Yoshiyuki Show

Influence of defects on electron emission from diamond films

The correlation between paramagnetic defects and the electron emission in diamond films, which were deposited by the chemical vapor deposition method, has been studied using electron-spin-resonance (ESR) and field-emission measurements. The paramagnetic defects, which are a carbon dangling bond in the diamond layer (Pdia-center: g=2.003, ΔHPP=3 Oe) and a carbon dangling bond in the nondiamond phase carbon region (Pac-center: g=2.003, ΔHPP=8 Oe), exist in the diamond films. Electron emission with high current density was observed for the diamond film, which contains high spin densities for both ESR centers, because electrons are efficiently transported to the diamond surface through the defect-induced energy band(s) by hopping conduction.

Structural characterization of CVD diamond films using the ESR method

Abstract The early deposition stages of diamond films have been studied in detail as a function of growth time, using electron spin resonance methods. The defect center in the non-diamond phase carbon region (g = 2.003, ΔHpp = 8–14 Oe was observed from a sample deposited for 10 min. The defect center in the diamond layer (g = 2.003, ΔHpp = 3–5 Oe) was observed together with the defect center in non-diamond phase carbon after 20 min of growth time, and the intensity of the defect center in the diamond layer increased gradually with prolonged deposition time. Moreover, the relationship between defect structures and electrical resistance of the diamond film was discussed.

Characterization of Surface Conductive Diamond Layer Grown by Microwave Plasma Chemical Vapor Deposition

The electronic structure of the surface and defect density in diamond films as-grown and cooled in an oxygen ambient after deposition have been investigated by means of electron energy loss and electron spin resonance spectroscopies. As-grown diamond films contain an amorphous carbon phase and a larger amount of defects in the surface region compared with the bulk region.

Anticorrosion coating of carbon nanotube/polytetrafluoroethylene composite film on the stainless steel bipolar plate for proton exchange membrane fuel cells

Composite film of carbon nanotube (CNT) and polytetrafluoroethylene (PTFE) was formed from dispersion fluids of CNT and PTFE. The composite film showed high electrical conductivity in the range of 0.1-13 S/cm and hydrophobic nature. This composite film was applied to stainless steel (SS) bipolar plates of the proton exchange membrane fuel cell (PEMFC) as anticorrosion film. This coating decreased the contact resistance between the surface of the bipolar plate and the membrane electrode assembly (MEA) of the PEMFC. The output power of the fuel cell is increased by 1.6 times because the decrease in the contact resistance decreases the series resistance of the PEMFC. Moreover, the coating of this composite film protects the bipolar plate from the surface corrosion.

Structural changes in CVD diamond film by boron and nitrogen doping

Abstract The effect of impurity atoms in the defect structures of a diamond film has been studied by electron spin resonance (ESR). It has been observed that introducing boron atoms into the diamond film during chemical vapor deposition (CVD) reduces paramagnetic defects (Pdia and Pac centers) by decreasing the activation barrier, which leads to a disappearance of the defects. On the other hand, the nitrogen doping introduces both defects and donor electrons in the diamond films.

Electric double-layer capacitor fabricated with addition of carbon nanotube to polarizable electrode

Electrical double-layer capacitor (EDLC) was fabricated with addition of carbon nanotube (CNT) to polarization electrodes as a conducting material. The CNT addition reduced the series resistance of the EDLC by one-twentieth, while the capacitance was not increased by the CNT addition. The low series resistance leaded to the high electrical energy stored in the EDLC. In this paper, the dependence of the series resistance, the specific capacitance, the energy, and the energy efficiencies on the CNT addition is discussed.

The electron emissions from nitrogen doped diamond film (effects of defects)

Abstract The influence of the defects introduced into the diamond film by nitrogen doping, on an electron emission has been studied by the electron spin resonance (ESR) method. It was observed that a large amount of nitrogen doping (N/C=1∼10) caused the crystal quality to deteriorate through the introduction of a paramagnetic defect into the diamond film. The current density of the electron emission was increased to 250 μA/cm 2 with an increase of defect density within the diamond film.

Photoemission characteristics of diamond films

In this study, we investigate the photoelectric emission from CVD diamond films. These diamond samples present NEA properties due to their as-grown surfaces terminated with hydrogen atoms. Photocathodes are characterised by UV pulsed laser-induced photoelectric measurements and photoelectric threshold measurements because the photoelectric emission is strongly dependant on the electron affinity of the diamond surface. Photoelectric threshold measurements show the existence of a sub-bandgap signal associated to a defect-band level for both samples, with the lowest value obtained for the highest defect-density diamond film. Moreover, the quantum efficiency of undoped diamond is measured at 213 nm as a function of the CH4 concentration. The highest quantum efficiency value is measured for the highest defect-density diamond film. Surface bonds modifications occurring during a prolonged laser irradiation are responsible for the decrease in the photoemissive performances of diamond films. # 2000 Elsevier Science B.V. All rights reserved.

ESR characterization of defects produced in diamond surface by B ion implantation

The defects produced by B ion implantation into CVD diamond films have been investigated by the electron spin resonance (ESR) method. The ESR analysis revealed the P ac -center ( g = 2.003, ΔH PP = 10-16 Oe), which originates from carbon dangling bonds in the non-diamond phase carbon region. When the dose of B ion increased from 1 X 10 13 to 1 X 10 16 ions/cm 2 , the spin density of the P ac -center in the implanted region increased from 1.5 X 10 19 to 3.2 X 10 20 spins/cm 3 and ΔH PP also increased from 10 to 16 Oe, while ΔH PP decreased from 20 to 2.6 Oe in the case of N ion implantation. The spin density of the P ac -center and the ΔH PP strongly depends on B ion doses.

UV picosecond laser-induced changes on chemical vapor deposited diamond surface investigated by photoelectric charge measurements and surface analysis

Abstract In this paper, we investigate UV picosecond laser-induced effects on undoped chemical vapor deposited (CVD) diamond surfaces as a function of irradiation time. Diamond films are negative electron affinity (NEA) emitters and contain defects (non-diamond phases). Surface analysis is performed before and after laser irradiation, in order to clearly demonstrate surface structural transformations. A diamond peak shift after pulsed laser irradiation is determined by micro-Raman analysis and correlated to stress variations in diamond. The post-irradiated diamond surface reactivity with ambient air is studied by X-ray photoelectron spectroscopy (XPS). XPS results show surface bonding modifications due to carbon–oxygen interaction enhanced by UV pulsed laser irradiation.