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Shiv Nadar University

(SoNS) School of Natural Sciences

In this paper, structural and electrical studies of A-site lanthanum-substituted Sr1-xLaxBi 2Nb2O9; x=0.0-0.5 ceramics are reported. The introduction of lanthanum produces pore-free microstructure upto x=0.3. A diffuse ferroelectric to paraelectric phase transition is observed in the doped samples and positive temperature coefficient of resistance (PTCR) is observed in x=0.0, 0.4 and 0.5 samples whereas x=0.1-0.3 samples show negative temperature coefficient of resistance (NTCR). Curie temperature decreases continuously with increase in lanthanum content. © 2005 Elsevier B.V. All rights reserved.

Physics

World University root node

Physica B: Condensed Matter

Structural and electrical studies in La-substituted SrBi2Nb 2O9 ferroelectric ceramics

In this paper, structural and dielectric studies of Sr1-xA xBi2Nb2O9 (A = La, Pb and x = 0.2) ceramics are reported. Tetragonal strain decreases on introduction of lanthanum while it increases for the lead doped sample. Addition of lead increases Curie temperature and sample with lanthanum content shows remarkable decrease in Curie temperature with broadened dielectric peak. The sample with x = 0.0 shows a rapid fall in dielectric constant value above 100 KHz. The lanthanum and lead doped samples show reduced dielectric loss values with frequency. © 2005 Elsevier B.V. All rights reserved.

Materials Letters

Dielectric studies of la and Pb doped SrBi2Nb2O 9 ferroelectric ceramic

Using a 100 MeV Au beam, the surface roughening kinetics of relaxed Si1-xGex alloy films for x = 0.5 and 0.7 are studied by means of ex-situ atomic force microscopy (AFM). Swift heavy ion (SHI) irradiation induced surface roughening behavior is demonstrated using the trend in variation of β as a function of fluence when the data are analyzed in terms of the Edwards-Wilkinson (EW) model. By employing the EW model, the observed surface roughening is explained on the basis of the competition between SHI induced sputtering and smoothening through redeposition of the sputtered atoms. The composition dependent variation of surface morphology with increasing fluence is discussed in the light of the strain distribution along the sample surface. © 2006 Elsevier Ltd. All rights reserved.

Solid State Communications

Surface roughening in Si1-xGex alloy films by 100 MeV Au: Composition dependency

We demonstrate a gradual surface modification process of relaxed Si0.5Ge0.5 alloy films by 100 MeV Au beam with fluence varying between 5 × 1010 and 1 × 1012 ions/cm2 at 80 K by means of atomic force microscopy (AFM). Presence of Ge quantum dots (QDs) was found in the virgin sample. The disappearance of the QDs were noticed when the samples were irradiated with a fluence of 5 × 1010 ions/cm2. Craters were found developing at a fluence of 1 × 1011 ions/cm2. Apart from the evolution of the craters, blisters were also detected at a fluence of 1 × 1012 ions/cm2. Variation of the average root mean square value of the surface roughness as a function of fluence was examined. © 2006 Elsevier B.V. All rights reserved.

Surface Science

Impact of 100 MeV Au on the surface of relaxed Si0.5Ge0.5 alloy films studied by atomic force microscopy

In this paper we report recent advances in pulsed-laser-deposited AlN thin films for high-temperature capping of SiC, passivation of SiC-based devices, and fabrication of a piezoelectric MEMS/NEMS resonator on Pt-metallized SiCySi. The AlN films grown using the reactive laser ablation technique were found to be highly stoichiometric, dense with an optical band gap of 6.2 eV, and with a surface smoothness of less than 1 nm. A low-temperature buffer-layer approach was used to reduce the lattice and thermal mismatch strains. The dependence of the quality of AlN thin films and its characteristics as a function of processing parameters are discussed. Due to high crystallinity, near-perfect stoichiometry, and high packing density, pulsed-laser-deposited AlN thin films show a tendency to withstand high temperatures up to 1600°C, and which enables it to be used as an anneal capping layer for SiC wafers for removing ion-implantation damage and dopant activation. The laser-deposited AlN thin films show conformal coverage on SiC-based devices and exhibit an electrical break-down strength of 1.66 MV/cm up to 350°C when used as an insulator in Ni/AlN/SiC metal-insulator-semi-conductor (MIS) devices. Pulsed laser deposition (PLD) AlN films grown on Pt/SiCVSi (100) substrates for radio-frequency microelectrical and mechanical systems and nanoelectrical and mechanical systems (MEMS and NEMS) demonstrated resonators having high Q values ranging from 8,000 to 17,000 in the frequency range of 2.5-0.45 MHz. AlN thin films were characterized by x-ray diffraction, Rutherford backscattering spectrometry (in normal and oxygen resonance mode), atomic force microscopy, ultraviolet (UV)-visible spectroscopy, and scanning electron microscopy. Applications exploiting characteristics of high bandgap, high bond strength, excellent piezoelectric characteristics, extremely high chemical inertness, high electrical resistivity, high breakdown strength, and high thermal stability of the pulsed-laser-deposited thin films have been discussed in the context of emerging developments of SiC power devices, for high-temperature electronics, and for radio frequency (RF) MEMS.

