Very thin films of tellurium, with mean thickness up to 100 A, were deposited in ultra high vacuum at room temperature on a Si(100) 2 x 1 surface, and were exposed to different amounts of O-2 and to the atmosphere. Ultraviolet photoelectron spectroscopy, X-ray photoelectron spectroscopy and low energy electron diffraction spectroscopy were performed in order to investigate the reactivity of the Te/Si(100) system towards oxygen. The Si(100) 2 x 1 surface is found to chemisorb O-2 and to saturate with approximate to 500 Langmuir. In contrast, the tellurium films are not active either towards oxygen or towards the atmosphere for a few minutes: no changes are detectable in the UPS and XPS spectra and LEED patterns of samples with the Si(100) surface completely covered by Te. With deposition of 1 A of tellurium the silicon substrate is not completely covered, and the sample can chemisorb a lower amount of oxygen with respect to the pure Si(100) 2 x 1 surface. The tellurium film thus acts as a protective barrier against the oxidation of silicon.
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