| Abstract
| - Self-assembled monolayers (SAMs) of hybrid ω-(4′-methylbiphenyl-4-yl) alkaneselenolates CH3(C6H4)2(CH2)nSe (BPnSe, n = 2−6) on Au(111) substrates, prepared at room temperature, were studied using scanning tunneling microscopy. Molecularly resolved images reveal that all BPnSe species form well-ordered SAMs on Au(111), with rotational domains having typically a size of ca. 30−80 nm, which is about 5 times larger than their thiol analogues prepared at the same conditions. Two types of structures are alternatingly adopted depending on the parity of the number of the methylene units in the aliphatic linker of the BPnSe molecules. The unit cell of BPnSe SAMs with n = odd can be described as close to a commensurate oblique (2√3 × √3)R30° structure with two molecules per unit cell. The molecular arrangement in BPnSe SAMs with n = even can be described by anisotropic expansion of the above structure along its shorter unit cell vector. This expansion is, however, irregular so that the respective unit vector in this direction cannot be defined. As a result of this expansion, BPnSe SAMs with n = even are characterized by about 22−28% lower packing density than those with n = odd. For all systems, partial reorientation of the Au(111) step edges was observed upon SAM formation, indicating significant mobility of the topmost gold atoms induced by the adsorbates. The results for BPnSe/Au(111) systems are discussed in view of the previously reported spectroscopic data and compared with the analogous results for the BPnS/Au(111) films.
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