Table of contents

Vacuum ultraviolet (VUV) photons are known to modify the bulk chemical composition of 193 nm photoresist, typically penetrating ∼100 nm and depleting carbon–oxygen bonds. Fourier transform infrared transmission measurements as a function of VUV photon fluence demonstrate that VUV-induced bond breaking occurs over a period of time. We present a model based on the idea that VUV photons initially deplete near-surface O-containing bonds, leading to deeper, subsequent penetration and more bond losses, until the remaining near-surface C–C bonds are able to absorb the incident radiation. Fitted model photoabsorption cross-sections compare well with the literature values.

An n-type Zn_1−x−yBe_xMg_yO thin film was deposited on a p-type Si substrate by pulsed laser deposition to obtain a solar-blind photodetector. The spectral response characteristic with a cutoff wavelength of 280 nm was demonstrated to realize the photodetection of the solar-blind wave zone. The responsivity of the device was improved by inserting an Al-doped ZnO (AZO) contact layer, which was expected to enhance the carrier collection efficiency significantly. Correspondingly, the peak responsivity was improved from 0.003 to 0.11 A W⁻¹ at zero bias, and a high external quantum efficiency of 53% at 270 nm was achieved. The fast rise time reached 20 ns. This work demonstrated the possibility of a wurtzite ZnO based oxide system to realize high performance zero-biased solar-blind photodetectors.

A new neutron resonant transmission (NRT) detector for epithermal neutron imaging has been designed and built for the ANCIENT CHARM project, which is developing a set of complementary neutron imaging methods for analysis of cultural heritage objects. One of the techniques being exploited is NRT with the aim of performing bulk elemental analysis. The 16-pixel prototype NRT detector consists of independent crystals of 2 × 2 mm pixel size, which allow for 2D position-sensitive transmission measurements with epithermal neutrons. First results obtained at the ISIS pulsed spallation neutron source are presented.

We compare the characteristics of photonic crystal (PC) light-emitting diodes (LEDs) with the same hole pattern density of 12 ea µm⁻². The PC LED with periodic hole structure demonstrated an increased output power, improved external efficiency at high current operation and uniform radiation owing to the periodic nanoscale features generating a photonic band gap (PBG), when compared with those of the random hole (RH) LED. The electroluminescence images obtained by confocal scanning electroluminescence microscopy (CSEM) show the difference of light emission propagation from the random and periodic structures.

Zinc oxide (ZnO) is a wide band gap semiconductor material with attractive features for light emitting devices, photovoltaics, chemical sensors and spintronics. In the past 10 yr ZnO has attracted tremendous interest from the materials science and semiconductor physics research communities, and in this review recent progress in (i) bulk growth, (ii) understanding of the role of hydrogen and (iii) formation of high-quality Schottky barrier (SB) diodes, are discussed for single crystalline ZnO. In (i), the emphasis is put on hydrothermally grown material and how the concentration of intentional and unintentional impurities, such as In and Li, can be controlled and modified by high temperature treatment and defect engineering involving vacancy clusters. In (ii), different possible configurations of hydrogen as a shallow donor are evaluated based on results from calculations employing the density-functional-theory as well as from experimental studies of local vibrational modes using Fourier transform infrared spectroscopy. Further, hydrogen is demonstrated to be very reactive and the interaction with zinc vacancies, group I and group V elements, and transition metals are elucidated. Moreover, the diffusion of hydrogen is found to be rapid and limited by the concentration of traps in hydrothermal samples, and it is argued that isolated (free) hydrogen is not very likely to exist in ZnO at room temperature. In (iii), a compilation of the literature data illustrates that the SB heights for metals deposited on n-type samples have no correlation with the metal work function, violating the fundamental Schottky–Mott model. The role of surface preparation cannot be overestimated and in several cases an oxidation of the surface prior to metal deposition is shown to be beneficial for the formation of high barrier SB diodes. The effects of near-surface defects, such as oxygen vacancies, and contact inhomogeneity are also addressed. However, in spite of the significant progress made in the past 5–7 years, a thorough understanding of the SB formation to ZnO is still lacking. Finally, results from characterization of electrically active point defects employing the SB contacts and junction spectroscopic techniques are reviewed and the identification of some prominent bandgap states is critically evaluated.

