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Sensors and Actuators B 160 (2011) 1346– 1351

Contents lists available at SciVerse ScienceDirect

Sensors and Actuators B: Chemical

j o ur nal homep a ge: www.elsev ier .com/ locate /snb

ynthesis of In2O3–ZnO core–shell nanowires and their application in gas sensing

andan Singha,∗, Andrea Ponzonib, Raju Kumar Guptaa, Pooi See Leea,∗, Elisabetta Cominib

School of Materials Science and Engineering, Nanyang Technological University, 50 Nanyang Avenue, Singapore 639798, SingaporeSensor, CNR-IDASC and University of Brescia, Via Valotti 9, 25133 Brescia, Italy

r t i c l e i n f o

rticle history:eceived 18 July 2011eceived in revised form9 September 2011ccepted 22 September 2011vailable online 1 October 2011

a b s t r a c t

Heteronanostructures are very promising gas sensor materials due to their high surface area and hybridproperties. In2O3–ZnO core–shell nanowires are synthesized via two-step growth process. The as-deposited shell is made up of grainy polycrystalline ZnO coated on the single crystalline In2O3 core.The sensing properties of pristine In2O3 and In2O3–ZnO core–shell nanowires are investigated for differ-ent gases. In2O3–ZnO core–shell nanowires are found to possess better response towards the CO, H2 andethanol while pristine In O nanowires has shown a superior response towards the NO . The high sen-

eywords:ore–shell nanowiresanowire networkolycrystallineas sensorensitivity

2 3 2

sitivity and dynamic repeatability have shown in these sensors reveal that the core–shell nanowires arepromising as sensitive and reliable chemical sensors. The gas sensing mechanism of these heterostruc-tured nanowires is discussed in detail.

© 2011 Elsevier B.V. All rights reserved.

. Introduction

Nanostructured metal oxides are the key materials for develop-ent of semiconducting gas sensors with improved gas-sensing

roperties [1–7]. One-dimensional (1D) nanostructures such asanowires, nanorods and nanobelts have become the focus of

ntensive investigation in the past decade as potential build-ng blocks for nanoscale devices and sensors [4,6,7]. Metal oxidemainly In2O3, SnO2 and ZnO) nanowires have been widely stud-ed in the field of chemical sensing due to their excellent electricalnd optical properties, with the ease of fabrication [1,3,5]. Sensoresponse and selectivity have been greatly improved by using func-ional layers on the surface of nanostructure such as noble metalsr metal oxides layer [1,2].

Heterostructured 1D nanomaterials have received great atten-ion due to their unique properties, which give more versatileunctions compared with monolithic nanomaterials when used foranoscale devices [2,8–13]. Complex structures of different oxidesave been obtained by properly combining vapor–liquid–solidVLS) and vapor–solid (VS) condensation: core–shell [14],ore–multishell [2], longitudinal [15] and branched heterostruc-

ures [16]. The heterostructures are being strongly investigated forts functional properties arising from the interconnected junctions.mongst the heterostructures, core–shell nanostructures have

∗ Corresponding authors. Tel.: +65 6790 6661; fax: +65 6790 9081.E-mail addresses: nand0005@ntu.edu.sg (N. Singh), pslee@ntu.edu.sg (P.S. Lee).

925-4005/$ – see front matter © 2011 Elsevier B.V. All rights reserved.oi:10.1016/j.snb.2011.09.073

been found attractive in chemical sensors [17–25]. For example;SnO2–ZnO, ZnO–CdS, ZnO–ZnS coaxial nanocables and CuO–SnO2p–n junction nanorods were applied as O2, NO2, NH3 and H2Sgas sensors [17,20,21,23–25]. Compared to a pristine nanorodbased gas sensor, the coaxial nanocable based gas sensor showeda superior response. For example; ZnO–CdS coaxial nanocableshave shown enhanced sensitivity towards NH3 [20]. Its superiorperformance has been attributed to the increased surface area ofZnO–CdS coaxial nanocables after deposition of a CdS shell on thesurface of the ZnO nanorods [20]. Zhu et al. have reported the �-Fe2O3–ZnO core–shell nanorods that dramatically improved theethanol sensing when compared to the pristine �-Fe2O3 nanorods[25].

