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Sample records for superlattice strength enhancement

  1. 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.

  2. 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.

  3. 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.

  4. Synthesis of Bulk Nanostructured DO22 Superlattice of Ni3(Mo, Nb with High Strength, High Ductility, and High Thermal Stability

    Directory of Open Access Journals (Sweden)

    H. M. Tawancy

    2012-01-01

    Full Text Available We show that a bulk nanostructured material combining high strength, high ductility, and high thermal stability can be synthesized in a Ni-Mo-Nb alloy with composition approaching Ni3(Mo, Nb. By means of a simple aging treatment at 700°C, the grains of the parent face-centered cubic phase are made to transform into nanosized ordered crystals with DO22 superlattice maintaining a size of 10–20 nm after up to 100 hours of aging and corresponding room-temperature yield strength of 820 MPa and tensile ductility of 35%. Deformation of the superlattice is found to predominantly occur by twinning on {111} planes of the parent phase. It is concluded that, although the respective slip systems are suppressed, most of the twinning systems are preserved in the DO22 superlattice enhancing the ductility.

  5. 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...

  6. Coercivity enhancement in (Co/CoO)n superlattices

    Science.gov (United States)

    Polisetty, Srinivas; Binek, Christian

    2009-03-01

    The temperature dependence of the coercivity is studied in (Co/CoO)n periodic multilayer thin film superstructures below and above the exchange bias blocking temperature. The ferromagnetic Co thin films are grown with the help of MBE at a base pressure of 10E-10 m.bar whereas antiferromagnetic CoO thin films are grown from in-situ oxidized Co. The thicknesses of these films are monitored by reflection high energy electron diffraction (RHEED). A mean-field theory^1 is outlined which provides an analytic and intuitive expression for the enhancement of the coercivity of the ferromagnet which experiences the exchange coupling with a neighboring antiferromagnet. An experimental approach is developed allowing to determine the interface susceptibility of an individual antiferromagnetic pinning layer by systematic change in the thickness of the antiferromagnet thin films in various sets of superlattice samples measured at different temperatures, respectively. The experiment enables us to separate out the intrinsic coercivity from the contribution induced by exchange coupling at the interface. It is the goal of our study to evidence or disprove if it is simply this susceptibility of the reversible interface magnetization creating the spin drag effect and by that the coercivity enhancement. Financial support by NSF through CAREER DMR-0547887, NRI and Nebraska MRSEC. ^1G. Scholten, K. D. Usadel, and U. Nowak, Phys. Rev B. 71, 064413 (2005).

  7. 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...

  8. Noise-enhanced spontaneous chaos in semiconductor superlattices at room temperature

    Science.gov (United States)

    Alvaro, M.; Carretero, M.; Bonilla, L. L.

    2014-08-01

    Physical systems exhibiting fast spontaneous chaotic oscillations are used to generate high-quality true random sequences in random number generators. The concept of using fast practical entropy sources to produce true random sequences is crucial to make storage and transfer of data more secure at very high speeds. While the first high-speed devices were chaotic semiconductor lasers, the discovery of spontaneous chaos in semiconductor superlattices at room temperature provides a valuable nanotechnology alternative. Spontaneous chaos was observed in 1996 experiments at temperatures below liquid nitrogen. Here we show spontaneous chaos at room temperature appears in idealized superlattices for voltage ranges where sharp transitions between different oscillation modes occur. Internal and external noises broaden these voltage ranges and enhance the sensitivity to initial conditions in the superlattice snail-shaped chaotic attractor thereby rendering spontaneous chaos more robust.

  9. Ion-bombardment-enhanced diffusion during the growth of sputtered superlattice thin films

    Energy Technology Data Exchange (ETDEWEB)

    Eltoukhy, A.H.; Greene, J.E.

    1978-08-15

    A technique is presented for determining the enhancement in solid-state diffusion caused by low-energy ion bombardment. In this technique, superlattice films are grown under varying conditions of ion bombardment and the amplitude of the resulting composition modulation wave is determined by analyzing x-ray diffraction satellite peaks surrounding the central Bragg peaks. The amplitude is in turn related to the enhanced diffusion coefficient D* (x) which may be expressed as D*/sub 0/ exp(-x/delta) where delta is a characteristic diffusion length of the ion-bombardment-produced defects. This approach was confirmed experimentally using InSb/GaSb superlattice structures grown by multitarget sputtering, each sample having equilayer thicknesses between 12 and 30 A. D* was found to increase as the sputtering pressure was decreased. Measured values of D* averaged over the enhanced diffusion region were on the order of 10/sup -17/ cm/sup 2//sec compared to a thermal interdiffusion coefficient of approximately 10/sup -22/ cm/sup 2//sec at the film growth temperature of 250 /sup 0/C.

  10. First-principles calculations of thermoelectric properties of TiN/MgO superlattices: The route for an enhancement of thermoelectric effects in artificial nanostructures

    Energy Technology Data Exchange (ETDEWEB)

    Takaki, Hirokazu; Kobayashi, Kazuaki; Shimono, Masato [National Institute for Materials Science (NIMS), 1-1 Namiki, Tsukuba, Ibaraki 305-0044 (Japan); Kobayashi, Nobuhiko [Institute of Applied Physics, University of Tsukuba, 1-1-1 Tennodai, Tsukuba, Ibaraki 305-8573 (Japan); Hirose, Kenji [Smart Energy Research Laboratories, NEC Corporation, 34 Miyukigaoka, Tsukuba, Ibaraki 305-8501 (Japan)

    2016-01-07

    We present the thermoelectric properties of TiN/MgO superlattices employing first-principles calculation techniques. The Seebeck coefficients, the electrical conductances, the thermal conductances, and the figure of merit are investigated employing electrical and thermal transport calculations based on density functional theory combined with the nonequilibrium Green's function and nonequilibrium molecular dynamics simulation methods. The TiN/MgO superlattices with a small lattice mismatch at the interfaces are ideal systems to study the way for an enhancement of thermoelectric properties in artificial nanostructures. We find that the interfacial scattering between the two materials in the metal/insulator superlattices causes the electrical conductance to change rapidly, which enhances the Seebeck coefficient significantly. We show that the figure of merit for the artificial superlattice nanostructures has a much larger value compared with that of the bulk material and changes drastically with the superlattice configurations at the atomistic level.

  11. 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.

  12. 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.

  13. Enhancing Carrier Injection Using Graded Superlattice Electron Blocking Layer for UVB Light-Emitting Diodes

    KAUST Repository

    Janjua, Bilal

    2014-12-01

    We have studied enhanced carrier injection by having an electron blocking layer (EBL) based on a graded superlattice (SL) design. Here, we examine, using a selfconsistent 6 × 6 k.p method, the energy band alignment diagrams under equilibrium and forward bias conditions while also considering carrier distribution and recombination rates (Shockley-Read-Hall, Auger, and radiative recombination rates). The graded SL is based on AlxGa1-xN (larger bandgap) Al0:5Ga0:5N (smaller bandgap) SL, where x is changed from 0.8 to 0.56 in steps of 0.06. Graded SL was found to be effective in reducing electron leakage and enhancing hole injection into the active region. Due to our band engineering scheme for EBL, four orders-of-magnitude enhancement were observed in the direct recombination rate, as compared with the conventional bulk EBL consisting of Al0:8Ga0:2N. An increase in the spatial overlap of carrier wavefunction was obtained due to polarization-induced band bending in the active region. An efficient single quantum-well ultraviolet-B light-emitting diode was designed, which emits at 280 nm. This is the effective wavelength for water disinfection application, among others.

  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. Enhanced thermoelectric figure-of-merit in thermally robust, nanostructured superlattices based on SrTiO3

    KAUST Repository

    Abutaha, Anas I.

    2015-03-24

    Thermoelectric (TE) metal oxides overcome crucial disadvantages of traditional heavy-metal-alloy-based TE materials, such as toxicity, scarcity, and instability at high temperatures. Here, we report the TE properties of metal oxide superlattices, composed from alternating layers of 5% Pr3+-doped SrTiO3-δ (SPTO) and 20% Nb5+-doped SrTiO3-δ (STNO) fabricated using pulsed laser deposition (PLD). Excellent stability is established for these superlattices by maintaining the crystal structure and reproducing the TE properties after long-time (20 h) annealing at high temperature (∼1000 K). The introduction of oxygen vacancies as well as extrinsic dopants (Pr3+ and Nb5+), with different masses and ionic radii, at different lattice sites in SPTO and STNO layers, respectively, results in a substantial reduction of thermal conductivity via scattering a wider range of phonon spectrum without limiting the electrical transport and thermopower, leading to an enhancement in the figure-of-merit (ZT). The superlattice composed of 20 SPTO/STNO pairs, 8 unit cells of each layer, exhibits a ZT value of 0.46 at 1000 K, which is the highest among SrTiO3-based thermoelectrics. © 2015 American Chemical Society.