Mg_0.9Mn_0.1In_xFe_2−x O₄ (x = 0.1 and 0.2) and Mg_0.9Mn_0.1Al_yFe_2−y O₄ (y = 0.1, 0.5 and 0.7) ferrites, with improved initial permeability and extremely low relative loss factor (RLF), were synthesized by the citrate precursor technique. Structural studies were made by using the x-ray diffraction technique and scanning electron microscopy (SEM), which confirm the formation of single-phase spinel structure. The size of the particle was of the order of ∼0.5 µm for the samples sintered at 1200 °C, which is smaller than that obtained for ferrite powders by the conventional ceramic method. The magnetic properties such as initial permeability and RLF with frequency, in the range 0.1–20 MHz, at different temperatures have been investigated. Initial permeability (μ_i) attains a very high value, 17342, for the In³⁺ doped ferrite series and for the Al³⁺ doped ferrite series the maximum value is 3785. The RLF was found to have low values and is of the order of 10⁻⁵–10⁻⁴ in the frequency range 0.1–20 MHz. In addition to this, an increase in the value of μ_i was observed with the rise in the temperature for all the series of ferrites.

To improve the magnetic properties, nickel hollow spheres (NHSs) were surface-modified with a cellular Co structure by a facile electroless cobalt plating route. The microstructures and properties of the modified NHSs were characterized by field emission scanning electron microscopy, x-ray diffraction, Brunauer–Emmett–Teller specific surface area and a vibrating sample magnetometer. Microwave properties were evaluated by mixing NHSs with polyvinyl butyral as coaxial samples. The SEM images showed that the NHSs were coated by the Co cellular films, which not only increased the specific surface area but also enhanced the coercivity and magnetization. Also, the modified NHSs composites presented low R_{L min} values below −30 dB at thicknesses between 1.0 and 2.0 mm, and exhibited a broad absorption bandwidth ΔW at 'thin' thickness.

Ferromagnetism is realized by implanting 300 keV Gd ions into MgO single crystals, with T_c well above room temperature. Structural and magnetic investigations reveal no detectable second phase. Ferromagnetism is absent in MgO crystals implanted by nonmagnetic ions, which implies that the lattice defects created by destructive implantation cannot account for the observed ferromagnetism in the Gd implanted MgO alone. The ferromagnetic behaviour disappears in the Gd implanted MgO after annealing to eliminate the lattice defects. The long-range ferromagnetic ordering in the Gd as-implanted MgO crystal is likely to be stabilized by defect-mediated exchange between magnetic moments localized on Gd ions.

Electromagnetic (EM) characteristics of superparamagnetic graphite-coated FeNi₃ nanocapsules were studied at 2–18 GHz. Compared with FeNi₃ nanoparticles coated by an amorphous oxide layer, the natural resonance and attenuation properties of the graphite-coated FeNi₃ nanocapsules were dramatically enhanced, due to the coating of the graphite. Graphite layers can restrain the growth of FeNi₃ nanocapsules, increase the resistivity, enhance the resonance frequency, keep the real part of permeability almost constant at high frequency and increase the magnetic loss. As a result of enhanced natural resonance and attenuation properties, the FeNi₃/C nanocapsules exhibit good EM absorption properties.

A simple structured tunable negative refractive index (n) metamaterial (TNIM) has been designed, fabricated and tested in a Q-band rectangular waveguide. The structure consists of one slab of single crystalline scandium-doped barium hexaferrite (Sc-BaM), aligned parallel to two rows of periodic copper wires. The magnetic field tunable passband is measured indicating the occurrence of negative n. The centre frequency of the 5 GHz wide passband, having a transmission peak of −13 dB, is shifted linearly from 40.9 to 43.9 GHz by varying the bias field (H) from 4.0 to 7.0 kOe. The impact of ferrite volume factor (FVF) of the Sc-BaM slab upon the performance of the TNIM composite has been studied qualitatively. A tradeoff effect is illustrated in which the desirable negative permeability (μ) of the ferrite is offset by the detrimental impact of its dielectric property in suppressing the negative permittivity (ε) of the nearby plasmonic wires.

Interband tunnel diodes are widely used to electrically interconnect the individual subcells in multi-junction solar cells. Tunnel diodes have to operate at high current densities and low voltages, especially when used in concentrator solar cells. They represent one of the most critical elements of multi-junction solar cells and the fluctuations of the peak current in the diodes have an essential impact on the performance and reliability of the devices. Recently we have found that GaAs tunnel diodes exhibit extremely high peak currents that can be explained by resonant tunnelling through defects homogeneously distributed in the junction. Experiments evidence rather large fluctuations of the peak current in the diodes fabricated from the same wafer. It is a challenging task to clarify the reason for such large fluctuations in order to improve the performance of the multi-junction solar cells. In this work we show that the large fluctuations of the peak current in tunnel diodes can be caused by relatively small fluctuations of the dopant concentration. We also show that the fluctuations of the peak current become smaller for deeper energy levels of the defects responsible for the resonant tunnelling.

