KTaO3(001) Preparation Methods in Vacuum: Effects on Surface Stoichiometry, Crystallography, and in-gap States

Abstract

KTaO3 single crystals with different orientations are used as substrates for the epitaxial growth of thin films and/or as hosts for two-dimensional electron gases. Due to the polar nature of the KTaO3(001) surface, one can expect difficulties and challenges to arise in its preparation. Maintaining good insulating characteristics without adding undesirable in-gap electronic states, obtaining good crystalline order up to the top surface layer, a sufficiently flat surface, and complete cleanliness of the surface (without water, C or OH contaminants), are in general difficult conditions to accomplish simultaneously. Cleaving in vacuum is likely the best option for obtaining a clean surface. However, since KTaO3 is cubic and lacks a well-defined cleavage plane, this method is notsuitable for sample growth or reproducible device fabrication. Here, we systematically evaluate the effect of typical preparation methods applied on the surfaces of KTaO3(001) single crystals. In particular, we used annealing in vacuum at different temperatures, light sputtering with Ar+ ions at low energy (500 eV) followed by annealing, heavy Ar+ ion bombardment and annealing, and grazing Ar+ ion bombardment under continuous azimuthal rotation combined with both annealing in vacuum and in O2 atmosphere. Possible side effects after each treatment are evaluated by a combination of techniques, including low-energy ion scattering at forward angles, Auger electron spectroscopy, low-energy electron energy loss, X-ray photoelectron spectroscopy, low-energy electron diffraction, and time of flightsecondary ion mass spectrometry. Advantages and shortcomings of each preparation method are discussed in detail.

30 pages, 8 figures

References in corpus (19)

• Electric Field Control of the LaAlO${}_3$/SrTiO${}_3$ Interface Ground State
• Creation and control of a two-dimensional electron liquid at the bare SrTiO3 surface
• A high-mobility two-dimensional electron gas at the heteroepitaxial spinel/perovskite complex oxide interface of γ-Al2O3/SrTiO3
• Discovery of two-dimensional anisotropic superconductivity at KTaO${}_3$ (111) interfaces
• Two-dimensional superconductivity at the surfaces of KTaO3 gated with ionic liquid
• Quasiparticle dynamics and spin-orbital texture of the SrTiO3 two-dimensional electron gas
• Zener Tunneling Between Landau Orbits in a High-Mobility Two-Dimensional Electron Gas
• Theory of the SrTiO3 Surface State Two-Dimensional Electron Gas
• Observation of two-dimensional superconductivity at the LaAlO3/KTaO3(110) heterointerface
• Spin-charge interconversion in KTaO${}_3$ two-dimensional electron gases
• Superfluid stiffness of a KTaO3-based two-dimensional electron gas
• Band Structure and Spin-Orbital Texture of the (111)-KTaO3 Two-Dimensional Electron Gas
• Coexistence of two- and three-dimensional Shubnikov-de Haas oscillations in Ar^+ -irradiated KTaO_3
• Direct visualization of Rashba-split bands and spin/orbital-charge interconversion at KTaO${}_3$ interfaces
• Oxygen vacancy induced electronic structure modification of KTaO${}_3$
• A switchable two-dimensional electron gas based on ferroelectric Ca:SrTiO${}_3$
• Molecular Beam Epitaxy of KTaO${}_3$
• Intrinsic magnetism in KTaO${}_3$ heterostructures
• High stability 2D electron gases formed in Si3N4/Al//KTaO3 heterostructures: synthesis and in-depth interfacial characterization