Table of contents

Microfluidic technologies have emerged recently as a promising new route for the fabrication of uniform emulsions. In this paper, we review microfluidic methods for synthesizing uniform streams of droplets and bubbles, focusing on those that utilize pressure-driven flows. Three categories of microfluidic geometries are discussed, including co-flowing streams, cross-flowing streams, and flow focusing devices. In each category we summarize observations that have been reported to date in experiments and numerical simulations. We describe these results in the context of physical mechanisms for droplet breakup, and simple theoretical models that have been proposed. Applications of droplets in microfluidic devices are briefly reviewed.

The magnetic behaviour of well-dispersed monodisperse Fe₃O₄ nanoparticles with sizes varying between 6.6 and 17.8 nm prepared in a non-aqueous medium was investigated. The smaller nanocrystals exhibit superparamagnetism with the blocking temperatures increasing with the particle size, whereas the biggest particles are ferromagnetic at room temperature. The saturation magnetization values are slightly smaller than that of the bulk material, suggesting the existence of a disordered spin configuration on their surface. The thickness of the magnetically inert shell was estimated from the size variation of the magnetization at 1.9 Å. The dipole–dipole interactions between the particles were tuned by changing the interparticle distances, e.g. by diluting the nanopowders in a non-magnetic matrix at concentrations ranging from 0.25 to 100 wt%. As the strength of the interactions is decreased with dilution, the energy barrier is substantially lowered; this will induce a drastic decrease of both the blocking temperatures and the coercivity with decreasing concentration of the nanoparticles.

We report on the effect of Fe substitution in the self doped manganite, La_0.87Mn_1−xFe_xO₃ in the composition range 0 ⩽ x ⩽ 0.15. The electrical resistivity (ρ) and dc magnetization were measured as a function of temperature, field and time. The metal to semiconducting transition is clearly observed for x ⩽ 0.02, while a semiconducting temperature dependence of resistivity is noticed for x ⩾ 0.08. The compound with x = 0.05 shows interesting features of ρ in field-cooled (FC) condition such as bifurcation in the zero-field cooled and FC temperature dependence, weak thermal hysteresis and memory effect. We observe the enhancement of colossal magnetoresistance by the Fe substitution in the low substitution range. The paramagnetic to ferromagnetic transition (T_c) is found to decrease with increasing x. The large thermal hysteresis in magnetization under FC condition is noticed for x ⩽ 0.02, which is different in character for the composition range 0.05 ⩽ x ⩽ 0.15. The relaxation of magnetization indicates the ferromagnetic (FM) character for x = 0, while the coexistence of FM and glassy components is observed for x ⩾ 0.02. The glassy magnetic phase increases with the increase in Fe substitution. The inhomogeneous phase separation between FM and glassy magnetic phases has been proposed to explain the magnetic and electrical transport properties of La_0.87Mn_1−xFe_xO₃.

Magnetic fields generated by current lines are the standard way of switching between resistance (R) states in magnetic random access memories. A less common but technologically more interesting alternative to achieve R-switching is to use an electrical current crossing the tunnel barrier. Such current induced magnetization switching (CIMS) or current induced switching (CIS) effects were recently observed in thin magnetic tunnel junctions, and attributed to spin transfer (CIMS) or electromigration of atoms into the insulator (CIS). In this work, electromigration-driven resistance changes (resistive switching) are superimposed with thermally induced pinned layer reversal (magnetic switching), producing a reproducible, three-state memory device. The tunnel junctions under study show a tunnel magnetoresistance of 14% with a RA product of 50 Ω µm². The reversible electromigration-driven resistance changes amount to 7–8% of the full resistance change and more than 10⁴R-switching events can be current induced without significant damage to the tunnel junction. Typical critical current densities are of the order of 2 × 10⁶ A cm⁻².

x-cut Nd : MgO : LiNbO₃ wafers are implanted with 3 MeV O⁺ ions at a dose of 6 × 10¹⁴ cm⁻², directly using a photoresist mask consisting of a series of open stripes of width 10 µm. The extraordinary refractive index (RI) experiences positive changes with respect to the bulk after ion bombardment and post-implantation annealing; therefore, channel waveguide structures are formed in the implanted regions. The near field intensity distributions of the transverse-electric modes are obtained by an end-fire coupling arrangement. The modal simulation result shows the reasonableness of the reconstructed RI profiles, which is helpful in designing practical waveguide devices produced by the ion implantation technique.

Field emission (FE) from a single-layer ultra-thin semiconductor film cathode (SUSC) on a metal substrate has been investigated theoretically. The self-consistent quantum FE model is developed by synthetically considering the energy band bending and electron scattering. As a typical example, we calculate the FE properties of ultra-thin AlN film with an adjustable film thickness from 1 to 10 nm. The calculated results show that the FE characteristic is evidently modulated by varying the film thickness, and there is an optimum thickness of about 3 nm. Furthermore, a four-step FE mechanism is suggested such that the distinct FE current of a SUSC is rooted in the thickness sensitivity of its quantum structure, and the optimum FE properties of the SUSC should be attributed to the change in the effective potential combined with the attenuation of electron scattering.

