Amorphous Ag Research Articles

Reflection mode X-ray absorption spectroscopy: new applications in surface science research

Reflection mode grazing incidence X-ray absorption spectroscopy (GIXAFS) was applied for the in situ investigation of solid/liquid interfaces. Results obtained during the active dissolution of metals are presented. In the case of silver in neutral or weakly acidic Na 2SO 4 solutions (pH 6.5), the formation of an Ag–O species at the surface of the Ag-electrode can be proven, i.e. the active dissolution proceeds via a non-protecting surface layer, the thickness of which was estimated to be about 5 nm. The atomic short-range order of this surface layer is different from polycrystalline silver oxides (Ag 2O and AgO) and relates to a more disordered or amorphous Ag 1+ oxide.

Surface-enhanced Raman scattering from ordered Ag nanocluster arrays

We have examined the effect of ordered silver nanocluster substrates on the surface-enhanced Raman spectrum of rhodamine 6G (R6G). Triangular shaped silver nanocluster arrays with order on the approximately 100 mum range were prepared using nanosphere lithography. Direct comparisons of R6G surface-enhanced Raman spectroscopy (SERS) signals between ordered nanocluster regions and amorphous Ag regions prepared under identical deposition conditions provide strong evidence of an electromagnetic field enhancement attributed to the unique nanocluster morphology. We have obtained order of magnitude enhancement factors for both 200 and 90 nm Ag nanocluster SERS substrates relative to Ag films.

AgAsS2 amorphous chalcogenide films prepared by pulsed laser deposition

A pulsed laser deposition technique has been applied to prepare amorphous ternary Ag–As–S films without an annealing process after the deposition. The films were prepared from AgAsS2 bulk glass using a KrF excimer laser. Energy-dispersive X-ray analysis and Rutherford backscattering were used to obtain the composition of the studied films. VASE ellipsometry has been used to determine optical properties and homogeneity of the index of refraction. Comparison of two models is presented.

The competing crystalline and amorphous solid solutions in the Ag–Cu system

Upon nonequilibrium processing using vapor quenching or mechanical alloying, the supersaturated fcc solid solution predominates over the amorphous solution in the Ag–Cu system. The thermodynamic and kinetic origins of this phase selection are explored. The enthalpy of formation of both solutions has been determined as a function of composition using calorimetry measurements and molecular dynamics (MD) simulations. The enthalpy of the fcc solution is found to be lower than that of the competing amorphous phase. The preference for the fcc crystalline state is enhanced by the low kinetic barrier to crystallization of the amorphous solution, which occurred during quenching even when high cooling rates were employed or during annealing at low temperatures. Consequently, the retention of an amorphous Ag–Cu solution required kinetic trapping using ultrahigh quenching rates achievable only under stringent vapor deposition conditions or in MD simulations. However, transmission electron microscopy revealed the presence of local regions of amorphous Ag–Cu after cold rolling of multilayers of elemental Ag and Cu foils at room temperature. This result of partial amorphization demonstrates the possibility of mechanically driven solid-state amorphization in a system with a positive heat of mixing.

Ag, Ge and Sn reference samples for elastic peak electron spectroscopy (EPES), used for experimental determination of the inelastic mean free path and the surface excitation parameter

Reference samples are needed for experimental determination of the inelastic mean free path (IMFP) of electrons by elastic peak electron spectroscopy (EPES). High-quality (microcrystalline mirror) Ni reference samples were used for IMFP measurements. For surface excitation parameter experiments, new types of reference samples are needed. They should exhibit pronounced surface-loss spectra, such as amorphous Ge (aGe), Sn and Ag. A new procedure is presented for their preparation. Microcrystalline Ag and Sn reference samples were deposited on highly polished (by Buehler alumina alpha micropolish 1C) brass (60% Cu, 40% Zn) substrates. Electrolytic deposition was used for Ag and for Sn and resulted in excellent surface quality. The average surface roughness γ av was checked by scanning tunnelling microscopy or atomic force microscopy before and after Ar + ion bombardment cleaning. Typical γ av values were 4-6 nm for Ag, 3-4 nm for Sn and 2-4 nm for brass substrate. The aGe sample was deposited by magnetron sputtering or by evaporation in a high vacuum on an Si substrate. Its γ av was 4-5 nm. The samples were studied by EPES/reflection electron energy-loss spectroscopy, covering the 0.2-5 keV energy range, with the ESA 31 HSA electron spectrometer. The IMFP of Sn was determined by EPES. The surface excitation parameters for the Si, Ge and Sn samples were determined from their inelastic scattering cross-section spectra. For Ag the surface excitation parameter was estimated by using the above reference samples.

