Ag Peak Research Articles

Effect of Polyethylenimine on the Selectivity of Determining Silver(I) by Stripping Voltammetry in the Presence of Copper(II)

It has been proposed that a water-soluble complexing polymer, polyethylenimine (PEI), be used to lower intermetallic interactions at the surface of solid electrodes in the determination of Ag(I) by stripping voltammetry in the presence of Cu(II). The introduction of PEI in the binary Ag(I)–Cu(II) system weakened the effect of Cu(II) on the anodic peak of Ag(I) and enhanced the selectivity in determining Ag(I) in the presence of excess amounts of Cu(II). With the use of PEI, Ag(I) can be determined at a Cu(II)-to-Ag(I) concentration ratio of 1000 : 1, compared to that of 20 : 1 in the absence of the polymer.

Electrochemical lithiation of the ternary silver sulfide Ag 4Hf 3S 8

Electrochemical lithiation of cubic Ag 4Hf 3S 8 that possesses both a two-dimensional (2D) array and a 3D channel of octahedral metal vacancy sites has been studied using an organic electrolyte lithium ion cell, Li/1 M LiPF 6 in propylene carbonate/Ag 4Hf 3S 8, under low constant current discharge conditions. Lithiation processes are discussed on the basis of proposed models originating from the inherent structural nature of Ag 4Hf 3S 8. The X-ray powder diffraction (XRD) lines for the lithiated phase shifted to slightly higher angles than those of Ag 4Hf 3S 8, and native Ag peaks were found in the XRD pattern, indicating that the intercalation of a certain amount of Li + induced reduction of Ag + and subsequent removal of Ag atoms from the host. The intercalated Li + became the building constituent instead of the original Ag +, which led to a structural reformation of the host material. The lattice constant of the lithiated phase, Li x Ag y Hf 3S 8 ( x+ y≤7, y≅0), was shortened by about 0.5 Å in comparison with that of Ag 4Hf 3S 8. It was ascertained from Rietveld analyses of XRD patterns at several discharge steps that the structures of lithiated phases could be solved without changing the original space group of Ag 4Hf 3S 8 and that electrochemical lithiation of Ag 4Hf 3S 8 proceeded topochemically conserving the Hf 3S 8 framework structure. The cell showed a long plateau at around 2.2–2.0 V up to the incorporation of about 3 mol Li +.

Moisture degradation mechanism of silver-based low-emissivity coatings

Moisture deterioration of low-emissivity (Low-E) coatings with layer structures of oxide/silver/oxide/glass, oxide/silver/glass, silver/oxide/glass, and silver/glass were investigated. All the films were formed by r.f. magnetron sputtering. Zinc oxide (ZnO) and tin oxide (SnO2) films were used as oxide layers. The coatings were analyzed using X-ray diffraction (XRD) and scanning electron microscopy (SEM). The storage for 144h at 50°C, 95% relative humidity was adopted as a moisture test. Only the silver film formed on the ZnO underlayer showed a crystalline state of the Ag(111) peak before the moisture test. The coating with the crystalline silver layer was more stable against moisture, however the moisture test generated silver migration partly, so that shallow dimples were formed. On the other hand, the coating with an amorphous silver layer was less stable, and the moisture test changed its structure into the crystalline form and brought about strong silver agglomeration. Judging from these results, it was concluded that the silver migration induced by moisture triggered a reduction of the ZnO–Ag interfacial adhesive force and caused the moisture-induced deterioration (the peeling of the top oxide layer).

Polypyrrole Films Doped with an Electroactive Sulfonated Chelating Reagent: Electrochemical Characterization and the Detection of Metal Ions

Polypyrrole films doped with the electroactive chelating reagent 3-(2-pyridyl)-5,6-diphenyl-4,4′-disulfonate-1,2,4-triazine (PDTDS2–) were prepared and characterized. The electroactive azo bond in PDTDS2– was detected in the polymer film by cyclic voltammetry. The ratio of pyrrole to PDTDS2– in the films (as evaluated from azo reduction and polymer growth charges) was 11.7:1 (s =2.03, n=38), quite close to the expected ratio of 8:1 for a doubly charged anion-doped film. The azo bond electrochemistry in the polypyrrole exhibited Nernstian pH behavior (ΔEf/Δ pH=–54.7±1.3 mV dec–1). Copper detection by medium-exchange cyclic voltammetry at these films was examined and it was found that both reduction and stripping, oxidation responses were obtained but the latter was better as it was narrower and larger in magnitude. Thinner films gave better copper responses and detection of Cu2+ down to 1×10 –6 mol dm–3 was possible at films prepared with a growth charge of about 40 μC. Selectivity was evaluated in mixture experiments and a range of commonly occurring ions did not interfere in the Cu2+ electrochemical detection. The most severe interferents were mercury(II) and EDTA; new voltammetric peaks for Ag(I) and Hg(II) were observed.

