Photoelectrochemical Reactions at Semiconductor Diamond Films

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Recently, a diamond electrode has been attractive since this electrode is a new carbon material following sp^2 carbon materials such as graphite and HOPG.The excellent features of this electrode have been reported by many groups : (1) remarkably large potential window, (2) good electrochemical response to the redox systems, (3) extremely small background current.A diamond electrode behaves as a p-type semiconductor with the band gap of 5.5 eV by doping boron in the film. When the laser light (193 nm/6.4eV) from Arf excimer laser was irradiated on the p-diamond electrode immersed in the electrolyte solution, hydrogen evolution which requires negative polarization in the dark condition occurred at significantly positive potential (+1.0V vs.SCE). On the other hand, almost no photocurrent was observed when the laser light from KrF or XeF excimer laser (248 nm/5.0 eV and 351 nm/3.53eV,respectively) was irradiated on the diamond electrode. These results indicated that the interband transit ted electron by the irradiation of ArF excimer laser light was accepted by proton in the electrolyte solution and, then, hydrogen evolution occurred. It is also confirmed that the flat band potential of the diamond electrode was 0.9V vs SCE by the electrochemical impedance measurement and the energy position of the conduction band of the p-diamond should be about -4.20V vs.SCE.Cobsequently, boron-doped p-diamond electrode became extremely reductive surface by the photo-irradiation.Applications of the p-diamond electrode as a biosensor was also investigated.