Disorder–Order Transformation of Trithiocyanuric Acid Adlayer on a Au(111) Surface Induced by Electrode Potential

Abstract

Self-assembled monolayers (SAMs) of trithiocyanuric acid (TTCA) on Au(111) surfaces are investigated by scanning tunneling microscopy (STM), cyclic voltammetry, and density functional theory calculation (DFT). The SAM exhibits a wormlike disordered structure from 1.0 V to 260 mV vs RHE (reversible hydrogen electrode). At 260 mV, an irreversible disorder–order phase transformation occurs and results in an ordered striped phase. High resolution STM images and DFT calculations suggest that TTCA molecules are parallel to each other within the stripes, which prompts the π–π stacking interactions between the molecules. Each molecule adsorbs vertically on the substrate via two S atoms and one heterocyclic N atom anchoring on the surface at the bridge sites and the top site, respectively. This adsorption geometry promises the SAM with good stability (binding energy 3.27 eV) and free reactive S terminals. The high stability and free S terminals of the TTCA SAM makes it a promising scaffold for applications in mole...