Table of contents

Soft x-ray lasers in the 3.5–50 nm wavelength range have been developed in many laboratories. The shortest wavelengths and highest output irradiances have been produced using plasmas created by optical lasers as the lasing medium. The optical laser is focused into a line on a solid target and the x-ray laser action occurs by amplification along the line with sufficiently high gain that mirrors are not needed. Population inversions are produced by free-electron collisions exciting bound electrons into metastable levels in neon- and nickel-like ions. This topical review presents a summary of the atomic, plasma and propagation physics of x-ray lasers created in this way.

Single-phase Nd₃Fe_26.8−xCo_xV_2.2 compounds with Nd₃(Fe,Ti)₂₉-type structure have been synthesized successfully for x = 0–12; and their structures and magnetic properties were investigated by x-ray diffraction and magnetic measurements. The Curie temperature increases drastically with increasing Co content from 500 K for x = 0–847 K for x = 12. All the compounds show a spin reorientation transition as temperature decreases. Spin reorientation temperature T_sr shows an increasing tendency with the exception of a minimum at around x = 6. Saturation magnetization increases monotonically with increasing Co content, which can be understood in terms of a rigid band model. The anisotropy field at 5 K decreases with increasing Co content. All the compounds show easy-plane-type anisotropy at room temperature and the series of the compounds is not suitable for permanent materials.

Physical parameters such as dielectric constant and susceptibility of dilute Fe₃O₄ ferrofluids derived directly from attenuated total reflection (ATR) and ferromagnetic resonance, respectively, were exploited to delineate the corresponding Faraday rotation angles with respect to applied magnetic fields. Theoretical estimation was compared with experimental measurements ensuring that the effective medium theory is admittedly correct and ATR is a prominent method to study the magneto-optical effect of ferrofluids.

Isotropic TbMn₆Sn₆ was prepared by mechanical milling and subsequent annealing. Although the crystalline grain size was a little larger than 15 nm, no remanence enhancement resulting from intergrain exchange coupling was observed. The coercivity μ₀H_c = 0.96 T at 293 K was much larger than that expected from magnetocrystalline anisotropy. The smallest effective anisotropy constant is suggested to be 0.25 MJ m⁻³ when the coercivity mechanism is controlled by coherent rotation of magnetization in a single-domain grain. The contributions of shape anisotropy and magnetoelastic anisotropy are considered in order to explain the large coercivity in the magnets.

The influence of sputtered SiO₂ over-layer on the SAW propagation characteristics of a 128° rotated Y-cut X-propagating lithium niobate SAW filter has been studied. Experimentally measured SAW phase velocity and temperature coefficient of delay (TCD), with varying SiO₂ over-layer thickness, show a significant deviation from the theoretically calculated values using the bulk material parameters of SiO₂. The observed deviation is attributed to the differences in the material parameters (density, elastic and dielectric constants and their temperature coefficient) of the deposited SiO₂ over-layer. The density and the dielectric constant of the deposited SiO₂ layer were determined separately, and the elastic constants and their temperature coefficients were estimated by fitting the experimental velocity and TCD data, respectively. The deviation in the dielectric constant and the density in comparison to the bulk was insignificant, and the estimated values of the elastic constants (C₁₁ = 0.75×10¹¹ N m⁻² and C₄₄ = 0.225×10¹¹ N m⁻²) were found to be lower, and the respective temperature coefficients (5.0×10⁻⁴ °C⁻¹ and 2.0×10⁻⁴ °C⁻¹) were high in comparison to the bulk material parameters.

Potassium hydrogen phthalate crystal is a good nonlinear optical system. Its electro-optic coefficient r₁₃₁ is measured for a wavelength of 670 nm and it is found to be of the order of that of urea crystal (1.06 pm V⁻¹). The dispersion study for the effective Pockels coefficients r_eff = r₁₁₃−r₁₁₂, is carried out for this crystal, and the electronic part of the electro-optic coefficient is shown to play an important role in the potassium hydrogen phthalate crystal. The electro-optical dispersion birefringence constant is found to be −1.11. Modulators based on KAP possess good figure of merits. The figure of merit that has been measured, corresponding to the wavelength of 670 nm is 9.5 pm V⁻¹.

A series of Er³⁺-doped PbWO₄ crystals have been grown by the Czochralski method with good optical quality. Optical absorbance, x-ray excited luminescence, photoluminescence and excitation spectra have been investigated in these Er³⁺-doped PbWO₄ crystals. Efficient luminescence from Er³⁺ ions doped in PbWO₄ is reported. With increasing luminescence of rare earth Er³⁺ ions in PbWO₄ : Er³⁺, the intrinsic luminescence of the PbWO₄ host is seen to decrease intensively. It was demonstrated that excitation into the PbWO₄ host is followed by an efficient energy transfer towards Er³⁺ ions. The excitation bands of Er³⁺ ions overlap with the luminescence spectra of the PbWO₄ host, which supports the hypothesis of resonant energy transfer from host to Er³⁺ ions. Annealing at higher temperature results in further enhancement of the luminescence of Er³⁺ ions in the PbWO₄ host.

