Thermal recrystallization of physical vapor deposition based germanium thin films on bulk silicon (100)

We demonstrate a simple, low‐cost, and scalable process for obtaining uniform, smooth surfaced, high quality mono‐crystalline germanium (100) thin films on silicon (100). The germanium thin films were deposited on a silicon substrate using plasma‐assisted sputtering based physical vapor deposition. They were crystallized by annealing at various temperatures ranging from 700 °C to 1100 °C. We report that the best quality germanium thin films are obtained above the melting point of germanium (937 °C), thus offering a method for in‐situ Czochralski process. We show well‐behaved high‐κ /metal gate metal–oxide–semiconductor capacitors (MOSCAPs) using this film. (© 2013 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Transfer of radioactivity from soil to vegetation in Rechna Doab,Pakistan

In Rechna Doab, samples of the most common vegetation, perennial grass Desmostachya bipinnata (dab), were collected along with soil samples from 29 sites. Natural radioactivity of ²²⁶Ra, ²³²Th/²²⁸Ac and ⁴⁰K was measured by using high purity germanium-based gamma ray spectrometer. Activity concentration levels of ²²⁶Ra, ²³²Th/²²⁸Ac and ⁴⁰K in soil were found to be 46.8±6.2 (36.0–57.6), 61.4±5.9 (48.2–73.2) and 644.8±73.9 (537.7–868.4) Bq kg^?1 (dry mass), respectively, and those in vegetation were 2.74±1.70 (1.00–6.39), 2.24±0.59 (1.56–2.61) and 172.72±113.37 (53.14–469.24) Bq kg^?1 (dry mass), respectively. The measured values of the activity concentration in vegetation are comparable with some other international data. Calculated soil to vegetation transfer factors of ²²⁶Ra, ²²⁸Ac and ⁴⁰K were 0.06±0.03 (0.02–0.14), 0.04±0.01 (0.03–0.04) and 0.26±0.16 (0.09–0.69). The mean outdoor absorbed dose rate in air for the area under study was determined as 8.22 nGy h^?1 and the mean indoor absorbed dose rate in air was 11.52 nGy h^?1. The total annual effective dose to the general public from the vegetation was found to be (0.02–0.16) mSv, which is below the recommended limit value of 1 mSv y^?1 for the general public. The dab vegetation under study was found to be radiologically safe for the population and environment.     

Luminescence characteristics of K2Ca2(SO4)3:Eu,Tb micro- and nanocrystalline phosphor

K₂Ca₂(SO₄)₃ microcrystalline pure, doped with Eu, Tb and co-doped with Eu, Tb was prepared by solid-state diffusion method. Nanoparticles of these phosphors were also prepared by the chemical co-precipitation method. The formation of the compounds was confirmed by XRD. The particle size was calculated by broadening of the XRD peaks using Scherrer's formula. The particle size of nanocrystalline powder material was approximately found to be around 20 nm. Thermoluminescence and photoluminescence were studied to see the effect of co-doping and particle size. Tb³⁺ co-doping decreases the intensity in the Eu²⁺ doped phosphor due to the energy transfer and multiple de-excitations through various radiative and non-radiative processes. The sensitivity of K₂Ca₂(SO₄)₃:Eu,Tb microcrystalline phosphor was around 15 times more than LiF-TLD 100 and 7 times more than CaSO₄:Dy. A high temperature peak (615 K) was observed in case of the nanoparticles, which was attributed to a particle size induced phase transition. This was confirmed by differential scanning calormetry measurements. The decrease in the sensitivity in case of nanoparticles is attributed to the particle size effect i.e. volume to surface ratio. Theoretical analysis of the glow curves was done by glow curve convolution deconvolution method to calculate trapping parameters of various peaks.     

Harmonic and Intermodulation Performance of Fabry-Perot Intensity Modulator

Abstract

In this article, a mathematical model for the transfer function of the Fabry-Perot intensity modulator is presented. The model, basically a cosine-series function, can be used to obtain closed-form expressions for the amplitudes of the harmonic and intermodulation products of the Fabry-Perot intensity modulator driven by a multi-frequency radio frequency voltage. The special case of a Fabry-Perot intensity modulator driven by an equal-amplitude two-frequency radio frequency voltage is considered in detail, and the results are compared, whenever possible, with previously published experimental and numerically obtained results.     

Absorption intensities for the 4-0 through 7-0 overtone bands of HCl

We have measured the absorption intesities for a number of rotation-vibration lines in the 4-0 through 7-0 overtone bands of HCl utilizing a Fourier transform spectrometer and a 409.6 m path length White cell. Individual line strengths, band strengths, dipole matrix elements, and Herman-Wallis factors are presented.     

