Kousuke Moritani

Stable structures of a rolled seamless belt of atoms arranged in a two-dimensional honeycomb lattice such as a carbon nano-belt, transit from a ring-shaped structure with a rotational invariance to folded structures as the circumference of the belt increases. Using molecular mechanics, we consider the size dependence of the structures obtained by simulated annealing. In addition, the relationship between the variety of metastable structures and the rate of temperature decrease during annealing is also examined. Furthermore, we investigate the effects of the van der Waals interaction between the surfaces on the structural transitions.

Since molecular cluster ion beams are expected to have various chemical effects, they are promising candidates for improving the secondary ion yield of Tof-SIMS. However, in order to clarify the effect and its mechanism, it is necessary to generate molecular cluster ion beams with various chemical properties and systematically examine it. In this study, we have established a method to stably form various molecular cluster ion beams from relatively small amounts of liquid materials for a long time by the bubbling method. Furthermore, we applied the cluster ion beams of water, methanol, methane, and benzene to the primary beam of SIMS and compared the molecular ion yields of aspartic acid. The effect of enhancing the yields of [M+H](+) ion of aspartic acid was found to be the largest for the water cluster and small for the methane and benzene clusters. These results indicate that the chemical effect contributes to the desorption/ionization process of organic molecules by the molecular cluster ion beam.

In contrast to a convex droplet, the particles contained in a suspended droplet accumulate near its bottom and can reflect light passing through it. The intensity of the light scattered by the particles near the bottom depends on the radius of curvature of the droplet at the bottom, and therefore this enables the detection of the shape change of the droplet with high sensitivity. We show that during the evaporation of a water droplet containing gold particles, the intensity of the scattered light initially increases gradually, after which it decreases rapidly immediately before the droplet evaporates completely. This change elucidates that the suspended droplet is rapidly flattened after its radius of curvature decreases, and the particles contained in it strongly affect its evaporation process, particularly for small droplets. This phenomenon can be used to more brightly illuminate the surface of a droplet relative to the interior.

We developed a gas cluster ion beam (GCIB) source in conjunction with a two rotating electric fields (REFs)-type mass filter. The REFs method is suitable for a mass filter of a massive cluster ion beam because masses can be separated from a continuous ion beam with a constant mass resolution in all mass ranges. In principle, the mass range is unlimited. Using this apparatus, we measured the size distribution of an Ar cluster ion beam. The REFs method has a wide mass range of at least 40 similar to 160,000 Da. The peak cluster size of the Ar cluster ion beam generated in this apparatus is 900. The annular patterns projected onto a fluorescent screen by Ar+ indicate that the maximum estimated mass resolution (M/Delta M) for the REFs mass filter is 86 for the full width at half maximum (FWHM) at a beam diameter of 0.12 mm (empty set). This mass filter should realize new applications of size-selected massive cluster ion beams as well as the study of cluster physics.