combinatorial thin film synthesis for developments of … thin film synthesis for developments of...
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[Abstract Guideline (Leave two lines for presentation number)] Combinatorial thin film synthesis for developments of new high dielectric constant thin film materials *T. Nagata1)2), S. Kumaragurubaran1), Y. Suzuki1)3), K. Takahashia1)4), S.-G. Ri1)4), Y. Tsunekawa1)4), S. Suzuki1)4), and T. Chikyow1) 1)National Institute for Materials Science, Tsukuba, Ibaraki, Japan, 2) JST-PRESTO, Kawaguchi, Saitama, Japan, 3)Meiji University, Kawasaki, Kanagawa, Japan, 4) COMET Inc., c/o NIMS, Tsukuba, Ibaraki, Japan *[email protected] Keywords: Combinatorial synthesis, dielectrics, film capacitor, high-k,
The development of high-dielectric constant thin film materials is essential for future active and passive nanoelectronics devices. Recently we developed high-dielectric constant thin film materials for thin film capacitor and gate dielectrics by combinatorial technique.
Compound semiconductor based power devices such as SiC require high-temperature operational passive devices such as a capacitor. SiC based active devices are capable of operating over 250°C. For module and system level advancement, the high-temperature operational passive should be developed urgently. In the case of capacitors, current available capacitors can efficiently function up to 175°C only. Therefore, a thin-film capacitor that can be operated at high-temperatures and integrated monolithically in the proximity of active device should be developed. The BaTiO3 based relaxor ferroelectrics with a high dielectric constant (> 200) and free of hazardous elements, are promising candidates.1) Among the BaTiO3 based relaxor ferroelectrics, we have chosen x[BaTiO3]-(1-x)[Bi(Mg2/3Nb1/3)O3] (BT-BMN) due to its high dielectric constant and temperature stability in the bulk form.2) However, a thin-film process of this ceramic is not available yet. Moreover, the control of Bi composition, which affects on dielectric constant and ferroelectricity strongly, is challenging due to high volatility of Bi.3)4)
In this context, high throughput combinatorial synthesis method is effective in the fast optimization of the Bi composition. In this paper, we have developed a thin-film processing technology for BT-BMN films by employing combinatorial pulse laser deposition method. The composition spread film was formed by ablating stoichiometric and 10 wt% rich BT-BMN targets alternatively and employing a moving mask to form alternative thickness gradient layers. XPS spectrum on the composition spread film showed a linear variation of Bi from stoichiometric to 10 wt% Bi excess regions. Scanning nonlinear dielectric microscopy revealed that the 7 wt% Bi excess region showed the disappearance of ferroelectricity and the high dielectric constant. The dielectric constant is close to 250 and the stability is <13% from room temperature to 400°C, which are very promising as a high-temperature dielectric medium. It is possible to achieve higher dielectric constant and better thermal stability of dielectric constant if film is produced from Bi-7 wt% enriched target with a controlled crystallization processes.
In the presentation, we will also briefly introduce the development of high-k gate materials for a Ge channel, which has been attracting a lot of attention as a replacement for the Si channel used in current Si-based metal-oxide-semiconductor (CMOS) devices.5) References 1) D.-K. Kwon et al., J. Am. Ceram. Soc. 87, 1088 (2004). 2) R. K. Malhan, et al., Patent No. US 8,194,392,B2 (Jun.5, 2012). 3) S. Kumaragurubaran, et al., Jpn. J. Appl. Phys 54, 04DH02 (2015). 4) S. Kumaragurubaran, et al., Thin Solid Films, 592, 29 (2015). 5) T. Nagata, et al., Thin Solid Films, 591, 105 (2015).
Fig. 1: Temperature dependency of dielectric constant (lines + solid symbols) and dielectric loss (lines) of combinatorial thin-film annealed at 800 °C.
Growth of an ultra-thin crystalline AlOx tunnel barrier layer on GaAs-based
surfaces for robust spin injection
*N. Nishizawa, S. Shimbo, R. Roca, and H. Munekata Institute of Innovative Research, Tokyo Institute of Technology *[email protected]
Keywords: Molecular beam epitaxy, tunnel barrier, density of interface state, spin injection, spintronics
Formation of an ultra-thin oxide tunnel barrier layer is indispensable for sufficient spin transport across a
ferromagnetic metal and a semiconductor. However, in the system consisting of amorphous AlOx on GaAs-based
structure, the prominent spin injection endurable for device applications has not been achieved so far, which is also in
MgO/GaAs system. That is because of the high density of interface-states due to the dangling-bonds at the interface.
We reported, in this paper, the preparation and characterization of a high quality, ultra-thin, crystalline AlOx layer (-
AlOx) on a GaAs-based structure [1], and show its usefulness on spin-photonic devices, spin-polarized light emitting
diodes (spin-LEDs) [2, 3] and spin-polarized photo-diodes (Spin-PDs) [4].
Important issues to obtain the clean interface between AlOx and GaAs is to promote the creation of As-Al bonds at
the interface and reduce the oxidation of topmost As layer by oxidation process. In order to obtain homogeneous As-Al
bonds without generating interface traps, aluminum epitaxial layer was grown on GaAs surface by using a molecular
beam epitaxy (MBE) system. The thickness of Al epilayer is 5.5 Å because oxygen penetration depth into aluminum
metal surface is known to be 4-6 Å. The oxidation at room temperature with dry air at 1 atm would not involve the excess
kinetic energy with surface Al atoms that generate dangling bonds at Al/GaAs interface, yielding fully-oxidized, 7.0-Å
thick AlOx layer on un-oxidized GaAs layer. The resultant AlOx layer shows distinct single crystalline feature reminiscent
of the -phase Al2O3 in the transmission electron microscope (TEM) observations, as shown in Fig.1.
The I-V curves through the structure consisting of 100-nm Al / 1.0-nm -AlOx / 300-nm n-GaAs / n-GaAs(001)
show nearly symmetric characteristic. These features strongly suggest that the carrier transport is dominated by the
tunneling through an -AlOx layer. Fitting with Simmons’ equation [5] to the IV curves of the forward bias region has
yielded the barrier height of 2.8 eV with barrier thickness of 1.0 nm. The C-V characteristics of the same structure exhibit
the behavior which is typical for MIS structure (Fig.2). Using admittance spectra obtained by the C-V measurements, the
interface trap density is estimated to be Dit ~ 3 1011 cm-2eV-1, which is far less than that for amorphous AlOx/GaAs
systems, Dit 1013 cm-2eV-1. The large barrier height and low Dit both indicate the realization of high quality an-AlOx
layer and clean interface. Thickness and epi-growth condition dependences will be discussed at the time of presentation.
The contribution of the -AlOx layer on spin injection was evaluated by measuring circular polarization (PCP) of
electroluminescence (EL) emitted from spin-LED devices which consists of AlGaAs/GaAs double heterostructures and
a Fe/-AlOx spin injection contact. PCP of EL from the samples is low in the low current region, whereas it increases
steeply and reaches close to the pure PCP when J > 100 A/cm2. This enhancement of PCP suggests the appearance for
some spin-dependent nonlinear effect in the high current regime, which is ensured by robust spin injection with the -
AlOx layer. Conversely, sufficient spin extraction from semiconductor to ferromagnetic metal is also observed in a spin-
PD device comprising Fe/-AlOx/p-GaAs structure.
References:
1) N. Nishizawa et al., JAP 114 033507 (2013).
2) N. Nishizawa et al., APL 104, 111102 (2014).
3) N. Nishizawa et al., PNAS early (online) edition: doi/10.1073/pnas.1609839114 .
4) R. Roca et al., JJAP in press.
5) J. G. Simmons J. Appl. Phys. 34, 1793 (1963).
Annealing Time Dependence of Sol-gel Derived CuGaO2 Films
K. Matsuyama, K. Obara, A. Ziana, T. Endo, W. Ikesugi, T. Aoki, and *K. Uesugi Division of Information and Electronic Engineering, Muroran Institute of Technology *[email protected]
Keywords: CuGaO2, CuGa2O4, Cu2O, sol-gel
Wurtzite-type CuGaO21) is a narrow-bandgap material that absorbs the visible light. It is expected as
solar cell absorbers with high photoelectric conversion efficiency. However, it is difficult to manufacture
because it is a metastable structure. Wurtzite-type CuGaO2 powder has been reported, but it is necessary to
form CuGaO2 films for device application. In this study, we report the fabrication process of CuGaO2 films
by a sol-gel method.
Acetylacetonatogallium (GaC18H21O6) and copper acetate monohydrate (CuC4H8O5) were used as a
solute, 2-propanol (C3H8O) was used as a solvent, and monoethanolamine (H7NC2O) was used as an
additive. A CuGaO sol solution was prepared by mixing them and stirring at 50°C for 2 hours. After the sol
solutions were coated on glass substrates, they were annealed in the N2 atmosphere at 100°C for 5 min
followed by 300°C for 10 min. Then they were crystallized by annealing at 300°C for 1~ 6 hours to fabricate
the CuGaO2 films.
Although delafossite-type CuGaO2 films with the wide-bandgap energy were formed at the high
temperature of 800°C,2) the films which annealed at 300°C showed the red shift of the optical absorption
edge, as shown in Fig. 1. The transmittance decreased at around 800 nm, and absorption occurred in the
visible light region. However, the blue shift of the absorption edge occurred as the annealing time became
longer than 6 hours. Fig. 2 shows the optical bandgap estimated from the absorption edge. The films which
annealed for 1 hour was the amorphous-like structure, but wurtzite-type CuGaO2 films were fabricated by
annealing for 6 hours at 300°C. The bandgap energy of the CuGaO2 film was estimated to be 1.75 eV. In
addition, the growth of the grain boundary of CuGa2O4 phase was observed on the film surface. When
annealing time increased further, Cu2O phase became dominant. The formation of CuGa2O4 and Cu2O by
the phase separation could be decreased by annealing time and control of the power of the infrared heating
furnace, the CuGaO2 films with the narrow-bandgap can be prepared by the sol-gel method.
References
1) T. Omata, H. Nagatani, I. Suzuki, M. Kita, H. Yanagi, and N. Ohashi., J. Am. Chem. Soc., 136, 3378-
3381 (2014).
2) A. Alias, M. Sakamoto, T. Kimura, and K. Uesugi., Jap. J. Appl. Phys., 51(3), 035503 (2012).
.
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]
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[eV
]
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CuGaO2
CuGa2O4
Cu2O
Fig. 2. Annealing time dependence of optical
bandgap of the films.
Fig. 1. Transmittance spectra of the films prepared
by annealing at 300°C for 1~36 hours.
Abstract Guideline (Leave two lines for presentation number)
Mesostructured SrTiO3/BaTiO3 Hybrid Films by Surfactant-Templated
Sol-Gel Pathway with Robust Ferroelectricity
M. B. Zakaria
1)2), A. Matsuda
1), T. Nagata
1), M. Osada
1)3),*Y. Yamauchi
1)4), and
*T. Chikyow
1)3)
1) National Institute for Materials Science (NIMS), 1-1 Namiki, Tsukuba, Ibaraki 305-0044, Japan,
2) Department of
Chemistry, Faculty of Science, Tanta University, Tanta, Gharbeya 31527, Egypt, 3)
Facility of Science and
Engineering, Waseda University, Ohkubo 3-4-1, Shinjuku, Tokyo, 169-8555, Japan, 4)
Australian Institute for
Innovative Materials (AIIM), University of Wollongong, Squires Way, North Wollongong, NSW 2500, Australia. *[email protected] and [email protected]
Keywords: Mesostructures, SrTiO3/BaTiO3, Hybrid Films, Sol-gel synthesis, Robust Ferroelectricity
Ferroelectric materials are useful for many applications
ranging from memories, electronic transducers to energy
harvesting devices.1 Here we report a new class of highly
stable ferroelectric material, i.e., a mesostructured
SrTiO3/BaTiO3 composite film, by surfactant-templated
sol-gel method (Fig. 1A). Owing to the concave surface
geometry and abundant hetero-interface between SrTiO3
(STO) and BaTiO3 (BTO) phases, a large number of strains
can be created in the composite film, thereby leading to
dramatic enhancement of ferroelectric property.
Recent researches on stain engineering have opened a
novel approach to apply BTO and STO in high-temperature
ferroelectric applications. High-strain energy through
substrate-controlled and coherent in-plane biaxial strain can
facilitate a large enhancement in Tc and remanent polarization
(Pr) in various ferroelectrics.2 Horizontal strains within
layered heterostructures has been widely studied so far.3
Currently, coherent in-plane biaxial strain has attracted much
attention. However, these previous approaches have several
disadvantages, for example, some physical vapor deposition
(PVD) processes (e.g., pulse laser deposition, molecular beam
epitaxy) are complicated and cannot be extended to general
synthetic methodology as easily as chemical routes such as
sol-gel approach.
For practical applications, a facile process that can
introduce high strains into materials is highly desirable for
reducing the production costs and times. Our mesostructured
STO/BTO composite films showed the highest dielectric
constant among all reported STO/BTO composites, as
illustrated in Figs. 1B and C. The presenting new concept
would be useful for preparing other hetero-nanostructures. Further manipulation of dielectric materials should
improve their ferroelectricity and would create new solid-state property for next-generation optoelectronic devices
in future.
References 1) a) J. Ma, J. M. Hu, Z. Li, and C. W. Nan, Adv. Mater., 23, 1062-1087 (2011), b) J. M. Hu, Z. Li, J. Wang, J. Ma,
Y. H. Lin, and C. W. Nan, J. Appl. Phys., 108, 043909 (2010), c) J. Ma, Z. Shi, and C. W. Nan, Adv. Mater., 19,
2571-2573 (2007).
2) a) J. H. Haeni, P. Irvin, W. Chang, R. Uecker, P. Reiche, Y. L. Li, S. Choudhury, W. Tian, M. E. Hawley, B.
Craigo, A. K. Tagantsev, X. Q. Pan, S. K. Streiffer, L. Q. Chen, S. W. Kirchoefer, J. Levy, and D. G. Schlom,
Nature, 430, 758-761 (2004), b) K. J. Choi, M. Biegalski, Y. L. Li, A. Sharan, J. Schubert, R. Uecker, P. Reiche, Y.
B. Chen, X. Q. Pan, V. Gopalan, L. Q. Chen, D. G. Schlom, and C. B. Eom, Science, 306, 1005-1009 (2004).
3) a) R. Xu, M. Shen, S. Ge, Z. Gan, and W. Cao, Thin Solid Films, 406, 113-117 (2002), b) H. Tabata, H. Tanaka,
T. Kawai, and M. Okuyama, Jpn. J. Appl. Phys., 34, 544-547 (1995).
Fig. 1. A) Synthetic concept of mesostructured STO/BTO composite films prepared by introducing BTO crystalline phase into mesoporous STO film, insets are SEM images of STO and BTO calcined at 800 °C. B) Temperature-dependent dielectric constant for mesostructured ST/BT composite calcined at 1000
ºC. For comparison, both mesoporous STO and BTO films calcined at 1000 ºC are also measured. C) Local piezoelectric hysteresis loops measured by piezoresponse force microscopy
(PFM).
Role of H2O in the characterization of the IWOH films prepared by reactive plasma deposition *F. Y. Meng, J. H. Shi, Y. W. Liu, and Z. X. Liu Research Center for New Energy Technology, Shanghai Institute of Microsystem and Information Technology (SIMIT), Shanghai 200050, P. R. China *[email protected] Keywords: IWOH film, Hall mobility, passivation, grain boundaries. Transparent conductive oxides (TCO) are widely used as electrodes in various optoelectronic devices, like light embittering diodes and photovoltaics devices, including amorphous/crystalline silicon heterojunction (SHJ) solar cells. In particular, W-doped In2O3 (IWO) is very attractive for transparent contacts in high-efficiency SHJ technology owing to its high mobility. Recently, H2O or H2 were introduced into the process chamber during deposition to fabricate high-mobility TCO films such as IO:H1), ICO:H2), and ITO:H3) so on.
In this work, H2O-doped IWO (IWOH) films were deposited by reactive plasma deposition (RPD) technique at around 100. The target is W-doped In2O3 (1.0 wt%), the ultimate vacuum pressure of the process chamber was 7.5x10-7 Torr. High-purity Ar and O2 gases were introduced into the chamber together with a small amount of DI water, and the working pressure was kept constant at around 3.0x10-3 Torr during the deposition process. Meanwhile, the oxygen partial pressure of O2/Ar was stable at 1.2x10-3 Torr to optimize the H2O flow rate. The thickness of all the samples was controlled at 100nm by modulating the tray speed of RPD. The electrical properties of IWOH films were changed greatly as shown in Fig. 1 when H2O vapor took part in the formation of IWOH films, the mobility was obviously improved after the post annealing (PA) treatment. Based on the measurement of Hall Effect, it was found in comparison with the IWO films without H2O introduction that the Hall mobility of IWOH was increased 33% in Fig. 1(a) when H2O flow rate ratio was 2.0%. Simultaneously, the resistivity decreased around 26% in Fig. 1(b). However, the carrier concentration was varied a little from 1.0x1020 cm-3 to 2.1x1020 cm-3 although H2O flow rate ratio was modulated from 0 to 3.0%, which indicated that the films can suffer from less parasitic free carrier absorption in infrared wavelengths.
0.0 0.5 1.0 1.5 2.0 2.5 3.040
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H2O flow rate ratio (%)
Hall m
obilit
y(cm
2 /Vs)
(a)
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7.0
7.5
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H2O flow rate ratio (%)
Resis
tivity
(x10
-4 Ω
cm
)
(b)
4.0
4.5
5.0
5.5
6.0
6.5
7.0
7.5
8.0
Fig. 1. Dependence of electric characterization of IWOH films on H2O flow rate ratio
In order to deeply understand the effect of H2O introduction on the characterization of IWOH films, besides Hall Effect, we would conduct x-ray photoelectron spectroscopy (XPS) on the IWOH samples before and after PA treatment to probe the role of H2O. In addition, the microstructure properties of the samples would be investigated by x-ray diffraction (XRD). The optical parameters would be discussed in combination with the measurements of UV/VIS/NIR spectrophotometer and spectroscopic ellipsometer. It was deduced that the improvement of the electrical properties probably originated from the grain boundary passivation or the intragrain passivation of OH- or H+ or H2O-related species produced in the reactive plasma atmosphere. Considering that the TCO films are usually applied as the contact electrodes in the optoelectronic devices, the
environmental stability of IWOH films at 85 and 85% relative humidity would be tested and analyzed. Main References: 1) T. Koida, H. Fujiwara, M. Kondo, Appl. Phys. Express, 1, 041501 (2008). 2) E. Kobayashi, Y. Watabe, T. Yamamoto, Y. yamada, Sol. Energy Mater. Sol. Cells, 149, 75-80(2016). 3) B. Macco, H. C. M. Knoops, and W. M. M. Kessels, ACS Appl. Mater. Interfaces, 7(30), 16723 (2015).
Electrical Characteristics of a- and b-Axis-Oriented Bismuth Titanate Thin Films Formed on Si(100) Substrates by Chemical Solution Deposition *A. Kohno and T. Tajiri Department of Applied Physics, Faculty of Science, Fukuoka University *[email protected] Keywords: ferroelectric thin film, bismuth layer-structured ferroelectrics, ferroelectric transistor memory, capacitance-voltage hysteresis, X-ray analysis
One of the attractive applications of ferroelectric materials has been non-volatile memory. Especially, ferroelectric field-effect transistor (FeFET) has been expected as a memory cell suitable for higher integrated density and lower power consumption. From the viewpoint of size scaling of transistor structure, the research on materials properties, including thickness effect, of the thinner films becomes important, and the crystal orientation control of ferroelectric film formed on Si substrate is further of importance for the hysteresis characteristics. Bismuth titanate (Bi4Ti3O12) is well known as the bismuth-layer-structured perovskite ferroelectrics. Especially, lanthanum-substituted bismuth titanate (Bi4-xLaxTi3O12: BLT) has attracted attention as a Pb-free ferroelectric material since its remarkable fatigue free behavior and good ferroelectric properties were reported1). Furthermore, we have reported that the preferred crystal orientation was observed in the sub-100nm thick BLT films formed directly on Si(100) substrates by using chemical solution deposition method and ferroelectric hysteresis loops related with the crystal orientation of BLT thin film were confirmed in capacitance-voltage (C-V) characteristics of metal-ferroelectric-semiconductor (MFS) capacitor2), 3). From the discussion of the previous reports the formation of crystal orientation in the films seemed to be caused by nucleation at the Si surface and subsequent grain growth during the crystallization. Based on the thought on this crystal grain growth model, the thinner BLT films must be highly a- and b-axis-orientated films, resulting in their good polarization characteristics even in thinner film. In this research, we have formed BLT films, of which thickness is thinner than 30nm, directly on Si(100), and investigated the crystal orientation, electrical characteristics, and their thickness dependences.
