Papers by Author: Mohamad Roumie

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Authors: R. Mawassi, R. Awad, Mohamad Roumie, M. Kork, I. Hassan
Abstract: The major limitation of Bi-system superconductor applications is the intergrain weak links and weak flux pinning capability producing low critical current density of the Bibased phases. In order to enhance these characteristics and other superconducting properties, effective flux pinning centers are introduced into high temperature superconductors. In this work, different weight percentages of ZnO nano oxide were introduced at the final stage of the Bi1.8Pb0.4Sr2Ca2Cu3O10-y superconductor preparation process. Phase characterization was completed by X-ray diffraction (XRD). Exact constitution of the samples was determined using particle induced X-ray emission (PIXE). Granular and microstructure were investigated using scanning electron microscopy (SEM). Electrical resistivity as function of the temperature was carried to evaluate the relative performance of samples, and finally, E-J characteristic curves were obtained at 77K. Using 0.4 ZnO weight percentage, the electrical and granular properties were greatly enhanced, indicating more efficient pinning mechanisms. A critical current density of 949 A/cm2 was obtained which represents more than twice the value obtained for the pure sample (Jc= 445 A/cm2).
Authors: Sayed Abboudy, Maher Soueidan, Qassem Al Asaad, Laurent Auvray, Gabriel Ferro, Mohamad Roumie, Bilal Nsouli
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.
Authors: Wassim Kassem, Malek Tabbal, Mohamad Roumie
Abstract: Thin coatings of Tungsten were deposited on substrates fabricated by pre-depositing graphite thin layers on Si(100) wafers. We ablate pure W target using a 20 ns KrF excimer laser (248 nm) in an Ar ambient. The effect of background gas pressure, substrate temperature, and laser fluence, on the properties of the deposited W layers is studied using several techniques including X-Ray Diffraction, Atomic Force Microscopy, surface profilometry, and Rutherford Back-Scattering spectrometry. Our results indicate that the deposited layers consist of the well-crystallized body-centered-cubic α-W phase with bulk-like properties, particularly for films deposited at a substrate temperature of 450°C, laser fluence greater than 400mJ, and pressure of about 10mTorr.
Authors: Mohamad Roumie, Sayed Abboudy, Maryam Al Sabbagh, Husam Abu-Safe, Maher Soueidan, Bilal Nsouli
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.
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