大坂 藍

For high-performance spintronic applications with Co-based Heusler alloys, we explore Si1−xGex(111) grown by liquid phase epitaxy (LPE) with Al–Ge mixed paste, where x is the Ge content. By annealing the screen printed Al–Ge paste on a Si(111) substrate, a continuous Si1−xGex(111) layer with a smooth interface between the Si1−xGex layer and Si substrate is epitaxially grown. The surface with residual paste is polished and treated by chemical mechanical polishing and a catalyst referred etching (CARE) process, resulting in a reduction of the root-mean-square roughness to 0.52 nm over a large-scale area. After the surface treatments of the LPE-Si1−xGex, we can obtain Si0.93Ge0.07(111) to epitaxially grow one of the Co-based Heusler alloys, Co2FeSi. The magnetic properties and intermixing at the Co2FeSi/LPE-Si0.93Ge0.07(111) interface are consistent with those at the Co2FeAl0.5Si0.5/Si(111) and the Co2FeAl0.5Si0.5/Ge(111) interfaces. The Al–Ge-paste-induced LPE-Si1−xGex(111) and the CARE process for the surface are quite effective for the growth of Co-based Heusler alloys in future SiGe-based spintronic devices.

Abstract We investigate resistance switching in proton-memristive NdNiO₃ film devices via the diffusional migration of a proton dopant by using electric field control. Lattice strain is found to play a significant role in determining proton migration within NdNiO₃ thin film. Compressive strain can accelerate the migration, resulting in a switching efficiency of 28.22% which is significantly higher than 0.21% on a tensile-strained device. The results demonstrate the significance of strain engineering and will guide the development of the design of multifunctional perovskite devices for emerging iontronics memory and computing applications.

The creation of three-dimensional (3D) geometrical shapes with atomically ordered surfaces and the investigation of their physical properties are major steps contributing to the development of a new paradigm in surface science. We produced a 3D-patterned Si sample with atomically flat and reconstructed {111} facet surfaces, and investigated its structural and physical properties. To apply the conventional techniques in surface science to 3D samples with various oriented surfaces, instead of two-dimensional planar samples, an appropriate relationship between the crystallographic surface ordering on the 3D-archi-tected surfaces and the angle-resolved photoelectron spectroscopy (ARPES) setup considering the configuration in 3D space is indispensable. The distinctive and complex low-energy electron diffraction (LEED) patterns reflecting the 3D-arranged facet surfaces showed the realization of atomically reconstructed facet surfaces on 3D-patterned Si. Surface states of the 3D-patterned Si{111} surfaces are mapped by ARPES by considering the 3D geometrical relationship. The selection of the appropriate alignment of the incident electron beam (light) for the target surfaces allows the clear observation of the band dispersion from the produced {111}7×7 facet surfaces in 3D space. Our demonstration of accessibility of ARPES technique could provide useful guidelines for new methodologies, giving a fundamental understanding of 3D-shape-induced novel functionalities.

Unlike normal hydrogen doping in a H2gas atmosphere assisted by precious metal catalysts at high temperatures, the cost-effective hydrogenation of rare-earth nickelate (RNiO3) thin films in acid solution with abundant protons supplies a tunable protonation-induced phase transition via the internal mechanism of electron-proton synergistic co-doping under ambient conditions. Here, we report the first ever large-area hydrogenation of a millimeter-scale NdNiO3film by metal-acid treatment, which leads to marked changes in optical and electrical transport properties corresponding to the hydrogen-induced electronic phase transition. We found that reflectance and conductance modulations are governed by the concentration of protons in NNO, which is controlled by the crystal facet orientation, which in turn affects the proton doping speed. The effect of the crystal orientation on the speed of protonation may be due to anisotropic hydrogen diffusion owing to the existence of an energetically favored channel along the [001] direction in the NdNiO3film. Our work provides a green route for the development of electronic devices based on nickelates with hydrogenation.