Polycrystalline Silver Foils Research Articles

Size Effect in Silver Oxidation By Nitrogen Dioxide

X-ray photoelectron spectroscopy is applied to study at room temperature and pressure of 10–5 Torr the interaction of NO2 with a model sample obtained by thermal deposition of silver on the graphite surface. Scanning tunneling microscopy shows that in this case, silver particles with a size of D = 4–11 nm are formed on the surface. For comparison, polycrystalline silver foil is studied under similar conditions. It is found that such a treatment leads to silver oxidation in the Ag/C sample while the foil remains unchanged under these conditions.

Chemical Reaction of Polar Phthalocyanines on Silver: Chloroaluminum Phthalocyanine and Fluoroaluminum Phthalocyanine

Interface properties of chloroaluminum(III) phthalocyanine (AlClPc) and fluoroaluminum(III) phthalocyanine (AlFPc) on different silver surfaces have been studied using X-ray and ultraviolet photoemission spectroscopy (XPS and UPS) and X-ray absorption spectroscopy (XAS). Both polycrystalline silver foil and silver single crystals were used as a substrate. In all cases a chemical reaction was detected by XPS, visible as additional species in chlorine or fluorine core level spectra. However, UPS spectra show additional intensity in vicinity of the Fermi edge only for monolayer coverages of AlClPc and AlFPc on silver foil. Possible scenarios for the different interaction on polycrystalline and single-crystalline silver surfaces are discussed. The roughness of the substrate may influence the strength of the interaction significantly.

Energy level alignment and interface states at α-sexithiophene/Ag interfaces

We present a combined X-ray and ultraviolet photoemission study of the interface between the thiophene based organic semiconductor α-sexithiophene (6T) and silver. Thermally evaporated organic films were deposited in several steps without breaking the vacuum on polycrystalline silver foils. Subsequently, the films were characterized via photoemission spectroscopy. These series of spectra allowed the determination of the energy level alignment at the interface. Our results provide evidence that chemical interaction takes place between flat lying α-6T molecules and the silver surface resulting in interface electronic levels. From the observed well defined molecular orbitals we have analyzed the energy level alignment and have found an interface dipole of −0.7 eV and a hole injection barrier of about 1.8 eV.

Role of phosphates in the promotion of silver catalysts for partial oxidation: I. Structure and properties of phosphates on the surface of polycrystalline silver

The chemical composition, structure, and properties of an H3PO4-promoted polycrystalline silver foil are studied by XPS. The surface of the doped sample contains oxygen in two states with binding energies of 531.1 and 533.0 eV. Heat treatment results in silver clusters distributed in the polyphosphate matrix. It follows from TDS data that the surface of the promoted catalyst contains a strongly bound oxygen species that desorbs at ~900 K. It is believed that the silver clusters stabilized by the phosphate matrix are active sites on the surface of the phosphorus-promoted catalyst.

Oxidation of a polycrystalline silver foil by reaction with ozone

The surface oxidation of a polycrystalline silver foil by reaction with ozone (5 mol% O 3 in O 2) at 300 K and ambient pressure was investigated. The morphology, microstructure and chemical composition of the oxide scale which developed on the foil surface during exposure to ozone was characterised by scanning electron microscopy (SEM), powder X-ray diffraction (XRD), Raman spectroscopy and X-ray photoelectron spectroscopy (XPS). The surface of silver foil was rapidly oxidised upon contact with ozone, initially producing a thick Ag 2O protective film. After 10 min reaction, the oxide film thickness was around 8–10 μm. SEM analysis revealed that Ag 2O film thickening occurred via a discontinuous film growth mechanism. Growth stresses, resulting from the large lattice volume mismatch between the oxide and the metal, caused the oxide film to crack and flake extensively during development. Spallation of the oxide film exposed fresh silver metal to ozone, which lead to further Ag 2O deposition. The continued recurrence of this process resulted in the formation a thick, discontinuous Ag 2O film on the silver foil. After foil exposure to ozone for 300 min, the oxide film thickness was 17–20 μm. Furthermore, Ag 2O at the surface of the oxide film was slowly oxidised to AgO with prolonged exposure to ozone. The combined results of our experimental studies were used to develop a better understanding of the oxidation of silver surfaces by O 3.

Antiferromagnetic ordering in silver at picokelvin temperatures

Silver nuclei form an antiferromagnetic spin system in which the conduction-electron-mediated indirect Ruderman-Kittel exchange interaction dominates over the nuclear dipolar forces. We have studied magnetic ordering by measuring the dynamic susceptibility of polycrystalline silver foils down to about 0.5 nK ( S > 0.4 R In2) using SQUID-NMR techniques. We obtain T c=(560±60) pK for the transition temperature at B = 0 and B c = 100 μT for the critical field extrapolated to T = 0.

