Solution phase post-modification of a trimesic acid network on Au(111) with Zn(2+) ions.

Solution phase post-modification of a trimesic acid (TMA) network on Au(111) with Zn(2+) ions was found to induce transformation of a bar-featured scanning tunneling microscopy image of (5√3 × 5√3) to a chevron-pair image of (10√3 × 10√3). Voltammetric determination of Zn coverage in the modified TMA network supports the fact that the chevron feature consists of three TMA molecules combined via two coordination bonds between Zn(2+) ions and carboxylates of TMA.

Formation of single-layered Pt islands on Au(111) using irreversible adsorption of Pt and selective adsorption of CO to Pt.

This communication compares two different multiple deposition routes of Pt on Au(111), using irreversible adsorption of Pt precursor ions and selective adsorption of CO. A scanning tunneling microscopy study revealed that the conventional route, not utilizing CO, produced multiple-layered Pt cluster islands, while the CO route, employing CO, formed single-layered Pt islands exclusively. The role of CO selectively adsorbed on pre-existing Pt islands was to prevent additional irreversible adsorption of Pt precursor ions onto Pt islands. Cyclic voltammetric works disclosed that the CO and hydrogen coverages on single-layered Pt islands were higher than those on multiple-layered ones, and that the Pt islands on Au were more effective in adsorbing CO than hydrogen.

Adsorptive behavior of dimethylglyoxime on Au(111).

Dimethylglyoxime (DMG) adsorbed on Au(111) was investigated using electrochemical scanning tunneling microscopy (STM) and X-ray photoelectron spectroscopy (XPS). STM experiments revealed three different structures of adsorbed DMG at open circuit potential (~0.07 V versus Ag/AgCl): (2√3×2√3)R30°-α, (2√3×4√3)R30°-ß, and (2√3×4√3)R30°-γ. The coverage of adsorbed DMG obtained using XPS was 0.33. A combination of structural and quantitative information identified the adsorbed DMG as an anionic tetramer, held together by intermolecular hydrogen bonding and arrayed in three ordered patterns. Domains of adsorbed DMG underwent phase transitions between the observed structures, most likely due to the influence of the STM tip. However, a significant correlation between the observed structures and the imaging conditions was not found. The ordered layers existed only at open circuit potential as evidenced by their disappearance when the potential was shifted to 0.2 or -0.15 V. The ordered layers were also removed by immersion in a solution of Ni(2+), implying that the adsorbed DMG was converted to a soluble dimer complex with the Ni(2+) ion. This particular observation is discussed in terms of the rigidity of the organic network.

Preoxidation of CO on Os-modified Pt(111): a comparison with Ru-modified Pt(111).

The variation in CO adsorption structures during the preoxidation of CO on Os-modified Pt(111) (Pt(111)/Os) was investigated using cyclic voltammetry and electrochemical scanning tunneling microscopy. The spontaneous deposition of Os on Pt(111) resulted in randomly scattered islands with a coverage range of 0.13-0.54. During preoxidation on Pt(111)/Os, a phase transition from (2 × 2)-α to (√19 × âˆš19) via the transient structures of (2 × 2)-ß and (1 × 1) took place as on unmodified Pt(111). As the amount of Os increased, however, the transient structures of (2 × 2)-ß and (1 × 1) appeared at lower potentials with higher populations. When the population of the transient structures was greater than 50%, an oxidative CO stripping process took place to the structure of (√19 × âˆš19), completing the preoxidation. These observations strongly support the idea that the presence of Os increases the mobility of adsorbed CO by electronic modification of the Pt(111) surface (electronic effect). In addition, the results obtained with Pt(111)/Os were compared with those of Pt(111)/Ru.

Selective adsorption of dithiolate-modified multi-wall carbon nanotubes onto alkanethiol self-assembled monolayers on Au(111).

Dithiolate-modified multi-wall carbon nanotubes (MWCNTs) adsorb selectively on the self-assembled monolayers (SAMs) of alkanethiols on a Au surface: the long dithiolates attached to the MWCNTs anchor the massive MWCNTs onto the Au surface by replacing the shorter thiolates of SAMs.