Permanent iridium modifier deposited on tungsten and zirconium-treated platforms in electrothermal atomic absorption spectrometry: vaporization of bismuth, silver and tellurium

The stabilizing role of permanent iridium modifier deposited on tungsten-treated (WTP) and zirconium-treated (ZrTP) platforms of transversely heated graphite atomizer (THGA) was studied in detail by electrothermal atomic absorption spectrometry (ETAAS) and different surface techniques in model experiments for Ag, Bi and Te. The comparison of the stabilizing efficiency of permanent Ir modifier on WTP and ZrTP and each of the single components, reveals the better effect of Ir on WTP and Ir itself. The extent of analyte losses during pre-atomization and the strength of analyte association with the modifier were estimated by the plotting of `differential vaporization curves'. The existence of double peaks of Ag, Bi and Te in WTP and Ir on WTP was confirmed and possible reasons for their formation were discussed. The absorbance profiles presented as differential curves reveal an existence of at least two different types of precursors determining processes of atom generation. The observed differences in the behavior of Ir permanent modifier on WTP and ZrTP, respectively, were explained by the different extent of iridium–tungsten and iridium–zirconium interaction and surface distribution. XRF, ESCA and SEM studies reveal non-uniform distribution of the modifier on the graphite substrate and the presence of oxide containing species on the surface.

Characterization of Silver Binding in Cryptomelane by X-ray Absorption Spectroscopy

ABSTRACTUsing silver K-edge extended X-ray absorption fine structure (EXAFS) spectroscopy, two different samples of silver-containing manganese oxide were analyzed in the fluorescence mode. For the first sample, silver ions from solution were sorbed onto one synthetic manganese oxide phase, namely cryptomelane (KxMn8O16, where l<x<2). The second sample was a silvermanganese oxide from Colorado. From the EXAFS analysis, silver was found to occupy two different sites in the synthetic sample. The natural samples from Colorado also exhibited a very similar coordination distances as the synthetic samples. In the low temperature spectrum of the synthetic sample at 10 K, the Ag-O peak was found to be missing and the amplitude of the Ag- Ag peak was approximately three times larger than the corresponding room temperature sample.

Transient photoinduced absorption of one-dimensional excitons and biexcitons during lattice relaxation

Transient photoinduced absorption spectra of one-dimensional excitons and biexcitons coupled with lattice vibrations are calculated with a two-band model by molecular dynamics. It is shown that the absorption peaks corresponding to the transition from photoexcited Bu excitons to Ag excitons and the lowest biexciton shift as self-trapping proceeds, where the former shifts to higher energy and the latter to lower energy. This difference is understood by means of the relaxation energy of Bu, Ag excitons and the biexciton. The transient absorbance change near the Bu to Ag peak is also discussed.

Metal overlayers on organic functional groups of self-organized molecular assemblies. V. Ion scattering spectroscopy and x-ray photoelectron spectroscopy of Ag/COOH interfaces

In the present work, x-ray photoelectron spectroscopy (XPS) and ion scattering spectroscopy (ISS) were used to characterize mercaptoundecanoic acid [MUA, HS(CH2)10 COOH] and mercaptohexadecanoic acid [MHA, HS(CH2)15COOH] self-assembled monolayers (SAMs) before and after depositing up to 1.0 nm Ag at ∼10−7 Torr. Results from XPS O 1s, Ag 3d, and C 1s spectra do not indicate that a complex is formed (no chemical shifts) between Ag and the COOH of MUA or MHA at 295 K. Although no direct evidence for Ag/COOH interactions is evident, the initial value for ISS Ag peak intensities for 1.0 nm of Ag on COOH of MHA is unchanged after 1 h and is only reduced to 68% of the initial value after 15 h. For MUA, the ISS Ag peak intensity for 1.0 nm is constant for about 5 min and is gradually reduced until it is not detectable about 90 min after Ag deposition. These results and those we obtained earlier for Ag on octadecanethiol [ODT, HS(CH2)17CH3] might be explained by weak or no interactions between Ag and COOH and by different defect densities in the SAMs. The initial Ag ISS peak intensity for 1.0 nm Ag on MHA increases from 295 K as the SAM temperature is reduced to reach a maximum at about 200 K. The increased ISS intensity from Ag/COOH vs Ag/CH3 is consistent with lower defect densities in the MHA vs ODT.