  16. Enhancing chaotic behavior at room temperature in GaAs/(Al,Ga)As superlattices

    Science.gov (United States)

    Ruiz-Garcia, M.; Essen, J.; Carretero, M.; Bonilla, L. L.; Birnir, B.

    2017-02-01

    Previous theoretical and experimental work has put forward 50-period semiconductor superlattices as fast, true random number generators at room temperature. Their randomness stems from feedback between nonlinear electronic dynamics and stochastic processes that are intrinsic to quantum transitions. This paper theoretically demonstrates that shorter superlattices with higher potential barriers contain fully chaotic dynamics over several intervals of the applied bias voltage compared to the 50-period device which presented a much weaker chaotic behavior. The chaos arises from deterministic dynamics, hence it persists even in the absence of additional stochastic processes. Moreover, the frequency of the chaotic current oscillations is higher for shorter superlattices. These features should allow for faster and more robust generation of true random numbers.

  17. 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.

  18. Piezoelectric Enhancement of (PbTiO3)m/(BaTiO3)n Ferroelectric Superlattices through Domain Engineering

    Energy Technology Data Exchange (ETDEWEB)

    Hong, Liang; Wu, Pingping; Li, Yulan; Gopalan, Venkatraman; Eom, C.B.; Schlom, Darrell G.; Chen, Long-Qing

    2014-11-20

    The phase diagram of (PbTiO3)m/(BaTiO3)n ferroelectric superlattices was computed using the phase-field approach as a function of layer volume fraction and biaxial strain to tune ferroelectric properties through domain engineering. Two interesting domain structures are found: one with mixed Bloch-Néel-Ising domain wall structures and the other with stabilized monoclinic phases. The polarization of the monoclinic phase is able to rotate from out-of-plane to in-plane or vice versa under an electric field, and thus facilitates the domain reversal of rhombohedral domains. This contributes significantly to both reduced coercive fields and enhanced piezoelectric responses.

  19. 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.

  20. Enhancement of radiation tolerance with the use of a doping superlattice solar cell

    Science.gov (United States)

    Slocum, Michael A.; Forbes, David V.; Hubbard, Seth M.

    2014-03-01

    Solar cells utilizing doping superlattices in the active region of the device have been proposed as an alternative design to increase radiation hardness. Multiple diodes are connected together in parallel, where each diode can be as thin or thick as the design requires. Thinning the doped layers reduces the diffusion length requirements ensuring efficient carrier collection and maintenance of short circuit current. Experimental comparisons between nipi and a conventional pin solar cells that were irradiated with 1 MeV electrons at fluences from 4x1014 to 2x1015 e-/cm2 show much more efficient maintenance of efficiency for the nipi design, maintaining nearly 100% efficiency up to a final dose of 2x1015 e-/cm2. Further simulations have indicated that the efficient maintenance of voltage and fill factor are likely due to traps created in the nipi solar cell during the fabrication process. Beginning of life voltage and efficiency values can be improved significantly by limiting the trap density, while this has a minor impact on the efficiency comparison between a nipi and conventional device with respect to radiation.

  1. Corner strength enhancement of high strength cold-formed steel at normal room and elevated temperatures

    Institute of Scientific and Technical Information of China (English)

    Ju CHEN; Wei-liang JIN

    2008-01-01

    In this study,the suitability of current design methods for the 0.2% proof yield strength of the comer regions for high strength cold-formed steel at norrnal room temperature was investigated.The current standard predictions are generally accurate for outer comer specimen but conservative for inner comer specimen.Based on the experimental results,an analytical model to predict the comer strength of high strength cold-formed steel at normal room temperature was also proposed.The comparison indicated that the proposed model predicted well the comer strength of high strength cold-formed steel not only at normal room temperature but also at elevated temperatures.It is shown that the predictions obtained from the proposed model agree well with the test results.Generally the comer strength enhancement of high strength cold-formed steel decreases when the temperature increases.

  2. Zinc alloy enhances strength and creep resistance

    Energy Technology Data Exchange (ETDEWEB)

    Machler, M. [Fisher Gauge Ltd., Peterborough, Ontario (Canada). Fishercast Div.

    1996-10-01

    A family of high-performance ternary zinc-copper-aluminum alloys has been developed that provides higher strength, hardness, and creep resistance than the traditional zinc-aluminum alloys Zamak 3, Zamak 5, and ZA-8. Designated ACuZinc, mechanical properties comparable to those of more expensive materials make it suitable for high-load applications and those at elevated temperatures. This article describes the alloy`s composition, properties, and historical development.

  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. Strength of Intentional Effort Enhances the Sense of Agency

    Directory of Open Access Journals (Sweden)

    Rin Minohara

    2016-08-01

    Full Text Available Sense of agency refers to the feeling of controlling one’s own actions, and the experience of controlling external events with one’s actions. The present study examined the effect of strength of intentional effort on sense of agency. We manipulated the strength of intentional effort using three types of buttons that differed in the amount of force required to depress them. We used a self-attribution task as an explicit measure of sense of agency. The results indicate that strength of intentional effort enhanced self-attribution when action-effect congruency was unreliable. We concluded that intentional effort importantly affects the integration of multiple cues affecting explicit judgments of agency when the causal relationship action and effect was unreliable.

  5. Carbon Nanotube Bonding Strength Enhancement Using Metal "Wicking" Process

    Science.gov (United States)

    Lamb, James L.; Dickie, Matthew R.; Kowalczyk, Robert S.; Liao, Anna; Bronikowski, Michael J.

    2012-01-01

    Carbon nanotubes grown from a surface typically have poor bonding strength at the interface. A process has been developed for adding a metal coat to the surface of carbon nano tubes (CNTs) through a wicking process, which could lead to an enhanced bonding strength at the interface. This process involves merging CNTs with indium as a bump-bonding enhancement. Classical capillary theory would not normally allow materials that do not wet carbon or graphite to be drawn into the spacings by capillary action because the contact angle is greater than 90 degrees. However, capillary action can be induced through JPL's ability to fabricate oriented CNT bundles to desired spacings, and through the use of deposition techniques and temperature to control the size and mobility of the liquid metal streams and associated reservoirs. A reflow and plasma cleaning process has also been developed and demonstrated to remove indium oxide, and to obtain smooth coatings on the CNT bundles.

  6. 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

  7. Dramatically enhanced electrical breakdown strength in cellulose nanopaper

    Directory of Open Access Journals (Sweden)

    Jianwen Huang

    2016-09-01

    Full Text Available Electrical breakdown behaviors of nanopaper prepared from nanofibrillated cellulose (NFC were investigated. Compared to conventional insulating paper made from micro softwood fibers, nanopaper has a dramatically enhanced breakdown strength. Breakdown field of nanopaper is 67.7 kV/mm, whereas that of conventional paper is only 20 kV/mm. Air voids in the surface of conventional paper are observed by scanning electron microscope (SEM. Further analyses using mercury intrusion show that pore diameter of conventional paper is around 1.7 μm, while that of nanopaper is below 3 nm. Specific pore size of nanopaper is determined to be approximately 2.8 nm by the gas adsorption technique. In addition, theoretical breakdown strengths of nanopaper and conventional paper are also calculated to evaluate the effect of pore size. It turns out that theoretical values agree well with experimental data, indicating that the improved strength in nanopaper is mainly attributed to the decreased pore size. Due to its outstanding breakdown strength, this study indicates the suitability of nanopaper for electrical insulation in ultra-high voltage convert transformers and other electrical devices.

  8. Dramatically enhanced electrical breakdown strength in cellulose nanopaper

    Science.gov (United States)

    Huang, Jianwen; Zhou, Yuanxiang; Zhou, Zhongliu; Liu, Rui

    2016-09-01

    Electrical breakdown behaviors of nanopaper prepared from nanofibrillated cellulose (NFC) were investigated. Compared to conventional insulating paper made from micro softwood fibers, nanopaper has a dramatically enhanced breakdown strength. Breakdown field of nanopaper is 67.7 kV/mm, whereas that of conventional paper is only 20 kV/mm. Air voids in the surface of conventional paper are observed by scanning electron microscope (SEM). Further analyses using mercury intrusion show that pore diameter of conventional paper is around 1.7 μ m , while that of nanopaper is below 3 nm. Specific pore size of nanopaper is determined to be approximately 2.8 nm by the gas adsorption technique. In addition, theoretical breakdown strengths of nanopaper and conventional paper are also calculated to evaluate the effect of pore size. It turns out that theoretical values agree well with experimental data, indicating that the improved strength in nanopaper is mainly attributed to the decreased pore size. Due to its outstanding breakdown strength, this study indicates the suitability of nanopaper for electrical insulation in ultra-high voltage convert transformers and other electrical devices.

