Monocrystalline Silver Research Articles

Effect of the crystal face orientation and alloying with gold on the properties of thin anodic films of Ag(I) oxide: I. Photocurrent

The anodic formation of nano-size anodic films of Ag(I) oxide on polycrystalline silver and Ag-Au alloys, as well as on low-index monocrystalline silver faces in 0.1 M KOH, is studied. Based on the data of photocurrent measurements, the n-kind of the oxide film conductivity is determined. Replacing the polycrystalline silver with monocrystals, as well as adding a small amount of gold atoms to its lattice (X[Au] <= 4 at. %), results in substantial structure ordering of the oxide due to the decrease in the deviation from the stoichiometric composition. The structure-dependent parameters of Ag(I) oxide (the optical absorption coefficient α, the concentration of donor defects ND, the width of the spatial charge region W, and the Debye screening length LD) are determined by the silver crystal face orientation, the gold content, and the film formation potential. At E = 0.52 V, the series of changes in these characteristics correlate with the series of reticular density. An increase in E breaks the series and increases the deviation of the composition from the stoichiometric Ag2O composition.

Preparation of amine coated silver nanoparticles using triethylenetetramine

This article presents a simple method towards the preparation of functionalized silver nanoparticles in a continuous medium. Silver nanoparticles were obtained through AgNO3 chemical reduction in ethanol and triethylenetetramine was used to stabilize and functionalize the metal. The product was characterized with X-ray diffraction (XRD), Fourier-transformed infrared spectroscopy (FTIR), UV-visible spectroscopy, thermal gravimetric analysis (TGA) and transmission electron microscopy (TEM). Monocrystalline silver particles with cubic structure and an average size of 20 nm were obtained. The results reveal that it is possible to synthesize Ag nanoparticles functionalized with amine groups and that particle size is influenced by the processing route.

ANODIC formation of thin Cu(I) and Ag(I) oxide films on Cu‐Au and Ag—Au alloys

AbstractThe anodic dissolution of Cu, Ag and their alloys with gold under the conditions of the formation of copper or silver oxides was examined by the technique of cyclic voltammetry, chronoammetry and photopotential measurements. The anodic formation and cathodic reduction of Cu(I) oxide on copper and Cu‐Au alloys or Ag(I) oxide on silver and Ag‐Au alloys with XAu≤30 at.% are controlled by migration in the oxide film. The peculiarity of Ag‐Au system is connected with the duplex structure of the oxide film and the initial selective dissolution of silver from Ag15Au and Ag30Au alloys. Ag2O oxide is an n‐type semiconductor with an excess of silver atoms. Oxide layers formed on monocrystalline silver are more stoichiometric than the layer formed on polycrystalline Ag. Copyright © 2008 John Wiley &amp; Sons, Ltd.

Surface Plasmon Mediated Interference Phenomena in Low-Q Silver Nanowire Cavities

Optical excitation of surface plasmons in wet-chemically grown monocrystalline silver nanowires ( approximately 100 nm diameter and up to a few tens of micrometers length) is studied by broadband imaging spectroscopy. Surface plasmons excited by an incident light beam in the so-called Kretschmann-Raether configuration give optical interference phenomena in the spectral domain. These spectral oscillations are interpreted in terms of Fabry-Perot cavity modes for surface plasmons in silver nanowires and allow for a direct experimental determination of the surface plasmon group velocity and cavity losses.

Determining some structure-sensitive characteristics of nano-sized anodic Ag(I) oxide from photopotential spectroscopy

A relatively simple device involving a set of LEDs and a digital processing of the signal is developed for in situ photopotential and photocurrent spectroscopy of thin semiconductors including oxide films under conditions of discretely changed light wavelength. Decreases in the electrode potential and photopotential of Ag(I) oxide with time upon the anodic effect are shown to obey different kinetic regularities, namely, logarithmic and exponential respectively. Photopotential measurements revealed n-type conductivity in thin (6 to 22 nm) semiconductor Ag2O films potentiostatically formed on either poly or monocrystalline silver (111) with a band gap of 3.1 eV. The structural disordering of the oxide is minimum at a potential of 0.490 V, which corresponds to nearly a midpoint of the anodic peak shoulder of the voltammogram. The concentration of donor defects in an Ag2O film grown on a “smooth” polycrystalline silver is lower than that on an ultrafine-dispersed silver, but higher than on Ag(111) monocrystal. A linear dependence of the photoresponse on the light beam power is found, and the spectral dependence of the photopotential is discussed. The photopotential dependence on the film thickness, as well as crystalline and microstructural state of the silver surface means that the photoresponse is determined by the bulk rather than superficial electronic states, and the film thickness is smaller than the Debye shielding length.

