Co–Pt–W thin films electrodeposited from sulphate–gluconate baths

Co–Pt–W magnetic thin films were electrodeposited from gluconate baths. Electrochemical characterization (polarization behaviors and transient curves), microstructure and magnetic properties were investigated. It turned out that increase in gluconate concentration and bath pH shifted the deposition potential to more negative potentials. Microstructure of electrodeposited Co–Pt–W thin films was affected by the bath pH and gluconate concentration enormously. Samples obtained from Co–sulphate–gluconate at pH 8.0 and gluconate concentration 0.3 mol L^?1 exhibited single hcp phase with strong (0 0 1) PO. VSM and MFM measurement showed that perpendicular magnetic anisotropy occurred in the Co–Pt–W thin films prepared under these conditions.     

Electrical percolation threshold in Ag–DLC nanocomposite films prepared by RF-sputtering and RF-PECVD in acetylene plasma

Silver–diamond like carbon (Ag–DLC) nanocomposite films were deposited on glass and silicon substrates by co-deposition of RF-sputtering and RF-PECVD method in acetylene plasma. The effects of deposition time on creation of conductive percolation pathway in Ag–DLC nanocomposite films were investigated. The films were characterized by XRD pattern, AFM images, UV–Vis and FTIR spectra. Pressure of chamber’s variation over time was illustrated the rate of carbon and silver deposition changing. The results showed that nanoparticles’ size and surface roughness was increased by increasing deposition time. Surface plasmon resonance peak’s red shift in optical absorption spectra of samples could be depends on silver nanoparticles’ scale up. Based on electrical measurements, electrical percolation threshold was observed only in the film with 35 min deposition time. Pathway was created for electric current by Ag nanoparticles’ moving in carbon matrix due to sp³ bonds and silver content in the films. The aging effect was studied for sample #2 in the threshold of percolation, where obtained Ag nanoparticles memorize its previous pathway. This investigation provides a better understanding for electric properties of Ag–DLC nanocomposite based on the percolation theory.     

Thermal stability and electrical properties of Ag–Ti films and Ti/Ag/Ti films prepared by sputtering

Ag–Ti (100 nm) alloy film, and Ti/Ag (100 nm) double-layer and Ti/Ag (100 nm)/Ti triple-layer films were prepared by rf sputtering to investigate the effect of Ti on suppression of agglomeration of the Ag thin film caused by thermal treatment. Scanning electron microscopy revealed that the Ag–Ti and Ti/Ag/Ti films had high thermal stability. X-ray photoelectron spectroscopy analysis showed that the surfaces of both kinds of films were covered with a TiO₂ layer after annealing, which was considered to be the key factor for improvement of the thermal stability of the films. In addition, scratch tests indicated improvement of the adhesive strength of the Ti/Ag/Ti film to the SiO₂ substrate due to the underlying Ti film layer, which effectively promoted suppression of Ag agglomeration. However, the resistivity of the Ag–Ti films increased abruptly with increasing Ti content due to the impurity scattering effect, and minimum usage of the alloying element was required to achieve low resistivity. In contrast, the Ti/Ag/Ti film exhibited both low resistivity and high thermal stability.     

A study on electrodeposited Co–Mo alloys thin films

Cobalt–Molybdenum (Co–Mo) induced electrodeposition has been studied from a sulphate bath on Ru electrodes at pH 4. The conditions of electrodeposition of Co–Mo alloys were determined using the cyclic voltametry at different ions concentration ratios. The theoretical model of Scharifker-Hills was used to analyse the current transients for studying the first stage of nucleation of Co–Mo alloys. The electrodeposited coatings were analysed by scanning electron microscopy, X-rays diffraction and alternating gradient force magnetometer techniques. The cyclic voltametry shows that the codeposition of Co–Mo alloys was accompanied by concurrent reactions such as the formation of the molybdenum oxides and the hydrogen evolution reaction. For the electrodeposited Co–Mo, the nucleation is in good agreement with the instantaneous nucleation and three-dimensional (3D) diffusion-limited growth. Co–Mo thin films of an hcp structure have been obtained, and the electrodeposition parameters such as the applied potential have a great influence on the structure, morphology and magnetic properties.     

