Table of contents

ZnO is attracting considerable attention for its possible application to light-emitting sources due to its advantages over GaN. We review the recent progress in the growth of ZnO epitaxial films, doping control, device fabrication processes including etching and ohmic contact formation, and finally the prospects for fabrication and characteristics of ZnO light-emitting diodes.

Micro- and nano-scale devices are used in electronics, micro-electro- mechanical, bio-analytical and medical components. An essential step for the fabrication of such small scale devices is photolithography. Photolithography requires a master mask to transfer micrometre or sub-micrometre scale patterns onto a substrate. The requirement of a physical, rigid mask can impede progress in applications which require rapid prototyping, flexible substrates, multiple alignment and 3D fabrication. Alternative technologies, which do not require the use of a physical mask, are suitable for these applications. In this paper mask-less methods of micro- and nano-scale fabrication have been discussed. The most common technique, which is the laser direct imaging (LDI), technique has been applied to fabricate micrometre scale structures on printed circuit boards, glass and epoxy. LDI can be combined with chemical methods to deposit metals, inorganic materials as well as some organic entities at the micrometre scale. Inkjet technology can be used to fabricate micrometre patterns of etch resists, organic transistors as well as arrays for bioanalysis. Electrohydrodynamic atomisation is used to fabricate micrometre scale ceramic features. Electrochemical methodologies offer a variety of technical solutions for micro- and nano-fabrication owing to the fact that electron charge transfer can be constrained to a solid–liquid interface. Electrochemical printing is an adaptation of inkjet printing which can be used for rapid prototyping of metallic circuits. Micro-machining using nano-second voltage pulses have been used to fabricate high precision features on metals and semiconductors. Optimisation of reactor, electrochemistry and fluid flow (EnFACE) has also been employed to transfer micrometre scale patterns on a copper substrate. Nano-scale features have been fabricated by using specialised tools such as scanning tunnelling microscopy, atomic force microscopy and focused ion beam. The methodologies adopted for nano-fabrication have analogies with the micrometre scale patterning methods. Currently, the resolution of mask-less techniques is lower than that of lithographic methods using a physical mask. However, in future, hybridisation or combination of the mask-less methods could lead to high resolution and higher precision micro- and nano-scale patterning methods.

Magnetic anisotropy and magnetization reversal of Al/Co/V/MgO(0 0 1) thin films have been investigated. The films were fabricated by magnetron sputtering. The roles of both Co and V layers thicknesses have been studied. Magnetic characterization has been carried out by transverse susceptibility (TS) measurements and hysteresis loops. Cobalt is grown in the hcp structure on V with the c axis parallel to the film plane. Two types of hcp Co crystal are grown with the c axes perpendicular to each other. This structure gives rise to a fourfold magnetic anisotropy. When the V layer thickness is below 40 Å a superimposed uniaxial anisotropy develops, the effect of which is a depression in the TS, in agreement with theoretical calculations. This uniaxial anisotropy is induced by the substrate and due to a discontinuous growth of the V layer. For hcp Co grown on V, the magnetic anisotropy rapidly increases with Co layer thickness. In this case, unexpected shifted hysteresis loops along the hard axes were observed when the films were not saturated. This has been explained by taking into account the magnetization reversal along the hard axis: it proceeds via magnetization rotation of some portions of the film at high fields, and by domain wall motion of the rest of the film at lower field values.

Electron drift velocity caused by E × B motion is measured with the help of a Mach probe in a rf planar magnetron sputtering discharge at different powers of 25, 50 and 75 W. Radial variation of the drift velocity is observed at all the powers with the maximum velocity in the racetrack region. The electron temperature and ion density are also found to exhibit radial variation. The drift velocity in the near target region is found to have a higher value than the sheath edge. The sheath structure measured with the help of an emissive probe exhibits radial variation with the strongest electric field in the racetrack region. The maximum extension of the sheath is approximately 2.5 cm from the target. The results of electron drift velocity measurements are explained in terms of the measured variation of the magnetic field and cathode sheath structure. Quite good agreement is observed between the drift velocities measured from Mach probe characteristics and sheath characteristics.

We have investigated the electronic transport properties of resistivity, magnetoresistance and the Hall effect on epitaxial and polycrystalline Fe₃Si thin films. The electrical transport measurements reveal the microstructure which has not been clarified from x-ray diffraction and/or scanning electron microscopy. We show that (1 0 0)-oriented epitaxial film 36 nm thick on MgO(1 1 1) exhibits ferromagnetic-tunnelling conduction, (1 1 0)-oriented epitaxial film 36 nm thick on yttria stabilized zirconia [YSZ(1 1 1)] is in a percolated region, and polycrystalline film 36 nm thick on Al₂O₃(1 1 0) and (1 0 0)-oriented epitaxial film 150 nm thick on MgAl₂O₄(1 0 0) have metallic conduction. These results imply that the electrical transport measurements are a powerful tool for evaluating the microstructure of the samples. The coefficients of the skew and the side-jump scatterings in the extraordinary Hall effect, and the quadratic temperature coefficient of resistivity observed on (1 0 0)-oriented epitaxial film 150 nm thick on MgAl₂O₄ show that Fe₃Si is a ferromagnetic metal where the effective electron mass is slightly enhanced compared with Fe, Co and Ni due to the electron–electron correlation.

