Structural analysis, electronic properties, and band gaps of a graphene nanoribbon: A new 2D materials

Science.gov (United States)

Dass, Devi

2018-03-01

Graphene nanoribbon (GNR), a new 2D carbon nanomaterial, has some unique features and special properties that offer a great potential for interconnect, nanoelectronic devices, optoelectronics, and nanophotonics. This paper reports the structural analysis, electronic properties, and band gaps of a GNR considering different chirality combinations obtained using the pz orbital tight binding model. In structural analysis, the analytical expressions for GNRs have been developed and verified using the simulation for the first time. It has been found that the total number of unit cells and carbon atoms within an overall unit cell and molecular structure of a GNR have been changed with the change in their chirality values which are similar to the values calculated using the developed analytical expressions thus validating both the simulation as well as analytical results. Further, the electronic band structures at different chirality values have been shown for the identification of metallic and semiconductor properties of a GNR. It has been concluded that all zigzag edge GNRs are metallic with very small band gaps range whereas all armchair GNRs show both the metallic and semiconductor nature with very small and high band gaps range. Again, the total number of subbands in each electronic band structure is equal to the total number of carbon atoms present in overall unit cell of the corresponding GNR. The semiconductors GNRs can be used as a channel material in field effect transistor suitable for advanced CMOS technology whereas the metallic GNRs could be used for interconnect.

Amniotic band-like structures | Govender | Obstetrics and ...

African Journals Online (AJOL)

Intra-amniotic band-like structures are seen fairly commonly on routine obstetric scans, especially during the first and second trimesters of pregnancy. It is important to establish the cause for such findings in order to determine their clinical significance and to assess prognosis. The vast majority of band-like structures are ...

Wakefield Band Partitioning in LINAC Structures

International Nuclear Information System (INIS)

Jones, Roger M

2003-01-01

In the NLC project multiple bunches of electrons and positrons will be accelerated initially to a centre of mass of 500 GeV and later to 1 TeV or more. In the process of accelerating 192 bunches within a pulse train, wakefields are excited which kick the trailing bunches off axis and can cause luminosity dilution and BBU (Beam Break Up). Several structures to damp the wakefield have been designed and tested at SLAC and KEK and these have been found to successfully damp the wakefield [1]. However, these 2π/3 structures suffered from electrical breakdown and this has prompted us to explore lower group velocity structures operating at higher fundamental mode phase advances. The wakefield partitioning amongst the bands has been found to change markedly with increased phase advance. Here we report on general trends in the kick factor and associated wakefield band partitioning in dipole bands as a function of phase advance of the synchronous mode in linacs. These results are applicable to both TW (travelling wave) and SW (standing wave) structures

Band-Structure of Thallium by the LMTO Method

DEFF Research Database (Denmark)

Holtham, P. M.; Jan, J. P.; Skriver, Hans Lomholt

1977-01-01

by an energy gap. The 6d and 7s bands were found to be far above the Fermi level and the 5d states were found to be far below it. Fermi surface properties and the electronic specific heat are computed and compared with experiment. The joint density of states has also been computed and is in reasonable...... and p bands for the HCP structure. Energy bands have been evaluated both with and without spin-orbit coupling which is particularly large in thallium. Energy bands close to the Fermi level were found to be mainly 6p like in character. The 6s states lay below the 6p bands and were separated from them......The relativistic band structure of thallium has been calculated using the linear muffin-tin orbital (LMTO) method. The positions and extents of the bands were found to follow the Wigner-Seitz rule approximately, and the origin of the dispersion of the bands was established from the canonical s...

The Marvels of Electromagnetic Band Gap (EBG) Structures

Science.gov (United States)

2003-11-01

terminology of "Electromagnetic conference papers and journal articles dealing with Band- gaps (EBG)". Recently, many researchers the characterizations...Band Gap (EBG) Structures 9 utilized to reduce the mutual coupling between Structures: An FDTD/Prony Technique elements of antenna arrays. based on the...Band- Gap of several patents. He has had pioneering research contributions in diverse areas of electromagnetics,Snteructure", Dymposiget o l 21 IE 48

Band structures in near spherical 138Ce

Science.gov (United States)

Bhattacharjee, T.; Chanda, S.; Bhattacharyya, S.; Basu, S. K.; Bhowmik, R. K.; Das, J. J.; Pramanik, U. Datta; Ghugre, S. S.; Madhavan, N.; Mukherjee, A.; Mukherjee, G.; Muralithar, S.; Singh, R. P.

2009-06-01

The high spin states of N=80138Ce have been populated in the fusion evaporation reaction 130Te( 12C, 4n) 138Ce at E=65 MeV. The γ transitions belonging to various band structures were detected and characterized using an array of five Clover Germanium detectors. The level scheme has been established up to a maximum spin and excitation energy of 23 ℏ and 9511.3 keV, respectively, by including 53 new transitions. The negative parity ΔI=1 band, developed on the 6536.3 keV 15 level, has been conjectured to be a magnetic rotation band following a semiclassical analysis and comparing the systematics of similar bands in the neighboring nuclei. The said band is proposed to have a four quasiparticle configuration of [πgh]⊗[. Other band structures are interpreted in terms of multi-quasiparticle configurations, based on Total Routhian Surface (TRS) calculations. For the low and medium spin states, a shell model calculation using a realistic two body interaction has been performed using the code OXBASH.

High power experimental studies of hybrid photonic band gap accelerator structures

Directory of Open Access Journals (Sweden)

JieXi Zhang

2016-08-01

Full Text Available This paper reports the first high power tests of hybrid photonic band gap (PBG accelerator structures. Three hybrid PBG (HPBG structures were designed, built and tested at 17.14 GHz. Each structure had a triangular lattice array with 60 inner sapphire rods and 24 outer copper rods sandwiched between copper disks. The dielectric PBG band gap map allows the unique feature of overmoded operation in a TM_{02} mode, with suppression of both lower order modes, such as the TM_{11} mode, as well as higher order modes. The use of sapphire rods, which have negligible dielectric loss, required inclusion of the dielectric birefringence in the design. The three structures were designed to sequentially reduce the peak surface electric field. Simulations showed relatively high surface fields at the triple point as well as in any gaps between components in the clamped assembly. The third structure used sapphire rods with small pin extensions at each end and obtained the highest gradient of 19  MV/m, corresponding to a surface electric field of 78  MV/m, with a breakdown probability of 5×10^{-1} per pulse per meter for a 100-ns input power pulse. Operation at a gradient above 20  MV/m led to runaway breakdowns with extensive light emission and eventual damage. For all three structures, multipactor light emission was observed at gradients well below the breakdown threshold. This research indicated that multipactor triggered at the triple point limited the operational gradient of the hybrid structure.

16O+16O molecular nature of the superdeformed band of 32S and the evolution of the molecular structure

International Nuclear Information System (INIS)

Kimura, Masaaki; Horiuchi, Hisashi

2004-01-01

The relation between the superdeformed band of 32 S and 16 O+ 16 O molecular bands is studied by the deformed-basis antisymmetrized molecular dynamics with the Gogny D1S force. It is found that the obtained superdeformed band members of S have a considerable amount of the 16 O+ 16 O component. Above the superdeformed band, we have obtained two excited rotational bands which have more prominent character of the 16 O+ 16 O molecular band. These three rotational bands are regarded as a series of 16 O+ 16 O molecular bands which were predicted by using the unique 16 O- 16 O optical potential. As the excitation energy and principal quantum number of the relative motion increase, the 16 O+ 16 O cluster structure becomes more prominent but at the same time, the band members are fragmented into several states

Band structure of CdTe under high pressure

International Nuclear Information System (INIS)

Jayam, Sr. Gerardin; Nirmala Louis, C.; Amalraj, A.

2005-01-01

The band structures and density of states of cadmium telluride (CdTe) under various pressures ranging from normal to 4.5 Mbar are obtained. The electronic band structure at normal pressure of CdTe (ZnS structure) is analyzed and the direct band gap value is found to be 1.654 eV. CdTe becomes metal and superconductor under high pressure but before that it undergoes structural phase transition from ZnS phase to NaCl phase. The equilibrium lattice constant, bulk modulus and the phase transition pressure at which the compounds undergo structural phase transition from ZnS to NaCl are predicted from the total energy calculations. The density of states at the Fermi level (N(E F )) gets enhanced after metallization, which leads to the superconductivity in CdTe. In our calculation, the metallization pressure (P M = 1.935 Mbar) and the corresponding reduced volume ((V/V 0 ) M = 0.458) are estimated. Metallization occurs via direct closing of band gap at Γ point. (author)

Intrinsic properties of high-spin band structures in triaxial nuclei

Science.gov (United States)

Jehangir, S.; Bhat, G. H.; Sheikh, J. A.; Palit, R.; Ganai, P. A.

2017-12-01

The band structures of 68,70Ge, 128,130,132,134Ce and 132,134,136,138Nd are investigated using the triaxial projected shell model (TPSM) approach. These nuclei depict forking of the ground-state band into several s-bands and in some cases, both the lowest two observed s-bands depict neutron or proton character. It was discussed in our earlier work that this anomalous behaviour can be explained by considering γ-bands based on two-quasiparticle configurations. As the parent band and the γ-band built on it have the same intrinsic structure, g-factors of the two bands are expected to be similar. In the present work, we have undertaken a detailed investigation of g-factors for the excited band structures of the studied nuclei and the available data for a few high-spin states are shown to be in fair agreement with the predicted values.

Band connectivity for topological quantum chemistry: Band structures as a graph theory problem

Science.gov (United States)

Bradlyn, Barry; Elcoro, L.; Vergniory, M. G.; Cano, Jennifer; Wang, Zhijun; Felser, C.; Aroyo, M. I.; Bernevig, B. Andrei

2018-01-01

The conventional theory of solids is well suited to describing band structures locally near isolated points in momentum space, but struggles to capture the full, global picture necessary for understanding topological phenomena. In part of a recent paper [B. Bradlyn et al., Nature (London) 547, 298 (2017), 10.1038/nature23268], we have introduced the way to overcome this difficulty by formulating the problem of sewing together many disconnected local k .p band structures across the Brillouin zone in terms of graph theory. In this paper, we give the details of our full theoretical construction. We show that crystal symmetries strongly constrain the allowed connectivities of energy bands, and we employ graph theoretic techniques such as graph connectivity to enumerate all the solutions to these constraints. The tools of graph theory allow us to identify disconnected groups of bands in these solutions, and so identify topologically distinct insulating phases.

Band structures in Sierpinski triangle fractal porous phononic crystals

International Nuclear Information System (INIS)

Wang, Kai; Liu, Ying; Liang, Tianshu

2016-01-01

In this paper, the band structures in Sierpinski triangle fractal porous phononic crystals (FPPCs) are studied with the aim to clarify the effect of fractal hierarchy on the band structures. Firstly, one kind of FPPCs based on Sierpinski triangle routine is proposed. Then the influence of the porosity on the elastic wave dispersion in Sierpinski triangle FPPCs is investigated. The sensitivity of the band structures to the fractal hierarchy is discussed in detail. The results show that the increase of the hierarchy increases the sensitivity of ABG (Absolute band gap) central frequency to the porosity. But further increase of the fractal hierarchy weakens this sensitivity. On the same hierarchy, wider ABGs could be opened in Sierpinski equilateral triangle FPPC; whilst, a lower ABG could be opened at lower porosity in Sierpinski right-angled isosceles FPPCs. These results will provide a meaningful guidance in tuning band structures in porous phononic crystals by fractal design.

Band structures in Sierpinski triangle fractal porous phononic crystals

Energy Technology Data Exchange (ETDEWEB)

Wang, Kai; Liu, Ying, E-mail: yliu5@bjtu.edu.cn; Liang, Tianshu

2016-10-01

In this paper, the band structures in Sierpinski triangle fractal porous phononic crystals (FPPCs) are studied with the aim to clarify the effect of fractal hierarchy on the band structures. Firstly, one kind of FPPCs based on Sierpinski triangle routine is proposed. Then the influence of the porosity on the elastic wave dispersion in Sierpinski triangle FPPCs is investigated. The sensitivity of the band structures to the fractal hierarchy is discussed in detail. The results show that the increase of the hierarchy increases the sensitivity of ABG (Absolute band gap) central frequency to the porosity. But further increase of the fractal hierarchy weakens this sensitivity. On the same hierarchy, wider ABGs could be opened in Sierpinski equilateral triangle FPPC; whilst, a lower ABG could be opened at lower porosity in Sierpinski right-angled isosceles FPPCs. These results will provide a meaningful guidance in tuning band structures in porous phononic crystals by fractal design.

BAND STRUCTURE OF NON-STEIOCHIOMETRIC LARGE-SIZED NANOCRYSTALLITES

Directory of Open Access Journals (Sweden)

I.V.Kityk

2004-01-01

Full Text Available A band structure of large-sized (from 20 to 35nm non-steichiometric nanocrystallites (NC of the Si2-xCx (1.04 < x < 1.10 has been investigated using different band energy approaches and a modified Car-Parinello molecular dynamics structure optimization of the NC interfaces. The non-steichiometric excess of carbon favors the appearance of a thin prevailingly carbon-contained layer (with thickness of about 1 nm covering the crystallites. As a consequence, one can observe a substantial structure reconstruction of boundary SiC crystalline layers. The numerical modeling has shown that these NC can be considered as SiC reconstructed crystalline films with thickness of about 2 nm covering the SiC crystallites. The observed data are considered within the different one-electron band structure methods. It was shown that the nano-sized carbon sheet plays a key role in a modified band structure. Independent manifestation of the important role played by the reconstructed confined layers is due to the experimentally discovered excitonic-like resonances. Low-temperature absorption measurements confirm the existence of sharp-like absorption resonances originating from the reconstructed layers.

Band Structure Characteristics of Nacreous Composite Materials with Various Defects

Science.gov (United States)

Yin, J.; Zhang, S.; Zhang, H. W.; Chen, B. S.

2016-06-01

Nacreous composite materials have excellent mechanical properties, such as high strength, high toughness, and wide phononic band gap. In order to research band structure characteristics of nacreous composite materials with various defects, supercell models with the Brick-and-Mortar microstructure are considered. An efficient multi-level substructure algorithm is employed to discuss the band structure. Furthermore, two common systems with point and line defects and varied material parameters are discussed. In addition, band structures concerning straight and deflected crack defects are calculated by changing the shear modulus of the mortar. Finally, the sensitivity of band structures to the random material distribution is presented by considering different volume ratios of the brick. The results reveal that the first band gap of a nacreous composite material is insensitive to defects under certain conditions. It will be of great value to the design and synthesis of new nacreous composite materials for better dynamic properties.

Analysis on X-band structure breakdown at GLCTA

International Nuclear Information System (INIS)

Suehara, T.; Sanuki, T.; Komamiya, S.; Higo, T.; Hayano, H.; Terunuma, N.; Saeki, T.; Watanabe, K.; Hayakawa, A.; Tsukada, Y.

2004-01-01

We have built a new monitoring system for accelerator structure breakdown in the X-band high-gradient test facility at KEK (GLCTA: Global Linear Collider Test Accelerator). An X-band test structure KX01 (made by KEK) has been processed at GLCTA and we have been collecting data for about 3 months using this breakdown monitoring system. We describe overview of the monitoring system and preliminary result of breakdown analysis of the structure. (author)

Maximizing band gaps in plate structures

DEFF Research Database (Denmark)

Halkjær, Søren; Sigmund, Ole; Jensen, Jakob Søndergaard

2006-01-01

periodic plate using Bloch theory, which conveniently reduces the maximization problem to that of a single base cell. Secondly, we construct a finite periodic plate using a number of the optimized base cells in a postprocessed version. The dynamic properties of the finite plate are investigated......Band gaps, i.e., frequency ranges in which waves cannot propagate, can be found in elastic structures for which there is a certain periodic modulation of the material properties or structure. In this paper, we maximize the band gap size for bending waves in a Mindlin plate. We analyze an infinite...... theoretically and experimentally and the issue of finite size effects is addressed....

Electronic band structure of lithium, sodium and potassium fluorides

International Nuclear Information System (INIS)

Jouanin, C.; Albert, J.P.; Gout, C.

1975-01-01

A mixed tight-binding, pseudopotential method is proposed to calculate the energy band structure of large-gap crystals and is tested here on LiF, NaF and KF. Three-centre terms are included in the determination of the valence bands by the tight-binding method and for the conduction bands we use a pseudopotential model proposed by Bassani and Giuliano, modified for the positive ions. By taking into account the polarization corrections, transitions calculated from the energy band structures are compared with experimental data and the agreement is generally good

Band structure analysis in SiGe nanowires

Energy Technology Data Exchange (ETDEWEB)

Amato, Michele [' Centro S3' , CNR-Istituto Nanoscienze, via Campi 213/A, 41100 Modena (Italy); Dipartimento di Scienze e Metodi dell' Ingegneria, Universita di Modena e Reggio Emilia, via Amendola 2 Pad. Morselli, I-42100 Reggio Emilia (Italy); Palummo, Maurizia [European Theoretical Spectroscopy Facility (ETSF) (Italy); CNR-INFM-SMC, Dipartimento di Fisica, Universita di Roma, ' Tor Vergata' , via della Ricerca Scientifica 1, 00133 Roma (Italy); Ossicini, Stefano, E-mail: stefano.ossicini@unimore.it [' Centro S3' , CNR-Istituto Nanoscienze, via Campi 213/A, 41100 Modena (Italy) and Dipartimento di Scienze e Metodi dell' Ingegneria, Universita di Modena e Reggio Emilia, via Amendola 2 Pad. Morselli, I-42100 Reggio Emilia (Italy) and European Theoretical Spectroscopy Facility - ETSF (Italy) and Centro Interdipartimentale ' En and Tech' , Universita di Modena e Reggio Emilia, via Amendola 2 Pad. Morselli, I-42100 Reggio Emilia (Italy)

2012-06-05

One of the main challenges for Silicon-Germanium nanowires (SiGe NWs) electronics is the possibility to modulate and engine their electronic properties in an easy way, in order to obtain a material with the desired electronic features. Diameter and composition constitute two crucial ways for the modification of the band gap and of the band structure of SiGe NWs. Within the framework of density functional theory we present results of ab initio calculations regarding the band structure dependence of SiGe NWs on diameter and composition. We point out the main differences with respect to the case of pure Si and Ge wires and we discuss the particular features of SiGe NWs that are useful for future technological applications.

Band structure analysis in SiGe nanowires

International Nuclear Information System (INIS)

Amato, Michele; Palummo, Maurizia; Ossicini, Stefano

2012-01-01

One of the main challenges for Silicon-Germanium nanowires (SiGe NWs) electronics is the possibility to modulate and engine their electronic properties in an easy way, in order to obtain a material with the desired electronic features. Diameter and composition constitute two crucial ways for the modification of the band gap and of the band structure of SiGe NWs. Within the framework of density functional theory we present results of ab initio calculations regarding the band structure dependence of SiGe NWs on diameter and composition. We point out the main differences with respect to the case of pure Si and Ge wires and we discuss the particular features of SiGe NWs that are useful for future technological applications.

Border Structure of Intercalary Heterochromatin Bands of Drosophila melanogaster Polytene Chromosomes.

Science.gov (United States)

Khoroshko, V A; Zykova, T Yu; Popova, O O; Zhimulev, I F

2018-03-01

The precise genomic localization of the borders of 62 intercalary heterochromatin bands in Drosophila polytene chromosomes was determined. A new type of bands containing chromatin of different states was identified. This type is a combination of the gray band and the intercalary heterochromatin band, creating a genetic structure that with a light microscope is identified as a continuous band. The border structure of such bands includes the coding regions of genes with ubiquitous activity.

Effect of correlation on the band structure of α-cerium

International Nuclear Information System (INIS)

Rao, R.S.; Singh, R.P.

1975-01-01

The electronic band structure of f.c.c. phase of the rare earth metal cerium (α-cerium) has been calculated using a formulation of the crystal potential where correlation also has been included in addition to exchange. The Green's function method of Korringa-Kohn and Rostoker has been used due to obvious advantages in calculation. The calculations indicate that the s-d bands are hybridized with the f-levels but the f-bands are fairly narrow and lie slightly above the Fermi level. The structure of the bands is qualitatively similar to those of calculations by others except for a general shift of the entire set of bands by about 0.1 Ryd. Thd density of states has also been calculated from the bands obtained. The spin susceptibility of α-cerium has also been calculated using the Kohn-Sham method. However, the calculated additional contributions to the band structure values cannot still explain the large experimental values reported in the literature. (author)

The cellular approach to band structure calculations

International Nuclear Information System (INIS)

Verwoerd, W.S.

1982-01-01

A short introduction to the cellular approach in band structure calculations is given. The linear cellular approach and its potantial applicability in surface structure calculations is given some consideration in particular

Electronic band structure

International Nuclear Information System (INIS)

Grosso, G.

1986-01-01

The aim of this chapter is to present, in detail, some theoretical methods used to calculate electronic band structures in crystals. The basic strategies employed to attack the problem of electronic-structure calculations are presented. Successive sections present the basic formulations of the tight-binding, orthogonalized-plane-wave, Green'sfunction, and pseudopotential methods with a discussion of their application to perfect solids. Exemplifications in the case of a few selected problems provide further insight by the author into the physical aspects of the different methods and are a guide to the use of their mathematical techniques. A discussion is offered of completely a priori Hartree-Fock calculations and attempts to extend them. Special aspects of the different methods are also discussed in light of recently published related work

Novel structural flexibility identification in narrow frequency bands

International Nuclear Information System (INIS)

Zhang, J; Moon, F L

2012-01-01

A ‘Sub-PolyMAX’ method is proposed in this paper not only for estimating modal parameters, but also for identifying structural flexibility by processing the impact test data in narrow frequency bands. The traditional PolyMAX method obtains denominator polynomial coefficients by minimizing the least square (LS) errors of frequency response function (FRF) estimates over the whole frequency range, but FRF peaks in different structural modes may have different levels of magnitude, which leads to the modal parameters identified for the modes with small FRF peaks being inaccurate. In contrast, the proposed Sub-PolyMAX method implements the LS solver in each subspace of the whole frequency range separately; thus the results identified from a narrow frequency band are not affected by FRF data in other frequency bands. In performing structural identification in narrow frequency bands, not in the whole frequency space, the proposed method has the following merits: (1) it produces accurate modal parameters, even for the modes with very small FRF peaks; (2) it significantly reduces computation cost by reducing the number of frequency lines and the model order in each LS implementation; (3) it accurately identifies structural flexibility from impact test data, from which structural deflection under any static load can be predicted. Numerical and laboratory examples are investigated to verify the effectiveness of the proposed method. (paper)

Optimum design of band-gap beam structures

DEFF Research Database (Denmark)

Olhoff, Niels; Niu, Bin; Cheng, Gengdong

2012-01-01

The design of band-gap structures receives increasing attention for many applications in mitigation of undesirable vibration and noise emission levels. A band-gap structure usually consists of a periodic distribution of elastic materials or segments, where the propagation of waves is impeded...... or significantly suppressed for a range of external excitation frequencies. Maximization of the band-gap is therefore an obvious objective for optimum design. This problem is sometimes formulated by optimizing a parameterized design model which assumes multiple periodicity in the design. However, it is shown...... in the present paper that such an a priori assumption is not necessary since, in general, just the maximization of the gap between two consecutive natural frequencies leads to significant design periodicity. The aim of this paper is to maximize frequency gaps by shape optimization of transversely vibrating...

Development of Electromagnetic Band Gap Structures in the Perspective of Microstrip Antenna Design

Directory of Open Access Journals (Sweden)

Md. Shahidul Alam

2013-01-01

Full Text Available Electromagnetic band gap (EBG technology has become a significant breakthrough in the radio frequency (RF and microwave applications due to their unique band gap characteristics at certain frequency ranges. Since 1999, the EBG structures have been investigated for improving performances of numerous RF and microwave devices utilizing the surface wave suppression and the artificial magnetic conductor (AMC properties of these special type metamaterial. Issues such as compactness, wide bandwidth with low attenuation level, tunability, and suitability with planar circuitry all play an important role in the design of EBG structures. Remarkable efforts have been undertaken for the development of EBG structures to be compatible with a wide range of wireless communication systems. This paper provides a comprehensive review on various EBG structures such as three-, two-, and one-dimensional (3D, 2D, and 1D EBG, mushroom and uniplanar EBG, and their successive advancement. Considering the related fabrication complexities, implementation of vialess EBG is an attractive topic for microwave engineers. For microstrip antennas, EBG structures are used in diversified ways, which of course found to be effective except in some cases. The EBG structures are also successfully utilized in antenna arrays for reducing the mutual coupling between elements of the array. Current challenges and limitations of the typical microstrip antennas and different EBG structures are discussed in details with some possible suggestions. Hopefully, this survey will guide to increasing efforts towards the development of more compact, wideband, and high-efficient uniplanar EBG structures for performance enhancement of antenna and other microwave devices.

Phononic band gap structures as optimal designs

DEFF Research Database (Denmark)

Jensen, Jakob Søndergaard; Sigmund, Ole

2003-01-01

In this paper we use topology optimization to design phononic band gap structures. We consider 2D structures subjected to periodic loading and obtain the distribution of two materials with high contrast in material properties that gives the minimal vibrational response of the structure. Both in...

Design of an X-band accelerating structure using a newly developed structural optimization procedure

Energy Technology Data Exchange (ETDEWEB)

Huang, Xiaoxia [Shanghai Institute of Applied Physics, Chinese Academy of Sciences, Shanghai 201800 (China); University of Chinese Academy of Sciences, Beijing 100049 (China); Fang, Wencheng; Gu, Qiang [Shanghai Institute of Applied Physics, Chinese Academy of Sciences, Shanghai 201800 (China); Zhao, Zhentang, E-mail: zhaozhentang@sinap.ac.cn [Shanghai Institute of Applied Physics, Chinese Academy of Sciences, Shanghai 201800 (China); University of Chinese Academy of Sciences, Beijing 100049 (China)

2017-05-11

An X-band high gradient accelerating structure is a challenging technology for implementation in advanced electron linear accelerator facilities. The present work discusses the design of an X-band accelerating structure for dedicated application to a compact hard X-ray free electron laser facility at the Shanghai Institute of Applied Physics, and numerous design optimizations are conducted with consideration for radio frequency (RF) breakdown, RF efficiency, short-range wakefields, and dipole/quadrupole field modes, to ensure good beam quality and a high accelerating gradient. The designed X-band accelerating structure is a constant gradient structure with a 4π/5 operating mode and input and output dual-feed couplers in a racetrack shape. The design process employs a newly developed effective optimization procedure for optimization of the X-band accelerating structure. In addition, the specific design of couplers providing high beam quality by eliminating dipole field components and reducing quadrupole field components is discussed in detail.

Band structure of superlattice with δ-like potential

International Nuclear Information System (INIS)

Gashimzade, N.F.; Gashimzade, F.M.; Hajiev, A.T.

1993-08-01

Band structure of superlattice with δ-like potential has been calculated taking into account interaction of carriers of different kinds. Superlattices of semiconductors with degenerated valence band and zero-gap semiconductors have been considered. For the latter semimetal-semiconductor transition has been obtained. (author). 8 refs, 1 fig

Band structural properties of MoS2 (molybdenite)

International Nuclear Information System (INIS)

Gupta, V.P.

1980-01-01

Semiconductivity and superconductivity in MoS 2 (molybdenite) can be understood in terms of the band structure of MoS 2 . The band structural properties of MoS 2 are presented here. The energy dependence of nsub(eff) and epsilon(infinity)sub(eff) is investigated. Using calculated values of nsub(eff) and epsilon(infinity)sub(eff), the Penn gap has been determined. The value thus obtained is shown to be in good agreement with the reflectivity data and also with the value obtained from the band structure. The Ravindra and Srivastava formula has been shown to give values for the isobaric temperature gradient of Esub(G)[(deltaEsub(G)/deltaT)sub(P)], which are in agreement with the experimental data, and the contribution to (deltaEsub(G)/deltaT)sub(P) due to the electron lattice interaction has been evaluated. In addition, the electronic polarizability has been calculated using a modified Lorentz-Lorenz relation. (author)

Ab-initio electronic band structure calculations for beryllium chalcogenides

International Nuclear Information System (INIS)

Kalpana, G.; Pari, G.; Yousuf, Mohammad

1997-01-01

The first principle tight-binding linear muffin-tin orbital method within the local density approximation (LDA) has been used to calculate the ground state properties, structural phase transition and pressure dependence of band gap of BeS, BeSe and BeTe. We have calculated the energy-volume relations for these compounds in the B3 and B8 phases. The calculated lattice parameters, bulk modulus and the pressure-volume relation were found to be in good agreement with the recent experimental results. The calculated B3→B8 structural transition pressure for BeS, BeSe and BeTe agree well with the recent experimental results. Our calculations show that these compounds are indirect band gap (Γ-X) semiconductors at ambient conditions. The calculated band gap values are found to be underestimated by 20-30% which is due to the usage of LDA. After the structural transition to the B8 phase, BeS continues to be indirect band gap semiconductors and ultimately above 100 GPa it metallises, BeSe and BeTe are metallic at the B3→B8 structural transition. (author)

Measuring the band structures of periodic beams using the wave superposition method

Science.gov (United States)

Junyi, L.; Ruffini, V.; Balint, D.

2016-11-01

Phononic crystals and elastic metamaterials are artificially engineered periodic structures that have several interesting properties, such as negative effective stiffness in certain frequency ranges. An interesting property of phononic crystals and elastic metamaterials is the presence of band gaps, which are bands of frequencies where elastic waves cannot propagate. The presence of band gaps gives this class of materials the potential to be used as vibration isolators. In many studies, the band structures were used to evaluate the band gaps. The presence of band gaps in a finite structure is commonly validated by measuring the frequency response as there are no direct methods of measuring the band structures. In this study, an experiment was conducted to determine the band structure of one dimension phononic crystals with two wave modes, such as a bi-material beam, using the frequency response at only 6 points to validate the wave superposition method (WSM) introduced in a previous study. A bi-material beam and an aluminium beam with varying geometry were studied. The experiment was performed by hanging the beams freely, exciting one end of the beams, and measuring the acceleration at consecutive unit cells. The measured transfer function of the beams agrees with the analytical solutions but minor discrepancies. The band structure was then determined using WSM and the band structure of one set of the waves was found to agree well with the analytical solutions. The measurements taken for the other set of waves, which are the evanescent waves in the bi-material beams, were inaccurate and noisy. The transfer functions at additional points of one of the beams were calculated from the measured band structure using WSM. The calculated transfer function agrees with the measured results except at the frequencies where the band structure was inaccurate. Lastly, a study of the potential sources of errors was also conducted using finite element modelling and the errors in

Photonic band edge assisted spontaneous emission enhancement from all Er3+ 1-D photonic band gap structure

Science.gov (United States)

Chiasera, A.; Meroni, C.; Varas, S.; Valligatla, S.; Scotognella, F.; Boucher, Y. G.; Lukowiak, A.; Zur, L.; Righini, G. C.; Ferrari, M.

2018-06-01

All Er3+ doped dielectric 1-D Photonic Band Gap Structure was fabricated by rf-sputtering technique. The structure was constituted by of twenty pairs of SiO2/TiO2 alternated layers doped with Er3+ ions. The scanning electron microscopy was used to check the morphology of the structure. Transmission measurements put in evidence the stop band in the range 1500 nm-1950 nm. The photoluminescence measurements were obtained by optically exciting the sample and detecting the emitted light in the 1.5 μm region at different detection angles. Luminescence spectra and luminescence decay curves put in evidence that the presence of the stop band modify the emission features of the Er3+ ions.

Mid-frequency Band Dynamics of Large Space Structures

Science.gov (United States)

Coppolino, Robert N.; Adams, Douglas S.

2004-01-01

High and low intensity dynamic environments experienced by a spacecraft during launch and on-orbit operations, respectively, induce structural loads and motions, which are difficult to reliably predict. Structural dynamics in low- and mid-frequency bands are sensitive to component interface uncertainty and non-linearity as evidenced in laboratory testing and flight operations. Analytical tools for prediction of linear system response are not necessarily adequate for reliable prediction of mid-frequency band dynamics and analysis of measured laboratory and flight data. A new MATLAB toolbox, designed to address the key challenges of mid-frequency band dynamics, is introduced in this paper. Finite-element models of major subassemblies are defined following rational frequency-wavelength guidelines. For computational efficiency, these subassemblies are described as linear, component mode models. The complete structural system model is composed of component mode subassemblies and linear or non-linear joint descriptions. Computation and display of structural dynamic responses are accomplished employing well-established, stable numerical methods, modern signal processing procedures and descriptive graphical tools. Parametric sensitivity and Monte-Carlo based system identification tools are used to reconcile models with experimental data and investigate the effects of uncertainties. Models and dynamic responses are exported for employment in applications, such as detailed structural integrity and mechanical-optical-control performance analyses.

Characterization of band structure for transverse acoustic phonons in Fibonacci superlattices by a bandedge formalism

International Nuclear Information System (INIS)

Hsueh, W J; Chen, R F; Tang, K Y

2008-01-01

We present a divergence-free method to determine the characteristics of band structures and projected band structures of transverse acoustic phonons in Fibonacci superlattices. A set of bandedge equations is formulated to solve the band structures for the phonon instead of using the traditional dispersion relation. Numerical calculations show band structures calculated by the present method for the Fibonacci superlattice without numerical instability, which may occur in traditional methods. Based on the present formalism, the band structure for the acoustic phonons has been characterized by closure points and the projected bandgaps of the forbidden bands. The projected bandgaps are determined by the projected band structure, which is characterized by the cross points of the projected bandedges. We observed that the band structure and projected band structure and their characteristics were quite different for different generation orders and the basic layers for the Fibonacci superlattice. In this study, concise rules to determine these characteristics of the band structure and the projected band structure, including the number and the location of closure points of forbidden bands and those of projected bandgaps, in Fibonacci superlattices with arbitrary generation order and basic layers are proposed.

Fluctuation diamagnetism in two-band superconductors

Science.gov (United States)

Adachi, Kyosuke; Ikeda, Ryusuke

2016-04-01

Anomalously large fluctuation diamagnetism around the superconducting critical temperature has been recently observed in iron selenide (FeSe) [Kasahara et al. (unpublished)]. This indicates that superconducting fluctuations (SCFs) play a more significant role in FeSe, which supposedly has a two-band structure, than in the familiar single-band superconductors. Motivated by the data on FeSe, SCF-induced diamagnetism is examined in a two-band system, on the basis of a phenomenological approach with a Ginzburg-Landau functional. The obtained results indicate that the SCF-induced diamagnetism may be more enhanced than that in a single-band system due to the existence of two distinct fluctuation modes. Such enhancement of diamagnetism unique to a two-band system seems consistent with the large diamagnetism observed in FeSe, though still far from a quantitative agreement.

Polarization-dependent diffraction in all-dielectric, twisted-band structures

Energy Technology Data Exchange (ETDEWEB)

Kardaś, Tomasz M.; Jagodnicka, Anna; Wasylczyk, Piotr, E-mail: pwasylcz@fuw.edu.pl [Photonic Nanostructure Facility, Institute of Experimental Physics, Faculty of Physics, University of Warsaw, Pasteura 5, 02-093 Warszawa (Poland)

2015-11-23

We propose a concept for light polarization management: polarization-dependent diffraction in all-dielectric microstructures. Numerical simulations of light propagation show that with an appropriately configured array of twisted bands, such structures may exhibit zero birefringence and at the same time diffract two circular polarizations with different efficiencies. Non-birefringent structures as thin as 3 μm have a significant difference in diffraction efficiency for left- and right-hand circular polarizations. We identify the structural parameters of such twisted-band matrices for optimum performance as circular polarizers.

Phononic Band Gaps in 2D Quadratic and 3D Cubic Cellular Structures.

Science.gov (United States)

Warmuth, Franziska; Körner, Carolin

2015-12-02

The static and dynamic mechanical behaviour of cellular materials can be designed by the architecture of the underlying unit cell. In this paper, the phononic band structure of 2D and 3D cellular structures is investigated. It is shown how the geometry of the unit cell influences the band structure and eventually leads to full band gaps. The mechanism leading to full band gaps is elucidated. Based on this knowledge, a 3D cellular structure with a broad full band gap is identified. Furthermore, the dependence of the width of the gap on the geometry parameters of the unit cell is presented.

Quasiparticle band structure of rocksalt-CdO determined using maximally localized Wannier functions.

Science.gov (United States)

Dixit, H; Lamoen, D; Partoens, B

2013-01-23

CdO in the rocksalt structure is an indirect band gap semiconductor. Thus, in order to determine its band gap one needs to calculate the complete band structure. However, in practice, the exact evaluation of the quasiparticle band structure for the large number of k-points which constitute the different symmetry lines in the Brillouin zone can be an extremely demanding task compared to the standard density functional theory (DFT) calculation. In this paper we report the full quasiparticle band structure of CdO using a plane-wave pseudopotential approach. In order to reduce the computational effort and time, we make use of maximally localized Wannier functions (MLWFs). The MLWFs offer a highly accurate method for interpolation of the DFT or GW band structure from a coarse k-point mesh in the irreducible Brillouin zone, resulting in a much reduced computational effort. The present paper discusses the technical details of the scheme along with the results obtained for the quasiparticle band gap and the electron effective mass.

Systematic design of phononic band-gap materials and structures by topology optimization

DEFF Research Database (Denmark)

Sigmund, Ole; Jensen, Jakob Søndergaard

2003-01-01

Phononic band-gap materials prevent elastic waves in certain frequency ranges from propagating, and they may therefore be used to generate frequency filters, as beam splitters, as sound or vibration protection devices, or as waveguides. In this work we show how topology optimization can be used...... to design and optimize periodic materials and structures exhibiting phononic band gaps. Firstly, we optimize infinitely periodic band-gap materials by maximizing the relative size of the band gaps. Then, finite structures subjected to periodic loading are optimized in order to either minimize the structural...

Deformed configurations, band structures and spectroscopic ...

Indian Academy of Sciences (India)

2014-03-20

Mar 20, 2014 ... The deformed configurations and rotational band structures in =50 Ge and Se nuclei are studied by deformed Hartree–Fock with quadrupole constraint and angular momentum projection. Apart from the `almost' spherical HF solution, a well-deformed configuration occurs at low excitation. A deformed ...

Investigation on cored-eutectic structure in Ni60/WC composite coatings fabricated by wide-band laser cladding

Energy Technology Data Exchange (ETDEWEB)

Ma, Qunshuang, E-mail: maqunshuang@126.com; Li, Yajiang, E-mail: yajli@sdu.edu.cn; Wang, Juan, E-mail: jwang@sdu.edu.cn; Liu, Kun, E-mail: liu_kun@163.com

2015-10-05

Highlights: • Perfect composite coatings were fabricated using wide-band laser cladding. • Special cored-eutectic structure was synthesized in Ni60/WC composite coatings. • Cored-eutectic consists of hard carbide compounds and fine lamellar eutectic of M{sub 23}C{sub 6} carbides and γ-Ni(Fe). • Wear resistance of coating layer was significantly improved due to precipitation of M{sub 23}C{sub 6} carbides. - Abstract: Ni60 composite coatings reinforced with WC particles were fabricated on the surface of Q550 steel using LDF4000-100 fiber laser device. The wide-band laser and circular beam laser used in laser cladding were obtained by optical lens. Microstructure, elemental distribution, phase constitution and wear properties of different composite coatings were investigated. The results showed that WC particles were partly dissolved under the effect of wide-band fiber laser irradiation. A special cored-eutectic structure was synthesized due to dissolution of WC particles. According to EDS and XRD results, the inside cores were confirmed as carbides of M{sub 23}C{sub 6} enriched in Cr, W and Fe. These complex carbides were primarily separated out in the molten metal when solidification started. Eutectic structure composed of M{sub 23}C{sub 6} carbides and γ-Ni(Fe) grew around carbides when cooling. Element content of Cr and W is lower at the bottom of cladding layer. In consequence, the eutectic structure formed in this region did not have inside carbides. The coatings made by circular laser beam were composed of dendritic matrix and interdendritic eutectic carbides, lacking of block carbides. Compared to coatings made by circular laser spot, the cored-eutectic structure formed in wide-band coatings had advantages of well-distribution and tight binding with matrix. The uniform power density and energy distribution and the weak liquid convection in molten pool lead to the unique microstructure evolution in composite coatings made by wide-band laser

Surface band structures on Nb(001)

International Nuclear Information System (INIS)

Fang, B.; Lo, W.; Chien, T.; Leung, T.C.; Lue, C.Y.; Chan, C.T.; Ho, K.M.

1994-01-01

We report the joint studies of experimental and theoretical surface band structures of Nb(001). Angle-resolved photoelectron spectroscopy was used to determine surface-state dispersions along three high-symmetry axes bar Γ bar M, bar Γ bar X, and bar M bar X in the surface Brillouin zone. Ten surface bands have been identified. The experimental data are compared to self-consistent pseudopotential calculations for the 11-layer Nb(001) slabs that are either bulk terminated or fully relaxed (with a 12% contraction for the first interlayer spacing). The band calculations for a 12% surface-contracted slab are in better agreement with the experimental results than those for a bulk-terminated slab, except for a surface resonance near the Fermi level, which is related to the spin-orbit interaction. The charge profiles for all surface states or resonances have been calculated. Surface contraction effects on the charge-density distribution and the energy position of surface states and resonances will also be discussed

Polarimetric and Structural Properties of a Boreal Forest at P-Band and L-Band

Science.gov (United States)

Tebaldini, S.; Rocca, F.

2010-12-01

With this paper we investigate the structural and polarimetric of the boreal forest within the Krycklan river catchment, Northern Sweden, basing on multi-polarimetric and multi-baseline SAR surveys at P-Band and L-Band collected in the framework of the ESA campaign BioSAR 2008. The analysis has been carried out by applying the Algebraic Synthesis (AS) technique, recently introduced in literature, which provides a theoretical framework for the decomposition of the backscattered signal into ground-only and volume-only contributions, basing on both baseline and polarization diversity. The availability of multiple baselines allows the formation of a synthetic aperture not only along the azimuth direction but also in elevation. Accordingly, the backscattered echoes can be focused not only in the slant range, azimuth plane, but in the whole 3D space. This is the rationale of the SAR Tomography (T-SAR) concept, which has been widely considered in the literature of the last years. It follows that, as long as the penetration in the scattering volume is guaranteed, the vertical profile of the vegetation layer is retrieved by separating backscatter contributions along the vertical direction, which is the main reason for the exploitation of Tomographic techniques at longer wavelengths. Still, the capabilities of T-SAR are limited to imaging the global vertical structure of the electromagnetic scattering in a certain polarization. It then becomes important to develop methodologies for the investigation of the vertical structure of different Scattering Mechanisms (SMs), such as ground and volume scattering, in such a way as to derive information that can be delivered also outside the field of Radar processing. This is an issue that may become relevant at longer wavelengths, such as P-Band, where the presence of multiple scattering arising from the interaction with terrain could hinder the correct reconstruction of the forest structure. The availability of multiple polarizations

Complete flexural vibration band gaps in membrane-like lattice structures

International Nuclear Information System (INIS)

Yu Dianlong; Liu Yaozong; Qiu Jing; Wang Gang; Zhao Honggang

2006-01-01

The propagation of flexural vibration in the periodical membrane-like lattice structure is studied. The band structure calculated with the plane wave expansion method indicates the existence of complete gaps. The frequency response function of a finite periodic structure is simulated with finite element method. Frequency ranges with vibration attenuation are in good agreement with the gaps found in the band structure. Much larger attenuations are found in the complete gaps comparing to those directional ones. The existence of complete flexural vibration gaps in such a lattice structure provides a new idea for vibration control of thin plates

Band structure of an electron in a kind of periodic potentials with singularities

Science.gov (United States)

Hai, Kuo; Yu, Ning; Jia, Jiangping

2018-06-01

Noninteracting electrons in some crystals may experience periodic potentials with singularities and the governing Schrödinger equation cannot be defined at the singular points. The band structure of a single electron in such a one-dimensional crystal has been calculated by using an equivalent integral form of the Schrödinger equation. Both the perturbed and exact solutions are constructed respectively for the cases of a general singular weak-periodic system and its an exactly solvable version, Kronig-Penney model. Any one of them leads to a special band structure of the energy-dependent parameter, which results in an effective correction to the previous energy-band structure and gives a new explanation for forming the band structure. The used method and obtained results could be a valuable aid in the study of energy bands in solid-state physics, and the new explanation may trigger investigation to different physical mechanism of electron band structures.

Compact electromagnetic bandgap structures for notch band in ultra-wideband applications.

Science.gov (United States)

Rotaru, Mihai; Sykulski, Jan

2010-01-01

This paper introduces a novel approach to create notch band filters in the front-end of ultra-wideband (UWB) communication systems based on electromagnetic bandgap (EBG) structures. The concept presented here can be implemented in any structure that has a microstrip in its configuration. The EBG structure is first analyzed using a full wave electromagnetic solver and then optimized to work at WLAN band (5.15-5.825 GHz). Two UWB passband filters are used to demonstrate the applicability and effectiveness of the novel EBG notch band feature. Simulation results are provided for two cases studied.

Tunable band structures of polycrystalline graphene by external and mismatch strains

Institute of Scientific and Technical Information of China (English)

Jiang-Tao Wu; Xing-Hua Shi; Yu-Jie Wei

2012-01-01

Lacking a band gap largely limits the application of graphene in electronic devices.Previous study shows that grain boundaries (GBs) in polycrystalline graphene can dramatically alter the electrical properties of graphene.Here,we investigate the band structure of polycrystalline graphene tuned by externally imposed strains and intrinsic mismatch strains at the GB by density functional theory (DFT) calculations.We found that graphene with symmetrical GBs typically has zero band gap even with large uniaxial and biaxial strain.However,some particular asymmetrical GBs can open a band gap in graphene and their band structures can be substantially tuned by external strains.A maximum band gap about 0.19 eV was observed in matched-armchair GB (5,5) | (3,7) with a misorientation of θ =13° when the applied uniaxial strain increases to 9％.Although mismatch strain is inevitable in asymmetrical GBs,it has a small influence on the band gap of polycrystalline graphene.

Multi-cavity locally resonant structure with the low frequency and broad band-gaps

Directory of Open Access Journals (Sweden)

Jiulong Jiang

2016-11-01

Full Text Available A multi-cavity periodic structure with the characteristic of local resonance was proposed in the paper. The low frequency band-gap structure was comparatively analyzed by the finite element method (FEM and electric circuit analogy (ECA. Low frequency band-gap can be opened through the dual influence of the coupling’s resonance in the cavity and the interaction among the couplings between structures. Finally, the influence of the structural factors on the band-gap was analyzed. The results show that the structure, which is divided into three parts equally, has a broader effective band-gap below the frequency of 200 Hz. It is also proved that reducing the interval between unit structures can increase the intensity of the couplings among the structures. And in this way, the width of band-gap would be expanded significantly. Through the parameters adjustment, the structure enjoys a satisfied sound insulation effect below the frequency of 500Hz. In the area of low frequency noise reduction, the structure has a lot of potential applications.

Topological Magnon Bands in a Kagome Lattice Ferromagnet.

Science.gov (United States)

Chisnell, R; Helton, J S; Freedman, D E; Singh, D K; Bewley, R I; Nocera, D G; Lee, Y S

2015-10-02

There is great interest in finding materials possessing quasiparticles with topological properties. Such materials may have novel excitations that exist on their boundaries which are protected against disorder. We report experimental evidence that magnons in an insulating kagome ferromagnet can have a topological band structure. Our neutron scattering measurements further reveal that one of the bands is flat due to the unique geometry of the kagome lattice. Spin wave calculations show that the measured band structure follows from a simple Heisenberg Hamiltonian with a Dzyaloshinkii-Moriya interaction. This serves as the first realization of an effectively two-dimensional topological magnon insulator--a new class of magnetic material that should display both a magnon Hall effect and protected chiral edge modes.

Valence band structure of binary chalcogenide vitreous semiconductors by high-resolution XPS

International Nuclear Information System (INIS)

Kozyukhin, S.; Golovchak, R.; Kovalskiy, A.; Shpotyuk, O.; Jain, H.

2011-01-01

High-resolution X-ray photoelectron spectroscopy (XPS) is used to study regularities in the formation of valence band electronic structure in binary As x Se 100−x , As x S 100−x , Ge x Se 100−x and Ge x S 100−x chalcogenide vitreous semiconductors. It is shown that the highest occupied energetic states in the valence band of these materials are formed by lone pair electrons of chalcogen atoms, which play dominant role in the formation of valence band electronic structure of chalcogen-rich glasses. A well-expressed contribution from chalcogen bonding p electrons and more deep s orbitals are also recorded in the experimental valence band XPS spectra. Compositional dependences of the observed bands are qualitatively analyzed from structural and compositional points of view.

Valence band structure of binary chalcogenide vitreous semiconductors by high-resolution XPS

Energy Technology Data Exchange (ETDEWEB)

Kozyukhin, S., E-mail: sergkoz@igic.ras.ru [Russian Academy of Science, Institute of General and Inorganic Chemistry (Russian Federation); Golovchak, R. [Lviv Scientific Research Institute of Materials of SRC ' Carat' (Ukraine); Kovalskiy, A. [Lehigh University, Department of Materials Science and Engineering (United States); Shpotyuk, O. [Lviv Scientific Research Institute of Materials of SRC ' Carat' (Ukraine); Jain, H. [Lehigh University, Department of Materials Science and Engineering (United States)

2011-04-15

High-resolution X-ray photoelectron spectroscopy (XPS) is used to study regularities in the formation of valence band electronic structure in binary As{sub x}Se{sub 100-x}, As{sub x}S{sub 100-x}, Ge{sub x}Se{sub 100-x} and Ge{sub x}S{sub 100-x} chalcogenide vitreous semiconductors. It is shown that the highest occupied energetic states in the valence band of these materials are formed by lone pair electrons of chalcogen atoms, which play dominant role in the formation of valence band electronic structure of chalcogen-rich glasses. A well-expressed contribution from chalcogen bonding p electrons and more deep s orbitals are also recorded in the experimental valence band XPS spectra. Compositional dependences of the observed bands are qualitatively analyzed from structural and compositional points of view.

Shell model description of band structure in 48Cr

International Nuclear Information System (INIS)

Vargas, Carlos E.; Velazquez, Victor M.

2007-01-01

The band structure for normal and abnormal parity bands in 48Cr are described using the m-scheme shell model. In addition to full fp-shell, two particles in the 1d3/2 orbital are allowed in order to describe intruder states. The interaction includes fp-, sd- and mixed matrix elements

Enhancement of phononic band gaps in ternary/binary structure

International Nuclear Information System (INIS)

Aly, Arafa H.; Mehaney, Ahmed

2012-01-01

Based on the transfer matrix method (TMM) and Bloch theory, the interaction of elastic waves (normal incidence) with 1D phononic crystal had been studied. The transfer matrix method was obtained for both longitudinal and transverse waves by applying the continuity conditions between the consecutive unit cells. Dispersion relations are calculated and plotted for both binary and ternary structures. Also we have investigated the corresponding effects on the band gaps values for the two types of phononic crystals. Furthermore, it can be observed that the complete band gaps are located in the common frequency stop-band regions. Numerical simulations are performed to investigate the effect of different thickness ratios inside each unit cell on the band gap values, as well as unit cells thickness on the central band gap frequency. These phononic band gap materials can be used as a filter for elastic waves at different frequencies values.

Changing optical band structure with single photons

Science.gov (United States)

Albrecht, Andreas; Caneva, Tommaso; Chang, Darrick E.

