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Sample records for hybrid superlattice structure

  1. Phoxonic Hybrid Superlattice.

    Science.gov (United States)

    Alonso-Redondo, Elena; Huesmann, Hannah; El Boudouti, El-Houssaine; Tremel, Wolfgang; Djafari-Rouhani, Bahram; Butt, Hans-Juergen; Fytas, George

    2015-06-17

    We studied experimentally and theoretically the direction-dependent elastic and electromagnetic wave propagation in a supported film of hybrid PMMA (poly[methyl-methacrylate])-TiO2 superlattice (SL). In the direction normal to the layers, this one-dimensional periodic structure opens propagation band gaps for both hypersonic (GHz) phonons and near-UV photons. The high mismatch of elastic and optical impedance results in a large dual phoxonic band gap. The presence of defects inherent to the spin-coating fabrication technique is sensitively manifested in the band gap region. Utilizing Brillouin light scattering, phonon propagation along the layers was observed to be distinctly different from propagation normal to them and can, under certain conditions (SL thickness and substrate elasticity), reveal the nanomechanical properties of the constituent layers. Besides the first realization of unidirectional phoxonic behavior, hybrid (soft-hard) periodic materials are a promising simple platform for opto-acoustic interactions and applications such as filters and Bragg mirrors.

  2. Electronic structure modeling of InAs/GaSb superlattices with hybrid density functional theory

    Science.gov (United States)

    Garwood, T.; Modine, N. A.; Krishna, S.

    2017-03-01

    The application of first-principles calculations holds promise for greatly improving our understanding of semiconductor superlattices. Developing a procedure to accurately predict band gaps using hybrid density functional theory lays the groundwork for future studies investigating more nuanced properties of these structures. Our approach allows a priori prediction of the properties of SLS structures using only the band gaps of the constituent materials. Furthermore, it should enable direct investigation of the effects of interface structure, e.g., intermixing or ordering at the interface, on SLS properties. In this paper, we present band gap data for various InAs/GaSb type-II superlattice structures calculated using the generalized Kohn-Sham formulation of density functional theory. A PBE0-type hybrid functional was used, and the portion of the exact exchange was tuned to fit the band gaps of the binary compounds InAs and GaSb with the best agreement to bulk experimental values obtained with 18% of the exact exchange. The heterostructures considered in this study are 6 monolayer (ML) InAs/6 ML GaSb, 8 ML InAs/8 ML GaSb and 10 ML InAs/10 ML GaSb with deviations from the experimental band gaps ranging from 3% to 11%.

  3. Complex band structure and superlattice electronic states

    Science.gov (United States)

    Schulman, J. N.; McGill, T. C.

    1981-04-01

    The complex band structures of the bulk materials which constitute the alternating layer (001) semiconductor-semiconductor superlattice are investigated. The complex bands near the center of the Brillouin zone in the [001] direction are studied in detail. The decay lengths of superlattice states whose energies lie in the bulk band gaps of one of the semiconductors are determined from the dispersion curves of these bands for imaginary k-->. This method is applied using a tight-binding band-structure calculation to two superlattices: the AlAs-GaAs superlattice and the CdTe-HgTe superlattice. The decay lengths of AlAs-GaAs superlattice conduction-band minimum states are found to be substantially shorter than those for the CdTe-HgTe superlattice. These differences in the decay of the states in the two superlattices result in differences in the variation of the conduction-band effective masses with the thickness of the AlAs and CdTe layers. The conduction-band effective masses increase more rapidly with AlAs thickness in the AlAs-GaAs superlattice than with CdTe thickness in the CdTe-HgTe superlattice.

  4. Coherent quantum transport features in carbon superlattice structures

    Science.gov (United States)

    McIntosh, R.; Henley, S. J.; Silva, S. R. P.; Bhattacharyya, S.

    2016-10-01

    Whilst resonant transmission is well understood and can be fully harnessed for crystalline superlattices, a complete picture has not yet emerged for disordered superlattices. It has proven difficult to tune resonant transmission in disordered diamond-like carbon (DLC) superlattices as conventional models are not equipped to incorporate significant structural disorder. In this work, we present concurrent experimental and theoretical analysis which addresses resonant transmission in DLC superlattices. Devices were fabricated by growing alternate layers of DLC with different percentages of sp3 hybridized carbon.Coherent quantum transport effects were demonstrated in these structurally disordered DLC superlattices through distinct current modulation with negative differential resistance (NDR) in the current-voltage (I-V) measurements. A model was developed using tight-binding calculations assuming a random variation of the hopping integral to simulate structural (bond-length) disorder. Calculations of the I-V characteristics compliment the interpretation of the measurements and illustrate that while DLC superlattice structures are unlike their classical counterparts, the near-field structural order will help with the confinement of quantised states. The present model provides an empirical guide for tailoring the properties of future devices, giving rise to much hope that carbon electronics operating at high frequencies over large areas can now be developed.

  5. Magnetic structure of holmium-yttrium superlattices

    DEFF Research Database (Denmark)

    Jehan, D.A.; McMorrow, D.F.; Cowley, R.A.;

    1993-01-01

    that the superlattices have high crystallographic integrity: the structural coherence length parallel to the growth direction is typically almost-equal-to 2000 angstrom, while the interfaces between the two elements are well defined and extend over approximately four lattice planes. The magnetic structures were......We present the results of a study of the chemical and magnetic structures of a series of holmium-yttrium superlattices and a 5000 angstrom film of holmium, all grown by molecular-beam epitaxy. By combining the results of high-resolution x-ray diffraction with detailed modeling, we show...... determined using neutron-scattering techniques. The moments on the Ho3+ ions in the superlattices form a basal-plane helix. From an analysis of the superlattice structure factors of the primary magnetic satellites, we are able to determine separately the contributions made by the holmium and yttrium...

  6. Revisiting HOPG superlattices: Structure and conductance properties

    Science.gov (United States)

    Patil, Sumati; Kolekar, Sadhu; Deshpande, Aparna

    2017-04-01

    Superlattices observed on highly oriented pyrolytic graphite (HOPG) have been studied extensively by scanning tunnelling microscopy (STM). The interest in the study of graphite superlattices has seen a resurgence since the discovery of graphene. Single layer graphene, bilayer graphene, and few layer graphene can now be grown on different substrates. The adherence of graphene to various substrates often leads to a periodic out-of-plane modulation and superlattices due to lattice mismatch. In this paper, we report STM imaging and scanning tunnelling spectroscopy (STS) of different kinds of superlattices on HOPG characterized by a variation in lattice periodicities. Our study also shows evidence of the displacement of the topmost HOPG layer by scanning different areas of the same superlattice. A correlation between the lattice periodicity with its conductance properties is derived. The results of this work are important for understanding the origin of the superlattice structure on HOPG. Investigation of such superlattices may open up possible ways to modify two dimensional electron systems to create materials with tailored electronic properties.

  7. Spin-dependent terahertz oscillator based on hybrid graphene superlattices

    Energy Technology Data Exchange (ETDEWEB)

    Díaz, E.; Miralles, K.; Domínguez-Adame, F. [GISC, Departamento Física de Materiales, Universidad Complutense, E-28040 Madrid (Spain); Gaul, C., E-mail: cgaul@pks.mpg.de [Max Planck Institute for the Physics of Complex Systems, 01187 Dresden (Germany)

    2014-09-08

    We theoretically study the occurrence of Bloch oscillations in biased hybrid graphene systems with spin-dependent superlattices. The spin-dependent potential is realized by a set of ferromagnetic insulator strips deposited on top of a gapped graphene nanoribbon, which induce a proximity exchange splitting of the electronic states in the graphene monolayer. We numerically solve the Dirac equation and study Bloch oscillations in the lowest conduction band of the spin-dependent superlattice. While the Bloch frequency is the same for both spins, we find the Bloch amplitude to be spin dependent. This difference results in a spin-polarized ac electric current in the THz range.

  8. Electrical transport engineering of semiconductor superlattice structures

    Science.gov (United States)

    Shokri, Aliasghar

    2014-04-01

    We investigate the influence of doping concentration on band structures of electrons and electrical transmission in a typical aperiodic semiconductor superlattice consisting of quantum well and barrier layers, theoretically. For this purpose, we assume that each unit cell of the superlattice contains alternately two types of material GaAs (as a well) and GaAlAs (as a barrier) with six sublayers of two materials. Our calculations are based on the generalized Kronig-Penny (KP) model and the transfer matrix method within the framework of the parabolic conductance band effective mass approximation in the coherent regime. This model reduces the numerical calculation time and enables us to use the transfer matrix method to investigate transport in the superlattices. We show that by varying the doping concentration and geometrical parameters, one can easily block the transmission of the electrons. The numerical results may be useful in designing of nanoenergy filter devices.

  9. Electrical transport engineering of semiconductor superlattice structures

    Energy Technology Data Exchange (ETDEWEB)

    Shokri, Aliasghar, E-mail: aashokri@tpnu.ac.ir

    2014-04-01

    We investigate the influence of doping concentration on band structures of electrons and electrical transmission in a typical aperiodic semiconductor superlattice consisting of quantum well and barrier layers, theoretically. For this purpose, we assume that each unit cell of the superlattice contains alternately two types of material GaAs (as a well) and GaAlAs (as a barrier) with six sublayers of two materials. Our calculations are based on the generalized Kronig–Penny (KP) model and the transfer matrix method within the framework of the parabolic conductance band effective mass approximation in the coherent regime. This model reduces the numerical calculation time and enables us to use the transfer matrix method to investigate transport in the superlattices. We show that by varying the doping concentration and geometrical parameters, one can easily block the transmission of the electrons. The numerical results may be useful in designing of nanoenergy filter devices.

  10. Ultrafast structural dynamics of perovskite superlattices

    Energy Technology Data Exchange (ETDEWEB)

    Woerner, M.; Korff Schmising, C. von; Zhavoronkov, N.; Elsaesser, T. [Max-Born-Institut fuer Nichtlineare Optik und Kurzzeitspektroskopie, Berlin (Germany); Bargheer, M. [Universitaet Potsdam, Institut fuer Physik und Astronomie, Potsdam (Germany); Vrejoiu, I.; Hesse, D.; Alexe, M. [Max-Planck-Institut fuer Mikrostrukturphysik, Halle (Germany)

    2009-07-15

    Femtosecond X-ray diffraction provides direct insight into the ultrafast reversible lattice dynamics of materials with a perovskite structure. Superlattice (SL) structures consisting of a sequence of nanometer-thick layer pairs allow for optically inducing a tailored stress profile that drives the lattice motions and for limiting the influence of strain propagation on the observed dynamics. We demonstrate this concept in a series of diffraction experiments with femtosecond time resolution, giving detailed information on the ultrafast lattice dynamics of ferroelectric and ferromagnetic superlattices. Anharmonically coupled lattice motions in a SrRuO{sub 3}/PbZr{sub 0.2}Ti{sub 0.8}O{sub 3} (SRO/PZT) SL lead to a switch-off of the electric polarizations on a time scale of the order of 1 ps. Ultrafast magnetostriction of photoexcited SRO layers is demonstrated in a SRO/SrTiO{sub 3} (STO) SL. (orig.)

  11. Theory of silicon superlattices - Electronic structure and enhanced mobility

    Science.gov (United States)

    Moriarty, J. A.; Krishnamurthy, S.

    1983-01-01

    A realistic tight-binding band-structure model of silicon superlattices is formulated and used to study systems of potential applied interest, including periodic layered Si-Si(1-x)Ge(x) heterostructures. The results suggest a possible new mechanism for achieving enhanced transverse carrier mobility in such structures: reduced transverse conductivity effective masses associated with the superlattice band structure. For electrons in 100-line-oriented superlattices, a reduced conductivity mass arises intrinsically from the lower symmetry of the superlattice and its unique effect on the indirect bulk silicon band gap. An order of magnitude estimate of the range of mobility enhancement expected from this mechanism appears to be consistent with preliminary experimental results on Si-Si(1-x)Ge(x) superlattices.

  12. Electronic structure of superlattices of graphene and hexagonal boron nitride

    KAUST Repository

    Kaloni, Thaneshwor P.

    2011-11-14

    We study the electronic structure of superlattices consisting of graphene and hexagonal boron nitride slabs, using ab initio density functional theory. We find that the system favors a short C–B bond length at the interface between the two component materials. A sizeable band gap at the Dirac point is opened for superlattices with single graphene layers but not for superlattices with graphene bilayers. The system is promising for applications in electronic devices such as field effect transistors and metal-oxide semiconductors.

  13. Manganites in Perovskite Superlattices: Structural and Electronic Properties

    KAUST Repository

    Jilili, Jiwuer

    2016-07-13

    structure of bulk CaMnO3 and LaNiO3. An onsite Coulomn interaction term U is tested for both the Mn and Ni atoms. G-type antiferromagnetism and insulating properties of CaMnO3 are reproduced with U = 3 eV and ferromagnetic ordering is favorable when CaMnO3 is strained to the substrate lattice constant. This implies that the CaMnO3 magnetism is sensitive to both strain and the U parameter. Antiparallel orientation of the Mn and Ti moments has been found experimentally in the BiMnO3/SrTiO3 superlattice. By introducing O defects at different layers, we find similar patterns when the defect is located in the BiO layer. The structural, electronic and magnetic properties are analysed. Strong hybridization between the d3z2−r2 orbitals of the Mn and Ti atoms near the O defect is found. The effect of uniaxial strain for the formation of a two-dimensional electron gas and the interfacial Ti magnetic moments of the (LaMnO3)2/(SrTiO3)2 superlattice are investigated. By tuning the strain state from compressive to tensile, we predict under which conditions the spin-polarization of the electron gas is enhanced. Since the thickness ratio of the superlattice correlates with the strain state, we also study the structural, electronic and magnetism trends of (LaMnO3)n/(SrTiO3)m superlattices with varying layer thicknesses. The main finding is that half-metallicity will vanish for n, m > 8. Reduction of the minority band gaps with increasing n and m originates mainly from an energetic downshift of the Ti dxy states. Along with these, the interrelation between the interface geometry and the electronic properties of the antiferromagnetic/ferromagnetic superlattice BiFeO3/ La0.7Sr0.3MnO3 is investigated. The magnetic and optical properties are also analysed by first principles calculations. The half-metallic character of bulk La0.7Sr0.3MnO3 is maintained in the superlattice, which implies potential applications on spintronics and memory devices.

  14. The structural and magnetic properties of holmium/scandium superlattices

    DEFF Research Database (Denmark)

    Bryn-Jacobsen, C.; Cowley, R.A.; McMorrow, D.F.;

    1997-01-01

    The properties of Ho/Sc superlattices grown by molecular beam epitaxy (MBE) have been investigated using X-ray and neutron diffraction techniques. Structural studies reveal the novel existence of more than one a lattice parameter. Examining the magnetic properties, it is found that the Ho 4f...

  15. Magnetic structures of holmium-lutetium alloys and superlattices

    DEFF Research Database (Denmark)

    Swaddling, P.P.; Cowley, R.A.; Ward, R.C.C.;

    1996-01-01

    Alloys and superlattices of Ho and Lu have been grown using molecular beam epitaxy and their magnetic structures determined using neutron-scattering techniques. The 4f moments in the alloys form a helix at all compositions with the moments aligned in the basal plane perpendicular to the wave vector...

  16. Electronic structure of a graphene superlattice with massive Dirac fermions

    Energy Technology Data Exchange (ETDEWEB)

    Lima, Jonas R. F., E-mail: jonas.iasd@gmail.com [Instituto de Ciencia de Materiales de Madrid (CSIC) - Cantoblanco, Madrid 28049 (Spain)

    2015-02-28

    We study the electronic and transport properties of a graphene-based superlattice theoretically by using an effective Dirac equation. The superlattice consists of a periodic potential applied on a single-layer graphene deposited on a substrate that opens an energy gap of 2Δ in its electronic structure. We find that extra Dirac points appear in the electronic band structure under certain conditions, so it is possible to close the gap between the conduction and valence minibands. We show that the energy gap E{sub g} can be tuned in the range 0 ≤ E{sub g} ≤ 2Δ by changing the periodic potential. We analyze the low energy electronic structure around the contact points and find that the effective Fermi velocity in very anisotropic and depends on the energy gap. We show that the extra Dirac points obtained here behave differently compared to previously studied systems.

  17. Hybrid Hamiltonian and Green's Function Approach for Studying Native Point Defect Levels in Semiconductor Compounds and Superlattices

    Science.gov (United States)

    Krishnamurthy, Srini; Van Orden, Derek; Yu, Zhi-Gang

    2016-09-01

    We have developed a hybrid method that can be applied to study isolated defects in semiconductor compounds and superlattices. The method is a combination of (1) a long-range tight-binding (TB) Hamiltonian, (2) a first-principles Hamiltonian, and (3) a Green's function (GF) formalism. The calculation of the GF requires accurate energy band structure, wave functions, and defect potentials. The TB Hamiltonian with sp 3 orbitals basis ensures accurate band gaps and band masses while providing the functional form for the wave functions. We calculated the band gaps of InAs/GaSb and InAs/InAsSb strained-layer superlattices and found them to agree well with measurements. The change in potentials caused by native point defects (NPDs) was obtained from a first-principles method using Spanish Initiative for Electronic Simulations with Thousands of Atoms, which also uses sp 3 basis. We describe the method of calculating NPD energy levels in compounds and superlattices, obtain some defect levels in GaAs, InAs, InSb, and GaSb compounds, and provide details of the NPD-level calculations.

  18. Isolated structures in two-dimensional optical superlattice

    Science.gov (United States)

    Zou, Xin-Hao; Yang, Bao-Guo; Xu, Xia; Tang, Peng-Ju; Zhou, Xiao-Ji

    2017-10-01

    Overlaying commensurate optical lattices with various configurations called superlattices can lead to exotic lattice topologies and, in turn, a discovery of novel physics. In this study, by overlapping the maxima of lattices, a new isolated structure is created, while the interference of minima can generate various "sublattice" patterns. Three different kinds of primitive lattices are used to demonstrate isolated square, triangular, and hexagonal "sublattice" structures in a two-dimensional optical superlattice, the patterns of which can be manipulated dynamically by tuning the polarization, frequency, and intensity of laser beams. In addition, we propose the method of altering the relative phase to adjust the tunneling amplitudes in "sublattices". Our configurations provide unique opportunities to study particle entanglement in "lattices" formed by intersecting wells and to implement special quantum logic gates in exotic lattice geometries.

  19. Nonlinear thermoelectric efficiency of superlattice-structured nanowires

    Science.gov (United States)

    Karbaschi, Hossein; Lovén, John; Courteaut, Klara; Wacker, Andreas; Leijnse, Martin

    2016-09-01

    We theoretically investigate nonlinear ballistic thermoelectric transport in a superlattice-structured nanowire. By a special choice of nonuniform widths of the superlattice barriers—analogous to antireflection coating in optical systems—it is possible to achieve a transmission which comes close to a square profile as a function of energy. We calculate the low-temperature output power and power-conversion efficiency of a thermoelectric generator based on such a structure and show that the efficiency remains high also when operating at a significant power. To provide guidelines for experiments, we study how the results depend on the nanowire radius, the number of barriers, and on random imperfections in barrier width and separation. Our results indicate that high efficiencies can indeed be achieved with today's capabilities in epitaxial nanowire growth.

  20. Isolated Structures in Two-Dimensional Optical Superlattice

    CERN Document Server

    Zou, Xinhao; Xu, Xia; Tang, Pengju; Zhou, Xiaoji

    2016-01-01

    Overlaying commensurate optical lattices with various configurations called superlattices can lead to exotic lattice topologies and, in turn, a discovery of novel physics. In this study, by overlapping the maxima of lattices, a new isolated structure is created, while the interference of minima can generate various "sublattice" patterns. Three different kinds of primitive lattices are used to demonstrate isolated square, triangular, and hexagonal "sublattice" structures in a two-dimensional optical superlattice, the patterns of which can be manipulated dynamically by tuning the polarization, frequency, and intensity of laser beams. In addition, we propose the method of altering the relative phase to adjust the tunneling amplitudes in "sublattices." Our configurations provide unique opportunities to study particle entanglement in "lattices" formed by intersecting wells and to implement special quantum logic gates in exotic lattice geometries.

  1. Strain-tunable half-metallicity in hybrid graphene-hBN monolayer superlattices

    Energy Technology Data Exchange (ETDEWEB)

    Meng, Fanchao, E-mail: fanchao.meng@mail.mcgill.ca [Department of Mining and Materials Engineering, McGill University, Montréal, QC H3A 0C5 (Canada); Zhang, Shiqi [School of Electrical, Computer and Energy Engineering, Arizona State University, Tempe, AZ 85281 (United States); Lee, In-Ho [Korea Research Institute of Standards and Science, 1 Doryong-Dong, Yuseong-Gu, Daejeon 305-600 (Korea, Republic of); Jun, Sukky [Department of Mechanical Engineering, University of Wyoming, Laramie, WY 82071 (United States); Ciobanu, Cristian V., E-mail: cciobanu@mines.edu [Department of Mechanical Engineering, Colorado School of Mines, Golden, CO 80401 (United States)

    2016-07-01

    Highlights: • Armchair superlattices have a bandgap modulated by the deformed domain widths. • Strain and domain width lead to novel spin-dependent behavior for zigzag boundaries. • Limits for spin-dependent bandgap and half-metallic behavior have been charted. - Abstract: As research in 2-D materials evolves toward combinations of different materials, interesting electronic and spintronic properties are revealed and may be exploited in future devices. A way to combine materials is the formation of spatially periodic domain boundaries in an atom-thick monolayer: as shown in recent reports, when these domains are made of graphene and hexagonal boron nitride, the resulting superlattice has half-metallic properties in which one spin component is (semi)metallic and the other is semiconductor. We explore here the range of spin-dependent electronic properties that such superlattices can develop for different type of domain boundaries, domain widths, and values of tensile strain applied to the monolayer. We show evidence of an interplay between strain and domain width in determining the electronic properties: while for armchair boundaries the bandgap is the same for both spin components, superlattices with zigzag boundaries exhibit rich spin-dependent behavior, including different bandgaps for each spin component, half-metallicity, and reversal of half-metallicity. These findings can lead to new ways of controlling the spintronic properties in hybrid-domain monolayers, which may be exploited in devices based on 2-D materials.

  2. Structure and magnetic properties of thin films and superlattices

    CERN Document Server

    Bentall, M J

    2002-01-01

    Thin layers of rare earth elements and Laves phase superlattices were grown using molecular beam epitaxy. Their structure and magnetic properties have been probed using x-ray and neutron scattering, magnetisation measurements and high resolution electron microscopy. When holmium is grown on yttrium, the x-ray scattering from layers with a thickness below T sub c ' 115 A is characteristic of a pseudomorphic layer with the same in-plane lattice parameter as the yttrium substrate to within 0.05%. For layers above T sub c ' there is a sharp reduction in misfit strain which is probably due to the creation of edge dislocations. When gadolinium is grown on yttrium, no sharp change of strain of the thin layer was observed up to a thickness of 2920 A. This is characteristic of a pseudomorphic layer, and a failure to nucleate dislocations. For the Laves phase superlattices, a study of the x-ray scattering near several Bragg reflections revealed the presence of numerous superlattice peaks, showing that the samples exhib...

  3. Low dark current N structure superlattice MWIR photodetectors

    Science.gov (United States)

    Salihoglu, Omer; Muti, Abdullah; Turan, Rasit; Ergun, Yuksel; Aydinli, Atilla

    2014-06-01

    Commercially available read out integrated circuits (ROICs) require the FPA to have high dynamic resistance area product at zero bias (R0A) which is directly related to dark current of the detector. Dark current arises from bulk and surface contributions. Recent band structure engineering studies significantly suppressed the bulk contribution of the type-II superlattice infrared photodetectors (N structure, M structure, W structure). In this letter, we will present improved dark current results for unipolar barrier complex supercell superlattice system which is called as "N structure". The unique electronic band structure of the N structure increases electron-hole overlap under bias, significantly. N structure aims to improve absorption by manipulating electron and hole wavefunctions that are spatially separated in T2SLs, increasing the absorption while decreasing the dark current. In order to engineer the wavefunctions, we introduce a thin AlSb layer between InAs and GaSb layers in the growth direction which also acts as a unipolar electron barrier. Despite the difficulty of perfect lattice matching of InAs and AlSb, such a design is expected to reduce dark current. Experiments were carried out on Single pixel with mesa sizes of 100 × 100 - 700 × 700 μm photodiodes. Temperature dependent dark current with corresponding R0A resistance values are reported.

  4. Fine structure of the exciton electroabsorption in semiconductor superlattices

    Science.gov (United States)

    Monozon, B. S.; Schmelcher, P.

    2017-02-01

    Wannier-Mott excitons in a semiconductor layered superlattice (SL) are investigated analytically for the case that the period of the superlattice is much smaller than the 2D exciton Bohr radius. Additionally we assume the presence of a longitudinal external static electric field directed parallel to the SL axis. The exciton states and the optical absorption coefficient are derived in the tight-binding and adiabatic approximations. Strong and weak electric fields providing spatially localized and extended electron and hole states, respectively, are studied. The dependencies of the exciton states and the exciton absorption spectrum on the SL parameters and the electric field strength are presented in an explicit form. We focus on the fine structure of the ground quasi-2D exciton level formed by the series of closely spaced energy levels adjacent from the high frequencies. These levels are related to the adiabatically slow relative exciton longitudinal motion governed by the potential formed by the in-plane exciton state. It is shown that the external electric fields compress the fine structure energy levels, decrease the intensities of the corresponding optical peaks and increase the exciton binding energy. A possible experimental study of the fine structure of the exciton electroabsorption is discussed.

  5. Laser induced structural transformation in chalcogenide based superlattices

    Science.gov (United States)

    Zallo, Eugenio; Wang, Ruining; Bragaglia, Valeria; Calarco, Raffaella

    2016-05-01

    Superlattices made of alternating layers of nominal GeTe and Sb2Te3 have been studied by micro-Raman spectroscopy. A structural irreversible transformation into ordered GeSbTe alloy is induced by high power laser light exposure. The intensity ratio of anti-Stokes and Stokes scattering under laser illumination gives a maximum average temperature in the sample of 177 °C. The latter is lower than the growth temperature and of 400 °C necessary by annealing to transform the structure in a GeSbTe alloy. The absence of this configuration after in situ annealing even up to 300 °C evidences an electronic excitation induced-transition which brings the system into a different and stable crystalline state.

  6. Engineering the electronic structure of graphene superlattices via Fermi velocity modulation

    Science.gov (United States)

    Lima, Jonas R. F.

    2017-01-01

    Graphene superlattices have attracted much research interest in the last years, since it is possible to manipulate the electronic properties of graphene in these structures. It has been verified that extra Dirac points appear in the electronic structure of the system. The electronic structure in the vicinity of these points has been studied for a gapless and gapped graphene superlattice and for a graphene superlattice with a spatially modulated energy gap. In each case a different behavior was obtained. In this work we show that via Fermi velocity engineering it is possible to tune the electronic properties of a graphene superlattice to match all the previous cases studied. We also obtained new features of the system never observed before, reveling that the electronic structure of graphene is very sensitive to the modulation of the Fermi velocity. The results obtained here are relevant for the development of novel graphene-based electronic devices.

  7. Photonic band structure of one-dimensional aperiodic superlattices composed of negative refraction metamaterials

    Science.gov (United States)

    Tyc, Michał H.; Salejda, Włodzimierz; Klauzer-Kruszyna, Agnieszka; Tarnowski, Karol

    2007-05-01

    The dispersion relation for polarized light transmitting through a one-dimensional superlattice composed of aperiodically arranged layers made of ordinary dielectric and negative refraction metamaterials is calculated with finite element method. Generalized Fibonacci, generalized Thue-Morse, double-periodic and Rudin-Shapiro superlattices are investigated, using their periodic approximants. Strong dispersion of metamaterials is taken into account. Group velocities and effective refraction indices in the structures are calculated. The self-similar structure of the transmission spectra is observed.

  8. Structural and magnetic properties of holmium-scandium alloys and superlattices

    DEFF Research Database (Denmark)

    Bryn-Jacobsen, C.; Cowley, R.A.; McMorrow, D.F.

    1997-01-01

    The properties of Ho-Sc alloys and superlattices grown by molecular-beam epitaxy have been investigated using x-ray and neutron-diffraction techniques. Structural studies reveal that the alloy samples have different a lattice parameters for the Sc-seed layer and the Ho:Sc alloy grown on top...... of the seed layer; while the superlattices have different a lattice parameters for the Sc seed, and for both the Ho and Sc in the superlattice layers. The structural characteristics are related to the large lattice mismatches (of the order 7%) between the constituent elements. The magnetic moments....... It is found that a good description of the dependence of T-N upon concentration is given by a virtual-crystal model where the peak in the conduction-electron susceptibility varies linearly between that of the pure constituents. In the superlattices, the moments also form a basal-plane helix at T...

  9. Structure property relationships of nitride superlattice hard coatings prepared by pulsed laser deposition

    Science.gov (United States)

    Patel, Nitin

    Today, more than 40% of all cutting tools used in machining applications are covered with coatings. Coatings improve wear resistance, increase tool life, enable use at higher speed, and broaden the application range. Superlattices, where thin layers (typically deposited in an alternating fashion, are widely used commercially. Importantly, the hardness value of a superlattice (e.g. TiN/AlN) can significantly exceed the rule of mixture value. Superlattice coatings built from crystallographically dissimilar materials are not widely studied but hold promise for improvements in performance by allowing for both hardness and toughness to be simultaneously optimized. This is what this thesis is concerned with: a structure-property comparison of isostructural superlattices with corresponding non-isostructural superlattices. In order to grow both isostructural and non-isostructural superlattices from the same set of materials, it is necessary to grow monolithic films in different phases. Towards this end, the synthesis of different phases of AlN, (Ti,Al)N, TaN, and TiN was investigated. Films were grown by pulsed laser deposition in two different chambers that had different base pressures to study the effect of background gases on the phases and orientations of the films. Growth of AlN and (Ti,Al)N films is strongly affected in a chamber that had a base pressure of 10-6 Torr, but the films adopt their stable nitride structures in a chamber with the lower base pressure of 10-8 Torr. TaN adopts either the cubic rock salt structure or its stable hexagonal structure, depending on the growth temperature, while TiN grows as rock salt in all conditions. Single crystal epitaxial superlattices were then grown with different compositions, periodicities, and crystallographic orientations to compare the effect of chemistry, nanostructure, and crystallographic texture on hardness. Finally, the structure-property relationships of non-isostructural (cubic/hexagonal) superlattices are

  10. Study on band gap structure of Fibonacci quantum superlattices by using the transfer matrix method

    Science.gov (United States)

    Ferrando, V.; Castro-Palacio, J. C.; Marí, B.; Monsoriu, J. A.

    2014-02-01

    The scattering properties of particles in a one-dimensional Fibonacci sequence based potential have been analyzed by means of the Transfer Matrix Method. The electronic band gaps are examined comparatively with those obtained using the corresponding periodic potentials. The reflection coefficient shows self-similar properties for the Fibonacci superlattices. Moreover, by using the generalized Bragg's condition, the band gaps positions are derived from the golden mean involved in the design of the superlattice structure.

  11. InN/GaN Superlattices: Band Structures and Their Pressure Dependence

    DEFF Research Database (Denmark)

    Gorczyca, Iza; Suski, Tadek; Staszczak, Grzegorz;

    2013-01-01

    with one monolayer of InN and 40 monolayers of GaN. The results are compared with calculations performed for different types of superlattices: InN/GaN, InGaN/GaN, and InN/InGaN/GaN with single monolayers of InN and/or InGaN. The superlattices are simulated by band structure calculations based on the local......Creation of short-period InN/GaN superlattices is one of the possible ways of conducting band gap engineering in the green-blue range of the spectrum. The present paper reports results of photoluminescence experiments, including pressure effects, on a superlattice sample consisting of unit cells...

  12. ``N'' structure for type-II superlattice photodetectors

    Science.gov (United States)

    Salihoglu, Omer; Muti, Abdullah; Kutluer, Kutlu; Tansel, Tunay; Turan, Rasit; Ergun, Yuksel; Aydinli, Atilla

    2012-08-01

    In the quest to raise the operating temperature and improve the detectivity of type II superlattice (T2SL) photodetectors, we introduce a design approach that we call the "N structure." N structure aims to improve absorption by manipulating electron and hole wavefunctions that are spatially separated in T2SLs, increasing the absorption while decreasing the dark current. In order to engineer the wavefunctions, we introduce a thin AlSb layer between InAs and GaSb layers in the growth direction which also acts as a unipolar electron barrier. Unlike the symmetrical insertion of AlSb into GaSb layers, N design aims to exploit the shifting of the electron and hole wavefunctions under reverse bias. With cutoff wavelength of 4.3 μm at 77 K, temperature dependent dark current and detectivity measurements show that the dark current density is 3.6 × 10-9 A/cm2, under zero bias. Photodetector reaches background limited infrared photodetection (BLIP) condition at 125 K with the BLIP detectivity (D*BLIP) of 2.6 × 1010 Jones under 300 K background and -0.3 V bias voltage.

  13. The magnetic structure of holmium-erbium superlattices

    Energy Technology Data Exchange (ETDEWEB)

    McMorrow, D.F. [Risoe National Lab., Roskilde (Denmark); Simpson, J.A.; Cowley, R.A.; Jehan, D.A.; Ward, R.C.C.; Wells, M.R. [Oxford Physics, Clarendon Lab. (United Kingdom); Thurston, T.R.; Gibbs, D. [Brookhaven National Lab., Upton, NY (United States)

    1994-06-01

    The effect of completing crystal-field anisotropies on magnetic order has been investigated in a series of Ho/Er superlattices using neutron and resonant x-ray magnetic diffraction techniques. The neutron diffraction reveals that for temperatures in the interval T{sub N}(Er) {le} T {le} T{sub N}(Ho) the Ho basal-plane order propagates coherently through the paramagnetic Er, and that below T{sub N}(Er) the longitudinal component of the Er moments fails to order across the Ho block. The magnetic superlattice peaks observed in the x-ray scattering display an anomalous energy dependence: a sharp resonance is found at L{sub III}(Ho), with no resonance visible at L{sub III}(Er). These results are discussed with reference to models of exchange in metallic superlattices.

  14. Structural and electronic properties of germanene/MoS2 monolayer and silicene/MoS2 monolayer superlattices

    OpenAIRE

    Li, Xiaodan; Wu, Shunqing; Zhou, Sen; Zhu, Zizhong

    2014-01-01

    Superlattice provides a new approach to enrich the class of materials with novel properties. Here, we report the structural and electronic properties of superlattices made with alternate stacking of two-dimensional hexagonal germanene (or silicene) and a MoS2 monolayer using the first principles approach. The results are compared with those of graphene/MoS2 superlattice. The distortions of the geometry of germanene, silicene, and MoS2 layers due to the formation of the superlattices are all r...

  15. The chemical and magnetic structures of holmium-yttrium and holmium-lutetium superlattices

    DEFF Research Database (Denmark)

    McMorrow, D.F.; Jehan, D.A.; Swaddling, P.P.;

    1993-01-01

    We present the results of a study of the chemical and magnetic structures of Ho/Y and Ho/Lu superlattices, all grown by molecular beam epitaxy. By combining the results of high-resolution X-ray diffraction with detailed modelling we show that the superlattices have high crystallographic integrity......: the average structural coherence length in the growth direction is approximately 2000 angstrom, while the interfaces between the two elements are well defined, extending over approximately four lattice planes. The magnetic structures were determined using neutron scattering techniques. In the case of the Ho...

  16. Coherent magnetic structures in terbium/holmium superlattices

    DEFF Research Database (Denmark)

    Bryn-Jacobsen, C.; Cowley, R.A.; McMorrow, D.F.;

    1997-01-01

    Neutron-scattering techniques have been used to investigate the magnetic properties of three Tb/Ho superlattices grown by molecular-beam epitaxy. It is revealed that for temperatures in the range T = 10 to T-N(Ho)approximate to 130 K, there is a basal-plane ferromagnetic alignment of Tb moments...

  17. Formation of uniform magnetic structures and epitaxial hydride phases in Nd/Pr superlattices

    DEFF Research Database (Denmark)

    Goff, J.P.; Bryn-Jacobsen, C.; McMorrow, D.F.;

    1997-01-01

    , and that the stacking sequence is coherent over many bilayer repeats. The neutron measurements show that for the hexagonal sites of the dhcp structure, the Nd magnetic order propagates coherently through the Pr, whereas the order on the cubic sites is either suppressed or confined to single Nd blocks. It is also shown...... that the singlet ground state of Pr is perturbed to produce a local moment on the hexagonal sites, so that in some cases there is a uniform magnetic structure throughout the superlattice. These results cast new light on the theory of magnetic interactions in rare-earth superlattices. Within a few months of growth...

  18. Synchrotron X-Ray Study on Structures of Ni80Fe20/Cu Superlattices

    Institute of Scientific and Technical Information of China (English)

    XU Ming; LUO Guang-Ming; CHAI Chun-Lin; YANG Tao; MAI Zhen-Hong; LAI Wu-Yan; WU Zhong-Hua; WANG De-Wu

    2001-01-01

    We have shown that, in contrast to the results in the literature, the Bragg peak intensity of Ni80Fe20/Cu superlattices is enhanced at the incident x-ray energy slightly higher than the absorption edge of the heavier element (Cu). The atomic density at Ni80Fe20/Cu interface was analysed by the diffraction anomalous fine structure technology with the incident angle of x-ray fixed at the first Bragg peak. Our results demonstrate the epitaxy growth of Ni80Fe20/Cu superlattices. Upon annealing, the epitaxity of Ni80Fe20/Cu multilayers becomes poor but the local crystallinity in each layer is improved.

  19. Study of the electronic structure and half-metallicity of CaMnO3/BaTiO3 superlattice

    Science.gov (United States)

    Wang, Kai; Jiang, Wei; Chen, Jun-Nan; Huang, Jian-Qi

    2016-09-01

    In this paper, the electronic structure, magnetic properties and half-metallicity of the CaMnO3/BaTiO3 superlattice are investigated by employing the first-principle calculation based on density functional theory within the GGA or GGA + U exchange-correlation functional. The CaMnO3/BaTiO3 superlattice is constructed by the cubic CaMnO3 and the tetragonal ferroelectric BaTiO3 growing alternately along (0 0 1) direction. The cubic CaMnO3 presents a robust half-metallicity and a metastable ferromagnetic phase. Its magnetic moment is an integral number of 3.000 μB per unit cell. However, the CaMnO3/BaTiO3 superlattice has a stable ferromagnetic phase, for which the magnetic moment is 12.000 μB per unit cell. It also retains the robust half-metallicity which mainly results from the strong hybridization between Mn and O atoms. The results show that the constructed CaMnO3/BaTiO3 superlattice exhibits superior magnetoelectric properties. It may provide a theoretical reference for the design and preparation of new multiferroic materials.

  20. The magnetic phase diagram and zero field structure of holmium-lutetium superlattices

    Energy Technology Data Exchange (ETDEWEB)

    Swaddling, P.P. [Clarendon Laboratory, Oxford University, Oxford (United Kingdom); McMorrow, D.F. [Risoe National Laboratory, Roskilde (Denmark); Cowley, R.A. [Clarendon Laboratory, Oxford University, Oxford (United Kingdom); Simpson, J.A. [Clarendon Laboratory, Oxford University, Oxford (United Kingdom); Wells, M.R. [Clarendon Laboratory, Oxford University, Oxford (United Kingdom); Ward, R.C.C. [Clarendon Laboratory, Oxford University, Oxford (United Kingdom); Clausen, K.N. [Risoe National Laboratory, Roskilde (Denmark); Collins, M.F. [Dept of Physics and Astronomy, McMaster University, Hamilton (Canada); Buyers, W.J.L. [AECL, Chalk River, Ontario (Canada)

    1995-02-09

    Neutron diffraction has been used to study the magnetic structure of a series of Ho/Lu superlattices. In zero field a transition to a ferromagnetic phase of Ho is observed at low temperatures, and the stability of this phase has been investigated by applying a magnetic field in the basal plane. ((orig.)).

  1. Electronic structure of atomically coherent square semiconductor superlattices with dimensionality below two

    NARCIS (Netherlands)

    Kalesaki, E.; Evers, W.H.; Vanmaekelbergh, D.; Delerue, C.

    2013-01-01

    The electronic structure of recently synthesized square superlattices with atomic coherence composed of PbSe, CdSe, or CdTe nanocrystals (NCs) attached along {100} facets is investigated using tight-binding calculations. In experimental realizations of these systems [W. H. Evers et al., Nano Lett. 1

  2. Artificial semiconductor/insulator superlattice channel structure for high-performance oxide thin-film transistors.

    Science.gov (United States)

    Ahn, Cheol Hyoun; Senthil, Karuppanan; Cho, Hyung Koun; Lee, Sang Yeol

    2013-01-01

    High-performance thin-film transistors (TFTs) are the fundamental building blocks in realizing the potential applications of the next-generation displays. Atomically controlled superlattice structures are expected to induce advanced electric and optical performance due to two-dimensional electron gas system, resulting in high-electron mobility transistors. Here, we have utilized a semiconductor/insulator superlattice channel structure comprising of ZnO/Al2O3 layers to realize high-performance TFTs. The TFT with ZnO (5 nm)/Al2O3 (3.6 nm) superlattice channel structure exhibited high field effect mobility of 27.8 cm(2)/Vs, and threshold voltage shift of only < 0.5 V under positive/negative gate bias stress test during 2 hours. These properties showed extremely improved TFT performance, compared to ZnO TFTs. The enhanced field effect mobility and stability obtained for the superlattice TFT devices were explained on the basis of layer-by-layer growth mode, improved crystalline nature of the channel layers, and passivation effect of Al2O3 layers.

  3. Zigzag-Shaped Superlattices on the Basis of Graphene Nanoribbons: Structure and Electronic Properties

    Science.gov (United States)

    Saroka, V. A.; Batrakov, K. G.

    2016-09-01

    The paper focuses on superlattices consisting of two coplanar fragments of one-layer graphene nanoribbons that have different width and are connected at an angle. Classification of such superlattices was carried out; their electronic properties were studied using the tight-binding method. It was demonstrated that in superlattices consisting of two fragments of graphene nanoribbons with armchair edges connected at an angle of 60°, the band gap can be regulated by the number of dimeric carbon atom chains of one of the fragments. In that case one can observe a periodic dependence of the band gap on the number of chains with a characteristic period equal to three dimeric chains. The number of dimeric chains of the second superlattice fragment regulates the average band gap value near which the periodic oscillations occur, as well as the amplitude of those oscillations. Therefore, one can accomplish a sufficiently precise band gap tuning for such structures. Such tuning can find its wide application in the booming carbon nanoelectronics industry when creating generators, amplifiers and sensors in the nanochains.

  4. Theoretical study of magnetism and electronic structure of Fe{sub 3}/Cr{sub n}(1 1 0) superlattices

    Energy Technology Data Exchange (ETDEWEB)

    Hu Haiquan [College of Physics Science and Information Engineering, Liaocheng University, Liaocheng 252059 (China)], E-mail: huhq@lcu.edu.cn; Li Hengshuai [College of Physics Science and Information Engineering, Liaocheng University, Liaocheng 252059 (China)], E-mail: hengshuaili@sina.com; Wang Yuanxu [College of Physics and Electron, Henan University, Kaifeng 475001 (China); Ren Zhongming [College of Car and Traffic Engineering, Liaocheng University, Liaocheng 252059 (China)

    2008-03-01

    The electronic structure and magnetism of Fe{sub 3}/Cr{sub n}(1 1 0) (n=1, 3, 5) superlattices (SL) with varying layer thickness have been studied using the full-potential linearized augmented plane-wave (FLAPW) method within the first-principle formalism. The results show that the ferromagnetic state is the preferable phase in the ground state. The magnetic moments of the Fe layers are slightly modified by the presence of the Cr layers. The Cr magnetic moments alternate direction from layer to layer, and an antiferromagnetic coupling between Fe and Cr at the interfacial layer is seen. The magnetic moments of the Cr layers are suppressed because there is a strong hybridization between d-states of both Fe and Cr atoms. Only a small moment is found in the Cr layer. The Cr moment alignment is determined by a delicate balance between the different magnetic interaction.

  5. Structural and magnetic properties of an InGaAs/Fe3Si superlattice in cylindrical geometry

    Science.gov (United States)

    Deneke, Ch; Schumann, J.; Engelhard, R.; Thomas, J.; Müller, C.; Khatri, M. S.; Malachias, A.; Weisser, M.; Metzger, T. H.; Schmidt, O. G.

    2009-01-01

    The structure and magnetic properties of an InGaAs/Fe3Si superlattice in a cylindrical geometry are investigated by electron microscopy techniques, x-ray diffraction and magnetometry. To form a radial superlattice, a pseudomorphic InGaAs/Fe3Si bilayer has been released from its substrate self-forming into rolled-up microtubes. Oxide-free interfaces as well as areas of crystalline bonding are observed and an overall lattice mismatch between succeeding layers is determined. The cylindrical symmetry of the final radial superlattice shows a significant effect on the magnetization behavior of the rolled-up layers.

  6. Structural simulation of superlattices in lithium aluminates; Simulacion estructural de superredes en aluminatos de litio

    Energy Technology Data Exchange (ETDEWEB)

    Carrera G, L.M.; Basurto S, R. [Instituto Nacional de Investigaciones Nucleares, A.P. 18-1027, 11801 Mexico D.F. (Mexico)

    1997-07-01

    Among the materials to be used on the tritium generator cover of the future fusion reactors the lithium aluminate ({gamma} - LiAlO{sub 2}) is one of the more studied. In this work it is presented the superlattice structural simulation that presents to {gamma} - LiAlO{sub 2} as main phase and to {alpha} - LiAlO{sub 2} as the secondary phase. The simulation is developed considering that as the two phases present different symmetry ({gamma} - LiAlO{sub 2} is tetrahedral and {alpha} - LiAlO{sub 2} is hexahedral) it is had a superlattice LUCS type (Layered Ultrathin Coherent Structure) that is it presents an structure in coherent ultrathin layers since it is what implicates a lesser energy of formation. (Author)

  7. Structural and electronic properties of germanene/MoS2 monolayer and silicene/MoS2 monolayer superlattices

    Science.gov (United States)

    Li, Xiaodan; Wu, Shunqing; Zhou, Sen; Zhu, Zizhong

    2014-03-01

    Superlattice provides a new approach to enrich the class of materials with novel properties. Here, we report the structural and electronic properties of superlattices made with alternate stacking of two-dimensional hexagonal germanene (or silicene) and a MoS2 monolayer using the first principles approach. The results are compared with those of graphene/MoS2 superlattice. The distortions of the geometry of germanene, silicene, and MoS2 layers due to the formation of the superlattices are all relatively small, resulting from the relatively weak interactions between the stacking layers. Our results show that both the germanene/MoS2 and silicene/MoS2 superlattices are manifestly metallic, with the linear bands around the Dirac points of the pristine germanene and silicene seem to be preserved. However, small band gaps are opened up at the Dirac points for both the superlattices due to the symmetry breaking in the germanene and silicene layers caused by the introduction of the MoS2 sheets. Moreover, charge transfer happened mainly within the germanene (or silicene) and the MoS2 layers (intra-layer transfer), as well as some part of the intermediate regions between the germanene (or silicene) and the MoS2 layers (inter-layer transfer), suggesting more than just the van der Waals interactions between the stacking sheets in the superlattices.

  8. Density functional theory investigation of titanium-tungsten superlattices: Structure and mechanical properties

    Science.gov (United States)

    Rudin, Sven P.

    2012-11-01

    Titanium (Ti) exhibits the body-centered crystal structure only at high temperatures. The temperature range of this so-called β-Ti phase can be expanded by alloying Ti with tungsten (W). Rather than placing the W atoms in the β-Ti crystal at random, this work applies density functional theory calculations to explore the consequences of an orderly placement in Ti/W superlattice structures. In all examples the W layer remains bcc-like. The stacking direction of the Ti/W superlattice drives the core of the Ti layer toward either a locally hcp- or ω-Ti structure, though the latter is mechanically unstable for all but the thinnest W layers. The relative thicknesses of the W and Ti layers as well as the stacking direction influence the formation energies, which consistently fall within a range corresponding roughly to room temperature. Superlattices allow a choice of stacking direction and layer thicknesses, both strongly influencing the material's strength, though not improving the mechanical properties as observed for Ti with randomly placed W particles.

  9. Electronic Structures and Giant Magnetoresistance of Co/Cu Superlattices with Different Orientations

    Institute of Scientific and Technical Information of China (English)

    SHANG Jia-Xiang; ZHAO Xiao-Dan

    2006-01-01

    @@ The electronic structures of Co3 Cu3 superlattices with the orientations of (100), (110) and (111) are calculated by the first-principle method within the framework of the density functional theory. It has been found that the spin-dependent scattering and charge transfers are prominent at interfaces compared to the interior layers for the three orientation superlattices. We also evaluate the magnetoresistance ratio by using the two-current model The results show that the giant magnetoresistance ratio decreases in the order of (110), (100), (111) orientations for Co3Cu3 models (49. 4%, 37. 7%, 29.3%, respectively). Further analysis shows that an expansion of average atomic volume would enhance the magnetic moment of Co, which is consistent with other calculation and experimental results. In addition, the giant magnetoresistance effect is analysed from the point of charge transfer.

  10. Electronic structure and optical properties of (BeTen/(ZnSem superlattices

    Directory of Open Access Journals (Sweden)

    Caid M.

    2016-03-01

    Full Text Available The structural, electronic and optical properties of (BeTen/(ZnSem superlattices have been computationally evaluated for different configurations with m = n and m≠n using the full-potential linear muffin-tin method. The exchange and correlation potentials are treated by the local density approximation (LDA. The ground state properties of (BeTen/(ZnSem binary compounds are determined and compared with the available data. It is found that the superlattice band gaps vary depending on the layers used. The optical constants, including the dielectric function ε(ω, the refractive index n(ω and the refractivity R(ω, are calculated for radiation energies up to 35 eV.

  11. Synchrotron X—Ray Study on Structures of Ni80Fe20/Cu Superlattices

    Institute of Scientific and Technical Information of China (English)

    杨涛; 麦振洪; 赖武彦; 吴忠华; 王德武; XUMing; 罗光明; 柴春林

    2001-01-01

    We have shown that,in contrast to the results in the literature,the Bragg peak intensity of Ni80Fe20/Cu superlattices is enhanced at the incident x-ray energy slightly higher than the absorption edge of the heavier element(Cu).The atomic density at Ni80Fe20/Cu interface was analysed by the diffraction anomalous fine structure technology with the incident angle of x-ray fixed at the first Bragg peak.Our results demonstrate the epitaxy growth of Ni80Fe20/Cu superlattices.Upon annealing,the epitaxity of Ni80Fe20/Cu multilayers becomes poor but the local crystallinity in each layer is improved.

  12. Phonon modes of MgB2: super-lattice structures and spectral response.

    Science.gov (United States)

    Alarco, Jose A; Chou, Alison; Talbot, Peter C; Mackinnon, Ian D R

    2014-11-28

    Micrometre-sized MgB2 crystals of varying quality, synthesized at low temperature and autogenous pressure, are compared using a combination of Raman and infra-red (IR) spectroscopy. These data, which include new peak positions in both spectroscopies for high quality MgB2, are interpreted using DFT calculations on phonon behaviour for symmetry-related structures. Raman and IR activity additional to that predicted by point group analyses of the P6/mmm symmetry are detected. These additional peaks, as well as the overall shapes of calculated phonon dispersion (PD) models are explained by assuming a double super-lattice, consistent with a lower symmetry structure for MgB2. A 2× super-lattice in the c-direction allows a simple correlation of the pair breaking energy and the superconducting gap by activation of corresponding acoustic frequencies. A consistent physical interpretation of these spectra is obtained when the position of a phonon anomaly defines a super-lattice modulation in the a-b plane.

  13. Hybrid matrix method for stable numerical analysis of the propagation of Dirac electrons in gapless bilayer graphene superlattices

    Science.gov (United States)

    Briones-Torres, J. A.; Pernas-Salomón, R.; Pérez-Álvarez, R.; Rodríguez-Vargas, I.

    2016-05-01

    Gapless bilayer graphene (GBG), like monolayer graphene, is a material system with unique properties, such as anti-Klein tunneling and intrinsic Fano resonances. These properties rely on the gapless parabolic dispersion relation and the chiral nature of bilayer graphene electrons. In addition, propagating and evanescent electron states coexist inherently in this material, giving rise to these exotic properties. In this sense, bilayer graphene is unique, since in most material systems in which Fano resonance phenomena are manifested an external source that provides extended states is required. However, from a numerical standpoint, the presence of evanescent-divergent states in the eigenfunctions linear superposition representing the Dirac spinors, leads to a numerical degradation (the so called Ωd problem) in the practical applications of the standard Coefficient Transfer Matrix (K) method used to study charge transport properties in Bilayer Graphene based multi-barrier systems. We present here a straightforward procedure based in the hybrid compliance-stiffness matrix method (H) that can overcome this numerical degradation. Our results show that in contrast to standard matrix method, the proposed H method is suitable to study the transmission and transport properties of electrons in GBG superlattice since it remains numerically stable regardless the size of the superlattice and the range of values taken by the input parameters: the energy and angle of the incident electrons, the barrier height and the thickness and number of barriers. We show that the matrix determinant can be used as a test of the numerical accuracy in real calculations.

  14. Low-Temperature Thermal Conductance in Superlattice Nanowire with Structural Defect

    Institute of Scientific and Technical Information of China (English)

    WANG Xin-Jun; LIU Jing-Feng; LI Shui

    2008-01-01

    Using the scattering-matrix cascading method, we investigate the effect of structural defect on the acoustic phonon transmission and thermal conductance in the superlattice nanowire at low temperatures. In the present system, the phonon transmissions exhibit quite complex oscillatory behaviour. It is found that a lateral defect in an otherwise periodic structure significantly decrease the thermal conductance and completely washes away the transmission quantization. However, the appreciable transmission quantization survives in the presence of a longitudinal defect whereas a good quantization plateau of thermal conductance emerges below the universal level in a wide temperature range with the lateral defect.

  15. Structural parameters and their effects on the electronic transport properties in aperiodic superlattice profile

    Science.gov (United States)

    Bendahma, F.; Djelti, R.; Bentata, S.

    2016-08-01

    The aperiodic GaAs/AlxGa1-xAs superlattices (SL) with trimer disorder have been studied in this paper. The transfer-matrix technique and the exact Airy function formalism have been used to determine the miniband structure, the transmission coefficient, the resonance energy and resonant tunneling time (RTT). Although the disorder localizes the states on average, our numerical calculations show that the localization length of the states becomes more extended when the disorder is correlated (trimer case). We have also found that the RTT is of the order of several femtoseconds.

  16. Photodetectors based on intersubband transitions using III-nitride superlattice structures

    Energy Technology Data Exchange (ETDEWEB)

    Hofstetter, Daniel; Baumann, Esther; Giorgetta, Fabrizio R; Theron, Ricardo [University of Neuchatel, 1 A.-L. Breguet, 2000 Neuchatel (Switzerland); Wu, Hong; Schaff, William J; Dawlaty, Jahan; George, Paul A; Eastman, Lester F; Rana, Farhan [Cornell University, Phillips Hall, Ithaca, NY 14853 (United States); Kandaswamy, Prem K; Leconte, Sylvain; Monroy, Eva [Equipe mixte CEA-CNRS Nanophysique et Semiconducteurs, INAC/SP2M/PSC, CEA-Grenoble, 17 rue des Martyrs, 38054 Grenoble cedex 9 (France)

    2009-04-29

    We review our recent progress on the fabrication of near-infrared photodetectors based on intersubband transitions in AlN/GaN superlattice structures. Such devices were first demonstrated in 2003, and have since then seen a quite substantial development both in terms of detector responsivity and high speed operation. Nowadays, the most impressive results include characterization up to 3 GHz using a directly modulated semiconductor laser and up to 13.3 GHz using an ultra-short pulse solid state laser.

  17. Superlattice band structure: New and simple energy quantification condition

    Energy Technology Data Exchange (ETDEWEB)

    Maiz, F., E-mail: fethimaiz@gmail.com [University of Cartage, Nabeul Engineering Preparatory Institute, Merazka, 8000 Nabeul (Tunisia); King Khalid University, Faculty of Science, Physics Department, P.O. Box 9004, Abha 61413 (Saudi Arabia)

    2014-10-01

    Assuming an approximated effective mass and using Bastard's boundary conditions, a simple method is used to calculate the subband structure for periodic semiconducting heterostructures. Our method consists to derive and solve the energy quantification condition (EQC), this is a simple real equation, composed of trigonometric and hyperbolic functions, and does not need any programming effort or sophistic machine to solve it. For less than ten wells heterostructures, we have derived and simplified the energy quantification conditions. The subband is build point by point; each point presents an energy level. Our simple energy quantification condition is used to calculate the subband structure of the GaAs/Ga{sub 0.5}Al{sub 0.5}As heterostructures, and build its subband point by point for 4 and 20 wells. Our finding shows a good agreement with previously published results.

  18. Electronic and optical properties of 4.2 μm"N" structured superlattice MWIR photodetectors

    Science.gov (United States)

    Salihoglu, O.; Hostut, M.; Tansel, T.; Kutluer, K.; Kilic, A.; Alyoruk, M.; Sevik, C.; Turan, R.; Ergun, Y.; Aydinli, A.

    2013-07-01

    We report on the development of a new structure for type II superlattice photodiodes that we call the "N" design. In this new design, we insert an electron barrier between InAs and GaSb in the growth direction. The barrier pushes the electron and hole wavefunctions towards the layer edges and under bias, increases the overlap integral by about 25% leading to higher detectivity. InAs/AlSb/GaSb superlattices were studied with density functional theory. Both AlAs and InSb interfaces were taken into account by calculating the heavy hole-light hole (HH-LH) splittings. Experiments were carried out on single pixel photodiodes by measuring electrical and optical performance. With cut-off wavelength of 4.2 μm at 120 K, temperature dependent dark current and detectivity measurements show that the dark current is 2.5 × 10-9 A under zero bias with corresponding R0A resistance of 1.5 × 104 Ω cm2 for the 500 × 500 μm2 single pixel square photodetectors. Photodetector reaches BLIP condition at 125 K with the BLIP detectivity (DBLIP∗) of 2.6 × 1010 Jones under 300 K background and -0.3 V bias voltage.

  19. Structure direction of II-VI semiconductor quantum dot binary nanoparticle superlattices by tuning radius ratio.

    Science.gov (United States)

    Chen, Zhuoying; O'Brien, Stephen

    2008-06-01

    We report a nanoparticle radius ratio dependent study of the formation of binary nanoparticle superlattices (BNSLs) of CdTe and CdSe quantum dots. While keeping all other parameters identical in the system, the effective nanoparticle radius ratio, gamma(eff), was tuned to allow the formation of five different BNSL structures, AlB(2), cub-NaZn(13), ico-NaZn(13), CaCu(5), and MgZn(2). For each structure, gamma(eff) is located close to a local maximum of its space-filling factor, based on a model for space filling principles. We demonstrate the ability to select specific BNSLs based solely on gamma(eff), highlighting the role of entropic forces as a driver for self-assembly.

  20. Formation of Superlattices of Gold Nanoparticles Using Ostwald Ripening in Emulsions: Transition from fcc to bcc Structure.

    Science.gov (United States)

    Schmitt, Julien; Hajiw, Stéphanie; Lecchi, Amélie; Degrouard, Jéril; Salonen, Anniina; Impéror-Clerc, Marianne; Pansu, Brigitte

    2016-06-30

    An efficient method to form 3D superlattices of gold nanoparticles inside oil emulsion droplets is presented. We demonstrate that this method relies on Ostwald ripening, a well-known phenomenon occurring during the aging of emulsions. The key point is that the nanoparticle concentration inside the smaller droplets is increasing very slowly with time, thus inducing the crystallization of the nanoparticles into superlattices. Using oil-in-water emulsions doped with hydrophobic gold nanoparticles, we demonstrate that this method is efficient for different types of oils (toluene, cyclohexane, dodecane, and hexadecane). 3D superlattices of the nanoparticles are obtained, with dimensions reaching a hundred nanometers. The kinetics of the crystallization depends on the solubility of the oil in water but also on the initial concentration of the gold nanoparticles in oil. This method also provides an innovative way to obtain the complete phase diagram of nanoparticle suspensions with concentration. Indeed, during this slow crystallization process, a transition from a disordered suspension to a fcc structure is observed, followed by a transition toward a bcc structure. This evolution with time provides key results to understand the role played by the ligands located at the surface of the nanoparticles in order to control the type of superlattices which are formed.

  1. Ab initio study of structural and electronic properties of (GaN)n/(AlN)n superlattices

    Science.gov (United States)

    Djoudi, L.; Merabet, M.; Dahmane, F.; Boucharef, M.; Benalia, S.; Rached, D.

    2016-10-01

    Structural and electronic properties of binary GaN and AlN compounds and their superlattices (SLs) (GaN)n/(AlN)n are investigated using the first-principles full potential linear muffin-tin orbitals method (FP-LMTO). The exchange-correlation potential is treated with the local density approximation of Perdew and Wang (LDA-PW). The ground-state properties are determined for the bulk materials GaN, AlN, and their superlattices (GaN)n/(AlN)n) in cubic phase. The calculated structural properties of GaN and AlN compounds are in good agreement with available experimental and theoretical data. It is found that AlN exhibit an indirect fundamental band gap while that GaN and the superlattices (SLs) exhibit a direct fundamental band gap, which might make the superlattices (GaN)n/(AlN)n materials promising and useful for optoelectronic applications. The fundamental band gap decreases with increasing the number of monolayer.

  2. Direct spectroscopic identification of the magnetic structure of the interface of Mn{sub 3}O{sub 4}/Fe{sub 3}O{sub 4} superlattices

    Energy Technology Data Exchange (ETDEWEB)

    Chen, C.L., E-mail: clchen@phys.sinica.edu.tw [Institutes of Physics, Academia Sinica, Taipei, Taiwan (China); Dong, C.L., E-mail: dong.cl@nsrrc.org.tw [National Synchrotron Radiation Research Center, Hsinchu, Taiwan (China); Chern, G. [Department of Physics, National Chung-Cheng University, Chiayi, Taiwan (China); Kumar, K. [Department of Science, Institute of Technology Tallaght (ITT Dublin), Tallaght, Dublin 24 (Ireland); Lin, H.J.; Chen, C.T. [National Synchrotron Radiation Research Center, Hsinchu, Taiwan (China); Chang, C.L. [Department of Physics, Tamkang University, Tamsui, Taiwan (China); Fujimori, A. [Department of Physics, University of Tokyo, Bunkyo-ku, Tokyo 113-0033 (Japan)

    2014-11-25

    Highlights: • Electronic structure of interfacial layer of superlattices is studied with XAS. • Magnetic property of interface in superlattices is studied by XMCD. • Antiparallel coupling between two ferrimagnetic layers is characterized. • MnFe{sub 2}O{sub 4}-like interface formed in Fe{sub 3}O{sub 4}/Mn{sub 3}O{sub 4} superlattices is identified. • Interfacial layer critically affects the magnetic properties of the superlattices. - Abstract: In this study, Fe and Mn L{sub 2,3}-edge X-ray absorption spectroscopy (XAS) and X-ray magnetic circular dichroism (XMCD) are performed on a series of Mn{sub 3}O{sub 4}/Fe{sub 3}O{sub 4} superlattices with various layer thicknesses to investigate the effect of the interface on the magnetic properties of the superlattices. XAS and XMCD spectral analyses indicate the presence of antiparallel interlayer magnetic coupling between the layers of Fe{sub 3}O{sub 4} and Mn{sub 3}O{sub 4}, which are both ferrimagnetic, in the Mn{sub 3}O{sub 4}/Fe{sub 3}O{sub 4} superlattices. Results suggest that interlayer magnetic coupling between the Mn{sub 3}O{sub 4} and Fe{sub 3}O{sub 4} layers in the superlattice is affected by the magnetic property of the interface region. The magnetic response of the superlattices is dominated by Fe{sub 3}O{sub 4} at high Fe{sub 3}O{sub 4} layer thicknesses and by the interface as the thickness declines. Findings reveal the formation of an interface that is likely composed of MnFe{sub 2}O{sub 4}. The interface critically influences the magnetic properties of the Mn{sub 3}O{sub 4}/Fe{sub 3}O{sub 4} superlattices.

  3. Ab Initio Investigation of the Structural and Electronic Properties of HgTe/CdTe Superlattices

    Science.gov (United States)

    Laref, A.; Alsagri, M.; Laref, S.; Luo, S. J.

    2017-08-01

    We carried out first-principle calculations to examine the impact of layer periodicity and strain on the structural and electronic features of HgTe/CdTe superlattices (SLs). The full-potential linearized augmented plane wave methodology is used to determine the electronic characteristics of these CdTe-HgTe heterojunctions. The CdTe and HgTe layers have a strong effect on the emerged fundamental energy gap of the SLs owing to the peculiar quantum confinement effect. The impact of layer thickness changes and strain are indispensable for engineering the energy band gap of HgTe/CdTe SLs. This could lead to an enormous development in the optoelectronic characteristics of these SLs, which may result in their broad applications in electronic devices.

  4. Electronic Structure of Si1-xIVx/Si Superlattices on Si(001)

    Institute of Scientific and Technical Information of China (English)

    CHEN Jie; L(U) Tie-Yu; HUANG Mei-Chun

    2007-01-01

    We have preformed systematical ab initio studies of the structural and electronic properties of short-period Si1-xIVx/Si (x = 0.125, 0.25, 0.5,IV=Ge, Sn) superlattices (SLs) grown along the [001] direction on bulk Si. The present calculations reveal that the Si0.875 Ge0.125/Si, Si0.75 Ge0.25/Si and Si0.875Sn0.125/Si axe the Γ-point direct bandgap semiconductors. The technological importance lies in the expectation that the direct gap Si1-xIVx/Si SLs may be used as components in integrated optoelectronic devices, in conjunction with the already well-established and highly advanced silicon technology.

