Effect of interface structure on film polarization and surface chemistry in ultra-thin TiO2/BaTiO3 Heterostructures

Jain, Chandini

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https://hdl.handle.net/2142/49664 Copy

Description

Title

Effect of interface structure on film polarization and surface chemistry in ultra-thin TiO2/BaTiO3 Heterostructures

Author(s)

Jain, Chandini

Issue Date

2014-05-30T17:03:40Z

Director of Research (if dissertation) or Advisor (if thesis)

Ertekin, Elif

Department of Study

Mechanical Sci & Engineering

Discipline

Mechanical Engineering

Degree Granting Institution

University of Illinois at Urbana-Champaign

Degree Name

M.S.

Degree Level

Thesis

Keyword(s)

• photocatalyst
• tio2
• batio3
• interface
• oxides
• polarization

Abstract

Advances in modern computational techniques have provided us with the ability to develop a fundamental understanding of complex material phenomenon down to an atomic scale and manipulate these properties for desired effects at larger lengths scales. It has become increasingly realistic to optimize and tailor material properties for potential applications in electronics, nanotechnology and energy harvesting. For example, when disparate oxides are integrated together in a heteroepitaxial system, the atomic-scale structure of the interface can dramatically influence the resulting properties of the material system. In this work, using first-principles total-energy electronic structure methods based on density functional theory, we investigate how the photocatalytic activity of anatase titanium dioxide ultra-thin films can be tuned via heteroepitaxial integration with a polarizable perovskite such as barium titanate. We explore several titanium dioxide/barium titanate heterostructures with varying interfacial geometry to elucidate how interface composition can control film polarization, in turn tailoring the surface reactivity. The polarization of the BaTiO3 is expected to affect the surface chemistry TiO2 thin film and adsorption energy of water molecules on the surface. However, thin-film perovskites such as BaTiO3 are subject to depolarization fields, and do not display ferroelectricity as in the bulk form. Therefore, the interface between the perovskite and TiO2 needs to be engineered to recover polarization. To maintain polarization, we perform first principles calculations based on density functional theory (DFT) varying both interface boundary conditions and interfacial composition of the heterostructure. Our first-principles calculations demonstrate that structurally imposed boundary conditions at the interface stabilize preferred orientations and magnitudes of polarization. However, the system is dominated by the interface effects, which eliminate any ferroelectric tendency. The direction and magnitude of this interface-induced polarization in the film also affects chemisorption of water molecules on surface of titanium dioxide. Tuning the molecular adsorption on surfaces can result in selectively augmented or suppressed reaction pathways, thereby potentially improving photocatalytic efficiency of the semiconductor photocatalyst.

Graduation Semester

2014-05

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http://hdl.handle.net/2142/49664

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Copyright 2014 Chandini Jain

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