Ag Grains Research Articles

In-situ evolution of temperature dependent attenuation coefficients of plasmonic silver nanostructures

With a growing interest in high temperature applications of plasmonic metal nanostructures, the morphological modulation and the evolution of optical constants of these plasmonic nanostructures have become important both from fundamental growth dynamics point of view and from optical applications viewpoint. In the present investigation, set of plasmonic silver nanostructures (thickness range 5–25 nm) have been grown by e-beam evaporation technique with varying deposition time. They have been subjected to temperature dependent in-situ spectroscopic ellipsometry measurements for optical analysis at room temperatures (25 °C) and at various elevated temperatures (80 °C–530 °C). The evolutions of optical and surface morphological parameters of these Ag nanostructures as a function of thicknesses have also been investigated. The optical attenuation coefficients (400–700 nm) of these Ag nanostructures are found to evolve in a different fashion depending upon thickness controlled nano-morphology. For low thickness films (5–16 nm), which consists of discrete Ag grains, the light attenuation coefficient initially decreases up to ∼130 °C and subsequently increases with increasing temperature up to 300 °C. This is due to the competition of two counteracting phenomena of reduction of electron-grain boundary scattering and increase in LSPR absorption effect due to temperature induced grain expansion. In contrast, for the relatively thicker films (>16 nm), the optical attenuation coefficient was found to decrease with increasing temperature due to dominance of former effect over later which is caused by larger grain size and network-like nano-morphology. The investigated temperature dependent evolution of optical properties is relevant in studies of physical processes at elevated temperatures and also for accurate modeling of plasmonic devices in high-temperature applications.

Microstructure evolution and highly sensitive surface enhanced Raman scattering properties of self-formation dual-scale Ag nanoparticles/ Ag-Zr alloy film

• Simple method was proposed to prepare monodisperse Ag particles/Ag-Zr films. • Ag nanoparticles (NPs) directly formed on the surface of as-deposited Ag-Zr films. • Size, number and nanogap of Ag NPs are sensitive to Ag-Zr film thickness. • Ag NP/Ag-Zr granular film displays effective Raman enhanced properties. Ag-22%Zr alloy films with different thicknesses were fabricated on flexible polyimide substrate by co-sputtering method. It is interested in finding that a lot of Ag nanoparticles are spontaneously formed on the as-deposited Ag-Zr films at room temperature. The phase, crystal structure, particle number and size, and surface enhanced Raman scattering (SERS) properties of as-deposited and annealed Ag-Zr alloy films were characterized by X-ray diffraction, high resolution transmission electron microscope, field emission scanning electron microscope and Raman spectrometer, respectively. Results show that Zr grains dispersed around Ag grains and had a coherent growth relation with Ag grains in the alloy film. Dual scale Ag nanoparticles were formed on the annealed Ag-Zr alloy films without template. An intense SERS effect was obtained by covering the Ag layer on the Ag-Zr alloy films. The SERS substrate showed good repeatability and revealed high sensitivity of enhancement factor with the detection limit concentration of Rhodamine 6G as low as 5 × 10-15 mol/L. It was demonstrated that the nanogaps between Ag nanoparticles behaved as hot spots, and thus enhanced local electromagnetic fields substantially. Furthermore, densely and uniformly distributed Ag nanoparticles enlarged the surface roughness and the surface area, resulting in further enhanced Raman signals.

Nano-Ag Particles Embedded in C-Matrix: Preparation, Properties and Application in Cell Metabolism.

The application of nano-Ag grains as antiviral and antibacterial materials is widely known since ancient times. The problem is the toxicity of the bulk or big-size grain materials. It is known that nano-sized silver grains affect human and animal cells in some medical treatments. The aim of this study is to investigate the influence of nano-Ag grains embedded in a carbonaceous matrix on cytotoxicity, genotoxicity in fibroblasts, and mutagenicity. The nanocomposite film is composed of silver nanograins embedded in a carbonaceous matrix and it was obtained via the PVD method by deposition from two separated sources of fullerenes and silver acetate powders. This method allows for the preparation of material in the form of a film or powder, in which Ag nanograins are stabilized by a carbon network. The structure and morphology of this material were studied using SEM/EDX, XRD, and Raman spectroscopy. The toxicology studies were performed for various types of the material differing in the size of Ag nanograins. Furthermore, it was found that these properties, such as cell viability, genotoxicity, and mutagenicity, depend on Ag grain size.

