Hajime Shirai

Rf microplasma jet at atmospheric pressure: characterization and application to thin film processing

A novel rf microplasma jet at atmospheric pressure was successfully generated using a single needle tube electrode. The atmospheric He discharge was characterized using optical emission spectroscopy with the inner hole diameter of the needle electrode and the flow rate of gas as variables. Preliminary results of the application of microplasma jets to thin film processing are given, i.e. silicon oxidation and the synthesis of carbon nanostructures including amorphous carbon, graphite, and nanotubes. A metal-oxide-semiconductor structure using the silicon oxidized layer formed by the O2/He plasma showed good rectification behaviour. The effects of gas flow velocity and inner diameter of the needle tube electrode on the carbon nanostructure and deposition area are discussed.This article was due to be published in Volume 36, issue 23 of Journal of Physics D: Applied Physics. To access this special issue please follow this link http://www.iop.org/EJ/toc/0022-3727/36/23

The characterization of radio-frequency discharge using electrolyte solution as one electrode at atmospheric pressure

Atmospheric pressure discharges driven by radio-frequency source were generated using electrolyte solution as one electrode. The electron density calculated from the Stark broadening of Hβ (486.1u2009nm) was in the order of 1015u2009cm−3 and showed a parabolic shape with the pH value of the solution. The simulated gas temperature increased from 950 to 2750u2009K as the input power increased from 12 to 40u2009W. We found that the plasma exposure was accompanied with the acidification of the solution electrode; it was ascribed to the dissolution of nitrogen-related compounds, such as HNO2, HNO3 and NxOy which originate from the oxidation of nitrogen in air. Also, solute atom line emission was observed in the plasma zone and evaporation was demonstrated to play an important role in the solute transport.

Role of oxygen atoms in the growth of magnetron sputter-deposited ZnO films

The role of oxygen atoms in the growth of magnetron sputter-deposited ZnO films was studied by alternating the deposition of a several-nanometer-thick ZnO layer and the O2/Ar mixture plasma exposure, i.e., layer-by-layer technique. The film crystallization promoted with suppressing the oxygen vacancy and interstitial defects by adjusting the exposure condition of O2/Ar plasma. These findings suggest that the chemical potential of oxygen atom determine the film crystallization as well as the electronic state. The diffusion and effusion of oxygen atoms at the growing surface play a role of thermal annealing, promoted the film crystallization as well as the creation and the annihilation of oxygen and zinc related defects. The role of oxygen atoms reaching at the film-growing surface is discussed in term of chemical annealing. The possible oxygen diffusion mechanism is proposed.

Rapid Recrystallization of Amorphous Silicon Utilizing Very-High-Frequency Microplasma Jet at Atmospheric Pressure

The rapid recrystallization of amorphous silicon (a-Si) utilizing a very-high-frequency (VHF) plasma jet of argon (Ar) at atmospheric pressure is investigated. A highly crystallized polycrystalline Si film is synthesized by optimizing the translating velocity of the substrate stage and the flow rate of argon. The temperature of the plasma exposure area reaches 1350±300 °C and the recrystallization of a-Si proceeded with time constants of 30–50 ms. The effects of the translating velocity of the substrate stage and the flow rate of argon on the rapid recrystallization of a-Si are demonstrated along with its mechanism.

Surface chemistry and preferential crystal orientation on the H and Cl terminated silicon surface

Surface chemistry and determining factors of the preferential crystal orientation are discussed through the deposition studies on hydrogenated chlorinated crystalline silicon films by rf plasma-enhanced chemical vapor deposition of a dichlorosilane, SiH2Cl2, and H2 mixture. The growth of randomly oriented crystal Si films occurred from the initial growth stage. On the other hand, the incubation layer of amorphous Si was formed in the initial stage, and subsequently, the growth of (220) preferred crystal orientation proceeded. They are determined by the thermal abstraction of H from the growing surface at substrate temperature above 350°C. Higher degree of Cl termination was effective in suppressing the oxygen incorporation into the Si network, although it did not contribute directly to the preferred crystal orientation. The insertion of atomic hydrogen to the Si–Si back bond in the subsurface region promoted the SiHClx complex formation, which was the most possible nucleation site for promoting the (220) ...

Synthesis of Well-Aligned Carbon Nanotubes Using a High-Density RF Inductive Coupling Plasma

Growth of vertically well-aligned carbon nanotubes was demonstrated utilizing high-density rf inductive coupling plasma-enhanced chemical vapor deposition of methane. A sufficient supply of CH4-related precursors as well as a rapid large number of dangling bonds at the top surface due to a negative substrate dc bias are essential for promoting the deposition rate of vertically well-aligned carbon nanotubes. Rapid deposition at 60 A/s of vertically well-aligned multi-walled carbon nanotubes was achieved using pure methane (50 sccm) by adjusting the plasma conditions.

Structure and Carrier-Transport in a-Si:H, a-Si(Ge): H Films Prepared by Chemical Annealing

The stability and opto-electric properties of a-Si:H films fabricated by “chemical annealing (CA)” with excited states of He (He*) were systematically investigated. The films made by the CA mode showed a high photoconductivity due to a low level of defect density, 2×10 15 cm -3 , and improvement in the stability against light soaking. A marked improvement was also found in the hole-transport in films fabricated by the CA. The structural relaxation on the growing surface was also enhanced by addition of a small amount of Ge.

Rapid Crystallization of Amorphous Silicon Utilizing the Plasma Annealing at Atmospheric Pressure

The rapid crystallization of amorphous silicon utilizing the rf inductive coupling thermal plasma jet of argon is demonstrated. Highly crystallized a-Si films were fabricated on th -SiO 2 and textured a-Si:H:B/SnO 2 /glass by adjusting the translational velocity of the substrate stage. The H concentration in the films decreased from 10 21 cm -3 to 10 19 cm -3 with no marked increases in oxygen and nitrogen impurity concentrations and defect density. The crystallization proceeds from the bottom to front surface in terms of the volume expansion during the solidification and crystallization of liquid Si.