Research and development in Materials Science and Engineering, mainly experimental Solid State Physics (electronic and thermal transport properties), Cryophysics and Nanotechnology.
Synthetic diamond is used in applications ranging from abrasives, tool coatings, bearing surfaces... more Synthetic diamond is used in applications ranging from abrasives, tool coatings, bearing surfaces, microelectronics and optics to corrosion protection. The first artificial synthesis used high-pressure techniques to produce diamond as the thermodynamically stable form, but it can also be grown at low pressures as a metastable carbon phase. Here we report the production of high-purity cubic diamond microparticles (10–100 µm), which form in a highly concentrated carbon-vapour phase, followed by deposition of the crystals on the substrate. The carbon-vapour phase is generated by thermal activation of graphite, and the fast initial growth-rates of diamond, in the range 100–500 µm s-1, are at least two orders of magnitude higher than previously reported. We expect that tuning of experimental parameters to optimize the density of the carbon-vapour phase will allow us to grow larger diamond crystals, thereby opening a wider range of potential practical applications.
: It was found that the thermoelectric power of polycrystalline bismuth increases with decreasing... more : It was found that the thermoelectric power of polycrystalline bismuth increases with decreasing thickness at room temperature. Parallel galvanomagnetic and resistivity measurements indicate that the mean free paths of the charge carriers remain unchanged in the range of thickness investigated. Applying Herring's simplified formula, combined with the law of emf's in parallel extended to three band conduction, it was found that a phonon-drag mechanism could explain the observed increase in TEP and the order of magnitude of the effect. The expected variation of the diffusion thermoelectric power with temperature in the range 80-300K was also computed, using the correct band structure and the temperature dependence of the density of free carriers. Besides, it was found that at 80K, the magnetoresistance is not the same for thin foils, whether the magnetic field is perpendicular or parallel to the surface of the foil. Some interesting features are noted about the low-field galv...
In the present work, the effect of carbon nanotubes (CNTs) addition on the electrical conductivit... more In the present work, the effect of carbon nanotubes (CNTs) addition on the electrical conductivity and mechanical properties of thermoplastic polymers was investigated. CNTs were incorporated into the polymer matrix either in high concentrations (masterbatch) or as an additive in small quantity (dilution source of masterbatches in a polymeric binder). Masterbatches containing a 5-20 % by weight of CNTs and composites obtained through their addition in polypropylene-the actual content of CNTs in polymer 0.1 and 0.01 wt. %-were synthesized and characterized by mechanical tests and scanning electron microscopy. Also, the frequency dependence of the AC electrical conductivity of masterbatches and dilute composites were measured. It has been shown that the introduction of masterbatches containing 10 wt. % of CNT provides a more efficient reinforcement of the composite than those using masterbatches with 5 and 20 wt. % of CNTs. It is also found that the alternating current (AC) conductivities display two or three regions: regions of constant conductivity and regions where the conductivity increases with increasing frequency (following the percolation scaling law). It was also observed that the conductivity increases drastically with increasing CNT content in the investigated concentration range (from 0 to 20 wt. %).
Ferrite nanoparticles of basic composition Ni 0.5 Zn 0.5 Fe 2 O 4 are synthesized for the first t... more Ferrite nanoparticles of basic composition Ni 0.5 Zn 0.5 Fe 2 O 4 are synthesized for the first time through molten salt method using Fe 1.61 O 3 , Ni 0.47 (OH) 2 , and Zn 0.98 O as non-standard Moroccan raw materials. The effect of various parameters such as annealing temperature and time on crystalline structure of Ni-Zn ferrite has been investigated. The TGA analysis shows the thermal behavior of the reagents mixture. The X-ray diffraction pattern confirmed the single phase, high crystalline and cubic structure with Fd3m space group, and average crystallite size of 29 nm. The Fourier transform infrared spectra (FT-IR) shows two fundamental absorption bands (v 1 and v 2) that are attributed to the stretching vibration of tetrahedral and octahedral sites, observed in spinel structure, in the wave number range of 400-600 cm À1. Particle size are evaluated by using transmission electron microscopy and proved that they have a cubical shape. EDS result confirms the purity of the Ni-Zn nanoferrite powder. Magnetic measurements reveal a weak ferrimagnetic behavior at low temperature and superparamagnetism at high temperature.