Yb–Bi co-doped germanosilicate glasses were prepared and their optical properties and optical amplification were investigated. Compared with single Bi-doped glasses, apparent enhancement in emission intensity, luminescence lifetime and optical gain was observed in Yb–Bi co-doped glasses with an excitation at 980 or 808 nm. The slope of the optical gain coefficient with the 808 nm excitation is much higher than that with 980 nm. The influences of Yb co-doping on the photoluminescence and gain properties of glasses with excitation at 808 nm were investigated and discussed. The highest gain coefficient at 1300 nm reaches 4.34 dB cm⁻¹ and 1.08 dB cm⁻¹ for the 808 nm and 980 nm excitations, respectively. The stimulated emission cross-section of the Yb–Bi co-doped glass with the 808 and 980 nm excitations was also estimated. Yb–Bi co-doped germanosilicate glasses are available for broadband amplification with either 980 or 808 nm excitation.

We report the electronic excitation induced controlled tuning of the surface plasmon resonance (SPR) wavelength of Ag nanoparticles (NPs) in fullerene C₇₀ matrix. The transformation of fullerene C₇₀ into amorphous carbon (a:C) under ion irradiation is used to tune the SPR wavelength of C₇₀–Ag nanocomposite thin films. A 100 nm blue shift was recorded for irradiation at a fluence of 3 × 10¹³ ions cm⁻² by 120 MeV Ag ions. A growth of Ag NPs from 7.0 ± 0.8 to 11.0 ± 0.4 nm with increasing fluence was observed by transmission electron microscopy and it is explained in the framework of thermal spike model. The transformation of fullerene C₇₀ into amorphous carbon with ion irradiation was confirmed by Raman spectroscopy. This work demonstrates the possibility to locally excite the SPR at a desired wavelength and therefore, acquiring multiple SPR bands at a single substrate which could be useful in developing more efficient optical sensors.

Nanoparticles (NPs) decorated ZnO/TiO₂ core/shell nanorod arrays were fabricated on transparent conductive glass substrates by sequential plasma deposition and post-annealing processes for dye-sensitized solar cells (DSSCs) applications. The NPs decorated ZnO/TiO₂ nanorods were composed of single-crystalline ZnO nanorods, homogeneously coated thin TiO₂ shells and entirely covered anatase TiO₂ NPs. The photocurrent density of the composite electrode was largely enhanced due to the enlarged surface area, the dark current was suppressed and the open-circuit voltage was increased because of the energy barrier formed at the interface between the ZnO core and the TiO₂ shell. The increased photocurrent and open-circuit voltage led to an improvement of twice the energy conversion efficiency.

Ferriprotoporphyrin IX chloride (haemin)-functionalized Al-doped zinc oxide (ZnO) is used for nitric oxide (NO) sensing at room temperature. The devices show high selectivity to NO against CO₂ and O₂. There is no such selectivity without haemin. Porous ZnO film made by a polystyrene sphere template is used to provide a high surface area. In comparison with non-porous ZnO film with low surface area, both the sensitivity and the response speed of the sensor made by porous ZnO are clearly improved. NO concentration down to 1 ppm can be detected. The response time is 20 s. The sensor is reversible after purging with pure nitrogen for about 100 s. Such a device is able to detect real-time variation of NO which is a vital physiological signalling molecule.

We report a complete switching of catalyst particle location from the base to the tip of carbon nanotubes when grown on microscale bimetallic scrolls by simply varying the growth temperature from 400 to 450 °C. The complete switching of catalyst particle location occurs in the very narrow temperature window of 50 °C. This is attributed to the miscible and reactive properties of the bimetallic layer with the substrate. The study suggests that the switching can be manipulated by supplying silicon from the substrate by reduction in silicon dioxide to the bimetallic layer.

The diode-pumped dual-frequency microchip Nd : YAG laser with tunable frequency difference is presented. The gain medium used is a microchip 2 mm in thickness for miniaturized and integrated design. Two quarter-wave plates are placed into the laser cavity and the intra-cavity birefringence produces two orthogonally linearly polarized modes. The rotation of one of the two quarter-wave plates introduces a controlled and variable cavity birefringence which causes a variable frequency difference between the two orthogonally polarized modes. The frequency difference can be tuned through the whole cavity free spectral range. The obtained frequency difference ranges from 14 MHz to 1.5 GHz. The variation of the beat frequency over a period of 10 min is less than 10 kHz. The lock-in between modes is not found. Experimental results are presented, which match well with the theoretical analysis based on Jones matrices.

