Wetting Of Ag Research Articles

Achieving excellent wetting of inactive Ag on C/C composites by a low-temperature surface modification strategy

Carbon fiber reinforced carbon matrix (C/C) composites are one of the most promising thermal lightweight materials. However, the inferior wettability of inactive metals on C/C composites severely limits their application for joining alloys in industrial structures. In this study, successful wetting of inactive Ag on C/C composites is achieved via a low-temperature surface modification strategy. After surface modification using a chromium carbide (CrC) layer, the contact angle of Ag droplets on C/C substrates decreases significantly from 158° to 26°. Results of microstructure analysis indicate that no new reaction phases are generated during the wetting process. The wetting and spreading process of Ag droplets on CrC modified C/C substrates are promoted by the diffusion from Ag to CrC layer, which is found for the first time in this study. This study provides a novel surface modification concept for the wetting of C/C composites and other carbon materials.

Exploring the role of Mn–Co spinel coating on Crofer 22 APU in adjusting reactions with the Ag based sealant during reactive air brazing

In this work, the Mn–Co spinel coating is successfully employed to control adverse reactions at the Crofer 22 APU interconnect/Ag–CuO braze interface through blocking their direct contact. The Mn–Co spinel coating is fabricated on the Crofer 22 APU before reactive air brazing (RAB). Wetting of Ag–CuO braze on the Mn–Co spinel coated Crofer 22 APU is studied. Ag-8mol%CuO braze is used to successfully braze the Mn–Co spinel coated Crofer 22 APU and YSZ at 1050 °C for 30 min in air. The Crofer 22 APU is protected well by the Mn–Co spinel coating during RAB, avoiding its oxidation and the outward diffusion of Fe and Cr. The long-term stability of joints is also evaluated in air at 800 °C for 200 h. The Mn–Co spinel coating effectively mitigates further degradation of the joint caused by oxidation at the interconnect/braze interface.

Insights into effects of O-incorporated Ag nanoparticles as wetting seeds toward improving Ag wetting on oxides

Ag wetting on oxides is essential for implementing exceptional layered Ag superstructures with simultaneous ultralow losses in electrical conductance and optical transmittance. This goal is difficult to achieve by conventional synthetic techniques involving the incorporation of heterogeneous transition metals or metalloids into Ag as wetting inducers as they cause detrimental optoelectrical changes. This study provides novel insights into the use of homogeneous Ag wetting seeds to improve the wetting of Ag on oxides. We investigated the effect of atomic O incorporation on the improvement of Ag wetting by monitoring its participation in and contribution to the Ag clustering and layering processes. Minimal incorporation of dissolved atomic O as a surfactant into the Ag nanoparticles transposed the nanoparticle evolution path from a complete to incomplete coalescence mode at significantly reduced thicknesses, which was attributed to a reduction in the nanoparticle free energy. The size and shape of the O-incorporated Ag nanoparticles were precisely controlled to accelerate the wetting transition of Ag on ZnO substrates by circumventing the transmutation effect of O. These results demonstrate a notable strategy for accomplishing a rapid Ag wetting transition toward a completely continuous layer with ultralow optoelectrical losses.

Enhanced liquid metal wetting on oxide surfaces via patterned particles

Liquid metals typically do not intrinsically wet oxide surfaces due to chemical dissimilarity, preventing the formation of well-bonded interfaces in many applications. This paper investigates how the wetting and spreading of liquid silver (Ag) droplets on oxide surfaces can be enhanced via patterned nickel (Ni) particles using multiscale modeling. First, a force field (FF) for an Ag/yttria-stabilized-zirconia system was developed by fitting the interfacial binding energy to density-functional theory (DFT) calculations. Then, molecular dynamics (MD) simulations using these FF parameters revealed that the good wetting of Ag on Ni caused Ag droplets to be attracted to the Ni particles, promoting spreading. Thus, the optimal hexagonal Ni pattern was shown to enhance the wetting area by 224% compared to a bare oxide surface. Second, an analytical model predicting the maximum possible enhancement in wetting area as a function of the intrinsic wetting angle, size of the Ag droplet, and size of the Ni particles was derived and validated with MD simulations, to generalize this method to other substrates. Both the analytical model and MD results suggested that the ability of Ni patterns to enhance the Ag wetting area becomes more significant as the wettability of substrate becomes worse.