BaSnO₃ crystallizes in a cubic perovskite structure and exhibits insulating behaviour. It can be made conducting by reducing a small fraction of Sn⁴⁺ into Sn²⁺ under an O₂-free atmosphere. This can be achieved through the solid solution Ba_1−xLa_xSnO_3−δ which is a mixed phase for x > 0.02, behaviour readily understood in terms of the lone pair cation Sn²⁺. The magnetic susceptibility was measured down to 4.2 K and is less than 1.7 × 10⁻⁵ emu cgs mol⁻¹ consistent with collective electron behaviour. The Mössbauer spectrum exhibits a wide unsplit peak with a quadrupole doublet of 3.18 mm s⁻¹ and an isomer shift of 0.12 mm s⁻¹ characteristic of Sn⁴⁺and corroborating the delocalization of the stereo chemical pair 5s². The band gap E_g was found to be 3.12 eV; further indirectly allowed inter-band transition occurs at 2.85 eV. The transport properties of Ba_0.98La_0.02SnO_3−δ indicate n-type conductivity (σ_300 K = 4.03 Ω⁻¹ cm⁻¹), little temperature dependence, with an activation energy ΔE of ∼1 meV and an electron mobility μ_300 K ∼ 0.1 cm² V⁻¹ s⁻¹, thermally activated. The conduction occurs by small polaron hopping between mixed valence Sn^4+/2+ ions. The observed conductivity is greater than that coming from La-substitution with one-electron doping implying the existence of oxygen vacancies. The electrons are believed to travel in the Sn-5s conduction band with an effective mass of 3.7 m_o. The non-linear dependence of Ln σ versus T⁻¹ at low temperatures could result from a predominant variable range hopping as suggested by the linear variation of log σ versus T^−0.25. The electron localization may be attributed to the random distribution of lanthanum as well as oxygen vacancies.

We have prepared light emitting nanocrystallline porous silicon (PS) layers by electrochemical anodization of crystalline silicon (c-Si) wafer and characterized the c-Si/PS heterojunctions using temperature dependence of dark current–voltage (I–V) characteristics. The reverse bias I–V characteristics of c-Si/PS heterojunctions are found to behave like the Schottky junctions where carrier transport is mainly governed by the carrier generation-recombination in the depletion region formed on the PS side. Fermi level of c-Si gets pinned to the defect levels at the interface resulting in ln(I) ∝ V^1/2. The barrier height in the reverse bias condition is shown to be equal to the band offset at the conduction band edges. An energy band diagram for the c-Si/PS heterojunction is proposed.

Si nanocrystals (NCs) were embedded in synthetic silica opals by means of Si-ion implantation or opal impregnation with porous-Si suspensions. In both types of sample photoluminescence (PL) is strongly Bragg-reflection attenuated (up to 75%) at the frequency of the opal stop-band in a direction perpendicular to the (1 1 1) face of the perfect hcp opal structure. Time-resolved PL shows a rich distribution of decay rates, which contains both shorter and longer decay components compared with the ordinary stretched exponential decay of Si NCs. This effect reflects changes in the spontaneous emission rate of Si NCs due to variations in the local density of states of real opal containing defects.

The fibre laser has been receiving great attention due to its advantages of high efficiency, high power and high beam quality, and is expected to be one of the most desirable heat sources for high-speed and deep-penetration welding. In this study, therefore, in bead-on-plate welding of Type 304 stainless steel plates with 6 kW fibre laser, the effects of laser power, power density and welding speed on the formation of sound welds were investigated with four laser beams of 130, 200, 360 and 560 µm in spot diameter, and their welding phenomena were clarified with high-speed video cameras and an x-ray transmission real-time imaging system. The weld beads showed a keyhole type of penetration at any diameter, and the maximum penetration of 11 mm in depth was obtained at 130 µm spot diameter and 0.6 m min⁻¹ welding speed. It was found that the laser power density exerted a remarkable effect on the increase in weld penetration at higher welding speeds, and sound partially penetrated welds without welding defects such as porosity, underfilling or humping could be produced at wide process windows of welding speeds between 4.5 and 10 m min⁻¹ with fibre laser beams of 360 µm or 560 µm in spot diameter. The high-speed video observation pictures and the x-ray images of the welding phenomena at 6 m min⁻¹ welding speed and 360 µm spot diameter show that a sound weld bead was formed owing to a long molten pool suppressing and accommodating spattering and a stable keyhole generating no bubbles from the tip, respectively.

The thermal degradation of a blue-colour emitting phosphor, CaMgSi₂O₆ : Eu²⁺(CMS : Eu²⁺), synthesized by a conventional solid-state reaction was investigated by crystal structure refinement and electron paramagnetic resonance (EPR). When the CMS : Eu²⁺ was annealed at a temperature ranging from 500 to 1100 °C in air, the intensities of photoluminescence (PL) and EPR peaks, which were attributed to the transition of Eu²⁺ ions from the excited state (4f⁶5d) to the ground state (4f⁷), remained stable until 700 °C, whereas the intensities of samples annealed from 800 to 1100 °C rapidly decreased. The crystal structure refinement, EPR and PL measurements for CMS : Eu²⁺ at various annealing temperatures showed that the degree of oxidation of Eu²⁺ played an important role in the occurrence of thermal degradation in CMS : Eu²⁺.

Different models dealing with localized and semi-localized transitions, namely Chen–Halperin, Mandowski and the model based on the Braunlich–Scharmann (BS) approach are compared. It has been found that for recombination dominant situations (r < 1 where r is the retrapping parameter for localized transitions), the TSL glow curves arising from localized recombination coincide with all three models whereas for r ≫ 1, the three models differ. This implies that for localized transitions under recombination dominant situations, the Chen–Halperin model is the best representative of the thermally stimulated luminescence (TSL) process.

It has also been found that for the TSL glow curves arising from delocalized recombination in Mandowski's semi-localized transitions model, the double peak structure of the TSL glow curve is a function of the radiation dose as well as of the heating rate. Further, the double peak structure of the TSL glow curves arising from delocalized recombination disappears at low doses as well as at higher heating rates. It has also been found that the TSL glow curves arising from delocalized recombination in the semi-localized transitions model based on the BS approach do not exhibit double peak structure as observed in the Mandowski semi-localized transitions model.

