Influence of multi-interfacial structure on mechanical and tribological properties of TiSiN/Ag multilayer coatings

The TiSiN/Ag multilayer coatings with bilayer periods of ~50, 65, 80, 115, 150, and 410 nm have been deposited on Ti6Al4 V alloy by arc ion plating. In order to improve the adhesion of the TiSiN/Ag multilayer coatings, TiN buffer layer was first deposited on titanium alloy. The multi-interfacial TiSiN/Ag layers possess alternating TiSiN and Ag layers. The TiSiN layers display a typical nanocrystalline/amorphous microstructure, with nanocrystalline TiN and amorphous Si₃N₄. TiN nanocrystallites embed in amorphous Si₃N₄ matrix exhibiting a fine-grained crystalline structure. The Ag layers exhibit ductile nanocrystalline metallic silver. The coatings appear to be a strong TiN (200)-preferred orientation for fiber texture growth. Moreover, the grain size of TiN decreases with the decrease of the bilayer periods. Evidence concluded from transmission electron microscopy revealed that multi-interfacial structures effectively limit continuous growth of single (200)-preferred orientation coarse columnar TiN crystals. The hardness of the coatings increases with the decreasing bilayer periods. Multi-interface can act as a lubricant, effectively hinder the cracks propagation and prevent aggressive seawater from permeating to substrate through the micro-pores to some extent, reducing the friction coefficient and wear rates. It was found that the TiSiN/Ag multilayer coating with a bilayer period of 50 nm shows an excellent wear resistance due to the fine grain size, high hardness, and silver-lubricated transfer films formed during wear tests.     

Effect of various single metallic seed-layers on the magnetic properties of Co/Pd multilayers

We studied the effects of Pd, Ru, and Ta seed-layers on the perpendicular magnetic properties of Co/Pd multilayers, promising materials for high-density magnetic recording media. Among the various seeds, the Ta seed-layer demonstrated a large coercivity and most highly promoted fcc (111) preferred orientation of the Co/Pd multilayer. We also patterned films into island arrays with sizes of 2 × 2 μm², 5 × 5 μm², and 10 × 10 μm² to investigate the effect of size on the magnetic properties. The coercivity increased as the island size decreased. The 2 × 2 μm² patterned Co/Pd multilayer with the Ta seed-layer showed a coercivity about six times greater than that of the un-patterned film. This increase can be explained by a change in the magnetization reversal mechanism from domain wall propagation to domain rotation.     

Structure characterization of Pd/Co/Pd tri-layer films epitaxially grown on MgO single-crystal substrates

Pd/Co/Pd tri-layer films were prepared on MgO substrates of (001), (111), and (011) orientations at room temperature by ultra high vacuum rf magnetron sputtering. The detailed film structures around the Co/Pd and the Pd/Co interfaces are investigated by reflection high energy electron diffraction. Pd layers of (001)_fcc, (111)_fcc, and (011)_fcc orientations epitaxially grow on the respective MgO substrates. Strained fcc-Co(001) single-crystal layers are formed on the Pd(001)_fcc layers by accommodating the fairly large lattice mismatch between the Co and the Pd layers. On the Co layers,, Pd polycrystalline layers are formed. When Co films are formed on the Pd(111)_fcc and the Pd(011)_fcc layers, atomic mixing is observed around the Co/Pd interfaces and fcc-CoPd alloy phases are coexisting with Co crystals. The Co crystals formed on the Pd(111)_fcc layers consist of hcp(0001) + fcc(111) and Pd(111)_fcc epitaxial layers are formed on the Co layers. Co crystals epitaxially grow on the Pd(011)_fcc layers with two variants, hcp(11?00) and fcc(111). On the Co layers, Pd(011)_fcc epitaxial layers are formed.     

Experimental investigation on constitutive behaviour of superconducting powder BSCCO

As a superconducting material, Bi 2233/Ag tape needs high-critical transport current density J _c, which is influenced by the uniform deformation and density of BSCCO powder in filaments during the forming process. The aim of this paper is to investigate the constitutive behaviour of BSCCO powder. The modified Drucker–Prager/Cap model is introduced to describe the constitutive behaviour of BSCCO powder. A series of cyclic loading experiments for BSCCO powder in a cylinder die were carried out. Based on the experiments, the relationships between the radial stress and the axial stress were obtained, and the parameters in the constitutive model were calculated. By pushing the compact powder from the die, the coefficient of friction between the BSCCO powder and the cylinder die was determined. Finally, the modified Drucker–Prager/Cap model is proposed and used to simulate the confined compression test of BSCCO powder.     

