Adsorption-induced self-organization is a new concept for “wet process” techniques for preparing highly ordered molecular adlayers by spontaneous adsorption in aqueous solution. The essential step is a thermodynamically controlled “mild” adsorption, which makes possible rapid surface diffusion and adsorption/desorption equilibrium. 2D-supramolecular structures of various molecules were possible to be constructed by choosing a proper substrate and an electrode potential, that is controlled adsorption STM visualization of highly ordered molecules provides fundamental data on intermolecular interactions.
Self-assembled monolayers of thiols have been studied by electrochemical scanning tunneling microscopy (EC-STM) in solution, which successfully disclosed the interfacial structures of the monolayers on Au(111) electrodes. 3-mercaptopropionic acid (MPA) monolayers exhibited an ordered structure defined as (3×3), and it is expected that intermolecular hydrogen bonding exists between the carboxylic acid head groups of the monolayer. The ES-STM showed large and small phase boundaries of the MPA monolayers. A two-component self-assembled monolayer of MPA and decanethiol (C10SH) exhibited phase-separated domain structures consisting of each component. It was also visualized that MPA and C10SH domains have ordered structures of (3×3) and p(3×2√3R-30o), respectively.
Adsorption of sulfuric acid anions (HSO4− or SO42−) on single crystal electrodes of platinum and palladium in 0.05 M H2SO4 has been studied using infrared reflection absorption spectroscopy (IRAS). Both Pt(111) and Pd(111) electrodes provide a single IRAS band around 1200 cm−1 in the region above 1000 cm−1. Two bands appear around 1200 and 1100 cm−1 with Pt(100), Pt(110) and Pt(S)-[n(111)×(111)] electrodes. The intensity of the lower frequency band is enhanced with the increase of the step atom density. The IRAS spectra of Pd(100), Pd(110) and stepped surface of Pd (Pd(311)) differ completely from those of Pt electrodes: a single band is observed around 1200 cm−1. Adsorbed geometry and adsorption site of the anion are discussed. The reduction of CO2 is deactivated remarkably by the adsorption of sulfuric acid anion on the Pt(S)-[n(111)×(111)] electrodes. Active site for the CO2 reduction is also discussed.
We investigated the chemical states of the interfaces between hydrofluoric acid solution and a silicon (Si) substrate using infrared absorption spectroscopy in multiple internal reflection geometry (MIR-IRAS). At the initial stage of porous Si formation, Si atoms on the outermost layer were removed and those on the second layer were terminated with hydrogen atoms to generate monohydride species bonded to hydride species (SiH*). The data of time evolution of the hydride species density obtained by etching simulation using the Monte Carlo method agreed fairly well with the experimental data. And it was found that the etching rate of SiH* is comparable to that of dihydride species (SiH2). At the high anodic current density region, where anodic current density is constant but anodic potential oscillates, we observed generation of suboxide Si(O3)-H at a minimum anodic potential. However, the suboxide was dissolved in the solution immediately after an increase in the anodic potential. This indicates that the formation and dissolution of an inhomogeneous oxide layer play an important role for the galvanostatic oscillation.
Sustainable metal nanocontacts were fabricated under controlled electrochemical potential in solution. Metal nanocontacts of Cu, Ag, Ni, Pd, and Pb were fabricated via electrochemical etching or deposition at a gap of sustainable thin Au wires in solution. Relatively stable behavior of the conductance quantization exhibiting a unit value was apparent at the contacts of Cu, Ag, Ni, and Pd at room temperature. Conductance quantization behavior of the Pb contact was rather unstable in comparison with other metals. Mechanical stability of Au nanocontact was also examined by controlling electrochemical potential in various solutions containing ClO4−, SO42− and Cl− ions.
The concept of our research with the aim at giving potential-regulated dynamic movements to adsorbed molecular assemblies and nano-substances on the electrode surfaces was described. The importance of extending the target entities to be moved from amphiphiles to dendrimers and surface-modified metal nanoparticles was emphasized. Results of electrochemical measurements were used to demonstrate the potential-dependent changes in adsorption structures for three different types of substances at a Au(111) electrode in aqueous solution. The substances include amphiphiles bearing a terminal 4-pyridyl (Py) group, poly(amideamine) dendrimer the periphery of which was totally modified with Py groups, and a Au nanoparticle containing Py groups in its surface protecting layer. For example, potential-regulated reversible movements of the dendrimer, that is, partial adsorption-desorption as well as orientation change of peripheral Py groups, were achieved for the first time.
Some electrochemical reactions spontaneously oscillates and forms a pattern on the electrode surface. These are caused by the non-linearity embedded in the reaction. We are interested in these phenomena in electrochemistry in terms of analogy between coupled electrochemical oscillators and neural oscillators, and synthesis of functional materials utilizing self-organization. In this article, we will present some of our recent works on the topics of (1) collective behaviors of coupled electrochemical oscillators and their analogy to neural network, (2) spontaneous synthesis of one dimensional layered nanostructures of copper metal and cuprous oxide, and (3) formation of a quantum contact through which the electronic conductance is quantized by 2e2/h.
DLC (Diamond-Like Carbon), a kind of the hard carbon film, has such features as the lowest friction coefficient among various ceramic coating materials, high hardness, and less damage in the counterparts. Because of these features, many developments regarding the application for various kinds of sliding parts are in progress. However, people now call other films DLC, too, even though they are different from those defined in ‘80 s. Moreover, new manufacturing methods such as sputtering and cathodic arc ion-plating are now used in addition to the conventional ones such as the radio frequency (rf) plasma assisted chemical vapor deposition (PACVD) and the ion beam deposition. It is required to use these DLCs properly for each usage. Another topic in these days is a flexible DLC film that uses rubber as the substrate material instead of the generally used ones such as metals and ceramics. This new DLC film is applied to the rubber seal ring (O-ring) for zoom lens system of 35 mm compact cameras.