Potential-dependent reconstruction at ordered Au(100)-aqueous interfaces as probed by atomic-resolution scanning tunneling microscopy (original) (raw)
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Surface Science, 1993
The electrode potential-induced formation and dissipation dynamics of the hexagonal ("hex") reconstruction on ordered Au(100) in perchloric and sulfuric acid electrolytes has been studied by means of in-situ scanning tunneling microscopy (STM). The real-space/real-time evolution of surface structures associated with the potential-dependent hex 1 (1 X 1) phase transition was examined on timescales down to ca I s by acquiring STM images during appropriate potential sweeps and steps (dubbed here "potentiodynamic STM"). Extensive hex domains can be formed by slow cooling following flame annealing and/or by holding the potential at values significantly below the potential of zero charge for the (I x 1) surface. The sharp removal of the reconstruction seen voltammetrically, during positive-going potential sweeps, is accompanied by rapid (< I s) formation of arrays of ordered (I x 1) clusters, created from the release of the ca 24% additional gold atoms utilized in the (5 x 27) and related hex structures compared with the (1 x 1) substrate. These clusters are significantly, twofold, larger (ca 4-6 nm) when formed in sulfuric acid electrolyte, due probably to an enhanced surface mobility in the presence of adsorbed sulfate. The reverse (I x 1)-hex transition at negative electrode charges is markedly slower. The hex domains appear initially as long thin (few atom-wide) strands, formed on (I x 1) terraces by adatom diffusion primarily from cluster sites. This mechanism is augmented close to terrace edges by a "wavefront-like" motion of atomic rows. Further development of the hex domains occurs partly by aggregation of very thin hex strings, but primarily by a uniform broadening of thicker strands. The considerable prospects for utilizing potentiodynamic STM to explore local CRA&I TAB nanoscale processes associated with reconstruction and other potential-induced ')u;'ced phase transitions is noted in the light of these findings.
The Journal of Physical Chemistry, 1993
The effect of iodide chemisorption on the nanoscale real-space dynamics associated with the electrode potentialinduced formation and removal of the hexagonal reconstruction on Au(100) in aqueous solution has been examined by means of in-situ scanning tunneling microscopy under potentiodynamic conditions. Unlike in "nonadsorbing" media such as perchloric acid where the (1 X 1)-(hex) phase change is slow (t l / z-10 min), requiring adatom diffusion from terrace edges, the potential-induced transition in iodide can be remarkably rapid (C0.2 s). The latter features facile large-scale (ca. 10-20 nm) gold mass transport emanating from former (1 X 1) terraces as well as from terrace edges. The likely roles of chemisorption in inducing such remarkably rapid reconstruction are briefly discussed.
We investigated the effects of tunneling current on scanning tunneling microscopy (STM) images of 1-octanethiol (OT) and 1-decanethiol (DT) self-assembled monolayers (SAMs). At a low tunneling current, the domain boundaries and ordered alkanethiol molecules were clearly resolved. As the tunneling current was increased at a constant bias voltage, however, the STM images showed disordered structures of the OT and DT SAMs. As the tunneling current was reduced back to low values, the ordered structures of the alkanethiol molecules reappeared. The reversibility of the process suggests that the sulfur head groups did not rearrange under any of the tunneling current conditions. On the basis of our observations, which are inconsistent with the standard model for STM imaging of molecules on metal surfaces, we consider the STM imaging mechanism in terms of a two-region tunneling junction model.
Journal of Electroanalytical Chemistry, 1999
The adsorption and desorption of pyridine (Py) adlayers prepared on Au(111) terraces were studied by in-situ scanning tunnelling microscopy (STM) and conventional voltammetry using an aqueous 0.1 M HClO 4 + 10 − 4 M Py solution at 298 K. The applied potential covered the range 0.15 VB EB1.2 V (vs. SHE), i.e. potentials above and below E pzc , the potential of zero charge of Au(111). In the range E pzc BE B0.96 V, hexagonal (4 × 4) ordered domains corresponding to Py molecules adsorbed vertically on the Au(111) surface coexist with disordered adlayer domains, but for EB E pzc , the ordered adlayer structure disappears leaving uncovered Au(111) domains. Similarly, for E \0.96 V, the (4 ×4) adlayer lattice is removed completely leading to a bare Au(111) surface. By stepping E backwards to a value in the range E pzc B EB0.96 V, the readsorption of Py takes place and the (4×4) adlayer domains are recovered in a few minutes. STM data offer the possibility of discussing anion adsorption and the early electroformation stages of the OH-containing adlayer on Au(111) terraces.
The Bulletin of the Korean Chemical Society , 2011
We investigated the effects of tunneling current on scanning tunneling microscopy (STM) images of 1-octanethiol (OT) and 1-decanethiol (DT) self-assembled monolayers (SAMs). At a low tunneling current, the domain boundaries and ordered alkanethiol molecules were clearly resolved. As the tunneling current was increased at a constant bias voltage, however, the STM images showed disordered structures of the OT and DT SAMs. As the tunneling current was reduced back to low values, the ordered structures of the alkanethiol molecules reappeared. The eversibility of the process suggests that the sulfur head groups did not rearrange under any of the tunneling current conditions. On the basis of our observations, which are inconsistent with the standard model for STM imaging of molecules on metal surfaces, we consider the STM imaging mechanism in terms of a two-region tunneling junction model.
Bulletin of the Korean Chemical Society, 2011
We investigated the effects of tunneling current on scanning tunneling microscopy (STM) images of 1-octanethiol (OT) and 1-decanethiol (DT) self-assembled monolayers (SAMs). At a low tunneling current, the domain boundaries and ordered alkanethiol molecules were clearly resolved. As the tunneling current was increased at a constant bias voltage, however, the STM images showed disordered structures of the OT and DT SAMs. As the tunneling current was reduced back to low values, the ordered structures of the alkanethiol molecules reappeared. The reversibility of the process suggests that the sulfur head groups did not rearrange under any of the tunneling current conditions. On the basis of our observations, which are inconsistent with the standard model for STM imaging of molecules on metal surfaces, we consider the STM imaging mechanism in terms of a two-region tunneling junction model.