Self-Assembled Monolayers On Gold, Platinum And Copper Single Crystal Surface: ECSTM And Molecular Simulation Study

Molecular self-assembly has attracted researchers' interest since 1980s, which is a crossing subject among the fields of condensed physics, materials science, synthesized chemistry, structure chemistry, biology science, nanometer materials and electronic device. Organic compounds including nitrogen and sulfur atoms could form well-ordered SAMs on noble metals.Electrochemical scanning tunneling microscopy(ECSTM) could be used to study the surface state of electrode and adsorption structure of adsorbate at molecular and atomic level. Molecular simulation could be used to obtain structure information (including structure, dynamics, thermodynamics and so on.) and to study the relationship between these information and functionality.In this thesis, ECSTM and molecular simulation were combined to investigate adsorption of 1-hexanethiol and benzenethiol on Au(100) and Pt(100), and adsorption of 1,5-diphenylcarbazide on Cu(111) surface to explain the formation mechanism of SAMs at molecular and atomic level.1. ECSTM study of adsorption of 1-hexanethiol on reconstructured and unreconstructured Au(100) surface.We have used in situ STM to examine the spatial structures of 1-hexanethoil (HT) adsorbed on Au(100) electrode in perchloric acid. Twoordered adlattices of HT, identified as (2(2^1/2)×10^1/2 and (2(2^1/2)×3(2^1/2))R45°, were observed on the unreconstructed Au(100)-(1 ×1) when the potential was held at 0.8V and 0.1V, respectively. The former was more prominent. HT admolecules interacted repulsively and were immobile on Au(100) at the initial stage of adsorption. High-quality STM molecular images aided with molecular modeling showed that HT admolecules were adsorbed at two types of adsorption sites, namely the 2-fold bridge and 4-fold hollow sites. A disordered-to-order phase transition was observed as the pressure within the adlayer increased with coverage to a near saturation level. HT admolecules were also adsorbed in an ordered form on the reconstructed Au(100)-"hex", but they were adsorbed so weakly that high-quality STM imaging was not achieved.