Detailed measurements of ion energy distributions (IEDs) originating at different stages of a pulsed vacuum arc are studied. It is shown that for a variety of cathode materials (Al, Mg, Ti and Zr), the directed energies per charge unit of ion originating at the initial stage of the arc, i.e. in 25 µs after ignition, are close to each other and are, approximately, as much as E_dir/Z ≈ 70 eV. A non-Maxwellian shape of these IEDs that is due to the presence of significant 'tails' of ions accelerated up to energies of a few hundred eletronvolts is found. In 100 µs after the arc ignition the directed energies relax to values that are close, principally, to values that have been measured earlier elsewhere. It is found that the 'anomalously' accelerated ions propagate within a narrow angle that is as much as, approximately, ±15° in relation to the plasma flux axis. These characteristics suggest that beyond the commonly adopted gas-dynamic mechanism of ion acceleration in cathode micro-jets, at the initial stage of a pulsed arc the mechanism of additional ion acceleration is presented, which is due, obviously, to a self-consistent electric field arising in front of the plasma macro-jet.

Luminescent ZnO nanoparticles have been synthesized on silicon and quartz substrates under extremely non-equilibrium conditions of energetic ion condensation during the post-focus phase in a dense plasma focus (DPF) device. Ar⁺, O⁺, Zn⁺ and ZnO⁺ ions are generated as a result of interaction of hot and dense argon plasma focus with the surfaces of ZnO pellets placed at the anode. It is found that the sizes, structural and photoluminescence (PL) properties of the ZnO nanoparticles appear to be quite different on Si(1 0 0) and quartz substrates. The results of x-ray diffractometry and atomic force microscopy show that the ZnO nanoparticles are crystalline and range in size from 5–7 nm on Si(1 0 0) substrates to 10–38 nm on quartz substrates. Room-temperature PL studies reveal strong peaks related to excitonic bands and defects for the ZnO nanoparticles deposited on Si (1 0 0), whereas the excitonic bands are not excited in the quartz substrate case. Raman studies indicate the presence of E2 (high) mode for ZnO nanoparticles deposited on Si(1 0 0).

Laser plasma is produced with a boron nitride (BN) particle-included water droplet as a target and a pre/main laser pulse scheme in which the pre-pulse is sent to explosively vaporize the droplet. Shadowgraph measurement of the exploded BN particle-included droplet shows that the water block expands at a velocity of about 200 m s⁻¹, which is much higher than the expansion velocity of the BN particles (less than 5 m s⁻¹). Extreme ultraviolet (EUV) emission around 4.86 nm from BN particles is enhanced to more than a factor of 2 with the dual-pulse scheme in comparison with the case of shooting the droplet with a single laser pulse. The enhancement of EUV emission is attributed to an increased main laser energy absorption by the BN particles after explosive vaporization of the droplet.

Silicon-on-insulator (SOI) wafers were etched by an energetic chlorine neutral beam obtained by the low-angle forward reflection of an ion beam, and the surface roughness of the etched wafers was compared with that of the SOI wafers etched by an energetic chlorine ion beam. When the ion beam was used to etch the silicon layer of the SOI wafers, the surface roughness was not significantly changed even though the use of higher ion bombardment energy slightly decreased the surface roughness of the SOI wafer. However, when the chlorine neutral beam was used instead of the chlorine ion beam having a similar beam energy, the surface roughness of the SOI wafer was significantly improved compared with that etched by the chlorine ion beam. By etching about 150 nm silicon from the SOI wafer having a 300 nm-thick top silicon layer with the chlorine neutral beam at the energy of 500 eV, the rms surface roughness of 1.5 Å could be obtained with the etch rate of about 750 Å min⁻¹.

The expansion of a copper laser produced plasma across a 320 mT magnetic field was investigated using time- and space-resolved optical emission spectroscopy. Time-of-flight Langmuir probe ion measurements were used to characterize the plume expansion in the absence of the magnetic field. The spectroscopy measurements reveal that the magnetic field gives rise to substantial confinement of the plasma emission. The field also leads to significant enhancement of the intensity of some of the neutral and ion emission lines.

