Diffusion Of Silver Research Articles

Field-assisted diffusion of silver in SnO2 thin films

Tin oxide films are known for their wide spread applications in the field of optoelectronics as transparent conductors and as atmosphere sensitive ceramic pellets for chemical sensor fabrication. Forming durable ohmic contacts to these films is vitally necessary for the effective performance and long life of almost all such devices. Silver electrodes are commonly considered as low resistance ohmic contacts to many metal-oxide semiconductors. Particularly in devices operating at elevated temperatures, silver migration can considerably decrease useful device lifetime. Here, we study the performance of silver electrodes paste printed on SnO2 thin films and show that the I-V characteristics of the silver/SnO2 contact changes with operating time at elevated temperatures. SnO2 films are grown on alumina substrates by ultrasonic spray pyrolysis technique. A pair of Ag electrodes are paste-printed on the surface of the grown films followed by a heat-treatment step to stabilize the deposits. The as-fabricated Ag/SnO2 contacts present ohmic characteristics. Continuous application of DC voltages to the samples operating at 350 °C results in a significant drop in the devices’ resistance. The results originate from field-assisted migration of silver ions from the anode to the cathode electrode and formation of Ag micro-filaments in the polycrystalline SnO2 layer.

Grain boundary complexions in silicon carbide

AbstractUnderstanding the diffusion and release of fission products in nuclear fuels is of great relevance for ensuring high levels of safety of these materials. The origin of the diffusion of silver in TRISO (Tristructural Isotropic) coated fuel particles has remained an open challenge in the study of this type of fuel despite 40 years of development. In this work, we propose that the existence of grain boundary complexions and complexion transitions might be responsible for the complex diffusion behavior observed with silver. We have identified three types of the Dillon‐Harmer complexions in SiC (clean grain boundary, a disordered layer with a ~0.6 nm of thickness, and an intergranular amorphous film) through ultra‐high resolution transmission electron microscopy.

ICP-MS measurement of silver diffusion coefficient in graphite IG-110 between 1048K and 1284K

Silver-110m has been shown to permeate intact silicon carbide and pyrolytic carbon coating layers of the TRISO fuel particles during normal High Temperature Gas-Cooled Reactor (HTGR) operational conditions. The diffusion coefficients for silver in graphite IG-110 measured using a release method designed to simulate HTGR conditions of high temperature and flowing helium in the temperature range 1048–1253 K are reported. The measurements were made using spheres milled from IG-110 graphite that were infused with silver using a pressure vessel technique. The Ag diffusion was measured using a time release technique with an ICP-MS instrument for detection. The results of this work are:DAg,IG−110=(6.6×10−4m2s)exp(−1.74×105JmolRT)The measured activation energy of 174 kJ/mol compares well with the range of values [154–193 kJ/mol] reported in the literature for LTI pyrocarbon. The measured pre-exponential D0 value of 6.60 × 10−4 m2/s is similar to the value of 5.3 × 10−4 m2/s reported for Russian LTI pyrocarbon.

Fabrication and Microscopic and Spectroscopic Characterization of Planar, Bimetallic, Micro- and Nanopatterned Surfaces.

Micropatterns and nanopatterns of gold embedded in silver and titanium embedded in gold have been prepared by combining either photolithography or electron-beam lithography with a glue-free template-stripping procedure. The obtained patterned surfaces have been topographically characterized using atomic force microscopy and scanning electron microscopy, showing a very low root-mean-square roughness (<0.5 nm), high coplanarity between the two metals (maximum height difference ≈ 2 nm), and topographical continuity at the bimetallic interface. Spectroscopic characterization using X-ray photoelectron spectroscopy (XPS), time-of-flight secondary-ion mass spectrometry (ToF-SIMS), and Auger electron spectroscopy (AES) has shown a sharp chemical contrast between the two metals at the interface for titanium patterns embedded in gold, whereas diffusion of silver into gold was observed for gold patterns embedded in silver. Surface flatness combined with a high chemical contrast makes the obtained surfaces suitable for applications involving functionalization with molecules by orthogonal adsorption chemistries or for instrumental calibration. The latter possibility has been tested by determining the image sharpness and the analyzed area on circular patterns of different sizes for each of the spectroscopic techniques applied for characterization.This is the first study in which the analyzed area has been determined using XPS and AES on a flat surface, and the first example of a method for determining the analyzed area using ToF-SIMS.

