Electrophoretic deposition of polyetheretherketone (PEEK) and PEEK/Bioglass® coatings on NiTi shape memory alloy wires

Polyetheretherketone (PEEK) and PEEK/Bioglass® coatings were produced on shape memory alloy (NiTi, Nitinol®) wires using electrophoretic deposition (EPD). Best results were achieved with suspensions of PEEK powders in ethanol in the range (1–6 wt%), using a deposition time of 5 minutes and applied voltage of 20 Volts. EPD using these parameters led to high quality PEEK coatings with a homogeneous microstructure along the wire length and a uniform thickness of up to 15 μm without development of cracks or the presence of large voids. Suspensions of PEEK powders in ethanol with addition of Bioglass® particles (0.5–2 wt%) (size < 5 μm) were used to produce PEEK/Bioglass® coatings. Sintering was carried out as a post EPD process in order to densify the coatings and to improve the adhesion of the coatings to the substrate. The sintering temperature was 340 °C, sintering time 20 min and heating rate 300 °C/h. Sintering led to uniform and dense PEEK and PEEK/Bioglass® coatings without any cracks. The bioactive behaviour of PEEK/Bioglass® composite coatings was investigated by immersion in acellular simulated body fluid (SBF) for up to two weeks. As expected, hydroxyapatite crystals formed on the surface of the coated wires after 1 week in SBF, confirming the bioactive character of the coatings. The results have demonstrated for the first time that EPD is a very convenient method to obtain homogeneous and uniform bioactive PEEK and PEEK/Bioglass® coatings on Nitinol® wires for biomedical applications.     

Geometric confinement of directly deposited features on hydrophilic rough surfaces using a sacrificial layer

It is challenging to achieve high definition for inkjet-printed features on hydrophilic rough surfaces. In this study, a spreading diameter of ~5 mm was observed for a 10 pL inkjet droplet when it impacted onto a hydrophilic rough surface. A new geometric confinement method was employed to facilitate a much higher inkjet printing definition in the range of ~50 μm. A layer of water-soluble polyacrylic acid (PAA) was spin-coated onto a hydrophilic rough surface and then inkjet patterned. Subsequently, the PAA was made water-insoluble by subjecting the sample to a heat treatment with temperatures above 170 °C. The change in solubility of PAA during the heat treatment is found to be a crucial factor, which enables the physical confinement of the subsequently inkjet printed aqueous-based droplets. The thickness of the spin-coated sample also plays a critical role in the effectiveness of the physical confinement. The effectiveness of the proposed approach was demonstrated with an inkjet patterning process, in which a dielectric layer of 200 nm SiN _x on a textured silicon wafer was selectively etched using 10 pL inkjet-printed droplets resulting in a line width of ~75 μm. When using a 1 pL printhead, the etched line width was as fine as ~30 μm.     

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.     

Deposition of hBN+Cu layer through electrical discharge process using green compact electrode

In the current investigation, solid-lubricant surfaces were prepared onto the mild steel work piece by means of electrical discharge coating process in electrical discharge machine (EDM). Hexagonal boron nitride (hBN) and copper (Cu) powder-based green compact electrodes, prepared in hot mounting press were used as an EDM tool. The loosely bonded material particles from the compact tool were transported to the mild steel surface. With the change of process parameters (powder mixture ratio, duty factor, and peak current), the variation in surface morphology, micro-hardness and tribological properties of hBN-Cu coating layer has been discussed. Following the investigation, field emission scanning electron microscopic (FESEM) images of coating indicated fewer gaps and pores for the powder lubricant mixing ratio of hBN: Cu/50:50, peak current value of 10 A and duty factor value of 70%. X-ray diffraction plot composed of prominent peaks of BN, Cu, along with Fe₂O₃ (intermetallic compound). Micro-hardness value of lubricant surfaces drastically reduced to the minimum of 75.76 HV (coating layer) from 180 HV (substrate). Moreover, pin on disk tribological test indicated the lubrication effect of hBN particles by revealing a major drop in wear value from 95.75 µm (work piece) to 1.52 µm (coating) and friction coefficient from 0.9 (work piece) to 0.1 (coating).     