The gas temperature (T_g) dependence of nucleation and growth processes of hydrocarbon nanoparticles in low pressure Ar/CH₄ RF discharges has been investigated. Measuring the electron density with the microwave cavity resonance technique allowed us to monitor nucleation processes on small (µs) time scales. On larger time scales, coagulation times and growth rates are determined by means of measuring the phase angle between the RF voltage and current in correlation with laser light scattering. The experimental results show a significant gas temperature dependence of both powder nucleation and growth processes. Within the measured gas temperature range (20–130 °C) the particle growth rate decreases by a factor of ∼3.7, while the coagulation time increases by a factor of ∼6.5 with increasing T_g. Moreover, in this paper we present a simplified model which uses the experimentally determined growth rates and coagulation times to predict the value of the critical density of nanometre sized neutral particles, necessary to initiate coagulation. This model estimates a critical density of 3.5 × 10¹⁵ m⁻³ at room temperature which decreases with increasing temperature.

We consider a continuous optical discharge (COD) sustained by a vertically directed weakly focused CO₂ laser beam, in a gravitational field. We used a full two-dimensional radiative gas-dynamic numerical model for the COD, which uses realistic quasi optics and takes refraction of the laser radiation in the plasma properly into account in the description of the laser beam propagation. The model is applied to calculate the parameters of the COD in a converging CO₂ laser beam in free air atmosphere as a function of the laser power. We also demonstrate the effect of the selection of spectral groups, used in the multi-group diffusion approximation of the thermal radiation transport, on the model solutions.

An absolute intensity measurement (AIM) technique is presented that combines the absolute measurements of the line and the continuum emitted by strongly ionizing argon plasmas. AIM is an iterative combination of the absolute line intensity–collisional radiative model (ALI–CRM) and the absolute continuum intensity (ACI) method. The basis of ALI–CRM is that the excitation temperature T₁₃ determined by the method of ALI is transformed into the electron temperature T_e using a CRM. This gives T_e as a weak function of electron density n_e. The ACI method is based on the absolute value of the continuum radiation and determines the electron density in a way that depends on T_e. The iterative combination gives n_e and T_e. As a case study the AIM method is applied to plasmas created by torche à injection axiale (TIA) at atmospheric pressure and fixed frequency at 2.45 GHz. The standard operating settings are a gas flow of 1 slm and a power of 800 W; the measurements have been performed at a position of 1 mm above the nozzle. With AIM we found an electron temperature of 1.2 eV and electron density values around 10²¹ m⁻³. There is not much dependence of these values on the plasma control parameters (power and gas flow). From the error analysis we can conclude that the determination of T_e is within 7% and thus rather accurate but comparison with other studies shows strong deviations. The n_e determination comes with an error of 40% but is in reasonable agreement with other experimental results.

Photoluminescent properties of ZnGa₂O₄ : Mn phosphor thin films grown on Si and quartz substrate using the pulsed laser deposition technique under different deposition conditions (i.e. oxygen partial pressure and substrate temperature) are reported. The charge transfer band (283 nm) excitation of the phosphor exhibited green emission (504 nm) due to electronic transition from ⁴G(⁴T₁)–⁶S(⁶A₁) of 3d⁵ Mn²⁺ ions. The SEM image with elemental composition analysis shows a change in the film porosity and the Ga/Zn ratio with respect to variation in the oxygen partial pressure during the growth of the thin films at a constant temperature (650 °C). The changes in the emission intensity of the films are attributed to the variation in oxygen and Zn content (low vapour pressure) with respect to the change in O₂ partial pressure.

Numerical simulation for the adhesive contact between a sphere and a half-space is employed. The numerical simulation is performed for a realistic surface force law based on the Lennard-Jones potential between molecules with the Derjaguin approximation. The result is compared with the two-dimensional Maugis model, which uses the Dugdale law. It is found that the Maugis model gives good results, approximating those obtained by the numerical simulation. It is also found that the usual Maugis parameter governs the transition from the two-dimensional JKR model to the two-dimensional rigid cylinder contact. But the rigid body limit found using the Maugis model is different from that found using the numerical simulation.

This work explores the surface treatment of copolymer materials with fluorinated carbonyl groups in various mole fractions by ultraviolet irradiation and ion-beam (IB) bombardment and its effect on liquid crystal (LC) surface alignments. X-ray photoemission spectroscopic analysis confirms that the content of the grafted CF₂ side chains dominates the pretilt angle. A significant increase in oxygen content is responsible for the increase in the polar surface energy during IB treatment. Finally, the polar component of the surface energy dominates the pretilt angle of the LCs.

We report on the x-ray analysis of non-capped InAs/AlAs(0 0 1) quantum dot systems grown at temperatures ranging from 480 up to 530 °C. A constant amount of InAs has been deposited resulting in a growth stage where coherently strained dots and plastically relaxed clusters coexist. It is found that with an increase in deposition temperature the average size of elastically strained dots increases without changes in their chemical composition and surface density. The observed process is in accordance with the InAs volume decrease stored in plastically relaxed clusters. The results establish the crucial role of strain-induced material intermixing between strained InAs dots and the AlAs substrate over the investigated growth temperature range.

