Diffusion Of Silver Research Articles

Electron beam effects in Ge–Se thin films and resistance change memory devices

Chalcogenide glasses are the advanced materials of choice for the emerging nanoionic memory devices – conductive bridge random access memory (CBRAM). To understand the nature of the effects occurring in these devices under influence of electron-beam radiation, the interaction of blanked chalcogenide films and nanostructured films containing chalcogenide glass and silver (Ag) source are studied. Raman spectroscopy, energy-dispersive X-ray spectroscopy and X-ray diffraction are used for establishing the structural and compositional effects occurring under radiation. They have strong compositional dependence with the stoichiometric compositions being most stable showing less structural changes after radiation. These effects are associated with the availability of lone-pair electrons, their participation in the bonding configurations and the coupling of electron states in the bandgap. They are further enhanced in the bilayers by silver diffusion in the chalcogenide matrix, as a result of interaction with electrons. These effects are used to interpret the electrical performance of CBRAM devices after radiation. The devices are characterized by their resistance states, threshold voltage and endurance. Those based on selenium-rich and stoichiometric composition undergo continuous parameters changes with increase in the radiation dose while in the devices based on germanium-rich composition a counter play of the structural changes and expulsion of silver occur.

Numerical Study on Silver Diffusion Joints of Coated Conductors by Finite-Element Method

Given the length limitations of commercial coated conductors, joint is very important for their practical applications. Silver diffusion joints are regarded to be promising in the superconducting applications without operation in persistent current mode. This paper presents a 3-D numerical model of silver diffusion joints. The current distributions in the contact layers and their effect on the joint resistance are systematically studied by varying silver layer thickness, length, and width of contact area. It is investigated that the width of the contact area has an inverse proportion to the simulated joint resistances in the range of 2-12 mm like a normal conductor. However, the relationship between the contact length and the simulated joint resistance has an evident deviation from the inverse proportion, because the current distribution in silver layers is highly nonuniform and gives rise to a smaller “silver usage ratio” when the contact length is longer. Based on the hypothesis that the sheet resistivity of ReBCO-Ag and Ag-Ag interfaces is uniformly distributed and is affected by the “silver usage ratio” to the same extent as the bulk resistance of the silver layers, the joint resistances derived from our model are in good agreement with the experimental results.

Ag diffusion in SiC high-energy grain boundaries: Kinetic Monte Carlo study with first-principle calculations

The diffusion of silver (Ag) impurities in high energy grain boundaries (HEGBs) of cubic (3C) silicon carbide (SiC) is studied using an ab initio based kinetic Monte Carlo (kMC) model. This study assesses the hypothesis that the HEGB diffusion is responsible for Ag release in Tristructural-Isotropic (TRISO) fuel particles, and provides a specific example to increase understanding of impurity diffusion in highly disordered grain boundaries. The HEGB environment was modeled by an amorphous SiC (a-SiC), which approximately represents the local environments of HEGBs. The structure and stability of Ag defects were calculated using ab initio methods based on Density Functional Theory (DFT). The defect energetics suggested that the fastest diffusion takes place via an interstitial mechanism in a-SiC and that is what is modeled. Interstitial sites were identified by a gridded search and transition states were computed using the climbing image nudged elastic band method. The formation energy of Ag interstitials (relative to bulk Ag) and the Kinetic Resolved Activation (EKRA) energies between them were well approximated with Gaussian distributions that were then sampled in the kMC. The diffusion of Ag was simulated with the effective medium model using kMC. Ag diffusion coefficients were estimated for the temperature range of 1200–1600°C. Ag in a HEGB is predicted to exhibit an Arrhenius type diffusion and with a diffusion prefactor and effective activation energy of (2.73±1.09)×10−10m2s−1 and 2.79±0.18eV, respectively. The comparison between HEGB results to other theoretical studies suggested not only that GB diffusion is predominant over bulk diffusion, but also that the HEGB is one of fastest grain boundary paths for Ag diffusion in SiC. The Ag diffusion coefficient in the HEGB shows a good agreement with ion-implantation measurements, but is 2–3 orders of magnitude lower than the reported diffusion coefficient values extracted from integral release measurements on in- and out-of- pile samples. The discrepancy between GB diffusion and integral release measurements suggests that other contributions are responsible for fast release of Ag in some experiments and we propose that these contributions may arise from radiation enhanced diffusion.

