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In this paper we explain the temperature dependence of excitonic effective mass and charge carrier conduction mechanism occurs in CH3NH3PbI3−xClx thin films prepared by chemical dip coating (CDC), spray pyrolysis (Spray) and repeated dipping-withdrawing (Dipping). Hall Effect study confirmed that prepared CH3NH3PbI3−xClx samples are p-type semiconductor having carrier concentration of the order of ~ 1016 cm−3. The charge carrier mobility, mean free path and mean free life time were found to decrease with increasing temperature due to polaronic effect. The excitonic effective mass is estimated to (0.090–0.196)me and excitonic binding energy (15–33) meV, well consistent with Wannier-Mott hydrogenic model and the nature of exciton is likely to be Mott-Wannier type. From electrical measurement, it was observed that charge carrier conduction in CH3NH3PbI3−xClx is governed by migration of $${\mathrm{I}}^{-}$$ I - and CH3N $${\mathrm{H}}_{3}^{+}$$ H 3 + vacancies and vacancy-assisted diffusion processes depending on temperature.

In this paper, Ba-doped SnO2 (SnO2:Ba), Mg-doped SnO2 (SnO2:Mg) and Ce-doped SnO2 (SnO2:Ce) nanostructured thin films were prepared on the glass substrate via a simple and low-cost nebulizer spray pyrolysis method. The crystal structure and morphology of all the samples were investigated by X-ray diffraction (XRD) and field-emission-scanning electron microscopy (FE-SEM), respectively. XRD results suggest that all the samples are polycrystalline with the tetragonal rutile structure. FE-SEM analysis exhibits a uniform surface morphology with homogenous distribution of grains. The transmittance measurement suggests that SnO2:Ba sample exhibits high transparency above 90% in the visible region. We find that doping causes an increase in the band gap, this behavior is explained by the Burstein–Moss effect. Two emission bands in the ultraviolet and visible regions are observed in the photoluminescence spectra. Hall effect measurement reveals that all the samples are degenerate and exhibit n-type semiconducting nature with carrier concentration in the order of 1018 cm−3. Ba doping induces the lowest resistivity of 0.047 Ω·cm associated with an increase in carrier concentration of 8.38 × 1018 cm−3 and mobility of 15.87 cm2 V−1 s−1. In contrast, the incorporation of Mg and Ce in SnO2 reduces the mobility and conductivity, which may be associated with the grain boundary scattering.

The Galactic Center is surrounded by two giant plasma lobes known as the Fermi Bubbles, extending ~10 kpc both above and below the Galactic plane. Spectroscopic observations of Fermi Bubble directions at radio, ultraviolet, and optical wavelengths have detected multi-phase gas clouds thought to be embedded within the bubbles referred to as Fermi Bubble high-velocity clouds (FB HVCs). While these clouds have kinematics that can be modeled by a biconical nuclear wind launched from the Galactic center, their exact origin is unknown because, until now, there has been little information on their heavy-metal abundance (metallicity). Here we show that FB HVCs have a wide range of metallicities from, This version of the article has been accepted for publication on Nature Astronomy after peer review. This version is not the Version of Record (https://doi.org/10.1038/s41550-022-01720-0) and does not reflect post-acceptance improvements, or any corrections

Hydrostatic pressure dependent structural, electronic, elastic and optical properties of Heusler compounds Cr2YAl (Y=Mn, Co) are investigated by the first-principles calculations. Present study shows good agreement between the calculated and experimental values of lattice parameters of these compounds. The gradual decrease of lattice parameter and unit cell volume with the increase of pressure eliminates the possibility of phase transition up to the considered pressure range 0–30 GPa. The absence of negative frequency in the phonon dispersion curves at various external pressures up to 30 GPa confirm the dynamical stability of these compounds. The values of Pugh's ratio, Poisson's ratio and Cauchy pressure indicate the ductility of Cr2CoAl while those criteria confirm the brittleness of Cr2MnAl. Pressure dependent behaviour of the elastic constants of these compounds shows the mechanical stability over the studied pressure range (0–30 GPa). Crystal stiffening of both the compounds is indicated by the increase of Debye temperature with increasing hydrostatic pressure. The pressure dependent band structure and density of states (DOS) calculations reveal the half- and the near half-metallic behaviour of Cr2MnAl and Cr2CoAl, respectively up to 20 GPa while those disappears at pressure around 30 GPa. The variations of optical constants with pressure is consistent with the results of the electronic structure calculations. High reflectivity (>45%) of both the compounds makes them attractive for optoelectronic device applications., Heusler compound, First-principles calculations, Elastic constants, Electronic properties, Half-metal.

