Valence Band Structure of InAs1−xBix and InSb1−xBix Alloy Semiconductors Calculated Using Valence Band Anticrossing Model

Science.gov (United States)

Samajdar, D. P.; Dhar, S.

2014-01-01

The valence band anticrossing model has been used to calculate the heavy/light hole and spin-orbit split-off energies in InAs1−xBix and InSb1−xBix alloy systems. It is found that both the heavy/light hole, and spin-orbit split E + levels move upwards in energy with an increase in Bi content in the alloy, whereas the split E − energy for the holes shows a reverse trend. The model is also used to calculate the reduction of band gap energy with an increase in Bi mole fraction. The calculated values of band gap variation agree well with the available experimental data. PMID:24592181

Features of carrier tunneling between the silicon valence band and metal in devices based on the Al/high-K oxide/SiO_2/Si structure

International Nuclear Information System (INIS)

Vexler, M. I.; Grekhov, I. V.

2016-01-01

The features of electron tunneling from or into the silicon valence band in a metal–insulator–semiconductor system with the HfO_2(ZrO_2)/SiO_2 double-layer insulator are theoretically analyzed for different modes. It is demonstrated that the valence-band current plays a less important role in structures with HfO_2(ZrO_2)/SiO_2 than in structures containing only silicon dioxide. In the case of a very wide-gap high-K oxide ZrO_2, nonmonotonic behavior related to tunneling through the upper barrier is predicted for the valence-band–metal current component. The use of an insulator stack can offer certain advantages for some devices, including diodes, bipolar tunnel-emitter transistors, and resonant-tunneling diodes, along with the traditional use of high-K insulators in a field-effect transistor.

Spectroscopic determination of valence band parameters in InP

International Nuclear Information System (INIS)

Lewis, R.A.; Lough, B.C.C.

2003-01-01

Full text: The general form of the Hamiltonian for an electron or hole in a semiconductor has been given by Luttinger. The valence band is characterised by three parameters - γ 1 , γ 2 , γ 3 -now commonly known as the Luttinger parameters. Despite many investigations there is still considerable uncertainty regarding the Luttinger parameters of InP. The situation has been reviewed by Hackenberg et al. These authors themselves sought to determine the Luttinger parameters by hot-electron luminescence and discovered that many Luttinger parameter triplets were consistent with their data. We employ a spectroscopic approach to estimating valence-band parameters in InP. Calculations have been made for both the unperturbed energy levels and the energy levels in a magnetic field of acceptor impurities in semiconductors characterised by different Luttinger parameters. We compare our recent experimental data for the transitions associated with the Zn acceptor impurity in InP in magnetic fields up to 30 T to determine the most appropriate set of valence-band parameters for InP

Valence band structure of PDMS surface and a blend with MWCNTs: A UPS and MIES study of an insulating polymer

Energy Technology Data Exchange (ETDEWEB)

Schmerl, Natalya M.; Khodakov, Dmitriy A.; Stapleton, Andrew J.; Ellis, Amanda V.; Andersson, Gunther G., E-mail: gunther.andersson@flinders.edu.au

2015-10-30

Graphical abstract: - Highlights: • Valence electron spectroscopy was performed on an insulating polymer using different charge compensation methods. • MWCNT were embedded in PDMS and found to be the most effective method for reducing the charging of the insulating polymer. • The valence band spectrum of PDMS was obtained via MIES and UPS. • Ion scattering spectroscopy was used to determine the concentration depth profile of the PDMS in the sample. - Abstract: The use of polydimethylsiloxane (PDMS) is increasing with new technologies working toward compact, flexible and transparent devices for use in medical and microfluidic systems. Electronic characterization of PDMS and other insulating materials is difficult due to charging, yet necessary for many applications where the interfacial structure is vital to device function or further modification. The outermost layer in particular is of importance as this is the area where chemical reactions such as surface functionalization will occur. Here, we investigate the valence band structure of the outermost layer and near surface area of PDMS through the use of metastable induced photoelectron spectroscopy (MIES) paired with ultraviolet photoelectron spectroscopy (UPS). The chemical composition of the samples under investigation were measured via X-ray photoelectron spectroscopy (XPS), and the vertical distribution of the polymer was shown with neutral impact collision ion scattering spectroscopy (NICISS). Three separate methods for charge compensation are used for the samples, and their effectiveness is compared.

Band width and multiple-angle valence-state mapping of diamond

International Nuclear Information System (INIS)

Jimenez, I.; Terminello, L.J.; Sutherland, D.G.J.

1997-01-01

The band width may be considered the single most important parameter characterizing the electronic structure of a solid. The ratio of band width and Coulomb repulsion determines how correlated or delocalized an electron system is. Some of the most interesting solids straddle the boundary between localized and delocalized, e.g. the high-temperature superconductors. The bulk of the band calculations available today is based on local density functional (DF) theory. Even though the Kohn-Sham eigenvalues from that theory do not represent the outcome of a band-mapping experiment, they are remarkably similar to the bands mapped via photoemission. Strictly speaking, one should use an excited state calculation that takes the solid's many-body screening response to the hole created in photoemission into account. Diamond is a useful prototype semiconductor because of its low atomic number and large band width, which has made it a long-time favorite for testing band theory. Yet, the two experimental values of the band width of diamond have error bars of ±1 eV and differ by 3.2 eV. To obtain an accurate valence band width for diamond, the authors use a band-mapping method that collects momentum distributions instead of the usual energy distributions. This method has undergone extensive experimental and theoretical tests in determining the band width of lithium fluoride. An efficient, imaging photoelectron spectrometer is coupled with a state-of-the-art undulator beam line at the Advanced Light Source to allow collection of a large number of data sets. Since it takes only a few seconds to take a picture of the photoelectrons emitted into a 84 degrees cone, the authors can use photon energies as high as 350 eV where the cross section for photoemission from the valence band is already quite low, but the emitted photoelectrons behave free-electron-like. This make its much easier to locate the origin of the inter-band transitions in momentum space

Band width and multiple-angle valence-state mapping of diamond

Energy Technology Data Exchange (ETDEWEB)

Jimenez, I.; Terminello, L.J.; Sutherland, D.G.J. [Lawrence Berkeley National Lab., CA (United States)] [and others

1997-04-01

The band width may be considered the single most important parameter characterizing the electronic structure of a solid. The ratio of band width and Coulomb repulsion determines how correlated or delocalized an electron system is. Some of the most interesting solids straddle the boundary between localized and delocalized, e.g. the high-temperature superconductors. The bulk of the band calculations available today is based on local density functional (DF) theory. Even though the Kohn-Sham eigenvalues from that theory do not represent the outcome of a band-mapping experiment, they are remarkably similar to the bands mapped via photoemission. Strictly speaking, one should use an excited state calculation that takes the solid`s many-body screening response to the hole created in photoemission into account. Diamond is a useful prototype semiconductor because of its low atomic number and large band width, which has made it a long-time favorite for testing band theory. Yet, the two experimental values of the band width of diamond have error bars of {+-}1 eV and differ by 3.2 eV. To obtain an accurate valence band width for diamond, the authors use a band-mapping method that collects momentum distributions instead of the usual energy distributions. This method has undergone extensive experimental and theoretical tests in determining the band width of lithium fluoride. An efficient, imaging photoelectron spectrometer is coupled with a state-of-the-art undulator beam line at the Advanced Light Source to allow collection of a large number of data sets. Since it takes only a few seconds to take a picture of the photoelectrons emitted into a 84{degrees} cone, the authors can use photon energies as high as 350 eV where the cross section for photoemission from the valence band is already quite low, but the emitted photoelectrons behave free-electron-like. This make its much easier to locate the origin of the inter-band transitions in momentum space.

A Comparison of the Valence Band Structure of Bulk and Epitaxial GeTe-based Diluted Magnetic Semiconductors

International Nuclear Information System (INIS)

Pietrzyk, M.A.; Kowalski, B.J.; Orlowski, B.A.; Knoff, W.; Story, T.; Dobrowolski, W.; Slynko, V.E.; Slynko, E.I.; Johnson, R.L.

2010-01-01

In this work we present a comparison of the experimental results, which have been obtained by the resonant photoelectron spectroscopy for a set of selected diluted magnetic semiconductors based on GeTe, doped with manganese. The photoemission spectra are acquired for the photon energy range of 40-60 eV, corresponding to the Mn 3p → 3d resonances. The spectral features related to Mn 3d states are revealed in the emission from the valence band. The Mn 3d states contribution manifests itself in the whole valence band with a maximum at the binding energy of 3.8 eV. (authors)

The Synthesis of NiO/TiO2 Heterostructures and Their Valence Band Offset Determination

Directory of Open Access Journals (Sweden)

Z. H. Ibupoto

2014-01-01

Full Text Available In this work, a heterojunction based on p-type NiO/n-type TiO2 nanostructures has been prepared on the fluorine doped tin oxide (FTO glass substrate by hydrothermal method. Scanning electron microscopy (SEM and X-Ray diffraction techniques were used for the morphological and crystalline arrays characterization. The X-ray photoelectron spectroscopy was employed to determine the valence-band offset (VBO of the NiO/TiO2 heterojunction prepared on FTO glass substrate. The core levels of Ni 2p and Ti 2p were utilized to align the valence-band offset of p-type NiO/n-type TiO2 heterojunction. The valence band offset was found to be ∼0.41 eV and the conduction band was calculated about ∼0.91 eV. The ratio of conduction band offset and the valence-band offset was found to be 2.21.

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).

Valence band structure and density of states effective mass model of biaxial tensile strained silicon based on k · p theory

International Nuclear Information System (INIS)

Kuang Qian-Wei; Liu Hong-Xia; Wang Shu-Long; Qin Shan-Shan; Wang Zhi-Lin

2011-01-01

After constructing a stress and strain model, the valence bands of in-plane biaxial tensile strained Si is calculated by k · p method. In the paper we calculate the accurate anisotropy valance bands and the splitting energy between light and heavy hole bands. The results show that the valance bands are highly distorted, and the anisotropy is more obvious. To obtain the density of states (DOS) effective mass, which is a very important parameter for device modeling, a DOS effective mass model of biaxial tensile strained Si is constructed based on the valance band calculation. This model can be directly used in the device model of metal—oxide semiconductor field effect transistor (MOSFET). It also a provides valuable reference for biaxial tensile strained silicon MOSFET design. (condensed matter: electronic structure, electrical, magnetic, and optical properties)

Nature of the valence band states in Bi2(Ca, Sr, La)3Cu2O8

International Nuclear Information System (INIS)

Wells, B.O.; Lindberg, P.A.P.; Shen, Z.; Dessau, D.S.; Spicer, W.E.; Lindau, I.; Mitzi, D.B.; Kapitulnik, A.

1990-01-01

We have used photoemission spectroscopy to examine the symmetry of the occupied states of the valence band for the La doped superconductor Bi 2 (Ca, Sr, La) 3 Cu 2 O 8 . While the oxygen states near the bottom of the 7 eV wide valence band exhibit predominantly O 2p z symmetry, the states at the top of the valence band extending to the Fermi level are found to have primarily O 2p x and O 2p y character. We have also examined anomalous intensity enhancements in the valence band feature for photon energies near 18 eV. These enhancements, which occur at photon energies ranging from 15.8 to 18.0 eV for the different valence band features, are not consistent with either simple final state effects or direct O2s transitions to unoccupied O2p states

Crossover and valence band Kβ X-rays of chromium oxides

International Nuclear Information System (INIS)

Fazinic, Stjepko; Mandic, Luka; Kavcic, Matjaz; Bozicevic, Iva

2011-01-01

Kβ X-ray spectra of chromium metal and selected chromium oxides were measured twice using medium resolution flat crystal spectrometer and high resolution spectrometer employing Johansson geometry after excitation with 2 MeV proton beams. The positions and intensities of crossover (Kβ'') and valence (Kβ 2,5 ) band X-rays relative to the primary Kβ X-ray components were extracted in a consistent way. The results were compared with the existing data obtained by proton and photon induced ionization mechanisms and theoretical predictions. The obtained results in peak relative positions and intensities were analyzed in order to study dependence on the chromium oxidation states and chromium-oxygen bond lengths in selected chromium oxides. Our results obtained by both spectrometers confirm that the linear trend observed for the valence peak relative energy shift as a function of chromium oxidation number does not depend on the experimental resolution. Experimental results for normalized intensities (i.e. relative intensities divided with the number of chromium-oxygen pairs) of crossover and valence band X-rays obtained by both spectrometers are in very good agreement, and follow exponential relationship with the average Cr-O bond lengths in corresponding chromium oxides. The observed trends in crossover and valence X-rays normalized intensities could be used to measure the average chromium-oxygen bond length in various chromium oxides, with the sum of both crossover and valence X-ray normalized intensities being the most sensitive measure.

Valence band offset of β-Ga2O3/wurtzite GaN heterostructure measured by X-ray photoelectron spectroscopy.

Science.gov (United States)

Wei, Wei; Qin, Zhixin; Fan, Shunfei; Li, Zhiwei; Shi, Kai; Zhu, Qinsheng; Zhang, Guoyi

2012-10-10

A sample of the β-Ga2O3/wurtzite GaN heterostructure has been grown by dry thermal oxidation of GaN on a sapphire substrate. X-ray diffraction measurements show that the β-Ga2O3 layer was formed epitaxially on GaN. The valence band offset of the β-Ga2O3/wurtzite GaN heterostructure is measured by X-ray photoelectron spectroscopy. It is demonstrated that the valence band of the β-Ga2O3/GaN structure is 1.40 ± 0.08 eV.

Convergence of valence bands for high thermoelectric performance for p-type InN

International Nuclear Information System (INIS)

Li, Hai-Zhu; Li, Ruo-Ping; Liu, Jun-Hui; Huang, Ming-Ju

2015-01-01

Band engineering to converge the bands to achieve high valley degeneracy is one of effective approaches for designing ideal thermoelectric materials. Convergence of many valleys in the valence band may lead to a high Seebeck coefficient, and induce promising thermoelectric performance of p-type InN. In the current work, we have systematically investigated the electronic structure and thermoelectric performance of wurtzite InN by using the density functional theory combined with semiclassical Boltzmann transport theory. Form the results, it can be found that intrinsic InN has a large Seebeck coefficient (254 μV/K) and the largest value of Z e T is 0.77. The transport properties of p-type InN are better than that of n-type one at the optimum carrier concentration, which mainly due to the large Seebeck coefficient for p-type InN, although the electrical conductivity of n-type InN is larger than that of p-type one. We found that the larger Seebeck coefficient for p-type InN may originate from the large valley degeneracy in the valence band. Moreover, the low minimum lattice thermal conductivity for InN is one key factor to become a good thermoelectric material. Therefore, p-type InN could be a potential material for further applications in the thermoelectric area.

Valence band electronic structure and band alignment of LaAlO{sub 3}/SrTiO{sub 3}(111) heterointerfaces

Energy Technology Data Exchange (ETDEWEB)

Gabel, J.; Scheiderer, P.; Zapf, M.; Schuetz, P.; Sing, M.; Claessen, R. [Physikalisches Institut and Roentgen Center for Complex Material Systems (RCCM), Universitaet Wuerzburg (Germany); Schlueter, C.; Lee, T.L. [Diamond Light Source, Didcot (United Kingdom)

2015-07-01

As in the famous LaAlO{sub 3}(LAO)/SrTiO{sub 3}(STO) (001) a two-dimensional electron system (2DES) also forms at the interface between LAO and STO in (111) orientation. A distinct feature of the (111) interface is its peculiar real space topology. Each bilayer represents a buckled honeycomb lattice similar to graphene which is known theoretically to host various topologically non-trivial states. Bilayer STO in proximity to the interface can be regarded as a three-orbital generalization of graphene with enhanced electron correlations making it a promising candidate for the realization of strongly correlated topological phases. We have investigated the electronic structure of the LAO/STO (111) heterostructure in relation to the oxygen vacancy concentration which we can control by synchrotron light irradiation and oxygen dosing. With hard X-ray photoemission we study the core levels, whereas resonant soft X-ray photoemission is used to probe the interfacial valence band (VB) states. Two VB features are found: a peak at the Fermi level associated with the 2DES and in-gap states at higher binding energies attributed to oxygen vacancies. By varying the oxygen vacancy contribution we can tune the emergence of the VB states and engineer the interfacial band alignment.

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

Valence-band and core-level photoemission study of single-crystal Bi2CaSr2Cu2O8 superconductors

International Nuclear Information System (INIS)

Shen, Z.; Lindberg, P.A.P.; Wells, B.O.; Mitzi, D.B.; Lindau, I.; Spicer, W.E.; Kapitulnik, A.

1988-01-01

High-quality single crystals of Bi 2 CaSr 2 Cu 2 O 8 superconductors have been prepared and cleaved in ultrahigh vacuum. Low-energy electron diffraction measurements show that the surface structure is consistent with the bulk crystal structure. Ultraviolet photoemission and x-ray photoemission experiments were performed on these well-characterized sample surfaces. The valence-band and the core-level spectra obtained from the single-crystal surfaces are in agreement with spectra recorded from polycrystalline samples, justifying earlier results from polycrystalline samples. Cu satellites are observed both in the valence band and Cu 2p core level, signaling the strong correlation among the Cu 3d electrons. The O 1s core-level data exhibit a sharp, single peak at 529-eV binding energy without any clear satellite structures

Valency and molecular structure

CERN Document Server

Cartmell, E

1977-01-01

Valency and Molecular Structure, Fourth Edition provides a comprehensive historical background and experimental foundations of theories and methods relating to valency and molecular structures. In this edition, the chapter on Bohr theory has been removed while some sections, such as structures of crystalline solids, have been expanded. Details of structures have also been revised and extended using the best available values for bond lengths and bond angles. Recent developments are mostly noted in the chapter on complex compounds, while a new chapter has been added to serve as an introduction t

First determination of the valence band dispersion of CH3NH3PbI3 hybrid organic-inorganic perovskite

Science.gov (United States)

Lee, Min-I.; Barragán, Ana; Nair, Maya N.; Jacques, Vincent L. R.; Le Bolloc'h, David; Fertey, Pierre; Jemli, Khaoula; Lédée, Ferdinand; Trippé-Allard, Gaëlle; Deleporte, Emmanuelle; Taleb-Ibrahimi, Amina; Tejeda, Antonio

2017-07-01

The family of hybrid organic-inorganic halide perovskites is in the limelight because of their recently discovered high photovoltaic efficiency. These materials combine photovoltaic energy conversion efficiencies exceeding 22% and low-temperature and low-cost processing in solution; a breakthrough in the panorama of renewable energy. Solar cell operation relies on the excitation of the valence band electrons to the conduction band by solar photons. One factor strongly impacting the absorption efficiency is the band dispersion. The band dispersion has been extensively studied theoretically, but no experimental information was available. Herein, we present the first experimental determination of the valence band dispersion of methylammonium lead halide in the tetragonal phase. Our results pave the way for contrasting the electronic hopping or the electron effective masses in different theories by comparing to our experimental bands. We also show a significant broadening of the electronic states, promoting relaxed conditions for photon absorption, and demonstrate that the tetragonal structure associated to the octahedra network distortion below 50 °C induces only a minor modification of the electronic bands, with respect to the cubic phase at high temperature, thus minimizing the impact of the cubic-tetragonal transition on solar cell efficiencies.

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

Accounting for many-body correlation effects in the calculation of the valence band photoelectron emission spectra of ferromagnets

International Nuclear Information System (INIS)

Minar, J.; Chadov, S.; Ebert, H.; Chioncel, L.; Lichtenstein, A.; De Nadai, C.; Brookes, N.B.

2005-01-01

The influence of dynamical correlation effects on the valence band photoelectron emission of ferromagnetic Fe, Co and Ni has been investigated. Angle-resolved as well as angle-integrated valence band photoelectron emission spectra were calculated on the basis of the one-particle Green's function, which was obtained by using the fully relativistic Korringa-Kohn-Rostoker method. The correlation effects have been included in terms of the electronic self-energy which was calculated self-consistently within Dynamical Mean-Field Theory (DMFT). In addition a theoretical approach to calculate high-energy angle-resolved valence band photoelectron emission spectra is presented

Auger electron emission initiated by the creation of valence-band holes in graphene by positron annihilation.

Science.gov (United States)

Chirayath, V A; Callewaert, V; Fairchild, A J; Chrysler, M D; Gladen, R W; Mcdonald, A D; Imam, S K; Shastry, K; Koymen, A R; Saniz, R; Barbiellini, B; Rajeshwar, K; Partoens, B; Weiss, A H

2017-07-13

Auger processes involving the filling of holes in the valence band are thought to make important contributions to the low-energy photoelectron and secondary electron spectrum from many solids. However, measurements of the energy spectrum and the efficiency with which electrons are emitted in this process remain elusive due to a large unrelated background resulting from primary beam-induced secondary electrons. Here, we report the direct measurement of the energy spectra of electrons emitted from single layer graphene as a result of the decay of deep holes in the valence band. These measurements were made possible by eliminating competing backgrounds by employing low-energy positrons (holes by annihilation. Our experimental results, supported by theoretical calculations, indicate that between 80 and 100% of the deep valence-band holes in graphene are filled via an Auger transition.

The complex band structure for armchair graphene nanoribbons

International Nuclear Information System (INIS)

Zhang Liu-Jun; Xia Tong-Sheng

2010-01-01

Using a tight binding transfer matrix method, we calculate the complex band structure of armchair graphene nanoribbons. The real part of the complex band structure calculated by the transfer matrix method fits well with the bulk band structure calculated by a Hermitian matrix. The complex band structure gives extra information on carrier's decay behaviour. The imaginary loop connects the conduction and valence band, and can profoundly affect the characteristics of nanoscale electronic device made with graphene nanoribbons. In this work, the complex band structure calculation includes not only the first nearest neighbour interaction, but also the effects of edge bond relaxation and the third nearest neighbour interaction. The band gap is classified into three classes. Due to the edge bond relaxation and the third nearest neighbour interaction term, it opens a band gap for N = 3M − 1. The band gap is almost unchanged for N = 3M + 1, but decreased for N = 3M. The maximum imaginary wave vector length provides additional information about the electrical characteristics of graphene nanoribbons, and is also classified into three classes

Spin-dependent electron-phonon coupling in the valence band of single-layer WS₂

DEFF Research Database (Denmark)

Hinsche, Nicki Frank; Ngankeu, Arlette S.; Guilloy, Kevin

2017-01-01

The absence of inversion symmetry leads to a strong spin-orbit splitting of the upper valence band of semiconducting single-layer transition-metal dichalchogenides such as MoS2 or WS2. This permits a direct comparison of the electron-phonon coupling strength in states that only differ by their spin....... Here, the electron-phonon coupling in the valence band maximum of single-layer WS2 is studied by first-principles calculations and angle-resolved photoemission. The coupling strength is found to be drastically different for the two spin-split branches, with calculated values of λK=0.0021 and 0.......40 for the upper and lower spin-split valence band of the freestanding layer, respectively. This difference is somewhat reduced when including scattering processes involving the Au(111) substrate present in the experiment but it remains significant, in good agreement with the experimental results....

Interplay of Coulomb interactions and disorder in three-dimensional quadratic band crossings without time-reversal symmetry and with unequal masses for conduction and valence bands

Science.gov (United States)

Mandal, Ipsita; Nandkishore, Rahul M.

2018-03-01

Coulomb interactions famously drive three-dimensional quadratic band crossing semimetals into a non-Fermi liquid phase of matter. In a previous work [Nandkishore and Parameswaran, Phys. Rev. B 95, 205106 (2017), 10.1103/PhysRevB.95.205106], the effect of disorder on this non-Fermi liquid phase was investigated, assuming that the band structure was isotropic, assuming that the conduction and valence bands had the same band mass, and assuming that the disorder preserved exact time-reversal symmetry and statistical isotropy. It was shown that the non-Fermi liquid fixed point is unstable to disorder and that a runaway flow to strong disorder occurs. In this paper, we extend that analysis by relaxing the assumption of time-reversal symmetry and allowing the electron and hole masses to differ (but continuing to assume isotropy of the low energy band structure). We first incorporate time-reversal symmetry breaking disorder and demonstrate that there do not appear any new fixed points. Moreover, while the system continues to flow to strong disorder, time-reversal-symmetry-breaking disorder grows asymptotically more slowly than time-reversal-symmetry-preserving disorder, which we therefore expect should dominate the strong-coupling phase. We then allow for unequal electron and hole masses. We show that whereas asymmetry in the two masses is irrelevant in the clean system, it is relevant in the presence of disorder, such that the `effective masses' of the conduction and valence bands should become sharply distinct in the low-energy limit. We calculate the RG flow equations for the disordered interacting system with unequal band masses and demonstrate that the problem exhibits a runaway flow to strong disorder. Along the runaway flow, time-reversal-symmetry-preserving disorder grows asymptotically more rapidly than both time-reversal-symmetry-breaking disorder and the Coulomb interaction.

Giant Cu 2p Resonances in CuO Valence-Band Photoemission

NARCIS (Netherlands)

Tjeng, L.H.; Chen, C.T.; Ghijsen, J.; Rudolf, P.; Sette, F.

1991-01-01

We report the observation of a giant resonance in the Cu 2p resonant-photoemission spectra of CuO. The study allows the unambiguous identification of the local Cu 3d8 configuration in the valence-band photoemission spectrum, providing conclusive evidence for the charge-transfer nature of the

The localized effect of the Bi level on the valence band in the dilute bismuth GaBixAs1-x alloy

Science.gov (United States)

Zhao, Chuan-Zhen; Zhu, Min-Min; Wang, Jun; Wang, Sha-Sha; Lu, Ke-Qing

2018-05-01

The research on the temperature dependence of the band gap energy of the dilute bismuth GaBixAs1-x alloy has been done. It is found that its temperature insensitiveness is due to the enhanced localized character of the valence band state and the small decrease of the temperature coefficient for the conduction band minimum (CBM). The enhanced localized character of the valence band state is the main factor. In order to describe the localized effect of the Bi levels on the valence band, the localized energy is introduced into the Varshni's equation. It is found that the effect of the localized Bi level on the valence band becomes strong with increasing Bi content. In addition, it is found that the pressure dependence of the band gap energy of GaBixAs1-x does not seem to be influenced by the localized Bi levels. It is due to two factors. One is that the pressure dependence of the band gap energy is mainly determined by the D CBM of GaBixAs1-x. The D CBM of GaBixAs1-x is not influenced by the localized Bi levels. The other is that the small variation of the pressure coefficient for the D valence band maximum (VBM) state of GaBixAs1-x can be cancelled by the variation of the pressure coefficient for the D CBM state of GaBixAs1-x.

Valence band offset of wurtzite InN/SrTiO3 heterojunction measured by x-ray photoelectron spectroscopy

Directory of Open Access Journals (Sweden)

Li Zhiwei

2011-01-01

Full Text Available Abstract The valence band offset (VBO of wurtzite indium nitride/strontium titanate (InN/SrTiO3 heterojunction has been directly measured by x-ray photoelectron spectroscopy. The VBO is determined to be 1.26 ± 0.23 eV and the conduction band offset is deduced to be 1.30 ± 0.23 eV, indicating the heterojunction has a type-I band alignment. The accurate determination of the valence and conduction band offsets paves a way to the applications of integrating InN with the functional oxide SrTiO3.

Electronic properties and bonding in Zr Hx thin films investigated by valence-band x-ray photoelectron spectroscopy

Science.gov (United States)

Magnuson, Martin; Schmidt, Susann; Hultman, Lars; Högberg, Hans

2017-11-01

The electronic structure and chemical bonding in reactively magnetron sputtered Zr Hx (x =0.15 , 0.30, 1.16) thin films with oxygen content as low as 0.2 at.% are investigated by 4d valence band, shallow 4p core-level, and 3d core-level x-ray photoelectron spectroscopy. With increasing hydrogen content, we observe significant reduction of the 4d valence states close to the Fermi level as a result of redistribution of intensity toward the H 1s-Zr 4d hybridization region at ˜6 eV below the Fermi level. For low hydrogen content (x =0.15 , 0.30), the films consist of a superposition of hexagonal closest-packed metal (α phase) and understoichiometric δ -Zr Hx (Ca F2 -type structure) phases, while for x =1.16 , the films form single-phase Zr Hx that largely resembles that of stoichiometric δ -Zr H2 phase. We show that the cubic δ -Zr Hx phase is metastable as thin film up to x =1.16 , while for higher H contents the structure is predicted to be tetragonally distorted. For the investigated Zr H1.16 film, we find chemical shifts of 0.68 and 0.51 eV toward higher binding energies for the Zr 4 p3 /2 and 3 d5 /2 peak positions, respectively. Compared to the Zr metal binding energies of 27.26 and 178.87 eV, this signifies a charge transfer from Zr to H atoms. The change in the electronic structure, spectral line shapes, and chemical shifts as a function of hydrogen content is discussed in relation to the charge transfer from Zr to H that affects the conductivity by charge redistribution in the valence band.

Tunneling emission of electrons from semiconductors' valence bands in high electric fields

International Nuclear Information System (INIS)

Kalganov, V. D.; Mileshkina, N. V.; Ostroumova, E. V.

2006-01-01

Tunneling emission currents of electrons from semiconductors to vacuum (needle-shaped GaAs photodetectors) and to a metal (silicon metal-insulator-semiconductor diodes with a tunneling-transparent insulator layer) are studied in high and ultrahigh electric fields. It is shown that, in semiconductors with the n-type conductivity, the major contribution to the emission current is made by the tunneling emission of electrons from the valence band of the semiconductor, rather than from the conduction band

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

Characterization of MBE-grown InAlN/GaN heterostructure valence band offsets with varying In composition

Energy Technology Data Exchange (ETDEWEB)

Jiao, Wenyuan, E-mail: wyjiaonju@gmail.com; Kong, Wei; Li, Jincheng; Kim, Tong-Ho; Brown, April S. [Department of Electrical and Computer Engineering, Duke University, Durham, NC, 27708 (United States); Collar, Kristen [Department of Physics, Duke University, Durham, NC, 27708 (United States); Losurdo, Maria [CNR-NANOTEC, Istituto di Nanotecnologia, via Orabona, 4-70126 Bari (Italy)

2016-03-15

Angle-resolved X-ray photoelectron spectroscopy (XPS) is used in this work to experimentally determine the valence band offsets of molecular beam epitaxy (MBE)-grown InAlN/GaN heterostructures with varying indium composition. We find that the internal electric field resulting from polarization must be taken into account when analyzing the XPS data. Valence band offsets of 0.12 eV for In{sub 0.18}Al{sub 0.82}N, 0.15 eV for In{sub 0.17}Al{sub 0.83}N, and 0.23 eV for In{sub 0.098}Al{sub 0.902}N with GaN are obtained. The results show that a compositional-depended bowing parameter is needed in order to estimate the valence band energies of InAlN as a function of composition in relation to those of the binary endpoints, AlN and InN.

Characterization of MBE-grown InAlN/GaN heterostructure valence band offsets with varying In composition

Directory of Open Access Journals (Sweden)

Wenyuan Jiao

2016-03-01

Full Text Available Angle-resolved X-ray photoelectron spectroscopy (XPS is used in this work to experimentally determine the valence band offsets of molecular beam epitaxy (MBE-grown InAlN/GaN heterostructures with varying indium composition. We find that the internal electric field resulting from polarization must be taken into account when analyzing the XPS data. Valence band offsets of 0.12 eV for In0.18Al0.82N, 0.15 eV for In0.17Al0.83N, and 0.23 eV for In0.098Al0.902N with GaN are obtained. The results show that a compositional-depended bowing parameter is needed in order to estimate the valence band energies of InAlN as a function of composition in relation to those of the binary endpoints, AlN and InN.

A Combined Theoretical and Experimental View on Valence and Conduction Band Densities of States of Lead Halide Perovskites

Science.gov (United States)

Kronik, Leeor; Endres, James; Egger, David A.; Kulbak, Michael; Kerner, Ross A.; Zhao, Lianfeng; Silver, Scott H.; Hodes, Gary; Rand, Barry P.; Cahen, David; Kahn, Antoine

We present results for the valence and conduction band density of states (DOS), measured via ultraviolet and inverse photoemission spectroscopies for three lead halide perovskites. Specifically, the DOS of MAPbI3, MAPbBr3, and CsPbBr3, grown on different substrates, are compared. Theoretical DOS, calculated via hybrid density functional theory and including spin-orbit coupling, are compared to experimental data. The agreement between experiment and theory, obtained after correcting the latter for quantitative discrepancies, leads to the identification of valence and conduction band spectral features. In particular, this comparison allows for precise determination of the energy position of the band edges, namely ionization energies and electron affinities of these materials. We find an unusually low DOS at the valence band maximum (VBM) of these systems, which confirms and generalizes previous findings of strong band dispersion and low DOS at the VBM of MAPbI3. This calls for special attention when using electron spectroscopy to determine the frontier electronic states of lead halide perovskites.

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.

Optical gain and gain suppression of quantum-well lasers with valence band mixing

International Nuclear Information System (INIS)

Ahn, D.; Chuang, S.L.

1990-01-01

The effects of valence band mixing on the nonlinear gains of quantum-well lasers are studied theoretically. The authors' analysis is based on the multiband effective-mass theory and the density matrix formalism with intraband relaxation taken into account. The gain and the gain-suppression coefficient of a quantum-well laser are calculated from the complex optical susceptibility obtained by the density matrix formulation with the theoretical dipole moments obtained from the multiband effective-mass theory. The calculated gain spectrum shows that there are remarkable differences (both in peak amplitude and spectral shape) between our model with valence band mixing and the conventional parabolic band model. The shape of the gain spectrum calculated by the authors' model becomes more symmetric due to intraband relaxation together with nonparabolic energy dispersions and is closer to the experimental observations when compared with the conventional method using the parabolic band model and the multiband effective-mass calculation without intraband relaxation. Both give quite asymmetric gain spectra. Optical intensity in the GaAs active region is estimated by solving rate equations for the stationary states with nonlinear gain suppression. The authors calculate the mode gain for the resonant mode including the gain suppression, which results in spectral hole burning of the gain spectrum

Deduction of the chemical state and the electronic structure of Nd{sub 2}Fe{sub 14}B compound from X-ray photoelectron spectroscopy core-level and valence-band spectra

Energy Technology Data Exchange (ETDEWEB)

Wang, Jing; Liang, Le [School of Materials Science and Engineering, Shanghai Jiao Tong University, Shanghai 200240 (China); Zhang, Lanting, E-mail: lantingzh@sjtu.edu.cn, E-mail: lmsun@sjtu.edu.cn [School of Materials Science and Engineering, Shanghai Jiao Tong University, Shanghai 200240 (China); Hirano Institute for Materials Innovation, Shanghai Jiao Tong University, Shanghai 200240 (China); Sun, Limin, E-mail: lantingzh@sjtu.edu.cn, E-mail: lmsun@sjtu.edu.cn [Instrumental Analysis Center, Shanghai Jiao Tong University, Shanghai 200240 (China); Hirano, Shinichi [Hirano Institute for Materials Innovation, Shanghai Jiao Tong University, Shanghai 200240 (China)

2014-10-28

Characterization of chemical state and electronic structure of the technologically important Nd{sub 2}Fe{sub 14}B compound is attractive for understanding the physical nature of its excellent magnetic properties. X-ray photoelectron spectroscopy (XPS) study of such rare-earth compound is important and also challenging due to the easy oxidation of surface and small photoelectron cross-sections of rare-earth 4f electrons and B 2p electrons, etc. Here, we reported an investigation based on XPS spectra of Nd{sub 2}Fe{sub 14}B compound as a function of Ar ion sputtering time. The chemical state of Fe and that of B in Nd{sub 2}Fe{sub 14}B compound can be clearly determined to be 0 and −3, respectively. The Nd in Nd{sub 2}Fe{sub 14}B compound is found to have the chemical state of close to +3 instead of +3 as compared with the Nd in Nd{sub 2}O{sub 3}. In addition, by comparing the valence-band spectrum of Nd{sub 2}Fe{sub 14}B compound to that of the pure Fe, the contributions from Nd, Fe, and B to the valence-band structure of Nd{sub 2}Fe{sub 14}B compound is made more clear. The B 2p states and B 2s states are identified to be at ∼11.2 eV and ∼24.6 eV, respectively, which is reported for the first time. The contribution from Nd 4f states can be identified both in XPS core-level spectrum and XPS valence-band spectrum. Although Nd 4f states partially hybridize with Fe 3d states, Nd 4f states are mainly localized in Nd{sub 2}Fe{sub 14}B compound.

Theory of two-photon absorption by exciton states in cubic semiconductors with degenerate valence bands

International Nuclear Information System (INIS)

Nguyen Ai Viet; Nguyen Toan Thang.

1987-06-01

The coefficient of the absorption of two polarized photons is calculated for direct band gap semiconductors with degenerate valence bands. Wannier-Mott exciton states are included in both the intermediate and final states. Numerical calculations are performed for ZnSe and are compared with Sondergeld's experimental and theoretical results. (author). 11 refs, 2 tabs

Valence band electronic structure of Ho-doped La0.67Ca0.33MnO3 using ultra-violet photoemission spectroscopy

Science.gov (United States)

Rout, S. K.; Mukharjee, R. N.; Mishra, D. K.; Roul, B. K.; Sekhar, B. R.; Dalai, M. K.

2017-05-01

In this manuscript we report the valence band electronic structure of Ho doped La0.67Ca0.33MnO3 using ultraviolet photoemission spectroscopy. We compared the density of states of La0.67Ca0.33MnO3, La0.67Ca0.3Ho0.03MnO3 and La0.64Ho0.03Ca0.33MnO3 near the Fermi level at various temperatures. Significant amount of changes have been observed at higher temperatures (220 K and 300 K) where the near Fermi level density of states increases with Ho doping into La0.67Ca0.33MnO3 indicating the enhancement of magnitude of change in metallicity (conductivity).

Internal-strain effect on the valence band of strained silicon and its correlation with the bond angles

Energy Technology Data Exchange (ETDEWEB)

Inaoka, Takeshi, E-mail: inaoka@phys.u-ryukyu.ac.jp; Yanagisawa, Susumu; Kadekawa, Yukihiro [Department of Physics and Earth Sciences, Faculty of Science, University of the Ryukyus, 1 Senbaru, Nishihara, Okinawa 903-0213 (Japan)

2014-02-14

By means of the first-principles density-functional theory, we investigate the effect of relative atom displacement in the crystal unit cell, namely, internal strain on the valence-band dispersion of strained silicon, and find close correlation of this effect with variation in the specific bond angles due to internal strain. We consider the [111] ([110]) band dispersion for (111) ((110)) biaxial tensility and [111] ([110]) uniaxial compression, because remarkably small values of hole effective mass m* can be obtained in this dispersion. Under the practical condition of no normal stress, biaxial tensility (uniaxial compression) involves additional normal compression (tensility) and internal strain. With an increase in the internal-strain parameter, the energy separation between the highest and second-highest valence bands becomes strikingly larger, and the highest band with conspicuously small m* extends remarkably down to a lower energy region, until it intersects or becomes admixed with the second band. This is closely correlated with the change in the specific bond angles, and this change can reasonably explain the above enlargement of the band separation.

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.

Determination of the impact of Bi content on the valence band energy of GaAsBi using x-ray photoelectron spectroscopy

Directory of Open Access Journals (Sweden)

K. Collar

2017-07-01

Full Text Available We investigate the change of the valence band energy of GaAs1-xBix (0valence band energy per addition of 1 % Bi is determined for strained and unstrained thin films using a linear approximation applicable to the dilute regime. Spectroscopic ellipsometry (SE was used as a complementary technique to determine the change in GaAsBi bandgap resulting from Bi addition. Analysis of SE and XPS data together supports the conclusion that ∼75% of the reduction in the bandgap is in the valence band for a compressively strained, dilute GaAsBi thin film at room temperature.

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.

On the theory of phonoriton in cubic semiconductors with a degenerate valence band

International Nuclear Information System (INIS)

Nguyen Ai Viet; Nguyen Thi Que Huong; Le Qui Thong

1992-10-01

The ''phonoriton'' is an elementary excitation constructed from an exciton polariton and phonon in semiconductors under intense excitation by an electromagnetic wave near the exciton resonance (L.V. Keldysh and A.L. Ivanov, 1982). In this paper we develop a theory of phonoriton in direct band gap cubic semiconductor with a degenerate valence band using the simple model of J.L. Birman and B.S. Wang (1990). In addition to experimental proofs of the existence of phonoriton we propose an experiment to measure its flight time. (author). 33 refs

Experimental determination of conduction and valence bands of semiconductor nanoparticles using Kelvin probe force microscopy

International Nuclear Information System (INIS)

Zhang Wen; Chen Yongsheng

2013-01-01

The ability to determine a semiconductor’s band edge positions is important for the design of new photocatalyst materials. In this paper, we introduced an experimental method based on Kelvin probe force microscopy to determine the conduction and valence band edge energies of semiconductor nanomaterials, which has rarely been demonstrated. We tested the method on six semiconductor nanoparticles (α-Fe 2 O 3 , CeO 2 , Al 2 O 3 , CuO, TiO 2 , and ZnO) with known electronic structures. The experimentally determined band edge positions for α-Fe 2 O 3 , Al 2 O 3 , and CuO well matched the literature values with no statistical difference. Except CeO 2 , all other metal oxides had a consistent upward bias in the experimental measurements of band edge positions because of the shielding effect of the adsorbed surface water layer. This experimental approach may outstand as a unique alternative way of probing the band edge energy positions of semiconductor materials to complement the current computational methods, which often find limitations in new synthetic or complex materials. Ultimately, this work provides scientific foundation for developing experimental tools to probe nanoscale electronic properties of photocatalytic materials, which will drive breakthroughs in the design of novel photocatalytic systems and advance the fundamental understanding of material properties.

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.

