Table of contents

Spin-polarized light sources are a new class of devices in which the radiative recombination of spin-polarized carriers results in luminescence exhibiting a net circular polarization. The operation principles and design of spin-polarized light sources are discussed. A comprehensive review of experimental work on spin-polarized light-emitting diodes and surface-emitting lasers is provided, concluding with a discussion of future prospects.

The magnetic and magnetostrictive properties of polycrystalline Co_1−xMn_xFe₂O₄ (0 ⩽ x ⩽ 0.4) have been studied. Although the Curie temperature decreases continuously with increasing concentration of Mn, the magnetization remains high up to x = 0.3 and unexpectedly low coercivity is observed for this composition showing an unusual magnetostrictive behaviour. This composition shows a relatively larger magnetostriction at low fields. Moreover, the strain derivative which is the slope of the magnetostriction curve at low magnetic fields is almost doubled and the field at which maximum magnetostriction is observed is reduced to almost half for 30% of Mn substitution. The results show that x ≈ 0.3 in Co_1−xMn_xFe₂O₄ is an optimum composition with superior magnetostrictive properties for many applications.

First-principles spin polarized calculations have been implemented by using the Discrete Molecular (DMol3) package to investigate the strengthening effects of alloying addition including Nb, Mo, V and Co in a cubic solid solution of Fe–Ga alloys. Mayer bond order values were used to evaluate the atomic bond strengths in the alloys and were then used to assess the alloying strengthening characteristics. Results from the calculations suggest that the transition metal Nb achieves the best strengthening effect in Fe–Ga alloys. The solid solution strengthening follows a decreasing order trend from larger to smaller from Nb, Mo, V to Co. The effect of Ga on individual bond strength variations between Fe and alloying elements and also on alloying strengthening was examined.

Tunnelling junctions with a SrTiO₃ barrier, one La_0.7Sr_0.3MnO₃ electrode and one Fe₃O₄ electrode were fabricated by pulsed laser deposition. The magnetization, current–voltage characteristics and magnetoresistance of the junctions were measured. The junction magnetoresistance was always negative, strongly bias-dependent at low temperatures and vanished with increasing temperature above about 135 K. Its field dependence was not correlated with the field dependence of the magnetization. This junction magnetoresistance is attributed to indirect tunnelling—as evidenced by current–voltage characteristics—between the Fe₃O₄ and the La_0.7Sr_0.3MnO₃ electrodes.

Magnetic suspension systems have shown a great deal of promise in the field of microrobotics. This paper discusses the performance of a new large gap magnetic suspension system developed by the researchers. The magnetic drive unit consists of six electromagnets attached to a soft iron pole piece and yoke. Levitation of an 11.19 g microrobot prototype is demonstrated for step, ramp and periodic input trajectories using PID control. The working envelope of the microrobot is 30 × 22 × 20 mm³, with an RMS error on the order of 18 µm in the vertical direction and 8 µm in the horizontal direction. It is demonstrated that the levitated microrobot is able to track the desired trajectory precisely and that the system has potential application for micromanipulation.

A CoAlO thin film was found to have good soft magnetic properties and gigahertz frequency response when it had a thickness of tens of nanometres. Increasing the thickness by more than 100 nm rapidly increased the coercivity and seriously degraded the high frequency response. A multilayering technique (laminating the magnetic layer with oxide spacers) was exploited to improve the magnetic properties in thick films. AlO_x and SiO_x were used as the oxide spacing layers in this experiment. For the 105 nm CoAlO films, the easy and hard axis coercivities were reduced by more than 8 times by introducing 2 nm AlO_x or 5 nm SiO_x spacers. With our optimum lamination [CoAlO (52.5 nm)/AlO_x (2 nm)]₇, good soft magnetic properties (easy and hard axis coercivities: 21 and 14 Oe and effective anisotropy field: 54 Oe) and high frequency response (real permeability: >200 up to ∼2 GHz) were successfully obtained in a multilayer film at a thickness of 380 nm. The changes in the microstructures and film stress with the introduction of the oxide spacers are discussed in this paper.

We report results of magnetization and differential scanning calorimetry measurements in the ferromagnetic shape memory alloy Ni₅₄Fe₁₉Ga₂₇. This alloy undergoes an austenite–martensite phase transition in its ferromagnetic state. The nature of the ferromagnetic state, both in the austenite and the martensite phase, is studied in detail. The ferromagnetic state in the martensite phase is found to have higher anisotropy energy as compared with the austenite phase. The estimated anisotropy constant is comparable to that of a well-studied ferromagnetic shape memory alloy system NiMnGa. Further, the present study highlights various interesting features accompanying the martensitic transition (MT). These features suggest the possibility of either a premartensitic transition and/or an inter-MT in this system.

