Electrodeposition of Co-Ni-Cu/Cu multilayers: 1. Composition, structure and magnetotransport properties

Co-Ni-Cu/Cu multilayers have been deposited from a sulfate/sulfamate bath by controlling the current and the potential for the deposition of the magnetic and the copper layer, respectively. The magnetic layer thickness was varied between 1.2 nm and 12 nm, while the Cu layer thickness was in the range of 1.1-2.3 nm. Alloys with direct current have also been produced for comparison. All multilayer deposits exhibited a face centered cubic structure, while a small amount of hexagonal close packed phase was also present in the d.c. deposited alloys. The composition analysis showed that the codeposition of Co and Ni can be classified as anomalous codeposition for both d.c. and compositionally modulated deposits, regardless of the simultaneous deposition of Cu. The composition of the magnetic layer was affected by its layer thickness. This finding led to the conclusion that there must be a composition gradient in the magnetic layer in the growth direction. The magnetoresistance of the multilayers increased with increasing copper layer thickness, while the superparamagnetic contribution in the magnetoresistance increased with decreasing deposition current density of the magnetic layers.     

Preparation and Characterisation of Electrodeposited Ni—Cu/Cu Multilayers

Ni–Cu/Cu multilayers have been, grown from a single electrolyte under potentiostatic conditions at different electrolyte pH values. The current-time transients recorded during deposition indicated different growth modes of the Ni–Cu layers. Structural characterisation by X-ray diffraction revealed that the multilayers have the same crystal structure and texture as their (1 0 0) textured polycrystalline Cu substrate. Scanning electron microscopy showed that the films grown at low pH (2.2) have smoother surfaces than those grown at high pH (3.0). Energy dispersive X-ray analysis revealed that the magnetic layers of the multilayers electrodeposited at high pH contain much more Cu compared to those deposited at low pH. Anisotropic magnetoresistance was found for nominal Cu layer thicknesses below 0.6 nm, and giant magnetoresistance (GMR) above 0.6 nm. The shape of the magnetoresistance curves for GMR multilayers indicated the predominance of a superparamagnetic contribution, possibly due to the discontinuous nature of the magnetic layer. For multilayers with the same bilayer and total thicknesses, the GMR magnitude decreased as the electrolyte pH increased. Besides possible structural differences, this may have come from a strong increase in the Cu content of the magnetic layers since this causes a nearly complete loss of ferromagnetism at room temperature.     

Characterisation of CoNi(Cu)/Cu multilayers deposited from a citrate electrolyte in a flow channel cell

CoNi(Cu)/Cu multilayers consisting of 50 and 200 bi-layers were deposited from a citrate electrolyte in a flow channel cell by a dual pulse plating technique. The dissolution of the ferromagnetic components during pulse plating was studied using an oscilloscope and cyclic voltammetry. It was found that the dissolution was suppressed due to the passivation of the ferromagnetic layers before the deposition of an atomic layer of nonmagnetic component on them. The passivation was a function of the nickel ion concentration in the electrolyte. X-ray studies showed that the deposit had a preferred crystal orientation of [1 1 1] and suggested the formation of a super-lattice. Atomic force microscopy studies showed a four-fold increase of the roughness of the ferromagnetic surface with increasing layer thickness from 6 to 10 nm, whereas the roughness of the nonmagnetic surface only changed slightly with increasing layer thickness. The multilayers exhibit giant magnetoresistance.     

Co/Cu纳米多层膜的电化学制备及其微观结构的表征

以(110)高择优的Cu片为基底,在硫酸盐镀液中采用单槽双脉冲控电位电沉积法制备了Co/Cu纳米多层膜。采用X射线衍射(XRD)和扫描电镜(SEM)分别对多层膜的微观结构和形貌进行了表征。结果表明,Co/Cu多层膜具有良好周期性,多层膜的微结构和表面形貌与表层的金属层紧密相关,也与Co和Cu镀层厚度及其相对厚度、周期数相关。硼酸的加入有利于改善Co/Cu多层膜的层状结构。     