The chemical solutions were prepared by mixing the BLT precursor solution (Kanto Chemical Co., Inc.), the BiO precursor solution (Enhanced Metal Organic Decomposition materials), and Butyl acetates (BA) solution. The mixture ratio of these solutions was a major factor to control the film thickness and crystal phase. The hydrogen terminated Si(100) substrates were prepared by chemical cleaning and subsequent HF solution treatment. Soon after the HF treatment, the mixed precursor solutions were deposited on the Si(100) substrates by spin-coating. After the samples were dried on a hot plate at 150C for 30 min, the films were crystallized at 550 C for 2 hours in a pure oxygen gas atmosphere by a furnace. For electrical measurements the gold electrodes were fabricated on the films.
Figure 1 shows the X-ray diffraction profiles: the intensity is normalized by Si(400) peak. The BLT film thicknesses were determined by X-ray reflectivity analysis. As shown in Fig. 1 the 200 diffraction intensity increased with reducing the BLT thickness. The a- and b-axis orientations were confirmed by pole-figure measurements of XRD. The atomic force microscope and transmission electron microscope observations revealed that the BLT films consisted of the small grains. The clockwise hysteresis loops were clearly observed in capacitance-voltage (C-V) characteristics of Au/BLT/p-Si capacitors even in the case of ~ 18nm film, as shown in Fig. 2. The formation of crystal orientation and thickness dependence of the electrical characteristics are discussed.
References 1) B. H. Park et al.: Nature 401 (1999) 682. 2) A. Kohno et al.: Mater. Res. Soc. Symp. Proc. 784 (2004) 497. 3) T. Tajiri et al.: IEEE Trans. on Ultrasonics, Ferroelectrics, and
Frequency Control 54 (2007) 2574.
Fig. 1 X-ray diffraction of BLT films on Si(100) substrates.
Fig. 2 C-V characteristics of the MFS capacitors.
Single-Crystalline GeSn Formation on Transparent Substrate and Its
Optoelectronic Applications
*T. Hosoi, H. Oka, T. Shimura, and H. Watanabe Osaka University, Suita, Osaka, Japan *[email protected]
Keywords: GeSn, Thin Film Transistor, Crystallization, Photoluminescence
Monolithic integration of high-performance CMOS and optoelectronic devices is a key technology for realizing
3D-IC and on-chip sensing system. Germanium-Tin (GeSn) alloy is one of the most promising materials for
optoelectronic applications because its energy band structure can be modulated by incorporating Sn and introducing
strain. The significant enhancement of carrier mobility and indirect-to-direct transition are predicted by theoretical
calculations [1]. The direct bandgap of GeSn corresponds to the wavelength of 25 m, which is suitable for
near-infrared (NIR) imaging and biochemical sensing. Despite the above mentioned advantages, low solid solubility
of Sn in Ge and large lattice mismatch between Ge and Sn are severe obstacles for the epitaxial growth of GeSn
layer. Furthermore, it is known that the epitaxially grown Ge(Sn) layer exhibits p-type behavior without intentional
doping probably due to point defects. Although GeSn layer with a Sn content of 12.6% has been formed by
non-equilibrium low-temperature epitaxial CVD growth on virtual Ge substrate (Si with Ge buffer layer) [2], further
improvement in crystalline quality and technique to control strain and doping concentration are highly desired.
Meanwhile, the formation of single crystalline GeSn layer on amorphous layers and transparent substrates is also an
important challenge for monolithic integration of GeSn-based optoelectronic devices. Solid-phase crystallization at
low temperature and laser annealing of amorphous GeSn layer on SiO2 have previously been demonstrated, but the
resulting GeSn layer was poly-crystalline and hence the degraded carrier mobility and optical properties. Therefore,
we focused on single-crystalline GeSn formation on both SiO2/Si and quartz substrate based on liquid-phase growth.
The GeSn-on-insulator structure (GeSn/SiO2/Si) can be formed by lateral liquid-phase epitaxy (LLPE) [3]. In
this technique, amorphous GeSn wire with a width of about 1-10 m surrounded by SiO2 layer but partly connected
to Si seed was annealed at a temperature above the melting point of GeSn, leading to the LLPE growth from the
seed along the GeSn wire during cooling. The advantage of this method is to confine dislocations within the seed
region thus obtaining tensile-strained single-crystalline GeSn layer on SiO2 layer with high-crystallinity. It should be
noted that the excess Sn atoms were swept out toward the growth direction, resulting in Sn precipitation at the end
of wire. The Sn content in the wire was estimated to be about 1% except for 6% near the Sn precipitation. Raman
spectroscopy revealed that 0.30.5% tensile-strain was induced in GeSn wire due to the difference in thermal
expansion coefficient between GeSn and Si. The photoluminescence (PL) peak obtained from Ge0.94Sn0.06 was
appeared at 0.66 eV (red-shifted by 0.14 eV with respect to Ge), indicating a direct bandgap narrowing by Sn
incorporation and tensile strain. However, the Si diffusion from seed-region extended over 200 m and thus lower
PL intensity at the middle part of GeSn wire was concerned.
We have recently succeeded in liquid-phase growth of a tensile-strained single-crystalline GeSn wire on quartz
substrate without using crystal seed [4, 5]. Although liquid-phase growth mostly results in poly-crystallization due to
spontaneous nucleation, Si-free single-crystalline GeSn wire was formed by locally melting a wire to induce
nucleation at liquid/solid interface. The Sn content and tensile-strain in GeSn wire were estimated to be 2.6% and
0.6%, respectively. The PL peak from GeSn was observed at 0.61 eV (red-shifted by 0.19 eV with respect to Ge) and
its intensity was 36 times higher than the bulk Ge. We also fabricated top-gate single-crystalline GeSn MOSFET on
a quartz substrate and obtained well-behaved accumulation-mode p-FET operation. A peak field-effect hole mobility
as high as 423 cm2/Vs was achieved. These results clearly indicate an excellent crystal quality of GeSn and mobility
enhancement due to Sn incorporation and tensile strain, which will be a novel platform for monolithic optoelectronic
integration.
References 1) K. L. Low, Y. Yang, G. Han, W. Fan, and Y. C. Yeo, J. Appl. Phys., 112, 103715 (2012).
2) S. Wirths, R. Geiger, N. von den Driesch, G. Mussler, T. Stoica, S. Mantl, Z. Ikonic, M. Luysberg, S. Chiussi, J.
M. Hartmann, H. Sigg, J. Faist, D. Buca, and D. Grützmacher, Nat. Photonics, 9, 88 (2015).
3) T. Shimura, M. Matsue, K. Tominaga, K. Kajimura, T. Amamoto, T. Hosoi, and H. Watanabe, Appl. Phys. Lett.,
107, 221109 (2015).
4) H. Oka, M. Koyama, T. Tomita, T. Amamoto, K. Tominaga, S. Tanaka, T. Hosoi, T. Shimura and H. Watanabe,
IEDM Tech. Dig., 580 (2016),
5) H. Oka, T. Amamoto, M. Koyama, Y. Imai, S. Kimura, T. Hosoi, T. Shimura and H. Watanabe, Appl. Phys. Lett.,
110, 032104 (2017).
Influence of growth temperature of embedded indium-oxynitride quantum dots on contact performance of ITO on III-nitride light-emitting diodes Chih-Yung Chiang, Zhong-Yi Liang, and *Wen-Cheng Ke Department of Materials Science and Engineering, National Taiwan University of Science and Technology, Taipei 106, Taiwan *[email protected] Keywords: LEDs, Ohmic contact, ITO, p-GaN
In recent years, the light-emitting diodes (LEDs) were widely used in lighting applications. Increasing injection current was a necessary approach for achieving a higher brightness of LEDs. Thus, Ohmic contact with a low specific contact resistance plays a crucial role to decrease the power dissipation. Traditional indium-tin-oxide (ITO) on p-GaN layer of LEDs exhibits a non-Ohmic behavior, because of the barrier height was formed at the interface between ITO and p-GaN layer. A lot of methods were proposed for overcoming the contact issue of ITO on p-GaN layer, such as InGaN interlayer, Ag nanoparticle, NiOx interlayer and InON QDs interlayer [1] etc. In order to achieve a lower specific contact resistance of ITO/p-GaN, contact annealing process at ~600 oC in the nitrogen ambient need to be done in a typical LED chip process. The high contact annealing temperature would change the Mg distribution in p-GaN layer, result in a high specific contact resistance of ITO/p-GaN. In this study, a low specific contact resistance of ITO/p-GaN can be achieved by embedded an indium-oxynitride (InON) quantum dots (QDs) interlayer without any contact annealing process. The growth temperature and growth time were optimized for improving specific contact resistance and optical transmittance. In Fig. 1, the atomic-force microscopy (AFM) image show the InON QDs grown on sapphire substrate with diameter of 50 nm and density of 1.9×109 cm-2. In Fig.2, it was shown that the InON QDs grown at 450 oC in 1-min exhibit a low specific contact resistance of 5.3×10-4 Ω-cm2. The optical transmittance of 450 oC-InON QDs on double polishing sapphire was ~ 91%. The experimental results indicated that the InON QDs interlayer was a potential approach for achieving good contact performances of ITO on LEDs.
Reference: 1) W. C. Ke, F. W. Lee, C. Y. Yang, W. K. Chen and H. P. Huang, J. Appl. Phys., 118, 155303 (2015).
400 450 500 550
5.0x10-4
1.0x10-3
1.5x10-3
2.0x10-3
2.5x10-3
3.0x10-3
C (
-cm
2 )
InON QDs growth temperature (oC)
Fig. 1. AFM images of InON QDs grown on sapphire. Fig. 2. Specific contact resistance of ITO on LEDs with embedded InON QDs interlayer grown at various temperatures.
Damage mechanisms for the irradiated PEEK by low energy proton
Hongxia Li1, Jianqun Yang1, Xingji Li1*, Chaoming Liu1, Shangli Dong1 1School of Materials Science and Engineering, Harbin Institute of Technology, Harbin 150001, China
Corresponding author: Xingji Li (Address: 92 West Dazhi Street, Nangang District, Harbin, China,
150001; E-mail: [email protected]; Phone: +8645186412462)
Keyword: PEEK, damage mechanism, GISAXS, irradiation, proton
Abstract: Poly ether ether ketone (PEEK) is a polymer widely used in space applications, such as
electrical components, structural materials, thermal blankets, solar cell paddles, etc due to its high
thermal stability, resistant to chemical damage and excellent mechanical properties. When PEEK is used
in space, it is easy to suffer from charged particles radiation damage, especially in low-energy protons.
However, less studies about damage mechanisms of PEEK exposed to low-energy protons became
available so far. In this paper, based on low-energy protons with 170keV, the damage mechanisms of
PEEK were studied by synchrotron radiation grazing
incidence small angle X ray scattering (GISAXS),
differential scanning calorimetry (DSC), electron
paramagnetic resonance (EPR) spectroscopy, Fourier
transform infrared Spectroscopy (FTIR) and X-ray
photoelectron spectroscopy (XPS). GISAXS
analyses show that the low-energy protons obviously
influence the microstructure on the near surface of
PEEK, as the Fig.1. The near surface of the unirradiated samples exists long period and layered
characteristics. With increasing the fluence, X-ray incidence angle corresponding to the disappearance
of the long period and layered characteristics decreases. DSC results show that the irradiation has little
effect on the crystallinity of the polymer. EPR analyses show the formation of free radicals. From FTIR
and XPS analyses that the low energy proton could damage ketone and benzene ring structure of PEEK,
causing damage of the integrity of molecular chain, and then disappearance of the long period and layered
characteristics, leading to the mechanical performance degradation of the PEEK. This research results
could provide PEEK related theoretical foundation for application in aerospace field.
Fig.1 PEEK with different incident angles of GISAXS
scattering pattern
Structural, Optical, and Photoelectrochemical Characterization of Thin Films of an Axially Chiral Bibenzo[c]phenanthrene Diol Md. Nazmul Kayes1), M. Shahabuddin1), M. Jalil Miah2), M. Karikomi1), E. Nasuno1), N. Kato1), and *K. Iimura1) 1) Graduate School of Engineering, Utsunomiya University, Tochigi, Japan, 2) Department of Mechanical and Chemical Engineering, Islamic University of Technology, Gazipur, Bangladesh. *[email protected] Keywords: thin films, photocurrent, circular dichroism spectra
The use of organic materials in the photovoltaic technology plays a vital role in energy production through an environmentally friendly and sustainable way. The active layers of organic materials having photo-response are of interest for future applications in solar cells. In the present study, thin films of an amphiphilic axially chiral bibenzo[c]phenanthrene diol (later denoted as BIPOL) have been prepared by the Langmuir-Blodgett (LB) and spin coating (SP) techniques, and their film structure and optical properties, and photoelectrochemical response have also been evaluated.
The surface pressure-molecular area isotherms of racemic mixture and enantiomers of BIPOL at 25oC commonly showed a plateau region followed by a steep increase of surface pressure. The thin films were prepared on solid substrates at several molecular areas by the scooping-up method and were characterized by UV-vis spectroscopy, photoluminescence spectroscopy (PL), X-ray reflectometry (XR), atomic force microscopy (AFM) and circular dichroism spectroscopy (CD). A large stokes shift was found in the photoluminescence spectra. The formation of condensed-phase micro-domains were observed in AFM images for all BIPOLs. The domains had the thickness larger than that expected for a monolayer and thus correspond to the multilayer regions in the film. The multilayer formation was also confirmed by XR analysis, and would be due to less hydrophilicity of the BIPOL molecules. CD spectra of R and S isomers of BIPOL in solution and in LB film on quartz substrate were shown in Fig. 1. The isomers showed the clear response to circularly polarized light, whereas no response was observed for the racemic mixture. A photochemical response was evaluated for LB and SP films on FTO substrates by a three electrode system, and was found that both films produced photocurrent responding to light illumination (Fig. 2). These observations imply that the thin films of BIPOL enantiomers may have circularly polarized light responsive optoelectronic function [1]. References [1] Ying Yang, Rosenildo Correa da Costa, Matthew J. Fuchter and Alasdair J. Campbel, Nature Photonics, 7, 634-638 (2013).
Fig. 1: CD spectra of isomers and racemic mixture of BIPOL in solution and in film on quartz substrate.
Fig. 2: Photocurrent response for the films of BIPOL prepared on FTO substrates by the LB and SP techniques.
-90
-60
-30
0
30
60
90
200 300 400 500
∆ε
/ M-1
cm-1
Wavelength, λ / nm
S (in sol.)R (in sol.)S (in film)R (in film)Racemic (in film)
0
0.1
0.2
0.3
0 200 400 600
Pho
tocu
rren
t / µ
Acm
-2
Time / s
LBSP
UV Photosensing Characters of Zinc-Tin Oxide (ZTO) Thin Film Transistors Fabricated via Spin-Coating and Inkjet Printing I-Wen Wang, Wei-Yao Lai, Ho-Lin Tsai, Jeng-Ting Li, *Jen-Sue Chen, In-Gann Chen, Weng-Sing Hwang Department of Materials Science and Engineering, National Cheng Kung University, Tainan, Taiwan *[email protected] Keywords: Photo-sensitivity, Thin Film Transistor, Zinc-Tin Oxide, Solution process Amorphous oxide thin film transistors applied as photosensing devices are receiving increasing attention due to their high electron mobility, gate bias modulation and signal amplification. In this work, we choose zinc-tin oxide (ZTO) instead of indium-gallium-zinc oxide (IGZO) to avoid expensive In and Ga elements. Due to the large bandgap of Zn-based oxide semiconductors (>3.3eV), the photoresponse is in the UV region. We have fabricated the ZTO active layers via two solution processes: spin-coating and inkjet printing. The purpose of using solution process is owing to its advantages of low cost and feasibility for large area deposition. With thickness less than 10 nm, the ZTO TFT exhibits a good field-effect mobility of ~10 cm2/Vs, small subthreshold slope of ~0.5 V/decade and high on/off current ratio of ~107. With light illumination of 405 nm wavelength and power density upto 0.5 mW/cm2, the light-intensity dependent transfer (ID-VG) characteristics of spin-coated and inkjet printed ZTO TFT devices are shown in Fig. 1.
Fig. 1 Transfer characteristics of (a) spin-coated and (b) inkjet printed ZTO TFT devices, as a function of light intensity (wavelength=405 nm). Accordingly, the light sensitivity is in the order of 105~106 for the ID-off region of both ZTO TFT devices. The light responsibility reaches around 170 A/W for spin-coated ZTO TFT while the responsibility of reaches 280 A/W for the inkjet printed ZTO TFT. Additionally, since the photo-induced current is gate bias dependent, both solution-processed ZTO TFTs demonstrate the potential photosensing capabilities with tunable light sensitivity and responsibility. References 1) Jeng-Ting Li, Li-Chih Liu, Po-Hsien Ke, Jen-Sue Chen, Jiann-Shing Jeng, Journal of Physics D: Applied Physics 49, 115104 (2016) 2) Li-Chih Liu, Jen-Sue Chen, and Jiann-Shing Jeng*, Applied Physics Letters 105, 023509 (2014).
Controllable epitaxial growth and physical properties of low dimensional Si
based materials
*Z. M. Jiang1), Y. J. Ma1)2), C. Zeng3), Z. Zhong1) and J. S. Xia3) 1) Department of Physics, Fudan University, Shanghai 200433, China, 2) Shanghai Institute of Microsystem and
Information Technology, 3) Huazhong University of Science and Technology * [email protected]
Keywords: Controllable growth, MBE, GeSi quantum dot, Nanocavity, Patterned substrate
Considering the fact that Si is the most prominent material for micro- and nano-electronics and the compatibility
between GeSi nanostructures and Si complementary metal-oxide-semiconductor (CMOS) technology, improving
electronic and photonic properties of Si by incorporation of Ge or GeSi nanostructures have long been desirable. In
addition, for device applications, size uniformity and spatial ordering as well as addressable site of these GeSi
nanostructures are highly expected. In the past decades, integration of patterned substrate and self-assembled growth
techniques has been demonstrated to be an effective approach to control nucleation position, uniformity and
ordering of these GeSi nanostructures.
In this paper, we first present results on the growth of ordered low density Ge quantum dots (QDs) on patterned
Si substrates and the controllable growth of Ge single QD and double QD nanostructures on nanohole-patterned Si
substrates via molecular beam epitaxy. Their growth mechanism is investigated. Surface chemical potential model is
used to elucidate the nucleation and growth of those ordered QDs. Then we report PL properties from a Ge single
QD embedded in a L3-type photonic crystal nanocavity. The growth of site-controlled Ge QDs on patterned
silicon-oxide-insulator substrates as well as the accurate embedding of a Ge single QD into a modified L3-type slab
cavity is demonstrated in detail. A sharp resonant luminescence peak is observed at 1498.8 nm, which is enhanced
by more than three orders of magnitude. Our devices provide a CMOS-compatible way of developing silicon-based
low-power consuming light emitters, and are promising for realizing on-chip single photon sources.
