Hirofumi Shimura

Evaluation of Morphology and Size Distribution of Silicon and Titanium Oxide Nanoparticles Generated by Laser Ablation

Nanometer-sized particles of silicon and titanium oxide were generated by irradiating solid targets using a nanosecond pulsed-Nd : YAG laser in a low pressure atmosphere. A low pressure differential mobility analyzer (LP-DMA) was used to classify the size of the generated particles. The LP-DMA and electron microscopes (SEM and TEM) were used to measure the change in the size distribution and morphology of the generated particles with laser power density and system pressure. The size distribution of both silicon and titanium oxide ranged from two to one hundred nanometers in diameter depending on the laser power density and pressure. From the high resolution TEM observation and electron diffraction, it was found that the generated titanium oxide nanoparticles were composed of a ‘core’ of faceted metallic single crystals with an oxide layer shell’.

Irradiation of CW-CO2 laser on a powder target. Formation of fullerene film from graphite powder

Abstract A process was investigated to irradiate a continuous-wave CO 2 laser (4.5 kW) on graphite powder with a mean diameter of 5 μm in a flow of Ar or He gas at 30 or 200 Torr. The film produced on a Ni substrate in the Ar flow at 200 Torr showed the Raman bands of C 60 and C 70 , and the C 60 /C 70 ratio was estimated to be 5/1 by MALDI-TOF mass spectrometry. The film formation process is discussed on the basis of an analysis of laser-irradiated powder, which included 0.01 wt% of C 60 , by UV–Vis absorption, and by observations of the plumes and SEM images.

Ion beam charging of silicon nanoparticles in helium background gas: Design of the ion beam aerosol charger

An ion beam aerosol charger that ionizes aerosol nanoparticles of less than 10 nm diameter using an ion beam was designed for use in the electrostatic manipulation of gas-suspended nanoparticles. Pulsed laser ablation of a solid target in a high purity helium gas under pressure of 2–10 Torr (266–1330 Pa) was employed to fabricate nanometer-sized silicon particles. The ion beam, which was generated by cold cathode Penning ionization of He atoms, was accelerated with an energy of 0–5 keV, penetrated a skimmer located within the differential pumping system, and then entered the aerosol ionization chamber. The silicon nanoparticles were both positively and negatively charged by the direct impact of the ion beam or the secondary electrons generated from the surrounding He gas. The change in the concentration of ions and charged aerosols was measured by ion probes. It was found that the concentration of charged particles was drastically increased to 2–50 times that at baseline.

Tribological Properties of MoS2-Coated Gray Cast Irons with Some Different Matrix Phases under the Boundary Lubricating Conditions

In this study, Fe-2.0Si-4.6C (mass%) gray cast iron disk specimens with three different matrix phases were coated with MoS2 using pressure spraying, and the friction and wear properties of the specimens were investigated against AISI52100 steel and polytetrafluoroethylene balls under the lubrication of oil using an Optimol SRV friction tester. When AISI52100 steel balls were used as the paired material, all of the MoS2-coated gray cast iron specimens showed lower friction coefficients and higher wear resistance than the non-coated disk specimens. On the other hand, MoS2-coated gray cast iron specimens exhibited higher friction coefficients than non-coated disk specimens for the most part, when polytetrafluoroethylene balls were used as the paired material.

Multi-oxides thin film formation on iron-base metal by YVO4 pulsed laser color marking