Valence and conduction band offsets at low-k a-SiO{sub x}C{sub y}:H/a-SiC{sub x}N{sub y}:H interfaces

Energy Technology Data Exchange (ETDEWEB)

King, Sean W., E-mail: sean.king@intel.com; Brockman, Justin; French, Marc; Jaehnig, Milt; Kuhn, Markus [Logic Technology Development, Intel Corporation, Hillsboro, Oregon 97124 (United States); French, Benjamin [Ocotillo Materials Laboratory, Intel Corporation, Chandler, Arizona 85248 (United States)

2014-09-21

In order to understand the fundamental electrical leakage and reliability failure mechanisms in nano-electronic low-k dielectric/metal interconnect structures, we have utilized x-ray photoelectron spectroscopy and reflection electron energy loss spectroscopy to determine the valence and conduction band offsets present at interfaces between non-porous and porous low-k a-SiO{sub x}C{sub y}:H interlayer dielectrics and a-SiC{sub x}N{sub y}:H metal capping layers. The valence band offset for such interfaces was determined to be 2.7±0.2 eV and weakly dependent on the a-SiOC:H porosity. The corresponding conduction band offset was determined to be 2.1±0.2 eV. The large band offsets indicate that intra metal layer leakage is likely dominated by defects and trap states in the a-SiOC:H and a-SiCN:H dielectrics.

Characterization of the Valence and Conduction Band Levels of n = 1 2D Perovskites: A Combined Experimental and Theoretical Investigation

KAUST Repository

Silver, Scott

2018-02-13

This study presents a combined experimental and theoretical study of the electronic structure of two 2D metal halide perovskite films. Ultraviolet and inverse photoemission spectroscopies are performed on solution-processed thin films of the n = 1 layered perovskite butylammonium lead iodide and bromide, BA2PbI4 and BA2PbBr4, characterized by optical absorption and X-ray diffraction, to determine their valence and conduction band densities of states, transport gaps, and exciton binding energies. The electron spectroscopy results are compared with the densities of states determined by density functional theory calculations. The remarkable agreement between experiment and calculation enables a detailed identification and analysis of the organic and inorganic contributions to the valence and conduction bands of these two hybrid perovskites. The electron affinity and ionization energies are found to be 3.1 and 5.8 eV for BA2PbI4, and 3.1 and 6.5 eV for BA2PbBr4. The exciton binding energies are estimated to be 260 and 300 meV for the two materials, respectively. The 2D lead iodide and bromide perovskites exhibit significantly less band dispersion and a larger density of states at the band edges than the 3D analogs. The effects of using various organic ligands are also discussed.

Valence instabilities as a source of actinide system inconsistencies

International Nuclear Information System (INIS)

Sandenaw, T.A.

1979-01-01

Light actinide elements alone, and in some of their alloys, may exist as a static or dynamic mixture of two configurations. Such a state can explain both a resistivity maximum and lack of magnetic order observed in so many actinide materials, and still be compatible with the existence of f-electrons in narrow bands. Impurity elements may stabilize slightly different intermediate valence states in U, Np, and Pu, thus contributing to inconsistencies in published results. The physical property behavior of mixed-valence, rare-earth compounds is very much like that observed in development of antiphase (martensitic) structures. Martensitic transformations in U, Np, and Pu, from high-temperature b. c. c. to alpha phase, may be a way of ordering an alloy-like metal of mixed or intermediate valence. The relative stability of each phase structure may depend upon its electron-valence ratio. A Hubbard model for electron correlations in a narrow energy band has been invoked in most recent theories for explaining light actinide behavior. Such a model may also be applicable to crystal symmetry changes in martensitic transformations in actinides

Instanton contributions to the valence band of the double Sine-Gordon potential

International Nuclear Information System (INIS)

Ricotta, R.M.; Escobar, C.O.

1982-01-01

The energy dispersion relation for the valence band of the double sine-Gordon potential is calculated, approximating the tunneling amplitude by a sum of contributions of multi-instantons and anti-instatons trajectories. The interesting feature of this potential is that they have to deal with two types of instantons, as there are two different potential barriers within one period of the potential. The results with the standard WKB approximation are compared. (Author) [pt

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.

Features of the core-valence luminescence and electron energy band structure of A1-xCsxCaCl3 (A = K,Rb) crystals

International Nuclear Information System (INIS)

Chornodolskyy, Ya; Stryganyuk, G; Syrotyuk, S; Voloshinovskii, A; Rodnyi, P

2007-01-01

From luminescence spectroscopy of CsCaCl 3 , Rb 1-x Cs x CaCl 3 and K 1-x Cs x CaCl 3 crystals, we have found evidence for intrinsic and impurity core-valence luminescence due to the radiative recombination of valence electrons with the holes of intrinsic or impurity 5p Cs + core states. The structural similarity of core-valence luminescence spectra has been revealed for the A 1-x Cs x CaCl 3 (A = K,Rb) crystals investigated. The electron energy structure of the CsCaCl 3 crystal has been calculated using the pseudopotential approach taking into account the gradient corrections for the exchange-correlation energy. The calculated density of the electronic states of CsCaCl 3 has been compared with corresponding parameters obtained from the analysis of core-valence luminescence spectra

Bond-Valence Constraints on Liquid Water Structure

International Nuclear Information System (INIS)

Bickmore, Barry R.; Rosso, Kevin M.; Brown, I. David; Kerisit, Sebastien N.

2009-01-01

The recent controversy about the structure of liquid water pits a new model involving water molecules in relatively stable rings-and-chains structures against the standard model that posits water molecules in distorted tetrahedral coordination. Molecular dynamics (MD) simulations 'both classical and ab initio' almost uniformly support the standard model, but since none of them can yet reproduce all the anomalous properties of water, they leave room for doubt. We argue that it is possible to evaluate these simulations by testing them against their adherence to the bond-valence model, a well known, and quantitatively accurate, empirical summary of the behavior of atoms in the bonded networks of inorganic solids. Here we use the results of ab initio molecular dynamics simulations of ice, water, and several solvated aqueous species to show that the valence sum rule (the first axiom of the bond-valence model,) is followed in both solid and liquid bond networks. We then test MD simulations of water, employing several popular potential models, against this criterion and the experimental O-O radial distribution function. It appears that most of those tested cannot satisfy both criteria well, except TIP4P and TIP5P. If the valence sum rule really can be applied to simulated liquid structures, then it follows that the bonding behaviors of atoms in liquids are in some ways identical to those in solids. We support this interpretation by showing that the simulations produce O-H-O geometries completely consistent with the range of geometries available in solids, and the distributions of instantaneous valence sums reaching the atoms in both the ice and liquid water simulations are essentially identical. Taken together, this is powerful evidence in favor of the standard distorted tetrahedral model of liquid water structure

A study of the valence shell electronic states of s-triazine by photoabsorption spectroscopy and ab initio calculations

Energy Technology Data Exchange (ETDEWEB)

Holland, D.M.P., E-mail: david.holland@stfc.ac.uk [Daresbury Laboratory, Daresbury, Warrington, Cheshire WA4 4AD (United Kingdom); Shaw, D.A. [Daresbury Laboratory, Daresbury, Warrington, Cheshire WA4 4AD (United Kingdom); Stener, M.; Decleva, P. [Dipartimento di Scienze Chimiche e Farmaceutiche, Università degli Studi di Trieste, Via L. Giorgieri, I-34127 Trieste (Italy); Consorzio Interuniversitario Nazionale per la Scienze e Tecnologia dei Materiali, INSTM, Unità di Trieste (Italy); CNR-IOM, Trieste (Italy); Coriani, S. [Dipartimento di Scienze Chimiche e Farmaceutiche, Università degli Studi di Trieste, Via L. Giorgieri, I-34127 Trieste (Italy); Consorzio Interuniversitario Nazionale per la Scienze e Tecnologia dei Materiali, INSTM, Unità di Trieste (Italy); Aarhus Institute of Advanced Studies, Aarhus University, 8000 Aarhus C (Denmark)

2016-09-30

Highlights: • The valence shell photoabsorption spectrum of s-triazine has been measured. • Electronic structure calculated with TDDFT and coupled cluster approaches. • Assignments proposed for Rydberg and valence states. • Mixing between Rydberg and valence states important. - Abstract: The absolute photoabsorption cross section of s-triazine has been measured between 4 and 40 eV, and is dominated by bands associated with valence states. Structure due to Rydberg excitations is both weak and irregular. Jahn-Teller interactions affect the vibronic structure observed in the Rydberg absorption bands due to excitation from the 1e″ or 6e′ orbitals. The interpretation of the experimental spectrum has been guided by transition energies and oscillator strengths, for Rydberg and valence states, calculated with the time-dependent version of density functional theory and with the coupled cluster linear response approach. The theoretical studies indicate that Rydberg/Rydberg and Rydberg/valence mixing is important.

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)

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.

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.

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.

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.

Clustering of low-valence particles: structure and kinetics.

Science.gov (United States)

Markova, Olga; Alberts, Jonathan; Munro, Edwin; Lenne, Pierre-François

2014-08-01

We compute the structure and kinetics of two systems of low-valence particles with three or six freely oriented bonds in two dimensions. The structure of clusters formed by trivalent particles is complex with loops and holes, while hexavalent particles self-organize into regular and compact structures. We identify the elementary structures which compose the clusters of trivalent particles. At initial stages of clustering, the clusters of trivalent particles grow with a power-law time dependence. Yet at longer times fusion and fission of clusters equilibrates and clusters form a heterogeneous phase with polydispersed sizes. These results emphasize the role of valence in the kinetics and stability of finite-size clusters.

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

Dimensionality and its effects upon the valence electronic structure of ordered metallic systems

International Nuclear Information System (INIS)

Tobin, J.G.

1983-07-01

The system c(10x2)Ag/Cu(001) was investigated with Angle-Resolved Photoemission (ARP), Low Energy Electron Diffraction (LEED) and Auger Electron Spectroscopy (AES). LEED and AES provided the calibration of a quartz microbalance used to measure the amount of silver evaporated onto the copper single crystal and also established the monolayer geometrical structure at one monolayer exposure. An off-normal ARP bandmapping study performed with polarized HeI and NeI radiation demonstrated the electronically two-dimensional nature of the silver d-bands at coverages of near one monolayer. The states at the surface Brillouin Zone center were assigned upon the basis of their polarization dependences and a structural model of hexagonal symmetry. A normal emission ARP experiment was performed at the Stanford Synchrotron Radiation Laboratory (SSRL) over the photon energy range of 6 to 32 eV. Data from it documented the evolution of the valence electronic structure of the silver overlayer from a two-dimensional hexagonal valence to a three-dimensional behavior converging towards that of bulk Ag(111). A structural study was attempted using the ARP technique of Normal Emission Photoelectron Diffraction over the photon energy range of 3.4 to 3.7 keV at SSRL, the results of which are inconclusive

Decay of Wannier-Mott excitons interacting with acoustic phonon in semiconductors with a degenerate valence band

International Nuclear Information System (INIS)

Nguyen Toan Thang; Nguyen Ai Viet; Nguyen Hong Quang

1987-06-01

Decay probabilities of light and heavy excitons interacting with acoustic phonons in cubic semiconductors with a degenerate valence band are calculated. The numerical results for GaAs showed that the decay probability of the light exciton is much greater than that of the heavy one. (author). 10 refs, 1 fig

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.

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, 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.

Valence holes observed in nanodiamonds dispersed in water

Science.gov (United States)

Petit, Tristan; Pflüger, Mika; Tolksdorf, Daniel; Xiao, Jie; Aziz, Emad F.

2015-02-01

Colloidal dispersion is essential for most nanodiamond applications, but its influence on nanodiamond electronic properties remains unknown. Here we have probed the electronic structure of oxidized detonation nanodiamonds dispersed in water by using soft X-ray absorption and emission spectroscopies at the carbon and oxygen K edges. Upon dispersion in water, the π* transitions from sp2-hybridized carbon disappear, and holes in the valence band are observed.Colloidal dispersion is essential for most nanodiamond applications, but its influence on nanodiamond electronic properties remains unknown. Here we have probed the electronic structure of oxidized detonation nanodiamonds dispersed in water by using soft X-ray absorption and emission spectroscopies at the carbon and oxygen K edges. Upon dispersion in water, the π* transitions from sp2-hybridized carbon disappear, and holes in the valence band are observed. Electronic supplementary information (ESI) available: Experimental methods, details on XAS/XES normalization and background correction procedures. See DOI: 10.1039/c4nr06639a

Photoemission investigation of the ZnSe/CdTe heterojunction band discontinuity

International Nuclear Information System (INIS)

Nelson, A.J.

1995-01-01

Synchrotron radiation soft x-ray photoemission spectroscopy and reflection high-energy electron diffraction were used to investigate the structural and electronic properties at the ZnSe/CdTe(100) heterojunction interface. ZnSe overlayers were sequentially grown in steps on p-type CdTe(100) single crystals at 200 degree C. In situ photoemission measurements were acquired after each growth in order to observe changes in the valence band electronic structure as well as changes in the Cd 4d, Zn 3d, and Te 4d core lines. The results were used to correlate the interfacial chemistry with the electronic structure and to directly determine the ZnSe/CdTe heterojunction valence band discontinuity and the consequent heterojunction band diagram. Results of these measurements reveal that the valence band offset is ΔE v =0.20 eV. copyright 1995 American Institute of Physics

Valence and conduction band offsets of β-Ga2O3/AlN heterojunction

Science.gov (United States)

Sun, Haiding; Torres Castanedo, C. G.; Liu, Kaikai; Li, Kuang-Hui; Guo, Wenzhe; Lin, Ronghui; Liu, Xinwei; Li, Jingtao; Li, Xiaohang

2017-10-01

Both β-Ga2O3 and wurtzite AlN have wide bandgaps of 4.5-4.9 and 6.1 eV, respectively. We calculated the in-plane lattice mismatch between the (-201) plane of β-Ga2O3 and the (0002) plane of AlN, which was found to be 2.4%. This is the smallest mismatch between β-Ga2O3 and binary III-nitrides which is beneficial for the formation of a high quality β-Ga2O3/AlN heterojunction. However, the valence and conduction band offsets (VBO and CBO) at the β-Ga2O3/AlN heterojunction have not yet been identified. In this study, a very thin (less than 2 nm) β-Ga2O3 layer was deposited on an AlN/sapphire template to form the heterojunction by pulsed laser deposition. High-resolution X-ray photoelectron spectroscopy revealed the core-level (CL) binding energies of Ga 3d and Al 2p with respect to the valence band maximum in individual β-Ga2O3 and AlN layers, respectively. The separation between Ga 3d and Al 2p CLs at the β-Ga2O3/AlN interface was also measured. Eventually, the VBO was found to be -0.55 ± 0.05 eV. Consequently, a staggered-gap (type II) heterojunction with a CBO of -1.75 ± 0.05 eV was determined. The identification of the band alignment of the β-Ga2O3/AlN heterojunction could facilitate the design of optical and electronic devices based on these and related alloys.

Valence-band discontinuities of wurtzite GaN, AlN, and InN heterojunctions measured by x-ray photoemission spectroscopy

International Nuclear Information System (INIS)

Martin, G.; Botchkarev, A.; Rockett, A.; Morkoc, H.

1996-01-01

The valence-band discontinuities at various wurtzite GaN, AlN, and InN heterojunctions were measured by means of x-ray photoemission spectroscopy. A significant forward endash backward asymmetry was observed in the InN/GaN endash GaN/InN and InN/AlN endash AlN/InN heterojunctions. The asymmetry was understood as a piezoelectric strain effect. We report the valence band discontinuities for InN/GaN=1.05±0.25 eV, GaN/AlN=0.70±0.24 eV, and InN/AlN=1.81±0.20 eV, all in the standard type I lineup. These values obey transitivity to within the experimental accuracy. Tables of photoemission core level binding energies are reported for wurtzite GaN, AlN, and InN. copyright 1996 American Institute of Physics

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

Valence and conduction band offsets of β-Ga2O3/AlN heterojunction

KAUST Repository

Sun, Haiding

2017-10-16

Both β-Ga2O3 and wurtzite AlN have wide bandgaps of 4.5–4.9 and 6.1 eV, respectively. We calculated the in-plane lattice mismatch between the (−201) plane of β-Ga2O3 and the (0002) plane of AlN, which was found to be 2.4%. This is the smallest mismatch between β-Ga2O3 and binary III-nitrides which is beneficial for the formation of a high quality β-Ga2O3/AlN heterojunction. However, the valence and conduction band offsets (VBO and CBO) at the β-Ga2O3/AlN heterojunction have not yet been identified. In this study, a very thin (less than 2 nm) β-Ga2O3 layer was deposited on an AlN/sapphire template to form the heterojunction by pulsed laser deposition. High-resolution X-ray photoelectron spectroscopy revealed the core-level (CL) binding energies of Ga 3d and Al 2p with respect to the valence band maximum in individual β-Ga2O3 and AlN layers, respectively. The separation between Ga 3d and Al 2p CLs at the β-Ga2O3/AlN interface was also measured. Eventually, the VBO was found to be −0.55 ± 0.05 eV. Consequently, a staggered-gap (type II) heterojunction with a CBO of −1.75 ± 0.05 eV was determined. The identification of the band alignment of the β-Ga2O3/AlN heterojunction could facilitate the design of optical and electronic devices based on these and related alloys.

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 of Si/Ge core-shell nanowires along the [110] direction modulated by external uniaxial strain

International Nuclear Information System (INIS)

Peng Xihong; Tang Fu; Logan, Paul

2011-01-01

Strain modulated electronic properties of Si/Ge core-shell nanowires along the [110] direction were reported, on the basis of first principles density-functional theory calculations. In particular, the energy dispersion relationship of the conduction/valence band was explored in detail. At the Γ point, the energy levels of both bands are significantly altered by applied uniaxial strain, which results in an evident change of the band gap. In contrast, for the K vectors far away from Γ, the variation of the conduction/valence band with strain is much reduced. In addition, with a sufficient tensile strain (∼1%), the valence band edge shifts away from Γ, which indicates that the band gap of the Si/Ge core-shell nanowires experiences a transition from direct to indirect. Our studies further showed that effective masses of charge carriers can also be tuned using the external uniaxial strain. The effective mass of the hole increases dramatically with tensile strain, while strain shows a minimal effect on tuning the effective mass of the electron. Finally, the relation between strain and the conduction/valence band edge is discussed thoroughly in terms of site-projected wavefunction characters.

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.)

Valence band photoemission studies of clean metals

International Nuclear Information System (INIS)

Wehner, P.S.

1978-04-01

The application of Angle-Resolved Photoelectron Spectroscopy (ARPES) to crystalline solids and the utilization of such studies to illuminate several questions concerning the detailed electronic structure of such materials, are discussed. Specifically, by construction of a Direct Transition (DT) model and the utilization of energy-dependent angle-resolved normal photoemission in the photon energy range 32 eV < or = hν < or = 200 eV, the bulk band structure of copper is experimentally mapped out along three different directions in the Brillouin Zone; GAMMA to K, GAMMA to L, and GAMMA to X. In addition, various effects which influence the obtainable resolution in vector k-space, namely, thermal disorder, momentum broadening, and band mixing, are discussed and are shown to place severe limitations on the applicability of the DT model. Finally, a model for Angle-Resolved X-ray Photoelectron Spectroscopy (ARXPS) based on the symmetry of the initial-state wavefunctions is presented and compared to experimental results obtained from copper single crystals

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.

Interface termination and band alignment of epitaxially grown alumina films on Cu-Al alloy

Science.gov (United States)

Yoshitake, Michiko; Song, Weijie; Libra, Jiří; Mašek, Karel; Šutara, František; Matolín, Vladimír; Prince, Kevin C.

2008-02-01

Epitaxial ultrathin alumina films were grown on a Cu-9 at. % Al(111) substrate by selective oxidation of Al in the alloy in ultrahigh vacuum. The photoelectron spectra of Al 2p and valence band were measured in situ during oxidation. By analyzing multiple peaks of Al 2p, the interface atomic structure was discussed. The energy difference between the Fermi level of the substrate and the valence band maximum of alumina (band offset) was obtained. The relation between the interface atomic structure and the band offset was compared with the reported first-principles calculations. A novel method for controlling the band offset was proposed.

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.

Effect of temperature on the valency bands of HDO in water in the liquid and solid states. Effects on the analysis of heavy water using infra-red absorption; Effet de temperature sur les bandes de valence de HDO dans l'eau a l'etat liquide et a l'etat solide - consequences pour l'analyse de l'eau lourde par absorption infra-rouge

Energy Technology Data Exchange (ETDEWEB)

Ceccaldi, M [Commissariat a l' Energie Atomique, Saclay (France). Centre d' Etudes Nucleaires

1964-07-01

After, a description of the technique used, a qualitative examination is made of the influence of the temperature on the {nu}{sub OH}(3,400 cm{sup -1}) and {nu}{sub OD} (2,500 cm{sup -1}) valence bands of HDO in the liquid state and then during the passage to the solid state. Quantitative examination with two cells of different thickness makes it possible to define the influence of temperature on the residual absorption of the pure liquid (D{sub 2}O or H{sub 2}O and on the valency bands ({nu}{sub OH} and {nu}{sub OD} respectively). It is found that a similar change occurs in the two bands but that the changes in the background are very different. During the passage from the liquid to the solid state the shape of the bands varies considerably but little change occurs in the total intensity. It has been possible to express these results in a simple form which is directly applicable to analytical problems. (authors) [French] Apres un rappel de la technique utilisee, on examine qualitativement l'influence de la temperature sur les bandes de valence {nu}{sub OH} (3400 cm{sup -1}) et {nu}{sub OD} (2500 cm{sup -1}) de HDO a l'etat liquide puis le passage a l'etat solide. L'examen quantitatif, avec deux cuves d'epaisseurs differentes, permet de preciser l'influence de la temperature sur l'absorption residuelle du liquide pur (D{sub 2}O ou H{sub 2}O) et sur les bandes de valence ( {nu}{sub OH} et {nu}{sub OD} respectivement). On constate une evolution parallele de ces bandes mais un comportement tres different du fond continu. Lors du passage de l'etat liquide a l'etat solide, la forme des bandes varie considerablement mais non l'intensite totale. On a pu formuler ces resultats sous une forme simple applicable directement aux problemes analytiques. (auteurs)

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.

Ultrawide band gap amorphous oxide semiconductor, Ga–Zn–O

Energy Technology Data Exchange (ETDEWEB)

Kim, Junghwan, E-mail: JH.KIM@lucid.msl.titech.ac.jp [Materials and Structures Laboratory, Tokyo Institute of Technology, Mailbox R3-4, 4259 Nagatsuta, Midori-ku, Yokohama (Japan); Miyokawa, Norihiko; Sekiya, Takumi; Ide, Keisuke [Materials and Structures Laboratory, Tokyo Institute of Technology, Mailbox R3-4, 4259 Nagatsuta, Midori-ku, Yokohama (Japan); Toda, Yoshitake [Materials Research Center for Element Strategy, Tokyo Institute of Technology, Mailbox SE-6, 4259 Nagatsuta, Midori-ku, Yokohama (Japan); Hiramatsu, Hidenori; Hosono, Hideo; Kamiya, Toshio [Materials and Structures Laboratory, Tokyo Institute of Technology, Mailbox R3-4, 4259 Nagatsuta, Midori-ku, Yokohama (Japan); Materials Research Center for Element Strategy, Tokyo Institute of Technology, Mailbox SE-6, 4259 Nagatsuta, Midori-ku, Yokohama (Japan)

2016-09-01

We fabricated amorphous oxide semiconductor films, a-(Ga{sub 1–x}Zn{sub x})O{sub y}, at room temperature on glass, which have widely tunable band gaps (E{sub g}) ranging from 3.47–4.12 eV. The highest electron Hall mobility ~ 7 cm{sup 2} V{sup −1} s{sup −1} was obtained for E{sub g} = ~ 3.8 eV. Ultraviolet photoemission spectroscopy revealed that the increase in E{sub g} with increasing the Ga content comes mostly from the deepening of the valence band maximum level while the conduction band minimum level remains almost unchanged. These characteristics are explained by their electronic structures. As these films can be fabricated at room temperature on plastic, this achievement extends the applications of flexible electronics to opto-electronic integrated circuits associated with deep ultraviolet region. - Highlights: • Incorporation of H/H{sub 2}O stabilizes the amorphous phase. • Ultrawide band gap (~ 3.8 eV) amorphous oxide semiconductor was fabricated. • The increase in band gap comes mostly from the deepening of the valence band maximum level. • Donor level is more likely aligned to the valence band maximum level.

Chemical state analysis of heat-treated 6, 13-bis(triisopropylsilylethynyl) pentacene investigated by XPS valence band spectra, XANES spectra and first-principles calculation

International Nuclear Information System (INIS)

Muro, Maiko; Natsume, Yutaka; Kikuma, Jun; Setoyama, Hiroyuki

2014-01-01

X-ray photoelectron spectroscopy (XPS) valence band spectra reflect the chemical bonding states. To take this advantage, we tried to interpret experimental spectra by the occupied density of states (DOS) based on first principles calculation. In this work, we discussed XPS and X-ray Absorption Near Edge Structure (XANES) spectra of 6, 13-bis(triisopropylsilylethynyl) pentacene (TIPS-Pen), which is well known as an organic semiconductor. We studied chemical structure change of TIPS-Pen caused by heat-treatment at 300degC under nitrogen and under the air. It has been suggested that the structural change of pentacene skeleton by Diels-Alder type reaction occurs in both cases. In addition, the sample heat-treated under the air showed desorption of the isopropyl group and increase of oxygen concentration. (author)

Band structure of semiconductors

CERN Document Server

Tsidilkovski, I M

2013-01-01

Band Structure of Semiconductors provides a review of the theoretical and experimental methods of investigating band structure and an analysis of the results of the developments in this field. The book presents the problems, methods, and applications in the study of band structure. Topics on the computational methods of band structure; band structures of important semiconducting materials; behavior of an electron in a perturbed periodic field; effective masses and g-factors for the most commonly encountered band structures; and the treatment of cyclotron resonance, Shubnikov-de Haas oscillatio

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 valence band-offset in a PbSe/ZnO heterojunction by x-ray photoelectron spectroscopy

Energy Technology Data Exchange (ETDEWEB)

Li Lin; Qiu Jijun; Weng Binbin; Yuan Zijian; Shi Zhisheng [School of Electrical and Computer Engineering, University of Oklahoma, Norman, Oklahoma 73019 (United States); Li Xiaomin; Gan Xiaoyan [State Key Laboratory of High Performance Ceramics and Superfine Microstructures, Shanghai Institute of Ceramics, Chinese Academy of Sciences, Shanghai 200050 (China); Sellers, Ian R. [Deparment of Physics, University of Oklahoma, Norman, Oklahoma 73019 (United States)

2012-12-24

A heterojunction of PbSe/ZnO has been grown by molecular beam epitaxy. X-ray photoelectron spectroscopy was used to directly measure the valence-band offset (VBO) of the heterojunction. The VBO, {Delta}E{sub V}, was determined as 2.51 {+-} 0.05 eV using the Pb 4p{sup 3/2} and Zn 2p{sup 3/2} core levels as a reference. The conduction-band offset, {Delta}E{sub C}, was, therefore, determined to be 0.59 {+-} 0.05 eV based on the above {Delta}E{sub V} value. This analysis indicates that the PbSe/ZnO heterojunction forms a type I (Straddling Gap) heterostructure.

Polarization Dependent Bulk-sensitive Valence Band Photoemission Spectroscopy and Density Functional Theory Calculations: Part I. 3d Transition Metals

Science.gov (United States)

Ueda, Shigenori; Hamada, Ikutaro

2017-12-01

The X-ray polarization dependent valence band HAXPES spectra of 3d transition metals (TMs) of Ti-Zn were measured to investigate the orbital resolved electronic structures by utilizing that the fact the photoionization cross-section of the atomic orbitals strongly depends on the experimental geometry. We have calculated the HAXPES spectra, which correspond to the cross-section weighted densities of states (CSW-DOSs), where the DOSs were obtained by the density functional theory calculations, and we have determined the relative photoionization cross-sections of the 4s and 4p orbitals to the 3d orbital in the 3d TMs. The experimentally obtained bulk-sensitive 3d and 4s DOSs were good agreement with the calculated DOSs in Ti, V, Cr, and Cu. In contrast, the deviations between the experimental and calculated 3d DOSs for Mn, Fe, Co, Ni were found, suggesting that the electron correlation plays an important role in the electronic structures for these materials.

Resonant photoemission at core-level shake-up thresholds: Valence-band satellites in nickel

International Nuclear Information System (INIS)

Bjoerneholm, O.; Andersen, J.N.; Wigren, C.; Nilsson, A.; Nyholm, R.; Ma; Ortensson, N.

1990-01-01

Three-hole satellites (3d 7 final-state configuration) in the nickel valence-band photoelectron spectrum have been identified at 13 and 18 eV binding energy with use of synchrotron radiation from the MAX storage ring. The three-hole satellites show resonances at photon energies close to the threshold for excitation of 3p 5 3d 9 core-hole shake-up states. The 13-eV satellite also shows a resonance directly at the 3p threshold. This is interpreted as an interference between the direct three-hole ionization and a shake-up transition in the Auger decay of the 3p hole. This shake-up process is also identified directly in the M 2,3 M 4,5 M 4,5 Auger spectrum

Hetero-gate-dielectric double gate junctionless transistor (HGJLT) with reduced band-to-band tunnelling effects in subthreshold regime

International Nuclear Information System (INIS)

Ghosh, Bahniman; Mondal, Partha; Akram, M. W.; Bal, Punyasloka; Salimath, Akshay Kumar

2014-01-01

We propose a hetero-gate-dielectric double gate junctionless transistor (HGJLT), taking high-k gate insulator at source side and low-k gate insulator at drain side, which reduces the effects of band-to-band tunnelling (BTBT) in the sub-threshold region. A junctionless transistor (JLT) is turned off by the depletion of carriers in the highly doped thin channel (device layer) which results in a significant band overlap between the valence band of the channel region and the conduction band of the drain region, due to off-state drain bias, that triggers electrons to tunnel from the valence band of the channel region to the conduction band of the drain region leaving behind holes in the channel. These effects of band-to-band tunnelling increase the sub-threshold leakage current, and the accumulation of holes in the channel forms a parasitic bipolar junction transistor (n–p–n BJT for channel JLT) in the lateral direction by the source (emitter), channel (base) and drain (collector) regions in JLT structure in off-state. The proposed HGJLT reduces the subthreshold leakage current and suppresses the parasitic BJT action in off-state by reducing the band-to-band tunnelling probability. (semiconductor devices)

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.

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

Effects of surface condition on the work function and valence-band position of ZnSnN2

Science.gov (United States)

Shing, Amanda M.; Tolstova, Yulia; Lewis, Nathan S.; Atwater, Harry A.

2017-12-01

ZnSnN2 is an emerging wide band gap earth-abundant semiconductor with potential applications in photonic devices such as solar cells, LEDs, and optical sensors. We report the characterization by ultraviolet photoelectron spectroscopy and X-ray photoelectron spectroscopy of reactively radio-frequency sputtered II-IV-nitride ZnSnN2 thin films. For samples transferred in high vacuum, the ZnSnN2 surface work function was 4.0 ± 0.1 eV below the vacuum level, with a valence-band onset of 1.2 ± 0.1 eV below the Fermi level. The resulting band diagram indicates that the degenerate bulk Fermi level position in ZnSnN2 shifts to mid-gap at the surface due to band bending that results from equilibration with delocalized surface states within the gap. Brief (< 10 s) exposures to air, a nitrogen-plasma treatment, or argon-ion sputtering caused significant chemical changes at the surface, both in surface composition and interfacial energetics. The relative band positioning of the n-type semiconductor against standard redox potentials indicated that ZnSnN2 has an appropriate energy band alignment for use as a photoanode to effect the oxygen-evolution reaction.

Band structure and optical properties of sinusoidal superlattices: ZnSe1-xTex

International Nuclear Information System (INIS)

Yang, G.; Lee, S.; Furdyna, J. K.

2000-01-01

This paper examines the band structure and optical selection rules in superlattices with a sinusoidal potential profile. The analysis is motivated by the recent successful fabrication of high quality ZnSe 1-x Te x superlattices in which the composition x varies sinusoidally along the growth direction. Although the band alignment in the ZnSe 1-x Te x sinusoidal superlattices is staggered (type II), they exhibit unexpectedly strong photoluminescence, thus suggesting interesting optical behavior. The band structure of such sinusoidal superlattices is formulated in terms of the nearly-free-electron (NFE) approximation, in which the superlattice potential is treated as a perturbation. The resulting band structure is unique, characterized by a single minigap separating two wide, free-electron-like subbands for both electrons and holes. Interband selection rules are derived for optical transitions involving conduction and valence-band states at the superlattice Brillouin-zone center, and at the zone edge. A number of transitions are predicted due to wave-function mixing of different subband states. It should be noted that the zone-center and zone-edge transitions are especially easy to distinguish in these superlattices because of the large width of the respective subbands. The results of the NFE approximation are shown to hold surprisingly well over a wide range of parameters, particularly when the period of the superlattice is short. (c) 2000 The American Physical Society

Energy shift and conduction-to-valence band transition mediated by a time-dependent potential barrier in graphene

Science.gov (United States)

Chaves, Andrey; da Costa, D. R.; de Sousa, G. O.; Pereira, J. M.; Farias, G. A.

2015-09-01

We investigate the scattering of a wave packet describing low-energy electrons in graphene by a time-dependent finite-step potential barrier. Our results demonstrate that, after Klein tunneling through the barrier, the electron acquires an extra energy which depends on the rate of change of the barrier height with time. If this rate is negative, the electron loses energy and ends up as a valence band state after leaving the barrier, which effectively behaves as a positively charged quasiparticle.

Simultaneous Conduction and Valence Band Quantization in Ultrashallow High-Density Doping Profiles in Semiconductors

Science.gov (United States)

Mazzola, F.; Wells, J. W.; Pakpour-Tabrizi, A. C.; Jackman, R. B.; Thiagarajan, B.; Hofmann, Ph.; Miwa, J. A.

2018-01-01

We demonstrate simultaneous quantization of conduction band (CB) and valence band (VB) states in silicon using ultrashallow, high-density, phosphorus doping profiles (so-called Si:P δ layers). We show that, in addition to the well-known quantization of CB states within the dopant plane, the confinement of VB-derived states between the subsurface P dopant layer and the Si surface gives rise to a simultaneous quantization of VB states in this narrow region. We also show that the VB quantization can be explained using a simple particle-in-a-box model, and that the number and energy separation of the quantized VB states depend on the depth of the P dopant layer beneath the Si surface. Since the quantized CB states do not show a strong dependence on the dopant depth (but rather on the dopant density), it is straightforward to exhibit control over the properties of the quantized CB and VB states independently of each other by choosing the dopant density and depth accordingly, thus offering new possibilities for engineering quantum matter.

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.)

Impact of band structure and transition matrix elements on polarization properties of the photoluminescence of semipolar and nonpolar InGaN quantum wells

Energy Technology Data Exchange (ETDEWEB)

Schade, L.; Schwarz, U.T. [Department of Microsystems Engineering, University of Freiburg, Georges-Koehler-Allee 103, 79108 Freiburg (Germany); Fraunhofer Institute for Applied Solid State Physics (IAF), Tullastrasse 72, 79108 Freiburg (Germany); Wernicke, T. [Institute of Solid State Physics, Technical University, Hardenbergstrasse 36, 10623 Berlin (Germany); Weyers, M. [Ferdinand-Braun-Institut fuer Hoechstfrequenztechnik, Gustav-Kirchhoff-Strasse 4, 12489 Berlin (Germany); Kneissl, M. [Institute of Solid State Physics, Technical University, Hardenbergstrasse 36, 10623 Berlin (Germany); Ferdinand-Braun-Institut fuer Hoechstfrequenztechnik, Gustav-Kirchhoff-Strasse 4, 12489 Berlin (Germany)

2011-03-15

Partial or full linear polarization is characteristic for the spontaneous emission of light from semipolar and nonpolar InGaN quantum wells. This property is an implication of the crystalline anisotropy as a basic property of the wurtzite structure. The influence of this anisotropy on the band structure and the transition matrix elements was calculated by a k.p-method for arbitrary quantum well orientations with respect to the c-axis; results are shown here in detail. Optical polarization is a direct consequence of a broken symmetry, mainly affecting the transition matrix elements from the conduction to the valence bands. Furthermore, the strain of the InGaN quantum well strongly depends on the crystal orientation of the substrate, resulting in a valence band mixing. The composition of the eigenfunctions has emerged to be most important for the polarization dependence of strained semipolar and nonpolar InGaN QW. The matrix elements, in combination with the thermal occupation of the bands, determine the polarization of the spontaneously emitted light. Our photoluminescence measurements of nonpolar QW match well with this model. However, in contrast to calculations with standard band parameters, the two topmost subbands show a larger separation in the emitted energy. (Copyright copyright 2011 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim)

Probing the graphite band structure with resonant soft-x-ray fluorescence

Energy Technology Data Exchange (ETDEWEB)

Carlisle, J.A.; Shirley, E.L.; Hudson, E.A. [Lawrence Berkeley National Lab., CA (United States)] [and others

1997-04-01

Soft x-ray fluorescence (SXF) spectroscopy using synchrotron radiation offers several advantages over surface sensitive spectroscopies for probing the electronic structure of complex multi-elemental materials. Due to the long mean free path of photons in solids ({approximately}1000 {angstrom}), SXF is a bulk-sensitive probe. Also, since core levels are involved in absorption and emission, SXF is both element- and angular-momentum-selective. SXF measures the local partial density of states (DOS) projected onto each constituent element of the material. The chief limitation of SXF has been the low fluorescence yield for photon emission, particularly for light elements. However, third generation light sources, such as the Advanced Light Source (ALS), offer the high brightness that makes high-resolution SXF experiments practical. In the following the authors utilize this high brightness to demonstrate the capability of SXF to probe the band structure of a polycrystalline sample. In SXF, a valence emission spectrum results from transitions from valence band states to the core hole produced by the incident photons. In the non-resonant energy regime, the excitation energy is far above the core binding energy, and the absorption and emission events are uncoupled. The fluorescence spectrum resembles emission spectra acquired using energetic electrons, and is insensitive to the incident photon`s energy. In the resonant excitation energy regime, core electrons are excited by photons to unoccupied states just above the Fermi level (EF). The absorption and emission events are coupled, and this coupling manifests itself in several ways, depending in part on the localization of the empty electronic states in the material. Here the authors report spectral measurements from highly oriented pyrolytic graphite.

Valence band electronic structure of Nb{sub 2}Pd{sub 1.2}Se{sub 5} and Nb{sub 2}Pd{sub 0.95}S{sub 5} 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)

2017-03-15

We present a comparative study of our valence band photoemission results on Nb{sub 2}Pd{sub 1.2}Se{sub 5} and Nb{sub 2}Pd{sub 0.95}S{sub 5} superconductors which are supported by our DFT based electronic structure calculations. We observe that the VB spectra of both the compounds are qualitatively similar, except for some slight differences in the binding energy positions of all the features. This could be due to the unequal electronegativities of Se and S atom. The calculated density of states (DOS) reveals that the VB features are mainly composed of Pd-Se/S hybridized states. The nature of DOS originating from the distinctly coordinated Pd atoms is different. Further, various Pd-4d and Nb-4d states crossing the Fermi level (E{sub f}) signifies the multiband character of these compounds. In addition, we find a temperature dependent pseudogap in Nb{sub 2}Pd{sub 0.95}S{sub 5} which is absent in Nb{sub 2}Pd{sub 1.2}Se{sub 5}.

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.

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.

Ab-initio calculation of the valence-band offset at strained GaAs/InAs (001) heterojunction

International Nuclear Information System (INIS)

Tit, N.; Peressi, M.

1993-06-01

We present a self consistent pseudopotential calculation of the valence band offset (VBO) at GaAs/InAs (001) strained heterojunction, which is chose as an example of the isovalent polar with common-anion lattice mismatched heterojunctions. The effects of strain are studied by looking at the variation of the VBO versus the in plane lattice constant, which is imposed by the substrate. Our results show that the VBO can be tuned by about 0.17 eV going from GaAs to InAs substrates. Comparison of our work with the available experimental and theoretical results is also discussed. (author). 25 refs, 3 figs, 5 tabs

Defect induced structural inhomogeneity, ultraviolet light emission and near-band-edge photoluminescence broadening in degenerate In ₂ O ₃ nanowires

Energy Technology Data Exchange (ETDEWEB)

Mukherjee, Souvik; Sarkar, Ketaki; Wiederrecht, Gary P.; Schaller, Richard D.; Gosztola, David J.; Stroscio, Michael A.; Dutta, Mitra

2018-03-01

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 (VO) 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 VO 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.

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.

Intermediate valence spectroscopy

International Nuclear Information System (INIS)

Gunnarsson, O.; Schoenhammer, K.

1987-01-01

Spectroscopic properties of intermediate valence compounds are studied using the Anderson model. Due to the large orbital and spin degeneracy N/sub f/ of the 4f-level, 1/N/sub f/ can be treated as a small parameter. This approach provides exact T = 0 results for the Anderson impurity model in the limit N/sub f/ → ∞, and by adding 1/N/sub f/ corrections some properties can be calculated accurately even for N/sub f/ = 1 or 2. In particular valence photoemission and resonance photoemission spectroscopies are studied. A comparison of theoretical and experimental spectra provides an estimate of the parameters in the model. Core level photoemission spectra provide estimates of the coupling between the f-level and the conduction states and of the f-level occupancy. With these parameters the model gives a fair description of other electron spectroscopies. For typical parameters the model predicts two structures in the f-spectrum, namely one structure at the f-level and one at the Fermi energy. The resonance photoemission calculation gives a photon energy dependence for these two peaks in fair agreement with experiment. The peak at the Fermi energy is partly due to a narrow Kondo resonance, resulting from many-body effects and the presence of a continuous, partly filled conduction band. This resonance is related to a large density of low-lying excitations, which explains the large susceptibility and specific heat observed for these systems at low temperatures. 38 references, 11 figures, 2 tables

Creation of quasi-Dirac points in the Floquet band structure of bilayer graphene.