Minority-carrier lifetimes in ultrananocrystalline diamond/amorphous carbon composite films prepared by coaxial arc plasma deposition *N. Nishikawa1), S. Takeichi1), T. Hanada1), H. Gima1), S. Tategami2), A. Iwamoto2), H. Takeda2),
A. Fukuyama2), and T. Yoshitake1) 1) Kyushu University, Fukuoka, Japan, 2) University of Miyazaki, Miyazaki, Japan
*[email protected] Keywords: ultrananocrystalline diamond, minority-carrier lifetime, new candidate for photovoltaics
1. Introduction Ultrananocrystalline diamond (UNCD)/hydrogenated amorphous carbon (a-C:H) composite (UNCD/a-C:H) films are composed of a large number of UNCD grains with diameters of less than 10 nm and an a-C:H matrix.1,2) The existence of a lot of grain boundaries1) is a structural specific to UNCD/a-C:H, which might be an origin of the appearance of energy levels in the band gap of dimaond3) and large absorption coefficients in the visible and ultraviolet ranges.1,4) In our previous research, we successfully realized the control of conduction type of UNCD/a-C:H by doing boron and nitrogen5,6), and fabricated heterostructural pn-junctions with singlecrystalline Si,7-9) and we confirmed the rectifying action and photodetection in the heterojunctions7). However, there have never been researches on the minority-carrier lifetime in UNCD/a-C:H. In this research, we experimentally measured the minority-carrier lifetime of typical samples with a µ-PCD apparatus. 2. Experimental UNCD/a-C:H films were prepared on insulating Si substrates by coaxial arc plasma deposition (CAPD) with graphite targets. Boron doping was made by using a boron-blended graphite target. Nitrogen-doped films were prepared in a nitrogen and hydrogen mixed gas atmosphere. 3. Results Figure 1 shows the time-dependence of the microwave reflectivity in voltage. There are obvious differences in the decay curves among the samples. The minority-carrier lifetime as for thin films is estimated by using the following equation.
The estimated minority-carrier lifetimes are shown in Table. 1. Hydrogenation evidently lengthens the lifetime, which implies that dangling bonds that act as trap centers are terminated by atomic hydrogen. The lifetime was slightly shortened by boron and nitrogen doping. The details are going to be reported at the conference. Acknowledgements: This work was partially supported by the Advanced Low Carbon Technology Research and Development Program (ALCA) of the Japan Science and Technology Agency (JST), the Yoshida Science and Education Promotion Association, and JSPS KAKENHI Grant Number 15H04127. References: 1) T. Yoshitake et al. JJAP 46 (2007) L936, 2) T. Yoshitake et al. JJAP 48 (2009) 020222, 3) P. Zapol et al. Phys. Rev. B 65 (2001) 045403, 4) A. Nagano et al. Diamond & Related Materials 17 (2008) 1199-1202 5) S. Ohmagari et al., JJAP 49 (2010) 031302, 6) S. Al-Riyami et al., APEX 3 (2010) 115102, 7) S. Ohmagari et al., JJAP 50 (2011) 035101, 8) S. Ohmagari et al, JJAP 51 (2012) 090123, 9) S. Ohmagari et al., JJAP 53 (2014) 050307.
Table. 1. Minority-carrier lifetimes in typical samples
Sample name Sample Lifetime (μs)
Sample A UNCD/a-C 0.0062
Sample B UNCD/a-C:H 1.58
Sample C UNCD/a-C:H (N 4at.%) 0.4
Sample D UNCD/a-C:H (B 0.5at.%) 1.08
Fig. 1. Microwave reflectivity in voltage plotted in (a) linear and (b) log scales against time.
0 1 20
200
400
time (µs)
Vol
tage
(mV
)
Sample A
Sample C
Sample D
Sample B
0 1 2100
101
102
103
time (µs)
Log(
Vol
tage
) (m
V)
Sample B
Sample D
Sample C
Sample A
Improved Carrier Mobility in High-conductive Si Nanocrystals via B doping
D. Shan1)2), D. K. Li1), *J. Xu1), and K. J. Chen1) 1)School of Electronic Science and Engineering and Jiangsu Provincial Key Laboratory of Advanced Photonic and
Electronic Materials, Nanjing University, Nanjing, 210093, China 2)School of Electronicand Information Engineering, Yangzhou Polytechnic Institute,Yangzhou225127, China
Keywords: Si nanocrystals, Boron-doped, Enhanced electronic properties
Si nano-crystals (Si NCs) have attracted more and more attention in recently years since they can be applied
in many kinds of nano-electronic and optoelectronic devices. However, the carrier mobility in Si NCs is
quite low and how to improve the carrier mobility in Si NCs is currently one of the challenge topics. It is
well known that doping in semiconductors can increase the conductivity but reduce the carrier mobility due to the
strong impurity scattering. Here, we report a
novel experimental result that the hole
mobility can be enhanced by nanoscale B
doping at suitable concentrations. The boron
(B)-doped Si NCs were fabricated by annealing
the doped amorphous Si thin films. The
enhanced hole mobility as high as 17.8
cm2/V·s is achieved by nanoscale B doping,
which is ten times more than that of
un-doped Si NCs (1.6 cm2/V·s) a shown in
Fig.1. Meanwhile, the sample exhibits the
very high conductivity (~4×102 S/cm). It is
suggested that B doping in Si NCs not only
induces the enhanced conductivity due to
the increase of hole concentrations but also
improve the carrier mobility. The possible
mechanism will be discussed in the talk.
Our results demonstrate that introduction of
the suitable impurities such as B or P in Si
NCs is a novel way to modulate the
electronic structures as well as the physical
properties of Si NCs to further improve the device performance based on micro- or nano-crystalline Si
materials. This work is supported by the ‘973 Program’ (2013CB632101), NSFC (11274155) and PAPD.
References :
1) J. Y. W. Seto, J. Appl. Phys. 46, 5247 (1975).
2) D. Shan, M. Q. Qian, Y. Ji, X. F. Jiang, J. Xu and K. J. Chen, Nanomaterials 6, 233 (2016).
3) R. Guerra and S. Ossicini, J. Am. Chem. Soc. 136, 4404 (2014). 4) P. Lu, W. W. Mu, J. Xu, et al., Sci Rep., 6, 22888 (2016).
Fig. 1. Room temperature Hall mobilities and dark conductivities of un-doped and B-doped nc-Si films with various doping concentration.
0.0 0.5 1.0 50
5
10
15
20
25
Hall mobility
FB (sccm)
Ha
ll M
ob
ilit
y
(
cm
2/V
s)
10-8
10-6
10-4
10-2
100
102
104
Dark conductivity
Da
rk
Co
nd
ucti
vit
y (
Scm
-1)
Electrically Contacting Self-Assembled PbS Nanocrystals Using Graphene
*H.P.A.G. Astier1), J.M. Fruhman1), L. Eyre1), B. Ehrler4), M. Böhm1), P.R. Kidambi2), U. Sassi2),
D. De Fazio2), J.P. Griffiths1), B.J. Robinson3), S. Hofmann2), A.C. Ferrari2), and C.J.B. Ford1) 1) Cavendish Laboratory, JJ Thomson Av. CB3 0HE, Cambridge, UK, 2) Cambridge Graphene Centre, 9 JJ Thomson
Av. CB3 0FA, Cambridge, UK, 3) Department of Physics, University of Lancaster, Lancaster LA1 4YB, UK, 4) Center for Nanophotonics, AMOLF, Science Park 104, 1098 XG, Amsterdam, The Netherlands *[email protected]
Keywords: graphene, quantum dot, single electron, self-assembly
Using molecular junctions as electrical
components often implies low scalability and complex
fabrication: horizontal architectures generally require
costly and sequential processes such as electron-beam
lithography1), whilst vertical stacking using metal
evaporation can damage the molecules or cause short
circuits2). Architectures based on molecular self-
assembled monolayers (SAMs) and graphene have
enabled molecular tunnel junctions to be built with a
yield of 90%3). Here, we use graphene to make arrays
of ~1µm2 junctions contacting SAMs of PbS
nanocrystals (5nm diameter) as quantum dots to
obtain films with more complex low-dimensional
transport characteristics. Our junctions exhibit
Coulomb blockade5) in the nanocrystals (Fig. 2) with
a yield above 40% before optimisation, thus
demonstrating single-electron effects in a robust and scalable
architecture. The design is adapted for electron-beam
lithography to contact areas down to nanometre sizes. This
enables a statistical comparison of transport over a large range
of nanocrystal numbers, from single digits up to tens of
thousands. Topographical imaging combining atomic force
microscopy (AFM) and ultra-sonic force microscopy (UFM)
allows us to investigate the conduction parameters in these
complex films in relation to their mechanical aspect6) (Fig. 3).
References:
1) D.L. Klein et al., Appl. Phys. Lett. 68, 2574 (1996).
2) H. Haick et al., J. Phys. Chem. C, 111, 2318 (2007).
3) G. Wang et al., Adv. Mater, 23, 755 (2011).
4) H. Jeong et al., Nanotechnology 26, 025601 (2015).
5) U. Meirav and E. B. Foxman, Sem. Sci. Tech. 11,
255 (1996).
6) B.J. Robinson and O.V. Kolosov, Nanoscale 6,
10806 (2014).
Fig. 1. Self-assembled PbS nanocrystal junction. The nanocrystals form a dense monolayer supporting the graphene top electrode.
Fig. 2. Left: I-V measurements of a self-assembled PbS nanocrystal junction exhibiting a Coulomb staircase (curves are offset vertically for clarity). Right: Detail of a self-assembled PbS nanocrystal contacted as a quantum dot.
Fig. 3. Topographical profile of junctions (a) with PbS SAM and no graphene, (b) after graphene transfer. The AFM records height profile (z-axis) whereas UFM records the stiffness response of a surface (colour scale, where brighter is stiffer).
(a) (b)
Enhanced visible-light emission from Quantum dots sensitized GeO2/Ge
perfect absorptive hetero-nano pyramids
*S. L. Shinde1), T. D. Dao1), S. Ishii1), L. W. Nien1), K. K. Nanda2) and T. Nagao1)3) 1)National Institute for Materials Science, Tsukuba, Ibaraki, Japan, 2)Indian Institute of Science, Bangalore, India 3)Hokkaido University, Kita-ku, Sapporo, Japan *[email protected]
Keywords: Germanium oxide, Defects, Visible light emission, Quantum dots.
Through the development of LEDs in the near ultraviolet and blue wavelengths, solid-state lighting (SSL) is
considered as a major promising technology for general illumination.[1,2] Various oxide and sulfide based phosphor materials, quantum dots (QDs) and organic dyes have been developed, and several strategies have been proposed to
generate white light in combination with ultraviolet/blue LEDs.[1,2] An alternative to rare earth or transition
metals-based phosphors are defects containing wide-bandgap (WBG) oxides such as silica, zirconates, aluminates,
Ga2O3, ZnO, and GeO2 etc. However, most of the defect containing WBG oxide phosphors has very low absorption
efficiency for visible light, making them impractical to coat on blue LED to generate white light. Therefore
compatibility of strong absorption (for UV/blue light) together with efficient PL are major requirement for the
practical phosphor materials.
Germanium dioxide (GeO2) is a WBG oxide with fascinating electronic and optical properties have been reported to have violet and blue luminescence,[3,4] However, due to its wide band gap nature, the absorption of GeO2
in the visible region is rather limited. It is known that by the formation of nanostructrures at the Ge and Si surfaces,
high density of impurity defects and structural defects in the lattice are formed, and the light absorption are
significantly increased in the visible to near infrared region.
We demonstrate the nearly perfect
absorption and quantum dots-mediated
enhanced visible light emissions from
defect engineered Ge nanopyramids. High-resolution 3D
photoluminescence (PL) imaging of
the pyramid structure elucidated the
position dependency of defects and
their emission: Stronger
photoluminescence yield was observed
at the nanopyramid tips (Fig. 1a), which
is correlated to the efficient light nanofocusing at the tips where increased defect density and roughness at the interface between Ge and surface oxide (GeO2) also takes place. Furthermore, the visible light emissions from this
GeO2/Ge interface can be enhanced ~15-fold when CdTe quantum dots (QDs) are adsorbed on the GeO2/Ge system
(Fig. 1b). The enhanced luminescence of our structure can be attributed to the extraordinary light harvesting
property of pyramid structure; strong anti-reflection effect, pronounced defect formation at the nanopyramid tips,
and anomalous resonant energy transfer between GeO2 defects and CdTe QDs. The proposed methodology can be
applied to other nano-structured wide bandgap materials to turn them into solar light harvesters and bright white
light-emitting phosphors.
References:
1) E. F. Schubert and J. K. Kim, Science, 308, 1274-1278(2005).
2) M. Shang, C. Li and J. Lin, Chem. Soc. Rev., 43, 1372-1386(2014).
3) S. C. Vanithakumari and K. K. Nanda, Adv. Mater., 21, 3581-3584(2009).
4) S. L. Shinde and K. K. Nanda, Cryst. Eng. Comm., 15, 1043-1046(2013).
Fig. 1. (a) SEM image of pyramids of GeO2/Ge and (b) Schematic of enhance visible-light emission from near perfect absorptive nano-pyramids of CdTe/GeO2/Ge.
High Density Formation of Fe-silicide Nanodots and Their Magnetic Properties S. Ishida, K. Makihara, M. Ikeda, A. Ohta, and S. Miyazaki Graduate School of Engineering, Nagoya University, Furo-cho, Chikusa-ku, Nagoya 464-8603, Japan
Phone:+81-52-789-2727, Fax:+81-52-789-3168, Email:[email protected]
Keywords: Nanodot, Fe3Si, remote H2 plasma
Ferromagnetic Fe3Si nanodots (NDs) have attracted attention as a promising material for application in spintronic
devices [1, 2], because DO3 ordered Fe3Si has a high spin polarization [3]. For the application of Fe3Si-NDs to
devices such as magnetoresistive random access memory, high-density formation and control of crystalline phase of
NDs are one of major concerns. Recently, we have demonstrated the formation of Fe-silicide NDs with an areal
density as high as ~1011 cm-2 by exposure of ultrathin Fe/a-Si/Fe tri-layer films to remote H2 plasma (H2-RP) without
external heating [4]. In this work, to improve the controllability of areal dot density and size, we formed Fe3Si-NDs
by exposing ultrathin Fe on Si-NDs, which were self-assembled on the SiO2 layer by LPCVD using SiH4, to a remote
H2-RP without external heating, and characterized their magnetic properties.
After conventional wet-chemical cleaning steps of n+-type Si(100) substrates, ~2.7nm-thick SiO2 was grown on the
substrates by dry O2 oxidation at 1000ºC. The SiO2 surface was dipped into a 0.1% HF solution to obtain uniform
surface termination with OH bonds. Then, Si-NDs were formed from the thermal decomposition of pure SiH4 under
66Pa at 590ºC. After that, a ~1-nm-thick Fe layer was deposited uniformly on the Si-NDs by electron beam
evaporation, where the areal density and size of Si-NDs, and Fe film thickness were designed with a stoichiometric
ratio of Fe:Si = 3:1. Subsequently, the Fe/Si-NDs stack structure was exposed to a H2-RP without external heating.
The plasma was generated by inductive coupling with an external single-turn antenna connected to a 60-MHz
generator through a matching circuit. The VHF power and the gas pressure were kept constant at 500 W and 20Pa,
respectively. The exposure time was 10 min.
Atomic force microscope images of Si-QDs and Fe/Si-QDs stack exposed to H2-RP confirm that the areal dot density
(~2.4×1011 cm-2) remains unchanged before and after the Fe deposition on the Si-NDs and the subsequent H2-RP
exposure, while the dot height was increased by ~6.5 nm (Fig.1). This result is explained by the agglomeration of
Fe on the underlying Si-NDs due to the local heating of sample surface caused by the recombination of atomic
hydrogens on the Fe film surface to from H2 molecules, which enhances the surface diffusion of Fe atoms on the
sample surface. To characterize magnetic properties of the NDs, in-plane magnetization curves (M-H curves) were
measured within a magnetic field range of ±1kOe by an alternation gradient magnetometer at room temperature (Fig.
2). The M-H curve shows ferromagnetic property with the coercivity, meaning the formation of ferromagnetic NDs.
The result suggests that silicidation reaction occurred simultaneously with the agglomeration of Fe atoms on the Si-
NDs to form Fe3Si phase.
In conclusion, we demonstrated a novel technique for the formation of Fe3Si-NDs on thermally grown SiO2 with
areal density as high as ~1011 cm-2, in which the agglomeration with cohesive action of Fe on Si-NDs accompanied
with silicidation reaction was promoted by H2-RP exposure without external heating.
Acknowledgements
This work was supported in part by Grant-in Aids for Young Scientists
(A) 16H06083 from the Ministry of Education, Culture, Sports,
Science and Technology, Japan.
Reference
[1] Y. Nakamura, et al., Jpn. J. Appl. Phys. 50, 015501 (2011).
[2] M. Naito, et al., Thin Solid Films 539, 108 (2013).
[3] A. Ionescu, et al., Phys. Rev. B 71, 1 (2005).
[4] H. Zhang, et al., Jpn. J. Appl. Phys. 55, 01AE20 (2016).
Fig. 1 AFM images of Si-NDs (a) and Fe/Si-NDs stack structure before (b) and after H2-RP exposure (c).
Fig. 2 In-plane magnetization curves of Fe/Si-NDs stack structure exposed to H2-RP, which was measured at room temperature.
Abstract Guideline (Leave two lines for presentation number) Applications of the Materials Genome Initiative to Advanced Thin Film Materials
*M. L. Green1, N. Nguyen1, Z. Trautt1, A. Zakutayev2, J. Perkins2, and T. Chikyow3 1National Institute of Standards and Technology (NIST), USA, 2National Renewable Energy Laboratory (NREL), USA, 3National Institute of Materials Science, Japan *[email protected] (Corresponding author) Keywords: Novel thin film materials, Materials Genome Initiative, high-throughput materials science, data curation, metrology. The Materials Genome Initiative (MGI) has as its main goal the discovery, optimization, and commercial deployment of advanced materials twice as fast as today’s practice, and at reduced cost. Therefore, the MGI has important applications for novel, advanced thin film materials. Thus far, the MGI has resulted in significant progress in computational simulation, modeling, and predictions of materials properties. However, prodigious amounts of experimental data are necessary to inform and validate these computational models. High-throughput experimentation (HTE), which enables accelerated synthesis and testing of materials, is uniquely suited to rapidly generate such high quality experimental data1. However, there remain serious challenges that the materials community must overcome to enable widespread deployment of an MGI-type approach to novel materials development. For example, data, both experimental and simulated, must be made discoverable, accessible, and interoperable. Further, even one “brick and mortar” high-throughput experimental facility would be very costly, whereas multiple facilities dedicated to different materials classes (e.g., electronic materials, catalysts, photovoltaics, thermoelectrics) would be needed. Therefore, I will introduce the concept of a “High Throughput Experimental Materials Virtual Laboratory” (HTE-MVL) to facilitate MGI-driven research. The virtual laboratory would consist of an integrated, delocalized network of high-throughput synthesis and characterization tools, as well as a best-in-class, configurable data curation system, consisting of NIST, NREL, NIMS (and other) materials resource registries and materials data repositories. Ultimately, users of the HTE-MVL, such as researchers at national labs, universities, and industry, could leverage it to facilitate the rapid development and commercialization of novel materials, devices and products. I will discuss actual experimental results, generated using the HTE-MVL model, for advanced thin film materials.
Schematic illustration of the High-throughput Experimental Materials Virtual Laboratory (HTE-MVL).
1) “Applications of High Throughput (Combinatorial) Methodologies to Electronic, Magnetic, Optical, and Energy-related Materials,” Martin L. Green, Ichiro Takeuchi, and Jason R. Hattrick-Simpers, Journal of Applied Physics (Applied Physics Reviews), 113 (23), (2013).