Self-assembly mechanism of platelike silver mesocrystal

In this letter, two-dimensional monocrystalline silver mesocrystals with about 5–20μm in size and 70nm in thickness were, for the first time, large-scale synthesized within a facile and organic-free replacement reaction system. The growth process and mechanism of silver mesoscopic plates are discussed in detail. An oriented nucleation and self-assembly coarsening process were suggested to describe the formation of monocrystalline silver mesocrystals. The kinetically dominated route reported here can be extended to other metals to synthesize the mesoscopic morphology.

Thermal and electrical properties of crystalline silver bromide

Simultaneous measurements of the thermal conductivity, thermal diffusivity and heat capacity per unit volume of monocrystalline silver bromide (AgBr), using the Gustafsson probe, in the temperature range 77–350 K are reported. Both thermal conductivity and thermal diffusivity follow Eucken's law in the temperature region studied. The heat capacity at constant pressure (CP), determined from the volumetric heat capacity, agrees with the calculated value at room temperature. The ratio of the thermal conductivity (λ) of AgBr and AgCl calculated from the Leibfried–Schlömann formula is in excellent agreement with the ratio λ(AgBr)/λ(AgCl) measured experimentally. The dielectric constant and loss factor of crystalline AgBr are also reported as a function of frequency in the range 100 Hz–1 MHz at room temperature.

Adsorption of thiourea on monocrystalline silver electrodes in neutral solution

Impedance spectroscopy and radiometric method have been used in the study of thiourea (TU) adsorption on monocrystalline silver electrodes of basal indices: (1 1 1), (1 0 0) and (1 1 0) in neutral solution. The dependence of the surface concentration of TU on the electrode potential and on the bulk concentration was determined for each studied surface. From radiometric measurements it follows that adsorption of TU on silver electrodes takes place in the entire range of applied potentials. The process of adsorption is practically reversible with respect to the electrode potential (in the range of the double layer) and the bulk concentration of TU. Differential capacity of silver electrodes in 0.01 M NaClO 4 solution containing TU of concentrations from 10 −6 to 5 × 10 −4 M has been measured. The isotherms of TU adsorption, determined from the capacitance and radiometric measurements have been compared and the Gibbs energy of adsorption was calculated. The values of limiting surface concentration of adsorbed TU as well as the Gibbs energy of adsorption depend on the plane of Ag electrode and follow the sequence: Ag(1 1 1) > Ag(1 0 0) > Ag(1 1 0) which is in agreement with the surface density of Ag atoms.

Electronic effects in SERS by liquid water

AbstractBy exploiting the attenuated total reflection (ATR)–Otto configuration, surface‐enhanced Raman scattering of water at monocrystalline copper and silver electrodes in 0.1 M Na2SO4 was observed at cathodic electrode potentials with hydrogen evolution at a laser wavelength of 647.1 nm. The proposed enhancement model is based on the condition that the upshift of the Fermi level of the electrode and the absorption of one laser photon allow an electron of the electrode at the Fermi level to reach the lower level of the energy band of delocalized electrons in liquid water. The electron interaction with the water molecules in the first hydration shell of cations in the Helmholtz plane is so‐called impulse scattering, which is the short‐time, non‐resonant excursion to the anionic ground state of molecules known for a long time in low‐energy electron scattering from free molecules. Copyright © 2005 John Wiley &amp; Sons, Ltd.

