Electronic Structure of Methoxy-, Bromo-, and Nitrobenzene Grafted onto Si(111)

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• 作者：Ralf Hunger ; Wolfram Jaegermann ; Alexandra Merson ; Yoram Shapira ; Christian Pettenkofer ; Jö ; rg Rappich
• 刊名：Journal of Physical Chemistry B
• 出版年：2006
• 出版时间：August 10, 2006
• 年：2006
• 卷：110
• 期：31
• 页码：15432 - 15441
• 全文大小：333K
• 年卷期：v.110,no.31(August 10, 2006)
• ISSN：1520-5207

文摘

The properties of Si(111) surfaces grafted with benzene derivatives were investigated using ultravioletphotoemission spectroscopy (UPS) and X-ray photoelectron spectroscopy (XPS). The investigated materialswere nitro-, bromo-, and methoxybenzene layers (-C₆H₄-X, with X = NO₂, Br, O-CH₃) deposited fromdiazonium salt solutions in a potentiostatic electrochemical process. The UPS spectra of the valence bandregion are governed by the molecular orbital density of states of the adsorbates, which is modified from theisolated state in the gas phase due to molecule-molecule and molecule-substrate interaction. Depending onthe adsorbate, clearly different emission features are observed. The analysis of XPS intensities clearly provesmultilayer formation for bromo- and nitrobenzene in agreement with the amount of charge transferred duringthe grafting process. Methoxybenzene forms only a sub-monolayer coverage. The detailed analysis of bindingenergy shifts of the XPS emissions for determining the band bending and the secondary electron onset inUPS spectra for determining the work function allow one to discriminate between surface dipole layers-changing the electron affinity-and band bending, affecting only the work function. Thus, complete energyband diagrams of the grafted Si(111) surfaces can be constructed. It was found that silicon surface engineeringcan be accomplished by the electrochemical grafting process using nitrobenzene and bromobenzene: silicon-derived interface gap states are chemically passivated, and the adsorbate-related surface dipole effects anincrease of the electron affinity.