Nano silver diffusion behaviour on conductive polymer during doping process for high voltage application

Conductive polymer had opened a new era of engineering for microelectronics and semiconductor applications. However, it is still a challenge for high voltage applications due to lower electrical conductivity compare to metals. This results tremendous energy losses during transmission and restricts its usage. In order to address such problem a novel method was investigated using nano silver particle doped iodothiophene since silver is the highest electrical conductive material. The experiments were carried out to study the organometallic diffusion behaviour of nanosilver doped iodothiophene with different concentration of iodothiophene. Five different mixing ratio between nanosilver and the solution of iodothiophene dissolved in diethyl ether were used which are 1:1.25, 1:1.5, 1:2.5, 1:3 and l:5. It was revealed that there is an effective threshold concentration of which the nano silver evenly distributed and there was no coagulation observed. These parameters laid the foundation of better doping process between the nano silver and the polymer significantly which would contribute developing conductive polymer towards high voltage application for industries that are vulnerable to corrosive environment.

Impulse Pressure Assisted Diffusion Bonding of Low Carbon Steel Using Silver Interlayer

In the present study, impulse pressure assisted diffusion bonding of low carbon steel was carried out using silver interlayer. To study the influence of input process parameters namely bonding temperature (T), maximum pulse pressure (P), and number of pulses (N), experiments of diffusion bonding were conducted according to the Taguchi L9 orthogonal array. To reveal the typical bond interface characteristics, selected samples were examined by scanning electron microscopy (FESEM) equipped with energy dispersive spectroscopy (EDS). The EDS analysis revealed a diffusion affected zone at the interface due to the diffusion of silver and iron across the interface. Lap joints were developed to measure the shear strength of the diffusion bonds. The optimum level of bonding temperature, maximum pulse pressure and number of pulses (875 °C, 10 MPa and 10 pulses) were identified. The ANOVA results indicated that bonding temperature had the highest statistical effect of 66.37% on shear strength followed by number of pulses and maximum pulse pressure. The fracture surface of the lap joints was also examined by FESEM and X-ray diffraction analysis.

Study on Growth Process of Ag(In, Ga)Se2 Films by a Three-Stage Co-Evaporation Method Using Molecular Beam Epitaxy Apparatus

Ag(In, Ga)Se2 (AIGS) has been considered as a promising candidate material for the top cell of chalcopyrite-based tandem solar cells. In this work, the process of (AIGS) film growth by a three-stage molecular beam epitaxy method is studied. The diffusion of silver and grain growth of AIGS films from the first stage-deposited (In, Ga)2Se3 is investigated. Energy dispersive spectroscopy mapping is used to reveal the distribution of silver in the film during each stage of the deposition process. A sharp silver accumulation at the surface of the film at the early stage of the deposition process is observed. This has led to the formation of a silver-rich phase, which gradually diffused into the film to produce a homogeneous distribution. X-ray diffraction results illustrate the phase changes of AIGS films. Based on the result, a growth model for AIGS films from the first stage to the second stage is suggested as (In, Ga)2Se3 → Ag9 (In, Ga)Se6 at the surface and (In, Ga)2Se3 at the bottom of the film → silver-rich AIGS film. During the third stage, the silver-rich film was converted to silver-poor film. The performance of AIGS solar cells fabricated from various samples was compared, and a highest efficiency of 7.1% was obtained.

Antimicrobial Effectiveness of Bioactive Silver Nanoparticles Synthesized by Actinomycetes HGG16n Strain.

Biologically synthetized silver nanoparticles are promising antimicrobial agent. Flow cytometry, well diffusion methods, colony-forming units (CFU) and spectroscopic approach are commonly used in antimicrobial study. The aim of this study was investigation of effectiveness of Bio- AgNPs synthesized by Actinomycetes HGG16n using fluorescence flow cytometry method as an alternative to the standard ones (well and disc diffusion method). Flow cytometry technique was applied to monitor the antibacterial effect of biocolloidal silver and its combination with various commercial antibiotics against selected pathogens. The observed effectiveness was confirmed by fluorescence micrographs. Silver nanoparticles synthesized by Actinomycetes HGG 16n strain were as effective antimicrobial agent as the tested commercial antibiotics. Escherichia coli, Klebsiella pneumoniae, Proteus mirabilis, Salmonella infantis and Bacillus subtilis strains are not able to create the resistant mechanisms under treatment of biocolloidal silver. Furthermore, the flow cytometry technique was more sensitive than disc and well diffusion and confirmed the effectiveness of BioAgNPs against all tested bacterial cells. Precipitation and limited diffusion of biocolloidal silver was observed by using well diffusion method. Specificity and selection of antimicrobial approach are related with different nature of lowmolecular compounds (e.g. antibiotic) compared with biocolloids. An alternative method, flow cytometry was designed for antimicrobial study of biocolloidal silver nanoparticles and compared to the classical microbial techniques. Moreover, this work highlights the development of novel and inexpensive antimicrobial agent for most oral and skin infections caused by Gram (+) and Gram (-) bacteria.