  5. ON THE CHARACTERIZATION OF METALLIC SUPERLATTICE STRUCTURES BY X—RAY DIFFRACTION

    Institute of Scientific and Technical Information of China (English)

    MINGXU; WenxueYU; 等

    1999-01-01

    To solve the problem on the microstructural characterization of metallic superlattices,taking the NiFe/Cu superlattices as example,we show that the sturctures of metallic superlattices can be characterized exactly by combining low-angle X-ray diffraction with high-angle X-ray diffraction.First,we determine exactly the total film thickness by a straightforward and precise method based on a modified Bragg law from the subsidiary maxima around the low-angle X-ray diffraction peak.Then.by combining with the simulation of high-angle X-ray diffraction.we obtain the sturctural parameters such as the superlattice period,the sublayer and buffer thickness,This characterization procedure is also applicable to other types of metallic superlattices.

  6. InN/GaN Superlattices: Band Structures and Their Pressure Dependence

    DEFF Research Database (Denmark)

    Gorczyca, Iza; Suski, Tadek; Staszczak, Grzegorz

    2013-01-01

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

  7. Improved structural and electrical properties in native Sb2Te3/GexSb2Te3+x van der Waals superlattices due to intermixing mitigation

    Directory of Open Access Journals (Sweden)

    Stefano Cecchi

    2017-02-01

    Full Text Available Superlattices made of Sb2Te3/GeTe phase change materials have demonstrated outstanding performance with respect to GeSbTe alloys in memory applications. Recently, epitaxial Sb2Te3/GeTe superlattices were found to feature GexSb2Te3+x blocks as a result of intermixing between constituting layers. Here we present the epitaxy and characterization of Sb2Te3/GexSb2Te3+x van der Waals superlattices, where GexSb2Te3+x was intentionally fabricated. X-ray diffraction, Raman spectroscopy, scanning transmission electron microscopy, and lateral electrical transport data are reported. The intrinsic 2D nature of both sublayers is found to mitigate the intermixing in the structures, significantly improving the interface sharpness and ultimately the superlattice structural and electrical properties.

  8. Superlattice structure of Ce{sup 3+}-doped BaMgF{sub 4} fluoride crystals - x-ray diffraction, electron spin-resonance, and optical investigations

    Energy Technology Data Exchange (ETDEWEB)

    Yamaga, M.; Hattori, K. [Department of Electrical and Electronic Engineering, Faculty of Engineering, Gifu University, Gifu (Japan); Kodama, N. [Department of Materials Science and Engineering, Faculty of Engineering and Resource Science, Akita University, Akita (Japan); Ishizawa, N. [Materials and Structures Laboratory, Tokyo Institute of Technology, Yokohama (Japan); Honda, M. [Faculty of Science, Naruto University of Education, Naruto (Japan); Shimamura, K.; Fukuda, T. [Institute for Materials Research, Tohoku University, Sendai (Japan)

    2001-09-14

    The x-ray diffraction patterns for Ce{sup 3+}-doped BaMgF{sub 4} (BMF) crystals suggest the existence of superlattice structure. The superlattice model is consistent with the characterization of the 4f{sup 1} ground state of Ce{sup 3+} as a probe ion using the electron spin-resonance (ESR) technique. The distinct Ce{sup 3+} luminescence spectra with different peak energies and lifetimes also support the superlattice model. Although the detailed superlattice structure could not be analysed using the diffraction spots, a model has been proposed, taking into account the eight Ce{sup 3+} polyhedra with different anion coordinations in the unit cell of the BMF crystal obtained from the ESR experiments. (author)

  9. Structural, Dynamic, and Vibrational Properties during Heat Transfer in Si/Ge Superlattices: A Car-Parrinello Molecular Dynamics Study

    CERN Document Server

    Ji, Pengfei; Yang, Mo

    2016-01-01

    The structural, dynamic, and vibrational properties during the heat transfer process in Si/Ge superlattices, are studied by analyzing the trajectories generated by the ab initio Car-Parrinello molecular dynamics simulation. The radial distribution functions and mean square displacements are calculated and further discussions are made to explain and probe the structural changes relating to the heat transfer phenomenon. Furthermore, the vibrational density of states of the two layers (Si/Ge) are computed and plotted to analyze the contributions of phonons with different frequencies to the heat conduction. Coherent heat conduction of the low frequency phonons is found and their contributions to facilitate heat transfer are confirmed. The Car-Parrinello molecular dynamics simulation outputs in the work show reasonable thermophysical results of the thermal energy transport process and shed light on the potential applications of treating the heat transfer in the superlattices of semiconductor materials from a quant...

  10. Optimization of thermoelectric properties for rough nano-ridge GaAs/AlAs superlattice structure

    Science.gov (United States)

    Wu, Chao-Wei; Wu, Yuh-Renn

    2016-11-01

    In this paper, optimizations of thermoelectric(TE) properties for the rough surface of the nano-ridge GaAs/AlAs superlattice(SL) structure are investigated. The nano-ridge featured with rough surface at both sides of the SL structure is introduced, where the modification of the phonon spatial confinement and phonon surface roughness scattering are taken into account. The elastic continuum model is employed to calculate the phonon dispersion relation and the related phonon group velocity. Reported experimental results with SL structures were used for verification of our model. The lattice thermal conductivity, electrical conductivity, Seebeck coefficient, and electronic thermal conductivity are calculated by Boltzmann transport equations and relaxation time approximation. Simulation results show that the nano-ridge SL structure with certain periodicity and phonon surface roughness scattering have strong influences on the TE properties. Highest ZT in our calculation is 1.285 at 300K and the ZT value of 3.04 is obtained at 1000K.

  11. Structural and optical investigation of InAsxP1-x/InP strained superlattices

    Science.gov (United States)

    Lamberti, C.; Bordiga, S.; Boscherini, F.; Mobilio, S.; Pascarelli, S.; Gastaldi, L.; Madella, M.; Papuzza, C.; Rigo, C.; Soldani, D.; Ferrari, C.; Lazzarini, L.; Salviati, G.

    1998-01-01

    We report a complete characterization of InAsxP1-x/InP (0.05superlattices epitaxially grown by low pressure metalorganic chemical vapor deposition and by chemical beam epitaxy. Samples were obtained by both conventional growth procedures and by periodically exposing the just-grown InP surface to an AsH3 flux. Using the latter procedure, very thin InAsxP1-x/InP layers (10-20 Å) are obtained by P↔As substitutions effects. Arsenic composition of the so obtained layers depends both on AsH3 flux intensity and exposure times. Samples have been characterized by means of high resolution x-ray diffraction, high resolution transmission electron microscopy, 4 K photoluminescence, and extended x ray absorption fine structure spectroscopy. The combined use of high resolution x-ray diffraction and of 4 K photoluminescence, with related simulations, allows us to predict both InAsP composition and width, which are qualitatively confirmed by electron microscopy. Our study indicates that the effect of the formation of thin InAsP layers is due to the As incorporation onto the InP surface exposed to the As flux during the AsH3 exposure, rather than the residual As pressure in the growth chamber during InP growth. Arsenic K-edge extended x-ray absorption fine structure analysis shows that the first shell environment of As at these interfaces is similar to that found in bulk InAsxP1-x alloys of similar composition. In particular we measure an almost constant As-In bond length (within 0.02 Å), independent of As concentration; this confirms that epitaxy with InP is accompanied by local structural distortions, such as bond angle variations, which accommodate the nearly constant As-In bond length. In our investigation we characterize not only very high quality heterostructures but also samples showing serious interface problems such as nonplanarity and/or a consistent chemical spread along the growth axis. In the study presented here we thus propose a general method, based on

  12. Experimental evidence of improved thermoelectric properties at 300K in Si/Ge superlattice structures

    Energy Technology Data Exchange (ETDEWEB)

    Venkatasubramanian, R.; Colpitts, T.; Watko, E.; Malta, D. [Research Triangle Inst., Research Triangle Park, NC (United States)

    1997-04-01

    The authors have found that it may be possible to obtain significant enhancement in ZT at 300 K, over conventional bulk SiGe alloys, through the use of Si/Ge Superlattice (SL) structures. The Seebeck coefficient in Si/Ge SL structures was observed to increase rapidly with decreasing SL period with no loss of electrical conductivity. The carrier mobilities in Si/Ge SLs were higher than in a comparable thin-film Si/Ge alloy. The best power factor of the short-period Si/Ge SLs is 112.2 {micro}W/K{sup 2} cm, over five-fold better than state-of-the-art n-type, bulk SiGe alloys. Approximately a two to four-fold reduction in thermal conductivity in short-period SL structures, compared to bulk SiGe alloy, was observed. The authors estimate at least a factor of five improvement over current state-of-the-art SiGe alloys, in several Si/Ge SL samples with periodicity of {approximately}45 to 75 {angstrom}. The results of this study are promising, but tentative due to the possible effects of substrate and the developmental nature of the thermoelectric property measurements.

  13. Comparing the structural stability of PbS nanocrystals assembled in fcc and bcc superlattice allotropes.

    Science.gov (United States)

    Bian, Kaifu; Wang, Zhongwu; Hanrath, Tobias

    2012-07-04

    We investigated the structural stability of colloidal PbS nanocrystals (NCs) self-assembled into superlattice (SL) allotropes of either face-centered cubic (fcc) or body-centered cubic (bcc) symmetry. Small-angle X-ray scattering analysis showed that the NC packing density is higher in the bcc than in the fcc SL; this is a manifestation of the cuboctahedral shape of the NC building block. Using the high-pressure rock-salt/orthorhombic phase transition as a stability indicator, we discovered that the transition pressure for NCs in a bcc SL occurs at 8.5 GPa, which is 1.5 GPa higher than the transition pressure (7.0 GPa) observed for a fcc SL. The higher structural stability in the bcc SL is attributed primarily to the effective absorption of loading force in specific SL symmetry and to a lesser extent to the surface energy of the NCs. The experimental results provide new insights into the fundamental relationship between the symmetry of the self-assembled SL and the structural stability of the constituent NCs.

  14. Enhanced tunnel transport in disordered carbon superlattice structures incorporated with nitrogen

    Science.gov (United States)

    Katkov, Mikhail V.; Bhattacharyya, Somnath

    2012-06-01

    The possibility for enhanced tunnel transport through the incorporation of nitrogen in a quasi-one dimensional superlattice structure of amorphous carbon (a -C) made of sp2-C and sp3-C rich phases is shown by using a tight-binding model. The proposed superstructure can be described by a set of disordered graphite-like carbon clusters (acting as quantum wells) separated by a thin layer of diamond-like carbon (barriers) where the variation of the width and depth of the carbon clusters significantly control the electron transmission peaks. A large structural disorder in the pure carbon system, introduced through the variation of the bond length and associated deformation potential for respective carbon phases, was found to suppress the sharp features of the transmission coefficients. A small percentage of nitrogen addition to the carbon clusters can produce a distinct transmission peak at the low energy; however, it can be practically destroyed due to increase of the level of disorder of carbon sites. Whereas pronounced resonance peaks, both for C and N sites can be achieved through controlling the arrangement of the nitrogen sites of increased concentration within the disordered sp2-C clusters. The interplay of disorder associated with N and C sites illustrated the tunable nature of resistance of the structures as well as their characteristic times.

  15. Magnetism by interfacial hybridization and p-type doping of MoS(2) in Fe(4)N/MoS(2) superlattices: a first-principles study.

    Science.gov (United States)

    Feng, Nan; Mi, Wenbo; Cheng, Yingchun; Guo, Zaibing; Schwingenschlögl, Udo; Bai, Haili

    2014-03-26

    Magnetic and electronic properties of Fe4N(111)/MoS2(√3 × √3) superlattices are investigated by first-principles calculations, considering two models: (I) Fe(I)Fe(II)-S and (II) N-S interfaces, each with six stacking configurations. In model I, strong interfacial hybridization between Fe(I)/Fe(II) and S results in magnetism of monolayer MoS2, with a magnetic moment of 0.33 μB for Mo located on top of Fe(I). For model II, no magnetism is induced due to weak N-S interfacial bonding, and the semiconducting nature of monolayer MoS2 is preserved. Charge transfer between MoS2 and N results in p-type MoS2 with Schottky barrier heights of 0.5-0.6 eV. Our results demonstrate that the interfacial geometry and hybridization can be used to tune the magnetism and doping in Fe4N(111)/MoS2(√3 × √3) superlattices.

  16. Magnetism by interfacial hybridization and p-type doping of MoS2 in Fe4N/MoS2 superlattices: A first-principles study

    KAUST Repository

    Feng, Nan

    2014-03-26

    Magnetic and electronic properties of Fe4N(111)/MoS 2(√3 × √3) superlattices are investigated by first-principles calculations, considering two models: (I) FeIFe II-S and (II) N-S interfaces, each with six stacking configurations. In model I, strong interfacial hybridization between FeI/Fe II and S results in magnetism of monolayer MoS2, with a magnetic moment of 0.33 μB for Mo located on top of Fe I. For model II, no magnetism is induced due to weak N-S interfacial bonding, and the semiconducting nature of monolayer MoS2 is preserved. Charge transfer between MoS2 and N results in p-type MoS2 with Schottky barrier heights of 0.5-0.6 eV. Our results demonstrate that the interfacial geometry and hybridization can be used to tune the magnetism and doping in Fe4N(111)/MoS2(√3 × √3) superlattices. © 2014 American Chemical Society.

  17. Ultrafast switching in nanoscale phase-change random access memory with superlattice-like structures.

    Science.gov (United States)

    Loke, Desmond; Shi, Luping; Wang, Weijie; Zhao, Rong; Yang, Hongxin; Ng, Lung-Tat; Lim, Kian-Guan; Chong, Tow-Chong; Yeo, Yee-Chia

    2011-06-24

    Phase-change random access memory cells with superlattice-like (SLL) GeTe/Sb(2)Te(3) were demonstrated to have excellent scaling performance in terms of switching speed and operating voltage. In this study, the correlations between the cell size, switching speed and operating voltage of the SLL cells were identified and investigated. We found that small SLL cells can achieve faster switching speed and lower operating voltage compared to the large SLL cells. Fast amorphization and crystallization of 300 ps and 1 ns were achieved in the 40 nm SLL cells, respectively, both significantly faster than those observed in the Ge(2)Sb(2)Te(5) (GST) cells of the same cell size. 40 nm SLL cells were found to switch with low amorphization voltage of 0.9 V when pulse-widths of 5 ns were employed, which is much lower than the 1.6 V required by the GST cells of the same cell size. These effects can be attributed to the fast heterogeneous crystallization, low thermal conductivity and high resistivity of the SLL structures. Nanoscale PCRAM with SLL structure promises applications in high speed and low power memory devices.

  18. Resonant tunnelling assisted electrical switching in amorphous-carbon multilayer-superlattice structures

    Science.gov (United States)

    Bhattacharyya, Somnath; Silva, S. R. P.

    2007-03-01

    Negative differential resistance (NDR) in an amorphous carbon (a-C) double barrier resonant tunnel diode (DB-RTD) with an estimated cut-off frequency well into the gigahertz regime is reported [1]. Presently we extend this work in carbon multi-layer superlattice structures by showing room temperature resonant tunnelling and establish a high value of the phase coherence length of ˜10 nm for low-dimensional amorphous materials. By applying a high bias, these structures are modified with reversible current switching of up to four orders of magnitude with a NDR signature and multiple peaks representative of resonant tunnelling in the ON state. In addition to the formation of filamentary channels by applying high bias, all these features are also explained using concepts based on tunnelling through the interface of the carbon layers, quantum-dot heterostructures and the presence of a confined two dimensional electron gas. This switching behavior and its tunability have been tested by applying a microwave signal up to 100 GHz which suggest the potential for novel high-speed memory devices. [1] S. Bhattacharyya, S.J. Henley, E. Mendoza, L.G-Rojas, J. Allam and S.R.P. Silva, Nature Mater. 5, 19 (2006).

  19. Hybrid Simulation of Composite Structures

    DEFF Research Database (Denmark)

    Høgh, Jacob Herold

    Hybrid simulation is a substructural method combining a numerical simulation with a physical experiment. A structure is thereby simulated under the assumption that a substructure’s response is well known and easily modelled while a given substructure is studied more accurately in a physical...... of freedom. In this dissertation the main focus is to develop hybrid simulation for composite structures e.g. wind turbine blades where the boundary between the numerical model and the physical experiment is continues i.e. in principal infinite amount of degrees of freedom. This highly complicates...

  20. High quantum efficiency Type-II superlattice N-structure photodetectors with thin intrinsic layers

    Science.gov (United States)

    Ergun, Yuksel; Hostut, Mustafa; Tansel, Tunay; Muti, Abdullah; Kilic, Abidin; Turan, Rasit; Aydinli, Atilla

    2013-06-01

    We report on the development of InAs/AlSb/GaSb based N-structure superlattice pin photodiode. In this new design, AlSb layer in between InAs and GaSb layers acts as an electron barrier that pushes electron and hole wave functions towards the GaSb/InAs interface to perform strong overlap under reverse bias. Experimental results show that, with only 20 periods of intrinsic layers, dark current density and dynamic resistance at -50 mV bias are measured as 6x10-3 A/cm2 and 148 Ωcm2 at 77K, respectively. Under zero bias, high spectral response of 1.2A/W is obtained at 5 μm with 50% cut-off wavelengths (λc) of 6 μm. With this new design, devices with only 146 nm thick i-regions exhibit a quantum efficiency of 42% at 3 μm with front-side illimunation and no anti-reflection coatings.

  1. Magnetism in lanthanide superlattices

    DEFF Research Database (Denmark)

    Goff, J.P.; Sarthour, R.S.; McMorrow, D.F.

    2000-01-01

    Neutron diffraction studies of heavy rare-earth superlattices have revealed the stabilization of novel magnetic phases chat are not present in bulk materials. The most striking result is the propagation of the magnetic ordering through nonmagnetic spacer materials. Here we describe some recent X......-ray magnetic resonant scattering studies of light rare-earth superlattices, which illuminate the mechanism of interlayer coupling, and provide access to different areas of Physics. such as the interplay between superconductivity and magnetism. Magnetic X-ray diffraction is found to be particularly well suited...... to the study of the modulated magnetic structures in superlattices, and provides unique information on the conduction-electron spin-density wave responsible for the propagation of magnetic order. (C) 2000 Elsevier Science B.V. All rights reserved....

  2. Magnetic Rare-Earth Superlattices

    DEFF Research Database (Denmark)

    Majkrzak, C.F.; Gibbs, D.; Böni, P.

    1988-01-01

    The magnetic structures of several single‐crystal, magnetic rare‐earth superlattice systems grown by molecular‐beam epitaxy are reviewed. In particular, the results of recent neutron diffraction investigations of long‐range magnetic order in Gd‐Y, Dy‐Y, Gd‐Dy, and Ho‐Y periodic superlattices...... are presented. In the Gd‐Y system, an antiphase domain structure develops for certain Y layer spacings, whereas modified helical moment configurations are found to occur in the other systems, some of which are commensurate with the chemical superlattice wavelength. References are made to theoretical interaction...

  3. Hybrid Tower, Designing Soft Structures

    DEFF Research Database (Denmark)

    Ramsgaard Thomsen, Mette; Tamke, Martin; Holden Deleuran, Anders;

    2015-01-01

    predictions about the inherent interdependency and material dependent performance of the hybrid structure and (2) the inter-scalar design strategies for specification and fabrication. The first investigation focuses on the design pipelines developed between the implementation of realtime physics...... (membrane reinforcement strategy) and micro scale (design of bespoke textile membrane). The paper concludes with a post construction analysis. Comparing structural and environmental data, the predicted and the actual performance of tower are evaluated and discussed....

  4. Hybrid composite laminate structures

    Science.gov (United States)

    Chamis, C. C.; Lark, R. F. (Inventor)

    1977-01-01

    An invention which relates to laminate structures and specifically to essentially anisotropic fiber composite laminates is described. Metal foils are selectively disposed within the laminate to produce increased resistance to high velocity impact, fracture, surface erosion, and other stresses within the laminate.

  5. Magnetic rare earth superlattices

    DEFF Research Database (Denmark)

    Majkrzak, C.F.; Kwo, J.; Hong, M.;

    1991-01-01

    Advances in molecular beam epitaxy deposition techniques have recently made it possible to grow, an atomic plane at a time, single crystalline superlattices composed of alternating layers of a magnetic rare earth, such as Gd, Dy, Ho, or Er, and metallic Y, which has an identical chemical structure...

  6. Enhancement in figure-of-merit with superlattices structures for thin-film thermoelectric devices

    Energy Technology Data Exchange (ETDEWEB)

    Venkatasubramanian, R.; Colpitts, T.

    1997-07-01

    Thin-film superlattice (SL) structures in thermoelectric materials are shown to be a promising approach to obtaining an enhanced figure-of-merit, ZT, compared to conventional, state-of-the-art bulk alloyed materials. In this paper the authors describe experimental results on Bi{sub 2}Te{sub 3}/Sb{sub 2}Te{sub 3} and Si/Ge SL structures, relevant to thermoelectric cooling and power conversion, respectively. The short-period Bi{sub 2}Te{sub 3} and Si/Ge SL structures appear to indicate reduced thermal conductivities compared to alloys of these materials. From the observed behavior of thermal conductivity values in the Bi{sub 2}Te{sub 3}/Sb{sub 2}Te{sub 3} SL structures, a distinction is made where certain types of periodic structures may correspond to an ordered alloy rather than an SL, and therefore, do not offer a significant reduction in thermal conductivity values. The study also indicates that SL structures, with little or weak quantum-confinement, also offer an improvement in thermoelectric power factor over conventional alloys. They present power factor and electrical transport data in the plane of the SL interfaces to provide preliminary support for the arguments on reduced alloy scattering and impurity scattering in Bi{sub 2}Te{sub 3}/Sb{sub 2}Te{sub 3} and Si/Ge SL structures. These results, though tentative due to the possible role of the substrate and the developmental nature of the 3-{omega} method used to determine thermal conductivity values, suggest that the short-period SL structures potentially offer factorial improvements in the three-dimensional figure-of-merit (ZT3D) compared to current state-of-the-art bulk alloys. An approach to a thin-film thermoelectric device called a Bipolarity-Assembled, Series-Inter-Connected Thin-Film Thermoelectric Device (BASIC-TFTD) is introduced to take advantage of these thin-film SL structures.

  7. Structurally induced magnetization in a La2/3Sr4/3MnO4 superlattice

    Energy Technology Data Exchange (ETDEWEB)

    Shah, Amish B. [Argonne National Lab. (ANL), Argonne, IL (United States); Nelson-Cheeseman, Brittany B. [Argonne National Lab. (ANL), Argonne, IL (United States); Subramanian, Ganesh [Arizona State Univ., Tempe, AZ (United States); Bhattacharya, Anand [Argonne National Lab. (ANL), Argonne, IL (United States); Spence, John C.H. [Arizona State Univ., Tempe, AZ (United States)

    2012-03-16

    A structural transition has been observed in a digital superlattice of La2/3Sr4/3MnO4, which is correlated to a magnetization enhancement upon cooling the sample. The artificial superlattices were grown layer-by-layer using ozone-assisted molecular beam epitaxy (MBE). Electron diffraction experiments show a phase transition below 150K in nanopatches of the superlattice, which coincides with an enhanced magnetization starting below 110K. Furthermore, atomic scale electron energy loss spectroscopy (EELS) shows changes in the Mn L2,3 and O K edges, which are related to valence, strain, and the atomic coordination within nanopatches. Atomic resolution image and EELS showing variations of oxygen and lanthanum signature edges in a La2/3Sr4/3MnO4 supperlattice.

  8. Electronic structure and magnetic couplings in metallic superlattices with diffuse interfaces

    Science.gov (United States)

    Stoeffler, Daniel; Gautier, François

    1992-02-01

    The real-space tight-binding method allows one to describe the magnetic order and the interlayer magnetic couplings (IMC) in Fe 3Cr n superlattices. In this paper we extend our previous study on Fe 3Cr n to Co 3Cr n and Ni 6Cr n superlattices. We obtain similar results for the IMC except that for Co 3Cr n the oscillations are obtained only after a "preasymptotic" ferromagnetic coupling regime ( n > 8). Then, we explore the role of diffuse interfaces by assuming as a first step the existence of ordered interfacial compounds (OIC). We show that the IMC oscillations are strongly perturbed and can be strongly damped by frustration effects on the Cr-OIC interfaces.

  9. Mn in misch-metal based superlattice metal hydride alloy - Part 1 structural, hydrogen storage and electrochemical properties

    Science.gov (United States)

    Young, K.; Wong, D. F.; Wang, L.; Nei, J.; Ouchi, T.; Yasuoka, S.

    2015-03-01

    The structural, gaseous phase hydrogen storage, and electrochemical properties of a series of Mn-modified misch-metal based superlattice metal hydride alloys were investigated in part one of this two-part series of papers. X-ray diffraction analysis showed that these alloys are all multi-phased compositions with different abundances of AB2, AB3, A2B7, AB4, and AB5 phases. Substitution of Ni in the B-site by Mn promotes AB5 phase formation and decreases both gaseous phase and electrochemical capacities due to the reduction in the abundance of main hexagonal A2B7 phase. AC impedance and magnetic susceptibility measurement were employed to characterize the surface of Mn-free and Mn-modified alloys and show deterioration in surface catalytic ability as the Mn-content increases. Mn-modification adversely affected misch-metal based superlattice metal hydride alloy properties such as phase homogeneity, capacity, cycle stability, high-rate performance, and surface reaction.

  10. Hybrid Composite Cryogenic Tank Structure

    Science.gov (United States)

    DeLay, Thomas

    2011-01-01

    A hybrid lightweight composite tank has been created using specially designed materials and manufacturing processes. The tank is produced by using a hybrid structure consisting of at least two reinforced composite material systems. The inner composite layer comprises a distinct fiber and resin matrix suitable for cryogenic use that is a braided-sleeve (and/or a filamentwound layer) aramid fiber preform that is placed on a removable mandrel (outfitted with metallic end fittings) and is infused (vacuum-assisted resin transfer molded) with a polyurethane resin matrix with a high ductility at low temperatures. This inner layer is allowed to cure and is encapsulated with a filamentwound outer composite layer of a distinct fiber resin system. Both inner and outer layer are in intimate contact, and can also be cured at the same time. The outer layer is a material that performs well for low temperature pressure vessels, and it can rely on the inner layer to act as a liner to contain the fluids. The outer layer can be a variety of materials, but the best embodiment may be the use of a continuous tow of carbon fiber (T-1000 carbon, or others), or other high-strength fibers combined with a high ductility epoxy resin matrix, or a polyurethane matrix, which performs well at low temperatures. After curing, the mandrel can be removed from the outer layer. While the hybrid structure is not limited to two particular materials, a preferred version of the tank has been demonstrated on an actual test tank article cycled at high pressures with liquid nitrogen and liquid hydrogen, and the best version is an inner layer of PBO (poly-pphenylenebenzobisoxazole) fibers with a polyurethane matrix and an outer layer of T-1000 carbon with a high elongation epoxy matrix suitable for cryogenic temperatures. A polyurethane matrix has also been used for the outer layer. The construction method is ideal because the fiber and resin of the inner layer has a high strain to failure at cryogenic

  11. Electronic Band Structures and Optical Properties of Type-II Superlattice Photodetectors with Interfacial Effect

    Science.gov (United States)

    2012-01-18

    MWIR and LWIR superlattice photodiodes,” Infrared Phys. Techn. 50, 187–190 (2007). 21. A. Khoshakhlagh, E. Plis, S. Myers, Y. D. Sharma, L. R. Dawson...quantum efficiency (QE) spectra [19,20] for a mid-wave infrared (MWIR) detector with a 3.6 μm cutoff wavelength and a long-wave infrared detector ( LWIR ...1016 cm−3 (dashed), NA = 5×1015 cm−3 (solid). different thicknesses, and the calibration is automatically included during the spectral response

  12. Multiferroicity in Perovskite Manganite Superlattice

    Science.gov (United States)

    Tao, Yong-Mei; Jiang, Xue-Fan; Liu, Jun-Ming

    2016-08-01

    Multiferroic properties of short period perovskite type manganite superlattice ((R1MnO3)n/(R2MnO3)n (n=1,2,3)) are considered within the framework of classical Heisenberg model using Monte Carlo simulation. Our result revealed the interesting behaviors in Mn spins structure in superlattice. Apart from simple plane spin cycloid structure which is shown in all manganites including bulk, film, and superlattice here in low temperature, a non-coplanar spiral spin structure is exhibited in a certain temperature range when n equals 1, 2 or 3. Specific heat, spin-helicity vector, spin correlation function, spin-helicity correlation function, and spin configuration are calculated to confirm this non-coplanar spiral spin structure. These results are associated with the competition among exchange interaction, magnetic anisotropy, and Dzyaloshinskii-Moriya interaction. Supported by the National Natural Science Foundation of China (NSFC) under Grant No. 11447136

  13. Land/groove optical recording with GeTe/Sb2Te3 superlattice-like structure

    Institute of Scientific and Technical Information of China (English)

    Wei Qiang(墙威); Luping Shi; Towchong Chong; Yang Cao(曹阳)

    2004-01-01

    A superlattice-like (SLL) structure was applied to phase-change optical recording. The recording layer consisting of alternating thin layers of two different phase-change materials, GeTe and Sb2Tes, were grown by magnetron sputtering on polycarbonate substrates. Land/groove optical recording was adopted to suppress crosstalk and obtain a large track density. Dynamic properties of the SLL disc were investigated with the shortest 1T pulse duration of 8 ns. Clear eye pattern was observed after 10000 direct overwrite cycles. Erasability above 20 dB was achieved at a constant linear velocity of 19 m/s. Carrier-noise ratio (CNR) kept above 46 dB when the recording frequency reaches 21 MHz. The SLL phase change optical disc demonstrates a better recording performance than the Ge1Sb2Te4 and Ge1Sb4Te7 discs in terms of CNR, erasability, and overwrite jitter.

  14. Electronic transport and band structures of GaAs/AlAs nanostructures superlattices for near-infrared detection

    Science.gov (United States)

    Barkissy, Driss; Nafidi, Abdelhakim; Boutramine, Abderrazak; Benchtaber, Nassima; Khalal, Ali; El Gouti, Thami

    2017-01-01

    We report here the theoretical calculations of band structures E( d 1), E( k z , k p ) and effective mass along the growth axis and in the plane of GaAs/Al x Ga1- x As superlattices, in the envelope function formalism. The effect of valence band offset, well thickness and temperature on the band structures, has been also studied. Our results show that a transition from indirect to direct band gap in (GaAs) m /(AlAs)4 takes place between m = 5 and 6 monolayers at room temperature. Samples (GaAs)9/(AlAs)4 and GaAs( d 1 = 10 nm)/Al0.15Ga0.85As( d 2 = 15 nm) have a direct band gap of 1.747 eV at room temperature and 1.546 eV at T = 30 mK, respectively. Their corresponding cutoff wavelengths are located in the near infrared region. We have interpreted the photoluminescence measurements of Ledentsov et al. in GaAs( d 1 = 2.52 nm)/AlAs ( d 1 = 1.16 nm) and the oscillations in the magnetoresistance observed by Kawamura et al. in GaAs/Al0.15Ga0.85As superlattice. In the later, the existence of discrete quantized levels along the growth direction z indicates extremely low interactions between adjacent wells leading to the use in parallel transport. The position of Fermi level predicts that this sample exhibits n-type conductivity. These results were compared and discussed with the available data in the literature and can be used as a guide for the design of infrared nanostructured detectors.

  15. Effect of Interface Bond Type on the Structure of InAs/GaSb Superlattices Grown by Metalorganic Chemical Vapor Deposition

    Institute of Scientific and Technical Information of China (English)

    LI Li-Gong; LIUShu-Man; LUO Shuai; YANG Tao; WANG Li-Jun; LIUFeng-Qi; YE Xiao-Ling; XU Bo; WANG Zhan-Guo

    2011-01-01

    InAs/GaSb type-II superlattices were grown on (100) GaSb substrates by meta.lorga.nic chemical vapor deposition. Raman scattering spectroscopy reveals that it is possible to grow superlattices with almost pure GaAs-like and mixed-like (plane of mixed As and Sb atoms that connect the GaSb and lnAs layers) interfaces. Introducing the InSb-like interface results in nanopipes and As contamination of the GaSb layers. X-ray diffraction and atomic force microscopy demonstrate that the superlattices with a mixed-like interface have better morphology and crystalline quality.%InAs/GaSb type-Ⅱ superlattices were grown on (100) GaSb substrates by metalorganic chemical vapor deposition.Raman scattering spectroscopy reveals that it is possible to grow superlattices with almost pure GaAs-like and mixed-like (plane of mixed As and Sb atoms that connect the GaSb and InAs layers) interfaces.Introducing the InSb-like interface results in nanopipes and As contamination of the GaSb layers.X-ray diffraction and atomic force microscopy demonstrate that the superlattices with a mixed-like interface have better morphology and crystalline quality.InAs/GaSb type-Ⅱ superlattices (SLs) have been shown to be a promising alternative to the existing HgCdTe and quantum well infrared detectors.[1,2]This material system can be tailored over a wide range of infrared wavelength from 3 to more than 30 μm by changing the thicknesses of the InAs and GaSb layers.Using the same technique,the Auger recombination rate can be significantly reduced in InAs/GaSb SLs,which is especially important for realizing high-performance infrared detectors at room temperature.[3,4] Furthermore,due to the large electron effective mass of the SL structures,the bandto-band tunneling current is intrinsically small compared to that of HgCdTe.[5] Since both the anion and the cation change across the interface (IF) of the InAs/GaSb SL,two types of interfaces are possible,InSb-like and GaAs-like.It has been shown that the

  16. Nearest-neighbor sp3s* tight-binding parameters based on the hybrid quasi-particle self-consistent GW method verified by modeling of type-II superlattices

    Science.gov (United States)

    Sawamura, Akitaka; Otsuka, Jun; Kato, Takashi; Kotani, Takao

    2017-06-01

    We report the determination of parameters for the nearest-neighbor sp3s* tight-binding (TB) model for GaP, GaAs, GaSb, InP, InAs, and InSb at 0, 77, and 300 K based on the hybrid quasi-particle self-consistent GW (QSGW) calculation and their application to a type II (InAs)/(GaSb) superlattice. The effects of finite temperature have been incorporated empirically by adjusting the parameter for blending the exchange-correlation terms of the pure QSGW method and local density approximation, in addition to the usage of experimental lattice parameters. As expected, the TB band gap shrinks with temperature and asymptotically with superlattice period when it is large. In addition, a bell curve in the band gap in the case of small superlattice period and slight and remarkable anisotropy in effective masses of electron and hole, both predicted by the hybrid QSGW method, respectively, are reproduced.

  17. Anisotropy in layered half-metallic Heusler alloy superlattices

    Energy Technology Data Exchange (ETDEWEB)

    Azadani, Javad G.; Munira, Kamaram; Sivakumar, Chockalingam; Butler, William H. [Center for Materials for Information Technology, University of Alabama, Tuscaloosa, Alabama 35487 (United States); Department of Physics and Astronomy, University of Alabama, Tuscaloosa, Alabama 35487 (United States); Romero, Jonathon [Department of Physics and Astronomy, University of Alabama, Tuscaloosa, Alabama 35487 (United States); Ma, Jianhua; Ghosh, Avik W. [Department of Electrical and Computer Engineering, University of Virginia, Charlottesville, Virginia 22904 (United States)

    2016-01-28

    We show that when two Heusler alloys are layered in the [001], [110], or [111] directions for various thicknesses to form a superlattice, the Slater-Pauling rule may still be satisfied and the resulting superlattice is often half-metallic with gaps comparable to or larger than those of its constituents. In addition, uniaxial magnetocrystalline anisotropy is induced because of the differences in the electronic structure of the two Heuslers in the superlattice. Various full-full, full-half, and half-half Heusler superlattices are studied, and potential half-metallic superlattices with perpendicular magnetocrystalline anisotropy are identified.

  18. Enhanced infrared detectors using resonant structures combined with thin type-II superlattice absorbers

    Science.gov (United States)

    Goldflam, M. D.; Kadlec, E. A.; Olson, B. V.; Klem, J. F.; Hawkins, S. D.; Parameswaran, S.; Coon, W. T.; Keeler, G. A.; Fortune, T. R.; Tauke-Pedretti, A.; Wendt, J. R.; Shaner, E. A.; Davids, P. S.; Kim, J. K.; Peters, D. W.

    2016-12-01

    We examined the spectral responsivity of a 1.77 μm thick type-II superlattice based long-wave infrared detector in combination with metallic nanoantennas. Coupling between the Fabry-Pérot cavity formed by the semiconductor layer and the resonant nanoantennas on its surface enables spectral selectivity, while also increasing peak quantum efficiency to over 50%. Electromagnetic simulations reveal that this high responsivity is a direct result of field-enhancement in the absorber layer, enabling significant absorption in spite of the absorber's subwavelength thickness. Notably, thinning of the absorbing material could ultimately yield lower photodetector noise through a reduction in dark current while improving photocarrier collection efficiency. The temperature- and incident-angle-independent spectral response observed in these devices allows for operation over a wide range of temperatures and optical systems. This detector paradigm demonstrates potential benefits to device performance with applications throughout the infrared.

  19. Epitaxy, thin films and superlattices

    Energy Technology Data Exchange (ETDEWEB)

    Jagd Christensen, Morten

    1997-05-01

    This report is the result of structural investigations of 3d transition metal superlattices consisting of Fe/V, Cr/Mn, V/Mn and Fe/Mn, and a structural and magnetic study of a series of Ho/Pr alloys. The work includes preparation and characterization of substrates as well as growth of thin films and Fe/V superlattices by molecular beam epitaxy, including in-situ characterization by reflection high energy electron diffraction and Auger electron spectroscopy. Structural characterization has been done by x-ray diffraction and neutron diffraction. The x-ray diffraction experiments have been performed on the rotating copper anode at Risoe, and at synchrotron facilities in Hamburg and Brookhaven, and the neutron scattering was done at the Danish research reactor DR3 at Risoe. In addition to longitudinal scans, giving information about the structural parameters in the modulation direction, non-specular scans were also performed. This type of scans gives information about in-plane orientation and lattice parameters. From the analysis, structural information is obtained about lattice parameters, epitaxial strain, coherence lengths and crystallographic orientation for the superlattice systems, except Fe/Mn superlattices, which could not be modelled. For the Ho/Pr alloys, x-ray magnetic scattering was performed, and the crystal and magnetic structure was investigated. (au) 14 tabs.; 58 ills., 96 refs.

  20. Structure and lattice dynamics of GaN and AlN. Ab-initio investigations of strained polytypes and superlattices

    Energy Technology Data Exchange (ETDEWEB)

    Wagner, Jan-Martin

    2004-10-14

    In this dissertation, ab-initio investigations of the strain influence on vibrational properties of GaN and AlN as well as of short-period GaN/AlN superlattices are presented. Based on densityfunctional theory and density-functional perturbation theory, for differently strained structures complete phonon spectra and related properties are calculated using the local-density approximation and norm-conserving pseudopotentials. (orig.)

  1. Ultra-Lightweight Hybrid Structured Mirror Project

    Data.gov (United States)

    National Aeronautics and Space Administration — MMCC is proposing herewith a hybrid structured mirror that combines the advantages of SiC membrane and magnesium graphite composite. The significance of magnesium...

  2. Superlattice Structures, Electronic Properties, and Spin Dynamics of the Partially Cu-Extracted Phase for the Composite Crystal System CuxV4O11

    Science.gov (United States)

    Onoda, Masashige; Tamura, Asato

    2017-02-01

    The crystal structures, electronic properties, and spin dynamics of CuxV4O11 with 1.2 ≤ x system, are explored through measurements of x-ray four-circle diffraction, electrochemistry, electrical resistivity, thermoelectric power, magnetization, and electron paramagnetic resonance. This system has superlattice structures mainly ascribed to the partial ordering of Cu ions. Cu1.78V4O11 is triclinic with space group Pbar{1} and the double supercell of the V4O11 substructure of the composite crystal. The significantly Cu-extracted crystal Cu1.40V4O11 has a quadruple supercell with space group P1. The electron transport for V ions is nonmetallic owing to the polaronic nature and/or phonon softening and to the random potential of Cu ions. The Curie-Weiss-type paramagnetism basically originates from the Cu2+ chain coordinated octahedrally, and the EPR relaxation at low temperatures is understood through the exchange mechanism for the dipole-dipole and anisotropic exchange interactions. The near absence of paramagnetic behaviors of V4+ ions might be due to the spin-singlet ladder model or alternating-exchange chain model depending on the superlattice structure and valence distribution. The electrochemical performance of Li rechargeable batteries using this superlattice system is about 300 A h kg-1 at voltages above 2 V.

  3. Superlattice Thermoelectric Materials and Devices

    Science.gov (United States)

    Venkatasubramanian, Rama

    2002-03-01

    We have recently demonstrated a significant enhancement in thermoelectric figure-of-merit (ZT) at 300K, of about 2.4 in p-type Bi2Te3/Sb2Te3 superlattices, using the concept of phonon-blocking electron-transmitting superlattice structures [1]. The phonon blocking arises from a complex localization-like behavior for phonons in nano-structured superlattices and the electron transmission is facilitated by optimal choice of band-offsets in these semiconductor hetero-structures. We will also discuss the ZT 1.2 results in n-type Bi2Te3/Bi2Te3-xSex superlattices and our initial understanding on the reasons behind the less-than-dramatic performance of these materials compared to the p-type superlattices. Due to the high ZT of the material, devices potentially offer high coefficient of performance (COP) in solid-state refrigeration. The thin-film devices, resulting from rather simple microelectronic processing, allow high cooling power densities to be achieved for a variety of high-power electronic applications. We have obtained 32K and 40K sub-ambient cooling at 298K and 353K, respectively, in these superlattice micro-thermoelements with potential localized active-cooling power densities approaching 700 W/cm2. In addition to high-performance (in terms of COP) and power densities, these thin-film microdevices are also extremely fast-acting, within 10 microsec and about a factor of 23,000 better than bulk thermoelectric technology. Thus, these are of significance for preventing thermal run-away in high-power electronics. We will present results to demonstrate this concept with infrared imaging of cooling/heating with superlattice micro-devices. We will also discuss outstanding issues such as heat removal from the heat sink towards the full exploitation of this technology. In addition, we will compare the state-of-the-art with other thin-film superlattice materials and device concepts. [1] R. Venkatasubramanian, E. Siivola, T. Colpitts, and B.C. O’Quinn, Thin

  4. Structural and optical properties of InAs/InAsSb superlattices grown by metal organic chemical vapor deposition for mid-wavelength infrared photodetectors

    Energy Technology Data Exchange (ETDEWEB)

    Ning, Zhen-Dong, E-mail: ningzd@semi.ac.cn [School of Materials Science and Engineering, Harbin Institute of Technology, Harbin 150001 (China); Liu, Shu-Man, E-mail: liusm@semi.ac.cn [Key Laboratory of Semiconductor Materials Science, Institute of Semiconductors, Chinese Academy of Sciences, Beijing 100083 (China); Luo, Shuai; Ren, Fei; Wang, Feng-Jiao; Yang, Tao; Liu, Feng-Qi [Key Laboratory of Semiconductor Materials Science, Institute of Semiconductors, Chinese Academy of Sciences, Beijing 100083 (China); Wang, Zhan-Guo [School of Materials Science and Engineering, Harbin Institute of Technology, Harbin 150001 (China); Key Laboratory of Semiconductor Materials Science, Institute of Semiconductors, Chinese Academy of Sciences, Beijing 100083 (China); Zhao, Lian-Cheng [School of Materials Science and Engineering, Harbin Institute of Technology, Harbin 150001 (China)

    2016-04-15

    Graphical abstract: - Highlights: • Structural and optical properties of InAs/InAsSb superlattices were investigated. • Temperature dependent photoluminescence emission was investigated in detail. • The Varshni and Bose–Einstein parameters were obtained. - Abstract: InAs/InAsSb superlattices were grown on (0 0 1) GaSb substrates by metal organic chemical vapor deposition for potential applications as mid-infrared optoelectronic devices. X-ray diffraction, transmission electron microscopy, photoluminescence emission and spectral photoconductivity were used to characterize the grown structures. Generally, photoluminescence emission measurements of InAs/InAsSb superlattices were performed over the temperature range from 11 K to 300 K. The Varshni and Bose–Einstein parameters were determined. Low-temperature photoluminescence measurements showed peaks at 3–5 μm, while photoconductance results showed strong spectral response up to room temperature, when the photoresponse onset was extended to 5.5 μm. The photoluminescence emission band covers the CO{sub 2} absorption peak making it suitable for application in CO{sub 2} detection.

  5. Exchange bias in Fe/Cr double superlattices.

    Energy Technology Data Exchange (ETDEWEB)

    Jiang, J. S.; Felcher, G. P.; Inomata, A.; Goyette, R.; Nelson, C.; Bader, S. D.

    1999-11-30

    Utilizing the oscillatory interlayer exchange coupling in Fe/Cr superlattices, we have constructed ''double superlattice'' structures where a ferromagnetic (F) and an antiferromagnetic (AF) Fe/Cr superlattice are coupled through a Cr spacer. The minor hysteresis loops in the magnetization are shifted from zero field, i.e., the F superlattice is exchange biased by the AF one. The double superlattices are sputter-deposited with (211) epitaxy and possess uniaxial in-plane magnetic anisotropy. The magnitude of the bias field is satisfactorily described by the classic formula for collinear spin structures. The coherent structure and insensitivity to atomic-scale roughness makes it possible to determine the spin distribution by polarized neutron reflectivity, which confirms that the spin structure is collinear. The magnetic reversal behavior of the double superlattices suggests that a realistic model of exchange bias needs to address the process of nucleating local reverse domains.

  6. Structural phase transition and superlattice misfit strain of RFeAsO (R=La,Pr,Nd,Sm)

    Science.gov (United States)

    Ricci, A.; Poccia, N.; Joseph, B.; Barba, L.; Arrighetti, G.; Ciasca, G.; Yan, J.-Q.; McCallum, R. W.; Lograsso, T. A.; Zhigadlo, N. D.; Karpinski, J.; Bianconi, A.

    2010-10-01

    The tetragonal-to-orthorhombic structural phase transition (SPT) in LaFeAsO (La-1111) and SmFeAsO (Sm-1111) single crystals measured by high-resolution x-ray diffraction is found to be sharp while the RFeAsO (R=La,Nd,Pr,Sm) polycrystalline samples show a broad continuous SPT. Comparing the polycrystalline and the single-crystal 1111 samples, the critical exponents of the SPT are found to be the same while the correlation length critical exponents are found to be very different. These results imply that the lattice fluctuations in 1111 systems change in samples with different surface to volume ratio that is assigned to the relieve of the temperature-dependent superlattice misfit strain between active iron layers and the spacer layers in 1111 systems. This phenomenon that is missing in the AFe2As2 (A=Ca,Sr,Ba) “122” systems, with the same electronic structure but different for the thickness and the elastic constant of the spacer layers, is related with the different maximum superconducting transition temperature in the 1111 (55 K) versus 122 (35 K) systems and implies the surface reconstruction in 1111 single crystals.

  7. Synthesis and crystal structure of a Pr5Ni19 superlattice alloy and its hydrogen absorption-desorption property.

    Science.gov (United States)

    Iwase, Kenji; Sakaki, Kouji; Matsuda, Junko; Nakamura, Yumiko; Ishigaki, Toru; Akiba, Etsuo

    2011-05-16

    The intermetallic compound Pr(5)Ni(19), which is not shown in the Pr-Ni binary phase diagram, was synthesized, and the crystal structure was investigated by X-ray diffraction (XRD) and transmission electron microscopy (TEM). Two superlattice reflections with the Sm(5)Co(19)-type structure (002 and 004) and the Pr(5)Co(19)-type structure (003 and 006) were observed in the 2θ region between 2° and 15° in the XRD pattern using Cu Kα radiation. Rietveld refinement provided the goodness-of-fit parameter S = 6.7 for the Pr(5)Co(19)-type (3R) structure model and S = 1.7 for the Sm(5)Co(19)-type (2H) structure model, indicating that the synthesized compound has a Sm(5)Co(19) structure. The refined lattice parameters were a = 0.50010(9) nm and c = 3.2420(4) nm. The high-resolution TEM image also clearly revealed that the crystal structure of Pr(5)Ni(19) is of the Sm(5)Co(19) type, which agrees with the results from Rietveld refinement of the XRD data. The P-C isotherm of Pr(5)Ni(19) in the first absorption was clearly different from that in the first desorption. A single plateau in absorption and three plateaus in desorption were observed. The maximum hydrogen storage capacity of the first cycle reached 1.1 H/M, and that of the second cycle was 0.8 H/M. The 0.3 H/M of hydrogen remained in the metal lattice after the first desorption process.

  8. A hybrid piezoelectric structure for wearable nanogenerators

    Energy Technology Data Exchange (ETDEWEB)

    Lee, Minbaek; Wang, Sihong; Wang, Zhong Lin [School of Materials Science and Engineering, Georgia Institute of Technology, Atlanta, GA 30332 (United States); Chen, Chih-Yen [School of Materials Science and Engineering, Georgia Institute of Technology, Atlanta, GA 30332 (United States); Department of Materials Science and Engineering, National Tsing-Hua University, Hsinchu, 30013 (China); Cha, Seung Nam; Park, Yong Jun; Kim, Jong Min [Frontier Research Lab, Samsung Advanced Institute of Technology, Samsung Electronics, Gyeonggi-Do 446-712 (Korea, Republic of); Chou, Li-Jen [Department of Materials Science and Engineering, National Tsing-Hua University, Hsinchu, 30013 (China)

    2012-04-03

    A hybrid-fiber nanogenerator comprising a ZnO nanowire array, PVDF polymer and two electrodes is presented. Depending on the bending or spreading action of the human arm, at an angle of {proportional_to}90 , the hybrid fiber reaches electrical outputs of {proportional_to}0.1 V and {proportional_to}10 nA cm{sup -2}. The unique structure of the hybrid fiber may inspire future research in wearable energy-harvesting technology. (Copyright copyright 2012 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim)

  9. Theory of THz harmonic generation in semiconductor superlattices (Conference Presentation)

    Science.gov (United States)

    Pereira, Mauro F.; Winge, David O.; Wacker, Andreas

    2016-10-01

    Superlattices are artificial structures with a wide range of applications and open possibilities for controlling and study transport and optical [M.F. Pereira Jr., Phys. Rev. B 52, (1995)] properties of semiconductors. In this work, we start from the full Nonequilibrium Greens Functions approach [A. Wacker et a, IEEE Journal of Sel. Top. in Quantum Electron.,19 1200611, (2013),T. Schmielau and M.F. Pereira, Appl. Phys. Lett. 95 231111, (2009)] to obtain Voltage-Current curves and compare them with experiments. By adjusting the numerical solutions of the corresponding Dyson equations to a simple model, analytical solutions are given for the nonlinear response of a biased superlattice under sub-THz radiation. The frequency multiplication process leading to multiple harmonicgeneration is described. This hybrid approach leads to predictive simulations and may have important application for a new generation of devices where the superlattices are used as both sources and detectors and may be particular useful for high resolution transient spectroscopy [A.A. Yablokov et at, IEEE Transactions on THz Science and Technology 5, 845 (2015)].

  10. Structurally induced magnetization in a La{sub 2/3}Sr{sub 4/3}MnO{sub 4} superlattice

    Energy Technology Data Exchange (ETDEWEB)

    Shah, Amish B. [Frederick Seitz Materials Research Laboratory, University of Illinois at Urbana-Champaign, 104 S. Goodwin Ave., Urbana, IL 61801 (United States); Department of Physics, Arizona State University, Tempe, AZ 85287 (United States); Nelson-Cheeseman, Brittany B.; Bhattacharya, Anand [Center for Nanoscale Materials and Materials Science Division, Argonne National Laboratory, Argonne, IL 60439 (United States); Subramanian, Ganesh; Spence, John C.H. [Department of Physics, Arizona State University, Tempe, AZ 85287 (United States)

    2012-07-15

    A structural transition has been observed in a digital superlattice of La{sub 2/3}Sr{sub 4/3}MnO{sub 4}, which is correlated to a magnetization enhancement upon cooling the sample. These artificial superlattices were grown layer-by-layer using ozone-assisted molecular beam epitaxy (MBE). Electron diffraction experiments show a phase transition below 150 K in nanopatches of the superlattice, which coincides with an enhanced magnetization starting below 110 K. Atomic scale electron energy loss spectroscopy (EELS) also shows changes in the Mn L{sub 2,3} and O K edges, which are related to valence, strain, and the atomic coordination within nanopatches. Atomic resolution image and EELS showing variations of oxygen and lanthanum signature edges in a La{sub 2/3}Sr{sub 4/3}MnO{sub 4} supperlattice. (Copyright copyright 2012 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim)

  11. Strong reduction of the lattice thermal conductivity in superlattices and quantum dot superlattices

    Science.gov (United States)

    Fomin, V. M.; Nika, D. L.; Cocemasov, A. I.; Isacova, C. I.; Schmidt, O. G.

    2012-06-01

    Thermal transport is theoretically investigated in the planar Si/Ge superlattices and Si/Ge quantum dot superlattices. The phonon states in the considered nanostructures are obtained using the Face-centered Cubic Cell model of lattice dynamics. A significant reduction of the lattice thermal conductivity is revealed in both considered structures in a wide range of temperatures from 100 K to 400 K. This effect is explained by the removal of the high-energy and high-velocity phonon modes from the heat flux due to their localization in superlattice segments and the phonon scattering on the interfaces. The obtained results show prospects of the planar superlattices and quantum-dot superlattices for thermoelectric and thermo-insulating applications.

  12. Euro hybrid materials and structures. Proceedings

    Energy Technology Data Exchange (ETDEWEB)

    Hausmann, Joachim M.; Siebert, Marc (eds.)

    2016-08-01

    In order to use the materials as best as possible, several different materials are usually mixed in one component, especially in the field of lightweight design. If these combinations of materials are joined inherently, they are called multi material design products or hybrid structures. These place special requirements on joining technology, design methods and manufacturing and are challenging in other aspects, too. The eight chapters with manuscripts of the presentations are: Chapter 1- Interface: What happens in the interface between the two materials? Chapter 2 - Corrosion and Residual Stresses: How about galvanic corrosion and thermal residual stresses in the contact zone of different materials? Chapter 3 - Characterization: How to characterize and test hybrid materials? Chapter 4 - Design: What is a suitable design and dimensioning method for hybrid structures? Chapter 5 - Machining and Processing: How to machine and process hybrid structures and materials? Chapter 6 - Component Manufacturing: What is a suitable manufacturing route for hybrid structures? Chapter 7 - Non-Destructive Testing and Quality Assurance: How to assure the quality of material and structures? Chapter 8 - Joining: How to join components of different materials?.

  13. Polyadic Cantor superlattices with variable lacunarity.

    Science.gov (United States)

    Jaggard, D L; Jaggard, A D

    1997-02-01

    Reflection and transmission properties of polyadic fractal superlattices are formulated, solved analytically, and characterized for variations in stage of growth, fractal dimension, and lacunarity. This is the first time to our knowledge that the effect of lacunarity on wave interactions with such structures has been considered. The results are summarized by families of reflection data that we denote twist plots. A new doubly recursive computational technique efficiently provides the reflection and transmission coefficients for a large class of Cantor superlattices with numerous interfaces.

  14. Aging in Magnetic Superlattices

    Science.gov (United States)

    Mukherjee, Tathagata; Pleimling, Michel; Binek, Christian

    2010-03-01

    Aging phenomena can be observed in non-equilibrium systems with slow relaxation dynamics. Magnetic specimens with well defined interactions and dimensions can serve as model systems for universal aspects of aging. Magnetic thin films provide access to a wide range of microscopic parameters. Superlattice structures allow tuning the intra and inter-plane exchange and enable geometrical confinement of the spin fluctuations. We use Co/Cr thin film superlattices to study magnetic aging. The static and dynamic magnetic properties are affected via the Co and Cr film thicknesses. The Curie temperature of the Co films is reduced from the bulk value by geometrical confinement. Cr provides antiferromagnetic coupling between the Co films. In-plane magnetic set fields of some 10-100 mT are applied and the sample is exposed to the latter for various waiting times. After removing the field, relaxation of the magnetization is recorded via longitudinal Kerr-magnetometry and SQUID. The relaxation data are analyzed by scaling plots revealing universal aspects of aging. Financial support by NRI, and NSF through EPSCoR, Career DMR-0547887, DMR-0904999, and MRSEC.

  15. Study of hybrid orientation structure wafer*

    Institute of Scientific and Technical Information of China (English)

    Tan Kaizhou; Zhang Jing; Xu Shiliu; Zhang Zhengfan; Yang Yonghui; Chen Jun; Liang Tao

    2011-01-01

    Two types of 5 μm thick hybrid orientation structure wafers, which were integrated by (110) or (100) orientation silicon wafers as the substrate, have been investigated for 15-40 V voltage ICs and MEMS sensor applications. They have been obtained mainly by SOI wafer bonding and a non-selective epitaxy technique, and have been presented in China for the first time. The thickness of BOX SiO2 buried in wafer is 220 nm. It has been found that the quality of hybrid orientation structure with (100) wafer substrate is better than that with (110) wafer substrate by “Sirtl defect etching of HOSW”.

  16. Current responsivity of semiconductor superlattice THz-photon detectors

    DEFF Research Database (Denmark)

    Ignatov, Anatoly A.; Jauho, Antti-Pekka

    1999-01-01

    The current responsivity of a semiconductor superlattice THz-photon detector is calculated using an equivalent circuit model which takes into account the finite matching efficiency between a detector antenna and the superlattice in the presence of parasitic losses. Calculations performed for curr......The current responsivity of a semiconductor superlattice THz-photon detector is calculated using an equivalent circuit model which takes into account the finite matching efficiency between a detector antenna and the superlattice in the presence of parasitic losses. Calculations performed...... for currently available superlattice diodes show that both the magnitudes and the roll-off frequencies of the responsivity are strongly influenced by an excitation of hybrid plasma-Bloch oscillations which are found to be eigenmodes of the system in the THz-frequency band. The expected room temperature values...

  17. Superlattice Optical Bistability Research.

    Science.gov (United States)

    2014-09-26

    multilayer heterojunction and superlattice device applications. 2.0 Growth Studies The MBE growth of mercury compound is still relatively new and novel...These superlattices are grown by molecular beam epitaxy in a MBE system specifically designed to handle mercury . MBE is an ultrahigh vacuum evaporative...therefore the growth process is not as well understood as that of III-V semiconductor - compounds . In HgTe-CdTe superlattices the CdTe deposition is

  18. Tetragonal-strain-induced local structural modifications in InAsxP1-x/InP superlattices: A detailed x-ray-absorption investigation

    Science.gov (United States)

    Pascarelli, S.; Boscherini, F.; Lamberti, C.; Mobilio, S.

    1997-07-01

    We report a comprehensive investigation of the local structure around As in thin InAsxP1-x strained layers in InAsxP1-x/InP superlattices by fluorescence-detected x-ray-absorption fine structure; seven superlattice samples are studied as a function of composition, and compared to six unstrained, bulk samples of similar composition. Contributions up to the third coordination shell around As are clearly visible in the spectra, and are analyzed taking into account important multiple-scattering contributions. Results show that structural modifications due to tetragonal distortion appear mainly in the second and third coordination shells, while nearest-neighbor bond lengths remain closer to the values in unstrained bulk alloys. This implies that in semiconductor alloys tetragonal strain accommodation is mainly obtained through bond-angle distortions, in analogy to the situation in bulk pseudobinary alloys. A model which combines macroscopic elastic theory and the known local structure in bulk pseudobinary alloys is presented, and is found to fit the data very well.

  19. Spin-dependent optical superlattice

    Science.gov (United States)

    Yang, Bing; Dai, Han-Ning; Sun, Hui; Reingruber, Andreas; Yuan, Zhen-Sheng; Pan, Jian-Wei

    2017-07-01

    We propose and implement a lattice scheme for coherently manipulating atomic spins. Using a vector light shift and a superlattice structure, we demonstrate experimentally its capability on addressing spins in double wells and square plaquettes with subwavelength resolution. The quantum coherence of spin manipulations is verified through measuring atom tunneling and spin exchange dynamics. Our experiment presents a building block for engineering many-body quantum states in optical lattices for realizing quantum simulation and computation tasks.

  20. Self-consistent photonic band structure of dielectric superlattices containing nonlinear optical materials.

    Science.gov (United States)

    Lousse, V; Vigneron, J P

    2001-02-01

    The theory of photonic crystals is extended to include the optical Kerr effect taking place in weak third-order, nonlinear materials present in the unit cell. The influence on the dispersion relations of the illumination caused by a single Bloch mode transiting through the crystal structure is examined. Special attention is given to the modification of the photonic gap width and position. Assuming an instantaneous change of refractive index with illumination, the nonlinear band structure problem is solved as a sequence of ordinary, linear band structure calculations, carried out in a plane-wave field representation.

  1. On the structural characterization of InAs/GaSb type-II superlattices: The effect of interfaces for fixed layer thicknesses

    Energy Technology Data Exchange (ETDEWEB)

    Arikan, Bulent, E-mail: bulentarikanx@gmail.com [Anadolu University, Physics Department, Yunusemre Campus, 26470 Eskisehir (Turkey); Korkmaz, Guven [Anadolu University, Physics Department, Yunusemre Campus, 26470 Eskisehir (Turkey); Suyolcu, Yusuf Eren [Anadolu University, Graduate School of Sciences, Advanced Technologies Research Unit: Nanotechnology, Yunusemre Campus, 26470 Eskisehir (Turkey); Aslan, Bulent; Serincan, Ugur [Anadolu University, Physics Department, Yunusemre Campus, 26470 Eskisehir (Turkey)

    2013-12-02

    We report on the detailed epitaxial growth conditions for type-II InAs/GaSb superlattice (SL) structures designed for mid-wave infrared detection. The mismatch between the GaSb buffer and the SL is precisely controlled by engineering the InSb-like interfaces for fixed InAs and GaSb layer thicknesses in the SL. High resolution X-ray diffraction and cross-sectional high resolution transmission electron microscopy analyses were performed to determine the mismatch and the thicknesses. It was shown that the in-plane lattice mismatch to the GaSb buffer is inversely proportional to the interface thickness for the samples presented here. The effect of the interfaces on the structure was also confirmed by room temperature transmission measurements: features were red-shifted as the interface thickness is increased. - Highlights: • Growth conditions are discussed in detail for type-II InAs/GaSb superlattices. • Interface thicknesses are systematically changed for fixed InAs and GaSb layers. • Shown that in-plane mismatch is inversely proportional to the interface thickness • The mismatch is precisely controlled by engineering the InSb-like interfaces.

  2. Properties of ultra-thin vanadium layers in V/Ru superlattices

    Science.gov (United States)

    Liscio, F.; Maret, M.; Meneghini, C.; Hazemann, J. L.; Albrecht, M.

    2007-12-01

    The properties of ultra-thin vanadium layers in V/Ru(0001) superlattices grown by molecular beam epitaxy were studied. The atomic structure of V was investigated by various methods including reflection high-energy electron diffraction (RHEED), x-ray diffraction (XRD) and polarized x-ray-absorption fine structure (PXAFS). It appears that, for up to three atomic layers, V adopts a slightly distorted hexagonal-close-packed (hcp) structure induced by pseudomorphic growth on Ru(0001). By increasing the V thickness to four atomic layers, this structure almost completely relaxes towards the body-centered-cubic (bcc) bulk structure. This sharp structural transition is also manifested in the electronic properties. A reduced superconducting transition temperature between 0.6 and 1.05 K was found in the bcc V/hcp Ru superlattice, while superconductivity is quenched in the superlattice with hexagonal V. This behavior might be linked to the existence of a ferromagnetic ground state of the metastable V induced by the hybridization of the d-bands at the hcp V/Ru interface, as predicted from first-principles density-functional theory.

  3. Properties of ultra-thin vanadium layers in V/Ru superlattices

    Energy Technology Data Exchange (ETDEWEB)

    Liscio, F [Science et Ingenierie des Materiaux et Procedes, INPGrenoble, CNRS-UJF, BP75, 38402 Saint Martin d' Heres (France); Maret, M [Science et Ingenierie des Materiaux et Procedes, INPGrenoble, CNRS-UJF, BP75, 38402 Saint Martin d' Heres (France); Meneghini, C [Dipartimento Di Fisica, Universita di Roma Tre, 00146-Rome (Italy); Hazemann, J L [Institut Neel, MCMF, CNRS, BP 166, 38042 Grenoble (France); Albrecht, M [Department of Physics, University of Konstanz, D-78457 Konstanz (Germany)

    2007-12-05

    The properties of ultra-thin vanadium layers in V/Ru(0001) superlattices grown by molecular beam epitaxy were studied. The atomic structure of V was investigated by various methods including reflection high-energy electron diffraction (RHEED), x-ray diffraction (XRD) and polarized x-ray-absorption fine structure (PXAFS). It appears that, for up to three atomic layers, V adopts a slightly distorted hexagonal-close-packed (hcp) structure induced by pseudomorphic growth on Ru(0001). By increasing the V thickness to four atomic layers, this structure almost completely relaxes towards the body-centered-cubic (bcc) bulk structure. This sharp structural transition is also manifested in the electronic properties. A reduced superconducting transition temperature between 0.6 and 1.05 K was found in the bcc V/hcp Ru superlattice, while superconductivity is quenched in the superlattice with hexagonal V. This behavior might be linked to the existence of a ferromagnetic ground state of the metastable V induced by the hybridization of the d-bands at the hcp V/Ru interface, as predicted from first-principles density-functional theory.

  4. MBE growth and characterisation of light rare-earth superlattices

    DEFF Research Database (Denmark)

    Ward, R.C.C.; Wells, M.R.; Bryn-Jacobsen, C.

    1996-01-01

    The molecular beam epitaxy growth techniques which have already successfully produced a range of heavy rare-earth superlattices have now been extended to produce superlattices of two light rare-earth elements, Nd/Pr, as well as superlattices and alloy films of a heavy/light system, Ho/Pr. High......-resolution X-ray diffraction analysis shows the Nd/Pr superlattices to be of high structural quality, while the Ho/Pr superlattices are significantly less so. In the Ho/Pr superlattices, Pr is found to retain its bulk dhcp crystal structure even in thin layers (down to 6 atomic planes thick) sandwiched between...... thick layers of hcp Ho. In addition, neutron diffraction studies of the He/Pr superlattices have shown that the helical Ho magnetic order is not coherent through the dhcp Pr layers, in contrast to previous hcp/hcp superlattices Ho/Y, Ho/Lu and Ho/Er. The series of Ho:Pr alloy films has shown structural...