Suppression of Silver Diffusion in Borosilicate Glass‐Based Low‐Temperature Cofired Ceramics by Copper Oxide Addition

The silver diffusion behavior in the low‐temperature cofired ceramic (LTCC) comprising of borosilicate glass and alumina was investigated in this work. Transmission electron microscope (TEM) analysis revealed that silver ions diffused into LTCC materials through the glass phase. The addition of copper oxide in the LTCC materials can suppress the silver diffusion during the sintering process because of the enhanced crystallization of borosilicate glass, which leads to the quick increase in glass viscosity and retards the silver diffusion. Thermal dynamic analysis confirmed that the diffusion coefficient of silver in the copper‐oxide‐modified LTCC materials was largely reduced.

A small molecule norspermidine in combination with silver ion enhances dispersal and disinfection of multi-species wastewater biofilms.

Detrimental biofilms have become a great concern in many areas due to their strong resistance and insensitivity to traditional antimicrobial agents. Norspermidine is a potent small molecule for biofilm dispersal. In this study, silver ion, a conventional inorganic biocide, was combined with norspermidine and used for control and removal of multi-species biofilms formed by a mixed culture from wastewater treatment systems. Results showed that silver ion (0.01-1mg/L) treatment alone failed to remove the existing wastewater biofilms. Norspermidine at the concentrations of 500-1000μM was capable to disrupt and disperse the existing biofilms with a biofilm reduction of 21-34% after 24-h exposure. The combined treatment with norspermidine (500μM) and silver ion (0.01mg/L) increased biofilm reduction to 48% (24-h exposure). The combined treatment also enhanced biofilm disinfection ratio (82%, 2-h exposure) by 2.0- and 2.6-folds compared to norspermidine (27%) or silver ion (23%) treatment alone, respectively. Confocal laser scanning microscopic (CLSM) observations found that norspermidine could disrupt biofilm matrix and promote biofilm dispersal via breaking down exopolysaccharides. The combined treatment increased the reduction in biofilm cell density and viability, possibly due to the damage of biofilm matrix, enhanced silver ion diffusion in biofilms, and increased biofilm sensitivity. These findings indicate that the combination of a small molecule norspermidine with a traditional biocide silver ion presents a novel strategy to remove and kill biofilms, which have a potential application in addressing wastewater biofilm-related issues.

Characterization of surface Ag nanoparticles in nanocomposite a-C:Ag coatings by grazing incidence X-ray diffraction at sub-critical angles of incidence

Silver diffusion within nanocomposite films and/or toward the film surface is often observed during annealing of the silver-based nanocomposite films. In order to control and/or minimize this process, it is crucial to characterize the aggregated silver nanoparticles on the films surface. In this paper grazing incidence X-ray diffraction (GIXRD) with both sub-critical and supra-critical angles of incidence is used to characterize the Ag nanoparticles distribution, shape and structure both inside the matrix and on the nanocomposite film surface. The nanocomposite carbon coating containing Ag nanoparticles (a-C:Ag) was deposited by dc magnetron sputtering. The coatings were analyzed by GIXRD using fixed incident angles both below and above the critical angle for total reflection. By using sub-critical angles it was possible to eliminate diffraction from the bulk material allowing to estimate the size distribution of the nanoparticles sitting on the surface. The results obtained by GIXRD analysis were checked through comparison with the observations made by both TEM and SEM analysis. The proposed methodology can be used to characterized nanoparticles deposition on a surface and/or island formation during film growth as long an adequate substrate with high critical angle for total reflection is used.