The mixed halide CH3NH3PbI3−xClx crystalline thin film has been prepared by two-step solution-processed repeated dip coating method at an ambient atmosphere. X-ray diffraction study reveals the presence of tetragonal and cubic phases in deposited film. Raman study confirms the metal halide bond in the inorganic framework and organic CH3 stretching/bending of C–H bond in CH3NH3PbI3−xClx perovskite. Scanning electron microscopy shows that cuboid and polyhedral-like crystal grains of 100 nm to 2 μm may find applications in optoelectronics. The perovskite CH3NH3PbI3−xClx thin film shows high spectral absorption coefficient of the order of 106 m−1. In optical band gap study, we found the coexistence of cubic and tetragonal perovskite phases. The energy band gap is dominated by cubic phase having Eg = 2.50 eV over tetragonal phase with band gap Eg = 1.67 eV. The room-temperature photoluminescence study confirms band edge, shallow and deep-level emissions. The temperature-dependent cathodoluminescence study shows red, green and ultraviolet emissions. The dominating green luminescence evolved for cubic phase at 2.51 eV. The red and ultraviolet emissions are also found for mixed-phase CH3NH3PbI3−xClx thin film, suitable for preparation of light-emitting devices.

Intermetallic compounds with CaAl2Si2-type structure have been studied extensively due to their exciting set of physical properties. Among various alumo-germanides, MgAl2Ge2 is the new representative of CaAl2Si2-type structures. Our previous study explores the structural aspects, mechanical behaviors and electronic features of intermetallic MgAl2Ge2. The present work discloses the results of optoelectronic, thermodynamic and vibrational properties of MgAl2Ge2 via density functional theory-based investigations. The band structure calculations suggest that MgAl2Ge2 possesses slight electronic anisotropy and the compound is metallic. The Fermi surface topology reveals that both electron- and hole-like sheets are present in MgAl2Ge2. The electron charge density map indicates toward the dominance of covalent bonding in MgAl2Ge2. The optical parameters are found to be independent of the state of the polarization of incident electric field. The large value of the reflectivity in the visible-to-ultraviolet region up to ~ 15 eV suggests that MgAl2Ge2 might be a good candidate as coating material to avoid solar heating. The thermodynamic properties have been calculated using the quasi-harmonic Debye approximation. We have found indications of lattice instability at the Brillouin zone boundary in the trigonal $$P\overline{3}m1$$ P 3 ¯ m 1 phase from the phonon dispersion curves. However, the compound might be stable at elevated temperature and as a function of pressure. All the theoretical findings herein have been compared with the reported results (where available). Various implications of our results have been discussed in detail. Graphic abstract

In this paper we explain the temperature dependence of excitonic effective mass and charge carrier conduction mechanism occurs in CH3NH3PbI3−xClx thin films prepared by chemical dip coating (CDC), spray pyrolysis (Spray) and repeated dipping-withdrawing (Dipping). Hall Effect study confirmed that prepared CH3NH3PbI3−xClx samples are p-type semiconductor having carrier concentration of the order of ~ 1016 cm−3. The charge carrier mobility, mean free path and mean free life time were found to decrease with increasing temperature due to polaronic effect. The excitonic effective mass is estimated to (0.090–0.196)me and excitonic binding energy (15–33) meV, well consistent with Wannier-Mott hydrogenic model and the nature of exciton is likely to be Mott-Wannier type. From electrical measurement, it was observed that charge carrier conduction in CH3NH3PbI3−xClx is governed by migration of \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$${\mathrm{I}}^{-}$$\end{document}I- and CH3N \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$${\mathrm{H}}_{3}^{+}$$\end{document}H3+ vacancies and vacancy-assisted diffusion processes depending on temperature.

DESI will precisely constrain cosmic expansion and the growth of structure by collecting $\sim$35 million redshifts across $\sim$80% of cosmic history and one third of the sky to study Baryon Acoustic Oscillations (BAO) and Redshift Space Distortions (RSD). We present a preliminary target selection for an Emission Line Galaxy (ELG) sample, which will comprise about half of all DESI tracers. The selection consists of a $g$-band magnitude cut and a $(g-r)$ vs. $(r-z)$ color box, which we validate using HSC/PDR2 photometric redshifts and DEEP2 spectroscopy. The ELG target density should be $\sim$2400 deg$^{-2}$, with $\sim$65% of ELG redshifts reliably within a redshift range of $0.6, Comment: 4 pages, 1 figure; published in Res. Notes AAS

