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Shiv Nadar University

(SoNS) School of Natural Sciences

Light-emitting centers in alkali-ion-implanted α quartz have been investigated with respect to the solid phase epitaxial growth of the ion irradiation induced amorphous zone. Cathodoluminescence was studied under the conditions of chemical epitaxy in annealing the samples, implanted with 2.5 × 10 16 50 keV Na ions/cm 2 or 175 keV Rb ions/cm 2, in 18O 2 atmosphere in the temperature range of 673-1173 K. In addition to the known intrinsic subbands at 2.40, 2.79, and 4.30 eV, which previously were associated with specific defects in the silica matrix, a strong violet band at 3.65 eV and a band at 3.25 eV have been identified. Both are intimately correlated with the presence of the implanted alkali atoms and recrystallization process. With respect to the 3.25 eV band reported in the literature, they are discussed to be correlated with the presence of nanoclusters in Si-enriched, and Ge- and Sn-implanted SiO 2 structures. © 2006 American Institute of Physics.

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Physics

Fulltext

Applied Physics Letters

Light-emitting defects and epitaxy in alkali-ion-implanted α quartz

The laterally nonsymmetric aza cryptand Lo readily forms mononuclear inclusion complexes with metal ions like CuII, Ni II, AgI, TlI, and so forth. However, when the secondary amines present in the three bridges are substituted by a cyanomethyl group to yield a new cryptand L, its metal-binding properties are drastically altered. Thus, while Lo binds AgI at the tren end, showing AgN4 coordination, in L, the bridgehead nitrogen atoms are pulled inside to form a two-coordinate complex of AgI and none of the O or N atoms present in the three bridges are involved in coordination. This is probably the first example where the two bridgehead atoms are pulled inside to the maximum to bind the metal ion. Likewise, the TlI ion shows TlN4 coordination with Lo, while in L it is loosely bound at the tren end, showing TlN3 coordination. Upon treatment with a AgI salt, the TlI can be replaced almost instantaneously. On the other hand, with copper(II) tetrafluoroborate salt in moist DMF, two of the cyanide groups in L are converted to carboxylic acid groups and bind the metal ion from outside. The CuII ion in this complex shows distorted octahedral coordination where the two O atoms from the two carboxylic acid groups and the two corresponding N atoms in the two bridges are bound equatorially. The two axial sites are occupied by the nearby bridgehead N atom and the O atom of a DMF molecule. All five complexes and the free ligands are characterized by spectroscopic and X-ray crystallographic studies. © Wiley-VCH Verlag GmbH &amp; Co. KGaA, 2006.

Chemistry

European Journal of Inorganic Chemistry

Alteration in the binding property of a laterally nonsymmetric aza cryptand toward CuII, AgI, and TlI ions upon derivatization with a cyanomethyl group

We have generalized the Pisarsky-Wilczek model of studying the U A(1) phase transition in π0, η and η′ system by incorporating the chiral phase transition. The mass-squared matrix of the neutral pseudoscalar mesons is revisited explicitly from the chiral effective action which necessitates the mixing among the unmixed states to get the physical states. The derivation of the mass spectra of the neutral pseudoscalar mesons shows that apart from their masses, the mixing angles also become temperature dependent. Based on the dilute instanton gas approximation we show that, the UA(1) phase transition along with the chiral phase transition plays an important role in the process of hadronization of the quark-gluon plasma with the quarks of three flavors. © World Scientific Publishing Company.

Modern Physics Letters A

Chiral and UA(1) phase transitions in π0, η and η′ mesons

Epitaxial thin films of gallium iron oxide (GaFeO3) are grown on (0 0 1) silicon by pulsed laser deposition (PLD) using yttrium-stabilized zirconia (YSZ) buffer layer. The crystalline template buffer layer is in situ PLD grown through the step of high-temperature stripping of the intrinsic silicon surface oxide. The X-ray diffraction pattern shows c-axis orientation of YSZ and b-axis orientation of GaFeO3 on Si (1 0 0) substrate. The ferromagnetic transition temperature (TC∼215K) is in good agreement with the bulk data. The films show a large nonlinear second harmonic Kerr rotation of ∼15° in the ferromagnetic state. © 2005 Elsevier B.V. All rights reserved.

Journal of Magnetism and Magnetic Materials

Large second-harmonic kerr rotation in GaFeO3 thin films on YSZ buffered silicon

Translation initiation of hepatitis C virus RNA occurs via ribosome binding to an 'internal ribosome entry site (IRES)' located in the 5′untranslated region of the viral RNA. The principle interaction between the 40S ribosomal subunit and the HCV IRES has been shown to be largely factor independent, which is followed by the joining of the 60S ribosomal subunit to form functional 80S complex. However several additional cellular proteins have been reported to bind to HCV IRES and enhance the initiation of translation. In order to identify novel factors involved in the ribosome assembly during internal initiation of HCV RNA, northwestern screening of a HeLa cDNA expression library was performed, using HCV IRES RNA as probe. We demonstrate here, that human ribosomal protein L18a, a constituent of 60S subunit, interacts with HCV IRES RNA. This interaction was further confirmed by using a recombinant protein similar to L18a (sL18a), cloned from human blood. Interestingly, addition of increasing concentration of the purified recombinant sL18a protein, showed moderate stimulation of HCV IRES activity in the in vitro translation assay. These observations suggest that the human L18a might influence the HCV IRES mediated translation. © Springer-Verlag 2005.

