Comparison of the Photoelectrochemical Behavior of H-Terminated and Methyl-Terminated Si(111) Surfaces in Contact with a Series of One-Electron, Outer-Sphere Redox Couples in CH3CN

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• 作者：Ronald L. Grimm ; Matthew J. Bierman ; Leslie E. O鈥橪eary ; Nicholas C. Strandwitz ; Bruce S. Brunschwig ; Nathan S. Lewis
• 刊名：The Journal of Physical Chemistry C
• 出版年：2012
• 出版时间：November 8, 2012
• 年：2012
• 卷：116
• 期：44
• 页码：23569-23576
• 全文大小：329K
• 年卷期：v.116,no.44(November 8, 2012)
• ISSN：1932-7455

文摘

The photoelectrochemical behavior of methyl-terminated p-type and n-type Si(111) surfaces was determined in contact with a series of one-electron, outer-sphere, redox couples that span >1 V in the Nernstian redox potential, E(A/A^{鈥?/sup>), of the solution. The dependence of the current vs potential data, as well as of the open-circuit photovoltage, V_oc, on E(A/A鈥?/sup>) was compared to the behavior of H-terminated p-type and n-type Si(111) surfaces in contact with these same electrolytes. For a particular E(A/A鈥?/sup>) value, CH₃-terminated p-Si(111) electrodes showed lower V_oc values than H-terminated p-Si(111) electrodes, whereas CH₃-terminated n-Si(111) electrodes showed higher V_oc values than H-terminated n-Si(111) electrodes. Under 100 mW cm鈥? of ELH-simulated Air Mass 1.5 illumination, n-type H鈥揝i(111) and CH₃鈥揝i(111) electrodes both demonstrated nonrectifying behavior with no photovoltage at very negative values of E(A/A鈥?/sup>) and produced limiting V_oc values of >0.5 V at very positive values of E(A/A鈥?/sup>). Illuminated p-type H鈥揝i(111) and CH₃鈥揝i(111) electrodes produced no photovoltage at positive values of E(A/A鈥?/sup>) and produced limiting V_oc values in excess of 0.5 V at very negative values of E(A/A鈥?/sup>). In contact with CH₃CN-octamethylferrocene+/0, differential capacitance vs potential experiments yielded a 鈭?.40 V shift in flat-band potential for CH₃-terminated n-Si(111) surfaces relative to H-terminated n-Si(111) surfaces. Similarly, in contact with CH₃CN-1,1鈥?dicarbomethoxycobaltocene+/0, the differential capacitance vs potential data indicated a 鈭?.25 V shift in the flat-band potential for CH₃-terminated p-Si(111) electrodes relative to H-terminated p-Si(111) electrodes. The observed trends in V_oc vs E(A/A鈥?/sup>), and the trends in the differential capacitance vs potential data are consistent with a negative shift in the interfacial dipole as a result of methylation of the Si(111) surface. The negative dipole shift is consistent with a body of theoretical and experimental comparisons of the behavior of CH₃鈥揝i(111) surfaces vs H鈥揝i(111) surfaces, including density functional theory of the sign and magnitude of the surface dipole, photoemission spectroscopy in ultrahigh vacuum, the electrical behavior of Hg/Si contacts, and the pH dependence of the current鈥損otential behavior of Si electrodes in contact with aqueous electrolytes.}