2017-11-01

Achieving strong interactions between individual photons enables a wide variety of exciting possibilities in quantum information science and many-body physics. Cold atoms interfaced with nanophotonic structures have emerged as a platform to realize novel forms of nonlinear interactions. In particular, when atoms are coupled to a photonic crystal waveguide, long-range atomic interactions can arise that are mediated by localized atom-photon bound states. We theoretically show that in such a system, the absorption of a single photon can change the band structure for a subsequent photon. This occurs because the first photon affects the atoms in the chain in an alternating fashion, thus leading to an effective period doubling of the system and a new optical band structure for the composite atom-nanophotonic system. We demonstrate how this mechanism can be engineered to realize a single-photon switch, where the first incoming photon switches the system from being highly transmissive to highly reflective, and analyze how signatures can be observed via non-classical correlations of the outgoing photon field.

Correlation of Photocatalytic Activity with Band Structure of Low-dimensional Semiconductor Nanostructures

Science.gov (United States)

Meng, Fanke

Photocatalytic hydrogen generation by water splitting is a promising technique to produce clean and renewable solar fuel. The development of effective semiconductor photocatalysts to obtain efficient photocatalytic activity is the key objective. However, two critical reasons prevent wide applications of semiconductor photocatalysts: low light usage efficiency and high rates of charge recombination. In this dissertation, several low-dimensional semiconductors were synthesized with hydrothermal, hydrolysis, and chemical impregnation methods. The band structures of the low-dimensional semiconductor materials were engineered to overcome the above mentioned two shortcomings. In addition, the correlation between the photocatalytic activity of the low-dimensional semiconductor materials and their band structures were studied. First, we studied the effect of oxygen vacancies on the photocatalytic activity of one-dimensional anatase TiO2 nanobelts. Given that the oxygen vacancy plays a significant role in band structure and photocatalytic performance of semiconductors, oxygen vacancies were introduced into the anatase TiO2 nanobelts during reduction in H2 at high temperature. The oxygen vacancies of the TiO2 nanobelts boosted visible-light-responsive photocatalytic activity but weakened ultraviolet-light-responsive photocatalytic activity. As oxygen vacancies are commonly introduced by dopants, these results give insight into why doping is not always beneficial to the overall photocatalytic performance despite increases in absorption. Second, we improved the photocatalytic performance of two-dimensional lanthanum titanate (La2Ti2 O7) nanosheets, which are widely studied as an efficient photocatalyst due to the unique layered crystal structure. Nitrogen was doped into the La2Ti2O7 nanosheets and then Pt nanoparticles were loaded onto the La2Ti2O7 nanosheets. Doping nitrogen narrowed the band gap of the La2Ti 2O7 nanosheets by introducing a continuum of states by the valence

Band Gap Properties of Magnetoelectroelastic Grid Structures with Initial Stress

International Nuclear Information System (INIS)

Wang Yi-Ze; Li Feng-Ming

2012-01-01

The propagation of elastic waves in magnetoelectroelastic grid structures is studied. Band gap properties are presented and the effects of the magnetoelectroelastic coupling and initial stress are considered. Numerical calculations are performed using the plane-wave expansion method. The results show that the band gap width can be tuned by the initial stress. It is hoped that our results will be helpful for designing acoustic filters with magnetoelectroelastic materials and grid structures

High-order harmonic generation from a two-dimensional band structure

Science.gov (United States)

Jin, Jian-Zhao; Xiao, Xiang-Ru; Liang, Hao; Wang, Mu-Xue; Chen, Si-Ge; Gong, Qihuang; Peng, Liang-You

2018-04-01

In the past few years, harmonic generation in solids has attracted tremendous attention. Recently, some experiments of two-dimensional (2D) monolayer or few-layer materials have been carried out. These studies demonstrated that harmonic generation in the 2D case shows a strong dependence on the laser's orientation and ellipticity, which calls for a quantitative theoretical interpretation. In this work, we carry out a systematic study on the harmonic generation from a 2D band structure based on a numerical solution to the time-dependent Schrödinger equation. By comparing with the 1D case, we find that the generation dynamics can have a significant difference due to the existence of many crossing points in the 2D band structure. In particular, the higher conduction bands can be excited step by step via these crossing points and the total contribution of the harmonic is given by the mixing of transitions between different clusters of conduction bands to the valence band. We also present the orientation dependence of the harmonic yield on the laser polarization direction.

Energy band structure tailoring of vertically aligned InAs/GaAsSb quantum dot structure for intermediate-band solar cell application by thermal annealing process.

Science.gov (United States)

Liu, Wei-Sheng; Chu, Ting-Fu; Huang, Tien-Hao

2014-12-15

This study presents an band-alignment tailoring of a vertically aligned InAs/GaAs(Sb) quantum dot (QD) structure and the extension of the carrier lifetime therein by rapid thermal annealing (RTA). Arrhenius analysis indicates a larger activation energy and thermal stability that results from the suppression of In-Ga intermixing and preservation of the QD heterostructure in an annealed vertically aligned InAs/GaAsSb QD structure. Power-dependent and time-resolved photoluminescence were utilized to demonstrate the extended carrier lifetime from 4.7 to 9.4 ns and elucidate the mechanisms of the antimony aggregation resulting in a band-alignment tailoring from straddling to staggered gap after the RTA process. The significant extension in the carrier lifetime of the columnar InAs/GaAsSb dot structure make the great potential in improving QD intermediate-band solar cell application.

Band Structure and Quantum Confined Stark Effect in InN/GaN superlattices

DEFF Research Database (Denmark)

Gorczyca, I.; Suski, T.; Christensen, Niels Egede

2012-01-01

InN/GaN superlattices offer an important way of band gap engineering in the blue-green range of the spectrum. This approach represents a more controlled method than the band gap tuning in quantum well systems by application of InGaN alloys. The electronic structures of short-period wurtzite InN/G...... wells and barriers one may tune band gaps over a wide spectral range, which provides flexibility in band gap engineering.......InN/GaN superlattices offer an important way of band gap engineering in the blue-green range of the spectrum. This approach represents a more controlled method than the band gap tuning in quantum well systems by application of InGaN alloys. The electronic structures of short-period wurtzite In......N/GaN(0001) superlattices are investigated, and the variation of the band gap with the thicknesses of the well and the barrier is discussed. Superlattices of the form mInN/nGaN with n ≥ m are simulated using band structure calculations in the Local Density Approximation with a semiempirical correction...

Emission bands of phosphorus and calculation of band structure of rare earth phosphides

International Nuclear Information System (INIS)

Al'perovich, G.I.; Gusatinskij, A.N.; Geguzin, I.I.; Blokhin, M.A.; Torbov, V.I.; Chukalin, V.I.; AN SSSR, Moscow. Inst. Novykh Khimicheskikh Problem)

1977-01-01

The method of x-ray emission spectroscopy has been used to investigate the electronic structure of monophosphides of rare-earth metals (REM). The fluorescence K bands of phosphorus have been obtained in LaP, PrP, SmP, GdP, TbP, DyP, HoP, ErP, TmP, YbP, and LuP and also the Lsub(2,3) bands of phosphorus in ErP, TmP, YbP, and LuP. Using the Green function technique involving the muffin-tin potential, the energy spectrum for ErP has been calculated in the single-electron approximation. The hystogram of electronic state distribution N(E) is compared with the experimental K and Lsub(2,3) bands of phosphorus in ErP. The agreement between the main details of N(E) and that of x-ray spectra allows to state that the model used provides a good description of the electron density distribution in crystals of REM monophosphides. In accordance with the character of the N(E) distribution the compounds under study are classified as semimetals or semiconductors with a very narrow forbidden band

Band structure of Mgsub(x)Znsub(1-x)Te alloys

International Nuclear Information System (INIS)

Laugier, A.; Montegu, B.; Barbier, D.; Chevallier, J.; Guillaume, J.C.; Somogyi, K.

1980-01-01

The band structure of Mgsub(x)Znsub(1-x)Te alloys is studied using a double beam wavelength modulated system in first derivative mode. Modulated reflectivity measurements are made from 82 to 300 K within spectral range 2500 to 5400 A. Structures corresponding to the E 0 , E 0 + Δ 0 , E 1 , E 1 + Δ 1 , e 1 and e 1 + Δ 1 critical points are indexed on the basis of existing band calculations for ZnTe. (author)

Band structures and localization properties of aperiodic layered phononic crystals

Energy Technology Data Exchange (ETDEWEB)

Yan Zhizhong, E-mail: zzyan@bit.edu.cn [Department of Applied Mathematics, Beijing Institute of Technology, Beijing 100081 (China); Zhang Chuanzeng [Department of Civil Engineering, University of Siegen, D-57078 Siegen (Germany)

2012-03-15

The band structures and localization properties of in-plane elastic waves with coupling of longitudinal and transverse modes oblique propagating in aperiodic phononic crystals based on Thue-Morse and Rudin-Shapiro sequences are studied. Using transfer matrix method, the concept of the localization factor is introduced and the correctness is testified through the Rytov dispersion relation. For comparison, the perfect periodic structure and the quasi-periodic Fibonacci system are also considered. In addition, the influences of the random disorder, local resonance, translational and/or mirror symmetries on the band structures of the aperiodic phononic crystals are analyzed in this paper.

Magnon band structure and magnon density in one-dimensional magnonic crystals

International Nuclear Information System (INIS)

Qiu, Rong-ke; Huang, Te; Zhang, Zhi-dong

2014-01-01

By using Callen's Green's function method and the Tyablikov and Anderson–Callen decoupling approximations, we systematically study the magnon band structure and magnon density perpendicular to the superlattice plane of one-dimensional magnonic crystals, with a superlattice consisting of two magnetic layers with ferromagnetic (FM) or antiferromagnetic (AFM) interlayer exchange coupling. The effects of temperature, interlayer coupling, anisotropy and external magnetic field on the magnon-energy band and magnon density in the K x -direction are investigated in three situations: a) the magnon band of magnetic superlattices with FM interlayer coupling, b) separate and c) overlapping magnon bands of magnetic superlattices with AFM interlayer coupling. In the present work, a quantum approach is developed to study the magnon band structure and magnon density of magnonic crystals and the results are beneficial for the design of magnonic-crystal waveguides or gigahertz-range spin-wave filters. - Highlights: • A quantum approach has been developed to study the magnon band of magnonic crystals. • The separate and overlapping magnon bands of magnetic superlattices are investigated. • The results are beneficial for the design of gigahertz-range spin-wave filters

Magnon band structure and magnon density in one-dimensional magnonic crystals

Energy Technology Data Exchange (ETDEWEB)

Qiu, Rong-ke, E-mail: rkqiu@163.com [Shenyang University of Technology, Shenyang 110870 (China); Huang, Te [Shenyang University of Technology, Shenyang 110870 (China); Zhang, Zhi-dong [Shenyang National Laboratory for Materials Science, Institute of Metal Research, Chinese Academy of Sciences, Shenyang 110016 (China)

2014-11-15

By using Callen's Green's function method and the Tyablikov and Anderson–Callen decoupling approximations, we systematically study the magnon band structure and magnon density perpendicular to the superlattice plane of one-dimensional magnonic crystals, with a superlattice consisting of two magnetic layers with ferromagnetic (FM) or antiferromagnetic (AFM) interlayer exchange coupling. The effects of temperature, interlayer coupling, anisotropy and external magnetic field on the magnon-energy band and magnon density in the K{sub x}-direction are investigated in three situations: a) the magnon band of magnetic superlattices with FM interlayer coupling, b) separate and c) overlapping magnon bands of magnetic superlattices with AFM interlayer coupling. In the present work, a quantum approach is developed to study the magnon band structure and magnon density of magnonic crystals and the results are beneficial for the design of magnonic-crystal waveguides or gigahertz-range spin-wave filters. - Highlights: • A quantum approach has been developed to study the magnon band of magnonic crystals. • The separate and overlapping magnon bands of magnetic superlattices are investigated. • The results are beneficial for the design of gigahertz-range spin-wave filters.

Collective motions and band structures in A = 60 to 80, even--even nuclei

International Nuclear Information System (INIS)

Hamilton, J.H.; Robinson, R.L.; Ramayya, A.V.

1978-01-01

Evidence for and the theoretical understanding of the richness of the collective band structures as illustrated by at least seven bands seen in levels of 68 Ge, 74 Se are reviewed. The experimental data on even-even nuclei in the A = 60 to 80 region have now revealed a wide variety of collective bands with different structures. The even parity yrast cascades alone are seen to involve multiple collective structures. In addition to the ground-state bands, strong evidence is presented for both neutron and proton rotation-aligned bands built on the same orbital, (g 9 / 2 ) 2 , in one nucleus. Several other nuclei also show the crossing of RAL bands around the 8 + level in this region. Evidence continues to be strong experimentally and supported theoretically that there is some type of shape transition and shape coexistence occurring now both in the Ge and Se isotopes around N = 40. Negative parity bands with odd and even spins with very collective nature are seen in several nuclei to high spin. These bands seem best understood in the RAL model. Very collective bands with ΔI = 1, extending from 2 + to 9 + are seen with no rotation-alignment. The purity of these bands and their persistence to such high spin establish them as an independent collective mode which is best described as a gamma-type vibration band in a deformed nucleus. In addition to all of the above bands, new bands are seen in 76 Kr and 74 Se. The nature of these bands is not presently known. 56 references

Hubbard-U band-structure methods

DEFF Research Database (Denmark)

Albers, R.C.; Christensen, Niels Egede; Svane, Axel

2009-01-01

The last decade has seen a large increase in the number of electronic-structure calculations that involve adding a Hubbard term to the local-density approximation band-structure Hamiltonian. The Hubbard term is then determined either at the mean-field level or with sophisticated many......-body techniques such as using dynamical mean-field theory. We review the physics underlying these approaches and discuss their strengths and weaknesses in terms of the larger issues of electronic structure that they involve. In particular, we argue that the common assumptions made to justify such calculations...

Structure of collective bands and deformations in 74,76Kr

International Nuclear Information System (INIS)

Tripathy, K.C.; Sahu, R.

2000-01-01

The structure of collective bands in 74,76 Kr is studied within the framework of the deformed configuration mixing shell model based on Hartree-Fock states. The active single-particle orbits are 1p 3/2 , 0f 5/2 , 1p 1/2 and 0g 9/2 with 56 Ni as the inert core. A modified Kuo interaction has been used for the above configuration space. The 74 Kr nucleus is found to be the most deformed nucleus among the krypton isotopes which is in agreement with experiment. The deformation is found to decrease for the 76 Kr isotope. The calculated positive- and negative-parity bands agree quite well with the experiment for both the nuclei. A number of excited bands is also predicted. We have also calculated B(E2) values and compared them with available experimental data. The structure of the strongly coupled band built on K = 4 (+) in 76 Kr is also studied. (author)

Photonic band structures in one-dimensional photonic crystals containing Dirac materials

International Nuclear Information System (INIS)

Wang, Lin; Wang, Li-Gang

2015-01-01

We have investigated the band structures of one-dimensional photonic crystals (1DPCs) composed of Dirac materials and ordinary dielectric media. It is found that there exist an omnidirectional passing band and a kind of special band, which result from the interaction of the evanescent and propagating waves. Due to the interface effect and strong dispersion, the electromagnetic fields inside the special bands are strongly enhanced. It is also shown that the properties of these bands are invariant upon the lattice constant but sensitive to the resonant conditions

Self-consistent, relativistic, ferromagnetic band structure of gadolinium

International Nuclear Information System (INIS)

Harmon, B.N.; Schirber, J.; Koelling, D.D.

1977-01-01

An initial self-consistent calculation of the ground state magnetic band structure of gadolinium is described. A linearized APW method was used which included all single particle relativistic effects except spin-orbit coupling. The spin polarized potential was obtained in the muffin-tin form using the local spin density approximation for exchange and correlation. The most striking and unorthodox aspect of the results is the position of the 4f spin-down ''bands'' which are required to float just on top of the Fermi level in order to obtain convergence. If the 4f states (l = 3 resonance) are removed from the occupied region of the conduction bands the magnetic moment is approximately .75 μ/sub B//atom; however, as the 4f spin-down states are allowed to find their own position they hybridize with the conduction bands at the Fermi level and the moment becomes smaller. Means of improving the calculation are discussed

Electronic band structure in porous silicon studied by photoluminescence and photoluminescence excitation spectroscopy

International Nuclear Information System (INIS)

Lee, Ki-Won; Kim, Young-You

2004-01-01

In this research, we used photoluminescence (PL) and photoluminescence excitation (PLE) to visualize the electronic band structure in porous silicon (PS). From the combined results of the PLE measurements at various PL emission energies and the PL measurements under excitation at various PLE absorption energies, we infer that three different electronic band structures, originating from different luminescent origins, give rise to the PL spectrum. Through either thermal activation or diffusive transfer, excited carriers are moved to each of the electronic band structures.

A Compact UWB Band-Pass Filter Using Embedded Circular Slot Structures for Improved Upper Stop-band Performance

DEFF Research Database (Denmark)

Shen, Ming; Ren, Jian; Mikkelsen, Jan Hvolgaard

2016-01-01

structures into the ring resonator. This is different from conventional designs using cascaded bandstop/low-pass filters for stop-band response suppression, which usually leads to big circuit sizes. And hence the proposed approach can reduce the circuit size significantly. A prototype filter with a compact...... size (13.6 mm×6.75 mm) has been implemented for experimental validation. The measured results show a −3 dB frequency band from 3.4 GHz to 11.7 GHz and > 20 dB upper stop-band suppression from 12.5 GHz to 20GHz....

Topological Classification of Crystalline Insulators through Band Structure Combinatorics

Science.gov (United States)

Kruthoff, Jorrit; de Boer, Jan; van Wezel, Jasper; Kane, Charles L.; Slager, Robert-Jan

2017-10-01

We present a method for efficiently enumerating all allowed, topologically distinct, electronic band structures within a given crystal structure in all physically relevant dimensions. The algorithm applies to crystals without time-reversal, particle-hole, chiral, or any other anticommuting or anti-unitary symmetries. The results presented match the mathematical structure underlying the topological classification of these crystals in terms of K -theory and therefore elucidate this abstract mathematical framework from a simple combinatorial perspective. Using a straightforward counting procedure, we classify all allowed topological phases of spinless particles in crystals in class A . Employing this classification, we study transitions between topological phases within class A that are driven by band inversions at high-symmetry points in the first Brillouin zone. This enables us to list all possible types of phase transitions within a given crystal structure and to identify whether or not they give rise to intermediate Weyl semimetallic phases.

Solving complex band structure problems with the FEAST eigenvalue algorithm

Science.gov (United States)

Laux, S. E.

2012-08-01

With straightforward extension, the FEAST eigenvalue algorithm [Polizzi, Phys. Rev. B 79, 115112 (2009)] is capable of solving the generalized eigenvalue problems representing traveling-wave problems—as exemplified by the complex band-structure problem—even though the matrices involved are complex, non-Hermitian, and singular, and hence outside the originally stated range of applicability of the algorithm. The obtained eigenvalues/eigenvectors, however, contain spurious solutions which must be detected and removed. The efficiency and parallel structure of the original algorithm are unaltered. The complex band structures of Si layers of varying thicknesses and InAs nanowires of varying radii are computed as test problems.

Two-band superconductor magnesium diboride

International Nuclear Information System (INIS)

Xi, X X

2008-01-01

This review focuses on the most important features of the 40 K superconductor MgB 2 -the weakly interacting multiple bands (the σ and π bands) and the distinct multiple superconducting energy gaps (the σ and π gaps). Even though the pairing mechanism of superconductor MgB 2 is the conventional electron-phonon coupling, the prominent influence of the two bands and two gaps on its properties sets it apart from other superconductors. It leads to markedly different behaviors in upper critical field, vortex structure, magnetoresistance and many other superconducting and normal-state properties in MgB 2 from single-band superconductors. Further, it gives rise to new physics that does not exist in single-band superconductors, such as the internal Josephson effects between the two order parameters. These unique phenomena depend sensitively on scattering inside and between the two bands, and the intraband and interband scattering can be modified by chemical substitution and irradiation. MgB 2 has brought unprecedented attention to two-band superconductivity, which has been found to exist in other old and new superconductors. The legacy of MgB 2 will be long lasting because of this, as well as the lessons it teaches in terms of the search for new phonon-mediated higher T c superconductors

Band structure and phonon properties of lithium fluoride at high pressure

Energy Technology Data Exchange (ETDEWEB)

Panchal, J. M., E-mail: amitjignesh@yahoo.co.in [Government Engineering College, Gandhinagar 382028, Gujarat (India); Department of Physics, University School of Sciences, Gujarat University, Ahmedabad 380009, Gujarat (India); Joshi, Mitesh [Government Polytechnic for Girls, Athwagate, Surat395001, Gujarat (India); Gajjar, P. N., E-mail: pngajjar@rediffmail.com [Department of Physics, University School of Sciences, Gujarat University, Ahmedabad 380009, Gujarat (India)

2016-05-23

High pressure structural and electronic properties of Lithium Fluoride (LiF) have been studied by employing an ab-initio pseudopotential method and a linear response scheme within the density functional theory (DFT) in conjunction with quasi harmonic Debye model. The band structure and electronic density of states conforms that the LiF is stable and is having insulator behavior at ambient as well as at high pressure up to 1 Mbar. Conclusions based on Band structure, phonon dispersion and phonon density of states are outlined.

Band structure and phonon properties of lithium fluoride at high pressure

International Nuclear Information System (INIS)

Panchal, J. M.; Joshi, Mitesh; Gajjar, P. N.

2016-01-01

High pressure structural and electronic properties of Lithium Fluoride (LiF) have been studied by employing an ab-initio pseudopotential method and a linear response scheme within the density functional theory (DFT) in conjunction with quasi harmonic Debye model. The band structure and electronic density of states conforms that the LiF is stable and is having insulator behavior at ambient as well as at high pressure up to 1 Mbar. Conclusions based on Band structure, phonon dispersion and phonon density of states are outlined.

Two-dimensional microwave band-gap structures of different ...

Indian Academy of Sciences (India)

- stant and/or magnetic permeability (or in particular impedance) are periodic and the propagation of electromagnetic waves is forbidden at certain frequencies when allowed to pass through these structures. This is similar to the electronic band.

Volume and surface photoemission from tungsten. I. Calculation of band structure and emission spectra

DEFF Research Database (Denmark)

Christensen, N. Egede; Feuerbacher, B.

1974-01-01

is obtained from an ad hoc potential based on a Dirac-Slater atomic calculation for the ground-state configuration and with full Slater exchange in the atomic as well as in the crystal potential. The selection of this best potential is justified by comparing the calculated band structure to Fermi...... of states. The present work includes a crude estimate of this surface density of states, which is derived from the bulk band structure by narrowing the d bands according to an effective number of neighbors per surface atom. Estimates of surface relaxation effects are also included.......The electronic energy-band structure of tungsten has been calculated by means of the relativistic-augmented-plane-wave method. A series of mutually related potentials are constructed by varying the electronic configuration and the amount of Slater exchange included. The best band structure...

Analysis of photonic band-gap (PBG) structures using the FDTD method

DEFF Research Database (Denmark)

Tong, M.S.; Cheng, M.; Lu, Y.L.

2004-01-01

In this paper, a number of photonic band-gap (PBG) structures, which are formed by periodic circuit elements printed oil transmission-line circuits, are studied by using a well-known numerical method, the finite-difference time-domain (FDTD) method. The results validate the band-stop filter...... behavior of these structures, and the computed results generally match well with ones published in the literature. It is also found that the FDTD method is a robust, versatile, and powerful numerical technique to perform such numerical studies. The proposed PBG filter structures may be applied in microwave...

On electronic structure of polymer-derived amorphous silicon carbide ceramics

Science.gov (United States)

Wang, Kewei; Li, Xuqin; Ma, Baisheng; Wang, Yiguang; Zhang, Ligong; An, Linan

2014-06-01

The electronic structure of polymer-derived amorphous silicon carbide ceramics was studied by combining measurements of temperature-dependent conductivity and optical absorption. By comparing the experimental results to theoretical models, electronic structure was constructed for a carbon-rich amorphous silicon carbide, which revealed several unique features, such as deep defect energy level, wide band-tail band, and overlap between the band-tail band and defect level. These unique features were discussed in terms of the microstructure of the material and used to explain the electric behavior.

Research on the Band Gap Characteristics of Two-Dimensional Phononic Crystals Microcavity with Local Resonant Structure

Directory of Open Access Journals (Sweden)

Mao Liu

2015-01-01

Full Text Available A new two-dimensional locally resonant phononic crystal with microcavity structure is proposed. The acoustic wave band gap characteristics of this new structure are studied using finite element method. At the same time, the corresponding displacement eigenmodes of the band edges of the lowest band gap and the transmission spectrum are calculated. The results proved that phononic crystals with microcavity structure exhibited complete band gaps in low-frequency range. The eigenfrequency of the lower edge of the first gap is lower than no microcavity structure. However, for no microcavity structure type of quadrilateral phononic crystal plate, the second band gap disappeared and the frequency range of the first band gap is relatively narrow. The main reason for appearing low-frequency band gaps is that the proposed phononic crystal introduced the local resonant microcavity structure. This study provides a good support for engineering application such as low-frequency vibration attenuation and noise control.

Tuning the band gap in hybrid tin iodide perovskite semiconductors using structural templating.

Science.gov (United States)

Knutson, Jeremy L; Martin, James D; Mitzi, David B

2005-06-27

Structural distortions within the extensive family of organic/inorganic hybrid tin iodide perovskite semiconductors are correlated with their experimental exciton energies and calculated band gaps. The extent of the in- and out-of-plane angular distortion of the SnI4(2-) perovskite sheets is largely determined by the relative charge density and steric requirements of the organic cations. Variation of the in-plane Sn-I-Sn bond angle was demonstrated to have the greatest impact on the tuning of the band gap, and the equatorial Sn-I bond distances have a significant secondary influence. Extended Hückel tight-binding band calculations are employed to decipher the crystal orbital origins of the structural effects that fine-tune the band structure. The calculations suggest that it may be possible to tune the band gap by as much as 1 eV using the templating influence of the organic cation.

Study of multi-quasiparticle band structures in 197Tl using α beam

International Nuclear Information System (INIS)

Mukherjee, G.; Nandi, S.; Pai, H.

2016-01-01

Study of the multi-quasiparticle (qp) states and the band structures built on them in the neutron deficient Tl nuclei in A ∼ 190 mass region provides useful information on particle-hole interaction in the heavy nuclei. In order to investigate the multi-qp band structures we have studied the excited states in 197 Tl by gamma ray spectroscopy

Electronic band structure of magnetic bilayer graphene superlattices

International Nuclear Information System (INIS)

Pham, C. Huy; Nguyen, T. Thuong; Nguyen, V. Lien

2014-01-01

Electronic band structure of the bilayer graphene superlattices with δ-function magnetic barriers and zero average magnetic flux is studied within the four-band continuum model, using the transfer matrix method. The periodic magnetic potential effects on the zero-energy touching point between the lowest conduction and the highest valence minibands of pristine bilayer graphene are exactly analyzed. Magnetic potential is shown also to generate the finite-energy touching points between higher minibands at the edges of Brillouin zone. The positions of these points and the related dispersions are determined in the case of symmetric potentials.

Band structure and optical properties of opal photonic crystals

OpenAIRE

Pavarini, E.; Andreani, L. C.; Soci, C.; Galli, M.; Marabelli, F.; Comoretto, D.

2005-01-01

A theoretical approach for the interpretation of reflectance spectra of opal photonic crystals with fcc structure and (111) surface orientation is presented. It is based on the calculation of photonic bands and density of states corresponding to a specified angle of incidence in air. The results yield a clear distinction between diffraction in the direction of light propagation by (111) family planes (leading to the formation of a stop band) and diffraction in other directions by higher-order...

Simulation of the Band Structure of Graphene and Carbon Nanotube

International Nuclear Information System (INIS)

Mina, Aziz N; Awadallah, Attia A; Ahmed, Riham R; Phillips, Adel H

2012-01-01

Simulation technique has been performed to simulate the band structure of both graphene and carbon nanotube. Accordingly, the dispersion relations for graphene and carbon nanotube are deduced analytically, using the tight binding model and LCAO scheme. The results from the simulation of the dispersion relation of both graphene and carbon nanotube were found to be consistent with those in the literature which indicates the correctness of the process of simulation technique. The present research is very important for tailoring graphene and carbon nanotube with specific band structure, in order to satisfy the required electronic properties of them.

High gradient test of X-band accelerating structure at GLCTA

International Nuclear Information System (INIS)

Watanabe, K.; Higo, T.; Hayano, H.; Terunuma, N.; Saeki, T.; Kudo, N.; Sanuki, T.; Seuhara, T.

2004-01-01

GLCTA (Global Linear Collider Test Accelerator) is the high power test facility for X-band acceleration. We have installed an X-band 60cm structure in April 2004 and have been processing it for more than 3 months. Now it is under test on long-term operation. We report here the installation process and high power test result to date. (author)

Temperature-induced band shift in bulk γ-InSe by angle-resolved photoemission spectroscopy

Science.gov (United States)

Xu, Huanfeng; Wang, Wei; Zhao, Yafei; Zhang, Xiaoqian; Feng, Yue; Tu, Jian; Gu, Chenyi; Sun, Yizhe; Liu, Chang; Nie, Yuefeng; Edmond Turcu, Ion C.; Xu, Yongbing; He, Liang

2018-05-01

Indium selenide (InSe) has recently become popular research topics because of its unique layered crystal structure, direct band gap and high electron mobilities. In this work, we have acquired the electronic structure of bulk γ-InSe at various temperatures using angle-resolved photoemission spectroscopy (ARPES). We have also found that as the temperature decreases, the valence bands of γ-InSe exhibit a monotonic shift to lower binding energies. This band shift is attributed to the change of lattice parameters and has been validated by variable temperature X-ray diffraction measurements and theoretical calculations.

Band structures in two-dimensional phononic crystals with periodic Jerusalem cross slot

Science.gov (United States)

Li, Yinggang; Chen, Tianning; Wang, Xiaopeng; Yu, Kunpeng; Song, Ruifang

2015-01-01

In this paper, a novel two-dimensional phononic crystal composed of periodic Jerusalem cross slot in air matrix with a square lattice is presented. The dispersion relations and the transmission coefficient spectra are calculated by using the finite element method based on the Bloch theorem. The formation mechanisms of the band gaps are analyzed based on the acoustic mode analysis. Numerical results show that the proposed phononic crystal structure can yield large band gaps in the low-frequency range. The formation mechanism of opening the acoustic band gaps is mainly attributed to the resonance modes of the cavities inside the Jerusalem cross slot structure. Furthermore, the effects of the geometrical parameters on the band gaps are further explored numerically. Results show that the band gaps can be modulated in an extremely large frequency range by the geometry parameters such as the slot length and width. These properties of acoustic waves in the proposed phononic crystals can potentially be applied to optimize band gaps and generate low-frequency filters and waveguides.

Band structure and optical properties of opal photonic crystals

Science.gov (United States)

Pavarini, E.; Andreani, L. C.; Soci, C.; Galli, M.; Marabelli, F.; Comoretto, D.

2005-07-01

A theoretical approach for the interpretation of reflectance spectra of opal photonic crystals with fcc structure and (111) surface orientation is presented. It is based on the calculation of photonic bands and density of states corresponding to a specified angle of incidence in air. The results yield a clear distinction between diffraction in the direction of light propagation by (111) family planes (leading to the formation of a stop band) and diffraction in other directions by higher-order planes (corresponding to the excitation of photonic modes in the crystal). Reflectance measurements on artificial opals made of self-assembled polystyrene spheres are analyzed according to the theoretical scheme and give evidence of diffraction by higher-order crystalline planes in the photonic structure.

Experimental Studies of W-Band Accelerator Structures at High Field

Energy Technology Data Exchange (ETDEWEB)

Hill, Marc E

2001-02-09

A high-gradient electron accelerator is desired for high-energy physics research, where frequency scalings of breakdown and trapping of itinerant beamline particles dictates operation of the accelerator at short wavelengths. The first results of design and test of a high-gradient mm-wave linac with an operating frequency at 91.392 GHz (W-band) are presented. A novel approach to particle acceleration is presented employing a planar, dielectric lined waveguide used for particle acceleration. The traveling wave fields in the planar dielectric accelerator (PDA) are analyzed for an idealized structure, along with a circuit equivalent model used for understanding the structure as a microwave circuit. Along with the W-band accelerator structures, other components designed and tested are high power rf windows, high power attenuators, and a high power squeeze-type phase shifter. The design of the accelerator and its components where eased with the aide of numerical simulations using a finite-difference electromagnetic field solver. Manufacturing considerations of the small, delicate mm-wave components and the steps taken to reach a robust fabrication process are detailed. These devices were characterized under low power using a two-port vector network analyzer to verify tune and match, including measurements of the structures' fields using a bead-pull. The measurements are compared with theory throughout. Addition studies of the W-band structures were performed under high power utilizing a 11.424 GHz electron linac as a current source. Test results include W-band power levels of 200 kW, corresponding to fields in the PDA of over 20 MV/m, a higher gradient than any collider. Planar accelerator devices naturally have an rf quadrupole component of the accelerating field. Presented for the first time are the measurements of this effect.

Study of band structure in 78,80Sr using Triaxial Projected Shell Model

International Nuclear Information System (INIS)

Behera, N.; Naik, Z.; Bhat, G.H.; Sheikh, J.A.; Palit, R.; Sun, Y.

2017-01-01

The purpose of present work is to carry out a systematic study of the yrast-band and gamma-band structure for the even-even 78-80 Sr nuclei using Triaxial Projected Shell Model (TPSM) approach. These nuclei were chosen because 78 Sr has well developed side band(unassigned configuration) and 80 Sr has well developed band observed experimentally

Proceedings of wide band gap semiconductors

International Nuclear Information System (INIS)

Moustakas, T.D.; Pankove, J.I.; Hamakawa, Y.

1992-01-01

This book contains the proceedings of wide band gap semiconductors. Wide band gap semiconductors are under intense study because of their potential applications in photonic devices in the visible and ultraviolet part of the electromagnetic spectrum, and devices for high temperature, high frequency and high power electronics. Additionally, due to their unique mechanical, thermal, optical, chemical, and electronic properties many wide band gap semiconductors are anticipated to find applications in thermoelectric, electrooptic, piezoelectric and acoustooptic devices as well as protective coatings, hard coatings and heat sinks. Material systems covered in this symposium include diamond, II-VI compounds, III-V nitrides, silicon carbide, boron compounds, amorphous and microcrystalline semiconductors, chalcopyrites, oxides and halides. The various papers addressed recent experimental and theoretical developments. They covered issues related to crystal growth (bulk and thin films), structure and microstructure, defects, doping, optoelectronic properties and device applications. A theoretical session was dedicated to identifying common themes in the heteroepitaxy and the role of defects in doping, compensation and phase stability of this unique class of materials. Important experimental milestones included the demonstrations of bright blue injection luminescence at room temperatures from junctions based on III-V nitrides and a similar result from multiple quantum wells in a ZnSe double heterojunction at liquid nitrogen temperatures

Bulk band structure of Bi2Te3

DEFF Research Database (Denmark)

Michiardi, Matteo; Aguilera, Irene; Bianchi, Marco

2014-01-01

-electron full-potential linearized augmented-plane-wave (FLAPW) formalism, fully taking into account spin-orbit coupling. Quasiparticle effects produce significant changes in the band structure of Bi2Te3 when compared to LDA. Experimental and calculated results are compared in the spectral regions where...

Structure determination of human Lck unique and SH3 domains by nuclear magnetic resonance spectroscopy

Directory of Open Access Journals (Sweden)

Willbold Dieter

2003-05-01

Full Text Available Abstract Background Protein tyrosine kinases are involved in signal transduction pathways that regulate cell growth, differentiation, activation and transformation. Human lymphocyte specific kinase (Lck is a 56 kDa protein involved in T-cell- and IL2-receptor signaling. Three-dimensional structures are known for SH3, SH2 and kinase domains of Lck as well as for other tyrosine kinases. No structure is known for the unique domain of any Src-type tyrosine kinase. Results Lck(1–120 comprising unique and SH3 domains was structurally investigated by nuclear magnetic resonance spectroscopy. We found the unique domain, in contrast to the SH3 part, to have basically no defined structural elements. The solution structure of the SH3 part could be determined with very high precision. It does not show significant differences to Lck SH3 in the absence of the unique domain. Minor differences were observed to the X-ray structure of Lck SH3. Conclusion The unique domain of Lck does not contain any defined structure elements in the absence of ligands and membranes. Presence of the unique domain is not relevant to the three-dimensional structure of the Lck SH3 domain.

Photo field emission spectroscopy of the tantalum band structure

International Nuclear Information System (INIS)

Kleint, Ch.; Radon, T.

1978-01-01

Photo field emission (PFE) currents of clean and barium covered tantalum tips have been measured with single lines of the mercury arc spectrum and phase-sensitive detection. Field strength and work function were determined from Fowler-Nordheim plots of the FE currents. Shoulders in the PFE current-voltage characteristics could be correlated to transitions in the band structure of tantalum according to a recently proposed two-step PFE model. A comparison with the relativistic calculations of Mattheiss and the nonrelativistic bands of Petroff and Viswanathan shows that Mattheiss' bands are more appropriate. Beside direct transitions several nondirect transitions from the different features composing the upper two density of states maxima below the Fermi edge of tantalum have been found. (Auth.)

The structure of collective bands in 72Ge

International Nuclear Information System (INIS)

Tripathy, K.C.; Sahu, R.

1999-01-01

In recent years, extensive experimental studies of nuclei in the mass region A=80 have led to exciting discoveries of large ground state deformations, coexistence of shapes, band crossings, rapid variations of structure with changing nucleon numbers etc. A theoretical study of 72 Ge is presented

Design for maximum band-gaps in beam structures

DEFF Research Database (Denmark)

Olhoff, Niels; Niu, Bin; Cheng, Gengdong

2012-01-01

This paper aims to extend earlier optimum design results for transversely vibrating Bernoulli-Euler beams by determining new optimum band-gap beam structures for (i) different combinations of classical boundary conditions, (ii) much larger values of the orders n and n-1 of adjacent upper and lower...

High Power Test of an X-Band Slotted-IRIS Accelerator Structure at NLCTA

International Nuclear Information System (INIS)

Doebert, S.; Fandos, R.; Grudiev, A.; Heikkinen, S.; Rodriquez, J.A.; Taborelli, M.; Wuensch, W.; Adolphsen, Chris E.; Laurent, L.

2007-01-01

The CLIC study group at CERN has built two X-band HDS (hybrid damped structure) accelerating structures for high-power testing in NLCTA at SLAC. These accelerating structures are novel with respect to their rf- design and their fabrication technique. The eleven-cell constant impedance structures, one made out of copper and one out of molybdenum, are assembled from clamped high-speed milled quadrants. They feature the same heavy higher-order-mode damping as nominal CLIC structures achieved by slotted irises and radial damping waveguides for each cell. The X-band accelerators are exactly scaled versions of structures tested at 30 GHz in the CLIC test facility, CTF3. The results of the X-band tests are presented and compared to those at 30 GHz to determine frequency scaling, and are compared to the extensive copper data from the NLC structure development program to determine material dependence and make a basic validation of the HDS design

Band structure of hydrogenated Si nanosheets and nanotubes

International Nuclear Information System (INIS)

Guzman-Verri, G G; Lew Yan Voon, L C

2011-01-01

The band structures of fully hydrogenated Si nanosheets and nanotubes are elucidated by the use of an empirical tight-binding model. The hydrogenated Si sheet is a semiconductor with an indirect band gap of about 2.2 eV. The symmetries of the wavefunctions allow us to explain the origin of the gap. We predict that, for certain chiralities, hydrogenated Si nanotubes represent a new type of semiconductor, one with coexisting direct and indirect gaps of exactly the same magnitude. This behavior is different from that governed by the Hamada rule established for non-hydrogenated carbon and silicon nanotubes. A comparison to the results of an ab initio calculation is made.

Band structures of 4f and 5f materials studied by angle-resolved photoelectron spectroscopy.

Science.gov (United States)

Fujimori, Shin-ichi

2016-04-20

Recent remarkable progress in angle-resolved photoelectron spectroscopy (ARPES) has enabled the direct observation of the band structures of 4f and 5f materials. In particular, ARPES with various light sources such as lasers (hν ~ 7 eV) or high-energy synchrotron radiations (hν >/~ 400 eV) has shed light on the bulk band structures of strongly correlated materials with energy scales of a few millielectronvolts to several electronvolts. The purpose of this paper is to summarize the behaviors of 4f and 5f band structures of various rare-earth and actinide materials observed by modern ARPES techniques, and understand how they can be described using various theoretical frameworks. For 4f-electron materials, ARPES studies of CeMIn5(M = Rh, Ir, and Co) and YbRh2Si2 with various incident photon energies are summarized. We demonstrate that their 4f electronic structures are essentially described within the framework of the periodic Anderson model, and that the band-structure calculation based on the local density approximation cannot explain their low-energy electronic structures. Meanwhile, electronic structures of 5f materials exhibit wide varieties ranging from itinerant to localized states. For itinerant U5f compounds such as UFeGa5, their electronic structures can be well-described by the band-structure calculation assuming that all U5f electrons are itinerant. In contrast, the band structures of localized U5f compounds such as UPd3 and UO2 are essentially explained by the localized model that treats U5f electrons as localized core states. In regards to heavy fermion U-based compounds such as the hidden-order compound URu2Si2, their electronic structures exhibit complex behaviors. Their overall band structures are generally well-explained by the band-structure calculation, whereas the states in the vicinity of EF show some deviations due to electron correlation effects. Furthermore, the electronic structures of URu2Si2 in the paramagnetic and hidden-order phases are

8-band and 14-band kp modeling of electronic band structure and material gain in Ga(In)AsBi quantum wells grown on GaAs and InP substrates

Energy Technology Data Exchange (ETDEWEB)

Gladysiewicz, M.; Wartak, M. S. [Faculty of Fundamental Problems of Technology, Wroclaw University of Technology, Wybrzeze Wyspianskiego 27, 50-370 Wroclaw (Poland); Department of Physics and Computer Science, Wilfrid Laurier University, Waterloo, Ontario N2L 3C5 (Canada); Kudrawiec, R. [Faculty of Fundamental Problems of Technology, Wroclaw University of Technology, Wybrzeze Wyspianskiego 27, 50-370 Wroclaw (Poland)

2015-08-07

The electronic band structure and material gain have been calculated for GaAsBi/GaAs quantum wells (QWs) with various bismuth concentrations (Bi ≤ 15%) within the 8-band and 14-band kp models. The 14-band kp model was obtained by extending the standard 8-band kp Hamiltonian by the valence band anticrossing (VBAC) Hamiltonian, which is widely used to describe Bi-related changes in the electronic band structure of dilute bismides. It has been shown that in the range of low carrier concentrations n < 5 × 10{sup 18 }cm{sup −3}, material gain spectra calculated within 8- and 14-band kp Hamiltonians are similar. It means that the 8-band kp model can be used to calculate material gain in dilute bismides QWs. Therefore, it can be applied to analyze QWs containing new dilute bismides for which the VBAC parameters are unknown. Thus, the energy gap and electron effective mass for Bi-containing materials are used instead of VBAC parameters. The electronic band structure and material gain have been calculated for 8 nm wide GaInAsBi QWs on GaAs and InP substrates with various compositions. In these QWs, Bi concentration was varied from 0% to 5% and indium concentration was tuned in order to keep the same compressive strain (ε = 2%) in QW region. For GaInAsBi/GaAs QW with 5% Bi, gain peak was determined to be at about 1.5 μm. It means that it can be possible to achieve emission at telecommunication windows (i.e., 1.3 μm and 1.55 μm) for GaAs-based lasers containing GaInAsBi/GaAs QWs. For GaInAsBi/Ga{sub 0.47}In{sub 0.53}As/InP QWs with 5% Bi, gain peak is predicted to be at about 4.0 μm, i.e., at the wavelengths that are not available in current InP-based lasers.

Effect of pressure on the structural properties and electronic band structure of GaSe

Energy Technology Data Exchange (ETDEWEB)

Schwarz, U.; Olguin, D.; Syassen, K. [Max-Planck-Institut fuer Festkoerperforschung, Heisenbergstrasse 1, 70569 Stuttgart (Germany); Cantarero, A. [Department of Materials Sciences, University of Valencia, 46000 Burjasot (Spain); Hanfland, M. [European Synchrotron Radiation Facility, BP 220, 38043 Grenoble (France)

2007-01-15

The structural properties of GaSe have been investigated up to 38 GPa by monochromatic X-ray diffraction. The onset of the phase transition from the {epsilon}-GaSe to a disordered NaCl-type structural motif is observed near 21 GPa. Using the experimentally determined lattice parameters of the layered {epsilon}-phase as input, constrained ab-initio total energy calculations were performed in order to optimize the internal structural parameters at different pressures. The results obtained for the nearest-neighbor Ga-Se distance agree with those derived from recent EXAFS measurements. In addition, information is obtained on the changes of Ga-Ga and Se-Se bond lengths which were not accessible to a direct experimental determination yet. Based on the optimized structural parameters, we report calculations of band gap changes of {epsilon}-GaSe under pressure. The optical response and electronic band structure of the metallic high-pressure phase of GaSe are discussed briefly. (copyright 2007 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

Electronic structure investigation of MoS2 and MoSe2 using angle-resolved photoemission spectroscopy and ab initio band structure studies.

Science.gov (United States)

Mahatha, S K; Patel, K D; Menon, Krishnakumar S R

2012-11-28

Angle-resolved photoemission spectroscopy (ARPES) and ab initio band structure calculations have been used to study the detailed valence band structure of molybdenite, MoS(2) and MoSe(2). The experimental band structure obtained from ARPES has been found to be in good agreement with the theoretical calculations performed using the linear augmented plane wave (LAPW) method. In going from MoS(2) to MoSe(2), the dispersion of the valence bands decreases along both k(parallel) and k(perpendicular), revealing the increased two-dimensional character which is attributed to the increasing interlayer distance or c/a ratio in these compounds. The width of the valence band and the band gap are also found to decrease, whereas the valence band maxima shift towards the higher binding energy from MoS(2) to MoSe(2).

Band structure, band offsets, substitutional doping, and Schottky barriers of bulk and monolayer InSe

Science.gov (United States)

Guo, Yuzheng; Robertson, John

2017-09-01

We present a detailed study of the electronic structure of the layered semiconductor InSe. We calculate the band structure of the monolayer and bulk material using density functional theory, hybrid functionals, and G W . The band gap of the monolayer InSe is calculated to be 2.4 eV in screened exchange hybrid functional, close to the experimental photoluminescence gap. The electron affinities and band offsets are calculated for vertical stacked-layer heterostructures, and are found to be suitable for tunnel field effect transistors (TFETs) in combination with WS e2 or similar. The valence-band edge of InSe is calculated to lie 5.2 eV below the vacuum level, similar to that for the closed shell systems HfS e2 or SnS e2 . Hence InSe would be suitable to act as a p -type drain in the TFET. The intrinsic defects are calculated. For Se-rich layers, the Se adatom (interstitial) is found to be the most stable defect, whereas for In-rich layers, the Se vacancy is the most stable for the neutral state. Antisites tend to have energies just above those of vacancies. The Se antisite distorts towards a bond-breaking distortion as in the EL2 center of GaAs. Both substitutional donors and acceptors are calculated to be shallow, and effective dopants. They do not reconstruct to form nondoping configurations as occurs in black phosphorus. Finally, the Schottky barriers of metals on InSe are found to be strongly pinned by metal induced gap states (MIGS) at ˜0.5 eV above the valence-band edge. Any interfacial defects would lead to a stronger pinning at a similar energy. Overall, InSe is an effective semiconductor combining the good features of 2D (lack of dangling bonds, etc.) with the good features of 3D (effective doping), which few others achieve.

Energy band structure of Cr by the Slater-Koster interpolation scheme

International Nuclear Information System (INIS)

Seifu, D.; Mikusik, P.

1986-04-01

The matrix elements of the Hamiltonian between nine localized wave-functions in tight-binding formalism are derived. The symmetry adapted wave-functions and the secular equations are formed by the group theory method for high symmetry points in the Brillouin zone. A set of interaction integrals is chosen on physical ground and fitted via the Slater-Koster interpolation scheme to the abinito band structure of chromium calculated by the Green function method. Then the energy band structure of chromium is interpolated and extrapolated in the Brillouin zone. (author)

Electronic structure of the misfit layer compound (SnS)(1.20)TiS2 : Band structure calculations and photoelectron spectra

NARCIS (Netherlands)

Fang, CM; deGroot, RA; Wiegers, GA; Haas, C

1996-01-01

In order to understand the electronic structure of the incommensurate misfit layer compound (SnS)(1.20)TiS2 we carried out an ab initio band structure calculation in the supercell approximation. The band structure is compared with that of the components 1T-TiS2 and hypothetical SnS with a similar

Electronic structure of the misfit layer compound (SnS)1.20TiS2 : band structure calculations and photoelectron spectra

NARCIS (Netherlands)

Fang, C.M.; Groot, R.A. de; Wiegers, G.A.; Haas, C.

1996-01-01

In order to understand the electronic structure of the incommensurate misfit layer compound (SnS)1.20TiS2 we carried out an ab initio band structure calculation in the supercell approximation. The band structure is compared with that of the components 1T-TiS2 and hypothetical SnS with a similar

Cherenkov oscillator operating at the second band gap of leakage waveguide structures

Directory of Open Access Journals (Sweden)

Kyu-Ha Jang

2016-10-01

Full Text Available An electromagnetic wave source operating around second band gaps of metallic grating structures is presented. The considered metallic grating structures are not perfect periodic but inhomogeneously structured within a period to have a second band gap where the wavelength is equal to the period of the structures. The radiation mechanism by an electron beam in the structures is different from the well-known Smith-Purcell radiation occurring in perfect periodic grating structures. That is, the radiating wave has a single frequency and the radiation is unidirectional. When the energy of the electron beam is synchronized at the standing wave point in the dispersion curves, strong interaction happens and coherent radiation perpendicular to the grating surface is generated with relatively lower starting oscillation current.

The band gap variation of a two dimensional binary locally resonant structure in thermal environment

Directory of Open Access Journals (Sweden)

Zhen Li

2017-01-01

Full Text Available In this study, the numerical investigation of thermal effect on band gap dynamical characteristic for a two-dimensional binary structure composed of aluminum plate periodically filled with nitrile rubber cylinder is presented. Initially, the band gap of the binary structure variation trend with increasing temperature is studied by taking the softening effect of thermal stress into account. A breakthrough is made which found the band gap being narrower and shifting to lower frequency in thermal environment. The complete band gap which in higher frequency is more sensitive to temperature that it disappears with temperature increasing. Then some new transformed models are created by changing the height of nitrile rubber cylinder from 1mm to 7mm. Simulations show that transformed model can produce a wider band gap (either flexure or complete band gap. A proper forbidden gap of elastic wave can be utilized in thermal environment although both flexure and complete band gaps become narrower with temperature. Besides that, there is a zero-frequency flat band appearing in the first flexure band, and it becomes broader with temperature increasing. The band gap width decreases trend in thermal environment, as well as the wider band gap induced by the transformed model with higher nitrile rubber cylinder is useful for the design and application of phononic crystal structures in thermal environment.

Comparison and fit of the two and six band k.p models for the band edge structure of Pbsub(1-x)Snsub(x)Te

International Nuclear Information System (INIS)

Weissman, Y.

