Molecular interactions with ferroelectric surfaces
Abstract
The presence of spontaneous polarization in ferroelectric materials leads to some interesting phenomena at ferroelectric surfaces. In the present work, the effects of polarization on the surface chemical reactivity of two ferroelectric metal oxide compounds, barium titanate (BaTiO3 ) and lithium niobate (LiNbO3 ), are studied using temperature programmed desorption (TPD) in ultrahigh vacuum. The interactions of various molecules, including methanol, carbon dioxide, water, and pyridine, with the single crystal surfaces are examined. It is shown that oxygen vacancy defects play an important role in the adsorption and reaction of methanol and carbon dioxide on BaTiO 3 (001) at room temperature. An in situ poling technique used to control the polarization of BaTiO3 crystals during TPD measurements is discussed. The effect of polarization on weak interactions of water, methanol, and pyridine with the stoichiometric surface of LiNbO 3 (0001) is determined by comparing the TPD spectra of these molecules on the c+ and c- crystal surfaces. The desorption energies are found to be consistently greater on the c+ surface by a few kJ per mole. A possible electrostatic mechanism for this effect is investigated by performing pyroelectric voltage measurements in vacuum. It is shown that the magnitude of pyroelectric-induced surface charging at ferroelectric surfaces is proportional to the heating rate of the material. The kinetics of screening charge relaxation is also examined by analysis of the pyroelectric data.
Subject Area
Materials science
Recommended Citation
John Garra,
"Molecular interactions with ferroelectric surfaces"
(January 1, 2009).
Dissertations available from ProQuest.
Paper AAI3363357.
http://repository.upenn.edu/dissertations/AAI3363357
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