Table of contents

The effects of ion bombardment on polymer surfaces can be profound, with implications for all plasma-based pattern transfer processes that involve the use of polymer etch masks in lithography and etching. We report results from molecular dynamics (MD) simulations of Ar⁺ (100 eV) sputtering of oxygen-containing polymers. The MD data are compared with available experimental results, with special focus on the so-called Ohnishi parameter, which has been shown to correlate with sputtering yields for many O-containing polymers. The MD simulations match the measured data as well as the published correlations. We present a quantitative model of sputtering for these polymers that shows why the Ohnishi parameter (a function of the polymer composition) is proportional to the steady-state sputtering yield. However, we also show that the Ohnishi parameter does not correlate with yields for other polymers, including polyfluoroethylene and polyethylene. The MD simulations show that the validity of this parametrization is dependent on whether or not the sputtering of the polymer transitions between ion-induced scissioning and cross-linking at steady state.

Neutron imaging can provide two- or three-dimensional, spatially resolved images of the internal structure of bulk samples that are not accessible by other techniques, making it a unique tool with many potential applications. The method is now well established and is available at neutron sources worldwide. This review will give a survey of the technique of neutron imaging with a special focus on neutron tomography; the basics of the method as well as the technology of instrumentation will be outlined, and the techniques will be illustrated by representative applications. While the first part of the paper focuses on conventional attenuation contrast imaging, the second part reviews and critically assesses recent methodical developments.

We present an experimental and theoretical study of the low-field dynamics of current-driven vortex oscillations in nanocontacts based on spin-valve multilayers. These oscillations appear as low-frequency (250–500 MHz) excitations in the electrical power spectrum which arise from variations in the giant magnetoresistance. We show that the vortex oscillations, once nucleated at large fields applied perpendicular to the film plane, persist at zero applied magnetic fields. Some training effects on the oscillation frequency and linewidth are also observed for small in-plane magnetic fields.

To probe magnetic ordering in single crystals of La_1−xMnO₃ (x = 0.01, 0.05, 0.13) and in ceramics of LaMn_1−yO₃ (y = 0, 0.02, 0.06), the X-band electron magnetic resonance measurements were carried out in the temperature range 5 K ⩽ T ⩽ 600 K. The temperature dependences of doubly integrated intensity of electron paramagnetic resonance signal and its linewidth were fitted with known theoretical models modified for taking into account the different mechanisms of spin relaxation. Both experimental data and fitting results evidence that vacancies in Mn- and La-sites dope the carriers, which induces ferromagnetic double exchange interaction in parent LaMnO₃. However, strong structural and chemical disorder of La_1−xMnO₃ crystals makes the ferromagnetic ground state eventually impossible even at x = 0.13. In marked contrast, better structural/chemical homogeneity together with a stronger impact of Mn-site vacancies on mixed manganese valence and double exchange are characteristic for LaMn_1−yO₃ ceramics. As a result, the LaMn_0.94O₃ compound appears to be ferromagnetic-like ordered and demonstrates band-like character of the doped carriers. It is shown that 'self-doped' LaMnO₃ may be considered as a model system for studying both transition from antiferromagnetic to ferromagnetic-like magnetic ground state in La manganites upon doping and the influence of structural/chemical disorder on such a transition.

Using a combination of x-ray diffraction, transmission electron microscopy, room temperature (RT) and in-field Mössbauer studies and dc magnetization, the structural and magnetic properties of nano-sized Cu_0.25Co_0.25Zn_0.5Fe₂O₄, prepared by the chemical co-precipitation method, have been studied. Although the crystallite sizes are only of about 40 nm, these samples show a very large magnetic moment at RT. The moment of 81 A m² kg⁻¹ obtained in one of the samples is comparable to one of the largest reported values in spinel ferrites as that found in bulk CoFe₂O₄. This can be explained in terms of the enhancement in the B–B interaction because of the distortion in the octahedral B site due to the presence of the Jahn–Teller cation Cu at this site. The dependence of magnetic properties on the α-Fe₂O₃ content has also been investigated.

