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 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.

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 sp2 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.

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 Vs(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.

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.

Polystyrene thin films undergo treatment by cold plasma produced from DC point-to-plane low- pressure (4 mbar) discharge in O2 and Ar. The surface tension highly increases (more than 70% for O2 plasma and 60% for Ar plasma) by applying as weak as 200 μA discharge mean current. The treatment time required for obtain the maximum wettability is double in the case of Ar (~60 s). Important increase in surface polar component takes place while the dispersive component decreases, regardless of the gas used. Oxygen-functionalities (10–12%) graft the first 5 nm of surface and the surface polarity is decupled, in both gases. The main part (>99.8% for O2 and >97% for Ar) of the treatment time corresponds to a relaxation phase of the discharge (post-discharge time) and, thus, the role of long lifetime excited particles (>3 eV) in the activation of the polymer surface is emphasized. An ionization front having velocity ~104–106 m/s (higher in O2 than in Ar) crosses the gap starting from the anode and propagating towards the cathode. The arrival of this wave at the cathode region boosts the cathode secondary processes. The secondary electrons amplify the discharge current and trigger off the initiation of a new ionization front, stronger than the first one, which establishes the glow discharge regime. These fronts (weaker in Ar discharge) are suggested as the main mechanisms for the cold plasma production and active particles generation for the polymer treatment.

We estimated the temperature of the gas phase surrounding a Y2O3 sample melted at the focus of a solar furnace by comparing the fluorescence spectra of YO molecule A2Π1/2-X2Σ+, A2Π3/2-X2Σ+, B2Σ+-X2Σ+ systems and simulated spectra (two temperature model). If A3/2 and B systems can be described by a simple formulation for the calculation of upper and lower states energies, we have had, despite the poor resolution of our instrument, to use a full formulation and particularly introduce the Λ doubling terms, to satisfactorily describe the A1/2 system. At low pressure the discrepancies between rotational and vibrational temperatures and the weakness of the fits suggest that the populations of internal levels do not follow Boltzmann distributions mainly close to the vaporizing surface. The temperatures determined at higher pressures (50 hPa) on the three systems are consistent each others and supposed representative of that of the gas phase.

We introduce a method to measure liquid absorption into paper based on measuring white light reflected from it. The method was used with 49.8–51.7 g/m2 pilot papers, whose hydrophobicity was tuned by their fiber content and furnish. In addition, one of the samples was internally sized. Impact wetting was used where a droplet of mineral oil, isopropanol or deionized water was applied to the paper surface opposite to the one facing the monitor. The volume of liquid per droplet was (0.9±0.2) μl to (1.3±0.1) μl. The sample was illuminated with an ordinary 20 W light bulb from above. The light intensity reflected off the sample was recorded with a fast charge-coupled camera during the liquid penetration. Optical changes in the paper sample were studied by calculating the average intensity of the reflected light from a selected area. The results showed that the speed of pore wetting, mainly in the z-direction, could be measured with each liquid-sample combination. Hence a digital camera based light reflection measurement can provide information about thickness direction liquid transport in paper.