Ag Grains Research Articles

Magnetic and transport properties of Co–Ag nanocrystalline particles

Co–Ag nanocrystalline films deposited by Pulsed Laser Deposition were irradiated by excimer laser at different values of energy fluence. The microstructural modifications induced by such treatment were investigated (by atomic force, scanning and transmission electron microscopies) and correlated with the magnetic and magnetotransport properties. The results indicate that laser irradiation favors the silver grain growth and induces a segregation of a fraction of Co, driven by the interface energy, to sites energetically more favorable like Ag grain boundaries (as small grains with diameters less than 5 nm, to be compared to ≈10 nm in the as-deposited sample) and the film/substrate interface. Such microstructural variation leads to changes in the magnetic behavior and to an increase of the magnetoresistance below 10 kOe.

Structure and Magnetism of Co and CoAg Nanocrystals

AbstractMonodisperse, air-stable Co/CoO and CoAg55 nanoparticles with a mean diameter of about 11 nm have been synthesized using methods of colloidal chemistry. High resolution transmission electron microscopy (TEM) and Electron Energy-Loss Spectroscopy (EELS) element-specific TEM images reveal a multiply-twinned fcc Co metallic core covered with a 2-2.5 nm thick CoO shell. The lattice parameters are in agreement with those of bulk Co and CoO. A shift of the hysteresis loop of 0.4 T, induced by field CoOling of the Co/CoO particles, indicates a strong unidirectional exchange anisotropy due to the interaction between the ferromagnetic Co core and the antiferromagnetic CoO shell. CoAg55 composite particles consist of grains of fcc Co and fcc Ag. No evidence for alloy formation was observed. Electron energy-loss and X-ray microanalysis indicate that Co is predominantly found in the surface region of the particles. SQUID magnetometry shows that at room temperature the CoAg55 particles are superparamagnetic while at 90 K a hysteresis loop was detected with a coercive field of 0.07 T and a remanent magnetization of 32 % of the saturation value.

Investigation on roughness of silver thin films inside silica capillaries for hollow waveguides

A metal (Ag)/dielectric (AgI) hollow glass waveguide is a novel and flexible fiber for the delivery of high-power IR laser radiation. The surface roughness of the Ag films is one of the key factors that greatly influence the attenuation of the waveguides. In this paper, with the wet chemistry deposition, Ag thin films were successfully fabricated in silica capillaries, whose inner diameter was 0.53 mm. By means of atomic force microscopy (AFM), the metallization process and roughness of the Ag thin films were analyzed. It can be concluded that as the volume of AgNO 3 solution increased, the needed silver deposition time increased, and the size of the Ag grains enlarged, resulting in an incremental increase in the surface roughness of the Ag thin films. IR transmission results show that the attenuation of the waveguides increases with an increase in the surface roughness of the Ag thin films and augments when the input power increases.

Wetting and structural transition induced by segregation at grain boundaries: a monte carlo study.

Wetting of the Sigma = 5 (310) <001> symmetrical tilt grain boundary (GB) close to the solubility limit in the Cu(Ag) solid solution has been observed by means of Monte Carlo simulations at T = 600 K. More precisely, a finite thickness film almost pure in Ag, separating the two initial Cu(Ag) grains, can be obtained from a critical intergranular germ induced by the strong segregation of Ag in the GB. As this film is actually a single crystal, this implies a complete rearrangement of the GB core structure. Thus the initial GB is replaced by two Cu(Ag)/Ag(Cu) interfaces. Evidence is presented for the increase of the film thickness when approaching the solubility limit, as expected in wetting phenomena.

Localization of strain in metal matrix composites studied by a scanning electron microscope-based grating method.

The deformation characteristics of the metal matrix composites Ag/Ni and Al/Al2O3 are studied at microstructural level by a scanning electron microscopebased grating method and finite element (FE) simulation. The measured strain was found to localize in narrow bands in the ductile matrix of both composites. In the case of the Al/Al2O3 composite, the bands are preferentially initiated in Al regions adjacent to the interface of large Al2O3 particles, leading to local strain maxima. The band positions found in the Ag/Ni composite are also affected by the less deformable Ni phase, but strain localization first occurs by sliding of single Ag grains sometimes located away from the Ni phase. Using a FE model of real phase geometry and measured border displacements as boundary conditions, the simulation agrees reasonably with the experiment. The differences in the case of the Al/Al2O3 composite are due to particle cracks and voids at the particle/matrix interface. This effect was found in the experiment but not considered in modelling. For the Ag/Ni composite the band positions agree fairly well. However, the level and gradient of strain is clearly different as the crystallographic orientation of the Ag grains was not accounted for in modelling.

