The electrode pair and nanogap fabrication: The pair of facing Au (99.99%) electrodes were fabricated by an optical-lithography technique on an n-type Si wafer of <111> orientation that was covered with 2-mm, thermally oxidized silicon layer. The initial separation was typically 2mm. The electrochemical fabrication of the nanogap electrodes was realized by using a CHI631A electrochemical workstation (CHI Co., USA). The deposition current in chronopotentiometry was 0.1mAcm 2. The electroplating solution was 15mm KAu(CN)2, with 0.3mm K3C6H5O7 and 0.3mm KH2PO4 as supporting electrolytes. These optimized experimental parameters, especially the current density, ensure that the Au deposits in a uniform and compact manner, which ensures a reasonably good stability of the fabricated nanogap in both solution and air. When the electroplating solution was diluted by a factor of 100, that is, the electroplating solution was 0.15mm KAu(CN)2 with 3mm K3C6H5O7 and 3mm KH2PO4, the largest fabricated gap width was about 10nm. All solutions were prepared with analytical grade reagents and Milli-Q water. The nanogap electrodes with a gap larger than 1nm were characterized with a LEO1530 scanning electron microscope (LEO Co., Germany). The nanogap electrodes with gaps smaller than 1nm were characterized with a Keithley 4200 semiconductor characterization system to measure the corresponding I-V curve of the gap.

Silver adlayer can be formed on Au single crystal surfaces by surface-induced dissociation of Ag coordinated complex precursor [(dptap-Ag)2](NO3)2, where dptap denotes 2-(2-pyridylimino)-2H-1,2,4-thia-diazolo [2,3-a] pyridine, by immersing in the acetonitrile containing such a complex. STM study shows (4×4) and (√2×√p2) adlayer structures on Au(1 1 1) and Au(1 0 0), respectively, resembling the Ag UPD adlayer structures on the corresponding Au single crystal electrodes at high underpotential shifts. The formation of the Ag adlayer is confirmed by XPS study, and computational calculations suggest a mechanism of surfaceinduced weakening and dissociation of the (electrostatic) Ag-N bond by charge transfer from the Au surface.

We report an in situ STM study of a potential-dependent long-range surface restructuring of Au(1 1 1) electrode in neat 1-butyl-3-methylimidazolium tetrafluoroborates (BMIBF4) ionic liquid. Au(1 1 1) undergoes a significant long-range surface restructuring upon cathodic excursion to 1.0V vs. Pt quasi-reference. The restructuring involves the formation of tiny pits, which then develops into a stable worm-like network with an average width of the network grids ～2nm. Electrochemical annealing occurs at the cathodic limit with the presence of a reduction product of cation BMIþ. A smooth surface is recovered with the appearance of the typical (√3×22) reconstruction of Au(1 1 1). The surface restructuring is reestablished upon anodic excursion to 1.3V after the adsorbed reduction product is oxidized. The long-range surface restructuring phenomenon is tentatively explained as a result of partial charge transfer to the weakly adsorbed BMIþ, which reduces the metal-metal cohesive energy. In addition, the synergetic effect of the counter anion BF-4 may also be involved. The results provide a knowledge of Au(1 1 1) electrode behavior in the neat ionic liquid and are beneficial to understanding in situ STM results involving surface morphological changes in such a media.

This Letter presents a study on the oxidation of electrochemically deposited Sn monolayer on Au(1 1 1) surface and STM tip-induced reduction of as-prepared ultra thin SnO film. A threshold bias of 0.6 V (tip negative) at a low tunneling current of ～50 pA is required to image the as-formed SnO thin film by STM, typical of a semiconductor characteristic. Increasing the tunneling current to ～2 nA leads to the reduction of the SnO back to Sn. Based on the energy level calculation for the SnO, a mechanism involving direct electron tunneling is proposed to account for the tipinduced reduction.

Diffusion coupled oscillatory behavior of the Au IHCI system was investigated in the presence of substrate "feedback" of the scanning electrochemical microscopic (SECM) system. It is shown that the amplitude of current oscillation can be increased significantly with a slight decrease in the oscillation frequency when the Pt substrate is positioned close to the small Au oscillating electrode. Such a "feedback" effect of the substrate may also become the driving force to induce current oscillation at the potential where normally electrodissolution occurs. The use of SECM to distinguish the types of oscillation mechanism of chosen systems is demonstrated by further fulfillment of a similar experiment on the surface process controlled potential oscillation system of Pt IHCHO. For this purpose, a special home-made galvanostat-potentiostat was employed which is generally necessary for studies of surface process controlled oscillation and may also be useful for studies of diffusion coupled oscillation under current control. It is shown that such an investigation under SECM configuration may provide insight into the oscillatory behavior from a new point of view.