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Now showing items 1 - 16 of 36

  • Carbon multicharged ions emission from femtosecond laser plume

    Balki, Oguzhan   Rahman, Md. Mahmudur   Abdel-Fattah, Mahmoud Hanafy   Elsayed-Ali, Hani E.  

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  • Carbon multicharged ion generation from laser-spark ion source

    Rahman, Md. Mahmudur   Balki, Oguzhan   Elsayed-Ali, Hani E.  

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  • Multicharged carbon ion generation from laser plasma

    Balki, Oguzhan   Elsayed-Ali, Hani E.  

    Carbon ions generated by ablation of a carbon target using an Nd:YAG laser pulse (wavelength lambda =3D 1064 nm, pulse width tau =3D 7 ns, and laser fluence of 10-110 J cm(-2)) are characterized. Time-of-flight analyzer, a three-mesh retarding field analyzer, and an electrostatic ion energy analyzer are used to study the charge and energy of carbon ions generated by laser ablation. The dependencies of the ion signal on the laser fluence, laser focal point position relative to target surface, and the acceleration voltage are described. Up to C4+ ions are observed. When no acceleration voltage is applied between the carbon target and a grounded mesh in front of the target, ion energies up to similar to 400 eV/charge are observed. The time-of-flight signal is analyzed for different retarding field voltages in order to obtain the ion kinetic energy distribution. The ablation and Coulomb energies developed in the laser plasma are obtained from deconvolution of the ion time-of-flight signal. Deconvolution of the time-of-flight ion signal to resolve the contribution of each ion charge is accomplished using data from a retarding field analysis combined with the time-of-flight signal. The ion energy and charge state increase with the laser fluence. The position of the laser focal spot affects the ion generation, with focusing similar to 1.9 mm in front of the target surface yielding maximum ions. When an external electric field is applied in an ion drift region between the target and a grounded mesh parallel to the target, fast ions are extracted and separated, in time, due to increased acceleration with charge state. Published by AIP Publishing.
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  • Synthesis of Cerium-Doped Titania Nanoparticles and Nanotubes

    Cao, Wei   Suzuki, Takuya   Elsayed-Ali, Hani E.   Abdel-Fattah, Tarek M.  

    Cerium-doped titania nanoparticles and nanotubes were synthesized via hydrothermal processes. X-Ray Diffraction revealed that cerium-doped titania nanoparticles have an anatase crystal structure, while cerium-doped titania nanotubes have an H2Ti3O7-type structure. Scanning electron microscopy and high resolution transmission electron microscopy showed that both types of titania are well crystallized with relatively uniform size distribution. The photocatalytic degradation of methylthioninium chloride known as methylene blue dye was tested and both cerium-doped titania nanoparticles and nanotubes. The preliminary photocatalytic degradation of Methylene Blue data showed significantly improved visible light photocatalytic activities as compared to commercial titania powders.
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  • Spark discharge coupled laser multicharged ion source

    Shaim, Md. Haider A.   Elsayed-Ali, Hani E.  

    A spark discharge is coupled to a laser multicharged ion source to enhance ion generation. The laser plasma triggers a spark discharge with electrodes located in front of the ablated target. For an aluminum target, the spark discharge results in significant enhancement in the generation of multicharged ions along with higher charge states than observed with the laser source alone. When a Nd:YAG laser pulse (wavelength 1064 nm, pulse width 7.4 ns, pulse energy 72 mJ, laser spot area on target 0.0024 cm(2)) is used, the total multicharged ions detected by a Faraday cup is 1.0 nC with charge state up to Al3+. When the spark amplification stage is used (0.1 mu F capacitor charged to 5.0 kV), the total charge measured increases by a factor of similar to 9 with up to Al6+ charge observed. Using laser pulse energy of 45 mJ, charge amplification by a factor of similar to 13 was observed for a capacitor voltage of 4.5 kV. The spark discharge increases the multicharged ion generation without increasing target ablation, which solely results from the laser pulse. This allows for increased multicharged ion generation with relatively low laser energy pulses and less damage to the surface of the target. (C) 2015 AIP Publishing LLC.
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  • Properties of Cu(In,Ga,Al)Se-2 thin films fabricated by magnetron sputtering

    Hameed, Talaat A.   Cao, Wei   Mansour, Bahiga A.   Elzawaway, Inas K.   Abdelrazek, El-Metwally M.   Elsayed-Ali, Hani E.  

