This study explains processes for the characterization by acoustic microscopy of materials presenting, along a thickness d close to the surface, a gradient in elastic properties in direction perpendicular to the surface. The method, modelling the non-homogeneous area by a finite number of layers of the same thickness, is sensitive to the factor fd (f is the working frequency) and to the nature of the gradient profile. The study of the dispersion of the Rayleigh velocity as a function of frequency shows that the shape of the curve Maynly depends on the gradient profile and on the structure (surface material and bulk material). When the numerical derivative of the dispersion curves presents inflexion points, they can be linked to the depth and to the nature of the profile. Modelling of the materials displaying a gradient shows that, in some cases, the plot of the curvature of the dispersion curves as a function of frequency is a useful means of characterization.

A sensitivity factor for electron mobility with respect to the tunnel oxide thickness in a floating gate electron-tunneling MOSFET of n-channel is defined. To this end, a field-dependent mobility is assumed.

A hollow cathode source with a specially designed cusp magnetic field Bz(r,θ) provides clustering environment to the sputtered carbon atoms and ions. Source's distinctive features are its sooting properties that depend upon the two well-defined regions within the discharge. The cusp field drives both of these regions but in different modes – one region ionizes the source gas, introduces the sputtered C from the hollow cathode while the other is the collision dominated gyrational motion of the C+ ions along Bz(r,θ) contours. Tunability of plasma's discharge characteristics provides the tool to investigate clustering in the sooting plasma.

Recently a new nematic bistable pixel, using simple monostable planar anchorings, has been proposed [4−6]. This pixel can be switched between two textures, having the same boundary conditions but different optical properties: one texture (U) is undistorted, whereas the other one (T) is characterized by the presence of a half-turn twist. The U → T switching was obtained by abruptly dropping the driving electric field. A slow decrease of the driving electric field favors the T → U transition. The electric field fall rate discriminates the kind of coupling between the boundary surfaces, hydrodynamic or elastic. Here we show the same behavior of this system by using square electric field pulses. We present experimental results concerning the critical values (amplitude and duration) of the driving signals, for which the elastic and the hydrodynamic effects are balanced and we measure their optimized values. Our results are in reasonable agreement with the theoretical predictions obtained by a simplified model.

RHEED controlled ultra-thin buffer layers of SrTiO3 have been deposited on (100) MgO by pulsed laser deposition to growth YBaCuO films for microwave applications. A buffer layer with a thickness between 2 and 15 nm, i.e. 5 to 40 unit cells of SrTiO3, is sufficient to expand to more than 60 °C the range of deposition temperatures leading to low microwave surface resistance. The Rs values are as good as those obtained on LaAlO3 substrates with a slighly lower magnetic field dependency. The SrTiO3 seed layer induces an oriented epitaxial growth with YBCO [100] // MgO [100] over this range of deposition temperatures.

The behaviour of pyrite in the process of mechanical milling in air has been examined. Milled powders were characterized by scanning electron microscopy, Mössbauer spectroscopy working in transmission geometry and X-ray diffraction. In the presence of oxygen, pyrite can readily be transformed to ferrous sulphate monohydrate, which indicates that the Fe(II) goes from a low-spin state to to a high-spin state. The transformation mechanism is saturated after about 60 hours milling, but however it can be markedly prolonged by further ageing at room temperature. The results also indicate that mechanical milling is a useful room temperature process of material production.

Slip patterning is influenced by both the distribution of Frank-Read sources in the bulk crystal and the dislocation interactions before emerging at the surface. The fine structure of slip lines is also highly dependent on the intrinsic nature of Frank-Read sources and particularly on their pinning points and external dislocation network, which is often not considered. In this paper, different types of Frank-Read sources are reviewed and the direct effects are described and discussed of these dislocation multiplication mechanisms on the step fine structure at the surface.

