In an effort to understand complex scattering phenomena, characteristics of optical waves such as polarization, angular spectrum, and temporal coherence have been extensively studied. In this article we will review several applications where the coherence properties of broad-band radiation offer unique sensing and diagnostic capabilities.

Photoconductivity studies were carried out on GaS single crystals prepared from melt by directional solidification. We studied the effect of light intensity, applied voltage on both the photoconductivity and the lifetime of carriers. The V-I characteristics and the absorption spectra were checked for different sample thickness. The present investigation was extended to study the spectral distribution of the photocurrent for GaS. It was found that the photocurrent curves are practically independent on the bias voltage. The energy gap for GaS was found to be 2.5 eV.

The capacitance between two adjacent nodes on an infinite square grid of identical capacitors can easily be found by superposition, and the solution is found by exploiting the symmetry of the grid. The mathematical problem presented in this work involves the solution of an infinite set of linear, inhomogeneous difference equations which are solved by the method of separation of variables.

The present 14 volts automotive electrical system will soon become 42 volts. For these future automotive applications, development of 80 volts power MOSFETs exhibiting low on-resistance is desired. The “FLoating Island” MOSFET (FLIMOSFET) is one of the new candidates to break the silicon limit, which is the “specific on-resistance/breakdown voltage” trade-off limit of conventional power MOSFETs. In this paper, the “FLoating Island” concept has been implemented on silicon: new vertical N-channel FLIMOSFETs (FLYMOS™) dedicated to automotive applications (below 100 volts) have been fabricated for the first time, using two steps epitaxy process. Experimental results show that the FLYMOS™ transistor exhibit a breakdown voltage of 73 volts but also an improved specific on-resistance compared to conventional VDMOSFETs (33% reduction of the specific on-resistance for the same breakdown voltage). In other words, in terms of “specific on-resistance/breakdown voltage” trade-off, the FLYMOS™ transistor is one of the best MOS devices in low voltage applications. These measurements validate the “FLoating Island” concept and the efficiency of the original edge cell that is used in the FLYMOS™ technology.

A single and simple graph is proposed, to visualize the impact of all the numerous parameters playing a role in the metal-oxide-semiconductor (MOS) transistor characteristics: doping and permittivity of the semiconductor, thickness, permittivity and charge of the oxide, temperature, and finally gate, drain and substrate voltages. In addition, MOS structure and capacitance properties are presented.

In this paper we develop arguments about the part of traps involved in the electronic conductivity of the 8-tris-hydroxyquinoline aluminium (Alq3) studied in the conventional electronic structure ITO/Alq3/Al. After the presentation of general models and some topical discussions about the expression of the mobility in organic materials, we present results obtained by photodipolar absorption, which is a thermo-photo-dielectric effect, and by impedance spectroscopy measurements. This last method permits to define the equivalent circuit that can be designed as a single capacitor C p and parallel resistor R p network with a series resistance $R_{s} \approx $ 50 $\rm \Omega $ located on the anode side; the log – log plot R p as a function of the dc bias voltage gives a linear law that can be seen in a first time as a consequence of a Trapped Charge Limited current (TCL); this TCL law could be improved with the introduction of a field dependent mobility. Indeed, the photodipolar absorption leads to more convincing arguments because this method acts as a probe to highlight the traps: in particular, we show that the optical pumping of electrons on trap levels gives a clear increase in the dielectric absorption generated by the reorientation of dipoles associated with trapped charges; the trap depth is located around E t = 0.19 eV, which is a value in good agreement with theoretical calculations or thermoluminescence measurements.

We consider possible magnetic symmetries of two-dimensional square lattices with circular ferrite rods magnetized by a uniform dc magnetic field. These structures can be used as tunable and nonreciprocal photonic crystals. Classification of eigenmodes in such crystals and compatibility relations are discussed on the basis of magnetic group theory and the theory of (co)representations. Some general electromagnetic properties of the magnetic crystals such as change in the basic domain of the Brillouin zone, change of symmetry in limiting cases, bidirectionality and nonreciprocity, symmetry relations for the waves and lifting of eigenwave degeneracies by dc magnetic field are also discussed.

xGeO2-(1-x)SiO2 films ( $0.1\le x\le 0.4$ ) were deposited by flame hydrolysis deposition (FHD) on Si substrates and annealed to 1150 °C for 2 h for consolidation in air. Then the films were irradiated perpendicularly to KrF excimer laser after being hydrogen loaded to enhance the photosensitivity to UV light. X-ray photoelectron spectroscopy (XPS) was used in order to characterize the purity of the films. The film was also studied using atomic force microscopy (AFM) to determine the analytical details of the microstructure. Film thickness and refractive index were measured by variable angle spectroscopic ellipsometry (VASE). The maximum positive 0.339% and negative 0.235% refractive index changes at 1550 nm were obtained after irradiation.

