Nobuhiro Aya

Fabrication of silicon nanostructured films by deposition of size-selected nanoparticles generated by pulsed laser ablation

Nanostructured films composed of size-controlled silicon nanoparticles were fabricated by pulsed laser ablation in helium background gas. The size distribution of the silicon nanoparticles in the gas phase was controlled and measured by the electrostatic size classification technique using a differential mobility analyzer coupled with an electrometer. The microstructures and crystallinity of the as-deposited and size-classified nanostructured films were analyzed by scanning electron microscopy and Raman spectroscopy, respectively. The effects of the background gas pressure and particle size on the morphology of the films are discussed.

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.

Synthesis of size-selected silicon nanoparticles by laser ablation

Abstract Using a laser ablation process under low pressure conditions in combination with a LP-DMA, we were able to fabricate size-selected charged silicon nanoparticles. By measuring the concentration and estimating the time required to cover the surface, it was found that this process can be used in QD material processing. The effect of system pressure and laser conditions on the size distribution of particles will be also discussed in the presentation.

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.

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.