We have synthesized a novel dye material of N,N'-bis[4-(N,N'-diphenylamino)-benzalidene] diaminomaleonitrile (BAP), as a dopant for red-light-emitting electroluminescent (EL) device. We fabricated several types of EL devices by doping BAP into tris(8-quinoline) aluminium (Alq₃) as the light-emitting layer, and investigated their EL properties. BAP has symmetric conjugated structure and could give sharp and intense photoluminescence in the red region. When BAP was doped into Alq₃, the device gave bright red EL with the maximum intensity of about 6700 cd m⁻² together with the contribution of Alq₃ emission. By introducing rubrene as an assist-dopant, the maximum EL intensity increased to 15 700 cd m⁻² when the bias voltage was 14.5 V. However, complete energy transfer to BAP has not been achieved.

We have studied the characteristics of intersubband absorption of polarized infrared (IR) radiation in as-grown and annealed self-organized InAs/GaAs quantum dots. It is observed that with the increase of annealing time and temperature, the dots tend to flatten and behave more like quantum wells. As a result, their sensitivity to TE (in-plane)-polarized light decreases and that to TM (out-of-plane)-polarized light increases. The effect could be utilized for the realization of polarization-sensitive IR detectors.

We present calculated values of transport properties (viscosity, thermal and electrical conductivities) of argon, copper and argon–copper thermal plasmas at equilibrium and non-equilibrium. In addition, combined ordinary and thermal diffusion coefficients, as defined by Murphy, are also given. The calculations are performed in the temperature range 300–25 000 K and at atmospheric pressure.

For all these calculations, we use a recent theory developed by Rat to determine the transport properties like, for example, viscosity or combined diffusion coefficients in non-equilibrium plasma (note that equilibrium is only a specific case). We also take great care in evaluating the collision integrals necessary to calculate the transport coefficients (especially the Cu–X interactions). At equilibrium, our results are compared with published values obtained theoretically and experimentally. Moreover, to our knowledge, there are no accessible data for these non-equilibrium argon–copper plasmas.

The equations for a one-dimensional `generationless' plasma containing two species of positive ion are derived and examined computationally in the steady state. When the ions have different masses, their drift speeds are different, and there is the potential for instability.

This instability is examined here, in the locally uniform plasma approximation, for the situation of nearly collisionless plasmas.

It is concluded that the situation may be weakly unstable and lead to the generation of noise near the plasma edge, but that the plasma parameters themselves are unlikely to be materially affected.

In recent years, there has been an increased interest in capacitively coupled plasma discharges which are operated with two frequencies. An analytical sheath model for a capacitively coupled radio-frequency plasma discharge operated with two frequencies is proposed and studied under the assumptions of a time-independent, collisionless ion motion. Expressions are obtained for the time-average electric potential within the sheath, nonlinear motion of the electron sheath boundary and nonlinear instantaneous sheath voltage. The derived model is valid under the condition that the low frequency (lf) electric field E_lf in the sheath is much higher than the high frequency (hf) electric field E_hf. This condition is fulfilled within typical dual frequency conditions. It is shown, however, that the hf electric field modifies the sheath structure significantly because of the electron response to E_hf. This model has been compared to particle-in-cell plasma simulations, finding good quantitative agreement. We present the dependence of the maximum sheath width and the dc sheath voltage drop on the hf/lf current ratio and on the hf/lf frequency ratio.

Interaction of deuterium plasma of streams and shock-waves (velocities up to 5×10⁷ cm s⁻¹) and fast ion beams (50–150 keV) generated in a dense plasma focus (DPF) device with low-activated austenitic steel, 25Cr12Mn20W, and ferritic steel, 10Cr9W, specimens positioned in the cathode part of DPF chamber has been investigated. If the power flux density of both types of irradiation is about q = 10⁵–10⁷ W cm⁻², then ion implantation into a surface layer of the materials was observed. An increase of this parameter till q = 10⁷–10⁸ W cm⁻² results in the so-called `detachment' effect (screening of the specimen surface by a cold plasma cloud). When the power flux density is increased up to q = 10<sup>9</sup>–10<sup>10</sup> W cm<sup>−2</sup>, the evaporated plasma cloud becomes of the same temperature as the plasma of the shock-wave, and melting and evaporation of material from the specimen surface appears to be very strong, thus the so-called `broken-implantation' takes place.

