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The evolution of the multipolar structure of the magnetic field of isolated neutron stars is studied assuming the currents to be confined to the crust. Lower orders (≤ 25) of multipole are seen to evolve in a manner similar to the dipole suggesting little or no evolution of the expected pulse shape. We also study the multifrequency polarization position angle traverse of PSR B0329+54 and find a significant frequency dependence above 2.7 GHz. We interpret this as an evidence of strong multipolar magnetic field present in the radio emission region.
When women have a history of anorexia nervosa (AN), the advice given about becoming pregnant, and about the management of pregnancies, has usually been cautious. This study compared the pregnancy outcomes of women with and without a history of AN.
Women with a confirmed diagnosis of AN who had presented to psychiatric services in North East Scotland from 1965 to 2007 were identified. Those women with a pregnancy recorded in the Aberdeen Maternal and Neonatal Databank (AMND) were each matched by age, parity and year of delivery of their first baby with five women with no history of AN. Maternal and foetal outcomes were compared between these two groups of women. Comparisons were also made between the mothers with a history of AN and all other women in the AMND.
A total of 134 women with a history of AN delivered 230 babies and the 670 matched women delivered 1144 babies. Mothers with AN delivered lighter babies but this difference did not persist after adjusting for maternal body mass index (BMI) in early pregnancy. Standardized birthweight (SBW) scores suggested that the AN mothers were more likely to produce babies with intrauterine growth restriction (IUGR) [relative risk (RR) 1.54, 95% confidence interval (CI) 1.11–2.13]. AN mothers were more likely to experience antepartum haemorrhage (RR 1.70, 95% CI 1.09–2.65).
Mothers with a history of AN are at increased risk of adverse pregnancy outcomes. The magnitude of these risks is relatively small and should be appraised holistically by psychiatric and obstetric services.
Prior to 2009 dengue fever had not been reported in the Andaman and Nicobar archipelago. In 2009, a few patients with dengue fever-like illness were reported, some of whom tested positive for dengue antibodies. In 2010, 516 suspected cases were reported, including some with dengue haemorrhagic fever (DHF) and dengue shock syndrome (DSS); 80 (15·5%) were positive for dengue antibodies. DENV RNA was detected in five patients and PCR-based typing showed that three of these belonged to serotype 1 and two to serotype 2. This was confirmed by sequence typing. Two clones of dengue virus, one belonging to serotype 1 and the other to serotype 2 appeared to be circulating in Andaman. Emergence of severe diseases such as DHF and DSS might be due to recent introduction of a more virulent strain or because of the enhancing effect of sub-neutralizing levels of antibodies developed due to prior infections. There is a need to revise the vector-borne disease surveillance system in the islands.
The effect of anthanum substitution (0-20%) on phase formation, structural evolution and electrical properties of SrBi2Ta2O9 (SBT) ceramics were investigated. X-ray diffraction studies revealed that phase pure SBT bulk samples can be synthesized with lanthanum doping without any phase segregation. Raman spectroscopy was used to understand the lattice vibrational characteristics of La substituted SBT compound. The ferroelectric soft mode at 27 cm−1 was shifted towards the lower frequencies at room temperature with increase in La concentrations. The octahedral stretching mode (O-Ta-O) did not influenced by La substitution in SBT. The x-ray photoemission spectroscopy measurements showed the decrease of binding energy of Bi 4f core levels (5/2 and 7/2) upon La substitution in SBT. The dielectric constant was increased from 120 to 190 up to 10% La doping and decreased with further increase in La concentration.