1975-10-01

The band edge structure of Pbsub(1-x)Snsub(x)Te is derived in detail using a two band ellipsoidal model and compared with a more rigorous calculation based on six bands. A quantitative comparison is made for two values of the energy gap, corresponding to the cases where x=0 and x=0.17. It was found that, for the occupied states in nondegenerate materials, both models are practically equivalent. Discrepancies may occur only in high degeneracies or deep inversion layers. The agreement between both models was significantly improved by introducing an effective energy gap in the two band model. It is suggested that the use of the effective energy gap may improve the agreement between the two band model and experiment whenever the details of the band edge structure enter the interpretation of the experimental results. (author)

ELECTRONIC-STRUCTURE OF THE MISFIT-LAYER COMPOUND (SNS)(1.17)NBS2 DEDUCED FROM BAND-STRUCTURE CALCULATIONS AND PHOTOELECTRON-SPECTRA

NARCIS (Netherlands)

FANG, CM; ETTEMA, ARHF; HAAS, C; WIEGERS, GA; VANLEUKEN, H; DEGROOT, RA

1995-01-01

In order to understand the electronic structure of the misfit-layer compound (SnS)(1.17)NbS2 we carried out an ab initio band-structure calculation of the closely related commensurate compound (SnS)(1.20)NbS2. The band structure is compared with calculations for NbS2 and for hypothetical SnS with

Results from the CLIC X-Band Structure Test Program at NLCTA

International Nuclear Information System (INIS)

Adolphsen, C.

2009-01-01

As part of a SLAC-CERN-KEK collaboration on high gradient X-band structure research, several prototype structures for the CLIC linear collider study have been tested using two of the high power (300 MW) X-band rf stations in the NLCTA facility at SLAC. These structures differ in terms of their fabrication (brazed disks and clamped quadrants), gradient profile (amount by which the gradient increases along the structure, which optimizes efficiency and maximizes sustainable gradient) and HOM damping (use of slots or waveguides to rapidly dissipate dipole mode energy). The CLIC goal in the next few years is to demonstrate the feasibility of a CLIC-ready baseline design and to investigate alternatives that could increase efficiency. This paper summarizes the high gradient test results from NLCTA in support of this effort.

Doping-dependent quasiparticle band structure in cuprate superconductors

NARCIS (Netherlands)

Eder, R; Ohta, Y.; Sawatzky, G.A

1997-01-01

We present an exact diagonalization study of the single-particle spectral function in the so-called t-t'-t ''-J model in two dimensions. As a key result, we find that hole doping leads to a major reconstruction of the quasiparticle band structure near (pi,0): whereas for the undoped system the

Evidence of ion intercalation mediated band structure modification and opto-ionic coupling in lithium niobite

Science.gov (United States)

Shank, Joshua C.; Tellekamp, M. Brooks; Doolittle, W. Alan

2015-01-01

The theoretically suggested band structure of the novel p-type semiconductor lithium niobite (LiNbO2), the direct coupling of photons to ion motion, and optically induced band structure modifications are investigated by temperature dependent photoluminescence. LiNbO2 has previously been used as a memristor material but is shown here to be useful as a sensor owing to the electrical, optical, and chemical ease of lithium removal and insertion. Despite the high concentration of vacancies present in lithium niobite due to the intentional removal of lithium atoms, strong photoluminescence spectra are observed even at room temperature that experimentally confirm the suggested band structure implying transitions from a flat conduction band to a degenerate valence band. Removal of small amounts of lithium significantly modifies the photoluminescence spectra including additional larger than stoichiometric-band gap features. Sufficient removal of lithium results in the elimination of the photoluminescence response supporting the predicted transition from a direct to indirect band gap semiconductor. In addition, non-thermal coupling between the incident laser and lithium ions is observed and results in modulation of the electrical impedance.

Evidence of ion intercalation mediated band structure modification and opto-ionic coupling in lithium niobite

International Nuclear Information System (INIS)

Shank, Joshua C.; Tellekamp, M. Brooks; Doolittle, W. Alan

2015-01-01

The theoretically suggested band structure of the novel p-type semiconductor lithium niobite (LiNbO 2 ), the direct coupling of photons to ion motion, and optically induced band structure modifications are investigated by temperature dependent photoluminescence. LiNbO 2 has previously been used as a memristor material but is shown here to be useful as a sensor owing to the electrical, optical, and chemical ease of lithium removal and insertion. Despite the high concentration of vacancies present in lithium niobite due to the intentional removal of lithium atoms, strong photoluminescence spectra are observed even at room temperature that experimentally confirm the suggested band structure implying transitions from a flat conduction band to a degenerate valence band. Removal of small amounts of lithium significantly modifies the photoluminescence spectra including additional larger than stoichiometric-band gap features. Sufficient removal of lithium results in the elimination of the photoluminescence response supporting the predicted transition from a direct to indirect band gap semiconductor. In addition, non-thermal coupling between the incident laser and lithium ions is observed and results in modulation of the electrical impedance

The use of Wannier function in the calculations of band structure of covalent crystals

International Nuclear Information System (INIS)

Lu Dong; Yang Guang

1985-10-01

A variational procedure has been used to build up Wannier functions to study the energy bands of diamond, silicon and α-tin. For the case of silicon the Wannier function, density of charge and band structure are calculated self-consistently and a simple method in a non-self-consistent way has been used to compute the band structure of diamond, silicon and α-tin. The method seems to be effective to describe the electronic properties of covalent crystals. (author)

Measurement of valence band structure in arbitrary dielectric films

International Nuclear Information System (INIS)

Uhm, Han S.; Choi, Eun H.

2012-01-01

A new way of measuring the band structure of various dielectric materials using the secondary electron emission from Auger neutralization of ions is introduced. The first example of this measurement scheme is the magnesium oxide (MgO) films with respect to the application of the films in the display industries. The density of state in the valence bands of MgO film and MgO film with a functional layer (FL) deposited over a dielectric surface reveals that the density peak of film with a FL is considerably less than that of film, thereby indicating a better performance of MgO film with functional layer in display devices. The second example of the measurement is the boron-zinc oxide (BZO) films with respect to the application of the films to the development of solar cells. The measurement of density of state in BZO film suggests that a high concentration of boron impurity in BZO films may enhance the transition of electrons and holes through the band gap from the valence to the conduction band in zinc oxide crystals; thereby improving the conductivity of the film. Secondary electron emission by the Auger neutralization of ions is highly instrumental for the determination of the density of states in the valence band of dielectric materials.

QUANTITATIVE ANALYSIS OF BANDED STRUCTURES IN DUAL-PHASE STEELS

Directory of Open Access Journals (Sweden)

Benoit Krebs

2011-05-01

Full Text Available Dual-Phase (DP steels are composed of martensite islands dispersed in a ductile ferrite matrix, which provides a good balance between strength and ductility. Current processing conditions (continuous casting followed by hot and cold rolling generate 'banded structures' i.e., irregular, parallel and alternating bands of ferrite and martensite, which are detrimental to mechanical properties and especially for in-use properties. We present an original and simple method to quantify the intensity and wavelength of these bands. This method, based on the analysis of covariance function of binary images, is firstly tested on model images. It is compared with ASTM E-1268 standard and appears to be more robust. Then it is applied on real DP steel microstructures and proves to be sufficiently sensitive to discriminate samples resulting from different thermo-mechanical routes.

Quasiparticle semiconductor band structures including spin-orbit interactions.

Science.gov (United States)

Malone, Brad D; Cohen, Marvin L

2013-03-13

We present first-principles calculations of the quasiparticle band structure of the group IV materials Si and Ge and the group III-V compound semiconductors AlP, AlAs, AlSb, InP, InAs, InSb, GaP, GaAs and GaSb. Calculations are performed using the plane wave pseudopotential method and the 'one-shot' GW method, i.e. G(0)W(0). Quasiparticle band structures, augmented with the effects of spin-orbit, are obtained via a Wannier interpolation of the obtained quasiparticle energies and calculated spin-orbit matrix. Our calculations explicitly treat the shallow semicore states of In and Ga, which are known to be important in the description of the electronic properties, as valence states in the quasiparticle calculation. Our calculated quasiparticle energies, combining both the ab initio evaluation of the electron self-energy and the vector part of the pseudopotential representing the spin-orbit effects, are in generally very good agreement with experimental values. These calculations illustrate the predictive power of the methodology as applied to group IV and III-V semiconductors.

Band structure in Platinum nuclei (A ∼ 182)

International Nuclear Information System (INIS)

Popescu, D.G.

1991-01-01

In this thesis, the author studies the band structure in Platinum nuclei and has divided his work in 5 parts: in the first, the author makes a general presentation of nucleus physics with a high angular momentum and introduces to the deformed nucleus notion -axial, triaxial or mixing of different deformations. The notion of form co-existence will be used to interpret the experimental results. In the second part, the author describes the detection means which have been used to make measurements. An abstract of theoretical notions, usefull for the understanding of fusion-evaporation reaction is presented. The author explains the details, performances and different modes of using of 'Chateau de cristal' and others used spectrometers. In the third part, the author presents all experimental data. He has effected γ coincidence measurements for Pt, Au and Ir nuclei. In the fourth part, for a classical analysis or an interpretation in the frame of cranking model the author presents theoretical models which are adapted at the study of high spin states and band structures

Band structures of two dimensional solid/air hierarchical phononic crystals

International Nuclear Information System (INIS)

Xu, Y.L.; Tian, X.G.; Chen, C.Q.

2012-01-01

The hierarchical phononic crystals to be considered show a two-order “hierarchical” feature, which consists of square array arranged macroscopic periodic unit cells with each unit cell itself including four sub-units. Propagation of acoustic wave in such two dimensional solid/air phononic crystals is investigated by the finite element method (FEM) with the Bloch theory. Their band structure, wave filtering property, and the physical mechanism responsible for the broadened band gap are explored. The corresponding ordinary phononic crystal without hierarchical feature is used for comparison. Obtained results show that the solid/air hierarchical phononic crystals possess tunable outstanding band gap features, which are favorable for applications such as sound insulation and vibration attenuation.

Band structures of two dimensional solid/air hierarchical phononic crystals

Energy Technology Data Exchange (ETDEWEB)

Xu, Y.L.; Tian, X.G. [State Key Laboratory for Mechanical Structure Strength and Vibration, Xi' an Jiaotong University, Xi' an 710049 (China); Chen, C.Q., E-mail: chencq@tsinghua.edu.cn [Department of Engineering Mechanics, AML and CNMM, Tsinghua University, Beijing 100084 (China)

2012-06-15

The hierarchical phononic crystals to be considered show a two-order 'hierarchical' feature, which consists of square array arranged macroscopic periodic unit cells with each unit cell itself including four sub-units. Propagation of acoustic wave in such two dimensional solid/air phononic crystals is investigated by the finite element method (FEM) with the Bloch theory. Their band structure, wave filtering property, and the physical mechanism responsible for the broadened band gap are explored. The corresponding ordinary phononic crystal without hierarchical feature is used for comparison. Obtained results show that the solid/air hierarchical phononic crystals possess tunable outstanding band gap features, which are favorable for applications such as sound insulation and vibration attenuation.

Role of the Z band in the mechanical properties of the heart.

Science.gov (United States)

Goldstein, M A; Schroeter, J P; Michael, L H

1991-05-01

In striated muscle the mechanism of contraction involves the cooperative movement of contractile and elastic components. This review emphasizes a structural approach that describes the cellular and extracellular components with known anatomical, biochemical, and physical properties that make them candidates for these contractile and elastic components. Classical models of contractile and elastic elements and their underlying assumptions are presented. Mechanical properties of cardiac and skeletal muscle are compared and contrasted and then related to ultrastructure. Information from these approaches leads to the conclusion that the Z band is essential for muscle contraction. Our review of Z band structure shows the Z band at the interface where extracellular components meet the cell surface. The Z band is also the interface from cell surface to myofibril, from extra-myofibrillar to myofibril, and finally from sarcomere to sarcomere. Our studies of Z band in defined physiologic states show that this lattice is an integral part of the contractile elements and can function as an elastic component. The Z band is a complex dynamic lattice uniquely suited to play several roles in muscle contraction.

The quasiparticle band structure of zincblende and rocksalt ZnO.

Science.gov (United States)

Dixit, H; Saniz, R; Lamoen, D; Partoens, B

2010-03-31

We present the quasiparticle band structure of ZnO in its zincblende (ZB) and rocksalt (RS) phases at the Γ point, calculated within the GW approximation. The effect of the p-d hybridization on the quasiparticle corrections to the band gap is discussed. We compare three systems, ZB-ZnO which shows strong p-d hybridization and has a direct band gap, RS-ZnO which is also hybridized but includes inversion symmetry and therefore has an indirect band gap, and ZB-ZnS which shows a weaker hybridization due to a change of the chemical species from oxygen to sulfur. The quasiparticle corrections are calculated with different numbers of valence electrons in the Zn pseudopotential. We find that the Zn(20+) pseudopotential is essential for the adequate treatment of the exchange interaction in the self-energy. The calculated GW band gaps are 2.47 eV and 4.27 eV respectively, for the ZB and RS phases. The ZB-ZnO band gap is underestimated compared to the experimental value of 3.27 by ∼ 0.8 eV. The RS-ZnO band gap compares well with the experimental value of 4.5 eV. The underestimation for ZB-ZnO is correlated with the strong p-d hybridization. The GW band gap for ZnS is 3.57 eV, compared to the experimental value of 3.8 eV.

Valley-dependent band structure and valley polarization in periodically modulated graphene

Science.gov (United States)

Lu, Wei-Tao

2016-08-01

The valley-dependent energy band and transport property of graphene under a periodic magnetic-strained field are studied, where the time-reversal symmetry is broken and the valley degeneracy is lifted. The considered superlattice is composed of two different barriers, providing more degrees of freedom for engineering the electronic structure. The electrons near the K and K' valleys are dominated by different effective superlattices. It is found that the energy bands for both valleys are symmetric with respect to ky=-(AM+ξ AS) /4 under the symmetric superlattices. More finite-energy Dirac points, more prominent collimation behavior, and new crossing points are found for K' valley. The degenerate miniband near the K valley splits into two subminibands and produces a new band gap under the asymmetric superlattices. The velocity for the K' valley is greatly renormalized compared with the K valley, and so we can achieve a finite velocity for the K valley while the velocity for the K' valley is zero. Especially, the miniband and band gap could be manipulated independently, leading to an increase of the conductance. The characteristics of the band structure are reflected in the transmission spectra. The Dirac points and the crossing points appear as pronounced peaks in transmission. A remarkable valley polarization is obtained which is robust to the disorder and can be controlled by the strain, the period, and the voltage.

Engineering the electronic band structures of novel cubic structured germanium monochalcogenides for thermoelectric applications

Science.gov (United States)

Ul Haq, Bakhtiar; AlFaify, S.; Ahmed, R.; Butt, Faheem K.; Laref, A.; Goumri-Said, Souraya; Tahir, S. A.

2018-05-01

Germanium mono-chalcogenides have received considerable attention for being a promising replacement for the relatively toxic and expensive chalcogenides in renewable and sustainable energy applications. In this paper, we explore the potential of the recently discovered novel cubic structured (π-phase) GeS and GeSe for thermoelectric applications in the framework of density functional theory coupled with Boltzmann transport theory. To examine the modifications in their physical properties, the across composition alloying of π-GeS and π-GeSe (such as π-GeS1-xSex for x =0, 0.25, 0.50, 0.75, and 1) has been performed that has shown important effects on the electronic band structures and effective masses of charge carriers. An increase in Se composition in π-GeS1-xSex has induced a downward shift in their conduction bands, resulting in the narrowing of their energy band gaps. The thermoelectric coefficients of π-GeS1-xSex have been accordingly influenced by the evolution of the electronic band structures and effective masses of charge carriers. π-GeS1-xSex features sufficiently larger values of Seebeck coefficients, power factors and figures of merit (ZTs), which experience further improvement with an increase in temperature, revealing their potential for high-temperature applications. The calculated results show that ZT values equivalent to unity can be achieved for π-GeS1-xSex at appropriate n-type doping levels. Our calculations for the formation enthalpies indicate that a π-GeS1-xSex alloying system is energetically stable and could be synthesized experimentally. These intriguing characteristics make π-GeS1-xSex a promising candidate for futuristic thermoelectric applications in energy harvesting devices.

Evidence of ion intercalation mediated band structure modification and opto-ionic coupling in lithium niobite

Energy Technology Data Exchange (ETDEWEB)

Shank, Joshua C.; Tellekamp, M. Brooks; Doolittle, W. Alan, E-mail: alan.doolittle@ece.gatech.edu [Department of Electrical and Computer Engineering, Georgia Institute of Technology, Atlanta, Georgia 30332 (United States)

2015-01-21

The theoretically suggested band structure of the novel p-type semiconductor lithium niobite (LiNbO{sub 2}), the direct coupling of photons to ion motion, and optically induced band structure modifications are investigated by temperature dependent photoluminescence. LiNbO{sub 2} has previously been used as a memristor material but is shown here to be useful as a sensor owing to the electrical, optical, and chemical ease of lithium removal and insertion. Despite the high concentration of vacancies present in lithium niobite due to the intentional removal of lithium atoms, strong photoluminescence spectra are observed even at room temperature that experimentally confirm the suggested band structure implying transitions from a flat conduction band to a degenerate valence band. Removal of small amounts of lithium significantly modifies the photoluminescence spectra including additional larger than stoichiometric-band gap features. Sufficient removal of lithium results in the elimination of the photoluminescence response supporting the predicted transition from a direct to indirect band gap semiconductor. In addition, non-thermal coupling between the incident laser and lithium ions is observed and results in modulation of the electrical impedance.

Estimating tropical forest structure using LIDAR AND X-BAND INSAR

Science.gov (United States)

Palace, M. W.; Treuhaft, R. N.; Keller, M. M.; Sullivan, F.; Roberto dos Santos, J.; Goncalves, F. G.; Shimbo, J.; Neumann, M.; Madsen, S. N.; Hensley, S.

2013-12-01

Tropical forests are considered the most structurally complex of all forests and are experiencing rapid change due to anthropogenic and climatic factors. The high carbon stocks and fluxes make understanding tropical forests highly important to both regional and global studies involving ecosystems and climate. Large and remote areas in the tropics are prime targets for the use of remotely sensed data. Radar and lidar have previously been used to estimate forest structure, with an emphasis on biomass. These two remote sensing methods have the potential to yield much more information about forest structure, specifically through the use of X-band radar and waveform lidar data. We examined forest structure using both field-based and remotely sensed data in the Tapajos National Forest, Para, Brazil. We measured multiple structural parameters for about 70 plots in the field within a 25 x 15 km area that have TanDEM-X single-pass horizontally and vertically polarized radar interferometric data. High resolution airborne lidar were collected over a 22 sq km portion of the same area, within which 33 plots were co-located. Preliminary analyses suggest that X-band interferometric coherence decreases by about a factor of 2 (from 0.95 to 0.45) with increasing field-measured vertical extent (average heights of 7-25 m) and biomass (10-430 Mg/ha) for a vertical wavelength of 39 m, further suggesting, as has been observed at C-band, that interferometric synthetic aperture radar (InSAR) is substantially more sensitive to forest structure/biomass than SAR. Unlike InSAR coherence versus biomass, SAR power at X-band versus biomass shows no trend. Moreover, airborne lidar coherence at the same vertical wavenumbers as InSAR is also shown to decrease as a function of biomass, as well. Although the lidar coherence decrease is about 15% more than the InSAR, implying that lidar penetrates more than InSAR, these preliminary results suggest that X-band InSAR may be useful for structure and

Monolithic dual-band HgCdTe infrared detector structure

CSIR Research Space (South Africa)

Parish, G

1997-07-01

Full Text Available A monolithic HgCdTe photoconductive device structure is presented that is suitable for dual-band optically registered infrared photodetection in the two atmospheric transmission windows of 3-5 mu m and 8-12 mu m, which correspond to the mid...

Band Structure Analysis of La0.7Sr0.3MnO3 Perovskite Manganite Using a Synchrotron

Directory of Open Access Journals (Sweden)

Hong-Sub Lee

2015-01-01

Full Text Available Oxide semiconductors and their application in next-generation devices have received a great deal of attention due to their various optical, electric, and magnetic properties. For various applications, an understanding of these properties and their mechanisms is also very important. Various characteristics of these oxides originate from the band structure. In this study, we introduce a band structure analysis technique using a soft X-ray energy source to study a La0.7Sr0.3MnO3 (LSMO oxide semiconductor. The band structure is formed by a valence band, conduction band, band gap, work function, and electron affinity. These can be determined from secondary electron cut-off, valence band spectrum, O 1s core electron, and O K-edge measurements using synchrotron radiation. A detailed analysis of the band structure of the LSMO perovskite manganite oxide semiconductor thin film was established using these techniques.

Metal-like Band Structures of Ultrathin Si {111} and {112} Surface Layers Revealed through Density Functional Theory Calculations.

Science.gov (United States)

Tan, Chih-Shan; Huang, Michael H

2017-09-04

Density functional theory calculations have been performed on Si (100), (110), (111), and (112) planes with tunable number of planes for evaluation of their band structures and density of states profiles. The purpose is to see whether silicon can exhibit facet-dependent properties derived from the presence of a thin surface layer having different band structures. No changes have been observed for single to multiple layers of Si (100) and (110) planes with a consistent band gap between the valence band and the conduction band. However, for 1, 2, 4, and 5 Si (111) and (112) planes, metal-like band structures were obtained with continuous density of states going from the valence band to the conduction band. For 3, 6, and more Si (111) planes, as well as 3 and 6 Si (112) planes, the same band structure as that seen for Si (100) and (110) planes has been obtained. Thus, beyond a layer thickness of five Si (111) planes at ≈1.6 nm, normal semiconductor behavior can be expected. The emergence of metal-like band structures for the Si (111) and (112) planes are related to variation in Si-Si bond length and bond distortion plus 3s and 3p orbital electron contributions in the band structure. This work predicts possession of facet-dependent electrical properties of silicon with consequences in FinFET transistor design. © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

Theoretical study of band structure of odd-mass {sup 115,117}I isotopes

Energy Technology Data Exchange (ETDEWEB)

Singh, Dhanvir, E-mail: singh1472phy@gmail.com; Kumar, Amit, E-mail: akbcw2@gmail.com; Sharma, Chetan, E-mail: chetan24101985@gmail.com [Research Scholar, Department of Physics and Electronics, University of Jammu, Jammu-180006 (India); Singh, Suram, E-mail: suramsingh@gmail.com [Assistant Professor, Department of Physics, Govt. Degree College, Kathua-184101 (India); Bharti, Arun, E-mail: arunbharti-2003@yahoo.co.in [Professor, Department of Physics and Electronics, University of Jammu, Jammu-180006 (India)

2016-05-06

By using the microscopic approach of Projected Shell Model (PSM), negative-parity band structures of odd mass neutron-rich {sup 115,117}I nuclei have been studied with the deformed single-particle states generated by the standard Nilsson potential. For these isotopes, the band structures have been analyzed in terms of quasi-particles configurations. The phenomenon of back bending in moment of inertia is also studied in the present work.

Density Functional Theory Calculations Revealing Metal-like Band Structures for Ultrathin Ge {111} and {211} Surface Layers.

Science.gov (United States)

Tan, Chih-Shan; Huang, Michael Hsuan-Yi

2018-05-21

To find out if germanium should also possess facet-dependent electrical conductivity properties, surface state density functional theory (DFT) calculations were performed on 1-6 layers of Ge (100), (110), (111), and (211) planes. Tunable Ge (100) and (110) planes always present the same semiconducting band structure with a band gap of 0.67 eV expected of bulk germanium. In contrast, 1, 2, 4, and 5 layers of Ge (111) and (211) plane models show metal-like band structures with continuous density of states (DOS) throughout the entire band. For 3 and 6 layers of Ge (111) and (211) plane models, the normal semiconducting band structure was obtained. The plane layers with metal-like band structures also show Ge-Ge bond length deviations and bond distortions, as well as significantly different 4s and 4p frontier orbital electron count and their relative percentages integrated over the valence and conduction bands from those of the semiconducting state. These differences should contribute to strikingly dissimilar band structures. The calculation results suggest observation of facet-dependent electrical conductivity properties of germanium materials, and transistors made of germanium may also need to consider the facet effects with shrinking dimensions approaching 3 nm. © 2018 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Infrared absorption, multiphonon processes and time reversal effect on Si and Ge band structure

International Nuclear Information System (INIS)

Kunert, H.W.; Machatine, A.G.J.; Malherbe, J.B.; Barnas, J.; Hoffmann, A.; Wagner, M.R.

2008-01-01

We have examined the effect of Time Reversal Symmetry (TRS) on vibrational modes and on the electronic band structure of Si and Ge. Most of the primary non-interacting modes are not affected by TRS. Only phonons originating from high symmetry lines S and A of the Brillouin Zone (BZ) indicate extra degeneracy. Selection rules for some two and three phonons originating from high symmetry lines are determined. The states of electrons and holes described by electronic band structure due to spin-inclusion are assigned by spinor representations of the double space group. Inclusion of the TRS into the band structure results in extra degeneracy of electrons and holes, and therefore optical selection rules suppose to be modified

X-BAND LINEAR COLLIDER R and D IN ACCELERATING STRUCTURES THROUGH ADVANCED COMPUTING

International Nuclear Information System (INIS)

Li, Z

2004-01-01

This paper describes a major computational effort that addresses key design issues in the high gradient accelerating structures for the proposed X-band linear collider, GLC/NLC. Supported by the US DOE's Accelerator Simulation Project, SLAC is developing a suite of parallel electromagnetic codes based on unstructured grids for modeling RF structures with higher accuracy and on a scale previously not possible. The new simulation tools have played an important role in the R and D of X-Band accelerating structures, in cell design, wakefield analysis and dark current studies

From lattice Hamiltonians to tunable band structures by lithographic design

Science.gov (United States)

Tadjine, Athmane; Allan, Guy; Delerue, Christophe

2016-08-01

Recently, new materials exhibiting exotic band structures characterized by Dirac cones, nontrivial flat bands, and band crossing points have been proposed on the basis of effective two-dimensional lattice Hamiltonians. Here, we show using atomistic tight-binding calculations that these theoretical predictions could be experimentally realized in the conduction band of superlattices nanolithographed in III-V and II-VI semiconductor ultrathin films. The lithographed patterns consist of periodic lattices of etched cylindrical holes that form potential barriers for the electrons in the quantum well. In the case of honeycomb lattices, the conduction minibands of the resulting artificial graphene host several Dirac cones and nontrivial flat bands. Similar features, but organized in different ways, in energy or in k -space are found in kagome, distorted honeycomb, and Lieb superlattices. Dirac cones extending over tens of meV could be obtained in superlattices with reasonable sizes of the lithographic patterns, for instance in InAs/AlSb heterostructures. Bilayer artificial graphene could be also realized by lithography of a double quantum-well heterostructure. These new materials should be interesting for the experimental exploration of Dirac-based quantum systems, for both fundamental and applied physics.

An open-structure sound insulator against low-frequency and wide-band acoustic waves

Science.gov (United States)

Chen, Zhe; Fan, Li; Zhang, Shu-yi; Zhang, Hui; Li, Xiao-juan; Ding, Jin

2015-10-01

To block sound, i.e., the vibration of air, most insulators are based on sealed structures and prevent the flow of the air. In this research, an acoustic metamaterial adopting side structures, loops, and labyrinths, arranged along a main tube, is presented. By combining the accurately designed side structures, an extremely wide forbidden band with a low cut-off frequency of 80 Hz is produced, which demonstrates a powerful low-frequency and wide-band sound insulation ability. Moreover, by virtue of the bypass arrangement, the metamaterial is based on an open structure, and thus air flow is allowed while acoustic waves can be insulated.

Band structures of phononic crystal composed of lattices with different periodic constants

International Nuclear Information System (INIS)

Hu, Jia-Guang; Xu, Wen

2014-01-01

With a square lattice mercury and water system being as the model, the band structures of nesting and compound phononic crystals with two different lattice constants were investigated using the method of the supercell plane wave expansion. It was observed that large band gaps can be achieved in low frequency regions by adjusting one of the lattice constants. Meanwhile, effects similar to interstitial impurity defects can be achieved with the increase of lattice constant of the phononic crystal. The corresponding defect modes can be stimulated in band gaps. The larger the lattice constant, the stronger the localization effect of defect modes on the wave. In addition, the change of the filling fraction of impurity exerts great influence on the frequency and localization of defect modes. Furthermore, the change of the position of impurity has notable influence on the frequency of defect modes and their localization. However, the geometry structure and orientation of impurity have little effect on the frequency of defect modes and their localization in the band gap.

Electrical properties and band structures of Pb1-x Snx Te alloys

International Nuclear Information System (INIS)

Ocio, Miguel

1972-01-01

Both p type alloys Pb 0.72 Sn 0.28 Te and Pb 0.53 Sn 0.47 Te have been studied in the present work. The main obtained results are the following: the materials have a two-valence band structure, the first band following non-parabolic Cohen's dispersion law; at low temperatures, carriers are scattered by ionized impurities; the Coulomb potentials being screened almost completely, impurities act like neutral centers. At room temperature, scattering by acoustic modes can explain lattice mobility behavior; reversing of the thermo-power, for samples with carrier densities of about 10 20 cm -3 , is possibly due to inter-band scattering between both valence bands; a very simple picture of the band parameters variations as a function of alloy fraction is suggested. (author) [fr

Triple photonic band-gap structure dynamically induced in the presence of spontaneously generated coherence

International Nuclear Information System (INIS)

Gao Jinwei; Bao Qianqian; Wan Rengang; Cui Cuili; Wu Jinhui

2011-01-01

We study a cold atomic sample coherently driven into the five-level triple-Λ configuration for attaining a dynamically controlled triple photonic band-gap structure. Our numerical calculations show that three photonic band gaps with homogeneous reflectivities up to 92% can be induced on demand around the probe resonance by a standing-wave driving field in the presence of spontaneously generated coherence. All these photonic band gaps are severely malformed with probe reflectivities declining rapidly to very low values when spontaneously generated coherence is gradually weakened. The triple photonic band-gap structure can also be attained in a five-level chain-Λ system of cold atoms in the absence of spontaneously generated coherence, which however requires two additional traveling-wave fields to couple relevant levels.

SINGLE-BAND, TRIPLE-BAND, OR MULTIPLE-BAND HUBBARD MODELS

NARCIS (Netherlands)

ESKES, H; SAWATZKY, GA

1991-01-01

The relevance of different models, such as the one-band t-J model and the three-band Emery model, as a realistic description of the electronic structure of high-T(c) materials is discussed. Starting from a multiband approach using cluster calculations and an impurity approach, the following

Electronic structure of the copper oxides: Band picture versus correlated behavior

Energy Technology Data Exchange (ETDEWEB)

Pickett, W E; Cohen, R E; Singh, D [Naval Research Lab., Washington, DC (USA); Krakauer, H [Coll. of William and Mary, Williamsburg, VA (USA)

1989-12-01

In the 2 1/2 years since the discovery of the high temperature superconducting copper oxides, a great deal has been learned from experiment about their behavior. From the theoretical side, there continues to be developments both within the band picture and from the model Hamiltonian viewpoint emphasizing correlations. In this paper we discuss briefly these complementary viewpoints in relation to certain of the experimental data. Due to our background in the band structure area, we approach the discussion by evaluating which phenomena can be (or has been) accounted for by the standard band approach, and point out which properties appear to require more intricate treatments of correlation. (orig.).

Relativistic band-structure calculations for electronic properties of actinide dioxides

International Nuclear Information System (INIS)

Maehira, Takahiro; Hotta, Takashi

2007-01-01

Energy band structures of actinide dioxides AnO 2 (An=Th, U, Np, and Pu) are investigated by a relativistic linear augmented-plane-wave method with the exchange-correlation potential in a local density approximation (LDA). It is found in common that the energy bands in the vicinity of the Fermi level are mainly due to the hybridization between actinide 5f and oxygen 2p electrons. By focusing on the crystalline electric field states, we point out the problem in the application of the LDA to AnO 2

Electronic structure of SnS deduced from photoelectron spectra and band-structure calculations

NARCIS (Netherlands)

Ettema, A.R.H.F.; Groot, R.A. de; Haas, C.; Turner, T.S.

1992-01-01

SnS is a layer compound with a phase transition from a high-temperature β phase to a low-temperature α phase with a lower symmetry. Ab initio band-structure calculations are presented for both phases. The calculations show that the charge distributions in the two phases are very similar. However,

Electronic band structures of binary skutterudites

Energy Technology Data Exchange (ETDEWEB)

Khan, Banaras [Center for Computational Materials Science, University of Malakand, Chakdara (Pakistan); Department of Physics, University of Malakand, Chakdara (Pakistan); Aliabad, H.A. Rahnamaye [Department of Physics, Hakim Sabzevari University, Sabzevar (Iran, Islamic Republic of); Saifullah [Center for Computational Materials Science, University of Malakand, Chakdara (Pakistan); Department of Physics, University of Malakand, Chakdara (Pakistan); Jalali-Asadabadi, S. [Department of Physics, Faculty of Science, University of Isfahan (UI), 81744 Isfahan (Iran, Islamic Republic of); Khan, Imad [Center for Computational Materials Science, University of Malakand, Chakdara (Pakistan); Department of Physics, University of Malakand, Chakdara (Pakistan); Ahmad, Iftikhar, E-mail: ahma5532@gmail.com [Center for Computational Materials Science, University of Malakand, Chakdara (Pakistan); Department of Physics, University of Malakand, Chakdara (Pakistan)

2015-10-25

The electronic properties of complex binary skutterudites, MX{sub 3} (M = Co, Rh, Ir; X = P, As, Sb) are explored, using various density functional theory (DFT) based theoretical approaches including Green's Function (GW) as well as regular and non-regular Tran Blaha modified Becke Jhonson (TB-mBJ) methods. The wide range of calculated bandgap values for each compound of this skutterudites family confirm that they are theoretically as challenging as their experimental studies. The computationally expensive GW method, which is generally assume to be efficient in the reproduction of the experimental bandgaps, is also not very successful in the calculation of bandgaps. In this article, the issue of the theoretical bandgaps of these compounds is resolved by reproducing the accurate experimental bandgaps, using the recently developed non-regular TB-mBJ approach, based on DFT. The effectiveness of this technique is due to the fact that a large volume of the binary skutterudite crystal is empty and hence quite large proportion of electrons lie outside of the atomic spheres, where unlike LDA and GGA which are poor in the treatment of these electrons, this technique properly treats these electrons and hence reproduces the clear electronic picture of these compounds. - Highlights: • Theoretical and experimental electronic band structures of binary skutterudites are reviewed. • The literature reveals that none of the existing theoretical results are consistent with the experiments. • GW, regular and non-regular TB-mBJ methods are used to reproduce the correct results. • The GW and regular TB-mBJ results are better than the available results in literature. • However, non-regular TB-mBJ reproduces the correct experimental band structures.

Electronic band structures of binary skutterudites

International Nuclear Information System (INIS)

Khan, Banaras; Aliabad, H.A. Rahnamaye; Saifullah; Jalali-Asadabadi, S.; Khan, Imad; Ahmad, Iftikhar

2015-01-01

The electronic properties of complex binary skutterudites, MX 3 (M = Co, Rh, Ir; X = P, As, Sb) are explored, using various density functional theory (DFT) based theoretical approaches including Green's Function (GW) as well as regular and non-regular Tran Blaha modified Becke Jhonson (TB-mBJ) methods. The wide range of calculated bandgap values for each compound of this skutterudites family confirm that they are theoretically as challenging as their experimental studies. The computationally expensive GW method, which is generally assume to be efficient in the reproduction of the experimental bandgaps, is also not very successful in the calculation of bandgaps. In this article, the issue of the theoretical bandgaps of these compounds is resolved by reproducing the accurate experimental bandgaps, using the recently developed non-regular TB-mBJ approach, based on DFT. The effectiveness of this technique is due to the fact that a large volume of the binary skutterudite crystal is empty and hence quite large proportion of electrons lie outside of the atomic spheres, where unlike LDA and GGA which are poor in the treatment of these electrons, this technique properly treats these electrons and hence reproduces the clear electronic picture of these compounds. - Highlights: • Theoretical and experimental electronic band structures of binary skutterudites are reviewed. • The literature reveals that none of the existing theoretical results are consistent with the experiments. • GW, regular and non-regular TB-mBJ methods are used to reproduce the correct results. • The GW and regular TB-mBJ results are better than the available results in literature. • However, non-regular TB-mBJ reproduces the correct experimental band structures

Imaging the Nanoscale Band Structure of Topological Sb

OpenAIRE

Soumyanarayanan, Anjan; Yee, Michael M.; He, Yang; Lin, Hsin; Gardner, Dillon R.; Bansil, Arun; Lee, Young S.; Hoffman, Jennifer E.

2013-01-01

Many promising building blocks of future electronic technology - including non-stoichiometric compounds, strongly correlated oxides, and strained or patterned films - are inhomogeneous on the nanometer length scale. Exploiting the inhomogeneity of such materials to design next-generation nanodevices requires a band structure probe with nanoscale spatial resolution. To address this demand, we report the first simultaneous observation and quantitative reconciliation of two candidate probes - La...

Analysis of photonic band gap in novel piezoelectric photonic crystal

Science.gov (United States)

Malar Kodi, A.; Doni Pon, V.; Joseph Wilson, K. S.

2018-03-01

The transmission properties of one-dimensional novel photonic crystal having silver-doped novel piezoelectric superlattice and air as the two constituent layers have been investigated by means of transfer matrix method. By changing the appropriate thickness of the layers and filling factor of nanocomposite system, the variation in the photonic band gap can be studied. It is found that the photonic band gap increases with the filling factor of the metal nanocomposite and with the thickness of the layer. These structures possess unique characteristics enabling one to operate as optical waveguides, selective filters, optical switches, integrated piezoelectric microactuators, etc.

L-band brightness temperature disaggregation for use with S-band and C-band radiometer data for WCOM

Science.gov (United States)

Yao, P.; Shi, J.; Zhao, T.; Cosh, M. H.; Bindlish, R.

2017-12-01

There are two passive microwave sensors onboard the Water Cycle Observation Mission (WCOM), which includes a synthetic aperture radiometer operating at L-S-C bands and a scanning microwave radiometer operating from C- to W-bands. It provides a unique opportunity to disaggregate L-band brightness temperature (soil moisture) with S-band C-bands radiometer data. In this study, passive-only downscaling methodologies are developed and evaluated. Based on the radiative transfer modeling, it was found that the TBs (brightness temperature) between the L-band and S-band exhibit a linear relationship, and there is an exponential relationship between L-band and C-band. We carried out the downscaling results by two methods: (1) downscaling with L-S-C band passive measurements with the same incidence angle from payload IMI; (2) downscaling with L-C band passive measurements with different incidence angle from payloads IMI and PMI. The downscaling method with L-S bands with the same incident angle was first evaluated using SMEX02 data. The RMSE are 2.69 K and 1.52 K for H and V polarization respectively. The downscaling method with L-C bands is developed with different incident angles using SMEX03 data. The RMSE are 2.97 K and 2.68 K for H and V polarization respectively. These results showed that high-resolution L-band brightness temperature and soil moisture products could be generated from the future WCOM passive-only observations.

Band structure engineering for ultracold quantum gases in optical lattices

International Nuclear Information System (INIS)

Weinberg, Malte

2014-01-01

The energy band structure fundamentally influences the physical properties of a periodic system. It may give rise to highly exotic phenomena in yet uncharted physical regimes. Ultracold quantum gases in optical lattices provide an ideal playground for the investigation of a large variety of such intriguing effects. Experiments presented here address several issues that require the systematic manipulation of energy band structures in optical lattices with diverse geometries. These artificial crystals of light, generated by interfering laser beams, allow for an unprecedented degree of control over a wide range of parameters. A major part of this thesis employs time-periodic driving to engineer tunneling matrix elements and, thus, the dispersion relation for bosonic quantum gases in optical lattices. Resonances emerging in the excitation spectrum due to the particularly strong forcing can be attributed to multi-photon transitions that are investigated systematically. By changing the sign of the tunneling, antiferromagnetic spin-spin interactions can be emulated. In a triangular lattice this leads to geometrical frustration with a doubly degenerate ground state as the simultaneous minimization of competing interactions is inhibited. Moreover, complex-valued tunneling matrix elements can be generated with a suitable breaking of time-reversal symmetry in the driving scheme. The associated Peierls phases mimic the presence of an electromagnetic vector gauge potential acting on charged particles. First proof-of-principle experiments reveal an excellent agreement with theoretical calculations. In the weakly interacting superfluid regime, these artificial gauge fields give rise to an Ising-XY model with tunable staggered magnetic fluxes and a complex interplay between discrete and continuous symmetries. A thermal phase transition from an ordered ferromagnetic- to an unordered paramagnetic state could be observed. In the opposite hard-core boson limit of strong interactions

A first principle study of band structure of III-nitride compounds

Energy Technology Data Exchange (ETDEWEB)

Ahmed, Rashid [Centre for High Energy Physics University of the Punjab, Lahore-54590 (Pakistan)]. E-mail: rasofi@hotmail.com; Akbarzadeh, H. [Department of Physics, Isfahan University of Technology, 841546 Isfahan (Iran, Islamic Republic of); Fazal-e-Aleem [Centre for High Energy Physics University of the Punjab, Lahore-54590 (Pakistan)

2005-12-15

The band structure of both phases, zinc-blende and wurtzite, of aluminum nitride, indium nitride and gallium nitride has been studied using computational methods. The study has been done using first principle full-potential linearized augmented plane wave (FP-LAPW) method, within the framework of density functional theory (DFT). For the exchange correlation potential, generalized gradient approximation (GGA) and an alternative form of GGA proposed by Engel and Vosko (GGA-EV) have been used. Results obtained for band structure of these compounds have been compared with experimental results as well as other first principle computations. Our results show a significant improvement over other theoretical work and are closer to the experimental data.

The Development of Layered Photonic Band Gap Structures Using a Micro-Transfer Molding Technique

International Nuclear Information System (INIS)

Kevin Jerome Sutherland

2001-01-01

Photonic band gap (PBG) crystals are periodic dielectric structures that manipulate electromagnetic radiation in a manner similar to semiconductor devices manipulating electrons. Whereas a semiconductor material exhibits an electronic band gap in which electrons cannot exist, similarly, a photonic crystal containing a photonic band gap does not allow the propagation of specific frequencies of electromagnetic radiation. This phenomenon results from the destructive Bragg diffraction interference that a wave propagating at a specific frequency will experience because of the periodic change in dielectric permitivity. This gives rise to a variety of optical applications for improving the efficiency and effectiveness of opto-electronic devices. These applications are reviewed later. Several methods are currently used to fabricate photonic crystals, which are also discussed in detail. This research involves a layer-by-layer micro-transfer molding ((mu)TM) and stacking method to create three-dimensional FCC structures of epoxy or titania. The structures, once reduced significantly in size can be infiltrated with an organic gain media and stacked on a semiconductor to improve the efficiency of an electronically pumped light-emitting diode. Photonic band gap structures have been proven to effectively create a band gap for certain frequencies of electro-magnetic radiation in the microwave and near-infrared ranges. The objective of this research project was originally two-fold: to fabricate a three dimensional (3-D) structure of a size scaled to prohibit electromagnetic propagation within the visible wavelength range, and then to characterize that structure using laser dye emission spectra. As a master mold has not yet been developed for the micro transfer molding technique in the visible range, the research was limited to scaling down the length scale as much as possible with the current available technology and characterizing these structures with other methods

The Development of Layered Photonic Band Gap Structures Using a Micro-Transfer Molding Technique

Energy Technology Data Exchange (ETDEWEB)

Sutherland, Kevin Jerome [Iowa State Univ., Ames, IA (United States)

2001-01-01

Photonic band gap (PBG) crystals are periodic dielectric structures that manipulate electromagnetic radiation in a manner similar to semiconductor devices manipulating electrons. Whereas a semiconductor material exhibits an electronic band gap in which electrons cannot exist, similarly, a photonic crystal containing a photonic band gap does not allow the propagation of specific frequencies of electromagnetic radiation. This phenomenon results from the destructive Bragg diffraction interference that a wave propagating at a specific frequency will experience because of the periodic change in dielectric permitivity. This gives rise to a variety of optical applications for improving the efficiency and effectiveness of opto-electronic devices. These applications are reviewed later. Several methods are currently used to fabricate photonic crystals, which are also discussed in detail. This research involves a layer-by-layer micro-transfer molding ({mu}TM) and stacking method to create three-dimensional FCC structures of epoxy or titania. The structures, once reduced significantly in size can be infiltrated with an organic gain media and stacked on a semiconductor to improve the efficiency of an electronically pumped light-emitting diode. Photonic band gap structures have been proven to effectively create a band gap for certain frequencies of electro-magnetic radiation in the microwave and near-infrared ranges. The objective of this research project was originally two-fold: to fabricate a three dimensional (3-D) structure of a size scaled to prohibit electromagnetic propagation within the visible wavelength range, and then to characterize that structure using laser dye emission spectra. As a master mold has not yet been developed for the micro transfer molding technique in the visible range, the research was limited to scaling down the length scale as much as possible with the current available technology and characterizing these structures with other methods.

Design and Analysis of a Triple Stop-band Filter Using Ratioed Periodical Defected Microstrip Structure

Science.gov (United States)

Jiang, Tao; Wang, Yanyan; Li, Yingsong

2017-07-01

In this paper, a triple stop-band filter with a ratioed periodical defected microstrip structure is proposed for wireless communication applications. The proposed ratioed periodical defected microstrip structures are spiral slots, which are embedded into a 50 Ω microstrip line to obtain multiple stop-bands. The performance of the proposed triple stop-band filter is investigated numerically and experimentally. Moreover, the equivalent circuit model of the proposed filter is also established and discussed. The results are given to verify that the proposed triple stop-band filter has three stop bands at 3.3 GHz, 5.2 GHz, 6.8 GHz to reject the unwanted signals, which is promising for integrating into UWB communication systems to efficiently prevent the potential interferences from unexpected narrowband signals such as WiMAX, WLAN and RFID communication systems.

Electronic structure of the misfit-layer compound (SnS)1.17NbS2 deduced from band-structure calculations and photoelectron spectra

NARCIS (Netherlands)

Fang, C.M.; Ettema, A.R.H.F.; Haas, C.; Wiegers, G.A.; Leuken, H. van; Groot, R.A. de

1995-01-01

In order to understand the electronic structure of the misfit-layer compound (SnS)1.17NbS2 we carried out an ab initio band-structure calculation of the closely related commensurate compound (SnS)1.20NbS2. The band structure is compared with calculations for NbS2 and for hypothetical SnS with

Electronic structures and band gaps of chains and sheets based on phenylacetylene units

International Nuclear Information System (INIS)

Kondo, Masakazu; Nozaki, Daijiro; Tachibana, Masamitsu; Yumura, Takashi; Yoshizawa, Kazunari

2005-01-01

We investigate the electronic structures of polymers composed of π-conjugated phenylacetylene (PA) units, m-PA-based and p-PA-based wires, at the extended Hueckel level of theory. It is demonstrated that these conjugated systems should have a variety of electric conductance. All of the one-dimensional (1D) chains and the two-dimensional (2D) sheet based on the m-PA unit are insulators with large band gaps of 2.56 eV because there is no effective orbital interaction with neighboring chains. On the other hand, p-PA-based 1D chains have relatively small band gaps that decrease with an increase in chain width (1.17-1.74 eV) and are semiconductive. The p-PA-based sheet called 'graphyne', a 2D-limit of the p-PA-based 1D chains, shows a small band gap of 0.89 eV. The variety of band electronic structures is discussed in terms of frontier crystal orbitals

Quasiparticle band gap of organic-inorganic hybrid perovskites: Crystal structure, spin-orbit coupling, and self-energy effects

Science.gov (United States)

Gao, Weiwei; Gao, Xiang; Abtew, Tesfaye A.; Sun, Yi-Yang; Zhang, Shengbai; Zhang, Peihong

2016-02-01

The quasiparticle band gap is one of the most important materials properties for photovoltaic applications. Often the band gap of a photovoltaic material is determined (and can be controlled) by various factors, complicating predictive materials optimization. An in-depth understanding of how these factors affect the size of the gap will provide valuable guidance for new materials discovery. Here we report a comprehensive investigation on the band gap formation mechanism in organic-inorganic hybrid perovskites by decoupling various contributing factors which ultimately determine their electronic structure and quasiparticle band gap. Major factors, namely, quasiparticle self-energy, spin-orbit coupling, and structural distortions due to the presence of organic molecules, and their influences on the quasiparticle band structure of organic-inorganic hybrid perovskites are illustrated. We find that although methylammonium cations do not contribute directly to the electronic states near band edges, they play an important role in defining the band gap by introducing structural distortions and controlling the overall lattice constants. The spin-orbit coupling effects drastically reduce the electron and hole effective masses in these systems, which is beneficial for high carrier mobilities and small exciton binding energies.

Structure of collective bands and deformations in {sup 74,76}Kr

Energy Technology Data Exchange (ETDEWEB)

Tripathy, K.C. [Physics Department, F M College, Balasore, 756 001 (India); Sahu, R. [Physics Department, Berhampur University, Berhampur, 760 007 (India)

2000-08-01

The structure of collective bands in {sup 74,76}Kr is studied within the framework of the deformed configuration mixing shell model based on Hartree-Fock states. The active single-particle orbits are 1p{sub 3/2}, 0f{sub 5/2}, 1p{sub 1/2} and 0g{sub 9/2} with {sup 56}Ni as the inert core. A modified Kuo interaction has been used for the above configuration space. The {sup 74}Kr nucleus is found to be the most deformed nucleus among the krypton isotopes which is in agreement with experiment. The deformation is found to decrease for the {sup 76}Kr isotope. The calculated positive- and negative-parity bandsagree quite well with the experiment for both the nuclei. A number of excited bands is also predicted. We have also calculated B(E2) values and compared them with available experimental data. The structure of the strongly coupled band built on K = 4{sup (+)} in {sup 76}Kr is also studied. (author)

Effect of eddy current damping on phononic band gaps generated by locally resonant periodic structures

Science.gov (United States)

Ozkaya, Efe; Yilmaz, Cetin

2017-02-01

The effect of eddy current damping on a novel locally resonant periodic structure is investigated. The frequency response characteristics are obtained by using a lumped parameter and a finite element model. In order to obtain wide band gaps at low frequencies, the periodic structure is optimized according to certain constraints, such as mass distribution in the unit cell, lower limit of the band gap, stiffness between the components in the unit cell, the size of magnets used for eddy current damping, and the number of unit cells in the periodic structure. Then, the locally resonant periodic structure with eddy current damping is manufactured and its experimental frequency response is obtained. The frequency response results obtained analytically, numerically and experimentally match quite well. The inclusion of eddy current damping to the periodic structure decreases amplitudes of resonance peaks without disturbing stop band width.

Theoretical studies on band structure and optical properties of 3C-SiC by FPLAPW

International Nuclear Information System (INIS)

Xu, P.; Xie, C.; Xu, F.; Pan, H.