CALCULATION STUDIES OF SPATIAL DISTRIBUTION OF THE ABSORBED DOSE RATE FOR VARIOUS SEEDS

Purpose . Conducting computational studies of dosimetric characteristics of microsources with the radionuclide I‑125, pilot production of which is established in the research and production complex of isotope and radiopharmaceuticals, JSC “State Scientific Centre of the Russian Federation — Institute for Physics and Power Engineering named after A. I. Leypunsky” (SSC RF IPPE). Sources of production IPPE are similar to the model 6711 of the company Nicomed Amersham, dosimetric characteristics of which are standardized in accordance with the TG43 AAPM formalism. Materials and methods. Microsourse «SEED No. 6711» (model of the company Nicomed Amersham) is hermetically sealed in a titanium capsule silver rod covered with a thin layer of radioactive I‑125. The half-life of iodine‑125 is 59,43 days. In the process of decay of I‑125 is converted into the Te‑125. Calculation of parameters of microsources and their comparison with the standard model 6711 is carried out with use of the computer code MCNP. Results . The method of calculation of the basic dosimetric characteristics of the microsourse SSC RF-IPPE in accordance with the TG43 formalism is developed. A comparative analysis of experimental data and calculated results by MCNP code, which allowed to identify possible reasons for differences, is performed. The estimated dose characteristics and recommended standard data for dose characteristics of micro «SEED No. 6711» are compared. Conclusions . There are two possible reasons for the differences between experimental and calculated results. The first one may be the roughness of the surface of a silver rod or diffusion of radioactive iodine in silver. The second reason might be the difference of the cross sections of the characteristic radiation of silver used in MCNP code. In the comparison of calculated dose characteristics and recommended standard the role of the application activity is very important. In compliance with the standard conditions on the composition of the environment, water phantom and air with 40% humidity, the results obtained are outside the acceptable difference of 3% from the recommended data. While the variation of only the thickness of the deposition of radioactive material in the 0–10 mkm change dosimetric characteristics in the range of 15–20%.

Electromechanical Performance Study on Silver Diffusion Joints of REBCO Coated Conductors under Axial Tensile Stress

Silver diffusion method is a promising candidate for joining the second generation high temperature superconducting tapes that can achieve a joint resistance of nΩ level while retaining full critical current. In this study, silver diffusion joints with joint resistance as low as <; 2 nΩ was demonstrated. The performance of silver diffusion joints under axial tension load, which is considered as a key parameter for their practical applications, was also systematically studied. It was investigated that the nominal critical axial tensile stress of the unlaminated silver diffusion joint fabricated by the coated conductor tapes from Shanghai Superconductor Co., Ltd. was in the range of 430-480 MPa, which is significantly lower than that of the single tape (approximately 590 MPa) and could hardly be improved by increasing the overlap length from 1 to 10 cm or by modifying the configuration from the lap-type to the enhanced bridge-type. According to the experimental results, the failure mechanism of silver diffusion joints under tensile stress was discussed. Based on which, a post-lamination process was proposed to alleviate the local stress concentration. The laminated silver diffusion and single straight tape exhibited consistent behavior under axial tension load and, therefore, the same critical axial tensile stress.

Ag-doped titanium dioxide gas sensor

Titanium dioxide has been utilized for the fabrication of oxygen sensitive ceramic bodies. In this work, disk-shaped TiO2 pellets are fabricated by the sintering of the press- formed anatase powder at 1000°C. Two silver contacts are printed on one of the top base of each sample. Silver wire segments are connected to the printed electrodes. It is shown that the gradual diffusion of silver into titanium dioxide from the electrodes profoundly affects the resistive properties of the ceramic samples. SEM, XRD and EDAX analyses are carried out to determine the position of the silver diffused in the structure. At 35°C, before silver diffusion, the electrical resistance of the device decreases ten times in response to the presence of 3000 ppm ethanol contamination. Sensitivity (Rair/Rgas) to reducing gases is severely affected by the silver doping level in the titanium dioxide. The progress of silver diffusion continuously decreases the sensitivity till it become less than one. Further progress in silver diffusion brings the devices to the condition at which the resistance increases at the presents of reducing gases. In this condition, inverse sensitivities (Rgas/Rair) as large as 103 are demonstrated.

