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

International Nuclear Information System (INIS)

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

1997-01-01

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

Conduction band-edge d-states in high-k dielectrics due to Jahn-Teller term splittings

International Nuclear Information System (INIS)

Lucovsky, G.; Fulton, C.C.; Zhang, Y.; Luning, J.; Edge, L.; Whitten, J.L.; Nemanich, R.J.; Schlom, D.G.; Afanase'v, V.V.

2005-01-01

X-ray absorption spectroscopy (XAS) is used to study conduction band edge electronic structure of high-k transition metal (TM) and trivalent lanthanide series rare earth (RE) oxide dielectrics. Empty TM/RE d-states are studied by intra-atomic transitions originating in core level spin-orbit split p-states, and conduction band states are studied in inter-atomic transitions which originate in the oxygen atom 1s core level state. In non-crystalline Zr and Hf silicate alloys, the local bonding symmetry, or crystal field splits these d-states into doubly and triply degenerate features. In nano-crystalline oxides, there are additional d-state splittings due to contributions of more distant neighbors that completely remove d-state degeneracies via the Jahn-Teller effect mechanism. This gives rise to highly localized band edge states that are electronically active in photoconductivity, internal photoemission, and act as bulk traps in metal oxide semiconductor (MOS) devices

Tunable Band Gap and Conductivity Type of ZnSe/Si Core-Shell Nanowire Heterostructures

Directory of Open Access Journals (Sweden)

Yijie Zeng

2014-10-01

Full Text Available The electronic properties of zincblende ZnSe/Si core-shell nanowires (NWs with a diameter of 1.1–2.8 nm are calculated by means of the first principle calculation. Band gaps of both ZnSe-core/Si-shell and Si-core/ZnSe-shell NWs are much smaller than those of pure ZnSe or Si NWs. Band alignment analysis reveals that the small band gaps of ZnSe/Si core-shell NWs are caused by the interface state. Fixing the ZnSe core size and enlarging the Si shell would turn the NWs from intrinsic to p-type, then to metallic. However, Fixing the Si core and enlarging the ZnSe shell would not change the band gap significantly. The partial charge distribution diagram shows that the conduction band maximum (CBM is confined in Si, while the valence band maximum (VBM is mainly distributed around the interface. Our findings also show that the band gap and conductivity type of ZnSe/Si core-shell NWs can be tuned by the concentration and diameter of the core-shell material, respectively.

Electronic conduction in doped multiferroic BiFeO3

Science.gov (United States)

Yang, Chan-Ho; Seidel, Jan; Kim, Sang-Yong; Gajek, M.; Yu, P.; Holcomb, M. B.; Martin, L. W.; Ramesh, R.; Chu, Y. H.

2009-03-01

Competition between multiple ground states, that are energetically similar, plays a key role in many interesting material properties and physical phenomena as for example in high-Tc superconductors (electron kinetic energy vs. electron-electron repulsion), colossal magnetoresistance (metallic state vs. charge ordered insulating state), and magnetically frustrated systems (spin-spin interactions). We are exploring the idea of similar competing phenomena in doped multiferroics by control of band-filling. In this paper we present systematic investigations of divalent Ca doping of ferroelectric BiFeO3 in terms of structural and electronic conduction properties as well as diffusion properties of oxygen vacancies.

Electron currents associated with an auroral band

International Nuclear Information System (INIS)

Spiger, R.J.; Anderson, H.R.

1975-01-01

Measurements of electron pitch angle distributions and energy spectra over a broad auroral band were used to calculate net electric current carried by auroral electrons in the vicinity of the band. The particle energy spectrometers were carried by a Nike-Tomahawk rocket launched from Poker Flat, Alaska, at 0722 UT on February 25, 1972. Data are presented which indicate the existence of upward field-aligned currents of electrons in the energy range 0.5-20 keV. The spatial relationship of these currents to visual structure of the auroral arc and the characteristics of the electrons carrying the currents are discussed

Electron currents associated with an auroral band

Science.gov (United States)

Spiger, R. J.; Anderson, H. R.

1975-01-01

Measurements of electron pitch angle distributions and energy spectra over a broad auroral band were used to calculate net electric current carried by auroral electrons in the vicinity of the band. The particle energy spectrometers were carried by a Nike-Tomahawk rocket launched from Poker Flat, Alaska, at 0722 UT on February 25, 1972. Data are presented which indicate the existence of upward field-aligned currents of electrons in the energy range 0.5-20 keV. The spatial relationship of these currents to visual structure of the auroral arc and the characteristics of the electrons carrying the currents are discussed.

Electron band theory 1952-1962

International Nuclear Information System (INIS)

Lomer, W.M.

1980-01-01

Work undertaken by the Theoretical Physics Division between 1952 and 1965 to obtain an understanding of electrons in metals, with uranium and the actinides and the structurally-important transition metals as the main targets is examined. A main result of that period was a conviction that the majority of the physical properties of all metals, except the 4f rare-earth series and the actinides beyond uranium, were dominated by band effects which could be described well enough for most purposes by simple one-electron calculations with simple self-consistent fields. The period from 1960 on showed increasingly clearly the necessity of incorporating relativistic spin-orbit coupling terms in the heavy metals, and some 'local exchange field' correction to the fields close to nuclei. The problems of the non-local interaction of spins - highly important for alloy theory and for antiferromagnetic instability -required the evolution of computers large enough to produce wave-functions at all wave-vectors for all bands so that the susceptibility at arbitrary wave-vector could be computed. This work has not proved to be very illuminating so far, and much interest again focusses today on heuristic arguments that give qualitative descriptions of band structures, such as canonical d-bands to account for crystal structure. (UK)

H-tailored surface conductivity in narrow band gap In(AsN)

Energy Technology Data Exchange (ETDEWEB)

Velichko, A. V., E-mail: amalia.patane@nottingham.ac.uk, E-mail: anton.velychko@nottingham.ac.uk; Patanè, A., E-mail: amalia.patane@nottingham.ac.uk, E-mail: anton.velychko@nottingham.ac.uk; Makarovsky, O. [School of Physics and Astronomy, The University of Nottingham, Nottingham NG7 2RD (United Kingdom); Capizzi, M.; Polimeni, A. [Dipartimento di Fisica, Sapienza Università di Roma, Piazzale A. Moro 2, 00185 Roma (Italy); Sandall, I. C.; Tan, C. H. [Department of Electronic and Electrical Engineering, The University of Sheffield, Sheffield S1 3JD (United Kingdom); Giubertoni, D. [Center for Materials and Microsystems—Fondazione Bruno Kessler, via Sommarive 18, 38123 Povo, Trento (Italy); Krier, A.; Zhuang, Q. [Physics Department, Lancaster University, Lancaster LA1 4YB (United Kingdom)

2015-01-12

We show that the n-type conductivity of the narrow band gap In(AsN) alloy can be increased within a thin (∼100 nm) channel below the surface by the controlled incorporation of H-atoms. This channel has a large electron sheet density of ∼10{sup 18 }m{sup −2} and a high electron mobility (μ > 0.1 m{sup 2}V{sup −1}s{sup −1} at low and room temperature). For a fixed dose of impinging H-atoms, its width decreases with the increase in concentration of N-atoms that act as H-traps thus forming N-H donor complexes near the surface.

Electrons in feldspar II: A consideration of the influence of conduction band-tail states on luminescence processes

DEFF Research Database (Denmark)

Poolton, H.R.J.; Ozanyan, K.B.; Wallinga, J.

2002-01-01

consider what influence the band tails have on the luminescence properties of feldspar, where electrons travel through the sample prior to recombination. The work highlights the dominant role that 0.04-0.05-eV phonons play in both the luminescence excitation and emission processes of these materials...

The determination of the conduction mechanism and optical band gap of fluorescein sodium salt

International Nuclear Information System (INIS)

Yakuphanoglu, Fahrettin; Sekerci, Memet; Evin, Ertan

2006-01-01

The electrical conductivity and optical properties of fluorescein sodium salt in the temperature range of 295-370 K have been investigated. Various conduction models described in the literature were used to elucidate the charge transport mechanism of the compound. It is found that the charge transfer mechanism of the compound is understood in terms of grain boundary scattering. It can be evaluated that the obtained electronic parameters such as mobility, conductivity at room temperature, activation energy and optical band gap suggest that the compound is an organic semiconductor

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

International Nuclear Information System (INIS)

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

2005-01-01

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

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

Energy Technology Data Exchange (ETDEWEB)

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

2017-06-01

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

Lanthanide 4f-electron binding energies and the nephelauxetic effect in wide band gap compounds

International Nuclear Information System (INIS)

Dorenbos, Pieter

2013-01-01

Employing data from luminescence spectroscopy, the inter 4f-electron Coulomb repulsion energy U(6, A) in Eu 2+/3+ impurities together with the 5d-centroid energy shift ϵ c (1,3+,A) in Ce 3+ impurities in 40 different fluoride, chloride, bromide, iodide, oxide, sulfide, and nitride compounds has been determined. This work demonstrates that the chemical environment A affects the two energies in a similar fashion; a fashion that follows the anion nephelauxetic sequence F, O, Cl, Br, N, I, S, Se. One may then calculate U(6, A) from well established and accurate ϵ c (1,3+,A) values which are then used as input to the chemical shift model proposed in Dorenbos (2012) [19]. As output it provides the chemical shift of 4f-electron binding energy and therewith the 4f-electron binding energy relative to the vacuum energy. In addition this method provides a tool to routinely establish the binding energy of electrons at the top of the valence band (work function) and the bottom of the conduction band (electron affinity) throughout the entire family of inorganic compounds. How the electronic structure of the compound and lanthanide impurities therein change with type of compound and type of lanthanide is demonstrated. -- Highlights: ► A relationship between 5d centroid shift and 4f-electron Coulomb repulsion energy is established. ► Information on the absolute 4f-electron binding energy of lanthanides in 40 compounds is provided. ► A new tool to determine absolute binding energies of electrons in valence and conduction bands is demonstrated

Conduction band mass determinations for n-type InGaAs/InAlAs single quantum wells

Energy Technology Data Exchange (ETDEWEB)

Jones, E.D.; Reno, J.L. [Sandia National Labs., Albuquerque, NM (United States); Kotera, Nobuo [Kyushu Inst. of Tech., Iizuka, Fukuoka (Japan); Wang, Y. [Florida State Univ., Tallahassee, FL (United States). National High Magnetic Field Lab.

1998-05-01

The authors report the measurement of the conduction band mass in n-type single 27-ML-wide InGaAs/InAlAs quantum well lattice matched to InP using two methods: (1) Magnetoluminescence spectroscopy and (2) far-infrared cyclotron resonance. The magnetoluminescence method utilizes Landau level transitions between 0 and 14 T at 1.4 K. The far infrared cyclotron resonance measurements were made at 4.2 K and to fields as large up to 18 T. The 2D-carrier density N{sub 2D} = 3 {times} 10{sup 11} cm{sup {minus}2} at low temperatures. The magnetoluminescence technique yielded an effective conduction-band mass of m{sub c} = 0.062m{sub 0} while the far infrared cyclotron resonance measurements gave m{sub c} = 0.056m{sub 0}, where m{sub 0} is the free electron mass. Both measurements show no evidence for any significant conduction-band nonparabolicity.

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.

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.

Transparent Conducting Oxides for Photovoltaics: Manipulation of Fermi Level, Work Function and Energy Band Alignment

Directory of Open Access Journals (Sweden)

Diana E. Proffit

2010-11-01

Full Text Available Doping limits, band gaps, work functions and energy band alignments of undoped and donor-doped transparent conducting oxides Zn0, In2O3, and SnO2 as accessed by X-ray and ultraviolet photoelectron spectroscopy (XPS/UPS are summarized and compared. The presented collection provides an extensive data set of technologically relevant electronic properties of photovoltaic transparent electrode materials and illustrates how these relate to the underlying defect chemistry, the dependence of surface dipoles on crystallographic orientation and/or surface termination, and Fermi level pinning.

Controlling the conduction band offset for highly efficient ZnO nanorods based perovskite solar cell

International Nuclear Information System (INIS)

Dong, Juan; Shi, Jiangjian; Li, Dongmei; Luo, Yanhong; Meng, Qingbo

2015-01-01

The mechanism of charge recombination at the interface of n-type electron transport layer (n-ETL) and perovskite absorber on the carrier properties in the perovskite solar cell is theoretically studied. By solving the one dimensional diffusion equation with different boundary conditions, it reveals that the interface charge recombination in the perovskite solar cell can be suppressed by adjusting the conduction band offset (ΔE C ) at ZnO ETL/perovskite absorber interface, thus leading to improvements in cell performance. Furthermore, Mg doped ZnO nanorods ETL has been designed to control the energy band levels. By optimizing the doping amount of Mg, the conduction band minimum of the Mg doped ZnO ETL has been raised up by 0.29 eV and a positive ΔE C of about 0.1 eV is obtained. The photovoltage of the cell is thus significantly increased due to the relatively low charge recombination

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

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...

Conductivity-limiting bipolar thermal conductivity in semiconductors

Science.gov (United States)

Wang, Shanyu; Yang, Jiong; Toll, Trevor; Yang, Jihui; Zhang, Wenqing; Tang, Xinfeng

2015-01-01

Intriguing experimental results raised the question about the fundamental mechanisms governing the electron-hole coupling induced bipolar thermal conduction in semiconductors. Our combined theoretical analysis and experimental measurements show that in semiconductors bipolar thermal transport is in general a “conductivity-limiting” phenomenon, and it is thus controlled by the carrier mobility ratio and by the minority carrier partial electrical conductivity for the intrinsic and extrinsic cases, respectively. Our numerical method quantifies the role of electronic band structure and carrier scattering mechanisms. We have successfully demonstrated bipolar thermal conductivity reduction in doped semiconductors via electronic band structure modulation and/or preferential minority carrier scatterings. We expect this study to be beneficial to the current interests in optimizing thermoelectric properties of narrow gap semiconductors. PMID:25970560

Electronic band structure and optical properties of antimony selenide under pressure

Energy Technology Data Exchange (ETDEWEB)

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

2016-05-23

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

Band-to-Band Tunneling-Dominated Thermo-Enhanced Field Electron Emission from p-Si/ZnO Nanoemitters.

Science.gov (United States)

Huang, Zhizhen; Huang, Yifeng; Xu, Ningsheng; Chen, Jun; She, Juncong; Deng, Shaozhi

2018-06-13

Thermo-enhancement is an effective way to achieve high performance field electron emitters, and enables the individually tuning on the emission current by temperature and the electron energy by voltage. The field emission current from metal or n-doped semiconductor emitter at a relatively lower temperature (i.e., current saturation was observed in the thermo-enhanced field emission measurements. The emission current density showed about ten-time enhancement (from 1.31 to 12.11 mA/cm 2 at 60.6 MV/m) by increasing the temperature from 323 to 623 K. The distinctive performance did not agree with the interband excitation mechanism but well-fit to the band-to-band tunneling model. The strong thermo-enhancement was proposed to be benefit from the increase of band-to-band tunneling probability at the surface portion of the p-Si/ZnO nanojunction. This work provides promising cathode for portable X-ray tubes/panel, ionization vacuum gauges and low energy electron beam lithography, in where electron-dose control at a fixed energy is needed.

Analysis of the electrical conduction in CdHgTe crystals

International Nuclear Information System (INIS)

Dziuba, Z.

1987-01-01

The electrical conduction versus magnetic field in p-like CdHgTe samples at 77 K is investigated by analysing the conductivity tensor components. The electrical conduction is mainly due to electrons in the conduction band and low-mobility carriers in an impurity band. In the investigated samples Cd/sub x/Hg/sub 1-x/Te with the composition x approximately 0.17 the concentration of electrons in the conduction band is higher than the intrinsic one and in samples with the composition close to HgTe the concentration of electrons in the conduction band is equal to or lower than the intrinsic one. The model of a half-filled impurity band situated close to the bottom of the conduction band is proposed to account for the concentration of electrons in the conduction band. (author)

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.

f-electron systems: pushing band theory

International Nuclear Information System (INIS)

Koelling, D.D.

1991-01-01

The f-electron orbitrals have always been the ''incomplete atomic shells acting as local moments, and weakly interacting with the remaining electronic structure'' in the minds of most people. So examining them using a band theory where one views them as itinerant was once - and to some extent even today still is - considered with some skepticism. Nonetheless, a very significant community has successfully utilized band theory as a probe of the electronic structure of the appropriate actinides and rare earths. Those people actually using the approach would be the first to declare that it is not the whole solution. Instead, one is pushing and even exceeding its limit of applicability. However, the apropriate procedure is to push the model consistently to its limits, patch where possible, and then look to see where discrepancies remain. I propose to offer a selected review of past developments (emphasizing the career to data of A.J. Freeman in this area), offer a list of interesting puzzles for the future, and then make some guesses as to the techniques one might want to use. (orig.)

k-dependent spectrum and optical conductivity near metal-insulator transition in multi-orbital hubbard bands

International Nuclear Information System (INIS)

Miura, Oki; Fujiwara, Takeo

2006-01-01

We apply the dynamical mean field theory (DMFT) combined with the iterative perturbation theory (IPT) to the doubly degenerate e g and the triply degenerate f 2g bands on a simple cubic lattice and a body-centered cubic lattice and calculate the spectrum and optical conductivity in arbitrary electron occupation. The spectrum simultaneously shows the effects of multiplet structure together with the electron ionization and affinity levels of different electron occupations, coherent peaks at the Fermi energy in the metallic phase and an energy gap at an integer filling of electrons for sufficiently large Coulomb U. We also discuss the critical value of the Coulomb U for degenerate orbitals on a simple cubic lattice and a body-centered cubic lattice. (author)

Electric conductivity of polyethylene during pulsed electron-beam irradiation at ETA

International Nuclear Information System (INIS)

Fiorito, R.B.; Miller, P.J.; Stern, S.H.

1986-01-01

The motivation for this work is two-fold: first, the authors want to understand the basic physics of the interaction of an intense electron beam with condensed matter. Intensity is the key word in the sense that many projectiles might act coherently or incoherently to alter significantly the medium through which they pass. During the pulse of an intense electron beam through a material which is ordinarily dielectric, the conductivity increases by 10 to 15 orders of magnitude. This effect is related to the promotion of charge carriers to the conduction band and to the mobility and lifetime of those carriers in that band. Therefore, there is a physically interesting system which is measurable in real time. It is a system which interrelates beam energy-deposition, charge-carrier concentration, material temperature, and carrier mobility. The second motivation for these experiments is methodological. If the authors can understand the relationship between conductivity and energy deposition, they might be able to develop this technique into a diagnostic of the dose-depth relationship in material subject to very-high dose and high dose-rate irradiation (≥ 1 Grad in ≤ 25 nsec). This relationship is inaccessible to measurement by means of conventional dosimetry. 14 references

Model Development for MODIS Thermal Band Electronic Crosstalk

Science.gov (United States)

Chang, Tiejun; Wu, Aisheng; Geng, Xu; Li, Yonghonh; Brinkman, Jake; Keller, Graziela; Xiong, Xiaoxiong

2016-01-01

MODerate-resolution Imaging Spectroradiometer (MODIS) has 36 bands. Among them, 16 thermal emissive bands covering a wavelength range from 3.8 to 14.4 m. After 16 years on-orbit operation, the electronic crosstalk of a few Terra MODIS thermal emissive bands developed substantial issues that cause biases in the EV brightness temperature measurements and surface feature contamination. The crosstalk effects on band 27 with center wavelength at 6.7 m and band 29 at 8.5 m increased significantly in recent years, affecting downstream products such as water vapor and cloud mask. The crosstalk effect is evident in the near-monthly scheduled lunar measurements, from which the crosstalk coefficients can be derived. The development of an alternative approach is very helpful for independent verification.In this work, a physical model was developed to assess the crosstalk impact on calibration as well as in Earth view brightness temperature retrieval. This model was applied to Terra MODIS band 29 empirically to correct the Earth brightness temperature measurements. In the model development, the detectors nonlinear response is considered. The impact of the electronic crosstalk is assessed in two steps. The first step consists of determining the impact on calibration using the on-board blackbody (BB). Due to the detectors nonlinear response and large background signal, both linear and nonlinear coefficients are affected by the crosstalk from sending bands. The second step is to calculate the effects on the Earth view brightness temperature retrieval. The effects include those from affected calibration coefficients and the contamination of Earth view measurements. This model links the measurement bias with crosstalk coefficients, detector non-linearity, and the ratio of Earth measurements between the sending and receiving bands. The correction of the electronic cross talk can be implemented empirically from the processed bias at different brightness temperature. The implementation

Electronic pairing mechanism due to band modification with increasing pair number

International Nuclear Information System (INIS)

Mizia, J.

1995-01-01

It is shown that a shift of an electron band with electron occupation number n, which is changing during the transition to the superconducting state, can lower the total energy of the system. In fact it will bring a negative contribution to the pairing potential, which is proportional to the product of the electron band shift with occupation number and the charge transfer during the transition to the superconducting state. The shift of the electron band comes from the change of stresses and the change of correlation effects in the CuO 2 plane with n, that in turn is caused by the changing oxygen concentration. This model explains the phenomenological success of Hirsch's model, which gives no explanation how the band shift in energy can give rise to superconductivity. (orig.)

Measurement of the band gap by reflection electron energy loss spectroscopy

Energy Technology Data Exchange (ETDEWEB)

Vos, Maarten, E-mail: maarten.vos@anu.edu.au [Electronic Materials Engineering Department, Research School of Physics and Engineering, The Australian National University, Canberra 0200 (Australia); King, Sean W. [Logic Technology Development, Intel Corporation, Hillsboro, OR 97124 (United States); French, Benjamin L. [Ocotillo Materials Laboratory, Intel Corporation, Chandler, AZ 85248 (United States)

2016-10-15

Highlights: • Semiconductors are measured (without surface preparation) using REELS. • At low beam energies it is difficult to measure band gap due to surface impurities. • At very high energies it is difficult to measure band gap due to recoil effect. • At intermediate energies (around 5 keV) one obtains a good estimate of the band gap. - Abstract: We investigate the possibilities of measuring the band gap of a variety of semiconductors and insulators by reflection electron energy loss spectroscopy without additional surface preparation. The band gap is a bulk property, whereas reflection energy loss spectroscopy is generally considered a surface sensitive technique. By changing the energy of the incoming electrons, the degree of surface sensitivity can be varied. Here, we present case studies to determine the optimum condition for the determination of the band gap. At very large incoming electron energies recoil effects interfere with the band gap determination, whereas at very low energies surface effects are obscuring the band gap without surface preparation. Using an incoming energy of 5 keV a reasonable estimate of the band gap is obtained in most cases.

Measurement of the band gap by reflection electron energy loss spectroscopy

International Nuclear Information System (INIS)

Vos, Maarten; King, Sean W.; French, Benjamin L.

2016-01-01

Highlights: • Semiconductors are measured (without surface preparation) using REELS. • At low beam energies it is difficult to measure band gap due to surface impurities. • At very high energies it is difficult to measure band gap due to recoil effect. • At intermediate energies (around 5 keV) one obtains a good estimate of the band gap. - Abstract: We investigate the possibilities of measuring the band gap of a variety of semiconductors and insulators by reflection electron energy loss spectroscopy without additional surface preparation. The band gap is a bulk property, whereas reflection energy loss spectroscopy is generally considered a surface sensitive technique. By changing the energy of the incoming electrons, the degree of surface sensitivity can be varied. Here, we present case studies to determine the optimum condition for the determination of the band gap. At very large incoming electron energies recoil effects interfere with the band gap determination, whereas at very low energies surface effects are obscuring the band gap without surface preparation. Using an incoming energy of 5 keV a reasonable estimate of the band gap is obtained in most cases.

Spatially resolved band alignments at Au-hexadecanethiol monolayer-GaAs(001) interfaces by ballistic electron emission microscopy

Energy Technology Data Exchange (ETDEWEB)

Junay, A.; Guézo, S., E-mail: sophie.guezo@univ-rennes1.fr; Turban, P.; Delhaye, G.; Lépine, B.; Tricot, S.; Ababou-Girard, S.; Solal, F. [Département Matériaux-Nanosciences, Institut de Physique de Rennes, UMR 6251, CNRS-Université de Rennes 1, Campus de Beaulieu, Bât 11E, 35042 Rennes Cedex (France)

2015-08-28

We study structural and electronic inhomogeneities in Metal—Organic Molecular monoLayer (OML)—semiconductor interfaces at the sub-nanometer scale by means of in situ Ballistic Electron Emission Microscopy (BEEM). BEEM imaging of Au/1-hexadecanethiols/GaAs(001) heterostructures reveals the evolution of pinholes density as a function of the thickness of the metallic top-contact. Using BEEM in spectroscopic mode in non-short-circuited areas, local electronic fingerprints (barrier height values and corresponding spectral weights) reveal a low-energy tunneling regime through the insulating organic monolayer. At higher energies, BEEM evidences new conduction channels, associated with hot-electron injection in the empty molecular orbitals of the OML. Corresponding band diagrams at buried interfaces can be thus locally described. The energy position of GaAs conduction band minimum in the heterostructure is observed to evolve as a function of the thickness of the deposited metal, and coherently with size-dependent electrostatic effects under the molecular patches. Such BEEM analysis provides a quantitative diagnosis on metallic top-contact formation on organic molecular monolayer and appears as a relevant characterization for its optimization.

Energies of conduction bands in dielectric liquids

International Nuclear Information System (INIS)

Holroyd, R.

1975-01-01

The properties of excess electrons in non-polar liquids depend on the relative energies of the trapped and conducting states. We have measured the energies of the conducting states, denoted V 0 , for about twenty non-polar liquids. Two methods were used: In one the work functions of metals immersed in the liquid were measured. In the other, solutes (TMPD) were photoionized in the liquid and V 0 calculated from the wavelength at which ionization onsets occur. A wide variation in conduction state energies is observed from a high of +0.21 eV for tetradecane to a low of --0.60 eV for tetramethylsilane. In general V 0 shifts to more negative values with increasing molecular symmetry, and correlates well with electron mobility. The photoionization results indicate that V 0 decreases with increasing temperature. In mixtures V 0 is linearly dependent on mole fraction. It was found empirically for n-hexane-neopentane mixtures that μ = 0.34 exp [--15.2(V 0 )]. This equation relating V 0 to the electron mobility also applies approximately to pure hydrocarbons. Thus the role of the conduction state energy in influencing electron mobilities and photoionization onsets is established and recent evidence indicates V 0 also influences the rates of electron reactions in these liquids

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

Electronic band structures of binary skutterudites

Energy Technology Data Exchange (ETDEWEB)

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

2015-10-25

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

Electronic band structures of binary skutterudites

International Nuclear Information System (INIS)

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

2015-01-01

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

Electronic transport properties of Ti-impurity band in Si

Energy Technology Data Exchange (ETDEWEB)

Olea, J; Gonzalez-Diaz, G; Pastor, D; Martil, I [Departamento de Fisica Aplicada III (Electricidad y Electronica), Facultad de Ciencias, Fisicas, Universidad Complutense, E-28040 Madrid (Spain)

2009-04-21

In this paper we show that pulsed laser melted high dose implantation of Ti in Si, above the Mott transition, produces an impurity band (IB) in this semiconductor. Using the van der Pauw method and Hall effect measurements we find strong laminated conductivity at the implanted layer and a temperature dependent decoupling between the Ti implanted layer (TIL) and the substrate. The conduction mechanism from the TIL to the substrate shows blocking characteristics that could be well explained through IB theory. Using the ATLAS code we can estimate the energetic position of the IB at 0.36 eV from the conduction band, the density of holes in this band which is closely related to the Ti atomic density and the hole mobility in this band. Band diagrams of the structure at low and high temperatures are also simulated in the ATLAS framework. The simulation obtained is fully coherent with experimental results.

Electronic transport properties of Ti-impurity band in Si

International Nuclear Information System (INIS)

Olea, J; Gonzalez-Diaz, G; Pastor, D; Martil, I

2009-01-01

In this paper we show that pulsed laser melted high dose implantation of Ti in Si, above the Mott transition, produces an impurity band (IB) in this semiconductor. Using the van der Pauw method and Hall effect measurements we find strong laminated conductivity at the implanted layer and a temperature dependent decoupling between the Ti implanted layer (TIL) and the substrate. The conduction mechanism from the TIL to the substrate shows blocking characteristics that could be well explained through IB theory. Using the ATLAS code we can estimate the energetic position of the IB at 0.36 eV from the conduction band, the density of holes in this band which is closely related to the Ti atomic density and the hole mobility in this band. Band diagrams of the structure at low and high temperatures are also simulated in the ATLAS framework. The simulation obtained is fully coherent with experimental results.

Spin-resolved conductance of Dirac electrons through multibarrier arrays

Science.gov (United States)

Dahal, Dipendra; Gumbs, Godfrey; Iurov, Andrii

We use a transfer matrix method to calculate the transmission coefficient of Dirac electrons through an arbitrary number of square potential barrier in gapped monolayer graphene(MLG) and bilayer graphene (BLG). The widths of barriers may not be chosen equal. The shift in the angle of incidence and the width of the barrier required for resonance are investigated numerically for both MLG and BLG. We compare the effects due to energy gap on these two transmission coefficient for each of these two structures (MLG and BLG). We present our results as functions of barrier width, height as well as incoming electron energy as well as band gap and examine the conditions for which perfect reflection or transmission occurs. Our transmission data are further used to calculate conductivity.

A multi-band, multi-level, multi-electron model for efficient FDTD simulations of electromagnetic interactions with semiconductor quantum wells

Science.gov (United States)

Ravi, Koustuban; Wang, Qian; Ho, Seng-Tiong

2015-08-01

We report a new computational model for simulations of electromagnetic interactions with semiconductor quantum well(s) (SQW) in complex electromagnetic geometries using the finite-difference time-domain method. The presented model is based on an approach of spanning a large number of electron transverse momentum states in each SQW sub-band (multi-band) with a small number of discrete multi-electron states (multi-level, multi-electron). This enables accurate and efficient two-dimensional (2-D) and three-dimensional (3-D) simulations of nanophotonic devices with SQW active media. The model includes the following features: (1) Optically induced interband transitions between various SQW conduction and heavy-hole or light-hole sub-bands are considered. (2) Novel intra sub-band and inter sub-band transition terms are derived to thermalize the electron and hole occupational distributions to the correct Fermi-Dirac distributions. (3) The terms in (2) result in an explicit update scheme which circumvents numerically cumbersome iterative procedures. This significantly augments computational efficiency. (4) Explicit update terms to account for carrier leakage to unconfined states are derived, which thermalize the bulk and SQW populations to a common quasi-equilibrium Fermi-Dirac distribution. (5) Auger recombination and intervalence band absorption are included. The model is validated by comparisons to analytic band-filling calculations, simulations of SQW optical gain spectra, and photonic crystal lasers.

Engineering flat electronic bands in quasiperiodic and fractal loop geometries

Energy Technology Data Exchange (ETDEWEB)

Nandy, Atanu, E-mail: atanunandy1989@gmail.com; Chakrabarti, Arunava, E-mail: arunava_chakrabarti@yahoo.co.in

2015-11-06

Exact construction of one electron eigenstates with flat, non-dispersive bands, and localized over clusters of various sizes is reported for a class of quasi-one-dimensional looped networks. Quasiperiodic Fibonacci and Berker fractal geometries are embedded in the arms of the loop threaded by a uniform magnetic flux. We work out an analytical scheme to unravel the localized single particle states pinned at various atomic sites or over clusters of them. The magnetic field is varied to control, in a subtle way, the extent of localization and the location of the flat band states in energy space. In addition to this we show that an appropriate tuning of the field can lead to a re-entrant behavior of the effective mass of the electron in a band, with a periodic flip in its sign. - Highlights: • Exact construction of eigenstates with flat and dispersive bands is reported. • Competition between translational order and growth of aperiodicity is discussed. • The effect of magnetic field on the location of flat band states is shown. • Flux tunable re-entrant behavior of the effective mass of electron is studied.

Band offsets of n-type electron-selective contacts on cuprous oxide (Cu{sub 2}O) for photovoltaics

Energy Technology Data Exchange (ETDEWEB)

Brandt, Riley E., E-mail: rbrandt@alum.mit.edu, E-mail: buonassisi@mit.edu; Lee, Yun Seog; Buonassisi, Tonio, E-mail: rbrandt@alum.mit.edu, E-mail: buonassisi@mit.edu [Massachusetts Institute of Technology, Cambridge, Massachusetts 02139 (United States); Young, Matthew; Dameron, Arrelaine; Teeter, Glenn [National Renewable Energy Laboratory, Golden, Colorado 80401 (United States); Park, Helen Hejin; Chua, Danny; Gordon, Roy G. [Harvard University, Cambridge, Massachusetts 02139 (United States)

2014-12-29

The development of cuprous oxide (Cu{sub 2}O) photovoltaics (PVs) is limited by low device open-circuit voltages. A strong contributing factor to this underperformance is the conduction-band offset between Cu{sub 2}O and its n-type heterojunction partner or electron-selective contact. In the present work, a broad range of possible n-type materials is surveyed, including ZnO, ZnS, Zn(O,S), (Mg,Zn)O, TiO{sub 2}, CdS, and Ga{sub 2}O{sub 3}. Band offsets are determined through X-ray photoelectron spectroscopy and optical bandgap measurements. A majority of these materials is identified as having a negative conduction-band offset with respect to Cu{sub 2}O; the detrimental impact of this on open-circuit voltage (V{sub OC}) is evaluated through 1-D device simulation. These results suggest that doping density of the n-type material is important as well, and that a poorly optimized heterojunction can easily mask changes in bulk minority carrier lifetime. Promising heterojunction candidates identified here include Zn(O,S) with [S]/[Zn] ratios >70%, and Ga{sub 2}O{sub 3}, which both demonstrate slightly positive conduction-band offsets and high V{sub OC} potential. This experimental protocol and modeling may be generalized to evaluate the efficiency potential of candidate heterojunction partners for other PV absorbers, and the materials identified herein may be promising for other absorbers with low electron affinities.

Role of electron-electron interactions in the RKKY theory of magnetism

International Nuclear Information System (INIS)

Cooke, J.F.

1978-10-01

The theory of magnetism in heavy rare earth metals is based on the RKKY theory. In this formalism the indirect exchange interaction between the local 4f spins is mediated by the conduction electrons. When carried to second order in the 4f-conduction electron interaction, traditional perturbation theory leads to a Heisenberg-like interaction between the local spins which depends on the electronic energy bands and 4f-conduction electron exchange matrix elements. This derivation neglects the detailed behavior of electron-electron interaction within the conduction band, which is known to be important in metallic systems. By using an equation of motion method, an expression for the inelastic neutron scattering cross-section has been derived which includes, in an approximate way, this electron-electron interaction. The results of this calculation indicate that spin-wave peaks can be broadened and shifted if the spin-wave band lies near the conduction electron Stoner continuum. The origin of this effect is similar to that found in itinerant electron systems where the spin-wave band actually intersects the Stoner continuum, resulting in the disappearance of the spin-wave mode

Role of electron-electron interactions in the RKKY theory of magnetism

International Nuclear Information System (INIS)

Cooke, J.F.

1979-01-01

The theory of magnetism in heavy rare earth metals is based on the RKKY theory. In this formalism the indirect exchange interaction between the local 4f spins is mediated by the conduction electrons. When carried to second order in the 4f-conduction electron interaction, traditional pertubation theory leads to a Heisenberg-like interaction between the local spins which depends on the electronic energy bands and 4f-conduction electron exchange matrix elements. This derivation neglects the detailed behavior of electron-electron interaction within the conduction band, which is known to be important in metallic systems. By using an equation of motion method, an expression for the inelastic neutron scattering cross-section has been derived which includes, in an approximate way, this electron-electron interaction. The results of this calculation indicate that spin-wave peaks can be broadened and shifted if the spin-wave band lies near the conduction electron Stoner continuum. The origin of this effect is similar to that found in itinerant electron systems where the spin-wave band actually intersects the Stoner continuum, resulting in the disappearance of the spin-wave mode

The Electronic Thermal Conductivity of Graphene.

Science.gov (United States)

Kim, Tae Yun; Park, Cheol-Hwan; Marzari, Nicola

2016-04-13

Graphene, as a semimetal with the largest known thermal conductivity, is an ideal system to study the interplay between electronic and lattice contributions to thermal transport. While the total electrical and thermal conductivity have been extensively investigated, a detailed first-principles study of its electronic thermal conductivity is still missing. Here, we first characterize the electron-phonon intrinsic contribution to the electronic thermal resistivity of graphene as a function of doping using electronic and phonon dispersions and electron-phonon couplings calculated from first-principles at the level of density-functional theory and many-body perturbation theory (GW). Then, we include extrinsic electron-impurity scattering using low-temperature experimental estimates. Under these conditions, we find that the in-plane electronic thermal conductivity κe of doped graphene is ∼300 W/mK at room temperature, independently of doping. This result is much larger than expected and comparable to the total thermal conductivity of typical metals, contributing ∼10% to the total thermal conductivity of bulk graphene. Notably, in samples whose physical or domain sizes are of the order of few micrometers or smaller, the relative contribution coming from the electronic thermal conductivity is more important than in the bulk limit, because lattice thermal conductivity is much more sensitive to sample or grain size at these scales. Last, when electron-impurity scattering effects are included we find that the electronic thermal conductivity is reduced by 30 to 70%. We also find that the Wiedemann-Franz law is broadly satisfied at low and high temperatures but with the largest deviations of 20-50% around room temperature.

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.

Relationship between electronic structure and electric conductivity of double rhodium oxides from X-ray spectral data

International Nuclear Information System (INIS)

Firsov, M.N.; Nefedov, V.I.; Shaplygin, I.S.