Multi-oxidized thin films were fabricated by applying laser color marking technique on a stainless steel surface with laser irradiation using an YVO4 pulsed-laser at 30 kHz in atmospheric conditions. These multi-oxidized thin films emitted several colors including purple, violet, ultramarine, orange, and green. Using this technique, these mono-colors were produced on the surface according to the scanning repetition number and laser power. Results of XRD analyses for the colored areas showed several types of oxides consisting of FeO, Fe3O4, CrO, Cr2O3, Cr3O4, NiO, Ni2O3, NiCr2O4, and their mixed oxides, which consisted of oxygen vacancy structures. Each of these oxides has its original color for each composition and structure if the mono-phase area producing it shows clear mono-color corresponding to the composition and structure.Multi-oxidized thin films were fabricated by applying laser color marking technique on a stainless steel surface with laser irradiation using an YVO4 pulsed-laser at 30 kHz in atmospheric conditions. These multi-oxidized thin films emitted several colors including purple, violet, ultramarine, orange, and green. Using this technique, these mono-colors were produced on the surface according to the scanning repetition number and laser power. Results of XRD analyses for the colored areas showed several types of oxides consisting of FeO, Fe3O4, CrO, Cr2O3, Cr3O4, NiO, Ni2O3, NiCr2O4, and their mixed oxides, which consisted of oxygen vacancy structures. Each of these oxides has its original color for each composition and structure if the mono-phase area producing it shows clear mono-color corresponding to the composition and structure.

Fabrication of well-defined silicon and titanium oxide nanoparticles by laser ablation

Nanometer-sized particles of silicon and titanium dioxide were generated by Nd:YAG laser ablation of solid substrates in a low pressure atmosphere. A low-pressure differential mobility analyzer (LP-DMA) was used to control the size of generated particles. The LP-DMA and a transmission electron microscopy (TEM) were used to measure the change in size distribution and morphology of nanoparticles with laser power and pressure. Finally, we succeeded to synthesize the almost spherical nanoparticles of 2-50 nm in diameter.

Fullerene synthesis from carbon powder using CW-CO2 laser

A semi-continuous process for the synthesis of fullerenes is described. This novel process incorporated a carbon powder feed system in combination with a continuous-wave CO2 laser irradiation source. The carbon powder contained no fullerenes but did contain graphite crystals and amorphous carbons of selected particle sizes (5, 10, or 20 μm), and selected irregular or spherical particle shapes. The method was successfully used to deposit C60 and C70 powders and films continuously. Laser irradiation of the carbon powder produced an observable laser plume. The experimental results and mechanism for the process are discussed.

Laser glazing of pure iron using high-power CO{sub 2}-gas laser

The surface of pure iron was glazed with a high-power CO2-gas laser to improve its surface hardness. The conditions of the CO2-gas laser were 1.6x105 W/cm2, continuous wave and multi mode at 5 kW. This laser beam was irradiated on the pure iron (99.9 wt%) surface under an Ar-gas (0.2 torr) atmosphere. The size of iron was 14x17x70 mm3. Microvickers hardness increased to 530 Hv (laser irradiated surface) from 257 Hv (substrate surface). The mechanism of increased hardness was analyzed with scanning electron microscopy and X-ray diffraction of the surfaces of both the laser irradiated and substrate iron. The SEM images showed that the laser glazed surface consisted of cross packed grains but the substrate surface included many micro pores. The hardened area had no boundary with its substrate and also had no cracks. From the results of XRD measurements, the patterns of the glazed surface partly changed to the amorphous phase and the relative intensity of (200) peak par (110) peak of δ-Fe changed to smaller than that of the substrate. These results suggested that the reasons for the increased hardness of the laser glazed surface were the disappearance of micro pores and the appearance of fine grains and amorphous phase.The surface of pure iron was glazed with a high-power CO2-gas laser to improve its surface hardness. The conditions of the CO2-gas laser were 1.6x105 W/cm2, continuous wave and multi mode at 5 kW. This laser beam was irradiated on the pure iron (99.9 wt%) surface under an Ar-gas (0.2 torr) atmosphere. The size of iron was 14x17x70 mm3. Microvickers hardness increased to 530 Hv (laser irradiated surface) from 257 Hv (substrate surface). The mechanism of increased hardness was analyzed with scanning electron microscopy and X-ray diffraction of the surfaces of both the laser irradiated and substrate iron. The SEM images showed that the laser glazed surface consisted of cross packed grains but the substrate surface included many micro pores. The hardened area had no boundary with its substrate and also had no cracks. From the results of XRD measurements, the patterns of the glazed surface partly changed to the amorphous phase and the relative intensity of (200) peak par (110) peak of δ-Fe changed to smaller t...