Photoinduced anisotropy in the ion-conducting amorphous semiconductor Ag–As–S

Amorphous Ag–As–S films become birefringent and their surfaces are modified when exposed to linearly polarized light. The photoinduced birefringence is positive with a magnitude of +0.01, which is in contrast with that (−0.001) of As 2S 3 . The refractive index change appears with an anisotropic surface deformation, which consists of two kinds of patterns. One is fringes in an illuminated spot and the other is streaks as cat's whiskers radiating from the spot. Compositional measurements show that the fringe accompanies an Ag-content modification of ∼5 at.%. The photoinduced anisotropy in Ag–As–S films is assumed to be caused by photo-electro–ionic interaction.

In situ Raman scattering studies of the amorphous and crystalline Si nanoparticles

We report on in situ studies of the vibrational properties of Si nanoparticles and ultrathin layers grown by dc magnetron sputtering in ultrahigh vacuum on amorphous MgO and Ag buffer layers. The average thickness of the Si layers ranged from monolayer coverage up to 200 Å. Transmission electron microscopy has been used to determine size and shape of the Si nanoparticles. Changes in the phonon spectra of Si nanoparticles during the crystallization process have been studied by interference enhanced Raman scattering technique. Marked size-dependences in the phonon density of states and the relaxation of the k-vector conservation with decrease in size of the Si nanoparticles have been detected. The transition between crystalline- and amorphous-like behavior takes place in the particles with an average number of Si atoms equal to (7±2)×10 2.

Disproportionation of Ag(II) to Ag(I) and Ag(III) in Fluoride Systems and Syntheses and Structures of (AgF+)2AgF4-MF6- Salts (M = As, Sb, Pt, Au, Ru)

Interaction of Ag(+) salts in anhydrous liquid hydrogen fluoride, aHF, with AgF(4)(-) salts gives amorphous red-brown diamagnetic Ag(I)Ag(III)F(4), which transforms exothermally to brown, paramagnetic, microcrystalline Ag(II)F(2) below 0 degrees C. Ag(I)Au(III)F(4) prepared from Ag(+) and AuF(4)(-) in aHF has a tetragonal unit cell and a KBrF(4) type lattice, with a = 5.788(1) Å, c = 10.806(2) Å, and Z = 4. Blue-green Ag(II)FAsF(6) disproportionates in aHF (in the absence of F(-) acceptors) to colorless Ag(I)AsF(6) and a black pseudotrifluoride, (Ag(II)F(+))(2)Ag(III)F(4)(-)AsF(6)(-). The latter and other (AgF)(2)AgF(4)MF(6) salts are also generated by oxidation of AgF(2) or AgF(+) salts in aHF with F(2) or in solutions of O(2)(+)MF(6)(-) salts (M = As, Sb, Pt, Au, Ru). Single crystals of (AgF)(2)AgF(4)AsF(6) were grown from an AgFAsF(6)/AsF(5) solution in aHF standing over AgF(2) or AgFBF(4), with F(2) as the oxidant. They are monoclinic, P2/c, at 20 degrees C, with a = 5.6045(6) Å, b = 5.2567(6) Å, c = 7.8061(8) Å, beta = 96.594(9) degrees, and Z = 1. The structure consists of (AgF)(n)()(n)()(+) chains (F-Ag-F = 180 degrees, Ag-F-Ag = 153.9(11) degrees, Ag-F = 2.003(4) Å), parallel to c, that enclose stacks of alternating AgF(4)(-) and AsF(6)(-), each anion making bridging contact with four Ag(II) cations of the four surrounding chains "caging" them. There is no registry between the ordered array in one "cage" and that in any neighboring "cage". The F-ligand anion bridges between the anions and, with the Ag(II) of the chains, generates a trifluoride-like structure. (AgF)(2)AgF(4)AsF(6) [like other (AgF)(n)()(n)()(+) salts] is a temperature-independent paramagnet except for a Curie "tail" below 50 K.