1983-01-01

Quantum yield spectra of X-ray photoemission of O K - and Rh M 3 -bands of double rhodium oxides with Be, Mg, Ca, Sr, Ba, Cd, V, Nb, Ta, Mo, W are obtained. Quantum yield spectra are analogous to absorption spectra and reflect vacant states in a crystal, in particular, the quantum yield spectrum of O K-band is associated with oxygen vacant states of p-symmetry while Rh M 3 -band spectrum with rhomium vacant states of d-symmetry. In all rhodium compounds investigated the first vacant band is formed by the rhodium 4d-states. The forbidden zone between the last occupied and first free states of rhodiUm has a small width (eV fractions), which explains the semiconductor character of electric conductivity of the investigated compounds. Electric resistance variation in investigated series of rhodium compounds is in agreement with peculiarities of their electronic structure and entirely depends on variation in the electron density on rhodium atoms

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

International Nuclear Information System (INIS)

Lee, Ki-Won; Kim, Young-You

2004-01-01

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

Bunch monitor for an S-band electron linear accelerator

International Nuclear Information System (INIS)

Otake, Yuji; Nakahara, Kazuo

1991-01-01

The measurement of bunch characteristics in an S-band electron linear accelerator is required in order to evaluate the quality of accelerated electron beams. A new-type bunch monitor has been developed which combines micro-stripline technology with an air insulator and wall-current monitoring technology. The obtained time resolution of the monitor was more than 150 ps. This result shows that the monitor can handle the bunch number of an S-band linac. The structure of the monitor is suitable for being installed in the vacuum area, since it is constructed of only metal and ceramic parts. It can therefore easily be employed in an actual machine

Electronic structures, elastic properties, and minimum thermal conductivities of cermet M{sub 3}AlN

Energy Technology Data Exchange (ETDEWEB)

Wang, Jin [Faculty of Materials and Energy, Southwest University, Chongqing 400715 (China); Key Laboratory of Liquid–Solid Structural Evolution and Processing of Materials, Ministry of Education, Shandong University, Jinan 250061 (China); Chen, ZhiQian, E-mail: chen_zq@swu.edu.cn [Faculty of Materials and Energy, Southwest University, Chongqing 400715 (China); Li, ChunMei; Li, Feng; Nie, ChaoYin [Faculty of Materials and Energy, Southwest University, Chongqing 400715 (China)

2014-08-15

The electronic structures and elastic anisotropies of cubic Ti{sub 3}AlN, Zr{sub 3}AlN, and Hf{sub 3}AlN are investigated by pseudopotential plane-wave method based on density functional theory. At the Fermi level, the electronic structures of these compounds are successive with no energy gap between conduct and valence bands, and exhibit metallicity in ground states. In valence band of each partial density of states, the different orbital electrons indicate interaction of corresponding atoms. In addition, the anisotropy of Hf{sub 3}AlN is found to be significantly different from that of Ti{sub 3}AlN and Zr{sub 3}AlN, which involve the differences in the bonding strength. It is notable that Hf{sub 3}AlN is a desired thermal barrier material with the lowest thermal conductivity at high temperature among the three compounds. - Graphical abstract: 1.Young's moduli of anti-perovskite Ti{sub 3}AlN, Zr{sub 3}AlN, and Hf{sub 3}AlN in full space. 2.Electron density differences on crystal planes (1 0 0), (2 0 0), and (1 1 0) of anti-perovskite Zr{sub 3}AlN. - Highlights: • We calculated three anti-perovskite cermets with first-principles theory. • We illustrated 3D Young modulus and found the anomalous anisotropy. • We explained the anomaly and calculated the minimum thermal conductivities.

Electron thermal conduction in LASNEX

International Nuclear Information System (INIS)

Munro, D.; Weber, S.

1994-01-01

This report is a transcription of hand-written notes by DM dated 29 January 1986, transcribed by SW, with some clarifying comments added and details specific to running the LASNEX code deleted. Reference to the esoteric measurement units employed in LASNEX has also been deleted by SW (hopefully, without introducing errors in the numerical constants). The report describes the physics equations only, and only of electron conduction. That is, it does not describe the numerical method, which may be finite difference or finite element treatment in space, and (usually) implicit treatment in time. It does not touch on other electron transport packages which are available, and which include suprathermal electrons, nonlocal conduction, Krook model conduction, and modifications to electron conduction by magnetic fields. Nevertheless, this model is employed for the preponderance of LASNEX simulations

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.

Terra MODIS Band 27 Electronic Crosstalk Effect and Its Removal

Science.gov (United States)

Sun, Junqiang; Xiong, Xiaoxiong; Madhavan, Sriharsha; Wenny, Brian

2012-01-01

The MODerate-resolution Imaging Spectroradiometer (MODIS) is one of the primary instruments in the NASA Earth Observing System (EOS). The first MODIS instrument was launched in December, 1999 on-board the Terra spacecraft. MODIS has 36 bands, covering a wavelength range from 0.4 micron to 14.4 micron. MODIS band 27 (6.72 micron) is a water vapor band, which is designed to be insensitive to Earth surface features. In recent Earth View (EV) images of Terra band 27, surface feature contamination is clearly seen and striping has become very pronounced. In this paper, it is shown that band 27 is impacted by electronic crosstalk from bands 28-30. An algorithm using a linear approximation is developed to correct the crosstalk effect. The crosstalk coefficients are derived from Terra MODIS lunar observations. They show that the crosstalk is strongly detector dependent and the crosstalk pattern has changed dramatically since launch. The crosstalk contributions are positive to the instrument response of band 27 early in the mission but became negative and much larger in magnitude at later stages of the mission for most detectors of the band. The algorithm is applied to both Black Body (BB) calibration and MODIS L1B products. With the crosstalk effect removed, the calibration coefficients of Terra MODIS band 27 derived from the BB show that the detector differences become smaller. With the algorithm applied to MODIS L1B products, the Earth surface features are significantly removed and the striping is substantially reduced in the images of the band. The approach developed in this report for removal of the electronic crosstalk effect can be applied to other MODIS bands if similar crosstalk behaviors occur.

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.

Indium oxide—a transparent, wide-band gap semiconductor for (opto)electronic applications

International Nuclear Information System (INIS)

Bierwagen, Oliver

2015-01-01

The present review takes a semiconductor physics perspective to summarize the state-of-the art of In 2 O 3 in relation to applications. After discussing conventional and novel applications, the crystal structure, synthesis of single-crystalline material, band-structure and optical transparency are briefly introduced before focussing on the charge carrier transport properties. The issues of unintentional n-type conductivity and its likely causes, the surface electron accumulation, and the lack of p-type conductivity will be presented. Intentional doping will be demonstrated to control the electron concentration and resistivity over a wide range, but is also subject to compensation. The control of the surface accumulation in relation to Schottky and ohmic contacts will be demonstrated. In the context of scattering mechanisms, the electron mobility and its limits will be discussed. Finally, the Seebeck coefficient and its significance will be shown, and ferromagnetic doping of In 2 O 3 will be critically discussed. With this overview most if not all ingredients for the use of In 2 O 3 as semiconductor material in novel or improved conventional devices will be given. (invited review)

The sensitivity of the electron transport within bulk zinc-blende gallium nitride to variations in the crystal temperature, the doping concentration, and the non-parabolicity coefficient associated with the lowest energy conduction band valley

Energy Technology Data Exchange (ETDEWEB)

Siddiqua, Poppy; O' Leary, Stephen K., E-mail: stephen.oleary@ubc.ca [School of Engineering, The University of British Columbia, 3333 University Way, Kelowna, British Columbia V1V 1V7 (Canada)

2016-09-07

Within the framework of a semi-classical three-valley Monte Carlo simulation approach, we analyze the steady-state and transient electron transport that occurs within bulk zinc-blende gallium nitride. In particular, we examine how the steady-state and transient electron transport that occurs within this material changes in response to variations in the crystal temperature, the doping concentration, and the non-parabolicity coefficient associated with the lowest energy conduction band valley. These results are then contrasted with those corresponding to a number of other compound semiconductors of interest.

Conduction band offset at the InN/GaN heterojunction

International Nuclear Information System (INIS)

Wang Kejia; Lian Chuanxin; Su Ning; Jena, Debdeep; Timler, John

2007-01-01

The conduction-band offset between GaN and InN is experimentally determined. InN/n-type GaN isotype heterojunctions grown by molecular beam epitaxy are observed to exhibit Schottky-junction like behavior based on rectifying vertical current flow. From capacitance-voltage measurements on the heterojunction, the Schottky barrier height is found to be ∼0.94 eV. The photocurrent spectroscopy measurement by backside illumination reveals an energy barrier height of 0.95 eV across the heterojunction, consistent with the capacitance measurement. By combining electrical transport, capacitance-voltage, and photocurrent spectroscopy measurement results, the conduction band offset between InN and GaN is estimated to be ΔE C =1.68±0.1 eV

Ka-Band Electronically Steered CubeSat Antenna, Phase II

Data.gov (United States)

National Aeronautics and Space Administration — Kymeta Government Solutions (KGS) designed, analyzed, built, tested, and delivered a small, lightweight, low-cost, low-power electronically steered Ka-band prototype...

A simple model for conduction band states of nitride-based double heteroestructures

Energy Technology Data Exchange (ETDEWEB)

Gaggero-Sager, L M; Mora-Ramos, M E, E-mail: lgaggero@uaem.m [Facultad de Ciencias, Universidad Autonoma del Estado de Morelos, Av. Universidad 1001, CP 62209, Cuernavaca, Morelos (Mexico)

2009-05-01

In this work we propose an analytical expression for the approximate modeling of the potential energy function describing conduction band bending in III-V nitride quantum wells. It is an alternative approach to the self-consistent Poisson-Schoedinger calculation. The model considers the influence of the many electron system and the built-in electric field inside the well. Hartree and exchange contributions are included along the lines of a local-density Thomas-Fermi-based theory. The effects due to the modulated doping in the barriers is also considered. We report the calculation of the energy spectrum as a function of several input parameters: alloy composition in the barriers, barrier doping concentration, and quantum well width. Our results could be of usefulness in the study of optoelectronic properties in this kind of systems.

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.

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

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

Science.gov (United States)

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

1997-02-01

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

Quantifying electronic band interactions in van der Waals materials using angle-resolved reflected-electron spectroscopy.

Science.gov (United States)

Jobst, Johannes; van der Torren, Alexander J H; Krasovskii, Eugene E; Balgley, Jesse; Dean, Cory R; Tromp, Rudolf M; van der Molen, Sense Jan

2016-11-29

High electron mobility is one of graphene's key properties, exploited for applications and fundamental research alike. Highest mobility values are found in heterostructures of graphene and hexagonal boron nitride, which consequently are widely used. However, surprisingly little is known about the interaction between the electronic states of these layered systems. Rather pragmatically, it is assumed that these do not couple significantly. Here we study the unoccupied band structure of graphite, boron nitride and their heterostructures using angle-resolved reflected-electron spectroscopy. We demonstrate that graphene and boron nitride bands do not interact over a wide energy range, despite their very similar dispersions. The method we use can be generally applied to study interactions in van der Waals systems, that is, artificial stacks of layered materials. With this we can quantitatively understand the 'chemistry of layers' by which novel materials are created via electronic coupling between the layers they are composed of.

A Unifying Perspective on Oxygen Vacancies in Wide Band Gap Oxides.

Science.gov (United States)

Linderälv, Christopher; Lindman, Anders; Erhart, Paul

2018-01-04

Wide band gap oxides are versatile materials with numerous applications in research and technology. Many properties of these materials are intimately related to defects, with the most important defect being the oxygen vacancy. Here, using electronic structure calculations, we show that the charge transition level (CTL) and eigenstates associated with oxygen vacancies, which to a large extent determine their electronic properties, are confined to a rather narrow energy range, even while band gap and the electronic structure of the conduction band vary substantially. Vacancies are classified according to their character (deep versus shallow), which shows that the alignment of electronic eigenenergies and CTL can be understood in terms of the transition between cavity-like localized levels in the large band gap limit and strong coupling between conduction band and vacancy states for small to medium band gaps. We consider both conventional and hybrid functionals and demonstrate that the former yields results in very good agreement with the latter provided that band edge alignment is taken into account.

Periodic Anderson model with correlated conduction electrons: Variational and exact diagonalization study

Science.gov (United States)

Hagymási, I.; Itai, K.; Sólyom, J.

2012-06-01

We investigate an extended version of the periodic Anderson model (the so-called periodic Anderson-Hubbard model) with the aim to understand the role of interaction between conduction electrons in the formation of the heavy-fermion and mixed-valence states. Two methods are used: (i) variational calculation with the Gutzwiller wave function optimizing numerically the ground-state energy and (ii) exact diagonalization of the Hamiltonian for short chains. The f-level occupancy and the renormalization factor of the quasiparticles are calculated as a function of the energy of the f orbital for a wide range of the interaction parameters. The results obtained by the two methods are in reasonably good agreement for the periodic Anderson model. The agreement is maintained even when the interaction between band electrons, Ud, is taken into account, except for the half-filled case. This discrepancy can be explained by the difference between the physics of the one- and higher-dimensional models. We find that this interaction shifts and widens the energy range of the bare f level, where heavy-fermion behavior can be observed. For large-enough Ud this range may lie even above the bare conduction band. The Gutzwiller method indicates a robust transition from Kondo insulator to Mott insulator in the half-filled model, while Ud enhances the quasiparticle mass when the filling is close to half filling.

Some Effective Tight-Binding Models for Electrons in DNA Conduction: A Review

International Nuclear Information System (INIS)

Yamada, H.; Iguchi, K.

2010-01-01

Quantum transport for DNA conduction has been widely studied with interest in application as a candidate in making nanowires as well as interest in the scientific mechanism. In this paper, we review recent works concerning the electronic states and the conduction/transfer in DNA polymers. We have mainly investigated the energy-band structure and the correlation effects of localization property in the two- and three-chain systems (ladder model) with long-range correlation as a simple model for electronic property in a double strand of DNA by using the tight-bindingmodel. In addition, we investigated the localization properties of electronic states in several actual DNA sequences such as bacteriophages of Escherichia coli, human-chromosome 22, compared with those of the artificial disordered sequences with correlation. The charge-transfer properties for poly(dA)-poly(dT) and poly(dG)-poly(dC) DNA polymers are also presented in terms of localization lengths within the frameworks of the polaron models due to the coupling between the charge carriers and the lattice vibrations of the double strand of DNA

The electronic band parameters calculated by the Kronig-Penney method for Cd1-xZnxS quantum dot superlattices

International Nuclear Information System (INIS)

Sakly, A.; Safta, N.; Mejri, H.; Lamine, A. Ben

2009-01-01

This work reports on a theoretical study of superlattices based on Cd 1-x Zn x S quantum dots embedded in an insulating material. We show, in particular, how this system can be assumed to a series of flattened cylindrical quantum dots with a finite barrier height at the boundary. In this paper, are also reviewed the approximations needed to calculate the band edges of the Cd 1-x Zn x S superlattices with use of the Kronig-Penney model. The electronic states and the electron effective masses of both Γ 1 - and Γ 2 -minibands have been computed as a function of zinc composition for different inter-quantum dot separations. As is found, the CdS system is appropriate to give rise a superlattice behavior for conduction electrons in a relatively large range of inter-sheet separations. An attempt to explain the electron band parameters calculated will be presented.

Electronic Conductivity of Doped-Lanthanum Gallate Electrolytes

Science.gov (United States)

Yamaji, Katsuhiko; Xiong, Yue Ping; Kishimoto, Haruo; Horita, Teruhisa; Sakai, Natsuko; Brito, Manuel E.; Yokokawa, Harumi

Electronic conductivity of doped lanthanum gallate electrolytes were determined by using a Hebb-Wagner type polarization cell. Electronic conductivity of cobalt-doped, La0.8Sr0.2Ga0.8Mg0.15Co0.5O3-δ (LSGMC), and non cobalt-doped, La0.8Sr0.2Ga0.8Mg0.2O2.8 (LSGM8282), were measured as a function of oxygen partial pressures. The electronic conductivity of LSGM8282 showed a linear dependence on p(O2)1/4 in the higher p(O2) region, which is attributed to the electronic hole conductivity. The electronic conductivity of LSGMC showed a linear dependence on p(O2)1/6 in the higher p(O2) region. LSGMC has higher electronic conductivity than LSGM, and the conductivity was not clearly changed with temperatures between 600 and 800 °C. In lower p(O2) region, the electronic conductivity data have poor reproducibility and did not show any dependence on p(O2) because of the degradation of the electrolytes in severe reducing atmospheres.

Kinks in the σ band of graphene induced by electron-phonon coupling.

Science.gov (United States)

Mazzola, Federico; Wells, Justin W; Yakimova, Rositza; Ulstrup, Søren; Miwa, Jill A; Balog, Richard; Bianchi, Marco; Leandersson, Mats; Adell, Johan; Hofmann, Philip; Balasubramanian, T

2013-11-22

Angle-resolved photoemission spectroscopy reveals pronounced kinks in the dispersion of the σ band of graphene. Such kinks are usually caused by the combination of a strong electron-boson interaction and the cutoff in the Fermi-Dirac distribution. They are therefore not expected for the σ band of graphene that has a binding energy of more than ≈3.5 eV. We argue that the observed kinks are indeed caused by the electron-phonon interaction, but the role of the Fermi-Dirac distribution cutoff is assumed by a cutoff in the density of σ states. The existence of the effect suggests a very weak coupling of holes in the σ band not only to the π electrons of graphene but also to the substrate electronic states. This is confirmed by the presence of such kinks for graphene on several different substrates that all show a strong coupling constant of λ≈1.

Visualizing One-Dimensional Electronic States and their Scattering in Semi-conducting Nanowires

Science.gov (United States)

Beidenkopf, Haim; Reiner, Jonathan; Norris, Andrew; Nayak, Abhay Kumar; Avraham, Nurit; Shtrikman, Hadas

One-dimensional electronic systems constitute a fascinating playground for the emergence of exotic electronic effects and phases, within and beyond the Tomonaga-Luttinger liquid paradigm. More recently topological superconductivity and Majorana modes were added to that long list of phenomena. We report scanning tunneling microscopy and spectroscopy measurements conducted on pristine, epitaxialy grown InAs nanowires. We resolve the 1D electronic band structure manifested both via Van-Hove singularities in the local density-of-states, as well as by the quasi-particle interference patterns, induced by scattering from surface impurities. By studying the scattering of the one-dimensional electronic states off various scatterers, including crystallographic defects and the nanowire end, we identify new one-dimensional relaxation regimes and yet unexplored effects of interactions. Some of these may bear implications on the topological superconducting state and Majorana modes therein. The authors acknowledge support from the Israeli Science Foundation (ISF).

Post-precipitation bias in band-tailed pigeon surveys conducted at mineral sites

Science.gov (United States)

Overton, C.T.; Schmitz, R.A.; Casazza, Michael L.

2005-01-01

Many animal surveys to estimate populations or index trends include protocol prohibiting counts during rain but fail to address effects of rainfall preceding the count. Prior research on Pacific Coast band-tailed pigeons (Patagioenas fasciata monilis) documented declines in use of mineral sites during rainfall. We hypothesized that prior precipitation was associated with a short-term increase in use of mineral sites following rain. We conducted weekly counts of band-tailed pigeons at 19 Pacific Northwest mineral sites in 2001 and 20 sites in 2002. Results from regression analysis indicated higher counts ???2 days after rain (11.31??5.00% [x????SE]) compared to ???3 days. Individual index counts conducted ???2 days after rain were biased high, resulting in reduced ability to accurately estimate population trends. Models of band-tailed pigeon visitation rates throughout the summer showed increased mineral-site counts during both June and August migration periods, relative to the July breeding period. Our research supported previous studies recommending that mineral-site counts used to index the band-tailed pigeon population be conducted during July. We further recommend conducting counts >3 days after rain to avoid weather-related bias in index estimation. The design of other population sampling strategies that rely on annual counts should consider the influence of aberrant weather not only coincident with but also preceding surveys if weather patterns are thought to influence behavior or detection probability of target species.

Electronic Energy Levels and Band Alignment for Aqueous Phenol and Phenolate from First Principles.

Science.gov (United States)

Opalka, Daniel; Pham, Tuan Anh; Sprik, Michiel; Galli, Giulia

2015-07-30

Electronic energy levels in phenol and phenolate solutions have been computed using density functional theory and many-body perturbation theory. The valence and conduction bands of the solvent and the ionization energies of the solutes have been aligned with respect to the vacuum level based on the concept of a computational standard hydrogen electrode. We have found significant quantitative differences between the generalized-gradient approximation, calculations with the HSE hybrid functional, and many-body perturbation theory in the G0W0 approximation. For phenol, two ionization energies below the photoionization threshold of bulk water have been assigned in the spectrum of Kohn-Sham eigenvalues of the solution. Deprotonation to phenolate was found to lift a third occupied energy level above the valence band maximum of the solvent which is characterized by an electronic lone pair at the hydroxyl group. The second and third ionization energies of phenolate were found to be very similar and explain the intensity pattern observed in recent experiments using liquid-microjet photoemission spectroscopy.

Role of Electronic Structure In Ion Band State Theory of Low Energy Nuclear Reactions

Science.gov (United States)

Chubb, Scott

2004-03-01

The Nuts and Bolts of our Ion Band State (IBS) theory of low energy nuclear reactions (LENR's) in palladium-deuteride (PdD) and palladium-hydride (PdH) are the electrons that hold together or tear apart the bonds (or lack of bonds) between deuterons (d's) or protons (p's) and the host material. In PdDx and PdH_x, this bonding is strongly correlated with loading: in ambient loading conditions (x< 0. 6), the bonding in hibits IBS occupation. As x arrow 1, slight increases and decreases in loading can lead to vibrations (which have conventionally been thought to occur from phonons) that can induce potential losses or increases of p/d. Naive assumptions about phonons fail to include these losses and increases. These effects can occur because neither H or D has core electrons and because in either PdD or PdH, the electrons near the Fermi Energy have negligible overlap with the nucleus of either D or H. I use these ideas to develop a formal justification, based on a generalization of conventional band theory (Scott Chubb, "Semi-Classical Conduction of Charged and Neutral Particles in Finite Lattices," 2004 March Meeting."), for the idea that occupation of IBS's can occur and that this can lead to nuclear reactions.

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.

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

CERN Document Server

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

1998-01-01

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

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.

Band Gap Modulated by Electronic Superlattice in Blue Phosphorene.

Science.gov (United States)

Zhuang, Jincheng; Liu, Chen; Gao, Qian; Liu, Yani; Feng, Haifeng; Xu, Xun; Wang, Jiaou; Zhao, Jijun; Dou, Shi Xue; Hu, Zhenpeng; Du, Yi

2018-05-22

Exploring stable two-dimensional materials with appropriate band gaps and high carrier mobility is highly desirable due to the potential applications in optoelectronic devices. Here, the electronic structures of phosphorene on a Au(111) substrate are investigated by scanning tunneling spectroscopy, angle-resolved photoemission spectroscopy (ARPES), and density functional theory (DFT) calculations. The substrate-induced phosphorene superstructure gives a superlattice potential, leading to a strong band folding effect of the sp band of Au(111) on the band structure. The band gap could be clearly identified in the ARPES results after examining the folded sp band. The value of the energy gap (∼1.1 eV) and the high charge carrier mobility comparable to that of black phosphorus, which is engineered by the tensile strain, are revealed by the combination of ARPES results and DFT calculations. Furthermore, the phosphorene layer on the Au(111) surface displays high surface inertness, leading to the absence of multilayer phosphorene. All these results suggest that the phosphorene on Au(111) could be a promising candidate, not only for fundamental research but also for nanoelectronic and optoelectronic applications.

Optical conductivity calculation of a k.p model semiconductor GaAs incorporating first-order electron-hole vertex correction

Science.gov (United States)

Nurhuda, Maryam; Aziz Majidi, Muhammad

2018-04-01

The role of excitons in semiconducting materials carries potential applications. Experimental results show that excitonic signals also appear in optical absorption spectra of semiconductor system with narrow gap, such as Gallium Arsenide (GaAs). While on the theoretical side, calculation of optical spectra based purely on Density Functional Theory (DFT) without taking electron-hole (e-h) interactions into account does not lead to the appearance of any excitonic signal. Meanwhile, existing DFT-based algorithms that include a full vertex correction through Bethe-Salpeter equation may reveal an excitonic signal, but the algorithm has not provided a way to analyze the excitonic signal further. Motivated to provide a way to isolate the excitonic effect in the optical response theoretically, we develop a method of calculation for the optical conductivity of a narrow band-gap semiconductor GaAs within the 8-band k.p model that includes electron-hole interactions through first-order electron-hole vertex correction. Our calculation confirms that the first-order e-h vertex correction reveals excitonic signal around 1.5 eV (the band gap edge), consistent with the experimental data.

Structure of conduction electrons on polysilanes

Energy Technology Data Exchange (ETDEWEB)

Ichikawa, Tsuneki [Hokkaido Univ., Sapporo (Japan); Kumagai, Jun

1998-10-01

The orbital structures of conduction electrons on permethylated oligosilane, Si{sub 2n}(CH{sub 3}){sub 2n+2}(n = 2 - 8), and poly(cyclohexylmethylsilane) have been determined by the electron spin-echo envelope modulation signals of the radical anions of these silanes in a deuterated rigid matrix at 77 K. The conduction electron on permethylated oligosilane is delocalized over the entire main chain, whereas that on poly(cyclohexylmethylsilane) is localized on a part of the main chain composed of about six Si atoms. Quantum-chemical calculations suggest that Anderson localization due to fluctuation of {sigma} conjugation by conformational disorder of the main chain is responsible for the localization of both the conduction electron and the hole. (author)

Effect of conduction band nonparabolicity on the optical properties in ...

Indian Academy of Sciences (India)

the bulk conduction band edge, the correction due to nonparabolicity can be important. [9,10]. In a narrow QW under a strong magnetic field, the optical absorption coefficients calculated with the nonparabolicity correction shows remarkable deviation from results obtained using parabolic energy approximation [11].

Band Alignment Determination of Two-Dimensional Heterojunctions and Their Electronic Applications

KAUST Repository

Chiu, Ming-Hui

2018-05-09

Two-dimensional (2D) layered materials such as MoS2 have been recognized as high on-off ratio semiconductors which are promising candidates for electronic and optoelectronic devices. In addition to the use of individual 2D materials, the accelerated field of 2D heterostructures enables even greater functionalities. Device designs differ, and they are strongly controlled by the electronic band alignment. For example, photovoltaic cells require type II heterostructures for light harvesting, and light-emitting diodes benefit from multiple quantum wells with the type I band alignment for high emission efficiency. The vertical tunneling field-effect transistor for next-generation electronics depends on nearly broken-gap band alignment for boosting its performance. To tailor these 2D layered materials toward possible future applications, the understanding of 2D heterostructure band alignment becomes critically important. In the first part of this thesis, we discuss the band alignment of 2D heterostructures. To do so, we firstly study the interlayer coupling between two dissimilar 2D materials. We conclude that a post-anneal process could enhance the interlayer coupling of as-transferred 2D heterostructures, and heterostructural stacking imposes similar symmetry changes as homostructural stacking. Later, we precisely determine the quasi particle bandgap and band alignment of the MoS2/WSe2 heterostructure by using scan tunneling microscopy/spectroscopy (STM/S) and micron-beam X-ray photoelectron spectroscopy (μ-XPS) techniques. Lastly, we prove that the band alignment of 2D heterojunctions can be accurately predicted by Anderson’s model, which has previously failed to predict conventional bulk heterostructures. In the second part of this thesis, we develop a new Chemical Vapor Deposition (CVD) method capable of precisely controlling the growth area of p- and n-type transition metal dichalcogenides (TMDCs) and further form lateral or vertical 2D heterostructures. This

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

Science.gov (United States)

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

2014-12-01

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

Method of forming electronically conducting polymers on conducting and nonconducting substrates

Science.gov (United States)

Murphy, Oliver J. (Inventor); Hitchens, G. Duncan (Inventor); Hodko, Dalibor (Inventor); Clarke, Eric T. (Inventor); Miller, David L. (Inventor); Parker, Donald L. (Inventor)

2001-01-01

The present invention provides electronically conducting polymer films formed from photosensitive formulations of pyrrole and an electron acceptor that have been selectively exposed to UV light, laser light, or electron beams. The formulations may include photoinitiators, flexibilizers, solvents and the like. These solutions can be used in applications including printed circuit boards and through-hole plating and enable direct metallization processes on non-conducting substrates. After forming the conductive polymer patterns, a printed wiring board can be formed by sensitizing the polymer with palladium and electrolytically depositing copper.

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.

An L-Band Polarized Electron PWT Photoinjector for the International Linear Collider (ILC)

CERN Document Server

Yu, David; Chen Ping; Lundquist, Martin; Luo, Yan; Smirnov, Alexei Yu

2005-01-01

A multi-cell, standing-wave, L-band, p-mode, plane-wave-transformer (PWT) photoinjector with an integrated photocathode in a novel linac structure is proposed by DULY Research Inc. as a polarized electron source. The PWT photoinjector is capable of operation in ultra high vacuum and moderate field gradient. Expected performance of an L-band polarized electron PWT injector operating under the parameters for the International Linear Collider is presented. The projected normalized transverse rms emittance is an order of magnitude lower than that produced with a polarized electron dc gun followed by subharmonic bunchers.

Effects of Conducting Instruction on the Musical Performance of Beginning Band Students.

Science.gov (United States)

Kelly, Steven N.

1997-01-01

Investigates the effects of conducting instruction on beginning band students' individual rhythmic performance, group rhythmic performance, group performance of legato and staccato, and group performance of phrasing and dynamics. The students represented diverse ethnic and cultural backgrounds. Concludes the conducting instruction is a useful tool…

Determination of the band alignment of a-IGZO/a-IGMO heterojunction for high-electron mobility transistor application

Energy Technology Data Exchange (ETDEWEB)

Zhang, Yi-Yu; Qian, Ling-Xuan; Liu, Xing-Zhao [School of Microelectronics and Solid-State Electronics, University of Electronic Science and Technology of China, Chengdu (China); State Key Laboratory of Electronic Thin Films and Integrated Devices, Chengdu (China)

2017-10-15

In the past decade, amorphous InGaZnO thin film transistors (a-IGZO TFTs) have become a very promising candidate for application in flat panel displays (FPDs). However, it is difficult to break through the mobility bottleneck of a-IGZO TFTs to obtain mobilities higher than 100 cm{sup 2} V{sup -1} s{sup -1}, thus limiting their use in more advanced applications. Construction of a high-electron mobility transistor (HEMT) based on a heterojunction structure could provide a solution for this problem. In this work, the band alignment of a-IGZO and amorphous InGaMgO (a-IGMO) heterojunction has been investigated using X-ray photoelectron spectroscopy (XPS) and transmission spectra measurements. The valence band (ΔE{sub V}) and conduction band offsets (ΔE{sub C}) were determined as 0.09 and 0.83 eV, respectively. The ΔE{sub C} was large enough to construct a potential well that could favor the appearance of a two-dimensional electron gas (2DEG). Hence, the achievement of an HEMT based on a-IGZO/a-IGMO heterojunction can be expected. Moreover, band bending contributed greatly to such a large ΔE{sub C}, and thus to the formation of electrical confinement structure. Our findings suggest that a-IGZO/a-IGMO heterojunction is a potential candidate for constructing a HEMT and thus breaking through the mobility bottleneck of a-IGZO-based TFTs for the applications in next-generation electronic products. (copyright 2017 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim)

Determination of the band alignment of a-IGZO/a-IGMO heterojunction for high-electron mobility transistor application

International Nuclear Information System (INIS)

Zhang, Yi-Yu; Qian, Ling-Xuan; Liu, Xing-Zhao

2017-01-01

In the past decade, amorphous InGaZnO thin film transistors (a-IGZO TFTs) have become a very promising candidate for application in flat panel displays (FPDs). However, it is difficult to break through the mobility bottleneck of a-IGZO TFTs to obtain mobilities higher than 100 cm"2 V"-"1 s"-"1, thus limiting their use in more advanced applications. Construction of a high-electron mobility transistor (HEMT) based on a heterojunction structure could provide a solution for this problem. In this work, the band alignment of a-IGZO and amorphous InGaMgO (a-IGMO) heterojunction has been investigated using X-ray photoelectron spectroscopy (XPS) and transmission spectra measurements. The valence band (ΔE_V) and conduction band offsets (ΔE_C) were determined as 0.09 and 0.83 eV, respectively. The ΔE_C was large enough to construct a potential well that could favor the appearance of a two-dimensional electron gas (2DEG). Hence, the achievement of an HEMT based on a-IGZO/a-IGMO heterojunction can be expected. Moreover, band bending contributed greatly to such a large ΔE_C, and thus to the formation of electrical confinement structure. Our findings suggest that a-IGZO/a-IGMO heterojunction is a potential candidate for constructing a HEMT and thus breaking through the mobility bottleneck of a-IGZO-based TFTs for the applications in next-generation electronic products. (copyright 2017 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim)

Tunneling conductance of a two-dimensional electron gas with Dresselhaus spin-orbit coupling

International Nuclear Information System (INIS)

Srisongmuang, B.; Ka-oey, A.

2012-01-01

We theoretically studied the spin-dependent charge transport in a two-dimensional electron gas with Dresselhaus spin-orbit coupling (DSOC) and metal junctions. It is shown that the DSOC energy can be directly measured from the tunneling conductance spectrum. We found that spin polarization of the conductance in the propagation direction can be obtained by injecting from the DSOC system. We also considered the effect of the interfacial scattering barrier (both spin-flip and non-spin-flip scattering) on the overall conductance and the spin polarization of the conductance. It is found that the increase of spin-flip scattering can enhance the conductance under certain conditions. Moreover, both types of scattering can increase the spin polarization below the branches crossing of the energy band. - Highlights: → DSOC energy can be directly measured from tunneling conductance spectrum. → Spin polarization of conductance in the propagation direction can be obtained by injecting from DSOC system. → Both types of scattering can increase spin polarization.

Electron Elevator: Excitations across the Band Gap via a Dynamical Gap State.

Science.gov (United States)

Lim, A; Foulkes, W M C; Horsfield, A P; Mason, D R; Schleife, A; Draeger, E W; Correa, A A

2016-01-29

We use time-dependent density functional theory to study self-irradiated Si. We calculate the electronic stopping power of Si in Si by evaluating the energy transferred to the electrons per unit path length by an ion of kinetic energy from 1 eV to 100 keV moving through the host. Electronic stopping is found to be significant below the threshold velocity normally identified with transitions across the band gap. A structured crossover at low velocity exists in place of a hard threshold. An analysis of the time dependence of the transition rates using coupled linear rate equations enables one of the excitation mechanisms to be clearly identified: a defect state induced in the gap by the moving ion acts like an elevator and carries electrons across the band gap.

Electronic band structure of TiFese2 in ferromagnetic phase

International Nuclear Information System (INIS)

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

2011-01-01

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

Band-gap creation by icosahedral symmetry in nearly-free-electron materials

International Nuclear Information System (INIS)

Carlsson, A.E.

1993-01-01

A series of numerical electronic density-of-states calculations is performed for rational approximants to a model one-electron potential based on icosahedrally arranged plane-wave components. It is found that high-order approximants can have band gaps even if the low-order approximants do not; furthermore, the magnitude of the gap increases with the order of the approximant. The results are interpreted via a two- and three-wave analysis of the energy eigenvalues at the pseudo-Jones-zone faces and edges. It is also found that the mechanism of band-gap reduction in the rational approximants is the presence of a small density of gap states. An analytic calculation shows that these gap states result from a splitting of threefold and pseudothreefold states at the valence-band edge when the icosahedral symmetry is broken. The splitting is proportional to the error with which the ratio between the approximant indices approximates τ, the golden mean. Finally, an application to the AlCuLi system is presented

Band-selective filter in a zigzag graphene nanoribbon.

Science.gov (United States)

Nakabayashi, Jun; Yamamoto, Daisuke; Kurihara, Susumu

2009-02-13

Electric transport of a zigzag graphene nanoribbon through a steplike potential and a barrier potential is investigated by using the recursive Green's function method. In the case of the steplike potential, we demonstrate numerically that scattering processes obey a selection rule for the band indices when the number of zigzag chains is even; the electrons belonging to the "even" ("odd") bands are scattered only into the even (odd) bands so that the parity of the wave functions is preserved. In the case of the barrier potential, by tuning the barrier height to be an appropriate value, we show that it can work as the "band-selective filter", which transmits electrons selectively with respect to the indices of the bands to which the incident electrons belong. Finally, we suggest that this selection rule can be observed in the conductance by applying two barrier potentials.

Optical and electronic properties of 2 H -Mo S2 under pressure: Revealing the spin-polarized nature of bulk electronic bands

Science.gov (United States)

Brotons-Gisbert, Mauro; Segura, Alfredo; Robles, Roberto; Canadell, Enric; Ordejón, Pablo; Sánchez-Royo, Juan F.

2018-05-01

Monolayers of transition-metal dichalcogenide semiconductors present spin-valley locked electronic bands, a property with applications in valleytronics and spintronics that is usually believed to be absent in their centrosymmetric (as the bilayer or bulk) counterparts. Here we show that bulk 2 H -Mo S2 hides a spin-polarized nature of states determining its direct band gap, with the spin sequence of valence and conduction bands expected for its single layer. This relevant finding is attained by investigating the behavior of the binding energy of A and B excitons under high pressure, by means of absorption measurements and density-functional-theory calculations. These results raise an unusual situation in which bright and dark exciton degeneracy is naturally broken in a centrosymmetric material. Additionally, the phonon-assisted scattering process of excitons has been studied by analyzing the pressure dependence of the linewidth of discrete excitons observed at the absorption coefficient edge of 2 H -Mo S2 . Also, the pressure dependence of the indirect optical transitions of bulk 2 H -Mo S2 has been analyzed by absorption measurements and density-functional-theory calculations. These results reflect a progressive closure of the indirect band gap as pressure increases, indicating that metallization of bulk Mo S2 may occur at pressures higher than 26 GPa.

Room-Temperature-Synthesized High-Mobility Transparent Amorphous CdO-Ga2O3 Alloys with Widely Tunable Electronic Bands.

Science.gov (United States)

Liu, Chao Ping; Ho, Chun Yuen; Dos Reis, Roberto; Foo, Yishu; Guo, Peng Fei; Zapien, Juan Antonio; Walukiewicz, Wladek; Yu, Kin Man

2018-02-28

In this work, we have synthesized Cd 1-x Ga x O 1+δ alloy thin films at room temperature over the entire composition range by radio frequency magnetron sputtering. We found that alloy films with high Ga contents of x > 0.3 are amorphous. Amorphous Cd 1-x Ga x O 1+δ alloys in the composition range of 0.3 < x < 0.5 exhibit a high electron mobility of 10-20 cm 2 V -1 s -1 with a resistivity in the range of 10 -2 to high 10 -4 Ω cm range. The resistivity of the amorphous alloys can also be controlled over 5 orders of magnitude from 7 × 10 -4 to 77 Ω cm by controlling the oxygen stoichiometry. Over the entire composition range, these crystalline and amorphous alloys have a large tunable intrinsic band gap range of 2.2-4.8 eV as well as a conduction band minimum range of 5.8-4.5 eV below the vacuum level. Our results suggest that amorphous Cd 1-x Ga x O 1+δ alloy films with 0.3 < x < 0.4 have favorable optoelectronic properties as transparent conductors on flexible and/or organic substrates, whereas the band edges and electrical conductivity of films with 0.3 < x < 0.7 can be manipulated for transparent thin-film transistors as well as electron transport layers.

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

Science.gov (United States)

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

2018-05-01

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

Kinks in the σ Band of Graphene Induced by Electron-Phonon Coupling

DEFF Research Database (Denmark)

Mazzola, Federico; Wells, Justin; Yakimova, Rosita

2013-01-01

Angle-resolved photoemission spectroscopy reveals pronounced kinks in the dispersion of the band of graphene. Such kinks are usually caused by the combination of a strong electron-boson interaction and the cutoff in the Fermi-Dirac distribution. They are therefore not expected for the band...... of graphene that has a binding energy of more than 3:5 eV. We argue that the observed kinks are indeed caused by the electron-phonon interaction, but the role of the Fermi-Dirac distribution cutoff is assumed by a cutoff in the density of states. The existence of the effect suggests a very weak coupling...

