Ion channeling in textured polycrystalline diamond films.

Channeling of Hhighplus and H highplus/sub2 ions of energies between 1.0 and 2.0 MeV in (100)-textured polycristalline diamond films grown by microwave plasma-assisted chemical-vapor deposition has been observed with Rutherford backscattering. The width of the orientational distribution of the diamond crystallites as deduced from the measured projectile velocity dependence of the observed channeling angular scans amounted to about 1 degree

Chemical vapour deposition and characterization of smooth -100-faceted diamond films.

Smoot (100)-faceted diamond films have been prepared by microwave-assisted chemical vapour deposition from CH4-H2 mixtures. Growth has been controlled by in-situ laser interferometry. Under appropriate growth conditions, the films show a fibre texture with the (100) fibre axis normal to the substrate. The surface is completely formed by well-aligned coplanar (100) facets. The structure and morphology of these films have been characterized by X-ray diffraction, ion channelling and angle-resolved optical scattering measurements. Fibre textures with an angular spread of the (100) directions as narrow as 1 degree have been observed. The coplanar (100) facets form an optically smooth surface, exhibiting pronounced specular reflection. The dependence of the texture formation and surface morphology on film thickness and deposition parameters, including substrate temperature and gas composition, has been studied. For lower than optimum growth temperatures the surface becomes rough as (111) fac ets develop in addition to the (still coplanar) (100) facets. For higher than optimum growth temperatures the size of the (100) facets increases and the texture axis tilts away from (100). By varying the gas composition, any texture axis between (100) and (110) can be established. Computer based growth simulations have been performed on the basis of evolutionary selection of specific crystallite orientations. It is shown that a growth parameter alpha=3 (exp 1/2) V100/V111, i.e. the ratio of the growth rates on (100) and (111) faces, determines the structure and morphology of the films. A novel two-step growth process based on the control of alpha permits the independent optimization of texture axis and surface morphology, offering the possibility to obtain smooth faceted diamond films for arbitrary film thickness

Active sites for outer-sphere, inner-sphere, and complex multistage electrochemical reactions at polycrystalline boron-doped diamond electrodes (pBDD) revealed with scanning electrochemical cell microscopy (SECCM)

The local rate of heterogeneous electron transfer (HET) at polycrystalline boron-doped diamond (pBDD) electrodes has been visualized at high spatial resolution for various aqueous electrochemical reactions, using scanning electrochemical cell microscopy (SECCM), which is a technique that uses a mobile pipet-based electrochemical cell as an imaging probe. As exemplar systems, three important classes of electrode reactions have been investigated: outer-sphere (one-electron oxidation of ferrocenylmethyltrimethylammonium (FcTMA+)), inner-sphere (one-electron oxidation of Fe2+), and complex processes with coupled electron transfer and chemical reactions (oxidation of serotonin). In all cases, the pattern of reactivity is similar: the entire pBDD surface is electroactive, but there are variations in activity between different crystal facets which correlate directly with differences in the local dopant level, as visualized qualitatively by field-emission scanning electron microscopy (FE-SEM). No evidence was found for enhanced activity at grain boundaries for any of the reactions. The case of serotonin oxidation is particularly interesting, as this process is known to lead to deterioration of the electrodes, because of blocking by reaction products, and therefore cannot be studied with conventional scanning electrochemical probe microscopy (SEPM) techniques. Yet, we have found this system nonproblematic to study, because the meniscus of the scanning pipet is only in contact with the surface investigated for a brief time and any blocking product is left behind as the pipet moves to a new location. Thus, SECCM opens up the possibility of investigating and visualizing much more complex heterogeneous electrode reactions than possible presently with other SEPM techniques