Table of contents

Using an electron microprobe, we measured and characterized the Nd³⁺ ion diffusion across a boundary between Nd doped and undoped ceramic yttrium aluminium garnet (YAG) for different temperature ramps and hold times and temperatures. The results show significant Nd ion diffusion on the order of micrometres to tens of micrometres depending on the time and temperature of sintering. The data fit well a model including bulk diffusion, grain boundary diffusion and grain growth. Grain boundary diffusion dominates and grain growth limits grain boundary diffusion by reducing the total cross-sectional area of grain boundaries.

We fabricate transparent MgAl₂O₄ nano-ceramics, which are composed of 40 nm grains, by sintering under high pressure and low temperatures. Analysis of the grain size, differential strains, yield strength and porosity obtained from transmission electron microscopy and x-ray diffraction indicates that the pores at the grain boundary triple junctions can retard grain boundary migration and thus prevent grain growth. It is found that the relatively high density for MgAl₂O₄ nano-ceramics produced at low-temperature and high pressure is attributed mainly to the large energy in the grain exteriors. The decrease in the transparency with increasing temperature (>700 °C) is therefore a result of the light scattering at large pores. On the basis of these results, we propose a mechanism of transparency in MgAl₂O₄ nano-ceramics.

This work comprises a new dc plasma application in the metallurgical–mechanical field, called plasma assisted heat treatment, and it presents the first results for annealing. Annealing treatments were performed in 90% reduction cold-rolled niobium samples at 900 °C and 60 min, in two different heating ways: (a) in a hollow cathode discharge (HCD) configuration and (b) in a plasma oven configuration. The evolution of the samples' recrystallization was determined by means of the microstructure, microhardness and softening rate characterization. The results indicate that plasma species (ions and neutrals) bombardment in HCD plays an important role in the recrystallization process activation and could lead to technological and economical advantages considering the metallic materials' heat treatment application.

During the last two decades atmospheric (or high) pressure non-thermal plasmas in and in contact with liquids have received a lot of attention in view of their considerable environmental and medical applications. The simultaneous generation of intense UV radiation, shock waves and active radicals makes these discharges particularly suitable for decontamination, sterilization and purification purposes. This paper reviews the current status of research on atmospheric pressure non-thermal discharges in and in contact with liquids. The emphasis is on their generation mechanisms and their physical characteristics.

The growth of reactively sputtered TiN films is discussed. First, an overview of the existing models in the literature that describe the development of the orientation and microstructure is given. Then, these models are critically confronted with the results of experiments published in the literature and performed by the authors. The latter experiments focus especially on the determination of the energy flux and atomic N/Ti flux towards the substrate and lead to the conclusion that these fluxes towards the substrate play a key role in the growth of the TiN films. This relation between these fluxes and the microstructure of the TiN films gives further evidence to the previously published extended structure zone model.

Ferromagnetic microtubes are fabricated by the deterministic release of thin magnetic films from a photoresist sacrificial layer. Crucial steps towards the fabrication of well positioned and uniform single rolled-up tubes are presented, where the final and main approach consists of releasing angled deposited magnetic films by dissolving an underlying patterned photoresist layer. Microtubes from soft magnetic Ni₈₀Fe₂₀ films and Co/Pt multilayer stacks with perpendicular magnetic anisotropy are obtained with predefined lengths and diameters down to 1.5 µm. The nonlinear rotational dynamics of the tubes in viscous fluids is investigated. Sensitivities to viscosity variations for tubes with different lengths are observed and suggest their potential application as single sensing probes in a wide range of viscosities. Moreover, the variation in the characteristic critical frequency of the rotational motion for chains of magnetically coupled microtubes agrees with the expected changes in the theoretical shape factor of cylindrical particles. Evidence of tube remagnetization during the rotation opens the way to investigate properties such as the switching fields of individual tubes.

The ferromagnetically coupled cobalt ion is observed to create a magnetocrystalline anisotropy in the PrNi_5−xCo_x structure above a critical composition of x = 2. The competition of the anisotropy energies between Co and Pr sublattices gives rise to a spin reorientation (SR) phenomenon in PrNi_5−xCo_x compounds at a low temperature (∼150 K) which is then followed by a magnetic transition at a higher temperature. Co-doping has a strong influence on the Curie temperature, changing it from ∼60 K (x = 1.95) to ∼537 K (x = 3). The magnetic entropy change is associated with SR as well as a magnetic transition, and correspondingly a large full width at half maximum (δT_FWHM) is obtained for this series of compounds. For example, the PrNi_2.85Co_2.15 compound presents δT_FWHM = 166 K at a 1 T field. This series therefore has an appreciable relative cooling power, which makes this material a suitable magnetic refrigerant over a large temperature span.

The system consisting of a magnetophotonic crystal (MPC) and a medium with negative permittivity was studied both experimentally and theoretically. The medium was prepared as a set of conductive wires—wire medium (WM). The MPC elementary cell comprises three layers (air, ferrite and quartz). The Tamm state (TS) position in a stop band was calculated depending on the thickness of the air layer in an MPC elementary cell and on the value of the WM negative permittivity. Using the experimental value of the TS frequency the inverse problem was solved and the effective permittivity of the WM bounding the MPC was obtained.

Well-dispersed Fe₃O₄ nanocrystals were synthesized by a simple hydrothermal method. The as-synthesized products were characterized by field emission scanning electron microscopy, transmission electron microscopy, selected area electron diffraction, x-ray diffraction, vibrating sample magnetometer and vector network analysis. The complex permittivity and permeability of paraffin wax and Fe₃O₄ with different Fe₃O₄ volume fractions were measured to increase linearly with the increase in the volume fraction of Fe₃O₄. The magnetic loss was caused mainly by natural resonance, which is in good agreement with the Kittel equation results. When the matching thickness is 3 mm, the calculated reflection loss reaches a maximum value of −21.2 dB at 8.16 GHz with 30% volume fraction of Fe₃O₄.

High-quality cobalt nanowires have been grown by focused-electron-beam-induced deposition (FEBID) and their magnetic and transport properties determined. The nanowires contain up to about 95% Co atomic percentage, as measured by EDX spectroscopy, which remarkably represents a high value compared with other metal deposits grown by the same technique. The Co content has been found to correlate with the beam current used for the growth. The magnetotransport properties have been studied on individual nanowires through 4-probe measurements. For the nanowires with the highest Co content, the resistivity at room temperature is low (∼40 µΩ cm), and shows metallic temperature dependence. The magnetotransport properties clearly demonstrate the ferromagnetic nature of the nanowire, with a saturation magnetization of M_s = 1329 ± 20 emu cm⁻³, very close to the bulk one. Due to the local character of this type of growth at targeted places and its high lateral resolution, these results pave the way for the creation of magnetic nanostructures and devices with the full potentiality of high-quality Co.

The local setting of magnetic anisotropy by low fluence Co ion implantation in amorphous magnetic thin films is demonstrated. For a wide range of ion fluences no structural changes occur and the adjustment of anisotropy is reversible. A quantitative relationship between the anisotropy change and the atomic displacements is found. Magnetic domain investigations of the purely magnetically patterned stripes reveal an effective quasi-cubic anisotropy below a critical width for orthogonal magnetic anisotropy alignment. The method of ion-annealing allows for a local setting of anisotropy without irreversible structural and magnetic alterations.

We report a new kind of high sensitivity magnetic sensor based on a tilted cross-junction which combines both the planar Hall effect (PHE) and magnetoresistance (MR) to enhance the sensitivity and linearity of the sensor. The sensitivity of this hybrid sensor is enhanced by about 30% when the cross-junction is tilted at an angle of 45° compared with a normal cross sensor junction. In this case, a sensitivity of 9.5 µV Oe⁻¹ is reached. Systematic investigations on the role of PHE and MR revealed that the transverse PHE component is always constant with tilt angle variations and it dominates the linearity of the hybrid sensor whereas the longitudinal MR component was the reason for improving the sensor sensitivity. The obtained results of the tilted cross-junction were described successfully using the first order approximation of the Stoner–Wohlfarth energy term.

