Subsequent Electroless Deposition Research Articles

Epoxy Resin-Assisted Cu Catalytic Printing for Flexible Cu Conductors on Smooth and Rough Substrates.

Flexible copper conductors have been extensively utilized in flexible and wearable electronics. They can be fabricated by using a variety of patterning techniques such as vacuum deposition, photolithography, and various printing techniques. However, vacuum deposition and photolithography are costly and result in material wastage. Moreover, traditional printing inks require posttreatment, which can damage flexible substrates, or grafting polymers, which involve complex processes to adhere to flexible substrates. Therefore, this study proposes a facile method of fabricating flexible metal patterns with high electrical conductivities and remarkable bonding forces on a diverse range of flexible substrates. Catalytic ink was prepared by using a mixture of epoxy resin, copper nanopowder, and nanosilica. The ink was applied to a variety of flexible substrates, including a poly(ethylene terephthalate) (PET) film, polyimide film, and filter paper, using screen printing to establish a bridge layer for subsequent electroless deposition (ELD). The catalytic efficiency was significantly improved by treating the cured ink patterns with air plasma. The fabricated flexible metals exhibited excellent adhesion and desirable electrical conductivity. The sheet resistance of the copper layer on the PET substrate decreased to 9.2 mΩ/□ after 150 min of ELD. The resistance of the flexible metal on the PET substrate increased by only 3.125% after 5000 bending cycles. The flexible metals prepared in this study demonstrated good foldability, and the samples with filter paper and PET substrates failed after 40 and 70 folds, respectively. A pressure sensor with a bottom electrode consisting of a copper interdigital electrode on a PET substrate displayed favorable sensing performance.

Design of bimetallic 3D-printed electrocatalysts via galvanic replacement to enhance energy conversion systems

3D-printing (also known as additive manufacturing) has recently emerged as an appealing technology to fight against the mainstream use of carbon-based fossil fuels by the large-scale, decentralized, and sustainable manufacturing of 3D-printed electrodes for energy conversion devices. Although promising strides have been made in this area, the tunability and implementation of cost-effective metal-based 3D-printed electrodes is a challenge. Herein, a straightforward method is reported to produce bimetallic 3D-printed electrodes with built-in noble metal catalysts via galvanic replacement. For this goal, a commercially available copper/polylactic acid composite filament has been exploited for the fabrication of Cu-based 3D-printed electrodes (3D-Cu) using fused filament fabrication (FFF) technology. The subsequent electroless deposition of an active noble metal catalyst (viz. Pd) onto the 3D-Cu surface has been carried out via galvanic exchange. A detailed electrochemical study run by scanning electrochemical microscopy (SECM) has revealed that the resulting bimetallic 3D-PdCu electrode exhibits enhanced capabilities by energy conversion related reactions —hydrogen evolution reaction (HER) and oxygen reduction reaction (ORR)— when compared with the monometallic 3D-Cu counterpart. Thus, this simple functionalization approach provides a custom way for manufacturing functional metal-based 3D-printed electronics harboring noble metal catalysts to improve energy-converting applications on-demand and beyond.

Fabrication of fractal structured soot templated titania-silver nano-surfaces for photocatalysis and SERS sensing

A novel approach of candle soot templated TiO2/Ag nanostructures to fabricate highly active photocatalyst and self-cleaning Surface-Enhanced Raman Scattering (SERS) substrates is demonstrated. A three-stage synthetic approach involves the replication of the fractal structure of candle soot in forming a high surface area porous TiO2 nanostructure using chemical vapour deposition and subsequent electroless deposition of silver nanoparticles on the high surface area fractal network that resulted in the formation of TiO2/Ag nanostructures. The unique morphology of TiO2/Ag renders these materials to exhibit photocatalytic and SERS activity. These surfaces showed an enhanced photocatalytic effect due to the Schottky junction which increases the recombination time of the charge carriers. The size and the coverage of the silver nanoparticles were optimized to obtain high conversion towards photocatalytic degradation of a model dye molecule such as Rhodamine B (RhB). The same substrate was also shown to enhance the Raman scattering spectra of RhB. The SERS activity of the substrate can be regenerated by photocatalytic cleaning the substrates. Overall, this present work demonstrated that fractal structured TiO2/Ag materials can be synthesized using fractal soot structures and this multi-functional material offers good potential in those applications, where photo-catalysis, SERS sensing, and self-cleaning sensing multifunctionality are required.

