Table of contents

In-plane defects have been introduced into graphene nanosheets by treatment with hydrochloric acid. Acid treatment induces bond cleavage in the C–C network via electrophilic attack. These resultant vacancy sites will then undergo further reactions with the surrounding ambient to produce C–O and C–H bonds. A σ^* resonance at 287 eV in the carbon K-edge x-ray absorption spectra is observed with acid treatment and is assigned to C–O states. Theoretical modelling of a di-vacancy in a graphene bilayer reproduces all essential features of this resonance and in addition predicts a metallic conductivity of states around this vacancy. The possibility of engineering the properties of graphene via the routes explored here is an important step towards establishing strategies for building devices based on this material.

The nematic (N) to smectic A (SmA) phase transitions in binary mixtures of the 6th (D6AOB) and 7th (D7AOB) members of alkylazoxybenzene series have been studied using high-precision calorimetry at 10, 20, 30, 50, 75 and 100 wt% of D7AOB concentrations. The temperature range of the nematic phase on six binary mixtures was wide, and it was dependent on the concentration of D7AOB and the ratio of transition temperatures T_NA/T_NI changes from 0.889 for 10 wt% D7AOB to 0.951 for 100 wt% D7AOB. The ratio of specific-heat amplitudes above and below the nematic to smectic (NA) transition, A⁺/A⁻, remains ∼1.0. The value of specific-heat exponent, α, changes from 0.1 to 0.4, implying variations from three-dimensional Ising type behaviour to mean field tricritical type behaviour, respectively, when the concentration of D7AOB increased from 10 wt% to 100 wt%.

An Au film modified by vanadium pentoxide (V₂O₅) has been investigated as the anode for injecting holes in organic light-emitting devices (OLEDs). It is found that OLEDs with the V₂O₅ modified Au anode have much lower driving voltages and much higher current efficiencies (four times higher) as compared with the OLEDs with bare Au as anode. The results of ultraviolet photoelectron spectroscopy and UV–visible spectrometer analysis indicate that the Au anode treated by V₂O₅ has a smaller barrier height and thus facilitates hole injection, apart from a high optical transparency of Au/V₂O₅. For the OLEDs with Au/V₂O₅ anode, the driving voltage is decreased by 13 V and the maximum current efficiency (4.1 cd A⁻¹) is four times higher as compared with that of the bare Au anode device (∼0.9 cd A⁻¹). The OLEDs with Au/V₂O₅ anode also have about 1.4 times higher efficiency than that of the OLEDs (∼2.8 cd A⁻¹) with ITO/V₂O₅ anode.

The termination of the edge of wafers in reactive ion etching reactors is important for obtaining uniform fluxes of reactants across the substrate. Structures such as focus rings (FRs) are often used to improve the uniformity of fluxes. There is a gap of hundreds of micrometres to a few mm between the edge of the wafer and the FR for mechanical clearance. Plasma penetration into the gap can produce particle forming films and erosion of consumable parts. In this paper, we discuss results from a computational investigation of ion energy and angular distributions incident into the wafer–focus ring gap. The geometry and electrical properties of the FR can skew the angle and limit the extent of energies of ions penetrating into the gap.

We present a novel way to obtain heavily nitrogen doped anatase TiO₂ films by using a solid-state nitrogen source. Epitaxial growth of the films was realized by introducing one unit-cell seed layer, which was indicated by reflection high-energy electron diffraction as intensity oscillation. Results of x-ray diffraction and x-ray photoelectron spectroscopy confirmed that the films were in the anatase phase heavily doped with nitrogen of ∼15 at%. The films obtained exhibited considerable narrowing of the optical bandgap, resulting in an enhancement of absorption in the visible-light region.

Recent progress in the development of barium strontium titanate thin film varactors for room temperature tunable microwave devices applications is reviewed, with emphasis on efforts towards the improvement in the quality of BST thin films and the fabrication issues crucial for the performance of microwave devices based on BST varactors. The paper provides examples of tunable microwave devices employing BST varactors. Other thin film materials currently competing with BST thin films are discussed. Topics which deserve further investigation are suggested.

Nanocomposite powders comprising Sm–Co–Fe intermetallic phases and Fe(Co) were synthesized by high-energy ball milling and were consolidated into bulk magnets by the spark-plasma sintering (SPS) technique. While the microstructure of the SPS samples was characterized by transmission electron microscopy (TEM), the solubility of Fe in different phases was investigated using Mössbauer spectroscopy. TEM studies revealed that the spark-plasma sintered sample has Sm(Co,Fe)₅ as a major phase with Sm₂(Co,Fe)₁₇, Sm(Co,Fe)₂ and Fe(Co) as secondary phases. The size of the nanocrystalline grains of all these phases was found to be in the range 50–100 nm. The Mössbauer spectra of the as-milled powders exhibited two different subspectra: a sextet corresponding to the Fe phase and a broad sextet associated with the Fe(Co) phase; while that of the SPS sample showed four different subspectra: a sextet corresponding to Fe and other three sextets corresponding to the Fe(Co), Sm(Co,Fe)₅ and Sm₂(Co,Fe)₁₇ phases; these results are in accordance with the TEM observation. Recoil magnetization and reversible susceptibility measurements revealed magnetically single phase behaviour of the SPS magnets.

