STM Study of Terephthalic Acid Self-Assembly on Au(111):  Hydrogen-Bonded Sheets on an Inhomogeneous Substrate

The adsorption and ordering of the molecule terephthalic acid (TPA), 1,4-benzene-dicarboxylic acid C 6 H 4 (COOH) 2, on the reconstructed Au(111) surface has been studied in situ in ultrahigh vacuum by scanning tunneling microscopy (STM) at room temperature. Two-dimensional (2D) self-assembled supramolecular domains evolve, wherein the well-known one-dimensional (1D) carboxyl H-bond pairing scheme is identified. Since the individual molecules occupy a distinct adsorption site and the supramolecular ordering usually extends over several substrate reconstruction domains, a significant variation in hydrogen bond lengths is encountered, which illustrates the versatility of hydrogen bridges in molecular engineering at surfaces. Ab initio calculations for a 1D H-bonded molecular chain provide insight into the limited geometric response of the molecules in different local environments.