National Center for Physics

Islamabad, Pakistan

National Center for Physics

Islamabad, Pakistan

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Motapothula M.,National University of Singapore | Dang Z.Y.,National University of Singapore | Venkatesan T.,National University of Singapore | Breese M.B.H.,National University of Singapore | And 2 more authors.
Physical Review Letters | Year: 2012

We report channeling patterns where clearly resolved effects of the narrow {111} planes are observed in axial and planar alignments for 2Â MeV protons passing through a 55Â nm [001] silicon membrane. At certain axes, such as â?̈213â?© and â?̈314â?©, the offset in atomic rows forming the narrow {111} planes results in shielding from the large potential at the wide {111} planes, producing a region of shallow, asymmetric potential from which axial channeling patterns have no plane of symmetry. At small tilts from such axes, different behavior is observed from the wide and narrow {111} planes. At planar alignment, distinctive channeling effects due to the narrow planes are observed. As a consequence of the shallow potential well at the narrow planes, incident protons suffer dechanneled trajectories which are excluded from channeling within the wide planes, resulting in an anomalously large scattered beam at {111} alignment. © 2012 American Physical Society.


Saeed A.,International Islamic University, Islamabad | Alia N.,National Center for Physics | Syed W.A.,International Islamic University, Islamabad
Chalcogenide Letters | Year: 2013

Tin antimony sulfide (SnSb2S4) thin film was deposited on ultrasonically cleaned soda lime glass substrate by vacuum thermal evaporation technique at10-4 Torr chamber pressure. The deposited thin films were annealed at 150°C in tube furnace in the presence of argon gas. For characterization, thin films were subjected to X-ray diffraction (XRD), SEM, EDS and J.A. Woollam variable angle ellipsometry (VASE) for structural, surface morphological, elemental composition and optical properties respectively. The film has ntype conductivity, confirmed by hot point probe technique. The film has good optical, structural and electrical properties extremely suitable for the use as non-toxic, environmental friendly absorbing layer in solar cell.


Masood W.,Pakistan Institute of Nuclear Science and Technology | Masood W.,National Center for Physics | Eliasson B.,Ruhr University Bochum | Eliasson B.,Umeå University
Physics of Plasmas | Year: 2011

A model for nonlinear ion waves in an unmagnetized plasma with relativistically degenerate electrons and cold fluid ions is presented here. The inertia is given here by the ion mass while the restoring force is provided by the relativistic electron degeneracy pressure, and the dispersion is due to the deviation from charge neutrality. A nonlinear Korteweg-de Vries equation is derived for small but finite amplitude waves and is used to study the properties of localized ion acoustic solitons for parameters relevant for dense astrophysical objects such as white dwarf stars. Different degrees of relativistic electron degeneracy are discussed and compared. © 2011 American Institute of Physics.


Khurram A.A.,National Center for Physics | Ali N.,National Center for Physics | Rakha S.A.,National Center for Physics | Zhou P.,University of Electronic Science and Technology of China | Munir A.,National Center for Physics
IEEE Transactions on Electromagnetic Compatibility | Year: 2014

A simple and fast coating method of honeycomb cores for microwave absorption has been described. The honeycomb cores with two different thicknesses (5 and 20 mm) coated with thermoplastic resin filled with carbon powder as lossy filler in 5, 10, 15, and 20 wt% have been tested for microwave absorption in 2-18-GHz frequency range. The 5-mm-thick honeycomb has shown absorption bandwidth of 14 GHz for maximum absorption of-6 dB (75%) with 15 wt%. filler content. However, the percentage of the filler was decreased to 10 wt% in 20-mm-thick honeycomb absorber for maximum absorption over a wide frequency range. The honeycomb sample with 10 wt% filler has bandwidth of 18 GHz for-7 dB (80%) reflection loss. The reflection loss measurements of coated honeycomb cores have also shown that use of E-glass fiber/epoxy composite can enhance the performance of the honeycomb absorber. The combination of a microwave absorbing nanocomposite and the coated honeycombs has been resulted in inferior absorption properties in 2-18-GHz frequency range. © 2014 IEEE.


Abbas S.M.,National Center for Physics | Abbas S.M.,Quaid-i-Azam University | Hussain S.T.,National Center for Physics | Ali S.,Quaid-i-Azam University | And 3 more authors.
Electrochimica Acta | Year: 2013

In this study, functionalized carbon nanotubes (CNTs) with good conductivity and high surface area are anchored with mesoporous Co 3O4 nanoparticles by a facile chemical co-precipitation method. Electrochemical characterizations show that Co3O 4/CNT nanocomposite delivers a capacity of 873 mAh g-1 after 50 cycles at a current density of 100 mA g-1. When the current density is increased to 250, 350 and 500 mA g-1, it still maintains a capacity of 895, 834 and 757 mAh g-1, respectively. The high capacity, rate capability and good cycling ability of Co3O 4/CNT nanocomposite are attributed to the intimate interaction between the CNTs and Co3O4 nanoparticles. The CNTs not only enhance the conductivity of Co3O4 nanoparticles but also improve the structure stability of Co3O4 nanoparticles. Furthermore, the mesoporous structure of Co3O 4 nanoparticles is available to the transfer of electrolyte. Our results demonstrate that CNTs reinforced Co3O4 nanocomposite could be a promising anode material for high capacity lithium-ion batteries. © 2013 Elsevier Ltd. All rights reserved.


