Table of contents

During the past two decades, diamond-like carbon (DLC) films have attracted an overwhelming interest from both industry and the research community. These films offer a wide range of exceptional physical, mechanical, biomedical and tribological properties that make them scientifically very fascinating and commercially essential for numerous industrial applications. Mechanically, certain DLC films are extremely hard (as hard as 90 GPa) and resilient, while tribologically they provide some of the lowest known friction and wear coefficients. Their optical and electrical properties are also extraordinary and can be tailored to meet the specific requirements of a given application. Because of their excellent chemical inertness, these films are resistant to corrosive and/or oxidative attacks in acidic and saline media. The combination of such a wide range of outstanding properties in one material is rather uncommon, so DLC can be very useful in meeting the multifunctional application needs of advanced mechanical systems. In fact, these films are now used in numerous industrial applications, including razor blades, magnetic hard discs, critical engine parts, mechanical face seals, scratch-resistant glasses, invasive and implantable medical devices and microelectromechanical systems. DLC films are primarily made of carbon atoms that are extracted or derived from carbon-containing sources, such as solid carbon targets and liquid and gaseous forms of hydrocarbons and fullerenes. Depending on the type of carbon source being used during the film deposition, the type of bonds (i.e. sp¹, sp², sp³) that hold carbon atoms together in DLC may vary a great deal and can affect their mechanical, electrical, optical and tribological properties. Recent systematic studies of DLC films have confirmed that the presence or absence of certain elemental species, such as hydrogen, nitrogen, sulfur, silicon, tungsten, titanium and fluorine, in their microstructure can also play significant roles in their properties. The main goal of this review paper is to highlight the most recent developments in the synthesis, characterization and application of DLC films. We will also discuss the progress made in understanding the fundamental mechanisms that control their very unique friction and wear behaviours. Novel design concepts and the principles of superlubricity in DLC films are also presented.

The magnetic properties of conventional amorphous microwires are determined by the radial, azimuthal and axial internal stresses induced both during the preparation process and during suitable thermal treatments. We propose a theoretical model in order to determine the total internal stresses induced during the 'complete' dc Joule-heating thermal treatment (heating–crystallization–cooling). We have started from the internal stresses values obtained in the preparation process and we have found that: (i) maximal values of the axial, azimuthal and radial stresses obtained after the thermal treatment are larger than the corresponding values obtained in the preparation process, the differences being of about 350 MPa, 150 MPa and 200 MPa, respectively; (ii) the dimensions of the cylindrical inner core increase significantly (with ∼15.2%); this fact involves the appearance of a large Barkhausen effect in low axially applied magnetic fields; and (iii) the reduced remanence increases from 0.46 to 0.70.

Magnetic levitation of miniaturized objects is investigated in this paper. A magnetic levitation setup is built to implement one-dimensional magnetic levitation motion. It was observed that as the levitated object becomes smaller, magnetic levitation suffers more from undesired vibrations. As a solution, eddy current damping is offered and implemented successfully by placing conductive plates close to the levitated object. An analytical expression for damping coefficient is derived. Experimentally, it is shown that eddy current damping can reduce the RMS positioning error to the level of more than one third of its original value for a 0.386 g object levitated in an air-gap region of 290 mm. The proposed system has the potential to be used for micro-manipulation purposes in a high motion range of 39.8 mm.

A Fe nanowires-filled amorphous carbon nanotubes (FeNW-filled a-CNTs) array was synthesized by sequential growth of electrodeposited Fe nanowires and subsequent chemical vapour deposition of amorphous CNTs in the nanochannels of alumina template. Structural characterizations of as-prepared FeNW-filled a-CNTs were carried out via field emission scanning electron microscope (FE-SEM), x-ray diffraction (XRD), elemental mapping, high-resolution transmission electron microscope (HRTEM) and Raman scattering. The formation mechanism of such Fe/C nanoheterostructure was proposed according to the detailed HRTEM analyses. Furthermore, the room temperature magnetic property of the as-prepared FeNW-filled a-CNTs array was also investigated, and obvious anisotropic behaviour in magnetization was observed.

Radio-frequency experimental measurements of magnetically coupled chains of L-C resonators supporting magneto-inductive (MI) waves are presented. MI waveguides are constructed using printed circuit board (PCB) inductors and external capacitors. Methods for increasing the nearest-neighbour coupling and reducing the non-nearest neighbour coupling using double-sided PCBs are demonstrated. Conditions for low propagation loss are determined, and a method of approximate matching to 50 Ω transmission lines is presented. Propagation losses of 0.12 dB per element and coupling losses of 0.4 dB are achieved, using elements with Q-factors of 110 at ≈150 MHz frequency. Simple recursive Fabry–Perot filters are demonstrated by inserting reflectors into the waveguide.