Science.gov (United States)

Cheung, W M; Chan, K S

2017-06-01

We study the Floquet quasi-energy band structure of bilayer graphene when it is illuminated by two laser lights with frequencies [Formula: see text] and [Formula: see text] using Floquet theory. We focus on the dynamical gap formed by the conduction band with Floquet index  =  -1 and the valence band with Floquet index  =  +1 to understand how Dirac points can be formed. It is found that the dynamical gap does not have rotation symmetry in the momentum space, and quasi-Dirac points, where the conduction and valence bands almost touch, can be created when the dynamical gap closes along some directions with suitably chosen radiation parameters. We derive analytical expressions for the direction dependence of the dynamical gaps using Lowdin perturbation theory to gain a better understanding of the formation of quasi-Dirac points. When both radiations are circularly polarized, the gap can be exactly zero along some directions, when only the first and second order perturbations are considered. Higher order perturbations can open a very small gap in this case. When both radiations are linearly polarized, the gap can be exactly zero up to the fourth order perturbation and more than one quasi-Dirac point is formed. We also study the electron velocity around a dynamical gap and show that the magnitude of the velocity drops to values close to zero when the k vector is near to the gap minimum. The direction of the velocity also changes around the gap minimum, and when the gap is larger in value the change in the velocity direction is more gradual. The warping effect does not affect the formation of a Dirac point along the k x axis, while it prevents its formation when there is phase shift between the two radiations.

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.

Electronic structure study of wide band gap magnetic semiconductor (La0.6Pr0.4)0.65Ca0.35MnO3 nanocrystals in paramagnetic and ferromagnetic phases

Science.gov (United States)

Dwivedi, G. D.; Joshi, Amish G.; Kumar, Shiv; Chou, H.; Yang, K. S.; Jhong, D. J.; Chan, W. L.; Ghosh, A. K.; Chatterjee, Sandip

2016-04-01

X-ray circular magnetic dichroism (XMCD), X-ray photoemission spectroscopy (XPS), and ultraviolet photoemission spectroscopy (UPS) techniques were used to study the electronic structure of nanocrystalline (La0.6Pr0.4)0.65Ca0.35MnO3 near Fermi-level. XMCD results indicate that Mn3+ and Mn4+ spins are aligned parallel to each other at 20 K. The low M-H hysteresis curve measured at 5 K confirms ferromagnetic ordering in the (La0.6Pr0.4)0.65Ca0.35MnO3 system. The low temperature valence band XPS indicates that coupling between Mn3d and O2p is enhanced and the electronic states near Fermi-level have been suppressed below TC. The valence band UPS also confirms the suppression of electronic states near Fermi-level below Curie temperature. UPS near Fermi-edge shows that the electronic states are almost absent below 0.5 eV (at 300 K) and 1 eV (at 115 K). This absence clearly demonstrates the existence of a wide band-gap in the system since, for hole-doped semiconductors, the Fermi-level resides just above the valence band maximum.

Studies on the valence electronic structure of Fe and Ni in FexNi1−x ...

Indian Academy of Sciences (India)

structure of Fe and Ni in various Fex Ni1−x alloys. Since Kβ-to-Kα X-ray intensity ratio has been reported [2–7] to be a sensitive physical parameter to investigate the changes in the valence electronic structure of 3d-transition metals [2], we have undertaken the study of the valence electronic structure of Fe and Ni in the Fex ...

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.

Effect of phase formation on valence band photoemission and photoresonance study of Ti/Ni multilayers using synchrotron radiation

International Nuclear Information System (INIS)

Bhatt, Pramod; Chaudhari, S.M.

2006-01-01

This paper presents investigation of Ti-Ni alloy phase formation and its effect on valence band (VB) photoemission and photoresonance study of as-deposited as well as annealed Ti/Ni multilayers (MLs) up to 600 deg. C using synchrotron radiation. For this purpose [Ti (50 A)/Ni (50 A)]X 10 ML structures were deposited by using electron-beam evaporation technique under ultra-high vacuum (UHV) conditions. Formation of different phases of Ti-Ni alloy due to annealing treatment has been confirmed by the X-ray diffraction (XRD) technique. The XRD pattern corresponding as-deposited ML sample shows crystalline nature of both Ti and Ni deposited layers, whereas 300 deg. C annealed ML sample show solid-state reaction (SSR) leading to amorphization and subsequent recrystallisation at higher temperatures of annealing (≥400 deg. C) with the formation of TiNi, TiNi 3 and Ti 2 Ni alloy phases. The survey scans corresponding to 400, 500 and 600 deg. C annealed ML sample shows interdiffusion and intermixing of Ni atoms into Ti layers leading to chemical Ti-Ni alloys phase formation at interface. The corresponding recorded VB spectra using synchrotron radiation at 134 eV on as-deposited ML sample with successive sputtering shows alternately photoemission bands due to Ti 3d and Ni 3d, respectively, indicating there is no mixing of the consequent layers and any phase formation at the interface during deposition. However, ML samples annealed at higher temperatures of annealing, particularly at 400, 500 and 600 deg. C show a clear shift in Ni 3d band and its satellite peak position to higher BE side indicates Ti-Ni alloy phase formation. In addition to this, reduction of satellite peak intensity and Ni 3d density of states (DOS) near Fermi level is also observed due to Ti-Ni phase formation with higher annealing temperatures. The variable photon energy VB measurements on as-deposited and ML samples annealed at 400 deg. C confirms existence and BE position of observed Ni 3d satellite

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

Band termination in the N=Z nucleus 44Ti

International Nuclear Information System (INIS)

Ur, C.A.; Lenzi, S.M.; Martinez-Pinedo, G.

1998-01-01

Nuclei in the vicinity of the middle of the 1f 7/2 shell show strong prolate deformation at low spins resulting in rotational-like band structures. With increasing angular momentum the structure of these nuclei evolves through triaxial and spherical shapes. Recently, band terminating states corresponding to fully aligned configurations of valence nucleons in the f 7/2 shell have been reported. Further increase of the angular momentum can be achieved by particle excitations on the higher shell. This will result in high energy γ-ray transitions as it was observed in 50 Cr. We have investigated the structure of 44 Ti up to the band termination. Excited states in 44 Ti have been populated via the 28 Si + 24 Mg at 110 MeV beam energy. The target consisted of ∼0.5 mg/cm 2 of 24 Mg deposited on a gold backing. Gamma-rays were detected with the GASP multidetector array composed by 40 HPGe Compton-suppressed detectors and the inner ball built of 80 BGO detectors. The preliminary level scheme of 44 Ti, as determined in our work, is presented. This nucleus has 2 valence protons and 2 valence neutrons filling the f 7/2 shell. The band terminating state corresponding to their total alignment is the 12 + state. Several γ-rays transitions above this state have been identified. Also, we have identified two negative parity bands strongly connected to the yrast positive parity structure. Such structures have also been observed in other two even-even N=Z nuclei in the f 7/2 shell, namely, 44 Cr and 52 Fe, but they were less populated. The structure of 44 Ti is also interesting from the point of view of the cross-conjugate symmetry. Comparing the level structure of 44 Ti and the one of its cross-conjugate nucleus at the other end of the shell, 52 Fe, it can be noticed that up to spin 10ℎ their structure is very similar, but in 44 Ti the band terminating state 12 + is not below the 10 + state as in the case of 52 Fe. This was related to a reminiscent degree of collectivity in the

Observation of the c-f hybridization effect in valence-transition system EuPtP

Energy Technology Data Exchange (ETDEWEB)

Anzai, Hiroaki; Ichiki, Katsuya [Graduate School of Engineering, Osaka Prefecture University, Sakai (Japan); Schwier, Eike F.; Iwasawa, Hideaki; Arita, Masashi; Sato, Hitoshi; Shimada, Kenya; Namatame, Hirofumi; Taniguchi, Masaki [Hiroshima Synchrotron Radiation Center, Hiroshima University, Higashi-Hiroshima (Japan); Mitsuda, Akihiro; Wada, Hirofumi [Graduate School of Science, Kyushu University, Fukuoka (Japan); Mimura, Kojiro [Graduate School of Engineering, Osaka Prefecture University, Sakai (Japan); Hiroshima Synchrotron Radiation Center, Hiroshima University, Higashi-Hiroshima (Japan)

2017-06-15

We study the electronic structure of EuPtP, which exhibits two first-order valence transitions at T{sub 1} = 247 K and T{sub 2} = 201 K, using angle-resolved photoemission spectroscopy. Below T{sub 2}, we observe an energy gap at the crossing point of the bulk Eu 4f and conduction bands. The shape of band dispersions is described by a hybridization-band picture based on the periodic Anderson model. Our results demonstrate the c-f hybridization effect in the low-temperature phase of EuPtP. (copyright 2017 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim)

Large shift and small broadening of Br2 valence band upon dimer formation with H2O: an ab initio study.

Science.gov (United States)

Franklin-Mergarejo, Ricardo; Rubayo-Soneira, Jesus; Halberstadt, Nadine; Ayed, Tahra; Bernal-Uruchurtu, Margarita I; Hernández-Lamoneda, Ramón; Janda, Kenneth C

2011-06-16

Valence electronic excitation spectra are calculated for the H(2)O···Br(2) complex using highly correlated ab initio potentials for both the ground and the valence electronic excited states and a 2-D approximation for vibrational motion. Due to the strong interaction between the O-Br and the Br-Br stretching motions, inclusion of these vibrations is the minimum necessary for the spectrum calculation. A basis set calculation is performed to determine the vibrational wave functions for the ground electronic state and a wave packet simulation is conducted for the nuclear dynamics on the excited state surfaces. The effects of both the spin-orbit interaction and temperature on the spectra are explored. The interaction of Br(2) with a single water molecule induces nearly as large a shift in the spectrum as is observed for an aqueous solution. In contrast, complex formation has a remarkably small effect on the T = 0 K width of the valence bands due to the fast dissociation of the dihalogen bond upon excitation. We therefore conclude that the widths of the spectra in aqueous solution are mostly due to inhomogeneous broadening. © 2011 American Chemical Society

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.

Electronic structure of germanium selenide investigated using ultra-violet photo-electron spectroscopy

Science.gov (United States)

Mishra, P.; Lohani, H.; Kundu, A. K.; Patel, R.; Solanki, G. K.; Menon, Krishnakumar S. R.; Sekhar, B. R.

2015-07-01

The valence band electronic structure of GeSe single crystals has been investigated using angle resolved photoemission spectroscopy (ARPES) and x-ray photoelectron spectroscopy. The experimentally observed bands from ARPES, match qualitatively with our LDA-based band structure calculations along the Γ-Z, Γ-Y and Γ-T symmetry directions. The valence band maximum occurs nearly midway along the Γ-Z direction, at a binding energy of -0.5 eV, substantiating the indirect band gap of GeSe. Non-dispersive features associated with surface states and indirect transitions have been observed. The difference in hybridization of Se and Ge 4p orbitals leads to the variation of dispersion along the three symmetry directions. The predominance of the Se 4pz orbitals, evidenced from theoretical calculations, may be the cause for highly dispersive bands along the Γ-T direction. Detailed electronic structure analysis reveals the significance of the cation-anion 4p orbitals hybridization in the valence band dispersion of IV-VI semiconductors. This is the first comprehensive report of the electronic structure of a GeSe single crystal using ARPES in conjugation with theoretical band structure analysis.

Electronic structure of germanium selenide investigated using ultra-violet photo-electron spectroscopy

International Nuclear Information System (INIS)

Mishra, P; Lohani, H; Sekhar, B R; Kundu, A K; Menon, Krishnakumar S R; Patel, R; Solanki, G K

2015-01-01

The valence band electronic structure of GeSe single crystals has been investigated using angle resolved photoemission spectroscopy (ARPES) and x-ray photoelectron spectroscopy. The experimentally observed bands from ARPES, match qualitatively with our LDA-based band structure calculations along the Γ–Z, Γ–Y and Γ–T symmetry directions. The valence band maximum occurs nearly midway along the Γ–Z direction, at a binding energy of −0.5 eV, substantiating the indirect band gap of GeSe. Non-dispersive features associated with surface states and indirect transitions have been observed. The difference in hybridization of Se and Ge 4p orbitals leads to the variation of dispersion along the three symmetry directions. The predominance of the Se 4p z orbitals, evidenced from theoretical calculations, may be the cause for highly dispersive bands along the Γ–T direction. Detailed electronic structure analysis reveals the significance of the cation–anion 4p orbitals hybridization in the valence band dispersion of IV–VI semiconductors. This is the first comprehensive report of the electronic structure of a GeSe single crystal using ARPES in conjugation with theoretical band structure analysis. (paper)

Valency and type conversion in CuInSe2 with H2 plasma exposure: A photoemission investigation

International Nuclear Information System (INIS)

Nelson, A.J.; Frigo, S.P.; Rosenberg, R.

1993-01-01

The effect of H 2 plasma exposure on CuInSe 2 was studied by synchrotron radiation soft-x-ray photoemission spectroscopy. The low-power H 2 plasma was generated with a commercial electron cyclotron resonance plasma source using pure H 2 with the plasma exposure being performed at 200 degree C. In situ photoemission measurements were acquired after each plasma exposure in order to observe changes in the valence-band electronic structure as well as changes in the In 4d and Se 3d core lines. The results were correlated in order to relate changes in surface chemistry to the electronic structure. These measurements indicate that the H 2 plasma exposure type converts the CuInSe 2 surface to an n-type surface as well as converting the In +3 valency state to an In +1 valency state

Crystal structure and band gap determination of HfO2 thin films

NARCIS (Netherlands)

Cheynet, M.C.; Pokrant, S.; Tichelaar, F.D.; Rouvière, J.L.

2007-01-01

Valence electron energy loss spectroscopy (VEELS) and high resolution transmission electron microscopy (HRTEM) are performed on three different HfO2 thin films grown on Si (001) by chemical vapor deposition (CVD) or atomic layer deposition (ALD). For each sample the band gap (Eg) is determined by

Decoding emotional valence from electroencephalographic rhythmic activity.

Science.gov (United States)

Celikkanat, Hande; Moriya, Hiroki; Ogawa, Takeshi; Kauppi, Jukka-Pekka; Kawanabe, Motoaki; Hyvarinen, Aapo

2017-07-01

We attempt to decode emotional valence from electroencephalographic rhythmic activity in a naturalistic setting. We employ a data-driven method developed in a previous study, Spectral Linear Discriminant Analysis, to discover the relationships between the classification task and independent neuronal sources, optimally utilizing multiple frequency bands. A detailed investigation of the classifier provides insight into the neuronal sources related with emotional valence, and the individual differences of the subjects in processing emotions. Our findings show: (1) sources whose locations are similar across subjects are consistently involved in emotional responses, with the involvement of parietal sources being especially significant, and (2) even though the locations of the involved neuronal sources are consistent, subjects can display highly varying degrees of valence-related EEG activity in the sources.

Energy band alignment of antiferroelectric (Pb,La)(Zr,Sn,Ti)O{sub 3}

Energy Technology Data Exchange (ETDEWEB)

Klein, Andreas, E-mail: aklein@surface.tu-darmstadt.de [Technische Universität Darmstadt, Institute of Materials Science, Surface Science Division, Jovanka-Bontschits-Straße 2, 64287 Darmstadt (Germany); Lohaus, Christian [Technische Universität Darmstadt, Institute of Materials Science, Surface Science Division, Jovanka-Bontschits-Straße 2, 64287 Darmstadt (Germany); Reiser, Patrick [Technische Universität Darmstadt, Institute of Materials Science, Surface Science Division, Jovanka-Bontschits-Straße 2, 64287 Darmstadt (Germany); InnovationLab GmbH, Speyerer Straße 4, 69115 Heidelberg (Germany); Dimesso, Lucangelo [Technische Universität Darmstadt, Institute of Materials Science, Surface Science Division, Jovanka-Bontschits-Straße 2, 64287 Darmstadt (Germany); Wang, Xiucai; Yang, Tongqing [Tongji University, Key Laboratory of Advanced Civil Engineering Materials (Ministry of Education), Functional Materials Research Laboratory, College of Materials Science and Engineering, Cao’an Road 4800, Shanghai 201804 (China)

2017-06-15

Highlights: • Energy band alignment of antiferroelectric PLZST studied by XPS. • A deconvolution procedure is applied to study band alignment of insulating materials. • Contribution of Pb 6s orbitals leads to higher valence band maximum. • Ferroelectric polarization does not contribute to valence band maximum energy. • The variation of Schottky barrier heights indicates no Fermi level pinning in PLZST. - Abstract: The energy band alignment of antiferroelectric (Pb,La)(Zr,Sn,Ti)O{sub 3} is studied with photoelectron spectroscopy using interfaces with high work function RuO{sub 2} and low work function Sn-doped In{sub 2}O{sub 3} (ITO). It is demonstrated how spectral deconvolution can be used to determine absolute Schottky barrier heights for insulating materials with a high accuracy. Using this approach it is found that the valence band maximum energy of (Pb,La)(Zr,Sn,Ti)O{sub 3} is found to be comparable to that of Pb- and Bi-containing ferroelectric materials, which is ∼1 eV higher than that of BaTiO{sub 3}. The results provide additional evidence for the occupation of the 6s orbitals as origin of the higher valence band maximum, which is directly related to the electrical properties of such compounds. The results also verify that the energy band alignment determined by photoelectron spectroscopy of as-deposited electrodes is not influenced by polarisation. The electronic structure of (Pb,La)(Zr,Sn,Ti)O{sub 3} should enable doping of the material without strongly modifying its insulating properties, which is crucial for high energy density capacitors. Moreover, the position of the energy bands should result in a great freedom of selecting electrode materials in terms of avoiding charge injection.

The stabilities and electron structures of Al-Mg clusters with 18 and 20 valence electrons

Science.gov (United States)

Yang, Huihui; Chen, Hongshan

2017-07-01

The spherical jellium model predicts that metal clusters having 18 and 20 valence electrons correspond to the magic numbers and will show specific stabilities. We explore in detail the geometric structures, stabilities and electronic structures of Al-Mg clusters containing 18 and 20 valence electrons by using genetic algorithm combined with density functional theories. The stabilities of the clusters are governed by the electronic configurations and Mg/Al ratios. The clusters with lower Mg/Al ratios are more stable. The molecular orbitals accord with the shell structures predicted by the jellium model but the 2S level interweaves with the 1D levels and the 2S and 1D orbitals form a subgroup. The clusters having 20 valence electrons form closed 1S21P61D102S2 shells and show enhanced stability. The Al-Mg clusters with a valence electron count of 18 do not form closed shells because one 1D orbital is unoccupied. The ionization potential and electron affinity are closely related to the electronic configurations; their values are determined by the subgroups the HOMO or LUMO belong to. Supplementary material in the form of one pdf file available from the Journal web page at http://https://doi.org/10.1140/epjd/e2017-80042-9

Electronic structure of the Ga1-xCr xN studied by high-energy photoemission spectroscopy

International Nuclear Information System (INIS)

Kim, J.J.; Makino, H.; Yao, T.; Takata, Y.; Kobayashi, K.; Yamamoto, T.; Hanada, T.; Cho, M.W.; Ikenaga, E.; Yabashi, M.; Miwa, D.; Nishino, Y.; Tamasaku, K.; Ishikawa, T.; Shin, S.

2005-01-01

Valence band spectra of Ga 1-x Cr x N have been investigated by high-energy photoemission spectroscopy at the photon energy of 5.95 keV. Cr doping does introduce a novel electronic structure in the bandgap and causes some change in valence band structure. Based on the first-principle calculation, Cr-associated electronic levels in the bandgap are assigned to nonbonding and antibonding d states while the change of the valence band suggests that the Ga 4s originated states are significantly modified through hybridization with the Cr 3d orbital. The present result evidences that the Ga valence electrons are considerably modified through the interaction with the second nearest-neighbour Cr atoms

Electronic structure of multiferroic BiFeO3 by resonant soft-x-ray emission spectroscopy

Energy Technology Data Exchange (ETDEWEB)

Higuchi, Tohru; Higuchi, T.; Liu, Y.-S.; Yao, P.; Glans, P.-A.; Guo, Jinghua; Chang, C.; Wu, Z.; Sakamoto, W.; Itoh, N.; Shimura, T.; Yogo, T.; Hattori, T.

2008-07-11

The electronic structure of multiferroic BiFeO{sub 3} has been studied using soft-X-ray emission spectroscopy. The fluorescence spectra exhibit that the valence band is mainly composed of O 2p state hybridized with Fe 3d state. The band gap corresponding to the energy separation between the top of the O 2p valence band and the bottom of the Fe 3d conduction band is 1.3 eV. The soft-X-ray Raman scattering reflects the features due to charge transfer transition from O 2p valence band to Fe 3d conduction band. These findings are similar to the result of electronic structure calculation by density functional theory within the local spin-density approximation that included the effect of Coulomb repulsion between localized d states.

Pressure-induced valence and structure change in some anti-Th3P4 structure rare earth compounds

International Nuclear Information System (INIS)

Werner, A.; Hochheimer, H.D.; Jayaraman, A.; Bucher, E.

1981-01-01

The anti-Th 3 P 4 structure compounds Yb 4 Bi 3 and Yb 4 Sb 3 have been investigated to 350 kbar by high pressure X-ray diffraction, using the diamond anvil cell. From the P-V data it is found that Yb 4 Bi 3 and Yb 4 Sb 3 are much more compressible, compared to Sm 4 Bi 3 before the valence transition. This suggests that a continuous change in the valence state of Yb takes place with pressure in the two compounds and that they may be in the mixed valent state already at ambient pressure. The ''collapsed'' anti-Th 3 P 4 structure becomes unstable in Yb 4 Bi 3 and Yb 4 Sb 3 and new lines appear at high pressure, that fit the NaCl structure. The latter structure change seems to occur also in the electronically collapsed Sm 4 Bi 3 . The results are presented and discussed. (Auth.)

X-ray spectra and electronic structure of the Ca3Ga2Ge3О12 compound

Science.gov (United States)

Shcherba, I. D.; Kostyk, L. V.; Noga, H.; Bekenov, L. V.; Uskokovich, D.; Jatsyk, B. M.

2017-09-01

The band structure of Ca3Ga2Ge3О12 with the garnet structure has been determined for the first time by X-ray emission and photoelectron spectroscopy. It has been established that the bottom of the valence band is formed by Ge d states, which are not dominant in the chemical bonding. Strong hybridization of oxygen 2s states with 4p states of Ga and Ge revealed by the presence of an extra structure in the X-ray emission spectra has been found. The middle of the valence band has been demonstrated to be occupied by d states of Ga, while Ga and Ge 4рstates with a considerable admixture of oxygen 2p states form the top of the valence band.

Influence of changes in the valence electronic configuration on the structure of L-X-ray spectra of molybdenum

International Nuclear Information System (INIS)

Polasik, M; Koziol, K; Slabkowska, K; Czarnota, M; Pajek, M

2009-01-01

Extensive multiconfiguration Dirac-Fock (MCDF) calculations with the inclusion of the transverse (Breit) interaction and QED corrections have been carried out on molybdenum to explain the dependence of the structure of Lα 1,2 and Lβ 1 lines on the changes in configurations of the valence electrons belonging to two different configuration types: three open-shell 4d 6-r 5s r (r = 2,1,0) configurations and one closed-shell 4d 4 3/2 5s 2 configuration. It has been found that the MCDF predictions for open-shell valence configurations (4d 4 5s 2 , 4d 5 5s 1 , 4d 6 5s 0 ) much better reproduce observed structure of Lα 1,2 lines in X-ray spectra of molybdenum than closed-shell 4d 4 3/2 5s 2 valence configuration. The influence of changes in the valence electronic configuration on the structure of L-X-ray spectra of molybdenum is noticeable. Moreover, the observation of the shapes of L-X-ray spectra seems to be very good method to investigate the changes of the valence electronic configuration caused by the chemical environment.

Structural and magnetic characterization of mixed valence Co(II, III)xZn1−xO epitaxial thin films

International Nuclear Information System (INIS)

Negi, D.S.; Loukya, B.; Dileep, K.; Sahu, R.; Shetty, S.; Kumar, N.; Ghatak, J.; Pachauri, N.; Gupta, A.; Datta, R.

2014-01-01

In this article, we report on the Co atom incorporation, secondary phase formation and composition-dependent magnetic and optical properties of mixed valence Co(II, III) x Zn 1−x O epitaxial thin films grown by pulsed laser deposition. The intended total Co concentration is varied between ∼6–60 at.% with relatively higher concentration of +3 over +2 charge state. Mixed valence Co(II, III) shows high solubility in ZnO (up to 38 at.%) and ferromagnetism is observed in samples with total Co incorporation of ∼29 and 38 at.%. Electron diffraction pattern and high resolution transmission electron microscopy images reveal single crystalline nature of the thin films with wurtzite structure. Co oxide interlayer, with both rock salt and spinel structure, are observed to be formed between the substrate and wurtzite film for total Co concentration at ∼17 at.% and above. Magnetization shows composition dependence with a saturation moment value of ∼93 emu cm −3 and a coercive field of ∼285 Oe observed for ∼38 at.% Co:ZnO films. Ferromagnetism was not observed for films with Co concentration 17 and 9 at.%. The Co oxide interlayer does not show any ferromagnetism. All the films are n-type with carrier concentration ∼10 19 cm −3 . The observed magnetism is probably resulting from direct antiferromagntic exchange interaction between Co 2+ and Co 3+ ions favored by heavy Co alloying giving rise to ferrimagnetism in the system. - Highlights: • Mixed valence Co doped ZnO ferromagnetic single crystal thin film. • Secondary phase formation in terms of CoO and Co3O4 and magnetism is observed only for high Co alloying. • Cathodoluminescence (CL) data showing increase in band gap with Co concentrations

Electronic structure of the rotation twin stacking fault in β-ZnS

International Nuclear Information System (INIS)

Northrup, J.E.; Cohen, M.L.

1981-01-01

The electronic structure of the rotation twin stacking fault in β-ZnS is calculated with the self-consistent pseudopotential method. The stacking fault creates a potential barrier of approx.0.07 eV and induces the localization of stacking-fault resonances near the top of the valence band. Stacking-fault states are also predicted to exist in the various gaps in the projected valence-band structure

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

Chemical states and electronic structure of a HfO(-2)/Ge(001) interface

International Nuclear Information System (INIS)

Seo, Kang-ill; McIntyre, Paul C.; Stanford U., Materials Sci. Dept.; Sun, Shiyu; Lee, Dong-Ick; Pianetta, Piero; SLAC, SSRL; Saraswat, Krishna C.; Stanford U., Elect. Eng. Dept.

2005-01-01

We report the chemical bonding structure and valence band alignment at the HfO 2 /Ge (001) interface by systematically probing various core level spectra as well as valence band spectra using soft x-rays at the Stanford Synchrotron Radiation Laboratory. We investigated the chemical bonding changes as a function of depth through the dielectric stack by taking a series of synchrotron photoemission spectra as we etched through the HfO 2 film using a dilute HF-solution. We found that a very non-stoichiometric GeO x layer exists at the HfO 2 /Ge interface. The valence band spectra near the Fermi level in each different film structure were carefully analyzed, and as a result, the valence band offset between Ge and GeO x was determined to be ΔE v (Ge-GeO x ) = 2.2 ± 0.15 eV, and that between Ge and HfO 2 , ΔE v (Ge-HfO 2 ) = 2.7 ± 0.15 eV

Investigation of structural, electronic and anisotropic elastic properties of Ru-doped WB{sub 2} compound by increased valence electron concentration

Energy Technology Data Exchange (ETDEWEB)

Surucu, Gokhan, E-mail: g_surucu@yahoo.com [Ahi Evran University, Department of Electric and Energy, 40100, Kirsehir (Turkey); Gazi University, Photonics Application and Research Center, 06500, Ankara (Turkey); Kaderoglu, Cagil [Ankara University, Department of Engineering Physics, 06100, Ankara (Turkey); Deligoz, Engin; Ozisik, Haci [Aksaray University, Department of Physics, 68100, Aksaray (Turkey)

2017-03-01

First principles density functional theory (DFT) calculations have been used to investigate the structural, anisotropic elastic and electronic properties of ruthenium doped tungsten-diboride ternary compounds (W{sub 1−x}Ru{sub x}B{sub 2}) for an increasing molar fraction of Ru atom from 0.1 to 0.9 by 0.1. Among the nine different compositions, W{sub 0.3}Ru{sub 0.7}B{sub 2} has been found as the most stable one due to the formation energy and band filling theory calculations. Moreover, the band structures and partial density of states (PDOS) have been computed for each x composition. After obtaining the elastic constants for all x compositions, the secondary results such as Bulk modulus, Young’s modulus, Poisson’s ratio, Shear modulus, and Vickers Hardness of polycrystalline aggregates have been derived and the relevant mechanical properties have been discussed. In addition, the elastic anisotropy has been visualized in detail by plotting the directional dependence of compressibility, Poisson ratio, Young’s and Shear moduli. - Highlights: • Effects of Ru substitution in WB{sub 2} using increased valence electron concentration. • Structural, electronic, mechanic and elastic properties for increasing Ru content. • Considered alloys are incompressible, brittle, stiffer and high hard materials.

Structure of s - p bonded metal clusters with 8, 20 and 40 valence electrons

International Nuclear Information System (INIS)

Kumar, V.

1992-10-01

From studies on some clusters of metals and semiconductors, there appear some similarities in the structure of clusters with a given number of atoms and having the number of valence electrons corresponding to a shell closing. Here we present results of the atomic and electronic structure of a few other clusters with 20 and 40 valence electrons, namely Sb 4 , Sn 5 and Sb 8 using the density functional molecular dynamics method. We suggest that the similarities in the structure and deviation from them may help to understand bonding characteristics in clusters and its evolution to bulk behaviour. Our results on Sb 8 cluster are preliminary but indicate that above room temperature its structure is two weakly interacting tetrahedra which is in general agreement with the observation of predominently antimony tetramers at T > 300 K. (author). 16 refs, 2 figs

Dirac Cones, Topological Edge States, and Nontrivial Flat Bands in Two-Dimensional Semiconductors with a Honeycomb Nanogeometry

Directory of Open Access Journals (Sweden)

E. Kalesaki

2014-01-01

Full Text Available We study theoretically two-dimensional single-crystalline sheets of semiconductors that form a honeycomb lattice with a period below 10 nm. These systems could combine the usual semiconductor properties with Dirac bands. Using atomistic tight-binding calculations, we show that both the atomic lattice and the overall geometry influence the band structure, revealing materials with unusual electronic properties. In rocksalt Pb chalcogenides, the expected Dirac-type features are clouded by a complex band structure. However, in the case of zinc-blende Cd-chalcogenide semiconductors, the honeycomb nanogeometry leads to rich band structures, including, in the conduction band, Dirac cones at two distinct energies and nontrivial flat bands and, in the valence band, topological edge states. These edge states are present in several electronic gaps opened in the valence band by the spin-orbit coupling and the quantum confinement in the honeycomb geometry. The lowest Dirac conduction band has S-orbital character and is equivalent to the π-π^{⋆} band of graphene but with renormalized couplings. The conduction bands higher in energy have no counterpart in graphene; they combine a Dirac cone and flat bands because of their P-orbital character. We show that the width of the Dirac bands varies between tens and hundreds of meV. These systems emerge as remarkable platforms for studying complex electronic phases starting from conventional semiconductors. Recent advancements in colloidal chemistry indicate that these materials can be synthesized from semiconductor nanocrystals.

Electronic structure simulation of chromium aluminum oxynitride by discrete variational-Xα method and X-ray photoelectron spectroscopy

International Nuclear Information System (INIS)

Choi, Youngmin; Chang, Hyunju; Lee, Jae Do; Kim, Eunah; No, Kwangsoo

2002-01-01

We use a first-principles discrete variational (DV)-Xα method to investigate the electronic structure of chromium aluminum oxynitride. When nitrogen is substituted for oxygen in the Cr-Al-O system, the N2p level appears in the energy range between O2p and Cr3d levels. Consequently, the valence band of chromium aluminum oxynitride becomes broader and the band gap becomes smaller than that of chromium aluminum oxide, which is consistent with the photoelectron spectra for the valence band using X-ray photoelectron spectroscopy (XPS) and ultraviolet photoelectron spectroscopy (UPS). We expect that this valence band structure of chromium aluminum oxynitride will modify the transmittance slope which is a requirement for photomask application. (author)

Band-structure calculations of noble-gas and alkali halide solids using accurate Kohn-Sham potentials with self-interaction correction

International Nuclear Information System (INIS)

Li, Y.; Krieger, J.B.; Norman, M.R.; Iafrate, G.J.

1991-01-01

The optimized-effective-potential (OEP) method and a method developed recently by Krieger, Li, and Iafrate (KLI) are applied to the band-structure calculations of noble-gas and alkali halide solids employing the self-interaction-corrected (SIC) local-spin-density (LSD) approximation for the exchange-correlation energy functional. The resulting band gaps from both calculations are found to be in fair agreement with the experimental values. The discrepancies are typically within a few percent with results that are nearly the same as those of previously published orbital-dependent multipotential SIC calculations, whereas the LSD results underestimate the band gaps by as much as 40%. As in the LSD---and it is believed to be the case even for the exact Kohn-Sham potential---both the OEP and KLI predict valence-band widths which are narrower than those of experiment. In all cases, the KLI method yields essentially the same results as the OEP

The energy band structure of A{sub x}Fe{sub 2}Se{sub 2} (A = K, Rb) superconductors

Energy Technology Data Exchange (ETDEWEB)

Zabidi, Noriza A. [Physics Department, Centre for Defence Foundation Studies, Universiti Pertahanan Nasional Malaysia, Kuala Lumpur 59200 (Malaysia); Azhan, Muhd. Z. [Defence Science Department, Faculty of Defence Science and Technology, Universiti Pertahanan Nasional Malaysia, Kuala Lumpur 59200 (Malaysia); Rosli, A. N. [Faculty of Science and Technology, Universiti Sains Islam Malaysia, Nilai 71800, Negeri Sembilan (Malaysia); Shrivastava, Keshav N. [School of Physics, University of Hyderabad, Hyderabad 500046 (India)

2014-03-05

We study the band structure of antiferromagnetic A{sub x}Fe{sub 2}Se{sub 2} (A = K, Rb) superconductors by using first-principles electronic structure calculations which is density functional theory. In the vicinity of iron-vacancy, we identify the valence electrons of A{sub x}Fe{sub 2}Se{sub 2} will be filled up to the Fermi level and no semiconducting gap is observed. Hence, the A{sub x}Fe{sub 2}Se{sub 2} is a metallic instead of semiconducting which leads to superconductivity in the orbital-selective Mott phase. Similarly, there is non-vanishing density of states at the Fermi level.

Electronic structure and optical properties of defect chalcopyrite HgGa2Se4

Science.gov (United States)

Gabrelian, B. V.; Lavrentyev, A. A.; Vu, Tuan V.; Parasyuk, O. V.; Khyzhun, O. Y.

2018-01-01

We report on studies from an experimental and theoretical viewpoint of the electronic structure of mercury digallium selenide, HgGa2Se4, a very promising optoelectronic material. In particular, the method of X-ray photoelectron spectroscopy (XPS) was used to evaluate binding energies of the constituent element core electrons and the shape of the valence band for pristine and Ar+-ion bombarded surfaces of HgGa2Se4 single crystal. First principles band-structure calculations were performed in the present work using the augmented plane wave + local orbitals (APW+lo). These calculations indicate that the Se 4p states are the main contributors at the top and in the upper portion of the valence band with slightly smaller contributions of the Ga 4p states in the upper portion of the band as well. Further, the central portion of the valence band is determined mainly by contributions of the Ga 4s states, and the Hg 5d states are the principal contributors to the bottom of the valence band. These theoretical data are in fair agreement when matching on a common energy scale of the X-ray emission bands giving information on the energy distribution of the Se 4p and Ga 4p states and the XPS valence-band spectrum of the HgGa2Se4 crystal. The principal optical constants are elucidated from the DFT calculations.

Structure and Magnetic Properties of a Mixed-Valence Heptanuclear Manganese Cluster.

Science.gov (United States)

Abbati, Gian Luca; Cornia, Andrea; Fabretti, Antonio C.; Caneschi, Andrea; Gatteschi, Dante

1998-07-27

Two novel polynuclear manganese(II,III) complexes have been synthesized by exploiting controlled methanolysis. A one-pot reaction of MnCl(2), NaOMe, dibenzoylmethane (Hdbm), and O(2) in anhydrous methanol, followed by recrystallization from MeOH/CHCl(3) mixtures, afforded the alkoxomanganese complexes [Mn(7)(OMe)(12)(dbm)(6)].CHCl(3).14MeOH (2) and [Mn(2)(OMe)(2)(dbm)(4)] (3). Complex 2 crystallizes in trigonal space group R&thremacr; with a = 14.439(2) Å, alpha = 86.34(1) degrees, and Z = 1. Complex 3 crystallizes in triclinic space group P&onemacr; with a = 9.612(1) Å, b = 10.740(1) Å, c = 13.168(1) Å, alpha = 80.39(1) degrees, beta = 87.66(1) degrees, gamma = 83.57(1) degrees, and Z = 1. The solid-state structure of 2 comprises a [Mn(6)(OMe)(12)(dbm)(6)] "crown" with crystallographically imposed 6-fold symmetry plus a central manganese ion. The layered Mn/O core mimics a fragment of the manganese oxide mineral lithiophorite. Conductivity measurements confirmed the nonionic character of 2 and suggested a mixed-valence Mn(II)(3)Mn(III)(4) formulation. The metrical parameters of the core were analyzed with the aid of bond-valence sum calculations. The central ion is essentially a valence-trapped Mn(II) ion, whereas the average Mn-O distances for the manganese ions of the "crown" are consistent with the presence of two Mn(II) and four Mn(III) ions. However, (1)H NMR spectra in solution strongly support valence localization and suggest that the observed solid-state structure may be a result of static disorder effects. Magnetic susceptibility vs T and magnetization vs field data at low temperature are consistent with an S = (17)/(2) ground state. Complex 3 is a symmetric alkoxo-bridged dimer. The two high-spin Mn(III) ions are antiferromagnetically coupled with J = 0.28(4) cm(-)(1), g = 1.983(2), and D = -2.5(4) cm(-)(1).

Observation of Rydberg transitions from the inner valence shell of ethane

International Nuclear Information System (INIS)

Dillon, M.A.; Tanaka, H.; Spence, D.

1987-01-01

The electron impact spectrum of ethane has been examined in a region that includes ionization out of the inner valence shell. One diffuse structure and a progression of ten vibrational bands have been found in a 4 eV range below and to some degree overlapping the 2 A 2 /sub u/ ion threshold. Evidence indicates that the observed transitions belong to the symmetry forbidden Rydberg series (2a 2 /sub u/) 2 →(2a 2 /sub u/, npσ or npπ)

Band Offsets at the Interface between Crystalline and Amorphous Silicon from First Principles

Science.gov (United States)

Jarolimek, K.; Hazrati, E.; de Groot, R. A.; de Wijs, G. A.

2017-07-01

The band offsets between crystalline and hydrogenated amorphous silicon (a -Si ∶H ) are key parameters governing the charge transport in modern silicon heterojunction solar cells. They are an important input for macroscopic simulators that are used to further optimize the solar cell. Past experimental studies, using x-ray photoelectron spectroscopy (XPS) and capacitance-voltage measurements, have yielded conflicting results on the band offset. Here, we present a computational study on the band offsets. It is based on atomistic models and density-functional theory (DFT). The amorphous part of the interface is obtained by relatively long DFT first-principles molecular-dynamics runs at an elevated temperature on 30 statistically independent samples. In order to obtain a realistic conduction-band position the electronic structure of the interface is calculated with a hybrid functional. We find a slight asymmetry in the band offsets, where the offset in the valence band (0.29 eV) is larger than in the conduction band (0.17 eV). Our results are in agreement with the latest XPS measurements that report a valence-band offset of 0.3 eV [M. Liebhaber et al., Appl. Phys. Lett. 106, 031601 (2015), 10.1063/1.4906195].

The valence electron structure and property analysis of TiC

Institute of Scientific and Technical Information of China (English)

无

2001-01-01

The valence electron structure of TiC was calculated by using the empirical electron theory of solids and molecules. The calculated results show that with the increase of temperature the number of common electrons of TiC increases, which indicates that TiC has a good thermal sta-bility; and there exists a close relationship between hardness and brittleness of TiC. According to the number of lattice electrons, the differences among the crystals with different structures can be explained qualitatively. Using the "bond- strengthening factor", the differences of hardness among the crystals with different structures can also be qualitatively explained to some extent.

Electronic structure of metallic glasses

International Nuclear Information System (INIS)

Oelhafen, P.; Lapka, R.; Gubler, U.; Krieg, J.; DasGupta, A.; Guentherodt, H.J.; Mizoguchi, T.; Hague, C.; Kuebler, J.; Nagel, S.R.

1981-01-01

This paper is organized in six sections and deals with (1) the glassy transition metal alloys, their d-band structure, the d-band shifts on alloying and their relation to the alloy heat of formation (ΔH) and the glass forming ability, (2) the glass to crystal phase transition viewed by valence band spectroscopy, (3) band structure calculations, (4) metallic glasses prepared by laser glazing, (5) glassy normal metal alloys, and (6) glassy hydrides

Attractive electron correlation in wide band gap semiconductors by electron-photon interaction

International Nuclear Information System (INIS)

Takeda, Hiroyuki; Yoshino, Katsumi

2004-01-01

We theoretically demonstrate attractive electron correlation in wide band gap semiconductors by electron-photon interaction. At low temperature, wavevectors of electromagnetic waves absorbed in wide band gap semiconductors cannot be neglected for wavevectors of electron waves; that is, electromagnetic waves affect the movements of electrons. In particular, attractive interaction occurs between two electrons when one electron changes from a valence band to a conduction band and the other electron changes from a conduction band to a valence band

Electronic structure simulation of chromium aluminum oxynitride by discrete variational-X{alpha} method and X-ray photoelectron spectroscopy

Energy Technology Data Exchange (ETDEWEB)

Choi, Youngmin; Chang, Hyunju; Lee, Jae Do [Korea Research Inst. of Chemical Technology, Taejon (Korea); Kim, Eunah; No, Kwangsoo [Korea Advanced Inst. of Science and Technology, Taejon (Korea)

2002-09-01

We use a first-principles discrete variational (DV)-X{alpha} method to investigate the electronic structure of chromium aluminum oxynitride. When nitrogen is substituted for oxygen in the Cr-Al-O system, the N2p level appears in the energy range between O2p and Cr3d levels. Consequently, the valence band of chromium aluminum oxynitride becomes broader and the band gap becomes smaller than that of chromium aluminum oxide, which is consistent with the photoelectron spectra for the valence band using X-ray photoelectron spectroscopy (XPS) and ultraviolet photoelectron spectroscopy (UPS). We expect that this valence band structure of chromium aluminum oxynitride will modify the transmittance slope which is a requirement for photomask application. (author)

Spectroscopy of 9Be and observation of neutron halo structure in the states of positive parity rotational band

Directory of Open Access Journals (Sweden)

Demyanova A.S.