This paper focuses on monitoring of carbon nanotube (CNT) network development during the cure of unsaturated polyester nanocomposites by means of electrical impedance spectroscopy. A phenomenological model of the dielectric response is developed using equivalent circuit analysis. The model comprises two parallel RC elements connected in series, each of them giving rise to a semicircular arc in impedance complex plane plots. An established inverse modelling methodology is utilized for the estimation of the parameters of the corresponding equivalent circuit. This allows a quantification of the evolution of two separate processes corresponding to the two parallel RC elements. The high frequency process, which is attributed to CNT aggregates, shows a monotonic decrease in characteristic time during the cure. In contrast, the low frequency process, which corresponds to inter-aggregate phenomena, shows a more complex behaviour explained by the interplay between conductive network development and the cross-linking of the polymer.

Thermally stimulated luminescence spectroscopy has been applied to study the deep centres in unintentionally doped high resistivity GaN epilayers grown by the metal organic chemical vapour deposition method on c-sapphire substrates. Two trap states with activation energies of 0.12 and 0.62 eV are evaluated from two luminescence peaks at 141.9 and 294.7 K in the luminescence curve. Our spectroscopy measurement, in combination with more accurate first-principles studies, provided insights into the microscopic origin of these levels. Our investigations suggest that the lower level at 0.12 eV might originate from C_N, which behaves as a hole trap state; the deeper level at 0.62 eV can be correlated with V_Ga that corresponds to the yellow luminescence band observed in low-temperature photoluminescence spectra.

This work presents a study of tellurite glasses doped with Eu³⁺ and Au nanoparticles. Luminescence of Eu³⁺ ions in the yellow–red region was examined as a function of Au nanoparticles concentration, while the thermal lens technique furnished the thermal diffusivity of the samples. The influence of the nanoparticles concentration on the thermal diffusivity of the glass and the Eu³⁺ luminescence is discussed.

Using the carbon nanotube (CNT) as the 1D building block, various 2D covalent CNT networks are theoretically built. The specific heat of these CNT networks is calculated by the quantized molecular structural mechanics method. The effect of the geometric parameters of networks on their specific heat is found to be small at all temperature levels. At high temperatures this effect even vanishes. A general formula for the specific heat of these 2D CNT networks is given. This formula depends only on the building block of the networks. Besides, the specific heat per unit area of these CNT networks with different geometric properties are also explored and found to be extremely low. The predicted thermal properties of the CNT networks reveal their potential applications in fabricating excellent loudspeakers.

Quantum ab initio simulations were carried out to study the CdSiO₃ triclinic crystal. Unit cell parameters and atomic positions were optimized to find a minimum total energy within the density functional theory (DFT) formalism in both the local density and generalized gradient approximations, LDA and GGA, respectively. Analysis of the Kohn–Sham electronic band structure shows that there are two very close indirect band gaps E_g(Z → Γ) = 2.57 eV (2.79 eV) and E_g(Q → Γ) = 2.59 eV (2.81 eV) for the GGA-PBE (LDA-CAPZ) computations, and a direct band gap E_g(Γ → Γ) = 2.57, 2.63 eV (2.85 eV). Effective masses for holes and electrons were estimated by parabolic fitting along different directions at the valence band maximum and conduction band minimum, and they are very anisotropic. A comparison with previously reported data for triclinic CaSiO₃ (wollastonite) using the LDA-CAPZ exchange-correlation functional reveals that the substitution of calcium by cadmium changes the localization of the valence band maximum in reciprocal space and decreases the band gap energies. Optical properties (dielectric function, optical absorption) for incident light polarized along different crystalline planes were computed, the optical absorption for incident light with polarization along the 0 1 0 crystalline plane being the smallest for energies near the main band gap due to the spatial disposition of the SiO₄ tetrahedra and CdO₆ octahedra chains that build up the structure of triclinic CdSiO₃.

ZnO thin films were grown using pulsed laser deposition by ablating a Zn target in various mixtures of O₂ and N₂. The presence of N₂ during deposition was found to affect the growth of the ZnO thin films and their optical properties. Small N₂ concentrations during growth led to strong acceptor-related photoluminescence (PL), while larger concentrations affected both the intensity and temperature dependence of the emission peaks. In addition, the PL properties of the annealed ZnO thin films are associated with the N₂ concentration during their growth. The possible role of nitrogen in ZnO growth and annealing is discussed.

