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Shiv Nadar University

(SoNS) School of Natural Sciences

Physics

World University root node

Physical Review B

Ab initio Wannier-function-based correlated calculations of Born effective charges of crystalline Li 2 O and LiCl

The impact of rapid thermal annealing (RTA) in producing samples by sequential implantation of Si and Er ions into a 200 nm SiO2 layer combined with different annealing cycles as well as the corresponding roomerature visible and infrared photoluminescence (PL) have been studied. The Er-related PL intensity at 1533 nm for the samples prepared by implanting Si with subsequent annealing, followed by Er implantation, and final annealing (type I) was found to be stronger than the one produced similarly but without the first annealing step (type II). In fact, the 1533 nm peak intensity in the optimized RTA processed sample is comparable to the PL yield of the furnace-annealed sample. Moreover, the excitation wavelength (405 nm) was found to be suitable for exciting the Si=O related point defects in the SiO2 layer and can provide a PL band with a maximum at ∼580 nm. While this band was further intensified in the presence of Si nanocrystals (Si NCs), it became weaker by introducing additional Er3+ ions with a concomitant rise of the 1533 nm Er PL, confirming the visible range pumping of Er3+. The detailed spectral analyses suggest that the 580 nm band is the result of the excitation/deexcitation mechanism in molecule such as states in the Si=O or the Si=O state mediated recombination of carriers in Si NCs according to the model proposed by [Wolkin, Phys. Rev. Lett. 82, 197 (1999)]. The samples were further characterized by transmission electron microscopy and Fourier-transform infrared spectroscopy. The time-resolved PL measurements and a modeling by rate equations were also performed to determine and justify the energy migration mechanism from Si NC to the neighboring Er3+. © 2008 American Institute of Physics.

Fulltext

Journal of Applied Physics

Influence of annealing on the Er luminescence in Si-rich SiO2 layers coimplanted with Er ions

During crystallization experiments two new polymorphs of the highly-active organic nonlinear optical (NLO) material 3-methyl-4-methoxy-4′- nitrostilbene (MMONS) have been discovered. Crystallization conditions of all three polymorphs and their characterization via crystal structure determination from single crystal X-ray diffraction data at 100 K have been discussed in detail. Two of the polymorphs exhibit different conformations, while a third polymorph incorporates both conformers as well as disorder. Comparisons between various types of intermolecular contacts in these three polymorphic forms have been quantified via Hirshfeld surface analysis. © The Royal Society of Chemistry.

Chemistry

CrystEngComm

Polymorphism in 3-methyl-4-methoxy-4′-nitrostilbene (MMONS), a highly active NLO material

Hexagonal and cubic MgxZn1-xO thin films corresponding to optical band gaps of 3.52 eV, 4 eV and 6.42 eV for x = 0.15, 0.28 and 0.85 compositions were grown by pulsed laser deposition technique. The crystalline quality of the films was investigated by X-ray diffraction-rocking curve measurements and indicated a high degree of crystallinity with narrow FWHM's of 0.21°-0.59°. Rutherford back scattering-channeling spectroscopy provides channeling yields of 7-14% indicating the good crystalline quality of the thin films. X-Ray photoelectron spectroscopy measurements clearly indicated different level of oxidation states of Mg and Zn. © 2007 Elsevier B.V. All rights reserved.

Optical Materials

Structural and chemical analysis of pulsed laser deposited MgxZn1-xO hexagonal (x = 0.15, 0.28) and cubic (x = 0.85) thin films

Ion implantation is a promising route for doping quartz with luminescent impurity atoms and growing photoactive nanoparticles of them. The present work focuses on cathodoluminescence (CL) and epitaxy during or after Na, Rb, Cs, Ge, and Ba ion implantation as well as Rb/Ge double implantation in crystalline α-quartz, under the conditions of dynamic, chemical or laser epitaxy. In addition to the known intrinsic sub-bands in the CL spectra, which have been associated with specific defects in the silica matrix, very intense blue or violet bands were found. They are correlated with the implanted ion species and follow their thermal behaviour. The quantum efficiency and possible origins of the blue/violet CL emission for various ions and processing treatments will be discussed. The case of double Rb/Ge implantation appears to be very promising with respect to a combination of a high CL output and full chemical epitaxy. © 2006 Elsevier B.V. All rights reserved.