We propose an effective admittance (EA) method to design antireflection structures for two-dimensional photonic crystals (PCs). We demonstrate that a compact and efficient antireflection structure, which is difficult to obtain by the conventional admittance matching method, can be readily designed by the EA method. The antireflection structure consists of an air slot resonant cavity that is constructed only with the materials that constitute the PC. Compared with a bare PC, the reflection from a PC with an antireflection structure is reduced by two orders of magnitude over a wide bandwidth. To confirm the presented EA method, finite-difference time-domain (FDTD) simulations are performed, and the results from the FDTD and the EA method are in good agreement.

A long wave infrared InAs-InGaAs quantum-dot (QD) infrared photodetector (QDIP) with a peak detection wavelength of 9.9 µm and operating temperature of over 170 K is reported. Peak specific photodetectivity D* of 3.8 × 10⁹ cm Hz^1/2 W⁻¹ and 1.3 × 10⁸ cm Hz^1/2 W⁻¹ were obtained at the detector temperature T = 78 K and T = 170 K, respectively. A large photoresponsivity of 4.6 A W⁻¹ and high photoconductive (PC) gain of > 144 were demonstrated at T = 170 K. The high temperature performance is attributable to the dark current reduction by the double Al_0.2Ga_0.8As barrier layers employed in the QDIP and the high PC gain at the elevated temperature. The performance demonstration indicates that the QDIP with double current-blocking barriers is promising for high-temperature long wave infrared photodetection.

Crystals of NaLa(WO₄)₂ : Ho³⁺ were grown by the Czochralski method. The spectroscopic properties have been investigated at room temperature. Intensity parameters, radiative lifetimes and branching ratios have been calculated in the framework of Judd–Ofelt theory. The luminescence spectra measured under 450 nm pumping are dominated by a strong green emission in the 550 nm region connected with the ⁵S₂ + ⁵F₄ → ⁵I₈ transition. The stimulated emission cross-section for this transition was estimated. The luminescence decay curve of the ⁵S₂ + ⁵F₄ level was also measured at room temperature.

Top-emitting organic light-emitting devices with different-thickness top Ag cathodes were fabricated. The tris (8-hydroxyquinoline) aluminium based device with a 23 nm thick Ag cathode shows a maximum efficiency of 11.1 cd A⁻¹ and the brightness of the device can reach 560 cd m⁻² at 4 V. The blueshift of the resonant wavelength (RW) in the devices with increasing thickness of the top Ag cathode was observed. The theoretical simulation was described by a model based on the Fabry–Perot microcavity structure. The results indicated that both RW and the efficiency of the devices are Ag thickness dependent.

The side-illumination-enhanced photovoltaic effect has been studied in La_0.9Sr_0.1MnO₃/Si heterojunctions fabricated by laser molecular beam epitaxy. When a He–Ne laser illuminated the La_0.9Sr_0.1MnO₃ film surface, a stable photovoltage was produced and the responsivity is ∼0.17 mV mW⁻¹. An enhancement of the photovoltaic effect occurred when the La_0.9Sr_0.1 MnO₃/Si interface was illuminated directly by side illumination, and the steady responsivity reached ∼6.87 mV mW⁻¹. This work demonstrates an effective way to improve the photovoltaic responsivity of the perovskite oxide heterojunctions.

This work examines the nonlinear interaction of waves in a layered periodic structure that consists of alternating semiconductor layers, namely, nonlinear and linear layers. The nonlinearity under study is due to that of the free carrier current. To study nonlinear processes, we use the three-wave interaction method that is applicable to bounded and periodic structures. It is shown that the phase of the nonlinear matrix element of interacting waves depends on the physical and geometrical parameters of the layers of which the structure is fabricated. As a result, the energy pumping can take place from a wave with a minimum frequency to that with a maximum one.

Adsorption and desorption of the filling gas, by the electrodes, the insulator and chamber materials of plasma focus devices, have been suggested as probable causes for the fluctuations in their neutron yield. This work describes analysis of data, aimed at looking for evidence to support this hypothesis. Before starting each series of discharges, a vacuum around 10⁻⁶ Torr is achieved. The filling gas, pure deuterium, is maintained under static conditions. A sudden fall of the initial pressure, around 5%, is systematically observed after the first shot in each series, before creeping back at an almost constant rate, in successive shots. On the other hand, for the first shot with fresh filling gas, the neutron yield is always low and systematically increases for the second one. The pressure evolution for the following shots shows no correlation with the neutron yield fluctuations. Thus, except for the first two shots, we find no evidence to support the hypothesis that the neutron yield fluctuations are related to an adsorption–desorption process. It is also observed that a tendency exists for the last shots of each series to yield a larger number of neutrons but with a larger dispersion. This study has been done with both solid and hollow anodes, showing qualitatively similar results in both cases.

The identification of sterilization agents is mandatory to achieve sterilization mechanisms in low-pressure discharges. A detailed account of each agent is required for improvements, development and establishment of plasma sterilization as an alternative to traditional sterilization processes. Sterilization agents are VUV and UV radiation, photodesorption producing volatile species and etching of spore coat and membrane. This work focuses on VUV and UV radiation as a sterilization agent of Bacillus atrophaeus spores. Four wavelength ranges are distinguished: the emission spectra above 300 nm, above 235 nm, above 112 nm and a full emission spectrum including active species. The range from 235 up to 300 nm without active species is identified to be the most capable for sterilizing Bacillus atrophaeus spores.

When Bohm diffusion is incorporated, the magnetic induction equation can be transformed into a type of heat equation which allows exact analytical solutions (Lee and Ryu 2004 Phys. Plasmas11 5462). This equation can admit amplification solutions for the axisymmetric magnetic field, if the diffusion velocity satisfies a certain condition. This paper discusses the case of the azimuthal field and finds that there are also analytical solutions which can amplify the magnetic field.