2014-03-01

Full Text Available The differential cross sections of the 9Be + α inelastic scattering at 30 MeV were measured at the tandem of Tsukuba University. All the known states of 9Be up to energies ~ 12 MeV were observed and decomposed into three rotational bands, each of them having a cluster structure consisting of a 8Be core plus a valence neutron in one of the sub-shells: p3/2−, s1/2+ and p1/2−. Existence of a neutron halo in the positive parity states was confirmed.

Surface-site-selective study of valence electronic structures of clean Si(100)-2x1 using Si-L23VV Auger electron-Si-2p photoelectron coincidence spectroscopy

International Nuclear Information System (INIS)

Kakiuchi, Takuhiro; Nagaoka, Shinichi; Hashimoto, Shogo; Fujita, Narihiko; Tanaka, Masatoshi; Mase, Kazuhiko

2010-01-01

Valence electronic structures of a clean Si(100)-2x1 surface are investigated in a surface-site-selective way using Si-L 23 VV Auger electron-Si-2p photoelectron coincidence spectroscopy. The Si-L 23 VV Auger electron spectra measured in coincidence with Si-2p photoelectrons emitted from the Si up-atoms or Si 2nd-layer of Si(100)-2x1 suggest that the position where the highest density of valence electronic states located in the vicinity of the Si up-atoms is shifted by 0.8 eV towards lower binding energy relative to that in the vicinity of the Si 2nd-layer. Furthermore, the valence band maximum in the vicinity of the Si up-atoms is indicated to be shifted by 0.1 eV towards lower binding energy relative to that in the vicinity of the Si 2nd-layer. These results are direct evidence of the transfer of negative charge from the Si 2nd-layer to the Si up-atoms. (author)

Comparison of moments from the valence structure function with QCD predictions

International Nuclear Information System (INIS)

Groot, J.G.H. de; Hansl, T.; Holder, M.; Knobloch, J.; May, J.; Paar, H.P.; Palazzi, P.; Para, A.; Ranjard, F.; Schlatter, D.; Steinberger, J.; Suter, H.; Rueden, W. von; Wahl, H.; Whitaker, S.; Williams, E.G.H.; Eisele, F.; Kleinknecht, K.; Lierl, H.; Spahn, G.; Willutzki, H.J.; Dorth, W.; Dydak, F.; Geweniger, C.; Hepp, V.; Tittel, K.; Wotschack, J.; Bloch, P.; Devaux, B.; Loucatos, S.; Maillard, J.; Merlo, J.P.; Peyaud, B.; Rander, J.; Savoy-Navarro, A.; Turlay, R.; Navarria, F.L.

1979-01-01

Moments (both ordinary and Nachtmann) of the nucleon valence structure function measured in high Q 2 γFe scattering are presented, supplemented by data from deep inelastic eD scattering. These data seem to agree with QCD predictions for vector gluons. The QCD parameter Λ is found to be of the order 0.5 GeV. (Auth.)

Determination of band alignment in the single-layer MoS2/WSe2 heterojunction

KAUST Repository

Chiu, Ming-Hui; Zhang, Chendong; Shiu, Hung-Wei; Chuu, Chih-Piao; Chen, Chang-Hsiao; Chang, Chih-Yuan S.; Chen, Chia-Hao; Chou, Mei-Yin; Shih, Chih-Kang; Li, Lain-Jong

2015-01-01

The emergence of two-dimensional electronic materials has stimulated proposals of novel electronic and photonic devices based on the heterostructures of transition metal dichalcogenides. Here we report the determination of band offsets in the heterostructures of transition metal dichalcogenides by using microbeam X-ray photoelectron spectroscopy and scanning tunnelling microscopy/spectroscopy. We determine a type-II alignment between MoS2 and WSe2 with a valence band offset value of 0.83 eV and a conduction band offset of 0.76 eV. First-principles calculations show that in this heterostructure with dissimilar chalcogen atoms, the electronic structures of WSe2 and MoS2 are well retained in their respective layers due to a weak interlayer coupling. Moreover, a valence band offset of 0.94 eV is obtained from density functional theory, consistent with the experimental determination.

Determination of band alignment in the single-layer MoS2/WSe2 heterojunction

KAUST Repository

Chiu, Ming-Hui

2015-07-16

The emergence of two-dimensional electronic materials has stimulated proposals of novel electronic and photonic devices based on the heterostructures of transition metal dichalcogenides. Here we report the determination of band offsets in the heterostructures of transition metal dichalcogenides by using microbeam X-ray photoelectron spectroscopy and scanning tunnelling microscopy/spectroscopy. We determine a type-II alignment between MoS2 and WSe2 with a valence band offset value of 0.83 eV and a conduction band offset of 0.76 eV. First-principles calculations show that in this heterostructure with dissimilar chalcogen atoms, the electronic structures of WSe2 and MoS2 are well retained in their respective layers due to a weak interlayer coupling. Moreover, a valence band offset of 0.94 eV is obtained from density functional theory, consistent with the experimental determination.

Electron and hole photoemission detection for band offset determination of tunnel field-effect transistor heterojunctions

International Nuclear Information System (INIS)

Li, Wei; Zhang, Qin; Kirillov, Oleg A.; Levin, Igor; Richter, Curt A.; Gundlach, David J.; Nguyen, N. V.; Bijesh, R.; Datta, S.; Liang, Yiran; Peng, Lian-Mao; Liang, Xuelei

2014-01-01

We report experimental methods to ascertain a complete energy band alignment of a broken-gap tunnel field-effect transistor based on an InAs/GaSb hetero-junction. By using graphene as an optically transparent electrode, both the electron and hole barrier heights at the InAs/GaSb interface can be quantified. For a Al 2 O 3 /InAs/GaSb layer structure, the barrier height from the top of the InAs and GaSb valence bands to the bottom of the Al 2 O 3 conduction band is inferred from electron emission whereas hole emissions reveal the barrier height from the top of the Al 2 O 3 valence band to the bottom of the InAs and GaSb conduction bands. Subsequently, the offset parameter at the broken gap InAs/GaSb interface is extracted and thus can be used to facilitate the development of predicted models of electron quantum tunneling efficiency and transistor performance

Evolution of optical properties and band structure from amorphous to crystalline Ga2O3 films

Science.gov (United States)

Zhang, Fabi; Li, Haiou; Cui, Yi-Tao; Li, Guo-Ling; Guo, Qixin

2018-04-01

The optical properties and band structure evolution from amorphous to crystalline Ga2O3 films was investigated in this work. Amorphous and crystalline Ga2O3 films were obtained by changing the growth substrate temperatures of pulsed laser deposition and the crystallinity increase with the rising of substrate temperature. The bandgap value and ultraviolet emission intensity of the films increase with the rising of crystallinity as observed by means of spectrophotometer and cathodoluminescence spectroscopy. Abrupt bandgap value and CL emission variations were observed when amorphous to crystalline transition took place. X-ray photoelectron spectroscopy core level spectra reveal that more oxygen vacancies and disorders exist in amorphous Ga2O3 film grown at lower substrate temperature. The valence band spectra of hard X-ray photoelectron spectroscopy present the main contribution from Ga 4sp for crystalline film deposited at substrate temperature of 500 oC, while extra subgap states has been observed in amorphous film deposited at 300 oC. The oxygen vacancy and the extra subgap density of states are suggested to be the parts of origin of bandgap and CL spectra variations. The experimental data above yields a realistic picture of optical properties and band structure variation for the amorphous to crystalline transition of Ga2O3 films.

Angle-resolved photoemission study and first-principles calculation of the electronic structure of LaSb2

International Nuclear Information System (INIS)

Acatrinei, Alice I; Browne, D; Losovyj, Y B; Young, D P; Moldovan, M; Chan, Julia Y; Sprunger, P T; Kurtz, Richard L

2003-01-01

In this work we present valence band studies of LaSb 2 using angle-resolved photoelectron spectroscopy with synchrotron radiation and compare these data with band structure calculations. Valence band spectra reveal that Sb 5p states are dominant near the Fermi level and are hybridized with the La 5d states just below. The calculations show a fair agreement with the experimentally determined valence band spectra, allowing an identification of the observed features. We measured some dispersion for kbar, especially for Sb 5p states; no significant dispersion was found for k || . (letter to the editor)

Band structure engineering for ultracold quantum gases in optical lattices

International Nuclear Information System (INIS)

Weinberg, Malte

2014-01-01

the same system maps onto a quantum spin-1/2 XY model. Owing to the quantum nature of the pseudospins, geometrical frustration leads to a highly degenerate ground state which can result in exotic valence bond spin-liquid phases. First signatures of an order-by-disorder effect emerge in this regime. A complementary approach to the manipulation of the band structure is investigated in a honeycomb potential. By rotating the quantization field of the system, the statedependent energy offset between the twofold atomic basis of the hexagonal Bravais lattice can be adjusted. This purposeful breaking of inversion symmetry enables the continuous opening of an energy gap at the Dirac points of the honeycomb band structure. In addition, a striking influence of the band gap onto the lifetimes for atoms in the first excited energy band is observed. In the last part of the thesis, both experimental manipulation techniques are discussed with respect to future applications for ultracold quantum gases in non-cubic optical lattices.

Pressure-induced changes in the electronic structure of americium metal

Science.gov (United States)

Söderlind, Per; Moore, K. T.; Landa, A.; Sadigh, B.; Bradley, J. A.

2011-08-01

We have conducted electronic-structure calculations for Am metal under pressure to investigate the behavior of the 5f-electron states. Density-functional theory (DFT) does not reproduce the experimental photoemission spectra for the ground-state phase where the 5f electrons are localized, but the theory is expected to be correct when 5f delocalization occurs under pressure. The DFT prediction is that peak structures of the 5f valence band will merge closer to the Fermi level during compression indicating the presence of itinerant 5f electrons. Existence of such 5f bands is argued to be a prerequisite for the phase transitions, particularly to the primitive orthorhombic AmIV phase, but does not agree with modern dynamical-mean-field theory (DMFT) results. Our DFT model further suggests insignificant changes of the 5f valence under pressure in agreement with recent resonant x-ray emission spectroscopy, but in contradiction to the DMFT predictions. The influence of pressure on the 5f valency in the actinides is discussed and is shown to depend in a nontrivial fashion on 5f-band position and occupation relative to the spd valence bands.

Absolute band structure determination on naturally occurring rutile with complex chemistry: Implications for mineral photocatalysis on both Earth and Mars

Science.gov (United States)

Li, Yan; Xu, Xiaoming; Li, Yanzhang; Ding, Cong; Wu, Jing; Lu, Anhuai; Ding, Hongrui; Qin, Shan; Wang, Changqiu

2018-05-01

Rutile is the most common and stable form of TiO2 that ubiquitously existing on Earth and other terrestrial planets like Mars. Semiconducting mineral such as rutile-based photoredox reactions have been considered to play important roles in geological times. However, due to the inherent complexity in chemistry, the precision determination on band structure of natural rutile and the theoretical explanation on its solar-driven photochemistry have been hardly seen yet. Considering the multiple minor and trace elements in natural rutile, we firstly obtained the single-crystal crystallography, mineralogical composition and defects characteristic of the rutile sample by using both powder and single crystal X-ray diffraction, electron microprobe analysis and X-ray photoelectron spectroscopy. Then, the band gap was accurately determined by synchrotron-based O K-edge X-ray absorption and emission spectra, which was firstly applied to natural rutile due to its robustness on compositions and defects. The absolute band edges of the rutile sample was calculated by considering the electronegativity of the atoms, band gap and point of zero charge. Besides, after detecting the defect energy levels by photoluminescence spectra, we drew the schematic band structure of natural rutile. The band gap (2.7 eV) of natural rutile was narrower than that of synthetic rutile (3.0 eV), and the conduction and valence band edges of natural rutile at pH = pHPZC were determined to be -0.04 V and 2.66 V (vs. NHE), respectively. The defect energy levels located at nearly the middle position of the forbidden band. Further, we used theoretical calculations to verify the isomorphous substitution of Fe and V for Ti gave rise to the distortion of TiO6 octahedron and created vacancy defects in natural rutile. Based on density functional theory, the narrowed band gap was interpreted to the contribution of Fe-3d and V-3d orbits, and the defect energy state was formed by hybridization of O-2p and Fe/V/Ti-3d

Band structure engineering and vacancy induced metallicity at the GaAs-AlAs interface

KAUST Repository

Upadhyay Kahaly, M.

2011-09-20

We study the epitaxial GaAs-AlAs interface of wide gap materials by full-potential density functional theory. AlAsthin films on a GaAs substrate and GaAsthin films on an AlAs substrate show different trends for the electronic band gap with increasing film thickness. In both cases, we find an insulating state at the interface and a negligible charge transfer even after relaxation. Differences in the valence and conduction band edges suggest that the energy band discontinuities depend on the growth sequence. Introduction of As vacancies near the interface induces metallicity, which opens great potential for GaAs-AlAs heterostructures in modern electronics.

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)

Geometrical and band-structure effects on phonon-limited hole mobility in rectangular cross-sectional germanium nanowires

International Nuclear Information System (INIS)

Tanaka, H.; Mori, S.; Morioka, N.; Suda, J.; Kimoto, T.

2014-01-01

We calculated the phonon-limited hole mobility in rectangular cross-sectional [001], [110], [111], and [112]-oriented germanium nanowires, and the hole transport characteristics were investigated. A tight-binding approximation was used for holes, and phonons were described by a valence force field model. Then, scattering probability of holes by phonons was calculated taking account of hole-phonon interaction atomistically, and the linearized Boltzmann's transport equation was solved to calculate the hole mobility at low longitudinal field. The dependence of the hole mobility on nanowire geometry was analyzed in terms of the valence band structure of germanium nanowires, and it was found that the dependence was qualitatively reproduced by considering an average effective mass and the density of states of holes. The calculation revealed that [110] germanium nanowires with large height along the [001] direction show high hole mobility. Germanium nanowires with this geometry are also expected to exhibit high electron mobility in our previous work, and thus they are promising for complementary metal-oxide-semiconductor (CMOS) applications

Determination of the valence-band offset of CdS/CIS solar cell devices by target factor analysis

Energy Technology Data Exchange (ETDEWEB)

Niles, D.W.; Contreras, M.; Ramanathan, K.; Noufi, R. [National Renewable Energy Lab., Golden, CO (United States)

1996-05-01

X-ray photoemission spectroscopy (XPS) is used to determine and compare the valence-band offsets ({Delta}E{sub v}) for CdS grown by chemical bath deposition on single-crystal and thin-film CuInSe{sub 2} (CIS). The thin-film CIS device was suitable for photovoltaic energy production. By sputtering through the CdS/CIS interface and reducing the depth profile with target factor analysis, the magnitude of {Delta}E{sub v} was determined to be {Delta}E{sub v} = 1.06 {+-} 0.15 eV for both the single-crystal and thin-film interfaces. This determination of {Delta}E{sub v} is about 0.25 eV larger than many previously reported estimations CdS grown by physical vapor deposition on CIS and helps explain the record performance of CdS/CIS photovoltaic devices.

Band offsets and electronic structures of interface between In{sub 0.5}Ga{sub 0.5}As and InP

Energy Technology Data Exchange (ETDEWEB)

Cai, Genwang [School of Physical Science and Engineering and Key Laboratory of Materials Physics of Ministry of Education of China, Zhengzhou University, Zhengzhou 450052 (China); College of Science, Henan University of Technology, Zhengzhou 450001 (China); Wang, Changhong; Wang, Weichao [College of Electronic Information and Optical Engineering, Nankai University, Tianjin 300071 (China); Liang, Erjun, E-mail: ejliang@zzu.edu.cn [School of Physical Science and Engineering and Key Laboratory of Materials Physics of Ministry of Education of China, Zhengzhou University, Zhengzhou 450052 (China)

2016-02-07

III–V semiconductor interfacing with high-κ gate oxide is crucial for the high mobility metal-oxide-semiconductor field transistor device. With density functional theory calculations, we explored the band offsets and electronic structures of the In{sub 0.5}Ga{sub 0.5}As/InP interfaces with various interfacial bondings. Among six different bonding interfaces, we found that P-In(Ga) bonding interface showed the highest stability. Local density of states calculations was adopted to calculate the band offsets. Except for the metallic interface, we noticed that neither valence band offset nor conduction band offset depended on the interfacial bondings. For the most stable P-In(Ga) interface, we did not observe any gap states. Furthermore, we explored the P-In(Ga) interfaces with interfacial P-As exchange defects, which slightly modified the interface stability and the band offsets but did not produce any gap states. These findings provide solid evidence that InP could serve as a promising interfacial passivation layer between III–V material and high-κ oxide in the application of high mobility devices.

XPS study on the electronic structure of hydrided Ti-V, Ti-Nb and Ti-Mo alloys

International Nuclear Information System (INIS)

Tanaka, Kazuhide; Aoki, Hiromasa

1989-01-01

Effects of hydrogenation on the core and valence electronic structures of β(bcc)-stabilized Ti-25at%V, Ti-50at%Nb and Ti-20at%Mo alloys are studied with XPS technique using monochromatized Al K α radiation. Small but uniform binding-energy shifts are observed upon hydrogenation for all the core spectra measured. Their valence-band spectra are significantly distorted, providing an evidence of the formation of metal-hydrogen bonding bands in these Ti alloys. Interrelations between the core binding-energy shifts and the valence-band distortion are discussed. (orig.)

Thermal evolution of the band edges of 6H-SiC: X-ray methods compared to the optical band gap

International Nuclear Information System (INIS)

Miedema, P.S.; Beye, M.; Könnecke, R.; Schiwietz, G.; Föhlisch, A.

2014-01-01

Highlights: • Conduction band minima (CBM) of 6H-SiC are estimated with Si 2p XAS. • Valence band maxima (VBM) of 6H-SiC are estimated with non-resonant Si 2p XES. • Temperature-dependent VBM and CBM of 6H-SiC show asymmetric band gap closing. • XAS, XES and RIXS band gap estimates are compared with the optical band gap. • XAS + XES versus optical band gap provides core-excitonic screening energies. - Abstract: The band gap of semiconductors like silicon and silicon carbide (SiC) is the key for their device properties. In this research, the band gap of 6H-SiC and its temperature dependence were analyzed with silicon 2p X-ray absorption spectroscopy (XAS), X-ray emission spectroscopy (XES) and resonant inelastic X-ray scattering (RIXS) allowing for a separate analysis of the conduction-band minimum (CBM) and valence-band maximum (VBM) components of the band gap. The temperature-dependent asymmetric band gap shrinking of 6H-SiC was determined with a valence-band slope of +2.45 × 10 −4 eV/K and a conduction-band slope of −1.334 × 10 −4 eV/K. The apparent asymmetry, e.g., that two thirds of the band-gap shrinking with increasing temperature is due to the VBM evolution in 6H-SiC, is similar to the asymmetry obtained for pure silicon before. The overall band gap temperature-dependence determined with XAS and non-resonant XES is compared to temperature-dependent optical studies. The core-excitonic binding energy appearing in the Si 2p XAS is extracted as the main difference. In addition, the energy loss of the onset of the first band in RIXS yields to values similar to the optical band gap over the tested temperature range

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.

Electronic Structures of Purple Bronze KMo6O17 Studied by X-Ray Photoemission Spectra

Science.gov (United States)

Qin, Xiaokui; Wei, Junyin; Shi, Jing; Tian, Mingliang; Chen, Hong; Tian, Decheng

X-ray photoemission spectroscopy study has been performed for the purple bronze KMo6O17. The structures of conduction band and valence band are analogous to the results of ultraviolet photoemission spectra and are also consistent with the model of Travaglini et al., but the gap between conduction and valence band is insignificant. The shape of asymmetric and broadening line of O-1s is due to unresolved contributions from the many inequivalent oxygen sites in this crystal structure. Mo 3d core-level spectrum reveals that there are two kinds of valence states of Molybdenum (Mo+5 and Mo+6). The calculated average valence state is about +5.6, which is consistent with the expectation value from the composition of this material. The tail of Mo-3d spectrum toward higher binding energy is the consequence of the excitation of electron-hole pairs with singularity index of 0.21.

Micro-Valences: Affective valence in neutral everyday objects

Directory of Open Access Journals (Sweden)

Sophie eLebrecht

2012-04-01

Full Text Available Affective valence influences both our cognition and our perception of the world. Indeed, the speed and quality with which we recognize objects in a visual scene can vary dramatically depending on its affective content. However, affective processing of visual objects has been typically studied using only stimuli with strong affective valences (e.g., guns or roses. Here we explore whether affective valence must be strong or obvious to exert an effect on our perception. We conclude that the majority of objects carry some affective valence (micro-valences and, thus, nominally neutral objects are not really neutral. Functionally, the perception of valence in everyday objects facilitates perceptually-driven choice behavior, decision-making, and affective responses.

Strongly correlated impurity band superconductivity in diamond: X-ray spectroscopic evidence

Directory of Open Access Journals (Sweden)

G. Baskaran

2006-01-01

Full Text Available In a recent X-ray absorption study in boron doped diamond, Nakamura et al. have seen a well isolated narrow boron impurity band in non-superconducting samples and an additional narrow band at the chemical potential in a superconducting sample. We interpret the beautiful spectra as evidence for upper Hubbard band of a Mott insulating impurity band and an additional metallic 'mid-gap band' of a conducting 'self-doped' Mott insulator. This supports the basic framework of a recent theory of the present author of strongly correlated impurity band superconductivity (impurity band resonating valence bond, IBRVB theory in a template of a wide-gap insulator, with no direct involvement of valence band states.

Valence electron structure of cast iron and graphltization behaviour criterion of elements

Institute of Scientific and Technical Information of China (English)

刘志林; 李志林; 孙振国; 杨晓平; 陈敏

1995-01-01

The valence electron structure of common alloy elements in phases of cast iron is calculated- The relationship between the electron structure of alloy elements and equilibrium, non-equilibrium solidification and graphitization is revealed by defining the bond energy of the strongest bond in a phase as structure formation factor S. A criterion of graphitization behaviour of elements is advanced with the critical value of the structure formation factor of graphite and the n of the strongest covalent bond in cementite. It is found that this theory conforms to practice very well when the criterion is applied to the common alloy elements.

Electronic structure study of wide band gap magnetic semiconductor (La{sub 0.6}Pr{sub 0.4}){sub 0.65}Ca{sub 0.35}MnO{sub 3} nanocrystals in paramagnetic and ferromagnetic phases

Energy Technology Data Exchange (ETDEWEB)

Dwivedi, G. D.; Chou, H.; Yang, K. S.; Jhong, D. J.; Chan, W. L. [Department of Physics, National Sun Yat-sen University, Kaohsiung 80424, Taiwan (China); Joshi, Amish G. [CSIR-National Physical Laboratory, Dr. K. S. Krishnan Road, New Delhi 110012 (India); Kumar, Shiv; Ghosh, A. K. [Department of Physics, Banaras Hindu University, Varanasi 221005 (India); Chatterjee, Sandip, E-mail: schatterji.app@iitbhu.ac.in [Department of Physics, Indian Institute of Technology (Banaras Hindu University), Varanasi 221005 (India)

2016-04-25

X-ray circular magnetic dichroism (XMCD), X-ray photoemission spectroscopy (XPS), and ultraviolet photoemission spectroscopy (UPS) techniques were used to study the electronic structure of nanocrystalline (La{sub 0.6}Pr{sub 0.4}){sub 0.65}Ca{sub 0.35}MnO{sub 3} near Fermi-level. XMCD results indicate that Mn{sup 3+} and Mn{sup 4+} spins are aligned parallel to each other at 20 K. The low M-H hysteresis curve measured at 5 K confirms ferromagnetic ordering in the (La{sub 0.6}Pr{sub 0.4}){sub 0.65}Ca{sub 0.35}MnO{sub 3} system. The low temperature valence band XPS indicates that coupling between Mn3d and O2p is enhanced and the electronic states near Fermi-level have been suppressed below T{sub C}. The valence band UPS also confirms the suppression of electronic states near Fermi-level below Curie temperature. UPS near Fermi-edge shows that the electronic states are almost absent below 0.5 eV (at 300 K) and 1 eV (at 115 K). This absence clearly demonstrates the existence of a wide band-gap in the system since, for hole-doped semiconductors, the Fermi-level resides just above the valence band maximum.

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

Multiplet effects in the electronic structure of intermediate-valence compounds

DEFF Research Database (Denmark)

Thunström, P.; Di Marco, I.; Grechnev, A.

2009-01-01

We present an implementation of the Hubbard-I approximation based on the exact solution of the atomic many-body problem incorporated in a full-potential linear muffin-tin orbital method of density-functional theory. Comparison between calculated and measured x-ray photoemission spectra reveal a g...... a good agreement for intermediate valence systems in open crystal structures such as YbInCu4, SmB6, and YbB12. Spectral features of the unoccupied states of SmB6 are predicted....

Electronic structure and optical properties of prominent phases of ...

Indian Academy of Sciences (India)

Santosh singh

2017-06-19

Jun 19, 2017 ... Our calculated band structure shows that there is a significant presence of O-2p and Ti-3d hybridization in the valence bands. ... (E ) to the c-axis, a high degree of fine structure exists ..... [4] S B Zhang, J. Phys. Condens.

Complex band structure and electronic transmission eigenchannels

DEFF Research Database (Denmark)

Jensen, Anders; Strange, Mikkel; Smidstrup, Soren

2017-01-01

and complex band structure, in this case individual eigenchannel transmissions and different complex bands. We present calculations of decay constants for the two most conductive states as determined by complex band structure and standard DFT Landauer transport calculations for one semi-conductor and two...

Analysis of the valence electronic structures and calculation of the physical properties of Fe,Co,and Ni

Institute of Scientific and Technical Information of China (English)

无

2009-01-01

The valence electronic structures of Fe, Co and Ni have been investigated with Empirical Electron Theory of Solids and Molecules. The magnetic moments, Curie temperature, cohesive energy and melting point have been calculated according to the valence electronic structure. These calculations fit the experimental data very well. Based on the calculations, the magnetic moments are proportional to the number of 3d magnetic electrons. Curie temperatures are related to the magnetic electrons and the bond lengths between magnetic atoms. Cohesive energies increase with the increase of the number of covalent electrons, and the decrease of the number of magnetic and dumb pair electrons. The melting point is mainly related to the number of covalent electron pairs distributed in the strongest bond. The contribution from the lattice electrons is very small, the dumb pair electrons weaken the melting point; however, the contribution to melting point of the magnetic electrons can be neglected. It reveals that the magnetic and thermal properties are closely related to the valence electronic structures, and the changes or transitions between the electrons obviously affect the physical properties.

Evolution of optical properties and band structure from amorphous to crystalline Ga2O3 films

Directory of Open Access Journals (Sweden)

Fabi Zhang

2018-04-01

Full Text Available The optical properties and band structure evolution from amorphous to crystalline Ga2O3 films was investigated in this work. Amorphous and crystalline Ga2O3 films were obtained by changing the growth substrate temperatures of pulsed laser deposition and the crystallinity increase with the rising of substrate temperature. The bandgap value and ultraviolet emission intensity of the films increase with the rising of crystallinity as observed by means of spectrophotometer and cathodoluminescence spectroscopy. Abrupt bandgap value and CL emission variations were observed when amorphous to crystalline transition took place. X-ray photoelectron spectroscopy core level spectra reveal that more oxygen vacancies and disorders exist in amorphous Ga2O3 film grown at lower substrate temperature. The valence band spectra of hard X-ray photoelectron spectroscopy present the main contribution from Ga 4sp for crystalline film deposited at substrate temperature of 500 oC, while extra subgap states has been observed in amorphous film deposited at 300 oC. The oxygen vacancy and the extra subgap density of states are suggested to be the parts of origin of bandgap and CL spectra variations. The experimental data above yields a realistic picture of optical properties and band structure variation for the amorphous to crystalline transition of Ga2O3 films.

Modeling direct band-to-band tunneling: From bulk to quantum-confined semiconductor devices

Science.gov (United States)

Carrillo-Nuñez, H.; Ziegler, A.; Luisier, M.; Schenk, A.

2015-06-01

A rigorous framework to study direct band-to-band tunneling (BTBT) in homo- and hetero-junction semiconductor nanodevices is introduced. An interaction Hamiltonian coupling conduction and valence bands (CVBs) is derived using a multiband envelope method. A general form of the BTBT probability is then obtained from the linear response to the "CVBs interaction" that drives the system out of equilibrium. Simple expressions in terms of the one-electron spectral function are developed to compute the BTBT current in two- and three-dimensional semiconductor structures. Additionally, a two-band envelope equation based on the Flietner model of imaginary dispersion is proposed for the same purpose. In order to characterize their accuracy and differences, both approaches are compared with full-band, atomistic quantum transport simulations of Ge, InAs, and InAs-Si Esaki diodes. As another numerical application, the BTBT current in InAs-Si nanowire tunnel field-effect transistors is computed. It is found that both approaches agree with high accuracy. The first one is considerably easier to conceive and could be implemented straightforwardly in existing quantum transport tools based on the effective mass approximation to account for BTBT in nanodevices.

Modeling direct band-to-band tunneling: From bulk to quantum-confined semiconductor devices

International Nuclear Information System (INIS)

Carrillo-Nuñez, H.; Ziegler, A.; Luisier, M.; Schenk, A.

2015-01-01

A rigorous framework to study direct band-to-band tunneling (BTBT) in homo- and hetero-junction semiconductor nanodevices is introduced. An interaction Hamiltonian coupling conduction and valence bands (CVBs) is derived using a multiband envelope method. A general form of the BTBT probability is then obtained from the linear response to the “CVBs interaction” that drives the system out of equilibrium. Simple expressions in terms of the one-electron spectral function are developed to compute the BTBT current in two- and three-dimensional semiconductor structures. Additionally, a two-band envelope equation based on the Flietner model of imaginary dispersion is proposed for the same purpose. In order to characterize their accuracy and differences, both approaches are compared with full-band, atomistic quantum transport simulations of Ge, InAs, and InAs-Si Esaki diodes. As another numerical application, the BTBT current in InAs-Si nanowire tunnel field-effect transistors is computed. It is found that both approaches agree with high accuracy. The first one is considerably easier to conceive and could be implemented straightforwardly in existing quantum transport tools based on the effective mass approximation to account for BTBT in nanodevices

Modeling direct band-to-band tunneling: From bulk to quantum-confined semiconductor devices

Energy Technology Data Exchange (ETDEWEB)

Carrillo-Nuñez, H.; Ziegler, A.; Luisier, M.; Schenk, A. [Integrated Systems Laboratory ETH Zürich, Gloriastrasse 35, 8092 Zürich (Switzerland)

2015-06-21

A rigorous framework to study direct band-to-band tunneling (BTBT) in homo- and hetero-junction semiconductor nanodevices is introduced. An interaction Hamiltonian coupling conduction and valence bands (CVBs) is derived using a multiband envelope method. A general form of the BTBT probability is then obtained from the linear response to the “CVBs interaction” that drives the system out of equilibrium. Simple expressions in terms of the one-electron spectral function are developed to compute the BTBT current in two- and three-dimensional semiconductor structures. Additionally, a two-band envelope equation based on the Flietner model of imaginary dispersion is proposed for the same purpose. In order to characterize their accuracy and differences, both approaches are compared with full-band, atomistic quantum transport simulations of Ge, InAs, and InAs-Si Esaki diodes. As another numerical application, the BTBT current in InAs-Si nanowire tunnel field-effect transistors is computed. It is found that both approaches agree with high accuracy. The first one is considerably easier to conceive and could be implemented straightforwardly in existing quantum transport tools based on the effective mass approximation to account for BTBT in nanodevices.

Levels of valence

Directory of Open Access Journals (Sweden)

Vera eShuman

2013-05-01

Full Text Available The distinction between the positive and the negative is fundamental in our emotional life. In appraisal theories, in particular in the component process model of emotion (Scherer, 1984, 2010, qualitatively different types of valence are proposed based on appraisals of (unpleasantness, goal obstructiveness/conduciveness, low or high power, self- (incongruence, and moral badness/goodness. This multifaceted conceptualization of valence is highly compatible with the frequent observation of mixed feelings in real life. However, it seems to contradict the one-dimensional conceptualization of valence often encountered in psychological theories, and the notion of valence as a common currency used to explain choice behavior. Here, we propose a framework to integrate the seemingly disparate conceptualizations of multifaceted valence and one-dimensional valence by suggesting that valence should be conceived at different levels, micro and macro. Micro-valences correspond to qualitatively different types of evaluations, potentially resulting in mixed feelings, whereas one-dimensional macro-valence corresponds to an integrative common currency to compare alternatives for choices. We propose that conceptualizing levels of valence may focus research attention on the mechanisms that relate valence at one level (micro to valence at another level (macro, leading to new hypotheses and addressing various concerns that have been raised about the valence concept, such as the valence-emotion relation.

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.

Relativistic quasiparticle band structures of Mg2Si, Mg2Ge, and Mg2Sn: Consistent parameterization and prediction of Seebeck coefficients

Science.gov (United States)

Shi, Guangsha; Kioupakis, Emmanouil

2018-02-01

We apply density functional and many-body perturbation theory calculations to consistently determine and parameterize the relativistic quasiparticle band structures of Mg2Si, Mg2Ge, and Mg2Sn, and predict the Seebeck coefficient as a function of doping and temperature. The quasiparticle band gaps, including spin-orbit coupling effects, are determined to be 0.728 eV, 0.555 eV, and 0.142 eV for Mg2Si, Mg2Ge, and Mg2Sn, respectively. The inclusion of the semicore electrons of Mg, Ge, and Sn in the valence is found to be important for the accurate determination of the band gaps of Mg2Ge and Mg2Sn. We also developed a Luttinger-Kohn Hamiltonian and determined a set of band parameters to model the near-edge relativistic quasiparticle band structure consistently for all three compounds that can be applied for thermoelectric device simulations. Our calculated values for the Seebeck coefficient of all three compounds are in good agreement with the available experimental data for a broad range of temperatures and carrier concentrations. Our results indicate that quasiparticle corrections are necessary for the accurate determination of Seebeck coefficients at high temperatures at which bipolar transport becomes important.

Levels of Valence

Science.gov (United States)

Shuman, Vera; Sander, David; Scherer, Klaus R.

2013-01-01

The distinction between the positive and the negative is fundamental in our emotional life. In appraisal theories, in particular in the component process model of emotion (Scherer, 1984, 2010), qualitatively different types of valence are proposed based on appraisals of (un)pleasantness, goal obstructiveness/conduciveness, low or high power, self-(in)congruence, and moral badness/goodness. This multifaceted conceptualization of valence is highly compatible with the frequent observation of mixed feelings in real life. However, it seems to contradict the one-dimensional conceptualization of valence often encountered in psychological theories, and the notion of valence as a common currency used to explain choice behavior. Here, we propose a framework to integrate the seemingly disparate conceptualizations of multifaceted valence and one-dimensional valence by suggesting that valence should be conceived at different levels, micro and macro. Micro-valences correspond to qualitatively different types of evaluations, potentially resulting in mixed feelings, whereas one-dimensional macro-valence corresponds to an integrative “common currency” to compare alternatives for choices. We propose that conceptualizing levels of valence may focus research attention on the mechanisms that relate valence at one level (micro) to valence at another level (macro), leading to new hypotheses, and addressing various concerns that have been raised about the valence concept, such as the valence-emotion relation. PMID:23717292

Energetic band structure of Zn3P2 crystals

Science.gov (United States)

Stamov, I. G.; Syrbu, N. N.; Dorogan, A. V.

2013-01-01

Optical functions n, k, ε1, ε2 and d2ε2/dE2 have been determined from experimental reflection spectra in the region of 1-10 eV. The revealed electronic transitions are localized in the Brillouin zone. The magnitude of valence band splitting caused by the spin-orbital interaction ΔSO is lower than the splitting caused by the crystal field ΔCR in the center of Brillouin zone and L and X points. The switching effects are investigated in Zn3P2 crystals. The characteristics of experimental samples with electric switching, adjustable resistors, and time relays based on Zn3P2 are presented.

Ab initio valence calculations in chemistry

CERN Document Server

Cook, D B

1974-01-01

Ab Initio Valence Calculations in Chemistry describes the theory and practice of ab initio valence calculations in chemistry and applies the ideas to a specific example, linear BeH2. Topics covered include the Schrödinger equation and the orbital approximation to atomic orbitals; molecular orbital and valence bond methods; practical molecular wave functions; and molecular integrals. Open shell systems, molecular symmetry, and localized descriptions of electronic structure are also discussed. This book is comprised of 13 chapters and begins by introducing the reader to the use of the Schrödinge

Band-to-band transitions, selection rules, effective mass, and excitonic contributions in monoclinic β -Ga2O3

Science.gov (United States)

Mock, Alyssa; Korlacki, Rafał; Briley, Chad; Darakchieva, Vanya; Monemar, Bo; Kumagai, Yoshinao; Goto, Ken; Higashiwaki, Masataka; Schubert, Mathias

2017-12-01

We employ an eigenpolarization model including the description of direction dependent excitonic effects for rendering critical point structures within the dielectric function tensor of monoclinic β -Ga2O3 yielding a comprehensive analysis of generalized ellipsometry data obtained from 0.75-9 eV. The eigenpolarization model permits complete description of the dielectric response. We obtain, for single-electron and excitonic band-to-band transitions, anisotropic critical point model parameters including their polarization vectors within the monoclinic lattice. We compare our experimental analysis with results from density functional theory calculations performed using the Gaussian-attenuation-Perdew-Burke-Ernzerhof hybrid density functional. We present and discuss the order of the fundamental direct band-to-band transitions and their polarization selection rules, the electron and hole effective mass parameters for the three lowest band-to-band transitions, and their excitonic contributions. We find that the effective masses for holes are highly anisotropic and correlate with the selection rules for the fundamental band-to-band transitions. The observed transitions are polarized close to the direction of the lowest hole effective mass for the valence band participating in the transition.

Bands dispersion and charge transfer in β-BeH2

Science.gov (United States)

Trivedi, D. K.; Galav, K. L.; Joshi, K. B.

2018-04-01

Predictive capabilities of ab-initio method are utilised to explore bands dispersion and charge transfer in β-BeH2. Investigations are carried out using the linear combination of atomic orbitals method at the level of density functional theory. The crystal structure and related parameters are settled by coupling total energy calculations with the Murnaghan equation of state. Electronic bands dispersion from PBE-GGA is reported. The PBE-GGA, and PBE0 hybrid functional, show that β-BeH2 is a direct gap semiconductor with 1.18 and 2.40 eV band gap. The band gap slowly decreases with pressure and beyond l00 GPa overlap of conduction and valence bands at the r point is observed. Charge transfer is studied by means of Mullikan population analysis.

The role of the core in degeneracy of chiral candidate band doubling

International Nuclear Information System (INIS)

Timar, J.; Sohler, D.; Vaman, C.; SUNY, Stony Brook, NY; Starosta, K.; Fossan, D.B.; Koike, T.; Tohoku Univ., Sendai; Lee, I.Y.; Macchiavelli, A.O.

2005-01-01

Complete text of publication follows. Nearly degenerate ΔI=1 rotational bands have been observed recently in several odd-odd nuclei in the A ∼ 130 and A ∼ 100 mass regions. The properties of these doublet bands have been found to agree with the scenario of spontaneous formation of chirality and disagree with other possible scenarios. However, the most recent results obtained from life-time experiments for some chiral candidate nuclei in the A ∼ 130 mass region seem to contradict the chiral interpretation of the doublet bands in these nuclei based on the observed differences in the absolute electromagnetic transition rates; the transition rates expected for chiral doublets are predicted to be very similar. Therefore it is interesting to search for new types of experimental data that may provide further possibilities to distinguish between alternative interpretations, and may uncover new properties of the mechanism that is responsible for the band doubling in these nuclei. Such a new type of experimental data was found by studying the chiral candidate bands in neighboring Rh nuclei. High-spin states of 103 Rh were studied using the 96 Zr( 11 B,4n) reaction at 40 MeV beam energy and chiral partner candidate bands have been found in it. As a result of this observation a special quartet of neighboring chiral candidate nuclei can be investigated for the first time. With this quartet identified a comparison between the behavior of the nearly degenerate doublet bands belonging to the same core but to different valence quasiparticle configurations, as well as belonging to different cores but to the same valence quasiparticle configuration, becomes possible. The comparison shows that the energy separation of these doublet band structures depends mainly on the core properties and only at less extent on the valence quasiparticle coupling. This observation sets up new criteria for the explanations of the band doublings, restricting the possible scenarios and providing

Change in crystalline structure and band alignment in atomic-layer-deposited HfO{sub 2} on InPusing an annealing treatment

Energy Technology Data Exchange (ETDEWEB)

Kang, Yu-Seon; Kim, Dae-Kyoung; Cho, Mann-Ho [Institute of Physics and Applied Physics, Yonsei University, Seoul 120-749 (Korea, Republic of); Seo, Jung-Hye [Division of Materials Science, Korea Basic Science Institute, Daejeon 305-333 (Korea, Republic of); Shon, Hyun Kyong; Lee, Tae Geol [Korea Research Institute of Standards and Science, Daejeon 305-540 (Korea, Republic of); Cho, Young Dae; Kim, Sun-Wook; Ko, Dae-Hong [Department of Material Science and Engineering, Yonsei University, Seoul 120-749 (Korea, Republic of); Kim, Hyoungsub [School of Advanced Materials Science and Engineering, Sungkyunkwan University, Suwon 440-746 (Korea, Republic of)

2013-08-15

Changes in structural characteristics and band alignments of atomic-layer-deposited HfO{sub 2} films on InP (001) as a function of annealing temperature and film thickness were investigated using various analytical techniques. After an annealing at temperatures over 500 C, the HfO{sub 2} films were converted into a fully crystalline structure with a tetragonal phase with no detectable interfacial layer between the film and the InP substrate. In-P-O states, produced by interfacial reactions, were increased during the post deposition annealing (PDA) process and oxides were detected in the surface region of the HfO{sub 2} film, indicating that In and P atoms had out-diffused. The E{sub g} value of the as-grown HfO{sub 2} film was found to be 5.80 {+-} 0.1 eV. After the PDA treatment, the optical band gap and valence band offset values were significantly affected by the interfacial oxide states between the HfO{sub 2} film and InP substrate. Moreover, band bending in InP, due to negative space charges generated by an unstable P-rich interfacial state during atomic layer deposition process was decreased after the annealing treatment. (copyright 2013 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim)

Band structures in fractal grading porous phononic crystals

Science.gov (United States)

Wang, Kai; Liu, Ying; Liang, Tianshu; Wang, Bin

2018-05-01

In this paper, a new grading porous structure is introduced based on a Sierpinski triangle routine, and wave propagation in this fractal grading porous phononic crystal is investigated. The influences of fractal hierarchy and porosity on the band structures in fractal graidng porous phononic crystals are clarified. Vibration modes of unit cell at absolute band gap edges are given to manifest formation mechanism of absolute band gaps. The results show that absolute band gaps are easy to form in fractal structures comparatively to the normal ones with the same porosity. Structures with higher fractal hierarchies benefit multiple wider absolute band gaps. This work provides useful guidance in design of fractal porous phononic crystals.