We report the significant enhancement of low-field magnetization and magnetoresistance (MR) in La_2/3Ca_1/3MnO₃ (LCMO) compounds with 5 at.% nano-MgO addition in the form of both nanoparticle and nanowire. It is found that the magnetization of the nano-MgO added compounds is highly sensitive to a low applied field below 7 kOe compared with the MgO-free LCMO. In addition, the enhancement of low-field MR is found in nano-MgO added compounds and the enhancement for the nanowire MgO-added composite is more remarkable than that for the nanoparticle MgO-added one. Moreover, two ferromagnetic phases with low-T_C and high-T_C in nano-MgO added compounds are observed. These results demonstrate that the low-field transport and magnetic properties of LCMO compounds can be effectively manipulated by controlling the morphology and dispersion of the insulating barrier using nano-MgO addition.

The interfacial ferromagnetic/antiferromagnetic exchange coupling and ferromagnetic and antiferromagnetic anisotropies of polycrystalline ferromagnetic/antiferromagnetic exchange biased bilayers of NiFe/MnPt grown by RF sputtering have been investigated with quasi-static and dynamic measurements for different MnPt and NiFe thicknesses. The dynamic properties have been investigated through complex permeability frequency spectra measurements in the 100 MHz–3 GHz range. An effective field is deduced from dynamic measurements. A sharp enhancement of this effective field appears above a critical MnPt thickness (4.7 nm) lower than the critical thickness for the appearance of the easy axis hysteresis loop shift (7.8 nm). We observe also a strong enhancement of the damping parameter for the former thickness. This may be attributed to the superparamagnetic to antiferromagnetic transition in the antiferromagnetic layer. The anisotropy constant of the antiferromagnetic layer determined with dynamic measurements is in agreement with the one deduced from static measurements. The interface exchange energy J_E deduced from dynamic measurement is twice higher than the one obtained with hysteresis loop measurements. The dispersion relation of the resonance frequency of imaginary part of the permeability shows hysteretic behaviour and discontinuities when measured in presence of a static magnetic field applied along the easy axis of the ferromagnetic layer. This is attributed to partial magnetization switching by rotation mechanism in the ferromagnetic layer.

Metal coated microcantilevers are used as transducers of their electrochemical environment. Using the metallic layer of these cantilevers as a working electrode allows one to modify the electrochemical state of the cantilever surface. Since the mechanical behaviour of micrometre scale objects is significantly surface-driven, this environment modification induces bending of the cantilever. Using a full-field interferometric measurement set-up to monitor the objects then provides an optical phase map, which is found to originate from both electrochemical and mechanical effects. The scaling of the electrochemically-induced phase with respect to the surface charge density is modelled according to Gouy–Chapman–Stern theory, whereas the relationship between the mechanical effect and the surface charge density is analysed. An identification technique is described to determine a modelling of the electroelastic coupling and to identify the spatial charge density distribution from full-field phase measurements. Minimizing the least-squares gap between the measured phase and a statically admissible phase field, the mechanical effect is found to be charge-driven. The charge density field is also found to be singular on the cantilever edge, and the shear stress versus charge density is found to be non-linear.

Polycrystalline n-ZnO/p-Cu₂O heterojunctions have been fabricated by low-temperature eletrodepositions of ZnO and Cu₂O layers in aqueous solutions. The condition for forming the Cu₂O layer significantly reflected the electrical rectification characteristic and the photovoltaic performance, and the heterojunction fabricated under optimized conditions showed an excellent electrical rectification characteristic and a photovoltaic performance of 1.28% in conversion efficiency under an AM 1.5 illumination.

Several solid polymers of technical importance such as polytetrafluoroethylene, polyvinylidenefluoride, ethylene-tetrafluoroethylene-copolymer, polyetheretherketone and polypropylene show a long-lasting, spectrally broad luminescence after irradiation with ultraviolet light of low intensity. With a sensitive photo detection system the luminescence decay is registered for several hours. The decay curves can be approximated by an inverse power law with fractional exponent, partly showing a pronounced temperature dependence. Qualitatively, the luminescence emission can be understood as arising from a radiative recombination of trapped charges that diffuse under thermal activation.

