We have studied the ageing effects on the photoluminescence (PL) of porous silicon (PS) prepared by anodisation in HF solution of low concentration (3% ). It was found that the PL behaviour within oxidation is different from that elaborated in habitual condition. The natural oxidation of PS layers shows two opposite behaviours of the PL before stabilisation. The PL intensity decreases significantly after an initial strong and fast increase. At low temperature, the PL exhibits large band and multi-peaks structures. It was shown by electron paramagnetic resonance (EPR) and Raman measurements that a possible phase transition from crystalline to amorphous phase can occur. We show that each transformation is related to preparation conditions.

A new varistor system of SnO2·Ni2O3·Nb2O5 exhibits the relative dissatisfactory physical and electrical properties. The effect of cobalt oxide on the properties of the SnO2·Ni2O3·Nb2O5 varistors was investigated by measuring the densities, permittivities, the current-voltage properties and the properties of the defect barriers. It is found that the sample doped with 0.25 mol% Co2O3 exhibits the abnormal poorer electrical properties than the samples without Co2O3 dopants. However, the sample doped with 6.0 mol% Co2O3 exhibits the highest nonlinear coefficient ($\alpha=17.24$) and reference electrical field ($E_{\rm B}=561$ V/mm), although the sample doped with 1.0 mol% Co2O3 exhibits the highest densities ($\rho =6.87$ g/cm3) and permittivities. The sample with 6.0 mol% Co2O3 bears the highest barriers, but the sample with 1.0 mol% Co2O3 shows the narrowest barriers. The investigation of the sintering temperature shows that the samples sintered at 1450 °C exhibit the better physical and electrical properties. The results were discussed and the defect barrier model was also introduced to explain.

A study on the influence of tabletting pressure upon the internal morphology of Fe2O3-Cr2O3 catalytic system shows the behaviour of that system at crystallite level or even below it. On increasing tabletting pressure of catalytic powder, remanent stresses are left in the tablets formed which can be calculated in terms of the remanent strain. The macrostresses are constant and small at tabletting pressures ranging within 108 − 5 × 108 Pa and increase linearly between 6 × 108 and 14 × 108 Pa. The microstresses take measurable values only in samples tabletted at pressures higher than 7 × 108 Pa. Besides the formation of remanent stresses, the increase of tabletting pressure brings about the overall change of porous structure and mechanical resistance of the catalytic system. The remanent stresses that appeared at tabletting result in cracks along some planes which, in most instances, are parallel to the planar faces of tablets. The maximum acceptable tabletting pressure of the catalytic system studied amounts to 5 × 108 Pa.

The martensitic transition of a Cu-Al-Ni single crystal has been studied by isothermal mechanical spectroscopy and in situ transmission electron microscopy (TEM) observations. A damping instability (with time) has been found at low frequency at the beginning of the transition. At the same time, TEM study has evidenced the presence of thin martensite plates which appear just at the beginning of the (massive) martensite formation and growth. The martensite plate growth rate is quite low and non continuous. While high internal friction in the transition domain is usually associated with the mobility between martensite/austenite interfaces, the present internal friction anomaly has been ascribed to the unstable motions of the first martensite plates.

PbO-As2O3 glasses containing different concentrations of Cr2O3 (ranging from 0 to 0.4 mol% ) were prepared. The differential thermal analysis, IR and optical absorption spectral studies of these glasses were carried out; from these studies, the variations in the values of glass transition and crystallization temperatures, optical band gap and the shifting of symmetrical bending vibrational frequency band were observed with increase in concentration of Cr2O3. Magnetic susceptibilities for these glasses were also determined and Cr3+ ion concentration was estimated. In addition, detailed studies on dielectric properties viz., dielectric constant ε, loss tan δ, ac conductivity $\sigma_{\rm ac}$ and dielectric breakdown strength were investigated. Using the results of these studies, the structural modifications taking place in the glass network were discussed in the light of Cr3+ ion concentration.

