Bombarding energy dependence of bonding structure in amorphous carbon interlayer and its effect on diamond nucleation

The bombarding energy dependence of bonding structure in amorphous carbon i nterlayer and its effect on diamond nucleation density (Nd) were studied. A morphous carbon (a-C) interlayer was deposited by magnetron sputtering. Int erestingly, the intensity ratio (I-D/I-G) Of the D band (similar to 1400 cm (-1)) to the G band (1570 cm(-1)) in the Raman spectra and the optical band gap of the a-C film were found to be inversely proportional to the sputter ing power, that is, to bombarding energy, When diamond was subsequently dep osited at 800 degrees C by microwave plasma chemical vapor deposition (CVD) , diamond could be grown only on the interlayers with higher I-D/I-G (great er than or equal to 2.20), and Nd was increased up to 2 x 10(6)/cm(2) with the increase of I-D/I-G ratio, that is, with the decrease of the bombarding energy. We experimentally confirmed that the amount of the sp(3) bonded ca rbon clusters within the interlayer was dependent on the bombarding energy of the particles, determining the diamond nucleation density. We suggest th at the transformation of the amorphous carbon into graphitic carbon should be effectively prevented for the diamond nucleation on the a-C interlayer.