Shunjiro Fujii

Single-wall carbon nanotubes (SWCNTs) are promising materials for electronic applications, such as transparent electrodes and thin-film transistors. However, the dispersion of isolated SWCNTs into solvents remains an important issue for their practical applications. SWCNTs are commonly dispersed in solvents via ultrasonication. However, ultrasonication damages SWCNTs, forming defects and cutting them into short pieces, which significantly degrade their electrical and mechanical properties. Herein, we demonstrate a novel approach toward the large-scale dispersion of long and isolated SWCNTs by using hydrodynamic cavitation. Considering the results of atomic force microscopy and dynamic light-scattering measurements, the average length of the SWCNTs dispersed via the hydrodynamic cavitation method is larger than that of the SWCNTs dispersed by using an ultrasonic homogenizer.

Copper oxide nanowires with good crystallinity and high aspect ratio have been attractive for use in high-performance optical and electronic devices. In this work, we fabricated copper oxide nanowires by thermal oxidation method. Copper oxide nanowires were fabricated at various heating times, keeping at a heating temperature of 500℃. When the heating time was over 30 minutes, the average width of the nanowires reached about 100 nm. It was observed that the bottom part of the nanowire was thick compared to the top part. We investigated the detailed structure by using micro-raman spectroscopy and electron backscatter diffraction (EBSD). From the results of raman spectra and EBSD crystal orientation mappings, it was found that Cu₂O/CuO heterostructure is formed at the thick region of the nanowire. Two type of heterostructures were confirmed, namely Cu₂O(110)/CuO(001) and Cu₂O(110)/CuO(110).

The chemical vapor transport method was used in this research to synthesize MoS2 bulk. Through mechanical exfoliation, we limited the thickness of MoS2 flakes from 1 to 3 μm. In order to fabricate a p-n homogeneous junction, we used oxygen plasma treatment to transform the MoS2 characteristics from n-type to p-type to fabricate a p-n homogenous junction and demonstrate the charge neutrality point shift from −80 to +102 V successfully using FET measurement. The MoS2 p-n homogeneous junction diode showed an excellent p-n characteristic curve during the measurements and performed great rectifying behavior with 1-10 Vpp in the half-wave rectification experiment. This work demonstrated that MoS2 flake had great potential for p-n diodes that feature significant p-n characteristics and rectifying behavior.

To clarify the nature of defects presented in neutron (n)-irradiated highly oriented pyrolytic graphite (HOPG), in situ X-ray diffraction (XRD) observation at room temperature (RT) and high pressure was conducted with synchrotron radiation (SPring-8). We focused on the graphite (002) [G(002)] peak under compression to 18.1 GPa and also under decompression. For comparison, unirradiated HOPG was also placed in the same high-pressure cell. We found that the G(002) peak can be represented by two components, the S and L peaks, for the n-irradiated HOPG, whereas it can be represented by only one component for the unirradiated HOPG. The d-spacing for the n-irradiated and unirradiated HOPG samples gradually decreased with increasing pressure. At 18.1 GPa, the d-spacing of the S peak of the irradiated sample became almost the same as that of the unirradiated one, but that of the L peak was larger. Under decompression, the behavior of the d-spacing was almost opposite to that under compression, and the d-spacing was restored to its value before compression. Also, taking account of the changes in the peak widths, we referred to and considered irradiation-induced defects of interstitial-type defects existing between the basal planes and in-plane defects of dislocation dipoles as possible defects that affect the changes in the G(002) peak.