Effects of laser-textured surface pattern on the wetting behavior and composition optimization of brazing filler: experimental study and numerical simulation

To reduce interface brittle compounds of brazed joints, laser-textured surface pattern was used instead of excessive active element to enhance the wetting behavior of brazing filler on Ti3SiC2 ceramic substrate. The cylindrical surface pattern was designed by theoretical calculation and examined by numerical simulation. The numerical simulation results showed that the cylindrical surface pattern can not only effectively reduce the wetting angle on the substrate surface, but also greatly accelerate the spreading process of brazing filler. The results of wetting experiment showed that the wettability of Ag–Cu–2Ti (wt. %) brazing filler on Ti3SiC2 with cylindrical surface pattern sufficiently increased compared with that on smooth surface, which were consistent with the theoretical calculation and numerical simulation results. The titanium content in Ag–Cu–Ti that suitable for the brazing of Ti3SiC2 even could be reduced from 4.5 to 2.0 wt. %. The novel method provides a feasible route for promoting the wetting behavior and achieving composition optimization of brazing filler.

Single-crystalline silver nanowire arrays directly synthesized onto substrates by template-assisted chemical wetting

Silver (Ag) nanowire arrays have attracted extensive research attention for their outstanding electrochemical detection sensitivity and optical properties. The most frequently used technology for fabricating Ag nanowire arrays is electrodeposition within the pores of anodic aluminium oxide (AAO) templates. In this paper, single-crystalline Ag nanowire arrays were grown by the capillary wetting of molten Ag inside the nanopores of AAO templates at a temperature of 970 °C. To improve the infiltration height for the molten Ag in the capillaries of the AAO templates, copper oxide (CuO) was added as a supplement because it can improve the wetting behavior between molten Ag and AAO templates. After the Ag nanowire arrays were embedded within the AAO pores, a novel hydrothermal etching method was proposed to remove the AAO templates because AAO showed a phase transition, which made it difficult to remove the AAO after heating at 970 °C. To test the properties of the obtained Ag nanowire arrays, the surface-enhanced Raman scattering performance was also studied.

Pinhole-free TiO2/Ag(O)/ZnO configuration for flexible perovskite solar cells with ultralow optoelectrical loss.

Perovskite solar cells (PSCs) fabricated on transparent polymer substrates are considered a promising candidate as flexible solar cells that can emulate the advantages of organic solar cells, which exhibit considerable freedom in their device design thanks to their light weight and mechanically flexibility while achieving high photocurrent conversion efficiency, comparable to that of their conventional counterparts fabricated on rigid glasses. However, the full realization of highly efficient, flexible PSCs is largely prevented by technical difficulties in simultaneously attaining a transparent electrode with efficient charge transport to meet the specifications of PSCs. In this study, an effective strategy for resolving this technical issue has been devised by proposing a simple but highly effective technique to fabricate an efficient, multilayer TiO2/Ag(O)/ZnO (TAOZ) configuration. This configuration displays low losses in optical transmittance and electrical conductivity owing to its completely continuous, ultrathin metallic Ag(O) transparent electrode, and any notable current leakage is suppressed by its pinhole-free TiO2 electron transport layer. These features are a direct consequence of the rapid evolution of Ag(O) and TiO2 into ultrathin, completely continuous, pinhole-free layers owing to the dramatically improved wetting of metallic Ag(O) with a minimal dose of oxygen (ca. 3 at%) during sputtering. The TAOZ configuration exhibits an average transmittance of 88.5% in the spectral range of 400–800 nm and a sheet resistance of 8.4 Ω sq−1 while demonstrating superior mechanical flexibility to that of the conventional TiO2 on ITO configuration. The photocurrent conversion efficiency of flexible PSCs is significantly improved by up to 11.2% thanks to an optimum combination of optoelectrical performance and pinhole-free morphologies in the TAOZ configuration.

Ultrathin Silver Film Electrodes with Ultralow Optical and Electrical Losses for Flexible Organic Photovoltaics.

