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Structural, electronic and magnetic properties of cobalt doped Ten (n = 6, 8, 10, 12) clusters have been reported using first principle calculations. We have observed that addition of cobalt results in change in structures of Te clusters. CoTe10 has low symmetry while binding energy/atom is large compared to other CoTen (n = 6, 8, 12) clusters. From charge density difference it has been observed that transition metal is more electronegative since there is maximum accumulation of charge. CoTe10 cluster is found to have large HOMO-LUMO gap which indicates its energetic stability than other studied clusters. Projected density of states reveal that 3d electrons are responsible for induction of magnetism in Te clusters. Our study shows hybridization between d-states of Co and p-states of Te. Stability of CoTen clusters have been determined from vibrational frequencies. We have also reported the Raman spectra of Co-doped Te clusters. [ABSTRACT FROM AUTHOR]

Systematic density functional theory (DFT) calculations have been performed to explore the interaction energetics, and electronic properties of Te8 cluster adsorbed on the h-BN surface. The interaction of Te8 cluster with BN sheet is due to weak Van-der-Waals forces at a distance of 4.33Å. The h-BN exhibits a wide band gap semiconducting nature with tuneability of band gap from 4.78 to 1.96 eV, with adsorption of Te8 cluster. HOMO-LUMO gap, density of states (DOS), projected density of states (PDOS) plots and electron charge density difference are also reported. [ABSTRACT FROM AUTHOR]

Structural and electronic properties of Tellurium cluster (Ten) and their cations (Ten2+) (n = 6, 8) have been studied theoretically using VASP within generalized gradient approximation. Ground state geometries and higher energy isomers of these clusters have been examined on the basis of total free energy calculations. Lowest energy isomers of neutral clusters are ring like structures whereas the lowest energy isomers of cations are polyhedral cages. HOMO–LUMO gap in cationic clusters is small compared to its neutral clusters. Removal of two electrons from the neutral cluster raises the free energy. Analysis of free energy, HOMO-LUMO gap and density of states (DOS) show that neutral cluster are more stable than their cations. [ABSTRACT FROM AUTHOR]

In the underdoped regime of the cuprate phase diagram, the modified version of the Resonance Valence Bond (RVB) model by Yang, Rice and Zhang (YRZ) captures the strong electronic correlation effects very well as corroborated by the ARPES and many other experiments. However, under a non-equilibrium transport setting, YRZ says nothing about the scattering mechanisms of the charge carriers. In the present investigation we include, in a very simplified way, the scattering of charge carriers due to antiferromagnetic type spin waves (ASW). The effect of ASW excitations on conductivity has been studied by changing combined life times of the included process. It has been found that there is a qualitative change in the conductivity in the right direction. The theoretical conductivity reproduces qualitatively the experimental one. [ABSTRACT FROM AUTHOR]

A review of our recent investigations related to the ac transport properties in the psedogapped state of cuprate high temperature superconductors is presented. For our theoretical calculations we use a phenomenological Green's function proposed by Yang, Rice and Zhang (YRZ). This is based upon the renormalized mean-field theory of the Hubbard model and takes into account the strong electron-electron interaction present in Cuprates. The pseudogap is also taken into account through a proposed self energy. We have tested the form of the Green's function by computing ac conductivity of cuprates and then compared with experimental results. We found agreement between theory and experiment in reproducing the doping evolution of ac conductivity but there is a problem with absolute magnitudes and their frequency dependence. This shows a partial success of the YRZ ansatz. The ways to rectify it are suggested and worked out. [ABSTRACT FROM AUTHOR]

In this paper we have studied the effect of Ag addition on electrical properties of Se80.5Bi1.5Te18-yAgy (y = 1.0, 1.5 and 2.0 at. %) glassy system by using digital picometer (Keithley, model 6487) in the voltage range 0-300V. I-V study reveals that the glassy alloys under study exhibit ohmic behavior at low voltage and non-ohmic at high voltage. The field dependence studies for pellets reveal the ohmic nature of current for voltage less than 60V and non-ohmic nature of current for voltage greater than 60V. At higher voltage, greater than 60V, thermal effects come into plays which result in an increase in electrical conductivity. The d.c. conductivity is found to increase with an increase in Ag content. The conduction mechanism is discussed in terms of Poole-Frenkel conduction mechanism. The linearity of the plots between ln(I) and V1/2 shows that the conduction mechanism in the higher voltage range is of Poole-Frenkel type. [ABSTRACT FROM AUTHOR]