  5. FABRICATION OF PHOTONIC CRYSTAL WITH SUPERLATTICES

    Institute of Scientific and Technical Information of China (English)

    SUN Cheng; Chen Haihua; Zhang Jizhong; Wei Hongmei; Gu Zhongze

    2006-01-01

    A novel technique was used to fabricate three-dimensional photonic crystals with superlattices. The super structure was fabricated by assembling monodispersed microspheres in the grooves of the scales of morpho butterfly, which makes the photonic crystal being composed of two kinds of different photonic structures (natural groove structure of butterfly wing and artificial microspherical colloids arrangement). The superstructural photonic crystal exhibits some unique optical properties different from both the butterfly wing and the colloidal crystal. The approach exhibited here provides a new way for fabricate photonic crystals with superlattices.

  6. Kinematic Analysis of a Hybrid Structure

    Directory of Open Access Journals (Sweden)

    Q.J. Duan

    2012-11-01

    Full Text Available This paper presents a kinematic analysis and simulation of a hybrid structure applied to the new design cable-suspended feed structure (CSFS for the next generation of large spherical radio telescopes. First, considering the requirement that feeds should be tilted from 40° to 60° and that the tracking precision in steady state is 4mm, a novel design of the feed supporting structure including a cable-cabin structure, an AB axis structure and a Stewart platform is performed. Next, kinematic analysis and the simulation of the CSFS are done. Simulations have been developed in combination with the 50m CSFS model, which demonstrate the effectiveness and feasibility of the proposed three-level cable-suspended feed system.

  7. Effect of InSb/In0.9Al0.1Sb superlattice buffer layer on the structural and electronic properties of InSb films

    Science.gov (United States)

    Zhao, Xiaomeng; Zhang, Yang; Guan, Min; Cui, Lijie; Wang, Baoqiang; Zhu, Zhanping; Zeng, Yiping

    2017-07-01

    The effect of InSb/In0.9Al0.1Sb buffer layers on InSb thin films grown on GaAs (0 0 1) substrate by molecular beam epitaxy (MBE) is investigated. The crystal quality and the surface morphology of InSb are characterized by XRD and AFM. The carrier transport property is researched through variable temperature hall test. The sharp interface between InSb/In0.9Al0.1Sb is demonstrated important for the high quality InSb thin film. We try different superlattice buffer layers by changing ratios, 2-0.5, thickness, 300-450 nm, and periods, 20-50. According to the function of the dislocation density to the absolute temperature below 150 K with different periods of SL buffers, we can find that the number of periods of superlattice is a major factor to decrease the density of threading dislocations. With the 50 periods SL buffer layer, the electron mobility of InSb at the room temperature and liquid nitrogen cooling temperature is ∼63,000 and ∼4600 cm2/V s, respectively. We deduce that the interface in the SL structure works as a filter layer to prevent the dislocation propagating to the upper InSb thin films.

  8. Electronic Band Structure and New Magneto-transport Properties in p-type Semiconductor Medium-infrared HgTe / CdTe Superlattice

    Science.gov (United States)

    Nafidi, Ab.; EL Abidi, A.; El Kaaouachi, A.; Nafidi, Ah.

    2005-06-01

    We report here the band structure and new magneto-transport results for HgTe (56 Å) / CdTe (30 Å) superlattice grown by molecular beam epitaxy (MBE). The angular dependence of the transverse magnetoresistance follows the two-dimensional (2D) behaviour. At low temperature, the sample exhibits p type conductivity with a concentration of 1.84×1012 cm-2 and a Hall mobility of 8200 cm2/Vs. The observed Shubnikov-de Haas effect gives a carrier density of 1.80×1012 cm-2. The superlattice heavy holes dominate the conduction in plane with an effective mass of 0.297 m0 and Fermi energy (2D) of 14 meV. In intrinsic regime, the measured gap Eg = 190 meV agree well with calculated Eg(Γ, 300 K) =178 meV. The formalism used here predicts that the system is semiconductor, for our HgTe to CdTe thickness ratio d1/d2 = 1,87, when d2 < 140 Å. In our case, d2=30 Å and Eg (Γ, 4.2 K) = 111 meV. In spite of it, the sample exhibits the features typical of a p type semiconductor and is a medium-infrared detector (7 μm< λ< 11 μm).

  9. Structural refinement of artificial superlattices by the X-ray diffraction method

    CERN Document Server

    Ishibashi, Y; Tsurumi, T

    1999-01-01

    This paper reports a structural refinement of BaTiO sub 3 (BTO)/SrTiO sub 3 (STO) artificially superstructured thin films. The refinement was achieved by taking into account the effect of interdiffusion between BTO and STO. The samples were prepared by a molecular-beam epitaxy method on SrTiO sub 3 (001) substrate at 600 .deg. C. The phonon model was employed to simulate the X-ray diffraction (XRD) profiles. A discrepancy was observed in the intensities of the satellite peaks when the effect of the interdiffusion between BTO and STO was not incorporated in the simulation. In successive simulations, the concentration profile due to the interdiffusion was first calculated according to Fick's second law, and then the coefficients of the Fourier series describing the lattice distortion and the modulation of the structure factor were determined. The XRD profiles thus simulated almost completely agreed with those observed. This indicates that XRD analysis with the calculation process proposed in this study will ena...

  10. Hybrid Method Simulation of Slender Marine Structures

    DEFF Research Database (Denmark)

    Christiansen, Niels Hørbye

    This present thesis consists of an extended summary and five appended papers concerning various aspects of the implementation of a hybrid method which combines classical simulation methods and artificial neural networks. The thesis covers three main topics. Common for all these topics...... is that they deal with time domain simulation of slender marine structures such as mooring lines and flexible risers used in deep sea offshore installations. The first part of the thesis describes how neural networks can be designed and trained to cover a large number of different sea states. Neural networks can...... that a single neural network can cover all relevant sea states. The applicability and performance of the present hybrid method is demonstrated on a numerical model of a mooring line attached to a floating offshore platform. The second part of the thesis demonstrates how sequential neural networks can be used...

  11. Plasmonic Enhanced Type-II Superlattice Focal Plane Arrays Project

    Data.gov (United States)

    National Aeronautics and Space Administration — SVT Associates proposes an novel type II superlattice structure to extend the cutoff wavelength and CBIRD SL photo diode structure with unipolar barriers to suppress...

  12. Magnetic properties of rare earth superlattices

    CERN Document Server

    Wilkins, C J T

    2001-01-01

    Single-crystal Tm/Y and Tm/Lu superlattices have been grown using molecular beam epitaxy and their chemical structures have been determined using X-ray diffraction. Magnetisation measurements have revealed a more complicated phase diagram than that of pure Tm. Application of a field along the c-direction gave rise to an extra transition, and transitions were detected for the superlattices when the field was applied along the b-axis. In neutron diffraction studies, c-axis longitudinally modulated magnetic structures were found for both Tm/Y and Tm/Lu, which propagate coherently through the non-magnetic layers. In the case of Tm/Lu superlattices, there is evidence for ordering of the basal plane components.

  13. Dynamic square superlattice of Faraday waves

    Science.gov (United States)

    Kahouadji, Lyes; Chergui, Jalel; Juric, Damir; Shin, Seungwon; Tuckerman, Laurette

    2014-11-01

    Faraday waves are computed in a 3D container using BLUE, a code based on a hybrid Front-Tracking/Level-set algorithm for Lagrangian tracking of arbitrarily deformable phase interfaces. A new dynamic superlattice pattern is described which consists of a set of square waves arranged in a two-by-two array. The corners of this array are connected by a bridge whose position oscillates in time between the two diagonals.

  14. X-ray reflectivity and atomic force microscopy studies of MOCVD grown AlxGa1-xN/GaN superlattice structures*

    Institute of Scientific and Technical Information of China (English)

    Wang Yuanzhang; Li Jinchai; Li Shuping; Chen Hangyang; Liu Dayi; Kang Junyong

    2011-01-01

    The grazing incidence X-ray reflectivity (GIXR) technique and atomic force microscopy (AFM) were exploited to obtain an accurate evaluation of the surfaces and interfaces for metalorganic chemical vapor deposition grown AlxGa1-xN/GaN superlattice structures. The X-ray diffraction results have been combined with reflectivity data to evaluate the layer thickness and Al mole fraction in the AlGaN layer. The presence ora smooth interface is responsible for the observation of intensity oscillation in GIXR, which is well correlated to step flow observation in AFM images of the surface. The structure with a low Al mole fraction (x = 0.25) and thin well width has a rather smooth surface for the Rrms of AFM data value is 0.45 nm.

  15. Electronic properties of superlattices on quantum rings

    Science.gov (United States)

    da Costa, D. R.; Chaves, A.; Ferreira, W. P.; Farias, G. A.; Ferreira, R.

    2017-04-01

    We present a theoretical study of the one-electron states of a semiconductor-made quantum ring (QR) containing a series of piecewise-constant wells and barriers distributed along the ring circumference. The single quantum well and the superlattice cases are considered in detail. We also investigate how such confining potentials affect the Aharonov–Bohm like oscillations of the energy spectrum and current in the presence of a magnetic field. The model is simple enough so as to allow obtaining various analytical or quasi-analytical results. We show that the well-in-a-ring structure presents enhanced localization features, as well as specific geometrical resonances in its above-barrier spectrum. We stress that the superlattice-in-a-ring structure allows giving a physical meaning to the often used but usually artificial Born–von-Karman periodic conditions, and discuss in detail the formation of energy minibands and minigaps for the circumferential motion, as well as several properties of the superlattice eigenstates in the presence of the magnetic field. We obtain that the Aharonov–Bohm oscillations of below-barrier miniband states are reinforced, owing to the important tunnel coupling between neighbour wells of the superlattice, which permits the electron to move in the ring. Additionally, we analysis a superlattice-like structure made of a regular distribution of ionized impurities placed around the QR, a system that may implement the superlattice in a ring idea. Finally, we consider several random disorder models, in order to study roughness disorder and to tackle the robustness of some results against deviations from the ideally nanostructured ring system.

  16. Electronic properties of superlattices on quantum rings.

    Science.gov (United States)

    da Costa, D R; Chaves, A; Ferreira, W P; Farias, G A; Ferreira, R

    2017-04-26

    We present a theoretical study of the one-electron states of a semiconductor-made quantum ring (QR) containing a series of piecewise-constant wells and barriers distributed along the ring circumference. The single quantum well and the superlattice cases are considered in detail. We also investigate how such confining potentials affect the Aharonov-Bohm like oscillations of the energy spectrum and current in the presence of a magnetic field. The model is simple enough so as to allow obtaining various analytical or quasi-analytical results. We show that the well-in-a-ring structure presents enhanced localization features, as well as specific geometrical resonances in its above-barrier spectrum. We stress that the superlattice-in-a-ring structure allows giving a physical meaning to the often used but usually artificial Born-von-Karman periodic conditions, and discuss in detail the formation of energy minibands and minigaps for the circumferential motion, as well as several properties of the superlattice eigenstates in the presence of the magnetic field. We obtain that the Aharonov-Bohm oscillations of below-barrier miniband states are reinforced, owing to the important tunnel coupling between neighbour wells of the superlattice, which permits the electron to move in the ring. Additionally, we analysis a superlattice-like structure made of a regular distribution of ionized impurities placed around the QR, a system that may implement the superlattice in a ring idea. Finally, we consider several random disorder models, in order to study roughness disorder and to tackle the robustness of some results against deviations from the ideally nanostructured ring system.

  17. High performance hybrid magnetic structure for biotechnology applications

    Science.gov (United States)

    Humphries, David E [El Cerrito, CA; Pollard, Martin J [El Cerrito, CA; Elkin, Christopher J [San Ramon, CA

    2009-02-03

    The present disclosure provides a high performance hybrid magnetic structure made from a combination of permanent magnets and ferromagnetic pole materials which are assembled in a predetermined array. The hybrid magnetic structure provides means for separation and other biotechnology applications involving holding, manipulation, or separation of magnetic or magnetizable molecular structures and targets. Also disclosed are further improvements to aspects of the hybrid magnetic structure, including additional elements and for adapting the use of the hybrid magnetic structure for use in biotechnology and high throughput processes.

  18. Effect of La0.7Sr0.3MnO3 crystal structures on magnetization of (1 1 1) oriented La0.7Sr0.3MnO3-SrRuO3 superlattices

    Science.gov (United States)

    Behera, B. C.; Padhan, P.; Prellier, W.

    2016-05-01

    A series of superlattices consisting of 15 bilayers of ferromagnetic La0.7Sr0.3MnO3 (LSMO) and SrRuO3 (SRO) were grown with either stacking order on (1 1 1) oriented SrTiO3 (STO) substrates using the pulsed laser deposition technique. The Raman spectra of these superlattices show the existence of rhombohedral and orthorhombic crystal structures of LSMO in (111)STO/[11-unit cell (u.c.) LSMO/n-u.c. SRO]X15 superlattices with n  =  2 and 3. Interestingly, the Raman spectra of (1 1 1)STO/[11-u.c. SRO/n-u.c. LSMO]X15 superlattices with n  =  2 and 3 show only the orthorhombic structure of LSMO. The (1 1 1)STO/[11-u.c. LSMO/n-u.c. SRO]X15 superlattices exhibit enhanced magnetization with weak antiferromagnetic coupling whereas reduced magnetization with strong antiferromagnetic coupling is observed in (1 1 1)STO/[11-u.c. SRO/n-u.c. LSMO]X15 superlattices. The observed magnetic properties of these superlattices can be explained by the interfacial structural coupling, as evident from their Raman spectra which suggest a modification in the stereochemistry of Mn at the interfaces.

  19. Energy Band Calculations for Maximally Even Superlattices

    Science.gov (United States)

    Krantz, Richard; Byrd, Jason

    2007-03-01

    Superlattices are multiple-well, semiconductor heterostructures that can be described by one-dimensional potential wells separated by potential barriers. We refer to a distribution of wells and barriers based on the theory of maximally even sets as a maximally even superlattice. The prototypical example of a maximally even set is the distribution of white and black keys on a piano keyboard. Black keys may represent wells and the white keys represent barriers. As the number of wells and barriers increase, efficient and stable methods of calculation are necessary to study these structures. We have implemented a finite-element method using the discrete variable representation (FE-DVR) to calculate E versus k for these superlattices. Use of the FE-DVR method greatly reduces the amount of calculation necessary for the eigenvalue problem.

  20. Structural and electrical properties of InAs/GaSb superlattices grown by metalorganic vapor phase epitaxy for midwavelength infrared detectors

    Energy Technology Data Exchange (ETDEWEB)

    Arikata, Suguru; Kyono, Takashi [Semiconductor Technologies Laboratory, Sumitomo Electric Industries, LTD., Hyogo (Japan); Miura, Kouhei; Balasekaran, Sundararajan; Inada, Hiroshi; Iguchi, Yasuhiro [Transmission Devices Laboratory, Sumitomo Electric Industries, LTD., Yokohama (Japan); Sakai, Michito [Sensor System Research Group, Japan Aerospace Exploration Agency (JAXA), Tsukuba, Ibaraki (Japan); Katayama, Haruyoshi [Space Technology Directorate I, Japan Aerospace Exploration Agency (JAXA), Tsukuba, Ibaraki (Japan); Kimata, Masafumi [College of Science and Engineering, Ritsumeikan University, Shiga (Japan); Akita, Katsushi [Sumiden Semiconductor Materials, LTD., Hyogo (Japan)

    2017-03-15

    InAs/GaSb superlattice (SL) structures were fabricated on GaSb substrates by metalorganic vapor phase epitaxy (MOVPE) toward midwavelength infrared (MWIR) photodiodes. Almost defect-free 200-period SLs with a strain-compensation interfacial layer were successfully fabricated and demonstrate an intense photoluminescence peak centered at 6.1 μm at 4 K and an external quantum efficiency of 31% at 3.5 μm at 20 K. These results indicate that the high-performance MWIR detectors can be fabricated in application with the InAs/GaSb SLs grown by MOVPE as an attractive method for production. (copyright 2017 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim)

  1. Thermal etching rate of GaN during MOCVD growth interruption in hydrogen and ammonia ambient determined by AlGaN/GaN superlattice structures

    Science.gov (United States)

    Zhang, Feng; Ikeda, Masao; Zhang, Shuming; Liu, Jianping; Tian, Aiqin; Wen, Pengyan; Cheng, Yang; Yang, Hui

    2017-10-01

    Thermal etching effect of GaN during growth interruption in the metalorganic chemical vapor deposition reactor was investigated in this paper. The thermal etching rate was determined by growing a series of AlGaN/GaN superlattice structures with fixed GaN growth temperature at 735 °C and various AlGaN growth temperature changing from 900 °C to 1007 °C. It was observed that the GaN layer was etched off during the growth interruption when the growth temperature ramped up to AlGaN growth temperature. The etching thickness was determined by high resolution X-ray diffractometer and the etching rate was deduced accordingly. An activation energy of 2.53 eV was obtained for the thermal etching process.

  2. Tunneling in quantum superlattices with variable lacunarity

    Energy Technology Data Exchange (ETDEWEB)

    Villatoro, Francisco R. [Departamento de Lenguajes y Ciencias de la Computacion, Universidad de Malaga, E-29071 Malaga (Spain); Monsoriu, Juan A. [Departamento de Fisica Aplicada, Universidad Politecnica de Valencia, E-46022 Valencia (Spain)], E-mail: jmonsori@fis.upv.es

    2008-05-19

    Fractal superlattices are composite, aperiodic structures comprised of alternating layers of two semiconductors following the rules of a fractal set. The scattering properties of polyadic Cantor fractal superlattices with variable lacunarity are determined. The reflection coefficient as a function of the particle energy and the lacunarity parameter present tunneling curves, which may be classified as vertical, arc, and striation nulls. Approximate analytical formulae for such curves are derived using the transfer matrix method. Comparison with numerical results shows good accuracy. The new results may be useful in the development of band-pass energy filters for electrons, semiconductor solar cells, and solid-state radiation sources up to THz frequencies.

  3. Sculptured 3D twister superlattices embedded with tunable vortex spirals.

    Science.gov (United States)

    Xavier, Jolly; Vyas, Sunil; Senthilkumaran, Paramasivam; Denz, Cornelia; Joseph, Joby

    2011-09-01

    We present diverse reconfigurable complex 3D twister vortex superlattice structures in a large area embedded with tunable vortex spirals as well as dark rings, threaded by vortex helices. We demonstrate these tunable complex chiral vortex superlattices by the superposition of relatively phase engineered plane waves. The generated complex 3D twister lattice vortex structures are computationally as well as experimentally analyzed using various tools to verify the presence of phase singularities. Our observation indicates the application-specific flexibility of our approach to tailor the transverse superlattice spatial irradiance profile of these longitudinally whirling vortex-cluster units and dark rings.

  4. [Hybridization of crucian carp, Carassius carassius (Linnaeus, 1758), in Ukrainian reservoirs and genetic structure of hybrids].

    Science.gov (United States)

    Mezhzheryn, S V; Kokodyĭĭ, S V; Kulysh, A V; Verlat'iĭĭ, D B; Fedorenko, L V

    2012-01-01

    Hybridization of crucian carps Carassius carassius in polyspecific crucian populations of reservoirs of Ukraine and genetic structure of the hybrids were investigated using biochemical gene marking and cytometric procedure. The fact of wide hybridization between C. auratus and C. carassius was proved to be true by large number of hybrids which can form populations consisting only from hybrid individuals. Hybrids C. auratus x C. carassius were diploid, tryploid and in exceptional cases tetraploid; females and males which most likely breed by hybridogenesis. Besides, some clonal hybrids C. carassius x C. gibelio-1 appearing as tetraploid females, and one triploid female C. carassius x Tinca tinca were revealed. It is supported that hybridization of alien C. auratus with endemic C. carassius became one of mechanisms of replacement and depressions of populations of the last.

  5. Structural evidence for enhanced polarization in a commensurate short-period BaTiO3/SrTiO3 superlattice

    Science.gov (United States)

    Tian, W.; Jiang, J. C.; Pan, X. Q.; Haeni, J. H.; Li, Y. L.; Chen, L. Q.; Schlom, D. G.; Neaton, J. B.; Rabe, K. M.; Jia, Q. X.

    2006-08-01

    A short-period (BaTiO3)6/(SrTiO3)5 superlattice was characterized by x-ray diffraction and transmission electron microscopy. The superlattice is epitaxially oriented with the c axes of BaTiO3 and SrTiO3 normal to the (001) surface of the SrTiO3 substrate. Despite the large in-plane lattice mismatch between BaTiO3 and SrTiO3 (˜2.2%), the superlattice interfaces were found to be nearly commensurate. The crystallographic c /a ratio of the superlattice was measured and the results agree quantitatively with first-principles calculations and phase-field modeling. The agreement supports the validity of the enhanced spontaneous polarization predicted for short-period BaTiO3/SrTiO3 superlattices.

  6. Fe-Substitution for Ni in Misch Metal-Based Superlattice Hydrogen Absorbing Alloys—Part 1. Structural, Hydrogen Storage, and Electrochemical Properties

    Directory of Open Access Journals (Sweden)

    Kwo-Hsiung Young

    2016-11-01

    Full Text Available The effects of Fe partially replacing Ni in a misch metal-based superlattice hydrogen absorbing alloy (HAA were studied. Addition of Fe increases the lattice constants and abundance of the main Ce2Ni7 phase, decreases the NdNi3 phase abundance, and increases the CaCu5 phase when the Fe content is above 2.3 at%. For the gaseous phase hydrogen storage (H-storage, Fe incorporation does not change the storage capacity or equilibrium pressure, but it does decrease the change in both entropy and enthalpy. With regard to electrochemistry, >2.3 at% Fe decreases both the full and high-rate discharge capacities due to the deterioration in both bulk transport (caused by decreased secondary phase abundance and consequent lower synergetic effect and surface electrochemical reaction (caused by the lower volume of the surface metallic Ni inclusions. In a low-temperature environment (−40 °C, although Fe increases the reactive surface area, it also severely hinders the ability of the surface catalytic, leading to a net increase in surface charge-transfer resistance. Even though Fe increases the abundance of the beneficial Ce2Ni7 phase with a trade-off for the relatively unfavorable NdNi3 phase, it also deteriorates the electrochemical performance due to a less active surface. Therefore, further surface treatment methods that are able to increase the surface catalytic ability in Fe-containing superlattice alloys and potentially reveal the positive contributions that Fe provides structurally are worth investigating in the future.

  7. Time-resolved photoluminescence of type-II quantum dots and isoelectronic centers in Zn-Se-Te superlattice structures

    Science.gov (United States)

    Cheung, M. C.-K.; Cartwright, A. N.; Sellers, I. R.; McCombe, B. D.; Kuskovsky, I. L.

    2008-01-01

    Spectrally and time-resolved photoluminescence of a ZnTe /ZnSe superlattice reveals a smooth transition of the photoluminescence (PL) lifetime from ˜100ns at 2.35eV to less than a few nanoseconds at 2.8eV. The significant increase of the lifetime in the low energy region is strong evidence to support the formation of type-II quantum dots (QDs), since in these nanostructures the spatial separation of carriers is increased. The shorter lived emission above 2.5eV is attributed to excitons bound to Te isoelectronic centers in the ZnSe matrix. The smooth transition of the PL lifetime confirms that clusters of these Te atoms evolve into type-II ZnTe /ZnSe QDs.

  8. Hybrid Testing of Composite Structures with Single-Axis Control

    DEFF Research Database (Denmark)

    Waldbjørn, Jacob Paamand; Høgh, Jacob Herold; Stang, Henrik

    2013-01-01

    a hybrid testing platform is introduced for single-component hybrid testing. In this case, the boundary between the numerical model and experimental setup is defined by multiple Degrees-Of-Freedoms (DOFs) which highly complicate the transferring of response between the two substructures. Digital Image......Hybrid testing is a substructuring technique where a structure is emulated by modelling a part of it in a numerical model while testing the remainder experimentally. Previous research in hybrid testing has been performed on multi-component structures e.g. damping fixtures, however in this paper...... Correlation (DIC) is therefore implemented for displacement control of the experimental setup. The hybrid testing setup was verified on a multicomponent structure consisting of a beam loaded in three point bending and a numerical structure of a frame. Furthermore, the stability of the hybrid testing loop...

  9. Superlattice-Induced Insulating States and Valley-Protected Orbits in Twisted Bilayer Graphene

    Science.gov (United States)

    Cao, Y.; Luo, J. Y.; Fatemi, V.; Fang, S.; Sanchez-Yamagishi, J. D.; Watanabe, K.; Taniguchi, T.; Kaxiras, E.; Jarillo-Herrero, P.

    2016-09-01

    Twisted bilayer graphene (TBLG) is one of the simplest van der Waals heterostructures, yet it yields a complex electronic system with intricate interplay between moiré physics and interlayer hybridization effects. We report on electronic transport measurements of high mobility small angle TBLG devices showing clear evidence for insulating states at the superlattice band edges, with thermal activation gaps several times larger than theoretically predicted. Moreover, Shubnikov-de Haas oscillations and tight binding calculations reveal that the band structure consists of two intersecting Fermi contours whose crossing points are effectively unhybridized. We attribute this to exponentially suppressed interlayer hopping amplitudes for momentum transfers larger than the moiré wave vector.

  10. Breaking Dense Structures: Proving Stability of Densely Structured Hybrid Systems

    Directory of Open Access Journals (Sweden)

    Eike Möhlmann

    2015-06-01

    Full Text Available Abstraction and refinement is widely used in software development. Such techniques are valuable since they allow to handle even more complex systems. One key point is the ability to decompose a large system into subsystems, analyze those subsystems and deduce properties of the larger system. As cyber-physical systems tend to become more and more complex, such techniques become more appealing. In 2009, Oehlerking and Theel presented a (de-composition technique for hybrid systems. This technique is graph-based and constructs a Lyapunov function for hybrid systems having a complex discrete state space. The technique consists of (1 decomposing the underlying graph of the hybrid system into subgraphs, (2 computing multiple local Lyapunov functions for the subgraphs, and finally (3 composing the local Lyapunov functions into a piecewise Lyapunov function. A Lyapunov function can serve multiple purposes, e.g., it certifies stability or termination of a system or allows to construct invariant sets, which in turn may be used to certify safety and security. In this paper, we propose an improvement to the decomposing technique, which relaxes the graph structure before applying the decomposition technique. Our relaxation significantly reduces the connectivity of the graph by exploiting super-dense switching. The relaxation makes the decomposition technique more efficient on one hand and on the other allows to decompose a wider range of graph structures.

  11. ZnSe/ZnSeTe Superlattice Nanotips

    Directory of Open Access Journals (Sweden)

    Young SJ

    2010-01-01

    Full Text Available Abstract The authors report the growth of ZnSe/ZnSeTe superlattice nanotips on oxidized Si(100 substrate. It was found the nanotips exhibit mixture of cubic zinc-blende and hexagonal wurtzite structures. It was also found that photoluminescence intensities observed from the ZnSe/ZnSeTe superlattice nanotips were much larger than that observed from the homogeneous ZnSeTe nanotips. Furthermore, it was found that activation energies for the ZnSe/ZnSeTe superlattice nanotips with well widths of 16, 20, and 24 nm were 76, 46, and 19 meV, respectively.

  12. ZnSe/ZnSeTe Superlattice Nanotips

    Science.gov (United States)

    2010-01-01

    The authors report the growth of ZnSe/ZnSeTe superlattice nanotips on oxidized Si(100) substrate. It was found the nanotips exhibit mixture of cubic zinc-blende and hexagonal wurtzite structures. It was also found that photoluminescence intensities observed from the ZnSe/ZnSeTe superlattice nanotips were much larger than that observed from the homogeneous ZnSeTe nanotips. Furthermore, it was found that activation energies for the ZnSe/ZnSeTe superlattice nanotips with well widths of 16, 20, and 24 nm were 76, 46, and 19 meV, respectively. PMID:20672085

  13. Growth, Nitrogen Vacancy Reduction and Solid Solution Formation in Cubic GaN Thin Films and the Subsequent Fabrication of Superlattice Structures Using AlN and InN

    Science.gov (United States)

    1992-06-01

    AD-A253 331 Semiannual Report Growth, Nitrogen Vacancy Reduction and Solid Solution Formation in Cubic GaN Thin Films and the Subsequent Fabrication...Growth, Nitrogen Vacancy Reduction and Solid Solution Formation in Cubic GaN Thin Films and the Subsequent Fabrication of Superlattice Structures Using...34 substrates, such as using a graded AlxGal-xN solid solution as a buffer layer. E. Conclusion We have shown that in the use of our modified gas source MBE

  14. Structural, electronic properties and enhancement of electrical polarization in Er2NiMnO6/La2NiMnO6 superlattice by first-principles calculations

    Directory of Open Access Journals (Sweden)

    Haipeng Lu

    2016-03-01

    Full Text Available Employing first-principles calculations, structural, electronic properties of new multiferroic material Er2NiMnO6/La2NiMnO6 perovskite superlattice are investigated. This structure is computed as monoclinic phase with obvious distortion. The average in-plane anti-phase rotation angle, average out-of-plane in-phase rotation angle and other microscopic features are reported in this paper. Ni and Mn are found in this superlattice that stay high spin states. These microscopic properties play important roles in multiferroic properties. Based on these microscopic features, the relationship between the direction of spontaneous polarization and the order of substitution in neighboring A-O layers is explained. Finally, we try to enhance the electrical polarization magnitude by 32% by altering the previous superlattice as LaEr2NiMnO7 structure. Our results show that both repulsion force of A site rare earth ions and the arrangement of B site ions can exert influences on spontaneous polarization.

  15. Genetic structure in a dynamic baboon hybrid zone corroborates behavioural observations in a hybrid population

    NARCIS (Netherlands)

    Charpentier, M J E; Fontaine, M C; Cherel, E; Renoult, J P; Jenkins, T; Benoit, L; Barthès, N; Alberts, S C; Tung, J

    2012-01-01

    Behaviour and genetic structure are intimately related: mating patterns and patterns of movement between groups or populations influence the movement of genetic variation across the landscape and from one generation to the next. In hybrid zones, the behaviour of the hybridizing taxa can also impact

  16. Superlattice Intermediate Band Solar Cell on Gallium Arsenide

    Science.gov (United States)

    2015-02-09

    AFRL-RV-PS- AFRL-RV-PS- TR-2015-0048 TR-2015-0048 SUPERLATTICE INTERMEDIATE BAND SOLAR CELL ON GALLIUM ARSENIDE Alexandre Freundlich...SUBTITLE 5a. CONTRACT NUMBER FA9453-13-1-0232 Superlattice Intermediate Band Solar Cell on Gallium Arsenide 5b. GRANT NUMBER 5c. PROGRAM ELEMENT NUMBER...band solar cell incorporating low dimensional structures made with dilute nitrogen alloys of III-V semiconductors is investigated theoretically and

  17. Interface bands in carbon nanotube superlattices

    Energy Technology Data Exchange (ETDEWEB)

    Jaskolski, W.; Pelc, M. [Instytut Fizyki UMK, Grudziadzka 5, 87-100 Torun (Poland); Santos, H.; Chico, L. [Instituto de Ciencia de Materiales de Madrid, Consejo Superior de Investigaciones Cientificas, Cantoblanco, 28049 Madrid (Spain); Ayuela, A. [Centro de Fisica de Materiales CSIC-UPV/EHU, Departamento de Fisica de Materiales (Facultad de Quimicas), and Donostia International Physics Center (DIPC), 20080 Donostia (Spain)

    2010-02-15

    We study the electronic band structure of several carbon nanotube superlattices built of two kinds of intermolecular junctions: (12, 0)/(6, 6) and (8, 0)/(14, 0). In particular, we focus on the energy bands originating from interface states. We find that in case of the metallic (12, 0)/(6, 6) superlattices, the interface bands change periodically their character from bonding- to antibonding-like vs. increasing length of the (6, 6) tube. We show that these changes are related to the decay of the charge density Friedel oscillations in the metallic (6, 6) tube. However, when we explore other chiralities without rotational symmetry, no changes in bondingantibonding character are observed for semiconductor superlattices, as exemplified in the case of (8, 0)/(14, 0) superlattices. Our results indicate that unless metallic tubes are employed in the junctions, the bonding-antibonding crossings are not present (copyright 2010 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

  18. Carbon-coated nanoparticle superlattices for energy applications

    Science.gov (United States)

    Li, Jun; Yiliguma, Affa; Wang, Yifei; Zheng, Gengfeng

    2016-07-01

    Nanoparticle (NP) superlattices represent a unique material architecture for energy conversion and storage. Recent reports on carbon-coated NP superlattices have shown exciting electrochemical properties attributed to their rationally designed compositions and structures, fast electron transport, short diffusion length, and abundant reactive sites via enhanced coupling between close-packed NPs, which are distinctive from their isolated or disordered NP or bulk counterparts. In this minireview, we summarize the recent developments of highly-ordered and interconnected carbon-coated NP superlattices featuring high surface area, tailorable and uniform doping, high conductivity, and structure stability. We then introduce the precisely-engineered NP superlattices by tuning/studying specific aspects, including intermetallic structures, long-range ordering control, and carbon coating methods. In addition, these carbon-coated NP superlattices exhibit promising characteristics in energy-oriented applications, in particular, in the fields of lithium-ion batteries, fuel cells, and electrocatalysis. Finally, the challenges and perspectives are discussed to further explore the carbon-coated NP superlattices for optimized electrochemical performances.

  19. Silicone-containing aqueous polymer dispersions with hybrid particle structure.

    Science.gov (United States)

    Kozakiewicz, Janusz; Ofat, Izabela; Trzaskowska, Joanna

    2015-09-01

    In this paper the synthesis, characterization and application of silicone-containing aqueous polymer dispersions (APD) with hybrid particle structure are reviewed based on available literature data. Advantages of synthesis of dispersions with hybrid particle structure over blending of individual dispersions are pointed out. Three main processes leading to silicone-containing hybrid APD are identified and described in detail: (1) emulsion polymerization of organic unsaturated monomers in aqueous dispersions of silicone polymers or copolymers, (2) emulsion copolymerization of unsaturated organic monomers with alkoxysilanes or polysiloxanes with unsaturated functionality and (3) emulsion polymerization of alkoxysilanes (in particular with unsaturated functionality) and/or cyclic siloxanes in organic polymer dispersions. The effect of various factors on the properties of such hybrid APD and films as well as on hybrid particles composition and morphology is presented. It is shown that core-shell morphology where silicones constitute either the core or the shell is predominant in hybrid particles. Main applications of silicone-containing hybrid APD and related hybrid particles are reviewed including (1) coatings which show specific surface properties such as enhanced water repellency or antisoiling or antigraffiti properties due to migration of silicone to the surface, and (2) impact modifiers for thermoplastics and thermosets. Other processes in which silicone-containing particles with hybrid structure can be obtained (miniemulsion polymerization, polymerization in non-aqueous media, hybridization of organic polymer and polysiloxane, emulsion polymerization of silicone monomers in silicone polymer dispersions and physical methods) are also discussed. Prospects for further developments in the area of silicone-containing hybrid APD and related hybrid particles are presented.

  20. Manipulation of electronic structure via alteration of local orbital environment in [(SrIrO3)m,(SrTi O3)] (m =1 ,2 ,and ∞ ) superlattices

    Science.gov (United States)

    Kim, So Yeun; Kim, Choong H.; Sandilands, L. J.; Sohn, C. H.; Matsuno, J.; Takagi, H.; Kim, K. W.; Lee, Y. S.; Moon, S. J.; Noh, T. W.

    2016-12-01

    We investigated the electronic structure of [(SrIrO3)m,(SrTi O3)] (m =1 ,2 ,and ∞ ) superlattice (SL) thin films with optical spectroscopy and first principles calculations. Our optical results confirmed the existence of the Jeff= 1 /2 states in SL samples, similar to the bulk Ruddlesden-Popper series S rn+1I rnO3 n +1 iridates. Apart from this similarity, in the SL samples, we observed red shifts of the characteristic optical excitations in the Jeff= 1 /2 state and an enhancement of the low-energy spectral weight, which implies a reduction in the effective electron correlation for bands near the Fermi energy. The density functional theory plus Coulomb interactions (DFT +U ) calculations suggested that the SrTi O3 layer intervened between SrIr O3 layers in the SLs activated additional hopping channels between the Ir ions, thus increasing the bandwidth and reducing the effective strength of the correlations. This paper demonstrates that fabrication of iridium-based heterostructures can be used to finely tune electronic structures via alteration of their local orbital environments.

  1. Structural and mechanical properties of Laponite-PEG hybrid films.

    Science.gov (United States)

    Shikinaka, Kazuhiro; Aizawa, Kazuto; Murakami, Yoshihiko; Osada, Yoshihito; Tokita, Masatoshi; Watanabe, Junji; Shigehara, Kiyotaka

    2012-03-01

    Inorganic/organic hybrids were obtained by the sol-gel type organic modification reaction of Laponite sidewalls with poly(ethylene glycol) (PEG) bearing alkoxysiloxy terminal functionality. By casting an aqueous dispersion of the hybrid, the flexible and transparent hybrid films were obtained. Regardless of the inorganic/organic component ratio, the hybrid film had the ordered structure of Laponite in-plane flat arrays. The mechanical strength of hybrid films was drastically improved by the presence of cross-linking among alkoxysilyl functionalities of PEG terminals and the absence of PEG crystallines. Hybrid films, especially those that consisted of PEG with short chain, showed good mechanical properties that originate from quasi-homogeneous dispersion of components due to anchoring of PEG terminal to Laponite sidewall and interaction of PEG to Laponite surface.

  2. Ultrasound focusing images in superlattices

    Energy Technology Data Exchange (ETDEWEB)

    Narita, Michiko; Tanaka, Yukihiro; Tamura, Shin-ichiro [Department of Applied Physics, Hokkaido University, Sapporo (Japan)

    2002-03-04

    We study theoretically ultrasound focusing in periodic multilayered structures, or superlattices, by solving the wave equation with the Green function method and calculating the transmitted ultrasound amplitude images of both the longitudinal and transverse modes. The constituent layers assumed are elastically isotropic but the periodically stacked structure is anisotropic. Thus anisotropy of ultrasound propagation is predicted even at low frequencies and it is enhanced significantly at higher frequencies due to the zone-folding effect of acoustic dispersion relations. An additional effect studied is the interference of ultrasound (known as the internal diffraction), which can be recognized when the propagation distance is comparable to the ultrasound wavelength. Numerical examples are developed for millimetre-scale Al/polymer multilayers used recently for imaging experiment with surface acoustic waves. (author)

  3. Picosecond luminescence approach to vertical transport in GaAs/GaAlAs superlattices

    Science.gov (United States)

    Deveaud, B.; Chomette, A.; Lambert, B.; Regreny, A.; Romestain, R.; Edel, P.

    1986-03-01

    Picosecond luminescence of GaAs/GaAlAs superlattices has been measured at 5 K. Asymetrical structures where one larger well is introduced at 9000 Å from the surface are studied. It is then possible to estimate the mean transfer time of photoexcited carriers through 9000 Å of superlattice. This time is found to be about 4 nsec in a 40/40 Å superlattice and 800 psec in a 30/30 Å one. This evidences the rather high mobility of small period superlattices in the growth direction.

  4. Advanced fiber-composite hybrids--A new structural material

    Science.gov (United States)

    Chamis, C. C.; Lark, R. F.; Sullivan, T. L.

    1974-01-01

    Introduction of metal foil as part of matrix and fiber composite, or ""sandwich'', improves strength and stiffness for multidirectional loading, improves resistance to cyclic loading, and improves impact and erosion resistance of resultant fiber-composite hybrid structure.

  5. Magnetic Graphene Nanohole Superlattices

    CERN Document Server

    Yu, Decai; Liu, Miao; Liu, Wei; Liu, Feng

    2008-01-01

    We investigate the magnetic properties of nano-holes (NHs) patterned in graphene using first principles calculations. We show that superlattices consisting of a periodic array of NHs form a new family of 2D crystalline "bulk" magnets whose collective magnetic behavior is governed by inter-NH spin-spin interaction. They exhibit long-range magnetic order well above room temperature. Furthermore, magnetic semiconductors can be made by doping magnetic NHs into semiconducting NH superlattices. Our findings offer a new material system for fundamental studies of spin-spin interaction and magnetic ordering in low dimensions, and open up the exciting opportunities of making engineered magnetic materials for storage media and spintronics applications.

  6. Designing CNC Knit for Hybrid Membrane And Bending Active Structures

    DEFF Research Database (Denmark)

    Tamke, Martin; Holden Deleuran, Anders; Gengnagel, Christoph

    2015-01-01

    Recent advances in computation allow for the integration of design and simulation of highly interrelated systems, such as hybrids of structural membranes and bending active elements. The engaged complexities of forces and logistics can be mediated through the development of materials with project...... means to design, specify, make and test CNC knit as material for hybrid structures in architectural scale. This paper shares the developed process, identifies challenges, potentials and future work...

  7. Identification of an organic semiconductor superlattice structure of pentacene and perfluoro-pentacene through resonant and non-resonant X-ray scattering

    Energy Technology Data Exchange (ETDEWEB)

    Kowarik, S.; Weber, C. [Humboldt-Universität zu Berlin, Institut für Physik, Newtonstr. 15, 12489 Berlin (Germany); Hinderhofer, A.; Gerlach, A.; Schreiber, F. [Universität Tübingen, Institut für Angewandte Physik, Auf der Morgenstelle 10, 72076 Tübingen (Germany); Wang, C.; Hexemer, A. [Advanced Light Source, Lawrence Berkeley National Laboratory, Berkeley, CA 94720 (United States); Leone, S. R. [Departments of Chemistry and Physics, University of California, and Lawrence Berkeley National Laboratory, Berkeley, CA 94720 (United States)

    2015-11-15

    Highly crystalline and stable molecular superlattices are grown with the smallest possible stacking period using monolayers (MLs) of the organic semiconductors pentacene (PEN) and perfluoro-pentacene (PFP). Superlattice reflections in X-ray reflectivity and their energy dependence in resonant soft X-ray reflectivity measurements show that PFP and PEN MLs indeed alternate even though the coherent ordering is lost after ∼ 4 ML. The observed lattice spacing of 15.9 Å in the superlattice is larger than in pure PEN and PFP films, presumably because of more upright standing molecules and lack of interdigitation between the incommensurate crystalline PEN and PFP layers. The findings are important for the development of novel organic quantum optoelectronic devices.

  8. Identification of an organic semiconductor superlattice structure of pentacene and perfluoro-pentacene through resonant and non-resonant X-ray scattering

    Directory of Open Access Journals (Sweden)

    S. Kowarik

    2015-11-01

    Full Text Available Highly crystalline and stable molecular superlattices are grown with the smallest possible stacking period using monolayers (MLs of the organic semiconductors pentacene (PEN and perfluoro-pentacene (PFP. Superlattice reflections in X-ray reflectivity and their energy dependence in resonant soft X-ray reflectivity measurements show that PFP and PEN MLs indeed alternate even though the coherent ordering is lost after ∼ 4 ML. The observed lattice spacing of 15.9 Å in the superlattice is larger than in pure PEN and PFP films, presumably because of more upright standing molecules and lack of interdigitation between the incommensurate crystalline PEN and PFP layers. The findings are important for the development of novel organic quantum optoelectronic devices.

  9. Tunneling of electrons through semiconductor superlattices

    Indian Academy of Sciences (India)

    C L Roy

    2002-11-01

    The purpose of the present paper is to report a study of tunneling of electrons through semiconductor superlattices (SSL); specially, we have analysed diverse features of transmission coefficient of SSL. The SSL we have considered is Ga0.7Al0.3As–GaAs which has been drawing considerable attention during the recent past on account of some typical features of its band structure. We have indicated how our results would help fabrication of ultra high speed devices.

  10. Hybrid Optimization in the Design of Reciprocal Structures

    DEFF Research Database (Denmark)

    Parigi, Dario; Kirkegaard, Poul Henning; Sassone, Mario

    2012-01-01

    The paper presents a method to generate the geometry of reciprocal structures by means of a hybrid optimization procedure. The geometry of reciprocal structures where elements are sitting on the top or in the bottom of each other is extremely difficult to predict because of the non...... is then applied to a recent example of free-form reciprocal structure....

  11. Design of Hybrid Solid Polymer Electrolytes: Structure and Properties

    Science.gov (United States)

    Bronstein, Lyudmila M.; Karlinsey, Robert L.; Ritter, Kyle; Joo, Chan Gyu; Stein, Barry; Zwanziger, Josef W.

    2003-01-01

    This paper reports synthesis, structure, and properties of novel hybrid solid polymer electrolytes (SPE's) consisting of organically modified aluminosilica (OM-ALSi), formed within a poly(ethylene oxide)-in-salt (Li triflate) phase. To alter the structure and properties we fused functionalized silanes containing poly(ethylene oxide) (PEO) tails or CN groups.

  12. Thermoelectric properties of thin film and superlattice structure of IV-VI and V-VI compound semiconductors; Thermoelektrische Eigenschaften duenner Schichten und Uebergitterstrukturen von IV-VI- und V-VI-Verbundhalbleitern

    Energy Technology Data Exchange (ETDEWEB)

    Blumers, Mathias

    2012-02-29

    The basic material property governing the efficiency of thermoelectric applications is the thermoelectric figure of merit Z=S{sup 2}.{sigma}/k, where S is the Seebeck-coefficient, {sigma} is the electrical conductivity and k the thermal conductivity. A promising concept of increasing Z by one and two dimensional quantum well superlattices (QW-SL) was introduced in the early 1990s in terms of theoretical predictions. The realization of such low dimensional systems is done by use of semiconductor compounds with different energy gaps. The ambition of the Nitherma project was to investigate the thermoelectric properties of superlattices and Multi-Quantum-Well-structures (MQW) made of Pb{sub 1-x}Sr{sub x}Te and Bi{sub 2}(Se{sub x}Te{sub 1-x}){sub 3}, respectively. Therefore SL- and MQW-structures of this materials were grown and Z was determined by measuring of S, {sigma} and {kappa} parallel to the layer planes. Aim of this thesis is the interpretation of the transport measurements (S,{sigma},{kappa}) of low dimensional structures and the improvement of preparation and measurement techniques. The influence of low dimensionality on the thermal conductivity in SL- and MQW-structures was investigated by measurements on structures with different layer thicknesses. In addition, measurements of the Seebeck-coefficient were performed, also to verify the results of the participating groups.

  13. Electronic structure and thermoelectric properties of (Mg2X)2 / (Mg2Y)2 (X, Y = Si, Ge, Sn) superlattices from first-principle calculations

    Science.gov (United States)

    Guo, San-Dong

    2016-05-01

    To identify thermoelectric materials containing abundant, low-cost and non-toxic elements, we have studied the electronic structures and thermoelectric properties of (Mg2X)2/ (Mg2Y)2 (X, Y = Si, Ge, Sn) superlattices with state-of-the-art first-principles calculations using a modified Becke and Johnson (mBJ) exchange potential. Our results show that (Mg2Ge)2/ (Mg2Sn)2 and (Mg2Si)2/ (Mg2Sn)2 are semi-metals using mBJ plus spin-orbit coupling (mBJ + SOC), while (Mg2Si)2/ (Mg2Ge)2 is predicted to be a direct-gap semiconductor with a mBJ gap value of 0.46 eV and mBJ + SOC gap value of 0.44 eV. Thermoelectric properties are predicted by through solving the Boltzmann transport equations within the constant scattering time approximation. It is found that (Mg2Si)2/ (Mg2Ge)2 has a larger Seebeck coefficient and power factor than (Mg2Ge)2/ (Mg2Sn)2 and (Mg2Si)2/ (Mg2Sn)2 for both p-type and n-type doping. The detrimental influence of SOC on the power factor of p-type (Mg2X)2/ (Mg2Y)2 (X, Y = Si, Ge, Sn) is analyzed as a function of the carrier concentration, but there is a negligible SOC effect for n-type. These results can be explained by the influence of SOC on their valence and conduction bands near the Fermi level.

  14. Calibrated and Interactive Modelling of Form-Active Hybrid Structures

    DEFF Research Database (Denmark)

    Quinn, Gregory; Holden Deleuran, Anders; Piker, Daniel

    2016-01-01

    Form-active hybrid structures (FAHS) couple two or more different structural elements of low self weight and low or negligible bending flexural stiffness (such as slender beams, cables and membranes) into one structural assembly of high global stiffness. They offer high load-bearing capacity...... materially-informed sketching. Making use of a projection-based dynamic relaxation solver for structural analysis, explorative design has proven to be highly effective....

  15. Jaynes Cummings Photonic Superlattices

    CERN Document Server

    Longhi, Stefano

    2011-01-01

    A classical realization of the Jaynes-Cummings (JC) model, describing the interaction of a two-level atom with a quantized cavity mode, is proposed based on light transport in engineered waveguide superlattices. The optical setting enables to visualize in Fock space dynamical regimes not yet accessible in quantum systems, providing new physical insights into the deep strong coupling regime of the JC model. In particular, bouncing of photon number wave packets in Hilbert space and revivals of populations are explained as generalized Bloch oscillations in an inhomogeneous tight-binding lattice.

  16. Nafion–clay hybrids with a network structure

    KAUST Repository

    Burgaz, Engin

    2009-05-01

    Nafion-clay hybrid membranes with a unique microstructure were synthesized using a fundamentally new approach. The new approach is based on depletion aggregation of suspended particles - a well-known phenomenon in colloids. For certain concentrations of clay and polymer, addition of Nafion solution to clay suspensions in water leads to a gel. Using Cryo-TEM we show that the clay particles in the hybrid gels form a network structure with an average cell size in the order of 500 nm. The hybrid gels are subsequently cast to produce hybrid Nafion-clay membranes. Compared to pure Nafion the swelling of the hybrid membranes in water and methanol is dramatically reduced while their selectivity (ratio of conductivity over permeability) increases. The small decrease of ionic conductivity for the hybrid membranes is more than compensated by the large decrease in methanol permeability. Lastly the hybrid membranes are much stiffer and can withstand higher temperatures compared to pure Nafion. Both of these characteristics are highly desirable for use in fuel cell applications, since a) they will allow the use of a thinner membrane circumventing problems associated with the membrane resistance and b) enable high temperature applications. © 2009 Elsevier Ltd. All rights reserved.

  17. Interlayer diffusion studies of a Laves phase exchange spring superlattice.

    Science.gov (United States)

    Wang, C; Kohn, A; Wang, S G; Ward, R C C

    2011-03-23

    Rare earth Laves phase (RFe(2)) superlattice structures grown at different temperatures are studied using x-ray reflectivity (XRR), x-ray diffraction, and transmission electron microscopy. The optimized molecular beam epitaxy growth condition is matched with the XRR simulation, showing minimum diffusion/roughness at the interfaces. Electron microscopy characterization reveals that the epitaxial growth develops from initial 3D islands to a high quality superlattice structure. Under this optimum growth condition, chemical analysis by electron energy loss spectroscopy with high spatial resolution is used to study the interface. The analysis shows that the interface roughness is between 0.6 and 0.8 nm and there is no significant interlayer diffusion. The locally sharp interface found in this work explains the success of simple structural models in predicting the magnetic reversal behavior of Laves exchange spring superlattices.

  18. Predicting Chiral Nanostructures, Lattices and Superlattices in Complex Multicomponent Nanoparticle Self-Assembly

    KAUST Repository

    Hur, Kahyun

    2012-06-13

    "Bottom up" type nanoparticle (NP) self-assembly is expected to provide facile routes to nanostructured materials for various, for example, energy related, applications. Despite progress in simulations and theories, structure prediction of self-assembled materials beyond simple model systems remains challenging. Here we utilize a field theory approach for predicting nanostructure of complex and multicomponent hybrid systems with multiple types of short- and long-range interactions. We propose design criteria for controlling a range of NP based nanomaterial structures. In good agreement with recent experiments, the theory predicts that ABC triblock terpolymer directed assemblies with ligand-stabilized NPs can lead to chiral NP network structures. Furthermore, we predict that long-range Coulomb interactions between NPs leading to simple NP lattices, when applied to NP/block copolymer (BCP) assemblies, induce NP superlattice formation within the phase separated BCP nanostructure, a strategy not yet realized experimentally. We expect such superlattices to be of increasing interest to communities involved in research on, for example, energy generation and storage, metamaterials, as well as microelectronics and information storage. © 2012 American Chemical Society.

  19. Nanofiber of ultra-structured aluminum and zirconium oxide hybrid.

    Science.gov (United States)

    Kim, Hae-Won; Kim, Hyoun-Ee

    2006-02-01

    An internally ultrastructured Al- and Zr-oxide hybrid was developed into a nanofiber. As a precursor for the generation of nanofiber, a hybridized sol was prepared using the Pechini-type sol-gel process, whereby the Al- and Zr-metallic ions were to be efficiently distributed and stabilized within the polymeric network. The hybridized sol was subsequently electrospun and heat treated to a nanofiber with diameters of tens to hundreds of nanometers. The internal structure of the nanofiber was organized at the molecular level, with the Al- and Zr-oxide regions being interspaced at distances of less than ten nanometers. This ultrastructured Al- and Zr-oxide hybrid nanofiber is considered to be potentially applicable in numerous fields.

  20. Topologically ordered magnesium-biopolymer hybrid composite structures.

    Science.gov (United States)

    Oosterbeek, Reece N; Seal, Christopher K; Staiger, Mark P; Hyland, Margaret M

    2015-01-01

    Magnesium and its alloys are intriguing as possible biodegradable biomaterials due to their unique combination of biodegradability and high specific mechanical properties. However, uncontrolled biodegradation of magnesium during implantation remains a major challenge in spite of the use of alloying and protective coatings. In this study, a hybrid composite structure of magnesium metal and a biopolymer was fabricated as an alternative approach to control the corrosion rate of magnesium. A multistep process that combines metal foam production and injection molding was developed to create a hybrid composite structure that is topologically ordered in all three dimensions. Preliminary investigations of the mechanical properties and corrosion behavior exhibited by the hybrid Mg-polymer composite structures suggest a new potential approach to the development of Mg-based biomedical devices.

  1. Photon BLOCH oscillations in porous silicon optical superlattices.

    Science.gov (United States)

    Agarwal, V; del Río, J A; Malpuech, G; Zamfirescu, M; Kavokin, A; Coquillat, D; Scalbert, D; Vladimirova, M; Gil, B

    2004-03-01

    We report the first observation of oscillations of the electromagnetic field in an optical superlattice based on porous silicon. These oscillations are an optical equivalent of well-known electronic Bloch oscillations in crystals. Elementary cells of our structure are composed by microcavities whose coupling gives rise to the extended collective modes forming optical minigaps and minibands. By varying thicknesses of the cavities along the structure axis, we have created an effective electric field for photons. A very high quality factor of the confined optical state of the Wannier-Stark ladder may allow lasing in porous silicon-based superlattices.

  2. High-Detectivity Type-II Superlattice Detectors for 6-14 um Infrared Applications Project

    Data.gov (United States)

    National Aeronautics and Space Administration — SVT Associates proposes an novel type II superlattice structure to extend the cutoff wavelength and CBIRD SL photo diode structure with unipolar barriers to suppress...

  3. Molecular dynamics simulation of thermal conductivities of superlattice nanowires

    Institute of Scientific and Technical Information of China (English)

    杨决宽; 陈云飞; 颜景平

    2003-01-01

    Nonequilibrium molecular dynamics simulations were carried out to investigate heat transfer in superlattice nanowires. Results show that for fixed period length superlattice nanowires, the ratio of the total interfacial thermal resistance to the total thermal resistance and the effective thermal conductivities are invariant with the changes in interface numbers. Increasing the period length leads to an increase in the average interfacial thermal resistance, which indicates that the interfacial thermal resistance depends not only on the materials that constitute the alternating segments of superlattice nanowires, but also on the lattice strain throughout the segments. The modification of the lattice structure due to the lattice mismatch should be taken into account in the acoustic mismatch model. Simulation results also demonstrated the size confinement effect on the thermal conductivities for low dimensional structures, i.e. the thermal conductivities and the interfacial thermal resistance increase as the nanowire cross-sectional area increases.

  4. Defect enhanced spin and valley polarizations in silicene superlattices

    Science.gov (United States)

    Li, Wen; Lu, Wei-Tao; Li, Yun-Fang; Han, Hai-Hua

    2017-04-01

    We studied the effect of a defect of superlattice on the spin and valley dependent transport properties in silicene, where there is an abnormal barrier in height. It is found that the transmission resonance is greatly suppressed, because the symmetry of superlattice structure is destroyed by the defect. The spin-up and spin-down electrons near the K and K ‧ valleys are dominated by different effective superlattices and defects. Therefore, the conductances are strongly dependent on the spin and valley of electron. By adjusting the defect strength properly, the spin and valley polarizations could be dramatically enhanced in a wide energy region. Furthermore, the result suggests an application of the structure as a defect-controlled switch.

  5. Nonlinear optical response in Kronig-Penney type graphene superlattice in terahertz regime

    Science.gov (United States)

    Jiang, Lijuan; Yuan, Rui-Yang; Zhao, Xin; Lv, Jing; Yan, Hui

    2015-05-01

    The terahertz nonlinear optical response in Kronig-Penney (KP) type graphene superlattice is demonstrated. The single-, triple- and quintuple-frequencies of the fifth-order nonlinear responses are investigated for different frequencies and temperatures with the angle φ along the periodicity of the superlattice toward the external field tuning from 0 to π/2. The results show that the fifth-order nonlinear optical conductance of graphene superlattice is enhanced in the terahertz regime when φ = 0, i.e. an external field is applied along the periodicity of the superlattice. The fifth-order nonlinear optical conductances at φ = 0 for different frequencies and temperatures are calculated. The results show that the nonlinear optical conductance is enhanced in low frequency and low temperature. Our results suggest that KP type graphene superlattices are preferred structures for developing graphene-based nonlinear photonics and optoelectronics devices.

  6. Structural properties of maize hybrids established by infrared spectra

    Directory of Open Access Journals (Sweden)

    Radenović Čedomir N.

    2015-01-01

    Full Text Available This paper discusses the application of the infrared (IR spectroscopy method for determination of structural properties of maize hybrid grains. The IR spectrum of maize grain has been registered in the following hybrids: ZP 341, ZP 434 and ZP 505. The existence of spectral bands varying in both number and intensity, as well as their shape, frequency and kinetics have been determined. They have been determined by valence oscillations and deformation oscillations of the following organic compounds: alkanes, alkenes, alkynes, amides, alcohols, ethers, carboxylic acids, esters and aldehydes and ketones, characteristic for biogenic compounds such as carbohydrates, proteins and lipids. In this way, possible changes in the grain structure of observed maize hybrids could be detected.

  7. Acoustoelectric effect in semiconductor superlattice

    Science.gov (United States)

    Mensah, S. Y.; Allotey, F. K. A.; Adjepong, S. K.

    1993-10-01

    Acoustoelectric effect in semiconductor superlattice has been studied for acoustic wave whose wavelength lambda = 2pi/q is smaller than the mean free path of the electrons l (where ql approaches 1). Unlike the homogeneous bulk material where Weinreich relation is independent of the wave number q in the superlattice we observe a dependence on q i.e. spatial dispersion. In the presence of applied constant field E a threshold value was obtained where the acoustoelectric current changes direction.

  8. Fibonacci quasiregular graphene-based superlattices: Quasiperiodicity and its effects on the transmission, transport and electronic structure properties

    Science.gov (United States)

    García-Cervantes, H.; Madrigal-Melchor, J.; Martínez-Orozco, J. C.; Rodríguez-Vargas, I.

    2015-12-01

    We study the transmission, transport and electronic structure properties of aperiodic Fibonacci monolayer graphene-based structures (AFGBSs). The transfer matrix method has been implemented to obtain the transmittance, linear-regime conductance and electronic structure. In particular, we have studied two types of aperiodic graphene-based structures: (1) electrostatic AFGBSs (EAFGBSs), structures formed with electrostatic potentials, and (2) substrate AFGBSs (SAFGBSs), obtained alternating substrates that can open and non-open, such as SiC and SiO2, an energy bandgap on graphene. We have found that the transmission properties can be modulated readily by changing the main parameters of the systems: well and barrier widths, energy and angle of incident electrons and the degree of aperiodicity. In the case of the linear-regime conductance turns out that it diminishes various orders of magnitude increasing the barrier width for SAFGBSs. On the contrary, Klein tunneling sustains the conductance in EAFGBSs. Calculating the electronic structure or miniband-structure formation and its fragmentation we establish a direct connection between the conductance peaks and the opening, closure and degeneration of energy minibands for both EAFGSLs and SAFGSLs.

  9. Fibonacci quasiregular graphene-based superlattices: Quasiperiodicity and its effects on the transmission, transport and electronic structure properties

    Energy Technology Data Exchange (ETDEWEB)

    García-Cervantes, H.; Madrigal-Melchor, J.; Martínez-Orozco, J.C.; Rodríguez-Vargas, I., E-mail: isaac@fisica.uaz.edu.mx

    2015-12-01

    We study the transmission, transport and electronic structure properties of aperiodic Fibonacci monolayer graphene-based structures (AFGBSs). The transfer matrix method has been implemented to obtain the transmittance, linear-regime conductance and electronic structure. In particular, we have studied two types of aperiodic graphene-based structures: (1) electrostatic AFGBSs (EAFGBSs), structures formed with electrostatic potentials, and (2) substrate AFGBSs (SAFGBSs), obtained alternating substrates that can open and non-open, such as SiC and SiO{sub 2}, an energy bandgap on graphene. We have found that the transmission properties can be modulated readily by changing the main parameters of the systems: well and barrier widths, energy and angle of incident electrons and the degree of aperiodicity. In the case of the linear-regime conductance turns out that it diminishes various orders of magnitude increasing the barrier width for SAFGBSs. On the contrary, Klein tunneling sustains the conductance in EAFGBSs. Calculating the electronic structure or miniband-structure formation and its fragmentation we establish a direct connection between the conductance peaks and the opening, closure and degeneration of energy minibands for both EAFGSLs and SAFGSLs.

  10. XRR investigations of II-VI and III-nitrid based DBR-structures, multilayers and superlattices.

    Energy Technology Data Exchange (ETDEWEB)

    Hildebrand, Radowan; Schmidt, Thomas; Zargham, Ardalan; Speckmann, Moritz; Kruse, Carsten; Hommel, Detlef; Falta, Jens [Institute of Solid State Physics, University of Bremen (Germany)

    2008-07-01

    Thin layers, especially distributed bragg reflectors (DBR), are important components in vertical cavity surface emitting laser (VCSEL)- structures. The investigation of AlN/InGaN and MgS/ZnCdSe DBR structures with the method of X-ray reflection (XRR) enables the determination of electron density, multilayer thickness and roughness of the interfaces. Reducing the roughness is of peculiar interest to achieve high reflective DBRs.

  11. LDA+U study on fully relaxed LaTiO{sub 3} and (SrTiO{sub 3}){sub m}(LaTiO{sub 3}){sub n} superlattice structures

    Energy Technology Data Exchange (ETDEWEB)

    Ahn, Hyo Shin [Korea Institute of Science and Technology, Seoul (Korea, Republic of); Seoul National University, Seoul (Korea, Republic of); Cuong, Do Duc; Lee, Jai Chan [Sungkyunkwan University, Suwon (Korea, Republic of); Han, Seung Wu [Ewha Womans University, Seoul (Korea, Republic of)

    2006-10-15

    Using LDA+U (where LDA stands for local-density-approximation and U for on-site coulomb energy) method, we study the structural and electronic properties of LaTiO{sub 3} and (SrTiO{sub 3}){sub m}(LaTiO{sub 3}){sub n} superlattice structures. Lattice vectors, as well as ionic positions, are relaxed to minimize the LDA+U energy functional. We find that the inclusion of the U term increases the lattice parameters and leads to larger distortions of oxygen octahedra in LaTiO{sub 3} and that the overall agreement with experiment is improved compared to LDA results. In the superlattice, we find that octahedral distortions around the La layer lower the total energy. The ionic relaxations, especially those of Ti atoms near the La layer, affect the spatial distribution of doped electrons, leading to a broader charge profile than the case without ionic relaxation. The corresponding Ti{sup 3+} profile is in good agreement with the electron-energy-loss spectroscopy data.

  12. Hybrid Spintronic Structures With Magnetic Oxides and Heusler Alloys

    DEFF Research Database (Denmark)

    Xu, Y. B.; Hassan, S. S. A.; Wong, P. K. J.;

    2008-01-01

    Hybrid spintronic structures, integrating half-metallic magnetic oxides and Heusler alloys with their predicted high spin polarization, are important for the development of second-generation spintronics with high-efficient spin injection. We have synthesized epitaxial magnetic oxide Fe3O4 on GaAs...

  13. Exploratory Topology Modelling of Form-Active Hybrid Structures

    DEFF Research Database (Denmark)

    Holden Deleuran, Anders; Pauly, Mark; Tamke, Martin;

    2016-01-01

    The development of novel form-active hybrid structures (FAHS) is impeded by a lack of modelling tools that allow for exploratory topology modelling of shaped assemblies. We present a flexible and real-time computational design modelling pipeline developed for the exploratory modelling of FAHS tha...

  14. Superconducting superlattices 2: Native and artificial

    Energy Technology Data Exchange (ETDEWEB)

    Bozovic, I.; Pavuna, D. [eds.

    1998-12-31

    This volume is composed of 26 papers presented at the symposium. Topics covered include the following: high-{Tc} superlattices: intrinsic and artificial; low-{Tc} superlattices and multilayers; and theory.

  15. Hybridized Nano-Structure Composed of Metal and Polydiacetylene

    Institute of Scientific and Technical Information of China (English)

    H. Oikawa; A. Masuhara; T. Onodera; H. Kasai; H. Nakanishi

    2005-01-01

    @@ 1Introduction Polydiacetylene (PDA) is one of the promising candidates for organic third-order nonlinear optical (NLO) material, due to fast optical responsibility and easy processability in comparison with semiconductors etc. The magnitude of NLO property, however, is not still sufficient for the devices applications. Neeves, et al[1] theoretically predicted the enhancement of NLO property for core-shell type hybridized nanocrystal (NC) composed of PDA and metal. In the present study, we have prepared the two kinds of core-shell type hybridized nano-structure, and investigated their optical properties.

