Alteration of Ti 2p XPS spectrum for titanium oxide by low-energy Ar ion bombardment

Alteration of Ti 2p XPS spectra for TiO2 single crystal was measured during Ar ion sputtering. The acceleration voltage of Ar ion bombardment ranged from 10 V to 2 kV. Components of Ti2+ and Ti3+ as reduced states have appeared, in addition to the Ti4+ state, after ion bombardment at 2 kV. However, although a small amount of Ti3+ has been observed in the case of 10 V bombardment, the Ti2+ component has not appeared. The intensities of the reduced states (Ti2+ and/or Ti3+) that have appeared at each acceleration voltage reach constant values after a long sputtering time. This saturation shows that the surface reaches an equilibrium state between the sputtered atoms and implanted ions. Moreover, the intensities of the reduced states increase with increasing accelerating voltage of the primary ions. The alteration by 10 V ion bombardment suggests that there is a critical energy for reduction to the Ti2+ state. Copyright (C) 2002 John Wiley Sons, Ltd.