A theoretical study of parametric amplification in magnetoinductive waveguides comprising metamaterial elements is presented. It is shown that phase-matching conditions can be satisfied in coupled waveguides by tailoring the dispersion characteristic of magnetoinductive waves. The corresponding formulation for parametric amplification is developed ab initio and analysed for a number of special cases. The problem of loss compensation in metamaterials by means of parametric amplification of magnetoinductive waves is studied in more detail.

FeTaN thin films with uniaxial anisotropy were fabricated by sputtering and patterned into strips with width of 21 µm, separation gap of 10 µm and angular displacement of 0° to 90° from the magnetic easy axis of the unpatterned films. The effective magnetic anisotropy field was effectively modified in both value and direction dependent on the displacement angle. The unpatterned thin films had a maximum permeability of μ'∼700, μ''∼1000 and a ferromagnetic resonance frequency of ∼1.1 GHz. After patterning, the ferromagnetic resonance frequency was found to be ranging from 1 to 1.8 GHz as the angular displacement was varied, indicating that this method is a viable way of tuning the ferromagnetic resonance frequency. These results were well explained according to the well-known Kittel's formula assuming two fold anisotropies in the patterned films.

The influence of swift heavy (180 MeV ¹⁰⁷Ag¹⁴⁺) ion irradiation on Au/n-Si Schottky diode characteristics has been analysed using in situ current–voltage (I–V) characterization. The values of the Schottky barrier height (SBH), the ideality factor and series resistance R_s for each irradiation fluence have been obtained from the forward bias I–V characteristics. For an unirradiated diode, the SBH and ideality factor were 0.74 ± 0.01 eV and 1.71, respectively. The barrier height decreases to 0.69 ± 0.01 eV as the fluence increases to a value of 1 × 10¹¹ ions cm⁻². It is found that after an irradiation fluence of 1 × 10¹¹ ions cm⁻² the SBH remains immune to further irradiation up to a fluence of 5 × 10¹² ions cm⁻². The observed behaviour is interpreted on the basis of energy loss mechanisms of energetic ions at the metal–semiconductor interface and irradiation-induced defects.

The photocurrent generated in single-walled carbon nanotube bundles upon camera flash illumination has been studied under different ambient pressures and light intensities. The results show that the intensity of photocurrent depends closely on the ambient pressure and light intensity. With the ambient pressure reduced, the photocurrent exhibits a logarithmic growth behaviour. Meanwhile, the photocurrent increases with the increase in light intensity. In this work, a dynamic model is employed to unveil the origins of the observed photocurrent. A much smaller lifetime of photocarriers (∼10 ms) is observed than that needed for gas molecular desorption or photodesorption (seconds or longer). Our results are consistent with the model of Schottky barriers being responsible for photocurrent generation.

A series of Al doped ZnO (ZnO : Al) films with different Al concentrations have been deposited on glass substrates using the sol–gel spin coating technique and the effect of Al concentrations on the structural, electrical, optical and photoresponse properties have been investigated. The XRD results show the presence of peaks due to the reflections of the planes from a wurtzite type of ZnO structure. The surface morphology shows that the grains become non-uniform and smaller in size as the Al doping level increases. For 1–2% Al doping, the film attains highest carrier concentration of about ∼2.7 × 10¹⁹ cm⁻³ and lowest resistivity of ∼2 × 10⁻² Ω cm. The excitonic nature in the absorption spectrum disappears for doping above 1%. The band gap increases with the increase in the Al concentration. The photoconductivity studies show that although the photoresponse properties are degraded due to incorporation of Al atoms, the 1% Al doped film shows the best photoresponse properties within the doping limit up to 5%.

High-power laser cutting is extensively used in many industrial applications. An important weakness of this process is the formation of striations (regular lines down the cut surface), which affect the quality of the surfaces produced. The elimination of striation formation is of considerable importance, since it could open up a variety of novel high-precision applications. This study presents the results of oxygen-assisted laser cutting of EN43 mild steel sheets, using a high-power fibre laser. Striation-free laser cuts are demonstrated for cutting 1 and 2 mm thick mild steel sheets. The optimal operating windows are presented and a mathematical method is proposed to estimate the critical speed at which striation-free cut can be obtained.

A new method to extract the angle of refraction data in diffraction enhanced imaging computed tomography (DEI-CT) is proposed in this paper. In this method the projective data of the refractive angle can be extracted from only one set of projective image data with the sample rotational angle range from 0° to 360°. This method not only much simplifies the process in the experiment of DEI-CT but can also get rid of some misalignments between two sets of projective image data with the sample rotational angle range from 0° to 180°, which are taken at the high angle and the low angle of the analyzer crystal, respectively. Using this method, the refractive index and the two derivatives of the refractive index in the plane perpendicular to the rotational axis of the sample can be reconstructed with higher quality than that done by the former ways. Experimental results confirm the new method.