Electromagnetic (EM) wave absorption properties of the paraffin–Fe(Mn)/ferrite nanocapsule composite (with 40 wt% nanocapsules) were investigated in the 2–18 GHz frequency range. The Fe(Mn)/ferrite nanocapsules synthesized by arc-discharging have a core–shell structure with cores 10–30 nm in diameter and shells about 5 nm in thickness. The reflection loss (RL) calculated from the measured permittivity and permeability was found to exceed −20 dB in the 13–15 GHz range for a thickness of about 1.75–1.95 mm. The optimal RL is −28.2 dB at about 14 GHz with 1.84 mm thickness. RL values exceeding −10 dB were obtained for the absorber of 1.7 mm thickness in the range 12.7–17.1 GHz, which almost covered the whole Ku-band (12.4–18 GHz). The excellent EM wave absorption properties of the Fe(Mn)/ferrite nanocapsules significantly depend on the core–shell microstructure and the match of dielectric and magnetic losses.

Mn-doped CuCrO₂ polycrystalline semiconductors were synthesized by the sol–gel method. The valence state of the Mn ions in the CuCr_1−xMn_xO₂ samples was identified as 3+ by analysing their lattice parameters, their electrical properties and their x-ray photoelectron spectra. The temperature dependence of the susceptibility of all samples exhibits paramagnetic behaviour at high temperature. For x = 0.20 the samples exhibit a clear ferromagnetic (FM) transition at 120 K. Clear hysteresis loops indicate that FM order exists in the Mn-doped samples at 50 K. All samples behave like semiconductors. The electrical and magnetic properties indicate that the ferromagnetism can be attributed to the double exchange interaction between the Mn³⁺ and Cr³⁺ in CuCr_1−xMn_xO₂ semiconductors.

We report the high temperature transport and thermoelectric properties of Ca_1−xR_xMnO₃(R = La, Y and Ce) perovskites in the electron-doped range. The substitution of different valence ions has a similar effect on the thermoelectric properties of this system. Resistivity and thermopower change regularly as the enhancement of doping level; they are both determined mainly by electron concentration. Thermal conductivity is dependent mainly on the weight of R ions, and it decreases monotonically with increasing doping content. The optimal electron concentration is around 0.1–0.12 for thermoelectric performance; in this range the ZT value of Ca_0.9La_0.1MnO₃ exceeds 0.12 at 1000 K, exhibiting a good high temperature thermoelectric applied potential. Besides, the hopping nature of the charge carriers is well explained in the framework of polaron theory. The high temperature thermopower values which are inconsistent with nominal Mn³⁺ ion configuration are also discussed.

A large reversible magnetocaloric effect over a wide temperature region has been observed in the compound Dy₂In. For a magnetic-field change of 5 T, the maximum magnetic-entropy change −ΔS_M is 9.2 J kg⁻¹ K⁻¹ at 126 K. The full width at half maximum (δT_FWHM) of the −ΔS_M versus T curve has a high value of 80 K and the relative cooling power (RCP) is as high as 736 J kg⁻¹ with no hysteresis losses. In particular, a large reversible −ΔS_M (4.6 J kg⁻¹ K⁻¹), large δT_FWHM (50 K) and large RCP (230 J kg⁻¹) are also achieved for a low field change of 2 T. Therefore, Dy₂In may be an interesting material for low-temperature magnetic refrigeration.

V-doped anatase TiO₂ films were fabricated by a non-vacuum liquid phase deposition (LPD) technique on glass substrates. All as-prepared films are amorphous, which are highly crystallized to be anatase TiO₂ after air or vacuum annealing at 600 °C. A nanocrystal structure with a grain size of about 10 nm was confirmed by XRD and high resolution transmission electron microscopy (HRTEM). It is found that in the LPD process, the in situ substitution of Ti by V ions occurred, and V atoms were distributed very uniformly in the TiO₂ matrix. The air-annealed V_0.025Ti_0.975O₂ samples are paramagnetic, while the vacuum annealed samples clearly exhibit room-temperature ferromagnetism (FM) with a magnetic moment of 1.1 μ_B/V. Our results unambiguously show that oxygen vacancies play a critical role in generating FM in doped TiO₂ and an F-centre mechanism for diluted FM is confirmed.

We model effective energy landscapes of a multispin Co nanoparticle with fcc internal structure, cubic magnetocrystalline anisotropy and truncated octahedral shape, varying the strength of the Néel surface anisotropy. The results show the increment of the effective anisotropy (defined through the energy barriers) due to the presence of surface anisotropy. Large surface anisotropy values are shown to change the sign of the cubic anisotropy and to induce a strong second cubic anisotropy constant. Numerically evaluated energy barrier values are fitted to the experimentally measured ones in Co nanoparticles with various cappings. The deduced local values of surface anisotropy are of the order of ∼0.4J–0.7J, where J is the exchange parameter.

The wave number of transverse spatial structures in broad-area vertical-cavity surface-emitting lasers (VCSELs) is controlled via frequency-selective feedback from an external self-imaging cavity in a broad range of wave numbers and emission frequencies. The selected states follow the dispersion curves of the free-running laser. A control range of about 2.5 µm⁻¹ in spatial frequency space and 2.5 nm in emission wavelength was obtained for square VCSELs and of about 3 µm⁻¹ and 8 nm for circular VCSELs having a different dispersion curve. By spatial filtering in Fourier space, the shape of the structures can also be controlled to some extent. It is argued that the feedback techniques are useful to 'probe' emission states of the free-running laser.

In an organic bulk-heterojunction (BHJ) solar cell there is a constant electric field (V_bi − V)/d (where V_bi is the built-in voltage, V is the applied voltage and d is the sample thickness) in the active layer. Current–voltage (J–V) characteristics of an organic BHJ solar cell based on a blend of poly(3-hexylethiophene) (P3HT) and phenyl [6,6] C₆₀ butyric acid methyl ester (PCBM) have been modelled by solving drift and diffusion equations taking into account the constant electric field. We fabricated the BHJ solar cells and measured their J–V characteristics. A comparison of the observed characteristics with theory shows excellent agreement. The diffusion component of the current dominates for V < V_bi and the current is not space charge limited.

The spectroscopic properties of Er³⁺/Yb³⁺ co-doped 50SiO₂–10Al₂O₃–20ZnF₂–20SrF₂ glass and glass ceramic containing SrF₂ nanocrystals were investigated. The formation of SrF₂ nanocrystals in the glass ceramic was confirmed by XRD. The oscillator strengths for several transitions of the Er³⁺ ions in the glass ceramic have been obtained and the Judd–Ofelt parameters were then determined. The XRD result and Judd–Ofelt parameters suggested that Er³⁺ and Yb³⁺ ions had efficiently enriched in the SrF₂ nanocrystals in the glass ceramic. The lifetime of excited states has been used to reveal the surroundings of luminescent Er³⁺ and Yb³⁺ and energy transfer (ET) mechanism between Er³⁺ and Yb³⁺. Much stronger upconversion luminescence and longer lifetime of the Er³⁺/Yb³⁺ co-doped glass ceramic were observed in comparison with the Er³⁺/Yb³⁺ co-doped glass, which could be ascribed to more efficient ET from Yb³⁺ to Er³⁺ due to the enrichment of Yb³⁺ and Er³⁺ and the shortening of the distance between lanthanide ions in the precipitated SrF₂ nanocrystals.

Er³⁺ doped Ni–Si–O compounds deposited by the magnetron sputtering technique are investigated. Compared with the optimized photoluminescence (PL) of Er³⁺ in Si-rich Si oxide, the PL of Er³⁺ in the compounds is strikingly enhanced in the ranges 500–900 nm and 1470–1650 nm. This enhancement and the appearance of many sharp peaks around 1.54 µm in the spectra depend on the Ni content and the annealing temperature. Two-order enhancement in the range 1470–1650 nm is achieved for the Ni–Si–O compound with 25 at.% Ni after 1150 °C annealing. The above experiments indicate that Ni induces new local environments around Er³⁺, which are responsible for PL enhancement and appearance of sharp peaks.

