Table of contents

After a brief history of plasma arc cutting (PAC) is given, its types and abilities are discussed. Experimental data (unfortunately, little is available) on plasma parameters are reviewed. The status of contemporary understanding of the process involved in PAC is presented. The main emphasis is on those processes that determine the technological abilities of the method. Along with the existing theories reviewed, we propose qualitative hypotheses on some of these processes. Among them are: dependence of the cyclic cathode erosion on the rate of current increase, double arcing and the role of insulating inclusions at the nozzle orifice on double arcing, dross formation and the shape of the kerf.

Gas phase nanoparticle production, manipulation and deposition is of primary importance for the synthesis of nanostructured materials and for the development of industrial processes based on nanotechnology. In this review we present and discuss this approach, introducing cluster sources, nanoparticle formation and growth mechanisms and the use of aerodynamic focusing methods that are coupled with supersonic expansions to obtain high intensity cluster beams with a control on nanoparticle mass and spatial distribution. The implication of this technique for the synthesis of nanostructured materials is also presented and applications are highlighted.

FePt particles 6 nm in size are produced by argon/nitrogen sputtering and gas-phase condensation. Marked changes in the atomic structure and morphology of the particles occur upon addition of nitrogen to the sputter gas. Electron energy loss spectroscopy and x-ray absorption spectroscopy show that nitrogen is incorporated in the particles in molecular and compound form. In situ sintering of the particles drives out the nitrogen causing enhanced diffusion leading to the preference of the L1₀ structure over the multiply twinned icosahedral structure, which forms in the absence of nitrogen in the sputter gas.

The magnetic and mechanical dynamics of nanometre-sized magnetic particles with a uniaxial anisotropy excited by ac magnetic fields is studied using the classical theory approach in the Lagrangian formalism. Through the magnetic anisotropy between the magnetic moment and the lattice, the nanoparticle is coupled with the magnetic moment and then driven into a mechanical precession mode by the ac magnetic fields. Mechanical resonance can be achieved along with the magnetic resonance at frequencies and with resonance amplitudes that depend strongly upon both the magnetic and the mechanical properties of the nanoparticles. The dynamics manifests itself in magnetic susceptibility and energy dissipation, which are discussed in great detail in this article.

The kinetics of multilayer deposition of colloidal particles (hematite (α-Fe₂O₃), chromium (hydrous) oxide (Cr(OH)₃, rod-like akageneite (β-FeOOH) and magnetite (Fe₃O₄) in distilled water) on C1018 steel beads is studied under the influence of magnetic fields. The study is conducted using a packed column technique under the conditions of constant flow rate (3 cm min⁻¹) and pH value (11). The rate of deposition increases rapidly in a magnetic field which remains constant and at a late-stage deposition multilayers are formed. A model of multilayer deposition is proposed. The model involves new parameters which characterize the multilayer deposition probability.

Zn_1−xFe_xO films were prepared by the radio-frequency (rf) magnetron sputtering technique on n-Si substrates with a composite target of a ceramic polycrystalline ZnO containing several Fe pieces on the surface. X-ray photoelectron spectroscopy study of the Zn_1−xFe_xO films shows that Fe in the as-deposited film exists mainly in the form of Fe²⁺. And x-ray diffraction spectra show that all the films exhibited c-axis orientation. The room temperature photoluminescence (PL) properties of the Zn_1−xFe_xO films were also discussed. Two obvious PL peaks appear at 378 nm and 414 nm, respectively. It is interesting that there is a tendency of redshift for the peak at 378 nm and that the PL intensity increases slightly for the peak at 414 nm as the Fe concentration increases. Discussions have been given to explain the different phenomena.

