In situ scanning tunneling microscopy of maleic acid and fumaric acid adsorbed on Pt(111)

Adsorption of cis- and trans-butene dicarboxylic acids commonly known as ma leic acid and fumaric acid, respectively, on Pt(111) electrodes was investi gated in HF solution using in situ scanning tunneling microscopy (STM). It was confirmed that both molecules are strongly adsorbed on the Pt(111) surf ace in the potential range of double-layer charging. High-resolution STM im ages revealed internal molecular structures of maleic acid and fumaric acid . A molecule of maleic acid had a triangular shape, while a zigzag shape wa s observed for fumaric acid. Although several packing arrangements were fou nd to form in small domains, major domains had (root 13 x root 13)R14 degre es and (2 root3 x 2 root3)R30 degrees structures for maleic acid and fumari c acid, respectively. These differences were explained in terms of the diff erence in conformation between the cis- and trans-isomers. (C) 2001 Elsevie r Science B.V. All rights reserved.