We report the preparation and the optical studies on tellurium rich glasses thin films. The thin films of Se30Te70-x Snx system for x= 0, 1.5, 2.5 and 4.5 glassy alloys prepared by melt quenching technique are deposited on the glass substrate using vacuum thermal evaporation technique. The analysis of absorption spectra in the spectral range 400nm-4000 nm at room temperature obtained from UV-VIS-NIR spectrophotometer [Perkin Elmer Lamda-750] helps us in the optical characterization of the thin films under study. The absorption spectrum fitting method is applied by using the Tauc's model for estimating the optical band gap and the width of the band tail of the thin films. The optical band gap is calculated and is found to decrease with the Sn content. [ABSTRACT FROM AUTHOR]

In the present study, we have investigated the impact of Pb content on the physical parameters in Se-Te-Pb system via average coordination number, constraints, the fraction of floppy modes, cross-linking density, lone pairs electrons, heat of atomization, mean bond energy, cohesive energy and electronegativity. The bulk samples have been prepared by using melt quenching technique. X-ray diffraction pattern of various samples indicates the amorphous nature of investigated glassy alloys. It is observed that average coordination number, average number of constraints and cross-linking density increase with Pb content. However, lone-pair electrons, floppy modes, average heat of atomization, cohesive energy and mean bond energy are found to decrease with Pb atomic percentage. [ABSTRACT FROM AUTHOR]

We investigates the electronic structure and optical properties of Li atom/ion intercalated armchair (6, 6) SiNT. A semiconductor to metallic transition was found for Li atom intercalation, while the band gap reduces considerably in case of Li ion intercalation. A large value of reflection and absorption has been observed for metallic and semiconducting systems. In case of atom intercalation, the system under study shows reflectivity in the infrared (IR) region and behaves as non-absorbing transparent conductors in the visible region. [ABSTRACT FROM AUTHOR]

First principal study of structural and electronic properties of black phosphorene with Si induced quantum dot (QD) has been investigated within density functional theory (DFT). Electronic band structure and corresponding density of states (DOS) show the drastic decrease in band gap in the presence of the quantum dot. A band gap of 1.08 eV in pristine black phosphorene has been reduced to 0.07 eV by creation of a Si induced QD. An induced magnetic moment of 1.2 μB has also been observed for phosphorene containing this quantum dot, a possible way of tailoring properties of black phosphorene. [ABSTRACT FROM AUTHOR]

We report the calorimetric study of amorphous Se30Te70-x Snx alloys for x= 0, 1.5, 2.5, 4.5 in terms of kinetic parameters. The DSC curves recorded at four different heating rates are analyzed to determine the transition temperatures, activation energy, thermal stability, glass forming ability. The crystallization process has been investigated using Kissinger, Matusita, Augis and Bennett, and Gao and Wang models. Various kinetic parameters have been calculated for a better understanding of the growth mechanism. The glass transition temperatures Tg, onset crystallization Tc, peak crystallization Tp, and melting temperature Tm are found to increase with the increase in Sn content. The system under investigation is found to be thermally stable for at lower at% of Sn. The values of parameters HR, Hw, and S indicate that Glass forming ability (GFA) decays with an increase in Sn content. [ABSTRACT FROM AUTHOR]

We report the Plasmon characteristics in stage-1 graphene intercalation compounds (GIC's), using the massless Dirac fermion (MDF) gas approximation. With the discussion of the weak and the strong c-axis coupling at graphene-intercalant hetrojunction plasmon characteristics of GIC's are predicted. We have found a reasonable agreement between our results and the experimental results of Ritsko and Rice. [ABSTRACT FROM AUTHOR]

Using first principles density functional theoretical calculations, the present paper reports a systematic study of phonon dispersion curves in pristine carbon (CNT) and silicon nanotubes (SiNT) having chirality (6,6) in the armchair configuration . Some of the phonon modes are found to have negative frequencies which leads to instability of the systems under study. The number of phonon branches has been found to be thrice as much as the number of atoms. The frequency of the higher optical bands varies from 1690 to 1957 cm-1 for CNT(6,6) while it is 596 to 658 cm-1 for SiNT. [ABSTRACT FROM AUTHOR]