Strain localization band width evolution by electronic speckle pattern interferometry strain rate measurement

Energy Technology Data Exchange (ETDEWEB)

Guelorget, Bruno [Institut Charles Delaunay-LASMIS, Universite de technologie de Troyes, FRE CNRS 2848, 12 rue Marie Curie, B.P. 2060, 10010 Troyes Cedex (France)], E-mail: bruno.guelorget@utt.fr; Francois, Manuel; Montay, Guillaume [Institut Charles Delaunay-LASMIS, Universite de technologie de Troyes, FRE CNRS 2848, 12 rue Marie Curie, B.P. 2060, 10010 Troyes Cedex (France)

2009-04-15

In this paper, electronic speckle pattern interferometry strain rate measurements are used to quantify the width of the strain localization band, which occurs when a sheet specimen is submitted to tension. It is shown that the width of this band decreases with increasing strain. Just before fracture, this measured width is about five times wider than the shear band and the initial sheet thickness.

Sub-band gap photo-enhanced secondary electron emission from high-purity single-crystal chemical-vapor-deposited diamond

International Nuclear Information System (INIS)

Yater, J. E.; Shaw, J. L.; Pate, B. B.; Feygelson, T. I.

2016-01-01

Secondary-electron-emission (SEE) current measured from high-purity, single-crystal (100) chemical-vapor-deposited diamond is found to increase when sub-band gap (3.06 eV) photons are incident on the hydrogenated surface. Although the light does not produce photoemission directly, the SEE current increases by more than a factor of 2 before saturating with increasing laser power. In energy distribution curves (EDCs), the emission peak shows a corresponding increase in intensity with increasing laser power. However, the emission-onset energy in the EDCs remains constant, indicating that the bands are pinned at the surface. On the other hand, changes are observed on the high-energy side of the distribution as the laser power increases, with a well-defined shoulder becoming more pronounced. From an analysis of this feature in the EDCs, it is deduced that upward band bending is present in the near-surface region during the SEE measurements and this band bending suppresses the SEE yield. However, sub-band gap photon illumination reduces the band bending and thereby increases the SEE current. Because the bands are pinned at the surface, we conclude that the changes in the band levels occur below the surface in the electron transport region. Sample heating produces similar effects as observed with sub-band gap photon illumination, namely, an increase in SEE current and a reduction in band bending. However, the upward band bending is not fully removed by either increasing laser power or temperature, and a minimum band bending of ∼0.8 eV is established in both cases. The sub-band gap photo-excitation mechanism is under further investigation, although it appears likely at present that defect or gap states play a role in the photo-enhanced SEE process. In the meantime, the study demonstrates the ability of visible light to modify the electronic properties of diamond and enhance the emission capabilities, which may have potential impact for diamond-based vacuum electron

Band structure and unconventional electronic topology of CoSi

Science.gov (United States)

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

2018-04-01

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

Hydrogen production by Tuning the Photonic Band Gap with the Electronic Band Gap of TiO2

KAUST Repository

Waterhouse, G. I. N.; Wahab, A. K.; Al-Oufi, M.; Jovic, V.; Anjum, Dalaver H.; Sun-Waterhouse, D.; Llorca, J.; Idriss, H.

2013-01-01

Tuning the photonic band gap (PBG) to the electronic band gap (EBG) of Au/TiO2 catalysts resulted in considerable enhancement of the photocatalytic water splitting to hydrogen under direct sunlight. Au/TiO2 (PBG-357 nm) photocatalyst exhibited superior photocatalytic performance under both UV and sunlight compared to the Au/TiO2 (PBG-585 nm) photocatalyst and both are higher than Au/TiO2 without the 3 dimensionally ordered macro-porous structure materials. The very high photocatalytic activity is attributed to suppression of a fraction of electron-hole recombination route due to the co-incidence of the PBG with the EBG of TiO2 These materials that maintain their activity with very small amount of sacrificial agents (down to 0.5 vol.% of ethanol) are poised to find direct applications because of their high activity, low cost of the process, simplicity and stability.

Hydrogen production by Tuning the Photonic Band Gap with the Electronic Band Gap of TiO2

KAUST Repository

Waterhouse, G. I. N.

2013-10-10

Tuning the photonic band gap (PBG) to the electronic band gap (EBG) of Au/TiO2 catalysts resulted in considerable enhancement of the photocatalytic water splitting to hydrogen under direct sunlight. Au/TiO2 (PBG-357 nm) photocatalyst exhibited superior photocatalytic performance under both UV and sunlight compared to the Au/TiO2 (PBG-585 nm) photocatalyst and both are higher than Au/TiO2 without the 3 dimensionally ordered macro-porous structure materials. The very high photocatalytic activity is attributed to suppression of a fraction of electron-hole recombination route due to the co-incidence of the PBG with the EBG of TiO2 These materials that maintain their activity with very small amount of sacrificial agents (down to 0.5 vol.% of ethanol) are poised to find direct applications because of their high activity, low cost of the process, simplicity and stability.

Relativistic band-structure calculations for electronic properties of actinide dioxides

International Nuclear Information System (INIS)

Maehira, Takahiro; Hotta, Takashi

2007-01-01

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

Lithium-modulated conduction band edge shifts and charge-transfer dynamics in dye-sensitized solar cells based on a dicyanamide ionic liquid.

Science.gov (United States)

Bai, Yu; Zhang, Jing; Wang, Yinghui; Zhang, Min; Wang, Peng

2011-04-19

Lithium ions are known for their potent function in modulating the energy alignment at the oxide semiconductor/dye/electrolyte interface in dye-sensitized solar cells (DSCs), offering the opportunity to control the associated multichannel charge-transfer dynamics. Herein, by optimizing the lithium iodide content in 1-ethyl-3-methylimidazolium dicyanamide-based ionic liquid electrolytes, we present a solvent-free DSC displaying an impressive 8.4% efficiency at 100 mW cm(-2) AM1.5G conditions. We further scrutinize the origins of evident impacts of lithium ions upon current density-voltage characteristics as well as photocurrent action spectra of DSCs based thereon. It is found that, along with a gradual increase of the lithium content in ionic liquid electrolytes, a consecutive diminishment of the open-circuit photovoltage arises, primarily owing to a noticeable downward movement of the titania conduction band edge. The conduction band edge displacement away from vacuum also assists the formation of a more favorable energy offset at the titania/dye interface, and thereby leads to a faster electron injection rate and a higher exciton dissociation yield as implied by transient emission measurements. We also notice that the adverse influence of the titania conduction band edge downward shift arising from lithium addition upon photovoltage is partly compensated by a concomitant suppression of the triiodide involving interfacial charge recombination. © 2011 American Chemical Society

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

Science.gov (United States)

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

2015-12-01

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

Giant modulation of the electronic band gap of carbon nanotubes by dielectric screening

NARCIS (Netherlands)

Aspitarte, Lee; McCulley, Daniel R.; Bertoni, Andrea; Island, J.O.; Ostermann, Marvin; Rontani, Massimo; Steele, G.A.; Minot, Ethan D.

2017-01-01

Carbon nanotubes (CNTs) are a promising material for high-performance electronics beyond silicon. But unlike silicon, the nature of the transport band gap in CNTs is not fully understood. The transport gap in CNTs is predicted to be strongly driven by electron-electron (e-e) interactions and

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

International Nuclear Information System (INIS)

Saxena, Prapti; Sanyal, Sankar P

2006-01-01

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

Conductance in double quantum well systems

International Nuclear Information System (INIS)

Hasbun, J E

2003-01-01

The object of this paper is to review the electronic conductance in double quantum well systems. These are quantum well structures in which electrons are confined in the z direction by large band gap material barrier layers, yet form a free two-dimensional Fermi gas within the sandwiched low band gap material layers in the x-y plane. Aspects related to the conductance in addition to the research progress made since the inception of such systems are included. While the review focuses on the tunnelling conductance properties of double quantum well devices, the longitudinal conductance is also discussed. Double quantum well systems are a more recent generation of structures whose precursors are the well known double-barrier resonant tunnelling systems. Thus, they have electronic signatures such as negative differential resistance, in addition to resonant tunnelling, whose behaviours depend on the wavefunction coupling between the quantum wells. As such, the barrier which separates the quantum wells can be tailored in order to provide better control of the device's electronic properties over their single well ancestors. (topical review)

Conducting polymer based biomolecular electronic devices

Indian Academy of Sciences (India)

Conducting polymers; LB films; biosensor microactuators; monolayers. ... have been projected for applications for a wide range of biomolecular electronic devices such as optical, electronic, drug-delivery, memory and biosensing devices.

Interfacial electron-transfer equilibria and flat-band potentials of α-Fe2O3 and TiO2 colloids studied by pulse radiolysis

International Nuclear Information System (INIS)

Dimitrijevic, N.M.; Savic, D.; Micic, O.I.; Nozik, A.J.

1984-01-01

The kinetics and equilibria of electron transfer between methylviologen cation radicals and α-Fe 2 O 3 or TiO 2 colloidal particles were studied with the pulse-radiolysis technique. The rates of electron transfer to both colloids are lower than those predicted for a diffusion-controlled reaction. For higher pHs (TiO 2 , pH > 2; α-Fe 2 O 3 , pH > 9) the established equilibrium MV + in equilibrium MV 2+ + (e - )/sub coll/ is strongly influenced by the MV 2+ concentration and pH. The MV + equilibrium concentration can be exploited to derive the flat-band potential of the semiconductor colloids. The method for determining the flat-band potential of the particles is independent of whether the injected electrons are free or trapped, and whether the electrons raise the bulk Fermi level toward the conduction band or just produce a space charge. The flat-band potentials for both colloids appear to be somewhat more negative (-0.1 to -0.2 V) than the corresponding single-crystal electrodes. Also, the flat-band potentials become slightly more negative with increasing radiation dose (initial MV + concentration). The effect of absorbed radiation dose is explained by the corresponding changes in the ratio of oxidized to reduced forms of the redox couple, which in turn changes the adsorbed ionic charge on the semiconductor surface. For colloidal particles of TiO 2 stabilized by poly(vinyl alcohol) (PVA), the flat-band potentials were almost the same as those for PVA-free TiO 2 sols. The decrease of particle diameter from 800 to 70 A does not affect the value of the flat-band potentials for TiO 2 and α-Fe 2 O 3 colloids. 28 references, 9 figures

Contributions of conduction band offset to the enhanced separation efficiency of photoinduced charges for SrTiO3/Bi2O3 heterojunction semiconductor

International Nuclear Information System (INIS)

Zhang, Zhenlong; Zhu, Jichun; Li, Shengjun; Mao, Yanli

2014-01-01

SrTiO 3 /Bi 2 O 3 heterojunction semiconductor was prepared and characterized by X-ray diffraction, UV–vis absorption spectrum, and scanning electron microscope, surface photovoltage spectroscopy, and photoluminescence spectroscopy. The surface photovoltage spectra indicate that the separation efficiency of photoinduced charges for SrTiO 3 /Bi 2 O 3 was enhanced compared with that of SrTiO 3 or Bi 2 O 3 . The energy band diagram of SrTiO 3 /Bi 2 O 3 heterojunction was directly determined with X-ray photoelectron spectroscopy, and the conduction band offset between SrTiO 3 and Bi 2 O 3 was quantified to be 0.28±0.03 eV. The photoluminescence spectra display that the recombination rate of photoinduced carriers for SrTiO 3 /Bi 2 O 3 decreases compared with that of SrTiO 3 or Bi 2 O 3 , which is mainly due to the energy levels matching between them. Therefore the enhanced separation efficiency of photoinduced charges is resulting from the energy difference between the conduction band edges of SrTiO 3 and Bi 2 O 3 . -- Graphical abstract: Enhanced separation efficiency for SrTiO 3 /Bi 2 O 3 is resulting from the energy difference between the conduction band edges. Highlights: ●Heterojunction semiconductor of SrTiO 3 /Bi 2 O 3 was prepared. ●SrTiO 3 /Bi 2 O 3 presents enhanced separation efficiency. ●Conduction band offset between SrTiO 3 and Bi 2 O 3 is quantified. ●Recombination rate of SrTiO 3 /Bi 2 O 3 decreases compared with single phases

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.

Dopant controlled trap-filling and conductivity enhancement in an electron-transport polymer

Energy Technology Data Exchange (ETDEWEB)

Higgins, Andrew, E-mail: aehiggin@princeton.edu, E-mail: kahn@princeton.edu; Kahn, Antoine, E-mail: aehiggin@princeton.edu, E-mail: kahn@princeton.edu [Department of Electrical Engineering, Princeton University, Princeton, New Jersey 08544-5263 (United States); Mohapatra, Swagat K.; Barlow, Stephen; Marder, Seth R. [Center for Organic Photonics and Electronics and School of Chemistry and Biochemistry, Georgia Institute of Technology, Atlanta, Georgia 30332-0400 (United States)

2015-04-20

Charge transport in organic semiconductors is often inhibited by the presence of tail states that extend into the band gap of a material and act as traps for charge carriers. This work demonstrates the passivation of acceptor tail states by solution processing of ultra-low concentrations of a strongly reducing air-stable organometallic dimer, the pentamethylrhodocene dimer, [RhCp*Cp]{sub 2}, into the electron transport polymer poly([N,N′-bis(2-octyldodecyl)-naphthalene-1,4,5,8-bis(dicarboximide) -2,6-diyl]-alt-5,5′-(2,2′-bithiophene)), P(NDI{sub 2}OD-T{sub 2}). Variable-temperature current-voltage measurements of n-doped P(NDI{sub 2}OD-T{sub 2}) are presented with doping concentration varied through two orders of magnitude. Systematic variation of the doping parameter is shown to lower the activation energy for hopping transport and enhance film conductivity and electron mobility.

Electronic Conductivity of Vanadium-Tellurite Glass-Ceramics

DEFF Research Database (Denmark)

Kjeldsen, Jonas; Yue, Yuanzheng; Bragatto, Caio B.

2013-01-01

In this paper, we investigate the electronic conductivity of 2TeO2-V2O5 glass-ceramics with crystallinity ranging from 0 to 100 wt.%, i.e., from entirely amorphous to completely crystalline. The glass is prepared by the melt quenching technique, and the crystal is prepared by subsequent heat...... spectroscopy. We find similar activation energies for both glass and crystal, implying that they have similar conduction mechanisms, i.e., thermally activated hopping. The electronic conductivity of 2TeO2-V2O5 glass is about one order of magnitude higher than that of the corresponding crystal......, and a percolation phenomenon occurs at a glass fraction of 61 wt.%, increasing from a lower conductivity in the crystal to a higher conductivity in the glass. We explain the behavior of electronic conduction in the 2TeO2-V2O5 glass-ceramics by considering constriction effects between particles as well...

Electronic Band Structure of BaCo_{2}As_{2}: A Fully Doped Ferropnictide Analog with Reduced Electronic Correlations

Directory of Open Access Journals (Sweden)

N. Xu

2013-01-01

Full Text Available We report an investigation with angle-resolved photoemission spectroscopy of the Fermi surface and electronic band structure of BaCo_{2}As_{2}. Although its quasinesting-free Fermi surface differs drastically from that of its Fe-pnictide cousins, we show that the BaCo_{2}As_{2} system can be used as an approximation to the bare unoccupied band structure of the related BaFe_{2-x}Co_{x}As_{2} and Ba_{1-x}K_{x}Fe_{2}As_{2} compounds. However, our experimental results, in agreement with dynamical-mean-field-theory calculations, indicate that electronic correlations are much less important in BaCo_{2}As_{2} than in the ferropnictides. Our findings suggest that this effect is due to the increased filling of the electronic 3d shell in the presence of significant Hund’s exchange coupling.

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.

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)

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.

Morphology, optical and ionic conductivity studies of electron beam irradiated polymer electrolyte film

Science.gov (United States)

Devendrappa, H.; Yesappa, L.; Niranjana, M.; Ashokkumar, S. P.; Vijeth, H.; Ganesh, S.

2018-04-01

The effects of electron beam (EB) irradiation on morphology, optical properties and ionic conductivity of (PVdF-co-HFP: LiClO4=90:10, PHL10) electrolyte films. The FESEM image reveal increasing porous morphology with increasing EB dose confirms the polymer degradation as result more amorphousity. The optical absorbance was found to be increase with red shift in UV region and direct optical band gaps was found decreased upon EB dose from 3.70 eV to 2.65 eV. The ionic conductivity increases slowly in lower frequency, whereas rapidly increases at the high frequency and found about 8.28×10-4 S/cm at 120 kGy dose. The obtained results suggest that the physical properties of polymer electrolytes can be changed using EB irradiation as requirement.

Electron conductivity model for dense plasmas

International Nuclear Information System (INIS)

Lee, Y.T.; More, R.M.

1984-01-01

An electron conductivity model for dense plasmas is described which gives a consistent and complete set of transport coefficients including not only electrical conductivity and thermal conductivity, but also thermoelectric power, and Hall, Nernst, Ettinghausen, and Leduc--Righi coefficients. The model is useful for simulating plasma experiments with strong magnetic fields. The coefficients apply over a wide range of plasma temperature and density and are expressed in a computationally simple form. Different formulas are used for the electron relaxation time in plasma, liquid, and solid phases. Comparisons with recent calculations and available experimental measurement show the model gives results which are sufficiently accurate for many practical applications

Band gap tuning of amorphous Al oxides by Zr alloying

DEFF Research Database (Denmark)

Canulescu, Stela; Jones, N. C.; Borca, C. N.

2016-01-01

minimum changes non-linearly as well.Fitting of the energy band gap values resulted in a bowing parameter of 2 eV. The band gap bowing of themixed oxides is assigned to the presence of the Zr d-electron states localized below the conduction bandminimum of anodized Al2O3.......The optical band gap and electronic structure of amorphous Al-Zr mixed oxides, with Zr content ranging from4.8 to 21.9% were determined using vacuum ultraviolet (VUV) and X-ray absorption spectroscopy (XAS). Thelight scattering by the nano-porous structure of alumina at low wavelengths...... was estimated based on the Miescattering theory. The dependence of the optical band gap of the Al-Zr mixed oxides on Zr content deviatesfrom linearity and decreases from 7.3 eV for pure anodized Al2O3 to 6.45 eV for Al-Zr mixed oxide with Zrcontent of 21.9%. With increasing Zr content, the conduction band...

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.

Optical conductivity of topological insulator thin films

International Nuclear Information System (INIS)

Li, L. L.; Xu, W.; Peeters, F. M.

2015-01-01

We present a detailed theoretical study on the optoelectronic properties of topological insulator thin film (TITFs). The k·p approach is employed to calculate the energy spectra and wave functions for both the bulk and surface states in the TITF. With these obtained results, the optical conductivities induced by different electronic transitions among the bulk and surface states are evaluated using the energy-balance equation derived from the Boltzmann equation. We find that for Bi 2 Se 3 -based TITFs, three characteristic regimes for the optical absorption can be observed. (i) In the low radiation frequency regime (photon energy ℏω<200 meV), the free-carrier absorption takes place due to intraband electronic transitions. An optical absorption window can be observed. (ii) In the intermediate radiation frequency regime (200<ℏω<300 meV), the optical absorption is induced mainly by interband electronic transitions from surface states in the valance band to surface states in the conduction band and an universal value σ 0 =e 2 /(8ℏ) for the optical conductivity can be obtained. (iii) In the high radiation frequency regime (ℏω>300 meV), the optical absorption can be achieved via interband electronic transitions from bulk and surface states in the valance band to bulk and surface states in the conduction band. A strong absorption peak can be observed. These interesting findings indicate that optical measurements can be applied to identify the energy regimes of bulk and surface states in the TITF

Measurement of valence band structure in arbitrary dielectric films

International Nuclear Information System (INIS)

Uhm, Han S.; Choi, Eun H.

2012-01-01

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

Conduction mechanism in Polyaniline-flyash composite material for shielding against electromagnetic radiation in X-band & Ku band

Directory of Open Access Journals (Sweden)

Avanish Pratap Singh

2011-06-01

Full Text Available β–Naphthalene sulphonic acid (β–NSA doped polyaniline (PANI–flyash (FA composites have been prepared by chemical oxidative polymerization route whose conductivity lies in the range 2.37–21.49 S/cm. The temperature dependence of electrical conductivity has also been recorded which shows that composites follow Mott's 3D–VRH model. SEM images demonstrate that β–NSA leads to the formation of the tubular structure with incorporated flyash phase. TGA studies show the improvement in thermal stability of composites with increase in loading level of flyash. Complex parameters i.e. permittivity (ɛ* = ɛ′- iɛ″ and permeability (μ*=μ′- iμ″ of PANI-FA composites have been calculated from experimental scattering parameters (S11 & S21 using theoretical calculations given in Nicholson–Ross and Weir algorithms. The microwave absorption properties of the composites have been studied in X-band (8.2 – 12.4 GHz & Ku–Band (12.4 – 18 GHz frequency range. The maximum shielding effectiveness observed was 32dB, which strongly depends on dielectric loss and volume fraction of flyash in PANI matrix.

Influence of energy band alignment in mixed crystalline TiO2 nanotube arrays: good for photocatalysis, bad for electron transfer

Science.gov (United States)

Mohammadpour, Raheleh

2017-12-01

Despite the wide application ranges of TiO2, the precise explanation of the charge transport dynamic through a mixed crystal phase of this semiconductor has remained elusive. Here, in this research, mixed-phase TiO2 nanotube arrays (TNTAs) consisting of anatase and 0-15% rutile phases has been formed through various annealing processes and employed as a photoelectrode of a photovoltaic cell. Wide ranges of optoelectronic experiments have been employed to explore the band alignment position, as well as the depth and density of trap states in TNTAs. Short circuit potential, as well as open circuit potential measurements specified that the band alignment of more than 0.2 eV exists between the anatase and rutile phase Fermi levels, with a higher electron affinity for anatase; this can result in a potential barrier in crystallite interfaces and the deterioration of electron mobility through mixed phase structures. Moreover, a higher density of shallow localized trap states below the conduction band with more depth (133 meV in anatase to 247 meV in 15% rutile phase) and also deep oxygen vacancy traps have been explored upon introducing the rutile phase. Based on our results, employing TiO2 nanotubes as just the electron transport medium in mixed crystalline phases can deteriorate the charge transport mechanism, however, in photocatalytic applications when both electrons and holes are present, a robust charge separation in crystalline anatase/rutile interphases will result in better performances.

Band gap tuning of amorphous Al oxides by Zr alloying

Energy Technology Data Exchange (ETDEWEB)

Canulescu, S., E-mail: stec@fotonik.dtu.dk; Schou, J. [Department of Photonics Engineering, Technical University of Denmark, 4000 Roskilde (Denmark); Jones, N. C.; Hoffmann, S. V. [ISA, Department of Physics and Astronomy, Aarhus University, 8000 Aarhus (Denmark); Borca, C. N.; Piamonteze, C. [Swiss Light Source, Paul Scherrer Institut, 5232 Villigen PSI (Switzerland); Rechendorff, K.; Nielsen, L. P.; Almtoft, K. P. [Danish Technological Institute, Kongsvang Alle 29, 8000 Aarhus (Denmark); Gudla, V. C.; Bordo, K.; Ambat, R. [Department of Mechanical Engineering, Technical University of Denmark, 2800 Kgs-Lyngby (Denmark)

2016-08-29

The optical band gap and electronic structure of amorphous Al-Zr mixed oxides with Zr content ranging from 4.8 to 21.9% were determined using vacuum ultraviolet and X-ray absorption spectroscopy. The light scattering by the nano-porous structure of alumina at low wavelengths was estimated based on the Mie scattering theory. The dependence of the optical band gap of the Al-Zr mixed oxides on the Zr content deviates from linearity and decreases from 7.3 eV for pure anodized Al{sub 2}O{sub 3} to 6.45 eV for Al-Zr mixed oxides with a Zr content of 21.9%. With increasing Zr content, the conduction band minimum changes non-linearly as well. Fitting of the energy band gap values resulted in a bowing parameter of ∼2 eV. The band gap bowing of the mixed oxides is assigned to the presence of the Zr d-electron states localized below the conduction band minimum of anodized Al{sub 2}O{sub 3}.

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.

Paramagnetic resonance and electronic conduction in organic semiconductors

International Nuclear Information System (INIS)

Nechtschein, M.

1963-01-01

As some organic bodies simultaneously display semi-conducting properties and a paramagnetism, this report addresses the study of conduction in organic bodies. The author first briefly recalls how relationships between conductibility and Electron Paramagnetic Resonance (EPR) can be noticed in a specific case (mineral and metallic semiconductors). He discusses published results related to paramagnetism and conductibility in organic bodies. He reviews various categories of organic bodies in which both properties are simultaneously present. He notably addresses radical molecular crystals, non-radical molecular crystals, charge transfer complexes, pyrolyzed coals, and pseudo-ferromagnetic organic structures. He discusses the issue of relationships between conduction (charge transfer by electrons) and ERP (which reveals the existence of non-paired electrons which provide free spins)

Statistical analysis of the electronic crosstalk correction in Terra MODIS Band 27

Science.gov (United States)

Madhavan, Sriharsha; Sun, Junqiang; Xiong, Xiaoxiong; Wenny, Brian N.; Wu, Aisheng

2014-10-01

The first MODerate-resolution Imaging Spectroradiometer (MODIS), also known as the Proto-Flight model (PFM), is on-board the Terra spacecraft and has completed 14 years of on orbit flight as of December 18, 2013. MODIS remotely senses the Earth in 36 spectral bands, with a wavelength range from 0.4 μm to 14.4 μm. The 36 bands can be subdivided into two groups based on their spectral responsivity as Reflective Solar Bands (RSBs) and Thermal Emissive Bands (TEBs). Band 27 centered at 6.77 μm is a TEB used to study the global water vapor distribution. It was found recently that this band has been severely affected by electronic crosstalk. The electronic crosstalk magnitude, its on-orbit change and calibration impact have been well characterized in our previous studies through the use of regularly scheduled lunar observations. Further, the crosstalk correction was implemented in Earth view (EV) images and quantified the improvements of the same. However, improvements remained desirable on several fronts. Firstly, the effectiveness of the correction needed to be analyzed spatially and radiometrically over a number of scenes. Also, the temporal aspect of the correction had to be investigated in a rigorous manner. In order to address these issues, a one-orbit analysis was performed on the Level 1A (L1A) scene granules over a ten year period from 2003 through 2012. Results have been quantified statistically and show a significant reduction of image striping, as well as removal of leaked signal features from the neighboring bands. Statistical analysis was performed by analyzing histograms of the one-orbit granules at a scene and detector level before and after correction. The comprehensive analysis and results reported in this paper will be very helpful to the scientific community in understanding the impacts of crosstalk correction on various scenes and could potentially be applied for future improvements of band 27 calibration and, therefore, its retrieval for the

Electron-beam-induced conduction in dielectrics

Energy Technology Data Exchange (ETDEWEB)

Acris, F C; Davies, P M; Lewis, T J [University Coll. of North Wales, Bangor (UK). School of Electronic Engineering Science

1976-03-14

A model for the enhanced conduction induced in dielectric films under electron bombardment while electrically stressed is discussed. It is assumed that the beam produces a virtual electrode at the end of its range in the dielectric and, as a consequence, the induced conduction is shown to depend on the properties of that part of the dielectric beyond the range of the beam. This model has also been discussed recently by Nunes de Oliviera and Gross. In the present treatment, it is shown how the model permits investigation of beam scattering and carrier generation and recombination processes. Experiments on electron-bombardment-induced conduction of thin (72 to 360 nm) films of anodic tantalum oxide are reported and it is shown that the theoretical model provides a very satisfactory explanation of all features of the results including the apparent threshold energy for enhanced conduction.

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.

Band-to-band tunneling distance analysis in the heterogate electron–hole bilayer tunnel field-effect transistor

Energy Technology Data Exchange (ETDEWEB)

Padilla, J. L., E-mail: jose.padilladelatorre@epfl.ch [Nanoelectronic Devices Laboratory, École Polytechnique Fédérale de Lausanne, Lausanne CH-1015 (Switzerland); Departamento de Electrónica y Tecnología de los Computadores, Universidad de Granada, Avda. Fuentenueva s/n, 18071 Granada (Spain); Palomares, A. [Departamento de Matemática Aplicada, Universidad de Granada, Avda. Fuentenueva s/n, 18071 Granada (Spain); Alper, C.; Ionescu, A. M. [Nanoelectronic Devices Laboratory, École Polytechnique Fédérale de Lausanne, Lausanne CH-1015 (Switzerland); Gámiz, F. [Departamento de Electrónica y Tecnología de los Computadores, Universidad de Granada, Avda. Fuentenueva s/n, 18071 Granada (Spain)

2016-01-28

In this work, we analyze the behavior of the band-to-band tunneling distance between electron and hole subbands resulting from field-induced quantum confinement in the heterogate electron–hole bilayer tunnel field-effect transistor. We show that, analogously to the explicit formula for the tunneling distance that can be easily obtained in the semiclassical framework where the conduction and valence band edges are allowed states, an equivalent analytical expression can be derived in the presence of field-induced quantum confinement for describing the dependence of the tunneling distance on the body thickness and material properties of the channel. This explicit expression accounting for quantum confinement holds valid provided that the potential wells for electrons and holes at the top and bottom of the channel can be approximated by triangular profiles. Analytical predictions are compared to simulation results showing very accurate agreement.

Strain-induced enhancement of thermoelectric performance of TiS2 monolayer based on first-principles phonon and electron band structures

Science.gov (United States)

Li, Guanpeng; Yao, Kailun; Gao, Guoying

2018-01-01

Using first-principle calculations combined with Boltzmann transport theory, we investigate the biaxial strain effect on the electronic and phonon thermal transport properties of a 1 T (CdI2-type) structural TiS2 monolayer, a recent experimental two-dimensional (2D) material. It is found that the electronic band structure can be effectively modulated and that the band gap experiences an indirect-direct-indirect transition with increasing tensile strain. The band convergence induced by the tensile strain increases the Seebeck coefficient and the power factor, while the lattice thermal conductivity is decreased under the tensile strain due to the decreasing group velocity and the increasing scattering chances between the acoustic phonon modes and the optical phonon modes, which together greatly increase the thermoelectric performance. The figure of merit can reach 0.95 (0.82) at an 8 percent tensile strain for the p-type (n-type) doping, which is much larger than that without strain. The present work suggests that the TiS2 monolayer is a good candidate for 2D thermoelectric materials, and that biaxial strain is a powerful tool with which to enhance thermoelectric performance.

Electron-phonon relaxation and excited electron distribution in gallium nitride

Energy Technology Data Exchange (ETDEWEB)

Zhukov, V. P. [Institute of Solid State Chemistry, Urals Branch of the Russian Academy of Sciences, Pervomayskaya st. 91, Yekaterinburg (Russian Federation); Donostia International Physics Center (DIPC), P. Manuel de Lardizabal 4, 20018 San Sebastian (Spain); Tyuterev, V. G., E-mail: valtyut00@mail.ru [Donostia International Physics Center (DIPC), P. Manuel de Lardizabal 4, 20018 San Sebastian (Spain); Tomsk State Pedagogical University, Kievskaya st. 60, Tomsk (Russian Federation); Tomsk State University, Lenin st. 36, Tomsk (Russian Federation); Chulkov, E. V. [Donostia International Physics Center (DIPC), P. Manuel de Lardizabal 4, 20018 San Sebastian (Spain); Tomsk State University, Lenin st. 36, Tomsk (Russian Federation); Departamento de Fisica de Materiales, Facultad de Ciencias Qumicas, UPV/EHU and Centro de Fisica de Materiales CFM-MPC and Centro Mixto CSIC-UPV/EHU, Apdo. 1072, 20080 San Sebastian (Spain); Echenique, P. M. [Donostia International Physics Center (DIPC), P. Manuel de Lardizabal 4, 20018 San Sebastian (Spain); Departamento de Fisica de Materiales, Facultad de Ciencias Qumicas, UPV/EHU and Centro de Fisica de Materiales CFM-MPC and Centro Mixto CSIC-UPV/EHU, Apdo. 1072, 20080 San Sebastian (Spain)

2016-08-28

We develop a theory of energy relaxation in semiconductors and insulators highly excited by the long-acting external irradiation. We derive the equation for the non-equilibrium distribution function of excited electrons. The solution for this function breaks up into the sum of two contributions. The low-energy contribution is concentrated in a narrow range near the bottom of the conduction band. It has the typical form of a Fermi distribution with an effective temperature and chemical potential. The effective temperature and chemical potential in this low-energy term are determined by the intensity of carriers' generation, the speed of electron-phonon relaxation, rates of inter-band recombination, and electron capture on the defects. In addition, there is a substantial high-energy correction. This high-energy “tail” largely covers the conduction band. The shape of the high-energy “tail” strongly depends on the rate of electron-phonon relaxation but does not depend on the rates of recombination and trapping. We apply the theory to the calculation of a non-equilibrium distribution of electrons in an irradiated GaN. Probabilities of optical excitations from the valence to conduction band and electron-phonon coupling probabilities in GaN were calculated by the density functional perturbation theory. Our calculation of both parts of distribution function in gallium nitride shows that when the speed of the electron-phonon scattering is comparable with the rate of recombination and trapping then the contribution of the non-Fermi “tail” is comparable with that of the low-energy Fermi-like component. So the high-energy contribution can essentially affect the charge transport in the irradiated and highly doped semiconductors.

Using Electronic Mail to Conduct Survey Research.

Science.gov (United States)

Thach, Liz

1995-01-01

Describes public and private online networks and the characteristics of electronic mail. Reviews the literature on survey research conducted via electronic mail, and examines the issues of design, implementation, and response. A table displays advantages and disadvantages of electronic mail surveys. (AEF)

Printable Transparent Conductive Films for Flexible Electronics.

Science.gov (United States)

Li, Dongdong; Lai, Wen-Yong; Zhang, Yi-Zhou; Huang, Wei

2018-03-01

Printed electronics are an important enabling technology for the development of low-cost, large-area, and flexible optoelectronic devices. Transparent conductive films (TCFs) made from solution-processable transparent conductive materials, such as metal nanoparticles/nanowires, carbon nanotubes, graphene, and conductive polymers, can simultaneously exhibit high mechanical flexibility, low cost, and better photoelectric properties compared to the commonly used sputtered indium-tin-oxide-based TCFs, and are thus receiving great attention. This Review summarizes recent advances of large-area flexible TCFs enabled by several roll-to-roll-compatible printed techniques including inkjet printing, screen printing, offset printing, and gravure printing using the emerging transparent conductive materials. The preparation of TCFs including ink formulation, substrate treatment, patterning, and postprocessing, and their potential applications in solar cells, organic light-emitting diodes, and touch panels are discussed in detail. The rational combination of a variety of printed techniques with emerging transparent conductive materials is believed to extend the opportunities for the development of printed electronics within the realm of flexible electronics and beyond. © 2018 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Band rejection filter for measurement of electron cyclotron emission during electron cyclotron heating

International Nuclear Information System (INIS)

Iwase, Makoto; Ohkubo, Kunizo; Kubo, Shin; Idei, Hiroshi.

1996-05-01

For the measurement of electron cyclotron emission from the high temperature plasma, a band rejection filter in the range of 40-60 GHz is designed to reject the 53.2 GHz signal with large amplitude from the gyrotron for the purpose of plasma electron heating. The filter developed with ten sets of three quarters-wavelength coupled by TE 111 mode of tunable resonant cavity has rejection of 50 dB and 3 dB bandwidth of 500 MHz. The modified model of Tschebysheff type for the prediction of rejection is proposed. It is confirmed that the measured rejection as a function of frequency agrees well with the experimental results for small coupling hole, and also clarified that the rejection ratio increases for the large coupling hole. (author)

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.

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

African Journals Online (AJOL)

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

Neoclassical electron heat conduction in tokamaks performed by the ions

International Nuclear Information System (INIS)

Ware, A.A.

1987-07-01

The increment to neoclassical ion heat conduction caused by electron collisions is shown to act like electron heat conduction since the energy is taken from and given back to the electrons at each diffusion step length. It can exceed electron neoclassical heat conduction by an order of magnitude

Detecting Kondo Entanglement by Electron Conductance

Science.gov (United States)

Yoo, Gwangsu; Lee, S.-S. B.; Sim, H.-S.

2018-04-01

Quantum entanglement between an impurity spin and electrons nearby is a key property of the single-channel Kondo effects. We show that the entanglement can be detected by measuring electron conductance through a double quantum dot in an orbital Kondo regime. We derive a relation between the entanglement and the conductance, when the SU(2) spin symmetry of the regime is weakly broken. The relation reflects the universal form of many-body states near the Kondo fixed point. Using it, the spatial distribution of the entanglement—hence, the Kondo cloud—can be detected, with breaking of the symmetry spatially nonuniformly by electrical means.

Electron Band Alignment at Interfaces of Semiconductors with Insulating Oxides: An Internal Photoemission Study

Directory of Open Access Journals (Sweden)

Valeri V. Afanas'ev

2014-01-01

Full Text Available Evolution of the electron energy band alignment at interfaces between different semiconductors and wide-gap oxide insulators is examined using the internal photoemission spectroscopy, which is based on observations of optically-induced electron (or hole transitions across the semiconductor/insulator barrier. Interfaces of various semiconductors ranging from the conventional silicon to the high-mobility Ge-based (Ge, Si1-xGex, Ge1-xSnx and AIIIBV group (GaAs, InxGa1-xAs, InAs, GaP, InP, GaSb, InSb materials were studied revealing several general trends in the evolution of band offsets. It is found that in the oxides of metals with cation radii larger than ≈0.7 Å, the oxide valence band top remains nearly at the same energy (±0.2 eV irrespective of the cation sort. Using this result, it becomes possible to predict the interface band alignment between oxides and semiconductors as well as between dissimilar insulating oxides on the basis of the oxide bandgap width which are also affected by crystallization. By contrast, oxides of light elements, for example, Be, Mg, Al, Si, and Sc exhibit significant shifts of the valence band top. General trends in band lineup variations caused by a change in the composition of semiconductor photoemission material are also revealed.

