REBCO (RE = rare earth) based high temperature superconducting (HTS) wires are now being utilized for the development of electric and electromagnetic devices for various industrial, scientific and medical applications. In the last several years, the increasing efforts in using the so-called second generation (2G) HTS wires for some of the applications require a further increase in their engineering current density (Je). The applications are those typically related to high magnetic fields where the higher Je of a REBCO wire, in addition to its higher irreversibility fields and higher mechanical strength, is already a major advantage over other superconducting wires. An effective way to increase the Je is to decrease the total thickness of a wire, for which using a thinner substrate becomes an obvious and attractive approach. By using our IBAD-MOCVD (ion beam assisted deposition-metal organic chemical vapor deposition) technology we have successfully made 2G HTS wires using a Hastelloy® C276 substrate that is only 30 μm in thickness. By using this thinner substrate instead of the typical 50 μm thick substrate and with a same critical current (Ic), the Je of a wire can be increased by 30% to 45% depending on the copper stabilizer thickness. In this paper, we report the fabrication and characterization of the 2G HTS wires made on the 30 μm thick Hastelloy® C276 substrate. It was shown that with the optimization in the processing protocol, the surface of the thinner Hastelloy® C276 substrate can be readily electropolished to the quality needed for the deposition of the buffer stack. Same in the architecture as that on the standard 50 μm thick substrate, the buffer stack made on the 30 μm thick substrate showed an in-plane texture with a Δϕ of around 6.7° in the LaMnO3 cap layer. Low-temperature in-field transport measurement results suggest that the wires on the thinner substrate had achieved equivalent superconducting performance, most importantly the Ic, as those on the 50 μm thick substrate. It is expected the 2G HTS wires made on the 30 μm thick Hastelloy® C276 substrate, the thinnest and with the highest Je to date, will greatly benefit such applications as high field magnets and high current cables.

In order to achieve high efficiency thin film polycrystalline silicon (poly-Si) solar cells on insulating substrate, we have developed a novel crystallization method of amorphous silicon (a-Si), an inverted aluminum-induced layer exchange (inverted-ALILE) method, where a metallic aluminum layer remains between the crystallized p þ -layer and a glass substrate to function a back contact in contrast to the conventional ALILE method. Crystallization process of a-Si during inverted-ALILE was observed in-situ by optical microscope. The crystallized film was analyzed using Raman measurement, X-ray photoelectron spectroscopy (XPS) and electron back scatter diffraction (EBSD). Those analyses indicated poly-Si thin film with large grain size and preferential orientation of (100). The prepared poly-Si layer was applied to thin film solar cell and we confirmed a significant improvement in series resistance as compared to a conventional ALILE method.

The optical emission behaviors of Ar, He, and Ar+He plasmas generated in air using an atmospheric pressure microwave plasma source have been studied employing optical emission spectroscopy (OES). Emissions from various source gas species and air were observed. The variations in the intensities and intensity ratios of specific emissions as functions of the microwave power and gas flow rate were analyzed to investigate the relationship between the emission behavior and the plasma properties. We find that dependence of the emission behavior on the input microwave power is mainly determined by variations in electron density and electron temperature in the plasmas. On the other hand, under different gas flow rate conditions, changes in the density of the source gas atoms also significantly affect the emissions. Interestingly, when plasma is generated using an Ar+He mixture, emissions from excited He atoms disappear while a strong Hα signal appears. The physics behind these behaviors is discussed in detail.

A microwave-induced plasma source is developed and is applied for the fast deposition of crystalline silicon films. In this paper, the plasma source is diagnosed first. Electron density, electron temperature, and discharge gas temperature of the plasmas generated in ambient air are studied using the optical emission spectroscopy method. The electron density is estimated by analyzing the Stark broadening of the hydrogen Hβ emission profile and is found to be as high as >1015 cm−3 over wide conditions. The Boltzmann plot method is used to calculate the electron temperature, which shows a value smaller than 1 eV. Analysis of the rotational structure of OH molecular emission reveals a discharge gas temperature in a range of ∼400–800 °C. Preliminary efforts of using the plasma source for Si film fast deposition are performed at a reduced pressure by using SiCl4 as the source gas. A fast deposition rate of 150 nm/s has been achieved for Si film with a high Raman crystallinity of Ic/Ia>10 even without using substrate heating and under a low H2 dilution condition. Mechanisms for these results are discussed in detail.

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