Bimetallic aggregates at surfaces: spectromicroscopy study of Pt–Ag interaction on graphite

The formation of bimetallic Pt/Ag alloy in an amorphous Ag film supported on highly oriented pyrolitic graphite has been investigated with scanning photoemission and scanning tunneling microscopy. This spatially resolved study reveals that alloying strongly depends on the morphology of the deposited metal. Whereas little metal intermixing is found in small Ag clusters (50 Å), efficient alloying is observed in much larger heterogeneous structures. Subsequent annealing results in a decrease of the exposed alloy component, due to segregation of the two metal species.

In Situ Studies of the Vibrational and Electronic Properties of Si Nanoparticles

AbstractWe report on in situ studies of the vibrational properties of ultra-thin Si layers grown by dc magnetron sputtering in ultrahigh vacuum on amorphous MgO and Ag buffer layers. The average thickness of the Si layers ranged from monolayer coverage up to 200 Å. The interference enhanced Raman scattering technique has been used to study changes in the phonon spectra of Si nanoparticles during the crystallization process. Marked size-dependencies in the phonon density of states of the Si quantum dots and the relaxation of the k-vector conservation condition with decrease in size of the Si nanoparticles have been detected. Electron energy loss spectra have been collected for amorphous and crystallized Si nanoparticles on SiO2 buffer layers and the difference in the onset of the electronic transitions have been found.

Optical, electrical, and structural properties of amorphous Ag–Ge–S and Ag–Ge–Se films and comparison of photoinduced and thermally induced phenomena of both systems

To understand the nature of Ag-rich chalcogenide glasses, the optical, electrical, and structural properties of evaporated amorphous (Ge0.3S0.7)100−xAgx and (Ge0.3Se0.7)100−yAgy films have been examined and compared with each other over a wide compositional range in Ag content. The maximum Ag content for the amorphous films was 67 at. % for the S-based system and 40 at. % for the Se-based system. The physical properties of both systems depended significantly on the Ag content but the compositional trends resembled each other. All the photoinduced and thermally induced phenomena observed for the S-based system were also observed for the Se-based system but with the compositional ranges shifted to lower Ag concentration: the photo- and thermal bleachings (0≤y<22 for the Se-based system, 0≤x<40 for the S-based system), the photoinduced surface deposition (PSD) of metallic Ag phenomenon, and the phase separation on annealing (25<y≤40, 50<x≤67). The Se-based system was found to exhibit the PSD phenomenon at low Ag concentrations where the S-based system never exhibits this effect.

Interaction of amorphous fluoropolymer with metal

The bonding structure of an amorphous fluoropolymer, AF 1600, with Al, Ag, Au, and Cu were examined using x-ray photoelectron spectroscopy. 100 Å thick films of AF 1600 were deposited on various metal films. AlF3 was found at the AF 1600/Al interface. F detached from the −CF3 functional group of the AF 1600, diffused into the Al/Al2O3 matrix and formed AlF3. The diffusion depth of F is estimated to be ≳150 Å. An Al film was evaporated onto an AF 1600 film. The Al film was then mechanically peeled off and the remaining polymer surface examined. AlF3 was again found. For the spin-on AF 1600 film on Ag, Au, and Cu, no chemical reaction between the metal and the polymer were found.

Ion-conducting amorphous semiconductor AgAsS

Optical, electrical and photoelectric properties of amorphous AgAsS have been studied. The material possesses an optical band-gap of 2 eV, while the electrical conductivity is governed by Ag+ ionic motion. Conventional photoconduction does not appear, but photovoltaic effects are detected. The material exhibits a photoinduced chemical modification phenomenon, which can be accounted for by assuming coupled ion-hole motions.

Structure and bonding in photodiffused amorphous Ag-GeSe2 thin films.

Grazing-incidence x-ray scattering (GIXS) techniques have been used to study the local and intermediate-range order in photodiffused amorphous Ag-${\mathrm{GeSe}}_{2}$ thin films and a variety of Ag-Ge-Se alloys. Using synchrotron-radiation sources, the GIXS technique can be used in conjunction with radial-distribution-function analysis, differential anomalous x-ray scattering, and differential distribution-function analysis to study the structure of very thin amorphous films. With these techniques, we have determined that the local atomic structure of Ag-${\mathrm{GeSe}}_{2}$ films satisfies a model where Se-Ag dative bonds are formed, one Se-Ag covalent bond is formed for each Ag atom added (below a critical composition), and Ge-Ge bonds are created as Ag is added. This last result significantly modifies the intermediate-range order in this system.