Ag grain boundary diffusion and segregation in Cu: Measurements in the types B and C diffusion regimes

Grain boundary (GB) diffusion of 110mAg in polycrystalline Cu was measured under the conditions of the Harrinson's type B (962–675 K) and type C (565–452 K) diffusion regimes. In the B-type diffusion regime, the triple product P= sδD gb ( s is the segregation factor and δ the GB width) was found to follow the Arrhenius law P=(1.4 +0.6 −0.4)·10 −15·exp{−[(69.1±2.5)kJ·mol −1]/ RT} m 3 s −1. The measurements under the C regime conditions directly established the temperature dependence of the GB diffusion coefficient D gb , D gb =(1.7 +0.7 −0.5)·10 −4· exp{−[(108.6±1.9) kJ· mol −1]/RT} m 2 s −1. Combining both results and assuming as usual δ≅5·10 −10 m the segregation factor s was determined to follow an Arrhenius dependence s=s 0 exp(−H s /RT) with the pre-exponential factor s 0=(1.6 +1.4 −1.0)·10 −2 and the segregation enthalpy H s=−39.5±4.0 kJ·mol −1. Experimental conditions were analyzed to figure the factors resulting in the curvature of the radiotracer profiles. Probable non-linear segregation was shown to give only marginal (if any) effect. The initial parts of the profiles are well described by accounting for the GB motion during diffusion anneal. The analysis shows that a hypothetial dislocation-enhanced volume diffusion at low temperatures cannot disturb the C-regime conditions in the present experiments. The very small tracer concentrations applied in the types B and C diffusion measurements indeed allow us to establish equilibrium GB segregation at negligible concentrations of solute atoms. The results are compared with the available literature data obtained by direct measurements with non-negligible solute concentrations.

Grain Boundary Motion during Ag and Cu Grain Boundary Diffusion in Cu Polycrystals

Grain boundary (GB) motion in high-purity Cu material (5N8 and 5N Cu) is investigated using the results of radiotracer GB diffusion measurements with tracers exhibiting fundamental differences in the solute-matrix atom interactions. The results on GB solute diffusion of Ag (revealing a miscibility gap in the Ag-Cu phase diagram) and Au (forming intermetallic compounds with Cu) in Cu and on Cu self-diffusion are analyzed. The initial parts of the Ag and Cu penetration profiles turned out to be substantially curved. The profile curvature is explained via the effect of GB motion during 110m Ag and 64Cu GB penetration. The activation enthalpies of GB motion in these two independent measurements occurred to be very close, 95 and 103 kJ/mol, respectively. Moreover, these values turn out to be close, but still somewhat larger than the activation enthalpy of Cu GB self-diffusion in Cu material of the same very high purity, Q Cu gb = 72 kJ/mol. Although tracer diffusion measurements of Au GB diffusion in Cu yielded only limited information on GB motion, the absolute values of GB velocities are consistent with those calculated from the Ag and Cu GB diffusion data.

Depth profile of tritium in plasma exposed CX-2002U

Depth profiles of the Ag grains density in autoradiographs, which represent tritium concentration in CX-2002U samples exposed to high flux D/T particles under various conditions, were examined and the apparent diffusion coefficients were estimated from the profiles. Plasma discharge generating D/T atomized particles with low energies increases tritium inventory in the samples by introducing high tritium concentration on the surface exposed and following diffusion process into the deep region with apparent diffusion coefficients (1.7×10 −16 m 2/s at 293 K and 2.3×10 −15 m 2/s at 573 K), which are much larger than the diffusion coefficients in the bulk reported. Oxygen RF-plasma exposure might be effective to remove tritium retained even at a fairly deep region in carbon fiber composite (CFC) components.

Growth and properties of NdBCOAg large grains for device applications

Nd 1+xBa 2−xCu 3O y (NdBCO) bulk materials are known to have superior superconducting properties than YBa 2Cu 3O 7−δ (YBCO). However, several barriers need to be overcome prior to the development of reliable fabrication techniques for these materials. One of these barriers is the required tight control of processing oxygen partial pressure p( O 2), which dictates the degree of Nd 3+ substitution onto Ba 2+-site and consequently affects both T c and J c . In addition, it is difficult to find an appropriate seed with similar lattice structure to and higher melting point than NdBCO, due to its nearly the highest peritectic temperature in the REBCO series. This paper focuses on establishing the growth conditions of Ag-doped, and hence melting point depressed, NdBCO large grains under high p( O 2) of 1–5% using NdBCO seeds introduced either at room temperature or near the peritectic temperature of NdBCOAg. The superconducting properties of the large NdBCOAg grains fabricated following the optimized conditions were also characterized.

