Faces Of Silver Single Crystals Research Articles

Electron transfer through single-crystal silver electrode/n-decanthiol monolayer/NaNO3 solution interfaces

The kinetics of Ru[(NH3)6]3+ reduction in 1 M NaNO3 solution at Ag(210) and Ag(111) singlecrystal electrodes modified by n-decanthiol monolayer is studied by electrochemical impedance spectroscopy and cyclic voltammetry. By using these two methods, standard rate constants of the redox reaction involving Ru[(NH3)6]3+/2+ redox couple in the absence and in the presence of the n-decanthiol film were estimated. The equivalent circuit describing the experimental data in the presence of the self-assembled organic monolayer and in the absence of redox reaction is an electrical circuit comprising a large resistance (∼106 Ω) connected in parallel with a capacitance (∼10−8 F). Analysis of kinetic data and extrapolation of Tafel lines resulted in the determination of the rate constant at unmodified Ag-electrode, which is characteristic of very fast heterogeneous electron transfer. The calculated rate constants for n-decanthiol-modified silver singlecrystal faces (210) and (111) in 1 M NaNO3 solution (pH 6.3) equal 4.63 × 10−5 and 3.05 × 10−5 cm/s, respectively. The results are compared with the data at hand reported by different authors for gold electrodes in indifferent electrolyte solution in the absence and in the presence of self-assembled monolayer.

Electrochemical behavior of silver single-crystal electrodes in 1 M NaNO3 solution in the absence and in the presence of decanethiol films

The surface properties of silver single-crystal faces (111) and (210) in 1 M NaNO3 aqueous solution in the absence and in the presence of monolayer n-decanethiol (DT) films are studied by the methods of cyclic voltammetry and electrochemical impedance using the meniscus contact technique. It is experimentally shown that, in the potential range from 0 to −0.5 V, the faradaic processes are absent and low currents are recorded on the unmodified silver surfaces. It is shown that the DT molecules, which are adsorbed on the nonoxidized surfaces of silver faces, spontaneously form (during 72 h) compact structurized films. The films are stable in the air and in the electrolyte solutions and totally block the surfaces of both faces. The impedance spectra, which were measured for each interface in a wide range of frequencies, are analyzed and interpreted. The measurements were performed by the use of the corresponding empirical equivalent circuits containing perfect and imperfect analogs of electrical circuits; complex nonlinear least squares (CNLS) regression method was applied for the calculations. The capacitance, ohmic resistance, and adsorbed monolayer thickness were estimated.

The role of crystal imperfections in electrochemical phase formation and growth

The role of different crystal imperfections and surface inhomogeneities in the processes of electrochemical phase formation and crystal growth is discussed on the basis of experimental results obtained by electrodeposition of metals on native and foreign single crystal substrates in selected model systems. The major role of screw dislocations in the electrochemical growth of real crystals is demonstrated in the case of silver electrodeposition on silver single crystal faces prepared by the so-called capillary technique. Experimental results show that the electrochemical spiral growth of silver crystal faces with low dislocation density can be used for a preparation of surfaces with a defined and uniform density of monatomic steps. Combined electrochemical and in situ scanning probe microscopy (SPM) studies of underpotential deposition (UPD) of metals on foreign single crystal substrates show that surface inhomogeneities induce a stepwise formation of different low-dimensional (0D, 1D, and 2D) metal phases. The thermodynamic, kinetic, and structural aspects of the stepwise formation of Me phases of different dimensionality in the UPD range are discussed on an atomic level using results of electrochemical and in situ SPM measurements in various systems. Keywords: electrocrystallization, screw dislocations, spiral growth, surface inhomogeneities, underpotential deposition, low-dimensional phases, scanning tunneling microscopy.

Modelling transformation processes in underpotential lead adsorbate on Ag(111)

The transformation processes at low coverage of lead underpotential adsorbate on quasiperfect (111) faces of silver single crystals are discussed in view of the influence of the atomic surface relief on the process kinetics. The results are compared with those on real silver electrodes. A conclusion is made that on quasi-perfect electrodes the transformation processes take place predominantly on the atomically smooth terraces while on real electrodes these processes occur both on the terraces and at the steps of the surface. This effect is explained to be due to the different step density on the electrode surfaces studied.

Elementary growth kinetics of silver electrocrystallization

The elementary processes of electrochemical growth of cubic faces of silver single crystals were investigated after the so-called capillary method by means of in situ laser Michelson interferometry. Data were obtained about the motion of dislocation generated steps during electrocrystallization from a stagnant solution. It was proved that step motion proceeds after the direct incorporation mechanism, with bulk diffusion field overlap, leading to deviation from linearity in the step velocity/overvoltage dependence at higher hillock slopes. The true value of the step kinetic coefficient for the studied face was determined: β = 1.2 cm/s. In acidified solutions β is much smaller: β = 0.17 cm/s. Interferometric measurements of hillock slope versus overvoltage dependencies allowed us to determine the Burgers vectors of the leading growth dislocation sources. The free surface energy of the step riser was determined without any additional suppositions: for pH ≅ 5 it was 130 erg/cm 2 and for pH ≅ 1 it was 110 erg/cm 2.

