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Band Structure (band + structure)
Kinds of Band Structure Terms modified by Band Structure Selected AbstractsChemInform Abstract: Ab initio Calculations of Electronic Band Structure and Charge Densities of Zinc Blende-Type GaN, BN and Their Solid Solution B0.5Ga0.5N.CHEMINFORM, Issue 51 2008Rabah Riane Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a "Full Text" option. The original article is trackable via the "References" option. [source] DFT Study of Effects of Potassium Doping on Band Structure of Crystalline Cuprous AzideCHINESE JOURNAL OF CHEMISTRY, Issue 12 2008Wei-Hua ZHU Abstract The structure and defect formation energies of the K-doped CuN3 were studied using density functional theory within the generalized gradient approximation. The results show that the K-doping breaks the azide symmetry and causes asymmetric atomic displacement. As the K-doping level increases, the band gap of the doped system gradually increases. The K impurity is easily incorporated into the crystal thermodynamically. The Cu vacancy is easily created thermodynamically and the K impurity can serve as nucleation centers for vacancy clustering. Finally the effects of K-doping concentrations on the sensitivity of CuN3 were understood based on electronic structures. [source] ChemInform Abstract: Syntheses, Crystal and Band Structures, and Magnetic and Optical Properties of New CsLnCdTe3 (Ln: La, Pr, Nd, Sm, Gd,Tm, and Lu).CHEMINFORM, Issue 16 2008Yi Liu Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a "Full Text" option. The original article is trackable via the "References" option. [source] Semiempirical electronic structure calculation on Ca and Pb apatitesINTERNATIONAL JOURNAL OF QUANTUM CHEMISTRY, Issue 4 2009Maria Matos Abstract A systematic study is made on the electronic structure of stoichiometric calcium and lead apatites, using the tight binding extended Hückel method (eHT). The aim is to investigate the applicability of the semiempirical theory to study this family of compounds. A10(BO4)6X2 (A = Ca, Pb) apatites, differing by substitutions in the BO4 tetrahedral unit (B = P, As, and V) and X-channel ion (X = OH, Cl), are considered. The calculations show that eHT is suitable to describe basic properties especially concerning trends with atomic substitution and geometry changes. Band structure, Mulliken charge distribution, and bond orders are in good agreement with results of ab initio density functional theory (DFT) found in the literature. Large variations in the optical gap due to vanadium and lead substitutions are newly found. Changes in the anion X-channel affect the optical gap, which is in close agreement with DFT results. Analysis involving subnets are performed to determine the role of halogenic orbitals in the electronic structure of chloroapatites, showing evidence of covalent Cl bonding. It was also found that PbOH bonding in hydroxy-vanadinite Pb10(VO4)6(OH)2, recently synthesized, is weaker than that of CaOH in vanadate Ca10(VO4)6(OH)2. Arsenium is found to be more weakely bound to the O-tetrahedron than phosphorous, although CaO bond is increased with the substitution. We investigate, in addition, the electronic structure of a model system Ca10(AsO4)6(OH)2, obtained from direct As substitution in the vanadate Ca10(VO4)6(OH)2. © 2008 Wiley Periodicals, Inc. Int J Quantum Chem, 2009 [source] Band structure and optical properties of SbSeI: density-functional calculationPHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 10 2007Harun Akkus Abstract The electronic structure and linear optical properties of the ferroelectric semiconductor SbSeI are calculated in the nonpolar phase using the density functional methods in the generalized gradient approximation. The obtained electronic band structure shows that SbSeI has an indirect forbidden gap of 1.65 eV. The linear photon-energy-dependent dielectric functions and some optical functions such as absorption and extinction coefficients, refractive index, energy-loss function, reflectivity and optical conductivity are calculated. Moreover, some important optical parameters such as the effective number of valence electrons and the effective optical dielectric constant are calculated. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Band structure of a harmonically confined electron with an impenetrable boundaryPHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 2 2004W. Hai Abstract We study finite-size effects of the spatially bounded quantum systems exemplified by a single-electron quantum dot with a harmonic potential and an impenetrable boundary. A general solution of the corresponding Schrödinger equation is obtained and the unique special solution for any energy is derived from the normalization and boundary conditions. The classical-mechanically allowable eigenenergies form the continuous spectrum or piecewise continuous bands with the minimum value being much less than the zero point energy of a free harmonic oscillator. As the increase of the confining size, the band widths reduce and the energies finally close to the discrete level of the free oscillator. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Density functional crystal orbital study of cyano-substituted poly(para -phenylene-vinylene) and poly(quinoxaline-vinylene)INTERNATIONAL JOURNAL OF QUANTUM CHEMISTRY, Issue 8 2006F. Bartha Abstract We have calculated the optical and electronic properties of several conjugated organic polymers: poly(p -phenylene-vinylene) (PPV) and its derivatives. Cyano substitutions on the phenylene ring: poly(2,5-dicyano- p -phenylene-vinylene) (2,5-DCN-PPV) and on the vinylene linkage: poly(p -phenylene-7(,8)-(di)cyano-vinylene) are considered. In addition, poly(quinoxaline-vinylene) (PQV) is studied. The infinite isolated quasi-1D chains are treated with periodic boundary conditions, using atomic basis sets. In a comparative study of PPV, some issues regarding the selection of the functionals and basis sets are discussed and excitation energies derived from time-dependent and from ordinary methods are compared. It is concluded that for these polymers the calculations are informative at the B3LYP/6-31G** density functional theory (DFT) level. The absolute values might change with improved methods, but the similarity of the polymers suggests that the relative characterization is adequate. Band structures are communicated along with characteristics of the highest occupied and the lowest unoccupied crystal orbitals (HOCO and LUCO). Electron affinities, ionization potentials, valence and conduction bandwidths, and effective masses at the bandgap are given. © 2006 Wiley Periodicals, Inc. Int J Quantum Chem, 2006 [source] Refractive index dispersion of relaxor ferroelectric 0.9Pb(Zn1/3Nb2/3)O3 -0.1PbTiO3 single crystalCRYSTAL RESEARCH AND TECHNOLOGY, Issue 2 2009Chongjun He Abstract The refractive indices of 0.9Pb(Zn1/3Nb2/3)O3 -0.1PbTiO3 single crystal at different wavelengths have been measured by the minimum deviation method at room temperature, and their dispersion equations are obtained. The parameters connected to the energy band structure are obtained by fitting single-oscillator dispersion equation. Despersion energies are found to take on covalent crystal values. (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Ciliated band structure in planktotrophic and lecithotrophic larvae of Heliocidaris species (Echinodermata: Echinoidea): a demonstration of conservation and changeACTA ZOOLOGICA, Issue 3 2001M. Byrne Abstract The evolution of lecithotrophic (non-feeding) development in sea urchins is associated with reduction or loss of structures found in the planktotrophic (feeding) echinopluteus larvae. Reductions or losses of larval feeding structures include pluteal arms, their supporting skeleton and the ciliated band that borders them. The barrel-shaped lecithotrophic larva of Heliocidaris erythrogramma has, at its posterior end, two or three ciliated band segments comprised of densely packed, elongate cilia. These cilia may be expressions of the epaulettes that would have been present in an ancestral larval form, represented today by the feeding echinopluteus of H. tuberculata. We compared the development and cellular organization of the larval ciliary structures of both Heliocidaris species to assess whether the ciliary bands of H. erythrogramma are expressions of the feeding ciliated band or epaulettes of an echinopluteus. Epaulette development in feeding larvae of H. tuberculata involves separation of specific parts of the ciliated band from the rest of the feeding ciliated band, hyperplastic addition of ciliated cells and hypertrophic growth of the cilia. Like epaulettes, the ciliated bands of H. erythrogramma are composed of long spindle-shaped cells arranged in a cup-shaped collection that bulges into the blastocoel; and these cells have elongated cilia. In their developmental origin and topological arrangement however, the ciliated