Fabrication and Characterization of Nanowire Devices
Hardev Singh VirkProfessor Emeritus, Eternal
University, Baru Sahib (HP), India
Birth of Nanotechnology“There's Plenty of Room at the Bottom” • On December 29, 1959, Richard P. Feynman
gave the seminal talk at a meeting at Caltech of the American Physical Society. He presented a vision of the precise manipulation of atoms and molecules so as to achieve amazing advances in information technology, mechanical devices, medical devices, and other areas.
Changing Idea into Reality
Eric Drexler of MIT, the Chemist, established the modern field of nanotechnology, with a draft of his seminal Ph.D. thesis in the mid 1980s. His 1991 doctoral thesis at MIT was revised and published as the book "Nanosystems, Molecular Machinery Manufacturing and Computation" (1992), which received the Association of American Publishers award for Best Computer Science Book of 1992.
The Incredible Tininess of Nano
Billions of nanometersA two meter tall male istwo billion nanometers.
The pinhead sized dot is a million nm
Biological cells size isThousands of nm
DNA Molecules are about 2.5 nm in width
Hydrogen atom spans 0.1 nm2 Uranium atoms span 1 nm
• AFM Imaging of ATOMS of GOLD (Au 111)
Atomic Lattice Structure of HOPG in 3D Topography using Atomic Force Microscope
Introduction to Nanowires
Nanowires of metallic and semi-conducting materials have drawn a lot of research interest because of their potential applications in fields like nanoelectronics, opto-electronics and sensors. Nanowires exhibit unique electrical, magnetic, optical, thermoelectric and chemical properties compared to their bulk counterpart. Electronic conduction takes place both by bulk conduction and through tunneling mechanism.
Special Characteristics
• Nanowires exhibit high density of electronic state.
• They have diameter-dependant band gap.• They show enhanced surface scattering of
electrons and phonons.• They have increased excitation energy, high
surface to volume ratio and large aspect ratio.
Fundamental Features• One-dimensionality• – Wire diameter: several nm ~ hundreds of nm’s• – Aspect ratio: L:D >10:1• Material integrity• – Single crystalline nanostructure• Availability of numerous materials• – Superconductor, metal, semiconductor, insulator • Unique physical properties• – Large surface-to-volume ratio• – High transport/carrier mobility• – Quantum confinement/tunable band structure
Quantum Confinement Effects
– Quantum dots (0-D): confined states, and no freely moving ones
– Nanowires (1-D): particles travel only along the wire direction
– Quantum wells (2-D): confines particles within a thin layer
There is no confinement effect in Bulk materials.Refer to energy distribution.
Chemical Routes of Synthesis• Solution-Based Synthesis• – Solution-Liquid-Solid (SLS) Method• – Solvothermal Chemical Synthesis• – Template-Based Synthesis• Gas-Phase Synthesis• – Vapor-Liquid-Solid (VLS) Method• -- Laser abrasion• -- PVD• -- CVD (LPCVD, MOCVD)• – Vapor-Solid (VS) Method• – Oxide-Assisted Growth (OAG)
Growth of Semiconductor Nanowiresby VLS method
Laser ablation overcomes thermodynamic equilibrium constraints and enables liquid nanocluster formation.
GaN Nanowires Grown by VLS method
SEM image of GaN nanowires of diameters 10nm and lengths on the order of 10m (Huang et al., 2002).
ZnO Nanowires on Sapphire by VLS method
SEM images of ZnO nanowire arrays grown on a sapphire substrate, (a) shows patterned growth, (b) shows a higher resolution image of the parallel alignment of the nanowires, and (c) shows the hexagonal cross-section of the nanowires (Huang et al., 2001).
Nano-Lasers using ZnO Nanowires
ZnO nanowires grown by VLS method. Emission spectrum from ZnO nanowires.