Improving the wetting ability of Ag on chemically heterogeneous oxides is technically important to fabricate ultrathin, continuous films that would facilitate the minimization of optical and electrical losses to develop qualified transparent Ag film electrodes in the state-of-the-art optoelectronic devices. This goal has yet to be attained, however, because conventional techniques to improve wetting of Ag based on heterogeneous metallic wetting layers are restricted by serious optical losses from wetting layers. Herein, we report on a simple and effective technique based on the partial oxidation of Ag nanoclusters in the early stages of Ag growth. This promotes the rapid evolution of the subsequently deposited pure Ag into a completely continuous layer on the ZnO substrate, as verified by experimental and numerical evidence. The improvement in the Ag wetting ability allows the development of a highly transparent, ultrathin (6 nm) Ag continuous film, exhibiting an average optical transmittance of 94% in the spectral range 400-800 nm and a sheet resistance of 12.5 Ω sq-1, which would be well-suited for application to an efficient front window electrode for flexible solar cell devices fabricated on polymer substrates.

Microstructure and properties of Ag–Ti3SiC2 contact materials prepared by pressureless sintering

Ti3SiC2-reinforced Ag-matrix composites are expected to serve as electrical contacts. In this study, the wettability of Ag on a Ti3SiC2 substrate was measured by the sessile drop method. The Ag–Ti3SiC2 composites were prepared from Ag and Ti3SiC2 powder mixtures by pressureless sintering. The effects of compacting pressure (100–800 MPa), sintering temperature (850–950°C), and soaking time (0.5–2 h) on the microstructure and properties of the Ag–Ti3SiC2 composites were investigated. The experimental results indicated that Ti3SiC2 particulates were uniformly distributed in the Ag matrix, without reactions at the interfaces between the two phases. The prepared Ag–10wt%Ti3SiC2 had a relative density of 95% and an electrical resistivity of 2.76 × 10-3 mΩ·cm when compacted at 800 MPa and sintered at 950°C for 1 h. The incorporation of Ti3SiC2 into Ag was found to improve its hardness without substantially compromising its electrical conductivity; this behavior was attributed to the combination of ceramic and metallic properties of the Ti3SiC2 reinforcement, suggesting its potential application in electrical contacts.

Computational design of metal oxides to enhance the wetting and adhesion of silver-based brazes on yttria-stabilized-zirconia

Ag–CuO is a broadly used reactive air brazing (RAB) system for effectively bonding ceramics and metal interfaces, especially for sealing yttria-stabilized zirconia (YSZ) to metals in solid-oxide fuel cells (SOFCs). To understand the superior performance of this braze, density functional theory (DFT) calculations were employed to investigate two mechanisms that can potentially increase the work of adhesion (Wadh) and hence reduce the wetting angle of Ag on YSZ. It was found while the formation of Ag–dissolved O clusters at the Ag–YSZ interface can promote wetting, a much greater wetting angle reduction comes from the formation of CuO interlayers between Ag and YSZ. Further, the Wadh of an Ag/CuO and CuO/YSZ interface was found to be significantly higher than that of an Ag/YSZ interface. Based on simulation-obtained insights into metal to oxide bond formation, a simple descriptor was developed to predict the Ag/oxide interface energies, the Ag/oxide Wadh, and to search for potential oxide interlayers capable of promoting the wetting and adhesion of Ag on YSZ. Many simple metal oxides (single cation) were examined, however their Wadh with Ag were less than that of an Ag/CuO interface. Expanding the search to multi-cation oxides led to several promising candidates, such as CuAlO2, CuGaO2, and Cu3TiO4; all of which are also stable in the reducing SOFC conditions. Depending upon their solubility in molten Ag, these newly-identified oxides could either be pre-applied as wetting promoting interlayers or directly incorporated into Ag to form new reactive air brazes.

Wetting of Ag, Au, and BeO by melts of B2O3 and B2O3 + PbO

Wetting of Ag, Au, and BeO by B2O3 and B2O3 + PbO melts depending on temperature is investigated. It is shown that the strongest interaction of such melts occurs with BeO.

Wetting and Interfacial Behaviors of Molten Ag, Cu and Ag-28Cu on WC-8Co Cemented Carbide

The wetting and spreading of molten Cu, Ag and Ag-28Cu (wt.%) on the WC-Co cemented carbide were investigated by the sessile drop technique at different temperatures, and the interfacial behaviors of the metal/WC-Co couples were analyzed by scanning electron microscopy (SEM) coupled with energy dispersive spectroscopy (EDS). The experimental results showed that the testing temperature and the composition of drop can play a key role in the wetting and spreading, and the good wettability with contact angle of less than 40o can be obtained. Moreover, the strongest interactions can be produced between the molten Cu and the WC-Co substrate at the higher temperature of 1100 oC due to the strong interdiffusion and solid solution between Cu and Co, resulting in the lowest equilibrium contact angle of ~0o. In addition, smooth and clean interfaces, without formation of visible interfacial reaction layer, were observed in all the three wetting systems. This work may also provide guidance to brazing of the cemented carbide.