Using new ultraviolet (UV) spectra of five background quasars from the Cosmic Origins Spectrograph on the Hubble Space Telescope, we analyze the low-latitude (|b|=20-30 degree) regions of the Fermi Bubbles, the giant gamma-ray emitting lobes at the Galactic Center. We combine these data with previous UV and atomic hydrogen (HI) datasets to build a comprehensive picture of the kinematics and metal column densities of the cool outflowing clouds entrained in the Fermi Bubbles. We find that the number of UV absorption components per sightline decreases as a function of increasing latitude, suggesting that the outflowing clouds become less common with increasing latitude. The Fermi Bubble HI clouds are accelerated up to b~7 degree, whereas when we model the UV Fermi Bubbles clouds deprojected flow velocities, we find that they are flat or even accelerating with distance from the Galactic center. This trend, which holds in both the northern and southern hemispheres, indicates that the nuclear outflow accelerates clouds throughout the Fermi Bubbles or has an acceleration phase followed by a coasting phase. Finally, we note the existence of several blueshifted high-velocity clouds at latitudes exceeding ~30 degree, whose velocities cannot be explained by gas clouds confined to the inside of the gamma-ray defined Fermi Bubbles. These anomalous velocity clouds are likely in front of the Fermi Bubbles and could be remnants from past nuclear outflows. Overall, these observations form a valuable set of empirical data on the properties of cool gas in nuclear winds from star-forming galaxies., Comment: 26 pages, 12 figures, Accepted for publication in ApJ

© 2018 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim Organolead mixed-halide perovskites capable of emitting multiple colors not only allow the fabrication of compact devices but also improves the functionality of light emitting devices beyond conventional displays. Here we demonstrate a cost-effective chemical dip-coating technique to grow highly reproducible methylammonium-lead-halide perovskite film, which exhibits highly efficient multi-color emissions of red, green and ultraviolet. The power- and temperature-resolved cathodoluminescence analyses reveal that these emissions are attributed to localized excitions with thermal activation energies of 27, 29 and 57 meV. The non-linear fitting of these emission band widths within the frame work of Boson model reveals that excitons are strongly coupled to the lattice with energy of 28 meV, which is consistent with the Raman measurement. This work presents an effective method for the deposition of high-quality and large-area perovskite film, which could be useful for high-performance multi-color display devices.

The Fermi Bubbles are two giant gamma-ray emitting lobes extending 55$^{\circ}$ above and below the Galactic Center. While the Northern Bubble has been extensively studied in ultraviolet (UV) absorption, little is known about the gas kinematics of the southern Bubble. We use UV absorption-line spectra from the Cosmic Origins Spectrograph (COS) on the Hubble Space Telescope to probe the southern Fermi Bubble using a sample of 17 background AGN projected behind or near the Bubble. We measure the incidence of high-velocity clouds (HVC), finding that four out of six sightlines passing through the Bubble show HVC absorption, versus six out of eleven passing outside. We find strong evidence that the maximum absolute LSR velocity of the HVC components decreases as a function of galactic latitude within the Bubble, for both blueshifted and redshifted components, as expected for a decelerating outflow. We explore whether the column-density ratios SiIV/SiIII, SiIV/SiII and SiIII/SiII correlate with the absolute galactic latitude within the Bubble. These results demonstrate the use of UV absorption-line spectroscopy to characterize the kinematics and ionization conditions of embedded clouds in the Galactic Center outflow., Comment: Accepted for publication in the ApJ. 17 pages, 7 figures, 15 figures in appendix will be available online in the ApJ

First-principles calculations are employed to investigate and compare the structural, elastic and optical properties of tantalum hemicarbide Ta2C and tantalum monocarbide TaC. Calculated lattice constants of these carbides are in good agreement with available theoretical and experimental results. The mechanical stability of these carbides is affirmed by the estimated values of elastic constants. The estimated values of Vickers hardness indicate that TaC is harder than Ta2C. The values of Pugh’s ratio and Poisson’s ratio suggest the brittle nature of both Ta2C and TaC. The optical properties of Ta2C along two polarization directions [001] and [100] are studied in details for the first time. Our study shows that the optical properties of both Ta2C and TaC compounds compliment the electronic structure calculations. Optical constants of Ta2C show significant dependence of the state of polarization of the incident electric field, and predict this material as optically anisotropic.

Most existing studies of the angular momentum evolution of young stellar populations have focused on the youngest (1-3 Myr) T Tauri stars. In contrast, the angular momentum distributions of older T Tauri stars (4-10 Myr) have been less studied, even though they hold key insight to understanding stellar angular momentum evolution at a time when protoplanetary disks have largely dissipated and when models therefore predict changes in the rotational evolution that can in principle be tested. We present a study of photometric variability among 1,974 confirmed T Tauri members of various sub-regions of the Orion OB1 association, and with ages spanning 4-10 Myr, using optical time-series from three different surveys. For 564 of the stars (~32% of the weak-lined T Tauri stars and ~13% of the classical T Tauri stars in our sample) we detect statistically significant periodic variations which we attribute to the stellar rotation periods, making this one of the largest samples of T Tauri star rotation periods yet published. We observe a clear change in the overall rotation period distributions over the age range 4-10 Myr, with the progressively older sub-populations exhibiting systematically faster rotation. This result is consistent with angular momentum evolution model predictions of an important qualitative change in the stellar rotation periods starting at ~5 Myr, an age range for which very few observational constraints were previously available., Accepted for publication in the Astronomical Journal. 16 pages, full appendices will be available in the electronic journal

