Paper SS1-WeA5
Preparation of TiO₂ Nanocrystals by Oxidation of Ti-Au Surface Alloys

Wednesday, October 22, 2008, 3:00 pm, Room 208

The formation of TiO₂ nanoparticles on a non-reactive, single-crystal noble metal substrate is useful for studies of nanocatalytic reactions. The formation of Ti-Au surface alloy on Au(111) surface and the growth of TiO₂ nanocrystals from the surface alloy have been studied with scanning tunneling microscopy (STM), scanning tunneling spectroscopy (STS) and Auger electron spectroscopy (AES). In our study, titanium was vapor deposited on Au(111) surface at 200 K. STM images show that Ti nucleates at the elbows of the surface herringbone reconstruction. At low Ti coverages (< 0.3 ML) extensive surface alloying occurs already at 400 K through island – substrate atomic exchange. Yet even at 900 K some amount of Ti stays near the surface. The exposure of the sample at 900 K to the flux of O₂ leads to oxidation of this sub-surface Ti and to growth of TiO₂ nanocrystals. At low initial Ti coverages (< 0.1 ML) the majority of the crystallites have triangular shape and at higher coverage, we observe hexagonal and ridge-like crystallite formation. The results of our experiments form an interesting comparison to recent studies of TiO₂ nanocrystals formed via reaction of vapor-deposited Ti on water multilayers on Au(111).