Optimization of seeding conditions for the fabrication of c-axis-oriented large NdBCO–Ag grains

NdBCO large-grain materials can improve the performance of engineering devices based on superconducting bulk materials if c-axis-oriented large grains can be produced in large quantities under simple processing conditions. This study concentrates on exploring the factors dictating the seeding behavior and the subsequent growth morphology of Ag-doped NdBCO grains under relatively high oxygen partial pressure using NdBCO seeds and a simple processing system. It was found that seeding temperature, aspect ratio of seed, and amount of Ag were all important factors affecting the success rate of inducing c-axis-oriented growths. With the optimized seeding conditions and in view of the simplicity of the processing system, the processing conditions derived from this study could lead to the up-scaling of NdBCO–Ag large-grain materials production.

The microstructural development of Ag/Ni multilayers during annealing

Abstract By use of transmission electron microscopy, including electron-energy-loss spectroscopy with image filtering techniques, and X-ray diffraction, the change in microstructure during annealing of -textured Ag/Ni multilayers has been studied. The multilayer break-up proceeds by the formation of Ag and Ni grains which grow at the expense of the multilayer. The driving force originates from the interface energy and large stresses in the multilayers. The grain growth was monitored with time by in-situ X-ray diffraction and an activation energy was derived which suggests that the diffusional mass transport takes place along grain boundaries and interfaces. The texture was preserved during the destratification of the multilayer which indicates that the Ag and Ni grains are not formed by a process of nucleation and growth but rather by the growth of individual layers.

Selective External Oxidation of the Intermetallic Compound, BaAg5

The selective oxidation of has been examined at 650–680°C in flowing . Under these conditions, a continuous external barium oxide scale formed. Depletion of Ba from the underlying led to the formation of a continuous Ag layer between the oxide scale and the . Ba was only detected along grain boundaries in the continuous Ag layer, which was consistent with the negligible solubility reported for Ba in bulk Ag. The local thickness of the continuous Ag layer was inversely correlated to the local Ag grain size. Subsequent experiments with Ag‐clad revealed that surface oxide formation commenced at exposed Ag grain boundaries. specimens clad with fine grained Ag foil exhibited more extensive oxide formation in a given time than specimens clad with coarse grained Ag foil. These observations confirmed that outward Ba migration through the continuous Ag layer occurred preferentially along Ag grain boundaries. This work demonstrates that an intermetallic compound may undergo external oxidation even when a continuous metallic (or intermetallic) layer, that possesses a low solubility for the oxidizable element, forms under the oxide scale. © 2000 The Electrochemical Society. All rights reserved.

Ion-beam modification of Co/Ag multilayers I: Structural evolution and magnetic response

We describe the effects of 1 MeV Si+ ion-beam irradiation on a sputtered Co/Ag multilayer with layer thicknesses of 5 Å for Co and 25 Å for Ag, thicknesses for which the magnetoresistance is maximum in the as-deposited sample. X-ray diffraction, magnetization, and magnetoresistance measurements all point to the conclusion that the Co is initially dispersed through the Ag and segregates completely upon ion-beam bombardment. Throughout the process both Ag and Co grains maintain a high degree of texture, essentially face centered cubic (111). The magnetization behavior evolves from superparamagnetic to mixed superparamagnetic–ferromagnetic with ion dose whereas the room-temperature magnetoresistance decreases from 12% to 1.5% upon irradiation up to 5×1016 Si+/cm2. Simple models taking into account the size distribution of the Co particles have been used to analyze these phenomena in order to quantify the particle size distribution.

A new direct process to prepare YBa 2Cu 3O 7− δ films on biaxially textured Ag{110}〈211〉

YBa 2Cu 3O 7− δ (YBCO) films were successfully prepared on biaxially textured Ag{110}〈211〉 substrates by using pulsed laser deposition. X-ray diffraction results showed that the degree of preferential orientation of Ag{110}〈211〉 substrates varied with increasing annealing temperature. With a thin template layer deposited at low temperature, YBCO film with c-axis orientation and in-plane biaxial alignment could be obtained at high deposition temperature. Scanning electron microscopy observation revealed that YBCO grains enlarged, but Ag grains on the surface of the YBCO films became smaller with increasing deposition temperature. At optimal deposition conditions, Ag atoms diffuse into the YBCO grain boundaries, and then fill in the weak-link regions in the YBCO film, resulting in the easier conduction. J c value of 5×10 5 A/cm 2 was obtained at 77 K and zero magnetic field for the best YBCO film in our work.

