[en] Chemically vapour deposited diamond is commonly synthesized from activated hydrogen-rich, carbon/hydrogen gas mixtures under conditions which should, from a thermodynamic equilibrium point of view, favour the production of graphite. Much remains to be understood about why diamond, and not graphite, forms under these conditions. However, it is well known that the presence of atomic hydrogen, is crucial to the success of diamond deposition. As part of an attempt to better understand the deposition process, a thermodynamic analysis of the process was performed on diamond (111) faces in hydrogen rich environments. It is shown that the key role of atomic hydrogen is to inhibit the reconstruction of the (111) face to an sp²-bonded structure, which would provide a template for graphite, rather than diamond formation. The model correctly predicts experimentally determined trends in growth rate and diamond film quality as a function of methane concentration in the stating gas mixture. 17 refs., 4 figs

[en] When Fe is exposed to the plasma environment suitable for the chemical vapor deposition (CVD) of diamond, the surface is rapidly covered with a thick layer graphitic soot and C swiftly diffuses into the Fe substrate. Once the soot reaches a critical thickness, diamond films nucleate and grow on top of it. However, adhesion of the film to the substrate is poor due to the lack of structural integrity of the soot layer, A thin coating of TiN on the Fe can act to prevent diffusion and soot formation. Diamond readily grows upon the TiN via an a-C interface layer, but the a-C/TiN interface is weak and delamination occurs at this interface. In order to try and improve the adhesion, the use of a high dose Ti implant was investigated to replace the TiN coating. 7 refs., 6 figs

[en] The behaviour of longitudinal and transverse optical phonons in cubic Al_xGa_l-xN are derived theoretically as a function of the concentration x (0≤x≤1). The calculation is based on a Modified Random Element Isodisplacement model which considers the interactions from the nearest neighbor and second neighbor atoms. We find one-mode behavior in Al_xGa_l-xN where the phonon frequency in general varies continuously and approximately linearly with x. (author)

[en] The Raman spectrum of an amorphous, fully sp³-bonded carbon network is presented. The reduced Raman spectrum agrees closely with the calculated density of states of diamond. The results have been obtained from nanoclusters produced deep inside a single crystal diamond irradiated with MeV He ions. The deep implantation creates amorphous sp³ bonded C clusters along the ion tracks, within a largely intact diamond matrix. The matrix maintains the clusters under high pressure, preventing the relaxation to sp² bonded structures. Sharp peaks associated with defect structures unique to MeV ion implantation are observed at 1422, 1447, 1467, 1496, 1540, 1563, 1631, 1649, 1683 and 1726 cm^-1. A shoulder is also observed in the reduced Raman spectrum at about 1120cm^-1 which is tentatively attributed to quantum confinement effects in the carbon nanoclusters. The results provide the Raman signature that might be expected from tetrahedrally bonded amorphous carbon films with no graphite-like amorphous components. 14 refs., 4 figs

[en] Polarized micro-Raman spectra of chemically vapour deposited diamond films are presented. It is shown that important parameters often extracted from the Raman spectra such as the ratio of the diamond to non-diamond component of the films and the estimation of the level of residual stress depend on the orientation of the diamond crystallites with respect to the polarization of the incident laser beam. The dependence originates from the fact that the Raman scattering from the non-diamond components in the films is almost completely depolarized whilst the scattering from the diamond components is strongly polarized. The results demonstrate the importance of taking polarization into account when attempting to use Raman spectroscopy in even a semi-quantitative fashion for the assessment of the purity, perfection and stress in CVD diamond films. 8 refs., 1 tab. 2 figs

[en] The effects of scanned 2 MeV He⁺ and 1.4 MeV H⁺ microbeam irradiation on unimplanted and P implanted diamond are discussed. Although diamond was found to be resistant to lattice defect production, it was found to swell very rapidly in comparison with other materials, giving rise to serious swelling induced dechanneling at scan edges at relatively low doses (10¹⁷/cm² for 2 MeV He⁺). Microbeams annealed the damage due to a 1.5 μm deep Phosphorus implantation at a dose of 10¹⁵P⁺/cm². The implantation damage was reduced at a dose of (1.6 x 10¹⁷/cm²) by up to 21 % for 2 MeV He⁺ irradiation, up to 16% for high flux 1.4 MeV H⁺ irradiation and 12% for low flux H⁺ irradiation. For the choice of analysis beam, all these beam effects were found to be most significant for He⁺ microbeams, so H⁺ microbeams should be used for analysis of diamond unless high depth resolution is required. 13 refs., 10 figs

[en] High-resolution transmission electron microscopy, electron diffraction and parallel electron energy loss spectroscopy are used to analyse nanocrystalline diamond powder. Grains of diameter in the range 2- 10 nm were found aggregated together; the grain boundaries were essentially a grossly disordered (amorphous) intergranular phase. Analysis of the plasmon loss-function indicated mass density of 3.30 g/cm³, compared with 3.51 g/cm³ for a chemically-vapour-deposited diamond. The core-loss spectra showed virtually pure sp³ bonding overall although some exposed surfaces were coated with two or three graphitic layers. Two peaks were observed in the low energy loss-function, one at 34 eV was characteristic of the volume plasmon typically observed in crystalline diamond, a second peak at ∼ 23 eV for larger grains, shifted to lower energies as the particle size decreased (to 19.5 eV for 2.8 nm diameter) and at the same time it increased in intensity, becoming stronger than the volume plasmon for a 2.8 nm crystal. these results are interpreted using theoretical results for surface plasmons in small spherical particles. 19 refs., 1 tab., 5 figs

[en] Recent investigations shows that an enhanced nitrogen content of carbo-nitride films improves wear resistance, hardness, tribological and other properties of these films. The present work reports on the properties of nitrogen rich carbon films produced by an intense gas discharge between carbon electrodes in a nitrogen atmosphere. The energy of the discharge, initial nitrogen pressure, number of discharges and geometry are varied to establish their effect on the nitrogen content and the mechanical, structural and morphological characteristics of the deposited carbon-nitride films. The structural diagnostics include optical and scanning electron microscopy, as well as Auger and Raman Spectroscopes and Rutherford Backscattering. The C-N films formed fell into two categories, differing in morphology and mechanical properties. Type I are C-N films, containing up to 35 at. % nitrogen, and which have an amorphous structure. These films are formed at relatively low plasma shock pressure and exhibit relatively low microhardness, ∼ 2 GPa. In a relatively narrow range of the plasma shock pressure and temperature the second type of C-N deposition is observed consisting of high density, closely-packed crystal-like grains growing perpendicular to the substrate surface and displaying a cauliflower-like morphology. The microhardness of these films reaches 15 GPa, as measured by the Vickers method. 14 refs., 7 figs

[en] Abstract only. 3 refs

[en] Surface conductivity measurements have been conducted on ion implanted glassy carbon (GC). Ion species included C, Xe and Si with doses ranging from 10¹⁴ to 10¹⁸ ions/cm². Ion beam irradiation has been found to increase the resistivity of GC by up to five orders of magnitude. 9 refs., 1 fig