Electronic and magnetic peculiarities of La2NiO4+δ are discussed emphasizing charge and spin ordering phenomena. Macroscopic measurements of conductivity (dc, optical) and magnetic susceptibility on samples of well-known oxygen stoichiometries agree to show anomalies where this peculiar ordering is expected. Our data account for the heterogeneous nature of the magnetism. The susceptibility which is quasi temperature independent in a large T range is modeled by a system of spins cluster.

The chemical bonding of different {111} Cu–MgO interfaces obtained by internal oxidation of (Cu, Mg) alloys at T = 900 °C and for an high oxygen activity of ao2 = 10−8, is studied by transmission electron energy loss spectroscopy (EELS) at high spatial resolution. For polar {111} interfaces (Cu and MgO in topotactical or pseudotwin orientation), it is shown that the terminating lattice plane in magnesia is occupied by oxygen atoms. An important charge transfer is identified at the interface, yielding Cu–L ELNES features corresponding to those of Cu1+ (Cu(I)) in its oxide. O–K edge fine structures at the interface are also modified: an edge enlargement and the presence of a low energy shoulder confirm the bonding of oxygen to Cu1+. Consistent with these results, the Mg–L edge is never modified compared to the MgO bulk phase. Specifically adapted to the heterophase interfaces, a spatial difference method, based on normalised spectra (NSD), is applied to estimate the relative contribution of the ELNES signal in the interface area. In the present case of high oxygen activity, the number of copper atoms in the Cu(I) oxidized state corresponds to a total occupancy of the outermost metal plane at the interface.

Electron mean free path (λa) has been investigated using Ballistic Electron Emission Microscopy (BEEM). Using the average collector current computed from large scale BEEM images and a model in which the current exponentially decreases in terms of metal thickness, a constant value of λa = 11 nm has been calculated in the 1–1.8 eV electron energy range. On small scale images, the study of well-defined BEEM doMayns shows that either λa or the interface transmission factor (or both) may differ from their average values. These local variations from one grain to another are interpreted as interface defects and channeling of the electron beam due to the electronic and crystallographic of the gold layer.

Very fine, 10% vol/vol, n-hexadecane and n-octadecane oil-in-water emulsions, stabilized by sodium dodecyl sulfate, have been prepared. Due to the very small size of the oil droplets, these emulsions are susceptible to undergo Ostwald ripening and/or coalescence. The maturation of the emulsions was studied over several months by three different techniques: ultrasonic attenuation spectroscopy, static light scattering and dynamic light scattering. Ultrasonic spectroscopy measurements between 0.5 and 10 MHz appeared as the most convenient technique for monitoring the changes in the size of such droplets. Moreover, the correlation of the results from the three different techniques allows a complete determination of the particle size and polydispersity during the ageing.

Although the risk of embrittlement of materials exposed to liquid metals has been recognized for many years, its prediction reMayns problematical insofar as the knowledge of the mechanisms involved in the phenomenon is limited. However, Liquid Metal Embrittlement (LME) is of prime interest because the risk of damage exists wherever the handling of liquid metals is required in various industrial or scientifical fields (chemical plants, power-producing systems, soldering process, ...). The interest for this phenomenon needs thus to be pursued. The present paper reviews experimental results about the occurrence of LME and the influence of different parameters, and presents a number of mechanisms which have been proposed to explain LME.

A linear transformation f(S) of configurational entropy with length scale dependent coefficients as a measure of spatial inhomogeneity is considered. When a final pattern is formed with periodically repeated initial arrangement of point objects the value of the measure is conserved. This property allows for computation of the measure at every length scale. Its remarkable sensitivity to the deviation (per cell) from a possible maximally uniform object distribution for the length scale considered is comparable to behaviour of strictly mathematical measure h introduced by Garncarek et al. in [2]. Computer generated object distributions reveal a correlation between the two measures at a given length scale for all configurations as well as at all length scales for a given configuration. Some examples of complementary behaviour of the two measures are indicated.

