Epitaxy and Atomic Structure Determination of Au/Tio 2 Interfaces by Combined EBSD and HRTEM
- PDF / 2,242,657 Bytes
- 6 Pages / 417.6 x 639 pts Page_size
- 94 Downloads / 185 Views
ABSTRACT We have studied the effects of deposition conditions on the epitaxial orientation of Au or TiO 2( 10) and on the atomic structure of Au/TiO 2 interfaces by combined EBSD and HRTEM. Two experimental conditions were explored consisting of deposition of a 12 nim Au film at 300K followed by annealing at 770K and direct deposition of a 12 rim Au film at 770K. Deposition at 300K followed by annealing at 770K give rise to a (llI)Au//(ll0)TjO2 epitaxial orientation relationship, while direct deposition at 700K temperature give rise to an epitaxial orientation relationship given by (1l2)A^//(l10)TiO2. For both orientations, two epitaxial variants are observed which are twin related. The (1 12 )Au//(1 10)TiO2 orientation has been found to minimize the interfacial lattice misfit while maximizing the number of Au-Ti bonds across the interface. INTRODUCTION Metals on oxide systems are important in numerous applications ranging from catalysts to gas sensors. The Au/ TiO2 system is of particular interest because of its high activity for low temperature oxidation of CO and its good sensitivity as CO gas sensor [1, 2]. These beneficial effects are caused in part by a unique yet unknown synergistic effect between Au islands and the TiO 2 substrate. Therefore, recent studies have been conducted on model TiO2( 110) surfaces to understand the interaction mechanisms, growth mode and surface chemical reactions [3, 4]. In this study, we are reporting results on the effect of substrate temperature and preparation method on epitaxial orientation relationship of Au islands formed on TiO 2(1 10). Preliminary results on the atomic structure of the Au/TiO 2 interfaces are also presented. EXPERIMENTS The Au films were grown on TiO 2(l 10) substrates by vapor deposition in a UHV chamber. Details on TiO 2 surface preparation and deposition method have been presented elsewhere [3]. Two deposition conditions were studied. The first one consists of deposition of a 12nm thick Au film at 300K, followed by annealing at 775K for 1 hour (Sample A). The second one consists of direct deposition of a l2nm film on a TiO 2 substrate maintained at 775K (Sample B). The samples were then transferred in air to the LEO 982 Field Emission Scanning Electron microscope (FESEM) for imaging and diffraction. Electron Backscatter Diffraction (EBSD) patterns were taken from individual Au particles using the Opal system (Oxford Instruments). With this system, a spatial resolution of the order of 80 nm has been achieved for Au [5]. High resolution transmission electron microscopy (HRTEM) was done using a Philips CM-300 on samples viewed in cross-section. 235 Mat. Res. Soc. Symp. Proc. Vol. 589 0 2001 Materials Research Society
RESULTS AND DISCUSSION
Orientation of Au films deposited at 300K and annealed at 770K (Sample A) A typical HRSEM image of a 12nm Au film deposited a 300K and annealed at 775K is shown in Fig.1 revealing a discontinuous Au film consisting of discrete Au particles with an average size of 250 nm. In this tilted SEM view, it can be seen that th
Data Loading...
