Yoshifumi Ikoma 교수

Si(100) wafers were subjected to severe plastic deformation under a pressure of 24 GPa using high-pressure torsion (HPT). Si wafers were plastically deformed at room temperature. HPT-processed samples were composed of metastable body centered cubic Si-III and rhombohedral Si-XII phases in the initial cubic diamond Si-I. The volume fraction of metastable phases increased with increasing plastic strain. Successive annealing at 873 K led to the reverse transformation of metastable phases. A broad p

Severe plastic deformation (SPD) has been widely studied in order to enhance the strength and ductility of metallic materials. Among various SPD processing techniques, high-pressure torsion (HPT) can be applied to various brittle materials including semiconductors. In this overview, we report on the HPT processing of Si, Ge, and compound semiconductor GaAs. When crystalline Si was subjected to HPT, metastable body-centered-cubic (bcc) Si-III and rhombohedral Si-XII as well as amorphous regions w

We have developed a new method for epitaxial growth of ultrathin (∼nm) 3C-SiC films on Si(100) by pulsed supersonic free jets of methylsilane (CH 3 SiH 3 ). It was found that pit formation at the SiC/Si(100) interface was suppressed by increasing the pulse width and the surface roughness was decreased by decreasing the number of CH 3 SiH 3 jet pulses. A linear relationship was observed between the film thickness and the pulse number in the thin film region of less than ≈40 nm, while the growth r

Artificially designing the crystal orientation and facets of noble metal nanoparticles is important to realize unique chemical and physical features that are very different from those of noble metals in bulk geometries. However, relative to their counterparts synthesized in wet-chemical processes, vapor-depositing noble metal nanoparticles with the desired crystallographic features while avoiding any notable impurities is quite challenging because this task requires breaking away from the thermo

We have investigated the epitaxial growth of multilayer structures of Si/3C–SiC/Si(100) by pulsed supersonic free jets of methylsilane (CH3SiH3) for SiC growth and trisilane (Si3H8) for Si growth. Epitaxial Si layers were obtained only on very thin (≈3 nm) 3C–SiC epitaxial layers, while polycrystalline Si was grown on thicker 3C–SiC layers. It was also found that the transition regions with a thickness of ≈1 nm existed at the interface between epitaxial 3C–SiC and Si layers by high-resolution tr

Grain refinement of GaAs was achieved by application of severe plastic deformation through high-pressure torsion (HPT). Ultrafine-grained structures including nanograins were produced by the HPT processing under 24 GPa. An intense photoluminescence (PL) peak in the near infrared corresponding to the band gap of GaAs disappeared after the HPT processing but subsequent annealing gave rise not only to restoration of the original band-gap-related peak but also to an additional PL peak in the visible

Ag wetting on oxides is essential for implementing exceptional layered Ag superstructures with simultaneous ultralow losses in electrical conductance and optical transmittance. This goal is difficult to achieve by conventional synthetic techniques involving the incorporation of heterogeneous transition metals or metalloids into Ag as wetting inducers as they cause detrimental optoelectrical changes. This study provides novel insights into the use of homogeneous Ag wetting seeds to improve the we

Germanium has been processed by high-pressure torsion (HPT) under a nominal pressure of 24 GPa at room temperature and cryogenic temperature. The samples processed at room temperature were composed of a diamond-cubic Ge-I phase and a metastable tetragonal Ge-III phase. The formation of Ge-III was significantly suppressed and Ge-I and an amorphous phase, in addition to a small amount of body-centred-cubic Ge-IV, appeared in the case of cryogenic HPT processing at 100 K. The Ge-IV phase gradually

Thermodynamically stable stoichiometric and higher oxidation states are known to be detrimental to the electrical and optical performances of Ag electrodes. In contrast, thermodynamically less stable or unstable suboxidation states entailing extreme O deficiencies are scarcely understood because the tenuous or null trace of O in suboxidized Ag domains is difficult to detect. This paper presents an experimental confirmation and numerical interpretation of the extreme suboxidation of Ag-layered el