When GaN and Si Tango, Thermal Mismatches are Overcome for Thick GaN-on-Si Vertical Power Devices A. Tanaka1), W. Choi2), R. Chen2), and *S. A. Dayeh1,2) 1)Materials Science and Engineering Program, University of California San Diego 2)Department of Electrical and Computer Engineering, University of California San Diego *[email protected] Keywords: Gallium Nitride on Silicon, Metalorganic Chemical Vapor Deposition (MOCVD), Selective Area Growth, Vertical Field Effect Transistors, High Power Devices
Since the great emergence of high-brightness gallium nitride (GaN) blue LEDs in 1990s, GaN has been also vowed as a strong contender for next-generation high power devices with high frequency of operation due to its superb material characteristics. The ability to grow thick drift layers of GaN on Si using conventional Metal Organic Chemical Vapor Deposition (MOCVD) is a long-cherished desire to achieve vertical high power GaN devices and to hold high voltage in the vertical direction. However, but the the huge thermal mismatch between GaN and Si inhibits the growth of thick crack-free GaN layers on Si. The development of bulk GaN substrate growth technologies such as Na-flux, hydride vapor phase epitaxy and ammonothermal methods, vertical GaN devices with high quality thick drift layers are becoming more feasible1),2) despite remaining challenges of cost, reliability and uniformity issues for these growth techniques.
In this work, we shed new light on GaN growth on Si again by a thorough study on selective area growth of thick (>10 µm) and crack-free GaN-on-Si by MOCVD. We performed mechanistic studies to understand cracking associated with thermal stresses and created structures to accommodate these stresses in order to grow layers with center thicknesses exceeding 19 µm of crack-free GaN on Si. From time dependent growth studies on SAG GaN-on-Si, we identified the cracking planes in GaN to be of the 0110 family and recognized that the 0111 type growth facets can transfer the thermal mismatch stresses from the crack planes to the surface. We then tailored our growth structure and conditions to preferentially form the 0111 SAG GaN-on-Si facets3) which reduced the stresses in the GaN dots as validated by Raman spectra peak shift and resulted in crack-free 19 µm thick GaN-on-Si. The threading dislocation density also decreased as the GaN film thickness increased and was verified by cross-sectional transmission electron microscopy (TEM). The lowest dislocation density we achieved is 1.1 x 107 cm-2 at the surface of the 19 µm GaN dot which is nearly one order of magnitude lower than state-of-the-arts value of 9.7x107 cm-2 for GaN-on-Si.4) We then fabricated vertical Schottky and pn junctions and demonstrated the first vertical GaN-on-Si metal-insulator-field-effect-transistor (MISFET) with over 19 µm GaN drift layer as shown in Fig. 1 exhibiting ~107 Ion/Ioff ratio and a threshold voltage of ~7V. This level of performance for GaN-on-Si MISFETs approaches that achieved on GaN-on-GaN devices and further optimizations are still required to achieve high breakdown voltages and low Ron. The Si CMOS integration of gate drive circuits for the vertical GaN power device is underway and will be presented in the conference. References: 1) H. Ohta et al., IEEE Electron Device Letter 36, 1180 (2015). 2) H. Nie et al., IEEE Electron Device Letter 35, 939 (2014). 3) A. Tanaka et al., Scientific Reports 5, 17314 (2015). 4) S. L. Selvaraj et al., IEEE Electron Device Letter 33, 1375 (2012).
Fig. 1 (a) Schematic structure of the GaN vertical MISFET on Si. (b) Side view SEM image of the MISFET device. (c) Transfer and (d) output characteristics showing on/off ratio ~107 and threshold voltage ~7V.
0 1 2 3 4 50.00.20.40.60.81.01.21.41.6
after stressWG = 50x2 = 100 µm
VG,max=20 V, DVG=-2 V
I D [m
A]
VD [V]
100µm
a. b.
c. d.
Direct laser writing of single walled carbon nanotubes for high performance
gas sensors
*A. Palla Papavlu
1), M. Dinescu
1), A. Wokaun
2), and T. Lippert
2)3)
1)National Institute for Lasers, Plasma, and Radiation Physics, Atomistilor 409, Magurele, Romania,
2) Research
with Neutrons and Muons Division, Paul Scherrer Institut, 5232 PSI-Villigen, Switzerland, 3)
Laboratory of
Inorganic Chemistry, ETH Zürich, Zürich, Switzerland *[email protected] (Corresponding author)
Keywords: laser direct writing, carbon nanotubes, sensors, ammonia, hydrogen peroxide
The area of printed electronics enables new applications ranging from low-cost, disposable analytical devices to
large-area sensor networks. In this work, research challenges and opportunities focusing on processing and
system-level integration of carbon nanotubes for enabling practical applications, i.e. chemiresistor gas sensors, are
presented.
The large-scale application of semiconducting single-walled
carbon nanotubes (SWCNTs) for printed electronics requires scalable,
repeatable, as well as non-contaminating assembly techniques.
This paper describes a rapid, solvent-free procedure for the fabrication of
sensitive sensors based on carbon nanotubes on flexible surfaces that
overcomes challenges associated with solvent-assisted chemical
functionalization and integration of these materials into devices.
The sensor fabrication technique is based on the laser-induced forward transfer
(LIFT) process assisted by a triazene polymer layer for the spatial transfer of
single walled carbon nanotubes. A schematic drawing of the transfer process is
shown in figure 1. LIFT is a simple process where a laser beam is focused
through a transparent substrate onto a material film to be transferred. Every
single pulse promotes the transfer of the thin film material onto a substrate that
is usually placed parallel and facing the thin film at very short distances.
With LIFT, SWCNTs are transferred, with a transfer yield of nearly 100%, Figure 1. Scheme of the sensor
fabrication process
to fabricate chemiresistive devices. The as printed carbon material maintains its original geometry, and the chemical
and structural properties with high fidelity. In addition, the performance, i.e. the sensitivity, resolution, and response
time of the laser-printed flexible sensor devices was evaluated by exposure of the sensors to different toxic vapors.
Different sensitivities and selectivity to the selected analytes i.e. acetone, ethanol, ammonia, H2O2, etc. have been
measured thus proving the feasibility of LIFT for applications in flexible sensing devices.
Lithography-free planar perfect absorbers for wide acceptance angle and
polarization-independent spectrally selective infrared devices
Tung Anh Doan 1,2) , Thang Duy Dao1) , Shatoshi Ishii1), *Tadaaki Nagao1,2) 1)International Center for Materials, Nanoarchitectonics (MANA), National Institute for Materials Science (NIMS),
Tsukuba, Ibaraki 305-0044, Japan, 2)Department of Condensed Matter Physics, Hokkaido University, Sapporo
060-0810, Japan. *[email protected]
Keywords: lithography-free, tri-layer planar films, wide incident angle, polarization-independent,
spectrally-selective perfect absorber.
Since the first experimental demonstration of metamaterial perfect absorber (MPA) [1], many efforts have been
made to obtain MPAs that have wide incident angle and polarization independence suitable for practical applications
such as for energy harvesting, bio-chemical sensing [2], light emission [3] and infrared (IR) sensing [4]. In most of the preceding studies, periodic metamaterial structures were fabricated by elaborate lithographic techniques which
showed significant angle dependence on the incident beam direction. In this paper, we demonstrate lithography-free,
tri-layer planar films with wide acceptance angle and polarization independent feature with wavelength-selective
perfect absorption. The proposed device can be realized by simple fabrication process and is operative in the near to
mid-IR regime. The structure consists of a dielectric middle layer sandwiched between a thin metallic top layer and
a thick metallic bottom layer (Fig. 1. a).
It is shown that near perfect absorption can be achieved due to the coupling of incident IR radiation to the
fundamental Fabry-Perot resonance mode. The perfect absorption peak is almost unchanged until the incident angle
reaches ±70 degrees for either transverse electric or magnetic polarization (Fig. 1. b). The geometrical parameters of
the three layers (Au, Ag or W as metallic layers and Si and Al2O3 as a dielectric layer) of the structure are determined and optimized by the numerical electromagnetic simulation and then fabricated by sputtering deposition.
The proposed results open up great opportunities for realizing cost-effective spectrally selective perfect absorbers
with reduced fabrication process in the IR regime which can be easily integrated with complementary metal oxide
semiconductor (CMOS) technology for IR signal processing, circuitry or image sensing for night vision. It is also
applicable for thermal detection for human sensors as well as cost-effective IR light sources with high efficiency.
Acknowledgements
This work was supported by CREST program from Japan Science and Technology Agency (JST), and KAKENHI
program from Japan Society for the Promotion of Science (JSPS).
References:
1) N. I. Landy, S. Sajuyigbe, J. J. Mock, D. R. Smith, and W. J. Padilla, Phys. Rev. Lett., 100, 207402 (2008).
2) Chen, K., Dao, T. D., Ishii, S., Aono, M., and Nagao, T., Advanced Functional Materials., 42, 6637-6643 (2015).
3) Yokoyama, T. Dao T.D., Chen, K., Ishii, S. , Sugavaneshwar, R.P. , Kitajima, M., and Nagao, T., Advanced
Optical Materials., 4 (12), 1987-1992 (2016).
4) Dao, T.D., Ishii, S., Yokoyama, T., Sawada, T., Sugavaneshwar, R.P., Chen, K., and Nagao, T., ACS Photonics.,
3 (7), 1271-1278 (2016).
Fig. 1. (a) Schematic representation of spectrally-selective perfect absorber. (b) Simulated absorption spectra of the tri-layer planar W/Si/W perfect absorber with regard to the incident angle.
6th
WMO Symposium on Data Assimilation -- 2013
Metal Oxide Nanostructures – An Approach for High Performance Resistive
Random-Access Memory
Dewei Chu, Adnan Youins and Sean Li
School of Materials Science and Engineering, The University of New South Wales, NSW 2052, Australia
Nanocapacitors are the key component in resistive random access memory (RRAM) for next
generation nanometre scaled electronic devices. It is believed that bottom up approach is a
cost effective technique compared with the other nanotechnologies. In this work, we report a
novel procedure for fabricating high performance nanocapacitors by using oxide nanocubes as
colloidal building blocks. The nanocubes of CeO2, which was synthesised with hydrothermal
methodology, were used to build the nanocapacitors through the capillary force assisted self-
assembly approach. Such a synthesis results in a large area of high quality ordered structure
with several square millimetres due to the narrow size and shape distributions of nanocubes in
non-polar organic solvents. The as-fabricated nanocapacitors exhibited excellent resistive
switching properties with very large ON/OFF ratios, good reliability and stability. These
demonstrate the developed technique is a promising approach for the fabrication of next
generation RRAM devices.
Multi-level Resistive Switching Achieved by Multi-layer Thin Film of Pure
and Mn-doped SnO2 Nanoparticles
Z. Xu,
*D. Chu, A. Younis, and S. Li
School of materials science and engineering, Faculty of Science, University of New South Wales, Sydney, Australia *[email protected]
Keywords: Metal oxides; Multi-layer thin film; Multi-level resistive switching; Self-assembly nanoparticles
Well self-assembled pure and Mn-doped SnO2 nanocrystals were synthesized by interface solvothermal method,
which is ideal for highly homogeneous large scale thin film deposition on flexible substrates for various electric
devices. Mn-doped SnO2 shows very good resistive switching with high On/Off ratio (over 103), endurance and
retention characteristics. More important, the resistive state can be tuned by multi-layer fabrication by alternate pure
SnO2 and Mn-doped SnO2 nanoparticle layer, which improved the memory capacity of resistive switching
effectively. Thus, such a method provides transparent, multi-level resistive switching for next generation
non-volatile memory applications.
Abstract Guideline (Leave two lines for presentation number)
Micro-Tensile Testing of Pulse Electroplated Gold for Application as Movable
Structure in MEMS Device
S. Yanagida1)2), *T.-F.M. Chang1)2), C.-Y. Chen1)2), T. Nagoshi3), D. Yamane1)2), K. Machida1)2)4),
K. Masu1)2), and M. Sone1)2) 1)Tokyo Institute of Technology, Yokohama, Kanagawa, Japan, 2)CREST, Japan Science and Technology Agency, 3)National Institute of Advanced Industrial Science and Technology, 4)NTT Advanced Technology Corporation *[email protected]
Keywords: Electroplated gold, Micro-tensile test, Hall-Petch relationship, MEMS accelerometer
Au materials are often used as micro-components in
MEMS devices because of their high electrical
conductivity, chemical stability, corrosion resistance,
and ductility. An enhancement in the sensitivity of a
MEMS is reported when using Au-based movable
structures as the key component [1]. The improved
sensitivity is mostly contributed by the high density of
Au. Density of Au is about 10 times higher than that of
silicon, which is currently the commonly used material
in MEMS accelerometers. In addition, the high density
is promising in further miniaturization of MEMS
accelerometers. For application of materials in MEMS,
it is necessary to clarify the mechanical property in micro-scale.
Mechanical behaviors of materials in small dimensions are different
from that of bulk materials, which is known as the sample size effect
[2]. Au is known to be a relatively soft metallic material, therefore, it
is especially important to evaluate the micro-mechanical property for
the applications in MEMS.
In this study, two kinds of electroplated Au samples were
evaluated. One was prepared by constant current electroplating (CE),
and the other was by pulse current electroplating (PE). Micro-tensile
specimens having dimensions of 10 × 10 × 40 μm3 were fabricated
by focus ion beam (FIB), as shown in Fig. 1, and tested by a testing
machine specially designed for micro-sized specimens.
Average grain sizes for the CE and the PE were 1.6 and 0.3 μm,
respectively. Both specimens showed concentrated deformation and
necking in part of the specimen after the tensile test as shown in Fig.
2. Engineering stress-strain curves of the specimens show that the
flow stresses are decreased in the plastic deformation region caused
by the necking. The results show that effects of the necking are
enlarged and amounts of the elongation is decreased similar to
ductile materials when dimensions of the specimen are in micro-scale.
0.2% proof stresses for the CE and the PE are 316 and 387 MPa,
respectively. Maximum stresses (when the elastic deformation is
finished) for the CE and the PE are 344 and 457 MPa, respectively.
Generally, yield stress of Au materials is 100~200 MPa. The Au
samples prepared by electroplating, especially for PE, both showed
higher strengths caused by grain boundary strengthening mechanism.
The results obtained in this study correspond well with the
Hall-Petch relationship.
References:
1) D. Yamane, T. Konishi, T. Matsushima, K. Machida, H. Toshiyoshi and K. Masu, Appl. Phys. Lett., 104, 74102
(2014).
2) M. D. Uchic, D.M. Dimiduk, J.N. Florando, and W.D. Nix, Science, 305, 986-989 (2004).
3) Y. Kihara, T. Nagoshi, T.-F.M. Chang, H. Hosoda, T. Sato and M. Sone, Mater. Lett., 153, 36-39 (2015).
Fig. 1 Fabrication process of the micro-specimen by
FIB.
Fig. 2 SEM images of the tensile
specimens: (a) CE sample before the
test, (b) PE sample before the test, (c)
CE sample after the test, and (d) PE
sample after the test.
Presentation number
Deformation Behavior of Electroplated Gold Micro-Pillars for MEMS
Accelerometers
*C.-Y.Chen1)2), Y. Yoshiba1)2), T.-F. M. Chang1)2), T. Nagoshi3), D. Yamane1)2), K. Machida4), K.
Masu1)2), and M. Sone1)2) 1)Tokyo Institute of Technology, Yokohama, Kanagawa, Japan, 2)CREST, Japan Science and Technology Agency, 3)National Institute of Advanced Industrial Science and Technology, 4)NTT Advanced Technology Corporation *[email protected]
Keywords: micro-compression test, electroplating, MEMS, texture, nano-crystal
Au materials have been studied as a structure materials for micro-electro-mechanical systems (MEMS) devices
because Au possesses high chemical stability, corrosion resistance, electrical conductivity, and especially high
density (19.30 gcm-3). Yamane et al. proposed Au-based MEMS accelerometers could attain a much higher
sensitivity than that of conventional Si-based MEMS accelerometers1). The Au-based MEMS accelerometer
fabricated by electroplating is compatible with post-CMOS process. This fabrication process enables to achieve
CMOS-MEMS integration, which could further reduce MEMS device size. Therefore, electroplating is a potential
candidate in fabrication of Au micro-components used in MEMS2,3).
Cyanide-based Au electrolyte is commonly used in industry because of its high stability even though it has
toxicity. In this study, Au films electroplated from cyanide-based electrolyte showed unusual mechanical properties,
such as brittle fracture and much higher yield stress of 650 MPa than that of bulk Au4). Moreover, columnar
textures/grains of Au film may have great influence on the mechanical properties. Micro-compression tests were
conducted with different loading direction, which was parallel/perpendicular to the grain growth direction. The Au
film shows strong anisotropy of deformation behavior and mechanical properties because of nano-columnar Au
grains embedded in micro-columnar textures. To the best of our knowledge, there is no report of texture orientation
dependent mechanical properties of polycrystalline Au film, and this study provides essential information especially
for Au-based MEMS accelerometers design.
References:
1) D. Yamane, T. Konishi, T. Matsushima, K. Machida, H. Toshiyoshi, K. Masu, Appl. Phys. Lett., 104, 074102
(2014).
2) C.-Y. Chen, M. Yoshiba, T. Nagoshi, T.-F.M. Chang, D. Yamane, K. Machida, K. Masu, M. Sone,
Electrochem. Commun., 67, 51-54 (2016).
3) H. Tang, C.-Y. Chen, T. Nagoshi, T.-F.M. Chang, D. Yamane, K. Machida, K. Masu, M. Sone, Electrochem.
Commun., 72, 126-130 (2016).
4) M. Yoshiba, C.-Y. Chen, T.-F.M. Chang, T. Nagoshi, D. Yamane, K. Machida, K. Masu, M. Sone, Mater.
Trans., 57, 1257-1260 (2016).
Fig. 1. SIM images of (a) (b) Au micro-pillar 1 and (c) (d) micro-pillar 2 before and after compression test.
Perpendicular Magnetic Properties of [CoPt/AZO/Ag] Multilayered Films for
Magneto-optical Chemical Sensing Applications
*H. Yamane
1), Y. Kondo
1), Y. Isaji
2), K. Takeda
2), and M. Kobayashi
2)
1) Akita Industrial Technology Center, Araya, Akita 010-1623, Japan,
2) Chiba Institute of Technology
Keywords: perpendicular magnetic, magneto-optical, CoPt, chemical sensor
Improvements in magneto-optical (MO) effects due to plasmon resonances and magneto-photonic crystals have
been extensively studied. A huge MO Kerr rotation angle (K) can be obtained by an optical interference (cavity)
effect in perpendicular magnetic multilayers consisting of [magnetic metal/optical interference dielectric/reflection
metal] stacked structures. We recently reported a new type of chemical sensor using the MO cavity effect.1,2)
The
MO cavity sensors require good perpendicular magnetic properties. In this research, we investigated the
perpendicular magnetic properties of [CoPt/AZO/Ag] multilayered films.
Samples were fabricated by magnetron sputtering onto a glass
substrate with a 10-nm-thick Al-doped ZnO (AZO) seed layer. The MO
cavities consisted of multilayered structures including hcp-Co80Pt20
perpendicular magnetic, AZO optical interference and Ag reflection
layers. Figure 1 shows the polar Kerr spectra of the CoPt(5 nm)/Ag(100
nm) stacked films with and without a 60-nm-thick AZO intermediate
layer. A large Kerr rotation angle of approximately 20 degrees was
obtained by inserting the AZO intermediate layer. This MO
enhancement is due to the MO cavity effect, in which the AZO
intermediate layer acts as an optical interference layer. The MO cavity
can be used as optical chemical sensors because the MO properties of
the stacked films are sensitive to the optical conditions of film surface.
The AZO intermediate layer was also effective to improve the
perpendicular magnetic properties of the CoPt layer. As described in Fig.
1, the [CoPt/AZO/Ag] stacked films indicated an ideal square polar
Kerr loop. The XRD measurements suggested that this magnetic
improvement was due to the improvement of CoPt crystallinity. The
perpendicular magnetic anisotropy of the hcp(001) oriented CoPt film is
decreased by the fluctuation of the crystalline orientation. Figure 2
shows the in-plane XRD profiles of CoPt/Ag stacked films with and
without a 2-nm-thick AZO intermediate layer. Both films show two
diffractions from the CoPt layer at low and high angle regions. These
peaks are identified as the diffractions from the hcp(100) plane and from
the hcp(110) and/or fcc(220) planes, respectively. The ratio of the
intensities of these peaks can be used as an index for the stacking faults
in hcp(001) orientated films. The ratio of the integrated intensities
(IL/IH) was increased from 1.16 to 1.36 by inserting the AZO layer into
the CoPt/Ag interface, i.e. the AZO layer was effective to reduce the
content of stacking faults in the CoPt film along the surface normal.