Experimental Study of Electronic Quantum Interference, Photonic Crystal Cavity, Photonic Band Edge Effects for Optical Amplification

Science.gov (United States)

2016-01-26

AFRL-RV-PS- AFRL-RV-PS- TR-2016-0003 TR-2016-0003 EXPERIMENTAL STUDY OF ELECTRONIC QUANTUM INTERFERENCE , PHOTONIC CRYSTAL CAVITY, PHOTONIC BAND...EDGE EFFECTS FOR OPTICAL AMPLIFICATION Shawn-Yu Lin Rensselaer Polytechnic Institute 110 8th Street Troy, New York 12180 26 Jan 2016 Final Report...2014 – 11 Jan 2016 4. TITLE AND SUBTITLE Experimental Study of Electronic Quantum Interference , Photonic Crystal Cavity, Photonic Band Edge Effects

Electronic structures and valence band splittings of transition metals doped GaNs

International Nuclear Information System (INIS)

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

2007-01-01

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

Damping effect of the inner band electrons on the optical absorption and bandwidth of metal nanoparticles

Energy Technology Data Exchange (ETDEWEB)

Ochoo, Lawrence, E-mail: lawijapuonj@yahoo.com; Migwi, Charles; Okumu, John [Kenyatta University, Physics Department (Kenya)

2012-12-15

Conflicts and discrepancies around nanoparticle (NP) size effect on the optical properties of metal NPs of sizes below the mean free path of electron can be traced to the internal damping effect of the hybrid resonance of the inner band (IB) and the conduction band (CB) electrons of the noble metals. We present a scheme to show how alternative mathematical formulation of the physics of interaction between the CB and the IB electrons of NP sizes <50 nm justifies this and resolves the conflicts. While a number of controversies exist between classical and quantum theories over the phenomenological factors to attribute to the NP size effect on the absorption bandwidth, this article shows that the bandwidth behavior can be well predicted from a different treatment of the IB damping effect, without invoking any of the controversial phenomenological factors. It finds that the IB damping effect is mainly frequency dependent and only partly size dependent and shows how its influence on the surface plasmon resonance can be modeled to show the influence of NP size on the absorption properties. Through the model, it is revealed that strong coupling of IB and CB electrons drastically alters the absorption spectra, splitting it into distinctive dipole and quadrupole modes and even introduce a behavioral switch. It finds a strong overlap between the IB and the CB absorptions for Au and Cu but not Ag, which is sensitive to the NP environment. The CB modes shift with the changing refractive index of the medium in a way that can allow their independent excitation, free of influence of the IB electrons. Through a hybrid of parameters, the model further finds that metal NP sizes can be established not only by their spectral absorption peak locations but also from a proper correlation of the peak location and the bandwidth (FWHM).

Band resolution of optical spectra of solvated electrons in water, alcohols, and tetrahydrofuran

International Nuclear Information System (INIS)

Jou, F.-Y.; Freeman, G.R.

1979-01-01

The optical absorption spectra of solvated electrons in water, alcohols, and tetrahydrofuran are empirically resolved into two Gaussian bands and a continuum tail. The first Gaussian band covers most of the low energy side of the spectrum. The second Gaussian band lies at an energy slightly above that of the absorption maximum of the total spectrum. With the exception of tert-butyl alcohol, in water and alcohols the following were observed: (a) the first Gaussian bands have the same half-width, but the oscillator strength in water is about double that in an alcohol; (b) the second Gaussian bands have similar half-widths and oscillator strengths; (c) the continuum tails have similar half-widths, yet that in water possesses only about one third as much oscillator strength as the one in alcohol. In tert-butyl alcohol and tetrahydrofuran the first Gaussian band and the continuum tail each carry nearly half of the total oscillator strength. (author)

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

Science.gov (United States)

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

2016-01-01

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

Organic photovoltaic cell incorporating electron conducting exciton blocking layers

Science.gov (United States)

Forrest, Stephen R.; Lassiter, Brian E.

2014-08-26

The present disclosure relates to photosensitive optoelectronic devices including a compound blocking layer located between an acceptor material and a cathode, the compound blocking layer including: at least one electron conducting material, and at least one wide-gap electron conducting exciton blocking layer. For example, 3,4,9,10 perylenetetracarboxylic bisbenzimidazole (PTCBI) and 1,4,5,8-napthalene-tetracarboxylic-dianhydride (NTCDA) function as electron conducting and exciton blocking layers when interposed between the acceptor layer and cathode. Both materials serve as efficient electron conductors, leading to a fill factor as high as 0.70. By using an NTCDA/PTCBI compound blocking layer structure increased power conversion efficiency is achieved, compared to an analogous device using a conventional blocking layers shown to conduct electrons via damage-induced midgap states.

The two bands model for the high temperature conductivity of the binary rare earth alloys

International Nuclear Information System (INIS)

Borgiel, W.

1983-09-01

The formula for the high temperature spin disorder resistivity for the concentrated Asub(1-x)Bsub(x)C alloys where A,B is an element of Rare Earth (RE) is determined on the basis of two bands model and the coherent potential approximation (CPA). The conductivity given by the 5d bands coming from the RE compounds has been taken into account

Electrostatic noise bands associated with the electron gyrofrequency and plasma frequency in the outer magnetosphere

International Nuclear Information System (INIS)

Shaw, R.R.

1975-01-01

Naturally occurring noise bands near the electron plasma frequency are frequently detected by the University of Iowa plasma wave experiment on the IMP 6 satellite in the region from just inside the plasmapause to radial distances of about 10 earth radii in the outer magnetosphere. The electric field strength of these noise bands is usually small with electric field spectral densities near 10 -15 volts 2 meter -2 Hz -1 . A wave magnetic field has been detected only in a few unusually intense cases, and in these cases the magnetic field energy density is several orders of magnitude smaller than the electric field energy density. The bands are observed at all magnetic latitudes covered by the IMP 6 orbit (parallelγ/sub m/parallel less than or equal to 45 0 ) and appear to be a permanent feature of the outer magnetosphere. They are found at all local times and occur least frequently in the quadrant from 18 to 24 hours. The bands appear to consist of two distinct spectral types, diffuse and narrow. In both types the center frequency of the noise band is bounded by consecutive harmonics of the electron gyrofrequency, and the bands occur most often between harmonics that are near the local electron plasma frequency. These bands appear to merge continuously into two types of plasma wave emissions that are found in dissimilar regions of the magnetosphere (upper hybrid resonance noise, also called Region 3 noise, inside the plasmasphere and (n + 1/2)f/sub g/ harmonics in the outer magnetosphere). It is suggested that this smooth merging is caused by changes in the plasma wave dispersion relation that occur as the spacecraft moves from the cold plasma within the plasmasphere into the warm non-Maxwellian plasma found in the outer magnetosphere

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.

Indication for a K/sup π/ = 0- octupole band in 150Nd from electron scattering

International Nuclear Information System (INIS)

Creswell, C.; Hirsch, A.; Bertozzi, W.; Heisenberg, J.; Kowalski, S.; Sargent, C.P.; Turchinetz, W.; Dieperink, A.

1978-01-01

Recent electron scattering results on the 0.850 MeV level of 150 Nd, when analyzed in terms of the interacting boson model, are inconsistent with the interpretation of this level as a pure J/sup π/(K) = 2 + (0) state. Very recent (n,n'γ) work has shown this level to be a 1 - , 2 + doublet. Assuming this level to be the band head of a ''K/sup π/ = 0 - '' octupole band, a simple model is used to predict electron scattering form factors for the 0.850 MeV state and a 3 - octupole level observed at 0.931 MeV. Comparison is made between these predicted form factors and recent electron scattering data

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

NARCIS (Netherlands)

ESKES, H; SAWATZKY, GA

1991-01-01

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

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 .

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.

Electron conductance in curved quantum structures

DEFF Research Database (Denmark)

Willatzen, Morten; Gravesen, Jens

2010-01-01

is computationally fast and provides direct (geometrical) parameter insight as regards the determination of the electron transmission coefficient. We present, as a case study, calculations of the electron conductivity of a helically shaped quantum-wire structure and discuss the influence of the quantum......A differential-geometry analysis is employed to investigate the transmission of electrons through a curved quantum-wire structure. Although the problem is a three-dimensional spatial problem, the Schrodinger equation can be separated into three general coordinates. Hence, the proposed method...

Electronic Transport Properties of Carbon-Nanotube Networks: The Effect of Nitrate Doping on Intratube and Intertube Conductances

Science.gov (United States)

Ketolainen, T.; Havu, V.; Jónsson, E. Ö.; Puska, M. J.

2018-03-01

The conductivity of carbon-nanotube (CNT) networks can be improved markedly by doping with nitric acid. In the present work, CNTs and junctions of CNTs functionalized with NO3 molecules are investigated to understand the microscopic mechanism of nitric acid doping. According to our density-functional-theory band-structure calculations, there is charge transfer from the CNT to adsorbed molecules indicating p -type doping. The average doping efficiency of the NO3 molecules is higher if the NO3 molecules form complexes with water molecules. In addition to electron transport along individual CNTs, we also study electron transport between different types (metallic, semiconducting) of CNTs. Reflecting the differences in the electronic structures of semiconducting and metallic CNTs, we find that in addition to turning semiconducting CNTs metallic, doping further increases electron transport most efficiently along semiconducting CNTs as well as through the junctions between them.

Quantum conductance of zigzag graphene oxide nanoribbons

International Nuclear Information System (INIS)

Kan, Zhe; Nelson, Christopher; Khatun, Mahfuza

2014-01-01

The electronic properties of zigzag graphene oxide nanoribbons (ZGOR) are presented. The results show interesting behaviors which are considerably different from the properties of the perfect graphene nanoribbons (GNRs). The theoretical methods include a Huckel-tight binding approach, a Green's function methodology, and the Landauer formalism. The presence of oxygen on the edge results in band bending, a noticeable change in density of states and thus the conductance. Consequently, the occupation in the valence bands increase for the next neighboring carbon atom in the unit cell. Conductance drops in both the conduction and valence band regions are due to the reduction of allowed k modes resulting from band bending. The asymmetry of the energy band structure of the ZGOR is due to the energy differences of the atoms. The inclusion of a foreign atom's orbital energies changes the dispersion relation of the eigenvalues in energy space. These novel characteristics are important and valuable in the study of quantum transport of GNRs

Optical Conductivity in a Two-Dimensional Extended Hubbard Model for an Organic Dirac Electron System α-(BEDT-TTF2I3

Directory of Open Access Journals (Sweden)

Daigo Ohki

2018-03-01

Full Text Available The optical conductivity in the charge order phase is calculated in the two-dimensional extended Hubbard model describing an organic Dirac electron system α -(BEDT-TTF 2 I 3 using the mean field theory and the Nakano-Kubo formula. Because the interband excitation is characteristic in a two-dimensional Dirac electron system, a peak structure is found above the charge order gap. It is shown that the peak structure originates from the Van Hove singularities of the conduction and valence bands, where those singularities are located at a saddle point between two Dirac cones in momentum space. The frequency of the peak structure exhibits drastic change in the vicinity of the charge order transition.

Photoconductivities from band states and a dissipative electron dynamics: Si(111) without and with adsorbed Ag clusters

International Nuclear Information System (INIS)

Vazhappilly, Tijo; Hembree, Robert H.; Micha, David A.

2016-01-01

A new general computational procedure is presented to obtain photoconductivities starting from atomic structures, combining ab initio electronic energy band states with populations from density matrix theory, and implemented for a specific set of materials based on Si crystalline slabs and their nanostructured surfaces without and with adsorbed Ag clusters. The procedure accounts for charge mobility in semiconductors in photoexcited states, and specifically electron and hole photomobilities at Si(111) surfaces with and without adsorbed Ag clusters using ab initio energy bands and orbitals generated from a generalized gradient functional, however with excited energy levels modified to provide correct bandgaps. Photoexcited state populations for each band and carrier type were generated using steady state solution of a reduced density matrix which includes dissipative medium effects. The present calculations provide photoexcited electronic populations and photoinduced mobilities resulting from applied electric fields and obtained from the change of driven electron energies with their electronic momentum. Extensive results for Si slabs with 8 layers, without and with adsorbed Ag clusters, show that the metal adsorbates lead to substantial increases in the photomobility and photoconductivity of electrons and holes

High gain harmonic generation free electron lasers enhanced by pseudoenergy bands

Directory of Open Access Journals (Sweden)

Takashi Tanaka

2017-08-01

Full Text Available We propose a new scheme for high gain harmonic generation free electron lasers (HGHG FELs, which is seeded by a pair of intersecting laser beams to interact with an electron beam in a modulator undulator located in a dispersive section. The interference of the laser beams gives rise to a two-dimensional modulation in the energy-time phase space because of a strong correlation between the electron energy and the position in the direction of dispersion. This eventually forms pseudoenergy bands in the electron beam, which result in efficient harmonic generation in HGHG FELs in a similar manner to the well-known scheme using the echo effects. The advantage of the proposed scheme is that the beam quality is less deteriorated than in other existing schemes.

Vibrational and electronic excitation of hexatriacontane thin films by low energy electron impact

International Nuclear Information System (INIS)

Vilar, M.R.; Schott, M.; Pfluger, P.

1990-01-01

Thin polycrystalline films of hexatriacontane (HTC) were irradiated with low energy (E=0.5--15 eV) electrons, and off-specular backscattered electron spectra were measured. Below E∼7 eV, single and multiple vibrational excitations only are observed, which relax the electrons down to the bottom of the HTC conduction band. Due to the negative electron affinity of HTC, thermal electrons are emitted into vacuum. Structure in the backscattered electron current at kinetic energies about 1.5 and 4 eV are associated to conduction band density of states. Above E∼7 eV, the dominant losses correspond to electronic excitations, excitons, or above a threshold (energy of the electron inside the HTC film) at 9.2±0.1 eV, electron--hole pair generation. The latter process is very efficient and reaches a yield of the order of one ∼11 eV. Evidence for chemical reaction above E∼4 eV is observed

Broad-band conductivity and dielectric spectroscopy of composites of multiwalled carbon nanotubes and poly(ethylene terephthalate) around their low percolation threshold

Science.gov (United States)

Nuzhnyy, D.; Savinov, M.; Bovtun, V.; Kempa, M.; Petzelt, J.; Mayoral, B.; McNally, T.

2013-02-01

Composites of multiwalled carbon nanotubes with poly(ethylene terephthalate) (PET-MWCNT) with up to 3 vol% MWCNTs were prepared and characterized by broad-band AC conductivity and dielectric spectroscopy up to the infrared range using several techniques. A very low electrical percolation threshold of 0.07 vol% MWCNTs was revealed from the low-frequency conductivity plateau as well as from DC conductivity, whose values show the same critical power dependence on MWCNT concentration with the exponent t = 4.3. Above the plateau, the AC conductivity increases with frequency up to the THz range, where it becomes overlapped with the absorption of vibrational modes. The temperature dependence down to ˜5 K has shown semiconductor behaviour with a concentration-independent but weakly temperature-dependent small activation energy of ˜3 meV. The behaviour is compatible with the previously suggested fluctuation-induced tunnelling conductivity model through a thin (˜1 nm) polymer contact layer among the adjacent MWCNTs within percolated clusters. At higher frequencies, deviations from the simple universal conductivity behaviour are observed, indicating some distribution of energy barriers for an electron hopping mechanism.

Joint density of states of wide-band-gap materials by electron energy loss spectroscopy

International Nuclear Information System (INIS)

Fan, X.D.; Peng, J.L.; Bursill, L.A.

1998-01-01

Kramers-Kronig analysis for parallel electron energy loss spectroscopy (PEELS) data is developed as a software package. When used with a JEOL 4000EX high-resolution transmission electron microscope (HRTEM) operating at 100 keV this allows us to obtain the dielectric function of relatively wide band gap materials with an energy resolution of approx 1.4 eV. The imaginary part of the dielectric function allows the magnitude of the band gap to be determined as well as the joint-density-of-states function. Routines for obtaining three variations of the joint-density of states function, which may be used to predict the optical and dielectric response for angle-resolved or angle-integration scattering geometries are also described. Applications are presented for diamond, aluminum nitride (AlN), quartz (SiO 2 ) and sapphire (Al 2 O 3 ). The results are compared with values of the band gap and density of states results for these materials obtained with other techniques. (authors)

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

Science.gov (United States)

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

2016-01-01

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

Dopant induced single electron tunneling within the sub-bands of single silicon NW tri-gate junctionless n-MOSFET

Science.gov (United States)

Uddin, Wasi; Georgiev, Yordan M.; Maity, Sarmistha; Das, Samaresh

2017-09-01

We report 1D electron transport of silicon junctionless tri-gate n-type transistor at 4.2 K. The step like curve observed in the current voltage characteristic suggests 1D transport. Besides the current steps for 1D transport, we found multiple spikes within individual steps, which we relate to inter-band single electron tunneling, mediated by the charged dopants available in the channel region. Clear Coulomb diamonds were observed in the stability diagram of the device. It is shown that a uniformly doped silicon nanowire can provide us the window for the single electron tunnelling. Back-gate versus front-gate color plot, where current is in a color scale, shows a crossover of the increased conduction region. This is a clear indication of the dopant-dopant interaction. It has been shown that back-gate biasing can be used to tune the coupling strength between the dopants.

Localisation assisted by the lattice relaxation and the optical absorption of extra-framework electrons in 12CaO.Al2O3

International Nuclear Information System (INIS)

Sushko, Peter V.; Shluger, Alexander L.; Hayashi, Katsuro; Hirano, Masahiro; Hosono, Hideo

2005-01-01

The crystalline framework of a complex oxide 12CaO.7Al 2 O 3 (C12A7) is built from positively charged sub-nanometer cages able to trap electrons. An embedded cluster approach is used to study the electronic structure and optical properties of electron-containing C12A7 for different concentration of extra-framework electrons. Our results suggest that the conduction band of the C12A7 consists of a relatively narrow band of empty cage states (cage conduction band) with one-electron energies between 5.5 and 6.1 eV above the top of the valence band (VB), and a framework conduction band at about 6.7 - 7.0 eV above the to of the VB. The gap between the cage conduction band and the framework conduction band is estimated to be about 1 - 1.5 eV. The energies of the lowest optical transitions from the top of the valence band to the cage conduction band are predicted to be at 5.2 - 5.5 eV. The extra-electrons occupy cage states, which split from the cage conduction band to about 4 eV above the top of the VB. The extra-framework electrons introduce two absorption bands with the experimental peaks at 0.4 eV and 2.8 eV. These bands are assigned to the inter-cage charge transfer and the intra-cage s-p transitions respectively. The changes in the optical absorption spectra as a function of the extra-electrons concentration are also discussed

Electron correlation influenced magnetic phase transitions in f-electron systems

International Nuclear Information System (INIS)

Frauenheim, T.; Ropke, G.

1980-01-01

The temperature-induced phase transition (on lowering the temperature) antiferromagnet-ferromagnet in the heavy rare earth and some of actinide compounds is qualitatively explained in the scope of a two-band Hubbard model and the more complex RKKY model as the result of electron correlation effects in the conduction bands. (orig.)

Large-Area Chemical Vapor Deposited MoS2 with Transparent Conducting Oxide Contacts toward Fully Transparent 2D Electronics

KAUST Repository

Dai, Zhenyu

2017-09-08

2D semiconductors are poised to revolutionize the future of electronics and photonics, much like transparent oxide conductors and semiconductors have revolutionized the display industry. Herein, these two types of materials are combined to realize fully transparent 2D electronic devices and circuits. Specifically, a large-area chemical vapor deposition process is developed to grow monolayer MoS2 continuous films, which are, for the first time, combined with transparent conducting oxide (TCO) contacts. Transparent conducting aluminum doped zinc oxide contacts are deposited by atomic layer deposition, with composition tuning to achieve optimal conductivity and band-offsets with MoS2. The optimized process gives fully transparent TCO/MoS2 2D electronics with average visible-range transmittance of 85%. The transistors show high mobility (4.2 cm2 V−1 s−1), fast switching speed (0.114 V dec−1), very low threshold voltage (0.69 V), and large switching ratio (4 × 108). To our knowledge, these are the lowest threshold voltage and subthreshold swing values reported for monolayer chemical vapor deposition MoS2 transistors. The transparent inverters show fast switching properties with a gain of 155 at a supply voltage of 10 V. The results demonstrate that transparent conducting oxides can be used as contact materials for 2D semiconductors, which opens new possibilities in 2D electronic and photonic applications.

Band gap and defect states of MgO thin films investigated using reflection electron energy loss spectroscopy

Directory of Open Access Journals (Sweden)

Sung Heo

2015-07-01

Full Text Available The band gap and defect states of MgO thin films were investigated by using reflection electron energy loss spectroscopy (REELS and high-energy resolution REELS (HR-REELS. HR-REELS with a primary electron energy of 0.3 keV revealed that the surface F center (FS energy was located at approximately 4.2 eV above the valence band maximum (VBM and the surface band gap width (EgS was approximately 6.3 eV. The bulk F center (FB energy was located approximately 4.9 eV above the VBM and the bulk band gap width was about 7.8 eV, when measured by REELS with 3 keV primary electrons. From a first-principles calculation, we confirmed that the 4.2 eV and 4.9 eV peaks were FS and FB, induced by oxygen vacancies. We also experimentally demonstrated that the HR-REELS peak height increases with increasing number of oxygen vacancies. Finally, we calculated the secondary electron emission yields (γ for various noble gases. He and Ne were not influenced by the defect states owing to their higher ionization energies, but Ar, Kr, and Xe exhibited a stronger dependence on the defect states owing to their small ionization energies.

Sub-band-gap absorption in Ga2O3

Science.gov (United States)

Peelaers, Hartwin; Van de Walle, Chris G.

2017-10-01

β-Ga2O3 is a transparent conducting oxide that, due to its large bandgap of 4.8 eV, exhibits transparency into the UV. However, the free carriers that enable the conductivity can absorb light. We study the effect of free carriers on the properties of Ga2O3 using hybrid density functional theory. The presence of free carriers leads to sub-band-gap absorption and a Burstein-Moss shift in the onset of absorption. We find that for a concentration of 1020 carriers, the Fermi level is located 0.23 eV above the conduction-band minimum. This leads to an increase in the electron effective mass from 0.27-0.28 me to 0.35-0.37 me and a sub-band-gap absorption band with a peak value of 0.6 × 103 cm-1 at 3.37 eV for light polarized along the x or z direction. Both across-the-gap and free-carrier absorption depend strongly on the polarization of the incoming light. We also provide parametrizations of the conduction-band shape and the effective mass as a function of the Fermi level.

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 band electronic structure of Pd based ternary chalcogenide superconductors

Energy Technology Data Exchange (ETDEWEB)

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

2016-12-15

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

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

International Nuclear Information System (INIS)

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

2005-01-01

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

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

Science.gov (United States)

Dass, Devi

2018-03-01

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

A class of monolayer metal halogenides MX{sub 2}: Electronic structures and band alignments

Energy Technology Data Exchange (ETDEWEB)

Lu, Feng; Wang, Weichao; Luo, Xiaoguang; Cheng, Yahui; Dong, Hong; Liu, Hui; Wang, Wei-Hua, E-mail: whwangnk@nankai.edu.cn [Department of Electronics and Tianjin Key Laboratory of Photo-Electronic Thin Film Device and Technology, Nankai University, Tianjin 300071 (China); Xie, Xinjian [School of Materials Science and Engineering, Hebei University of Technology, Tianjin 300130 (China)

2016-03-28

With systematic first principles calculations, a class of monolayer metal halogenides MX{sub 2} (M = Mg, Ca, Zn, Cd, Ge, Pb; M = Cl, Br, I) has been proposed. Our study indicates that these monolayer materials are semiconductors with the band gaps ranging from 2.03 eV of ZnI{sub 2} to 6.08 eV of MgCl{sub 2}. Overall, the band gap increases with the increase of the electronegativity of the X atom or the atomic number of the metal M. Meanwhile, the band gaps of monolayer MgX{sub 2} (X = Cl, Br) are direct while those of other monolayers are indirect. Based on the band edge curvatures, the derived electron (m{sub e}) and hole (m{sub h}) effective masses of MX{sub 2} monolayers are close to their corresponding bulk values except that the m{sub e} of CdI{sub 2} is three times larger and the m{sub h} for PbI{sub 2} is twice larger. Finally, the band alignments of all the studied MX{sub 2} monolayers are provided using the vacuum level as energy reference. These theoretical results may not only introduce the monolayer metal halogenides family MX{sub 2} into the emerging two-dimensional materials, but also provide insights into the applications of MX{sub 2} in future electronic, visible and ultraviolet optoelectronic devices.

Inter-spin distance determination using L-band (1-2 GHz) non-adiabatic rapid sweep electron paramagnetic resonance (NARS EPR)

Science.gov (United States)

Kittell, Aaron W.; Hustedt, Eric J.; Hyde, James S.

2014-01-01

Site-directed spin-labeling electron paramagnetic resonance (SDSL EPR) provides insight into the local structure and motion of a spin probe strategically attached to a molecule. When a second spin is introduced to the system, macromolecular information can be obtained through measurement of inter-spin distances either by continuous wave (CW) or pulsed electron double resonance (ELDOR) techniques. If both methodologies are considered, inter-spin distances of 8 to 80 Å can be experimentally determined. However, there exists a region at the upper limit of the conventional X-band (9.5 GHz) CW technique and the lower limit of the four-pulse double electron-electron resonance (DEER) experiment where neither method is particularly reliable. The work presented here utilizes L-band (1.9 GHz) in combination with non-adiabatic rapid sweep (NARS) EPR to address this opportunity by increasing the upper limit of the CW technique. Because L-band linewidths are three to seven times narrower than those at X-band, dipolar broadenings that are small relative to the X-band inhomogeneous linewidth become observable, but the signal loss due to the frequency dependence of the Boltzmann factor, has made L-band especially challenging. NARS has been shown to increase sensitivity by a factor of five, and overcomes much of this loss, making L-band distance determination more feasible [1]. Two different systems are presented and distances of 18–30 Å have been experimentally determined at physiologically relevant temperatures. Measurements are in excellent agreement with a helical model and values determined by DEER. PMID:22750251

Radiative shocks with electron thermal conduction

International Nuclear Information System (INIS)

Borkowski, Kazimierz.

1988-01-01

The authors studies the influence of electron thermal conduction on radiative shock structure for both one- and two-temperature plasmas. The dimensionless ratio of the conductive length to the cooling length determines whether or not conduction is important, and shock jump conditions with conduction are established for a collisionless shock front. He obtains approximate solutions with the assumptions that the ionization state of the gas is constant and the cooling rate is a function of temperature alone. In the absence of magnetic fields, these solutions indicate that conduction noticeably influences normal-abundance interstellar shocks with velocities 50-100 km s -1 and dramatically affects metal-dominated shocks over a wide range of shock velocities. Magnetic fields inhibit conduction, but the conductive energy flux and the corresponding decrease in the post-shock electron temperature may still be appreciable. He calculates detailed steady-state radiative shock models in gas composed entirely of oxygen, with the purpose of explaining observations of fast-moving knots in Cas A and other oxygen-rich supernova remnants (SNRs). The O III ion, whose forbidden emission usually dominates the observed spectra, is present over a wide range of shock velocities, from 100 to 170 kms -1 . All models with conduction have extensive warm photoionization zones, which provides better agreement with observed optical (O I) line strengths. However, the temperatures in these zones could be lowered by (Si II) 34.8 μm and (Ne II) 12.8 μm cooling if Si and Ne are present in appreciable abundance relative to O. Such low temperatures would be inconsistent with the observed (O I) emission in oxygen-rich SNRs

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

Energy Technology Data Exchange (ETDEWEB)

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

2015-11-02

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

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

Science.gov (United States)

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

2015-11-01

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

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

International Nuclear Information System (INIS)

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

2015-01-01

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

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.

Oxygen effects on the interfacial electronic structure of titanyl phthalocyanine film: p-Type doping, band bending and Fermi level alignment

International Nuclear Information System (INIS)

Nishi, Toshio; Kanai, Kaname; Ouchi, Yukio; Willis, Martin R.; Seki, Kazuhiko

2006-01-01

The effect of oxygen doping on titanyl phthalocyanine (TiOPc) film was investigated by ultraviolet photoelectron spectroscopy (UPS). The electronic structure of the interface formed between TiOPc films deposited on highly oriented pyrolytic graphite (HOPG) was clearly different between the films prepared in ultrahigh vacuum (UHV) and under O 2 atmosphere (1.3 x 10 -2 Pa). The film deposited in UHV showed downward band bending characteristic of n-type semiconductor, possibly due to residual impurities working as unintentional n-type dopants. On the other hand, the film deposited under O 2 atmosphere showed upward band bending characteristic of p-type semiconductor. Such trends, including the conversion from n- to p-type, are in excellent correspondence with reported field effect transistor characteristics of TiOPc, and clearly demonstrates that bulk TiOPc film was p-doped with oxygen. In order to examine the Fermi level alignment between TiOPc film and the substrate, the energy of the highest occupied molecular orbital (HOMO) of TiOPc relative to the Fermi level of the conductive substrate was determined for various substrates. The alignment between the Fermi level of conductive substrate and Fermi level of TiOPc film at fixed energy in the bandgap was not observed for the TiOPc film prepared in UHV, possibly because of insufficient charge density in the TiOPc film. This situation was drastically changed when the TiOPc film exposed to O 2 , and clear alignment of the Fermi level fixed at 0.6 eV above the HOMO with the Fermi level of the conducting substrate was observed, probably by p-type doping effect of oxygen. These are the first direct and quantitative information about bulk oxygen doping from the viewpoint of the electronic structure. These results suggest that similar band bending with Fermi level alignment may be also achieved for other organic semiconductors under practical device conditions, and also call for caution at the comparison of experimental

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.

Electron transfer from electronic excited states to sub-vacuum electron traps in amorphous ice

International Nuclear Information System (INIS)

Vichnevetski, E.; Bass, A.D.; Sanche, L.

2000-01-01

We investigate the electron stimulated yield of electronically excited argon atoms (Ar * ) from monolayer quantities of Ar deposited onto thin films of amorphous ice. Two peaks of narrow width ( - electron-exciton complex into exciton states, by the transfer of an electron into a sub-vacuum electron state within the ice film. However, the 10.7 eV feature is shifted to lower energy since electron attachment to Ar occurs within small pores of amorphous ice. In this case, the excess electron is transferred into an electron trap below the conduction band of the ice layer

On averaging the Kubo-Hall conductivity of magnetic Bloch bands leading to Chern numbers

International Nuclear Information System (INIS)

Riess, J.

1997-01-01

The authors re-examine the topological approach to the integer quantum Hall effect in its original form where an average of the Kubo-Hall conductivity of a magnetic Bloch band has been considered. For the precise definition of this average it is crucial to make a sharp distinction between the discrete Bloch wave numbers k 1 , k 2 and the two continuous integration parameters α 1 , α 2 . The average over the parameter domain 0 ≤ α j 1 , k 2 . They show how this can be transformed into a single integral over the continuous magnetic Brillouin zone 0 ≤ α j j , j = 1, 2, n j = number of unit cells in j-direction, keeping k 1 , k 2 fixed. This average prescription for the Hall conductivity of a magnetic Bloch band is exactly the same as the one used for a many-body system in the presence of disorder

Amplification of transcutaneous and percutaneous bone-conduction devices with a test-band in an induced model of conductive hearing loss.

Science.gov (United States)

Park, Marn Joon; Lee, Jae Ryung; Yang, Chan Joo; Yoo, Myung Hoon; Jin, In Suk; Choi, Chi Ho; Park, Hong Ju

2016-11-01

Transcutaneous devices have a disadvantage, the dampening effect by soft tissue between the bone and devices. We investigated hearing outcomes with percutaneous and transcutaneous devices using test-bands in an induced unilateral conductive hearing loss. Comparison of hearing outcomes of two devices in the same individuals. The right ear was plugged in 30 subjects and a test-band with devices (Cochlear™ Baha® BP110 Power and Sophono® Alpha-2 MPO™) was applied on the right mastoid tip with the left ear masked. Sound-field thresholds, speech recognition thresholds (SRTs), and word recognition scores (WRSs) were compared. Aided thresholds of Sophono were significantly better than those of Baha at most frequencies. Sophono WRSs (86 ± 12%) at 40 dB SPL and SRTs (14 ± 5 dB HL) were significantly better than those (73 ± 24% and 23 ± 8 dB HL) of Baha. However, Sophono WRSs (98 ± 3%) at 60 dB SPL did not differ from Baha WRSs (95 ± 12%). Amplifications of the current transcutaneous device were not inferior to those of percutaneous devices with a test-band in subjects with normal bone-conduction thresholds. Since the percutaneous devices can increase the gain when fixed to the skull by eliminating the dampening effect, both devices are expected to provide sufficient hearing amplification.

The effect of driven electron-phonon coupling on the electronic conductance of a polar nanowire

Energy Technology Data Exchange (ETDEWEB)

Mardaani, Mohammad, E-mail: mohammad-m@sci.sku.ac.ir; Rabani, Hassan, E-mail: rabani-h@sci.sku.ac.ir [Department of Physics, Faculty of Science, Shahrekord University, P. O. Box 115, Shahrekord (Iran, Islamic Republic of); Nanotechnology Research Center, Shahrekord University, 8818634141 Shahrekord (Iran, Islamic Republic of); Esmaili, Esmat; Shariati, Ashrafalsadat [Department of Physics, Faculty of Science, Shahrekord University, P. O. Box 115, Shahrekord (Iran, Islamic Republic of)

2015-08-07

A semi-classical model is proposed to explore the effect of electron-phonon coupling on the coherent electronic transport of a polar chain which is confined between two rigid leads in the presence of an external electric field. To this end, we construct the model by means of Green's function technique within the nearest neighbor tight-binding and harmonic approximations. For a time-periodic electric field, the atomic displacements from the equilibrium positions are obtained precisely. The result is then used to compute the electronic transport properties of the chain within the Peierls-type model. The numerical results indicate that the conductance of the system shows interesting behavior in some special frequencies. For each special frequency, there is an electronic quasi-state in which the scattering of electrons by vibrating atoms reaches maximum. The system electronic conductance decreases dramatically at the strong electron-phonon couplings and low electron energies. In the presence of damping forces, the electron-phonon interaction has a less significant effect on the conductance.

The effect of driven electron-phonon coupling on the electronic conductance of a polar nanowire

International Nuclear Information System (INIS)

Mardaani, Mohammad; Rabani, Hassan; Esmaili, Esmat; Shariati, Ashrafalsadat

2015-01-01

A semi-classical model is proposed to explore the effect of electron-phonon coupling on the coherent electronic transport of a polar chain which is confined between two rigid leads in the presence of an external electric field. To this end, we construct the model by means of Green's function technique within the nearest neighbor tight-binding and harmonic approximations. For a time-periodic electric field, the atomic displacements from the equilibrium positions are obtained precisely. The result is then used to compute the electronic transport properties of the chain within the Peierls-type model. The numerical results indicate that the conductance of the system shows interesting behavior in some special frequencies. For each special frequency, there is an electronic quasi-state in which the scattering of electrons by vibrating atoms reaches maximum. The system electronic conductance decreases dramatically at the strong electron-phonon couplings and low electron energies. In the presence of damping forces, the electron-phonon interaction has a less significant effect on the conductance

Correlation between morphology, electron band structure, and resistivity of Pb atomic chains on the Si(5 5 3)-Au surface

International Nuclear Information System (INIS)

Jałochowski, M; Kwapiński, T; Łukasik, P; Nita, P; Kopciuszyński, M

2016-01-01

Structural and electron transport properties of multiple Pb atomic chains fabricated on the Si(5 5 3)-Au surface are investigated using scanning tunneling spectroscopy, reflection high electron energy diffraction, angular resolved photoemission electron spectroscopy and in situ electrical resistance. The study shows that Pb atomic chains growth modulates the electron band structure of pristine Si(5 5 3)-Au surface and hence changes its sheet resistivity. Strong correlation between chains morphology, electron band structure and electron transport properties is found. To explain experimental findings a theoretical tight-binding model of multiple atomic chains interacting on effective substrate is proposed. (paper)

Electronic band-gap modified passive silicon optical modulator at telecommunications wavelengths.

Science.gov (United States)

Zhang, Rui; Yu, Haohai; Zhang, Huaijin; Liu, Xiangdong; Lu, Qingming; Wang, Jiyang

2015-11-13

The silicon optical modulator is considered to be the workhorse of a revolution in communications. In recent years, the capabilities of externally driven active silicon optical modulators have dramatically improved. Self-driven passive modulators, especially passive silicon modulators, possess advantages in compactness, integration, low-cost, etc. Constrained by a large indirect band-gap and sensitivity-related loss, the passive silicon optical modulator is scarce and has been not advancing, especially at telecommunications wavelengths. Here, a passive silicon optical modulator is fabricated by introducing an impurity band in the electronic band-gap, and its nonlinear optics and applications in the telecommunications-wavelength lasers are investigated. The saturable absorption properties at the wavelength of 1.55 μm was measured and indicates that the sample is quite sensitive to light intensity and has negligible absorption loss. With a passive silicon modulator, pulsed lasers were constructed at wavelengths at 1.34 and 1.42 μm. It is concluded that the sensitive self-driven passive silicon optical modulator is a viable candidate for photonics applications out to 2.5 μm.

Influence of non-collisional laser heating on the electron dynamics in dielectric materials

Science.gov (United States)

Barilleau, L.; Duchateau, G.; Chimier, B.; Geoffroy, G.; Tikhonchuk, V.

2016-12-01

The electron dynamics in dielectric materials induced by intense femtosecond laser pulses is theoretically addressed. The laser driven temporal evolution of the energy distribution of electrons in the conduction band is described by a kinetic Boltzmann equation. In addition to the collisional processes for energy transfer such as electron-phonon-photon and electron-electron interactions, a non-collisional process for photon absorption in the conduction band is included. It relies on direct transitions between sub-bands of the conduction band through multiphoton absorption. This mechanism is shown to significantly contribute to the laser heating of conduction electrons for large enough laser intensities. It also increases the time required for the electron distribution to reach the equilibrium state as described by the Fermi-Dirac statistics. Quantitative results are provided for quartz irradiated by a femtosecond laser pulse with a wavelength of 800 nm and for intensities in the range of tens of TW cm-2, lower than the ablation threshold. The change in the energy deposition induced by this non-collisional heating process is expected to have a significant influence on the laser processing of dielectric materials.

The thermodynamical foundation of electronic conduction in solids

Science.gov (United States)

Bringuier, E.

2018-03-01

In elementary textbooks, the microscopic justification of Ohm’s local law in a solid medium starts with Drude’s classical model of electron transport and next discusses the quantum-dynamical and statistical amendments. In this paper, emphasis is laid instead upon the thermodynamical background motivated by the Joule-Lenz heating effect accompanying conduction and the fact that the conduction electrons are thermalized at the lattice temperature. Both metals and n-type semiconductors are considered; but conduction under a magnetic field is not. Proficiency in second-year thermodynamics and vector analysis is required from an undergraduate university student in physics so that the content of the paper can be taught to third-year students. The necessary elements of quantum mechanics are posited in this paper without detailed justification. We start with the equilibrium-thermodynamic notion of the chemical potential of the electron gas, the value of which distinguishes metals from semiconductors. Then we turn to the usage of the electrochemical potential in the description of near-equilibrium electron transport. The response of charge carriers to the electrochemical gradient involves the mobility, which is the reciprocal of the coefficient of the effective friction force opposing the carrier drift. Drude’s calculation of mobility is restated with the dynamical requirements of quantum physics. Where the carrier density is inhomogeneous, there appears diffusion, the coefficient of which is thermodynamically related to the mobility. Next, it is remarked that the release of heat was ignored in Drude’s original model. In this paper, the flow of Joule heat is handled thermodynamically within an energy balance where the voltage generator, the conduction electrons and the host lattice are involved in an explicit way. The notion of dissipation is introduced as the rate of entropy creation in a steady state. The body of the paper is restricted to the case of one

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.