We present two statistical analytical approaches to estimate the particle size distribution of magnetic nanoparticles. They are termed best linear unbiased estimator and linear minimum mean square error estimator. These approaches are implemented and quantified within the formalism of linear unbiased estimation theory. To illustrate the efficiency of the proposed approaches, we give two examples of the application to the particle size distribution analysis in ferrofluids with normal and lognormal samples. In both cases we compare the reconstruction distributions using our methods with those calculated via the electron microscopy images of the ferrofluid particles.

Pure, La³⁺ doped at A site, V⁵⁺ doped at B site, and La³⁺ and V⁵⁺ co-doped multiferroic BiFeO₃ ceramics: BiFeO₃ (BFO), Bi_0.85La_0.15FeO₃ (BLF), BiFe_0.97V_0.03O₃ (BFV), Bi_0.85La_0.15Fe_0.97V_0.03O₃ (BLFV), etc were successfully prepared by a rapid liquid sintering technique. X-ray diffraction indicated that these ceramics were of polycrystalline perovskite structures, accompanied with a tiny residual Bi₂O₃ phase. It was found that, among these ceramics, BLFV ceramic exhibited the best electrical properties. The leakage current density of BLFV ceramic was only 2.1 × 10⁻⁶ A cm⁻² at 10 kV cm⁻¹, two and one orders of magnitude lower than those of the BLF and BFV ceramics, respectively. In the measuring frequency of 4 KHz–1 MHz, the dielectric constants and losses of this sample exhibited slight variation and the lowest loss tangent was 0.08. The sample had a relatively saturated ferroelectric hysteresis loop. These suggested that the co-doped BiFeO₃ ceramic by La³⁺ and V⁵⁺ at A and B sites showed advantages in application over the pure BFO, doped BLF and BFV ceramics, respectively.

A facile solvothermal route was developed to prepare flower-like Co microcrystals composed of Co nanoplates, in which water/ethanol mixture was used as solvent and ethylenediamine tetraacetic acid sodium was used as complexing agent, respectively. X-ray diffraction pattern showed that the synthesized Co microcrystals were present in hexagonal close-packed phase and x-ray photoelectron spectroscopy analysis indicated that the surface of the sample was oxidized. Scanning electron microscope images revealed that each of the flowery Co microcrystals was composed of several pieces of Co plates with uniform thickness of ca 200 nm. It was found that the solvents played a crucial role in determining the morphology of the Co products and the introduction of a certain amount of ethanol was indispensable for the formation of flower-shaped morphology. Magnetic measurement at room temperature indicated that the coercivity (H_c) of the flower-like Co microcrystals came up to 407.3 Oe, which was much higher than that of bulk Co metal.

A study on a three-energy-level system in asymmetric Al_xGa_1−xN/GaN double quantum wells has been performed by solving the Schrödinger and Poisson equations self-consistently. It is found that the resonance between the second subband (the 2 subband) and the 3 subband occurs when the Al composition of the right well is 0.54. The energy separation between the 2 and 3 subbands is a minimum which is up to 145 meV. The absorption coefficient of the intersubband transition (ISBT) between the first and second subbands (the 1–2 ISBT) approximately equals that of the 1–3 ISBT, provided that the Al composition of the right well is 0.54. The wavelengths of the 1–2 and 1–3 ISBTs are 1.55 µm and 1.31 µm, respectively. These results suggest promising applications to two-colour devices operating within the optical communication wavelength range.

By two examples of dissimilar physical phenomena causing thermophysical effects, the unique capabilities of one of the up-to-date methods of experimental physics—focal plane array (FPA) based infrared (IR) thermography (IRT), are demonstrated distinctly. Experimenters inexperienced in IRT can grasp how this method provides a means for combining real-time visualization with quantitative analysis. A narrow-band short-wavelength IR camera was used in the experiments. It is discussed and stated that IRT is best matched and suited to the next two test conditions—when a heated specimen is thin and when heat is generated in the immediate region of a surface of a solid. The first prerequisite is realized in the search for directional patterns of combined low-power radiation sources with the use of the IRT-aided method. The second one is realized in studies of water vapour adsorption on uneven (irregular) surfaces of solid materials. With multiple swatches taken from a set of different fabrics and used as experimental samples, a sharp distinction between adsorptivities of their surfaces is strikingly illustrated by IRT time-domain measurements exhibiting the associated thermal effect ranging within an order of magnitude. It is justified that the described IRT-aided test can find practical implementation at least in the light industry. Emissivities of different fabrics are evaluated experimentally with the described reflection method based on the narrow spectral range of IRT. On the basis of direct IR observations, attention is paid to the need for close control over the surface temperature increase while the adsorption isotherms are being measured. Sensitivity of the FPA-based IRT method, as applied to examine the kinetics of initial stages of adsorption of gaseous molecules on the solid surface, is evaluated analytically and quantitatively. The relationship between the amount of adsorbate and the measurable excess of adsorbent temperature is found. It is discovered that the method makes it possible to control nano-quantities of the adsorbed matter, namely, it is sensitive to an incipient molecular film of 1/300-monolayer effective thickness.

