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A general formulation is employed to study and quantitatively ascertain the effect of plasma broadening of intrinsic autoionizing (AI) resonances in photoionization cross sections. In particular, R-matrix data for iron ions described in the previous paper in the RMOP series (RMOP-II, hereafter RMOP2) are used to demonstrate underlying physical mechanisms due to electron collisions, ion microfields (Stark), thermal Doppler effects, core excitations, and free–free transitions. Breit–Pauli R-matrix cross sections for a large number of bound levels of Fe ions are considered, 454 levels of Fe XVII, 1184 levels of Fe XVIII and 508 levels of Fe XIX. Following a description of theoretical and computational methods, a sample of results is presented to show significant broadening and shifting of AI resonances due to extrinsic plasma broadening as a function of temperature and density. The redistribution of AI resonance strengths broadly preserves their integrated strengths as well as the naturally intrinsic asymmetric shapes of resonance complexes which are broadened, smeared and flattened, eventually dissolving into the bound-free continua. [ABSTRACT FROM AUTHOR]

An extended version of the R -matrix methodology is presented for calculation of radiative parameters for improved plasma opacities. Contrast and comparisons with existing methods primarily relying on the distorted wave approximation are discussed to verify accuracy and resolve outstanding issues, particularly with reference to the opacity project (OP). Among the improvements incorporated are: (i) large-scale Breit–Pauli R -matrix calculations for complex atomic systems including fine structure, (ii) convergent close coupling wave function expansions for the (e + ion) system to compute oscillator strengths and photoionization cross sections, (iii) open and closed shell iron ions of interest in astrophysics and experiments, (iv) a treatment for plasma broadening of autoionizing resonances as function of energy-temperature-density dependent cross sections, (v) a 'top-up' procedure to compare convergence with R -matrix calculations for highly excited levels, and (vi) spectroscopic identification of resonances and bound (e + ion) levels. The present R -matrix monochromatic opacity spectra are fundamentally different from OP and lead to enhanced Rosseland and Planck mean opacities. An outline of the work reported in other papers in this series and those in progress is presented. Based on the present re-examination of the OP work, opacities of heavy elements might require revisions in high temperature-density plasma sources. [ABSTRACT FROM AUTHOR]

To investigate the completeness of coupled channel (CC) Breit–Pauli R-matrix (BPRM) calculations for opacities we employ the relativistic distorted wave (RDW) method to complement ('top-up') and compare the BPRM photoionization cross sections for high- n ℓ levels of both Fe xvii and Fe xviii. Good agreement is found with background photoionization cross sections using these two methods, which also ensures the correct matching of bound level cross sections for completeness. In order to top-up the CC-BPRM calculations, bound–bound transitions involving additional bound levels, and a large number of doubly-excited quasi-bound levels corresponding to BPRM autoionizing resonances described in the paper RMOPII are calculated using the RDW method. Photoionization cross sections in the high energy region are also computed and compared up to about 500 Ry, and contributions from higher core level excitations than BPRM are considered. The effect of configuration interaction is investigated, which plays a significant role in correctly reproducing some background cross sections. Due to the fact that the additional RDW levels correspond to high- n ℓ bound levels that are negligibly populated according to the Mihalas–Hummer–Däppen equation-of-state (paper I), the effect on opacities is expected to be small. [ABSTRACT FROM AUTHOR]

Iron is the dominant heavy element that plays an important role in radiation transport in stellar interiors. Owing to its abundance and large number of bound levels and transitions, iron ions determine the opacity more than any other astrophysically abundant element. A few iron ions constitute the abundance and opacity of iron at the base of the convection zone (BCZ) at the boundary between the solar convection and radiative zones and are the focus of the present study. Together, Fe xvii, Fe xviii and Fe xix represent 85% of iron ion fractions, 20%, 39% and 26% respectively, at the BCZ physical conditions of temperature T ∼ 2.11 × 10 6 K and electron density N e = 3.1 × 10 22 c.c. We report the most extensive R -matrix atomic calculations for these ions for bound–bound and bound–free transitions, the two main processes of radiation absorption. We consider wavefunction expansions with 218 target or core ion fine structure levels of Fe xviii for Fe xvii, 276 levels of Fe xix for Fe xviii, in the Breit–Pauli R -matrix (BPRM) approximation, and 180 LS terms (equivalent to 415 fine structure levels) of Fe xx for Fe xix calculations. These large target expansions, which include core ion excitations to n = 2,3,4 complexes, enable accuracy and convergence of photoionization cross sections, as well as the inclusion of high lying resonances. The resulting R -matrix datasets include 454 bound levels for Fe xvii, 1,174 levels for Fe xviii, and 1,626 for Fe xix up to n ⩽ 10 and l = 0–9. Corresponding datasets of oscillator strengths for photoabsorption are: 20 951 transitions for Fe xvii, 141 869 for Fe xviii, and 289 291 for Fe xix. Photoionization cross sections have been obtained for all bound fine structure levels of Fe xvii and Fe xviii, and for 900 bound LS states of Fe xix. Selected results demonstrating prominent characteristic features of photoionization are presented, particularly the strong Seaton photoexcitation-of-core resonances formed via high-lying core excitations with Δ n = 1 that significantly impact bound–free opacity. [ABSTRACT FROM AUTHOR]