Structural antiferrodistortive phase transitions have been studied in mixed disordered perovskites Rb1−xKxCaF3 crystals over a wide concentration range (0 < x < 1) by Raman spectroscopy and a full group theory analysis has been carried out. Raman spectra have been indexed in all phases and a “one mode” behavior is evidenced. The influence of the cationic substitution on the mechanism driving the transitions is characterized by: i) the disappearance of the strong first-order character of the low temperature transition in RbCaF3; ii) the continuous evolution of the Raman spectra as a function of temperature, with no sharp indication of a transition except for the classical soft mode behavior; iii) the persistence of hard Raman modes even in the ideal cubic phase; iiii) the appearance of a broad central component associated with relaxation processes. Finally, the results of lattice dynamics calculations, when compared to inelastic neutron scattering measurements, show that the classical virtual crystal model fails. These results are examined in terms of a simple displacive transition for these fluoro-perovskites in which the interactions between F6 octahedra are anisotropic and the importance of the substitutional disorder is highlighted.

We study the atomic structure of $\{112\} \Sigma = 3$ twin boundaries consisting of a stacking of six $\{111\}$ planes and characterized by a resulting Burger vector equal to zero. The twins were imaged by HRTEM. We develop image processing to localize the silicon and carbon atoms in each grain and thus to deduce their stacking and to calculate the possible rotation and translation of one grain with respect to the other with an accuracy greater than 0.1%. We show that there is no rigid body translation between the two grains. However, models derived from Möller or Pond et al. are not suitable. We propose an alternative model which is in close agreement with the asymmetrical contrast of the twin boundary.

The high intensity of concentrated solar radiation obtained with the Odeillo (France) solar furnace facilities can be used to produce carbon nanotubes by direct vaporization of carbon bi-metal targets under inert gas atmosphere. Electron microscope pictures and Raman spectra show that the structure of the produced carbon nanotubes is likely to depend on experimental conditions and that the growth of single-wall or multi-walled carbon nanotubes can be favored.

The viability of sculptured thin film (STF) implementations of Šolc fan and folded filters for optical detection and determination of gas concentration is established. A nanoscopic–to–continuum model is devised for predicting the electromagnetic (optical) response of a STF Šolc filter whose void regions are filled with a chemically non–reacting gas. Ultra–narrow band–pass features in the transmission spectrum are shown to shift with the gas concentration.

The inelastic and elastic cross-sections of an interacting electron beam with MgO, SiO2, and Al2O3 have been calculated and tabulations are provided for primary electron energies lower than 10 keV. By using the tabulated cross-sections, a Monte-Carlo simulation is utilized to obtain the backscattering coefficient in the energy range 1–10 keV

This paper is aimed at the characterization of Electric Power Drive Systems based on the Induction Machine fed by Multi-level Voltage-source inverters, to be used within instantaneous torque and flux control methodologies. The input/output transfer function for a N-level inverter is discussed and the correspondent available output voltage vectors, as well as the input sequences that give them rise, represented in the stationary Park reference plane. Concerning the induction machine characterization, an analytical study on the torque and stator flux instantaneous behavior is made, demonstrating that the first one highly depends on the delivered torque and speed. In consequence, a sampling scale predictive model of the induction machine is deduced in order to make possible the optimal choice of the inverter configuration for a sampling period. Finally, a DEADBEAT based control law is discussed and simulated as an illustration example of both the voltage-inverter and induction machine models presented within this paper.

High power laser shocks with a 0.6 ns pulse duration have been used to study the debonding of coatings electrolytically deposited on the opposite face of the substrate than the one shocked. Experiments have been carried out on various substrate/coating systems such as stainless steel/copper or nickel and hastelloy X/platinum. Experimentally, a lower intensity debonding threshold has been determined for each of these systems. On the other hand, an upper threshold above which a systematic removal of the coating is obtained has been evidenced. By the numerical simulation of these experiments, a traction range for debonding at the interface has been determined for the three systems. A significant difference for the adhesion levels of these systems has been evidenced using this method. Thus, the possibility to use the laser shock technique as a non destructive adhesion test for coatings of some tens microns is clearly demonstrated.