Conventional Electroless Deposition Research Articles

Conformal cobalt nanoshell deposition on nanoporous gold: A candidate for selective phosphate sensing

Conformal deposition of a Co nanoshell of tailorable thickness (1.5–7.1 nm) on the internal surfaces of nanoporous gold (NPG) was achieved by adapting conventional electroless deposition conditions to circumvent sheath-only deposition on its external surface. Confining electroless deposition onto the ligaments of NPG is challenging as it demands mass transport through the porous network with non-homogeneous deposition likely due to concurrent depletion of the species to be deposited. Spatially-controlled Co electroless deposition into NPG's pores required the sequential addition of dimethylamine borane (DMAB) as reducing agent and an ultra-low concentration of Co ions. DMAB is drawn into the hydrophilic serpentine pores of NPG in a pre-immersion step with temperature elevation prior to addition of Co ions to yield Co@NPG composite. Deposition at planar gold under these conditions was not achieved, emphasising NPG's heightened intrinsic catalytic activity. XPS revealed the presence of cobalt oxide in the nanoshell. Preliminary exploration of oxidized Co@NPG nanocomposite as a potentiometric phosphate sensor revealed a linear dynamic range of 0.10–500 ppm. The facile, exclusively liquid-phase non-conventional electroless deposition approach unveils a new design strategy for a diverse range of core-shell nanoporous catalysts as prospective electrodes in fuel cells, energy conversion devices and sensors.

The Preparation of Pd/Foam-Ni Electrode and Its Electrocatalytic Hydrodechlorination for Monochlorophenol Isomers

Noble metal palladium modified foamed nickel electrode (Pd/foam-Ni) was prepared by electrodeposition method. The fabricated electrode showed better catalytic performance than the Pd/foam-Ni prepared by conventional electroless deposition. The catalysts were characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and transmission electron microscopy (TEM). Electrocatalytic activity of the Pd/Ni was studied for the hydrodechlorination of monochlorophenol isomers. The Pd/Ni exhibited good catalytic activity for 3-chlorophenol (3-CP). Complete decomposition of chlorophenol isomers could be achieved within 2 h, and the hydrodechlorination process conformed to the pseudo-first-order kinetic model. It showed a supreme stability after recycling for 5 times. The Pd/Ni exhibited a promising application prospect with high effectiveness and low Pd loading.

Synthesizing amorphous Ni-P micro-/nano-composites with perfect roundness or embryo-like structures

The ability to manipulate the morphology and structure of core-shell materials on a micro/nano scale can further control their physical and chemical properties, leading to the wider applications. Herein, the conventional electroless deposition technique for metal alloy films on solid substrates was adapted to synthesize the Ni-P micro/nano-composites in solution under high temperature and high pressure through the hydrothermal method. The obtained amorphous Ni-P composites exhibit perfect roundness with the multilayer structure of concentric circle. By controlling the erosion condition in HNO3, the special embryo-like structure was obtained where a solid microsphere is encircled by a layer of hollow globular ultrathin film with the thickness smaller than 50 nm. A round hole opens on the surface of the embryo-like structure. The reaction or formation mechanism was tentatively discussed. The methods can be used to produce the special micro-/nano-structures of metal phosphide.

Synthesis of Vertically Conformal ZnO/CuO Core–Shell Nanowire Arrays by Electrophoresis-Assisted Electroless Deposition

Vertically conformal ZnO/CuO core–shell nanowire (NW) arrays with high aspect ratios were synthesized by electrophoresis-assisted electroless deposition (EAELD) of CuO onto preformed ZnO NWs. Using this method, conformal CuO seeds were successfully formed on long ZnO NWs by the electrostatic attachment of colloidal Cu2O NPs under the solution and subsequent thermal oxidation. Using the CuO seeds, conformal CuO shell to core ZnO NWs were successfully fabricated by kinetic-limited deposition in the solution, which overcame the inherent diffusion limitations of conventional electroless deposition. This experimental evidence and thermodynamic modeling results are presented to validate the proposed EAELD mechanism. The vertically conformal hetero-nanostructure arrays developed in this work are a promising platform for applications such as solar cells and catalysts because of the maximized junction areas and active sites.

Arc plasma deposition of Pd seeding for Cu electroless deposition

Arc plasma deposition (APD) has been used for surface treatment of glass and polyimide (PI) substrates for Cu electroless deposition (ELD). The thickness of Cu ELD films increased linearly with time up to 2,000 nm on glass and 3,400 nm on PI substrates. Resistivity of Cu ELD films on glass (1.4–3.4 μΩ cm) and on PI (4.1–5.8 μΩ cm) was lower than that reported for conventional ELD processes (5–10 μΩ cm). The adhesion strength of Cu ELD films produced by our process was as good as, or better than, that for conventional Cu ELD films. APD is an effective, simple, and dry method for deposition of the seed layer for ELD on the surfaces of insulating materials.