High-energy band structure of gold

DEFF Research Database (Denmark)

Christensen, N. Egede

1976-01-01

The band structure of gold for energies far above the Fermi level has been calculated using the relativistic augmented-plane-wave method. The calculated f-band edge (Γ6-) lies 15.6 eV above the Fermi level is agreement with recent photoemission work. The band model is applied to interpret...

True photonic band-gap mode-control in VCSEL structures

DEFF Research Database (Denmark)

Romstad, F.; Madsen, M.; Birkedal, Dan

2003-01-01

Photonic band-gap mode confinement in novel nano-structured large area VCSEL structures is confirmed by the amplified spontaneous emission spectrum. Both guide and anti-guide VCSEL structures are experimentally characterised to verify the photonic band-gap effect.......Photonic band-gap mode confinement in novel nano-structured large area VCSEL structures is confirmed by the amplified spontaneous emission spectrum. Both guide and anti-guide VCSEL structures are experimentally characterised to verify the photonic band-gap effect....

Band structure of a three-dimensional topological insulator quantum wire in the presence of a magnetic field.

Science.gov (United States)

Liu, Zhe; Jiang, Liwei; Zheng, Yisong

2016-07-13

By means of a numerical diagonalization approach, we calculate the electronic structure of a three-dimensional topological insulator (3DTI) quantum wire (QW) in the presence of a magnetic field. The QW can be viewed as a 3DTI film with lateral surfaces, when its rectangular cross section has a large aspect ratio. Our calculation indicates that nonchiral edge states emerge because of the confined states at the lateral surfaces. These states completely cover the valence band region among the Landau levels, which reasonably account for the absence of the [Formula: see text] quantum Hall effect in the relevant experimental works. In an ultrathin 3DTI film, inversion between the electron-type and hole-type bands occurs, which leads to the so-called pseudo-spin Hall effect. In a 3DTI QW with a square cross section, a tilting magnetic field can establish well-defined Landau levels in all four surfaces. In such a case, the quantum Hall edge states are localized at the square corners, characterized by the linearly crossing one-dimensional band profile. And they can be shifted between the adjacent corners by simply rotating the magnetic field.

Valence electronic structure of tantalum carbide and nitride

Institute of Scientific and Technical Information of China (English)

FAN; ChangZeng

2007-01-01

The valence electronic structures of tantalum carbide (TaC) and tantalum nitride (TaN) are studied by using the empirical electronic theory (EET). The results reveal that the bonds of these compounds have covalent, metallic and ionic characters. For a quantitative analysis of the relative strength of these components, their ionicities have been calculated by implanting the results of EET to the PVL model. It has been found that the ionicity of tantalum carbide is smaller than that of tantalum nitride. The EET results also reveal that the covalent electronic number of the strongest bond in the former is larger than that of the latter. All these suggest that the covalent bond of TaC is stronger than that of TaN, which coincides to that deduced from the first-principles method.……

Valence electronic structure of tantalum carbide and nitride

Institute of Scientific and Technical Information of China (English)

无

2007-01-01

@@ The valence electronic structures of tantalum carbide (TaC) and tantalum nitride (TaN) are studied by using the empirical electronic theory (EET). The results reveal that the bonds of these compounds have covalent, metallic and ionic characters. For a quantitative analysis of the relative strength of these components, their ionicities have been calculated by implanting the results of EET to the PVL model. It has been found that the ionicity of tantalum carbide is smaller than that of tantalum nitride. The EET results also reveal that the covalent electronic number of the strongest bond in the former is larger than that of the latter. All these suggest that the covalent bond of TaC is stronger than that of TaN, which coincides to that deduced from the first-principles method.

Theoretical band structure of the superconducting antiperovskite oxide Sr3-xSnO

Science.gov (United States)

Ikeda, Atsutoshi; Fukumoto, Toshiyuki; Oudah, Mohamed; Hausmann, Jan Niklas; Yonezawa, Shingo; Kobayashi, Shingo; Sato, Masatoshi; Tassel, Cédric; Takeiri, Fumitaka; Takatsu, Hiroshi; Kageyama, Hiroshi; Maeno, Yoshiteru

2018-05-01

In order to investigate the position of the strontium deficiency in superconductive Sr3-xSnO, we synthesized and measured X-ray-diffraction patterns of Sr3-xSnO (x ∼ 0.5). Because no clear peaks originating from superstructures were observed, strontium deficiency is most likely to be randomly distributed. We also performed first-principles band-structure calculations on Sr3-xSnO (x = 0, 0.5) using two methods: full-potential linearized-augmented plane-wave plus local orbitals method and the Korringa-Kohn-Rostoker Green function method combined with the coherent potential approximation. We revealed that the Fermi energy of Sr3-xSnO in case of x ∼ 0.5 is about 0.8 eV below the original Fermi energy of the stoichiometric Sr3SnO, where the mixing of the valence p and conduction d orbitals are considered to be small.

In-clustering induced anomalousbehavior of band gap in InAlN and InGaN

DEFF Research Database (Denmark)

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

2010-01-01

Electronic band structure calculations of In containing ternary nitride alloys are presented showing a strong modification of the band gap, EG and its pressure coefficient, dEG/dp, as a function of In-content. Two different arrangements of In atoms are considered: uniform and clustered. It is shown...... that Indium clustering is the additional, large factor leading to the unusual bowings of the band gaps and their pressure coefficients. The theoretical results are compared with experimental data on variations of EG with In content. In the analysis of observed phenomena we point out the particular role...... of the uppermost valence band....

Valence one-electron and shake-up ionization bands of fluorene, carbazole and dibenzofuran

International Nuclear Information System (INIS)

Reza Shojaei, S.H.; Morini, Filippo; Deleuze, Michael S.

2013-01-01

Highlights: • The photoelectron spectra of the title compounds are assigned in details. • Shake-up lines are found to severely contaminate both π- and σ-ionization bands. • σ-ionization onsets are subject to severe vibronic coupling complications. • We compare the results of OVGF, ADC(3) and TDDFT calculations. - Abstract: A comprehensive study of the He (I) ultra-violet photoelectron spectra of fluorene, carbazole and dibenzofuran is presented with the aid of one-particle Green’s Function calculations employing the outer-valence Green’s Function (OVGF) approach and the third-order algebraic diagrammatic construction [ADC(3)] scheme, along with Dunning’s correlation consistent basis sets of double and triple zeta quality (cc-pVDZ, cc-pVTZ). Extrapolations of the ADC(3) results for the outermost one-electron π-ionization energies to the cc-pVTZ basis set enable theoretical insights into He (I) measurements within ∼0.15 eV accuracy, up to the σ-ionization onset. The lower ionization energy of carbazole is the combined result of mesomeric and electronic relaxation effects. OVGF/cc-pVDZ or OVGF/cc-pVTZ pole strengths smaller than 0.85 systematically corroborate a breakdown of the orbital picture of ionization at the ADC(3) level. Comparison is made with calculations of the lowest doublet–doublet excitation energies of the radical cation of fluorene, by means of time-dependent density functional theory (TDDFT)

Structural, electronic structure, and band alignment properties at epitaxial NiO/Al{sub 2}O{sub 3} heterojunction evaluated from synchrotron based X-ray techniques

Energy Technology Data Exchange (ETDEWEB)

Singh, S. D., E-mail: devsh@rrcat.gov.in; Das, Arijeet; Ajimsha, R. S.; Upadhyay, Anuj; Kamparath, Rajiv; Mukherjee, C.; Misra, P.; Rai, S. K.; Sinha, A. K.; Ganguli, Tapas [Raja Ramanna Centre for Advanced Technology, Indore, Madhya Pradesh 452013 (India); Nand, Mangla; Jha, S. N. [Bhabha Atomic Research Centre, Mumbai, Maharashtra 400085 (India); Shukla, D. K.; Phase, D. M. [UGC-DAE Consortium for Scientific Research, Khandwa Road, Indore, Madhya Pradesh 452017 (India)

2016-04-28

The valence band offset value of 2.3 ± 0.2 eV at epitaxial NiO/Al{sub 2}O{sub 3} heterojunction is determined from photoelectron spectroscopy experiments. Pulsed laser deposited thin film of NiO on Al{sub 2}O{sub 3} substrate is epitaxially grown along [111] direction with two domain structures, which are in-plane rotated by 60° with respect to each other. Observation of Pendellosung oscillations around Bragg peak confirms high interfacial and crystalline quality of NiO layer deposited on Al{sub 2}O{sub 3} substrate. Surface related feature in Ni 2p{sub 3/2} core level spectra along with oxygen K-edge soft X-ray absorption spectroscopy results indicates that the initial growth of NiO on Al{sub 2}O{sub 3} substrate is in the form of islands, which merge to form NiO layer for the larger coverage. The value of conduction band offset is also evaluated from the measured values of band gaps of NiO and Al{sub 2}O{sub 3} layers. A type-I band alignment at NiO and Al{sub 2}O{sub 3} heterojunction is also obtained. The determined values of band offsets can be useful in heterojunction based light emitting devices.

Transport in bilayer and trilayer graphene: band gap engineering and band structure tuning

Science.gov (United States)

Zhu, Jun

2014-03-01

Controlling the stacking order of atomically thin 2D materials offers a powerful tool to control their properties. Linearly dispersed bands become hyperbolic in Bernal (AB) stacked bilayer graphene (BLG). Both Bernal (ABA) and rhombohedral (ABC) stacking occur in trilayer graphene (TLG), producing distinct band structures and electronic properties. A symmetry-breaking electric field perpendicular to the sample plane can further modify the band structures of BLG and TLG. In this talk, I will describe our experimental effort in these directions using dual-gated devices. Using thin HfO2 film deposited by ALD as gate dielectric, we are able to apply large displacement fields D > 6 V/nm and observe the opening and saturation of the field-induced band gap Eg in bilayer and ABC-stacked trilayer graphene, where the conduction in the mid gap changes by more than six decades. Its field and temperature dependence highlights the crucial role played by Coulomb disorder in facilitating hopping conduction and suppressing the effect of Eg in the tens of meV regime. In contrast, mid-gap conduction decreases with increasing D much more rapidly in clean h-BN dual-gated devices. Our studies also show the evolution of the band structure in ABA-stacked TLG, in particular the splitting of the Dirac-like bands in large D field and the signatures of two-band transport at high carrier densities. Comparison to theory reveals the need for more sophisticated treatment of electronic screening beyond self-consistent Hartree calculations to accurately predict the band structures of trilayer graphene and graphenic materials in general.

Band alignment of type I at (100ZnTe/PbSe interface

Directory of Open Access Journals (Sweden)

Igor Konovalov

2016-06-01

Full Text Available A junction of lattice-matched cubic semiconductors ZnTe and PbSe results in a band alignment of type I so that the narrow band gap of PbSe is completely within the wider band gap of ZnTe. The valence band offset of 0.27 eV was found, representing a minor barrier during injection of holes from PbSe into ZnTe. Simple linear extrapolation of the valence band edge results in a smaller calculated band offset, but a more elaborate square root approximation was used instead, which accounts for parabolic bands. PbSe was electrodeposited at room temperature with and without Cd2+ ions in the electrolyte. Although Cd adsorbs at the surface, the presence of Cd in the electrolyte does not influence the band offset.

Clustering of germanium atoms in silica glass responsible for the 3.1 eV emission band studied by optical absorption and X-ray absorption fine structure analysis

International Nuclear Information System (INIS)

Yoshida, Tomoko; Muto, Shunsuke; Yuliati, Leny; Yoshida, Hisao; Inada, Yasuhiro

2009-01-01

Correlation between the 3.1 eV emission band and local atomic configuration was systematically examined for Ge + implanted silica glass by UV-vis optical absorption spectroscopy and X-ray absorption fine structure (XAFS) analysis. The 2.7 eV emission band, commonly observed in defective silica, was replaced by the sharp and intense 3.1 eV emission band for the Ge + fluence > 2 x 10 16 cm -2 , in which UV-vis absorption spectra suggested clustering of Ge atoms with the size ∼1 nm. XAFS spectroscopy indicated that the Ge atoms were under coordinated with oxygen atoms nearly at a neutral valence state on average. The present results are consistent with the previous ESR study but imply that the small Ge clusters rather than the O=Ge: complexes (point defects) are responsible for the 3.1 eV emission band.

Valence nucleons in self-consistent fields

International Nuclear Information System (INIS)

Di Toro, M.; Lomnitz-Adler, J.

1978-01-01

An iterative approach to determine directly the best Hartree-Fock one-body density rho is extended by expressing rho in terms of a core and a valence part and allowing for general crossings of occupied and unoccupied levels in the valence part. Results are shown for 152 Sm and a microscopic analysis of the core structure of deformed light nuclei is carried out. (author)

Theoretical and experimental studies of the ZnSe/CuInSe2 heterojunction band offset

International Nuclear Information System (INIS)

Nelson, A.J.; Schwerdtfeger, C.R.; Wei, S.; Zunger, A.; Rioux, D.; Patel, R.; Hoechst, H.

1993-01-01

We report first-principles band structure calculations that show that ZnSe/CuInSe 2 has a significant valence band offset (VBO, ΔE v ): 0.70±0.05 eV for the relaxed interface and 0.60±0.05 eV for the coherent interface. These large values demonstrate the failure of the common anion rule. This is traced to a stronger Cu,d-Se,p level repulsion in CuInSe 2 than the Zn,d-Se,p repulsion in ZnSe. The VBO was then studied by synchrotron radiation soft x-ray photoemission spectroscopy. ZnSe overlayers were sequentially grown in steps on n-type CuInSe 2 (112) single crystals at 200 degree C. In situ photoemission measurements were acquired after each growth in order to observe changes in the valence band electronic structure as well as changes in the In 4d and Zn 3d core lines. Results of these measurements reveal that the VBO is ΔE v =0.70±0.15 eV, in good agreement with the first-principles prediction

Electronic structure of lanthanide scandates

Science.gov (United States)

Mizzi, Christopher A.; Koirala, Pratik; Marks, Laurence D.

2018-02-01

X-ray photoelectron spectroscopy, ultraviolet photoelectron spectroscopy, and density functional theory calculations were used to study the electronic structure of three lanthanide scandates: GdSc O3,TbSc O3 , and DySc O3 . X-ray photoelectron spectra simulated from first-principles calculations using a combination of on-site hybrid and GGA +U methods were found to be in good agreement with experimental x-ray photoelectron spectra. The hybrid method was used to model the ground state electronic structure and the GGA +U method accounted for the shift of valence state energies due to photoelectron emission via a Slater-Janak transition state approach. From these results, the lanthanide scandate valence bands were determined to be composed of Ln 4 f ,O 2 p , and Sc 3 d states, in agreement with previous work. However, contrary to previous work the minority Ln 4 f states were found to be located closer to, and in some cases at, the valence band maximum. This suggests that minority Ln 4 f electrons may play a larger role in lanthanide scandate properties than previously thought.

Photoelectron spectroscopic study on electronic structure of butterfly-templated ZnO

Energy Technology Data Exchange (ETDEWEB)

Kamada, Masao; Sugiyama, Harue; Takahashi, Kazutoshi; Guo, Qixin [Synchrotron Light Application Center, Saga University, Honjo 1, Saga 840-8502 (Japan); Gu, Jiajun; Zhang, Wang; Fan, Tongxiang; Zhang, Di [State Key Laboratory of Metal Matrix Composites, Shanghai Jiaotong University, Shanghai 200030 (China)

2010-06-15

Biological systems have complicated hierarchical architecture involving nano-structures inside, and are expected as another candidate for new nano-templates. The present work reports the photoelectron spectroscopic study on electronic structure of the butterfly-templated ZnO that were successfully produced from butterfly wings. Ultraviolet Photoelectron Spectrum (UPS) of the butterfly-templated ZnO shows clearly the valence band and a Zn-3d peak, indicating that the butterfly-templated ZnO has the same electronic structure as bulk ZnO. However, the details show that the energy positions of the Zn-3d level and the valence-band structure are different between them. The present results indicate that the bonding interaction between Zn-4sp and O-2p orbitals is stronger in the butterfly-templated ZnO, probably due to the nano-structures inside. Important parameters such as band bending and electron affinity are also obtained. The larger band bending and the lower electron affinity are found in the butterfly-templated ZnO (copyright 2010 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

Study of interfaces and band offsets in TiN/amorphous LaLuO3 gate stacks

KAUST Repository

Mitrovic, Ivona Z.

2011-07-01

TiN/LaLuO3 (LLO) gate stacks formed by molecular beam deposition have been investigated by X-ray photoelectron spectroscopy, medium energy ion scattering, spectroscopic ellipsometry, scanning transmission electron microscopy, electron energy loss spectroscopy and atomic force microscopy. The results indicate an amorphous structure for deposited LLO films. The band offset between the Fermi level of TiN and valence band of LLO is estimated to be 2.65 ± 0.05 eV. A weaker La-O-Lu bond and a prominent Ti2p sub-peak which relates to Ti bond to interstitial oxygen have been identified for an ultra-thin 1.7 nm TiN/3 nm LLO gate stack. The angle-dependent XPS analysis of Si2s spectra as well as shifts of La4d, La3d and Lu4d core levels suggests a silicate-type with Si-rich SiOx LLO/Si interface. Symmetrical valence and conduction band offsets for LLO to Si of 2.2 eV and the bandgap of 5.5 ± 0.1 eV have been derived from the measurements. The band alignment for ultra-thin TiN/LLO gate stack is affected by structural changes. Copyright © 2011 Published by Elsevier B.V. All rights reserved.

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

First-principle natural band alignment of GaN / dilute-As GaNAs alloy

Directory of Open Access Journals (Sweden)

Chee-Keong Tan

2015-01-01

Full Text Available Density functional theory (DFT calculations with the local density approximation (LDA functional are employed to investigate the band alignment of dilute-As GaNAs alloys with respect to the GaN alloy. Conduction and valence band positions of dilute-As GaNAs alloy with respect to the GaN alloy on an absolute energy scale are determined from the combination of bulk and surface DFT calculations. The resulting GaN / GaNAs conduction to valence band offset ratio is found as approximately 5:95. Our theoretical finding is in good agreement with experimental observation, indicating the upward movements of valence band at low-As content dilute-As GaNAs are mainly responsible for the drastic reduction of the GaN energy band gap. In addition, type-I band alignment of GaN / GaNAs is suggested as a reasonable approach for future device implementation with dilute-As GaNAs quantum well, and possible type-II quantum well active region can be formed by using InGaN / dilute-As GaNAs heterostructure.

A first-principles study of the electronic structure of the sulvanite compounds

Energy Technology Data Exchange (ETDEWEB)

Osorio-Guillen, J.M., E-mail: jorge.osorio@fisica.udea.edu.co [Instituto de Fisica, Universidad de Antioquia, Medellin A.A. 1226 (Colombia); Espinosa-Garcia, W.F. [Instituto de Fisica, Universidad de Antioquia, Medellin A.A. 1226 (Colombia)

2012-03-15

We have investigated by means of first-principles total energy calculations the electronic structure of the sulvanite compounds: Cu{sub 3}VS{sub 4}, Cu{sub 3}NbS{sub 4} and Cu{sub 3}TaS{sub 4}; the later is a possible candidate as a p-type transparent conductor with potential applications in solar cells and electrochromic devices. The calculated electronic structure shows that these compounds are indirect band gap semiconductors, with the valence band maximum located at the R-point and the conduction band minimum located at the X-point. The character of the valence band maximum is dominated by Cu d-states and the character of the conduction band minimum is due to the d-states of the group five elements. From the calculated charge density and electron localisation function we can conclude that the sulvanite compounds are polar covalent semiconductors.

Peculiarities of electronic structure of silicon-on-insulator structures and their interaction with synchrotron radiation

Directory of Open Access Journals (Sweden)

Vladimir A. Terekhov

2015-09-01

Full Text Available SOI (silicon-on-insulator structures with strained and unstrained silicon layers were studied by ultrasoft X-ray emission spectroscopy and X-ray absorption near edge structure spectroscopy with the use of synchrotron radiation techniques. Analysis of X-ray data has shown a noticeable transformation of the electron energy spectrum and local partial density of states distribution in valence and conduction bands in the strained silicon layer of the SOI structure. USXES Si L2,3 spectra analysis revealed a decrease of the distance between the L2v′ и L1v points in the valence band of the strained silicon layer as well as a shift of the first two maxima of the XANES first derivation spectra to the higher energies with respect to conduction band bottom Ec. At the same time the X-ray standing waves of synchrotron radiation (λ~12–20 nm are formed in the silicon-on-insulator structure with and without strains of the silicon layer. Moreover changing the synchrotron radiation grazing angle θ by 2° leads to a change of the electromagnetic field phase to the opposite.

Determination of the surface band bending in InxGa1−xN films by hard x-ray photoemission spectroscopy

Directory of Open Access Journals (Sweden)

Mickael Lozac'h, Shigenori Ueda, Shitao Liu, Hideki Yoshikawa, Sang Liwen, Xinqiang Wang, Bo Shen, Kazuaki Sakoda, Keisuke Kobayashi and Masatomo Sumiya

2013-01-01

Full Text Available Core-level and valence band spectra of InxGa1−xN films were measured using hard x-ray photoemission spectroscopy (HX-PES. Fine structure, caused by the coupling of the localized Ga 3d and In 4d with N 2s states, was experimentally observed in the films. Because of the large detection depth of HX-PES (~20 nm, the spectra contain both surface and bulk information due to the surface band bending. The InxGa1−xN films (x = 0–0.21 exhibited upward surface band bending, and the valence band maximum was shifted to lower binding energy when the mole fraction of InN was increased. On the other hand, downward surface band bending was confirmed for an InN film with low carrier density despite its n-type conduction. Although the Fermi level (EF near the surface of the InN film was detected inside the conduction band as reported previously, it can be concluded that EF in the bulk of the film must be located in the band gap below the conduction band minimum.

Effect of hydrogen on the diode properties of reactively sputtered amorphous silicon Schottky barrier structures

International Nuclear Information System (INIS)

Morel, D.L.; Moustakas, T.D.

1981-01-01

The diode properties of reactively sputtered hydrogenated amorphous silicon Schottky barrier structures (a-SiH/sub x/ /Pt) have been investigated. We find a systematic relation between the changes in the open circuit voltage, the barrier height, and the diode quality factor. These results are accounted for by assuming that hydrogen incorporation into the amorphous silicon network removes states from the top of the valence band and sharpens the valence-band tail. Interfacial oxide layers play a significant role in the low hydrogen content, and low band-gap regime

Structural, optical and electronic properties of K2Ba(NO3)4 crystal

Science.gov (United States)

Isaenko, L. I.; Korzhneva, K. E.; Goryainov, S. V.; Goloshumova, A. A.; Sheludyakova, L. A.; Bekenev, V. L.; Khyzhun, O. Y.

2018-02-01

Nitrate crystals reveal nonlinear optical properties and could be considered as converters of laser radiation in the short-wave region. The conditions for obtaining and basic properties of K2Ba(NO3)4 double nitrate crystals were investigated. Crystal growth was implemented by slow cooling in the temperature range of 72-49 °C and low rate evaporation. The structural analysis of K2Ba(NO3)4 formation on the basis of two mixed simple nitrate structures is discussed. The main groups of oscillations in K2Ba(NO3)4 crystal were revealed using Raman and IR spectroscopy, and the table of vibrations for this compound was compiled. The electronic structure of K2Ba(NO3)4 was elucidated in the present work from both experimental and theoretical viewpoints. In particular, X-ray photoelectron spectroscopy (XPS) was employed in the present work to measure binding energies of the atoms constituting the titled compound and its XPS valence-band spectrum for both pristine and Ar+ ion-bombarded surfaces. Further, total and partial densities of states of constituent atoms of K2Ba(NO3)4 have been calculated. The calculations reveal that the O 2p states dominate in the total valence-band region of K2Ba(NO3)4 except of its bottom, where K 3p and Ba 5p states are the principal contributors, while the bottom of the conduction band is composed mainly of the unoccupied O 2p states, with somewhat smaller contributions of the N 2p∗ states as well. With respect to the occupation of the valence band by the O 2p states, the present band-structure calculations are confirmed by comparison on a common energy scale of the XPS valence-band spectrum and the X-ray emission O Kα band for the K2Ba(NO3)4 crystal under study. Furthermore, the present calculations indicate that the K2Ba(NO3)4 compound is a direct-gap material.

Micro-Valences: Affective valence in neutral everyday objects

OpenAIRE

Sophie eLebrecht; Moshe eBar; Lisa F Barrett; Michael J Tarr

2012-01-01

Affective valence influences both our cognition and our perception of the world. Indeed, the speed and quality with which we recognize objects in a visual scene can vary dramatically depending on its affective content. However, affective processing of visual objects has been typically studied using only stimuli with strong affective valences (e.g., guns or roses). Here we explore whether affective valence must be strong or obvious to exert an effect on our perception. We conclude that the maj...

Valence band photoemission from in-situ grown GaAs(100)-c(4 x 4)

Czech Academy of Sciences Publication Activity Database

Jiříček, Petr; Cukr, Miroslav; Bartoš, Igor; Adell, M.; Strasser, T.; Schattke, W.

2006-01-01

Roč. 56, č. 1 (2006), s. 21-26 ISSN 0011-4626. [Symposium on Surface Physics /10./. Praha, 11.07.2005-15.07.2005] R&D Projects: GA ČR(CZ) GA202/04/0994 Institutional research plan: CEZ:AV0Z10100521 Keywords : GaAs(100)-c(4X4) * surface states * band structure * structure plot Subject RIV: BM - Solid Matter Physics ; Magnetism Impact factor: 0.568, year: 2006

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 ...

Design of medium band gap Ag-Bi-Nb-O and Ag-Bi-Ta-O semiconductors for driving direct water splitting with visible light.

Science.gov (United States)

Wang, Limin; Cao, Bingfei; Kang, Wei; Hybertsen, Mark; Maeda, Kazuhiko; Domen, Kazunari; Khalifah, Peter G

2013-08-19

Two new metal oxide semiconductors belonging to the Ag-Bi-M-O (M = Nb, Ta) chemical systems have been synthesized as candidate compounds for driving overall water splitting with visible light on the basis of cosubstitution of Ag and Bi on the A-site position of known Ca2M2O7 pyrochlores. The low-valence band edge energies of typical oxide semiconductors prevents direct water splitting in compounds with band gaps below 3.0 eV, a limitation which these compounds are designed to overcome through the incorporation of low-lying Ag 4d(10) and Bi 6s(2) states into compounds of nominal composition "AgBiM2O7". It was found that the "AgBiTa2O7" pyrochlores are in fact a solid solution with an approximate range of Ag(x)Bi(5/6)Ta2O(6.25+x/2) with 0.5 semiconductors with the onset of strong direct absorption at 2.72 and 2.96 eV, respectively. Electronic structure calculations for an ordered AgBiNb2O7 structure show that the band gap reduction and the elevation of the valence band primarily result from hybridized Ag d(10)-O 2p orbitals that lie at higher energy than the normal O 2p states in typical pyrochlore oxides. While the minimum energy gap is direct in the band structure, the lowest energy dipole allowed optical transitions start about 0.2 eV higher in energy than the minimum energy transition and involve different bands. This suggests that the minimum electronic band gap in these materials is slightly smaller than the onset energy for strong absorption in the optical measurements. The elevated valence band energies of the niobate and tantalate compounds are experimentally confirmed by the ability of these compounds to reduce 2 H(+) to H2 gas when illuminated after functionalization with a Pt cocatalyst.

Determination of band offsets at strained NiO and MgO heterojunction for MgO as an interlayer in heterojunction light emitting diode applications

Energy Technology Data Exchange (ETDEWEB)

Singh, S.D., E-mail: devsh@rrcat.gov.in [Raja Ramanna Centre for Advanced Technology, Indore, Madhya Pradesh 452013 (India); Nand, Mangla [Bhabha Atomic Research Centre, Mumbai, Maharashtra 400085 (India); Ajimsha, R.S.; Upadhyay, Anuj; Kamparath, Rajiv; Mukherjee, C.; Misra, P.; Sinha, A.K. [Raja Ramanna Centre for Advanced Technology, Indore, Madhya Pradesh 452013 (India); Jha, S.N. [Bhabha Atomic Research Centre, Mumbai, Maharashtra 400085 (India); Ganguli, Tapas [Raja Ramanna Centre for Advanced Technology, Indore, Madhya Pradesh 452013 (India)

2016-12-15

Highlights: • Valence band offset at NiO/MgO heterojunction is experimentally determined. • Experimentally determined value of 2.3 ± 0.4 eV is significantly larger than the predicted from theoretical calculations. • The value of valence band offset is in corroboration with that estimated from the band transitivity model. • Our result can be used to predict accurately carrier transport and electroluminescence mechanisms for heterojunction LEDs. - Abstract: Valence band offset of 2.3 ± 0.4 eV at strained NiO/MgO heterojunction is determined from photoelectron spectroscopy (PES) measurements. The determined value of valence band offset is larger than that is predicted from first principle calculations, but is in corroboration with that obtained from band transitivity rule. Our PES result indicates a larger value of the valence band offset at strained NiO/MgO heterojunction and can be used to predict accurately carrier transport and electroluminescence mechanisms for n-ZnO/MgO/p-NiO and p-NiO/MgO/n-GaN heterojunction light emitting diodes.

Tailoring band structure and band filling in a simple cubic (IV, III)-VI superconductor

Science.gov (United States)

Kriener, M.; Kamitani, M.; Koretsune, T.; Arita, R.; Taguchi, Y.; Tokura, Y.

2018-04-01

Superconductivity and its underlying mechanisms are one of the most active research fields in condensed-matter physics. An important question is how to enhance the transition temperature Tc of a superconductor. In this respect, the possibly positive role of valence-skipping elements in the pairing mechanism has been attracting considerable interest. Here we follow this pathway and successfully enhance Tc up to almost 6 K in the simple chalcogenide SnTe known as a topological crystalline insulator by doping the valence-skipping element In substitutionally for the Sn site and codoping Se for the Te site. A high-pressure synthesis method enabled us to form single-phase solid solutions Sn1 -xInxTe1 -ySey over a wide composition range while keeping the cubic structure necessary for the superconductivity. Our experimental results are supported by density-functional theory calculations which suggest that even higher Tc values would be possible if the required doping range was experimentally accessible.

Band gap of corundumlike α -Ga2O3 determined by absorption and ellipsometry

Science.gov (United States)

Segura, A.; Artús, L.; Cuscó, R.; Goldhahn, R.; Feneberg, M.

2017-07-01

The electronic structure near the band gap of the corundumlike α phase of Ga2O3 has been investigated by means of optical absorption and spectroscopic ellipsometry measurements in the ultraviolet (UV) range (400-190 nm). The absorption coefficient in the UV region and the imaginary part of the dielectric function exhibit two prominent absorption thresholds with wide but well-defined structures at 5.6 and 6.3 eV which have been ascribed to allowed direct transitions from crystal-field split valence bands to the conduction band. Excitonic effects with large Gaussian broadening are taken into account through the Elliott-Toyozawa model, which yields an exciton binding energy of 110 meV and direct band gaps of 5.61 and 6.44 eV. The large broadening of the absorption onset is related to the slightly indirect character of the material.

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

The observation of valence band change on resistive switching of epitaxial Pr{sub 0.7}Ca{sub 0.3}MnO{sub 3} film using removable liquid electrode

Energy Technology Data Exchange (ETDEWEB)

Lee, Hong-Sub; Park, Hyung-Ho, E-mail: hhpark@yonsei.ac.kr [Department of Materials Science and Engineering, Yonsei University, Seodaemun-Ku, Seoul 120-749 (Korea, Republic of)

2015-12-07

The resistive switching (RS) phenomenon in transition metal oxides (TMOs) has received a great deal of attention for non-volatile memory applications. Various RS mechanisms have been suggested as to explain the observed RS characteristics. Many reports suggest that changes of interface and the role of oxygen vacancies originate in RS phenomena; therefore, in this study, we use a liquid drop of mercury as the top electrode (TE), epitaxial Pr{sub 0.7}Ca{sub 0.3}MnO{sub 3} (PCMO) (110) film of the perovskite manganite family for RS material, and an Nb-doped (0.7 at. %) SrTiO{sub 3} (100) single crystal as the substrate to observe changes in the interface between the TE and TMOs. The use of removable liquid electrode Hg drop as TE not only enables observation of the RS characteristic as a bipolar RS curve (counterclockwise) but also facilitates analysis of the valence band of the PCMO surface after resistive switching via photoelectron spectroscopy. The observed I-V behaviors of the low and high resistance states (HRS) are explained with an electrochemical migration model in PCMO film where accumulated oxygen vacancies at the interface between the Hg TE and PCMO (110) surface induce the HRS. The interpreted RS mechanism is directly confirmed via valence band spectrum analysis.

Reformulated tight binding calculation for band discontinuity at CdTe/Hg xCd1-xTe heterointerfaces and their type I-type III transitions

International Nuclear Information System (INIS)

Ekpunobi, A.J.

2005-01-01

A recently reformulated tight binding method is used to calculate the valence band discontinuity at the CdTe/Hg x Cd 1-x Te interface in the s 2 p 2 configuration. The calculated valence band discontinuity of 0.31 eV at CdTe/HgTe interface is in good agreement with self-consistent calculation and accepted experimental value. Calculations were extended to alloy interfaces, which enabled the investigation of the band-offset problem at the transition point. Both valence band discontinuity ratio and conduction band discontinuity ratio show inflexions at the transition point

Photoelectron spectra and electronic structure of some spiroborate complexes

Energy Technology Data Exchange (ETDEWEB)

Vovna, V.I.; Tikhonov, S.A.; Lvov, I.B., E-mail: lvov.ib@dvfu.ru; Osmushko, I.S.; Svistunova, I.V.; Shcheka, O.L.

2014-12-15

Highlights: • The electronic structure of three spiroborate complexes—boron 1,2-dioxyphenylene β-diketonates has been investigated. • UV and X-ray photoelectron spectra have been interpreted. • DFT calculations have been used for interpretation of spectral bands. • The binding energy of nonequivalent carbon and oxygen atoms were measured. • The structure of X-ray photoelectron spectra of the valence electrons is in good agreement with the energies and composition of Kohn–Sham orbitals. - Abstract: The electronic structure of the valence and core levels of three spiroborate complexes – boron 1,2-dioxyphenylene β-diketonates – has been investigated by methods of UV and X-ray photoelectron spectroscopy and quantum chemical density functional theory. The ionization energy of π- and n-orbitals of the dioxyphenylene fragment and β-diketonate ligand were measured from UV photoelectron spectra. This made it possible to determine the effect of substitution of one or two methyl groups by the phenyl in diketone on the electronic structure of complexes. The binding energy of nonequivalent carbon and oxygen atoms were measured from X-ray photoelectron spectra. The results of calculations of the energy of the valence orbitals of complexes allowed us to refer bands observed in the spectra of the valence electrons to the 2s-type levels of carbon and oxygen.

Electronic structure of nanoparticles of substoichometric hexagonal tungsten oxides

International Nuclear Information System (INIS)

Khyzhun, O Y; Solonin, Y M

2007-01-01

X-ray photoelectron spectroscopy (XPS), X-ray emission spectroscopy (XES) and X-ray absorption spectroscopy (XAS) methods were used to study the electronic structure of hexagonal h-WO 3 and h-WO 2.8 nanoparticles. For comparison, nanopowder substoichiometric monoclinic tungsten oxides with close content of oxygen atoms, namely m-WO 3 and m-WO 2.77 compounds, were also investigated. For the mentioned oxides, XPS valence-band and corelevel spectra, XES O Kα bands and XAS W L III and O 1s edges were derived. The XPS valence-band spectra and O Kα emission bands in the mentioned hexagonal and monoclinic tungsten oxides were compared on a common energy scale. Both the O Kα bands and XPS valence-band spectra broaden somewhat in the sequences h-WO 3 → h-WO 2.8 and m-WO 3 → m-WO 2.77 , with the half-widths of the spectra being somewhat higher for the hexagonal oxides as compared with those for the monoclinic compounds. The effective positive charge state of tungsten atoms in h-WO 2.8 is very close to that in m-WO 2.77 , but the negative charge states of oxygen atoms are close to each other for all the tungsten oxides under consideration

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...

Relation between plasmons and the valence-band density-of-states in polymethylmethacrylate - influence of ion irradiation on damage selectivity

International Nuclear Information System (INIS)

Moliton, J.P.; Jussiaux, C.; Trigaud, T.; Lazzaroni, R.; Lhost, O.; Bredas, J.L.; Kihn, Y.; Sevely, J.

1996-01-01

A physical model is presented that aims at rationalizing the selectivity of bond breakage observed when polymethylmethacrylate is irradiated by ions in the 10-500 keV energy range. This model, previously proposed by Brandt and Ritchie, is based on electronic collective effects. The coupling between the pure plasma oscillation at omega(p) and the oscillation of free electrons at [omega(k0)(2)](1/2) makes the whole electronic population resonant at the frequency omega(rp) = (omega(p)(2) + [omega(k0)(2)])(1/2). By computing the valence-band density of states, we calculate [omega(k0)(2)] and then deduce the theoretical value of omega(rp). On the other hand, we provide an experimental measurement of omega(rp) and study its dependence on ion fluence by electron-energy-loss spectroscopy. The validity of the model of Brandt and Ritchie is then discussed in the light of both theoretical and experimental data. (author)

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.

Breakdown of rotational symmetry at semiconductor interfaces; a microscopic description of valence subband mixing

International Nuclear Information System (INIS)

Cortez, S.; Krebs, O.; Voisin, P.

2000-01-01

The recently discovered in-plane optical anisotropy of [001]-grown quantum wells offers a new theoretical and experimental insight into the electronic properties of semiconductor interfaces. We first discuss the coupling of X and Y valence bands due to the breakdown of rotation inversion symmetry at a semiconductor hetero-interface, with special attention to its dependence on effective parameters such as valence band offset. The intracell localization of Bloch functions is explained from simple theoretical arguments and evaluated numerically from a pseudo-potential microscopic model. The role of envelope functions is considered, and we discuss the specific case of non-common atom interfaces. Experimental results and applications to interface characterization are presented. These calculations give a microscopic justification, and establish the limits of the heuristic 'H BF ' model. (author)

BAND ALIGNMENT OF ULTRATHIN GIZO/SiO2/Si HETEROSTRUCTURE DETERMINED BY ELECTRON SPECTROSCOPY

Directory of Open Access Journals (Sweden)

Hee Jae Kang2

2011-11-01

Full Text Available Amorphous GaInZnO (GIZO thin films are grown on SiO2/Si substrate by the RF magnetron sputtering method. By thecombination of measured band gaps from reflection energy loss spectroscopy (REELS spectra and valence band fromX-ray photo-electron spectroscopy (XPS spectra, we have demonstrated the energy band alignment of GIZO thin films.The band gap values are 3.2 eV, 3.2 eV, 3.4eV and 3.6eV for the concentration ratios of Ga: In: Zn in GIZO thin filmsare 1:1:1, 2:2:1, 3:2:1 and 4:2:1, respectively. These are attributed to the larger band gap energy of Ga2O3 comparedwith In2O3 and ZnO. The valence band offsets (ΔEv decrease from 2.18 to 1.68 eV with increasing amount of Ga inGIZO thin films for GIZO1 to GIZO4, respectively. These experimental values of band gap and valence band offsetwill provide the further understanding in the fundamental properties of GIZO/SiO2/Si heterostructure, which will beuseful in the design, modeling and analysis of the performance devices applications.

Valence evaluation with approaching or withdrawing cues: directly testing valence-arousal conflict theory.

Science.gov (United States)

Wang, Yan Mei; Li, Ting; Li, Lin

2017-07-19

The valence-arousal conflict theory assumes that both valence and arousal will trigger approaching or withdrawing tendencies. It also predicts that the speed of processing emotional stimuli will depend on whether valence and arousal trigger conflicting or congruent motivational tendencies. However, most previous studies have provided evidence of the interaction between valence and arousal only, and have not provided direct proof of the interactive links between valence, arousal and motivational tendencies. The present study provides direct evidence for the relationship between approach-withdrawal tendencies and the valence-arousal conflict. In an empirical test, participants were instructed to judge the valence of emotional words after visual-spatial cues that appeared to be either approaching or withdrawing from participants. A three-way interaction (valence, arousal, and approach-withdrawal tendency) was observed such that the response time was shorter if participants responded to a negative high-arousal stimulus after a withdrawing cue, or to a positive low-arousal stimulus after an approaching cue. These findings suggest that the approach-withdrawal tendency indeed plays a crucial role in valence-arousal conflict, and that the effect depends on the congruency of valence, arousal and tendency at an early stage of processing.

Influence of the aggregate state on band structure and optical properties of C60 computed with different methods

Science.gov (United States)

Pal, Amrita; Arabnejad, Saeid; Yamashita, Koichi; Manzhos, Sergei

2018-05-01

C60 and C60 based molecules are efficient acceptors and electron transport layers for planar perovskite solar cells. While properties of these molecules are well studied by ab initio methods, those of solid C60, specifically its optical absorption properties, are not. We present a combined density functional theory-Density Functional Tight Binding (DFTB) study of the effect of solid state packing on the band structure and optical absorption of C60. The valence and conduction band edge energies of solid C60 differ on the order of 0.1 eV from single molecule frontier orbital energies. We show that calculations of optical properties using linear response time dependent-DFT(B) or the imaginary part of the dielectric constant (dipole approximation) can result in unrealistically large redshifts in the presence of intermolecular interactions compared to available experimental data. We show that optical spectra computed from the frequency-dependent real polarizability can better reproduce the effect of C60 aggregation on optical absorption, specifically with a generalized gradient approximation functional, and may be more suited to study effects of molecular aggregation.