Jointing of Coated Conductors by Using Nano-particle Metal Pastes

Development of a jointing technique of coated conductors is important for all applications, such as superconducting magnets, cables, etc. Low resistance jointing techniques by means of silver diffusion [1] and for superconducting joints[2] have been reported so far. Since these processes were carried out at higher temperatures than the O2 annealing temperature for appropriate carrier doping to the REBa2Cu3O7-d (REBCO) crystals and resulted in oxygen deficiency in the REBCO crystals, long time O2 annealing was required for compensation of this oxygen deficiency. Because the long time and high temperature post annealing is an inappropriate process as on-site technology, solder jointing technology has been widely accepted, in general, for practical applications. However, the resistance of the solder joint is 50 - 100 nΩ, and then the Joule heat generation in the joint region is a serious problem and must be solved. Consequently, we have studied a new jointing technique by using the pastes containing of silver or gold nano-particles. Because the Ic value of GdBCO was deteriorated with higher temperature heat treatment, we have tried to develop a jointing technology with the low temperature (below 200°C). We used the nano-particle metal pastes (∼5nm) which contained dispersants around the chemically active surface of nano-particles and dissociates at low temperatures and achieved the low resistance joint (∼ 3nΩ, 10 x 160mm2, 77K) as well as no Ic degradation without O2 post annealing.

Ag precipitation at the free interface of multilayer NiCuZn ferrites/LTCC components

The diffusion and precipitation of silver and copper in low-dielectric-constant low temperature cofired ceramics (LTCC) for multilayer NiCuZn ferrites/LTCC components are investigated in this study. Ag precipitation is formed at the free interface between NiCuZn ferrites and LTCC for multilayer NiCuZn ferrites/LTCC components after cofiring. During the heating stage Cu+ will segregate into the grain boundary from the NiCuZn ferrites due to the low oxygen partial pressure inside the sample and then dissolve into LTCC near the interface between NiCuZn ferrites and LTCC. Cu+ in glass would diffuse from the interior toward the surface and become oxidized into Cu2+ or precipitated as the CuO phase at the surface. To maintain charge neutrality this process requires an outward diffusion of Cu+ and Ag+ from the interior toward the free surface. The reduction of Ag+ into Ag on the free surface is accelerated by Cu+ oxidation.

The measurement of silver diffusivity in zirconium carbide to study the release behavior of 110mAg in the ZrC TRISO-coated nuclear fuel particle

The tri-structural isotropic (TRISO) coated particle fuel has been developed and used for high temperature gas-cooled reactors (HTGRs). It provides a unique robustness of the first barrier for the fission products. The TRISO fuel particle has typically consisted of a UO2 or UCO kernel, surrounded by successive layers of porous carbon, dense inner pyrocarbon, silicon carbide, and dense outer pyrocarbon. During operation, however, the SiC layer has been known to release radioactive silver 110mAg which makes maintenance more difficult and thus costly. Zirconium carbide has been considered as a promising alternative to the SiC fission product barrier. ZrC exhibits high temperature stability and possibly possesses superior Pd resistance, while the retention properties especially for silver have not been adequately studied.To help elucidate the diffusive behavior of silver in the ZrC coating of the TRISO-coated particle, a new diffusion experimental technique, called the encapsulating source method, has been developed by constructing a constant source diffusion couple between ZrC and Ag gas originated from Zr–Ag solid solution. Scanning electron microscopy (SEM), wavelength-dispersive X-ray spectroscopy (WDS), electron backscatter diffraction (EBSD) and optical methods were used to analyze the diffusion couple annealed at 1500 °C. The resultant diffusion coefficient of Ag in single-crystalline ZrC0.84 at 1500 °C was experimentally determined to be about 2.8 (±1.2) × 10−17 m2/s.