An “OFF-to-ON” shape memory polymer conductor for early fire disaster alarming

• Silver coated SMP conductor was fabricated by electroless deposition process. • ON-OFF switching of SMP conductor can be achieved via temperature variation. • The SMP conductor realized fast early fire alarm in fire simulation. • Thermal simulation verified the wide response range of the SMP conductor. Casualties and severe damages of environmental resources resulted from wildfires are to some extent caused by belated evacuating personnel and fighting fires. It is considered that if the timely detection of the high temperature signal can be achieved in the early stage of fire disaster, the duly rescue actions brought by the early fire alarming can extensively avoid casualty accidents and the detrimental fire spread. Therefore, in this work, we fabricate a cross-linked polycaprolactone (PCL) network, and based on its shape memory property and subsequent electroless deposition process, we prepare a smart conductor with ability of switching between non-conductive and conductive at low and high temperatures respectively. Outdoor experiments present that this electrically “OFF-to-ON” conductor can effectively respond to a fire and play a crucial role in early fire alarming under simulated fire scene. The finite element analysis simulation results further prove the advantages of this material over the traditional thermocouple in detecting temperature changes.

One‐step anchored polymers via phenolamine bionic design on textile‐based heater for application in personal heat management

AbstractFlexible electronic fabrics urgently need to solve the problem of adhesion between the conductive layer and the fabric substrates. Inspired by phenamine bionics, we designed and fabricated copper nanoparticle conductive network/nylon 6 woven fabric (CNNs/NWF) wearable heaters through rapid co‐deposited of tannic acid and polyethyleneimine (PEI) by using CuSO4/H2O2 as a trigger. The grafted TA/PEI interface is capable of anchoring on the fabric surface via covalent and non‐covalent bonds on the one hand and providing an ideal platform to absorb and reduce catalyst Ag+ to facilitate subsequent electroless deposition on the other. Furthermore, the electrical heater could rise temperature from 14.6 to 152.6°C within 90 s under 1.5 V voltage, better than that of recently reported literature. The heater had a splendid conductivity (sheet resistance R0 ≈ 0.0086 Ω sq−1) and remain stable after 1000 bending cycle tests (normalized resistance R/R0 ≈ 2.5). Furthermore, the heater could meet 50 standard washing tests, satisfying the essential needs of the wearable devices. The deviation between the simulated data and the measured data was no more than 10% by the simulation of the finite elemental analysis. This study might provide a viable source for wearable heating devices.

Polymer-Assisted Metallization of Mammalian Cells.

Developing biotemplating techniques to translate microorganisms and cultured mammalian cells into metallic biocomposites is of great interest for biosensors, electronics, and energy. The metallization of viruses and microbial cells is successfully demonstrated via a genetic engineering strategy or electroless deposition. However, it is difficult to transform mammalian cells into metallic biocomposites because of the complicated genes and the delicate morphological features. Herein, "polymer-assisted cell metallization" (PACM) is reported as a general method for the transformation of mammalian cells into metallic biocomposites. PACM includes a first step of in situ polymerization of functional polymer on the surface and in the interior of the mammalian cells, and a subsequent electroless deposition of metal to convert the polymer-functionalized cells into metallic biocomposites, which retain the micro- and nanostructures of the mammalian cells. This new biotemplating method is compatible with different cell types and metals to yield a wide variety of metallic biocomposites with controlled structures and properties.

Enhancement of the second harmonic signal of nonlinear crystals by self-assembled gold nanoparticles.

In second harmonic generation (SHG), the energy of two incoming photons, e.g., from a femtosecond laser, can be combined in one outgoing photon of twice the energy, e.g., by means of a nonlinear crystal. The SHG efficiency, however, is limited. In this work, the harvested signal is maximized by composing a hybrid system consisting of a nonlinear crystal with a dense coverage of plasmonic nanostructures separated by narrow gaps. The method of self-assembled diblock-copolymer-based micellar lithography with subsequent electroless deposition is employed to cover the whole surface of a lithium niobate (LiNbO3) crystal. The interaction of plasmonic nanostructures with light leads to a strong electric near-field in the adjacent crystal. This near-field is harnessed to enhance the near-surface SHG signal from the nonlinear crystal. At the plasmon resonance of the gold nanoparticles, a pronounced enhancement of about 60-fold SHG is observed compared to the bare crystal within the confocal volume of a laser spot.