A sensor device composed of nanowires with a single crys-talline core and a polycrystalline shell possesses advantages overdevices made of monolithic nanowires or polycrystalline thinfilms. Such core–shell nanowires enhance both receptor and trans-ducer functions of the device. For example, the polycrystallineouter shell serves to provide abundant adsorbing sites for gasmolecules [26], this may enhance the receptor function. Secondly,the single crystalline core allows fast transport of charge carrierduring the interaction of gas molecules with the nanowire andenhances the transducer functions. The main objective of this workis to distinguish the advantages of heterostructures over mono-

lithic nanostructures in the sensing and selectivity of differentclass of gases, namely the reducing and oxidizing gases. In thiswork 1D core–shell nanostructures were synthesized using anevaporation–condensation method where single crystalline In2O3

ctuators B 160 (2011) 1346– 1351 1347

nca

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wtflAwttsncBtegdi

3

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Fig. 1. FESEM images of (a) as grown In2O3 nanowire serving as core, (b) afterdeposition of the ZnO shell layer and inset shows the magnified view of the hetero-structure surface, (c) device, (d) the area selected in red square (For interpretation

N. Singh et al. / Sensors and A

anowire serves as a core in the heterostructure with a grainy poly-rystalline shell of ZnO. Sensing properties of these nanowires withnd without ZnO shell have been investigated.

. Experimental details

In2O3–ZnO core–shell nanowires were synthesized in a hori-ontal double tube VLS furnace in a two-step growth process [27].n the first step, core In2O3 nanowires were synthesized at 900 ◦Csing 9 nm gold layer as catalyst for the nanowire growth. Therowth was carried out on alumina substrate with growth dura-ion of 30 min. In the second step, smaller growth duration of 5 minas used for the ZnO shell deposition on the In2O3 core without

atalyst. The source temperature and the argon flow rate were keptonstant at 900 ◦C and 50 sccm respectively, as in the first step. Finalroducts on the alumina substrate were collected near the coolernd (450–500 ◦C) of the tube. The morphology, crystallinity andomposition of as synthesized products were characterized by fieldmission scanning electron microscope (FESEM) on a JEOL 7600Fcanning electron microscope operated at 5 kV and high resolutionransmission electron micrographs (HRTEM), selected area electroniffraction (SAED) patterns and Energy dispersive X-ray (EDX) ofingle nanowire were collected using a JEOL JEM 2100F microscopet an accelerating voltage of 200 kV.

For the fabrication of sensors, a platinum interdigitated elec-rode structure was deposited by sputtering over the pristine In2O3nd In2O3–ZnO core–shell nanowires. A Pt heater was depositedn the backside of the alumina substrate of 2 mm × 2 mm for pre-ise heating. The distance between the interdigitated contacts was00 �m. The sensor operating temperature was achieved by apply-

ng a constant voltage to the heater, using the same Pt resistancelso as a thermometer. The selection of substrate for the sensorlatform plays an important role especially in higher tempera-ure operations. Higher working temperature can produce leakagehrough the substrate which deteriorates the sensor performance.o it is useful to use a poor electronic conducting substrate withigh thermal conductivity (e.g. alumina) for the high working tem-erature resistor based devices.

The responses of the core–shell nanowires to different gasesere evaluated by measuring the resistance/conductance varia-

ion upon exposure to various concentrations of different gases. Theow-through technique was used to test the gas sensing properties.

constant synthetic air flux (0.3 l/min) at atmospheric pressureas used as gas carrier for the dispersion of the analyte gases in

he desired concentration. All measurements were performed in aemperature-stabilized sealed chamber at 20 ◦C under 50% RH. Theensor conductance was monitored by the volt-amperometric tech-ique at a constant bias voltage (1 V). The sensing properties wereharacterized at working temperatures between 100 and 400 ◦C.efore sensing measurements, all samples were pre-stabilized athe working temperature for 10 h. Various concentrations of differ-nt gases were obtained by diluting a premixed concentration ofas in air. The sensor response (S) was defined as the ratio of theevice resistance (conductance) in oxidizing (reducing) gas to that

n air respectively.

