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Porous tungsten (W) nanostructure formation was performed for the first time using a helium (He) arc discharge plasma under sub-atmospheric pressure of 80 kPa. Scanning electron microscope observations showed that micron-sized bubble and hole structures were formed in the W substrate at a surface temperature of 1700 °C, indicating He penetration into the W substrate. At the surface temperature of 800 °C, surface blackening of the W substrate due to the He plasma irradiation for two hours was found. The unique surface morphology has a W nanofiber network with a thickness of ~10 µm which consists of assembly of W nanoparticles with a diameter of 20–30 nm. It was suggested that an interaction between W vapor evaporated from the W electrodes and the surrounding He plasma plays a key role for physical processes of the nanostructured W formation identified in this study. It could be formed due to a process of cluster–cluster aggregation of W nanoparticles produced by nucleation and condensation from the W vapor phase. The W nanoparticle network deposition is considered to be a new process for the porous W nanostructure formation as an alternative to standard fuzz formation associated by bubble formation on the surface of base W substrate. [ABSTRACT FROM AUTHOR]

The tungsten vapour produced from the electrodes during short arc lamp operation is transported by gas convection and then deposited on the inner quartz bulb wall to form a tungsten thin film, causing the wall to blacken. We have been able to consider important phenomena for the first time by developing a unified numerical simulation model incorporating relevant sub-models. These include the absorption of the radiant energy due to blackening of the lamp and the temporal variation in the lamp parameters. The validity of the numerical simulation model is first evaluated by comparison with experimental results. The basic characteristics of the lamp obtained using the model is found to be in good agreement with the experimental results and other research results. The influence of the bulb wall blackening is then examined. The temperature of the bulb is shown strongly affected by convective heat transfer from the hot gas, and the temperature rise of the bulb after blackening is found to be primarily governed by the absorption of the radiant energy by the tungsten thin film. Through the increase in the bulb temperature, the gas temperature in the bulb is also increased. This raises the operating pressure, which increases the stress on the bulb wall. Consequently, it is demonstrated that the probability of breakage gradually increases with time due to the blackening by tungsten vapour deposition. [ABSTRACT FROM AUTHOR]

A new technology for obtaining nanostructure on silicon surface for potential applications to optical devices is represented. Scanning electron microscope analysis indicated a grown nanostructure of dense forest consisting of long cylindrical needle cones with a length of approximately 300 nm and a mutual distance of approximately 200 nm. Raman spectroscopy and spectrophotometry showed a good crystallinity and photon trapping, and reduced light reflectance after helium plasma exposure. The present technique consists of a simple maskless process that circumvents the use of chemical etching liquid, and utilizes soft ion bombardment on silicon substrate, keeping a good crystallinity. [ABSTRACT FROM AUTHOR]