Diamond particles have been prepared from CH
4 H
2 gas mixtures on Si and Al substrates by a pulsed discharge (PD) plasma chemical vapor deposition (CVD) method at low substrate temperatures of nearby 500°C, and their structural changes as a function of PD conditions have been investigated to make clear the possibility of the diamond deposition on the Al substrate. The crystalline quality of the diamond deposited on the Si substrate became superior when the discharge time (Td) in the repetition period of the pulse was shortened from 2 to 0.5 ms under the constant non-discharge time (Tn) of 3 ms. The longer Tn at constant Td was also effective to improve the crystalline quality. When the deposition was performed on the Al substrate under the constant Td=0.5 ms, Al
4C
3 was formed at short Tn of 2 ms, and diamond was formed at longer Tn of 3 ms. The increase of the current at the beginning of the discharge by means of inserting a condenser and a resistor between the electrodes was also effective to deposit diamond component. These results showed PD plasma CVD method was effective to improve the crystalline quality, and could deposit the diamond on the Al substrate at low substrate temperature.
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