A direct mathematical approach is presented to calculate the absolute full-energy peak (photopeak) efficiency and coincidence correction of hyper pure germanium (HPGe) detectors for extended circular disc sources. The calculation of the full-energy peak efficiency is based on elliptic integration and its validity was checked by comparison with experimental measurements. Extensive experimental readings have been carried out; gamma sources containing several radionuclides covering the energy range from 60 to 1836 keV were used. By comparison, the theoretical and experimental full-energy peak efficiency values are in good agreement; the overall percentage error is less than 3%.

Carefully prepared bulk ceramic specimens of In₂O₃ and Sn-doped In₂O₃ (ITO) were analysed with x-ray and UV photoelectron spectroscopy before and after heat treatment in vacuum and oxygen atmosphere. The results on ex situ prepared ceramic specimens were shown to be comparable to those of in situ deposited-measured thin films in terms of core levels, Fermi levels and ionization potentials. This suggests a viable path for rapid synthesis and screening of surface electronic-defect properties for other transparent conducting oxides (TCO) materials. A strong correlation exists between the surface electronic-defect structure of In₂O₃-based TCOs and their underlying electronic-defect structure, owing to the unique crystal-defect properties of the bixbyite structure. This leads to formation of a chemical depletion at the surface and the formation of a peroxide surface species for higher preparation temperatures. The results are discussed with respect to the use of ITO as hole injection electrode in organic light emitting devices.

Buried silicon carbide (SiC) was synthesized at room temperature using implantation of 150 keV C⁺ ions in n-type Si (100) and Si (111) substrates. The dose of implanted C⁺ was varied from 4 × 10¹⁷ to 8 × 10¹⁷ cm⁻². Post-implantation annealing at 1000° C for 30 min was carried out in inert ambience. Rutherford backscattering spectroscopy, x-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy and Raman spectroscopy were employed to characterize the samples. FTIR and Raman spectroscopic techniques in combination with the XRD analysis confirmed the development of the β-SiC phase in the samples. The average size of the SiC precipitates was estimated to be 9 nm from XRD analysis.

We report here a straightforward and rapid microwave–hydrothermal route providing an easy synthesis of Eu³⁺ doped La₂O₃ nanowhiskers. The nanostructured Eu³⁺ doped La₂O₃ is characterized by x-ray diffraction studies, scanning electron microscopy and photoluminescence (PL). The emission spectrum shows transitions from the excited 5D₀ state to ⁷F_J (J = 0, 1, 2, 3, 4) levels of the Eu³⁺ ion. The most intense peak around 611 nm is due to the ⁵D₀ → ⁷F₂ transition, expected from the Judd–Ofelt selection rules. PL spectra measurements demonstrate that the lanthanum oxide nanowhisker shows higher PL intensity.

A three-dimensional hydrodynamic model is developed to simulate a post-discharge reactor placed downstream from a flowing microwave discharge in N₂–O₂ used for plasma sterilization. The temperature distribution and the density distributions of NO(B ²Π) molecules and O(³P) atoms, which are known to play a central role in the sterilization process, are obtained in the reactor in the case of discharges at 915 and 2450 MHz, pressure range 1–8 Torr and N₂–xO₂ mixture composition, with x = 0.2–2%. Excluding the flow direction, sufficiently low temperatures ideal for sterilization have been found in most parts of the reactor. The highest NO(B) and O(³P) concentrations at the reactor entrance are achieved at the highest pressure values investigated here. However, these larger densities rapidly decrease within a few centimetres below the values obtained at lower pressure. On the contrary, at low pressure the density distributions of NO(B) and O(³P) are quasi-homogeneous in most of the horizontal planes. At 8 Torr the densities increase orders of magnitude in the reactor as the gas flow increases from 1 × 10³ to 4 × 10³ sccm, while at 2 Torr this increase does not reach even one order of magnitude. In agreement with the experiment, the densities of NO(B) and O(³P) have been found to increase at 2 Torr as the O₂ percentage increases in the discharge gas mixture, whereas at 8 Torr the density of NO(B) decreases with O₂ percentage and the O(³P) density presents only minor changes.

