THE DILUTION EFFECT OF NOBLE-GASES ON THE STRUCTURE AND COMPOSITION OF CHEMICALLY VAPOR-DEPOSITED DIAMOND FILMS

Diamond thin films were prepared by decomposition of methane and hydrogen in a microwave plasma discharge. The dilution effect of noble gases on the deposition of diamond film was investigated by scanning electron microscopy, optical emission spectroscopy, X-ray diffraction and Raman spectroscopy. It was found that the introduction of noble gases changes the morphology of the diamond film from triangular {111} to square {100} facets and leads to fewer crystalline defects. Such results are more pronounced for Ar and Ne but less pronounced for He, Kr and Xe. The noble gases can be regarded as efficient dilution gases in the diamond deposition by inducing additional ion-molecule and excited atom-molecule reactions. As a result, the nucleation and growth of diamond have been enhanced, and the formation of non-diamond carbon phases has been substantially suppressed through the reaction of noble gases in methane and hydrogen plasmas. The results indicate that the diamond films prepared in this way were frequently deposited on a buffer layer composite of crystalline graphite and non-crystalline form of carbon.