ELECTRON-MICROSCOPY STUDY OF DEFECTS IN SYNTHETIC DIAMOND LAYERS

Defects contained in synthetic diamond epitaxial layers are studied by transmission electron microscopy and high-resolution electron microscopy (HREM). Coherent twinning on {111} planes was found to be the dominant defect in chemically vapour deposited diamond thin films. HREM images reveal areas exhibiting a threefold periodicity due to overlapping SIGMA = 3 twins. SIGMA = 9 interfaces, present when two of these second-order twins overlap, are observed as well. HREM images of a 60-degrees as well as of a pure screw ribbon viewed along the direction of the ribbon allow us to determine the stacking-fault energy in diamond, yielding a mean value of 209 +/- 26 mJ m-2. This is significantly smaller than previously determined values, based on the application of the weak-beam method to ribbons parallel to the foil. Atomic-scale models are proposed for a number of complex defect configurations which are observed in the diamond epitaxial layers, for example, twinning dislocations, interaction between stacking faults and interaction between a stacking-fault and a twin interface.