RESEARCH PROJECTS
Determination of second order reduction factors for icosahedral Jahn-Teller Systems The vibronic coupling in C60 and other icosahedral
molecules can greatly affect the magnitude of electronic interactions such
as spin-orbit, zeeman or strains effects. This particular aspect of the
vibronic coupling can be moduled by introducing appropriate reduction factors
in novel effective electronic hamiltonians used to describe the type of
interaction considered. Three main J-T systems are considered: T1Ä
h., G Ä (g Ä
h) and H Ä (g + h1 + h2).
Analytical calculations are used in conjunction with numerical calculations
to determine most of the second order isotropic reduction factors related
to these systems. M. Abou-Ghantous, C. Bates*, J. Duun*. (Supported
by URB.)
Magnons localized on surface steps: a theoretical model In this project, we present the solution of the full magnetic
problem arising from the absence of magnetic translation symmetry in two
dimensions due to an extended magnetic surface step on the surface boundary
of an insulating magnetic substrate. The calculation concerns in particular
the spin fluctuation dynamics of a magnetic atomic step in the surface
of a ferromagnetic simple cubic lattice, the spin order being in the direction
normal to surface boundary. Only exchange interactions are considered between
the localized magnon modes propagating along the step, their fields, being
evanescent in the plane normal to the step direction. (Accepted in the
European Journal of Physics B: Condensed Matter, 1999). M. Abou-Ghantous,
A. Khater*.
Synthesis of nitride thin films using plasma assisted pulsed laser deposition In this work, we are investigating the synthesis of carbon
nitride (CNx) and gallium nitride (GaN) thin films by pulsed
laser deposition assisted by a nitrogen radio-frequency surface wave plasma.
The growth of the films takes place through the interaction of the excimer
laser ablated species and the nitrogen atoms produced by the nitrogen plasma.
Such a deposition system is particularly attractive for the deposition
of nitride films because it offers the possibility of independently controlling
the laser ablation plasma and the N atom flux. It has indeed been shown
that the nitrogen atoms appreciably enhance the nitrogen content in the
CNx layers. Furthermore, epitaxial GaN films have been grown
with this system at a deposition temperature of 850 oC. Physical
and chemical characterization of the films is presently under way to correlate
between the properties of the layers and the deposition conditions. M.
Chaker*, M. Tabbal, P. Mérel*. (Supported in part by Natural
Sciences and Engineering Research Council of Canada (NSERC); Micronet and
URB.)
Supersymmetric D-branes in curved backgrounds In preparation. A. H. Chamseddine.
Chiral anomalies in the spectral action CAMS-98-05, Sep 1998. 7pp. (To appear in the book 'Quantum
Groups and Fundamental Physical Interactions', ed. D. Kastler, published
by Nova Science Publ. Co.) e-Print Archive: hep-th/9809148. A. H. Chamseddine.
Calabi-yau black holes and enhancement of supersymmetry in five-dimensions CAMS-99-01, Mar 1999. 12pp. e-Print Archive: hep-th/9903046.
A.
H. Chamseddine, W. A. Sabra.
Investigation of paramagnetic centers in diamond films produced by chemical vapor deposition Paramagnetic centers in plasma assisted chemical vapor deposition
(CVD) diamond films are being investigated using electron paramagnetic
resonance (EPR). The effect of the introduction of various amounts of gases,
such as nitrogen and carbon dioxide, on growth parameters is being investigated,
particularly at low substrate temperatures. A number of paramagnetic enters,
thus created, are being investigated as a function of gas mixture content
and substrate temperature. T. Christidis, M. Tabbal, S. Isber, J. Stiegler
*.
Production of the radioactive 26Al in massive stars We investigate the production or destruction of the radioactive
nucleus 26Al in massive stars during their hydrogen-helium-carbon-Neon
and oxygen burning phases. We use up-dated nuclear reactions involved in
the Mg Al cycle, and up-dated input physics in the stellar model. This
radioactive nucleus of 106 years decay time is observable through
its 1.809 MeV g -ray lines and is an indicator
for the current nucleosynthesis processes in the Galaxy. Paper in preparation:
26Al
production in massive stars. M. El Eid, A. Champagne*, C. Illiadis*,
B. Meyer*. (Supported by University of North Carolina.)
Stellar nucleosynthesis in massive stars Massive stars of masses (15-30) solar masses are evolved through
their advanced burning phases including the central oxygen burning. The
formation of the heavy elements by the s-process nucleosynthesis is investigated.