Stretchable conductive Ni@Fe3O4@Polyester fabric strain sensor with negative resistance variation and electromagnetic interference shielding

Abstract Soft textile-based electronic devices are promising for the development of flexible strain sensors, and useful in the fields of manufacturing, smart robots, and wearable health monitoring. In this study, we fabricated a flexible, highly responsive, and electrically conductive hierarchical Ni@Fe3O4 textile strain sensor (Ni@PET-g-PAO/Fe3O4) by radiation-induced graft polymerization, in-situ formation of Fe3O4, and subsequent electroless deposition of nickel (Ni) on a polyester (PET) fabric. Compared with the previously reported strain sensors, our hierarchical strain sensor exhibited reveals a distinctive negative resistance variation and was an excellent stretchable conductor with the increase in strain. Fe3O4 acted as a joint component by improving the adhesion of the conductive Ni layer to the support and reducing the influence of the thermal deformation of the organic fiber on the sensitivity, while enhancing the magnetic properties of the Ni metal layer. This provided the multifunctional strain sensor with excellent robust performances. The strain sensor exhibited a fast and repeatable response and displayed long-term stability in the strain range of 0–40% and an operation frequency of 0.05–1 Hz. In addition, the strain sensor was used to detect and monitor finger bending, wrist twisting, and walking. Moreover, the strain sensor could be sewed into clothing to monitor human motions. In addition, the strain sensor exhibited excellent electromagnetic interference shielding efficiency and magnetic response. Therefore, this study provided a general and effective strategy to design smart wearable devices with high performances.

Mesoporous Si–Cu nanocomposite anode for a lithium ion battery produced by magnesiothermic reduction and electroless deposition

Copper deposited mesoporous silicon was fabricated by magnesiothermic reduction and electroless deposition and its electrochemical properties as an anode for lithium ion batteries were investigated. The 300–400 nm sized mesoporous Si particles were synthesized by magnesiothermic reduction of SiO2 nanospheres prepared by the Stöber method. The mesopores of Si particles were effectively decorated with Cu using Sn sensitization/Pd activation and subsequent Cu electroless deposition. The homogeneous distribution of Cu inside the mesoporous Si particles was confirmed by high resolution transmission electron microscopy images and energy dispersive spectroscopy mapping on the cross-sectional specimen prepared by a focused ion beam. The mesoporous Si–Cu nanocomposite exhibited high initial Coulombic efficiency, long cycle stability, and high rate capability, delivering a high capacity of 1569 mAh g−1 after 200 cycles at the current density of 1000 mA g−1. The improved electrochemical performance in a mesoporous Si–Cu nanocomposite was attributed to the high electrical conductivity, high Li+ ion mobility, and structural stability to restrict the aggregation and pulverization of active materials.

Silver Mesh Electrodes via Electroless Deposition-Coupled Inkjet-Printing Mask Technology for Flexible Polymer Solar Cells.

The application of metal grids as flexible transparent electrodes (FTEs) in optoelectronic devices is significantly influenced by poor adhesion and thickness difference between the metal and the substrate, resistance distribution uniformity, and a high annealing temperature. Direct inkjet printing of the metal mesh can overcome junction resistance while maintaining high conductivity, but the metal mesh thickness is still unsatisfactory. In addition, inkjet printing of mechanically durable metal FTEs directly on flexible substrates is challenging because of the high-temperature sintering treatment. Electroless deposition is a well-established method for low-cost and large-scale deposition of metal films. Here, ultrathin and ultraflexible Ag mesh@polydopamine (PDA)/poly(ethylene terephthalate) (PET) FTEs were fabricated by integrating inkjet-printed polymer matrices on a PDA-modified flexible PET substrate to form consecutive patterns as a mask and performing subsequent electroless deposition of the Ag mesh. The FTEs exhibit an excellent sheet resistance (Rs) of 9 Ω/sq with 89.9% transmittance. The resultant polymer solar cells show a superior power conversion efficiency (PCE) of 10.24% with 1 cm2 area and feature excellent flexural endurance (81% of initial PCE after 1500 bending cycles) and operational reliability (83% of initial PCE after 30 days). This ecofriendly and large-area fabrication technique has potential for future commercial applications of wearable electronics.

A Nature-Inspired, Flexible Substrate Strategy for Future Wearable Electronics.