Study on preparation of Co–Pt–W alloy films by electrodeposition

Abstract

Co–Pt–W alloy films were prepared by the electroplating method to replace costly sputtering on a copper substrate. Effects of different pH values and current densities on composition, microstructure and magnetic properties of films were investigated. With the rise in pH values, the amounts of tungsten and cobalt decrease simultaneously as a result of less tungstate oxides in higher OH– concentration solution. Almost all the deposited films were crystalline and formed fcc CoPt(111) and hcp CoPt(002). Co–Pt–W alloy films intend to change from fcc to hcp structure when the current density was >20 mA cm^?2. It was found that hcp structures of Co–Pt–W alloy films possess high coercivity performance. Moreover, higher pH values induced lower saturation magnetisation while higher current densities could result in larger saturation magnetisation. Dissimilar surface morphology could be detected under different current densities. With increasing the current density, grains of films tend to agglomerate and grow perpendicularly to substrate. Bigger agglomerated particles and ‘hill-like’ structure could be observed when the current density was up to 30 mA cm^?2.     

Fabricating Au–Ag core-shell composite films for surface-enhanced Raman scattering

Surface-enhanced Raman scattering (SERS) integrates high levels of sensitivity with spectroscopic precision, and thus, has tremendous potential for chemical and biomolecular sensing. The key to the wider application of Raman spectroscopy using roughened metallic surfaces is the development of highly enhancing substrates for analytical purposes, i.e., for better detection sensitivity of trace contaminants and pollutants. Here, we have prepared Au, Ag, AuAg multilayer, and Au@Ag films on glass substrates for SERS-active substrates. The Au@Ag film shows a much stronger SERS signal for trans-bis(4-pyridyl)ethylene (BPE) molecules than those from pure Au, Ag, and AuAg films, indicating the Au@Ag film is more powerful than pure Au, Ag, and AuAg film as SERS active substrates. The enhanced surface Raman scattering signals were attributed to the local field enhancement in the core-shell structure.     

Combined in situ electrochemical impedance spectroscopy–UV/Vis and AFM studies of Ag nanoparticle stability in perfluorinated films

In situ electrochemical–UV/Vis spectroscopic analysis in combination with AFM measurements were performed to study the reactivity of Ag nanoparticles sandwiched in between two polytetrafluoroethylene (PTFE) films. The electrolyte uptake in the film was correlated with the onset of the changes in the surface plasmon resonance by measuring the film capacitance and the surface plasmon resonance peak simultaneously as a function of the exposure time. AFM studies indicate that both particle ripening and Ag dissolution take place and the dissolution kinetics was shown to decrease with increasing covering film thickness.     

Effects of Co additions on electromigration behaviors in Sn–3.0 Ag–0.5 Cu-based solder joint

As the miniaturization trend of electronic packing industry, electromigration (EM) has become a critical issue for fine pitch packaging. The EM effects on microstructure evolution of intermetallic compound layer (IMC) in Sn–3.0 Ag–0.5 Cu + XCo (X = 0, 0.05, 0.2 wt%) solder joint was investigated. Findings of this study indicated that current stressing of Sn–3.0 Ag–0.5 Cu–0.2 Co solder joint with 10⁴ A/cm² at 50 °C for 16 days, no remarkable EM damages exhibited in solder matrix. Whereas, after current stressing at 150 °C for 1 and 3 days, Sn–3.0 Ag–0.5 Cu specimens showed obvious polarity effect between cathode and anode. Different morphology changes were also observed at both sides. After current stressing for 1 day, two IMC layers, Cu₆Sn₅ and Cu₃Sn, with wave type morphology formed at cathode. Sn phases were also observed inside in the IMC layer. However, only Cu₆Sn₅ formed in anode. Three days later, Sn phases were found in anode. Besides, Co additions, aging treatment, Ag₃Sn, and other IMCs improved the resistance of EM by the evidence of retarding polarity effect.     