The role of the plasma in laser–metal interaction is of considerable interest due to its influence in the energy transfer mechanism in industrial laser materials processing. A 10 kW CO₂ laser was used to study its interaction with aluminium under an argon environment. The objective was to determine the absorption and refraction of the laser beam through the plasma during the processing of aluminium. Laser processing of aluminium is becoming an important topic for many industries, including the automobile industry. The spectroscopic relative line to continuum method was used to determine the electron temperature distribution within the plasma by investigating the 4158 Å Ar I line emission and the continuum adjacent to it. The plasmas are induced in 1.0 atm pure Ar environment over a translating Al target, using f/7 and 10 kW CO₂ laser. Spectroscopic data indicated that the plasma composition and behaviour were Ar-dominated. Experimental results indicated the plasma core temperature to be 14 000–15 300 K over the incident range of laser powers investigated from 5 to 7 kW. It was found that 7.5–29% of the incident laser power was absorbed by the plasma. Cross-section analysis of the melt pools from the Al samples revealed the absence of any key-hole formation and confirmed that the energy transfer mechanism in the targets was conduction dominated for the reported range of experimental data.

Experiments were conducted in a detachable vacuum chamber for Cu vacuum arc with arc current in the range 19–24 A. Experimental results indicated that the gap distance had a distinct influence on the characteristics of the random walk of the cathode spot (CS) for the gap distance adopted, i.e. d = 4.8 mm and d = 6.8 mm. It was found that the increase in the gap distance could lead to a larger diffusion parameter. Based on the dynamics of fragments constituting the CS, it was proposed that with a longer gap distance, the magnetic interaction between fragments would be strengthened. It would result in the increase of the mean step length of the CS and the decrease of the mean step time, which would lead to a larger diffusion parameter as observed. The plasma density in the region of the CS was also found to decrease with the increase in the gap distance. It would result in the CS having a higher probability of jumping to the contaminated region but not to the vicinity of the existing crater.

The aim of this work is to analyse and discuss a spectroscopic method of diagnosis based on the Stark broadening of emission lines to determine the electron density and temperature in atmospheric-pressure plasmas. Usually, when the electron temperature is previously known, the Stark broadening of certain spectral lines spontaneously emitted by the plasma is used to determine the electron density in a rapid and inexpensive way. However, comparing two or more broadening of lines can allow us to diagnose the electron density and temperature simultaneously. To carry out this cross-point method, we must know the Stark broadening dependence on the electron temperature and density for different lines. In this work we have used the first three Balmer series hydrogen lines, whose Stark broadenings were calculated by means of a recent micro-field model existing in the bibliography. The experimental study was made in argon and hydrogen plasma flames. The plasmas were produced at 2.45 GHz by an axial injection torch, which can operate at atmospheric pressure under different experimental conditions to produce appropriate plasmas in 'open air'. The flame produced in this way is a two-temperature plasma, so it is not in local thermodynamic equilibrium. Moreover, by means of the Boltzmann-plot modified with the p⁻⁶ law, we found for the hydrogen plasma that most of the observable atomic states were ruled by the excitation–saturation balance. With this method we could also determine the electron temperature.

A two-temperature thermal non-equilibrium model is developed and applied to the three-dimensional and time-dependent simulation of the flow inside a dc arc plasma torch. A detailed comparison of the results of the non-equilibrium model with those of an equilibrium model is presented. The fluid and electromagnetic equations in both models are approximated numerically in a fully-coupled approach by a variational multi-scale finite element method. In contrast to the equilibrium model, the non-equilibrium model did not need a separate reattachment model to produce an arc reattachment process and to limit the magnitude of the total voltage drop and arc length. The non-equilibrium results show large non-equilibrium regions in the plasma–cold-flow interaction region and close to the anode surface. Marked differences in the arc dynamics, especially in the arc reattachment process, and in the magnitudes of the total voltage drop and outlet temperatures and velocities between the models are observed. The non-equilibrium results show improved agreement with experimental observations.

Based on the two-temperature magnetohydrodynamic model, a high-current vacuum arc (HCVA) in vacuum interrupters is simulated and analysed. The phenomenon of plasma backflow in arc column is found, which is ultimately ascribed to the strong magnetic pinch effect of HCVA. Due to plasma backflow, the maximal value of ion density at the cathode side is not located at the centre of the cathode side, but at the paraxial region of the cathode side, that is to say, ion density appears to sag at the centre of the cathode side (arc column seems to be divided into two parts). The sag of light intensity is also found by experiments.

Nb_0.06Sn_xTi_0.94−xO₂ (x ≤ 0.3) thin films were grown by a pulsed-laser deposition method with varying Sn concentration. Through a combinatorial technique, we find that Sn concentration can reach a maximum of about x = 0.3 while maintaining the stable anatase phase and epitaxy. A doping concentration dependence of the refractivity is revealed, in which refractivity reduction at a wavelength of λ = 500 nm is estimated to be 12.4% for Nb_0.06Sn_0.3 Ti_0.64O₂ thin film. Sn doping induced band-gap blue shift can be contributed to the mixing of extended Sn 5s orbitals with the conduction band of TiO₂. Low resistivity on the order of 10⁻⁴ Ω cm at room temperature and high internal transmittance of more than 95% in the visible light region are exhibited for Nb_0.06Sn_x Ti_0.94−xO₂ thin films (x ≤ 0.2). Optical and transport analyses demonstrate that doping Sn into Nb_0.06 Ti_0.94O₂ can reduce the refractivity while maintaining low resistivity and high transparency.

In this paper we report a detailed description of the laser cleaning procedure and emission performance measurement on a pulsed laser deposited Mg film. During the tests performed after the end of each cleaning operation we have observed an increase in quantum efficiency (QE) in time. Then the QE apparently stabilizes at a remarkably higher value. The study of this phenomenon and its relation to chemical composition of the residual gases of vacuum environment is important because it determines both the achievable QE value and the lifetime of the Mg film based cathode. Moreover, the stability of the QE at remarkably high values has been revealed for a time scale of several days after each laser cleaning process, in our vacuum conditions. The adsorption of reactive chemical species leading to the lowering of the Mg work function is discussed.

