Contact electrification and triboelectrification are well-known in the case of dissimilar materials, however the case of charge exchange during friction between nominally identical insulating materials is less documented. We experimentally investigated the triboelectrification between two smooth monocrystalline $\alpha $-Al2O3 (sapphire) antagonists by surface force measurements with a Surface Force Apparatus (SFA). The force between a sphere and a plane, both in sapphire, was measured as a function of the sphere-plane distance D, before and after nano-friction tests, under dry argon atmosphere. Respective contributions of van der Waals, water meniscus and electrostatic forces were determined. The estimated Hamaker constant was in good agreement with the Lifshitz theory, and the dominant meniscus attraction at low separation could be overcome with small radius sphere. We demonstrated that electrostatic forces were generated by the nano-friction test and we quantified the adhesion that results from this contact-electrification. In the first stage of the unloading process, the short range electrostatic force was found to vary both with time and distance D. Experimental results were correlated with surface densities of mobile charges on the two surfaces, and the time-dependence was related to classical surface transport phenomena on alumina surfaces.

This paper investigates the dielectric properties of various air/SF6 gas mixtures based upon a cylindrical spacer model with adhering particle on the surface under homogeneous field conditions. The investigation involves a comparison with pure SF6. The flashover field strength for clean and particle contaminated spacer surface under lightning impulse (LI) and alternating voltage (AC) stress is determined. The results of the investigations show the sensitivity of air/SF6 gas mixtures to conducting particles on spacer surfaces for gas pressure up to 1000 kPa. Moreover, the correspondence between pure SF6 and air/SF6 gas mixtures for AC and LI flashover field strength range from 50 to 178 kV/cm is determined. Conclusions are drawn about the ability of air/SF6 gas mixtures to serve as technically efficient media for long Gas Insulated Transmission Lines (GITL). The results shed light on the issue of the SF6 reduction and the particle detectability in GITL.

Low dielectric constant materials (low-k) are used as interlevel dielectrics in integrated circuits. This paper concerns the etching process of these materials in high density plasma with the aim to provide some insights concerning the etch mechanisms. Materials studied are methylsilsesquioxane (MSQ) polymers, either dense (SiOC) or containing 40% of porosity (porous SiOC). Amorphous hydrogenated silicon carbide (SiC) material, used as hard mask and/or etch stop layer, is also investigated. Etch is performed in an inductively coupled reactor using fluorocarbon gases, which have proven to be very successful in the etch of conventional SiO2. First, etching with hexafluoroethane (C2F$_{6})$ is performed. Although etch rates are high, etch selectivities with respect to SiC are weak. So, oxygen, argon, and hydrogen are added to C2F6 with the aim of improving selectivities. The best selectivity is obtained for the C2F6/H2 (10%–90%) mixture. To understand etch rate and selectivity variations, plasma analyses by optical emission spectroscopy are correlated to surface analysis using X-Ray Photoelectron Spectroscopy (XPS). In general, atomic fluorine concentration in the plasma explains the etch rate, while the presence of a fluorocarbon layer on the surface is well correlated to the selectivity. To ensure that the etch process does not affect materials properties, and particularly their dielectric constant, bulk analysis by Fourier Transformed Infra-Red spectroscopy and images by Scanning Electron Microscopy have also been carried out.

The structure and magnetic properties of the nanoparticles of immiscible system Co20Cu80 prepared by means of arc-discharge, have been studied in detail. The diameters of the particles are about 20 ~ 30 nm and a core/shell structure forms. The cores are Co-Cu solutions, which show some small Co precipitates, encapsulated with a shell of cupper oxide or cobalt oxide as observed by means of high-resolution transmission electron microscope (HRTEM) and energy dispersive X-ray (EDS). The loop shift in the hysteresis loop indicates the existence of the exchange bias between ferromagnetic and antiferromagnetic components at low temperatures. A block temperature about 180 K has been observed for as-deposited nanoparticles. For the annealed nanoparticles, the thermal magnetization at low temperatures is satisfied with Bloch's law. 


We modify the Sedov theory to describe plasma shock waves generated in a pulsed laser ablating process. Under reasonable asymptotic behavior and boundary conditions, the propagating rules in global free space (including near areas and mid-far areas) of pulsed-laser-induced shock waves are established for the first time. In particular, the temporal behavior of energy causing a difference in the propagation characteristics between the practical plasma shock wave and the ideal shock wave in a point explosion model is detailedly discussed. The theoretical results calculated with our model are in good agreement with the corresponding experimental data. In addition, some important free parameters which could not directly be obtained from other previous works are determined naturally on the basis of our model.