Theoretical study of electronic absorption spectroscopy of propadienylidene molecule vis-â-vis the observed diffuse interstellar bands

International Nuclear Information System (INIS)

Reddy, Samala Nagaprasad; Mahapatra, S.

2012-01-01

Highlights: ► Theoretical study of spectroscopy and dynamics of electronically excited l-C 3 H 2 . ► Construction of ab initio electronic potential energy and diabatic coupling surfaces. ► First principles study of nuclear dynamics on excited electronic states. ► Findings reveal l-C 3 H 2 is a potential molecular carrier of diffuse interstellar bands. ► Electronically excited l-C 3 H 2 decays by ultrafast nonradiative internal conversion. -- Abstract: Observation of broad and diffuse interstellar bands (DIBs) at 4881 Å and 5440 Å assigned to the optical absorption spectrum of Y-shaped propadienylidene (H 2 C=C=C:) molecule is theoretically examined in this paper. This molecule apparently absorbs in the same wavelength region as the observed DIBs and was suggested to be a potential carrier of these DIBs. This assignment mostly relied on the experimental data from radioastronomy and laboratory measurements. Motivated by these available experimental data we attempt here a theoretical study and investigate the detailed electronic structure and nuclear dynamics underlying the electronic absorption bands of propadienylidene molecule. Our results show that this molecule indeed absorbs in the wavelength region of the recorded DIBs. Strong nonadiabatic coupling between its energetically low-lying electronic states plays major role, initiates ultrafast internal conversion and contributes to the spectral broadening. Theoretical findings are finally compared with the available experimental and theoretical data and discussed in connection with the recorded DIBs.

Optimization of a triode-type cusp electron gun for a W-band gyro-TWA

Science.gov (United States)

Zhang, Liang; Donaldson, Craig R.; He, Wenlong

2018-04-01

A triode-type cusp electron gun was optimized through numerical simulations for a W-band gyrotron traveling wave amplifier. An additional electrode in front of the cathode could switch the electron beam on and off instantly when its electric potential is properly biased. An optimal electron beam of current 1.7 A and a velocity ratio (alpha) of 1.12 with an alpha spread of ˜10.7% was achieved when the triode gun was operated at 40 kV.

Hydrostatic pressure and conduction band non-parabolicity effects on the impurity binding energy in a spherical quantum dot

International Nuclear Information System (INIS)

Sivakami, A.; Mahendran, M.

2010-01-01

The binding energy of a shallow hydrogenic impurity in a spherical quantum dot under hydrostatic pressure with square well potential is calculated using a variational approach within the effective mass approximation. The effect of conduction band non-parabolicity on these energies is also estimated. The binding energy is computed for GaAs spherical quantum dot as a function of dot size, hydrostatic pressure both in the presence and absence of the band non-parabolicity effect. Our results show that (i) the hydrostatic pressure increases the impurity binding energy when dot radius increases for a given pressure, (ii) the hydrostatic pressure with the band non-parabolicity effect effectively increases the binding energy such that the variation is large for smaller dots and (iii) the maximum contribution by the non-parabolicity effect is about 15% for narrow dots. Our results are in good agreement with Perez-Merchancano et al. [J. Phys. Condens. Matter 19 (2007) 026225] who have not considered the conduction band non-parabolicity effect.

Electron transport in heavily doped GdN

Science.gov (United States)

Maity, T.; Trodahl, H. J.; Natali, F.; Ruck, B. J.; Vézian, S.

2018-01-01

We report measurements of electron transport phenomena in the intrinsic ferromagnetic semiconductor GdN doped with 1.3 ×1021cm-3 electrons. The conductivity, carrier concentration, and thermoelectric power are compared with expectations based on an LSDA+U band structure. In the ferromagnetic state the carriers fill the majority-spin conduction band pockets to the bottom of the minority-spin band. The resistance implies an electron mobility of 18 cm2V-1s-1 at zero temperature, and in turn a mean-free path of 10-30 nm. Spin disorder scattering rapidly reduces the mobility near the 70 K Curie temperature (TC). The thermoelectric power is negative in the paramagnetic phase, as expected for a n -type conductor, with a magnitude that is in agreement with the Fermi energy implied by the band structure. The thermopower reverses sign to be positive in the ferromagnetic phase, which correlates with a strongly temperature-dependent electron diffusion from spin-disorder scattering that increases rapidly as the temperature rises toward TC.

Electronic structure and electron dynamics at Si(100)

Energy Technology Data Exchange (ETDEWEB)

Weinelt, M. [Universitaet Erlangen-Nuernberg, Lehrstuhl fuer Festkoerperphysik, Erlangen (Germany); Max-Born-Institut, Berlin (Germany); Kutschera, M.; Schmidt, R.; Orth, C.; Fauster, T. [Universitaet Erlangen-Nuernberg, Lehrstuhl fuer Festkoerperphysik, Erlangen (Germany); Rohlfing, M. [International University Bremen, School of Engineering and Science, P.O. Box 750 561, Bremen (Germany)

2005-02-01

The electronic structure and electron dynamics at a Si(100) surface is studied by two-photon photoemission (2PPE). At 90 K the occupied D{sub up} dangling-bond state is located 150{+-}50 meV below the valence-band maximum (VBM) at the center of the surface Brillouin zone anti {gamma} and exhibits an effective hole mass of (0.5{+-}0.15)m{sub e}. The unoccupied D{sub down} band has a local minimum at anti {gamma} at 650{+-}50 meV above the VBM and shows strong dispersion along the dimer rows of the c(4 x 2) reconstructed surface. At 300 K the D{sub down} position shifts comparable to the Si conduction-band minimum by 40 meV to lower energies but the dispersion of the dangling-bond states is independent of temperature. The surface band bending for p-doped silicon is less than 30 meV, while acceptor-type defects cause significant and preparation-dependent band bending on n-doped samples. 2PPE spectra of Si(100) are dominated by interband transitions between the occupied and unoccupied surface states and emission out of transiently and permanently charged surface defects. Including electron-hole interaction in many-body calculations of the quasi-particle band structure leads us to assign a dangling-bond split-off state to a quasi-one-dimensional surface exciton with a binding energy of 130 meV. Electrons resonantly excited to the unoccupied D{sub down} dangling-bond band with an excess energy of about 350 meV need 1.5{+-}0.2 ps to scatter via phonon emission to the band bottom at anti {gamma} and relax within 5 ps with an excited hole in the occupied surface band to form an exciton living for nanoseconds. (orig.)

Electronic conductance of quantum wire with serial periodic potential structures

International Nuclear Information System (INIS)

Fayad, Hisham M.; Shabat, Mohammed M.; Abdus Salam International Centre for Theoretical Physics, Trieste

2000-08-01

A theory based on the total transfer matrix is presented to investigate the electronic conductance in a quantum wire with serial periodic potentials. We apply the formalism in computation of the electronic conductance in a wire with different physical parameters of the wire structure. The numerical results could be used in designing some future quantum electronic devices. (author)

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.

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.

Dynamical electron-phonon coupling, G W self-consistency, and vertex effect on the electronic band gap of ice and liquid water

Science.gov (United States)

Ziaei, Vafa; Bredow, Thomas

2017-06-01

We study the impact of dynamical electron-phonon (el-ph) effects on the electronic band gap of ice and liquid water by accounting for frequency-dependent Fan contributions in the el-ph mediated self-energy within the many-body perturbation theory (MBPT). We find that the dynamical el-ph coupling effects greatly reduce the static el-ph band-gap correction of the hydrogen-rich molecular ice crystal from-2.46 to -0.23 eV in great contrast to the result of Monserrat et al. [Phys. Rev. B 92, 140302 (2015), 10.1103/PhysRevB.92.140302]. This is of particular importance as otherwise the static el-ph gap correction would considerably reduce the electronic band gap, leading to considerable underestimation of the intense peaks of optical absorption spectra of ice which would be in great disagreement to experimental references. By contrast, the static el-ph gap correction of liquid water is very moderate (-0.32 eV), and inclusion of dynamical effects slightly reduces the gap correction to -0.19 eV. Further, we determine the diverse sensitivity of ice and liquid water to the G W self-consistency and show that the energy-only self-consistent approach (GnWn ) exhibits large implicit vertex character in comparison to the quasiparticle self-consistent approach, for which an explicit calculation of vertex corrections is necessary for good agreement with experiment.

The influence of band Jahn-Teller effect and magnetic order on the magneto-resistance in manganite systems

Energy Technology Data Exchange (ETDEWEB)

Rout, G.C., E-mail: gcr@iopb.res.i [Condensed Matter Physics Group, Department of Applied Physics and Ballistics, F.M. University, Balasore, Orissa 756019 (India); Parhi, Nilima [Department of Physics, M.P.C. (Autonomous) College, Baripada, Orissa 757001 (India); Behera, S.N. [Institute of Material Science, Bhubaneswar 751004 (India)

2009-08-01

A model calculation is presented in order to study the magneto-resistivity through the interplay between magnetic and structural transitions for the manganite systems. The model consists of an orbitally doubly degenerate conduction band and a periodic array of local moments of the t{sub 2g} electrons. The band electrons interact with the local t{sub 2g} electrons via the s-f hybridization. The phonons interact with the band electrons through static and dynamic band Jahn-Teller (J-T) interaction. The model Hamiltonian including the above terms is solved for the single particle Green's functions and the imaginary part of the self-energy gives the electron relaxation time. Thus the magneto-resistivity (MR) is calculated from the Drude formula. The MR effect is explained near the magnetic and structural transition temperatures.

A model study of tunneling conductance spectra of ferromagnetically ordered manganites

Science.gov (United States)

Panda, Saswati; Kar, J. K.; Rout, G. C.

2018-02-01

We report here the interplay of ferromagnetism (FM) and charge density wave (CDW) in manganese oxide systems through the study of tunneling conductance spectra. The model Hamiltonian consists of strong Heisenberg coupling in core t2g band electrons within mean-field approximation giving rise to ferromagnetism. Ferromagnetism is induced in the itinerant eg electrons due to Kubo-Ohata type double exchange (DE) interaction among the t2g and eg electrons. The charge ordering (CO) present in the eg band giving rise to CDW interaction is considered as the extra-mechanism to explain the colossal magnetoresistance (CMR) property of manganites. The magnetic and CDW order parameters are calculated using Zubarev's Green's function technique and solved self-consistently and numerically. The eg electron density of states (DOS) calculated from the imaginary part of the Green's function explains the experimentally observed tunneling conductance spectra. The DOS graph exhibits a parabolic gap near the Fermi energy as observed in tunneling conductance spectra experiments.

Wurtzite/zinc-blende electronic-band alignment in basal-plane stacking faults in semi-polar GaN

Science.gov (United States)

Monavarian, Morteza; Hafiz, Shopan; Izyumskaya, Natalia; Das, Saikat; Özgür, Ümit; Morkoç, Hadis; Avrutin, Vitaliy

2016-02-01

Heteroepitaxial semipolar and nonpolar GaN layers often suffer from high densities of extended defects including basal plane stacking faults (BSFs). BSFs which are considered as inclusions of cubic zinc-blende phase in wurtzite matrix act as quantum wells strongly affecting device performance. Band alignment in BSFs has been discussed as type of band alignment at the wurtzite/zinc blende interface governs the response in differential transmission; fast decay after the pulse followed by slow recovery due to spatial splitting of electrons and heavy holes for type- II band alignment in contrast to decay with no recovery in case of type I band alignment. Based on the results, band alignment is demonstrated to be of type II in zinc-blende segments in wurtzite matrix as in BSFs.

Direct current hopping conductance in one-dimensional diagonal disordered systems

Institute of Scientific and Technical Information of China (English)

Ma Song-Shan; Xu Hui; Liu Xiao-Liang; Xiao Jian-Rong

2006-01-01

Based on a tight-binding disordered model describing a single electron band, we establish a direct current (dc) electronic hopping transport conductance model of one-dimensional diagonal disordered systems, and also derive a dc conductance formula. By calculating the dc conductivity, the relationships between electric field and conductivity and between temperature and conductivity are analysed, and the role played by the degree of disorder in electronic transport is studied. The results indicate the conductivity of systems decreasing with the increase of the degree of disorder, characteristics of negative differential dependence of resistance on temperature at low temperatures in diagonal disordered systems, and the conductivity of systems decreasing with the increase of electric field, featuring the non-Ohm's law conductivity.

The electrical conductivity of an interacting electron gas

International Nuclear Information System (INIS)

Kojima, D.Y.

1977-01-01

A manybody theory by the propagator method developed by Montroll and Ward for the equilibrium statistical mechanics, is reformulated to describe the electrical conductivity for an electron gas system containing impurity. The theory includes electron-impurity interaction to the infinite order and electron-electron interaction to the first order exchange effect. The propagator used by Montroll and Ward is separated into two propagators, each of which satisfies either Bloch or Schroedinger equation, to utilize the perturbation method. Correct counting of graphs are presented. Change in the relaxation time due to the electron-electron interaction is explicity shown and compared with recent works [pt

Enhancement of dye-sensitized solar cells performances by improving electron density in conduction band of nanostructure TiO2 electrode with using a metalloporphyrin as additional dye

International Nuclear Information System (INIS)

Mojiri-Foroushani, M.; Dehghani, H.; Salehi-Vanani, N.

2013-01-01

Highlights: ► N719 and ZnTCPP dyes were used in a sequential adsorption process. ► By using two dyes, improved the performance of the cell. ► Density of electrons in the conduction band of TiO 2 electrodes improved. -- Abstract: A zinc(II)-porphyrin dye with four carboxyphenyl moiety of ancillary (ZnTCPP) was studied as a sensitizer in combination with a ruthenium complex (N719) in co-sensitized solar cells. The high molar extinction coefficient (ε) of porphyrin dyes leads to high light absorption in the dye-sensitized TiO 2 electrode. In spite of the high ε of porphyrin dyes, they usually have a narrow absorption band and also to suffer from dye aggregation due to their planar structural nature. This causes lower efficiencies of the DSSCs for the porphyrins than the ruthenium complexes. Co-sensitization of two or more dyes with complementary absorption spectra on TiO 2 film is an important method to further enhance the IPCE response and energy conversion efficiency of dye-sensitized solar cells. Interestingly, when the ZnTCPP electrode was used to assemble a co-sensitized solar cell by additional adsorption of N719 dye, the efficiency improved to 6.35% (in comparison to N719 that the efficiency was 4.74%). The results indicated that the co-sensitized device shows enhancements of photovoltaic performance not only in short-circuit current density (J SC ) but also in open-circuit voltage (V OC ). In the present study we have been shown that co-sensitization of a zinc(II)-porphyrin with N719 dye changes the energy levels of the TiO 2 electrode and in result produces further improvement for its device performance

Electron heat conduction and suprathermal particles

International Nuclear Information System (INIS)

Bakunin, O.G.; Krasheninnikov, S.I.

1991-01-01

As recognized at present, the applicability of Spitzer-Harm's theory on electron heat conduction along the magnetic field is limited by comparatively small values of the thermal electron mean free path ratio, λ to the characteristic length of changes in plasma parameters, L: γ=λ/L≤10 -2 . The stationary kinetic equation for the electron distribution function inhomogeneous along the x-axis f e (v,x) allows one to have solutions in the self-similar variables. The objective of a given study is to generalize the solutions for the case of arbitrary Z eff , that will allow one to compare approximate solutions to the kinetic equation with the precise ones in a wide range of parameters. (author) 8 refs., 2 figs

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....

Observation of total electron content and irregularities in electron density using GHz band radiowaves emitted from satellite

International Nuclear Information System (INIS)

Ogawa, Tadahiko; Fujita, Masaharu; Awaka, Jun.

1978-01-01

The experiments to investigate the influence of troposphere on millimeter and sub-millimeter wave propagation were carried out, using the engineering test satellite -- 2 (ETS-2) which became the Japanese first stationary satellite and carries the transmitter emitting beacon waves of 1.7, 11.5 and 34.5 GHz coherent each other. By these experiments, it was found that the waves of 1.7 and 11.5 GHz were affected by the ionosphere. The measurement of total electron content using GHz band waves was the first trial in the world, and is capable of grasping its change with higher accuracy than conventional methods. Scintillation of 1.7 GHz is mainly the phenomenon during night, and it was revealed that it has a peak at 22.30 local time and occurred through the radiowave scattering owing to the irregularities of the ionosphere. It is also suggested that some plasma instability is generated in the place where electron density gradient in the ionosphere is large, and the irregularities of fine scale are produced, assuming from GHz band scintillations at the time of magnetic storm. The relations among wave number spectrum, scintillation frequency spectrum and S4 index (statistical quantity to give estimate for scintillation amplitude) can be derived by the weak scattering theory (Simple scattering theory). As seen above, the diagnosis of plasma disturbances in the ionosphere is feasible by the simultaneous observations of total electron content and scintillation. (Wakatsuki, Y.)

Photon- and electron-induced surface voltage in electron spectroscopies on ZnSe(0 0 1)

International Nuclear Information System (INIS)

Cantoni, M.; Bertacco, R.; Brambilla, A.; Ciccacci, F.

2009-01-01

The surface band bending in ZnSe(0 0 1), as a function of the temperature, is investigated both in the valence band (by photoemission) and in the conduction band (by inverse photoemission and absorbed current spectroscopies). Two different mechanisms are invoked for interpreting the experimental data: the band bending due to surface states, and the surface voltage induced by the incident beam. While the latter is well known in photoemission (surface photovoltage), we demonstrate the existence of a similar effect in inverse photoemission and absorbed current spectroscopies, induced by the incident electrons instead of photons. These results point to the importance of considering the surface voltage effect even in electron-in techniques for a correct evaluation of the band bending.

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

International Nuclear Information System (INIS)

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

2016-01-01

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

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

Energy Technology Data Exchange (ETDEWEB)

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

2016-10-15

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

Electron energies in metals

International Nuclear Information System (INIS)

Mahan, G.D.; Tennessee Univ., Knoxville, TN

1991-01-01

The modern era of electron-electron interactions began a decade ago. Plummer's group initiated a program of using angular resolved photoemission to examine the band structure of the simple metals. Beginning with aluminum, and carrying on to sodium and potassium, they always found that the occupied energy bands were much narrower than expected. For example, the compressed energy bands for metallic potassium suggest a band effective mass of m* = 1.33m e . This should be compared to the band mass found from optical conductivity m*/m e = 1.01 ± 0.01. The discrepancy between these results is startling. It was this great difference which started my group doing calculations. Our program was two-fold. On one hand, we reanalyzed the experimental data, in order to see if Plummer's result was an experimental artifact. On the other hand, we completely redid the electron-electron self-energy calculations for simple metals, using the most modern choices of local-field corrections and vertex corrections. Our results will be reported in these lectures. They can be summarized as following: Our calculations give the same effective masses as the older calculations, so the theory is relatively unchanged; Our analysis of the experiments suggests that the recent measurements of band narrowing are an experimental artifact. 38 refs., 9 figs

Mechanisms of fine extinction band development in vein quartz: new insights from correlative light and electron microscopy

Science.gov (United States)

Derez, Tine; Van Der Donck, Tom; Plümper, Oliver; Muchez, Philippe; Pennock, Gill; Drury, Martyn R.; Sintubin, Manuel

2017-07-01

Fine extinction bands (FEBs) (also known as deformation lamellae) visible with polarized light microscopy in quartz consist of a range of nanostructures, inferring different formation processes. Previous transmission electron microscopy studies have shown that most FEB nanostructures in naturally deformed quartz are elongated subgrains formed by recovery of dislocation slip bands. Here we show that three types of FEB nanostructure occur in naturally deformed vein quartz from the low-grade metamorphic High-Ardenne slate belt (Belgium). Prismatic oriented FEBs are defined by bands of dislocation walls. Dauphiné twin boundaries present along the FEB boundaries probably formed after FEB formation. In an example of two sub-rhombohedral oriented FEBs, developed as two sets in one grain, the finer FEB set consists of elongated subgrains, similar to FEBs described in previous transmission electron microscopy studies. The second wider FEB set consists of bands with different dislocation density and fluid-inclusion content. The wider FEB set is interpreted as bands with different plastic strain associated with the primary growth banding of the vein quartz grain. The nanometre-scale fluid inclusions are interpreted to have formed from structurally bounded hydroxyl groups that moreover facilitated formation of the elongate subgrains. Larger fluid inclusions aligned along FEBs are explained by fluid-inclusion redistribution along dislocation cores. The prismatic FEB nanostructure and the relation between FEBs and growth bands have not been recognized before, although related structures have been reported in experimentally deformed quartz.

X-ray absorption and reflection as probes of the GaN conduction bands: Theory and experiments

Energy Technology Data Exchange (ETDEWEB)

Lambrecht, W.R.L.; Rashkeev, S.N.; Segall, B. [Case Western Reserve Univ., Cleveland, OH (United States)] [and others

1997-04-01

X-ray absorption measurements are a well-known probe of the unoccupied states in a material. The same information can be obtained by using glancing angle X-ray reflectivity. In spite of several existing band structure calculations of the group III nitrides and previous optical studies in UV range, a direct probe of their conduction band densities of states is of interest. The authors performed a joint experimental and theoretical investigation using both of these experimental techniques for wurtzite GaN.

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

DEFF Research Database (Denmark)

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

2013-01-01

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

Temperature Dependence of the Spin-Hall Conductivity of a Two-Dimensional Impure Rashba Electron Gas in the Presence of Electron-Phonon and Electron-Electron Interactions

Science.gov (United States)

Yavari, H.; Mokhtari, M.; Bayervand, A.

2015-03-01

Based on Kubo's linear response formalism, temperature dependence of the spin-Hall conductivity of a two-dimensional impure (magnetic and nonmagnetic impurities) Rashba electron gas in the presence of electron-electron and electron-phonon interactions is analyzed theoretically. We will show that the temperature dependence of the spin-Hall conductivity is determined by the relaxation rates due to these interactions. At low temperature, the elastic lifetimes ( and are determined by magnetic and nonmagnetic impurity concentrations which are independent of the temperature, while the inelastic lifetimes ( and related to the electron-electron and electron-phonon interactions, decrease when the temperature increases. We will also show that since the spin-Hall conductivity is sensitive to temperature, we can distinguish the intrinsic and extrinsic contributions.

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.

Adjustment of Conduction Band Edge of Compact TiO2 Layer in Perovskite Solar Cells Through TiCl4 Treatment.

Science.gov (United States)

Murakami, Takurou N; Miyadera, Tetsuhiko; Funaki, Takashi; Cojocaru, Ludmila; Kazaoui, Said; Chikamatsu, Masayuki; Segawa, Hiroshi

2017-10-25

Perovskite solar cells (PSCs) without a mesoporous TiO 2 layer, that is, planar-type PSCs exhibit poorer cell performance as compared to PSCs with a porous TiO 2 layer, owing to inefficient electron transfer from the perovskite layer to the compact TiO 2 layer in the former case. The matching of the conduction band levels of perovskite and the compact TiO 2 layer is thus essential for enhancing PSC performance. In this study, we demonstrate the shifting of the conduction band edge (CBE) of the compact TiO 2 layer through a TiCl 4 treatment, with the aim of improving PSC performance. The CBE of the compact TiO 2 layer was shifted to a higher level through the TiCl 4 treatment and then shifted in the opposite direction, that is, to a lower level, through a subsequent heat treatment. These shifts in the CBE were reflected in the PSC performance. The TiCl 4 -treated PSC showed an increase in the open-circuit voltage of more than 150 mV, as well as a decrease of 100 mV after being heated at 450 °C. On the other hand, the short-circuit current decreased after the treatment but increased after heating at temperatures higher than 300 °C. The treated PSC subjected to subsequent heating at 300 °C exhibited the best performance, with the power conversion efficiency of the PSC being 17% under optimized conditions.

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

Formation of a conducting LaAlO3/SrTiO3 interface studied by low-energy electron reflection during growth

Science.gov (United States)

van der Torren, A. J. H.; Liao, Z.; Xu, C.; Gauquelin, N.; Yin, C.; Aarts, J.; van der Molen, S. J.

2017-12-01

The two-dimensional electron gas occurring between the band insulators SrTiO3 and LaAlO3 continues to attract considerable interest, due to the possibility of dynamic control over the carrier density and due to ensuing phenomena such as magnetism and superconductivity. The formation of this conducting interface is sensitive to the growth conditions, but despite numerous investigations there are still questions about the details of the physics involved. In particular, not much is known about the electronic structure of the growing LaAlO3 layer at the growth temperature (around 800°C) in oxygen (pressure around 5 ×10-5 mbar), since analysis techniques at these conditions are not readily available. We developed a pulsed laser deposition system inside a low-energy electron microscope in order to study this issue. The setup allows for layer-by-layer growth control and in situ measurements of the angle-dependent electron reflection intensity, which can be used as a fingerprint of the electronic structure of the surface layers during growth. By using different substrate terminations and growth conditions we observe two families of reflectivity maps, which we can connect either to samples with an AlO2-rich surface and a conducting interface or to samples with a LaO-rich surface and an insulating interface. Our observations emphasize that substrate termination and stoichiometry determine the electronic structure of the growing layer, and thereby the conductance of the interface.

Conduction mechanism studies on electron transfer of disordered system

Institute of Scientific and Technical Information of China (English)

徐慧; 宋祎璞; 李新梅

2002-01-01

Using the negative eigenvalue theory and the infinite order perturbation theory, a new method was developed to solve the eigenvectors of disordered systems. The result shows that eigenvectors change from the extended state to the localized state with the increase of the site points and the disordered degree of the system. When electric field is exerted, the electrons transfer from one localized state to another one. The conductivity is induced by the electron transfer. The authors derive the formula of electron conductivity and find the electron hops between localized states whose energies are close to each other, whereas localized positions differ from each other greatly. At low temperature the disordered system has the character of the negative differential dependence of resistivity and temperature.

Matrix elements of intraband transitions in quantum dot intermediate band solar cells: the influence of quantum dot presence on the extended-state electron wave-functions

International Nuclear Information System (INIS)

Nozawa, Tomohiro; Arakawa, Yasuhiko

2014-01-01

The intraband transitions which are essential for quantum dot intermediate band solar cells (QD IBSCs) are theoretically investigated by estimating the matrix elements from a ground bound state, which is often regarded as an intermediate band (IB), to conduction band (CB) states for a structure with a quantum dot (QD) embedded in a matrix (a QD/matrix structure). We have found that the QD pushes away the electron envelope functions (probability densities) from the QD region in almost all quantum states above the matrix CB minimum. As a result, the matrix elements of the intraband transitions in the QD/matrix structure are largely reduced, compared to those calculated assuming the envelope functions of free electrons (i.e., plane-wave envelope functions) in a matrix structure as the final states of the intraband transitions. The result indicates the strong influence of the QD itself on the intraband transitions from the IB to the CB states in QD IBSC devices. This work will help in better understanding the problem of the intraband transitions and give new insight, that is, engineering of quantum states is indispensable for the realization of QD IBSCs with high solar energy conversion efficiencies. (paper)

Paramagnetic resonance and electronic conduction in organic semiconductors; Resonance paramagnetique et conduction electroniques dans les semi-conducteurs organiques

Energy Technology Data Exchange (ETDEWEB)

Nechtschein, M. [Commissariat a l' energie atomique et aux energies alternatives - CEA, Laboratoire de Resonance Magnetique (France)

1963-07-01

As some organic bodies simultaneously display semi-conducting properties and a paramagnetism, this report addresses the study of conduction in organic bodies. The author first briefly recalls how relationships between conductibility and Electron Paramagnetic Resonance (EPR) can be noticed in a specific case (mineral and metallic semiconductors). He discusses published results related to paramagnetism and conductibility in organic bodies. He reviews various categories of organic bodies in which both properties are simultaneously present. He notably addresses radical molecular crystals, non-radical molecular crystals, charge transfer complexes, pyrolyzed coals, and pseudo-ferromagnetic organic structures. He discusses the issue of relationships between conduction (charge transfer by electrons) and ERP (which reveals the existence of non-paired electrons which provide free spins)

Optical and electrical properties of some electron and proton irradiated polymers

International Nuclear Information System (INIS)

Mishra, R.; Tripathy, S.P.; Sinha, D.; Dwivedi, K.K.; Ghosh, S.; Khathing, D.T.; Mueller, M.; Fink, D.; Chung, W.H.

2000-01-01

Ion beam treatment studies have been carried out to investigate the potential for improvements in conductivity properties of the polymers Polytetrafluroethylene (PTFE), Polyimide (PI), Polyethyleneterepthalate (PET) and Polypropylene (PP), after 2 MeV electron and 62 MeV proton irradiation. The shift in optical absorption edges as observed by UV-VIS spectra of the irradiated polymers has been correlated to the optical band-gap using Tauc's expression. A decrease in the optical band-gap has been observed in irradiated PP and PTFE, but no considerable change was found for the optical band-gaps of PET and PI. Further AC conductivity measurements confirmed an increase in conductivity in electron irradiated PP

Electron Gas Dynamic Conductivity Tensor on the Nanotube Surface in Magnetic Field

Directory of Open Access Journals (Sweden)

A. M. Ermolaev

2011-01-01

Full Text Available Kubo formula was derived for the electron gas conductivity tensor on the nanotube surface in longitudinal magnetic field considering spatial and time dispersion. Components of the degenerate and nondegenerate electron gas conductivity tensor were calculated. The study has showed that under high electron density, the conductivity undergoes oscillations of de Haas-van Alphen and Aharonov-Bohm types with the density of electrons and magnetic field changes.

Electronic and optical properties of ZrB12 and YB6. Discussion on electron-phonon coupling

International Nuclear Information System (INIS)

Teyssier, J.; Kuzmenko, A.; Marel, D. van der; Lortz, R.; Junod, A.; Filippov, V.; Shitsevalova, N.

2006-01-01

We report the optical properties of high-quality single crystals of low temperature superconductors zirconiumdodecaboride ZrB 12 (T c =5.95 K) and yttrium hexaboride YB 6 (T c =7.15 K) in the range 6 meV-4.6 eV at room temperature. The experimental optical conductivity was extracted from the analysis of the reflectivity in the infrared range and ellipsometry measurement of the dielectric function in the visible range. The electronic band structure of these compounds was calculated by the self-consistent full-potential LMTO method and used to compute the interband part of the optical conductivity and the plasma frequency Ω p . A good agreement was observed between the interband part of the experimental optical conductivities and the band structure calculations. Different methods combining optical spectroscopy, resistivity, specific heat measurements and results of band structure calculations are used to determine the electron-phonon coupling constant. (copyright 2006 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

Electron Hole Plasma in Solids Induced by Ultrashort XUV Laser Pulses

International Nuclear Information System (INIS)

Rethfeld, B.; Medvedev, N.

2013-01-01

Irradiation of solids with ultrashort XUV laser pulses leads to an excitation of electrons from the valence band and deeper shells to the conduction band leading to a nonequilibrium highly energetic electron hole plasma. We investigate the transient electron dynamics in a solid semiconductor and metal (silicon and aluminum, respectively) under irradiation with a femtosecond VUV to XUV laser pulse as used in experiments with the Free Electron Laser FLASH at DESY in Hamburg, Germany. Applying the Asymptotical Trajectory Monte-Carlo technique, we obtain the transient energy distribution of the excited and ionized electrons within the solid. Photon absorption by electrons in different bands and secondary excitation and ionization processes are simulated event by event. The method was extended in order to take into account the electronic band structure and Pauli's principle for electrons in the conduction band. In this talk we review our results on the dynamics of the transient electron-hole plasma, in particular its transient density and energy distribution in dependence on laser and material parameters. For semiconductors we introduce the concept of an ''effective energy gap'' for collective electronic excitation, which can be applied to estimate the free electron density after high-intensity ultrashort XUV laser pulse irradiation. For aluminum we demonstrate that the electronic spectra depend on the relaxation kinetics of the excited electronic subsystem. Experimentally observed spectra of emitted photons from irradiated aluminum can be explained well with our results. (author)

Theory of super-para-electric large polaron for gigantic photo-enhancements of dielectric constant and electronic conductivity in SrTiO3

International Nuclear Information System (INIS)

Yu Qiu; Nasu, Keiichiro

2005-01-01

In connection with the recent experimental discoveries on gigantic photoenhancements of the electronic conductivity and the quasi-static dielectric susceptibility in SrTiO 3 , we theoretically study a photo-generation mechanism of a charged ferroelectric domain in this quantum dielectric. The photo-generated electron, being quite itinerant in the 3d band of Ti 4+ , is assumed to couple weakly but quadratically with soft-anharmonic T 1u phonons in this quantum dielectric. The photo-generated electron is also assumed to couple strongly but linearly with the breathing type high energy phonons. Using a tight binding model for electron, we will show that these two types of electron-phonon couplings result in two types of polarons, a 'super-para-electric (SPE) large polaron' with a quasi-global parity violation, and an 'off-centre type self-trapped polaron' with only a local parity violation. We will also show that this SPE large polaron is nothing else but a singly charged (e - ) and conductive ferroelectric (or SPE) domain with a quasi macroscopic size. This polaron or domain is also shown to have a high mobility and a large quasi-static dielectric susceptibility

Charge recombination processes in minerals studied using optically stimulated luminescence and time-resolved exo-electrons

International Nuclear Information System (INIS)

Tsukamoto, Sumiko; Murray, Andrew; Ankjaergaard, Christina; Jain, Mayank; Lapp, Torben

2010-01-01

A time-resolved optically stimulated exo-electron (TR-OSE) measurement system has been developed using a Photon Timer attached to a gas-flow semi-proportional pancake electron detector within a Risoe TL/OSL reader. The decay rate of the exo-electron emission after the stimulation pulse depends on the probability of (1) escape of electrons into the detector gas from the conduction band by overcoming the work function of the material and (2) thermalization of electrons in the conduction band, and subsequent re-trapping/recombination. Thus, we expect the exo-electron signal to reflect the instantaneous electron concentration in the conduction band. In this study, TR-OSE and time-resolved optically stimulated luminescence (TR-OSL) were measured for the first time using quartz, K-feldspar and NaCl by stimulating the samples using pulsed blue LEDs at different temperatures between 50 and 250 0 C after beta irradiation and preheating to 280 0 C. The majority of TR-OSE signals from all the samples decayed much faster than TR-OSL signals irrespective of the stimulation temperatures. This suggests that the lifetime of OSL in these dosimeters arises mainly from the relaxation of an excited state of the recombination centre, rather than from residence time of an electron in the conduction band.

Experimental study of energy harvesting in UHF band

International Nuclear Information System (INIS)

Bernacki, Ł; Gozdur, R; Salamon, N

2016-01-01

A huge progress of down-sizing technology together with trend of decreasing power consumption and, on the other hand, increasing efficiency of electronics give the opportunity to design and to implement the energy harvesters as main power sources. This paper refers to the energy that can be harvested from electromagnetic field in the unlicensed frequency bands. The paper contains description of the most popular techniques and transducers that can be applied in energy harvesting domain. The overview of current research and commercial solutions was performed for bands in ultra-high frequency range, which are unlicensed and where transmission is not limited by administrative arrangements. During the experiments with Powercast’s receiver, the same bands as sources of electromagnetic field were taken into account. This power source is used for conducting radio-communication process and excess energy could be used for powering the extra electronic circuits. The paper presents elaborated prototype of energy harvesting system and the measurements of power harvested in ultra-high frequency range. The evaluation of RF energy harvesters for powering ultra-low power (ULP) electronic devices was performed based on survey and results of the experiments. (paper)

Theory of the negative differential conductivity effect in semiconductor superlattices

International Nuclear Information System (INIS)

Vo Hong Anh; Nguyen Hong Shon; Le Vu Ky

1990-01-01

A new mechanism of the negative differential conductivity (NDC) effect in semiconductor superlattices (SL) is proposed and analysed that is due to the conduction electron trapping by donor centers. It is shown that the NDC effect occurs for sufficently high (but reasonable) impurity concentration and not too large value of the τ ε /τ c ratio (where τ ε is the electron energy relaxation time and τ c the electron life time in the conduction band) when the applied d.c. electric field reaches certain critical value defined by the physical parameters of the sample. (author). 8 refs, 2 figs

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

Directory of Open Access Journals (Sweden)

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.

Implementation of electronic crosstalk correction for terra MODIS PV LWIR bands

Science.gov (United States)

Geng, Xu; Madhavan, Sriharsha; Chen, Na; Xiong, Xiaoxiong

2015-09-01

The MODerate-resolution Imaging Spectroradiometer (MODIS) is one of the primary instruments in the fleet of NASA's Earth Observing Systems (EOS) in space. Terra MODIS has completed 15 years of operation far exceeding its design lifetime of 6 years. The MODIS Level 1B (L1B) processing is the first in the process chain for deriving various higher level science products. These products are used mainly in understanding the geophysical changes occurring in the Earth's land, ocean, and atmosphere. The L1B code is designed to carefully calibrate the responses of all the detectors of the 36 spectral bands of MODIS and provide accurate L1B radiances (also reflectances in the case of Reflective Solar Bands). To fulfill this purpose, Look Up Tables (LUTs), that contain calibration coefficients derived from both on-board calibrators and Earth-view characterized responses, are used in the L1B processing. In this paper, we present the implementation mechanism of the electronic crosstalk correction in the Photo Voltaic (PV) Long Wave InfraRed (LWIR) bands (Bands 27-30). The crosstalk correction involves two vital components. First, a crosstalk correction modular is implemented in the L1B code to correct the on-board Blackbody and Earth-View (EV) digital number (dn) responses using a linear correction model. Second, the correction coefficients, derived from the EV observations, are supplied in the form of LUTs. Further, the LUTs contain time stamps reflecting to the change in the coefficients assessed using the Noise Equivalent difference Temperature (NEdT) trending. With the algorithms applied in the MODIS L1B processing it is demonstrated that these corrections indeed restore the radiometric balance for each of the affected bands and substantially reduce the striping noise in the processed images.