2004-01-01

Full text: SiC has attracted more interests because of its great technological importance in microelectronic and photoelectronic devices. We have studied the band structure and optical properties of 3C-SiC by using a Full Potential Linearized Augmented Plane Waves (FPLAPW) method. The partial density of states (DOS) of Si and C atoms as well as the band structure of 3C-SiC are presented. The calculated band gap is 1.30eV, which is much less than the experimental value. It is attributed to a deficiency of the local density theory. The imaginary part of the dielectric function has been obtained directly from the band structure calculation. With the band gap correction, the real part of the dielectric function has been derived from the imaginary part by Kramers Kronig (K-K) dispersion relationship. The calculated results are in good agreement with the results measured by Petalas et al. by using ultraviolet spectroscopic ellipsometry in the photon energy range of 5eV-10eV. The band-to-band transition can be identified from the critical points exhibited in the calculated dielectric function, which is consistent with the experimental results of Petalas et al. The refractive index, extinction coefficient and reflectivity have also been calculated from obtained dielectric function, which are in agreement with the experimental results of Logothetidis and Lambrecht

Ab initio electronic band structure study of III-VI layered semiconductors

Science.gov (United States)

Olguín, Daniel; Rubio-Ponce, Alberto; Cantarero, Andrés

2013-08-01

We present a total energy study of the electronic properties of the rhombohedral γ-InSe, hexagonal ɛ-GaSe, and monoclinic GaTe layered compounds. The calculations have been done using the full potential linear augmented plane wave method, including spin-orbit interaction. The calculated valence bands of the three compounds compare well with angle resolved photoemission measurements and a discussion of the small discrepancies found has been given. The present calculations are also compared with recent and previous band structure calculations available in the literature for the three compounds. Finally, in order to improve the calculated band gap value we have used the recently proposed modified Becke-Johnson correction for the exchange-correlation potential.

Band structure dynamics in indium wires

Science.gov (United States)

Chávez-Cervantes, M.; Krause, R.; Aeschlimann, S.; Gierz, I.

2018-05-01

One-dimensional indium wires grown on Si(111) substrates, which are metallic at high temperatures, become insulating below ˜100 K due to the formation of a charge density wave (CDW). The physics of this transition is not conventional and involves a multiband Peierls instability with strong interband coupling. This CDW ground state is readily destroyed with femtosecond laser pulses resulting in a light-induced insulator-to-metal phase transition. The current understanding of this transition remains incomplete, requiring measurements of the transient electronic structure to complement previous investigations of the lattice dynamics. Time- and angle-resolved photoemission spectroscopy with extreme ultraviolet radiation is applied to this end. We find that the transition from the insulating to the metallic band structure occurs within ˜660 fs, which is a fraction of the amplitude mode period. The long lifetime of the transient state (>100 ps) is attributed to trapping in a metastable state in accordance with previous work.

Electronic band structures and optical properties of type-II superlattice photodetectors with interfacial effect.

Science.gov (United States)

Qiao, Peng-Fei; Mou, Shin; Chuang, Shun Lien

2012-01-30

The electronic band structures and optical properties of type-II superlattice (T2SL) photodetectors in the mid-infrared (IR) range are investigated. We formulate a rigorous band structure model using the 8-band k · p method to include the conduction and valence band mixing. After solving the 8 × 8 Hamiltonian and deriving explicitly the new momentum matrix elements in terms of envelope functions, optical transition rates are obtained through the Fermi's golden rule under various doping and injection conditions. Optical measurements on T2SL photodetectors are compared with our model and show good agreement. Our modeling results of quantum structures connect directly to the device-level design and simulation. The predicted doping effect is readily applicable to the optimization of photodetectors. We further include interfacial (IF) layers to study the significance of their effect. Optical properties of T2SLs are expected to have a large tunable range by controlling the thickness and material composition of the IF layers. Our model provides an efficient tool for the designs of novel photodetectors.

Calculation of band alignments and quantum confinement effects in zero- and one-dimensional pseudomorphic structures

International Nuclear Information System (INIS)

Yang, M.; Sturm, J.C.; Prevost, J.

1997-01-01

The strain field distributions and band lineups of zero-dimensional and one-dimensional strained pseudomorphic semiconductor particles inside a three-dimensional matrix of another semiconductor have been studied. The resulting strain in the particle and the matrix leads to band alignments considerably different from that in the conventional two-dimensional (2D) pseudomorphic growth case. The models are first applied to an ideal spherical and cylindrical Si 1-x Ge x particle in a large Si matrix. In contrast to the 2D case, the band alignments for both structures are predicted to be strongly type II, where the conduction-band edge and the valence-band edge of the Si matrix are both significantly lower than those in the Si 1-x Ge x inclusion, respectively. Band lineups and the lowest electron endash heavy-hole transition energies of a pseudomorphic V-groove Si 1-x Ge x quantum wire inside a large Si matrix have been calculated numerically for different size structures. The photoluminescence energies of a large Si 1-x Ge x V-groove structure on Si will be lower than those of conventional 2D strained Si 1-x Ge x for similar Ge contents. copyright 1997 The American Physical Society

Photonic band structure calculations using nonlinear eigenvalue techniques

International Nuclear Information System (INIS)

Spence, Alastair; Poulton, Chris

2005-01-01

This paper considers the numerical computation of the photonic band structure of periodic materials such as photonic crystals. This calculation involves the solution of a Hermitian nonlinear eigenvalue problem. Numerical methods for nonlinear eigenvalue problems are usually based on Newton's method or are extensions of techniques for the standard eigenvalue problem. We present a new variation on existing methods which has its derivation in methods for bifurcation problems, where bordered matrices are used to compute critical points in singular systems. This new approach has several advantages over the current methods. First, in our numerical calculations the new variation is more robust than existing techniques, having a larger domain of convergence. Second, the linear systems remain Hermitian and are nonsingular as the method converges. Third, the approach provides an elegant and efficient way of both thinking about the problem and organising the computer solution so that only one linear system needs to be factorised at each stage in the solution process. Finally, first- and higher-order derivatives are calculated as a natural extension of the basic method, and this has advantages in the electromagnetic problem discussed here, where the band structure is plotted as a set of paths in the (ω,k) plane

Electronic band structure, optical, dynamical and thermodynamic properties of cesium chloride (CsCl from first-principles

Directory of Open Access Journals (Sweden)

Bingol Suat

2015-01-01

Full Text Available The geometric structural optimization, electronic band structure, total density of states for valence electrons, density of states for phonons, optical, dynamical, and thermodynamical features of cesium chloride have been investigated by linearized augmented plane wave method using the density functional theory under the generalized gradient approximation. Ground state properties of cesium chloride are studied. The calculated ground state properties are consistent with experimental results. Calculated band structure indicates that the cesium chloride structure has an indirect band gap value of 5.46 eV and is an insulator. From the obtained phonon spectra, the cesium chloride structure is dynamically stable along the various directions in the Brillouin zone. Temperature dependent thermodynamic properties are studied using the harmonic approximation model.

Hybrid functional band gap calculation of SnO6 containing perovskites and their derived structures

International Nuclear Information System (INIS)

Lee, Hyewon; Cheong, S.W.; Kim, Bog G.

2015-01-01

We have studied the properties of SnO 6 octahedra-containing perovskites and their derived structures using ab initio calculations with different density functionals. In order to predict the correct band gap of the materials, we have used B3LYP hybrid density functional, and the results of B3LYP were compared with those obtained using the local density approximation and generalized gradient approximation data. The calculations have been conducted for the orthorhombic ground state of the SnO 6 containing perovskites. We also have expended the hybrid density functional calculation to the ASnO 3 /A'SnO 3 system with different cation orderings. We propose an empirical relationship between the tolerance factor and the band gap of SnO 6 containing oxide materials based on first principles calculation. - Graphical abstract: (a) Structure of ASnO 3 for orthorhombic ground state. The green ball is A (Ba, Sr, Ca) cation and the small (red) ball on edge is oxygen. SnO 6 octahedrons are plotted as polyhedron. (b) Band gap of ASnO 3 as a function of the tolerance factor for different density functionals. The experimental values of the band gap are marked as green pentagons. (c) ASnO 3 /A'SnO 3 superlattices with two types cation arrangement: [001] layered structure and [111] rocksalt structure, respectively. (d) B3LYP hybrid functional band gaps of ASnO 3 , [001] ordered superlattices, and [111] ordered superlattices of ASnO 3 /A'SnO 3 as a function of the effective tolerance factor. Note the empirical linear relationship between the band gap and effective tolerance factor. - Highlights: • We report the hybrid functional band gap calculation of ASnO 3 and ASnO 3 /A'SnO 3 . • The band gap of ASnO 3 using B3LYP functional reproduces the experimental value. • We propose the linear relationship between the tolerance factor and the band gap

Band structure and Fermi surface of UPd2Al3 studied by angle-resolved photoemission spectroscopy

International Nuclear Information System (INIS)

Fujimori, Shin-ichi; Saitoh, Yuji; Okane, Tetsuo; Yamagami, Hiroshi; Fujimori, Atsushi; Haga, Yoshinori; Yamamoto, Etsuji; Onuki, Yoshichika

2007-01-01

We have observed the band structure and Fermi surfaces of the heavy Fermion superconductor UPd 2 Al 3 by angle-resolved photoemission experiments in the soft X-ray region. We observed renormalized quasi-particle bands in the vicinity of the Fermi level and strongly dispersive bands on the higher binding energy side. Our observation suggests that the structure previously assigned to contributions from localized states in the U 5f spectrum has strong energy dispersions

Bose-Einstein condensates in optical lattices: Band-gap structure and solitons

International Nuclear Information System (INIS)

Louis, Pearl J. Y.; Kivshar, Yuri S.; Ostrovskaya, Elena A.; Savage, Craig M.

2003-01-01

We analyze the existence and stability of spatially extended (Bloch-type) and localized states of a Bose-Einstein condensate loaded into an optical lattice. In the framework of the Gross-Pitaevskii equation with a periodic potential, we study the band-gap structure of the matter-wave spectrum in both the linear and nonlinear regimes. We demonstrate the existence of families of spatially localized matter-wave gap solitons, and analyze their stability in different band gaps, for both repulsive and attractive atomic interactions

Fermi Surface and Band Structure of (Ca,La)FeAs2 Superconductor from Angle-Resolved Photoemission Spectroscopy

International Nuclear Information System (INIS)

Liu Xu; Liu De-Fa; Zhao Lin; Guo Qi; Mu Qing-Ge; Chen Dong-Yun; Shen Bing; Yi He-Mian; Huang Jian-Wei; He Jun-Feng; Peng Ying-Ying; Liu Yan; He Shao-Long; Liu Guo-Dong; Dong Xiao-Li; Zhang Jun; Ren Zhi-An; Zhou Xing-Jiang; Chen Chuang-Tian; Xu Zu-Yan

2013-01-01

The (Ca,R)FeAs 2 (R=La, Pr, etc.) superconductors with a signature of superconductivity transition above 40 K possess a new kind of block layers that consist of zig-zag As chains. We report the electronic structure of the new (Ca,La)FeAs 2 superconductor investigated by both band structure calculations and high resolution angle-resolved photoemission spectroscopy measurements. Band structure calculations indicate that there are four hole-like bands around the zone center Γ(0,0) and two electron-like bands near the zone corner M(π, π) in CaFeAs 2 . In our angle-resolved photoemission measurements on (Ca 0.9 La 0.1 )FeAs 2 , we have observed three hole-like bands around the Γ point and one electron-like Fermi surface near the M(π, π) point. These results provide important information to compare and contrast with the electronic structure of other iron-based compounds in understanding the superconductivity mechanism in the iron-based superconductors. (express letter)

Reconstruction of Band Structure Induced by Electronic Nematicity in an FeSe Superconductor

Science.gov (United States)

Nakayama, K.; Miyata, Y.; Phan, G. N.; Sato, T.; Tanabe, Y.; Urata, T.; Tanigaki, K.; Takahashi, T.

2014-12-01

We have performed high-resolution angle-resolved photoemission spectroscopy on an FeSe superconductor (Tc˜8 K ), which exhibits a tetragonal-to-orthorhombic structural transition at Ts˜90 K . At low temperature, we found splitting of the energy bands as large as 50 meV at the M point in the Brillouin zone, likely caused by the formation of electronically driven nematic states. This band splitting persists up to T ˜110 K , slightly above Ts, suggesting that the structural transition is triggered by the electronic nematicity. We have also revealed that at low temperature the band splitting gives rise to a van Hove singularity within 5 meV of the Fermi energy. The present result strongly suggests that this unusual electronic state is responsible for the unconventional superconductivity in FeSe.

Banded Structures in Electron Pitch Angle Diffusion Coefficients from Resonant Wave Particle Interactions

Science.gov (United States)

Tripathi, A. K.; Singhal, R. P.; Khazanov, G. V.; Avanov, L. A.

2016-01-01

Electron pitch angle (D (alpha)) and momentum (D(pp)) diffusion coefficients have been calculated due to resonant interactions with electrostatic electron cyclotron harmonic (ECH) and whistler mode chorus waves. Calculations have been performed at two spatial locations L = 4.6 and 6.8 for electron energies 10 keV. Landau (n = 0) resonance and cyclotron harmonic resonances n = +/-1, +/-2,...+/-5 have been included in the calculations. It is found that diffusion coefficient versus pitch angle (alpha) profiles show large dips and oscillations or banded structures. The structures are more pronounced for ECH and lower band chorus (LBC) and particularly at location 4.6. Calculations of diffusion coefficients have also been performed for individual resonances. It is noticed that the main contribution of ECH waves in pitch angle diffusion coefficient is due to resonances n = +1 and n = +2. A major contribution to momentum diffusion coefficients appears from n = +2. However, the banded structures in D alpha and Dpp coefficients appear only in the profile of diffusion coefficients for n = +2. The contribution of other resonances to diffusion coefficients is found to be, in general, quite small or even negligible. For LBC and upper band chorus waves, the banded structures appear only in Landau resonance. The Dpp diffusion coefficient for ECH waves is one to two orders smaller than D alpha coefficients. For chorus waves, Dpp coefficients are about an order of magnitude smaller than D alpha coefficients for the case n does not = 0. In case of Landau resonance, the values of Dpp coefficient are generally larger than the values of D alpha coefficients particularly at lower energies. As an aid to the interpretation of results, we have also determined the resonant frequencies. For ECH waves, resonant frequencies have been estimated for wave normal angle 89 deg and harmonic resonances n = +1, +2, and +3, whereas for whistler mode waves, the frequencies have been calculated for angle

Relativistic band-structure calculations for CeTIn sub 5 (T=Ir and Co) and analysis of the energy bands by using tight-binding method

CERN Document Server

Maehira, T; Ueda, K; Hasegawa, A

2003-01-01

In order to investigate electronic properties of recently discovered heavy fermion superconductors CeTIn sub 5 (T=Ir and Co), we employ the relativistic linear augmented-plane-wave (RLAPW) method to clarify the energy band structures and Fermi surfaces of those materials. The obtained energy bands mainly due to the large hybridization between Ce 4 f and In 5 p states well reproduce the Fermi surfaces consistent with the de Haas-van Alphen experimental results. However, when we attempt to understand magnetism and superconductively in CeTIn sub 5 from the microscopic viewpoint, the energy bands obtained in the RLAPW method are too complicated to analyze the system by further including electron correlations. Thus, it is necessary to prepare a more simplified model, keeping correctly the essential characters of the energy bands obtained in the band-structure calculation. For the purpose, we construct a tight-binding model for CeTIn sub 5 by including f-f and p-p hoppings as well as f-p hybridization, which are ex...

High-spin structure of 121Xe: triaxiality, band termination and signature inversion

International Nuclear Information System (INIS)

Timar, J.; Paul, E.S.; Beausang, C.W.; Joyce, M.J.; Sharpey-Schafer, J.F.

1995-01-01

High-spin states of the odd-neutron 121 Xe nucleus have been studied with Eurogam using the 96 Zr( 30 Si, 5n) 121 Xe fusion-evaporation reaction. The level scheme has been extended up to a tentative spin of 67/2h at an excitation energy of ∼ 14 MeV. Several new rotational bands have been observed and the previously known bands extended. Two of them lose their regular character at high spins, which may be interpreted as transition from collective behaviour to a regime of noncollective oblate states. The deduced high-spin structure is compared to Woods-Saxon TRS cranking and CSM calculations. Configurations of the bands have been suggested. The νh 1 1/2 band is interpreted as having a triaxial shape. Signature inversion and an unexpectedly large staggering of the B(M1)/B(E2) ratios has been found for one of the bands. Enhanced E1 transitions have been observed between the νd 5/2 and the νh 1 1/2 bands. (orig.)

Structure of the lowest excited 0/sup +/ rotational band of /sup 16/O

Energy Technology Data Exchange (ETDEWEB)

Ikebata, Yasuhiko; Suekane, Shota

1983-10-01

The structure of the lowest excited 0/sup +/ rotational band is investigated by using the extended Nilsson model wave functions with angular momentum projection and the B1 interaction, two-body LS-force of the Skyrme type and the Coulomb interaction. The results obtained show good agreement with energy interval in this band.

Valence band electronic structure of Pd based ternary chalcogenide superconductors

Energy Technology Data Exchange (ETDEWEB)

Lohani, H. [Institute of Physics, Sachivalaya Marg, Bhubaneswar 751005 (India); Homi Bhabha National Institute, Training School Complex, Anushakti Nagar, Mumbai 400085 (India); Mishra, P. [Institute of Physics, Sachivalaya Marg, Bhubaneswar 751005 (India); Goyal, R.; Awana, V.P.S. [National Physical Laboratory(CSIR), Dr. K. S. Krishnan Road, New Delhi 110012 (India); Sekhar, B.R., E-mail: sekhar@iopb.res.in [Institute of Physics, Sachivalaya Marg, Bhubaneswar 751005 (India); Homi Bhabha National Institute, Training School Complex, Anushakti Nagar, Mumbai 400085 (India)

2016-12-15

Highlights: • VB Photoemission study and DFT calculations on Pd based ternary superconductors are presented. • Nb{sub 2}Pd{sub 0.95}S{sub 5} shows a temperature dependent pseudogap. • VB spectral features of ternary superconductors are correlated to their structural geometry. - Abstract: We present a comparative study of the valence band electronic structure of Pd based ternary chalcogenide superconductors Nb{sub 2}Pd{sub 0.95}S{sub 5}, Ta{sub 2}Pd{sub 0.97}S{sub 6} and Ta{sub 2}Pd{sub 0.97}Te{sub 6} using experimental photoemission spectroscopy and density functional based theoretical calculations. We observe a qualitatively similarity between valence band (VB) spectra of Nb{sub 2}Pd{sub 0.95}S{sub 5} and Ta{sub 2}Pd{sub 0.97}S{sub 6}. Further, we find a pseudogap feature in Nb{sub 2}Pd{sub 0.95}S{sub 5} at low temperature, unlike other two compounds. We have correlated the structural geometry with the differences in VB spectra of these compounds. The different atomic packing in these compounds could vary the strength of inter-orbital hybridization among various atoms which leads to difference in their electronic structure as clearly observed in our DOS calculations.

Band structure and unconventional electronic topology of CoSi

Science.gov (United States)

Pshenay-Severin, D. A.; Ivanov, Y. V.; Burkov, A. A.; Burkov, A. T.

2018-04-01

Semimetals with certain crystal symmetries may possess unusual electronic structure topology, distinct from that of the conventional Weyl and Dirac semimetals. Characteristic property of these materials is the existence of band-touching points with multiple (higher than two-fold) degeneracy and nonzero Chern number. CoSi is a representative of this group of materials exhibiting the so-called ‘new fermions’. We report on an ab initio calculation of the electronic structure of CoSi using density functional methods, taking into account the spin-orbit interactions. The linearized \

Electronic Band Structure of Helical Polyisocyanides.

Science.gov (United States)

Champagne, Benoît; Liégeois, Vincent; Fripiat, Joseph G; Harris, Frank E

2017-10-19

Restricted Hartree-Fock computations are reported for a methyl isocyanide polymer (repeating unit -C═N-CH 3 ), whose most stable conformation is expected to be a helical chain. The computations used a standard contracted Gaussian orbital set at the computational levels STO-3G, 3-21G, 6-31G, and 6-31G**, and studies were made for two line-group configurations motivated by earlier work and by studies of space-filling molecular models: (1) A structure of line-group symmetry L9 5 , containing a 9-fold screw axis with atoms displaced in the axial direction by 5/9 times the lattice constant, and (2) a structure of symmetry L4 1 that had been proposed, containing a 4-fold screw axis with translation by 1/4 of the lattice constant. Full use of the line-group symmetry was employed to cause most of the computational complexity to depend only on the size of the asymmetric repeating unit. Data reported include computed bond properties, atomic charge distribution, longitudinal polarizability, band structure, and the convoluted density of states. Most features of the description were found to be insensitive to the level of computational approximation. The work also illustrates the importance of exploiting line-group symmetry to extend the range of polymer structural problems that can be treated computationally.

Reducing support loss in micromechanical ring resonators using phononic band-gap structures

Energy Technology Data Exchange (ETDEWEB)

Hsu, Feng-Chia; Huang, Tsun-Che; Wang, Chin-Hung; Chang, Pin [Industrial Technology Research Institute-South, Tainan 709, Taiwan (China); Hsu, Jin-Chen, E-mail: fengchiahsu@itri.org.t, E-mail: hsujc@yuntech.edu.t [Department of Mechanical Engineering, National Yunlin University of Science and Technology, Douliou, Yunlin 64002, Taiwan (China)

2011-09-21

In micromechanical resonators, energy loss via supports into the substrates may lead to a low quality factor. To eliminate the support loss, in this paper a phononic band-gap structure is employed. We demonstrate a design of phononic-crystal (PC) strips used to support extensional wine-glass mode ring resonators to increase the quality factor. The PC strips are introduced to stop elastic-wave propagation by the band-gap and deaf-band effects. Analyses of resonant characteristics of the ring resonators and the dispersion relations, eigenmodes, and transmission properties of the PC strips are presented. With the proposed resonator architecture, the finite-element simulations show that the leaky power is effectively reduced and the stored energy inside the resonators is enhanced simultaneously as the operating frequencies of the resonators are within the band gap or deaf bands. Realization of a high quality factor micromechanical ring resonator with minimized support loss is expected.

Reducing support loss in micromechanical ring resonators using phononic band-gap structures

International Nuclear Information System (INIS)

Hsu, Feng-Chia; Huang, Tsun-Che; Wang, Chin-Hung; Chang, Pin; Hsu, Jin-Chen

2011-01-01

In micromechanical resonators, energy loss via supports into the substrates may lead to a low quality factor. To eliminate the support loss, in this paper a phononic band-gap structure is employed. We demonstrate a design of phononic-crystal (PC) strips used to support extensional wine-glass mode ring resonators to increase the quality factor. The PC strips are introduced to stop elastic-wave propagation by the band-gap and deaf-band effects. Analyses of resonant characteristics of the ring resonators and the dispersion relations, eigenmodes, and transmission properties of the PC strips are presented. With the proposed resonator architecture, the finite-element simulations show that the leaky power is effectively reduced and the stored energy inside the resonators is enhanced simultaneously as the operating frequencies of the resonators are within the band gap or deaf bands. Realization of a high quality factor micromechanical ring resonator with minimized support loss is expected.

Numerical and Experimental Investigation of Stop-Bands in Finite and Infinite Periodic One-Dimensional Structures

DEFF Research Database (Denmark)

Domadiya, Parthkumar Gandalal; Manconi, Elisabetta; Vanali, Marcello

2016-01-01

Adding periodicity to structures leads to wavemode interaction, which generates pass- and stop-bands. The frequencies at which stop-bands occur are related to the periodic nature of the structure. Thus structural periodicity can be shaped in order to design vibro-acoustic filters for reducing...... method deals with the evaluation of a vibration level difference (VLD) in a finite periodic structure embedded within an infinite one-dimensional waveguide. This VLD is defined to predict the performance in terms of noise and vibration insulation of periodic cells embedded in an otherwise uniform...

Photonic band gap structure simulator

Science.gov (United States)

Chen, Chiping; Shapiro, Michael A.; Smirnova, Evgenya I.; Temkin, Richard J.; Sirigiri, Jagadishwar R.

2006-10-03

A system and method for designing photonic band gap structures. The system and method provide a user with the capability to produce a model of a two-dimensional array of conductors corresponding to a unit cell. The model involves a linear equation. Boundary conditions representative of conditions at the boundary of the unit cell are applied to a solution of the Helmholtz equation defined for the unit cell. The linear equation can be approximated by a Hermitian matrix. An eigenvalue of the Helmholtz equation is calculated. One computation approach involves calculating finite differences. The model can include a symmetry element, such as a center of inversion, a rotation axis, and a mirror plane. A graphical user interface is provided for the user's convenience. A display is provided to display to a user the calculated eigenvalue, corresponding to a photonic energy level in the Brilloin zone of the unit cell.

Autopsy on an RF-Processed X-band Travelling Wave Structure

International Nuclear Information System (INIS)

Le Pimpec, Frederic

2002-01-01

In an effort to locate the cause(s) of high electric-field breakdown in x-band accelerating structures, we have cleanly-autopsied (no debris added by post-operation structure disassembly) an RF-processed structure. Macroscopic localization provided operationally by RF reflected wave analysis and acoustic sensor pickup was used to connect breakdowns to autopsied crater damage areas. Surprisingly, the microscopic analyses showed breakdown craters in areas of low electric field. High currents induced by the magnetic field on sharp corners of the input coupler appears responsible for the extreme breakdown damage observed

Efficient band structure modulations in two-dimensional MnPSe3/CrSiTe3 van der Waals heterostructures

Science.gov (United States)

Pei, Qi; Wang, Xiaocha; Zou, Jijun; Mi, Wenbo

2018-05-01

As a research upsurge, van der Waals (vdW) heterostructures give rise to numerous combined merits and novel applications in nanoelectronics fields. Here, we systematically investigate the electronic structure of MnPSe3/CrSiTe3 vdW heterostructures with various stacking patterns. Then, particular attention of this work is paid on the band structure modulations in MnPSe3/CrSiTe3 vdW heterostructures via biaxial strain or electric field. Under a tensile strain, the relative band edge positions of heterostructures transform from type-I (nested) to type-II (staggered). The relocation of conduction band minimum also brings about a transition from indirect to direct band gap. Under a compressive strain, the electronic properties change from semiconducting to metallic. The physical mechanism of strain-dependent band structure may be ascribed to the shifts of the energy bands impelled by different superposition of atomic orbitals. Meanwhile, our calculations manifest that band gap values of MnPSe3/CrSiTe3 heterostructures are insensitive to the electric field. Even so, by applying a suitable intensity of negative electric field, the band alignment transition from type-I to type-II can also be realized. The efficient band structure modulations via external factors endow MnPSe3/CrSiTe3 heterostructures with great potential in novel applications, such as strain sensors, photocatalysis, spintronic and photoelectronic devices.

Electronic structure and optical properties of Cs2HgI4: Experimental study and band-structure DFT calculations

Science.gov (United States)

Lavrentyev, A. A.; Gabrelian, B. V.; Vu, V. T.; Shkumat, P. N.; Myronchuk, G. L.; Khvyshchun, M.; Fedorchuk, A. O.; Parasyuk, O. V.; Khyzhun, O. Y.

2015-04-01

High-quality single crystal of cesium mercury tetraiodide, Cs2HgI4, has been synthesized by the vertical Bridgman-Stockbarger method and its crystal structure has been refined. In addition, electronic structure and optical properties of Cs2HgI4 have been studied. For the crystal under study, X-ray photoelectron core-level and valence-band spectra for pristine and Ar+-ion irradiated surfaces have been measured. The present X-ray photoelectron spectroscopy (XPS) results indicate that the Cs2HgI4 single crystal surface is very sensitive with respect to Ar+ ion-irradiation. In particular, Ar+ bombardment of the single crystal surface alters the elemental stoichiometry of the Cs2HgI4 surface. To elucidate peculiarities of the energy distribution of the electronic states within the valence-band and conduction-band regions of the Cs2HgI4 compound, we have performed first-principles band-structure calculations based on density functional theory (DFT) as incorporated in the WIEN2k package. Total and partial densities of states for Cs2HgI4 have been calculated. The DFT calculations reveal that the I p states make the major contributions in the upper portion of the valence band, while the Hg d, Cs p and I s states are the dominant contributors in its lower portion. Temperature dependence of the light absorption coefficient and specific electrical conductivity has been explored for Cs2HgI4 in the temperature range of 77-300 K. Main optical characteristics of the Cs2HgI4 compound have been elucidated by the first-principles calculations.

Study on the Effect of Secondary Banded Structure on the Fatigue Property of Non-Quenched and Tempered Micro Alloyed Steel

Science.gov (United States)

Yajie, Cheng; Qingliang, Liao; Yue, Zhang

Due to composition segregation and cooling speed, streamline or banded structure were often obtained in the thermal forming parts along the direction of parts forming. Generally speaking, banded structure doesn't decrease the longitudinal mechanical properties, so the secondary banded structure can't get enough attention. The effect of secondary banded structure on the fatigue properties of micro alloyed DG20Mn and 35CrMo steel was investigated using the axial tensile fatigue test of stress ratio of 0.1. The result shows that secondary banded structure was obtained in the center of the steel parts, because of the composition segregation and the lower cooling rate in center part of steel. Secondary banded structure has no significant effect on axial tensile properties of both DG20Mn and 35CrMo, but decreases the axial tensile fatigue performance of DG20Mn steel. This study suggests that under the high cyclic tensile stress, multi-source damage cracks in steel initiated by large strain of pearlite of secondary banded structure, which is larger than damage strain, is the major factor of the decrease of fatigue life of steel.

Development of small C-band standing-wave accelerator structure

International Nuclear Information System (INIS)

Miura, S.; Takahashi, A.; Hisanaga, N.; Sekido, H.; Yoshizumi, A.

2000-01-01

We have newly developed a compact C-band (5712 MHz) standing-wave accelerator for the medical product/waste sterilization applications. The accelerator consists of an electron gun operating at 25 kV DC followed by a single-cell pre-buncher and 3-cell buncher section, and 11-cell of the side-coupled standing-wave accelerating structure. The total length including the electron gun is about 600 mm. The first high-power test was performed in March 2000, where the accelerator successively generated the electron beam of 9 MeV energy and 160 mA peak-current at 3.8 MW RF input power. Mitsubishi Heavy Industry starts to serve the sterilization systems using C-band accelerator reported here, and also supplies the accelerator components for the medical oncology applications. (author)

Design of UWB Monopole Antenna with Dual Notched Bands Using One Modified Electromagnetic-Bandgap Structure

Directory of Open Access Journals (Sweden)

Hao Liu

2013-01-01

Full Text Available A modified electromagnetic-bandgap (M-EBG structure and its application to planar monopole ultra-wideband (UWB antenna are presented. The proposed M-EBG which comprises two strip patch and an edge-located via can perform dual notched bands. By properly designing and placing strip patch near the feedline, the proposed M-EBG not only possesses a simple structure and compact size but also exhibits good band rejection. Moreover, it is easy to tune the dual notched bands by altering the dimensions of the M-EBG. A demonstration antenna with dual band-notched characteristics is designed and fabricated to validate the proposed method. The results show that the proposed antenna can satisfy the requirements of VSWR < 2 over UWB 3.1–10.6 GHz, except for the rejected bands of the world interoperability for microwave access (WiMAX and the wireless local area network (WLAN at 3.5 GHz and 5.5 GHz, respectively.

Design of UWB Monopole Antenna with Dual Notched Bands Using One Modified Electromagnetic-Bandgap Structure

Science.gov (United States)

Xu, Ziqiang

2013-01-01

A modified electromagnetic-bandgap (M-EBG) structure and its application to planar monopole ultra-wideband (UWB) antenna are presented. The proposed M-EBG which comprises two strip patch and an edge-located via can perform dual notched bands. By properly designing and placing strip patch near the feedline, the proposed M-EBG not only possesses a simple structure and compact size but also exhibits good band rejection. Moreover, it is easy to tune the dual notched bands by altering the dimensions of the M-EBG. A demonstration antenna with dual band-notched characteristics is designed and fabricated to validate the proposed method. The results show that the proposed antenna can satisfy the requirements of VSWR WLAN) at 3.5 GHz and 5.5 GHz, respectively. PMID:24170984

Strain effect on graphene nanoribbon carrier statistic in the presence of non-parabolic band structure

International Nuclear Information System (INIS)

Izuani Che Rosid, N A; Ahmadi, M T; Ismail, Razali

2016-01-01

The effect of tensile uniaxial strain on the non-parabolic electronic band structure of armchair graphene nanoribbon (AGNR) is investigated. In addition, the density of states and the carrier statistic based on the tight-binding Hamiltonian are modeled analytically. It is found that the property of AGNR in the non-parabolic band region is varied by the strain. The tunable energy band gap in AGNR upon strain at the minimum energy is described for each of n-AGNR families in the non-parabolic approximation. The behavior of AGNR in the presence of strain is attributed to the breakable AGNR electronic band structure, which varies the physical properties from its normality. The linear relation between the energy gap and the electrical properties is featured to further explain the characteristic of the deformed AGNR upon strain. (paper)

Crystal structure, electrical properties and electronic band structure of tantalum ditelluride

CERN Document Server

Vernes, A; Bensch, W; Heid, W; Naether, C

1998-01-01

Motivated by the unexpectedly strong influence of the Te atoms on the structural and bonding properties of the transition metal tellurides, we have performed a detailed study of TaTe sub 2. Experimentally, this comprises a crystal structure determination as well as electrical resistivity measurements. The former analysis leads to an accurate update of the structural data reported in the 1960s, while the latter provides evidence for the mainly electronic character of scattering processes leading to the electrical conductivity. In addition, the electronic properties of TaTe sub 2 have been calculated using the TB-LMTO method. The partial density of states reflects the close connection of the Ta zigzag chains and the Te-Te network. This finding explains the charge transfer in the system in a rather simple way. The orthogonal-orbital character of the bands proved the existence of pi-bonds. The Fermi-surface study supports the interpretation of the experimental resistivity measurements. (author)

Estimation of photonic band gap in the hollow core cylindrical multilayer structure

Science.gov (United States)

Chourasia, Ritesh Kumar; Singh, Vivek

2018-04-01

The propagation characteristic of two hollow core cylindrical multilayer structures having high and low refractive index contrast of cladding regions have been studied and compared at two design wavelengths i.e. 1550 nm and 632.8 nm. With the help of transfer matrix method a relation between the incoming light wave and outgoing light wave has been developed using the boundary matching technique. In high refractive index contrast, small numbers of layers are sufficient to provide perfect band gap in both design wavelengths. The spectral position and width of band gap is highly depending on the optical path of incident light in all considered cases. For sensing application, the sensitivity of waveguide can be obtained either by monitoring the width of photonic band gap or by monitoring the spectral shift of photonic band gap. Change in the width of photonic band gap with the core refractive index is larger in high refractive index contrast of cladding materials. However, in the case of monitoring the spectral shift of band gap, the obtained sensitivity is large for low refractive index contrast of cladding materials and further it increases with increase of design wavelength.

Banded Structures in Electron Pitch Angle Diffusion Coefficients from Resonant Wave-Particle Interactions

Science.gov (United States)

Tripathi, A. K.; Singhal, R. P.; Khazanov, G. V.; Avanov, L. A.

2016-01-01

Electron pitch angle (D(sub (alpha alpha))) and momentum (D(sub pp)) diffusion coefficients have been calculated due to resonant interactions with electrostatic electron cyclotron harmonic (ECH) and whistler mode chorus waves. Calculations have been performed at two spatial locations L=4.6 and 6.8 for electron energies less than or equal to 10 keV. Landau (n=0) resonance and cyclotron harmonic resonances n= +/- 1, +/-2, ... +/-5 have been included in the calculations. It is found that diffusion coefficient versus pitch angle (alpha) profiles show large dips and oscillations or banded structures. The structures are more pronounced for ECH and lower band chorus (LBC) and particularly at location 4.6. Calculations of diffusion coefficients have also been performed for individual resonances. It is noticed that the main contribution of ECH waves in pitch angle diffusion coefficient is due to resonances n=+1 and n=+2. A major contribution to momentum diffusion coefficients appears from n=+2. However, the banded structures in D(sub alpha alpha) and D(sub pp) coefficients appear only in the profile of diffusion coefficients for n=+2. The contribution of other resonances to diffusion coefficients is found to be, in general, quite small or even negligible. For LBC and upper band chorus waves, the banded structures appear only in Landau resonance. The D(sub pp) diffusion coefficient for ECH waves is one to two orders smaller than D(sub alpha alpha) coefficients. For chorus waves, D(sub pp) coefficients are about an order of magnitude smaller than D(sub alpha alpha) coefficients for the case n does not equal 0. In case of Landau resonance, the values of D(sub pp) coefficient are generally larger than the values of D(sub alpha alpha) coefficients particularly at lower energies. As an aid to the interpretation of results, we have also determined the resonant frequencies. For ECH waves, resonant frequencies have been estimated for wave normal angle 89 deg and harmonic resonances

The structure of rotational bands in alpha-cluster nuclei

Directory of Open Access Journals (Sweden)

Bijker Roelof

2015-01-01

Full Text Available In this contribution, I discuss an algebraic treatment of alpha-cluster nuclei based on the introduction of a spectrum generating algebra for the relative motion of the alpha-clusters. Particular attention is paid to the discrete symmetry of the geometric arrangement of the α-particles, and the consequences for the structure of the rotational bands in the 12C and 16O nuclei.

Largely Tunable Band Structures of Few-Layer InSe by Uniaxial Strain.

Science.gov (United States)

Song, Chaoyu; Fan, Fengren; Xuan, Ningning; Huang, Shenyang; Zhang, Guowei; Wang, Chong; Sun, Zhengzong; Wu, Hua; Yan, Hugen

2018-01-31

Because of the strong quantum confinement effect, few-layer γ-InSe exhibits a layer-dependent band gap, spanning the visible and near infrared regions, and thus recently has been drawing tremendous attention. As a two-dimensional material, the mechanical flexibility provides an additional tuning knob for the electronic structures. Here, for the first time, we engineer the band structures of few-layer and bulk-like InSe by uniaxial tensile strain and observe a salient shift of photoluminescence peaks. The shift rate of the optical gap is approximately 90-100 meV per 1% strain for four- to eight-layer samples, which is much larger than that for the widely studied MoS 2 monolayer. Density functional theory calculations well reproduce the observed layer-dependent band gaps and the strain effect and reveal that the shift rate decreases with the increasing layer number for few-layer InSe. Our study demonstrates that InSe is a very versatile two-dimensional electronic and optoelectronic material, which is suitable for tunable light emitters, photodetectors, and other optoelectronic devices.

Electronic structures and valence band splittings of transition metals doped GaNs

International Nuclear Information System (INIS)

Lee, Seung-Cheol; Lee, Kwang-Ryeol; Lee, Kyu-Hwan

2007-01-01

For a practical viewpoint, presence of spin splitting of valence band in host semiconductors by the doping of transition metal (TM) ions is an essential property when designing a diluted magnetic semiconductors (DMS) material. The first principle calculations were performed on the electronic and magnetic structure of 3d transition metal doped GaN. V, Cr, and Mn doped GaNs could not be candidates for DMS materials since most of their magnetic moments is concentrated on the TM ions and the splittings of valence band were negligible. In the cases of Fe, Co, Ni, and Cu doped GaNs, on the contrary, long-ranged spin splitting of valence band was found, which could be candidates for DMS materials

Effect of structural distortion on the electronic band structure of NaOsO3 studied within density functional theory and a three-orbital model

Science.gov (United States)

Mohapatra, Shubhajyoti; Bhandari, Churna; Satpathy, Sashi; Singh, Avinash

2018-04-01

Effects of the structural distortion associated with the OsO6 octahedral rotation and tilting on the electronic band structure and magnetic anisotropy energy for the 5 d3 compound NaOsO3 are investigated using the density functional theory (DFT) and within a three-orbital model. Comparison of the essential features of the DFT band structures with the three-orbital model for both the undistorted and distorted structures provides insight into the orbital and directional asymmetry in the electron hopping terms resulting from the structural distortion. The orbital mixing terms obtained in the transformed hopping Hamiltonian resulting from the octahedral rotations are shown to account for the fine features in the DFT band structure. Staggered magnetization and the magnetic character of states near the Fermi energy indicate weak coupling behavior.

Hybrid functional band gap calculation of SnO{sub 6} containing perovskites and their derived structures

Energy Technology Data Exchange (ETDEWEB)

Lee, Hyewon [Department of Physics, Pusan National University, Pusan 609-735, Republic of South Korea (Korea, Republic of); Cheong, S.W. [Rutgers Center for Emergent Materials and Department of Physics and Astronomy, Rutgers University, Piscataway, NJ 08854 (United States); Kim, Bog G., E-mail: boggikim@pusan.ac.kr [Department of Physics, Pusan National University, Pusan 609-735, Republic of South Korea (Korea, Republic of)

2015-08-15

We have studied the properties of SnO{sub 6} octahedra-containing perovskites and their derived structures using ab initio calculations with different density functionals. In order to predict the correct band gap of the materials, we have used B3LYP hybrid density functional, and the results of B3LYP were compared with those obtained using the local density approximation and generalized gradient approximation data. The calculations have been conducted for the orthorhombic ground state of the SnO{sub 6} containing perovskites. We also have expended the hybrid density functional calculation to the ASnO{sub 3}/A'SnO{sub 3} system with different cation orderings. We propose an empirical relationship between the tolerance factor and the band gap of SnO{sub 6} containing oxide materials based on first principles calculation. - Graphical abstract: (a) Structure of ASnO{sub 3} for orthorhombic ground state. The green ball is A (Ba, Sr, Ca) cation and the small (red) ball on edge is oxygen. SnO{sub 6} octahedrons are plotted as polyhedron. (b) Band gap of ASnO{sub 3} as a function of the tolerance factor for different density functionals. The experimental values of the band gap are marked as green pentagons. (c) ASnO{sub 3}/A'SnO{sub 3} superlattices with two types cation arrangement: [001] layered structure and [111] rocksalt structure, respectively. (d) B3LYP hybrid functional band gaps of ASnO{sub 3}, [001] ordered superlattices, and [111] ordered superlattices of ASnO{sub 3}/A'SnO{sub 3} as a function of the effective tolerance factor. Note the empirical linear relationship between the band gap and effective tolerance factor. - Highlights: • We report the hybrid functional band gap calculation of ASnO{sub 3} and ASnO{sub 3}/A'SnO{sub 3}. • The band gap of ASnO{sub 3} using B3LYP functional reproduces the experimental value. • We propose the linear relationship between the tolerance factor and the band gap.

Study of band structure of some odd proton Eu isotopes

International Nuclear Information System (INIS)

Pandit, Rakesh K.; Rani Devi; Khosa, S.K.

2016-01-01

Much work has been done on the odd-Z, odd-A nuclei in the rare earth region because of occurrence of fascinating variety of structures of nuclei in this mass region. The Eu nuclei are in the transitional deformation region and it provides an opportunity to investigate theoretically the deformation changes with mass number and excitation energy besides to study the structure of their excited states. The 153 Eu nucleus has been well studied over the last two decades. The aim of the present work is to study in detail the band structure of some odd-Z nuclei

Degenerate band edge laser

Science.gov (United States)

Veysi, Mehdi; Othman, Mohamed A. K.; Figotin, Alexander; Capolino, Filippo

2018-05-01

We propose a class of lasers based on a fourth-order exceptional point of degeneracy (EPD) referred to as the degenerate band edge (DBE). EPDs have been found in parity-time-symmetric photonic structures that require loss and/or gain; here we show that the DBE is a different kind of EPD since it occurs in periodic structures that are lossless and gainless. Because of this property, a small level of gain is sufficient to induce single-frequency lasing based on a synchronous operation of four degenerate Floquet-Bloch eigenwaves. This lasing scheme constitutes a light-matter interaction mechanism that leads also to a unique scaling law of the laser threshold with the inverse of the fifth power of the laser-cavity length. The DBE laser has the lowest lasing threshold in comparison to a regular band edge laser and to a conventional laser in cavities with the same loaded quality (Q ) factor and length. In particular, even without mirror reflectors the DBE laser exhibits a lasing threshold which is an order of magnitude lower than that of a uniform cavity laser of the same length and with very high mirror reflectivity. Importantly, this novel DBE lasing regime enforces mode selectivity and coherent single-frequency operation even for pumping rates well beyond the lasing threshold, in contrast to the multifrequency nature of conventional uniform cavity lasers.

Graphene-insulator-semiconductor capacitors as superior test structures for photoelectric determination of semiconductor devices band diagrams

Directory of Open Access Journals (Sweden)

K. Piskorski

2018-05-01

Full Text Available We report on the advantages of using Graphene-Insulator-Semiconductor (GIS instead of Metal-Insulator-Semiconductor (MIS structures in reliable and precise photoelectric determination of the band alignment at the semiconductor-insulator interface and of the insulator band gap determination. Due to the high transparency to light of the graphene gate in GIS structures large photocurrents due to emission of both electrons and holes from the substrate and negligible photocurrents due to emission of carriers from the gate can be obtained, which allows reliable determination of barrier heights for both electrons, Ee and holes, Eh from the semiconductor substrate. Knowing the values of both Ee and Eh allows direct determination of the insulator band gap EG(I. Photoelectric measurements were made of a series of Graphene-SiO2-Si structures and an example is shown of the results obtained in sequential measurements of the same structure giving the following barrier height values: Ee = 4.34 ± 0.01 eV and Eh = 4.70 ± 0.03 eV. Based on this result and results obtained for other structures in the series we conservatively estimate the maximum uncertainty of both barrier heights estimations at ± 0.05 eV. This sets the SiO2 band gap estimation at EG(I = 7.92 ± 0.1 eV. It is shown that widely different SiO2 band gap values were found by research groups using various determination methods. We hypothesize that these differences are due to different sensitivities of measurement methods used to the existence of the SiO2 valence band tail.

Graphene-insulator-semiconductor capacitors as superior test structures for photoelectric determination of semiconductor devices band diagrams

Science.gov (United States)

Piskorski, K.; Passi, V.; Ruhkopf, J.; Lemme, M. C.; Przewlocki, H. M.

2018-05-01

We report on the advantages of using Graphene-Insulator-Semiconductor (GIS) instead of Metal-Insulator-Semiconductor (MIS) structures in reliable and precise photoelectric determination of the band alignment at the semiconductor-insulator interface and of the insulator band gap determination. Due to the high transparency to light of the graphene gate in GIS structures large photocurrents due to emission of both electrons and holes from the substrate and negligible photocurrents due to emission of carriers from the gate can be obtained, which allows reliable determination of barrier heights for both electrons, Ee and holes, Eh from the semiconductor substrate. Knowing the values of both Ee and Eh allows direct determination of the insulator band gap EG(I). Photoelectric measurements were made of a series of Graphene-SiO2-Si structures and an example is shown of the results obtained in sequential measurements of the same structure giving the following barrier height values: Ee = 4.34 ± 0.01 eV and Eh = 4.70 ± 0.03 eV. Based on this result and results obtained for other structures in the series we conservatively estimate the maximum uncertainty of both barrier heights estimations at ± 0.05 eV. This sets the SiO2 band gap estimation at EG(I) = 7.92 ± 0.1 eV. It is shown that widely different SiO2 band gap values were found by research groups using various determination methods. We hypothesize that these differences are due to different sensitivities of measurement methods used to the existence of the SiO2 valence band tail.

Ab initio electronic band structure calculation of InP in the wurtzite phase

Science.gov (United States)

Dacal, Luis C. O.; Cantarero, Andrés

2011-05-01

We present ab initio calculations of the InP band structure in the wurtzite phase and compare it with that of the zincblende phase. In both calculations, we use the full potential linearized augmented plane wave method as implemented in the WIEN2k code and the modified Becke-Johnson exchange potential, which provides an improved value of the bandgap. The structural optimization of the wurtizte InP gives a=0.4150 nm, c=0.6912 nm, and an internal parameter u=0.371, showing the existence of a spontaneous polarization along the growth axis. As compared to the ideal wurtzite structure (that with the lattice parameter derived from the zincblende structure calculations), the actual wurtzite structure is compressed (-1.3%) in plane and expanded (0.7%) along the c-direction. The value of the calculated band gaps agrees well with recent optical experiments. The calculations are also consistent with the optical transitions found using polarized light.

Magnetic phase diagrams from non-collinear canonical band theory

DEFF Research Database (Denmark)

Shallcross, Sam; Nordstrom, L.; Sharma, S.

2007-01-01

A canonical band theory of non-collinear magnetism is developed and applied to the close packed fcc and bcc crystal structures. This is a parameter-free theory where the crystal and magnetic symmetry and exchange splitting uniquely determine the electronic bands. In this way, we are able...... hybridization, and on this basis we are able to analyze the microscopic reasons behind the occurrence of non-collinear magnetism in the elemental itinerant magnets....... to construct phase diagrams of magnetic order for the fcc and bcc lattices. Several examples of non-collinear magnetism are seen to be canonical in origin, in particular, that of gamma-Fe. In this approach, the determination of magnetic stability results solely from changes in kinetic energy due to spin...

Electronic band structure study of colossal magnetoresistance in Tl 2Mn 2O 7

Science.gov (United States)

Seo, D.-K.; Whangbo, M.-H.; Subramanian, M. A.

1997-02-01

The electronic structure of Tl 2Mn 2O 7 was examined by performing tight binding band calculations. The overlap between the Mn t 2g- and Tl 6 s-block bands results in a partial filling of the Tl 6 s-block bands. The associated Fermi surface consists of 12 cigar-shape electron pockets with each electron pocket about {1}/{1000} of the first Brillouin zone in size. The Tl 6 s-block bands have orbital contributions from the Mn atoms, and the carrier density is very low. These are important for the occurrence of a colossal magnetoresistance in Tl 2Mn 2O 7.

Phononic band gaps and vibrations in one- and two-dimensional mass-spring structures

DEFF Research Database (Denmark)

Jensen, Jakob Søndergaard

2003-01-01

The vibrational response of finite periodic lattice structures subjected to periodic loading is investigated. Special attention is devoted to the response in frequency ranges with gaps in the band structure for the corresponding infinite periodic lattice. The effects of boundaries, viscous dampin...

Multiple band structure in 156Er

International Nuclear Information System (INIS)

Sunyar, A.W.; Der Mateosian, E.; Kistner, O.C.; Johnson, A.; Lumpkin, A.H.; Thieberger, P.

1976-01-01

The 142 Nd( 18 O,4n) 156 Er reaction at 90-95 MeV was used to study 156 Er high-spin states to spin 24. In addition to the background ground-state band, two well developed off-spin side bands, one of each parity, were observed. (Auth.)

Pressure-Induced Structural Evolution and Band Gap Shifts of Organometal Halide Perovskite-Based Methylammonium Lead Chloride.

Science.gov (United States)

Wang, Lingrui; Wang, Kai; Xiao, Guanjun; Zeng, Qiaoshi; Zou, Bo

2016-12-15

Organometal halide perovskites are promising materials for optoelectronic devices. Further development of these devices requires a deep understanding of their fundamental structure-property relationships. The effect of pressure on the structural evolution and band gap shifts of methylammonium lead chloride (MAPbCl 3 ) was investigated systematically. Synchrotron X-ray diffraction and Raman experiments provided structural information on the shrinkage, tilting distortion, and amorphization of the primitive cubic unit cell. In situ high pressure optical absorption and photoluminescence spectra manifested that the band gap of MAPbCl 3 could be fine-tuned to the ultraviolet region by pressure. The optical changes are correlated with pressure-induced structural evolution of MAPbCl 3 , as evidenced by band gap shifts. Comparisons between Pb-hybrid perovskites and inorganic octahedra provided insights on the effects of halogens on pressure-induced transition sequences of these compounds. Our results improve the understanding of the structural and optical properties of organometal halide perovskites.