  16. Structural, chemical, and thermoelectric properties of Bi{sub 2}Te{sub 3} Peltier materials. Bulk, thin films, and superlattices

    Energy Technology Data Exchange (ETDEWEB)

    Peranio, Nicola

    2008-07-01

    In this work, the nature of the natural nanostructure (nns) was analysed and the correlations to the transport coefficients, particularly the lattice thermal conductivity, is discussed. Experimental methods are presented for the first time, yielding an accurate quantitative analysis of the chemical composition and of stress fields in Bi{sub 2}Te{sub 3} and in compounds with similar structural and chemical microstructures. This work can be subdivided as follows: (I) N-type Bi{sub 2}(Te{sub 0.91}Se{sub 0.09}){sub 3} and p-type (Bi{sub 0.26}Sb{sub 0.74}){sub 1.98}(Te{sub 0.99}Se{sub 0.01}){sub 3.02} bulk materials synthesised by the Bridgman technique. (II) Bi{sub 2}Te{sub 3} thin films and Bi{sub 2}Te{sub 3}/Bi{sub 2}(Te{sub 0.88}Se{sub 0.12}){sub 3} superlattices epitaxially grown by molecular beam epitaxy (MBE) on BaF{sub 2} substrates with periods of {delta}-12 nm at the Fraunhofer-Institut fuer Physikalische Messtechnik (IPM). (III) Experimental methods, i.e., TEM specimen preparation, high-accuracy quantitative chemical analysis by EDX in the TEM, and image simulations of dislocations and the nns according to the two-beam dynamical diffraction theory. The nns was analysed in detail by stereomicroscopy and by image simulation and was found to be a pure sinusoidal displacement field with (i) a displacement vector parallel to <5,-5,1> and an amplitude of about 10 pm and (ii) a wave vector parallel to {l_brace}1,0,10{r_brace} and a wavelength of 10 nm. The results obtained here showed a significant amount of stress in the samples, induced by the nns which was still not noticed and identified. Both kinds of nanostructures, artificial (ans) and natural (nns) nanostructures, yielded in thermoelectric materials a low lattice thermal conductivity which was beneficial for the thermoelectric figure of merit ZT. (orig.)

  17. Spontaneous Superlattice Formation in Nanorods through PartialCation Exchange

    Energy Technology Data Exchange (ETDEWEB)

    Robinson, Richard D.; Sadtler, Bryce; Demchenko, Denis O.; Erdonmez, Can K.; Wang, Lin-Wang; Alivisatos, A. Paul

    2007-03-14

    Lattice mismatch strains are widely known to controlnanoscale pattern formation in heteroepitaxy, but such effects have notbeen exploited in colloidal nanocrystal growth. We demonstrate acolloidal route to synthesizing CdS-Ag2S nanorod superlattices throughpartial cation exchange. Strain induces the spontaneous formation ofperiodic structures. Ab initio calculations of the interfacial energy andmodeling of strain energies show that these forces drive theself-organization. The nanorod superlattices exhibit high stabilityagainst ripening and phase mixing. These materials are tunablenear-infrared emitters with potential applications as nanometer-scaleoptoelectronic devices.

  18. Binding Graphene Sheets Together Using Silicon: Graphene/Silicon Superlattice

    Directory of Open Access Journals (Sweden)

    Zhang Yong

    2010-01-01

    Full Text Available Abstract We propose a superlattice consisting of graphene and monolayer thick Si sheets and investigate it using a first-principles density functional theory. The Si layer is found to not only strengthen the interlayer binding between the graphene sheets compared to that in graphite, but also inject electrons into graphene, yet without altering the most unique property of graphene: the Dirac fermion-like electronic structure. The superlattice approach represents a new direction for exploring basic science and applications of graphene-based materials.

  19. The intensive terahertz electroluminescence induced by Bloch oscillations in SiC natural superlattices.

    Science.gov (United States)

    Sankin, Vladimir; Andrianov, Alexandr; Petrov, Alexey; Zakhar'in, Alexey; Lepneva, Ala; Shkrebiy, Pavel

    2012-10-09

    : We report on efficient terahertz (THz) emission from high-electric-field-biased SiC structures with a natural superlattice at liquid helium temperatures. The emission spectrum demonstrates a single line, the maximum of which shifts linearly with increases in bias field. We attribute this emission to steady-state Bloch oscillations of electrons in the SiC natural superlattice. The properties of the THz emission agree fairly with the parameters of the Bloch oscillator regime, which have been proven by high-field electron transport studies of SiC structures with natural superlattices.

  20. Calculation of hybrid joints used in modern aerospace structures

    Directory of Open Access Journals (Sweden)

    Marcel STERE

    2011-12-01

    Full Text Available The state – of - the art of aeronautical structures show that parts are manufactured and subsequently assembled with the use of fasteners and/ or bonding. Adhesive bonding is a key technology to low weight, high fatigue resistance, robustness and an attractive design for cost structures.The paper results resolve significant problems for two groups of end-users:1 for the aerospace design office: a robust procedure for the design of the hybrid joint structural components;2 for the aeronautical repair centres: a useful procedure for structural design and analysis with significant cost savings.

  1. Indium-bump-free antimonide superlattice membrane detectors on a silicon substrates

    Science.gov (United States)

    Zamiri, M.; Klein, B.; Schuler, T.; Myers, S.; Cavallo, F.; Krishna, S.

    2016-05-01

    We present an approach to realize antimonide based superlattices on silicon substrates without using conventional Indium-bump hybridization. In this approach, PIN based superlattice detectors are grown on top of a 60 nm Al0.6Ga0.4Sb sacrificial layer on a GaSb host substrate. Following the growth, the individual pixels are transferred using our epitaxiallift off technique, which consists of a wet-etch to undercut the pixels followed by a dry-stamp process to transfer the pixels to a silicon substrate prepared with a gold layer. Structural and optical characterization of the transferred pixels was done using an optical microscope, scanning electron microscopy and photoluminescence. The interface between the transferred pixels and the new substrate was abrupt and no significant degradation in the optical quality was observed. An Indium-bump-free membrane detector was then fabricated using this approach. Spectral response measurements provided a 100% cut-off wavelength of 4.3 μm at 77 K. The performance of the membrane detector was compared to a control detector on the as-grown substrate. The membrane detector was limited by surface leakage current. The proposed approach could pave the way for wafer-level integration of photonic detectors on silicon substrates, which could dramatically reduce the cost of these detectors.

  2. Van der Waals trilayers and superlattices: Modification of electronic structures of MoS2 by intercalation

    OpenAIRE

    Lu, N.; Guo, H. Y.; L. Wang; Wu, X. J.; Zeng, X. C.

    2014-01-01

    We perform a comprehensive first-principles study of the electronic properties of van der Waals (vdW) trilayers via intercalating a two-dimensional (2D) monolayer (ML = BN, MoSe2, WS2, or WSe2) between MoS2 bilayer to form various MoS2/ML/MoS2 sandwich trilayers. We find that the BN monolayer is the most effective sheet to decouple the interlayer vdW coupling of the MoS2 bilayer, and the resulting sandwich trilayer can recover the electronic structures of the MoS2 monolayer, particularly the ...

  3. Double Sided Si(Ge)/Sapphire/III-Nitride Hybrid Structure

    Science.gov (United States)

    Park, Yeonjoon (Inventor); Choi, Sang Hyouk (Inventor)

    2016-01-01

    One aspect of the present invention is a double sided hybrid crystal structure including a trigonal Sapphire wafer containing a (0001) C-plane and having front and rear sides. The Sapphire wafer is substantially transparent to light in the visible and infrared spectra, and also provides insulation with respect to electromagnetic radio frequency noise. A layer of crystalline Si material having a cubic diamond structure aligned with the cubic direction on the (0001) C-plane and strained as rhombohedron to thereby enable continuous integration of a selected (SiGe) device onto the rear side of the Sapphire wafer. The double sided hybrid crystal structure further includes an integrated III-Nitride crystalline layer on the front side of the Sapphire wafer that enables continuous integration of a selected III-Nitride device on the front side of the Sapphire wafer.

  4. Magnetic Bloch oscillations in nanowire superlattice rings.

    Science.gov (United States)

    Citrin, D S

    2004-05-14

    The recent growth of semiconductor nanowire superlattices encourages hope that Bloch-like oscillations in such structures formed into rings may soon be observed in the presence of a time-dependent magnetic flux threading the ring. These magnetic Bloch oscillations are a consequence of Faraday's law; the time-dependent flux produces an electromotive force around the ring, thus leading to the Bloch-like oscillations. In the spectroscopic domain, generalized Wannier-Stark states are found that are manifestations of the emf-induced localization of the states.

  5. Brain anatomical structure segmentation by hybrid discriminative/generative models.

    Science.gov (United States)

    Tu, Z; Narr, K L; Dollar, P; Dinov, I; Thompson, P M; Toga, A W

    2008-04-01

    In this paper, a hybrid discriminative/generative model for brain anatomical structure segmentation is proposed. The learning aspect of the approach is emphasized. In the discriminative appearance models, various cues such as intensity and curvatures are combined to locally capture the complex appearances of different anatomical structures. A probabilistic boosting tree (PBT) framework is adopted to learn multiclass discriminative models that combine hundreds of features across different scales. On the generative model side, both global and local shape models are used to capture the shape information about each anatomical structure. The parameters to combine the discriminative appearance and generative shape models are also automatically learned. Thus, low-level and high-level information is learned and integrated in a hybrid model. Segmentations are obtained by minimizing an energy function associated with the proposed hybrid model. Finally, a grid-face structure is designed to explicitly represent the 3-D region topology. This representation handles an arbitrary number of regions and facilitates fast surface evolution. Our system was trained and tested on a set of 3-D magnetic resonance imaging (MRI) volumes and the results obtained are encouraging.

  6. Investigation of miniband formation and optical properties of strain-balanced InGaAs/GaAsP superlattice structure embedded in p-i-n GaAs solar cells

    Science.gov (United States)

    Fukuyama, Atsuhiko; Matsuochi, Kouki; Nakamura, Tsubasa; Takeda, Hideaki; Toprasertpong, Kasidit; Sugiyama, Masakazu; Nakano, Yoshiaki; Suzuki, Hidetoshi; Ikari, Tetsuo

    2017-08-01

    To improve the superlattice (SL) solar cell performance, we carried out an accurate estimation of transition energies and miniband widths and focused on understanding of the optical properties of the SL structure using piezoelectric photothermal (PPT), photoreflectance (PR), and photoluminescence (PL) methods. Solar cell structure samples with different barrier thicknesses from 2.0 to 7.8 nm in quantum wells were prepared. From the PR and theoretical calculation, the formation of a miniband was confirmed. The PL peak showed a redshift and a decrease in signal intensity with decreasing barrier thickness, which were explained by carrier separation as a consequence of electron transportation through the miniband without recombination. The PPT signal intensities of the SL were still large even for the 2.0-nm-barrier-thickness sample. It is conceivable that the multiple-phonon emission during carrier transport through the miniband was detected. The usefulness of multidimensional investigation by using the above three methods is clearly demonstrated.

  7. Hybrid Optimization in the Design of Reciprocal Structures

    DEFF Research Database (Denmark)

    Parigi, Dario; Kirkegaard, Poul Henning; Sassone, Mario

    2012-01-01

    that explore the global domain of solutions as genetic algorithms (GAs). The benchmark tests show that when the control on the topology is required the best result is obtained by a hybrid approach that combines the global search of the GA with the local search of a GB algorithm. The optimization method......The paper presents a method to generate the geometry of reciprocal structures by means of a hybrid optimization procedure. The geometry of reciprocal structures where elements are sitting on the top or in the bottom of each other is extremely difficult to predict because of the non....... In this paper it is shown that the geometrically compatible position of the elements could be determined by local search algorithm gradient-based (GB). However the control on which bar sit on the top or in the bottom at each connection can be regarded as a topological problem and require the use of algorithms...

  8. In Situ Production of Graphene-Fiber Hybrid Structures

    DEFF Research Database (Denmark)

    Akia, Mandana; Cremar, Lee; Chipara, Mircea

    2017-01-01

    We report a scalable method to obtain a new material where large graphene sheets form webs linking carbon fibers. Film-fiber hybrid nonwoven mats are formed during fiber processing and converted to carbon structures after a simple thermal treatment. This contrasts with multistep methods that atte......We report a scalable method to obtain a new material where large graphene sheets form webs linking carbon fibers. Film-fiber hybrid nonwoven mats are formed during fiber processing and converted to carbon structures after a simple thermal treatment. This contrasts with multistep methods...... a capillarity effect that promoted the formation of thin veils, which become graphene sheets upon dehydration by sulfuric acid vapor followed by carbonization (at relatively low temperatures, below 800 °C). These veils extend over several micrometers within the pores of the fiber network, and consist...

  9. Hybrid proper orthogonal decomposition formulation for linear structural dynamics

    Science.gov (United States)

    Placzek, A.; Tran, D.-M.; Ohayon, R.

    2008-12-01

    Hybrid proper orthogonal decomposition (PODh) formulation is a POD-based reduced-order modeling method where the continuous equation of the physical system is projected on the POD modes obtained from a discrete model of the system. The aim of this paper is to evaluate the hybrid POD formulation and to compare it with other POD formulations on the simple case of a linear elastic rod subject to prescribed displacements in the perspective of building reduced-order models for coupled fluid-structure systems in the future. In the first part of the paper, the hybrid POD is compared to two other formulations for the response to an initial condition: an approach based on the discrete finite elements equation of the rod called the discrete POD (PODd), and an analytical approach using the exact solution of the problem and consequently called the analytical POD (PODa). This first step is useful to ensure that the PODh performs well with respect to the other formulations. The PODh is therefore used afterwards for the forced motion response where a displacement is imposed at the free end of the rod. The main contribution of this paper lies in the comparison of three techniques used to take into account the non-homogeneous Dirichlet boundary condition with the hybrid POD: the first method relies on control functions, the second on the penalty method and the third on Lagrange multipliers. Finally, the robustness of the hybrid POD is investigated on two examples involving firstly the introduction of structural damping and secondly a nonlinear force applied at the free end of the rod.

  10. Hybrid competitive strategies, organizational structure, and firm performance

    OpenAIRE

    Pertusa Ortega, Eva María

    2008-01-01

    Comunicación presentada en SMS 28th Annual International Conference, Cologne, Germany, October 12-15, 2008. This paper analyzes the internal characteristics of organizational structure which have an influence on the development of hybrid competitive strategies and their link to firm performance. The study examines a sample of large Spanish firms belonging to different sectors by means of the Partial Least Squares (PLS) technique, using formative dimensions for competitive strategy and orga...

  11. Optical Properties of Self-Organized PbS Quantum Dot Superlattices

    Institute of Scientific and Technical Information of China (English)

    YE Chang-Hui; YAO Lian-Zeng; MU Ji-Mei; SHI Gang; ZHANG Li-De

    2000-01-01

    Self-organization of PbS into quantum dot superlattices has been demonstrated for the first time, and hexaplanar colloidal crystals 1 - 10 μm in size made from PbS quantum dots 3 - 6 nm in diameter are revealed in transmissionelectron microscope micrographs, and the inner structures of the superlattices can be seen by a high resolution transmission electron microscopy. The optical absorption and photoluminescence spectra have been recorded. The ordering of the superlattices is crucial for the understanding of the fundamental properties of quantum-dot arrays, as well as for their optimal utilization in optical and electronic applications.

  12. Perovskite Superlattices as Tunable Microwave Devices

    Science.gov (United States)

    Christen, H. M.; Harshavardhan, K. S.

    2003-01-01

    Experiments have shown that superlattices that comprise alternating epitaxial layers of dissimilar paraelectric perovskites can exhibit large changes in permittivity with the application of electric fields. The superlattices are potentially useful as electrically tunable dielectric components of such microwave devices as filters and phase shifters. The present superlattice approach differs fundamentally from the prior use of homogeneous, isotropic mixtures of base materials and dopants. A superlattice can comprise layers of two or more perovskites in any suitable sequence (e.g., ABAB..., ABCDABCD..., ABACABACA...). Even though a single layer of one of the perovskites by itself is not tunable, the compositions and sequence of the layers can be chosen so that (1) the superlattice exhibits low microwave loss and (2) the interfacial interaction between at least two of the perovskites in the superlattice renders either the entire superlattice or else at least one of the perovskites tunable.

  13. Polarized light source based on graphene-nanoribbon hybrid structure

    Science.gov (United States)

    Xu, Pengfei; Zhang, Han; Qian, Haoliang; Chen, Bigeng; Jiang, Xiaoshun; Wu, Yuanpeng; Liu, Xiaowei; Liu, Xu; Yang, Qing

    2017-07-01

    Nanoscale light source is the key element for on-chip integrated optical communication system. As an important property of light source, polarization can be exploited to improve the information capacity of optical communication and the sensitivity of optical sensing. We demonstrate a novel TE-polarized light source based on graphene-nanoribbon (G-NR) hybrid structure. Thanks to the polarizing dependent absorption along graphene layer, the random polarized emission of nanoribbon (NR) can be transferred into the same TE polarization. In addition, lasing action in G-NR hybrid structure is also investigated. We attribute the polarization control to the differential attenuation of electromagnetic modes in graphene. Our simulation revealed electromagnetic field distribution and far field polar images of TE and TM modes in nanoribbon, which is consistent with experimental results. The compact G-NR hybrid structure light source offers a new way to realize the polarization controllable nanoscale light source and facilitate the practical applications of nanowire or nanoribbon light source.

  14. Nanodevices based on Membrane-Carbon Nanotube Hybrid Structures

    Science.gov (United States)

    Jin, Hye Jun; Kim, Tae Hyun; Namgung, Seon; Hong, Seunghun; Lee, Sang Hun; Park, Tai Hyun

    2010-03-01

    Proteins in cell membrane have been drawing attention due to their versatile functionalities such as ion transfer for neuronal activity and selective binding for sensory systems. However, it is still very difficult to manipulate and study those proteins because they easily lose their functionalities without lipid membranes. We developed a method to coat lipid membranes containing various functional membrane proteins on single-walled carbon nanotube (swCNT)-based field effect transistors (FETs). In this hybrid structure, the activity of membrane proteins can be monitored by underlying swCNT-FETs, allowing us to easily study the functionalities of membrane proteins. Furthermore, we built advanced devices based on these hybrid structures. For an example, we coated lipid membrane containing `olfactory receptors' on swCNT-FETs, resulting in `bioelectric nose' systems. The bioelectric nose system had high sensitivity and human nose-like selectivity to odorant molecules. This talk will also discuss about the future prospect of these membrane-CNT hybrid structures.

  15. Development of Hybrid Product Breakdown Structure for NASA Ground Systems

    Science.gov (United States)

    Monaghan, Mark W.; Henry, Robert J.

    2013-01-01

    The Product Breakdown Structure is traditionally a method of identification of the products of a project in a tree structure. It is a tool used to assess, plan, document, and display the equipment requirements for a project. It is part of a product based planning technique, and attempts to break down all components of a project in as much detail as possible, so that nothing is overlooked. The PBS for ground systems at the Kennedy Space Center is being developed to encompass the traditional requirements including the alignment of facility, systems, and components to the organizational hierarchy. The Ground Operations Product Breakdown Structure is a hybrid in nature in that some aspects of a work breakdown structure will be incorporated and merged with the Architecture Concept of Operations, Master Subsystem List, customer interface, and assigned management responsibility. The Ground Operations Product Breakdown Structure needs to be able to identify the flexibility of support differing customers (internal and external) usage of ground support equipment within the Kennedy Space Center launch and processing complex. The development of the Product Breakdown Structure is an iterative activity Initially documenting the organization hierarchy structure and relationships. The Product Breakdown Structure identifies the linkage between the customer program requirements, allocation of system resources, development of design goals, and identification logistics products. As the Product Breakdown Structure progresses the incorporation of the results of requirement planning for the customer occurs identifying facility needs and systems. The mature Product Breakdown Structure is baselined with a hierarchical drawing, the Product Breakdown Structure database, and an associated document identifying the verification of the data through the life cycle of the program/product line. This paper will document, demonstrate, and identify key aspects of the life cycle of a Hybrid Product

  16. Einstein's Photoemission from Quantum Confined Superlattices.

    Science.gov (United States)

    Debbarma, S; Ghatak, K P

    2016-01-01

    This paper is dedicated to the 83th Birthday of Late Professor B. R. Nag, D.Sc., formerly Head of the Departments of Radio Physics and Electronics and Electronic Science of the University of Calcutta, a firm believer of the concept of theoretical minimum of Landau and an internationally well known semiconductor physicist, to whom the second author remains ever grateful as a student and research worker from 1974-2004. In this paper, an attempt is made to study, the Einstein's photoemission (EP) from III-V, II-VI, IV-VI, HgTe/CdTe and strained layer quantum well heavily doped superlattices (QWHDSLs) with graded interfaces in the presence of quantizing magnetic field on the basis of newly formulated electron dispersion relations within the frame work of k · p formalism. The EP from III-V, II-VI, IV-VI, HgTe/CdTe and strained layer quantum wells of heavily doped effective mass superlattices respectively has been presented under magnetic quantization. Besides the said emissions, from the quantum dots of the aforementioned heavily doped SLs have further investigated for the purpose of comparison and complete investigation in the context of EP from quantum confined superlattices. Using appropriate SLs, it appears that the EP increases with increasing surface electron concentration and decreasing film thickness in spiky manners, which are the characteristic features of such quantized hetero structures. Under magnetic quantization, the EP oscillates with inverse quantizing magnetic field due to Shuvnikov-de Haas effect. The EP increases with increasing photo energy in a step-like manner and the numerical values of EP with all the physical variables are totally band structure dependent for all the cases. The most striking features are that the presence of poles in the dispersion relation of the materials in the absence of band tails create the complex energy spectra in the corresponding HD constituent materials of such quantum confined superlattices and effective electron

  17. The Role of Ligand Packing Frustration in Body-Centered Cubic (bcc) Superlattices of Colloidal Nanocrystals.

    Science.gov (United States)

    Goodfellow, Brian W; Yu, Yixuan; Bosoy, Christian A; Smilgies, Detlef-M; Korgel, Brian A

    2015-07-02

    This paper addresses the assembly of body centered-cubic (bcc) superlattices of organic ligand-coated nanocrystals. First, examples of bcc superlattices of dodecanethiol-capped Au nanocrystals and oleic acid-capped PbS and PbSe nanocrystals are presented and examined by transmission electron microscopy (TEM) and grazing incidence small-angle X-ray scattering (GISAXS). These superlattices tend to orient on their densest (110) superlattice planes and exhibit a significant amount of {112} twinning. The same nanocrystals deposit as monolayers with hexagonal packing, and these thin films can coexist with thicker bcc superlattice layers, even though there is no hexagonal plane in a bcc lattice. Both the preference of bcc in bulk films over the denser face-centered cubic (fcc) superlattice structure and the transition to hexagonal monolayers can be rationalized in terms of packing frustration of the ligands. A model is presented to calculate the difference in entropy associated with capping ligand packing frustration in bcc and fcc superlattices.

  18. Evolving random fractal Cantor superlattices for the infrared using a genetic algorithm.

    Science.gov (United States)

    Bossard, Jeremy A; Lin, Lan; Werner, Douglas H

    2016-01-01

    Ordered and chaotic superlattices have been identified in Nature that give rise to a variety of colours reflected by the skin of various organisms. In particular, organisms such as silvery fish possess superlattices that reflect a broad range of light from the visible to the UV. Such superlattices have previously been identified as 'chaotic', but we propose that apparent 'chaotic' natural structures, which have been previously modelled as completely random structures, should have an underlying fractal geometry. Fractal geometry, often described as the geometry of Nature, can be used to mimic structures found in Nature, but deterministic fractals produce structures that are too 'perfect' to appear natural. Introducing variability into fractals produces structures that appear more natural. We suggest that the 'chaotic' (purely random) superlattices identified in Nature are more accurately modelled by multi-generator fractals. Furthermore, we introduce fractal random Cantor bars as a candidate for generating both ordered and 'chaotic' superlattices, such as the ones found in silvery fish. A genetic algorithm is used to evolve optimal fractal random Cantor bars with multiple generators targeting several desired optical functions in the mid-infrared and the near-infrared. We present optimized superlattices demonstrating broadband reflection as well as single and multiple pass bands in the near-infrared regime.

  19. Structural and magnetic properties of FeF sub 2 (001)/ZnF sub 2 (001) and FeF sub 2 (110)/ZnF sub 2 (110) superlattices

    CERN Document Server

    Yamazaki, H

    2003-01-01

    Using the molecular beam epitaxy technique, fluoride superlattices of FeF sub 2 (001)/ZnF sub 2 (001) and FeF sub 2 (110)/ZnF sub 2 (110) were prepared on single-crystal substrates, Al sub 2 O sub 3 (101-bar 0) and MgO(100), respectively. In addition to structural characterization, dependence of the Neel temperature on the thickness of the FeF sub 2 (001) and (110) layers was investigated in detail. The observed periodic variations of the Neel temperature with a period of 1 atomic monolayer were discussed in terms of an interface-topographical frustration due to the competing exchange interactions of J sub 2 and J sub 3.

  20. Influence of Fermi velocity engineering on electronic and optical properties of graphene superlattices

    Energy Technology Data Exchange (ETDEWEB)

    Aram, Tahereh Nemati [Research Institute for Applied Physics and Astronomy, University of Tabriz, Tabriz (Iran, Islamic Republic of); Université Grenoble Alpes, Institut Neel, 38042 Grenoble (France); Asgari, Asghar, E-mail: asgari@tabrizu.ac.ir [Research Institute for Applied Physics and Astronomy, University of Tabriz, Tabriz (Iran, Islamic Republic of); School of Electrical, Electronic and Computer Engineering, The University of Western Australia, Crawley, WA 6009 (Australia)

    2015-06-05

    In this paper, using Kronig–Penney model, the electronic states in graphene-based superlattices with various substrates and considering exact electron Fermi velocity values are investigated. The analysis of our results clearly indicates that the difference between Fermi velocity values of gaped and gapless graphene regions determines the patency rate of band gap. Also, using transfer matrix method (TMM) the absorbance spectrum of mentioned structures is calculated. The more important result is that the absorbance of these structures is significantly near zero. - Highlights: • The electronic states in graphene superlattices with various substrates are investigated. • The exact electron Fermi velocity values are considered. • Using TMM the absorbance spectrum of two graphene-based superlattices is calculated. • The widest (narrowest) energy band gap belong to quartz–SiC (quartz–h-BN) superlattice.

  1. Hybrid open public space of landscape elements and built structure

    Directory of Open Access Journals (Sweden)

    Gordana Bence

    2008-01-01

    Full Text Available The trend today in the cities in Europe and elsewhere is in combining landscape elements, built structure and different uses into a complex urban structure. Physical and program interweaving of landscape elements and built structure enables the consumers daily practice of leisure programs – relaxation, recreation and experiencing other cultural, educational and social events in the public green space. On the basis of determinate social changes and new approaches in urban planning practice, analyses of architectural and urban case studies from the point of view of integrating the landscape elements into the urban structure, the article defines the phenomenon of hybrid open public space and proposes methodical guidelines for the planning.

  2. Phonon-induced polariton superlattices

    DEFF Research Database (Denmark)

    de Lima, Jr., M. M.; Poel, Mike van der; Santos, P. V.;

    2006-01-01

    We show that the coherent interaction between microcavity polaritons and externally stimulated acoustic phonons forms a tunable polariton superlattice with a folded energy dispersion determined by the phonon population and wavelength. Under high phonon concentration, the strong confinement of the...... of the optical and excitonic polariton components in the phonon potential creates weakly coupled polariton wires with a virtually flat energy dispersion....

  3. Electron transport across a quantum wire embedding a saw-tooth superlattice

    Institute of Scientific and Technical Information of China (English)

    Chen Yuan-Ping; Yan Xiao-Hong; Lu Mao-Wang; Deng Yu-Xiang

    2004-01-01

    By developing the recursive Green function method, the transport properties through a quantum wire embedding a finite-length saw-tooth superlattice are studied in the presence of magnetic field. The effects of magnetic modulation and the geometric structures of the superlattice on transmission coefficient are discussed. It is shown that resonant electron gas. The transmission spectrum can be tailored to match requirements through adjusting the size of saw-tooth quantum dot and field strength.

  4. Tunable Negative Differential Resistance in Planer Graphene Superlattice Resonant Tunneling Diode

    OpenAIRE

    Sattari-Esfahlan, S. M.; Fouladi-Oskuei, J.; S. Shojaei

    2017-01-01

    In this paper, we report on the controllable negative differential resistance (NDR) in a proposed planar graphene superlattice structure. High value of peak to valley ratio (PVR) is predicted. This is significant because of appearance of NDR with high PVR at low biases. Our finding is important since beside the other potential applications of the graphene, proposes implementation of the graphene based superlattice in electronic devices such as resonant tunneling diode and filters.

  5. Moire superlattice effects in graphene/boron-nitride van der Waals heterostructures

    Energy Technology Data Exchange (ETDEWEB)

    Wallbank, John R.; Chen, Xi; Fal' ko, Vladimir I. [Department of Physics, Lancaster University, Lancaster (United Kingdom); Mucha-Kruczynski, Marcin [Department of Physics, University of Bath (United Kingdom)

    2015-06-15

    Van der Waals heterostructures of graphene and hexagonal boron nitride feature a moire superlattice for graphene's Dirac electrons. Here, we review the effects generated by this superlattice, including a specific miniband structure featuring gaps and secondary Dirac points, and a fractal spectrum of magnetic minibands known as Hofstadter's butterfly. (copyright 2015 by WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim)

  6. Self-Organization of PbS into Quantum Dots Superlattices

    Institute of Scientific and Technical Information of China (English)

    2000-01-01

    Self-organization of PbS into quantum dots superlattices is demonstrated for the first time, and hexaplanar colloidal crystals 1-10m m in size made from PbS quantum dots 4nm in diameter are shown in Transmission Electron Microscope (TEM) micrograph, and the inner structures of the superlattices can be seen from the High Resolution Transmission Electron Microscope (HRTEM).

  7. Heterojunction and superlattice detectors for infrared to ultraviolet

    Science.gov (United States)

    Perera, A. G. U.

    2016-07-01

    The interest in Infrared and Ultraviolet detectors has increased immensely due to the emergence of important applications over a wide range of activities. Detectors based on free carrier absorption known as Hetero-junction Interfacial Workfunction Internal Photoemission (HEIWIP) detectors and variations of these heterojunction structures to be used as intervalence band detectors for a wide wavelength region are presented. Although this internal photoemission concept is valid for all semiconductor materials systems, using a well-studied III-V system of GaAs/AlxGa1-x As to cover a wide wavelength range from UV to far-infrared (THz) is an important development in detector technology. Using the intervalence band (heavy hole, light hole and split off) transitions for high operating temperature detection of mid Infrared radiation is also discussed. A promising new way to extend the detection wavelength threshold beyond the standard threshold connected with the energy gap in a GaAs/AlxGa1-x As system is also presented. Superlattice detector technology, which is another promising detector architecture, can be optimized using both Type I and Type II heterostructures. Here the focus will be on Type II Strained Layer (T2SL) Superlattice detectors. T2SL Superlattices based on InAs/(In,GA)Sb have made significant improvements demonstrating focal plane arrays operating around 80 K and with multiple band detection capability. A novel spectroscopic method to evaluate the band offsets of both heterojunction and superlattice detectors is also discussed.

  8. Structural and electronic properties of hybrid silicon-germanium nanosheets

    Directory of Open Access Journals (Sweden)

    F. L. Pérez Sánchez

    2014-12-01

    Full Text Available Using first principles molecular calculations, based on the Density Functional Theory (DFT, structural and electronic properties of hybrid graphene—like silicon—germanium circular nanosheets of hexagonal symmetry are investigated. The exchange—correlation functional of Perdew—Wang (PW in the local spin density approximation (LSDA based on the pseudopotentials of Dolg—Bergnre is applied. The finite extension nanosheets are represented by the CnHm—like cluster model with mono—hydrogenated armchair edges. Changes of the physicochemical properties were analyzed to learn on the chemical composition. We have obtained that the corrugation of the hybrid nanosheets is maintained (with respect to the pristine nanosheets of Ge and Si and is more pronounced when there is a high percentage of germanium. Moreover, hybrid nanosheets have ionic bonds (polarity in the interval from 0.18 to 0.77 D and exhibit a semimetal behavior. Three types of chemical compositions are considered: 1 the one—one relationship, 2 formation of Ge dimers and 3 formation of Ge hexagons. In each case it is observed an increase in the chemical reactivity. Finally, analyzing the work function we conclude that in cases 1 and 2 the chemical compositions improve the efficiency of the field emission and thereby they could expand the scope of nanotechnology applications.

  9. Highly Polarized Electrons from GaAs-GaAsP and InGaAs-AlGaAs Strained Layer Superlattice Photocathodes

    CERN Document Server

    Nakanishi, T; Kuwahara, M; Naniwa, K; Nishitani, T; Okumi, S; Yamamoto, N; Yasui, K

    2004-01-01

    GaAs-GaAsP strained layer superlattice photocathode has been developed for highly polarized electron beams. This cathode achieved a maximum polarization of 92% with a quantum efficiency of 0.5%. Criteria for achieving the highest polarization together with high quantum efficiency using superlattice photocathodes are discussed based on experimental spin-resolved quantum efficiency spectra of GaAs-AlGaAs, InGaAs-AlGaAs and GaAs-GaAsP superlattice structures.

  10. Aging in Co/Cr Superlattices

    Science.gov (United States)

    Mukherjee, T.; Pleimling, M.; Binek, Ch.

    2009-03-01

    Aging phenomena are observed in various systems brought into non-equilibrium and subsequently showing slow relaxation dynamics. Magnetic specimens with well defined interactions and dimensions can serve as model systems for universal aspects of aging. Magnetic thin films provide access to a wide range of microscopic parameters. Superlattice structures allow tuning the intra and inter-plane exchange and enable geometrical confinement of the spin fluctuations. We use Co/Cr thin film superlattices to study magnetic aging. The static and dynamic properties are affected via the Co and Cr film thicknesses. TC of the Co films is reduced from the bulk value by geometrical confinement. Non-ergodic behavior sets in at a tunable temperature T^* in a range of some 100K above zero. Cr provides antiferromagnetic coupling between the Co films. Non-equilibrium spin states are set via low field cooling in 5mT in-plane magnetic field to below T^*. Next various in-plane magnetic set fields of some 10-100 mT are applied and the sample is exposed to the latter for various waiting times tw, respectively. After removing the field, relaxation of the magnetization is recorded via longitudinal Kerr-magnetometry. The relaxation data are analyzed by scaling plots revealing universal aspects of aging. Financial support by Teledyne-Isco, NRI, and NSF through EPSCoR, Career DMR-0547887, and MRSEC.

  11. Thermodynamics of Co/Cr superlattices

    Science.gov (United States)

    Mukherjee, T.; Sahoo, S.; Skomski, R.; Sellmyer, D. J.; Binek, Ch.

    2008-03-01

    Progress in ultra thin film growth has resulted in many novel surface and interface induced properties of artificial heterostuctures. Here, we study magnetic superlattices of ultrathin Co and Cr films grown by Molecular Beam Epitaxy methodology at a base pressure below 1x10-10 mbar. Our approach is based on controlling two distinct magnetic degrees of freedom. First, the critical temperature, Tc, of individual Co films is tailored via geometrical confinement of the correlation length perpendicular to the film. Various thickness dependent values, Tc(d), between zero and the bulk Curie temperature of 1388 K are realized. Second, the Tc-tailored Co films are antiferromagnetically coupled through Cr interlayer films. The oscillating coupling strength is tailored via the Cr interlayer thickness. The resulting thermodynamic properties of such Co/Cr superlattices are studied with the help of SQUID magnetometry. Particular emphasis is laid on tailoring magnetic entropy changes in the vicinity of room temperature. X-ray diffraction and X-ray reflectivity are used to correlate structural data with the magnetic properties.

  12. Improved hybrid optimization algorithm for 3D protein structure prediction.

    Science.gov (United States)

    Zhou, Changjun; Hou, Caixia; Wei, Xiaopeng; Zhang, Qiang

    2014-07-01

    A new improved hybrid optimization algorithm - PGATS algorithm, which is based on toy off-lattice model, is presented for dealing with three-dimensional protein structure prediction problems. The algorithm combines the particle swarm optimization (PSO), genetic algorithm (GA), and tabu search (TS) algorithms. Otherwise, we also take some different improved strategies. The factor of stochastic disturbance is joined in the particle swarm optimization to improve the search ability; the operations of crossover and mutation that are in the genetic algorithm are changed to a kind of random liner method; at last tabu search algorithm is improved by appending a mutation operator. Through the combination of a variety of strategies and algorithms, the protein structure prediction (PSP) in a 3D off-lattice model is achieved. The PSP problem is an NP-hard problem, but the problem can be attributed to a global optimization problem of multi-extremum and multi-parameters. This is the theoretical principle of the hybrid optimization algorithm that is proposed in this paper. The algorithm combines local search and global search, which overcomes the shortcoming of a single algorithm, giving full play to the advantage of each algorithm. In the current universal standard sequences, Fibonacci sequences and real protein sequences are certified. Experiments show that the proposed new method outperforms single algorithms on the accuracy of calculating the protein sequence energy value, which is proved to be an effective way to predict the structure of proteins.

  13. Healing Temperature of Hybrid Structures Based on Genetic Algorithm

    Institute of Scientific and Technical Information of China (English)

    赵中伟; 陈志华; 刘红波

    2016-01-01

    The healing temperature of suspen-dome with stacked arches(SDSA)and arch-supported single-layer lattice shell structures was investigated based on the genetic algorithm. The temperature field of arch under solar radiation was derived by FLUENT to investigate the influence of solar radiation on the determination of the healing temperature. Moreover, a multi-scale model was established to apply the complex temperature field under solar radiation. The change in the mechanical response of these two kinds of structures with the healing temperature was discussed. It can be concluded that solar radiation has great influence on the healing temperature, and the genetic algorithm can be effectively used in the optimization of the healing temperature for hybrid structures.

  14. Magnetic structure of La0.7Sr0.3MnO3/La0.7Sr0.3FeO3 superlattices

    Energy Technology Data Exchange (ETDEWEB)

    Arenholz, E.; van der Laan, G.; Yang, F.; Kemik, N.; Biegalski, M.D.; Christen, H.M.; Takamura, Y.

    2009-01-10

    Using x-ray magnetic dichroism we characterize the magnetic order in La{sub 0.7}Sr{sub 0.3}MnO{sub 3} (LSMO)/La{sub 0.7}Sr{sub 0.3}FeO{sub 3} (LSFO) superlattices with 6 unit cell thick sublayers. The LSMO layers exhibit a reduced Curie temperature compared to the bulk while antiferromagnetic order in the LSFO layers persists up to the bulk Neel temperature. Moreover, we find that aligning the LSMO magnetization by a magnetic field within the (001) surface plane leads to a reorientation of the Fe moments as well maintaining a perpendicular orientation of Fe and Mn moments. This perpendicular alignment is due to the frustrated exchange coupling at the LSMO/LSFO interface.

  15. Simple theoretical analysis of the Einstein’s photoemission from quantum confined superlattices

    Science.gov (United States)

    Pahari, S.; Bhattacharya, S.; Roy, S.; Saha, A.; De, D.; Ghatak, K. P.

    2009-11-01

    In this paper, we study the Einstein's photoemission from III-V, II-VI, IV-VI and HgTe/CdTe quantum well superlattices (QWSLs) with graded interfaces and quantum well effective mass superlattices in the presence of a quantizing magnetic field on the basis of newly formulated dispersion relations in the respective cases. Besides, the same has been studied from the afore-mentioned quantum dot superlattices and it appears that the photoemission oscillates with increasing carrier degeneracy and quantizing magnetic field in different manners. In addition, the photoemission oscillates with film thickness and increasing photon energy in quantum steps together with the fact that the solution of the Boltzmann transport equation will introduce new physical ideas and new experimental findings under different external conditions. The influence of band structure is apparent from all the figures and we have suggested three applications of the analyses of this paper in the fields of superlattices and microstructures.

  16. Thermal conductivity measurement of InGaAs/InGaAsP superlattice thin films

    Institute of Scientific and Technical Information of China (English)

    CHEN Zhen; YANG Juekuan; ZHUANG Ping; CHEN Minhua; ZHU Jian; CHEN Yunfei

    2006-01-01

    The thermal conductivities of InGaAs/InGaAsP superlattices with different period lengths were measured from 100 to 320 K using 3ω method.In this temperature range, the thermal conductivities were found to decrease with an increase in temperature. For the period length-dependant thermal conductivity, the minimum value does exist at a certain period length, which demonstrates that at a short period length, superlattice thermal conductivity increases with a decrease in the period length. When the period is longer than a certain period length, the interface thermal resistance dominates in phonon transport. The experimental and theoretical results confirmed the previous predictions from the lattice dynamics analysis, i.e. with the increase in period length, the dominant mechanisms of phonon transport in superlattices will shift from wave mode to particle mode. This is crucial for the cutoff of the phonons and lays a sound foundation for the design of superlattice structures.

  17. Analytical Study of Electromagnetic Wave in Superlattice

    Institute of Scientific and Technical Information of China (English)

    LIN Chang; ZHANG Xiu-Lian

    2004-01-01

    The theoretical description of soliton solutions and exact analytical solutions in the sine-Gordon equation is extended to superlattice physics. A family of interesting exact solutions and a new exact analytical solution have been obtained for the electromagnetic wave propagating through a superlattice. In more general cases, the vector potential along the propagating direction obeys the sine-Gordon equation. Some mathematical results of theoretical investigation are given for different cases in superlattices.

  18. Self-Organized Growth of Alloy Superlattices

    Energy Technology Data Exchange (ETDEWEB)

    Chason, E.; Floro, J.A.; Follstaedt, D.M.; Lagally, M.G.; Liu, F.; Tersoff, J.; Venezuela, P.

    1998-10-19

    We predict theoretically and demonstrate experimentally the spontaneous formation of a superlattice during crystal growth. When a strained alloy grows by "step flow", the steps at the surface form periodic bunches. The resulting modulated strain biases the incorporation of the respective alloy components at different steps in the bunch, leading to the formation of a superlattice. X-ray diffraction and electron microscopy for SiGe grown on Si give clear evidence for such spontaneous superlattice formation.

  19. Multistability, chaos, and random signal generation in semiconductor superlattices

    Science.gov (United States)

    Ying, Lei; Huang, Danhong; Lai, Ying-Cheng

    2016-06-01

    Historically, semiconductor superlattices, artificial periodic structures of different semiconductor materials, were invented with the purpose of engineering or manipulating the electronic properties of semiconductor devices. A key application lies in generating radiation sources, amplifiers, and detectors in the "unusual" spectral range of subterahertz and terahertz (0.1-10 THz), which cannot be readily realized using conventional radiation sources, the so-called THz gap. Efforts in the past three decades have demonstrated various nonlinear dynamical behaviors including chaos, suggesting the potential to exploit chaos in semiconductor superlattices as random signal sources (e.g., random number generators) in the THz frequency range. We consider a realistic model of hot electrons in semiconductor superlattice, taking into account the induced space charge field. Through a systematic exploration of the phase space we find that, when the system is subject to an external electrical driving of a single frequency, chaos is typically associated with the occurrence of multistability. That is, for a given parameter setting, while there are initial conditions that lead to chaotic trajectories, simultaneously there are other initial conditions that lead to regular motions. Transition to multistability, i.e., the emergence of multistability with chaos as a system parameter passes through a critical point, is found and argued to be abrupt. Multistability thus presents an obstacle to utilizing the superlattice system as a reliable and robust random signal source. However, we demonstrate that, when an additional driving field of incommensurate frequency is applied, multistability can be eliminated, with chaos representing the only possible asymptotic behavior of the system. In such a case, a random initial condition will lead to a trajectory landing in a chaotic attractor with probability 1, making quasiperiodically driven semiconductor superlattices potentially as a reliable

  20. High-temperature crystallization of nanocrystals into three-dimensional superlattices

    Science.gov (United States)

    Wu, Liheng; Willis, Joshua J.; McKay, Ian Salmon; Diroll, Benjamin T.; Qin, Jian; Cargnello, Matteo; Tassone, Christopher J.

    2017-08-01

    Crystallization of colloidal nanocrystals into superlattices represents a practical bottom-up process with which to create ordered metamaterials with emergent functionalities. With precise control over the size, shape and composition of individual nanocrystals, various single- and multi-component nanocrystal superlattices have been produced, the lattice structures and chemical compositions of which can be accurately engineered. Nanocrystal superlattices are typically prepared by carefully controlling the assembly process through solvent evaporation or destabilization or through DNA-guided crystallization. Slow solvent evaporation or cooling of nanocrystal solutions (over hours or days) is the key element for successful crystallization processes. Here we report the rapid growth (seconds) of micrometre-sized, face-centred-cubic, three-dimensional nanocrystal superlattices during colloidal synthesis at high temperatures (more than 230 degrees Celsius). Using in situ small-angle X-ray scattering, we observe continuous growth of individual nanocrystals within the lattices, which results in simultaneous lattice expansion and fine nanocrystal size control due to the superlattice templates. Thermodynamic models demonstrate that balanced attractive and repulsive interparticle interactions dictated by the ligand coverage on nanocrystal surfaces and nanocrystal core size are responsible for the crystallization process. The interparticle interactions can also be controlled to form different superlattice structures, such as hexagonal close-packed lattices. The rational assembly of various nanocrystal systems into novel materials is thus facilitated for both fundamental research and for practical applications in the fields of magnetics, electronics and catalysis.

  1. Structural and Morphological Investigation for Water-Processed Graphene Oxide/Single-Walled Carbon Nanotubes Hybrids

    Science.gov (United States)

    Muda, M. R.; Ramli, M. M.; Mat Isa, S. S.; Halin, D. S. C.; Talip, L. F. A.; Mazelan, N. S.; Anhar, N. A. M.; Danial, N. A.

    2017-06-01

    New group of materials derived from hybridization of single walled carbon nanotubes (SWCNTs) and graphene oxide (GO) which resulting novel three dimensional (3D) materials generates an outstanding properties compared to corresponding SWCNTs and GO/Graphene. In this paper, we describe a simple approach using water processing method to develop integrated rGO/GO-SWCNT hybrids with different hybrid ratios. The hybrid ratios were varied into three divided ratio and the results were compared between pristine SWCNTs and GO in order to investigate the structural density and morphology of these carbonaceous materials. With an optimized ratio of rGO/GO-SWCNT, the hybrid shows a well-organized hybrid film structures with less defects density sites. The optimized mixture ratio emphasized the important of both rGO and SWCNTs in the hybrid structures. Morphological structural and defects density degrees were examined by Field Emission Scanning Electron Microscopy (FESEM) and Raman spectroscopy.

  2. Structural Organization of Enzymes of the Phenylacetate Catabolic Hybrid Pathway

    Directory of Open Access Journals (Sweden)

    Andrey M. Grishin

    2015-06-01

    Full Text Available Aromatic compounds are the second most abundant class of molecules on the earth and frequent environmental pollutants. They are difficult to metabolize due to an inert chemical structure, and of all living organisms, only microbes have evolved biochemical pathways that can open an aromatic ring and catabolize thus formed organic molecules. In bacterial genomes, the phenylacetate (PA utilization pathway is abundant and represents the central route for degradation of a variety of organic compounds, whose degradation reactions converge at this pathway. The PA pathway is a hybrid pathway and combines the dual features of aerobic metabolism, i.e., usage of both oxygen to open the aromatic ring and of anaerobic metabolism—coenzyme A derivatization of PA. This allows the degradation process to be adapted to fluctuating oxygen conditions. In this review we focus on the structural and functional aspects of enzymes and their complexes involved in the PA degradation by the catabolic hybrid pathway. We discuss the ability of the central PaaABCE monooxygenase to reversibly oxygenate PA, the controlling mechanisms of epoxide concentration by the pathway enzymes, and the similarity of the PA utilization pathway to the benzoate utilization Box pathway and β-oxidation of fatty acids.

  3. Structural Organization of Enzymes of the Phenylacetate Catabolic Hybrid Pathway.

    Science.gov (United States)

    Grishin, Andrey M; Cygler, Miroslaw

    2015-06-12

    Aromatic compounds are the second most abundant class of molecules on the earth and frequent environmental pollutants. They are difficult to metabolize due to an inert chemical structure, and of all living organisms, only microbes have evolved biochemical pathways that can open an aromatic ring and catabolize thus formed organic molecules. In bacterial genomes, the phenylacetate (PA) utilization pathway is abundant and represents the central route for degradation of a variety of organic compounds, whose degradation reactions converge at this pathway. The PA pathway is a hybrid pathway and combines the dual features of aerobic metabolism, i.e., usage of both oxygen to open the aromatic ring and of anaerobic metabolism-coenzyme A derivatization of PA. This allows the degradation process to be adapted to fluctuating oxygen conditions. In this review we focus on the structural and functional aspects of enzymes and their complexes involved in the PA degradation by the catabolic hybrid pathway. We discuss the ability of the central PaaABCE monooxygenase to reversibly oxygenate PA, the controlling mechanisms of epoxide concentration by the pathway enzymes, and the similarity of the PA utilization pathway to the benzoate utilization Box pathway and β-oxidation of fatty acids.

  4. Ion beam studies in strained layer superlattices

    CERN Document Server

    Pathak, A P; Bhattacharya, D P; Dev, B N; Ghosh, S; Goswami, D K; Lakshmi-Bala, S; Nageswara-Rao, S V S; Satyam, P V; Siddiqui, A M; Srivastava, S K; Turos, A

    2002-01-01

    The potential device application of semiconductor heterostructures and strained layer superlattices has been highlighted. Metal organic chemical vapour deposition grown In sub 0 sub . sub 5 sub 3 Ga sub 0 sub . sub 4 sub 7 As/InP lattice-matched structure has been irradiated by 130 MeV Ag sup 1 sup 3 sup + and studied by RBS/Channelling using 3.5 MeV He sup 2 sup + ions. Ion irradiation seems to have induced a finite tensile strain in the InGaAs layer, indicating thereby that ion beam mixing occurs at this energy. Other complementary techniques like high resolution XRD and STM are needed to conclude the structural modifications in the sample.

  5. Nonreciprocal Multiferroic Superlattices with Broken Parity Symmetry

    Science.gov (United States)

    Tang, Zhenghua; Zhang, Weiyi

    Multiferroic materials are characterized by the coexistence of ferroelectric and ferromagnetic (or antiferromagnetic) orders, the coupling to lattice vibration can be invoked either through piezoelectric or piezomagnetic effects. In this paper, the polaritonic band structures of multiferroic superlattices composed of oppositely polarized domains are investigated using the generalized transfer matrix method. For the primitive cell with broken parity symmetry, the polaritonic band structure is asymmetrical with respect to the forward and backward propagation directions (nonreciprocality). In particular, the band extreme points move away from the Brillouin zone center. This asymmetry in band-gap positions and widths can be used to design compact one-way optical isolators, while the extremely slow light velocities near the asymmetrical upper edges of lower bands includes the essential ingredients for designing slow light devices.

  6. Structure of Solvent-Free Nanoparticle−Organic Hybrid Materials

    KAUST Repository

    Yu, Hsiu-Yu

    2010-11-16

    We derive the radial distribution function and the static structure factor for the particles in model nanoparticleorganic hybrid materials composed of nanoparticles and attached oligomeric chains in the absence of an intervening solvent. The assumption that the oligomers form an incompressible fluid of bead-chains attached to the particles that is at equilibrium for a given particle configuration allows us to apply a density functional theory for determining the equilibrium configuration of oligomers as well as the distribution function of the particles. A quasi-analytic solution is facilitated by a regular perturbation analysis valid when the oligomer radius of gyration R g is much greater than the particle radius a. The results show that the constraint that each particle carries its own share of the fluid attached to itself yields a static structure factor that approaches zero as the wavenumber approaches zero. This result indicates that each particle excludes exactly one other particle from its neighborhood. © 2010 American Chemical Society.

  7. Preparation of Ionic Silsesquioxanes with Regular Structures and Their Hybridization

    Directory of Open Access Journals (Sweden)

    Yoshiro Kaneko

    2012-01-01

    Full Text Available This paper deals with our recent studies on the preparation of ionic silsesquioxanes (SQs with regular structures. Cationic ladder-like polySQs (PSQs with hexagonally stacked structures were successfully prepared by the sol-gel reactions of amino group-containing organotrialkoxysilanes in strong acid aqueous solutions. Self-organization of an ion pair (a salt prepared from the amino group in the organotrialkoxysilane and an acid is the key factor for the formation of such regular structures of the PSQs. It is also reported that the control of the conformational structure of the PSQs was performed by the introduction of the chiral moieties. In addition, we investigated the correlation between the of acid-catalysts and the structures of SQs prepared by the hydrolytic condensation of amino group-containing organotrialkoxysilane, that is, the use of the superacid aqueous solution resulted in the formation of cage-like octaSQ, while the ladder-like PSQs with hexagonally stacked structures were formed from the strong acid aqueous solutions under the same reaction conditions. Furthermore, anion-exchange behaviors of the cationic ladder-like PSQ were investigated with various organic and inorganic compounds, such as anionic surfactants, a polymer, and layered clay minerals, to obtain the functional hybrid materials.

  8. Static and Dynamic Analyses of Long-Span Spatial Steel-Cable-Membrane Hybrid Structures

    Institute of Scientific and Technical Information of China (English)

    丁阳; 彭翼; 李忠献

    2003-01-01

    With the increment of the complexity of structural systems and the span of spatial structures, the interactions between parts of the structures, especially between some flexible substructures, become too complex to be analyzed clearly. In this paper, taking an actual gymnasium of a long-span spatial steel-cable-membrane hybrid structure as the calculation model, the static and dynamic analyses of the hybrid structures are performed by employing the global analysis of the whole hybrid structure and the substructural analysis of the truss arch substructure, the cable-membrane substructure, etc. In addition, the comparison of stresses and displacements of structural members in the global and substructural analyses is made. The numerical results show that serious errors exist in the substructural analysis of the hybrid structure, and the global analysis is necessary for the hybrid structure under the excitation of static loads and seismic loads.

  9. Design of MWIR Type-II Superlattices for Infrared Photon Detectors

    Science.gov (United States)

    Grein, Christoph

    The Type II InAs/GaInSb and InAs/InAsSb superlattices are material systems for implementation as photodetector absorbers in infrared imaging applications. In addition to cutoff wavelengths spanning the infrared spectrum, they offer degrees of freedom in their materials design (e.g. layer thicknesses, alloy compositions, number of layers in one superlattice period) that permit the optimization of an infrared photon detector's figures of merit such as detectivity through the tuning of material properties like generation/recombination lifetimes and optical absorption. We describe efforts to obtain accurate electronic band structures of superlattice semiconductors with infrared energy gaps, and employing them to evaluate nonradiative minority carrier lifetimes. Simple device models are utilized to suggest potential performance enhancements that arise from employing superlattices as infrared absorber. We also discuss current efforts to simulate the molecular beam epitaxial growth of InAs/InAsSb superlattices to predict dominant native point defects and other growth nonidealities. Design of MWIR Type-II Superlattices for Infrared Photon Detectors.

  10. Hybrid density functional theory band structure engineering in hematite.

    Science.gov (United States)

    Pozun, Zachary D; Henkelman, Graeme

    2011-06-14

    We present a hybrid density functional theory (DFT) study of doping effects in α-Fe(2)O(3), hematite. Standard DFT underestimates the band gap by roughly 75% and incorrectly identifies hematite as a Mott-Hubbard insulator. Hybrid DFT accurately predicts the proper structural, magnetic, and electronic properties of hematite and, unlike the DFT+U method, does not contain d-electron specific empirical parameters. We find that using a screened functional that smoothly transitions from 12% exact exchange at short ranges to standard DFT at long range accurately reproduces the experimental band gap and other material properties. We then show that the antiferromagnetic symmetry in the pure α-Fe(2)O(3) crystal is broken by all dopants and that the ligand field theory correctly predicts local magnetic moments on the dopants. We characterize the resulting band gaps for hematite doped by transition metals and the p-block post-transition metals. The specific case of Pd doping is investigated in order to correlate calculated doping energies and optical properties with experimentally observed photocatalytic behavior.

  11. Assortative mating and the maintenance of population structure in a natural hybrid zone.

    Science.gov (United States)

    Culumber, Zachary W; Ochoa, Olivia M; Rosenthal, Gil G

    2014-08-01

    Understanding the factors that give rise to natural hybrid zones and govern their dynamics and structure is important to predicting the evolutionary consequences of hybridization. Here we use a combination of multigenerational population genetic data, mating patterns from a natural population, behavioral assays, and mark-recapture data within clinal hybrid zones of the genus Xiphophorus to test the role of assortative mating in maintaining population structure and the potential for ongoing genetic exchange between heterospecifics. Our data demonstrate that population structure is temporally robust and driven largely by assortative mating stemming from precopulatory isolation between pure species. Furthermore, mark-recapture data revealed that rates of migration within the same stream reach are far below the level needed to support population structure. In contrast to many empirical studies of natural hybrid zones, there appeared to be no hybrid male dysfunction or discrimination against hybrid males by pure parental females, and hybrid females mated and associated with pure species and hybrid males at random. Despite strong isolation between pure parentals, hybrids therefore can act as a conduit for genetic exchange between heterospecifics, which has been shown to increase the tempo of evolutionary change. Additionally, our findings highlight the complexity of natural hybrid zone dynamics, demonstrating that sexual and ecological selection together can give rise to patterns that do not fit classical models of hybrid zone evolution.

  12. Growth kinetics and structural perfection of (InN)1/(GaN)1-20 short-period superlattices on +c-GaN template in dynamic atomic layer epitaxy

    Science.gov (United States)

    Kusakabe, Kazuhide; Hashimoto, Naoki; Itoi, Takaomi; Wang, Ke; Imai, Daichi; Yoshikawa, Akihiko

    2016-04-01

    The growth kinetics and structural perfection of (InN)1/(GaN)1-20 short-period superlattices (SPSs) were investigated with their application to ordered alloys in mind. The SPSs were grown on +c-GaN template at 650 °C by dynamic atomic layer epitaxy in conventional plasma-assisted molecular beam epitaxy. It was found that coherent structured InN/GaN SPSs could be fabricated when the thickness of the GaN barrier was 4 ML or above. Below 3 ML, the formation of SPSs was quite difficult owing to the increased strain in the SPS structure caused by the use of GaN as a template. The effective or average In composition of the (InN)1/(GaN)4 SPSs was around 10%, and the corresponding InN coverage in the ˜1 ML-thick InN wells was 50%. It was found that the effective InN coverage in ˜1 ML-thick InN wells could be varied with the growth conditions. In fact, the effective In composition could be increased up to 13.5%, i.e., the corresponding effective InN coverage was about 68%, by improving the capping/freezing speed by increasing the growth rate of the GaN barrier layer.

  13. Growth kinetics and structural perfection of (InN){sub 1}/(GaN){sub 1–20} short-period superlattices on +c-GaN template in dynamic atomic layer epitaxy

    Energy Technology Data Exchange (ETDEWEB)

    Kusakabe, Kazuhide; Hashimoto, Naoki; Wang, Ke; Imai, Daichi [Center for SMART Green Innovation Research, Chiba University, 1-33 Yayoi-cho, Inage-ku, Chiba 263-8522 (Japan); Itoi, Takaomi [Graduate School of Engineering, Chiba University, 1-33 Yayoi-cho, Inage-ku, Chiba 263-8522 (Japan); Yoshikawa, Akihiko, E-mail: yoshi@faculty.chiba-u.jp [Center for SMART Green Innovation Research, Chiba University, 1-33 Yayoi-cho, Inage-ku, Chiba 263-8522 (Japan); Graduate School of Engineering, Kogakuin University, Hachioji, Tokyo 192-0015 (Japan)

    2016-04-11

    The growth kinetics and structural perfection of (InN){sub 1}/(GaN){sub 1–20} short-period superlattices (SPSs) were investigated with their application to ordered alloys in mind. The SPSs were grown on +c-GaN template at 650 °C by dynamic atomic layer epitaxy in conventional plasma-assisted molecular beam epitaxy. It was found that coherent structured InN/GaN SPSs could be fabricated when the thickness of the GaN barrier was 4 ML or above. Below 3 ML, the formation of SPSs was quite difficult owing to the increased strain in the SPS structure caused by the use of GaN as a template. The effective or average In composition of the (InN){sub 1}/(GaN){sub 4} SPSs was around 10%, and the corresponding InN coverage in the ∼1 ML-thick InN wells was 50%. It was found that the effective InN coverage in ∼1 ML-thick InN wells could be varied with the growth conditions. In fact, the effective In composition could be increased up to 13.5%, i.e., the corresponding effective InN coverage was about 68%, by improving the capping/freezing speed by increasing the growth rate of the GaN barrier layer.

  14. Interwell excitons in GaAs superlattices

    DEFF Research Database (Denmark)

    Birkedal, Dan; Sayed, Karim El; Sanders, G.;

    1997-01-01

    The formation of spatially indirect excitons in superlattices with narrow minibands is investigated experimentally. The interwell exciton is similar to the first Wannier-Stark localized exciton of an electrically biased superlattice. However, in the present case the localization is mediated by th...

  15. Plant hybrid zones affect biodiversity: Tools for a genetic-based understanding of community structure

    Energy Technology Data Exchange (ETDEWEB)

    Whitham, T.G.; Martinsen, G.D.; Keim, P. [Northern Arizona Univ., Flagstaff, AZ (United States); Floate, K.D. [Agriculture and Agri-Food Canada, Lethbridge, Alberta (Canada); Dungey, H.S. [Univ. of Tasmania, Hobart, Tasmania (Australia)]|[Queensland Forest Research Inst., Gympie, Queensland (Australia); Potts, B.M. [Univ. of Tasmania, Hobart, Tasmania (Australia)

    1999-03-01

    Plant hybrid zones are dynamic centers of ecological and evolutionary processes for plants and their associated communities. Studies in the wild and in gardens with synthetic crosses showed that hybrid eucalypts supports the greatest species richness and abundances of insect and fungal taxa. In an updated review of 152 case studies of taxa associated with diverse hybridizing systems, there were 43 (28%) cases of hybrids being more susceptible than their parent species, 7 (5%) resistant, 35 (23%) additive, 35 (23%) dominant, and 32 (21%) showed no response to hybridization. Thus, most taxa respond to hybrids in ways that result in equal or greater abundance, and hybrids tend to accumulate the taxa of their parent species. These studies suggest that genetic-based plant traits affect the distribution of many species and that the variation in hybrids can be used as tools to examine the genetic components of community structure and biodiversity.

  16. Long range energy transfer in graphene hybrid structures

    Science.gov (United States)

    Gonçalves, Hugo; Bernardo, César; Moura, Cacilda; Ferreira, R. A. S.; André, P. S.; Stauber, Tobias; Belsley, Michael; Schellenberg, Peter

    2016-08-01

    In this work we quantify the distance dependence for the extraction of energy from excited chromophores by a single layer graphene flake over a large separation range. To this end hybrid structures were prepared, consisting of a thin (2 nm) layer of a polymer matrix doped with a well chosen strongly fluorescent organic molecule, followed by an un-doped spacer layer of well-defined thicknesses made of the same polymer material and an underlying single layer of pristine, undoped graphene. The coupling strength is assessed through the variation of the fluorescence decay kinetics as a function of distance between the graphene and the excited chromophore molecules. Non-radiative energy transfer to the graphene was observed at distances of up to 60 nm a range much greater than typical energy transfer distances observed in molecular systems.

  17. Structural Acoustic Response of Shape Memory Alloy Hybrid Composite Panels

    Science.gov (United States)

    Turner, Travis L.

    1996-01-01

    A method has been developed to predict the structural acoustic response of shape memory alloy hybrid composite panels subjected to acoustic excitation. The panel is modeled by a finite element analysis and the radiated field is predicted using Rayleigh's integral. Transmission loss predictions for the case of an aluminum panel excited by a harmonic acoustic pressure are shown to compare very well with a classical analysis. Predictions of the normal velocity response and transmitted acoustic pressure for a clamped aluminum panel show excellent agreement with experimental measurements. Predicted transmission loss performance for a composite panel with and without shape memory alloy reinforcement are also presented. The preliminary results demonstrate that the transmission loss can be significantly increased with shape memory alloy reinforcement.

  18. Hybrid nano-structure for enhanced energy storage devices

    Science.gov (United States)

    Shuvo, Mohammad Arif Ishtiaque

    The goal of this research is to develop electrode materials using various nano-structure hybrids for improved energy storage devices. Enhancing the performance of energy storage device has been gaining tremendous attention since it holds the key solution to advance renewable energy usage thus reduce the consumption of fossil fuels. The application of energy storage devices such as super-capacitor and Li-ion-battery has seen significant growth; however, it is still limited mainly by charge/discharge rate and energy density. One of the solutions is to use nano-structure materials, which offer higher power at high energy density and improved stability during the charge discharge cycling of ions in and out of the storage electrode material. In this research, carbon-based materials (e.g. porous carbon, graphene) in conjunction with metal oxides such as CeO2 nanoparticles/TiO2 nanowires are synthesized utilizing low temperature hydrothermal method for the fabrication of advanced electrode materials. Scanning Electron Microscopy (SEM), Transmission Electron Microscopy (TEM), X-ray Diffraction (XRD), Thermogravimetric Analysis (TGA), X-ray Photoelectron Spectroscopy (XPS), and Fourier Transformation Infrared Spectroscopy (FTIR) were used for materials characterization. Poentio-galvanostat, battery analyzer, and Electrochemical Impedance Spectroscopy (EIS) were used for evaluating the electrochemical performance. The testing results have shown that a maximum 500% higher specific capacitance could be obtained using porous carbon/CeO2 instead of porous carbon for super-capacitor application and microwave exfoliated graphene oxide/TiO2 nanowire hybrid provides up to 80% increment of specific capacity compared to porous carbon anode for Li-ion-battery application.

  19. Hybrid optical-fibre/geopolymer sensors for structural health monitoring of concrete structures

    Science.gov (United States)

    Perry, M.; Saafi, M.; Fusiek, G.; Niewczas, P.

    2015-04-01

    In this work, we demonstrate hybrid optical-fibre/geopolymer sensors for monitoring temperature, uniaxial strain and biaxial strain in concrete structures. The hybrid sensors detect these measurands via changes in geopolymer electrical impedance, and via optical wavelength measurements of embedded fibre Bragg gratings. Electrical and optical measurements were both facilitated by metal-coated optical fibres, which provided the hybrid sensors with a single, shared physical path for both voltage and wavelength signals. The embedded fibre sensors revealed that geopolymer specimens undergo 2.7 mɛ of shrinkage after one week of curing at 42 °C. After curing, an axial 2 mɛ compression of the uniaxial hybrid sensor led to impedance and wavelength shifts of 7 × 10-2 and -2 × 10-4 respectively. The typical strain resolution in the uniaxial sensor was 100 μ \\varepsilon . The biaxial sensor was applied to the side of a concrete cylinder, which was then placed under 0.6 mɛ of axial, compressive strain. Fractional shifts in impedance and wavelength, used to monitor axial and circumferential strain, were 3 × 10-2 and 4 × 10-5 respectively. The biaxial sensor’s strain resolution was approximately 10 μ \\varepsilon in both directions. Due to several design flaws, the uniaxial hybrid sensor was unable to accurately measure ambient temperature changes. The biaxial sensor, however, successfully monitored local temperature changes with 0.5 °C resolution.