  9. Unexpected enhancements and reductions of rf spin resonance strengths

    Directory of Open Access Journals (Sweden)

    M. A. Leonova

    2006-05-01

    Full Text Available We recently analyzed all available data on spin-flipping stored beams of polarized protons, electrons, and deuterons. Fitting the modified Froissart-Stora equation to the measured polarization data after crossing an rf-induced spin resonance, we found 10–20-fold deviations from the depolarizing resonance strength equations used for many years. The polarization was typically manipulated by linearly sweeping the frequency of an rf dipole or rf solenoid through an rf-induced spin resonance; spin-flip efficiencies of up to 99.9% were obtained. The Lorentz invariance of an rf dipole’s transverse ∫Bdl and the weak energy dependence of its spin resonance strength E together imply that even a small rf dipole should allow efficient spin flipping in 100 GeV or even TeV storage rings; thus, it is important to understand these large deviations. Therefore, we recently studied the resonance strength deviations experimentally by varying the size and vertical betatron tune of a 2.1  GeV/c polarized proton beam stored in COSY. We found no dependence of E on beam size, but we did find almost 100-fold enhancements when the rf spin resonance was near an intrinsic spin resonance.

  10. Photon strength and the low-energy enhancement

    Energy Technology Data Exchange (ETDEWEB)

    Wiedeking, M. [iThemba LABS, P.O. Box 722, Somerset West 7129 (South Africa); Bernstein, L. A.; Bleuel, D. L.; Burke, J. T.; Hatarik, R.; Lesher, S. R.; Scielzo, N. D. [Physical and Life Sciences Directorate, Lawrence Livermore National Laboratory, Livermore, California 94551 (United States); Krtička, M. [Faculty of Mathematics and Physics, Charles University, V Holešovickách 2, Prague 8 (Czech Republic); Allmond, J. M. [Department of Physics, University of Richmond, Virginia 23173 (United States); Basunia, M. S.; Fallon, P.; Firestone, R. B.; Lake, P. T.; Lee, I-Y.; Paschalis, S.; Petri, M.; Phair, L. [Nuclear Science Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720 (United States); Goldblum, B. L. [Department of Nuclear Engineering, University of California, Berkeley, California 94720 (United States)

    2014-08-14

    Several measurements in medium mass nuclei have reported a low-energy enhancement in the photon strength function. Although, much effort has been invested in unraveling the mysteries of this effect, its physical origin is still not conclusively understood. Here, a completely model-independent experimental approach to investigate the existence of this enhancement is presented. The experiment was designed to study statistical feeding from the quasi-continuum (below the neutron separation energy) to individual low-lying discrete levels in {sup 95}Mo produced in the (d, p) reaction. A key aspect to successfully study gamma decay from the region of high-level density is the detection and extraction of correlated particle-gamma-gamma events which was accomplished using an array of Clover HPGe detectors and large area annular silicon detectors. The entrance channel excitation energy into the residual nucleus produced in the reaction was inferred from the detected proton energies in the silicon detectors. Gating on gamma-transitions originating from low-lying discrete levels specifies the state fed by statistical gamma-rays. Any particle-gamma-gamma event in combination with specific energy sum requirements ensures a clean and unambiguous determination of the initial and final state of the observed gamma rays. With these requirements the statistical feeding to individual discrete levels is extracted on an event-by-event basis. The results are presented and compared to {sup 95}Mo photon strength function data measured at the University of Oslo.

  11. Caffeine enhances upper body strength in resistance-trained women

    Directory of Open Access Journals (Sweden)

    Penhollow Tina

    2010-05-01

    Full Text Available Abstract Background Research has indicated that low-to-moderate dosages of caffeine supplementation are ergogenic for sustained endurance efforts as well as high-intensity exercise. The effects of caffeine supplementation on strength-power performance are equivocal, with some studies indicating a benefit and others demonstrating no change in performance. The majority of research that has examined the effects of caffeine supplementation on strength-power performance has been carried out in both trained and untrained men. Therefore, the purpose of this study was to determine the acute effects of caffeine supplementation on strength and muscular endurance in resistance-trained women. Methods In a randomized manner, 15 women consumed caffeine (6 mg/kg or placebo (PL seven days apart. Sixty min following supplementation, participants performed a one-repetition maximum (1RM barbell bench press test and repetitions to failure at 60% of 1RM. Heart rate (HR and blood pressure (BP were assessed at rest, 60 minutes post-consumption, and immediately following completion of repetitions to failure. Results Repeated measures ANOVA indicated a significantly greater bench press maximum with caffeine (p ≤ 0.05 (52.9 ± 11.1 kg vs. 52.1 ± 11.7 kg with no significant differences between conditions in 60% 1RM repetitions (p = 0.81. Systolic blood pressure was significantly greater post-exercise, with caffeine (p Conclusions These findings indicate a moderate dose of caffeine may be sufficient for enhancing strength performance in resistance-trained women.

  12. Enhancing the strength of an optical trap by truncation.

    Directory of Open Access Journals (Sweden)

    Vanessa R M Rodrigues

    Full Text Available Optical traps (tweezers are beginning to be used with increasing efficacy in diverse studies in the biological and biomedical sciences. We report here results of a systematic study aimed at enhancing the efficiency with which dielectric (transparent materials can be optically trapped. Specifically, we investigate how truncation of the incident laser beam affects the strength of an optical trap in the presence of a circular aperture. Apertures of various sizes have been used by us to alter the beam radius, thereby changing the effective numerical aperture and intensity profile. We observe significant enhancement of the radial and axial trap stiffness when an aperture is used to truncate the beam compared to when no aperture was used, keeping incident laser power constant. Enhancement in trap stiffness persists even when the beam intensity profile is modulated. The possibility of applying truncation to multiple traps is explored; to this end a wire mesh is utilized to produce multiple trapping that also alters the effective numerical aperture. The use of a mesh leads to reduction in trap stiffness compared to the case when no wire mesh is used. Our findings lead to a simple-to-implement and inexpensive method of significantly enhancing optical trapping efficiency under a wide range of circumstances.

  13. Creep strength and rupture ductility of creep strength enhanced ferritic steels

    Energy Technology Data Exchange (ETDEWEB)

    Kushima, Hideaki; Sawada, Kota; Kimura, Kazuhiro [National Inst. for Materials Science, Tsukuba, Ibaraki (Japan)

    2010-07-01

    Creep strength and rupture ductility of Creep Strength Enhanced Ferritic (CSEF) steels were investigated from a viewpoint of stress dependence in comparison with conventional low alloy ferritic creep resistant steels. Inflection of stress vs. time to rupture curve was observed at 50% of 0.2% offset yield stress for both CSEF and conventional ferritic steels. Creep rupture ductility tends to decrease with increase in creep exposure time, however, those of conventional low alloy steels indicate increase in the long-term. Creep rupture ductility of the ASME Grades 92 and 122 steels indicates drastic decrease with decrease in stress at 50% of 0.2% offset yield stress. Stress dependence of creep rupture ductility of the ASME Grades 92 and 122 steels is well described by stress ratio to 0.2% offset yield stress, regardless of temperature. Drop of creep rupture ductility is caused by inhomogeneous recovery at the vicinity of prior austenite grain boundary, and remarkable drop of creep rupture ductility of CSEF steels should be derived from those stabilized microstructure. (orig.)

  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. 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. Dressing spray enhances the adhesive strength of surgical dressing tapes

    Directory of Open Access Journals (Sweden)

    Sarifakioglu Evren

    2006-01-01

    Full Text Available Background: The use of surgical adhesive tapes after minor surgical and dermatologic operations is widespread. Their use reduces the wound tension and separation and they ultimately improve the postoperative scar. The most commonly used wound adhesives to enhance the adhesiveness of the surgical tapes, are tincture of benzoin and mastisol. Aim: The purpose of the present study is to demonstrate the role of adhesive power of dressing spray with the adhesive tape application on the skin, which is widely used in clinics after the skin closure. Methods: Fifteen volunteers who were chosen among the medical personnel of the hospital comprised the study group. The skin of the flexor aspect of the 1/3 middle forearm of the subjects was used as the procedure region. The data is collected in the first, second and eighth days of the study. At the first stage of the study, an adhesive wound closure tape was applied to the skin without any compound of adhesives (group A. In the second and third stages, a thin coat of transparent film dressing spray (group B and an adhesive compound of tincture of benzoin (group C were applied to the skin before the adhesive tape placement, respectively. Different values of weights ranging between 50-900 gm were hanged by hooking into the center of the adhesive tape. The weights that caused complete separations of the tape from the skin after exactly 20 seconds were recorded in all groups. The data was analyzed by using Friedman test in order to calculate statistical significance between groups A, B and C. Results: The difference in adhesive power between control and groups B and C was found to be highly significant ( p < 0.05. Compound tincture of benzoin was observed to have greatest adhesive strength. Transparent film dressing spray was not as efficient as tincture of benzoin, but when compared with the control group, it enhanced the tape adhesion by 2-fold. Conclusion: The results indicated that dressing spray tested has

  18. 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....