Wettability of Ag nanocluster on Cu-Ni alloys: A computational approach

The conductive pastes containing Ag particles are used for patterning the electrodes of electronic devices such as solar cells and touch screen panels. Although Cu@Ag type metal particles have been tried as a substitute instead of Ag for cost reduction, the dewetting of Ag from Cu core during the processes has limited the use of Cu as a core metal. In this work, to investigate the Cu-Ni alloys as the core metal, we analyze the surface structures of Cu-Ni alloys and measure the compatibility between Ag and Cu-Ni alloys as wells as Cu and Ni by calculating the contact angles of Ag droplet on the metal surfaces using molecular dynamics simulations. As the Ni content of Cu-Ni alloys increases, the contact angle decreases: the contact angles for Cu, Cu3Ni, CuNi, CuNi3, and Ni are 69.6, 52.6, 50.5, 45.1, and 8.9°, respectively. Therefore, the wettability of Ag on the Cu-Ni alloys is improved with the Ni content in the Cu-Ni alloys. This result indicates that the Cu-Ni alloys could be good candidates as the core metal to be used in the metal particles for the conductive pastes.

Effects of rare earth La on microstructure and properties of Ag–21Cu–25Sn alloy ribbon prepared by melt spinning

Abstract Ag–21Cu–25Sn alloy ribbon as a promising intermediate temperature alloy solder (400–600 °C) was prepared by melt spinning technique in this paper. Rare earth La was added into Ag–21Cu–25Sn alloy to refine the microstructures and improve the wettabilities of as-prepared alloy solders. The phase constitutions, microstructures, melting temperatures and wettabilities of selected specimens were respectively tested. The results showed that the dominant phase constitutions of Ag–21Cu–25Sn– x La alloy ribbons were Ag 3 Sn and Cu 3 Sn. The grain size of Ag–21Cu–25Sn– x La alloy decreased with the addition of La increasing. La addition reduced the melting temperatures of Ag–21Cu–25Sn– x La alloy ribbons, and effectively improved the wettabilities of the alloy ribbons. When the addition of La was 0.5 wt%, the wettability of as-prepared alloy solder achieved the optimal value of 158 cm 2 g −1 under brazing temperature 600 °C and dwell time 15 min. In addition, raising brazing temperature and prolonging dwell time could improve the wettability of Ag–21Cu–25Sn– x La alloy ribbon.

Wetting of noble metals by Bi2O3-based melts

The wetting of Ag, Pt, Pd, Au, and Ir by Bi2O3-GeO2 (SiO2, TiO2, B2O3, ZnO) melts has been studied as a function of the melt temperature and composition. It is shown that the melts most weakly interact with iridium.

Improvement of transparent silver thin film anodes for organic solar cells with a decreased percolation threshold of silver

Organic solar cells (OSCs) using thermally evaporated Ag thin films as the transparent anode are investigated with poly(3-hexylthiophene) (P3HT) and [6,6]-phenyl-C61-butyric acid methyl ester (PCBM) films as the active layer. The optimal power conversion efficiency (PCE) of 2.57% is obtained for the device with the 11nm thick Ag layer, namely the percolation threshold of Ag. Then an interlayer of MoO3 between the Ag anode and glass substrate is introduced. Two different thicknesses of MoO3 (2nm or 10nm) are chosen here, corresponding to the unclosed or closed MoO3 layer, respectively. It is observed that the introduction of the MoO3 interlayer can effectively improve the wetting of Ag on the substrate and reduce the percolation threshold of Ag. When the MoO3 thickness is 10nm, since the surface energy of Ag (γ=1.25Jm−2) is higher than that of MoO3 (γ=0.06Jm−2), the Ag–Ag interactions are stronger than the Ag-substrate interactions, weakening the surface-modifying effect. In contrast, since the 2nm thick unclosed MoO3 layer may create preferred nucleation sites on the substrate to enhance the lateral growth of Ag film effectively, a very low sheet resistance of 9.32 Ω/□ and a relatively high transmittance are obtained for MoO3 (2 nm)/Ag (9 nm) anode. The PCE of corresponding OSCs can be improved to 2.71%, comparable to that of ITO-based reference OSCs (PCE of 2.85%). From our results, it is concluded that the performance of the Ag thin film electrode can be improved by decreasing the percolation threshold of Ag with a MoO3 interlayer (especially when the MoO3 layer is thin). It may be instructive for the further research of metal thin film electrodes.

