PHYSICS

Publication Record

Abou Ghantous, M., and A. Khater. 1999. Magnons localised on surface steps: A theoretical model. The European Physical Journal B 12:335–341.

Isber, S., T. Christidis, M. Tabbal, S. Charar, and M. Goiran. 2001. High-frequency EPR of CO²⁺ in CdSe. Physica B 293:304–307.

Kortz, U., S. Isber, M. Dickman, and D. Ravot. 2000. Sandwich-type silicotungstates: Structure and magnetic properties of the dimeric polyoxoanions [{SiM2W9O34(H2O)}2]12- (M = Mn2+, Cu2+, Zn2+). Inorganic Chemistry.

Kortz, U., Y. P. Jeannin, A. Tézé, G. Hervé , and S. Isber. 1999. A novel dimeric Ni-substituted b-Keggin silicotungstate: Structure and magnetic properties of K12[{b-SiNi2W10O36(OH)2(H2O)}2]×20H2O Inorganic Chemistry.

Merel, P., M. Chaker, M. Tabbal, and H. Pepin. 2001. Structural and electrical characteristics of epitaxial GaN thin films grown using a hybrid pulsed laser deposition system. Applied Surface Science.

Misra, S. K., S. Isber, J. A. Capobianco, and E. Cavalli. 1999. Electron paramagnetic resonance of Er3+ doped in YVO4: Hyperfine parameters. Journal of Chemical Physics.

Misra, S. K., S. Isber, and P. Chand. 2000. Single anisotropy of Cr³⁺ in zinc maleate tetrahydrate crystal Zn(C₄H₃O₄)₂.4H₂O (ZMTH) study by EPR. Physica B 291:105–109.

Misra, S. K., S. Isber, and L. Li. 1999. Electron paramagnetic resonance of Gd³⁺ in Praseodymium triacetate tetrahydrate. Physica B 269:278–283.

Qiu, Q., J. L. Dunn, C. A. Bates, M. Abou Ghantous, and V. Polinger. 2000. Reduction factors for the Icosahedral T_1uxh_g Jahn-Teller systems. Physical Review B 62 (23):16155–16166.

Tabbal, M., S. Isber, T. Christidis, M. A. El Khakani, and M. Chaker. 2000. Effect of deposition temperature on the optical transmission and paramagnetic centers in pulsed laser deposited amorphous silicon carbide thin films. Journal of Applied Physics 88:5127.

Tabbal, M., M. Kazopoulo, T. Christidis, and S. Isber. 2001. Enhancement of the molecular nitrogen dissociation levels by Ar dilution in surface wave sustained plasmas. Applied Physics Letters.

Tabbal, M., P. Merel, M. Chaker, M. A. El Khakani, E. G. Herbert, and B. N. Lucas. 1999. Synthesis of diamond like carbon films by PLD: Optimization of process parameters. Surface and Coatings Technology.

Tabbal, M., P. Merel, M. Chaker, and H. Pepin. 2001. Pulsed laser deposition of c-axis oriented aluminum nitride thin films on silicon. European Physical Journal Applied Physics.

The, L., M. F. El Eid, and B. S. Meyer. 2000. A new study of the s-process in massive stars. Astrophysical Journal 533:998–1015.

Abstracts, Conferences, and Proceedings

Abou Ghantous, M., J. Dunn, and C. A. Bates. September, 2000. General aspects on Jahn-Teller effects in cubic and icosahedral symmetries. Petra-School of Physics: Physics of new materials. Invited speaker, Amman, Jordan.

Abou Ghantous, M., J. Dunn, V. Polinger, and C. A. Bates. August 2000. Franck-Condon approximation for second order reduction factors: Application to vibronic reduction in fullerenes. Invited Speaker. Petra-School of Physics: Physics of New Materials, Boston, USA.

Abou Ghantous, M., and A. Khater. September 2000. Spin and vibration modes on surface atomic steps and other surface nanostructures: The matching method. Petra-School of Physics: Physics of new materials. Invited speaker, Amman, Jordan.

———. September 2000. Magnon and phonons localised on surface nanostructures. Petra-School of Physics: Physics of New Materials, Amman, Jordan.

Christidis, T., M. Tabbal, S. Isber, M. A. El Khakani, and M. Chaker. June 2001. Comparative ESR study of hydrogenated and non-hydrogenated amorphous silicon carbide thin films. European Materials Research Society, Strasbourg, France.

