Masahito Matsui

Oxygen partial pressure dependences of a–c phase ratio, crystallinity, surface roughness and in-plane orientation in YBCO thin film depositions by IBS

YBa2Cu3OX thin films were grown on MgO by ion beam sputtering at various substrate temperatures TS and oxygen partial pressures PO with a supply of either oxygen molecules or plasma (PL) to study fundamental crystal growth of perovskite oxide. Growth of the a-phase dominates at low TS while that of the c-phase dominates at high TS. This indicates that a thermal surface migration is an important mechanism for the a/c orientations. The c-phase dominates at lower PO, and it decreases while the a-phase increases with increasing PO at TS = 600 ?C. This is interpreted by a particle energy assisted surface migration controlled by collision between sputtered particles and the supplied oxygen species. The two results indicate that the surface migration is a crucial factor for the a/c orientations. The a-phase growth is enhanced by PL due to two mechanisms, the collision retarded surface migration, and plasma energy assisted atomic rearrangement and surface energy reduction. Intragrain and intergrain crystallinities show a regular correlation of PO dependences at TS = 600 ?C, while a PO dependence of surface roughness shows an inverse correlation with the intragrain and intergrain crystallinities. The mixed film can release a strain energy from interior grain to ambient media, then it has good crystallinity but a rough surface. In contrast, the pure single a-phase film has poor crystallinities but the smoothest surface because the strain energy is stored in the interior. In-plane orientation is improved by increasing the a-phase ratio, and in-plane crystallinity can be improved by PL.

Double-layer fabrication of cubic-manganites/hexagonal-ZnO on various substrates by ion beam sputtering, and variable electrical property

Hetero double-layers of LaBaMnO3 (LBMO)/ZnO were fabricated by ion beam sputtering on substrates of MgO, sapphire (SP), LaAlO3 (LAO), and SrTiO3 (STO). All the surfaces of substrates, ZnO and LBMO have step-terrace morphology. The p-LBMO/n-ZnO/SP shows junction rectification at different temperatures. The junction resistance follows from colossal magnetoresistance (CMR) of LBMO based on DEC model. The different LBMO/ZnO junctions on the different substrates show different junction behaviors at room temperatures. LBMO/ZnO/STO has the largest rectification factor of 210. After running measurement currents, LBMO/ZnO/STO shows current?voltage (I?V) switchings. LBMO/ZnO/MgO shows very clear switching and large hysteresis between upward and downward voltage sweeps. These are interpreted by CMR and DEC model, and phase separation. The switching is caused by disconnection of percolation path consisting of ferromagnetic metallic grains. The higher resistant state cannot be quickly transformed back to the lower resistant state during the downward sweep.

Evolution of I-V Characteristics and Photo Effects of Heterojunction LBMO/ZnO Prepared by IBS

The hetero p-n junctions of LBMO/ZnO were fabricated by ion beam sputtering. The sample shows clear temperature-dependent rectifying current (I)-voltage (V) characteristics, and junction resistance vs temperature curve is reflected by the CMR nature based on DEC model. The sample shows two-step switching, then the I-V is composed of very-low-resistance (VLR), low-resistance (LR) and high-resistance (HR) regions. The whole I-V behavior is changed by measurement running current. The switching is caused by the spot current, and the original VLR is restored when the current is reduced. The mechanism of switching is proposed in terms of the percolation paths composed of metallic FM-grains. Photo illumination effect on the I-V was investigated. The currents are increased in VLR and HR regions by the illumination. Two origins are possible, electronic process due to hole injection, and phase process. The percolation path might be reinforced by the light.

Hetero-epitaxial Growth of Cubic La(Sr)MnO3 on Hexagonal ZnO, In-Plane Orientations of La(Sr)MnO3 (001), (110), and (111) Phases

Hexagonal ZnO was grown on a hexagonal (001) sapphire substrate. Then cubic La(Sr)MnO3 (LSMO) was grown on a ZnO underlayer by ion beam sputtering at various substrate temperatures to obtain double-layers of LSMO/ZnO and to investigate hetero-epitaxial orientation growth. Out-of-plane (001)-oriented ZnO was grown with an in-plane orientation of [100](001)ZnO ∥ [110](001)sapphire (B-mode). Three phases of LSMO with out-of-plane (001), (110), and (111) orientations were grown on (001) ZnO generally. However, each single phase of LSMO could be grown only by controlling the deposition conditions. We achieved the in-plane orientation growth of LSMO, [110](001)LSMO ∥ [100](001)ZnO (B-mode), [10](110)LSMO ∥ [100](001)ZnO (A-mode), and [10](111)LSMO ∥ [110](001)ZnO (B-mode). The A-mode is defined as the mode in which both in-plane fundamental axes are parallel. The B-mode entails no parallel axes. The LSMO(001)- and (110)-grains have three equivalent in-plane domains, and the LSMO(111)-grain has a single domain. Lattice matching calculation can be used to partially interpret the orientation growth.

Rheology and nonhydrostatic pressure evaluation of solidified oils including Daphne oils by observing microsphere deformation

The rheological properties of solidified oils including Daphne 7373 and 7474 under high pressure up to 5 GPa were evaluated by observing the large plastic deformation of metal microspheres due to nonhydrostatic pressurization in these oils using a diamond-anvil pressure cell. The solidification pressures determined by the onset pressures of deformation for aluminum microspheres are about 0.6 GPa for traction oils, 1.2 GPa for mineral oils, and 1.79 GPa for Daphne 7373 at 24 °C. Microsphere deformation for Daphne 7474 was not observed up to 3.51 GPa. Shear stresses of the solidified oils were estimated from the deformed Cu microspheres, treating them as stress sensors based on several assumptions.

FABRICATION OF LSMO SINGLE LAYERS AND LSMO/YBCO DOUBLE LAYERS

(La, Sr)MnO3 (LSMO) single-layer and LSMO/YBCO double-layer films have been grown on LAO and MgO substrates using ion beam sputtering. For LSMO single-layer films, the highly epitaxial films can be grown at lower substrate temperatures down to 500°C. The epitaxy of the films, which is degraded with increasing TS, can be restored by supply of plasma oxygen. Smaller lattice mismatch of LSMO on LAO gives two-dimensional step-and-terrace type growth, whereas on MgO grain type growth is observed due to larger mismatch. For the double-layer films, LSMO layer can be grown epitaxially on a-oriented YBCO underlayer, but a part of the underlying a-YBCO is changed into c-YBCO during the deposition of overlayer. For c-YBCO underlayer, a part of the underlying c-YBCO is changed into (110)-oriented phase after the deposition of overlayer. Then it is necessary to deposit the overlayer at lower temperatures.

Plastic Deformations of Micro-Spheres by Solidified Lubricants and Lubricants’ Shear Stress Under Very High Pressure

In order to grasp the possibility of evaluating shear properties for solidified lubricants under high pressure, plastic deformations of metal micro-spheres (about 0.07mm) in solidified lubricants were evaluated by employing a diamond-anvil pressure cell (DAC). Large deformations (2–5 times larger than the original sphere dimensions) were observed for CVT oil and ester oil up to 6 GPa at 23–25°C. Deformation starting pressure agreed with the solidified pressure. These deformations were caused by the non-hydrostatic pressure in the solidified lubricants. Shear stresses of the solidified lubricants were tentatively and roughly estimated from the plastic deformations of the spheres based on some assumptions. They almost agreed with the mean shear stress (traction force / hertzian contact area) from traction test.Copyright