The influence of post-annealing treatment on the wettability of Ag+/Na+ ion-exchanged soda-lime glasses

In this paper, the effect of thermal annealing and the duration of ion-exchange on the wetting parameters of the Ag+/Na+ ion-exchanged glasses have been reported. The analysis of wetting angle in different post-annealing temperatures shows that the wetting angle is increased by increasing the annealing temperature. The wetting parameters of Ag+/Na+ ion-exchanged glasses at different ion-exchanged periods of time have been also investigated. Scanning electron microscopy (SEM), UV–Visible spectroscopy and Fourier transform infrared (FTIR) spectroscopy have been used for determination of surface morphology and composition analysis of the prepared samples. The results of SEM show changes in the surface of the samples for different post-annealing temperatures. The optical characterization using UV–Vis spectroscopy shows an increase in the intensity of the absorption peak with increasing the ion-exchange duration. The FTIR spectroscopy confirms the formation of silver oxide material on the surface of Ag+/Na+ ion-exchanged glasses.

Ultrasmooth Silver Thin Film on PEDOT:PSS Nucleation Layer for Extended Surface Plasmon Propagation

Poly(3,4-ethylene dioxythiophene):poly(styrene sulfonate) (PEDOT:PSS) layers are used as the nucleation (seed) layer to reduce surface roughness of the overlying silver (Ag). The technique leads to ultrasmooth Ag thin films with a minimum surface roughness of 0.8 nm. The mechanism contributing to the improvement is explained on the basis of better wetting of Ag on PEDOT:PSS, and properties of the nucleation layer on the aspects of surface energy, surface adhesive force, and surface morphology influencing Ag wetting and growth pattern are being discussed. The surface plasmon resonance (SPR) shows significant improvement, in terms of the Figure of Merits (FOM), as the surface roughness on Ag films is reduced. A lower light scattering and longer plasmon propagation of maximum 15.3 μm are also realized on a smoother Ag surface. The results indicate great potential on the application of combined PEDOT:PSS/Ag structure as an effective and economically feasible design solution for plasmonic and optical metamaterials devices.

Non-reactive versus dissolutive wetting of Ag–Cu alloys on Cu substrates

The fundamental issues of equilibrium and non-equilibrium (dissolutive) wetting and spreading in the liquid Ag/solid Cu system are studied by the dispensed drop technique. To this end, wetting experiments of Cu, both mono- and poly-crystalline, with two types of Ag–Cu alloys, one non-saturated and the other saturated in copper, are performed at 900 °C in high vacuum by the dispensed drop technique. The results are compared with those given in the literature for the same or similar systems as well as with model predictions.

Dissolutive wetting of Ag on Cu: A molecular dynamics simulation study

Reactive wetting in the eutectic AgCu system is studied with molecular dynamics simulations. As Ag(l) spreads on the Cu surface, Cu dissolves into the liquid. The results for reactive wetting are compared to simulations in which no mixing is permitted, demonstrating that wetting kinetics are enhanced by dissolution reactions. The time dependent radius of the droplet R( t) is used to quantify kinetics for the wetting geometry of an infinitely long cylinder spreading on a substrate. Data show that, when dissolution is dominant, spreading is well described by R( t) ∼ ( R 0 t) 1/2, where R 0 is the starting cylinder radius. Contact angle θ( t) data were calculated via a method that accounts for structure near the contact region and compared to data obtained using circular fits to the droplet profile. Significant differences were observed due to molecular scale structure that rapidly evolves near the contact line. This structure exhibits markedly lower θ than what is predicted from droplet profile data and it is proposed to exist throughout most stages of dissolutive wetting. Simulations of AgCu binary liquids spreading on Cu demonstrate that wetting kinetics decrease with increasing Cu in the liquid, further emphasizing that wetting kinetics are intrinsically linked to dissolution kinetics. After dissolution is complete, a Ag-rich monolayer of atoms advances diffusively across the Cu surface.