Physica B: Condensed Matter

Luminescence and epitaxy of ion-implanted α-quartz

Data fusion originally referred to the process of combining multi-sensor data from different sources such that the resulting information/model is in some sense better than would be possible when these sources where used individually. In this paper the data fusion concept is extended to molecular drug design. Rather than using data from different sensor sources, different descriptor sets are used to predict activities or responses for a set of molecules. Data fusion techniques are applied in order to improve the predictive (QSAR) model on test data. In this case this type of data fusion is referred to as auto-fusion. An effective auto-fusion functional model and alternative architectures are proposed for a predictive molecular design or QSAR model to model and predict the binding affinity to the human serum albumin. © Springer-Verlag Berlin Heidelberg 2007.

Lecture Notes in Computer Science (including subseries Lecture Notes in Artificial Intelligence and Lecture Notes in Bioinformatics)

Data fusion and auto-fusion for Quantitative Structure-Activity Relationship (QSAR)

The structure of l-ornithine hydrochloride, C5H13N2O Cl-, has been redetermined at 100 K by single-crystal X-ray diffraction within a project that aims to generate accurate bond-distance restraints for the invariom refinement of proteins. The high-resolution data were subject to an invariom and a multipole refinement, and the resulting electron densities on a grid were compared. Improvements in the conventional R factor obtained by multipole modelling were smaller than in other structures containing solely the elements CHNO owing to Cl core scattering. Cruickshanks diffraction-component precision index and Stevens &amp; Coppens suitability factor are discussed. © International Union of Crystallography 2007.

Acta Crystallographica Section B: Structural Science

Redetermination, invariom-model and multipole refinement of L-ornithine hydrochloride

Although reliable determination of the molecular dipole moment from experimental charge density analyses on molecular crystals is a challenging undertaking, these values are becoming increasingly common experimental results. We collate all known experimental determinations and use this database to identify broad trends in the dipole moment enhancements implied by these measurements as well as outliers for which enhancements are pronounced. Compelling evidence emerges that molecular dipole moments from X-ray diffraction data can provide a wealth of information on the change in the molecular charge distribution that results from crystal formation. Most importantly, these experiments are unrivalled In their potential to provide this information in such detail and deserve to be exploited to a much greater extent. The considerable number of experimental determinations now available has enabled us to pinpoint those studies that merit further attention, either because they point unequivocally to a considerable enhancement in the crystal (of 50% or more), or because the experimental determinations suggest enhancements of 100% or more - much larger than independent theoretical estimates. In both cases further detailed experimental and theoretical studies are indicated. © 2007 Wiley-VCH Verlag GmbH & Co. KGaA.

ChemPhysChem

Dipole moment enhancement in molecular crystals from X-ray diffraction data

4H-SiC samples implanted with 1020 Al were annealed at various temperatures with a BN/AIN or graphite cap, and there morphological, structural, and electrical properties are compared. No blow holes were observed in either cap. Some Si out-diffuses through the graphite cap which results in a rougher surface and a structurally modified region near the surface. The BN/AlN cap annealed at 1800°C cannot be readily removed, whereas the graphite cap can be removed easily after any annealing temperature. The sheet resistances for both types of samples were about the same.

Materials Science Forum

Comparison of graphite and BN/AIN annealing caps for ion implanted SiC

The paper describes the major circulation changes in the eastern Indian Ocean during last 5 million years based on variation in planktic foraminiferal assemblages in various ODP and DSDP cores examined by various workers. The Late Miocene/Pliocene transition is characterized by weakening of the Leeuwin Current and migration of the polar front towards north. The early Pliocene is marked by closing of the Indonesian Seaway for surface waters and strengthening of the Leeuwin Current, a general warming of the surface waters and thickening of the mixed layer in the eastern Indian Ocean. The Late Pliocene and Pleistocene witnessed severe climatic fluctuations and episodic weakening and strengthening of the Leeuwin Current in response to either ENSO induced changes in the Western Pacific Warm Pool or lowering of sea level and reduction in Indonesian throughflow due to ice sheet expansion.