The Effect of Co Content and Annealing Temperatures on the Resistivity in Ag-Co Films.

Ag-Co films with ultra-high resistivity were prepared on polyimide by magnetron sputtering. The effect of Co content and annealing temperatures on the resistivity and microstructure of Ag-Co films has been thoroughly investigated and the relation between resistivity and microstructure has been discussed. Results show that thicker Ag-Co films without annealing present lower resistivity due to better crystallinity. However, thin Ag-Co films (≤21 nm) annealed at 360 °C present ultra-high film resistivity because of the formation of diffusion pits on the film surface which blocks the transmission of electrons in films to increase film resistivity. Inversely, the resistivity of thick Ag-Co films (≥45 nm) annealed at 360 °C is much less than that annealed at lower than 260 °C owing to no diffusion pits. Furthermore, the addition of Co inhibits the growth of Ag grains and limits the migration of electrons in Ag-Co films further, also resulting in the increase of Ag-Co films’ resistivity.

Investigation of the AgCl Formation Mechanism on the Ag Wire Surface for the Fabrication of a Marine Low-Frequency-Electric-Field-Detection Ag/AgCl Sensor Electrode.

One of the most widely used electric field sensors for low-frequency electric field detection (LFEFD) in seawater uses the Ag/AgCl electrode. The surface structure of the electrode including AgCl layers plays a critical role in the electrode’s electrochemical performance required for the sensor. In this study, the sequential AgCl formation process under the constant current was examined on the Ag wire in an electrode size for actual applications, and an optimal electrode surface structure was suggested for the LFEFD Ag/AgCl sensor. Upon mild anodization (0.2 mA/cm2) in 3.3 M KCl solution that permits us to follow the AgCl formation process manageably, Ag dissolution from the wire surface begins leaving cavities on the surface, with the accompanied growth of initial Ag grains. During this period, AgCl deposits in sizes of about several micrometers to 10 μm with crystal planes also form primarily along scratch lines on the wire surface, but in a partial scale. Then, with further anodization, the assumed thin AgCl deposits start to form, covering a large portion of the wire surface. They grow to become deposits in sizes of about several micrometers to 10 μm with no clear facet planes next to one another and are connected to form the network structure, representing the main developing mode of the AgCl deposits. While they cover all the surface, AgCl deposits also form on the surface of the already formed ones, making multiple AgCl layers. All these deposits develop through the nucleation process with a relatively high surface energy barrier, and their formation rate is solely controlled by the release rate of Ag+ from the wire, thus by the applied current magnitude. The Ag/AgCl electrode with a thick AgCl layer and many holes in the AgCl surface structure like microchannels is considered to work effectively for the LFEFD sensor in terms of both detection sensitivity and service lifetime.

Microstructural Analysis and Mechanical Characterization of Shape Memory Alloy Ni-Ti-Ag Synthesized by Casting Route

The purpose of the current research is to study the microstructure and mechanical properties of Ni-Ti-Ag shape memory alloys prepared by the casting route. Ag (grain size at 1 mm) was incorporated into Ni-Ti alloys at varying percentages of weight (0, 1.5, 3 and 4.5 wt.% Ag) to produce shape memory alloys using a Vacuum Arc Re-melting (VAR) furnace. Microstructural analysis was defined by FESEM microscopy and XRD examinations, while the transformation temperatures of the Ni-Ti-Ag shape memory alloy were determined by DSC examination. On the other hand, determination of mechanical properties was carried out using micro-hardness and compressive tests. The results of this work show that Ag was dispersed homogeneously into the Ni-Ti alloy. Moreover, two primary phases (austenite phase and martensite phase) emerged with few impurities. The results of the XRD examination show that the number of Ag peaks increased with the increase in weight percentage of Ag. The transformation temperature of the austenitic phase was defined as −1.6 °C by DSC. The mechanical characterizations increased with the increase in weight percentages of Ag (1.5, 3 and 4.5 wt.%), and significantly affected the mechanical properties of the Ni-Ti alloy. An improvement in compressive strength (42.478%) was found for the alloy with 3 wt.% Ag, while the micro-hardness results show a slight decrease in micro-hardness (8.858%) for the alloy with 4.5 wt.% Ag.