We used an in-plane magnetized electrode and a perpendicular to film plane magnetized multilayer electrode in a magnetic tunnel junction to generate the active part of a magnetic field sensor able to measure large fields. When the applied field is normal to the junction surface, the magnetization of the multilayer electrode is fixed while the moment of the in-plane magnetized electrode rotates towards the applied field. This generates a linear variation of tunnel junction resistance with the applied field. The use of tunnel junctions with all their known advantages makes this structure attractive for measuring large magnetic fields, of up to several kG.

In previously published papers [G. Musa et al., Rom. Rep. Phys. 49, 195 (1997); G. Musa et al., Eur. Phys. J. Appl. Phys. 4, 165 (1998)] we reported a drastic change of time evolution of the barrier discharge current at the addition of hydrogen to neon–filling gas of the discharge device. Both, discharge current and discharge emitted light durations increase at least five times. We established that the main explanation of the above mentioned behavior consists in the negative-positive ion recombination, process which has one of the largest known cross–section [M.A. Lieberman and A.J. Lichtenberg, Principles of plasma discharges and material processing (John Wiley & Sons, N.Y., 1994)]. The first condition to have negative-positive ions recombination is to use as filling gas of the discharge device an electronegative–electropositive gas mixture [G. Musa et al., ESCAMPIG-16, Grenoble France, 2002, Vol. 2, p. 29; G. Musa et al., J. Phys. D: Appl. Phys. 18, 2119 (1985); A. Baltog et al., Contrib. Plasma Phys. 40, 537 (2000); G. Musa and A. Baltog, Contrib. Plasma Phys. 43, 210 (2003)]. Additional conditions must be fulfilled in order to ensure enough density of negative ions necessary for such a recombination process. An increased “consumption” of electrons is necessary to produce needed negative ions. Consequently, the wall polarization process is slowing down with subsequent increase of the light emission and discharge current duration. Possible use of this increase of light emission at electronegative gas addition to the filling gas neon as a mean to increase the discharge light generation efficiency is considered.

A range of silicon-based optical thin films have been deposited in a matrix distributed electron cyclotron resonance (MDECR) reactor. Process parameters were optimized in order to obtain optical quality thin films at low substrate temperatures and high deposition rates without post-deposition treatment. Stoichiometric silica films have been deposited at the rates up to 70 nm/min at temperatures lower than 150 °C. Oxynitride films with a controllable refractive index ranging from 1.46 to 1.86 have been obtained from SiH4/O2/N2 mixtures. Real time process control by multichannel ellipsometry has been implemented and successfully applied for the deposition of silica, silicon oxynitrides and amorphous silicon. Better than 0.3% in thickness accuracy was achieved in high rate deposition of silica layers of various predefined thickness. Refractive indices were determined in real-time with an absolute precision of 0.005–0.02. The control algorithm was used for fabrication of multilayer optical filters. The results show that the MDECR concept coupled with real-time process control by ellipsometry can be technology of choice for the deposition of interference coatings.

2K+ to K + K2+ and K to K3+ provide a reaction with a net enthalpy equal to one and three times the potential energy of atomic hydrogen, respectively. The presence of these gaseous ions or atoms with thermally dissociated hydrogen formed a so-called resonance transfer (rt)-plasma having strong VUV emission with a stationary inverted Lyman population. Significant line broadening of the Balmer $\alpha $, $\beta $, and $\gamma $ lines of 18 eV was observed, compared to 3–4 eV from a hydrogen microwave plasma. Emission from rt-plasmas occurred even when the electric field applied to the plasma was zero. The reaction was exothermic since excess power of 20 mW cm−3 was measured by Calvet calorimetry. An energetic catalytic reaction was proposed involving a resonant energy transfer between hydrogen atoms and 2K+ or K to form very stable novel hydride ions H−(1/p) called hydrino hydrides having a fractional principal quantum numbers p = 2 and p = 4, respectively. Characteristic emission was observed from K2+ and K3+ that confirmed the resonant nonradiative energy transfer of 27.2 eV and 3 × 27.2 eV from atomic hydrogen to 2K+ and K, respectively. The product hydride ion H−(1/4) was observed spectroscopically at 110 nm corresponding to its predicted binding energy of 11.2 eV. The 1H MAS NMR spectrum of novel compound KH*Cl relative to external tetramethylsilane (TMS) showed a large distinct upfield resonance at −4.4 corresponding to an absolute resonance shift of −35.9 ppm that matched the theoretical prediction of p = 4. A novel peak of KH*I at −1.5 ppm relative to TMS corresponding to an absolute resonance shift of –33.0 ppm matched the theoretical prediction of p = 2. The predicted catalyst reactions, position of the upfield-shifted NMR peaks for H−(1/4) and H−(1/2), and spectroscopic data for H−(1/4) were found to be in agreement with the experimental observations as well as previously reported spectroscopic data for H−(1/2) and analysis of KH*Cl and KH*I containing these hydride ions.