In this paper, we report on the growth and fabrication of thin film Si photovoltaic devices on photonic structures which were fabricated on steel and PEN and Kapton substrates. Both amorphous Si and thin film nanocrystalline Si devices were fabricated. The 2 dimensional photonic reflector structures were designed using a scattering matrix theory and consisted of appropriately designed holes/pillars which were imprinted into a polymer layer coated onto PEN, Kapton and stainless steel substrates. The photonic structures were coated with a thin layer of Ag and ZnO. Both single junction and tandem junction (amorphous/amorphous and amorphous/nanocrystalline) cells were fabricated on the photonic layers. It was observed that the greatest increase in short circuit current and efficiency in these cells due to the use of photonic reflectors was in nanocrystalline Si cells, where an increase in current approaching 30% (compared to devices fabricated on flat substrates) was obtained for thin (∼ 1 micrometer thick i layers) films of nano Si deposited on steel structures. The photonic structures (which were nanoimprinted into a polymer) were shown to stand up to temperatures as large as 300 C, thereby making such structures practical when a steel (or glass) of kapton substrate is used. Detailed measurements and discussion of quantum efficiency and device performance for various photonic back reflector structures on steel, kapton and PEN substrates will be presented in the paper.
Graded-band-gap CuIn1−xGaxSe2 (CIGS) absorbers with Ga/Ga+In value in the 20%-30% range have a demonstrated efficiency of 18.8%. For CdS-containing devices, the shortcircuit current density (Jsc) has almost reached its expected maximum. However, the open-circuit voltage of CIGS solar cells is limited by the surface microstructure and chemistry. In this work, we examine the microstructural properties and chemistry of CIGS. We also attempted to correlate the above observations and device performance.
We have grown SrBi2Ta2O9 (SBT) thin films on various bottom electrodes such as Pt/TiO2/SiO2/Si (Pt) and LaNiO3/Pt/TiO2/SiO2/Si (LNO) substrates. The substrate temperature and oxygen pressure for the SBT film was maintained at 500 °C and 200 mTorr. As-grown films were post-annealed at a temperature of 800 °C. X-ray diffraction studies revealed that as-grown films were amorphous and crystallized to single phase after annealing. The difficulty of obtaining lowest Raman modes of SBT on platinized silicon substrate was overcome by using conducting oxide electrodes. Films grown on platinized silicon showed maximum value of remanent polarization (2Pr ∼ 21.5 μC/cm2) with coercive field (Ec) of ∼ 67 kV/cm. The degradation of ferroelectric properties of the films was observed with the introduction of 50 nm conducting LaNiO3 electrode at the interface of Pt and SBT film, which was attributed to high resistivity of the oxide electrode layers. Leakage current density was studied with the consideration of the Schottky emission model. The barrier height of the films grown on Pt and LNO were estimated to be 1.27 eV and 1.12 eV, respectively. The reduction of barrier height was attributed to the lower work function of the LNO electrode.
In this paper we report on the ability of rapid thermal annealing (1050C, 45s) and furnace annealing (900C, 30min) to partially break up the interfacial oxide in bipolar transistors with different oxide thicknesses at the polysilicon/silicon interface. We have obtained the different oxide thicknesses either by performing different ex situ cleans (RCA clean or RCA clean + HF dip) before Low Pressure Chemical Vapor Deposition (LPCVD) of polysilicon, or by using a cluster tool for polysilicon deposition with the ability to perform an in situ clean and then allowing the growth of different oxide thicknesses at the interface prior to polysilicon deposition. For the in situ cleaned devices, it is observed that after the interface anneal, the current gain increases with increasing oxide thicknesses, but with little penalty in terms of higher emitter resistance, Re. This indicates that by controllably increasing the interfacial oxide thickness and by subsequent annealing to partially break up the interfacial oxide, higher current gains can be obtained with little sacrifice in terms of higher Re.
The dielectric response of La- and Dy- doped BiFeO3 thin films to electric- and magnetic fields was measured at microwave frequencies (up to 12GHz) in a temperature range from 25 °C to 300 °C. Interesting phenomena were observed. Significant oscillations in the C(f) characteristic which were unaffected by the electric field or by elevated temperature but which were dampened by a magnetic field. We also observed ‘N’-type I-V characteristics. A possible explanation for this mesoscopic response is the presence of structural features that cause resonance (e.g. grains, grain-boundaries, domains, domain walls etc), with a contribution strong enough to be averaged by the system. The exact origin of these features is unknown at present.