bands of H. erythrogramma correspond more closely with parts of the pluteal feeding ciliated band than with epaulettes. The larvae of this echinoid appear to develop epaulette-like bands from parts of the original (but reduced) feeding ciliated band. The evolution of development in H. erythrogramma has thus involved both conservation and change in echinopluteal ciliary structures. [source] Building Niobate Nanoparticles with Hexaniobate Lindqvist IonsEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 10 2010Hua Tong Abstract We present a general method to fabricate niobate nanoparticles (NPs) by using hexaniobate Lindqvist ions as niobium source. First, soft-chemical synthesis was adopted to prepare amorphous compound NPs, which subsequently served as parent bodies, affording not only nanoscale size but also optimal compositions and elements for the final annealed nanocrystalline niobates. By this method, a series of nanocrystalline niobates, including MNbO4 (M = In, Ga, Fe), MNb2O6 (M = Ba, Sr, Ni, Cd, Pb), MxFe1,xNbO4 (M = In, Ga), MxNi1,xNb2O6 (M = Ba, Sr), and (AgNb)1,x(SrTi)xO3, were successfully prepared. Experimental results presented herein show that the compositions and components of niobate NPs can be adjusted as desired, markedly influencing the crystal phase, energy band structure, and photocatalytic performance of the niobate NPs. [source] Crossing an Interface: Ferroelectric Control of Tunnel Currents in Magnetic Complex Oxide HeterostructuresADVANCED FUNCTIONAL MATERIALS, Issue 15 2010Michael Hambe Abstract Experimental results on entirely complex oxide ferromagnetic/ferroelectric/ferromagnetic tunnel junctions are presented in which the tunneling magnetoresistance is modified by applying low electric field pulses to the junctions. The experiments indicate that ionic displacements associated with the polarization reversal in the ferroelectric barrier affect the complex band structure at ferromagnetic,ferroelectric interfaces. The results are discussed in the framework of the theoretically predicted magnetoelectric interface effect and may lead to novel multistate memory devices. [source] Conductive Nanostructures of MMX ChainsADVANCED FUNCTIONAL MATERIALS, Issue 9 2010Alejandro Guijarro Abstract Crystals of [Pt2(n -pentylCS2)4I] show a transition from semiconductor to metallic with the increase of the temperature (conductivity is 0.3,1.4,S,·,cm,1 at room temperature) and a second metallic,metallic transition at 330,K, inferred by electrical conductivity measurements. X-ray diffraction studies carried out at different temperatures (100, 298, and 350,K) confirm the presence of three different phases. The valence-ordering of these phases is analyzed using structural, magnetic, and electrical data. Density functional theory calculations allow a further analysis of the band structure derived for each phase. Nanostructures adsorbed on an insulating surface show electrical conductivity. These results suggest that MMX-polymer-based nanowires could be suitable for device applications. [source] Chemical bonding in ternary magnesium hydridesINTERNATIONAL JOURNAL OF QUANTUM CHEMISTRY, Issue 3 2003Emilio Orgaz Abstract The electronic structure of various alkali and alkaline,earth magnesium-based hydrides was investigated in detail. These types of crystalline compounds show MgH4 or MgH6 units ordered within a light-metal framework. We investigated the nature of the chemical bonding in these units by means of quantum chemical calculations of several related clusters. The properties of the charge density of the clusters, within the framework of the theory of atoms in molecules, was analyzed. A further set of computations of the band structure of the solid hydrides was conducted using a state-of the-art density functional-based method and the mechanism of stabilization of the MgH units is discussed. It was found that the properties obtained at the molecular level correlate well with those of the solid crystals, indicating the molecular nature of the extended systems in which the units MgHx, x = 4, 6, are stabilized by means of MgH closed-shell interactions. © 2003 Wiley Periodicals, Inc. Int J Quantum Chem 94: 150,164, 2003 [source] Relativistic effects in the optical response of HgSe by time-dependent density functionals theoryINTERNATIONAL JOURNAL OF QUANTUM CHEMISTRY, Issue 4-5 2001P. L. de Boeij Abstract We treat the dominant relativistic effects in the optical response properties of mercury selenide using time-dependent