Atomic mechanism of twin formation in CVD diamond films

Abstract

The macro-texture, grain boundary distribution and surface morphology in CVD free standing diamond films deposited with different methane concentrations were observed by X ray diffraction, electron backscatter diffraction and SEM. The atom stacking process of twins on {111} planes of diamond crystal were studied. It is shown that the twins form easily on {111} planes because of the 〈111〉 60° orientation relationship of first order twin and the stacking structure of {111} planes. At low methane concentration, carbon atoms tend to deposit on {111} planes with lower surface energy, which facilitates the formation of twins by means of rotating deposition of carbon atoms, while the high twinning frequency weakens the texture. With increasing methane concentration the {001} planes with lower growing activation energy become the main frontal growth fronts, and only those grains with 〈001〉 crystal direction which is parallel to the surface normal can continuously grow, so that the probability of twin nucleation decreases. In addition, second_order twins were found in diamond film, and their formation mechanism was analyzed.