The ionization distribution of a small scale rotating cylindrical magnetron discharge is simulated by a Monte Carlo based program. The simulation describes the high energy electron trajectories and the interaction between these electrons and the sputtering gas, which finally leads to the ionization distribution. By radial projection of the ionization positions on the target surface, the erosion track dimensions can be correctly simulated. The discrepancy between the simulation and the experiments shows the need to modify the experimental design and to control the alignment between the central axis of the target tube and the magnet configuration in a better way.

A particle-in-cell simulation of beam extraction through a hole in contact with plasma was developed. Particular emphasis was placed on plasma moulding over the hole, ion neutralization in high aspect ratio holes and the energy and angular distributions of the residual ions and fast neutrals in the beam downstream of the hole. When the sheath thickness is much smaller than the diameter of the hole, plasma moulding is severe, and the resulting ion and neutral beams are highly divergent. When the sheath thickness is much larger than the hole diameter, plasma moulding is weak, and collimated beams may be extracted. The angular distribution of fast neutrals peaks off axis, less so for smaller diameters and deep holes. Larger diameters and shallow holes (more plasma moulding) yield narrower ion energy distributions. The fast neutral energy distribution is predicted to be similar to that of ions, but it is shifted to lower energies.

The last part of a numerical study of low-pressure nitrogen cold plasma created by a pulsed discharge in a point-to-plane geometry at 4 Torr is presented.

The present work deals with the discharge and plasma behaviour during the falling part of a rectangular shaped applied voltage pulse and completes our investigation of the discharge under the stress of this voltage shape.

The relative model is based on fluid description of the cold plasma, on Poisson's equation for the electric field and on balance equations for the excited population taking into account only the most important generation and decay mechanisms of the radiative B ³Π_g, C ³Π_u and the metastables states of nitrogen, according to the conclusions of our recent work (Potamianou et al 2003 Eur. Phys. J. Appl. Phys.22 179–88). Results for space and time evolution of the charged particles densities, electric field, potential and electron current density are reported. According to these results, a non-neutral channel is formed that evolves slowly and ends in the formation of a double layer. Excited particle distributions are presented and the influence of the electron current density discussed. It seems that, in this kind of discharge, creation of active particles is not only due to electron current density but also physicochemical mechanisms. The obtained results will help to determine optimal conditions for polymer surface treatment.

The spectral radiance of the 185 and 254 nm lines in two positive column mercury discharge lamps was measured over a wide range of operating conditions. The lamps had internal diameters of 5 and 23 mm. Argon was used as a carrier gas. The lamps were operated with cold spot temperatures of 20, 40 and 60 °C. At each of these temperatures, results were obtained for five currents ranging from 20 to 100 mA for the 5 mm lamp and from 200 to 1000 mA for the 23 mm lamp. For each current studied, results were determined for argon pressures ranging from 66.6 to 666 Pa (0.5 to 5.0 Torr) in the 5 mm lamp and 26.6 to 666 Pa (0.2 to 5.0 Torr) in the 23 mm lamp. An argon miniarc was used as the radiometric standard. By calibrating the spectral response of the optical system with a well-characterized mercury pencil lamp, results were obtained for 12 additional Hg lines from 289 to 579 nm. For the 23 mm lamp the electric field in the positive column was measured. For this lamp the radiated power as a percentage of input power was also determined. The results provide an experimental basis for validating computer models of Hg fluorescent lamp discharges.

The dynamics of laser-produced plasma (LPP) and its shockwave-induced density jump (SIDJ) were investigated in low-pressure ambient air during the laser pulse using an optical interferometer. A tiny SIDJ could be observed clearly in ambient air with pressure as low as 3 Torr even during the rising edge of a 7 ns laser pulse. It was shown that the density jump and ionization could seed laser-induced ambient air breakdown at a relatively low pressure, which could significantly reduce laser energy deposited in the LPP. The ionization of the density jump was confirmed by dynamic emission imaging.

A two-dimensional (axially symmetric) computational model of the microdischarge formation in a barrier discharge for short (1–2 mm) gaps in air at atmospheric pressure is proposed. A non-homogeneous electric field, caused by a residual non-uniform charging of the dielectric barriers, is considered as an important reason for the filament formation by a Townsend mechanism. The ion–electron emission from the dielectric covering the cathode is treated as the principal secondary process; the secondary emission coefficient in the model is selected to be consistent with the Paschen voltage. For an applied sinusoidal voltage, this follows the microdischarge development on a microsecond scale. It is shown that even a slight inhomogeneity of the initial electric field leads to the formation of a narrow microdischarge channel.