The investigation addresses the effect of magnetizing field on the magnetic properties of melt spun Ni_52.84Mn_19.6Ga_27.56 (at%) alloy ribbons. Magnetization behaviour at different fields was observed using a superconducting quantum interference device magnetometer for heating and cooling cycles. The plots showed distinct changes in magnetization around the characteristic temperatures at austenitic start and finish (A_S, A_F), martensitic start and finish (M_S, M_F). With increasing field A_S, M_F were unaffected. In the range of martensitic start and its finish temperature, the zero field cooled and field cooled measurements indicated magnetization drops indicating antiferromagnetic interactions, which is characteristic of the martensitic phase formation. It was shown from x-ray diffraction analysis that the low martensitic fraction in the majority austenite phase induced the splitting in the L2₁ austenitic ordering. This was further corroborated by the evidence of a few martensitic plates around grain boundaries at room temperature which is close to martensitic start temperature.

High magnetization nanoparticles coated with a biocompatible polymer have attracted considerable interest in recent times as potential materials for biomedical applications associated with targeted drug delivery, detection and the treatment of cancer. This paper considers the use of sodium borohydride reduction of metal salts to form Fe based nanoparticles coated with carboxyl terminated polyethylene glycol (cPEG). By mixing the reactants in a Y-junction, the synthesis produces uniform nanoparticles in the size range 10–20 nm with a core–shell structure. The particles are subsequently coated with a 1–3 nm thick layer of cPEG. These nanoparticles are soft ferromagnets with H_c = 400 Oe. Exciting these nanoparticles with a 4 Oe, 500 kHz alternating magnetic field leads to particle heating with a maximal increase in the saturation temperature as the particle size is decreased. For the largest particles considered here, the temperature reaches 35 °C with a 10 mg sample mass whilst for the smallest nanoparticles considered the temperature exceeds 40 °C.

We study the dynamical response of suspensions of single-domain magnetic nanoparticles. The effect of sample parameters on Néel and Brownian relaxation times which characterize the response is studied. Their effect on the ac susceptibility is also investigated. As the relaxation times are strongly size dependent we study the effect of polydispersity on the response functions next. A procedure to extract particle-size distribution in polydisperse samples from Cole–Cole plots is provided. Further, the presence of attractive and repulsive interactions amongst MNP yields a distribution of clusters of varying sizes. We propose a model incorporating the phenomena of aggregation and fragmentation to understand the formation of clusters and their distributions. Finally, we compare our numerical results with the experimental data. These comparisons are satisfactory.

Performance of devices such as magnetic random access memories crucially depends on magnetic switching time. By numerical simulations we show that ultra-fast (in the sub-nanosecond range) magnetic reversal in nanoparticles can be achieved with a single pulse of magnetic field oriented at some specific angles with respect to the magnetic moment. These angles form the areas of ballistic reversal (with no magnetization ringing). We show that the size of these areas increases with decreasing pulse duration, which allows reaching of the sub-nanosecond reversal for a pulse duration of the order of dozen(s) of ps. When changing the magnetic field, the areas of ballistic reversal move along the equator of the unitary sphere, and eventually merge with each other. For appropriate choice of the azimuthal angle, one can reach magnetic reversal along a trajectory located in or out of the easy plane.

Poly(vinylidene fluoride trifluoroethylene) and ZnO were employed for nonvolatile memory thin film transistors as ferroelectric gate insulator and oxide semiconducting channel layers, respectively. It was proposed that the thickness of the ZnO layer be carefully controlled for realizing the lower programming voltage, because the serially connected capacitor by the formation of a fully depleted ZnO channel had a critical effect on the off programming voltage. The fabricated memory transistor with Al/P(VDF–TrFE) (80 nm)/Al₂O₃ (4 nm)/ZnO (5 nm) exhibits encouraging behaviour such as a memory window of 3.8 V at the gate voltage of −10 to 12 V, and 10⁷on/off ratio, and a gate leakage current of 10⁻¹¹ A.