Effects of the anion in glycine-containing electrolytes on the mechanical properties of electrodeposited Co–Ni films

Tailoring of the mechanical properties (e.g., hardness, Young's modulus or wear characteristics) of Co–Ni electrodeposits has been accomplished by changing the anion (sulphate versus chloride ions) in glycine-containing solutions at 80 °C, while maintaining all the other electroplating conditions unaltered. Galvanostatic deposition on metalized silicon substrates at 5–40 mA cm⁻² produced well adherent Co–Ni films with varying surface finish, chemical composition (50–83 wt% Co), morphology and structure. The deposition from chloride salts yielded matte grey, cobalt-rich Co–Ni films with hexagonal close-packed structure and crystallite sizes around 65–85 nm. Films obtained under the same electrodeposition conditions from sulphate salts were Ni-rich, displayed smoother surfaces and smaller crystallite sizes (30–40 nm) belonging mainly to the face-centered cubic phase. The crystallite size played a key role on the mechanical properties of the films, while the composition and the phase percentage had little effect. It is thus demonstrated that the nature of the anion induces a large tunability both in the microstructure and mechanical properties of the deposits. In particular, the nanoindentation hardness could be varied between 1.6 and 7.1 GPa, while the Young's modulus ranged between 122 and 181 GPa.     

Antibacterial and tribological properties of TaN–Cu,TaN–Ag,and TaN–(Ag,Cu) nanocomposite thin films

In this study, attempts were made to prepare and characterize TaN–(Cu,Ag) nanocomposite films by using a hybrid approach combining reactive co-sputtering and rapid thermal annealing at various temperatures to induce the formation of soft metal particles in the matrix or on the surface. The films’ properties and their antiwear and antibacteria behaviors were compared with those previously studied TaN–Cu and TaN–Ag films. All three types of TaN–(soft metal) films showed good tribological properties due to the lubricious Ag and/or Cu layers. It was also found that the antibacteria efficiency of TaN–(Ag,Cu) film against either Escherichia coli or Staphylococcus aureus could be much improved, comparing with that of TaN–Ag or TaN–Cu film. The synergistic effect due to the coexistence of Ag and Cu is obvious. The annealing temperature used to develop TaN–(Cu,Ag) films with good antibacterial and antiwear behaviors could be as low as 250 °C. The lowering of the annealing temperature made these films applicable onto low-melting-point materials, such as polymers.     

A selective ethanol gas sensor based on spray-derived Ag–ZnO thin films

A simple and cost-effective spray pyrolysis technique was employed to synthesize silver-doped zinc oxide (Ag–ZnO) thin films on the glass substrates from aqueous solutions of zinc acetate and silver nitrate precursors at 450 °C. The effects of Ag doping on structural, morphological, and gas-sensing properties of films were examined. The X-ray diffraction spectra of the Ag–ZnO films showed the polycrystalline nature having hexagonal crystal structure. Scanning electron microscopy (SEM) images of the pure ZnO films revealed the uniform distribution of the spherical grains (~80 nm size). Tiny Ag nanoparticles are clearly visualized in the SEM of Ag–ZnO films. The investigation of the effect of Ag doping on the gas-sensing properties of the Ag–ZnO revealed that the 15 % Ag-doped ZnO sample has the highest gas sensitivity (85 %) and excessive Ag doping in ZnO degraded the gas sensitivity. A possible mechanism of Ag–ZnO-based sensor sensitivity to the target gas is also proposed.     