Preferred location for conducting filament formation in thin-film nano-ionic electrolyte: study of microstructure by atom-probe tomography

Atom-probe tomography of Ag-photodoped amorphous thin-film Ge40S60, the material of interest in nano-ionic memory and lateral geometry MEMS technologies, reveals regions with two distinct compositions on a nanometer length-scale. One type of region is Ag-rich and of a size typically extending beyond the measured sample volume of ~40 × 40 × 80 nm3. These type-I regions contain aligned nanocolumns, ~5 nm wide, that are the likely location for reversible diffusion of Ag+ ions and associated growth/dissolution of conducting filaments. The nanocolumns become relatively Ag-rich during the photodoping, and the pattern of Ag enrichment originates from the columnar-porous structure of the as-deposited film that is to some extent preserved in the electrolyte after photodoping. Type-II regions have lower Ag content, are typically 10–20 nm across, and appear to conform to the usual description of the photoreaction products of the optically-induced dissolution and diffusion of silver in a thin-film chalcogenide. The microstructure, with two types of region and aligned nanocolumns, is present in the electrolyte after photodoping without any applied bias, and is important for understanding switching mechanisms, and writing and erasing cycles, in programmable-metallization-cell memory.

Influence of Nanoeffects on the Oxidation of Cr–C/Ag Thin Films Containing Silver Nanoparticles

AbstractWell‐controlled functionalization of carbide‐based nanocomposite films with noble‐metal surface nanoparticles of different sizes may lead to new materials with novel multifunctional properties. In this work, magnetron sputtering was used to deposit nanocomposite films comprising amorphous chromium carbide (a‐CrCx), amorphous carbon (a‐C), and a minority of silver in the form of embedded nanoclusters. Up to 5⋅1010 surface nanoparticles per cm2 with different size distributions were also found to be formed, owing to the diffusion of silver from the bulk of the film. The influences of these conductive nanoparticles on the electrochemical behavior of the films were investigated in dilute sulfuric acid. Although silver is a noble metal, the oxidation potential of the nanoparticles was about 0.4 V more negative than the Ag+/Ag standard potential, meaning that the nanoparticles were oxidized in the Cr passive potential region. While this effect can mainly be explained by a low concentration of Ag+ in the electrolyte, the sizes of the nanoparticles and interactions with the matrix were also found to be important. Scanning electron microscopy and X‐ray photoelectron spectroscopy were used to analyze the surface chemistries. As Ag can be replaced by other noble metals, the concept is of general interest for further studies.

Effect of lithium and silver diffusion in single-stack and tandem OLED devices

A study of metal (Li, Ag) diffusion has been carried out in an archetypal OLED device based on N,N′-di(1-naphthyl)-N,N′-diphenyl-(1,1′-biphenyl)-4,4′-diamine|tris(8-hydroxyquinolinato) aluminum|4,7-diphenyl-1,10-phenanthroline (NPB|Alq3|Bphen). Using single-stack and two-stack tandem OLED structures with variations of layer thicknesses and metal layer placements, we have found that Ag vapor-deposited on Alq3 layer can diffuse or penetrate deep into Alq3, up to ∼2,000 Å, causing luminescence quenching. This diffusion can be substantially prevented by a thin layer of Li or Bphen deposited on Alq3 prior to the deposition of Ag. In contrast, Li diffusion in either Alq3 or Bphen is limited to about 50–100 Å. Li appears to be able to diffuse into Bphen irrespective of the order of Li and Bphen depositions.

Antibacterial properties and reduction of MRSA biofilm with a dressing combining polyabsorbent fibres and a silver matrix.

