The kinetics of structural changes in anionic adlayers on stepped Au(111)s electrodes from sulfuric acid solutions

Batch fabrication of gold-gold nanogaps by E-beam lithography and electrochemical deposition

We report on the successful development of a well-controlled two-step batch nano-fabrication process to achieve nanometer-size gaps at the wafer scale. The technique is based on an optimized electron-beam lithography process, which enables the fabrication of nanogaps in the range (15 ± 4) nm. Following this first step, the feedback-controlled electrochemical deposition of gold from an aqueous HAuCl4-based electrolyte is applied to further reduce the size of the gap down to about 0.3-1.0 nm. This protocol was successfully demonstrated by fabricating more than 385 nanogaps on a 4 inch wafer. The reproducible fabrication of nanogaps in the range between 0.3 and 1.0 nm opens up new perspectives for addressing the electrical and reactivity properties of single molecules and clusters in confined space under well-controlled conditions.

Electrochemical modification of surface morphology of Au/Ti bilayer films deposited on a Si prism for in situ surface-enhanced infrared absorption (SEIRA) spectroscopy

Surface-enhanced infrared absorption (SEIRA)-active Au/Ti bilayer films sputter deposited on Si substrates have been prepared by an electrochemical annealing (ECA) treatment for the first time. The application of Au/Ti bilayer films on Si substrates to the spectroscopic technique is a promising alternative to the conventional technique using directly deposited Au films on Si substrates, offering excellent adhesive durability of the deposited metal films. However, Au/Ti bilayer films have never been selected for the spectroscopy technique because the films in the as-prepared state exhibit relatively smooth surface morphology: the excitation of the localized surface plasmon is vital to achieving SEIRA enhancements but could hardly be observed on the smooth morphology. It is shown by ex situ scanning tunneling microscopy measurements that the unfavorable smooth morphology of the as-prepared Au/Ti bilayer films can be modified by the ECA treatment to a reasonably rough, island-structure morphology similar to that of the conventional SEIRA-active Au films. In situ infrared absorption spectroscopy of adsorbed sulfate anions has been conducted on the Au/Ti bilayer film both before and after ECA treatment. The spectroscopy measurements demonstrate that the SEIRA activity of the film after being subjected to the treatment is significantly improved so that the technique could detect adsorbates on the film electrodes even with the submonolayer coverage. As an additional benefit, the ECA treatment has brought about a substantial increase in the fraction of Au(111) domains on the polycrystalline Au film surfaces. Accordingly, this approach enables us to prepare SEIRA-active Au films having sufficient adhesion to the Si substrates as well as the highly preferred (111) orientation.

Interaction of cytidine 5'-monophosphate with Au(111): an in situ infrared spectroscopic study

The interaction of cytidine 5'-monophosphate (CMP) with gold surfaces is studied by means of in situ infrared spectroscopy and cyclic voltammetry at the Au(111)|aqueous solution interface. Similar to other nucleic acid components, cytidine 5'-monophosphate is chemisorbed on the surface at positive potentials, and the amount of adsorbed CMP increases with the potential. Subtractively normalized interfacial Fourier-transform infrared spectroscopy (SNIFTIRS) is used to identify the adsorbed and desorbed species. Upon electrochemical desorption, the molecules released in solution are unprotonated on the N3 atom. Striking similarities are found between the spectrum of adsorbed CMP and the solution spectrum of protonated CMP. The origin of such similarities is discussed. The results strongly suggest that chemisorption occurs through the N3 atom of the pyrimidine ring. A comparison is drawn with cytidine, whose electrochemical and spectroscopic behaviors are also investigated.

On a New Phase Transition in the Cu/Au(111)/H2SO4 System

A new pair of current spikes has been found in the cyclic voltammogram of Au(111) in an acidic copper sulphate solution, indicative of a phase transition in the Cu adlayer. The spike potential is well inside the bulk deposition region and hence, the new feature can be observed only at low Cu++ concentration, when bulk deposition is slow. The charge under the spike correlates linearly with extent of the (√3 × √3)R30° structure, up to 40μCcm-2 for the fully developed superstructure. The spike potential shifts with the sulphate concentration and hence, this feature is assigned to the desorption of sulphate from the well-known honey comb structure of the Cu upd layer.