Complete Structural Phases for Self-Assembled Methylthiolate Monolayers on Au(111)

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Abstract

The structure of self-assembled methylthiolate monolayers on Au(111) as a function of surface coverage has been investigated using scanning tunneling microscopic imaging, and complete structural phases are obtained. A full layer (1/3 ML) of methylthiolate organizes into a long-range ordered (3 x 4) phase with chiral domains. The domain boundary has a local (3 x 4 root 3)-rect structure. Gradual removal of methylthiolate by partial thermal desorption leads first to the formation of a local (7 x root 3)-rect phase with coverage equal to 0.286 ML. This (7 x root 3)-rect phase is found to coexist with the (3 x 4) phase and a disordered phase. As the coverage is reduced to below 0.28 ML, stripes parallel to the < 11 (2) over bar > directions appear. All the phases are made from the basic, CH3S-Au-SCH3, structural motif. Cis-trans transformation of the CH3S-Au-SCH3 unit is observed. For an isolated CH3S-Au-SCH3 unit, both methyl groups have equal probability of contributing to the cis-trans transformation at 77 K. Within the stripe phase, only one of the methyl groups actively participates in cis-trans transformation while the other group remains as a spectator.
Original languageEnglish
Pages (from-to)21234-21244
Number of pages11
JournalJournal of Physical Chemistry C
Volume117
Issue number41
Publication statusPublished - 2013

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