Flexibility plays a vital role in wearable electronics. Repeated bending often leads to the dramatic decrease of conductivity because of the numerous microcracks formed in the metal coating layer, which is undesirable for flexible conductors. Herein, conductive textile-based tactile sensors and metal-coated polyurethane sponge-based bending sensors with superior flexibility for monitoring human touch and arm motions are proposed, respectively. Tannic acid, a traditional mordant, is introduced to attach to various flexible substrates, providing a perfect platform for catalyst absorbing and subsequent electroless deposition (ELD). By understanding the nucleation, growth, and structure of electroless metal deposits, the surface morphology of metal nanoparticles can be controlled in nanoscale with simple variation of the plating time. When the electroless plating time is 20 min, the normalized resistance (R/R0 ) of as-made conductive fibers is only 1.6, which is much lower than a 60 min ELD sample at the same conditions (R/R0 ≈ 5). This is because a large number of unfilled gaps between nanoparticles prevent metal films from cracking under bending. Importantly, the Kelvin problem is relevant to deposited conductive coatings because metallic cells have a honeycomb-like structure, which is a rationale to explain the relationships of conductivity and flexibility.

Effect of Activation Site Density on Copper Encapsulation of MWCNTs by Electroless Deposition

Importance of the activation site density on final encapsulation of multi-walled carbon nanotubes (MWCNTs) with copper was investigated in this study. MWCNTs, sensitized with tin and activated with silver, were used as precursors to prepare copper-decorated nanotubes. The effect of activation bath pH was found to be critical to control the density of silver-activation sites and to produce uniform encapsulation of carbon nanotubes (CNTs) with copper in the subsequent electroless deposition method. The morphology of the copper decorated nanotubes was studied using Field Emission Gun Scanning Electron Microscope (FEG SEM) and Energy Dispersive Spectroscopy (EDS).

Surface Activation of Polymers Assisted By Picosecond Laser Pulses for Selective Metallization Via Electroless Deposition

The preparation of metallic tracks on non-conductive or semi-conductive substrates is attracting a strong scientific interest due to its useful applications in integrated circuit technology and its potential for miniaturization. The selective metallization on dielectric substrates can be carried out via laser-assisted direct writing techniques These involve processes such as thermally induced deposition, surface modification for subsequent electroless deposition as well as photocatalysis-mediated deposition among others [1]. Furthermore, a well-known methodology for producing metal tracks onto polymeric substrates is the so-called laser direct structuring (LDS) technology and is widely used for producing molded interconnect devices (MIDs). Conventional LDS uses polymeric materials loaded with a small amount of metallic compound (e.g. Pd particles) which after laser ablation can be released for catalyzing a further electroless plating process. Organometallic complexes based on palladium (Pd2+), copper (Cu2+) [2] as well as metal oxide composites of copper−chromium oxide (CuO·Cr2O3) or antimony-doped tin oxide (ATO) [3] have been used as catalyst sources for LDS technology in the last years. The active material is finely dispersed in the polymeric matrix and can be chemically modified by laser ablation in order to play a role as catalyst in a subsequent electroless deposition process. However, although the LDS method offers flexibility and freedom for 3D patterning design, the addition of those special additives (catalyst sources) is required in order to make the polymeric material suitable for LDS. This paper will discuss a simple methodology for patterning metal tracks onto the polymeric substrate polybutylene terephthalate (PBT). The selective metallization process consists of three main steps: (1) surface patterning and activation with picosecond-laser pulses in a dry processing environment; (2) treatment of the substrate in PdCl2 seeding solution, and (3) selective metallization of the substrate via electroless copper deposition. It was found that, besides a significant surface roughening, the use of ultra-short laser pulses promoted the chemical modification of the polymeric surface in a manner that the surface acquires the ability to reduce Pd-ions into metallic Pd clusters during a subsequent treatment in PdCl2 solution. The laser parameters as well as the concentration and the temperature of the PdCl2 solution were investigated and correlated with the surface morphology, the formation of Pd clusters as well as with the characteristics of the copper layers. The copper features were homogeneous and exhibited well defined geometries. Moreover, the adhesive properties of the copper structures were investigated. Tape tests showed that the copper structures exhibited good adhesion to the PBT substrate and this is ascribed to the high roughness obtained via laser patterning. The copper layers exhibit low electrical resistivity values and therefore show great potential for applications in electronic devices even with 3D complex geometries.

A simple method of fabricating nickel-coated cotton fabrics for wearable strain sensor

Conductive fabrics have achieved significant attention in the field of wearable electronics. Herein, a novel and simple method was developed to fabricate nickel-coated cotton fabrics. Triazine groups were bonded onto the cotton fabrics through treating by cyanuric chloride solution to absorb silver ions and to form a catalytical layer on the fabrics, which could successfully initiate the subsequent electroless deposition (ELD) of nickel (Ni). The cyanuric chloride concentration and ELD time were optimized. Compared to conventional methods, superior conductivity as well as good adhesion was obtained because of the stable affinity of triazine groups to metals. The surface conductivity of the as-prepared Ni-coated fabrics was as high as 21.82 S cm−1. The strain sensing properties of the Ni-coated fabrics were studied, demonstrating high sensitivity and rapid response. These attractive properties of the Ni-coated cotton fabrics suggest that the proposed method is expected to be used in the fabrication of wearable strain sensors.