A self-assembled Ag nanoparticle agglomeration process on graphene for enhanced light output in GaN-based LEDs

We introduce Ag nanoparticles fabricated by a self-assembled agglomeration process in order to enhance the electrical properties, adhesive strength, and reliability of the graphene spreading layer in inorganic-based optoelectronic devices. Here, we fabricated InGaN/GaN multi-quantum-well (MQW) blue LEDs having various current spreading layers: graphene only, graphene with Ag nanoparticles covering the surface, and graphene with Ag nanoparticles only in selectively patterned micro-circles. Although the Ag nanoparticles were found to act as an additional current path that increases the current spreading, optical properties such as transmittance also need to be considered when the Ag nanoparticles are combined with graphene. As a result, LEDs having a graphene spreading layer with Ag nanoparticles formed in selectively patterned micro-circles displayed more uniform and stable light emission and 1.7 times higher light output power than graphene only LEDs.     

Structure and electrical properties of PMN-PZT micro-actuator deposited by tape-casting process

A potential application for Pb(Mg_1/3Nb_2/3)O₃-Pb(Zr_0.52T{i}_0.48)O₃ (PMN-PZT) piezoelectric material is micro positioning and actuation for hard disk drives. And this material was developed and the processing of a piezoelectric multilayer element for stacking and co-firing Ag/Pd electroded tape casting layers was investigated. The formation mechanisms of PMN-PZT ternary solid solution prepared by the mixed oxides techniques has been characterized by differential thermal analysis (DTA) and thermal gravimetric analysis (TGA). The sintered microstructure and composition of the PMN-PZT multilayer elements were investigated by scanning electron microscope (SEM), and X-ray spectrometer (EDX). The data from DTA/TGA stress the importance of a slow debonding from room temperature to 500 C. The joining of the electrode to the PMN-PZT layer confirms that the internal electrodes are well defined and is well interconnected to the PMN-PZT layer. The ferroelectric polarization-electric (P-E) hysteresis loops of the piezoelectric films were also measured. The remanent polarization and coercive field calculated from the P-E curves decreased with decreasing the number of PMN-PZT multilayer films from 10-layer to 4-layer. After that, a novel U-type micro-actuator attached to each side via piezoelectric elements was also practically measured by laser Doppler vibrometer in order to testify the driving mechanics of it. The highest displacement/voltage sensitivity of 1.496 m/±20 V is achieved by the micro-actuator with two 10-layer elements. The corresponding resonance frequency of the sway mode is high at 12 kHz.     

Co-Firing Characteristics of Cordierite Tapes with Ag/Pd for High Frequency Chip Inductors

As a new electronic material, low-temperature sintering, low-dielectric cordierite tapes exhibit great potential in the manufacturing of high frequency inductors. While the co-firing of cordierite dielectric material with conductive metal in lower sintering temperature is always a difficulty, and it directly affects the practical application of the inductors. In this paper, the prepared cordierite tapes with low-sintering temperature, low dielectric constant, and low losses were used as matrix material, and the co-firing characteristics of cordierite tapes with Ag/Pd was preliminary studied to investigate the feasibility in the manufacturing process. Deformation, pores, and delaminations are three main defects of the co-fired samples. With an Al₂O₃ powders and press blocks assisted process, good co-firing effect of cordierite tapes with Ag/Pd can be obtained at 900 °C. The co-firing interface of cordierite tape and Ag/Pd is very dense and no obvious element migration is detected. The paper is contributed to the manufacture of high frequency inductors.     

Density Gradients in Multilayer Compacted Iron Powder Parts

The use of multilayer compaction to form powder metal (P/M)components, is encouraging. With this process, a part is formed by successively compacting layers of powder. The formation of parts with larger than conventional height to diameter ratios is possible. Multilayer compaction also reduces the density gradients normally observed in large parts from conventional double action compaction. Optimization of the layer thickness based on the powder characteristics can lead to greatly reduced density gradients.

The physical properties of multilayer compacted components are investigated as a function of layer thickness. The research has been performed with two iron powders of varying characteristics. The compressibility of the powder versus the layer thickness is discussed and related to the density distribution in the component.     