We report on an experimental study of the charge transfer dynamics in a P3HT : PCBM blend by means of a femtosecond fluorescence up-conversion technique. Using two-photon excitation we probe the exciton dynamics in P3HT and a P3HT : PCBM blend with a weight ratio of 1 : 1 at excitation densities of up to 6 × 10¹⁸ cm⁻³. In both samples we find strongly nonexponential decay traces compatible with (i) diffusion-limited exciton–exciton annihilation and (ii) diffusion-limited donor–acceptor charge transfer in the polymer blend. Additionally, our results indicate that in the P3HT : PCBM blend about 50% of the photogenerated excitons undergo a prompt charge transfer process on a time scale of about 150 fs. Our study shows that fluorescence spectroscopy with femtosecond time resolution is a powerful technique for probing ultrafast charge transfer processes in solar cell materials.

Multi-wavelength second-harmonic generation in an aperiodic poled LiTaO₃ superlattice was studied. By fitting the measured data of phase-matching wavelengths and temperatures, the temperature-dependent Sellmeier equation of the LiTaO₃ crystal has been determined. This work provides a new method to measure the refractive index of the nonlinear crystal and its dispersion and therefore, is of benefit to the study of the quasi-phase-matching technique.

We report on the implementation of InGaN/GaN-based light-emitting diodes (LEDs) structures on Si(1 1 0) oriented substrates grown by metal–organic vapour phase epitaxy. The total thickness of the completely crack-free device structures on Si(1 1 0) substrates amounts to 2.5 µm exhibiting a comparable or even better layer quality than identical LED structures grown on standard Si(1 1 1) substrates. This result can be explained by a more suited epitaxial relation between the c-plane of the high-temperature AlN seed layer and the Si(1 1 0) surface. The crystallographic structure of the LEDs was analysed by x-ray diffraction and the optical properties were investigated by photo- and electroluminescence. The improved crystallographic quality on Si(1 1 0) goes in line with a higher peak intensity in the photoluminescence measurements. Furthermore, a bright bluish light emission at 490 nm is obtained by an electrical excitation at room temperature.

The effects of strain on the conduction mechanism in heterostructures consisting of strained nano-thin 3C–SiC films on Si are reported. These films exhibit significantly different electrical behaviours than the bulk material. Strained nano-thin 3C–SiC films were grown on n-type Si substrates by gas source molecular beam epitaxy. Reflection high-energy electron diffraction patterns show that these films are about 3% strained relative to the SiC lattice constant. In order to investigate the electrical properties of thin film structures, Al, Cr and Pt contacts to a nano-thin film 3C–SiC were deposited and characterized. The I–V measurements of the strained nano-thin films demonstrate back-to-back Schottky diode characteristics and the band offsets due to the biaxial tensile strain introduced within the 3C–SiC films were calculated and simulated. Based on the experimental and simulation results, an empirical model for the current transport in the heterostructures based on strained nano-thin films has been proposed. It was found that due to the band alignment of this structure, current is constrained at the surface which allows use of nano-thin films as surface sensors.

Distributed Bragg reflectors (DBRs) based on chalcogenide glasses showing stopbands in the near-infrared range were designed and fabricated by thermal evaporation combined with the oblique angle deposition technique. This technique allows the deposition of alternate thin films of predetermined optical constants, leading to the fabrication of multilayer structures of tailored optical behaviour based entirely on a single glass composition. Moreover, exploratory work has been performed by determining the spectral shift of the DBRs due to chemical infiltration within their nanoporosity. These promising experimental results suggest that the chalcogenide-based reflectors can be used in the field of chemical sensing.

Novel phosphorus-doped and undoped single crystal ZnO nanotetrapods were fabricated on sapphire by a simple chemical vapour deposition method, using phosphorus pentoxide (P₂O₅) as the dopant source. The optical properties of the samples were investigated by photoluminescence (PL) spectroscopy. Low-temperature PL measurements of phosphorus-doped and undoped samples were compared, and the results indicated a decrease in deep level defects due to the incorporation of a phosphorus acceptor dopant. The PL spectrum of the phosphorus-doped sample at 10 K exhibited several acceptor-bound exciton related emission peaks. The effect of phosphorus doping on the optical characteristics of the samples was investigated by excitation intensity and temperature dependent PL spectra. The acceptor-binding energies of the phosphorus dopant were estimated to be about 120 meV, in good agreement with the corresponding theoretical and experimental values in phosphorus-doped ZnO films and nanowires.

We present photocurrent power-enhancement calculations of a carbon nanotube p–n junction electromagnetically coupled to a highly efficient photonic structure. Particular attention is paid to a GaAs photonic structure specifically modified to increase the intensity of infrared light onto the nanotube region for effective energy conversion. Using finite-difference time-domain calculations, we compute a significant increase in electric field intensity in the nanotube region which enables an estimation of power efficiency. These results demonstrate the potential of using a photonic structure to couple large-scale infrared sources with carbon nanotubes while still retaining all the unique optoelectronic properties found at the nanoscale.

The resistive switching characteristics of MnO_x thin film were investigated for resistive random access memory (ReRAM) applications. The devices in the form of metal–insulator–metal structure exhibited reversible resistive switching behaviour under both sweeping voltages and voltage pulses. Formation and rupture of conductive filaments were proposed to explain the resistive switching. When Al was used as the top electrode instead of Pt, the device had a better endurance performance. Additionally, the Pt/MnO_x/Al device showed fast switching speed and long retention ability. The experiment result suggested that Pt/MnO_x/Al device had a potentiality for practical memory application.

An Yb³⁺: YAl₃(BO₃)₄/YAl₃(BO₃)₄ composite is obtained by the segmented crystal growth method. Diode-pumped laser operation is demonstrated in the 2.0 mm thick, (0 0 1)-oriented composite with a 0.8 mm thick, 9.5 at% Yb³⁺ : YAl₃(BO₃)₄ crystal segment. Under the absorbed pump power of 11.9 W, quasi-continuous-wave output powers of 0.82 W with a slope efficiency of nearly 20% and of 0.3 W with a slope efficiency of 10.5% around 1040 nm are achieved in hemispherical and plano–plano cavities, respectively.

A waveguide amplifier with a large core was fabricated by the vapour transport method, which allows the dense dispersion of DCM into the PMMA plate inhibiting its aggregation. The cladding layer of the amplifier was formed by the dispersal of organofluorine compounds with a low refractive index. Amplification of the signal beam at 650 nm was observed upon top pumping with a pulsed laser at 488 nm. The gain of the amplifier was 3.76 dB cm⁻¹ at the maximum and was one order of magnitude greater than that of a fibre optical amplifier.

We demonstrate efficient white organic light-emitting devices (WOLEDs) based on an orange phosphorescent iridium complex bis(2-(2-fluorphenyl)-1,3-benzothiozolato-N, C^2')iridium(acetylacetonate) in combination with blue phosphorescent dye bis[(4, 6-difluorophenyl)-pyridinato-N,C²)](picolinato) Ir(III) and red phosphorescent dye bis[1-(phenyl)isoquinoline] iridium (III) acetylanetonate. By introducing a thin layer of 4, 7-diphenyl-1,10-phenanthroline between blue and red emission layers, the diffusion of excitons is confined and white light can be obtained. WOLEDs with the interlayer all have a higher colour rendering index (>82) than the device without it (76). One device has the maximum current efficiency of 17.6 cd A⁻¹ and a maximum luminance of 39 050 cd m⁻². The power efficiency is 8.7 lm W⁻¹ at 100 cd m⁻². Furthermore, the device has good colour stability and the CIE coordinates just change from (0.394, 0.425) to (0.390, 0.426) with the luminance increasing from 630 to 4200 cd m⁻².