Ca₃Sc₂Si₃O₁₂ : Ce³⁺ phosphors with a single phase and fine size were successfully obtained at a lower temperature (1100 °C) using the gel-combustion method compared with the conventional solid-state reaction method (about 1500 °C). The crystal phase and the microstructure of the phosphors and their photoluminescence were investigated. The particle size is about 1 µm, which is much less than that obtained by the solid-state reaction. Smaller particle size can reduce internal scattering when particles are mixed with silicon and coated onto a blue light-emitting diode (LED). A bright green emission is observed, which is attributed to the characteristic emissions from 5d–²F_5/2 and 5d–²F_7/2 transitions of Ce³⁺. The excitation spectra show a broad and strong absorption at about 460 nm, suggesting that it is very suitable for use as a colour converter in white LEDs. The decay time of the gel-combustion phosphor is 54.65 ns.

The response characteristic of a femtosecond low temperature GaAs (LT-GaAs) photoconductive switch formed in a coplanar waveguide at different voltage biases is studied with the femtosecond photocurrent autocorrelation measurement technique. The experimental results show that the switching time increases when the bias voltage is increased from 10³ to 10⁵ V cm⁻¹. We provide a physical model, combining the potential barrier lowering (the Frenkel–Poole effect) and the field-enhanced thermal ionization, to give a complete explanation to the response characteristic of the LT-GaAs photoconductive switch at larger varying bias fields ranging from 10³ to 10⁵ V cm⁻¹.

A high density 'blue' mode has been observed when operating the Helicon Double Layer Thruster (HDLT) with xenon. Using a Langmuir probe and a retarding field energy analyser (RFEA), the plasma source and exhaust have been characterized at various radio frequency (RF) powers and operating pressures. When operating at low RF powers, the HDLT prototype is shown to be in a capacitively coupled mode. As the RF power is increased, a discrete mode transition occurs over a small RF power range (at about 625 W at 0.45 mTorr) and the plasma inside the source increases in density significantly and changes to a bright white/blue colour. This high density mode exhibits hysteresis, and radial measurements inside the source reveal a centrally peaked profile that is indicative of a helicon wave-sustained discharge. The quality, or Q, factor of the matching box is determined as a function of RF power and is shown to decrease in the high density mode, consistent with the increase in plasma density observed. The xenon exhaust of the HDLT prototype is investigated axially with the Langmuir probe and the RFEA and is shown to follow a Boltzmann expansion with an electron temperature of about 6 eV.

The dispersion relation and the growth rate of a dust ion-acoustic wave propagating in a complex superthermal plasma containing elongated and rotating dust particles are kinetically investigated by employing Vlasov–Maxwell equations. The negatively charged dust particles are assumed to rotate around an axis perpendicular to the direction of elongation. The condition for an unstable dust ion-acoustic wave is obtained in terms of the rotation frequency and the wave number. In the low frequency regime, the growing mode of the wave is found to be enhanced by the increase in dust particle rotation frequency. However, the dust charge state does not affect the growth rate so much, especially in the high δ = n_i0/n_e0 regime.

High-pressure argon plasma, excited by a high-current pulsed volume discharge, has been investigated. Spatial-time VUV–VIS emission kinetics were used for the plasma diagnostics. A homogeneous discharge was obtained at a pressure of up to 10 bar. It was revealed that the spectral shape of the UV–VIS photorecombination continuum is a sensitive diagnostic tool for the constriction of the discharge. This shape changes because of the difference of the positive charge carriers in the arc (atomic Ar⁺ ions) and homogeneous (molecular ions) phases of the discharge. The intensity of this continuum is proportional to the square of the electron density. The experimental data and modelling show that the heating of electrons after the main excitation pulse is a very undesirable process. It suppresses the recombination flow in plasma, thus the kinetics of all excited species are spread in time with a decrease in the excimers densities. The electron collision-induced mixing effectively converts the reservoir of long-lived triplet molecules to fast-emitted singlet excimers. This mechanism is dominant in the production of singlet excimers.