density functional theory (TDDFT). The scalar relativistic effects have been included within the zeroth-order regular approximation (ZORA) in both the ground-state DFT calculations and in the time-dependent response calculations. Within this approximation the HgSe crystal is found to be a semimetal. In a previous study [J Chem Phys 2001, 114, 1860] we have shown that TDDFT/ZORA can be applied successfully to narrow-gap semiconductors, such as indium antimonide, that become semimetallic within the local density approximation when scalar relativistic effects are included. Results are given for the band structure, the static dielectric constant ,,, and the dielectric function ,(,) of HgSe, and these results are compared with the similar ones for InSb. We find considerably improved results for the dielectric function of HgSe when relativistic effects are included. © 2001 John Wiley & Sons, Inc. Int J Quantum Chem, 2001 [source] Studies of electron transfer dynamics in particle-surface interactionsISRAEL JOURNAL OF CHEMISTRY, Issue 1-2 2005Vladimir A. EsaulovArticle first published online: 10 MAR 2010 A review of recent work on electron transfer processes leading to neutralization of positive ions and formation of negative ions is presented. Experiments were performed on simple jellium-like metal surfaces, transition metals, and specific characteristics of electronic band structure were investigated for some cases, revealing differences in electron transfer processes between surfaces of the same element. It was shown that electronegative adsorbates like oxygen and chlorine provoke strong changes in electron transfer rates, which are akin to promotion and poisoning of reactions at surfaces. The results of experiments on Auger neutralization of He+ ions on Ag surfaces and H, and F, formation on Ag and Pd surfaces are presented and compared with recent theoretical treatments of these processes. The effect of adsorbates is illustrated by the example of chlorine adsorption on silver. Directions where further theoretical effort would considerably advance the understanding of these phenomena are delineated. [source] Dispersion in the Mott insulator UO2: A comparison of photoemission spectroscopy and screened hybrid density functional theory,JOURNAL OF COMPUTATIONAL CHEMISTRY, Issue 13 2008Lindsay E. Roy Abstract We present a comparison between the screened hybrid density functional theory of Heyd, Scuseria, and Enzerhof (HSE06) and high-resolution photoemission (PES) measurement on a single crystal of UO2. Angle-resolved photoemission data show a slight dispersion in the f -orbital derived bands in good agreement with the HSE band structure. The effect of spin-orbit coupling on the HSE band gap has also been calculated and found to be negligible. © 2008 Wiley Periodicals, Inc. J Comput Chem, 2008 [source] A QSO host galaxy and its Ly, emission at z= 6.43,MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 2 2009Tomotsugu Goto ABSTRACT Host galaxies of highest redshift quasi-stellar objects (QSOs) are of interest; they provide us with a valuable opportunity to investigate physics relevant to the starburst,active galactic nuclei (AGN) connection at the earliest epoch of the Universe, with the most luminous black holes. Here, we report an optical detection of an extended structure around a QSO at z= 6.43 in deep z,- and zr -band images of the Subaru/Suprime-Cam. Our target is CFHQS J2329-0301 (z= 6.43), the highest redshift QSO currently known. We have carefully subtracted a point spread function (PSF) constructed using nearby stars from the images. After the PSF (QSO) subtraction, a structure in the z, band extends more than 4 arcsec on the sky (Re= 11 kpc), and, thus, is well resolved (16, detection). The PSF-subtracted zr -band structure is in a similar shape to that in the z, band, but less significant with a 3, detection. In the z, band, a radial profile of the QSO+host shows a clear excess over that of the averaged PSF in 0.8,3 arcsec radius. Since the z, band includes a Ly, emission at z= 6.43, we suggest the z, flux is a mixture of the host (continuum light) and its Ly, emission, whereas the zr -band flux is from the host. Through a SED modelling, we estimate 40 per cent of the PSF-subtracted z,-band light is from the host (continuum) and 60 per cent is from Ly, emission. The absolute magnitude of the host is M1450=,23.9 (cf. M1450=,26.4 for the QSO). A lower limit of the SFR(Ly,) is 1.6 M, yr,1 with stellar mass ranging from 6.2 × 108 to 