Table of contents

A sputter-deposited SmCo₅ thin film with perpendicular magnetic anisotropy has been developed. The Sm–Co film, composed of [Co (0.41 nm)/Sm (0.31 nm)]₃₅, was prepared by sputtering on a Cu (100 nm)/glass substrate at various substrate temperatures. The coercivity was found to increase rapidly at 325–345°C and to be much greater in the direction perpendicular to the film surface than in the film plane. By using in-plane x-ray diffractometry, reflection peaks of the Sm–Co film deposited at 325–345°C were confirmed to originate from the SmCo₅ phase, and the film showed a preferred orientation of the c-axis in the direction perpendicular to the film surface. The Co/Sm laminate structure deposited on the Cu seedlayer at an appropriate substrate temperature was found to be the key to promoting crystallization of the SmCo₅ with its c-axis oriented perpendicular to the film surface.

In this note, we re-examine one-dimensional diffusion experiments of high concentration aqueous CuSO₄ into deionized water carried out by Carey A E et al (1995 Water Resources Res.31 2213–18). We show that spreading of concentrated CuSO₄ fronts does not conform to the t^1/2 relation expected from Fick's hypothesis but is subdiffusive; i.e. the cumulated concentration of CuSO₄ increases much slower than t^1/2. Occurrence of subdiffusion of CuSO₄ fronts can be related to the fact that the diffusion coefficient, D(C), of aqueous CuSO₄ decreases with increasing C, as previously predicted in Küntz M and Lavallée P (2003 J. Phys. D: Appl. Phys.36 1135–42). This result supports our initial assumption that non-Fickian diffusion is the rule in all concentration-dependent diffusivity processes, i.e. in diffusion processes involving variation of the diffusion coefficient, D(C), with the concentration of the transported quantity, C. A simple 'offer and demand' model is proposed that accounts qualitatively well for all the available experimental data. Spreading fronts are subdiffusive for D(C) decreasing with C, superdiffusive for increasing D(C) and scale as t^1/2 only for constant D.

Fe/Mo multilayers were prepared by electron beam evaporation. The magnetoresistance (MR) properties of the multilayers changed significantly with the thickness of Mo layers in the films. When the thickness of nonmagnetic Mo layers reached 3.0 nm, the MR effect of the multilayers transformed from a negative to a positive one. The curve of MR is easily saturated at relatively low applied magnetic fields. The MR ratio of [Fe(1.5 nm)/Mo(1.0 nm)]₄₂ multilayers with a typical negative MR effect can reach an absolute value of 0.1%, and that of [Fe(1.5 nm)/Mo(5.0 nm)]₁₅ multilayers with a typical positive MR effect can reach a value of 0.42%. Antiferromagnetic interlayer coupling can be observed in our films at room temperature. The origin of the MR variation is discussed according to three contributions, i.e. ordinary MR, induced by Lorentz force, anisotropic MR and the MR induced by spin-dependent scattering between the interfaces of the magnetic–nonmagnetic layers.

Arrays of multi-walled carbon nanotubes (MWCNTs) were fabricated by pyrolysis of iron phthalocyanine (FePc). A silicon wafer and a stainless steel plate were used as the substrates. MWCNTs grown on the silicon wafer were packed closely to each other and were thus well aligned, while those grown on the stainless steel plate had a low density and were oriented randomly. Field emission was achieved from the MWCNT arrays on both substrates. The turn-on electric fields of the silicon-based and stainless steel-based arrays were measured to be 1.9 V µm⁻¹ and 3.4 V µm⁻¹, respectively. The emission site distribution was also studied using a transparent anode. The field emission from the MWCNTs on the silicon substrate occurred mainly at the edge regions, while that from the MWCNTs on the stainless steel substrate exhibited a much better uniformity. We attribute this disparity in the emission site distribution to the screening effect of the electric field.