Many-Scale Investigations of Deformation Behavior of Polycrystalline Composites: II-Micro-Macro Simultaneous FE and Discrete Dislocation Dynamics Simulation.

The current work numerically investigates commercial polycrystalline Ag/17vol.%SnO composite tensile deformation behavior with available experimental data. Such composites are useful for electric contacts and have a highly textured initial material status after hot extrusion. Experimentally, the initial sharp fiber texture and the number of 3-twins were reduced due to tensile loading. The local inhomogeneous distribution of hardness and Young’s modulus gradually decreased from nanoindentation tests, approaching global homogeneity. Many-scale simulations, including micro-macro simultaneous finite element (FE) and discrete dislocation dynamics (DDD) simulations, were performed. Deformation mechanisms on the microscale are fundamental since they link those on the macro- and nanoscale. This work emphasizes micromechanical deformation behavior. Such FE calculations applied with crystal plasticity can predict local feature evolutions in detail, such as texture, morphology, and stress flow in individual grains. To avoid the negative influence of boundary conditions (BCs) on the result accuracy, BCs are given on the macrostructure, i.e., the microstructure is free of BCs. The particular type of 3D simulation, axisymmetry, is preferred, in which a 2D real microstructural cutout with 513 Ag grains is applied. From FE results, 3-twins strongly rotated to the loading direction (twins disappear), which, possibly, caused other grains to rotate away from the loading direction. The DDD simulation treats the dislocations as discrete lines and can predict the resolved shear stress (RSS) inside one grain with dependence on various features as dislocation density and lattice orientation. The RSS can act as the link between the FE and DDD predictions.

Damage Analysis in Ag Nanoparticle Interconnect Line Under High-Density Electric Current

Abstract Printed electronics (PEs) have attracted attention for the fabrication of microscale electronic circuits. PEs use conductive inks which include metal nanoparticles. The conductive ink can be printed on flexible substrates for wearable devices using ink-jet printers and roll-to-roll methods. With the scaling down of electric devices, the current density and Joule heating in the device lines increase, and electromigration (EM) damage becomes significant. EM is a transportation phenomenon of metallic atoms caused by the electron wind under high-density current. Reducing the EM damage is extremely important to enhance the device reliability. With the progress in miniaturization of the metal nanoparticle ink lines, EM problem needs to be solved for ensuring the reliability of these lines. We know that the formation of aggregates and cathode damages occur due to a current loading. The diffusion path of atoms due to the EM has not been identified under the high-density current loading. In this study, a high-density electric current loading was applied to an Ag nanoparticle line. The line specimens were prepared using a lift-off method. After the current loading tests, observations were conducted using a laser microscope and scanning electron microscope. A local decrease in the line thickness and scale-shaped slit-like voids were observed due to the high-density current loading. Moreover, the microstructure of the line was modified by enlarging the Ag grain. From the results, we identified that a dominant diffusion occurred at the Ag grain boundary due to the EM.

Wide range tunability of surface plasmon resonance of nanostructured Ag deposited by off-axis magnetron sputtering

In this work, nanostructured Ag showing size distribution dependent tunable surface plasmon resonance (SPR) are grown on glass substrate using off-axis DC magnetron sputtering at a sputtering power of 74 W. Argon gas pressure is set at 8.0 Pa and the deposition time is varied in the range 5–300 s. The structural, morphological, and optical properties are examined by using X-ray diffractometer (XRD), field emission scanning electron microscope (FESEM), and UV–Visible spectrophotometer. XRD patterns of all samples reveal characteristic (111) and (200) peaks of fcc Ag. Broad XRD peaks suggest formation of nanosized Ag crystallites with mean crystallite size of 3 nm. FESEM images depict near spherical Ag grains up to 120 s deposition time and elongated grains with greater substrate coverage with extended deposition time of 300 s. SPR features are well distinct in the optical absorption spectra which are highly sensitive to the deposition time. Within a short deposition time of 5–60 s, nanostructured Ag demonstrates wide range SPR tunability from 438 nm to 530 nm. It is observed that the variations in the size distribution as estimated from FESEM images are crucial to observe systematic red shift of SPR with increasing deposition time. Nanosized Ag produced by off-axis magnetron sputtering may be used as a vital component in plasmonic devices and sensors.