We study the conditions to perform micro-spectroscopy with a sub-wavelength lateral resolution in the wavelength spectral range from 3 to 20 μm, taking advantage of the infrared spectral signature of different chemical species. We utilised CLIO, a free electron laser, as the photon source. The transmitted photons were collected by either fluoride or chalcogenide glass fibres. Fibre tips were obtained through chemical etching by organic solvents. Metallisation of the tips permits to achieve lateral resolution of the order of the tip size. However, parasitic propagation of the light in the film reduces the contrast between irradiated and non-irradiated zones. We exemplify our set up with near-field infrared spectra obtained for polymer thin films deposited onto silicon wafers.

Hf70Cu25Rh5 and Hf70Cu25Ir5 amorphous alloys were prepared by a single roller melt-spinning method and the crystallization processes were studied by X-ray diffraction, differential scanning calorimetry and transmission electron microscopy. For both of the two alloys, the crystallization proceeds through the reactions of Am${\to}$I-phase${\to}$Hf2Cu+α-Hf, where Am and I-phase represent the amorphous and icosahedral quasicrystalline phases, respectively. Under optimum annealing conditions, the particle size of the I-phase is 10−25 and 10−20 nm for Rh- and Ir-containing alloys, respectively. Considering the fact that the crystallization process of Hf70Cu30 amorphous alloy does not accompany the precipitation of an I-phase, the present result demonstrates that the addition of Rh or Ir is significant. It is suggested that icosahedron-like atomic clusters exist in the amorphous state of Hf70Cu25Rh5 and Hf70Cu25Ir5 alloys, which serve as the seeds for the precipitation of the I-phase in the initial crystallization process.

Stoichiometric In2S3 films were prepared by thermal evaporation technique onto clean glass substrates. According to X-ray investigations, the as-deposited films were in amorphous state. Both the ac conductivity and dielectric constants were measured in the frequency range 100 Hz−100 kHz at different temperatures. Different parameters such as the frequency exponent parameter s, the density of states near the Fermi level $N(E_{\rm F})$, the activation energy $(\Delta E)$ and the optical band gap Eg of In2S3 amorphous thin films were estimated. The hopping conduction was recognized as the conduction mechanism for the investigated films.

This paper presents a new method of switching management for four quadrant switches (FQS) of matrix converters. By discriminating the FQS command orders, it is possible to lay down the FQS configuration (transistor or diode). The presented method uses the load current sign and zero closeness information to ensure good sequencing of command orders. By using Mealy state machines, we simplify the existing state diagrams for any phase number switching cell. The successful results on a three-phase switching cell, without oversized power circuit, validate this new state diagram structure.

Ga2Te3 has been prepared in bulk and thin film forms. The composition of films has been checked using energy dispersive X-ray (EDX) spectroscopy technique. X-ray diffraction (XRD) measurements have showed that the Ga2Te3 films evaporated at room temperature substrates were amorphous. Investigation of the I-V characteristics in amorphous Ga2Te3 films reveals that it is typical for a memory switch. The thickness dependence of the mean value of the switching voltage Vth is linear in the investigated range and Vth decreases exponentially with temperature in the range (298−393 K). The switching voltage activation energy (ε) calculated from the temperature dependence of Vth is found to be 0.277 eV. Electrical conduction activation energy ($E_{\sigma}$) is found to be (0.564 eV). The agreement between the obtained value of the ratio $\varepsilon/E_{\sigma}$ (0.49) and its value derived theoretically (0.5) suggests that the switching phenomenon in amorphous Ga2Te3 films is explained according to an electrothermal model for the switching process. The transmittance (T) of Ga2Te3 thin films, has been measured over the wavelength range 400−2500 nm. From an analysis of the transmittance data, the optical constants, the refractive index (n) and the extinction coefficient (k), have been determined. Similarly the absorption coefficient (α) measurements, have been evaluated. Allowed nondirect transitions with optical energy gap ($E_{\rm g}^{\rm opt}$) of 1.15 eV have been obtained.