Metal overlayers on self-organized molecular assemblies. IV. Ion scattering spectroscopy of the Ag/CH3 interface

Ion scattering spectroscopy (ISS) of vacuum deposited Ag on octadecanethiol (ODT, HS(CH2)17CH3) organized molecular assemblies (OMAs) provides a means of studying interfacial structure at metal/organic interfaces under controlled conditions. The OMAs were self-assembled onto gold films on silicon 〈100〉 substrates. ISS compositional depth profiles of the Ag/CH3 interface were performed at a number of temperatures between 113 and 293 K. Results from these experiments show clearly that Ag penetrates rapidly through ODT above ∼200 K. The changes in ISS Ag peak intensities as a function of time and temperature provide evidence for the formation of Ag clusters at the ODT/Au interface after penetration of Ag. Changes in deposition rate between 0.003 and 0.015 nm/s yielded little difference in corresponding ISS depth profiles. Over a range of ion beam current densities from 0.06 to 2.0 μA/cm2, scaled compositional depth profiles were found to be comparable within experimental error.

Agglomeration of submonolayer Ag films on Si(111) induced by the interaction with atomic hydrogen

We have used Auger electron spectroscopy to characterize the agglomeration of Ag layers with coverages of 0.2 to 1.2 ML induced by the interaction with atomic hydrogen. Originally uniform Ag films agglomerate during the interaction with atomic hydrogen to form Ag islands. The model calculations of Ag and Si Auger peak intensities after complete Ag agglomeration have been performed for the case of island growth. Our results have shown that the height of Ag islands increases with the increase of the original Ag coverage, while the total area covered by Ag islands is constant and independent of the original Ag coverage.

An investigation of molecular beam epitaxy “in-situ” grown Ag/GaAs schottky diodes

Electrical properties of molecular beam epitaxy “in-situ” grown Ag on (001) GaAs Schottky diodes were investigated. X-ray rocking curves show a (111) main peak for “in-situ” Ag grown at low temperature. During annealing, the main peak of Ag rotates from (111) to (200) to closely match that of the underlying GaAs lattice. The barrier height, 0.991 eV (determined by C-V measurement), decreases whereas doping concentration increases with increasing annealing temperature. Interdiffusion and the formation of some compound phases were also observed during annealing. A simple model, in which Ga dissociates from GaAs resulting in an increase in uncompensated ions at the metal-semiconductor interface, is proposed to explain the observation that carrier concentrations increase after annealing.

Spectrometer corrections for a retarding field analyser used for elastic peak electron spectroscopy and auger electron spectroscopy

Elastic peak electron spectroscopy using a retarding field analyser (RFA) proved to be an efficient tool for several applications. The advantage of RFA lies in its simultaneous LEED-AES application, in its large aperture averaging angular effects and in the possibility of surface analysis with the elastic peak. The difficulty of the RFA is its poor energy resolution integrating also the background adjacent to the peak observed (elastic or Auger peak) and producing peak distortion. Spectrometer correction was made by determining the spectral distribution function of the RFA energy window, using an approach of sum of Gaussians. Parameters of the Gaussian functions have been determined by decomposition of elastic peak spectra measured with an RFA Riber OPR-304 on Ag. Ag and Au elastic peaks at 1 and 2 keV energy were compared with highly resolved spectra obtained with a hemispherical analyser. Calculated elastic peak spectra exhibited reasonable agreement with experimental data obtained with the RFA spectrometer.

Structural, magnetic and electronic properties of non-equilibrium FeAg alloys

Wide concentration ranges of disordered bcc or fcc FeAg alloys have been produced by sputter-deposition. They are ferromagnetic at low temperatures. The average hyperfine field and the magnetic moment of Fe atoms are larger than those of pure Fe, because the substitution of Fe by Ag with a larger atomic size expands the atomic volume of Fe and enhances the spin polarization. In fcc FeAg alloys, the quadrupole splitting analysis of Mössbauer spectra indicates no remarkable segregation in the as-sputtered state, while it shows a continuous growth of fcc Fe clusters by aging and a phase transformation to bcc by annealing above 520 K. X-ray photoemission spectroscopy studies of these alloys reveal individual Fe and Ag peaks. The concentration dependence of peak intensities and peak positions indicate that Fe and Ag electronically intermix.