Two methodologies are presented allowing to find the current density on a revolution surface to obtain a given 3D magnetic field distribution. The combination of the Biot-Savart law and the superposition theory is used to establish an algebraic relationship between the predefined magnetic field and the searched current density. Basically, two approaches are used: the continuous approach, in which the current density is modeled by an analytical function and the discrete method where the searched current density is given by a list of values that match a mesh of the magnet support. Furthermore, the use of the spherical harmonic development of the predefined magnetic field leads to a compact formulation of the inverse problem. The proposed matrix methodology has been developed for any magnet having a revolution axis (revolution magnets). A computer code which uses both approaches has been developed and gives good simulation results, which show an interesting prospects for new magnet design.

High-velocity convective and radiative drying of an optical fibre coated with an aqueous polymeric suspension is considered. This study is divided into two parts: drying is first experimentally tested using a semi-industrial device, then a heat and mass transfer model between the fibre and its environment is proposed and discretised. The comparison of experimental and numerical results consolidates the assumptions of the present model and thus allows to consider it in future to dimension an industrial coating-drying process.

An effort for better understanding of main parameters influence to polystyrene thin films treatment under DC point-to-plane low-pressure discharge in nitrogen is attempted. Voltage-current curves and discharge repetitive current impulses for various gap lengths and gas pressures, in absence and in presence of polystyrene thin films in the cold plasma reactor, evidence that in any case a normal glow discharge regime is established. Atactic polystyrene thin films underlie treatment under the above regime and hydrophilic surfaces are obtained. Wettability is characterized, under certain experimental protocols, by contact angle measurements along the films treated for various gap lengths (d = 0.5, 1, 2 cm), gas pressures (p = 2-10 mbar), gas flow rates (Q = 1-1110$ sccm) and times (ttr = 0-600 s). The best treatment takes place opposite to the point electrode, in an area around the discharge symmetry axis, proving non-homogeneous surface treatment. Atomic Force Microscopy (AFM) shows that this fact does not relate to surface morphological changes. The experimental results confirm that the above treatment yields polystyrene films with very good wettability (typical contact angles: 5-15°) avoiding any obvious material degradation. Ageing effects are introduced but the final wettability in comparison to that before the treatment is increased. The role of excited neutrals and reactive particles with long radiative lifetime (metastables states) is emphasized and seems to lead to polymer treatment through diffusion mechanisms.

The experimental determination of the iron losses created in a localized zone of an electric machine is a difficult operation. We try to verify and to valid by local thermal measurements the sum of local iron losses. To realize our verification, we determine the optimal measurement conditions by calculation and simulation before the realization of a prototype specially designed for this operation. This structure represents a part of an electric machine, with emphasis on inhomogeneous flux distribution areas. This device permits to obtain an experimental temperature mapping which is compared to the calculated temperature distribution obtained by finite elements modelling.

The plasmadynamics of a stationary plasma thruster (SPT-100) plume in the very-near-field region have been studied by using a two-dimensional axisymmetric numerical code based on a combination of Particle-in-Cell (PIC) simulation for ion component (Xe+ and Xe++) and fluid description for electrons. In particular we have solved the electron momentum conservation equation (including collisional and magnetic effects) and the electron energy conservation equation (including collisional effects). Due to the difference between electron and ion Larmor radius and to the effect of the thruster wall, the quasi-neutrality hypothesis can be violated in the very-near-field plume region and the electric field must be computed accordingly. The xenon atom flowfield is calculated analytically. The model allows a unitary rationalization of several experimental observations.

