COMPARATIVE 2ND-HARMONIC GENERATION AND X-RAY PHOTOELECTRON-SPECTROSCOPY STUDIES OF THE UV CREATION AND O-2 HEALING OF TI3+ DEFECTS ON (110)RUTILE TIO2 SURFACES
An. Shultz et al., COMPARATIVE 2ND-HARMONIC GENERATION AND X-RAY PHOTOELECTRON-SPECTROSCOPY STUDIES OF THE UV CREATION AND O-2 HEALING OF TI3+ DEFECTS ON (110)RUTILE TIO2 SURFACES, Surface science, 339(1-2), 1995, pp. 114-124
SHG studies on polished and etched (110) rutile TiO2 single-crystal su
rfaces suggest that above band gap, low-energy (4.7 eV) ultraviolet ph
otons create stable Ti3+ surface defects in UHV. Such defects can be h
ealed by subsequently exposing the surface to O-2 gas. These results a
re similar to recently reported measurements on polished and etched (0
01) rutile single-crystal surfaces. Observations on the (001) surfaces
were interpreted as the photodesorption and re-adsorption of molecula
r oxygen bound loosely to Ti3+ defects on the surface as a Ti4+:O-2(-)
complex. For the current (110) study, XPS was used to confirm the def
ect type and to quantify the density of Ti3+ defects created. Defects
on the surfaces studied using XPS were generated using photons of even
lower energy (3.4 eV), indicating that the oxygen species removed was
very loosely bound. The same defect creation and healing processes we
re also observed on a nearly defect-free thermally annealed single-cry
stal surface using XPS. Whether bridging oxygen ions on the (110) surf
ace or O-2(-) tons are the photo-labile species has yet to be determin
ed. Transient photodesorption of O-2 at high oxygen pressure also was
observed using SHG. SHG has proven to be a sensitive probe of surface
defects, consistent with XPS results, under conditions ranging from UH
V to atmospheric.