Probing Transient Valence Orbital Changes with Picosecond Valence-to-Core X-ray Emission Spectroscopy

DEFF Research Database (Denmark)

March, Anne Marie; Assefa, Tadesse A.; Boemer, Christina

2017-01-01

We probe the dynamics of valence electrons in photoexcited [Fe(terpy)2]2+ in solution to gain deeper insight into the Fe ligand bond changes. We use hard X-ray emission spectroscopy (XES), which combines element specificity and high penetration with sensitivity to orbital structure, making...... valence orbitals to the nascent core-hole. Vtc-XES offers particular insight into the molecular orbitals directly involved in the light-driven dynamics; a change in the metal ligand orbital overlap results in an intensity reduction and a blue energy shift in agreement with our theoretical calculations...... and more subtle features at the highest energies reflect changes in the frontier orbital populations....

Synchrotron Studies of Narrow Band and Low-Dimensional Materials. Final Report for July 1, 1990 --- December 31, 2002

International Nuclear Information System (INIS)

Allen, J. W.

2003-01-01

This report summarizes a 12-year program of various kinds of synchrotron spectroscopies directed at the electronic structures of narrow band and low-dimensional materials that display correlated electron behaviors such as metal-insulator transitions, mixed valence, superconductivity, Kondo moment quenching, heavy Fermions, and non-Fermi liquid properties

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)

Valence photoelectron spectrum of KBr: Effects of electron correlation

International Nuclear Information System (INIS)

Calo, A.; Huttula, M.; Patanen, M.; Aksela, H.; Aksela, S.

2008-01-01

The valence photoelectron spectrum has been measured for molecular KBr. Experimental energies of the main and satellite structures have been compared with the results of ab initio calculations based on molecular orbital theory including configuration and multiconfiguration interaction approaches. Comparison between the experimental KBr spectrum and previously reported Kr valence photoelectron spectrum has also been performed in order to find out if electron correlation is of the same importance in the valence ionized state of KBr as in the corresponding state of Kr

Madelung and Hubbard interactions in polaron band model of doped organic semiconductors

Science.gov (United States)

Png, Rui-Qi; Ang, Mervin C.Y.; Teo, Meng-How; Choo, Kim-Kian; Tang, Cindy Guanyu; Belaineh, Dagmawi; Chua, Lay-Lay; Ho, Peter K.H.

2016-01-01

The standard polaron band model of doped organic semiconductors predicts that density-of-states shift into the π–π* gap to give a partially filled polaron band that pins the Fermi level. This picture neglects both Madelung and Hubbard interactions. Here we show using ultrahigh workfunction hole-doped model triarylamine–fluorene copolymers that Hubbard interaction strongly splits the singly-occupied molecular orbital from its empty counterpart, while Madelung (Coulomb) interactions with counter-anions and other carriers markedly shift energies of the frontier orbitals. These interactions lower the singly-occupied molecular orbital band below the valence band edge and give rise to an empty low-lying counterpart band. The Fermi level, and hence workfunction, is determined by conjunction of the bottom edge of this empty band and the top edge of the valence band. Calculations are consistent with the observed Fermi-level downshift with counter-anion size and the observed dependence of workfunction on doping level in the strongly doped regime. PMID:27582355

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 structures in the nematic elastomers phononic crystals

Energy Technology Data Exchange (ETDEWEB)

Yang, Shuai [Department of Mechanics, School of Civil Engineering, Beijing Jiaotong University, Beijing 100044 (China); School of Civil Engineering and Architecture, Anyang Normal University, Anyang 455000 (China); Liu, Ying, E-mail: yliu5@bjtu.edu.cn [Department of Mechanics, School of Civil Engineering, Beijing Jiaotong University, Beijing 100044 (China); Liang, Tianshu [Department of Mechanics, School of Civil Engineering, Beijing Jiaotong University, Beijing 100044 (China)

2017-02-01

As one kind of new intelligent materials, nematic elastomers (NEs) represent an exciting physical system that combines the local orientational symmetry breaking and the entropic rubber elasticity, producing a number of unique physical phenomena. In this paper, the potential application of NEs in the band tuning is explored. The band structures in two kinds of NE phononic crystals (PCs) are investigated. Through changing NE intrinsic parameters, the influence of the porosity, director rotation and relaxation on the band structures in NE PCs are analyzed. This work is a meaningful try for application of NEs in acoustic field and proposes a new intelligent strategy in band turning.

Band structures in the nematic elastomers phononic crystals

International Nuclear Information System (INIS)

Yang, Shuai; Liu, Ying; Liang, Tianshu

2017-01-01

As one kind of new intelligent materials, nematic elastomers (NEs) represent an exciting physical system that combines the local orientational symmetry breaking and the entropic rubber elasticity, producing a number of unique physical phenomena. In this paper, the potential application of NEs in the band tuning is explored. The band structures in two kinds of NE phononic crystals (PCs) are investigated. Through changing NE intrinsic parameters, the influence of the porosity, director rotation and relaxation on the band structures in NE PCs are analyzed. This work is a meaningful try for application of NEs in acoustic field and proposes a new intelligent strategy in band turning.

16O + 16O molecular structures of superdeformed states in S isotopes

Science.gov (United States)

Taniguchi, Y.

2017-06-01

Structures of excited states in S isotopes are investigated by 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 positive- and negative-parity superdeformed (SD) bands are predicted in 33-36S except for negative-parity states in 36S. The SD bands have structures of 16O + 16O + valence neutron(s) in molecular orbitals around the two 16O cores in a cluster picture. The configurations of the valence neutron(s) in the SD states are δ and/or π molecular orbitals.

Band Alignment at GaN/Single-Layer WSe2 Interface

KAUST Repository

Tangi, Malleswararao

2017-02-21

We study the band discontinuity at the GaN/single-layer (SL) WSe2 heterointerface. The GaN thin layer is epitaxially grown by molecular beam epitaxy on chemically vapor deposited SL-WSe2/c-sapphire. We confirm that the WSe2 was formed as an SL from structural and optical analyses using atomic force microscopy, scanning transmission electron microscopy, micro-Raman, absorbance, and microphotoluminescence spectra. The determination of band offset parameters at the GaN/SL-WSe2 heterojunction is obtained by high-resolution X-ray photoelectron spectroscopy, electron affinities, and the electronic bandgap values of SL-WSe2 and GaN. The valence band and conduction band offset values are determined to be 2.25 ± 0.15 and 0.80 ± 0.15 eV, respectively, with type II band alignment. The band alignment parameters determined here provide a route toward the integration of group III nitride semiconducting materials with transition metal dichalcogenides (TMDs) for designing and modeling of their heterojunction-based electronic and optoelectronic devices.

Band Alignment at GaN/Single-Layer WSe2 Interface

KAUST Repository

Tangi, Malleswararao; Mishra, Pawan; Tseng, Chien-Chih; Ng, Tien Khee; Hedhili, Mohamed N.; Anjum, Dalaver H.; Alias, Mohd Sharizal; Wei, Nini; Li, Lain-Jong; Ooi, Boon S.

2017-01-01

We study the band discontinuity at the GaN/single-layer (SL) WSe2 heterointerface. The GaN thin layer is epitaxially grown by molecular beam epitaxy on chemically vapor deposited SL-WSe2/c-sapphire. We confirm that the WSe2 was formed as an SL from structural and optical analyses using atomic force microscopy, scanning transmission electron microscopy, micro-Raman, absorbance, and microphotoluminescence spectra. The determination of band offset parameters at the GaN/SL-WSe2 heterojunction is obtained by high-resolution X-ray photoelectron spectroscopy, electron affinities, and the electronic bandgap values of SL-WSe2 and GaN. The valence band and conduction band offset values are determined to be 2.25 ± 0.15 and 0.80 ± 0.15 eV, respectively, with type II band alignment. The band alignment parameters determined here provide a route toward the integration of group III nitride semiconducting materials with transition metal dichalcogenides (TMDs) for designing and modeling of their heterojunction-based electronic and optoelectronic devices.

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.

Fluorescence properties of valence-controlled Eu2+ and Mn2+ ions in aluminosilicate glasses

International Nuclear Information System (INIS)

Van Tuyen, Ho; Nonaka, Takamasa; Yamanaka, Ken-ichi; Chau, Pham Minh; Quy Hai, Nguyen Thi; Quang, Vu Xuan; Nogami, Masayuki

2017-01-01

Controlling of valence states of metal ions doped in glasses has attracted considerable interest due to the possibility of looking toward optical applications. In this study, new Na 2 O-Al 2 O 3 -SiO 2 glasses were developed to dope Eu 2+ and Mn 2+ with well controlled valence states by heating in H 2 gas atmosphere, and the changes in the valence state of doped-ions and their fluorescence properties were investigated using visible and infrared optical absorption spectroscopies, X-ray absorption fine structure spectroscopy, and fluorescence spectroscopy. Among Eu 3+ , Mn 3+ and Mn 2+ ions incorporated in the as-prepared glasses, the Eu 3+ and Mn 3+ ions were reduced to Eu 2+ and Mn 2+ ions, respectively, by heating in H 2 gas and OH bonds were concurrently formed. The fluorescence spectra of glasses heated in H 2 exhibited broad emission bands at 450 and 630 nm wavelength, assigned to the Eu 2+ and Mn 2+ , respectively, ions, in which the fluorescence intensity at 450 nm was observed to decrease with increasing Mn 2+ ion content. The increased fluorescence intensities were analyzed as the energy transfer from Eu 2+ to Mn 2+ ions and the energy transfer efficiency was estimated with a concentration of Eu 2+ and Mn 2+ ions.

A study of the valence shell electronic states of s-triazine by photoabsorption spectroscopy and ab initio calculations

DEFF Research Database (Denmark)

Holland, D.M.P.; Shaw, D.A.; Stener, Mauro

2016-01-01

absorption bands due to excitation from the 1e00 or 6e0 orbitals. The interpretation of the experimental spectrum has been guided by transition energies and oscillator strengths, for Rydberg and valence states, calculated with the time-dependent version of density functional theory and with the coupled...... cluster linear response approach. The theoretical studies indicate that Rydberg/Rydberg and Rydberg/valence mixing is important....

Band alignment of B0.14Al0.86N/Al0.7Ga0.3N heterojunction

KAUST Repository

Sun, Haiding; Park, Young Jae; Li, Kuang-Hui; Torres Castanedo, C. G.; Alowayed, Abdulmohsen; Detchprohm, Theeradetch; Dupuis, Russell D.; Li, Xiaohang

2017-01-01

Owing to large bandgaps of BAlN and AlGaN alloys, their heterojunctions have the potential to be used in deep ultraviolet and power electronic device applications. However, the band alignment of such junctions has not been identified. In this work, we investigated the band-offset parameters of a BAlN/AlGaN heterojunction grown by metalorganic vapor phase epitaxy. These specific compositions were chosen to ensure a sufficiently large band offset for deep ultraviolet and power electronic applications. High resolution transmission electron microscopy confirmed the high structural quality of the heterojunction with an abrupt interface and uniform element distribution. We employed high resolution X-ray photoemission spectroscopy to measure the core level binding energies of B 1s and Ga 2p with respect to the valence band maximum of BAlN and AlGaN layers, respectively. Then, we measured the energy separation between the B 1s and Ga 2p core levels at the interface of the heterojunction. The valence band offset was determined to be 0.40 ± 0.05 eV. As a consequence, we identified a staggered-gap (type-II) heterojunction with the conduction band offset of 1.10 ± 0.05 eV. The determination of the band alignment of the BAlN/AlGaN heterojunction facilitates the design of optical and electronic devices based on such junctions.

Band alignment of B0.14Al0.86N/Al0.7Ga0.3N heterojunction

KAUST Repository

Sun, Haiding

2017-09-21

Owing to large bandgaps of BAlN and AlGaN alloys, their heterojunctions have the potential to be used in deep ultraviolet and power electronic device applications. However, the band alignment of such junctions has not been identified. In this work, we investigated the band-offset parameters of a BAlN/AlGaN heterojunction grown by metalorganic vapor phase epitaxy. These specific compositions were chosen to ensure a sufficiently large band offset for deep ultraviolet and power electronic applications. High resolution transmission electron microscopy confirmed the high structural quality of the heterojunction with an abrupt interface and uniform element distribution. We employed high resolution X-ray photoemission spectroscopy to measure the core level binding energies of B 1s and Ga 2p with respect to the valence band maximum of BAlN and AlGaN layers, respectively. Then, we measured the energy separation between the B 1s and Ga 2p core levels at the interface of the heterojunction. The valence band offset was determined to be 0.40 ± 0.05 eV. As a consequence, we identified a staggered-gap (type-II) heterojunction with the conduction band offset of 1.10 ± 0.05 eV. The determination of the band alignment of the BAlN/AlGaN heterojunction facilitates the design of optical and electronic devices based on such junctions.

Reformulated tight binding calculation for band discontinuity at CdTe/Hg {sub x}Cd{sub 1-x}Te heterointerfaces and their type I-type III transitions

Energy Technology Data Exchange (ETDEWEB)

Ekpunobi, A.J. [Department of Physics and Industrial Physics, Nnamdi Azikiwe University, P.M.B. 5025, Awka, Anambra State (Nigeria)

2005-02-25

A recently reformulated tight binding method is used to calculate the valence band discontinuity at the CdTe/Hg {sub x}Cd{sub 1-x}Te interface in the s{sup 2}p{sup 2} configuration. The calculated valence band discontinuity of 0.31 eV at CdTe/HgTe interface is in good agreement with self-consistent calculation and accepted experimental value. Calculations were extended to alloy interfaces, which enabled the investigation of the band-offset problem at the transition point. Both valence band discontinuity ratio and conduction band discontinuity ratio show inflexions at the transition point.

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.

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 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.

Band offsets of novel CoTiO{sub 3}/Ag{sub 3}VO{sub 4} heterojunction measured by X-ray photoelectron spectroscopy

Energy Technology Data Exchange (ETDEWEB)

Wangkawong, Kanlayawat [Department of Chemistry, Faculty of Science, Chiang Mai University, Chiang Mai 50200 (Thailand); Tantraviwat, Doldet [Thai Microelectronics Center (TMEC), National Electronics and Computer Technology Center (NECTEC), Chachoengsao 24000 (Thailand); Phanichphant, Sukon [Materials Science Research Centre, Faculty of Science, Chiang Mai University, Chiang Mai 50200 (Thailand); Inceesungvorn, Burapat, E-mail: binceesungvorn@gmail.com [Department of Chemistry, Faculty of Science, Chiang Mai University, Chiang Mai 50200 (Thailand)

2015-01-01

Highlights: • Band lineup of novel CoTiO{sub 3}/Ag{sub 3}VO{sub 4} composite is determined by semidirect XPS method. • The composite forms a type-II staggered heterojunction. • Valence and conduction-band offsets are 0.2 ± 0.3 and −0.6 ± 0.3 eV, respectively. • Band lineup determination is needed for understanding charge transfer at interfaces. - Abstract: The energy band diagram and band offsets of the novel CoTiO{sub 3}/Ag{sub 3}VO{sub 4} heterojunction photocatalyst are investigated by X-ray photoelectron spectroscopy for the first time. Excluding the strain effect, the valence-band and conduction-band offsets are determined to be 0.2 ± 0.3 eV and −0.6 ± 0.3 eV, respectively. The CoTiO{sub 3}/Ag{sub 3}VO{sub 4} composite forms a type-II heterojunction, for which the photogenerated charge carriers could be effectively separated. The results suggest that determination of the energy band structure is crucial for understanding the photogenerated charge transfer mechanism at the interfaces, hence the corresponding photocatalytic activity and would also be beneficial to the design of new and efficient heterostructure-based photocatalysts.

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....

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.

Instantaneous band gap collapse in VO{sub 2} caused by photocarrier doping

Energy Technology Data Exchange (ETDEWEB)

Herzog, Marc; Wegkamp, Daniel; Wolf, Martin; Staehler, Julia [Fritz-Haber-Institut der MPG, Berlin (Germany); Xian, Lede; Cudazzo, Pierluigi [Univ. del Pais Vasco, San Sebastian (Spain); European Theoretical Spectroscopy Facility (ETSF) (France); Gatti, Matteo [European Theoretical Spectroscopy Facility (ETSF) (France); Ecole Polytechnique, Palaiseau (France); McGahan, Christina L.; Marvel, Robert E.; Haglund, Richard F. [Vanderbilt Univ., Nashville, Tennessee (United States); Rubio, Angel [Fritz-Haber-Institut der MPG, Berlin (Germany); Univ. del Pais Vasco, San Sebastian (Spain); European Theoretical Spectroscopy Facility (ETSF) (France); MPI for the Structure and Dynamics of Matter, Hamburg (Germany)

2015-07-01

We have investigated the controversially discussed mechanism of the insulator-to-metal transition (IMT) in VO{sub 2} by means of femtosecond time-resolved photoelectron spectroscopy (trPES). Our data show that photoexcitation transforms insulating monoclinic VO{sub 2} quasi-instantaneously into a metal without an 80 fs structural bottleneck for the photoinduced electronic phase transition. First-principles many-body perturbation theory calculations reveal an ultrahigh sensitivity of the VO{sub 2} band gap to variations of the dynamically screened Coulomb interaction thus supporting the fully electronically driven isostructural IMT indicated by our trPES results. We conclude that the ultrafast band structure renormalization is caused by photoexcitation of carriers from localized V 3d valence states, strongly changing the screening before significant hot-carrier relaxation or ionic motion has occurred.

Valencies of the lanthanides

OpenAIRE

Johnson, David A.; Nelson, Peter G.

2018-01-01

The valencies of the lanthanides vary more than was once thought. In addition to valencies associated with a half-full shell, there are valencies associated with a quarter- and three-quarter-full shell. This can be explained on the basis of Slater’s theory of many-electron atoms. The same theory explains the variation in complexing constants in the trivalent state (the “tetrad effect”). Valency in metallic and organometallic compounds is also discussed.

Electrical and photoelectric properties of Si-based metal–insulator–semiconductor structures with Au nanoparticles at the insulator–semiconductor interface

Energy Technology Data Exchange (ETDEWEB)

Koryazhkina, M. N., E-mail: mahavenok@mail.ru; Tikhov, S. V.; Gorshkov, O. N.; Kasatkin, A. P.; Antonov, I. N. [Lobachevsky State University of Nizhny Novgorod (NNSU) (Russian Federation)

2016-12-15

It is shown that the formation of Au nanoparticles at the insulator–silicon interface in structures with a high density of surface states results in a shift of the Fermi-level pinning energy at this interface towards the valence-band ceiling in silicon and in increasing the surface-state density at energies close to the Fermi level. In this case, a band with a peak at 0.85 eV arises on the photosensivity curves of the capacitor photovoltage, which is explained by the photoemission of electrons from the formed Au-nanoparticle electron states near the valence-band ceiling in silicon.

Valence and Magnetic Transitions in YbMn2Ge2-Applied Pressure

International Nuclear Information System (INIS)

Hofmann, M.; Link, P.; Campbell, S.J.; Goncharenko, I.

2005-01-01

Full text: Rare-earth intermetallic compounds containing ytterbium exhibit a wide range of interesting and unusual physical and magnetic properties. This occurs mainly as a result of their mixed valence states (II/III) or changes from one valence state to the other. We have recently determined the magnetic structures of tetragonal YbMn 2 Ge 2 (I4/mmm) by powder neutron diffraction experiments and demonstrated that YbMn 2 Ge 2 has a planar antiferromagnetic structure below T N1 ∼ 510 K with a canted antiferromagnetic structure below T N2 ∼ 185 K. As applied pressure favours changes in the valence character of intermediate valence systems and correspondingly influences the magnetic behaviour, we have investigated the effects of applied pressure on YbMn 2 Ge 2 . Analyses of our in situ neutron diffraction experiments (T=1.5-300 K; p=0-2.7 GPa), reveal a distinct change in magnetic structure and a sharp drop in the a-lattice parameter above ∼ 1.4 GPa with the changes associated with a valence transition. A full account of these effects will be discussed in relation to our current photoelectron spectroscopy measurements of YbMn 2 Ge 2 . (authors)

Valence effects of sorption: laboratory control of valence state

International Nuclear Information System (INIS)

Meyer, R.E.; Arnold, W.D.; Case, F.I.

1984-01-01

Estimation of the rates of migration of nuclides from nuclear waste repositories required knowledge of the interaction of these nuclides with the components of the geological formations in the path of the migration. These interactions will be dependent upon the valence state and speciation of the nuclide. If the valence state is not known, then there can be little confidence in use of the data for safety analysis. An electrochemical method of valence state control was developed which makes use of a porous electrode in a flow system containing a column of the adsorbent. By use of this method and solvent extraction analyses of the valence states, a number of reactions of interest to HLW repositories were investigated. These include the reduction of Np(V) and Tc(VII) by crushed basalt and other minerals. For the reduction of Np(V) by basalt, the experiments indicate that sorption on basalt increases with pH and that most of the Np is reduced to Np(IV). The adsorbed Np(IV) is very difficult to remove from the basalt. For the experiments with Tc(VII), the results are considerably more complicated. The results of these experiments are used to assess some of the techniques and methods currently used in safety analyses of proposed HLW repositories. Perhaps the most important consideration is that predictive modeling of valence change reactions, such as the reduction of Np(V) and Tc(VII), must be used with considerable caution, and the occurrence of such reactions should be verified as best as possible with experiments using valence state control and analyses. 13 references, 3 figures, 1 table

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)

Effect of single vacancy on the structural, electronic structure and magnetic properties of monolayer graphyne by first-principles

Energy Technology Data Exchange (ETDEWEB)

Yun, Jiangni, E-mail: niniyun@nwu.edu.cn; Zhang, Yanni; Xu, Manzhang; Wang, Keyun; Zhang, Zhiyong

2016-10-01

The effect of single vacancy on the structural, electronic and magnetic properties of monolayer graphyne is investigated by the first-principles calculations. The calculated results reveal that single vacancy can result in the spin polarization in monolayer graphyne and the spin polarization is sensitive to local geometric structure of the vacancy. In the case of monolayer graphyne with one single vacancy at the sp{sup 2} hybridized C site, the vacancy introduces rather weakly spin-polarized, flat bands in the band gap. Due to the localization nature of the defect-induced bands, the magnetic moment is mainly localized at the vacancy site. As for the monolayer graphyne with one single vacancy at the sp hybridized C site, one defect-induced state which is highly split appears in the band gap. The spin-up band of the defect-induced state is highly dispersive and shows considerable delocalization, suggesting that the magnetic moment is dispersed around the vacancy site. The above magnetization in monolayer graphyne with one single vacancy is possibly explained in terms of the valence-bond theory. - Graphical abstract: Calculated band structure of the monolayer graphyne without (a) and with one single vacancy at Vb site (b) and at Vr site(c), respectively. Blue and red lines represent the spin-up and spin-down bands, respectively. For the sake of clarity, the band structure near the Fermi energy is also presented on the right panel. The Fermi level is set to zero on the energy scale. - Highlights: • A Jahn-Teller distortion occurs in monolayer graphyne with single vacancy. • The spin polarization is sensitive to local geometric structure of the vacancy. • Vacancy lying at sp{sup 2} hybridized C site introduces weakly spin-polarized defect bands. • A strong spin splitting occurs when the vacancy lies at sp hybridized C site. • The magnetization is explained in terms of the valence-bond theory.

Ab-initio valence band spectra of Al, In doped ZnO

International Nuclear Information System (INIS)

Palacios, P.; Sanchez, K.; Wahnon, P.

2009-01-01

We present the structural and electronic characterization of n-doped (Aluminium or Indium) ZnO and the effect of the doping on the calculated photoelectron spectroscopy (PES) spectra. The fully-relaxed calculations have been made using the density functional theory, including a Hubbard correlation term that increases the Zn-3d states binding energy, and which matches the experimental values. The effect of Oxygen vacancies is also included in our study. Our results show that the new Al or In-donor levels appearing in the conduction band hybridize with the Oxygen-2p states and help decrease the resistivity of these doped systems as was found experimentally. The calculated PES spectra show a small enhancement in the intensity close to the chemical potential as a result of these new Al or In levels

A study of the valence shell spectroscopic and thermodynamic properties of trifluoronitrosomethane cations

International Nuclear Information System (INIS)

Graham, D.M.; Powis, I.; Underwood, J.G.; Shaw, D.A.; Holland, D.M.P.

2012-01-01

Highlights: ► Fragmentation processes in CF 3 NO have been studied using mass spectrometry. ► Singly charged atomic fragments have been observed. ► Experimental appearance energies have been compared to thermochemical estimates. ► Hartree Fock transition energies and oscillator strengths have been calculated. - Abstract: A time-of-flight mass spectrometry study has been carried out to investigate the fragmentation processes occurring in trifluoronitrosomethane (CF 3 NO) as a result of valence shell photoionisation. Synchrotron radiation has been used to record spectra in the photon energy range ∼10–42 eV, and appearance energies have been determined for 10 fragment ions. At high excitation energies, singly charged atomic fragments have been observed. For the main dissociation channels, leading to the formation of NO + , CF 2 + or CF 3 + , the experimental appearance energies have been compared with thermochemical estimates, and a satisfactory agreement has been found. Structure observed in the total ion yield curve has been interpreted with the aid of excited state transition energies and oscillator strengths obtained in a time-dependent Hartree Fock calculation. The theoretical results show that configuration interaction strongly affects many of the valence states. A HeI excited photoelectron spectrum of CF 3 NO has been measured and the orbital ionisation energies have been compared with theoretical values computed using the Outer Valence Green’s Function approach. A large Franck–Condon gap is observed between the 12a′ (n - ) and the 11a ′ state bands, in accord with the calculated vertical ionisation energies of 10.87 and 16.32 eV for the 12a′ (n − ) and the 11a′ (n + ) orbitals, respectively. In the ion yield curve, the corresponding energy range is strongly influenced by autoionising valence states.

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 Structure of Eu6C60

Institute of Scientific and Technical Information of China (English)

WANG Xiao-Xiong; LI Hong-Nian; XU Ya-Bo; WANG Peng; ZHANG Wen-Hua; XU Fa-Qiang

2009-01-01

We study the valence band of Eu-intercalated C60 by synchrotron radiation photoelectron spectroscopy to un-derstand the ferromagnetism (FM) and the giant magnetoresistance (GMR) of Eu6C60. The results reveal the semiconducting property and the remarkable 5d6s-π hybridization. Eu-C60 bonding has both ionic and covalent contributions. No more than half the 5d6s electrons transfer from Eu to the LUMO derived band of C60, and the LUMO+1 derived band is not filled. The remaining valence electrons of Eu, together with some π (LUMO, HOMO and HOMO-1) electrons, constitute the covalent bond. The electronic structure implies that the magnetic coupling in Eu6C60 should be through the intra-atomic f-sd exchange and the medium of the π electrons. The possibility of the GMR being tunnelling magnetoresistance is ruled out.

Structural and electronic properties of wurtzite Bx Al1-x N from first-principles calculations

KAUST Repository

Zhang, Muwei

2017-06-14

The structural and electronic properties of wurtzite BAlN (0≤x≤1) are studied using density functional theory. The change of lattice parameters with increased B composition shows small bowing parameters and thus slightly nonlinearity. The bandgap exhibits strong dependence on the B composition, where transition from direct to indirect bandgap occurs at a relatively low B composition (x∼0.12) is observed, above which the bandgap of BAlN maintained indirect, thus desirable for low-absorption optical structures. The Γ-A and Γ-K indirect bandgaps are dominant at lower and higher B compositions, respectively. Density of states (DOS) of the valence band is susceptible to the B incorporation. Strong hybridization of Al, B, and N in p-states leads to high DOS near the valence band maximum. The hybridization of Al and B in s-states at lower B compositions and p-states of B at higher B compositions give rise to high DOS near lower end of the upper valence band. Charge density analysis reveals the B-N chemical bond is more covalent than the Al-N bond. This will lead to more covalent crystal with increasing B composition. Dramatic change of the heavy hole effective mass is found due to significant curvature increase of the band by minor B incorporation.

Structural and electronic properties of wurtzite Bx Al1-x N from first-principles calculations

KAUST Repository

Zhang, Muwei; Li, Xiaohang

2017-01-01

The structural and electronic properties of wurtzite BAlN (0≤x≤1) are studied using density functional theory. The change of lattice parameters with increased B composition shows small bowing parameters and thus slightly nonlinearity. The bandgap exhibits strong dependence on the B composition, where transition from direct to indirect bandgap occurs at a relatively low B composition (x∼0.12) is observed, above which the bandgap of BAlN maintained indirect, thus desirable for low-absorption optical structures. The Γ-A and Γ-K indirect bandgaps are dominant at lower and higher B compositions, respectively. Density of states (DOS) of the valence band is susceptible to the B incorporation. Strong hybridization of Al, B, and N in p-states leads to high DOS near the valence band maximum. The hybridization of Al and B in s-states at lower B compositions and p-states of B at higher B compositions give rise to high DOS near lower end of the upper valence band. Charge density analysis reveals the B-N chemical bond is more covalent than the Al-N bond. This will lead to more covalent crystal with increasing B composition. Dramatic change of the heavy hole effective mass is found due to significant curvature increase of the band by minor B incorporation.

Energetic band structure of Zn{sub 3}P{sub 2} crystals

Energy Technology Data Exchange (ETDEWEB)

Stamov, I.G. [Tiraspol State Corporative University, Lablocicin Street 5, 2069 Tiraspol (Moldova, Republic of); Syrbu, N.N., E-mail: sirbunn@yahoo.com [Technical University of Moldova, 168 Stefan cel Mare Avenue, 2004 Chisinau (Moldova, Republic of); Dorogan, A.V. [Technical University of Moldova, 168 Stefan cel Mare Avenue, 2004 Chisinau (Moldova, Republic of)

2013-01-01

Optical functions n, k, {epsilon}{sub 1}, {epsilon}{sub 2} and d{sup 2}{epsilon}{sub 2}/dE{sup 2} have been determined from experimental reflection spectra in the region of 1-10 eV. The revealed electronic transitions are localized in the Brillouin zone. The magnitude of valence band splitting caused by the spin-orbital interaction {Delta}{sub SO} is lower than the splitting caused by the crystal field {Delta}{sub CR} in the center of Brillouin zone and L and X points. The switching effects are investigated in Zn{sub 3}P{sub 2} crystals. The characteristics of experimental samples with electric switching, adjustable resistors, and time relays based on Zn{sub 3}P{sub 2} are presented.

But for the Bad, There Would Not Be Good: Grounding Valence in Brightness through Shared Relational Structures

Science.gov (United States)

Lakens, Daniel; Semin, Gun R.; Foroni, Francesco

2012-01-01

Light and dark are used pervasively to represent positive and negative concepts. Recent studies suggest that black and white stimuli are automatically associated with negativity and positivity. However, structural factors in experimental designs, such as the shared opposition in the valence (good vs. bad) and brightness (light vs. dark) dimensions…

Importance-truncated shell model for multi-shell valence spaces

Energy Technology Data Exchange (ETDEWEB)

Stumpf, Christina; Vobig, Klaus; Roth, Robert [Institut fuer Kernphysik, TU Darmstadt (Germany)

2016-07-01

The valence-space shell model is one of the work horses in nuclear structure theory. In traditional applications, shell-model calculations are carried out using effective interactions constructed in a phenomenological framework for rather small valence spaces, typically spanned by one major shell. We improve on this traditional approach addressing two main aspects. First, we use new effective interactions derived in an ab initio approach and, thus, establish a connection to the underlying nuclear interaction providing access to single- and multi-shell valence spaces. Second, we extend the shell model to larger valence spaces by applying an importance-truncation scheme based on a perturbative importance measure. In this way, we reduce the model space to the relevant basis states for the description of a few target eigenstates and solve the eigenvalue problem in this physics-driven truncated model space. In particular multi-shell valence spaces are not tractable otherwise. We combine the importance-truncated shell model with refined extrapolation schemes to approximately recover the exact result. We present first results obtained in the importance-truncated shell model with the newly derived ab initio effective interactions for multi-shell valence spaces, e.g., the sdpf shell.

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

Electronic structure of ZrX2 (X = Se, Te)

Science.gov (United States)

Shkvarin, A. S.; Merentsov, A. I.; Shkvarina, E. G.; Yarmoshenko, Yu. M.; Píš, I.; Nappini, S.; Titov, A. N.

2018-03-01

The electronic structure of the ZrX2 (X = Se, Te) compounds has been studied using photoelectron, resonant photoelectron and X-ray absorption spectroscopy, theoretical calculations of the X-ray absorption spectra, and density of electronic states. It was found that the absorption spectra and valence band spectra are influenced by the chalcogen type. The results of the multiplet calculation of the Zr4+ atom show that the change in the splitting in the crystal field, which is described by the 10Dq parameter, is due to the change in the ratio of covalent and ionic contributions to the chemical bond. The resonance band near the Fermi level in the valence band spectra is observed for ZrTe2 in the Zr 3p-4d resonant excitation mode. The extent of photon energy indicates the charge localization on the Zr atom. Similar resonance band for ZrSe2 is absent; it indicates the presence of a gap at the Fermi level.

Semiempirical search for oxide superconductors based on bond valence sums

International Nuclear Information System (INIS)

Tanaka, S.; Fukushima, N.; Niu, H.; Ando, K.

1992-01-01

Relationships between crystal structures and electronic states of layered transition-metal oxides are analyzed in the light of bond valence sums. Correlations between the superconducting transition temperature T c and the bond-valence-sum parameters are investigated for the high-T c cuprate compounds. Possibility of making nonsuperconducting oxides superconducting is discussed. (orig.)

Effect of valence on the electromigration in silver

International Nuclear Information System (INIS)

Nguyen Van Doan

1970-01-01

It is shown that the apparent effective valence Z B ** of a solute deduced from experiments differs from the true effective valence Z B * defined in the atomic models by a corrective term due to the 'vacancy flow effect'. The experimental results suggest that this corrective term is very important and that it is negative for transition elements; this hypothesis is confirmed for the case of iron in a copper matrix. For the elements to the right of silver in the periodic table, where the correction can be neglected, the effective valence of the solute varies linearly with z (z + 1), z being the difference between the valency of the solute and the solvent; in contrast, the further the solute is from the solvent in the periodic table the more nearly the electronic structure of the ion at the saddle point resembles that of the ion at the equilibrium position. (author) [fr

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)

Control of Ge1-x-ySixSny layer lattice constant for energy band alignment in Ge1-xSnx/Ge1-x-ySixSny heterostructures

Science.gov (United States)

Fukuda, Masahiro; Watanabe, Kazuhiro; Sakashita, Mitsuo; Kurosawa, Masashi; Nakatsuka, Osamu; Zaima, Shigeaki

2017-10-01

The energy band alignment of Ge1-xSnx/Ge1-x-ySixSny heterostructures was investigated, and control of the valence band offset at the Ge1-xSnx/Ge1-x-ySixSny heterointerface was achieved by controlling the Si and Sn contents in the Ge1-x-ySixSny layer. The valence band offset in the Ge0.902Sn0.098/Ge0.41Si0.50Sn0.09 heterostructure was evaluated to be as high as 330 meV, and its conduction band offset was estimated to be 150 meV by considering the energy bandgap calculated from the theoretical prediction. In addition, the formation of the strain-relaxed Ge1-x-ySixSny layer was examined and the crystalline structure was characterized. The epitaxial growth of a strain-relaxed Ge0.64Si0.21Sn0.15 layer with the degree of strain relaxation of 55% was examined using a virtual Ge substrate. Moreover, enhancement of the strain relaxation was demonstrated by post-deposition annealing, where a degree of strain relaxation of 70% was achieved after annealing at 400 °C. These results indicate the possibility for enhancing the indirect-direct crossover with a strained and high-Sn-content Ge1-xSnx layer on a strain-relaxed Ge1-x-ySixSny layer, realizing preferable carrier confinement by type-I energy band alignment with high conduction and valence band offsets.

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...

Photoionization cross-sections of ground and excited valence levels of actinides

Directory of Open Access Journals (Sweden)

Yarzhemsky Victor G.

2012-01-01

Full Text Available The photoionization cross-sections of ground and excited atomic states of actinide atoms were calculated by the Dirac-Fock-Slater method for two excitation energies of X-ray radiation (1253.6 eV and 1486.6 eV. These data are required for calculations of intensities of X-ray photoelectron spectra of actinide compound valence bands and interpretation of experimental spectra.

Valence electronic properties of porphyrin derivatives.

Science.gov (United States)

Stenuit, G; Castellarin-Cudia, C; Plekan, O; Feyer, V; Prince, K C; Goldoni, A; Umari, P

2010-09-28

We present a combined experimental and theoretical investigation of the valence electronic structure of porphyrin-derived molecules. The valence photoemission spectra of the free-base tetraphenylporphyrin and of the octaethylporphyrin molecule were measured using synchrotron radiation and compared with theoretical spectra calculated using the GW method and the density-functional method within the generalized gradient approximation. Only the GW results could reproduce the experimental data. We found that the contribution to the orbital energies due to electronic correlations has the same linear behavior in both molecules, with larger deviations in the vicinity of the HOMO level. This shows the importance of adequate treatment of electronic correlations in these organic systems.

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...

Reconstructing the energy band electronic structure of pulsed laser deposited CZTS thin films intended for solar cell absorber applications

Science.gov (United States)

Pandiyan, Rajesh; Oulad Elhmaidi, Zakaria; Sekkat, Zouheir; Abd-lefdil, Mohammed; El Khakani, My Ali

2017-02-01

We report here on the use of pulsed KrF-laser deposition (PLD) technique for the growth of high-quality Cu2ZnSnS4 (CZTS) thin films onto Si, and glass substrates without resorting to any post sulfurization process. The PLD-CZTS films were deposited at room temperature (RT) and then subjected to post annealing at different temperatures ranging from 200 to 500 °C in Argon atmosphere. The X-ray diffraction and Raman spectroscopy confirmed that the PLD films crystallize in the characteristic kesterite CZTS structure regardless of their annealing temperature (Ta), but their crystallinity is much improved for Ta ≥ 400 °C. The PLD-CZTS films were found to exhibit a relatively dense morphology with a surface roughness (RMS) that increases with Ta (from ∼14 nm at RT to 70 nm at Ta = 500 °C with a value around 40 nm for Ta = 300-400 °C). The optical bandgap of the PLD-CZTS films, was derived from UV-vis transmission spectra analysis, and found to decrease from 1.73 eV for non-annealed films to ∼1.58 eV for those annealed at Ta = 300 °C. These band gap values are very close to the optimum value needed for an ideal solar cell absorber. In order to achieve a complete reconstruction of the one-dimensional energy band structure of these PLD-CZTS absorbers, we have combined both XPS and UPS spectroscopies to determine their chemical bondings, the position of their valence band maximum (relative to Fermi level), and their work function values. This enabled us to sketch out, as accurately as possible, the band alignment of the heterojunction interface formed between CZTS and both CdS and ZnS buffer layer materials.

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 offsets in ITO/Ga2O3 heterostructures

Science.gov (United States)

Carey, Patrick H.; Ren, F.; Hays, David C.; Gila, B. P.; Pearton, S. J.; Jang, Soohwan; Kuramata, Akito

2017-11-01

The valence band offsets in rf-sputtered Indium Tin Oxide (ITO)/single crystal β-Ga2O3 (ITO/Ga2O3) heterostructures were measured with X-Ray Photoelectron Spectroscopy using the Kraut method. The bandgaps of the component materials in the heterostructure were determined by Reflection Electron Energy Loss Spectroscopy as 4.6 eV for Ga2O3 and 3.5 eV for ITO. The valence band offset was determined to be -0.78 ± 0.30 eV, while the conduction band offset was determined to be -0.32 ± 0.13 eV. The ITO/Ga2O3 system has a nested gap (type I) alignment. The use of a thin layer of ITO between a metal and the Ga2O3 is an attractive approach for reducing contact resistance on Ga2O3-based power electronic devices and solar-blind photodetectors.

Multiband model of the valence-band electronic structure in cylindrical GaAs nanowires

Directory of Open Access Journals (Sweden)

Čukarić Nemanja A.

2010-01-01

Full Text Available We compute the hole states in the GaAs free-standing nanowires, and in the GaAs/(Al,GaAs core-shell nanowires of type I-s, which are grown along the [100] direction. The hole states are extracted from the 4-band Luttinger-Kohn Hamiltonian, which explicitly takes into account mixing between the light and heavy holes. The axial aproximation is adopted, which allowed classification of states according to the total angular monentum (fz when expressed in units of the Planck constant. The envelope functions are expanded in Bessel functions of the first kind. The dispersion relations of the subbands E(kz obtained by the devised method do not resemble parabolas, which is otherwise a feature of the dispersion relations of the conduction subbands. Furthermore, the energy levels of holes whose total orbital momentum is fz=1/2 are shown to cross for a free-standing wire. The low energy fz=1/2 states are found to anticross, but these anticrossings turn into crossings when the ratio of the inner and outer radius of the core-shell wire takes a certain value. The influence of the geometric parameters on the dispersion relations is considered for both free standing and core-shell nanowires.

Density functional study of electronic structure, elastic and optical properties of MNH2 (M=Li, Na, K, Rb)

International Nuclear Information System (INIS)

Babu, K Ramesh; Vaitheeswaran, G

2014-01-01

We report a systematic first principles density functional study on the electronic structure, elastic and optical properties of nitrogen based solid hydrogen storage materials LiNH 2 , NaNH 2 , KNH 2 , and RbNH 2 . The ground state structural properties are calculated by using standard density functional theory, and also dispersion corrected density functional theory. We find that van der Waals interactions are dominant in LiNH 2 whereas they are relatively weak in other alkali metal amides. The calculated elastic constants show that all the compounds are mechanically stable and LiNH 2 is found to be a stiffer material among the alkali metal amides. The melting temperatures are calculated and follow the order RbNH 2 2 2 2 . The electronic band structure is calculated by using the Tran–Blaha modified Becke–Johnson potential and found that all the compounds are insulators, with a considerable band gap. The [NH 2 ] − derived states completely dominate in the entire valence band region while the metal atom states occupy the conduction band. The calculated band structure is used to analyze the different interband optical transitions occurring between valence and conduction bands. Our calculations show that these materials have considerable optical anisotropy. (paper)

Determination of band-structure parameters of Pbsub(1-x)Snsub(x)Te narrow-gap semiconductor from infrared Faraday rotation

International Nuclear Information System (INIS)

Sizov, F.F.; Lashkarev, G.V.; Martynchuk, E.K.