Simultaneous quantitation of seven elements by an X-ray fluorescence system for the microsphere method

An automated X-ray fluorescence system with a low Compton background was designed utilizing a metal filter, electronic devices, polarized X-rays for element excitation, a Si(Li) detector, and a commercially available X-ray tube. Rb, Mo, Ag, I, La, and Gd were tested in order to select a single optimal filter. A low Compton background and a high count rate over a wide spectral range were obtained with a filter optimized for Ag. Regions of interest were chosen for K alpha peaks of Zr, Mo, Rh, Ag, Sn, I, and Ba. The net K alpha peak areas were computed by subtracting the K beta counts from the total net counts in the regions of interest. An excellent linear relation was obtained between the computed K alpha net counts and their concentrations. The net count rates (c.p.m./p.p.m.) were 29.34 (Zr), 46.56 (Mo), 69.78 (Rh), 81.60 (Ag), 77.75 (Sn), 70.30 (I) and 74.13 (Ba). It is concluded that all seven elements can be used for nonradioactive microspheres with satisfactory counting statistics for simultaneous measurements of regional blood flows.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Capture of Ag atoms in defects produced by low-energy Ar + ion bombardment on the Si(111) surface

By means of LEED and Na +-ISS, we have studied the behaviour of 2/3 ML Ag atoms deposited on Si(111) surface bombarded by a 1 keV Ar + ion beam. With the Ar ion doses ranging from 1.0x10 15 to 3x10 15 ions/cm 2, we observed on the surface a definite decrease in the Ag single scattering peak intensity as the substrate temperature increased. The Ag peak intensity minimum was seen at about 400°C. Further increase of the substrate temperature led to the recovery of the Ag peak intensity. The Ag peak intensity maximum appeared at temperatures around 580°C. In the temperature region between 450 and 580°C corresponding to the above recovery of the Ag peak intensity, the 3 × 3 LEED pattern was observed. After comparison with the behaviour for the non-dosed surface, the above observation was attributed to the capture of Ag atoms in defects induced by the Ar + ion bombardment.

Electrochemical behaviour of tellurium and silver telluride at rotating glassy carbon electrode

Electrodeposition of tellurium and silver is performed at rotating glassy carbon disc electrodes. First the mechanism of deposition of tellurium is investigated, and a well defined wave may be observed close to − 0.4 V/ sce. On the plateau of this wave a small peak may be noticed at − 0.7 V/ sce, and is due to reduction of Te(0) into Te(—II), but a chemical reaction occurs simultaneously between Te(—II) and Te(IV), reaching the electrode by convection and diffusion, to lead again to Te(0), and consequently the thickness of the deposit increases. Conversely, with a non-rotating electrode, the Te(IV) species reach electrode only by diffusion and in lesser amounts than in the above case; so the peak at − 0.7 V/ sce is large since the tellurium deposit dissolves by reduction int Te(—II). The electrodeposition of silver telluride Ag 2 Te is investigated with several concentration ratio of Ag(I) and Te(IV). One may observe the progressive changes in the shape and magnitude of the oxidation peaks of Ag and Te. For a Ag(I)Te(IV) ratio close to 0.8 it has been observed that quasi pure Ag 2 Te is obtained. The elementary composition of the deposit was confirmed by X-ray analysis.

Proteolytic Cleavage of Human von Willebrand Factor Induced by Enzyme(s) Released From Polymorphonuclear Cells

In vivo fragmentation of the von Willebrand factor antigen (vWF:Ag) molecule has been demonstrated on radiocrossed immunoelectrophoresis (CIE) in the plasma from patients with disseminated intravascular coagulation, in factor VIII concentrates, and in normal serum. Experiments reported here show that polymorphonuclear (PMN) cells contain a non-calcium-dependent protease(s) that when released and incubated with vWF:Ag results in an additional vWF:Ag peak on radio-CIE. Production of fragments of vWF:Ag by incubation with PMN cells occurred in a time-dependent manner. The protease(s) responsible was inhibited by diisopropyl fluorophosphate, soybean trypsin inhibitor, and aprotinin, but not by benzamidine, azide, epicron, or hirudin. Citrate, EDTA, and leupeptin also had no effect on the PMN cell enzyme's activity, indicating that the enzyme(s) is not calcium dependent. The PMN cell enzyme responsible for vWF:Ag fragmentation is located intracellularly and released by freezethaw lysis or cell activation by calcium or the calcium ionophore A23187.