Christidis, T., M. Tabbal, S. Isber, P. Merel, and M. Chaker. September 2000. Effect of nitrogen incorporation on the paramagnetic centers in pulsed laser deposited amorphous carbon thin films. Diamond 2000, Porto, Portugal.

El Eid, M. F., A. Champagne, and W. Shaya. 1999. Nucleosyntin red giant and super giant stars. In the proceedings of the International Symposium on Nuclei in the Cosmos, p. 123. Paris: Edition Frontieres. (The symposium took place on July 6–11, 1998, Volos, Greece.)

Merel, P., M. Chaker, H. Pepin, and M. Tabbal. 1999. Epitaxial growth of GaN thin films using a hybrid pulsed laser deposition system. Materials Research Society Symposium Proceedings.

Tabbal, M. October 1999. Environmental and biotechnological applications of plasma-based processes. Int. Conf. on Biotechnologies as a Catalyst for National Development, Beirut, Lebanon.

Tabbal, M., T. Christidis, S. Isber, A. El-Khakani, P. Merel, and M. Chaker. April 2001. Paramagnetic centers in carbon based films. Materials Research Society: Spring Meeting, San Francisco, California, USA.

Tabbal, M., M. Kazopoulo, T. Christidis, and S. Isber. May 2000. Characterization of a nitrogen surface wave discharge for the deposition of nitride thin films. 2nd French-Lebanese Conference on Materials Science, Beirut, Lebanon.

———. November 2000. Investigation of nitrogen atom production in Ar/N2 and He/N2 surface wave plasmas. LAAS Science Meeting, Beirut, Lebanon.

Tabbal, M., P. Merel, and M. Chaker. 1999. Synthesis of nitride thin films by pulsed laser deposition assisted by a nitrogen surface wave plasma. Proceedings of 14th International Symposium on Plasma Chemistry (ISPC-14), Prague, Czech Republic.

———. June 2001. Remote plasma assisted pulsed laser deposition of CNx and GaN thin films. European Materials Research Society, Strasbourg, France.

Tabbal, M., P. Merel, M. Chaker, T. Christidis, and S. Isber. June 2000. Effect of laser intensity on the physical and microstructural properties of carbon nitride thin films synthesized by plasma assisted pulsed laser deposition. Gordon Research Conference on Laser Interaction with Materials, Andover, New Hampshire, USA.

Research Projects

Carbon 60 and icosahedral systems

Theoretical analysis and models to determine the reductions factors for vibronic coupling required for interpretation of experimental data. Abou Ghantous, M., and Nottingham University.

Completed or in progress at AUB

The Franck Condon approximation for Second Order reduction factors “in Fullerenes”

Papers to be submitted to Journal of Physic: Condensed Matter. Abou Ghantous, M., C. A. Bates, J. Dunn, and V. Polinger.

Calculation of spin modes on magnetic surface clusters

Accepted in Surface Sciences Letters. Abou Ghantous, M with Khater, A.

Pulsed laser deposition of nitride thin films

We use pulsed laser deposition (PLD) assisted by a nitrogen remote plasma to synthesize nitride thin films, namely, Carbon nitride (CNx) and gallium nitride (GaN). Chemical analysis of the CNx layers shows that the presence of nitrogen atoms in the remote plasma enhances the nitrogen incorporation in the films ranging between 16 to 25 % atomic. For GaN, High Resolution X-Ray Diffraction (XRD) measurements indicate that the crystalline quality of the films depends critically on atomic nitrogen to gallium flux ratio that reaches the substrate during film growth. Smooth GaN films with narrow GaN(0002) rocking curves (FWHM = 80 arcsec) have been synthesized at a substrate temperature as low as 750ºC. The effect of the various operating parameters, such as laser intensity, background pressure, and plasma power, on the growth and properties of both types of films will be investigated. Chaker, M., M. Tabbal, and P. Merel.

Supported by Natural Science and Engineering Research Council of Canada (NSERC)
Completed or in progress at Institut national de recherche scientifique (INRS), Canada

V-band electron paramagnetic resonance

A 75-GHz Electron Paramagnetic Resonance spectrometer is being built, using a Gunn diode and a cylindrical reflection cavity. The spectrometer will eventually be used to investigate EPR spectra from carbon-based thin films that seem to possess paramagnetic centers with small g anisotropy or very similar g-values. It will be also used to investigate metallic semiconductor crystals doped with rare earth ions. Christidis, T., S. Isber, and M. Tabbal.