Silicon carbide (SiC) is widely recognized as the leading candidate to replace silicon in micro-electro-mechanical systems devices operating in harsh environments. In this work, cantilevers and bridges in SiC are designed, fabricated and evaluated between room temperature (RT) and 600 °C. The active material is a cubic poly-SiC film deposited on a poly-Si layer which is separated from the Si substrate by a thermal oxide. From surface profiling and optical observations, it is deduced that an average residual strain of +5 × 10⁻⁴ is present in the 2.7 µm thick film, with a gradient of 2.5 × 10⁻⁴ µm⁻¹. The structures are excited either mechanically or electrostatically. Their resonance frequency is measured by laser Doppler velocimetry and used to derive the Young's modulus and residual stress in the heteroepitaxial layer (330± 45 GPa and 200± 20 MPa, respectively). The temperature coefficient of Young's modulus is found to be −53± 2 ppm K⁻¹ in the range RT to ∼ 300 °C, while an analytical expression is given for the temperature dependence of the Young's modulus between RT and 500 °C. The residual tensile stress is found to depend on temperature in a complex manner.

Rare earth fluoride (REF₃, RE = La, Ce, Pr, Sm, Er, Yb, Y) films were deposited on Ge(1 1 1) and silicon wafers in order to determine optical constants from the near infrared up to the high frequency tail of the reststrahlen band. The FT-IR transmission spectrum and the reflection spectrum were used to examine the infrared optical properties of the fluorides. The optical constants of the films in the infrared spectrum from 2 to 20 µm were calculated using the classical Lorentz oscillator model by fitting the transmission spectrum. The reflective spectrum of the fluorides on silicon was used to demonstrate the absorption difference in this region. It is found that the extinction coefficients of rare earth fluorides films with Pnma structure (REF₃, RE = Y, Yb, Er) are larger than the other fluorides films with structure (REF₃, RE = La, Ce, Pr, Sm) from 15 to 20 µm.

Photorefractive gratings were produced in a C₆₀-doped nematic liquid crystal cell under the application of two coherent beams and a nonbiased sinusoidal ac electric field. The beam coupling and diffraction of the ac electric field assisted gratings were studied systematically. A stable asymmetric energy transference was obtained. Diffraction was observed when the angle (between the normal of the cell and the bisector of the writing beams) was 0°, and the dependence of diffraction efficiency on the peak-to-peak value of the ac voltage was similar to that at an incidence angle of 45°, suggesting that the role of the ac field was to facilitate the charge separation, and the space-charge field (SCF) originated predominantly from the diffusion of the ac electric field assisted photo-induced carriers under the application of nonuniform illumination and an applied ac field. The grating was produced by director reorientation induced by the cooperation of the SCF and the applied ac electric field. A self-erasing phenomenon was observed in this cell. An explanation in terms of the movement of two kinds of carriers with opposite signs was proposed.

We propose an analytical model of the photocurrent efficiency dependence on the light intensity in organic semiconductors. The influence of the thickness of sample, space charge effects and recombination of charge on the loss of photocurrent has been considered. We demonstrate that the presented model is the enhancement of an analytical model reported recently by Rappaport et al (2005 J. Appl. Phys.98 033714). The method to identify and separate regions where the role of bimolecular recombination or the space charge dominates in the photocurrent is presented. The developed model can be useful for the modelling of the loss photocurrent in organic photovoltaic cells.

Double waveguides were produced in potassium titanyl phosphate (KTiOPO₄ or KTP) by ion exchange in pure RbNO₃ at 340 °C for 45 min, and subsequently ion implantation with 500 keV O ions at a dose of 1 × 10¹⁵ ions cm⁻². By the prism-coupling method the guided mode spectra as well as the refractive index profiles of the ion-exchanged sample were determined. The relative value of the refractive index distribution of the ion implanted KTP sample in the z direction was simulated, which indicates the formation of double waveguides. The field pattern of the propagation light in the waveguide was collected and studied by the end-coupling method. The near-field pattern of two planar operating waveguides was observed, one upon the other. The irradiation damage as well as the Rb distribution was analysed by means of the Rutherford backscattering spectrometry technique.

This paper is aimed at evaluating the electric field, the corona onset voltage and the corona current in negatively stressed needle-to-meshed plate gaps as compared with the case of using a flat plate. The charge simulation method is used for calculating the electric field in the gap. The onset voltage is evaluated based on the calculated field and the criterion for self-recurring single electron-avalanches in the ionization-zone around the needle tip. The corona current–voltage characteristics were measured for thin and thick needles at two gap spacings with meshed and flat plates. The corona currents with meshed plates are lower than those with a flat plate; even the corona onset voltage with the flat plate is higher than that with the meshed plate.

