Keisuke Niwase

Generation of giant carbon hollow spheres from C60 fullerene by shock-compression

Abstract We report on the generation of carbon hollow spheres up to several micrometers in diameter on an internal hollow surface of the recovered sample from C 60 fullerene powder after shock-compression up to 57 GPa. Scanning electron microscopy demonstrates see-through spheres, a collapsed one like a Ping-Pong ball and bowl type objects, suggesting that the spheres are empty. Raman spectroscopy reveals that the carbon hollow spheres are in highly graphitized state of which crystalline size is several hundred of nanometers. The possible formation mechanism is proposed.

Self-Organized Nanostructures Generated on Au, Ag and Cu Surfaces by Low-Temperature Electron Irradiation

We describe a new type of self-organized nanostructure for Au, Ag and Cu thin foils irradiated with high-energy electrons at around 100 K. The nanostructure appears on the electron exit surface and consists of aligned grooves which developed parallel to the surface, and nanoholes and hillocks which grew parallel to the electron beam. The groove pattern depends on the irradiation direction, the surface orientation, and the kind of metal. After about 1000 s of irradiation, penetration of the foil by grooves and holes occurs, finally leading to the formation of nanoslits or nanoparticles. These structures are probably the smallest ones generated so far on each metal surface. It is suggested that some irradiation-induced effects are closely related to the generation of nanostructures.

Micro-Raman Study on Structure Evolution of Graphite Exposed to Intense Thermal Shock Load

A small area of a fine grain graphite block was exposed to intense thermal shock load at 9.6 GW/m2 and investigated by micro-Raman spectroscopy. Raman spectra of the loaded area show a reduction of the intensity ratio of D and G peaks in comparison with the one of unloaded graphite, indicating the ordering of graphitic structure even for as short as 5 ms. Raman spectra of the surrounding area, on the other hand, exhibited broad features of amorphous carbon, indicating a carbon deposits from the loaded area. The broad spectra showed a strong positional dependence, reflecting the temperature gradient of the block induced by the shock load. Fitting analysis of the Raman spectra clearly shows two linear relationships between the G-peak width (FWHMG) and the peak intensity ratio (ID / IG), corresponding to two steps of ordering process of the amorphous carbon deposits.

Void formation close to stacking fault tetrahedra in heavily electron irradiated pure Ag and Cu

Abstract Pure Ag and Cu foils were irradiated with 1.25 MeV electrons at temperatures between 110 and 323 K in a high voltage electron microscope. For Ag foils irradiated at 300 K, SFT form an inhomogeneous lattice at first and then voids appear, the sites of which correspond to the SFT-lattice positions. Also at 270 K voids were found after a homogeneous formation of the SFT lattice, however, below 240 K voids were not observed. Void formation after SFT formation was also found for Cu specimens irradiated above 300 K. The nucleation process of voids is discussed in terms of the effect of a small amount of solute or gas atoms, which were segregated to SFT clusters under irradiation.

Quenchable compressed graphite synthesized from neutron-irradiated highly oriented pyrolytic graphite in high pressure treatment at 1500 °C

The super hard material of “compressed graphite” (CG) has been reported to be formed under compression of graphite at room temperature. However, it returns to graphite under decompression. Neutron-irradiated graphite, on the other hand, is a unique material for the synthesis of a new carbon phase, as reported by the formation of an amorphous diamond by shock compression. Here, we investigate the change of structure of highly oriented pyrolytic graphite (HOPG) irradiated with neutrons to a fluence of 1.4 × 1024 n/m2 under static pressure. The neutron-irradiated HOPG sample was compressed to 15 GPa at room temperature and then the temperature was increased up to 1500 °C. X-ray diffraction, high-resolution transmission electron microscopy on the recovered sample clearly showed the formation of a significant amount of quenchable-CG with ordinary graphite. Formation of hexagonal and cubic diamonds was also confirmed. The effect of irradiation-induced defects on the synthesis of quenchable-CG under high pressur...

Transformation from C60 fullerene into carbon spheres by shock compression

Here, we report a partially facetted carbon sphere of about 20 μm in diameter on the outer surface of the recovered sample from C60 fullerene powder after shock-compression. The sphere has two hexagonal facets locating almost parallel to each other. Spotty contrast is observed on the roundish particle but not on the facetted area. Micro-Raman spectroscopy revealed that the facetted area is in a highly graphitized state but not the roundish area.

Cooling Rate Threshold in Transformation of C60 Fullerene to Amorphous Diamond and Highly Disordered Carbon in SCARQ Experiments

C60 films on gold substrates (film thickness of 6–20 μm) were prepared. These films were shock compressed to 48 GPa and recovered using “shock compression and rapid quenching (SCARQ)” technique. The recovered samples were amorphous diamond, when the initial thickness of the sample was less than 10 μm, and disordered carbon, when the initial thickness was 20 μm. The temperature history of the sample was estimated by one‐dimensional thermal diffusion analysis. It was revealed that there was a lower limit of cooling rate for recovery of amorphous diamond. The chemical bond change of carbon after shock compression was also discussed.