This study was designed to evaluate the antibacterial activity of a wound dressing which combines polyacrylate fibres and a silver lipido-colloid matrix (UrgoClean Ag, silver polyabsorbent dressing), against biofilm of methicillin-resistant Staphylococcus aureus (MRSA). Samples of silver polyabsorbent dressing and the neutral form of this dressing (UrgoClean) were applied to biofilms of MRSA formed on a collagen I-coated surface, cultured for 24 hours. Different exposure times were tested (1, 2, 4 and 7 days) without dressing change. The biofilm reduction was quantified by using culture methods and by confocal laser scanning microscopy experiments. The application of the silver polyabsorbent dressing resulted in a significant decrease of the biofilm population by a log reduction of 4.6, after 24 hours of exposure. Moreover, the antibiofilm activity was maintained for 7 days with reduction values up to 4 log (reduction of biofilm superior to 99.99%). The application of the neutral dressing also induced a significant reduction of the concentration of sessile cells after 1 day (about 0.90 log). The results obtained with this neutral form of the dressing showed that the polyacrylate fibres were able to exert a mechanical disruption of the biofilm architecture. These in vitro experiments demonstrated that silver polyabsorbent dressing was able to strongly reduce the biofilm of MRSA. The antibiofilm mechanism of this dressing can be explained by a dual action of the polyabsorbent fibres (based on ammonium polyacrylate polymer around an acrylic core) which induced a mechanical disruption of the biofilm matrix and/or a sequestration of sessile cells, and the diffusion of silver ions which produced bactericidal activity. This study was supported by Laboratoires Urgo (Dijon). P. Janod is an employee of Laboratoires Urgo. The company had no influence on the experimental design and the interpretation of the results.

Gold and silver diffusion in germanium: a thermodynamic approach

Diffusion properties are technologically important in the understanding of semiconductors for the efficent formation of defined nanoelectronic devices. In the present study we employ experimental data to show that bulk materials properties (elastic and expansivity data) can be used to describe gold and silver diffusion in germanium for a wide temperature range (702–1177 K). Here we show that the so-called cBΩ model thermodynamic model, which assumes that the defect Gibbs energy is proportional to the isothermal bulk modulus and the mean volume per atom, adequately metallic diffusion in germanium.

Advanced wire bonding for high reliability and high temperature applications

Abstract The next generation of switches for power electronic will be based on white band gap (WBG) semiconductor GaN or SiC. This materials supports higher switching current and high frequency. White band gap semiconductors enables higher application temperature. Certainly, high temperature capability is also to discuss in combination with high number of thermal cycles. For a frame module concept shows these paper a comparison of different joining techniques with the focus on the reliability issue on wire and ribbon bonding. Beside to the 1000 passive thermal cycles from −40°C to +125°C there are active thermals cycles for technology qualification required [3]. Depending on the application and mission profile a high thermal cycling capability is necessary. For this reason, new high temperature joining techniques for die attach, e.g. Silver sintering or diffusion soldering, were developed in the recent past [4]. All of this new joining techniques focusing on higher electrical, thermal and thermo-mechanical performance of power modules. By using an optimized metallization system for the WBG the numbers of thermal cycles can be increased and the maximum operating temperature advanced up to 300°C. In these new temperature regions silicon semiconductors will be substituted by WBG semiconductors. The present work shows an active power cycling capability of different wire and ribbon bonds and the failure mechanism will be discussed. A calculation model explained the reliability for the different wire diameter and the impact of bonding materials. This reliability calculation explain the thermo-mechanical effects and based on materials and geometry data and is not optimized for evidence. Through these physical background understanding more than 1.000.000 thermal cycles with a 150 K temperature swing from +30°C to +180°C are now possible. These is a the basic knowledge for a design for reliability based on current, mission profile and reliability optimization for future high end applications with wire or ribbon bonding technique.

Quantitatively in Situ Imaging Silver Nanowire Hollowing Kinetics.

We report the in situ investigation of the morphological evolution of silver nanowires to hollow silver oxide nanotubes using transmission X-ray microscopy (TXM). Complex silver diffusion kinetics and hollowing process via the Kirkendall effect have been captured in real time. Further quantitative X-ray absorption analysis reveals the difference between the longitudinal and radial diffusions. The diffusion coefficient of silver in its oxide nanoshell is, for the first time, calculated to be 1.2 × 10-13 cm2/s from the geometrical parameters extracted from the TXM images.

The effect of heat treatment on the microstructure and diffusion of silver in pyrolytic carbon coatings

It is well accepted that TRISO (tristructural isotropic) coated nuclear fuel particles are capable of retaining fission products up to 1600 °C, however above this temperature fission products can diffuse through the pyrolytic carbon (PyC) and silicon carbide coatings that act as the containment barriers in this fuel. Despite decades of research and development, little is known on the origin of this fuel temperature limit. In order to understand the origin of this fuel temperature PyC coatings produced by fluidized bed chemical vapor deposition were heat treated at 1000 °C, 1400 °C and 1700 °C for 200 h in an innert atmosphere. We have observed that above 1400 °C the anisotropy, domain size and level of graphitization increases to twice its original value. Furthermore, at 1700 °C some samples exhibited the formation of nano-pores, which could be the origin of the maximum fuel temperature limit or at least contribute to it. The increased diffusivity of elements due to microstructural changes was corroborated by silver diffusion experiments. Furthermore, we have observed that not all the samples suffer the same level of graphitization, thus suggesting that some PyC coatings can maintain their capability to retain fission products even after temperature excursions above 1600 °C.