STM studies in underpotential—overpotential metal deposition

The deposition of lead on “real” silver single crystal faces in the so-called underpotential ( upd) and overpotential ( opd) ranges was studied by in situ STM with atomic resolution. The results are compared with previous electrochemical, morphological, and in situ EXAFS and GIXS investigations. The STM images on bare substrates show regular hexagonal and quadratic lattices for the (111) and (100) planes, respectively, without any reconstructions. At high coverages in the upd range, well-ordered lead adlayers are observed on both substrate orientations. The lead monolayer on Ag(111) was found to be incommensurate, close packed, and rotated by about 4–5° with respect to the substrate. This agrees with previous GIXS measurements and indicates internal compressive strain within the adlayer. In contrast, lead on Ag(100) forms a superlattice structure which has a much lower adatom density than a hexagonal close-packed layer. The symmetry and interatomic distances are close to a c(2 × 2)Pb overlayer. In the opd range, 3-D lead crystallites are formed. On both substrate orientations, the contact plane of the lead crystallites is the close-packed (111) plane. At low overpotentials, the lead crystallites on Ag(111) grow epitaxially, rotated by about 5° with respect to the substrate. On Ag(100), two different orientations of lead crystallites in parallel to both [110] crystallographic directions of the substrate are observed. The nucleation rate of lead depends not only on the overpotential, but also on the initial polarization state in the upd range using an upd opd transient technique. Nucleation and growth may proceed either inside the imperfect and strained upd-adlayer or on top of it according to the Stranski-Krastanov mechanism.

Underpotential deposition and electrocrystallization of metals: an in situ scanning tunnelling microscopy study with lateral atomic resolution

The formation of well ordered 2D metal adsorbate layers in the underpotential range and 3D metal deposits in the overpotential range on foreign substrates has been studied in the model system Ag(hkl)/Pb2+ byin situ scanning tunnelling microscopy (STM) under defined potential control with lateral atomic resolution. The results are compared to electrochemical, morphological, in situ EXAFS and GIXS investigations. In situ STM provides an excellent atomic view of the initial steps of underpotential deposition (UPD) and electrocrystallization of lead onto (100) and (111) silver single-crystal faces. The results indicate a Stranski-Krastanov mechanism of 3D nucleation and growth in this system.

Superficial structure of gold and silver faces and adsorption from liquid phase

Are the structures of gold and silver single-crystal faces when in contact with aqueous solutions the ones described by ideal models and/or those observed in UHV ? Comparison of some results obtained by traditional electrochemical methods : with models and with results obtained by in-situ physical methods is discussed, first for the potential of zero charge in the case of no or slight specific adsorption, then for adsorption of halide ions and finally for underpotential deposition of metal ions on a substrate of a foreign metal.

Noise analysis in metal deposition—expectations and limits

The application of electrochemical noise analysis (ENA) on the electrocrystallization processes of metals is discussed on the basis of the well-known nucleation and growth mechanisms studied experimentally by transient techniques of silver deposition on quasi-perfect silver single crystal faces. Simulations of simplified 2-D nucleation and mononuclear growth mechanisms show that the nucleation and propagation rates are reflected in the power spectrum and the autocorrelation function. The analysis of data becomes difficult if both the nucleation and propagation rates are Poissonian distributed. First experimental results obtained for the silver deposition on quasi-perfect silver single crystal faces and the copper deposition on polycrystalline microelectrodes are reported.

A modification of the last step of surface preparation for gold and silver single crystal faces

A modification of the last step of surface preparation for gold and silver single crystal faces

Surface structural effects in electrocatalysis

The dependence of electrocatalytic effects on the structural properties of two-dimensional (2-D) metal adsorbates formed by underpotential deposition (UPD) of Pb, Tl and Bi on gold and silver single crystal faces of (111), (110) and (100) orientation is demonstrated for various electro-reduction reactions in acid solutions. Positive and negative electrocatalytic effects are observed depending on the metal substrate/adsorbate combination, on the degree of metal adsorbate coverage as well as on the type of redox reaction. Specificity of bond formations of reactants, intermediates and/or products with respect to the structural arrangement of the adatoms may explain the observed dependence on the crystallographic orientation of the substrate.