Structure and giant magnetoresistance of laser irradiated Ag/Co multilayers

The Ag/Co multilayers (MLs) showing the giant magnetoresistance (GMR) were thermally processed by excimer laser irradiation at the fluence up to 0.25 J cm −2 with 1–200 pulses. An increase of the GMR ratio from 7.5–15% at 4.2 K was observed for MLs with Ag layers composed of randomly oriented Ag grains at lower laser fluences when MLs were not melted. For textured Ag/Co ML the effect of irradiation on GMR was minor. The behavior of different MLs under laser irradiation vs. their structure is discussed.

Formation of granular-like structure of Ag/Co multilayers by excimer laser irradiation

The electron beam deposited Ag/Co multilayers (MLs) showing the giant magnetoresistance (GMR) were thermally processed by XeCl excimer laser irradiation at the fluences between 0.1 and 0.25 J/cm 2 with 1–200 pulses. An increase of the GMR ratio from 7.5 to 15% at 4.2 K was observed for ML with Ag layers composed of randomly oriented Ag grains at lower laser fluences when the ML was not yet melted. The magnetization M(T) curves of the irradiated samples indicate the presence of granular like component, while the anisotropy of GMR due to layering persists. For Ag/Co ML with coherent structure the effect of irradiation on GMR was minor.

Structures of Ag/ZnO, Ag/WO&lt;SUB&gt;3&lt;/SUB&gt; and Ag/Al-oxide Nanocrystalline Composites Prepared by Gas Evaporation and &lt;I&gt;in-situ&lt;/I&gt; Compaction

Ag/ZnO, Ag/WO 3 and Ag/Al-oxide nanocrystalline composites were prepared by gas evaporation and successive in-situ compaction. The structures were observed by high-resolution transmission electron microscopy. The metal oxide grains in these composites were hardly deformed during the compaction at 2.0 GPa, while the Ag grains deformed along the external shape of the neighboring metal oxide grains. The Ag grains act as an adhesive between the metal oxide grains, resulting in a decrease in void formation.

Surface Microstructure and Magnetic Properties of Laser-Processed Granular Co-Ag Films

ABSTRACTCo-Ag films prepared by Pulsed Laser Deposition and showing GMR in the as deposited state, have been irradiated by excimer laser: the chemical and structural modification induced by such treatment have been studied by XPS and by atomic force and electron microscopies. The pulsed laser irradiation favors the nucleation of nanosized Co grains at Ag grain boundaries, resulting in an enhancement of the magnetoresistivity at low fields and low temperature. Indeed, after laser treatment, a doubled field sensitivity (δGMR/δH) at T=I0K, with respect to the untreated samples, has been observed. The correlation with the observed magnetic properties variations, is discussed.

Radiotracer Diffusion of Ni and Ag in Ag and Ni Grain Boundaries and Oriented Ag/Ni Interphase Boundaries

Grain boundary and interphase boundary diffusion has been investigated in the system Ag/Ni using the radiotracer serial sectioning technique. Ni segregation in Ag grain boundaries is strongly temperature dependent leading to the conclusion that Ni atoms are located mainly in the bulk planes adjacent to the grain boundary. From interphase boundary diffusion measurements in (110) oriented Ag/Ni interphase boundaries it can be deduced that the structure of this interphase boundary is incoherent.

Clustering process of the cuprate phase in Ag-added BPSCCO composites

The clustering of cuprate grains in sintered composites of Ag-added (Bi, Pb)–Sr–Ca–Cu–O (Tc≈110 K) has been investigated in particular reference to the percolation process. The material consists of two phases: metallic grains of Ag and superconducting cuprate-grains of (Bi, Pb)2Sr2Ca2Cu3Ox (2223 phase). The resistivity ρ at 77 K is a decreasing function of Ag-volume fraction f, the contribution from the superconducting clusters being concealed. However, when the temperature T is further lowered enough, ρ changes stepwise into an increasing function, showing the obvious contribution from the superconducting clusters. This transition is realized when the superconducting weak-link is enhanced by lowering T, and is featured by the two dimensional character of the percolation process of the cuprate clusters.