Localized conductive patterning via focused electron beam reduction of graphene oxide

Energy Technology Data Exchange (ETDEWEB)

Kim, Songkil; Henry, Mathias [George W. Woodruff School of Mechanical Engineering, Georgia Institute of Technology, Atlanta, Georgia 30332 (United States); Kulkarni, Dhaval D.; Zackowski, Paul; Jang, Seung Soon; Tsukruk, Vladimir V. [School of Materials Science and Engineering, Georgia Institute of Technology, Atlanta, Georgia 30332 (United States); Fedorov, Andrei G., E-mail: agf@gatech.edu [George W. Woodruff School of Mechanical Engineering, Georgia Institute of Technology, Atlanta, Georgia 30332 (United States); Parker H. Petit Institute for Bioengineering and Bioscience, Georgia Institute of Technology, Atlanta, Georgia 30332 (United States)

2015-03-30

We report on a method for “direct-write” conductive patterning via reduction of graphene oxide (GO) sheets using focused electron beam induced deposition (FEBID) of carbon. FEBID treatment of the intrinsically dielectric graphene oxide between two metal terminals opens up the conduction channel, thus enabling a unique capability for nanoscale conductive domain patterning in GO. An increase in FEBID electron dose results in a significant increase of the domain electrical conductivity with improving linearity of drain-source current vs. voltage dependence, indicative of a change of graphene oxide electronic properties from insulating to semiconducting. Density functional theory calculations suggest a possible mechanism underlying this experimentally observed phenomenon, as localized reduction of graphene oxide layers via interactions with highly reactive intermediates of electron-beam-assisted dissociation of surface-adsorbed hydrocarbon molecules. These findings establish an unusual route for using FEBID as nanoscale lithography and patterning technique for engineering carbon-based nanomaterials and devices with locally tailored electronic properties.

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.

A stretchable and screen-printable conductive ink for stretchable electronics

Science.gov (United States)

Mohammed, Anwar; Pecht, Michael

2016-10-01

Stretchable electronics can offer an added degree of design freedom and generate products with unprecedented capabilities. Stretchable conductive ink serving as interconnect, is a key enabler for stretchable electronics. This paper focuses on the development of a stretchable and screen printable conductive ink which could be stretched more than 500 cycles at 20% strain while maintaining electrical and mechanical integrity. The screen printable and stretchable conductive ink developed in this paper marks an important milestone for this nascent technology.

Electronic band structure, magnetic, transport and thermodynamic properties of In-filled skutterudites InxCo4Sb12

International Nuclear Information System (INIS)

Leszczynski, J; Da Ros, V; Lenoir, B; Dauscher, A; Candolfi, C; Masschelein, P; Hejtmanek, J; Kutorasinski, K; Tobola, J; Smith, R I; Stiewe, C; Müller, E

2013-01-01

The thermoelectric and thermodynamic properties of polycrystalline In x Co 4 Sb 12 (0.0 ⩽ x ⩽ 0.26) skutterudites were investigated and analysed between 2 and 800 K by means of electrical resistivity, thermopower, thermal conductivity and specific heat measurements. Hall effect, sound velocity and thermal expansion measurements were also made in order to gain insights into the transport and elastic properties of these compounds. The impact of the In filling on the crystal structure as well as the thermal dynamics of the In atoms were tracked down to 4 K using powder neutron diffraction experiments. Analyses of the transport data were compared with the evolution of the electronic band structure with x determined theoretically within the Korringa–Kohn–Rostoker method with the coherent potential approximation. These calculations indicate that In gives rise to a remarkably large p-like density of states located at the conduction band edge. The electrical properties show typical trends of heavily doped semiconductors regardless of the In content. The thermal transport in CoSb 3 is strongly influenced by the presence of In in the voids of the crystal structure resulting in a drop in the lattice thermal conductivity values in the whole temperature range. The low value of the Grüneisen parameter suggests that this decrease mainly originates from enhanced mass-fluctuations and point-defect scattering mechanisms. The highest thermoelectric figure of merit ZT ∼ 1.0 at 750 K was achieved at the maximum In filling fraction, i.e. for x = 0.26. (paper)

Electron doping through lithium intercalation to interstitial channels in tetrahedrally bonded SiC

Energy Technology Data Exchange (ETDEWEB)

Sakai, Yuki [Department of Applied Physics, The University of Tokyo, 7-3-1, Hongo, Bunkyo-ku, Tokyo 113-8656 (Japan); Center for Computational Materials, Institute for Computational Engineering and Sciences, The University of Texas at Austin, Austin, Texas 78712 (United States); Oshiyama, Atsushi [Department of Applied Physics, The University of Tokyo, 7-3-1, Hongo, Bunkyo-ku, Tokyo 113-8656 (Japan)

2015-11-07

We report on first-principles calculations that clarify the effect of lithium atom intercalation into zinc blende 3C-silicon carbide (3C-SiC) on electronic and structural properties. Lithium atoms inside 3C-SiC are found to donate electrons to 3C-SiC that is an indication of a new way of electron doping through the intercalation. The electrons doped into the conduction band interact with lithium cations and reduce the band spacing between the original valence and conduction bands. We have also found that a silicon monovacancy in 3C-SiC promotes the lithium intercalation, showing that the vacancy generation makes SiC as a possible anode material for lithium-ion battery.

Flat electronic bands in fractal-kagomé network and the effect of perturbation

Energy Technology Data Exchange (ETDEWEB)

Nandy, Atanu, E-mail: atanunandy1989@gmail.com; Chakrabarti, Arunava, E-mail: arunava-chakrabarti@yahoo.co.in [Department of Physics, University of Kalyani, Kalyani, West Bengal - 741235 (India)

2016-05-06

We demonstrate an analytical prescription of demonstrating the flat band [FB] states in a fractal incorporated kagomé type network that can give rise to a countable infinity of flat non-dispersive eigenstates with a multitude of localization area. The onset of localization can, in principle, be delayed in space by an appropriate choice of energy regime. The length scale, at which the onset of localization for each mode occurs, can be tuned at will following the formalism developed within the framework of real space renormalization group. This scheme leads to an exact determination of energy eigenvalue for which one can have dispersionless flat electronic bands. Furthermore, we have shown the effect ofuniform magnetic field for the same non-translationally invariant network model that has ultimately led to an‘apparent invisibility’ of such staggered localized states and to generate absolutely continuous sub-bands in the energy spectrum and again an interesting re-entrant behavior of those FB states.

Wide Band to ''Double Band'' upgrade

International Nuclear Information System (INIS)

Kasper, P.; Currier, R.; Garbincius, P.; Butler, J.

1988-06-01

The Wide Band beam currently uses electrons obtained from secondary photon conversions to produce the photon beam incident on the experimental targets. By transporting the positrons produced in these conversions as well as the electrons it is possible to almost double the number of photons delivered to the experiments per primary beam proton. 11 figs

Diode laser spectroscopy of oxygen electronic band at 760 nm

International Nuclear Information System (INIS)

Lucchesini, A.; De Rosa, M.; Gozzini, S.

1998-01-01

Collisional broadening and shift coefficients have been obtained by analyzing the line shapes of oxygen absorptions in the 760 nm electronic band. By using a diode laser spectrometer with commercially available etherostructure Al x Ga 1-x As diode lasers operating in 'free-running mode', line shape parameters have been collected at room temperature by varying the gas pressure. A systematic study has been carried on seven absorption lines by scanning the diode laser emission wavelength around the gas resonances. The weak absorption lines have been detected by using the wavelength modulation (WM) spectroscopy technique with second-harmonic detection

Electrical conduction at domain walls in multiferroic BiFeO3

Science.gov (United States)

Seidel, Jan; Martin, Lane; He, Qing; Zhan, Qian; Chu, Ying-Hao; Rother, Axel; Hawkridge, Michael; Maksymovych, Peter; Yu, Pu; Gajek, Martin; Balke, Nina; Kalinin, Sergei; Gemming, Sybille; Wang, Feng; Catalán, Gustau; Scott, James; Spaldin, Nicola; Orenstein, Joseph; Ramesh, Ramamoorthy

2009-03-01

We report the observation of room temperature electronic conductivity at ferroelectric domain walls in BiFeO3. The origin and nature of the observed conductivity is probed using a combination of conductive atomic force microscopy, high resolution transmission electron microscopy and first-principles density functional computations. We show that a structurally driven change in both the electrostatic potential and local electronic structure (i.e., a decrease in band gap) at the domain wall leads to the observed electrical conductivity. We estimate the conductivity in the wall to be several orders of magnitude higher than for the bulk material. Additionally we demonstrate the potential for device applications of such conducting nanoscale features.

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.

Towards double-functionalized small diamondoids: selective electronic band-gap tuning

International Nuclear Information System (INIS)

Adhikari, Bibek; Fyta, Maria

2015-01-01

Diamondoids are nanoscale diamond-like cage structures with hydrogen terminations, which can occur in various sizes and with a diverse type of modifications. In this work, we focus on the structural alterations and the effect of doping and functionalization on the electronic properties of diamondoids, from the smallest adamantane to heptamantane. The results are based on quantum mechanical calculations. We perform a self-consistent study, starting with doping the smallest diamondoid, adamantane. Boron, nitrogen, silicon, oxygen, and phosphorus are chosen as dopants at sites which have been previously optimized and are also consistent with the literature. At a next step, an amine- and a thiol- group are separately used to functionalize the adamantane molecule. We mainly focus on a double functionalization of diamondoids up to heptamantane using both these atomic groups. The effect of isomeration in the case of tetramantane is also studied. We discuss the higher efficiency of a double-functionalization compared to doping or a single-functionalization of diamondoids in tuning the electronic properties, such as the electronic band-gap, of modified small diamondoids in view of their novel nanotechnological applications. (paper)

Mechanical design and fabrication of the VHF-gun, the Berkeley normal-conducting continuous-wave high-brightness electron source

Science.gov (United States)

Wells, R. P.; Ghiorso, W.; Staples, J.; Huang, T. M.; Sannibale, F.; Kramasz, T. D.

2016-02-01

A high repetition rate, MHz-class, high-brightness electron source is a key element in future high-repetition-rate x-ray free electron laser-based light sources. The VHF-gun, a novel low frequency radio-frequency gun, is the Lawrence Berkeley National Laboratory (LBNL) response to that need. The gun design is based on a normal conducting, single cell cavity resonating at 186 MHz in the VHF band and capable of continuous wave operation while still delivering the high accelerating fields at the cathode required for the high brightness performance. The VHF-gun was fabricated and successfully commissioned in the framework of the Advanced Photo-injector EXperiment, an injector built at LBNL to demonstrate the capability of the gun to deliver the required beam quality. The basis for the selection of the VHF-gun technology, novel design features, and fabrication techniques are described.

Band-to-band and inner shell excitation VIS-UV photoluminescence of quaternary InAlGaN alloys

International Nuclear Information System (INIS)

Fukui, K.; Naoe, S.; Okada, K.; Hamada, S.; Hirayama, H.

2006-01-01

Visible and ultraviolet photoluminescence and photoluminescence excitation spectra of quaternary InAlGaN alloys were measured. The excitation photon energy covers from band edge to 180 eV, near both nitrogen K (∝400 eV) and aluminium K (∝1.5 keV) inner shell energy region. From photoluminescence excitation spectra photoluminescence intensity per incident photon number varies in proportion to incident photon energy. This result implies that many conduction band electron - valence band hole pairs which are responsible for photoluminescence are produced by high energy excitation. Time resolved decay curves were also measured in the same energy region. No effect of high energy excitation on time resolved decay measurements suggests a role of indium on the photoluminescence mechanism in InAlGaN system. (copyright 2006 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

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.

Preliminary design and optimization of a G-band extended interaction oscillator based on a pseudospark-sourced electron beam

Energy Technology Data Exchange (ETDEWEB)

Yin, Y., E-mail: yong.yin@strath.ac.uk, E-mail: yinyong@uestc.edu.cn [School of Physical Electronics, University of Electronic Science and Technology of China, Chengdu 610054 (China); Department of Physics, Scottish Universities Physics Alliance, University of Strathclyde, Glasgow G4 0NG (United Kingdom); He, W.; Zhang, L.; Yin, H.; Cross, A. W. [Department of Physics, Scottish Universities Physics Alliance, University of Strathclyde, Glasgow G4 0NG (United Kingdom)

2015-07-15

The design and simulation of a G-band extended interaction oscillator (EIO) driven by a pseudospark-sourced electron beam is presented. The characteristic of the EIO and the pseudospark-based electron beam were studied to enhance the performance of the newly proposed device. The beam-wave interaction of the EIO can be optimized by choosing a suitable pseudospark discharging voltage and by widening the operating voltage region of the EIO circuit. Simulation results show that a peak power of over 240 W can be achieved at G-band using a pseudospark discharge voltage of 41 kV.

Observation of an electron band above the Fermi level in FeTe0.55Se0.45 from in-situ surface doping

International Nuclear Information System (INIS)

Zhang, P.; Ma, J.; Qian, T.; Richard, P.; Ding, H.; Xu, N.; Xu, Y.-M.; Fedorov, A. V.; Denlinger, J. D.; Gu, G. D.

2014-01-01

We used in-situ potassium (K) evaporation to dope the surface of the iron-based superconductor FeTe 0.55 Se 0.45 . The systematic study of the bands near the Fermi level confirms that electrons are doped into the system, allowing us to tune the Fermi level of this material and to access otherwise unoccupied electronic states. In particular, we observe an electron band located above the Fermi level before doping that shares similarities with a small three-dimensional pocket observed in the cousin, heavily electron-doped KFe 2−x Se 2 compound.

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.

Quantification and impact of nonparabolicity of the conduction band of indium tin oxide on its plasmonic properties

International Nuclear Information System (INIS)

Liu, Xiaoge; Park, Junghyun; Kang, Ju-Hyung; Yuan, Hongtao; Cui, Yi; Hwang, Harold Y.; Brongersma, Mark L.

2014-01-01

Doped indium tin oxide (ITO) behaves as a Drude metal with a plasma frequency that is controlled by its free carrier density. In this work, we systematically tune this frequency across the mid-infrared range by annealing treatments in a reducing environment that produce high electron concentrations (∼10 21  cm −3 ). The changes in ITO's optical properties that result from the changes in carrier density are measured by attenuated total reflection measurements. These optical frequency measurements are complemented by Hall measurements to obtain a comprehensive picture of the Drude response of the ITO films. It was found that a complete description of the optical properties at very high carrier densities needs to account for the nonparabolicity of the conduction band of ITO and a reduced carrier mobility. More specifically, an increase in carrier concentration from 6.2 × 10 19  cm −3 to 1.4 × 10 21  cm −3 comes with a change of the effective electron mass from 0.35 m 0 to 0.53 m 0 and a decrease in the optical frequency mobility from about 20 cm 2  V −1  s −1 to 9 cm 2  V −1  s −1

On electronic structure of polymer-derived amorphous silicon carbide ceramics

Science.gov (United States)

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

2014-06-01

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

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.

Electrochemically oxidized electronic and ionic conducting nanostructured block copolymers for lithium battery electrodes.

Science.gov (United States)

Patel, Shrayesh N; Javier, Anna E; Balsara, Nitash P

2013-07-23

Block copolymers that can simultaneously conduct electronic and ionic charges on the nanometer length scale can serve as innovative conductive binder material for solid-state battery electrodes. The purpose of this work is to study the electronic charge transport of poly(3-hexylthiophene)-b-poly(ethylene oxide) (P3HT-PEO) copolymers electrochemically oxidized with lithium bis(trifluoromethanesulfonyl) imide (LiTFSI) salt in the context of a lithium battery charge/discharge cycle. We use a solid-state three-terminal electrochemical cell that enables simultaneous conductivity measurements and control over electrochemical doping of P3HT. At low oxidation levels (ratio of moles of electrons removed to moles of 3-hexylthiophene moieties in the electrode), the electronic conductivity (σe,ox) increases from 10(-7) S/cm to 10(-4) S/cm. At high oxidation levels, σe,ox approaches 10(-2) S/cm. When P3HT-PEO is used as a conductive binder in a positive electrode with LiFePO4 active material, P3HT is electrochemically active within the voltage window of a charge/discharge cycle. The electronic conductivity of the P3HT-PEO binder is in the 10(-4) to 10(-2) S/cm range over most of the potential window of the charge/discharge cycle. This allows for efficient electronic conduction, and observed charge/discharge capacities approach the theoretical limit of LiFePO4. However, at the end of the discharge cycle, the electronic conductivity decreases sharply to 10(-7) S/cm, which means the "conductive" binder is now electronically insulating. The ability of our conductive binder to switch between electronically conducting and insulating states in the positive electrode provides an unprecedented route for automatic overdischarge protection in rechargeable batteries.

Cellulose nanocrystal: electronically conducting polymer nanocomposites for supercapacitors

OpenAIRE

Liew, Soon Yee

2012-01-01

This thesis describes the use of cellulose nanocrystals for the fabrication of porous nanocomposites with electronic conducting polymers for electrochemical supercapacitor applications. The exceptional strength and negatively charged surface functionalities on cellulose nanocrystals are utilised in these nanocomposites. The negatively charged surface functionalities on cellulose nanocrystals allow their simultaneous incorporation into electropolymerised, positively charged conducting polymer ...

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.

Effect of superconductivity on the cubic to tetragonal structural transition due to a two-fold degenerate electronic band

International Nuclear Information System (INIS)

Ghatak, S.K.; Khanra, B.C.; Ray, D.K.

1978-01-01

The effect of the BCS superconductivity on the cubic to tetragonal structural transition arising from a two-fold degenerate electronic band is investigated within the mean field approximation. The phase diagram of the two transitions is given for a half filled esub(g)-band. Modification of the two transitions when they are close together is also discussed. (author)

Conductance oscillation in graphene-nanoribbon-based electronic Fabry-Perot resonators

International Nuclear Information System (INIS)

Zhang Yong; Han Mei; Shen Linjiang

2010-01-01

By using the tight-binding approximation and the Green's function method, the quantum conductance of the Fabry-Perot-like electronic resonators composed of zigzag and metallic armchair edge graphene nanoribbons (GNRs) was studied numerically. Obtained results show that due to Fabry-Perot-like electronic interference, the conductance of the GNR resonators oscillates periodically with the Fermi energy. The effects of disorders and coupling between the electrodes and the GNR on conductance oscillations were explored. It is found that the conductance oscillations appear at the strong coupling and become resonant peaks as the coupling is very weak. It is also found that the strong disorders in the GNR can smear the conductance oscillation periods. In other words, the weak coupling and the strong disorders all can blur the conductance oscillations, making them unclearly distinguished.

Electronic structure classifications using scanning tunneling microscopy conductance imaging

International Nuclear Information System (INIS)

Horn, K.M.; Swartzentruber, B.S.; Osbourn, G.C.; Bouchard, A.; Bartholomew, J.W.

1998-01-01

The electronic structure of atomic surfaces is imaged by applying multivariate image classification techniques to multibias conductance data measured using scanning tunneling microscopy. Image pixels are grouped into classes according to shared conductance characteristics. The image pixels, when color coded by class, produce an image that chemically distinguishes surface electronic features over the entire area of a multibias conductance image. Such open-quotes classedclose quotes images reveal surface features not always evident in a topograph. This article describes the experimental technique used to record multibias conductance images, how image pixels are grouped in a mathematical, classification space, how a computed grouping algorithm can be employed to group pixels with similar conductance characteristics in any number of dimensions, and finally how the quality of the resulting classed images can be evaluated using a computed, combinatorial analysis of the full dimensional space in which the classification is performed. copyright 1998 American Institute of Physics

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.

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

Science.gov (United States)

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

2016-01-01

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

Microstructural evolution in adiabatic shear bands of copper at high strain rates: Electron backscatter diffraction characterization

International Nuclear Information System (INIS)

Tang Lin; Chen Zhiyong; Zhan Congkun; Yang Xuyue; Liu Chuming; Cai Hongnian

2012-01-01

The microstructural evolution of adiabatic shear bands in annealed copper with different large strains at high strain rates has been investigated by electron backscatter diffraction. The results show that mechanical twinning can occur with minimal contribution to shear localization under dynamic loading. Elongated ultrafine grains with widths of 100–300 nm are observed during the evolution of the adiabatic shear bands. A rotational dynamic recrystallization mechanism is proposed to explain the formation of the elongated ultrafine grains. - Highlights: ► The microstructural evolution of ASB is studied by electron backscatter diffraction. ► Twinning can occur in ASB while the contribution to shear localization is slight. ► Elongated ultrafine grains are observed during the evolution process of ASB. ► A possible mechanism is proposed to explain the microstructure evolution of ASB.

Detecting Electron Transport of Amino Acids by Using Conductance Measurement

Directory of Open Access Journals (Sweden)

Wei-Qiong Li

2017-04-01

Full Text Available The single molecular conductance of amino acids was measured by a scanning tunneling microscope (STM break junction. Conductance measurement of alanine gives out two conductance values at 10−1.85 G0 (1095 nS and 10−3.7 G0 (15.5 nS, while similar conductance values are also observed for aspartic acid and glutamic acid, which have one more carboxylic acid group compared with alanine. This may show that the backbone of NH2–C–COOH is the primary means of electron transport in the molecular junction of aspartic acid and glutamic acid. However, NH2–C–COOH is not the primary means of electron transport in the methionine junction, which may be caused by the strong interaction of the Au–SMe (methyl sulfide bond for the methionine junction. The current work reveals the important role of the anchoring group in the electron transport in different amino acids junctions.

Optical band gap of ZnO thin films deposited by electron beam evaporation

International Nuclear Information System (INIS)

Nadeem, M. Y.; Ali, S. L.; Wasiq, M. F.; Rana, A. M.

2006-01-01

Optical band gap of ZnO thin films deposited by electron beam evaporation at evaporation rates ranging 5 As/sup -1/ to 15 As /sup -1/ and thickness ranging 1000A to 3000A is presented. Deposited films were annealed at 573K for one and half hour. The variations in the optical band gap were observed and showed decreasing behavior from 3.15 eV, 3.05 eV, from 3.18 eV to 3.10 eV and from 3.19 eV to 3.18 eV for films with respective thickness 1000A, 2000 A, 3000 A on increasing the evaporation rate from 5 As/sup-1/ to As/sup -1/ by keeping thickness constant. (author)

Comparative study of electron conduction in azulene and naphthalene

Indian Academy of Sciences (India)

Wintec

tional or electronic devices. Recent advances in experi- mental techniques have allowed ... stimulates us to study the electronic conduction in azulene molecule and to compare that with its isomer, naphthalene. ..... ernment of India, for funding and (SD) acknowledges CSIR,. Government of India, for a research fellowship.

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

International Nuclear Information System (INIS)

Peterman, D.J.

1980-01-01

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

Electron Raman scattering in quantum well wires

International Nuclear Information System (INIS)

Zhao Xiangfu; Liu Cuihong

2007-01-01

Electron Raman scattering (ERS) is investigated in a semiconductor quantum well wire (QWW) of cylindrical geometry for T=0K and neglecting phonon-assisted transitions. The differential cross-section (DCS) involved in this process is calculated as a function of a scattering frequency and the cylindrical radius. Electron states are confined within a QWW. Single parabolic conduction and valence bands are assumed. The selection rules are studied. Singularities in the spectra are interpreted for various cylindrical radii. ERS discussed here can provide direct information about the electron band structure of the system

S-band 300 W pulsed solid state microwave amplifier development for driving high power klystrons for electron accelerators

International Nuclear Information System (INIS)

Mohania, Praveen; Shrivastava, Purushottam; Hannurkar, P.R.

2005-01-01

S-Band Microwave electron accelerators like microtrons and linear accelerators need pulsed microwaves from few megawatts to tens of megawatts to accelerator the electrons to desired energy and intensity. Klystron tube based driver amplifiers were used to drive the high power klystrons, which need microwave power from few tens of watts to 1 kW depending on tube output power and gain. A endeavour was initiated at Centre for Advanced Technology to develop state of art solid state S-band microwave amplifiers indigenously to drive the klystron tubes. A modular design approach was used and individual modules up to 160 W power levels were developed and tested. Finally combining 160 W modules will give up to 300 W output power. Several more modules can be combined to achieve even high power levels. Present paper describes the developmental efforts of 300 W S-band solid-state amplifiers and related microwave technologies. (author)

First-principle study of the electronic band structure and the effective mass of the ternary alloy GaxIn1-xP

Science.gov (United States)

Yang, H. Q.; Song, T. L.; Liang, X. X.; Zhao, G. J.

2015-01-01

In this work, the electronic band structure and the effective mass of the ternary alloy GaxIn1-xP are studied by the first principle calculations. The software QUANTUM ESPRESSO and the generalized gradient approximation (GGA) for the exchange correlations have been used in the calculations. We calculate the lattice parameter, band gap and effective mass of the ternary alloy GaxIn1-xP for the Ga composition x varying from 0.0 to 1.0 by the step of 0.125. The effect of the Ga composition on the lattice parameter and the electronic density of states are discussed. The results show that the lattice parameter varies with the composition almost linearly following the Vegard's law. A direct-to-indirect band-gap crossover is found to occur close to x = 0.7. The effective masses are also calculated at Γ(000) high symmetry point along the [100] direction. The results show that the band gap and the electron effective mass vary nonlinearly with composition x.

Band gap engineering strategy via polarization rotation in perovskite ferroelectrics

International Nuclear Information System (INIS)

Wang, Fenggong; Grinberg, Ilya; Rappe, Andrew M.

2014-01-01

We propose a strategy to engineer the band gaps of perovskite oxide ferroelectrics, supported by first principles calculations. We find that the band gaps of perovskites can be substantially reduced by as much as 1.2 eV through local rhombohedral-to-tetragonal structural transition. Furthermore, the strong polarization of the rhombohedral perovskite is largely preserved by its tetragonal counterpart. The B-cation off-center displacements and the resulting enhancement of the antibonding character in the conduction band give rise to the wider band gaps of the rhombohedral perovskites. The correlation between the structure, polarization orientation, and electronic structure lays a good foundation for understanding the physics of more complex perovskite solid solutions and provides a route for the design of photovoltaic perovskite ferroelectrics

Differential cross sections for electron impact excitation of the electronic bands of phenol

Energy Technology Data Exchange (ETDEWEB)

Neves, R. F. C. [School of Chemical and Physical Sciences, Flinders University, GPO Box 2100, Adelaide SA 5001 (Australia); Instituto Federal do Sul de Minas Gerais, Campus Poços de Caldas, Minas Gerais (Brazil); Departamento de Física, UFJF, Juiz de Fora, Minas Gerais (Brazil); Jones, D. B. [School of Chemical and Physical Sciences, Flinders University, GPO Box 2100, Adelaide SA 5001 (Australia); Lopes, M. C. A.; Nixon, K. L. [Departamento de Física, UFJF, Juiz de Fora, Minas Gerais (Brazil); Silva, G. B. da [School of Chemical and Physical Sciences, Flinders University, GPO Box 2100, Adelaide SA 5001 (Australia); Universidade Federal de Mato Grosso, Barra do Garças, Mato Grosso (Brazil); Duque, H. V. [School of Chemical and Physical Sciences, Flinders University, GPO Box 2100, Adelaide SA 5001 (Australia); Departamento de Física, UFJF, Juiz de Fora, Minas Gerais (Brazil); Oliveira, E. M. de; Lima, M. A. P. [Instituto de Física “Gleb Wataghin,” Universidade Estadual de Campinas, 13083-859 Campinas, São Paulo (Brazil); Costa, R. F. da [Centro de Ciências Naturais e Humanas, Universidade Federal do ABC, 09210-580 Santo André, São Paulo (Brazil); Varella, M. T. do N. [Instituto de Física, Universidade de São Paulo, CP 66318, 05315-970 São Paulo (Brazil); Bettega, M. H. F. [Departamento de Física, Universidade Federal do Paraná, CP 19044, 81531-990 Curitiba, Paraná (Brazil); and others

2015-03-14

We report results from a joint theoretical and experimental investigation into electron scattering from the important organic species phenol (C{sub 6}H{sub 5}OH). Specifically, differential cross sections (DCSs) have been measured and calculated for the electron-impact excitation of the electronic states of C{sub 6}H{sub 5}OH. The measurements were carried out at energies in the range 15–40 eV, and for scattered-electron angles between 10{sup ∘} and 90{sup ∘}. The energy resolution of those experiments was typically ∼80 meV. Corresponding Schwinger multichannel method with pseudo-potentials calculations, with and without Born-closure, were also performed for a sub-set of the excited electronic-states that were accessed in the measurements. Those calculations were conducted at the static exchange plus polarisation (SEP)-level using a minimum orbital basis for single configuration interaction (MOBSCI) approach. Agreement between the measured and calculated DCSs was typically fair, although to obtain quantitative accord, the theory would need to incorporate even more channels into the MOBSCI.

Extended two-temperature model for ultrafast thermal response of band gap materials upon impulsive optical excitation

Energy Technology Data Exchange (ETDEWEB)

Shin, Taeho [Department of Chemistry, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139-4307 (United States); Samsung Advanced Institute of Technology, Suwon 443-803 (Korea, Republic of); Teitelbaum, Samuel W.; Wolfson, Johanna; Nelson, Keith A., E-mail: kanelson@mit.edu [Department of Chemistry, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139-4307 (United States); Kandyla, Maria [Department of Chemistry, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139-4307 (United States); Theoretical and Physical Chemistry Institute, National Hellenic Research Foundation, Athens 116-35 (Greece)

2015-11-21

Thermal modeling and numerical simulations have been performed to describe the ultrafast thermal response of band gap materials upon optical excitation. A model was established by extending the conventional two-temperature model that is adequate for metals, but not for semiconductors. It considers the time- and space-dependent density of electrons photoexcited to the conduction band and accordingly allows a more accurate description of the transient thermal equilibration between the hot electrons and lattice. Ultrafast thermal behaviors of bismuth, as a model system, were demonstrated using the extended two-temperature model with a view to elucidating the thermal effects of excitation laser pulse fluence, electron diffusivity, electron-hole recombination kinetics, and electron-phonon interactions, focusing on high-density excitation.

Electronic energy states of HfSe/sub 2/ and NbSe/sub 2/ by low energy electron loss spectroscopy study

Energy Technology Data Exchange (ETDEWEB)

Ito, T; Iwami, M; Hiraki, A [Osaka Univ., Suita (Japan). Faculty of Engineering

1981-06-01

Low energy electron loss spectroscopy (ELS) study was performed on 1T-HfSe/sub 2/ (group IVB metal compound) and 2H-NbSe/sub 2/ (group VB metal compound) by using incident electron energies of 30-250 eV. From the loss data in the second derivative form, maxima in density-of-states in the conduction band of the compounds were deduced through the information on the filled core states by X-ray photoelectron spectroscopy. The conduction band of the transition-metal dichalcogenides could be divided into two parts. The results are discussed in relation to the previous work on WS/sub 2/ (group VIB metal compound), and also to proposals based on band calculations and experimental studies on the transition-metal dichalcogenides with constituent metals of group IVB, VB and VIB.

Multiphoton electronic-spin generation and transmission spectroscopy in n-type GaAs

Energy Technology Data Exchange (ETDEWEB)

Idrish Miah, M., E-mail: m.miah@griffith.edu.a [Department of Physics, University of Chittagong, Chittagong 4331 (Bangladesh)

2011-01-17

Multiphoton electronic-spin generation in semiconductors was investigated using differential transmission spectroscopy. The generation of the electronic spins in the semiconductor samples were achieved by multiphoton pumping with circularly polarized light beam and was probed by the spin-resolved transmission of the samples. The electronic spin-polarization of conduction band was estimated and was found to depend on the delay of the probe beam, temperature as well as on the multiphoton pumping energy. The temperature dependence showed a decrease of the spin-polarization with increasing temperature. The electronic spin-polarization was found to depolarize rapidly for multiphoton pumping energy larger than the energy gap of the split-off band to the conduction band. The results were compared with those obtained in one-photon pumping, which shows that an enhancement of the electronic spin-polarization was achieved in multiphoton pumping. The findings resulting from this investigation might have potential applications in opto-spintronics, where the generation of highly polarized electronic spins is required.

Multiphoton electronic-spin generation and transmission spectroscopy in n-type GaAs

International Nuclear Information System (INIS)

Idrish Miah, M.

2011-01-01

Multiphoton electronic-spin generation in semiconductors was investigated using differential transmission spectroscopy. The generation of the electronic spins in the semiconductor samples were achieved by multiphoton pumping with circularly polarized light beam and was probed by the spin-resolved transmission of the samples. The electronic spin-polarization of conduction band was estimated and was found to depend on the delay of the probe beam, temperature as well as on the multiphoton pumping energy. The temperature dependence showed a decrease of the spin-polarization with increasing temperature. The electronic spin-polarization was found to depolarize rapidly for multiphoton pumping energy larger than the energy gap of the split-off band to the conduction band. The results were compared with those obtained in one-photon pumping, which shows that an enhancement of the electronic spin-polarization was achieved in multiphoton pumping. The findings resulting from this investigation might have potential applications in opto-spintronics, where the generation of highly polarized electronic spins is required.

Microbial interspecies electron transfer via electric currents through conductive minerals

Science.gov (United States)

Kato, Souichiro; Hashimoto, Kazuhito; Watanabe, Kazuya

2012-01-01

In anaerobic biota, reducing equivalents (electrons) are transferred between different species of microbes [interspecies electron transfer (IET)], establishing the basis of cooperative behaviors and community functions. IET mechanisms described so far are based on diffusion of redox chemical species and/or direct contact in cell aggregates. Here, we show another possibility that IET also occurs via electric currents through natural conductive minerals. Our investigation revealed that electrically conductive magnetite nanoparticles facilitated IET from Geobacter sulfurreducens to Thiobacillus denitrificans, accomplishing acetate oxidation coupled to nitrate reduction. This two-species cooperative catabolism also occurred, albeit one order of magnitude slower, in the presence of Fe ions that worked as diffusive redox species. Semiconductive and insulating iron-oxide nanoparticles did not accelerate the cooperative catabolism. Our results suggest that microbes use conductive mineral particles as conduits of electrons, resulting in efficient IET and cooperative catabolism. Furthermore, such natural mineral conduits are considered to provide ecological advantages for users, because their investments in IET can be reduced. Given that conductive minerals are ubiquitously and abundantly present in nature, electric interactions between microbes and conductive minerals may contribute greatly to the coupling of biogeochemical reactions. PMID:22665802

Spin- and valley-dependent electronic band structure and electronic heat capacity of ferromagnetic silicene in the presence of strain, exchange field and Rashba spin-orbit coupling

Science.gov (United States)

Hoi, Bui Dinh; Yarmohammadi, Mohsen; Kazzaz, Houshang Araghi

2017-10-01

We studied how the strain, induced exchange field and extrinsic Rashba spin-orbit coupling (RSOC) enhance the electronic band structure (EBS) and electronic heat capacity (EHC) of ferromagnetic silicene in presence of external electric field (EF) by using the Kane-Mele Hamiltonian, Dirac cone approximation and the Green's function approach. Particular attention is paid to investigate the EHC of spin-up and spin-down bands at Dirac K and K‧ points. We have varied the EF, strain, exchange field and RSOC to tune the energy of inter-band transitions and consequently EHC, leading to very promising features for future applications. Evaluation of EF exhibits three phases: Topological insulator (TI), valley-spin polarized metal (VSPM) and band insulator (BI) at given aforementioned parameters. As a new finding, we have found a quantum anomalous Hall phase in BI regime at strong RSOCs. Interestingly, the effective mass of carriers changes with strain, resulting in EHC behaviors. Here, exchange field has the same behavior with EF. Finally, we have confirmed the reported and expected symmetry results for both Dirac points and spins with the study of valley-dependent EHC.

Electronic conductivity studies on oxyhalide glasses containing TMO

Energy Technology Data Exchange (ETDEWEB)

Vijayatha, D. [R& D Center, Bharatiar University, Coimbatore, Tamil Nadu (India); Department of Physics, Gurunanak Institute of Technology, Hyderabad -040 (India); Viswanatha, R. [Solid State and Structural Chemistry Unit, Indian Institute of Science, Bangalore 560012 (India); Sujatha, B. [Department of Electronics and Communcation, MSRIT, Bangalore 560054 (India); Narayana Reddy, C., E-mail: nivetejareddy@gmail.com [Department of Physics, Sree Siddaganga College of Arts, Science and Commerce, Tumkur 572102 (India)

2016-05-06

Microwave-assisted synthesis is cleaner, more economical and much faster than conventional methods. The development of new routes for the synthesis of solid materials is an integral part of material science and technology. The electronic conductivity studies on xPbCl{sub 2} – 60 PbO – (40-x) V{sub 2}O{sub 5} (1 ≥ x ≤ 10) glass system has been carried out over a wide range of composition and temperature (300 K to 423 K). X-ray diffraction study confirms the amorphous nature of the samples. The Scanning electron microscopic studies reveal the formation of cluster like morphology in PbCl{sub 2} containing glasses. The d.c conductivity exhibits Arrhenius behaviour and increases with V{sub 2}O{sub 5} concentration. Analysis of the results is interpreted in view Austin-Mott’s small polaron model of electron transport. Activation energies calculated using regression analysis exhibit composition dependent trend and the variation is explained in view of the structure of lead-vanadate glass.

Conductivity of the electron-impurity system

International Nuclear Information System (INIS)

Goettig, S.

1983-09-01

The free-carrier absorption of electromagnetic radiation due to the presence of static scatterers is examined taking into account the electron-electron interaction, the plasma-phonon polar coupling and the plasma anisotropy. For the case of strong coupling in the isotropic plasma the absorption due to the collective-mode excitation processes is, for frequencies just above the plasmon-like collective mode frequency, shown to be dominant over the absorption due to single-particle excitations. The expression for the frequency-dependent absorptive part of the conductivity due to the long-wavelength collective-mode excitations is derived for the case of multicomponent anisotropic degenerate plasma (e.g. lead chalcogenides). The results are discussed in detail and compared with available experimental data for n-PbSe. The comparison with the previous theories is also given. (author)

From lattice Hamiltonians to tunable band structures by lithographic design

Science.gov (United States)

Tadjine, Athmane; Allan, Guy; Delerue, Christophe

2016-08-01

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

Tuning of electronic band gaps and optoelectronic properties of binary strontium chalcogenides by means of doping of magnesium atom(s)- a first principles based theoretical initiative with mBJ, B3LYP and WC-GGA functionals

Science.gov (United States)

Debnath, Bimal; Sarkar, Utpal; Debbarma, Manish; Bhattacharjee, Rahul; Chattopadhyaya, Surya

2018-02-01

First principle based theoretical initiative is taken to tune the optoelectronic properties of binary strontium chalcogenide semiconductors by doping magnesium atom(s) into their rock-salt unit cells at specific concentrations x = 0.0, 0.25, 0.50, 0.75 and 1.0 and such tuning is established by studying structural, electronic and optical properties of designed binary compounds and ternary alloys employing WC-GGA, B3LYP and mBJ exchange-correlation functionals. Band structure of each compound is constructed and respective band gaps under all the potential schemes are measured. The band gap bowing and its microscopic origin are calculated using quadratic fit and Zunger's approach, respectively. The atomic and orbital origins of electronic states in the band structure of any compound are explored from its density of states. The nature of chemical bonds between the constituent atoms in each compound is explored from the valence electron density contour plots. Optical properties of any specimen are explored from the computed spectra of its dielectric function, refractive index, extinction coefficient, normal incidence reflectivity, optical conductivity optical absorption and energy loss function. Several calculated results are compared with available experimental and earlier theoretical data.

Quantum conductance of 4,4-bipyridine molecular junctions: Role of electrode work function and local d band

DEFF Research Database (Denmark)

Rauba, J.M.C.; Strange, Mikkel; Thygesen, Kristian Sommer

2008-01-01

conductance than the Pt-BPD junction due to the smaller work function of Au as compared to Pt. On the other hand, coupling to the local d band is stronger in the case of Pt and this broadens the LUMO resonance. We find that these effects largely outbalance each other leading to conductances of 0.01G(0) and 0......-principles results within a simple single-level model....

