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We constructed a simple device, which utilized laser-induced breakdown spectroscopy to image H2 gas leaking from the surfaces of hydrogen fuel cells to ambient air. Nanosecond laser pulses of wavelength lambda=532 nm emitted from a neodymium-doped yttrium aluminum garnet laser were first compressed to a pulse length Deltat<1 ns using a stimulated Brillouin backscattering cell. Relay-imaging optics then focused this beam onto the H(2) leak and initiated the breakdown plasma. The Balmer-alpha (H-alpha) emission that emerged from this was collected with a 2-m-long macrolens assembly with a 90-mm-diameter image area, which covered a solid angle of approximately 1 x 10(-3)pi steradians seen from the plasma. The H-alpha light was isolated by two 100-mm-diameter interference filters with a 2 nm bandpass, and imaged by a thermoelectrically cooled charge-coupled device camera. By scanning the position of the laser focus, the spatial distribution of H2 gas over a 90-mm-diameter area was photographed with a spatial resolution of < or = 5 mm. Photoionization of the water vapor in the air caused a strong H-alpha background. By using pure N2 as a buffer gas, H2 leaks with rates of <1 cc/min were imaged. We also studied the possibilities of detecting He, Ne, or Xe gas leaks.

A low-temperature plasma oxidation of GaAs (lower than 100 °C) has been realized. The oxidation apparatus mainly consists of a quartz tube chamber, a low-power rf oscillator and an electrical magnet. The oxidation rate can be controlled in the range 100–600 Å/min by changing the magnetic field perpendicularly applied to the sample. The interface state density between p-type GaAs and its oxide film is the order of 1010 cm−2 eV−1 around 0.5 eV from the top of the valence band. This low state density suggests that the oxide film can be applied to various GaAs MOS devices. For the oxide film of n-type GaAs, an anomalous frequency dispersion in the MOS capacitance is found in the accumulation region. This anomaly is very similar to that observed in anodic oxidation.