Study on the formation mechanism of the glaze film formed on Ni/Ag composites

The results of the study on the sliding wear behavior of a Ni/Ag-15at% material showed that the well-compacted glaze film mainly consisting of NiO, Ni and Ag was formed on the contact surface at 600°C, which played an important part in decreasing friction coefficients. Microscopic observations showed the film possessed a multi-layered structure with silver-rich, outer layer and moderately-oxidized, non-silver-containing inner layer. The formation of the multi-layered structure is believed to have developed as a result of the joint factors involving repeated oxidization, fracturing, mixing and consolidation, followed by heat-induced silver diffusion from the dense wear debris layer to the outmost surface under the flash temperature. The effect of the second diffusion and coalescence of silver on the tribological performance of the Ni/Ag material was briefly discussed.

Direct observation of conductive filament formation in Alq3 based organic resistive memories

This work explores resistive switching mechanisms in non-volatile organic memory devices based on tris(8-hydroxyquinolie)aluminum (Alq3). Advanced characterization tools are applied to investigate metal diffusion in ITO/Alq3/Ag memory device stacks leading to conductive filament formation. The morphology of Alq3/Ag layers as a function of the metal evaporation conditions is studied by X-ray reflectivity, while depth profile analysis with X-ray photoelectron spectroscopy and time-of-flight secondary ion mass spectrometry is applied to characterize operational memory elements displaying reliable bistable current-voltage characteristics. 3D images of the distribution of silver inside the organic layer clearly point towards the existence of conductive filaments and allow for the identification of the initial filament formation and inactivation mechanisms during switching of the device. Initial filament formation is suggested to be driven by field assisted diffusion of silver from abundant structures formed during the top electrode evaporation, whereas thermochemical effects lead to local filament inactivation.

A model for silver ion catalysis of chalcopyrite (CuFeS2) dissolution

Atmospheric leaching of chalcopyrite in sulfuric acid solutions is a slow process due to its passivation. Silver ions have been shown to catalyze this process and increase the oxidation rate. In this study the interaction between silver ions and chalcopyrite has been investigated in silver-containing sulfuric acid solutions. The silver concentration of the test solutions was between 0 and 10ppm. In situ Mott–Schottky analysis and X-ray photoelectron spectroscopy (XPS) were respectively applied to study chalcopyrite's semiconductor properties and silver diffusion into the chalcopyrite passive film. Results of the Mott–Schottky experiments showed that the addition of silver to the solution increases the apparent capacitance of the chalcopyrite passive film owing to changes in the semiconductor properties of the film. The measured capacitance was shown to be time dependent for the first 15min of the experiment (i.e. sample immersion in solution) and after this elapsed time the capacitance stayed constant. XPS results showed that silver atoms diffuse about 18nm below the chalcopyrite surface.A model is proposed for silver ion catalyzed chalcopyrite electro-dissolution. In this model it is assumed that silver cations adsorb to the electrode surface and form Ag2S. The formation of each Ag2S molecule on the surface requires the creation of a sulfur vacancy and a pair of holes in the passive film. The effect of both the sulfur vacancy and the pair of holes is an increase in the dissolution kinetics of chalcopyrite.

Mitigation of membrane biofouling through surface modification with different forms of nanosilver

Membrane biofouling is a serious problem limiting widespread application of membrane technology. Modification of membranes using silver nanoparticles appears to be a promising option for mitigating biofouling.NADIR® UP150 ultrafiltration membranes made of polyethersulfone were modified with different forms of nanosilver through (i) diffusion of silver ions with subsequent reduction, (ii) addition of polyethyleneimine-capped silver nanoparticles, and (iii) thermal-pressure fixation of silver-modified nanofibres. The modified membranes for any changes in permeability, antimicrobial properties, silver leaching and contact angle were examined.All modified membranes displayed antimicrobial properties. Both membranes modified through diffusion of silver and polyethyleneimine-capped silver nanoparticles method mitigated biofouling. These membranes also showed slightly higher permeability than the unmodified control, while silver-modified nanofibre membranes had the lowest permeability of all the membranes tested. Filtration results corresponded well with contact angle measurements. All modified membranes exhibited low levels of silver leaching over time.