Effects of weak nonlinearity on dispersion relations and frequency band-gaps of periodic structures

DEFF Research Database (Denmark)

Sorokin, Vladislav; Thomsen, Jon Juel

2015-01-01

of these for nonlinear problems is impossible or cumbersome, since Floquet theory is applicable for linear systems only. Thus the nonlinear effects for periodic structures are not yet fully uncovered, while at the same time applica-tions may demand effects of nonlinearity on structural response to be accounted for....... The present work deals with analytically predicting dynamic responses for nonlinear continuous elastic periodic structures. Specifically, the effects of weak nonlinearity on the dispersion re-lation and frequency band-gaps of a periodic Bernoulli-Euler beam performing bending os-cillations are analyzed......The analysis of the behaviour of linear periodic structures can be traced back over 300 years, to Sir Isaac Newton, and still attracts much attention. An essential feature of periodic struc-tures is the presence of frequency band-gaps, i.e. frequency ranges in which waves cannot propagate...

Low band gap frequencies and multiplexing properties in 1D and 2D mass spring structures

International Nuclear Information System (INIS)

Aly, Arafa H; Mehaney, Ahmed

2016-01-01

This study reports on the propagation of elastic waves in 1D and 2D mass spring structures. An analytical and computation model is presented for the 1D and 2D mass spring systems with different examples. An enhancement in the band gap values was obtained by modeling the structures to obtain low frequency band gaps at small dimensions. Additionally, the evolution of the band gap as a function of mass value is discussed. Special attention is devoted to the local resonance property in frequency ranges within the gaps in the band structure for the corresponding infinite periodic lattice in the 1D and 2D mass spring system. A linear defect formed of a row of specific masses produces an elastic waveguide that transmits at the narrow pass band frequency. The frequency of the waveguides can be selected by adjusting the mass and stiffness coefficients of the materials constituting the waveguide. Moreover, we pay more attention to analyze the wave multiplexer and DE-multiplexer in the 2D mass spring system. We show that two of these tunable waveguides with alternating materials can be employed to filter and separate specific frequencies from a broad band input signal. The presented simulation data is validated through comparison with the published research, and can be extended in the development of resonators and MEMS verification. (paper)

The Electronic Band Structure of Platinum Oxide (PtO) | Omehe ...

African Journals Online (AJOL)

We have performed the electronic band structure of the bulk and monolayer of PtO using the full potential linear muffin-tin orbital and the projector augmented wave method with the density functional theory. We applied the LDA and LDA+U scheme to both methods. It was found out that the LDA calculation of bulk PtO ...

Band structure properties of (BGa)P semiconductors for lattice matched integration on (001) silicon

Energy Technology Data Exchange (ETDEWEB)

Hossain, Nadir; Sweeney, Stephen [Advanced Technology Institute and Department of Physics, University of Surrey, Guildford, Surrey GU2 7XH (United Kingdom); Hosea, Jeff [Advanced Technology Institute and Department of Physics, University of Surrey, Guildford, Surrey GU2 7XH, UK and Ibnu Sina Institute for Fundamental Science Studies, Universiti Teknologi Malaysia, Johor Bahru 81310 (Malaysia); Liebich, Sven; Zimprich, Martin; Volz, Kerstin; Stolz, Wolfgang [Material Sciences Center and Faculty of Physics, Philipps-University, 35032 Marburg (Germany); Kunert, Bernerdette [NAsP III/V GmbH, Am Knechtacker 19, 35041 Marburg (Germany)

2013-12-04

We report the band structure properties of (BGa)P layers grown on silicon substrate using metal-organic vapour-phase epitaxy. Using surface photo-voltage spectroscopy we find that both the direct and indirect band gaps of (BGa)P alloys (strained and unstrained) decrease with Boron content. Our experimental results suggest that the band gap of (BGa)P layers up to 6% Boron is large and suitable to be used as cladding and contact layers in GaP-based quantum well heterostructures on silicon substrates.

Low frequency phononic band structures in two-dimensional arc-shaped phononic crystals

International Nuclear Information System (INIS)

Xu, Zhenlong; Wu, Fugen; Guo, Zhongning

2012-01-01

The low frequency phononic band structures of two-dimensional arc-shaped phononic crystals (APCs) were studied by the transfer matrix method in cylindrical coordinates. The results showed the first phononic band gaps (PBGs) of APCs from zero Hz with low modes. Locally resonant (LR) gaps were obtained with higher-order rotation symmetry, due to LR frequencies corresponding to the speeds of acoustic waves in the materials. These properties can be efficiently used in a structure for low frequencies that are forbidden, or in a device that permits a narrow window of frequencies. -- Highlights: ► We report a new class of quasi-periodic hetero-structures, arc-shaped phononic crystals (APCs). ► The results show the first PBGs start with zero Hz with low modes. ► Locally resonant (LR) gaps were obtained with higher-order rotation symmetry, due to LR frequencies corresponding to the speeds of acoustic waves in the materials.

Two-band tariff for domestic use: Italian Electricity Board rate structure

International Nuclear Information System (INIS)

Barteselli, R.

1992-01-01

ENEL (the Italian National Electricity Board) has begun to introduce a new rate structure for households: the 'two-band tariff'. This article is an effort to examine in principle how the new tariff could optimize load management when applied to the whole household sector

Observations of Multi-band Structures in Double Star TC-1 PEACE Electron and HIA Ion Data

Science.gov (United States)

Mohan Narasimhan, K.; Fazakerley, A. N.; Grimald, S.; Dandouras, I. S.; Mihaljcic, B.; Kistler, L. M.; Owen, C. J.

2015-12-01

Several authors have reported inner magnetosphere observations of proton distributions confined to narrow energy bands in the range 1 - 25 keV (Smith and Hoffman (1974), etc). These structures have been described as "nose structures", with reference to their appearance in energy-time spectrograms and are also known as "bands" if they occur for extended periods of time. Multi-nose structures have been observed if 2 or more noses appear at the same time (Vallat et al., 2007). Gaps between "noses" (or "bands") have been explained in terms of the competing corotation, convection and magnetic gradient drifts. Charge exchange losses in slow drift paths for steady state scenarios and the role of substorm injections have also been considered (Li et al., 2000; Ebihara et al., 2004). We analyse observations of electron and ion multi-band structures frequently seen in Double-Star TC1 PEACE and HIA data. We present results from statistical surveys conducted using data from the duration of the mission. Furthermore, using a combination of both statistics and simulations, we test previous theories as to possible formation mechanisms and explore other possible explanations.

TDRSS S-shuttle unique receiver equipment

Science.gov (United States)

Weinberg, A.; Schwartz, J. J.; Spearing, R.

1985-01-01

Beginning with STS-9, the Tracking and Date Relay Satellite system (TDRSS) will start providing S- and Ku-band communications and tracking support to the Space Shuttle and its payloads. The most significant element of this support takes place at the TDRSS White Sands Ground Terminal, which processes the Shuttle return link S- and Ku-band signals. While Ku-band hardware available to other TDRSS users is also applied to Ku-Shuttle, stringent S-Shuttle link margins have precluded the application of the standard TDRSS S-band processing equipment to S-Shuttle. It was therfore found necessary to develop a unique S-Shuttle Receiver that embodies state-of-the-art digital technology and processing techniques. This receiver, developed by Motorola, Inc., enhances link margins by 1.5 dB relative to the standard S-band equipment and its bit error rate performance is within a few tenths of a dB of theory. An overview description of the Space Shuttle Receiver Equipment (SSRE) is presented which includes the presentation of block diagrams and salient design features. Selected, measured performance results are also presented.

Electronic band structure and optical properties of the cubic, Sc, Y and La hydride systems

International Nuclear Information System (INIS)

Peterman, D.J.

1980-01-01

Electronic band structure calculations are used to interpret the optical spectra of the cubic Sc, Y and La hydride systems. Self-consistent band calculations of ScH 2 and YH 2 were carried out. The respective joint densities of states are computed and compared to the dielectric functions determined from the optical measurements. Additional calculations were performed in which the Fermi level or band gap energies are rigidly shifted by a small energy increment. These calculations are then used to simulate the derivative structure in thermomodulation spectra and relate the origin of experimental interband features to the calculated energy bands. While good systematic agreement is obtained for several spectral features, the origin of low-energy interband transitions in YH 2 cannot be explained by these calculated bands. A lattice-size-dependent premature occupation of octahedral sites by hydrogen atoms in the fcc metal lattice is suggested to account for this discrepancy. Various non-self-consistent calculations are used to examine the effect of such a premature occupation. Measurements of the optical absorptivity of LaH/sub x/ with 1.6 2 lattice. These experimental results also suggest that, in contrast to recent calculations, LaH 3 is a small-band-gap semiconductor

Polar semiconductor heterojunction structure energy band diagram considerations

International Nuclear Information System (INIS)

Lin, Shuxun; Wen, Cheng P.; Wang, Maojun; Hao, Yilong

2016-01-01

The unique nature of built-in electric field induced positive/negative charge pairs of polar semiconductor heterojunction structure has led to a more realistic device model for hexagonal III-nitride HEMT. In this modeling approach, the distribution of charge carriers is dictated by the electrostatic potential profile instead of Femi statistics. The proposed device model is found suitable to explain peculiar properties of GaN HEMT structures, including: (1) Discrepancy in measured conventional linear transmission line model (LTLM) sheet resistance and contactless sheet resistance of GaN HEMT with thin barrier layer. (2) Below bandgap radiation from forward biased Nickel Schottky barrier diode on GaN HEMT structure. (3) GaN HEMT barrier layer doping has negligible effect on transistor channel sheet charge density.

Polar semiconductor heterojunction structure energy band diagram considerations

Energy Technology Data Exchange (ETDEWEB)

Lin, Shuxun; Wen, Cheng P., E-mail: cpwen@ieee.org; Wang, Maojun; Hao, Yilong [Institute of Microelectronics, Peking University, Beijing (China)

2016-03-28

The unique nature of built-in electric field induced positive/negative charge pairs of polar semiconductor heterojunction structure has led to a more realistic device model for hexagonal III-nitride HEMT. In this modeling approach, the distribution of charge carriers is dictated by the electrostatic potential profile instead of Femi statistics. The proposed device model is found suitable to explain peculiar properties of GaN HEMT structures, including: (1) Discrepancy in measured conventional linear transmission line model (LTLM) sheet resistance and contactless sheet resistance of GaN HEMT with thin barrier layer. (2) Below bandgap radiation from forward biased Nickel Schottky barrier diode on GaN HEMT structure. (3) GaN HEMT barrier layer doping has negligible effect on transistor channel sheet charge density.

An Optimized, Grid Independent, Narrow Band Data Structure for High Resolution Level Sets

DEFF Research Database (Denmark)

Nielsen, Michael Bang; Museth, Ken

2004-01-01

enforced by the convex boundaries of an underlying cartesian computational grid. Here we present a novel very memory efficient narrow band data structure, dubbed the Sparse Grid, that enables the representation of grid independent high resolution level sets. The key features our new data structure are...

Band structure and orbital character of monolayer MoS2 with eleven-band tight-binding model

Science.gov (United States)

Shahriari, Majid; Ghalambor Dezfuli, Abdolmohammad; Sabaeian, Mohammad

2018-02-01

In this paper, based on a tight-binding (TB) model, first we present the calculations of eigenvalues as band structure and then present the eigenvectors as probability amplitude for finding electron in atomic orbitals for monolayer MoS2 in the first Brillouin zone. In these calculations we are considering hopping processes between the nearest-neighbor Mo-S, the next nearest-neighbor in-plan Mo-Mo, and the next nearest-neighbor in-plan and out-of-plan S-S atoms in a three-atom based unit cell of two-dimensional rhombic MoS2. The hopping integrals have been solved in terms of Slater-Koster and crystal field parameters. These parameters are calculated by comparing TB model with the density function theory (DFT) in the high-symmetry k-points (i.e. the K- and Γ-points). In our TB model all the 4d Mo orbitals and the 3p S orbitals are considered and detailed analysis of the orbital character of each energy level at the main high-symmetry points of the Brillouin zone is described. In comparison with DFT calculations, our results of TB model show a very good agreement for bands near the Fermi level. However for other bands which are far from the Fermi level, some discrepancies between our TB model and DFT calculations are observed. Upon the accuracy of Slater-Koster and crystal field parameters, on the contrary of DFT, our model provide enough accuracy to calculate all allowed transitions between energy bands that are very crucial for investigating the linear and nonlinear optical properties of monolayer MoS2.

Metal-induced gap states in ferroelectric capacitors and its relationship with complex band structures

Science.gov (United States)

Junquera, Javier; Aguado-Puente, Pablo

2013-03-01

At metal-isulator interfaces, the metallic wave functions with an energy eigenvalue within the band gap decay exponentially inside the dielectric (metal-induced gap states, MIGS). These MIGS can be actually regarded as Bloch functions with an associated complex wave vector. Usually only real values of the wave vectors are discussed in text books, since infinite periodicity is assumed and, in that situation, wave functions growing exponentially in any direction would not be physically valid. However, localized wave functions with an exponential decay are indeed perfectly valid solution of the Schrodinger equation in the presence of defects, surfaces or interfaces. For this reason, properties of MIGS have been typically discussed in terms of the complex band structure of bulk materials. The probable dependence on the interface particulars has been rarely taken into account explicitly due to the difficulties to include them into the model or simulations. We aim to characterize from first-principles simulations the MIGS in realistic ferroelectric capacitors and their connection with the complex band structure of the ferroelectric material. We emphasize the influence of the real interface beyond the complex band structure of bulk materials. Financial support provided by MICINN Grant FIS2009-12721-C04-02, and by the European Union Grant No. CP-FP 228989-2 ``OxIDes''. Computer resources provided by the RES.

Investigation of the Band Structure of Graphene-Based Plasmonic Photonic Crystals.

Science.gov (United States)

Qiu, Pingping; Qiu, Weibin; Lin, Zhili; Chen, Houbo; Tang, Yixin; Wang, Jia-Xian; Kan, Qiang; Pan, Jiao-Qing

2016-09-09

In this paper, one-dimensional (1D) and two-dimensional (2D) graphene-based plasmonic photonic crystals (PhCs) are proposed. The band structures and density of states (DOS) have been numerically investigated. Photonic band gaps (PBGs) are found in both 1D and 2D PhCs. Meanwhile, graphene-based plasmonic PhC nanocavity with resonant frequency around 175 THz, is realized by introducing point defect, where the chemical potential is from 0.085 to 0.25 eV, in a 2D PhC. Also, the bending wvaguide and the beam splitter are realized by introducing the line defect into the 2D PhC.

Optical properties of Nb and Mo calculated from augmented-plane-wave band structures

International Nuclear Information System (INIS)

Pickett, W.E.; Allen, P.B.

1975-01-01

Nonrelativistic band calculations of Mattheiss for Nb and Petroff and Viswanathan for Mo are used to calculate the imaginary part epsilon 2 of the dielectric function for these metals. The structure resulting from interband transitions in the frequency range 0.1--0.5 Ry is found to give fairly good agreement with experiment. The calculation indicates that structure in epsilon 2 can arise from transitions away from symmetry points and lines in the Brillouin zone. The difficulty in distinguishing between the direct and indirect transition models for epsilon 2 is shown to arise from a lack of strong optical critical points. Predictions of the rigid-band model for the optical properties of Nb-Mo alloys are presented

Harnessing the bistable composite shells to design a tunable phononic band gap structure

Science.gov (United States)

Li, Yi; Xu, Yanlong

2018-02-01

By proposing a system composed of an array of bistable composite shells immersed in air, we develop a new class of periodic structure to control the propagation of sound. Through numerical investigation, we find that the acoustic band gap of this system can be switched on and off by triggering the snap through deformation of the bistable composite shells. The shape of cross section and filling fraction of unit cell can be altered by different number of bistable composite shells, and they have strong impact on the position and width of the band gap. The proposed concept paves the way of using the bistable structures to design a new class of metamaterials that can be enable to manipulate sound.

Tight binding electronic band structure calculation of achiral boron nitride single wall nanotubes

International Nuclear Information System (INIS)

Saxena, Prapti; Sanyal, Sankar P

2006-01-01

In this paper we report the Tight-Binding method, for the electronic structure calculations of achiral single wall Boron Nitride nanotubes. We have used the contribution of π electron only to define the electronic band structure for the solid. The Zone-folding method is used for the Brillouin Zone definition. Calculation of tight binding model parameters is done by fitting them to available experimental results of two-dimensional hexagonal monolayers of Boron Nitride. It has been found that all the boron nitride nanotubes (both zigzag and armchair) are constant gap semiconductors with a band gap of 5.27eV. All zigzag BNNTs are found to be direct gap semiconductors while all armchair nanotubes are indirect gap semiconductors. (author)

Importance of doping, dopant distribution, and defects on electronic band structure alteration of metal oxide nanoparticles: Implications for reactive oxygen species

International Nuclear Information System (INIS)

Saleh, Navid B.; Milliron, Delia J.; Aich, Nirupam; Katz, Lynn E.; Liljestrand, Howard M.; Kirisits, Mary Jo

2016-01-01

Metal oxide nanoparticles (MONPs) are considered to have the potency to generate reactive oxygen species (ROS), one of the key mechanisms underlying nanotoxicity. However, the nanotoxicology literature demonstrates a lack of consensus on the dominant toxicity mechanism(s) for a particular MONP. Moreover, recent literature has studied the correlation between band structure of pristine MONPs to their ability to introduce ROS and thus has downplayed the ROS-mediated toxicological relevance of a number of such materials. On the other hand, material science can control the band structure of these materials to engineer their electronic and optical properties and thereby is constantly modulating the pristine electronic structure. Since band structure is the fundamental material property that controls ROS-producing ability, band tuning via introduction of dopants and defects needs careful consideration in toxicity assessments. This commentary critically evaluates the existing material science and nanotoxicity literature and identifies the gap in our understanding of the role of important crystal structure features (i.e., dopants and defects) on MONPs' electronic structure alteration as well as their ROS-generation capability. Furthermore, this commentary provides suggestions on characterization techniques to evaluate dopants and defects on the crystal structure and identifies research needs for advanced theoretical predictions of their electronic band structures and ROS-generation abilities. Correlation of electronic band structure and ROS will not only aid in better mechanistic assessment of nanotoxicity but will be impactful in designing and developing ROS-based applications ranging from water disinfection to next-generation antibiotics and even cancer therapeutics. - Highlights: • Metal oxide nanoparticles (MONPs) produce reactive oxygen species (ROS) • Band structure of pristine MONPs is different than those with dopants/defects • Dopants/defects modulate

Importance of doping, dopant distribution, and defects on electronic band structure alteration of metal oxide nanoparticles: Implications for reactive oxygen species

Energy Technology Data Exchange (ETDEWEB)

Saleh, Navid B., E-mail: navid.saleh@utexas.edu [Department of Civil, Architectural, and Environmental Engineering, University of Texas, Austin, TX 78712 (United States); Milliron, Delia J. [McKetta Department of Chemical Engineering, University of Texas, Austin, TX 78712 (United States); Aich, Nirupam [Department of Civil, Structural and Environmental Engineering, University at Buffalo, The State University of New York, Buffalo, NY, 14260 (United States); Katz, Lynn E.; Liljestrand, Howard M.; Kirisits, Mary Jo [Department of Civil, Architectural, and Environmental Engineering, University of Texas, Austin, TX 78712 (United States)

2016-10-15

Metal oxide nanoparticles (MONPs) are considered to have the potency to generate reactive oxygen species (ROS), one of the key mechanisms underlying nanotoxicity. However, the nanotoxicology literature demonstrates a lack of consensus on the dominant toxicity mechanism(s) for a particular MONP. Moreover, recent literature has studied the correlation between band structure of pristine MONPs to their ability to introduce ROS and thus has downplayed the ROS-mediated toxicological relevance of a number of such materials. On the other hand, material science can control the band structure of these materials to engineer their electronic and optical properties and thereby is constantly modulating the pristine electronic structure. Since band structure is the fundamental material property that controls ROS-producing ability, band tuning via introduction of dopants and defects needs careful consideration in toxicity assessments. This commentary critically evaluates the existing material science and nanotoxicity literature and identifies the gap in our understanding of the role of important crystal structure features (i.e., dopants and defects) on MONPs' electronic structure alteration as well as their ROS-generation capability. Furthermore, this commentary provides suggestions on characterization techniques to evaluate dopants and defects on the crystal structure and identifies research needs for advanced theoretical predictions of their electronic band structures and ROS-generation abilities. Correlation of electronic band structure and ROS will not only aid in better mechanistic assessment of nanotoxicity but will be impactful in designing and developing ROS-based applications ranging from water disinfection to next-generation antibiotics and even cancer therapeutics. - Highlights: • Metal oxide nanoparticles (MONPs) produce reactive oxygen species (ROS) • Band structure of pristine MONPs is different than those with dopants/defects • Dopants/defects modulate

Metamaterial Combining Electric- and Magnetic-Dipole-Based Configurations for Unique Dual-Band Signal Enhancement in Ultrahigh-Field Magnetic Resonance Imaging.

Science.gov (United States)

Schmidt, Rita; Webb, Andrew

2017-10-11

Magnetic resonance imaging and spectroscopy (MRI and MRS) are both widely used techniques in medical diagnostics and research. One of the major thrusts in recent years has been the introduction of ultrahigh-field magnets in order to boost the sensitivity. Several MRI studies have examined further potential improvements in sensitivity using metamaterials, focusing on single frequency applications. However, metamaterials have yet to reach a level that is practical for routine MRI use. In this work, we explore a new metamaterial implementation for MRI, a dual-nuclei resonant structure, which can be used for both proton and heteronuclear magnetic resonance. Our approach combines two configurations, one based on a set of electric dipoles for the low frequency band, and the second based on a set of magnetic dipoles for the high frequency band. We focus on the implementation of a dual-nuclei metamaterial for phosphorus and proton imaging and spectroscopy at an ultrahigh-field strength of 7 T. In vivo scans using this flexible and compact structure show that it locally enhances both the phosphorus and proton transmit and receive sensitivities.

Modelling the metal–semiconductor band structure in implanted ohmic contacts to GaN and SiC

International Nuclear Information System (INIS)

Pérez-Tomás, A; Fontserè, A; Placidi, M; Jennings, M R; Gammon, P M

2013-01-01

Here we present a method to model the metal–semiconductor (M–S) band structure to an implanted ohmic contact to a wide band gap semiconductor (WBG) such as GaN and SiC. The performance and understanding of the M–S contact to a WBG semiconductor is of great importance as it influences the overall performance of a semiconductor device. In this work we explore in a numerical fashion the ohmic contact properties to a WBG semiconductor taking into account the partial ionization of impurities and analysing its dependence on the temperature, the barrier height, the impurity level band energy and carrier concentration. The effect of the M–S Schottky barrier lowering and the Schottky barrier inhomogeneities are discussed. The model is applied to a fabricated ohmic contact to GaN where the M–S band structure can be completely determined. (paper)

Observation of dark-current signals from the S-band structures of the SLAC linac

International Nuclear Information System (INIS)

Assmann, R.; Decker, F.J.; Seidel, M.; Siemann, R.H.; Whittum, D.

1997-07-01

It is well known that the electro-magnetic fields in high-gradient RF structures can cause electron emission from the metallic structure walls. If the emitted electrons are captured and accelerated by the accelerating fields so-called dark-current is induced. Dark-currents have been measured and studied for various RF-structures. In this paper the authors present measurements of RF induced signals for the SLC S-band structures. For nominal gradients of 17 MV/m it is shown that the dark-current can be strong enough to significantly reduce the signal-to-noise ratio of the SLC beam wire scanners. They also show results from RF measurements in the dipole band. The measurements are compared to more direct observations of dark-current and it is tried to connect the results to possible effects on the accelerated particle beam

Optical properties and electronic band structure of AgInSe2

International Nuclear Information System (INIS)

Ozaki, Shunji; Adachi, Sadao

2006-01-01

Optical properties of a chalcopyrite semiconductor AgInSe 2 have been studied by optical absorption, spectroscopic ellipsometry (SE), and thermoreflectance (TR) measurements. The measurements reveal distinct structures at energies of the critical points in the Brillouin zone. By performing the band-structure calculation, these critical points have been successfully assigned to specific points in the Brillouin zone. (copyright 2006 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (Abstract Copyright [2006], Wiley Periodicals, Inc.)

Exploiting Unique Structural and Functional Properties of Malarial Glycolytic Enzymes for Antimalarial Drug Development

Directory of Open Access Journals (Sweden)

Asrar Alam

2014-01-01

Full Text Available Metabolic enzymes have been known to carry out a variety of functions besides their normal housekeeping roles known as “moonlighting functions.” These functionalities arise from structural changes induced by posttranslational modifications and/or binding of interacting proteins. Glycolysis is the sole source of energy generation for malaria parasite Plasmodium falciparum, hence a potential pathway for therapeutic intervention. Crystal structures of several P. falciparum glycolytic enzymes have been solved, revealing that they exhibit unique structural differences from the respective host enzymes, which could be exploited for their selective targeting. In addition, these enzymes carry out many parasite-specific functions, which could be of potential interest to control parasite development and transmission. This review focuses on the moonlighting functions of P. falciparum glycolytic enzymes and unique structural differences and functional features of the parasite enzymes, which could be exploited for therapeutic and transmission blocking interventions against malaria.

Weakly nonlinear dispersion and stop-band effects for periodic structures

DEFF Research Database (Denmark)

Sorokin, Vladislav; Thomsen, Jon Juel

of frequency band-gaps, i.e. frequency ranges in which elastic waves cannot propagate. Most existing analytical methods in the field are based on Floquet theory [1]; e.g. this holds for the classical Hill’s method of infinite determinants [1,2], and themethod of space-harmonics [3]. However, application...... of these methods for studying nonlinear problems isimpossible or cumbersome, since Floquet theory is applicable only for linear systems. Thus the nonlinear effects for periodic structures are not yet fully uncovered, while at the same time applications may demand effects of nonlinearity on structural response...... to be accounted for.The paper deals with analytically predicting dynamic response for nonlinear elastic structures with a continuous periodic variation in structural properties. Specifically, for a Bernoulli-Euler beam with aspatially continuous modulation of structural properties in the axial direction...

Band gap structure modification of amorphous anodic Al oxide film by Ti-alloying

DEFF Research Database (Denmark)

Canulescu, Stela; Rechendorff, K.; Borca, C. N.

2014-01-01

The band structure of pure and Ti-alloyed anodic aluminum oxide has been examined as a function of Ti concentration varying from 2 to 20 at. %. The band gap energy of Ti-alloyed anodic Al oxide decreases with increasing Ti concentration. X-ray absorption spectroscopy reveals that Ti atoms...... are not located in a TiO2 unit in the oxide layer, but rather in a mixed Ti-Al oxide layer. The optical band gap energy of the anodic oxide layers was determined by vacuum ultraviolet spectroscopy in the energy range from 4.1 to 9.2 eV (300–135 nm). The results indicate that amorphous anodic Al2O3 has a direct...

Constructing Repairable Meta-Structures of Ultra-Broad-Band Electromagnetic Absorption from Three-Dimensional Printed Patterned Shells.

Science.gov (United States)

Song, Wei-Li; Zhou, Zhili; Wang, Li-Chen; Cheng, Xiao-Dong; Chen, Mingji; He, Rujie; Chen, Haosen; Yang, Yazheng; Fang, Daining

2017-12-13

Ultra-broad-band electromagnetic absorption materials and structures are increasingly attractive for their critical role in competing with the advanced broad-band electromagnetic detection systems. Mechanically soft and weak wax-based materials composites are known to be insufficient to serve in practical electromagnetic absorption applications. To break through such barriers, here we developed an innovative strategy to enable the wax-based composites to be robust and repairable meta-structures by employing a three-dimensional (3D) printed polymeric patterned shell. Because of the integrated merits from both the dielectric loss wax-based composites and mechanically robust 3D printed shells, the as-fabricated meta-structures enable bear mechanical collision and compression, coupled with ultra-broad-band absorption (7-40 and 75-110 GHz, reflection loss  smaller than -10 dB) approaching state-of-the-art electromagnetic absorption materials. With the assistance of experiment and simulation methods, the design advantages and mechanism of employing such 3D printed shells for substantially promoting the electromagnetic absorption performance have been demonstrated. Therefore, such universal strategy that could be widely extended to other categories of wax-based composites highlights a smart stage on which high-performance practical multifunction meta-structures with ultra-broad-band electromagnetic absorption could be envisaged.

Design, realization and test of C-band accelerating structures for the SPARC-LAB linac energy upgrade

International Nuclear Information System (INIS)

Alesini, D.; Bellaveglia, M.; Biagini, M.E.; Boni, R.; Brönnimann, M.; Cardelli, F.; Chimenti, P.; Clementi, R.; Di Pirro, G.; Di Raddo, R.; Ferrario, M.; Ficcadenti, L.; Gallo, A.; Kalt, R.; Lollo, V.; Palumbo, L.; Piersanti, L.; Schilcher, T.

2016-01-01

The energy upgrade of the SPARC-LAB photo-injector at LNF-INFN (Frascati, Italy) has been originally conceived replacing one low gradient (13 MV/m) 3 m long SLAC type S-band traveling wave (TW) section with two 1.4 m long C-band accelerating sections. Due to the higher gradients reached by such structures, a higher energy beam can be obtained within the same accelerator footprint length. The use of C-band structures for electron acceleration has been adopted in a few FEL linacs in the world, among others, the Japanese Free Electron Laser at SPring-8 and the SwissFEL at Paul Scherrer Institute (PSI). The C-band sections are traveling wave, constant impedance structures with symmetric input and output axial couplers. Their design has been optimized for the operation with a SLED RF pulse compressor. In this paper we briefly review their design criteria and we focus on the construction, tuning, low and high-power RF tests. We also illustrate the design and realization of the dedicated low level RF system that has been done in collaboration with PSI in the framework of the EU TIARA project. Preliminary experimental results appear to confirm the operation of such structures with accelerating gradients larger than 35 MV/m.

Design, realization and test of C-band accelerating structures for the SPARC-LAB linac energy upgrade

Energy Technology Data Exchange (ETDEWEB)

Alesini, D.; Bellaveglia, M.; Biagini, M.E.; Boni, R. [INFN Laboratori Nazionali di Frascati, Via Enrico Fermi 40, 00044, Frascati (Italy); Brönnimann, M. [Paul Scherrer Institut, 5232 Villigen (Switzerland); Cardelli, F. [INFN Sezione di Roma, P.le Aldo Moro 2, 00185, Roma (Italy); Università di Roma “La Sapienza”, P.le Aldo Moro 2, 00185, Roma (Italy); Chimenti, P.; Clementi, R.; Di Pirro, G.; Di Raddo, R.; Ferrario, M. [INFN Laboratori Nazionali di Frascati, Via Enrico Fermi 40, 00044, Frascati (Italy); Ficcadenti, L. [INFN Sezione di Roma, P.le Aldo Moro 2, 00185, Roma (Italy); Università di Roma “La Sapienza”, P.le Aldo Moro 2, 00185, Roma (Italy); Gallo, A. [INFN Laboratori Nazionali di Frascati, Via Enrico Fermi 40, 00044, Frascati (Italy); Kalt, R. [Paul Scherrer Institut, 5232 Villigen (Switzerland); Lollo, V. [INFN Laboratori Nazionali di Frascati, Via Enrico Fermi 40, 00044, Frascati (Italy); Palumbo, L. [INFN Sezione di Roma, P.le Aldo Moro 2, 00185, Roma (Italy); Università di Roma “La Sapienza”, P.le Aldo Moro 2, 00185, Roma (Italy); Piersanti, L., E-mail: luca.piersanti@lnf.infn.it [INFN Sezione di Roma, P.le Aldo Moro 2, 00185, Roma (Italy); Università di Roma “La Sapienza”, P.le Aldo Moro 2, 00185, Roma (Italy); Schilcher, T. [Paul Scherrer Institut, 5232 Villigen (Switzerland)

2016-11-21

The energy upgrade of the SPARC-LAB photo-injector at LNF-INFN (Frascati, Italy) has been originally conceived replacing one low gradient (13 MV/m) 3 m long SLAC type S-band traveling wave (TW) section with two 1.4 m long C-band accelerating sections. Due to the higher gradients reached by such structures, a higher energy beam can be obtained within the same accelerator footprint length. The use of C-band structures for electron acceleration has been adopted in a few FEL linacs in the world, among others, the Japanese Free Electron Laser at SPring-8 and the SwissFEL at Paul Scherrer Institute (PSI). The C-band sections are traveling wave, constant impedance structures with symmetric input and output axial couplers. Their design has been optimized for the operation with a SLED RF pulse compressor. In this paper we briefly review their design criteria and we focus on the construction, tuning, low and high-power RF tests. We also illustrate the design and realization of the dedicated low level RF system that has been done in collaboration with PSI in the framework of the EU TIARA project. Preliminary experimental results appear to confirm the operation of such structures with accelerating gradients larger than 35 MV/m.

Ballistic-electron-emission spectroscopy of AlxGa1-xAs/GaAs heterostructures: Conduction-band offsets, transport mechanisms, and band-structure effects

International Nuclear Information System (INIS)

OShea, J.J.; Brazel, E.G.; Rubin, M.E.; Bhargava, S.; Chin, M.A.; Narayanamurti, V.

1997-01-01

We report an extensive investigation of semiconductor band-structure effects in single-barrier Al x Ga 1-x As/GaAs heterostructures using ballistic-electron-emission spectroscopy (BEES). The transport mechanisms in these single-barrier structures were studied systematically as a function of temperature and Al composition over the full compositional range (0≤x≤1). The initial (Γ) BEES thresholds for Al x Ga 1-x As single barriers with 0≤x≤0.42 were extracted using a model which includes the complete transmission probability of the metal-semiconductor interface and the semiconductor heterostructure. Band offsets measured by BEES are in good agreement with previous measurements by other techniques which demonstrates the accuracy of this technique. BEES measurements at 77 K give the same band-offset values as at room temperature. When a reverse bias is applied to the heterostructures, the BEES thresholds shift to lower voltages in good agreement with the expected bias-induced band-bending. In the indirect band-gap regime (x>0.45), spectra show a weak ballistic-electron-emission microscopy current contribution due to intervalley scattering through Al x Ga 1-x As X valley states. Low-temperature spectra show a marked reduction in this intervalley current component, indicating that intervalley phonon scattering at the GaAs/Al x Ga 1-x As interface produces a significant fraction of thisX valley current. A comparison of the BEES thresholds with the expected composition dependence of the Al x Ga 1-x As Γ, L, and X points yields good agreement over the entire composition range. copyright 1997 The American Physical Society

Effects of thermo-order-mechanical coupling on band structures in liquid crystal nematic elastomer porous phononic crystals.

Science.gov (United States)

Yang, Shuai; Liu, Ying

2018-08-01

Liquid crystal nematic elastomers are one kind of smart anisotropic and viscoelastic solids simultaneously combing the properties of rubber and liquid crystals, which is thermal sensitivity. In this paper, the wave dispersion in a liquid crystal nematic elastomer porous phononic crystal subjected to an external thermal stimulus is theoretically investigated. Firstly, an energy function is proposed to determine thermo-induced deformation in NE periodic structures. Based on this function, thermo-induced band variation in liquid crystal nematic elastomer porous phononic crystals is investigated in detail. The results show that when liquid crystal elastomer changes from nematic state to isotropic state due to the variation of the temperature, the absolute band gaps at different bands are opened or closed. There exists a threshold temperature above which the absolute band gaps are opened or closed. Larger porosity benefits the opening of the absolute band gaps. The deviation of director from the structural symmetry axis is advantageous for the absolute band gap opening in nematic state whist constrains the absolute band gap opening in isotropic state. The combination effect of temperature and director orientation provides an added degree of freedom in the intelligent tuning of the absolute band gaps in phononic crystals. Copyright © 2018 Elsevier B.V. All rights reserved.

Terahertz emission from CdHgTe/HgTe quantum wells with an inverted band structure

Energy Technology Data Exchange (ETDEWEB)

Vasilyev, Yu. B., E-mail: Yu.Vasilyev@mail.ioffe.ru [Russian Academy of Sciences, Ioffe Physical–Technical Institute (Russian Federation); Mikhailov, N. N. [Russian Academy of Sciences, Rzhanov Institute of Semiconductor Physics, Siberian Branch (Russian Federation); Vasilyeva, G. Yu.; Ivánov, Yu. L.; Zakhar’in, A. O.; Andrianov, A. V. [Russian Academy of Sciences, Ioffe Physical–Technical Institute (Russian Federation); Vorobiev, L. E.; Firsov, D. A. [Peter the Great Saint-Petersburg Polytechnic University (Russian Federation); Grigoriev, M. N. [Ustinov Baltic State Technical University “VOENMEKh” (Russian Federation); Antonov, A. V.; Ikonnikov, A. V.; Gavrilenko, V. I. [Russian Academy of Sciences, Institute for Physics of Microstructures (Russian Federation)

2016-07-15

The terahertz electroluminescence from Cd{sub 0.7}Hg{sub 0.3}Te/HgTe quantum wells with an inverted band structure in lateral electric fields is experimentally detected and studied. The emission-spectrum maximum for wells 6.5 and 7 nm wide is near 6 meV which corresponds to interband optical transitions. The emission is explained by state depletion in the valence band and conduction band filling due to Zener tunneling, which is confirmed by power-law current–voltage characteristics.

Electronic band structure of TiFese2 in ferromagnetic phase

International Nuclear Information System (INIS)

Jahangirli, Z.A.; Mimura, K.; Shim, Y.; Mamedov, N.T.; Wakita, K.; Orudzhev, G.S.; Jahangirli, Z.A.

2011-01-01

Electronic band structure of crystalline TiFeSe 2 has been calculated using full-potential method of Linear Augmented Plane Wave (LAPW) in density-functional approach with exchange-correlation potential taken in Generalized Gradient Approximation (GGA). The chemical bond in TiFeSe 2 is shown to be metallic because energies of 3d-electrons localized at iron atoms are close to Fermi energy level

Importance of complex band structure and resonant states for tunneling

Czech Academy of Sciences Publication Activity Database

Dederichs, P. H.; Mavropoulos, Ph.; Wunnicke, O.; Papanikolaou, N.; Bellini, V.; Zeller, R.; Drchal, Václav; Kudrnovský, Josef

2002-01-01

Roč. 240, - (2002), s. 108-113 ISSN 0304-8853 R&D Projects: GA AV ČR IAA1010829; GA ČR GA202/00/0122; GA MŠk OC P5.30 Grant - others:TSR(XX) 01398 Institutional research plan: CEZ:AV0Z1010914 Keywords : magnetoresistance * tunneling * band structure * interface effects Subject RIV: BM - Solid Matter Physics ; Magnetism Impact factor: 1.046, year: 2002

Band structures in a two-dimensional phononic crystal with rotational multiple scatterers

Science.gov (United States)

Song, Ailing; Wang, Xiaopeng; Chen, Tianning; Wan, Lele

2017-03-01

In this paper, the acoustic wave propagation in a two-dimensional phononic crystal composed of rotational multiple scatterers is investigated. The dispersion relationships, the transmission spectra and the acoustic modes are calculated by using finite element method. In contrast to the system composed of square tubes, there exist a low-frequency resonant bandgap and two wide Bragg bandgaps in the proposed structure, and the transmission spectra coincide with band structures. Specially, the first bandgap is based on locally resonant mechanism, and the simulation results agree well with the results of electrical circuit analogy. Additionally, increasing the rotation angle can remarkably influence the band structures due to the transfer of sound pressure between the internal and external cavities in low-order modes, and the redistribution of sound pressure in high-order modes. Wider bandgaps are obtained in arrays composed of finite unit cells with different rotation angles. The analysis results provide a good reference for tuning and obtaining wide bandgaps, and hence exploring the potential applications of the proposed phononic crystal in low-frequency noise insulation.

Compton profiles and band structure calculations of CdS and CdTe

International Nuclear Information System (INIS)

Heda, N.L.; Mathur, S.; Ahuja, B.L.; Sharma, B.K.

2007-01-01

In this paper we present the isotropic Compton profiles of zinc-blende CdS and CdTe measured at an intermediate resolution of 0.39 a.u. using our 20 Ci 137 Cs Compton spectrometer. The electronic band structure calculations for both the zinc-blende structure compounds and also wurtzite CdS have been undertaken using various schemes of ab-initio linear combination of atomic orbitals calculations implemented in CRYSTAL03 code. The band structure and Mulliken's populations are reported using density functional scheme. In case of wurtzite CdS, our theoretical anisotropies in directional Compton profiles are compared with available experimental data. In case of both the zinc-blende compounds, the isotropic experimental profiles are found to be in better agreement with the present Hartree-Fock calculations. A study of the equal-valence-electron-density experimental profiles of zinc-blende CdS and CdTe shows that the CdS is more ionic than CdTe. (copyright 2007 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

Complex band structures of transition metal dichalcogenide monolayers with spin–orbit coupling effects

International Nuclear Information System (INIS)

Szczęśniak, Dominik; Ennaoui, Ahmed; Ahzi, Saïd

2016-01-01

Recently, the transition metal dichalcogenides have attracted renewed attention due to the potential use of their low-dimensional forms in both nano- and opto-electronics. In such applications, the electronic and transport properties of monolayer transition metal dichalcogenides play a pivotal role. The present paper provides a new insight into these essential properties by studying the complex band structures of popular transition metal dichalcogenide monolayers (MX 2 , where M   =  Mo, W; X   =  S, Se, Te) while including spin–orbit coupling effects. The conducted symmetry-based tight-binding calculations show that the analytical continuation from the real band structures to the complex momentum space leads to nonlinear generalized eigenvalue problems. Herein an efficient method for solving such a class of nonlinear problems is presented and yields a complete set of physically relevant eigenvalues. Solutions obtained by this method are characterized and classified into propagating and evanescent states, where the latter states manifest not only monotonic but also oscillatory decay character. It is observed that some of the oscillatory evanescent states create characteristic complex loops at the direct band gap of MX 2 monolayers, where electrons can directly tunnel between the band gap edges. To describe these tunneling currents, decay behavior of electronic states in the forbidden energy region is elucidated and their importance within the ballistic transport regime is briefly discussed. (paper)

Complex band structures of transition metal dichalcogenide monolayers with spin-orbit coupling effects

Science.gov (United States)

Szczęśniak, Dominik; Ennaoui, Ahmed; Ahzi, Saïd

2016-09-01

Recently, the transition metal dichalcogenides have attracted renewed attention due to the potential use of their low-dimensional forms in both nano- and opto-electronics. In such applications, the electronic and transport properties of monolayer transition metal dichalcogenides play a pivotal role. The present paper provides a new insight into these essential properties by studying the complex band structures of popular transition metal dichalcogenide monolayers (MX 2, where M  =  Mo, W; X  =  S, Se, Te) while including spin-orbit coupling effects. The conducted symmetry-based tight-binding calculations show that the analytical continuation from the real band structures to the complex momentum space leads to nonlinear generalized eigenvalue problems. Herein an efficient method for solving such a class of nonlinear problems is presented and yields a complete set of physically relevant eigenvalues. Solutions obtained by this method are characterized and classified into propagating and evanescent states, where the latter states manifest not only monotonic but also oscillatory decay character. It is observed that some of the oscillatory evanescent states create characteristic complex loops at the direct band gap of MX 2 monolayers, where electrons can directly tunnel between the band gap edges. To describe these tunneling currents, decay behavior of electronic states in the forbidden energy region is elucidated and their importance within the ballistic transport regime is briefly discussed.

Structure design for a 500 GeV S-band linear collider

International Nuclear Information System (INIS)

Hahne, P.; Holtkamp, N.; Klatt, R.; Weiland, T.

1991-01-01

Constant gradient structures with an accelerating gradient of 20 MeV per meter are commonly used with S-band frequency. The well known features of these travelling wave tubes provide a dedicated design for their use in the next generation linear collider. Some of the required design parameters for this tubes are presented within the whole concept of this collider with an active length of about 30 km. The choice of these parameters is explained and calculations concerning the structure are presented

L-Band SAR Backscatter Related to Forest Cover, Height and Aboveground Biomass at Multiple Spatial Scales across Denmark

DEFF Research Database (Denmark)

Joshi, Neha P.; Mitchard, Edward T A; Schumacher, Johannes

2015-01-01

may be confounded by variations in biophysical forest structure (density, height or cover fraction) and differences in the resolution of satellite and ground data. Here, we attempt to quantify the effect of these factors by relating L-band ALOS PALSAR HV backscatter and unique country-wide Li...

Uniqueness of the joint measurement and the structure of the set of compatible quantum measurements

Science.gov (United States)

Guerini, Leonardo; Terra Cunha, Marcelo

2018-04-01

We address the problem of characterising the compatible tuples of measurements that admit a unique joint measurement. We derive a uniqueness criterion based on the method of perturbations and apply it to show that extremal points of the set of compatible tuples admit a unique joint measurement, while all tuples that admit a unique joint measurement lie in the boundary of such a set. We also provide counter-examples showing that none of these properties are both necessary and sufficient, thus completely describing the relation between the joint measurement uniqueness and the structure of the compatible set. As a by-product of our investigations, we completely characterise the extremal and boundary points of the set of general tuples of measurements and of the subset of compatible tuples.

Photonic band structures solved by a plane-wave-based transfer-matrix method.

Science.gov (United States)

Li, Zhi-Yuan; Lin, Lan-Lan

2003-04-01

Transfer-matrix methods adopting a plane-wave basis have been routinely used to calculate the scattering of electromagnetic waves by general multilayer gratings and photonic crystal slabs. In this paper we show that this technique, when combined with Bloch's theorem, can be extended to solve the photonic band structure for 2D and 3D photonic crystal structures. Three different eigensolution schemes to solve the traditional band diagrams along high-symmetry lines in the first Brillouin zone of the crystal are discussed. Optimal rules for the Fourier expansion over the dielectric function and electromagnetic fields with discontinuities occurring at the boundary of different material domains have been employed to accelerate the convergence of numerical computation. Application of this method to an important class of 3D layer-by-layer photonic crystals reveals the superior convergency of this different approach over the conventional plane-wave expansion method.

Photonic band structures solved by a plane-wave-based transfer-matrix method

International Nuclear Information System (INIS)

Li Zhiyuan; Lin Lanlan

2003-01-01

Transfer-matrix methods adopting a plane-wave basis have been routinely used to calculate the scattering of electromagnetic waves by general multilayer gratings and photonic crystal slabs. In this paper we show that this technique, when combined with Bloch's theorem, can be extended to solve the photonic band structure for 2D and 3D photonic crystal structures. Three different eigensolution schemes to solve the traditional band diagrams along high-symmetry lines in the first Brillouin zone of the crystal are discussed. Optimal rules for the Fourier expansion over the dielectric function and electromagnetic fields with discontinuities occurring at the boundary of different material domains have been employed to accelerate the convergence of numerical computation. Application of this method to an important class of 3D layer-by-layer photonic crystals reveals the superior convergency of this different approach over the conventional plane-wave expansion method

QUANTUM-MECHANICAL MODELING OF SPATIAL AND BAND STRUCTURE OF Y3AL5O12 SCINTILLATION CRYSTAL

Directory of Open Access Journals (Sweden)

I. I. Vrubel

2016-05-01

Full Text Available Spatial and electronic structures of a unit cell of yttrium-aluminum garnet have been studied. Quantum-mechanical model have been presented. Semi-empirical methods PM6 and PM7 have been used for geometry optimization of the crystal unit cell. Band structure has been calculated within density functional theory with the use of PBE exchange-correlation functional. Histograms of metal-oxygen distances for equilibrium geometry have been constructed. Comparison of the used methods has been carried out and recommendation about their applicability for such problems was given. The single-particle wave functions and energies have been calculated. The bandgap was estimated. The band structure was plotted. It was shown that the method gives reliable results for spatial and band structure of Y3Al5O12 scintillation crystal. The results of this work can be used for improvement of characteristics of garnet scintillation crystals.

Electronic structure of Ag8GeS6

Directory of Open Access Journals (Sweden)

D.I. Bletskan

2017-04-01

Full Text Available For the first time, the energy band structure, total and partial densities of states of Ag8GeS6 crystal were calculated using the ab initio density functional method in LDA and LDA+U approximations. Argyrodite is direct-gap semiconductor with the calculated band gap width Egd = 1.46 eV in the LDA+U approximation. The valence band of argyrodite contains four energy separated groups of occupied subzones. The unique feature of electron-energy structure of Ag8GeS6 crystal is the energy overlapping between the occupied d-states of Ag atoms and the delocalized valence p-states of S atoms in relatively close proximity to the valence band top.

Engineered band structure for an enhanced performance on quantum dot-sensitized solar cells

Energy Technology Data Exchange (ETDEWEB)

Jin, Bin Bin [Key Laboratory of Macromolecular Science of Shaanxi Province and School of Materials Science and Engineering, Shaanxi Normal University, Xi' an 710062 (China); Department of Chemical Engineering, Institute of Chemical Industry, Shaanxi Institute of Technology, Xi' an 710300 (China); Wang, Ye Feng [School of Chemistry and Chemical Engineering, Shaanxi Normal University, Xi' an 710062 (China); Wei, Dong; Chen, Yu; Zeng, Jing Hui, E-mail: jhzeng@ustc.edu [Key Laboratory of Macromolecular Science of Shaanxi Province and School of Materials Science and Engineering, Shaanxi Normal University, Xi' an 710062 (China); Cui, Bin [School of Chemistry and Materials Science, Northwestern University, Xi' an 710620 (China)

2016-06-20

A photon-to-current efficiency of 2.93% is received for the Mn-doped CdS (MCdS)-quantum dot sensitized solar cells (QDSSCs) using Mn:ZnO (MZnO) nanowire as photoanode. Hydrothermal synthesized MZnO are spin-coated on fluorine doped tin oxide (FTO) glass with P25 paste to serve as photoanode after calcinations. MCdS was deposited on the MZnO film by the successive ionic layer adsorption and reaction method. The long lived excitation energy state of Mn{sup 2+} is located inside the conduction band in the wide bandgap ZnO and under the conduction band of CdS, which increases the energetic overlap of donor and acceptor states, reducing the “loss-in-potential,” inhibiting charge recombination, and accelerating electron injection. The engineered band structure is well reflected by the electrochemical band detected using cyclic voltammetry. Cell performances are evidenced by current density-voltage (J-V) traces, diffuse reflectance spectra, transient PL spectroscopy, and incident photon to current conversion efficiency characterizations. Further coating of CdSe on MZnO/MCdS electrode expands the light absorption band of the sensitizer, an efficiency of 4.94% is received for QDSSCs.

First-principles study on band structures and electrical transports of doped-SnTe

Directory of Open Access Journals (Sweden)

Xiao Dong

2016-06-01

Full Text Available Tin telluride is a thermoelectric material that enables the conversion of thermal energy to electricity. SnTe demonstrates a great potential for large-scale applications due to its lead-free nature and the similar crystal structure to PbTe. In this paper, the effect of dopants (i.e., Mg, Ca, Sr, Ba, Eu, Yb, Zn, Cd, Hg, and In on the band structures and electrical transport properties of SnTe was investigated based on the first-principles density functional theory including spin–orbit coupling. The results show that Zn and Cd have a dominant effect of band convergence, leading to power factor enhancement. Indium induces obvious resonant states, while Hg-doped SnTe exhibits a different behavior with defect states locating slightly above the Fermi level.

