IUVSTA 15th International Vacuum Congress (IVC-15), AVS 48th International Symposium (AVS-48), 11th International Conference on Solid Surfaces (ICSS-11)
    Surface Science Monday Sessions
       Session SS1-MoP

Paper SS1-MoP3
High Spatial Resolution Soft X-ray Photoemission Study of WO3 Thin Films

Monday, October 29, 2001, 5:30 pm, Room 134/135

Session: Electronic Structure Poster Session
Presenter: L. Lozzi, University of L'Aquila, Italy
Authors: L. Lozzi, University of L'Aquila, Italy
M. Passacantando, University of L'Aquila, Italy
S. Santucci, University of L'Aquila, Italy
S. La Rosa, Sincrotrone Trieste SCpa, Italy
N. Yu Svetchnikov, Sincrotrone Trieste SCpa, Italy
Correspondent: Click to Email
Tungsten trioxide (WO3) is a wide gap n-type semiconductor and it is the subject of an intense both theoretical and experimental studies because of its interesting applications, such as gas sensors towards different gases, like NO2 and H2S, and as electrochromic film. Many of these possible applications are mainly due to the oxygen vacancies. For example, in the sensing mechanism, the gas species are adsorbed on the surface changing the concentration of the free electrons on the surface. These electrons are present on the surface because of the oxygen vacancies. The variation of this concentration modifies the electrical conductivity of the film. Similarly, the presence of substoichiometric WO3-x compounds, determines the optical properties of these films. An important parameter in the preparation of WO3 thin films is the thermal treatment following the sample growth. For example it has been shown that the gas sensitivity and response time are strongly influenced by the annealing procedure, because of the phase transitions induced by the annealing. In this work the WO3 surface chemical composition has been studied by means of high resolution soft X-ray photoemission spectroscopy. We have studied the surface properties of both as deposited samples and samples after annealing in air at high temperatures. Valence band and W 4f core levels have been analysed on different samples positions and high resolution maps have been acquired. The valence band spectra have shown W 5d density of state at the Fermi level, indicating the presence of metallic tungsten on the surface. This has been confirmed by the W 4f signal, which present both metallic and oxidized phases. The high resolution maps, obtained following both valence and core states, have clearly evidenced the presence non stoichiometric areas and of some metallic islands.