PNNL

Abstract

Surfaces of titanium dioxide in both rutile and anatase polymorphs have attracted significant attention in catalysis and photochemistry. The (110) orientation of rutile, and to a lesser extent other rutile orientations, have been studied on an atomic scale, yielding information on surface structure and chemical reactivity. In contrast, the thermal and photochemistry of well-defined, single-crystal anatase surfaces had not been investigated, largely because of the metastable nature of anatase , as well as the lack of availability of high-quality surfaces. Here we describe a study of the adsorption and photoreactivity of an organic adlayer, trimethyl acetate (TMA), on structurally-excellent anatase (001) epitaxial thin films grown by oxygen plasma assisted molecular beam epitaxy (OPAMBE). High-resolution scanning tunneling microscopy (STM), x-ray photoelectron spectroscopy (XPS), and photodesorption spectrometry have been used to study the chemisorptions and ultraviolet (UV) light-induced photodecomposition of TMA in ultrahigh vacuum. UV light promotes hole-mediated photodecomposition of TMA, resulting in decarboxylation to yield tert-butyl radical and CO2. The photochemical rate constant is equal to that measured for OPAMBE grown rutile TiO2(110) surfaces.