Preparation of layered bioceramic hydroxyapatite/sodium titanate coatings on titanium substrates using a hybrid technique of alkali-heat treatment and electrochemical deposition

Bioceramic hydroxyapatite/sodium titanate coating on sandblasted titanium substrate was fabricated by a three-step process. At first, the sandblasted titanium substrate was coated with a flake-like sodium titanate layer by alkali-heat treatment. In the second step, the alkali-heat treated titanium substrate was hydrothermal treated at 180 °C for 4 h with calcium solutions. In the third step, the hydroxyapatite (HA) coating was deposited onto the hydrothermal treated layer via electrochemical deposition method. The surface topography and roughness of the coatings were determined by field emission scanning electron microscope (FESEM) and a mechanical contact profilometer, respectively. The surface compositions were evaluated by X-ray diffraction (XRD), energy-dispersive X-ray spectrum (EDS), and X-ray photoelectron spectroscopy (XPS). The EDS, XPS, and XRD analysis confirm the presence of element Ca, Ca²⁺, and CaTiO₃ on sodium titanate layer after hydrothermal treatment with Ca(NO₃)₂ solution, respectively. FESEM micrograph shows the rod/needle-shaped crystallites are highly densely packed on the calcium-ion-containing layer with an average size of ~50 nm in diameter. The results indicate that the sodium titanate layer containing Ca²⁺ ions possesses higher ability to induce HA formation compared with the pure sodium titanate layer. It is revealed that surface composition plays an important role in the electrochemical deposition of HA. The calcium-ion-containing layer probably makes the nucleation of HA easy and effectively promotes orientated growth of HA on flake-like sodium titanate surface. The sodium titanate layer possesses a lower corrosion current density and a higher corrosion potential than sandblasted-Ti substrate. The sodium titanate layer should act as a barrier to the release of metal ions from metallic substrate to physiological solutions and thus reducing the electrochemical reaction rate.     

Ultrathin metal layer, ITO film and ITO/Cu/ITO multilayer towards transparent antenna

The authors have investigated radioelectrical performances of monopole antennas fabricated from transparent conducting films. Ultrathin copper layer, Indium Tin Oxide (ITO) film and ITO/Cu/ITO multilayer have been deposited by r.f. sputtering. For each sample, sheet resistance, optical transparency, radioelectrical performances have been evaluated and discussed. This research shows that multilayer technology is suitable for UHF band applications.     

Magnetic Proximity Effects in V/Fe Superconductor/Ferromagnet Single Bilayer Revealed by Waveguide-Enhanced Polarized Neutron Reflectometry

Polarized neutron reflectometry is used to study the magnetic proximity effect in a superconductor/ferromagnet (SC/FM) system of composition Cu(32 nm)/ V(40 nm)/Fe(1 nm)/MgO. In contrast to previous studies, here a single SC/FM bilayer, is studied and multilayer artefacts are excluded. The necessary signal enhancement is achieved by waveguide resonance, i.e., preparing the V(40 nm)/Fe(1 nm) SC/FM bilayer sandwiched by the highly reflective MgO substrate and Cu top layer, respectively. A new magnetic state of the system was observed at temperatures below 0.7T _C manifested in a systematic change in the height and width of the waveguide resonance peak. Upon increasing the temperature from 0.7T _C to T _C, a gradual decay of this state is observed, accompanied by a 5% growth of the diffuse scattering. This behavior can be explained in a natural way by the polarization of the superconducting electrons upon the SC transition, i.e., an appearance of additional induced magnetization within the SC, due to the proximity of the FM layer.     

Transparent conductive and infrared reflective AZO/Cu/AZO multilayer film prepared by RF magnetron sputtering

AZO/Cu/AZO multilayer films were prepared on glass substrate by radio frequency magnetron sputtering technology. The prepared films were investigated by a four-point probe system, X-ray diffraction, optical transmittance spectra, scanning electron microscope, atomic force microscopy and Fourier transform infrared spectroscopy. The results showed that Cu inner layer started forming a continuous film at the thickness around 11 nm. The prepared AZO/Cu/AZO samples exhibited the visible transmittance of 60–80 % and sample with 15 nm Cu inner layer showed the highest infrared reflection rate of 67 % in FIR region and the lowest sheet resistance of 16.6 Ω/sq. The proper visible transmittance and infrared reflection property of the AZO/Cu/AZO multilayer film make it a promising candidate for future energy conservation materials.     