Energy science: Fast track for silver.

A solid composite material has been made that conducts electricity through the rapid transport of silver ions, which diffuse faster than in some liquids. The material holds promise for applications in charge-storage devices. See Article p.159 Materials that conduct both electrons and ions are important technologically for use in electrodes, permeation membranes, sensors and catalysts. They often consist of two or more components in a composite, with each mode of conduction catered for separately. This paper shows that a composite of the 'super-ionic' conductor rubidium silver iodide (RbAg4I5) and the electronic conductor graphite exhibits extremely fast diffusion of silver ions at the interface between the two materials, generating both a silver excess and a silver deficiency, analogous to single-phase mixed conductors, even though such behaviour is not possible in the individual phases.

Nanolayered solid electrolyte (GeSe2)30(Sb2Se3)30(AgI)40/AgI: A new hypothesis for the conductivity mechanism in layered AgI

Using the laser ablation method, films comprised of alternating layers of AgI and (GeSe2)30(Sb2Se3)30(AgI)40 glass were obtained. Individual layer thickness amounts to 10÷15nm, and the total number of layers is about 100. X-ray diffraction (XRD) and film conductivity measurements were carried out during several cycles of heating up to 200°C and cooling to room temperature. It was established that after three cycles of thermal processing specific lateral conductivity of the film is equal to 0.3Scm−1 and conductivity activation energy is equal to 0.07eV at room temperature. Attempts to explain such a high conductivity value based on XRD results did not yield satisfactory results. However, our first-principle calculations within the density functional theory (DFT) showed that in the free layer composed of four AgI planes a rearrangement occurs, resulting in formation of the stable structure of two silver planes on the inside and two iodine planes on the outside (I–Ag–Ag–I). Rearrangement of similar stack of eight or twelve atomic planes results in formation of two or three I–Ag–Ag–I layers loosely bound to each other, accordingly. This suggests that increase in specific conductivity growth of multilayer film as a consequence of cyclic heating and cooling may be connected with AgI stratification on its boundary with chalcogenide glass and following stabilization of layered phases mentioned above. The existence of an empty space between the layers that is constrained by iodine ion planes should facilitate silver ion diffusion along the layers.

Effects of high-dose hydrogen implantation on defect formation and dopant diffusion in silver implanted ZnO crystals

This work reports on the effects of a deep high-dose hydrogen ion implant on damage accumulation, defect retention, and silver diffusion in silver implanted ZnO crystals. Single-crystal ZnO samples were implanted with Ag ions in a region ∼150 nm within the surface, and some of these samples were additionally implanted with hydrogen ions to a dose of 2 × 1016 cm−2, close to the depth ∼250 nm. Rutherford backscattering/ion channeling measurements show that crystal damage caused by Ag ion implantation and the amount of defects retained in the near surface region following post-implantation annealing were found to diminish in the case with the H implantation. On the other hand, the additional H ion implantation resulted in a reduction of substitutional Ag atoms upon post-implantation annealing. Furthermore, the presence of H also modified the diffusion properties of Ag atoms in ZnO. We discuss these findings in the context of the effects of nano-cavities on formation and annihilation of point defects as well as on impurity diffusion and trapping in ZnO crystals.

Silver recovery from simulated photographic baths by electrochemical deposition avoiding Ag2S formation

Aiming at recovering silver from a simulated photographic wastewater, a study on electrochemical deposition with modulated current was developed. In cathodic potentials where hydrogen formation occurs, Ag2S formation was noticed over the electrode due to parasitic reactions. Therefore, in a galvanostatic process, the electrodeposition would only be feasible if conducted under current control to avoid Ag2S formation. An electrochemical flow reactor was used for silver electrodeposition under current control using a stainless steel plate. The modulated current values for the electrodeposition were calculated according to the limiting current kinetic control, applying the mass transfer coefficient calculated from experimental values of diffusion coefficient of silver ions and diffusion layer thickness. Silver electrodeposition was achieved at high efficiency rates, low energy consumption and without the presence of parasitic reactions. The highly negative potentials were avoided when the limiting current was applied and, consequently, sulfur sulfide was not formed over silver deposit. The modulated current electrodeposition of silver revealed to be a feasible process to recover silver from spent photographic baths.