This work describes the thermoluminescence (TL) response of silica-based materials irradiated with thermal neutrons. These materials have the compositions (mol %) (60 + x)SiO₂–(30 − x)Na₂O–5MgO–5Al₂O₃, where x = 0, 5, 10 and 15. The irradiation was carried out in the fluence range 1 × 10¹⁴ – 1 × 10¹⁷ neutron cm⁻². These glassy materials gave two TL glow peaks at around 473 and 643 K. The intensity ratio of these peaks is found to vary with varying SiO₂/Na₂O ratios. The peak at 473 K is more prominent at the ratio SiO₂/Na₂O = 75/15, while the intensity of the other one at 643 K increases by decreasing the value of this ratio. The former peak is attributed to both 'AlO₄' hole centres and non-bridging oxygen (NBO) ion centres induced by neutrons irradiation, while the latter one could be ascribed to (NBO) ion centres introduced by the network modifiers, Na⁺ ions. The TL response against the neutron beam fluences of the material having the ratio SiO₂/Na₂O = 75/15 is found to show sublinearity in the above-mentioned range of fluence (using the area under the curve method). The other features such as high sensitivity and simple glow curve structure might be good indicators for this material to be used as a dosimeter in several applications such as thermal neutrons or in food irradiation.

Sr₃Al₁₀SiO₂₀–SrAl₁₂O₁₉, doped with Eu²⁺, Cr³⁺ and (Eu²⁺ + Cr³⁺) is prepared by solid-state reaction and energy transfer from Eu²⁺ to Cr³⁺ in the phase of Sr₃Al₁₀SiO₂₀ is the focus of investigation. The spectrum of Sr₃Al₁₀SiO₂₀–SrAl₁₂O₁₉ : Eu²⁺ shows f–d emission bands at 460 and 400 nm. Cr³⁺ doped Sr₃Al₁₀SiO₂₀–SrAl₁₂O₁₉ yields emission lines at 688 and 696 nm and a broad emission band between 650 and 750 nm. The photoluminescence study and fluorescence lifetime measurements demonstrate efficient energy transfer from Eu²⁺ to Cr³⁺ in Sr₃Al₁₀SiO₂₀ : Eu²⁺, Cr³⁺. The emission lines peak at 688 nm and 696 nm, which, respectively, originate from ²E–⁴A₂ transitions in the phases of SrAl₁₂O₁₉ and Sr₃Al₁₀SiO₂₀. The broad emission band of Cr³⁺ between 650 and 750 nm in the phase of Sr₃Al₁₀SiO₂₀ is considered to be the ⁴T₂–⁴A₂ transition by calculating the strength of the octahedral crystal field Dq, the Racah parameters B and C as well as by constructing the Tanabe–Sugano diagram.

High-quality ZnO epitaxial films were grown by pulsed-laser deposition on Si (1 1 1) substrates with a thin γ-Al₂O₃ buffer layer. The epitaxial γ-Al₂O₃ buffer layer consists of two (1 1 1) oriented domains rotated 60° from each other against the surface normal, which yields the in-plane epitaxial relationship or . The crystalline quality and optical properties of ZnO epi-layers were studied by x-ray diffraction and photoluminescence measurements. A clear correlation between ZnO deep-level emission (DLE) to near-band edge (NBE) emission intensity ratio and the width of the ϕ-scan across off-normal reflection was observed. The NBE linewidth also exhibits strong dependence on the width of the ZnO (0 0 2) rocking curve. These observations indicate the NBE and DLE emissions are mainly affected by the edge and screw type dislocations, respectively.

Thermal flow characteristics of air plasma jets generated by a non-transferred plasma torch with hollow electrodes are experimentally and numerically investigated in order to provide more reliable scientific and technical information, which has been insufficient for their practical applications to material and environmental industries. In this work, a thermal plasma torch of hollow electrode type is first designed and fabricated, and similarity criteria for predicting operational conditions for the scale-up to high-power torches are derived from the arc voltage characteristics measured with various operating and geometry conditions of the torch. The thermal flow characteristics of air plasma jets ejected from the torch are measured by enthalpy probe diagnostics and turn out to have relatively low temperatures of around 3000–7000 K, but show features of other unique properties, such as high energy flux, broad high temperature region and long plasma jet with moderate axial velocity, which are promising for their applications to material syntheses and hazardous waste treatments. Such high enthalpy at a relatively low temperature of air thermal plasma compared with the argon one is due to the high thermal energy residing in the vibrational and rotational states and oxygen dissociation, besides the translational states in monatomic gases such as argon. It is expected that this high specific enthalpy of the air plasma will enable material and environmental industries to treat a large amount of precursors and waste materials effectively at a lower temperature for a longer residence time by the low plasma velocity. It is also found from the measurements that the turbulence intensity influenced by the size of the electrode diameter has a significant effect on the axial and radial profiles of plasma jet properties and that a longer plasma jet is more readily achievable with a larger electrode diameter reducing the turbulence intensity in the external region of the torch. In the numerical studies based on magnetohydrodynamics (MHD) theory, a precise three-dimensional transient numerical model for the internal arc discharge plasma of the torch has been developed along with a practical two-dimensional stationary one for the external thermal plasma jet by considering highly localized distributions of arc roots with circumferential non-uniformity on the electrode wall surfaces, so that more reliable and realistic descriptions on the arc thermal plasma properties become feasible both inside and outside the torch. The numerical calculation results are compared with the experimental data obtained from the probe measurements and found to be in good agreement with them.

This paper analyses the dynamic process of groove filling and the resulting weld pool fluid flow in gas metal arc welding of thick metals with V groove. Filler droplets carrying mass, momentum, thermal energy and sulfur species are periodically impinged onto the workpiece. The complex transport phenomena in the weld pool, caused by the combined effect of droplet impingement, gravity, electromagnetic force, surface tension and plasma arc pressure, were investigated to determine the transient weld pool shape and distributions of velocity, temperature and sulfur species in the weld pool. It was found that the groove provides a channel which can smooth the flow in the weld pool, leading to poor mixing between the filler metal and the base metal.

