Self-Assembled Monolayers and Biointerface

Abstract

Growth processes of self-assembled monolayers(SAMs) were studied by scanning tunneling microscopy(STM), surface plasmom spectroscopy(SPS), thermal desorption spectroscopy (TDS), X-ray photoelectron spectroscopy (XPS), and high resolution electron energy loss spectroscopy(HREELS). A new equilibrium state for alkanethiol SAMs different from previously reported phase was confirmed for the first time. While the conventional final equilibrium state was interpreted as the homogeneous adsorption sites on three-fold hollow on Au(111),the existence of a new equilibrium state shows that there are three adsorption sites: hollow, bridge and on-top sites on Au(111),suggesting that the previously accepted phase is still nuder nonequilibrium. As a result of this study, temporal development of interfacial reaction and dimerization problems were discussed in more detail. Furthermore, structural order and disorder processes during SAM formation were investigated in dialkyl sulfide, dialkyl disulfide, and aromatic thiol system. For example, molecularly resolved STM image clearly revealed that cyclohexanethiol(CHT) SAMs have an oblique unit cell consisting three adsorbed molecules, which can be described as the (5)Rsuperstructure. The superstructure observed for CHT SAMs on Au(111) is comparable to that observed for the conventional alkanethiol or aromatic thiol SAMs. The formation of such a unique superstructure is attributed to the adsorption geometry with the stable chair conformation, i.e., the equatorial and axial chair conformation, for the flexible aliphatic ring in the CHT molecules. In this study, we revealed that the structure rigidity of the molecular backbone is an important parameter for determining the molecular packing structure of SAMs. In order to demonstrate the further capacity of SAMs and establish an efficient methodology for future application to biological systems, studies of immobilization of biological macromolecules are now in progress and some preliminary result will be discussed in the workshop from viewpoints of biointerface and spatio-temporal functions.