  20. Spatio-temporal changes in the genetic structure of the Passerina bunting hybrid zone.

    Science.gov (United States)

    Carling, Matthew D; Zuckerberg, Benjamin

    2011-03-01

    Although theoretical models predict that the structure of a hybrid zone can change under a variety of scenarios, only a few empirical studies of hybrid zones have unequivocally demonstrated zone movement. These studies are rare because few data sets exist that include repeated, temporally spaced, samples of the same hybrid zone. We analysed mitochondrial DNA haplotype data from samples separated by 40-45 years from across the Passerina amoena (Lazuli Bunting) and Passerina cyanea (Indigo Bunting) hybrid zone to investigate whether the genetic structure of this zone has changed during that interval. Both cline and generalized linear mixed modelling analyses uncovered a significant narrowing and a substantial westward shift of the Passerina bunting hybrid zone, clearly illustrating hybrid zone movement. The cause of the change may be due to a combination of ecological, demographic and behavioural factors. Our results predict that the width of the hybrid zone will continue to narrow over time, a finding consistent with reinforcement theory.

  1. Aberration Corrected Scanning Transmission Electron Microscopy of (Ca , Sr)Fe2O5 Brownmillerite superlattices

    Science.gov (United States)

    Mukherjee, Debangshu; Stone, Greg; Moon, Eun Ju; Young, Joshua; Gopalan, Venkatraman; Rondinelli, James; May, Steven; Alem, Nasim

    The brownmillerite phase A2B2O5 consists of ordered oxygen vacancies in alternate perovskite layers forming chiral tetrahedral chains. The handedness of these tetrahedral chains control the polarization of the structure. The current study focuses on 1-1 brownmillerite superlattices grown on a SrTiO3 substrates using molecular beam epitaxy. The B-site in this structure is iron throughout the superlattice film, while the A-site alternates between calcium and strontium in the superlattice layers. In this study, we use atomic resolution aberration corrected scanning transmission electron microscopy (STEM) to investigate the structure and chemistry of the film-substrate interface as well as the chemical structure of the superlattice. Atom positions are determined to measure displacement vectors of A-site cations in the superlattice structure. D.M., G.A.S., V.G. and N.A. were supported by the National Science Foundation under Grant No. DMR-1420620. E.J.M. and S.J.M. were supported by the National Science Foundation under Grant No. DMR-1151649.

  2. Optical constants of GaAs-AlGaAs superlattices and multiple quantum wells

    Science.gov (United States)

    Kahen, K. B.; Leburton, J. P.

    1986-01-01

    The optical properties of GaAs-Al sub x Ga sub 1-xAs superlattices are calculated as a function of the frequency and superlattice structure. The comutations are performed using a partition method which combines the vectors k.p method with the pseudopotential technique. The influence of the super-structure on the electronic properties of the systems is accounted for by appropriate quantization conditions. The anisotropy and structure dependence of the dielectric constant result mainly from the contribution of the gamma region while the contributions of the other regions of the Brillouin zone are rather insensitive to the superlattice structure. The superlattice index of refraction values are shown to attain maxima at the various quantized transition energies, where for certain structures, the difference between the refractive indices of the superlattices and its corresponding Al sub x Ga sub 1-xAs alloy can be as large as 2%. In general results are in good agreement with the experimental data.

  3. Reversible solvent vapor-mediated phase changes in nanocrystal superlattices.

    Science.gov (United States)

    Goodfellow, Brian W; Korgel, Brian A

    2011-04-26

    Colloidal nanocrystals are being explored for use in a variety of applications, from solar cells to transistors to medical diagnostics and therapy. Ordered assemblies of nanocrystals, or superlattices, are one particularly interesting class of these materials, in which the nanocrystals serve as modular building blocks to construct nanostructures by self-assembly with spatial and temporal complexity and unique properties. From a fundamental perspective, the nanocrystals are simple molecular models that can be manipulated and studied to test statistical mechanical and thermodynamic models of crystallization and disorder. An article by Bian et al. in this issue of ACS Nano reports surprising new phase behavior in semiconductor nanocrystal superlattices: reversible transitions between non-close-packed body-centered cubic (bcc) and body-centered tetragonal (bct) structures, and close-packed face-centered cubic (fcc) structures, observed by real-time in situ grazing incidence small-angle X-ray scattering (GISAXS) measurements, upon solvent vapor exposure and increased interparticle separation. These studies offer new insight and raise new questions about superlattice structure and the forces that control self-assembly. Accompanying computer simulations show that ligand-ligand interactions are important. Furthermore, it appears that ligand-coated nanocrystals have more in common with soft microphase-separated materials, like diblock copolymers and surfactant assemblies, than previously realized.

  4. A novel organic-inorganic hybrid tandem solar cell with inverted structure

    Science.gov (United States)

    Bahrami, A.; Faez, R.

    2017-04-01

    A novel organic-inorganic hybrid tandem solar cell with inverted structure is proposed. This efficient double-junction hybrid tandem solar cell consists of a single-junction hydrogenated amorphous silicon (a-Si:H) subcell with n-i-p structure as front cell and a P3HT:PCBM organic subcell with inverted structure as back cell. In order to optimize the hybrid tandem cell, we have performed a simulation based on transfer matrix method. We have compared the characteristics of this novel structure with a conventional structure. As a result, a power conversion efficiency (PCE) of 6.1 and 24% improvement compared to the conventional hybrid tandem cell was achieved. We also discuss the high potential of this novel structure for realizing high-stability organic-inorganic hybrid photovoltaic devices.

  5. Optoelectronic Properties of Hybrid Titania Nanotubes/Hematite Nanoparticles Structures

    Science.gov (United States)

    Wang, Lili; Panaitescu, Eugen; Menon, Latika

    2015-03-01

    TiO2/Fe2O3 nanostructures are becoming promising alternatives for improving cost effectiveness (in /W) of emerging photovoltaic devices such as dye sensitized or metal-insulator-semiconductor solar cells, combining the low cost, earth abundance and stability of the materials with the enhanced performance offered by the nanoscale architecture. We investigated novel, high quality titania/hematite composites, namely hematite nanoparticle decorated titania nanotube arrays, which were obtained by a simple, inexpensive and easily scalable two-step process, electrochemical anodization of titanium followed by forced hydrolysis. The titania nanotubular scaffold provides a large active surface area, while the iron oxide nanoparticles significantly broaden the light absorption range into the visible region. The morphological and structural characteristics of the samples were analyzed by scanning electron microscopy (SEM), X-ray diffraction (XRD) and transmission electron microscopy (TEM). The light absorption efficiency was measured by diffuse reflectance spectroscopy (DRS), and the optoelectronic behavior of the hybrid structures was analyzed by IV measurements under simulated solar illumination. The influence of the synthesis process and the structure design on the photovoltaic performance is currently investigated for optimal device prototyping.

  6. Photoacoustic transformation of Bessel light beams in magnetoactive superlattices

    Energy Technology Data Exchange (ETDEWEB)

    Mityurich, G. S., E-mail: George-mityurich@mail.ru [Belarusian Trade and Economics University of Consumer Cooperatives (Belarus); Chernenok, E. V.; Sviridova, V. V.; Serdyukov, A. N. [Gomel State University (Belarus)

    2015-03-15

    Photoacoustic transformation of the TE mode of a Bessel light beam (BLB) has been studied for piezoelectric detection in short-period superlattices formed by magnetoactive crystals of bismuth germanate (Bi{sub 12}GeO{sub 20}) and bismuth silicate (Bi{sub 12}SiO{sub 20}) types. It is shown that the resulting signal amplitude can be controlled using optical schemes of BLB formation with a tunable cone angle. A resonant increase in the signal amplitude has been found in the megahertz range of modulation frequencies and its dependences on the BLB modulation frequency, geometric sizes of the two-layer structure and piezoelectric transducer, radial coordinate of the polarization BLB mode, and dissipative superlattice parameters are analyzed.

  7. Thermodynamics and Magnetocaloric properties of Fe/Cr Superlattices

    Science.gov (United States)

    Mukherjee, T.; Michalski, S.; Skomski, R.; Sellmyer, D. J.; Binek, Ch.

    2011-03-01

    We explore MC properties of tailored Fe/Cr superlattices involving simple 3d metals. Our multilayers are fabricated by pulsed laser deposition with emphasis on maximizing magnetic entropy changes near room temperature. We use nanostructuring to tailor magnetic interaction and exploit geometrical confinement in order to fit the FM to paramagnetic transition temperature of the FM constituent films. In concert this leads to an optimized global metamagnetic transition maximizing the isothermal entropy change. Thermodynamic and MC properties of such Fe/Cr superlattices are studied with the help of SQUID magnetometry. Entropy changes are deduced via the Maxwell relation in single phase regions and via the Clausis-Clapeyron relations at first order metamagnetic transitions, X-ray diffraction and X-ray reflectivity are used to correlate structural data with the magnetic properties. Financial support by NRI, and NSF through EPSCoR, Career DMR-0547887, and MRSEC Grant No. 0820521.

  8. Resonant tunnelling in a Fibonacci bilayer graphene superlattice

    Energy Technology Data Exchange (ETDEWEB)

    Mukhopadhyay, S.; Sinha, C. [Department of Theoretical Physics, Indian Association for the Cultivation of Science, Jadavpur, Kolkata, West Bengal (India); Biswas, R. [Department of Physics, PK College, Contai, Purba Medinipur, West Bengal (India)

    2010-02-15

    The transmission coefficients (TCs) and angularly averaged conductance for quasi-particle transport are studied for a bilayer graphene superlattice arranged according to the Fibonacci sequence. The transmission is found to be symmetric around the superlattice growth direction and highly sensitive to the direction of the quasi-particle incidence. The transmission spectra are fragmented and appear in groups due to the quasi-periodicity of the system. The average conductance shows interesting structures sharply dependent on the height of the potential barriers between two graphene strips. The low-energy conductance due to Klein transmission is substantially modified by the inclusion of quasi-periodicity in the system. (Abstract Copyright [2010], Wiley Periodicals, Inc.)

  9. Phonons in Ge/Si superlattices with Ge quantum dots

    CERN Document Server

    Milekhin, A G; Pchelyakov, O P; Schulze, S; Zahn, D R T

    2001-01-01

    Ge/Si superlattices with Ge quantum dots obtained by means of molecular-beam epitaxy were investigated by means of light Raman scattering under resonance conditions. These structures are shown to have oscillation properties of both two-dimensional and zero-dimensional objects. Within spectrum low-frequency range one observes twisted acoustic phonons (up to 15 order) typical for planar superlattices. Lines of acoustic phonons are overlapped with a wide band of continuous emission. Analysis of frequencies of Ge and Ge-Si optical phonons shows that Ge quantum dots are pseudoamorphous ones and mixing of Ge and Si atoms is a negligible one. One detected low-frequency shift of longitudinal optical phonons at laser excitation energy increase (2.54-2.71 eV)

  10. Blind Evaluation of Hybrid Protein Structure Analysis Methods based on Cross-Linking.

    Science.gov (United States)

    Belsom, Adam; Schneider, Michael; Brock, Oliver; Rappsilber, Juri

    2016-07-01

    Hybrid methods combine experimental data and computational modeling to analyze protein structures that are elusive to structure determination. To spur the development of hybrid methods, we propose to test them in the context of the CASP experiment and would like to invite experimental groups to participate in this initiative.

  11. Depth-Resolved Composition and Electronic Structure of Buried Layers and Interfaces in a LaNiO{sub 3}/SrTiO{sub 3} Superlattice from Soft- and Hard- X-ray Standing-Wave Angle-Resolved Photoemission

    Energy Technology Data Exchange (ETDEWEB)

    Eiteneer, D. [Department of Physics, University of California, Davis, California 95616 (United States); Materials Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720 (United States); Pálsson, G.K., E-mail: gunnar.palsson@physics.uu.se [Department of Physics, University of California, Davis, California 95616 (United States); Materials Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720 (United States); Nemšák, S. [Department of Physics, University of California, Davis, California 95616 (United States); Materials Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720 (United States); Peter-Grünberg-Institut PGI-6, Forschungszentrum Julich, 52425 Julich (Germany); Gray, A.X. [Department of Physics, University of California, Davis, California 95616 (United States); Materials Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720 (United States); Stanford Institute for Materials and Energy Sciences, SLAC National Accelerator Laboratory, Menlo Park, California 94025 (United States); Kaiser, A.M. [Department of Physics, University of California, Davis, California 95616 (United States); Materials Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720 (United States); Son, J.; LeBeau, J. [Materials Department, University of California, Santa Barbara, California 93106 (United States); Conti, G. [Department of Physics, University of California, Davis, California 95616 (United States); Materials Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720 (United States); and others

    2016-08-15

    Highlights: • Depth resolved electronic structure of LaNiO{sub 3}/SrTiO{sub 3} superlattices is measured. • The structure is determined by x-ray standing wave angle-resolved photoemission. • Similarity to the electronic structure of La{sub 0.7}Sr{sub 0.3}MnO{sub 3}/SrTiO{sub 3} is discussed. - Abstract: LaNiO{sub 3} (LNO) is an intriguing member of the rare-earth nickelates in exhibiting a metal-insulator transition for a critical film thickness of about 4 unit cells [Son et al., Appl. Phys. Lett. 96, 062114 (2010)]; however, such thin films also show a transition to a metallic state in superlattices with SrTiO{sub 3} (STO) [Son et al., Appl. Phys. Lett. 97, 202109 (2010)]. In order to better understand this transition, we have studied a strained LNO/STO superlattice with 10 repeats of [4 unit-cell LNO/3 unit-cell STO] grown on an (LaAlO{sub 3}){sub 0.3}(Sr{sub 2}AlTaO{sub 6}){sub 0.7} substrate using soft x-ray standing-wave-excited angle-resolved photoemission (SWARPES), together with soft- and hard- x-ray photoemission measurements of core levels and densities-of-states valence spectra. The experimental results are compared with state-of-the-art density functional theory (DFT) calculations of band structures and densities of states. Using core-level rocking curves and x-ray optical modeling to assess the position of the standing wave, SWARPES measurements are carried out for various incidence angles and used to determine interface-specific changes in momentum-resolved electronic structure. We further show that the momentum-resolved behavior of the Ni 3d e{sub g} and t{sub 2g} states near the Fermi level, as well as those at the bottom of the valence bands, is very similar to recently published SWARPES results for a related La{sub 0.7}Sr{sub 0.3}MnO{sub 3}/SrTiO{sub 3} superlattice that was studied using the same technique (Gray et al., Europhysics Letters 104, 17004 (2013)), which further validates this experimental approach and our conclusions. Our

  12. Interface disorder and transport properties in HTC/CMR superlattices

    Energy Technology Data Exchange (ETDEWEB)

    Haberkorn, N.; Guimpel, J.; Sirena, M.; Steren, L.B.; Campillo, G.; Saldarriaga, W.; Gomez, M.E

    2004-08-01

    The physical properties of superlattices are affected by interface disorder, like roughness and interdiffusion. X-ray diffraction allows its measurement through modeling and structure refinement. The high-T{sub c} RBa{sub 2}Cu{sub 3}O{sub 7} (RBCO) and colossal magnetoresistance La{sub x}A{sub 1-x}MnO{sub 3} (LAMO) perovskites are interesting superlattice partners given their similar lattice parameters and because the combination of magnetic and superconducting properties is interesting for both basic and applied research. We have investigated the structural and transport properties of YBCO/La{sub 2/3}Ca{sub 1/3}MnO{sub 3} and GdBCO/La{sub 0.6}Sr{sub 0.04}MnO{sub 3} superlattices grown by sputtering on (1 0 0)MgO. We find a roughness of 1 RBCO unit cell and a 30% interdiffusion in the same length from the interfaces for all samples. The superconducting behavior is found strongly dependent on the LAMO layer thickness.

  13. Shape-Anisotropy Driven Symmetry Transformations in Nanocrystal Superlattice Polymorphs

    KAUST Repository

    Bian, Kaifu

    2011-04-26

    Despite intense research efforts by research groups worldwide, the potential of self-assembled nanocrystal superlattices (NCSLs) has not been realized due to an incomplete understanding of the fundamental molecular interactions governing the self-assembly process. Because NCSLs reside naturally at length-scales between atomic crystals and colloidal assemblies, synthetic control over the properties of constituent nanocrystal (NC) building blocks and their coupling in ordered assemblies is expected to yield a new class of materials with remarkable optical, electronic, and vibrational characteristics. Progress toward the formation of suitable test structures and subsequent development of NCSL-based technologies has been held back by the limited control over superlattice spacing and symmetry. Here we show that NCSL symmetry can be controlled by manipulating molecular interactions between ligands bound to the NC surface and the surrounding solvent. Specifically, we demonstrate solvent vapor-mediated NCSL symmetry transformations that are driven by the orientational ordering of NCs within the lattice. The assembly of various superlattice polymorphs, including face-centered cubic (fcc), body-centered cubic (bcc), and body-centered tetragonal (bct) structures, is studied in real time using in situ grazing incidence small-angle X-ray scattering (GISAXS) under controlled solvent vapor exposure. This approach provides quantitative insights into the molecular level physics that controls solvent-ligand interactions and assembly of NCSLs. Computer simulations based on all-atom molecular dynamics techniques confirm several key insights gained from experiment. © 2011 American Chemical Society.

  14. Spectral properties of Fibonacci superlattices formed using armchair graphene nanoribbons

    Science.gov (United States)

    Korol, A. M.; Litvynchuk, S. I.; Bagliuk, S. V.; Lazarenko, M. V.

    2016-03-01

    We discuss and analyze the dependence spectra of the transmission coefficient T on the quasiparticle energy E of one variety of graphene-based Fibonacci superlattices (SL). The SL is built from armchair graphene nanoribbons (GNR), and the quasi-periodicity is produced by metal-like (MGNR) and semiconductor (SCGNR) ribbons, placed along the lattice growth axis in accordance with the Fibonacci sequence, which are used as individual SL elements. It is shown that the difference in the values of quantized transverse quasi-momentum of electrons in MGNR and SCGNR is enough to form an effective quasi-periodic modulation in the examined structure (no additional factors required), and the optimal nanoribbon width range for this purpose is determined. We also analyzed the dependence of the spectral properties of the test structure on the geometric parameters of the superlattice, and the external electrostatic potential. We paid particular attention to the fact that each Fibonacci generation had a Dirac superlattice band gap. The results of the study can be useful in the determination of optimal parameters for graphene-based nanoelectronic devices.

  15. Shape-anisotropy driven symmetry transformations in nanocrystal superlattice polymorphs.

    Science.gov (United States)

    Bian, Kaifu; Choi, Joshua J; Kaushik, Ananth; Clancy, Paulette; Smilgies, Detlef-M; Hanrath, Tobias

    2011-04-26

    Despite intense research efforts by research groups worldwide, the potential of self-assembled nanocrystal superlattices (NCSLs) has not been realized due to an incomplete understanding of the fundamental molecular interactions governing the self-assembly process. Because NCSLs reside naturally at length-scales between atomic crystals and colloidal assemblies, synthetic control over the properties of constituent nanocrystal (NC) building blocks and their coupling in ordered assemblies is expected to yield a new class of materials with remarkable optical, electronic, and vibrational characteristics. Progress toward the formation of suitable test structures and subsequent development of NCSL-based technologies has been held back by the limited control over superlattice spacing and symmetry. Here we show that NCSL symmetry can be controlled by manipulating molecular interactions between ligands bound to the NC surface and the surrounding solvent. Specifically, we demonstrate solvent vapor-mediated NCSL symmetry transformations that are driven by the orientational ordering of NCs within the lattice. The assembly of various superlattice polymorphs, including face-centered cubic (fcc), body-centered cubic (bcc), and body-centered tetragonal (bct) structures, is studied in real time using in situ grazing incidence small-angle X-ray scattering (GISAXS) under controlled solvent vapor exposure. This approach provides quantitative insights into the molecular level physics that controls solvent-ligand interactions and assembly of NCSLs. Computer simulations based on all-atom molecular dynamics techniques confirm several key insights gained from experiment.

  16. Super-hybrid composites - An emerging structural material

    Science.gov (United States)

    Chamis, C. C.; Lark, R. F.; Sullivan, T. L.

    1975-01-01

    Specimens of super-hybrids and advanced fiber composites were subjected to extensive tests to determine their mechanical properties, including impact and thermal fatigue. The super-hybrids were fabricated by a procedure similar to that reported by Chamis et al., (1975). Super-hybrids subjected to 1000 cycles of thermal fatigue from -100 to 300 F retained over 90% of their longitudinal flexural strength and over 75% of their transverse flexural strength; their transverse flexural strength may be as high as 8 times that of a commercially supplied boron/1100-Al composite. The thin specimen Izod longitudinal impact resistance of the super-hybrids was twice that of the boron/110-Al material. Super-hybrids subjected to transverse tensile loads exhibited nonlinear stress-strain relationships. The experimentally determined initial membrane (in-plane) and bending elastic properties of super-hybrids were predicted adequately by linear laminate analysis.

  17. Analysis of SMA Hybrid Composite Structures using Commercial Codes

    Science.gov (United States)

    Turner, Travis L.; Patel, Hemant D.

    2004-01-01

    A thermomechanical model for shape memory alloy (SMA) actuators and SMA hybrid composite (SMAHC) structures has been recently implemented in the commercial finite element codes MSC.Nastran and ABAQUS. The model may be easily implemented in any code that has the capability for analysis of laminated composite structures with temperature dependent material properties. The model is also relatively easy to use and requires input of only fundamental engineering properties. A brief description of the model is presented, followed by discussion of implementation and usage in the commercial codes. Results are presented from static and dynamic analysis of SMAHC beams of two types; a beam clamped at each end and a cantilevered beam. Nonlinear static (post-buckling) and random response analyses are demonstrated for the first specimen. Static deflection (shape) control is demonstrated for the cantilevered beam. Approaches for modeling SMAHC material systems with embedded SMA in ribbon and small round wire product forms are demonstrated and compared. The results from the commercial codes are compared to those from a research code as validation of the commercial implementations; excellent correlation is achieved in all cases.

  18. Optical properties of hybrid semiconductor-metal structures

    Energy Technology Data Exchange (ETDEWEB)

    Kreilkamp, L.E.; Pohl, M.; Akimov, I.A.; Yakovlev, D.R.; Bayer, M. [Experimentelle Physik 2, Technische Universitaet Dortmund, 44221 Dortmund (Germany); Belotelov, V.I.; Zvezdin, A.K. [A.M. Prokhorov General Physics Institute, Russian Academy of Sciences, 119992 Moscow (Russian Federation); Karczewski, G.; Wojtowicz, T. [Institute of Physics, Polish Academy of Sciences, 02668 Warsaw (Poland); Rudzinski, A.; Kahl, M. [Raith GmbH, Konrad-Adenauer-Allee 8, 44263 Dortmund (Germany)

    2012-07-01

    We study the optical properties of hybrid nanostructures comprising a semiconductor CdTe quantum well (QW) separated by a thin CdMgTe cap layer of 40 nm from a patterned gold film. The CdTe/CdMgTe QW structure with a well width of 10nm was grown by molecular beam epitaxy. The one-dimensional periodic gold films on top were made using e-beam lithography and lift-off process. The investigated structures can be considered as plasmonic crystals because the metal films attached to the semiconductor are patterned with a period in the range from 475 to 600 nm, which is comparable to the surface plasmon-polariton (SPP) wavelength. Angle dependent reflection spectra at room temperature clearly show plasmonic resonances. PL spectra taken at low temperatures of about 10 K under below- and above-barrier illumination show significant modifications compared to the unstructured QW sample. The number of emission lines and their position shift change depending on the excitation energy. The role of exciton-SPP coupling and Schottky barrier at the semiconductor-metal interface are discussed.

  19. Hybrid surface structures for efficiency enhancement of fluorescent SiC for white LED application

    DEFF Research Database (Denmark)

    Ou, Yiyu; Xiong, Meng; Lu, Weifang

    Hybrid structures contain structures in both micro- and nano-meter scale have been fabricated on fluorescent SiC by applying a fast fabrication method. Luminescence efficiency of f-SiC was enhanced significantly compared with normal nanostructures....

  20. The Tower: Modelling, Analysis and Construction of Bending Active Tensile Membrane Hybrid Structures

    DEFF Research Database (Denmark)

    Holden Deleuran, Anders; Schmeck, Michel; Charles Quinn, Gregory

    2015-01-01

    as combining two or more structural concepts and materials together to create a stronger whole. The paper presents the methods used and developed for design, simulation, evaluation and production, as well as the challenges and obstacles to overcome to build a complex hybrid tower structure in an outside......The project is the result of an interdisciplinary research collaboration between CITA, KET and Fibrenamics exploring the design of integrated hybrid structures employing bending active elements and tensile membranes with bespoke material properties and detailing. Hybrid structures are defined here...

  1. Exact Surface States in Photonic Superlattices

    CERN Document Server

    Xie, Qiongtao

    2012-01-01

    We develop an analytical method to derive exact surface states in photonic superlattices. In a kind of infinite bichromatic superlattices satisfying some certain conditions, we analytically obtain their in-gap states, which are superpositions of finite numbers of unstable Bloch waves. By using the unstable in-gap states, we construct exactly several stable surface states in various photonic superlattices. We analytically explore the parametric dependence of these exact surface states. Our analysis provides an exact demonstration for the existence of surface states and would be also helpful to understand surface states in other lattice systems.

  2. Thermoelectric properties of strontium titanate superlattices incorporating niobium oxide nanolayers

    KAUST Repository

    Sarath Kumar, S. R.

    2014-04-22

    A novel superlattice structure based on epitaxial nanoscale layers of NbOx and Nb-doped SrTiO3 is fabricated using a layer-by-layer approach on lattice matched LAO substrates. The absolute Seebeck coefficient and electrical conductivity of the [(NbOx) a/(Nb-doped SrTiO3)b]20 superlattices (SLs) were found to increase with decreasing layer thickness ratio (a/b ratio), reaching, at high temperatures, a power factor that is comparable to epitaxial Nb-doped SrTiO3 (STNO) films (∼0.7 W m-1 K-1). High temperature studies reveal that the SLs behave as n-type semiconductors and undergo an irreversible change at a varying crossover temperature that depends on the a/b ratio. By use of high resolution X-ray photoelectron spectroscopy and X-ray diffraction, the irreversible changes are identified to be due to a phase transformation from cubic NbO to orthorhombic Nb2O5, which limits the highest temperature of stable operation of the superlattice to 950 K. © 2014 American Chemical Society.

  3. A new hybrid coding for protein secondary structure prediction based on primary structure similarity.

    Science.gov (United States)

    Li, Zhong; Wang, Jing; Zhang, Shunpu; Zhang, Qifeng; Wu, Wuming

    2017-03-16

    The coding pattern of protein can greatly affect the prediction accuracy of protein secondary structure. In this paper, a novel hybrid coding method based on the physicochemical properties of amino acids and tendency factors is proposed for the prediction of protein secondary structure. The principal component analysis (PCA) is first applied to the physicochemical properties of amino acids to construct a 3-bit-code, and then the 3 tendency factors of amino acids are calculated to generate another 3-bit-code. Two 3-bit-codes are fused to form a novel hybrid 6-bit-code. Furthermore, we make a geometry-based similarity comparison of the protein primary structure between the reference set and the test set before the secondary structure prediction. We finally use the support vector machine (SVM) to predict those amino acids which are not detected by the primary structure similarity comparison. Experimental results show that our method achieves a satisfactory improvement in accuracy in the prediction of protein secondary structure.

  4. Hybrid Composites for LH2 Fuel Tank Structure

    Science.gov (United States)

    Grimsley, Brian W.; Cano, Roberto J.; Johnston, Norman J.; Loos, Alfred C.; McMahon, William M.

    2001-01-01

    The application of lightweight carbon fiber reinforced plastics (CFRP) as structure for cryogenic fuel tanks is critical to the success of the next generation of Reusable Launch Vehicles (RLV). The recent failure of the X-33 composite fuel tank occurred in part due to microcracking of the polymer matrix, which allowed cryogen to permeate through the inner skin to the honeycomb core. As part of an approach to solve these problems, NASA Langley Research Center (LaRC) and Marshall Space Flight Center (MSFC) are working to develop and investigate polymer films that will act as a barrier to the permeation of LH2 through the composite laminate. In this study two commercially available films and eleven novel LaRC films were tested in an existing cryogenics laboratory at MSFC to determine the permeance of argon at room temperature. Several of these films were introduced as a layer in the composite to form an interleaved, or hybrid, composite to determine the effects on permeability. In addition, the effects of the interleaved layer thickness, number, and location on the mechanical properties of the composite laminate were investigated. In this initial screening process, several of the films were found to exhibit lower permeability to argon than the composite panels tested.

  5. Temperature-Dependent X-ray Diffraction Measurements of Infrared Superlattices Grown by MBE

    Directory of Open Access Journals (Sweden)

    Charles J. Reyner

    2016-11-01

    Full Text Available Strained-layer superlattices (SLSs are an active research topic in the molecular beam epitaxy (MBE and infrared focal plane array communities. These structures undergo a >500 K temperature change between deposition and operation. As a result, the lattice constants of the substrate and superlattice are expected to change by approximately 0.3%, and at approximately the same rate. However, we present the first temperature-dependent X-ray diffraction (XRD measurements of SLS material on GaSb and show that the superlattice does not contract in the same manner as the substrate. In both InAs/InAs0.65Sb0.35 and In0.8Ga0.2As/InAs0.65Sb0.35 SLS structures, the apparent out-of-plane strain states of the superlattices switch from tensile at deposition to compressive at operation. These changes have ramifications for material characterization, defect generation, carrier lifetime, and overall device performance of superlattices grown by MBE.

  6. Investigation of Anisotropic Thermal Conductivity of GaAs/AlAs Superlattices

    Science.gov (United States)

    Li, Ran

    The thermal conductivities of superlattices are essential to improve the properties of thermoelectrics and optoelectronics; however, limited results in relation to both the in-plane and cross-plane thermal conductivities have been reported. A convenient, effective, and accurate experimental method is required to improve the current research on the thermal properties of superlattices. We conducted an experimental research study on two GaAs/AlAs superlattice samples with a total superlattice layer thickness of 2 microm using a combination of the 2-omega and 3-omega techniques. The samples have period thicknesses of 4 nm and 10 nm, respectively. To explore the thermal conductivities of the substrate and insulation layer of the superlattice samples indirectly, a controlled sample with the same structure, but without a superlattice layer, is used. We obtained the thermal conductivities of the GaAs substrate and insulation layer (SiO2 thin film) using the 3-omega technique and FEM simulation model. We also explored the deviation of the experimental results of the 2-omega technique from the Fourier's Law through the controlled sample. These parameters obtained from the controlled sample are used in the data analysis in the following superlattice research. In the superlattice study, we combine the 3-omega and 2-omega techniques to characterize the anisotropic thermal conductivity of GaAs/AlAs superlattice from the same wafer. The in-plane thermal conductivity, cross-plane thermal conductivity, and anisotropy are obtained from the same wafer by comparing the experimental results with the FEM simulated results. This combination works fine in general and demonstrates a significant reduction in thermal conductivity compared to that of equivalent bulk materials. Superlattices with different period thicknesses but the same total superlattice thickness present a significant difference in both the in-plane and cross-plane thermal conductivities of the superlattices. However, we

  7. A Hybrid Structure for Data Aggregation in Wireless Sensor Network

    Directory of Open Access Journals (Sweden)

    Hedieh Sajedi

    2014-01-01

    Full Text Available In recent years, wireless sensor networks have been used for various applications such as environmental monitoring, military and medical applications. A wireless sensor network uses a large number of sensor nodes that continuously collect and send data from a specific region to a base station. Data from sensors are collected from the study area in the common scenario of sensor networks. Afterward, sensed data is sent to the base station. However, neighboring sensors often lead to redundancy of data. Transmission of redundant data to the base station consumes energy and produces traffic, because process is run in a large network. Data aggregation was proposed in order to reduce redundancy in data transformation and traffic. The most popular communication protocol in this field is cluster based data aggregation. Clustering causes energy balance, but sometimes energy consumption is not efficient due to the long distance between cluster heads and base station. In another communication protocol, which is based on a tree construction, because of the short distance between the sensors, energy consumption is low. In this data aggregation approach, since each sensor node is considered as one of the vertices of a tree, the depth of tree is usually high. In this paper, an efficient hierarchical hybrid approach for data aggregation is presented. It reduces energy consumption based on clustering and minimum spanning tree. The benefit of combining clustering and tree structure is reducing the disadvantages of previous structures. The proposed method firstly employs clustering algorithm and then a minimum spanning tree is constructed based on cluster heads. Our proposed method was compared to LEACH which is a well-known data aggregation method in terms of energy consumption and the amount of energy remaining in each sensor network lifetime. Simulation results indicate that our proposed method is more efficient than LEACH algorithm considering energy

  8. Direct probing of vertical electron movement in superlattices by sub-picosecond luminescence

    Science.gov (United States)

    Deveaud, B.; Chomette, A.; Clérot, F.; Lambert, B.; Auvray, P.; Gauneau, M.; Regreny, A.

    Vertical transport in GaAs/AlGaAs superlattices is probed in structures with graded composition. Such structures allow boi to impose a quasi-electric field to the carriers and to evidence the carrier movement by the temporal changes in the luminescence lineshape. The fit of this lineshape by a drift-diffusion model gives the transport properties of electrons. High mobility of the electrons is evidenced for the shortest period superlattices, in agreement with previous optical measurements. Smaller mobilities are observed when the miniband width becomes smaller.

  9. Fabrication of Si/SiO2 Superlattice Microwire Array Solar Cells Using Microsphere Lithography

    Directory of Open Access Journals (Sweden)

    Shigeru Yamada

    2016-01-01

    Full Text Available A fabrication process for silicon/silicon dioxide (Si/SiO2 superlattice microwire array solar cells was developed. The Si/SiO2 superlattice microwire array was fabricated using a microsphere lithography process with polystyrene particles. The solar cell shows a photovoltaic effect and an open-circuit voltage of 128 mV was obtained. The limiting factors of the solar cell performance were investigated from the careful observations of the solar cell structures. We also investigated the influence of the microwire array structure on light trapping in the solar cells.

  10. Structural investigation of the zirconium-titanium based amino trimethylene phosphonate hybrid coating on aluminum alloy

    Institute of Scientific and Technical Information of China (English)

    Shuanghong WANG; Changsheng LIU; Fengjun SHAN

    2009-01-01

    A zirconium-titanium based amino trimethylene phosphonate hybrid coating on AA6061 aluminum alloys was formed by dipping in a fluorotitanate/zirconate acid and amino trimethylene phosphonic acid (ATMP) solution for improving the lacquer adhesion and corrosion resistance as a substitute of chromate coatings. The morphol-ogy and structure of the hybrid coating were studied by means of scanning electror microscopy (SEM) and atomic force microscopy (AFM). The surface compositior and structure characteristics were also investigated by means of X-ray photoelectron spectroscopy (XPS) and Fourier transformation infra-red spectroscopy (FTIR). The results of SEM and AFM show that the hybrid coating present piece particle distrib-ution which is much denser than that of the zirconium-titanium coating. The results of XPS and FTIR indicate that the hybrid coating is a hybrid composite structure composed of both the zirconium-titanium and amino trimethylene phosphonate coat-ings.

  11. Temperature Histories of Structural Steel Laser and Hybrid Laser-GMA Welds Calculated Using Multiple Constraints

    Science.gov (United States)

    2015-12-10

    Naval Research Laboratory Washington, DC 20375-5320 NRL/MR/6390--15-9665 Temperature Histories of Structural Steel Laser and Hybrid Laser-GMA Welds...NUMBER OF PAGES 17. LIMITATION OF ABSTRACT Temperature Histories of Structural Steel Laser and Hybrid Laser-GMA Welds Calculated Using Multiple...202) 767-2601 Inverse thermal analyses of structural steel deep-penetration welds are presented. These analyses employ a methodology that is in terms of

  12. Controllable spin and valley polarized current through a superlattice of normal/ferromagnetic/normal silicene junction

    Science.gov (United States)

    Rashidian, Z.; Hajati, Y.; Rezaeipour, S.; Baher, S.

    2017-02-01

    The spin and valley transports in a superlattice of normal/ferromagnetic/normal silicene junction are studied theoretically. Transport properties in particular valley-resolved conductance, spin and valley polarization have been computed by the Landauer Buttiker formula. We achieve fully valley and spin polarized current in the superlattice N/F/N structure. Our findings also imply that by increasing the number of ferromagnetic barriers, the onset of fully spin and valley polarized current always occur for lower values of staggered potential(Δz/E) and length of the ferromagnetic region (Kf L) in the silicene supelattice structure as compared with N/F/N silicene junction. Fully spin and valley polarizations make silicene superlattice a suitable candidate for spin-valleytronics applications.

  13. Optically and Electrically Tunable Dirac Points and Zitterbewegung in Graphene-Based Photonic Superlattices

    CERN Document Server

    Deng, Hanying; Malomed, Boris A; Chen, Xianfeng; Panoiu, Nicolae C

    2015-01-01

    We demonstrate that graphene-based photonic superlattices provide a versatile platform for electrical and all-optical control of photonic beams with deep-subwavelength accuracy. Specifically, by inserting graphene sheets into periodic metallo-dielectric structures one can design optical superlattices that posses photonic Dirac points (DPs) at frequencies at which the spatial average of the permittivity of the superlattice, $\\bar{ \\varepsilon}$, vanishes. Similar to the well-known zero-$\\bar{n}$ bandgaps, we show that these zero-$\\bar{\\varepsilon}$ DPs are highly robust against structural disorder. We also show that, by tuning the graphene permittivity via the optical Kerr effect or electrical doping, one can induce a spectral variation of the DP exceeding \\SI{30}{\

  14. Effect of secondary structure on the thermodynamics and kinetics of PNA hybridization to DNA hairpins

    DEFF Research Database (Denmark)

    Kushon, S A; Jordan, J P; Seifert, J L

    2001-01-01

    structures in both target and probe molecules are shown to depress the melting temperatures and free energies of the probe-target duplexes. Kinetic analysis of hybridization yields reaction rates that are up to 160-fold slower than hybridization between two unstructured strands. The thermodynamic and kinetic...

  15. A Best Practice Modular Design of a Hybrid Course Delivery Structure for an Executive Education Program

    Science.gov (United States)

    Klotz, Dorothy E.; Wright, Thomas A.

    2017-01-01

    This article highlights a best practice approach that showcases the highly successful deployment of a hybrid course delivery structure for an Operations core course in an Executive MBA Program. A key design element of the approach was the modular design of both the course itself and the learning materials. While other hybrid deployments may stress…

  16. A Best Practice Modular Design of a Hybrid Course Delivery Structure for an Executive Education Program

    Science.gov (United States)

    Klotz, Dorothy E.; Wright, Thomas A.

    2017-01-01

    This article highlights a best practice approach that showcases the highly successful deployment of a hybrid course delivery structure for an Operations core course in an Executive MBA Program. A key design element of the approach was the modular design of both the course itself and the learning materials. While other hybrid deployments may stress…

  17. Interwell excitons in GaAs superlattices

    DEFF Research Database (Denmark)

    Birkedal, Dan; Sayed, Karim El; Sanders, G.;

    1996-01-01

    The formation of spatially indirect excitons in superlattices with narrow minibands is theoretically and experimentally investigated. We identify the experimental conditions for the observation of interwell excitons and find a distinct excitonic state energetically located between the Is exciton ...

  18. A Structural Model Decomposition Framework for Hybrid Systems Diagnosis

    Science.gov (United States)

    Daigle, Matthew; Bregon, Anibal; Roychoudhury, Indranil

    2015-01-01

    Nowadays, a large number of practical systems in aerospace and industrial environments are best represented as hybrid systems that consist of discrete modes of behavior, each defined by a set of continuous dynamics. These hybrid dynamics make the on-line fault diagnosis task very challenging. In this work, we present a new modeling and diagnosis framework for hybrid systems. Models are composed from sets of user-defined components using a compositional modeling approach. Submodels for residual generation are then generated for a given mode, and reconfigured efficiently when the mode changes. Efficient reconfiguration is established by exploiting causality information within the hybrid system models. The submodels can then be used for fault diagnosis based on residual generation and analysis. We demonstrate the efficient causality reassignment, submodel reconfiguration, and residual generation for fault diagnosis using an electrical circuit case study.

  19. Interface Properties of InAs/AlSb Superlattices Characterized by Grazing Incidence X-Ray Reflectivity

    Institute of Scientific and Technical Information of China (English)

    LI Zhi-Hua; GUO Li-Wei; WU Shu-Dong; WANG Wen-Xin; HUANG Qi; ZHOU Jun-Ming

    2005-01-01

    @@ Two kinds of superlattice interfaces of InAs/AlSb superlattices are realized in an optimized interface growth process, where one is AlAs-like and the other is InSb-like grown on a relaxed AlSb buffer layer. The superlattice properties such as interface roughness and layer thickness are studied by grazing incidence x-ray reflectivity. The reflectivity curves are simulated by standard software till the simulation curves match well with the experimental curves. The simulation indicates that AlAs-like interfaces are much rougher than InSb-like interfaces. Grazing incidence x-ray reflectivity is also discussed as a powerful tool to assessing the structure properties of superlattices.

  20. Cross-sectional scanning thermal microscopy of ErAs/GaAs superlattices grown by molecular beam epitaxy.

    Science.gov (United States)

    Park, K W; Krivoy, E M; Nair, H P; Bank, S R; Yu, E T

    2015-07-03

    Scanning thermal microscopy has been implemented in a cross-sectional geometry, and its application for quantitative, nanoscale analysis of thermal conductivity is demonstrated in studies of an ErAs/GaAs nanocomposite superlattice. Spurious measurement effects, attributable to local thermal transport through air, were observed near large step edges, but could be eliminated by thermocompression bonding to an additional structure. Using this approach, bonding of an ErAs/GaAs superlattice grown on GaAs to a silicon-on-insulator wafer enabled thermal signals to be obtained simultaneously from Si, SiO2, GaAs, and ErAs/GaAs superlattice. When combined with numerical modeling, the thermal conductivity of the ErAs/GaAs superlattice measured using this approach was 11 ± 4 W m(-1) K(-1).

  1. Hybrid Structures for Surface-Enhanced Raman Scattering: DNA Origami/Gold Nanoparticle Dimer/Graphene.

    Science.gov (United States)

    Prinz, Julia; Matković, Aleksandar; Pešić, Jelena; Gajić, Radoš; Bald, Ilko

    2016-10-01

    A combination of three innovative materials within one hybrid structure to explore the synergistic interaction of their individual properties is presented. The unique electronic, mechanical, and thermal properties of graphene are combined with the plasmonic properties of gold nanoparticle (AuNP) dimers, which are assembled using DNA origami nanostructures. This novel hybrid structure is characterized by means of correlated atomic force microscopy and surface-enhanced Raman scattering (SERS). It is demonstrated that strong interactions between graphene and AuNPs result in superior SERS performance of the hybrid structure compared to their individual components. This is particularly evident in efficient fluorescence quenching, reduced background, and a decrease of the photobleaching rate up to one order of magnitude. The versatility of DNA origami structures to serve as interface for complex and precise arrangements of nanoparticles and other functional entities provides the basis to further exploit the potential of the here presented DNA origami-AuNP dimer-graphene hybrid structures.

  2. A gold hybrid structure as optical coupler for quantum well infrared photodetector

    Energy Technology Data Exchange (ETDEWEB)

    Ding, Jiayi; Li, Qian; Jing, Youliang [National Laboratory for Infrared Physics, Shanghai Institute of Technical Physics, Chinese Academy of Sciences, 500 Yu Tian Road, Shanghai 200083 (China); Chen, Xiaoshuang, E-mail: xschen@mail.sitp.ac.cn; Li, Zhifeng; Li, Ning; Lu, Wei [National Laboratory for Infrared Physics, Shanghai Institute of Technical Physics, Chinese Academy of Sciences, 500 Yu Tian Road, Shanghai 200083 (China); Synergetic Innovation Center of Quantum Information and Quantum Physics, University of Science and Technology of China, Hefei, Anhui 230026 (China)

    2014-08-28

    A hybrid structure consisting of a square lattice of gold disk arrays and an overlaying gold film is proposed as an optical coupler for a backside-illuminated quantum well infrared photodetector (QWIP). Finite difference time-domain method is used to numerically simulate the reflection spectra and the field distributions of the hybrid structure combined with the QWIP device. The results show that the electric field component perpendicular to the quantum well is strongly enhanced when the plasmonic resonant wavelength of the hybrid structure coincides with the response one of the quantum well infrared photodetector regardless of the polarization of the incident light. The effect of the diameter and thickness of an individual gold disk on the resonant wavelength is also investigated, which indicates that the localized surface plasmon also plays a role in the light coupling with the hybrid structure. The coupling efficiency can exceed 50 if the structural parameters of the gold disk arrays are well optimized.

  3. Analytical Study of Electromagnetic Wave in Superlattice

    Institute of Scientific and Technical Information of China (English)

    LINChang; ZHANGXiu-Lian

    2004-01-01

    The theoretical description of soliton solutions and exact analytical solutions in the sine-Gordon equation is extended to superlattice physics. A family of interesting exact solutions and a new exact analytical solution have been obtained for the electromagnetic wave propagating through a superlattice. In more general cases, the vector potential along the propagating direction obeys the sine-Gordon equation. Some mathematical results of theoretical investigation are given for different cases in supedattices.

  4. HgTe-CdTe SUPERLATTICES

    OpenAIRE

    Smith, D; Mcgill, T.

    1984-01-01

    We report on a theoretical study of the electronic properties of HgTe-CdTe superlattices. The band gap as a function of layer thickness, effective masses normal to the layer plane and tunneling length are compared to the corresponding (Hg, Cd)Te alloys. We find that the superlattice possesses a number of properties that may make it superior to the corresponding alloy as an infrared material.

  5. ON THE STABILIZATION OF THE LINEAR HYBRID SYSTEM STRUCTURE

    Directory of Open Access Journals (Sweden)

    Kirillov

    2014-11-01

    Full Text Available The linear control hybrid system, consisting of a fi- nite set of subsystems (modes having different dimensions, is considered. The moments of reset time are determined by some complementary function – evolutionary time. This function satisfies the special complementary ordinary differential equation. The mode stabilization problem is solved for some class of piecewise linear controls. The method of stabilization relies on the set of invariant planes, the existence of which is due to the special form of the hybrid system.

  6. Extraordinary Magnetoresistance Effect in Semiconductor/Metal Hybrid Structure

    KAUST Repository

    Sun, Jian

    2013-06-27

    In this dissertation, the extraordinary magnetoresistance (EMR) effect in semiconductor/metal hybrid structures is studied to improve the performance in sensing applications. Using two-dimensional finite element simulations, the geometric dependence of the output sensitivity, which is a more relevant parameter for EMR sensors than the magnetoresistance (MR), is studied. The results show that the optimal geometry in this case is different from the geometry reported before, where the MR ratio was optimized. A device consisting of a semiconductor bar with length/width ratio of 5~10 and having only 2 contacts is found to exhibit the highest sensitivity. A newly developed three-dimensional finite element model is employed to investigate parameters that have been neglected with the two dimensional simulations utilized so far, i.e., thickness of metal shunt and arbitrary semiconductor/metal interface. The simulations show the influence of those parameters on the sensitivity is up to 10 %. The model also enables exploring the EMR effect in planar magnetic fields. In case of a bar device, the sensitivity to planar fields is about 15 % to 20 % of the one to perpendicular fields. 5 A “top-contacted” structure is proposed to reduce the complexity of fabrication, where neither patterning of the semiconductor nor precise alignment is required. A comparison of the new structure with a conventionally fabricated device shows that a similar magnetic field resolution of 24 nT/√Hz is obtained. A new 3-contact device is developed improving the poor low-field sensitivity observed in conventional EMR devices, resulting from its parabolic magnetoresistance response. The 3-contact device provides a considerable boost of the low field response by combining the Hall effect with the EMR effect, resulting in an increase of the output sensitivity by 5 times at 0.01 T compared to a 2-contact device. The results of this dissertation provide new insights into the optimization of EMR devices

  7. Spin-dependent Seebeck effects in a graphene superlattice p–n junction with different shapes

    Science.gov (United States)

    Zhou, Benhu; Zhou, Benliang; Yao, Yagang; Zhou, Guanghui; Hu, Ming

    2017-10-01

    We theoretically calculate the spin-dependent transmission probability and spin Seebeck coefficient for a zigzag-edge graphene nanoribbon p–n junction with periodically attached stubs under a perpendicular magnetic field and a ferromagnetic insulator. By using the nonequilibrium Green’s function method combining with the tight-binding Hamiltonian, it is demonstrated that the spin-dependent transmission probability and spin Seebeck coefficient for two types of superlattices can be modulated by the potential drop, the magnetization strength, the number of periods of the superlattice, the strength of the perpendicular magnetic field, and the Anderson disorder strength. Interestingly, a metal to semiconductor transition occurs as the number of the superlattice for a crossed superlattice p–n junction increases, and its spin Seebeck coefficient is much larger than that for the T-shaped one around the zero Fermi energy. Furthermore, the spin Seebeck coefficient for crossed systems can be much pronounced and their maximum absolute value can reach 528 μV K-1 by choosing optimized parameters. Besides, the spin Seebeck coefficient for crossed p–n junction is strongly enhanced around the zero Fermi energy for a weak magnetic field. Our results provide theoretical references for modulating the thermoelectric properties of a graphene superlattice p–n junction by tuning its geometric structure and physical parameters.

  8. MgO/Cu2O Superlattices: Growth of Epitaxial Two-Dimensional Nanostructures

    Science.gov (United States)

    Yang, M. J.; Wadekar, P. V.; Hsieh, W. C.; Huang, H. C.; Lin, C. W.; Chou, J. W.; Liao, C. H.; Chang, C. F.; Seo, H. W.; You, S. T.; Tu, L. W.; Lo, I. K.; Ho, N. J.; Yeh, S. W.; Liao, H. H.; Chen, Q. Y.; Chu, W. K.

    2016-12-01

    Alternated stacking of dissimilar layers can produce novel superlattice materials with multiple functionalities. The majority of such work reported in literature on epitaxial superlattices has been on alternating layers with the same space group (SG) and crystal structure (CS), whereas superlattices with the same CS but different SG have not been studied as much. We have grown superlattices with two well-known oxide materials, viz. cuprite (Cu2O, CS = cubic and SG = Pn bar{3} m) and magnesium oxide (MgO, CS = cubic, SG = Fm bar{3} m). An MgO buffer layer grown near 650°C at the film-substrate interface was found to be essential to achieving reasonable long-range atomic order. Grazing-angle x-ray diffraction, x-ray reflectivity, and electron diffraction analyses as well as transmission electron microscopy were used to investigate the interface abruptness, smoothness, and general crystallinity of the individual layers. Interdiffusion between MgO and Cu2O near interfacial regions places a limit of 250°C on the growth temperature for fabrication of superlattices with reasonably sharp interfaces.

  9. Structural and optical characterization of InAs/GaSb type-II superlattices: Influence of the change in InAs and GaSb layer thicknesses for fixed InSb-like interfaces

    Energy Technology Data Exchange (ETDEWEB)

    Arikan, Bulent, E-mail: bulentarikanx@gmail.com; Korkmaz, Melih; Aslan, Bulent; Serincan, Uğur

    2015-08-31

    In this article, we report on the molecular beam epitaxy growth and characterization of a 140 period InAs/GaSb type-II superlattice structure designed for mid infrared detection. Thickness of a period was systematically altered in each sample by changing the thickness of InAs (GaSb) layers from 9 to 7 monolayers (ML) for a fixed GaSb (InAs) layer at 9 ML (7 ML). The same InSb-like strain compensation interface was used for all samples. High resolution X-ray diffraction analysis, spectral responsivity and external quantum efficiency (QE) measurements were performed to express the effects of layer thickness variations on both structural and photodetector features. The decrease in the InAs thickness resulted in the increased mismatch from 0 to + 1626 ppm and the blue shift in the 50% cut-off wavelength (λ{sub c}) from 5.41 to 4.36 μm at 77 K. The additional decrease in GaSb thickness caused further increase in the mismatch up to + 1791 ppm. The steepness of the photoresponse at the absorption band edge was quantified and presented comparatively with different photodetector parameters and material properties for a complete picture. The highest optical response was obtained from sample having 8 ML InAs and 9 ML GaSb with λ{sub c} = 4.76 μm and QE = 23.7% at 4 μm. - Highlights: • Detailed growth conditions for InAs/GaSb SLs designed for infrared detection • Precisely engineering the λ{sub c} and the ∆a{sub ⊥}/a by controlling the SL layer thicknesses • InAs layer thickness changes are more effective than the GaSb on the λ{sub c} and ∆a{sub ⊥}/a.

  10. On the structural and physicochemical properties of gamma irradiated UHMWPE/silane hybrid

    Energy Technology Data Exchange (ETDEWEB)

    Shafiq, Muhammad [Advanced Polymer Laboratory, Department of Metallurgy and Materials Engineering, Pakistan Institute of Engineering and Applied Sciences, 45650 Islamabad (Pakistan); Mehmood, Malik Sajjad [Advanced Polymer Laboratory, Department of Metallurgy and Materials Engineering, Pakistan Institute of Engineering and Applied Sciences, 45650 Islamabad (Pakistan); Department of Basic Sciences and Humanities, University of Engineering and Technology, 47050 Taxila (Pakistan); Yasin, Tariq, E-mail: yasintariq@yahoo.com [Advanced Polymer Laboratory, Department of Metallurgy and Materials Engineering, Pakistan Institute of Engineering and Applied Sciences, 45650 Islamabad (Pakistan)

    2013-12-16

    This study has been carried to investigate the influence of gamma rays on the structural and physicochemical properties of UHMWPE/silane hybrid. UHMWPE was mixed with vinyltriethoxysilane (VTES) and compression molded sheets were irradiated at different doses of gamma rays. Fourier transform infrared spectroscopy indicated the formation of siloxane linkages in hybrids, which were found to be shifted towards lower wave number upon irradiation. The X-ray diffraction patterns showed significant increase in the percentage crystallinity of hybrid upon gamma irradiation, especially at 65 kGy absorbed dose. Scanning electron micrographs showed good consolidation and compaction with no surface defects. Moreover, the rough topography was changed to smooth ripple-like appearance upon γ-irradiation. Thermal analysis revealed that irradiated hybrids exhibited higher onset thermal degradation temperature, peak melting temperature, and crystalline lamellae thickness compared with the water treated hybrid. In addition, the tensile testing confirmed an increase of 41% and 133% in yield strength and Young's modulus in 100 kGy irradiated hybrid respectively than that of water treated hybrid. We hope that the irradiated UHMWPE/silane hybrids can be used in various high-strength applications such as total joint replacements, pickers for textile machinery, lining for coal chutes and dump trucks. - Highlights: • UHMWPE/silane hybrids have been prepared and irradiated using gamma rays. • The structural analysis revealed the formation siloxane linkages in the hybrid. • The crystallinity, thermal stability and mechanical properties of hybrids were improved with irradiation. • The irradiated hybrids can be used in various high-strength applications.

  11. Advanced Ceramic Matrix Composites with Multifunctional and Hybrid Structures

    Science.gov (United States)

    Singh, Mrityunjay; Morscher, Gregory N.

    2004-01-01

    Ceramic matrix composites are leading candidate materials for a number of applications in aeronautics, space, energy, and nuclear industries. Potential composite applications differ in their requirements for thickness. For example, many space applications such as "nozzle ramps" or "heat exchangers" require very thin (structures whereas turbine blades would require very thick parts (> or = 1 cm). Little is known about the effect of thickness on stress-strain behavior or the elevated temperature tensile properties controlled by oxidation diffusion. In this study, composites consisting of woven Hi-Nicalon (trademark) fibers a carbon interphase and CVI SiC matrix were fabricated with different numbers of plies and thicknesses. The effect of thickness on matrix crack formation, matrix crack growth and diffusion kinetics will be discussed. In another approach, hybrid fiber-lay up concepts have been utilized to "alloy" desirable properties of different fiber types for mechanical properties, thermal stress management, and oxidation resistance. Such an approach has potential for the C(sub I)-SiC and SiC(sub f)-SiC composite systems. CVI SiC matrix composites with different stacking sequences of woven C fiber (T300) layers and woven SiC fiber (Hi-Nicalon (trademark)) layers were fabricated. The results will be compared to standard C fiber reinforced CVI SiC matrix and Hi-Nicalon reinforced CVI SiC matrix composites. In addition, shear properties of these composites at different temperatures will also be presented. Other design and implementation issues will be discussed along with advantages and benefits of using these materials for various components in high temperature applications.

  12. Ferromagnet / superconductor oxide superlattices

    Science.gov (United States)

    Santamaria, Jacobo

    2006-03-01

    The growth of heterostructures combining oxide materials is a new strategy to design novel artificial multifunctional materials with interesting behaviors ruled by the interface. With the (re)discovery of colossal magnetoresistance (CMR) materials, there has been renewed interest in heterostructures involving oxide superconductors and CMR ferromagnets where ferromagnetism (F) and superconductivity (S) compete within nanometric distances from the interface. In F/S/F structures involving oxides, interfaces are especially complex and various factors like interface disorder and roughness, epitaxial strain, polarity mismatch etc., are responsible for depressed magnetic and superconducting properties at the interface over nanometer length scales. In this talk I will focus in F/S/F structures made of YBa2Cu3O7 (YBCO) and La0.7Ca0.3MnO3 (LCMO). The high degree of spin polarization of the LCMO conduction band, together with the d-wave superconductivity of the YBCO make this F/S system an adequate candidate for the search of novel spin dependent effects in transport. We show that superconductivity at the interface is depressed by various factors like charge transfer, spin injection or ferromagnetic superconducting proximity effect. I will present experiments to examine the characteristic distances of the various mechanisms of superconductivity depression. In particular, I will discuss that the critical temperature of the superconductor depends on the relative orientation of the magnetization of the F layers, giving rise to a new giant magnetoresistance effect which might be of interest for spintronic applications. Work done in collaboration with V. Peña^1, Z. Sefrioui^1, J. Garcia-Barriocanal^1, C. Visani^1, D. Arias^1, C. Leon^1 , N. Nemes^2, M. Garcia Hernandez^2, S. G. E. te Velthuis^3, A. Hoffmann^3, M. Varela^4, S. J. Pennycook^4. Work supported by MCYT MAT 2005-06024, CAM GR- MAT-0771/2004, UCM PR3/04-12399 Work at Argonne supported by the Department of Energy, Basic

  13. Surface photovoltage spectroscopy of quantum wells and superlattices

    Energy Technology Data Exchange (ETDEWEB)

    Bachrach-Ashkenasy, N.; Kronik, L.; Shapira, Y. [Department of Physical Electronics, Faculty of Engineering, Tel-Aviv University, Ramat-Aviv 69978 (Israel); Rosenwaks, Y.; Hanna, M.C. [National Renewable Energy Laboratory, Golden, Colorado 80401 (United States); Leibovitch, M.; Ram, P. [Physics Department, Brooklyn College of the City University of New York, Brooklyn, New York 11210 (United States)

    1996-02-01

    Surface photovoltage spectroscopy (SPS) has been employed to monitor optical transitions in quantum well and superlattice structures at room temperature. Excellent agreement is found between theoretical predictions of heavy hole and electron energy level positions and the observed transitions. The results show that using this technique, the complete band diagram of the quantum structure may be constructed. SPS emerges as a powerful tool capable of monitoring optical transitions above the lowest one in a simple to interpret, contactless, and nondestructive way. {copyright} {ital 1996 American Institute of Physics.}

  14. Type II superlattice technology for LWIR detectors

    Science.gov (United States)

    Klipstein, P. C.; Avnon, E.; Azulai, D.; Benny, Y.; Fraenkel, R.; Glozman, A.; Hojman, E.; Klin, O.; Krasovitsky, L.; Langof, L.; Lukomsky, I.; Nitzani, M.; Shtrichman, I.; Rappaport, N.; Snapi, N.; Weiss, E.; Tuito, A.

    2016-05-01

    SCD has developed a range of advanced infrared detectors based on III-V semiconductor heterostructures grown on GaSb. The XBn/XBp family of barrier detectors enables diffusion limited dark currents, comparable with MCT Rule-07, and high quantum efficiencies. This work describes some of the technical challenges that were overcome, and the ultimate performance that was finally achieved, for SCD's new 15 μm pitch "Pelican-D LW" type II superlattice (T2SL) XBp array detector. This detector is the first of SCD's line of high performance two dimensional arrays working in the LWIR spectral range, and was designed with a ~9.3 micron cut-off wavelength and a format of 640 x 512 pixels. It contains InAs/GaSb and InAs/AlSb T2SLs, engineered using k • p modeling of the energy bands and photo-response. The wafers are grown by molecular beam epitaxy and are fabricated into Focal Plane Array (FPA) detectors using standard FPA processes, including wet and dry etching, indium bump hybridization, under-fill, and back-side polishing. The FPA has a quantum efficiency of nearly 50%, and operates at 77 K and F/2.7 with background limited performance. The pixel operability of the FPA is above 99% and it exhibits a stable residual non uniformity (RNU) of better than 0.04% of the dynamic range. The FPA uses a new digital read-out integrated circuit (ROIC), and the complete detector closely follows the interfaces of SCD's MWIR Pelican-D detector. The Pelican- D LW detector is now in the final stages of qualification and transfer to production, with first prototypes already integrated into new electro-optical systems.

  15. Engineering of hydrogenated two-dimensional h-BN/C superlattices as electrostatic substrates.

    Energy Technology Data Exchange (ETDEWEB)

    Liu, Zhun; Zhong, Xiaoliang; Yan, Hui; Wang, Ru-Zhi

    2016-01-14

    Hybridized two-dimensional materials incorporating domains from the hexagonal boron nitride (h-BN) and graphene is an interesting branch of materials science due to their highly tunable electronic properties. In the present study, we investigate the hydrogenated two-dimensional (2D) h-BN/C superlattices (SLs) with zigzag edges using first-principles calculations. We found that the domain width, the phase ratio, and the vertical dipole orientation all have significant influence on the stability of SLs. The electronic reconstruction is associated with the lateral polar discontinuities at the zigzag edges and the vertically polarized (B2N2H4)(m) domains, which modifies the electronic structures and the spatial potential of the SLs significantly. Furthermore, we demonstrate that the hydrogenated 2D h-BN/C SLs can be applied in engineering the electronic structure of graphene: laterally-varying doping can be achieved by taking advantage of the spatial variation of the surface potential of the SLs. By applying an external vertical electric field on these novel bidirectional heterostructures, graphene doping levels and band offsets can be tuned to a wide range, such that the graphene doping profile can be switched from the bipolar (p-n junction) to unipolar (n(+)-n junction) mode. It is expected that such bidirectional heterostructures provide an effective approach for developing novel nanoscale electronic devices and improving our understanding of the fundamentals of low-dimensional materials.

  16. Phonon-pumped terahertz gain in n-type GaAs/AlGaAs superlattices

    Science.gov (United States)

    Sun, Gregory; Soref, Richard A.

    2001-05-01

    Local population inversion and far-IR gain are proposed and theoretically analyzed for an unbiased n-doped GaAs/Al0.15Ga0.85As superlattice pumped solely by phonons. The lasing transition occurs at the Brillouin zone boundary of the superlattice wave vector kz between the two conduction minibands CB1 and CB2 of the opposite curvature in kz space. The proposed waveguided structure is contacted above and below by heat sinks at 300 K and 77 K, respectively. Atop the superlattice, a heat buffer layer confines longitudinal optical phonons for enhanced optical-phonon pumping of CB1 electrons. A gain of 345 cm-1 at 4.5 THz is predicted for a doping density of 2.8×1016cm-3.

  17. Synthesis and electrical properties of In2O3(ZnO)m superlattice nanobelt

    Institute of Scientific and Technical Information of China (English)

    唐欣月; 高红; 武立立; 温静; 潘思明; 刘欣; 张喜田

    2015-01-01

    One-dimensional (1D) In2O3(ZnO)m superlattice nanobelts are synthesized by chemical vapor deposition method. The formation of In2O3(ZnO)m superlattice is verified by the high-resolution transmission electron microscopy images. The typical zigzag boundaries could be clearly observed. An additional peak at 614 cm−1 is found in the Raman spec-trum, which may correspond to the superlattice structure. The study about the electrical transport properties reveals that the In2O3(ZnO)m nanobelts exhibit peculiar nonlinear I–V characteristics even under the Ohmic contact measurement con-dition, which are different from the Ohmic behaviors of the In-doped ZnO nanobelts. The photoelectrical measurements show the differences in photocurrent property between them, and their transport mechanisms are also discussed.

  18. Wannier-Stark localization and terahertz electroluminescence of natural SiC superlattice

    Energy Technology Data Exchange (ETDEWEB)

    Sankin, V. I.; Andrianov, A. V.; Petrov, A. G.; Zakhar' in, A. O. [A.F. Ioffe Physical Technical Institute, 194021 St. Petersburg (Russian Federation)

    2013-12-04

    We report on efficient terahertz electroluminescence in the region of 1.5-2 THz from high electric field biased 6H-SiC n{sup +}−n{sup −}−n{sup +} structures with a natural superlattice at 7 K. The properties of the terahertz emission allow it to be attributed to spontaneous radiation resulting from electron Bloch oscillations in SiC natural superlattice. The use of the unique object, namely, natural superlattice of SiC allowed us to demonstrate a whole series of remarkable effects of Wannier-Stark localization and to get the intensive terahertz emission under steady-state electrical excitation of Bloch oscillations.

  19. Optical Fiber/Nanowire Hybrid Structures for Efficient Three-Dimensional Dye-Sensitized Solar Cells

    KAUST Repository

    Weintraub, Benjamin

    2009-11-09

    Wired up: The energy conversion efficiency of three-dimensional dye-sensitized solar cells (DSSCs) in a hybrid structure that integrates optical fibers and nanowire arrays is greater than that of a two-dimensional device. Internal axial illumination enhances the energy conversion efficiency of a rectangular fiber-based hybrid structure (see picture) by a factor of up to six compared to light illumination normal to the fiber axis from outside the device.