Moreover, the magnetic properties of the [CoPt/AZO/Ag] stacked films
were influenced by an AZO overcoat layer fabricated on the top of
stacked films. As described in Fig. 3, the AZO overcoat layer reduced
the squareness ratio of polar Kerr loops (blue). This magnetic
deterioration can be suppressed by air exposure for the CoPt layer (red).
High energy XPS measurements suggested that this phenomenon was
due to the difference in surface oxidized condition of the CoPt layer.
This study was partly supported by JSPS KAKENHI (Grant
No.26390091) and SPring-8 (Proposal No.2016A1226).
References:
1) H. Yamane et al., Materials Transactions, 57, 892-897 (2016),
2) H. Yamane et al., Digest of MNC 2016, 10P-7-21 (2016).
Fig. 1. Polar Kerr spectra of CoPt/Ag stacked films with and without AZO intermediate layer.
Fig. 2. In-plane XRD profiles for CoPt/Ag stacked films with and without AZO
intermediate layer.
Fig. 3. Effect of air exposure on perpendicular magnetic properties of [AZO/CoPt/AZO/Ag]
stacked films.
Large-scale growth of high-quality 2D layered materials for transparent,
flexible and high performance photodetector
Z. Q. Zheng, J. D. Yao, G. W. Yang*
State Key Laboratory of Optoelectronic Materials and Technologies, Nanotechnology
Research Center, School of Materials Science & Engineering, Sun Yat-sen University,
Guangzhou 510275, Guangdong, P. R. China.
Because of their exotic electronic and optical attributes, layered materials have
generated immense interest for application in next generation electronics and
optoelectronic devices, including solar cells, light-emitting diodes and transistors. For
photodetection applications, high performance photodetectors have attracted
significant attention owing to their widely applications. Compared with traditional
photodetectors which are typically based on conventional semiconductor materials
(e.g. silicon), layered materials-based optoelectronic devices often exhibit higher
responsivity and even faster response due to their strong light-matter interaction
properties and large surface-to-volume ratio.
In recent years, transparent and flexible photodetectors, which are unreachable
with standard rigid technology, hold the promise to open up unprecedented
applications in innovative wearable optoelectronic system. These characteristics have
initiated different strategies to develop layered material-based transparent and flexible
photodetectors with demonstrated high efficiency. However, several key challenges
lie ahead before such layered materials can be integrated into complex circuits,
because the traditional methods do not provide large-area coverage and systematic
control of the film thickness.
To overcome these issues, we introduce pulsed-laser deposition (PLD) for the
deposition of centimeter-scale superior quality multilayer In2Se3 and WSe2 film on
multiple substrates, including transparent polyimide (PI), conventional SiO2/Si,
commercial PI and transparent sapphire substrates. Compared with traditional
approaches, PLD is a scalable deposition technique that can render fairly
stoichiometric atomic species transfer from a target precisely onto a substrate, and
offers well thickness control based on the number of pulses. Especially, the fabricated
devices on transparent PI substrate conduct a flexible transparent property and
broadband photoresponse ranging from 370 to 1064 nm. In addition, the resulting
WSe2 photoresistor demonstrates stable photo-switching behavior and high
responsivity of 0.92 A/W. On the other hand, benefit from the direct bandgap of
In2Se3, a photodetector with excellent responsivity of 20.5 A/W and detectivity of
6.02×1011
Jones is demonstrated2. Accordingly, these finding indicate a possible new
strategy for the design and integration of flexible, transparent and broadband
photodetectors based on large-area layered materials films, with great potential for
practical applications in the wearable optoelectronic devices.
Ultra-flexible Freestanding ZnO Nanosheets: A Novel Material for Highly
Sensitive Chemiresistive Sensors
*Ganesh Kumar Mani1) Kousei Miyakoda2), Asuka Saito2), Yutaka Yasoda2), Gaku Tsuruzoe2),
Kazuyoshi Tsuchiya1), 3) 1) Micro / Nano Technology Center, Tokai University, 4-1-1 Kitakaname, Hiratsuka, Kanagawa, 259-1292, Japan. 2) Graduate School of Science and Technology, Tokai University, 4-1-1 Kitakaname, Hiratsuka, Kanagawa, 259-
1292, Japan. 3) Department of Precision Engineering, Tokai University, 4-1-1 Kitakaname, Hiratsuka, Kanagawa, 259-1292,
Japan.
[email protected] (Ganesh Kumar Mani)
Keywords: Nanosheets, gas sensor, ammonia, ZnO, PLLA
Exhaled human breath consists mixture of numerous organic and
inorganic compounds with concentrations ranging from ppb to ppm.
Currently, number of biomarkers were identified in breath samples that
could be used to identify the diseases. Among which ammonia (NH3)
has been proposed as a potential biomarker in monitoring hemodialysis
(HD) adequacy. In the last few decades, many materials have been
developed for NH3 sensor, but still there is a huge demand for highly
sensitive, flexible and suitable to integrate with embedded systems is
needed. In this scenario, free standing nanosheets may offer excellent
flexibility as well as high gas sensitivity, moreover can be deposited on
biocompatible substrates like Poly lactic acid (PLLA). Many
nanomaterials can be deposited on single nanosheets and can be used a
skin patch. At first, polyvinyl alcohol (PVA)/PLLA layers were initially
spin coated on Si substrates and then zinc oxide (ZnO) was deposited
on PLLA by RF magnetron sputtering technique. Then, PVA layer was
sacrificed in water and free standing PLLA/ZnO layer was collected. Finally the PLLA/ZnO nanosheets were
transferred into interdigitated electrode for sensing studies. Meanwhile, their structural, elemental and morphological
properties were investigated by XRD, EDS, XPS and FE-SEM. To probe the selectivity nature of the sensing elements,
PLLA/ZnO nanosheets were tested with three different vapours. Results showed that, the sensing response towards
ammonia was higher than others. The transient resistance response, stability, response and recovery times were also
investigated.
References 1. G. K. Mani and J. B. B. Rayappan, Sensors Actuators B Chem., 183, 459–466 (2013).
2. 1 G. K. Mani and J. B. B. Rayappan, Mater. Sci. Eng. B, 191, 41–50 (, 2015).
Fig. 1 Flexibility of the free standing nanosheets on
interdigitated electrode
Resistive Based Microfluidic pH Sensor: A Novel Approach
*Ganesh Kumar Mani1), Dhviya Ponnusamy1), Madoka Morohoshi2), Hiroshi Kimura3), Yuta
Sunami1), 4), Kazuyoshi Tsuchiya1), 4) 1) Micro / Nano Technology Center, Tokai University, 4-1-1 Kitakaname, Hiratsuka, Kanagawa, 259-1292, Japan. 2) Graduate School of Science and Technology, Tokai University, 4-1-1 Kitakaname, Hiratsuka, Kanagawa, 259-
1292, Japan. 3) Department of Mechanical Engineering, Tokai University, 4-1-1 Kitakaname, Hiratsuka, Kanagawa, 259-1292,
Japan. 4) Department of Precision Engineering, Tokai University, 4-1-1 Kitakaname, Hiratsuka, Kanagawa, 259-1292,
Japan.
[email protected] (Ganesh Kumar Mani)
Keywords: ZnO, thin film, microfluidics, sensitivity, pH
Precise montioring of pH in microlitre liquids is desired for many
biomedical applications. Since today, there is no adequate microfludic
device was fabricated with low cost and high sensitivity. The present study
is concerned about the development of highly sensitive solid state
resistance based microfluidic pH sensor for Bio-MEMS applications. At
first the microfludic channel was prepared in polydimethysiloxane (PDMS)
using the master pattern created in acryl by computer numerical control
(CNC) micro milling machine. ZnO thin film was deposited on glass
substrates (20 x 20 mm) by RF sputtering technique. Finally, glass with
ZnO thn film and PDMS microfludic device bonder via. plasma bonding.
pH sensing studies were done by potentiometric method according the
resistance change in ZnO. . The pH level of each test solution was
confirmed by a commercial pH glass-electrode. The sensitivity of the developed microfluidic device was validated by
passing various pH buffer solutions for a period of time at room temperature through the microfluidic channel with
the support of syringe pump. The fabricated sensor exhibited the super – Nernstian response of 50 mV/pH. The pH
sensing measurements show reproducible potentials for each pH value with shorter response times.
References 1. G. K. Mani, M. Morohoshi and Y. Yasoda, ACS Appl. Mater. Interfaces, 9, 5193–5203 (2017).
Fig. 1 Schematic of the proposed microfluidic pH
sensor
I-V characteristics of nanowire based resistive change memory T. Aono1), K. Sugawa1), T. Shimizu2), S. Shingubara2), K. Takase1)
1)College of Science and Technology, Nihon University, Chiyoda-ku, Tokyo 101-8308, Japan 2)Graduate School of Science and Engineering, Kansai University, Suita, Osaka 564-8680, Japan
E-mail: [email protected] Keywords : ReRAM, Nanowires,
1. INTRODUCTION
Resistive switching random access memory (ReRAM) has been expected to a next generation memory due to high-speed response, non-volatility, low power consumption [1]. However, poor reproducibility of a switching voltage hinders the practical application. According to a filament model, many kinds and number of filaments made at the soft breakdown of an insulator are thought to be the origin. In our previous studies, we employed anodic porous alumina (APA) with ordered nanoholes as the insulator of ReRAM because nanoholes are expected to inhibit the growth of conductive filaments spacially. In the result, we succeeded in suppression of the switching voltage variation [2].
Looking at the top view of SEM image of APA (Fig. 1), we notice no restriction along the dashed lines. It means that there exist a division indicating a bulk property. In this study, a nanowire based insulator has been focused on to confine the filaments omnidirectionally.
2. EXPERIMENTS Nickel nanowires were buried into nanoholes of APA using electroplating method, where nickel sulfate was
used as an electrolyte solution. The exposed Ni nanowires were obtained by chemical etching the alumina layer. The nanowires were oxidized by oxygen plasma for 1, 3, 5 min. The surface morphology of nanowires was investigated by a field emission scanning electron microscope (FE-SEM). For a contact preparation, Indium solder was used against the top electrode. The bottom electrode was a residual aluminum substrate. The I-V characteristics of NiO nanowires were measured by a standard two-probe method at room temperature, where the current was limited to 1 mA in a SET process guard the device from a complete dielectric breakdown.
3. RESULTS Figure 2 (a) ~ (c) shows the cross-sectional SEM images of NiO nanowires. The diameter and the length are
about 40 nm and 600 nm, respectively. Significant oxidation time dependence was not found in the shape. Figure 2 (d) ~ (f) show the I-V characteristics. In case of 1 min oxidation, a relatively wide distribution of the switching voltage is measured. The distribution range narrows at once in 3 min oxidation and widens again in 5 min oxidation. 1 min oxidation state is near the bulk state even though the oxidation thickness seems to be the thinnest. In this study, plasma source was used for the oxidation. So, long time oxidation makes the film amorphous by high kinetic energy of oxygen. The relatively high current found in the RESET process in case of 3 min oxidation might be due to poor crystallinity of the NiO thin film. Thickness of the NiO thickens for longer oxidation time and many filaments can exist in the film. This leads to the wide switching voltage distribution again.
References [1] M. J. Lee et al. Nano Lett. 9, 1475 (2009). [2] Y. Tanimoto et al. Jpn. J. Appl. Phys 54, 06FH05 (2015).
Fig. 2 Cross-sectional SEM images of NiO nanowire (a) ~ (c) and the I-V cures of NiO nanowire ReRAM(red lines for SET, blue lines for RESET processes)
Fig. 1 The top view of APA nanoholes
200 nm
Oxidation : 1 min
500 nm
(a) Oxidation : 5 min
500 nm
(c)Oxidation : 3 min
500 nm
(b)
(d) (e) (f)10
-10 10
-8 10
-6 10
-4
10-2
100
Cur
rent
[A]
3210Voltage [V]
Oxidation : 1 min78 cycle
10-10
10-8
10-6
10-4
10-2
100
Cur
rent
[A]
3210Voltage [V]
Oxidation : 3 min32 cycle
10-10
10-8
10-6
10-4
10-2
100
Cur
rent
[A]
3210Voltage [V]
Oxidation : 5 min36 cycle
Highly Sensitive Trimethylamine Sensor based on VOx-TiOx Thin Films
M. Veena, M. Abinaya, P. Deepak Raj, *M. Sridharan Functional Nanomaterials & Devices Laboratory, Centre for Nanotechnology & Advanced Biomaterials and School
of Electrical & Electronics Engineering, SASTRA University, Thanjavur - 613 401, India.
*e-mail: [email protected] (M.Sridharan)
Keywords: Metal oxides, thin films, sputtering, trimethylamine,
Detection of toxic, pollutant and combustible gases is important for environmental safety and indoor air
quality monitoring. Especially, short-chain amines like trimethylamine (TMA) play a critical role in petrochemical
and pesticide industries. The allowed exposure limit according to National Institute for Occupational Safety and Health
(NIOSH) is 10 ppm. But the available sensor technologies for TMA do not satisfy all the ideal conditions. Transition
metal mixed oxides especially vanadium–titanium mixed oxides (VOx-TiOx) have attracted more towards TMA
detection due to their heterojunction formation, improved selectivity as well reliable phase transitions resulted in good
electrical properties. Hence, in this present work, VOx-TiOx thin films were deposited using DC magnetron sputtering
technique. The structural properties of the films clearly revealed the formation of mixed oxide. The morphological
features were investigated using field-emission scanning electron microscopy and atomic force microscopy
techniques. Room temperature TMA sensing characteristics were done with various concentration levels of TMA and
the observed results are shown in Fig. 1. Also, the sensitivity was greatly improved in mixed oxides compared to mono
oxide (VOx) (Inset to Fig.1). Furthermore, selectivity, transient resistance response, stability were investigated.
References
1. G. Korotcenkov et al., Mater. Sci. Forum, pp. 223–229, 2016
2. Mauro Epifani et al., Journal of Physical Chemistry C, pp. 20697–20705, 2013
3. Maria Cristina Carottaa et al., Journal of the European Ceramic Society, pp. 1409–1413,2004
0 100 200 300 400 50050
60
70
80
90
100
Se
ns
or
Re
sp
on
se
(S
)
Concentration (PPM)
Room temperature response
Vox Vox-TiOx0
20
40
60
80
Sen
so
r R
es
po
ns
e (
S)
100 PPM TMA
Fig 1: Sensor response towards different concentration of TMA vapours
Correlation of Electron Dynamics and Coloration of UV induced Tungsten Oxide *Y. Lee1), G. Shim1) and H. Seo1)2) 1) Department of Energy Systems Research, Ajou University, Suwon 16499, Republic of Korea 2) Department of Materials Science and Engineering, Ajou University, Suwon 16499, Republic of Korea *[email protected] Keywords :WO3, Photochromic, Polaron, pump-probe, UV
Coloration of WO3 has been attracted much attention in various chromic effect such as photo, electro and gasochromic. Polaron theory for explaining the photochromic mechanism has been intensively studied.1) In case of reduced WO3, electron-phonon coupling as polaron gives a rise to near infrared (NIR) absorption, leading to visible coloration. Also, conduction transport is achieved via electron hopping transport between W5+ and W6+ valence state.2) Various approach is used to investigate coloration such as structural, optical, electrical, and chemical characteristic. However, physical characteristic of WO3 in terms of dynamics of excited electrons is relatively deficient than others due to requirement of femto-second laser. Relaxation of excited electrons gives critical information for observing e-phonon coupling as decay time of the process is attributed to such as e-e, e-phonon and phonon-phonon scattering.3) Therefore, the approach to observe a relaxation process will be helpful to unveil correlation between coloration and polaron effect. For ultrafast-time transient spectroscopy, pump-probe spectroscopy is suitable to investigate e-phonon coupling because femto-second laser pulse with shorter than pico-seconds is available to observe e-phonon relaxation. In this study, the nanoporous WO3 films was deposited by RF magneton sputtering with a surface water bonded columnar structure confirmed by Fourier transform infrared spectroscopy. Optical band gap is found at 3.1 eV. UV-vis measurement shows significant NIR absorption after UV light. Reduced W5+ state after UV in 5 % H2/N2 gas is observed using Raman and X-ray photoelectron spectroscopy and O/W ratio is calculated to WO2.74. Change in electronic structure is found from mid-gap state to n-type characteristic with H incorporated sub-peak after UV light by using ultraviolet photoelectron spectroscopy. Pump for excitation (700 nm) – probe for response of material (1000 nm) time transient spectroscopy offered footprint of e-phonon coupling. Fast decay is achieved in 2 pico-seconds and then long time decay over 10 pico-seconds. From obtained results, we confirmed that the coloration is closely attributed to e-phonon coupling. The result from pump-probe measurement demonstrates that excited electrons (or hot electrons) is resonant with NIR probe laser and slowly decay in colored film due to interaction between NIR and e-phonon coupling. In conclusion, this study help to understand correlation between coloration of WO3 and dynamics of electrons.
References 1) E. K. H. SALJE, Eur. J. Solid State Inorg. Chem., 31, 805-821 (1994), 2) Yuping He, Zhenyu Wu, Limin Fu, Chaorong Li, Yanming Miao, Li Cao, Haiming Fan, and Bingsuo Zou, Chem. Mater., 15, 4039-4045(2003). 3) STEPHAN LINK, MOSTAFA A. EL-SAYED, Int. Reviews in Physical Chemistry, 19, 409-453, (2000)
Fig. 1. Normalized transmittance signal of pump (700 nm) – probe (1000 nm) before and after UV light in H2
Cosputtering crystal synthesis and gas sensing performance of cerium-doped tin dioxide thin films with various cerium concentrations
*Y.-C. Liang1), C.-M. Lee1) , and Y.-J. Lo1) 1) Institute of Materials Engineering, National Taiwan Ocean University, Keelung, 202 Taiwan *[email protected] Keywords: Cosputtering, oxides, gas sensor, thin film, doping
The Ce-doped SnO2 thin films with various cerium concentrations were prepared using cosputtering of Sn and Ce metallic targets with different Ce sputtering powers. Tin dioxide (SnO2) is an n-type semiconductor with excellent optical and electrical properties. This semiconducting metal oxide is commercially used for technological devices because of its numerous advantages, including low cost, high chemical stability, high sensitivity to various toxic gases, and compatibility with microfabrication processes. However, for application in gas-sensing devices, its gas-sensing performance requires further improvement for the specific detection of particular gases with high sensitivity. Incorporation of some additives into SnO2 is another approach for improving the gas-sensing performance of SnO2 because doping can alter its structure and grain size or introduce surface defects. These factors are advantageous for enhancing the gas-sensing responses of SnO2 toward specific test gases.
In this study, the Ce-doped SnO2 thin films with various cerium concentrations were prepared using cosputtering of Sn and Ce metallic targets with different Ce sputtering powers. The thin-film growth temperature was maintained at 300 °C with an Ar/O2 ratio of 25:15; the gas pressure during sputtering thin-film deposition was fixed at 2.67 Pa. The as-prepared Ce-doped SnO2 thin films contained cerium in the concentration range 1.2–4.5 at% and exhibited a columnar grain feature with a high crystallinity. The surface roughness of the Ce-doped SnO2 thin films increased with the cerium concentration in the films. As exhibited in Fig. 1 that the cerium doping into the SnO2 thin film increased the surface crystallite size of the film. Moreover, increasing the Ce sputtering power led to the formation of an increased number of oxygen vacancies and Ce4+ ions near the Ce-doped SnO2 thin film surface. The gas sensors made from undoped and Ce-doped SnO2 thin films were placed in a closed vacuum chamber, and various concentrations of ethanol vapor (50, 100, 250, 500, and 750 ppm) were introduced into the test chamber, using synthetic air as the carrier gas. The gas sensing response of the thin-film sensors to ethanol vapor is defined as the Ra/Rg. Ra is the sensor electrical resistance in the absence of target gas and Rg is that in the target gas. The increased number of oxygen vacancies and Ce4+ ions and surface roughness of the 4.5 at% Ce-doped SnO2 thin films prepared using a relatively high Ce sputtering power considerably improved the ethanol-gas-sensing responses of the films in this study. References : 1) Y.C. Liang, C.M. Lee, J. Applied Physics 120, 135306 (2016). 2)Y.C. Liang, C.M. Lee, Y.R. Lo, RSC Adv. 7, 4724 (2017). 3) Y.C. Liang, Y.R. Cheng, CrystEngComm 17, 5801(2015).