The polyphase multipactor, i.e. the non-resonant form of secondary electron emission rf discharges in vacuum, has been analysed and studied experimentally. The multipactor discharge was observed in an evacuated standard rectangular waveguide through which pulsed high-power microwave radiation in the decimeter wavelength range was transmitted. The power interval in which the two-sided (between the wide walls of the waveguide) multipactor appeared has been determined. It is found that there is a characteristic delay time for the onset of the multipactor breakdown as compared with the time at which the microwave power is applied. The dependence of this delay time on the microwave power has been established. The experimental results are compared with results of numerical simulations which make it possible to estimate the secondary emission properties of the waveguide walls. Reasons for some observed discrepancies between numerical results and experimental data are discussed as well as the nature of the observed multipactor delay.

The metastable atom population distribution in a free expanding uranium vapour generated by electron beam (e-beam) heating is expected to depart from its original value near the source due to atom–atom collisions and interaction with electrons of the e-beam generated plasma co-expanding with the vapour. To investigate the dynamics of the electron–atom and atom–atom interactions at different e-beam powers (or source temperatures), probing of the atomic population in ground (0 cm⁻¹) and 620 cm⁻¹ metastable states of uranium was carried out by the absorption technique using a hollow cathode discharge lamp. The excitation temperature of vapour at a distance ∼30 cm from the source was calculated on the basis of the measured ratio of populations in 620 to 0 cm⁻¹ states and it was found to be much lower than both the source temperature and estimated translational temperature of the vapour that is cooled by adiabatic free expansion. This indicated relaxation of the metastable atoms by collisions with low energy plasma electrons was so significant that it brings the excitation temperature below the translational temperature of the vapour. So, with increase in e-beam power and hence atom density, frequent atom–atom collisions are expected to establish equilibrium between the excitation and translational temperatures, resulting in an increase in the excitation temperature (i.e. heating of vapour). This has been confirmed by analysing the experimentally observed growth pattern of the curve for excitation temperature with e-beam power. From the observed excitation temperature at low e-beam power when atom–atom collisions can be neglected, the total de-excitation cross section for relaxation of the 620 cm⁻¹ state by interaction with low energy electrons was estimated and was found to be ∼10⁻¹⁴ cm². Finally using this value of cross section, the extent of excitational cooling and heating by electron–atom and atom–atom collisions are described at higher e-beam powers.

Measurements of x-ray emission spectra generated by 10–20 keV electrons impinging normally on bulk targets of pure elements Ti (Z = 22), W (Z = 74) and Pt (Z = 78) have been performed using an experimental setup developed for studying electron–atom/molecule collisions in our laboratory. Values extracted from the experimental data for bremsstrahlung yield, integrated yield and mean energy of the bremsstrahlung radiation beam for the above collision systems have been compared with the simulation results obtained from the general purpose Monte Carlo simulation code PENELOPE. The comparisons are found to show a satisfactory agreement between them within their statistical uncertainties. Some apparent mismatches are observed for which possible causes and their origins are discussed.

A simple robust method is presented to determine the densities of metastable and resonant species in low temperature, low pressure argon and argon-diluted plasmas. The ratios of spectral lines which correspond to transitions from common upper states to resonant or metastable lower states are measured with low resolution optical spectrographs. Photon reabsorption makes these ratios sensitive to the population densities of the lower states. The concept of escape factors is used to develop a set of nonlinear equations for the line ratios, which does not depend on the densities of the upper states. By means of a least squares method, the equations can be solved for metastable and resonant state population densities. The method does not depend on the nature of the excitation process, which makes it superior to other spectroscopic techniques in situations where the electron energy distribution is not known.

A hybrid model, called the hybrid plasma equipment model, was used to study Ar/Cl₂ inductively coupled plasmas used for the etching of Si. The effects of substrate bias, source power and gas pressure on the plasma characteristics and on the fluxes and energies of plasma species bombarding the substrate were observed. A comparison with experimentally measured etch rates was made to investigate how the etch process is influenced and which plasma species mainly account for the etch process. First, the general plasma characteristics are investigated at the following operating conditions: 10% Ar 90% Cl₂ gas mixture, 5 mTorr total gas pressure, 100 sccm gas flow rate, 250 W source power, −200 V dc bias at the substrate electrode and an operating frequency of 13.56 MHz applied to the coil and to the substrate electrode. Subsequently, the pressure is varied from 5 to 80 mTorr, the substrate bias from −100 to −300 V and the source power from 250 to 1000 W. Increasing the total gas pressure results in a decrease of the etch rate and a less anisotropic flux to the substrate due to more collisions of the ions in the sheath. Increasing the substrate bias has an effect on the energy of the ions bombarding the substrate and to a lesser extent on the magnitude of the ion flux. When source power is increased, it was found that, not the energy, but the magnitude of the ion flux is increased. The etch rate was more influenced by a variation of the substrate bias than by a variation of the source power, at these operating conditions. These results suggest that the etch process is mainly affected by the energy of the ions bombarding the substrate and the magnitude of the ion flux, and to a lesser extent by the magnitude of the radical flux.