Highlights nZVI is used as Fenton-like reagent for activation of Zn leaching from the BFS. nZ... more Highlights nZVI is used as Fenton-like reagent for activation of Zn leaching from the BFS. nZVI has positive effect on kinetics of Zn leaching though with some loss of efficiency. A complex ultrasonic-assisted method for BFS recycling is proposed.
Abstract NiO nanostructured powders were synthesized by an ultrasonic spray pyrolysis (USP) techn... more Abstract NiO nanostructured powders were synthesized by an ultrasonic spray pyrolysis (USP) technique. The powders were characterized using low temperature adsorption (BET), X-ray diffraction, scanning electron microscopy (SEM), and a transmission electron microscopy (TEM). The final product of the ultrasonic spray pyrolysis is hollow microspheres with 5–7 μm in diameter. The microspheres are built from nanoparticles with 40–60 nm in diameter.
Using recent experimental data on their temperature variation, the in-plane electrical and therma... more Using recent experimental data on their temperature variation, the in-plane electrical and thermal conductivities of low stage graphite acceptor intercalation compounds are analyzed. A 2D model is used for the electrical resistivity to interpret the data and some features specific to 2D conduction are underlined. After introducing the various mechanisms responsible for thermal conduction, the effect of intercalation on the thermal conductivity of pristine graphites is discussed.
The Science and Technology of Carbon Nanotubes, 1999
Publisher Summary This chapter introduces the main electronic features of CNTs and some general a... more Publisher Summary This chapter introduces the main electronic features of CNTs and some general aspects of electronic conduction and transmission. The main experimental results obtained on the electrical resistivity of MWCNT and SWCNT and the very recent data relative to the thermopower of SWCNT bundles have also been presented. MWCNTs behave as an ultimate carbon fiber revealing specific 2D quantum transport features at low temperatures; weak localization and universal conductance fluctuations. At high temperature its electrical conductivity is described by means of the semiclassical models which were successful in describing graphite. At low temperature, they reveal 2D quantum transport features, one of them being observed in bulk carbons and graphites (weak localization), while the other can only be observed in a mesoscopic form (universal conductance fluctuations). Single-walled CNTs (SWCNTs) behave as pure quantum wires, which, if limited in length, reduce to quantum dots. Eeach type of CNT has its own features which are strongly dependent on the dimensionality of the electronic gas. The chapter also discusses the effect of intercalation on the electrical resistivity of SWCNT bundles and some potential applications.
We have developed a reliable lithographic method to pattern thin gold films by locally exposing a... more We have developed a reliable lithographic method to pattern thin gold films by locally exposing a thin layer of an electron beam resist with the tip of a scanning tunneling microscope (STM). The exposure of the resist layer is induced by applying a voltage ...
... As a result of the pioneering measurements of X(T) for NiCl2-GIC, CoCl2-GIC, and FeCl3-GIC by... more ... As a result of the pioneering measurements of X(T) for NiCl2-GIC, CoCl2-GIC, and FeCl3-GIC by Karimov et al.1'2 and ... Recent characterization of the sam-ples used in the present study by electron microscopy, 123 however, has shown that within the intercalate layers, the ...
The temperature dependences of the Fermi energies for electrons and holes in Bismuth are computed... more The temperature dependences of the Fermi energies for electrons and holes in Bismuth are computed in the range 80-300°K, taking into account the non-parabolicity and non-ellipsoidicity of the conduction band. The partial diffusion thermoelectric powers for electrons and holes, and the total diffusion thermoelectric power in the two principal directions are then deduced. Computed values are compared with recent experimental data.
