Search

We developed an ion beam figuring system that utilizes electrostatic deflection. The system can produce an arbitrary shape by deterministically scanning the ion beam. The scan of the ion beam, which can be precisely controlled using only an electrical signal, enables us to avoid degradation of the mirror shape caused by imperfect acceleration or deceleration of a mechanically scanning stage. Additionally, this surface figuring method can easily be combined with X-ray metrology because the workpiece remains fixed during the figuring. We evaluated the figuring accuracy of the system by fabricating a plano-elliptical mirror for X-ray focusing. A mirror with a shape error of 1.4 nm root mean square (RMS) with a maximum removal depth of 992 nm, which corresponds to figuring accuracy of 0.14% RMS, was achieved. After the second shape corrections, an elliptical shape with a shape error of approximately 1 nm peak-to-valley, 0.48 nm RMS could be fabricated. Then, the mirror surface was smoothed by a low-energy ion beam. Consequently, a micro-roughness of 0.117 nm RMS, measured by atomic force microscopy, was achieved over an area of 1 x 1 μm². [ABSTRACT FROM AUTHOR]

In order to advance the mass production of graphene devices, it is beneficial to avoid the difficulty graphene transfer process. Direct precipitation of graphene using a tungsten capping layer is convenient for this purpose, and is quite simple and compatible with conventional semiconductor fabrication processes. In this study, multilayer graphene was directly precipitated on a wafer of GaN-based blue LEDs to form a transparent electrode. The fabricated LED exhibited superior I–V characteristics and emitted blue luminescence around the probe of the electrode. [ABSTRACT FROM AUTHOR]

In this study, the direct growth of multilayer graphene from amorphous carbon on a sapphire (0001) substrate by precipitation using a nickel catalyst layer and a tungsten capping layer was examined. The findings revealed that a tungsten carbide layer was formed on top of the catalyst, and this suppressed the diffusion of carbon atoms upwards towards the surface. This caused the graphene layer to precipitate below the catalyst layer rather than above it. Under optimized growth conditions, Raman spectroscopy indicated that a high-quality graphene layer was formed with a low D/G peak intensity ratio of 0.10. [ABSTRACT FROM AUTHOR]

Aluminum oxide was investigated as a mask material for the selective growth of GaN by liquid phase electroepitaxy in comparison with SiO2, SiN, and W. SiO2 and W masks were dissolved in a solution and many polycrystals were generated on the SiN mask. Therefore, these masks are not suitable for selective growth. On the other hand, aluminum oxide was found durable in the solution, and growth selectivity was also achieved. Then, microchannel epitaxy was conducted using the aluminum mask by liquid phase electroepitaxy. Not only the selective growth but also the lateral growth of c-plane GaN with a width of about 8 µm was successfully achieved using the aluminum oxide mask. [ABSTRACT FROM AUTHOR]

To shorten the duration of x-ray pulses, we present a nonlinear optical technique using atoms with core-hole vacancies (core-hole atoms) generated by inner-shell photoionization. The weak Coulomb screening in the core-hole atoms results in decreased absorption at photon energies immediately above the absorption edge. By employing this phenomenon, referred to as saturable absorption, we successfully reduce the duration of x-ray free-electron laser pulses (photon energy: 9.000 keV, duration: 6-7 fs, fluence: 2.0-3.5×105 J/cm²) by ∼35%. This finding that core-hole atoms are applicable to nonlinear x-ray optics is an essential stepping stone for extending nonlinear technologies commonplace at optical wavelengths to the hard x-ray region. [ABSTRACT FROM AUTHOR]