We demonstrate an integral gated mode single photon detector at telecom wavelengths. The charge number of an avalanche pulse rather than the peak current is monitored for single photon detection. The transient spikes in conventional gated mode operation are cancelled completely by integrating, which enables one to effectively improve the performance of single photon detector with the same avalanche photodiode. This method achieved a detection efficiency of 29.9% at the dark count probability per gate equal to 5.57 × 10⁻⁶/gate (1.11 × 10⁻⁶ ns⁻¹) at 1550 nm.

We present an investigation on the magnetoresistance (MR) properties and lateral photoeffect (LPE) of thin Co films deposited on Si substrates with a thin native oxide layer. A marked transition on the transport properties of our films was observed around 250 K. The thinnest Co film exhibits the largest MR of 17.5%. We explain the transport and magnetotransport properties by the conducting channel switching from the upper metallic film to the Si inversion layer. Besides the MR, a large lateral photovoltage which depends in a linear way on the incident light spot position measured on the metallic film was also investigated. The largest open-circuit position sensitivity is 27.6 mV mm⁻¹. The LPE was discussed in terms of metal–semiconductor junction.

Thermal lensing in an end-pumped Tm,Ho:YLF laser crystal has been investigated with a theoretical model of continuous-wave quasi-three-level laser. Considering energy transfer upconversion (ETU) and ground-state reabsorption, the rate equations are given. The influence of ETU on the fractional thermal loading is calculated, and the results show that the latter critically depends on the pump-to-mode size ratio. The temperature distributions of a Tm,Ho : YLF crystal for different pump powers have been analysed. The output power and the focal length of the thermal lens as a function of pump power are obtained in experiment. The experimental results are compared with the theoretical results, and the experimental results show that the theoretical results are reasonable.

Detailed polarized spectral properties of a 3.2 at.% Yb³⁺ : Li₂Gd₄(MoO₄)₇ crystal, including absorption cross-section, emission cross-section, up-conversion spectrum and intrinsic fluorescence lifetime, were investigated. The laser potentiality was also evaluated and the results show that this crystal is a good candidate for tunable and ultrashort pulse lasers.

SF₆ is generally treated as thermally stable and inert for applications below 500 °C. This work investigates the thermal stability of pure SF₆ gas under 1.2 atm pressure between 200 and 450 °C in the presence of construction metals (Cu, Al), without any applied electric field. The obtained experimental results indicate that SF₆ may react with metallic surfaces forming solid and gaseous by-products, either in the gas matrix or diffused in the metallic surfaces. The phenomenon is enhanced in the presence of adsorbed moisture. For copper surfaces, sulfide layers are formed. By-products are not formed for pure Al surfaces. However, when Al is covered by a few micrometres thick Al₂O₃ film, hot SF₆ molecules have a structure change effect, i.e. reduce porosity in the oxide and in the substrate, provide smooth transition layers Al/Al₂O₃ and increase the Al₂O₃ layer width. In the presence of moisture this phenomenon is significantly intensified and a diffused overlayer of AlF₃ also forms. The by-products in the gas matrix are mainly sulfur oxides for hot spot temperatures below 300 °C, while at higher temperatures oxyfluorides SO₂F_x and HF are mainly formed. These by-products are either toxic or corrosive. Thus, the thermal stability issue of SF₆ may have to be reconsidered.

Atmospheric pressure corona discharges are industrially employed to treat large areas of commodity polymer sheets by creating new surface functional groups. The most common processes use oxygen containing discharges to affix oxygen to hydrocarbon polymers, thereby increasing their surface energy and wettability. The process is typically continuous and is carried out in a web configuration with film speeds of tens to hundreds of cm s⁻¹. The densities and relative abundances of functional groups depend on the gas composition, gas flow rate and residence time of the polymer in the discharge zone which ultimately determine the magnitude and mole fractions of reactive fluxes to the surface. In this paper, results are discussed from a two-dimensional computational investigation of the atmospheric pressure plasma functionalization of a moving polypropylene sheet in repetitively pulsed He/O₂/H₂O discharges. O and OH typically initiate surface processing by hydrogen abstraction. These species are regenerated during every plasma pulse but are also largely consumed during the inter-pulse period. Longer-lived species such as O₃ accumulate over many pulses and convect downstream with the gas flow. Optimizing the interplay between local rapid reactions, such as H abstraction which occurs dominantly in the discharge zone, and non-local slower processes, such as surface–surface reactions, may enable the customization of the relative abundance of surface functional groups.

Absolute total dissociation cross sections, σ_t,diss, by electron-impact are reported for CHF₃ and C₃F₈ from 10 to 300 eV using the chemical gettering technique described by Winters and Inokuti (1982 Phys. Rev. A 25 1420). Data are concentrated in the near-threshold region (10–30 eV). The thresholds for dissociation of CHF₃ and C₃F₈ are determined to be 10.4 eV and 11.9 eV, respectively. Ionization thresholds occur at 16 eV for CHF₃ and 16.2 eV for C₃F₈. Neutral dissociation cross sections of both CHF₃ and C₃F₈ are obtained by subtracting the ionization cross sections, σ_t,ion, from the total dissociation cross sections, σ_t,diss.