The preparation of laminated ceramic composites using paint technology

Ceramic paints comprising ceramic powder, dispersant, resin and solvent were prepared by high speed mixing. The powders were alumina and alumina with 20 vol% zirconia. Alternate layers of paint having thicknesses of 20–30 m were deposited by the random deposition of droplets from a conventional paint spray gun operating on compressed air. Laminates of up to 1 mm were produced. The microstructure of the multilayer ceramic wafers produced by drying, thermolysis and sintering is reported. The method avoids the thermolamination step associated with tape casting and allows laminates to be prepared on contoured fugitive substrates.     

Electrochemical synthesis of Ag/Co multilayered nanowires in porous polycarbonate membranes

The electrodeposition of Ag/Co multilayers into 20 μm thick ion track etched polycarbonate membranes with pore diameter of 120 nm were studied using a single bath containing cobalt sulphate, silver cyanide and potassium pyrophosphate. Cyclic voltammetry and transmission electron microscopy (TEM) was used to determine deposition conditions for pure Ag and 97 wt.% Co layers. The Co rich metallic nanowires were deposited at −1100 mV and the Ag nanowires were deposited at −600 mV vs. Ag/AgCl. By using Faraday's law and linear relation between the charges passed during the time interval for each metal layers and bilayer thickness, a current efficiency of 58% was determined for pulsed deposition of Co. This implies that hydrogen or initial layer re-dissolution of Co during Ag deposition consumes 31% of the charge passed during Co deposition. Multilayered nanowires with 8 and 15 nm thick Ag and Co rich layers, respectively, exhibit well-defined layers in TEM. X-ray diffraction investigations of 20 μm long, Ag, Co and Ag/Co multilayered nanowires show that the Ag deposits exhibited a f.c.c. 〈111〉 texturing while the Co deposit exhibited basal plane diffraction of h.c.p. (002) and f.c.c. (111). Magnetic measurements on Ag/Co multilayered nanowires have been made with the external field parallel and perpendicular to the film plane on two series of multilayers: thickness of Co (50 and 15 nm)/Ag (8 nm). In the case of longer cylinder (t_Co=50 nm) the axis along the wire starts to become the easy axis (lower saturation field) as expected in the limit where t_Ag=0 (case of single Co nanowires), due to the shape anisotropy.     

Electrical characteristics and detailed interfacial structures of Ag/Ni metallization on polycrystalline thermoelectric SnSe

SnSe is a promising thermoelectric material with a high figure of merit in single crystal form, which has stimulated continuous research on polycrystalline SnSe. In this study, we investigated a metallization techniques for polycrystalline SnSe to achieve highly efficient and practical SnSe thermoelectric modules. The Ag/Ni metallization layers were formed on pristine polycrystalline SnSe using various deposition technique: sputter coating Ni, powder Ni and foil Ni by spark plasma sintering. Structural analysis demonstrated that the microstructure and contact resistance could be different according to the metallization process, despite using the same metals. The Ag/Ni metallization layer using foil Ni acted as an effective diffusion barrier and minimized electrical contact resistance(2.3 × 10~(-4) Ω cm~2). A power loss in the thermoelectric module of only 5% was demonstrated using finite element simulation.     

In-situ deposition of Pd nanoparticles on tubular halloysite template for initiation of metallization

Halloysite template has a tubular microstructure; its wall has a multi-layer aluminosilicate structure. A new catalytic method is adopted here, through the in-situ reduction of Pd ions on the surface of tubular halloysite by methanol to initiate electroless plating; the detailed deposition features of Pd nanoparticles are investigated for the first time. The results indicate that an in-situ reduction and deposition of Pd occurs at room temperature, in which the halloysite template plays an important role. Impurities in halloysite (such as ferric oxide) influence the formation and distribution of the Pd nanoparticles. The Pd nanoparticles are of a non-spherical shape in most cases, which would be caused by the irregular appearance of halloysite. No intercalation of the nanoparticles occurs between the aluminosilicate layers in the halloysite. The diameter of Pd nanoparticles increases with time; the average diameter ranges from 1 nm to 4 nm. Pd nanoparticles on a halloysite template can catalyze electroless deposition of Ni to prepare a novel nano-sized cermet at low cost. This practicable catalytic method could also be used on other clay substrates for the initiation of metallization.     

