SrTiO3 Capping Layer Research Articles

Highly tunable skyrmion-like polar nanodomains for high-density ferroelectric hard disks

Emerging topological polar domains have a wide range of potential applications in electronic devices. It is critical to accurately manipulate these topological domains by electrical fields and explore their exotic properties for making more energy-efficient high-density non-volatile memories. Herein, we demonstrate that skyrmion-like polar nanodomains appear at room temperature in SrTiO3/PbTiO3 bilayer heterostructures by balancing the elastic and electrostatic energies via varying the SrTiO3 capping layer thickness. These polar nanodomains, stable at room temperature, can be electrically written, erased, and rewritten into the bilayer by applying an appropriate bias on the conductive tip of an atomic force microscope. The lateral size and location of these polar nanodomains can be precisely controlled. Moreover, ring-shaped conductive domain walls are observed around these polar nanodomains, with on/off ratios of more than two orders of magnitude with respect to the ferroelectric background. Based on these characteristics, the polar nanodomains can be created, erased, and probed electrically, suggesting applications for high-density ferroelectric hard disks.

Oxygen Vacancy Engineering for Highly Tunable Ferromagnetic Properties: A Case of SrRuO3 Ultrathin Film with a SrTiO3 Capping Layer

AbstractOxide heterostructures have great potential for spintronics applications due to their well‐defined heterointerfaces and vast functionalities. To integrate such compelling features into practical spintronics devices, effective control of the magnetic switching behavior is key. Here, continuous control of the magnetic coercive field in SrTiO3/SrRuO3 ultrathin heterostructures is achieved by oxygen vacancy (VO) engineering. Pulsed laser deposition of an oxygen‐deficient SrTiO3 capping layer can trigger VO migration into the SrRuO3 layer while avoiding the formation of Ru vacancies. Moreover, by varying the thickness and growth conditions of the SrTiO3 capping layer, the value of the coercive field (HC) in the ferromagnetic SrRuO3 layer can be continuously tuned. The maximum enhancement of HC at 5 K is 3.2 T. Such a wide‐range tunability of HC may originate from a VO‐induced enhancement of perpendicular magnetic anisotropy and domain wall pinning. This study offers effective approaches for controlling physical properties of oxide heterostructures via VO engineering, which may facilitate the development of oxide‐based functional devices.

Tuning the carrier density in SrTiO3/LaTiO3/SrTiO3 quantum wells

We discuss methods of built-in carrier density control in SrTiO3/LaTiO3/SrTiO3 heterostructures that exhibit quasi-two-dimensional carrier confinement in an interfacial quantum well. Unlike the electronically similar LaAlO3/SrTiO3 heterostructures, where the polar discontinuity at the interface defines the accumulated carrier density, the LaTiO3 heterostructures offer two means of carrier density control—changing the La doping level and utilizing the effect of surface depletion through the change in the SrTiO3 capping layer thickness. Dynamic carrier tuning over a limited range is possible by the application of a back-gate bias, which primarily affects the depth distribution of carriers. We find that small changes in the pre-annealing conditions of a SrTiO3 substrate can have a dramatic effect on the low-temperature sheet resistance of the heterostructures.

Localized Control of Curie Temperature in Perovskite Oxide Film by Capping-Layer-Induced Octahedral Distortion.

With reduced dimensionality, it is often easier to modify the properties of ultrathin films than their bulk counterparts. Strain engineering, usually achieved by choosing appropriate substrates, has been proven effective in controlling the properties of perovskite oxide films. An emerging alternative route for developing new multifunctional perovskite is by modification of the oxygen octahedral structure. Here we report the control of structural oxygen octahedral rotation in ultrathin perovskite SrRuO_{3} films by the deposition of a SrTiO_{3} capping layer, which can be lithographically patterned to achieve local control. Using a scanning Sagnac magnetic microscope, we show an increase in the Curie temperature of SrRuO_{3} due to the suppression octahedral rotations revealed by the synchrotron x-ray diffraction. This capping-layer-based technique may open new possibilities for developing functional oxide materials.

