Table of contents

In this rapid communication, we present the new electromagnetic resonant cavity properties of the gold nanoshell. The gold nanoshell is regarded as a nanometre electromagnetic resonant cavity, and the cavity resonance displays tunability controlled by the radii of the dielectric core. The main mode of nanocavity resonant absorption is obtained, which shows a redshift during the reaction of the gold nanoshells. The classical electrodynamics theory is used to describe this gold-coated mini nanoshell cavity, and it shows agreement with experimental results.

We present the photoluminescence characterization of pure and 0.2 mol% samarium-doped zirconium oxide, prepared by the sol-gel process and annealed at 1000 °C to stabilize the monoclinic phase. Under excitation at 320 nm the Sm³⁺-doped monoclinic zirconium oxide shows strong emission at the green (569 nm) and red (607, 613 and 618 nm) bands, corresponding to the ⁴G_7/2→⁶H_9/2 and ⁴F_3/2→⁶H_9/2 samarium transitions, respectively; whereas the undoped sample only shows a broadband emission centred at 495 nm. The main mechanism that allows the samarium emission under UV excitation appears to be non-radiative energy transfer from the ZrO₂ host to the Sm³⁺ ions.

The Debye equation with slit-smeared small angle x-ray scattering (SAXS) data is extended from an ideal two-phase system to a pseudo two-phase system with the presence of the interface layer, and a simple accurate solution is proposed to determine the average thickness of the interface layer in porous materials. This method is tested by experimental SAXS data, which were measured at 25 °C, of organo-modified mesoporous silica prepared by condensation of tetraethoxysilane (TEOS) and methyltriethoxysilane (MTES) using non-ionic neutral surfactant as template under neutral condition.

Variable-range-hopping (VRH) conduction that has been ascribed to the formation of graphite sp² bonds, can be generated in diamond by means of high dose ion implantation. With increasing implantation temperature, the ion doses required to generate this conduction increase owing to some form of self-annealing. Similar behaviour has been reported for the formation of amorphous material in silicon. Morehead and Crowder (1970 Radiat. Eff.6 27) developed a model based on displacement spikes to describe this process in silicon. Prawer and Kalish (1995 Phys. Rev. B 51 15711) adapted this model to describe the onset of VRH conduction in diamonds that they had implanted with 100 keV C⁺ and 320 keV Xe⁺ at different temperatures. In this study it is assumed that the latter ions could not have formed displacement spikes in diamond. Equations, based on interstitial-vacancy generation and recombination, are then derived to describe the processes of damage formation and annealing in diamond during ion implantation, and applied to the data of Prawer and Kalish. The model fits the latter data well, and is also consistent with recent results on interstitial-vacancy generation, and the interactions of these defects, in electron-irradiated diamonds.

In this work, we report about the analysis of structural, physical, and gas-sensing properties of a new sensing material made by mixing In₂O₃ and SeO₂. The In₂O₃/SeO₂ thin films have been obtained by thermal evaporation of In:Se in a 2:1 ratio and subsequent thermal annealing in an oxygen flow. In order to investigate the structure and the morphology of the films obtained, high-resolution transmission electron microscopy, small-area electron diffraction, and digital image processing were performed on thermally annealed films. The Hall effect and resistivity measurements of such films have been carefully analysed. In addition, In₂O₃/SeO₂ mixed oxide films were tested in a controlled atmosphere and the electrical conductance changes were measured as a function of temperature.

The sensing behaviour of such films has been analysed according to an adsorption kinetic model, which related the conductivity variation to gas concentrations, time exposure, and working temperature.

In this investigation, we have studied the effect of negative bias voltage on the properties of a sputtered Ta layer deposited at high Ar pressure (13.3 Pa) which is used as a diffusion barrier in a Cu/Ta/Si structure focusing on its silicidation process. According to Rutherford backscattering spectrometry, the Cu(85 nm)/Ta(100 nm, unbiased)/Si(111) structure was found to be stable up to 300 °C in a N₂ environment for 30 min. At a temperature of 450 °C, TaSi₂ was formed at the Ta/Si(111) interface, and the Ta diffusion barrier completely failed. By applying various negative bias voltages ranging from 0 to -150 V, an optimum bias voltage of V_b = -50 V for the sputtered Ta layer was found from scanning electron microscopy and four-point-probe resistivity measurements. In addition, the normalized ion flux (n_i), defined as the ratio of Ar⁺ ion flux to Ta flux, was determined to be 7.5 for optimum experimental conditions. As a result, the biased Ta layer was used as a diffusion barrier between Cu and Si; it showed a low resistivity of 99 µΩ cm, a density of about 14.1 g cm^-3 with a good surface morphology and a contribution of bcc-Ta phase structure of about 65%. The Cu(50 nm)/Ta(50 nm, biased)/Si(111) structure was demonstrated to be thermally stable under perfect conditions up to 500 °C and TaSi₂ formation in an N₂ environment for 30 min was retarded up to 700 °C.