Lattice dynamical and electronic transition changes due to V and Co doped ZnO have been investigated using optical techniques. Vanadium and Co doped ZnO pellets were prepared using conventional ceramic processing route and thin films were fabricated by pulsed laser deposition. Raman spectra of Zn1-xVxO targets showed many additional peaks in the range of 230 to 350 cm-1 and 750 to 900 cm-1. Integrated intensities of these additional modes decreased with increase of temperature as similar to the host ZnO modes, which precludes electronic Raman scattering to be the origin. Raman peaks for stoichiometric Zn3(VO4)2 and Zn2V2O7 compounds also had additional peaks that can be attributed to the secondary phases formed in the compositions of Zn1-xVxO. Raman spectra of Zn1-xCoxO showed no additional modes besides ZnO modes, however, the intensity of the second order peak at 540 cm-1 was increased due to Co doping. Thin films of Zn1-xCoxO exhibited highly c-axis orientation deposited on (001)Al2O3 substrates. The optical absorption of the films showed that the band gap decreased with increase of Co concentrations at room temperature along with the sub bandgap absorptions due to d-d transitions of Co2+.
Alternating layers of Ni and Nb with a total thickness of 1060Å, and Ni and Cr with a total thickness of 840Å were deposited by electron beam evaporation on silicon. The individual layer thicknesses were adjusted in such a way as to obtain 50/50 at% compositions of Ni-Nb and Ni-Cr; the thicknesses were around 100Å for Ni and 170Å for Nb, and 100Å of Ni and 110Å of Cr. The films were bombarded with 350 keV Cr+ ions at a dose of 2 × 10 ions cm. RBS and TEM techniques were used to study the mixing and microstructure. Almost complete mixing and amorphization have been observed for the Ni-Nb system. Ni-Cr film has revealed very little mixing compared to Ni-Nb film and the microstructure remained polycrystalline. Sputter (rf) deposited Ni-Cr film also remained polycrystalline both before and after ion irradiation. The Ni-Cr System appears to be an exception to the structural difference rule for amorphous phase formation by ion irradiation.
An investigation of the ion beam mixing of Mo and Ta layers with 304 stainless steel and the potentiodynamic polarization behavior of the modified surfaces are described.
Alternating thin layers (<100Å) of stainless steel (304) and either Mo or Ta were deposited by electron beam evaporation. Ion mixing was performed with 2 MeV Ni+ at a fluence of 5 × 1016cm−2. Examination of the mixed surfaces with TEN revealed characteristics of the amorphous phase and in some cases being embedded with crystalline regions for both Mo and Ta mixed stainless steel surfaces. The amorphous surfaces were tested for their corrosion behavior in 1M H2SO4 and O.1M NaCl solutions by the potentiodynamic polarization method. Significantly improved corrosion behavior were obtained for modified surfaces compared to unmodified stainless steel.
0.6 µm-wide lines of high Tc Y-Ba-Cu-O have been fabricated by direct laser writing on mirror-like thin films which were grown by laser deposition without post annealing. Laser ablation etching had no effect on the Tc and Jc until the lines were < 1µm wide. The 0.6 µm-wide strip showed some degradation of Tc and Jc. The critical current densities for these patterned lines were measured to be ∼5×106 A/cm2 at 50 K.
The feasibility of fabricating Nb-Nb silicide microstructure by Physical Vapor Deposition with sufficient control of impurities has been investigated. It is demonstrated that electron beam evaporation can satisfy the requirement of impurity control under appropriate vacuum condition. In elemental layered structure of Nb and Si, NbSi2 is the first phase formed upon annealing. It was found that, at 600°C, the growth rate of NbSi2 phase at the interface of Nb and Si is 35Å/min. The Nb5Si3 phase nucleates at a higher temperature (around 900°C) at the interface of Nb and NbSi2. In the case of co-deposited film with overall composition around Nb5 Si3, NbSi2 formation is by-passed. Thus, multilayers of Nb/NbSi2 or Nb/Nb5Si3 can be formed from layered elemental deposition and subsequent heat treatment under controlled conditions by adjusting the starting thicknesses of the films. Alternate elemental and co-deposition and subsequent or in-situ heat treatment can directly form the layered Nb/desired silicide composite. Multilayers of Nb/NbSi2 and Nb/Nb5Si3 with layer thicknesses below 500Å have been formed from layered elemental deposition.