Measurements are presented of the time resolved cathode and anode falls of high frequency fluorescent lamps for a range of discharge currents typically encountered in dimming mode. Measurements were performed with the movable anode technique. Supporting spectroscopic emission measurements were made of key transitions (argon 420.1 nm and mercury 435.8 nm), whose onset coincide with cathode fall equalling the value associated with the energy, relative to the ground state, of the upper level of the respective transition. The measurements are in general agreement with the well-known understanding of dimmed lamp operation: peak cathode fall decreases with increasing lamp current and with increasing auxiliary coil heating. However, the time dependence of the measurements offers additional insight.

A two-dimensional arc magnetohydrodynamic model is presented to study the effects of metallic vapour and gassing material on air switching arc motion based on different mixture plasma properties (pure air, 99% air–1% Cu, 99% air–1% Ag, 99% air–1% Fe, 90% air–10% PA6). It demonstrates that metallic vapours may cool the arc central region and reduce the arc motion velocity, and iron vapours have the strongest action compared with copper and silver vapours; the gassing material may improve the arc motion velocity. In addition, the effect of the net emission coefficient model and the grey body radiation model on the calculation results for pure air arc motion is compared. To verify the simulation results partially, using the integrated imaging diagnostics system, experiments are carried out to measure the average velocity of arc motion with one model chamber.

This paper presents the results of an experimental study of rf capacitive discharge in low-pressure SF₆. The rf discharge in SF₆ is shown to exist not only in weak-current (α-) and strong-current (γ-) modes but also in a dissociative δ-mode. This δ-mode is characterized by a high degree of SF₆ dissociation, high plasma density, electron temperature and active discharge current, and it is intermediate between α- and γ-modes. The δ-mode appears due to a sharp increase in the dissociation rate of SF₆ molecules via electron impact starting after a certain threshold value of rf voltage. At the same time the threshold ionization energy of SF_x (x = 1–5) radicals formed is below the ionization potential of SF₆ molecules. The double layer existing in the anode phase of the near-electrode sheath is shown to play an important role in sustaining the α- mode as well as the δ-mode but it is not a cause of the rf discharge transition from α- to δ-mode.

The first corona inception in a divergent electric field is affected by atmospheric parameters. The effect of humidity is a little-debated question and a summary review is first proposed in this paper. Then we present experimental results performed in two different high voltage laboratories. Those two laboratories are located at different latitudes (Germany and northern Argentina) in order to put in evidence the effect of humidity on the inception voltage. At high humidity levels, the standard deviation of the probability distributions is clearly reduced whereas the influence of humidity upon the mean values is made up by quite a large discrepancy in the data. Nevertheless, the critical volume model allows the experimental probability distributions to be calculated with the proviso that the negative ion density directly involved in the primary electron production rate is field dependent and not constant as previously assumed. The calculations show that the total negative ion density is exponentially linked to the humidity.

The dynamics of high energetic electrons (⩾11.7 eV) in a modified industrial confined dual-frequency capacitively coupled RF discharge (Exelan, Lam Research Inc.), operated at 1.937 MHz and 27.118 MHz, is investigated by means of phase resolved optical emission spectroscopy. Operating in a He–O₂ plasma with small rare gas admixtures the emission is measured, with one-dimensional spatial resolution along the discharge axis. Both the low and high frequency RF cycle are resolved. The diagnostic is based on time dependent measurements of the population densities of specifically chosen excited rare gas states. A time dependent model, based on rate equations, describes the dynamics of the population densities of these levels. Based on this model and the comparison of the excitation of various rare gas states, with different excitation thresholds, time and space resolved electron temperature, propagation velocity and qualitative electron density as well as electron energy distribution functions are determined. This information leads to a better understanding of the dual-frequency sheath dynamics and shows, that separate control of ion energy and electron density is limited.

The dependence of the electron density and the mean ion energy relative to the ground electrode on the driving frequency (13.56–156 MHz) is investigated in capacitively coupled argon plasmas. It is found that at constant rf power, the electron density increases with the driving frequency then starts to level off after reaching some transition frequency. When the driving frequency exceeds this transition frequency, almost all rf power is spent on electron heating and the electron density remains unchanged even when the frequency continues to increase. The measured data is compared with the results from an inhomogeneous plasma model. The variations of the measured electron density and mean ion energy are found to be consistent with the scaling between the electron heating and the ion acceleration power and their dependence on driving frequency, as obtained earlier by Godyak.