High energy ion beam induced Ag diffusion within amorphous Ag:GeSe2

High energy ion beam induced Ag diffusion within amorphous Ag:GeSe2

Study of the physical properties of an amorphous Ag FIC at low temperatures

An amorphous silver ion conductor 0.79(AgI)0.21(Ag 2O B 2O 3) has been prepared by quenching and been examined by DTA and XRDA. The a.c. conductivities of the material in the temperature range of 100–300K have been measured. The electronic conductivities are negligible in the temperature range investigated. Below 150K a deviation from the Arrhenius relation has been found. The thermoelectric power of the specimens has been measured at 100–300K and the Ag + transport heat has been calculated. The influence of magnetic field of 3000–10000 Gauses on the impedance and the thermoelectric power has been studied at 135–280K, but no effect has been detected.

Amorphous CuAg Films with High Stability

Films produced by quenching CuAg vapour onto cooled substrates at liquid nitrogen temperature are investigated using electron microscopy, electron diffraction, and electrical resistivity measurements. In the composition range from 30 to 70 at% Cu the as-quenched films are amorphous, and within the range of 35 to 63 at% Cu the amorphous phase is stable above room temperature with a maximum crystallization temperature Tc = 381 K at 47.5 at% Cu. Crystallization results in the formation of a supersaturated f.c.c. solid solution which decomposes in a second crystallization step. The effect of deposition rate, film thickness, temperature, and surface of the substrate, and most importantly of the composition on the transition temperatures is investigated. A comparative study of the formation of amorphous phases in a wide variety of Cu-based alloys is presented. Dunne Schichten werden durch Abschrecken eines CuAg-Dampfgemisches auf 77 K gekuhlte Substrate hergestellt und elektronenmikroskopisch und resistometrisch untersucht. Im Konzentrationsbereich von 30 bis 70 At% Cu kondensieren die Schichten amorph. Zwischen 35 und 63 At% Cu ist der amorphe Zustand oberhalb Raumtemperatur stabil (maximale Kristallisationstemperatur von 381 K bei 47,5 At% Cu). Bei der Kristallisation wird eine ubersattigte feste Losung mit kubisch flachenzentrierter Struktur gebildet. In einer weiteren Umwandlung entmischt sich die metastabile feste Losung. Der Einflus von Aufdampfgeschwindigkeit, Schichtdicke, Temperatur und Oberflache der Substrate und besonders der Konzentration auf die Umwandlungstemperaturen wird untersucht. In einer theoretischen Behandlung im Hinblick auf die Bildung amorpher Phasen wird das System CuAg mit anderen Cu-Legierungen verglichen.

Excitation of plasmons by fast electrons in thin amorphous and crystalline AgCu films

Excitation of plasmons by fast electrons in thin amorphous and crystalline AgCu films

A comparison between the structures of amorphous and liquid Ag–Cu and Cu–Mg alloys

Amorphous films of AgCu and CuMg2, approximately 3000 Å in thickness, were prepared by co-evaporation of Ag and Cu, and Cu and Mg, respectively, onto 25 μm thick Be sheets, held at liquid nitrogen temperature. Mo Kα X-rays were used as a radiation probe to determine the structure of the films, at room temperature, and of the liquid alloys of Cu with 50 at.% Ag and with 0 and 67 at.% Mg at 50°C above the liquidus temperature. With the transmission technique, the interference functions (or structure factors) I(K) were determined in the range of K = 4π sin θ/λ between 0.8 Å−1 and 12.5 Å−1, and then Fourier transformed to obtain the radial distribution functions (RDF). The I(K) and RDF of the amorphous AgCu and CuMg2 films were compared with those of the liquid Ag–Cu and Cu–Mg alloys, respectively. It was found that the structures of the amorphous and liquid Ag–Cu alloys were similar with a more well defined short-range order occurring in the solid alloys, whose I(K) exhibited the well known shoulder on the second peak. The I(K) and RDF of the amorphous CuMg2 and the liquid Cu–Mg alloys cannot be explained by a common structure, although I(K) showed a small premaximum below the first main peak in both the amorphous and liquid alloys, a feature observed in many liquid Mg alloys.