Functional coating deposition using plasma is broadly used in industrial application working at a pressure ranging from low pressure discharges (a few Pascals) to atmospheric plasmas. The active gas (silane is selected for this study) is often diluted in a gas that helps in stabilizing the discharge like helium or argon. In addition, the discharge can be polluted by uncontrolled external gas source like air or oxygen coming from water adsorbed in reactor walls. In this paper, we study the interactions taking place within the bulk of a capacitively coupled plasma and study the impact of these reactions on the flux of species moving towards the substrate and so the impact on the composition of deposited film. A one-dimensional fluid model is presented for the modelling of radio frequency capacitively coupled plasmas in a mixture of silane/helium, including small concentrations of O₂ and N₂. In total, 48 different species (electrons, ions, neutrals, radicals and excited species) are considered in the model. After a sensitivity study, 27 electron–neutral and 76 chemical reactions (i.e. ion–neutral and neutral–neutral reactions) were maintained in the fluid model. The fluid model itself consists of a set of mass balance equations (i.e. one for every species), the electron energy equation and the Poisson equation. The reaction rate coefficients of the electron–neutral reactions, as a function of average electron energy, are obtained from a Boltzmann model. The reaction rate coefficients of the ion–neutral and neutral–neutral reactions are assumed to be constant. It is found that helium does not affect the silane plasma chemistry drastically. The incorporation of small amounts of air (containing about 82% N₂ and 18% O₂) in a silane/helium plasma, however, influences the plasma chemistry to a large extent. A large number of nitrogen species (i.e. N₂, N, N₂⁺), and species containing oxygen (i.e. SiH₃O SiO, OH and others), are present in the discharge at relatively high densities (i.e. of the order of 10¹⁴–10¹⁷ m⁻³).

A model of stationary direct current discharges in atmospheric-pressure air is developed that accounts for deviation of plasma state from the local thermodynamic equilibrium. It is shown that at the current range 0.01–0.1 A a change in the dominant ionization mechanism takes place, from ionization by electron impact at low currents to associative ionization in atomic collisions at high currents. Results of the calculation of discharge parameters over a wide current range are presented. Calculated plasma parameters agree with the available experimental data.

Electrically deformed single crystal mirrors will be a vital part of a first generation of scanning helium microscope (SHeM). Optimized mirrors will be used to focus thermal energy helium atoms into a surface-sensitive, low-energy probe, with a resolution that depends upon the precise mirror shape. Here, we present surface profilometry measurements of a prototype atom mirror. A temporal phase-stepping Mach–Zender fibre interferometer is used to profile the mirror surface with an accuracy of a few tens of nanometres. Results are compared with the theory of small deflections of an elastic thin plate. Our experiments suggest that relatively simple apparatus can induce the mirror profiles required to demagnify a conventional helium source into a microprobe suitable for a SHeM. Use of elliptical boundary conditions in the clamping mechanism afford biaxial bending in the crystal whilst a simple double-electrode design is demonstrated to be capable of asymmetric control of the mirror deformation.

Optical transmission measurements are commonly used for the routine determination of thin film optical constants. This paper presents an overview of the different methods of evaluating these transmission data, leading to values for the complex refractive index. Three different groups of methods are distinguished using: (1) at least two different optical measurements; (2) dispersion relations or general physical constraints to approximate the behaviour of the wavelength-dependent refractive index; and (3) a `virtual' measurement as a second variable. The methods from groups (2) and (3) (requiring only a single transmission measurement) are treated in more detail and are evaluated in terms of their accuracy.

Near-surface composition and tribological behaviour of plasma nitrided commercially pure (CP) Ti have been investigated using x-ray diffraction, nuclear reaction analysis, scanning electron microscopy, wear assays with stainless steel Gracey scaler and sonic apparatus, and friction coefficient measurements. The total wear behaviour can be divided into two steps. The first step is the growth of an oxynitride layer. The second step is the breakdown of the oxynitride layer during which debris is produced, increasing the friction coefficient. Each sample exhibits features that correlate with the near-surface composition. For instance, the presence of thin layers of ε-Ti₂N and δ-TiN precipitating on the near-surface region control the transition from the first to the second step.

A three-dimensional impedance network model for describing the frequency dependent electrical properties of composite materials has been developed. The considered compounds consist of conducting particles dispersed in an insulating matrix and the ratio between the conductivities of the two phases is around seven decades. The character of the contacts between the particles will have a critical effect on the electrical characteristics. Two different types of contacts, represented by edge and face connections, are taken into account. A sharp edge connection gives an extremely localized field enhancement. Instead of trying to resolve this rapidly diverging electric field, an equivalent circuit element that reproduces the overall behaviour of the edge contact was introduced. The distribution of the filler grains also affects the electrical properties. The large agglomerates that appear in random distributions are not representative of the well-dispersed real materials. Several methods to create a more even than random dispersion of the conducting particles were therefore utilized. Simulations were performed and compared to measurements on ethylene–propylene–diene monomer rubber filled with silicon carbide grains. The calculations reproduce the general characteristics of the experimental results.