The initial relations and the description of a method for calculating the composition and thermodynamic properties of a closed gaseous system in thermodynamic equilibrium at constant pressure and temperature are given. The essence of the method consists in the minimization of the Gibbs energy of a system in ideal state. The calculation algorithm is implemented by the Tmdgas program in the C++ language. This program is part of the database system TheCoufal, available to interested parties at http://www.feec.vutbr.cz/~coufal/. The method described was used to calculate the thermodynamic properties of a system of products of the dissociation and ionization of H₂O. The results have been tabulated for pressures of 1, 5 and 20 bar at temperatures ranging from ambient temperature to 50 kK.

Infrared (IR) continuum radiation from the arc of a metal halide high intensity discharge lamp was measured and modelled. There are three contributions to the near IR continuum from free electrons: electron–Hg atom bremsstrahlung, electron–ion bremsstrahlung and electron–ion recombination radiation. Electron–Hg atom bremsstrahlung is the most important of these. The radiation transport model utilized empirical Hg density, arc temperature and electron density maps. The line width of the Hg 7¹S₀ to 6¹P₁ resonance broadened transition was used to determine the arc core Hg density. The arc temperature as a function of radius was determined using the radiance of the Hg 9860, 7311 and 7166 cm⁻¹ lines. Relative densities of neutral Dy atoms and Dy ions as a function of radius were found using an Abel inversion of the relative line radiance of selected Dy I and Dy II lines. A Saha analysis was used to determine the electron density in the lamp. The continuum is 73% of the total near IR radiation in the 4000–12 800 cm⁻¹ range.

A high power radio wave, launched into the polar ionosphere at angle θ with the earth's magnetic field from a ground-based transmitter in the vicinity of twice the electron cyclotron frequency (2.75 MHz), is reported to create an airglow at an effective radiated power (ERP) = 10 MW. We interpret this result as a consequence of parametric decay of the radio wave into an electron Bernstein wave (EBW) and an ion acoustic wave (IAW). The oscillatory velocity of electrons due to the pump couples with the density perturbation due to the IAW to produce a current, driving the Bernstein mode. The latter, in connection with the pump, exerts a ponderomotive force on electrons, driving the IAW. The growth rate of the parametric instability is maximum for θ = 0. At the same time, for any given value of θ, the growth rate increases with and attains a maximum around b ∼ 2, then falls gradually. The EBW produces energetic electrons via cyclotron damping. These electrons collide with the neutral atoms of the plasma to excite them to higher energy states. As the excited atoms return to lower energy states, they radiate in the visible.

Non-self-sustained positive and negative dc corona discharges were studied in point–plane gap at atmospheric pressure in nitrogen and in a nitrogen–oxygen mixture. Discharges were triggered by UV radiation. Current–voltage characteristics were recorded for a wide range of voltages and the waveforms of current pulses arising were recorded. Regularities found in the case of positive corona are explainable assuming that initial charge carriers are introduced into the discharge gap due the photoeffect at the plane electrode. Due to the photoionization in the oxygen–nitrogen mixture burst pulses arise. Study of negative corona showed that the electron emission from an electrode coated by a thin layer of TiO₂ cannot be explained by a simple photoeffect mechanism. It was found that the emission is a field-depending multistep-mechanism, which is controlled by the conductance of the metal-dielectric interface.

We report measurements of the breakdown curves of an rf capacitive discharge in low pressure silane. The electron drift velocity was determined from the locations of the turning point and of the minimum in the breakdown curves in the range E/p = 145–1292 V cm⁻¹ Torr⁻¹. We compare our results to values calculated from the published cross-sections in the range E/p = 1–2000 V cm⁻¹ Torr⁻¹ and data calculated in other papers and find good agreement.

A global model for electronegative plasmas in a pressure range of 0.1–100 Pa is used to investigate the dissociation of the precursor in O₂/SiCl(CH₃)₃ discharges. Microwave power is fed to the plasma by an annular waveguide ring with slotted line radiators on the inner side (SLAN) that is operated at 2.45 GHz. The modelling of the ECR plasma discharge and its application to the plasma enhanced chemical vapour deposition (PECVD) of silicon oxide films are reported. In the case of an oxygen discharge, theoretical values of the main plasma parameters (electron density and temperature and atomic oxygen population) are presented as a function of both pressure and electromagnetic power. The model results are compared with the experimental results obtained by optical emission spectroscopy, obtaining reasonably good agreement. The application of the model to the study of the PECVD of SiO₂ film from O₂/SiCl(CH₃)₃ mixtures has enabled us to determine that the fragmentation of the SiCl(CH₃)₃ molecule takes place mainly by electron impact dissociation, while the growth rate seems to be controlled by oxidation processes. Finally the influence of the precursor in the discharge has been studied. According to the model, in a first order approximation the insertion of the precursor causes an increase in the electron density due to the lower ionization threshold of the SiCl(CH₃)₃ molecule.

