Single Crystal Silver Surfaces Research Articles

Adsorption of acrolein on single-crystal surfaces of silver: Density functional studies

Silver selectively catalyzes the hydrogenation of the C O group of α, β-unsaturated aldehydes, indicating preferential adsorption-induced activation of this bond compared to the adjacent C C bond. Using a density functional method and periodic slab models, we studied the propensity of the flat Ag(1 1 0) and the stepped Ag(2 2 1) surfaces to activate the C O bond of adsorbed acrolein. Our calculations show acrolein to interact only weakly with all adsorption sites under study (by at most 35 kJ mol −1), resulting in very limited bond activation. Therefore, we conclude that other active sites on silver catalysts participate in the experimentally observed selective hydrogenation.

Coadsorption of hydrogen and potassium on silver single crystal surfaces

Adsorption and coadsorption of H 2 (D 2) and potassium on the single crystal silver surfaces (111) and (110) have been studied using TPD, angle-resolved TPD, work function measurements and LEED. Atomic hydrogen was used to cover the silver surfaces, since a very high activation barrier for molecular adsorption exists. From the Ag(111) surface hydrogen desorbs in a single peak with a close to second order reaction and a desorption energy of 7 kcal/mol. Hydrogen desorption from Ag(110) is characterized by two overlapping desorption peaks which are very sensitive to small amounts of water coadsorption. Angular distributions of the desorption probability following a cos 2.5Θ and a cos 3.5Θ function for Ag(111) and Ag(110) were observed, respectively. Upon hydrogen saturation (0.65 ML) on Ag(111) the work function increases by 240 meV. Coadsorbed potassium shifts the desorption temperature for H 2 dramatically by 250 K to higher temperature on both surfaces. Simultaneous desorption of hydrogen and potassium on both silver surfaces with a ratio of 1 K-atom to 4 H 2 molecules indicates a strong potassium-hydrogen interaction in the coadsorbate.

A device for performing surface-plasmon-polariton-assisted Raman scattering from adsorbates on single-crystal silver surfaces

We describe the theory, design, and performance of a new surface-plasmon-polariton-(SPP) assisted Raman scattering instrument that exploits the Kretschmann geometry. In contrast to previous methods, our device allows the entire SPP emission cone to be collected, thus optimizing the detected Raman intensity. This advantage makes surface Raman scattering from adsorbates on relatively smooth or single-crystal silver films possible with routine optics and electronics in the rest of the system. We demonstrate the concept with data acquired from a monolayer of paranitrosodimethylanaline (pNDMA) on nearly smooth polycrystalline Ag and single-crystal Ag(111) with air or liquid as the ambient medium.

Second harmonic generation studies of anionic adsorption on polycrystalline and single crystal silver surfaces

Adsorption of anions on single crystal and polycrystalline silver surfaces has been monitored with optical second harmonic generation. Potentials inves

Unenhanced raman spectroscopy of benzene adsorbed on single crystal silver surfaces: Evidence for surface selection rules

We have interpreted the unenhanced Raman spectra of perdeuterobenzene adsorbed in submonolayer quantities on the (111) and (110) surfaces of silver to

Electrochemical behaviour of silver and gold single-crystal surfaces covered with a monolayer of adsorbed sulphur

The behaviour of sulphur adsorbed at a silver and gold/electrolyte interface has been studied by a combination of radiotracer and classical electrochemical methods. Sulphur forms stable monolayers on single-crystal silver surfaces in aqueous NaF between −0.4 and −1.0 V (MSE). The double-layer capacity is substantially lowered and the pzc shfted. The sulphur can be removed by cathodic treatment, but the silver surface cannot be returned to its original clean condition by this method.

Electrochemical behaviour of silver and gold single-crystal surfaces covered with a monolayer of adsorbed sulphur

The behaviour of sulphur adsorbed at a silver and gold/electrolyte interface has been studied by a combination of radiotracer and classical electrochemical methods. Sulphur forms stable monolayers on single-crystal silver surfaces in aqueous NaF between −0.4 and −1.0 V (MSE). The double-layer capacity is substantially lowered and the pzc shfted. The sulphur can be removed by cathodic treatment, but the silver surface cannot be returned to its original clean condition by this method.