We determine the yield of these heavy elements from massive stars, especially
the effect of the carbon-burning shell on the synthesis of the s-elements
is carefully studied. Publications in progress: A new study of the s-process
Nucleosynthesis in Massive stars (Astrophysical Journal, 1999), s-process
in the Carbon-burning shell in Massive stars.
M. El Eid, B. Meyer*,
L. The*. (Supported in part by URB; Clemson University.)
Magnetic properties of small gap semiconductor SnTe-doped europium Magnetization of Sn1-xEuxTe (x = 6.0%)
was measured at 2.0 K in magnetic fields H up to 9 Tesla. A magnetization
“ramp” due to pairs was observed in all samples. This ramp consisted of
well-resolved Magnetization steps (MST) arising from pairs. The ramp were
used to determine the value J/kB = -0.52 K for the dominant
antiferromagnetic exchange constant. Electron paramagnetic resonance measurements
on Sn1-xEuxTe powder show a single line with a landé
factor of 1.985 ± 0.005. S. Isber,
T. Christidis, M. Tabbal, S. Charar*, A. Errebbah*. (Supported in part
by URB; Centre National de la Recherche Scientifique [CNRS-France].)
Single anisotropy of Cr3+ in zinc maleate tetrahydrate crystal Zn(C4H3O4)2.4H2O (ZMTH) study by EPR X-band (9.27 GHz) EPR spectra have been recorded on a single
crystal of Cr3+ doped Zn(C4H3O4)2.4H2O
for several orientations of the external magnetic field at room and liquid
helium temperatures. All the EPR line positions observed were simultaneously
fitted in a least-squares procedure employing numerical diagonalization
in order to determine the landé factors and the axial distortion
parameter (D). The relative intensities of lines at liquid helium temperature
indicate the absolute sign of the parameter D to be negative. S. Isber,
S. K. Misra*, P. Chand*. (Supported by Natural Sciences and Engineering
Research Council of Canada (NSERC).)
Coil-stretch transitions in star-branched macromolecules Coil-stretch transition in a dilute solution of star-branched
polymers in a longitudinal hydrodynamic flow is investigated theoretically
by scaling analysis and numerical calculations based on solving equations
of motion. The analysis is based on calculating the viscous friction forces
on different branches of a macromolecule as functions of the flow rate
and the deformation of all the branches. The next stage of the project
will require stability analysis for two different scenarios: uniform stretching
or uncoiling in a cascade of transitions. L. I. Klushin.
Phase segregation in random heteropolymers under deformation Replica method is applied to calculate the free energy density
in a collapsed random copolymer at low temperature. Effects of applying
external tension are investigated. Project in a preliminary investigation
stage. L. I. Klushin. (Supported by Russian Foundation for Basic
Research.)
Exactly solvable models for phase transitions in polymeric brushes containing minority chains Exact analytical calculation of the partition function for
an ideal polymer chain interacting with the surroundings in a grafted brush
was calculated. The aim of the research is to investigate the complete
phase diagram of the system, which should include the adsorption-desorption
and the adsorption-stretching transitions. Analytical calculations are
used in conjunction with numerical calculations based on the transfermatrix
technique. L. I. Klushin, A.M. Skvortsov*, A. A. Gorbunov*. (Supported
by Russian Foundation for Basic Research.)
Investigation of paramagnetic defects in pulsed laser deposited thin films by electron spin resonance In this project, paramagnetic defects in pulsed laser deposited
amorphous silicon carbide (a-SiC) and diamond-like-carbon (DLC) thin films
are investigated using Electron Spin Resonance (ESR). It is found that
dangling bonds are the most commonly encountered defect in such films and
their presence can affect the electronic, optical and mechanical properties
of the films. For the a-SiC films, the behavior of the intensity and line
shape of the ESR signal as deposition temperature is increased, indicates
the onset of some long-range order in the films deposited at temperatures
above 600oC. For the DLC films, the effect of the laser intensity
on the ESR signal is currently under investigation. A study of the power
saturation of the ESR signal of the films will also be conducted to get
more insight on the microstructure of such technologically attractive materials.
