Sensors and Actuators B 118 (2006) 156–162 SnO 2 /MoO 3 -nanostructure and alcohol detection J. Arbiol a,b,∗ , J.R. Morante b , P. Bouvier c , T. Pagnier c , E.A. Makeeva d , M.N. Rumyantseva d , A.M. Gaskov d a TEM-MAT, SCT, Universitat de Barcelona, Llu´ ıs Sol´ e i Sabar´ ıs 1-3, E-08028 Barcelona, CAT, Spain b EME, Departament d’Electr ` onica, Universitat de Barcelona, E-08028 Barcelona, CAT, Spain c LEPMI-ENSEEG, 1130, rue de la Piscine, BP 75, Saint Martin d’H` eres 38402, France d Chemistry Department, Moscow State University, 1-3 Leninskie Gory, 119992 Moscow, Russia Available online 23 May 2006 Abstract SnO 2 /MoO 3 mixed samples from 0 to 100 mol% MoO 3 have been prepared by using the sol–gel method and calcined at 500 ◦ C during 24 h. The sensor response of the samples towards alcohols, C n H 2n+1 OH (n = 1–4), and NH 3 will be interpreted in terms of the acid–base properties of the nanocomposites. To support it, a detailed high-resolution transmission electron microscopy, electron energy loss spectroscopy and RAMAN analysis have been performed allowing to determine the structural, morphological and compositional evolution of this nanostructured binary system. The change on the sensing characteristics related with the Mo content on samples is explained attending to these analytical characterization results that point out the presence of Mo 2 O 3 in the very small grain of SnO 2 , about 2.5 nm, before their segregation in determining the sensing characteristics. © 2006 Elsevier B.V. All rights reserved. Keywords: SnO 2 /MoO 3 ; Semiconductor gas sensor; Nanometal oxide binary systems; Surface acidity; HRTEM; EELS; Raman 1. Introduction In late 1990s, SnO 2 and MoO 3 mixtures were shown to have excellent catalytic properties for selective oxidation of methanol and other organic compounds [1]. It is well known that the addition of metals or metal oxides with catalytic prop- erties can influence on the gas sensing behavior of the SnO 2 material [2–10]. In this case, the addition of MoO 3 to SnO 2 has been proposed as an outstanding alternative to modify the sensor response to certain gas species as the presence of Mo atoms at the surface of SnO 2 changes the acidity performances which varies mainly its reactivity with alcohols, ammonia or amine groups. Nowadays, these performances have strengthened the practical interest on nanocomposites of SnO 2 (semiconducting oxide) and MoO 3 (d-metal oxide exhibiting catalytic activity) for the devel- opment of resistive gas sensors as the catalytic characteristics in this nano-binary system are enhanced [11–15], presenting a very high active surface value. SnO 2 /MoO 3 composites are n-type semiconductors, just as the constituent oxides [12–14]. The introduction of molybdenum ∗ Corresponding author. E-mail address: arbiol@ub.edu (J. Arbiol). URL: http://nun97.el.ub.es/∼arbiol. notably reduces the electrical conductivity of SnO 2 in air, and, according to the previous literature, it may be associated either with the transfer of electrons trapped at oxygen vacancies (V 0 •• and V 0 • ) to Mo 6+ ions [14,15], Mo 6+ + V 0 • = Mo 5+ + V 0 •• (1) Mo 6+ + 2V 0 • = Mo 4+ + 2V 0 •• (2) or with the formation of Mo i 5+ interstitials in the structure of SnO 2 by the quasi-chemical reaction [12,13] Mo Sn 6+ + e ′ = Mo i 5+ (3) Thus, it is assumed SnO 2 could contain Mo ions in three different oxidation states [11–13]: Mo 6+ , Mo 5+ , and Mo 4+ . Ivanovskaya et al. [12] from electron spin resonance (ESR) measurement have corroborated that some Mo atoms present Mo i 5+ state in enough concentration to justify the conductivity diminution. Up to now, the gas-sensing properties of SnO 2 –MoO 3 materials have only been investigated at low MoO 3 contents (≤35 mol%). Furthermore, only a very few works have been devoted to obtain a morphological and structural characteriza- tion of the SnO 2 /MoO 3 binary system in order to justify the modified sensing characteristics. All these results encouraged 0925-4005/$ – see front matter © 2006 Elsevier B.V. All rights reserved. doi:10.1016/j.snb.2006.04.021