Fluorocarbon (C:F) and nitrogen-doped fluorocarbon (C:F:N) thin films are deposited by RF magnetron sputtering using a polytetrafluoroethylene (PTFE) target and Ar or Ar/N2 sputtering gas. Properties of C:F:N films are compared to those of C:F films. They are studied using X-ray Photoelectron Spectroscopy (XPS), Infra-Red (IR) transmission spectroscopy, Thermo-Gravimetric Analysis (TGA), impedance spectroscopy, and current-voltage measurements. By adding nitrogen to the sputtering gas, XPS shows that nitrogen substitutes for fluorine leading to a decrease in the relative concentration of CFx species, to an increase in C-C bonds, and to the appearance of specific CFN bonds. There is also a new IR band at 1350 cm-1 whose origin is uncertain (CN bonds or disordered sp 2 carbon). Thermal stability is not improved upon nitrogen addition (the C:F and C:F:N films both decompose above 200 °C). Dielectric properties (dielectric constant and loss) are only slightly affected by nitrogen doping. The DC transport properties are modified upon nitrogen addition (C:F:N films display a higher resistivity and a supra-linear behaviour at high fields indicative of field-enhanced tunnelling transport).

In 2001 we have published a paper [1] in which an ultrasonic method using a large bandwidth transducer with a spherical lens and based on acoustic waves separation near the focal region was presented. We have shown that compared to traditional acoustic microscopy (acoustic signature) the size of the zone analysed on bulk samples was highly reduced. This method is now extended to thin films on bulk substrates. Experimental dispersion curves for thin DLC (Diamond Like Carbon) films on steel are presented. The ultrasonic velocity of leaky Sezawa mode is assessed on a large bandwidth even in zones where the transducer is not very efficient. We show that the signal processing used enlarges the frequency domain explored. Such an element is essential for inverse problem treatment and coating elastic modulus calculation. Once again we show that the length of defocusing can by highly reduced. Hence, the zone analysed on the sample is smaller.

Magnetic compensation of gravity forces, similar to the space conditions of “microgravity”, needs the production of a uniform magnetic force field. We derive here a basic mathematical result that shows the impossibility to establish exact gravity compensation in a finite volume. The imperfection of compensation can be, however, quantified and a relation is derived between homogeneity accuracy and compensation volume in a cylindrical symmetry. We study how the use of inserts made of saturated ferromagnetic materials can modify the homogeneity of magnetic force field. In order to illustrate this result, an iron insert has been numerically calculated for the particular case of gravity compensation of H2 in a 10 T superconducting coil. An experimental test has been carried out on a H2 vapour bubble very close to its gas-liquid critical point. Near the critical point the gas-liquid interfacial tension is vanishing, then any bubble deformation from the ideal spherical shape reveals the non-homogeneities in the magnetic compensation force.

This paper examines the role of interfaces in the polymericinsulating films under the scope of their dielectric strength. PET(Polyethylene terephthalate) films of different thickness are puttogether forming a planar sample of a typical thickness of $200~\mu$ m and subjected to AC ramp voltage, until the dielectricbreakdown. The role of interface as a potential barrier forelectrons was examined as well as the influence of interfacenumber for a standard thickness. Experiments were also executedfor investigating the role of the position of the first, thesecond and the last interface in the sample. All the experimentswere executed with the same voltage rising rate, the breakdown ACvoltage V b was measured and the dielectric strength F b was calculated. It was shown that interfaces act as deep trappingcenters for electrons giving rise to the sample dielectricstrength for sort time experiments. Moreover the thinner the firstfilm, the higher the dielectric strength for the sample. It wasalso found that the position of the second interface does not playan important role in the process.

The effect of disorder caused by MeV heavy ionirradiation on the tunnel magnetoresistance (TMR) of magnetictunnel junctions is investigated. Two types of tunnel junctions,viz. Co/Al2O3/Ni80Fe20 and Co/Gd-dopedAl2O3/Ni80Fe20 are studied. Upon 70 MeV Si ionirradiation at a fluence of $5\times10^{11}$  ions/cm2, the undopedjunctions show relatively small but irreversible change, while theGd-doped junctions show a huge reduction, in TMR. In both casesjunctions were completely destroyed by 200 MeV Ag ion irradiationat a fluence of $1 \times 10^{11}$ ions/cm2. The results areattributed to the modification of the barrier and the neighboringinterfaces caused by the high energy density deposited by incidentions.

X-ray diffraction, Mössbauer spectroscopy, Scanning Electron Microscopy (SEM) and Transmission Electron Microscopy (TEM) techniques were used to characterize the Fe-C phases in the soots synthesized by the DC arc discharge method. Various equilibrium and non-equilibrium Fe-C compounds were identified, with fractions depending on both the location in the reactor and the helium gas pressure. The soots obtained are composed of the same five phases (C-graphite, α-Fe, γ-Fe, Fe3C and Fe5C2) whatever the helium gas pressure and wherever they are situated in the reactor. However, the location in the reactor has a considerable influence on the size of the particles in the nanostructure. The Fe-C compounds in the Pyrex vessel samples (CL) seem only to be present in the form of nanoparticles embedded in an amorphous gangue, while the water-cooled copper cylinder samples (RS) contain, in addition to these nanoparticles, large composite crystalline particles.