Prediction of double layer parameters: The case of silver

The electron work functions (Φ) of the single crystal faces of silver have been estimated from experimental data with evaporated thin films and compared with the directly measured values. The values of Φ derived from the electrochemical data are shown to agree fairly well with the experimental values. A work function—potential of zero charge plot has been obtained showing regularities in the behaviour of silver single crystal faces. The surface potential associated with adsorbed water molecules derived from the above plot is used to predict the values of the inner layer capacity at the potential of zero charge, C i, which turns out to agree satisfactorily with the available experimental data. Finally, peak potentials for desorption of amyl alcohol are predicted on the basis of the values of C i and Φ. Again, good agreement is found between the calculated and the experimental values, and the three main faces are shown to be arranged in a regular sequence. The picture emerging from this approach is discussed in terms of hydrophilicity concepts. Difficult aspects which do not render the physical interpretation conclusive are pinpointed. Double layer parameters for experimental conditions not yet investigated have been calculated and tabulated, and some areas for future research are outlined.

ChemInform Abstract: ADSORPTION OF SULFATE ION ON GROWTH STEPS OF (111) AND (100) FACES OF SILVER SINGLE CRYSTALS

Chemischer InformationsdienstVolume 15, Issue 11 Physical Inorganic Chemistry ChemInform Abstract: ADSORPTION OF SULFATE ION ON GROWTH STEPS OF (111) AND (100) FACES OF SILVER SINGLE CRYSTALS T. VITANOV, T. VITANOVSearch for more papers by this authorA. POPOV, A. POPOVSearch for more papers by this author T. VITANOV, T. VITANOVSearch for more papers by this authorA. POPOV, A. POPOVSearch for more papers by this author First published: March 13, 1984 https://doi.org/10.1002/chin.198411032Read the full textAboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinkedInRedditWechat No abstract is available for this article. Volume15, Issue11March 13, 1984 RelatedInformation

Adsorption of SO2−4 on growth steps of (111) and (100) faces of silver single crystals

Adsorption of SO2−4 on growth steps of (111) and (100) faces of silver single crystals

Adsorption of SO 42− on growth steps of (111) and (100) faces of silver single crystals

The effect of the growth-step density of electrolytically grown (111) and (100) faces of silver single crystals in diluted solutions of Na 2SO 4 was studied. A weak specific adsorption of SO 4 2− is found on the steps only. The charge of the ions adsorbed was estimated quantitatively. The enhanced adsorption on the steps has been discussed.

LEED, AES and thermal desorption study of iodine chemisorption on the silver (100), (111) and (110) faces

The chemisorption of iodine vapor on the three low index faces of silver single crystals has been studied by combined LEED, AES and thermal desorption mass spectrometry. By exposure to gaseous iodine, only a c(2 × 2) phase is found on Ag(100), while on Ag(111) and Ag(110) several structures are observed depending on the iodine coverage. On all the three faces, the saturation coverage is about the same. Further iodine uptake leads to the formation of a thin layer of epitactic silver iodide, which, upon heating, undergoes structural changes before desorption.

Leed, aes and thermal desorption study of iodine chemisorption on the silver (100), (111) and (110) faces

The chemisorption of iodine vapor on the three low index faces of silver single crystals has been studied by combined LEED, AES and thermal desorption mass spectrometry. By exposure to gaseous iodine, only a c(2×2) phase is found on Ag(100), while on Ag(111) and Ag(110) several structures are observed depending on the iodine coverage. On all the three faces, the saturation coverage is about the same. Further iodine uptake leads to the formation of a thin layer of epitactic silver iodide, which, upon heating, undergoes structural changes before desorption.

Electrical double layer on (111) and (100) faces of silver single crystals in solutions containing ClO−4 and F−

The differential capacitance-potential dependence C(E) of electrolytically grown (111) and (100) faces of silver single crystals in diluted solutions of NaClO4 and KF was studied. Comparison with results obtained in KF solutions shows a concentration-independent shift of Emin to more negative potentials and higher values of the reciprocal slope of the C−1 vs. Cd−1 plots. The data obtained have been explained as due to a weak specific adsorption of ClO4− which is stronger on the (100) face. The influence of water in the double layer on the adsorption has been discussed.

Electrical double layer on (111) and (100) faces of silver single crystals in solutions containing ClO 4− and F −

The differential capacitance-potential dependence C( E) of electrolytically grown (111) and (100) faces of silver single crystals in diluted solutions of NaClO 4 and KF was studied. Comparison with results obtained in KF solutions shows a concentration-independent shift of E min to more negative potentials and higher values of the reciprocal slope of the C −1 vs. C d −1 plots. The data obtained have been explained as due to a weak specific adsorption of ClO 4 − which is stronger on the (100) face. The influence of water in the double layer on the adsorption has been discussed.

Sulfur overlayers on the low-index faces of silver

The two-dimensional phases formed by sulfur on the (100), (111) and (110) faces of silver single crystals were studied by standard LEED-Auger techniques. On each face, different structures were observed depending on the coverage and the temperature. Most of the phases showed complex LEED diagrams. A remarkable similarity, however, was found among the structures of the phases observed at maximum coverage on the three faces. For these phases, tentative structural models are suggested and discussed.