. Results and discussion

FESEM image in Fig. 1(a) shows the typical morphology of In2O3anowires which serves as core in the heterostructure. The aseposited In2O3 nanowires were found to be single crystalline with

verage diameter of ∼150 nm and a length of 5–20 �m randomlyistributed on the alumina substrate. In the second step, ZnO shell

ayer was deposited on the In2O3 nanowires core, without usingny catalyst. The growth duration in second growth step was kept

of the references to color in this figure legend, the reader is referred to the web ver-sion of the article.) in (c). (e) The wide area EDX pattern obtained from the as growncore–shell nanowire sample.

short (5 min) to maintain a small ZnO shell thickness. The mor-phology of the as synthesized core–shell nanowires is shown inFig. 1(b). A grainy ZnO shell layer covering the nanowire core can beobserved in the inset of Fig. 1(b). These granules on the surface werefound polycrystalline ZnO which is discussed later in this section.Fig. 1(c) and (d) shows the SEM image of the as fabricated deviceand nanostructures at the channel of the device respectively. Thepresence of Zn, In and O was confirmed by the broad area energydispersive X-ray spectroscopy (EDS) study on the as grown samples(Fig. 1e). Sharp peaks of Zn (L-line), In (L-series) and O (K-line) wereobtained.

Detailed study of the crystal structure and composition of thesingle core–shell nanowire was performed under TEM. Fig. 2(a)shows the TEM image of a typical In2O3–ZnO core–shell nanowirewith the granular ZnO on the surface. HRTEM image (Fig. 2b) andSAED patterns in Fig. 2(c and d) reveal the single crystalline core(cubic indium oxide) and poly crystalline ZnO shell. The SAED pat-terns are indexed for single crystalline cubic phase of In2O3 alongzone axis (ZA) [1 0 2] and the polycrystalline rings were obtained forthe wurtzite ZnO. In the polycrystalline phase, collective reflectionsfrom the various planes construct ring patterns in the diffrac-tion space. Thus, the ring patterns confirm that the ZnO shell is

polycrystalline. Starting from the inner ring, A, B, C and D corre-spond to the reflection from wurtzite ZnO planes of (1 0 0), (0 0 2),(1 0 2) and (1 1 0) respectively. To further investigate the composi-tion of core–shell nanowires, a TEM-EDS (energy dispersive X-ray

1348 N. Singh et al. / Sensors and Actuat

Fig. 2. TEM analysis of (a) as grown hetero-structure showing the grainy outersurface, (b) HRTEM image of the same, (c) SAED pattern obtained from the outershell shows the polycrystalline diffraction rings of wurtzite ZnO, (d) SAED patternobtained from the core area of the heterostructure, shows the diffraction patternos

ssmneo

for both devices. It was observed that the ZnO–In2O3 nanowire

f a single crystalline cubic phase of the In2O3 and (e) demonstrates the TEM-EDStudy, a line profile obtained from a single nanowire (shown in the inset).

pectroscopy) study was performed on a single nanowire. Fig. 2(e)hows the TEM-EDS concentration line profiles of Zn, O and In,easured along the cross section of the In2O3–ZnO core–shell

anowire. As clearly shown, Zn is located at the outer surface, cov-ring the nanowire core. In contrast, In is located in the interiorr core of the nanowire. This proves the formation of In2O3–ZnO

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Fig. 3. A representative plot of dynamic sensor responses obtained from the devices

ors B 160 (2011) 1346– 1351

core–shell nanowires. The elemental mapping performed on theIn2O3–ZnO heterostructure is shown in supporting information S1,which further confirms the formation of core–shell nanostructure.

The VLS growth mechanism for the core In2O3 nanowires withgold serving as the catalyst in the nanowire growth is discussedelsewhere [27]. ZnO shell was deposited without using any catalyst;as a result random nucleation of ZnO on the In2O3 nanowire leadsto the formation of granular structures. The growth of ZnO in poly-crystalline form is related to the short deposition duration and lowsynthesis temperature. These unique structures with single crys-talline core and polycrystalline shell possess certain advantageswhen used as a chemical sensor. The grainy and rough outer sur-face of the nanostructure creates abundant adsorption sites for thegas molecules [26], which enhance the sensor receptor function.In addition, the presence of homo and hetero nanojunctions in themultiple nanowires network create different potential barriers onthe electrons percolation paths. ZnO has been previously used as ashell on SnO2, TiO2 and Fe2O3 in a core–shell structure to enhancethe gas sensing properties [23–25]. It is noteworthy that the ZnOshells in these prior works are single crystalline [23–25]. Lao et al.[28] have reported the formation of In2O3–ZnO heterostructureswith In2O3 core and ZnO secondary arms. It has been observed thatone step growth of the hierarchical (In2O3 core and ZnO secondaryarms) structure forms single crystalline nanostructures.