SLAC High Gradient Testing of a KEK X-Band Accelerator Structure

International Nuclear Information System (INIS)

Loewen, Rod

2000-01-01

The high accelerating gradients required for future linear colliders demands a better study of field emission and RF breakdown in accelerator structures. Changes in structure geometry, vacuum pumping, fabrication methods, and surface finish can all potentially impact the conditioning process, dark current emission, and peak RF power handling capability. Recent tests at SLAC of KEK's ''M2'' travelling wave x-band accelerator section provides an opportunity to investigate some of these effects by comparing its performance to previously high power tested structures at SLAC. In addition to studying ultimate power limitations, this test also demonstrates the use of computer automated conditioning to reach practical, achievable gradients

STATUS OF X-BAND STANDING WAVE STRUCTURE STUDIES AT SLAC

International Nuclear Information System (INIS)

Dolgashev, Valery A.

2003-01-01

The linacs proposed for the Next Linear Collider (NLC) and Japanese Linear Collider (JLC) would contain several thousand X-Band accelerator structures that would operate at a loaded gradient of 50 MV/m. An extensive experimental and theoretical program is underway at SLAC, FNAL and KEK to develop structures that reliably operate at this gradient. The development of standing wave structures is a part of this program. The properties of standing wave structures allow them to operate at the loaded gradient in contrast to traveling wave structures that need conditioning to the unloaded gradient (65 MV/m for NLC/JLC). The gradients in the standing structures tested thus far have been limited by input coupler breakdowns. The behavior of these breakdowns is consistent with a model of pulsed heating due to high magnetic fields. New input couplers have been designed to reduce maximum magnetic fields. This paper discusses design considerations related to high power performance, wakefield suppression and results of high power tests of prototype standing wave structures

Breakdown Characteristics Study on an 18 Cell X-band Structure

International Nuclear Information System (INIS)

Wang, F

2008-01-01

A CLIC designed 18 cells, low group velocity (2.4% to 1.0% c), X-band (11.4 GHz) accelerator structure (denoted T18) was designed at CERN, its cells were built at KEK, and it was assembled and tested at SLAC. An interesting feature of this structure is that the gradient in the last cell is about 50% higher than that in the first cell. This structure has been RF conditioned at SLAC NLCTA for about 1400 hours where it incurred about 2200 breakdowns. This paper presents the characteristics of these breakdowns, including (1) the breakdown rate dependence on gradient, pulse width and conditioning time, (2) the breakdown distribution along the structure, (3) relation between breakdown and pulsed heating dependence study and (4) electric field decay time for breakdown changing over the whole conditioning time. Overall, this structure performed very well, having a final breakdown rate of less than 1e-6/pulse/m at 106 MV/m with 230 ns pulse width

Breakdown Characteristics Study on an 18 Cell X-band Structure

International Nuclear Information System (INIS)

Wang Faya

2009-01-01

A CLIC designed 18 cells, low group velocity (2.4% to 1.0% c), X-band (11.4 GHz) accelerator structure (denoted T18) was designed at CERN, its cells were built at KEK, and it was assembled and tested at SLAC. An interesting feature of this structure is that the gradient in the last cell is about 50% higher than that in the first cell. This structure has been RF conditioned at SLAC NLCTA for about 1400 hours where it incurred about 2200 breakdowns. This paper presents the characteristics of these breakdowns, including 1) the breakdown rate dependence on gradient, pulse width and conditioning time, 2) the breakdown distribution along the structure, 3) relation between breakdown and pulsed heating dependence study and 4) electric field decay time for breakdown changing over the whole conditioning time. Overall, this structure performed very well, having a final breakdown rate of less than 1e-6/pulse/m at 106 MV/m with 230 ns pulse width.

Modelling band-to-band tunneling current in InP-based heterostructure photonic devices

NARCIS (Netherlands)

van Engelen, J.P.; Shen, L.; van der Tol, J.J.G.M.; Smit, M.K.; Kockaert, P.; Emplit, P.; Gorza, S.-P.; Massar, S.

2015-01-01

Some semiconductor photonic devices show large discontinuities in the band structure. Short tunnel paths caused by this band structure may lead to an excessive tunneling current, especially in highly doped layers. Modelling of this tunnelling current is therefore important when designing photonic

High-gradient experiment on X-band disk-loaded structures

International Nuclear Information System (INIS)

Higo, T.; Taniuchi, T.; Yamamoto, M.; Odagiri, J.; Tokumoto, S.; Mizuno, H.; Takata, K.; Wilson, I.; Wuensch, W.

1993-09-01

The high-gradient performance of two travelling-wave X-band accelerating structures 20 cm long has been studied. One of the structures, KEK, was conditioned up to an average accelerating gradient (Eav) of 68 MV/m in 600 hours, while the other, CERN, reached 85 MV/m in 50 hours. In the latter case the maximum output power was fed from the SLED system and the maximum field inside the structure was 138 MV/m. This maximum level was limited by the available power from the klystron. Operation at the Eav=50 MV/m level was found to be stable for both structures. The associated dark current at this level was less than a few μA for CERN but 20 to 30 μA for KEK. Since the two electrical designs are almost the same the difference in dark current must be attributed to the difference in the two fabrication techniques. Modified Fowler-Northeim plots of downstream dark current showed a change of slope, a kink, around 50 to 60 MV/m above which the field enhancement factor was substantially increased. (author)

Band structure of comb-like photonic crystals containing meta-materials

Science.gov (United States)

Weng, Yi; Wang, Zhi-Guo; Chen, Hong

2007-09-01

We study the transmission properties and band structure of comb-like photonic crystals (PC) with backbones constructed of meta-materials (negative-index materials) within the frame of the interface response theory. The result shows the existence of a special band gap at low frequency. This gap differs from the Bragg gaps in that it is insensitive to the geometrical scaling and disorder. In comparison with the zero-average-index gap in one-dimensional PC made of alternating positive- and negative-index materials, the gap is obviously deeper and broader, given the same system parameters. In addition, the behavior of its gap-edges is also different. One gap-edge is decided by the average permittivity whereas the other is only subject to the changing of the permeability of the backbone. Due to this asymmetry of the two gap-edges, the broadening of the gap could be realized with much freedom and facility.

Band-structure-based collisional model for electronic excitations in ion-surface collisions

International Nuclear Information System (INIS)

Faraggi, M.N.; Gravielle, M.S.; Alducin, M.; Silkin, V.M.; Juaristi, J.I.

2005-01-01

Energy loss per unit path in grazing collisions with metal surfaces is studied by using the collisional and dielectric formalisms. Within both theories we make use of the band-structure-based (BSB) model to represent the surface interaction. The BSB approach is based on a model potential and provides a precise description of the one-electron states and the surface-induced potential. The method is applied to evaluate the energy lost by 100 keV protons impinging on aluminum surfaces at glancing angles. We found that when the realistic BSB description of the surface is used, the energy loss obtained from the collisional formalism agrees with the dielectric one, which includes not only binary but also plasmon excitations. The distance-dependent stopping power derived from the BSB model is in good agreement with available experimental data. We have also investigated the influence of the surface band structure in collisions with the Al(100) surface. Surface-state contributions to the energy loss and electron emission probability are analyzed

Tuning the band structure of graphene nanoribbons through defect-interaction-driven edge patterning

Science.gov (United States)

Du, Lin; Nguyen, Tam N.; Gilman, Ari; Muniz, André R.; Maroudas, Dimitrios

2017-12-01

We report a systematic analysis of pore-edge interactions in graphene nanoribbons (GNRs) and their outcomes based on first-principles calculations and classical molecular-dynamics simulations. We find a strong attractive interaction between nanopores and GNR edges that drives the pores to migrate toward and coalesce with the GNR edges, which can be exploited to form GNR edge patterns that impact the GNR electronic band structure and tune the GNR band gap. Our analysis introduces a viable physical processing strategy for modifying GNR properties by combining defect engineering and thermal annealing.

Efficient evaluation of epitaxial MoS2 on sapphire by direct band structure imaging

Science.gov (United States)

Kim, Hokwon; Dumcenco, Dumitru; Fregnaux, Mathieu; Benayad, Anass; Kung, Yen-Cheng; Kis, Andras; Renault, Olivier; Lanes Group, Epfl Team; Leti, Cea Team

The electronic band structure evaluation of two-dimensional metal dichalcogenides is critical as the band structure can be greatly influenced by the film thickness, strain, and substrate. Here, we performed a direct measurement of the band structure of as-grown monolayer MoS2 on single crystalline sapphire by reciprocal-space photoelectron emission microscopy with a conventional laboratory ultra-violet He I light source. Arrays of gold electrodes were deposited onto the sample in order to avoid charging effects due to the insulating substrate. This allowed the high resolution mapping (ΔE = 0.2 eV Δk = 0.05 Å-1) of the valence states in momentum space down to 7 eV below the Fermi level. The high degree of the epitaxial alignment of the single crystalline MoS2 nuclei was verified by the direct momentum space imaging over a large area containing multiple nuclei. The derived values of the hole effective mass were 2.41 +/-0.05 m0 and 0.81 +/-0.05 m0, respectively at Γ and K points, consistent with the theoretical values of the freestanding monolayer MoS2 reported in the literature. HK acknowledges the french CEA Basic Technological Research program (RTB) for funding.

Sensitive criterion for chirality; Chiral doublet bands in 104Rh59

International Nuclear Information System (INIS)

Koike, T.; Starosta, K.; Vaman, C.; Ahn, T.; Fossan, D.B.; Clark, R.M.; Cromaz, M.; Lee, I.Y.; Macchiavelli, A.O.

2003-01-01

A particle plus triaxial rotor model was applied to odd-odd nuclei in the A ∼ 130 region in order to study the unique parity πh11/2xνh11/2 rotational bands. With maximum triaxiality assumed and the intermediate axis chosen as the quantization axis for the model calculations, the two lowest energy eigenstates of a given spin have chiral properties. The independence of the quantity S(I) on spin can be used as a new criterion for chirality. In addition, a diminishing staggering amplitude of S(I) with increasing spin implies triaxiality in neighboring odd-A nuclei. Chiral quartet bases were constructed specifically to examine electromagnetic properties for chiral structures. A set of selection rules unique to chirality was derived. Doublet bands built on the πg9/2xνh11/2 configuration have been discovered in odd-odd 104Rh using the 96Zr(11B, 3n) reaction. Based on the discussed criteria for chirality, it is concluded that the doublet bands observed in 104Rh exhibit characteristic chiral properties suggesting a new region of chirality around A ∼110. In addition, magnetic moment measurements have been performed to test the πh11/2xνh11/2 configuration in 128Cs and the πg9/2xνh11/2 configuration in 104Rh

Effect of initial structure on strengthening and properties of the 35NKhTYu alloy bands

International Nuclear Information System (INIS)

Vorontsov, N.M.; Shugaenko, V.K.; Drapiko, P.E.; Chernyakova, L.E.; Patseka, R.F.

1978-01-01

Variation in the structure, mechanical strength, plasticity, and elasticity of thin (about 0.15 mm thick) bands of 36NKhTYu alloy after their cold rolling to the reduction degree up to 70% was examined. The influence of the cold plastic deformation on the dislocation structure of the alloy has been determined. By resorting to the method of transmission electron microscopy, the distribution of dislocations depending on the reduction degree has been shown. The character of the influence of the initial structure of bands after their plastic deformation on the process of decomposition of the solid solution and the formation of γ 1 -phase in tempering and a variation in the mechanical properties of 36NKhTYu alloy have been established

Band structure of one-dimensional doped photonic crystal with three level atoms using the Fresnel coefficients method

Science.gov (United States)

Jafari, A.; Rahmat, A.; Bakkeshizadeh, S.

2018-01-01

We consider a one-dimensional photonic crystal (1DPC) composed of double-layered dielectrics. Electric permittivity and magnetic permeability of this crystal depends on the incident electromagnetic wave frequency. We suppose that three level atoms have been added to the second layer of each dielectric and this photonic crystal (PC) has been doped. These atoms can be added to the layer with different rates. In this paper, we have calculated and compared the band structure of the mentioned PC considering the effect of added atoms to the second layer with different rates through the Fresnel coefficients method. We find out that according to the effective medium theory, the electric permittivity of the second layer changes. Also the band structure of PC for both TE and TM polarizations changes, too. The width of bandgaps related to “zero averaged refractive index” and “Bragg” increases. Moreover, new gap branches appear in new frequencies at both TE and TM polarizations. In specific state, two branches of “zero permittivity” gap appear in the PC band structure related to TM polarization. With increasing the amount of the filling rate of total volume with three level atoms, we observe a lot of changes in the PC band structure.

Effect of species structure and dielectric constant on C-band forest backscatter

Science.gov (United States)

Lang, R. H.; Landry, R.; Kilic, O.; Chauhan, N.; Khadr, N.; Leckie, D.

1993-01-01

A joint experiment between Canadian and USA research teams was conducted early in Oct. 1992 to determine the effect of species structure and dielectric variations on forest backscatter. Two stands, one red pine and one jack pine, in the Petawawa National Forestry Institute (PNFI) were utilized for the experiment. Extensive tree architecture measurements had been taken by the Canada Centre for Remote Sensing (CCRS) several months earlier by employing a Total Station surveying instrument which provides detailed information on branch structure. A second part of the experiment consisted of cutting down several trees and using dielectric probes to measure branch and needle permittivity values at both sites. The dielectric and the tree geometry data were used in the George Washington University (GWU) Vegetation Model to determine the C band backscattering coefficients of the individual stands for VV polarization. The model results show that backscatter at C band comes mainly from the needles and small branches and the upper portion of the trunks acts only as an attenuator. A discussion of variation of backscatter with specie structure and how dielectric variations in needles for both species may affect the total backscatter returns is provided.

Analysis of photonic band-gap structures in stratified medium

DEFF Research Database (Denmark)

Tong, Ming-Sze; Yinchao, Chen; Lu, Yilong

2005-01-01

in electromagnetic and microwave applications once the Maxwell's equations are appropriately modeled. Originality/value - The method validates its values and properties through extensive studies on regular and defective 1D PBG structures in stratified medium, and it can be further extended to solving more......Purpose - To demonstrate the flexibility and advantages of a non-uniform pseudo-spectral time domain (nu-PSTD) method through studies of the wave propagation characteristics on photonic band-gap (PBG) structures in stratified medium Design/methodology/approach - A nu-PSTD method is proposed...... in solving the Maxwell's equations numerically. It expands the temporal derivatives using the finite differences, while it adopts the Fourier transform (FT) properties to expand the spatial derivatives in Maxwell's equations. In addition, the method makes use of the chain-rule property in calculus together...

Crystal structure and energy band and optical properties of phosphate Sr3P4O13

International Nuclear Information System (INIS)

Zhang, Y.-C.; Cheng, W.-D.; Wu, D.-S.; Zhang, H.; Chen, D.-G.; Gong, Y.-J.; Kan, Z.-G.

2004-01-01

A single crystal of the compound Sr 3 P 4 O 13 has been found and the crystal structure has been characterized by means of single crystal X-ray diffraction analysis. The compound crystallizes in triclinic system and belongs to space group P1-bar. It builds up from SrO 7 polyhedra and P 4 O 13 -6 anions and has a layered structure, and the Sr atoms are located in the interlayer space. The absorption and luminescence spectrum of Sr 3 P 4 O 13 microcrystals have been measured. The calculated results of crystal energy band structure by the DFT show that the solid state of Sr 3 P 4 O 13 is an isolator with direct band gap. The calculated total and partial density of states indicate that the top valence bands are contributions from P 3p and O 2p states and low conduction bands mostly originate from Sr atomic states. The calculated optical response functions expect that the Sr 3 P 4 O 13 is a low refractive index, and it is possible that the Sr 3 P 4 O 13 is used to make transparent material between the UV and FR light zone

Unique Reversible Crystal-to-Crystal Phase Transition – Structural and Functional Properties of Fused Ladder Thienoarenes

KAUST Repository

Abe, Yuichiro

2017-08-15

Donor-acceptor type molecules based on fused ladder thienoarenes, indacenodithiophene (IDT) and dithienocyclopenta-thienothiophene (DTCTT), coupled with benzothiadiazole, are prepared and their solid-state structures are investigated. They display a rich variety of solid phases ranging from amorphous glass states to crystalline states, upon changes in the central aromatic core and side group structures. Most notably, the DTCTT-based derivatives showed reversible crystal-to-crystal phase transitions in heating and cooling cycles. Unlike what has been seen in π−conjugated molecules variable temperature XRD revealed that structural change occurs continuously during the transition. A columnar self-assembled structure with slip-stacked π−π interaction is proposed to be involved in the solid-state. This research provides the evidence of unique structural behavior of the DTCTT-based molecules through the detailed structural analysis. This unique structural transition paves the way for these materials to have self-healing of crystal defects, leading to improved optoelectronic properties.

Unique Reversible Crystal-to-Crystal Phase Transition – Structural and Functional Properties of Fused Ladder Thienoarenes

KAUST Repository

Abe, Yuichiro; Savikhin, Victoria; Yin, Jun; Grimsdale, Andrew C.; Soci, Cesare; Toney, Michael F.; Lam, Yeng Ming

2017-01-01

Donor-acceptor type molecules based on fused ladder thienoarenes, indacenodithiophene (IDT) and dithienocyclopenta-thienothiophene (DTCTT), coupled with benzothiadiazole, are prepared and their solid-state structures are investigated. They display a rich variety of solid phases ranging from amorphous glass states to crystalline states, upon changes in the central aromatic core and side group structures. Most notably, the DTCTT-based derivatives showed reversible crystal-to-crystal phase transitions in heating and cooling cycles. Unlike what has been seen in π−conjugated molecules variable temperature XRD revealed that structural change occurs continuously during the transition. A columnar self-assembled structure with slip-stacked π−π interaction is proposed to be involved in the solid-state. This research provides the evidence of unique structural behavior of the DTCTT-based molecules through the detailed structural analysis. This unique structural transition paves the way for these materials to have self-healing of crystal defects, leading to improved optoelectronic properties.

Reply to ``Comment on `Band structure engineering of graphene by strain: First-principles calculations' ''

Science.gov (United States)

Gui, Gui; Li, Jin; Zhong, Jianxin

2009-10-01

We reply to the Comment by Farjam and Rafii-Tabar [Phys. Rev. B 80, 167401 (2009)] on our paper [Phys. Rev. B 78, 075435 (2008)]. We show that the gap opening found in our paper is due to the use of a small number of k points in the calculation which prevents revealing the sharp contact of the two bands near K or R . Once a large number of k points is used, the density-functional theory (DFT) VASP codes give the same conclusion as obtained by Farjam and Rafii-Tabar by using the QUANTUM-ESPRESSO codes, namely, there is no gap opening in the band structure of graphene under small planar strain. We also point out that all other results in our paper remain correct, except for the conclusion of the gap opening. The results demonstrate the importance of using a large number of k points for determining the gap width of the band structure of graphene under strain as well as the validity of the DFT VASP codes for the system.

Calculated high-pressure structural properties, lattice dynamics and quasi particle band structures of perovskite fluorides KZnF3, CsCaF3 and BaLiF3.

Science.gov (United States)

Vaitheeswaran, G; Kanchana, V; Zhang, Xinxin; Ma, Yanming; Svane, A; Christensen, N E

2016-08-10

A detailed study of the high-pressure structural properties, lattice dynamics and band structures of perovskite structured fluorides KZnF3, CsCaF3 and BaLiF3 has been carried out by means of density functional theory. The calculated structural properties including elastic constants and equation of state agree well with available experimental information. The phonon dispersion curves are in good agreement with available experimental inelastic neutron scattering data. The electronic structures of these fluorides have been calculated using the quasi particle self-consistent [Formula: see text] approximation. The [Formula: see text] calculations reveal that all the fluorides studied are wide band gap insulators, and the band gaps are significantly larger than those obtained by the standard local density approximation, thus emphasizing the importance of quasi particle corrections in perovskite fluorides.

Observation of states beyond band termination in 156,157,158Er and strongly deformed structures in 173,174,175Hf

International Nuclear Information System (INIS)

Riley, M A; Djongolov, M K; Evans, A O

2006-01-01

High-spin terminating bands in heavy nuclei were first identified in nuclei around 158 Er 90 . While examples of terminating states have been identified in a number of erbium isotopes, almost nothing is known about the states lying beyond band termination. In the present work, the high-spin structure of 156,157,158 Er has been studied using the Gammasphere spectrometer. The subject of triaxial superdeformation and 'wobbling' modes in Lu nuclei has rightly attracted a great deal of attention. Very recently four strongly or superdeformed (SD) sequences have been observed in 174 Hf, and cranking calculations using the Ultimate Cranker code predict that such structures may have significant triaxial deformation. We have performed two experiments in an attempt to verify the possible triaxial nature of these bands. A lifetime measurement was performed to confirm the large (and similar) deformation of the bands. In addition, a high-statistics, thin-target experiment took place to search for linking transitions between the SD bands, possible wobbling modes, and new SD band structures

Band structure of cavity-type hypersonic phononic crystals fabricated by femtosecond laser-induced two-photon polymerization

Energy Technology Data Exchange (ETDEWEB)

Rakhymzhanov, A. M.; Utegulov, Z. N., E-mail: zhutegulov@nu.edu.kz, E-mail: fytas@mpip-mainz.mpg.de [Department of Physics, School of Science and Technology, Nazarbayev University, Astana 010000 (Kazakhstan); Optics Laboratory, National Laboratory Astana, Nazarbayev University, Astana 10000 (Kazakhstan); Gueddida, A. [Institut d' Electronique, Microélectronique et Nanotechnologie, 59650 Villeneuve d' Ascq (France); LPMR, Département de Physique, Faculté des Sciences, Université Mohamed I, 60000 Oujda (Morocco); Alonso-Redondo, E. [Max Planck Institute of Polymer Research, Ackermannweg 10, 55128 Mainz (Germany); Perevoznik, D.; Kurselis, K. [Laser Zentrum Hannover e.V., 30419 Hannover (Germany); Chichkov, B. N. [Laser Zentrum Hannover e.V., 30419 Hannover (Germany); Institute of Laser and Information Technologies RAS, Moscow, 142092 Troitsk (Russian Federation); El Boudouti, E. H. [LPMR, Département de Physique, Faculté des Sciences, Université Mohamed I, 60000 Oujda (Morocco); Djafari-Rouhani, B. [Institut d' Electronique, Microélectronique et Nanotechnologie, 59650 Villeneuve d' Ascq (France); Fytas, G., E-mail: zhutegulov@nu.edu.kz, E-mail: fytas@mpip-mainz.mpg.de [Max Planck Institute of Polymer Research, Ackermannweg 10, 55128 Mainz (Germany); Department of Materials Science, University of Crete and FORTH, 71110 Heraklion (Greece)

2016-05-16

The phononic band diagram of a periodic square structure fabricated by femtosecond laser pulse-induced two photon polymerization is recorded by Brillouin light scattering (BLS) at hypersonic (GHz) frequencies and computed by finite element method. The theoretical calculations along the two main symmetry directions quantitatively capture the band diagrams of the air- and liquid-filled structure and moreover represent the BLS intensities. The theory helps identify the observed modes, reveals the origin of the observed bandgaps at the Brillouin zone boundaries, and unravels direction dependent effective medium behavior.

Energy band structure and electrical properties of Ga-oxide/GaN interface formed by remote oxygen plasma

Science.gov (United States)

Yamamoto, Taishi; Taoka, Noriyuki; Ohta, Akio; Truyen, Nguyen Xuan; Yamada, Hisashi; Takahashi, Tokio; Ikeda, Mitsuhisa; Makihara, Katsunori; Nakatsuka, Osamu; Shimizu, Mitsuaki; Miyazaki, Seiichi

2018-06-01

The energy band structure of a Ga-oxide/GaN structure formed by remote oxygen plasma exposure and the electrical interface properties of the GaN metal–oxide–semiconductor (MOS) capacitors with the SiO2/Ga-oxide/GaN structures with postdeposition annealing (PDA) at various temperatures have been investigated. Reflection high-energy electron diffraction and X-ray photoelectron spectroscopy clarified that the formed Ga-oxide layer is neither a single nor polycrystalline phase with high crystallinity. We found that the energy band offsets at the conduction band minimum and at the valence band maximum between the Ga-oxide layer and the GaN surface were 0.4 and 1.2 ± 0.2 eV, respectively. Furthermore, capacitance–voltage (C–V) characteristics revealed that the interface trap density (D it) is lower than the evaluation limit of Terman method without depending on the PDA temperatures, and that the SiO2/Ga-oxide stack can work as a protection layer to maintain the low D it, avoiding the significant decomposition of GaN at the high PDA temperature of 800 °C.

Band alignment studies of Al2O3/CuGaO2 and ZnO/CuGaO2 hetero-structures grown by pulsed laser deposition

International Nuclear Information System (INIS)

Ajimsha, R.S.; Das, Amit K.; Joshi, M.P.; Kukreja, L.M.

2014-01-01

Highlights: • Band offset studies at the interface of Al 2 O 3 /CuGaO 2 and ZnO/CuGaO 2 hetero-structures were performed using X-ray photoelectron spectroscopy. • Valance band offsets (VBO) of these hetero-structures were obtained from respective XPS peak positions and VB spectra using Kraut's equation. • Al 2 O 3 /CuGaO 2 interface exhibited a type I band alignment with valance band offset (VBO) of 4.05 eV whereas type II band alignment was observed in ZnO/CuGaO 2 hetero-structure with a VBO of 2.32 eV. • Schematic band alignment diagram for the interface of these hetero-structures has been constructed. • Band offset and alignment studies of these heterojunctions are important for gaining insight to the design of various optoelectronic devices based on such hetero-structures. - Abstract: We have studied the band offset and alignment of pulsed laser deposited Al 2 O 3 /CuGaO 2 and ZnO/CuGaO 2 hetero-structures using photoelectron spectroscopy. Al 2 O 3 /CuGaO 2 interface exhibited a type I band alignment with valance band offset (VBO) of 4.05 eV whereas type II band alignment was observed in ZnO/CuGaO 2 hetero-structure with a VBO of 2.32 eV. Schematic band alignment diagram for the interface of these hetero-structures has been constructed. Band offset and alignment studies of these heterojunctions are important for gaining insight to the design of various optoelectronic devices based on such hetero-structures

Large-area 2D periodic crystalline silicon nanodome arrays on nanoimprinted glass exhibiting photonic band structure effects

International Nuclear Information System (INIS)

Becker, C; Lockau, D; Sontheimer, T; Rech, B; Schubert-Bischoff, P; Rudigier-Voigt, E; Bockmeyer, M; Schmidt, F

2012-01-01

Two-dimensional silicon nanodome arrays are prepared on large areas up to 50 cm 2 exhibiting photonic band structure effects in the near-infrared and visible wavelength region by downscaling a recently developed fabrication method based on nanoimprint-patterned glass, high-rate electron-beam evaporation of silicon, self-organized solid phase crystallization and wet-chemical etching. The silicon nanodomes, arranged in square lattice geometry with 300 nm lattice constant, are optically characterized by angular resolved reflection measurements, allowing the partial determination of the photonic band structure. This experimentally determined band structure agrees well with the outcome of three-dimensional optical finite-element simulations. A 16% photonic bandgap is predicted for an optimized geometry of the silicon nanodome arrays. By variation of the duration of the selective etching step, the geometry as well as the optical properties of the periodic silicon nanodome arrays can be controlled systematically. (paper)

Dual-band frequency selective surface with large band separation and stable performance

Science.gov (United States)

Zhou, Hang; Qu, Shao-Bo; Peng, Wei-Dong; Lin, Bao-Qin; Wang, Jia-Fu; Ma, Hua; Zhang, Jie-Qiu; Bai, Peng; Wang, Xu-Hua; Xu, Zhuo

2012-05-01

A new technique of designing a dual-band frequency selective surface with large band separation is presented. This technique is based on a delicately designed topology of L- and Ku-band microwave filters. The two band-pass responses are generated by a capacitively-loaded square-loop frequency selective surface and an aperture-coupled frequency selective surface, respectively. A Faraday cage is located between the two frequency selective surface structures to eliminate undesired couplings. Based on this technique, a dual-band frequency selective surface with large band separation is designed, which possesses large band separation, high selectivity, and stable performance under various incident angles and different polarizations.

Band structure of ABC-trilayer graphene superlattice

International Nuclear Information System (INIS)

Uddin, Salah; Chan, K. S.

2014-01-01

We investigate the effect of one-dimensional periodic potentials on the low energy band structure of ABC trilayer graphene first by assuming that all the three layers have the same potential. Extra Dirac points having the same electron hole crossing energy as that of the original Dirac point are generated by superlattice potentials with equal well and barrier widths. When the potential height is increased, the numbers of extra Dirac points are increased. The dispersions around the Dirac points are not isotropic. It is noted that the dispersion along the k y direction for k x  = 0 oscillates between a non-linear dispersion and a linear dispersion when the potential height is increased. When the well and barrier widths are not identical, the symmetry of the conduction and valence bands is broken. The extra Dirac points are shifted either upward or downward depending on the barrier and well widths from the zero energy, while the position of the central Dirac point oscillates with the superlattice potential height. By considering different potentials for different layers, extra Dirac points are generated not from the original Dirac points but from the valleys formed in the energy spectrum. Two extra Dirac points appear from each pair of touched valleys, so four Dirac points appeared in the spectrum at particular barrier height. By increasing the barrier height of superlattice potential two Dirac points merge into the original Dirac point. This emerging and merging of extra Dirac points is different from the equal potential case

Quasiparticle excitations in valence-fluctuation materials: effects of band structure and crystal fields

International Nuclear Information System (INIS)

Brandow, B.H.

1985-01-01

Evidence is now quite strong that the elementary hybridization model is the correct way to understand the lattice-coherent Fermi liquid regime at very low temperatures. Many-body theory leads to significant renormalizations of the input parameters, and many of the band-theoretic channels for hybridization are suppressed by the combined effects of Hund's-rule coupling, crystal-field splitting, and the f-f Coulomb repulsion U. Some exploratory calculations based on this picture are described, and some inferences are drawn about the band structures of several heavy-fermion materials. These inferences can and should be tested by suitably modified band-theoretic calculations. We find evidence for a significant Baber-scattering contribution in the very-low-temperature resistivity. A new mechanism is proposed for crossover from the coherent Fermi-liquid regime to the incoherent dense-Kondo regime. 28 refs

Specific features of band structure and optical anisotropy of Cu{sub 2}CdGeSe{sub 4} quaternary compounds

Energy Technology Data Exchange (ETDEWEB)

Brik, M.G., E-mail: brik@fi.tartu.ee [College of Mathematics and Physics, Chongqing University of Posts and Telecommunications, Chongqing 400065 (China); Institute of Physics, University of Tartu, Riia 142, Tartu 51014 (Estonia); Institute of Physics, Jan Dlugosz University, Armii Krajowej 13/15, PL-42200 Czestochowa (Poland); Parasyuk, O.V. [Department of Chemistry, Eastern European National University, Voli 13, Lutsk 43025 (Ukraine); Myronchuk, G.L. [Department of Physics, Eastern European National University, Voli 13, Lutsk 43025 (Ukraine); Kityk, I.V. [Institute of Materials Science and Engineering, Technical University of Czestochowa, Al. Armii Krajowej 19, 42-200 Czestochowa (Poland)

2014-09-15

Complex theoretical and experimental studies of the band structure and optical functions of a new Cu{sub 2}CdGeSe{sub 4} quaternary crystal are reported. The benchmark band structure calculations were performed using the first-principles methods. As a result, the structural, electronic, optical and elastic properties of Cu{sub 2}CdGeSe{sub 4} were calculated in the general gradient approximation (GGA) and local density approximation (LDA). The calculated dielectric function and optical absorption spectra exhibit some anisotropic behavior. Detailed analysis of the band energy dispersion and effective space charge density helped in establishing the origin of the band structure anisotropy. All calculated properties are compared with the experimental data. An additional comparison with a similar crystal of Cu{sub 2}CdGeSe{sub 4} allowed to reveal the role played by the anions (S or Se) in formation of the optical properties of these two materials. - Highlights: • The structural, electronic, optical properties of Cu{sub 2}CdGeSe{sub 4} were calculated. • Pressure effects on these properties were modeled. • Comparison with a similar compound of Cu{sub 2}CdGeS{sub 4} was performed.

Investigation of band structure of {sup 103,105}Rh using microscopic computational technique

Energy Technology Data Exchange (ETDEWEB)

Kumar, Amit, E-mail: akbcw2@gmail.com [Research Scholar, Department of Physics and Electronics, University of Jammu, Jammu-180006 (India); Singh, Suram, E-mail: suramsingh@gmail.com [Assistant Professor, Department of Physics Govt. Degree College, Kathua-184142 (India); Bharti, Arun, E-mail: arunbharti-2003@yahoo.co.in [Professor, Department of Physics and Electronics, University of Jammu, Jammu-180006 (India)

2015-08-28

The high-spin structure in {sup 61}Cu nucleus is studied in terms of effective two body interaction. In order to take into account the deformed BCS basis, the basis states are expanded in terms of the core eigenfunctions. Yrast band with some other bands havew been obtained and back-bending in moment of inertia has also been calculated and compared with the available experimental data for {sup 61}Cu nucleus. On comparing the available experimental as well as other theoretical data, it is found that the treatment with PSM provides a satisfactory explanation of the available data.

Measurements of higher order modes in a 30 cm long X-band structure

International Nuclear Information System (INIS)

Xiao, L.; Liang, Y.; Tong, D.; Zhang, H.

2001-01-01

The use of a cage of metallic wires as a bead is proposed to measure the higher order modes (HOMs) in an X-band accelerating structure. These long thin wires can isolate the longitudinal electric field component from other field components and produce sufficient frequency shift in bead-pull measurements. In the setup described in this paper, the bead is made by sputtering silver film onto a thin nylon line through a specially designed fixture. The cage has a size of approximately 0.5 mm in diameter, 2 mm in length and more than six metallic wires of less than 0.1 mm in width. The fabrication and calibration of the cage are described. The longitudinal electric fields of the lowest passband dipole mode TM 110 in a 30 cm long X-band structure are measured by bead-pull measurements. Results are compared with the calculated ones obtained from URMELT-code

Adsorbate-induced modification of electronic band structure of epitaxial Bi(111) films

Energy Technology Data Exchange (ETDEWEB)

Matetskiy, A.V., E-mail: mateckij@iacp.dvo.ru [Institute of Automation and Control Processes FEB RAS, 5 Radio Street, 690041 Vladivostok (Russian Federation); Bondarenko, L.V.; Tupchaya, A.Y.; Gruznev, D.V. [Institute of Automation and Control Processes FEB RAS, 5 Radio Street, 690041 Vladivostok (Russian Federation); Eremeev, S.V. [Institute of Strength Physics and Materials Science, 634021 Tomsk (Russian Federation); Tomsk State University, 634050 Tomsk (Russian Federation); Zotov, A.V. [Institute of Automation and Control Processes FEB RAS, 5 Radio Street, 690041 Vladivostok (Russian Federation); School of Natural Sciences, Far Eastern Federal University, 690950 Vladivostok (Russian Federation); Department of Electronics, Vladivostok State University of Economics and Service, 690600 Vladivostok (Russian Federation); Saranin, A.A. [Institute of Automation and Control Processes FEB RAS, 5 Radio Street, 690041 Vladivostok (Russian Federation); School of Natural Sciences, Far Eastern Federal University, 690950 Vladivostok (Russian Federation)

2017-06-01

Highlights: • Modification of electronic properties of ultrathin Bi films by adsorbates is demonstrated. • Due to electron doping from Cs adatoms, surface-state bands shift to higher binding energies. • As a result, only electron pockets are left in the Fermi map. • Tin acts as an acceptor dopant for Bi, shifting Fermi level upward. • As a result, only hole pockets are left in the Fermi map. - Abstract: Changes of the electronic band structure of Bi(111) films on Si(111) induced by Cs and Sn adsorption have been studied using angle-resolved photoemission spectroscopy and density functional theory calculations. It has been found that small amounts of Cs when it presents at the surface in a form of the adatom gas leads to shifting of the surface and quantum well states to the higher binding energies due to the electron donation from adsorbate to the Bi film. In contrast, adsorbed Sn dissolves into the Bi film bulk upon heating and acts as an acceptor dopant, that results in shifting of the surface and quantum well states upward to the lower binding energies. These results pave the way to manipulate with the Bi thin film electron band structure allowing to achieve a certain type of conductivity (electron or hole) with a single spin channel at the Fermi level making the adsorbate-modified Bi a reliable base for prospective spintronics applications.

Structural Evolution of a Warm Frontal Precipitation Band During GCPEx

Science.gov (United States)

Colle, Brian A.; Naeger, Aaron; Molthan, Andrew; Nesbitt, Stephen

2015-01-01

A warm frontal precipitation band developed over a few hours 50-100 km to the north of a surface warm front. The 3-km WRF was able to realistically simulate band development, although the model is somewhat too weak. Band genesis was associated with weak frontogenesis (deformation) in the presence of weak potential and conditional instability feeding into the band region, while it was closer to moist neutral within the band. As the band matured, frontogenesis increased, while the stability gradually increased in the banding region. Cloud top generating cells were prevalent, but not in WRF (too stable). The band decayed as the stability increased upstream and the frontogenesis (deformation) with the warm front weakened. The WRF may have been too weak and short-lived with the band because too stable and forcing too weak (some micro issues as well).

Enhancement of computer program SPECTRAN to provide optional synthesis of 1/12 octave-band and critical-band spectra from 1/3 octave-band spectra

Energy Technology Data Exchange (ETDEWEB)

Chang, Young-Soo [Argonne National Lab., IL (United States); Liebich, R.E. [Raytheon Environmental Services Company, Cambridge, MA (United States)

1997-07-01

This paper describes greatly enhanced version of the computer program SPECTRAN, which was initially presented in Paper No. 96-RA104.01, at the A&WMA 89th Annual Meeting in June 1996. The program has had three basic upgrades since that time. The first is provision of an option to use either batch-mode input from previously prepared data files or a {open_quotes}user-friendly{close_quotes} interactive input routine. The latter is primarily for first-time users and those having only one, or very few, spectra to process. The second improvement is the synthesis of 1/12 octave-band spectra from 1/3 octave-band spectra, with {open_quotes}tone correction,{close_quotes} in a manner similar to that used in the original version of the program. The third fundamental improvement is addition of a unique new capability to synthesize classic {open_quotes}critical-band{close_quotes} spectra from 1/3 octave-band input spectra. Critical-band spectra are also termed {open_quotes}equivalent-rectangular-bandwidth (ERB){close_quotes} and {open_quotes}equal-contribution-to-speech (ECS){close_quotes} spectra.

Dual-band frequency selective surface with large band separation and stable performance

International Nuclear Information System (INIS)

Zhou Hang; Qu Shao-Bo; Lin Bao-Qin; Wang Jia-Fu; Ma Hua; Zhang Jie-Qiu; Peng Wei-Dong; Bai Peng; Wang Xu-Hua; Xu Zhuo

2012-01-01

A new technique of designing a dual-band frequency selective surface with large band separation is presented. This technique is based on a delicately designed topology of L- and Ku-band microwave filters. The two band-pass responses are generated by a capacitively-loaded square-loop frequency selective surface and an aperture-coupled frequency selective surface, respectively. A Faraday cage is located between the two frequency selective surface structures to eliminate undesired couplings. Based on this technique, a dual-band frequency selective surface with large band separation is designed, which possesses large band separation, high selectivity, and stable performance under various incident angles and different polarizations. (electromagnetism, optics, acoustics, heat transfer, classical mechanics, and fluid dynamics)

Band-notched spiral antenna

Science.gov (United States)

Jeon, Jae; Chang, John

2018-03-13

A band-notched spiral antenna having one or more spiral arms extending from a radially inner end to a radially outer end for transmitting or receiving electromagnetic radiation over a frequency range, and one or more resonance structures positioned adjacent one or more segments of the spiral arm associated with a notch frequency band or bands of the frequency range so as to resonate and suppress the transmission or reception of electromagnetic radiation over said notch frequency band or bands.

Ultra-Thin Multi-Band Polarization-Insensitive Microwave Metamaterial Absorber Based on Multiple-Order Responses Using a Single Resonator Structure

Directory of Open Access Journals (Sweden)

Yong Zhi Cheng

2017-10-01

Full Text Available We design an ultra-thin multi-band polarization-insensitive metamaterial absorber (MMA using a single circular sector resonator (CSR structure in the microwave region. Simulated results show that the proposed MMA has three distinctive absorption peaks at 3.35 GHz, 8.65 GHz, and 12.44 GHz, with absorbance of 98.8%, 99.7%, and 98.3%, respectively, which agree well with an experiment. Simulated surface current distributions of the unit-cell structure reveal that the triple-band absorption mainly originates from multiple-harmonic magnetic resonance. The proposed triple-band MMA can remain at a high absorption level for all polarization of both transverse-electric (TE and transverse-magnetic (TM modes under normal incidence. Moreover, by further optimizing the geometric parameters of the CSRs, four-band and five-band MMAs can also be obtained. Thus, our design will have potential application in detection, sensing, and stealth technology.

Effects of the c-Si/a-SiO2 interfacial atomic structure on its band alignment: an ab initio study.

Science.gov (United States)

Zheng, Fan; Pham, Hieu H; Wang, Lin-Wang

2017-12-13

The crystalline-Si/amorphous-SiO 2 (c-Si/a-SiO 2 ) interface is an important system used in many applications, ranging from transistors to solar cells. The transition region of the c-Si/a-SiO 2 interface plays a critical role in determining the band alignment between the two regions. However, the question of how this interface band offset is affected by the transition region thickness and its local atomic arrangement is yet to be fully investigated. Here, by controlling the parameters of the classical Monte Carlo bond switching algorithm, we have generated the atomic structures of the interfaces with various thicknesses, as well as containing Si at different oxidation states. A hybrid functional method, as shown by our calculations to reproduce the GW and experimental results for bulk Si and SiO 2 , was used to calculate the electronic structure of the heterojunction. This allowed us to study the correlation between the interface band characterization and its atomic structures. We found that although the systems with different thicknesses showed quite different atomic structures near the transition region, the calculated band offset tended to be the same, unaffected by the details of the interfacial structure. Our band offset calculation agrees well with the experimental measurements. This robustness of the interfacial electronic structure to its interfacial atomic details could be another reason for the success of the c-Si/a-SiO 2 interface in Si-based electronic applications. Nevertheless, when a reactive force field is used to generate the a-SiO 2 and c-Si/a-SiO 2 interfaces, the band offset significantly deviates from the experimental values by about 1 eV.

Carrier-carrier relaxation kinetics in quantum well semiconductor structures with nonparabolic energy bands

DEFF Research Database (Denmark)

Dery, H.; Tromborg, Bjarne; Eisenstein, G.

2003-01-01

We describe carrier-carrier scattering dynamics in an inverted quantum well structure including the nonparabolic nature of the valance band. A solution of the semiconductor Bloch equations yields strong evidence to a large change in the temporal evolution of the carrier distributions compared to ...

Tinene: a two-dimensional Dirac material with a 72 meV band gap.

Science.gov (United States)

Cai, Bo; Zhang, Shengli; Hu, Ziyu; Hu, Yonghong; Zou, Yousheng; Zeng, Haibo

2015-05-21

Dirac materials have attracted great interest for both fundamental research and electronic devices due to their unique band structures, but the usual near zero bandgap of graphene results in a poor on-off ratio in the corresponding transistors. Here, we report on tinene, monolayer gray tin, as a new two-dimensional material with both Dirac characteristics and a remarkable 72 meV bandgap based on density functional theory calculations. Compared with silicene and germanene, tinene has a similar hexagonal honeycomb monolayer structure, but it has an obviously larger buckling height (∼0.70 Å). Interestingly, such a moderate buckling structure results in phonon dispersion without appreciable imaginary modes, indicating the strong dynamic stability of tinene. Significantly, a distinct transformation is discovered from the band structure that six Dirac cones would appear at high symmetry K points in the first Brillouin zone when gray tin is thinned from the bulk to monolayer, but a bandgap as large as 72 meV is still preserved. Considering the recent successful realization of silicene and germanene with a similar structure, the predicted stable tinene with Dirac characteristics and a suitable bandgap is a possibility for the "more than Moore" materials and devices.

Band structure and thermoelectric properties of half-Heusler semiconductors from many-body perturbation theory

Science.gov (United States)

Zahedifar, Maedeh; Kratzer, Peter

2018-01-01

Various ab initio approaches to the band structure of A NiSn and A CoSb half-Heusler compounds (A = Ti, Zr, Hf) are compared and their consequences for the prediction of thermoelectric properties are explored. Density functional theory with the generalized-gradient approximation (GGA), as well as the hybrid density functional HSE06 and ab initio many-body perturbation theory in the form of the G W0 approach, are employed. The G W0 calculations confirm the trend of a smaller band gap (0.75 to 1.05 eV) in A NiSn compared to the A CoSb compounds (1.13 to 1.44 eV) already expected from the GGA calculations. While in A NiSn materials the G W0 band gap is 20% to 50% larger than in HSE06, the fundamental gap of A CoSb materials is smaller in G W0 compared to HSE06. This is because G W0 , similar to PBE, locates the valence band maximum at the L point of the Brillouin zone, whereas it is at the Γ point in the HSE06 calculations. The differences are attributed to the observation that the relative positions of the d levels of the transition metal atoms vary among the different methods. Using the calculated band structures and scattering rates taking into account the band effective masses at the extrema, the Seebeck coefficients, thermoelectric power factors, and figures of merit Z T are predicted for all six half-Heusler compounds. Comparable performance is predicted for the n -type A NiSn materials, whereas clear differences are found for the p -type A CoSb materials. Using the most reliable G W0 electronic structure, ZrCoSb is predicted to be the most efficient material with a power factor of up to 0.07 W/(K2 m) at a temperature of 600 K. We find strong variations among the different ab initio methods not only in the prediction of the maximum power factor and Z T value of a given material, but also in comparing different materials to each other, in particular in the p -type thermoelectric materials. Thus we conclude that the most elaborate, but also most costly G W0

Novel semiconductor solar cell structures: The quantum dot intermediate band solar cell

International Nuclear Information System (INIS)

Marti, A.; Lopez, N.; Antolin, E.; Canovas, E.; Stanley, C.; Farmer, C.; Cuadra, L.; Luque, A.

2006-01-01

The Quantum Dot Intermediate Band Solar Cell (QD-IBSC) has been proposed for studying experimentally the operating principles of a generic class of photovoltaic devices, the intermediate band solar cells (IBSC). The performance of an IBSC is based on the properties of a semiconductor-like material which is characterised by the existence of an intermediate band (IB) located within what would otherwise be its conventional bandgap. The improvement in efficiency of the cell arises from its potential (i) to absorb below bandgap energy photons and thus produce additional photocurrent, and (ii) to inject this enhanced photocurrent without degrading its output photo-voltage. The implementation of the IBSC using quantum dots (QDs) takes advantage of the discrete nature of the carrier density of states in a 0-dimensional nano-structure, an essential property for realising the IB concept. In the QD-IBSC, the IB arises from the confined electron states in an array of quantum dots. This paper reviews the operation of the first prototype QD-IBSCs and discusses some of the lessons learnt from their characterisation

Novel semiconductor solar cell structures: The quantum dot intermediate band solar cell

Energy Technology Data Exchange (ETDEWEB)

Marti, A. [Instituto de Energia Solar-UPM, ETSIT de Madrid, Ciudad Universitaria sn, 28040 Madrid (Spain)]. E-mail: amarti@etsit.upm.es; Lopez, N. [Instituto de Energia Solar-UPM, ETSIT de Madrid, Ciudad Universitaria sn, 28040 Madrid (Spain); Antolin, E. [Instituto de Energia Solar-UPM, ETSIT de Madrid, Ciudad Universitaria sn, 28040 Madrid (Spain); Canovas, E. [Instituto de Energia Solar-UPM, ETSIT de Madrid, Ciudad Universitaria sn, 28040 Madrid (Spain); Stanley, C. [Department of Electronics and Electrical Engineering, University of Glasgow, Glasgow G12 8QQ (United Kingdom); Farmer, C. [Department of Electronics and Electrical Engineering, University of Glasgow, Glasgow G12 8QQ (United Kingdom); Cuadra, L. [Departamento de Teoria de la Senal y Comunicaciones- Escuela Politecnica Superior, Universidad de Alcala, Ctra. Madrid-Barcelona, km. 33600, 28805-Alcala de Henares (Madrid) (Spain); Luque, A. [Instituto de Energia Solar-UPM, ETSIT de Madrid, Ciudad Universitaria sn, 28040 Madrid (Spain)

2006-07-26

The Quantum Dot Intermediate Band Solar Cell (QD-IBSC) has been proposed for studying experimentally the operating principles of a generic class of photovoltaic devices, the intermediate band solar cells (IBSC). The performance of an IBSC is based on the properties of a semiconductor-like material which is characterised by the existence of an intermediate band (IB) located within what would otherwise be its conventional bandgap. The improvement in efficiency of the cell arises from its potential (i) to absorb below bandgap energy photons and thus produce additional photocurrent, and (ii) to inject this enhanced photocurrent without degrading its output photo-voltage. The implementation of the IBSC using quantum dots (QDs) takes advantage of the discrete nature of the carrier density of states in a 0-dimensional nano-structure, an essential property for realising the IB concept. In the QD-IBSC, the IB arises from the confined electron states in an array of quantum dots. This paper reviews the operation of the first prototype QD-IBSCs and discusses some of the lessons learnt from their characterisation.

Electronic band structure and optical properties of antimony selenide under pressure

Energy Technology Data Exchange (ETDEWEB)

Abhijit, B.K.; Jayaraman, Aditya; Molli, Muralikrishna, E-mail: muralikrishnamolli@sssihl.edu.in [Department of Physics, Sri Sathya Sai Institute of Higher Learning, Prasanthinilayam, 515 134 (India)

2016-05-23

In this work we present the optical properties of Antimony Selenide (Sb{sub 2}Se{sub 3}) under ambient conditions and under pressure of 9.2 GPa obtained using first principles calculations. We investigated the electronic band structure using the FP-LAPW method within the sphere of the density functional theory. Optical properties like refractive index, absorption coefficient and optical conductivity are calculated using the WIEN2k code.

16O + 16O + valence neutrons in molecular orbitals structures of positive- and negative-parity superdeformed bands in 34S

International Nuclear Information System (INIS)

Taniguchi, Yasutaka

2015-01-01

The structures of superdeformed (SD) states in 34 S have been investigated using the antisymmetrized molecular dynamics and generator coordinate method (GCM). The GCM basis wave functions are calculated via energy variation with a constraint on the quadrupole deformation parameter β. By applying the GCM after parity and angular momentum projections, the coexistence of two positive- and one negative-parity SD bands are predicted, and low-lying states and other deformed bands are obtained. The SD bands have structures of 16 O + 16 O + two valence neutrons in molecular orbitals around the two 16 O cores in a cluster picture. The configurations of the two valence neutrons are δ 2 and π 2 for the positive-parity SD bands and π 1 δ 1 for the negative-parity SD band. (author)

16O + 16O + valence neutrons in molecular orbitals structures of positive- and negative-parity superdeformed bands in 34S

International Nuclear Information System (INIS)

Taniguchi, Yasutaka

2014-01-01

The structures of superdeformed (SD) states in 34 S are investigated using the antisymmetrized molecular dynamics and generator coordinate method (GCM). The GCM basis wave functions are calculated via energy variation with a constraint on the quadrupole deformation parameter β. By applying the GCM after parity and angular momentum projections, the coexistence of two positive- and one negative-parity SD bands are predicted, and low-lying states and other deformed bands are obtained. The SD bands have structures of 16 O + 16 O + two valence neutrons in molecular orbitals around the two 16 O cores in a cluster picture. The configurations of the two valence neutrons are δ 2 and π 2 for the positive-parity SD bands and π 1 δ 1 for the negative-parity SD band

Photonic Band Structure of Dispersive Metamaterials Formulated as a Hermitian Eigenvalue Problem

KAUST Repository

Raman, Aaswath

2010-02-26

We formulate the photonic band structure calculation of any lossless dispersive photonic crystal and optical metamaterial as a Hermitian eigenvalue problem. We further show that the eigenmodes of such lossless systems provide an orthonormal basis, which can be used to rigorously describe the behavior of lossy dispersive systems in general. © 2010 The American Physical Society.