Ag-doped Bi₂(Te_0.95Se_0.05)₃ thermoelectric thin films (Ag: 0–0.5 wt%) with thickness of 800 nm have been deposited on glass substrates by the flash evaporation method at 473 K. The structure and morphology of the thin films were analysed by x-ray diffraction and field emission scanning electron microscopy, respectively. The effects of Ag doping concentration on the thermoelectric properties of the annealed thin films were investigated by room-temperature measurement of the Seebeck coefficient and electrical resistivity. The thermoelectric power factor was enhanced to 16.1 µW cm⁻¹ K⁻² at 0.2 wt% Ag doping. The Seebeck coefficients are positive with increasing Ag doping concentration from 0.25 to 0.5 wt%. And the thin films show p-type conduction.

Bi₂Te₃ plate-like crystals with homogeneous hexagonal morphology were rapidly synthesized using a microwave assisted wet chemical method in 30 min. These Bi₂Te₃ nanoplates possessed a fixed edge with a length of ∼0.5–2 µm, and the thickness was less than ∼100 nm. The n-type Bi₂Te₃ nanocomposites were prepared by consolidating mixtures of these nanoplates and mechanically alloyed powders using plasma activated sintering, and the effect of nanoplate addition on the thermoelectric properties of the nanocomposites was investigated. When the content of the doped nanoplates was 15 wt%, the lattice thermal conductivity of the Bi₂Te₃ nanocomposites decreased by 18% compared with that of the undoped compounds. A preliminary investigation showed that nanopowder addition was an effective way to decrease the thermal conductivity and increase the thermoelectric efficiency.

Adhesion and light-load friction are crucial to the effective operation of nano/micro-devices, which are dependent on physical and mechanical properties of two metals in contact. Electron work function (EWF) and elastic modulus of metals have been demonstrated to be dominant parameters for adhesion and light-load friction of metals. This paper presents the authors' recent studies to correlate the elastic properties of metal with the EWF. It is demonstrated that there exists a strong correlation between EWF and elastic behaviour. Such a correlation makes it possible to predict adhesion and elastic-contact friction mainly based on the EWF.

This paper reports an experimental and theoretical investigation of the indentation of a layered elastic solid, with special reference to the surface force apparatus (SFA). The contacting surfaces of the SFA comprise a 3-layer material: a thin mica surface layer on a thicker epoxy layer supported by a thick silica substrate. An existing finite element analysis of the deformation of ideal mica/epoxy/silica surfaces used in the SFA is adapted to compare with the experimental measurements of the variation of contact size with load, both with and without adhesion at the interface. This is in marked difference to the Johnson, Kendall and Roberts (JKR) theory for homogeneous solids. Experiments and finite element calculations were also carried out on the elastic indentation of a thin (5.5 µm) layer of mica on a very thick layer of epoxy (>100 µm). As input data for the calculations, the elastic moduli of the mica and epoxy were measured in separate indentation experiments. The stiffness of a layered solid can be expressed by an 'effective modulus' , which has been deduced from the experimental measurements and compared with the theoretical values with fair success. The work of adhesion is commonly measured in the SFA by observing the 'pull-off force' to separate the surfaces. The theory shows that, for a layered solid, the pull-force can vary significantly from the JKR value for a homogeneous solid. In particular, it was found that the mica surface energy, γ_sv, measured by SFA experiments using crossed cylinders of mean radius R, where the materials are layered and the mica/mica adhesion is high, can vary with the pull-off force F_p according to F_p/4πR < γ_sv < F_p/2πR, and for this particular experiment was given as γ_sv = F_p/3.5 πR as compared with γ_sv = F_p/3πR for homogeneous materials.

We have investigated the effect of ion bombardment during and after deposition on the structure and surface properties of semiconducting β-FeSi₂ thin films grown on n-Si(1 0 0) substrates at room temperature by unbalanced magnetron sputtering. The properties of β-FeSi₂ thin films were characterized with field emission gun scanning electron microscopy, atomic force microscopy, x-ray diffraction analysis and Raman spectroscopy. Ion bombardment of the films after deposition resulted in grain size refinement and decreased the crystallinity of the films. However, ion bombardment during deposition increased the crystallinity and grain size of the coatings. These modifications induced by ion bombardment are also expected to affect the photovoltaic performance.

A novel genetic algorithm (GA) utilizing independent component analysis (ICA) was developed for x-ray reflectivity (XRR) curve fitting. EFICA was used to reduce mutual information, or interparameter dependences, during the combinatorial phase. The performance of the new algorithm was studied by fitting trial XRR curves to target curves which were computed using realistic multilayer models. The median convergence properties of conventional GA, GA using principal component analysis and the novel GA were compared. GA using ICA was found to outperform the other methods with problems having 41 parameters or more to be fitted without additional XRR curve calculations. The computational complexity of the conventional methods was linear but the novel method had a quadratic computational complexity due to the applied ICA method which sets a practical limit for the dimensionality of the problem to be solved. However, the novel algorithm had the best capability to extend the fitting analysis based on Parratt's formalism to multiperiodic layer structures.

We study the influence of Mn doping on the vibrational properties of rf sputtered ZnO thin films. Raman spectra of the Mn doped ZnO samples reveal two additional vibrational modes, in addition to the host phonon modes, at 252 and 524 cm⁻¹. The intensity of the additional modes increases continuously with Mn concentration in ZnO and can be used as an indication of Mn incorporation in ZnO. The modes are assigned to the activation of ZnO silent modes due to relaxation of Raman selection rules produced by the breakdown of the translational symmetry of the crystal lattice with the incorporation of Mn at the Zn site. Furthermore, the A₁ (LO) mode is observed with very high intensity in the Raman spectra of undoped ZnO thin film and is attributed to the built-in electric field at the grain boundaries.

