Control of the Band-Edge Positions of Crystalline Si(111) by Surface Functionalization with 3,4,5-Trifluorophenylacetylenyl Moieties

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• 作者：Noah T. Plymale ; Anshul A. Ramachandran ; Allison Lim ; Bruce S. Brunschwig ; Nathan S. Lewis
• 刊名：Journal of Physical Chemistry C
• 出版年：2016
• 出版时间：July 7, 2016
• 年：2016
• 卷：120
• 期：26
• 页码：14157-14169
• 全文大小：631K
• 年卷期：0
• ISSN：1932-7455

文摘

Functionalization of semiconductor surfaces with organic moieties can change the charge distribution, surface dipole, and electric field at the interface. The modified electric field will shift the semiconductor band-edge positions relative to those of a contacting phase. Achieving chemical control over the energetics at semiconductor surfaces promises to provide a means of tuning the band-edge energetics to form optimized junctions with a desired material. Si(111) surfaces functionalized with 3,4,5-trifluorophenylacetylenyl (TFPA) groups were characterized by transmission infrared spectroscopy, X-ray photoelectron spectroscopy, and surface recombination velocity measurements. Mixed methyl/TFPA-terminated (MMTFPA) n- and p-type Si(111) surfaces were synthesized and characterized by electrochemical methods. Current density versus voltage and Mott–Schottky measurements of Si(111)–MMTFPA electrodes in contact with Hg indicated that the barrier height, Φ_b, was a function of the fractional monolayer coverage of TFPA (θ_TFPA) in the alkyl monolayer. Relative to Si(111)–CH₃ surfaces, Si(111)–MMTFPA samples with high θ_TFPA produced shifts in Φ_b of ≥0.6 V for n-Si/Hg contacts and ≥0.5 V for p-Si/Hg contacts. Consistently, the open-circuit potential (E_oc) of Si(111)–MMTFPA samples in contact with CH₃CN solutions that contained the 1-electron redox couples decamethylferrocenium/decamethylferrocene (Cp*₂Fe^+/0) or methyl viologen (MV^2+/+•) shifted relative to Si(111)–CH₃ samples by +0.27 V for n-Si and by up to +0.10 V for p-Si. Residual surface recombination limited the E_oc of p-Si samples at high θ_TFPA despite the favorable shift in the band-edge positions induced by the surface modification process.