Journal of Electronic Materials

Advances in pulsed-laser-deposited AlN Thin Films for high-temperature capping, device passivation, and piezoelectric-based RF MEMS/NEMS resonator applications

Random amplified polymorphic DNA (RAPD) technique was used as a tool for assessing genetic diversity and species relationships among 28 accessions of eggplant representing five species. Twenty-eight samples of eggplants were collected from different parts of the country. A total of 144 polymorphic amplified products were obtained from 14 decamer primers, which discriminated all the accessions. The value of Jaccard's coefficient ranged from 0.05 to 0.82. The similarity result indicates presence of high level of genetic diversity in eggplants and a dendrogram constructed by UPGMA method shows that S. incanum is closest to S. melongena followed by S. nigrum. Only one accession of S. nigrum and S. surattense was taken in the present study that showed grouping with each other. Genetically distinct genotypes identified using RAPD markers could be potential sources of germplasm for eggplant improvement.

Life Sciences

Current Science

Genetic diversity within the genus Solatium (Solanaceae) as revealed by RAPD markers

DNA replication takes place at five different stages during the life cycle of Plasmodium falciparum including the human and mosquito hosts. DNA replication initiation, the rate-determining step is poorly understood in Plasmodium. Here we show that PfMCM4 and PfORC1, two members of prereplication initiation complex are expressed specifically in the nucleus during the trophozoite and schizont stages of the asexual parasitic life cycle where maximum amount of DNA replication takes place. Further, we show that these proteins are also expressed in gametocytes, where DNA replication also occurs. These results expand our knowledge on these proteins and resolves discrepancies arising from previous studies with respect to the expression pattern of replication initiation proteins during the parasite's life cycle. © 2006 Federation of European Microbiological Societies. Published by Blackwell Publishing Ltd. All rights reserved.

Fulltext

FEMS Microbiology Letters

Analogous expression pattern of Plasmodium falciparum replication initiation proteins PfMCM4 and PfORC1 during the asexual and sexual stages of intraerythrocytic developmental cycle

Ion implantation is a promising route for doping quartz with luminescent impurity atoms and nanoparticles at moderate fluences. The present work focuses on the comparison of epitaxy and cathodoluminescence (CL) after Ba, Ge, Na and Rb ion implantation as well as Rb/Ge double implantation in α-quartz, under the conditions of either dynamic or chemical epitaxy. In addition to the known intrinsic sub-bands in the CL spectra, due to the silica matrix or electron irradiation, we were able to line up several new blue or violet bands with the implanted ion species and follow their thermal behaviour. In the case of Na and Rb ions, complete chemical epitaxy has been achieved, but only rather weak CL output. For Ba ions, almost complete dynamic epitaxy and fairly high CL efficiency have been realized, but no epitaxy for Ge implantation. The case of dual Rb/Ge ion implantation appears as the most promising route to gain a high CL light output and full epitaxy. © 2006 Elsevier B.V. All rights reserved.

Nuclear Instruments and Methods in Physics Research, Section B: Beam Interactions with Materials and Atoms

Cathodoluminescence and epitaxy after group-IV and alkali-ion implantation in α-quartz

In the course of a systematic investigation of dynamic, chemical, and laser-induced solid phase epitaxy of α-quartz after ion implantation, we have studied epitaxy and cathodoluminescence emission after 250 keV Cs-ion implantation and subsequent pulsed excimer laser treatment in air. Rutherford backscattering channelling analysis showed partial epitaxy for all the laser-irradiated samples; however, no full epitaxy was achieved. The optical properties of these samples were analyzed using cathodoluminescence spectroscopy, giving evidence of five emission bands at 2.42, 2.79, 3.25, 3.65, and 4.30 eV photon energy. Their intensity relation to the laser power and retained Cs-ion fraction are discussed and the present results will be compared with those obtained after chemical and dynamic epitaxy of quartz after alkali-ion, Ge, and Ba implantation. © 2005 Elsevier B.V. All rights reserved.

Applied Surface Science

Cathodoluminescence and epitaxy after laser annealing of Cs + -irradiated α-quartz

The reaction of poly(allyl azide) (PAA; number-average molecular weight = 1800 g/mol) with N-phenyl maleimide, 4,4′-bis(maleimidodiphenyl) ether, 4,4′-(bismaleimidodiphenyl) sulfone, and 1,6-bismaleimido hexane is described in this article. As indicated by Fourier transform infrared studies, the azido group reacted with the highly electron-deficient olefinic bond of N-phenyl maleimide or bismaleimides in a 3 + 2 cycloaddition reaction under mild reaction conditions. The curing of PAA with bismaleimides (10-30 phr) was monitored with differential scanning calorimetry. In freshly prepared samples of PAA and bismaleimides, a broad exothermic transition was observed in the temperature range of 150-280°C and could be attributed to the loss of N 2 from PAA and the curing of bismaleimides. The heat of the exothermic reaction (ΔH) depended on the structure and composition and was in the range of 800-1413 J/g. Isothermal heating in an air oven at 40°C (2 days) followed by 60°C (5-6 days) resulted in the conversion of a sticky, viscous liquid into an elastic, nonsticky material. No significant difference in the ΔH values of uncured and cured samples was observed, and this indicated the reaction of fewer azido groups with the bismaleimides (dipolarophiles). In the thermogravimetry traces, a mass loss was indicated in the temperature range of 130-280°C due to the loss of nitrogen from the azido group. © 2006 Wiley Periodicals, Inc.