ZnO thin films were grown by metal-organic chemical vapour deposition using methanol as oxidant. Rapid thermal annealing (RTA) was performed in an ambient of one atmosphere oxygen at 900 °C for 60 s. The RTA properties of the films have been characterized using scanning electron microscopy, x-ray diffraction, x-ray photoelectron spectroscopy, photoluminescence spectra and Hall measurement. The grains of the film were well coalesced and the surface became denser after RTA. The full-width at half maximum of rocking curves was only 496 arcsec. The ZnO films were also proved to have good optical quality. The Hall mobility increased to 43.2 cm² V⁻¹ s⁻¹ while the electron concentration decreased to 6.6 × 10¹⁶ cm⁻³. It is found that methanol is a potential oxidant for ZnO growth and the quality of ZnO film can be improved substantially through RTA.

The effect of electron-beam (eb) irradiation on the electrical, optical, thermal and structural properties of polyurethane-elastomer (Pu) sheets of thickness 0.076 mm was investigated. The samples were exposed to eb at ascending dose levels in the range 90–300 kGy. Optical properties and structural studies using Fourier transform infrared measurements and x-ray diffraction technique were performed on un-irradiated and irradiated samples. Dc-conductivity measurements were carried out in the temperature range 306–413 K. It was found that the electrical conductivity of polyurethane-elastomer increased due to eb irradiation via degradation mechanisms. Furthermore, the activation energy was calculated, as a function of the eb doses. Also, at the eb irradiation doses, in the range 200–300 kGy, radiation causes branching that reduces crystallinity and induces further lattice defects that may act as scattering centres and energy barriers for the flow of electric current. Thermal gravimetric analysis study indicates the degradation of Pu due to eb irradiation, which causes the samples to start decomposition later than un-irradiated ones. The differential thermal analysis measurements exhibit a significant change in their melting behaviour.

The mechanochemical milling technique is employed to synthesize Pb_1−xSn_xF₂ solid solutions (with x = 0.2–0.6) at room temperature. The obtained samples with x = 0.2–0.5 show x-ray powder diffraction patterns similar to the β-PbF₂ cubic structure, with the crystallite size in the range 25–29 nm. The ionic conductivity of the investigated materials, determined from impedance spectroscopy measurements, shows a maximum at x = 0.5, reaching a value of 2.28 × 10⁻³ S cm⁻¹ at room temperature. The electrical relaxation dynamics are studied in the electric modulus formalism in the frequency range 50 Hz–1 MHz over a wide temperature range. The conductivity relaxation time, for different compositions, is thermally activated with the same activation energy of the dc conduction. Scaling of the modulus spectra at different temperatures and compositions indicates that the relaxation dynamics are independent of temperature but depend on the microscopic structure and/or the concentration of mobile charge carriers. The frequency dependence of the dissipation factor, tan δ, shows a dielectric relaxation process, most probably originating from interfacial polarization.

A dense and uniform metal layer was completely coated on the surface of fly-ash cenosphere particles by either electroless plating or magnetron sputtering technique. The surface morphology and characteristics of the electroless and sputtered metal coatings have been compared and investigated by various characterization methods, including scanning electron microscopy, energy dispersion x-ray spectrum, x-ray photoelectron spectroscopy, optical microscopy and atomic force microscopy. The results indicate that the electroless plating process has a faster deposition rate as compared with the sputtering process, and the metal coating fabricated by electroless plating is rough as compared with the metal coating fabricated by magnetron sputtering. The Cu-coated fine cenospheres could be fabricated by the electroless plating technique.

In this paper, we report the dielectric spectroscopy of hexagonal boron nitride (h-BN) ceramic which has been widely used due to a very low dielectric coefficient. In order to obtain the relaxation time distributions of h-BN, the Havriliak–Negami empirical equation is selected to analyse the measured dielectric data due to the Cole–Cole plots of h-BN samples. In the processes of solving the empirical equation, a nonlinear least-square technique is used and the boundary condition for unknown parameters in the equation is defined. The relaxation time and its distribution parameters are obtained by this method. The polarization mechanisms are also discussed based on the obtained relaxation time distributions. This research may be helpful for applications of h-BN ceramic.

Polycrystalline KZnSO₄Cl : Eu and KMgSO₄Cl : Eu prepared by a wet chemical method have been studied for their thermoluminescence (TL) and photoluminescence (PL) characteristics. The PL emission spectra of the phosphor suggests the presence of Eu²⁺ and Eu³⁺ in the host compound occupying two different lattice sites. The TL glow curve of the KZnSO₄Cl : Eu compounds has a simple structure with prominent peaks at 200 and 290 °C, while KMgSO₄Cl : Eu peaks at 165 and 265 °C. The TL sensitivity of the phosphors is compared with CaSO₄ : Dy and is found to be 3.4 and 2.4 times less in KZnSO₄Cl : Eu and KMgSO₄Cl : Eu phosphors, respectively.

Neutron irradiation effects on the stress relaxation rate of Al–Cu–Mg alloy have been investigated. The specimens were exposed to 100 mC, Ra–Be neutron source of continuous energy 2–12 MeV for a period ranging from 4 to 16 days. Stress relaxation tests during the tensile tests at room temperature were performed at multiple stress levels up to the fracture using a universal testing machine. The comparison of the stress relaxation rate of irradiated specimens with that of an unirradiated one shows that the rate decreases after irradiation. The decrease becomes more pronounced as the exposure time increases. The activation energy to the movement of dislocations was found to be higher in irradiated specimens than in an unirradiated one. The analysis of results shows that the rate controlling process of stress relaxation in irradiated specimens is different from that of an unirradiated one. The micrographs of fractured surfaces in fact point to the changes that take place in the fracture mechanism before and after irradiation. These observations account for the decrease in the stress relaxation rate.