Facile preparation of high-performance elastically stretchable interconnects.

Sites on poly(dimethylsiloxane) are selected by ultraviolet exposure. In a subsequent electroless deposition, solid silver films are created on the selected sites only. In this way, facile vacuum-free deposition of electrodes from the liquid phase and their photoresist- and solvent-free patterning are realized. The technique enables reliable rigid-to-soft interconnects that are reversibly stretchable under arbitrary and changing stretching directions.

An aerosol-based soft lithography to fabricate nanoscale silver dots and rings for spectroscopic applications.

Site-selective deposition of aerosol Pd nanoparticles on a substrate was employed to fabricate nanoscale Ag dots and rings through a subsequent electroless deposition. The fabricated nanoscale dot and ring arrays respectively showed properties in surface-enhanced Raman (SER, with a 1.8 × 10(5) enhancement factor) and Fourier transform near infrared (FT-NIR, at 6153 cm(-1) absorption band) spectra.

Using an Office Inkjet Printer to Define the Formation of Copper Films on Paper

A low-cost fabrication process for forming conductive copper lines on paper is presented. An office inkjet printer was used to deposit desired patterns of silver nitrate and tannic acid solutions sequentially on paper. Silver nitrate was instantaneously reduced in situ on paper by tannic acid at room temperature to form silver nanoparticles, which acted as catalysts for the subsequent electroless deposition of copper. The copper films were 1.8 μm thick, and the sheet resistance of the copper film on paper was 9 Ω/□. A dual monopole ultrawide band antenna was fabricated on paper and its performance was equivalent to that of a similar antenna fabricated on a copper-film covered Kapton substrate using conventional lithographic processes. The paper-based conductive copper films fabricated using the facile process presented herein will aid the development of low-cost flexible circuits and sensors.

Electroless and electrolytic deposition of Co–SiC composite coatings on aluminum

Hydrometallurgical methods for production of Co–SiC composite coatings on aluminum were developed. The following consecutive stages were proposed: zincating of aluminum substrate in strong alkaline solutions (cementation, compact deposition, double dip), electroless cobalt deposition in an alkaline solution and, finally, electroless deposition or electrodeposition of the composites. All stages and appropriate reductant selection were essential to achieve good adherence of the multilayered system to the aluminum surface. It was found that double zincate treatment of the substrate and subsequent electroless deposition of cobalt layer (for 30min, in the presence of 0.3M maleic acid as a bath stabilizer) are essential steps to achieve good adherence of electroless or electrodeposited composites of high SiC contents (25–46wt%). Microscopic observations showed uniform composition and thickness of the individual layers over the cross-section of the samples. Microhardness of deposits was also determined: it increased from 35 HV for pure substrate to 604 HV for Al/Zn/Coel/Co–SiCel or 312 HV forAl/Zn/Coel/Co–SiCed systems.

Synthesis of carbon nanotube/Ni nanocomposite film by electrophoresis and electroless deposition without Pd pretreatment

Here we report the fabrication of carbon nanotubes (CNTs)/Ni nanocomposite film by electrophoretic deposition (EPD) and subsequent electroless deposition. The present technique requires no pretreatment with expensive Pd species for activation of the surface of CNTs. The EPD bath was modified with NiSO4·6H2O to form Ni clusters on the surface of CNTs. As a result, a thin Ni layer (6nm thickness) was fabricated on CNTs, forming a CNT/Ni nanocomposite film with a thickness of 5–10μm. The fabricated CNT/Ni film had nanoporous structure and exhibited electric double layer capacity and catalytic activities for decoloration of methyl orange.

Versatile Fabrication of Intact Three‐Dimensional Metallic Butterfly Wing Scales with Hierarchical Sub‐micrometer Structures

Spread your wings: Surface functionalization of butterfly wing scales and subsequent electroless deposition of different metals produces metallic replicas with 3D sub-micrometer structures (see picture). This approach converts complicated natural 3D bioorganic structures into various otherwise unavailable metal structures with optical, electronic, magnetic, thermal, or catalytic applications.