The electroluminescent properties in red organic light-emitting diodes (OLEDs) doped with polar and non-polar red emitting molecules were studied. The emission chrominance changed from red to orange along with the increase in the bias voltage in the devices doped with polar molecules; however, the emitted colour in the devices doped with non-polar molecules was unaffected by the bias voltage and the viewing angle. The reason was assumed to be the orientation of polar molecules under the electric field, so that non polar molecule is the optimum candidate for red emitting dopants used in red OLEDs to obtain stable chrominance.

We investigate and compare optical absorption, luminescence and scintillation properties of Pr-doped Y₃Al₅O₁₂, Lu₃Al₅O₁₂, Y₂SiO₅ and Lu₂SiO₅ single crystals. The processes determining the kinetics of the fast Pr³⁺ 5d–4f radiative transition are described. Among the studied host materials, only Lu₃Al₅O₁₂ presents neither any 5d₁–4f luminescence state nonradiative quenching nor Pr³⁺ ionization at room temperature. We evaluate the figure of merit of all materials for application as scintillators. The most promising system appears to be Lu₃Al₅O₁₂ : Pr, since it combines an elevated density of 6.67 g cm⁻³, a fast scintillation response dominated by a 21 ns decay time and a spectrally corrected light yield about 160% with respect to that of Bi₄Ge₃O₁₂ (BGO).

The pulsed chemical oxygen–iodine laser (COIL) development is aimed at many new applications. Pulsed electric discharge is most effective in turning COIL operation into the pulse mode by instant production of iodine atoms. A numerical model is developed for simulations of the pulsed COIL initiated by an electric discharge. The model comprises a system of kinetic equations for neutral and charged species, electric circuit equation, gas thermal balance equation and the photon balance equation. Reaction rate coefficients for processes involving electrons are found by solving the electron Boltzmann equation, which is re-calculated in a course of computations when plasma parameters changed. The processes accounted for in the Boltzmann equation include excitation and ionization of atoms and molecules, dissociation of molecules, electron attachment processes, electron–ion recombination, electron–electron collisions, second-kind collisions and stepwise excitation of molecules. The last processes are particularly important because of a high singlet oxygen concentration in gas flow from the singlet oxygen chemical generator. Results of numerical simulations are compared with experimental laser pulse waveforms. It is concluded that there is satisfactory agreement between theory and the experiment. The prevailing mechanism of iodine atom formation from the CF₃I donor in a very complex kinetic system of the COIL medium under pulse discharge conditions, based on their detailed numerical modelling and by comparing these results both with experimental results of other authors and their own experiments, is established. The dominant iodine atom production mechanism for conditions under study is the electron-impact dissociation of CF₃I molecules. It was proved that in the conditions of the experiment the secondary chemical reactions with O atoms play an insignificant role.

Precise etch depth control of ultra-thin HfO₂ (3.5 nm) films applied as a gate oxide material was investigated by using atomic layer etching (ALET) with an energetic Ar beam and BCl₃ gas. A monolayer etching condition of 1.2 Å/cycle with a low surface roughness and an unchanged surface composition was observed for ultra-thin, ALET-etched HfO₂ by supplying BCl₃ gas and an Ar beam at higher levels than the critical pressure and dose, respectively. When HfO₂-nMOSFET devices were fabricated by ALET, a 70% increase in the drain current and a lower leakage current were observed compared with the device fabricated by conventional reactive ion etching, which was attributed to the decreased structural and electrical damage.

The theoretical performance of a planar microscale ion generation device is analysed using the direct simulation Monte Carlo (DSMC) technique. The discrete motion and interactions of electrons and ions are modelled for atmospheric air as represented by N₂ and O₂. The ionization threshold of the device in air is found to be 70 V because of the effects of molecular excitations that reduce the energy of the free electrons and the nature of the collision cross sections. Additionally, microscale planar ionization devices are revealed to be inherently inefficient because of the loss of electrons and ions to the dielectric boundary. A multiscale simulation of the electrohydrodynamics is also conducted by extracting the ion–neutral interactions from the DSMC calculations and integrating them into a continuum-scale fluid dynamics model. The multiscale simulations show that the ion–neutral body force distribution for the planar devices is concentrated on the face of the cathode and therefore limits the impact of the force on the flow. A scale analysis confirms that the body force distribution is insufficient to induce high flow rates at this scale.

The density of neutral nitrogen atoms in a glass reactor was measured by two absolute methods: two-photon absorption laser induced fluorescence (TALIF) and catalytic probes. The source of N atoms was nitrogen plasma created in a quartz tube by surfatron microwave generator operating at 2.45 GHz and adjustable output power up to 300 W. The TALIF measurements were performed using a dye laser which was pumped by a YAG laser. At the exit of the dye laser, the beam frequency was doubled through a KDP crystal and then mixed in a BBO crystal. The wavelength of the output laser beam was chosen at 206.65 nm so two-photon absorption was suitable to excite nitrogen atoms from the ground state to the 5d ²D state. Absolute N density was determined by using calibration with krypton. Simultaneously, the N atom density was measured with a fiber optics catalytic probe (FOCP) with a well-activated iron catalytic tip. Measurements were performed by both methods at nitrogen flows between 0.2 and 2 l min⁻¹, and discharge powers between 60 and 300 W. At rather high nitrogen flows, the N atom density increased monotonically with increasing discharge power, while at lower flow saturation was observed. TALIF showed somewhat higher values than FOCP which was attributed to the accuracy of both methods. The main advantage of TALIF is a broader detection range, while FOCP is an extremely simple and inexpensive technique.

The ion saturation current to a spherical probe immersed into a plasma of high-pressure gas comprising two types of atoms is considered. Calculations were made for recombination controlled plasma in a wide range of R/L (ratio of probe radius to ionization length) from R/L ≪ 1 to R/L ≫ 1 and in a wide range of degrees of ionization. Electropositive ions are considered. Numerical results were obtained for high-pressure argon–hydrogen plasma with arbitrary argon–hydrogen composition. Temperature was considered constant throughout the near-probe plasma. Unlike the common presentation of the results of the calculations in graphical form, we present our results in the form of analytical expressions, which approximate the numerical results with reasonable accuracy. These analytical approximations allow an experimentalist to interpret the results of the measurements relatively easily. In the case of one sort of ions, the analytical approximation has an especially simple form. In the last section of the paper, the thermal layer around the probe is considered. It has been shown that the suggested formulae can be used, provided the plasma temperature is sufficiently high.

We investigated the interactions of atomic and molecular chlorine with plasma-conditioned stainless steel surfaces through both experiments and modelling. The recombination of Cl during adsorption and desorption of Cl₂ was characterized using a rotating-substrate technique in which portions of the cylindrical substrate surface are periodically exposed to an inductively coupled chlorine plasma and then to an Auger electron spectrometer in separate, differentially pumped chambers. After several hours of exposure to the Cl₂ plasma, the stainless steel substrate became coated with a Si-oxychloride-based layer (Fe : Si : O : Cl ≈ 1 : 13 : 13 : 3) due to chlorine adsorption and the erosion of the silica discharge tube. Desorption of Cl₂ from this surface was monitored through measurements of pressure rises in the Auger chamber as a function of substrate rotation frequency. Significant adsorption and desorption of Cl₂ was observed with the plasma off, similar to that observed previously on plasma-conditioned anodized aluminium surfaces, but with much faster desorption rates that are most likely attributable to the smoother and non-porous stainless steel surface morphology. When the plasma was turned on, a much larger pressure rise was observed due to Langmuir–Hinshelwood recombination of Cl atoms. Recombination coefficients, γ_Cl, ranged from 0.004 to 0.03 and increased with Cl-to-Cl₂ number density ratio. This behaviour was observed previously for anodized aluminium surfaces, and was explained by the blocking of Cl recombination sites by adsorbed Cl₂. Application of this variable recombination coefficient to the modelling of high-density chlorine plasmas gives a much better agreement with measured Cl₂ percent dissociations compared with predictions obtained with a recombination coefficient that is independent of plasma conditions.