Atomic-Scale Measurement of Structure and Chemistry of a Single-Unit-Cell Layer of LaAlO3 Embedded in SrTiO3

A single layer of LaAlO3 with a nominal thickness of one unit cell, which is sandwiched between a SrTiO3 substrate and a SrTiO3 capping layer, is quantitatively investigated by high-resolution transmission electron microscopy. By the use of an aberration-corrected electron microscope and by employing sophisticated numerical image simulation procedures, significant progress is made in two aspects. First, the structural as well as the chemical features of the interface are determined simultaneously on an atomic scale from the same specimen area. Second, the evaluation of the structural and chemical data is carried out in a fully quantitative way on the basis of the absolute image contrast, which has not been achieved so far in materials science investigations using high-resolution electron microscopy. Considering the strong influence of even subtle structural details on the electronic properties of interfaces in oxide materials, a fully quantitative interface analysis, which makes positional data available with picometer precision together with the related chemical information, can contribute to a better understanding of the functionality of such interfaces.

Leakage Current Behaviors of SrTiO3 Capped Mn-doped Polycrystalline BiFeO3 Thin Film

The polycrystalline Mn 1% doped BFO (BFMO) thin film was deposited on Pt(111)/Ti/SiO2/Si(100) substrate by pulsed laser deposition. A thin SrTiO3 capping layer was grown on top of deposited Bi(Fe0.99Mn0.01)O3 thin film. The structural and electrical properties of STO/BFMO thin film were investigated. By capping a thin STO on top of BFMO, leakage current density of capacitor was improved greatly compare to that of the pure BFMO without degrading ferroelectricity.

Termination control of electronic phases in oxide thin films and interfaces: LaAlO 3 /SrTiO 3 (001)

A wealth of intriguing properties emerge in the seemingly simple system composed of the band insulators LaAlO 3 and SrTiO 3 such as a two-dimensional electron gas, superconductivity and magnetism. In this paper, we review the current insight obtained from first principles calculations on the mechanisms governing the behaviour of thin LaAlO 3 films on SrTiO 3 (001). In particular, we explore the strong dependence of the electronic properties on the surface and interface termination, the finite film thickness, lattice polarization and defects. A further aspect that is addressed is how the electronic behaviour and functionality can be tuned by an SrTiO 3 capping layer, adsorbates and metallic contacts. Lastly, we discuss recent reports on the coexistence of magnetism and superconductivity in this system for what they might imply about the electronic structure of this system.

Chemical stability and transport properties of ultrathin La1.2Sr1.8Mn2O7 Ruddlesden–Popper films

Epitaxial La1.2Sr1.8Mn2O7 films with n=2 Ruddlesden–Popper structure were grown on SrTiO3 (001) substrates. Decomposition through water intercalation led to the disappearance of the metal-insulator transition in samples exposed to ambient atmosphere. Crystal damage was limited to the surface layer only, demonstrating the anisotropic nature of the water intercalation process. By protecting films with a SrTiO3 capping layer, the metal-insulator transition persisted down to 2.5 unit cell thick films. In thinner films, we propose a mechanism related to the loss of interlayer ferromagnetic order in favor of in-plane antiferromagnetism as a reason for the loss of the metallic state.

Effects of SrTiO3 capping in La2∕3Ca1∕3MnO3 electrodes of different orientations

We report on the study of the structural, magnetic, and electronic properties of SrTiO3 capped La2∕3Ca1∕3MnO3 electrodes grown on (001) and (110) SrTiO3 substrates. Magnetic properties of the (001) and (110) capped electrodes evolve differently when the capping layer thickness increases, revealing a reduction of the saturation magnetization for the (001) ones. Electronic properties are studied combining Mn55 nuclear magnetic resonance (NMR) and x-ray photoemission spectroscopy (XPS). NMR experiments highlight that electronic phase separation in the (001) electrodes is enhanced by the presence of the SrTiO3 capping layer and XPS measurements show that the electronic state of interfacial Mn ions from (001) electrode is more sensitive to the capping layer.