Ag : Si₃N₄ nanocermets were fabricated by the magnetron cosputtering method and were thermally treated at different temperatures. The off-resonant third-order nonlinear susceptibilities were determined to be of the order of 10⁻¹⁰ esu at 800 nm by the optical Kerr effect experiment. Further time-resolved pump–probe researches prove that heat treatment is a feasible way to improve the performance of ultrafast response for this material. The research results demonstrate that in addition to the common use in microelectronics, the Si₃N₄ nanocermets are promising in future applications in optical communication and photoelectric fields.

In-situ Sn-doped CdS thin films have been deposited successfully by the chemical bath deposition method using tartaric acid as a complexing agent. The films have been characterized by x-ray diffraction for structure determination, and microstructural parameters like crystallite size, rms strain and dislocation density have been calculated using x-ray line profile analysis. The composition of the films has been determined by x-ray photoelectron spectroscopy and energy dispersive x-ray analysis. Optical studies show that the band gap decreases significantly for pure CdS (2.39 eV) to 3.8 mol% of Sn-doped CdS (1.84 eV). A detailed PL study of CdS when doped with varying Sn concentrations has also been discussed. Temperature variation of the electrical resistivity of Sn-doped CdS thin films confirmed their semiconducting behaviour similar to the pure CdS. It also shows that doping of Sn in CdS makes a pronounced drop in the room temperature resistivity value from 10¹⁰–10³ Ω cm for pure CdS to 3.8 mol% of Sn-doped CdS, respectively.

Zinc selenide (ZnSe) thin films were deposited onto well cleaned silicon (100) and glass substrates at different substrate temperatures (483–589 K) using vacuum evaporation method under a vacuum of 4 × 10⁻³ Pa. The compositions of the deposited films were determined by Rutherford backscattering spectrometry and the percentage of iodine concentration is calculated as (ZnSe)I_0.001. The x-ray diffractograms reveal the cubic structure of the film oriented along the (111) direction. In optical studies, the transition of the deposited film is found to be a direct allowed transition. The optical energy gaps of the deposited films are found to be in the range from 2.72 to 2.60 eV. ZnSe/silicon Schottky diodes were fabricated. From the current–voltage measurement the ideality factor was found to be in the range 2.01–3.51. From the capacitance–voltage studies, the built in potential was found to be 1.51 V. The values of effective carrier concentration (N_A) and the barrier height are calculated as 4.37 × 10¹¹ cm⁻³ and 1.95 eV, respectively.

Two kinds of heterostructures have been proposed and investigated in this paper. One is called the SCSC heterostructure which is composed of two semi-infinite two dimensional phononic crystals (PCs) consisting of circular cylinders embedded in the square lattice with different filling fractions, and the other is named the RRTC heterostructure, which is composed of two semi-infinite PCs consisting of rectangular cylinders in a rectangular lattice and circular cylinders in a triangular lattice, respectively. The interface guided modes in the PC heterostructures with CCl₄ (mercury) cylinders in a mercury (CCl₄) host were analysed using the plane-wave expansion method in combination with a supercell technique. The results show that interface states are absent in the simple SCSC heterostructure, but they can be created either by lateral lattice slipping or by increasing the interface separation, and also the absolute gap width and the number of guided modes depends strongly on the relatively transverse displacement and longitudinal gliding. It is anticipated that the guided modes in such heterostructures can be engineered by adjusting the relative transverse or longitudinal displacement. For the RRTC hererostructure, it could generate interface guided modes states without any relative displacement.

A Monte Carlo simulation technique is used to investigate electron transport in carbon tetrafluoride (CF₄) for an arbitrary configuration of electric and magnetic fields. We investigate the way in which the transport coefficients and other swarm properties are influenced by the electric and magnetic field strengths and the angle between the fields. In addition, the sensitivity of transport data on the presence of non-conservative collisions (attachment/ionization) is analysed. It is found that the difference between the two sets of transport coefficients, bulk and flux, resulting from the explicit effects of non-conservative collisions, can be controlled either by the variation of the magnetic field strengths or by the angles between the fields. This study was initiated in order to obtain the transport data for input into the fluid models of magnetron and inductively coupled plasma discharges as well as several types of high energy particle detectors, and has resulted in a database of such transport data. Values and general trends in the profiles of mean energy, collision frequency, rate coefficients, drift velocity elements and diffusion tensor are reported here.