This paper presents a model describing the hysteresis in ferroelectric materials at moderate to high driving levels and from quasi-static frequency to high dynamics. To a quasi-static model, based on a simple mechanism related to the dry-friction concept, is added a polarization fractional derivative term to take into account the dynamical effects through the ferroelectric material. The fractional derivative term allows us to describe slow dynamical variations for the hysteresis area (frequency) loop on a large frequency bandwidth. These variations cannot be described using the usual dynamical term (ρ · dP/dt) physically linked to resistive damping. In the paper, an equivalent electrical circuit of the model is proposed.

Finally, the new approach and the physical insights are developed and discussed. Large numbers of simulated behaviour are compared with experimental results on a typical soft PZT ferroelectric ceramic (type Navy II piezoelectric transducer ceramic).

In this paper, the deformation behaviour of Zr₆₅ Cu_17.5Ni₁₀Al_7.5 metallic glasses with different amounts of free volume was investigated with nano- and micro-indentation. It was found that the plastic flow of the metallic glasses is closely related to the amount of free volume. The metallic glasses with more free volume exhibit more conspicuous serrations with a larger pop-in size during nanoindentation and more pronounced shear bands during micro-indentation. The effect of free volume on the deformation behaviour of the Zr-based metallic glasses is discussed in terms of free volume theory.

Lead-free ceramics (1-x)K_0.5Na_0.5(Nb_0.925Ta_0.075)O₃-xLiSbO₃ have been prepared by an ordinary sintering technique. Our results reveal that Li⁺ and Sb⁵⁺ diffuse into the K_0.5Na_0.5(Nb_0.925Ta_0.075)O₃ lattices to form a solid solution with a perovskite structure. The introduction of LiSbO₃ into K_0.5Na_0.5(Nb_0.925Ta_0.075)O₃ decreases the Curie temperature (T_c) slightly, but shifts the ferroelectric tetragonal–ferroelectric orthorhombic phase transition temperature (T_O−T) significantly to low temperatures. As a result, the ceramics have an orthorhombic phase at x ≤ 0.02 and tetragonal phase at x ≥ 0.04. Coexistence of the orthorhombic and tetragonal phases is formed at 0.02 < x < 0.04 near room temperature, leading to significant enhancements of the piezoelectric properties. For the ceramic with x = 0.035, the piezoelectric properties become optimum giving: piezoelectric coefficient d₃₃ = 244 pC N⁻¹, electromechanical coupling factors k_P = 51% and k_t = 46%, remanent polarization P_r= 20.1 µC cm⁻², coercive field E_c = 1.37 kV mm⁻¹ and Curie temperature T_c = 354 °C. The ceramic has good temporal and thermal stability, greatly improved electrical properties and a relatively high Curie temperature, suggesting that it is a promising lead-free replacement for lead-based piezoelectric ceramics.

Epitaxially-grown BFZO thin films with various amounts of Zr content were successfully fabricated on (0 0 1) Nb doped-SrTiO₃ substrates using the pulsed laser-beam deposition technique. The Zr substitution caused a substantial decrease in the leakage current density of the films. According to the analysis of the origin of the leakage current behaviour, the samples with x values smaller than 0.7 were found to show Poole–Frenkel (PF) type leakage properties at high electric fields, and the samples with larger x values exhibited Schottky-type behaviour. Regarding the x = 0.7 sample, it was considered that the currents of the PF- and Schottky-type behaviours determined the leakage properties of the samples, resulting in an intermediate state. The observed mechanism change is discussed in conjunction with the electronic band structure change, which may be caused by the increase in the relative amount of Zr ions, as well as by the change in the valence state of the Fe ions associated with Zr substitution.

The dielectric confinement effect on the blue shift ΔE_g(a) of the ZnO quantum dots (QDs) embedded in the SiO₂ matrix is evaluated by applying a multi-shell two-electron system model. The experimental measurement and the calculations of various dielectric structures indicate that the composite matrix structure provides a better estimation of the blue shift of the ZnO QDs–SiO₂ system than the multi-shell structure. The proportionality factor x defined in this work exhibits a dependence of the dielectric confinement energy on the specific dimension ratio (the b/a ratio) and the dielectric constant ε_matrix of the outer matrix. The result of the calculation also shows the limit of the two-electron system in estimating the ground-state energy of samples with high dot density. However, the correlation shows the existence of the strong dielectric confinement effect in ZnO QDs–SiO₂ thin films and allows a better understanding of the semiconductor QDs–dielectric systems.

The crystal structures for T₂[M(CN)₆] where T = Mn, Cd; M = Fe, Ru, Os, were refined from the corresponding XRD powder patterns using the Rietveld method in the hexagonal P-3 (147) space group with Z = 1. In the structure of these families of anhydrous hexacyanometallates (II) the N end of the CN group appears bifurcated, serving as a ligand for two neighbouring T metals. Such a coordination mode has not been reported before for transition metal hexacyanometallates but it is consistent with the magnetic properties and Mössbauer, IR and Raman spectra of the studied compounds. The anhydrous solids are obtained by dehydration of the corresponding octahydrates. In the hydrated form the metals (Mn, Cd) linked at the N ends have a mixed coordination sphere formed by three N atoms and three coordinated waters, with two of these latter forming bridges between two neighbouring metals. The loss of these structural waters leaves the metals (T) in an unstable state with only three ligands in their coordination sphere and a structural transformation involving a change in the CN group electronic configuration is induced. The metal coordination through bifurcated CN groups leads to a remarkable increase in the charge overlapping between the metal centres, which appears attractive for molecular magnet design.