A realistic threshold density for the lasing of excimers of about 5 × 10¹⁵ cm⁻³ was estimated (the gain coefficient is 0.05 cm⁻¹). This criterion could be realized in 10 bar of Ar by a homogeneous single pulse discharge pumping with a peak electron density of 2.4 × 10¹⁶ cm⁻³.

γ-Al₂O₃ crystalline nanoparticles (NPs) are for the first time produced by the arc-discharge in water method. The discharge is studied in situ during the NP formation by simultaneously recording the voltage and current waveforms, emitted light intensity and time-resolved optical emission spectra and snapshots of the discharge. The microstructure of the NPs is investigated by high-resolution transmission electron microscopy, the chemical purity is confirmed by x-ray photoelectron spectroscopy and the crystalline structure by x-ray diffraction. The results experimentally demonstrate the successive phases that lead to the supersaturation condition governing this gas-phase bottom–up process for dielectric NP production.

We present a comparison of blanket 193 nm photoresist (PR) roughening and chemical modifications of samples processed in a well-characterized argon (Ar) inductively coupled plasma (ICP) system and an ultra-high vacuum beam system. In the ICP system, PR samples are irradiated with Ar vacuum ultraviolet (VUV) and Ar ions, while in the vacuum beam system, samples are irradiated with either a Xe-line VUV source or Ar-lamp VUV source with Ar ions. Sample temperature, photon flux, ion flux and ion energy are controlled and measured. The resulting chemical modifications to bulk 193 nm PR and surface roughness are analysed with Fourier transform infrared (FTIR) spectroscopy and atomic force microscopy. We demonstrate that under VUV-only conditions in the vacuum beam and ICP (with no substrate bias applied) systems 193 nm PR does not roughen. However, roughness increases with simultaneous high energy (>70 eV) ion bombardment and VUV irradiation and is a function of VUV fluence, substrate temperature and photon-to-ion flux ratio. PR processed in the ICP system experiences increased etching, probably due to release of H- and O-containing gaseous products and subsequent chemical etching, in contrast to samples in the vacuum beam system where etch-products are rapidly pumped away. The surface roughness structure and behaviour, however, remain similar and this is attributed to the synergy between VUV-photon and positive ions.

Due to increased active surface area and high redox flexibility, the green rust- and ferrihydrite- (FH) coated sands appear promising materials in environmental applications such as reactive filtration processes for the elimination and fixation of pollutants in soils, sediments and contaminated water. Recently, different synthesis routes to prepare coatings of the ferric green rust (FGR) and FH minerals on quartz sand were reported (Khare et al 2008 Solid State Sci.10 1342), where the pre-synthesized minerals and the sand were mixed via either a dry or a wet contact, or the minerals were synthesized by a chemical reaction in the presence of sand. We performed scanning electron microscopy, magnetic and electron paramagnetic resonance (EPR) measurements of the coated sands, with the aim of determining magnetic properties of the coatings and to investigate whether the three deposition methods yield chemically identical coatings within each group (FGR-type or FH-type), just appearing in different volumes, or whether the different deposition methods also introduce physical/chemical differences within the coatings of the same group. The FGR-type coatings behave magnetically as a superparamagnetic system. The significantly different spin blocking temperatures of the FGR samples prepared by the 'dry-contact' and 'wet-contact' methods (those prepared by the 'wet-contact' method were about 40 K higher) reveal physical/chemical differences between the two nominally same coatings. The FH-type coatings are magnetically more homogeneous, being of a spin-glass type. Marginal differences between the FH coatings produced by the 'wet-contact' and 'reactive' synthesis routes were observed as well.