  19. Strength of Rocks Affected by Deformation Enhanced Grain Growth

    Science.gov (United States)

    Kellermann Slotemaker, A.; de Bresser, H.; Spiers, C.

    2005-12-01

    One way of looking into the possibility of long-term strength changes in the lithosphere is to study transient effects resulting from modifications of the microstructure of rocks. It is generally accepted that mechanical weakening may occur due to progressive grain size refinement resulting from dynamic recrystallization. A decrease in grain size may induce a switch from creep controlled by grain size insensitive dislocation mechanisms to creep governed by grain size sensitive (GSS) mechanisms involving diffusion and grain boundary sliding processes. This switch forms a well-known scenario to explain localization in the lithosphere. However, fine-grained rocks in localized deformation zones are prone to grain coarsening due to surface energy driven grain boundary migration (SED-GBM). This might harden the rock, affecting its role in localizing strain in the long term. The question has arisen if grain growth by SED-GBM in a rock deforming in the GSS creep field can be significantly affected by strain. The broad aim of this study is to shed more light onto this. We have experimentally investigated the microstructural and strength evolution of fine-grained (~0.6 μm) synthetic forsterite and Fe-bearing olivine aggregates that coarsen in grain size while deforming by GSS creep at elevated pressure (600 MPa) and temperature (850-1000 °C). The materials were prepared by `sol-gel' method and contained 0.3-0.5 wt% water and 5-10 vol% enstatite. We performed i) static heat treatment tests of various time durations involving hot isostatic pressing (HIP), and ii) heat treatment tests starting with HIP and continuing with deformation up to 45% axial strain at strain rates in the range 4x10-7 - 1x10-4 s-1. Microstructures were characterized by analyzing full grain size distributions and textures using SEM/EBSD. In addition to the experiments, we studied microstructural evolution in simple two-dimensional numerical models, combining deformation and SED-GBM by means of the

  20. Photon Strength and the Low-Energy Enhancement

    Energy Technology Data Exchange (ETDEWEB)

    Wiedeking, M; Bernstein, L A; Krticka, M; Bleuel, D L; Allmond, J M; Basunia, M S; Burke, J T; Fallon, P; Firestone, R B; Goldblum, B L; Hatarik, R; Lake, P T; Lee, I Y; Lesher, S R; Paschalis, S; Petri, M; Phair, L; Scielzo, N D

    2012-02-22

    The ability of atomic nuclei to emit and absorb photons with energy E{sub {gamma}} is known as the photon strength function f(E{sub {gamma}}). It has direct relevance to astrophysical element formation via neutron capture processes due to its central role in nuclear reactions. Studies of f(E{sub {gamma}}) have benefited from a wealth of data collected in neutron capture and direct reactions but also from newly commissioned inelastic photon scattering facilities. The majority of these experimental methods, however, rely on the use of models because measured {gamma}-ray spectra are simultaneously sensitive to both the nuclear level density and f(E{sub {gamma}}). As excitation energy increases towards the particle separation energies, the level density increases rapidly, creating the quasi-continuum. Nuclear properties in this excitation energy region are best characterized using statistical quantities, such as f(E{sub {gamma}}). A point of contention in studies of the quasi-continuum has been an unexpected and unexplained increase in f(E{sub {gamma}}) at low {gamma}-ray energies (i.e. below E{sub {gamma}} {approx}3 MeV) in a subset of light-to-medium mass nuclei. Ideally, a new model-independent experimental technique is required to address questions regarding the existence and origin of this low-energy enhancement in f(E{sub {gamma}}). Here such a model-independent approach is presented for determining the shape of f(E{sub {gamma}}) over a wide range of energies. The method involves the use of coupled high-resolution particle and {gamma}-ray spectroscopy to determine the emission of {gamma} rays from the quasi-continuum in a nucleus with defined excitation energy to individual discrete levels of known spins and parities. This method shares characteristics of two neutron capture-based techniques: the Average Resonance Capture (ARC) and the Two-Step Cascade analysis (TSC). The power of the new technique lies in the additional ability to positively identify primary

  1. Photon Strength and the Low-Energy Enhancement

    Energy Technology Data Exchange (ETDEWEB)

    Wiedeking, M; Bernstein, L A; Krticka, M; Bleuel, D L; Allmond, J M; Basunia, M S; Burke, J T; Fallon, P; Firestone, R B; Goldblum, B L; Hatarik, R; Lake, P T; Lee, I Y; Lesher, S R; Paschalis, S; Petri, M; Phair, L; Scielzo, N D

    2012-02-22

    The ability of atomic nuclei to emit and absorb photons with energy E{sub {gamma}} is known as the photon strength function f(E{sub {gamma}}). It has direct relevance to astrophysical element formation via neutron capture processes due to its central role in nuclear reactions. Studies of f(E{sub {gamma}}) have benefited from a wealth of data collected in neutron capture and direct reactions but also from newly commissioned inelastic photon scattering facilities. The majority of these experimental methods, however, rely on the use of models because measured {gamma}-ray spectra are simultaneously sensitive to both the nuclear level density and f(E{sub {gamma}}). As excitation energy increases towards the particle separation energies, the level density increases rapidly, creating the quasi-continuum. Nuclear properties in this excitation energy region are best characterized using statistical quantities, such as f(E{sub {gamma}}). A point of contention in studies of the quasi-continuum has been an unexpected and unexplained increase in f(E{sub {gamma}}) at low {gamma}-ray energies (i.e. below E{sub {gamma}} {approx}3 MeV) in a subset of light-to-medium mass nuclei. Ideally, a new model-independent experimental technique is required to address questions regarding the existence and origin of this low-energy enhancement in f(E{sub {gamma}}). Here such a model-independent approach is presented for determining the shape of f(E{sub {gamma}}) over a wide range of energies. The method involves the use of coupled high-resolution particle and {gamma}-ray spectroscopy to determine the emission of {gamma} rays from the quasi-continuum in a nucleus with defined excitation energy to individual discrete levels of known spins and parities. This method shares characteristics of two neutron capture-based techniques: the Average Resonance Capture (ARC) and the Two-Step Cascade analysis (TSC). The power of the new technique lies in the additional ability to positively identify primary

  2. 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...

  3. Enhanced shear strength of sodium bentonite using frictional additives

    Energy Technology Data Exchange (ETDEWEB)

    Schmitt, K.E. [GeoSyntec Consultants, Huntington Beach, CA (United States); Bowders, J.J.; Gilbert, R.B. [Univ. of Texas, Austin, TX (United States); Daniel, D.E. [Univ. of Illinois, Urbana, IL (United States)

    1997-12-31

    One of the most important obstacles to using geosynthetic clay liners (GCLs) in landfill cover systems is the low shear strength provided by the bentonitic portion of the GCL. In this study, the authors propose that granular, frictional materials might be added to the bentonite to form an admixture that would have greater shear strength than the bentonite alone while still raining low hydraulic conductivity. Bentonite was mixed with two separate granular additives, expanded shale and recycled to form mixtures consisting of 20-70% bentonite by weight. In direct shear tests at normal stresses of 34.5-103.5 kPa, effective friction angles were measured as 45{degrees} for the expanded 36{degrees} for the recycled glass, and 7{degrees} for the hydrated granular bentonite. The strength of the expanded shale mixtures increased nearly linearly as the percentage shale in the mixture increased, to 44{degrees} for a bentonite mixture with 80% shale. The addition of recycled glass showed little effect on the shear strength of the mixtures of glass and bentonite. Hydraulic conductivity measurements for both types of mixtures indicated a linear increase with log(k) as the amount of granular additive increased. For applications involving geosynthetic clay liners for cover systems, a mixture of 40% expanded shale and 60% bentonite is recommended, although further testing must be done. The 40/60 mixture satisfies the hydraulic equivalency requirement, with k = 5.1X10{sup -9} cm/sec, while increasing the shear strength parameters of the bentonitic mixture to {phi}{prime} = 17{degrees} and c{prime} = 0.

  4. Field-strength dependence of Gadolinium enhancement: Theory and implications

    Energy Technology Data Exchange (ETDEWEB)

    Elster, A.D. [Wake Forest Univ., Winston-Salem, NC (United States)

    1994-09-01

    The decision to use contrast in magnetic resonance (MR) examination has important diagnostic, economic, and medicolegal implications. The overwhelmng majority of published studies defining the clinical utility of gadolinium administration for neuroimaging have been performed at high fields. Are these conclusions about contrast agent use at high fields equally valid for low-field imaging? Is contrast enhancement at 1.5T the same as contrast enhancement at 0.15T? The relationship between field stregth and contrast enhancement is sufficiently complex that few readers will find it intuitively obvious. This commentary reviews and further develops the theoretical framework necessary to explain the field dependence of gadolinium enhancement in tissues.

  5. 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.