    Cu(In,Ga,Al)Se-2 (CIGAS) thin films were studied as an alternative absorber layer material to Cu(InxGa1-x)Se-2. CIGAS thin films with varying Al content were prepared by magnetron sputtering on Si(100) and soda-lime glass substrates at 350 degrees C, followed by postdeposition annealing at 520 degrees C for 5 h in vacuum. The film composition was measured by an electron probe micro-analyzer while the elemental depth profiles were determined by secondary ion mass spectrometry. X-ray diffraction studies indicated that CIGAS films are single phase with chalcopyrite structure and that the (112) peak clearly shifts to higher 2 theta values with increasing Al content. Scanning electron microscopy images revealed dense and well-defined grains, as well as sharp CIGAS/Si(100) interfaces for all films. Atomic force microscopy analysis indicated that the roughness of CIGAS films decreases with increasing Al content. The bandgap of CIGAS films was determined from the optical transmittance and reflectance spectra and was found to increase as Al content increased. (C) 2015 American Vacuum Society.
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  • VO2 Films Prepared by Atomic Layer Deposition and RF Magnetron Sputtering

    Tangirala, Madhavi   Zhang, Kai   Nminibapiel, David   Pallem, Venkateswara   Dussarrat, Christian   Cao, Wei   Adam, Thomas N.   Johnson, Corbet S.   Elsayed-Ali, Hani E.   Baumgart, Helmut  

    Among the many vanadium suboxides and different stoichiometries, VO2 has received considerable attention due to its remarkable metal-insulator transition (MIT) behavior, which causes a significant reversible change in its electrical and optical properties occurring across the phase transition at 67 degrees C. The initially amorphous VO2 thin films were fabricated by the emerging, Atomic Layer Deposition (ALD) technique with (tetrakis[ethylmethylamino] vanadium) {V(NEtMe)(4)} as precursor and H2O vapor as oxidation agent. For benchmarking we have also used the RF Magnetron Sputtering technique to deposit metallic vanadium thin films, which were later oxidized during furnace annealing. Post annealing of the as-deposited ALD films was performed in order to obtain the technologically important form of crystallized VO2 thin films using furnace annealing. All film depositions were carried out on native oxide covered (100) Si substrates. The conditions for successful furnace annealing are reported in terms of temperature and annealing gas composition and the physical characterization results are presented.
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  • Properties of Cu(In,Ga,Al)Se-2 thin films fabricated by pulsed laser deposition

    Chen, Weiru   Cao, Wei   Hameed, Talaat A.   Marsillac, Sylvain   Elsayed-Ali, Hani E.  

    Cu(In,Ga,Al)Se-2 (CIGAS) thin films were investigated as an alternative absorber layer to Cu(In, Ga) Se-2 (CIGS). CIGAS thin films were prepared by pulsed laser deposition on SiO2/Si(100) and glass substrates at 150 degrees C with different Al contents. The compositions of all films were measured by electron probe micro-analyzer. X-ray diffraction studies indicate that all the films are oriented along the [112] direction and that the (112) peak shifts to higher 2 theta value with increasing Al content. Scanning electron microscopy images show that dense and well-defined grains are formed as Al is incorporated into CIGS. Atomic force microscopy images indicate that the grain sizes and the roughness of the thin films decrease with increasing Al content. The bandgap of CIGAS thin films was determined from the optical spectra and was found to increase with increasing Al content.
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  • Electron Diffraction Studies of Structural Dynamics of Bismuth Nanoparticles

    Esmail, Ahmed R.   Bugayev, Aleksey   Elsayed-Ali, Hani E.  

    The lattice response of bismuth nanoparticles to femtosecond laser excitation is probed by ultrafast electron diffraction. The transient decay time after laser excitation is observed to be longer for diffraction from the (012) lattice planes compared to that from (110). From the position of the (012) diffraction peak, a transient lattice contraction due to hot electron blast force is observed over several picoseconds followed by expansion while the position of the (110) peak shows only expansion. The diffraction peak width :indicates partial disorder of the nanoparticles consistent with formation of a liquid shell as the lattice is heated.
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  • STM study of pulsed laser assisted growth of Ge quantum dot on Si(100)-(2 x 1)

    Er, Ali Oguz   Elsayed-Ali, Hani E.  

    Ge quantum dot formation on Si(1 0 0)-(2 x 1) by nanosecond pulsed laser deposition under laser excitation was investigated. Scanning tunneling microscopy was used to probe the growth mode and morphology. Excitation was performed during deposition using laser energy density of 25 100 mJ/cm(2). Faceted islands were achieved at a substrate temperature of similar to 250 degrees C only when using laser excitation. The island morphology changes with increased laser excitation energy density although the faceting of the individual islands remains the same. The size of the major length of islands increases with the excitation laser energy density. A purely electronic mechanism of enhanced surface diffusion of the Ge adatoms is proposed.
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  • Copper cation removal in an electrokinetic cell containing zeolite

    Elsayed-Ali, Omar H.   Abdel-Fattah, Tarek   Elsayed-Ali, Hani E.  