This paper is devoted first, to anisotropic distributions of stored electric charges in isotropic materials and second, to charge trapping and induced electrostatic potential in anisotropic dielectrics.

On the one hand, we examine the case of anisotropic trapped charge distributions in linear homogeneous isotropic insulators, obtained after an electron irradiation in a scanning electron microscope. This injection leads to the formation of a mirror image. We first establish the characteristics of the mirror image obtained from such anisotropic distribution by linking the mirror diameter to the curvature tensor of the equipotentials thanks to the geometric optics ansatz (GOA). Second, the equipotentials induced by the presence of an anisotropic charge distribution in such isotropic dielectrics have been determined in the case of homeoidal (ellipsoidal) distributions that generalize the classical spherical distributions. Then, for these homeoidal distributions in isotropic dielectrics, the features of the mirror image have been deduced from the previous GOA estimation. Elliptic mirrors can be obtained and calculated in the limit cases of such homeoidal distributions.

On the other hand, we consider the non-trivial case of a point charge lying at the interface between the vacuum and a linear homogeneous orthotropic anisotropic dielectric and the determination of its corresponding potential seen from the vacuum. This problem has already been solved in the case of transversal isotropic dielectrics (ε_x = ε_y = ε_r, ε_r ≠ ε_z), but we extend in this paper the classical dielectric image problem to the more general case where ε_x ≠ ε_y ≠ ε_z. The equivalent charge and the induced electrostatic potential are evaluated. For these anisotropic insulators, the equipotentials created by a point charge at the interface are found to be ellipsoids and this leads to an elliptic mirror image. The ratio between the two main axis values of the elliptic mirror is proportional to the square root of the ratio of the permittivities values in the plane of the interface. Finally these calculations are used to explain the experimental results obtained by the mirror method on a TiO₂ sample that is known to be an anisotropic dielectric.

With a point-to-plane geometry, the experimental investigation of the current–voltage characteristics in corona discharges demonstrated that existing empirical formulae met with some physical difficulties in explaining the results. By mathematically processing the experimental data and applying the updated knowledge of corona inception, a new general formula in characterizing the relationship of corona current–voltage was derived and expressed as I = K(V − V₀)ⁿ. It was demonstrated that the exponent n falls into a limited scope of 1.5–2.0, and there always exists an optimal exponent n in the scope, which can be determined by maximizing the R-square of regression. Of all the potentially influential factors, it was disclosed that the point radius has the strongest influence on the optimal exponent n, and the effects of ambient conditions and corona polarities are not noticeable. The optimal exponent n holds a fixed value of 2.0 for microscopic points and of 1.5 for large points with a radius in millimetres, but changes decreasingly with the radius for the points of microns. For given experimental conditions, the optimal exponent n almost does not change with the inter-electrode distance. Furthermore, it was demonstrated that the formula is applicable not only for both negative and positive coronas in point-to-plane geometries but also for both polarities in point-to-ring geometries. With the optimal exponent n, the formula can well explain the inconsistencies met by other existing formulae and best represent the characteristics of corona current–voltage with an accuracy of 1 µm.

A theoretical model of surface stress is developed in this paper for a microcantilever with varying widths, and a method for calculating the surface stress via static deflection, slope angle or radius at curvature of the cantilever beam is presented. This model assumes that surface stresses are uniformly distributed on one surface of the cantilever beam. Based on this stressor model and using the small deformation Euler–Bernoulli beam theory, a fourth-order ordinary differential governing equation with varying coefficients or an equivalent second-order integro-differential equation is derived. A simple approach is then proposed to determine the solution of the resulting equation, and a closed-form approximate solution with high accuracy can be obtained. For rectangular and V-shaped microfabricated cantilevers, the dependences of transverse deflection, slope and curvature of the beam on the surface stresses are given explicitly. The obtained results indicate that the zeroth order approximation of the stressor model reduces to the end force model with a linear curvature for a rectangular cantilever. For larger surface stresses, the curvature exhibits a non-linear behaviour. The predictions through the stressor model give higher accuracy than those from the end moment and end force models and satisfactorily agree with experimental data. The derived closed-form solution can serve as a theoretical benchmark for verifying numerically obtained results for microcantilevers as atomic force microscopy and micromechanical sensors.

A planar waveguide is fabricated by 3 MeV O²⁺ ion-implanted in MgO-doped lithium niobate, and the refractive index profiles of waveguides are reconstructed based on etching and ellipsometry techniques. The SRIM2003 code is used to simulate the damage distribution induced by implantation. The etching rate versus the etching depth is extracted and the relation between the etching rate and the damage profile is discussed. The index profile of this kind of waveguide is determined by etching in combination with the following ellipsometric measurements. Both ordinary and extraordinary index profiles in waveguide are obtained. The influence of damage profile on index profiles in waveguide, as well as that on waveguide properties is analysed.

We successfully used the sol–gel method to synthesize crack-free electrochromic (EC) tantalum pentoxide coatings on indium tin oxide glass at room temperatures. Colouring and bleaching states can be reversibly obtained with an applied voltage as low as 3.2 V. The achieved optical density modulation between the two states is estimated to be larger than 15%, which is the highest value among the reported tantalum oxide based EC films to date. Anomalous coloration, which is independent of the polarity of the biased voltage, is observed and explained by the double injection mechanism.