Abnormal microstructure evolution behaviors of annealed Ag-18.9 at% Co alloy film on flexible polyimide substrates

Ag-Co alloy films were fabricated at room temperature by magnetron sputtering. The results revealed that a large amount of polyhedral single-crystal Ag nanoparticles grow on the surface of Ag-Co alloy films, which is significantly different from the microstructure of Ag-Co alloy films on rigid substrates. Furthermore, after annealing, Ag atoms get enough energy to move toward the film surface and thus the mass and average size of Ag particles both increase with the increase of annealing temperatures. In addition, the average size of Ag particles decreases with the increase of annealing time but the particles per square micron increases. Amorphous Co is observed in the Ag-Co films and Ag grains in Ag-Co films become smaller, which indicates the growth of Ag grains is inhibited by Co. A new type of Ag particles / Ag-Co films with a convex structure is obtained and applied as SERS substrates, where the characteristic Raman spectra of 5 × 10−12 M R6G could be detected.

High performance Ag2Se/Ag/PEDOT composite films for wearable thermoelectric power generators

Herein, we report a Ag2Se/Ag/PEDOT (poly (3,4-ethylenedioxythiophene) composite film with a high thermoelectric performance and superior flexibility. First, we used PEDOT: poly (styrenesulfonate) (PSS) coated Se nanowires (NWs) as templates to prepare PEDOT:PSS coated Ag2Se/Ag composite powders, then Ag2Se/Ag/PEDOT composite films supported on porous nylon membrane were fabricated by vacuum assisted filtration and then hot pressing. An optimum composite film exhibits a high power factor of ∼1442.5 μW m−1 K−2, ultrahigh electrical conductivity (σ) of ∼5957.3 S cm−1 and superior flexibility (only 5.5% decrease in σ after 1000 times bending around a 4 mm radius rod) at RT. A certain amount of Ag phase in the composite film leads to an ultrahigh σ, while the PEDOT located at the interface between Ag and Ag2Se grains and at the surface of the Ag2Se grains causes the composite film with a low thermal conductivity. The excellent flexibility is due to the synergistic effect of the nylon membrane and PEDOT. Moreover, a 4-leg flexible thermoelectric power generator (f-TEG) assembled with the composite film shows a low internal resistance of ∼8 Ω, which makes it very possible to be integrated with a DC/DC converter for continually outputting power. The f-TEG produces a voltage of 5.6 mV and a maximum power of 1.8 μW (power density of 7.47 W m−2) at a temperature gradient of 27 K. This work provides an effective avenue for preparing high-performance flexible thermoelectric film with ultrahigh electrical conductivity.

From Unimolecular Template to Silver Nanocrystal Clusters: An Effective Strategy to Balance Antibacterial Activity and Cytotoxicity.