Application of low-voltage electrophoretic deposition to fabrication of direct methanol fuel cell electrode composite catalyst layer

In this study, the application of a low-voltage electrophoretic deposition (EPD) approach to the fabrication of DMFC electrode composite (i.e., catalyst/ionomer) catalyst layers using a CNT-supported PtRu (PtRu/CNT) anode nanocatalyst was investigated. In the operation of EPD, the PtRu/CNT electrocatalyst was first well mixed with a suitable amount of Nafion^® solution (ionomer dispersion) with or without the addition of HClO₄ as a supporting electrolyte and then electrophoretically deposited onto a non-catalyzed electrode base at a low applied DC voltage range of 0–5 V for 0–60 min. The resultant composite catalyst layer appeared to be thin and quite smooth exhibiting a lustrous texture particularly when the supporting electrolyte was employed in the suspension. Electrochemical impedance spectroscopy (EIS), however, showed that the coated composite catalyst layer exhibited a fairly high resistance indicating an excessive amount of ionomer was preferably deposited. Application of the fabricated electrode to a DMFC resulted in a cell performance with low but reasonable power density. These test results suggested that the low-voltage EPD could be a feasible approach to effective fabrication of DMFC electrode composite catalyst layers incorporated with CNT-supported electrocatalysts, although significant improvements are deemed to be necessary.     

Preparation of YBa2Cu3O7-x superconducting thick films by the electrophoretic deposition method

YBa₂Cu₃O_7-x thick films have been realised by the Electrophoretic Deposition method (EPD). The influence of several parameters (powder and iodine concentrations in the suspension, applied voltage and deposition time) on the EPD process has been studied by measuring the conductivity of the suspension and the amount of YBa₂Cu₃O_7-x particles deposited on the electrode. Superconducting coatings onto silver substrates have been produced by a multilayer process during different deposition times. The highest critical current density value of these coatings measured by the four-point probe method is about 10³ A/cm² (77 K), in a suitable range for magnetic shielding applications.     

Chemical Vapor Deposition of Bernal‐Stacked Graphene on a Cu Surface by Breaking the Carbon Solubility Symmetry in Cu Foils

The synthesis of Bernal‐stacked multilayer graphene over large areas is intensively investigated due to the value of this material's tunable electronic structure, which makes it promising for use in a wide range of optoelectronic applications. Multilayer graphene is typically formed via chemical vapor deposition onto a metal catalyst, such as Ni, a Cu–Ni alloy, or a Cu pocket. These methods, however, require sophisticated control over the process parameters, which limits the process reproducibility and reliability. Here, a new synthetic method for the facile growth of large‐area Bernal‐stacked multilayer graphene with precise layer control is proposed. A thin Ni film is deposited onto the back side of a Cu foil to induce controlled diffusion of carbon atoms through bulk Cu from the back to the front. The resulting multilayer graphene exhibits a 97% uniformity and a sheet resistance of 50 Ω sq^?1 with a 90% transmittance after doping. The growth mechanism is elucidated and a generalized kinetic model is developed to describe Bernal‐stacked multilayer graphene growth by the carbon atoms diffused through bulk Cu.     

Influence of substrate temperature on crystalline copper aluminium oxide thin films synthesized through chemical spray pyrolysis (CSP) technique

Copper aluminium oxide (CuAlO₂) of well ordered crystalline films were deposited on to glass substrates with Cu/Al ratio r = 0.8 at the substrate temperatures of 250, 300, 350, 400 and 450 °C. Films which were characterized had a thickness of the order of few micrometers. Films deposited at the optimized deposition temperature (450 °C) revealed well-crystalline CuAlO₂ phase with XRD peak at 2θ = 31.7° corresponds to (006) reflection. The peak positions of the core level XPS spectra, confirm the presence of delafossite CuAlO₂ phase. The optical transmission of 80 % has been observed in the visible spectrum. The obtained band gap energy is 4.1 eV. From the observed results it was evidenced that the substrate temperature has strong influence on the structural and optical properties of the spray pyrolysed copper aluminium oxide films.     

Synthesis and electrophoretic deposition of magnetic nickel ferrite nanoparticles

Powders with particle size ∼5–15 nm of nickel ferrite have been synthesized chemically from aqueous precursor solutions. From the structural and magnetic properties, it is determined that the synthetic material possesses high NiFe₂O₄ phase purity and controllable particle size. The optimum calcination temperature is found to be ∼500 °C, at which the NiFe₂O₄ particles exhibit a saturation magnetization of 2800 G, and a particle size of about 10 nm. The particles are then deposited onto silicon substrates by electrophoretic deposition (EPD) process. The Ni ferrite particles are suspended in a medium of isopropyl alcohol with magnesium nitrate and lanthanum nitrate salts as charging agents. The transportation of particles to the substrate surface is assisted by applied electric field and particles adhere to the substrate surface by a glycerol based surfactant. The magnetic response of the EPD film has been investigated by vibrating sample magnetometer (VSM) measurements.     