1.1 × 1010 M, when 100 Myr of age is assumed. The detection shows that a luminous QSO is already harboured by a large, star-forming galaxy in the early Universe only after ,840 Myr after the big bang. The host may be a forming giant galaxy, co-evolving with a super-massive black hole. [source] Synthesis and Comparative Study of Nano-TiO2 Over Degussa P-25 in Disinfection of WaterPHOTOCHEMISTRY & PHOTOBIOLOGY, Issue 3 2010S. Swetha Nanostructured TiO2 crystals were synthesized by gel to crystalline conversion. The crystals obtained were anatase form of titania averaging in 30 nm particles with an intrinsic band gap of 3.1 eV. The photocatalytic behavior was evaluated for the bactericidal effect in water, contaminated with the indicator organism Escherichia coli. The 100% photoinactivation of E. coli was achieved within 60 min with suspended nano-TiO2. The catalytic activity of synthesized nanosample was observed to be 2.6 times more than that of commercial TiO2 sample referred to as Degussa P-25. The photoinactivation of E. coli was tested with irradiation source of different wavelengths to substantiate the influence of particle size and nano crystallinity on electronic band structure. The photoactivity of nano titania enhanced to 1.625 times when the source of irradiation shifted from 360 to 400 nm while Degussa P-25 showed no change. [source] Optical anisotropy of A - and M -plane InN grown on free-standing GaN substratesPHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 5 2010P. Schley Abstract Wurtzite A - and M -plane InN films were grown by molecular beam epitaxy (MBE) on free-standing GaN substrates. Spectroscopic ellipsometry (SE) in the photon energy range from 0.56 up to 15,eV was applied in order to determine the ordinary and extraordinary complex dielectric function (DF) of InN. A distinct optical anisotropy was found over the whole energy range. The extraordinary absorption edge in comparison to the ordinary one is shifted to higher energies confirming previous studies. The investigations in the upper vacuum-ultraviolet (VUV) spectral range (9.5,15,eV) yielded transition energies for four critical points (CPs) of the band structure (BS) which have not been observed so far. [source] Optical properties of InN grown on Si(111) substratePHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 5 2010E. Sakalauskas Abstract A comprehensive characterization of the optical properties of wurtzite InN films grown by molecular beam epitaxy on Si(111) substrates is presented. Two types of films are investigated in this work: InN on AlN/Si(111) and InN on GaN/AlN/Si(111). Their properties are compared to a layer deposited on GaN/sapphire substrate. The dielectric function (DF) is obtained from spectroscopic ellipsometry (SE). The infrared studies yield the plasma frequency and thus the electron density, while the interband absorption is probed between 0.56 and 9.8,eV. For InN grown on Si(111) substrate, the absorption onset is slightly shifted to higher energies with respect to the InN film grown on GaN/sapphire which can be attributed to higher electron concentrations. Despite this, strongly pronounced optical transitions due to critical points of the band structure are found in the high-energy part of the DF. It emphasizes the already promising quality of the InN films on silicon. Band-gap renormalization (BGR), band filling, and strain are taken into account in order to estimate the intrinsic band gap of wurtzite InN. For the InN layers on silicon, we get a band gap between 0.66 and 0.685,eV. [source] Single impurity Anderson model and band anti-crossing in the Ga1,xInx Ny As1,y material systemPHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 1 2008Nikolaos Vogiatzis Abstract The role of the single-N impurity in the GaInNAs system is evaluated using the single impurity Anderson model. The N impurities can act either as scattering resonances or as bound states depending on their energy position. For the former case, using self-energy calculations and Matsubara Green's functions we investigate the nature of the mixed single-N state (energy broadening, shift). The effect of this interaction on the perturbed conduction subbands is also examined. The single impurity Anderson model results in a complex band structure. The real part of the band structure can be directly related to the dispersion obtained with the band anti-crossing model and is in very good agreement. The imaginary bandstructure contains further information about the mixing of the nitrogen state and the conduction band which is not contained within the band anti-crossing model. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Focusing effect of photonic crystal concave lenses made from porous dielectricsPHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 5 2004V. V. Sergentu Abstract In the present paper we show the photonic band structure and transmittance spectra of photonic crystal (PC) consisting of porous dielectric and compare the results with the earlier published. Frequency ranges, where PC can be ascribed an effective index of refraction, are given and approximately indicated on the transmittance spectra. This helps to identify optical elements' properties made of porous dielectric: lenses in our case. The focusing effect of PC concave lens, working in the long wavelength limit and spectral regions with a negative refractive index, is investigated. We prove the good focusing effect of such lenses that can be easily fabricated. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Theoretical resonant Raman spectra of nanotube (7,0) with point defectsPHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 11-12 2009Valentin N. Popov Abstract The Raman spectra of the nanotube (7,0) with point defects (monovacancy, divacancy, and Stone,Wales defect) were simulated in order to derive spectroscopic signatures of defective nanotubes. First, we calculated the electronic band structure and the phonon dispersion of the defective nanotubes using supercells within a non-orthogonal tight-binding model. We found that new optical transitions and Raman-active phonons appeared in comparison with the perfect nanotube. Secondly, we calculated the resonance Raman excitation profile for all Raman-active phonons of the defective nanotubes and simulated their Raman spectra at specific laser excitation energies. The predicted high-intensity Raman lines can be used as spectroscopic signatures of the defective nanotubes. [source] Structural, electronic and optical properties of lead zirconatePHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 11 2008J. Baedi Abstract The structure, the band structure, the total density of states, the dielectric function, the extinction coefficient and the refractive index have been calculated for lead zirconate (PbZrO3) using density functional theory (DFT). The full potential linearized augmented plane wave (FL-LAPW) method was used with the generalized gradient approximation (GGA). Calculations of the optical spectra have been performed for the energy range 0,28 eV. It is shown that the orthorhombic PbZrO3, which is optically negative, exhibits a biaxial birefringence and its refractive index is smallest along the a -axis (na (0) = 2.32, nb (0) = 2.36 and nc (0) = 2.34) which is close to the experimental value. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] The band structure of a layered Hg3TeCl4 crystal formed by energy states of HgCl2 and HgTe crystalsPHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 8 2008M. Sznajder Abstract The ab-initio calculated band structure of a not as yet investigated orthorhombic Hg3TeCl4 crystal (Pbca, D152h) was analyzed by means of the elementary energy-bands concept. It was demonstrated that this band structure originates from that of a layered HgCl2 dielectric deformed by the presence of the HgTe structural elements. Further, it was revealed that the valence band of Hg3TeCl4 is composed of the 8-branch elementary energy bands corresponding to the actual Wyckoff position c (x, y, z) of D152h group that indicates the presence of ionic and covalent contributions to the chemical bonding in the crystal. The existence of Davydov splitting in the 8-branch elementary energy band situated in the low-energy range of the valence band was observed, which is typical for layered crystals with a weak interlayer interaction between translationally nonequivalent structural units. It was shown that the anisotropy of the electron and hole effective masses does not correspond to the macroscopic anisotropy of the crystal and an explanation of this behaviour was proposed. The obtained parameters of the crystal (direct energy gap Eg = 2.49 eV as well as values of the estimated electron effective masses) indicate that it could find an application in optoelectronics. