Toshiaki Yasui

Changes in chemical structure and optical properties of polyimide films induced by ion bombardment

The effect of ion bombardment on the chemical structure and optical properties of polyimide films was investigated. Oxygen and nitrogen ion beams with energies in the range of 0.5–1.0 keV and doses between 1.7×1015 and 8.2×1016 ions/cm2 were irradiated on the films, and in situ x-ray photoelectron spectroscopy (XPS) and spectral transmittance analyses were carried out. The in situ XPS analyses showed that the addition reaction of oxygen and nitrogen atoms and desorption of components caused chemical structural changes in ion-bombarded polyimides. The in situ spectral analyses showed that the spectral transmittances of films were decreased by ion bombardment.

Diagnostic Experiment and Kinetic Model Analysis of Microwave CH4/H2 Plasmas for Deposition of Diamondlike Carbon Films

Medium-pressure CH4/H2 plasmas were generated in a discharge tube on the axis of a cylindrical 2.45-GHz-microwave TM011-mode-resonance cavity for chemical vapor deposition of diamondlike carbon films. Diamondlike carbon synthesis, plasma diagnostic measurements and kinetic model analyses were conducted to examine the correlation between plasma properties and film features. The characteristics of the calculated H-atom density of the excitation quantum level 4 agreed with those of the measured spectral intensity of the Hβ line. Consequently, high density ratios of C atoms to H atoms were required for deposition of diamondlike carbon. On the other hand, the density ratio of CH3 radicals to H atoms was considered to be closely related to the hardness of deposited diamondlike carbons.

Exposure of spacecraft polymers to energetic ions, electrons and ultraviolet light

Abstract The influence of high-energy charged-particle bombardment and UV light irradiation on chemical structure of polyimide films was investigated to clarify the mechanism of material degradation in space. The films were exposed to oxygen or nitrogen ion beams with 0.5 keV, to electron beams with 20–30 keV and to UV and visible light of 250–600 nm. X-ray photoelectron spectroscopic analysis showed structural changes of the exposed polymers. The optical properties of transmittance and reflectance were also found to be degraded.

X-ray Photoelectron Spectroscopy Study of the Interactions of O+ and N+ Ions with Polyimide Films

With an increase in the use of polyimides in aerospace applications, the degradation of polyimides caused in the space environment is receiving more attention. In this paper, a ground experiment in which polyimides were exposed to high-energy ions in the space plasma environment was carried out. The effects of oxygen or nitrogen ion bombardment on the chemical structure of polyimide films were investigated by X-ray photoelectron spectroscopy (XPS). The polyimides were exposed to ion beams with energies in the range of 0.5–1.0 keV and in doses between 1.7 ×1015 and 8.2 ×1016 ions/cm2. An in-situ XPS analysis was also carried out, and showed that the ion bombardment changed the chemical structure of the polyimides due to the addition of oxygen and nitrogen ions and the desorption of other components.

Effects of ion bombardment on polymer films

Abstract With an increase in the use of polymers for aerospace applications, the degradation of polymers in space is receiving more attention. In this paper, we studied the influences of ionic impact on the surface polymers of spacecraft. The effects of ion bombardment on the chemical structures and optical properties of polymer films were investigated. The specimens were polyimide and teflon films. Oxygen and nitrogen ion beams with energies in the range of 0.5–1.0 keV and doses between 1.7 × 10 15 and 8.2×10 16 ions cm −2 were exposed to the polymers. In-situ X-ray photoelectron spectroscopy (XPS) and spectral transmittance analyses were carried out on the polymers before and after ion bombardment. The in-situ XPS analyses showed that the addition reactions of oxygen and nitrogen atoms and desorption of components caused changes of chemical structures in the ion-bombarded polymers. The in-situ spectral analyses showed that the spectral transmittances were decreased by the ion bombardment.