Modifying Fe and Mn contents in GaFeO3 (GFO) enhances the magnetic properties, increases the magnetic transition temperature (TC) and reduces the leakage current. Here, we report structural, magnetic, and leakage current characteristics of manganese-doped gallium ferrite with different Fe-content, i.e. Ga2−xFexO3 (1 ≤ x ≤ 1.4) system. Structural characterization reveals that all the samples retain the orthorhombic phase with space group Pc21n for above amounts of doping. Magnetization of the samples with respect to temperature shows the lower magnetic transition temperature (TC) for pure GFO, i.e. 220 K, which increases to 345 K above room temperature (RT) for 2% Mn-doped Ga0.6Fe1.4O3 (GFMO3). Higher remanent magnetization (∼16 emu g−1) with a lower coercive field (∼4 kOe) is obtained for Mn-doped Ga0.6Fe1.4O3. We found the decrease of leakage current with doping of Mn. The observation of multiferroicity in these single-phase materials (i.e. GFO3 and GFMO3) at RT make them potential candidates for memory, multifunctional, and spintronics device applications. [ABSTRACT FROM AUTHOR]

We report on the study of high quality Pb(Zr,Ti)O3 thin films grown by radio-frequency magnetron sputtering on (0 0 0 1) ZnO with an MgO interfacial seed layer. A systematic investigation of the heterostructures has been performed by x-ray diffraction, atomic force microscopy (AFM) and ultraviolet–visible spectroscopy for the structural and optical properties, along with the electrical characterization and simulation. (0 1 1)-oriented perovskite phase was observed in Pb(Zr,Ti)O3 thin films which used the MgO seed layer, whereas the pyrochlore phase was dominant in the films deposited directly on ZnO. The surface morphology measured by AFM indicated that the introduction of the MgO interfacial seed layer promoted formation of a smooth surface and uniform grain structures in the thin films. The transmission spectra also showed an increase of the optical transmittance measured by ultraviolet–visible spectroscopy. The capacitance–voltage measurements exhibited butterfly-shaped capacitance curves which bear a resemblance to those of the typical metal–ferroelectric–metal structures. The characteristics of the polarization versus electric field were investigated by a simulation to understand the behaviour of the hysteresis loops in this metal–ferroelectric–insulator–semiconductor structure. [ABSTRACT FROM AUTHOR]

Low dimensional systems, nanowires (NWs), in particular, have exhibited excellent optical and electronic properties. Understanding the thermal properties in semiconductor NWs is very important for their applications in electronic devices. In the present study, the thermal conductivity of a freestanding silicon NW is estimated by employing Raman spectroscopy. The advantage of this technique is that the excitation source (laser) acts as both the heater and probe. The variations of the first-order Raman peak position of the freestanding silicon NW with respect to temperature and laser power are recorded. From the analysis of effective laser power absorbed by exposed silicon NW and a detailed Raman study along with the concept of longitudinal heat distribution in silicon NW, the thermal conductivity of the freestanding silicon NW of ∼112 nm diameter is estimated to be ∼53 W m−1 K− 1. [ABSTRACT FROM AUTHOR]