Fig. 1. Scanning electron microscope images: (a) undoped SnO2 thin film. (b) Ce-doped SnO2 thin film.
Synthesis and characterization of low-k porous SiO2/PLA films
C.W. Hsiao, T.H. Chang, and S.J. Shih *
Department of Materials Science and Engineering, National Taiwan University of Science and Technology, 43, Sec.
4 Keelung Road, Taipei10607, Taiwan
Keywords: low-k; hybrid film; SiO2; spray pyrolysis
Since smaller size of integrated circuit (IC) components yields higher speed and lower power consumption, which
means that more and more electronic components are allowed to be installed in a volume, however, reducing IC size
causes the signal delay (i.e. resistive-capacitive delay, or RC delay [1]). To minimize the RC delay, the common
strategy is to decrease the values of resistance and capacitance of interconnector. Regarding to reducing the value of
resistance, currently copper material is used to replace alumina material, and it is difficult to find lower resistance
than copper material. Therefore, the low dielectric constant (low-k) materials, decreasing interconnect capacitance,
play the important role for reducing RC delay. Furthermore, the low-k hybrid film is one of potential candidates
because of its superior thermal stability, high chemical resistibility, and low dielectric constant. This study used low
cost porous SiO2 [2] and biodegradable polylactic acid (PLA) to prepare the low-k hybrid film. Porous SiO2 were
synthesized by one-step spray pyrolysis. The starting material are tetraethyl orthosilicate (TEOS) and poly
oxyethylene-poly oxypropylene-poly oxyethylene (F127) as a porogen, and are dissolved into deionized water
becoming a solution. After the processes of atomization, evaporation and calcination, the solid/porous silicate
powders were collected by high voltage electrostatic deposition. Then, by adding 3wt% of porous SiO2 particles into
PLA polymer, the low-k hybrid films were fabricated.
In Figure 1, the scanning electron microscopy (SEM) images of SiO2
particles added with 50vol% F127 porogen, whereas the vol% is defined
as the percentage of the volume of F127 per the volume of TEOS, shows
that the SiO2 particles are porous on the surface. The pores are nanoscale
with average size about 66±22nm and most pores are uniformly dispersed
on the surface of particles. Some large particles collapse inward. The
particle size is around 730±440nm and in addition the particle sizes
become larger with increasing the amount of F127 surfactant. It shows
that the F127 concentration affected the surface morphology and size of
SiO2 particles.
The porosity of the particle is defined that the difference between the
volume of SiO2 powders added with F127 (V2) and the volume of SiO2
without adding F127 (V1) divides the volume of SiO2 powders added
F127 (V2), and the value is taken into percentage. In this study, the
porosities of the SiO2 powders increase with adding more F127. SiO2
powders were mixed into PLA polymer to fabricate hybrid thin film and
were measured the dielectric constant. In this study, the dielectric
constant of PLA hybrid film with solid SiO2 powder (0% of porosity) is
about 3.07. Furthermore, the dielectric constants value for hybrid film
decrease from 2.93 to 2.75 with increasing the porosity of SiO2 from
50.8% to 76.6%, as shown in Figure 2. This study shows that the 50vol%
of F127 sample has the largest porosity (~76.6%) and lowest dielectric
constant (~2.75). It presents that porous SiO2 material is a potential
candidate used on low-k material to improve the problem of RC delay.
References:
[1] J. Rubinstein, P. Penfield Jr, and M.A. Horowitz, Signal delay in RC tree networks, IEEE, 2, 202-211 (1983).
[2] D. Shamiryan, T. Abell, F. Iacopi, and K. Maex, Low-k dielectric materials, Mater. Today, 7, 34-39 (2004).
Investigation of ALD Co ultra thin film on Cu and SiO2
*C. W. Chen, C. Y. Su, and C. C. Kei
Instrument Technology Research Center, National Applied Research Laboratories *[email protected]
Keywords : ALD, Cobalt, ultra thin film, incubation, MFM
In the semiconductor industry, Cu has become the mainstream material as back-end interconnect due to its good
electric conductivity. However, it is easy for Cu to induce electromigration(EM), then voids form and cause
electrical functions failure. Using cobalt as a cover of Cu is one solution for this issue. Atomic layer
deposition(ALD) could deposit conformal ultra thin cobalt film; on the other hand, magnetic force
microscopy(MFM) could be a method to analyze the cobalt film incubation mechanism of ALD, especially with the
low cycle number film.
Cu and SiO2 are applied as substrates of ALD cobalt films to compare the incubation behavior at low cycle
number condition. We prepare ALD Co film with 70 cycle numbers on these two substrates and use MFM to scan
their surface. From the MFM mapping results in Figure 1, the Cu based sample shows the uniform distribution of
magnetic signal from Co , and the SiO2 based one shows no signal, relatively.
We consider ALD Co film has different incubation rates on Cu and SiO2, and it may form the continuous film
only after specific cycle numbers of Co have deposited. It would be quite important issue to investigate since the
thinner and thinner ultra thin Co film is demanding by semiconductor process, and the granular film’s characteristic
could be entirely different from continuous one.
Fig. 1. MFM mapping of ALD Co 70 cycle number on (a) Cu (b) SiO2 substrate
[Abstract Guideline] Unrevealing the catalyzed growth of freestanding graphene on SiC by Fe *F. Song1), K. C. Shen1)2), H. L. Sun1), Z. Jiang1), Y. B. Huang1), Y. Zou1), and J. W. Wells3) 1)Shanghai Synchrotron Radiation Facility and Shanghai Institute of Applied Physics, Chinese Academy of Sciences, 2010204, China 2) Department of Physics, Zhejiang University, 310027, China 3)Department of Physics, Norwegian University of Science and Technology, N-7491, Trondheim, Norway. *[email protected] (Corresponding author) Keywords: Band structure, ARPES, Graphene, SiC, Fe Graphene, the two-dimensional carbon allotrope, has become famous after its successful mechanical cleavage from graphite in 2004 [1]. With amazing properties such as the lightest and strongest material discoved on Earth, and the ability to conduct heat and electricity better than other materials, graphene is expected to be integrated into a huge number of applications. In order to promote the potential applications of graphene, fundamental understanding of the basic properties of is crucial, and therefore, numerous effors have been devoted to the fabrication and characterization of graphen film on various substrates [2]. While the fabrication plays an important role on graphene’s propeties, considerable work has been done to get directed or tailored growth of graphen layers on metal or semiconductor substrates. For example, doping is proved to be an efficient way to tuning the growth and correspondingly the properties. Herein, we thoroughly investiaged the growth of graphene on SiC substrate via the help of Fe film, where the graphene can be obtailed at much lower annealing temperature [3]. Most importantly, the intrinsic properties of Fe catalyzed graphen on SiC is revealed via angle-resolved photoemission spectrum, which clearly indicates the formation of almost free-standing graphene after the Fe film reacts with SiC, which releases free carbon atom floating onto the surface and a FeSiX complex with even more interesing behavior.
References 1) K. S. Novoselov1, A. K. Geim1, S. V. Morozov, D. Jiang, Y. Zhang, S. V. Dubonos, I. V. Grigorieva, A. A. Firsov, Science., 306, 666-669 (2004). 2) A. H. Castro Neto, F. Guinea, N. M. R. Peres, K. S. Novoselov, and A. K. Geim, Review of modern physics, 81, 109 (2009). 3) S. Cooil, F. Song, G.T. Williamsa, O.R. Roberts, D.P. Langstaff, B. Jørgensen, K. Høydalsvik, D.W. Breiby, E. Wahlström, D.A. Evans, J.W. Wells, Carbon, 50, 5099-5105 (2012).
Fig. 1. Band dispersion of graphene around K point, formed on SiC with the assistance of Fe’s catalyst.
Preparation of aluminum film by using low damaging sputtering for OLED negative electrode *Sangmo Kim and Kyung Hwan Kim Department of Electrical Engineering, Gachon University, Senongnam, Korea *[email protected] Keywords: Thin films, low damaging, sputtering, OLED, electrode
Organic-based electronic and optoelectronic device applications such as organic light emitting diodes (OLEDs), organic photovoltaics (OPVs), organic sensors, and organic memories have attracted highly attention due to their low cost, high performance, and flexibility, compare to conventional optoelectronic devices. To improve their higher performance, it is very important to prepare a high-quality metal cathode layer on organic layers [1]. Among a high-quality metal cathode with low work function and high electrical properties such Al, Al–Li, Mg–Ag, Ag, aluminum has been widely used as negative electrode materials due to high electron injection efficiency and chemical stability [3].
However, it is very difficult to deposit cathodes on organic layers without any damage due to their weak and sensitivity to radiation and the bombardment of energetic particles ejected from plasma by using conventional physical vapor deposition (PVD) such as a conventional sputtering technique (magnetron sputtering). In this study, we fabricated Al films by using low damaging sputtering for OLED negative electrode. Facing target sputtering (FTS), as a low plasma-damage-free sputtering technique, has been employed to prepare Al electrode. Figure 1 shows the diagrams of magnetic field between two targets and photo images while sputtering. By inserting York plate on the sputtering gun, we improved the uniformity of the magnet field and made higher density plasma at the center region of the gun. As shown in Figure 1, the plasma density in distributed magnetic field type is distributed uniformly in whole area between both targets. In case of the concentrated magnetic field, most of the λ-electrons are confined at center axis area of both targets, because the confining magnetic field density is higher than other area except near center axis. Therefore, the ionization rate of working gas is high at the center axis, between two targets, so the high-density plasma is formed in there [3]. Figure 2 shown the current-voltage (I-V) characteristics of as-prepared samples. The leakage-current density of OLEDs is more decreased at distributed magnetic field than former case. Therefore, we confirmed that the kinetic energy of particles could be controlled effectively by changing the confining magnetic field.
Fig. 1 Photo images of discharged plasma, schematic diagrams as a function of magnetic field; (a) concentration type and (d) distribution type.
Fig. 2 Current-voltage (CV) characteristics of OLEDs as a function of confining magnetic field; (a) concentrated magnetic field and (b) distributed magnetic field
References 1) I. G. Hill, A. Rajagopal, A. Kahn, and Y. Hu, Appl. Phys. Lett., 73, 662 (1998). 2) Y. Onai, T. Uchida, Y. Kasahara, K. Ichikawa, and Y. Hoshi, Thin Solid Films, 516, 5911–5915 (2008). 3) J. M. Moon and H. K. Kim, J. Elec. Soc., 155 (7), J187-J192 (2008)
The characteristics amorphous TiOx films deposited by electron beam
evaporation of Ti3O5 under different oxygen partial pressure
Sheng-En Huang, Wen-Jen Lee*
Department of Applied Physics, National Pingtung University, Taiwan.
*E-mail: [email protected] Keywords: TiOx film, optical coating, transmittance, optical bandgap, refractive index.
Amorphous titanium oxide (TiOx) films are widely applied to optical
coatings of lenses due to their high refractive index, high transparence in
visible light region, high hardness, and excellent chemical stability. [1-3]
In this work, TiOx films were deposited on n-type Si (100) wafers and
glass substrates by electron beam evaporation without any
substrate-heating. Ti3O5 was used as the starting material, which was
evaporated at different oxygen partial pressures for obtaining TiOx films
with different oxygen contains and properties. Before thin film deposition,
the vacuum chamber was pumped down to a base pressure of 2.50 × 10-7
torr for each depositing process. Then an oxygen gas was introduced to
vacuum chamber by mass flow controller (MFC) for creating different
process pressures via different oxygen flow rates. The depositing pressure
of TiOx films were about 7.20 × 10-6
, 4.60 × 10-5
, 7.10 × 10-5
, 9.80 × 10-5
,
and 1.25 × 10-4
torr for the oxygen flow rate of 0, 2, 4, 6, and 8 sccm,
respectively (shown in Fig. 1). The film deposition rate was monitored
with a quartz crystal microbalance (QCM) and controlled at about 1.0
angstrom per second. The film thicknesses were measured by surface
profilometer. The crystalline structures of films were examined by X-ray
diffractometer (XRD). The surface roughness and morphologies of films
were analysed by scanning probe microscope (SPM). The transmittance
and absorbance spectra of films were measured by UV-Visible-NIR
spectrophotometer, moreover, the optical bandgap of films were calculated
from the absorbance spectrum of films. The wavelength depended
refraction index (n) of films were measured by spectroscopic ellipsometer.
The results show that all films are amorphous structures due to
without any substrate-heating and the films have very smooth surface
morphologies with average roughness (Ra) of about 1.0 nm. Besides, the
thicknesses of films are slightly increased with increasing oxygen flow
rates (shown in Fig. 2) because higher oxygen flow rate creates higher
oxygen partial pressure, which increasing the reactive probability and
oxygen contents of TiOx films. In addition, the visible-light transmittance
and optical bandgaps of TiOx films are also slightly increased with
increasing oxygen partial pressure (shown in Fig. 3 and 4) that can also be
attributed to higher oxygen contents of films. However, the refractive
index of films are decreased with increasing oxygen partial pressure
(shown in Fig. 5) that can be attributed to that the film densities are
decreased with higher oxygen partial pressure because higher pressure
caused lower mean free path.
References:
[1] C. H. Heo, S.-B. Lee and J.-H. Boo, Thin Solid Films, 475, 183-188
(2005).
[2] M. Zhang, G. Lin, C. Dong and L. Wen, Surf. Coat. Technol., 201,
7252-725 (2007).
[3] O. Duyar, F. Placido and H. Z. Durusoy, J. Phys. D: Appl. Phys., 41,
095307 (2008).
Fig. 1. The process pressures and mean free
paths as a function of oxygen flow rate.
Fig. 2. Thickness variations of TiOx films
deposited at different oxygen flow rate.
Fig. 3. Transmittance spectra of TiOx films
deposited at different oxygen flow rate.
Fig. 4. The bandgap energies of TiOx films
extracted from a plot of (αhv)2 vs hv.
Fig. 5. Refractive index of TiOx films
deposited at different oxygen flow rate.
Thermodynamic Assessments of Reactivity at Metal/p-Zn3P2 Interfaces:
Relationship between Interface Structure and Carrier Transport Behavior
*R. Katsube and Y. Nose Department of Materials Science and Engineering, Kyoto University, Kyoto, Japan *[email protected]
Keywords: solar cells, zinc phosphide, chemical potential diagram, Schottky/Ohmic behavior
Carrier transport behavior of metal/semiconductor (M/S) junction is one of key factors in electronic devices. One of
physical properties which describe a character at a junction is Schottky barrier height (SBH). SBH of a certain M/S
junction is often predicted by the Schottky-Mott rule1,2) which assumes a simple contact of surfaces of isolated metal
and semiconductor. However, in most real M/S junctions, some interactions at interface such as atomic
interdiffusion, formation of intermediate compounds, and charge transfer affect carrier transport. This makes it
difficult to understand carrier transport behavior in M/S junctions.
Zinc phosphide (Zn3P2) is a potential candidate as a non-toxic alternative to CdTe3) which is an absorber of
commercial thin-film solar cells. The highest efficiency of Zn3P2-based solar cells was reported using Schottky
junction with Mg.4) Considering Schottky-type solar cells, SBH has a significant impact on conversion efficiency
because SBH would determines the maximum open circuit voltage of device. According to Wyeth and Catalano,5)
carrier transport across M/p-Zn3P2 junctions was also affected by interactions at interface, but reactivity of
M/p-Zn3P2 interfaces has never been studied systematically. In the present study, we thus experimentally and
theoretically investigated the interfacial structures together with current-voltage (I-V) characteristics in M/p-Zn3P2
junctions. As model cases, we selected Al/p-Zn3P2 and Ag/p-Zn3P2 junctions. The metals have the similar work
functions, 4.20 eV for Al and 4.28 eV for Ag.
The polycrystalline Zn3P2 ingots were prepared by a physical vapor transport technique.6) The ingots were
mechanically processed to obtain Zn3P2 plates with mirror surfaces. The metal electrodes were then deposited on the
Zn3P2 plates by thermal evaporation. The theoretical investigation on the reactivity was discussed based on chemical
potential diagram. The diagrams of M-P-Zn systems were constructed using the CHESTA code.7) The
thermodynamic data for the calculation were collected from the literatures.8–10)
Figure 1 shows the I-V curves of as-fabricated Ag/p-Zn3P2 and Al/p-Zn3P2 junctions. While the Ag/p-Zn3P2
junction is Ohmic, the Al/p-Zn3P2 junction shows Schottky behavior with anomaly large ideality factor of 2.7.
According to the chemical potential diagram as shown in Fig 2, the former junction is stable but the latter structure
is reactive. The reaction at Al/p-Zn3P2 interface results in formation of a semiconductor, AlP. This might be the
reason for the difference of the carrier transport properties. In the presentation, we will comprehensively discuss the
characteristics of M/p-Zn3P2 junctions with the chemical potential diagrams of the M-P-Zn systems.
References 1) W. Schottky, Zeitschrift für Physik, 113, 367–414 (1939). 2) N. F. Mott, Proc. the Royal Society A: Mathematical, Physical and Engineering Sciences, 171, 27–38 (2016). 3) R.P. Scott and A.C. Cullen, The Internal Journal of Life Cycle Assessment, 21, 29–43 (2015). 4) A. Catalano et al., Proc. 2nd E. C. Photovoltaic Solar Energy Conference, 440–446 (1979). 5) N.C. Wyeth and A. Catalano, Journal of Applied Physics, 51, 2286–2288 (1980). 6) R. Katsube and Y. Nose, submitted. 7) Chesta web site, http://www.aqua.mtl.kyoto-u.ac.jp/chestaEng.html (visited 1 March 2017). 8) T. Gómez-Acebo, Calphad, 22, 203–220 (1998). 9) I. Karakaya and W. T. Thompson, Bulletin of Alloy Phase Diagrams, 9, 232–236 (1988). 10) I. Barin, Thermochemical Data of Pure Substances, Wiley-VCH Verlag GmbH, Weinheim, Germany, (1995).
-50
0 0
0
-100
-50
-100
-50
-100
Ag(s)
Zn P (s)3 2
log( / a
tm)
p Ag
log(/ atm)
pP 4
log(
/ at
m)
pZn
P(red)
Zn(s) ZnP s2( )
AgP s2( )Ag P s3 11( )
Ag Zn s5 8( )AgZn s( )
AgZn s3( )(b)(a)
-100
-50
0 0
0
-100
-50
-100
-50
log( / atm)
p Al
log( / atm)
pP4
log(
/ at
m)
pZn
Zn P (s)3 2
Al(s)
Zn(s)ZnP s2( )
P(red)AlP(s)
Fig. 1. I-V characteristics of Ag/p-Zn3P2 and Al/p-Zn3P2 junctions.
Fig. 2. Chemical potential diagrams of (a) Al-P-Zn and (b) Ag-P-Zn system at 600 K.