Nanowire FabricationTemplate synthesis using polymer and
anodic alumina membranesElectrochemical deposition
Ensures fabrication of electrically continuous wires since only takes place on conductive surfaces
Applicable to a wide range of materialsHigh pressure injection
Limited to elements and heterogeneously-melting compounds with low melting points
Does not ensure continuous wires Does not work well for diameters < 30-40 nm
Chemical Vapor Deposition (CVD) or VLS technique Laser assisted techniques
Polymer Template Synthesis of Nanowires
Large Etched Ion TracksLarge Etched Ion Tracks
Anodization of aluminum Start with uniform layer of ~1m Al Al serves as the anode, Pt may serve as the
cathode, and 0.3M oxalic acid is the electrolytic solution
Low temperature process (2-50C) 40V is applied Anodization time is a function of sample size and
distance between anode and cathode Key Attributes of the process (per M. Sander)
Pore ordering increases with template thickness – pores are more ordered on bottom of template
Process always results in nearly uniform diameter pore, but not always ordered pore arrangement
Aspect ratios are reduced when process is performed when in contact with substrate
Anodic Alumina Template Preparation
Electrochemical mechanism• The overall reaction that takes place during
anodization is: 2Al + 3H2O => Al2O3 + 3H2
At the anode: 2Al + 3O2- => Al2O3 + 6e-
At the cathode:6H+ + 6e- ==> 3H2
• The Al is oxidized at the metal/oxide interface
• The oxide is etched away by the acid with the applied potential
• The pores are induced by the roughness of the top surface
TEM micrographs
(T. Sands/ HEMI group http://www.mse.berkeley.edu/groups/Sands/HEMI/nanoTE.html)
Anodic alumina (Al2O3) Template
100nmSi substrate
alumina template
(M. Sander)
Electrolytic CellElectrolytic Cell
Replica of Nanowires
Microtubule Fabrication
Electrochemical Synthesis
• Electrochemistry has been used to fabricate nanowires of Cu and heterojunctions of Cu-Se and Cd-S. The results of our investigations can be exploited for fabrication of nanodevices for application in opto-electronics and nano- electronics. During failure of our Experiments, exotic patterns ( nanoflowers, nanocrystals, nanobuds) were produced under nature’s self assembly.
Template Synthesis of Copper Template Synthesis of Copper NanowiresNanowires
The electro-deposition of metals is identical to The electro-deposition of metals is identical to an electroplating process. Polymer ITFs and anodic alumina and anodic alumina can be used as a template. The electrolyte used here is can be used as a template. The electrolyte used here is CuSO4.5H2O acidic solution. The rate of deposition of CuSO4.5H2O acidic solution. The rate of deposition of metallic film depends upon: current density, inter-metallic film depends upon: current density, inter-electrode distance, cell voltage, electrolyte electrode distance, cell voltage, electrolyte concentration, pH value and temperature etc. In our concentration, pH value and temperature etc. In our case, electrode distance was kept 0.5 cm and a current case, electrode distance was kept 0.5 cm and a current of 2mA was applied for 1 hour. The developed of 2mA was applied for 1 hour. The developed nanostructures were scanned under SEM for nanostructures were scanned under SEM for morphological and structural studies.morphological and structural studies.
Atomic Force Microscope(NT-MDT)
AFM image of hexagonal pores of AFM image of hexagonal pores of Anodic Alumina Membrane (AAM)Anodic Alumina Membrane (AAM)
SEM Images of Cu Nanowires using SEM Images of Cu Nanowires using Electrodeposition TechniqueElectrodeposition Technique
Copper Nanowire Bundles in AAMCopper Nanowire Bundles in AAM
Cu Nanowires under Constant CurrentCu Nanowires under Constant Current
Capping Effect of Current VariationCapping Effect of Current Variation
I-V Characteristics of Copper I-V Characteristics of Copper Nanowires grown in-situ in AAMNanowires grown in-situ in AAM
Copper Lillies grown due to over- Copper Lillies grown due to over- deposition of Copper in AAM deposition of Copper in AAM
A Garden of Copper NanoflowersA Garden of Copper NanoflowersA Garden of Copper NanoflowersA Garden of Copper Nanoflowers
Copper Nanoflowers grown in Polymer Template (100nm pores)
Copper Marigold Flower
SiC Crystalline Nanowire Flowers G. W. Ho (Nanotechnology, 2004)
Crystalline Nano-comb of ZnO NW H. Yan (JACS 2003)
SEM micrograph of Copper Buds
SEM micrograph of Nanocrystals of SEM micrograph of Nanocrystals of Polycrystalline CopperPolycrystalline Copper
XRD Spectrum of polycrystalline XRD Spectrum of polycrystalline Copper nanocrystalsCopper nanocrystals
Position [°2Theta] (Copper (Cu))
10 20 30 40 50 60 70
Counts
0
20000
40000
60000
36.6
37 [°
]38
.283
[°]
43.4
61 [°
]45
.448
[°]
48.9
20 [°
]50
.580
[°]
54.3
04 [°
]54
.956
[°]
64.8
09 [°
]
74.2
99 [°
]
KK1
XRD spectrum of Cu nanowiresXRD spectrum of Cu nanowires
Position [°2Theta] (Copper (Cu))
30 40 50 60 70 80 90
Counts
0
400
1600
Cu polycrystalline
SEM Image of CdS NanowiresSEM Image of CdS Nanowires
HRTEM image showing CdS Nanowire HRTEM image showing CdS Nanowire & Heterojunctions & Heterojunctions
I-V plot of CdS Nanowire arrays I-V plot of CdS Nanowire arrays showing RTD characteristics showing RTD characteristics
SEM image of Cu-Se NanowiresSEM image of Cu-Se Nanowires
Cu-Se nanowires exhibit p-n junction Cu-Se nanowires exhibit p-n junction diode characteristicsdiode characteristics
A Billion Dollar Question …
• What can nanowires offer for semiconductor nanoelectronics?