Kausar A.,Quaid-i-Azam University | Kausar A.,National Center for Physics | Zulfiqar S.,National University of Sciences and Technology | Sarwar M.I.,Quaid-i-Azam University
Polymer Reviews | Year: 2014

Currently, a lot of research efforts have been directed toward exploiting the special high-performance characteristics of polymers with sulfur in the backbone. Sulfur-containing polymers fall under various classes and cover an extremely broad property range. The impetus to their development resulted from the unique properties and success in their applications, depending upon the type of linkage introduced. This review basically sets out to explain the design, synthesis, properties, and applications of various sulfur-containing polymers especially polyamides, polyimides, poly(amide-imide)s, polybenzimidazoles, polyurethanes, polyesters, etc. Outstanding performance of these polymers came up from their structures having sulfur-based groups such as thiophene, sulfide, sulfone, thiazol, and thiourea. Thus these linkages endow special features to such functional polymers. The sulfur-containing polymers are also described here with reference to their relevance as optically active, liquid crystalline, flame retardant, and fuel cell materials. Several endeavors are underway to take advantage of incorporated sulfur moiety in the polymer backbone, as a consequence to ascertain their validity on the forefront of scientific investigations. © 2014 Copyright Taylor & Francis Group, LLC.


Gohar H.,National Center for Physics | Saifullah K.,Quaid-i-Azam University
General Relativity and Gravitation | Year: 2012

We study radiation of scalar particles from charged dilaton black holes. The Hamilton-Jacobi method has been used to work out the tunneling probability of outgoing particles from the event horizon of dilaton black holes. For this purpose we use WKB approximation to solve the charged Klein-Gordon equation. The procedure gives Hawking temperature for these black holes as well. © 2012 Springer Science+Business Media, LLC.


Kausar A.,Quaid-i-Azam University | Kausar A.,National Center for Physics | Zulfiqar S.,COMSATS Institute of Information Technology | Zulfiqar S.,The University of Nizwa | Sarwar M.I.,Quaid-i-Azam University
Polymer Degradation and Stability | Year: 2013

High performance segmented poly(urethane-thiourea)s (PUTs) were prepared via one-step reaction using a new thiourea- and pyridine-based aromatic diisocyanate, isophthaloyl bis (3-((4-isocyanatophenylcarbamoyloxy)pyridyl) thiourea) (IBPCOT) and 2,7-dihydroxy naphthalene (DHN) as hard segment, whereas 20, 50 and 80 mol% polyethylene glycol (PEG) constitute the soft segment. IBPCOT and PUTs were characterized by spectroscopic techniques, and the polymer properties such as solubility, crystallinity, molecular weight, chemical resistance, flame resistance and thermal stability were studied. Poly(urethane-thiourea)s possessed high molar mass (98-104 × 10 3) and amorphous structures. Thermogravimetric analysis revealed that polymers, with 20 and 50 mol% PEG content, were fairly stable above 500°C and possessed high glass transition temperature up to 278°C. The processable polyurethanes with outstanding thermal stability, flame retardancy and chemical resistance were, thus, obtained by decreasing the amount of polyol in polymer structure. PUTs also exhibited superior thermal stability, relative to typical polyurethanes, owing to the carefully designed rigid hard segment architecture (IBPCOT/DHN). © 2012 Elsevier Ltd. All rights reserved.


Kausar A.,National Center for Physics
Polymer - Plastics Technology and Engineering | Year: 2015

A facile route was adopted to graft polystyrene on poly(vinyl alcohol-co-ethylene) matrix. Poly(vinyl alcohol-co-ethylene)-graft-polystyrene (PVAE-g-PS) was then reinforced with two types of nanofillers, i.e., graphene oxide (GO) and nanodiamond functional graphene oxide (GO-ND). PVAE-g-PS/GO and PVAE-g-PS/GO-ND nanocomposite series reinforced with 0.1—5 wt.% nanofiller were fabricated by solution processing. Structure of nanofillers and composite was confirmed by FTIR. FESEM imaging revealed that nanodiamond functional GO platelets were fully incorporated into matrix. TGA demonstrated enhanced stability of PVAE-g-PS/GO-ND nanomposites containing GO-ND. Similarly, UL 94 and electrical conductivity measurement of GO-ND-based system were found to be superior compared to one of copolymer/GO. © 2015, Copyright © Taylor & Francis Group, LLC.


Ul-Ain B.,National Center for Physics | Zafar A.,Quaid-i-Azam University | Ahmed S.,Quaid-i-Azam University
Catalysis Science and Technology | Year: 2015

Nitrous oxide serves as a green propellant for space applications; however, an active and stable catalyst is required for its decomposition. A new class of material (X-type hexaferrites) was tested for this reaction for the first time. The catalysts were prepared by a co-precipitation method and a pure single hexagonal phase was confirmed by XRD and SEM. The developed pure and doped catalysts were found to be catalytically active for nitrous oxide decomposition reaction and the activity increased with increasing dopant content. However, Cr-Mn co-doped materials showed higher catalytic activity than Mn-doped samples. The cationic substitution and surface defects (oxygen vacancies) were found to be responsible for the upsurge of activity. The desired stability of the developed catalyst added to its potential for applicability. © The Royal Society of Chemistry 2015.

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