Interaction of sulfate ions with monocrystalline silver electrodes

The phenomenon of sulfate ion adsorption on monocrystalline silver surfaces was investigated quantitatively. The adsoprtion of sulfate from 0.1 M HClO 4 was found reversible with respect to the potential and also to the bulk concentration of sulfate. The adsorption isotherms as well as the surface concentration/potential dependences were determined radiometrically. The surface concentration sequence was found to be Ag(111)2Ag(110) >Ag(100). The thermodynamic parameters of adsorption were calculated by fitting experimental data to virial, Frumkin and Henry adsorption models. The sequence of sulfate adsorption on three basal silver planes from 0.1 M NaClO 4 was found to be quite different to that from an acidic supporting electrolyte, in agreement with the sequence of zero-charge potentials for the silver surfaces investigated.

Texture Development and Anisotropic Photoelastic Properties in Rolled Silver Chloride

Experimental and theoretical studies have been carried out in order to relate elastic anisotropy to optical anisotropy by means of photoelasticity. The fundamentals of anisotropic photoelasticity have been described. Specimens of monocrystalline and polycrystalline silver chloride have been submitted to tensile stress and relative retardation and extinction angles observed in polarized monochromatic light to show conformity to the theories which quantitatively relate the state of stress and optical phenomena. Textures of cold-rolled as well as of recrystallized silver chloride specimens were determined with an X-ray goniometer. Texture determining parameters such as degree of rolling and recrystallisation time and temperature have been varied. Textures found in silver chloride after various processing have been characterized.

Temperature dependence of the carrier mobility in Ag2Se layers grown on NaCl and SiOx substrates

Electrical propertics of monocrystalline and polycrystalline silver selenide thin films have been investigated in the temperature range of −196 to +150°C. Epitaxial and randomly oriented Ag2Se layers have been grown by vacuum deposition on NaCl and SiOx substrates, respectively. Special attention was paid to changes of the “mobility” (n-type conductivity) with temperature including the polymorphic phase transformation region (from 100 to 140 °C). The measurements have been performed in both directions of the temperature variation and a difference was found in the temperature of the phase transformation (hysteresis) depending upon the heating or cooling down conditions. A typical mobility of about 1000 cm2/Vs was found at room temperature. Shape and differences in the slopes of the mobility variations have been discussed.

On the stability of thin epitaxial films

The deposition of thin epitaxial layers from the vapour phase is a subject of broad and current interest. The authors have recently become aware of a particularly simple epitaxial system, (copper deposited on monocrystalline silver), for which the misfit is large, and where the two f.c.c. metals are essentially immiscible at the temperature of deposition. It is the purpose of this contribution to estimate the strain energy densities involved in the coherent deposition of copper on silver, and to evaluate the effect of coherency strains on the vapour pressure of the deposited material. The structure of copper overlays evaporated at room temperature and a pressure of about 10/sup -7/ Pa on the (111) plane of silver was investigated recently by Tyliszczak, De Crescenzi and Hitchcock. Their results indicate that layer-by-layer epitaxial growth occurs during the deposition of the first few monolayers. The copper atomic spacing is commensurate with the silver substrate. During later deposition the silver surface is covered with copper islands. At later states, the copper spacing corresponds to that of bulk copper. The lattice parameter of copper is about 0.361 nm while that of silver is 0.408 nm. Clearly, the first few layers of epitaxial copper are severelymore » strained and Hitchcock, in private communication, notes that these initial layers tend to re-evaporate readily. The authors examine a simple thermodynamic model to predict the increase in equilibrium vapour pressure arising from the epitaxial strain. The extra energy associated with this strain is calculated using linear elastic theory, with its accompanying simplifications. The calculation indicates that epitaxial growth on (100) planes would minimize this strain energy, in contrast to deposition on (111), which maximizes it.« less

Frequency response analysis of the Ag/Ag+ system: a partially active electrode approach

The dc and ac polarization behaviour of the Ag/Ag+ system was studied theoretically and experimentally. The model proposed is based on bulk diffusion towards a partially active electrode surface. The experimental data obtained on stationary and rotated disc electrodes of polycrystalline and monocrystalline silver in 0.1 M AgNo3 + 1.0 M HClO4 solution are interpreted in terms of different model parameters characterizing the dc and ac behaviour of the system quantitatively. It is demonstrated that surface relaxation may give rise to an inductive part in the ac-impedance diagram.