Recently several investigators reported on various means of generating cold plasma jets at atmospheric pressure. More interestingly, these jets turned out to be not continuous plasmas but trains of small high velocity plasma packets/bullets. However, until now little is known of the nature of these 'bullets'. Here we present experimental insights into the physical and chemical characteristics of bullets. We show that their time of initiation, their velocity and the distance they travel are directly dependent on the value of the applied voltage. We also show that these bullets can be controlled by the application of an external electric field. Using an intensified charge coupled device camera we report on their geometrical shape, which was revealed to be 'donut' shaped, therefore giving an indication that solitary surface ionization waves may be responsible for the creation of these bullets. In addition, using emission spectroscopy, we follow the evolution of various species along the trajectory of the bullets, in this way correlating the bullet propagation with the evolution of their chemical activity.

To precisely control the dielectric constant and the structure of a low-k SiOC film, we have developed a neutral-beam-enhanced chemical vapour deposition (NBECVD) method. Using Ar NBECVD, we can precisely control the dielectric constant and the film modulus of low-k SiOC deposited on Si substrates because this method avoids precursor dissociation that results from electron collisions and UV photons in plasma. Optimizing the ratio between Si–O and Si–(CH₃)_x as well as the proportions of linear (two-dimensional SiOC), network and cage (three-dimensional SiOC) structures by changing the precursor, we obtained a k value of 2.2 and a reasonable modulus by using dimethyl dimethoxy silane as a precursor. Additionally, the NBECVD process is applicable as a method for damage-free super-low-k film deposition on the underlying low-k film that is sensitive to damage by the plasma.

Gas phase and reactor wall-surface kinetics are coupled in a global model for SF₆ plasmas. A complete set of gas phase and surface reactions is formulated. The rate coefficients of the electron impact reactions are based on pertinent cross section data from the literature, which are integrated over a Druyvesteyn electron energy distribution function. The rate coefficients of the surface reactions are adjustable parameters and are calculated by fitting the model to experimental data from an inductively coupled plasma reactor, i.e. F atom density and pressure change after the ignition of the discharge. The model predicts that SF₆, F, F₂ and SF₄ are the dominant neutral species while and F⁻ are the dominant ions. The fit sheds light on the interaction between the gas phase and the reactor walls. A loss mechanism for SF_x radicals by deposition of a fluoro-sulfur film on the reactor walls is needed to predict the experimental data. It is found that there is a net production of SF₅, F₂ and SF₆, and a net consumption of F, SF₃ and SF₄ on the reactor walls. Surface reactions as well as reactions between neutral species in the gas phase are found to be important sources and sinks of the neutral species.

The threshold for microwave corona breakdown in a rectangular cavity is investigated using a direct variational approach. Good accuracy of the results is verified by a comparison with a full numerical solution of the relevant eigenvalue problem determining the breakdown threshold equation. The importance of the interplay between diffusion and attachment in setting the breakdown threshold is discussed. A comparison with experimental results shows very good agreement.

We report results from a combined optical interferometric and spectrally resolved imaging study on colliding laser produced aluminium plasmas. A Nomarski interferometer was used to probe the spatio-temporal distribution of electron densities at the collision front. Analysis of the resulting interferograms reveals the formation and evolution of a localized electron density feature with a well-defined profile reminiscent of a stagnation layer. Electron stagnation begins at a time delay of 10 ns after the peak of the plasma generating laser pulse. The peak electron density was found to exceed 10¹⁹ cm⁻³ and the layer remained well defined up to a time delay of ca 100 ns. Temporally and spectrally resolved optical imaging was also undertaken, to compare the Al⁺ ion distribution with that of the 2D electron density profile. This revealed nascent stagnation of singly charged ions at a delay time of 20 ns. We attribute these results to the effects of space charge separation in the seed plasma plumes.

We consider a continuous optical discharge (COD) sustained by a weakly focused CO₂ laser beam and stabilized by a cold gas flow incident in the direction of the laser radiation propagation. We develop and examine a two-dimensional radiative gas-dynamic model for COD which uses realistic quasi-optics and takes refraction of the laser radiation in the plasma properly into account in describing the laser beam propagation. The model is applied to calculate the parameters of COD in the air flow as functions of the laser power and inlet velocity of the incident flow.

Two-temperature thermodynamic and transport properties of argon–hydrogen and nitrogen–hydrogen plasma mixtures are presented, chemical equilibrium being achieved. The calculations of transport properties are carried out using the Chapman–Enskog method up to the third order; when electron temperature differs from that of heavy particles, calculations are performed following both a recent two-temperature theory by Rat et al that retains the coupling between electrons and heavy particles and a simplified decoupling theory proposed by Devoto. No relevant discrepancies between results obtained using these two approaches have been found, allowing the simplified method of Devoto to be still used in the computation of non-equilibrium transport properties like thermal conductivity, electrical conductivity and viscosity, with the exception of some diffusion coefficients. Results for composition, mass density, specific heat, thermal conductivity, electrical conductivity and viscosity of atmospheric pressure plasmas in the electron temperature range 300–40 000 K are reported.

A constructive approach to the theory of diffusion processes is proposed, which is based on application of both symmetry analysis and the method of modelling functions. An algorithm for construction of the modelling functions is suggested. This algorithm is based on the error function expansion (ERFEX) of experimental concentration profiles. The high-accuracy analytical description of the profiles provided by ERFEX approximation allows a convenient extraction of the concentration dependence of diffusivity from experimental data and prediction of the diffusion process. Our analysis is exemplified by its employment in experimental results obtained for surface diffusion of lithium on the molybdenum (1 1 2) surface precovered with dysprosium. The ERFEX approximation can be directly extended to many other diffusion systems.

This paper studies the surface instability of an elastic thin solid film lying on a rigid substrate and subjected to van der Waals-like surface interactions. The effect of film–substrate interfacial slippage is accounted for by using a simplified linear cohesive interface model. It is found that the interfacial slippage generally plays a destabilizing role in the surface instability of the thin film. For highly compressible films with Poisson's ratio smaller than 0.25, the surface wrinkling behaviour previously inconceivable in the case of a perfectly bonded interface is now feasible if film–substrate interface slipping is permitted. In addition, our linear perturbation analysis shows that the critical conditions for the onset of surface instability can be modulated by adjusting the slippery stiffness of the interface. The result might be helpful for developing novel techniques to create micro-/nanosized surface patterns.

This paper introduces a novel method for fabricating copper (Cu) oxide/activated carbon fibre (ACF) through the aerosol palladium (Pd) activation for use in electroless Cu deposition and heat treatment of Cu deposited ACF with nitric monoxide (NO) gas injection. Electroless Cu deposition was initiated by catalytically activating the ACF surface with spark generated Pd aerosol nanoparticles. The catalytically activated ACF was placed into a solution used for the electroless Cu deposition. Subjecting the Cu deposited ACF to a heat treatment in a NO/nitrogen (N₂) gas injection (1000 ppm NO) resulted in changes to the morphology of the Cu particles. As the temperature increased from 100 to 500 °C, the relative mass fraction of oxygen in the Cu particles increased from 3.6% to 14.2% and the fraction of Cu decreased from 41.2% to 34.1%, which was caused by the formation of Cu oxides (Cu₂O and CuO). The corresponding surface area and pore volume of the ACF decreased from 1019 m² g⁻¹ to 401 m² g⁻¹ and from 0.40 cm³ g⁻¹ to 0.18 cm³ g⁻¹, respectively. The morphological evolution and decrease in porosity were attributed to volume expansion of Cu particles during oxidation.

We have achieved in situ magnesium doping into nanocrystalline cubic boron nitride thin films during sputter deposition. It was clarified, through x-ray diffraction, Fourier transform infrared spectroscopy and x-ray photoelectron spectroscopy, that less than 1 at% magnesium doping does not significantly affect the growth of the cubic phase. Magnesium-doped films deposited in pure argon showed electric conductivity up to 10⁴ times higher than the undoped film. Although the Hall voltage was not reproduced reliably for most of the cases, the films containing 2.1 at% magnesium clearly revealed p-type conduction with carrier concentration and mobility of 4 × 10¹⁴ cm⁻³ and 6 cm² V⁻¹ s⁻¹, respectively, at 380 K. It was also found that the increase in electric conductivity with magnesium concentration was accompanied by the decrease in the relative amount of nitrogen in the film.