Fabrication and Characterization of Phosphorus Doped Si nanocrystals
D. Shan1)2), M. Q. Qian1), *J. Xu1), D. K. Li1), W. Li1) and K. J. Chen1) 1)
School of Electronic Science and Engineering and Jiangsu Provincial Key Laboratory of Advanced Photonic and
Electronic Materials, Nanjing University, Nanjing, 210093, China, 2)
School of Electronic and Information
Engineering, Yangzhou Polytechnic Institute,Yangzhou 225127, China *[email protected]
Keywords: Si nanocrystals, doping, characterization,
Recently, the studies on Phosphorus and/or Boron doping in Si nano-crystals (Si NCs) have been attracted much
attention since the doping can modulate the electronic structures and the related physical properties and it provides
an effective approach to improve the performance of nano- and opto-electronic devices based on Si NCs. Currently,
fabrication of doped Si NCs with controllable way and the characterization of prepared materials is one of the
interesting topics. Here, we fabricate the phosphorus
(P)-doped Si NCs by annealing the doped amorphous
Si thin films or doped amorphous Si-based multilayers
and investigate their microstructures and electronic
properties. For the single layer samples, the thermally
activated conduction dominates the carrier transport
process and the grain boundaries play an important role
in the Si nanocrystals films before doping. After P
doping, the conductivities are increased and the
conductivity activation energies are reduced
accordingly as shown in Fig.1. It can be concluded that
the carrier transport properties of the doped samples are
dominated by neutral impurities scattering mechanism
and phonon scattering in the different temperature
regions. For the multilayered samples containing
P-doped Si NCs, the room temperature conductivity
can also be enhanced by seven orders of magnitude
than the unintentionally-doped sample, reaching values
up to 110S/cm for heavily-doped sample. The
temperature-dependent carrier transport behaviors suggest the changes from Mott variable range hopping process to
thermally activation conduction process with the temperature. Moreover, the changes of Hall mobility before and
after P doping are also discussed in this work. This work is supported by the ‘973 Program’ (2013CB632101),
NSFC (11274155) and PAPD.
References :
1) S. K. Ray, S. Maikap, W. Banerjee and S. Das, J Phys D: Appl Phys., 46, 153001 (2013).
2) B. L.Oliva-Chatelain, T. M. Ticich and A. R. Barron, Nanoscale 8, 1733 (2016)
3) P. Lu, W. W. Mu, J. Xu, et al., Sci Rep., 6, 22888 (2016).
3) D. Shan, M. Q. Qian, Y. Ji, X. F. Jiang, J. Xu and K. J. Chen, Nanomaterials 6, 233 (2016).
Fig. 1. The temperature-dependent conductivities of nc-Si films before and after P doping.
Fig. 1 Room temperature EL spectra from a LED with Si-QDs with Ge core. Schematic illustration of LED structure is shown in the inset.
Formation of Si-based Quantum Dots on Sub-micron Si Wire Structures and
Their Electroluminescence
*M. Ikeda, L. Gao, K. Yamada, K. Makihara, A. Ohta, and S. Miyazaki Graduate School of Engineering, Nagoya University, Furo-cho, Chikusa-ku, Nagoya, Japan *[email protected]
Keywords: silicon quantum dot, germanium core, silicon wire, electroluminescence
Light emission from Si-based nanostructures such as Si and Ge quantum dots (QDs) has stimulated
considerable interest in the field of silicon-based photonics because of its potential to combine photonic processing
with electronic processing on a single Si chip [1, 2]. Much effort has been devoted to improve light emission
efficiency and stability, which includes not only the confinement of electron-hole pairs but also the use of strain and
impurity doping. Recently, we demonstrated room temperature photoluminescence from the Si-QDs with Ge core
with fairly broad spectra in a region of 0.6–0.8 eV originating from the radiative recombination of photogenerated
electron-hole pairs through the quantized states of Ge core [3, 4]. Since the silicon photonics is based on Si wire
waveguides, emitted light from Si-based nanostructures should be coupled with the optical mode of Si wire
structures. In this work, we extended our research work to the formation of high density Si-QDs with Ge core on
sub-micron patterned Si wire structures and characterized their electroluminescence (EL).
Sub-micron Si line and space patterns were fabricated by using electron beam lithography and dry etching,
where a line height, line width and space width were 300nm, 500nm and 400nm, respectively. After thermal
oxidation of the patterned substrates and a subsequent dip in a 0.1% HF solution to terminate the surface with OH
bonds, Si-QDs were formed on the patterned substrates by controlling the early stages of LPCVD using pure SiH4 at
560˚C with a pressure of 120 Pa. Then, highly selective depositions of Ge core and Si cap on the pre-grown
Si-QDs were carried out by the thermal decomposition of 10% GeH4 diluted with H2 at 490˚C with a pressure of 27
Pa and of pure SiH4 at 560˚C with a pressure as low as 2.7 Pa, respectively. For the surface passivation of the QDs,
~2nm-thick SiO2 was formed on the dot surface by exposing them to a remote O2 plasma at 500˚C.
To evaluate the formation of Si-QDs on the sub-micron Si wire structures, the areal density and size of the
Si-QDs were measured by high-resolution SEM. The areal dot density (1.4×1011cm-2) was the same on the top and
side surfaces of the Si wire, and space (bottom) surface in-between the Si wire. There were also no significant
changes in average dot diameters (~8.3 nm) and dot size distributions (FWHM: ~4.0 nm) among the top, side and
bottom surfaces of the Si wire structures. These results indicate that initial Si nucleation and growth occur
uniformly even on the sub-micron Si wire structures with the space width of 400nm. Based on these results,
Si-QDs with Ge core were formed on Si wire structures. Here, AFM topographic images taken after each step of
LPCVD on SiO2/p-Si without patterns confirm the formation of dots with an average height of ~7nm including a Ge
core with a size of ~2.5nm. EL measurements were carried
out at room temperature from a cleaved facet after the
formation of Al top and bottom electrodes. EL spectra show a
peak at ~0.78eV under application of pulsed biases in the
forward bias direction (Fig. 1). With an increase in the
applied bias, the EL intensity was increased with no significant
changes in a spectral shape. The observed EL can be
explained by the radiative recombination of electron-hole pairs
between quantized states in Ge core caused by hole injection
from the p-Si and electron injection from the Al-electrode.
Acknowledgements
This work was supported in part by Grant-in Aid for
Scientific Research (S) No. 15H05762 of MEXT, Japan and by
JSPS Core-to-Core Program of International Collaborative
Research Center on Atomically Controlled Processing for
Ultralarge Scale Integration. References 1) R. J. Walters et al., Nature Mat., 4, 143 (2005).
2) H. Takami et al., Jpn. J. Appl. Phys., 52, 04CG08 (2013).
3) K. Kondo et al., J. Appl. Phys., 119, 033103 (2016).
4) K. Yamada et al., ECS Trans., 75, 695 (2016).
Self-oscillation characteristics of oriented VO2 films on conductive TiN/Ti
layers
* T. Aoto1), K. Sato1), Md. Suruz Mian1), and K. Okimura1) 1) Graduate School of Engineering, Tokai University *[email protected]
Keywords: VO2, self-oscillation, sine-wave-like form, probe lode
Vanadium dioxide (VO2) shows a sharp insulator-metal transition (IMT) at around 341 K1). Since this transition
can also be triggered by voltage, VO2 is expected to be used as oscillation device due to voltage-triggered threshold
switching with negative-resistance. Recently, we reported growth of VO2 thin films2) and their self-oscillations
phenomena3) on conductive TiN/Ti layers. In this study, we report on (020)-oriented VO2 thin film growth on (111)-
oriented TiN layer. Utilizing this oriented VO2 thin films, we investigated the self-oscillation phenomena. In particular,
we attempted to quantify the probe load which is a factor influencing the self-oscillations characteristics.
The VO2 device was composed of (020)-oriented VO2 thin film on (111)-oriented conductive TiN layer.
Depositions of VO2 and TiN films were performed by RF magnetron sputtering. Figure 1 shows a schematic of the
experimental circuit for observing self-oscillations of the VO2 device. The circuit was composed of the VO2 device, a
DC power supply (Vs) and a resistance (Rs: 8 kΩ). Electrical contacting probe (radius: 25 µm) on the VO2 layer was
positively biased and the voltage drop of VO2 device was monitored by a digital oscilloscope. As many reports have
suggested, self-oscillation phenomenon occurs when the voltage exceeds a certain threshold value due to repeated
switching of resistance. In this study, we introduced load weight of the probes which contact on both the VO2 and TiN
films as a parameter affecting the oscillation characteristics. The load weight was quantitatively measured by weight
meter as shown in Fig. 1. Also, corresponding pressure of the probe was calculated by the load weight divided by the
contact area. In the measurements, probe load on TiN was set to 250 MPa, while probe load on VO2 was varied from
5 to 250 MPa.
Figure 2 shows self-oscillation waveforms obtained from the oriented VO2 thin films for different probe load.
As shown in Fig. 2 (a), sawtooth-wave-like form was obtained at probe load of 150 MPa. Similar oscillation waveform
was reported by Suruz Mian et al. 3) On the other hand, when the probe load on VO2 was at 5 MPa, sine-wave-like
form was obtained as shown in Fig. 2 (b). In this case, oscillation frequency reached 10 MHz which is the highest
value of the oscillation frequency for VO2 film reported so far. Thus, we realized high frequency oscillation from the
oriented VO2 thin film. In addition, the amplitude of sine-wave-like form in Fig. 2 (b) was 0.060V, which was smaller
than that in Fig. 2 (a). Table Ⅰ shows summary of oscillation characteristics based on probe load on VO2. When the
probe load was 5 MPa, rather higher oscillation frequency and smaller amplitude were observed than those of 150
MPa. We think that the smaller amplitude contribute to realize faster switching. It is required for oscillation device to
have controllability of oscillation frequency. Therefore, the oscillation characteristics shown in Table Ⅰ are considered
to be advantageous when we try to apply VO2 as oscillation device. In this presentation, we will describe details of
two kinds of oscillation characteristics from the oriented VO2 thin film.
Probe load on
VO2 150 MPa 5 MPa
Waveform Sawtooth-wave-
like form
Sine-wave-like
form
Oscillation frequency
850 kHz 10.0 MHz
Amplitude (ΔV) 1.3 V 0.060 V
Table Ⅰ Oscillation characteristics based on the probe load on VO2.
Fig. 2 Self-oscillation waveforms (a) probe load on VO2 is 150 MPa (b) probe load on VO2 is 5 MPa.
0
0.05
0.1
0.15
0.2
0.25
0 100 200 300
Vs = 23 V
T = 100 ns
(f = 10 MHz)
ΔV = 0.060V
Sine-wave-like form
Time (ns)
Probe load: 5 MPa
References 1) F. J. Morin: Phys. Rev. Lett. 3, 34 (1959).
2) Md. Suruz Mian and K. Okimura, J. Vac. Sci.
Technol. A 32, 041502 (2014).
3) Md. Suruz Mian, K. Okimura and J. Sakai J.
Appl. Phys. 117, 215305 (2015).
Probe load on
VO2 150 MPa 5 MPa
Waveform Sawtooth-wave-
like form Sine-wave-like
form
Oscillation
frequency 850 kHz 9.0 MHz
Amplitude (ΔV) 1.3 V 0.060 V
References 1) F. J. Morin: Phys. Rev. Lett. 3, 34 (1959).
2) Md. Suruz Mian and K. Okimura, J. Vac. Sci.
Technol. A 32, 041502 (2014).
3) Md. Suruz Mian, K. Okimura and J. Sakai J.
Appl. Phys. 117, 215305 (2015).
Fig. 1 Schematic of self-oscillation
experiment.
Oscilloscope
Rs = 8 kΩ
Rs = 8 kΩ
Vs
VO2
TiN
Ti
Si
Weight meter
0
0.5
1
1.5
2
2.5
0 1000 2000 3000 4000
Vs = 4.0 V
ΔV = 1.3 V T = 1180 ns
(f = 850 kHz)
Sawtooth-wave-like form (a)
Time (ns)
Volt
age o
f V
O2 (
V)
Volt
age o
f V
O2 (
V)
Probe load: 150 MPa
Probe load: 150 MPa
(b)
0.00
0.10
0.20
0.30
0.40
0.50
30 20 10 5 3
CoPt/nm
Coercivity (kOe)
without air exposure with
Influence of ZnO on magnetic properties of CoPt films
*K. takeda1), Y. Isaji1) , H.Yamane2), and M. Kobayashi1) 1) Chiba Institute of Technology, 2-17-1 Tsudanuma, Narashino, Chiba 275-0016, Japan, 2) Akita Industrial
Technology Center *[email protected]
Keywords: CoPt, Perpendicular magnetic, ZnO, AZO
1. Introduction: Currently, perpendicular magnetic recording is used for
the magnetic recording method of HDD and the like. In this
perpendicular magnetic recording system, high density recording is
possible as compared with the conventional in-plane magnetic recording
system. In this experiment, a stacked film in which AZO (ZnO doped
with Al) was used as a base layer by using CoPt for the magnetic layer,
and a laminated film of [AZO / CoPt / AZO] in which AZO was
sputtered onto CoPt as a protective layer, and before sputtering the AZO
protective layer After exposing to the atmosphere once, prepare a sample
on which an AZO protective layer is deposited. It is aimed to compare
and examine how the difference in fabrication conditions of the
fabricated sample affects the perpendicular magnetic properties.
2. Experimental method: Experimental samples were prepared using
magnetron sputtering equipment. The sample was prepared by sputtering
AZO as a seed layer on a glass substrate 150 to 0 nm, then sputtering
CoPt as 30 to 3 nm as a magnetic layer and sputtering 50 nm of AZO as a
protective layer of CoPt, A multilayer film was formed by sputtering a
protective layer after exposure to the atmosphere before sputtering the
protective layer. For the measurement of the magnetic properties of the
prepared samples, the Kerr effect and the VSM were used to measure the
maximum applied magnetic field at 15 kOe, respectively. Structural
analysis was also performed using X-ray diffraction.
3. Result: Figure 1 shows the influence of the AZO underlayer of the
fabricated sample on the CoPt magnetic layer. As can be seen from the
figure, the perpendicular magnetic properties occur only when the
underlayer AZO is present, and the perpendicular anisotropy is decreased
as the coercive force is larger at 10 nm than at the film thickness of 5 nm.
Further, a magnetic characteristic similar to 2 nm was obtained for a
sample of 25 nm. There was no significant difference in the sample of
the underlayer AZO having a film thickness of 25 to 150 nm. Next, the
influence of the film thickness of the CoPt magnetic layer on the
magnetic characteristics with the AZO underlayer set to 50 nm is shown
in FIG. 2 without (blue). From the figure, the coercivity tended to
increase as the thickness of the CoPt magnetic layer was thinner. Also,
the thinner the perpendicular magnetic properties are, the better the result
is. Next, the influence of the difference in CoPt film thickness on the coercive force when AZO of the protective
layer is sputtered is shown in FIG. 2 with (ash). As can be seen from the figure, the coercive force tended to be small
as a whole with the protective layer. The sample exposed to the atmospheric air when preparing the protective layer
is shown in air exposure in FIG. 2 (orange). As can be seen from the figure, when the protective layer was formed
by exposure to the air, no deterioration in magnetic properties was observed, and the same results as without the
protective layer were obtained with a slight decrease in coercive force compared with without protective layer .
Fig. 1 Influence of AZO film thickness
on perpendicular magnetic properties
Figure 2. Influence of thickness of CoPt
magnetic layer on coercive force under
each condition of "No protective layer,
protective layer and air exposure, with
protective layer"
-5kOe 5kOe
CoPt10nm / AZO 0nm
CoPt10nm / AZO 2nm
CoPt10nm / AZO 10nm
Effect of a metal interlayer placed under Au catalyst for making well-defined
microscale holes in Si substrate by metal-assisted chemical etching
*R. Niwa, T. Shimizu*, M. Matsumura1), T. Ito and S. Shingubara Graduate School of Science and Engineering, Kansai University. 1)Organization for Research and Development of Innovative Science and Technology, Kansai University,
Yamate-cho 3-3-35, Suita 564-8680, Osaka, Japan *[email protected]
Keywords: Si, Metal assisted chemical etching, Through-silicon via, Micro-nanofabrication, Nanowire
Etching of Si is a fundamental and important process for making through silicon via (TSV) in 3D-LSI.
The TSV requires microscale holes with a high aspect ratio. Wet chemical processes generally have an advantage of
low process-cost over dry etching which are carried out in vacuum systems. However, it is difficult for wet chemical
etching to make high aspect ratio holes because it tends to etch Si isotropically due to the inherent properties of wet
processes. Metal-assisted chemical etching (MACE) has the possibility of circumventing this problem because by
this method Si is etched only at the interface of metal catalyst and Si, which allows high selectivity and directivity of
holes formed in Si [1, 2]. However, improvements in the MACE process are necessary to bring the method to a level
applicable to making TSV. In this study we demonstrate usefulness of a metal interlayer interposed between the
metal catalyst and Si for formation of vertical microscale holes in Si (100) substrate by MACE.
In experiments, we used Au discs about 10 m in diameter and 20 nm in thickness, which were deposited
on Si substrate with a lift-off process of photolithography, as catalyst for MACE. For some samples, a Ti interlayer
with a thickness of 10 nm was placed between Au and Si substrate by depositing the Ti layer on Si substrate prior to
the deposition of the Au layer. MACE was carried out for these two kinds of Si samples with Au or Au/Ti catalyst
in a solution composed of 2.1 M HF, 1.7M H2O2, and H2O at 40 0C for 30 min.
Fig. 1 shows cross-sectional SEM images of Si substrates after MACE. When Au discs without a Ti
interlayer was used as the catalyst, no well-defined holes were formed, but many crooked tiny holes were formed in
Si over the area on which Au disc had been deposited, as shown in Fig. 1(a). This suggests that the Au disc was
split into small particles during MACE, and that each Au particle worked as etching catalyst, making a tiny crooked
hole. In contrast, when a Ti interlayer was placed between the Au layer and Si, straight holes about 10 m in
diameter, which is the same as the diameter of the Au/Ti discs, were formed in Si substrate to a depth of about 40
m after etching for 30 min, as shown in Fig. 1 (b). This result indicates the usefulness of the Ti interlayer for
making well-defined high aspect ratio holes in Si substrate by MACE. Although we have tested some other metals
for the interlayer, we have not obtained vertical holes in Si as good as the holes made with the Au/Ti catalyst.
Fig. 1 Cross-sectional SEM images of Si samples etched by MACE using (a) Au and (b) Au/Ti as catalysts.
[1] C. Lee, K. Tsujino, Y. Kanda, S. Ikeda and M. Matsumura. J. Mater. Chem., 18 (2008) 1015-1020.
[2] Z. Huang, N. Geyer, P. Werner, J. Boor and U. Goesele, Adv. Mat. 23 (2011) 285-308.
Metal composite for flexible interconnect
Electro-mechanical characteristics of metal/polymer composite film
Rei Satoh1),2), Jin Kawakita1), Yukihiro Sakamoto2) and Toyohiro Chikyow1)
1) National Institute for Materials Science 2) Chiba Institute of Technology Keywords (Composite material, Flexible interconnect, Electrical characteristics, Mechanical properties,
Simultaneous evaluation)
1. Introduction Flexible electronics such as stretchable healthcare device and foldable electronic paper are expected to
improve quality of business and human life. Flexible devices require flexibility for their components. The interconnect including micro wiring of the devices requires flexibility as well as high electric conductivity and
strong adhesiveness to the plastic substrate. In addition, an efficient process is necessary for fabrication of the interconnect. Although metals such as copper and silver have been used for the interconnect of the conventional electronic devices which are mostly rigid, the metal interconnect might be broken and peeled off
from the plastic substrate when they are bent and unbent repeatedly. Organic polymers have excellent mechanical properties as compared to metal Therefore, composites of polymer and metal have been studied in order to achieve both electrical conductivity and mechanical flexibility. So far, the following research results were reported; that conducive polymer/metal composite showed 2×10-4 Ω-1·cm-1 of conductivity two orders of
magnitude higher than the commercially available conductive polymer, more than 90% of adhesiveness onto various plastic materials, and 104 times of repeated bending with keeping electrical conduction. The electrical and mechanical behavior of the composite, however, are not clear when the composite is in motion. The
purpose of this research was to clarify dynamic electrical and mechanical characteristic of the conductive
polymer/metal composite film.
2. Experimental method
2－1. Preparation of specimen
A mixture of AgBF4 (1.0 mol·dm-3) and C4H5N (0.5 mol·dm-3) in acetonitrile was used as the reaction solution. It was dropped in the linear shape (1W×30L) on a polyimide sheet and dimethylpolysiloxane sheet
(20w×50L×0.02H) as the substrate. UV light (bright line: 436, 405, 365 nm in wavelength, and strength: 50 mW·cm-2) was irradiated on the reaction solution for 5 minutes and composite of polypyrrole doped with BF4 and metal silver was synthesized.
