Papers by Author: Bilal Nsouli

Abstract: The quantification of active ingredients (AI) in drugs is a crucial and important step in the drug quality control process. This is usually performed by using wet chemical techniques like LC-MS, UV spectrophotometry and other appropriate organic analytical methods. However, if the active ingredient contains specific heteroatoms (F, S, Cl…), elemental IBA like PIXE and PIGE techniques, using small tandem accelerator of 1-2 MV, can be explored for molecular quantification. IBA techniques permit the analysis of the sample under solid form, without any laborious sample preparations. In this work, we demonstrate the ability of the Thick Target PIXE technique for rapid and accurate quantification of both low and high concentrations of active ingredients in different commercial drugs. Fenofibrate, a chlorinated active ingredient, is present in high amounts in two different commercial drugs, its quantification was done using the relative approach to an external standard. On the other hand, Tiemonium methylsulfate which exists in relatively low amount in commercial drugs, its quantification was done using GUPIX simulation code (absolute quantification) The experimental aspects related to the quantification validity (use of external standards, absolute quantification, matrix effect,...) are presented and discussed.

Abstract: An absorber-emitter system was fabricated using a multi-layer structure of amorphous silicon and silicon oxide thin films. The layers were deposited using RF magnetron sputtering system. The thin films were alternated in a periodic structure to form a one-dimensional photonic crystal. Each period in the crystal consisted of one layer of 57 nm thick silicon and a 100 nm thick silicon oxide layer. Several samples were prepared consisted on different periods (N= 1, 2, 3, 4, 5 and 10). Rutherford Backscattering Spectrometry technique (RBS) was used to verify the number of layers and their alternation, checking the thicknesses and determine the real stoichiometry in each layer of Si and SiOx.

Abstract: In this work, the capability of the proton Induced γ-ray Emission (PIGE) technique to monitor a rapid, nondestructive and quantification of Boron in ultra-thin films of BxGa1-xAs deposited on GaAs substrate using MOCVD is discussed. In order to improve the sensitivity for B detection, a systematic study was undertaken using proton induced beam at three different energies (from 1.7, 2.4 and 3 MeV) with different tilting angles (0, 60° and 80°). Best conditions were found to be at 1.7 MeV and at 80° for proton energy and tilting angle within ten minutes of acquisition time.

Abstract: In this work the capability of the proton induced X-ray emission (PIXE) technique to monitor a rapid, non-destructive and accurate quantification of Al on or inside SiC is discussed. Optimization of PIXE acquisition parameters was performed using as reference, a thin Al film (2.5 nm) thermally evaporated onto silicon carbide substrate. In order to improve the sensitivity for Al detection and quantitative determination, a systematic study was undertaken using proton ion beam at different energies (from 0.2 to 3 MeV) with a different tilting angle (0°, 60°, and 80°). The limit of detection (LOD) was found to be lower than 0.02 nm. The optimum PIXE conditions (energy, angle) were applied for determining the Al doping concentration in thin (1 µm) 4H-SiC homoepitaxial layer. The Al concentration as determined by PIXE was found to be 3.9x1020 at/cm3 in good agreement with SIMS measurements, and the LOD was estimated to be 6x1018 at/cm3.

Abstract: In this work the capability of the proton induced X-ray emission (PIXE) technique to monitor a rapid, non-destructive and accurate quantification of Al on and in Si-based matrix is discussed. Optimization of PIXE acquisition parameters was performed using as reference a thin Al film (2.5 nm) thermally evaporated onto silicon substrate. In order to improve the sensitivity for Al detection and quantitative determination, a systematic study was undertaken using proton ion beam at different energies (from 0.3 to 3 MeV) with a different tilting angle (0°, 60°, and 80°). The limit of detection (LOD) was found to be lower than 0.2 nm. The optimum PIXE conditions (energy, angle) were applied for determining the Al doping concentration in thin (1 µm) 4H-SiC homoepitaxial layer. The Al concentration as determined by PIXE was found to be 3.9x1020 at/cm3 in good agreement with SIMS measurements, and the LOD was estimated to be 6x1018 at/cm3.

Abstract: In this paper we present a methodology to affect the stability of polytypes formation during heteroepitaxial growth of SiC on Si. This methodology is based on the investigation of growth related parameters. These parameters involve substrate temperature, effect of impurities on surface diffusion, strain, and super-saturation conditions as solved by using SSMBE growth (Solid Source molecular beam epitaxy).

Abstract: We report an optical study of 3C-SiC layers grown on 6H-SiC substrates by VLS mechanism using a Si-Ge melt. The photoluminescence and μ-Raman results show a clear and significant incorporation of germanium in the layers from the melt. A photoluminescence emission attributed to Ge related transitions is observed in the infrared region. μ-Raman spectra exhibit two peaks related to the Ge-Ge and Si-Ge bonds. From the characteristics of these Raman peaks, it was found that the amount of Ge incorporated inside the 3C layers increases with increasing Ge content of the melt. This has been verified by Particle-Induced X-rays Emission (PIXE) measurements which gave a Ge concentration varying from ~ 1x1019 to ~ 1x1020 at.cm-3. All these results suggest that Ge incorporates in the VLS grown 3C layers by forming Si-Ge-(C) nanoclusters.

Abstract: The growth kinetics of 3C-SiC heteroepitaxial layers on α-SiC substrates by Vapour-Liquid-Solid (VLS) mechanism in Ge-Si melts was investigated. Various parameters were studied such as temperature, melt composition, propane flux and substrate nature (polytype, polarity and misorientation). It was found that the growth rate increases with increasing temperature, propane flux, Si content of the melt and misorientation of the substrate. The calculated activation energy (from 4.7 to 6.6 kcal/mole depending on the substrate type) is very small suggesting that the limiting process is the diffusion of the dissolved carbon inside the melt. The carbon solubility inside the melt mainly affects the carbon dissolution kinetics from the gas phase. The results also suggest that surface effects are important through the layer polarity and crystalline quality.

Abstract: We report on the heteroepitaxial growth of 3C-SiC layers by Vapor-Liquid-Solid (VLS) mechanism on Si face 6H-SiC substrates, on-axis and 3.5° off. The Si-Ge melts, which Si content was varied from 10 to 50 at%, were fed by 3 sccm of propane. The growth temperature was varied from 1200 to 1600°C. It was found that 3C-SiC layers (either twinned or twinned free) form at low temperature while homoepitaxy is achieved at high temperature. The proposed growth mechanism involves the initial formation of 3C islands during the heating ramp (below 1200°C) and the dissolution of these islands when temperature increases. Geometrical aspects, such as the step density at the surface and the vertical component of the growth, are also considered to explain the difference observed between the on and off axis substrates.

Abstract: We report on the heteroepitaxial growth of 3C-SiC layers by Vapor-Liquid-Solid (VLS) mechanism on various α-SiC substrates, namely on- and off-axis for both 4H and 6H-SiC(0001), Si and C faces. The Si-Ge melts, which Si content was varied from 25 to 50 at%, were fed by 3 sccm of propane. The growth temperature was varied from 1200 to 1600°C. It was found that singledomain 3C-SiC layers can be obtained on 6H-SiC off and on-axis and 4H-SiC on-axis, while the other types of substrate gave twinned 3C-SiC material. As a general rule, one has to increase temperature when decreasing the Si content of the melt in order to avoid DPB formation. It was also found that twinned 3C-SiC layers form at low temperature while homoepitaxy is achieved at high temperature.