We report the effect of hydrogenation on the electrical properties of two series of metallorganic chemical vapour deposition-grown Al_xGa_1−xN samples with Al compositions x = 0.1 and 0.3. Using electrical characterization methods both shallow and deep centres were investigated. We observe a dominant donor level with a larger binding energy in the sample with x = 0.3. Interface defects are also observed between the Au and the AlGaN layer and their density increases with increasing x. Their presence is related to the high Al mole fraction which creates potential fluctuations at the surface of the sample. Hydrogenation results in a partial passivation of the shallow donor, the disappearance of interface defects, and the creation of a new shallow donor centre.

Polypyrrole (Ppy) was prepared by a photoelectropolymerization technique using different current densities on Ru-dye sensitized titanium dioxide nanoporous films. Solar cells were constructed using gold as the counter electrode with Ppy acting as the hole conductor and current–voltage characteristics were measured revealing initial efficiencies of 0.06%. Time–current profiles and x-ray photoelectron data confirmed that Ppy growth occurs within the TiO₂ pores and not at the extreme surface. Efficiency measurements of solar cells increased over one month and stabilized to nearly 1% this phenomenon being attributed to the intercalation of Li⁺ ions during the preparation step, which involved a dedoping process at a reduced potential and a soaking in LiClO₄ solution.

We have manufactured flexible field effect transistors with both polymeric and low molecular weight organic semiconductors onto a very thin (6.5 nm) gate insulator with capacitance in excess of 600 nF cm⁻². Gate insulators were prepared by anodization of a sputtered aluminium film on a Mylar plastic sheet. Anodization protocols in very dilute acid and in pure water, were explored and results compared.

Excitation of Na(3p) and K(4p) states by a high velocity non-transferred direct current plasma jet was studied. A turbulent nitrogen plasma jet was discharged into an atmosphere consisting of nitrogen and oxygen, laden with trace amounts of alkali. The line reversal temperatures of Na and K depend on the molar fraction of oxygen and may deviate considerably from the gas temperature. The reaction pressure was 0.1 MPa. The measured line reversal temperatures were reproduced by a simple chemical model. At temperatures near 2000 K non-equilibrium is caused by association of nitrogen atoms by the Zeldovich mechanism, which affects the vibrational temperature of nitrogen molecules. Near 1000 K excitation may also take place due to a chemiluminescent mechanism between alkali metals and ozone.

The knowledge of two-temperature transport coefficients is of interest in the modelling of flow in plasma processes and heat transfer. The transport coefficients in argon–helium plasmas at atmospheric pressure are calculated assuming that the kinetic electron temperature, T_e, is different from that of the heavy species, T_h. The electrical conductivity, the viscosity, the total thermal conductivity and the combined diffusion coefficients are calculated up to 30 000 K. The influence of the molar percentage of argon as well as that of the non-equilibrium parameter θ = T_e/T_h are investigated. The plasma composition is calculated using the modified Saha equation of van den Sanden et al. The most recent data to obtain collision integrals are also presented. It is shown that the viscosity and the combined diffusion coefficients strongly depend on θ, through the plasma composition and the collision integrals. The ion-dominated regime occurs all the more quickly as θ is high, resulting in a regime of interactions between charged species which induces a decrease of the viscosity and the combined diffusion coefficients. The electrical conductivity, which is directly linked to the electron number density, and the thermal conductivity increase as θ increases.

A reaction mechanism has been developed that is appropriate for the plasma aftertreatment of diesel exhaust gas. It is based on a simulated gas mixture containing propene, nitric oxide, nitrogen dioxide, oxygen and nitrogen. The reaction mechanism has been used to determine the end-products from the plasma processing and their concentrations using a chemical kinetics modelling procedure. It has been validated by a range of experiments using the same gas mixture with a packed bed, a dielectric barrier plasma reactor and a wide range of end-product analysis techniques. Using a wide range of experimental conditions has enabled us to validate the model and its predictions and to critically evaluate several alternative reaction mechanisms for the oxidation of propene and the formation of end-products in a more systematic and reliable manner than before.