2－2. Simultaneous evaluation of mechanical and electric properties
Mechanical property of the composite on polyimide was evaluated by a tensile test according to the Japanese Industrial Standards (JIS 7127) with a load cell of 9.8 N and at a tensile speed of 10 mm·min-1. During the
tensile test, the electric resistance between two ends of the specimens was measured.
3. Results and discussion Fig. 1 shows changes in applied force with tensile time of the polypyrrole/silver composite formed on
different plastic substrates. The strain was also indicated as the upper abscissa. In the specimen with the polyimide (PI) substrate, a breaking of the specimen, i.e. corresponding to the substrate was observed at a load
of 321 N at 63 sec after starting of the tensile test while the specimen with dimethylpolysiloxane (PDMS) substrate was broken at 181 N and 168 sec. Fig. 2 shows changes in electric resistance with tensile time of polypyrrole/silver composite formed on different plastic substrates. In the composite specimen formed on the
PI substrate, the electric resistance was increased with the time, i.e. the strain, and it exceeded the upper limit of measurement at 63 sec after starting of the tensile test. The former behaviour was explained by decreasing in contact area between the silver particles of the composite and the latter was due to breaking of both the
composite and the substrate at the same time. In the case of the specimen with the PDMS substrate, the electric resistance was almost constant from the tensile start to 55 sec and then increased gradually until 83 sec, jumped up to the upper limit of measurement at 89 sec through up and down behaviour. Considerable
difference of change in electric resistance between the substrates until breaking of the composite might be caused by actual tensile stress applied to the composite formed on the substrate with different shearing stress depending on adhesive status between the composite and the substrate. In addition, it is noted that the composite can be used until the polyimide substrate is broken in flexible electronic devices while the
mechanical behaviour of the composite until the composite is broken can be evaluated by using PDMS as the
substrate. The load stress and the strain at the breaking of the composite were calculated 158 N·mm-2 and 17.4% for the PI substrate and 113 N·mm-2 and 24.7% for the PDMS substrate, respectively. From these values, it was estimated that the composite was stretched 1.74 mm and 2.71 mm for the PI and PDMS
substrates, respectively at the breaking point by using the following formula; ɛ = ΔL/L (ɛ : strain, ΔL : deformation length and L : length before giving force).
From the elongation of metallic silver as one of the wiring materials is 23%, it is supposed that the composite
material used in this study can exhibit improvement up to 27.1% higher than that of metallic silver alone in terms of conductive elongation.
4. Conclusion This research succeeded in evaluating both mechanical and electrical properties of conductive
polymer/metal composite film simultaneously for the first time. Dynamic mechanical and electrical characteristic of the conductive polymer/metal composite film was clarified; the composite is superior to
metallic silver as the interconnect of the flexible devices and can be used until the polyimide substrate is broken.
Time / s
Ele
ctro
n r
esis
tan
ce/
MΩ
0.5
1.0
1.5
Time / s
Ap
pli
ed f
orc
e /
N
Strain/%
On PDMS substrate
On PI substrate
Composite’s break
Substrate’s break
Fig.1 Relationship between time (strain) and load of polypyrrole / silver composite formed on polydimethylpolysiloxane (PDMS) and polyimide substrates under
tensile test at 10 mm·min-1.
Fig.2 Changes in electric resistance of polypyrrole / silver composite formed on polydimethylpolysiloxane (PDMS) and polyimide substrates with time
under tensile test at 10 mm·min-1.
ｚ
On PDMS substrate
On PI substrate
Composite’s break
Investigation of Optical Absorption and Thickness of Phthalocyanine
Layer-by-layer Deposited Film using Optical Waveguide with Surface
Plasmon Resonance
D. Sato, M. Ishigooka, H. Oshikane, C. Lertvachirapaiboon, Y. Ohdaira, A. Baba, K. Shinbo, K.
Kato, and F. Kaneko Graduate School of Science and Technology, Niigata University, Niigata, Japan *[email protected]
Keywords: Optical waveguide spectroscopy, surface plasmon resonance (SPR), phthalocyanine, Kramers-Kronig
relation
Optical waveguide sensor is a useful method for investigating optical absorption of thin films.
1) Sensitive
observation can be conducted since the evanescent wave of reflected light is repeatedly absorbed by a deposited film
on the sensor. However, evaluation of the thickness of deposited film is difficult, and monitoring of transparent film
deposition is not possible using the method. In this study, optical absorption and film thickness were investigated
using an optical waveguide sensor with surface plasmon resonance (SPR) method.
The structure of prepared sensor is shown in Fig. 1. BK-7 glass substrate was used as a substrate. 45-nm-thick
Ag and 5-nm-thick Au films with 5-mm-width were consecutively vacuum evaporated. Then, transparent and
anionic poly(methyl methacrylate-co-methacrylic acid) (PMMA-co-PMAA) film was spin-coated. A cell to hold
solution was set on the sensor, and layer-by-layer (LbL) deposited film was prepared by putting aqueous solutions of
cationic and anionic molecules alternately. Cationic poly diallyldimethylammonium chloride (PDADMAC) and
anionic Alcian Blue, pyridine variant (AB) dye were used for film deposition. The optical absorption and SPR
properties due to film deposition were monitored at the part without (part A in Fig. 1) and with (part B in Fig. 1)
Ag/Au films, respectively. The s-polarized light component of output light (IS) was observed before LbL film
deposition and used as a reference. The p-polarized light components of output light (IPs) before and after film
deposition were also observed to investigate optical absorption and SPR properties.
Figure 2 shows output light spectra. SPR peak wavelength qualitatively redshifts with deposited film thickness,
and the PMMA-co-PMAA film thickness was adjusted to induce SPR at longer wavelength compared to optical
absorption band of AB. Before film deposition (curve 1), a peak at 840 nm was observed due to SPR. After film
deposition (1 bilayer, curve 2), a peak at 600 nm due to AB absorption was observed and the SPR peak redshifted.
As shown here, optical absorption of AB and SPR property can be simultaneously observed. Further film deposition
(5 bilayers, curve 3) resulted in an intense AB peak at 600 nm and more redshift of SPR peak. The output light
spectra were observed during the film deposition, and the film thickness for each deposition was investigated. The
sensor also allows us to investigate transparent film deposition.
Fig. 1 Sensor structure
Fig. 2 Output light spectra
Reference:
1) J.T. Bradshaw, S.B. Mendes, S.S. Saavedra, Anal. Chem. 74, 1751 (2002).
600 800 1000
0
0.1
0.2
Wavelength [nm]
log
10(I
S/I
P)
1
2
3
Improved Optoelectronic Performance of InGaN-based Light-Emitting Diodes Grown on a Micro-/Nano-scale Hybrid Patterned Sapphire Substrate *Chih-Yung Chiang, Zhong-Yi Liang, and Wen-Cheng Ke Department of Materials Science and Engineering, National Taiwan University of Science and Technology, Taipei 106, Taiwan *[email protected] Keywords: InGaN, LEDs, Patterned sapphire substrate, efficiency droop
Recent studies on substrate patterning in the nano-scale indicate a further reduction in the dislocation density and an enhancement in the light extraction efficiency of InGaN-based LEDs. LEDs grown on nano-patterned sapphire substrates (NPSSs) demonstrate improved light output power compared with those grown on micro-scale PSSs. Nano-imprinting is a mass-production technique for fabrication NPSSs. Until now, pattern loss issues, especially for small-sized and high-density nano-patterns, remain a technical bottleneck, because resin frequently sticks to the mold. Thus, reduction of the C-plane area in micro-scale PSS and pattern loss of small-sized nano-scale patterns in NPSSs, among other factors, limit LEDs grown on PSSs. To further improve the performance of LEDs using a PSS, a hybrid-PSS was proposed [1,2]: embedding nano-pattern structures onto a conventional micro-scale pattern of PSS (bare-PSS). The optoelectronic properties of LEDs grown on hybrid-PSS and bare-PSS are demonstrated and compared. Possible mechanisms are proposed to explain the improved luminous intensity and efficiency droop of InGaN-based LEDs grown on hybrid-PSS.
A hybrid patterned sapphire substrate (hybrid-PSS) was prepared using an anodic aluminum oxide etching mask to transfer nano-patterns onto a conventional patterned sapphire substrate with micro-scale patterns (bare-PSS). The threading dislocations (TDs) suppression of light-emitting diodes (LEDs) grown on a hybrid-PSS (HP-LED) exhibit a smaller reverse leakage current compared with that of LEDs grown on a bare-PSS (BP-LED). The combined effects of quantum confinement Stark effect and bandgap shrinkage of the InGaN well layer were considered to explain the large red-shifted EL peak wavelength under high injection currents. The calculated piezoelectric fields are 1.59 and 1.57 MVcm-1 respectively for BP-LED and HP-LED. The estimated LED chip temperatures rise from room temperature to 150C and 75C for BP-LED and HP-LED respectively at a 600-mA injection current. This smaller temperature rise of LED chip is attributed to the increased contact area between sapphire and the LED structural layer because of the embedded nano-pattern. Although the chip generates more heat at high injection currents, the accumulated heat can yet be removed outside the chip effectively. The high diffuse reflection (DR) rate of hybrid-PSS increases the escape probability of photons, resulting in an increase in the viewing angle of LEDs from 130 to 145. The efficiency droop was reduced from 46% to 35%, effects, which can be attributed to the elimination of TDs and strain relaxation by embedded nano-patterns. In addition, the light output power of HP-LED at 360-mA injection currents exhibits a ~22.3% enhancement, demonstrating that hybrid-PSSs are beneficial to applicate in high-power LEDs.
References : 1) W. C. Ke, W. K. Chen, F. Y. Hong, C. C. Ho, U.S. Patent 9,385,274, July 5, 2016. 2) W. C. Ke, F. W. Lee, C. Y. Chiang, Z. Y. Liang, W. K. Chen, and T. Y. Seong, ACS Appl. Mater. Interfaces, 8,
34520-34529 (2016).
Fig. 1. SEM image of hybrid-PSS.
Infrared light emission in dislocation-engineered silicon *CL Hsin1), CC Cheng2) and PL Liu3) 1) Department of Electrical Engineering, National Central University, Taoyuan, Taiwan 32001 2) Department of Physics, National Central University, Taoyuan, Taiwan, 32001 3) Graduate Institute of Precision Engineering, National Chung Hsing University, Taichung, Taiwan, 402 *[email protected] Keywords: dislocation array, network, photoluminescence, tunneling current, density of state One of the perspectives of the Si-based technology is the optical interconnect for data transmission and applications in optoelectronic integrated circuit. In this report, the engineered dislocation network was proposed and the atomic structure of the dislocation array was revealed by high-resolution transmission electron microscope (HRTEM) and scanning tunneling microscope (STM). The photoluminescence (PL) emission is strong and compatible with intrinsic Si characteristic peak, making it possible as light emitters in silicon. The analysis of dislocation array-induced scanning tunneling spectroscopy (STS) identified the presence of defect levels under the conduction band, compared with the occupied and unoccupied Kohn-Sham orbitals in the forbidden gap of Si derived from first-principles theoretical models. This study demonstrated the possibility of dislocation-induced optical transition from a theoretical and experimental perspective, which will be essential in the development of Si-based optoelectronic integrated circuit.
Fig. 1. PL of the (001)Si substrate (top, black-dashed line)and (001)Si substrate with dislocation array (bottom,red-solid line).
Figure 2. Correlation of DOS and dislocation networks. (a)STS I-V measurement and (b) the normalized conductance(dI/dV)/(I/V) of the Si substrate. (c) STS I-V measurementand (d) the normalized conductance (dI/dV)/(I/V) of the Sisubstrate with dislocation array.
Influence of surface treatment on CoPt film on magnetic properties
*Y. Isaji1), K. Takeda1), H. Yamane2), and M. Kobayashi1) 1) Chiba Institute of Technology, Narashino, Chiba, Japan, 2) Akita Industrial Technology Center, *[email protected]
Keywords: perpendicular magnetic, CoPt, HDD, magneto-optical
Currently, HDD is an indispensable high-density recording medium in society. In the HDD, a perpendicular
magnetic recording method is used, which is a method of recording so that the magnetization faces perpendicularly to
the recording surface. Commonly used CoPt films exhibit
high perpendicular magnetic anisotropy, but they are
greatly affected by underlying layers. Also, the
perpendicular magnetization film can be applied to a
sensor, but requires a protective layer. In our previous
studies, it was found that after the CoPt film formation, it
was taken out of the chamber and kept in the air for about
1 day, so that even if AZO(Al-doped ZnO) was formed
thereafter, almost no deterioration of the perpendicular
magnetic properties was suppressed. Figure 1 shows the
effect of air exposure on kerr loops of CoPt films. In this
research, we aimed mainly to investigate the influence on
magnetic properties by using oxygen plasma.
sample were fabricated by DC magnetron sputtering
onto glass substrate at room temperature. The ultimate
pressure was 1 × 10 -5 Pa or less and the Ar gas pressure
was 0.2 Pa. Plasma was generated at O 2 gas pressure of
1.5 Pa and power of 200 W, and surface treatment was
performed. The measurement of magnetic properties,
measurement was carried out by applying a magnetic field
in the direction perpendicular to the film surface with a
vibrating sample magnetometer (VSM) and a magneto-
optic kerr effect measuring device. For the analysis of the
crystal structure, evaluation was carried out using an X-
ray diffraction (XRD).
When AZO was formed directly on CoPt by only
5nm, the perpendicular magnetic properties were
deteriorated. Also, as the protective layer became thicker,
the perpendicular magnetic properties decreased in
proportion to it. After forming the CoPt film, O2 plasma
was generated for 60 seconds, and AZO film was formed.
As a result, similar to the atmospheric exposure, the
deterioration of the perpendicular magnetic properties
was suppressed. Figure 2 shows effect of plasma
treatment on kerr loops. Even when comparing the crystal
structures, since there is no significant change, it is
considered that a change in the electronic state occurs due
to bonding with oxygen on the extremely thin surface of
the CoPt surface, and the deterioration of the
perpendicular magnetic properties is suppressed. Figure 3
shows effect of plasma treatment on XRD.
Fig.1. Effect of air exposure on kerr loops
of CoPt films.
Fig.3. Effect of plasma treatment on XRD
Plasma
No plasma
Fig.2. Effect of plasma treatment on Kerr loops
Plasma
No plasma
Study on the Off-Stoichiometric Multiferroic Hexagonal YMnO3
G. Dixit 1*), P. Bazwan2), P. Kumar3), K. Asokan3)
1)Dept of Physics, G.B.P.U.A.&T.Pantnagar-263145, Uttarakhand, India,2)Amity School of Applied Sciences, AmityUniversity Gurgaon-122413, Haryana, India, 3)Materials Science Division, Inter University Accelerator Centre, NewDelhi-110067, India *[email protected] : Mutiferroic, Hexagonal Manganite, XRD, Dielectric
Multiferroic materials have attracted much interest during the recent years. Yttrium Manganite (YMnO3) is TypeII multiferroics which is regular ferroelectrics and also (anti)ferromagnetic. A number of reports are available for thestudy of electrical, magnetic and structural properties. It has been observed that if the concentration of Y or Mn ionsis changed by doping any foreign element at these two ion sites, the properties of the material are significantlyaffected without distorting the structure. Present work is motivated to observe the effect of different concentrationsof Y and Mn ions without doping any other element in the host lattice. Samples with different stoichiometries:YMnO3 (YMO), Y0.95MnO3 (5%Y deficiency- YMO:95Y), and YMn0.95O3 (5 % Mn deficiency- YMO:95Mn) wereprepared by solid state reaction method and characterised by various experimental techniques such as XRD, andSEM for their structural and morphological studies. Electrical behaviour is studied by dielectric properties. It hasbeen observed that the compounds with excess of Mn ions consist of extra phases of Mn oxides. The YMO and Mndeficient pellets seem to be more porous in comparison to the dense structure of Y deficient and Mn excesscompounds. Small crystallites and larger unit cell in comparison to YMO may be the reason for porosity in Mndeficient samples. Dielectric constant is found to decrease with frequency for all these compounds. At roomtemperature, Mn ions deficiency increases the dielectric constant of YMO, but high frequency and low temperaturecauses it to decrease. The Y ions deficiency does not seem to affect the electrical behaviour of YMO significantly.Based on these observations, it can be said that deficiency of Mn ions change microstructure and the electricalproperties of YMO more in comparison to Y deficient samples.
Fig 1 : Variation of dielectric constants with (a) low frequency (b) high frequency. Variation of dielectric losseswith (c) low frequency (d) high frequency for compounds of YMO, YMO:95Y and YMO:95Mn.
Graphene/TiO2 hybrid layer for simultaneous detection and degradation by a
one-step transfer and integration method
Xinxin Yu
1), Ranran Ca
1), Yuqing Song
3), Qiang Gao
1), Nan Pan
2), Mingzai Wu
1) and Xiaoping
Wang2),3)
1)
School of Physics and Material Science, Anhui University, Hefei 230601, PR China, 2)
Hefei National Laboratory
for Physical Sciences at the Microscale, University of Science and Technology of China, Hefei 230026, P R China, 3)
Department of Physics, University of Science and Technology of China, Hefei 230026, P R China *[email protected]
Keywords: graphene /TiO2, SERS, photocatalysis, functionalization, application,
During the past decades, researchers have made great efforts towards an ideal surface enhanced Raman
spectroscopy (SERS) substrate. Here a smart SERS-active flexible substrate was designed and its performance was
studied. The substrate is constructed by graphene and TiO2, and could be divided into two functional layers.
Graphene provide a flat hot surface for Raman enhancement, which could be ascribed to chemical enhancement.
TiO2 layer is an effective photocatalyst, which could induce photocatalytic decomposition of adsorbed molecules
under UV irradiation. Notably, such substrate was realized by one-step transfer method, followed by annealing. In
the synthesis process, a flexible TiO2 layer was produced by spin-coating on the CVD graphene and was used as a
support in the transfer process of graphene instead of PMMA, which could exclude contamination and avoid
degradation of the Raman enhancement performance. Combined detection with degradation of trace amounts of
analyte, the versatility of the SERS substrate is greatly enhanced and could be adapted to fit a wide range of sensing
and photocatalytic applications.
Fig 1. The scheme of the sense and degradation process.
References :
1) X. X. Yu, H. B. Cai, W. H. Zhang, X. J. Li, N. Pan, Y. Luo, X. P. Wang and J. G. Hou, ACS Nano, 5,
952-958(2011).
2) X. X. Yu, K. Lin, K.Q. Qiu, H. B. Cai, X. J. Li, J. Y. Liu, N. Pan, S. J. Fu, Y. Luo and X. P. Wang, Carbon, 50,
4512-4517(2012).
3) L.L. Zhang, Z. W. Bao, X. X. Yu*, P. Dai, J. Zhu, M.Z. Wu, G. Li, X.S. Liu, Z.Q. Sun, C.L. Chen, ACS Appl.
Mater. Interfaces, 8, 6431-6438(2016).
Coexistence of topological edge state and superconductivity in Bismuth ultrathin film
Hao-Hua Sun, Mei-Xiao Wang, Fengfeng Zhu, Guan-Yong Wang, Hai-Yang Ma, Zhu-
An Xu, Qing Liao, Yunhao Lu, Chun-Lei Gao, Yao-Yi Li, Canhua Liu, Dong Qian,
Dandan Guan,* and Jin-Feng Jia
Ultrathin freestanding Bismuth film is theoretically predicted to be one kind of two
dimensional topological insulators (TIs). Experimentally the topological nature of
bismuth strongly depends on the situations of the Bi films. Film thickness and
interaction with the substrate often change the topological properties of Bi films. Using
angle resolved photoemission spectroscopy (ARPES), scanning tunneling microscopy
or spectroscopy (STM/STS) and first-principle calculation (DFT), the properties of
Bi(111) ultrathin film grown on the NbSe2 superconducting substrate have been studied.
We find the band structures of the ultrathin film is quasi-freestanding, and 1D edge
state exists on Bi(111) film as thin as 3 bilayers (BLs). Superconductivity is also
detected on different layers of the film and the pairing potential exhibits an exponential
decay with the layer thicknesses. Thus, the topological edge states can co-exist with
superconductivity, which makes the system a good promising platform for exploring
Majorana fermions.