Time-domain THz transmission and FTIR reflectivity spectra of dense core–shell composites of the BaZr_0.2Ti_0.8O₃, BaZr_0.4Ti_0.6O₃, Ba_0.66Sr_0.34TiO₃ and Ba_0.45Sr_0.55TiO₃ compositions were studied in a broad temperature range of 10–900 K. The spectra were evaluated to obtain the complex dielectric functions and at room temperature they were compared with the prediction of the generalized brick-wall model based on the effective medium approximation. The model was analysed concerning the dielectric losses and electric-field tunability below the polar phonon frequency range. Whereas the predicted losses are much reduced compared with those of the cores, the observed enhanced losses in the THz range give evidence of an interdiffusion of the BaTiO₃ cores into the shells.

The simultaneous release of electrons and holes by what seems to be a single trap has been observed experimentally. We previously performed numerical simulations on a phenomenological model which showed similar behaviour. Here, we provide an analytical solution to this model. This model explains trends in radioluminescence, thermoluminescence and thermally stimulated conductivity of a material with one electron trap, one hole trap and one radiative recombination centre, in which thermal excitation of the electron trap occurs before that of the hole trap. It is shown that TL emission due to electron recombination at centres can be controlled by a hole trap and the electron recombination will have a peak shape associated with the hole trap's parameters. When this happens, the peaks in free electron concentration, free hole concentration and TL all occur nearly simultaneously. The analytical model allows this to be explained along with scaling laws and initial rise behaviour. Under the conditions illustrated by this model, the usual methods used to distinguish between electron traps and hole traps will give incorrect results.

We use a new approach to derive dielectric mixing rules for macroscopically homogeneous and isotropic multicomponent mixtures of anisotropic inhomogeneous dielectric particles. Two factors of anisotropy are taken into account, the shape of the particles and the anisotropy of the dielectric parameters of the particles' substances. Our approach is based upon the notion of macroscopic compact groups of particles and the procedure of averaging of the fields over volumes much greater than the typical scales of these groups. It enables us to effectively sum up the contributions from multiple interparticle re-emission and short-range correlation effects, represented by all terms in the infinite iterative series for the electric field strength and induction. The expression for the effective permittivity can be given the form of the Lorentz–Lorenz type, which allows us to determine the effective polarizabilities of the particles in the mixture. These polarizabilities are found as integrals over the regions occupied by the particles and taken of explicit functions of the principal components of the permittivity tensors of the particles' substances and the permittivity of the host medium. The case of a mixture of particles of ellipsoidal shape is considered in detail to exemplify the use of general formulae. As another example, Bruggeman-type formulae are derived under pertinent model assumptions. The ranges of validity of the results obtained are discussed as well.

In this paper, surface effects on the axial buckling and the transverse vibration of nanowires are examined by using the refined Timoshenko beam theory. The critical compression force of axial buckling and the natural frequency of nanowires are obtained analytically, in which the impacts of surface elasticity, residual surface stress, transverse shear deformation and rotary inertia have been included. The buckling and vibration behaviour of a nanowire is demonstrated to be size dependent, especially when its cross-sectional dimension reduces to nanometres. The surface effects with positive elastic constants tend to increase the critical compression force and the natural frequency, especially for slender nanowires, while the shear deformation lowers these values for stubby nanowires. This study may be helpful to accurately measure the mechanical properties of nanowires and to design nanowire-based devices and systems.

Surface radiation represents an important mechanism for heat loss at high temperatures. Thermal control may require improved heat dissipation of highly emitting surfaces in order to keep the maximum temperature below a certain critical value in high-temperature turbine systems. Emissivity allows determining the surface temperature based on thermal spectra measurement or thermal imaging of the turbine blades. In this study, the emissivities of different coating samples including the metal substrate have been measured over a wavelength range 0.4–1.08 µm in the temperature range 400–1150 °C and high values of emissivities are observed. The data are also compared with the theoretical values of emissivity. The comparison between the theory and experiment are, however, poor because the experimental data are obtained at high temperatures, while the theoretical values are calculated using the values of refraction and absorption indices at room temperature in the Fresnel reflection formula. The optical constants of the samples are computed by the Lorentz elastically bound electron theory of insulator and the Drude free-electron theory of metals.