Plasma immersion ion implantation (PIII) of insulating materials is quite challenging because of surface charging and capacitance effects. In this paper, we conduct a two-dimensional plasma–sheath simulation of PIII into insulating strips that have practical industrial applications. Our results reveal distortion of the plasma sheath above the parallel strips. Consequently, there exist horizontal components of the ion velocity affecting the implantation results in terms of both the incident ion dose and the penetration depth. The strip dimension is also found to exert a considerable influence on the implantation dynamics. When the strip is wider, the ion dose in the insulating strip is higher but the difference in the vertical velocity is quite small. This illustrates the importance of sample placement in the implantation process.

Changes in the cathodic arc attachment mode during a current step are studied both experimentally under well-defined and reproducible conditions, and by finite element calculations. A transition from diffuse to spot and back to diffuse attachment is observed as the response to the step. Spot formation is identified experimentally by a sharp peak in the light intensity in front of the cathode and a steep decrease in the lamp voltage. Numerical three-dimensional solutions of the thermal-conduction equation in the cathode body exposed to nonlinear surface heating give good quantitative agreement of the time course of the observed changes in attachment modes. The model that describes the heating by the near cathode layer uses a simpler equation for the ion current density than other models in the recent literature. The model describes how an excess energy flux is created in the layer in front of a spot, which cannot be transported back to the cathode by the ion current and must, therefore, be supplied to the arc. The calculated integral excess power shows a time course similar to the observed light intensity.

The products of a negative corona discharge in both pure CO₂ and mixtures of CO₂ + O₂ have been studied using a coaxial cylindrical electrode geometry with particular emphasis on the production of ozone. The discharge current in pure CO₂ was found to be highly sensitive to the presence of trace concentrations of molecular oxygen and to changes in the flow speed through the discharge. The effect of dissociative electron attachment to ozone on the discharge current was studied by measurements of ozone and CO production. The ozone concentration increases monotonically with increasing content of oxygen in the mixture with carbon dioxide, whereas the CO concentration exhibits a flat maximum for oxygen concentrations of around 4%. A simple kinetic model of the dominant chemical processes is described and compared with the experimental results.

A method for analysing thin films using a dual-waveguide interferometric technique is described. Alternate dual polarization addressing of the interferometer sensor using a ferroelectric liquid crystal polarization switch allowed the opto-geometrical properties (density and thickness) of adsorbed layers at a solid–liquid interface to be determined. Differences in the waveguide mode dispersion between the transverse electric and transverse magnetic modes allowed unique combinations of layer thickness and refractive index to be determined at all stages of the layer formation process. The technique has been verified by comparing the analysis of the surface adsorption of surfactants with data obtained using neutron scattering techniques, observing their behaviour on trimethylsilane coated silicon oxynitride surfaces. The data obtained were found to be in excellent agreement with analogous neutron scattering experiments and the precision of the measurements taken to be of the order of 40 pm with respect to adsorbed layer thicknesses. The study was extended to a series of surfactants whose layer morphology could be correlated with their hydrophilicity/lipophilicity balance. Those in the series with longer alkyl chains were observed to form thinner, denser layers at the hydrophobic solid/aqueous liquid interface and the degree of order attained at sub-critical micelle concentrations to be correlated with molecular fluidity.

The technique is expected to find utility with those interested in thin film analysis. An important and growing area of application is within the life sciences, especially in the field of protein structure and function.

Copper oxide thin films deposited on Si (100) by a filtered cathodic vacuum arc with and without substrate bias have been studied by atomic force microscopy, x-ray diffraction (XRD), x-ray photoelectron spectroscopy (XPS) and Raman spectroscopy. The results show that the substrate bias significantly affects the surface morphology, crystalline phases and texture. In the film deposited without bias, two phases—cupric oxide (CuO) and cuprous oxide (Cu₂O)—coexist as cross-evidenced by XRD, XPS and Raman analyses, whereas CuO is dominant concurrent with CuO (020) texture in the film deposited with bias. The film deposited with bias exhibits a more uniform and clearer surface morphology although both kinds of films are very smooth. Some explanations are given as well.

