Domain specific phenomena at ferroelectric perovskite surfaces

Dongbo Li, University of Pennsylvania

Abstract

Ferroelectric compounds are the basis of traditional electronic ceramic devices. The ferroelectric response is being explored as components in emerging nanoscale devices. At these length scales, the fundamental aspects of atomic structure and reactions at ferroelectric surfaces are critical to a range of device applications. In this dissertation, Scanning Probe Microscopy was employed to study the domain specific phenomena at ferroelectric perovskite surfaces. The primary aim of these studies is to acquire a detailed understanding of polarization related processes at ferroelectric surfaces and to generate new insights into basic mechanisms behind them. Using a combination of scanning tunneling microscopy (STM), non-contact atomic force microscopy (nc-AFM), and low energy electron diffraction (LEED), surface structure and stability of BaTiO3 (001) was investigated. It is discovered that this surface adopts a family of reconstructions, each depending on thermo-chemical history. Surface reconstruction evolution with temperature and chemical potential of environments was understood through density function theoretical (DFT) calculations that predict the surface diagram with thermodynamically most favorable surface phases under varying conditions. Theoretical calculations were done by A. Kolpak and A. Rappe. Comparisons of the results from the calculations with the STM and nc-AFM observations were used to construct atomic models for the reconstructed surfaces. The relationship between atomic domain polarization and local surface interactions was studied with two approaches. Using piezoforce microscopy (PFM) and scanning surface potential microscopy (SSPM), the interaction between electron injection and ferroelectric lattice was investigated. The observed polarization reorientation through surface charging was further explored to control domain structure at the nano-meter scale. The effect of electron beam dosage, current, and voltage was quantified for PZT thin films. By coupling the capability of scanning probes and/or electron beams to control the domain polarization at the nanometer scale to the specificity of photochemical reactions on ferroelectric domains, nanostructures with magnetic properties were assembled at ferroelectric surfaces. Using SSPM, the effect of polarization orientation on CO2 adsorption was examined and quantified, leading to the discovery of a sticking coefficient difference by a factor of 4 for opposite domains in both BaTiO 3 and lead zirconate titanate (PZT) crystals. The differences were discussed in terms of the possible adsorption mechanisms at surfaces. The molecular adsorption mechanism was deduced with reference to temperature programmed desorption (TPD) measurements from M. He and J. Vohs and DFT calculations from A. Kolpak and A. Rappe.

Subject Area

Materials science

Recommended Citation

Li, Dongbo, "Domain specific phenomena at ferroelectric perovskite surfaces" (2008). Dissertations available from ProQuest. AAI3309469.
https://repository.upenn.edu/dissertations/AAI3309469

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