This work addresses the instability of a ZnO substrate during metalorganic chemical vapour deposition (MOCVD) growth of GaN by using Al₂O₃ films deposited by atomic layer deposition (ALD) as a stabilizing transition layer on the Zn face of ZnO (0 0 0 1) substrates. A systematic study of Al₂O₃ films of different thicknesses (2–90 nm) under different ALDs and post-annealing conditions was carried out. However, this paper focuses on as-deposited 20 and 50 nm Al₂O₃ films that were transformed to polycrystalline α-Al₂O₃ phases after optimal annealing at 1100 °C for 10 min and 20 min, respectively. GaN layers were grown on ZnO substrates with these α-Al₂O₃ transition layers by MOCVD using NH₃ as a nitrogen source. Wurtzite GaN was observed by high resolution x-ray diffraction only on 20 nm Al₂O₃/ZnO substrates. Field-emission scanning electron microscopy showed a mirror-like surface, no etch pits and no film peeling in these samples. Room temperature photoluminescence showed a red-shift in the near band-edge emission of GaN, which may be related to oxygen incorporation forming a shallow donor-related level in GaN. Raman scattering also indicated the presence of a well-crystallized GaN layer on the 20 nm Al₂O₃/ZnO substrate.

Surface laser treatment of commercially pure titanium plates was performed in air using two different Nd : YAG sources delivering pulses of 5 and 35 ns. The laser fluence conditions were set to obtain with each source either yellow or blue surface layers. Nuclear reaction analysis (NRA) was used to quantify the amount of light elements in the formed layers. Titanium oxinitrides, containing different amounts of oxygen and nitrogen, were mainly found, except in the case of long pulses and high laser fluence, which led to the growth of titanium dioxide. The structure of the layers was studied by x-ray diffraction and Raman spectroscopy. In addition, reflectance spectra showed the transition from a metal-like behaviour to an insulating TiO₂-like behaviour as a function of the treatment conditions.

Modelling of the laser–target interaction on the basis of the Semak model was performed to understand the different compositions and properties of the layers. Numerical calculations showed that vaporization dominates in the case of short pulses, whereas a liquid-ablation regime is achieved in the case of 35 ns long pulses.

In this paper, the refractive index, extinction coefficient and optical band gap of xPbO–(1 − x)TiO₂ systems are determined by spectroscopic ellipsometry in the spectral range of wavelength 250–850 nm. All films are elaborated by mixed reactive thermal co-evaporation on a SiO₂/Si substrate. The Tauc–Lorentz model is used to extract the optical responses and characteristics of the layers. The best values of the fitted parameters are reported. The wavelength-by-wavelength numerical inversion, carried out without considering any fitting parameter, is also represented as another way to derive the optical constants of the layers. The refractive index and the extinction coefficient depend on the PbO content in xPbO–(1 − x)TiO₂ systems. The obtained values of the optical band gap are found to change between 2.54 and 3.38 eV. It is demonstrated here that the xPbO–(1 − x)TiO₂ systems with the studied compositions have an indirect optical band gap.

CaAl₂O₄ co-doped with Eu²⁺ and Er³⁺ were prepared by the solid-state reaction method and investigated for their photoluminescence properties. Broad band UV excited luminescence was observed for CaAl₂O₄ : Eu²⁺, Er³⁺ in the blue region due to transitions from the 4f⁶5d¹ to the 4f⁷ configuration of the Eu²⁺ ion. From the analysis of excitation and emission spectra, the crystal field splitting of the 5d states of Eu²⁺and the parameters of electron-vibrational interaction, such as the Huang–Rhys factor, effective phonon energy and zero-phonon line position of this system, were estimated for the first time.

We report on a detailed study of strain in freestanding Ge nanocrystals (NCs) by using x-ray diffraction (XRD) line profile analysis supported by high resolution transmission microscopy (HRTEM) imaging. Freestanding Ge NCs down to ∼7 nm size are synthesized by using the ball milling technique and investigated regarding the nature of strain. Detailed analysis of size and lattice strain in the NCs reveals that strain is anisotropic in the NCs. NC size and strain anisotropy factor are calculated by taking into consideration a dislocation contrast factor. The analysis further suggests that screw type dislocations are the main contributors to the strain anisotropy and the dislocation density and corresponding strain vary with crystallite size, with a maximum of both quantities for NCs produced after 20 h of milling. Direct evidence for strain caused by dislocations in individual NCs is provided from HRTEM imaging. Relaxation of strain is studied by differential scanning calorimetry, which shows a low temperature heat release at ∼310 °C, clearly indicating a kind of structural relaxation of the strained NCs. The methodology presented here is applicable for embedded as well as freestanding NCs of other materials. Implications of strain on the optical properties of Ge NCs are discussed.