M.
Tabbal, T. Christidis, S. Isber, M. A. El Khakani*, M. Chaker*, P. Mérel*.
(Supported by URB.)
Behrndt, K.*, Chamseddine, A.H., and Sabra, W.A., BPS Black Holes in n=2 five-dimensional ADS Supergravity. Physics Letter B, 442, 97-101, 1998. Bindilatti, V.*, Ter Haar, E.*, Oliviera, N. F.*, Liu, M. T.*, Shapira, Y.*, Gratens, X.*, Charar, S.*, Isber, S., Masr,i P.*, Averous, M.*, and Golacki, Z.*, Magnetization steps in Pb1-xEuxS: exchange and anisotropic interactions. Physical Review B, 57, 7854-7862, 1998. Birshtein, T. M.*., Mercurieva, A. A.*, Klushin, L. I., and Polotsky, A. A.*, Liquid-crystalline polymer brushes: deformation and microphase segregation. Computational and Theoretical Polymer Science, 8, 179-189, 1998. Chamseddine, A. H., Remarks on the Spectral action principle. Physics Letter B, 436, 84-90, 1998. Chamseddine, A. H., and Sabra, W. A., Admitting Killing Spinors in five-dimensions. Physics Letter B, 426, 36-42,1998. Gratens X.*, Arauzo, A. B.*, Breton, G.*, Charar, S.*, Averous, M.*, and Isber, S., EPR of PbEuSe layer and PbEuSe/PbSe superlatice grown by MBE. Physical Review B, 58, 877-881, 1998. Gratens, X.*, Charar, S.*, Averous, M.*, Isber, S., and Golacki, Z.*, Magnetic properties of the diluted magnetic semiconductor Pb1-xCexSe. Physical Review B, 56, 8199-8203, 1997. Gratens, X.*, Isber, S., Charar, S.*, Fau, C.*, Averous, M.*, Misra, S. K.*, and Golacki, Z.*, EPR study of fine and hyperfine interactions of Gd3+ in Bi2(1-x)Gd2xSe3 and Pb1-xGdxSe. Physical Review B, 55, 8075-8079, 1997. Herwig, F.*, Blocker, T.*, Schoenberner, D.*, and El Eid, M., Stellar Evolution of Low and Intermediate-Mass Stars. Astronomy Astrophysics, 324, L81-L84, 1997. Isber, S., Masri, P.*, Charar, S.*, Gratens, X.*, and Misra, S. K.*, Crystal field effect on the pair, open- and close-triplet cluster in PbEuSe. Journal of Physics C, 9, 10023-10032, 1997. Isber, S., Misra, S. K.*, Charar, S.*, Gratens, X.*, Averous,,M.*, and Golacki, Z.*, EPR of Eu2+ in the diluted magnetic semiconductors Pb1-xEuxS. Physical Review B, 56, 13724-13727, 1997. Klushin, L. I., Skvortsov, A. M.*, and Gorbunov, A. A.*, Adsorption of a macromolecule in an external field: an exactly solvable model with bicritical behavior. Physical Revue E, 56,1511-1521, 1997. Klushin, L. I., Kinetics of a homopolymer collapse: beyond the Rouse-Zimm scaling. Journal of Chemical Physics, 108, 7917-7920, 1998. Klushin, L. I., Birshtein , T. M.*, and Mercurieva, A. A.*, Microphase segregation in polymeric brushes under deformation: regular and singular phase diagrams. Macromolecular Theory and Simulations, 7, 483-496, 1998. Klushin, L. I., Skvortsov, A. M.*, and Gorbunov, A. A.*, An exactly solvable model with first- and second-order phase transitions. Physics-Uspekhi, 41, 639-649, 1998. Mérel, P.*, Chaker, M.*, Tabbal, M. and Moisan, M.*, The influence of atomic nitrogen flux on the composition of carbon nitride thin films. Applied Physics Letters, 71, 3814-3816, 1997. Mérel, P.*, Tabbal, M., Chaker, M.*, Ricard ,A.*, and Moisan M.*, Influence of the field frequency on the nitrogen atom yield in the remote plasma of an N2 high frequency discharge. Plasma Sources: Science and Technology, 7, 550-556,1998. Mérel, P.*, Tabbal, M., Moisa, S.*, Chaker, M.*, and Margot, J.