A novel electroless method to prepare a platinum electrocatalyst on diamond for fuel cell applications

A novel electroless deposition method was demonstrated to prepare a platinum electrocatalyst on boron doped diamond (BDD) substrates without the need for pre-activation. This green method addresses the uniformity and particle size issues associated with electrodeposition and circumvents the pre-activation procedure which is necessary for conventional electroless deposition. The inert BDD substrate formed a galvanic couple with an iron wire, to overcome the activation barrier associated with conventional electroless deposition on diamond, leading to the formation of Pt nanoparticles on the electrode surface in a galvanic process coupled to a chemical process. When sodium hypophosphite was employed as the reducing agent to drive the electroless reaction Pt deposits which were contaminated with iron and phosphorus resulted. In contrast, the reducing agent ascorbic acid gave rise to high purity Pt nanoparticles. Optimal deposition conditions with respect to bath temperature, pH value and stabilizing additives are identified. Using this approach, high purity and uniformly distributed platinum nanoparticles are obtained on the diamond electrode surface, which demonstrate a high electrochemical activity towards methanol oxidation.

Cu-filled through-hole electrode for ZnS using high adhesive strength Ni–P thin film

Zinc sulfide (ZnS) and related materials are important for applications in ultraviolet light emitting diodes, cathode ray tubes, flat panel displays and infrared ray (IR) windows. In order to utilize these optoelectronics devices in electronic products, 3D-packaging as well as wafer level packaging (WLP) are needed. The two methods used to achieve this are physical vapor deposition (PVD) and conventional electroless deposition processes. However, both these methods have problems. Films made by PVD are not always of uniform thickness if the substrate is not flat. On the other hand, films made by conventional electroless deposition have weak adhesive strength to substrates. In order to overcome these limitations, we developed a new electroless deposition process to form nickel–phosphorus (Ni–P) films. This process combines catalyzation (Cu deposition) and electroless deposition processes. The films made using the new process show high adhesive strength in tensile tests and also very uniform thickness. In addition, conformal Cu filling of through-holes was achieved by using this new electroless deposition process.

Preparation of Cu-Sn Layers on Polymer Substrate by Reduction-Diffusion Method Using Ionic Liquid Baths

A novel metallization of non-conductive epoxy substrate with Cu-Sn “speculum alloy,” or “white bronze,” was performed through successive electrochemical processes: (i) conventional electroless deposition of pure Cu layer and (ii) subsequent electrochemical alloying of the resulting pure Cu layer with Sn using an ionic liquid bath at 150°C, a medium-low temperature. Availability of the Sn quasi-reference electrode for the alloying was verified, and the resulting compact and adhesive Cu-Sn layers, composed of Cu6Sn5 and/or Cu3Sn intermetallic phases, were examined as an alternative to nickel plating. The abundance of the two intermetallic phases was found to be dependent on the alloying potential and duration, and was discussed in terms of alloy formation thermodynamics of the Cu-Sn system.

Anisotropic Deposition of Localized Electroless Nickel for Preferential Bridge Connection

Preferential bridge connection by localized electroless NiB deposition was investigated. The phenomenon of “bridge” formation by so-called extraneous deposition was utilized as a technique to perform the selective deposition of NiB on organic surfaces. The films used for bridging were preferentially deposited in the area between facing pads. The deposition proceeded in the direction perpendicular to the surfaces of the facing pads. The occurrence of this anisotropic deposition strongly depends on solution diffusion, and the fabrication of a connection could be controlled by changing the pattern and pad dimensions. This method does not use a resist pattern for selective deposition; thus, it is a high throughput maskless fabrication process for the connection between separated pads. Using this technology, a preferential bridge connection for a pad array with a pad width, a pad height, a distance of between the facing pads, and a pitch was fabricated. Moreover, the combined use of localized electroless deposition and conventional electroless deposition on the bridging film is expected to realize for pad-to-pad connections with low electric resistance.