Overview of progress in giant magnetoresistive sensors based onNiFe/Ag multilayers

The evolution of devices based on NiFe and Ag in thin film giant magnetoresistance (GMR) structures is reviewed and traced from the early continuous multilayer (CML) structures, through granular alloys (GAs) of NiFe and Ag, spin valves (SVs), discontinuous multilayers (DMLs), and the most recent patterned multilayer (PML) structures. The technological motivation far the development of these various structures, based in particular on field sensitivity as an important figure of merit, and their limitations is discussed. Although DMLs are shown to possess the highest sensitivity, 1.2%/Oe, it is shown that they are limited by noise. Various issues affecting the implementation of NiFe/Ag DML sensors are addressed with particular emphasis on noise, since presently noise gates the development of a successful sensor. The MR characteristics of DML sensors are examined as a function of different biasing schemes to reduce noise and improve linearity. It is shown that the transverse response of ten-layer DML sensors when transversely biased may give acceptable noise performance. This represents one of the two fundamental approaches to the reduction of noise in NiFe/Ag MLs, i.e. one based on the concept of increasing the number of easily switchable ferromagnetic “grains” in the structure. The other approach is based on the concept of a sensor consisting of single large domains in each NiFe layer which provided the impetus for the development of patterned multilayer (PML) devices. Finally, the GMR response of these PML structures is briefly discussed     

Multilayer amorphous hydrogenated carbon (a-C:H) and SiOx doped a-C:H films for optical applications

In this study SiO_x doped amorphous hydrogenated carbon (a-C:H) films were formed from hexamethyldisiloxane (with hydrogen transport gas) by closed drift ion beam deposition applying variable ion beam energy (300-800 eV). The band gap dependence on the deposition energy was determined and used in production of SiO_x doped a-C:H and a-C:H (formed from acetylene gas) multilayer (two and four layers) stack. Optical properties of the multilayer structures as well as individual layers were analysed in the UV-VIS-NIR range (200-1000 nm). It was shown that employing double or four layer systems, the reflectivity of the multilayer structure-crystalline silicon can be tuned to almost 0% at specific wavelength range (550-950 nm), important in solar cell applications.     

Preparation of NiO Buffer Layer by Direct Oxygenation of Ni Tape

Recently, Nickel-based alloys are widely used for textured substrates tapes. However, the deposition of oxide buffer layers on nickel tapes is required to stop the diffusion of nickel from the tape to superconducting layer and to improve the mismatch between the substrate and superconducting film. Biaxially textured NiO buffer layer is easily formed on cubic textured nickel tape by the technique called surface oxidation epitaxy. In this work, we developed a direct oxygenating method to make the NiO buffer layer on nickel tape. The nickel tape was directly oxygenated in different atmospheres. It is found that in inert atmosphere, a high quality NiO layer can be formed on the surface of the tape. The oxygenating conditions, including atmospheres and temperatures, and their influence on the structure of the NiO buffer layer, were studied in detail and discussed.     

Direct writing of metal nanoparticle films inside sealed microfluidic channels

Herein we demonstrate the ability to pattern Ag nanoparticle films of arbitrary geometry inside sealed PDMS/TiO2/glass microfluidic devices. The technique can be employed with aqueous solutions at room temperature under mild conditions. A 6 nm TiO2 film is first deposited onto a planar Pyrex or silica substrate, which is subsequently bonded to a PDMS mold. UV light is then exposed through the device to reduce Ag+ from an aqueous solution to create a monolayer-thick film of Ag nanoparticles. We demonstrate that this on-chip deposition method can be exploited in a parallel fashion to synthesize nanoparticles of varying size by independently controlling the solution conditions in each microchannel in which the film is formed. The film morphology was checked by atomic force microscopy, and the results showed that the size of the nanoparticles was sensitive to solution pH. Additionally, we illustrate the ability to biofunctionalize these films with ligands for protein capture. The results indicated that this could be done with good discrimination between addressed locations and background. The technique appears to be quite general, and films of Pd, Cu, and Au could also be patterned.     

Effect of addition of Ag on the microstructures and electrical properties of sol-gel derived SnO2 glass composites

The effect of addition of Ag on the microstructure and electrical properties of sol-gel derived SnO₂-glass composites was examined. Comparisons of the microstructures and electrical properties were carried out between glass composites prepared by a sol-gel method and a conventional one using glass frit. The glass composite gels and the SnO₂-glass powder mixtures containing AgNO₃ were calcined at 500 °C in order to decompose AgNO₃ into Ag and then fired at 900 °C. In the sol-gel derived glass composites, the grain growth of Ag was suppressed and Ag particles connected mutually at the boundaries of aggregated gel particles to form three-dimensional networks. Thus, the glass composite derived by the sol-gel method showed a high electrical conductivity and a positive temperature coefficient of resistance (TCR). The highly electrical conductive paths of Ag in the glass composite were effectively formed when powder compacts were formed at a higher pressure. On the other hand, in the glass composites prepared using SnO₂-glass powder mixtures, coarse-grained Ag particles were isolated in closed pores regardless of the forming pressure, and therefore did not contribute to electrical conduction in the glass composite.     