Carbon nanoparticles (CNPs) were grown in the subsurface-region of porous SiO₂ templates that had been subjected to plasma enhanced chemical vapour deposition. The over-layer multiwall carbon nanotubes (MWCNTs) grown in the surface region of the template were removed by a sonication process. Mechanical scrubbing of the template surface was used to remove the subsurface for investigation. The powder obtained was dispersed in ethanol onto copper-grids for characterization by electron microscopy, electron diffraction and micro-Raman spectroscopy. Elliptical, faceted and grape-shaped CNPs were observed by electron microscopy with electron diffraction patterns showing short range orderings. The Raman spectrum of the CNPs was found to be distinctly different from that of the over-layer MWCNTs in that the D-band (at ∼1385 cm⁻¹) merged with the G-band (at ∼1552 cm⁻¹). It seems that the CNPs in the subsurface-region grew simultaneously with the over-layer MWCNTs. A possible growth mechanism is proposed. The I–V characteristic of the CNPs, recorded by scanning tunnelling microscopy, was found to be asymmetric and characteristic of degenerately doped p–n junction diodes.

A weakly Ti-doped copper nitride (Cu₃N) film was prepared by cylindrical magnetron sputtering. The XPS results indicate that Ti atoms do not substitute for the Cu atoms but probably locate at the grain boundaries. The columnar grains size is about half of that of the undoped Cu₃N film and the surface is smoother. For weakly Ti-doped Cu₃N films, a dense layer appears on top of the columnar crystals. The RMS of the Cu film formed by annealing of the weakly Ti-doped Cu₃N film is more than twice larger than that of the film before annealing. Compared with the undoped Cu₃N film, it possesses fine thermal stability both in vacuum and in atmosphere.

Understanding nanofluidic behaviours in energetically unfavourable confining environments is essential for the development of high-performance nanoporous energy absorption systems. In the current study, the effect of liquid composition on defiltration in a hydrophobic nanoporous silica gel is investigated experimentally using two types of admixtures: carbamide of a relatively small molecular size and sodium bis(2-ethylhexyl) sulfosuccinate of a relatively large molecular size. By adding carbamide in the liquid phase, while the change in the solid–liquid interfacial tension is secondary, the defiltration volume can be lowered significantly, which can be related to the difficulties in gas phase formation and growth in nanopores. The factor of sodium bis(2-ethylhexyl) sulfosuccinate comes in mostly by affecting the liquid motions in relatively small nanopores.

This work employs a metal direct imprinting process, which possesses the characteristics of simplicity, low-cost and high resolution, for the fabrication of subwavelength structures on a metallic thin film. Herein, the mould featuring periodic line structures is manufactured by using E-beam lithography and followed by a dry etching process; meanwhile, the thin film is fabricated by sputtering Al on a silicon substrate. AFM section analyses are employed to measure imprinting depths of the subwavelength metallic structures and it is found that the uniformity of the imprinting depths is affected by the designed patterns, the material property of thin film and mould deformation. The process temperature and the mould filling that influence the transferred quality are investigated. In addition, TEM is also utilized to examine defects in the subwavelength metallic structures. Finally, good quality subwavelength metallic structures are fabricated under a pressure of 300 MPa for 60 s at room temperature. In this study, we have demonstrated that subwavelength metallic structures with a minimum linewidth of less than 100 nm on the Al thin film are successfully constructed by the metal direct imprinting process.

Deposition parameters were varied systematically to obtain NiO/Gd-doped CeO₂ composite films using the electrostatic spray deposition method. The microstructure and morphology of the obtained films were investigated using a scanning electron microscope and an x-ray diffractometer. The degree of wetting of aerosol droplets on substrates decreased in the order of silicon wafer > stainless steel > glass. For deposition on silicon wafers, a continuous, flat layer was formed first due to excellent wetting of aerosol droplets on the substrate. Isolated particles were then nucleated and precipitated from the subsequent landing droplets and scattered on the bottom layer due to the very limited wetting of aerosol droplets on the flat oxide layer. Preferential landing of aerosol droplets on the isolated particles and subsequent precipitation and agglomeration of the fine particles finally resulted in a cauliflower morphology. Higher deposition temperature and lower flow rate of precursor solution resulted in drier droplets and hence diminished wetting and favoured particle precipitation, preferential landing of aerosol droplets and subsequent particle agglomeration. Increasing substrate roughness also favoured preferential landing of aerosol droplets and particle agglomeration. The composition of the deposited films was in fairly good agreement with that of the starting solution as revealed by the inductively coupled plasma mass spectrometer.