We have found that liquid crystal (LC) can be aligned on an inkjet printed and air-buffed polyimide (PI) surface. Surface anisotropy is introduced by inkjet printing and air blowing from a PI ink cartridge and an empty cartridge of an inkjet printer, respectively. LC molecules align on the PI surfaces with the nano-scale grooves, which are validated with atomic force microscope images. The pretilt angles of the LCs could be varied from 0° to 90°, by controlling the composition of a mixture of homogeneous and homeotropic PIs.

We investigated the temperature-dependent transport properties of Pt/Nb-doped SrTiO₃ junctions, exhibiting rectifying and hysteretic behaviours. The conventional Schottky diode model failed to explain the current–voltage characteristics, since the estimated Richardson constant was too small. The temperature dependence of the barrier height and the ideality factor showed that the inhomogeneous barrier model described the experimental data well. The estimated interfacial potential fluctuation was dependent on the resistance states. This suggested that the spatial inhomogeneity could affect the resistive switching phenomena.

In the linearized hydrodynamic model metallic single-wall carbon nanotubes (SWCNTs) are assumed to be free electron gas layers. By considering the friction force due to the interaction of surface plasmon waves propagating along the metallic SWCNTs and graphite lattice we generalized the results on calculating the dispersion relation of SWCNTs with linearized hydrodynamic model. We obtained a more accurate dispersion relation and investigated the friction force dependence of dispersion relations for transverse magnetic and transverse electric propagations of two azimuthal modes.

We demonstrate the essential principles for performing a novel form of metastable-atom microscopy, namely focusing and scanning of a He 2³S beam. A magneto-optical lens, in conjunction with time-varying magnetic field components, has been used to scan a beam of He 2³S atoms across a sample surface in a manner analogous to other scanning probe techniques. The instrument developed is the first to apply methods in the laser manipulation of atoms specifically to the study of surfaces. With the lens in its current arrangement, a beam of He 2³S atoms with an intensity of ∼6 × 10¹² atoms s⁻¹ cm⁻² may be directed anywhere within a sample area of ∼64 mm² at a focal distance of 1.4 m and with a focal spot full-width at half-maximum of <2 mm. Such control over the intensity and position of the He 2³S beam greatly benefits the surface analysis technique of metastable de-excitation spectroscopy, as demonstrated with example spectra from a clean Si(1 1 1) 7 × 7 surface.

La_0.05Tb_0.95MnO₃/La_0.67Sr_0.33MnO₃/SrTiO₃ heterojunctions were fabricated by laser molecular-beam epitaxy. Dielectric properties as functions of temperature (77–320 K) and frequency (10²–10⁶ Hz) of these junctions were investigated in detail. The sample showed a notable magnetoresistive effect due to the contribution of the La_0.67Sr_0.33MnO₃ layer and a diffuse dielectric anomaly which was found to arise from Maxwell–Wagner (MW) relaxation. Both positive and negative magnetocapacitive behaviours were observed. These behaviours were found to be intimately linked to the dielectric anomaly and can be well explained based on the combined role of the MW effect and magnetoresistance.

The formation process of InAs quantum dots (QDs) on vicinal GaAs (1 0 0) substrates is studied by atomic force microscopy (AFM). It is found that after 1.2 MLs of InAs deposition, while the QDs with diameters less than the width of the multi-atomic steps are shrinking, the larger QDs are growing. Photoluminescence measurements of the uncapped QDs correspond well to the AFM structure observations of the QDs. We propose that the QDs undergo an anomalous coarsening process with modified growth kinetics resulting from the restrictions of the finite terrace sizes. A comparison between the QDs on the vicinal GaAs (1 0 0) substrates and the QDs on the exact GaAs (1 0 0) further verifies the effect of the multi-atomic steps on the formation of QDs.

Based on kinetic theory, a model is developed for the in-plane thermal conductivity of nanocrystalline metallic films, combining partially diffuse electron–surface scattering and grain-boundary impedance. The thickness and temperature dependent thermal conductivities are examined. The influence of electron–surface scattering on thermal transport is remarkable, especially for thinner films with a more specular film surface. In addition to electron–surface scattering, grain-boundary scattering also has a major influence on the size effect for thermal conductivity.

A simple model is presented that relates optical and mechanical properties of optical coating materials deposited by typical physical vapour deposition techniques to the porosity of the layers. In terms of this model, a clear correlation between thermal shift, mechanical stress and refractive index could be simulated. As a practical conclusion, it is found that a certain fraction of small nanosized pores in the films is essential in order to get a valuable balance between optical and mechanical coating properties.

Room temperature synthesis of ordered-vacancy-compounds (OVCs) and copper indium diselenide (CuInSe₂, CIS) by cation and anion exchange reactions of solid CdS thin films with CIS ionic solution in an alkaline chemical bath is reported. The growth parameters such as pH, deposition time and concentration of the solutions were optimized to achieve uniform thin films. Nanostructured CdS thin films (150 nm thick) prepared by chemical bath deposition are used for the deposition of OVC and CIS thin films. The ion exchange reaction between the CdS thin film and the CIS ionic solutions transforms the yellow colour CdS film into faint black, indicating the formation of OVC and CIS film. The resultant films were annealed in air at 200 °C for 1 h and further subjected to characterization using the x-ray diffraction, transmission electron microscopy, energy dispersive x-ray analysis, x-ray photoelectron spectroscopy, scanning electron microscopy, atomic force microscopy, optical absorption and electrical measurement techniques. The OVC and CuIn₃Se₅ nanodomains are observed in chalcopyrite CIS thin films and these films have nanostructured morphology onto amorphous/nanocrystalline phase of CdS. The OVC–CIS films are p-type with a band gap energy of 1.453 eV.

First-principles density functional theory electronic structure calculations were carried out for Cr-doped SrTiO₃ to evaluate the effect of Cr-doping on the band gap states and the photocatalytic activity of SrTiO₃. The defect formation energy is also investigated to determine the energy required for Cr-doping. Our results indicate that substituting Cr for Sr requires smaller formation energy than substituting Cr for Ti in the Cr-doped SrTiO₃ structures and the Cr atoms energetically prefer to partially take up some Sr sites, simultaneously partially some Ti sites. Some Cr 3d gap states appear near the bottom of the conduction band in the Cr-doped SrTiO₃ structures, which results in the decreased electron transition energy and thus the visible light absorption observed in the experiment. The correlations between the doped Cr atoms at different sites and the environmental O atoms may be responsible for the differences in the visible light photocatalytic activities for the doped SrTiO₃. Further research demonstrates that different dopant concentrations in Cr-doped SrTiO₃ do not bring significant changes in the electronic characteristics but may change a little the electron transition energy and weaken photocatalytic activity under visible light.

We report the ferroelectric and pyroelectric properties of the composite films of lithium tantalate (LT) nanoparticle in poly(vinylidene fluoride) PVDF matrix at different volume fractions of LT (f_LT = 0.047, 0.09 and 0.17). For an applied electric field of 150 kV cm⁻¹ the nonvolatile polarization of the composite was observed to increase from 0.014 µC cm⁻² at f_LT = 0 to 2.06 µC cm⁻² at f_LT = 0.17. For f_LT = 0.17, the composite films exhibit a saturated ferroelectric hysteresis loop with a remanent polarization (2P_r = 4.13 µC cm⁻²). Compared with pure poled PVDF the composite films also showed a factor of about five enhancement in the pyroelectric coefficient at f_LT = 0.17. When used in energy detection mode the pyroelectric voltage sensitivity of the composite films was found to increase from 3.93 to 18.5 V J⁻¹ with an increase in f_LT from 0.0 to 0.17.