Near-field thermal radiation can be several orders of magnitude higher than that between two black bodies. Previous studies have shown that the energy transfer between two semi-infinite media separated by a nanometre vacuum gap is maximized when the real part of the dielectric function is around −1 due to the excitement of surface waves. Real materials can exhibit such a behaviour only within a very small spectral interval. However, by tuning the different adjustable parameters of the dielectric functions, it is possible to estimate the maximum achievable near-field radiative transfer. In this study, the influence of each parameter in the Drude and the Lorentz models on the nanoscale radiation is investigated. Optimal values are obtained for these parameters that maximize the near-field heat flux, which can be more than an order of magnitude higher than previously calculated values for SiC and doped Si. The effect of temperature on the optimal parameters in the Drude model is also discussed. The results will guide future selection and design of materials for the enhancement in near-field heat transfer.

The behaviour of agitated submerged granular media is of wide relevance technologically and in nature. Recent modelling of such systems has invoked a kinetic theory description. Such descriptions involve the so-called granular temperature, which is directly related to the mean-square of the velocity fluctuations about the mean flow velocity. The better formulation of these models and their subsequent validation demand the experimental elucidation of the dynamics and granular temperature of submerged granular media undergoing excitation. Such elucidation, based on the non-invasive optical technique of diffusing wave spectroscopy (DWS), is reported here. The particle dynamics and granular temperature have been studied for a periodically forced submerged granular bed as a function of the forcing conditions. Rather unexpectedly, it was found that the granular temperature scaled with the square of the acceleration of the forcing rather than the square of the peak forcing velocity as in dry vibro-fluidized beds. It was also observed that the granular temperature increased with distance above the base of the bed where the forcing was applied.

The composite of α-Fe₂O₃/Zn₂SnO₄ was synthesized via a sol–gel route. Photoelectric properties are investigated by surface photovoltage spectroscopy and electric field-induced surface photovoltage spectroscopy. The photovoltaic response for the composite with the molar ratio 4 : 1 of α-Fe₂O₃ to Zn₂SnO₄ without bias is similar to that for the pristine α-Fe₂O₃ under positive bias. The results show that the modification of Zn₂SnO₄ can significantly improve the surface photovoltaic response of α-Fe₂O₃. The enhanced photogenerated charges separation could be ascribed to the good contact and energy level matching between α-Fe₂O₃ and Zn₂SnO₄. The high electron mobility and low rate of electron–hole recombination in Zn₂SnO₄ are also responsible for the improved photoelectric properties of α-Fe₂O₃.

The effects of additives on the distributions of lamellar morphology and orientation in sheared isotactic polypropylene were investigated using the small beam of synchrotron small-angle x-ray scattering. The Cu-phthalocyanine can template the lamellar orientation even under low shear rates, whereas the ultramarine blue cannot. The surface contact is suggested to play a role in stabilizing the formation of oriented nuclei which subsequently direct the growth of oriented lamellae. The additives have no notable effects on the long spacing in the shear region. However, at high shear rates, they decrease the thickness of crystalline lamellae or increase the thickness of amorphous lamellae. Since the additives increase the degree of volume crystalline in the shear region, the number of crystalline lamellae should be increased. The results are helpful in designing and selecting suitable additives for controlling lamellar morphology and orientation.

In this study, we investigated the influence of the surface modified BaTiO₃ nanoparticles on the electrical, thermophysical and micromechanical properties of ethylene-vinyl acetate (EVM) vulcanizates. Gamma-aminopropyl triethoxysilane was used as a silane coupling agent for the surface treatment of the BaTiO₃ nanoparticles. It was found that the incorporation of surface modified BaTiO₃ nanoparticles into the EVM matrix not only increased the permittivity, thermal conductivity and the mechanical strength but also showed a comparative dielectric loss tangent with pure EVM vulcanizates. In particular, the nanocomposites exhibit relatively high dielectric strength and good ductility even at the loading level of 50 vol%. The improved properties not only originate from the homogeneous dispersion of BaTiO₃ nanoparticles but also should be ascribed to the strong interfacial interaction between the surface modified BaTiO₃ nanoparticles and EVM matrix. We also investigated the dielectric relaxation behaviour of the BaTiO₃ filled EVM nanocomposites by using Jonscher's theory of universal dielectric response.