Synthetic diamond is used in applications ranging from abrasives, tool coatings, bearing surfaces... more Synthetic diamond is used in applications ranging from abrasives, tool coatings, bearing surfaces, microelectronics and optics to corrosion protection. The first artificial synthesis used high-pressure techniques to produce diamond as the thermodynamically stable form, but it can also be grown at low pressures as a metastable carbon phase. Here we report the production of high-purity cubic diamond microparticles (10–100 µm), which form in a highly concentrated carbon-vapour phase, followed by deposition of the crystals on the substrate. The carbon-vapour phase is generated by thermal activation of graphite, and the fast initial growth-rates of diamond, in the range 100–500 µm s-1, are at least two orders of magnitude higher than previously reported. We expect that tuning of experimental parameters to optimize the density of the carbon-vapour phase will allow us to grow larger diamond crystals, thereby opening a wider range of potential practical applications.
: It was found that the thermoelectric power of polycrystalline bismuth increases with decreasing... more : It was found that the thermoelectric power of polycrystalline bismuth increases with decreasing thickness at room temperature. Parallel galvanomagnetic and resistivity measurements indicate that the mean free paths of the charge carriers remain unchanged in the range of thickness investigated. Applying Herring's simplified formula, combined with the law of emf's in parallel extended to three band conduction, it was found that a phonon-drag mechanism could explain the observed increase in TEP and the order of magnitude of the effect. The expected variation of the diffusion thermoelectric power with temperature in the range 80-300K was also computed, using the correct band structure and the temperature dependence of the density of free carriers. Besides, it was found that at 80K, the magnetoresistance is not the same for thin foils, whether the magnetic field is perpendicular or parallel to the surface of the foil. Some interesting features are noted about the low-field galv...
In the present work, the effect of carbon nanotubes (CNTs) addition on the electrical conductivit... more In the present work, the effect of carbon nanotubes (CNTs) addition on the electrical conductivity and mechanical properties of thermoplastic polymers was investigated. CNTs were incorporated into the polymer matrix either in high concentrations (masterbatch) or as an additive in small quantity (dilution source of masterbatches in a polymeric binder). Masterbatches containing a 5-20 % by weight of CNTs and composites obtained through their addition in polypropylene-the actual content of CNTs in polymer 0.1 and 0.01 wt. %-were synthesized and characterized by mechanical tests and scanning electron microscopy. Also, the frequency dependence of the AC electrical conductivity of masterbatches and dilute composites were measured. It has been shown that the introduction of masterbatches containing 10 wt. % of CNT provides a more efficient reinforcement of the composite than those using masterbatches with 5 and 20 wt. % of CNTs. It is also found that the alternating current (AC) conductivities display two or three regions: regions of constant conductivity and regions where the conductivity increases with increasing frequency (following the percolation scaling law). It was also observed that the conductivity increases drastically with increasing CNT content in the investigated concentration range (from 0 to 20 wt. %).
Ferrite nanoparticles of basic composition Ni 0.5 Zn 0.5 Fe 2 O 4 are synthesized for the first t... more Ferrite nanoparticles of basic composition Ni 0.5 Zn 0.5 Fe 2 O 4 are synthesized for the first time through molten salt method using Fe 1.61 O 3 , Ni 0.47 (OH) 2 , and Zn 0.98 O as non-standard Moroccan raw materials. The effect of various parameters such as annealing temperature and time on crystalline structure of Ni-Zn ferrite has been investigated. The TGA analysis shows the thermal behavior of the reagents mixture. The X-ray diffraction pattern confirmed the single phase, high crystalline and cubic structure with Fd3m space group, and average crystallite size of 29 nm. The Fourier transform infrared spectra (FT-IR) shows two fundamental absorption bands (v 1 and v 2) that are attributed to the stretching vibration of tetrahedral and octahedral sites, observed in spinel structure, in the wave number range of 400-600 cm À1. Particle size are evaluated by using transmission electron microscopy and proved that they have a cubical shape. EDS result confirms the purity of the Ni-Zn nanoferrite powder. Magnetic measurements reveal a weak ferrimagnetic behavior at low temperature and superparamagnetism at high temperature.