Low energy argon differential sputtering yields and thresholds along the 〈110〉 and 〈100〉 directions from single crystal silver surfaces

Abstract The relative differential sputtering yields, dS, in a fixed small solid angle at various directions from a single crystal silver target under normal Ar+ ion bombardment (ion energy from threshold to about 100 eV) have been measured. The yields measured in the directions of various sputtering “spots” were: dS 1 in the 〈110〉 direction at about 60° from the (110) face;dS 2, 〈110〉 direction, 45° from (100) face;dS 3, 〈110〉 direction, 35° from (111) face;dS 4, 〈110〉 direction, normal to (110) face; and dS 5, 〈100〉 direction, normal to the (100) face. The magnitudes of the yields were: dS 1 ≃ dS 2 > dS 3. An order of magnitude lower were: dS 4 > dS 5. For the oblique 〈110〉 emissions, the curves of (dS) 1/2 vs. incident ion energy were linear for ion energies of about 20–50 eV; extrapolation of these curves to zero yield gave the following sputtering threshold energies: dS 1, 14 eV; dS 2, 18 eV; and dS 3, 23 eV.

Numerical Experiments on Scattering of Noble Gases from Single-Crystal Silver

Three-dimensional numerical experiments on the scattering of noble-gas atoms from single-crystal surfaces of silver are described. This numerical method can be very useful in determining the relative importance of different variables in the interactions although it cannot be expected to give quantitative agreement with individual cases until a better knowledge of the interatomic binding energies and the surface state is available. Most of the cases are for neon on the fcc (111) surface, but isolated cases of helium and argon on (111) and neon on (100) are included. The energies include those of effusive molecular beams from 300° to 45 000°K equivalent source temperatures (0.06 to 7.8 eV). Several interaction parameters describing mean energy and momentum exchanges and traces of the spatially resolved flux in the incident plane are given for most of the cases. Sample out-of-plane flux data and some typical data on spatially resolved energy are also given, and general trends for the rest of the data are described. The results give trapping probabilities that are much greater than those inferred from laboratory experience, and flux patterns that are significantly broader than those encountered in the experiments for the few cases that can be compared directly. The neon trends with increasing energy are quite similar to those of the Saltsburg and Smith experiments for xenon, with new effects appearing in the present results for energies higher than those of the laboratory experiments. These new effects include multiple peaks, one above and one below specular, and a broadening of the patterns with increasing incident energy. They are attributed to increased resolution of the surface atomic configuration due to deeper penetration of the potential field above the surface. The trends of the Logan, Keck, and Stickney hard-cube theory are shown in the present results at low incident energy, and the expected hard-sphere limit behavior is observed at very high incident energy, in agreement with the recent calculations of Goodman.

Recombination of Hydrogen, Nitrogen and Oxygen Atoms on Copper and Silver Single Crystal Surfaces

Abstract Recombination of hydrogen atoms, nitrogen atoms and oxygen atoms was carried out on single crystal surfaces of copper and silver subjected to various surface pre-treatments. With both the recombination of hydrogen atoms and that of nitrogen atoms, copper surfaces electrolytically polished have always higher activity than those chemically polished. The Cu(100) surface chemically etched by ammonium persulfate was more active than that etched by nitric acid for both hydrogen atoms and nitrogen atoms, whereas with the Cu(110) the opposite order of activity was obtained. For both silver and copper, no evidence was found to show the different order of activity between the recombination of hydrogen atoms and that of nitrogen atoms. Concerning the recombination of oxygen atoms on single crystal surfaces of silver, the (110) face was found to be more active than the (100) face in accord with the result of our earlier work about the recombination of hydrogen atoms on single crystal surfaces of copper.

The preparation of smooth single crystal surfaces of silver by an evaporation technique

Abstract An electron diffraction study has been made of the growth of evaporated silver layers on cleaved mica surfaces, with the substrate at various temperatures during the deposition. It is shown that good orientation (epitaxy) occurs over a wide range of temperatures, but that the nature of the orientation depends upon both the substrate temperature and the film thickness. Under certain conditions of proparation it is found that the surface of the silver deposit is very smooth on an atomic scale. These surfaces are of value as sub-strates for other experiments, both on epitaxy and on specimen preparation for high resolution electron microscopy of metals, and examples of these applications are quoted.

The initial stages of growth of oriented copper nuclei on single crystal surfaces of silver

Abstract Layers of metallic copper of less than 1 A in average thickness have been deposited in a controlled manner on to smooth (111) surfaces of silver inside an electron diffraction camera. It is found that an electron diffraction pattern from oriented copper nuclei appears suddenly at some critical thickness. This critical thickness decreases with increasing substrate temperature, being about 0.9 A at room temperature and 0.2 A at 300°c. Possibilities for the initial structure of the deposit, and for the change which occurs at the critical thickness, are considered, and the effect of substrate temperature is discussed.