SnS films have been deposited at room temperature by the chemical bath deposition technique. The films have been examined to evaluate their structure, morphology, composition and optical properties. SnS films were polycrystalline with an orthorhombic-herzenbergite structure. The lattice parameters and crystallite size of the sample have been calculated to be a = 4.39 Å, b = 11.17 Å, c = 3.97 Å with a/c = 1.106, and 67 nm, respectively. SnS films have been well crystallized in the form of cylindrical rods and the atomic ratio of Sn to S is 49.8 : 50.2. The optical properties of the sample have been studied using the transmittance and reflectance measurements as a function of wavelength between 190 and 3300 nm. The optical band gap is direct with a value of 1.31 eV. The refractive index and extinction coefficient as a function of wavelength for the film were investigated from the transmittance spectrum by applying the envelope method. The optical parameters of the material such as dielectric constants (n, k, ε₁ and ε_∞), plasma frequency ω_p and carrier concentration N_opt were also evaluated.

An exact analytical expression for the complex thermal impedance Z of multi-finger microelectronic components is presented in this paper. The integral transform technique has been used to obtain this expression and solve the three dimensional heat conduction equation directly in the frequency domain. Calculations were first performed for a single-finger on a single-layer structure in order to compare the results with those available in the literature and hence validate the solution. Generally, the comparison shows good agreement between our results and those given in most publications. When the structures are composed of several layers, the thermal impedance changes with the thermal conductivities and the thicknesses of the different layers. It is also affected by the thermal contact resistance between the layers. Some results illustrate the influence of these parameters. The case of a multi-finger component is then treated and the influence of distances between fingers is investigated. For all cases, the Nyquist diagram (i.e. Im(Z) versus Re(Z) for different pulsation values ω) is plotted. Mainly two zones are observed: one for the high frequencies and the other for the lower ones. The substrate dimensions are found to largely influence the scale of the low frequency zone whereas the distance between the fingers influences the higher one. Finally, the solution is applied to a multi-finger device in contact with a heat sink.

This work proposes a viewing angle switching (VAS) panel using twisted-nematic liquid-crystals (TN-LCs). Calculations reveal that, in a low voltage regime, a TN-LC behaves optically as a high twisted (∼90°) TN-LC in a vertical direction but as a low twisted (<25°) TN-LC in a horizontal direction. Additionally, a large difference in phase retardation of TN-LC from different viewing directions occurs at applied voltage 1.5V_th ⩽ V ⩽ 1.7V_th, where V_th is the threshold voltage of director reorientation. The large differences in the twisted angle and the phase retardation from different directions result in a large optically anisotropic behaviour of a TN-LC layer. The proposed VAS panel is developed using this large optically anisotropic behaviour of a TN-LC layer. Optical films are also used in the proposed VAS panel to enhance the optical anisotropy of a TN-LC layer. With the proposed panel, a display is only perceived clearly at a downward direction in a narrow viewing angle mode to ensure high privacy protection. Additionally, the proposed VAS panel achieves a high transmittance of 95%, making it highly promising for mobile device applications.

A three-dimensional finite element method program is developed to investigate the magnetoelectric (ME) coupling in multiferroic composites. For a bilayer plate, we show that: (1) the electric potential in the piezoelectric layer induced by the magnetic potential is not uniform but exhibits concentration near the edge/corner of the plate; (2) the mechanically clamped boundary condition can enhance the ME effect by a factor of 10 as compared with the traction-free case; (3) the ME effect in a composite plate is always stronger than that in the corresponding composite beam; (4) a large aspect ratio of the plate corresponds to an increased ME effect; (5) the in-plane longitudinal ME effect is larger than the out-of-plane one.

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