The behaviour of a periodic composite material depends not only on the properties of the constituent phases but also strongly on the microstructural texture of those phases such as spheres, lamellae and needles. This paper shows how to design the microstructure for a specific extremal bulk (effective) thermal conductivity in a three-phase composite medium. An inverse homogenization technique that is driven by the computational topology optimization algorithm is presented. Apart from benchmarking examples such as the Vigdergauz-type and sandwich-like architectures, a series of new single length-scale designs of microstructures are generated from this procedure. The topological design results are validated by comparing their conductivities against the empirical formulae in the two-phase composites. This study interestingly finds that the phase interfaces yielded from the topology optimization highly resemble the constant mean curvature surfaces. A comparison of their respective attainability with the Milton–Kohn physical bounds is made and the equivalence of these two sets of topologies is consequently justified.

The amorphous partial crystallization method has been applied to fabricate Ge–Te based bulk in situ thermoelectric amorphous/nanocrystal composites. High-resolution transmission electron microscopy showed that nanocrystals of only 4–8 nm were formed by nanoscale phase separation from the semiconductor amorphous matrix during annealing between the glass transition and the crystallization temperatures. The electrical conductivity and the thermoelectric power factor of the amorphous/nanocrystal composite annealed at 443 K for 2 h were about three orders of magnitude larger than those of the amorphous precursor. The amorphous nanocomposite exhibited a lower thermal conductivity and a higher figure of merit, compared with the crystalline GeTe alloy. This work provides a new approach to develop new bulk nanocomposites for thermoelectric applications.

Real time measurement of thermal diffusivity during the evolution of the light curing process in dental resins is reported using photothermal radiometry. The curing is induced by a non-modulated blue light beam, and at the same time, a modulated red laser beam is sent onto the sample, generating a train of thermal waves that produce modulated infrared radiation. The monitoring of this radiation permits to follow the time evolution of the process. The methodology is applied to two different commercially available light curing resin-based composites. In all cases thermal diffusivity follows a first order kinetics with similar stabilization characteristic times. Analysis of this kinetics permits to exhibit the close relationship of increase in thermal diffusivity with the decrease in monomer concentration and extension of the polymerization in the resin, induced by the curing light. It is also shown that the configuration in which the resin is illuminated by the modulated laser can be the basis for the development of an in situ technique for the determination of the degree of curing.

Using the scattering matrix method, we investigate the acoustic phonon transmission and thermal conductance in a quantum waveguide with two stubs at low temperatures. It is found that the threshold frequency of the onset of each phonon mode travelling through the quantum waveguide depends on the stub heights. The thermal conductance exhibits oscillatory decaying behaviour with the width between the two stubs due to the coupling effects between them. In addition, the transmission coefficient and thermal conductance are also sensitive to the widths and heights of the stubs. It is suggested that changing the geometric parameters of the stubs could provide an efficient way to control the thermal conductance of the proposed micro-structures artificially.

When high voltage is applied to distilled water filled in two glass beakers which are in contact, a stable water connection forms spontaneously, giving the impression of a floating water bridge. A detailed experimental analysis reveals static and dynamic structures as well as heat and mass transfer through this bridge.

We present a method based on induced currents in a cylindrical probe which allows analysis of the micro-particle charging processes in an aerosol. The micro particles were triboelectrically charged by passing through a dielectric tube coaxially mounted into the probe. The cylindrical probe enabled the quantification of particle charging without prior calibration of the probe. An analytic model was developed for the description of the measured induced currents and implemented into a computer simulation program. The combination of model simulations and an appropriate experimental setup revealed comprehensive data for the determination of the particles' electric charge against time of flight through the tube. In methodological proof of principle experiments, the formations of particle clouds with charges of different signs were observed using magnetite micro particles.

We report on the design of a stable optical limiter in the low laser power regime based on the thermal variation of refractive index in a novel nanocomposite material. The optical material, chloroaluminium-phthalocyanine (ClAlPc), is embedded in SiO₂-Nafion nanocomposite membrane (ClSNf) and its thermally induced nonlinear refractive index is characterized by the Z-scan technique with a low power cw He–Ne laser as the source. The value of nonlinear refractive index coefficient, n₂, is found to be about 1.11 × 10⁻¹¹ m² W⁻¹. The experiment is repeated with the dye doped in pure Nafion membrane (ClNf) and the results are compared with those of ClAlPc doped SiO₂–Nafion nanocomposite membrane. The value of n₂ is found to be 1.36 × 10⁻¹¹ m² W⁻¹ and is larger than that of the ClAlPc embedded SiO₂–Nafion nanocomposite membrane. The photostability of the dye-embedded membrane is studied by exposing the sample to cw He–Ne laser and monitoring its fluorescence emission intensity continuously. The samples are found to show large thermal lens effect and demonstrated to be good optical limiters in the low power regime. Whereas the optical properties of dye-doped Nafion appear to be slightly better than those of the dye embedded in silica and incorporated in Nafion, the latter is found to offer excellent photostability.

The mechanical model for the rectangular cantilever beam proposed by Zhang et al is solved analytically by the series solution with mathematical properties investigated in detail. The derived series solution is proved convergent, and restrained only by the small deflection presumed by the Euler–Bernoulli beam theorem, and is applicable for calculating the deflection and curvature for any value of the exerted axial stress. The formulae estimating the accuracy of the coefficients and the series solution are developed from Stirling's approximation for the gamma function. The condition on the axial stress is developed, by which the genuinely nonlinear curvature can be approximated by a linear function and the deflection can be calculated from the boundary condition by a cubic polynomial. The additional redundant boundary condition used in Zhang's work is discussed, which should be removed since it fails to fit the model by inducing errors for calculating the deflection and the curvature. The present series solution approach provides formal deflection–stress and curvature–stress relations for the design of a MEMS micro-cantilever system as a bio-detection device. For self-assembly applications, the adsorbing material can be identified by solving the exerted axial stress from the series solution.

On page 5654 of this article, the caption of figure 9 is correct but figures 9(a) and 9(b) should be interchanged.