No abstract

We have developed a large‐scale metal‐organic vapor phase epitaxy (MOVPE) reactor. The growth rates of AlN and AlGaN were compared with those calculated using the parasitic chemical reaction model. The calculated results were in good agreement with the experimental results over the entire 8″ wafer. To experimentally investigate the extent of the gas‐phase prereaction between the precursors and ammonia, the results of epitaxy were compared with those for a 6″‐type reactor. The growth of AlN and AlGaN at relatively high rates without any significant gas‐phase prereaction was demonstrated. (© 2013 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

We describe an atmospheric‐pressure MOVPE reactor with a capacity of 2 inch by 10 or 3 inch by 8. In this reactor, the parasitic reaction of particulate generation is suppressed by adopting a high‐flow‐speed design. As a result of suppressing of the parasitic reaction, we have also grown GaN at a growth rate of more than 28 μm/hr at atmospheric pressure. It is also important to grow a heterostructure of Al‐containing alloys continuously to enable device applications, while maintaining the proper growth conditions for other layers such as GaN:Mg. An Al0.09Ga0.91N layer has been grown at a growth rate of 1 μm/h at atmospheric pressure. In the production environment, it is also essential to operate a reactor under a stable condition. To this end, we have adopted ex‐situ dry cleaning of all reactor components with deposits on them after every growth run. Dry cleaning was conducted using chemical etching of the deposit by chlorine gas in a hot tube reactor at about 800 °C. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

We study the effects of hydrostatic pressure (HP) compression on the superconducting transition of severely strained Nb samples, whose grain sizes are reduced to the submicrometer level. Engineered granularity by high-pressure torsion (HPT) treatment changes the strength of coupling between submicrometer-scale grains and introduces lattice strain. We attempt to utilize the initially accumulated shear strain in the starting material for increasing the superconducting transition temperature Tc under HP compression. The HP effects on non-strained Nb have already been investigated in the pressure regime over 100 GPa by Struzhkin et al. [Phys. Rev. Lett. 79, 4262 (1997)], and Tc reportedly exhibited an increase from 9.2 to 9.9 K at approximately 10 GPa. (1) Slightly strained Nb in the HPT treatment exhibits the increase in Tc under HP due to the strengthening of the intergrain coupling, so the pressure scale of the pressure response observed by Struzhkin et al. is reduced to approximately one-seventh at the maximum. (2) Prominently strained Nb in the HPT treatment exhibits the increase in Tc under HP due to a reduction in structural symmetry at the unit-cell level: In a Nb sample subjected to HPT (6 GPa, 10 revolutions), Tc exceeds 9.9 K at approximately 2 GPa. According to our first-principle calculations, the reduction in the structural symmetry affords an increase in the density of states at the Fermi energy, thereby yielding a prominent increase in Tc at low pressures.

Hydrogen absorption and desorption through diffusive processes and the accompanying phase transformations in hydrogen storage materials have been investigated by x-ray diffraction, thermogravimetry, pressure-composition-temperature isotherms, and electrical resistance measurements. We use time- and temperature-dependent magnetic measurements to gain a detailed understanding of these phenomena in palladium hydride PdH0.64 prepared by severe plastic deformation via the high-pressure torsion method. The concept of our method is pursuing an increase in the ratio of the paramagnetic α-phase Pd+H to the diamagnetic β-phase PdH. An antiferromagnetic correlation appears between the paramagnetic moments of Pd at a low temperature and a huge discrete change in magnetization appears due to collective H desorption above room temperature. It is also verified that H diffusion and its desorption can be changed with the accumulation of the severe lattice strain.