Knowledge on the thickness, composition, and interfaces of thin films and multilayers is, in many systems, fundamental for the understanding and optimization of their properties. One of the techniques often applied to such studies is Rutherford backscattering (RBS). However, it has been very difficult to account for the effects of interface roughness in the data obtained, and the alternative has been to develop dedicated data analysis codes for particular problems where roughness plays a determinant role. In this work, the effect of roughness is taken into account in the data analysis by calculating the effect of roughness on the apparent energy resolution as a function of depth. This depends on the exact type of roughness, and three different models have been implemented: inhomogeneous layer thickness, corrugated sample, and rough substrate surface. Interfacial mixing in multilayers can also be analysed with the method developed. Automatic fits to the data can be performed in this way, where the roughness parameters are derived during the fit, providing a new tool for RBS analysis. The code is applied to several systems in order to test its validity and applicability. Systems which are hard to analyse by RBS have been chosen: Si/VS/ Si_0.65 Ge_0.35 300 nm/ Si_0.2 Ge_0.8 4 nm/ Si_0.65 Ge_0.35 15 nm/Si 3 nm thin films, where VS stands for a linearly composition-graded virtual substrate; and MgO /( Fe 25 Å/ Co 20 Å)₁₀ multilayers.

Magnetic tunnel junctions in the sub-micrometre range have been patterned by electron beam lithography. The hard reference electrode is composed of an artificial antiferromagnetic subsystem while the soft magnetic detection layer is Permalloy (NiFe). The magnetic switching characteristic is studied for various seed layers. For a polycrystalline iron seed line the magnetoresistance switching curve is irregular and not well behaved, while for a nonmagnetic seed layer (Ru) the reproducibility is good and the switching can be related to the shape of the element. We discuss possible coupling mechanisms and show that the magnetization reversal of the soft layer is mainly driven by the large stray fields of moving Néel-type domain walls in the Fe seed layer.

We have designed, fabricated and tested a soft x-ray device, which uses a capillary discharge to achieve neon-like argon lasing. The ceramic capillary has an inner diameter of 3 mm and a length of 150 mm. When operating the device with a current of 16 kA and dI/dt of 517.8 A ns^-1 at gas pressure of 26.7 Pa, lasing has been confirmed. Multi-pulse laser output has also been observed with a slightly higher current of 17.5 kA, and this indicates that there exist several configurations suitable for the Ne-like Ar lasing during one pinch process. This is the first observation of multi-pulse laser output.

A model for calculating the three-dimensional stationary geometric shape of the cutting front for laser fusion cutting is presented in this paper. The model relates the cut kerf geometry with the cut-through depth, various laser parameters such as power, speed, focus position and material thickness. In this model, the energy absorbed by the workpiece includes not only the direct energy from the laser beam but also the energy from the multiple reflections generated by the beam impinging on the cutting front of the cut kerf. The effects of multiple reflections are functions of the inclined angle of the cutting front and the cutting depth. The effects of various laser processing parameters, multiple reflections and inert gas pressure on the geometric shape of the cutting front have been analysed systematically and in detail. The model allows accurate prediction of the cut-through depth and cut-edge quality for a given set of process parameters. It also helps to explain the effect of focal position, cut-assist pressure and other parameters upon the cut-edge quality.

A mathematical model is developed to calculate the distribution of the gas flow field at the entrance, inside and exit of a laser cut kerf for inlet stagnation pressures ⩾5 bar for an inert assist gas jet exiting from a supersonic nozzle. A two-dimensional analytical method is adopted to locate approximately the position and shape of the detached shock above the cutting front surface according to the geometrical shape of the cutting front. A method of two-dimensional characteristics is applied to calculate the gas flow field distribution along the cutting front. The calculated results of the flow field distribution are simulated by the computer and can be used to estimate and analyse the cut-edge quality under different cutting conditions.