Possible explanation for the conductance of a single quantum unit in metallic carbon nanotubes

International Nuclear Information System (INIS)

Choi, Hyoung Joon; Ihm, Jisoon; Yoon, Young-Gui; Louie, Steven G.

1999-01-01

The quantum conductance of a metallic carbon nanotube with one end immersed in a jellium metal is studied. We find that the incident π * -band electrons, having a very high angular momentum with respect to the tube axis, go through the tube without being scattered by the free electrons in surrounding metal and contribute a quantum unit (2e 2 /h) to the conductance. On the other hand, the incident π-band electrons, with the p z atomic orbitals in phase along the tube circumference, experience strong resonant back-scattering because the low-angular-momentum states at the Fermi level have a dominantly metallic character in the nanotube-jellium metal coexistence region. These results provide a possible explanation for the experimentally observed conductance of one quantum unit instead of two for nanotubes with one end dipped into liquid metal such as mercury. (c) 1999 The American Physical Society

Experimental Benchmarking of Pu Electronic Structure

International Nuclear Information System (INIS)

Tobin, J.G.; Moore, K.T.; Chung, B.W.; Wall, M.A.; Schwartz, A.J.; Ebbinghaus, B.B.; Butterfield, M.T.; Teslich, N.E. Jr.; Bliss, R.A.; Morton, S.A.; Yu, S.W.; Komesu, T.; Waddill, G.D.; van der Laan, G.; Kutepov, A.L.

2008-01-01

The standard method to determine the band structure of a condensed phase material is to (1) obtain a single crystal with a well defined surface and (2) map the bands with angle resolved photoelectron spectroscopy (occupied or valence bands) and inverse photoelectron spectroscopy (unoccupied or conduction bands). Unfortunately, in the case of Pu, the single crystals of Pu are either nonexistent, very small and/or having poorly defined surfaces. Furthermore, effects such as electron correlation and a large spin-orbit splitting in the 5f states have further complicated the situation. Thus, we have embarked upon the utilization of unorthodox electron spectroscopies, to circumvent the problems caused by the absence of large single crystals of Pu with well-defined surfaces. Our approach includes the techniques of resonant photoelectron spectroscopy, x-ray absorption spectroscopy, electron energy loss spectroscopy, Fano Effect measurements, and Bremstrahlung Isochromat Spectroscopy, including the utilization of micro-focused beams to probe single-crystallite regions of polycrystalline Pu samples.

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

International Nuclear Information System (INIS)

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

1977-01-01

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

Electron quantum interferences and universal conductance fluctuations

International Nuclear Information System (INIS)

Benoit, A.; Pichard, J.L.

1988-05-01

Quantum interferences yield corrections to the classical ohmic behaviour predicted by Boltzmann theory in electronic transport: for instance the well-known ''weak localization'' effects. Furthermore, very recently, quantum interference effects have been proved to be responsible for statistically different phenomena, associated with Universal Conductance Fluctuations and observed on very small devices [fr

Ionic and electronic conductivity in lead-zirconate-titanate (PZT)

NARCIS (Netherlands)

Boukamp, Bernard A.; Pham thi ngoc mai, P.T.N.M.; Blank, David H.A.; Bouwmeester, Henricus J.M.

2004-01-01

Accurate impedance measurements on differently sized samples of lead–zirconate–titanate (PbZr0.53Ti0.47O3, PZT) have been analyzed with a CNLS procedure, resulting in the separation of the ionic and electronic conductivities over a temperature range from f150 to 630 jC. At 603 jC the electronic

Enhanced persistent red luminescence in Mn2+-doped (Mg,Zn)GeO3 by electron trap and conduction band engineering

Science.gov (United States)

Katayama, Yumiko; Kayumi, Tomohiro; Ueda, Jumpei; Tanabe, Setsuhisa

2018-05-01

The effect of Zn substitution on the persistent luminescence properties of MgGeO3:Mn2+-Ln3+ (Ln = Eu and Yb) red phosphors was investigated. The intensity of the persistent luminescence of the Eu3+ co-doped phosphors increased with increasing Zn content, whereas that of the Yb3+ co-doped samples decreased. For both series of lanthanide co-doped samples, the thermoluminescence (TL) glow peak shifted to the lower temperature side with increasing Zn content. These persistent luminescence properties were well explained in terms of lowering of the bottom of the conduction band relative to the ground state of the divalent lanthanide ions. Especially, in Eu3+ co-doped system, TL peak shifted from 520 K to 318 K by 50% Zn substitution. The persistent radiance of the (Mg0.5 Zn0.5)GeO3: Mn2+-Eu3+ sample at 1 h after ceasing UV light was 46 times stronger than that of MgGeO3:Mn2+-Eu3+, and 11 times stronger than that of ZnGa2O4: Cr3+ standard deep red persistent phosphor.

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].

Terahertz optical-Hall effect for multiple valley band materials: n-type silicon

International Nuclear Information System (INIS)

Kuehne, P.; Hofmann, T.; Herzinger, C.M.; Schubert, M.

2011-01-01

The optical-Hall effect comprises generalized ellipsometry at long wavelengths on samples with free-charge carriers placed within external magnetic fields. Measurement of the anisotropic magneto-optic response allows for the determination of the free-charge carrier properties including spatial anisotropy. In this work we employ the optical-Hall effect at terahertz frequencies for analysis of free-charge carrier properties in multiple valley band materials, for which the optical free-charge carrier contributions originate from multiple Brillouin-zone conduction or valence band minima or maxima, respectively. We investigate exemplarily the room temperature optical-Hall effect in low phosphorous-doped n-type silicon where free electrons are located in six equivalent conduction-band minima near the X-point. We simultaneously determine their free-charge carrier concentration, mobility, and longitudinal and transverse effective mass parameters.

Self-assembly of an electronically conductive network through microporous scaffolds.

Science.gov (United States)

Sebastian, H Bri; Bryant, Steven L

2017-06-15

Electron transfer spanning significant distances through a microporous structure was established via the self-assembly of an electronically conductive iridium oxide nanowire matrix enveloping the pore walls. Microporous formations were simulated using two scaffold materials of varying physical and chemical properties; paraffin wax beads, and agar gel. Following infiltration into the micropores, iridium nanoparticles self-assembled at the pore wall/ethanol interface. Subsequently, cyclic voltammetry was employed to electrochemically crosslink the metal, erecting an interconnected, and electronically conductive metal oxide nanowire matrix. Electrochemical and spectral characterization techniques confirmed the formation of oxide nanowire matrices encompassing lengths of at least 1.6mm, 400× distances previously achieved using iridium nanoparticles. Nanowire matrices were engaged as biofuel cell anodes, where electrons were donated to the nanowires by a glucose oxidizing enzyme. Copyright © 2017 Elsevier Inc. All rights reserved.

Self-similar variables and the problem of nonlocal electron heat conductivity

International Nuclear Information System (INIS)

Krasheninnikov, S.I.; Bakunin, O.G.

1993-10-01

Self-similar solutions of the collisional electron kinetic equation are obtained for the plasmas with one (1D) and three (3D) dimensional plasma parameter inhomogeneities and arbitrary Z eff . For the plasma parameter profiles characterized by the ratio of the mean free path of thermal electrons with respect to electron-electron collisions, γ T , to the scale length of electron temperature variation, L, one obtains a criterion for determining the effect that tail particles with motion of the non-diffusive type have on the electron heat conductivity. For these conditions it is shown that the use of a open-quotes symmetrizedclose quotes kinetic equation for the investigation of the strong nonlocal effect of suprathermal electrons on the electron heat conductivity is only possible at sufficiently high Z eff (Z eff ≥ (L/γ T ) 1/2 ). In the case of 3D inhomogeneous plasma (spherical symmetry), the effect of the tail electrons on the heat transport is less pronounced since they are spread across the radius r

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

Positron and electron energy bands in several ionic crystals using restricted Hartree-Fock method

Science.gov (United States)

Kunz, A. B.; Waber, J. T.

1981-08-01

Using a restricted Hartree-Fock formalism and suitably localized and symmetrized wave functions, both the positron and electron energy bands were calculated for NaF, MgO and NiO. The lowest positron state at Γ 1 lies above the vacuum level and negative work functions are predicted. Positron annihilation rates were calculated and found to be in good agreement with measured lifetimes.

A tight binding model study of tunneling conductance spectra of spin and orbitally ordered CMR manganites

Science.gov (United States)

Panda, Saswati; Sahoo, D. D.; Rout, G. C.

2018-04-01

We report here a tight binding model for colossal magnetoresistive (CMR) manganites to study the pseudo gap (PG) behavior near Fermi level. In the Kubo-Ohata type DE model, we consider first and second nearest neighbor interactions for transverse spin fluctuations in core band and hopping integrals in conduction band, in the presence of static band Jahn-Teller distortion. The model Hamiltonian is solved using Zubarev's Green's function technique. The electron density of states (DOS) is found out from the Green's functions. We observe clear PG near Fermi level in the electron DOS.

Electronic and optical properties of ZrB{sub 12} and YB{sub 6}. Discussion on electron-phonon coupling

Energy Technology Data Exchange (ETDEWEB)

Teyssier, J.; Kuzmenko, A.; Marel, D. van der; Lortz, R.; Junod, A. [Departement de Physique de la Matiere Condensee, Universite de Geneve, Quai Ernest-Ansermet 24, 1211 Geneve 4 (Switzerland); Filippov, V.; Shitsevalova, N. [Institute for Problems of Materials Science NANU, Kiev (Ukraine)

2006-09-15

We report the optical properties of high-quality single crystals of low temperature superconductors zirconiumdodecaboride ZrB{sub 12} (T{sub c}=5.95 K) and yttrium hexaboride YB{sub 6} (T{sub c}=7.15 K) in the range 6 meV-4.6 eV at room temperature. The experimental optical conductivity was extracted from the analysis of the reflectivity in the infrared range and ellipsometry measurement of the dielectric function in the visible range. The electronic band structure of these compounds was calculated by the self-consistent full-potential LMTO method and used to compute the interband part of the optical conductivity and the plasma frequency {omega}{sub p}. A good agreement was observed between the interband part of the experimental optical conductivities and the band structure calculations. Different methods combining optical spectroscopy, resistivity, specific heat measurements and results of band structure calculations are used to determine the electron-phonon coupling constant. (copyright 2006 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

A comparison of L-band and C-band rf guns as sources for inline-injection systems

International Nuclear Information System (INIS)

Gallardo, J.C.; Kirk, H.G.; Meyerer, T.

1994-12-01

We consider the beam dynamics associated with installing a BNL type 1 1/2 cell L-band or C-band rf gun before two TESLA L-band cryomodules. This system will deliver a 25 MeV electron beam with peak currents on the order of 100 A suitable for further magnetic compression. evaluate the injection systems utilizing the electron beam dynamic code PARMELA from the point of view of minimizing the transverse invariant emittance

Electronic structure and electron momentum density in TiSi

Energy Technology Data Exchange (ETDEWEB)

Ghaleb, A.M. [Department of Physics, College of Science, University of Kirkuk, Kirkuk (Iraq); Mohammad, F.M. [Department of Physics, College of Science, University of Tikreet, Tikreet (Iraq); Sahariya, Jagrati [Department of Physics, University College of Science, M.L. Sukhadia University, Udaipur 313001, Rajasthan (India); Sharma, Mukesh [Physics Division, Forensic Science Laboratory, Jaipur, Rajasthan (India); Ahuja, B.L., E-mail: blahuja@yahoo.com [Department of Physics, University College of Science, M.L. Sukhadia University, Udaipur 313001, Rajasthan (India)

2013-03-01

We report the electron momentum density in titanium monosilicide using {sup 241}Am Compton spectrometer. Experimental Compton profile has been compared with the theoretical profiles computed using linear combination of atomic orbitals (LCAO). The energy bands, density of states and Fermi surface structures of TiSi are reported using the LCAO and the full potential linearized augmented plane wave methods. Theoretical anisotropies in directional Compton profiles are interpreted in terms of energy bands. To confirm the conducting behavior, we also report the real space analysis of experimental Compton profile of TiSi.

A five-picosecond electron pulse from ANL (Argonne National Laboratory) L-Band Linac

International Nuclear Information System (INIS)

Cox, G.L.; Jonah, C.D.; Ficht, D.T.; Mavrogenes, G.S.; Sauer, M.C. Jr.

1989-01-01

The pulse-compression system of the Argonne National Laboratory Chemistry Division L-Band Linac, presented at the 1986 Linear Accelerator Conference at Stanford, California, has been completed. A five-picosecond-wide electron pulse containing 6 x 10 -9 coulomb charge has been achieved. Acceleration parameters and the pulse-width measurement technique are discussed, and future plans for the utilization of this pulse in radiation chemistry studies are presented. 5 refs., 4 figs

Conduction quantization in monolayer MoS2

Science.gov (United States)

Li, T. S.

2016-10-01

We study the ballistic conduction of a monolayer MoS2 subject to a spatially modulated magnetic field by using the Landauer-Buttiker formalism. The band structure depends sensitively on the field strength, and its change has profound influence on the electron conduction. The conductance is found to demonstrate multi-step behavior due to the discrete number of conduction channels. The sharp peak and rectangular structures of the conductance are stretched out as temperature increases, due to the thermal broadening of the derivative of the Fermi-Dirac distribution function. Finally, quantum behavior in the conductance of MoS2 can be observed at temperatures below 10 K.

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.

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 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.

Laser ablation under different electron heat conduction models in inertial confinement fusion

Science.gov (United States)

Li, Shuanggui; Ren, Guoli; Huo, Wen Yi

2018-06-01

In this paper, we study the influence of three different electron heat conduction models on the laser ablation of gold plane target. Different from previous studies, we concentrate on the plasma conditions, the conversion efficiency from laser into soft x rays and the scaling relation of mass ablation, which are relevant to hohlraum physics study in indirect drive inertial confinement fusion. We find that the simulated electron temperature in corona region is sensitive to the electron heat conduction models. For different electron heat conduction models, there are obvious differences in magnitude and spatial profile of electron temperature. For the flux limit model, the calculated conversion efficiency is sensitive to flux limiters. In the laser ablation of gold, most of the laser energies are converted into x rays. So the scaling relation of mass ablation rate is quite different from that of low Z materials.

Anomalous conductivity noise in gapped bilayer graphene heterostructure

Science.gov (United States)

Aamir, Mohammed Ali; Karnatak, Paritosh; Sai, T. Phanindra; Ghosh, Arindam

Bilayer graphene has unique electronic properties - it has a tunable band gap and also, valley symmetry and pseudospin degree of freedom like its single layer counterpart. In this work, we present a study of conductance fluctuations in dual gated bilayer graphene heterostructures by varying the Fermi energy and the band gap independently. At a fixed band gap, we find that the conductance fluctuations obtained by Fermi energy ensemble sampling increase rapidly as the Fermi energy is tuned to charge neutrality point (CNP) whereas the time-dependent conductance fluctuations diminish rapidly. This discrepancy is completely absent at higher number densities, where the transport is expected to be through the 2D bulk of the bilayer system. This observation indicates that near the CNP, electrical transport is highly sensitive to Fermi energy, but becomes progressively immune to time-varying disorder. A possible explanation may involve transport via edge states which becomes the dominant conduction mechanism when the bilayer graphene is gapped and Fermi energy is situated close to the CNP, thereby causing a dimensional crossover from 2D to 1D transport. Our experiment outlines a possible experimental protocol to probe intrinsic topological states in gapped bilayer graphene.

Optical conductivity of the Hubbard model

International Nuclear Information System (INIS)

Vicente Alvarez, J.J.; Balseiro, C.A.; Ceccatto, H.A.

1996-07-01

We study the response to a static electric field (charge stiffness) and the frequency-dependent conductivity of the Hubbard model in a resonant-valence-bond-type paramagnetic phase. This phase is described by means of a charge and spin rotational-invariant approach, based on a mixed fermion-boson representation of the original strongly correlated electrons. We found that the Mott transition at half filling is well described by the charge stiffness behaviour, and that the values for this quantity off half filling agree reasonably well with numerical results. Furthermore, for the frequency-dependent conductivity we trace back the origin of the band which appears inside the Hubbard gap to magnetic pair breaking. This points to a magnetic origin of midinfrared band in high-T c compounds, with no relation to superconductivity. (author). 12 refs, 2 tabs

Advances in X-Band and S-Band Linear Accelerators for Security, NDT, and Other Applications

CERN Document Server

Mishin, Andrey V

2005-01-01

At AS&E High Energy Systems Division, we designed several new advanced high energy electron beam and X-ray sources. Our primary focus has always been in building the world's most portable commercial X-band accelerators. Today, our X-band systems frequently exceed performance of the similar S-band machines, while they are more portable compared to the latter. The new designs of the X-band accelerators in the most practical energy range from 1 MeV to 6 MeV have been tested delivering outstanding results. Seventy 6 MeV X-band linacs systems have been produced. The most compact linac for security is used by AS&E in a self-shielded, Shaped Energy™ cargo screening system. We pioneered using the X-band linear accelerators for CT, producing high quality images of oil pipes and wood logs. An X-band linear accelerator head on a robotic arm has been used for electron beam radiation curing of an odd-shaped graphite composite part. We developed the broad-range 4 MeV to over 10 MeV energy-regulated X-band ...

Determination of band offsets at GaN/single-layer MoS2 heterojunction

KAUST Repository

Tangi, Malleswararao

2016-07-25

We report the band alignment parameters of the GaN/single-layer (SL) MoS2 heterostructure where the GaN thin layer is grown by molecular beam epitaxy on CVD deposited SL-MoS2/c-sapphire. We confirm that the MoS2 is an SL by measuring the separation and position of room temperature micro-Raman E1 2g and A1 g modes, absorbance, and micro-photoluminescence bandgap studies. This is in good agreement with HRTEM cross-sectional analysis. The determination of band offset parameters at the GaN/SL-MoS2 heterojunction is carried out by high-resolution X-ray photoelectron spectroscopy accompanying with electronic bandgap values of SL-MoS2 and GaN. The valence band and conduction band offset values are, respectively, measured to be 1.86 ± 0.08 and 0.56 ± 0.1 eV with type II band alignment. The determination of these unprecedented band offset parameters opens up a way to integrate 3D group III nitride materials with 2D transition metal dichalcogenide layers for designing and modeling of their heterojunction based electronic and photonic devices.

Determination of band offsets at GaN/single-layer MoS2 heterojunction

KAUST Repository

Tangi, Malleswararao; Mishra, Pawan; Ng, Tien Khee; Hedhili, Mohamed N.; Janjua, Bilal; Alias, Mohd Sharizal; Anjum, Dalaver H.; Tseng, Chien-Chih; Shi, Yumeng; Joyce, Hannah J.; Li, Lain-Jong; Ooi, Boon S.

2016-01-01

We report the band alignment parameters of the GaN/single-layer (SL) MoS2 heterostructure where the GaN thin layer is grown by molecular beam epitaxy on CVD deposited SL-MoS2/c-sapphire. We confirm that the MoS2 is an SL by measuring the separation and position of room temperature micro-Raman E1 2g and A1 g modes, absorbance, and micro-photoluminescence bandgap studies. This is in good agreement with HRTEM cross-sectional analysis. The determination of band offset parameters at the GaN/SL-MoS2 heterojunction is carried out by high-resolution X-ray photoelectron spectroscopy accompanying with electronic bandgap values of SL-MoS2 and GaN. The valence band and conduction band offset values are, respectively, measured to be 1.86 ± 0.08 and 0.56 ± 0.1 eV with type II band alignment. The determination of these unprecedented band offset parameters opens up a way to integrate 3D group III nitride materials with 2D transition metal dichalcogenide layers for designing and modeling of their heterojunction based electronic and photonic devices.

Determining the band gap and mean kinetic energy of atoms from reflection electron energy loss spectra

International Nuclear Information System (INIS)

Vos, M.; Marmitt, G. G.; Finkelstein, Y.; Moreh, R.

2015-01-01

Reflection electron energy loss spectra from some insulating materials (CaCO 3 , Li 2 CO 3 , and SiO 2 ) taken at relatively high incoming electron energies (5–40 keV) are analyzed. Here, one is bulk sensitive and a well-defined onset of inelastic excitations is observed from which one can infer the value of the band gap. An estimate of the band gap was obtained by fitting the spectra with a procedure that includes the recoil shift and recoil broadening affecting these measurements. The width of the elastic peak is directly connected to the mean kinetic energy of the atom in the material (Doppler broadening). The experimentally obtained mean kinetic energies of the O, C, Li, Ca, and Si atoms are compared with the calculated ones, and good agreement is found, especially if the effect of multiple scattering is taken into account. It is demonstrated experimentally that the onset of the inelastic excitation is also affected by Doppler broadening. Aided by this understanding, we can obtain a good fit of the elastic peak and the onset of inelastic excitations. For SiO 2 , good agreement is obtained with the well-established value of the band gap (8.9 eV) only if it is assumed that the intensity near the edge scales as (E − E gap ) 1.5 . For CaCO 3 , the band gap obtained here (7 eV) is about 1 eV larger than the previous experimental value, whereas the value for Li 2 CO 3 (7.5 eV) is the first experimental estimate

Electronic Conductivity of Polypyrrole−Dodecyl Benzene Sulfonate Complexes

DEFF Research Database (Denmark)

West, Keld; Bay, Lasse; Nielsen, Martin Meedom

2004-01-01

The electronic conductivity of the electroactive polymer polypyrrole-dodecyl benzene sulfonate (PPy-DBS) has been characterized as function of the redox level. The polymer was synthesized with different isomers of the dopant anions: the common mixed DBS tenside and three well-defined synthetic...

Electrical conductivity of hydrogen shocked to megabar pressures

International Nuclear Information System (INIS)

Weir, S.T.; Nellis, W.J.; Mitchell, A.C.

1993-08-01

The properties of ultra-high pressure hydrogen have been the subject of much experimental and theoretical study. Of particular interest is the pressure-induced insulator-to-metal transition of hydrogen which, according to recent theoretical calculations, is predicted to occur by band-overlap in the pressure range of 1.5-3.0 Mbars on the zero temperature isotherm. Extremely high pressures are required for metallization since the low-pressure band gap is about 15 eV. Recent static-pressure diamond anvil cell experiments have searched for evidence of an insulator-to-metal transition, but no conclusive evidence for such a transition has yet been supplied. Providing conclusive evidence for hydrogen metallization is difficult because no technique has yet been developed for performing static high-pressure electrical conductivity experiments at megabar pressures. The authors report here on electrical conductivity experiments performed on H 2 and D 2 multi-shocked to megabar pressures. Electrical conductivities of dense fluid hydrogen at these pressures and temperatures reached are needed for calculations of the magnetic fields of Jupiter and Saturn, the magnetic fields being generated by convective dynamos of hot, dense, semiconducting fluid hydrogen. Also, since electrical conduction at the pressure-temperature conditions being studied is due to the thermal excitation of charge carriers across the electronic band gap, these experiments yield valuable information on the width of the band gap at high densities

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

NARCIS (Netherlands)

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

1996-01-01

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

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

NARCIS (Netherlands)

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

1996-01-01

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

Mixed ionic-electronic conduction in Ni doped lanthanum gallate perovskites

Energy Technology Data Exchange (ETDEWEB)

Long, N.J.; Tuller, H.L.

1998-07-01

Lanthanum gallate is a promising material for monolithic fuel cells or oxygen pumps, i.e., one in which the electrolyte and electrodes are formed from a common phase. The authors have investigated La{sub 1{minus}x}Sr{sub x}Ga{sub 1{minus}y}Ni{sub y}O{sub 3} (LSGN{sub x{minus}y}) with x = 0.1 and y = 0.2 and 0.5 as a potential cathode material for such an electrochemical device. The {sigma}(PO{sub 2},T) for LSGN{sub 10--20} points to a p-type electronic conductivity at high PO{sub 2} and predominantly ionic conductivity at low PO{sub 2}. LSGN{sub 10-50} has an electronic conductivity suitable for SOFC applications of approximately 50 S/cm in air at high temperature. AC impedance spectroscopy on an electron blocking cell of the form M/LSG/LSGN/LSG/M was used to isolate the ionic conductivity in the LSGN{sub 10--20} material. The ionic conductivity was found to have a similar magnitude and activation energy to that of undoped LSG material with {sigma}{sub i} = 0.12 S/cm at 800 C and E{sub A} = 1.0 {+-} 0.1 eV. Thermal expansion measurements on the LSGN materials were characterized as a function of temperature and dopant level and were found to match that of the electrolyte under operating conditions.

Retrospective biodosimetry with small tooth enamel samples using K-Band and X-Band

International Nuclear Information System (INIS)

Gomez, Jorge A.; Kinoshita, Angela; Leonor, Sergio J.; Belmonte, Gustavo C.; Baffa, Oswaldo

2011-01-01

In an attempt to make the in vitro electron spin resonance (ESR) retrospective dosimetry of the tooth enamel a lesser invasive method, experiments using X-Band and K-Band were performed, aiming to determine conditions that could be used in cases of accidental exposures. First, a small prism from the enamel was removed and ground with an agate mortar and pestle until particles reach a diameter of approximately less than 0.5 mm. This enamel extraction process resulted in lower signal artifact compared with the direct enamel extraction performed with a diamond burr abrasion. The manual grinding of the enamel does not lead to any induced ESR signal artifact, whereas the use of a diamond burr at low speed produces a signal artifact equivalent to the dosimetric signal induced by a dose of 500 mGy of gamma irradiation. A mass of 25 mg of enamel was removed from a sound molar tooth previously irradiated in vitro with a dose of 100 mGy. This amount of enamel was enough to detect the dosimetric signal in a standard X-Band spectrometer. However using a K-Band spectrometer, samples mass between 5 and 10 mg were sufficient to obtain the same sensitivity. An overall evaluation of the uncertainties involved in the process in this and other dosimetric assessments performed at our laboratory indicates that it is possible at K-Band to estimate a 100 mGy dose with 25% accuracy. In addition, the use of K-Band also presented higher sensitivity and allowed the use of smaller sample mass in comparison with X-Band. Finally, the restoration process performed on a tooth after extraction of the 25 mg of enamel is described. This was conducted by dental treatment using photopolymerizable resin which enabled complete recovery of the tooth from the functional and aesthetic viewpoint showing that this procedure can be minimally invasive.

Retrospective biodosimetry with small tooth enamel samples using K-Band and X-Band

Energy Technology Data Exchange (ETDEWEB)

Gomez, Jorge A. [Departamento de Fisica, FFCLRP, Universidade de Sao Paulo, 14040-901 Ribeirao Preto, Sao Paulo (Brazil); Kinoshita, Angela [Departamento de Fisica, FFCLRP, Universidade de Sao Paulo, 14040-901 Ribeirao Preto, Sao Paulo (Brazil); Universidade Sagrado Coracao - USC, 17011-160 Bauru, Sao Paulo (Brazil); Leonor, Sergio J. [Departamento de Fisica, FFCLRP, Universidade de Sao Paulo, 14040-901 Ribeirao Preto, Sao Paulo (Brazil); Belmonte, Gustavo C. [Universidade Sagrado Coracao - USC, 17011-160 Bauru, Sao Paulo (Brazil); Baffa, Oswaldo, E-mail: baffa@usp.br [Departamento de Fisica, FFCLRP, Universidade de Sao Paulo, 14040-901 Ribeirao Preto, Sao Paulo (Brazil)

2011-09-15

In an attempt to make the in vitro electron spin resonance (ESR) retrospective dosimetry of the tooth enamel a lesser invasive method, experiments using X-Band and K-Band were performed, aiming to determine conditions that could be used in cases of accidental exposures. First, a small prism from the enamel was removed and ground with an agate mortar and pestle until particles reach a diameter of approximately less than 0.5 mm. This enamel extraction process resulted in lower signal artifact compared with the direct enamel extraction performed with a diamond burr abrasion. The manual grinding of the enamel does not lead to any induced ESR signal artifact, whereas the use of a diamond burr at low speed produces a signal artifact equivalent to the dosimetric signal induced by a dose of 500 mGy of gamma irradiation. A mass of 25 mg of enamel was removed from a sound molar tooth previously irradiated in vitro with a dose of 100 mGy. This amount of enamel was enough to detect the dosimetric signal in a standard X-Band spectrometer. However using a K-Band spectrometer, samples mass between 5 and 10 mg were sufficient to obtain the same sensitivity. An overall evaluation of the uncertainties involved in the process in this and other dosimetric assessments performed at our laboratory indicates that it is possible at K-Band to estimate a 100 mGy dose with 25% accuracy. In addition, the use of K-Band also presented higher sensitivity and allowed the use of smaller sample mass in comparison with X-Band. Finally, the restoration process performed on a tooth after extraction of the 25 mg of enamel is described. This was conducted by dental treatment using photopolymerizable resin which enabled complete recovery of the tooth from the functional and aesthetic viewpoint showing that this procedure can be minimally invasive.

High Peak Power Test and Evaluation of S-band Waveguide Switches

Science.gov (United States)

Nassiri, A.; Grelick, A.; Kustom, R. L.; White, M.

1997-05-01

The injector and source of particles for the Advanced Photon Source is a 2856-MHz S-band electron-positron linear accelerator (linac) which produces electrons with energies up to 650 MeV or positrons with energies up to 450 MeV. To improve the linac rf system availability, an additional modulator-klystron subsystem is being constructed to provide a switchable hot spare unit for each of the five exsisting S-band transmitters. The switching of the transmitters will require the use of SF6-pressurized S-band waveguide switches at a peak operating power of 35 MW. Such rf switches have been successfully operated at other accelerator facilities but at lower peak powers. A test stand has been set up at the Stanford Linear Accelerator Center (SLAC) Klystron Factory to conduct tests comparing the power handling characteristics of two WR-284 and one WR-340 switches. Test results are presented and their implications for the design of the switching system are discussed.

Tunable Electron-Electron Interactions in LaAlO_{3}/SrTiO_{3} Nanostructures

Directory of Open Access Journals (Sweden)

Guanglei Cheng

2016-12-01

Full Text Available The interface between the two complex oxides LaAlO_{3} and SrTiO_{3} has remarkable properties that can be locally reconfigured between conducting and insulating states using a conductive atomic force microscope. Prior investigations of “sketched” quantum dot devices revealed a phase in which electrons form pairs, implying a strongly attractive electron-electron interaction. Here, we show that these devices with strong electron-electron interactions can exhibit a gate-tunable transition from a pair-tunneling regime to a single-electron (Andreev bound state tunneling regime where the interactions become repulsive. The electron-electron interaction sign change is associated with a Lifshitz transition where the d_{xz} and d_{yz} bands start to become occupied. This electronically tunable electron-electron interaction, combined with the nanoscale reconfigurability of this system, provides an interesting starting point towards solid-state quantum simulation.

Temperature-Induced Large Broadening and Blue Shift in the Electronic Band Structure and Optical Absorption of Methylammonium Lead Iodide Perovskite.

Science.gov (United States)

Yang, Jia-Yue; Hu, Ming

2017-08-17

The power conversion efficiency of hybrid halide perovskite solar cells is profoundly influenced by the operating temperature. Here we investigate the temperature influence on the electronic band structure and optical absorption of cubic CH 3 NH 3 PbI 3 from first-principles by accounting for both the electron-phonon interaction and thermal expansion. Within the framework of density functional perturbation theory, the electron-phonon coupling induces slightly enlarged band gap and strongly broadened electronic relaxation time as temperature increases. The large broadening effect is mainly due to the presence of cation organic atoms. Consequently, the temperature-dependent absorption peak exhibits blue-shift position, decreased amplitude, and broadened width. This work uncovers the atomistic origin of temperature influence on the optical absorption of cubic CH 3 NH 3 PbI 3 and can provide guidance to design high-performance hybrid halide perovskite solar cells at different operating temperatures.

The electronic structure of core states under extreme compressions

International Nuclear Information System (INIS)

Straub, G.K.

1992-01-01

At normal density and for modest compressions, the electronic structure of a metal can be accurately described by treating the conduction electrons and their interactions with the usual methods of band theory. The core electrons remain essentially the same as for an isolated free atom and do not participate in the bonding forces responsible for creating a condensed phase. As the density increases, the core electrons begin to ''see'' one another as the overlap of the tails of wave functions can no longer be neglected. The electronic structure of the core electrons is responsible for an effective repulsive interaction that eventually becomes free-electron-like at very high compressions. The electronic structure of the interacting core electrons may be treated in a simple manner using the Atomic Surface Method (ASM). The ASM is a first-principles treatment of the electronic structure involving a rigorous integration of the Schroedinger equation within the atomic-sphere approximation. Solid phase wave functions are constructed from isolated atom wave functions and the band width W l and the center of gravity of the band C l are obtained from simple formulas. The ASM can also utilize analytic forms of the atomic wave functions and thus provide direct functional dependence of various aspects of the electronic structure. Of particular use in understanding the behavior of the core electrons, the ASM provides the ability to analytically determine the density dependence of the band widths and positions. The process whereby core states interact with one another is best viewed as the formation of narrow electron bands formed from atomic states. As the core-core overlap increases, the bands increase in width and mean energy. In Sec.3 this picture is further developed and from the ASM one obtains the analytic dependence on density of the relative motion of the different bands. Also in Sec. 3 is a discussion of the transition to free electron bands

Toxicity of metal oxide nanoparticles in Escherichia coli correlates with conduction band and hydration energies.

Science.gov (United States)

Kaweeteerawat, Chitrada; Ivask, Angela; Liu, Rong; Zhang, Haiyuan; Chang, Chong Hyun; Low-Kam, Cecile; Fischer, Heidi; Ji, Zhaoxia; Pokhrel, Suman; Cohen, Yoram; Telesca, Donatello; Zink, Jeffrey; Mädler, Lutz; Holden, Patricia A; Nel, Andre; Godwin, Hilary

2015-01-20

Metal oxide nanoparticles (MOx NPs) are used for a host of applications, such as electronics, cosmetics, construction, and medicine, and as a result, the safety of these materials to humans and the environment is of considerable interest. A prior study of 24 MOx NPs in mammalian cells revealed that some of these materials show hazard potential. Here, we report the growth inhibitory effects of the same series of MOx NPs in the bacterium Escherichia coli and show that toxicity trends observed in E. coli parallel those seen previously in mammalian cells. Of the 24 materials studied, only ZnO, CuO, CoO, Mn2O3, Co3O4, Ni2O3, and Cr2O3 were found to exert significant growth inhibitory effects; these effects were found to relate to membrane damage and oxidative stress responses in minimal trophic media. A correlation of the toxicological data with physicochemical parameters of MOx NPs revealed that the probability of a MOx NP being toxic increases as the hydration enthalpy becomes less negative and as the conduction band energy approaches those of biological molecules. These observations are consistent with prior results observed in mammalian cells, revealing that mechanisms of toxicity of MOx NPs are consistent across two very different taxa. These results suggest that studying nanotoxicity in E. coli may help to predict toxicity patterns in higher organisms.

A simplified approach to the band gap correction of defect formation energies: Al, Ga, and In-doped ZnO

Science.gov (United States)

Saniz, R.; Xu, Y.; Matsubara, M.; Amini, M. N.; Dixit, H.; Lamoen, D.; Partoens, B.

2013-01-01

The calculation of defect levels in semiconductors within a density functional theory approach suffers greatly from the band gap problem. We propose a band gap correction scheme that is based on the separation of energy differences in electron addition and relaxation energies. We show that it can predict defect levels with a reasonable accuracy, particularly in the case of defects with conduction band character, and yet is simple and computationally economical. We apply this method to ZnO doped with group III elements (Al, Ga, In). As expected from experiment, the results indicate that Zn substitutional doping is preferred over interstitial doping in Al, Ga, and In-doped ZnO, under both zinc-rich and oxygen-rich conditions. Further, all three dopants act as shallow donors, with the +1 charge state having the most advantageous formation energy. Also, doping effects on the electronic structure of ZnO are sufficiently mild so as to affect little the fundamental band gap and lowest conduction bands dispersion, which secures their n-type transparent conducting behavior. A comparison with the extrapolation method based on LDA+U calculations and with the Heyd-Scuseria-Ernzerhof hybrid functional (HSE) shows the reliability of the proposed scheme in predicting the thermodynamic transition levels in shallow donor systems.

Investigation on the optimal magnetic field of a cusp electron gun for a W-band gyro-TWA

Science.gov (United States)

Zhang, Liang; He, Wenlong; Donaldson, Craig R.; Cross, Adrian W.

2018-05-01

High efficiency and broadband operation of a gyrotron traveling wave amplifier (gyro-TWA) require a high-quality electron beam with low-velocity spreads. The beam velocity spreads are mainly due to the differences of the electric and magnetic fields that the electrons withstand the electron gun. This paper investigates the possibility to decouple the design of electron gun geometry and the magnet system while still achieving optimal results, through a case study of designing a cusp electron gun for a W-band gyro-TWA. A global multiple-objective optimization routing was used to optimize the electron gun geometry for different predefined magnetic field profiles individually. Their results were compared and the properties of the required magnetic field profile are summarized.

First–principle calculation of the elastic, band structure, electronic states, and optical properties of Cu–doped ZnS nanolayers

Energy Technology Data Exchange (ETDEWEB)

Lahiji, Mohammadreza Askaripour, E-mail: m.a.lahijiii@gmail.com [Department of applied mathematics, Astaneh Ashrafieh Branch, Islamic Azad University, Astaneh Ashrafieh (Iran, Islamic Republic of); Ziabari, Ali Abdolahzadeh, E-mail: ali.abd.ziabari@gmail.com [Nano Research Lab, Lahijan Branch, Islamic Azad University, P.O. Box: 1616, Lahijan (Iran, Islamic Republic of)

2016-11-15

The structural, elastic, electronic, and optical properties of undoped and Cu–doped ZnS nanostructured layers have been studied in the zincblende (ZB) phase, by first–principle approach. Density functional theory (DFT) has been employed to calculate the fundamental properties of the layers using full–potential linearized augmented plane–wave (FPLAPW) method. Mechanical analysis revealed that the bulk modulus increases with the increase of Cu content. Cu doping was found to reduce the band gap value of the material. In addition, DOS effective mass of the electrons and heavy holes was evaluated. Adding Cu caused the decrement/increment of transmission/reflectance of nanolayers in the UV–vis region. The substitution by Cu increased the intensity of the peaks, and a slight red shift was observed in the absorption peak. Moreover, the static dielectric constant, and static refractive index increased with Cu content. The optical conductivity also followed a similar trend to that of the dielectric constants. Energy loss function of the modeled compounds was also evaluated. All calculated parameters were compared with the available experimental and other theoretical results.

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.