Despite the utility and promise of carbon nanotubes (CNTs), their production is generally based on empirical principles. There are only a few CNT formation models that predict the dependence of their growth on various synthesis parameters. Typically, these do not incorporate a detailed mechanistic consideration of the various processes that are involved during CNT synthesis. We address this need and present a model for catalytic CNT growth that integrates various interdependent physical and chemical processes involved in CNT production. We validate the model by comparing its predictions with one set of experimental measurements from a previous study for cobalt (Co) catalyzed growth. A brief parametric study is presented subsequently. From an application perspective, the model is able to predict the growth rate of the CNT length and its dependence on the ambient temperature and gas-phase feedstock partial pressure.

An ordered array of n-type semiconductor spheres was interfaced with a matrix of p-type material to realize a distributed structure with face-centre-cubic symmetry. Both types have been realized by the use of functionalized single walled carbon nanotubes. The structures lack typical dc junction characteristics because of connectivity between p-type regions. They exhibit nonlinear optical characteristics (ac effect), which was attributed to the quadratic Stark effect.

The dewetting process of spinodally unstable thin film on rough substrates is considered. The theoretical consideration is based on the force model of substrate–film interactions. The competition between spinodal dewetting and dewetting due to substrate roughness is analysed and an analytical solution for the structure of the dewetted film has been discovered. We found conditions where the lateral periodicity of a substrate surface profile is smaller than the critical spinodal wavelength of a film and the roughness of the surface is large enough to initiate dewetting due to substrate roughness; then the dewetted film patterns repeat the substrate structure corresponding to lateral periodicity of a substrate surface profile. In other cases, the film spinodally dewets with a lateral scale close to the dominant spinodal wavelength.

The theory of the dewetting process developed for a model of substrate–film interaction forces was examined by an experimental investigation of the dewetting process of thin polystyrene (PS) films on chemically etched silicon substrates. In the dependence on PS films thickness and silicon roughness, various situations of dewetting were observed as follows: (i) if the wavelength of the substrate roughness is much larger than the critical spinodal wavelength of a film, then spinodal dewetting of the film is observed; (ii) if the wavelength of the substrate roughness is smaller than the critical wavelength of the film and the substrate roughness is larger in comparison with film thickness, then the dewetting due to substrate roughness is observed and the dewetted film patterns repeat the rough substrate structure; (iii) if the wavelength of the substrate roughness is smaller than the critical wavelength of the film and the substrate roughness is small in comparison with the film thickness, then spinodal dewetting proceeds.

ZnO nanoparticles were successfully coated on the surface of carbon nanotubes (CNTs) during the final stage of the growth process of CNTs using radio-frequency plasma enhanced chemical vapour deposition. During the coating process, Zn or ZnO particles with oxygen vacancies can be selectively anchored to the oxygen atom of the oxygen-containing groups on the surface of CNTs and can be perfectly oxidized by active oxygen atoms in the annealing process. The appropriate amount of coated nanoparticles effectively reduces the formation of various structural defects induced by oxygen or hydrogen atoms on the surface of the CNT wall, which can be evaluated through a decrease in the intensity ratio of disorder graphitic band (D peak) over graphitic C–C stretching band (G peak) in the Raman spectrum as well as a distinct decrease in the intensity peak, corresponding to C–H stretching vibration, in the infrared spectrum.

The grain boundary groove shapes for equilibrated solid aminomethylpropanediol, 2-amino-2 methyl-1.3 propanediol (AMPD) with its melt were directly observed by using a horizontal temperature gradient stage. From the observed grain boundary groove shapes, the Gibbs–Thomson coefficient (Γ), solid–liquid interfacial energy (σ_SL) and grain boundary energy (σ_gb) of AMPD have been determined to be (5.4 ± 0.5) × 10⁻⁸ K m, (8.5 ± 1.3) × 10⁻³ J m⁻² and (16.5 ± 2.8) × 10⁻³ J m⁻², respectively. The ratio of thermal conductivity of equilibrated liquid phase to solid phase for the AMPD has also been measured to be 1.12 at the melting temperature.

In-depth thickness mode ultrasonic deformations were monitored by hard (22 keV) x-ray diffraction in Bragg geometry on a Si (1 1 1) crystal. The ultrasonic thickness mode standing wave was applied with a PZT transducer coupled to the Si crystal. Measurements were taken on the time-integrated mode and also at different phases of the ultrasonic excitation in stroboscopic mode. In-depth (2 mm) x-ray stroboscopic measurements on Si showed dynamical strains that were enough to set the crystal out of the diffraction condition. This opens new possibilities for applications such as a stroboscopic gradient x-ray monochromator made out of Si at back-diffraction geometry and stress–strain curve determination of crystals.

Polycrystalline Cd_1−xZn_xTe films were grown on glass substrates over the full range of compositions (0 < x < 1) by metal–organic chemical vapour deposition at 480 °C. The films (∼5 µm thick) showed uniform texture oriented along the ⟨1 1 1⟩ direction, perpendicular to the substrate, independent of the film composition. The dependence of the lattice parameter of cubic Cd_1−xZn_xTe on the composition followed Vegard's law. The thick Cd_1−xZn_xTe films were shown to be of a single phase and structurally stable. The average grain size in the thick films was in the range 3–5 µm. The dominant imperfections in the films were twins (mostly Σ = 3) and dislocations. The x-ray diffraction (XRD) FWHM parameter reached a maximum at x = 0.5. Transmission electron microscopy (TEM) in situ heating in the range 200–400 °C caused plastic deformation in the grains without causing ordering effects. Optical absorption and low-temperature photoluminescence measurements confirmed the XRD and TEM results.

