CREATION OF VARIABLE CONCENTRATIONS OF DEFECTS ON TIO2,(110) USING LOW-DENSITY ELECTRON-BEAMS

Low density (similar to mu A/cm(2)) 0.48 and 1.0 keV electron beams have been used to create surface defects on a TiO2(110) surface. These electron-beam induced defects were examined primarily by X-ray photoelectron spectroscopy (XPS) with supporting ultraviolet photoemission spectroscopy (WS). Glancing and normal emission XPS spectra of nearly defect-free surfaces revealed that Ti atoms on the surface were similar to the bulk Ti, while some surface oxygen atoms were different from the bulk oxygen. XPS of Ti 2p(3/2) was used to quantify the defect concentration and to examine the defect electronic structure. Based on our calculation of defect concentrations and the comparison of our results with results and models from the literature, we conclude that oxygen vacancies induced by election beams in the current study are mostly from the bridging oxygen sites, in agreement with the previous work. A range of defect concentrations with similar electronic structure, mainly composed of Ti3+, have been induced by low-density electron beams. Beam energy and exposure were the experimental variables. The rates of defect formation at low beam exposure were beam-energy dependent, with a faster growth rate at 0.48 keV than at 1.0 keV. These defects were similar to those by thermal annealing in vacuum, but a higher concentration of defects could be obtained with longer beam exposure. However, the e-beam induced defects were different from those produced by Ar+ ion bombardment since both this and previous studies have found defects produced by Ar+ ion bombardment to be complex, with a variety of different local environments where oxygen and titanium surface atoms coexist.