Ghassan Younes

On the growth of 4H–SiC by low-temperature liquid phase epitaxy in Al rich Al–Si melts

Abstract The growth of 4H–SiC by low-temperature liquid phase epitaxy was studied in Al–Si melts. The temperature ranged from 1000°C to 1200°C. Some problems, which were sources of non-homogeneity of the growth or low reproducibility of the process, were identified and reviewed: (1) local delayed wetting of the seed by the melt, (2) morphological (3) presence of alumina particles on the liquid, (4) high reactivity of the melt with graphite at temperature above 1200°C, (5) formation of crystallites on the surface upon cooling. The solutions proposed to avoid or limit these problems are: (1) deposition of a Si layer before the growth, (2) careful backside gluing, (3) a two-step procedure involving the pre-dipping in the melt of a graphite rod on which alumina particles agglomerate, (4) growth at temperature lower than 1200°C. No solution was found to avoid the crystallites formation upon cooling.

Set-up, optimization and first set of samples at the radiocarbon laboratory in Lebanon

A new radiocarbon laboratory has been established recently at the Lebanese Atomic Energy Commission. This laboratory consists of benzene synthesis line and a low background liquid scintillation counter, Tri-Carb 3180 TR/SL for measurements with Bismuth Germanate (BGO) guard detector. The effectiveness of the benzene line was tested firstly by preparing benzene from a wood sample after carbide and acetylene receiving. Normalization and standardization of the liquid scintillation counter was carried out, as well as the Factor of Merit (E2/B) was determined for three different counting regions. To assure accuracy and reliability of results, reference materials were used. Based on z-score and u-score evaluation, as well as Student’s t-test, acceptable data were obtained from travertine and wood samples available through the International Atomic Energy Agency (IAEA-C2 and IAEA-C5), and humic acid (U) and murex shell (R) from the Fifth International Radiocarbon Intercomparison (VIRI). After that, a preliminary study was done, which is the base for future research in order to assess the anthropogenic impact and degree of environmental pollution in terms of radiocarbon isotope ratio (Δ14C) deduced from the Percent Modern Carbon or PMC. This work represents the results of four reference materials and those of five green grass samples. The Δ14C of green grass samples collected from two different clean zones were found to be 50‰ and 52‰, while the values of those collected from different polluted zones were 23‰, 7‰ and 15‰.

Growth of Nanocrystalline Translucent h-BN Films Deposited by CVD at High Temperature on SiC Substrates

h-BN layers were deposited on α-SiC substrates by CVD at high temperature (1500-1900°C) using B2H6 and NH3 diluted in Ar. Growth rates were in the 6-10 µm/h range. In all the conditions studied, the BN as deposited layers were found to be translucent to light, some having a light whitish aspect and other a more yellowish one. It was also observed that the deposit was not always adhesive. µ-Raman and TEM characterization showed that the layers were nano-crystalline with crystallite size < 10 nm. The growth rate was found temperature and N/B ratio dependent due to an N limited growth regime which is more pronounced above 1700°C.

COMPARATIVE STUDY OF THE INHIBITIVE ACTION BETWEEN THE BITTER ORANGE LEAF EXTRACT AND ITS CHEMICAL CONSTITUENT LINALOOL ON THE MILD STEEL CORROSION IN HCL SOLUTION

Bitter orange, Citrus Aurantium (CA), extract and one of its chemical constituents, Linalool, have been evaluated as a corrosion inhibitor for mild steel in 0.5 mol L hydrochloric acid (HCl) solution using potentiodynamic polarization, electrochemical impedance, Fourier transform infrared spectroscopy (FTIR), and atomic force spectroscopy (AFM) techniques. Functional groups of CA and Linalool were identified by FTIR spectroscopy. The Potentiodynamic polarization and electrochemical impedance studies showed that CA and Linalool act as mixed type inhibitors. The activation parameters showed that the corrosion inhibition takes place by spontaneous physical adsorption on the mild steel surface. Thermodynamic-kinetic model and Flory-Huggins isotherms were used to investigate the adsorption characteristics of CA and Linalool. The surface morphologies of mild steel specimens were studied using AFM, in which the surface roughness of the metal specimens on a micro scale was characterized.

Swift Quantification of Fenofibrate and Tiemonium methylsulfate Active Ingredients in Solid Drugs Using Particle Induced X-Ray Emission

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.