Cathodic electrophoretic deposition of barium titanate films from aqueous solution

Cathodic electrophoretic deposition (EPD) of barium titanate from aqueous suspensions was performed on nickel substrate. Cathodic deposition allows preparation of thin layers from aqueous solution on base metal electrodes, such as Ni or Cu, without creating an intermediate oxide layer during the deposition. This opens the opportunity to prepare complex shapes of dielectric layers onto base metals for co-firing, using relatively cheap and environmentally benign aqueous EPD. Stable barium titanate colloidal suspension with a concentration of 10 g/100 mL at pH of 9.2 has been prepared for the deposition. The characteristics of electrophoretic deposition of those positively charged particles onto cathode were investigated. A uniform and dense layer was obtained for films deposited at 3 V for 2 min. The calculated film thickness for the sintered layer at these conditions was ∼1 μm. The morphology can be controlled, and in particular the pore size and distribution can be controlled via the applied voltage. At low voltage a uniform layer can be obtained whereas at high voltage a large number of macropores appears in the deposit and their size increase with the increasing of the voltage due to gas bubble formation.     

TiOx/Ag/TiOx multilayer for application as a transparent conductive electrode and heat mirror

Amorphous TiO_x films and Ag layer were deposited by electron-beam evaporation on soda-lime glass at room temperature. The details regarding the structure, surface morphology, and optical properties of the as-prepared TiO_x films were examined by X-ray diffraction, scanning electron microscopy, and ultra-violet (UV) -visible-near-infrared (NIR) spectrometry. The TiO_x films exhibit amorphous phase with an optical band gap of 3.35 eV. The polygrains oriented along the (111) and (200) directions in the Ag films were adopted to supply carriers into the TiO_x film and lower the sheet resistance of the stacked layer. The multilayer exhibited a sufficiently large Ag thickness (>15 nm), low resistance, high UV transmittance, visible transmittance, and high NIR reflection. Dependence of Ag thickness, TiO_x bottom-layer, and TiO_x overlayer on the optical and electrical properties of TiO_x/Ag/TiO_x were explored. A figure of merit (FOM) was used to find an optimal structure for a multilayer with superior conductivity and visible transparency. An FOM of 9.8 × 10^?2 (Ω^?1) at the visible wavelength of 550 nm for a TiO_x/Ag/TiO_x stacked layer with an 18-nm-thick Ag and a 20-nm-thick TiO_x was achieved. The TiO_x/Ag/TiO_x sample annealed at 500 °C 10 min also shows a good thermal stability.     

Study of Ar + O2 deposition pressures on properties of pulsed laser deposited CdTe thin films at high substrate temperature

Cadmium telluride (CdTe) thin films deposited by pulsed laser deposition (PLD) on fluorine–tin–oxide substrates under different pressures of argon (Ar) + oxygen (O₂) at high substrate temperature (T_s = 500 °C) was reported in this paper. In our work, the CdTe thin films were prepared successfully at high T_s by inputting Ar + O₂. As reported, PLD-CdTe thin films were almost prepared at low substrate temperatures (<300 °C) under vacuum conditions. The deposition of CdTe thin films at high T_s by PLD is rarely reported. The influence of the Ar + O₂ gas pressure on thickness, structural performance, surface morphology, optical property and band gap (E_g) had been investigated respectively by Ambios probe level meter, X-ray diffraction (XRD), scanning electron microscopy (SEM) and UV–Vis spectrometer. Strong dependence of properties on the deposition pressures was revealed. In the range of Ar + O₂ gas pressure from 5 to 12 Torr, the deposition rate and the E_g of CdTe films vary in the range of 41.9–57.66 nm/min then to 35.26 nm/min and 1.51–1.54 eV then to 1.47 eV, respectively. The XRD diagrams showed that the as-deposited films were polycrystalline, and the main phase was cubic phase. However, the preferred orientation peak disappeared when the deposition pressure was higher. SEM images indicated that the CdTe film deposited at a higher deposition pressure was more uniform and had a higher compactness and a lower pinhole density. Furthermore, based on this thorough study, FTO/PLD-CdS (100 nm)/PLD-CdTe (~1.5 μm)/HgTe:Cu/Ag solar cells with an efficiency of 6.68 % and an area of 0.64 mm² were prepared successfully.     