Dissolution from electrodeposited copper–cobalt–copper sandwiches

The electrochemical behaviour of electrodeposited Co–Cu/Cu multilayers from citrate electrolytes was investigated using cyclic voltammetry and stripping techniques at a rotating ring disc electrode. Copper and cobalt–copper alloy sandwiches were deposited from an electrolyte containing 0.0125 M CuSO₄, 0.250 M CoSO₄ and 0.265 M trisodium citrate at two different pHs, 1.7 and 6.0. The Cu/Co–Cu/Cu sandwich is representative of a single layer in a Co–Cu/Cu multilayer deposit, which is known to exhibit unusual physical and magnetic properties. Results from cyclic voltammetry and detection of dissolving species at the ring showed that cobalt is stripped from a Cu/Co–Cu/Cu sandwich even when a copper layer as thick as 600 nm covers the Co–Cu alloy. Scanning electron microscopy showed that cobalt can dissolve from the deposit easily because the copper layer covering the Co–Cu alloy is porous. A separate series of experiments with Cu/Co–Ni–Cu/Cu sandwich showed that cobalt does not dissolve from these deposits because the addition of nickel stabilises cobalt in the Co–Ni–Cu alloy.     

Effect of sub-layer thickness on magnetic and giant magnetoresistance properties of Ni-Fe/Cu/Co/Cu multilayered nanowire arrays

Ni–Fe/Cu/Co/Cu multilayered nanowire arrays were electrodeposited into anodic aluminum oxide template by using dual-bath method at room temperature. Scanning electron microscopy and transmission electron micros-copy were used to characterize the morphology and structure of the multilayered nanowire arrays. Vibrating sample magnetometer and physical property measurement system were used to measure their magnetic and giant magnetoresistance (GMR) properties. The effect of sub-layer thickness on the magnetic and GMR proper-ties was investigated. The results indicate that magnetic properties of electrodeposited nanowires are not affect-ed obviously by Cu layer thickness, while magnetic layers (Ni–Fe and Co layers) have significant influence. In addition, GMR ratio presents an oscillatory behavior as Cu layer thickness changes. The magnetic and GMR properties of the multilayered nanowire arrays are optimum at room temperature for the material structure of Ni–Fe (25 nm)/Cu (15 nm)/Co (25 nm)/Cu (15 nm) with 30 deposition cycles.     

High-Temperature Reaction Between Cemented Tungsten Carbide and Copper

Interdiffusion in the system cemented tungsten carbide-molten copper has been studied in the range ≤1120°C with special emphasis on the effects of WC grain size and Co content. Techniques used for analyzing the diffusion layers obtained are EPMA, optical microscopy, and microhardness measurement. A Cu-bonded WC layer develops with simultaneous diffusion of Co from the cemented carbide into the bulk copper. The Cu-bonded WC layer grows until a Co-rich layer forms at the Cu/WC-Co interface; further heating pushes the Cu-bonded WC layer deep into the bulk cemented carbide without any significant change in layer thickness. When the WC grain size is reduced and the cobalt content increased, the penetration of copper into cemented carbides increases. A tentative mechanism of interdiffusion has been proposed based on the experimental results.     

电沉积Ni80Fe20/Cu纳米多层膜及其巨磁电阻效应

采用单槽控电位双脉冲技术在n-Si（111）晶面上制备了［Ni₈₀Fe₂₀/Cu］_n多层膜,用SEM观测了多层膜的断面形貌,利用X射线衍射（XRD）表征了多层膜的超晶格结构。采用四探针法研究了多层膜的巨磁电阻（GMR）性能,结果表明,多层膜的GMR值随着Cu层厚度的变化发生周期性振荡,随着NiFe层厚度的增加先增大后减小;当样品结构为［NiFe（1.6 nm）/Cu（2.6 nm）］₈₀时,GMR值可达6.4%;多层膜的最低饱和磁场仅为750Oe。磁滞回线测试结果表明,反铁磁耦合多层膜具有较小的矩形比,更适宜作为磁头材料。     

Effect of electrode configuration and mode of deposition on magnetoresistance in electrodeposited Co/Cu multilayers on n-Si by a fully electrochemical method

Electrodeposition of metallic multilayers on Si is normally preceded by the vapour deposition of a metallic layer. Since vapour deposition produces an additional step in the production process, direct electrodeposition of multilayers on Si is desirable. However, direct electrodeposition on Si has resulted in low magnetoresistance (MR) - of the order of 1% - at room temperature. With the use of (i) electroless plated copper back contact, (ii) composite potentiostatic pulses, (iii) horizontal electrode configuration and (iv) non-continuous mode of deposition, a room temperature MR of 5.8% has been achieved.     