The optical response of free standing graphene, with or without a perpendicular magnetic field, doping or gap, is studied theoretically by solving Maxwell's equations. Formulae for the reflection coefficient and the reflected polarization are derived in terms of the polarization of the incident electromagnetic wave in the microwave region, its angle of incidence and the azimuthal angle on the graphene plane. These formulae involve the conductivity tensor of graphene. The behaviour of the reflection coefficient and the reflected polarization with the variation of these parameters may be used to infer the optical conductivity tensor and the anisotropy of the conductivity (by this we mean the presence of non-vanishing off-diagonal components of the conductivity tensor). The conductivity of graphene is important since it provides indirect evidence of the effective relativistic dispersion of the energy of the quasi-particles involved.

This paper proposes a polaronic stacking fault defect model as the origin of the huge dielectric properties in CaCu₃Ti₄O₁₂ (CCTO) materials. The model reconciles the opposing views of researchers on both sides of the intrinsic versus extrinsic debate about the origin of the unusually high values of the dielectric constant measured for CCTO in its various forms. Therefore, by considering stacking fault as the origin of the high dielectric constant phenomena, it was shown that the internal barrier layer capacitance mechanism is enhanced by another similar, but different in nature, mechanism that operates in the nanoscale range due to polaron defects associated with stacking fault, a mechanism that was referred to as nanoscale barrier layer capacitance (NBLC). The NBLC approach explains the origin of the CCTO's huge dielectric constant coexisting with semiconducting features.

We present an experimental and theoretical method to simultaneously obtain the optical dispersion curves and the thermal properties of thin film samples. From the experimental and analytical perspectives, we establish the physical conditions to validate this novel approach. Similarly, the method is tested on thin films of aluminium nitride (AlN) deposited on quartz and crystalline silicon substrates. The experimental set-up is that used for the open photoacoustic cell pseudo-transmittance spectroscopy (OPC-PATS). The sample is illuminated with modulated light as a pre-condition to induce and detect photothermal waves. The amplitude of these waves is proportional to the optical absorption and to the thermal properties of the sample. This is displayed in the so-called pseudo-transmittance spectra that we report here. Theoretically, we extend a previously reported self-consistent method to provide, in addition to the refractive index and the extinction coefficient spectral curves, the ratio of the thermal to the optical transparency and the thermal conductivity. Although the current analysis is applied to the optical range, the conditions of the method are such that it can readily be extended to other wavelengths.

Hydrogen (H) incorporation into AlGaN/GaN heterostructures used in high electron mobility transistors, grown by different methods, is studied by high-resolution depth profiling. Samples grown on sapphire and Si(1 1 1) substrates by molecular-beam epitaxy and metal–organic vapour phase epitaxy; involving H-free and H-containing precursors, were analysed to evaluate the eventual incorporation of H into the wafer. The amount of H was measured by means of nuclear reaction analysis (NRA) using the ¹H(¹⁵N,αγ)¹²C reaction up to a depth of ∼110 nm into the heterostructures. Interestingly, the H profiles are similar in all the samples analysed, with an increasing H content towards the surface and a negligible H incorporation into the GaN layer (0.24 ± 0.08 at%) or at the AlGaN/GaN interface. Therefore, NRA shows that H uptake is not related to the growth process or technique employed and that H contamination may be due to external sources after growth. The eventual correlation between topographical defects on the AlGaN surface and the H concentration are also discussed.

Optical stimulation luminescence (OSL) signals can be obtained using continuous-wave optical stimulation (CW-OSL), the linear modulation optical stimulation method (LM-OSL) and the time-resolved optical stimulation (TR-OSL) method. During TR-OSL measurements, the stimulation and emission of luminescence are experimentally separated in time by using short light pulses. This paper presents new TR-OSL data for annealed high purity synthetic quartz, for marble and for commercially available iodized salt. A new type of behaviour for TR-OSL signals for quartz and iodized salt is presented, in which the OSL signal exhibits a nonmonotonic behaviour during optical stimulation; this type of behaviour has not been reported previously in the literature for quartz. Furthermore, a luminescence component with very long luminescence lifetime is reported for some quartz aliquots, which may be due to the presence of a delayed-OSL (DOSL) mechanism in quartz. A new kinetic model for TR-OSL in quartz is presented, which is based on a main electron trap and on several luminescence centres. The model is used to quantitatively fit several sets of experimental data of pulsed optically stimulated luminescence from quartz.

Vanadium oxide (VO_x) thin films were deposited on thermally grown silicon oxide substrates using a pure vanadium target in a pulsed dc sputtering technique. Film microstructure, electrical resistivity, temperature coefficient of resistance (TCR) and activation energy were studied as a function of the oxygen partial pressure (pO₂) and growth temperatures. The mixed valence VO_x thin films deposited at various substrate temperatures between 40 and 300 °C exhibited columnar grain structure even though the samples were found to be x-ray amorphous. The TCR and activation energies of the films increased from 0.4% (K⁻¹) to 2.4% (K⁻¹) and 0.04 eV to 0.28 eV, respectively, by controlling the pO₂ content between depositions. The charge carrier transport in the VO_x thin films was found to exhibit conventional and inverse Meyer–Neldel compensation mechanisms depending on the growth conditions.

Single crystal lanthanum hexaboride (LaB₆) field emission arrays with uniform tip structures have been achieved using the electrochemical etching method and the field emission characteristics are evaluated. A direct current voltage source is introduced in the etching process and phosphoric acid is used as the electrolyte solution. The SEM observation of the emitters reflects the feasibility of the electrochemical etching method for the fabrication of single crystal LaB₆ FEA. The turn-on field of LaB₆ FEA is low at 3.2 Vµm⁻¹ and the emission current exhibits high stability during the 20-minute operation. Furthermore, even at low vacuum (>1.5 × 10⁻⁵ Torr) it still exhibits good emission properties and a strong ability to withstand the ion bombardment, which is useful for low operation vacuum microelectronic devices.

The potential of hybrid polymer 49% poly(methyl methacrylate)-grafted natural rubber (MG49) and poly(methyl methacrylate) (PMMA) as a polymer host in solid polymer electrolyte film for rechargeable battery systems has been investigated. The hybrid films were prepared by the solution casting technique. The ionic conductivity was investigated by alternating current electrochemical impedance spectroscopy. The highest conductivity was 1.47 × 10⁻⁸ S cm⁻¹ at 20 wt% of LiClO₄. The observation on structural studies performed by x-ray diffraction showed that the crystallinity phase is reduced at the highest conductivity. Fourier transform infrared spectroscopy analysis showed that the interaction between lithium ion and oxygen atoms occurred at carbonyl (C=O) and ether (C–O–C) groups.

Tensile and fatigue properties of Cu–Ni multilayers with different nominal individual layer thicknesses (λ) (10–100 nm) on a polyimide substrate were investigated. The nominal yield strength and fatigue strength of the multilayer/polyimide composite as a function of λ were determined. The experimental results indicate that both yield and fatigue strengths increase as λ decreases until λ is less than 20 nm. Tensile and fatigue cracking behaviour were examined to understand the damage mechanism of the ultrafine metallic multilayers.

Structured ZnO films have been fabricated on soda-lime glass slides at a low temperature (80–85 °C) by a chemical bath deposition method in one step without seed layers. Mixed aqueous solutions of zinc sulfate, ammonia and thiourea were used at alkaline conditions. The influence of the ammonia concentration in the initial solution on the property of the deposited film was investigated systematically. The morphology, structural and optical properties of the deposited films were examined and characterized by x-ray diffraction (XRD), energy-dispersive spectroscopy x-ray diffraction (EDX), scanning electron microscopy (SEM), Raman spectroscopy and photoluminescence (PL) spectroscopy. Structural analyses with XRD, EDX and SEM revealed that the formed films exhibit a wurtzite hexagonal phase. The deposited film was more preferentially oriented in the (0 0 2) direction with an increase in the ammonia concentration from 0.75 to 2 mol l⁻¹. The optical-phonon E₂ mode at 437 cm⁻¹ in the Raman spectrum, together with the XRD and EDX analyses, showed that flower-like and columnar crystalline ZnO films were formed in two ammonia concentration ranges, 0.75–1.4 mol l⁻¹ and 1.6–2.0 mol l⁻¹, respectively. Furthermore, PL spectra showed strong and high intensity peaks of UV emission with suppressed green emission for these deposited ZnO films. ZnS films were formed with a high ammonia concentration of 3.0 M. The formation mechanisms of ZnO, Zn(OH)₂ and ZnS phases were discussed.

