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Supramolecular assembly of biphenyl dicarboxylic acid on Au(1 1 1)
Authors:N Zhu  T Komeda
Institution:a Institute of Multidisciplinary Research for Advanced Materials, Tohoku University, Katahira 2-1-1, Aoba-ku, Sendai 980-8577, Japan
b CREST, Japan Science and Technology Corporation (JST), Kawaguchi, Saitama 332-0112, Japan
Abstract:We investigate the structure of submonolayer film of 4,4′-biphenyl dicarboxylic acid (BDA) molecules on Au(1 1 1)-22 × √3 reconstructed surface with the use of scanning tunneling microscopy (STM). The BDA molecules form ordered structures on Au(1 1 1) surface which are commensurate with the substrate. We have concluded that the molecule-molecule interaction is mainly through hydrogen bonding formed by a straight dimer of BDA molecules. The straight dimer can be expressed as 4s + 2t or its six crystallographic equivalents using the unit vectors of the gold substrate of s and t. The length of hydrogen bonding (O-H-O) is estimated to be 0.31 nm assuming nearest neighbor distance of gold atoms of 0.275 nm. The ordering shows a clear contrast with the case of BDA on Cu(1 0 0) surface S. Stepanow, N. Lin, F. Vidal, A. Landa, M. Ruben, J.V. Barth, K. Kern, Nanoletters 5 (2005) 901] in which a square type of ordering of molecules is observed by the formation of hydrogen bonding between a carboxylate (COO) and a benzene ring. The clear difference of the ordered structure on Cu(1 0 0) and Au(1 1 1) surface demonstrates that the absence (presence) of deprotonation of carboxyl group of BDA molecule on Au(1 1 1) (Cu(1 0 0)) switches the straight and square type ordering of BDA molecules.
Keywords:Scanning tunneling microscopy  Crystallization  Self-assembly  Gold  Carboxylic acid  Low index single crystal surfaces  Metal-insulator interfaces
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