Variation of the morphology of silver surfaces by thermal and catalytic etching

The structural and morphological variations of the surfaces of polycrystalline silver foils upon heating in ultra-high vacuum (UHV) or in reacting gases related to methanol oxidation have been investigated using scanning electron microscopy (SEM) and reflection high-energy electron diffraction (RHEED). Thermal etching under UHV conditions with and without net evaporation of silver atoms results in two distinct restructural features: the formation of surface hill-and-valley structures including low-index faces, and the preferential development of (012) facets. In the presence of an oxygen atmosphere, as well as for conditions of methanol oxidation, a strong surface facetting occurs, depending on the composition and temperature. Flat facets, terrace-and-step structures, pits, as well as combinations thereof, may be formed, and the underlying mechanisms are qualitatively discussed on the basis of the related chemical processes and thermodynamic principles.

Anisotropy in the electron momentum distribution of silver.

The electron momentum anisotropy of silver has been studied by measuring the directional Compton profiles of silver single crystals with use of the radiation from an annular $^{241}\mathrm{Am}$ source. Three different samples, cut along the (100), (110), and (111) planes, were used. The experimental anisotropy has been compared with the results of two recent calculations. The agreement is very good with the model based on the linear combination of Gaussian orbitals (LCGO) and slightly worse with the augmented-plane-wave model. The directional average has also been measured with use of polycrystalline silver foil; the agreement with the LCGO model is again within the experimental error. A comparison with a previous experiment on polycrystalline silver is also done.

Metal-carbon stretching vibrations for CO on silver

Vibration bands for CO adsorbed on a polycrystalline silver foil have been seen in both the 2000 cm −1 region and the 400 cm −1 region with a RAIRS measurement using a commercial grating infrared spectrometer. The AgC stretching vibration band at 430 cm −1 results from an adsorbed CO molecule that desorbs between 200 and 300 K and has a CO stretching vibration band at 2060 cm −1. The integrated absorption coefficient of the AgC stretching band is about 0.03 of that of the CO stretching band.

On the adsorption of oxygen and potassium hydroxide on silver

Oxygen has been adsorbed on a polycrystalline silver foil at 0.1 MPa pressure and at temperatures between 290 and 870 K. The sample was transferred into an ultrahigh vacuum chamber and analyzed by X-ray photoelectron spectroscopy (XPS). The surface was covered by at most one monolayer of dissociatively adsorbed oxygen characterized by an O 1s binding energy of 529.9 eV. The same silver foil has also been impregnated with a highly hydrated layer of KOH. This layer was subsequently calcined in a stream of oxygen gas at 0.1 MPa and at 570 K. The resulting surface phase showed a K 2p 3 2 signal at 293.0 eV and a broad O 1s signal which was composed of at least two peaks at about 531 and 529.6 eV. The peak areas gave constant element K:O ratios of 1 : 2 up to 770 K. These XPS results were interpreted by a mixed oxyhydroxide phase containing K and Ag.

The physical and chemical characterization of electrochemically reformed silver surfaces

The effects of electrochemically oxidizing and reducing polycrystalline silver foils in aqueous chloride solutions are studied from a physical and chemical standpoint. Scanning electron microscopy indicates that the resulting surface is rough, consisting of nodular formations. Auger electron spectroscopic, secondary ion mass spectrometric and electrochemical results provide clear indication that a highly purified layer of metallic silver of increased surface area and activity is produced by the electrochemical reformation process. No evidence is found for the retention of intense Raman scatterers such as pyridine at these surfaces under ultrahigh vacuum conditions. The implications of the chemical and physical state of the reformed silver foils are discussed in the context of theories which have been proposed to explain the anomalously intense Raman spectra of scatterers adsorbed from solution onto these reformed silver surfaces. The origin of the 240 cm −1 Raman line commonly observed on electrochemically reformed silver is discussed and assigned to the Ag−Cl − stretching mode.

Temperaturabhängigkeit des Streuuntergrundes im Elektroneninterferenzdiagramm polykristalliner Silberschichten

The filtered and unfiltered intensities of electrons (30 to 50 kev) scattered in thin polycrystalline silver foils (300 to 1400 A) were measured by means of a retarding field apparatus in the temperature range from 170 to 380 °K. Further the absorption coefficients due to the inelastic and the different elastic scattering processes were determined.