Supported by URB
Completed or in progress at AUB

S-process nucleosynthesis in massive stars

Evolution models are constructed for massive stars through their advanced evolutionary phases by taking into account a complete description of nuclear fusion reactions that lead to the formation of heavy elements by the slow neutron capture process (referred to as s-process). El Eid, M., L. The, and B. Meyer.

Supported by URB and National Science Foundation (NSF), USA
Completed or in progress at AUB and Clemson University, South Carolina, USA

Production of radioactive isotopes in massive stars

The production of rare radioactive isotopes, like Al26, is investigated as it occurs during different phases of the evolution of massive stars. Up-dated nuclear reaction rates are included in these investigations. El Eid, M., L. The, B. Meyer, C. Illiadis, and A. Champagne.

Supported by National Science Foundation (NSF), USA
Completed or in progress at AUB, Clemson University, and University of North Carolina at Chapel Hill

Origin of the A and B presolar SiC grains

A and B SiC grains are identified in the residue of the Murchison carbonaceous meteorites. These peculiar grains are likely to have originated from AGB stars. However, the conditions under which they are produced are still poorly known. This project will deal with this issue, aiming at a better understanding of the evolution of AGB stars. El Eid, M., E. Zinner (PL), and S. Amari.

Supported by Cosmochemistry program of NASA
Completed or in progress at AUB, and University Washington in St. Louis

Electron spin resonance of Cr(2)CdCl(6).12H(2)O

X-Band (9.6GHz) ESR spectra have been recorded on a single crystal Cr(2)CdCl(6).12H(2)O for several orientations of the external magnetic field  at liquid helium temperature. A preliminary examination of the ESR line positions reveals that there exist two magnetically inequivalent sites of Cr(++) in the unit cell, characterized by considerably different values of the zero-field splitting (D). Isber, S.

Supported by URB
Completed or in progress at AUB

Single crystal growth and (EPR) study of diluted magnetic semiconductors

The authors are in the process of setting up a Bridgman technique to grow a single crystal, in particular a semimagnetic semiconductor. The set-up consists of a heating source (high temperature furnace 1200 K), quartz tubes, vacuum system, chemical products, stepper-motor and a PCI interface card to monitor the slow motion of the melt inside the furnace. This project will allow us to be self-sufficient and grow our crystal here at AUB. The grown samples will be first characterized by EPR versus temperature at the AUB Physics department, and second, by magnetization measurements versus magnetic field at the Université Montpellier II-France. Isber, S., T. Christidis, and M. Tabbal.

Supported by URB and Centre national de la Recherche Scientifique (CNRS), France
Completed or in progress at AUB

Development of a radio-frequency surface wave plasma N-atom source

The aim of this study is to develop a radio-frequency surface wave plasma N-atom source that can be used for future applications in the surface modification and synthesis of materials. The source is operated at 13.56 MHz, and at total gas pressures, ranging from 0.5 to 20 Torr, in nitrogen and in gas mixtures, such as Helium or Argon /Nitrogen. Optical Emission Spectroscopy will be used to monitor the N-atom production and the dissociation rate [N]/[N2] in the remote plasma, and to measure the rotational and vibrational temperatures of the gas. Experimental parameters, such as operating pressure, plasma power, tube diameter, and the rare gas concentration in the plasma, will be varied in order to determine the optimal plasma conditions leading to the most efficient dissociation of the N2 molecule. The results will be discussed in terms of the kinetics of the chemical reactions taking place in the plasma. Tabbal, M., T. Christidis, and S. Isber.

Supported by URB
Completed or in progress at AUB

Electron Paramagnetic Resonance of amorphous carbon nitride thin films

Electron Paramagnetic Resonance (EPR) is used to study the effect of nitrogen incorporation on the paramagnetic centers in pulsed laser deposited unhydrogenated amorphous carbon (a-C) and carbon nitride (CNx) thin films. For both a-C and a-CNx films, the g-value of the EPR signal was found to be close to 2.0028, and the EPR lineshapes were found to be pure Lorentzian. These two observations indicate that the paramagnetic centers in both types of films are most probably clustered graphitic carbon-related defects. The defect density (about 1020 spins/cm3) was found to increase with nitrogen content in the films. The exchange-narrowed EPR line width also shows an increase from 2.6 to 3.7 G as the nitrogen content in the films is varied from 25 to 17 %. It is thus suggested that nitrogen could induce bridging between adjacent paramagnetic centers thus modifying the mechanical and electrical properties of the films. Tabbal, M., T. Christidis, S. Isber, P. Merel, and M. Chaker.

Supported by URB

Completed or is in progress at AUB