Polypropylene metallized capacitors are of general use in power electronics because of their reliability, their self-healing capabilities, and their low price. Though the behavior of metallized coiled capacitors has been discussed, no work has been carried out on stacked and flattened metallized capacitors. The purpose of this article is to suggest an analytical model of resonance frequency, stray inductance and impedance of stacked capacitors. We first solve the equation of propagation of the magnetic potential vector (A) in the dielectric of an homogeneous material. Then, we suggest an original method of resolution, like the one used for resonant cavities, in order to present an analytical solution of the problem. Finally, we give some experimental results proving that the physical knowledge of the parameters of the capacitor (dimension of the component, and material constants), enables us to calculate an analytical model of resonance frequency, stray inductance and impedance of stacked capacitors.

We report the recent progress in the structuration of nanoporous silicon at a submicronic scale. Multilayered periodic structures, with low-roughness interfaces, and an index contrast of 0.6 are reported. Their strong photonic bandgap properties are demonstrated by the measurement of a reflectance up to 99.64% ± 0.01%, by mean of ring-down spectroscopy. This property is the base of a novel structure allowing an efficient guiding of light in a low-index layer. The submicronic structuration of the optical index of a planar waveguide along one direction of plane is also described, and a realistic map of the optical index, demonstrating a index contrast of 0.5, is unambiguously deduced from transmission spectra.

Fuzzy logic offers nowadays an interesting alternative to the designers of non linear control laws for electrical or electromechanical systems. However, due to the huge number of tuning parameters, this kind of control is only used in a few industrial applications. This paper proposes a new, very simple, on-site tuning strategy for a PID-like fuzzy logic controller. Thanks to the experimental designs methodology, we will propose sets of optimized pre-established settings for this kind of fuzzy controllers. The proposed parameters are only depending on one on-site open-loop identification test. In this way, this on-site tuning methodology has to be compared to the Ziegler-Nichols one's for conventional controllers. Experimental results (on a permanent magnets synchronous motor and on a DC/DC converter) will underline all the efficiency of this tuning methodology. Finally, the field of validity of the proposed pre-established settings will be given.

We report on characterisation of optical modes in InP microcavities formed by two-dimensional (2D) photonic crystals (PC) on a suspended membrane. Diffracted photoluminescence (PL) experiments and numerical calculations are associated in order to analyse the properties of PC microresonators and waveguides and to investigate the coupling between these two building blocks of PC based photonic integrated circuits.

A fully silicon CMOS compatible high voltage (H-V) integrated circuit has been developed that features 5-V high performance digital CMOS with H-V devices. The high voltage device has to support voltage drop upper 50 V between drain and source, both for NMOS and PMOS transistors. It will be placed only in the input and output circuit, for interface application. A lateral diffusion MOS (LDMOS) structure has been chosen, for its compatibility with 5 V CMOS devices. Two specific implants are introduced into the standard process. They create the high voltage N and P junctions. Numerical simulations are performed to determine specific implant characteristics. Moreover, a two-dimensional simulator gives best LDMOS dimensions. A process control monitor has been done according to these results. After the technological realization, a quantitative electrical characterization, as maximal breakdown voltage, determines the best architecture. These devices are modeled by the MOS SPICE2G Level3, which gives sufficient results for digital applications. A simple circuit, a 5 V-50 V buffer, is simulated, realized and characterized, to conclude this work.

We have developed a model of calculation of the induced current due to an electron beam. The expression for the electron beam induced current (EBIC) with an extended generation profile is obtained via the resolution of a steady state continuity equation by the Green function method, satisfying appropriated boundary conditions to the physical model. The generation profile takes into account the lateral diffusion, the effect of defects, dislocations and recombination surfaces besides the number of absorbed electrons and that of diffuse electrons as a function of the depth. In the case of a Schottky diode Au/GaAs obtained by metalorganic vapour phase epitaxy (MOVPE) method, the theoretical induced current profile is compared to the experimental one and to theoretical profiles whose analytical expressions are given by van Roosbroeck and Bresse. The minority carriers diffusion length Ln = 2 µm and the optical self-absorption coefficient a = 0.034 µm−1 can be deduced from the experimental current profile, measured by scanning electron microscopy. The theoretical curve, obtained from the proposed model is in a good agreement with the experimental one for surface recombination velocity 106 cm s−1 except for distances far from the depletion layer (x0 > 2.3 µm) where the photocurrent produced by the multiple process of the reabsorbed recombination radiation is preponderant. Our results are in agreement with those obtained by other experimental techniques on the same samples.