This work elucidates the basic mechanisms active in microstructure and the associated surface energy for a widely used bioinert ceramic, magnesia partially stabilized zirconia (MgO–PSZ) following CO₂ laser treatment. CO₂ laser irradiation results in rapid heating of the surface and consequently leads to the surface densification and crystal growth in the melted layer of the MgO–PSZ. There was an increase in the tetragonal phase after CO₂ laser treatment and columnar crystal structure in the upper-most layer and irregular grain in the heat affected zone. Various power densities of laser treatment brought about different microstructures on the modified MgO–PSZ. Contact angle measurement of a set of test liquids was used to estimate the surface energy of the MgO–PSZ before and after CO₂ laser treatment. It was found that the surface energy of MgO–PSZ had been enhanced after CO₂ laser treatment and its increase was related to the phase change (represented by microstructure) and crystal size of MgO–PSZ.

Photoreflectance (PR) is used to investigate the internal electric field of a series of ZnSe/GaAs heterostructures having different layer thicknesses. The room and low temperature PR spectra exhibited Franz–Keldysh oscillations at energies above the ZnSe band gap. From the period of these oscillations, the electric field at the ZnSe/GaAs interface was determined and behaviour decreasing with temperature was observed. The calculated values for the electric field (10–50 kV cm⁻¹) are in agreement with the typical values in semiconductors. The dependence of the electric field on the layer thickness is attributed to the presence of additional states introduced by the misfit dislocations that are formed to relieve the epilayer strain.

The effects of Mn doping on the ferroelectric properties of Pb(Zr_0.3Ti_0.7)O₃ (PZT) thin films on Pt/Ti/SiO₂/Si substrates have been investigated. The composition of the PZT and Mn doping level are Pb(Zr_0.3Ti_0.7)_1−xMn_xO₃ (x = 0,0.2,0.5,1,2,4 mol%). The PZT thin films doped with a small amount of Mn²⁺ (x ⩽ 1) showed almost no hysteretic fatigue up to 10¹⁰ switching bipolar pulse cycles, coupled with excellent retention properties. However, excessive additions of manganese made the fatigue behaviour worse. We propose that the addition of small amounts of Mn is able to reduce the oxygen vacancy concentration due to the combination of Mn²⁺ and oxygen vacancies in PZT films, forming Mn⁴⁺ ions. The interfacial layer between the Pt electrode and PZT films and Mn-doped PZT (x = 4) was detected by measuring the dielectric constant of thin films of different thickness. However, this interfacial layer was not detected in Mn-doped PZT (x = 1). These observations support the concept of the preferential electromigration of oxygen vacancies into sites in planes parallel to the electrodes, which is probably responsible for the hysteretic fatigue.

A model for the size-dependence of activation energy is developed. With the model and Fick's second law, relationships among the liner thickness, the working life and the working temperature of a TaN liner for Cu interconnects are predicted. The predicted results of the TaN liner are in good agreement with the experimental results. Moreover, the critical thicknesses of liners of some elements are calculated.

The perturbation method is developed to deal with the problem of determining the effective nonlinear conductivity of Kerr-like nonlinear media under an external ac electric field. As an example, we have considered the cylindrical inclusion embedded in a host under the sinusoidal external field E₁ sin (ωt) + E₃ sin (3ωt) with frequencies ω and 3ω. The potentials of composites at higher harmonics are derived in both local inclusion particle and host regions. The effective responses of bulk nonlinear composites at basic frequency and harmonics are given for cylindrical composites in the dilute limit. Moreover, the relationships between the nonlinear effective responses at the basic frequency and the third harmonics are derived.