    Zeolites are used in environmental remediation of soil or water to immobilize or remove toxic materials by cation exchange. An experiment was conducted to test the use a low electric field to direct the toxic cations towards the zeolite. An electrokinetic cell was constructed using carbon electrodes. Synthetic Linde Type A (LTA) zeolite was placed in the cell. Copper(II) chloride dissolved in water was used as a contaminant. The Cu(2+) concentration was measured for ten hours with and without an applied electric field. The removal of the Cu(2+) ions was accelerated by the applied field in the first two hours. For longer time, the electric field did not improve the removal rate of the Cu(2+) ions. The presence of zeolite and applied electric field complicates the chemistry near the cathode and causes precipitation of Cu(2+) ions as copper oxide on the surface of the zeolite. With increased electric field the zeolite farther away from the cathode had little cation exchange due to the higher drift velocity of the Cu(2+) ions. The results also show that, in the LTA Zeolite A pellets, the cation exchange of Cu is limited to a shell of several tens of micrometers. (C) 2010 Elsevier B.V. All rights reserved.
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  • Identification of single nanoparticles RID A-6029-2012

    Song, Yujun   Zhang, Zongsuo   Elsayed-Ali, Hani E.   Wang, Haining   Henry, Laurence L.   Wang, Ququan   Zou, Shengli   Zhang, Tao  

    The physicochemical properties of nanomaterials significantly depend on their three-dimensional (3D) morphologies (sizes, shapes and surface topography), the surrounding media, and their spatial arrangement. Systematically and precisely correlating these parameters with the related physicochemical properties of specific single nanoparticles (NPs) is a fundamental requirement for the discovery of their novel properties and applications, as well as for advancing the fundamental and practical knowledge required for the design and fabrication of new materials. In this article, the progress in the identification of the specific individual NP is summarized, including the in situ methods and the spatial-localization methods based on plasmonic NPs as model. Identification of single NPs based on local surface plasmon resonance observed by fluorescent inverted optical microscopy, dark-field microscopy, scanning near-field optical microscopy, atomic force microscopy, and transmission electron microscope are reviewed. Recent progress in the investigation of 3D morphology-dependent optical properties by these methods is described. Experimental and theoretical developments in single-NP identification for the purpose of understanding the physicochemical properties are discussed.
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  • Electronically enhanced surface diffusion during Ge growth on Si(100)

    Er, Ali Oguz   Elsayed-Ali, Hani E.  

    The effect of nanosecond pulsed laser excitation on surface diffusion during the growth of Ge on Si(100) at 250 degrees C was studied. In situ reflection high-energy electron diffraction was used to measure the surface diffusion coefficient while ex situ atomic force microscopy was used to probe the structure and morphology of the grown quantum dots. The results show that laser excitation of the substrate increases the surface diffusion during the growth of Ge on Si(100), changes the growth morphology, improves the crystalline structure of the grown quantum dots, and decreases their size distribution. A purely electronic mechanism of enhanced surface diffusion of the deposited Ge is proposed. (C) 2011 American Institute of Physics. [ doi: 10.1063/1.3567918]
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  • Laser-fluence effects on NbNx thin films fabricated by pulsed laser deposition

    Farha, Ashraf Hassan   Er, Ali Oguz   Ufuktepe, Yuksel   Elsayed-Ali, Hani E.  

    Niobium nitride films were deposited on Nb substrate using pulsed laser deposition (PLD) with a Q-switched Nd:YAG laser at different laser fluences. The film crystal structure and surface morphology were studied. The microstructure, texture and surface morphologies of the films were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), and atomic force microscope (AFM). Highly textured NbNx films were produced by PLD on niobium substrates at different laser fluences for constant background nitrogen pressure and substrate deposition temperature. When the fabrication parameters are fixed except the laser fluence, surface roughness, deposition rate, nitrogen content, and grain size increase together with increasing laser fluence. The nitrogen content in NbNx films increases with the laser fluence up to 15 J cm(-2) and decreases thereafter. The films exhibit highly textured structure with a preferential orientation of (1 1 0) parallel to the substrate. The NbNx layers are formed in mixed phase (cubic and hexagonal) with the ratio of hexagonal phase to cubic phase dependent on the laser fluence. These observations can be used to establish guidelines for optimizing the laser fluence to achieve the desired morphology and phase of the grown NbNx thin film. (c) 2011 Elsevier B.V. All rights reserved.
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  • Size effects on phonon response of bismuth nanoislands to ultrafast laser excitation

    Xiong, Hui   Esmail, Ahmed   Elsayed-Ali, Hani E.  

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  • Femtosecond pulsed laser deposition of Ge quantum dot growth on Si(100)-(2 x 1)

    Er, Ali Oguz   Elsayed-Ali, Hani E.  

    Ge quantum dots were grown on Si(1 0 0)-(2 x 1) by femtosecond pulsed laser deposition at various substrate temperatures using a femtosecond Ti:sapphire laser. In situ reflection high-energy electron diffraction and ex situ atomic force microscopy were used to analyze the film structure and morphology. The morphology of germanium islands on silicon was studied at different coverages. The results show that femtosecond pulsed laser deposition reduces the minimum temperature for epitaxial growth of Ge quantum dots to similar to 280 degrees C, which is 120 degrees C lower than previously observed in nanosecond pulsed laser deposition and more than 200 degrees C lower than that reported for molecular beam epitaxy and chemical vapor deposition. (C) 2011 Elsevier B.V. All rights reserved.
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