Based on the models for determining the geometry of the cutting front and the gas flow distribution inside the cut kerf of the laser fusion cutting process, the effects of the inlet stagnation pressure of the nozzle, the exit diameter of the supersonic nozzle, laser power, cutting speed and focal position upon the geometry of the cutting front and the flow field distribution which subsequently affect the cut edge quality are analysed in this paper. The theoretical predictions are verified by practical laser fusion cutting experiments using a high-power CO₂ laser, a supersonic nozzle and a high-pressure cut-assisted gas in the range of 5 bar and above. The theoretical predictions are used to explain the roughness, the ripple directions and the amount of dross on the experimental cut edges.

This paper reports on the measurement of the electron drift velocity, the density normalized effective ionization coefficients (α-η)/N, and the ratio η/α (η and α are the attachment and ionization coefficients, respectively), over a wide range of the density-reduced field strength, E/N, from 40 to 560 Td (1 Td = 10^-17 V cm²). From the measured values of (α-η)/N and η/α, the density normalized ionization and attachment coefficients were obtained. Further analysis of avalanche development past the first electron transit allowed us to derive the average mobility of both positive and negative ions. The mobility of negative ions was found to agree very well with Blanc's law at small fields, thereby indicating that the majority negative ion in the avalanche is SF₆^-. The critical field strength was found to vary almost linearly with the SF₆ content in the mixture, comparing well with previous measurements.

A model describing the chemical clustering kinetics in a low-pressure acetylene RF discharge has been developed. The model contains neutral chain and cyclic hydrocarbons, positive and negative ions, and electrons. The gas-phase chemistry includes neutral-neutral reactions, electron induced H-abstraction, electron attachment, and ion-ion neutralization. In addition, diffusion losses to the reactor walls are considered. The model predicts the time evolution of species concentrations and chemical reaction rates, and reveals the preferred clustering pathways. The clustering occurs mainly through addition of growth species and formation of linear molecules. However, the amount of aromatic hydrocarbons produced is not negligible even at room temperature and increases strongly with the gas temperature. The FTIR and NMR measurements performed indicate the presence of aromatic compounds in the particles produced.

Five necessary conditions for the so-called formal correctness of solutions of kinetic equations are formulated, which form a mathematical model of the reaction kinetics in HV circuit breakers after current zero for a given time-dependence of temperature and a given time-dependence of pressure or volume. The conditions are based on the mass action law, knowledge obtained from mathematical analysis of a system of ordinary differential equations, the principles of numerical analysis and the equilibrium-state principle of thermodynamics. Concrete solutions of kinetic equations are given and analysed for the products of SF₆ dissociation and ionization. Two models are considered. In one model, the temperature drops from 10 000 to 2500 K, in the other it drops from 12 000 K to room temperature. A comparison of the time-dependent composition with the equilibrium composition is offered for both models.

The (Ne + H₂) plasma in a hollow cathode glow discharge has been investigated. A theoretical description of (Ne + H₂) plasma has been made by considering the main elementary processes including the vibrational kinetics. Based on the results obtained from the model an emission method has been developed for H^- concentration measurement. The results obtained by this emission method are compared with those obtained by the photodetachment method.

This paper is devoted to calculation of the non-equilibrium composition in a SF₆ thermal plasma at atmospheric pressure. Non-equilibrium thermal plasmas are characterized by heavy species temperatures T_h below 9000 K with electron temperatures at the maximum three times higher than T_h when the latter is below 4000 K. Different theories have been used based on either multi-temperature plasmas, Saha-Potapov modified by André et al, van de Sanden et al, Cliteur et al, or kinetic calculations or the pseudo-equilibrium model, recently developed. This model gives results similar to those of kinetic calculations for N₂ and H₂ plasmas but with calculation times two orders magnitude faster. Pseudo-equilibrium calculation takes into account the reactions with low activation energies instead of ionization reactions, while keeping all the species present in the kinetic calculation. First, the theories are compared in a case already studied in the literature by Cliteur: a heavy species temperature T_h at 6000 K, with the electron temperature T_e varying between 6000 and 15 000 K. Comparison of the results shows that the multi-temperature calculations, except those of Cliteur, are far from kinetic especially for n_e and n_F^-. In addition, the pseudo-equilibrium model fits rather well with the kinetic calculations as long as molecular species are present in the plasma. Second, to calculate the composition of non-equilibrium thermal plasmas the ratio T_e/T_h is assumed to vary as the logarithm of the electron densities ratio n_e/n_c^max, n_e^max being the electron density over which equilibrium prevails, i.e. 10²³ m^-3. For kinetic reactions where electrons are involved (in the direct reaction while heavy species intervene in the reverse reaction), a temperature T* between T_e and T_h is defined. T* is calculated as a function of the electron flux to that of heavy species. The variation of T* with T_h is smoother than that of T_e. In such conditions again, there is an excellent agreement between kinetic and pseudo-equilibrium calculations performed at T*, which is not the case for multi-temperature calculations. These results demonstrate that the pseudo-equilibrium calculation developed for thermal plasma simple forming gases such as N₂ and H₂ can also be applied to more complex gases such as SF₆.