Investigations on ion transport properties of new Ag⁺ ion conducting electroactive solid polymer electrolyte (SPE) membranes (1 − x)PEO: x[0.7(0.75AgI : 0.25AgCl): 0.3MI] (M ≡ Rb, K), where x = 0 < x < 50 wt (%), are reported. A novel hot-press/solvent-free dry technique has been used for complexing/dissolving the salts into the PEO polymeric host. The two complexing salts [0.7(0.75AgI : 0.25AgCl): 0.3MI], recently investigated at the present laboratory, are the solid-solution-synthesized quaternary superionic solids in the polycrystalline phase which exhibited Ag⁺ ion conductivity σ ∼ 10⁻³ S cm⁻¹ at room temperature. The compositional (x) dependent conductivity (σ) studies identified the composition 70PEO : 30[0.7(0.75AgI : 0.25AgCl) : 0.3MI] as the optimum conducting composition (OCC) SPE films. σ-enhancement of approximately three orders of magnitude could be achieved in both OCC SPEs at room temperature from that of the pure polymeric host: PEO. To explain the σ-increase in OCC SPE films, ionic mobility (μ) has been determined experimentally at room temperature using the d.c. polarization transient ionic current (TIC) technique and, subsequently, the mobile ion concentration (n) has been evaluated from σ and μ data. The ionic transference number (t_ion) in OCC SPEs has been estimated from the TIC 'current–time' plot and, hence, the ionic drift velocity (v_d) has been evaluated. The phase identification and material characterization studies on both OCC SPEs have been done by XRD, SEM and DTA techniques. The temperature dependent studies on the ionic parameters, namely σ, μ, n, t_ion, v_d, provided a deeper insight to understand the ion conduction phenomenon in OCC SPEs along with the information regarding energies involved in different thermally activated processes. Thin film SPE batteries have been fabricated using the two OCCs: 70PEO: 30[0.7(0.75AgI : 0.25AgCl): 0.3RbI]; 70PEO: 30[0.7(0.75AgI : 0.25AgCl): 0.3KI] as electrolytes, sandwiched between the Ag-metal foil anode and the hot-pressed cathode film: (C + I₂ + SPE) in 1 : 1 : 1 wt (%). The cell potential discharge performances have been studied at room temperature under varying load conditions.

A hard anodization (HA) technique was employed using different mixtures of sulfuric/oxalic acid for fabrication of highly self-ordered alumina nanopore arrays. The sulfuric acid concentration was changed from 0.005 to 0.05 M and the anodization voltage was changed from 60 to 140 V. An optimum self-ordering was achieved in a wide range of interpore distances from 130 to 270 nm. For each mixture, there was a region of anodization voltage in which the self-ordering took place. The width of this region decreases with increasing sulfuric acid concentration. In these regions, the optimum voltages with the best self-ordering versus the sulfuric acid concentration follow a second order exponential decay function. Our investigations show that current–time characteristics at optimum anodization voltages were identical for all mixtures. For each electrolyte mixture, the interpore distance was dependent upon the anodization voltages with proportionality constants of 2.1 nm V⁻¹ and 2.2 nm V⁻¹ for high and low voltages, respectively. The porosity of the samples (about 3.5%) follows the porosity rule of HA.

Transparent conductive Dy-doped zinc oxide thin films have been deposited on glass substrates by pulsed laser deposition technique. The effects of post-deposition annealing treatment on structural, electrical and optical properties of the ZnO : (Dy) thin films were investigated. The films show high transparency and conductivity. Van der Pauw measurements reveal that the films are n-type degenerate semiconductors. The electrical resistivity of the films deposited at 300 °C is 2.74 × 10⁻⁴ Ω cm with a carrier density of 9.33 × 10²⁰ cm⁻³ and a Hall mobility of 24.48 cm² V⁻¹ s⁻¹. The resistivity can be further reduced to as low as 2.12 × 10⁻⁴ Ω cm by post-deposition annealing at 420 °C for 2 h in nitrogen. Post-annealing increased the grain size and surface roughness of the films. The average transmission of the ZnO : (Dy) films (with a thickness about 529 nm) in the visible range is above 80%. The optical direct band gap value of the films is about 3.7 eV, which is slightly dependent on the annealing treatment in nitrogen.

Carbon nanotubes will have extensive application in all areas of nano-technology, and in particular in the field of nano-fluidics, wherein they can be used for molecular separation, nano-scale filtering and as nano-pipes for conveying fluids. In the field of nano-medicine, nanotubes can be functionalized with various types of receptors to act as bio-sensors for the detection and elimination of cancer cells, or be used as bypasses and even neural connections. Modelling fluid flow inside nanotubes is a very challenging problem, since there is a complex interplay between the motion of the fluid and the stability of the walls. A critical issue in the design of nano-fluidic devices is the induced vibration of the walls, due to the fluid flow, which can promote structural instability. It has been established that the resonant frequencies depend on the flow velocity. We have studied, for the first time, the flow of viscous fluids through multi-walled carbon nanotubes, using the Euler–Bernoulli classical beam theory to model the nanotube as a continuum structure. Our aim has been to compute the effect of the fluid flow on the structural stability of the nanotubes, without having to consider the details of the fluid–walls interaction. The variations of the resonant frequencies with the flow velocity are obtained for both unembedded nanotubes, and when they are embedded in an elastic medium. It is found that a nanotube conveying a viscous fluid is more stable against vibration-induced buckling than a nanotube conveying a non-viscous fluid, and that the aspect ratio plays the same role in both cases.