In order to distinguish the performance of the pristine In2O3and core–shell In2O3–ZnO nanowires as a chemical sensor, thesensing properties towards oxidizing and reducing gases wereinvestigated in various concentrations under different work-ing temperature. Both types of nanowires were tested for CO(50–400 ppm), NO2 (0.2–1 ppm), ethanol (100–400 ppm) andhydrogen (1000–4000 ppm) within a working temperature range of100–400 ◦C. The gas flow rate was kept constant at 300 sccm duringthe whole experiment for all gases. Fig. 3 shows the typical sensorresponse plot for both types of nanowires towards different con-centrations of ethanol vapors. The first two cycles were measuredwith the same concentration to avoid any false response upon firstexposure.

Fig. 4 summarizes the sensor responses for various gaseswith different working temperature for both pristine In2O3 andcore–shell In2O3–ZnO nanowires. Fig. 5 depicts the comparison ofall the gases tested at the optimum working temperature for bothtypes of devices. A maximum sensor response for CO, H2 and NO2was obtained in the temperature range of 300–350 ◦C whereas forethanol the maximum sensor response was found near 350–400 ◦C

sensors show higher response towards CO, ethanol and hydrogengases (which are reducing species) compared to the oxidizing gasNO2 (Fig. 5). The NO2 concentrations used in the experiment were

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N. Singh et al. / Sensors and Actuators B 160 (2011) 1346– 1351 1349

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devic

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Fig. 4. Gas sensing profiles of (a) In2O3 and (b) In2O3–ZnO core–shell nanowire

elatively low compared to the other two gases, because of its highlyxidizing nature. On the other hand, pristine In2O3 nanowires showignificantly better response (maximum at 350 ◦C working temper-ture) towards 1 ppm NO2 which is almost 5.5 times higher thann2O3–ZnO core–shell nanowires. The pristine In2O3 nanowiresensor responds well to the NO2 gas when the working tempera-ure is higher than 200 ◦C. A low concentration of 200 ppb NO2 canead to a high sensor response of ∼5.4 (±9.3%) at 350 ◦C for pris-ine In2O3 nanowires (Supporting information S2). In contrast, theensor composed of core–shell nanowires showed a lower sensoresponse (∼1.45 ± 11.2%) with longer response time for the sameas concentration. In literature, pristine In2O3 nanowires have beenound to be highly sensitive and selective towards NO2 gas [29,30].

out et al. [29] have reported high sensor response of ∼44 for 1 ppmO2 at 150 ◦C from In2O3 nanowires (20 nm diameter) preparedy template assisted growth. Xu et al. [30] have reported a sensoresponse of ∼2.5 for 1 ppm NO2 at 250 ◦C from In2O3 nanowires inomparison to a sensor response of ∼17.5 for 1 ppm NO2 at 350 ◦Crom In2O3 nanowires in this work. Other metal oxide nanomateri-ls such as ZnO nanorods (1.4 at 100 ppb NO2) [31], SnO2 nanobelts2.3 at 300 ppb NO ) [32] and WO nanowires (21 at 10 ppm NO )

2 3 229] were also found to be attractive for NO2 detection.

For reducing gases, the responses of the devices were oppo-ite to the oxidizing gas (NO2). As evident in Figs. 4 and 5,

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ig. 5. The gas sensing performances of In2O3 and ZnO–In2O3 core–shell nanowiresith their respective optimized working temperatures are plotted with the same

as concentration for both types of nanowires: 4000 ppm H2 at 300 ◦C and 350 ◦C, ppm NO2 at 350 ◦C and 300 ◦C, 400 ppm CO at 350 ◦C and 400 ◦C, 400 ppm ethanolt 400 ◦C and 350 ◦C, for In2O3 and ZnO–In2O3, respectively.

es towards CO (100 ppm), NO2 (1 ppm), H2 (2000 ppm) and ethanol (100 ppm).