High intensity electron emission cathodes based on carbon nanotube films have been successfully fabricated. An investigation of the explosive field emission properties of the carbon nanotube cathode in a double-pulse mode was presented and a high emission current density of 245 A cm⁻² was obtained. The formation of the cathode plasma layer was proved and the production process of the electron beams from the cathode was explained. The time and space resolution of the electron beams flow from the cathode was investigated. The plasma expanded at a velocity of ∼8.17 cm µs⁻¹ towards the anode and influenced on the intensity and distribution of electron beams obviously. The formation of cathode plasma had no preferential position and the local enhancement of electron beams was random. This carbon nanotube cathode appears to be suitable for high-power microwave device applications.

CuCl is a I–VII semiconductor material with a direct band gap of ∼3.4 eV. It exhibits a zincblende structure (γ-phase) at low temperatures, up to ∼680 K. Unlike GaN, ZnO and related materials, CuCl has a relatively low lattice mismatch with Si (<0.4%) and a large excitonic binding energy (∼190 meV). This suggests the possibility of the fabrication of excitonic-based blue/UV optoelectronic devices on Si with relatively low threading dislocation densities. In this study, CuCl has been deposited and examined as a candidate material for the fabrication of these devices. X-ray diffraction (XRD) measurements confirmed that the deposited films were preferentially oriented in the (1 1 1) plane. Room temperature photoluminescence measurements reveal a strong Z₃ free exciton peak (3.232 eV). Both steady state dc and ac impedance spectroscopy experiments suggested that the deposited CuCl is a mixed ionic–electronic semiconductor material. An electronic conductivity of the order of 2.3 × 10⁻⁷ S cm⁻¹ was deduced to be in coexistence with Cu⁺ ionic conductivity using irreversible electrodes (Au), while a total conductivity of the order of 6.5 × 10⁻⁷ S cm⁻¹ was obtained using reversible electrodes (Cu) at room temperature. Further to this, we have identified some of the challenges in fabricating an optoelectronic device based on a CuCl/Si hybrid platform and propose some possible solutions.

Conducting ion-beam assisted CVD deposited a-C type DLC films can be patterned electro-oxidatively by masked and maskless probe-induced STM-based lithography. The former constitutes a parallel rapid processing technology, with the tip acting as a distant stationary electrode. The latter is a higher spatial resolution serial technology, with the tip defining a travelling local electro-chemical cell. The mechanism is based on electro-oxidative conversion of solid carbon to gaseous CO or CO₂ in the presence of an aqueous phase, either as a bulk fluid or as a thin adsorbed film. The process is constrained kinetically in the early stages by limitations on charge transport through the surface barrier at the fluid-to-solid interface and subsequently by the availability of oxidants and by their transport to reactive sites. The as-received surface is terminated by chemisorbed oxygen, leading to the formation of an insulating surface barrier. The threshold potential for initiation of conversion depends on the width of the barrier. The results may have implications for new technologies exploiting the properties of carbon-based materials, but may also add to the present understanding of the electrochemistry of carbon solids.

Large-quantity synthesis of single-crystalline perfectly hexagonal-shaped ZnO rods has been achieved through the thermal evaporation of metallic zinc powder in the presence of oxygen without the use of metal catalyst or additives. Detailed structural analyses confirm that the structures formed exhibit a wurtzite hexagonal phase and are preferentially oriented along the c-axis direction. Low-temperature photoluminescence shows that the exciton emission bound-to-neutral donor (D⁰X) and free-exciton dominate the edge emission region while the donor–acceptor pair (DAP) and its replica dominate the lower energy regions. With increased temperature, D⁰X decreases abruptly and is then suppressed, but with further increase in temperature (>100 K) the photoluminescence spectra are dominated by the DAP.

Inspired by the self-cleaning superhydrophobic taro leaf, a polystyrene (PS) film with superhydrophobic surface was obtained using a natural taro leaf as template. The water contact angle and the sliding angle of the superhydrophobic PS surface were 158° ± 1.6° and 3°, respectively. The PS surface was still superhydrophobic when contacting with black ink, fresh blood and even viscous glue water. SEM shows that the surface structure comprises many uniform papillae with the diameters ranging from 10 to 15 µm, which is similar to the surface structure of natural taro leaf. Such a special surface morphology may result in the superhydrophobic property.

