AVS 47th International Symposium
    Surface Science Tuesday Sessions
       Session SS-TuP

Paper SS-TuP35
Oxygen Loss and Recovering Induced by Ultra High Vacuum and Oxygen Annealing on WO3 Thin Film Surfaces

Tuesday, October 3, 2000, 5:30 pm, Room Exhibit Hall C & D

Session: Poster Session
Presenter: S. Santucci, University of L'Aquila, Italy
Authors: M. Pssacantando, University of L'Aquila, Italy
L. Lozzi, University of L'Aquila, Italy
C. Cantalini, University of L'Aquila, Italy
S. Santucci, University of L'Aquila, Italy
Correspondent: Click to Email
Thin films of WO3 with thickness in the range of 150 nm have been deposited onto silicon substrates by thermal evaporation. The films as deposited and annealed at 300 and 500°C in oxygen for 24 hours were submitted to UHV annealing. XPS measurements (W4f and valence band) show for the as deposited sample annealed at 200°C in steps of 50°C a marked increase of the metallic features of the surface attributable to oxygen loss. This film extracted from the UHV ambient and annealed in oxygen at 200° shows XPS features meaningful of a renewed oxygen incorporation which is again reduced by the UHV annealing demonstrating an evident reversibility towards the oxygen loss and recovery for this kind of sample. Also the WO3 film treated by oxygen annealing at 300° shows an increase of the metallic character of the film surface due to oxygen loss as a consequence of the UHV annealing up to 300°C but the sample extracted from the UHV ambient and submitted to a second annealing in oxygen at 300°C for 24 h recovers oxygen remaining substantially stable and scarcely influenced by successive UHV annealing. Finally the surface of the sample initially annealed in oxygen at 500°C appears at the XPS measurements evidently stable after the UHV annealing up to 500°C. These results have been confirmed by Scanning Tunneling Microscopy measurements which evidenced for the as deposited sample a narrowing of the band gap when the annealing temperature in UHV overcomes 300°C. Gas sensing towards NO2 of samples with UHV annealing modified surfaces have been also investigated giving encouraging results respect to the increase of the sensitivity of the sensor.