Paper SS1-ThM5
Monocrystalline TiO₂ Nanoparticles Growth on Au(111) Surface by RLAD Method

Thursday, October 18, 2007, 9:20 am, Room 608

Titanium oxide is a promising photocatalytic material and has been the subject of much research throughout the last two decades. Nanostructuring is one approach for tailoring the properties of a catalyst. Recently, two methods of preparation of titania nanoparticles on Au(111) surfaces were reported (Z. Song at al. 2005 and E. Farfan-Arribas et al. 2005); yet no light-induced chemistry was observed on such nanoparticles to date. In order to prepare photoactive nanoparticles, we have conducted an extensive STM study of the growth of TiO₂ on a Au(111) surface by Reactive Layer Assisted Deposition (RLAD). The method consists of physical vapor deposition of Ti on a predeposited layer of oxygen-containing reactant followed by annealing to a higher temperature that removes the excess of the reactant. In the experiments with water as a reactive layer, we investigated the dependence of morphology of the produced arrays of titania nanoparticles on the thickness of the water multilayers. At water coverages above 50 ML we found evidence for role of an intermediate liquid water layer formed as the temperature is increased. The dynamics of water evaporation, rather than the underlying Au surface reconstruction, determined the particle distribution on the surface in this case. This relatively thick water layer also has caused us to observe evidence of the titanium hydride formation. At temperatures above 300 K the hydride decomposed leaving the titanium buried under a gold layer. The typical size of initially formed titania nanoparticles was 1 nm. At more elevated temperatures, nanoparticles coalesced so that by a temperature of 900 K about 80 % of the titania material was converted into single-crystal, flat islands with edges parallel to Au [1-10] directions, with their heights being a multiple of 0.55 nm. The atomic structure of the islands will be discussed. We have also attempted to use NH₄NO₃ as a reactive layer and the corresponding results will be presented.