  6. 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)

  7. Enhanced stimulus strength improves visual cognition in aging and Alzheimer's disease.

    Science.gov (United States)

    Cronin-Golomb, Alice; Gilmore, Grover C; Neargarder, Sandy; Morrison, Sarah R; Laudate, Thomas M

    2007-10-01

    Deficits in visual cognition in Alzheimer's disease (AD) arise from neuropathological changes in higher-order association areas of the cortex and from defective input from lower-level visual processing areas. We investigated whether enhanced signal strength may lead to improvement of visual cognition in AD. We tested 35 individuals with probable AD, 35 age-matched elderly control (EC) and 58 young control (YC) adults on letter identification, word reading, picture naming, discrimination of unfamiliar faces, and pattern completion. The contrast sensitivity step-difference across an independent sample of AD and EC groups was used in calculating an image filter, from which we produced stimulus-strength conditions of low-degraded, medium-normal, and high-enhanced. Using this filter we created a hypothetical proximal-strength equivalence between AD at medium strength and EC at low strength, and between AD at high strength and EC at medium strength. For letter identification, word reading, picture naming, and face discrimination, medium strength elicited AD accuracy levels and reaction times that were similar to those of EC at low strength. On picture naming, increased strength reduced perceptual-type errors for EC and AD and random errors for AD. For word reading, high strength elicited AD accuracy levels and reaction times that were equivalent to those of EC at medium strength. We saw no effect of signal-strength manipulation on performance of pattern completion, possibly owing to the complex cognitive demands of that task or to the inadequacy of the filter for its images. The results indicate that putative AD-EC differences in cognition directly reflect contrast sensitivity differences between the groups. Enhancement of stimulus strength can ameliorate vision-based deficits and lead to improvement in some aspects of cognitive performance. These results suggest new non-pharmacological avenues to explore in the attempt to improve cognition in elderly adults and

  8. Enhancement of octupole strength in near spherical nuclei

    Energy Technology Data Exchange (ETDEWEB)

    Robledo, L.M. [Universidad Autonoma de Madrid, Dep. Fisica Teorica, Facultad de Ciencias, Madrid (Spain)

    2016-09-15

    The validity of the rotational formula used to compute E1 and E3 transition strengths in even-even nuclei is analyzed within the Generator Coordinate Method framework based on mean field wave functions. It turns out that those nuclei with spherical or near spherical shapes the E1 and E3 strengths computed with this formula are strongly underestimated and a sound evaluation of them requires angular-momentum projected wave functions. Results for several isotopic chains with proton number equal to or near magic numbers are analyzed and compared with experimental data. The use of angular-momentum projected wave functions greatly improves the agreement with the scarce experimental data. (orig.)

  9. Enhanced stability and mechanical strength of sodium alginate composite films.

    Science.gov (United States)

    Liu, Sijun; Li, Yong; Li, Lin

    2017-03-15

    This work aims to study how three kinds of nanofillers: graphene oxide (GO), ammonia functionalized graphene oxide (AGO), and triethoxylpropylaminosilane functionalized silica, can affect stability and mechanical strength of sodium alginate (SA) composite films. The filler/sodium alginate (SA) solutions were first studied by rheology to reveal effects of various fillers on zero shear viscosity η0. SA composite films were then prepared by a solution mixing-evaporation method. The structure, morphology and properties of SA composite films were characterized by Fourier transform infrared spectroscopy (FTIR), X-ray diffractometry (XRD), thermogravimetric analysis (TGA), field emission scanning electron microscopy (FESEM), contact angle and mechanical testing. Compared to GO and silica, the presence of AGO significantly improved the interaction between AGO and SA, which led to the increase in stability and mechanical strength of the resulting SA composite films. The tensile strength and elongation at break of AGO/SA composite film at 3wt% AGO loading were increased by 114.9% and 194.4%, respectively, in contrast to pure SA film. Furthermore, the stability of AGO/SA composite films at high temperatures and in a wet environment were better than that of silica/SA and GO/SA composite films. Copyright © 2016 Elsevier Ltd. All rights reserved.

  10. 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.

  11. Mechanical design of mussel byssus: material yield enhances attachment strength

    Science.gov (United States)

    Bell; Gosline

    1996-01-01

    The competitive dominance of mussels in the wave-swept rocky intertidal zone is in part due to their ability to maintain a secure attachment. Mussels are tethered to the substratum by a byssus composed of numerous extracellular, collagenous threads secreted by the foot. Each byssal thread has three serially arranged parts: a corrugated proximal region, a smooth distal region and an adhesive plaque. This study examines the material and structural properties of the byssal threads of three mussel species: Mytilus californianus, M. trossulus, and M. galloprovincialis. Tensile tests in general reveal similar material properties among species: the proximal region has a lower initial modulus, a lower ultimate stress and a higher ultimate strain than the distal region. The distal region also yields at a stress well below its ultimate value. In whole thread tests, the proximal region and adhesive plaque are common sites of structural failure and are closely matched in strength, while the distal region appears to be excessively strong. We propose that the high strength of the distal region is the byproduct of a material designed to yield and extend before structural failure occurs. Experimental and theoretical evidence is presented suggesting that thread yield and extensibility provide two important mechanisms for increasing the overall attachment strength of the mussel: (1) the reorientation of threads towards the direction of applied load, and (2) the 'recruitment' of more threads into tension and the consequent distribution of applied load over a larger cross-sectional area, thereby reducing the stress on each thread. This distal region yield behavior is most striking for M. californianus and may be a key to its success in extreme wave-swept environments.

  12. 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.

  13. Flexural strength enhancement of confined reinforced concrete columns

    OpenAIRE

    Pam, HJ; Ho, JCM

    2001-01-01

    As part of a continuing research study, this paper proposes a new design aid to calculate the actual moment capacity of confined reinforced concrete columns. Up to now the moment capacity of a reinforced concrete column is calculated based on the code's guidelines for an unconfined section. As most reinforced concrete columns contain transverse or confining reinforcement, which will enhance the column moment capacity, the actual moment capacity will be much higher than the unconfined moment c...

  14. 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.

  15. 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.

  16. 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...

  17. Is Enhanced-Eccentric Resistance Training Superior to Traditional Training for Increasing Elbow Flexor Strength?

    OpenAIRE

    Kaminski, Thomas W.; Barstow, Ian K.; Bishop, Mark D.

    2003-01-01

    Protocols for strengthening muscle are important for fitness, rehabilitation, and the prevention of myotendinous injuries. In trained individuals, the optimal method of increasing strength remains unclear. The purpose of this study was to compare the effects of a traditional method of strengthening with a method that allowed for enhanced-eccentric training, on changes in elbow flexor strength in trained subjects. Thirty-nine (8 male, 31 female) trained subjects with normal elbow function part...

  18. Can project managers signature strengths enhance project team resilience, and if so, how?

    OpenAIRE

    Kristensen, Anita Hultgren; Presttun, Hanne

    2016-01-01

    Purpose: The purpose of this thesis is to explore the relationship between signature strengths and the development and strengthening of resilience in teams within a project setting. More specifically, this thesis investigates whether project managers can use signature strengths to enhance project team resilience, and if so, how? Design/methodology/approach: Theories within positive psychology and project management will be used as a framework in this thesis. In particular, P...

  19. Non-random walk diffusion enhances the sink strength of semicoherent interfaces

    Science.gov (United States)

    Vattré, A.; Jourdan, T.; Ding, H.; Marinica, M.-C.; Demkowicz, M. J.

    2016-01-01

    Clean, safe and economical nuclear energy requires new materials capable of withstanding severe radiation damage. One strategy of imparting radiation resistance to solids is to incorporate into them a high density of solid-phase interfaces capable of absorbing and annihilating radiation-induced defects. Here we show that elastic interactions between point defects and semicoherent interfaces lead to a marked enhancement in interface sink strength. Our conclusions stem from simulations that integrate first principles, object kinetic Monte Carlo and anisotropic elasticity calculations. Surprisingly, the enhancement in sink strength is not due primarily to increased thermodynamic driving forces, but rather to reduced defect migration barriers, which induce a preferential drift of defects towards interfaces. The sink strength enhancement is highly sensitive to the detailed character of interfacial stresses, suggesting that `super-sink' interfaces may be designed by optimizing interface stress fields. Such interfaces may be used to create materials with unprecedented resistance to radiation-induced damage.

  20. 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.

