RESEARCH ARTICLE Copyright © 2012 American Scientific Publishers All rights reserved Printed in the United States of America Journal of Nanoelectronics and Optoelectronics Vol. 7, 1–7, 2012 SnO 2 Whiskers with Pd Nanoparticles for Gas Sensor Applications A. V. Zaytseva 1 , V. B. Zaytsev 2 ∗ , M. N. Rumyantseva 3 , A. M. Gaskov 3 , and A. A. Zhukova 3 1 Laboratory of Physicochemistry of Nanoparticles AETechnologies LTD, Sretensky bul., 7/1/8, 3, Moscow, 107045, Russia 2 Physics Department, Moscow State University, Leninskie gory, 119991, Russia 3 Chemistry Department, Moscow State University, Leninskie gory, 119991, Russia Promising for the gas sensing one-dimensional tin oxide (SnO 2 ) structures are reported. Antimony- doped SnO 2 single crystal whiskers have been synthesized by in situ doping process in horizontal flow reactor. The surface of the whiskers was modified with different amount of Pd and investigated by means of atomic force microscopy (AFM). The obtained AFM data are explained by a model of Pd nanoparticles growth on the whisker surface. Sensor performance of the whiskers with Pd coating was studied and an increase of the sensor signal towards 10 ppm of carbon monoxide is found for the whiskers covered by certain amount of Pd. Keywords: Tin Oxide, Whisker, Palladium, Nanoparticles, Gas Sensor. 1. INTRODUCTION Gas-sensor devices based on semiconducting oxides such as SnO 2 have a good performance to detect different dan- gerous gases such as CO, NO 2 etc. 1–3 One-dimensional (1D) crystals of SnO 2 , i.e., whiskers, are attracting a sig- nificant interest for gas sensor application. 4 Because of the single crystalline structure of whiskers they are markedly surpass nanoparticles in stability and charge carrier mobil- ity. Pure SnO 2 whiskers are rarely used because they are characterized by rather high electrical resistance. In order to increase the charge carrier concentration and thus the electrical conductivity of SnO 2 whiskers they are mod- ified by donor additives. 5–8 The improvement of sensi- tivity and selectivity of SnO 2 -based sensor materials can be achieved by surface modification with noble metal (Pt, Pd, Au) clusters. 9–14 We have synthesized antimony doped SnO 2 whiskers with low electrical resistance and modified their surfaces with Pd nanoparticles using an impregnation route. The mechanism of nucleation and growth of the deposited Pd nanoparticles is discussed in the framework of as-called Volmer-Weber Island growth. 15 The sensing properties towards carbon monoxide (CO) of individual whiskers and thick films made of whiskers with various amount of Pd nanoparticles have been investigated. Pd amounts on the ∗ Author to whom correspondence should be addressed. whisker surfaces are determined that provide highest sen- sitivity towards CO. 2. EXPERIMENTAL DETAILS Antimony doped tin dioxide whiskers were grown from SnO + Sb 2 O 3 mixture in a controlled gaseous environment in a flow reactor (see for details Refs. [16, 17]). Accord- ing to X-ray diffraction (XRD) and selected area elec- tron diffraction (SAED) data the whiskers consist of one phase, i.e., SnO 2 cassiterite. The SAED pattern revealed that whiskers are single-crystalline. Auger spectroscopy measurements showed that Sb is mainly distributed in the surface layer of the whiskers. 17 The concentration of Sb was determined by a method described in Ref. [17]. The whiskers of SnO 2 doped with 0.12 at.% of Sb were selected for surface modification by Pd catalyst. The cat- alyst deposition was performed by impregnation of 0.5 g of SnO 2 (Sb) whiskers with 1.1 mM of Pd(acac) 2 solution in ethanol in order to get 0.1, 0.2, 0.5, 1.0 or 2.0 wt.% Pd-modified whiskers. The Pd concentration in SnO 2 (Sb) whiskers was calculated by using the weight ratio of Pd to SnO 2 . The samples were annealed at 255  C for 24 hour in air to decompose Pd(acac) 2 . Individual whiskers were adhered using indium contacts on alumina substrates. The electrical resistance (R) of indi- vidual whiskers was measured using a V7E-42 voltmeter, which allows us the resistance measurements in the range J. Nanoelectron. Optoelectron. 2012, Vol. 7, No. 6 1555-130X/2012/7/001/007 doi:10.1166/jno.2012.1404 1