Ferroelectric domains have been investigated on the cross-section of Pb(Zr_0.55Ti_0.45)O₃ (PZT) thin film capacitors by scanning probe microscopy. The static domain images on the cross-section were obtained by the lateral piezoresponse force microscopy (LPFM) method, in which the ac voltage used to induce the converse piezoelectric effect was applied between the conductive tip and the bottom electrode. The polarization component normal to the substrate could be characterized via both d₃₃ and d₁₅ piezoelectric coefficients, which resulted in a high resolution of LPFM images. After a variable dc bias was applied between the top and the bottom electrodes, the variations of domain image on the cross-section were recorded by the LPFM immediately. Upon the application of low bias, new domain sites appeared near the PZT/Pt interface opposite to the initial polarization. Forward stretch of new domains was facilitated under the dc field approaching the coercive field E_c. Under a very high field (about three times of the E_c), the sidewise expansion of columnar domains was observed. However, the domains were only partially switched even though a very high field was applied. The observed domain growth process indicated a lower energy barrier for nucleation compared with that of domain wall motion. Possible reasons for the incomplete switching are the substantial influences of the interface and depolarization in thin film capacitors.

Zirconium oxynitride films were deposited onto glass and Si (1 0 0) substrates at room temperature by pulsed reactive dc magnetron sputtering of a metallic Zr target in an Ar/O₂/N₂ atmosphere. The structural, compositional and optical properties of the deposited films were found to depend on the ratio of nitrogen partial pressure to the total reactive gas partial pressure. Morphology investigation by atomic force microscopy showed that most of the zirconium oxynitride coatings have smooth surfaces (average roughness 2.5 nm). X-ray diffraction measurements revealed a change from the monoclinic zirconium oxide phase to the orthorhombic, and then a change to the cubic zirconium nitride phase upon changing the nitrogen content in the films. Optical properties of zirconium oxynitride films were analysed by a spectrophotometer and computer simulations. The calculated refractive index of transparent and semi-transparent films was found to be in the range 2.05–4.73 (at 650 nm). The optical band gap changed from 3.67 to 1.59 eV with changing nitrogen content. This study allows the elaboration process optimization and then the control of the film composition and properties, which is very interesting for a technological transfer.

Nanocomposite thin films containing Au nanoparticles embedded in a partially oxidized Si matrix were synthesized by the atom beam co-sputtering technique. Transmission electron microscopy studies revealed formation of Au nanoparticles in as-deposited films. The size distribution of Au nanoparticles was tailored by varying the metal fraction in the nanocomposite films. Increasing the metal fraction has been found to result in the formation of Au nanoparticles with a relatively narrower size distribution. The processes involving irradiation with energetic sputtered atoms arriving at the substrate are considered in nucleation and growth of Au nanoparticles at room temperature. The advantages of atom beam sputtering over ion implantation and ion beam mixing are also discussed.

The main features of ultra-short laser ablation of various materials (metals, semiconductors or insulators) have been studied through the complementary analyses of the plasma plume induced by laser irradiation, and of the deposited films. The generation of nanoparticles (in the 10–100 nm range) was observed and these findings were investigated in order to obtain information on the relevant parameters governing the formation of these nanoparticles. By the use of polyatomic targets, the non-congruent formation of nanoparticles was evidenced, demonstrating the existence of complex phenomena (phase separation, chemical reactions and interaction with the residual gas) during the laser–matter interaction and plasma expansion. An unexpected finding was the influence of the laser beam spot size on nanoparticle emission during femtosecond laser ablation. The comparison of these results with the currently admitted explanations of ultra-short laser–matter interactions clearly indicates that the existing models and simulations do not describe or explain the overall phenomena taking place during femtosecond laser ablation, and another approach has to be envisaged including the influence of the parameters evidenced in this work.

Asymmetrical properties of ion transport have been found in single conical nanopores and partly charged nano-channels. Recently, nanofluidic diodes based on this novel phenomenon have been fabricated. To generally understand the mechanism of the ionic current rectification, we study the ionic electric behaviours in several kinds of nanopores based on Poisson–Nernst–Planck equations. The calculated results show that for a partly charged nanopore, the geometry of the uncharged section, which might have been overlooked previously, has a substantial influence on current rectification. In addition, surface charge distribution is also an influential factor in current rectification. In particular, for a long homogeneously charged conical nanopore, the electrical and geometric properties of the section near the nanopore tip with a length of hundreds of nanometres are mainly responsible for the ionic current rectification. This result is consistent with the results of recent experiments on nanofluidic diodes.

This paper describes a study on the surface potential decay of corona charged low density polyethylene (LDPE) films. A conventional corona charging process is used to deposit charge on the surface of film and surface potential is measured by a compact JCI 140 static monitor. The results from corona charged multilayer sample reveal that the bulk process dominates charge decay. In addition, the pulsed-electro-acoustic (PEA) technique has been employed to monitor charge profiles in corona charged LDPE films. By using the PEA technique, we are able to monitor charge migration through the bulk. Charge profiles in corona charged multilayer sample are consistent with surface potential results. Of further significance, the charge profiles clearly demonstrate that double injection has taken place in corona charged LDPE films.