  20. A novel Michelson Fabry-Perot hybrid interference sensor based on the micro-structured fiber

    Science.gov (United States)

    Zhang, Yaxun; Zhang, Yu; Wang, Zhenzhen; Liu, Zhihai; Wei, Yong; Zhao, Enming; Yang, Xinghua; Zhang, Jianzhong; Yang, Jun; Yuan, Libo

    2016-09-01

    We propose and demonstrate a novel Michelson Fabry-Perot hybrid fiber interference sensor. By integrating a Michelson interferometer in a two-core fiber and a Fabry-Perot interferometer in a micro silica-capillary, we produce the Michelson Fabry-Perot hybrid interference sensor. Owing to the structure characteristic of the micro-structured fiber, this hybrid fiber interference sensor can achieve the measurement of the axial strain and radial bending simultaneously. The measurement sensitivity of the axial train is 0.015 nm/με and the measurement sensitivity of the radial bending is 1.393 nm/m-1.

  1. Fabrication and Crystal Structure of [ABO3 /REMO3] (A=Ca, La, B=Fe, Mn, RE=Bi, La, M=Fe, Fe0.8Mn0.2) Superlattices Grown by Pulsed Laser Deposition Method

    NARCIS (Netherlands)

    Watabe, Yuta; Iwata, Nobuyuki; Oikawa, Takahiro; Hashimoto, Takuya; Huijben, Mark; Rijnders, Guus; Yamamoto, Hiroshi

    2014-01-01

    In this study, we aim to synthesize novel materials that show ferromagnetic and ferroelectric properties with the magnetoelectric effect at room temperature. Nine types of superlattice were fabricated by stacking [7 units — ABO3/7 units — REMO3] for 14 times by pulsed laser deposition. From all reci

  2. Geographic variation in the structure of oak hybrid zones provides insights into the dynamics of speciation.

    Science.gov (United States)

    Zeng, Yan-Fei; Liao, Wan-Jin; Petit, Rémy J; Zhang, Da-Yong

    2011-12-01

    Studying geographic variation in the rate of hybridization between closely related species could provide a useful window on the evolution of reproductive isolation. Reinforcement theory predicts greater prezygotic isolation in areas of prolonged contact between recently diverged species than in areas of recent contact, which implies that old contact zones would be dominated by parental phenotypes with few hybrids (bimodal hybrid zones), whereas recent contact zones would be characterized by hybrid swarms (unimodal hybrid zones). Here, we investigate how the hybrid zones of two closely related Chinese oaks, Quercus mongolica and Q. liaotungensis, are structured geographically using both nuclear and chloroplast markers. We found that populations of Q. liaotungensis located around the Changbai Mountains in Northeast China, an inferred glacial refugium, were introgressed by genes from Q. mongolica, suggesting historical contact between the two species in this region. However, these introgressed populations form sharp bimodal hybrid zones with Q. mongolica. In contrast, populations of Q. liaotungensis located in North China, which show no sign of ancient introgression with Q. mongolica, form unimodal hybrid zones with Q. mongolica. These results are consistent with the hypothesis that selection against hybrids has had sufficient time to reinforce the reproductive barriers between Q. liaotungensis and Q. mongolica in Northeast China but not in North China.

  3. Resonant tunnelling and intersubband absorption in AlN - GaN superlattices

    Energy Technology Data Exchange (ETDEWEB)

    Baumann, E.; Giorgetta, F.R.; Hofstetter, D. [University of Neuchatel, 1 A.-L. Breguet, Neuchatel, 2000 (Switzerland); Wu, H.; Schaff, W.J.; Eastman, L.F. [Cornell University, Ithaca, NY 14850 (United States); Kirste, L. [Fraunhofer-Institute of Applied Solid State Physics, Tullastrasse 72, Freiburg, 79108 (Germany)

    2005-02-01

    We report on intersubband absorption and photovoltage measurements on regular GaN/AlN-based superlattice structures at 1.55 {mu}m. For high barriers, the photovoltage peaks at a higher energy than the absorbance spectrum due to the decrease of the tunnelling probability. The observed photovoltage is thus the macroscopic manifestation that the 2-dimensional electron gas at the top of the superlattice gets depleted by a vertical transport of electrons. (copyright 2005 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

  4. Non-binary Hybrid LDPC Codes: Structure, Decoding and Optimization

    CERN Document Server

    Sassatelli, Lucile

    2007-01-01

    In this paper, we propose to study and optimize a very general class of LDPC codes whose variable nodes belong to finite sets with different orders. We named this class of codes Hybrid LDPC codes. Although efficient optimization techniques exist for binary LDPC codes and more recently for non-binary LDPC codes, they both exhibit drawbacks due to different reasons. Our goal is to capitalize on the advantages of both families by building codes with binary (or small finite set order) and non-binary parts in their factor graph representation. The class of Hybrid LDPC codes is obviously larger than existing types of codes, which gives more degrees of freedom to find good codes where the existing codes show their limits. We give two examples where hybrid LDPC codes show their interest.

  5. PHASE TRANSITION PROPERTIES OF A TWO COMPONENT FINITE MAGNETIC SUPERLATTICE

    Institute of Scientific and Technical Information of China (English)

    WANG XIAO-GUANG; LIU NING-NING; PAN SHAO-HUA; YANG GUO-ZHEN

    2000-01-01

    We study an (l, n) finite superlattice, which consists of two alternative magnetic materials(components) of l and n atomic layers, respectively. Based on the Ising model, we examine the phase transition properties of the magnetic superlattice. By transfer matrix method we derive the equation for Curie temperature of the superlattice. Numerical results are obtained for the dependence of Curie temperature on the thickness and exchange constants of the superlattice.

  6. Hybrid structure of biotemplate-zinc-tin oxide for better optical, morphological and photocatalytic properties

    Science.gov (United States)

    Karpuraranjith, M.; Thambidurai, S.

    2017-03-01

    A new chitosan (as biotemplate)-zinc-tin oxide hybrid structure was successfully synthesized by a chemical precipitation method and annealed at 500 °C. We studied the structural changes, optical, thermal and photo catalytic properties. The chemical bonding of the Zn-O and Sn-O-Sn functional groups were confirmed by FT-IR absorption peaks appearing at 538 and 635 cm‑1. The different ratio of ZnO to SnO2 particles on the biotemplate matrix altered the morphology of the hybrids from an agglomerated state to a microcrystalline form confirmed by HR-SEM and TEM analysis. The formation of a Zn0.15Sn0.85O hybrid structure was observed in the visible light region, with an energy band gap of ∼3.19 eV and higher surface area of 98 m2 g‑1. The thermal property shows that CS-Zn0.15Sn0.85O has a higher thermal stability than a CS-Zn0.25Sn0.75O hybrid structure. The results demonstrate that the biotemplate-zinc-tin oxide hybrid structure has a reinforced effect compared to the other components. Therefore, a biotemplate-based zinc-tin oxide hybrid structure could be a promising material for better dye removal efficiency, which was obtained for ∼100 and 96% with MB and RY-15 dyes.

  7. Magnetocaloric effects in a freestanding and flexible graphene-based superlattice synthesized with a spatially confined reaction.

    Science.gov (United States)

    Zhu, Haiou; Xiao, Chong; Cheng, Hao; Grote, Fabian; Zhang, Xiaodong; Yao, Tao; Li, Zhou; Wang, Chengming; Wei, Shiqiang; Lei, Yong; Xie, Yi

    2014-06-03

    Superlattices have attracted great interest because of their tailorable electronic properties at the interface. However, the lack of an efficient and low-cost synthetic method represents a huge challenge to implement superlattices into practical applications. Herein, we report a space-confined nanoreactor strategy to synthesize flexible freestanding graphene-based superlattice nanosheets, which consist of alternately intercalated monolayered metal-oxide frameworks and graphene. Taking vanadium oxide as an example, clear-cut evidences in extended X-ray absorption fine structure, high-resolution transmission electron microscopy and infrared spectra have confirmed that the vanadium oxide frameworks in the superlattice nanosheets show high symmetry derived from the space-confinement and electron-donor effect of graphene layers, which enable the superlattice nanosheets to show emerging magnetocaloric effect. Undoubtedly, this freestanding and flexible superlattice synthesized from a low-cost and scalable method avoids complex transferring processes from growth substrates for final applications and thus should be beneficial to a wide variety of functionalized devices.

  8. Tensile properties of a boron/nitrogen-doped carbon nanotube–graphene hybrid structure

    Directory of Open Access Journals (Sweden)

    Kang Xia

    2014-03-01

    Full Text Available Doping is an effective approach that allows for the intrinsic modification of the electrical and chemical properties of nanomaterials. Recently, a graphene and carbon nanotube hybrid structure (GNHS has been reported, which extends the excellent properties of carbon-based materials to three dimensions. In this paper, we carried out a first-time investigation on the tensile properties of the hybrid structures with different dopants. It is found that with the presence of dopants, the hybrid structures usually exhibit lower yield strength, Young’s modulus, and earlier yielding compared to that of a pristine hybrid structure. For dopant concentrations below 2.5% no significant reduction of Young’s modulus or yield strength could be observed. For all considered samples, the failure is found to initiate at the region where the nanotubes and graphene sheets are connected. After failure, monatomic chains are normally observed around the failure region. Dangling graphene layers without the separation of a residual CNT wall are found to adhere to each other after failure with a distance of about 3.4 Å. This study provides a fundamental understanding of the tensile properties of the doped graphene–nanotube hybrid structures, which will benefit the design and also the applications of graphene-based hybrid materials.

  9. The doubly conditioned frequency spectrum does not distinguish between ancient population structure and hybridization

    KAUST Repository

    Eriksson, Anders

    2014-03-13

    Distinguishing between hybridization and population structure in the ancestral species is a key challenge in our understanding of how permeable species boundaries are to gene flow. The doubly conditioned frequency spectrum (dcfs) has been argued to be a powerful metric to discriminate between these two explanations, and it was used to argue for hybridization between Neandertal and anatomically modern humans. The shape of the observed dcfs for these two species cannot be reproduced by a model that represents ancient population structure in Africa with two populations, while adding hybridization produces realistic shapes. In this letter, we show that this result is a consequence of the spatial coarseness of the demographic model and that a spatially structured stepping stone model can generate realistic dcfs without hybridization. This result highlights how inferences on hybridization between recently diverged species can be strongly affected by the choice of how population structure is represented in the underlying demographic model. We also conclude that the dcfs has limited power in distinguishing between the signals left by hybridization and ancient structure. 2014 The Author.

  10. Magneto-fluorescent hybrid of dye and SPION with ordered and radially distributed porous structures

    Science.gov (United States)

    Gogoi, Madhulekha; Deb, Pritam

    2014-04-01

    We have reported the development of a silica based magneto-fluorescent hybrid of a newly synthesized dye and superparamagnetic iron oxide nanoparticles with ordered and radially distributed porous structure. The dye is synthesized by a novel yet simple synthetic approach based on Michael addition between dimer of glutaraldehyde and oleylamine molecule. The surfactant used for phase transformation of the dye from organic to aqueous phase, also acts as a structure directing agent for the porous structure evolution of the hybrid with radial distribution. The evolution of the radially distributed pores in the hybrids can be attributed to the formation of rod-like micelles containing nanoparticles, for concentration of micelles greater than critical micelle concentration. A novel water extraction method is applied to remove the surfactants resulting in the characteristic porous structure of the hybrid. Adsorption isotherm analysis confirms the porous nature of the hybrids with pore diameter ∼2.4 nm. A distinct modification in optical and magnetic property is observed due to interaction of the dye and SPION within the silica matrix. The integration of multiple structural components in the so developed hybrid nanosystem results into a potential agent for multifunctional biomedical application.

  11. Zener tunneling of light waves in an optical superlattice.

    Science.gov (United States)

    Ghulinyan, Mher; Oton, Claudio J; Gaburro, Zeno; Pavesi, Lorenzo; Toninelli, Costanza; Wiersma, Diederik S

    2005-04-01

    We report on the observation of Zener tunneling of light waves in spectral and time-resolved transmission measurements, performed on an optical superlattice made of porous silicon. The structure was designed to have two photonic minibands, spaced by a narrow frequency gap. A gradient in the refractive index was introduced to create two optical Wannier-Stark ladders and, at a critical value of the optical gradient, tunneling between energy bands was observed in the form of an enhanced transmission peak and a characteristic time dependence of the transmission.

  12. Passivation of MBE grown InGaSb/InAs superlattice photodiodes

    Science.gov (United States)

    Hill, Cory J.; Keo, Sam S.; Mumolo, Jason M.; Gunapala, Sarath D.

    2005-01-01

    We have performed wet chemical passivation tests on InGaSb/InAs superlattice photodiode structures grown molecular beam epitaxy. The details of the devices growth and characterization as well as the results of chemical passivation involving RuCl3 and H2SO4 with SiO2 dielectric depositions are presented.

  13. Coherent dynamics of interwell excitons in GaAs/AlxGa1-xAs superlattices

    DEFF Research Database (Denmark)

    Mizeikis, V.; Birkedal, Dan; Langbein, Wolfgang Werner;

    1997-01-01

    Coherent exciton dynamics in a GaAs/AlxGa1-xAs narrow-miniband superlattice is studied by spectrally resolved transient four-wave mixing. Coherent optical properties of the investigated structure are found to be strongly affected by the existence of two different heavy-hole excitonic states. One ...

  14. Heterogeneous genome divergence, differential introgression, and the origin and structure of hybrid zones.

    Science.gov (United States)

    Harrison, Richard G; Larson, Erica L

    2016-06-01

    Hybrid zones have been promoted as windows on the evolutionary process and as laboratories for studying divergence and speciation. Patterns of divergence between hybridizing species can now be characterized on a genomewide scale, and recent genome scans have focused on the presence of 'islands' of divergence. Patterns of heterogeneous genomic divergence may reflect differential introgression following secondary contact and provide insights into which genome regions contribute to local adaptation, hybrid unfitness and positive assortative mating. However, heterogeneous genome divergence can also arise in the absence of any gene flow, as a result of variation in selection and recombination across the genome. We suggest that to understand hybrid zone origins and dynamics, it is essential to distinguish between genome regions that are divergent between pure parental populations and regions that show restricted introgression where these populations interact in hybrid zones. The latter, more so than the former, reveal the likely genetic architecture of reproductive isolation. Mosaic hybrid zones, because of their complex structure and multiple contacts, are particularly good subjects for distinguishing primary intergradation from secondary contact. Comparisons among independent hybrid zones or transects that involve the 'same' species pair can also help to distinguish between divergence with gene flow and secondary contact. However, data from replicate hybrid zones or replicate transects do not reveal consistent patterns; in a few cases, patterns of introgression are similar across independent transects, but for many taxa, there is distinct lack of concordance, presumably due to variation in environmental context and/or variation in the genetics of the interacting populations.

  15. Probing Energy Levels of Large Array Quantum Dot Superlattice by Electronic Transport Measurement

    Science.gov (United States)

    Bisri, S. Z.; Degoli, E.; Spallanzani, N.; Krishnan, G.; Kooi, B.; Ghica, C.; Yarema, M.; Protesescu, L.; Heiss, W.; Kovalenko, M.; Pulci, O.; Ossicini, S.; Iwasa, Y.; Loi, M. A.

    2015-03-01

    Colloidal quantum dot superlattice (CQDS) emerges as new type of hybrid solids allowing easy fabrication of devices that exploits the quantum confinement properties of individual QD. This materials displays peculiar characters, making investigation of their transport properties nontrivial. Besides the bandgap variations, 0D nature of QD lead to the formation of discrete energy subbands. These subbands are crucial for multiple exciton generation (for efficient solar cell), thermoelectric material and multistate transistor. Full understanding of the CQDS energy level structure is vital to use them in complex devices. Here we show a powerful method to determine the CQDS electronic energy levels from their intrinsic charge transport characteristics. Via the use of ambipolar transistors with CQDS as active materials and gated using highly capacitive ionic liquid gating, Fermi energy can be largely tuned. It can access energy levels beyond QD's HOMO & LUMO. Ability to probe not only the bandgap, but also the discrete energy level from large assembly of QD at room temperature suggests the formation of energy minibands in this system.

  16. Weak Topological Insulators in PbTe/SnTe superlattice

    Science.gov (United States)

    Yang, Gang; Liu, Junwei; Fu, Liang; Duan, Wenhui; Liu, Chaoxing

    2014-03-01

    It is desirable to realize topological phases in artificial structures by engineering electronic band structures. In this paper, we investigate (PbTe)m(SnTe)2n-m superlattices along the [001] direction and find a robust weak topological insulator phase for a large variety of layer numbers m and 2 n - m . We confirm this topologically non-trivial phase by calculating Z2 topological invariants and topological surface states based on the first-principles calculations. We show that the folding of Brillouin zone due to the superlattice structure plays an essential role in inducing topologically non-trivial phases in this system. This mechanism can be generalized to other systems in which band inversion occurs at multiple momenta, and gives us a brand-new way to engineer topological materials in artificial structures. We acknowledge support from the Ministry of Science and Technology of China and the National Natural Science Foundation of China. LF is supported by the DOE Office of Basic Energy Sciences.

  17. Hybrid star structure with the Field Correlator Method

    Energy Technology Data Exchange (ETDEWEB)

    Burgio, G.F.; Zappala, D. [INFN, Catania (Italy)

    2016-03-15

    We explore the relevance of the color-flavor locking phase in the equation of state (EoS) built with the Field Correlator Method (FCM) for the description of the quark matter core of hybrid stars. For the hadronic phase, we use the microscopic Brueckner-Hartree-Fock (BHF) many-body theory, and its relativistic counterpart, i.e. the Dirac-Brueckner (DBHF). We find that the main features of the phase transition are directly related to the values of the quark-antiquark potential V{sub 1}, the gluon condensate G{sub 2} and the color-flavor superconducting gap Δ. We confirm that the mapping between the FCM and the CSS (constant speed of sound) parameterization holds true even in the case of paired quark matter. The inclusion of hyperons in the hadronic phase and its effect on the mass-radius relation of hybrid stars is also investigated. (orig.)

  18. Trust and Contracting in Agri-Food Hybrid Structures

    OpenAIRE

    Martino, Gaetano

    2007-01-01

    The paper aims at examining the hypothesis that the influence of trust on contract can be thought of as a dynamic factor of organizational choices in supply chains. The relationship between contract and trust is delineated on the basis of institutional environment, contractual incompleteness, safeguards and restrictive provisions. The interaction between individual and system elements in the formation of trust and its influence in hybrid contracting is considered. According to a New Instituti...

  19. A generalized hybrid transfinite element computational approach for nonlinear/linear unified thermal/structural analysis

    Science.gov (United States)

    Tamma, Kumar K.; Railkar, Sudhir B.

    1987-01-01

    The present paper describes the development of a new hybrid computational approach for applicability for nonlinear/linear thermal structural analysis. The proposed transfinite element approach is a hybrid scheme as it combines the modeling versatility of contemporary finite elements in conjunction with transform methods and the classical Bubnov-Galerkin schemes. Applicability of the proposed formulations for nonlinear analysis is also developed. Several test cases are presented to include nonlinear/linear unified thermal-stress and thermal-stress wave propagations. Comparative results validate the fundamental capablities of the proposed hybrid transfinite element methodology.

  20. Optical fiber-based core-shell coaxially structured hybrid cells for self-powered nanosystems

    Energy Technology Data Exchange (ETDEWEB)

    Pan, Caofeng; Zhu, Guang [School of Materials Science and Engineering, Georgia Institute of Technology, Atlanta, Georgia (United States); Guo, Wenxi [School of Materials Science and Engineering, Georgia Institute of Technology, Atlanta, Georgia (United States); State Key Laboratory of Physical Chemistry of Solid Surfaces, College of Chemistry and Chemical Engineering, Xiamen University, Xiamen 361005 (China); Dong, Lin [School of Materials Science and Engineering, Georgia Institute of Technology, Atlanta, Georgia (United States); School of Materials Science and Enginnering, Zhenzhou University, Zhenghou 450001 (China); Wang, Zhong Lin [School of Materials Science and Engineering, Georgia Institute of Technology, Atlanta, Georgia (United States); Beijing Institute of Nanoenergy and Nanosystems, Chinese Academy of Sciences, Beijing (China)

    2012-07-03

    An optical fiber-based 3D hybrid cell consisting of a coaxially structured dye-sensitized solar cell (DSSC) and a nanogenerator (NG) for simultaneously or independently harvesting solar and mechanical energy is demonstrated. The current output of the hybrid cell is dominated by the DSSC, and the voltage output is dominated by the NG; these can be utilized complementarily for different applications. The output of the hybrid cell is about 7.65 {mu}A current and 3.3 V voltage, which is strong enough to power nanodevices and even commercial electronic components. (Copyright copyright 2012 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim)

  1. Improved Thermoelectric Performance in Flexible Tellurium Nanowires/Reduced Graphene Oxide Sandwich Structure Hybrid Films

    Science.gov (United States)

    Gao, Jie; Liu, Chengyan; Miao, Lei; Wang, Xiaoyang; Peng, Ying; Chen, Yu

    2016-11-01

    With a high flexibility and an adjustable electronic structure, reduced graphene oxide (RGO) is a potential candidate for flexible thermoelectric materials. Here, we report that flexible RGO/tellurium nanowires (Te NWs)/RGO sandwich structure hybrid films are prepared on glass fabrics through the drop-cast method. The addition of 20 wt.% Te NWs into a RGO matrix remarkably improves the Seebeck coefficient from 15.2 μV/K to 89.7 μV/K while maintaining relatively high electrical conductivity, thus resulting in a one order of magnitude higher power factor value compared with the Te NWs. According to the values of carrier mobility and concentration of hybrid films, the improved thermoelectric properties are presented because of the energy filtering effect on the interfaces in hybrid films. This article suggests that RGO/Te NWs/RGO hybrid films would be promising for fabricating flexible energy sources.

  2. Structure improvement and electrochemical studies of bipolar nickel metal hydride batteries for hybrid electric vehicles

    Institute of Scientific and Technical Information of China (English)

    DENG Chao; SHI Peng-fei

    2006-01-01

    Nickel metal hydride battery in bipolar design offers some advantages for its application as a power storage system for electric and hybrid vehicles. This paper deals with the structure design and electrochemical studies of bipolar Ni/MH batteries for hybrid vehicles. An improvement is applied in bipolar battery design,and such bipolar Ni/MH batteries with 5 sub-cells have been assembled and investigated. Testing results show that bipolar batteries with improved structure have better compression tolerance and cycle performance than conventional ones. In addition, the improved bipolar batteries display excellent large current discharge ability and high power density. As simulating working conditions for hybrid vehicles, the batteries show good stability during pulse cycles, which verifies the possibility of being used as a power storage device on hybrid vehicles.

  3. Improved Thermoelectric Performance in Flexible Tellurium Nanowires/Reduced Graphene Oxide Sandwich Structure Hybrid Films

    Science.gov (United States)

    Gao, Jie; Liu, Chengyan; Miao, Lei; Wang, Xiaoyang; Peng, Ying; Chen, Yu

    2017-05-01

    With a high flexibility and an adjustable electronic structure, reduced graphene oxide (RGO) is a potential candidate for flexible thermoelectric materials. Here, we report that flexible RGO/tellurium nanowires (Te NWs)/RGO sandwich structure hybrid films are prepared on glass fabrics through the drop-cast method. The addition of 20 wt.% Te NWs into a RGO matrix remarkably improves the Seebeck coefficient from 15.2 μV/K to 89.7 μV/K while maintaining relatively high electrical conductivity, thus resulting in a one order of magnitude higher power factor value compared with the Te NWs. According to the values of carrier mobility and concentration of hybrid films, the improved thermoelectric properties are presented because of the energy filtering effect on the interfaces in hybrid films. This article suggests that RGO/Te NWs/RGO hybrid films would be promising for fabricating flexible energy sources.

  4. Novel fabrication technique of hybrid structure lens array for 3D images

    Science.gov (United States)

    Lee, Junsik; Kim, Junoh; Kim, Cheoljoong; Shin, Dooseub; Koo, Gyohyun; Won, Yong Hyub

    2016-03-01

    Tunable liquid lens arrays can produce three dimensional images by using electrowetting principle that alters surface tensions by applying voltage. This method has advantages of fast response time and low power consumption. However, it is challenging to fabricate a high fill factor liquid lens array and operate three dimensional images which demand high diopter. This study describes a hybrid structure lens array which has not only a liquid lens array but a solid lens array. A concave-shape lens array is unavoidable when using only the liquid lens array and some voltages are needed to make the lens flat. By placing the solid lens array on the liquid lens array, initial diopter can be positive. To fabricate the hybrid structure lens array, a conventional lithographic process in semiconductor manufacturing is needed. A negative photoresist SU-8 was used as chamber master molds. PDMS and UV adhesive replica molding are done sequentially. Two immiscible liquids, DI water and dodecane, are injected in the fabricated chamber, followed by sealing. The fabricated structure has a 20 by 20 pattern of cylindrical shaped circle array and the aperture size of each lens is 1mm. The thickness of the overall hybrid structure is about 2.8mm. Hybrid structure lens array has many advantages. Solid lens array has almost 100% fill factor and allow high efficiency. Diopter can be increased by more than 200 and negative diopter can be shifted to the positive region. This experiment showed several properties of the hybrid structure and demonstrated its superiority.

  5. Crystal Structure and Band Gap Engineering in Polyoxometalate-Based Inorganic-Organic Hybrids.

    Science.gov (United States)

    Roy, Soumyabrata; Sarkar, Sumanta; Pan, Jaysree; Waghmare, Umesh V; Dhanya, R; Narayana, Chandrabhas; Peter, Sebastian C

    2016-04-04

    We have demonstrated engineering of the electronic band gap of the hybrid materials based on POMs (polyoxometalates), by controlling its structural complexity through variation in the conditions of synthesis. The pH- and temperature-dependent studies give a clear insight into how these experimental factors affect the overall hybrid structure and its properties. Our structural manipulations have been successful in effectively tuning the optical band gap and electronic band structure of this kind of hybrids, which can find many applications in the field of photovoltaic and semiconducting devices. We have also addressed a common crystallographic disorder observed in Keggin-ion (one type of heteropolyoxometalate [POMs])-based hybrid materials. Through a combination of crystallographic, spectroscopic, and theoretical analysis of four new POM-based hybrids synthesized with tactically varied reaction conditions, we trace the origin and nature of the disorder associated with it and the subtle local structural coordination involved in its core picture. While the crystallography yields a centrosymmetric structure with planar coordination of Si, our analysis with XPS, IR, and Raman spectroscopy reveals a tetrahedral coordination with broken inversion symmetry, corroborated by first-principles calculations.

  6. Enhanced valley-resolved thermoelectric transport in a magnetic silicene superlattice

    Science.gov (United States)

    Niu, Zhi Ping; Zhang, Yong Mei; Dong, Shihao

    2015-07-01

    Electrons in two-dimensional crystals with a honeycomb lattice structure possess a valley degree of freedom in addition to charge and spin, which has revived the field of valleytronics. In this work we investigate the valley-resolved thermoelectric transport through a magnetic silicene superlattice. Since spin is coupled to the valley, this device allows a coexistence of the insulating transmission gap of one valley and the metallic resonant band of the other, resulting in a strong valley polarization Pv. Pv oscillates with the barrier strength V with its magnitude greatly enhanced by the superlattice structure. In addition, a controllable fully valley polarized transport and an on/off switching effect in the conductance spectra are obtained. Furthermore, the spin- and valley-dependent thermopowers can be controlled by V, the on-site potential difference between A and B sublattices and Fermi energy, and enhanced by the superlattice structure. Enhanced valley-resolved thermoelectric transport and its control by means of gate voltages make the magnetic silicene superlattice attractive in valleytronics applications.

  7. The Doubly Conditioned Frequency Spectrum Does Not Distinguish between Ancient Population Structure and Hybridization

    OpenAIRE

    Eriksson, Anders; Manica, Andrea

    2014-01-01

    Distinguishing between hybridization and population structure in the ancestral species is a key challenge in our understanding of how permeable species boundaries are to gene flow. The doubly conditioned frequency spectrum (dcfs) has been argued to be a powerful metric to discriminate between these two explanations, and it was used to argue for hybridization between Neandertal and anatomically modern humans. The shape of the observed dcfs for these two species cannot be reproduced by a model ...

  8. Strong coupling of Rydberg atoms and surface phonon polaritons on piezoelectric superlattices

    CERN Document Server

    Sheng, Jiteng; Shaffer, James P

    2016-01-01

    We propose a hybrid quantum system where the strong coupling regime can be achieved between a Rydberg atomic ensemble and propagating surface phonon polaritons on a piezoelectric superlattice. By exploiting the large electric dipole moment and long lifetime of Rydberg atoms as well as tightly confined surface phonon polariton modes, it is possible to achieve a coupling constant far exceeding the relevant decay rates. The frequency of the surface mode can be selected so it is resonant with a Rydberg transition by engineering the piezoelectric superlattice. We describe a way to observe the Rabi splitting associated with the strong coupling regime under realistic experimental conditions. The system can be viewed as a new type of optomechanical system.

  9. Ballistic miniband conduction in a graphene superlattice

    Science.gov (United States)

    Lee, Menyoung; Wallbank, John R.; Gallagher, Patrick; Watanabe, Kenji; Taniguchi, Takashi; Fal'ko, Vladimir I.; Goldhaber-Gordon, David

    2016-09-01

    Rational design of long-period artificial lattices yields effects unavailable in simple solids. The moiré pattern in highly aligned graphene/hexagonal boron nitride (h-BN) heterostructures is a lateral superlattice with high electron mobility and an unusual electronic dispersion whose miniband edges and saddle points can be reached by electrostatic gating. We investigated the dynamics of electrons in moiré minibands by measuring ballistic transport between adjacent local contacts in a magnetic field, known as the transverse electron focusing effect. At low temperatures, we observed caustics of skipping orbits extending over hundreds of superlattice periods, reversals of the cyclotron revolution for successive minibands, and breakdown of cyclotron motion near van Hove singularities. At high temperatures, electron-electron collisions suppress focusing. Probing such miniband conduction properties is a necessity for engineering novel transport behaviors in superlattice devices.

  10. Nanoscale Structure of Self-Assembling Hybrid Materials of Inorganic and Electronically Active Organic Phases

    Energy Technology Data Exchange (ETDEWEB)

    Sofos, M.; Goswami, D.A. Stone D.K.; Okasinski, J.S.; Jin, H.; Bedzyk, M.J.; Stupp, S.I. (NWU)

    2008-10-06

    Hybrid materials with nanoscale structure that incorporates inorganic and organic phases with electronic properties offer potential in an extensive functional space that includes photovoltaics, light emission, and sensing. This work describes the nanoscale structure of model hybrid materials with phases of silica and electronically active bola-amphiphile assemblies containing either oligo(p-phenylene vinylene) or oligo(thiophene) segments. The hybrid materials studied here were synthesized by evaporation-induced self-assembly and characterized by X-ray scattering techniques. Grazing-incidence X-ray scattering studies of these materials revealed the formation of two-dimensional hexagonally packed cylindrical micelles of the organic molecules with diameters between 3.1 and 3.6 nm and cylindrical axes parallel to the surface. During the self-assembly process at low pH, the cylindrical aggregates of conjugated molecules become surrounded by silica giving rise to a hybrid structure with long-range order. Specular X-ray reflectivity confirmed the long-range periodicity of the hybrid films within a specific range of molar ratios of tetraethyl orthosilicate to cationic amphiphile. We did not observe any long-range ordering in fully organic analogues unless quaternary ammonium groups were replaced by tertiary amines. These observations suggest that charge screening in these biscationic conjugated molecules by the mineral phase is a key factor in the evolution of long range order in the self-assembling hybrids.

  11. Enhanced non-radiative energy transfer in hybrid III-nitride structures

    Energy Technology Data Exchange (ETDEWEB)

    Smith, R. M.; Athanasiou, M.; Bai, J.; Liu, B.; Wang, T., E-mail: t.wang@sheffield.ac.uk [Department of Electrical and Electronic Engineering, University of Sheffield, Mappin Street, Sheffield S1 3JD (United Kingdom)

    2015-09-21

    The effect of surface states has been investigated in hybrid organic/inorganic white light emitting structures that employ high efficiency, nearfield non-radiative energy transfer (NRET) coupling. The structures utilize blue emitting InGaN/GaN multiple quantum well (MQW) nanorod arrays to minimize the separation with a yellow emitting F8BT coating. Surface states due to the exposed III-nitride surfaces of the nanostructures are found to reduce the NRET coupling rate. The surface states are passivated by deposition of a silicon nitride layer on the III-nitride nanorod surface leading to reduced surface recombination. A low thickness surface passivation is shown to increase the NRET coupling rate by 4 times compared to an un-passivated hybrid structure. A model is proposed to explain the increased NRET rate for the passivated hybrid structures based on the reduction in surface electron depletion of the passivated InGaN/GaN MQW nanorods surfaces.

  12. Enhanced non-radiative energy transfer in hybrid III-nitride structures

    Science.gov (United States)

    Smith, R. M.; Athanasiou, M.; Bai, J.; Liu, B.; Wang, T.

    2015-09-01

    The effect of surface states has been investigated in hybrid organic/inorganic white light emitting structures that employ high efficiency, nearfield non-radiative energy transfer (NRET) coupling. The structures utilize blue emitting InGaN/GaN multiple quantum well (MQW) nanorod arrays to minimize the separation with a yellow emitting F8BT coating. Surface states due to the exposed III-nitride surfaces of the nanostructures are found to reduce the NRET coupling rate. The surface states are passivated by deposition of a silicon nitride layer on the III-nitride nanorod surface leading to reduced surface recombination. A low thickness surface passivation is shown to increase the NRET coupling rate by 4 times compared to an un-passivated hybrid structure. A model is proposed to explain the increased NRET rate for the passivated hybrid structures based on the reduction in surface electron depletion of the passivated InGaN/GaN MQW nanorods surfaces.

  13. Resonance frequency in ferromagnetic superlattices

    Energy Technology Data Exchange (ETDEWEB)

    Qiu Rongke; Huang Andong [School of Science, Shenyang University of Technology, Shenyang 110870 (China); Li Da; Zhang Zhidong, E-mail: rkqiu@163.com [Shenyang National Laboratory for Materials Science, Institute of Metal Research and International Centre for Materials Physics, Chinese Academy of Sciences, Shenyang 110016 (China)

    2011-10-19

    The resonance frequency in two-layer and three-layer ferromagnetic superlattices is studied, using the Callen's Green function method, the Tyablikov decoupling approximation and the Anderson-Callen decoupling approximation. The effects of interlayer exchange coupling, anisotropy, external magnetic field and temperature on the resonance frequency are investigated. It is found that the resonance frequencies increase with increasing external magnetic field. In a parameter region of the asymmetric system, each sublayer corresponds to its own resonance frequency. The anisotropy of a sublayer affects only the resonance frequency corresponding to this sublayer. The stronger the anisotropy, the higher is the resonance frequency. The interlayer exchange coupling affects only the resonance frequencies belonging to the sublayers connected by it. The stronger the interlayer exchange coupling, the higher are the resonance frequencies. All the resonance frequencies decrease as the reduced temperature increases. The results direct the method to enhance and adjust the resonance frequency of magnetic multilayered materials with a wide band.

  14. Structural, magnetic, and superconducting properties of pulsed-laser-deposition-grown La1.85Sr0.15CuO4/La2/3Ca1/3MnO3 superlattices on (001)-oriented LaSrAlO4 substrates

    Science.gov (United States)

    Das, S.; Sen, K.; Marozau, I.; Uribe-Laverde, M. A.; Biskup, N.; Varela, M.; Khaydukov, Y.; Soltwedel, O.; Keller, T.; Döbeli, M.; Schneider, C. W.; Bernhard, C.

    2014-03-01

    Epitaxial La1.85Sr0.15CuO4/La2/3Ca1/3MnO3 (LSCO/LCMO) superlattices on (001)-oriented LaSrAlO4 substrates have been grown with pulsed laser deposition technique. Their structural, magnetic, and superconducting properties have been determined with in situ reflection high-energy electron diffraction, x-ray diffraction, specular neutron reflectometry, scanning transmission electron microscopy, electric transport, and magnetization measurements. We find that despite the large mismatch between the in-plane lattice parameters of LSCO (a =0.3779 nm) and LCMO (a =0.387 nm) these superlattices can be grown epitaxially and with a high crystalline quality. While the first LSCO layer remains clamped to the LaSrAlO4 substrate, a sizable strain relaxation occurs already in the first LCMO layer. The following LSCO and LCMO layers adopt a nearly balanced state in which the tensile and compressive strain effects yield alternating in-plane lattice parameters with an almost constant average value. No major defects are observed in the LSCO layers, while a significant number of vertical antiphase boundaries are found in the LCMO layers. The LSCO layers remain superconducting with a relatively high superconducting onset temperature of Tconset≈36 K. The macroscopic superconducting response is also evident in the magnetization data due to a weak diamagnetic signal below 10 K for H ∥ ab and a sizable paramagnetic shift for H ∥ c that can be explained in terms of a vortex-pinning-induced flux compression. The LCMO layers maintain a strongly ferromagnetic state with a Curie temperature of TCurie≈190 K and a large low-temperature saturation moment of about 3.5(1) μB per Mn ion. These results suggest that the LSCO/LCMO superlattices can be used to study the interaction between the antagonistic ferromagnetic and superconducting orders and, in combination with previous studies on YBa2Cu3O7-x/La2/3Ca1/3MnO3 superlattices, may allow one to identify the relevant mechanisms.

  15. Theory of Semiconducting Superlattices and Microstructures

    Science.gov (United States)

    1992-03-01

    Core excitons ir. superlattices We have developed the first theory of Hjalmarsor.- Frenke ’ core excitons in superlattices, and applied it to strained...technique has been described are accelerated. A kinetic tempcrature TK is defined as by Kirkpatrick et al.31 and uses thr Monte Carlo algo- the average...classical kinetic energy of the atoms, rithm of Metropolis et al.32 Monte Carlo steps are taken 3/2kTK=(l/N)4rn’mlv,, where i=1,2, . . . ,n is the

  16. Fabrication and characterization of materials and structures for hybrid organic-inorganic photonics

    Science.gov (United States)

    Haško, Daniel; Chovan, Jozef; Uherek, František

    2017-03-01

    Hybrid organic-inorganic integrated photonics integrate the organic material, as a part of active layer, with inorganic structure, and it is the organic component that extends the functionalities as compared to inorganic photonics. This paper presents the results of fabrication and characterization of inorganic and organic layers, as well as of hybrid organic-inorganic structures. Inorganic oxide and nitride materials and structures were grown using plasma enhanced chemical vapor deposition. As a substrate for tested organic layers and for preparation of multilayer structures, commercially available SiO2 created by thermal oxidation on Si was used. The hybrid organic-inorganic structures were prepared by spin coating of organic materials on SiO2/Si inorganic structures. As the basic photonics devices, the testing strip inorganic and organic waveguides were fabricated using reactive ion etching. The shape of fabricated testing waveguides was trapezoidal and etched structures were able to guide the radiation. The presented technology enabled to prepare hybrid organic-inorganic structures of comparable dimensions and shape. The fabricated waveguides dimensions and shape will be used for optimisation and design of new lithographic mask to prepare photonic components with required characteristics.

  17. Resonant x-ray scattering in perovskite manganite superlattice. Observation of 'orbital superlattice'

    CERN Document Server

    Kiyama, T; Ohsumi, H; Murakami, Y; Wakabayashi, Y; Izumi, M; Kawasaki, M; Tokura, Y

    2003-01-01

    We report the results of resonant X-ray scattering (RXS) measurement of superlattices which consist of La sub 0 sub . sub 4 sub 5 Sr sub 0 sub . sub 5 sub 5 MnO sub 3 and La sub 0 sub . sub 6 sub 0 Sr sub 0 sub . sub 4 sub 0 MnO sub 3 multilayers. An interference technique made it possible to observe RXS reflections from ferro-type orbital ordering in the superlattices. RXS can reveal the local circumstances around specific atoms in materials regulated atomically. In this experiment, we observed that the superlattice is actually composed of two kinds of layers with different lattice distortion states, presenting 'orbital superlattices', in which layers with different orbital states are stacked alternately in an atomic scale. (author)

  18. CONDENSED MATTER: ELECTRONIC STRUCTURE, ELECTRICAL, MAGNETIC, AND OPTICAL PROPERTIES: A theoretical study of harmonic generation in a short period AlGaN/GaN superlattice induced by a terahertz field

    Science.gov (United States)

    Chen, Jun-Feng; Hao, Yue

    2009-12-01

    Based on an improved energy dispersion relation, the terahertz field induced nonlinear transport of miniband electrons in a short period AlGaN/GaN superlattice is theoretically studied in this paper with a semiclassical theory. To a short period superlattice, it is not precise enough to calculate the energy dispersion relation by just using the nearest wells in tight binding method: the next to nearest wells should be considered. The results show that the electron drift velocity is 30% lower under a dc field but 10% higher under an ac field than the traditional simple cosine model obtained from the tight binding method. The influence of the terahertz field strength and frequency on the harmonic amplitude, phase and power efficiency is calculated. The relative power efficiency of the third harmonic reaches the peak value when the dc field strength equals about three times the critical field strength and the ac field strength equals about four times the critical field strength. These results show that the AlGaN/GaN superlattice is a promising candidate to convert radiation of frequency ω to radiation of frequency 3ω or even higher.

  19. The reflection and interference of electrons at the interface of superlattice

    Institute of Scientific and Technical Information of China (English)

    CHENG; Xingkui

    2002-01-01

    [1]Mukherji, D., Nag, B. R., Band structure of semiconductor superlattice, Phys. Rev., 1975,B12: 4338-4345.[2]Bastard, G., Superlattice band structure in the envelop-function approximation, Phys. Rev., 1981,B24: 5693-5697.[3]Ninno, D., Wong, K. B., Geh, M. A. et al., Optical transitions at confined resonance in(001)GaAs-Ga1-xAlxAs superlattice, Phys. Rev., 1985, B32: 2700-2702.[4]Cho, H. S., Prucnal, P. R., New formalism of the Kronig-Penney model with application to superlattice, Phys.Rev., 1987, B36: 3237-3242.[5]Adachi, S., GaAs, AlAs, and AlxGa1-xAs: Material parameters for use in research and device application, J. Appl. Phys., 1985, 58(3): R1-R29.[6]Levine, B. F., Bethea,C.G., Shen,V.O. et al., Tunable long-wavelength detectors using graded barrier quantum wells grown by electron beam source molecular beam epitaxy, Appl. Phys. Lett., 1990, 57(4): 383-385.

  20. Goos-Hänchen shifts in AA-stacked bilayer graphene superlattices

    Science.gov (United States)

    Zahidi, Youness; Redouani, Ilham; Jellal, Ahmed

    2016-07-01

    The quantum Goos-Hänchen shifts of the transmitted electron beam through an AA-stacked bilayer graphene superlattices are investigated. We found that the band structures of graphene superlattices can have more than one Dirac point, their locations do not depend on the number of barriers. It was revealed that any n-barrier structure is perfectly transparent at normal incidence around the Dirac points created in the superlattices. We showed that the Goos-Hänchen shifts display sharp peaks inside the transmission gap around two Dirac points (E =VB + τ, E =VW + τ), which are equal to those of transmission resonances. The obtained Goos-Hänchen shifts are exhibiting negative as well as positive behaviors and strongly depending on the location of Dirac points. It is observed that the maximum absolute values of the shifts increase as long as the number of barriers is increased. Our analysis is done by considering four cases: single, double barriers, superlattices without and with defect.

  1. Nanomechanical characterization of rod-like superlattice assembled from tobacco mosaic viruses

    Science.gov (United States)

    Wang, Haoran; Wang, Xinnan; Li, Tao; Lee, Byeongdu

    2013-01-01

    Tobacco mosaic virus (TMV) and TMV-derived materials have demonstrated their great potential in biomedical applications, where the mechanical properties are determining factors for their proper functionalities and structural integrity. Recently, it has been found that a superlattice structure can be formed by two-dimensional hexagonal packing TMV self-assembly in Barium ions solution. In parallel to the exploration of possible applications of TMV superlattice, the mechanical properties were characterized by the atomic force microscopy based nanoindentation. The elastic modulus of 2.14 GPa was obtained by application of the extended Johnson-Kendall-Roberts (JKR) model with the force vs sample deformation data. The adhesion force was taken into consideration, and an easy-to-implement approach of using the extended JKR model was proposed by processing both the theoretical model and the experimental data. Finite element analysis was conducted to evaluate the reinforcing effect of the like-charge forces between the TMVs and the mechanical properties of the TMV superlattice. Using the Halpin-Tsai model, the transverse elastic modulus of the superlattice sample varied within 2.00-4.38 GPa, depending on the indentation locations. Attraction-repulsion equilibrium was found to maintain the packing of TMVs. This provides useful information to address the sources of the attraction and repulsion forces to control the TMV assembly.

  2. The dependence of the tunneling characteristic on the electronic energy bands and the carrier’s states of Graphene superlattice

    Science.gov (United States)

    Yang, C. H.; Shen, G. Z.; Ao, Z. M.; Xu, Y. W.

    2016-09-01

    Using the transfer matrix method, the carrier tunneling properties in graphene superlattice generated by the Thue-Morse sequence and Kolakoski sequence are investigated. The positions and strength of the transmission can be modulated by the barrier structures, the incident energy and angle, the height and width of the potential. These carriers tunneling characteristic can be understood from the energy band structures in the corresponding superlattice systems and the carrier’s states in well/barriers. The transmission peaks above the critical incident angle rely on the carrier’s resonance in the well regions. The structural diversity can modulate the electronic and transport properties, thus expanding its applications.

  3. Beating the amorphous limit in thermal conductivity by superlattices design.

    Science.gov (United States)

    Mizuno, Hideyuki; Mossa, Stefano; Barrat, Jean-Louis

    2015-09-16

    The value measured in the amorphous structure with the same chemical composition is often considered as a lower bound for the thermal conductivity of any material: the heat carriers are strongly scattered by disorder, and their lifetimes reach the minimum time scale of thermal vibrations. An appropriate design at the nano-scale, however, may allow one to reduce the thermal conductivity even below the amorphous limit. In the present contribution, using molecular-dynamics simulation and the Green-Kubo formulation, we study systematically the thermal conductivity of layered phononic materials (superlattices), by tuning different parameters that can characterize such structures. We have discovered that the key to reach a lower-than-amorphous thermal conductivity is to block almost completely the propagation of the heat carriers, the superlattice phonons. We demonstrate that a large mass difference in the two intercalated layers, or weakened interactions across the interface between layers result in materials with very low thermal conductivity, below the values of the corresponding amorphous counterparts.

  4. Microemulsion-based synthesis of copper nanodisk superlattices

    Science.gov (United States)

    Sun, Lei; Zhao, Yanbao; Guo, Wenjing; Tao, Xiaojun; Zhang, Zhijun

    2011-06-01

    Nanocrystal superlattices (NCSs) comprised of self-assembled copper nanodisks were successfully synthesized in quaternary W/O microemulsions containing Span 80-Tween 80, liquid paraffin and n-butanol. Morphologies, structure and thermal properties of the Cu nanocrystals were characterized by means of X-ray diffraction (XRD), transmission electron microscopy (TEM), Fourier transform infrared (FT-IR) spectra, thermogravimetry (TG) and differential thermogravimetry (DTG). The reaction conditions which effect the growth of the Cu nanodisks were explored, and a mechanism for the formation of the Cu NCSs is proposed. XRD and TEM studies show that the as-synthesized Cu nanodisks exhibit a cubic crystal structure, and FT-IR and TG analysis show that the surfaces of the Cu nanodisks are covered with surfactants, which assist in the formation of the superlattice and prevent the oxidation of the Cu nanocrystals. Variation of the reaction parameters such as mass ratio of the surfactants and the presence of oleic acid is found to have a significant effect on the formation of the Cu nanodisks.

  5. Dimensional control of cobalt spin state in oxide superlattices

    Science.gov (United States)

    Jeong, Da Woon; Choi, W. S.; Okamoto, S.; Sohn, C. H.; Park, H. J.; Kim, J.-Y.; Lee, H. N.; Kim, K. W.; Moon, S. J.; Noh, T. W.

    2013-03-01

    Perovskite cobalt oxide is a very intriguing system with various spin states owing to the delicate balance between crystal field splitting and Hund exchange energy. In this talk, we show that its spin state can be altered through dimensional control, enabled by digital synthesis of perovskite cobalt oxide superlattices. We employed a few unit cells of LaCoO3 as an active magnetic layer, separated by LaAlO3 spacer layer. High quality [(LaCoO3) n (LaAlO3) n ]8 (n = 2, 6, and 10) superlattices were fabricated using pulsed laser epitaxy. Spectroscopic tools including x-ray absorption spectroscopy and optical spectroscopy revealed clear evolution of the electronic structure and resultant spin state by changing dimensionality. Specifically, the spin state changed from a high to a low spin state with a larger optical band gap, as the dimension reduced from 3D to 2D. Dynamic mean field calculation supported the critical role of dimensionality on the spin state and electronic structure of LaCoO3.

  6. Efficient light emission from inorganic and organic semiconductor hybrid structures by energy-level tuning.

    Science.gov (United States)

    Schlesinger, R; Bianchi, F; Blumstengel, S; Christodoulou, C; Ovsyannikov, R; Kobin, B; Moudgil, K; Barlow, S; Hecht, S; Marder, S R; Henneberger, F; Koch, N

    2015-04-15

    The fundamental limits of inorganic semiconductors for light emitting applications, such as holographic displays, biomedical imaging and ultrafast data processing and communication, might be overcome by hybridization with their organic counterparts, which feature enhanced frequency response and colour range. Innovative hybrid inorganic/organic structures exploit efficient electrical injection and high excitation density of inorganic semiconductors and subsequent energy transfer to the organic semiconductor, provided that the radiative emission yield is high. An inherent obstacle to that end is the unfavourable energy level offset at hybrid inorganic/organic structures, which rather facilitates charge transfer that quenches light emission. Here, we introduce a technologically relevant method to optimize the hybrid structure's energy levels, here comprising ZnO and a tailored ladder-type oligophenylene. The ZnO work function is substantially lowered with an organometallic donor monolayer, aligning the frontier levels of the inorganic and organic semiconductors. This increases the hybrid structure's radiative emission yield sevenfold, validating the relevance of our approach.

  7. Absorption enhancement and total absorption in a graphene-waveguide hybrid structure

    Science.gov (United States)

    Guo, Jun; Wu, Leiming; Dai, Xiaoyu; Xiang, Yuanjiang; Fan, Dianyuan

    2017-02-01

    We propose a graphene/planar waveguide hybrid structure, and demonstrate total absorption in the visible wavelength range by means of attenuated total reflectance. The excitation of planar waveguide mode, which has strong near field enhancement and increased light interaction length with graphene, plays a vital role in total absorption. We analyze the origin and physical insight of total absorption theoretically by using an approximated reflectance, and show how to design such hybrid structure numerically. Utilizing the tunability of doped graphene, we discuss the possible application in optical modulators. We also achieve broadband absorption enhancement in near-IR range by cascading multiple graphene-waveguide hybrid structures. We believe our results will be useful not only for potential applications in optical devices, but also for studying other two-dimension materials.

  8. Absorption enhancement and total absorption in a graphene-waveguide hybrid structure

    Directory of Open Access Journals (Sweden)

    Jun Guo

    2017-02-01

    Full Text Available We propose a graphene/planar waveguide hybrid structure, and demonstrate total absorption in the visible wavelength range by means of attenuated total reflectance. The excitation of planar waveguide mode, which has strong near field enhancement and increased light interaction length with graphene, plays a vital role in total absorption. We analyze the origin and physical insight of total absorption theoretically by using an approximated reflectance, and show how to design such hybrid structure numerically. Utilizing the tunability of doped graphene, we discuss the possible application in optical modulators. We also achieve broadband absorption enhancement in near-IR range by cascading multiple graphene-waveguide hybrid structures. We believe our results will be useful not only for potential applications in optical devices, but also for studying other two-dimension materials.

  9. Electronic band structure effects in monolayer, bilayer, and hybrid graphene structures

    Science.gov (United States)

    Puls, Conor

    Since its discovery in 2005, graphene has been the focus of intense theoretical and experimental study owing to its unique two-dimensional band structure and related electronic properties. In this thesis, we explore the electronic properties of graphene structures from several perspectives including the magnetoelectrical transport properties of monolayer graphene, gap engineering and measurements in bilayer graphene, and anomalous quantum oscillation in the monolayer-bilayer graphene hybrids. We also explored the device implications of our findings, and the application of some experimental techniques developed for the graphene work to the study of a complex oxide, Ca3Ru2O7, exhibiting properties of strongly correlated electrons. Graphene's high mobility and ballistic transport over device length scales, make it suitable for numerous applications. However, two big challenges remain in the way: maintaining high mobility in fabricated devices, and engineering a band gap to make graphene compatible with logical electronics and various optical devices. We address the first challenge by experimentally evaluating mobilities in scalable monolayer graphene-based field effect transistors (FETs) and dielectric-covered Hall bars. We find that the mobility is limited in these devices, and is roughly inversely proportional to doping. By considering interaction of graphene's Dirac fermions with local charged impurities at the interface between graphene and the top-gate dielectric, we find that Coulomb scattering is responsible for degraded mobility. Even in the cleanest devices, a band gap is still desirable for electronic applications of graphene. We address this challenge by probing the band structure of bilayer graphene, in which a field-tunable energy band gap has been theoretically proposed. We use planar tunneling spectroscopy of exfoliated bilayer graphene flakes demonstrate both measurement and control of the energy band gap. We find that both the Fermi level and

  10. Growth, Nitrogen Vacancy Reduction and Solid Solution Formation in Cubic GaN Thin Films and the Subsequent Fabrication of Superlattice Structures Using AIN and InN

    Science.gov (United States)

    1992-12-01

    AD-A258 804 Final Technical Report Ii Growth, Nitrogen Vacancy Reduction and Solid Solution Formation in Cubic GaN Thin Films and the Subsequent...Technical 6/1/86-12/31/92 4. TITLE AND SUBTITLE Growth, Nitrogen Vacancy Reduction and 5. FUNDING NUMBERS Solid Solution Formation in Cubic GaN Thin...According to the structural and chemical analyses, there is no reason to believe that a homogeneous solid solution close to this composition had

  11. CVD growth of graphene under exfoliated hexagonal boron nitride for vertical hybrid structures

    Energy Technology Data Exchange (ETDEWEB)

    Wang, Min [SKKU Advanced Institute of Nanotechnology (SAINT) (Korea, Republic of); Center for Human Interface Nanotechnology (HINT) (Korea, Republic of); Jang, Sung Kyu [SKKU Advanced Institute of Nanotechnology (SAINT) (Korea, Republic of); Song, Young Jae [SKKU Advanced Institute of Nanotechnology (SAINT) (Korea, Republic of); Department of Physics, Sungkyunkwan University (SKKU), Suwon 440-746 (Korea, Republic of); Lee, Sungjoo, E-mail: leesj@skku.edu [SKKU Advanced Institute of Nanotechnology (SAINT) (Korea, Republic of); Center for Human Interface Nanotechnology (HINT) (Korea, Republic of); College of Information and Communication Engineering, Sungkyunkwan University (SKKU), Suwon 440-746 (Korea, Republic of)

    2015-01-15

    Graphical abstract: We have demonstrated a novel yet simple method for fabricating graphene-based vertical hybrid structures by performing the CVD growth of graphene at an h-BN/Cu interface. Our systematic Raman measurements combined with plasma etching process indicate that a graphene film is grown under exfoliated h-BN rather than on its top surface, and that an h-BN/graphene vertical hybrid structure has been fabricated. Electrical transport measurements of this h-BN/graphene, transferred on SiO2, show the carrier mobility up to approximately 2250 cm{sup 2} V{sup −1} s{sup −1}. The developed method would enable the exploration of the possibility of novel hybrid structure integration with two-dimensional material systems. - Abstract: We have demonstrated a novel yet simple method for fabricating graphene-based vertical hybrid structures by performing the CVD growth of graphene at an h-BN/Cu interface. Our systematic Raman measurements combined with plasma etching process indicate that a graphene film is grown under exfoliated h-BN rather than on its top surface, and that an h-BN/graphene vertical hybrid structure has been fabricated. Electrical transport measurements of this h-BN/graphene, transferred on SiO{sub 2}, show the carrier mobility up to approximately 2250 cm{sup 2} V{sup −1} s{sup −1}. The developed method would enable the exploration of the possibility of novel hybrid structure integration with two-dimensional material systems.

  12. Sampling Enrichment toward Target Structures Using Hybrid Molecular Dynamics-Monte Carlo Simulations.

    Science.gov (United States)

    Yang, Kecheng; Różycki, Bartosz; Cui, Fengchao; Shi, Ce; Chen, Wenduo; Li, Yunqi

    2016-01-01

    Sampling enrichment toward a target state, an analogue of the improvement of sampling efficiency (SE), is critical in both the refinement of protein structures and the generation of near-native structure ensembles for the exploration of structure-function relationships. We developed a hybrid molecular dynamics (MD)-Monte Carlo (MC) approach to enrich the sampling toward the target structures. In this approach, the higher SE is achieved by perturbing the conventional MD simulations with a MC structure-acceptance judgment, which is based on the coincidence degree of small angle x-ray scattering (SAXS) intensity profiles between the simulation structures and the target structure. We found that the hybrid simulations could significantly improve SE by making the top-ranked models much closer to the target structures both in the secondary and tertiary structures. Specifically, for the 20 mono-residue peptides, when the initial structures had the root-mean-squared deviation (RMSD) from the target structure smaller than 7 Å, the hybrid MD-MC simulations afforded, on average, 0.83 Å and 1.73 Å in RMSD closer to the target than the parallel MD simulations at 310K and 370K, respectively. Meanwhile, the average SE values are also increased by 13.2% and 15.7%. The enrichment of sampling becomes more significant when the target states are gradually detectable in the MD-MC simulations in comparison with the parallel MD simulations, and provide >200% improvement in SE. We also performed a test of the hybrid MD-MC approach in the real protein system, the results showed that the SE for 3 out of 5 real proteins are improved. Overall, this work presents an efficient way of utilizing solution SAXS to improve protein structure prediction and refinement, as well as the generation of near native structures for function annotation.

  13. Hybrid experimental/analytical models of structural dynamics - Creation and use for predictions

    Science.gov (United States)

    Balmes, Etienne

    1993-01-01

    An original complete methodology for the construction of predictive models of damped structural vibrations is introduced. A consistent definition of normal and complex modes is given which leads to an original method to accurately identify non-proportionally damped normal mode models. A new method to create predictive hybrid experimental/analytical models of damped structures is introduced, and the ability of hybrid models to predict the response to system configuration changes is discussed. Finally a critical review of the overall methodology is made by application to the case of the MIT/SERC interferometer testbed.

  14. Compact hybrid cell based on a convoluted nanowire structure for harvesting solar and mechanical energy

    Energy Technology Data Exchange (ETDEWEB)

    Xu, Chen; Wang, Zhong Lin [School of Materials Science and Engineering, Georgia Institute of Technology, Atlanta, GA 30332 (United States)

    2011-02-15

    A fully integrated, solid-state, compact hybrid cell (CHC) that comprises ''convoluted'' ZnO nanowire structures for concurrent harvesting of both solar and mechanical energy is demonstrated. The compact hybrid cell is based on a conjunction design of an organic solid-state dye-sensitized solar cell (DSSC) and piezoelectric nanogenerator in one compact structure. The CHC shows a significant increase in output power, clearly demonstrating its potential for simultaneously harvesting multiple types of energy for powering small electronic devices for independent, sustainable, and mobile operation. (Copyright copyright 2011 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim)

  15. Hybrid local FEM/global LISA modeling of damped guided wave propagation in complex composite structures

    Science.gov (United States)

    Shen, Yanfeng; Cesnik, Carlos E. S.

    2016-09-01

    This paper presents a new hybrid modeling technique for the efficient simulation of guided wave generation, propagation, and interaction with damage in complex composite structures. A local finite element model is deployed to capture the piezoelectric effects and actuation dynamics of the transmitter, while the global domain wave propagation and interaction with structural complexity (structure features and damage) are solved utilizing a local interaction simulation approach (LISA). This hybrid approach allows the accurate modeling of the local dynamics of the transducers and keeping the LISA formulation in an explicit format, which facilitates its readiness for parallel computing. The global LISA framework was extended through the 3D Kelvin-Voigt viscoelasticity theory to include anisotropic damping effects for composite structures, as an improvement over the existing LISA formulation. The global LISA framework was implemented using the compute unified device architecture running on graphic processing units. A commercial preprocessor is integrated seamlessly with the computational framework for grid generation and material property allocation to handle complex structures. The excitability and damping effects are successfully captured by this hybrid model, with experimental validation using the scanning laser doppler vibrometry. To demonstrate the capability of our hybrid approach for complex structures, guided wave propagation and interaction with a delamination in a composite panel with stiffeners is presented.

  16. Absorption properties of type-II InAs/InAsSb superlattices measured by spectroscopic ellipsometry

    Energy Technology Data Exchange (ETDEWEB)

    Webster, P. T.; Riordan, N. A.; Liu, S.; Zhang, Y.-H.; Johnson, S. R., E-mail: shane.johnson@asu.edu [Center for Photonics Innovation and School of Electrical, Computer, and Energy Engineering, Arizona State University, Tempe, Arizona 85287 (United States); Steenbergen, E. H. [U.S. Air Force Research Laboratory, AFRL/RXAN, Wright Patterson, Ohio 45433 (United States); Synowicki, R. A. [J. A. Woollam Co., Inc., 645 M. Street, Suite 102, Lincoln, Nebraska 68508 (United States)

    2015-02-09

    Strain-balanced InAs/InAsSb superlattices offer access to the mid- to long-wavelength infrared region with what is essentially a ternary material system at the GaSb lattice constant. The absorption coefficients of InAs/InAsSb superlattices grown by molecular beam epitaxy on (100)-oriented GaSb substrates are measured at room temperature over the 30 to 800 meV photon energy range using spectroscopic ellipsometry, and the miniband structure of each superlattice is calculated using a Kronig-Penney model. The InAs/InAsSb conduction band offset is used as a fitting parameter to align the calculated superlattice ground state transition energy to the measured absorption onset at room temperature and to the photoluminescence peak energy at low temperature. It is observed that the ground state absorption coefficient and transition strength are proportional to the square of the wavefunction overlap and the ground state absorption coefficient approaches a maximum value of around 5780 cm{sup −1} as the wavefunction overlap approaches 100%. The absorption analysis of these samples indicates that the optical joint density of states is weakly dependent on the period thickness and Sb content of the superlattice, and that wavefunction overlap is the principal design parameter in terms of obtaining strong absorption in these structures.

  17. First-Principles Study of Electronic Structure of Type I Hybrid Carbon-Silicon Clathrates

    Science.gov (United States)

    Chan, Kwai S.; Peng, Xihong

    2016-08-01

    A new class of type I hybrid carbon-silicon clathrates has been designed using computational methods by substituting some of the Si atoms in the silicon clathrate framework with carbon atoms. In this work, the electronic structure of hybrid carbon-silicon clathrates with and without alkaline or alkaline-earth metal guest atoms has been computed within the density functional theory framework. The theoretical calculations indicate that a small number of carbon substitutions in the Si46 framework slightly reduces the density of states (DOS) near the band edge and narrows the bandgap of carbon-silicon clathrates. Weak hybridization of the conduction band occurs when alkaline metal (Li, Na, K) atoms are inserted into the structure, while strong hybridization of the conduction band occurs when alkaline-earth metal (Mg, Ca, Ba) atoms are inserted into the hybrid structure. Empty C y Si46- y clathrates within the composition range of 2 ≤ y ≤ 15 can be tuned to exhibit indirect bandgaps of 1.5 eV or less, and may be considered as potential electronic materials.

  18. Simple theoretical analysis of the photoemission from quantum confined effective mass superlattices of optoelectronic materials

    Directory of Open Access Journals (Sweden)

    Debashis De

    2011-07-01

    Full Text Available The photoemission from quantum wires and dots of effective mass superlattices of optoelectronic materials was investigated on the basis of newly formulated electron energy spectra, in the presence of external light waves, which controls the transport properties of ultra-small electronic devices under intense radiation. The effect of magnetic quantization on the photoemission from the aforementioned superlattices, together with quantum well superlattices under magnetic quantization, has also been investigated in this regard. It appears, taking HgTe/Hg1−xCdxTe and InxGa1−xAs/InP effective mass superlattices, that the photoemission from these quantized structures is enhanced with increasing photon energy in quantized steps and shows oscillatory dependences with the increasing carrier concentration. In addition, the photoemission decreases with increasing light intensity and wavelength as well as with increasing thickness exhibiting oscillatory spikes. The strong dependence of the photoemission on the light intensity reflects the direct signature of light waves on the carrier energy spectra. The content of this paper finds six different applications in the fields of low dimensional systems in general.

  19. Broadband mid-infrared superlattice light-emitting diodes

    Science.gov (United States)

    Ricker, R. J.; Provence, S. R.; Norton, D. T.; Boggess, T. F.; Prineas, J. P.

    2017-05-01

    InAs/GaSb type-II superlattice light-emitting diodes were fabricated to form a device that provides emission over the entire 3-5 μm mid-infrared transmission window. Variable bandgap emission regions were coupled together using tunnel junctions to emit at peak wavelengths of 3.3 μm, 3.5 μm, 3.7 μm, 3.9 μm, 4.1 μm, 4.4 μm, 4.7 μm, and 5.0 μm. Cascading the structure recycles the electrons in each emission region to emit several wavelengths simultaneously. At high current densities, the light-emitting diode spectra broadened into a continuous, broadband spectrum that covered the entire mid-infrared band. When cooled to 77 K, radiances of over 1 W/cm2 sr were achieved, demonstrating apparent temperatures above 1000 K over the 3-5 μm band. InAs/GaSb type-II superlattices are capable of emitting from 3 μm to 30 μm, and the device design can be expanded to include longer emission wavelengths.

  20. A Novel Organophosphorus Hybrid with Excellent Thermal Stability: Core-Shell Structure, Hybridization Mechanism, and Application in Flame Retarding Semi-Aromatic Polyamide.

