Electrochemical characterization of intrinsic hydrogen terminated single crystalline CVD diamond

摘要

Cyclic voltammetry experiments have been performed on high quality intrinsic hydrogen terminated single crystalline CVD diamond to characterize the electron transfer at the interface of the diamond/redox-electrolyte system. In vacuum these diamond films are insulating, but immersed into electrolyte solutions which contain Fe(CN)_6~(3-/4-) or Ru(NH_3)_6~(2+/3+) generates insulator-metal transition. The two redox systems have chemical potentials below the valence-band maximum E_(VBM) as calculated from the formal potentials. The same experiments applied with methyl viologen (MV) as redox couple results in no detectable electron exchange. MV has two levels, but both are above E_(VBM). The reversible electron exchange with Fe(CN)_6~(3-/4-) or Ru(NH_3)_6~(2+/3+) is rate limited, as peaks are broadened and shifted to higher and lower potentials. The results are compared with data available in the literature for high quality H-terminated boron doped (metallic) polycrystalline diamond which shows that the formal potentials are basically comparable. Electrochemical oxidation terminates the experiments as the surface conductivity is removed and films become highly resistive. The results are discussed using the transfer-doping and the Marcus-Gerischer models for interpretation.