Effect of Sb and Ag addition on the optical constants of SSe80.5Bi1.5Te18-yAy (A = Sb, Ag) and y = 2.0 at. %) thin films, prepared by thermal vacuum evaporation technique, is investigated using Swanepoel method. The optical constants i.e. refractive index (n), film thickness, absorption coefficient and optical energy gap are calculated from the transmission spectra. It has been found that refractive index increases with an increase in Sb or Ag content and the absorption coefficient is also found to increases with increase in optical energy. Whereas the optical band gap decreases with an increase in Sb content and increases with an increase in Ag content. Hence, the present results reveals that the addition of Sb and Ag produce remarkable change on the nonlinear optical properties of the thin film. [ABSTRACT FROM AUTHOR]

First principle calculations based on density functional theory have been used to study the structural, electronic and optical properties of infinite armchair (6,6) silicon nanotube. The cohesive energy of the studied SiNT has been found to be 4.45 eV/atom in comparison to cohesive energy 5.22 eV/atom of its bulk counterpart. Contrary to some published results in literature, the SiNT with (6,6) chirality does not appear to have zero band gap semiconductor since it shows band gap of 0.18 eV. Also the absorption egde of SiNT shifts towards the lower energy as compared to bulk and lies in the infrared region, as a consequence of decrease in dimensionality. [ABSTRACT FROM AUTHOR]

We present the first principles studies of semi-infinite phase engineered MoS2 along zigzag direction. The semiconducting (2H) and semi-metallic (1T’) phases are known to be stable in thin-film MoS2. We described the electronic and structural properties of the infinite array of 1T’/2H/1T’. It has been found that 1T’phase induced semi-metallic character in 2H phase beyond interface but, only Mo atoms in 2H phase domain contribute to the semi-metallic nature and S atoms towards semiconducting state. 1T’/2H/1T’ system can act as a typical n-p-n structure. Also high holes concentration at the interface of Mo layer provides further positive potential barriers. [ABSTRACT FROM AUTHOR]

We present first principal investigations on structural and electronic properties of in-plane phase engineered WSe2 with armchair type interface. The 2H and 1T phases of WSe2, joined along x-direction is a natural metal-semiconductor heterostructure and therefore shows potential for applications in 2D electronics and opto-electronics. The electronic properties transit towards metallic 1T region. No inflections across interface shows negligible mismatch strain which is unlike what has been reported for MoS2. Charge density analysis shows charge accumulation on 1T domain. This can lead to reduction of Schottky barrier heights at the metal-semiconductor junction. STM analysis confirms transition of 1T phase towards distorted 1T’ structure. The present results provide essential insights for nano-devices using 2D hybrid materials. [ABSTRACT FROM AUTHOR]

The dispersion parameters such as single-oscillator energy (E0), dispersive energy (Ed) and static refractive index (n0) of Sb doped quaternary thin films are studied in terms of Wemple-DiDomenico (WDD) single oscillator approach. Optical band gap (Eg) is determined from Tauc's extrapolation method and is found to decrease with an increase in Sb content. Tanaka's relation is found valid for the films under study. [ABSTRACT FROM AUTHOR]

In the present work the effect of Sn doping on the physical properties of, tellurium rich, Se30Te70-xSnx system is studied theoretically. The average coordination number, constraints, lone pair electrons and heat of atomization for Se30Te70-xSnx system are calculated for x = 0,1.5,2.5,5.5 using the well defined relations. The present study shows that the values of lone pair electrons and average single bond energy goes on decreasing with increasing Sn content whereas the average coordination number, constraints and heat of atomization increases with increase in the Sn content. [ABSTRACT FROM AUTHOR]

The effect of Bi on the structural and optical properties of Se82-xBixTe18 glassy alloys is studied, theoretically. Cohesive energy is calculated by using chemical bond approach and is found to decrease with increasing Bi content. Optical band gap of thin films is calculated by Shimakawa's relation. The optical band gap decreases with increase in Bi content. [ABSTRACT FROM AUTHOR]

We present the first principles studies of semi-infinite phase engineered MoS2 along zigzag direction. The semiconducting (2H) and semi-metallic (1T’) phases are known to be stable in thin-film MoS2. We described the electronic and structural properties of the infinite array of 1T’/2H/1T’. It has been found that 1T’phase induced semi-metallic character in 2H phase beyond interface but, only Mo atoms in 2H phase domain contribute to the semi-metallic nature and S atoms towards semiconducting state. 1T’/2H/1T’ system can act as a typical n-p-n structure. Also high holes concentration at the interface of Mo layer provides further positive potential barriers. [ABSTRACT FROM AUTHOR]