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Low energy quasiparticle dispersion of graphite by angle-resolved photoemission spectroscopyPHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 11 2007A. Grüneis Abstract The low energy electron dispersion in graphite is measured by angle-resolved photoemission spectroscopy. The measured photoemission intensity maxima are compared to a tight-binding calculation of the electronic band structure. We observe a strong trigonal warping of the equi-energy contour which is well reproduced by the calculations. Furthermore we clearly show that the concept of Dirac Fermions breaks down for AB stacked graphite. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Isostructural BaSi2, BaGe2 and SrGe2: electronic and optical propertiesPHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 7 2007D. B. Migas Abstract We have performed a theoretical study of the electronic band structure, density of states, dielectric function and absorption coefficient of isostructural BaSi2, BaGe2 and SrGe2 compounds by means of different ab initio methods. All materials are found to be indirect band-gap semiconductors displaying almost equal dispersion of bands close to the gap region. The energy gaps of 0.83, 0.57 and 0.44 eV are estimated for BaSi2, BaGe2 and SrGe2, respectively. Analysis of the absorption coefficient of BaSi2 in comparison with data for other semiconducting silicides indicates its prospects for a solar cell application. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] A theoretical investigation of ZnOxS1,x alloy band structurePHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 5 2007H. Rozale Abstract We report the properties of ordered ZnOxS1,x alloys calculated in various structures (CuAu,I, Cu3Au, Luzonite and Famatinite) using a first-principles total-energy formalism based on the hybrid full-potential augmented plane-wave plus local orbitals (APW + lo) method, within the local-density approximation (LDA). The calculated band gaps of the alloys are direct and range from 0.49 for O-rich to 1.55 eV for S-rich ZnOxS1,x. The non linear variation of the band gap energy is related to the large electronegativity difference between O and S. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Surface properties of the (001) surface of cubic PbZrO3 and PbTiO3PHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 2 2007*Article first published online: 30 OCT 200, Yuan Xu Wang Abstract The (001) surface of cubic PbZrO3 and PbTiO3 with the PbO and B(Ti or Zr)O2 -terminations has been investigated using a plane wave ultrasoft pseudopotential method within the density functional theory. The results of the grand thermodynamic potential show that only the PbO-terminated surface can exist. The different surface relaxation behavior of the PbO-terminated surface between PbZrO3 and PbTiO3 is mainly due to the larger cell volume of cubic PbZrO3 than cubic PbTiO3. The different surface dipole moments between PbZrO3 and PbTiO3 with both types terminations are discussed. The surface states appear on the band structure of the PbO-terminated surface for cubic PbZrO3. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Magnon energy gap and the magnetically structural symmetry in a three-layer ferrimagnetic superlatticePHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 8 2006Rong-ke Qiu Abstract The magnon energy band in a ferrimagnetic superlattice with three layers in a unit cell is studied by employing retarded Green's functions and the spin-wave method. Two modulated energy gaps ,,13 and ,,23 are evaluated systematically, which exist in the magnon energy band along the Kx -direction perpendicular to the plane of the superlattice. It is revealed that the energy gap ,,13 has a direct relation with the symmetry among the spin quantum numbers and the interlayer exchange couplings, while the energy gap ,,23 relates to the symmetry among these spin quantum numbers only. These symmetries differ from the symmetry of crystallographic point groups. We define the magnetically structural symmetry that is dominated mainly by the magnetic parameters. The absence of the energy gap at a certain condition means that the system has a high magnetically structural symmetry. The magnetically structural symmetry of the superlattice, which is an intrinsic property, strongly affects the magnon energy band structure and thus the magnetic behaviors of the system. Furthermore, two complete bandgaps are observed to extend through the Brillouin zone (referred to as "magnonic crystal") in this superlattice system. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] | |||||||||||||||||||