Silver nanomaterials have attracted a great deal of interest due to their broad-spectrum antimicrobial activity. However, it is still challenging to balance the high antibacterial efficiency with low damage to biological cells of silver nanostructures, especially when the diameter decreases to less than 10 nm. Here, we developed a new type of Ag nanohybrid material via a unimolecular micelle template method, which presents amazing antibacterial activities and almost noncytotoxicity. First, water-soluble multiarm star-shaped brushlike copolymer α-CD-g-[(PEO40-g-PAA50)-b-PEO5]18 was precisely synthesized and its micelle behavior in different solvents was revealed. Then, nanocrystal clusters assembled by Ag grains (Ag@Template NCs) were prepared through an in situ redox route using the unimolecular micelle of α-CD-g-[(PEO40-g-PAA50)-b-PEO5]18 as the soft template, AgNO3 as a precursor, and tetrabutylammonium borohydride (TBAB) as the reducing agent. The overall size of the achieved Ag@Template NCs is controlled by the template structure at around 40 nm (Dh in DMF), and the size of the Ag grain can be easily regulated from ∼1 to ∼5 nm by adjusting the feeding ratio of AgNO3/acrylic acid (AA) units in the template from 1:10 to 1:1. Benefitting from the structural design of the template, all Ag@Template NCs prepared here exhibit excellent dispersibility and chemical stability in different aqueous environments (neutral, pH = 5.5, and 0.9% NaCl physiological saline solution), which play a crucial role in the long-term storage and potential application in a complex physiological environment. The antibacterial and cytotoxicity tests indicate that Ag@Template NCs display much better performance than Ag nanoparticles (Ag NPs), which have a comparable overall size of ∼25 nm. The inhibitory capability of Ag@Template NCs to bacteria strongly depends on the grain size. Specifically, the Ag@Template-1 NC assembled by the smallest grains (1.6 ± 0.3 nm) presents the best antibacterial activity. For E. coli (-), the MIC value is as low as 5 μg/mL (0.36 μg/mL of Ag), while for S. aureus (+), the value is around 10 μg/mL (0.72 μg/mL of Ag). The survival rate of L02 cells and lactate dehydrogenase assay together illustrate the low cytotoxicity possessed by the prepared Ag@Template NCs. Therefore, the proposed Ag@Template NC structure successfully resolves the high reactivity, instability, and fast oxidation issues of the ultrasmall Ag nanoparticles, and integrates high antibacterial efficiency and nontoxicity to biological cells into one platform, which implies its broad potential application in biomedicine.

Critical processing temperature for high-performance protected silver mirrors

Silver (Ag) mirrors for astronomical telescopes consist of multiple metallic and dielectric thin films. Furthermore, the topmost surface of such Ag mirrors needs to be covered by a protection coating. While the protection coating is often deposited at room temperature and the entire mirrors are also handled at room temperature, various thin film deposition techniques offer protection coatings with improved characteristics when carried out at elevated temperatures. Thus, in this work, high-performance Ag mirrors were designed and fabricated with a new benchmark. The resulting Ag mirrors were annealed (i.e., post-fabrication annealing) at various temperatures to investigate the viability of introducing thermal processes during and/or after fabrication in improving overall optical performance and durability of protected silver mirrors. In our experiments, Ag mirror samples were deposited by electron-beam evaporation and subsequently annealed at various temperatures in the range from 60 {\deg}C to 300 {\deg}C, and then the mirror samples underwent an environmental stress test at 80 {\deg}C and 80% humidity for 10 days. While all the mirror samples annealed below 200 {\deg}C showed negligible corrosion after undergoing the stress testing, those annealed below 160 {\deg}C presented spectral reflectivity comparable to or higher than that of as-deposited reference samples. In contrast, the mirror samples annealed above 200 {\deg}C exhibited significant degradation after the stress testing. The comprehensive analysis indicated that delamination and voids caused by the growth of Ag grains during the annealing are the primary mechanisms of the degradation.

Telluride Mineralogy of the Deer Horn Au-Ag-Te-(Bi-Pb-W) Deposit, British Columbia: Implications for the Generation of Tellurides

