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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.

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

Transparent and conducting CdO and Cr doped CdO (CdO:Cr) crystalline films were prepared on glass substrate at 350 °C by cost effective spray pyrolysis technique. Structural analysis indicates CdO:Cr films are polycrystalline cubic structure comprises with spherical or semi-spherical nano-scale particles. The direct band gap energy of CdO was found to change with Cr doping. The photoluminescence (PL) spectra of CdO show extended band edge emissions accompanied by red emission originated from different impurity states. The optical dispersion parameters calculated using Wemple–DiDomenico single-oscillator model were found to vary with Cr concentration in CdO. The dispersion energy of oscillator found to decrease with increasing Cr concentration. Simultaneously, the variation of third-order nonlinear susceptibility with photon energy was found to decrease with increasing Cr concentrations. Hall study confirms that CdO and CdO:Cr films are n-type semiconductor having carrier concentration of the order of ∼1019 cm−3. The obtained physical properties of CdO film were improved by Cr doping which make them suitable for optoelectronic applications.

Al/ZnO: Al heterojunction was fabricated by depositing ZnO: Al film on Al substrate by spray pyrolysis technique at 220 °C substrate temperature. XRD, SEM and EDAX techniques were used to study the properties of thin films. Heterojunction properties were studied by I–V and C–V measurements. The fabricated Al/ZnO: Al junctions were rectifying in character. The room temperature ideality factors of Al/ZnO: Al junctions are found to vary from 2.56 to 5.45. The reverse saturation currents are 5.21 × 10−9, 1.35 × 10−6, 1.99 × 10−6, 9.99 × 10−7 and 1.02 × 10−7 A for Al/ZnO: Al junctions. Junction forward current depends on doping concentrations and temperature, whereas reverse saturation current remains independent for Al concentration. The built-in-potential calculated from capacitance for Al/ZnO: Al junctions are 2.74, 2.60, 2.0, 2.50 and 2.43 V corresponding to 1, 2, 3, 4 and 5 mol% of Al. X-ray diffraction study confirmed that the films are polycrystalline, orientated in (0 0 2) plane. Scanning electron microscopy study confirmed circular ring patterns with inside ribbon type structure for Al doped ZnO films.

Using plane-wave pseudopotential density functional theory (DFT), the first-principle calculations are performed to investigate the structural aspects, mechanical behaviors and electronic features of the newly synthesized CaAl2Si2-prototype intermetallic compound, MgAl2Ge2 for the first time and the results are compared with those calculated for its silicide and carbide counterparts MgAl2Si2 and MgAl2C2. The calculated lattice constants agree fairly well with their corresponding experimental values. The estimated elastic tensors satisfy the mechanical stability conditions for MgAl2Ge2 along with MgAl2Si2 and MgAl2C2. The level of elastic anisotropy increases following the sequence of X-elements Ge → Si → C. MgAl2Ge2 and MgAl2Si2 are expected to be ductile and damage tolerant, while MgAl2C2 is a brittle one. MgAl2Ge2 and MgAl2Si2 should exhibit better thermal shock resistance and low thermal conductivity and accordingly these can be used as thermal barrier coating (TBC) materials. The Debye temperature of MgAl2Ge2 is lowest among three intermetallic compounds. MgAl2Ge2 and MgAl2Si2 should exhibit metallic conductivity; while the dual characters of weak-metals and semiconductors are expected for MgAl2C2. The values of theoretical Vickers hardness for MgAl2Ge2, MgAl2Si2, and MgAl2C2 are 3.3, 2.7, and 7.7 GPa, respectively, indicating that these three intermetallics are soft and easily machinable.

