Masahiko Mitsuhashi

Modulation derived satellite peaks in x-ray reciprocal mapping on bismuth cuprate superconductor film

X-ray reciprocal space mapping (XRSM) was employed to investigate epitaxial Bi2Sr2Ca1Cu2Ox(Bi-2212) film. Ordinal cross section XRSM (ω-2θ) and plan view XRSM (ω-ψ) clearly indicated asymmetric intensity distribution of four satellite peaks caused by supercell structure of Bi-2212 film. Modulation vector estimated by XRSM was q=0.2b*+0.9c*. The XRSM image simulated by sawtooth wave vector showed good agreement with asymmetric satellite peaks observed on epitaxial film.

Effect of Buffer Layer on Epitaxial Growth of YSZ Deposited on Si Substrate by Slower Q-switched 266 nm YAG Laser

Yttria-stabilized zirconia (YSZ) was grown on Si(100) substrate by pulsed laser deposition (PLD). The laser used in this study was a 266 nm YAG laser with a second function generator modulating only the Q-switch while the primary generator modulated the flash lamp (slower Q-switch). Epitaxial growth was verified on YSZ film deposited without oxygen gas followed by primary deposition in oxygen atmosphere on Si substrate with a ~0.4-nm-thin oxide layer. The crystallinity was strongly dependent on the thickness of the buffer layer deposited prior to the primary deposition of YSZ. The epitaxial growth was confirmed by scan, and ω scan (rocking curve) showed the full width at half maximum (FWHM) of 1.1 deg. The required oxygen pressure for epitaxial growth was quite high compared to that of excimer deposition.

Evolution of Atomically Stepped Surface of Indium Tin Oxide Thin Films Grown on Nanoimprinted Glass Substrates

Indium tin oxide (ITO) thin films were deposited on atomically stepped glass substrates (step height of ~0.2 nm and separation of ~80 nm) by pulsed laser deposition. The atomically stepped glass was prepared via thermal nanoimprint using an atomically stepped sapphire mold. The surface morphology of the ITO thin film definitely reflected the atomically stepped pattern of the glass substrate surface. The step height and the separation of the ITO film surface were close to those of the nanoimprinted glass surface. The fast Fourier transform analysis of the atomic force microscopy image also confirmed the periodicity of the atomic-step pattern.

Room-Temperature Epitaxial Growth of (Li,Ni)O Thin Film with Li Content up to 60 mol %

NiO thin films containing up to 60 mol % Li were deposited on an ultra smooth sapphire (0001) substrate at room-temperature (RT) by the pulsed laser deposition (PLD) process. From in situ reflection high-energy electron diffraction (RHEED) and ex situ X-ray diffraction (XRD), it was found that the cubic NiO thin film containing 60 mol % Li, deposited at RT, could be epitaxially grown with (111) orientation; however the film became polycrystalline when deposited at 200 °C under the same atmosphere. These results indicate the possible exploration of novel growth of the oxide films using RT PLD process.

Fabrication of ferromagnetic Ni(111) nanoparticles embedded epitaxially in (Mg,Ni)O matrix by reduction of (Mg0.5Ni0.5)O(111) epitaxial thin film

The ferromagnetic Ni nanoparticles could be epitaxially dispersed in the (Mg,Ni)O matrix by the oxide reduction. For this purpose, the epitaxial (Mg0.5Ni0.5)O thin film was grown at room temperature by pulsed laser deposition and successively reduced at 700 °C in hydrogen gas atmosphere. X-ray diffraction confirmed in-plane and out-of-plane epitaxial precipitation of Ni nanoparticles in the (Mg,Ni)O matrix by selective reduction of the Ni–O part in the epitaxial (Mg0.5Ni0.5)O thin film. Atomic-scale analyses indicated uniform dispersion of Ni nanoparticles (~20 nm average size) in the (Mg,Ni)O matrix. Magnetic measurement confirmed ferromagnetic property of the Ni nanoparticle-containing (Mg,Ni)O thin films.

