Peter Leisner

Electrochemical deposition of Co nanowire arrays; quantitative consideration of concentration profiles

Electrodeposition of Co into ion track etched polycarbonate membranes by a chronoamperometric method has been studied. The concentration variation and diffusion limiting current during nanoprocessing for growth of Co in nanoelectrode applications are described for two regimes; in the vicinity of the electrode and at the mouth of pores. The behaviour of the as-deposited nanoelectrodes can be modelled as a recessed microelectrode. A diffusion controlled limiting current of the nanodes is studied by the Cottrell equation at short times, i.e. current αt−1/2. At longer times, a steady-state current is obtained due to gradually increasing radii, r, of the spherical diffusion zones from each recessed nanode, i.e. current α(1/(r+L)), where L is the membrane thickness. The experimental value of diffusion coefficient D for Co ions was found: D=2.5×10–5 cm2 s−1. XRD and TEM measurements on 250 nm diameter and 20 μm long Co nanowires showed a hexagonal closed packed phase with a 〈100〉 texturing. The nanowires exhibited an enhanced magnetic coercivity in comparison to bulk Co. The difference of saturation fields between the parallel and perpendicular orientation fields corresponds well to the expected demagnetisation field of 2πM=8796 Oe value due to the shape anisotropy in case of an infinite thin Co cylinder.

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 Faradays 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 (tCo=50 nm) the axis along the wire starts to become the easy axis (lower saturation field) as expected in the limit where tAg=0 (case of single Co nanowires), due to the shape anisotropy.

On texture formation of chromium electrodeposits

The microstructure, texture and hardness of electrodeposited hard, direct current (DC) chromium and pulsed reversed chromium has been investigated. These investigations suggest that the growth and texture of hard chromium is controlled by inhibition processes and reactions. Further, it has been established that codeposition of Cr2O3 nanoparticles is a general feature of DC chromium electrodeposition.

Current Efficiency and Crystallization Mechanism in Pulse Plating of Hard Chromium

The current efficiency of chromium deposition was investigated under conditions of periodic current reversal. It has been demonstrated that the relationship between the anodic and the cathodic charges, Qa/Qc, has a strong influence on the current efficiency and the structure of the deposit. A plausible model for the crystallization mechanism during periodic current reversal has been suggested. According to the model, an advantageous chromium structure is maintained during the deposition process because interstitial hydrogen in the chromium lattice is oxidized during the anodic period.

Methods for electrodepositing composition-modulated alloys

Abstract Materials exhibiting unique mechanical, physical and chemical properties can be obtained by combining thin layers of different metals or alloys forming a multilayered structure. Two general techniques exist for electrodepositing composition-modulated alloy (CMA) materials; dual-bath and single-bath plating. For both techniques a number of variation exist. The most suitable technique and variation for the manufacture of a certain CMA material is highly dependent on the metals included in the given CMA system and on the dimensions of the multilayered structure. In this paper, the main principles of the two electrochemical techniques and their variants are discussed.

Electrodeposition of compositionally modulated Au/Co alloy layers

Au/Co multilayers were electrodeposited from a single bath based on acid citrate, cobalt sulphate and gold cyanide electrolyte. The Taguchi statistical method was used for experiment planning and optimisation. X-ray diffraction (XRD) investigations of the structure showed that the Au deposits exhibited a polycrystalline fcc 〈1 1 1〉 structure with an estimated grain size of ∼7 nm, while the Co deposits exhibited a nano-polycrystalline fcc structure with an estimated grain size ranging between 2 and 28 nm and a strong in-plane texture. The XRD investigation of the multilayer structure also indicated an interface roughness of about 1.5 nm between the Au and Co layers.

Effect of annealing on the structure and hardness of Ni–P–W multilayered alloy coatings produced by pulse plating

Ni-P-W multilayered alloy coatings were deposited on copper foils by pulse plating, using a rotating cylinder electrode. They consisted of layers of high (Ni-5 wt.% P-45 wt.% W) and low (Ni-8 wt.% ...

Recent progress in pulse reversal plating of copper for electronics applications

Abstract Based on demands for modern printed circuit board (pcb) manufacturing, the copper electroplating process is discussed. Electroplating from an additive free solution using low frequency pulse reversal plating with superimposed cathodic pulsation is suggested, which meets the demands for precise dimensions, high ductility and conductivity, low costs and environmental friendliness.

Experimental analysis and modelling of textile transmission line for wearable applications

Purpose – The paper seeks, by means of measurement and modelling, to evaluate frequency dependent per‐unit‐length parameters of conductive textile transmission line (CTTL) for wearable applications and to study deterioration of these parameters when CTTL is subjected to washing.Design/methodology/approach – The studied transmission line is made of Nickel/Copper (Ni/Cu) plated polyester ripstop fabric and is subjected to standard 60°C cycle in a commercial off‐the‐shelf washing machine. The per‐unit‐length parameters (resistance and inductance) and characteristic impedance of the line are extracted from measurements before and after washing. Using the measurement data an equivalent circuit is created to model the degradation of the line. The circuit is then integrated in a three‐dimensional transmission line matrix (TLM) model of the transmission line.Findings – Both an electrical equivalent circuit and a TLM model are developed describing the degradation of the conductive textile when washed. A severe det...

CFD Aided Reflow Oven Profiling for PCB Preheating in a Soldering Process

A CFD-aided reflow oven profile prediction algorithm has been developed and applied to modelling of preheating of a PCB with non-uniform distribution of component thermal mass in a forced air convection solder reflow oven. The iterative algorithm combines an analytic approach with CFD modelling. It requires an experimentally validated CFD model of the solder reflow oven and a CFD model of the PCB as main inputs. Results of computational experiments have been presented to reveal good agreement between predicted PCB profiles and corresponding CFD calculations. Application guidelines contained in the description of the algorithm will assist potential users both during the virtual prototyping phase of a PCB including designing for assembly and in the phase of reflow oven profiling.