ABSTRACTThe Deer Horn deposit, located 150 km south of Smithers in west-central British Columbia, is an Eocene polymetallic system enriched in Au-Ag-Te with lesser amounts of Bi-Pb-W; the Au and Ag are hosted in Te-bearing minerals and Ag-rich gold (Au-Ag alloy). A quartz-sulfide vein system containing the main zones of Au-Ag-Te mineralization and attendant sericite alteration occurs in the hanging wall of a local, spatially related thrust fault and is genetically related to the nearby Eocene Nanika granodiorite intrusive suite. Tellurium-bearing minerals commonly form isolated euhedral to subhedral grains or composite grains (up to 525 μm in size) of Ag-, Bi-, Pb-, and Au-rich tellurium-bearing minerals (e.g., hessite, tellurobismuthite, volynskite, altaite, and petzite). Panchromatic cathodoluminescence imaging revealed four generations of quartz. Within remnant cores of quartz I, local oscillatory zoning occurs in quartz II. Fine-grained veinlets of quartz III and IV crosscut quartz I and II, showing evidence of at least two deformation events; late-forming veinlets of calcite crosscut all generations of quartz. The tellurides and Ag-rich gold occur in stage III quartz. Three types of fluid inclusions were observed in stage III and IV quartz: (1) aqueous liquid and vapor inclusions (L-V); (2) aqueous carbonic inclusions (L-L-V); and (3) carbonic inclusions (vapor-rich). Primary fluid inclusions related to the telluride mineralization within quartz III were tested with microthermometry, along with a few primary inclusions from quartz IV. Homogenization temperatures are 130.0–240.5 °C for L-V inclusions and 268.0–336.4 °C for L-L-V inclusions. Aqueous carbonic inclusions had solid CO2 melting temperatures from –62.1 to –56.8 °C, indicating the presence of ≈1 to 30 mol.% dissolved methane in these inclusions.The Deer Horn Au-Ag-Te-(Bi-Pb-W) deposit is a reduced intrusion-related gold system characterized by sheeted veins, metal zoning, low salinity aqueous-carbonic fluids, and a genetic relationship to an Eocene granodiorite. Values of δ34S of pyrite vary from –1.6 to 1.6 per mil and are compatible with a magmatic source of sulfur.

Influence of Co contents on the microstructure and SERS performance of self-formed Ag nanoparticles/Ag-Co alloy films on flexible substrates

Self-formed Ag nanoparticles/Ag-Co alloy films with various Co contents were fabricated by sputtering Ag-Co composite target. Effects of Co contents in Ag-Co films on the microstructure and SERS performance of nanoparticles/alloy films were thoroughly investigated through SEM, TEM and Raman spectrometer. Amorphous Co in Ag-Co films restricted the growth of Ag grains in the films and promoted the formation and growth of Ag nanoparticles on the film’s surface. The size and number of Ag nanoparticles grown on the surface were closely related to Co contents in Ag-Co films, Ag-Co film thicknesses and annealing temperatures. Ag nanoparticles/Ag-Co films covered with Ag layers performed ultra-sensitive Raman signals due to forming abundant active hot spots. This flexible SERS substrate could detect 10−12 mol/L Rhodamine 6G (R6G), which indicated that this novel type of Ag nanoparticles/Ag-Co alloy films could be used and applied as high-efficient SERS substrates.

The Effect of Aerophine 3418A Collector Dosage on Niğde (Ulukışla-Madenköy) Complex Pb-Zn Sulphide Ore Flotation

In this study, grinding + flotation experiments were performed on the sample of complex Pb-Zn sulphide ore taken from Niğde (Ulukışla-Madenköy) region in Turkey. According to the mineralogical analysis of the ore sample used in experimental studies, it was determined that the ore composition contains calcite, quartz, pyrite, chalcopyrite, hematite, goethite, limonite, gypsum, galena, sphalerite, jarosite, arsenopyrite and marcasite minerals. In addition, Au and Ag grains were found to be inclusions in hematite, goethite and jarosite minerals. The experiments were carried out at a solid ratio of 30%, a flow rate of 10 L/min, a stirring rate of 1250 rpm and pH = 9. In flotation tests, lime is used as the pH regulator, zinc sulphate, sodium silicate as the depressant, sodium isobutyl dithiophosphine as the collector and methyl isobutyl carbinol as the frother. In the flotation studies, the effect of Aerophine 3418A collector dosage on flotation was investigated. As a result, a lead concentrate of 55.13% Pb was obtained and it was found that this concentrate contained 2489 ppm of Ag. The amount of Aerophine 3418A collector was determined as 10 g/t.