We applied a time-resolved four-wave mixing technique for the determination of thermal diffusivity, sound velocity, thermo-optic and photoelastic coefficients in heavily doped n-type and p-type 4H–SiC substrates. Spatial modulation of thermal properties was achieved by intraband carrier excitation using a light-interference pattern at 1064 nm and subsequent carrier thermalization. Decay of the light-induced thermal grating at its various periods and sample temperatures was monitored by diffraction of a delayed probe pulse at 532 nm wavelength. The grating decay kinetics provided the thermal diffusivity D_T = 0.94 cm² s⁻¹, thermo-optic coefficient dn/dT = 3.6 × 10⁻⁵ K⁻¹ and effective photoelastic constant at 300 K. Temperature dependences of dn/dT and thermal expansion almost matched that of the heat capacity, C_p(T), and correlated well with the E_g(T) dependence.

Atomistic simulations are performed to investigate the torsional behaviour of abnormal double-walled carbon nanotubes (DWCNTs) with an interlayer distance of less than 0.34 nm and carbon nanowires (CNWs) made of linear carbon-atom chain (C-chain) encapsulated inside single-walled carbon nanotubes (SWCNTs) subject to torsional motion. The interaction between atoms is modelled using the second-generation reactive empirical bond-order potential coupled with the Lennard-Jones potential. These simulations indicate that the effect of the van der Waals (vdW) interaction is more significant for abnormal DWCNTs than for normal DWCNTs. The critical torsional moments of abnormal DWCNTs are considerably enhanced compared with those of corresponding normal DWCNTs. It is worth noting that the critical torsional moment does not always increase with a decrease in the interlayer distance of DWCNTs. Numerical results also show that the torsional behaviours of CNWs are influenced dramatically by the radius of CNWs. Compared with those of corresponding SWCNTs, the critical torsional moment and the critical torsional angle of CNW increase in CNWs of radius less than 0.4 nm and decrease in (6, 6) and (11, 0) CNWs with large radius.

In this paper a new equation for calculating the nanofluid viscosity by considering the Brownian motion of nanoparticles is introduced. The relative velocity between the base fluid and nanoparticles has been taken into account. This equation presents the nanofluid viscosity as a function of the temperature, the mean nanoparticle diameter, the nanoparticle volume fraction, the nanoparticle density and the base fluid physical properties. In developing the model a correction factor is introduced to take into account the simplification that was applied on the boundary condition. It is calculated by using very limited experimental data for nanofluids consisting of 13 nm Al₂O₃ nanoparticles and water and 28 nm Al₂O₃ nanoparticles and water. The predicted results are then compared with many other published experimental results for different nanofluids and very good concordance between these results is observed. Compared with the other theoretical models that are available in the literature, the presented model, in general, has a higher accuracy and precision.

Vibrothermography has proven to be a useful technique for the detection of cracks, which reveal themselves as heat sources when mechanically excited in vibrothermography experiments. In this work we present a method to evaluate the size and depth of buried heat sources in metallic samples, from lock-in vibrothermography measurements. We have developed a theoretical model allowing us to calculate the surface temperature produced by modulated buried heat sources of arbitrary shape and power distribution by integrating the contribution of point-like heat sources over the entire heat source extension. In order to test the validity of the model, we have chosen homogeneous and rectangular heat sources, perpendicular to the sample surface. We have prepared calibrated heat sources by attaching two flat pieces of stainless steel and controlling the tightness with screws. Measurements of the surface temperature by an infrared video camera have been compared with the predictions of the theoretical model. The agreement between experimental and theoretical results confirms that lock-in vibrothermography is an efficient tool not only to detect but also to characterize the geometrical parameters of inner heat sources.

Polyurethane-based nanocomposite films were prepared by incorporating carbon-coated SiC nanowires (SiC@C) into the polymer matrix. Electric field-induced strain measurements revealed that a loading of 0.5 wt% SiC@C increased the strain level by a factor of 1.7 at a moderate field strength (6.5 V µm⁻¹). Current–electric field characteristics and the film thickness dependence of strain demonstrated that the improvement of the electromechanical response was linked to a more pronounced space charge effect in the nanocomposite than in the polymer host. DSC measurements revealed that the level of phase mixing in the PU matrix remained unchanged after SiC@C filling; hence, the nano-objects themselves acted as charge traps.

We present an analytical two-dimensional (2D) model of a high current space charge limited (SCL) electron injection into a solid through a Schottky contact for a n⁺–i–n⁺ diode with constant mobility and no velocity overshoot effect. The amount of electron injection is limited by the barrier at the contact, which includes the effect of electron tunnelling through the Schottky barrier. For a given barrier height, the SCL current condition can be reached if the tunnelling current becomes dominant over the drift–diffusion current. An analytical scaling is present to show the enhancement of the SCL current due to finite contact size, which is verified by a 2D device simulator over a wide range of parameters.

In order to unveil the inner mechanisms that determine acetylene concentration, experimental studies on the effect of several parameters such as plasma torch power, hydrogen flux and coal flux were carried out from coal pyrolysis in a dc plasma torch. Xinjiang long flame coals including volatile constituents at a level of about 42% were used in the experiment. Under the following experimental conditions, namely plasma torch power, hydrogen flow rate and pulverized coal feed speed of 2.12 MW, 32 kg h⁻¹ and 900 kg h⁻¹, respectively, acetylene volume concentration of about 9.4% was achieved. The experimental results indicate that parameters such as plasma torch power and coal flux play important roles in the formation of acetylene. Acetylene concentration increases inconspicuously with hydrogen flux. A chemical thermodynamic equilibrium model using the free energy method is introduced in this paper to numerically simulate each experimental condition. The numerical results are qualitatively consistent with the experimental results. Two parameters, i.e. the gas temperature and the ratio of hydrogen/carbon, are considered to be the dominant and independent factors that determine acetylene concentration.

Depending on the emission current, a liquid-metal-ion-source produces microdroplets in addition to ions. A critical current defines the threshold of pure ion and mixed ion/droplet emission. According to previous theoretical work, this critical current depends on the liquid metal properties only. We found, that the critical current from capillary emitters is lower by about a factor of two compared with solid or porous needle emitters which are within the theoretically expected range. These results are of particular importance for applications that require pure ion emission.

We demonstrate a re-writable, high capacity holographic encoding technique for multiplexed bead-based suspension assays. The microparticles are made from SU8 doped with a photochromic diarylethene dye and manufactured using multilayer photolithography and dry etching. Each particle is encoded with a unique hologram, whose diffraction pattern consists of bright and dark regions, representing a binary number that identifies the particle. Theoretically up to 10²⁴ unique codes are available on a 100 µm particle using this method, when the code is read with a standard 2/3'' CMOS camera. Encoding capacities of 512 unique codes have been demonstrated on a 500 µm SU8 particle. The code is thermally stable for 3 days at 25 °C, and once written, the code can be erased and re-written once whilst still remaining readable. The code can be written into the particle during an assay experiment (no pre-encoding is required) and requires simple optics for reading.

Temperatures and vibrational populations are investigated experimentally and numerically in a CO–N₂–O₂ gas mixture. By spatially resolved Raman Q-branch spectra measurement, the strong vibrational excitation was observed in the gas mixtures at a high gas pressure. Numerical calculation, which incorporates both major processes of molecular energy transfer and diffusion of vibrationally excited species across the spatially nonuniform excitation region, provides indepth perception of vibrational kinetics of these diatomic molecular gas mixtures and is verified by the experimental data. The results demonstrate that strong vibrational nonequilibrium for all diatomic species can be sustained by the optical pumping method with a focused CO laser in a relatively cold (300–400 K) molecular gas mixture up to one atmospheric pressure. However, the results also demand further investigations on determining accurate rates of the V–V exchange gas mixture such as for N₂–O₂.