The adsorption of aromatic molecules at solid/liquid interface represents one important topic in surface science because of its close relationship with the surface catalysis, molecular-based nanostructure and nanodevices, and other surface physical chemistry phenomena. With the high-resolution images of molecular adlayer obtained by electrochemical scanning tunneling microscopy (STM), the abundant information about the adsorption structure and dynamics of aromatic molecules on electrode surfaces was obtained. The results are important to the understanding of the intermolecular and molecular-substrate interactions which govern the formation of adlayers. In the present review, the development of electrochemical STM was briefly reviewed and the progress of the study on the adsorption of aromatic compounds and their derivations on electrode surface was introduced. In particular, the attention is paid on the adsorption of hetero-cyclic aromatic compounds and other derivatives to elucidate the interaction of different functional groups with the substrate and the effect of molecule symmetry, electronic structure on the adsorption process.
It is very important to determine the structure at an electrode/electrolyte interface in situ not only for fundamental surface science but also for the applications related to nanotechnology. Surface X-ray scattering (SXS) technique is one of the most promising methods to determine the interfacial structure with a high space resolution in situ. Here we focus on the SXS technique, which is able to probe an atomic/molecular structure at buried interfaces, such as those of importance in electrochemistry. As an example, we described our results about the structural analyses of the electrochemical deposition processes of Pd and Ag on Au single crystal electrodes using in situ SXS technique.
A highly surface-sensitive vibrational spectroscopy, sum frequency generation (SFG), has been employed to investigate the interfacial structure of the Langmuir-Blodgett (LB) thin films on solid substrates. The SFG measurements demonstrate that the molecular structures at the surface layer of the even-numbered LB films of stearic acid considerably change both in air and in solution when Cd2+ cations are present. A flip-over model is proposed to explain the Cd2+-induced surface reorganization process.
A quartz crystal microbalance (QCM) having the capability of detecting the mass change of nanogram range was used to examine various interfacial processes at self-assembled monolayers (SAMs) of thiols, such as formation and desorption of SAMs, redox of ferrocene-terminated SAMs and acid dissociation of SAMs bearing -COOH and -NH2 functionalities. From the mass change due to ion association between charged functionalities of SAMs and electrolyte ions, the change in the microenvironment around the functionalities during the redox of SAM, and acid-base properties of SAMs both on open circuit and under potential control were evaluated. Because of high sensitivity of QCM and unique information obtained by using it, QCM will contribute greatly to the progress of nanoscience and nanotechnology, particularly those related to solid surfaces.
Four topics are presented on the electrode surfaces investigated using an ultrahigh vacuum-electrochemistry combined system: 1) Pt(100) reconstructed electrode, 2) adlayers of halides on electrodes, 3) formation of AgBr in solution, and 4) adlayer of p-xylene on Rh(111).
The electric double layer at electrolyte-electrode interface has been investigated by an experimental simulation under ultra high vacuum (UHV). In order to reproduce an electric double layer on an electrode surface, water is adsorbed on the surface treated with electrolyte components (HCl, Na and sulfuric acid) and CO. The coadsorption of water molecules with the electronegative and electropositive additives indicates the existence of various hydration structures or orientation of water molecules on the surfaces. By comparing the results under UHV conditions with those from in-situ electrode surfaces in solution, there appears to be a correlation between orientation of water molecules and electrode potential. Over-layer water molecules as well as adsorbed ones on the surface provides ordered or disordered structures that determine the electrode potential values.
Since the electrode interface phenomena have multiscale nature in space and time, the multiscale model from quantum to continuum level should be considered. In this article we describe the structure of the Pt(111)/dipolar liquid interface and the adsorption of sulfur on electrified Au(111) surface. The structure of the Pt(111)/dipolar liquid interface has been investigated by fully self-consistent combination of the first-principles calculation based on quantum mechanics for the metal and the reference hypernetted-chain (RHNC) theory for the liquid. The electronic density profile for the metal, density and orientational structure of liquid molecules, and electrostatic potential across the interface are discussed in detail. A dense layer of liquid molecules, which is ordered in terms of orientation, is formed near the metal surface, but this surface-induced structure extends about only three molecular diameters from the surface. This result is in agreement with the recent experimental observations. For S adsorption on electrified Au(111) surface the screening of the electron at metal surface and the change of the adsorption energy of sulfur are discussed briefly.
Recent topics of the use of reflectance difference spectroscopy (RDS) to control and characterize the Si-surface oxidation and the InAs wetting-layer formation are reviewed. It is shown that by measuring the RD-spectrum oscillation one can control the thickness of layer-by-layer Si-surface oxides in an atomic scale. Moreover, by analyzing the RD spectra, the atomic structure and component of the SiO2/Si interface is characterized. On the other hand, the RD-spectrum change in the InAs growth on GaAs substrate before the quantum-dot formation enables us to clarify not only a variety of surface atomic structures of InAs wetting layers, such as (1×3), (2×3), and (2×4), but also the cation-alloying dynamic process of InAs wetting layers.