Life Sciences

Archives of Virology

Human ribosomal protein L18a interacts with hepatitis C virus internal ribosome entry site

As one of the final steps in the bacterial growth cycle, daughter cells must be released from one another by cutting the shared peptidoglycan wall that separates them. In Escherichia coli, this delicate operation is performed by several peptidoglycan hydrolases, consisting of multiple amidases, lytic transglycosylases, and endopeptidases. The interactions among these enzymes and the molecular mechanics of how separation occurs without lysis are unknown. We show here that deleting the endopeptidase PBP 4 from strains lacking AmiC produces long chains of unseparated cells, indicating that PBP 4 collaborates with the major peptidoglycan amidases during cell separation. Another endopeptidase, PBP 7, fulfills a secondary role. These functions may be responsible for the contributions of PBPs 4 and 1 to the generation of regular cell shape and the production of normal biofilms. In addition, we find that the E. coli peptidoglycan amidases may have different substrate preferences. When the oo-carboxypeptidase PBP 5 was deleted, thereby producing cells with higher levels of pentapeptides, mutants carrying only AmiC produced a higher percentage of cells in chains, while mutants with active AmiA or AmiB were unaffected. The results suggest that AmiC prefers to remove tetrapeptides from peptidoglycan and that AmiA and AmiB either have no preference or prefer pentapeptides. Muropeptide compositions of the mutants corroborated this latter conclusion. Unexpectedly, amidase mutants lacking PBP 5 grew in long twisted chains instead of straight filaments, indicating that overall septal morphology was also defective in these strains. Copyright © 2006, American Society for Microbiology. All Rights Reserved.

Journal of Bacteriology

Daughter cell separation by penicillin-binding proteins and peptidoglycan amidases in Escherichia coli

There has been a keen interest in metal benzothiazoles, and specifically for zinc benzothiazole for applications involving broad emission such as white light organic light emitting diodes. The broad emission characteristic is normally attributed to occurrence of exciplexes and is believed to further broaden in electroluminescence from a bilayer device. In order to understand possible role of molecular level interaction in photoluminescence (PL), we study PL decay dynamics of zinc benzothiazole powder, thin film and a virtual alloy with a hole transport material TPD (prepared by stacking very thin alternate layers of the two materials). We observe significant hastening of the PL decay from powder and 'effective alloy' to the thin film. To unravel the nature of changes in decay dynamics, we employ both least square fitting, and time domain spectroscopy known as time analyzed transient spectroscopy (TATS). The efficacy of the later procedure in obtaining insights is demonstrated. Our results indicate that inter molecular interaction in the condensed phase significantly influence the life time of the radiative species in this material. © 2005 Elsevier B.V. All rights reserved.

Synthetic Metals

Time domain spectroscopic study of PL decay in zinc benzothiazole suitable for white light emitting OLEDs

2005 International Semiconductor Device Research Symposium

Surface and interface analysis of MgxZn1-xO cubic and hexagonal phases by X-ray photoelectron and rutherford back scattering spectroscopies

Ion implantation and recrystallization of quartz may be a very important process for photonic applications. We have investigated how laser irradiation can be used to epitaxially recrystallize layers of α-quartz, which were amorphized by 175 keV Rb + or 250 keV Cs + ion implantation at a fluence of 2.5 × 10 16 cm -2 . The samples were irradiated with pulses of a XeCl excimer laser (wavelength 308 nm, pulse length 55 ns, energy density 3.2-5 J/cm 2 ). The thickness of the amorphous layer and the quality of the recrystallized layer were analyzed by Rutherford Backscattering Channeling Spectroscopy. Partial epitaxial recrystallization was found for all laser-irradiated samples that proceeded faster for higher laser energy density, however no full epitaxy was achieved up to the maximum laser energy of 5 J/cm 2 . The degree of epitaxy was more or less the same for 20 or 200 laser shots. © 2005 Elsevier B.V. All rights reserved.

Applied Surface Science

Laser-induced epitaxial recrystallization after alkali-ion implantion into α-quartz

A method of forming a sheet of Ge nanocrystals in a SiO2 layer based on molecular beam epitaxy (MBE) and rapid thermal processing (RTF) is presented. The method takes advantage of the very high precision by which a very thin Ge layer can be deposited by MBE. With proper choice of process parameters the nanocrystal size can be varied between ∼3 and ∼8 nm and the area-density between ∼1×1011 and ∼1×10 12 dots/cm2. The tunneling oxide thickness is determined by the thickness of a thermally grown SiO2 layer, and is typically 4 nm. C-V measurements of MOS capacitors reveal hole and electron injection from the substrate into the nanocrystals. Memory windows of about 0.2 and 0.5 V for gate-voltage sweeps of 3 and 6 V, respectively, are achieved. © 2005 Materials Research Society.