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.     

Fabrication of network films of conducting polymer-linked polyoxometallate-stabilized carbon nanostructures

The ability of a Keggin-type polyoxometallate, phosphododecamolybdate (PMo₁₂O₄₀³⁻), to form stable anionic monolayers on carbon nanoparticles and multi-wall nanotubes is explored here to produce stable colloidal solutions of polyoxometallate covered carbon nanostructures and to disperse them within conducting polymer, poly(3,4-ethylenedioxythiophene), i.e. PEDOT, or polyaniline multilayer films. By repeated alternate treatments in the colloidal suspension of PMo₁₂O₄₀³⁻-protected carbon nanoparticles or nanotubes, and in the acid solution of a monomer (3,4-ethylenedioxythiophene or aniline), the amount of the material can be increased systematically (layer-by-layer) to form stable three-dimensional organized arrangements (networks) of interconnected organic and inorganic layers on electrode (e.g. glassy carbon) surfaces. In hybrid films, the negatively charged polyoxometallate-covered carbon nanostructures interact electrostatically with positively charged conducting polymer ultra-thin layers. Consequently, the attractive electrochemical charging properties of conducting polymers, reversible redox behavior of polyoxometallate, as well as the mechanical and electrical properties of carbon nanoparticles or nanotubes can be combined. The films are characterized by fast dynamics of charge transport, and they are of potential importance to electrocatalysis and charge storage in redox capacitors.     

Inhibition of steel corrosion by polyaniline coatings

Polyaniline (PANI) coatings were electrosynthesised on steel samples (13% and 4.44% Cr) using sulphuric and phosphoric acids as supporting electrolytes. Protective properties of PANI coatings in the supporting electrolytes were investigated by monitoring the open-circuit potential vs. time, and by applying electrochemical impedance spectroscopy. PANI layers have been found to provide corrosion protection. Thicker PANI layers at 530 mV vs. Ag/AgCl (3 mol dm⁻³ KCl) exhibit pure capacitive behaviour at low frequencies, and in addition a small resistance at high frequencies. Thinner layers at 530 mV exhibit a much higher resistance attributed to a higher degree of PANI-free electrode surface and/or to a significant amount of PANI transformed from emeraldine to leucoemeraldine form. The layer deposited in a phosphate solution appears to have better protective properties than the layer deposited in a sulphate solution. Therefore, PANI from phosphate solution was tested also in 0.1 mol dm⁻³ HCl. However, in the chloride-containing solution, the time of protection was significantly shorter.     

Development of a magnetic corrosion probe for nondestructive evaluation of concrete against corrosion of reinforcing bar

A new magnetic corrosion probe has been developed for nondestructive evaluation of concrete against corrosion of reinforcing bar. Two types of probes, a thin iron wire (probe A) and an iron-plated copper bar (probe B) were tested whether their changes in residual magnetization with progress of corrosion of iron could be detected using a superconducting interference device (SQUID) magnetometer. The preliminary tests carried out under an atmospheric condition showed that the residual magnetization became less intensive with progress of corrosion for both probes. Then the two types of probes were embedded in mortar for an accelerated corrosion test. The results showed that probe A scarcely corroded in mortar despite that reinforcing bar suffered from corrosion under the identical condition. The probe B corroded as reinforcing bar did, resulting in a sharp decrease in the residual magnetization. Thus, the probe of type B embedded in mortar can give a magnetic warning against degradation of surroundings regarding the corrosion of reinforcing bar.     

Bias sensitive multispectral structures for imaging applications

In this paper we present results on the optimization of an pinpii‘n’ type a-Si:H based three color detector with voltage controlled spectral sensitivity. The sensor element was fabricated on a glass covered with Indium Tin Oxide (ITO) and consists of a p-i-n a-SiC:H multilayer structure which faces the incident illumination, followed by a-SiC:H(-p)/a-SiC:H(-i)/a-Si:H(-i′)/a-SiC:H(-n′)/ITO heterostructure, that allows the optically addressed readout.Results show that this approach leads to regionally different collection parameters resulting in multispectral photodiodes. In the polychromatic operation mode different sensitivity ranges are programmed by switching between different biases so that the basic colors can be resolved with a single device. Positive bias is needed under blue irradiation and moderated reverse bias under green. The threshold voltage between green and red sensitivity depends on the thickness of the bottom a-SiC:H (-i) layer, and corresponds to the complete confinement of the absorbed green photons across the pinpi sequence. As the thickness of the a-Si:H i'-layer increases, the self-reverse effect due to the front absorption will be balanced by the decrease of the self-forward effect due to the back absorption shifting the threshold voltage to lower reverse bias.The various design parameters are discussed and supported by a 2D numerical simulation.     

Investigation of magnetization reversal in micron-sized stripes of epitaxial-grown (1 1 0) Laves phase DyFe2 films

A large-scale striped array of width 3.4 μm has been fabricated in 400-nm-thick epitaxial (1 1 0) DyFe₂ films with Laves phase structure using a UV direct write system. The magnetic and magneto-optical properties of the sample were characterized by a vibrating sample magnetometer and magneto-optical Kerr magnetometry, respectively. The close easy-axis [−1 1 0] direction, confirmed by VSM, was chosen for patterning. The MO Kerr loops reveal that an additional anisotropy can be induced by the shape of the stripes, which can obviously enhance the coercivity of the close easy-axis [−1 1 0] loop. The magnitude of this additional anisotropy was determined to be 4.2 × 10⁵ erg/cm³, which is not sufficient to change the coercivity of the hard-axis loop due to a large intrinsic anisotropy along the hard-axis [0 0 1] direction.     

制备超薄多层膜的自动转速控厚法

在转速控厚法的基础上 ,排除了射频溅射的电磁干扰 ,实现了自动转速控厚法。用这种方法镀制超薄多层膜时 ,可以实时记录下镀制每层膜的沉积时间、自动切换转速、完成设定周期后自动停止转动。自动转速控厚法与转速控厚法相比 ,明显降低了多层膜制备的劳动强度 ,提高了多层膜制备的成品率和监控精度。而且将在镀制复杂膜系多层膜时 ,具有更加明显的优势     

Properties of exchange biased Co/Co3O4 bilayer films

Co/Co₃O₄ bilayer films were fabricated by RF sputtering with Co and Co₃O₄ targets. Exchange bias effect in the bilayer films was observed at 80 K by vibrating sample magnetometer. The bias effect disappeared about 240 K slightly lower than the Néel point of CoO and much higher than the Néel temperature of Co₃O₄ about 40 K. To clarify the origin of the exchange bias effect, Auger and X-ray photoelectron spectroscopy were employed and CoO was found at a transition region from Co₃O₄ layer to Co layer due to oxygen diffusion during sputtering. The angular dependence of exchange bias field H_E was obtained to obey function of H_E(θ)=18.06 (kA/m)[−cos θ+0.22 cos 3θ+0.03 cos 5θ−0.01 cos 7θ+].     

Green's Function for Multilayers with Interfacial Membrane and Flexural Rigidities¹

A three-dimensional Green's function for a material system consisting of anisotropic and linearly elastic planar multilayers with interfacial membrane and flexural rigidities has been derived. The Stroh formalism and two-dimensional Fourier transforms are applied to derive the general solution for each homogeneous layer. The Green's function for the multilayers is then solved by imposing the surface boundary condition, the interfacial displacement continuity condition, and the interfacial traction discontinuity condition. The last condition is given by the membrane and bending equilibrium equations of the interphases modeled as Kirchhoff plates. Numerical results that demonstrate the validity and efficiency of the formulation are presented for the case of a stack of silicon thin films embedded in epoxy.