Proteolytic cleavage of human von Willebrand factor induced by enzyme(s) released from polymorphonuclear cells

In vivo fragmentation of the von Willebrand factor antigen (vWF:Ag) molecule has been demonstrated on radiocrossed immunoelectrophoresis (CIE) in the plasma from patients with disseminated intravascular coagulation, in factor VIII concentrates, and in normal serum. Experiments reported here show that polymorphonuclear (PMN) cells contain a non-calcium-dependent protease(s) that when released and incubated with vWF:Ag results in an additional vWF:Ag peak on radio- CIE. Production of fragments of vWF:Ag by incubation with PMN cells occurred in a time-dependent manner. The protease(s) responsible was inhibited by diisopropyl fluorophosphate, soybean trypsin inhibitor, and aprotinin, but not by benzamidine, azide, epicron, or hirudin. Citrate, EDTA, and leupeptin also had no effect on the PMN cell enzyme's activity, indicating that the enzyme(s) is not calcium dependent. The PMN cell enzyme responsible for vWF:Ag fragmentation is located intracellularly and released by freezethaw lysis or cell activation by calcium or the calcium ionophore A23187.

An electrochemical and ESCA study on the tarnishing of silver in solutions of different pS and pH values

The variation of the open circuit potential of Ag electrodes in solutions of varying pH values, and containing increasing concentrations of S 2-, is followed as a function of time until steady values, E st are reached. In all cases E st values are attained from positive potentials. The shift towards negative values depends on the ambient sulphide content, being more the higher the concentration. The E st—log[S 2-] plots are invariably S-shaped, denoting adsorption from solution. Before the inflexion linearity exists between E st and C s2-, and this is explained on the basis of a Gibbs' type adsorption model. Evidence is presented to support the conclusion that the adsorbed species at all pH values is the SH − ion. The variation of E st after inflexion follows the general relationship ▪ The relation indicates a 1ē electrode process, despite the fact that bulk Ag 2S forms quickly on the surface of the Ag electrodes. Galvanostatic reduction of the corrosion film formed on Ag electrodes in sulphidic solutions occurs in a single step corresponding to Ag 2S. Similarly, ESCA spectrograms of the films exhibit peaks for Ag and S. The sulphur 2 p peak shows two sublevels corresponding to S2 p 1 2 and S2 p 3 2 with a separation of 1.20 eV. The relative atomic concentrations of the Ag:S peaks is very near to 2:1, indicating that the film is formed of Ag 2S. The results of the present investigation strongly suggest that Ag 2S is formed chemically, consecutive to a 1ē electrode process. Ageing of the Ag/AgSH/Ag 2S electrode in sulphide-free solutions causes the electrode to respond theoretically to pS 2-, with a Nerstian slope of 0.029 V/log C unit.

Destruction of ristocetin cofactor by coagulation at 4°C

Ristocetin cofactor (VIIIR:RCo) and factor VIII-related antigen (VIIIR:Ag) were measured in anticoagulated and non-anticoagulated blood incubated at 4°C, room temperature (RT) or 37°C for 24 hours. A marked decrease in VIIIR:RCo, to almost undetectable levels, and a smaller decrease in VIIIR:Ag occurred when whole blood clotted at 4°C. These changes were slight 8r absent when blood clotted at RT or 37°C. VIIIR:RC8 lost at 4°C was not recoverable by further incubation at 37°C but the less-marked loss of VIIIR:Ag was partially recovered. In blood which had clotted at 4°C there was a change in the electrophoretic profile of VIIIR:Ag on crossed immunoelectrophoresis: there was more anodal migration of the VIIIR:Ag peak, consistent with a decrease in the mean molecular size. Further experiments showed that the decrease in VIIIR:RCo during coagulation at 4°C preceded the decrease in fibrinogen levels. In cell-free plasma VIIIR:RCo also decreased markedly when coagulation occurred at 4°C. The results show that loss of VIIIR:RCo occurs when blood is allowed to clot at 4°C: this is not due to cryoprecipitation and does not require the presence of blood cells. The data suggest that it is probably caused by plasma proteases activated early in the coagulation pathway.