Nitriding of Co–Cr–Mo alloy in nitrogen

Using the results of a thermodynamic analysis, a Co–Cr–Mo alloy was successfully nitrided in nitrogen at temperatures of 1073–1473 K. The near-surface microstructure of the treated Co–Cr–Mo alloy was characterized using X-ray diffraction, field-emission scanning electron microscopy, electron probe micro-analyzer, and transmission electron microscopy equipped with energy-dispersive X-ray spectroscopy. The results indicated that the highest nitriding efficiency was achieved at the treatment temperature of 1273 K, with the size and coverage of the nitride particles on sample's surface increasing with an increase in the treatment duration. After nitriding at 1273 K for 2 h, numerous nitride particles, consisting of an outer Cr₂N layer and an inner π phase layer, were formed on top of the nitrogen-containing γ phase, and some π phase also precipitated in the alloy matrix at the sub-surface level.     

Formation of microstructure in Ag–In–Sn solder alloys

Abstract

A metallographic study is reported of the phases and reactions that occur in Ag–In–Sn (Pb-free) solder alloys containing approximately 3 wt-%Ag and up to 10 wt-%In. Specimens were prepared by very slow unidirectional solidification and as small castings. Three different intermetallic compound phases and two different matrix phases were observed, depending on the In content of the alloy. The probable reactions that produce these phases are discussed and compared with data from the published ternary liquidus projection. This study was carried out in the Department of Materials Science and Engineering, University of Toronto, as part of the CMAP program.     

Interfacial reactions with and without current stressing at Sn–Co/Ag and Sn–Co/Cu solder joints

Sn–Co alloys are promising Pb-free solders, while plating layers and substrates of Ag and Cu are commonly encountered in electronic products. This study examines the interfacial reactions between Sn–0.25 wt% Co/Ag and Sn–0.25 wt% Co/Cu at 180 and 210 °C, with and without current stressing. CoSn₃ precipitates are found in the solder matrix in the as-prepared condition. In Sn–0.25 wt% Co/Ag couples, a continuous Ag₃Sn reaction phase layer is observed at the interface and Ag₃Sn phase particles are dispersed in the matrix, with and without current stressing. When there is a 500 A/cm² electrical current, the growth rate of the Ag₃Sn phase is not affected at either the cathode side or the anode side. However, the passage of an electrical current leads to the formation of needle-like Ag₃Sn phase particles in the solder matrix. In Sn–0.25 wt% Co/Cu couples, both Cu₆Sn₅ and Cu₃Sn reaction phases are formed at the interface, with and without current stressing. Cu₆Sn₅ precipitates, with a higher Co content, are found in the matrix, mostly nucleated on CoSn₃ precipitates. When there is a 500 A/cm² electrical current stressing, all the reaction phase layers are thicker and the anode interfaces are nonplanar. It is observed that there is cracking and that there are discontinuous Cu₆Sn₅ layers at the interface and that a significant amount of Cu₆Sn₅ phase in the matrix accompanies 500 A/cm² electrical current stressing.     

Phase transformations in the ternary Ag–Ga–Sb system

Phase diagram of the Ag–Ga–Sb ternary system was extrapolated using calculation of phase diagrams (CALPHAD) method. Phase transition temperatures of the alloys with compositions along three vertical sections with constant molar ratios Ga/Sb = 1, Ag/Ga = 1 and Ag/Sb = 1 were measured using differential scanning calorimetry (DSC). Scanning electron microscopy with energy dispersive X-ray spectroscopy (SEM/EDX) was used for identification of phases in equilibrated samples. Experimental results were compared with thermodynamic prediction.     