The electrocatalytic influence of underpotential lead adsorbates on the reduction of nitrobenzene and nitrosobenzene on silver single crystal surfaces in methanolic solutions

The electrocatalytic influence of underpotential lead adsorbates on the reduction of nitrobenzene (φ-NO 2) and nitrosobenzene (φ-NO) on poly- and monocrystalline silver electrodes was studied in methanolic solutions. On the bare, silver substrates φ-NO 2 and φ-NO reduced to phenylhydroxylamine (φ-NHOH) in neutral solutions and to anilin (φ-NH 2) in acid solutions. The underpotential deposition of lead on the silver substrates caused a partial inhibition of the φ-NO 2 and φ-NO reduction processes in acid solutions. The reduction of the intermediate φ-NHOH to φ-NH 2 was entirely inhibited by a complete coverage of the lead adsorbate. In the presence of Cl − ions in the electrolyte a pseudo-catalytic effect was found which is interpreted in terms of a competitive adsorption—desorption mechanism involving a replacement of specifically adsorbed chloride by the preferential adsorption of lead.

The influence of crystal orientation on the electron energy loss spectrum of monocrystalline silver films

In electron energy loss measurements (50 keV) on monocrystalline silver films in transmission the intensity of the 3.8 eV volume plasma loss is found to be dependent on the crystal orientation. If the crystal is tilted relatively to the electron beam by an angle α the elastic intensity I el in the primary direction oscillates by 10%, the intensity of the volume plasmon however varies much stronger similar to I el ; it can become even zero at certain angles α. The intensity of the surface loss is nearly proportional to the elastic intensity. An explanation of this phenomenon is missing. Presumably it must lie in the dynamic theory of electron diffraction.

Surface segregation: Comparison between theory and experiment

A theoretical description of the exchange of impurity atoms between the surface and the bulk is presented, with the assumption that desorption can be neglected. The analysis shows that the segregation isotherm — i.e. the relationship between surface coverage and volume concentration at thermodynamic equilibrium — can be readily deduced from the time dependence of surface coverage under out of equilibrium conditions. The desorption can be included in this description (in our case, we assume first order desorption). The dissolution of radioactive sulphur in monocrystalline silver was measured by AES. From the results the diffusion coefficient is derived. The segregation isotherm obtained is in good agreement with previous results of Bénard et al. The advantages of this method are outlined.

Sputtering experiments with silver single crystals and the channeling phenomena

Abstract Sputtering yields of monocrystalline silver under irradiation with 7-30 keV Ar+, Kr+ and Xe+ ions, not reported earlier, have been determined. The yield has been found to depend strongly on the orientation of the crystal and mass of the impinging ion. Onderdelinden's model based on Lindhard's theory of Channeling is found to describe satisfactorily, the observed orientation and ion-mass dependence of the yields for the ions of energy ∼10 keV or above. The role of the barrier potential approximated in the model in predicting the experimental results is discussed.

The coherent excitation of atoms moving through a crystal experimental results

Experimental results concerning to discovery of coherent Coulomb excitation for the He+ ions passing through monocrystalline silver film are reported.

Low temperature diffusion of cobalt and cadmium in silver

The diffusion of 109Cd and 60Co in monocrystalline silver was investigated over a temperature range from about 375 to 650°C using a chemical film sectioning technique. Penetration depths studied were limited to a region that has previously exhibited unusually steep penetration profiles for high temperature diffusion of 60Co in Ag. This anomalous behavior or “near-surface effect” is characterized by abnormally low diffusivities for penetration depths up to several microns from the surface. For both of the isotope tracers, a near-surface effect was observed at the higher temperatures of the range. However, the diffusivities measured at the lower temperatures were in agreement with extrapolations of hightemperature lattice diffusion data in the literature. An apparent transition in diffusion mechanism was noted from plots of the logarithm of the diffusivity vs. the reciprocal of the absolute temperature. The transitional behavior is described in terms of oxidation kinetics. A possible mechanism for the near surface effect, that has an activation energy and pre-exponential factor corresponding to that observed in the transition is discussed in detail.