• Nonlithographic & extremely cost-effective• Reduced phonon scattering: High carrier
mobility but reduced thermal conductance(?) • Tunable electrical/optical properties• Large surface-to-volume ratio: Sensor
sensitivity & memory programming efficiency
Advantages of 1-D Nanowires• High-quality single-crystal wires with nearly
perfect surface• Scalable nanostructure with precisely
controlled critical dimensions• Best cross-section for surround-gate CMOS• Very cost-effective materials synthesis• High transport low-dimensionality structure• May use as both device and interconnect for
ultra-compact logic (e.g., SRAM)
Nanowire Field-Effect Transistor
• Ambipolar transport• Carrier mobility study• Quantum effect
A single device for numerous applications
Device physics study
Quantum-Wire Device M. Bjork (Nano Letters, Sept. 2004)
1. In-situ control of nanowire synthesis allows design of strongly confined quantum mechanical systems inside nanowires, possibly useful for SET .2. Next-generation nanoelectronic devices with extremely-low power, high performance, and radiation tolerance.
3-D Nanowire Logic Chip H. Ng (Nano Letters, July 2004)
Si NW Thermal Conductance D. Li (APL Oct. 2003)
Thermoelectric (TE) Conversion E.J. Menke (Nano Letters, Oct. 2004)
Bismuth Telluride (Bi2Te3) nanowires
Role of Nanowires for Next-Generation Electronics
• The chemical and physical characteristics of nanowires, including composition, size,
electronic and optical properties, can be rationally controlled during synthesis in a predictable manner, thus making these materials attractive building blocks for assembling electronic and optoelectronics nanosystems.
Some Observations & Remarks• Nanotechnology will be the driving force for
next technology revolution.• Nanowires open door to a wonderland where
the next generation electronics would emerge.• Scope for innovating new synthesis method
and complex functional nanostructures.• New device and interconnect concepts will
emerge from horizon, driven by materials synthesis.
Our Publications
• My website: http:// drhsvirk.weebly.com for list of our published research papers. Go to www.docstoc.com for purchase of
reprints. Free download of Review Paper on Nanowires: visit: ttp://www.intechopen.com/articles/show• Chapter 20 of Book “Nanowires - Implementations and
Applications”, InTech Open, Abbass Hashim (Ed).
AcknowledgementsAcknowledgements
• Reimer Spohr & Christina Trautman (GSI, Darmstadt)Reimer Spohr & Christina Trautman (GSI, Darmstadt)• Sanjit Amrita Kaur (GND University, Amritsar)Sanjit Amrita Kaur (GND University, Amritsar)• Vishal, Gurmit, Sehdev & KK (DAVIET, Jalandhar)Vishal, Gurmit, Sehdev & KK (DAVIET, Jalandhar)• Dr SK Mehta, Chemistry Deptt. (PU, Chandigarh) Dr SK Mehta, Chemistry Deptt. (PU, Chandigarh) • CSIO Chandigarh & IIT Roorkee for FESEM & TEM facility.CSIO Chandigarh & IIT Roorkee for FESEM & TEM facility.• SEM & TEM facility (SAIF, PU, Chandigarh)SEM & TEM facility (SAIF, PU, Chandigarh)• Rajeev Patnaik (Geology Deptt., PU, Chandigarh)Rajeev Patnaik (Geology Deptt., PU, Chandigarh)• DAV MC, New Delhi for Research Grants.DAV MC, New Delhi for Research Grants.• Dr. MS Atwal, VC, Eternal University, Baru Sahib.Dr. MS Atwal, VC, Eternal University, Baru Sahib.
Thank You !!!