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。     

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.     

单晶硅上电沉积Cu/Co纳米多层膜及其巨磁电阻效应

采用双脉冲控电位技术在单晶硅上沉积了一系列Cu/Co纳米多层膜,调制波长从200nm到5nm不等.用扫描电镜及X射线衍射对多层膜的调制结构进行了表征.采用四探针法测试多层膜的巨磁电阻（GMR）效应,研究了GMR与调制波长（λ）、铜的子层厚度（δ_Cu）的关系：λ较大时,没有观察到明显的GMR效应;λ＜30nm时,GMR效应随λ减小而增大;而λ＜8nm时,GMR值随铜层厚度的变化周期性振荡.     

Monitoring Cu nodule formation using Ni marker layers

We have used Ni marker layers to study the evolution of the characteristic spheroidal nodule morphology in electrodeposited Cu films. Ultrathin Ni layers were electrodeposited in-between Cu layers, and cross sections prepared by electrochemical polishing. During growth of a typical spheroidal feature, the edge (i.e. where there is a discontinuity in the surface slope) traces out a straight line in the cross-sectional image. At high overpotential, the cross-sections show nodule-on-nodule growth, giving rise to the well known cauliflower morphology. Rotating disk electrode studies reveal that, surprisingly, the absolute diffusion layer thickness does not appear to play a major role in the development of spheres.     

添加剂对Cu/Co多层膜电结晶成核机理及磁性的影响

在硼酸镀液中以单晶S i(111)为基底用双槽法制备Cu/Co多层膜,在镀液中分别加入了镀铜添加剂2000#和镀钴添加剂5#。探讨了镀层电结晶成核机理,在基础镀液中铜电结晶为三维连续成核过程,钴电结晶在较低电位下为三维连续成核,在较高电位下为三维瞬时成核过程。加入添加剂后,铜、钴电结晶均为三维瞬时成核过程。测试了Cu/Co多层膜的磁性能;添加剂能提高多层膜的磁性能,无添加剂的Cu/Co多层膜的巨磁阻(GMR)值约为5%,而在加入了添加剂后,其GMR值高达52%。     

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。     

Optical properties of Ni and Cu nanowire arrays and Ni/Cu superlattice nanowire arrays

In this study, Ni and Cu nanowire arrays and Ni/Cu superlattice nanowire arrays are fabricated using standard techniques such as electrochemical deposition of metals into porous anodic alumina oxide templates having pore diameters of about 50 nm. We perform optical measurements on these nanowire array structures. Optical reflectance (OR) of the as-prepared samples is recorded using an imaging spectrometer in the wavelength range from 400 to 2,000 nm (i.e., from visible to near-infrared bandwidth). The measurements are carried out at temperatures set to be 4.2, 70, 150, and 200 K and at room temperature. We find that the intensity of the OR spectrum for nanowire arrays depends strongly on the temperature. The strongest OR can be observed at about T = 200 K for all samples in visible regime. The OR spectra for these samples show different features in the visible and near-infrared bandwidths. We discuss the physical mechanisms responsible for these interesting experimental findings. This study is relevant to the application of metal nanowire arrays as optical and optoelectronic devices.     

Fabrication of magnetic nanodot array using electrochemical deposition processes

We investigated fabrication processes of magnetic nanodot arrays for the ultra-high density magnetic recording media by using an electrodeposition. A CoZrNb underlayer was sputter-deposited on a glass disk substrate as a soft magnetic underlayer (SUL). Nano-patterns were formed on the substrate by UV-nanoimprint lithography (UV-NIL) and CoPt was electrodeposited into the nano-patterns. For obtaining uniform CoPt nanodot arrays with high perpendicular coercivities, we applied thin Cu intermediate layer on CoZrNb SUL and minimized its thickness. As a result, we obtained CoPt nanodot arrays with 150-nm diameter, 300-nm pitches, and 20-nm heights, which have uniform structures, on the substrates with the construction of Cu (1-2 nm)/CoZrNb (100 nm)/Cr (5 nm)/glass disk. The perpendicular coercivity of the CoPt nanodot arrays was as high as 5.4 kOe. From these results, we showed that the Cu intermediate layer with even 1-2 nm thick considerably improved the deposition condition on the substrates with CoZrNb SUL to successfully fabricate CoPt nanodot arrays with the diameter and pitches of 80 nm and 160 nm with sufficient uniformity.     

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.     

