EIS, CV and XPS experiments were carried out to address the evolution of H‐terminated BDD electrochemical properties under intensive use and air aging. A drastic drop of apparent electron transfer rate k0′ was thus recorded using Fe(CN6)3–/4– as the redox mediator by identifying components of the Randles equivalent circuit. Excellent agreement was observed between theoretical and experimental curves. The feasibility of recovering and stabilizing high reactivity and reversible behaviour by applying a suitable electrochemical post treatment was then demonstrated. Such a treatment was developed empirically and seemed to significantly improve the electrode performances. On the basis of our results, we claim that the electrochemical evolutions observed are strongly linked to chemical termination modifications and partial inactivation of the electrode surface. Further research on the mechanisms that govern electron mediation at the diamond surface would be of high interest for better control of diamond electrode stability and reactivity towards their applications for bio‐electronic devices. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Electrical transport properties of thin boron doped nanocrystalline diamond films with thicknesses of 60–500nm have been studied. The Raman spectra measured exhibit Fano resonances, characteristic for B concentrations close to the metal-to-insulator transition. Upon increasing the B concentration, the sp2 carbon related Raman resonances vanish. In such boron-doped nanocrystalline diamond films, a positive magnetoresistance could be observed at liquid helium temperatures. The boron doped diamond films show conductivity similar to that of B-doped epitaxial diamond without any significant contribution of the grain boundary transport, leading to the superconductive transition in nanocrystalline diamond at ∼1.66K.
Surface electronic states of the partially hydrogenated diamond C(100)-(2ϫ1):H surface were studied by near-edge x-ray absorption fine structure and C 1s core level photoemission. Partially hydrogenated surfaces were prepared by synchrotron irradiation of the monohydride-terminated surface or by hydrogen adsorption on the clean surface. A new surface core-exciton state produced at a photon energy of 282.5 eV has been assigned to single dangling bonds of the partially hydrogenated surface. Monitoring this new feature has been found to be a powerful method to study hydrogen kinetics during ͑i͒ photon irradiation of a fully hydrogenated diamond surface, ͑ii͒ adsorption of atomic hydrogen on a clean diamond surface, and ͑iii͒ photon irradiation of a fully hydrogenated surface followed by thermal annealing. From the analysis of dangling-bond distribution, it follows that no preferential pairing of hydrogen on the C-C dimers occurs during hydrogen adsorption at room temperature. In contrast, thermal annealing induces pairing of the single dangling bonds into the -bonded configuration, the pairing process being accompanied by hydrogen desorption. This observation suggests that the activation barrier of hydrogen thermal diffusion is only slightly lower than that of thermal desorption.
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