1977-01-01

The temeprature dependences of Faraday rotation in Pbsub(1-x)Snsub(x)Te of p type with the hole density 3x10 16 -2.2x10 18 cm -3 are studied in the range 40-370 K and in the spectral interval 4-16 μm. The analysis of interband Faraday rotation confirms a conclusion made by the authors earlier that the g factor for the c band (gsub(c)) is positive, for the v band (gsub(v))-negative and that [gsub(c)] > [gsub(v)]. The temperature dependences of carrier effective masses are investigated on the basis of the two-band model. It is demonstrated that for T < 200 K the Faraday effective mass of holes near the ceiling of the valency band varies in direct proportion to the width of the forbidden band. The temperature increase of the Faraday effective mass of current carriers, which is faster than that of the effective electron mass, is discovered, and this is related to the effect of the heavy hole band

Interfacial chemical bonding state and band alignment of CaF2/hydrogen-terminated diamond heterojunction

International Nuclear Information System (INIS)

Liu, J. W.; Liao, M. Y.; Cheng, S. H.; Imura, M.; Koide, Y.

2013-01-01

CaF 2 films are deposited on hydrogen-terminated diamond (H-diamond) by a radio-frequency sputter-deposition technique at room temperature. Interfacial chemical bonding state and band alignment of CaF 2 /H-diamond heterojunction are investigated by X-ray photoelectron spectroscopy. It is confirmed that there are only C-Ca bonds at the CaF 2 /H-diamond heterointerface. Valence and conductance band offsets of the CaF 2 /H-diamond heterojunciton are determined to be 3.7 ± 0.2 and 0.3 ± 0.2 eV, respectively. It shows a type I straddling band configuration. The large valence band offset suggests advantage of the CaF 2 /H-diamond heterojunciton for the development of high power and high frequency field effect transistors.

Evaluation of band alignment of α-Ga2O3/α-(Al x Ga1‑ x )2O3 heterostructures by X-ray photoelectron spectroscopy

Science.gov (United States)

Uchida, Takayuki; Jinno, Riena; Takemoto, Shu; Kaneko, Kentaro; Fujita, Shizuo

2018-04-01

The band alignment at an α-Ga2O3/α-(Al x Ga1‑ x )2O3 heterointerface, with different Al compositions (x), grown on a c-plane sapphire substrate was evaluated by X-ray photoelectron spectroscopy. The experimental results show that the heterointerface has the type-I band discontinuity with the valence band offsets of 0.090, 0.12, and 0.14 eV, and the conduction band offsets of 0.34, 0.79, and 1.87 eV, for x values of 0.1, 0.4, and 0.8, respectively. The small band offset for the valence band is attributed to the fact that the valence band of oxides is constituted by the localized O 2p level, which is dominated by the nature of oxygen atoms. The type-I band discontinuity is desirable for a variety of heterostructure devices.

Electronic structure and p-type doping of ZnSnN2

Science.gov (United States)

Wang, Tianshi; Janotti, Anderson; Ni, Chaoying

ZnSnN2 is a promising solar-cell absorber material composed of earth abundant elements. Little is known about doping, defects, and how the valence and conduction bands in this material align with the bands in other semiconductors. Using density functional theory with the the Heyd-Scuseria-Ernzerhof hybrid functional (HSE06), we investigate the electronic structure of ZnSnN2, its band alignment to other semiconductors, such as GaN and ZnO, the possibility of p-type doping, and the possible causes of the observed unintentional n-type conductivity. We find that the position of the valence-band maximum of ZnSnN2 is 0.55 eV higher than that of GaN, yet the conduction-band minimum is close to that in ZnO. As possible p-type dopants, we explore Li, Na, and K substituting on the Zn site. Finally, we discuss the cause of unintentional n-type conductivity by analyzing the position of the conduction-band minimum with respect to that of GaN and ZnO.

Electronic structure calculations on nitride semiconductors and their alloys

International Nuclear Information System (INIS)

Dugdale, D.

2000-09-01

Calculations of the electronic properties of AIN, GaN, InN and their alloys are presented. Initial calculations are performed using the first principles pseudopotential method to obtain accurate lattice constants. Further calculations then investigate bonding in the nitrides through population analysis and density of state calculations. The empirical pseudopotential method is also used in this work. Pseudopotentials for each of the nitrides are constructed using a functional form that allows strained material and alloys to be studied. The conventional k.p valence band parameters for both zincblende and wurtzite are obtained from the empirical band structure using two different methods. A Monte-Carlo fitting of the k.p band structure to the pseudopotential data (or an effective mass method for the zincblende structure) is used to produce one set. Another set is obtained directly from the momentum matrix elements and energy eigenvalues at the centre of the Brillouin zone. Both methods of calculating k.p parameters produce band structure in excellent agreement with the original empirical band calculations near the centre of the Brillouin zone. The advantage of the direct method is that it produces consistent sets of parameters, and can be used in studies involving a series of alloy compositions. Further empirical pseudopotential method calculations are then performed for alloys of the nitrides. In particular, the variation of the band gap with alloy composition is investigated, and good agreement with theory and experiment is found. The direct method is used to obtain k.p parameters for the alloys, and is contrasted with the fitting approach. The behaviour of the nitrides under strain is also studied. In particular. valence band offsets for nitride heterojunctions are calculated, and a strong forward- backward asymmetry in the band offset is found, in good agreement with other results in the literature. (author)

Electronic structure and optical properties of noncentrosymmetric LiGaGe{sub 2}Se{sub 6}, a promising nonlinear optical material

Energy Technology Data Exchange (ETDEWEB)

Lavrentyev, A.A.; Gabrelian, B.V.; Vu, V.T.; Ananchenko, L.N. [Department of Electrical Engineering and Electronics, Don State Technical University, 1 Gagarin Square, 344010 Rostov-on-Don (Russian Federation); Isaenko, L.I. [Laboratory of Crystal Growth, Institute of Geology and Mineralogy, SB RAS, 43 Russkaya Street, 630090 Novosibirsk (Russian Federation); Laboratory of Semiconductor and Dielectric Materials, Novosibirsk State University, 2 Pirogova Street, 630090 Novosibirsk (Russian Federation); Yelisseyev, A.; Krinitsin, P.G. [Laboratory of Crystal Growth, Institute of Geology and Mineralogy, SB RAS, 43 Russkaya Street, 630090 Novosibirsk (Russian Federation); Khyzhun, O.Y., E-mail: khyzhun@ipms.kiev.ua [Frantsevych Institute for Problems of Materials Science, National Academy of Sciences of Ukraine, 3 Krzhyzhanivsky Street, UA-03142 Kyiv (Ukraine)

2016-11-15

X-ray photoelectron core-level and valence-band spectra are measured for pristine and Ar{sup +} ion-bombarded surfaces of LiGaGe{sub 2}Se{sub 6} single crystal grown by Bridgman-Stockbarger technique. Further, electronic structure of LiGaGe{sub 2}Se{sub 6} is elucidated from both theoretical and experimental viewpoints. Density functional theory (DFT) calculations are made using the augmented plane wave +local orbitals (APW+lo) method to study total and partial densities of states in the LiGaGe{sub 2}Se{sub 6} compound. The present calculations indicate that the principal contributors to the valence band are the Se 4p states: they contribute mainly at the top and in the central portion of the valence band of LiGaGe{sub 2}Se{sub 6}, with also their significant contributions in its lower portion. The Ge 4s and Ge 4p states are among other significant contributors to the valence band of LiGaGe{sub 2}Se{sub 6}, contributing mainly at the bottom and in the central portion, respectively. In addition, the calculations indicate that the bottom of the conduction band is composed mainly from the unoccupied Ge s and Se p states. The present DFT calculations are supported experimentally by comparison on a common energy scale of the X-ray emission bands representing the energy distribution of the 4p states associated with Ga, Ge and Se and the XPS valence-band spectrum of the LiGaGe{sub 2}Se{sub 6} single crystal. The main optical characteristics of the LiGaGe{sub 2}Se{sub 6} compound are elucidated by the first-principles calculations.

Photoluminescence and Band Alignment of Strained GaAsSb/GaAs QW Structures Grown by MBE on GaAs

Directory of Open Access Journals (Sweden)

Nigamananda Samal

2010-02-01

Full Text Available An in-depth optimization of growth conditions and investigation of optical properties including discussions on band alignment of GaAsSb/GaAs quantum well (QW on GaAs by molecular beam epitaxy (MBE are reported. Optimal MBE growth temperature of GaAsSb QW is found to be 470 ± 10 °C. GaAsSb/GaAs QW with Sb content ~0.36 has a weak type-II band alignment with valence band offset ratio QV ~1.06. A full width at half maximum (FWHM of ~60 meV in room temperature (RT photoluminescence (PL indicates fluctuation in electrostatic potential to be less than 20 meV. Samples grown under optimal conditions do not exhibit any blue shift of peak in RT PL spectra under varying excitation.

Pulsed laser deposition of HfO{sub 2} thin films on indium zinc oxide: Band offsets measurements

Energy Technology Data Exchange (ETDEWEB)

Craciun, D.; Craciun, V., E-mail: valentin.craciun@inflpr.ro

2017-04-01

Highlights: • High quality amorphous IZO and HfO{sub 2} films were obtained by PLD technique. • XPS measurements were used to obtain the valence band alignment in HfO{sub 2}/IZO heterostructure. • A valence band offset (ΔE{sub V}) of 1.75 eV was obtained for the HfO{sub 2}/IZO heterostructure. • A conduction band offset (ΔE{sub C}) of 0.65 eV was estimated for the HfO{sub 2}/IZO heterostructure. - Abstract: One of the most used dielectric films for amorphous indium zinc oxide (IZO) based thin films transistor is HfO{sub 2}. The estimation of the valence band discontinuity (ΔE{sub V}) of HfO{sub 2}/IZO heterostructure grown using the pulsed laser deposition technique, with In/(In + Zn) = 0.79, was obtained from X-ray photoelectron spectroscopy (XPS) measurements. The binding energies of Hf 4d5, Zn 2p3 and In 3d5 core levels and valence band maxima were measured for thick pure films and for a very thin HfO{sub 2} film deposited on a thick IZO film. A value of ΔE{sub V} = 1.75 ± 0.05 eV was estimated for the heterostructure. Taking into account the measured HfO{sub 2} and IZO optical bandgap values of 5.50 eV and 3.10 eV, respectively, a conduction band offset ΔE{sub C} = 0.65 ± 0.05 eV in HfO{sub 2}/IZO heterostructure was then obtained.

Electronic structure of SnF{sub 3}: An example of valence skipper which forms charge density wave

Energy Technology Data Exchange (ETDEWEB)

Hase, I., E-mail: i.hase@aist.go.jp [National Institute of Advanced Industrial Science and Technology (AIST), Tsukuba 305-8568 (Japan); Yanagisawa, T. [National Institute of Advanced Industrial Science and Technology (AIST), Tsukuba 305-8568 (Japan); Kawashima, K. [IMRA Material R& D Co., LTD., Kariya, Aichi 448-0032 (Japan)

2016-11-15

Highlights: • We calculated the electronic structure of SnF{sub 3} and BaBiO{sub 3} from first principles. • As for SnF{sub 3}, charge-density-wave (CDW) is found, which agrees with the experiment. • As for BaBiO{sub 3}, CDW is not found, contrary to the experiment. • We conclude that the CDW is hard in SnF{sub 3} and is soft in BaBiO{sub 3}. - Abstract: In the present study we calculated the electronic structure of the valence skipping compound SnF{sub 3} and BaBiO{sub 3} from first-principles. We confirmed that the charge-density-wave (CDW) is formed in SnF{sub 3}, and the Sn atoms in two crystallographic different sites take the valence Sn{sup 2+} and Sn{sup 4+}. Structure optimization study reveals that this CDW is stable, though the atomic position is slightly different from the experimental data. This behavior is in contrast with the case of BaBiO{sub 3}, where the structure optimization leads to the uniform state, which means that two Bi sites are equivalent. The CDW state is hard in SnF{sub 3}, which means that the CDW gap is large enough and it is difficult to melt this CDW order.

Synthesis, structural, electronic and linear electro-optical features of new quaternary Ag2Ga2SiS6 compound

Science.gov (United States)

Piasecki, M.; Myronchuk, G. L.; Parasyuk, O. V.; Khyzhun, O. Y.; Fedorchuk, A. O.; Pavlyuk, V. V.; Kozer, V. R.; Sachanyuk, V. P.; El-Naggar, A. M.; Albassam, A. A.; Jedryka, J.; Kityk, I. V.

2017-02-01

For the first time phase equilibria and phase diagram of the AgGaS2-SiS2 system were successfully explored by differential thermal and X-ray phase analysis methods. Crystal structure of low-temperature (LT) modification of Ag2Ga2SiS6 (LT- Ag2Ga2SiS6) was studied by X-ray powder method and it belongs to tetragonal space group I-42d, with unit cell parameters a=5.7164(4) Å, c=9.8023(7) Å, V=320.32(7) Å3. Additional details regarding the crystal structure exploration are available at the web page Fachinformationszentrum Karlsruhe. X-ray photoelectron core-level and valence-band spectra were measured for pristine LT- Ag2Ga2SiS6 crystal surface. In addition, the X-ray photoelectron valence-band spectrum of LT-Ag2Ga2SiS6 was matched on a common energy scale with the X-ray emission S Kβ1,3 and Ga Kβ2 bands, which give information on the energy distribution of the S 3p and Ga 4p states, respectively. The presented X-ray spectroscopy results indicate that the valence S p and Ga p atomic states contribute mainly to the upper and central parts of the valence band of LT-Ag2Ga2SiS6, respectively, with a less significant contribution also to other valence-band regions. Band gap energy was estimated by measuring the quantum energy in the spectral range of the fundamental absorption. We have found that energy gap Eg is equal to 2.35 eV at 300 K. LT-Ag2Ga2SiS6 is a photosensitive material and reveals two spectral maxima on the curve of spectral photoconductivity spectra at λmax1 =590 nm and λmax2 =860 nm. Additionally, linear electro-optical effect of LT-Ag2Ga2SiS6 for the wavelengths of a cw He-Ne laser at 1150 nm was explored.

A detailed study of nucleon structure function in nuclei in the valence quark region

Energy Technology Data Exchange (ETDEWEB)

Bianchi, N. [INFN-Laboratori, Nazionali di Frascati (Italy)

1994-04-01

The so called {open_quotes}EMC effect{close_quotes} discovered during the 1980`s, has caused a big controversy in the community of nuclear and high energy physicists; during the last ten years, five experiments have been performed in different laboratories and several hundreds of papers about the possible interpretation of the modification of the nucleon structure function inside nuclei have been published. However, from the experimental point of view, the main goal of four experiments (EMC, BCDMS, NMC, FNAL) has been to emphasize the region of low x{sub b}, where shadowing effects appear. In the region of valence quarks and nuclear effects (x{sub b} > 0.1 - 0.2) the most reliable data presently available are from the SLAC E139 experiment performed in 1983 with only 80 hours of beam time. New precise data in the valence quark region are necessary to measure separate structure functions F{sub 2}(x{sub b}, Q{sup 2}) and R{sup lt}(x{sub b},Q{sup 2}) = {sigma}{sub l}/{sigma}{sub t}, and to investigate the real A-dependence of the ratio between bound and free-nucleon structure functions which is not completely defined by the SLAC data. Moreover, from the nuclear physics point of view, a measurement on some unexplored nuclei, like {sup 3}He and {sup 48}Ca, would be of great interest. The intermediate scaling region (0.1 < x{sub b} < 0.7) would be accessible at CEBAF if the machine energy will reach 6-8 GeV, as suggested by all the tests performed on the RF cavities. This physics program has been already presented in two letter of intents.

Electronic structure and exchange interactions in diluted semimagnetic semiconductors (Zn,Co)Se and (Zn,Mn)Se

Science.gov (United States)

Mašek, J.

1991-05-01

A comparative study of the electronic structure of (Zn,Co)Se and (Zn,Mn)Se is done by using a tight-binding version of the coherent potential approximation. The densities of states, relevant for a photoemission experiment, are calculated for a magnetically disordered phase. The exchange constant Jpd is obtained from the splitting of the valence band top in the ferromagnetic phase of the mixed crystal; Jdd is estimated from the energy of a spin reversal. We explain the large exchange constant in the Co-based systems as a result of efficient hybridization of the d-states with the valence band.

Valence-to-core-detected X-ray absorption spectroscopy

DEFF Research Database (Denmark)

Hall, Eleanor R.; Pollock, Christopher J.; Bendix, Jesper

2014-01-01

X-ray absorption spectroscopy (XAS) can provide detailed insight into the electronic and geometric structures of transition-metal active sites in metalloproteins and chemical catalysts. However, standard XAS spectra inherently represent an average contribution from the entire coordination...... environment with limited ligand selectivity. To address this limitation, we have investigated the enhancement of XAS features using valence-to-core (VtC)-detected XAS, whereby XAS spectra are measured by monitoring fluorescence from valence-to-core X-ray emission (VtC XES) events. VtC emission corresponds...... to transitions from filled ligand orbitals to the metal 1s core hole, with distinct energetic shifts for ligands of differing ionization potentials. VtC-detected XAS data were obtained from multiple valence emission features for a series of well-characterized Mn model compounds; taken together, these data...

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)

Excitations of one-valence-proton, one-valence-neutron nucleus {sup 210}Bi from cold-neutron capture

Energy Technology Data Exchange (ETDEWEB)

Cieplicka-Oryńczak, N. [INFN sezione di Milano, Via Celoria 16, 20133 Milano (Italy); Institute of Nuclear Physics, Polish Academy of Sciences, PL-31342 Kraków (Poland); Fornal, B.; Szpak, B. [Institute of Nuclear Physics, Polish Academy of Sciences, PL-31342 Kraków (Poland); Leoni, S.; Bottoni, S. [INFN sezione di Milano, Via Celoria 16, 20133 Milano (Italy); Università degli Studi di Milano, Via Celoria 16, 20133 Milano (Italy); Bazzacco, D. [Dipartimento di Fisica e Astronomia dell’Università, I-35131 Padova (Italy); INFN Sezione di Padova, I-35131 Padova (Italy); Blanc, A.; Jentschel, M.; Köster, U.; Mutti, P.; Soldner, T. [Institute Laue-Langevin, 6, rue Jules Horowitz, 38042 Grenoble Cedex 9 (France); Bocchi, G. [Università degli Studi di Milano, Via Celoria 16, 20133 Milano (Italy); France, G. de [GANIL, Bd. Becquerel, BP 55027, 14076 CAEN Cedex 05 (France); Simpson, G. [LPSC, Université Joseph Fourier Grenoble 1, CNRS/IN2P3, Institut National Polytechnique de Grenoble, F-38026 Grenoble Cedex (France); Ur, C. [INFN Sezione di Padova, Via F. Marzolo 8, I-35131 Padova (Italy); Urban, W. [Faculty of Physics, University of Warsaw, ul. Hoża 69, 02-681, Warszawa (Poland)

2015-10-15

The low-spin structure of one-proton, one-neutron {sup 210}Bi nucleus was investigated in cold-neutron capture reaction on {sup 209}Bi. The γ-coincidence measurements were performed with use of EXILL array consisted of 16 HPGe detectors. The experimental results were compared to shell-model calculations involving valence particles excitations. The {sup 210}Bi nucleus offers the potential to test the effective proton-neutron interactions because most of the states should arise from the proton-neutron excitations. Additionally, it was discovered that a few states should come from the couplings of valence particles to the 3{sup −} octupole vibration in {sup 208}Pb which provides also the possibility of testing the calculations involving the core excitations.

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)

Exciting imperfection. Real-structure effects in magnesium-, cadmium-, and zinc-oxide

Energy Technology Data Exchange (ETDEWEB)

Schleife, Andre

2010-07-01

We employ recent ab-initio methods and theoretical spectroscopy techniques that rely on heavy numerical calculations to describe electronic excitations in non-ideal crystals of three group-II oxides. We study the ideal equilibrium polymorphs of these oxides, for gaining a thorough understanding as well as the necessary confidence in our approaches to generalize and apply them to the electronic excitations in imperfect crystals. As such imperfections we take the influence of strain, the alloying of the different oxides, an intrinsic point defect, and free electrons in the lowest conduction band into account. We employ the DFT results as input in order to compute quasiparticle electronic structures, which are in good agreement with experimental findings. According to Hedin's equations for interacting electrons, the electron-hole interaction is taken into account by solving a Bethe-Salpeter equation for the polarization function. Thereafter the equilibrium polymorphs of ideal bulk MgO, ZnO, and CdO and investigates the structure of their valence and conduction bands are described. We present densities of states and effective masses, as well as natural band discontinuities. Furthermore, our description of the dielectric function, which takes excitonic effects into account, enables us to derive the electron-energy loss function. The influence of uniaxial and biaxial strain on the ordering of the valence bands in ZnO is investigated. In addition, we explore the electronic band structure of the non-equilibrium wurtzite structures of MgO and CdO. We predict valence-band splittings and band gaps as they might occur at interfaces of Mgo or CdO with ZnO substrates. Thereafter we study pseudobinary alloys by means of a cluster expansion method. Due to the different crystal structures of the respective oxides, i.e. rocksalt and wurtzite, the description of their heterostructural combination has to be achieved. The electronic and optical properties of the group-II oxide

Exciting imperfection. Real-structure effects in magnesium-, cadmium-, and zinc-oxide

International Nuclear Information System (INIS)

Schleife, Andre

2010-01-01

We employ recent ab-initio methods and theoretical spectroscopy techniques that rely on heavy numerical calculations to describe electronic excitations in non-ideal crystals of three group-II oxides. We study the ideal equilibrium polymorphs of these oxides, for gaining a thorough understanding as well as the necessary confidence in our approaches to generalize and apply them to the electronic excitations in imperfect crystals. As such imperfections we take the influence of strain, the alloying of the different oxides, an intrinsic point defect, and free electrons in the lowest conduction band into account. We employ the DFT results as input in order to compute quasiparticle electronic structures, which are in good agreement with experimental findings. According to Hedin's equations for interacting electrons, the electron-hole interaction is taken into account by solving a Bethe-Salpeter equation for the polarization function. Thereafter the equilibrium polymorphs of ideal bulk MgO, ZnO, and CdO and investigates the structure of their valence and conduction bands are described. We present densities of states and effective masses, as well as natural band discontinuities. Furthermore, our description of the dielectric function, which takes excitonic effects into account, enables us to derive the electron-energy loss function. The influence of uniaxial and biaxial strain on the ordering of the valence bands in ZnO is investigated. In addition, we explore the electronic band structure of the non-equilibrium wurtzite structures of MgO and CdO. We predict valence-band splittings and band gaps as they might occur at interfaces of Mgo or CdO with ZnO substrates. Thereafter we study pseudobinary alloys by means of a cluster expansion method. Due to the different crystal structures of the respective oxides, i.e. rocksalt and wurtzite, the description of their heterostructural combination has to be achieved. The electronic and optical properties of the group-II oxide alloys

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.

Lattice and Valence Electronic Structures of Crystalline Octahedral Molybdenum Halide Clusters-Based Compounds, Cs2[Mo6X14] (X = Cl, Br, I), Studied by Density Functional Theory Calculations.

Science.gov (United States)

Saito, Norio; Cordier, Stéphane; Lemoine, Pierric; Ohsawa, Takeo; Wada, Yoshiki; Grasset, Fabien; Cross, Jeffrey S; Ohashi, Naoki

2017-06-05

The electronic and crystal structures of Cs 2 [Mo 6 X 14 ] (X = Cl, Br, I) cluster-based compounds were investigated by density functional theory (DFT) simulations and experimental methods such as powder X-ray diffraction, ultraviolet-visible spectroscopy, and X-ray photoemission spectroscopy (XPS). The experimentally determined lattice parameters were in good agreement with theoretically optimized ones, indicating the usefulness of DFT calculations for the structural investigation of these clusters. The calculated band gaps of these compounds reproduced those experimentally determined by UV-vis reflectance within an error of a few tenths of an eV. Core-level XPS and effective charge analyses indicated bonding states of the halogens changed according to their sites. The XPS valence spectra were fairly well reproduced by simulations based on the projected electron density of states weighted with cross sections of Al K α , suggesting that DFT calculations can predict the electronic properties of metal-cluster-based crystals with good accuracy.

Change in optimum genetic algorithm solution with changing band discontinuities and band widths of electrically conducting copolymers

Science.gov (United States)

Kaur, Avneet; Bakhshi, A. K.

2010-04-01

The interest in copolymers stems from the fact that they present interesting electronic and optical properties leading to a variety of technological applications. In order to get a suitable copolymer for a specific application, genetic algorithm (GA) along with negative factor counting (NFC) method has recently been used. In this paper, we study the effect of change in the ratio of conduction band discontinuity to valence band discontinuity (Δ Ec/Δ Ev) on the optimum solution obtained from GA for model binary copolymers. The effect of varying bandwidths on the optimum GA solution is also investigated. The obtained results show that the optimum solution changes with varying parameters like band discontinuity and band width of constituent homopolymers. As the ratio Δ Ec/Δ Ev increases, band gap of optimum solution decreases. With increasing band widths of constituent homopolymers, the optimum solution tends to be dependent on the component with higher band gap.

Oxygen Evolution at Manganite Perovskite Ruddlesden-Popper Type Particles: Trends of Activity on Structure, Valence and Covalence

Directory of Open Access Journals (Sweden)

Majid Ebrahimizadeh Abrishami

2016-11-01

Full Text Available An improved understanding of the correlation between the electronic properties of Mn-O bonds, activity and stability of electro-catalysts for the oxygen evolution reaction (OER is of great importance for an improved catalyst design. Here, an in-depth study of the relation between lattice structure, electronic properties and catalyst performance of the perovskite Ca1−xPrxMnO3 and the first-order RP-system Ca2−xPrxMnO4 at doping levels of x = 0, 0.25 and 0.5 is presented. Lattice structure is determined by X-ray powder diffraction and Rietveld refinement. X-ray absorption spectroscopy of Mn-L and O-K edges gives access to Mn valence and covalency of the Mn-O bond. Oxygen evolution activity and stability is measured by rotating ring disc electrode studies. We demonstrate that the highest activity and stability coincidences for systems with a Mn-valence state of +3.7, though also requiring that the covalency of the Mn-O bond has a relative minimum. This observation points to an oxygen evolution mechanism with high redox activity of Mn. Covalency should be large enough for facile electron transfer from adsorbed oxygen species to the MnO6 network; however, it should not be hampered by oxidation of the lattice oxygen, which might cause a crossover to material degradation. Since valence and covalency changes are not entirely independent, the introduction of the energy position of the eg↑ pre-edge peak in the O-K spectra as a new descriptor for oxygen evolution is suggested, leading to a volcano-like representation of the OER activity.

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.

Valence states of cobalt and crystal structure peculiarities of solid solution YBa2Cu3-xCoxO6+σ

International Nuclear Information System (INIS)

Voronin, V.I.; Goshchinskij, B.N.; Mitberg, Eh.B.; Leonidov, I.A.; Kozhevnikov, V.L.

2000-01-01

Crystal structure of solid solution YBa 2 Cu 3-x Co x O 6+σ , where x = 0.2, 0.4, 0.6 and 0.8, is studied by the method of powder neutron diffraction. Charge states of the cation are calculated using the interatomic distances obtained. It is shown that cobalt in Cu1 position has valency 3 + and octahedral coordination at x = 0.2 and 0.4. Increase in doping degree involves both transition of a portion of cobalt ions in the positions mentioned to the state with valence 4 + and tetrahedral coordination and partial substitution of copper in Cu2 position [ru

Reconstructing the energy band electronic structure of pulsed laser deposited CZTS thin films intended for solar cell absorber applications

Energy Technology Data Exchange (ETDEWEB)

Pandiyan, Rajesh [Institut National de la Recherche Scientifique, Centre-Énergie, Matériaux et Télécommunications, 1650 Blvd. Lionel–Boulet, C.P. 1020, Varennes, QC J3X-1S2 (Canada); Oulad Elhmaidi, Zakaria [Institut National de la Recherche Scientifique, Centre-Énergie, Matériaux et Télécommunications, 1650 Blvd. Lionel–Boulet, C.P. 1020, Varennes, QC J3X-1S2 (Canada); University of Mohammed V, Faculty of Sciences, Materials Physics Laboratory, B.P. 1014 Rabat (Morocco); Sekkat, Zouheir [Optics & Photonics Center, Moroccan Foundation for Advanced Science, Innovation and Research, Rabat (Morocco); Abd-lefdil, Mohammed [University of Mohammed V, Faculty of Sciences, Materials Physics Laboratory, B.P. 1014 Rabat (Morocco); El Khakani, My Ali, E-mail: elkhakani@emt.inrs.ca [Institut National de la Recherche Scientifique, Centre-Énergie, Matériaux et Télécommunications, 1650 Blvd. Lionel–Boulet, C.P. 1020, Varennes, QC J3X-1S2 (Canada)

2017-02-28

Highlights: • High quality CZTS thin films grown by means of PLD technique without resorting to any post sulfurization process. • Effect of thermal annealing treatments (in the 200–500 °C range) on the structural, morphological and optoelectronic properties of PLD-CZTS films. • Experimental determination of key optoelectronic parameters (i.e.; E{sub g}, VBM, ϕ, I{sub p}, and χ) enabling the reconstruction of energy band electronic structure of the PLD-CZTS films. • Investigation on the energy band alignments of the heterojunction interface formed between CZTS and both CdS and ZnS buffer layer materials. - Abstract: We report here on the use of pulsed KrF-laser deposition (PLD) technique for the growth of high-quality Cu{sub 2}ZnSnS{sub 4} (CZTS) thin films onto Si, and glass substrates without resorting to any post sulfurization process. The PLD-CZTS films were deposited at room temperature (RT) and then subjected to post annealing at different temperatures ranging from 200 to 500 °C in Argon atmosphere. The X-ray diffraction and Raman spectroscopy confirmed that the PLD films crystallize in the characteristic kesterite CZTS structure regardless of their annealing temperature (T{sub a}), but their crystallinity is much improved for T{sub a} ≥ 400 °C. The PLD-CZTS films were found to exhibit a relatively dense morphology with a surface roughness (RMS) that increases with T{sub a} (from ∼14 nm at RT to 70 nm at T{sub a} = 500 °C with a value around 40 nm for T{sub a} = 300–400 °C). The optical bandgap of the PLD-CZTS films, was derived from UV–vis transmission spectra analysis, and found to decrease from 1.73 eV for non-annealed films to ∼1.58 eV for those annealed at T{sub a} = 300 °C. These band gap values are very close to the optimum value needed for an ideal solar cell absorber. In order to achieve a complete reconstruction of the one-dimensional energy band structure of these PLD-CZTS absorbers, we have combined both XPS and UPS

Computational Design of Flat-Band Material

Science.gov (United States)

Hase, I.; Yanagisawa, T.; Kawashima, K.

2018-02-01

Quantum mechanics states that hopping integral between local orbitals makes the energy band dispersive. However, in some special cases, there are bands with no dispersion due to quantum interference. These bands are called as flat band. Many models having flat band have been proposed, and many interesting physical properties are predicted. However, no real compound having flat band has been found yet despite the 25 years of vigorous researches. We have found that some pyrochlore oxides have quasi-flat band just below the Fermi level by first principles calculation. Moreover, their valence bands are well described by a tight-binding model of pyrochlore lattice with isotropic nearest neighbor hopping integral. This model belongs to a class of Mielke model, whose ground state is known to be ferromagnetic with appropriate carrier doping and on-site repulsive Coulomb interaction. We have also performed a spin-polarized band calculation for the hole-doped system from first principles and found that the ground state is ferromagnetic for some doping region. Interestingly, these compounds do not include magnetic element, such as transition metal and rare-earth elements.

Electronic structure of Ti4Fe2Ox as determined from first-principles APW + LO calculations and X-ray spectroscopy data

International Nuclear Information System (INIS)

Lavrentyev, A.A.; Gabrelian, B.V.; Shkumat, P.N.; Nikiforov, I.Ya.; Zavaliy, I.Yu.; Sinelnichenko, A.K.; Izvekov, A.V.; Khyzhun, O.Yu.

2010-01-01

Electronic properties of Ti 4 Fe 2 O oxide, a very promising hydrogen-storage material, were studied both from theoretical and experimental points of view employing the first-principles band-structure augmented plane wave + local orbitals (APW + LO) method with the WIEN2k code as well as X-ray photoelectron spectroscopy (XPS) and soft X-ray emission spectroscopy (SXES). Total and partial densities of states of the constituent atoms of Ti 4 Fe 2 O have been derived from the APW + LO calculations. The XPS valence-band spectra as well as the SXES Ti Lα, Fe Lα and O Kα bands have been measured for a series of Ti 4 Fe 2 O x oxides (x = 1.0, 0.5, and 0.25). The present APW + LO calculations reveal that, the O 2p-like states are the dominant contributors into the bottom of the valence band, whilst the top of the valence band and the bottom of the conduction band of Ti 4 Fe 2 O are dominated by contributions of the Fe 3d- and Ti 3d-like states. The APW + LO results are confirmed experimentally by a comparison on a common energy scale of the XPS valence-band spectra and the SXES Ti Lα, Fe Lα and O Kα bands of the Ti 4 Fe 2 O x oxides. The XPS Ti 2p, Fe 2p and O 1s core-level binding energies have been measured for the compounds under consideration.

Direct imaging of band profile in single layer MoS2 on graphite: quasiparticle energy gap, metallic edge states, and edge band bending.

Science.gov (United States)

Zhang, Chendong; Johnson, Amber; Hsu, Chang-Lung; Li, Lain-Jong; Shih, Chih-Kang

2014-05-14

Using scanning tunneling microscopy and spectroscopy, we probe the electronic structures of single layer MoS2 on graphite. The apparent quasiparticle energy gap of single layer MoS2 is measured to be 2.15 ± 0.06 eV at 77 K, albeit a higher second conduction band threshold at 0.2 eV above the apparent conduction band minimum is also observed. Combining it with photoluminescence studies, we deduce an exciton binding energy of 0.22 ± 0.1 eV (or 0.42 eV if the second threshold is use), a value that is lower than current theoretical predictions. Consistent with theoretical predictions, we directly observe metallic edge states of single layer MoS2. In the bulk region of MoS2, the Fermi level is located at 1.8 eV above the valence band maximum, possibly due to the formation of a graphite/MoS2 heterojunction. At the edge, however, we observe an upward band bending of 0.6 eV within a short depletion length of about 5 nm, analogous to the phenomena of Fermi level pinning of a 3D semiconductor by metallic surface states.

Praseodymium valency from crystal structure in Pr-Ba-Cu-O and (Y-Pr)-Ba-Cu-O single crystals

International Nuclear Information System (INIS)

Collin, G.; Albouy, P.A.; Monod, P.; Ribault, M.

1990-01-01

The substitution of Pr to Y leads to materials with a general formula (Y 1-v Pr v ) (Ba 2-x Pr x ) (Cu 3-y vac y ) O 6+x/2-y+z and with a structural transition around v + x' ∼ 0.5. For v + x 0.5 the crystals are tetragonal, La 1.5 Ba 1.5 Cu 3 O 7±z type, with the characteristic tri-twinning of this phase. The Pr valency, in the range 3-3.2 + depending on preparation conditions, is determined from interatomic distances. Orthorhombic crystals of Pr Ba Cu O prepared at high temperatures exhibit a high amount of defects, y ∼ 0.25 on the Cu(1) site and are semiconductors with a T -1/4 activation law attributed to the praseodymium valence fluctuation

The surface electronic structure of Y(0001)

International Nuclear Information System (INIS)

Searle, C.

1998-12-01

Yttrium has been grown epitaxially on W(110). The growth was monitored by using photoemission spectroscopy with a synchrotron radiation source. The film thickness has been gauged by the attenuation of the W 4f 7/2 bulk component. The films have been grown reproducibly and show a prominent surface state which is indicative of good order and low contamination. Angle-Resolved Ultra-Violet Photoemission Spectroscopy has been used to examine the valence band of these ultra-thin films. The films show a very different structure to the valence band of a bulk crystal of yttrium. The differences have been investigated by a series of model calculations using the LMASA-46 tight-binding LMTO program. The calculations suggest that the ultra-thin film surface state may be hybridised with a tungsten orbital having (x 2 - y 2 ) character. (author)

Valence electronic structure of cobalt phthalocyanine from an optimally tuned range-separated hybrid functional.

Science.gov (United States)

Brumboiu, Iulia Emilia; Prokopiou, Georgia; Kronik, Leeor; Brena, Barbara

2017-07-28

We analyse the valence electronic structure of cobalt phthalocyanine (CoPc) by means of optimally tuning a range-separated hybrid functional. The tuning is performed by modifying both the amount of short-range exact exchange (α) included in the hybrid functional and the range-separation parameter (γ), with two strategies employed for finding the optimal γ for each α. The influence of these two parameters on the structural, electronic, and magnetic properties of CoPc is thoroughly investigated. The electronic structure is found to be very sensitive to the amount and range in which the exact exchange is included. The electronic structure obtained using the optimal parameters is compared to gas-phase photo-electron data and GW calculations, with the unoccupied states additionally compared with inverse photo-electron spectroscopy measurements. The calculated spectrum with tuned γ, determined for the optimal value of α = 0.1, yields a very good agreement with both experimental results and with GW calculations that well-reproduce the experimental data.

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.

Fluorescence properties of valence-controlled Eu{sup 2+} and Mn{sup 2+} ions in aluminosilicate glasses

Energy Technology Data Exchange (ETDEWEB)

Van Tuyen, Ho [Duy Tan University, 3 Quang Trung, Hai Chau, Da Nang (Viet Nam); Nonaka, Takamasa; Yamanaka, Ken-ichi [Toyota Central R& D Labs., Inc., Nagakute, Aichi (Japan); Chau, Pham Minh; Quy Hai, Nguyen Thi; Quang, Vu Xuan [Duy Tan University, 3 Quang Trung, Hai Chau, Da Nang (Viet Nam); Nogami, Masayuki, E-mail: mnogami@mtj.biglobe.ne.jp [Toyota Physical and Chemical Research Institute, Nagakute, Aichi (Japan); Ton Duc Thang University, Ho Chi Minh City (Viet Nam); Duy Tan University, 3 Quang Trung, Hai Chau, Da Nang (Viet Nam)

2017-04-15

Controlling of valence states of metal ions doped in glasses has attracted considerable interest due to the possibility of looking toward optical applications. In this study, new Na{sub 2}O-Al{sub 2}O{sub 3}-SiO{sub 2} glasses were developed to dope Eu{sup 2+} and Mn{sup 2+} with well controlled valence states by heating in H{sub 2} gas atmosphere, and the changes in the valence state of doped-ions and their fluorescence properties were investigated using visible and infrared optical absorption spectroscopies, X-ray absorption fine structure spectroscopy, and fluorescence spectroscopy. Among Eu{sup 3+}, Mn{sup 3+} and Mn{sup 2+} ions incorporated in the as-prepared glasses, the Eu{sup 3+} and Mn{sup 3+} ions were reduced to Eu{sup 2+} and Mn{sup 2+} ions, respectively, by heating in H{sub 2} gas and OH bonds were concurrently formed. The fluorescence spectra of glasses heated in H{sub 2} exhibited broad emission bands at 450 and 630 nm wavelength, assigned to the Eu{sup 2+} and Mn{sup 2+}, respectively, ions, in which the fluorescence intensity at 450 nm was observed to decrease with increasing Mn{sup 2+} ion content. The increased fluorescence intensities were analyzed as the energy transfer from Eu{sup 2+} to Mn{sup 2+} ions and the energy transfer efficiency was estimated with a concentration of Eu{sup 2+}and Mn{sup 2+} ions.

Wavelet-based study of valence-arousal model of emotions on EEG signals with LabVIEW.

Science.gov (United States)

Guzel Aydin, Seda; Kaya, Turgay; Guler, Hasan

2016-06-01

This paper illustrates the wavelet-based feature extraction for emotion assessment using electroencephalogram (EEG) signal through graphical coding design. Two-dimensional (valence-arousal) emotion model was studied. Different emotions (happy, joy, melancholy, and disgust) were studied for assessment. These emotions were stimulated by video clips. EEG signals obtained from four subjects were decomposed into five frequency bands (gamma, beta, alpha, theta, and delta) using "db5" wavelet function. Relative features were calculated to obtain further information. Impact of the emotions according to valence value was observed to be optimal on power spectral density of gamma band. The main objective of this work is not only to investigate the influence of the emotions on different frequency bands but also to overcome the difficulties in the text-based program. This work offers an alternative approach for emotion evaluation through EEG processing. There are a number of methods for emotion recognition such as wavelet transform-based, Fourier transform-based, and Hilbert-Huang transform-based methods. However, the majority of these methods have been applied with the text-based programming languages. In this study, we proposed and implemented an experimental feature extraction with graphics-based language, which provides great convenience in bioelectrical signal processing.

Robust indirect band gap and anisotropy of optical absorption in B-doped phosphorene.

Science.gov (United States)

Wu, Zhi-Feng; Gao, Peng-Fei; Guo, Lei; Kang, Jun; Fang, Dang-Qi; Zhang, Yang; Xia, Ming-Gang; Zhang, Sheng-Li; Wen, Yu-Hua

2017-12-06

A traditional doping technique plays an important role in the band structure engineering of two-dimensional nanostructures. Since electron interaction is changed by doping, the optical and electrochemical properties could also be significantly tuned. In this study, density functional theory calculations have been employed to explore the structural stability, and electronic and optical properties of B-doped phosphorene. The results show that all B-doped phosphorenes are stable with a relatively low binding energy. Of particular interest is that these B-doped systems exhibit an indirect band gap, which is distinct from the direct one of pure phosphorene. Despite the different concentrations and configurations of B dopants, such indirect band gaps are robust. The screened hybrid density functional HSE06 predicts that the band gap of B-doped phosphorene is slightly smaller than that of pure phosphorene. Spatial charge distributions at the valence band maximum (VBM) and the conduction band minimum (CBM) are analyzed to understand the features of an indirect band gap. By comparison with pure phosphorene, B-doped phosphorenes exhibit strong anisotropy and intensity of optical absorption. Moreover, B dopants could enhance the stability of Li adsorption on phosphorene with less sacrifice of the Li diffusion rate. Our results suggest that B-doping is an effective way of tuning the band gap, enhancing the intensity of optical absorption and improving the performances of Li adsorption, which could promote potential applications in novel optical devices and lithium-ion batteries.

