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Observation of Substrate Orientation-Dependent Oxygen Defect Filling in Thin WO3−δ/TiO2 Pulsed Laser-Deposited Films with in Situ XPS at High Oxygen Pressure and Temperature
journal contribution
posted on 2012-09-11, 00:00 authored by Artur Braun, Funda Aksoy Akgul, Qianli Chen, Selma Erat, Tzu-Wen Huang, Naila Jabeen, Zhi Liu, Bongjin
S. Mun, Samuel S. Mao, Xiaojun ZhangSubstoichiometric tungsten oxide films of approximately
10 nm thickness
deposited with pulsed laser ablation on single-crystal TiO2 substrates with (001) and (110) orientation show defect states near
the Fermi energy in the valence-band X-ray photoelectron spectroscopy
(XPS) spectra. The spectral weight of the defect states is particularly
strong for the film grown on the (001) surface. In situ XPS under
an oxygen pressure of 100 mTorr shows that the spectral weight of
the defect states decreases significantly at 500 K for the film on
the (110) substrate, whereas that of the film grown on the (001) substrate
remains the same at a temperature up to 673 K. Furthermore, diffusion
of titanium from the substrate to the film surface is observed on
the (110) substrate, as is evidenced by the sudden appearance of the
Ti 2p core level signature above 623 K and below 673 K. The film grown
on the (001) surface does not show such an interdiffusion effect,
which suggests that the orientation of the substrate can have a significant
influence on the high-temperature integrity of the tungsten oxide
films. Quantitative analysis of the O 1s core level XPS spectra shows
that chemisorbed water from sample storage under ambient conditions
is desorbed during heating under oxygen exposure.