We present and discuss the results of an in situ IR study on the mechanism and kinetics of formic acid oxidation on a Pt film/Si electrode, performed in an attenuated total reflection (ATR) flow cell configuration under controlled mass transport conditions, which specifically aimed at elucidating the role of the adsorbed bridge-bonded formates in this reaction. Potentiodynamic measurements show a complex interplay between formation and desorption/oxidation of COad and formate species and the total Faradaic current. The notably faster increase of the Faradaic current compared to the coverage of bridge-bonded formate in transient measurements at constant potential, but with different formic acid concentrations, reveals that adsorbed formate decomposition is not rate-limiting in the dominant reaction pathway. If being reactive intermediate at all, the contribution of formate adsorption/decomposition to the reaction current decreases with increasing formic acid concentration, accounting for at most 15% for 0.2 M DCOOH at 0.7 VRHE. The rapid build-up/removal of the formate adlayer and its similarity with acetate or (bi-)sulfate adsorption/desorption indicate that the formate adlayer coverage is dominated by a fast dynamic adsorption-desorption equilibrium with the electrolyte, and that formate desorption is much faster than its decomposition. The results corroborate the proposal of a triple pathway reaction mechanism including an indirect pathway, a formate pathway, and a dominant direct pathway, as presented previously (Chen, Y. X.; et al. Angew. Chem. Int. Ed. 2006, 45, 981), in which adsorbed formates act as a site-blocking spectator in the dominant pathway rather than as an active intermediate.

The influence of the substrate and the deposition conditions-vapor deposition versus deposition from solution-on the structures formed upon self-assembly of deposited bis(terpyridine) derivative (2,4'-BTP) monolayers on different hexagonal substrates, including highly oriented pyrolytic graphite (HOPG), Au(111), and (111)-oriented Ag thin films, was investigated by high-resolution scanning tunneling microscopy and by model calculations of the intermolecular energies and the lateral corrugation of the substrate-adsorbate interaction. Similar quasi-quadratic network structures with almost the same lattice constants obtained on all substrates are essentially identical to the optimum configuration expected from an optimization of the adlayer structure with C-H...N-type bridging bonds as a structure-determining factor, which underlines a key role of the intermolecular interactions in adlayer order. Slight distortions from the optimum values to form commensurate adlayer structures on the metal substrates and the preferential orientation of the adlayer with respect to the substrate are attributed to the substrate-adsorbate interactions, specifically, the lateral corrugation in the substrate-adsorbate interaction upon lateral displacement and rotation of the adsorbed BTP molecules. The fact that similar adlayer structures are obtained on HOPG under ultrahigh vacuum conditions (solid|gas interface) and on HOPG in trichlorobenzene (solid|liquid interface) indicates that the intermolecular interactions are not severely affected by the solvent.

Scanning tunneling microscopy observations show that (i) the lattice mismatch between Ni and Ru leads to a sequence of increasingly relaxed structures in Ni films grown on Ru(0001), and (ii) the density of Ni islands changes drastically with the thickness of the underlying Ni film. The latter is associated with an increase in Ni mobility; from monolayer to three-layer Ni films a reduction in Ni adatom diffusion barrier of 300 meV is estimated. Such effects are shown to significantly affect film growth and, in this case, to promote smoother growth. New possibilities for obtaining smoother film growth for heteroepitaxial systems, in general, are discussed. PACS numbers: 68.55. -a, 61.16.Ch Epitaxial growth affords the opportunity to make materials with morphologies and chemical compositions which would not ordinarily occur in nature [1 -4]. By varying the experimental parameters of temperature, deposition rate, and, more recently, additive (surfactant) concentrations the characteristics of the growing film can be controlled to a certain extent [5 -12]. For heteroepitaxy further effects come into play, namely, the change in film structure due to the removal of strain, and the change in electronic properties with increasing film thickness. The strain results from the lattice mismatch between the substrate and the growing film. In this Letter we demonstrate that these surface modifications can have a drastic effect on the adatom mobilities, leading to layerdependent island densities. The structure of and adatom mobilities on films of different layer thicknesses were determined by scanning tunneling microscopy (STM). For these experiments we first prepared well-defined Ni films on a Ru (0001) substrate by deposition at 550 K. This temperature is sufficiently high to produce well-ordered surfaces and rather large terraces, but not high enough to create the equilibrium morphology of that system, which consists of 3D crystallites growing on a single Ni layer (Stranski-Krastanov growth) and which is obtained after deposition at or annealing to higher temperatures [13,14].On these thin film substrates we subsequently deposited small amounts of Ni in a second dose at room temperature. From the distribution and density of the Ni islands obtained after the second dose we gain insight into adatom diffusion on and among the various well-defined Ni layers. The results lead us to introduce layer dependent mobilities and island densities as a general concept for heteroepitaxy with substantial implications for growth descriptions and film morphologies.Deposition and STM imaging were carried out at p ( 3 x 10 " Pa, on carefully cleaned Ru(0001) substrates.Further details on the experimental setup and procedures and on the growth behavior of that system will be described elsewhere [14]. STM images were recorded in a pocket-sized STM at tunnel currents around 1 nA and bias voltages of 100 mV. The images are presented in either a top view representation, v .ih darker areas corresponding to lower levels, or in a bird's eye view with illu...

The self-organization of diblock copolymers into micellar structures in an appropriate solvent allows the deposition of well ordered arrays of pure metal and alloy nanoparticles on flat surfaces with narrow distributions in particle size and interparticle spacing. Here we investigated the influence of the materials (substrate and polymer) and deposition parameters (temperature and emersion velocity) on the deposition of metal salt loaded micelles by dip-coating from solution and on the order and inter-particle spacing of the micellar deposits and thus of the metal nanoparticle arrays resulting after plasma removal of the polymer shell. For identical substrate and polymer, variation of the process parameters temperature and emersion velocity enables the controlled modification of the interparticle distance within a certain length regime. Moreover, also the degree of hexagonal order of the final array depends sensitively on these parameters.

In situ Au3+--> reaction and dispersion of the resulting gold in the form of nanoparticles (NPs) in a reactive polymer medium, such as poly(vinyl alcohol) (PVA) molecules in hot water, are explored to devise a composite Au-PVA structure of self-standing films. The Au-NPs (0-2 wt%) tailor a violet to purple to a yellowish color of films from a colorless base polymer. A distinct surface interface (of thickness 2-5 nm) from the core (20-30 nm diameter) is resolved in transmission electron microscope images. The x-ray photoelectron spectrum (XPS) in the 81-91 eV range accounts for the effect which causes asymmetric shapes of the 4f(7/2) and 4f(5/2) Au bands. In a model structure, the asymmetry arises in the contribution of the surface Au atoms, which extend a chemical bridging with surface O atoms from the PVA molecules in a surface layer. A similar asymmetry also arises in C 1s and O 1s bands in the counterpart PVA molecules at 287.79 and 532.35 eV, respectively. At Au content as large as 2 wt%, no separate XPS band arises on a negligibly small fraction of surface Au atoms when Au-NPs have been grown in thin laminates (or cuboids and prisms).