Optimal control theory of an age-structured coronavirus disease model and the dynamical analysis of the underlying ordinary differential equation model having constant parameters

This paper addresses the dynamics of COVID-19 using the approach of age-structured modeling. A particular case of the model is presented by taking into account age-free parameters. The sub-model consisting of ordinary differential equations (ODEs) is investigated for possible equilibria, and qualitative aspects of the model are rigorously presented. In order to control the spread of the disease, we considered two age- and time-dependent non-pharmaceutical control measures in the age-structured model, and an optimal control problem using a general maximum principle of Pontryagin type is achieved. Finally, sample simulations are plotted which support our theoretical work.     

First principles investigation of protactinium-based oxide-perovskites for flexible opto electronic devices

The structural,elastic,mechanical,electronic,and optical properties of KPaO_3 and RbPaO_3 compounds are investigated from first-principles calculations by using the WIEN2 k code in the frame of local density approximation(LDA) and generalized gradient approximation(GGA).The calculated ground state quantities,such as lattice constant(α_0),ground state energy(E),bulk modulus(S),and their pressure derivative(B_p) are in reasonable agreement with the present analytical and previous theoretical results and available experimental data.Based on several elastic and mechanical parameters,the structural stability,hardness,stiffness and the brittle and ductile behaviors are discussed,which reveal that protactiniumbased oxide series of perovskites is mechanically stable and possesses weak resistance to shear deformation compared with resistance to unidirectional compression while flexible and covalent behaviors are dominated in them.The analysis of band profile through Trans-Blaha modified Becke-Johnson(TB-mBJ) potential highlights the underestimation of bandgap with traditional density functional theory(DFT) approximation.Specific contribution of electronic states is investigated by means of total and partial density of states and it can be evaluated that both compounds are(Γ-Γ) direct bandgap semiconductors.All fundamental optical properties are analyzed while attention is paid to absorption and reflection spectra to explore extensive absorptions and reflections of these compounds in high frequency regions.The present method represents an influential approach to calculating the whole set of elastic,mechanical,and opto-electronic parameters,which would conduce to the understanding of various physical phenomena and empower the device engineers to implement these materials in flexible opto-electronic applications.     

Effect of annealing on contact performance and electrical properties of p-type high purity germanium single crystal

Van de Pauw Hall measurement is an effective method to characterize the properties of semiconductors, such as bulk concentration, mobility, and resistivity, all of which are used to describe the purity level in the semiconductors. However, the performance of the ohmic contacts has a direct impact on the reliability and accuracy of the results obtained from the Van de Pauw Hall measurement. In the present work, the influences of different annealing techniques on the performance of the InSn ohmic contacts have been investigated using a High Purity Germanium (HPGe) crystal sample. The results show that the preferred annealing condition is at 400 °C for 1 hour, which has provided a significant improvement of the InSn contact quality and microscopic homogenization of the impurities in the HPGe crystal. The carrier concentration, charge mobility, and resistivity of the sample annealed at 400 °C for 1 hour are 5.772×10¹⁰/cm³, 1.883×10⁴× cm²/Vs, and 5.795×10³×Ω?cm at 77 K, respectively.     

Analytical Holographic Superconductor with Backreaction Using AdS 3/CFT 2

The holographic model for a two-dimensional superconductor has been investigated by considering the three-dimensional gravity in the bulk. To find the critical temperature, we used the Sturm–Liouville variational method. Where as the same method is applied for calculating the condensation of the dual operators on the boundary. We included the back reactions on the metric by a combination of the perturbation method of the fields with respect to the small parameter and then applying the variational integrals on the resulting equations of the motion. The critical temperature has been successfully obtained on the backreaction effects, and we showed that it dropped with a rise in the backreaction of the fields, and it makes the condensation harder. We can use our analytical results to support the numerical data which was reported previously.     

Structural, electronic, and optical properties of ZnOl_xSex alloys using first-principles calculations

The structural, electronic, and optical properties of binary ZnO, ZnSe compounds, and their ternary ZnOl_xSex alloys are computed using the accurate full potential linearized augmented plane wave plus local orbital （FP-LAPW ＋ lo） method in the rocksalt （B 1） and zincblende （B3） crystallographic phases. The electronic band structures, fundamental energy band gaps, and densities of states for ZnO1_xSex are evaluated in the range 0 〈 x 〈 1 using Wu-Cohen （WC） generalized gradient approximation （GGA） for the exchange-correlation potential. Our calculated results of lattice parameters and bulk modulus reveal a nonlinear variation for pseudo-binary and their ternary alloys in both phases and show a considerable deviation from Vegard＇s law. It is observed that the predicted lattice parameter and bulk modulus are in good agreement with the available experimental and theoretical data. We establish that the composition dependence of band gap is semi-metallic in B1 phase, while a direct band gap is observed in B3 phase. The calculated density of states is described by taking into account the contribution of Zn 3d, O 2p, and Se 4s, and the optical properties are studied in terms of dielectric functions, refractive index, reflectivity, and energy loss function for the B3 phase and are compared with the available experimental data.