Sn–In–Ag phase equilibria and Sn–In–(Ag)/Ag interfacial reactions

Experimental verifications of the Sn–In and Sn–In–Ag phase equilibria have been conducted. The experimental measurements of phase equilibria and thermodynamic properties are used for thermodynamic modeling by the CALPHAD approach. The calculated results are in good agreement with experimental results. Interfacial reactions in the Sn–In–(Ag)/Ag couples have been examined. Both Ag₂In and AgIn₂ phases are formed in the Sn–51.0 wt%In/Ag couples reacted at 100 and 150 °C, and only the Ag₂In phase is formed when reacted at 25, 50 and 75 °C. Due to the different growth rates of different reaction phases, the reaction layer at 100 °C is thinner than those at 25 °C, 50 °C, and 75 °C. In the Sn–20.0 wt%In/Ag couples, the ζ phase is formed at 250 °C and ζ/AgIn₂ phases are formed at 125 °C. Compared with the Sn–20 wt%In/Ag couples, faster interfacial reactions are observed in the Sn–20.0 wt%In–2.8 wt%Ag/Ag couples, and minor Ag addition to Sn–20 wt%In solder increases the growth rates of the reaction phases.     

Preparation and characterization of pyrolytically deposited (Co–V–O and Cr–V–O) thin films

The metal acetylacetonates of vanadium, cobalt and chromium were prepared from commercial reagents. The corresponding metal acetylacetonates were mixed in desired ratio and deposited on soda lime glass substrate by metal organic chemical vapor deposition technique. Mixed oxides thin films with atomic composition Co_0.31V_1.37O₅ and Cr_0.5V₂O₅ were obtained. A combination of Rutherford backscattering spectroscopy and energy-dispersive X-ray fluorescence was used for the transition element identification and atomic compositional study of the thin films. The thickness of the Co–V–O and Cr–V–O thin films was 166 and 127 nm, respectively. The optical spectra of the films were obtained using a Pye Unicam SP8-400 spectrophotometer in the ultraviolet/visible region. The result of the spectral analyses gave the optical bandgap energy of the materials. The temperature dependence of the electrical resistivity measured using the Van der Pauw method indicated that the materials are semiconducting. Their activation energy was obtained from plots of the natural logarithm of conductivity vs. the reciprocal of temperature. The sign of the thermopower shows that both materials are p-type semiconductors.     

Simple route for the synthesis of supercapacitive Co–Ni mixed hydroxide thin films

Facile synthesis of Co–Ni mixed hydroxides films with interconnected nanoparticles networks through two step route is successfully established. These films have been characterized by X-ray diffraction (XRD), Fourier transform infrared technique (FTIR), scanning electron microscopy (SEM) and wettability test. Co–Ni film formation is confirmed from XRD and FTIR study. SEM shows that the surface of Co–Ni films is composed of interconnected nanoparticles. Contact angle measurement revealed the hydrophilic nature of films which is feasible for the supercapacitor. The electrochemical performance of the film is evaluated by cyclic voltammetry, and constant-current charge/discharge cycling techniques. Specific capacitance of the Co–Ni mixed hydroxide electrode achieved 672 F g^?1. Impedance analysis shows that Co–Ni mixed hydroxide electrode provides less resistance for the intercalation and de-intercalation of ions. The Co–Ni mixed electrode exhibited good charge/discharge rate at different current densities. The results demonstrated that Co–Ni mixed hydroxide composite is very promising for the next generation high performance electrochemical supercapacitors.     

Phase separation in immiscible silver–copper alloy thin films

Far from equilibrium, immiscible nanocrystalline Ag–Cu alloy thin films of nominal composition Ag–40 at.% Cu have been deposited by co-sputter deposition. Both X-ray and electron diffraction studies indicate that the as-deposited films largely consist of nanocrystalline grains of a single alloyed face-centered cubic (fcc) phase. However, detailed three-dimensional atom probe tomography studies on the same films give direct evidence of a nanoscale phase separation within the columnar grains of the as-deposited Ag–Cu films. Subsequent annealing of these films at 200 °C leads to two effects; a more pronounced nanoscale separation of the Ag and Cu phases, as well as the early stages of recrystallization leading to the breakdown of the columnar grain morphology. Finally, annealing at a higher temperature of 390 °C for a long period of time leads to complete recrystallization, grain coarsening, and a complete phase separation into fcc Cu and fcc Ag phases.