The acrylamide polymer gel template method has been adopted to synthesize single phase Dy1–xGdxMnO3 (DGMO, x= 0, 0.05, 0.1, 0.15, 0.2) ceramics. The Rietveld refinement of x-ray diffraction patterns recorded at room temperature suggests that DGMO ceramics are stabilized in an orthorhombic crystal structure with a Pnma space group. Gd3+ cations play an important role in stabilizing the orthorhombic phase and the unit cell volume increases with x. We report the phonon spectra of pure and Gd-substituted DyMnO3 (DMO) and their mode assignments. Raman modes are softened with x due to the relaxation in the stiffness constants upon the increase in the volume of the unit cell. The magnetic transition temperatures corresponding to TN(Dy) and Tlock decrease with the increase in Gd concentration as inferred from the temperature dependent magnetization data (M–T curve). The magnetization value increases below TN(Dy) with the increase in the Gd concentration as observed from the M–T plot. The magnetic hysteresis loop is fitted to extract ferromagnetic and antiferromagnetic/paramagnetic contributions for each composition x. Fittings of M–H loops indicate the increase in the magnetic contribution below TN(Dy) upon increasing the Gd dopant concentrations, while that decreases above TN(Dy). The temperature dependent specific heat data identifies these magnetic transition temperatures TN(Dy), Tlock and TN(Mn). Furthermore, magnetic field dependencies on TN(Dy), Tlock and TN(Mn) are studied in an elaborate manner. Both DMO and DGMO samples are found to be viable candidates for magnetic refrigeration applications in cryogenic temperature region. [ABSTRACT FROM AUTHOR]

CdxZn1−xS (x = 0.0 to 1.0, at 0.1 interval) quantum dots (QDs) were synthesized by mechanical alloying of the stoichiometric mixture of elemental Cd, Zn and S powders at room temperature under Ar in record minimum time. The Cd0.5Zn0.5S QDs were formed after 25 min and the Cd0.1Zn0.9S QDs after 160 min of milling. The x-ray and high resolution transmission electron microscope characterizations reveal the presence of both major and minor zinc-blende and wurtzite phases and stacking faults in these QDs. Lattice parameters of both these phases decrease and the optical band-gaps increase continuously with increasing Zn concentrations. A very distinct change in colour of these QDs from blue to red is noticed with increasing Cd concentration from 0 to 1, indicating that optical band-gap varies with varying composition. [ABSTRACT FROM AUTHOR]

We demonstrate the growth temperature dependence of film thickness and surface roughness of ZnO films grown by atomic layer deposition using ozone as an oxidizer. The significantly low growth rate of the film using O3 precursor is attributed to the recombinative surface loss of O3. The variation of the spatial uniformity inferred from the surface roughness of the ZnO films and the O3 concentration was explained by a transition from reaction- to recombination-limited growth. We have fabricated a metal–oxide–semiconductor device, consisting of an insulating ZnO layer using an O3 source, between metallic and semiconducting Al : ZnO layers. The device demonstrates a remarkable resistive switching behaviour. The electrochemical migration of oxygen vacancies, which is created in the vicinity of the interface of ZnO semiconductor–ZnO insulator, drives the resistive switching behaviour. This significant result produced on the all-oxide-based device fabricated by atomic layer deposited ZnO can have significant impact for multifunctional applications. [ABSTRACT FROM AUTHOR]

In active galactic nucleus spectra, a series of Fe II multiplets form a pseudo-continuum that extends from the ultraviolet to the near-infrared (NIR). This emission is believed to originate in the broad-line region, and it has been known for a long time that pure photoionization fails to reproduce it in the most extreme cases, as does the collisional excitation alone. The most recent models by Sigut & Pradhan include details of the Fe II ion microphysics and cover a wide range in the ionization parameter log Uion = (– 3.0 → –1.3) and density log nH = (9.6 → 12.6). With the aid of such models and a spectral synthesis approach, we studied for the first time in detail the NIR emission of I Zw 1. The main goals were to confirm the role played by Lyα fluorescence mechanisms in the production of the Fe II spectrum and to construct the first semi-empirical NIR Fe II template that best represents this emission, consequently allowing its clean subtraction in other sources. A good overall match between the observed Fe II+Mg II features with those predicted by the best-fitted model was obtained, corroborating the Lyα fluorescence as a key process to understand the Fe II spectrum. The best model was fine-tuned by applying a deconvolution method to the observed Fe II+Mg II spectrum. This derived semi-empirical template was then fitted to the spectrum of Ark 564, showing that it nicely reproduced its observed Fe II+Mg II emission. Our work extends the current set of available Fe II templates into the NIR region. [ABSTRACT FROM AUTHOR]