The microstructure of Na_xTi_yNi_1−x−yO (abbreviated as NaTNO), a high dielectric material, has been investigated by scanning electron microscopy. Dielectric dispersion and complex impedance of NaTNO ceramics (in the frequency range 10–10⁷ Hz) are discussed. The relatively lower value of the dielectric constant (ε') of NaTNO compared with those of Li_xTi_yNi_1−x−yO (LTNO) and K_xTi_yNi_1−x−yO (KTNO) is attributed to the typical distinguishing behaviour of its microstructure. Ac impedance spectroscopic studies indicate that the internal barrier layer capacitance effect, arising from differing electrical properties of grains and grain boundaries, is responsible for high dielectric permittivity of this non-ferroelectric material. The ratios of dielectric dispersion strengths, in the low (<100 kHz) and high (>100 kHz) frequency ranges, increase with an increase in the Na content. Deviation of the measured ε' value of NaTNO from that predicted by the boundary layer capacitance mechanism is attributed to its typical microstructure.

The behaviour of electrocontact heating is investigated in a Sn60–Pb40 alloy by using the modified impression technique and dc electric current in the range from 0 to 2.5 A at 298 K. The localized temperature increases with the increase in electric current, and the temperature rise on the surface at thermal equilibrium state is proportional to the square of the electric current. The increase in the temperature is consistent with the results from the finite element simulation, taking account of the effect of the oxide layer and thermal contact resistance on the contact surface. The simulation results show that the thickness of the oxide layer has a strong influence on the thermal equilibrium state of the electrocontact heating. Microstructural observation indicates that the current stressing has no effect on the evolution of microstructures under the experimental conditions.

Calculations within the density functional theory approach were performed to obtain structural parameters, electronic band structure, carrier effective masses and optical absorption spectra in orthorhombic CaPbO₃. Both local density and generalized gradient approximations, LDA and GGA, respectively, were considered. A comparison reveals good agreement of the calculated lattice parameters with experimental results. A direct Γ → Γ one-electron energy band gap of 0.84 eV (0.94 eV) was obtained within the GGA (LDA) level of calculation, in contrast to a previous interpretation of experimental data pointing to a gap of only 0.43 eV. Comparting our results with band gap energies previously obtained for CaXO₃ crystals (X = C in calcite, X = Si in wollastonite and X = Ge,Sn,Pb in the orthorhombic phase), we note that the energy gap oscillates, but with an overall trend to decrease, as the atomic number of the X atomic species increases.

The luminescence properties of Er doped β-Ga₂O₃ and of the erbium gallium garnet Er₃Ga₅O₁₂ (ErGG) have been investigated both in the visible and in the infrared (IR) ranges by means of photoluminescence (PL). Doping of the β-Ga₂O₃ was obtained in two different ways: erbium ion implantation into β-Ga₂O₃ and high temperature annealing of a mixture of Er₂O₃ and Ga₂O₃ powders. X-ray diffraction shows that the latter samples present both β-Ga₂O₃ and ErGG phases. The PL studies demonstrate that the β-Ga₂O₃ in these samples is doped with erbium. The differences in the luminescence emission and excitation peaks of the Er³⁺ ions in these two hosts are studied through selective PL measurements. Strong near IR emission and weak green emission from Er³⁺ in the β-Ga₂O₃ matrix is obtained. The opposite is obtained for Er³⁺ in ErGG when excited under the same conditions. Room temperature luminescence is observed from erbium in the two hosts.

Both BiFeO₃/Bi_3.15Nd_0.85Ti₃O₁₂ (BNdT) bi-layers and BiFeO₃ thin films were grown on Pt/Ti/SiO₂/Si by the sol–gel method. While just a nearly linear dielectric response was observed in the BiFeO₃ film, the BiFeO₃/BNdT bi-layers exhibited a saturated ferroelectric hysteresis loop with a large remanent polarization (2P_r = 72 µC cm⁻²). This 2P_r value is also much higher than that (∼20 µC cm⁻² reported previously) of BNdT films. The large remanent polarization of bi-layers results dominantly from the giant polarization of the BiFeO₃ layer performed under an actual field of 607.4 kV cm⁻¹ when the BNdT layer acts as an insulating barrier, leading to almost a ten times increase in the breakdown field of the BiFeO₃ layer.

The pyroelectric current response is one of the most important features of ferro-piezoelectric materials. The polarization versus temperature curve is the main signature of the phase transitions in these materials. The integration of the thermally stimulated current (TSC) released by polarized samples on increasing T has been used to reproduce the polarization versus temperature behaviour. However, in the TSC current there are contributions coming from sample conductivity, released charges and ferroelectric relaxation, among others, that become more important for high T_c ferroelectrics. In this work a new approach of analysis of the TSC current is proposed to extract the 'true' pyroelectric current arising from the fluctuations of the temperature gradient applied to the sample. This new analysis is first tested with a well-known PZT ceramic and then applied to the study of phase stability and transitions in lead-free ferro-piezoelectric (Na_1−xLi_x)NbO₃ solid solution ceramics with 0 < x ≤ 0.12. Special emphasis is laid on the ferroelectric phase stabilization for the x = 0.5 sample.