High Microwave Absorption of Nano-Fe3O4 Deposited Electrophoretically on Carbon Fiber

Production of magnetite (nano-Fe₃O₄)-coated carbon fibers (MCCFs) composites using the electrophoretic deposition (EPD) technique has been investigated in the present research. Fe₃O₄ nano-powder was synthesized by the reduction of Fe (III)-tri-ethanolamine (TEA) in an aqueous alkaline solution. By the deposition of nano-Fe₃O₄ particles distributed stably in a suspension on the surface, a uniform and compact Fe₃O₄ thin-film was fabricated on nitric acid-treated carbon fiber. According to the results, the strongest reflection loss (RL) of MCCFs was recognized to be ?11 dB at 10.37 and 11.4 GHz for a layer of 1.7 mm in thickness. EPD was introduced as a suitable method for the production of MCCFs due to its low cost, easy productivity and time efficiency as well as the high absorption properties of the resulting MCCFs compared with the previous reported works.     

Deposition of Cu–Mn alloy film from supercritical carbon dioxide for advanced interconnects

Cu–Mn alloy films for microelectronic interconnects were deposited by H₂ reduction of bis(2,2,6,6-tetramethyl-3,5-heptanedionato)-copper(II) [Cu(tmhd)₂] and bis(penta-methylcyclopentadienyl)-manganese [Mn(pmcp)₂] in supercritical carbon dioxide (scCO₂). 20-nm thick and continuous Cu–Mn films with a smooth surface were deposited at the temperature of 210 °C. Manganese was found to be segregated to film surface and its content on the surface increased with increasing Mn precursor concentration in scCO₂. Mn addition by supercritical fluid deposition could improve surface quality of the Cu film. And electrical resistivity of the Cu–Mn films increased with the Mn contents in the film.     

Diffusion barrier performance of nano-structured and amorphous Ru-Ge diffusion barriers for copper metallization

In the experiment, nano-structured and amorphous ultrathin Ru-Ge interlayers (∼15 nm in thickness) were deposited between Cu(Ru) alloy film and Si substrate via co-sputtering functioning as preventive diffusion barrier layers. After annealing at different temperatures, X-ray diffraction and four-point probe method revealed that the amorphous Ru-Ge layer effectively suppressed the Cu diffusion into Si substrate up to a temperature of at least 873 K; however, it is less than 773 K for the nano-structured Ru-Ge layer. A self-formed amorphous multilayer of Ru(RuO_x)/RuGe_xCu_y could be attained by annealing Cu/Cu(Ru)/Ru-Ge(amorphous)/Si system at a very low temperature (even 473 K). The results proved that the amorphous Ru-Ge system could self-form the multilayer diffusion barrier before the diffusion reaction between Cu and Si and improved the thermal stability of the Cu interconnection significantly.     

Immobilization of Pt Nanoparticles via Rapid and Reusable Electropolymerization of Dopamine on TiO2 Nanotube Arrays for Reversible SERS Substrates and Nonenzymatic Glucose Sensors

Inspired by mussel‐adhesion phenomena in nature, polydopamine (PDA) coatings are a promising route to multifunctional platforms for decorating various materials. The typical self‐polymerization process of dopamine is time‐consuming and the coatings of PDA are not reusable. Herein, a reusable and time‐saving strategy for the electrochemical polymerization of dopamine (EPD) is reported. The PDA layer is deposited on vertically aligned TiO₂ nanotube arrays (NTAs). Owing to the abundant catechol and amine groups in the PDA layer, uniform Pt nanoparticles (NPs) are deposited onto the TiO₂ NTAs and can effectively prevent the recombination of electron–hole pairs generated from photo‐electrocatalysis and transfer the captured electrons to participate in the photo‐electrocatalytic reaction process. Compared with pristine TiO₂ NTAs, the as‐prepared Pt@TiO₂ NTA composites exhibit surface‐enhanced Raman scattering sensitivity for detecting rhodamine 6G and display excellent UV‐assisted self‐cleaning ability, and also show promise as a nonenzymatic glucose biosensor. Furthermore, the mussel‐inspired electropolymerization strategy and the fast EPD‐reduced nanoparticle decorating process presented herein can be readily extended to various functional substrates, such as conductive glass, metallic oxides, and semiconductors. It is the adaptation of the established PDA system for a selective, robust, and generalizable sensing system that is the emphasis of this work.