Photonic Band Structure of Dispersive Metamaterials Formulated as a Hermitian Eigenvalue Problem

KAUST Repository

Raman, Aaswath; Fan, Shanhui

2010-01-01

We formulate the photonic band structure calculation of any lossless dispersive photonic crystal and optical metamaterial as a Hermitian eigenvalue problem. We further show that the eigenmodes of such lossless systems provide an orthonormal basis, which can be used to rigorously describe the behavior of lossy dispersive systems in general. © 2010 The American Physical Society.

Wire measurement of impedance of an X-band accelerating structure

CERN Document Server

Baboi, N; Dolgashev, V A; Jones, R M; Lewandowski, J R; Tantawi, S G; Wang, J W

2004-01-01

Several tens of thousands of accelerator structures will be needed for the next generation of linear collders known as the GLC/NLC (Global Linear Collider/Next Linear Collider). To prevent the beam being driven into a disruptive BBU (Beam Break Up) mode or at the very least, the emittance being signifcantly diluted, it is important to damp down the wakefield left by driving bunches to a manageable level. Manufacturing errors and errors in design need to be measurable and compared with predictions. We develop a circuit model of wire-loaded X-band accelerator structures. This enables the wakefield (the inverse transform of the beam impedance) to be readily computed and compared with the wire measurement. We apply this circuit model to the latest series of accelerating for the GLC/NLC. This circuit model is based upon the single-cell model developed in [1] extended here to complete, multi-cell structures.

A High-Resolution Crystal Structure of a Psychrohalophilic α-Carbonic Anhydrase from Photobacterium profundum Reveals a Unique Dimer Interface.

Directory of Open Access Journals (Sweden)

Vijayakumar Somalinga

Full Text Available Bacterial α-carbonic anhydrases (α-CA are zinc containing metalloenzymes that catalyze the rapid interconversion of CO2 to bicarbonate and a proton. We report the first crystal structure of a pyschrohalophilic α-CA from a deep-sea bacterium, Photobacterium profundum. Size exclusion chromatography of the purified P. profundum α-CA (PprCA reveals that the protein is a heterogeneous mix of monomers and dimers. Furthermore, an "in-gel" carbonic anhydrase activity assay, also known as protonography, revealed two distinct bands corresponding to monomeric and dimeric forms of PprCA that are catalytically active. The crystal structure of PprCA was determined in its native form and reveals a highly conserved "knot-topology" that is characteristic of α-CA's. Similar to other bacterial α-CA's, PprCA also crystallized as a dimer. Furthermore, dimer interface analysis revealed the presence of a chloride ion (Cl- in the interface which is unique to PprCA and has not been observed in any other α-CA's characterized so far. Molecular dynamics simulation and chloride ion occupancy analysis shows 100% occupancy for the Cl- ion in the dimer interface. Zinc coordinating triple histidine residues, substrate binding hydrophobic patch residues, and the hydrophilic proton wire residues are highly conserved in PprCA and are identical to other well-studied α-CA's.

Diffusion properties of band 3 in human erythrocytes

Science.gov (United States)

Spector, Jeffrey O.

The plasma membrane of the human erythrocyte (RBC) is a six fold symmetric network held together at various pinning points by several multi-protein complexes. This unique architecture is what gives the RBC its remarkable material properties and any disruptions to the network can have severe consequences for the cell. Band 3 is a major transmembrane protein that plays the role of linking the fluid lipid bilayer to the cytoskeletal network. To interrogate the structural integrity of the RBC membrane we have tracked individual band 3 molecules in RBCs displaying a variety of pathologies that are all a consequence of membrane or network related defects. These diseases are spherocytosis, elliptocytosis, and pyropokilocytosis. We have also investigated the protein related diseases sickle cell, and south east asian ovalocytosis. To assess the impact that the network has on the dynamic organization of the cell we have also studied the mobility of band 3 in RBC progenitor cells. Individual band 3 molecules were imaged at 120 frames/second and their diffusion coefficients and compartment sizes recorded. The distributions of the compartment sizes combined with the information about the short and long time diffusion of band 3 has given us insight into the architecture of the membrane in normal and diseased cells. The observation that different membrane pathologies can be distinguished, even to the point of different molecular origins of the same disease, implies that the mobility of transmembrane proteins may be a useful tool for characterizing the "health" of the membrane.

Lam\\'e polynomials, hyperelliptic reductions and Lam\\'e band structure

OpenAIRE

Maier, Robert S.

2003-01-01

The band structure of the Lam\\'e equation, viewed as a one-dimensional Schr\\"odinger equation with a periodic potential, is studied. At integer values of the degree parameter l, the dispersion relation is reduced to the l=1 dispersion relation, and a previously published l=2 dispersion relation is shown to be partially incorrect. The Hermite-Krichever Ansatz, which expresses Lam\\'e equation solutions in terms of l=1 solutions, is the chief tool. It is based on a projection from a genus-l hype...

Glucose Absorption by the Bacillary Band of Trichuris muris.

Directory of Open Access Journals (Sweden)

Tina V A Hansen

2016-09-01

Full Text Available A common characteristic of Trichuris spp. infections in humans and animals is the variable but low efficacy of single-dose benzimidazoles currently used in mass drug administration programmes against human trichuriasis. The bacillary band, a specialised morphological structure of Trichuris spp., as well as the unique partly intracellular habitat of adult Trichuris spp. may affect drug absorption and perhaps contribute to the low drug accumulation in the worm. However, the exact function of the bacillary band is still unknown.We studied the dependency of adult Trichuris muris on glucose and/or amino acids for survival in vitro and the absorptive function of the bacillary band. The viability of the worms was evaluated using a motility scale from 0 to 3, and the colorimetric assay Alamar Blue was utilised to measure the metabolic activity. The absorptive function of the bacillary band in living worms was explored using a fluorescent glucose analogue (6-NBDG and confocal microscopy. To study the absorptive function of the bacillary band in relation to 6-NBDG, the oral uptake was minimised or excluded by sealing the oral cavity with glue and agarose.Glucose had a positive effect on both the motility (p < 0.001 and metabolic activity (p < 0.001 of T. muris in vitro, whereas this was not the case for amino acids. The 6-NBDG was observed in the pores of the bacillary band and within the stichocytes of the living worms, independent of oral sealing.Trichuris muris is dependent on glucose for viability in vitro, and the bacillary band has an absorptive function in relation to 6-NBDG, which accumulates within the stichocytes. The absorptive function of the bacillary band calls for an exploration of its possible role in the uptake of anthelmintics, and as a potential anthelmintic target relevant for future drug development.

A wave-bending structure at Ka-band using 3D-printed metamaterial

Science.gov (United States)

Wu, Junqiang; Liang, Min; Xin, Hao

2018-03-01

Three-dimensional printing technologies enable metamaterials of complex structures with arbitrary inhomogeneity. In this work, a 90° wave-bending structure at the Ka-band (26.5-40 GHz) based on 3D-printed metamaterials is designed, fabricated, and measured. The wave-bending effect is realized through a spatial distribution of varied effective dielectric constants. Based on the effective medium theory, different effective dielectric constants are accomplished by special, 3D-printable unit cells, which allow different ratios of dielectric to air at the unit cell level. In contrast to traditional, metallic-structure-included metamaterial designs, the reported wave-bending structure here is all dielectric and implemented by the polymer-jetting technique, which features rapid, low-cost, and convenient prototyping. Both simulation and experiment results demonstrate the effectiveness of the wave-bending structure.

Helical quantum states in HgTe quantum dots with inverted band structures.

Science.gov (United States)

Chang, Kai; Lou, Wen-Kai

2011-05-20

We investigate theoretically the electron states in HgTe quantum dots (QDs) with inverted band structures. In sharp contrast to conventional semiconductor quantum dots, the quantum states in the gap of the HgTe QD are fully spin-polarized and show ringlike density distributions near the boundary of the QD and spin-angular momentum locking. The persistent charge currents and magnetic moments, i.e., the Aharonov-Bohm effect, can be observed in such a QD structure. This feature offers us a practical way to detect these exotic ringlike edge states by using the SQUID technique.

Band structure calculation of GaSe-based nanostructures using empirical pseudopotential method

International Nuclear Information System (INIS)

Osadchy, A V; Obraztsova, E D; Volotovskiy, S G; Golovashkin, D L; Savin, V V

2016-01-01

In this paper we present the results of band structure computer simulation of GaSe- based nanostructures using the empirical pseudopotential method. Calculations were performed using a specially developed software that allows performing simulations using cluster computing. Application of this method significantly reduces the demands on computing resources compared to traditional approaches based on ab-initio techniques and provides receiving the adequate comparable results. The use of cluster computing allows to obtain information for structures that require an explicit account of a significant number of atoms, such as quantum dots and quantum pillars. (paper)

Correlation between electronic structure and energy band in Eu-doped CuInTe2 semiconductor compound with chalcopyrite structure

Institute of Scientific and Technical Information of China (English)

Tai Wang; Yong-Quan Guo; Shuai Li

2017-01-01

The Eu-doped Cu(In,Eu)Te2 semiconductors with chalcopyrite structures are promising materials for their applications in the absorption layer for thin-film solar cells due to their wider band-gaps and better optical properties than those of CulnTe2.In this paper,the Eu-doped CulnTe2 (Culn1-xEuxTe2,x =0,0.1,0.2,0.3) are studied systemically based on the empirical electron theory (EET).The studies cover crystal structures,bonding regularities,cohesive energies,energy levels,and valence electron structures.The theoretical values fit the experimental results very well.The physical mechanism of a broadened band-gap induced by Eu doping into CuInTe2 is the transitions between different hybridization energy levels induced by electron hopping between s and d orbitals and the transformations from the lattice electrons to valence electrons for Cu and In ions.The research results reveal that the photovoltaic effect induces the increase of lattice electrons of In and causes the electric resistivity to decrease.The Eu doping into CuInTe2 mainly influences the transition between different hybridization energy levels for Cu atoms,which shows that the 3d electron numbers of Cu atoms change before and after Eu doping.In single phase CuIn1-xEuxTe2,the number of valence electrons changes regularly with increasing Eu content,and the calculated band gap Eg also increases,which implies that the optical properties of Eu-doped CuIn1-xEuxTe2 are improved.

Multifunctional Binary Monolayers Ge xP y: Tunable Band Gap, Ferromagnetism, and Photocatalyst for Water Splitting.

Science.gov (United States)

Li, Pengfei; Zhang, Wei; Li, Dongdong; Liang, Changhao; Zeng, Xiao Cheng

2018-06-04

The most stable structures of two-dimensional Ge x P y and Ge x As y monolayers with different stoichiometries (e.g., GeP, GeP 2 , and GeP 3 ) are explored systematically through the combination of the particle-swarm optimization technique and density functional theory optimization. For GeP 3 , we show that the newly predicted most stable C2/ m structure is 0.16 eV/atom lower in energy than the state-of-the-art P3̅m1 structure reported previously ( Nano Lett. 2017, 17, 1833). The computed electronic band structures suggest that all the stable and metastable monolayers of Ge x P y are semiconductors with highly tunable band gaps under the biaxial strain, allowing strain engineering of their band gaps within nearly the whole visible-light range. More interestingly, the hole doping can convert the C2/ m GeP 3 monolayer from nonmagnetic to ferromagnetic because of its unique valence band structure. For the GeP 2 monolayer, the predicted most stable Pmc2 1 structure is a (quasi) direct-gap semiconductor that possesses a high electron mobility of ∼800 cm 2 V -1 s -1 along the k a direction, which is much higher than that of MoS 2 (∼200 cm 2 V -1 s -1 ). More importantly, the Pmc2 1 GeP 2 monolayer not only can serve as an n-type channel material in field-effect transistors but also can be an effective catalyst for splitting water.

Electronic band structure of Two-Dimensional WS2/Graphene van der Waals Heterostructures

Science.gov (United States)

Henck, Hugo; Ben Aziza, Zeineb; Pierucci, Debora; Laourine, Feriel; Reale, Francesco; Palczynski, Pawel; Chaste, Julien; Silly, Mathieu G.; Bertran, François; Le Fèvre, Patrick; Lhuillier, Emmanuel; Wakamura, Taro; Mattevi, Cecilia; Rault, Julien E.; Calandra, Matteo; Ouerghi, Abdelkarim

2018-04-01

Combining single-layer two-dimensional semiconducting transition-metal dichalcogenides (TMDs) with a graphene layer in van der Waals heterostructures offers an intriguing means of controlling the electronic properties through these heterostructures. Here, we report the electronic and structural properties of transferred single-layer W S2 on epitaxial graphene using micro-Raman spectroscopy, angle-resolved photoemission spectroscopy measurements, and density functional theory (DFT) calculations. The results show good electronic properties as well as a well-defined band arising from the strong splitting of the single-layer W S2 valence band at the K points, with a maximum splitting of 0.44 eV. By comparing our DFT results with local and hybrid functionals, we find the top valence band of the experimental heterostructure is close to the calculations for suspended single-layer W S2 . Our results provide an important reference for future studies of electronic properties of W S2 and its applications in valleytronic devices.

Determination of conduction and valence band electronic structure ...

Indian Academy of Sciences (India)

shifts in the rutile Ti d-band to lower energy with respect to anatase, i.e., ... requires excitation with UV light due to its wide band ... RIXS maps were compared to the theoretical results .... optical methods are insufficient, such as dark samples.

Band structure and dielectric function of TlInTe2

International Nuclear Information System (INIS)

Wakita, K.; Shim, Y.; Orudzhev, G.; Mamedov, N.; Hashimzade, F.

2006-01-01

The band structure of ternary chain TlInTe 2 was calculated with allowance for non-locality of ionic pseudo-potentials. The dielectric function, as well as the effective masses of holes and electrons, the effective number of valence electrons, and the function of characteristic losses were determined. The results of comparison between the calculated dielectric function and the one obtained ellipsometrically in the spectral range from 0.85 to 6 eV are quite favorable. (copyright 2006 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (Abstract Copyright [2006], Wiley Periodicals, Inc.)

Band Structure Engineering of Cs2AgBiBr6 Perovskite through Order-Disordered Transition: A First-Principle Study.

Science.gov (United States)

Yang, Jingxiu; Zhang, Peng; Wei, Su-Huai

2018-01-04

Cs 2 AgBiBr 6 was proposed as one of the inorganic, stable, and nontoxic replacements of the methylammonium lead halides (CH 3 NH 3 PbI 3 , which is currently considered as one of the most promising light-harvesting material for solar cells). However, the wide indirect band gap of Cs 2 AgBiBr 6 suggests that its application in photovoltaics is limited. Using the first-principle calculation, we show that by controlling the ordering parameter at the mixed sublattice, the band gap of Cs 2 AgBiBr 6 can vary continuously from a wide indirect band gap of 1.93 eV for the fully ordered double-perovskite structure to a small pseudodirect band gap of 0.44 eV for the fully random alloy. Therefore, one can achieve better light absorption simply by controlling the growth temperature and thus the ordering parameters and band gaps. We also show that controlled doping in Cs 2 AgBiBr 6 can change the energy difference between ordered and disordered Cs 2 AgBiBr 6 , thus providing further control of the ordering parameters and the band gaps. Our study, therefore, provides a novel approach to carry out band structure engineering in the mixed perovskites for optoelectronic applications.

Simultaneous Out-of-band Interference Rejection and Radiation Enhancement in an Electronic Product via an EBG Structure

DEFF Research Database (Denmark)

Ruaro, Andrea; Thaysen, Jesper; Jakobsen, Kaj Bjarne

2014-01-01

to achieve simultaneously both the enhancement of the antenna radiation efficiency and the shrinking of its dimensions, while making the device more resilient to out-of-band electromagnetic interference (EMI). The patterning of the ground plane allows, in fact, to effectively suppress higher-order resonances......This work presents an application of a planar electromagnetic band gap (EBG) structure with a perspective product implementation in the back of the mind. The focus is on the integration of such structure under the constraint of space and system coexistence. It is discovered that it is possible...... (alternatively, parallel plate noise) and decrease the radiation efficiency of the structure forbidding higher-order modes to propagate and subsequently be diffracted by the ground plane....

Single-Band and Dual-Band Infrared Detectors

Science.gov (United States)

Ting, David Z. (Inventor); Gunapala, Sarath D. (Inventor); Soibel, Alexander (Inventor); Nguyen, Jean (Inventor); Khoshakhlagh, Arezou (Inventor)

2017-01-01

Bias-switchable dual-band infrared detectors and methods of manufacturing such detectors are provided. The infrared detectors are based on a back-to-back heterojunction diode design, where the detector structure consists of, sequentially, a top contact layer, a unipolar hole barrier layer, an absorber layer, a unipolar electron barrier, a second absorber, a second unipolar hole barrier, and a bottom contact layer. In addition, by substantially reducing the width of one of the absorber layers, a single-band infrared detector can also be formed.

Structure of the Kπ = 4+ bands in 186,188Os

Science.gov (United States)

Phillips, A. A.; Garrett, P. E.; Bettermann, L.; Braun, N.; Burke, D. G.; Demand, G. A.; Faestermann, T.; Finlay, P.; Green, K. L.; Hertenberger, R.; Krü; cken, R.; Leach, K. G.; Schumaker, M. A.; Svensson, C. E.; Wirth, H.-F.; Wong, J.

2009-01-01

The structures of 3+ states in Os have been debated over several decades. Based on measured B(E2) values they were interpreted in 186-192Os as Kπ = 4+ two-phonon vibrations, whereas inelastic scattering, and (t,α) work imply a hexadecapole phonon description. To clarify the nature of these Kπ = 4+ bands in 186,188Os, we performed a (3He,d) reaction on 185,187Re targets using 30 MeV 3He beams and a Q3D spectrograph. Absolute cross sections were obtained for excited states up to 3 MeV at 9 angles from 5° to 50°. Results indicate a significant 5/2+[402]π+3/2+[402]π component in agreement with quasiparticle phonon model predictions for a single hexadecapole phonon structure.

Direct Measurement of the Band Structure of a Buried Two-Dimensional Electron Gas

DEFF Research Database (Denmark)

Miwa, Jill; Hofmann, Philip; Simmons, Michelle Y.

2013-01-01

We directly measure the band structure of a buried two dimensional electron gas (2DEG) using angle resolved photoemission spectroscopy. The buried 2DEG forms 2 nm beneath the surface of p-type silicon, because of a dense delta-type layer of phosphorus n-type dopants which have been placed there...

Structure of dipole bands in 106In

International Nuclear Information System (INIS)

Deo, A. Y.; Palit, R.; Naik, Z.; Joshi, P. K.; Mazumdar, I.; Sihotra, S.; Mehta, D.; Kumar, S.; Chakrabarti, R.; Kshetri, R.; Jain, H. C.

2009-01-01

High spin states in neutron-deficient 106 In were investigated using 78 Se( 32 S,p3n) reaction at 125 MeV. The level scheme is extended up to 7 MeV of excitation energy for the negative parity states constituting four dipole bands, and the positive parity states which mainly exhibit single-particle excitations are extended up to 5 MeV. Projected deformed Hartree-Fock calculations were carried out to understand the configurations of different bands in this nucleus.

O'nyong nyong virus molecular determinants of unique vector specificity reside in non-structural protein 3.

Directory of Open Access Journals (Sweden)

Kali D Saxton-Shaw

Full Text Available O'nyong nyong virus (ONNV and Chikungunya virus (CHIKV are two closely related alphaviruses with very different infection patterns in the mosquito, Anopheles gambiae. ONNV is the only alphavirus transmitted by anopheline mosquitoes, but specific molecular determinants of infection of this unique vector specificity remain unidentified. Fifteen distinct chimeric viruses were constructed to evaluate both structural and non-structural regions of the genome and infection patterns were determined through artificial infectious feeds in An. gambiae with each of these chimeras. Only one region, non-structural protein 3 (nsP3, was sufficient to up-regulate infection to rates similar to those seen with parental ONNV. When ONNV non-structural protein 3 (nsP3 replaced nsP3 from CHIKV virus in one of the chimeric viruses, infection rates in An. gambiae went from 0% to 63.5%. No other single gene or viral region addition was able to restore infection rates. Thus, we have shown that a non-structural genome element involved in viral replication is a major element involved in ONNV's unique vector specificity.

Structural mechanisms of formation of adiabatic shear bands

Directory of Open Access Journals (Sweden)

Mikhail Sokovikov

2016-10-01

Full Text Available The paper focuses on the experimental and theoretical study of plastic deformation instability and localization in materials subjected to dynamic loading and high-velocity perforation. We investigate the behavior of samples dynamically loaded during Hopkinson-Kolsky pressure bar tests in a regime close to simple shear conditions. Experiments were carried out using samples of a special shape and appropriate test rigging, which allowed us to realize a plane strain state. Also, the shear-compression specimens proposed in were investigated. The lateral surface of the samples was investigated in a real-time mode with the aid of a high-speed infra-red camera CEDIP Silver 450M. The temperature field distribution obtained at different time made it possible to trace the evolution of plastic strain localization. Use of a transmission electron microscope for studying the surface of samples showed that in the regions of strain localization there are parts taking the shape of bands and honeycomb structure in the deformed layer. The process of target perforation involving plug formation and ejection was investigated using a high-speed infra-red camera. A specially designed ballistic set-up for studying perforation was used to test samples in different impulse loading regimes followed by plastic flow instability and plug ejection. Changes in the velocity of the rear surface at different time of plug ejection were analyzed by Doppler interferometry techniques. The microstructure of tested samples was analyzed using an optical interferometer-profilometer and a scanning electron microscope. The subsequent processing of 3D deformation relief data enabled estimation of the distribution of plastic strain gradients at different time of plug formation and ejection. It has been found that in strain localization areas the subgrains are elongated taking the shape of bands and undergo fragmentation leading to the formation of super-microcrystalline structure, in which the

Unique double concentric ring organization of light harvesting complexes in Gemmatimonas phototrophica.

Directory of Open Access Journals (Sweden)

Marko Dachev

2017-12-01

Full Text Available The majority of life on Earth depends directly or indirectly on the sun as a source of energy. The initial step of photosynthesis is facilitated by light-harvesting complexes, which capture and transfer light energy into the reaction centers (RCs. Here, we analyzed the organization of photosynthetic (PS complexes in the bacterium G. phototrophica, which so far is the only phototrophic representative of the bacterial phylum Gemmatimonadetes. The isolated complex has a molecular weight of about 800 ± 100 kDa, which is approximately 2 times larger than the core complex of Rhodospirillum rubrum. The complex contains 62.4 ± 4.7 bacteriochlorophyll (BChl a molecules absorbing in 2 distinct infrared absorption bands with maxima at 816 and 868 nm. Using femtosecond transient absorption spectroscopy, we determined the energy transfer time between these spectral bands as 2 ps. Single particle analyses of the purified complexes showed that they were circular structures with an outer diameter of approximately 18 nm and a thickness of 7 nm. Based on the obtained, we propose that the light-harvesting complexes in G. phototrophica form 2 concentric rings surrounding the type 2 RC. The inner ring (corresponding to the B868 absorption band is composed of 15 subunits and is analogous to the inner light-harvesting complex 1 (LH1 in purple bacteria. The outer ring is composed of 15 more distant BChl dimers with no or slow energy transfer between them, resulting in the B816 absorption band. This completely unique and elegant organization offers good structural stability, as well as high efficiency of light harvesting. Our results reveal that while the PS apparatus of Gemmatimonadetes was acquired via horizontal gene transfer from purple bacteria, it later evolved along its own pathway, devising a new arrangement of its light harvesting complexes.

A Ku-band magnetically insulated transmission line oscillator with overmoded slow-wave-structure

Science.gov (United States)

Jiang, Tao; He, Jun-Tao; Zhang, Jian-De; Li, Zhi-Qiang; Ling, Jun-Pu

2016-12-01

In order to enhance the power capacity, an improved Ku-band magnetically insulated transmission line oscillator (MILO) with overmoded slow-wave-structure (SWS) is proposed and investigated numerically and experimentally. The analysis of the dispersion relationship and the resonant curve of the cold test indicate that the device can operate at the near π mode of the TM01 mode, which is useful for mode selection and control. In the particle simulation, the improved Ku-band MILO generates a microwave with a power of 1.5 GW and a frequency of 12.3 GHz under an input voltage of 480 kV and input current of 42 kA. Finally, experimental investigation of the improved Ku-band MILO is carried out. A high-power microwave (HPM) with an average power of 800 MW, a frequency of 12.35 GHz, and pulse width of 35 ns is generated under a diode voltage of 500 kV and beam current of 43 kA. The consistency between the experimental and simulated far-field radiation pattern confirms that the operating mode of the improved Ku-band MILO is well controlled in π mode of the TM01 mode. Project supported partly by the National Natural Science Foundation of China (Grant No. 61171021).

Touching points in the energy band structure of bilayer graphene superlattices

International Nuclear Information System (INIS)

Pham, C Huy; Nguyen, V Lien

2014-01-01

The energy band structure of the bilayer graphene superlattices with zero-averaged periodic δ-function potentials are studied within the four-band continuum model. Using the transfer matrix method, the study is mainly focused on examining the touching points between adjacent minibands. For the zero-energy touching points the dispersion relation derived shows a Dirac-like double-cone shape with the group velocity which is periodic in the potential strength P with the period of π and becomes anisotropic at relatively large P. From the finite-energy touching points we have identified those located at zero wave-number. It was shown that for these finite-energy touching points the dispersion is direction-dependent in the sense that it is linear or parabolic in the direction parallel or perpendicular to the superlattice direction, respectively. We have also calculated the density of states and the conductivity which demonstrates a manifestation of the touching points examined. (paper)

InN/GaN Superlattices: Band Structures and Their Pressure Dependence

DEFF Research Database (Denmark)

Gorczyca, Iza; Suski, Tadek; Staszczak, Grzegorz

2013-01-01

Creation of short-period InN/GaN superlattices is one of the possible ways of conducting band gap engineering in the green-blue range of the spectrum. The present paper reports results of photoluminescence experiments, including pressure effects, on a superlattice sample consisting of unit cells...... with one monolayer of InN and 40 monolayers of GaN. The results are compared with calculations performed for different types of superlattices: InN/GaN, InGaN/GaN, and InN/InGaN/GaN with single monolayers of InN and/or InGaN. The superlattices are simulated by band structure calculations based on the local...... density approximation (LDA) with a semi-empirical correction for the ‘‘LDA gap error’’. A similarity is observed between the results of calculations for an InGaN/GaN superlattice (with one monolayer of InGaN) and the experimental results. This indicates that the fabricated InN quantum wells may contain...

Electromagnetic Band Gap Structures: Practical Tips and Advice for Antenna Engineers

Directory of Open Access Journals (Sweden)

P. Kovacs

2012-04-01

Full Text Available In this paper we discuss the use of electromagnetic band gap (EBG structures in antenna engineering from a practical point of view. Our aim is to point out the most common mistakes and myths related to design, analysis and application of EBGs in the field of antennas. The paper could be helpful for beginners giving a short course on designing EBGs but also will bring novel findings for experts, investigating the effect of different number of unit cells on radiation characteristics of a planar antenna. An important part of the paper is the experiments showing the surface wave distribution over an EBG board and over the fabricated antennas with- and without the periodic structure.

Enhanced photocatalytic activity of titania with unique surface indium and boron species

Science.gov (United States)

Yu, Yanlong; Wang, Enjun; Yuan, Jixiang; Cao, Yaan

2013-05-01

Indium and boron co-doped TiO2 photocatalysts were prepared by a sol-gel method. The structure and properties of photocatalysts were characterized by XRD, BET, XPS, UV-vis DRS and PL techniques. It is found that boron is mainly doped into the lattice of TiO2 in interstitial mode, while indium is present as unique chemical species of O-In-Clx (x = 1 or 2) on the surface. Compared with pure TiO2, the narrowness of band gap of TiO2 doped with indium and boron is due to the mixed valence band formed by B2p of interstitial doped B ions hybridized with lattice O2p. And the surface state energy levels of O-In-Clx (x = 1 or 2) and B2O3 species were located at about 0.4 and 0.3 eV below the conduction band respectively, which could lead to significant absorption in the visible-light region and facilitated the effectually separation of photogenerated carriers. Therefore, indium and boron co-doped TiO2 showed the much higher photocatalytic activities than pure TiO2, boron doped TiO2 (TiO2-B) and indium doped TiO2 (TiO2-In) under visible and UV light irradiation.

Voltage tunable two-band MIR detection based on Si/SiGe quantum cascade injector structures

International Nuclear Information System (INIS)

Grydlik, M.; Rauter, P.; Meduna, M.; Fromherz, T.; Bauer, G.; Falub, C.; Dehlinger, G.; Sigg, H.; Gruetzmacher, D.

2004-01-01

We report the results of photocurrent spectroscopy in the mid-infrared (MIR) spectral region performed on p-type Si/SiGe cascade structures. The samples were grown by MBE and consist of a series of five SiGe quantum wells with ground states that can be coupled through thin Si barriers by aligning them in energy with an externally applied electric field E bi . Quantum wells and barriers are Boron doped to a level of 2.5 10 17 cm -3 . Our samples contain 10 sequences of the 5 quantum wells separated by 500 nm thick, undoped Si barriers. Vertical photocurrent spectroscopy has been performed for various electric fields applied perpendicular to the quantum wells at temperatures between 10 K and 100 K. Depending on the direction of the externally applied electric field relative to E bi , the photoresponse of our samples can be switched between two MIR detection bands with maxima at 230 meV and 400 meV. Due to the inversion asymmetry of the samples, at 0 V external voltage the samples deliver a short circuit current in the high-energy spectral band. Since the quantum cascades are formed in the valence band of the Si/SiGe structures, the quantum well transitions responsible for the observed photocurrents are allowed for radiation polarized parallel to the quantum wells. Therefore, these structures appear to be suitable for voltage tuneable MIR detection under normal incident radiation. By comparing the experimental results to model calculations, design strategies to optimize the responsivity of the Si/SiGe cascade structures are discussed. (author)

Elastic band prediction equations for combined free-weight and elastic band bench presses and squats.

Science.gov (United States)

Shoepe, Todd C; Ramirez, David A; Almstedt, Hawley C

2010-01-01

Elastic bands added to traditional free-weight techniques have become a part of suggested training routines in recent years. Because of the variable loading patterns of elastic bands (i.e., greater stretch produces greater resistance), it is necessary to quantify the exact loading patterns of bands to identify the volume and intensity of training. The purpose of this study was to determine the length vs. tension properties of multiple sizes of a set of commonly used elastic bands to quantify the resistance that would be applied to free-weight plus elastic bench presses (BP) and squats (SQ). Five elastic bands of varying thickness were affixed to an overhead support beam. Dumbbells of varying weights were progressively added to the free end while the linear deformation was recorded with each subsequent weight increment. The resistance was plotted as a factor of linear deformation, and best-fit nonlinear logarithmic regression equations were then matched to the data. For both the BP and SQ loading conditions and all band thicknesses tested, R values were greater than 0.9623. These data suggest that differences in load exist as a result of the thickness of the elastic band, attachment technique, and type of exercise being performed. Facilities should adopt their own form of loading quantification to match their unique set of circumstances when acquiring, researching, and implementing elastic band and free-weight exercises into the training programs.

Experimental and theoretical investigations of the electronic band structure of metal-organic frameworks of HKUST-1 type

Energy Technology Data Exchange (ETDEWEB)

Gu, Zhi-Gang [Institut für Funktionelle Grenzflächen (IFG), Karlsruher Institut für Technologie (KIT), Hermann-von-Helmholtz-Platz 1, 76344 Eggenstein-Leopoldshafen (Germany); State Key Laboratory of Structural Chemistry, Fujian Institute of Research on the Structure of Matter, Chinese Academy of Sciences, 350002 Fuzhou (China); Heinke, Lars, E-mail: Lars.Heinke@KIT.edu; Wöll, Christof [Institut für Funktionelle Grenzflächen (IFG), Karlsruher Institut für Technologie (KIT), Hermann-von-Helmholtz-Platz 1, 76344 Eggenstein-Leopoldshafen (Germany); Neumann, Tobias; Wenzel, Wolfgang; Li, Qiang; Fink, Karin [Institute of Nanotechnology (INT), Karlsruher Institut für Technologie (KIT), Hermann-von-Helmholtz-Platz 1, 76344 Eggenstein-Leopoldshafen (Germany); Gordan, Ovidiu D.; Zahn, Dietrich R. T. [Semiconductor Physics, Technische Universität Chemnitz, 09107 Chemnitz (Germany)

2015-11-02

The electronic properties of metal-organic frameworks (MOFs) are increasingly attracting the attention due to potential applications in sensor techniques and (micro-) electronic engineering, for instance, as low-k-dielectric in semiconductor technology. Here, the band gap and the band structure of MOFs of type HKUST-1 are studied in detail by means of spectroscopic ellipsometry applied to thin surface-mounted MOF films and by means of quantum chemical calculations. The analysis of the density of states, the band structure, and the excitation spectrum reveal the importance of the empty Cu-3d orbitals for the electronic properties of HKUST-1. This study shows that, in contrast to common belief, even in the case of this fairly “simple” MOF, the excitation spectra cannot be explained by a superposition of “intra-unit” excitations within the individual building blocks. Instead, “inter-unit” excitations also have to be considered.

Experimental and theoretical investigations of the electronic band structure of metal-organic frameworks of HKUST-1 type

Science.gov (United States)

Gu, Zhi-Gang; Heinke, Lars; Wöll, Christof; Neumann, Tobias; Wenzel, Wolfgang; Li, Qiang; Fink, Karin; Gordan, Ovidiu D.; Zahn, Dietrich R. T.

2015-11-01

The electronic properties of metal-organic frameworks (MOFs) are increasingly attracting the attention due to potential applications in sensor techniques and (micro-) electronic engineering, for instance, as low-k-dielectric in semiconductor technology. Here, the band gap and the band structure of MOFs of type HKUST-1 are studied in detail by means of spectroscopic ellipsometry applied to thin surface-mounted MOF films and by means of quantum chemical calculations. The analysis of the density of states, the band structure, and the excitation spectrum reveal the importance of the empty Cu-3d orbitals for the electronic properties of HKUST-1. This study shows that, in contrast to common belief, even in the case of this fairly "simple" MOF, the excitation spectra cannot be explained by a superposition of "intra-unit" excitations within the individual building blocks. Instead, "inter-unit" excitations also have to be considered.

Experimental and theoretical investigations of the electronic band structure of metal-organic frameworks of HKUST-1 type

International Nuclear Information System (INIS)

Gu, Zhi-Gang; Heinke, Lars; Wöll, Christof; Neumann, Tobias; Wenzel, Wolfgang; Li, Qiang; Fink, Karin; Gordan, Ovidiu D.; Zahn, Dietrich R. T.

2015-01-01

The electronic properties of metal-organic frameworks (MOFs) are increasingly attracting the attention due to potential applications in sensor techniques and (micro-) electronic engineering, for instance, as low-k-dielectric in semiconductor technology. Here, the band gap and the band structure of MOFs of type HKUST-1 are studied in detail by means of spectroscopic ellipsometry applied to thin surface-mounted MOF films and by means of quantum chemical calculations. The analysis of the density of states, the band structure, and the excitation spectrum reveal the importance of the empty Cu-3d orbitals for the electronic properties of HKUST-1. This study shows that, in contrast to common belief, even in the case of this fairly “simple” MOF, the excitation spectra cannot be explained by a superposition of “intra-unit” excitations within the individual building blocks. Instead, “inter-unit” excitations also have to be considered

Application of mid-infrared free-electron laser tuned to amide bands for dissociation of aggregate structure of protein.

Science.gov (United States)

Kawasaki, Takayasu; Yaji, Toyonari; Ohta, Toshiaki; Tsukiyama, Koichi

2016-01-01

A mid-infrared free-electron laser (FEL) is a linearly polarized, high-peak powered pulse laser with tunable wavelength within the mid-infrared absorption region. It was recently found that pathogenic amyloid fibrils could be partially dissociated to the monomer form by the irradiation of the FEL targeting the amide I band (C=O stretching vibration), amide II band (N-H bending vibration) and amide III band (C-N stretching vibration). In this study, the irradiation effect of the FEL on keratin aggregate was tested as another model to demonstrate an applicability of the FEL for dissociation of protein aggregates. Synchrotron radiation infrared microscopy analysis showed that the α-helix content in the aggregate structure decreased to almost the same level as that in the monomer state after FEL irradiation tuned to 6.06 µm (amide I band). Both irradiations at 6.51 µm (amide II band) and 8.06 µm (amide III band) also decreased the content of the aggregate but to a lesser extent than for the irradiation at the amide I band. On the contrary, the irradiation tuned to 5.6 µm (non-absorbance region) changed little the secondary structure of the aggregate. Scanning-electron microscopy observation at the submicrometer order showed that the angular solid of the aggregate was converted to non-ordered fragments by the irradiation at each amide band, while the aggregate was hardly deformed by the irradiation at 5.6 µm. These results demonstrate that the amide-specific irradiation by the FEL was effective for dissociation of the protein aggregate to the monomer form.

The band structure of carbonmonoxide on 2-D Au islands on graphene

KAUST Repository

Katsiev, Khabiboulakh

2014-06-01

The dispersion of the occupied molecular orbitals of carbon monoxide adsorbed on Au 2D islands, vapor-deposited on graphene/Ru(0 0 0 1), is seen to be wave vector dependent, as revealed by angle-resolved photoemission. The band dispersion is similar to CO monolayers adsorbed on many single crystal metal surfaces. Thus not only are the adsorbed gold islands on graphene flat and crystalline, as evident in the dispersion of the Au d-states, but the CO molecular adlayer is both molecular and ordered as well. The experimental angle-resolved photoemission combined with model calculations of the occupied CO band structure, suggest that, in spite of being a very weakly bound adsorbate, the CO adlayer on Au 2D islands on graphene is strongly hybridized to the Au layer. . © 2014 Elsevier B.V. All rights reserved.

Unique structural modulation of a non-native substrate by cochaperone DnaJ.

Science.gov (United States)

Tiwari, Satyam; Kumar, Vignesh; Jayaraj, Gopal Gunanathan; Maiti, Souvik; Mapa, Koyeli

2013-02-12

The role of bacterial DnaJ protein as a cochaperone of DnaK is strongly appreciated. Although DnaJ unaccompanied by DnaK can bind unfolded as well as native substrate proteins, its role as an individual chaperone remains elusive. In this study, we demonstrate that DnaJ binds a model non-native substrate with a low nanomolar dissociation constant and, more importantly, modulates the structure of its non-native state. The structural modulation achieved by DnaJ is different compared to that achieved by the DnaK-DnaJ complex. The nature of structural modulation exerted by DnaJ is suggestive of a unique unfolding activity on the non-native substrate by the chaperone. Furthermore, we demonstrate that the zinc binding motif along with the C-terminal substrate binding domain of DnaJ is necessary and sufficient for binding and the subsequent binding-induced structural alterations of the non-native substrate. We hypothesize that this hitherto unknown structural alteration of non-native states by DnaJ might be important for its chaperoning activity by removing kinetic traps of the folding intermediates.

Density-functional band-structure calculations for La-, Y-, and Sc-filled CoP3-based skutterudite structures

International Nuclear Information System (INIS)

Loevvik, O.M.; Prytz, O.

2004-01-01

The crystal structure, thermodynamic stability, and electronic structure of La-, Y-, and Sc-filled CoP 3 are predicted from density-functional band-structure calculations. The size of the cubic voids in the skutterudite structure is changed much less than the difference in size between the different filling atoms, and we expect that the larger rattling amplitude of the smaller Sc and Y atoms may decrease the lattice thermal conductivity of Sc- and Y-filled structures significantly compared to La-filled structures. The solubility of La, Y, and Sc in CoP 3 is calculated to be around 5, 3-6 %, and below 1% at 0 K, respectively. Based on similar systems, this is expected to increase considerably if Fe is substituted for Co. Fe substitution is also expected to compensate the increased charge carrier concentration of the filled structures that is seen in the calculated electron density of states. In conclusion, Sc- or Y-filled (FeCo)P 3 skutterudite structures are promising materials for thermoelectric applications

Synthesis, band structure, and optical properties of Ba2ZnV2O8

International Nuclear Information System (INIS)

Chen, D.-G.; Cheng, W.-D.; Wu, D.-S.; Zhang, H.; Zhang, Y.-C.; Gong, Y.-J.; Kan, Z.-G.

2004-01-01

A novel compound Ba 2 ZnV 2 O 8 has been synthesized in high temperature solution reaction and its crystal structure has been characterized by means of single crystal X-ray diffraction analysis. It crystallizes in monoclinic system and belongs to space group P2 1 /c with a=7.9050(16), b=16.149(3), c=6.1580(12)A, β=90.49(3). It builds up from 1-D branchy chains of [ZnV 2 O 8 4- ] ∞ , and the Ba 2+ cations are located in the space among these chains. The IR spectrum, ultraviolet-visible diffuse reflection integral spectrum and fluorescent spectra of this compound have been investigated. The calculated results of energy band structure by the density functional theory method show that the solid-state compound of Ba 2 ZnV 2 O 8 is an insulator with direct band gap of 3.48eV. The calculated total and partial density of states indicate that the top valence bands are contributions from the mixings of O-2p, V-3d, and Zn-3d states and low conduction bands mostly originate from unoccupied antibonding states between the V-3d and O-2p states. The V-O bonds are mostly covalence characters and Zn-O bonds are mostly ionic interactions, and the ionic interaction strength is stronger between the Ba-O than between the Zn-O. The refractive index of n x , n y , and n z is estimated to be 1.7453, 1.7469, and 1.7126, respectively, at wavelength of 1060nm for Ba 2 ZnV 2 O 8 crystal

FDTD method for computing the off-plane band structure in a two-dimensional photonic crystal consisting of nearly free-electron metals

Energy Technology Data Exchange (ETDEWEB)

Xiao Sanshui; He Sailing

2002-12-01

An FDTD numerical method for computing the off-plane band structure of a two-dimensional photonic crystal consisting of nearly free-electron metals is presented. The method requires only a two-dimensional discretization mesh for a given off-plane wave number k{sub z} although the off-plane propagation is a three-dimensional problem. The off-plane band structures of a square lattice of metallic rods with the high-frequency metallic model in the air are studied, and a complete band gap for some nonzero off-plane wave number k{sub z} is founded.

FDTD method for computing the off-plane band structure in a two-dimensional photonic crystal consisting of nearly free-electron metals

International Nuclear Information System (INIS)

Xiao Sanshui; He Sailing

2002-01-01

An FDTD numerical method for computing the off-plane band structure of a two-dimensional photonic crystal consisting of nearly free-electron metals is presented. The method requires only a two-dimensional discretization mesh for a given off-plane wave number k z although the off-plane propagation is a three-dimensional problem. The off-plane band structures of a square lattice of metallic rods with the high-frequency metallic model in the air are studied, and a complete band gap for some nonzero off-plane wave number k z is founded

The transfer to technology to manufacture the disk of X-band accelerator structure

International Nuclear Information System (INIS)

Ueno, Kenji; Kawamata, Hiroshi; Takatomi, Toshikazu; Kume, Tatsuya; Funahashi, Yoshisato

2005-01-01

We research the transfer of manufacturing technology on X-band structure disks. From this issue we confirm that the venders will be able to manufacture disks when they get the process sheet method and drawings. More it is clear that we have to consider the automation process in order to get the repeatability of the disks. (author)

Visible-light activity of N-LiInO{sub 2}: Band structure modifications through interstitial nitrogen doping

Energy Technology Data Exchange (ETDEWEB)

Xu, Kaiqiang [College of Material Science and Engineering, Hunan University, Changsha, 410082 (China); Xu, Difa, E-mail: xudifa@sina.com [Hunan Key Laboratory of Applied Environmental Photocatalysis, Changsha University, Changsha, 410022 (China); Zhang, Xiangchao; Luo, Zhuo; Wang, Yutang [Hunan Key Laboratory of Applied Environmental Photocatalysis, Changsha University, Changsha, 410022 (China); Zhang, Shiying, E-mail: cdzhangshiying@163.com [College of Material Science and Engineering, Hunan University, Changsha, 410082 (China); Hunan Key Laboratory of Applied Environmental Photocatalysis, Changsha University, Changsha, 410022 (China)

2017-01-01

Highlights: • The interstitial nitrogen doping into LiInO{sub 2} is achieved at low temperature. • The band gap narrowing to an extent of 2.8 eV from 3.5 eV is observed. • The doping favours charge carrier separation and photocatalytic activity. • Superoxide radical is the dominant active specie in the pollutant degradation. - Abstract: Element doping is a promising strategy to improve the photo-response and photocatalytic activity of semiconductor photocatalyst with a wide band gap. To reduce the band gap of LiInO{sub 2} that is considered as a novel photocatalyst, nitrogen-doped LiInO{sub 2} (N-LiInO{sub 2}) is successfully fabricated by treating LiInO{sub 2} and urea at 200 °C. It is found that interstitial instead of substitutional configurations are formed in the crystal structure of N-LiInO{sub 2} due to the low-treating temperature and rich-oxygen conditions. The interstitial N-doping forms a doping state with 0.6 eV above the valence band maximum and a defect state with 0.1 eV below the conduction band minimum, reducing the band gap of LiInO{sub 2} from 3.5 to 2.8 eV. N-LiInO{sub 2} exhibits higher photocatalytic activity towards methylene blue (MB) degradation under 380 nm light irradiation, which is 1.4 times that of pure LiInO{sub 2}. The enhanced photocatalytic activity of N-LiInO{sub 2} is attributed to the extended light absorption and the improved charge carrier separation, which result in more reactive species participating in the photcatalytic process. This work provides a further understanding on tuning the band structure of semiconductor photocatalyst by N-doping strategies.

Handbook of the band structure of elemental solids from Z = 1 to Z = 112

CERN Document Server

Papaconstantopoulos, Dimitris A

2015-01-01

This handbook presents electronic structure data and tabulations of Slater-Koster parameters for the whole periodic table. This second edition presents data sets for all elements up to Z = 112, Copernicium, whereas the first edition contained only 53 elements. In this new edition, results are given for the equation of state of the elements together with the parameters of a Birch fit, so that the reader can regenerate the results and derive additional information, such as Pressure-Volume relations and variation of Bulk Modulus with Pressure. For each element, in addition to the equation of state, the energy bands, densities of states, and a set of tight-binding parameters is provided. For a majority of elements, the tight-binding parameters are presented for both a two- and three-center approximation. For the hcp structure, new three-center tight-binding results are given. Other new material in this edition include: energy bands and densities of states of all rare-earth metals, a discussion of the McMillan-Gas...

Development of intermediate-scale structure at different altitudes within an equatorial plasma bubble: Implications for L-band scintillations

Science.gov (United States)

Bhattacharyya, A.; Kakad, B.; Gurram, P.; Sripathi, S.; Sunda, S.

2017-01-01

An important aspect of the development of intermediate-scale length (approximately hundred meters to few kilometers) irregularities in an equatorial plasma bubble (EPB) that has not been considered in the schemes to predict the occurrence pattern of L-band scintillations in low-latitude regions is how these structures develop at different heights within an EPB as it rises in the postsunset equatorial ionosphere due to the growth of the Rayleigh-Taylor instability. Irregularities at different heights over the dip equator map to different latitudes, and their spectrum as well as the background electron density determine the strength of L-band scintillations at different latitudes. In this paper, VHF and L-band scintillations recorded at different latitudes together with theoretical modeling of the scintillations are used to study the implications of this structuring of EPBs on the occurrence and strength of L-band scintillations at different latitudes. Theoretical modeling shows that while S4 index for scintillations on a VHF signal recorded at an equatorial station may be >1, S4 index for scintillations on a VHF signal recorded near the crest of the equatorial ionization anomaly (EIA) generally does not exceed the value of 1 because the intermediate-scale irregularity spectrum at F layer peak near the EIA crest is shallower than that found in the equatorial F layer peak. This also explains the latitudinal distribution of L-band scintillations. Thus, it is concluded that there is greater structuring of an EPB on the topside of the equatorial F region than near the equatorial F layer peak.

Origami-based mechanical metamaterials with tunable frequency band structures (Conference Presentation)

Science.gov (United States)

Yasuda, Hiromi; Pratt, Riley; Yang, Jinkyu

2017-04-01

We investigate wave dynamics in origami-based mechanical metamaterials composed of bellows-like origami structures, specifically the Tachi-Miura Polyhedron (TMP). One of the unique features of the TMP is that its structural deformations take place only along the crease lines, therefore the structure can be made of rigid plates and hinges. By utilizing this feature, we introduce linear torsional springs to model the crease lines and derive the force and displacement relationship of the TMP structure along the longitudinal direction. Our analysis shows strain softening/hardening behaviors in compression/tensile regions respectively, and the force-displacement curve can be manipulated by altering the initial configuration of the TMP (e.g., the initial folding angle). We also fabricate physical prototypes and measure the force-displacement behavior to verify our analytical model. Based on this static analysis on the TMP, we simplify the TMP structure into a linkage model, preserving the tunable strain softening/hardening behaviors. Dynamic analysis is also conducted numerically to analyze the frequency response of the simplified TMP unit cell under harmonic excitations. The simplified TMP exhibits a transition between linear and nonlinear behaviors, which depends on the amplitude of the excitation and the initial configuration. In addition, we design a 1D system composed of simplified TMP unit cells and analyze the relationship between frequency and wave number. If two different configurations of the unit cell (e.g., different initial folding angles) are connected in an alternating arrangement, the system develops frequency bandgaps. These unique static/dynamic behaviors can be exploited to design engineering devices which can handle vibrations and impact in an efficient manner.

Micromachined millimeter-wave photonic band-gap crystals

International Nuclear Information System (INIS)

Oezbay, E.; Michel, E.; Tuttle, G.; Biswas, R.; Sigalas, M.; Ho, K.

1994-01-01

We have developed a new technique for fabricating three-dimensional photonic band-gap crystals. Our method utilizes an orderly stacking of micromachined (110) silicon wafers to build the periodic structure. A structure with a full three-dimensional photonic band gap centered near 100 GHz was measured, with experimental results in good agreement with theoretical predictions. This basic approach described should be extendable to build structures with photonic band-gap frequencies ranging from 30 GHz to 3 THz

Mangrove vegetation structure in Southeast Brazil from phased array L-band synthetic aperture radar data

Science.gov (United States)

de Souza Pereira, Francisca Rocha; Kampel, Milton; Cunha-Lignon, Marilia

2016-07-01

The potential use of phased array type L-band synthetic aperture radar (PALSAR) data for discriminating distinct physiographic mangrove types with different forest structure developments in a subtropical mangrove forest located in Cananéia on the Southern coast of São Paulo, Brazil, is investigated. The basin and fringe physiographic types and the structural development of mangrove vegetation were identified with the application of the Kruskal-Wallis statistical test to the SAR backscatter values of 10 incoherent attributes. The best results to separate basin to fringe types were obtained using copolarized HH, cross-polarized HV, and the biomass index (BMI). Mangrove structural parameters were also estimated using multiple linear regressions. BMI and canopy structure index were used as explanatory variables for canopy height, mean height, and mean diameter at breast height regression models, with significant R2=0.69, 0.73, and 0.67, respectively. The current study indicates that SAR L-band images can be used as a tool to discriminate physiographic types and to characterize mangrove forests. The results are relevant considering the crescent availability of freely distributed SAR images that can be more utilized for analysis, monitoring, and conservation of the mangrove ecosystem.