Pulsed-laser-deposition technique was used to grow SrBi2Nb2O9 (SBN) thin films on platinized silicon substrates. The effect of annealing temperature and film thicknesses on the structural and electrical properties has been studied. The average grain size and rms surface roughness was found to increase with increasing annealing temperature. The degree of orientation along the (200) direction was increased with the film thicknesses. The remanent polarization was found to be increased with the film thicknesses and was attributed to the selftexturing characteristics of SBN films. Thin films with higher thickness (∼570 nm) exhibited high value of remanent polarization (∼38 ν/cm2) with coercive field of 185 kV/cm. There was a reduction of coercive field with the film thickness. The dielectric constant was observed to be independent of the film thickness. The increase in loss tangent with increasing film thicknesses was attributed to the reduction of dielectric breakdown strength of the films. The SBN thin films showed minimal fatigue characteristics and suitable material for memory devices.
Wide bandgap (∼6 eV) ZnO/MgO multilayer thin films have been fabricated using pulsed laser deposition technique from their respective targets on c-plane Al2O3 substrates. The thickness of single ZnO sublayer thickness was varied in the range of 0.75–2.5 nm with a fixed MgO sublayer thickness of 1 nm in order to achieve a total film thickness of ∼300 nm. The structural transition from hexagonal to cubic phase was observed with the decrease in the thickness of single ZnO layer from 2.5 to 0.75 nm that resulted in the increase in bandgap from 3.5 to 6.2 eV. Mg contents of the films were increased from 40 % to 60 % for hexagonal and cubic phases, respectively. The surface roughness and grain structure were not influenced much with the increase of Mg concentration. Resistivity of the films was increased six orders of magnitude with the increase in Mg incorporation. The post annealing at 750° C did not show any significant change in the crystal structure and the optical properties.
We have studied the influence of partial substitution of Ca (0%, 5%, 10% and 15%) on the structural and electrical properties of SrBi2Nb2O9 (SBN) thin films. Pulsed laser deposition technique was used to grow thin films on platinized silicon substrates. X-ray diffraction data confirmed the polycrystalline nature of the films with preferential orientation along the polarization axis. Incorporation of Ca at Sr-site of SBN reduced the lattice parameter and was attributed to the smaller ionic radii of Ca. The soft mode frequency at 29.5 cm-1 of SBN shifted towards higher wavenumber implied increasing the transition temperature upon Ca substitution. The grain sizes of SBN thin films vary from oval to rod like structures and improving the homogeneous distribution of grains with the increase in Ca contents. The ferroelectric properties of the films enhanced with maximum remanent polarization of 35.3 mC/cm2. The increase in the coercive field with incorporation of Ca at Sr-site was attributed to the higher electronegativity of Ca. The SBN thin films with the incoporation of Ca exhibited poor leakage current behavior. The reduction of dielectric permittivity with Ca concentration was attributed to the lower dielectric permittivity of CaBi2Nb2O9.
Pulsed laser deposition technique was used to fabricate Ba0.5Sr0.5TiO 3 (BST) thin-films on Pt/TiO 2/SiO2/Si substrates. The influence of thin interfacial layers of Ta2O5, TiO2, and ZrO2, on the structural and electrical properties of BST thin films was investigated. Insertion of interfacial layers does not affect the perovskite phase formation of BST thin films. Buffer layers helped to make uniform distribution of grains and resulted in a relative increase in the average grain size. The dielectric tunability of BST thin films was reduced with the presence of buffer layers. A BST thin film having a dielectric permitivity of 470 reduced to 337, 235 and 233 in the presence of Ta2O5, TiO2, and ZrO2 layers, respectively. The reduction of the relative dielectric permittivity of BST films with the insertion of interfacial layers was explained in terms of a series capacitance effect, due to the low dielectric constant of interfacial layers. The TiO2 layer did not show any appreciable change in the leakage current density. Deposition of thin Ta2O5 and ZrO2 interfacial layer on top of Pt reduced the leakage current density by an order of magnitude.