Surface structure and composition of nanocrystalline SnO 2 thin films obtained by Chemical Vapor Deposition
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Surface structure and composition of nanocrystalline SnO2 thin films obtained by Chemical Vapor Deposition Davide Barreca1, Elza Bontempi2, Laura E. Depero2, Cinzia Maragno3, Eugenio Tondello3 ISTM-CNR and INSTM - Department of Chemical Sciences - Padova University - Via Marzolo, 1 - 35131 Padova, Italy. 2 INFM and Structural Chemistry Laboratory – Department of Mechanical Engineering - Brescia University - Via Branze, 38 – 25123 Brescia, Italy. 3 Department of Chemical Sciences and INSTM - Padova University - Via Marzolo, 1 – 35131 Padova, Italy. 1
ABSTRACT Nanocrystalline SnO2 thin films were synthesized by Chemical Vapor Deposition on Si(100) and Al2O3 substrates using bis(diethylamino)dimethylstannane(IV) [(CH3)2Sn(N(C2H5)2)2] as precursor. Film growth was performed at 400-500°C in an O2(H2O)+N2 atmosphere, with the aim of studying the effects of the synthesis conditions on the coating properties. The sample chemical composition and surface morphology were analyzed by X-ray Photoelectron Spectroscopy (XPS) and Atomic Force Microscopy (AFM), while their structural features were investigated by Glancing Incidence X-ray Diffraction (GIXRD) and X-ray Reflectivity (XRR). In this paper, the attention is focused on the interplay between film nanostructure and morphology, with particular regard to the influence of the growth surface. INTRODUCTION The cassiterite tin dioxide (SnO2), an n-type semiconductor [1], has received a widespread attention for several technological applications, including transparent electrodes and conductors [2], solar cells, heterogeneous catalysts, and gas sensors for oxidable gases [3-6]. The functional properties of these systems are strongly dependent on defects nature as well as on crystallite size, chemical composition and surface morphology [7,8]. A thorough investigation of these characteristics is therefore a key-step in order to develop materials with tailored performances. Since the system features are appreciably influenced by the synthetic approach, different preparation techniques have been employed to obtain pure and doped SnO2 thin films. These include spray pyrolysis, magnetron sputtering, electron beam evaporation, ion-assisted deposition and sol-gel [5]. The Chemical Vapor Deposition (CVD) process is a valuable method since it allows a modulation of nanosystem properties by a suitable choice of the molecular precursor, together with an accurate control of the growth conditions. The present work focuses on the correlations between surface structure and composition of SnO2 nanocrystalline thin films obtained by CVD from [(CH3)2Sn(N(C2H5)2)2] in a nitrogen-wet oxygen reaction atmosphere. The main advantages of the used precursor have already been reported [9]. The films were deposited on Si(100) and α-Al2O3 in view of possible applications in gas sensing devices. Results concerning the influence of the synthesis parameters on the surface structure and composition of the layers are presented and discussed.
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EXPERIMENTAL DETAILS SnO2 films were deposited in a hot-
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