*, Direct evaluation of the sp3 carbon atom content in DLC thin films by XPS. Applied Surface Science, 136, 105-110,1998. Misra, S. K.*, and Isber, S., EPR of Kramers ions Er3+, Nd3+, Yb3+ and Ce3+ in Y(NO3)3,6H2O and Y2(SO4)3.8H2O: study of hyperfine transitions. Physica B, 253, 111-122, 1998. Misra, S. K.*, Isber, S., Capobianco, J. A.*, and Cavalli, E.*, Electron paramagnetic resonance of Er3+ doped in YVO4: hyperfine parameters. Journal of Chemical Physics, 240, 313-318, 1999. Misra, S. K.*, Isber, S., and Li, L.*, An EPR study of the phase transitions and Gd3+ zero-field splitting parameters in RbR(SO4)2.4H2O (R=Er, Dy, Pr, Nd, Sm, Eu). Journal of Physics C, 10, 10667-10677, 1998. Skvortsov, A. M.*, Klushin, L. I., and Gorbunov, A. A.*, Short and long chains in a polymer brush: a conformational transition. Macromolecules, 30, 1818-1827, 1997. Tabbal, M., Mérel, P.*, Chaker, M.*, El Khakani, M. A.*, Herbert, E. G.*, Lucas, B. N.* and O’Hern, M. E.*, Effect of laser intensity on the microstructural and mechanical properties of Pulsed Laser Deposited Diamond-Like-Carbon thin films. Journal of Applied Physics, 85, 3860-3865, 1999. Tabbal, M., Mérel, P.*, Moisa, S.*, Chaker, M.*, Gat,
E.*, Ricard, A.*, Moisan, M.*, and Gujrathi, S.*, XPS and FTIR analysis
of nitrogen incorporation in CNx thin films. Surface
and Coatings Technology, 98, 1092-1096, 1998.
ABSTRACTS,
PRESENTATIONS AND PROCEEDINGS
Chamseddine, A. H., Gauged n=4 Supergravity through Compactification and BPS Monopoles. The Sixth International Symposium on Particles, Strings and Cosmology, Boston, Massachusetts, 1998, Editor P. Nath, World Scientific, 734-741, 1999. El Eid, M., Champagne, A.*, and Shaya, W., Nucleosynthesis in Red Giant and Supergiant Stars (invited talk presented by M. E. El Eid). International Symposium on Nuclei in the cosmos, Volos, Greece, 6-11 July 1998. Edition Frontieres: Paris, 1999. Margot, J.*, Chaker, M.*, St-Onge, L.*, Tabbal, M., Aliouchouche, A.*, and Pauna O.*, High-frequency magnetoplasmas in electronegative gases. ICPIG XXIII conference, Toulouse, France, 1997. Journal de Physique IV, III, (10), 295-304, 1997. Mérel, P.*, Chaker, M.*, Pépin, H.*, and Tabbal, M., Epitaxial growth of GaN thin films using a hybrid pulsed laser deposition system. MRS Spring ‘99 Meeting, San Francisco, USA, 1999. Mérel, P.*, Chaker, M.*, Ricard, A.*, Moisan, M.*, and Tabbal, M., Influence of the applied field frequency on the concentration of nitrogen atoms produced by a N2 surface-wave discharge. ESCAMPIG 98 Conference, Dublin, Ireland, 1998. Mérel, P.*, Tabbal, M., Chaker, M.*, Ricard, A.*, and Moisan, M.*, A high flux N atom source based on a HF N2 discharge. ICPIG XXIII conference, Toulouse, France, 1997. Tabbal, M., Mérel, P.*, Chaker, M.*, El Khakani, M. A.*, Herbert, E. G.*, Lucas, B. N.*, and O’Hern, M. E.*, Synthesis of DLC thin films by PLD: Optimization of process parameters. 6th International Conference on Plasma Surface Engineering, Garmisch-Partenkirchen, Germany, 1998. Tabbal, M., Pauna, O.*, Chaker, M.*, and Margot, J.*, A surface
wave based high-density plasma source operated at 200 MHz. ICPIG XXIII
conference, Toulouse, France, 1997.
Shaya W., Element formation in giant and supergiant stars
(1999). M.El Eid.
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