Electroplating and magnetostructural characterization of multisegmented Co54Ni46/Co85Ni15 nanowires from single electrochemical bath in anodic alumina templates

Highly hexagonally ordered hard anodic aluminum oxide membranes, which have been modified by a thin cover layer of SiO₂ deposited by atomic layer deposition method, were used as templates for the synthesis of electrodeposited magnetic Co-Ni nanowire arrays having diameters of around 180 to 200 nm and made of tens of segments with alternating compositions of Co₅₄Ni₄₆ and Co₈₅Ni₁₅. Each Co-Ni single segment has a mean length of around 290 nm for the Co₅₄Ni₄₆ alloy, whereas the length of the Co₈₅Ni₁₅ segments was around 430 nm. The composition and crystalline structure of each Co-Ni nanowire segment were determined by transmission electron microscopy and selected area electron diffraction techniques. The employed single-bath electrochemical nanowire growth method allows for tuning both the composition and crystalline structure of each individual Co-Ni segment. The room temperature magnetic behavior of the multisegmented Co-Ni nanowire arrays is also studied and correlated with their structural and morphological properties.     

Isotropic magnetization response of electrodeposited nanocrystalline Ni–W alloy nanowire arrays

Isotropic magnetization response was demonstrated in electrodeposited nanocrystalline Ni–15 % W alloy nanowire arrays, which can be applied to nanoscale magnetic field sensors. The Ni–W alloy nanowire arrays were electrochemically synthesized on a nanochannel template electrode from an aqueous electrolytic solution. X-ray and electron diffraction patterns revealed that Ni–15 % W alloy deposits were composed of ultrafine crystal grains with a supersaturated solid solution phase. The magnetization of the Ni–15 % W alloy thin films reached saturation at around 2.5 kOe in a perpendicular direction to the film plane, whereas the pure Ni thin films hardly magnetized in the perpendicular direction. On the contrary, Ni–15 % W alloy nanowire arrays were easily magnetized, and reach saturation at around 1.0 kOe, even in a perpendicular direction to the array film plane that corresponds to the long-axis direction of the alloy nanowires.     

Electrochemical Surface Modification of Aluminium Sheets for Application to Nano-electronic Devices: Anodization Aluminium and Electrodeposition of Cobalt-Copper

A nano-porous anodized aluminium oxide layer was synthesized on the surface of bulk aluminium at a wide range of anodization voltages. The barrier layer at the pore bottom of anodized aluminium oxide layer was chemically etched to make good electrical contact for nanowires electrodeposited in the pores thus formed on metallic aluminium substrates. Cathodic polarization was examined at a wide range of cathode potentials to investigate the electrodeposition behaviour of Cu and Co into the pores. Co₈₁Cu₁₉/Cu multilayered nanowires were fabricated using a pulse-plating technique into the templates. Co-alloy layer and Cu layer thicknesses were adjusted to 10 nm, by controlling the deposition times. The temperature dependence of the resistance of Co₈₁Cu₁₉/Cu multilayered nanowires grown on the template presented clean metallic characteristics and a giant magnetoresistance (GMR) of 23% was reached at 4 K.     

Microstructure and mechanical properties of nanomultilayered AlTiN/Cu coatings prepared by a hybrid system of AIP and PDCMS

Due to its excellent lubricity and immiscibility with nitride phase, Cu has been added to nitrides to form a typical nanomultilayer structure. In this work, a hybrid deposition of AIP and PDCMS was applied to synthesize the multilayered AlTiN/Cu coatings, and the relationship between microstructure and mechanical properties was explored. The Cu-free AlTiN coating exhibited a c-TiAlN phase with a strong (200) preferred orientation. After adding Cu layer, the microstructure changed from a dense columnar structure into a featureless structure and then a fine-grained structure. As the Cu layer thickness reached 5.1 nm, the AlTiN/Cu(18.4 at.%) coating showed a double-phase of c-TiAlN and c-Cu. The thickness modulation period of Cu/AlTiN sublayer exhibited an excellent linear relationship with the content ratio of Cu/(Al + Ti). After adding Cu, the ion bombardment effect was weakened, the AlTiN/Cu(2.9 at.%) coating exhibited the lowest surface roughness of 18.9 nm, and the hardness gradually decreased from 34.6 to 13.2 GPa, accompanied by a relaxation of residual stress. Due to a high H/E* ratio, a maximum adhesion strength of 83.0 N was obtained at 2.9 at.% Cu.     

Electrodeposition of Ni-Co-Cu/Cu multilayers: 2. Calculations of the element distribution and experimental depth profile analysis

It has long been known that a concentration gradient can develop in electrodeposits along the growth direction as a result of the combined impact of anomalous codeposition and mass trasnport limitation of the reactants. It is shown in the present paper that this composition change in electrodeposited Co-Ni-Cu/Cu multilayers can be verified by secondary neutral mass spectrometry (SNMS). Various electrodeposited samples have been analyzed and the resulting composition profiles have been compared to the calculation based on the non-destructive analysis of the overall composition. The change of the Co:Ni ratio in the magnetic layer along the growth direction has been verified. A calculation method has been proposed by which the local composition of the magnetic layer can be estimated from the thickness dependence of the overall multilayer composition. It has also been shown that the deviation of the experimental depth profile data from the estimation based on the variation of the total composition with the Co-Ni-Cu layer thickness can be ascribed to the roughness increase during the sputtering in the SNMS instrument.     

