A first-principles study of the structural, electronic, optical, and vibrational properties for paramagnetic half-Heusler compound TiIrBi by GGA and GGA

The structural, electronic, optical, and vibrational properties of half-Heusler compound TiIrBi have been investigated by using the Generalized Gradient Approximation (GGA) and GGA plus modified Becke and Johnson (GGA + mBJ) functional within the Density Functional Theory (DFT). The obtained formation enthalpies and energy-volume curves for the three different atomic arrangements (alpha, beta and gamma) show that gamma phase is the most energetically favorable phase. Additionally, among the paramagnetic (PM), ferromagnetic (FM), and antiferromagnetic (AFM) magnetic systems considered for the gamma-phase of this compound, the paramagnetic system is found to be the most stable. The spin-polarized electronic band calculations of the TiIrBi compound demonstrate that this material has a semiconductor nature in both the majority and minority spin channels with the direct bandgap of 0.56 and 0.87 eV using the GGA and GGA + mBJ approach, respectively. The obtained formation enthalpy and phonon dispersion curves for gamma-crystal structure of TiIrBi compound show that this material is both thermodynamically and dynamically stable. We have also examined the optical properties by computing the optical parameters such as real and imaginary parts of the dielectric function, refractive index, extinction coefficient, optical conductivity, and reflectivity of the half-Heusler compound TiIrBi in the photon energy range of 0-16 eV. The collected results indicate that the TiIrBi compound has a direct bandgap semiconductor, which makes it a convenient material for technological applications in optoelectronics

Real Space Visualization of Thermomagnetic Irreversibility within Supercooling and Superheating Spinodals in Mn1.85Co0.15SbMn_{1.85}Co_{0.15}Sb using Scanning Hall Probe Microscopy

Phase coexistence across disorder-broadened and magnetic-field-induced first order antiferromagnetic to ferrimagnetic transition in polycrystalline $Mn_{1.85}Co_{0.15}Sb$ has been studied mesoscopically by Scanning Hall Probe Microscope at 120K and up to 5 Tesla magnetic fields. We have observed hysteresis with varying magnetic field and the evolution of coexisting antiferromagnetic and ferrimagnetic state on mesoscopic length scale. These studies show that the magnetic state of the system at low field depends on the path followed to reach 120 K. The low field magnetic states are mesoscopically different for virgin and second field increasing cycle when 120 K is reached by warming from 5K, but are the same within measurement accuracy when the measuring temperature of 120K is reached from 300K by cooling

Photoluminescence transient study of surface defects in ZnO nanorods grown by chemical bath deposition

Two deep level defects (2.25 and 2.03 eV) associated with oxygen vacancies (V$_o$) were identified in ZnO nanorods (NRs) grown by low cost chemical bath deposition. A transient behaviour in the photoluminescence (PL) intensity of the two V$_o$ states was found to be sensitive to the ambient environment and to NR post-growth treatment. The largest transient was found in samples dried on a hot plate with a PL intensity decay time, in air only, of 23 and 80 s for the 2.25 and 2.03 eV peaks, respectively. Resistance measurements under UV exposure exhibited a transient behaviour in full agreement with the PL transient indicating a clear role of atmospheric O$_2$ on the surface defect states. A model for surface defect transient behaviour due to band bending with respect to the Fermi level is proposed. The results have implications for a variety of sensing and photovoltaic applications of ZnO NRs

Scattering of elastic waves by periodic arrays of spherical bodies

We develop a formalism for the calculation of the frequency band structure of a phononic crystal consisting of non-overlapping elastic spheres, characterized by Lam\'e coefficients which may be complex and frequency dependent, arranged periodically in a host medium with different mass density and Lam\'e coefficients. We view the crystal as a sequence of planes of spheres, parallel to and having the two dimensional periodicity of a given crystallographic plane, and obtain the complex band structure of the infinite crystal associated with this plane. The method allows one to calculate, also, the transmission, reflection, and absorption coefficients for an elastic wave (longitudinal or transverse) incident, at any angle, on a slab of the crystal of finite thickness. We demonstrate the efficiency of the method by applying it to a specific example.Comment: 19 pages, 5 figures, Phys. Rev. B (in press

Single-particle and collective excitations in quantum wires made up of vertically stacked quantum dots: Zero magnetic field

We report on the theoretical investigation of the elementary electronic excitations in a quantum wire made up of vertically stacked self-assembled InAs/GaAs quantum dots. The length scales (of a few nanometers) involved in the experimental setups prompt us to consider an infinitely periodic system of two-dimensionally confined (InAs) quantum dot layers separated by GaAs spacers. The the Bloch functions and the Hermite functions together characterize the whole system. We then make use of the Bohm-Pines' (full) random-phase approximation in order to derive a general nonlocal, dynamic dielectric function. Thus developed theoretical framework is then specified to work within a (lowest miniband and) two-subband model that enables us to scrutinize the single-particle as well as collective responses of the system. We compute and discuss the behavior of the eigenfunctions, band-widths, density of states, Fermi energy, single-particle and collective excitations, and finally size up the importance of studying the inverse dielectric function in relation with the quantum transport phenomena. It is remarkable to notice how the variation in the barrier- and well-widths can allow us to tailor the excitation spectrum in the desired energy range. Given the advantage of the vertically stacked quantum dots over the planar ones and the foreseen applications in the single-electron devices and in the quantum computation, it is quite interesting and important to explore the electronic, optical, and transport phenomena in such systems

Impact of 50% ethanolic extract of Calendula officinalis (flower) on the reproductive function of male albino rats (Rattus norvegicus)

Oral administration to male rats of 200mg kg-1 body weight of an extract of Calendula officinalis flowers every day for 60 days did not cause loss of body weight, but decreased significantly the weight of the testis, epididymis, seminal vesicle and ventral prostate. Sperm motility as well as sperm density were reduced significantly, resulting in 80% loss of fertility.Serum testosterone levels showed highly significant reduction. Total protein and sialic acid in the testis, epididymis, seminal vesicles and ventral prostate decreased significantly, and testicular cholesterol was elevated. All measured haematological parameters were unchanged