Table of contents

Amorphous (PbBr₂)_0.9(CuBr)_0.1 films have been obtained by quench deposition of the mixture of PbBr₂ and CuBr. Upon crystallization of the films, Cu⁺ ions aggregate to form very small CuBr crystallites, which are uniformly embedded in the crystalline PbBr₂ matrix, exhibiting blue-shifted CuBr exciton absorption. Despite the precipitation of the CuBr crystallites, the resulting films retain a relatively flat surface (rms roughness, ~15 nm for films with ~800 nm thickness).

The preparation of a-SiOCF films from Si(OC₂H₅)₄, C₄F₈ and/or Ar using a plasma-enhanced chemical vapour deposition method is reported. The chemical bonding structures of the films are analysed by high-resolution x-ray photoelectron spectroscopy (XPS) and Fourier transform infrared (FTIR) spectroscopy. The results show that the films contain F-Si-O-Si, Si-OH, Si-O-Si, C-CF and C-F configurations. However, as for the film deposited from the feeding gases with Ar, a C-C configuration is also included in addition to the above-mentioned configurations. This indicates that the existence of Ar in the plasma leads to the formation of a fluorocarbon structure with a high degree of cross-linking. No evidence reveals the presence of a Si-C bond in the film, so it is believed that the fluorocarbon is perhaps embedded into the matrix of SiOF.

Vortices are seen in the magnetization distributions of rectangular magnetic elements in both experiments and micromagnetic simulations. To investigate the role of vortices during magnetization reversal, Ni₈₀Fe₂₀ elements 100 nm and 200 nm wide and 5-60 nm thick were fabricated by electron beam lithography and studied by high-resolution magnetic imaging in the transmission electron microscope. During reversal, vortices appeared near the ends of the elements, grew under an increasing reverse field, and disappeared after rapid switching. Maximum switching fields of 400 Oe for 100 nm wide elements and 200 Oe for 200 nm wide elements occurred for film thicknesses of 25-30 nm and above. Simulations showed that reversal in these elements always occurred by means of vortices, however the simulated switching fields were much higher than the experimentally observed values. Lower switching fields were obtained in the simulations when vortex creation was assisted by `defects' at the edges of the elements. However, to successfully simulate the magnitude and thickness dependence of the switching fields, it was necessary to start from an initial magnetic state which already contained a vortex.

A series of \mbox{Co-Al-O} granular thin films were fabricated by RF reactive sputtering at various oxygen fluxes, and the tunnelling magnetoresistance (TMR), phase composition, microstructure and the conductance mechanism of the films were systematically investigated. X-ray diffraction and transmission electron microscopy revealed that the metal granules in the films gradually change from an AlCo alloy phase to a pure Co phase, and the granules become smaller with increasing oxygen flux. The TMR also varied with an increase of the oxygen flux and exhibited a maximum of -7% at 1.7 vol% oxygen flux. A crossover of the temperature coefficient of resistivity (TCR) from positive to negative with the increase of the oxygen flux is observed, and zero TCR is obtained at 1.0 vol% oxygen flux, implying a change of the conduction mechanism. These behaviours of the TMR and the TCR can be ascribed to the influence of the oxygen flux on the phase composition and the microstructure.

This paper describes a novel and miniature probe for monitoring the velocity of the phase transition in aluminium powder under shock loading. Experimental results are presented that could suggest an explanation for the phenomena that are involved, and the possible consequences of these on the design of flux-compression generators are discussed.

The charge density per unit length, the longitudinal component of the electric field and the electron concentration behind the front of fast ionization wave, initiated by a nanosecond voltage pulse of negative polarity in air, N₂ and H₂, are reconstructed in the pressure range of 1-24 Torr. The breakdown initiation from the high-voltage electrode is investigated. The accumulation of the positive charge in the vicinity of the cathode at the initial moment of the time of discharge development is revealed; and the time dependence of the conduction current through the cathode is determined. Energy branching in the discharge is analysed in various gases. It is shown that the greater part of the energy (40-60%) in the whole range of parameters passes to excitation of electronic states of molecules, that a part of the energy input into high-energy degrees of freedom (ionization, dissociation) monotonically decreases with the pressure and that a part of low-energy ones (rotation, vibration) monotonically increases.

An analysis is presented of the oscillations of keyhole pressure and plasma radiation emitted during welding with a continuous wave (CW) CO₂ laser. Welding was done with a CW CO₂ laser, Photon Sources VFA 2500, operating at the power of 1.75 kW. The welded materials were mild and stainless steel sheets, 0.8-2 mm thick. The shielding gas was argon or helium. Oscillations of plasma radiation were registered in monochromatic or broad band radiation with the use of a photomultiplier or photodiode and pressure variations with a microphone in the frequency range of 20-2×10⁴ Hz. It has been found that the optical signal from the plasma plume is closely connected with the acoustic signal and that the source of the acoustic signal is the pulsating movement of the plasma plume. Spectral analysis of the measured oscillations shows differences in power spectra depending on the welding conditions. Generally, two intrinsic frequency peaks in the range of 0.5-4 kHz are always present but the amplitude, frequency and width of the peaks depend on the material and welding conditions. The results show that the optical and acoustic signals emitted during the welding process can be useful for process monitoring. The behaviour of the observed oscillations is characteristic for deterministic chaos. Considerable regularization of the process was observed as an effect of modulation of the laser beam. The modulation factor (P_{max -}P_min )/P_max was equal to 0.2 and the modulation frequency was 2 kHz. In this case, the intense peak corresponding to the modulation frequency was observed in the power spectrum together with smaller peaks corresponding to the harmonic frequencies.