Synthesis of Mica Thin Film by Pulsed Laser Deposition

Synthesis of crystalline biotite-mica thin films was examined by applying a two-step process: (1) low-temperature growth of the mica film precursor on an ultrasmooth sapphire (α-Al2O3 single crystal) substrate by pulsed laser deposition using a sintered biotite ceramics target and (2) post-annealing in vacuum. X-ray diffraction and Raman scattering spectroscopy confirmed that a c-axis-oriented polycrystalline biotite-mica thin film was obtained by post-annealing the 500 °C-grown film precursor at temperatures above 700 °C in vacuum. An atomic-scale pattern corresponding to that of the cleaved natural mica surface was observed on the surface of thin film by atomic force spectroscopy.

Fabrication of Ni/Al2O3/Ni Heteroepitaxial Junction by Post-Hydrogen Reduction of NiO/Al2O3/NiO Trilayered Epitaxial Thin Film

The fabrication of a Ni/Al2O3/Ni heteroepitaxial junction was achieved by the post-hydrogen reduction of a NiO/Al2O3/NiO trilayered epitaxial thin film grown by pulsed laser deposition. The top and bottom NiO layers were selectively reduced to Ni metal layers showing epitaxial relationships, while the Al2O3 interlayer remained. The crystallographic and interfacial characteristics were confirmed by X-ray diffraction analysis, reflection high-energy electron diffraction, and transmission electron microscopy. The fabricated Ni/Al2O3/Ni heteroepitaxial junction exhibited atomically sharp interfaces with no amorphous boundary layer.

Heavy Doping of Li + -ion into NiO Epitaxial Thin Films via Unequilibrium Room-temperature Processing for New Functionalization

NiO is a typical material for new p-type oxide semiconductors. Conductivity of NiO can be raised with Li + doping. In case of Li-heavy doping, we can obtain Li x NiO 2 (0.5 2 has been increased as an electrode material for rechargeable lithium cells. In this work, we tried to fabricate a novel NiO material with Li + -heavily doped by applying the pulsed laser-induced room temperature (R.T.) film process. Previously, we have succeeded in the epitaxial growth of various oxide thin films at R.T. such as Sn-doped In 2 O 3 transparent electrodes [1]. Although the many studies have been made on the deposition of NiO epitaxial thin film at low temperatures [2], there are few reports on fabrication and the conductive characteristic for Li-heavily doped NiO epitaxial films. The film deposition at R.T., which is the unequilibrium vapor phase process, is expected to result in different crystal structure and characteristics from the films grown at high-temperatures. A composition-adjusted thin film of Li x Ni 1-x O(0.10 2 O 3 )(0001) or MgO(100) substrates by pulsed laser deposition (PLD) technique in 10 −6 Torr of oxygen at R.T. and the high temperatures of 350 and 515°C. Crystalline properties of thin films deposited at R.T. or high temperatures were examined using reflection high energy electron diffraction (RHEED) and X-ray diffraction. For the Li-heavily doped NiO films(x>0.30) grown at R.T., a clear streak RHEED pattern showing epitaxial growth was observed. But the Li-heavily doped NiO films grown at high temperatures, exhibited the ring RHEED pattern, which indicates the policrystal growth of films. Electric conductivity of various Li-doped NiO thin films deposited at R.T. or high temperatures on sapphire (0001) substrates were measured by two-probe method. The interesting results were obtained that conductivity of the film was increased remarkably with an increase of Li-doping for R.T. deposition, but was not changed so much regardless of Li-doping for high-temperature depositions.

Effect of Strain on Supercell Structure of Bismuth Cuprate Superconducting Film

The multilayered structure of bismuth cuprate superconducting film (Bi2Sr2Ca1Cu2OX/Bi2Sr2Cu1OX) affects the supercell consisting of several unit cells as well as the lattice constant of each layer. A relatively thick film of epitaxial Bi2Sr2Ca1Cu2OX (Bi-2212) was prepared to determine its crystal structure and to compare with a reference film of ~1000 A thickness and a multilayered structure. As the Bi-2212 film grew continuously, the film was rotated by 32° around the surface normal with respect to the initial layer of Bi-2212. The angle can be interpreted according to the coincidence site lattice (CSL) with Σ 17 and 18.