Multilayer Co/Pd films with nanocrystalline and amorphous Co layers: Coercive force, random anisotropy, and exchange coupling of grains

The values of saturation magnetization M _s, exchange coupling constant A, local magnetic anisotropy field H _a, random anisotropy correlation radius R _c, and coercive force H _c were independently measured for multilayer Co/Pd films with nanocrystalline and amorphous Co layers. It is shown that variation of the coercive force H _c(t _Co) as a function of the cobalt layer thickness t _Co is related to changes in characteristics of the magnetic microstructure. The main factor determining changes in the ferromagnetic correlation radius R _f and the average anisotropy 〈K〉 of a magnetic block in multilayer Co/Pd films is variation of exchange coupling constant A(t ^Co).     

Development of refractory ohmic contact materials for gallium arsenide compound semiconductors

Recent strong demands for optoelectronic communication and portable telephones have encouraged engineers to develop optoelectronic devices, microwave devices, and high-speed devices using hetero-structural GaAs-based compound semiconductors. Although the GaAs crystal growth techniques had reached a level to control the compositional stoichiometry and crystal defects on a nearly atomic scale by the advanced techniques such as molecular beam epitaxy and metal organic chemical vapor deposition techniques, development of ohmic contact materials (which play a key role to inject external electric current from the metals to the semiconductors) was still on a trial-and-error basis.Our research efforts have been focused to develop low resistance, refractory ohmic contact materials to n-type GaAs using the deposition and annealing techniques, and it was found the growth of homo-or hetero-epitaxial intermediate semiconductor layers (ISL) on the GaAs surface was essential for the low resistance ohmic contact formation. In this paper, two typical examples of ohmic contact materials developed by forming ISL were given. The one was refractory NiGe-based ohmic contact material, which was developed by forming the homo-epitaxial ISL doped heavily with donors. This heavily doped ISL was discovered to be formed through the regrowth mechanism of GaAs layers at the NiGe/GaAs interfaces during annealing at elevated temperatures. To reduce the contact resistance further down to a value required by the device designers, an addition of small amounts of third elements to NiGe, which have strong binding energy with Ga, was found to be essential. These third elements contributed to increase the carrier concentration in ISL. The low resistance ohmic contact materials developed by forming homo-epitaxial ISL were Ni/M/Ge where a slash ‘/’ denotes the deposition sequence and M is an extremely thin (∼5 nm) layer of Au, Ag, Pd, Pt or In. The other was refractory In_xGa_1−xAs-based ohmic contact materials which were developed by forming the hetero-epitaxial ISL with low Schottky barrier to the contacting metals by growing the In_xGa_1−xAs layers on the GaAs substrate by sputter-depositing In_xGa_1−xAs targets and subsequently annealing at elevated temperatures. To reduce the contact resistance, it was found that this In_xGa_1−xAs (ISL) layer had to have In compositional gradient normal to the GaAs surface: the In concentration being rich at the metal/In_xGa_1−xAs interface and poor close to the In_xGa_1−xAs/GaAs interface. This concentration graded ISL reduced both the barrier heights at the metal/ISL and ISL/GaAs interfaces and reduced the contact resistance. The ohmic contact materials developed by forming hetero-epitaxial ISL was In_0.7Ga_0.3As/Ni/WN₂/W. These contact materials formed refractory compounds at the interfaces, which was also found to be essential to improve thermal stability of ohmic contacts used in the GaAs devices.     

Processing and microstructure of porous and dense PZT thick films on Al2O3

The processing of porous PZT thick-film ceramics on Al₂O₃ has been studied. The films were screen-printed from a thixotropic ink of PZT with a 58% solids content. The thick films were sintered between 1000 and 1150°C for 2 h. The sintered films show a 10 m thickness and an average pore diameter ranging from 1–2 m. The PZT forms a continuous skeleton that can be filled with the desired polymer. Dense and continuous PZT films were fabricated by screen-printing PZT ink on previously electroded Al₂O₃ substrates with Ag/Pd 70/30 paste. Densification of the PZT was obtained by sintering near the liquidus temperature of the Ag-Pd system.