The structure and electrical conductivity of vacuum-annealed WO3 thin films

被引:118
作者
Gillet, M
Aguir, K
Lemire, C
Gillet, E
Schierbaum, K
机构
[1] Univ Aix Marseille 3, Fac Sci St Jerome, CNRS, Lab Mat & Microelect Provence,UMR 6137, F-13397 Marseille 20, France
[2] Univ Dusseldorf, Inst Phys Kondensierten Mat, D-40225 Dusseldorf, Germany
关键词
tungsten oxide; surface conductivity; RHEED; sensors;
D O I
10.1016/j.tsf.2004.04.018
中图分类号
T [工业技术];
学科分类号
08 ;
摘要
We have investigated the surface structure of monoclinic WO3 thin films on alpha-Al2O3(0001) substrates during thermal treatments in ultra high vacuum and oxygen exposure. For an annealing temperature of 450 degreesC, reflection high-energy electron diffraction shows the formation of a second WO3 phase with a pseudo cubic structure and the partial reduction to metallic tungsten clusters on the WO3 surface. Electron energy loss spectrometry confirms these changes of the surface structure. The reverse process, i.e. the oxidation of W, occurs if the samples are heated in air at 450 degreesC. Under oxygen exposure films in the monoclinic WO3 phase follow a semiconductor like behaviour with an activation energy of - 0.34 eV Reduced WO3 films exhibit a metal-like conductivity with an activation energy of approximately zero. The temperature-dependent conductivities as well as the conductivity effects that we found upon CO exposures to the WO3 thin films depend much on the thermal pre-treatments and the associated surface structures. CO exposure leads to an increase of the conductivity; this acceptor-type interaction of CO with samples that have been annealed at 450 degreesC is explained by a dissociation into carbon and oxygen, the latter interacting with oxygen vacancies. (C) 2004 Published by Elsevier B.V
引用
收藏
页码:239 / 246
页数:8
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