Quasi-aligned Zn_1−xMg_xO nanorods have been synthesized on Si substrates by thermal evaporation. The Mg content (x) in Zn_1−xMg_xO nanorods was 0.23, higher than that in the source materials by a factor of about 1.9. Zn_1−xMg_xO (x = 0.23) nanorods showed a wurtzite ZnO structure with the c-axis constant of 0.5179 nm. The nanorods grew along the [0 0 0 1] crystal direction and had uniform and flat hexagonal planes with diameters of about 200 nm. Photoluminescence measurements revealed that the predominant ultraviolet (UV) emission of Zn_1−xMg_xO (x = 0.23) nanorods was centred at 3.78 eV, with a ∼0.51 eV blueshift from the UV emission line (3.27 eV) of ZnO nanorods. This blueshift indicated the bandgap engineering in nanostructures of Zn_1−xMg_xO ternary alloys.

Crystallization kinetics and structure of 20Li₂O–80TeO₂ glasses are studied using x-ray diffraction, Fourier transform infrared spectroscopy and differential scanning calorimetry techniques. XRD results show γ-TeO₂, α-TeO₂ and Li₂Te₂O₅ phase crystallization in the glass matrix. The infrared band structure of this glass is similar to that observed in glassy TeO₂. Activation energies were evaluated from Lorentzian three-peak deconvolution of the DSC crystallization peak recorded at different particle sizes. As the obtained activation values were very close, it was not possible to establish a hierarchy on the crystallization of this glass. In addition, the height of the Lorentzian peaks (δT_P1, δT_P2 and δT_P3) for each sample was measured and plotted against the nucleation temperature. The presence of two maxima at around 284 and 304 °C suggests at least two maximum nucleation temperatures in the studied 20Li₂O–80TeO₂ glass.

Lead-free ceramics (K_0.5Na_0.5)_1−xLi_x(Nb_1−ySb_y)O₃ have been prepared by an ordinary sintering technique. Li⁺ and Sb⁵⁺ diffuse into the K_0.5Na_0.5NbO₃ lattices to form a solid solution with the perovskite structure. The substitution of Li⁺ increases the Curie temperature T_c and shifts the ferroelectric tetragonal–ferroelectric orthorhombic phase transition (T_O–T) to low temperatures. On the other hand, the substitution of Sb⁵⁺ decreases T_c and has a minor effect on T_O–T. The coexistence of the orthorhombic and tetragonal phases at x = 0.06 and y = 0.06 near room temperature and the strong covalence of Sb lead to significant improvements in the piezoelectric properties. For the (K_0.5Na_0.5)_0.94Li_0.06(Na_0.94Sb_0.06)O₃ ceramic, piezoelectric constant d₃₃ = 212 pC N⁻¹, planar and thickness electromechanical coupling factors k_P = 46% and k_t = 47% and T_c = 358 °C. The donor-type doping of BaCO₃, SrCO₃ or Bi₂O₃ leads to further enhancements of the piezoelectric and ferroelectric properties.

The geometrical arrangement of single-molecule-high islands and the contact between them have large roles in determining the electrical properties of field effect transistors (FETs) based on monolayer-scale pentacene thin films. As the pentacene coverage increases through the submonolayer regime there is a percolation transition where islands come into contact and a simultaneous rapid onset of current. At coverages just above the percolation threshold, the electrical properties vary with geometrical changes in the contacts between the pentacene islands. At higher coverages, the FET mobility is much lower than the mobility measured by the van der Pauw method because of high contact resistances in monolayer-scale pentacene film devices. An increase in the van der Pauw mobility of holes as a function of pentacene coverage shows that second layer islands take part in charge transport.

The excitation and stability of surface waves on the interface of two compressible fluids moving with respect to each other in a two-dimensional channel is investigated. It is shown that in this case surface waves are always unstable. On the other hand, in this case the dispersion relation in the short and the long wavelength limits coincides with the dispersion relation in the compressible and the incompressible infinite fluid, respectively. Furthermore, surface wave excitation under resonant condition is investigated. It is concluded that due to the Cerenkov-like emission mechanism a sound wave propagates in the fluid at rest. In this case, the growth rate of the Cerenkov-like instability is compared with the growth rate of the instability for the excitation of the tangentially discontinuous surface wave. Likewise, using fluent software, surface wave excitation in two dimensions is simulated.

Using molecular-dynamics computer simulation, we study the material processes occurring for fixed laser fluence in a thin metal film induced by ultrafast laser irradiation. The simulation algorithm combines molecular-dynamics for the atom motion supplemented by an analytical solution of time dependence of the homogeneous electron dynamics. Our results show that the laser pulse duration influences virtually all material processes in the irradiated film: melting, build-up of compressive and tensile pressure, spallation and cluster formation. In particular, for the same laser fluence, a reduction of the laser pulse duration leads to more pronounced pressure peaks in the film, which may induce thermomechanical spallation of the sample, and—at higher fluences, where the ablated material forms a vapour cloud—to an increase in the number of large droplets in the vapour cloud. If the laser pulse duration is smaller than the electron–phonon relaxation time in the material, the latter quantity becomes dominant in limiting the material processes.