Characterization of Pd-free electroless Co-based cap selectively deposited on Cu surface via borane-based reducing agent

In this work, a highly selective and self-activated (Pd-free) Co-based deposition process for capping of Cu-lines is presented. TEM images of the cross-section of capped Cu-lines show no extraneous deposition, which translates to selectivity and direct deposition of Co-based alloy on the Cu surface without Pd-activation as a pretreatment step in conventional electroless deposition. Furthermore, an 8.6% increase in the sheet resistance(Rs) via Pd-activation process which is higher than that of the Co-based self-activated process indicates that Pd may diffuse into Cu line and induce Rs increase. Results from grazing incidence X-ray diffraction (GIXRD) analysis on as-deposited Co-based films reveal that it has a nano-crystalline structure. Such structure changes very little after annealing over 400 °C for 30 min. AES depth profiles also reveal a uniform distribution of the elemental components and extremely low B content. Additionally, Cu was not detected on Co cap film, indicating such films could serve as diffusion barrier layers to inhibit Cu diffusion.

Substrate-Enhanced Electroless Deposition of Metal Nanoparticles on Carbon Nanotubes

By simply supporting carbon nanotubes with a metal substrate of a redox potential lower than that of the metal ions to be reduced into nanoparticles, we have developed a facile yet versatile and effective substrate-enhanced electroless deposition (SEED) method for functionalizing nanotubes with a large variety of metal nanoparticles, including those otherwise impossible by more conventional electroless deposition methods, in the absence of any additional reducing agent. The nanotube-supported metal nanoparticles thus produced are electrochemically active, and the newly developed SEED process represents a significant advance in functionalization of carbon nanotubes with metal nanoparticles for a wide range of potential applications, including in advanced sensing and catalytic systems.

Comprehensive Characterization and Permeation Analysis of Thin Pd/Al2O3 Composite Membranes Prepared by Suction‐Assisted Electroless Deposition

In this work, suction‐assisted electroless deposition technique is proposed to prepare high hydrogen permselective Pd/Al2O3 composite membranes. Effects of suction pressure and plating time on the surface morphology and denseness of the resulting composite membranes have been investigated. Scanning electron microscopy (SEM), electron probe microscope analysis (EPMA), x‐ray diffractometry (XRD), and nitrogen permeability technique were used to characterize these membranes. Furthermore, the hydrogen permeability and selectivity of the composite membranes were also studied. The experimental result shows that the nitrogen permeability of the palladium (Pd) top layer is decreased with lowering the suction pressure. Under suction pressure of 3 kPa and plating time of 1 hr, a membrane with a perfectly dense 4.5 µm thick Pd layer can be obtained, whose H2/N2 selectivity is approaching infinite. As compared to the conventional electroless deposition, via suction assistance, the adhesion between the Pd top layer and Al2O3 support of the resulting membranes can be remarkably improved, and the thickness attained for complete denseness can also be reduced effectively. Based on the hydrogen permeation results, it is found that the rate‐limiting step for the hydrogen permeation through the Pd top layer is controlled by the surface reaction. Furthermore, the activation energy is estimated as 18 kJ/mol. This value is in a good agreement with those reported in literature for Pd layers thinner than 10 µm.

P H dependence of synchrotron x-ray induced electroless nickel deposition

We investigated the room temperature electroless nickel deposition on glass, induced by synchrotron x ray. By irradiating electrolytes with intense x ray the onset time for Ni reduction disappears at high electrolyte pH (>6.0) in sharp contrast with conventional electroless deposition. The time for Ni reduction in irradiated solution also decreases with increase in electrolyte pH. Consequently higher reduction rates in alkaline solutions (pH>8.0) raise the Ni nucleation density during deposition, as illustrated by homogeneous and complete coverage of the substrate by nanoparticles within a short period of 1 min. The enhancement in reduction rate is attributed to high redox efficiency of hydrated electrons produced by x ray as well as their redox potential enhancements under higher electrolyte pH conditions.

Selective Deposition of Metals on Plastics Used in the Construction of Microanalytical Devices: Photo-Directed Formation of Metal Features on PMMA

We describe here, for the first time, the use of amine-terminated poly(methyl methacrylate), AT-PMMA, surfaces as a substrate for the electroless deposition of Au nanoparticle films (Au-EDNPFs), the adsorptive deposition of Au colloids, the laterally patterned formation of Au-EDNPFs, and the use of the patterned Au-EDNPFs to form electrolessly deposited Ag films with micrometer features. Au-EDNPFs were formed by chemical reduction of AuCl4- films coordinated to AT-PMMA sheets. The Au-EDNPFs act as autocatalytic substrates for the conventional electroless deposition of Ag. Such Ag films can be used in the construction of functional Ag/AgCl reference electrodes. In addition, sequentially deposited, multilayer Au colloid films formed on the AT-PMMA surfaces are shown to be effective electrochemical working electrodes in aqueous media. In the final portion of the work, laterally patterned (selective) deposition of Ag films was accomplished by photoremoval of photolabile protecting groups attached to the amine...