    Science.gov (United States)

    Lin, Xue-Bao; Du, Shuang-Lan; Long, Jia-Wei; Chen, Li; Wang, Yu-Zhong

    2016-01-13

    An organophosphorous hybrid (BM@Al-PPi) with unique core-shell structure was prepared through hybridization reaction between boehmite (BM) as the inorganic substrate and phenylphosphinic acid (PPiA) as the organic modifier. Fourier transform infrared spectra (FTIR), solid state (31)P and (27)Al magic angle spinning nuclear magnetic resonance, X-ray diffraction, and element analysis were used to investigate the chemical structure of the hybrids, where the microrod-like core was confirmed as Al-PPi aggregates generated from the reaction between BM and PPiA, and those irregular nanoparticles in the shell belonged to residual BM. Compared with the traditional dissolution-precipitation process, a novel analogous suspension reaction mode was proposed to explain the hybridization process and the resulting product. Scanning electronic microscopy further proved the core-shell structure of the hybrids. BM exhibited much higher initial decomposition temperature than that of Al-PPi; therefore, the hybrid showed better thermal stability than Al-PPi, and it met the processing temperature of semi-aromatic polyamide (HTN, for instance) as an additive-type flame retardant. Limiting oxygen index and cone calorimetric analysis suggested the excellent flame-retardant performance and smoke suppressing activity by adding the resulting hybrid into HTN.

  1. Structural Synthesis of a Class of 2R2T Hybrid Mechanisms

    Institute of Scientific and Technical Information of China (English)

    TIAN Chunxu; FANG Yuefa; GUO Sheng

    2016-01-01

    Conventional overconstrained parallel manipulators have been widely studied both in industry and academia, however the structural synthesis of hybrid mechanisms with additional constraints is seldom studied, especially for the four degrees of freedom(DOF) hybrid mechanisms. In order to develop a manipulator with additional constraints, a class of important spatial mechanisms with coupling chains(CCs) whose motion type is two rotations and two translations(2R2T) is presented. Based on screw theory, the combination of different types of limbs which are used to construct parallel mechanisms and coupling chains is proposed. The basic types of the general parallel mechanisms and geometric conditions of the kinematic chains are given using constraint synthesis method. Moreover, the 2R2T motion pattern hybrid mechanisms which are derived by adding coupling chains between different serial kinematic chains(SKCs) of the corresponding parallel mechanisms are presented. According to the constraint analysis of the mechanisms, the movement relationship of the moving platform and the kinematic chains is derived by disassembling the coupling chains. At last, fourteen novel hybrid mechanisms with two or three serial kinematic chains are presented. The proposed novel hybrid mechanisms and construction method enrich the family of the spatial mechanisms and provide an instruction to design more complex hybrid mechanisms.

  2. Efficient Hybrid White Organic Light-Emitting Diodes for Application of Triplet Harvesting with Simple Structure

    CERN Document Server

    Hwang, Kyo Min; Lee, Sungkyu; Yoo, Han Kyu; Baek, Hyun Jung; Kim, Jwajin; Yoon, Seung Soo; Kim, Young Kwan

    2016-01-01

    In this study, we fabricated hybrid white organic light-emitting diodes (WOLEDs) based on triplet harvesting with simple structure. All the hole transporting material and host in emitting layer (EML) of devices were utilized with same material by using N,N'-di-1-naphthalenyl-N,N'-diphenyl-[1,1':4',1":4",1"'-quaterphenyl]-4,4"'-diamine (4P-NPD) which were known to be blue fluorescent material. Simple hybrid WOLEDs were fabricated three color with blue fluorescent and green, red phosphorescent materials. We was investigated the effect of triplet harvesting (TH) by exciton generation zone on simple hybrid WOLEDs. Characteristic of simple hybrid WOLEDs were dominant hole mobility, therefore exciton generation zone was expected in EML. Additionally, we was optimization thickness of hole transporting layer and electron transporting layer was fabricated a simple hybrid WOLEDs. Simple hybrid WOLED exhibits maximum luminous efficiency of 29.3 cd/A and maximum external quantum efficiency of 11.2%. Commission Internatio...

  3. Structural synthesis of a class of 2R2T hybrid mechanisms

    Science.gov (United States)

    Tian, Chunxu; Fang, Yuefa; Guo, Sheng

    2016-07-01

    Conventional overconstrained parallel manipulators have been widely studied both in industry and academia, however the structural synthesis of hybrid mechanisms with additional constraints is seldom studied, especially for the four degrees of freedom(DOF) hybrid mechanisms. In order to develop a manipulator with additional constraints, a class of important spatial mechanisms with coupling chains(CCs) whose motion type is two rotations and two translations(2R2T) is presented. Based on screw theory, the combination of different types of limbs which are used to construct parallel mechanisms and coupling chains is proposed. The basic types of the general parallel mechanisms and geometric conditions of the kinematic chains are given using constraint synthesis method. Moreover, the 2R2T motion pattern hybrid mechanisms which are derived by adding coupling chains between different serial kinematic chains(SKCs) of the corresponding parallel mechanisms are presented. According to the constraint analysis of the mechanisms, the movement relationship of the moving platform and the kinematic chains is derived by disassembling the coupling chains. At last, fourteen novel hybrid mechanisms with two or three serial kinematic chains are presented. The proposed novel hybrid mechanisms and construction method enrich the family of the spatial mechanisms and provide an instruction to design more complex hybrid mechanisms.

  4. A Carbon-Sulfur Hybrid with Pomegranate-like Structure for Lithium-Sulfur Batteries.

    Science.gov (United States)

    Shi, Yanting; Lv, Wei; Niu, Shuzhang; He, Yanbing; Zhou, Guangmin; Chen, Guohua; Li, Baohua; Yang, Quan-Hong; Kang, Feiyu

    2016-05-01

    A carbon-sulfur hybrid with pomegranate-like core-shell structure, which demonstrates a high rate performance and relatively high cyclic stability, is obtained through carbonization of a carbon precursor in the presence of a sulfur precursor (FeS2 ) and a following oxidation of FeS2 to sulfur by HNO3 . Such a structure effectively protects the sulfur and leaves enough buffer space after Fe(3+) removal and, at the same time, has an interconnected conductive network. The capacity of the obtained hybrid is 450 mA h g(-1) under the current density of 5 C. This work provides a simple strategy to design and prepare various high-performance carbon-sulfur hybrids for lithium-sulfur batteries.

  5. Ultracompact resonator with high quality-factor based on a hybrid grating structure

    DEFF Research Database (Denmark)

    Taghizadeh, Alireza; Mørk, Jesper; Chung, Il-Sug

    2015-01-01

    We numerically investigate the properties of a hybrid grating structure acting as a resonator with ultrahigh quality factor. This reveals that the physical mechanism responsible for the resonance is quite different from the conventional guided mode resonance (GMR). The hybrid grating consists...... of a subwavelength grating layer and an un-patterned high-refractive-index cap layer, being surrounded by low index materials. Since the cap layer may include a gain region, an ultracompact laser can be realized based on the hybrid grating resonator, featuring many advantages over high-contrast-grating resonator...... lasers. The effect of fabrication errors and finite size of the structure is investigated to understand the feasibility of fabricating the proposed resonator....

  6. Fast structural design and analysis via hybrid domain decomposition on massively parallel processors

    Science.gov (United States)

    Farhat, Charbel

    1993-01-01

    A hybrid domain decomposition framework for static, transient and eigen finite element analyses of structural mechanics problems is presented. Its basic ingredients include physical substructuring and /or automatic mesh partitioning, mapping algorithms, 'gluing' approximations for fast design modifications and evaluations, and fast direct and preconditioned iterative solvers for local and interface subproblems. The overall methodology is illustrated with the structural design of a solar viewing payload that is scheduled to fly in March 1993. This payload has been entirely designed and validated by a group of undergraduate students at the University of Colorado using the proposed hybrid domain decomposition approach on a massively parallel processor. Performance results are reported on the CRAY Y-MP/8 and the iPSC-860/64 Touchstone systems, which represent both extreme parallel architectures. The hybrid domain decomposition methodology is shown to outperform leading solution algorithms and to exhibit an excellent parallel scalability.

  7. Analysis of interference between two optical beams in a quasi-zero electric permittivity photonic crystal superlattice.

    Science.gov (United States)

    Li, Ziyuan; Hattori, Haroldo T

    2013-02-01

    A quasi-zero-average-index photonic crystal structure has been recently demonstrated by using the concept of complementary media. It consists of dielectric photonic crystal superlattices with alternating layers of negative index photonic crystals and positive index dielectric media. This photonic crystal structure has unique optical properties, such as phase-invariant field and self-collimation of light. In particular, the nanofabricated superlattices can be used in chip-scale optical interconnects and interferometers with quasi-zero-average phase difference. However, in potential interconnect applications, crosstalk between neighboring signals needs to be avoided. In this article, we study simulations of the interference of propagating electromagnetic waves in a quasi-zero electric permittivity photonic crystal superlattice. The simulations here are restricted to TM modes, with the main electric field along the vertical direction.

  8. Superlattices assembled through shape-induced directional binding.

    Science.gov (United States)

    Lu, Fang; Yager, Kevin G; Zhang, Yugang; Xin, Huolin; Gang, Oleg

    2015-01-01

    Organization of spherical particles into lattices is typically driven by packing considerations. Although the addition of directional binding can significantly broaden structural diversity, nanoscale implementation remains challenging. Here we investigate the assembly of clusters and lattices in which anisotropic polyhedral blocks coordinate isotropic spherical nanoparticles via shape-induced directional interactions facilitated by DNA recognition. We show that these polyhedral blocks--cubes and octahedrons--when mixed with spheres, promote the assembly of clusters with architecture determined by polyhedron symmetry. Moreover, three-dimensional binary superlattices are formed when DNA shells accommodate the shape disparity between nanoparticle interfaces. The crystallographic symmetry of assembled lattices is determined by the spatial symmetry of the block's facets, while structural order depends on DNA-tuned interactions and particle size ratio. The presented lattice assembly strategy, exploiting shape for defining the global structure and DNA-mediation locally, opens novel possibilities for by-design fabrication of binary lattices.

  9. 17.6%-Efficient radial junction solar cells using silicon nano/micro hybrid structures

    Science.gov (United States)

    Lee, Kangmin; Hwang, Inchan; Kim, Namwoo; Choi, Deokjae; Um, Han-Don; Kim, Seungchul; Seo, Kwanyong

    2016-07-01

    We developed a unique nano- and microwire hybrid structure by selectively modifying only the tops of microwires using metal-assisted chemical etching. The proposed nano/micro hybrid structure not only minimizes surface recombination but also absorbs 97% of incident light under AM 1.5G illumination, demonstrating outstanding light absorption compared to that of planar (59%) and microwire arrays (85%). The proposed hybrid solar cells with an area of 1 cm2 exhibit power conversion efficiencies (Eff) of up to 17.6% under AM 1.5G illumination. In particular, the solar cells show a high short-circuit current density (Jsc) of 39.5 mA cm-2 because of the high light-absorbing characteristics of the nanostructures. This corresponds to an approximately 61.5% and 16.5% increase in efficiency compared to that of a planar silicon solar cell (Eff = 10.9%) and a microwire solar cell (Eff = 15.1%), respectively. Therefore, we expect the proposed hybrid structure to become a foundational technology for the development of highly efficient radial junction solar cells.We developed a unique nano- and microwire hybrid structure by selectively modifying only the tops of microwires using metal-assisted chemical etching. The proposed nano/micro hybrid structure not only minimizes surface recombination but also absorbs 97% of incident light under AM 1.5G illumination, demonstrating outstanding light absorption compared to that of planar (59%) and microwire arrays (85%). The proposed hybrid solar cells with an area of 1 cm2 exhibit power conversion efficiencies (Eff) of up to 17.6% under AM 1.5G illumination. In particular, the solar cells show a high short-circuit current density (Jsc) of 39.5 mA cm-2 because of the high light-absorbing characteristics of the nanostructures. This corresponds to an approximately 61.5% and 16.5% increase in efficiency compared to that of a planar silicon solar cell (Eff = 10.9%) and a microwire solar cell (Eff = 15.1%), respectively. Therefore, we expect the

  10. A LINEAR HYBRID MODEL OF MSE AND BEM FOR FLOATING STRUCTURES IN COASTAL ZONES

    Institute of Scientific and Technical Information of China (English)

    ZHANG Jun; MIAO Guo-ping

    2006-01-01

    A linear hybrid model of Mild Slope Equation (MSE) and Boundary Element Method (BEM) is developed to study the wave propagation around floating structures in coastal zones. Both the wave refraction under the influence of topography and the wave diffraction by floating structures are considered. Hence, the model provides wave properties around the coastal floating structures of arbitrary shape but also the wave forces on and the hydrodynamic characteristics of the structures. Different approaches are compared to demonstrate the validity of the present hybrid model. Several numerical tests are carried out for the cases of pontoons under different circumstances. The results show that the influence of topography on the hydrodynamic characteristics of floating structures in coastal regions is important and must not be ignored in the most wave period range with practical interests.

  11. Optimal design of structures for earthquake loads by a hybrid RBF-BPSO method

    Institute of Scientific and Technical Information of China (English)

    Eysa Salajegheh; Saeed Gholizadeh; Mohsen Khatibina

    2008-01-01

    The optimal seismic design of structures requires that time history analyses (THA) be carried out repeatedly. This makes the optimal design process inefficient, in particular, if an evolutionary algorithm is used. To reduce the overall time required for structural optimization, two artificial intelligence strategies are employed. In the first strategy, radial basis function (RBF) neural networks are used to predict the time history responses of structures in the optimization flow. In the second strategy, a binary particle swarm optimization (BPSO) is used to find the optimum design. Combining the RBF and BPSO, a hybrid RBF-BPSO optimization method is proposed in this paper, which achieves fast optimization with high computational performance. Two examples are presented and compared to determine the optimal weight of structures under earthquake loadings using both exact and approximate analyses. The numerical results demonstrate the computational advantages and effectiveness of the proposed hybrid RBF-BPSO optimization method for the seismic design of structures.

  12. Phonon thermal transport in silicene-germanene superlattice: a molecular dynamics study

    Science.gov (United States)

    Wang, Xinyu; Hong, Yang; Chan, Paddy K. L.; Zhang, Jingchao

    2017-06-01

    Two-dimensional (2D) hybrid materials have drawn enormous attention in thermoelectric applications. In this work, we apply a molecular dynamics (MD) simulation to investigate the phonon thermal transport in silicene-germanene superlattice. A non-monotonic thermal conductivity of silicene-germanene superlattice with period length is revealed, which is due to the coherent-incoherent phonon conversion and phonon confinement mechanisms. We also calculate the thermal conductivity of a Si-Ge random mixing monolayer, showing a U-shaped trend. Because of the phonon mode localizations at Ge concentration of 80%, thermal conductivity varies dramatically at low doping regions. By changing the total length (L total), the infinite-length thermal conductivities of pure silicene, pure germanene, silicene-germanene superlattice, and Si-Ge random mixing monolayer are extracted as 16.08, 15.95, 5.60 and 4.47 W/m-K, respectively. The thermal boundary conductance (TBC) of the silicene-germanene is also evaluated, showing a small thermal rectification. At L total = 274.7 nm, the TBC of silicene to germanene is 620.49 MW/m2-K, while that of germanene to silicene is 528.76 MW/m2-K.

  13. A hybrid method for identification of structural domains

    Science.gov (United States)

    Hua, Yongpan; Zhu, Min; Wang, Yuelong; Xie, Zhaoyang; Li, Menglong

    2014-12-01

    Structural domains in proteins are the basic units to form various proteins. In the protein's evolution and functioning, domains play important roles. But the definition of domain is not yet precisely given, and the update cycle of structural domain databases is long. The automatic algorithms identify domains slowly, while protein entities with great structural complexity are on the rise. Here, we present a method which recognizes the compact and modular segments of polypeptide chains to identify structural domains, and contrast some data sets to illuminate their effect. The method combines support vector machine (SVM) with K-means algorithm. It is faster and more stable than most current algorithms and performs better. It also indicates that when proteins are presented as some Alpha-carbon atoms in 3D space, it is feasible to identify structural domains by the spatially structural properties. We have developed a web-server, which would be helpful in identification of structural domains (http://vis.sculab.org/~huayongpan/cgi-bin/domainAssignment.cgi).

  14. Optimization of hybrid antireflection structure integrating surface texturing and multi-layer interference coating

    Science.gov (United States)

    Kubota, Shigeru; Kanomata, Kensaku; Suzuki, Takahiko; Hirose, Fumihiko

    2014-10-01

    The antireflection structure (ARS) for solar cells is categorized to mainly two different techniques, i.e., the surface texturing and the single or multi-layer antireflection interference coating. In this study, we propose a novel hybrid ARS, which integrates moth eye texturing and multi-layer coat, for application to organic photovoltaics (OPVs). Using optical simulations based on the finite-difference time-domain (FDTD) method, we conduct nearly global optimization of the geometric parameters characterizing the hybrid ARS. The proposed optimization algorithm consists of two steps: in the first step, we optimize the period and height of moth eye array, in the absence of multi-layer coating. In the second step, we optimize the whole structure of hybrid ARS by using the solution obtained by the first step as the starting search point. The methods of the simple grid search and the Hooke and Jeeves pattern search are used for global and local searches, respectively. In addition, we study the effects of deviations in the geometric parameters of hybrid ARS from their optimized values. The design concept of hybrid ARS is highly beneficial for broadband light trapping in OPVs.

  15. Charge transfer-induced magnetic exchange bias and electron localization in (111)- and (001)-oriented LaNiO3/LaMnO3 superlattices

    Science.gov (United States)

    Wei, Haoming; Barzola-Quiquia, Jose Luis; Yang, Chang; Patzig, Christian; Höche, Thomas; Esquinazi, Pablo; Grundmann, Marius; Lorenz, Michael

    2017-03-01

    High-quality lattice-matched LaNiO3/LaMnO3 superlattices with monolayer terrace structure have been grown on both (111)- and (001)-oriented SrTiO3 substrates by pulsed laser deposition. In contrast to the previously reported experiments, a magnetic exchange bias is observed that reproducibly occurs in both (111)- and (001)-oriented superlattices with the thin single layers of 5 and 7 unit cells, respectively. The exchange bias is theoretically explained by charge transfer-induced magnetic moments at Ni atoms. Furthermore, magnetization data at low temperature suggest two magnetic phases in the superlattices, with Néel temperature around 10 K. Electrical transport measurements reveal a metal-insulator transition with strong localization of electrons in the superlattices with the thin LaNiO3 layers of 4 unit cells, in which the electrical transport is dominated by two-dimensional variable range hopping.

  16. Plasmon-gating photoluminescence in graphene/GeSi quantum dots hybrid structures

    Science.gov (United States)

    Chen, Yulu; Wu, Qiong; Ma, Yingjie; Liu, Tao; Fan, Yongliang; Yang, Xinju; Zhong, Zhenyang; Xu, Fei; Lu, Jianping; Jiang, Zuimin

    2015-01-01

    The ability to control light-matter interaction is central to several potential applications in lasing, sensing, and communication. Graphene plasmons provide a way of strongly enhancing the interaction and realizing ultrathin optoelectronic devices. Here, we find that photoluminescence (PL) intensities of the graphene/GeSi quantum dots hybrid structures are saturated and quenched under positive and negative voltages at the excitation of 325 nm, respectively. A mechanism called plasmon-gating effect is proposed to reveal the PL dependence of the hybrid structures on the external electric field. On the contrary, the PL intensities at the excitation of 405 and 795 nm of the hybrid structures are quenched due to the charge transfer by tuning the Fermi level of graphene or the blocking of the excitons recombination by excitons separation effect. The results also provide an evidence for the charge transfer mechanism. The plasmon gating effect on the PL provides a new way to control the optical properties of graphene/QD hybrid structures. PMID:26631498

  17. Structure of hybrid organic-inorganic sols for the preparation of hydrothermally stable membranes

    NARCIS (Netherlands)

    Castricum, H.L.; Sah, A.; Geenevasen, J.A.J.; Kreiter, R.; Blank, D.H.A.; Vente, J.F.; ten Elshof, J.E.

    2008-01-01

    A procedure for the preparation of hybrid sols for the synthesis of organic-inorganic microporous materials and thin film membranes is reported. We describe silane reactivity and sol structure for acid-catalysed colloidal sols from mixtures of either tetraethylorthosilicate (TEOS) and methyltriethox

  18. Effect of concrete creep and shrinkage on tall hybrid structures and its countermeasures

    Institute of Scientific and Technical Information of China (English)

    Pusheng SHEN; Hui FANG; Xinhong XIA

    2009-01-01

    This paper aims to study the different vertical displacements in tall hybrid-structures and the corresponding engineering measures. First, the method to calculate the different vertical displacements in tall hybrid-structures is presented. This method takes into account the effects of construction process by applying loads sequentially story by story. Based on the concrete creep and shrinkage calculation formula in American Concrete Institute (ACI)code, with the assumption that loads are increased linearly in members, the creep and shrinkage effects of members are analyzed by adopting two parameters named average load-aged-coefficient and average age-last coefficient. The effects of steel ratio on members creep are analyzed by age-adjusted module method (AEMM). The effects that core-tube were constructed in advance to outer steel frame were also considered. Then, based on the samplecalculation, the measures to effectively reduce the different vertical displacements in hybrid-structures are proposed. This method is simple and practical in the calculation of different vertical displacements in tall and super-tall hybrid-structures.

  19. Probing Structure and Composition of Nickel/Titanium Carbide Hybrid Interfaces at the Atomic Scale (Preprint)

    Science.gov (United States)

    2010-01-01

    The transition in structure and composition across the titanium carbide /nickel hybrid interface has been determined at near atomic resolution by...coupling high-resolution transmission electron microscopy with three-dimensional atom probe tomography. The titanium carbide phase adopts a rocksalt-type

  20. Photoluminescence in Er-implanted AlGaN/GaN superlattices and GaN epilayers

    Energy Technology Data Exchange (ETDEWEB)

    Sobolev, N.A.; Emel' yanov, A.M.; Sakharov, V.I.; Serenkov, I.T.; Shek, E.I.; Besyul' kin, A.I.; Lundin, W.V.; Shmidt, N.M.; Usikov, A.S.; Zavarin, E.E

    2003-12-31

    Photoluminescence (PL), structural and electrophysical properties of Al{sub 0.26}Ga{sub 0.74}N/GaN superlattices grown by metal-organic chemical vapor deposition, implanted by erbium (Er) ions with 1 MeV energy and 1x10{sup 15} cm{sup -2} dose as well as annealed at 700-1100 deg. C for 4 min in argon have been investigated. A comparison of the properties of the superlattices with that of the GaN epilayers grown, implanted and annealed at the same conditions is also given. The Er-related peak with a maximum at {lambda}{approx}1.54 {mu}m dominated and the defect-related emission band at {lambda}{approx}1-1.4 {mu}m was observed in the PL spectra of both types of samples. When the measurement temperature was increased from 80 to 300 K, practically the same temperature quenching of the Er-related intensity was observed in the superlattices and GaN epilayers implanted and annealed at the same conditions. The Er-related intensity at 300 K increased monotonically as the annealing temperature was raised from 700 to 1000 deg. C, but the intensity in the superlattices was higher by several times than that in the epilayers. A decrease of the Er-related PL intensity in the superlattice after annealing at 1100 deg. C is associated with the formation of non-radiative recombination centers.

  1. Effect of crystalline/amorphous interfaces on thermal transport across confined thin films and superlattices

    Science.gov (United States)

    Giri, Ashutosh; Braun, Jeffrey L.; Hopkins, Patrick E.

    2016-06-01

    We report on the thermal boundary resistances across crystalline and amorphous confined thin films and the thermal conductivities of amorphous/crystalline superlattices for Si/Ge systems as determined via non-equilibrium molecular dynamics simulations. Thermal resistances across disordered Si or Ge thin films increase with increasing length of the interfacial thin films and in general demonstrate higher thermal boundary resistances in comparison to ordered films. However, for films ≲3 nm, the resistances are highly dependent on the spectral overlap of the density of states between the film and leads. Furthermore, the resistances at a single amorphous/crystalline interface in these structures are much lower than those at interfaces between the corresponding crystalline materials, suggesting that diffusive scattering at an interface could result in higher energy transmissions in these systems. We use these findings, together with the fact that high mass ratios between amorphous and crystalline materials can lead to higher thermal resistances across thin films, to design amorphous/crystalline superlattices with very low thermal conductivities. In this regard, we study the thermal conductivities of amorphous/crystalline superlattices and show that the thermal conductivities decrease monotonically with increasing interface densities above 0.1 nm-1. These thermal conductivities are lower than that of the homogeneous amorphous counterparts, which alludes to the fact that interfaces non-negligibly contribute to thermal resistance in these superlattices. Our results suggest that the thermal conductivity of superlattices can be reduced below the amorphous limit of its material constituent even when one of the materials remains crystalline.

  2. Hybrid FDTD Analysis for Periodic On-Chip Terahertz (THZ) Structures

    Energy Technology Data Exchange (ETDEWEB)

    Hussein, Yasser A.; Spencer, James E.; /SLAC

    2005-06-07

    We present electromagnetic analysis and radiation efficiency calculations for on-chip terahertz (THz) structures based on a hybrid, finite-difference, time-domain (HFDTD) technique. The method employs the FDTD technique to calculate S-parameters for one cell of a periodic structure. The transmission ABCD matrix is then estimated and multiplied by itself n times to obtain the n-cell periodic structure ABCD parameters that are then converted back to S-parameters. Validation of the method is carried out by comparing the results of the hybrid technique with FDTD calculations of the entire periodic structure as well as with HFSS which all agree quite well. This procedure reduces the CPU-time and allows efficient design and optimization of periodic THz radiation sources. Future research will involve coupling of Maxwell's equations with a more detailed, physics-based transport model for higher-order effects.

  3. Analysis of Non-Conventional Hybrid MOSFET Structure for Gate Leakage Current

    Directory of Open Access Journals (Sweden)

    RANA Ashwani K.

    2011-10-01

    Full Text Available A non-conventional hybrid MOSFET (HMOSstructure has been proposed to reduce the gate leakagecurrent. This non-conventional hybrid MOSFET consistsof source/drain-to-gate non-overlap region and high-kgate stack. The gate leakage behaviour of HMOS hasbeen investigated with the help of compact analyticalmodel, which is backed by Sentaurus Simulation. Ourmodel sustains a very good agreement between the modeland TCAD result. It is found that HMOS structure hasreduced the gate leakage current to great extent ascompared to conventional overlapped MOSFETstructure.

  4. A HYBRID GRANULARITY PARALLEL ALGORITHM FOR PRECISE INTEGRATION OF STRUCTURAL DYNAMIC RESPONSES

    Institute of Scientific and Technical Information of China (English)

    Yuanyin Li; Xianlong Jin; Genguo Li

    2008-01-01

    Precise integration methods to solve structural dynamic responses and the corre-sponding time integration formula are composed of two parts: the multiplication of an exponential matrix with a vector and the integration term. The second term can be solved by the series solu-tion. Two hybrid granularity parallel algorithms are designed, that is, the exponential matrix and the first term are computed by the fine-grained parallel algorithm and the second term is com-puted by the coarse-grained parallel algorithm. Numerical examples show that these two hybrid granularity parallel algorithms obtain higher speedup and parallel efficiency than two existing parallel algorithms.

  5. Rechargeable Mg battery cathode TiS3 with d-p orbital hybridized electronic structures

    Science.gov (United States)

    Taniguchi, Kouji; Gu, Yunpeng; Katsura, Yukari; Yoshino, Takafumi; Takagi, Hidenori

    2016-01-01

    Rechargeable performance is realized in Mg batteries using a TiS3 cathode without the nanometer-scale downsizing of electrode particles. The specific capacity is about 80 mAh/g for the first 50 cycles at room temperature. This observed specific capacity is comparable to that of the prototype cathode for Mg batteries. First-principles calculation indicates that TiS3 is a semiconductor with d-p orbital hybridized electronic structures around the Fermi level. The reversible electrode performance is likely assisted by the delocalized electronic distribution over metal-ligand units through d-p orbital hybridization.

  6. Enantioselective Catalysis by Using Short, Structurally Defined DNA Hairpins as Scaffold for Hybrid Catalysts.

    Science.gov (United States)

    Marek, Jasmin J; Singh, Raghvendra P; Heuer, Andreas; Hennecke, Ulrich

    2017-05-02

    A new type of DNA metal complex hybrid catalyst, which is based on single-stranded DNA oligonucleotides, is described. It was shown that oligonucleotides as short as 14 nucleotides that fold into hairpin structures are suitable as nucleic acid components for DNA hybrid catalysts. With these catalysts, excellent enantioinduction in asymmetric Diels-Alder reactions with selectivity values as high as 96 % enantiomeric excess (ee) can be achieved. Molecular dynamics simulations indicate that a rather flexible loop combined with a rigid stem region provides DNA scaffolds with these high selectivity values. © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

  7. Preparation of Magnetic Hybrid Microspheres with Well-Defined Yolk-Shell Structure

    Directory of Open Access Journals (Sweden)

    Yuan Zhao

    2016-01-01

    Full Text Available A facile and efficient route was reported to prepare a kind of yolk-shell magnetic hybrid microspheres by suspension polymerization and calcinations method. The morphology, structure, and composition of the magnetic microspheres were characterized by FTIR, XRD, TEM, SEM, and TGA analysis. The vibrating-sample magnetometry (VSM results clearly showed that the magnetic particles were superparamagnetic with saturation magnetization of 32.82 emu/g which makes the microcomposites easily controlled by an external magnetic field. The results revealed that the magnetic hybrid microspheres might have important applications in magnetic bioseparation and drug delivery.

  8. Polarization dependence of the metamagnetic resonance of cut-wire-pair structure by using plasmon hybridization

    Energy Technology Data Exchange (ETDEWEB)

    Dung, Nguyen Van; Yoo, Young Joon; Lee, Young Pak [Hanyang University, Seoul (Korea, Republic of); Tung, Nguyen Thanh [KU Leuven, Leuven (Belgium); Tung, Bui Son; Lam, Vu Dinh [Vietnam Academy of Science and Technology, Hanoi (Viet Nam)

    2014-07-15

    The influence of lattice constants on the electromagnetic behavior of a cut-wire-pair (CWP) structure has been elucidated. In this report, we performed both simulations and experiments to determine the influence of polarization on the metamagnetic resonance of the CWP structure. The key finding is the result of an investigation on the plasmon hybridization between the two CWs, which showed that the polarization of the incident wave was affected. Good agreement between numerical simulation and measurement is achieved.

  9. Photon transport enhanced by transverse Anderson localization in disordered superlattices

    CERN Document Server

    Hsieh, Pin-Chun; McMillan, James; Tsai, Min-An; Lu, Ming; Panoiu, Nicolae; Wong, Chee Wei

    2014-01-01

    One of the daunting challenges in optical physics is to accurately control the flow of light at the subwavelength scale, by patterning the optical medium one can design anisotropic media. The light transport can also be significantly affected by Anderson localization, namely the wave localization in a disordered medium, a ubiquitous phenomenon in wave physics. Here we report the photon transport and collimation enhanced by transverse Anderson localization in chip-scale dispersion engineered anisotropic media. We demonstrate a new type of anisotropic photonic structure in which diffraction is nearly completely arrested by cascaded resonant tunneling through transverse guided resonances. By perturbing the shape of more than 4,000 scatterers in these superlattices we add structural disordered in a controlled manner and uncover the mechanism of disorder-induced transverse localization at the chip-scale. Arrested spatial divergence is captured in the power-law scaling, along with exponential asymmetric mode profil...

  10. Spin-polarized transport in graphene nanoribbon superlattices

    Institute of Scientific and Technical Information of China (English)

    Yu Xin-Xin; Xie Yue-E; OuYang Tao; Chen Yuan-Ping

    2012-01-01

    By the Green's function method,we investigate spin transport properties of a zigzag graphene nanoribbon superlattice (ZGNS) under a ferromagnetic insulator and edge effect.The exchange splitting induced by the ferromagnetic insulator eliminates the spin degeneracy,which leads to spin-polarized transport in structure.Spin-dependent minibands and minigaps are exhibited in the conductance profile near the Fermi energy.The location and width of the miniband are associated with the geometry of the ZGNS.In the optimal structure,the spin-up and spin-down minibands can be separated completely near the Fermi energy.Therefore,a wide,perfect spin polarization with clear stepwise pattern is observed,i.e.,the perfect spin-polarized transport can be tuned from spin up to spin down by varying the electron energy.

  11. Shape-controlled synthesis of palladium and copper superlattice nanowires for high-stability hydrogen sensors

    Science.gov (United States)

    Yang, Dachi; Carpena-Núñez, Jennifer; Fonseca, Luis F.; Biaggi-Labiosa, Azlin; Hunter, Gary W.

    2014-01-01

    For hydrogen sensors built with pure Pd nanowires, the instabilities causing baseline drifting and temperature-driven sensing behavior are limiting factors when working within a wide temperature range. To enhance the material stability, we have developed superlattice-structured palladium and copper nanowires (PdCu NWs) with random-gapped, screw-threaded, and spiral shapes achieved by wet-chemical approaches. The microstructure of the PdCu NWs reveals novel superlattices composed of lattice groups structured by four-atomic layers of alternating Pd and Cu. Sensors built with these modified NWs show significantly reduced baseline drifting and lower critical temperature (259.4 K and 261 K depending on the PdCu structure) for the reverse sensing behavior than those with pure Pd NWs (287 K). Moreover, the response and recovery times of the PdCu NWs sensor were of ~9 and ~7 times faster than for Pd NWs sensors, respectively.

  12. Improving hybrid statistical and physical forcefields through local structure enumeration.

    Science.gov (United States)

    Conway, Patrick; DiMaio, Frank

    2016-08-01

    Forcefields used in biomolecular simulations are comprised of energetic terms that are physical in nature, based on parameter fitting to quantum mechanical simulation or experimental data, or statistical, drawing off high-resolution structural data to describe distributions of molecular features. Combining the two in a single forcefield is challenging, since physical terms describe some, but not all, of the observed statistics, leading to double counting. In this manuscript, we develop a general scheme for correcting statistical potentials used in combination with physical terms. We apply these corrections to the sidechain torsional potential used in the Rosetta all-atom forcefield. We show the approach identifies instances of double-counted interactions, including electrostatic interactions between sidechain and nearby backbone, and steric interactions between neighboring Cβ atoms within secondary structural elements. Moreover, this scheme allows for the inclusion of intraresidue physical terms, previously turned off to avoid overlap with the statistical potential. Combined, these corrections lead to a forcefield with improved performance on several structure prediction tasks, including rotamer prediction and native structure discrimination.

  13. Enhanced hybrid search algorithm for protein structure prediction using the 3D-HP lattice model.

    Science.gov (United States)

    Zhou, Changjun; Hou, Caixia; Zhang, Qiang; Wei, Xiaopeng

    2013-09-01

    The problem of protein structure prediction in the hydrophobic-polar (HP) lattice model is the prediction of protein tertiary structure. This problem is usually referred to as the protein folding problem. This paper presents a method for the application of an enhanced hybrid search algorithm to the problem of protein folding prediction, using the three dimensional (3D) HP lattice model. The enhanced hybrid search algorithm is a combination of the particle swarm optimizer (PSO) and tabu search (TS) algorithms. Since the PSO algorithm entraps local minimum in later evolution extremely easily, we combined PSO with the TS algorithm, which has properties of global optimization. Since the technologies of crossover and mutation are applied many times to PSO and TS algorithms, so enhanced hybrid search algorithm is called the MCMPSO-TS (multiple crossover and mutation PSO-TS) algorithm. Experimental results show that the MCMPSO-TS algorithm can find the best solutions so far for the listed benchmarks, which will help comparison with any future paper approach. Moreover, real protein sequences and Fibonacci sequences are verified in the 3D HP lattice model for the first time. Compared with the previous evolutionary algorithms, the new hybrid search algorithm is novel, and can be used effectively to predict 3D protein folding structure. With continuous development and changes in amino acids sequences, the new algorithm will also make a contribution to the study of new protein sequences.

  14. Different proportions of C/KCu7S4 hybrid structure for high-performance supercapacitors

    Science.gov (United States)

    Dai, Shuge; Xi, Yi; Hu, Chenguo; Yue, Xule; Cheng, Lu; Wang, Guo

    2014-10-01

    KCu7S4 has the channel structure and minor resistance. Its double larger channels ensure that the ions can well exchange with other's, at the same time, can shorten the ionic diffusion path and improve the ionic and electronic transport. So KCu7S4 shows good electrochemical property. The paper reports a novel and high performance supercapacitor based on hybrid carbon particles and KCu7S4 (C/KCu7S4) electrode. For the hybrid structure with different proportions of C and KCu7S4, the C/KCu7S4 (1:10) hybrid supercapacitor shows preferable electrochemical performance and large specific capacitance (469 mF cm-2) at high charge-discharge rate (2 mA), still retaining ∼95% of the capacitance over 5000 cycles by charge-discharge process at a fixed current of 10 mA. Three supercapacitor units in series can light 50 light-emitting diodes (LEDs) for 2.5 min, 10 LEDs for 4 min, one LED for 5.5 min. The much-increased capacity, rate capability, and cycling stability may be attributed to the superionic conductive KCu7S4 nanowires and C/KCu7S4 hybrid structure, which improve ionic and electronic transport, enhance the kinetics of redox reactions through the electrode system.

  15. Impact Resistance of Lightweight Hybrid Structures for Gas Turbine Engine Fan Containment Applications

    Science.gov (United States)

    Hebsur, Mohan G.; Noebe, Ronald D.; Revilock, Duane M.

    2003-01-01

    The ballistic impact resistance of hybrid composite sandwich structures was evaluated with the ultimate goal of developing new materials or structures for potential gas turbine engine fan containment applications. The sandwich structures investigated consisted of GLARE-5 laminates as face sheets with lightweight cellular metallic materials such as honeycomb, foam, and lattice block as a core material. The impact resistance of these hybrid sandwich structures was compared to GLARE-5 laminates and 2024-T3 Al sheet, which were tested as a function of areal weight (material thickness). The GLARE-5 laminates exhibited comparable impact properties to that of 2024-T3 Al at low areal weights, even though there were significant differences in the static tensile properties of these materials. The GLARE-5, however, did have a greater ballistic limit than straight aluminum sheet at higher areal weights. Furthermore, there is up to a 25% advantage in ballistic limit for the GLARE-5/foam sandwich structures compared to straight 2024-T3 Al. But no advantage in ballistic limit was observed between any of the hybrid sandwich structures and thicker versions of GLARE-5. Recommendations for future work are provided, based on these preliminary data.

  16. Hybrid density functional study of the structural, bonding, and electronic properties of bismuth vanadate

    Science.gov (United States)

    Kweon, Kyoung E.; Hwang, Gyeong S.

    2012-10-01

    The structure and property prediction of metal oxides can significantly be improved by incorporating exact Hartree-Fock (HF) exchange into density functional theory (DFT), which is the so-called hybrid DFT. We explored the impact of HF exchange inclusion on the predicted structural, bonding, and electronic properties of bismuth vanadate (BiVO4), with particular attention to the difference between its monoclinic and tetragonal scheelite phases. The applied exchange-correlation (xc) functionals include the gradient corrected Perdew-Burke-Ernzerhof (PBE) and the PBE-HF hybrid functionals with HF exchange amounts of 10%, 25%, and 50%. We find that the PBE-HF25% yields a monoclinic structure in very close agreement with the experimentally determined structure, while the PBE-HF50% tends to overestimate the monoclinic distortion and the PBE/PBE-HF10% can hardly identify a distinct monoclinic configuration at ambient conditions. Electronic structure analysis reveals that the increasing monoclinic distortion with the amount of HF exchange is related to the enhancement of hybridization between Bi 6s-O 2p antibonding states and unoccupied Bi 6p states. The bonding mechanisms and band structures of the monoclinic and tetragonal phases of BiVO4 were also investigated, and we discuss how the predictions are sensitive to the xc functional choice.

  17. Proton Conduction in Sulfonated Organic-Inorganic Hybrid Monoliths with Hierarchical Pore Structure.

    Science.gov (United States)

    von der Lehr, Martin; Seidler, Christopher F; Taffa, Dereje H; Wark, Michael; Smarsly, Bernd M; Marschall, Roland

    2016-09-28

    Porous organic-inorganic hybrid monoliths with hierarchical porosity exhibiting macro- and mesopores are prepared via sol-gel process under variation of the mesopore size. Organic moieties in the pore walls are incorporated by substituting up to 10% of the silicon precursor tetramethylorthosilicate with bisilylated benzene molecules. After functionalization with sulfonic acid groups, the resulting sulfonated hybrid monoliths featuring a bimodal pore structure are investigated regarding proton conduction depending on temperature and relative humidity. The hierarchical pore system and controlled mesopore design turn out to be crucial for sulfonation and proton conduction. These sulfonated hybrid hierarchical monoliths containing only 10% organic precursor exhibit higher proton conduction at different relative humidities than sulfonated periodic mesoporous organosilica made of 100% bisilylated precursors exhibiting solely mesopores, even with a lower concentration of sulfonic acid groups.

  18. SYNTHESIS AND CHARACTERIZATION OF STRUCTURALLY WELL-DEFINED POLYMER-INORGANIC HYBRID NANOPARTICLES VIA ATRP

    Institute of Scientific and Technical Information of China (English)

    Jie Bai; Jie-bin Pang; Kun-yuan Qiu; Yen Wei

    2002-01-01

    Atom transfer radical polymerization (ATRP) using cuprous chloride/2,2'-bipyridine (bipy) was applied to graft polymerization of styrene on the surface of silica nanoparticles to synthesize polymer-inorganic hybrid nanoparticles. 2-(4-Chloromethylphenyl) ethyltriethoxysilane (CTES) was immobilized on the surface of silica nanoparticles through condensation reaction of the silanol groups on silica with triethoxysilane group of CTES. Then ATRP of St was initiated by this surface-modified silica nanoparticles bearing benzyl chloride groups, and formed PSt graft chains on the surface of silica nanoparticles. The thickness of the graft chains increased with reaction time. End group analysis confirmed the occurrence of ATRP. Thermal analysis indicated that thermal stabilization of these resulting hybrid nanoparticles also increases with polymerization conversion. The results above show that this "grafting from" reaction could be used for the preparation of polymer-inorganic hybrid nanoparticles with controlled structure of the polymer's end groups.

  19. First-principles study on the electronic and transport properties of periodically nitrogen-doped graphene and carbon nanotube superlattices

    Science.gov (United States)

    Xu, Fuming; Yu, Zhizhou; Gong, Zhirui; Jin, Hao

    2017-08-01

    Prompted by recent reports on √ 3 × √ 3 graphene superlattices with intrinsic inter-valley interactions, we perform first-principles calculations to investigate the electronic properties of periodically nitrogen-doped graphene and carbon nanotube nanostructures. In these structures, nitrogen atoms substitute one-sixth p of the carbon atoms in the pristine hexagonal lattices with exact periodicity to form perfect √ 3 × √ 3 superlattices of graphene and carbon nanotubes. Multiple nanostructures of √ 3 × √ 3 graphene ribbons and carbon nanotubes are explored, and all configurations show nonmagnetic and metallic behaviors. The transport properties of √ 3 × √ 3 graphene and carbon nanotube superlattices are calculated utilizing the non-equilibrium Green's function formalism combined with density functional theory. The transmission spectrum through the pristine and √ 3 × √ 3 armchair carbon nanotube heterostructure shows quantized behavior under certain circumstances.

  20. Transverse acoustic waves in piezoelectric ZnO/MgO and GaN/AlN Fibonacci-periodic superlattices

    Science.gov (United States)

    Martínez-Gutiérrez, D.; Velasco, V. R.

    2014-06-01

    This work studies the transverse acoustic waves, including the piezoelectric coupling, in Fibonacci superlattices formed by wurtzite ZnO/MgO and GaN/AlN, respectively. We examine also other superlattice structures formed by combining different kinds of Fibonacci sequences and finite periodic systems. The possibility to use different Fibonacci sequences including layers with double length of one of the constituent materials produces important modifications in the dispersion curves. The effect is more important in the lower frequency range and affects the gaps appearing in this frequency range. It is also possible to find narrow and flat bands cutting the original gaps and producing narrower ones. There are modes at different frequency ranges having spatial confinement in one of the constituent parts of the superlattice period.

  1. Electronic Structure Rearrangements in Hybrid Ribozyme/Protein Catalysis

    Science.gov (United States)

    Kang, Jiyoung; Kino, Hiori; Field, Martin J.; Tateno, Masaru

    2017-04-01

    We analyzed the electronic structural changes that occur in the reaction cycle of a biological catalyst composed of RNA and protein, and elucidated the dynamical rearrangements of the electronic structure that was obtained from our previous study in which ab initio quantum mechanics/molecular mechanics molecular dynamics simulations were performed. Notable results that we obtained include the generation of a reactive HOMO that is responsible for bond formation in the initial stages of the reaction, and the appearance of a reactive LUMO that is involved in the bond rupture that leads to products. We denote these changes as dynamical induction of the reactive HOMO (DIRH) and LUMO (DIRL), respectively. Interestingly, we also find that the induction of the reactive HOMO is enhanced by the formation of a low-barrier hydrogen bond (LBHB), which, to the best of our knowledge, represents a novel role for LBHBs in enzymatic systems.

  2. Enhanced Structural, Thermal, and Electrical Properties of Multiwalled Carbon Nanotubes Hybridized with Silver Nanoparticles

    Directory of Open Access Journals (Sweden)

    Yusliza Yusof

    2016-01-01

    Full Text Available The objective of this study is to evaluate the structural, thermal, and electrical properties of multiwalled carbon nanotubes (MWNT hybridized with silver nanoparticles (AgNP obtained via chemical reduction of aqueous silver salt assisted with sodium dodecyl sulphate (SDS as stabilizing agent. Transmission electron microscopy (TEM reveals microstructural analysis of the MWNT-Ag hybrids. The Fourier transform infrared (FTIR spectra prove the interactions between the AgNP and carboxyl groups of the MWNT. Raman spectra reveal that the D- to G-band intensity ratios ID/IG and ID′/IG increase upon the deposition of AgNP onto the surface of the MWNT. Thermogravimetric analysis (TGA shows that the MWNT-Ag hybrids decompose at a much faster rate and the weight loss decreased considerably due to the presence of AgNP. Nonlinearity of current-voltage (I-V curves indicates that electrical transport of pristine MWNT is enhanced when AgNP is induced as charge carriers in the MWNT-Ag hybrids. The threshold voltage Vth value for the MWNT doped with a maximum of 70 vol% of AgNP was substantially reduced by 65% relative to the pristine MWNT. The MWNT-Ag hybrids have a favourable electrical characteristic with a low threshold voltage that shows enhancement mode for field-effect transistor (FET applications.

  3. Structural Organization of Enzymes of the Phenylacetate Catabolic Hybrid Pathway

    OpenAIRE

    Grishin, Andrey M.; Miroslaw Cygler

    2015-01-01

    Aromatic compounds are the second most abundant class of molecules on the earth and frequent environmental pollutants. They are difficult to metabolize due to an inert chemical structure, and of all living organisms, only microbes have evolved biochemical pathways that can open an aromatic ring and catabolize thus formed organic molecules. In bacterial genomes, the phenylacetate (PA) utilization pathway is abundant and represents the central route for degradation of a variety of organic compo...

  4. A systematic study of polarized electron emission from strained GaAs/GaAsP superlattice photocathodes

    CERN Document Server

    Maruyama, T; Brachmann, A; Clendenin, J E; Garwin, E L; Harvey, S; Jiang, J; Kirby, R E; Prescott, C Y; Prepost, R; Moy, A M

    2004-01-01

    Spin-polarized electron photoemission has been studied for GaAs/GaAs$_{1-x}$P$_x$ strained superlattice cathodes grown by gas-source molecular beam epitaxy. The superlattice structural parameters are systematically varied to optimize the photoemission characteristics. The heavy-hole and light-hole transitions are reproducibly observed in quantum efficiency spectra, enabling direct measurement of the band energies and the energy splitting. Electron-spin polarization as high as 86% with over 1% quantum efficiency has been observed.

  5. Band gap engineering of ZnSnN2/ZnO (001) short-period superlattices via built-in electric field

    Science.gov (United States)

    Fang, D. Q.; Zhang, Y.; Zhang, S. L.

    2016-12-01

    Using density-functional-theory calculations combined with hybrid functional, we investigate the band gaps and built-in electric fields of ZnSnN2/ZnO (001) short-period superlattices. The band gap of ZnSnN2/ZnO (001) superlattice can be tuned from 1.9 eV to 0 eV by varying the thickness of both the ZnSnN2 and ZnO regions. Compared to the III-nitride superlattices, stronger built-in electric fields, induced by the polarizations, form inside the ZnSnN2/ZnO superlattices. The lowest electron and uppermost hole states are mainly localized at the two opposite interfaces of the superlattice, but the tails of the lowest electron states extend over several atomic layers. Based on the electrostatic argument, we demonstrate that variations of the band gap are approximately described by a geometric factor. The influence of the in-plane strain is also discussed. The results will be valuable in the design of ZnSnN2/ZnO heterostructures for electronics and optoelectronics applications.

  6. Superlattices: problems and new opportunities, nanosolids

    Directory of Open Access Journals (Sweden)

    Tsu Raphael

    2011-01-01

    Full Text Available Abstract Superlattices were introduced 40 years ago as man-made solids to enrich the class of materials for electronic and optoelectronic applications. The field metamorphosed to quantum wells and quantum dots, with ever decreasing dimensions dictated by the technological advancements in nanometer regime. In recent years, the field has gone beyond semiconductors to metals and organic solids. Superlattice is simply a way of forming a uniform continuum for whatever purpose at hand. There are problems with doping, defect-induced random switching, and I/O involving quantum dots. However, new opportunities in component-based nanostructures may lead the field of endeavor to new heights. The all important translational symmetry of solids is relaxed and local symmetry is needed in nanosolids.

  7. Screened exchange hybrid density functional for accurate and efficient structures and interaction energies.

    Science.gov (United States)

    Brandenburg, Jan Gerit; Caldeweyher, Eike; Grimme, Stefan

    2016-06-21

    We extend the recently introduced PBEh-3c global hybrid density functional [S. Grimme et al., J. Chem. Phys., 2015, 143, 054107] by a screened Fock exchange variant based on the Henderson-Janesko-Scuseria exchange hole model. While the excellent performance of the global hybrid is maintained for small covalently bound molecules, its performance for computed condensed phase mass densities is further improved. Most importantly, a speed up of 30 to 50% can be achieved and especially for small orbital energy gap cases, the method is numerically much more robust. The latter point is important for many applications, e.g., for metal-organic frameworks, organic semiconductors, or protein structures. This enables an accurate density functional based electronic structure calculation of a full DNA helix structure on a single core desktop computer which is presented as an example in addition to comprehensive benchmark results.

  8. Chlorine adlayer-templated growth of a hybrid inorganic-organic layered structure on Au(111)

    Science.gov (United States)

    Rzeźnicka, I. I.; Horino, H.; Yagyu, K.; Suzuki, T.; Kajimoto, S.; Fukumura, H.

    2016-10-01

    Growth of a hybrid inorganic-organic layered structure on the Au(111) surface using a one-step solution growth is reported. The hybrid structure is consist of 4,4‧-bipyridine [4,4‧-BiPyH2]2 + cations, Cl anions and Au adatoms, provided from substrate by means of the adsorbate-induced surface phase transition of a surface reconstruction. Its surface and bulk structures were characterized by scanning tunneling microscopy (STM), secondary ion mass spectrometry (SIMS), and Raman spectroscopy. STM results reveal growth of the first [4,4‧-BiPyH2]2 + layer on top of the p(√{ 3} ×√{ 3})" separators=", R 30 ° chlorine overlayer formed on the Au(111) surface. These two layers are found to provide a platform for a following three-dimensional growth facilitated by hydrogen bonding, aurophilic and π-π stacking interactions.

  9. Quasi-Static Single-Component Hybrid Simulation of a Composite Structure with Multi-Axis Control

    DEFF Research Database (Denmark)

    Høgh, J.; Waldbjørn, J.; Wittrup-Schmidt, J.

    2015-01-01

    This paper presents a quasi-static hybrid simulation performed on a single component structure. Hybrid simulation is a substructural technique, where a structure is divided into two sections: a numerical section of the main structure and a physical experiment of the remainder. In previous cases...... to evaluate the validity of the method, the results are compared to a test of the emulated structure – referred to here as the reference test. It was found that the error introduced by compliance in the load train was significant. Digital image correlation was for this reason implemented in the hybrid...

  10. Hybrid Direct Write Lithographic Strategies for Complex Hierarchical Structures

    Science.gov (United States)

    Singer, Jonathan P.

    With the number of alternative lithographic techniques for high resolution and 3D patterning rapidly increasing, there is a need to identify a set of scalable techniques which balances the ability to arbitrarily control every detail of a target pattern and to produce these complex patterns at a high rate. It is in this way that metamaterial devices put forward on a lab scale for applications such as phononics, photonics, and plasmonics can be realized in the industrial scale. This thesis, in approaching this challenge, utilizes combinations of patterning techniques, leveraging the ability for "large" scale alternative lithographic techniques, such as interference lithography or self-assembly, to create the same nanostructured morphology over a large area combined with laser direct write. The process of drawing a single line or isolated voxel can result in a hierarchical pattern defined by the latent motif of the larger-scale technique. The net resuh is to shift the burden of high resolution patterning from the direct write to the large scale technique, effectively decoupling the correlation between the level of detail and the patterning speed and control. More specifically, the following combinations with laser direct writing were investigated: (1) proximity field nanopatterning for the predefinition of diffraction-order-defined 3D resonators which were applied as "stand-up" plasmodic microresonators, (2) dewetting to conduct development-free 2D patterning of isolated sub-micron lines, and, via overlap effects, nanoscale ( <1 00 nm) gratings, (3) block copolymer self-assembly to initiate the simultaneous annealing and alignment of near-equilibrium microdomains from a metastable starting morphology, and (4) interference lithography to fabricate 3D sub-micron periodic and quasiperiodic hierarchical structures with controllable positioning and tunable fill fraction that has potential for applications to microphotonics. In conjunction with the experimental components

  11. Dynamic Behavior of Hybrid APM (Advanced Pore Morphology Foam and Aluminum Foam Filled Structures

    Directory of Open Access Journals (Sweden)

    Joerg Weise

    2012-06-01

    Full Text Available The aim of this work is to evaluate the effect of different densities of hybrid aluminum polymer foam on the frequency behavior of a foam filled steel structure with different ratios between steel and foam masses. The foam filled structure is composed of three steel tubes with a welded flange at both ends bolted together to form a portal grounded by its free ends. Structure, internal and ground constraints have been designed and manufactured in order to minimize nonlinear effects and to guarantee optimal constraint conditions. Mode shapes and frequencies were verified with finite elements models (FEM to be in the range of experimental modal analysis, considering the frequency measurement range limits for instrumented hammer and accelerometer. Selected modes have been identified with suitable modal parameters extraction techniques. Each structure has been tested before and after filling, in order to compute the percentage variation of modal parameters. Two different densities of hybrid aluminum polymer foam have been tested and compared with structures filled with aluminum foams produced using the powder compact melting technique. All the foam fillings were able to suppress high frequency membrane modes which results in a reduction of environmental noise and an increase in performance of the components. Low frequency modes show an increase in damping ratio only when small thickness steel frames are filled with either Hybrid APM or Alulight foam.

  12. Anisotropic temperature-dependent thermal conductivity by an Al2O3 interlayer in Al2O3/ZnO superlattice films

    Science.gov (United States)

    Lee, Won-Yong; Lee, Jung-Hoon; Ahn, Jae-Young; Park, Tae-Hyun; Park, No-Won; Kim, Gil-Sung; Park, Jin-Seong; Lee, Sang-Kwon

    2017-03-01

    The thermal conductivity of superlattice films is generally anisotropic and should be studied separately in the in-plane and cross-plane directions of the films. However, previous works have mostly focused on the cross-plane thermal conductivity because the electrons and phonons in the cross-plane direction of superlattice films may result in much stronger interface scattering than that in the in-plane direction. Nevertheless, it is highly desirable to perform systematic studies on the effect of interface formation in semiconducting superlattice films on both in-plane and cross-plane thermal conductivities. In this study, we determine both the in-plane and cross-plane thermal conductivities of Al2O3 (AO)/ZnO superlattice films grown by atomic layer deposition (ALD) on SiO2/Si substrates in the temperature range of 50–300 K by the four-point-probe 3-ω method. Our experimental results indicate that the formation of an atomic AO layer (0.82 nm) significantly contributes to the decrease of the cross-plane thermal conductivity of the AO/ZnO superlattice films compared with that of AO/ZnO thin films. The cross-plane thermal conductivity (0.26–0.63 W m‑1 K‑1 of the AO/ZnO superlattice films (with an AO layer of ∼0.82 nm thickness) is approximately ∼150%–370% less than the in-plane thermal conductivity (0.96–1.19 W m‑1 K‑1) of the corresponding film, implying significant anisotropy. This indicates that the suppression of the cross-plane thermal conductivity is mainly attributed to the superlattice, rather than the nanograin columnar structure in the films. In addition, we theoretically analyzed strong anisotropic behavior of the in-plane and cross-plane thermal conductivities of the AO/ZnO superlattice films in terms of temperature dependence.

  13. Thermoelectric properties of IV–VI-based heterostructures and superlattices

    Energy Technology Data Exchange (ETDEWEB)

    Borges, P.D., E-mail: pabloborges@ufv.br [Instituto de Ciências Exatas e Tec., Universidade Federal de Viçosa, Rio Paranaíba, MG (Brazil); Department of Physics, Texas State University, San Marcos, TX 78666 (United States); Petersen, J.E.; Scolfaro, L. [Department of Physics, Texas State University, San Marcos, TX 78666 (United States); Leite Alves, H.W. [Departamento de Ciências Naturais, Universidade Federal de São João Del Rei, Caixa Postal 110, São João Del Rei 36300-000, MG (Brazil); Myers, T.H. [Department of Physics, Texas State University, San Marcos, TX 78666 (United States)

    2015-07-15

    Doping in a manner that introduces anisotropy in order to reduce thermal conductivity is a significant focus in thermoelectric research today. By solving the semiclassical Boltzmann transport equations in the constant scattering time (τ) approximation, in conjunction with ab initio electronic structure calculations, within Density Functional Theory, we compare the Seebeck coefficient (S) and figure of merit (ZT) of bulk PbTe to PbTe/SnTe/PbTe heterostructures and PbTe doping superlattices (SLs) with periodically doped planes. Bismuth and Thallium were used as the n- and p-type impurities, respectively. The effects of carrier concentration are considered via chemical potential variation in a rigid band approximation. The impurity bands near the Fermi level in the electronic structure of PbTe SLs are of Tl s- and Bi p-character, and this feature is independent of the doping concentration or the distance between impurity planes. We observe the impurity bands to have a metallic nature in the directions perpendicular to the doping planes, yet no improvement on the values of ZT is found when compared to bulk PbTe. For the PbTe/SnTe/PbTe heterostructures, the calculated S presents good agreement with recent experimental data, and an anisotropic behavior is observed for low carrier concentrations (n<10{sup 18} cm{sup −3}). A large value of ZT{sub ||} (parallel to the growth direction) of 3.0 is predicted for n=4.7×10{sup 18} cm{sup −3} and T=700 K, whereas ZT{sub p} (perpendicular to the growth direction) is found to peak at 1.5 for n=1.7×10{sup 17} cm{sup −3}. Both electrical conductivity enhancement and thermal conductivity reduction are analyzed. - Graphical abstract: Figure of merit for PbTe/SnTe/PbTe heterostructure along the [0 0 1] direction, P.D. Borges, J.E. Petersen, L. Scolfaro, H.W. Leite Alves, T.H. Myers, Improved thermoelectric properties of IV–VI-based heterostructures and superlattices. - Highlights: • Thermoelectric properties of IV

  14. Magnetic anisotropy of [Co{sub 2}MnSi/Pd]{sub n} superlattice films prepared on MgO(001), (110), and (111) substrates

    Energy Technology Data Exchange (ETDEWEB)

    Matsushita, Naoki; Takamura, Yota; Fujino, Yorinobu; Nakagawa, Shigeki, E-mail: nakagawa@pe.titech.ac.jp [Department of Physical Electronics, Tokyo Institute of Technology, 2-12-1 Ookayama, Meguro-ku, Tokyo 152-8552 (Japan); Sonobe, Yoshiaki [Samsung R and D Institute Japan-Yokohama, 2-7, Sugasawa-cho, Tsurumi-ku, Yokohama-shi, Kanagawa-ken 230-0027 (Japan)

    2015-02-09

    Superlattice films with full-Heusler Co{sub 2}MnSi (CMS) alloy and Pd layers prepared on Pd-buffered MgO(001), (110), and (111) substrates were investigated. Crystal orientation and epitaxial relationship of Pd and CMS layers were analyzed from x-ray diffraction, pole figure measurements, and transmission electron microscope observation. Formation of the L2{sub 1}-ordered structure in the CMS layers was confirmed by observation of CMS(111) diffraction. Perpendicular magnetic anisotropy (PMA) was obtained in the [CMS (0.6 nm)/Pd (2 nm)]{sub 6} superlattice film formed using MgO(111) substrates although other superlattice films prepared using MgO(001) and (110) substrates showed in-plane and isotropic magnetic anisotropy, respectively. The perpendicular magnetic anisotropy energy constant K for the superlattice films prepared using MgO(111) substrate was estimated to be 2.3 Mergs/cm{sup 3}, and an interfacial anisotropy constant K{sub i} per one CMS-Pd interface in the superlattice films was estimated to be 0.16 ergs/cm{sup 2}. K{sub i} in superlattice films with various crystal orientations showed positive values, indicating that Pd/CMS interfaces had an ability to induce PMA regardless of their crystal orientation.

  15. Magnetic anisotropy of [Co2MnSi/Pd]n superlattice films prepared on MgO(001), (110), and (111) substrates

    Science.gov (United States)

    Matsushita, Naoki; Takamura, Yota; Fujino, Yorinobu; Sonobe, Yoshiaki; Nakagawa, Shigeki

    2015-02-01

    Superlattice films with full-Heusler Co2MnSi (CMS) alloy and Pd layers prepared on Pd-buffered MgO(001), (110), and (111) substrates were investigated. Crystal orientation and epitaxial relationship of Pd and CMS layers were analyzed from x-ray diffraction, pole figure measurements, and transmission electron microscope observation. Formation of the L21-ordered structure in the CMS layers was confirmed by observation of CMS(111) diffraction. Perpendicular magnetic anisotropy (PMA) was obtained in the [CMS (0.6 nm)/Pd (2 nm)]6 superlattice film formed using MgO(111) substrates although other superlattice films prepared using MgO(001) and (110) substrates showed in-plane and isotropic magnetic anisotropy, respectively. The perpendicular magnetic anisotropy energy constant K for the superlattice films prepared using MgO(111) substrate was estimated to be 2.3 Mergs/cm3, and an interfacial anisotropy constant Ki per one CMS-Pd interface in the superlattice films was estimated to be 0.16 ergs/cm2. Ki in superlattice films with various crystal orientations showed positive values, indicating that Pd/CMS interfaces had an ability to induce PMA regardless of their crystal orientation.

  16. Hierarchical structuring of liquid crystal polymer-Laponite hybrid materials.

    Science.gov (United States)

    Tritschler, Ulrich; Zlotnikov, Igor; Zaslansky, Paul; Aichmayer, Barbara; Fratzl, Peter; Schlaad, Helmut; Cölfen, Helmut

    2013-09-03

    Biomimetic organic-inorganic composite materials were fabricated via one-step self-organization on three hierarchical levels. The organic component was a polyoxazoline with pendent cholesteryl and carboxyl (N-Boc-protected amino acid) side chains that was able to form a chiral nematic lyotropic phase and bind to positively charged inorganic faces of Laponite. The Laponite particles formed a mesocrystalline arrangement within the liquid-crystal (LC) polymer phase upon shearing a viscous dispersion of Laponite nanoparticles and LC polymer in DMF. Complementary analytical and mechanical characterization techniques (AUC, POM, TEM, SEM, SAXS, μCT, and nanoindentation) covering the millimeter, micrometer, and nanometer length scales reveal the hierarchical structures and properties of the composite materials consisting of different ratios of Laponite nanoparticles and liquid-crystalline polymer.

  17. Subgap transport in silicene-based superconducting hybrid structures

    Science.gov (United States)

    Li, Hai

    2016-08-01

    We investigate the influences of exchange field and perpendicular electric field on the subgap transport in silicene-based ferromagnetic/superconducting (FS) and ferromagnetic/superconducting/ferromagnetic (FSF) junctions. Owing to the unique buckling structure of silicene, the Andreev reflection and subgap conductance can be effectively modulated by a perpendicular electric field. It is revealed that the subgap conductance in the FS junction can be distinctly enhanced by an exchange field. Remarkably, resorting to the tunable band gap of silicene, an exclusive crossed Andreev reflection (CAR) process in the FSF junction can be realized within a wide range of related parameters. Moreover, in the FSF junction the exclusive CAR and exclusive elastic cotunneling processes can be switched by reversing the magnetization direction in one of the ferromagnetic regions.

  18. Effective negative refractive index in ferromagnet-semiconductor superlattices.

    Science.gov (United States)

    Tarkanyan, Roland H; Niarchos, Dimitris G

    2006-06-12

    Problem of anomalous refraction of electromagnetic waves is analyzed in a superlattice which consists of alternating layers of ferromagnetic insulator and nonmagnetic semiconductor. Effective permittivity and permeability tensors are derived in the presence of an external magnetic field parallel to the plane of the layers. It is shown that in the case of the Voigt configuration, the structure behaves as a left-handed medium with respect to TE-type polarized wave, in the low-frequency region of propagation. The relative orientation of the Poynting vector and the refractive wave vector is examined in different frequency ranges. It is shown that the frequency region of existence for the backward mode can be changed using external magnetic field as tuning parameter.

  19. Tunable anisotropic superfluidity in an optical kagome superlattice

    Science.gov (United States)

    Zhang, Xue-Feng; Wang, Tao; Eggert, Sebastian; Pelster, Axel

    2015-07-01

    We study the phase diagram of the Bose-Hubbard model on the kagome lattice with a broken sublattice symmetry. Such a superlattice structure can naturally be created and tuned by changing the potential offset of one sublattice in the optical generation of the frustrated lattice. The superstructure gives rise to a rich quantum phase diagram, which is analyzed by combining quantum Monte Carlo simulations with the generalized effective potential Landau theory. Mott phases with noninteger filling and a characteristic order along stripes are found, which show a transition to a superfluid phase with an anisotropic superfluid density. Surprisingly, the direction of the superfluid anisotropy can be tuned by changing the particle number, the hopping strength, or the interaction. Finally, we discuss characteristic signatures of anisotropic phases in time-of-flight absorption measurements.