Magnetic anisotropy in isotropic and nanopatterned strongly exchange-coupled nanolayers

In this study, the fabrication of magnetic multilayers with a controlled value of the in-plane uniaxial magnetic anisotropy field in the range of 12 to 72 kA/m was achieved. This fabrication was accomplished by the deposition of bilayers consisting of an obliquely deposited (54°) 8-nm-thick anisotropic Co layer and a second isotropic Co layer that was deposited at a normal incidence over the first layer. By changing the thickness value of this second Co layer (X) by modifying the deposition time, the value of the anisotropy field of the sample could be controlled. For each sample, the thickness of each bilayer did not exceed the value of the exchange correlation length calculated for these Co bilayers. To increase the volume of the magnetic films without further modification of their magnetic properties, a Ta spacer layer was deposited between successive Co bilayers at 54° to prevent direct exchange coupling between consecutive Co bilayers. This step was accomplished through the deposition of multilayered films consisting of several (Co_{8 nm-54°}/Co_{X nm-0°}/Ta_{6 nm-54°}) trilayers.     

Some aspects of removal of copper and cobalt from mixed ion dilute solutions

Some aspects of the electrodeposition of copper and cobalt from aqueous sulphate solutions containing low concentrations of their ions were studied with a view to heavy metal removal via an electrochemical process. Both metals were deposited on a vitreous carbon rotating disc electrode. Deposits formed under different conditions were studied employing linear sweep voltammetry, scanning electron microscopy and EDAX surface analysis. Constant potential electrolysis was used to simulate recovery in a laboratory batch reactor. Copper can be deposited without cobalt interference at potentials as cathodic as –1.0 V despite high Co concentrations. At more negative potentials, both metals are deposited simultaneously, although the copper proportion in the binary mixture is greater than that corresponding to the solution concentration ratio. Voltammetry studies effected under conditions in which codeposition occurs show only minor changes in copper behaviour. On the other hand, cobalt behaviour exhibits significant modifications. Even though formation of an intermetallic compound is possible, ASVL and microscopy tests indicate cobalt deposition in different crystalline forms as the more probable cause. In turn, cobalt deposition depends on the polarization conditions of the electrode and on the cobalt and copper concentrations.     

Structure and Mechanical Properties of Copper/Niobium Multilayers

Copper/niobium multilayers prepared by sputtering onto Si substrates with layer thicknesses ranging from 11 to 5000 have been characterized by transmission electron microscopy and nanoindentation. The films are strongly textured with {110} close-packed planes of the bcc Nb parallel to the {111} close-packed planes of the fcc Cu and close-packed directions tending to be parallel as well. For the 11 layers, the Cu is found to grow pseudomorphically on Nb in the bcc structure. It is thought that, for thicker layers, the bcc Cu loses coherency and transforms martensitically to the fcc phase, thus resulting in the observed KurdjumovSachs orientation relationship. As the layer thickness, d , decreases from 5000 to 500, the hardness increases as d ^−1/2; i.e., it follows a HallPetch relationship so that hardening is due to grain boundaries and interfaces. The slope is the same as in pure Cu, but there is a large intercept which is ascribed to internal stresses and a large dislocation density. As the layer thickness decreases from 100 to 11, the hardness increases as (1/ d ) ℓn (0.69 d ), which is a line tension formulation such as would be expected for Orowan dislocation bowing between the layers. Again there is a large intercept which is ascribed to cutting through the Cu/Nb interfaces. The interfacial energy is calculated to be 0.46 J/m².     