A hybrid method is presented for the calculation of the interaction of a complicated shape ferrite-core eddy current testing probe with extremely small size cracks in a plate. The method is obtained by blending the boundary integral (BIM) and finite element (FEM) methods preserving their attractive properties, that is, the fast and accurate evaluation of the defect field and the versatility in specimen and probe geometry, respectively. FEM is applied for the computation of the electric field induced in the specimen without cracks. Using the obtained, so-called, incident field the BIM is used for the calculation of the field perturbation due to the presence of the cracks in the tested specimen. With the application of the presented hybrid calculations, a very fast and accurate method is developed for the solution of a problem that would pose considerable difficulties for either the FEM or the BIM if they were applied purely alone in the conventional way. The results of the calculations are compared with a large number of experimental data. The very good correlation between the measured and simulated probe responses proves the applicability of the presented method.

In-situ spectroscopic ellipsometry is known to be very sensitive, non-invasive technique for monitoring and control of thin film growth. In the production of optical interference coatings the refractive index of the material is usually assumed to remain constant within a single layer. Under such assumption only the optical thickness of the layer can be efficiently controlled. For modern complex structures, however, even insignificant deviation from the design, due to the shift in the refractive index, can be very detrimental to the resulting performance of the coating. Simultaneous real-time determination of refractive index and growth rate is necessary in order to comply with strict specifications. If the index departs from the target value, one has to adjust process parameters and, ultimately, perform re-calculation of the filter structure to compensate for an error. We will review the work performed in our laboratory during last few years. Development of several different control strategies will be discussed and their application to the control of PECVD of optical interference coatings demonstrated. Latest work is concerned with the advances in the closed-loop control of the fabrication of optical thin films by in-situ multi-wavelength phase-modulated kinetic ellipsometry using both, direct numerical inversion algorithm for the real-time reconstruction of refractive index and layer thickness and real-time least-squire fitting-based approach. These techniques have been tested on quarter-wave index optical filters as well as on inhomogeneous refractive index profiles and demonstrated efficiency and robustness.

High-frequency ultrasonic pulses at 36 MHz are used to measure velocity profiles in a complex fluid sheared in the Couette geometry. Our technique is based on time-domain cross-correlation of ultrasonic speckle signals backscattered by the moving medium. Post-processing of acoustic data allows us to record a velocity profile in 0.02–2 s with a spatial resolution of 40 μm over 1 mm. After a careful calibration using a Newtonian suspension, the technique is applied to a sheared lyotropic lamellar phase seeded with polystyrene spheres of diameter 3–10 μm. Time-averaged velocity profiles reveal the existence of inhomogeneous flows, with both wall slip and shear bands, in the vicinity of a shear-induced “layering” transition. Slow transient regimes and/or temporal fluctuations can also be resolved and exhibit complex spatio-temporal flow behaviors with sometimes more than two shear bands.

A series impedance method [Mason and Fair, Proc. IRE, 464 (1942); IEEE Standard on Piezoelectricity ANSI/IEEE Std 176-1987 (New York: The Institute of Electrical and Electronics Engeneers, 1987)] is the most popular way for investigation of piezoelectric properties of crystals. The AC voltage generated by a vibrating crystal achieves its maximum if a frequency of an exciting signal applied to the sample is equal to a resonance frequency of the sample. In this article a very simple experimental setup for piezoelectric measurements was described. Usually measurements of resonance frequencies are made at a constant temperature, which makes an experiment long-lasting. The experimental setup described below allows performance of the experiment in slow-change temperature regime.

We previously used the Pulsed Photoacoustic Spectroscopy to quantify sunscreen chromophore diffusion into human skin, and suggested a methodology to evaluate the time and the depth diffusion profile into human skin. In the present study we present the results obtained for the diffusion of an emulsion in human skin, which is used in the sunscreen compositions. This study shows, for the first time, a particular behaviour due to a chemical reaction inside the skin during the diffusion process. This result brings a particularly interesting technique through the PPAS spectroscopy, to evaluate in situ, the eventual chemical reactions that can occur during drug diffusion into human skin. Numerical simulation allows us to understand the impact of thermal, optical and geometrical parameters on the photoacoustic signal and thus the physics of the diffusion phenomenon. The present simulation shows clearly that the $t_{\max}$ values corresponding to the maximum of the photoacoustic signal magnitude, $\Delta P _{\max}$, decrease when the thickness, $\ell $, of the sample decrease. Conclusions about possibilities and limitations of the considered model are discussed.

We have developed an analytic solution to heat equation in vicinity of steel sample surface, heated by pulsed Gaussian laser beam, taking into account both heat transfer conduction and radiation. Then we performed a new calculation method to build up isothermal generative lines in vicinity of targeted surface. We tried to explain line distortion through comparison with some of our further studies that considered basically conduction phenomenon and that paradoxically performed non-Gaussian temperature experimental profiles.