In this work, the microhardness of plasma sprayed Al₂O₃ coatings was evaluated using the Vickers indentation technique, and the effects of measurement direction, location and applied loads were investigated. The measured data sets were then statistically analysed employing the Weibull distribution to evaluate their variability within the coatings. It was found that the Vickers hardness (VHN) increases with decreasing applied indenter load, which can be explained in terms of Kick's law and the Meyer index k of 1.93, as well as relating to the microstructural characteristics of plasma sprayed coatings and the elastic recovery taking place during indentation. In addition, VHN, measured on the cross section of coatings, was obviously higher than that on its top surface. The obtained Weibull modulus and variation coefficient indicate that the VHN was less variable when measured at a higher applied load and on the cross section of coating. The obvious dependence of the VHN on the specific indentation location within through-thickness direction was also realized. These phenomena described above in this work were related to the special microstructure and high anisotropic behaviour of plasma sprayed coatings.

The effect of sequential additions of Co₃O₄, Sb₂O₅ and CaCO₃ on the microstructure and electrical behaviour of SnO₂-based ceramics was investigated. Although without conferring varistor properties, Co₃O₄ additions promote densification in the material. Successive addition of Sb₂O₅ provides the sample varistor properties but with low nonlinearity coefficient (α = 5.7) and high electric field (E₁ = 2022 V cm⁻¹) at current density 10⁻³ A cm⁻³. Moreover, antimony oxide addition degrades the microstructure condition by inducing porosity. Subsequent addition of CaCO₃ promotes densification and grain growth. However, it does not lead to the increase in the nonlinearity coefficient. It only lowers the electric field, thus making the material suitable for lower voltage applications. Observed significant increase in the relative dielectric permittivity up to a factor of about 60 and 200 in the cases of antimony or antimony and calcium addition to SnO₂–Co₃O₄ (accompanied by the appearance of varistor effect) is due to the formation of barrier depletion layers at grain boundaries.

Spallation of materials induced by laser driven shock waves is generally produced under uniaxial (one-dimensional (1D)) deformation by irradiating a spot of diameter much greater than the sample thickness. Here, two-dimensional (2D) effects are introduced in shock wave propagation by drastically reducing the loaded spot. Experiments performed on aluminium samples detect the effect of lateral wave propagation, both on recovered samples and on time-resolved VISAR measurements. Damage zones are localized completely differently from that under uniaxial condition, according to the presence of 2D effects, and the signature of these 2D effects can be read on VISAR signals. Numerical simulations provide a full understanding of wave propagation and resulting damage in 1D or 2D configuration. Comparisons with experimental VISAR signals show the possibility of validating more accurately the dynamic damage criteria, including the 2D effects.

Local piezoresponse of individual grains in polycrystalline Pb_0.9125La_0.0975(Zr_0.65Ti_0.35)_0.976O₃ (PLZT 9.75/65/35) relaxor ceramics is studied using the scanning probe microscopy (SPM) technique. The observed piezoelectric contrast consisting of irregular (labyrinth-type) polarization patterns is attributed to the compositional disorder and consequent charge imbalance caused by high La concentration. A measure of this disorder, the polarization correlation length ξ, is directly determined using an autocorrelation analysis function implemented in the SPM software. The analysis of the obtained images shows that ξ taken at the scale ∼200 nm varies as a function of the position inside the grain notably decreasing upon approaching the grain boundary. As a result, the average correlation length taken over the entire grain is apparently dependent on the grain size saturating at about 2 µm. The obtained dependences are consistent with both the mechanical stress effect of impinging grains and the composition gradient in the PLZT grain and allows for better understanding of the dielectric properties of disordered ferroelectrics.

The important role of the anisotropy of elastic and piezoelectric properties in the relaxor-ferroelectric 0.93Pb(Zn_1/3Nb_2/3)O₃–0.07PbTiO₃ single crystal poled along [0 1 1] of the perovskite unit cell has been stated in connection with the formation of the piezoelectric response of the 2–2-type piezo-active composites based on this single crystal. Different examples of the 2–2 single crystal/polymer and 2–2–0 single crystal/porous polymer composites have been studied in this work. Based on the non-monotonic volume fraction and orientation dependences of effective piezoelectric coefficients and figures of merit of the 2–2-type composites, we have shown their advantages. These advantages are associated with a presence of high piezoelectric activity and sensitivity, with variations of the effective piezoelectric coefficients , , and within wide ranges along with signs of the piezoelectric coefficients of the 0.93Pb(Zn_1/3Nb_2/3)O₃–0.07PbTiO₃ single crystal. Experimental values measured by Zhang et al (2006 Appl. Phys. Lett.89 242908) obey the condition sgn that has a considerable influence on the piezoelectric performance and hydrostatic parameters of the studied 2–2 and 2–2–0 composites.