The two-dimensional dynamics of the radiation from a microdischarge for the case of the second positive and the first negative systems of nitrogen is simulated and compared with recent experimental data. The effects of the secondary emission coefficient and of a distribution of residual surface charges are investigated. It is shown that the level of inhomogeneity of the residual surface charge distribution does not affect the radius of the microdischarge channel, but affects its two-dimensional structure.

The proposed model explains satisfactorily the experimental results for the velocity of the cathode-directed ionizing wave and the emission of the N₂ second positive system from a microdischarge.

A detailed study of the mechanical interphase (IP) between an amine-cured epoxy and the amorphous thermoplastic polyvinylpyrrolidone (PVP) was performed. The amine curing agent was diaminodiphenylsulphone (DDS). With 170 °C, the curing temperature was close to the glass transition temperature of PVP. Using a depth-sensing indentation setup equipped with a Berkovich indenter, force penetration curves were measured at different positions on the cross-section of an epoxy/PVP/epoxy sandwich specimen. Profiles of the sample Young's modulus, E_s, the hardness, H, and the plasticity index, ψ, were analysed as a function of the distance from the epoxy/PVP interface. Each of these quantities showed significant variations. Furthermore, the profile of the ratio between the reduced modulus of the tip–sample contact, E_r, and the hardness is shown to reflect the profile of the plasticity index, that is the relative amount of plastic indentation work. A relationship is presented that allows the calculation of the plasticity index from the ratios E_r/H and h_f/h_c, where h_f and h_c denote the final depth and the contact depth, respectively. Although the Young's modulus shows strong variations, the hardness appears to be the most sensitive parameter for IP property variations. Three different zones can be identified from the hardness profile, with respective widths of ∼21.3, 52.5 and 160.9 µm, which add up to a total IP width of ∼234.7 µm. Zone Z1 is located next to the PVP layer. The outer edge of zone Z2 is located at a position similar to the one of the amine depletion zone. The latter was detected by means of energy-dispersive analysis of x-rays and its width is ∼71 µm. Inspection of the residual imprints shows a larger plastic deformation for zone Z1, in agreement with the high values of the plasticity index and of the creep deformations. From these grounds, the different IP zones are discussed in terms of the diffusion processes taking place during the epoxy curing procedure. Zone Z1 is associated with bi-directional interdiffusion across the initial interface. Zone Z3 can be attributed to long-ranging effects reaching far beyond the amine depletion zone.

Light scattering in thin films represents several essential microstructural, morphological and compositional parameters in thin film systems. Under the present investigation certain gadolinia, silica thin films and multilayer systems have been probed for their spectral scattering signals using the photophysics beamline of INDUS-1 synchrotron radiation source. The pulsed structure of synchrotron radiation and its interaction with certain non-wedge optical component has however led to the spectral interference (SI) modulations in scattering signals, which was tackled by an appropriate modelling and analysis technique. Under this technique the geometric mean of the SI amplitudes were computed and then de-convoluted into several Gaussian peaks. Each Gaussian peak was made to interfere with an appropriate temporally delayed peak having certain transformed amplitude factors. Superposition of all these Gaussian interference was computed and compared with the experimental profile in an iterative manner to determine the mean pulse delay introduced by the optical element. Finally the inverse fast Fourier transform of the experimental SI signal was carried out to compare the modelling results and both the approaches demonstrated a closed match. Spectral scattering signals recorded for various thin film layer combinations depicted close resemblances with the specular characteristics recorded using a spectrophotometric technique. This distinctly highlights the dominance of multilayer thin film interference phenomena on the spectral light scattering characteristics.

The purpose of this study was to compare the thermal resistance of a wetsuit fabricated from aerogel-syntactic foam hybrid insulation developed by Bardy et al [1] to a foam neoprene wetsuit. The thermal resistance of the hybrid wetsuit and a foam neoprene wetsuit was measured on a human test subject in water at 0.25 MPa (15.25 msw) of hyperbaric pressure. Measurements showed that although certain body regions of the hybrid wetsuit had a higher thermal resistance than foam neoprene, the overall thermal resistance of the hybrid wetsuit was 41% less than a foam neoprene wetsuit, and 51–88% less than predicted values. This was postulated, based on sample testing in water, to be due, in part, to increased heat flow through the hybrid insulation from water filled surface depressions at higher pressures. Other factors may have included water flow over the skin and the presence of thermal bridges in the insulation. Due to a smooth surface and tighter fit, the measured thermal resistance of the foam neoprene wetsuit was within 2–23% of the values predicted using data from Bardy et al [2]. It was concluded that unless the surface depressions can be eliminated, and alternative methods for a tighter fit achieved, foam neoprene provides more thermal protection.