The charge developed in an insulator by an electron beam has often been studied by following the evolution of the secondary electron emission of the target. However this latter proves to be insufficient when one attempts to correlate it with physical properties of the sample such as its density of traps and their spatial distribution. An important step would be to have access to the time evolution of the surface potential V s (t). However, this latter quantity is not easy to measure. In this paper, we propose a new method to measure the evolution of the surface potential by relating it to the X-ray emission induced by the electronic bombardment. More exactly, we show that there is a relation between the intensity of the characteristic peaks and the potential existing under the beam impact at a given instant of the charge. After having explained the method, we check its validity both experimentally and also by comparison with Monte Carlo simulations. We then present initial results obtained for amorphous SiO2 targets.

A fluid model has been used in this work to analyze the electric and energetic behavior of a low-pressure DC glow discharge in Ar chosen as a gas test. The governing equations are the first three moments of the Boltzmann transport equations under their complete form without using the classical-drift-diffusion approximation for the momentum transfer equation while the energy conservation equation involves both thermal and drift energies. In the framework of the local energy approximation, the basic data needed more particularly in the collision source terms for both momentum transfer and energy equations are determined from a multi term solution of Boltzmann equation. Due to the strong coupling with electric field obtained from Poisson equation and the high sheath gradients, the transport equations are numerically solved using a powerful Galerkin finite elements method. This model, after a validation from comparison with literature results, is then used to analyze the convective and drift energy effects on the electric discharge characteristics. Present results show a large influence of the convective term in comparison to the drift-diffusion approximation, mainly on the electric field and charged density profiles due to the antagonist effect induced by this term on the electron and ion motion which reinforces the charge space. Present results show also the discharge characteristic changes mainly in the sheath due to the drift energy consideration.

N-type silicon presents several advantages compared to p-type material, among them, the most important is the small capture cross sections of metallic impurities, which are neatly smaller. As a consequence lifetime and also diffusion length of minority carriers should be neatly higher in n-type than in p-type, for a given impurity concentration. This is of a paramount interest for multicrystalline silicon wafers, in which the impurity-extended crystallographic defects interaction governs the recombination strength of minority carriers. It is experimentally verified that in 1.2 $\rm \Omega $  cm raw wafers lifetimes about 200  $\mu $ s and diffusion lengths around 220 $\mu $ m are measured. These values increase strongly after gettering treatments like phosphorus diffusion or Al-Si alloying. Scan maps reveal that extended defects are poorly active, although in regions where the density of dislocations is higher than 106 cm-2. Abrupt $p^{+}n$ junctions are obtained by Al-Si alloying after annealing between 850 and 900 °C, which could be used for rear junction cells. Such cells can be processed by means of similar processing steps used to make conventional p-type base cells.

Fresnel lens has a long history in optics. This concept at non-optical wavelengths is also applicable. In this paper we report design and fabrication of a half and quarter wave dielectric Fresnel lens made of Plexiglas, and a Fresnel reflector at 11.1 GHz frequency. We made two lenses and one reflector at same frequency and compare their gain and radiation pattern to simulated results. Some methods for better focusing action will be introduced.

The non-uniformity of responsivity of photodiodes and thermal detectors limits the accuracy of their calibration. Spatial non-uniformity properties of a pyroelectric radiometer, a thermopile detector, silicon, germanium and indium gallium arsenide photodiodes are investigated in the scope of our work. Silicon type photodiodes showed best uniformity characteristics among the analysed photodiodes and detectors. Significant changes have been found in the spatial responsivity close to the band gap of silicon. The spatial responsivity of thermopile detector was measured at two different wavelengths and no wavelength dependence was observed.

Optical emission spectroscopy is used to characterize the production of active species as a function of hydrogen concentration in the mixture under different operating conditions. A major concern is to enhance the concentration of the active species by hydrogen addition that carry several electron volts energy above their ground states, and thus affect the surface chemistry. The emission intensity of the selected optical transitions of molecular and atomic species is measured to determine the functional dependence of their radiative states. The relative ground state molecular ion density [N2 +]is measured from the emission intensity of the first negative band head (λ = 391.4 nm, 0–0) by considering the fact that in low temperature plasma, ion with single charge is produced by the electron impact, and the ion density is proportional to the electron density. It is found that the concentration of the active species may be enhanced significantly by selecting an appropriate gas composition and operating parameters. The SS-304 samples are nitrided under the optimum conditions for 4, 8, 12 and 16 hours and hardness values are found to increase five times for 16 hours treatment time. The optimized discharge conditions are found favorable for plasma ion nitriding.