  20. Transport properties of graphene under periodic and quasiperiodic magnetic superlattices

    Energy Technology Data Exchange (ETDEWEB)

    Lu, Wei-Tao, E-mail: luweitao@lyu.edu.cn [School of Science, Linyi University, 276005 Linyi (China); Institute of Condensed Matter Physics, Linyi University, 276005 Linyi (China); Wang, Shun-Jin [Department of Physics, Sichuan University, 610064 Chengdu (China); Wang, Yong-Long; Jiang, Hua [School of Science, Linyi University, 276005 Linyi (China); Institute of Condensed Matter Physics, Linyi University, 276005 Linyi (China); Li, Wen [School of Science, Linyi University, 276005 Linyi (China)

    2013-08-15

    We study the transmission of Dirac electrons through the one-dimensional periodic, Fibonacci, and Thue–Morse magnetic superlattices (MS), which can be realized by two different magnetic blocks arranged in certain sequences in graphene. The numerical results show that the transmission as a function of incident energy presents regular resonance splitting effect in periodic MS due to the split energy spectrum. For the quasiperiodic MS with more layers, they exhibit rich transmission patterns. In particular, the transmission in Fibonacci MS presents scaling property and fragmented behavior with self-similarity, while the transmission in Thue–Morse MS presents more perfect resonant peaks which are related to the completely transparent states. Furthermore, these interesting properties are robust against the profile of MS, but dependent on the magnetic structure parameters and the transverse wave vector.

  1. Influence of impurity on electronic properties of carbon nanotube superlattices

    Directory of Open Access Journals (Sweden)

    AA Shokri

    2013-09-01

    Full Text Available   In this paper, electronic properties of single-wall armchair and zigzag carbon nanotubes (CNTs superlattices, n(12,0/m(6,6 and n(12,0/m(11,0 are investigated. For this reason, the topological defects of pentagon–heptagon pairs at interfaces of carbon hexagonal network appear. These defects break the symmetry of the system, and then change the electrical properties. The calculations include two parts: investigation of the structures in the absence and presence of the impurity effect, which are calculated by the nearest-neighbor tight binding model . Out numerical results can be useful in designing nanoelectronic devices based on carbon nanotubes.

  2. Titanium-based silicide quantum dot superlattices for thermoelectrics applications.

    Science.gov (United States)

    Savelli, Guillaume; Stein, Sergio Silveira; Bernard-Granger, Guillaume; Faucherand, Pascal; Montès, Laurent; Dilhaire, Stefan; Pernot, Gilles

    2015-07-10

    Ti-based silicide quantum dot superlattices (QDSLs) are grown by reduced-pressure chemical vapor deposition. They are made of titanium-based silicide nanodots scattered in an n-doped SiGe matrix. This is the first time that such nanostructured materials have been grown in both monocrystalline and polycrystalline QDSLs. We studied their crystallographic structures and chemical properties, as well as the size and the density of the quantum dots. The thermoelectric properties of the QDSLs are measured and compared to equivalent SiGe thin films to evaluate the influence of the nanodots. Our studies revealed an increase in their thermoelectric properties-specifically, up to a trifold increase in the power factor, with a decrease in the thermal conductivity-making them very good candidates for further thermoelectric applications in cooling or energy-harvesting fields.

  3. Domain-dependent electronic structure and optical absorption property in hybrid organic-inorganic perovskite.

    Science.gov (United States)

    Meng, Xiang; Zhang, Ruifeng; Fu, Zhongheng; Zhang, Qianfan

    2016-10-05

    Hybrid organic-inorganic perovskites, represented by materials in the CH3NH3PbI3 series, have become one of the most promising materials for solar cells with a high power conversion efficiency and low cost. The ordered Pb-I cage in such hybrid perovskites can induce the polarized cations to form a variety of polarization domains with long-range order, which will lead to the formation of specific atomic conformations or metastable crystalline phases, unique electronic band structures and optical absorption properties. Such domain-dependent characteristics play a critical role in the phase transition and service stability of such solar cells, and also open up the opportunity of tuning their electronic structure. In the present study, we systematically investigate the band structures and optical absorption properties of different electronically ordered domains in CH3NH3PbI3. By comparing different perovskites containing various cations, we have clarified the important influence of cation polarization on domain-dependent properties. Our results provide not only a possible pathway for the manipulation of band structure by applying an external field, but also a novel scheme for improving the performance and stability of hybrid perovskites.

  4. Carbon and metal nanotube hybrid structures on graphene as efficient electron field emitters

    Science.gov (United States)

    Heo, Kwang; Lee, Byung Yang; Lee, Hyungwoo; Cho, Dong-guk; Arif, Muhammad; Kim, Kyu Young; Choi, Young Jin; Hong, Seunghun

    2016-07-01

    We report a facile and efficient method for the fabrication of highly-flexible field emission devices by forming tubular hybrid structures based on carbon nanotubes (CNTs) and nickel nanotubes (Ni NTs) on graphene-based flexible substrates. By employing an infiltration process in anodic alumina oxide (AAO) templates followed by Ni electrodeposition, we could fabricate CNT-wrapped Ni NT/graphene hybrid structures. During the electrodeposition process, the CNTs served as Ni nucleation sites, resulting in a large-area array of high aspect-ratio field emitters composed of CNT-wrapped Ni NT hybrid structures. As a proof of concepts, we demonstrate that high-quality flexible field emission devices can be simply fabricated using our method. Remarkably, our proto-type field emission devices exhibited a current density higher by two orders of magnitude compared to other devices fabricated by previous methods, while maintaining its structural integrity in various bending deformations. This novel fabrication strategy can be utilized in various applications such as optoelectronic devices, sensors and energy storage devices.

  5. Genetic Segregation and Genomic Hybridization Patterns Support an Allotetraploid Structure and Disomic Inheritance for Salix Species

    Directory of Open Access Journals (Sweden)

    Gianni Barcaccia

    2014-09-01

    Full Text Available The Salix alba L. (white willow—Salix fragilis L. (crack willow complex includes closely related polyploid species, mainly tetraploid (2n = 4x = 76, which are dioecious and hence obligate allogamous. Because little is known about the genome constitution and chromosome behavior of these pure willow trees, genetic analysis of their naturally occurring interspecific polyploid hybrids is still very difficult. A two-way pseudo-testcross strategy was exploited using single-dose AFLP markers in order to assess the main inheritance patterns of tetraploid biotypes (disomy vs. tetrasomy in segregating populations stemmed from S. alba × S. fragilis crosses and reciprocals. In addition, a genomic in situ hybridization (GISH technology was implemented in willow to shed some light on the genome structure of S. alba and S. fragilis species, and their hybrids (allopolyploidy vs. autopolyploidy. The frequency of S. alba-specific molecular markers was almost double compared to that of S. fragilis-specific ones, suggesting the phylogenetic hypothesis of S. fragilis as derivative species from S. alba-like progenitors. Cytogenetic observations at pro-metaphase revealed about half of the chromosome complements being less contracted than the remaining ones, supporting an allopolyploid origin of both S. alba and S. fragilis. Both genetic segregation and genomic hybridization data are consistent with an allotetraploid nature of the Salix species. In particular, the vast majority of the AFLP markers were inherited according to disomic patterns in S. alba × S. fragilis populations and reciprocals. Moreover, in all S. alba against S. fragilis hybridizations and reciprocals, GISH signals were observed only on the contracted chromosomes whereas the non-contracted chromosomes were never hybridized. In conclusion, half of the chromosomes of the pure species S. alba and S. fragilis are closely related and they could share a common diploid ancestor, while the rest of

  6. Glassy Carbon Coating Deposited on Hybrid Structure of Composite Materials

    Directory of Open Access Journals (Sweden)

    Posmyk A.

    2016-06-01

    Full Text Available This paper presents a method of production metal matrix composites with aluminum oxide foam covered by glassy carbon layer used as reinforcement. The glassy carbon coating was formed for decreasing of friction coefficient and reducing the wear. In first step of technology liquid glassy carbon precursor is on ceramic foam deposited, subsequently cured and carbonated at elevated temperature. In this way ceramic foam is covered with glassy carbon coating with thickness of 2-8 μm. It provides desirable amount of glassy carbon in the structure of the material. In the next step, porous spheres with carbon coating are infiltrated by liquid matrix of Al-Cu-Mg alloy. Thereby, equable distribution of glassy carbon in composite volume is achieved. Moreover, typical problems for composites reinforced by particles like sedimentation, agglomeration and clustering of particles are avoided. Tribological characteristics during friction in air versus cast iron as a counterpart were made. Produced composites with glassy carbon layer are characterised by friction coefficient between 0.08-0.20, thus meeting the typical conditions for solid lubricants.

  7. sp3-hybridized framework structure of group-14 elements discovered by genetic algorithm

    Energy Technology Data Exchange (ETDEWEB)

    Nguyen, Manh Cuong [Ames Laboratory; Zhao, Xin [Ames Laboratory; Wang, Cai-Zhuang [Ames Laboratory; Ho, Kai-Ming [Ames Laboratory

    2014-05-01

    Group-14 elements, including C, Si, Ge, and Sn, can form various stable and metastable structures. Finding new metastable structures of group-14 elements with desirable physical properties for new technological applications has attracted a lot of interest. Using a genetic algorithm, we discovered a new low-energy metastable distorted sp3-hybridized framework structure of the group-14 elements. It has P42/mnm symmetry with 12 atoms per unit cell. The void volume of this structure is as large as 139.7Å3 for Si P42/mnm, and it can be used for gas or metal-atom encapsulation. Band-structure calculations show that P42/mnm structures of Si and Ge are semiconducting with energy band gaps close to the optimal values for optoelectronic or photovoltaic applications. With metal-atom encapsulation, the P42/mnm structure would also be a candidate for rattling-mediated superconducting or used as thermoelectric materials.

  8. Hydrostatic pressure and strain effects in short period InN/GaN superlattices

    DEFF Research Database (Denmark)

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

    2012-01-01

    The electronic structures of short-period pseudomorphically grown superlattices (SLs) of the form mInN/nGaN are calculated and the band gap variation with the well and the barrier thicknesses is discussed including hydrostatic pressure effects. The calculated band gap shows a strong dependence on...... strongly on the strain conditions and SL geometry, but weakly on the applied external hydrostatic pressure....

  9. Monolithic Integration of a DFB Superlattice Laser Using High Energy Ion Implantation

    Science.gov (United States)

    1991-02-13

    Considerations Relative to DFB/DBR Laser Fabrication .... 46 4.0 Materials Evaluation of Multi-Quantum Well/Superlattice Samples Fabricated by Molecular Beam...important to consider the disordering that can occur during annealing and its effects on device performance. 3.7 CONSIDERATIONS RELATIVE TO DFB/DBR LASER ... FABRICATION The structure examined in ts work is to be incorporated in a distributed feedback type laser. The resolution of the selective ion beam

  10. Wave-function reconstruction in a graded semiconductor superlattice

    DEFF Research Database (Denmark)

    Lyssenko, V. G.; Hvam, Jørn Märcher; Meinhold, D.

    2004-01-01

    We reconstruct a test wave function in a strongly coupled, graded well-width superlattice by resolving the spatial extension of the interband polarisation and deducing the wave function employing non-linear optical spectroscopy. The graded gap superlattice allows us to precisely control the dista...

  11. Hybrid Aluminum and Natural Fiber Composite Structure for Crash Safety Improvement

    Science.gov (United States)

    Helaili, S.; Chafra, M.; Chevalier, Y.

    There is a growing interest on pedestrian's protection in automotive safety standards. Pedestrians head impact is one of the most important tests. In this paper, a hybrid composite structure made from natural fiber and aluminum, which improve the head protection when impact is taken place, is presented. The structure is made from a honeycomb composite made from unidirectional and woven composites and a thin aluminum layer. A head impact model is developed. The number of hexagonal layers is fixed and the thickness of the aluminum layer of the honeycomb structure is varied. The specific absorption energy is then calculated.

  12. Development of Control Structure for Hybrid Wind Generators with Active Power Capability

    Directory of Open Access Journals (Sweden)

    Mehdi Niroomand

    2014-01-01

    Full Text Available A hierarchical control structure is proposed for hybrid energy systems (HES which consist of wind energy system (WES and energy storage system (ESS. The proposed multilevel control structure consists of four blocks: reference generation and mode select, power balancing, control algorithms, and switching control blocks. A high performance power management strategy is used for the system. Also, the proposed system is analyzed as an active power filter (APF with ability to control the voltage, to compensate the harmonics, and to deliver active power. The HES is designed with parallel DC coupled structure. Simulation results are shown for verification of the theoretical analysis.

  13. A computer simulation investigation into the stability of the AB2 superlattice in a binary hard sphere system

    NARCIS (Netherlands)

    Eldridge, M.D.; Madden, P.A.; Frenkel, D.

    1993-01-01

    The thermodynamic stability of the binary hard-sphere AB2 superlattice structure has been confirmed by means of computer simulations. This is consistent with the results of experimental studies of suspensions of hard-sphere colloidal particles. A fit of the Helmholtz free energy surface for the regi

  14. A hybrid analysis method for linear dynamic soil-structure interaction in time and frequency domain

    Institute of Scientific and Technical Information of China (English)

    丁海平; 廖振鹏

    2001-01-01

    A hybrid analysis method in time and frequency domains for linear soil-structure interaction is presented. First, the time domain solution of the system with Rayleigh damping excited by a short time impulse is obtained by the decoupling numerical simulation technique of near-field wave motion. Then, the corresponding frequency domain solution can be got by Fourier transform. According to the relationship between damping value and dynamic re-sponse of a system, the solution of the system with complex damping can be got by Taylor expansion. The hybrid method makes the best of decoupling and explicit algorithm in time domain, and increases the calculation efficien-cy for linear soil-structure interaction analysis.

  15. Tensile force identification in cable-stayed structures: Hybrid system identification algorithm and experimental verification

    Energy Technology Data Exchange (ETDEWEB)

    Noh, Myung Hyun [POSCO, Incheon (Korea, Republic of); Hu, Jong Wan [Incheon National University, Incheon (Korea, Republic of)

    2014-11-15

    In this study, we investigate a method to detect tensile forces in cable-stayed structures using the combined sensitivity updating method and the advanced hybrid microgenetic algorithm. The proposed method allows us not only to avoid the trap of minimum at initial searching stage but also to find their final solutions in better numerical efficiency. The validity of the technique is numerically verified using a set of dynamic data obtained from a simulation of the cable model modeled using the finite element method. Then, the hybrid algorithm is applied to vibrating sagged cables in the laboratory scale test. The results obtained are in good agreement with the semi-analytical solutions and experimental results reported by other investigators. The results indicate that the new method is computationally efficient in characterizing the tensile force variation for cable-stayed structures.

  16. Manipulating hybrid structures of polymer/a-Si for thin film solar cells

    Science.gov (United States)

    Peng, Ying; He, Zhiqun; Diyaf, Adel; Ivaturi, Aruna; Zhang, Zhi; Liang, Chunjun; Wilson, John I. B.

    2014-03-01

    A series of uniform polymer/amorphous silicon hybrid structures have been fabricated by means of solution-casting for polymer and radio frequency excited plasma enhanced chemical vapour deposition for amorphous silicon (a-Si:H). Poly(3,4-ethylene dioxythiophene):poly(styrene sulfonate) (PEDOT:PSS) functioned as a photoactive donor, while the silicon layer acted as an acceptor. It is found that matching the hole mobility of the polymer to the electron mobility of amorphous silicon is critical to improve the photovoltaic performance from hybrid cells. A three-layer p-i-n structure of ITO/PEDOT:PSS(200 nm)/i-Si(450 nm)/n-Si(200 nm)/Al with a power conversion efficiency of 4.78% under a standard test condition was achieved.

  17. Manipulating hybrid structures of polymer/a-Si for thin film solar cells

    Energy Technology Data Exchange (ETDEWEB)

    Peng, Ying; He, Zhiqun, E-mail: zhqhe@bjtu.edu.cn, E-mail: J.I.B.Wilson@hw.ac.uk; Zhang, Zhi; Liang, Chunjun [Key Laboratory of Luminescence and Optical Information, Ministry of Education, Institute of Optoelectronic Technology, Beijing Jiaotong University, Beijing 100044 (China); Diyaf, Adel; Ivaturi, Aruna; Wilson, John I. B., E-mail: zhqhe@bjtu.edu.cn, E-mail: J.I.B.Wilson@hw.ac.uk [SUPA, School of Engineering and Physical Sciences, Heriot-Watt University, Edinburgh EH14 4AS (United Kingdom)

    2014-03-10

    A series of uniform polymer/amorphous silicon hybrid structures have been fabricated by means of solution-casting for polymer and radio frequency excited plasma enhanced chemical vapour deposition for amorphous silicon (a-Si:H). Poly(3,4-ethylene dioxythiophene):poly(styrene sulfonate) (PEDOT:PSS) functioned as a photoactive donor, while the silicon layer acted as an acceptor. It is found that matching the hole mobility of the polymer to the electron mobility of amorphous silicon is critical to improve the photovoltaic performance from hybrid cells. A three-layer p-i-n structure of ITO/PEDOT:PSS(200 nm)/i-Si(450 nm)/n-Si(200 nm)/Al with a power conversion efficiency of 4.78% under a standard test condition was achieved.

  18. Effect of Different Structural Materials on Neutronic Performance of a Hybrid Reactor

    Science.gov (United States)

    Übeyli, Mustafa; Tel, Eyyüp

    2003-06-01

    Selection of structural material for a fusion-fission (hybrid) reactor is very important by taking into account of neutronic performance of the blanket. Refractory metals and alloys have much higher operating temperatures and neutron wall load (NWL) capabilities than low activation materials (ferritic/martensitic steels, vanadium alloys and SiC/SiC composites) and austenitic stainless steels. In this study, effect of primary candidate refractory alloys, namely, W-5Re, T111, TZM and Nb-1Zr on neutronic performance of the hybrid reactor was investigated. Neutron transport calculations were conducted with the help of SCALE 4.3 System by solving the Boltzmann transport equation with code XSDRNPM. Among the investigated structural materials, tantalum had the worst performance due to the fact that it has higher neutron absorption cross section than others. And W-5Re and TZM having similar results showed the best performance.

  19. Controlling Torque Distribution for Parallel Hybrid Vehicle Based on Hierarchical Structure Fuzzy Logic

    Institute of Scientific and Technical Information of China (English)

    HuangMiao-hua; JinGuo-dong

    2003-01-01

    The Hierarchical Structure Fuzzy Logic Control(HSFLC) strategies of torque distribute for Parallel Hybrid Electric Vehicle (PHEV) in the mocle of operation of the vehicle i. e. , acceleration, cruise, deceleration etc. have been studied. Using secondly developed the hybrid vehicle simulation tool ADVISOR, the dynamic model of PHEV has been set up by MATLAB/SIMULINK. The engine, motor as well as the battery characteristics have been studied. Simulation results show that the proposed hierarchical structured fuzzy logic control strategy is effective over the entire operating range of the vehicle in terms of fuel economy. Based on the analyses of the simulation results and driver's experiences, a fuzzy controller is designed and developed to control the torque distribution. The controller is evaluated via hardware-in-the-loop simulator (HILS). The results show that controller verify its value.

  20. Research Update: The electronic structure of hybrid perovskite layers and their energetic alignment in devices

    Directory of Open Access Journals (Sweden)

    Selina Olthof

    2016-09-01

    Full Text Available In recent years, the interest in hybrid organic–inorganic perovskites has increased at a rapid pace due to their tremendous success in the field of thin film solar cells. This area closely ties together fundamental solid state research and device application, as it is necessary to understand the basic material properties to optimize the performances and open up new areas of application. In this regard, the energy levels and their respective alignment with adjacent charge transport layers play a crucial role. Currently, we are lacking a detailed understanding about the electronic structure and are struggling to understand what influences the alignment, how it varies, or how it can be intentionally modified. This research update aims at giving an overview over recent results regarding measurements of the electronic structure of hybrid perovskites using photoelectron spectroscopy to summarize the present status.

  1. Two-dimensional Confinement of Heavy Fermions in Artificial Superlattices

    Science.gov (United States)

    Shishido, Hiroaki

    2011-03-01

    Low dimensionality and strong electron-electron Coulomb interactions are both key parameters for novel quantum states of condensed matter. A metallic system with the strongest electron correlations is reported in rare-earth and actinide compounds with f electrons, known as heavy-fermion compounds, where the effective mass of the conduction electrons are strikingly enhanced by the electron correlations up to some hundreds times the free electron mass. To date the electronic structure of all heavy-fermion compounds is essentially three-dimensional. We realized experimentally a two-dimensional heavy fermion system, adjusting the dimensionality in a controllable fashion. We grew artificial superlattices of CeIn 3 (m)/ LaIn 3 (n), in which m -layers of heavy-fermion antiferromagnet CeIn 3 and n -layers of a non-magnetic isostructual compound LaIn 3 are stacked alternately, by a molecular beam epitaxy. By reducing the thickness of the CeIn 3 layers, the magnetic order was suppressed and the effective electron mass was further enhanced. The Néel temperature becomes zero at around m = 2 , concomitant with striking deviations from the standard Fermi liquid low-temperature electronic properties. Standard Fermi liquid behaviors are, however, recovered under high magnetic field. These behaviors imply new ``dimensional tuning'' towards a quantum critical point. We also succeeded to fabricate artificial superlattices of a heavy fermion superconductor CeCoIn 5 and non-magnetic divalent Yb-compound YbCoIn 5 . Superconductivity survives even in CeCoIn 5 (3)/ YbCoIn 5 (5) films, while the thickness of CeCoIn 5 layer, 2.3 nm, is comparable to the c -axis coherence length ξc ~ 2 nm. This work has been done in collaboration with Y. Mizukami, S. Yasumoto, M. Shimozawa, H. Kontani, T. Shibauchi, T. Terashima and Y. Matsuda.superconductivity is realized in the artificial superlattices. This work has been done in collaboration with Y. Mizukami, S. Yasumoto, M. Shimozawa, H. Kontani, T

  2. Multi-locus estimates of population structure and migration in a fence lizard hybrid zone.

    Directory of Open Access Journals (Sweden)

    Adam D Leaché

    Full Text Available A hybrid zone between two species of lizards in the genus Sceloporus (S. cowlesi and S. tristichus on the Mogollon Rim in Arizona provides a unique opportunity to study the processes of lineage divergence and merging. This hybrid zone involves complex interactions between 2 morphologically and ecologically divergent subspecies, 3 chromosomal groups, and 4 mitochondrial DNA (mtDNA clades. The spatial patterns of divergence between morphology, chromosomes and mtDNA are discordant, and determining which of these character types (if any reflects the underlying population-level lineages that are of interest has remained impeded by character conflict. The focus of this study is to estimate the number of populations interacting in the hybrid zone using multi-locus nuclear data, and to then estimate the migration rates and divergence time between the inferred populations. Multi-locus estimates of population structure and gene flow were obtained from 12 anonymous nuclear loci sequenced for 93 specimens of Sceloporus. Population structure estimates support two populations, and this result is robust to changes to the prior probability distribution used in the Bayesian analysis and the use of spatially-explicit or non-spatial models. A coalescent analysis of population divergence suggests that gene flow is high between the two populations, and that the timing of divergence is restricted to the Pleistocene. The hybrid zone is more accurately described as involving two populations belonging to S. tristichus, and the presence of S. cowlesi mtDNA haplotypes in the hybrid zone is an anomaly resulting from mitochondrial introgression.

  3. Dispersing perylene diimide/SWCNT hybrids: structural insights at the molecular level and fabricating advanced materials.

    Science.gov (United States)

    Tsarfati, Yael; Strauss, Volker; Kuhri, Susanne; Krieg, Elisha; Weissman, Haim; Shimoni, Eyal; Baram, Jonathan; Guldi, Dirk M; Rybtchinski, Boris

    2015-06-17

    The unique properties of carbon nanotubes (CNT) are advantageous for emerging applications. Yet, the CNT insolubility hampers their potential. Approaches based on covalent and noncovalent methodologies have been tested to realize stable dispersions of CNTs. Noncovalent approaches are of particular interest as they preserve the CNT's structures and properties. We report on hybrids, in which perylene diimide (PDI) amphiphiles are noncovalently immobilized onto single wall carbon nanotubes (SWCNT). The resulting hybrids were dispersed and exfoliated both in water and organic solvents in the presence of two different PDI derivatives, PP2b and PP3a. The dispersions were investigated using cryogenic transmission electron microscopy (cryo-TEM), providing unique structural insights into the exfoliation. A helical arrangement of PP2b assemblies on SWCNTs dominates in aqueous dispersions, while a single layer of PP2b and PP3a was found on SWCNTs in organic dispersions. The dispersions were probed by steady-state and time-resolved spectroscopies, revealing appreciable charge redistribution in the ground state, and an efficient electron transfer from SWCNTs to PDIs in the excited state. We also fabricated hybrid materials from the PP2b/SWCNT dispersions. A supramolecular membrane was prepared from aqueous dispersions and used for size-selective separation of gold nanoparticles. Hybrid buckypaper films were prepared from the organic dispersions. In the latter, high conductivity results from enhanced electronic communication and favorable morphology within the hybrid material. Our findings shed light onto SWCNT/dispersant molecular interactions, and introduce a versatile approach toward universal solution processing of SWCNT-based materials.

  4. Plasmon nanoparticle superlattices as optical-frequency magnetic metamaterials.

    Science.gov (United States)

    Alaeian, Hadiseh; Dionne, Jennifer A

    2012-07-02

    Nanocrystal superlattices have emerged as a new platform for bottom-up metamaterial design, but their optical properties are largely unknown. Here, we investigate their emergent optical properties using a generalized semi-analytic, full-field solver based on rigorous coupled wave analysis. Attention is given to superlattices composed of noble metal and dielectric nanoparticles in unary and binary arrays. By varying the nanoparticle size, shape, separation, and lattice geometry, we demonstrate the broad tunability of superlattice optical properties. Superlattices composed of spherical or octahedral nanoparticles in cubic and AB(2) arrays exhibit magnetic permeabilities tunable between 0.2 and 1.7, despite having non-magnetic constituents. The retrieved optical parameters are nearly polarization and angle-independent over a broad range of incident angles. Accordingly, nanocrystal superlattices behave as isotropic bulk metamaterials. Their tunable permittivities, permeabilities, and emergent magnetism may enable new, bottom-up metamaterials and negative index materials at visible frequencies.

  5. Transverse magnetic mode along THz waveguides with biased superlattices

    Energy Technology Data Exchange (ETDEWEB)

    Aceituno, P. [Dpto. Fisica Basica, Universidad de La Laguna, La Laguna, 38206 Tenerife (Spain)], E-mail: paceitun@ull.es; Hernandez-Cabrera, A. [Dpto. Fisica Basica, Universidad de La Laguna, La Laguna, 38206 Tenerife (Spain); Vasko, F.T. [Institute of Semiconductor Physics, NAS Ukraine, Pr. Nauki 41, Kiev 03028 (Ukraine)

    2008-05-15

    We study the propagation of transverse magnetic modes arising from a waveguide consisting on a GaAs-based superlattice located at vacuum-dielectric interface. The transverse mode is generated by the ultrafast intersubband response of the superlattice subjected to a high-frequency electric field. The superlattice is also subjected to a homogeneous bias potential to get a biased superlattice with equipopulated levels. The heterostructure is analyzed through the tight-binding approximation, and considering the level broadening caused by different scattering processes (homogeneous and inhomogeneous broadening mechanisms). We pay special attention to the dispersion relations of the complex dielectric permittivity because of real and imaginary parts of this function play a key role in wide miniband superlattices.

  6. Diffraction anomalies in hybrid structures based on chalcogenide-coated opal photonic crystals

    CERN Document Server

    Voronov, M M; Yakovlev, S A; Kurdyukov, D A; Golubev, V G

    2014-01-01

    The results of spectroscopic studies of the diffraction anomalies (the so-called resonant Wood anomalies) in spatially-periodic hybrid structures based on halcogenide (GST225)-coated opal films of various thickness are presented. A theoretical analysis of spectral-angular dependencies of the Wood anomalies has been made by means of a phenomenological approach using the concept of the effective refractive index of waveguiding surface layer.

  7. Structural Stability of Functionalized Silicene Nanoribbons with Normal, Reconstructed, and Hybrid Edges

    OpenAIRE

    Sadegh Mehdi Aghaei; Ingrid Torres; Irene Calizo

    2016-01-01

    Silicene, a novel graphene-like material, has attracted a significant attention because of its potential applications for nanoelectronics. In this paper, we have theoretically investigated the structural stability of edge-hydrogenated and edge-fluorinated silicene nanoribbons (SiNRs) via first-principles calculations. Various edge forms of SiNRs including armchair edge, zigzag edge, Klein edge, reconstructed Klein edge, reconstructed pentagon-heptagon edge, and hybrid edges have been consider...

  8. The topological structure of the integral quantum Hall effect in magnetic semiconductor-superconductor hybrids

    Institute of Scientific and Technical Information of China (English)

    Ren Ji-Rong; Zhu Hui

    2009-01-01

    An unconventional integer quantum Hall regime was found in magnetic semiconductor-superconductor hybrids.By making use of the decomposition of the gauge potential on a U(1) principal fibre bundle over k-space, we study the topological structure of the integral Hall conductance. It is labeled by the Hopf index β and the Brouwer degree η. The Hall conductance topological current and its evolution is discussed.

  9. Hybrid Soft Soil Tire Model (HSSTM). Part 1: Tire Material and Structure Modeling

    Science.gov (United States)

    2015-04-28

    HYBRID SOFT SOIL TIRE MODEL (HSSTM). PART I: TIRE MATERIAL AND STRUCTURE MODELING Taheri, Sh.a,1, Sandu, C.a...model the dynamic behavior of the tire on soft soil , a lumped mass discretized tire model using Kelvin-Voigt elements is developed. To optimize the...terrains (such as sandy loam) and tire force and moments, soil sinkage, and tire deformation data were collected for various case studies based on a

  10. Facile preparation of smooth perovskite films for efficient meso/planar hybrid structured perovskite solar cells.

    Science.gov (United States)

    Zhang, Meng; Yu, Hua; Yun, Jung-Ho; Lyu, Miaoqiang; Wang, Qiong; Wang, Lianzhou

    2015-06-21

    Smooth organolead halide perovskite films for meso/planar hybrid structured perovskite solar cells were prepared by a simple compressed air blow-drying method under ambient conditions. The resultant perovskite films show high surface coverage, leading to a device power conversion efficiency of over 10% with an open circuit voltage up to 1.003 V merely using pristine poly(3-hexylthiophene) (P3HT) as a hole transporter.

  11. Nano- and micro-structured silicon for hybrid near-infrared photodetectors

    Science.gov (United States)

    Äńerek, V.; Głowacki, E. D.; Bednorz, M.; Demchyshyn, S.; Sariciftci, N. S.; Ivanda, M.

    2016-05-01

    Structuring surface and bulk of crystalline silicon on different length scales can significantly alter its properties and possibly improve the performance of opto-electronic devices and sensors based on silicon. Different dominant feature scales are responsible for modification of some of electronic and optical properties of silicon. Several easily reproducible chemical methods for facile structuring of silicon on nano and micro-scales, based on both electroless and anodic etching of silicon in hydrofluoric acid based etchants, and chemical anisotropic etching of silicon in basic environments, are presented. We show how successive micro and nano structuring creates hierarchical silicon surfaces, which can be used to simultaneously exploit the advantages of both structuring feature length scales. Finally, we demonstrate a large increase in photocurrent obtained from a hybrid structured silicon/organic near-infrared photodetector. Improved silicon/6,6'-dibromoindigo hybrid photodiodes were prepared by nano- and micro-structuring the silicon part of the heterojunction by wet chemical etching methods. Photocurrent and spectral responsivity were improved in comparison to planar diodes by up to two orders of magnitude by optimization of the silicon structuring process. We show that the improvement in photocurrent is not due to the increase in surface area or light trapping.

  12. Application of Nuclear Magnetic Resonance and Hybrid Methods to Structure Determination of Complex Systems.

    Science.gov (United States)

    Prischi, Filippo; Pastore, Annalisa

    2016-01-01

    The current main challenge of Structural Biology is to undertake the structure determination of increasingly complex systems in the attempt to better understand their biological function. As systems become more challenging, however, there is an increasing demand for the parallel use of more than one independent technique to allow pushing the frontiers of structure determination and, at the same time, obtaining independent structural validation. The combination of different Structural Biology methods has been named hybrid approaches. The aim of this review is to critically discuss the most recent examples and new developments that have allowed structure determination or experimentally-based modelling of various molecular complexes selecting them among those that combine the use of nuclear magnetic resonance and small angle scattering techniques. We provide a selective but focused account of some of the most exciting recent approaches and discuss their possible further developments.

  13. Hybrid metal-dielectric, slow wave structure with magnetic coupling and compensation

    Energy Technology Data Exchange (ETDEWEB)

    Smirnov, A.V., E-mail: asmirnov@radiabeam.com [RadiaBeam Systems LLC, 1713 Stewart St., Santa Monica, CA 90404 (United States); Savin, E. [RadiaBeam Systems LLC, 1713 Stewart St., Santa Monica, CA 90404 (United States); National Research Nuclear University “MEPhI”, Moscow 115409 (Russian Federation)

    2016-06-01

    A number of electron beam vacuum devices such as small radiofrequency (RF) linear accelerators (linacs) and microwave traveling wave tubes (TWTs) utilize slow wave structures which are usually rather complicated in production and may require multi-step brazing and time consuming tuning. Fabrication of these devices becomes challenging at centimeter wavelengths, at large number of cells, and when a series or mass production of such structures is required. A hybrid, metal-dielectric, periodic structure for low gradient, low beam current applications is introduced here as a modification of Andreev’s disk-and-washer (DaW) structure. Compensated type of coupling between even and odd TE01 modes in the novel structure results in negative group velocity with absolute values as high as 0.1c–0.2c demonstrated in simulations. Sensitivity to material imperfections and electrodynamic parameters of the disk-and-ring (DaR) structure are considered numerically using a single cell model.

  14. Multifunctional hybrid porous filters with hierarchical structures for simultaneous removal of indoor VOCs, dusts and microorganisms.

    Science.gov (United States)

    Zhao, Yang; Low, Ze-Xian; Feng, Shasha; Zhong, Zhaoxiang; Wang, Yong; Yao, Zhong

    2017-02-23

    Air purification often requires multiple layers of filters with different functions to remove various air pollutants, which lead to high pressure drop, high air flow path and frequent filter replacement. In this work, a novel multifunctional Ag@MWCNTs/Al2O3 hybrid filter with a depth-type hierarchical structure for simultaneous removal of fine particles, microorganisms and VOCs was designed and fabricated. The novel hybrid air filter showed leading air purification performances to date, achieving 82.24% degradation of formaldehyde at room temperature, 99.99% formaldehyde degradation at 55 °C and complete retention of indoor airborne microorganisms. The complete particle retention rate (100% retention) based on the most penetrating particle size (MPPS, aerodynamic diameter ≦300 nm) of Ag@MWCNTs/Al2O3 was achieved at an only 35.60% pressure drop compared with the pristine Al2O3 filter, leading to the highest quality factor (Qf) ever reported. Furthermore, the Ag@MWCNTs/Al2O3 hybrid filter showed excellent water repellency (water contact angle of 139.6 ± 2.9°), prolonging the service life of the filters and improving the air purification efficiency. The novel Ag@MWCNTs/Al2O3 hybrid filter exhibits remarkable air purification performance in both laboratory synthetic conditions as well as in the "real world" and shows great promise as an effective single replacement for multiple layers of air purifying filters.

  15. Optoelectronic Properties of Van Der Waals Hybrid Structures: Fullerenes on Graphene Nanoribbons

    Science.gov (United States)

    Correa, Julián David; Orellana, Pedro Alejandro; Pacheco, Mónica

    2017-01-01

    The search for new optical materials capable of absorbing light in the frequency range from visible to near infrared is of great importance for applications in optoelectronic devices. In this paper, we report a theoretical study of the electronic and optical properties of hybrid structures composed of fullerenes adsorbed on graphene and on graphene nanoribbons. The calculations are performed in the framework of the density functional theory including the van der Waals dispersive interactions. We found that the adsorption of the C60 fullerenes on a graphene layer does not modify its low energy states, but it has strong consequences for its optical spectrum, introducing new absorption peaks in the visible energy region. The optical absorption of fullerenes and graphene nanoribbon composites shows a strong dependence on photon polarization and geometrical characteristics of the hybrid systems, covering a broad range of energies. We show that an external electric field across the nanoribbon edges can be used to tune different optical transitions coming from nanoribbon–fullerene hybridized states, which yields a very rich electro-absorption spectrum for longitudinally polarized photons. We have carried out a qualitative analysis on the potential of these hybrids as possible donor-acceptor systems in photovoltaic cells. PMID:28336904

  16. Nacre-like hybrid films: Structure, properties, and the effect of relative humidity.

    Science.gov (United States)

    Abba, Mohammed T; Hunger, Philipp M; Kalidindi, Surya R; Wegst, Ulrike G K

    2015-03-01

    Functional materials often are hybrids composed of biopolymers and mineral constituents. The arrangement and interactions of the constituents frequently lead to hierarchical structures with exceptional mechanical properties and multifunctionality. In this study, hybrid thin films with a nacre-like brick-and-mortar microstructure were fabricated in a straightforward and reproducible manner through manual shear casting using the biopolymer chitosan as the matrix material (mortar) and alumina platelets as the reinforcing particles (bricks). The ratio of inorganic to organic content was varied from 0% to 15% and the relative humidities from 36% to 75% to determine their effects on the mechanical properties. It was found that increasing the volume fraction of alumina from 0% to 15% results in a twofold increase in the modulus of the film, but decreases the tensile strength by up to 30%, when the volume fraction of alumina is higher than 5%. Additionally, this study quantifies and illustrates the critical role of the relative humidity on the mechanical properties of the hybrid film. Increasing the relative humidity from 36% to 75% decreases the modulus and strength by about 45% and triples the strain at failure. These results suggest that complex hybrid materials can be manufactured and tailor made for specific applications or environmental conditions.

  17. Insect damages on structural, morphologic and composition of Bt maize hybrids to silage

    Directory of Open Access Journals (Sweden)

    Geraldo Balieiro Neto

    2013-03-01

    Full Text Available It was aimed to evaluate the effect of insect damage on the morphologic and structural characteristics and chemical composition from maize hybrids DKB 390 and AG 8088 with the Cry1Ab trait versus its nonbiotech counterpart. The GMO did not receive insecticide application and the conventional hybrids received one deltametrina (2.8% application at 42 days. The damages caused bySpodoptera frugiperda and Helicoverpa zea in hybrids with Cry1Ab were smaller than its nonbiotech counterpart. After harvest, 95 days after seedling plants were separated in stalks, ears, leafs, dead leafs and floral pennant. The experimental design was randomized block in factorial arrangement 2 x 2. The height of plant and height of ear, percentage and amount of dead leafs from hybrids with the Cry1Ab were higher than its nonbiotech counterpart. There was higher nutrients transfer from stalks to grain filling and smaller rate stalks:ear on transgenic plant. The quality of the transgenic plants can be better when harvest earlier, by increasing no fiber carbohydrates, but when harvest latter, by increasing stalk percentage and stalk lignin content.

  18. Enhanced Mechanical Performance of Bio-Inspired Hybrid Structures Utilising Topological Interlocking Geometry

    Science.gov (United States)

    Djumas, Lee; Molotnikov, Andrey; Simon, George P.; Estrin, Yuri

    2016-05-01

    Structural composites inspired by nacre have emerged as prime exemplars for guiding materials design of fracture-resistant, rigid hybrid materials. The intricate microstructure of nacre, which combines a hard majority phase with a small fraction of a soft phase, achieves superior mechanical properties compared to its constituents and has generated much interest. However, replicating the hierarchical microstructure of nacre is very challenging, not to mention improving it. In this article, we propose to alter the geometry of the hard building blocks by introducing the concept of topological interlocking. This design principle has previously been shown to provide an inherently brittle material with a remarkable flexural compliance. We now demonstrate that by combining the basic architecture of nacre with topological interlocking of discrete hard building blocks, hybrid materials of a new type can be produced. By adding a soft phase at the interfaces between topologically interlocked blocks in a single-build additive manufacturing process, further improvement of mechanical properties is achieved. The design of these fabricated hybrid structures has been guided by computational work elucidating the effect of various geometries. To our knowledge, this is the first reported study that combines the advantages of nacre-inspired structures with the benefits of topological interlocking.

  19. Tuning Structure and Properties of Graded Triblock Terpolymer-Based Mesoporous and Hybrid Films

    KAUST Repository

    Phillip, William A.

    2011-07-13

    Despite considerable efforts toward fabricating ordered, water-permeable, mesoporous films from block copolymers, fine control over pore dimensions, structural characteristics, and mechanical behavior of graded structures remains a major challenge. To this end, we describe the fabrication and performance characteristics of graded mesoporous and hybrid films derived from the newly synthesized triblock terpolymer, poly(isoprene-b-styrene-b-4-vinylpyridine). A unique morphology, unachievable in diblock copolymer systems, with enhanced mechanical integrity is evidenced. The film structure comprises a thin selective layer containing vertically aligned and nearly monodisperse mesopores at a density of more than 1014 per m2 above a graded macroporous layer. Hybridization via homopolymer blending enables tuning of pore size within the range of 16 to 30 nm. Solvent flow and solute separation experiments demonstrate that the terpolymer films have permeabilities comparable to commercial membranes, are stimuli-responsive, and contain pores with a nearly monodisperse diameter. These results suggest that moving to multiblock polymers and their hybrids may open new paths to produce high-performance graded membranes for filtration, separations, nanofluidics, catalysis, and drug delivery. © 2011 American Chemical Society.

  20. Investigation of a hybrid structure gaseous detector for ion backflow suppression suppression

    CERN Document Server

    Zhang, YuLian; Hu, BiTao

    2016-01-01

    A new concept for ion backflow suppression in future time projection chamber with Micropattern Gas Detectors readout is presented. It is a hybrid structure cascaded Gas Electron Multiplier with Micromegas with the goal to reduce ion backflow from the amplification region towards the drift volume. Gas Electron Multiplier also acting as a preamplifer and shares gas gain with Micromegas. In this way a lower voltage difference has to be applied to the Micromegas and risk of sparking is reduced. Feasibility tests for the hybrid detector is performed using an $^{55}$Fe X-ray source to evaluate the energy resolution, its gain properties and the ion backflow. %The properties of this novel structure in terms of gain and ion backflow are investigated. The energy resolution is better than 27$\\%$ FWHM for 5.9 keV X-rays. It is demonstrated that at a gain up to 6000, a backflow ratio less than 0.3$\\%$ is reachable in the hybrid readout structure.

  1. Contributions of each isotope in structural material on radiation damage in a hybrid reactor

    Science.gov (United States)

    Günay, Mehtap

    2016-11-01

    In this study, the fluids were used in the liquid first-wall, blanket and shield zones of the designed hybrid reactor system. In this study, salt-heavy metal mixtures consisting of 93-85% Li20Sn80 + 5% SFG-PuO2 and 2-10% UO2, 93-85% Li20Sn80 + 5% SFG-PuO2 and 2-10% NpO2, and 93-85% Li20Sn80 + 5% SFG-PuO2 and 2-10% UCO were used as fluids. In this study, the effect on the radiation damage of spent fuel-grade (SFG)-PuO2, UO2, NpO2 and UCO contents was investigated in the structural material of a designed fusion-fission hybrid reactor system. In the designed hybrid reactor system were investigated the effect on the radiation damage of the selected fluid according to each isotopes of structural material in the structural material for 30 full power years (FPYs). Three-dimensional analyses were performed using the most recent MCNPX-2.7.0 Monte Carlo radiation transport code and the ENDF/B-VII.0 nuclear data library.

  2. CPU-GPU hybrid accelerating the Zuker algorithm for RNA secondary structure prediction applications.

    Science.gov (United States)

    Lei, Guoqing; Dou, Yong; Wan, Wen; Xia, Fei; Li, Rongchun; Ma, Meng; Zou, Dan

    2012-01-01

    Prediction of ribonucleic acid (RNA) secondary structure remains one of the most important research areas in bioinformatics. The Zuker algorithm is one of the most popular methods of free energy minimization for RNA secondary structure prediction. Thus far, few studies have been reported on the acceleration of the Zuker algorithm on general-purpose processors or on extra accelerators such as Field Programmable Gate-Array (FPGA) and Graphics Processing Units (GPU). To the best of our knowledge, no implementation combines both CPU and extra accelerators, such as GPUs, to accelerate the Zuker algorithm applications. In this paper, a CPU-GPU hybrid computing system that accelerates Zuker algorithm applications for RNA secondary structure prediction is proposed. The computing tasks are allocated between CPU and GPU for parallel cooperate execution. Performance differences between the CPU and the GPU in the task-allocation scheme are considered to obtain workload balance. To improve the hybrid system performance, the Zuker algorithm is optimally implemented with special methods for CPU and GPU architecture. Speedup of 15.93× over optimized multi-core SIMD CPU implementation and performance advantage of 16% over optimized GPU implementation are shown in the experimental results. More than 14% of the sequences are executed on CPU in the hybrid system. The system combining CPU and GPU to accelerate the Zuker algorithm is proven to be promising and can be applied to other bioinformatics applications.

  3. Developing high-performance III-V superlattice IRFPAs for defense: challenges and solutions

    Science.gov (United States)

    Zheng, Lucy; Tidrow, Meimei; Aitcheson, Leslie; O'Connor, Jerry; Brown, Steven

    2010-04-01

    The antimonide superlattice infrared detector technology program was established to explore new infrared detector materials and technology. The ultimate goal is to enhance the infrared sensor system capability and meet challenging requirements for many applications. Certain applications require large-format focal plane arrays (FPAs) for a wide field of view. These FPAs must be able to detect infrared signatures at long wavelengths, at low infrared background radiation, and with minimal spatial cross talk. Other applications require medium-format pixel, co-registered, dual-band capability with minimal spectral cross talk. Under the technology program, three leading research groups have focused on device architecture design, high-quality material growth and characterization, detector and detector array processing, hybridization, testing, and modeling. Tremendous progress has been made in the past few years. This is reflected in orders-of-magnitude reduction in detector dark-current density and substantial increase in quantum efficiency, as well as the demonstration of good-quality long-wavelength infrared FPAs. Many technical challenges must be overcome to realize the theoretical promise of superlattice infrared materials. These include further reduction in dark current density, growth of optically thick materials for high quantum efficiency, and elimination of FPA processing-related performance degradation. In addition, challenges in long-term research and development cost, superlattice material availability, FPA chip assembly availability, and industry sustainability are also to be met. A new program was established in 2009 with a scope that is different from the existing technology program. Called Fabrication of Superlattice Infrared FPA (FastFPA), this 4-year program sets its goal to establish U.S. industry capability of producing high-quality superlattice wafers and fabricating advanced FPAs. It uses horizontal integration strategy by leveraging existing III

  4. Bimetallic PtAu superlattice arrays: Highly electroactive and durable catalyst for oxygen reduction and methanol oxidation reactions

    Science.gov (United States)

    Feng, Jiu-Ju; He, Li-Li; Fang, Rui; Wang, Qiao-Li; Yuan, Junhua; Wang, Ai-Jun

    2016-10-01

    Superlattice arrays, an important type of nanomaterials, have wide applications in catalysis, optic/electronics and energy storage for the synergetic effects determined by both individual metals and collective interactions. Herein, a simple one-pot solvothermal coreduction approach is developed for facile preparation of bimetallic PtAu alloyed superlattice arrays (PtAu SLAs) in oleylamine, with the assistance of urea via hydrogen bonding induced self-assembly. Urea is essential in morphology-controlled process and prevents PtAu nanoparticles from the disordered aggregation. The characterization and formation mechanism of PtAu SLAs are investigated in details. The as-synthesized hybrid nanocrystals exhibit enhanced electrocatalytic performances for oxygen reduction reaction (ORR) and methanol oxidation reaction (MOR) in alkaline electrolyte in comparison with commercial Pt-C (50%, wt.%) and Pt black catalysts.

  5. Reprint of : Three-terminal heat engine and refrigerator based on superlattices

    Science.gov (United States)

    Choi, Yunjin; Jordan, Andrew N.

    2016-08-01

    We propose a three-terminal heat engine based on semiconductor superlattices for energy harvesting. The periodicity of the superlattice structure creates an energy miniband, giving an energy window for allowed electron transport. We find that this device delivers a large power, nearly twice than the heat engine based on quantum wells, with a small reduction of efficiency. This engine also works as a refrigerator in a different regime of the system's parameters. The thermoelectric performance of the refrigerator is analyzed, including the cooling power and coefficient of performance in the optimized condition. We also calculate phonon heat current through the system and explore the reduction of phonon heat current compared to the bulk material. The direct phonon heat current is negligible at low temperatures, but dominates over the electronic at room temperature and we discuss ways to reduce it.

  6. Simple and Superlattice Turing Patterns in Reaction-Diffusion Systems Bifurcation, Bistability, and Parameter Collapse

    CERN Document Server

    Judd, S L; Judd, Stephen L.; Silber, Mary

    1998-01-01

    This paper investigates the competition between both simple (e.g. stripes, hexagons) and ``superlattice'' (super squares, super hexagons) Turing patterns in two-component reaction-diffusion systems. ``Superlattice'' patterns are formed from eight or twelve Fourier modes, and feature structure at two different length scales. Using perturbation theory, we derive simple analytical expressions for the bifurcation equation coefficients on both rhombic and hexagonal lattices. These expressions show that, no matter how complicated the reaction kinectics, the nonlinear reaction terms reduce to just four effective terms within the bifurcation equation coefficients. Moreover, at the hexagonal degeneracy -- when the quadratic term in the hexagonal bifurcation equation disappears -- the number of effective system parameters drops to two, allowing a complete characterization of the possible bifurcation results at this degeneracy. The general results are then applied to specific model equations, to investigate the stabilit...

  7. Tailored inter and intra layer exchange coupled superlattices for optimized magnetocaloric effect

    Science.gov (United States)

    Mukherjee, Tathagata; Michalski, S.; Skomski, R.; Sellmyer, D. J.; Binek, Ch.

    2012-02-01

    We explore Magnetocaloric (MC) properties of Fe/Cr superlattices with tailored inter- and intra-layer interaction using simple 3d metals. Our multilayers are fabricated by pulsed-laser deposition with emphasis on maximizing magnetic entropy changes near room temperature. NanostructuringootnotetextT. Mukherjee, S. Sahoo, R. Skomski, D. J. Sellmyer, and Ch. Binek, Phys. Rev. B 79, 144406 (2009). allows tailoring ferromagnetic and antiferromagnetic coupling. This in concert with finite size scaling of the ferromagnetic Fe films has the potential to lead to optimized MC materials. Thermodynamic and MC properties of such Fe/Cr superlattices are studied with the help of SQUID magnetometry. Entropy changes are deduced via the Maxwell relation in single phase regions, X-ray diffraction and X-ray reflectivity are used to correlate structural data with the magnetic properties.

  8. THz elastic dynamics in finite-size CoFeB-MgO phononic superlattices

    Science.gov (United States)

    Ulrichs, Henning; Meyer, Dennis; Müller, Markus; Wittrock, Steffen; Mansurova, Maria; Walowski, Jakob; Münzenberg, Markus

    2016-10-01

    In this article, we present the observation of coherent elastic dynamics in a nano-scale phononic superlattice, which consists of only 4 bilayers. We demonstrate how ultra-short light pulses with a length of 40 fs can be utilized to excite a coherent elastic wave at 0.535 THz, which persist over about 20 ps. In later steps of the elastic dynamics, modes with frequency of 1.7 THz and above appear. All these modes are related to acoustic band gaps. Thus, the periodicity strongly manifests in the wave physics, although the system under investigation has only a small number of spatial periods. To further illustrate this, we show how by breaking the translational invariance of the superlattice, these features can be suppressed. Discussed in terms of phonon blocking and radiation, we elucidate in how far our structures can be considered as useful building blocks for phononic devices.

  9. Space-time evolution of Gaussian wave packets through superlattices containing left-handed layers

    Energy Technology Data Exchange (ETDEWEB)

    Pereyra, P; Romero-Serrano, M [Departamento de Ciencias Basicas, Universidad Autonoma Metropolitana-Azcapotzalco, Mexico DF (Mexico); Robledo-Martinez, A, E-mail: ppereyra@correo.azc.uam.m, E-mail: a.robledo@mailaps.or [Departamento de EnergIa, Universidad Autonoma Metropolitana-Azcapotzalco, Mexico DF (Mexico)

    2009-05-01

    We study the space-time evolution of Gaussian electromagnetic wave packets moving through (L/R){sup n} superlattices, containing alternating layers of left and right-handed materials. We show that the time spent by the wave packet moving through arbitrary (L/R){sup n} superlattices are well described by the phase time. We show that in the particular case where the thicknesses d{sub L,R} and indices n{sub l,r} of the layers satisfy the condition d{sub L}|n{sub L}| = d{sub R}n{sub R}, the usual band structure becomes a sequence of isolated and equidistant peaks with negative phase times.

  10. Transfer matrix theory of monolayer graphene/bilayer graphene heterostructure superlattice

    Energy Technology Data Exchange (ETDEWEB)

    Wang, Yu, E-mail: ywang@semi.ac.cn [Department of Physics, Faculty of Science, Kunming University of Science and Technology, Kunming 650500 (China)

    2014-10-28

    We have formulated a transfer matrix method to investigate electronic properties of graphene heterostructure consisting of monolayer graphene and bilayer counterpart. By evaluating transmission, conductance, and band dispersion, we show that, irrespective of the different carrier chiralities in monolayer graphene and bilayer graphene, superlattice consisting of biased bilayer graphene barrier and monolayer graphene well can mimic the electronic properties of conventional semiconductor superlattice, displaying the extended subbands in the quantum tunneling regime and producing anisotropic minigaps for the classically allowed transport. Due to the lateral confinement, the lowest mode has shifted away from the charge neutral point of monolayer graphene component, opening a sizeable gap in concerned structure. Following the gate-field and geometry modulation, all electronic states and gaps between them can be externally engineered in an electric-controllable strategy.

  11. Transfer matrix theory of monolayer graphene/bilayer graphene heterostructure superlattice

    Science.gov (United States)

    Wang, Yu

    2014-10-01

    We have formulated a transfer matrix method to investigate electronic properties of graphene heterostructure consisting of monolayer graphene and bilayer counterpart. By evaluating transmission, conductance, and band dispersion, we show that, irrespective of the different carrier chiralities in monolayer graphene and bilayer graphene, superlattice consisting of biased bilayer graphene barrier and monolayer graphene well can mimic the electronic properties of conventional semiconductor superlattice, displaying the extended subbands in the quantum tunneling regime and producing anisotropic minigaps for the classically allowed transport. Due to the lateral confinement, the lowest mode has shifted away from the charge neutral point of monolayer graphene component, opening a sizeable gap in concerned structure. Following the gate-field and geometry modulation, all electronic states and gaps between them can be externally engineered in an electric-controllable strategy.

  12. Investigation of the magnetoresistivity in compositional superlattices under the influence of an intense electromagnetic wave

    Science.gov (United States)

    Hoi, Bui Dinh; Bau, Nguyen Quang; Nam, Nguyen Dinh

    2016-01-01

    The magnetoresistivity (MR) is theoretically calculated in a compositional semiconductor superlattice (CSSL), subjected to a crossed DC electric field and magnetic field, in the presence of an intense electromagnetic wave (EMW). The magnetic field is oriented along the growth direction of the CSSL and the electron-acoustic phonon interaction is taken into account at low temperature. Numerical results for the GaN/AlGaN CSSL show the Shubnikov-de Haas (SdH) oscillations in the MR whose period does not depend on the temperature and amplitude decreases with increasing temperature. The temperature dependence of the relative amplitude of these oscillations is in good agreement with other theories and experiments in some two-dimensional (2D) electron systems. The influence of the EMW as well as superlattice structure on the MR is discussed and compared with available theoretical and experimental results.

  13. Formation mechanism of dot-line square superlattice pattern in dielectric barrier discharge

    Energy Technology Data Exchange (ETDEWEB)

    Liu, Weibo; Dong, Lifang, E-mail: donglfhbu@163.com, E-mail: pyy1616@163.com; Wang, Yongjie; Zhang, Xinpu [College of Physics Science and Technology, Hebei University, Baoding 071002 (China); College of Quality and Technical Supervision, Hebei University, Baoding 071002 (China); Pan, Yuyang, E-mail: donglfhbu@163.com, E-mail: pyy1616@163.com [College of Quality and Technical Supervision, Hebei University, Baoding 071002 (China)

    2014-11-15

    We investigate the formation mechanism of the dot-line square superlattice pattern (DLSSP) in dielectric barrier discharge. The spatio-temporal structure studied by using the intensified-charge coupled device camera shows that the DLSSP is an interleaving of three different subpatterns in one half voltage cycle. The dot square lattice discharges first and, then, the two kinds of line square lattices, which form square grid structures discharge twice. When the gas pressure is varied, DLSSP can transform from square superlattice pattern (SSP). The spectral line profile method is used to compare the electron densities, which represent the amounts of surface charges qualitatively. It is found that the amount of surface charges accumulated by the first discharge of DLSSP is less than that of SSP, leading to a bigger discharge area of the following discharge (lines of DLSSP instead of halos of SSP). The spatial distribution of the electric field of the surface charges is simulated to explain the formation of DLSSP. This paper may provide a deeper understanding for the formation mechanism of complex superlattice patterns in DBD.

  14. Nanoengineering of an Si/MnGe quantum dot superlattice for high Curie-temperature ferromagnetism.

    Science.gov (United States)

    Nie, Tianxiao; Kou, Xufeng; Tang, Jianshi; Fan, Yabin; Lee, Shengwei; He, Qinglin; Chang, Li-Te; Murata, Koichi; Gen, Yin; Wang, Kang L

    2017-02-14

    The realization and application of spintronic devices would be dramatically advanced if room-temperature ferromagnetism could be integrated into semiconductor nanostructures, especially when compatible with mature silicon technology. Herein, we report the observation of such a system - an Si/MnGe superlattice with quantum dots well aligned in the vertical direction successfully grown by molecular beam epitaxy. Such a unique system could take full advantage of the type-II energy band structure of the Si/Ge heterostructure, which could trap the holes inside MnGe QDs, significantly enhancing the hole-mediated ferromagnetism. Magnetic measurements indeed found that the superlattice structure exhibited a Curie temperature of above 400 K. Furthermore, zero-field cooling and field cooling curves could confirm the absence of ferromagnetic compounds, such as Ge8Mn11 (Tc ∼ 270 K) and Ge3Mn5 (Tc ∼ 296 K) in our system. Magnetotransport measurement revealed a clear magnetoresistance transition from negative to positive and a pronounced anomalous Hall effect. Such a unique Si/MnGe superlattice sets a new stage for strengthening ferromagnetism due to the enhanced hole-mediation by quantum confinement, which can be exploited for realizing the room-temperature Ge-based spin field-effect transistors in the future.

  15. Stratigraphy of a diamond epitaxial three-dimensional overgrowth using doping superlattices

    Science.gov (United States)

    Lloret, F.; Fiori, A.; Araujo, D.; Eon, D.; Villar, M. P.; Bustarret, E.

    2016-05-01

    The selective doped overgrowth of 3D mesa patterns and trenches has become an essential fabrication step of advanced monolithic diamond-based power devices. The methodology here proposed combines the overgrowth of plasma-etched cylindrical mesa structures with the sequential growth of doping superlattices. The latter involve thin heavily boron doped epilayers separating thicker undoped epilayers in a periodic fashion. Besides the classical shape analysis under the scanning electron microscope relying on the appearance of facets corresponding to the main crystallographic directions and their evolution toward slow growing facets, the doping superlattices were used as markers in oriented cross-sectional lamellas prepared by focused ion beam and observed by transmission electron microscopy. This stratigraphic approach is shown here to be applicable to overgrown structures where faceting was not detectable. Intermediate growth directions were detected at different times of the growth process and the periodicity of the superlattice allowed to calculate the growth rates and parameters, providing an original insight into the planarization mechanism. Different configurations of the growth front were obtained for different sample orientations, illustrating the anisotropy of the 3D growth. Dislocations were also observed along the lateral growth fronts with two types of Burger vector: b 01 1 ¯ = /1 2 [ 01 1 ¯ ] and b 112 = /1 6 [ 112 ] . Moreover, the clustering of these extended defects in specific regions of the overgrowth prompted a proposal of two different dislocation generation mechanisms.

  16. [Characteristics of canopy structure of super high yielding japonica hybrid rice community].

    Science.gov (United States)

    Chen, Jinhong; Zhang, Guoping; Guo, Hengde; Mao, Guojuan

    2003-06-01

    In this paper, the characteristics of canopy structure, such as the numbers of seedling, panicle and grain, the distribution of dry matters in different canopy layers and different organs, and the distributions of LAI and of solar radiation in different canopy layers of super high yielding community of japonica hybrid rice were studied, in comparison with normal japonica rice. The results showed that the total the dry matter weight and the dry matter weight of layers below 40 cm, 40-60 cm, 60-80 cm and above 80 cm of japonica hybrid rice canopy were 32.29%, 29.12%, 13.95%, 16.45% and 100.17% higher those that of normal japonica rice, respectively. The ratios of dry leaf (photosynthetic organ) and of dry panicle (sink organ) weight to total dry weight were 24.8% and 12.8%, respectively, which were greater than those of normal japonica rice, while the ratios of dry sheath and stem (storage organs) weight were 33.6% and 28.9%, respectively, which were lower than those of normal japonica rice. The allotment of LAI in different layers of japonica hybrid rice canopy was reasonable, and the LAI of above 40 cm layer at full heading stage reached 5.44. The solar radiation was well-distributed inside japonica hybrid rice canopy, for example, the solar radiation in layers below 60 cm were 13.1%-37.0% higher, but 5.9%-12.2% lower above 60 cm than that of normal japonica rice. The extinction coefficients of solar radiation in layers below 20 cm, 20-40 cm, 40-60 cm and 60-80 cm of japonica hybrid rice canopy were 35.1%, 13.5%, 29.1% and 17.2% lower than that of normal japonica rice, respectively.

  17. Rate-prediction structure complexity analysis for multi-view video coding using hybrid genetic algorithms

    Science.gov (United States)

    Liu, Yebin; Dai, Qionghai; You, Zhixiang; Xu, Wenli

    2007-01-01

    Efficient exploitation of the temporal and inter-view correlation is critical to multi-view video coding (MVC), and the key to it relies on the design of prediction chain structure according to the various pattern of correlations. In this paper, we propose a novel prediction structure model to design optimal MVC coding schemes along with tradeoff analysis in depth between compression efficiency and prediction structure complexity for certain standard functionalities. Focusing on the representation of the entire set of possible chain structures rather than certain typical ones, the proposed model can given efficient MVC schemes that adaptively vary with the requirements of structure complexity and video source characteristics (the number of views, the degrees of temporal and interview correlations). To handle large scale problem in model optimization, we deploy a hybrid genetic algorithm which yields satisfactory results shown in the simulations.

  18. Design and Fabrication of a Novel Hybrid-Structure Heat Pipe for a Concentrator Photovoltaic

    Directory of Open Access Journals (Sweden)

    Heiu-Jou Shaw

    2012-10-01

    Full Text Available This study presents a design method to fabricate a novel hybrid-structure flat plate heat pipe (NHSP heat pipe for a concentrator photovoltaic. The NHSP heat pipe is composed of a flattened copper pipe and a sintered wick structure, and a coronary-stent-like rhombic copper mesh supports the structure. The coronary-stent-like supporting structure enhances the mechanical strength and shortens the reflux path of the working fluid. Experiments demonstrate that the sintered capillary heat pipe reduces the thermal resistance by approximately 72%, compared to a traditional copper mesh-screen heat pipe. Furthermore, it can reduce thermal resistance by 65% after a supporting structure is added to the heat pipe. The results show that the NHSP heat pipe provided the best performance for the concentrator photovoltaic, which can increase photoelectric conversion efficiency by approximately 3.1%, compared to an aluminum substrate.

  19. Cracked structure-acoustic coupling problems by hybrid fractal FE and BE methods

    Institute of Scientific and Technical Information of China (English)

    吴国荣; 仲伟芳

    2004-01-01

    Evaluation of the sound-structure interaction is important for effective control of noise and vibration in structural acoustic systems. Cracked elastic structure-sound interaction problems are studied by employing the hybrid fractal FEM and BEM. The degrees of freedom of the system can be reduced greatly through adopting fractal FEM in discretizing the cracked elastic structure; while the exterior acoustic field is calculated by BEM, which automatically satisfies Sommerfeld's radiation condition. Numerical examples are given and show that the resonant frequencies of the structure-acoustic coupled system decrease as the depth of the crack increases, and that the crack has a significant effect on the acoustical field in the vicinity of the crack tip.

  20. Active vibration control of hybrid smart structures featuring piezoelectric films and electrorheological fluids

    Science.gov (United States)

    Choi, Seung-Bok; Park, Yong-Kun; Cheong, ChaeCheon

    1996-05-01

    This paper presents a proof-of-concept investigation on an active vibration control of a hybrid smart structure (HSS) consisting of a piezoelectric film actuator (PFA) and an electro- rheological fluid actuator (ERFA). Firstly, an HSS beam is constructed by inserting a starch- based electro-rheological fluid into a hollow composite beam and perfectly bonding two piezoelectric films on the upper and lower surfaces of the structure as an actuator and as a sensor, respectively. As for the PFA, a neuro-sliding mode controller (NSC) incorporating neural networks with the concept of sliding mode control is formulated. On the other hand, the control scheme for the ERFA is developed as a function of excitation frequencies on the basis of field-dependent frequency responses. An experimental implementation for the PFA and ERFA is then established to perform an active vibration control of the HSS in the transient and forced vibrations. Both the increment of damping ratios and the suppression of tip deflections are evaluated in order to demonstrate control effectiveness of the PFA, the ERFA, and the hybrid actuation. The experimental results exhibit a superior ability of the hybrid actuation system to tailor elastodynamic responses of the HSS rather than a single class of actuation system alone.