Results are presented for the time evolution of photoemission in a 0.1 cm parallel-plane gap in atmospheric pressure air when a positive dc voltage is applied at one of the electrodes. The hydrodynamic set of equations is solved using the finite-element flux-corrected transport method in two dimensions. The time evolution of the electron distribution at the cathode and the variation of the spread of the electrons are examined during the avalanche, the avalanche-to-streamer transition and streamer propagation stages. Finally, the effect of the variation of the photoemission coefficient on the field distribution and the current waveform are presented.

We propose two methods for obtaining the atomic-like background for the x-ray absorption fine structure (XAFS): the methods of smoothing spline and of Bayesian smoothing. Both are capable of using the prior information, calculated or experimental, about the background. The XAFS signals obtained by these techniques are shown to be significantly corrected in comparison with standard methods. The method of Bayesian smoothing is the only method that gives the errors of approximation of the atomic-like background by an artificial smooth function. These errors are shown to be the main source of the uncertainty of the XAFS function.

This paper deals with oxidation phenomena observed on surfaces submitted to the action of corona-activated ambient air. The study was mainly performed with gold and silicon surfaces chosen for their great material stability. During the discharge, the surfaces become covered with micronic water droplets which look like granules. They grow in number with the duration of the sample exposure to the discharge, their mean size depending on the material, and they resist the vacuum of the electron scanning microscope, but not its electron beam, especially when it is focused on them. From a chemical point of view, the surfaces are now oxidized in a way comparable with what can be obtained in liquid electrochemical solutions and, apart from the electrode material oxides or hydroxides observed, one can also find nitrogen oxides, but in clearly smaller quantities.

Repetitive laser pulses deposit sufficient energy to provide uniform-like heating at the surface of a substrate. This improves the surface properties of the substrate so treated. In the present study, an analytical solution for the temperature distribution due to repetitive laser pulse heating with a convective boundary condition at the surface is obtained. A Laplace transformation method is used when obtaining the analytical solution for the heat transfer equation. The effects of the pulse parameter (β/γ) and the Biot number (Bi) on the resulting temperature profiles for the possible attainment of a steady temperature at the surface during repetitive laser pulse heating is explored. The consecutive pulses with decreasing intensities are employed in the analysis while Bi is varied as 2×10^-4⩽Bi⩽0.2. It is found that it is unlikely that the temperature profile follows the pulse profile. The effect of Bi on the temperature profiles resulted from the repetitive pulses becoming significant when Bi⩾10^-2.

We present some results of a theoretical investigation on the free flexural vibration of a slender prismatic rod containing the materials for which the elastic moduli in tension and compression may differ. For simplicity the rod considered possesses a longitudinal plane of symmetry, and the initial condition adjustment and support are also symmetric with respect to this plane. The equation of motion that we have derived is nonlinear, no matter how low the amplitude of flexural vibration is. The nonlinearity is based on the fact that the flexural rigidity of the rod depends on the sign of a local curvature of the bent rod treated as an elastic line. We investigated the particular solution that corresponds to the fundamental mode of flexural vibration. In this mode, the rod performs periodic, though not simple harmonic, vibration. The frequency of this vibration is derived as a function of the material and geometric properties of the rod investigated.

A general model that explains the mechanisms of the cleaning process of technological liquids and gases, and that estimates and controls the results of these processes, has not yet been found. It is possible to simulate the magnetic filtration of a technological medium by using electrical circuit theory. Characteristics of filtration processes under different regimes can be easily obtained by an appropriate change of nonlinearity parameters of the circuit. Furthermore, the presented model seems to be promising for non-magnetic filtration and other processes similar to filtration, such as separation, absorption, flotation and classification.

A novel route for the formation of nano-aggregates of aluminium by ion irradiation of a spin-cast metal-organic thin film of aluminium acetyl acetonate [((CH₃CO)₂CH)₃Al] is reported. Glancing angle x-ray diffraction studies on an irradiated sample show the formation of fcc aluminium clusters. Microstructural studies using transmission electron microscopy show the formation of aggregated branched nanoclusters of diameter ≈5-60 nm, which on increasing fluences interconnect through branches and form a network-like structure. Networked structures of aggregated Al clusters might have formed due to overlapping of multiple ion tracks at relatively higher fluences.

It was noted that the model of streamer pseudo-branching, proposed in `The role of photoionization in positive streamer dynamics' (Kulikovsky A A 2000 J. Phys. D: Appl. Phys.33 1514-24) in 2D geometry, cannot be vindicated within the frame of the physical model used in the article. It was also shown that the results of numerical simulation represented in the article are not repeatable.

The main results of the discussed work are summarized. The simple arguments of the authors of the comment do not prove streamer stability. The failure to reproduce our numerical results could be caused by the use of a coarse grid for photoionization calculations. A possible mechanism of streamer instability is briefly discussed.