the In2O3–ZnO core–shell nanowire sensor shows a significantlyimproved sensing property for reducing gases compared to thepristine In2O3 nanowire sensor. A sensor response of ∼7 (±3.1%)for 2000 ppm H2 was obtained from core–shell nanowires incomparison to ∼2 (±6.5%) for the pristine In2O3. A high sen-sor response of ∼265 (±7.1%) for 400 ppm ethanol at 350 ◦Cwas obtained from In2O3–ZnO nanowire compared to the max-imum sensor response of ∼17 (±4.5%) from the In2O3 nanowireat 400 ◦C for similar gas concentration (Fig. 5). This result showsthe high selectivity of the In2O3–ZnO nanowire for ethanol. Thedynamic repeatability was observed for different gases in thesame experiment by exposing the nanowires to the sensing gasesone after another for more than 26 h. The sensing performanceswere found to be repeatable and stable for all gases. In the lit-erature, Hwang et al. [13] have observed a slight increase inthe NO2 sensor response (from 1.6 to 2.3 for 10 ppm NO2) forZnO–SnO2 core–shell (with single crystalline SnO2 shell) nanowiresensor compared to the increase in the reducing gases sen-sor response (41–280 for 200 ppm ethanol, 2.5–8.3 for 200 ppmH2).

3.1. Sensing mechanism

In the network nanowire sensors with or without a shelllayer, there are abundant of junctions formed along the percola-tion path of charge carriers. Only the homointerfaces are formedat the junctions in the pristine In2O3 nanowire sensor. In con-trast, combinations of homo and heterointerfaces can be formedin the In2O3–ZnO core–shell nanowire sensor. The presence ofZnO shell layer creates heterojunctions (In2O3–ZnO) which pro-vides additional energy barrier at the junction, augmenting thechange in resistance of the nanowires towards gas exposure.In the sensing mechanism of such devices, the role of poly-crystalline shell layer and nanowire junctions are discussed. Asignificantly higher response for ethanol and H2 was obtained fromIn2O3–ZnO nanowires while pristine In2O3 nanowires showed abetter response for NO2 (Supporting information S2).

In the pristine In2O3 nanowires at high working temperature of100–400 ◦C, an electron depletion layer forms near the surface bythe chemisorption of oxygen species, which increases the deviceresistance. Upon gas exposure to the device, the surface becomesmore resistive or conductive depending on the oxidative or reduc-

tive interaction with gases, respectively. Along with the variationin resistance of the nanowire during gas exposure, energy barriersat the inter nanowire contacts have a profound effect on the finalresponse of the sensor device.

1350 N. Singh et al. / Sensors and Actuat

Fig. 6. Illustration of the charge transport through (a) homo-structures nanowirejunction followed by cross section contact and formation of an energy barrier at thejunction, (b) hetero-structured core–shell nanowire junction followed by the crosssectional view with two depletion regions and formation of three energy barriers att

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rication. N. Singh acknowledges the research scholarship providedby Nanyang Technological University, Singapore.

he interfaces.

Similar electron depletion layer forms at the surface of ZnOhell in the In2O3–ZnO core–shell nanowire (refer to Fig. 6b). Inhe In2O3–ZnO core–shell nanowire, an additional electron deple-ion layer forms at the In2O3–ZnO interface due to the differences inork function of the core and shell materials. The thicknesses of theepletion layers play a crucial role in the carrier transport betweenensing gas and nanowire material [13]. In the metal oxides, theepletion layer thickness exists in a range of 11–21 nm for a work-

ng temperature of 327–427 ◦C [33]. A thin shell layer may get fullyepleted resulting in complex effect on the sensing mechanism13].

Percolation paths of the electrons in the nanowires networkre composed of multiple nanojunctions with a potential barrier atach junction. The height of the potential barrier at the homojunc-ions mainly depends on the surface states, oxygen vacancies andhe depletion layer on the nanowire surface due to chemisorptionsf oxygen ions [34,35]. The potential barrier in the heterojunctionss more complex and depends on the work function and band gapifferences between the two materials forming heterostructure, asell as the presence of eventual surface states [36]. Because of the

omplexity of properly determining surface states, the band struc-ure is often approximated ignoring their effects and applying thenderson’s model [37]. In this frame, the barrier at the ZnO–In2O3

nterface is asymmetric, with a depletion layer building up in thenO side and an accumulation layer building up in the In2O3 side.

