Multicrystalline Mg 2 Si crystals were grown using a Brigdman method combined with a die-casting growth technique. Although molten and/or vapor-phase Mg at elevated growth temperatures exhibit high chemical reactivity with the surrounding crucible materials, the use of an alumina crucible with a BN coating allowed single phase crystal growth and Mg 2 Si of good crystalline quality. Incorporation of carbon into the Mg 2 Si was observed to form Mg 2 Si 1-x C x . For x=0.01 and 0.03, a lower thermal conductivity and higher figure of merit than those of Mg 2 Si were observed in the temperature range from room temperature to 773 K. The maximum figure of merit was 0.62 at 773 K for a Mg 2 Si 0.99 C 0.01 sample.
Melt growth of Mg 2 Si was conducted using the vertical Bridgman growth method. Because magnesium is highly reactive at the growth temperature (1358 K), crucible materials were chosen to avoid chemical reactions and sticking between the crucibles, the molten Mg 2 Si and magnesium vapor. Crucibles made of alumina, pyrolytic boron nitride (pBN), and hexagonal boron nitride (hBN) were examined. The use of a pBN crucible enabled in the suppression of chemical reactions involving molten Mg 2 Si and vaporized magnesium at elevated growth temperatures, resulting in no sticking of the grown crystal to the inner wall of the crucible. While the measured conductivity for samples grown using an alumina crucible was n-type for all of the temperatures that were investigated, the samples that were grown using a pBN crucible exhibited p-type conductivity. This correlates closely with unintentional boron incorporation during the growth process.
A differential absorption pulsed dye laser radar for NO2, concentration measurement was developed. A special laser resonator, which generates two wavelengths alternately, was devised for this laser radar. NO2 concentration, as an air pollutant, was measured automatically using a mini-computer in Kawasaki for 30 hours. Averaging one thousand 75 pps repetition signal data made it possible to detect a concentration as low as 5 ppb in a 2 km round trip path.
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