Norio Homma

Preparation of carbon nanoparticles by plasma-assisted pulsed laser deposition method : size and binding energy dependence on ambient gas pressure and plasma condition

Abstract Nanometer-size carbon particles were prepared on a Si substrate using pulsed laser deposition (PLD) assisted by radio frequency (RF) Ar plasma and were compared with ones prepared by PLD in vacuum and Ar gas. In both the plasma and gas ambiences, experiments were carried out in Ar pressure p Ar ranging from 0.13 to 13 Pa. The particle size increased as p Ar increased. However, the size obtained in the RF Ar plasma was approximately 1.5 times larger than that prepared in the Ar gas. An X-ray photoelectron spectroscopy (XPS) analysis revealed that the carbon film covered by the particles was in an amorphous state. The sp 3 /sp 2 carbon ratio of the film was evaluated by deconvolution of XPS carbon (1 s ) spectra into three components, which are attributed to diamond (sp 3 ), graphite (sp 2 ) and carbon oxide components. The highest sp 3 /sp 2 ratio was 0.4 in the Ar gas and Ar plasma at p Ar =0.13 Pa. The sp 3 /sp 2 ratio decreases monotonously, as the particle size increases. The ratio obtained in the Ar plasma is larger than that in the Ar gas. The effects of p Ar and plasma for nanoparticle characteristics are discussed.

Preparation of double layer film of boron and carbon by pulsed laser deposition

Abstract Double layer films of boron and carbon were prepared by pulsed laser deposition (PLD) on silicon substrates. The film surface morphology was examined by atomic force microscopy (AFM). The chemical composition of the elements, carbon, boron, silicon and oxygen, and bonding state of carbon atoms as a function of the depth from the film surface were analyzed by X-ray photoelectron spectroscopy (XPS) with argon ion sputtering technique. Carbon atoms bonded to boron (CB) were observed as well as carbon atoms bonded to carbon (CC).

Deposition of fine carbon particles using pulsed ArF laser ablation assisted by inductively coupled plasma

Abstract Carbon thin films containing many fine carbon particles were deposited by a pulsed ArF laser ablation technique assisted by inductively coupled plasma (ICP). The sizes of the particles were found to be ∼100 nm. The particles seemed to be coagulated from several finer particles of size ∼10 nm. When ICP was applied to a plume, the shape of the coagulated particles became spherical. The deposited surface was assumed to be diamond-like carbon based on the binding energy of carbon (1s) in the particle obtained by XPS spectra.

Observations of Suspension and Levitation Effects of Bulk High-Tc Superconductors in Microgravity Experiments.

We were successful in observing suspension and levitation effects of bulk high-T c superconductors (HTSCs) with a permanent magnet in microgravity experiments. Different results from experiments on Earth have been observed for a sintered Y–Ba–Cu–O sample levitated above a ring shape magnet. However, a melt processed sample showed no difference in suspended and levitated positions both on Earth and in microgravity. The different motions between sintered and melt processed HTSCs in microgravity can be explained by the difference in magnitude of the pinning force. It is shown that melt processed HTSCs for applications of suspension and levitation effects can be employed in space as on Earth.

Numerical evaluation of levitation force of a stack with high Tc superconducting thin films

Abstract Hysteresis of the levitation force with a permanent magnet and a high Tc superconducting (HTS) thin film is discussed from calculated shielding current distribution with macroscopic numerical simulation code. Shielding current density of the thin film can be roughly estimated from the measurement of the levitation force. The levitation force of a stack with the thin films is also compared with that of bulk HTS. Numerical evaluation is useful to explain the experimental results and to discuss applications of the HTS thin film.

Evaluation of motion of a high-Tc superconducting thin film in microgravity experiments

Abstract Motion of a high- T c superconducting (HTS) thin film was observed in microgravity experiments with a free fall drop shaft facility. The field-cooled thin film was suspended under a permanent magnet in the free fall experiments. When the magnet was rotated in microgravity, the thin film moved to a stable position where centrifugal force was balanced to restoring force caused by pinning of superconductor. The motion of the HTS thin film is numerically evaluated by using the frozen field model, which is based on an assumption that fluxoids are fixed at pinning points on the surface of the superconductor. The numerical evaluation is useful to explain the experimental results.

Observations of Suspension and Levitation Effects of Bulk HTSCs in Microgravity Experiments

We were successful in observing suspension and levitation effects of bulk high-Tc superconductors (HTSCs) with a permanent magnet in microgravity experiments. Different results from experiments on Earth have been observed for a sintered Y-Ba-Cu-O sample levitated above a ring shape magnet. However, a melt processed sample showed no difference in suspended and levitated positions both on Earth and in microgravity. Stable equilibrium of the melt processed sample is discussed from view points of pinning effect. It is shown that melt processed HTSCs for applications of suspension and levitation effects can be employed in space as on Earth.

Evaluation of levitation and suspension forces of a bulk HTSC in microgravity experiments

Abstract Levitation and suspension forces between a permanent magnet and a bulk high T c superconductor are examined in microgravity experiments. Different experimental results are obtained for a melt processed and a sintered Y-Ba-Cu-O samples. Stable equilibrium of the melt processed sample is discussed from view points of pinning effect.