High critical current density and high-tolerance superconductivity in high-entropy alloy thin films.

High-entropy alloy (HEA) superconductors-a new class of functional materials-can be utilized stably under extreme conditions, such as in space environments, owing to their high mechanical hardness and excellent irradiation tolerance. However, the feasibility of practical applications of HEA superconductors has not yet been demonstrated because the critical current density (Jc) for HEA superconductors has not yet been adequately characterized. Here, we report the fabrication of high-quality superconducting (SC) thin films of Ta-Nb-Hf-Zr-Ti HEAs via a pulsed laser deposition. The thin films exhibit a large Jc of >1 MA cm-2 at 4.2 K and are therefore favorable for SC devices as well as large-scale applications. In addition, they show extremely robust superconductivity to irradiation-induced disorder controlled by the dose of Kr-ion irradiation. The superconductivity of the HEA films is more than 1000 times more resistant to displacement damage than that of other promising superconductors with technological applications, such as MgB2, Nb3Sn, Fe-based superconductors, and high-Tc cuprate superconductors. These results demonstrate that HEA superconductors have considerable potential for use under extreme conditions, such as in aerospace applications, nuclear fusion reactors, and high-field SC magnets.

Enhanced anomalous magnetization in carbonyl iron by Ni+ ion beam irradiation.

We investigate the magnetic properties in carbonyl iron (CI) particles before and after Ni[Formula: see text] and H[Formula: see text] ion beam irradiation. Upon increasing temperatures, the saturation magnetization ([Formula: see text]) in hysteresis loops exhibits an anomalous increase at a high temperature for the unirradiated and the Ni[Formula: see text]-beam-irradiated samples, unlike in H[Formula: see text]-beam-irradiated sample. Moreover, the magnetization values at low and high temperatures are more intense after Ni[Formula: see text] beam irradiation, whereas after H[Formula: see text] beam irradiation those are remarkably suppressed. Hematite ([Formula: see text]-Fe[Formula: see text]O[Formula: see text]) phase introduced on the surface of our CI particles undergoes the Morin transition that was observed in our magnetization-temperature curves. The Morin transition causing canted antiferromagnetism above the Morin temperature was found in the unirradiated and Ni[Formula: see text]-beam-irradiated samples, but not in H[Formula: see text]-beam-irradiated sample. It is thus revealed that the CI particles undergoing the Morin transition cause the anomalous increase in [Formula: see text]. We may suggest that Ni[Formula: see text] ion beam increases uncompensated surface spins on the CI particles resulting in a more steep Morin transition and the intensified [Formula: see text]. Ion-beam irradiation may thus be a good tool for controlling the magnetic properties of CI particles, tailoring our work for future applications.

Enhanced efficiency of crystalline Si solar cells based on kerfless-thin wafers with nanohole arrays.

Several techniques have been proposed for kerfless wafering of thin Si wafers, which is one of the most essential techniques for reducing Si material loss in conventional wafering methods to lower cell cost. Proton induced exfoliation is one of promising kerfless techniques due to the simplicity of the process of implantation and cleaving. However, for application to high efficiency solar cells, it is necessary to cope with some problems such as implantation damage removal and texturing of (111) oriented wafers. This study analyzes the end-of-range defects at both kerfless and donor wafers and ion cutting sites. Thermal treatment and isotropic etching processes allow nearly complete removal of implantation damages in the cleaved-thin wafers. Combining laser interference lithography and a reactive ion etch process, a facile nanoscale texturing process for the kerfless thin wafers of a (111) crystal orientation has been developed. We demonstrate that the introduction of nanohole array textures with an optimal design and complete damage removal lead to an improved efficiency of 15.2% based on the kerfless wafer of a 48 µm thickness using the standard architecture of the Al back surface field.