A three-dimensional network model for performing non-linear time-dependent simulations of the electrical characteristics related to a composite material is presented. The considered compounds are represented by a cubic lattice and consist of conducting particles distributed in an insulating matrix. Earlier studies of the non-linear characteristics of silicon carbide (SiC) grains and of the linear frequency-dependent electrical properties of composites are combined and extended. The calculations are compared to measurements on ethylene–propylene–diene monomer rubber filled with angular SiC grains. The field-dependent conductivity measured for the unconsolidated SiC powder is used as input to the simulations. The model can manage the conductivity difference of seven decades between the constituents and the strong exponential non-linearity of the conducting particles. The network calculations replicate the experimental characteristic at high filler concentrations, where direct 'face' contacts between the filler grains dominate the behaviour. At lower concentrations, it is shown that indirect 'edge' contacts involving the polymer control the current transport also in the non-linear high field range. The general effective conductivity describing an edge connection in the linear case is no longer appropriate. Non-linear mechanisms in the polymer and the conducting grains within a field enhanced limited region around the contact need to be represented by an equivalent circuit element with a case-dependent resulting expression.

In this paper, we propose a modified coupling of modes (COM) approach, which can be used in the practical design of a layered surface acoustic wave (SAW) filter. Unlike the half-space SAW filter, frequency dependences of the COM parameters are included by using the effective permittivity approach of surface waves. Owing to the introduction of the COM model, the effects of propagation loss, electrode reflections, electrical transduction, acoustic reception, thin film loss and the distributed finger capacitance can be taken into accounts in the frequency analysis of the layered SAW filter. The frequency response of a two-port 440 MHz IDT/ZnO/R-plane sapphire layered SAW filter is analysed and compared with the existing experimental results. Results have shown good agreement between the calculated and experimental frequency responses.

From the theoretical point of view, the influence of the solid–gas interface on the effective thermal parameters in a two-layer structure of the photoacoustic technique is discussed. It is shown that the effective thermal parameters depend strongly upon the thermal resistance value associated with the solid–gas interface. New expressions for the effective thermal conductivity and thermal diffusivity in the low frequency limit are obtained. In the high frequency limit, the 'resonant' behaviour of the effective thermal diffusivity is maintained and a new complex dependence on frequency of the effective thermal conductivity is shown.

A periodic method is used to determine simultaneously both thermal conductivity and diffusivity of various polymer materials at room temperature. The sample is placed between two metallic plates and temperature modulation is applied on the front side of one of the metallic plates. The temperature at the front and rear sides of both plates is measured and the experimental transfer function is calculated. The theoretical thermal heat transfer function is calculated by the quadrupole method. Thermal conductivity and diffusivity are simultaneously identified from both real and imaginary parts of the experimental transfer function. The thermophysical parameters of several polymer samples (PTFE, PVDF and PA11) with different thicknesses (respectively, 5 mm, 2 mm and 300 µm) were studied and compared with values from the literature. The values identified for the thermal parameters are in good agreement with values from the literature for PTFE and PVDF samples; however, we show that the method reaches its limit for the thinner PA11 sample, owing to inadequacy of the thermal model.

Values of several parameters that affect calculation of heat transfer during fusion welding such as the arc efficiency, arc radius and the effective thermal conductivity of the liquid metal are not always readily available. Following an inverse approach, a smart model that embodies an iterative procedure for the optimization of multiple unknown variables within the framework of phenomenological laws that govern heat transfer and fluid flow in the weld pool is developed. The optimization scheme considers the sensitivity of computed weld geometry with the unknown parameters. The weld penetration was found to be sensitive to all the unknown variables considered. The weld width was influenced mainly by the arc efficiency and the arc radius. The initial values of the unknown variables did not affect their optimum values but affected the number of iterations necessary for convergence. The model could correctly learn values of multiple unknown parameters from only a few measurements of weld penetration and width and, based on the knowledge of these parameters, provided realistic predictions of heat transfer, fluid flow and weld geometry.