Electrochemical behaviour and physical properties of Cu/Co multilayers

Cobalt/copper multilayer formation was analysed over different substrates in order to control the bilayer thickness and quality of coatings. Using a sulphate-citrate bath, at pH 4.7, electrodeposition conditions were optimised to prepare good alternate Cu/Co layers with high efficiency, by minimising the oxidation of cobalt layers during copper deposition. For multilayers with cobalt and copper layers of several nanometers, direct observation by scanning electron microscopy (SEM) or tapping mode-atomic force microscopy (TMAFM) gives layer thickness in agreement with the value calculated from deposition charges. Therefore, this calculation has been used to estimate the thickness of the thinner layers for which direct observation was difficult or impossible. A relation between the response of different characterisation methods was found. When the thickness of each layer in Cu/Co multilayers is >1.8-2 nm, potentiodynamic stripping experiments show separate peaks related to cobalt and copper oxidation. In these conditions, magnetoresistance of the coating is low. For thinner layers, the stripping response shows overlapping peaks or even a single oxidation peak. In these conditions the magnetoresistance begin to increase.     

Effects of anodization and electrodeposition conditions on the growth of copper and cobalt nanostructures in aluminum oxide films

Anodic aluminum oxide (AAO) films were prepared by alternative current (ac) oxidation in sulfuric acid and phosphoric acid solution. The porous structure of the AAO templates was probed by ac electrodeposition of copper. AAO templates grown using an applied square waveform signal in cold sulfuric acid solution exhibit a greater pore density and a more homogeneous barrier layer. UV–vis–NIR reflectance spectra of the Cu/AAO assemblies exhibit a plasmon absorption peak centered at 580 nm, consistent with the formation of Cu nanostructures slightly larger than 10 nm in diameter. Spectroscopic data also indicate that there is little or no oxide layer surrounding the Cu nanostructures grown by ac electrodeposition. The effect of pH of the cobalt plating solution on the magnetic properties of the Co/AAO assemblies was also investigated. Co nanowire arrays electrodeposited at pH 5.5 in H₂SO₄-grown AAO templates exhibit a fair coercivity of 1325 Oe, a magnetization squarness of about 72%, and a significant effective anisotropy. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Preparation of multilayered Co/Pd nanostructure films by electroplating and their magnetic properties

Multilayered fcc Co/Pd nanostructure films, prepared by electrodeposition on an electropolished polycrystalline copper substrate using a dual cell method, exhibit a remanent perpendicular magnetic anisotropy which depends on the Co film thickness. By decreasing the Co layer thickness and setting the Pd monolayer thickness as 1 nm, the remanent magnetic ratio (the ratio of the remanent magnetization perpendicular to the film plane in relation to that found on the plane of the film) became large and exceeded 1 for a Co layer thickness of about 0.4 nm, which indicates that the easy axis of magnetization of the multilayered film changed from a direction parallel to the film plane to a direction perpendicular to it at this Co film thickness. The magnetic behavior of the heat treated Co/Pd multilayered film was measured and discussed.     

Electrodeposition of cobalt based ferro-magnetic metal nanowires in polycarbonate films with cylindrical nanochannels fabricated by heavy-ion-track etching

Polycarbonate films of thickness 30 μm were irradiated with heavy ions by applying a flux of 10⁸ ions cm⁻² to produce straight tracks perpendicular to the film surface. The tracks were preferentially etched in 6 M aqueous solution of sodium hydroxide to prepare cylindrical nanochannels. The channel diameters were tuned between 200 and 600 nm by varying the etching time. Co₈₁Cu₁₉ alloy nanowires were electrodeposited potentiostatically, while Co/Cu multilayered nanowires, consisting of alternating Co and Cu layers with thickness 10 nm, were synthesized by means of a pulse plating technique in channels of length 30 μm and diameter 200 nm. Co₈₁Cu₁₉ alloy nanowires showed an anisotropic magnetoresistance effect of 0.6%, and the giant magnetoresistance of Co/Cu multilayered nanowires reached up to 8.0%.     

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.     

NiO/Co/Cu/Co/NiFe自旋阀多层膜研究

采用射频磁控溅射方法制备了一系列自旋阀多层膜。在Cu/NiFe界面处插入适当厚度的Co薄层,可增强界面处的自旋相关散射,增大自旋阀的MR值。用绝缘材料NiO作钉扎层,在大磁场中淀积了NiO/Co/Cu/Co/NiFe底自旋阀,其最大MR值达6％。