A simplified analytical model is proposed to evaluate some characteristics of the arc jet generated with a dc plasma torch, in the restricted area of atmospheric plasma spraying conditions. The plasma inside the anode nozzle is considered as stationary and is divided into the arc column and a surrounding cold layer which electrically insulates the plasma from the nozzle wall. Radiation and processes related to the arc attachment at the electrodes are not explicitly taken into account. Heat conduction is evaluated by using Kirchoff's potential, which is described, as it is done also for the electrical conductivity, as a function of the gas specific enthalpy instead of temperature. The model is used to calculate the specific enthalpy radial distribution. From that, and by introducing a mean isentropic coefficient, it is possible to calculate the axial velocity of the plasma jet at the nozzle exit and to evaluate the different pressure contributions. The comparison between predicted and previously measured plasma jet velocities shows good agreement for various experimental conditions.

Application of a voltage pulse having a rise time of tens of nanoseconds to electrodes immersed in water results in streamer development and the formation of a highly conductive plasma channel between the electrodes. The electrical resistance of such channels decreases rapidly from a few ohms to a few tens of milliohms due to Joule heating resulting from the high current which flows through the plasma. The dynamics of the plasma resistance depend on the parameters of the discharge circuit and the medium in which the discharge takes place. The resistance of the channel reaches a minimum value approximately at the moment of the peak current for under-damped current oscillations. During the resistance collapse, the pressure inside the channel rises to several GPa, causing a rapid expansion of the channel which forms a cavity in the liquid resulting in a high power ultrasound pulse. The cavity expands to a maximum size which is dependent on the circuit driving the discharge and the properties of the plasma discharge channel. The cavity then collapses producing a second acoustic pulse. In this paper the dynamic resistance of the spark channel is described using a phenomenological model based on the plasma channel energy balance equation used by Braginskii. The model which links the hydrodynamic characteristics of the channel and the resulting cavity with the parameters of the electric driving circuit allows the development of the plasma channel and cavity to be predicted. The peak high-power ultrasound (HPU) pressures calculated using this approach are compared with the pressure values estimated by an analytical model which uses a constant value of the spark channel resistance derived from experimental data. Comparisons are also made with direct measurements of HPU output made using a Pinducer sensor. Although the model is based on a phenomenological description of the plasma channel dynamics and its resistance and requires the value of the spark constant, the results obtained using this approach provide a reasonable agreement with experimental measurements and could therefore be used for the estimation of HPU pulse characteristics in practical applications of spark discharges in water.

The problem of heating a film on a semi-infinite substrate with repetitive high negative bias voltage pulses in contact with a plasma is solved by using the Laplace integral transform technique. The plasma is composed of a collisionless presheath and sheath on an electrically negative film, which partially reflects and secondarily emits ions and electrons. The heating rate of the film attributable to the plasma, the presheath and the sheath, is determined by kinetic analysis. This work proposes a semi-analytical model to calculate the temperature and temperature gradient evolutions inside the film and substrate and provides quantitative results applicable to the control of the temperature evolution. The predicted surface temperature of the film as a function of time is found to agree well with the experimental data. A minimum exits in the temperature gradient profile at a certain depth below the surface. As the heating period progresses, the point of minimum temperature gradient moves towards the solid bulk of the film. The temperature evolution rises periodically and the heat flux evolution oscillates near the vicinity of the surface of the film. In a region beyond a certain depth, the above-mentioned phenomena disappear, and the temperature and temperature gradient evolutions rise monotonically. The effects of the dimensionless pulse duty cycle and the bias voltage on the temperature and temperature gradient profiles could be demonstrated. The temperature at the front surface of the film increases linearly with the pulse parameters. The results show that the temperature and temperature gradient profiles inside the film and substrate are strongly dependent on the pulse parameters.