schematic diagram is shown in Fig. 6.In nanowires network devices, charge carriers have to travel

hrough large number of inter-nanowire junctions present alonghe channel. In In2O3–ZnO core–shell nanowires, due to the largeresistance of the polycrystalline ZnO shell, charge carriers prefer

less resistive path through the single crystalline core in ordero reach another nanowire though the shell. At a heterointerfacebetween two In2O3–ZnO core–shell nanowires) there are threenergy barriers involved (shown in Fig. 6b). This consists of twoarriers at the heterointerfaces between In2O3–ZnO in each core

hell nanowire and one at the homointerface between the poly-rystalline ZnO shells of two nanowires. Charge carriers have toercolate through all three potential barriers (which are connected

n series) in order to reach to the other nanowire.

ors B 160 (2011) 1346– 1351

3.2. Reducing species

Exposure to reducing gases (such as ethanol, H2 and CO) reducesthe depletion layer thickness at the surface of pristine In2O3nanowires due to their electron donating nature, resulting in anincreased conductance of the device. In pristine In2O3 nanowires,the relative change in the conductance (sensor response) is limitedby the modulation of surface depletion layer. As a result reduc-ing gases show lower response on pristine In2O3 nanowires sensordevice. On the other hand, In2O3–ZnO core–shell nanowires withpolycrystalline ZnO shell consist more potential barriers (e.g. atsurface depletion layer, polycrystalline grain boundaries and het-erointerfaces) to be modulated during reducing gas exposure. Inaddition, polycrystalline ZnO creates more adsorption sites for thegas molecules. The combined effect of the polycrystalline ZnO shelllayer and modulation of potential barriers on the percolation pathupon gas exposure, defines the sensor behavior for different gases.The significant enhancements in the sensor response and selectiv-ity for the reducing gases (ethanol, H2) have been achieved by thepresence of polycrystalline ZnO shell on In2O3 nanowire core.

3.3. Oxidizing species

Pristine In2O3 nanowires showed higher sensor responsetowards oxidizing gas NO2 (Supporting information S2). The highsensor response of pristine In2O3 for NOx gases is well knownand described in literature [29,30]. On the other hand, In2O3–ZnOcore shell nanowires upon exposure to oxidizing gases, the initialdepletion layer (before exposure) in the ZnO shell further extendsand connects with the interface depletion layer (for the thin shelllayer). As a result the resistance of the device increases due to theformation of the large integrated depletion region. Under such con-ditions, during sensing in oxidizing environment, the oxidizing gasmolecules have to withdraw electrons from the nanowire core andthe electrons requires a larger energy to surmount the large inte-grated depletion region. This results in the low NO2 responses forthe In2O3–ZnO core–shell heterostructures. The relative change inthe current before and after exposure to NO2 is small due to theinitial large potential barrier height.

4. Conclusions

The role of polycrystalline ZnO shell layer in a core–shellnanowire has been investigated in the sensing of different classof gases, which was found to be playing a decisive role in selec-tive sensor response enhancement of reducing species. In addition,combinations of homo and heterointerfaces formed at the junc-tions in the In2O3–ZnO core–shell nanowires sensor improved thesensitivity towards reducing gases by lowering the potential bar-rier heights along the charge carrier path. However pristine In2O3nanowires show a better response towards NO2 (oxidizing gas).

Acknowledgements

We thank Nicola Poli for his technical support during device fab-

Appendix A. Supplementary data

Supplementary data associated with this article can be found, inthe online version, at doi:10.1016/j.snb.2011.09.073.

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Biographies

Nandan Singh completed his M.Tech. (Materials Science) in 2007 from Indian Insti-tute of Technology (IIT) Kharagpur, India. Currently he is pursuing his Ph.D. in NTUSingapore. His research focus is on synthesis of oxide semiconductor nanowires forthe application in chemical sensing and optoelectronic devices.

Andrea Ponzoni received his Ph.D. from University of Brescia, Italy. His researchfocus is on the study of metal oxides to prepare gas sensors based on differenttransduction principles including conductometric, SAW and diode devices.

Raju Kumar Gupta completed his Ph.D. from the National University of Singapore.His research focus is on the synthesis of semiconducting inorganic and organicnanowires.

Pooi See Lee is an Associate Professor from the School of Materials Science andEngineering, Nanyang Technological University, Singapore. Her research interest ison the synthesis of nanowires and their applications.

Elisabetta Comini received her Ph.D. in Material Science at the University of Brescia.She is presently working on chemical sensors with particular reference to depositionof thin films by PVD technique and electrical characterization of MOx thin films.In 2001 she has been appointed assistant professor at the university of Brescia,Italy.