P‐38: A Study on the Difference of Thermal Behavior by Crystallization Method

Indium‐Tin‐Oxide (ITO) / Ag (Silver) / ITO triple layer, are often used as anode electrodes, but when the Ag is eluted, they cause many problems, such as poor dark spots. In this paper, the thermal behavior of the upper ITO, which is presumed to be the most relevant, was observed to identify the cause of this defect. The ITO layer is deposited in an amorphous state during initial deposition to create a pattern. After patterning, it is crystallized by heat treatment to obtain electrical and physical characteristics. However, it was confirmed that partial crystallization was already in progress at initial deposition due to changes in thickness. Partial crystallization was mainly observed at the meeting points of the three Ag grains. It was also confirmed that the process of heat treatment led to different crystallization than the initial partial crystallization. The crystallization areas formed in these heterogeneous states showed different thermal behavior. Stress caused by different thermal behaviors accelerated as heat treatment progressed, producing pin‐holes after the heat treatment was completed. Thus, the number of pin‐holes increases as heterogeneous states increase, resulting in a difference in the level of Ag elution defect. In conclusion, a decrease in the number of triple points an Ag Grain meets can reduce dissimilarity and consequently reduce the probability of pin‐hole occurrence. Therefore, expanding the size of the Ag Grain is effective in reducing the defect of Ag elution.

Fracture mechanism of microporous Ag-sintered joint in a GaN power device with Ti/Ag and Ni/Ti/Ag metallization layer at different thermo-mechanical stresses

Ag sinter joining technology is emerging as a die attach material for next-generation power modules in high-temperature applications. Thermal shock test has revealed that the fracture characteristics and reliability of sintered Ag joint were influenced by thermo-mechanical stress. This was study conducted to understand the microstructure, vertical crack formation, and fracture behavior of sintered Ag joints which were designed with different metallization layers on a direct bonded aluminum (DBA) substrate, at different thermo-mechanical stresses during thermal shock tests. Two kinds of metallization layers were designed as Ti/Ag and Ni/Ti/Ag layers. A finite element model (FEM) simulation confirmed that the Ni layer prohibited Al hillock-like deformation and generates different thermo-mechanical stresses during the thermal shock test from − 50 °C to 250 °C. Depending on the degradation of the interfaces for both of the Ag-sintered joints, the sintered Ag grain necking thickness and microstructure characteristics including the Ag grain structures, which have a dominant influence on the bonding strength in terms of long-term reliability, are considerably different from the results by an electron back scatter diffraction (EBSD) analysis. This paper proposes a novel metallization technology that can induce joint fracture with complete recrystallization of sintered Ag joints by effectively suppressing interfacial degradation. The mechanism of this technology was systematically analyzed through experiments and FEM simulations.

Sputtering of Ag (111) nanotwinned films on Si (100) wafers for backside metallization of power devices

For improving the performance of backside metallization for power electronic devices, an innovative Ag film with ultra-high twin density is proposed in this study. Experimentally, nanotwinned Ag films with thicknesses ranging from 2 to 8 µm and a strong (111) preferred orientation were sputtered on Si (100) wafers with and without a Ti thin film. The results indicated that the coincident Σ3 twin and Σ9 near-twin boundaries in proportion to the total grain boundaries in this Ag nanotwinned film on Ti pre-coated Si (100) wafer were 50.8 % and 13.5 %, respectively. These Ag nanotwins had spacing of 2 to 50 nm, with an average spacing of about 12 nm, and were contained in columnar Ag grains grown normal to the Si wafer. The employment of a Ti interlayer of 0.1 µm thickness clearly improved the adhesion at the Ag/Si interface under peeling tests, resulting in a bonding strength of 1.7 MPa and a maximal indentation hardness of 2 GPa.

Ultra-high local plasticity in high-strength nanocomposites

We subjected an aged Cu-24wt%Ag ingot to cold drawing to create a high-strength nanostructured composite wire with both Cu-rich proeutectic and Ag-rich eutectic components. During the drawing, a fine lamellar structure (average spacing 20 ± 6 nm) developed in the proeutectic component, which contained a high density of Ag fibers (average width below 5 nm) embedded in the matrix. In the eutectic component, a relatively coarse structure developed, with an average Ag grain size around 100 nm. The result of such a bimodal size of Ag fibers was ultra-high bending plasticity, i.e., the drawn wire tolerated 59% bending strain at the outermost edge, 15 times its tensile elongation (3.6%). During our bending test, dynamic recovery and partial recrystallization occurred more near the inner edge than near the outer edge and primarily in the eutectic component. High bending strain caused some of the thicker Ag fibers to become discontinuous and lose their original alignment. This structural evolution increased local plasticity, resulting in an unexpectedly high achievable bending strain, which is unusual in nano-sized, Ag-fiber-reinforced high-strength composites.