The Boltzmann equation for ions and electrons in gases subject to arbitrarily oriented electric and magnetic fields is solved by a recently developed unified `multiterm' theory (White et al 1999a), and attention is focused on portrayal of the velocity distribution function. In particular, we take `slices' in velocity space to elucidate the effects of changing orientation angle, magnetic field strength and the ion to gas molecule mass ratio. The first results for electrons in CO₂ and ion swarms in electric and magnetic fields are presented in this way. The implications of symmetries are discussed.

By analysing switching current data i(t), produced by the reversal of domains, it was possible to extract detailed information concerning the behaviour of the switching kinetics in TGS crystals. The switching curves were fitted to a three-parameter nucleation and growth model based on Avrami statistical theory. By direct observation of the domain pattern during slow polarization reversal, by means of nematic liquid crystals, it was possible to verify the assumptions of the theory for crystal samples with both a spatially uniform and non-uniform distribution of domain nuclei.

Electroluminescence detected in many different polymers under uniform 50 Hz ac and dc fields exhibits a threshold-like character, i.e. the light emission increases supralinearly with the applied voltage above a critical value called the emission threshold. The significance of this threshold is not straightforward. It could be a true physical threshold corresponding to the onset of the luminescence excitation as opposed to a sensitivity-limited threshold without specific significance. This paper discusses this issue on the basis of electroluminescence analysis in several polymers used in electrical engineering, such as polyethylenes, polyesters and polyimides. The analysis relies on the consideration of the field dependence of the electroluminescence and its imaging in the sample plane. It is shown that the threshold-like character under a dc field reveals the onset of the electroluminescence excitation whereas it has no specific meaning under ac stress where the detection is sensitivity-limited. The significance of the luminescence-voltage characteristic, as regards the electrical ageing and its possible use for diagnostic purposes, is further considered.

Studies of the vibration-vibration (VV) exchange in CO molecules excited up to vibration quantum numbers v = 20 have been performed both theoretically and experimentally. A new kinetic model which takes into account the multi-quantum VV exchange in the temperature range T = 100-300 K is described for the first time. A description is given of the experimental methodology allowing for studies of the effects of the relaxation of the vibrational distribution after a sudden disturbance. The disturbance of the vibrational distribution is produced by a Q-switched short pulse of single line radiation in fundamental band. The relaxation is studied by measuring the laser pulse energy of the second pulse initiated by resonator Q-switching produced with a variable time delay relative to the first pulse. A set of kinetic rate constants accepted in the model for various gas temperatures, vibration level numbers and number of exchanged vibration quanta from 1 to 4 is presented. The good agreement between the experimental data and the results of the advanced theory is the first direct evidence in support of the multi-quantum exchange model.

An amplitude-modulated high-power laser propagating through a magnetized semiconductor exerts a ponderomotive force on free electrons at the modulation frequency Ω and excites a large amplitude lower hybrid wave. A second laser beam of frequency ω₂ propagating through this region is modulated by the density perturbation of the lower hybrid wave, leading to information transfer from one beam to the other. The modulation transfer is resonantly enhanced when the modulation frequency is near the lower hybrid frequency, Ω = ω_pcos θ/[ε_L + (ω²_p/ω²_c)sin ²θ]^1/2, where ω_p and ω_c are the electron plasma and cyclotron frequencies, ε_L is the lattice permittivity and θ is the angle magnetic field makes with the surface normal.