Zirconia (ZrO₂) nanoparticles have been synthesized by a novel two-reverse emulsion technique and combined with polypyrrole (PPY) to form ZrO₂–PPY nanocomposites. The complex impedance and dielectric permittivity of ZrO₂–PPY nanocomposite have been investigated as a function of frequency and temperature for different compositions. The optical band gap of zirconia decreases with increase in polymer concentration. Two electrical responses in the impedance spectra corresponding to the grain and grain boundary effects are analysed by an equivalent circuit. Activation energies are very small (35–70 meV). The samples exhibit a large dielectric constant and at room temperature it becomes about 12 000 at 0.7 KHz for the highest content of zirconia. The high dielectric response is mainly originated by Maxwell–Wagner polarization.

In the present study an inverse hyperbolic heat conduction problem is solved by the conjugate gradient method (CGM) in estimating the unknown boundary heat flux based on the boundary temperature measurements. Results obtained in this inverse problem will be justified based on the numerical experiments where three different heat flux distributions are to be determined. Results show that the inverse solutions can always be obtained with any arbitrary initial guesses of the boundary heat flux. Moreover, the drawbacks of the previous study for this similar inverse problem, such as (1) the inverse solution has phase error and (2) the inverse solution is sensitive to measurement error, can be avoided in the present algorithm. Finally, it is concluded that accurate boundary heat flux can be estimated in this study.

The effective flexural modulus of an ordinary homogeneous tube does not depend on its dimensions, whereas the moduli measured for some carbon nanotubes do. As an example of how the size-dependent effective flexural modulus can occur for a homogeneous sample, a tube made of material with different tensile and compressive moduli is considered. Such a tube is homogeneous with respect to its composition. But when it is bent, it behaves in some sense like a composite beam consisting of two different materials—compressed and extended parts of a tube. It was found that the effective flexural modulus of such tubes is a decreasing function of the ratio of the inner radius to the outer radius. This provides various types of modulus versus outer radius dependences; some of them resemble the dependences observed for carbon nanotubes.

The classical Richards equation describes infiltration into porous soil as a nonlinear diffusion process. Recent experiments have suggested that this process exhibits anomalous scaling behaviour. These observations suggest generalizing the classical Richards equation by introducing fractional time derivatives. The resulting fractional Richards equation with appropriate initial and boundary values is solved numerically in this paper. The numerical code is tested against analytical solutions in the linear case. Saturation profiles are calculated for the fully nonlinear fractional Richards equation. Isochrones and isosaturation curves are given. The cumulative moisture intake is found as a function of the order of the fractional derivative. These results are compared against experiment.

This paper presents a theoretical analysis of the dynamics of spherical metallic particles in electrostatic separators/sizers (ESSs). A computational algorithm is employed to depict the cylinder-type electrode arrangements applied in some electrostatic processes generating non-uniform electric fields. The ESS consists of a pair of conducting cylinders. The upper cylinder is energized by HVdc, while the lower one is grounded and mounted horizontally on a revolvable axis. The aim of this paper is to present a new electrode configuration and demonstrate the usefulness of numerical techniques for the evaluation of the particle's motion. A computer program was employed for analysing the behavior of spherical particles in a two-dimensional electrode arrangement that models the actual electric field configuration of cylinder-type electrostatic separators/sizers. The analysis is needed for the development of any new application of this cylinder-type electrode arrangement as an electrostatic separation method. The results reveal that the particle's motion depends on its radius and density and amplitude of the applied voltage. The actual granular mixtures with different specific mass and radius could be separated applying this cylinder-type electrostatic separation method; the lift voltage is an important parameter for separation. With a program for two-dimensional analysis of the electric field, the computational procedure presented in this paper could be employed for any particle shapes.

The governing continuum-based conservation equations for laminar 2D (with axisymmetry) convective micro-tube-flow of gas are numerically solved. These equations comprehensively incorporate the physical effects of variations of gas density with pressure and temperature, and gas viscosity and thermal conductivity with temperature. Their non-dimensionalization reveals the significance of variations in gas properties in convective micro-flows, and the role of the dimensionless groups, especially the Brinkman number/s. Even at very low Mach numbers, gas density variation is induced due to the significance of density–temperature sensitivity of gas, in micro-convection. The induced radial flow due to gas density and viscosity variations are numerically captured and results are generated considering different combinations of variable properties. Results indicate that laminar micro-convection characteristics are significantly affected in both quality and quantity, by physical effects induced by variations in gas properties.