  1. Enhancing psychological capital and personal growth initiative: working on strengths or deficiencies.

    Science.gov (United States)

    Meyers, Maria Christina; van Woerkom, Marianne; de Reuver, Renee S M; Bakk, Zsuzsa; Oberski, Daniel L

    2015-01-01

    Personal growth initiative (PGI), defined as being proactive about one's personal development, is critical to graduate students' academic success. Prior research has shown that students' PGI can be enhanced through interventions that focus on stimulating developmental activities. Within this study, we aimed to investigate whether an intervention that stimulates development in the area of one's personal strengths (strengths intervention) has more beneficial effects on students' PGI than an intervention that stimulates development in the area of individual deficiencies (deficiency intervention). We conducted 2 longitudinal field experiments to investigate the effects of the 2 interventions on students' PGI (Experiment 1) and the potential mediating role of psychological capital (PsyCap) in this regard (Experiment 2). In Experiment 1, 105 (N = 105) university students participated in either a strengths intervention or a deficiency intervention. Results indicated that the strengths intervention increased the students' PGI in the short but not in the long term, whereas the deficiency intervention did not affect PGI. Ninety students (N = 90) participated in Experiment 2, in which we slightly refined both interventions by putting a stronger emphasis on the ongoing development of strengths (strengths intervention) or correction of deficiencies (deficiency intervention) by adding posttraining assignments. Results suggested that participating in both interventions led to increases in PGI over a 3-month period, but that these increases were bigger for the strengths intervention group. Furthermore, the relationship between the strengths intervention and PGI was mediated by hope as one component of PsyCap.

  2. 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.

  3. 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.

  4. 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.

  5. Design of Hierarchically Cut Hinges for Highly Stretchable and Reconfigurable Metamaterials with Enhanced Strength.

    Science.gov (United States)

    Tang, Yichao; Lin, Gaojian; Han, Lin; Qiu, Songgang; Yang, Shu; Yin, Jie

    2015-11-25

    Applying hierarchical cuts to thin sheets of elastomer generates super-stretchable and reconfigurable metamaterials, exhibiting highly nonlinear stress-strain behaviors and tunable phononic bandgaps. The cut concept fails on brittle thin sheets due to severe stress concentration in the rotating hinges. By engineering the local hinge shapes and global hierarchical structure, cut-based reconfigurable metamaterials with largely enhanced strength are realized.

  6. Biomimetic design and assembly of organic-inorganic composite films with simultaneously enhanced strength and toughness.

    Science.gov (United States)

    Han, Jingbin; Dou, Yibo; Yan, Dongpeng; Ma, Jing; Wei, Min; Evans, David G; Duan, Xue

    2011-05-14

    Inorganic nanoplatelet reinforced polymer films were fabricated via alternate layer-by-layer assembly of layered double hydroxide (LDH) nanoplatelets with poly(vinyl alcohol) (PVA), which showed largely enhanced strength and good ductility simultaneously. © The Royal Society of Chemistry 2011

  7. 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.

  8. Increased residual force enhancement in older adults is associated with a maintenance of eccentric strength.

    Directory of Open Access Journals (Sweden)

    Geoffrey A Power

    Full Text Available Despite an age-related loss of voluntary isometric and concentric strength, muscle strength is well maintained during lengthening muscle actions (i.e., eccentric strength in old age. Additionally, in younger adults during lengthening of an activated skeletal muscle, the force level observed following the stretch is greater than the isometric force at the same muscle length. This feature is termed residual force enhancement (RFE and is believed to be a combination of active and passive components of the contractile apparatus. The purpose of this study was to provide an initial assessment of RFE in older adults and utilize aging as a muscle model to explore RFE in a system in which isometric force production is compromised, but structural mechanisms of eccentric strength are well-maintained. Therefore, we hypothesised that older adults will experience greater RFE compared with young adults. Following a reference maximal voluntary isometric contraction (MVC of the dorsiflexors in 10 young (26.1 ± 2.7 y and 10 old (76.0 ± 6.5 y men, an active stretch was performed at 15°/s over a 30° ankle joint excursion ending at the same muscle length as the reference MVCs (40° of plantar flexion. Any additional torque compared with the reference MVC therefore represented RFE. In older men RFE was ~2.5 times greater compared to young. The passive component of force enhancement contributed ~37% and ~20% to total force enhancement, in old and young respectively. The positive association (R(2 = 0.57 between maintained eccentric strength in old age and RFE indicates age-related mechanisms responsible for the maintenance of eccentric strength likely contributed to the observed elevated RFE. Additionally, as indicated by the greater passive force enhancement, these mechanisms may be related to increased muscle series elastic stiffness in old age.

  9. Intrinsic noncollinear magnetization in Fe/Cr superlattices

    Energy Technology Data Exchange (ETDEWEB)

    Yartseva, N.S., E-mail: yartseva@imp.uran.ru [Institute of Metal Physics, UD of RAS, Ekaterinburg 620990 (Russian Federation); Yartsev, S.V. [ZAO NPO “Spektr”, 14 Berezovskiy 623700 (Russian Federation); Demangeat, C. [UFR de Physique et d’Ingéniérie, Université de Strasbourg, 3 rue de l’Université, 67000 Strasbourg (France)

    2014-12-15

    Magnetic moments distribution in Fe{sub 3}Cr{sub n} superlattice series with fixed middle Fe monolayer and number of Cr monolayers (MLs) n from 1 to 45 is computed in the framework of collinear and noncollinear Periodic Anderson model. The superlattices are composed of layers in (0 0 1) and (1 1 0) plane with ideal interface. The total energy shows that noncollinear orientation of the magnetic moments remains the ground state for all superlattices with Cr thickness above 5 MLs. Distribution of the magnetic moments for Fe/Cr(0 0 1) superlattices depends on parity of the Cr MLs. For odd numbers Cr magnetic moments are canted and symmetrically distributed between the neighboring Fe slabs. The values of Cr moments are enhanced at the interface and weakened to the bulk in the middle. For even numbers of Cr MLs quasi-helicoidal magnetic moments distribution consisting of two interleaved spirals is found. The moments are screwing sequentially from Fe/Cr interface to perpendicular orientation, keeping the angles and moments for some successive MLs, and then continue screwing towards the next interface. In Fe/Cr(1 1 0) superlattices the magnetic moments of two nonequivalent atoms in the monolayer are canted to each other near Fe/Cr interface and then swing the direction on perpendicular to the fixed Fe moments. - Highlights: • Frustration destroys the collinear magnetization in Fe/Cr superlattices. • Spin spiral were investigated within basic noncollinear Periodic Anderson Model. • Total energy of the spin spiral is generally more stable than collinear magnetization. • Neither step nor alloying at the Fe/Cr interface is necessary for Spin Spiral stability. • The two interleaved spirals calculated are similar to Fishman’s helical state.

  10. 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.

  11. Titania doped triaxial porcelain: Enhancement of strength by controlled heat treatment

    Indian Academy of Sciences (India)

    Sunipa Bhattacharyya; Swapan Kumar Das; Kausik Dana; Nirendra Krishna Mitra

    2007-06-01

    Titania doped vitrified triaxial porcelain samples were subjected to controlled heat treatment at different temperatures of 600, 800 and 1000°C with a specific heating schedule. The results revealed that flexural strength of 800°C heat treated sample was significantly enhanced to 60 MPa from its original value of 40 MPa. XRD pattern revealed the formation of mullite in the system both before and after heat treatment and the differences in their growth was ascertained through SEM analysis. The present heat treatment process may be useful to produce high strength porcelain body from a common triaxial system.

  12. Structural control of metamaterial oscillator strength and electric field enhancement at terahertz frequencies

    DEFF Research Database (Denmark)

    Keiser, G. R.; Seren, H. R.; Strikwerda, Andrew C.

    2014-01-01

    The design of artificial nonlinear materials requires control over internal resonant charge densities and local electric field distributions. We present a MM design with a structurally controllable oscillator strength and local electric field enhancement at terahertz frequencies. The MM consists...... of a split ring resonator (SRR) array stacked above an array of closed conducting rings. An in-plane, lateral shift of a half unit cell between the SRR and closed ring arrays results in an increase of the MM oscillator strength by a factor of 4 and a 40% change in the amplitude of the resonant electric field...

  13. Level density of $^{56}$Fe and low-energy enhancement of $\\gamma$-strength function

    CERN Document Server

    Voinov, A V; Agvaanluvsan, U; Algin, E; Belgya, T; Brune, C R; Guttormsen, M; Hornish, M J; Massey, T; Mitchell, G E; Rekstad, J; Schiller, A; Siem, S

    2006-01-01

    The $^{55}$Mn$(d,n)^{56}$Fe differential cross section is measured at $E_d=7$ MeV\\@. The $^{56}$Fe level density obtained from neutron evaporation spectra is compared to the level density extracted from the $^{57}$Fe$(^3$He,$\\alpha\\gamma)^{56}$Fe reaction by the Oslo-type technique. Good agreement is found between the level densities determined by the two methods. With the level density function obtained from the neutron evaporation spectra, the $^{56}$Fe $\\gamma$-strength function is also determined from the first-generation $\\gamma$ matrix of the Oslo experiment. The good agreement between the past and present results for the $\\gamma$-strength function supports the validity of both methods and is consistent with the low-energy enhancement of the $\\gamma$ strength below $\\sim 4$ MeV first discovered by the Oslo method in iron and molybdenum isotopes.

