(213b) Influence of Ferroelectric Polarization On Palladium Thermal Stability On LiNbO3

Ferroelectric oxides such as LiNbO₃ are an interesting class of multifunctional oxides. The ability to manipulate the orientation of the ferroelectric dipoles in these materials via the application of an electric field has led to their proposed use in a variety of applications including non-volatile random access memories. While much is known about the bulk properties of these materials the effect of the orientation of the ferroelectric dipoles on surface properties has been much less explored. If surface reactivity is polarization dependent one might be able to use this property in the fabrication of nano-devices and to tailor the reactivity of catalytic surfaces. To explore this possibility in this study we have investigated the influence of the orientation of dipoles on the palladium deposition growth and thermal stability on ferroelectric LiNbO₃ surface. In ultra high vacuum (UHV) chamber, palladium was deposited on (0001) LiNbO₃ single crystal surface at room temperature with Auger Electron Spectroscopy (AES) measuring the metal deposition and substrate signal intensities. Different growth mode was observed from LiNbO₃ surface with different directions of dipole orientations. Palladium growth on the negative (c-) surface is more likely to follow a layer-by-layer mode compared with on the positive (c+) surface. When heat up the LiNbO₃ single crystal with palladium deposition, the palladium 3D island formation started at significantly lower temperature on the c+ surface than on the c- surface. To further study the impact of ferroelectric polarization on palladium agglomeration on LiNbO₃ and how agglomerated palladium particle size affects CO adsorption, temperature programmed desorption (TPD) was performed during the process of annealing the Pd/LiNbO₃ samples at various temperatures. Palladium on LiNbO₃ c- surface has higher CO adsorption coverage than the c+ surface at the same annealing temperature, which confirmed the Pd has a higher thermal stability on the c- termination surface than on the c+ termination. This study provides one of the first definitive examples of a systematic study on ferroelectric-polarization dependent metal thermal stability on the surface of a ferroelectric metal oxide.