Boron Doping during Vapor-Liquid-Solid Growth of Homoepitaxial 4H-SiC Layers

Vapor-Liquid-Solid was used for growing boron doped homoepitaxial SiC layers on 4HSiC( 0001) 8°off substrates. Si-based melts were fed by propane (5 sccm) in the temperature range 1450-1500°C. Two main approaches were studied to incorporate boron during growth : 1) adding elemental B in the initial melt, with two different compositions : Si90B10 and Si27Ge68B5; the growth was performed at 1500°C; 2) adding B2H6 (1 to 5 sccm) to the gas phase during growth with a melt composition of Si25Ge75; the growth was performed at 1450°C. In most cases, the growth time was limited by liquid loss due to wetting on the crucible walls. The longer growth duration (1h) was obtained when adding B2H6 to the gas phase. In the case of Si90B10 melt, the surface morphology exhibits large and parallel terraces whereas the step front is more undulated when adding Ge. Raman and photoluminescence characterizations performed on these layers confirmed the 4H polytype of the layers in addition to the presence of B which results in a strong B-N donor-acceptor band. Particle induced γ-ray emission was also used to detect B incorporation inside the grown layers.

Comparison between Ar and N2 for High-Temperature Treatment of 4H-SiC Substrates

4H-SiC seeds have been treated at high temperature (1650-1900°C) under A r or N2 in a sublimation like graphite crucible with SiC powder at the hotter pa rt. It was found that the surface morphology is significantly altered by the nature of the atmospher e. N2 gives a smoother surface for the low temperature range (< 1700°C) whereas at higher temperat ure it degrades compared to Ar. Thermodynamical calculations performed on the Si-C-N (Ar) syst em show that N2 plays an important role on the gas phase chemistry of decomposition of SiC by forming gaseous species of nitrides. It is found that the gas phase is C rich when N 2 is used at low temperature whereas it becomes Si rich at a temperature higher than 1700°C. The theoretical r sults correlate well with the graphitisation of the SiC powder.

Seasonal Variations of Radiocarbon Content in Plant Leaves in a 14 C-Depleted Area

The determination of radiocarbon content in biogenic samples such as tree leaves and short-lived plants is crucial when studying the anthropogenic impact on the ecosystem and for detecting any alteration in stable and radioactive CO 2 . A total of 76 samples of evergreen and deciduous tree leaves as well seasonal plants were collected in winter, spring, and summer. Sampling was carried out from rural villages located in Mount Lebanon Province, Lebanon. Based on the data obtained from a previous study carried out in autumn, which showed that the selected sites are characterized by depletion of 14 C caused by the releases of pollutants and CO 2 from a cement factory in the region, further investigation was carried out in the present work to determine possible significant seasonal variations in Δ 14 C values. Reference samples of identical species were collected in the same period from a clean zone. The conventional 14 C method was used to determine the carbon isotopic ratio. Δ 14 C data are compared to those obtained in autumn. 14 C concentration in the studied sites was significantly lower than in the clean area in all seasons. ANOVA tests showed that there is a significant seasonal variation for deciduous leaves and seasonal plants, while this difference was not significant in evergreen leaves. In addition, no significant variation was recognized for different species in the same season. DOI: 10.2458/azu_rc.57.18350

Occurrence and levels of pesticides in South Lebanon water

This study reviews the detection of pesticides in different surface and groundwater samples collected from South Litani region in South Lebanon during 2012. These have been analyzed using an optimized and validated solid phase extraction method followed by gas chromatography coupled with mass spectrometry. Organochlorine and organophosphate pesticides were mostly noted at levels below the recommended value for individual pesticide in water except pirimiphos-methyl that was recorded at 300.87 ng L−1 in groundwater sample, designated for drinking water and collected in February. DDE concentration exceeded 100 ng L−1 in both surface and groundwater in October. The reported results represent the first Lebanese statistical data illustrating the quantification of pesticides in water over a period of time. More importantly, it draws attention to the need of pesticides’ monitoring programs in the Lebanese water resources.

Kinetic studies of solute – solvent interactions in the solvolysis of trans -[Co(4- tert -butylpyridine) 4 Cl 2 )ClO 4 in organic-aqueous mixtures

The kinetics of solvolysis of trans-[Co(L)4 C12] C1O4 where (L-4-tert-butylpyr-idine) were followed spectrophotometrically in water-dioxane and water-dimethylsulfoxide media (0-60% v/v) over the temperature range (40-55°C). Non-linear plots were found for the logarithm of the rate constant of the first-order reaction versus the reciprocal of the relative permittivity, 3**r, of the mixed solvent. This behaviour can be attributed to the differential solvation of the initial and transition states of the complex. The enthalpies and entropies of activation showed compensating extrema with the mole fraction of solvent, leading to a small variation in the free energy of activation. By applying a free-energy cycle, it was found that the difference between the values of the free energy of transfer of the cations in the transition and initial states were negative, indicating that the cation in the transition state is more solvated than that in the initial state.