The following calculation method permits the evaluation of the transverse distribution of the field amplitude Ψ(x,y,z) propagating in a waveguide. This method is based on a standard method for propagation in free space, which is using the Fast Fourier Transform (FFT). It is very simple in practice, and it does not require a mode decomposition for the waveguide propagation. It uses the properties of periodicity and symmetry of the FFT in the transverse plane in order to take into account the influence of the waveguide. The advantage of this calculation method is the full compatibility with the case of a guided wave (waveguide propagation), an unguided wave (free space propagation) and any intermediate regime where the guiding occurs softly or only in a limited part of the waveguide; for example when an input wave is not guided at the entrance of the waveguide, and becomes guided at the end. In practice, these conditions are observed experimentally for example in the infrared “Free Electron Lasers”, which are broadband tunable lasers, and some of them are using a waveguide, in the center of the optical cavity, coupled with free space areas. The calculation method presented here works in this special configuration. On the other hand, although not using a mode decomposition, this method allows also a rapid decomposition in eigenmodes TEpq and TMpq. Using only one symmetry operator and one FFT, it gives the whole set of mode amplitudes.

A two-dimensional numerical code, previously developed for the modelling of a-Si:H deposition in a SiH4/H2 radio frequency cylindrical PECVD reactor, has been modified in order to perform the modelling of CH4/H2 mixtures in the same experimental configuration. This model, which includes electrical and chemical modules, takes into account the transport and the chemistry of the charged and neutral species. The results of the models have been compared to measurements. The calculated electrical power coupled to the plasma and the self-bias voltages are compared to the experimental ones. The calculated radical densities are compared to those measured by threshold ionization mass spectroscopy at the substrate centre. Moreover, the calculated radial distribution of the deposition rate is compared to profilometry measurements. Eventually, results obtained here in CH4/H2 are compared with those previously obtained in SiH4/H2 plasmas under similar experimental conditions.

We have developed a model for the calculation of the induced current due to an electron beam with an extended generation profile. The analytical expression of the electron beam induced current (EBIC) is obtained by solving the steady-state continuity equation using the Green function method. In the case of a sulphur doped (Ga0.7Al0.3As:N+/Ga0.7Al0.3As:P) sample prepared by metalorganic vapour phase epitaxy (MOVPE) method, the experimental current profile, measured by SEM enabled us to calculate the diffusion length of the minority carriers (Lp = 1 μm in the N region and Ln = 1.80 μm in the P region of the ternary sample). Far from the depletion layer, the experimental current profile measured provided us the optical self absorption coefficient of this sample: ap = 1.483 μm−1 in the N region and an = 0.167 μm−1 in the P region. According to our EBIC model, the width of the depletion layer of this sample is about 0.8 μm, while at elaboration of the sample, 10 years ago, the width of the depletion layer deduced from the characteristic curve I(V) was about 300−400 Å. This widening of the depletion layer is due to the ageing of the diode.

The transmission of breakdown plasma generated in water during laser shock processing experiments was investigated theoretically. A numerical model based on a rate equation formalism has been developed to calculate the characteristics (peak irradiance and duration) of the laser pulses transmitted through the breakdown plasmas generated in water. Results are in good agreement with previous experimental data for 25 ns−1064 nm laser pulses. Above 10 GW/cm2, the transmitted peak irradiance saturates and the transmission starts to decrease. The results have been extended to shorter wavelengths (532 and 355 nm). At 1064 nm, the breakdown process is dominated by avalanche ionization, whereas for shorter wavelengths, multiphoton ionization plays the major role.