Poly(aniline-co-o-anisidine) of copolymer coatings was synthesized on the copper surface (Cu) with two different amounts of p-toluenesulfonic acid (p-TSA) added to the aqueous sodium oxalate (NaOX) solution. The copper substrates in NaOX solutions containing p-TSA acid had a fairly reliable passive surface mainly due to the formation of copper (II) oxalate layer. The addition of p-TSA acid to the working electrolyte contributed to both the amount of copolymer deposition (growth) and that of copolymer coated per unit time of electropolymerization (growth rate). The growth of copolymer coating on Cu electrode was characterized by scanning electron microscopy. The corrosion performances of copolymer coatings were investigated in 3.5% NaCl solution with anodic polarization curves and electrochemical impedance spectroscopy. The results showed that p-TSA acid led to the diminishing of the permeability of the copolymer films. The copolymer coatings exhibited an effective barrier property on copper electrode and a remarkable anodic protection to substrate for longer exposure time.

For the first time, the thermo-emf is calculated in the two-temperatures approximation and taking into account non-equilibrium charge carriers. The results strongly differ from the results obtained in the one-temperature approximation. To emphasize the role played by these non-equilibrium charge carriers, it was considered a very thin semiconductor sample, so recombination processes and energy exchange processes are not present. The thermo-emf generated depends only on electron's parameters and Peltier's resistance appears.

Behaviour of bulk phonons propagating in clathrate compounds based on thiourea has been studied by Brillouin spectroscopy for different polarizations of incident and scattered beams. Elasto-optical coefficients p₁₂, p₁₃, p₄₄ and p₃₁ have been determined for host–guest type crystals. Pressure dependence of the intensity of excitations propagating in a structure of the host–guest type has been studied by the non-invasive method of Brillouin spectroscopy.

Optical and field emission (FE) properties of aligned single-crystalline ZnO nanorods, grown on aluminium substrate at 530 °C by the non-catalytic thermal evaporation process, have been examined. Raman-scattering and room-temperature PL spectra exhibit a strong and sharp optical phonon E₂ mode at 437 cm⁻¹ and a strong ultraviolet emission at 381 nm, respectively. The FE characterization shows that a turn-on field for the vertically aligned nanorods was 5.8 V µm⁻¹ and the emission current density reached to 0.061 mA cm⁻² at an applied electrical field of 9.0 V µm⁻¹ and shows no saturation. The field enhancement factor β was estimated, from the F–N plot, to be about ∼2.081 × 10³.

The effect of post-growth rapid thermal annealing on the optical characteristics of InAsN/InGaAs dot-in-a-well DWELL structures grown by molecular beam epitaxy on GaAs(1 0 0) has been studied. InAs/InGaAs DWELL structures have been used as a reference. Photoluminescence measurements of these samples show similar optical effects, such as a blueshift of the peak wavelength and a reduction of the full width of at half maximum PL emission, in both types of structures up to an annealing temperature of 750 °C. Nevertheless, at 850 °C, these effects are much more pronounced in the structures with N. These results suggest that an additional As–N interdiffusion process inside the InAsN quantum dots plays a dominant role in these effects at high annealing temperatures (850 °C) on InAsN/InGaAs structures.

Noise spectroscopy has been proposed as a means of extracting a more selective response from metallic oxide gas sensors. In this paper, we complete our previous models of adsorption–desorption (A–D) noise by taking into account the effect of the fluctuation of the adsorbed molecule's density, not only on the density of free carriers but also on their mobility. Using Wolkenstein's isotherm, combined with the electroneutrality and the fluctuation of both free electron density and mobility, we derive an exact expression for the A–D noise in the case of dissociative and non-dissociative chemisorption. The model shows that the power density spectrum of the fluctuation of the sensor's conductance has a cut-off frequency and a low frequency magnitude which are specifics of the adsorbed gas. The cut-off frequency is four orders of magnitude lower than the one we obtained without considering mobility fluctuations.

In this paper, a theoretical model is devised for analysing the effects of induced pressure gradients on electroosmotically driven nanopore flows within the continuum regime, without presuming the validity of the Boltzmann distribution of ionic charges. The charge density distributions are obtained from the conservation considerations of the individual ionic species and are subsequently employed to obtain the potential distribution. This is utilized in conjunction with the Navier–Stokes equation, to obtain a closed form expression of the fully developed steady-state velocity profiles within the nanochannel. From the theoretical analysis, it is revealed that channels with more severe electric double layer overlap effects are characterized with more significant impacts of the adverse pressure gradients induced on account of entrance and exit effects. These effects are found to be significantly more prominent for relatively shorter channels, in which case the induced pressure effects are found to be capable of resulting in a reduction in the flow rate even of the order of 10%. Such findings can be of potential importance for an accurate design of electrokinetically actuated nanofluidic systems in which the entrance and exit pressure losses cannot be trivially overruled.

Wave propagation in two-dimensional phononic crystals (PCs) with viscoelasticity is investigated using a finite-difference-time-domain (FDTD) method. The viscoelasticity is evaluated using the Kelvin–Voigt model with fractional derivatives (FDs) so that both the dispersion and dissipation are considered. Numerical approximation of FDs is integrated into the FDTD scheme to simulate wave propagation in such PCs. All the constituent materials are treated as isotropic and homogeneous. The gaps are substantially displaced and widened and the attenuation is noticeably enhanced due to the dispersion and dissipation of host material and the complicated multiple scattering between scatterers. These results indicate that the viscoelasticity of the damping host has significant influence on wave propagation in PCs and should be considered.