  14. Enhancement of Adhesive Strength of Ultrahigh Molecular Weight Polyethylene Fibers Prepared by Polar Polymer Implantation

    Institute of Scientific and Technical Information of China (English)

    YU Jun-rong; YANG Xin-ge; HU Zu-ming; LIU Zhao-feng

    2007-01-01

    A new technique was proposed to enhance the adhesive strength of ultrahigh molecular weight polyethylene (UHMWPE) fibers. Polar polymer was implanted into UHMWPE gel fibers during extracting process and can then be trapped en the surface of the fibers after subsequent ultra-drawing. The physical and chemical changes in the fiber structure were examined with scanning electron microscopy (SEM) and Fourier transform infrared (FTIR) spectroscopy. The mechanical and interfacial adhesion properties of UHMWPE fibers were investigated with tensile testing. The results showed that there wee polar groups on the surface of pretreated UHMWPE fiber. The interracial shear strength of UHMWPE fibers with epoxy resin was greatly improved without socrificing the excellent mechanical properties of fibers. After pretreated with ethylene/vinyl acetate copolymer (EVA), the shear strength of the interface between fiber and epoxy resin increased from 1.06 to 2.49 MPa, while the integrated mechanical properties of the pretreated UHMWPE fibers ware still optimal.

  15. 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

  16. 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.

  17. Enhancement and Mitigation Mechanisms of Protein Fouling of Ultrafiltration Membranes under Different Ionic Strengths.

    Science.gov (United States)

    Miao, Rui; Wang, Lei; Mi, Na; Gao, Zhe; Liu, Tingting; Lv, Yongtao; Wang, Xudong; Meng, Xiaorong; Yang, Yongzhe

    2015-06-02

    To determine further the enhancement and mitigation mechanisms of protein fouling, filtration experiments were carried out with polyvinylidene fluoride (PVDF) ultrafiltration (UF) membranes and bovine serum albumin (BSA) over a range of ionic strengths. The interaction forces, the adsorption behavior of BSA on the membrane surface, and the structure of the BSA adsorbed layers at corresponding ionic strengths were investigated. Results indicate that when the ionic strength increased from 0 to 1 mM, there was a decrease in the PVDF-BSA and BSA-BSA electrostatic repulsion forces, resulting in a higher deposition rate of BSA onto the membrane surface, and the formation of a denser BSA layer; consequently, membrane fouling was enhanced. However, at ionic strengths of 10 and 100 mM, membrane fouling and the BSA removal rate decreased significantly. This was mainly due to the increased hydration repulsion forces, which caused a decrease in the PVDF-BSA and BSA-BSA interaction forces accompanied by a decreased hydrodynamic radius and increased diffusion coefficient of BSA. Consequently, BSA passed more easily through the membrane and into permeate. There was less accumulation of BSA on the membrane surface. A more nonrigid and open structure BSA layer was formed on the membrane surface.

  18. Enhanced breakdown strength of multilayered films fabricated by forced assembly microlayer coextrusion

    Energy Technology Data Exchange (ETDEWEB)

    Mackey, Matt; Hiltner, Anne; Baer, Eric [Department of Macromolecular Science and Engineering, Case Western Reserve University, Cleveland, OH 44106-7202 (United States); Flandin, Lionel [LMOPS UMR 5041, CNRS Universite de Savoie, F-73376 Le Bourget Du Lac Cedex (France); Wolak, Mason A; Shirk, James S, E-mail: Anne.Hiltner@cwru.ed [US Naval Research Laboratory, Washington, DC 20375 (United States)

    2009-09-07

    There is a need in electronic systems and pulsed power applications for capacitors with high energy density. From a material standpoint, capacitive energy density improves with increasing dielectric constant and/or breakdown strength. Current state-of-the-art polymeric capacitors are, however, limited in that their dielectric constant is low (2-4). Our approach to improve polymer film capacitors is to combine, through microlayer coextrusion, two polymers with complementary properties: one with a high breakdown strength (polycarbonate) and one with a high dielectric constant (polyvinylidene fluoride-hexafluoropropylene). As opposed to the monolith controls, multilayered films with various numbers of layers and compositions subjected to a pulsed voltage exhibit treeing patterns that hinder the breakdown process. Consequently, substantially enhanced breakdown strengths are measured in the mutilayered films. It is further shown, by varying the overall film thickness, that the charge at the tip of the needle electrode is a key parameter that controls treeing. Based on the acquired data, a breakdown mechanism is formulated to explain the increased dielectric strengths. Using the understanding gained from these systems, selection and optimization of future layered structures can be carried out to obtain additional property enhancements.

  19. Magnetization-Enhanced Dislocation Motion and Decreased Yield Strength of 60Fe40Ni Alloy

    Institute of Scientific and Technical Information of China (English)

    2001-01-01

    Using a special constant deflection device, the changes in dislocation configuration ahead of a loaded crack tip for 60Fe40Ni alloy, before and after magnetization in a magnetic field, have been studied in TEM. The results showed that the magnetization for 60Fe40Ni alloy could enhance dislocation emission, multiplication and motion. Also, the mechanical properties of 60Fe40Ni alloy, in air and in the magnetic field respectively, have been investigated using the slow strain rate tension. And the results indicated that magnetization could make the yield strength corresponding to decrease by 26 percent, but did not influence the ultimate tensile strength and the fracture strain, which showed that magnetization could enhance plastic deformation.

  20. Structural control of metamaterial oscillator strength and electric field enhancement at terahertz frequencies

    Science.gov (United States)

    Keiser, G. R.; Seren, H. R.; Strikwerda, A. C.; Zhang, X.; Averitt, R. D.

    2014-08-01

    The design of artificial nonlinear materials requires control over internal resonant charge densities and local electric field distributions. We present a MM design with a structurally controllable oscillator strength and local electric field enhancement at terahertz frequencies. The MM consists of a split ring resonator (SRR) array stacked above an array of closed conducting rings. An in-plane, lateral shift of a half unit cell between the SRR and closed ring arrays results in an increase of the MM oscillator strength by a factor of 4 and a 40% change in the amplitude of the resonant electric field enhancement in the SRR capacitive gap. We use terahertz time-domain spectroscopy and numerical simulations to confirm our results. We show that the observed electromagnetic response in this MM is the result of image charges and currents induced in the closed rings by the SRR.

  1. Structural Control of Metamaterial Oscillator Strength and Electric Field Enhancement at Terahertz Frequencies

    CERN Document Server

    Keiser, George R; Strikwerda, Andrew C; Zhang, Xin; Averitt, Richard D

    2014-01-01

    The design of artificial nonlinear materials requires control over the internal resonant charge densities and local electric field distributions. We present a MM design with a structurally controllable oscillator strength and local electric field enhancement at terahertz frequencies. The MM consists of a split ring resonator (SRR) array stacked above an array of nonresonant closed conducting rings. An in-plane, lateral shift of a half unit cell between the SRR and closed ring arrays results in a decrease of the MM oscillator strength by a factor of 4 and a 40% change in the amplitude of the resonant electric field enhancement in the SRR capacitive gap. We use terahertz time-domain spectroscopy and numerical simulations to confirm our results and we propose a qualitative inductive coupling model to explain the observed electromagnetic reponse.

  2. Low-energy enhancement in the \\gamma-ray strength functions of $^{73,74}$Ge

    CERN Document Server

    Renstrøm, T; Utsumoniya, H; Schwengner, R; Goriely, S; Larsen, A C; Filipescu, D M; Gheorghe, I; Bernstein, L A; Bleuel, D L; Glodariu, T; Görgen, A; Guttormsen, M; Hagen, T W; Kheswa, B V; Lui, Y -W; Negi, D; Ruud, I E; Shima, T; Siem, S; Takahisa, K; Tesileanu, O; Tornyi, T G; Tveten, G M; Wiedeking, M

    2015-01-01

    The $\\gamma$-ray strength functions and level densities of $^{73,74}$Ge have been extracted up to the neutron separation energy S$_n$ from particle-$\\gamma$ coincidence data using the Oslo method. Moreover, the $\\gamma$-ray strength function of $^{74}$Ge above S$_n$ has been determined from photo-neutron measurements, hence these two experiments cover the range of E$_\\gamma \\approx$ 1-13 MeV for $^{74}$Ge. The obtained data show that both $^{73,74}$Ge display an increase in strength at low $\\gamma$ energies. The experimental $\\gamma$-ray strength functions are compared with $M1$ strength functions deduced from average $B(M1)$ values calculated within the shell model for a large number of transitions. The observed low-energy enhancements in $^{73,74}$Ge are adopted in the calculations of the $^{72,73}$Ge(n,$\\gamma$) cross sections, where there are no direct experimental data. Calculated reaction rates for more neutron-rich germanium isotopes are shown to be strongly dependent on the presence of the low-energy ...

  3. Structural Control of Metamaterial Oscillator Strength and Electric Field Enhancement at Terahertz Frequencies

    OpenAIRE

    Keiser, George R.; Seren, Huseyin R.; Strikwerda, Andrew C.; Zhang, Xin; Averitt, Richard D.