Astronomers are entering an era of {\mu}as-level astrometry utilizing the 5-decade-old IAU Galactic coordinate system that was only originally defined to $\sim$0{\deg}.1 accuracy, and where the dynamical centre of the Galaxy (Sgr A*) is located $\sim$0{\deg}.07 from the origin. We calculate new independent estimates of the North Galactic Pole (NGP) using recent catalogues of Galactic disc tracer objects such as embedded and open clusters, infrared bubbles, dark clouds, and young massive stars. Using these catalogues, we provide two new estimates of the NGP. Solution 1 is an "unconstrained" NGP determined by the galactic tracer sources, which does not take into account the location of Sgr A*, and which lies 90{\deg}.120$\,\pm\,$0{\deg}.029 from Sgr A*, and Solution 2 is a "constrained" NGP which lies exactly 90{\deg} from Sgr A*. The "unconstrained" NGP has ICRS position: $\alpha_{NGP}$ = 192{\deg}.729 $\,\pm\,$ 0{\deg}.035, $\delta_{NGP}$ = 27{\deg}.084 $\,\pm\,$ 0{\deg}.023 and $\theta\,$ = 122{\deg}.928 $\,\pm\,$ 0{\deg}.016. The "constrained" NGP which lies exactly 90{\deg} away from Sgr A* has ICRS position: $\alpha_{NGP}$ = 192{\deg}.728 $\,\pm\,$0{\deg}.010, $\delta_{NGP}$ = 26{\deg}.863 $\,\pm\,$ 0{\deg}.019 and $\theta\,$ = 122{\deg}.928 $\,\pm\,$ 0{\deg}.016. The difference between the solutions is likely due to the Sun lying above the Galactic midplane. Considering the angular separation between Sgr A* and our unconstrained NGP, and if one adopts the recent estimate of the Galactocentric distance for the Sun of $R_{0}$ = 8.2$\,\pm\,$0.1 kpc, then we estimate that the Sun lies $z_{\odot}$ $\simeq$ 17$\,\pm\,$5 pc above the Galactic midplane. Our value of $z_{\odot}$ is consistent with the true median of 55 previous estimates published over the past century of the Sun's height above the Galactic mid-plane ($z_{\odot}$ $\simeq$ 17$\,\pm\,$2 pc)., Comment: Accepted for publication in the MNRAS. 13 pages, 7 figures

Transparent and highly photoconductive nano-composite ZnO–CdO films were fabricated on glass substrate at 360 °C substrate temperature. X-ray diffraction (XRD) studies indicate that the films are nano-crystalline and contain a combination of hexagonal ZnO and cubic CdO structures. According to scanning electron microscopy (SEM) studies, the surface of the films is found to be rough over large areas favoring photo absorption. From the optical and electrical measurements, it is found that ZnO–CdO composite combines the properties of optical transparency in the visible region with a high electrical conductivity. Based on the characteristics of photoluminescence (PL) and photoconductivity, it seems that Zn/Cd = 3:1 nano-crystalline film is preferable for application as buffer layers in solar cells.

The forthcoming Dark Energy Spectroscopic Instrument (DESI) experiment plans to measure the effects of dark energy on the expansion of the Universe and create a $3$D map of the Universe using galaxies up to $z \sim 1.6$ and QSOs up to $z \sim 3.5$. In order to create this map, DESI will obtain spectroscopic redshifts of over $30$ million objects; among them, a majority are \oii emitting star-forming galaxies known as emission-line galaxies (ELGs). These ELG targets will be pre-selected by drawing a selection region on the $g - r$ vs. $r - z$ colour-colour plot, where high redshift ELGs form a separate locus from the lower redshift ELGs and interlopers. In this paper, we study the efficiency of three ELG target selection algorithms -- the final design report (FDR) cut based on the DEEP2 photometry, Number Density Modelling and Random Forest -- to determine how the combination of these three algorithms can be best used to yield a simple selection boundary that will be best suited to meet DESI's science goals. To do this, we selected $17$ small patches in the DESI footprint where we run the three target selection algorithms to pre-select ELGs based on their photometry. We observed the pre-selected ELGs using the MMT Binospec, which is similar in functionality to the DESI instrument, to obtain their spectroscopic redshifts and fluxes of $1054$ ELGs. By analysing the redshift and fluxing distribution of these galaxies, we find that although NDM performed the best, simple changes in the FDR definition would also yield sufficient performance., Comment: 16 pages, 9 figures, Accepted by the MNRAS on 2020 July 27