Heterojunction diodes of n-ZnO/p-Si (100) and n-ZnO:Al/p-Si (100) were fabricated by spray pyrolysis technique. X-ray diffraction (XRD), energy dispersive x-ray spectroscopy (EDX), and field emission scanning electron microscopy (FESEM) were used to characterize the as-prepared samples. The XRD pattern indicates the hexagonal wurzite structure of zinc oxide (ZnO) and Al-doped ZnO (AZO) thin films grown on Si (100) substrate. The compositional analysis by EDX indicates the presence of Al in the AZO structure. The FESEM image indicates the smooth and compact surface of the heterostructures. The current–voltage characteristics of the heterojunction confirm the rectifying diode behavior at different temperatures and illumination intensities. For low forward bias voltage, the ideality factors were determined to be 1.24 and 1.38 for un-doped and Al-doped heterostructures at room temperature (RT), respectively, which indicates the good diode characteristics. The capacitance–voltage response of the heterojunctions was studied for different oscillation frequencies. From the 1/C 2–V plot, the junction built-in potentials were found 0.30 V and 0.40 V for un-doped and Al-doped junctions at RT, respectively. The differences in built-in potential for different heterojunctions indicate the different interface state densities of the junctions. From the RT photoluminescence (PL) spectrum of the n-ZnO/p-Si (100) heterostructure, an intense main peak at near band edge (NBE) 378 nm (3.28 eV) and weak deep-level emissions (DLE) centered at 436 nm (2.84 eV) and 412 nm (3.00 eV) were observed. The NBE emission is attributed to the radiative recombination of the free and bound excitons and the DLE results from the radiative recombination through deep level defects.

This work illustrates thickness dependent physical properties of copper indium diselenide CuInSe 2 (CIS) thin films fabricated by a novel two stage electron-beam evaporation technique. Structural analysis exhibits CuInSe 2 phase chalcopyrite structure having preferred orientation in the (112) plane. Absorption coefficient of CIS films have been found very high and associated with band-to-band transition. The optical band gap displays a slight variation from 1.80 eV to 1.90 eV depending on film thickness. Photoluminescence (PL) study reveals the presence of acceptor-type defects in the films. Some other important optical constants, such as refractive index, real and imaginary parts of dielectric constant, optical conductivity and energy loss function are also calculated and found dependent on film thickness. Electrical conductivity measurement confirms CIS films are semiconducting in nature and the activation energy values indicate electrical transport is mainly thermally activated. Hall Effect study confirms CIS films are p-type having carrier concentration of the order of ∼10 26 m -3 .

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

Nanorod like crystalline CH3NH3PbI3-xClx thin film was prepared by spray pyrolysis at an ambient atmosphere. X-ray diffraction (XRD) and Raman studies reveal the tetragonal perovskite phase of spray deposited film. The optical band gap of CH3NH3PbI3-xClx is estimated to ~1.64 eV which is consistent with vacuum based deposited perovskites. The CH3NH3PbI3-xClx film exhibits a high absorption coefficient of the order of 106 m−1. Photoluminescence (PL) study suggests that band-to-band radiative recombination occurs in CH3NH3PbI3-xClx film. Cathodoluminescence study confirms the emission of 1.67 eV at 80 K and 1.80 eV at 300 K. In this study, the second harmonic generation at photon energy 3.6 eV is reported for the first time at room temperature (RT). It is noted that the band edge peak position at 1.67 eV is being diffused and shifted to 1.80 eV at RT while the second harmonic peak position at 3.6 eV remains unchanged.

Optical and photo-electrical properties of ZnO–CdO films with the ratio of Zn/Cd=1:0, 3:1, 1:1, 1:3 and 0:1 has been studied. XRD study confirms the combination of hexagonal ZnO and cubic CdO phase present in the polycrystalline sample. Atomic force microscopy results indicate that the crystal grains are agglomerated and surface roughness enhanced due to higher Cd concentration in ZnO. From optical studies, it is found that the transmittance and the band gap decreased as Cd content increased. Photoluminescence studies on ZnO–CdO films showed intense near-band edge emissions at room temperature and is attributed to recombination of excitons localized within band tail states likely caused by non-uniform Cd distribution in ZnO–CdO matrix. The dispersion of refractive index was analyzed by the Wemple–DiDomenico single-oscillator model. The third-order nonlinear polarizability is found high with higher concentration of cadmium at higher photon energies. Some other optical parameters such as dissipation factor, optical conductivity, interband transition strength, surface and volume energy loss have been calculated depending on dielectric constant evaluated from optical data. Finally, photoconductive gain and carrier lifetime have been calculated and found dependent on Zn/Cd ratio.

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

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

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