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.

Optoelectronic properties of valence-state-controlled amorphous niobium oxide

Science.gov (United States)

Onozato, Takaki; Katase, Takayoshi; Yamamoto, Akira; Katayama, Shota; Matsushima, Koichi; Itagaki, Naho; Yoshida, Hisao; Ohta, Hiromichi

2016-06-01

In order to understand the optoelectronic properties of amorphous niobium oxide (a-NbO x ), we have investigated the valence states, local structures, electrical resistivity, and optical absorption of a-NbO x thin films with various oxygen contents. It was found that the valence states of Nb ion in a-NbO x films can be controlled from 5+  to 4+  by reducing oxygen pressure during film deposition at room temperature, together with changing the oxide-ion arrangement around Nb ion from Nb2O5-like to NbO2-like local structure. As a result, a four orders of magnitude reduction in the electrical resistivity of a-NbO x films was observed with decreasing oxygen content, due to the carrier generation caused by the appearance and increase of an oxygen-vacancy-related subgap state working as an electron donor. The tunable optoelectronic properties of a-NbO x films by valence-state-control with oxygen-vacancy formation will be useful for potential flexible optoelectronic device applications.

Electronic Structure of TIBa(sub 2)CaCu(sub 2)O(sub 7-delta)

Science.gov (United States)

Vasquez, R. P.; Novikov, D. L.; Freeman, A. J.; Siegal, M. P.

1996-01-01

The core levels of TIBa(sub 2)CaCu(sub 2)O(sub 7-delta) epitaxial films have been measured with x-ray photoelectron spectroscopy (XPS). The valence electronic structure has been determined using the full-potential linear muffin tin orbital band structure method and measured with XPS.

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...

Electronic structure investigation of oxidized aluminium films with electron momentum spectroscopy

International Nuclear Information System (INIS)

Guo, X.; Canney, S.; Kheifets, A.S.; Vos, M.; Fang, Z.; Utteridge, S.; McCarthy, I.E.; Weigold, E.

1996-09-01

Electron momentum spectroscopy (EMS) of (e, 2e) measurements with oxidized aluminium thin films have been performed. Due to the surface sensitive mature of the EMS spectrometer employed the measured (e, 2e) events come from the front oxidized layer as viewed by the electron detectors. The measurements show clearly two major features in the spectral momentum density distribution and they are related to the upper valence band and the lower valence band of aluminum oxide. The first is a 'dual parabola' energy-momentum dispersion pattern spanning about 8 eV in the upper valence band. This 'dual parabola' pattern has been qualitatively reproduced by a linear muffin-tin orbital (LMTO) calculation on spherically averaged α-A1 2 O 3 with nearly the same energy span. In the lower valence band, the LMTO calculation indicates a dispersion spanning about 5 eV, and the measured spectral momentum density plot shows a similar 'bowl' shape but with less dispersion. The possible causes which blur the dispersion in the lower valence band are discussed. Other features in the spectral momentum density distribution are also discussed and compared with the LMTO calculation. 45 refs., 1 tab., 10 figs

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 ...

Valence-delocalization of the mixed-valence oxo-centered trinuclear iron propionates [FeIII2FeIIO(C2H5CO2)6(py)3[npy; n = 0, 1.5

International Nuclear Information System (INIS)

Nakamoto, Tadahiro; Katada, Motomi; Kawata, Satoshi; Kitagawa, Susumu; Sano, Hirotoshi; Konno, Michiko

1994-01-01

Mixed-valence trinuclear iron propionates [Fe III 2 Fe II O(C 2 H 5 CO 2 ) 6 (py) 3 [npy, where n = 0, 1.5, were synthesized and the structure of the pyridine-solvated complex was determined by single-crystal X-ray diffraction. Moessbauer spectra of the solvated propionate complex showed a temperature-dependent mixed-valence state related to phase transitions, reaching an almost delocalized valence state at room temperature. On the other hand, the non-solvated propionate showed a remarkable change of the spectral shape related to a phase transition, remaining in a localized valence state at higher temperatures up to room temperature. (orig.)

Experimental studies of narrow band effects in the actinides

Energy Technology Data Exchange (ETDEWEB)

Brodsky, M.B.

1976-01-01

In many actinide metallic systems the f-electrons exhibit band behavior. This is a consequence of direct f-f wave function overlap or hybridization of f-electrons with s-, p-, and d-electrons. The f-bands can be responsible for large electronic densities of states at the Fermi level which may lead to band magnetism of various types. Although the concept of valence instabilities must be approached cautiously especially in the light actinides, it would not be surprising to observe them in the future, especially in Am compounds.

Experimental studies of narrow band effects in the actinides

International Nuclear Information System (INIS)

Brodsky, M.B.

1976-01-01

In many actinide metallic systems the f-electrons exhibit band behavior. This is a consequence of direct f-f wave function overlap or hybridization of f-electrons with s-, p-, and d-electrons. The f-bands can be responsible for large electronic densities of states at the Fermi level which may lead to band magnetism of various types. Although the concept of valence instabilities must be approached cautiously especially in the light actinides, it would not be surprising to observe them in the future, especially in Am compounds

Electronic Structure and Band Alignment at the NiO and SrTiO ₃ p–n Heterojunctions

Energy Technology Data Exchange (ETDEWEB)

Zhang, Kelvin H. L. [Department of Materials Science & amp, Metallurgy, University of Cambridge, 27 Charles Babbage Road, Cambridge CB3 0FS, U.K.; Wu, Rui [Department of Materials Science & amp, Metallurgy, University of Cambridge, 27 Charles Babbage Road, Cambridge CB3 0FS, U.K.; Tang, Fengzai [Department of Materials Science & amp, Metallurgy, University of Cambridge, 27 Charles Babbage Road, Cambridge CB3 0FS, U.K.; Li, Weiwei [Department of Materials Science & amp, Metallurgy, University of Cambridge, 27 Charles Babbage Road, Cambridge CB3 0FS, U.K.; Oropeza, Freddy E. [Department of Materials, Imperial College London, Exhibition Road, London SW7 2AZ, U.K.; Qiao, Liang [School of Materials, The University of Manchester, Manchester M13 9PL, U.K.; Lazarov, Vlado K. [Department of Physics, University of York, Heslington, York YO10 5DD, U.K.; Du, Yingge [Physical Sciences Division, Physical & amp, Computational; Payne, David J. [Department of Materials, Imperial College London, Exhibition Road, London SW7 2AZ, U.K.; MacManus-Driscoll, Judith L. [Department of Materials Science & amp, Metallurgy, University of Cambridge, 27 Charles Babbage Road, Cambridge CB3 0FS, U.K.; Blamire, Mark G. [Department of Materials Science & amp, Metallurgy, University of Cambridge, 27 Charles Babbage Road, Cambridge CB3 0FS, U.K.

2017-07-25

Understanding the energetics at the interface including the alignment of valence and conduction bands, built-in potentials, and ionic and electronic reconstructions, is an important challenge in designing oxide interfaces that have controllable multi-functionalities for novel (opto-)electronic devices. In this work, we report detailed investigations on the hetero-interface of wide bandgap p-type NiO and n-type SrTiO3 (STO). We show that despite a large lattice mismatch (~7%) and dissimilar crystal structure, high-quality NiO and Li doped NiO (LNO) thin films can be epitaxially grown on STO(001) substrates through a domain matching epitaxy (DME) mechanism. X-ray photoelectron spectroscopy (XPS) studies indicate that NiO/STO heterojunctions form a type II “staggered” band alignment. In addition, a large built-in potential of up to 0.97 eV was observed at the interface of LNO and Nb doped STO (NbSTO). The LNO/NbSTO p-n heterojunctions exhibit a large rectification ratio of 2×103, but also a large ideality factor of 4.3. The NiO/STO p-n heterojunctions have important implication for applications in photocatalysis and photodetector as the interface provides favourable energetics for facile separation and transport of photogenerated electrons and holes.

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

New quaternary thallium indium germanium selenide TlInGe2Se6: Crystal and electronic structure

Science.gov (United States)

Khyzhun, O. Y.; Parasyuk, O. V.; Tsisar, O. V.; Piskach, L. V.; Myronchuk, G. L.; Levytskyy, V. O.; Babizhetskyy, V. S.

2017-10-01

Crystal structure of a novel quaternary thallium indium germanium selenide TlInGe2Se6 was investigated by means of powder X-ray diffraction method. It was determined that the compound crystallizes in the trigonal space group R3 with the unit cell parameters a = 10.1798(2) Å, c = 9.2872(3) Å. The relationship with similar structures was discussed. The as-synthesized TlInGe2Se6 ingot was tested with X-ray photoelectron spectroscopy (XPS) and X-ray emission spectroscopy (XES). In particular, the XPS valence-band and core-level spectra were recorded for initial and Ar+ ion-bombarded surfaces of the sample under consideration. The XPS data allow for statement that the TlInGe2Se6 surface is rigid with respect to Ar+ ion-bombardment. Particularly, Ar+ ion-bombardment (3.0 keV, 5 min duration, ion current density fixed at 14 μA/cm2) did not cause substantial modifications of stoichiometry in topmost surface layers. Furthermore, comparison on a common energy scale of the XES Se Kβ2 and Ge Kβ2 bands and the XPS valence-band spectrum reveals that the principal contributions of the Se 4p and Ge 4p states occur in the upper and central portions of the valence band of TlInGe2Se6, respectively, with also their substantial contributions in other portions of the band. The bandgap energy of TlInGe2Se6 at the level of αg=103 cm-1 is equal to 2.38 eV at room temperature.

Electronic structures of ReS sub 2 , ReSe sub 2 and TcS sub 2 in the real and the hypothetical undistorted structures

CERN Document Server

Fang, C M; Haas, C; Groot, R A D

1997-01-01

The transition-metal dichalcogenides ReX sub 2 (X = S or Se) and TcS sub 2 with a d sup 3 electron configuration have distorted CdCl sub 2 and Cd(OH) sub 2 structures, respectively, with the Re(Tc) atoms in each layer forming parallelogram-shaped connected clusters (diamond chain). Ab-initio band-structure calculations were performed for ReX sub 2 and TcS sub 2 , and the hypothetical undistorted 1T-TcS sub 2 and 3R-ReX sub 2 structures. The calculations show that ReS sub 2 , ReSe sub 2 and TcS sub 2 are semiconductors with energy gaps of about 1.0 eV, 0.5 eV and 0.7 eV, respectively, while for the undistorted structures the Fermi level is in the partly filled band of d sub x sub sup 2 sub - sub y sub sup 2 and d sub x sub y orbitals of the t sub 2 sub g manifold. X-ray photoemission spectra for the core levels and valence band of ReSe sub 2 and ReS sub 2 are presented. The valence x-ray photoemission spectra showed that ReS sub 2 is a p-type semiconductor with an energy gap of about 1.5 eV, while ReSe sub 2 i...

Energies of rare-earth ion states relative to host bands in optical materials from electron photoemission spectroscopy

Science.gov (United States)

Thiel, Charles Warren

There are a vast number of applications for rare-earth-activated materials and much of today's cutting-edge optical technology and emerging innovations are enabled by their unique properties. In many of these applications, interactions between the rare-earth ion and the host material's electronic states can enhance or inhibit performance and provide mechanisms for manipulating the optical properties. Continued advances in these technologies require knowledge of the relative energies of rare-earth and crystal band states so that properties of available materials may be fully understood and new materials may be logically developed. Conventional and resonant electron photoemission techniques were used to measure 4f electron and valence band binding energies in important optical materials, including YAG, YAlO3, and LiYF4. The photoemission spectra were theoretically modeled and analyzed to accurately determine relative energies. By combining these energies with ultraviolet spectroscopy, binding energies of excited 4fN-15d and 4fN+1 states were determined. While the 4fN ground-state energies vary considerably between different trivalent ions and lie near or below the top of the valence band in optical materials, the lowest 4f N-15d states have similar energies and are near the bottom of the conduction band. As an example for YAG, the Tb3+ 4f N ground state is in the band gap at 0.7 eV above the valence band while the Lu3+ ground state is 4.7 eV below the valence band maximum; however, the lowest 4fN-15d states are 2.2 eV below the conduction band for both ions. We found that a simple model accurately describes the binding energies of the 4fN, 4fN-1 5d, and 4fN+1 states. The model's success across the entire rare-earth series indicates that measurements on two different ions in a host are sufficient to predict the energies of all rare-earth ions in that host. This information provides new insight into electron transfer transitions, luminescence quenching, and valence

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.

Electronic structure of Al- and Ga-doped ZnO films studied by hard X-ray photoelectron spectroscopy

Directory of Open Access Journals (Sweden)

M. Gabás

2014-01-01

Full Text Available Al- and Ga-doped sputtered ZnO films (AZO, GZO are semiconducting and metallic, respectively, despite the same electronic valence structure of the dopants. Using hard X-ray photoelectron spectroscopy we observe that both dopants induce a band in the electronic structure near the Fermi level, accompanied by a narrowing of the Zn 3d/O 2p gap in the valence band and, in the case of GZO, a substantial shift in the Zn 3d. Ga occupies substitutional sites, whereas Al dopants are in both substitutional and interstitial sites. The latter could induce O and Zn defects, which act as acceptors explaining the semiconducting character of AZO and the lack of variation in the optical gap. By contrast, mainly substitutional doping is consistent with the metallic-like behavior of GZO.

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.

Fine structure and energy spectrum of exciton in direct band gap cubic semiconductors with degenerate valence bands

International Nuclear Information System (INIS)

Nguyen Toan Thang; Nguyen Ai Viet; Nguyen Que Huong

1987-06-01

The influence of the cubic structure on the energy spectrum of direct exciton is investigated, using the new method suggested by Nguyen Van Hieu and co-workers. Explicit expressions of the exciton energy levels 1S, 2S and 2P are derived. A comparison with the experiments and the other theory is done for ZnSe. (author). 10 refs, 1 fig., 2 tabs

Advantages of low beam energies in a TEM for valence EELS

Science.gov (United States)

Stöger-Pollach, M.; Pongratz, P.

2010-02-01

Since the availability of monochromators in transmission electron microscopes (TEMs), electron energy loss spectrometry (EELS) is widely used to determine band gaps and the dielectric properties of semiconductors on a nano-metre scale. Nevertheless, three physical effects hamper straightforward analysis: (a) relativistic energy losses, (b) the delocalization of the energy loss which is in the 10 nano-metreer range for valence losses, and (c) the presence of interface plasmons. When reducing the operation voltage of the TEM one can kill two birds with one stone: (a) the relativistic losses will disappear as soon as veinvestigated sample) and (b) the delocalization will decrease, because it also depends on the energy of the incident electron probe. The determination of the optical properties of quantum structures is discussed in the case of GaP/GaAs interface at 200 keV and 20 keV beam energy, respectively. Further, the influence of the delocalization of the energy loss signal is discussed theoretically and experimentally.

Electronic structure of α-SrB4O7: experiment and theory

International Nuclear Information System (INIS)

Atuchin, V V; Kesler, V G; Zaitsev, A I; Molokeev, M S; Aleksandrovsky, A S; Kuzubov, A A; Ignatova, N Y

2013-01-01

The investigation of valence band structure and electronic parameters of constituent element core levels of α-SrB 4 O 7 has been carried out with x-ray photoemission spectroscopy. Optical-quality crystal α-SrB 4 O 7 has been grown by the Czochralski method. Detailed photoemission spectra of the element core levels have been recorded from the powder sample under excitation by nonmonochromatic Al Kα radiation (1486.6 eV). The band structure of α-SrB 4 O 7 has been calculated by ab initio methods and compared to XPS measurements. It has been found that the band structure of α-SrB 4 O 7 is weakly dependent on the Sr-related states. (paper)

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.

X-ray photoelectron spectra structure and chemical bonding in AmO2

Directory of Open Access Journals (Sweden)

Teterin Yury A.

2015-01-01

Full Text Available Quantitative analysis was done of the X-ray photoelectron spectra structure in the binding energy range of 0 eV to ~35 eV for americium dioxide (AmO2 valence electrons. The binding energies and structure of the core electronic shells (~35 eV-1250 eV, as well as the relativistic discrete variation calculation results for the Am63O216 and AmO8 (D4h cluster reflecting Am close environment in AmO2 were taken into account. The experimental data show that the many-body effects and the multiplet splitting contribute to the spectral structure much less than the effects of formation of the outer (0-~15 eV binding energy and the inner (~15 eV-~35 eV binding energy valence molecular orbitals. The filled Am 5f electronic states were shown to form in the AmO2 valence band. The Am 6p electrons participate in formation of both the inner and the outer valence molecular orbitals (bands. The filled Am 6p3/2 and the O 2s electronic shells were found to make the largest contributions to the formation of the inner valence molecular orbitals. Contributions of electrons from different molecular orbitals to the chemical bond in the AmO8 cluster were evaluated. Composition and sequence order of molecular orbitals in the binding energy range 0-~35 eV in AmO2 were established. The experimental and theoretical data allowed a quantitative scheme of molecular orbitals for AmO2, which is fundamental for both understanding the chemical bond nature in americium dioxide and the interpretation of other X-ray spectra of AmO2.

Electronic structure and thermoelectric properties of bismuth telluride and bismuth selenide

CERN Document Server

Mishra, S K; Jepsen, O

1997-01-01

The electronic structures of the two thermoelectric materials Bi sub 2 Te sub 3 and Bi sub 2 Se sub 3 are studied using density-functional theory with the spin - orbit interaction included. The electron states in the gap region and the chemical bonding can be described in terms of pp sigma interaction between the atomic p orbitals within the 'quintuple' layer. For Bi sub 2 Se sub 3 , we find both the valence-band maximum as well as the conduction-band minimum, each with a nearly isotropic effective mass, to occur at the zone centre in agreement with experimental results. For Bi sub 2 Te sub 3 , we find that the six valleys for the valence-band maximum are located in the mirror planes of the Brillouin zone and they have a highly anisotropic effective mass, leading to an agreement between the de Haas-van Alphen data for the p-doped samples and the calculated Fermi surface. The calculated conduction band, however, has only two minima, instead of the six minima indicated from earlier experiments. The calculated S...

Structural and XPS studies of PSi/TiO2 nanocomposites prepared by ALD and Ag-assisted chemical etching

International Nuclear Information System (INIS)

Iatsunskyi, Igor; Kempiński, Mateusz; Nowaczyk, Grzegorz; Jancelewicz, Mariusz; Pavlenko, Mykola; Załęski, Karol; Jurga, Stefan

2015-01-01

Highlights: • Porous silicon/TiO 2 nanocomposites have been investigated. • Morphology and chemical composition of PSi/TiO 2 nanocomposites were established. • Valence-band XPS maximums for PSi/TiO 2 nanocomposites were found and analyzed. - Abstract: PSi/TiO 2 nanocomposites fabricated by atomic layer deposition (ALD) and metal-assisted chemical etching (MACE) were investigated. The morphology and phase structure of PSi/TiO 2 nanocomposites were studied by means of scanning electron microscopy (SEM), transmission electron microscopy (TEM) with an energy dispersive X-ray spectroscopy (EDX) and Raman spectroscopy. The mean size of TiO 2 nanocrystals was determined by TEM and Raman spectroscopy. X-ray photoelectron spectroscopy (XPS) was used to analyze the chemical elemental composition by observing the behavior of the Ti 2p, O 1s and Si 2p lines. TEM, Raman spectroscopy and XPS binding energy analysis confirmed the formation of TiO 2 anatase phase inside the PSi matrix. The XPS valence band analysis was performed in order to investigate the modification of PSi/TiO 2 nanocomposites electronic structure. Surface defects states of Ti 3+ at PSi/TiO 2 nanocomposites were identified by analyzing of XPS valence band spectra

UPS and DFT investigation of the electronic structure of gas-phase trimesic acid

Energy Technology Data Exchange (ETDEWEB)

Reisberg, L., E-mail: rebban@ut.ee [Institute of Physics, University of Tartu, W. Oswaldi 1, EE-50411 Tartu (Estonia); Pärna, R. [Institute of Physics, University of Tartu, W. Oswaldi 1, EE-50411 Tartu (Estonia); MAX IV Laboratory, Lund University, Fotongatan 2, 225 94 Lund (Sweden); Kikas, A.; Kuusik, I.; Kisand, V. [Institute of Physics, University of Tartu, W. Oswaldi 1, EE-50411 Tartu (Estonia); Hirsimäki, M.; Valden, M. [Surface Science Laboratory, Optoelectronics Research Centre, Tampere University of Technology, FIN-33101 Tampere (Finland); Nõmmiste, E. [Institute of Physics, University of Tartu, W. Oswaldi 1, EE-50411 Tartu (Estonia)

2016-11-15

Highlights: • In the current study outer valence band electronic structure of benzene-1,3,5-tricarboxylic acid was interpreted. • Experimental and calculated trimesic acid (TMA) spectrum were compared to ones of benzene and benzoic acid. • It is shown that similarities between MO energies and shapes for benzene and TMA exists. • Addition of carboxyl groups to the benzene ring clearly correlates with increasing binding energy of HOMO. - Abstract: Benzene-1,3,5-tricarboxylic acid (trimesic acid, TMA) molecules in gas-phase have been investigated by using valence band photoemission. The photoelectron spectrum in the binding energy region from 9 to 22 eV is interpreted by using density functional theory calculations. The electronic structure of TMA is compared with benzene and benzoic acid in order to demonstrate changes in molecular orbital energies induced by addition of carboxyl groups to benzene ring.

Effects of crystal structure and composition on the photocatalytic performance of Ta-O-N functional materials.

Science.gov (United States)

Liu, Qing-Lu; Zhao, Zong-Yan; Yi, Jian-Hong

2018-05-07

For photocatalytic applications, the response of a material to the solar spectrum and its redox capabilities are two important factors determined by the band gap and band edge position of the electronic structure of the material. The crystal structure and composition of the photocatalyst are fundamental for determining the above factors. In this article, we examine the functional material Ta-O-N as an example of how to discuss relationships among these factors in detail with the use of theoretical calculations. To explore how the crystal structure and composition influence the photocatalytic performance, two groups of Ta-O-N materials were considered: the first group included ε-Ta 2 O 5 , TaON, and Ta 3 N 5 ; the second group included β-Ta 2 O 5 , δ-Ta 2 O 5 , ε-Ta 2 O 5 , and amorphous-Ta 2 O 5 . Calculation results indicated that the band gap and band edge position are determined by interactions between the atomic core and valence electrons, the overlap of valence electronic states, and the localization of valence states. Ta 3 N 5 and TaON are suitable candidates for efficient photocatalysts owing to their photocatalytic water-splitting ability and good utilization efficiency of solar energy. δ-Ta 2 O 5 has a strong oxidation potential and a band gap suitable for absorbing visible light. Thus, it can be applied to photocatalytic degradation of most pollutants. Although a-Ta 2 O 5 , ε-Ta 2 O 5 , and β-Ta 2 O 5 cannot be directly used as photocatalysts, they can still be applied to modify conventional Ta-O-N photocatalysts, owing to their similar composition and structure. These calculation results will be helpful as reference data for analyzing the photocatalytic performance of more complicated Ta-O-N functional materials. On the basis of these findings, one could design novel Ta-O-N functional materials for specific photocatalytic applications by tuning the composition and crystal structure.

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

Electronic structure and photocatalytic activities of (Bi{sub 2−δ}Y{sub δ})Sn{sub 2}O{sub 7} solid solution

Energy Technology Data Exchange (ETDEWEB)

Fan, Wenjie; Hu, Jinli; Huang, Jing; Wu, Xin; Lin, Sen, E-mail: slin@fzu.edu.cn; Huang, Caijin; Qiu, Xiaoqing, E-mail: qiuxq@fzu.edu.cn

2015-12-01

Highlights: • (Bi{sub 2−δ}Y{sub δ})Sn2O7 solid solutions were synthesized by one-step hydrothermal method. • The contribution of Bi 6s orbitals to electronic structures can be continuously tuned. • The high photocatalytic activity should originate from the good band dispersions. - Abstract: A series of (Bi{sub 2−δ}Y{sub δ})Sn{sub 2}O{sub 7} solid solutions were prepared by a one-step hydrothermal method to investigate the correlation between the electronic structures and photocatalytic activity. All the (Bi{sub 2−δ}Y{sub δ})Sn{sub 2}O{sub 7} samples were characterized by X-ray diffraction, transmission electron microscopy, infrared and UV–vis absorption spectroscopy, and the Brunauer–Emmett–Teller technique. The effects of Bi 6s orbitals in (Bi{sub 2−δ}Y{sub δ})Sn{sub 2}O{sub 7} solid solutions on the electronic structures and photogradation of colorless 2-naphthol solution were investigated experimentally and theoretically. It is found that the introduction of Y{sup 3+} induces the shrinkage of the lattice of (Bi{sub 2−δ}Y{sub δ})Sn{sub 2}O{sub 7} solid solutions. Consequently, the contribution of Bi 6s orbitals to electronic structures of (Bi{sub 2−δ}Y{sub δ})Sn{sub 2}O{sub 7} solid solutions can be continuously tuned by Y{sup 3+} substitution for Bi{sup 3+}. Density function theory calculations reveal that the Bi 6s and O 2p states dominate the top of valence band of Bi{sub 2}Sn{sub 2}O{sub 7}, while the bottom of conduction band mainly consists of the states of Sn 5s, O 2p and Bi 6p. Once the Bi{sup 3+} ions are substituted by Y{sup 3+}, the intensity of Bi 6s states is weakening at the top of valence band while the bottom of conduction band retains the same feature observed for pure Bi{sub 2}Sn{sub 2}O{sub 7}. Moreover, the band dispersions of valence band and conduction band become narrower after Y{sup 3+} introduction into the lattice of (Bi{sub 2−δ}Y{sub δ})Sn{sub 2}O{sub 7} solid solutions. As a result, the

Electronic structure analysis of GaN films grown on r- and a-plane sapphire

Energy Technology Data Exchange (ETDEWEB)

Mishra, Monu; Krishna TC, Shibin; Aggarwal, Neha [Physics of Energy Harvesting Division, CSIR-National Physical Laboratory (CSIR-NPL), Dr. K.S. Krishnan Marg, New Delhi 110012 (India); Academy of Scientific and Innovative Research (AcSIR), CSIR-NPL Campus, Dr. K.S. Krishnan Marg, New Delhi 110012 (India); Vihari, Saket [Physics of Energy Harvesting Division, CSIR-National Physical Laboratory (CSIR-NPL), Dr. K.S. Krishnan Marg, New Delhi 110012 (India); Gupta, Govind, E-mail: govind@nplindia.org [Physics of Energy Harvesting Division, CSIR-National Physical Laboratory (CSIR-NPL), Dr. K.S. Krishnan Marg, New Delhi 110012 (India); Academy of Scientific and Innovative Research (AcSIR), CSIR-NPL Campus, Dr. K.S. Krishnan Marg, New Delhi 110012 (India)

2015-10-05

Graphical abstract: Substrate orientation induced changes in surface chemistry, band bending, hybridization states, electronic properties and surface morphology of epitaxially grown GaN were investigated via photoemission spectroscopic and Atomic Force Microscopic measurements. - Highlights: • Electronic structure and surface properties of GaN film grown on r/a-plane sapphire. • Downward band bending (0.5 eV) and high surface oxide is observed for GaN/a-sapphire. • Electron affinity and ionization energy is found to be higher for GaN/a-sapphire. - Abstract: The electronic structure and surface properties of epitaxial GaN films grown on r- and a-plane sapphire substrates were probed via spectroscopic and microscopic measurements. X-ray photoemission spectroscopic (XPS) measurements were performed to analyse the surface chemistry, band bending and valence band hybridization states. It was observed that GaN/a-sapphire display a downward band bending of 0.5 eV and possess higher amount of surface oxide compared to GaN/r-sapphire. The valence band (VB) investigation revealed that the hybridization corresponds to the interactions of Ga 4s and Ga 4p orbitals with N 2p orbital, and result in N2p–Ga4p, N2p–Ga4s{sup ∗}, mixed and N2p–Ga4s states. The energy band structure and electronic properties were measured via ultraviolet photoemission spectroscopic (UPS) experiments. The band structure analysis and electronic properties calculations divulged that the electron affinity and ionization energy of GaN/a-sapphire were 0.3 eV higher than GaN/r-sapphire film. Atomic Force Microscopic (AFM) measurements revealed faceted morphology of GaN/r-sapphire while a smooth pitted surface was observed for GaN/a-sapphire film, which is closely related to surface oxide coverage.

Conduction-band valley spin splitting in single-layer H-T l2O

Science.gov (United States)

Ma, Yandong; Kou, Liangzhi; Du, Aijun; Huang, Baibiao; Dai, Ying; Heine, Thomas

2018-02-01

Despite numerous studies, coupled spin and valley physics is currently limited to two-dimensional (2D) transition-metal dichalcogenides (TMDCs). Here, we predict an exceptional 2D valleytronic material associated with the spin-valley coupling phenomena beyond 2D TMDCs—single-layer (SL) H-T l2O . It displays large valley spin splitting (VSS), significantly larger than that of 2D TMDCs, and a finite band gap, which are both critically attractive for the integration of valleytronics and spintronics. More importantly, in sharp contrast to all the experimentally confirmed 2D valleytronic materials, where the strong valence-band VSS (0.15-0.46 eV) supports the spin-valley coupling, the VSS in SL H-T l2O is pronounced in its conduction band (0.61 eV), but negligibly small in its valence band (21 meV), thus opening a way for manipulating the coupled spin and valley physics. Moreover, SL H-T l2O possesses extremely high carrier mobility, as large as 9.8 ×103c m2V-1s-1 .

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.

Application of ESCA spectroscopy to the study of electronic structure of high temperature superconductors

International Nuclear Information System (INIS)

Dagoury, G.

1988-01-01

Characteristics of high T c oxide superconductors are very sensitive to slight variation of chemical composition, ESCA spectroscopy is used for identification of YBaCuO superconductivity. Binding energy of the different electronic levels and structure of valence band are determined [fr

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.

The chemical bond in inorganic chemistry the bond valence model

CERN Document Server

Brown, I David

2016-01-01

The bond valence model is a version of the ionic model in which the chemical constraints are expressed in terms of localized chemical bonds formed by the valence charge of the atoms. Theorems derived from the properties of the electrostatic flux predict the rules obeyed by both ionic and covalent bonds. They make quantitative predictions of coordination number, crystal structure, bond lengths and bond angles. Bond stability depends on the matching of the bonding strengths of the atoms, while the conflicting requirements of chemistry and space lead to the structural instabilities responsible for the unusual physical properties displayed by some materials. The model has applications in many fields ranging from mineralogy to molecular biology.

Size and alloying induced shift in core and valence bands of Pd-Ag and Pd-Cu nanoparticles

International Nuclear Information System (INIS)

Sengar, Saurabh K.; Mehta, B. R.; Govind

2014-01-01

In this report, X-ray photoelectron spectroscopy studies have been carried out on Pd, Ag, Cu, Pd-Ag, and Pd-Cu nanoparticles having identical sizes corresponding to mobility equivalent diameters of 60, 40, and 20 nm. The nanoparticles were prepared by the gas phase synthesis method. The effect of size on valence and core levels in metal and alloy nanoparticles has been studied by comparing the values to those with the 60 nm nanoparticles. The effect of alloying has been investigated by comparing the valence and core level binding energies of Pd-Cu and Pd-Ag alloy nanoparticles with the corresponding values for Pd, Ag, and Cu nanoparticles of identical sizes. These effects have been explained in terms of size induced lattice contractions, alloying induced charge transfer, and hybridization effects. The observation of alloying and size induced binding energy shifts in bimetallic nanoparticles is important from the point of view of hydrogen reactivity

Structural study and electronic band structure investigations of the solid solution Na xCu1-xIn5S8 and its impact on the Cu(In,Ga)Se2/In2S3 interface of solar cells

International Nuclear Information System (INIS)

Lafond, A.; Guillot-Deudon, C.; Harel, S.; Mokrani, A.; Barreau, N.; Gall, S.; Kessler, J.

2007-01-01

The present work reports investigations on the new In 2 S 3 containing Cu and/or Na compounds, which are expected to be formed at the Cu(In,Ga)Se 2 /In 2 S 3 interface. The knowledge of these materials properties is very important in order to better understand the operation of the devices based on these junction partners. It has been observed that a solid solution Na x Cu 1-x In 5 S 8 exists from CuIn 5 S 8 (x = 0) to NaIn 5 S 8 (x = 1) with a spinel-like structure. The single crystal structure determination shows that indium, copper and sodium atoms are statistically distributed on the tetrahedral sites. XPS investigations on the CuIn 5 S 8 , Na 0.5 Cu 0.5 In 5 S 8 and NaIn 5 S 8 compounds combined with the band gap changes reported in a previous work show that these variations are mainly due to valence band maximum shift; it is moved downward when x increases from 0 to 1. These observations are confirmed by the electron structure calculations based on the density functional theory, which additionally demonstrate that the pure sodium compound has direct gap whereas the copper-containing compounds have indirect gaps

Study of band terminating in the A ≅ 100 by EUROGAM

International Nuclear Information System (INIS)

Gizon, J.; Gizon, A.; Genevey, J.; Santos, D.; Nyako, B.M.; Timar, J.; Zolnai, L.; Boston, A.J.; Zoss, D.T.; Paul, E.S.; Semple, A.T.; O'Brien, N.J.; Parry, C.M.; Cata-Danil, Gh.; Bucurescu, D.; Afanasjev, A.V.; Ragnarsson, I.

1997-01-01

Terminating bands in nuclei in the A≅ 100 region have been investigated using the EUROGAM2 array. Results have been obtained for Pd (Z 46) and Rh (Z = 45) isotopes. In the nucleus 102 Pd, eight terminating configurations are identified. It is the first nucleus where terminating bands built on the valence space configurations and on core excited configurations are observed. Terminating bands have been also found in 103 Pd and 102 Rh. For 102 Rh it is the first case of band terminations identified in a doubly-odd nucleus below the Z = 50 shell closure. (authors)

Measurement of core level and band offsets at the interface of ITO/Hg_3In_2Te_6(1 1 0) heterojunction by synchrotron radiation photoelectron spectroscopy

International Nuclear Information System (INIS)

Li, Yapeng; Fu, Li; Sun, Jie; Ibrahim, Kurash; Wang, Jia-ou

2016-01-01

Highlights: • The valence band maximum of ITO film and MIT were measured to be 1.6 eV and 0.6 eV, respectively. • The concentration of In element presented a trend of increasing first and then decreasing from MIT to ITO. • The valence band offsets of the ITO/MIT(1 1 0) heterojunction was confirmed to be a type-II band alignment phenomenon. - Abstract: The Indium Tin Oxide (ITO) film was deposited on the surface of Hg_3In_2Te_6 (short for MIT) (1 1 0) for the fabrication of ITO/MIT(1 1 0) heterojunction by using the pulsed laser deposition method. In situ X-ray photoelectron spectroscopy was utilized to examine the band offsets and core level of ITO/MIT(1 1 0) heterojunctions. The result showed that the valence band maximum of ITO films and MIT(1 1 0) were 1.6 eV and 0.6 eV, respectively. Meanwhile, it was found that the binding energy of Te 3d, Sn 3d and Hg 4f remained unchanged during the ITO deposition process. However, the binding energy of O 1s and In 3d_5_/_2 increased about 0.3 eV and 0.2 eV, respectively, with the thickness increasing of ITO film from 3.5 nm to 5 nm. This may due to the elements diffusion at the interface region during the film growing process. According to the core level spectrum, it can be speculated that no significant chemical reaction occurred at the interface of ITO/MIT(1 1 0). In addition, the valence band offset of the ITO/MIT(1 1 0) heterojunction can be calculated to be −1 ± 0.15 eV by the means of the photoelectron spectroscopy methods. The conduction band offset is deduced to be −3.96 ± 0.15 eV from the known valence band offset value, indicating that the band offsets of ITO/MIT(1 1 0) heterojunction is a type-II band alignment.

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

Spin-polarized structural, elastic, electronic and magnetic properties of half-metallic ferromagnetism in V-doped ZnSe

Energy Technology Data Exchange (ETDEWEB)

Monir, M. El Amine.; Baltache, H. [Laboratoire de Physique Quantique de la Matière et de la Modélisation Mathématique (LPQ3M), Faculté des Sciences, Université de Mascara, Mascara 29000 (Algeria); Murtaza, G., E-mail: murtaza@icp.edu.pk [Materials Modeling Lab, Department of Physics, Islamia College University, Peshawar (Pakistan); Khenata, R., E-mail: khenata_rabah@yahoo.fr [Laboratoire de Physique Quantique de la Matière et de la Modélisation Mathématique (LPQ3M), Faculté des Sciences, Université de Mascara, Mascara 29000 (Algeria); Ahmed, Waleed K. [ERU, Faculty of Engineering, United Arab Emirates University, Al Ain (United Arab Emirates); Bouhemadou, A. [Laboratory for Developing New Materials and their Characterization, Department of Physics, Faculty of Science, University of Setif, 19000 Setif (Algeria); Omran, S. Bin [Department of Physics and Astronomy, College of Science, King Saud University, P.O. Box 2455, Riyadh 11451 (Saudi Arabia); Seddik, T. [Laboratoire de Physique Quantique de la Matière et de la Modélisation Mathématique (LPQ3M), Faculté des Sciences, Université de Mascara, Mascara 29000 (Algeria)

2015-01-15

Based on first principles spin-polarized density functional theory, the structural, elastic electronic and magnetic properties of Zn{sub 1−x}V{sub x}Se (for x=0.25, 0.50, 0.75) in zinc blende structure have been studied. The investigation was done using the full-potential augmented plane wave method as implemented in WIEN2k code. The exchange-correlation potential was treated with the generalized gradient approximation PBE-GGA for the structural and elastic properties. Moreover, the PBE-GGA+U approximation (where U is the Hubbard correlation terms) is employed to treat the “d” electrons properly. A comparative study between the band structures, electronic structures, total and partial densities of states and local moments calculated within both GGA and GGA+U schemes is presented. The analysis of spin-polarized band structure and density of states shows the half-metallic ferromagnetic character and are also used to determine s(p)-d exchange constants N{sub 0}α (conduction band ) and N{sub 0}β (valence band) due to Se(4p)–V(3d) hybridization. It has been clearly evidence that the magnetic moment of V is reduced from its free space change value of 3 µ{sub B} and the minor atomic magnetic moment on Zn and Se are generated. - Highlights: • Half metallicity origins by doping V in ZnSe. • PBE-GGA+U approximation is employed to treat the “d” electrons properly. • s(p)-d Exchange constants N{sub 0}α (conduction band ) and N{sub 0}β (valence band) are due to Se(4p)-V(3d) hybridization.

Ab initio calculation of band alignment of epitaxial La2O3 on Si(111 substrate

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Alberto Debernardi

2015-08-01

Full Text Available By means of plane wave pseudopotential method we have studied the electronic properties of the heterostructure formed by an high dielectric constant (k oxide, the hexagonal La2O3 epitaxially grown with (0001-orientation on Si (111 substrate. We found that for La2O3 both the dielectric constant along the growth direction and the band gap are larger in the epitaxial film than in the bulk. By super-cell techniques we have computed the band alignment of the junction finding a valence band offset and a conduction band offset of ~1.6 eV and ~1.7 eV respectively. We demonstrate that the band alignment can be engineered by δ-doping the interface: our simulations show that, by doping the interface with S or Se monolayer, the valence (conduction band offset increases (decreases of about 0.5 eV without the formation of spurious electronic states in the semiconductor band-gap. The simulation of the critical thickness of pseudomorphic Lanthana film complete the work. Our results are relevant for the realization of a new generation of devices based on ultra-scaled complementary metal oxides semiconductors (CMOS technology.

Ferromagnetic dinuclear mixed-valence Mn(II)/Mn(III) complexes: building blocks for the higher nuclearity complexes. structure, magnetic properties, and density functional theory calculations.

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Hänninen, Mikko M; Välivaara, Juha; Mota, Antonio J; Colacio, Enrique; Lloret, Francesc; Sillanpää, Reijo

2013-02-18

A series of six mixed-valence Mn(II)/Mn(III) dinuclear complexes were synthesized and characterized by X-ray diffraction. The reactivity of the complexes was surveyed, and structures of three additional trinuclear mixed-valence Mn(III)/Mn(II)/Mn(III) species were resolved. The magnetic properties of the complexes were studied in detail both experimentally and theoretically. All dinuclear complexes show ferromagnetic intramolecular interactions, which were justified on the basis of the electronic structures of the Mn(II) and Mn(III) ions. The large Mn(II)-O-Mn(III) bond angle and small distortion of the Mn(II) cation from the ideal square pyramidal geometry were shown to enhance the ferromagnetic interactions since these geometrical conditions seem to favor the orthogonal arrangement of the magnetic orbitals.

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...

Spin Dynamics and Magnetic Ordering in Mixed Valence Systems

DEFF Research Database (Denmark)

Shapiro, S. M.; Bjerrum Møller, Hans; Axe, J. D.

1978-01-01

. 0 meV at the transition to the alpha phase. The temperature independence of the susceptibility within the gamma phase cannot be simply reconciled with the temperature dependence of the valence within the gamma phase. TmSe is shown to order in a type I antiferromagnetic structure below T//N similar 3....... 2 K. The magnetic phase diagram is understood as a successive domain reorientation and a metamagnetic phase transition for T less than 3 K with increasing field. The mixed valence nature manifests itself in a reduced moment and a markedly altered crystal field. Another sample of TmSe with a lattice...

Enhancing Thermoelectric Performances of Bismuth Antimony Telluride via Synergistic Combination of Multiscale Structuring and Band Alignment by FeTe2 Incorporation.

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