铜离子在硫酸锌电解液深度净化除钴中的作用

对Cu2+在湿法炼锌浸出液锑盐法深度净化除钴过程中的作用进行了研究. 考察了钴离子浓度达到深度净化浓度([Co2+]<0.1 mg/L)的时间、低于该浓度的持续时间及所需初始铜离子浓度([Cu2+]0)等因素,综合衡量除钴效果,得到优化实验条件为：[Co2+]0=15 mg/L时,钴/锑质量比(Co/Sb)=2:1,[Cu2+]0=200 mg/L,达到深度净化浓度的时间和保持该浓度的时间分别是25和70 min;[Co2+]0=7.5 mg/L时,Co/Sb=2:1,[Cu2+]0=100 mg/L,达到和保持深度净化浓度的时间分别是40和55 min. 搅拌转速对除钴效果影响不大,高转速有利于钴返溶,返溶的原因可能是沉积的碱式钴盐溶解.     

Enhanced photovoltaic property by forming p-i-n structures containing Si quantum dots/SiC multilayers

Si quantum dots (Si QDs)/SiC multilayers were fabricated by annealing hydrogenated amorphous Si/SiC multilayers prepared in a plasma-enhanced chemical vapor deposition system. The thickness of amorphous Si layer was designed to be 4 nm, and the thickness of amorphous SiC layer was kept at 2 nm. Transmission electron microscopy observation revealed the formation of Si QDs after 900°C annealing. The optical properties of the Si QDs/SiC multilayers were studied, and the optical band gap deduced from the optical absorption coefficient result is 1.48 eV. Moreover, the p-i-n structure with n-a-Si/i-(Si QDs/SiC multilayers)/p-Si was fabricated, and the carrier transportation mechanism was investigated. The p-i-n structure was used in a solar cell device. The cell had the open circuit voltage of 532 mV and the power conversion efficiency (PCE) of 6.28%.

PACS

81.07.Ta; 78.67.Pt; 88.40.jj     

Anodic behaviour of one and two-layer coatings of Zn and Co electrodeposited from single and dual baths

One and two-layer Zn and Co coatings deposited from single and dual baths have been studied. During potentiodynamic stripping of a two-layer coating deposited from dual baths, containing either Zn2+ or Co2+, composed of a Co underlayer and a Zn overlayer, two separate peaks are observed, corresponding to the dissolution of both metals independently of one another. When the overlayer is of Co, the predominant part of the two-layer coating is stripped at the dissolution potential of pure Co coatings. In the anodic dissolution curve of a two-layer coating deposited from a single bath, containing both Zn2+ and Co2+, composed of a Zn layer with low (1.0%) Co content and a layer with high (6.5%) Co content, three anodic current peaks are observed. These are due to the dissolution of pure Zn and of Zn–Co alloy phases. The heights of the peaks and the potentials of their maxima do not depend on the order of layers but only on their thickness.     

Microstructure in electrodeposited copper layers; the role of the substrate

The microstructures of Cu layers, ranging in thickness from 3 to 12 μm, were investigated. The layers were electrodeposited from an acidic copper electrolyte onto two distinct substrate materials important for the micro-components industry: an Au layer with a pronounced 〈111〉-texture, and a nano-crystalline NiP layer. The evolutions of surface topography, morphology and crystallographic texture in the layers were investigated with scanning electron microscopy (SEM), transmission electron microscopy (TEM) and X-ray diffraction analysis, respectively. Distinct surface topographies were observed for Cu layers deposited on the Au and NiP substrates. Deposition onto the Au substrate resulted in a very smooth surface of all Cu layers, whereas the NiP substrate caused an irregular surface for 3-μm-thick layers of Cu. The crystallographic texture in the Cu layers in the first few micrometres depended strongly on the crystallographic texture in the substrate. The Cu crystallites inherited the 〈111〉-orientation of the Au substrate, whilst no preferred crystallographic orientation was observed in the Cu crystallites on the nano-crystalline NiP substrate. For Cu layers thicker than 3 μm a 〈110〉-fibre texture developed on both the substrates.     

