Unique domain structure of pi-conjugated tolanethioacetate self-assembled monolayers on Au(111)

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.     

Study of fibrinogen adsorption on self-assembled monolayers on Au(111) by atomic force microscopy

The adsorption of plasma protein fibrinogen on the self-assembled monolayers (SAMs) of n-hexadecyl mercaptan and citrate was investigated with atomic force microscopy (AFM). On the basis of the preparation of these two flat SAMs on Au(111), high-resolution AFM images of bovine fibrinogen were obtained with different protein concentrations. The results indicated that the surface chemical composition significantly affected the adsorption behavior of fibrinogen. Since fibrinogen plays a key role in the regulation of both haemostasis and thrombosis, high-resolution AFM imaging on SAMs is expected to be an effective approach to study the haemocompatibility of materials with different surface chemistry.     

Fast displacement and structural transition of cyclohexanethiol self-assembled monolayers by octanethiols on Au (111)

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 (5x2 radical10)R48 degrees structure of CHT SAMs to the ( radical3x radical3)R30 degrees or c(4x2) 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.     

Well-ordered structure of methylene blue monolayers on Au(111) surface: electrochemical scanning tunneling microscopy studies

Well-ordered structure of methylene blue (MB) monolayers on Au(111) surface has been successfully obtained by controlling the substrate potential. Electrochemical scanning tunneling microscopy (ECSTM) examined the monolayers of MB on Au(111) in 0.1 M HClO(4) and showed long-range ordered, interweaved arrays of MB with quadratic symmetry on the substrate in the potential range of double-layer charging. High-resolution ECSTM image further revealed the details of the MB monolayers structure of c(5 x 5 radical 3)rect and the flat-lying orientation of ad-molecules. The dependence of molecular organization on the substrate potential and the formation mechanism of well-ordered structure on Au(111) surface were investigated in detail. The obtained well-ordered structure at the interface between a metal and an aqueous electrolyte might possibly be used as high-density device for signal memory and templates for the advanced nanopatterning of surfaces.     

Effect of temperature on friction observed between a Si3N4 tip and a dodecanethiol self-assembled monolayer on Au(1 1 1)

Recent computational studies (Phys. Rev. Lett. 70 (1993) 1960; Phys. Rev. B 62 (2000) 17055) predicted that friction of ordered organic monolayer had characteristic dependence on temperature, where the maximum friction was observed around rotator transition point of the monolayer. This remained to be confirmed experimentally. Using a friction force microscope (FFM) combined with a temperature regulation module, we attempted to investigate such dependence on temperature (130 K-room temperature) on a self-assembled monolayer of dodecanethiol prepared on Au(1 1 1). The observed friction showed strong dependence on temperature and good agreement with the computational prediction.     

Formation of large ordered domains in benzenethiol self-assembled monolayers on Au(1 1 1) observed by scanning tunneling microscopy

Benzenethiol (BT) self-assembled monolayers (SAMs) on Au(1 1 1) were prepared as a function of solution temperature after immersion in a 1 mM ethanol solution for 1 day. The surface structures of BT SAMs were examined by means of scanning tunneling microscopy (STM). Although BT molecules usually form disordered SAMs containing the Au adatom islands at room temperature, we found that they formed two-dimensional ordered SAMs containing a large size domain at a high solution temperature of 50 or 75 °C. High-resolution STM imaging revealed that BT SAMs on Au(1 1 1) formed at 50 °C have a (2×3√2)R23° packing structure. From our STM study, we revealed that two-dimensional ordered BT SAMs on Au(1 1 1) can be obtained by changing the solution temperature.     

The effect of a gap between the poles of an attachable electromagnet and a tested component on coercimeter readings and methods for decreasing it (Review)

The main drawback of a coercimeter with attachable electromagnets (AEM) is its sensitivity to a random gap between electromagnet poles and a tested article formed in the process of inspection. The causes of such sensitivity are analyzed and the methods for decreasing it are considered.