Photoelectrochemical Reactions at Semiconductor Diamond Films

近年来，金刚石电极成为继石墨、HOPG等sp^2碳材料之后的新碳材料，受到广泛关注。（1）非常大的电位窗口，（2）对氧化还原体系的良好电化学响应，（3）本底电流极小，通过在膜中掺杂硼，金刚石电极表现为带隙为5.5eV的p型半导体。当Arf准分子激光（193 nm/6.4eV）照射在浸于电解质溶液中的p型金刚石电极上时，在明显的正电位（+1.0Vvs.SCE）下发生了在黑暗条件下需要负极化的析氢反应。当KrF和XeF准分子激光（分别为248 nm/5.0 eV和351 nm/3.53 eV）照射在金刚石电极上时，几乎没有观察到光电流。这些结果表明，在ArF准分子激光照射下，带间渡越电子被电解质溶液中的质子接受，从而发生析氢。通过电化学阻抗测量，证实了金刚石电极的平带电位为0.9Vvs SCE，p型金刚石的导带能量位置约为-4.20Vvs.SCE.在光照射下，钴、硼掺杂的p型金刚石电极成为极还原表面，并探讨了该电极作为生物传感器的应用.

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.