STM study of two-dimensional assemblies of tricarboxylic acid derivatives on Au(111)

Two-dimensional assemblies of tricarboxylic acid derivatives, 1,3,5-tris(carboxymethoxy)benzene (TCMB, C6H3(OCH2COOH)(3)) and 1,3,5-tris(3-carboxypropoxy)benzene (TCPB, C6H3(OCH2CH2CH2COOH)(3)), have been investigated on an Au(1 1 1) surface by electrochemical scanning tunneling microscopy in HClO4 solution. TCMB molecules are self-organized into a hexagonal network. Each molecule appears in a propeller shape, consistent with its chemical structure. The adlayer structure of TCPB molecules is significantly different from that of TCMB. Compared with their chemical structures, the difference can be attributed to the increase of the length of alkyl chains. In addition, the molecule-substrate interaction plays an important role in the formation of H-bonding in the two adlayers.