Thermal conductivity of electron-irradiated graphene

Science.gov (United States)

Weerasinghe, Asanka; Ramasubramaniam, Ashwin; Maroudas, Dimitrios

2017-10-01

We report results of a systematic analysis of thermal transport in electron-irradiated, including irradiation-induced amorphous, graphene sheets based on nonequilibrium molecular-dynamics simulations. We focus on the dependence of the thermal conductivity, k, of the irradiated graphene sheets on the inserted irradiation defect density, c, as well as the extent of defect passivation with hydrogen atoms. While the thermal conductivity of irradiated graphene decreases precipitously from that of pristine graphene, k0, upon introducing a low vacancy concentration, c reduction of the thermal conductivity with the increasing vacancy concentration exhibits a weaker dependence on c until the amorphization threshold. Beyond the onset of amorphization, the dependence of thermal conductivity on the vacancy concentration becomes significantly weaker, and k practically reaches a plateau value. Throughout the range of c and at all hydrogenation levels examined, the correlation k = k0(1 + αc)-1 gives an excellent description of the simulation results. The value of the coefficient α captures the overall strength of the numerous phonon scattering centers in the irradiated graphene sheets, which include monovacancies, vacancy clusters, carbon ring reconstructions, disorder, and a rough nonplanar sheet morphology. Hydrogen passivation increases the value of α, but the effect becomes very minor beyond the amorphization threshold.

Bending of conjugated molecular wires and its effect on electron conduction properties

International Nuclear Information System (INIS)

Das, Bidisa

2010-01-01

The electronic structure and electron transport properties of simple conjugated molecular wires like oligophenylene ethynylene (OPE) and oligophenylene vinylene (OPV) are studied under compression. If artificially confined to a given shorter length, the oligomers tend to bend and bending causes a loss in the overlap of the conjugated molecular orbitals. Theoretical modeling of electronic transport has been carried out for all undistorted and compressed OPE/OPV oligomers. OPV exists in step-like or V-like conformations and they have the same stability with very similar frontier molecular orbitals. The conductances of these molecular wires are calculated when inserted between two gold probes and the conductances for OPV are found to be comparable to OPE when the interfaces are same. The conductance decreases with bending due to the gradual loss in overlap of the molecular orbitals. It is also found that the conductances of the molecular wires decrease very strongly if the terminal sulfur atom is simultaneously bonded to hydrogen and a gold surface, thus reflecting the importance of the interface in determining the conductance in two-probe systems. From the conductance studies it may be concluded that if one or more benzene rings of OPE are rotated from coplanar conditions, the orthogonal molecular orbitals may completely block the electronic transport, rendering the molecule insulating.

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

NARCIS (Netherlands)

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

1995-01-01

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

Density changes in shear bands of a metallic glass determined by correlative analytical transmission electron microscopy

Energy Technology Data Exchange (ETDEWEB)

Rösner, Harald, E-mail: rosner@uni-muenster.de [Institut für Materialphysik, Westfälische Wilhelms-Universität Münster, Wilhelm-Klemm-Strasse 10, D-48149 Münster (Germany); Peterlechner, Martin [Institut für Materialphysik, Westfälische Wilhelms-Universität Münster, Wilhelm-Klemm-Strasse 10, D-48149 Münster (Germany); Kübel, Christian [Karlsruhe Institute of Technology (KIT), Institute of Nanotechnology (INT), Hermann-von-Helmholtz-Platz 1, D-76344 Eggenstein-Leopoldshafen (Germany); Karlsruhe Nano Micro Facility (KNMF), Karlsruhe Institute of Technology (KIT), D-76344 Eggenstein-Leopoldshafen (Germany); Schmidt, Vitalij [Institut für Materialphysik, Westfälische Wilhelms-Universität Münster, Wilhelm-Klemm-Strasse 10, D-48149 Münster (Germany); Wilde, Gerhard [Institut für Materialphysik, Westfälische Wilhelms-Universität Münster, Wilhelm-Klemm-Strasse 10, D-48149 Münster (Germany); Institute of Nanochemistry and Nanobiology, School of Environmental and Chemical Engineering, Shanghai University, Shanghai 200444 (China)

2014-07-01

Density changes between sheared zones and their surrounding amorphous matrix as a result of plastic deformation in a cold-rolled metallic glass (melt-spun Al{sub 88}Y{sub 7}Fe{sub 5}) were determined using high-angle annular dark-field (HAADF) detector intensities supplemented by electron-energy loss spectroscopy (EELS), energy-dispersive X-ray (EDX) and nano-beam diffraction analyses. Sheared zones or shear bands were observed as regions of bright or dark contrast arising from a higher or lower density relative to the matrix. Moreover, abrupt contrast changes from bright to dark and vice versa were found within individual shear bands. We associate the decrease in density mainly with an enhanced free volume in the shear bands and the increase in density with concomitant changes of the mass. This interpretation is further supported by changes in the zero loss and Plasmon signal originating from such sites. The limits of this new approach are discussed. - Highlights: • We describe a novel approach for measuring densities in shear bands of metallic glasses. • The linear relation of the dark-field intensity I/I{sub 0} and the mass thickness ρt was used. • Individual shear bands showed abrupt contrast changes from bright to dark and vice versa. • Density changes ranging from about −10% to +6% were found for such shear bands. • Mixtures of amorphous/medium range ordered domains were found within the shear bands.

Multi-band tight-binding calculation of electronic transport in Fe/trans-polyacetylene/Fe tunnel junctions

International Nuclear Information System (INIS)

Abedi Ravan, B

2012-01-01

In this paper, the electronic transport characteristics of Fe/trans-polyacetylene/Fe magnetic tunnel junctions (MTJs) are investigated using multi-band tight-binding calculations within the framework of nonequilibrium Green function theory. A CH 2 radical is added to different positions on the polymer chain and its effects on the tunnelling magnetoresistance of the MTJ are studied. The ferromagnetic electrodes are assumed to be single-band and their tight-binding parameters are chosen in such a way as to simulate the ab initio density functional calculations of the band structure of bcc-Fe along its [001] crystallographic direction. In building the Hamiltonian of the trans-polyacetylene (t-PA) chain, we have assumed an s orbital on the H atoms and one s and three p(p x ,p y ,p z ) orbitals on the C atoms, and the dimerization effects are taken into account. It is found that moving the radical out of the centre of the polymer chain enhances the tunnelling magnetoresistance of the MTJ.

Single-Band and Dual-Band Infrared Detectors

Science.gov (United States)

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

2017-01-01

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

Electron Raman scattering in a cylindrical quantum dot

International Nuclear Information System (INIS)

Zhong Qinghu; Yi Xuehua

2012-01-01

Electron Raman scattering (ERS) is investigated in a CdS cylindrical quantum dot (QD). The differential cross section is calculated as a function of the scattering frequency and the size of the QD. Single parabolic conduction and valence bands are assumed, and singularities in the spectrum are found and interpreted. The selection rules for the processes are also studied. The ERS studied here can be used to provide direct information about the electron band structure of these systems. (semiconductor physics)

Electronic properties of epitaxial 6H silicon carbide

International Nuclear Information System (INIS)

Wessels, B.W.; Gatos, H.C.

1977-01-01

The electrical conductivity and Hall coefficient were measured in the temperature range from 78 to 900 K for n-type epitaxially grown 6H silicon carbide. A many-valley model of the conduction band was used in the analysis of electron concentration as a function of temperature. From this analysis, the density of states mass to the free electron mass ratio per ellipsoid was calculated to be 0.45. It was estimated that the constant energy surface of the conduction band consists of three ellipsoids. The ionization energy of the shallowest nitrogen donor was found to be 105 meV, when the valley-orbit interaction was taken into account. The electron scattering mechanisms in the epitaxial layers were analyzed and it was shown that the dominant mechanism limiting electron mobility at high temperatures is inter-valley scattering and at low temperatures (200K), impurity and space charge scattering. A value of 360 cm 2 /V sec was calculated for the maximum room temperature Hall mobility expected for electrons in pure 6H SiC. The effect of epitaxial growth temperature on room temperature Hall mobility was also investigated. (author)

Stretchable, Twisted Conductive Microtubules for Wearable Computing, Robotics, Electronics, and Healthcare

OpenAIRE

Thanh Nho Do; Yon Visell

2017-01-01

Stretchable and flexible multifunctional electronic components, including sensors and actuators, have received increasing attention in robotics, electronics, wearable, and healthcare applications. Despite advances, it has remained challenging to design analogs of many electronic components to be highly stretchable, to be efficient to fabricate, and to provide control over electronic performance. Here, we describe highly elastic sensors and interconnects formed from thin, twisted conductive mi...

Influence of defects on the absorption edge of InN thin films: The band gap value

Science.gov (United States)

Thakur, J. S.; Danylyuk, Y. V.; Haddad, D.; Naik, V. M.; Naik, R.; Auner, G. W.

2007-07-01

We investigate the optical-absorption spectra of InN thin films whose electron density varies from ˜1017tõ1021cm-3 . The low-density films are grown by molecular-beam-epitaxy deposition while highly degenerate films are grown by plasma-source molecular-beam epitaxy. The optical-absorption edge is found to increase from 0.61to1.90eV as the carrier density of the films is increased from low to high density. Since films are polycrystalline and contain various types of defects, we discuss the band gap values by studying the influence of electron degeneracy, electron-electron, electron-ionized impurities, and electron-LO-phonon interaction self-energies on the spectral absorption coefficients of these films. The quasiparticle self-energies of the valence and conduction bands are calculated using dielectric screening within the random-phase approximation. Using one-particle Green’s function analysis, we self-consistently determine the chemical potential for films by coupling equations for the chemical potential and the single-particle scattering rate calculated within the effective-mass approximation for the electron scatterings from ionized impurities and LO phonons. By subtracting the influence of self-energies and chemical potential from the optical-absorption edge energy, we estimate the intrinsic band gap values for the films. We also determine the variations in the calculated band gap values due to the variations in the electron effective mass and static dielectric constant. For the lowest-density film, the estimated band gap energy is ˜0.59eV , while for the highest-density film, it varies from ˜0.60tõ0.68eV depending on the values of electron effective mass and dielectric constant.

Influence of energy bands on the Hall effect in degenerate semiconductors

International Nuclear Information System (INIS)

Wu, Chhi-Chong; Tsai, Jensan

1989-01-01

The influence of energy bands on the Hall effect and transverse magnetoresistance has been investigated according to the scattering processes of carriers in degenerate semiconductors such as InSb. Results show that the Hall angle, Hall coefficient, and transverse magnetoresistance depend on the dc magnetic field for both parabolic and nonparabolic band structures of semiconductors and also depend on the scattering processes of carriers in semiconductors due to the energy-dependent relaxation time. From their numerical analysis for the Hall effect, it is shown that the conduction electrons in degenerate semiconductors play a major role for the carrier transport phenomenon. By comparing with experimental data of the transverse magnetoresistance, it shows that the nonparabolic band model is better in agreement with the experimental work than the parabolic band model of semiconductors

Dynamic conductivity modified by impurity resonant states in doping three-dimensional Dirac semimetals

Science.gov (United States)

Li, Shuai; Wang, Chen; Zheng, Shi-Han; Wang, Rui-Qiang; Li, Jun; Yang, Mou

2018-04-01

The impurity effect is studied in three-dimensional Dirac semimetals in the framework of a T-matrix method to consider the multiple scattering events of Dirac electrons off impurities. It has been found that a strong impurity potential can significantly restructure the energy dispersion and the density of states of Dirac electrons. An impurity-induced resonant state emerges and significantly modifies the pristine optical response. It is shown that the impurity state disturbs the common longitudinal optical conductivity by creating either an optical conductivity peak or double absorption jumps, depending on the relative position of the impurity band and the Fermi level. More importantly, these conductivity features appear in the forbidden region between the Drude and interband transition, completely or partially filling the Pauli block region of optical response. The underlying physics is that the appearance of resonance states as well as the broadening of the bands leads to a more complicated selection rule for the optical transitions, making it possible to excite new electron-hole pairs in the forbidden region. These features in optical conductivity provide valuable information to understand the impurity behaviors in 3D Dirac materials.

Electron Transfer between Electrically Conductive Minerals and Quinones

Directory of Open Access Journals (Sweden)

Olga Taran

2017-07-01

Full Text Available Long-distance electron transfer in marine environments couples physically separated redox half-reactions, impacting biogeochemical cycles of iron, sulfur and carbon. Bacterial bio-electrochemical systems that facilitate electron transfer via conductive filaments or across man-made electrodes are well-known, but the impact of abiotic currents across naturally occurring conductive and semiconductive minerals is poorly understood. In this paper I use cyclic voltammetry to explore electron transfer between electrodes made of common iron minerals (magnetite, hematite, pyrite, pyrrhotite, mackinawite, and greigite, and hydroquinones—a class of organic molecules found in carbon-rich sediments. Of all tested minerals, only pyrite and magnetite showed an increase in electric current in the presence of organic molecules, with pyrite showing excellent electrocatalytic performance. Pyrite electrodes performed better than commercially available glassy carbon electrodes and showed higher peak currents, lower overpotential values and a smaller separation between oxidation and reduction peaks for each tested quinone. Hydroquinone oxidation on pyrite surfaces was reversible, diffusion controlled, and stable over a large number of potential cycles. Given the ubiquity of both pyrite and quinones, abiotic electron transfer between minerals and organic molecules is likely widespread in Nature and may contribute to several different phenomena, including anaerobic respiration of a wide variety of microorganisms in temporally anoxic zones or in the proximity of hydrothermal vent chimneys, as well as quinone cycling and the propagation of anoxic zones in organic rich waters. Finally, interactions between pyrite and quinones make use of electrochemical gradients that have been suggested as an important source of energy for the origins of life on Earth. Ubiquinones and iron sulfide clusters are common redox cofactors found in electron transport chains across all domains

Electron Transfer Between Electrically Conductive Minerals and Quinones

Science.gov (United States)

Taran, Olga

2017-07-01

Long-distance electron transfer in marine environments couples physically separated redox half-reactions, impacting biogeochemical cycles of iron, sulfur and carbon. Bacterial bio-electrochemical systems that facilitate electron transfer via conductive filaments or across man-made electrodes are well known, but the impact of abiotic currents across naturally occurring conductive and semiconducitve minerals is poorly understood. In this paper I use cyclic voltammetry to explore electron transfer between electrodes made of common iron minerals (magnetite, hematite, pyrite, pyrrhotite, mackinawite and greigite), and hydroquinones - a class of organic molecules found in carbon-rich sediments. Of all tested minerals, only pyrite and magnetite showed an increase in electric current in the presence of organic molecules, with pyrite showing excellent electrocatalytic performance. Pyrite electrodes performed better than commercially available glassy carbon electrodes and showed higher peak currents, lower overpotential values and a smaller separation between oxidation and reduction peaks for each tested quinone. Hydroquinone oxidation on pyrite surfaces was reversible, diffusion controlled, and stable over a large number of potential cycles. Given the ubiquity of both pyrite and quinones, abiotic electron transfer between minerals and organic molecules is likely widespread in Nature and may contribute to several different phenomena, including anaerobic respiration of a wide variety of microorganisms in temporally anoxic zones or in the proximity of hydrothermal vent chimneys, as well as quinone cycling and the propagation of anoxic zones in organic rich waters. Finally, interactions between pyrite and quinones make use of electrochemical gradients that have been suggested as an important source of energy for the origins of life on Earth. Ubiquinones and iron sulfide clusters are common redox cofactors found in electron transport chains across all domains of life and

Thermoelectric band engineering: The role of carrier scattering

Science.gov (United States)

Witkoske, Evan; Wang, Xufeng; Lundstrom, Mark; Askarpour, Vahid; Maassen, Jesse

2017-11-01

Complex electronic band structures, with multiple valleys or bands at the same or similar energies, can be beneficial for thermoelectric performance, but the advantages can be offset by inter-valley and inter-band scattering. In this paper, we demonstrate how first-principles band structures coupled with recently developed techniques for rigorous simulation of electron-phonon scattering provide the capabilities to realistically assess the benefits and trade-offs associated with these materials. We illustrate the approach using n-type silicon as a model material and show that intervalley scattering is strong. This example shows that the convergence of valleys and bands can improve thermoelectric performance, but the magnitude of the improvement depends sensitively on the relative strengths of intra- and inter-valley electron scattering. Because anisotropy of the band structure also plays an important role, a measure of the benefit of band anisotropy in the presence of strong intervalley scattering is presented.

Zero-phonon line and fine structure of the yellow luminescence band in GaN

Science.gov (United States)

Reshchikov, M. A.; McNamara, J. D.; Zhang, F.; Monavarian, M.; Usikov, A.; Helava, H.; Makarov, Yu.; Morkoç, H.

2016-07-01

The yellow luminescence band was studied in undoped and Si-doped GaN samples by steady-state and time-resolved photoluminescence. At low temperature (18 K), the zero-phonon line (ZPL) for the yellow band is observed at 2.57 eV and attributed to electron transitions from a shallow donor to a deep-level defect. At higher temperatures, the ZPL at 2.59 eV emerges, which is attributed to electron transitions from the conduction band to the same defect. In addition to the ZPL, a set of phonon replicas is observed, which is caused by the emission of phonons with energies of 39.5 meV and 91.5 meV. The defect is called the YL1 center. The possible identity of the YL1 center is discussed. The results indicate that the same defect is responsible for the strong YL1 band in undoped and Si-doped GaN samples.

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.

Digital base-band rf control system for the superconducting Darmstadt electron linear accelerator

Directory of Open Access Journals (Sweden)

M. Konrad

2012-05-01

Full Text Available The accelerating field in superconducting cavities has to be stabilized in amplitude and phase by a radio-frequency (rf control system. Because of their high loaded quality factor superconducting cavities are very susceptible for microphonics. To meet the increased requirements with respect to accuracy, availability, and diagnostics, the previous analog rf control system of the superconducting Darmstadt electron linear accelerator S-DALINAC has been replaced by a digital rf control system. The new hardware consists of two components: An rf module that converts the signal from the cavity down to the base-band and a field-programmable gate array board including a soft CPU that carries out the signal processing steps of the control algorithm. Different algorithms are used for normal-conducting and superconducting cavities. To improve the availability of the control system, techniques for automatic firmware and software deployment have been implemented. Extensive diagnostic features provide the operator with additional information. The architecture of the rf control system as well as the functionality of its components will be presented along with measurements that characterize the performance of the system, yielding, e.g., an amplitude stabilization down to (ΔA/A_{rms}=7×10^{-5} and a phase stabilization of (Δϕ_{rms}=0.8° for superconducting cavities.

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.

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

International Nuclear Information System (INIS)

Szczęśniak, Dominik; Ennaoui, Ahmed; Ahzi, Saïd

2016-01-01

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

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

Science.gov (United States)

Szczęśniak, Dominik; Ennaoui, Ahmed; Ahzi, Saïd

2016-09-01

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

Determining the band gap and mean kinetic energy of atoms from reflection electron energy loss spectra

Energy Technology Data Exchange (ETDEWEB)

Vos, M. [Atomic and Molecular Physics Laboratories, Research School of Physics and Engineering, Australian National University, Canberra ACT (Australia); Marmitt, G. G. [Atomic and Molecular Physics Laboratories, Research School of Physics and Engineering, Australian National University, Canberra ACT (Australia); Instituto de Fisica da Universidade Federal do Rio Grande do Sul, Avenida Bento Goncalves 9500, 91501-970 Porto Alegre, RS (Brazil); Finkelstein, Y. [Nuclear Research Center — Negev, Beer-Sheva 84190 (Israel); Moreh, R. [Physics Department, Ben-Gurion University of the Negev, Beer-Sheva 84105 (Israel)

2015-09-14

Reflection electron energy loss spectra from some insulating materials (CaCO{sub 3}, Li{sub 2}CO{sub 3}, and SiO{sub 2}) taken at relatively high incoming electron energies (5–40 keV) are analyzed. Here, one is bulk sensitive and a well-defined onset of inelastic excitations is observed from which one can infer the value of the band gap. An estimate of the band gap was obtained by fitting the spectra with a procedure that includes the recoil shift and recoil broadening affecting these measurements. The width of the elastic peak is directly connected to the mean kinetic energy of the atom in the material (Doppler broadening). The experimentally obtained mean kinetic energies of the O, C, Li, Ca, and Si atoms are compared with the calculated ones, and good agreement is found, especially if the effect of multiple scattering is taken into account. It is demonstrated experimentally that the onset of the inelastic excitation is also affected by Doppler broadening. Aided by this understanding, we can obtain a good fit of the elastic peak and the onset of inelastic excitations. For SiO{sub 2}, good agreement is obtained with the well-established value of the band gap (8.9 eV) only if it is assumed that the intensity near the edge scales as (E − E{sub gap}){sup 1.5}. For CaCO{sub 3}, the band gap obtained here (7 eV) is about 1 eV larger than the previous experimental value, whereas the value for Li{sub 2}CO{sub 3} (7.5 eV) is the first experimental estimate.

Electron transport through supported biomembranes at the nanoscale by conductive atomic force microscopy

International Nuclear Information System (INIS)

Casuso, I; Fumagalli, L; Samitier, J; Padros, E; Reggiani, L; Akimov, V; Gomila, G

2007-01-01

We present a reliable methodology to perform electron transport measurements at the nanoscale on supported biomembranes by conductive atomic force microscopy (C-AFM). It allows measurement of both (a) non-destructive conductive maps and (b) force controlled current-voltage characteristics in wide voltage bias range in a reproducible way. Tests experiments were performed on purple membrane monolayers, a two-dimensional (2D) crystal lattice of the transmembrane protein bacteriorhodopsin. Non-destructive conductive images show uniform conductivity of the membrane with isolated nanometric conduction defects. Current-voltage characteristics under different compression conditions show non-resonant tunneling electron transport properties, with two different conduction regimes as a function of the applied bias, in excellent agreement with theoretical predictions. This methodology opens the possibility for a detailed study of electron transport properties of supported biological membranes, and of soft materials in general

Electron transport through supported biomembranes at the nanoscale by conductive atomic force microscopy

Energy Technology Data Exchange (ETDEWEB)

Casuso, I [Department Electronica, Universitat de Barcelona and Laboratori de Nanobioenginyeria-IBEC, Parc CientIfic de Barcelona, Barcelona (Spain); Fumagalli, L [Department Electronica, Universitat de Barcelona and Laboratori de Nanobioenginyeria-IBEC, Parc CientIfic de Barcelona, Barcelona (Spain); Samitier, J [Department Electronica, Universitat de Barcelona and Laboratori de Nanobioenginyeria-IBEC, Parc CientIfic de Barcelona, Barcelona (Spain); Padros, E [Unitat de BiofIsica, Departamento de BioquImica i de Biologia Molecular, Facultat de Medicina i Centre d' Estudis en BiofIsica, Universitat Autonoma de Barcelona, Barcelona (Spain); Reggiani, L [CNR-INFM National Nanotechnology Laboratory, Dipartimento di Ingegneria dell' Innovazione, Universita di Lecce, Lecce (Italy); Akimov, V [CNR-INFM National Nanotechnology Laboratory, Dipartimento di Ingegneria dell' Innovazione, Universita di Lecce, Lecce (Italy); Gomila, G [Department Electronica, Universitat de Barcelona and Laboratori de Nanobioenginyeria-IBEC, Parc CientIfic de Barcelona, Barcelona (Spain)

2007-11-21

We present a reliable methodology to perform electron transport measurements at the nanoscale on supported biomembranes by conductive atomic force microscopy (C-AFM). It allows measurement of both (a) non-destructive conductive maps and (b) force controlled current-voltage characteristics in wide voltage bias range in a reproducible way. Tests experiments were performed on purple membrane monolayers, a two-dimensional (2D) crystal lattice of the transmembrane protein bacteriorhodopsin. Non-destructive conductive images show uniform conductivity of the membrane with isolated nanometric conduction defects. Current-voltage characteristics under different compression conditions show non-resonant tunneling electron transport properties, with two different conduction regimes as a function of the applied bias, in excellent agreement with theoretical predictions. This methodology opens the possibility for a detailed study of electron transport properties of supported biological membranes, and of soft materials in general.

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

Band engineering and rational design of high-performance thermoelectric materials by first-principles

Directory of Open Access Journals (Sweden)

Lili Xi

2016-06-01

Full Text Available Understanding and manipulation of the band structure are important in designing high-performance thermoelectric (TE materials. Our recent work has involved the utilization of band structure in various topics of TE research, i.e., the band convergence, the conductive network, dimensionality reduction by quantum effects, and high throughput material screening. In non-cubic chalcopyrite compounds, we revealed the relations between structural factors and band degeneracy, and a simple unity-η rule was proposed for selecting high performance diamond-like TE materials. Based on the deep understanding of the electrical and thermal transport, we identified the conductive network in filled skutterudites with the “phonon glass-electron crystal” (PGEC paradigm, and extended this concept to caged-free Cu-based diamond-like compounds. By combining the band structure calculations and the Boltzmann transport theory, we conducted a high-throughput material screening in half-Heusler (HH systems, and several promising compositions with high power factors were proposed out of a large composition collection. At last, we introduced the Rashba spin-splitting effect into thermoelectrics, and its influence on the electrical transport properties was discussed. This review demonstrated the importance of the microscopic perspectives for the optimization and design of novel TE materials.

Antimonene: Experiments and theory of surface conductivity

Science.gov (United States)

Palacios, Juan Jose; Ares, Pablo; Pakdel, Sahar; Paz, Wendel; Zamora, Felix; Gomez-Herrero, Julio

Very recently antimony has been demonstrated to be amenable to standard exfoliation procedures opening the possibility of studying the electronic properties of isolated few-layers flakes of this material, a.k.a. antimonene. Antimony is a topological semimetal, meaning that its electronic structure presents spin-split helical states (or Dirac cones) on the surface, but it is still trivially metallic in bulk. Antimonene, on the other hand, may present a much reduced electronic bulk contribution for a small number of layers. A novel technique to make electrical contacts on the surface of individual thin flakes (5-10 monolayers) has allowed us to measure the (surface) conductivity of these in ambient conditions. Our measurements show a high conductivity in the range of 1 - 2e2 / h , which we attribute to the surface Dirac electrons. We have also carried out theoretical work to address the origin of this value, in particular, the importance of scattering between the Dirac electrons and the bulk bands. Our calculations are based on density functional theory for the electronic structure and Kubo formalism for the conductivity, the latter considering random disorder and the presence of water. Ministerio de Economia y Competitividad, Grant FIS2016-80434-P.

Thermal conductivity of graphene with defects induced by electron beam irradiation

Science.gov (United States)

Malekpour, Hoda; Ramnani, Pankaj; Srinivasan, Srilok; Balasubramanian, Ganesh; Nika, Denis L.; Mulchandani, Ashok; Lake, Roger K.; Balandin, Alexander A.

2016-07-01

We investigate the thermal conductivity of suspended graphene as a function of the density of defects, ND, introduced in a controllable way. High-quality graphene layers are synthesized using chemical vapor deposition, transferred onto a transmission electron microscopy grid, and suspended over ~7.5 μm size square holes. Defects are induced by irradiation of graphene with the low-energy electron beam (20 keV) and quantified by the Raman D-to-G peak intensity ratio. As the defect density changes from 2.0 × 1010 cm-2 to 1.8 × 1011 cm-2 the thermal conductivity decreases from ~(1.8 +/- 0.2) × 103 W mK-1 to ~(4.0 +/- 0.2) × 102 W mK-1 near room temperature. At higher defect densities, the thermal conductivity reveals an intriguing saturation-type behavior at a relatively high value of ~400 W mK-1. The thermal conductivity dependence on the defect density is analyzed using the Boltzmann transport equation and molecular dynamics simulations. The results are important for understanding phonon - point defect scattering in two-dimensional systems and for practical applications of graphene in thermal management.We investigate the thermal conductivity of suspended graphene as a function of the density of defects, ND, introduced in a controllable way. High-quality graphene layers are synthesized using chemical vapor deposition, transferred onto a transmission electron microscopy grid, and suspended over ~7.5 μm size square holes. Defects are induced by irradiation of graphene with the low-energy electron beam (20 keV) and quantified by the Raman D-to-G peak intensity ratio. As the defect density changes from 2.0 × 1010 cm-2 to 1.8 × 1011 cm-2 the thermal conductivity decreases from ~(1.8 +/- 0.2) × 103 W mK-1 to ~(4.0 +/- 0.2) × 102 W mK-1 near room temperature. At higher defect densities, the thermal conductivity reveals an intriguing saturation-type behavior at a relatively high value of ~400 W mK-1. The thermal conductivity dependence on the defect density is

Electronically conductive perovskite-based oxide nanoparticles and films for optical sensing applications

Science.gov (United States)

Ohodnicki, Jr., Paul R; Schultz, Andrew M

2015-04-28

The disclosure relates to a method of detecting a change in a chemical composition by contacting a electronically conducting perovskite-based metal oxide material with a monitored stream, illuminating the electronically conducting perovskite-based metal oxide with incident light, collecting exiting light, monitoring an optical signal based on a comparison of the incident light and the exiting light, and detecting a shift in the optical signal. The electronically conducting perovskite-based metal oxide has a perovskite-based crystal structure and an electronic conductivity of at least 10.sup.-1 S/cm, where parameters are specified at the gas stream temperature. The electronically conducting perovskite-based metal oxide has an empirical formula A.sub.xB.sub.yO.sub.3-.delta., where A is at least a first element at the A-site, B is at least a second element at the B-site, and where 0.8perovskite-based oxides include but are not limited to La.sub.1-xSr.sub.xCoO.sub.3, La.sub.1-xSr.sub.xMnO.sub.3, LaCrO.sub.3, LaNiO.sub.3, La.sub.1-xSr.sub.xMn.sub.1-yCr.sub.yO.sub.3, SrFeO.sub.3, SrVO.sub.3, La-doped SrTiO.sub.3, Nb-doped SrTiO.sub.3, and SrTiO.sub.3-.delta..

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.

Electronic-Reconstruction-Enhanced Tunneling Conductance at Terrace Edges of Ultrathin Oxide Films.

Science.gov (United States)

Wang, Lingfei; Kim, Rokyeon; Kim, Yoonkoo; Kim, Choong H; Hwang, Sangwoon; Cho, Myung Rae; Shin, Yeong Jae; Das, Saikat; Kim, Jeong Rae; Kalinin, Sergei V; Kim, Miyoung; Yang, Sang Mo; Noh, Tae Won

2017-11-01

Quantum mechanical tunneling of electrons across ultrathin insulating oxide barriers has been studied extensively for decades due to its great potential in electronic-device applications. In the few-nanometers-thick epitaxial oxide films, atomic-scale structural imperfections, such as the ubiquitously existed one-unit-cell-high terrace edges, can dramatically affect the tunneling probability and device performance. However, the underlying physics has not been investigated adequately. Here, taking ultrathin BaTiO 3 films as a model system, an intrinsic tunneling-conductance enhancement is reported near the terrace edges. Scanning-probe-microscopy results demonstrate the existence of highly conductive regions (tens of nanometers wide) near the terrace edges. First-principles calculations suggest that the terrace-edge geometry can trigger an electronic reconstruction, which reduces the effective tunneling barrier width locally. Furthermore, such tunneling-conductance enhancement can be discovered in other transition metal oxides and controlled by surface-termination engineering. The controllable electronic reconstruction can facilitate the implementation of oxide electronic devices and discovery of exotic low-dimensional quantum phases. © 2017 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Electron beam induced conductivity in 'PET' and 'FEP'

International Nuclear Information System (INIS)

Walzade, S.J.; Jog, J.P.; Dake, S.B.; Bhoraskar, S.V.

1983-01-01

Electron Beam Induced Conductivity (EBIC), classified into EBIC (bulk) and EBIC (surface) have been measured in PET and FEP respectively. The peculiar oscillatory nature of the induced gain versus beam energy variations is explained in terms of the spatial distributions of the trapping centres near the surface of the polymers. (author)

Atomic-Monolayer MoS2 Band-to-Band Tunneling Field-Effect Transistor

KAUST Repository

Lan, Yann Wen

2016-09-05

The experimental observation of band-to-band tunneling in novel tunneling field-effect transistors utilizing a monolayer of MoS2 as the conducting channel is demonstrated. Our results indicate that the strong gate-coupling efficiency enabled by two-dimensional materials, such as monolayer MoS2, results in the direct manifestation of a band-to-band tunneling current and an ambipolar transport.

Electronic properties of electron and hole in type-II semiconductor nano-heterostructures

Science.gov (United States)

Rahul, K. Suseel; Souparnika, C.; Salini, K.; Mathew, Vincent

2016-05-01

In this project, we record the orbitals of electron and hole in type-II (CdTe/CdSe/CdTe/CdSe) semiconductor nanocrystal using effective mass approximation. In type-II the band edges of both valance and conduction band are higher than that of shell. So the electron and hole get confined in different layers of the hetero-structure. The energy eigen values and eigen functions are calculated by solving Schrodinger equation using finite difference matrix method. Based on this we investigate the effect of shell thickness and well width on energy and probability distribution of ground state (1s) and few excited states (1p,1d,etc). Our results predict that, type-II quantum dots have significant importance in photovoltaic applications.

Electronic properties of electron and hole in type-II semiconductor nano-heterostructures

Energy Technology Data Exchange (ETDEWEB)

Rahul, K. Suseel [Department of Physics, Central University of Kerala, Riverside Transit Campus, Kasaragod, Kerala. India (India); Department of Physics, Sri Vyasa NSS College, Wadakkancheri, Thrissur, Kerala, PIN:680623. India (India); Souparnika, C. [Department of Physics, Sri Vyasa NSS College, Wadakkancheri, Thrissur, Kerala, PIN:680623. India (India); Salini, K.; Mathew, Vincent, E-mail: vincent@cukerala.ac.in [Department of Physics, Central University of Kerala, Riverside Transit Campus, Kasaragod, Kerala. India (India)

2016-05-06

In this project, we record the orbitals of electron and hole in type-II (CdTe/CdSe/CdTe/CdSe) semiconductor nanocrystal using effective mass approximation. In type-II the band edges of both valance and conduction band are higher than that of shell. So the electron and hole get confined in different layers of the hetero-structure. The energy eigen values and eigen functions are calculated by solving Schrodinger equation using finite difference matrix method. Based on this we investigate the effect of shell thickness and well width on energy and probability distribution of ground state (1s) and few excited states (1p,1d,etc). Our results predict that, type-II quantum dots have significant importance in photovoltaic applications.

Hot phonon generation by split-off hole band electrons in AlxGa1-xAs alloys investigated by picosecond Raman scattering

International Nuclear Information System (INIS)

Jacob, J.M.; Kim, D.S.; Zhou, J.F.; Song, J.J.

1992-01-01

The initial generation of hot LO phonons by the relaxation of hot carriers in GaAs and Al x Ga 1-x As alloy semiconductors is studied. Within the initial 2ps of photoexcitation, only those electrons originating from the split-off hole bands are found to generate a significant number of I-valley hot phonons when photon energies of 2.33eV are used. A picosecond Raman scattering technique is used to determine the hot phonon occupation number in a series of MBE grown Al x Ga 1-x As samples with 0≤x≤0.39. The Stokes and anti-Stokes lines were measured for both GaAs-like and AlAs-like LO phonon modes to determine their occupation numbers. The authors observe a rapid decrease in the phonon occupation numbers as the aluminum concentration increases beyond x = 0.2. This rapid decrease is explained by considering only those electrons photoexcited from the split-off hole band. Almost all of the electrons originating from the heavy and light-hole bands are shown to quickly transfer and remain in the X and L valleys without generating significant numbers of hot LO phonons during the initial 2ps and at a carrier density of 10 17 cm -3 . A model based upon the instantaneous thermalization of hot electrons photoexcited from the split-off hole bands is used to fit the data. They have obtained very good agreement between experiment and theory. This work provides a clear understanding to the relaxation of Γ valley hot electrons by the generation of hot phonons on subpicosecond and picosecond time scales, which has long standing implications to previous time resolved Raman experiments

Highly Confined Electronic and Ionic Conduction in Oxide Heterostructures

DEFF Research Database (Denmark)

Pryds, Nini

2015-01-01

The conductance confined at the interface of complex oxide heterostructures provides new opportunities to explore nanoelectronic as well as nanoionic devices. In this talk I will present our recent results both on ionic and electronic conductivity at different heterostructures systems. In the first...... unattainable for Bi2O3-based materials, is achieved[1]. These confined heterostructures provide a playground not only for new high ionic conductivity phenomena that are sufficiently stable but also uncover a large variety of possible technological perspectives. At the second part, I will discuss and show our...

Towards Designing Environmentally Stable Conjugated Polymers with very Small Band-Gaps

International Nuclear Information System (INIS)

Hong, Sung Y.; Kim, Sung C.

2003-01-01

We have investigated substituent effect on the stabilization energies, and nucleus-independent chemical shifts of pentafulvalenes and on the electronic structures of the corresponding polypentafulvalenes to design environmentally stable semiconductive or conductive polymers. Geometrical optimizations of the molecules were carried out at the density functional level of theory with B3LYP hybrid functional and 6-311+G(d) basis set. Stabilization energies were estimated using isodesmic and homodesmotic reactions. As a criterion of aromaticity nucleus-independent chemical shifts of the molecules were computed using GIAO approach. For the polymers the geometrical parameters were optimized through AM1 band calculations and the electronic structures were obtained through modified extended Huckel band calculations. It is found that strong electronwithdrawing substituents increase isodesmic and homodesmotic stabilization energies of pentafulvalene, though it does not increase the aromaticity. Nitro-substituted pentafulvalene is estimated to have stabilization energy as much as azulene. However, substitution either with electron-donating groups or with electronwithdrawing groups does not significantly affect the electronic structures of polypentafulvalene and poly (vinylenedioxypentafulvalene)

Electronic, structural, and optical properties of crystalline yttria

International Nuclear Information System (INIS)

Xu, Y.; Gu, Z.; Ching, W.Y.

1997-01-01

The electronic structure of crystalline Y 2 O 3 is investigated by first-principles calculations within the local-density approximation (LDA) of the density-functional theory. Results are presented for the band structure, the total density of states (DOS), the atom- and orbital-resolved partial DOS, effective charges, bond order, and charge-density distributions. Partial covalent character in the Y-O bonding is shown, and the nonequivalency of the two Y sites is demonstrated. The calculated electronic structure is compared with a variety of available experimental data. The total energy of the crystal is calculated as a function of crystal volume. A bulk modulus B of 183 Gpa and a pressure coefficient B ' of 4.01 are obtained, which are in good agreement with compression data. An LDA band gap of 4.54 eV at Γ is obtained which increases with pressure at a rate of dE g /dP=0.012eV/Gpa at the equilibrium volume. Also investigated are the optical properties of Y 2 O 3 up to a photon energy of 20 eV. The calculated complex dielectric function and electron-energy-loss function are in good agreement with experimental data. A static dielectric constant of var-epsilon(0)=3.20 is obtained. It is also found that the bottom of the conduction band consists of a single band, and direct optical transition at Γ between the top of the valence band and the bottom of the conduction band may be symmetry forbidden. copyright 1997 The American Physical Society

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.