High-temperature platinum resistance thermometry: the problem with silver and the case for gold

The diffusion of silver through quartz at high temperatures leads to contamination of the platinum sensing element of high temperature platinum resistance thermometers. While some protection of the PRT element may be afforded by the application of appropriate electric fields, the contamination of the quartz elements of silver fixed points causes their premature failure. Contamination is evidenced by the yellowish colour imparted to the glass by the silver particles growing within the quartz glass matrix. The presence of silver as the contaminating element has been confirmed unambiguously through energy dispersive x-ray analysis and secondary ion mass spectrometry. To mitigate the risk of silver contamination, the gold point is proposed as an alternative calibration point. PRT resistance ratios measured at the freezing points of silver and gold in different laboratories at different times are highly correlated. This suggests that the ITS-90 reference function might be extrapolated to 1064.18 °C (the gold fixed point). However, it remains unclear from the gold and silver PRT resistance ratios from the literature whether extrapolation of the reference function leads to the correct value at the gold point. A direct comparison of gold fixed points may be required to resolve the inconsistencies. Additional PRT data may help resolve the discrepancy.

Ceramic Enamels as New Back Contacts for Cu (In, Ga) Se2-Based Photovoltaic Tile

In this work, we investigated the properties of silver and gold enamels as potential back contacts for Cu (In, Ga) Se2 (CIGS) solar cells. The enamels were deposited on ceramic tiles by nonvacuum printing techniques. Thus, we are proposing a development of integrated photovoltaic tile for the first time. We also explained the CIGS synthesis procedure using coprecipitation of selenite precursors. To deposit the precursor powders on the substrate, a doctor blade method is applied. The interface morphology between ceramic tile, back contact, and CIGS absorber was studied as a critical factor for the final solar cell performance. The thermal treatment effect on the back contact properties was also reported. Excellent compatibility between CIGS and gold layer was observed, keeping thickness and chemical composition adequate for photovoltaic applications. The band gap energy confirms assembly effectiveness. Unsatisfied results of silver diffusion toward CIGS absorber were obtained when silver enamels were used.

Silver diffusion over silicon surfaces with adsorbed tin atoms

Silver diffusion over the (111), (100), and (110) surfaces of silicon with preliminarily adsorbed tin atoms is studied by Auger electron spectroscopy and low-energy electron diffraction. Diffusion is observed only on the surface of Si(111)-2√3 × 2√3-Sn. The diffusion mechanism is established. It is found that the diffusion coefficient depends on the concentration of diffusing atoms. The diffusion coefficient decreases with increasing silver concentration, while the activation energy and the preexponential factor increase.

Ion beam analysis of golden threads from Romanian medieval textiles

In this study, metal threads from Romanian religious embroideries and precious velvet brocades dated from 15th to 18th century were analyzed by using IBA methods (PIXE and RBS) which, in comparison to the traditional analytical techniques (XRF, EDS), allowed the detection of their structures and accurate identification of the trace elements (detection limits of few tens of ppm). PIXE results confirmed that both types of the metal threads studied – wires and strips – have layered structures being made of fine silver, refined by cupellation, and gilded most probably with pure gold, and not of Au–Ag alloy, or gilded Ag–Cu alloy or Au–Ag–Cu alloy, as resulted from the previously performed SEM-EDS analysis. Trace elements of historical interest like lead, mercury and bismuth have been also possible to be detected by PIXE. The resulting elemental maps allowed us to identify the areas from which the metal thread structure and quantitative composition could be accurately determined. RBS measurements revealed that the gilding layer is separated from the silver bulk by an interface layer resulting through atomic diffusion of silver into the gold, which lead to the conclusion that the methods used for gilding were probably either the diffusion bonding or the fire gilding. The gilding layers thicknesses were estimated by PIXE with the GUPIX software and also determined from RBS measurements.