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Abstract:
ZnO, pretreated in oxygen for 12 h at 700°C and 760 Torr O2 (i.e. an oxygen-rich layer), shows a non-stationary thermolysis ( > 320°C) and photolysis (UV irradiation). After removal of about 400 monolayers from the 0001 face and 150 from the 000 face, thermal decomposition is negligible below 700°C. The photolysis (relative increase about 100% at first) could only be observed on the 0001 face over a range of about 100 monolayers. In addition the oxygen-rich films were characterized by SEM and XPS measurements. The XPS spectra qualitatively showed two different species of oxygen. The proposed model for the decomposition mechanism involves acceptor states in the forbidden gap and an established activation equilibrium via hole creation in the valence band due to UV radiation.