Lead-free (K_xNa_1−x)_1−yLi_yNb_0.80Ta_0.20O₃ ceramics have been prepared using the conventional solid-state reaction technique in ambience. A systematic study was carried out to examine the existence and influences of two speculated morphotropic phase boundaries (MPBs). The result shows that the widely-accepted MPB near x = 0.50 can be hardly recognized. All the (K_xNa_1−x)_0.97Li_0.03Nb_0.80Ta_0.20O₃ ceramics with x = 0.40–0.60 exhibit the high performance of piezoelectric constant d₃₃ ∼ 230 pC N⁻¹, planar electromechanical coupling coefficient k_p ∼ 48.5% and thickness coupling coefficient k_t over 36%. In contrast, the other MPB associating with the Li-content in a narrow compositional width of y = 0.03–0.04 shows a significant influence on the dielectric and piezoelectric properties. Similarity between the latter MPB and that in Pb(Zr,Ti)O₃ is also discussed.

The structure, electronic and magnetic properties of perovskite (1 − x)La_0.7Ca_0.3MnO₃(LCMO)/xCu (x is a mass percentage, x = 1%, 3%, 5%, 7%, 9%, 15%, 20%) have been studied. The nano-scale metal Cu powder was doped into the LCMO matrix. The results showed that some Cu element substituted for Mn ion in LCMO and the remainder resided in the grain boundaries in the form of a CuO phase because of the oxidation process when the Cu powder was sintered at high temperature in air. Cu existed in the form of Cu³⁺ ions in the samples at a low doping level (x ⩽ 3%) and Cu²⁺ ions appeared when x > 3%. Because of the larger ionic radius of Cu²⁺ ions compared with the average Mn radius, it is likely that the Cu²⁺ ions in the proximity of the grain boundaries tend to separate into the boundaries. An amorphous phase of the Cu element was formed in the grain boundaries, which respond to the unusual electrical and magnetic behaviours of the heavily doped samples. A maximum MR value (∼50%) around 210 K was observed in a magnetic field of 3000 Oe for the 5% doped samples. Besides the effect of Cu substituting for Mn ions in LCMO, the MR behaviour is also attributed to the properties of dopants which reside in the grain boundaries of the matrix grains.

Bulk AgPb_mSbTe_2+m compounds exhibit outstanding thermoelectric properties. It is believed that their preparation by a higher cooling rate could improve the homogeneity of these materials, and thereby one expects a certain impact on their thermoelectric properties. We have prepared AgPb₁₈Sb_1−xTe₂₀ compounds where x = 0.0, 0.1, 0.3 and 0.5 by quenching the melts in liquid nitrogen. High-resolution transmission electron microscopy has confirmed that the homogeneity of the samples is improved with respect to the samples prepared by furnace cooling. The decrease in the electric conductivity and the increase in the absolute value of the Seebeck coefficient, we ascribe to the improved homogeneity of the samples. The same effects on the conductivity and on the Seebeck coefficient are obtained with increasing Sb content. The influence of the Sb concentration are interpreted as follows: the number of Ag–Sb pairs and thereby the widening of the energy band increase with increasing Sb content.

An optical investigation was performed to investigate the formation of carbon in pseudo-micro-aluminized hexahydro-1,3,5-trinitro-1,3,5-triazine explosive powder explosion. X-ray diffraction analyses indicated that carbon was one of the major ingredients in the residue. Instantaneous emission spectra of C₂, AlO, CO and CO₂ showed that micro-aluminium promotes the ejected carbon at 3159 ± 50 K temperature and 6–8 MPa blast pressure. The convincing reason is that excess Al creates an O-poor environment.

The heat and mass transfer process in a solid–gas reactor is optimized based on constructal theory. The entropy generation minimization is taken as the optimization objective and a triangular element is taken as the elemental area. The aspect ratio of a triangular elemental area is optimized under constraint conditions. A number of optimal triangular elements are assembled to a new larger rectangular area and optimized again. The optimization is completed by continuing analogous work until the control area is covered. Analytical results are obtained. The effects of some parameters on minimum entropy generation are analysed by numerical examples. Smaller entropy generation can be obtained when the optimization for a given volume is carried out on the basis of triangular elements than those obtained on the basis of rectangular elements.