HREM and EXELFS investigation of local structure in thin CVD diamond films

Diamond coatings prepared by microwave plasma-assisted chemical vapour deposition (CVD) on silicon substrates have been studied by two complementary transmission electron microscopy techniques, high resolution electron microscopy (HREM) and extended energy loss fine structure spectroscopy (EXELFS). HREM observations allowed a wide range of growth defects, mainly based on coherent twinning on {111} planes, to be identified. But 5-fold twin centres were very rarely found, whereas the images often revealed extended areas exhibiting the perfect diamond structure, both observations indicating a film quality higher than usual for synthetic diamonds. Moreover, the radial distribution functions (RDFs) derived from EXELFS spectra confirmed that the material was guile well-ordered. Typical examples are given, of a [110] image exhibiting different twin and grain boundaries of types Sigma = 3, 9, 19, 27, 33 and 81, as well as one 5-fold twin centre, and of an extended perfect structure area viewed along the (111) direction. A particularly interesting defect configuration, consisting of three neighbouring dissociated dislocations, is also analysed: one of these, a pure extended-screw dislocation, allowed us to determine he intrinsic stacking-fault energy in diamond, yielding a value of 276 +/- 3 mJ m(-2), This value, although lower than the theoretical predictions, agrees very well with mean values previously determined from weak-beam experiments. (C) 1991 Elsevier Science S.A.