Anodic behaviour of composition modulated Zn–Co multilayers electrodeposited from single and dual baths

The anodic behaviour of composition modulated Zn–Co multilayers (CMM) electrodeposited from single and dual baths was studied. Multilayers with thickness of the individual sublayers 0.3 and 3.0m were electrodeposited galvanostatically. It was established that most of the CMM coatings obtained from dual baths dissolve at potentials that are close to those for pure Co coatings. CMM coatings obtained from a single bath dissolve at potentials between the dissolution potentials of pure Co and pure Zn coatings. With increase in the number of sublayers in CMM coatings with equal total thickness, deposited both from dual or single baths, regardless of their individual sublayer thickness and sequence, potentials of the stripping peaks are shifted positively.     

On oxidation and adhesion of copper‐filled PE

The IR‐spectroscopy and MVCIR technique were used to study the role of technological factors (filler content, film thickness) in oxidation of polyethylene coatings filled with copper powder. It was learned that copper powder introduced into polyethylene reduces the ultimate level of oxidation of both the outer surface layer and deep‐seated layers of the polymer; also, the layer thickness of the specimens oxidized at diffusion conditions was observed to be decreased. Besides, the oxidation gradient determined through the specimen thickness was decreased on increasing the filler content. For example, with copper concentration over 3 vol %, the ultimate level of oxidation within the polymer layer that undergoes diffusive oxidation remains unchanged. The filler exerts its influence on bonding of the coatings, first of all through variations in the oxidation level of the polymer layer bordering on the substrate. For example, at the filler concentration above 3 vol %, the achievable level of adhesional strength does not depend on the coat thickness (the coat thickness being smaller than that of the diffusively oxidized layer). In thicker coatings, oxidative transformations do not, in fact, take place in the zone of adhesional contact, and the adhesion strength remains unchanged during thermal treatment. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 80: 2047–2052, 2001     

Single-step functionalization of vertically aligned MWCNTs with Cu and Ni by chemical reduction of copper and nickel acetyl acetonate in benzyl alcohol

We report a one-step functionalization reaction of forests of vertically aligned multi-walled carbon nanotubes (MWCNTs) with Cu or Ni nanoparticles. The benzyl alcohol assisted deposition reaction reduces copper or nickel acetyl acetonate to metallic homogeneously distributed nanoparticles and a 1 μm thick metallic capping layer normal to the MWCNT forests. Scanning electron microscopy and transmission electron microscopy images reveal a trimodal diameter regime for the Cu nanoparticles and a bimodal distribution for the Ni nanoparticles. Electron energy loss spectroscopy (EELS) and X-ray diffraction measurements confirm the metallic form of the particles and layers; however EELS reveals surface oxidation of the Cu particles. The metallic layer on top of the functionalized MWCNT forests can serve as a back contact and is deposited simultaneously with the nanoparticles. Field emission measurements reveal a lower contact resistance than for samples prepared by metal sputtering. Comparison with a sputtering process shows the uniqueness of this new Cu functionalization method for CNTs.     

Electrodeposition of Co-Cu-Zn/Cu multilayers: influence of anomalous codeposition on the formation of ternary multilayers

Electrodeposited Co-Cu-Zn/Cu multilayers have been prepared with various control modes. It was found in all cases that the Zn content of the magnetic layer is higher than that in the corresponding dc-plated sample. The data of the composition analysis were elucidated by the assumption of anomalous codeposition of Zn and Co. When the less noble layer is deposited, a Zn-rich zone is produced first, then it is covered with a Co-rich layer. If exchange reaction was allowed during the pulse-plating, Co dissolved selectively while the Zn content of the Co-rich layer remained unchanged. The relative resistance of Zn against the exchange reaction is due to the limited accessibility of the Zn-rich zone of the sample rather than electrochemical reasons. The structure of the deposit was analyzed by X-ray diffraction (XRD). It was revealed that Zn incorporation leads to strongly textured deposits with (1 1 1) orientation. The Zn atoms also enlarge the lattice distances of all phases formed. The incorporation of Zn into the magnetic layer of the multilayers decreases the magnetoresistance of the samples.