Highlights nZVI is used as Fenton-like reagent for activation of Zn leaching from the BFS. nZ... more Highlights nZVI is used as Fenton-like reagent for activation of Zn leaching from the BFS. nZVI has positive effect on kinetics of Zn leaching though with some loss of efficiency. A complex ultrasonic-assisted method for BFS recycling is proposed.
Abstract NiO nanostructured powders were synthesized by an ultrasonic spray pyrolysis (USP) techn... more Abstract NiO nanostructured powders were synthesized by an ultrasonic spray pyrolysis (USP) technique. The powders were characterized using low temperature adsorption (BET), X-ray diffraction, scanning electron microscopy (SEM), and a transmission electron microscopy (TEM). The final product of the ultrasonic spray pyrolysis is hollow microspheres with 5–7 μm in diameter. The microspheres are built from nanoparticles with 40–60 nm in diameter.
Using recent experimental data on their temperature variation, the in-plane electrical and therma... more Using recent experimental data on their temperature variation, the in-plane electrical and thermal conductivities of low stage graphite acceptor intercalation compounds are analyzed. A 2D model is used for the electrical resistivity to interpret the data and some features specific to 2D conduction are underlined. After introducing the various mechanisms responsible for thermal conduction, the effect of intercalation on the thermal conductivity of pristine graphites is discussed.
The Science and Technology of Carbon Nanotubes, 1999
Publisher Summary This chapter introduces the main electronic features of CNTs and some general a... more Publisher Summary This chapter introduces the main electronic features of CNTs and some general aspects of electronic conduction and transmission. The main experimental results obtained on the electrical resistivity of MWCNT and SWCNT and the very recent data relative to the thermopower of SWCNT bundles have also been presented. MWCNTs behave as an ultimate carbon fiber revealing specific 2D quantum transport features at low temperatures; weak localization and universal conductance fluctuations. At high temperature its electrical conductivity is described by means of the semiclassical models which were successful in describing graphite. At low temperature, they reveal 2D quantum transport features, one of them being observed in bulk carbons and graphites (weak localization), while the other can only be observed in a mesoscopic form (universal conductance fluctuations). Single-walled CNTs (SWCNTs) behave as pure quantum wires, which, if limited in length, reduce to quantum dots. Eeach type of CNT has its own features which are strongly dependent on the dimensionality of the electronic gas. The chapter also discusses the effect of intercalation on the electrical resistivity of SWCNT bundles and some potential applications.
We have developed a reliable lithographic method to pattern thin gold films by locally exposing a... more We have developed a reliable lithographic method to pattern thin gold films by locally exposing a thin layer of an electron beam resist with the tip of a scanning tunneling microscope (STM). The exposure of the resist layer is induced by applying a voltage ...
... As a result of the pioneering measurements of X(T) for NiCl2-GIC, CoCl2-GIC, and FeCl3-GIC by... more ... As a result of the pioneering measurements of X(T) for NiCl2-GIC, CoCl2-GIC, and FeCl3-GIC by Karimov et al.1'2 and ... Recent characterization of the sam-ples used in the present study by electron microscopy, 123 however, has shown that within the intercalate layers, the ...
The temperature dependences of the Fermi energies for electrons and holes in Bismuth are computed... more The temperature dependences of the Fermi energies for electrons and holes in Bismuth are computed in the range 80-300°K, taking into account the non-parabolicity and non-ellipsoidicity of the conduction band. The partial diffusion thermoelectric powers for electrons and holes, and the total diffusion thermoelectric power in the two principal directions are then deduced. Computed values are compared with recent experimental data.
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Papers by Jean-Paul Issi