Ryuta Morishima

Room-temperature growth of a carbon nanofiber on the tip of conical carbon protrusions

Glassy carbon was Ar + -ion bombarded with a simultaneous Mo supply under ultrahigh vacuum conditions using a microprotrusion fabrication system that consists of a differentially pumped ion gun and a seed-material supply source. Conical protrusions were formed by sputtering with a seed supply, and carbon nanofibers (CNFs) grew on the tips even at room temperature. The length of CNFs reached up to ∼10 μm, and their diameter was almost uniform (50 nm) in the growth direction. The short CNFs aligned in the ion beam direction, whereas the long ones were non-aligned. The CNF growth on a glassy carbon surface was ascribed to the enhanced surface texturing and to the massive redeposition of C atoms onto cones, both of which are specific to the oblique ion bombardment: The former would lead to an increase in the number of possible nucleation sites for the CNF growth, and the C atoms arising from the latter process would migrate toward the conical tips, thus forming CNFs.

Synthesis of Ni Nanowire-Encapsulated Carbon Nanotubes

A novel method for synthesizing nanowire-encapsulated carbon nanotubes (CNTs) under a high-vacuum ambient is demonstrated. A mixture of acetylene (C2H2) and ammoniac (NH3) gases was effused through a molecular beam (MB)-nozzle onto a small area of a Ni mesh sample heated at 580°C using a newly developed MB-chemical vapor deposition (CVD) system. The densely distributed CNTs, which grew by the thermal decomposition of gases on the intensely gas-effused area, were almost identical in diameter (~9 nm) despite a large difference in length (0.1–1 µm), and were almost completely filled with a single Ni nanowire of 6 nm in diameter. CNTs with discontinuous filling or those without filling were not observed. On the basis of the detailed transmission electron microscopy (TEM), the base growth mode accompanied by the diffusion of catalyst Ni atoms toward the growth sites was proposed to account for an extremely high rate of filling with nanowire into CNTs.