[Show abstract][Hide abstract] ABSTRACT: Displacement of cyclohexanethiols (CHTs) self-assembled monolayers (SAMs) by octanethiols on Au (111) (OTs) was examined by scanning tunneling microscopy (STM) and contact angle measurements. We revealed that the fast displacement of CHT by OT takes place within a few minutes, and then displacement proceeds slowly to form the closely packed OT SAMs. The main driving force for the unusual fast displacement is due to the large increase of chemical interactions between the sulfur and gold atoms, and the van der Waals interactions between alkyl chains after displacement of CHT by OT. STM imaging clearly demonstrated the structural transitions from the (5 x 2 square root 10)R48 degrees structure of CHT SAMs to the (square root 3 x square root 3)R30 degrees or c(4 x 2) structures of OT SAMs via an intermediate phase that were often observed during alkanethiol SAM growth on gold. In this study, we found that CHT SAMs can be used as a new transient layer for the fabrication of nanostructures on a surface.
[Show abstract][Hide abstract] ABSTRACT: Octanethiol (OT) self-assembled monolayers (SAMs) were prepared on Au(111) by solution and ambient-pressure vapor deposition methods at 75°C. Surface structures were investigated with scanning tunneling microscopy (STM) to understand molecular-scale structural features of OT SAMs according to deposition method and temperature. OT SAMs prepared by solution deposition have large-ordered domains corresponding to ∼100nm with a c(4×2) superlattice, but disordered phases and structural defects in the ordered domains also formed from desorption of adsorbed molecules from the surface. However, high-quality OT SAMs were obtained by vapor deposition and showed large well-ordered domains of 20–50nm without formation of disordered phases. The formation of vacancy islands was markedly influenced by deposition method. This study demonstrated that the formation and structure of OT SAMs on Au(111) were influenced by deposition method and temperature.
Colloids and Surfaces A-physicochemical and Engineering Aspects - COLLOID SURFACE A. 01/2008; 313:324-327.
[Show abstract][Hide abstract] ABSTRACT: Surface structures of tolanethioacetate (TTA) self-assembled monolayers (SAMs) on Au(111), formed in a 0.5mM N,N'-dimethylformamide (DMF) solution, were investigated as a function of solution temperature by scanning tunneling microscopy (STM). The STM study revealed that thioacetyl-terminated TTA molecules on Au(111) did not form ordered SAMs at room temperature and 80 degrees C, whereas the adsorption of TTA molecules on Au(111) at a solution temperature of 50 degrees C led to the formation of two mixed phases: a disordered phase and a unique ordered phase, consisting rod-like domains, which can be described as a ( radical6x radical13)15 degrees superstructure. From this study, it was demonstrated that solution temperature is a key factor controlling the two-dimensional SAM structure of TTA molecules.