Modification of Au nanoparticles dispersed on carbon support using spontaneous deposition of Pt toward formic acid oxidation.

This work presents formic acid oxidation on Pt deposits on Au nanoparticles dispersed on Vulcan XC-72R. The Pt deposits were produced using spontaneous deposition method contacting the Au nanoparticles with solutions containing Pt complex ions in various concentrations. The Pt deposits were characterized using CO stripping coulometry, X-ray photoelectron spectroscopy, and inductively coupled plasma atomic emission spectroscopy. When the Pt concentration is 10(-5)-10(-4) M, the Pt deposits are nanoislands of monatomic height. In the concentration range of 10(-4)-10(-3) M, the Pt deposits are most likely two-layer-thick nanofeatures. As Pt concentration increases further, the deposits become wider and thicker. Voltammetric behavior of Pt deposits reveals that on Pt deposits, dehydrogenation path is activated at the expense of poison-forming dehydration path. Furthermore, chronoamperometric measurement of the catalytic activity of Pt deposits supports that the two-layer-thick Pt deposits are most efficient in formic acid oxidation among the studied Pt deposits on Au nanoparticles. The enhancement factor of the particular Pt deposits is 2 in terms of turnover frequency, compared with a commercial Pt catalyst. Details are discussed in conjunction with Pt deposits on Au(111).

Electrocatalytic oxidation of formic acid and methanol on Pt deposits on Au(111).

This work presents characteristics of Pt deposits on Au(111) obtained by the use of spontaneous deposition and investigated by electrochemical scanning tunneling microscopy (EC-STM). On such prepared and STM characterized Au(111)/Pt surfaces, we studied electrocatalytic oxidation of formic acid and methanol. We show that the first monatomic layer of Pt displays a (square root 3 x square root 3)R30 degrees surface structure, while the second layer is (1 x 1). After prolonged deposition, multilayer Pt deposits are formed selectively on Au(111) surface steps and are 1-20 nm wide and one to five layers thick. On the optimized Au(111)/Pt surface, formic acid oxidation rates are enhanced by a factor of 20 compared to those of pure Pt(111). The (square root 3 x square root 3)R30 degrees-Pt yields very low methanol oxidation rates, but the rates increase significantly with further Pt growth.

Electrochemical scanning tunneling microscopic observation of the preoxidation process of CO on Pt(111) electrode surface.

Presented are sequential images of CO on Pt(111), observed with electrochemical scanning tunneling microscopy, during its electrochemical preoxidation process. In the course of the well-known phase transition from the (2 x 2)-3CO-alpha structure to the (radical 19 x radical 19)R23.4 degrees-13CO structure, various structures were observed: (2 x 2)-3CO-beta (Chem. Comm. 2006, 2191-2193), (1 x 1)-CO, and (radical 13 x radical 13)R46.1 degrees-9CO. Based on an analysis of the populations of the structures averaged over imaging time and imaged location at the preoxidation potential range (0-0.25 V vs Ag/AgCl), the structures of CO domains changed sequentially in the order of (2 x 2)-3CO-alpha, (2 x 2)-3CO-beta, (1 x 1)-CO, (radical 13 x radical 13)R46.1 degrees-9CO, and (radical 19 x radical 19)R23.4 degrees-13CO as the potential shifted from 0 to 0.25 V. Such a sequential structural change demonstrates that the structures of (2 x 2)-3CO-beta, (1 x 1)-CO, and (radical 13 x radical 13)R46.1 degrees-9CO are transient ones during the preoxidation of CO on Pt(111). Discussed are the transient structures in terms of various aspects, such as the absence of CO in solution and the origin of compressed structures.

Electrochemical STM observation of new structures of CO adsorbed on a Pt(111) electrode surface.

Presented are two newly observed adstructures of adsorbed CO onto Pt(111), (2 x 2)-3CO-beta and (2 x 2)-4CO, observed during the structural evolution from the well-known (2 x 2)-3CO-alpha structure to the (square root 19 x square root 19)-13CO structure.