The surface topography and character of the deposited films formed from γ-aminopropyltriethoxysilane (KH-550) and dodecyltrimethoxysilane (WD-10) on a silicon dioxide substrate (0001) via vapour phase deposition was investigated using atomic force microscopy (AFM), x-ray photoelectron spectroscopy and static water contact angle measurement techniques. The surface topography of the silane films adsorbed on the silicon dioxide substrates is dissimilar with different silane coupling agents and different deposition conditions. The silane films adsorbed on the silicon dioxide substrate become rougher with the increasing time of the deposition, but become smoother with the increasing temperature of the silicon dioxide substrate. The character of the substrate surface was changed from a hydrophilic one to a hydrophobic one after KH-550 or WD-10 deposition, and the WD-10 treated silicon dioxide substrate has a larger contact angle (96.3°) than KH-550 treated substrate (78.7°) at the same deposition condition, which indicates that the WD-10 treated substrate is more hydrophobic than the KH-550 treated substrate.

By reactively sputtering Zr and Al₂O₃ targets in a gaseous mixture of Ar and N₂, ZrN/AlON nanomultilayers were synthesized to study the crystallization conditions for AlON layers and how they influence the characteristics of multilayers. The composition analysis indicated that some of the oxygen atoms were replaced by nitrogen atoms in Al₂O₃, leading to the formation of aluminium oxynitride, AlON, during the procedure of the Al₂O₃ target being sputtered in the gaseous mixture. Further investigations showed that when their thickness was limited to less than 1 nm, amorphous AlON layers were crystallized under the template effects of crystalline ZrN layers, and then coherent interfaces formed as a result. Correspondingly, the multilayers were remarkably strengthened with hardness approaching a maximum of 33 GPa. After the layer thickness of AlON exceeded the critical value of 1 nm, the subsequently deposited AlON grew amorphously and blocked the epitaxial growth of multilayers, accompanied by the decline of hardness. Yet, on the other hand, the integrated hardness of multilayers was not sensitive to the thickness of the ZrN template layers and its value was maintained a bit higher than 30 GPa in a wide range of ZrN layer thickness variations.

Laser micromachining of transparent materials is a promising technique for producing micro-optical elements. Several types of both direct (e.g. ablation) and indirect (e.g. laser-induced backside wet etching: LIBWE) procedures have already been developed and presented in the last two decades. Here we present a new method (laser-induced backside dry etching (LIBDE)) in the analogy of LIBWE for the micro and nanoprocessing of transparent materials.

In our experiments 1 mm thick fused silica plates were used as transparent work pieces. The plates were covered with 100 nm thick silver layers. The metal absorbing films were irradiated through the fused silica by a KrF excimer laser beam (λ = 248 nm, FWHM = 30 ns). The illuminated area was 1.05 mm² and the fluence on the silver–quartz interface varied in the range 0–1800 mJ cm⁻². We have provided evidence that LIBDE is more effective and simple than LIBWE, its etch rate being much higher at a given laser fluence. Our interference experiments proved that the LIBDE etching technique is suitable to fabricate gratings displaying submicrometre periods in transparent materials. On the basis of all these, it is suggested that this method may be useful to produce other nano and microoptical elements, too.

In the present work, a combination of Raman spectroscopy and grazing incidence x-ray reflectivity (GIXRR) techniques has been used for structural characterization of electron-beam evaporated [Si (5 nm)/Ge (5 nm)]_{× 10} and [Si (10 nm)/Ge (10 nm)]_{× 10} multilayer structures (MLS) as a function of annealing temperature. The Raman measurements show that in the case of both short and long period Si/Ge MLS, in addition to the normally observed Si–Si and Ge–Ge optical phonon modes, we also observe first order features from SiGe alloy, indicating the presence of intermixing and phase formation at the interface during deposition. Also the frequency and intensity of this alloy feature depends mainly on layer thicknesses and are enhanced in longer period MLS. These results are also supported by GIXRR and atomic force microscopy (AFM) measurements. However, in spite of the heavier interdiffusion during deposition, upon annealing at higher temperatures the longer period MLS shows a comparatively stable nature. The results are interpreted in terms of diffusion-induced structural changes in the MLS as a function of annealing temperature.

