| AVS 54th International Symposium | |
| Surface Science | Wednesday Sessions |
| Session SS1-WeM |
| Session: | Oxide Surface Reactivity |
| Presenter: | M. He, University of Pennsylvania |
| Authors: | D.B. Li, University of Pennsylvania M. He, University of Pennsylvania J. Garra, University of Pennsylvania D.A. Bonnell, University of Pennsylvania J.M. Vohs, University of Pennsylvania |
| Correspondent: | Click to Email |
Many perovskite oxides such as BaTiO3 undergo a phase transition from a ferroelectric tetragonal phase to a paraelectric cubic phase at readily accessible temperatures. In the ferroelectric state the material is polar and has a bulk electric dipole whose orientation can be controlled via application of an external electric field. While it has been suggested that the orientation of the ferroelectric dipole on the surface may affect adsorption and reaction of species from the gas phase, examples demonstrating the ferroelectric control of surface reactivity have to date been elusive. In this talk we will present what we believe are the first definitive examples of the influence of ferroelectric polarization on the surface reactivity of BaTiO3. In the first example, demonstrates the effect of ferroelectric polarization on the adsorption of CO2 on oxygen vacancies on the surface of a BaTiO3(001) single crystal. Sub-micron sized out-of-plane domains with the polarization oriented perpendicularly inward (c-) or outward (c+) from the surface were produced on the BaTiO3(001) sample using an AFM tip. Frequency modulation, scanning surface potential microscopy (FM-SSPM) was then employed to measure the potential change of the ferroelectric domains before and after exposure of the poled surface to CO2. It was observed that CO2 caused a larger decrease in the surface potential for c- domains relative to the c+ domains, indicating a difference in the amount of CO2 adsorbing on each domain. In the second example, the amount of methanol that adsorbed on an oriented, BaTiO3 thin film supported on TiO2(110) under UHV conditions was found to be dependent on the orientation of the ferroelectric dipole. In this case the sample was poled by heating above Tc and then placing it in contact with an electrode to which a small + or - voltage was applied. For a constant exposure, the amount of CH3OH that adsorbed at 300 K was found to increase in the following order c- > unpoled > c+. This result has been attributed to a polarization dependent interaction of weakly bound CH3OH molecules prior to dissociative adsorption at defect sites.