Effects of polarization on adsorption and reaction on ferroelectric surfaces.

摘要

The ability to manipulate dipole orientation in ferroelectric oxides holds promise as a method to tailor surface reactivity for specific applications. Since ferroelectric domains can be patterned at the nano-scale, domain-specific surfaces, which may provide a new method for fabrication of nano-scale devices. However, the effect of ferroelectric polarization on adsorption and surface reactivity is still not well understood. Therefore, in an effort to better understand how polarization influences surface reactivity, in this thesis project, well-defined model systems that consisted of gas-metal oxide interactions and metal-metal oxide interactions were studied. In particular, the two model systems that were studied included: BaTiO3 polycrystalline thin film and LiNbO3 (0001) single crystal. These model systems allowed the use of various surface sensitive spectroscopic techniques, including AES, XPS and TPD, especially for BaTiO3 thin film, the ferroelectric polarization can be manipulated in-situ, which allows accurate observation on even subtle desorption difference.;The results of this research project show that methanol and ethanol dissociatively adsorb on the surface and forms alkoxide and hydroxide intermediate precursor and the sticking coefficient is a function of ferroelectric polarization. The sticking coefficient of methanol on BaTiO3 surface is c- (negatively poled)> a (unpoled) > c+ (positively poled) while of ethanol on BaTiO3 surface is c+ > c- > a. Beyond sticking coefficient, the iv TPD results of BaTiO3 with ethanol and 2-fluoroethanol shows that ferroelectric polarization can also alter the intrinsic reactivity of the surface. On positively poled surface, the maximum reaction activation energy is 7kJ/mol's higher than from the a surface. In addition, in the Pd depositing on LiNbO3 single crystal, ferroelectric polarization can affect the stability of palladium deposition. It was observed the Pd deposited on LiNbO3 is more stable on the negatively charged surface compared to the positively charged surface. When appropriate, possible explanations of ferroelectric polarization effect on surface adsorption and reactivity were given.