Abstract
We have investigated the surface structure of monoclinic WO3 thin films on α-Al2O3(0001) substrates during thermal treatments in ultra high vacuum and oxygen exposure. For an annealing temperature of 450 °C, 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 °C. 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 °C is explained by a dissociation into carbon and oxygen, the latter interacting with oxygen vacancies.
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Disclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.