A broad-band three-dimensional (3D) isotropic left-handed metamaterial (LHM) is proposed in this paper. The 3D unit cell is composed of a dielectric cube with metallic Jerusalem crosses on all its six sides. A theoretical model was set up by using equivalent-circuit theory. The magnetic and electric resonant frequencies of the proposed LHM are always equal, which guarantees the existence of a left-handed band. Numerical simulations were carried out to verify the proposed LHM. The results show that the relative bandwidth reaches up to 44.6%; the left-handed band is independent of the polarization of incident waves and is almost the same for different incident angles. Thus, the proposed LHM is a good candidate as a broad-band 3D isotropic LHM.

We report on a study of the near-field sensitivity of a metal-dielectric near-field terahertz probe by time-domain terahertz spectroscopy. The obtained experimental data were analysed using principal component analysis. Principal components corresponding to the changes in the output terahertz pulse upon varying the probe–sample distance and reflecting the local anisotropy in a ferroelectric BaTiO₃ crystal were extracted and identified. Simulations of the pulse propagation within a model of the probe revealed very similar independent components.

Novel hybrid organic/inorganic nanocomposites made of metal oxide and conjugated polymer nanocomposite and its application in bulk-heterojunction solar cells were studied. The composite was composed of different concentrations of strontium titanate (SrTiO₃) and polyaniline doped phosphoric acid. The optimum concentration of strontium titanate was found to be 0.2 v/v. An inorganic–organic photovoltaic device with a structure of Ag/Pani–H₃PO₄–SrTiO₃/Al has been fabricated. The ideality factor value of the diode was found to be 1.8. This n value of the diode implies a deviation from ideal junction behaviour. The barrier height ϕ_b value for the diode was found to be 0.56 eV. The Ag/Pani–H₃PO₄–SrTiO₃/Al diode shows a photovoltaic behaviour with a maximum open-circuit voltage V_oc of 2.49 V, and short-circuit current I_sc of 5.6 mA under light illumination λ = 460 nm. The conversion efficiency was found to be 5.2%. It is evaluated that the Ag/Pani–H₃PO₄–SrTiO₃/Al diode is a good photodiode with calculated electronic parameters.

Visualization of Nd : YAG laser ablation of aluminium targets was performed by a shadowgraph apparatus capable of imaging the dynamics of ablation with nanosecond time resolution. Direct observations of vaporization, explosive phase change and shock waves were obtained. The influence of vaporization and phase explosion on shock wave velocity was directly measured. A significant increase in the shock wave velocity was observed at the onset of phase explosion. However, the shock wave behaviour followed the form of a Taylor–Sedov spherical shock below and above the explosive phase change threshold. The jump in the shock wave velocity above phase explosion threshold is attributed to the release of stored enthalpy in the superheated liquid surface. The energy released during phase explosion was estimated by fitting the transient shock wave position to the Taylor scaling rules. Results of temperature calculations indicate that the vapour temperature at the phase explosion threshold is slightly higher than the critical temperature at the early stages of the shock wave formation. The shock wave pressure nearly doubled when transitioning from normal vaporization to phase explosion.

The effect of voltage on flow rate within cone jet mode electrospraying has been investigated, with particular emphasis on the effect of emitter geometry. A set of experiments investigated the effect of the outer and inner diameters on the flow rate relationship to voltage, in cone jet mode electrospray. This was accomplished by the use of a high fidelity flow meter, capable of measuring changes in flow rate to a fraction of a nanolitre per second.

It has been previously demonstrated that there are two separate parameters that influence the flow rate sensitivity to voltage; the hydraulic resistance of the flow system, and the outer diameter of the emitter. By a simple derivation, the second of these two is explained by the variation of theoretical electric pressure with voltage, as the outer diameter is varied.

Good agreement is found between experimental and theoretical results, suggesting the simple theory reasonably explains the physics of the situation.

As well as elucidating the physics involved in electrospray—suggesting the electric field is an important controlling parameter within cone jet mode electrospray—the theoretical and experimental agreement has important implications for variable throttling of thrust in colloid thrusters, and could bring about better optimization of performance in other electrospray-employing fields.

The optical and electrical characteristics of pure, sodium- and lithium-doped potassium hydrogen tartrate crystals grown by the gel technique are reported. An optical absorption study conducted in the UV–Vis range of 200–800 nm reveals the transparency of these crystals in the entire visible range but not in the ultraviolet range. The optical band gap of pure potassium hydrogen tartrate crystals is found to be dependent on doping by Na or Li ions. The non-linear optical behaviour of these crystals is reported and explained. The electrical properties of pure and doped potassium hydrogen tartrate crystals are studied by measuring electrical resistivity from 80 to 300 K. It is shown that while pure potassium hydrogen tartrate crystal is an insulator at room temperature (300 K), doping by Na or Li ions makes it a semiconductor. The results have been explained in terms of the variable range hopping model.