Comparison Studies of Interfacial Electronic and Energetic Properties of LaAlO3/TiO2 and TiO2/LaAlO3 Heterostructures from First-Principles Calculations

Review of First-Principles Studies of TiO2: Nanocluster, Bulk, and Material Interface

TiO2 has extensive applications in the fields of renewable energy and environmental protections such as being used as photocatalysts or electron transport layers in solar cells. To achieve highly efficient photocatalytic and photovoltaic applications, ongoing efforts are being devoted to developing novel TiO2-based material structures or compositions, in which a first-principles computational approach is playing an increasing role. In this review article, we discuss recent computational and theoretical studies of structural, energetic, electronic, and optical properties of TiO2-based nanocluster, bulk, and material interface for photocatalytic and photovoltaic applications. We conclude the review with a discussion of future research directions in the field.

Thickness Control of the Spin-Polarized Two-Dimensional Electron Gas in LaAlO3/BaTiO3 Superlattices

We explored the possibility of increasing the interfacial carrier quantum confinement, mobility and conductivity in the (LaAlO₃)_n/(BaTiO₃)_n superlattices by thickness regulation using the first-principles electronic structure calculations. Through constructing two different interfacial types of LaAlO₃/BaTiO₃ superlattices, we discovered that the LaO/TiO₂ interface is preferred from cleavage energy consideration. We then studied the electronic characteristics of two-dimensional electron gas (2DEG) produced at the LaO/TiO₂ interface in the LaAlO₃/BaTiO₃ superlattices via spin-polarized density functional theory calculations. The charge carrier density of 2DEG has a magnitude of 10¹⁴ cm⁻² (larger than the traditional system LaAlO₃/SrTiO₃), which is mainly provided by the interfacial Ti 3d_xy orbitals when the thicknesses of LaAlO₃ and BaTiO₃ layers are over 4.5 unit cells. We have also revealed the interfacial electronic characteristics of the LaAlO₃/BaTiO₃ system, by showing the completely spin-polarized 2DEG mostly confined at the superlattice interface. The interfacial charge carrier mobility and conductivity are found to be converged beyond the critical thickness. Therefore, we can regulate the interfacial confinement for the spin-polarized 2DEG and quantum transport properties in LaAlO₃/BaTiO₃ superlattice via controlling the thicknesses of the LaAlO₃ and BaTiO₃ layers.

Tuning the Two-Dimensional Electron Gas at Oxide Interfaces with Ti-O Configurations: Evidence from X-ray Photoelectron Spectroscopy

A chemical redox reaction can lead to a two-dimensional electron gas at the interface between a TiO₂-terminated SrTiO₃ (STO) substrate and an amorphous LaAlO₃ capping layer. When replacing the STO substrate with rutile and anatase TiO₂ substrates, considerable differences in the interfacial conduction are observed. On the basis of X-ray photoelectron spectroscopy (XPS) and transport measurements, we conclude that the interfacial conduction comes from redox reactions, and that the differences among the materials systems result mainly from variations in the activation energies for the diffusion of oxygen vacancies at substrate surfaces.

First-principles studies of polar perovskite KTaO3 surfaces: structural reconstruction, charge compensation, and stability diagram

First-principles calculations predict a surface phase stability diagram for the polar perovskite KTaO₃.