Effect of ripple taper on band-gap overlap in a coaxial Bragg structure operating at terahertz frequency

International Nuclear Information System (INIS)

Ding Xueyong; Li Hongfan; Lv Zhensu

2012-01-01

Based on the mode-coupling method, numerical analysis is presented to demonstrate the influence of ripple taper on band-gap overlap in a coaxial Bragg structure operating at terahertz frequency. Results show that the interval between the band-gaps of the competing mode and the desired working mode is narrowed by use of positive-taper ripples, but is expanded if negative-taper ripples are employed, and the influence of the negative-taper ripples is obviously more advantageous than the positive-taper ripples; the band-gap overlap of modes can be efficiently separated by use of negative-taper ripples. The residual side-lobes of the frequency response in a coaxial Bragg structure with ripple taper also can be effectively suppressed by employing the windowing-function technique. These peculiarities provide potential advantage in constructing a coaxial Bragg cavity with high quality factor for single higher-order-mode operation of a high-power free-electron maser in the terahertz frequency range.

Effect of superconductivity on the cubic to tetragonal structural transition due to a two-fold degenerate electronic band

International Nuclear Information System (INIS)

Ghatak, S.K.; Khanra, B.C.; Ray, D.K.

1978-01-01

The effect of the BCS superconductivity on the cubic to tetragonal structural transition arising from a two-fold degenerate electronic band is investigated within the mean field approximation. The phase diagram of the two transitions is given for a half filled esub(g)-band. Modification of the two transitions when they are close together is also discussed. (author)

Quasiparticle band structure for the Hubbard systems: Application to α-CeAl2

International Nuclear Information System (INIS)

Costa-Quintana, J.; Lopez-Aguilar, F.; Balle, S.; Salvador, R.

1990-01-01

A self-energy formalism for determining the quasiparticle band structure of the Hubbard systems is deduced. The self-energy is obtained from the dynamically screened Coulomb interaction whose bare value is the correlation energy U. A method for integrating the Schroedingerlike equation with the self-energy operator is given. The method is applied to the cubic Laves phase of α-CeAl 2 because it is a clear Hubbard system with a very complex electronic structure and, moreover, this system provides us with sufficient experimental data for testing our method

Omnidirectional photonic band gap enlarged by one-dimensional ternary unmagnetized plasma photonic crystals based on a new Fibonacci quasiperiodic structure

Energy Technology Data Exchange (ETDEWEB)

Zhang Haifeng [College of Electronic and Information Engineering, Nanjing University of Aeronautics and Astronautics, Nanjing 210016 (China); Nanjing Artillery Academy, Nanjing 211132 (China); Liu Shaobin [College of Electronic and Information Engineering, Nanjing University of Aeronautics and Astronautics, Nanjing 210016 (China); State Key Laboratory of Millimeter Waves of Southeast University, Nanjing Jiangsu 210096 (China); Kong Xiangkun; Bian Borui; Dai Yi [College of Electronic and Information Engineering, Nanjing University of Aeronautics and Astronautics, Nanjing 210016 (China)

2012-11-15

In this paper, an omnidirectional photonic band gap realized by one-dimensional ternary unmagnetized plasma photonic crystals based on a new Fibonacci quasiperiodic structure, which is composed of homogeneous unmagnetized plasma and two kinds of isotropic dielectric, is theoretically studied by the transfer matrix method. It has been shown that such an omnidirectional photonic band gap originates from Bragg gap in contrast to zero-n gap or single negative (negative permittivity or negative permeability) gap, and it is insensitive to the incidence angle and the polarization of electromagnetic wave. From the numerical results, the frequency range and central frequency of omnidirectional photonic band gap can be tuned by the thickness and density of the plasma but cease to change with increasing Fibonacci order. The bandwidth of omnidirectional photonic band gap can be notably enlarged. Moreover, the plasma collision frequency has no effect on the bandwidth of omnidirectional photonic band gap. It is shown that such new structure Fibonacci quasiperiodic one-dimensional ternary plasma photonic crystals have a superior feature in the enhancement of frequency range of omnidirectional photonic band gap compared with the conventional ternary and conventional Fibonacci quasiperiodic ternary plasma photonic crystals.

Solvent micro-evaporation and concentration gradient synergistically induced crystallization of poly(L-lactide) and ring banded supra-structures with radial periodic variation of thickness

DEFF Research Database (Denmark)

Huang, Shaoyong; Li, Hongfei; Wen, Huiying

2014-01-01

The crystalline morphology and structure of poly(L-lactide) (PLLA) in a PLLA film-chloroform system were investigated by means of wide angle X-ray diffraction (WAXD), polarized optical microscopy (POM) and atomic force microscopy (AFM). Birefringent and nonbirefringent ring banded supra-structure......The crystalline morphology and structure of poly(L-lactide) (PLLA) in a PLLA film-chloroform system were investigated by means of wide angle X-ray diffraction (WAXD), polarized optical microscopy (POM) and atomic force microscopy (AFM). Birefringent and nonbirefringent ring banded supra......-structures with radial periodic variation of thickness were obtained, which were induced by micro-evaporation of solvents and concentration gradient of PLLA. The ring banded morphologies consisted of multilayer lamellar crystals, which is a manifestation of alternating ridge and valley bands of periodic variation...

Manipulation of Optoelectronic Properties and Band Structure Engineering of Ultrathin Te Nanowires by Chemical Adsorption.

Science.gov (United States)

Roy, Ahin; Amin, Kazi Rafsanjani; Tripathi, Shalini; Biswas, Sangram; Singh, Abhishek K; Bid, Aveek; Ravishankar, N

2017-06-14

Band structure engineering is a powerful technique both for the design of new semiconductor materials and for imparting new functionalities to existing ones. In this article, we present a novel and versatile technique to achieve this by surface adsorption on low dimensional systems. As a specific example, we demonstrate, through detailed experiments and ab initio simulations, the controlled modification of band structure in ultrathin Te nanowires due to NO 2 adsorption. Measurements of the temperature dependence of resistivity of single ultrathin Te nanowire field-effect transistor (FET) devices exposed to increasing amounts of NO 2 reveal a gradual transition from a semiconducting to a metallic state. Gradual quenching of vibrational Raman modes of Te with increasing concentration of NO 2 supports the appearance of a metallic state in NO 2 adsorbed Te. Ab initio simulations attribute these observations to the appearance of midgap states in NO 2 adsorbed Te nanowires. Our results provide fundamental insights into the effects of ambient on the electronic structures of low-dimensional materials and can be exploited for designing novel chemical sensors.

Tunable band structures in digital oxides with layered crystal habits

Science.gov (United States)

Shin, Yongjin; Rondinelli, James M.

2017-11-01

We use density functional calculations to show that heterovalent cation-order sequences enable control over band-gap variations up to several eV and band-gap closure in the bulk band insulator LaSrAlO4. The band-gap control originates from the internal electric fields induced by the digital chemical order, which induces picoscale band bending; the electric-field magnitude is mainly governed by the inequivalent charged monoxide layers afforded by the layered crystal habit. Charge transfer and ionic relaxations across these layers play secondary roles. This understanding is used to construct and validate a descriptor that captures the layer-charge variation and to predict changes in the electronic gap in layered oxides exhibiting antisite defects and in other chemistries.

Deformation bands and dislocation structures of [1-bar 5 5] coplanar double-slip-oriented copper single crystal under cyclic deformation

International Nuclear Information System (INIS)

Li, Y.; Li, S.X.; Li, G.Y.

2004-01-01

The features of surface morphology and dislocation structure of [1-bar 5 5] coplanar double-slip-oriented copper single crystal under cyclic deformation at a constant plastic shear strain amplitude of 2x10 -3 were studied using optical microscope (OP) and electron channelling contrast imaging (ECCI) in the scanning electron microscope (SEM). Experimental results show that there are two sets of the secondary type of deformation band (DBII) formed in the specimen. The geometry relationship of the two sets of deformation bands (DBs) and slip band (SB) are given. The habit planes of DBIIs are close to (1-bar 0 1) and (1-bar 1 0) plane, respectively. The surface dislocation structures in the specimen including vein, irregular dislocation cells and dislocation walls were also observed. The typical dislocation structure in DBII is the dislocation walls

Uranium(VI) coordination polymers with pyromellitate ligand: Unique 1D channel structures and diverse fluorescence

Energy Technology Data Exchange (ETDEWEB)

Zhang, Yingjie, E-mail: yzx@ansto.gov.au [Australian Nuclear Science and Technology Organization, Locked Bag 2001, Kirrawee DC, NSW 2232 (Australia); Bhadbhade, Mohan [Mark Wainwright Analytical Centre, University of New South Wales, Kensington, NSW 2052 (Australia); Karatchevtseva, Inna [Australian Nuclear Science and Technology Organization, Locked Bag 2001, Kirrawee DC, NSW 2232 (Australia); Price, Jason R. [Australian Synchrotron, 800 Blackburn Road, Clayton, VIC 3168 (Australia); Liu, Hao [Centre for Clean Energy Technology, School of Chemistry and Forensic Science, University of Technology Sydney, PO Box 123, Broadway, Sydney, NSW 2007 (Australia); Zhang, Zhaoming; Kong, Linggen [Australian Nuclear Science and Technology Organization, Locked Bag 2001, Kirrawee DC, NSW 2232 (Australia); Čejka, Jiří [Department of Mineralogy, National Museum, Václavské náměstí, 68, Prague 1, 115 79-CZ (Czech Republic); Lu, Kim; Lumpkin, Gregory R. [Australian Nuclear Science and Technology Organization, Locked Bag 2001, Kirrawee DC, NSW 2232 (Australia)

2015-03-15

Three new coordination polymers of uranium(VI) with pyromellitic acid (H{sub 4}btca) have been synthesized and structurally characterized. (ED)[(UO{sub 2})(btca)]·(DMSO)·3H{sub 2}O (1) (ED=ethylenediammonium; DMSO=dimethylsulfoxide) has a lamellar structure with intercalation of ED and DMSO. (NH{sub 4}){sub 2}[(UO{sub 2}){sub 6}O{sub 2}(OH){sub 6}(btca)]·~6H{sub 2}O (2) has a 3D framework built from 7-fold coordinated uranyl trinuclear units and btca ligands with 1D diamond-shaped channels (~8.5 Å×~8.6 Å). [(UO{sub 2}){sub 2}(H{sub 2}O)(btca)]·4H{sub 2}O (3) has a 3D network constructed by two types of 7-fold coordinated uranium polyhedron. The unique μ{sub 5}-coordination mode of btca in 3 enables the formation of 1D olive-shaped large channels (~4.5 Å×~19 Å). Vibrational modes, thermal stabilities and fluorescence properties have been investigated. - Graphical abstract: Table of content: three new uranium(VI) coordination polymers with pyromellitic acid (H{sub 4}btca) have been synthesized via room temperature and hydrothermal synthesis methods, and structurally characterized. Two to three dimensional (3D) frameworks are revealed. All 3D frameworks have unique 1D large channels. Their vibrational modes, thermal stabilities and photoluminescence properties have been investigated. - Highlights: • Three new coordination polymers of U(VI) with pyromellitic acid (H{sub 4}btca). • Structures from a 2D layer to 3D frameworks with unique 1D channels. • Unusual µ{sub 5}-(η{sub 1}:η{sub 2}:η{sub 1}:η{sub 2:}η{sub 1}) coordination mode of btca ligand. • Vibrational modes, thermal stabilities and luminescent properties reported.

Vibrational dynamics and band structure of methyl-terminated Ge(111)

Energy Technology Data Exchange (ETDEWEB)

Hund, Zachary M.; Nihill, Kevin J.; Sibener, S. J., E-mail: s-sibener@uchicago.edu [The James Franck Institute and Department of Chemistry, The University of Chicago, 929 E. 57" t" h Street, Chicago, Illinois 60637 (United States); Campi, Davide; Bernasconi, M. [Dipartimento di Scienza dei Materiali, Universita di Milano-Bicocca, Via Cozzi 53, 20125 Milano (Italy); Wong, Keith T.; Lewis, Nathan S. [Division of Chemistry and Chemical Engineering, Beckman Institute and Kavli Nanoscience Institute, California Institute of Technology, 210 Noyes Laboratory, 127-72, Pasadena, California 91125 (United States); Benedek, G. [Dipartimento di Scienza dei Materiali, Universita di Milano-Bicocca, Via Cozzi 53, 20125 Milano (Italy); Donostia International Physics Center (DIPC), Universidad del País Vasco (EHU), 20018 Donostia/San Sebastian (Spain)

2015-09-28

A combined synthesis, experiment, and theory approach, using elastic and inelastic helium atom scattering along with ab initio density functional perturbation theory, has been used to investigate the vibrational dynamics and band structure of a recently synthesized organic-functionalized semiconductor interface. Specifically, the thermal properties and lattice dynamics of the underlying Ge(111) semiconductor crystal in the presence of a commensurate (1 × 1) methyl adlayer were defined for atomically flat methylated Ge(111) surfaces. The mean-square atomic displacements were evaluated by analysis of the thermal attenuation of the elastic He diffraction intensities using the Debye-Waller model, revealing an interface with hybrid characteristics. The methyl adlayer vibrational modes are coupled with the Ge(111) substrate, resulting in significantly softer in-plane motion relative to rigid motion in the surface normal. Inelastic helium time-of-flight measurements revealed the excitations of the Rayleigh wave across the surface Brillouin zone, and such measurements were in agreement with the dispersion curves that were produced using density functional perturbation theory. The dispersion relations for H-Ge(111) indicated that a deviation in energy and lineshape for the Rayleigh wave was present along the nearest-neighbor direction. The effects of mass loading, as determined by calculations for CD{sub 3}-Ge(111), as well as by force constants, were less significant than the hybridization between the Rayleigh wave and methyl adlayer librations. The presence of mutually similar hybridization effects for CH{sub 3}-Ge(111) and CH{sub 3}-Si(111) surfaces extends the understanding of the relationship between the vibrational dynamics and the band structure of various semiconductor surfaces that have been functionalized with organic overlayers.

Vibrational dynamics and band structure of methyl-terminated Ge(111)

International Nuclear Information System (INIS)

th Street, Chicago, Illinois 60637 (United States))" data-affiliation=" (The James Franck Institute and Department of Chemistry, The University of Chicago, 929 E. 57th Street, Chicago, Illinois 60637 (United States))" >Hund, Zachary M.; th Street, Chicago, Illinois 60637 (United States))" data-affiliation=" (The James Franck Institute and Department of Chemistry, The University of Chicago, 929 E. 57th Street, Chicago, Illinois 60637 (United States))" >Nihill, Kevin J.; th Street, Chicago, Illinois 60637 (United States))" data-affiliation=" (The James Franck Institute and Department of Chemistry, The University of Chicago, 929 E. 57th Street, Chicago, Illinois 60637 (United States))" >Sibener, S. J.; Campi, Davide; Bernasconi, M.; Wong, Keith T.; Lewis, Nathan S.; Benedek, G.

2015-01-01

A combined synthesis, experiment, and theory approach, using elastic and inelastic helium atom scattering along with ab initio density functional perturbation theory, has been used to investigate the vibrational dynamics and band structure of a recently synthesized organic-functionalized semiconductor interface. Specifically, the thermal properties and lattice dynamics of the underlying Ge(111) semiconductor crystal in the presence of a commensurate (1 × 1) methyl adlayer were defined for atomically flat methylated Ge(111) surfaces. The mean-square atomic displacements were evaluated by analysis of the thermal attenuation of the elastic He diffraction intensities using the Debye-Waller model, revealing an interface with hybrid characteristics. The methyl adlayer vibrational modes are coupled with the Ge(111) substrate, resulting in significantly softer in-plane motion relative to rigid motion in the surface normal. Inelastic helium time-of-flight measurements revealed the excitations of the Rayleigh wave across the surface Brillouin zone, and such measurements were in agreement with the dispersion curves that were produced using density functional perturbation theory. The dispersion relations for H-Ge(111) indicated that a deviation in energy and lineshape for the Rayleigh wave was present along the nearest-neighbor direction. The effects of mass loading, as determined by calculations for CD 3 -Ge(111), as well as by force constants, were less significant than the hybridization between the Rayleigh wave and methyl adlayer librations. The presence of mutually similar hybridization effects for CH 3 -Ge(111) and CH 3 -Si(111) surfaces extends the understanding of the relationship between the vibrational dynamics and the band structure of various semiconductor surfaces that have been functionalized with organic overlayers

High power breakdown testing of a photonic band-gap accelerator structure with elliptical rods

Directory of Open Access Journals (Sweden)

Brian J. Munroe

2013-01-01

Full Text Available An improved single-cell photonic band-gap (PBG structure with an inner row of elliptical rods (PBG-E was tested with high power at a 60 Hz repetition rate at X-band (11.424 GHz, achieving a gradient of 128  MV/m at a breakdown probability of 3.6×10^{-3} per pulse per meter at a pulse length of 150 ns. The tested standing-wave structure was a single high-gradient cell with an inner row of elliptical rods and an outer row of round rods; the elliptical rods reduce the peak surface magnetic field by 20% and reduce the temperature rise of the rods during the pulse by several tens of degrees, while maintaining good damping and suppression of high order modes. When compared with a single-cell standing-wave undamped disk-loaded waveguide structure with the same iris geometry under test at the same conditions, the PBG-E structure yielded the same breakdown rate within measurement error. The PBG-E structure showed a greatly reduced breakdown rate compared with earlier tests of a PBG structure with round rods, presumably due to the reduced magnetic fields at the elliptical rods vs the fields at the round rods, as well as use of an improved testing methodology. A post-testing autopsy of the PBG-E structure showed some damage on the surfaces exposed to the highest surface magnetic and electric fields. Despite these changes in surface appearance, no significant change in the breakdown rate was observed in testing. These results demonstrate that PBG structures, when designed with reduced surface magnetic fields and operated to avoid extremely high pulsed heating, can operate at breakdown probabilities comparable to undamped disk-loaded waveguide structures and are thus viable for high-gradient accelerator applications.

Thermoelectric band engineering: The role of carrier scattering

Science.gov (United States)

Witkoske, Evan; Wang, Xufeng; Lundstrom, Mark; Askarpour, Vahid; Maassen, Jesse

2017-11-01

Complex electronic band structures, with multiple valleys or bands at the same or similar energies, can be beneficial for thermoelectric performance, but the advantages can be offset by inter-valley and inter-band scattering. In this paper, we demonstrate how first-principles band structures coupled with recently developed techniques for rigorous simulation of electron-phonon scattering provide the capabilities to realistically assess the benefits and trade-offs associated with these materials. We illustrate the approach using n-type silicon as a model material and show that intervalley scattering is strong. This example shows that the convergence of valleys and bands can improve thermoelectric performance, but the magnitude of the improvement depends sensitively on the relative strengths of intra- and inter-valley electron scattering. Because anisotropy of the band structure also plays an important role, a measure of the benefit of band anisotropy in the presence of strong intervalley scattering is presented.

Novel dielectric photonic-band-gap resonant cavity loaded in a gyrotron

International Nuclear Information System (INIS)

Chen Xiaoan; Liu Gaofeng; Tang Changjian

2010-01-01

A novel resonant cavity composed of a periodic, multilayer, dielectric photonic crystal is proposed. Using the transfer matrix method and the Bloch theorem for periodic systems, an analysis on the band-gap property of such a structure is made, and the basic electromagnetic property of the photonic-band-gap resonant cavity (PBGC) is preliminarily exhibited. The theoretical studies and the cold cavity simulation results obtained from a high-frequency structure simulator are presented. On the basis of the present research, such a PBGC is quite similar to the two-dimensional PBGC made of triangular lattices of metal rods with a defect at its centre, in which a frequency selectivity is similarly demonstrated. Because of its unique electromagnetic property, the cavity has many promising applications in active and passive devices operating in the millimetre, sub-millimetre, and even THz wave range. As a specific application, the feasibility of substituting the traditional cylindrical resonant cavity loaded in a gyrotron for a dielectric PBGC to achieve a transverse high-order operation is discussed under the consideration of the electromagnetic features of the cavity. The study shows the great potential value of such a cavity for gyrotron devices.

Spin splitting in band structures of BiTeX (X=Cl, Br, I) monolayers

Science.gov (United States)

Hvazdouski, D. C.; Baranava, M. S.; Stempitsky, V. R.

2018-04-01

In systems with breaking of inversion symmetry a perpendicular electric field arises that interacts with the conduction electrons. It may give rise to electron state splitting even without influence of external magnetic field due to the spin-orbital interaction (SOI). Such a removal of the spin degeneracy is called the Rashba effect. Nanostructure with the Rashba effect can be part of a spin transistor. Spin degeneracy can be realized in a channel from a material of this type without additive of magnetic ions. Lack of additive increases the charge carrier mobility and reliability of the device. Ab initio simulations of BiTeX (X=Cl, Br, I) monolayers have been carried out using VASP wherein implemented DFT method. The study of this structures is of interest because such sort of structures can be used their as spin-orbitronics materials. The crystal parameters of BiTeCl, BiTeBr, BiTeI have been determined by the ionic relaxation and static calculations. It is necessary to note that splitting of energy bands occurs in case of SOI included. The values of the Rashba coefficient aR (in the range from 6.25 to 10.00 eV·Å) have high magnitudes for spintronics materials. Band structure of monolayers structures have ideal Rashba electron gas, i.e. there no other energy states near to Fermi level except Rashba states.

Band parameters of phosphorene

DEFF Research Database (Denmark)

Lew Yan Voon, L. C.; Wang, J.; Zhang, Y.

2015-01-01

Phosphorene is a two-dimensional nanomaterial with a direct band-gap at the Brillouin zone center. In this paper, we present a recently derived effective-mass theory of the band structure in the presence of strain and electric field, based upon group theory. Band parameters for this theory...... are computed using a first-principles theory based upon the generalized-gradient approximation to the density-functional theory. These parameters and Hamiltonian will be useful for modeling physical properties of phosphorene....

Spectral element method for band-structure calculations of 3D phononic crystals

International Nuclear Information System (INIS)

Shi, Linlin; Liu, Na; Zhou, Jianyang; Zhou, Yuanguo; Wang, Jiamin; Liu, Qing Huo

2016-01-01

The spectral element method (SEM) is a special kind of high-order finite element method (FEM) which combines the flexibility of a finite element method with the accuracy of a spectral method. In contrast to the traditional FEM, the SEM exhibits advantages in the high-order accuracy as the error decreases exponentially with the increase of interpolation degree by employing the Gauss–Lobatto–Legendre (GLL) polynomials as basis functions. In this study, the spectral element method is developed for the first time for the determination of band structures of 3D isotropic/anisotropic phononic crystals (PCs). Based on the Bloch theorem, we present a novel, intuitive discretization formulation for Navier equation in the SEM scheme for periodic media. By virtue of using the orthogonal Legendre polynomials, the generalized eigenvalue problem is converted to a regular one in our SEM implementation to improve the efficiency. Besides, according to the specific geometry structure, 8-node and 27-node hexahedral elements as well as an analytic mesh have been used to accurately capture curved PC models in our SEM scheme. To verify its accuracy and efficiency, this study analyses the phononic-crystal plates with square and triangular lattice arrangements, and the 3D cubic phononic crystals consisting of simple cubic (SC), bulk central cubic (BCC) and faced central cubic (FCC) lattices with isotropic or anisotropic scatters. All the numerical results considered demonstrate that SEM is superior to the conventional FEM and can be an efficient alternative method for accurate determination of band structures of 3D phononic crystals. (paper)

Hybrid density functional theory study of Cu(In1−xGaxSe2 band structure for solar cell application

Directory of Open Access Journals (Sweden)

Xu-Dong Chen

2014-08-01

Full Text Available Cu(In1−xGaxSe2 (CIGS alloy based thin film photovoltaic solar cells have attracted more and more attention due to its large optical absorption coefficient, long term stability, low cost and high efficiency. However, the previous theoretical investigation of this material with first principle calculation cannot fulfill the requirement of experimental development, especially the accurate description of band structure and density of states. In this work, we use first principle calculation based on hybrid density functional theory to investigate the feature of CIGS, with B3LYP applied in the CuIn1−xGaxSe2 stimulation of the band structure and density of states. We report the simulation of the lattice parameter, band gap and chemical composition. The band gaps of CuGaSe2, CuIn0.25Ga0.75Se2, CuIn0.5Ga0.5Se2, CuIn0.75Ga0.25Se2 and CuInSe2 are obtained as 1.568 eV, 1.445 eV, 1.416 eV, 1.275 eV and 1.205 eV according to our calculation, which agree well with the available experimental values. The band structure of CIGS is also in accordance with the current theory.

Observations of 40-70 micron bands of ice in IRAS 09371 + 1212 and other stars

Science.gov (United States)

Omont, A.; Forveille, T.; Moseley, S. H.; Glaccum, W. J.; Harvey, P. M.; Likkel, L.; Loewenstein, R. F.; Lisse, C. M.

1990-01-01

IRAS 09371 + 1212 is still an absolutely unique object. This M giant star, with circumstellar CO and a spectacular bipolar nebula, displays unique IRAS FIR colors which had been attributed to strong emission in the 40-70-micron bands of ice, as subsequently supported by the observation of a strong 3.1-micron absorption band. The results of the KAO observations have confirmed its unusual nature: the far-infrared bands of ice are by far the strongest known. Its dust temperature, 50 K or less, is by far the lowest known for a late-type circumstellar envelope.

Valence band structures of InAs/GaAs quantum rings using the Fourier transform method

International Nuclear Information System (INIS)

Jia Boyong; Yu Zhongyuan; Liu Yumin

2009-01-01

The valence band structures of strained InAs/GaAs quantum rings are calculated, with the four-band k · p model, in the framework of effective-mass envelope function theory. When determining the Hamiltonian matrix elements, we develop the Fourier transform method instead of the widely used analytical integral method. Using Fourier transform, we have investigated the energy levels as functions of the geometrical parameters of the rings and compared our results with those obtained by the analytical integral method. The results show that the energy levels in the quantum rings change dramatically with the inner radius, outer radius, average radius, width, height of the ring and the distance between two adjacent rings. Our method can be adopted in low-dimensional structures with arbitrary shape. Our results are consistent with those in the literature and should be helpful for studying and fabricating optoelectronic devices

Numerical calculation of acoustic radiation from band-vibrating structures via FEM/FAQP method

Directory of Open Access Journals (Sweden)

GAO Honglin

2017-08-01

Full Text Available The Finite Element Method (FEM combined with the Frequency Averaged Quadratic Pressure method (FAQP are used to calculate the acoustic radiation of structures excited in the frequency band. The surface particle velocity of stiffened cylindrical shells under frequency band excitation is calculated using finite element software, the normal vibration velocity is converted from the surface particle velocity to calculate the average energy source (frequency averaged across intensity, frequency averaged across pressure and frequency averaged across velocity, and the FAQP method is used to calculate the average sound pressure level within the bandwidth. The average sound pressure levels are then compared with the bandwidth using finite element and boundary element software, and the results show that FEM combined with FAQP is more suitable for high frequencies and can be used to calculate the average sound pressure level in the 1/3 octave band with good stability, presenting an alternative to applying frequency-by-frequency calculation and the average frequency process. The FEM/FAQP method can be used as a prediction method for calculating acoustic radiation while taking the randomness of vibration at medium and high frequencies into consideration.

Enhanced photocatalytic activity of titania with unique surface indium and boron species

International Nuclear Information System (INIS)

Yu, Yanlong; Wang, Enjun; Yuan, Jixiang; Cao, Yaan

2013-01-01

Indium and boron co-doped TiO 2 photocatalysts were prepared by a sol–gel method. The structure and properties of photocatalysts were characterized by XRD, BET, XPS, UV–vis DRS and PL techniques. It is found that boron is mainly doped into the lattice of TiO 2 in interstitial mode, while indium is present as unique chemical species of O–In–Cl x (x = 1 or 2) on the surface. Compared with pure TiO 2 , the narrowness of band gap of TiO 2 doped with indium and boron is due to the mixed valence band formed by B2p of interstitial doped B ions hybridized with lattice O2p. And the surface state energy levels of O–In–Cl x (x = 1 or 2) and B 2 O 3 species were located at about 0.4 and 0.3 eV below the conduction band respectively, which could lead to significant absorption in the visible-light region and facilitated the effectually separation of photogenerated carriers. Therefore, indium and boron co-doped TiO 2 showed the much higher photocatalytic activities than pure TiO 2 , boron doped TiO 2 (TiO 2 –B) and indium doped TiO 2 (TiO 2 –In) under visible and UV light irradiation.

S-band and X-band integrated PWT photoelectron linacs

International Nuclear Information System (INIS)

Yu, D.; Newsham, D.; Zeng, J.; Rosenzweig, J.

2001-01-01

A compact high-energy injector, which has been developed by DULY Research Inc., will have wide scientific, industrial, and medical applications. The new photoelectron injector integrates the photocathode directly into a multicell linear accelerator. By focusing the beam with solenoids or permanent magnets, and producing high current with low emittance, high brightness and low energy spread are achieved. In addition to providing a small footprint and improved beam quality in an integrated structure, the compact system considerably simplifies external subsystems required to operate the photoelectron linac, including rf power transport, beam focusing, vacuum and cooling. The photoelectron linac employs an innovative Plane-Wave-Transformer (PWT) design, which provides strong cell-to-cell coupling, relaxes manufacturing tolerances and facilitates the attachment of external ports to the compact structure with minimal field interference. DULY Research Inc. under the support of the DOE Small Business Innovation Research (SBIR) program, has developed, constructed and installed a 20-MeV, S-band compact electron source at UCLA. Cold test results for this device are presented. DULY Research is also actively engaged in the development of an X-band photoelectron linear accelerator in a SBIR project. When completed, the higher frequency structure will be approximately three times smaller. Design considerations for this device are discussed following the S-band cold test results

Correlation between morphology, electron band structure, and resistivity of Pb atomic chains on the Si(5 5 3)-Au surface

International Nuclear Information System (INIS)

Jałochowski, M; Kwapiński, T; Łukasik, P; Nita, P; Kopciuszyński, M

2016-01-01

Structural and electron transport properties of multiple Pb atomic chains fabricated on the Si(5 5 3)-Au surface are investigated using scanning tunneling spectroscopy, reflection high electron energy diffraction, angular resolved photoemission electron spectroscopy and in situ electrical resistance. The study shows that Pb atomic chains growth modulates the electron band structure of pristine Si(5 5 3)-Au surface and hence changes its sheet resistivity. Strong correlation between chains morphology, electron band structure and electron transport properties is found. To explain experimental findings a theoretical tight-binding model of multiple atomic chains interacting on effective substrate is proposed. (paper)

Physical properties and band structure of reactive molecular beam epitaxy grown oxygen engineered HfO{sub 2{+-}x}

Energy Technology Data Exchange (ETDEWEB)

Hildebrandt, Erwin; Kurian, Jose; Alff, Lambert [Institute of Materials Science, Technische Universitaet Darmstadt, 64287 Darmstadt (Germany)

2012-12-01

We have conducted a detailed thin film growth structure of oxygen engineered monoclinic HfO{sub 2{+-}x} grown by reactive molecular beam epitaxy. The oxidation conditions induce a switching between (111) and (002) texture of hafnium oxide. The band gap of oxygen deficient hafnia decreases with increasing amount of oxygen vacancies by more than 1 eV. For high oxygen vacancy concentrations, defect bands form inside the band gap that induce optical transitions and p-type conductivity. The resistivity changes by several orders of magnitude as a function of oxidation conditions. Oxygen vacancies do not give rise to ferromagnetic behavior.

Band parameters of phosphorene

International Nuclear Information System (INIS)

Lew Yan Voon, L C; Wang, J; Zhang, Y; Willatzen, M

2015-01-01

Phosphorene is a two-dimensional nanomaterial with a direct band-gap at the Brillouin zone center. In this paper, we present a recently derived effective-mass theory of the band structure in the presence of strain and electric field, based upon group theory. Band parameters for this theory are computed using a first-principles theory based upon the generalized-gradient approximation to the density-functional theory. These parameters and Hamiltonian will be useful for modeling physical properties of phosphorene. (paper)

Band-gap and band-edge engineering of multicomponent garnet scintillators from first principles

Czech Academy of Sciences Publication Activity Database

Yadav, S.K.; Uberuaga, B.P.; Nikl, Martin; Jiang, C.; Stanek, C.R.

2015-01-01

Roč. 4, č. 5 (2015), "054012-1"-"054012-9" ISSN 2331-7019 R&D Projects: GA ČR GAP204/12/0805 Institutional support: RVO:68378271 Keywords : scintillator * electronic band gap structure * garnets * band gap engineering Subject RIV: BM - Solid Matter Physics ; Magnetism Impact factor: 4.061, year: 2015

Strain gradient drives shear banding in metallic glasses

Science.gov (United States)

Tian, Zhi-Li; Wang, Yun-Jiang; Chen, Yan; Dai, Lan-Hong

2017-09-01

Shear banding is a nucleation-controlled process in metallic glasses (MGs) involving multiple temporal-spatial scales, which hinders a concrete understanding of its structural origin down to the atomic scale. Here, inspired by the morphology of composite materials, we propose a different perspective of MGs as a hard particle-reinforced material based on atomic-scale structural heterogeneity. The local stable structures indicated by a high level of local fivefold symmetry (L5FS) act as hard "particles" which are embedded in the relatively soft matrix. We demonstrate this concept by performing atomistic simulations of shear banding in CuZr MG. A shear band is prone to form in a sample with a high degree of L5FS which is slowly quenched from the liquid. An atomic-scale analysis on strain and the structural evolution reveals that it is the strain gradient effect that has originated from structural heterogeneity that facilitates shear transformation zones (STZs) to mature shear bands. An artificial composite model with a high degree of strain gradient, generated by inserting hard MG strips into a soft MG matrix, demonstrates a great propensity for shear banding. It therefore confirms the critical role strain gradient plays in shear banding. The strain gradient effect on shear banding is further quantified with a continuum model and a mechanical instability analysis. These physical insights might highlight the strain gradient as the hidden driving force in transforming STZs into shear bands in MGs.

Momentum-Space Imaging of the Dirac Band Structure in Molecular Graphene via Quasiparticle Interference

Science.gov (United States)

Stephenson, Anna; Gomes, Kenjiro K.; Ko, Wonhee; Mar, Warren; Manoharan, Hari C.

2014-03-01

Molecular graphene is a nanoscale artificial lattice composed of carbon monoxide molecules arranged one by one, realizing a dream of exploring exotic quantum materials by design. This assembly is done by atomic manipulation with a scanning tunneling microscope (STM) on a Cu(111) surface. To directly probe the transformation of normal surface state electrons into massless Dirac fermions, we map the momentum space dispersion through the Fourier analysis of quasiparticle scattering maps acquired at different energies with the STM. The Fourier analysis not only bridges the real-space and momentum-space data but also reveals the chiral nature of those quasiparticles, through a set of selection rules of allowed scattering involving the pseudospin and valley degrees of freedom. The graphene-like band structure can be reshaped with simple alterations to the lattice, such as the addition of a strain. We analyze the effect on the momentum space band structure of multiple types of strain on our system. Supported by DOE, Office of Basic Energy Sciences, Division of Materials Sciences and Engineering under contract DE-AC02-76SF00515.

Band structure of TiO sub 2 -doped yttria-stabilized zirconia probed by soft-x-ray spectroscopy

CERN Document Server

Higuchi, T; Kobayashi, K; Yamaguchi, S; Fukushima, A; Shin, S

2003-01-01

The electronic structure of TiO sub 2 -doped yttria-stabilized zirconia (YSZ) has been studied by soft-X-ray emission spectroscopy (SXES) and X-ray absorption spectroscopy (XAS). The valence band is mainly composed of the O 2p state. The O 1s XAS spectrum exhibits the existence of the Ti 3d unoccupied state under the Zr 4d conduction band. The intensity of the Ti 3d unoccupied state increases with increasing TiO sub 2 concentration. The energy separation between the top of the valence band and the bottom of the Ti 3d unoccupied state is in accord with the energy gap, as expected from dc-polarization and total conductivity measurements. (author)

Study of the structure of yrast bands of neutron-rich 114-124Pd isotopes

Science.gov (United States)

Chaudhary, Ritu; Devi, Rani; Khosa, S. K.

2018-02-01

The projected shell model calculations have been carried out in the neutron-rich 114-124Pd isotopic mass chain. The results have been obtained for the deformation systematics of E(2+1) and E(4+1)/E({2}+1) values, BCS subshell occupation numbers, yrast spectra, backbending phenomena, B( E2) transition probabilities and g-factors in these nuclei. The observed systematics of E(2+1) values and R_{42} ratios in the 114-124Pd isotopic mass chain indicate that there is a decrease of collectivity as the neutron number increases from 68 to 78. The occurrence of backbending in these nuclei as well as the changes in the calculated B( E2) transition probabilities and g -factors predict that there are changes in the structure of yrast bands in these nuclei. These changes occur at the spin where there is crossing of g-band by 2-qp bands. The predicted backbendings and predicted values of B( E2)s and g-factors in some of the isotopes need to be confirmed experimentally.

Demonstration of molecular beam epitaxy and a semiconducting band structure for I-Mn-V compounds

International Nuclear Information System (INIS)

Jungwirth, T.; Novak, V.; Cukr, M.; Zemek, J.; Marti, X.; Horodyska, P.; Nemec, P.; Holy, V.; Maca, F.; Shick, A. B.; Masek, J.; Kuzel, P.; Nemec, I.; Gallagher, B. L.; Campion, R. P.; Foxon, C. T.; Wunderlich, J.

2011-01-01

Our ab initio theory calculations predict a semiconducting band structure of I-Mn-V compounds. We demonstrate on LiMnAs that high-quality materials with group-I alkali metals in the crystal structure can be grown by molecular beam epitaxy. Optical measurements on the LiMnAs epilayers are consistent with the theoretical electronic structure. Our calculations also reproduce earlier reports of high antiferromagnetic ordering temperature and predict large, spin-orbit-coupling-induced magnetic anisotropy effects. We propose a strategy for employing antiferromagnetic semiconductors in high-temperature semiconductor spintronics.

Current state of X-band accelerating structure high gradient test. Be held at high energy accelerator organization on April 15, 2005

International Nuclear Information System (INIS)

Watanabe, Ken; Higo, Toshiyasu

2005-01-01

XTF (X-band Test Facility, Old name is GLCTA) is the high gradient test facility for X-band acceleration. We have installed an X-band 60cm structure (KX01) in the April 2004 and have been processing it for more than 10 months. Now it is under test on long-term operation. We report here the high gradient test result to date. (author)

Defect induced structural inhomogeneity, ultraviolet light emission and near-band-edge photoluminescence broadening in degenerate In2O3 nanowires

Science.gov (United States)

Mukherjee, Souvik; Sarkar, Ketaki; Wiederrecht, Gary P.; Schaller, Richard D.; Gosztola, David J.; Stroscio, Michael A.; Dutta, Mitra

2018-04-01

We demonstrate here defect induced changes on the morphology and surface properties of indium oxide (In2O3) nanowires and further study their effects on the near-band-edge (NBE) emission, thereby showing the significant influence of surface states on In2O3 nanostructure based device characteristics for potential optoelectronic applications. In2O3 nanowires with cubic crystal structure (c-In2O3) were synthesized via carbothermal reduction technique using a gold-catalyst-assisted vapor-liquid-solid method. Onset of strong optical absorption could be observed at energies greater than 3.5 eV consistent with highly n-type characteristics due to unintentional doping from oxygen vacancy ({V}{{O}}) defects as confirmed using Raman spectroscopy. A combination of high resolution transmission electron microscopy, x-ray photoelectron spectroscopy and valence band analysis on the nanowire morphology and stoichiometry reveals presence of high-density of {V}{{O}} defects on the surface of the nanowires. As a result, chemisorbed oxygen species can be observed leading to upward band bending at the surface which corresponds to a smaller valence band offset of 2.15 eV. Temperature dependent photoluminescence (PL) spectroscopy was used to study the nature of the defect states and the influence of the surface states on the electronic band structure and NBE emission has been discussed. Our data reveals significant broadening of the NBE PL peak consistent with impurity band broadening leading to band-tailing effect from heavy doping.

Measurement of the nucleon structure function in the deep inelastic neutrino-iron scattering with a wide-band neutrino beam

International Nuclear Information System (INIS)

Flottmann, T.

1982-01-01

In this thesis the nucleon structure function xF 3 is determined from the inclusive measurement of the deep inelastic neutrino nucleon charged current interaction. The data were taken in the CERN wide band neutrino beam using the detector of the CERN-Dortmund-Heidelberg-Saclay collaboration. This detector serves at the same time as target, as hadron energy calorimeter and as muon spectrometer. One major aspect of this work was to study the possibility of using high statistics wide band beam data for structure function analysis. The systematic errors specific to this kind of beam are investigated. To obtain the differential cross sections about 100000 neutrino and 75000 antineutrino events in the energy range 20-200 GeV are analysed. The differential cross sections are normalized to the total cross sections, as measured in the narrow band beam by the same collaboration. The calculated structure function xF 3 shows significant deviations from scaling. These scaling violations are compared quantitatively with the predictions of quantum chromodynamics. (orig.) [de

Consideration of relativistic effects in band structure calculations based on the empirical tight-binding method

International Nuclear Information System (INIS)

Hanke, M.; Hennig, D.; Kaschte, A.; Koeppen, M.

1988-01-01

The energy band structure of cadmium telluride and mercury telluride materials is investigated by means of the tight-binding (TB) method considering relativistic effects and the spin-orbit interaction. Taking into account relativistic effects in the method is rather simple though the size of the Hamilton matrix doubles. Such considerations are necessary for the interesting small-interstice semiconductors, and the experimental results are reflected correctly in the band structures. The transformation behaviour of the eigenvectors within the Brillouin zone gets more complicated, but is, nevertheless, theoretically controllable. If, however, the matrix elements of the Green operator are to be calculated, one has to use formula manipulation programmes in particular for non-diagonal elements. For defect calculations by the Koster-Slater theory of scattering it is necessary to know these matrix elements. Knowledge of the transformation behaviour of eigenfunctions saves frequent diagonalization of the Hamilton matrix and thus permits a numerical solution of the problem. Corresponding results for the sp 3 basis are available

Three-dimensional ordered particulate structures: Method to retrieve characteristics from photonic band gap data

International Nuclear Information System (INIS)

Miskevich, Alexander A.; Loiko, Valery A.

2015-01-01

A method to retrieve characteristics of ordered particulate structures, such as photonic crystals, is proposed. It is based on the solution of the inverse problem using data on the photonic band gap (PBG). The quasicrystalline approximation (QCA) of the theory of multiple scattering of waves and the transfer matrix method (TMM) are used. Retrieval of the refractive index of particles is demonstrated. Refractive indices of the artificial opal particles are estimated using the published experimental data. - Highlights: • A method to retrieve characteristics of photonic crystals is proposed. • The method is based on the inverse problem solution using the photonic band gap data. • Retrieval of the refractive index of photonic crystal particles is demonstrated. • Retrieval results show inhomogeneous distribution of synthetic opal particle pores

Band-structure tailoring and surface passivation for highly efficient near-infrared responsive PbS quantum dot photovoltaics

Science.gov (United States)

Zhou, Ru; Niu, Haihong; Ji, Fengwei; Wan, Lei; Mao, Xiaoli; Guo, Huier; Xu, Jinzhang; Cao, Guozhong

2016-11-01

PbS is a promising light harvester for near-infrared (NIR) responsive quantum dot (QD) photovoltaics due to its narrow bulk band gap (0.41 eV) and large exciton Bohr radius (18 nm). However, the relatively low conduction band (CB) and high-density surface defects of PbS as two major drawbacks for its use in solar cells severely hamper the photovoltaic performance enhancement. In this work, a modified solution-based successive ionic layer adsorption and reaction (SILAR) utilizing mixed cationic precursors of Pb2+ and Cd2+ is explored, and such a scheme offers two benefits, band-structure tailoring and surface passivation. In-situ deposited CdS suppresses the excessive growth of PbS in the mesopores, thereby facilitating the favorable electron injection from PbS to TiO2 in view of the up-shifted CB level of QDs; the intimate interpenetration of two sulfides with each other leads to superior passivation of trap state defects on PbS, which suppresses the interfacial charge recombination. With the construction of photovoltaics based on such a hybrid (Pb,Cd)S/CdS configuration, impressive power conversion efficiency up to 4.08% has been reached, outperforming that of the conventional PbS/CdS pattern (2.95%). This work highlights the great importance of band-structure tailoring and surface passivation for constructing highly efficient PbS QD photovoltaics.

Band structure of metallic pyrochlore ruthenates Bi2Ru2O7 and Pb2Ru2O/sub 6.5/

International Nuclear Information System (INIS)

Hsu, W.Y.; Kasowski, R.V.; Miller, T.; Chiang, T.

1988-01-01

The band structure of Bi 2 Ru 2 O 7 and Pb 2 Ru 2 O/sub 6.5/ has been computed self-consistently from first principles for the first time by the pseudofunction method. We discover that the 6s bands of Bi and Pb are very deep and unlikely to contribute to the metallic behavior as previously believed. The unoccupied 6p bands, however, are only several eV above the Fermi energy and are mixed with the Ru 4d band at the Fermi surface via the framework O atoms, leading to band conduction and delocalized magnetic moments. The predicted location of the 6s bands and the location and width of the O 2p band are confirmed by synchrotron radiation and ultraviolet electron spectroscopy of single crystals

Determination of band structure parameters and the quasi-particle gap of CdSe quantum dots by cyclic voltammetry.

Science.gov (United States)

Inamdar, Shaukatali N; Ingole, Pravin P; Haram, Santosh K

2008-12-01

Band structure parameters such as the conduction band edge, the valence band edge and the quasi-particle gap of diffusing CdSe quantum dots (Q-dots) of various sizes were determined using cyclic voltammetry. These parameters are strongly dependent on the size of the Q-dots. The results obtained from voltammetric measurements are compared to spectroscopic and theoretical data. The fit obtained to the reported calculations based on the semi-empirical pseudopotential method (SEPM)-especially in the strong size-confinement region, is the best reported so far, according to our knowledge. For the smallest CdSe Q-dots, the difference between the quasi-particle gap and the optical band gap gives the electron-hole Coulombic interaction energy (J(e1,h1)). Interband states seen in the photoluminescence spectra were verified with cyclic voltammetry measurements.

Optical model with multiple band couplings using soft rotator structure

Science.gov (United States)

Martyanov, Dmitry; Soukhovitskii, Efrem; Capote, Roberto; Quesada, Jose Manuel; Chiba, Satoshi

2017-09-01

A new dispersive coupled-channel optical model (DCCOM) is derived that describes nucleon scattering on 238U and 232Th targets using a soft-rotator-model (SRM) description of the collective levels of the target nucleus. SRM Hamiltonian parameters are adjusted to the observed collective levels of the target nucleus. SRM nuclear wave functions (mixed in K quantum number) have been used to calculate coupling matrix elements of the generalized optical model. Five rotational bands are coupled: the ground-state band, β-, γ-, non-axial- bands, and a negative parity band. Such coupling scheme includes almost all levels below 1.2 MeV of excitation energy of targets. The "effective" deformations that define inter-band couplings are derived from SRM Hamiltonian parameters. Conservation of nuclear volume is enforced by introducing a monopolar deformed potential leading to additional couplings between rotational bands. The present DCCOM describes the total cross section differences between 238U and 232Th targets within experimental uncertainty from 50 keV up to 200 MeV of neutron incident energy. SRM couplings and volume conservation allow a precise calculation of the compound-nucleus (CN) formation cross sections, which is significantly different from the one calculated with rigid-rotor potentials with any number of coupled levels.

Band structure of Heusler compounds studied by photoemission and tunneling spectroscopy

Energy Technology Data Exchange (ETDEWEB)

Arbelo Jorge, Elena

2011-07-01

Heusler compounds are key materials for spintronic applications. They have attracted a lot of interest due to their half-metallic properties predicted by band structure calculations. The aim of this work is to evaluate experimentally the validity of the predictions of half metallicity by band structure calculations for two specific Heusler compounds, Co{sub 2}FeAl{sub 0.3}Si{sub 0.7} and Co{sub 2}MnGa. Two different spectroscopy methods for the analysis of the electronic properties were used: Angular Resolved Ultraviolet Photoemission Spectroscopy (ARUPS) and Tunneling Spectroscopy. Heusler compounds are prepared as thin films by RF-sputtering in an ultra high vacuum system. For the characterization of the samples, bulk and surface crystallographic and magnetic properties of Co{sub 2}FeAl{sub 0.3}Si{sub 0.7} and Co{sub 2}MnGa are studied. X-ray and electron diffraction reveal a bulk and surface crossover between two different types of sublattice order (from B2 to L2{sub 1}) with increasing annealing temperature. X-ray magnetic circular dichroism results show that the magnetic properties in the surface and bulk are identical, although the magnetic moments obtained are 5 % below from the theoretically predicted. By ARUPS evidence for the validity of the predicted total bulk density of states (DOS) was demonstrated for both Heusler compounds. Additional ARUPS intensity contributions close to the Fermi energy indicates the presence of a specific surface DOS. Moreover, it is demonstrated that the crystallographic order, controlled by annealing, plays an important role on broadening effects of DOS features. Improving order resulted in better defined ARUPS features. Tunneling magnetoresistance measurements of Co{sub 2}FeAl{sub 0.3}Si{sub 0.7} and Co{sub 2}MnGa based MTJ's result in a Co{sub 2}FeAl{sub 0.3}Si{sub 0.7} spin polarization of 44 %, which is the highest experimentally obtained value for this compound, although it is lower than the 100 % predicted. For Co

A theoretical study of pressure-induced phase transitions and electronic band structure of anti-A-sesquioxide type γ-Be3N2

International Nuclear Information System (INIS)

Paliwal, Uttam; Joshi, Kunj Bihari

2011-01-01

Structural parameters and electronic band structure of anti-A-sesquioxide (aAs) type γ-Be 3 N 2 are presented following the first-principles linear combination of atomic orbitals method within the framework of a posteriori density-functional theory implemented in the CRYSTAL code. Pressure-induced phase transitions among the four polymorphs α, β, cubic-γ and aAs-γ of Be 3 N 2 are examined. Enthalpy-pressure curves do not show the possibility of pressure-induced structural phase transition to the cubic-γ phase. However, α → aAs-γ and β → aAs-γ structural phase transitions are observed at 139 GPa and 93 GPa, respectively. Band structure calculations predict that aAs-γ Be 3 N 2 is an indirect semiconductor with 4.73 eV bandgap at L point. Variation of bandgap with pressure and deformation potentials are studied for the α, β and aAs-γ polymorphs. Pressure-dependent band structure calculations reveal that, within the low-pressure limit, bandgaps of β and aAs-γ increase with pressure unlike α-Be 3 N 2 .

Experimental determination of conduction and valence bands of semiconductor nanoparticles using Kelvin probe force microscopy