Polyimide (C₂₂H₁₀N₂O_5, PMDA-ODA, Kapton-H) samples were doped with phosphorous or boron and fluorine using the radiation assisted diffusion technique, with Co-60 gamma-rays over the dose range ∼64–384 kGy, at room temperature. The diffusion of phosphorus and fluorine was confirmed by the RBS technique and that of boron by the neutron depth profiling technique. The elemental concentration on the surface was studied by the XPS technique. The relative concentration of phosphorus, fluorine and boron increased with increasing dose of gamma-rays. The dielectric constant, ε', of the polyimide increased by ∼43% after phosphorus doping but decreased by ∼33% after boron and fluorine doping. The increase in ε' is attributed to the radiation induced chemical coupling of the phosphorus atoms across the intra-molecular polyimide chains. The down shift in ε' is attributed to the decrease in the degree of electronic polarization and to the increase in the free volume due to the diffused boron or fluorine atoms. For all the doped samples the dielectric constant, ε', decreased very slowly with increasing frequency, over the range 100 Hz–7 MHz. AFM results reveal that the surface morphology and the roughness of the doped polyimide are appreciably different than that of virgin polyimide.

The time and space resolved emission profiles of the CII line from the laser-blow-off (LBO) plumes of multilayered LiF-C thin film have been investigated using a laser-induced forward transfer technique. The evolution features of the 426.7 nm line were studied in different ambient environments ranging from high vacuum to 3 mbar of argon pressures and at various fluences of the ablating laser. It was found that many features of the plasma plume generated by the LBO method resemble that of plumes created in conventional laser produced plasma; however, a few differences were observed in their behaviour with regard to plume splitting and plume compression. A sudden change in the temporal profile was observed to occur at a distance about 4–6 mm away from the target. The variation of the plume structures observed at different fluences of the ablating laser is reported. The validity of the Rayleigh–Taylor instability, shock wave and drag force model in the present experiment are also discussed.

It is shown that the electrical transport in ferromagnet–ferroelectric–type La_0.67Ca_0.33MnO₃/BaTiO₃ composites fabricated by the sol–gel method strongly depends on sintering temperature (T_s). For the T_s > 1000 °C samples, the insulator–metal transition temperature (T_IM) decreases with increasing BaTiO₃ content and the magnetoresistance (MR) is enhanced at low temperature (T < T_IM). For the T_s = 1000 °C samples, the T_IM value initially increases with an increase of BaTiO₃ content and thereafter it decreases as BaTiO₃ content further increases. For the T_s = 900 °C samples, the T_IM value increases throughout the increase in BaTiO₃ content and MR is enhanced over the whole temperature range studied. The experimental results have been discussed in terms of the magnetoelectric coupling effect and the interfacial diffusion reaction, especially at grain boundaries.

In addition to our previous work, we report on further experimental results concerning Langmuir–Blodgett polyvinylidenefluoride-copolymer thin films. Polarization hysteresis loops and polarization switching behaviour of samples with thicknesses below 3 nm were measured. Also, the time and temperature comportments of the remanent polarization were investigated for various film thicknesses, ranging from 2.7 up to 63.8 nm. The remanent polarization shows a loss of about 10% over 3 decades of time, ranging from 100 to 2 · 10⁵ s. For thinner films, the remanent polarization exhibits the typical behaviour of a first-order transition, whereas for thicker samples a diffuse transition is found. Initial polarization curves obtained from the unpolarized state were finally measured. They are temperature and thickness dependent.