A series of Fe₂YSi (Y = Cr, Mn, Fe, Co, Ni) alloys were synthesized and their electronic and magnetic properties were studied both theoretically and experimentally. In particular, a novel Heusler alloy Fe₂CrSi single phase was synthesized by means of the melt-spinning method. First principles FLAPW calculations were performed on Fe₂YSi alloys. Based on the results, Fe₂CrSi is predicted to be a half-metallic ferromagnet with a spin moment of 2μ_B/f.u. and a gap of 0.42 eV. Fe₂MnSi is also half-metallic in the ferromagnetic state. The saturation magnetic moments at 5 K for this series of alloys fit the theoretical calculations well. Specifically, the saturation magnetic moment of Fe₂CrSi is 2.05μ_B/cell, which agrees with the ideal value of 2μ_B derived from the Slater–Pauling rule. The Curie temperatures of Fe₂YSi alloys are all higher than 500 K except for Fe₂MnSi, which has a T_C below room temperature. Finally, the effect of lattice distortion on the electronic and magnetic properties of Fe₂CrSi and Fe₂CoSi was studied. It is found that Fe₂CrSi is half-metallic from −3% to +1% uniform lattice distortion, and this character is preferred in systems containing large strain, such as melt-spun ribbons or thin films.

A polycrystalline ceramic of Sr₂SbMnO₆ (SSM) was fabricated using the powders obtained by the conventional solid-state reaction route. The dielectric measurements of the ceramic were carried out as a function of frequency (100 Hz–10 MHz) and temperature (190–360 K). SSM exhibited higher relative permittivity (∼2 × 10⁵ for 1 kHz at 360 K) than that for the recently known high permittivity ceramic CaCu₃Ti₄O₁₂ (CCTO). It decreased to a relatively low value (∼2 × 10³ for 1 kHz) on decreasing the temperature down to 195 K. The modified Cole–Cole equation that included the conductivity term was used to describe the dielectric spectra of the ceramic. Impedance spectroscopy was employed to determine the electrical parameters (resistance, capacitance and relaxation time) of the grain and the grain boundary. The grain and grain boundary conduction and the dielectric relaxation time followed an Arrhenius law associated with activation energies of 0.22 eV, 0.35 eV and 0.24 eV, respectively. Nearly equal activation energies for dielectric relaxation and grain conduction revealed a possibility of invoking a common mechanism to rationalize the permittivity data. The capacitance and resistance associated with the grain boundary were found to be higher than that associated with the grain to a great extent. The incidence of giant relative permittivity and the other experimental findings support the Maxwell–Wagner type of mechanism.

There are several techniques which combine atomic force microscopy with ultrasonics. In atomic force acoustic microscopy the cantilever is forced to ultrasonic vibrations while the tip is in contact with a sample surface. The various physical forces acting between the tip and the surface depend nonlinearly on the distance. Therefore linear approximations are restricted to tip–sample displacements covering small parts of the interaction force curve. This situation is realized for example at high static loads and small amplitudes of the cantilever and the sample surface vibrations. The nonlinearity of the forces becomes noticeable by generation of higher harmonics in the spectrum of the cantilever vibration. A frequency dependent transfer function can be derived from the model of the cantilever as a beam with constant cross-section using the differential equation for flexural vibrations. By multiplying the transfer function with experimental spectra the nonlinear contact and adhesion forces were calculated as a function of time. In situ measurements of the cantilever and the sample vibrations by a calibrated heterodyne Mach–Zehnder interferometer are presented. This allowed us to reconstruct the tip–sample interaction forces as a function of tip–sample distance.

A limitation on the extinction cross section, valid for all scatterers satisfying some basic physical assumptions, is investigated. The physical limitation is obtained from the holomorphic properties of the forward scattering dyadic. The analysis focuses on the consequences for materials with negative permittivity and permeability, i.e. metamaterials. From a broadband point of view, the limitations imply that there is no fundamental difference between metamaterials and ordinary materials with respect to scattering and absorption. The analysis is illustrated by three numerical examples of metamaterials modelled by temporal dispersion.

Using a combination of Drude and critical points models, we show that the permittivity of several metals can be more efficiently described than using the well-known Drude–Lorentz model. The numerical implementation in a finite-difference time-domain code together with a non-uniform grid enables the study of thin metallic intermediate layers often neglected in simulations but found in realistic resonant structures.

We investigate the influence of flaws on phonon transport and thermal conductance in a dielectric quantum wire. At extremely low temperatures, phonons are multiply scattered elastically by the flaws. We show that the main physical peculiarity of the phonon transfer in wires is due to the special features of phonon spectrum in the low-frequency region. A comparison between the thermal conductances is made when two typical flaws, longitudinal flaws (LF) or transverse flaws (TF), are introduced into acoustic phonon transport leads. It is found that (i) the behaviour of the thermal conductance versus temperature is qualitatively different for different types of flaws with the same area and (ii) the thermal conductance depends sensitively on the length L of TF, while the quantum wire with LF exhibits small quasi-periodic oscillatory thermal conductance behaviour.

Fluorescence sensitization of a 2,2'-([1,1'-biphenyl]–4,4'-diyldi-2,1-ethenediyl)-bis-benzenesulfonic acid disodium salt (Stilbene 3) solution in ethanol (EtOH) due to the presence in aqueous solution of ammonia is reported here. In this study sensitization of the dye solution due to the presence of ammonia was observed. It was also found that the observed sensitization is dynamic in nature. Sensitization of the fluorescence of the indicator also has full reversibility. An optical sensor for the detection of ammonia could thus be constructed using these properties of the dye and the sensitizer.