Plasma Generation by Resonant-Cavity Microwave Discharge and Its Applications for Material Processing

A 2.45-GHz-microwave plasma source with a resonant cavity was studied for material processing under medium to atmospheric pressures. Stable plasmas, with electron temperature and density of 1 to 5 eV and beyond the plasma cutoff density, respectively, were efficiently sustained in an ambient pressure of 10-2-10 kPa with hydrogen, helium, nitrogen, argon and a mixture of H2+2H2 (vol. rate). The operational characteristics of coupling efficiency and cavity length depended on gas species. From electric fields measured on the cavity inner wall, the electromagnetic field pattern of TM011 resonance mode was expected to be excited in the cavity over a wide range of operational conditions. In addition, operation of a plasmajet generator, into which the plasma source was modified, diamond film synthesis and surface modification due to atomic oxygen were demonstrated.

Thrust performance and plasma features of low-power Hall-effect thrusters

The closed-electron-drift Hall-effect accelerator is a promising thruster in space. The effects of magnetic field shape and strength on Hall thruster performance were studied using 1-kW-class THT-series Hall thrusters. The discharge current characteristics were sensitive to magnetic field shape and strength. The thrust for the THT-IIIA thruster with more intensive concentration of magnetic field near the acceleration channel exit, i.e., with a smaller magnetic field at the anode was slightly higher than that for the THT-III thruster. The THT-IIIA thruster could be stably operated at a higher magnetic field strength than that for the THT-III thruster. As a result, for the THT-IIIA thruster, a higher thrust efficiency was achieved with a lower discharge current and a higher thrust. Furthermore, Hall thruster flowfield analysis was made to understand inner physical phenomena. Both ionization and acceleration were found to efficiently occur in a thin region with a few mm thick near the acceleration channel exit. The calculated thruster performance roughly agreed with the experimental ones.

Electron cyclotron resonance plasma generation using a planar ring‐cusp magnetic field and a reentrant coaxial cavity

An electron cyclotron resonance (ECR) plasma source 16 cm in diameter using a planar ring‐cusp magnetic field and a reentrant coaxial cavity was developed. The planar ring‐cusp magnetic field produces a large‐area ECR surface. The reentrant coaxial cavity forces microwaves to be introduced into the ECR surface from an annular window of a discharge chamber sidewall. This plasma source generated large‐area, uniform, and stable plasmas. At 0.079 Pa of discharge chamber pressure for Ar, the plasma uniformity was 11.1% within a 12‐cm‐diam plane. Above 184 W of forward power, overdense plasmas were produced on the center axis at 0.079 Pa. The maximum Ar plasma density of 1.14×1011 cm−3 was achieved on the center axis at a discharge chamber pressure of 0.079 Pa with a forward power of 437 W.

Exposure of space material insulators to energetic ions

To understand degradation of materials due to ion bombardment in a space plasma environment, polymers of polyimide, polyetheretherketone and perfluoroalkoxy, and glasses coated with MgF2 were exposed to ion beams of oxygen and nitrogen with energy levels ranging from 600 eV to 5 keV. For the polymers, x‐ray photoelectron spectroscopic analysis showed that the addition reaction of oxygen or nitrogen atoms or the disruption or separation of various structural compounds occurred depending on ion energy and dose. For the glass plate, the coating layer of MgF2 was drastically sputtered.

Microwave Ion Source Using Resonant Cavity

Ring-cusped magnetic-field ion sources using 2.45-GHz-microwave resonant cavities were studied to develop high-performance compact ion sources for economically assisting material processings. The minimum flow rate required to sustain discharge was 10 sccm for weak-B-field off-resonance discharge in the TM011-mode-excitation cylindrical cavity, 6 sccm for weak-B-field discharge in the reentrant coaxial cavity, in which a stronger electric field was generated compared with that in the cylindrical cavity, and 3 sccm for electron cyclotron resonance (ECR) discharge in the cylindrical cavity. As a result of ion beam extraction, the highest mass utilization efficiency of 18.7% was achieved for ECR discharge.