A powerful fluid model to study the role of gas dynamics in a glow discharge considered as an excitation medium for XeCl lasers is presented. This model was employed using a numerical code including four strongly coupled parts: electric circuit equations, electron Boltzmann equation, kinetic equations and conservation equations. The theoretical formalism presented here is based on the two-dimensional Euler equations describing the perfect compressible fluid. The numerical calculations have been carried out considering the single shot regime and neglecting the gas flow. The monotonic upstream centred scheme for conservation laws corrections has been used in order to estimate the exchange flow surrounding the control volume walls. We show that the crossing discharge induces a thermal energy density enhancement located principally in the cavity centre.

A numerical simulation of isostatic compaction of monosized spheres by discrete element method is presented in this paper. The dynamic microstructural changes of the particle compact during compaction were first investigated in terms of mean packing density and coordination number, and then characterized using percolation theory. The constitutive relationship between density and pressure was also examined, moreover used to validate the empirical relations obtained by experiments.

We theoretically demonstrate thermal neutron diffusion in two-dimensional structures with periodic moderators composed of circular rods with square lattices. In such structures, damping constant regions in which thermal neutron diffusion cannot take place appear. We define these damping constant regions as diffusion band gaps. The diffusion band gaps significantly depend on the radius of the rod and the lattice constant. The moderators are assumed to be C and H₂O.

In the standard technique of beam energy resolution one uses the property of momentum dispersion by dipole magnets. It is shown that one can, alternatively, use three quadrupole magnets to select the beam momentum or energy. The lengths and magnetic fields of the quadrupoles can be adjusted to focus the particles of the required energy and simultaneously defocus the particles of higher or lower energies. For obtaining a very high resolving power one can use such triplets in cascade. The resolving powers of these are multiplicative, whereas in the case of dipoles one can use just two bending magnets for roughly doubling the resolving power. This method is different from the technique used in quadrupole mass filters where RF field is used in quadrupoles.

A peak-search method for high resolution gamma-ray spectroscopy, based entirely on spectrum convolution, is presented. The detection of the peak and determination of the peak position, width and area can be realized in successive steps, independent of each other. To realize each of the steps, the spectrum is convoluted with an appropriate near-optimal function. Analytical expressions for the uncertainties of positions, areas and widths can be derived. For resolving doublets the standard least-square technique is used, but on the convoluted spectra, avoiding the problems associated with the background component. The performance of the software package based on the proposed method was successfully tested against two standard sets of test spectra of the International Atomic Energy Agency and intercomparison with other peak-search packages proves that the proposed approach is robust and reliable.

Elastomers are of interest for use as deformation elements in pressure and force sensors. In this paper, a custom designed programmable elastomer test rig (PETR) developed in order to allow the routine mechanical evaluation (compression mode) of small elastomer structures (0.3–30 mm thick) is described and characterized. The mechanical properties of two polyurethane and two silicone rubbers were investigated using the PETR. Silastic silicone (Dow Corning 9161) was found to display relatively low hysteresis and good elasticity. More in-depth investigation of this material revealed that the elastic modulus and the hysteresis were independent of the amount of catalyst used in its preparation over the range 2–6% (w/w). The Zener model was found to provide a good representation of the actual stress–strain behaviour of test specimens subjected to load–unload tests at strain rates in the range 1.25–60% min⁻¹ (load rates 4–200 N min⁻¹) and dynamic tests at frequencies in the range 0.001–0.1 Hz. The combined hysteresis and creep for a 1 h test period was not greater than 4%, with the creep contribution being up to 2.3% and occurring in a manner predicted by the Zener model. Specimen form-factor strongly influenced both the elastic modulus and the hysteresis. Increasing the form-factor from 0.5 to 2.6 increased the elastic modulus from about 3.0 to 7.6 MPa while also increasing the hysteresis from 2.4% to 25.2%.

The direct observation of the self-combustion of structurally co-deformed elemental powders, in the course of the ball milling treatment, was possible by employing quartz transparent reaction vessels and a high-speed image acquiring system. The synthesis of a titanium–silicon system was chosen as a case study. Whereas the primary ignition appears to be linked to an impact event, the reaction spreads out because of the violent and continuous throwing out of burning particles inside the milling vial. The reaction reaches completion within milliseconds. The use of radiation pyrometers enabled us to register the combustion temperature, which reached the melting temperature of the reaction product and approached the adiabatic temperature of the process. Results indicate that the underlying reaction mechanism relies on liquid–solid diffusion as in the conventional self-sustaining high-temperature synthesis process. Important information of the ball–vial dynamics was also obtained by tracking the trajectory of the ball, which, due to being heated up to luminosity, became visible for several cycles of the reciprocating milling machine.