We have found that the effective thermal resistance of carbon nanofibre (CNF) arrays can be reduced significantly (by as much as 30%) by using rapid thermal annealing (RTA). The RTA was carried out in the temperature range 800–1050°C for about 1 min in the H₂ and N₂ atmosphere. We attribute the observed reduction in the thermal resistance to the improved quality of the CNF material, as well as to the decrease in the contact resistance at the interface between the array and its (silicon) substrate. The improvement in the quality of the CNF material has been established on the basis of the Raman spectroscopy. We suggest a suitable criterion ('figure of merit') to characterize the CNF material quality. A photothermal method is employed in our analysis to assess the level of the interfacial resistance. We conclude that RTA can result in substantial improvement in the thermal properties of the CNF materials. We also conclude that the application of Raman spectroscopy enables one to establish, in an effective and non-destructive fashion, a useful criterion of the CNF material quality.

The reduced mobility and diffusion coefficients of and O⁻ are calculated with a Monte Carlo simulation for the gas mixtures N₂–H₂O (50%, 50%) and O₂–N₂ (80%N₂, 20%O₂), respectively, from measured and calculated elastic and inelastic cross sections. These mobility and longitudinal diffusion coefficients have been compared with the standard Blanc's law and with the common mean energy (CME) procedure. Good agreement between these three calculation methods was found for the mobility and diffusion of in the N₂–H₂O mixture at high reduced fields where inelastic processes are relatively uninfluential. However, a strong deviation between Blanc's law and both CME procedure and our Monte Carlo calculations for the reduced mobility and the diffusion coefficient of in this gas mixture N₂–H₂O was observed at low reduced fields, because inelastic processes are significant. On the contrary, for the case of the N₂–O₂ mixture, where inelastic processes are small over the reduced electric field range 1–8000 Td, the three calculation methods led to similar results. The elastic collision cross sections used were determined from a semi-classical JWKB approximation by using a rigid core potential model for both symmetric and asymmetric , O⁻/O₂ and O⁻/N₂ ion–neutral systems. Moreover, the inelastic cross sections were extended to low energies from appropriate approximations. These cross section sets were validated from the good agreement between our Monte Carlo calculated reduced mobilities in N₂ and H₂O, O⁻ in O₂ and N₂ and either measured values for the systems and O⁻/O₂ or physical properties of the systems and O⁻/N₂.

In this work, a recursive algorithm to solve fin problems with temperature-dependent thermal conductivity is given. The algorithm is based on the Taylor series solution. The results are compared with the solutions obtained by the Adomian decomposition method (ADM) and with the numerical solutions as well. The results of the comparisons have shown that the ADM is just an approximation of the present study and the accuracy of the solution is also worse than the present algorithm.

The interdigital transducer (IDT) is a key component in surface-acoustic wave (SAW) and acousto-optical devices and has extensive applications in signal processing and optical communication at present. Properties of the acoustic field are mainly dominated by the geometric shapes of the electrodes (i.e. fingers) of the IDT and the piezoelectric characteristics of the substrate. However, the studies on excitation and acoustic wave field characteristics of IDTs are still not matured or perfect. In this paper, the 2D interface Green's function method (GFM) for simulating numerically the SAW field of IDTs with arbitrary finger shapes is presented. The electric charge densities originated from the electrostatic field and the generated SAW on the IDT electrodes are calculated first using the 2D interface GFM. Then the charge density distribution as the distributed source of SAW used to calculate the SAW field. IDT with arbitrary finger shapes can be treated. As an example, the properties of a SAW field generated by focused IDTs with the shape of concentric circular arc fingers on Y–Z LiNbO₃ and c-oriented PZT substrates are also analysed and discussed. The method can be applied to numerical analysis of IDTs with arbitrary finger shapes, such as broadband chirp transducers, curved-finger transducers and finger-length weighted transducers.