    2014-01-01

    The design of artificial nonlinear materials requires control over the internal resonant charge densities and local electric field distributions. We present a MM design with a structurally controllable oscillator strength and local electric field enhancement at terahertz frequencies. The MM consists of a split ring resonator (SRR) array stacked above an array of nonresonant closed conducting rings. An in-plane, lateral shift of a half unit cell between the SRR and closed ring arrays results i...

  4. Formation of size-controlled silicon nanocrystals in plasma enhanced chemical vapor deposition grown SiO{sub x}N{sub y}/SiO{sub 2} superlattices

    Energy Technology Data Exchange (ETDEWEB)

    Hartel, A.M., E-mail: andreas.hartel@imtek.uni-freiburg.de [IMTEK, Faculty of Engineering, Albert-Ludwigs-University Freiburg, Georges-Koehler-Allee 103, 79110 Freiburg (Germany); Hiller, D.; Gutsch, S. [IMTEK, Faculty of Engineering, Albert-Ludwigs-University Freiburg, Georges-Koehler-Allee 103, 79110 Freiburg (Germany); Loeper, P. [Fraunhofer Institute for Solar Energy Systems, Heidenhofstr. 2, 79110 Freiburg (Germany); Estrade, S. [MIND-IN2UB, Departament d' Electronica, Universitat de Barcelona, Marti i Franques 1, 08028 Barcelona (Spain); TEM-MAT, SCT- UB, Sole i Sabaris 1, 08028 Barcelona (Spain); Peiro, F.; Garrido, B. [MIND-IN2UB, Departament d' Electronica, Universitat de Barcelona, Marti i Franques 1, 08028 Barcelona (Spain); Zacharias, M. [IMTEK, Faculty of Engineering, Albert-Ludwigs-University Freiburg, Georges-Koehler-Allee 103, 79110 Freiburg (Germany)

    2011-10-31

    Size controlled silicon nanocrystals (SiNC) in silicon oxynitride matrix were prepared using plasma enhanced chemical vapor deposition. The as-deposited superlattices (SLs) and the corresponding bulk films were treated by thermal annealing. Hydrogen effusion was performed during the heating up by choosing a sufficiently low heating ramp. The phase separation of the layers into SiNCs and surrounding oxynitride matrix was studied at temperatures of up to 1150 {sup o}C. The influence of the annealing temperature on SiO{sub x}N{sub y}/SiO{sub 2} - SLs with varying SiO{sub x}N{sub y} layer thickness was investigated by several analytical techniques including variable angle spectroscopic ellipsometry, photoluminescence (PL) spectroscopy, x-ray photoelectron spectroscopy, Fourier transform infrared spectrometry (FTIR) and transmission electron microscopy (TEM). Before annealing FTIR investigations show in addition to the expected Si-O bonds also the formation of nitrogen and hydrogen related bonds. The shift of the Si-O-Si stretching vibration to higher wave numbers after annealing indicates phase separation. The disappearance of the hydrogen related bonds indicates the hydrogen effusion. The PL signal is rising significantly with increasing annealing temperature and the PL peak position is strongly related to the thickness of the SiO{sub x}N{sub y} sublayers due to quantum confinement effects. TEM investigations confirm the size-controlled growth of SiNCs within the oxynitride matrix. The role of incorporated nitrogen and hydrogen is discussed.

  5. Large enhancement of radiative strength for soft transisitons in the quasicontinuum

    CERN Document Server

    Voinov, A; Agvaanluvsan, U; Belgya, T; Chankova, R; Guttormsen, M; Mitchell, G E; Rekstad, J; Schiller, A; Siem, S

    2004-01-01

    Radiative strength functions (RSFs) for the 56,57-Fe nuclei below the separation energy are obtained from the 57-Fe(3-He,alpha gamma)56-Fe and 57-Fe(3-He,3-He' gamma)57-Fe reactions, respectively. An enhancement of more than a factor of ten over common theoretical models of the soft (E_gamma ~< 2 MeV) RSF for transitions in the quasicontinuum (several MeV above the yrast line) is observed. Two-step cascade intensities with soft primary transitions from the 56-Fe(n,2gamma)57-Fe reaction confirm the enhancement.

  6. IS ENHANCED-ECCENTRIC RESISTANCE TRAINING SUPERIOR TO TRADITIONAL TRAINING FOR INCREASING ELBOW FLEXOR STRENGTH?

    Directory of Open Access Journals (Sweden)

    Thomas W. Kaminski

    2003-06-01

    Full Text Available Protocols for strengthening muscle are important for fitness, rehabilitation, and the prevention of myotendinous injuries. In trained individuals, the optimal method of increasing strength remains unclear. The purpose of this study was to compare the effects of a traditional method of strengthening with a method that allowed for enhanced-eccentric training, on changes in elbow flexor strength in trained subjects. Thirty-nine (8 male, 31 female trained subjects with normal elbow function participated in this study. Subjects were rank-ordered according to isometric force production and randomly assigned to one of three training groups: control (CONT, traditional concentric/eccentric (TRAD, and concentric/enhanced-eccentric (NEG. The training groups completed 24 training sessions. An evaluator blinded to training group performed all testing. Mixed model ANOVA techniques were used to determine if differences existed in concentric one repetition maximum strength, and isometric force production among groups. Changes in peak and average isokinetic force production were also compared. Type 1 error was maintained at 5%. While both groups improved concentric one repetition maximum (NEG = 15.5%, TRAD = 13.8% neither training group statistically differed from changes demonstrated by the CONT group. Nor did either training group show significant improvements in isometric or isokinetic force production over the CONT group. These results do not support the superiority of enhanced-eccentric training for increasing force production in trained subjects.

  7. A scaffold-enhanced light-activated surgical adhesive technique: surface selection for enhanced tensile strength in wound repair

    Science.gov (United States)

    Soller, Eric C.; Hoffman, Grant T.; Heintzelman, Douglas L.; Duffy, Mark T.; Bloom, Jeffrey N.; McNally-Heintzelman, Karen M.

    2004-07-01

    An ex vivo study was conducted to determine the effect of the irregularity of the scaffold surface on the tensile strength of repairs formed using our Scaffold-Enhanced Biological Adhesive (SEBA). Two different scaffold materials were investigated: (i) a synthetic biodegradable material fabricated from poly(L-lactic-co-glycolic acid); and (ii) a biological material, small intestinal submucosa, manufactured by Cook BioTech. The scaffolds were doped with protein solder composed of 50%(w/v) bovine serum albumin solder and 0.5mg/ml indocyanine green dye mixed in deionized water, and activated with an 808-nm diode laser. The tensile strength of repairs performed on bovine thoracic aorta, liver, spleen, small intestine and lung, using the smooth and irregular surfaces of the above scaffold-enhanced materials were measured and the time-to-failure was recorded. The tensile strength of repairs formed using the irregular surfaces of the scaffolds were consistently higher than those formed using the smooth surfaces of the scaffolds. The largest difference was observed on repairs formed on the aorta and small intestine, where the repairs were, on average, 50% stronger using the irregular versus the smooth scaffold surfaces. In addition, the time-to-failure of repairs formed using the irregular surfaces of the scaffolds were between 50% and 100% longer than that achieved using the smooth surfaces of the scaffolds. It has previously been shown that distributing or dispersing the adhesive forces over the increased surface area of the scaffold, either smooth or irregular, produces stronger repairs than albumin solder alone. The increase in the absolute strength and longevity of repairs seen in this new study when the irregular surfaces of the scaffolds are used is thought to be due to the distribution of forces between the many independent micro-adhesions provided by the irregular surfaces.

  8. Longer Interset Rest Periods Enhance Muscle Strength and Hypertrophy in Resistance-Trained Men.

    Science.gov (United States)

    Schoenfeld, Brad J; Pope, Zachary K; Benik, Franklin M; Hester, Garrett M; Sellers, John; Nooner, Josh L; Schnaiter, Jessica A; Bond-Williams, Katherine E; Carter, Adrian S; Ross, Corbin L; Just, Brandon L; Henselmans, Menno; Krieger, James W

    2016-07-01

    Schoenfeld, BJ, Pope, ZK, Benik, FM, Hester, GM, Sellers, J, Nooner, JL, Schnaiter, JA, Bond-Williams, KE, Carter, AS, Ross, CL, Just, BL, Henselmans, M, and Krieger, JW. Longer interset rest periods enhance muscle strength and hypertrophy in resistance-trained men. J Strength Cond Res 30(7): 1805-1812, 2016-The purpose of this study was to investigate the effects of short rest intervals normally associated with hypertrophy-type training versus long rest intervals traditionally used in strength-type training on muscular adaptations in a cohort of young, experienced lifters. Twenty-one young resistance-trained men were randomly assigned to either a group that performed a resistance training (RT) program with 1-minute rest intervals (SHORT) or a group that employed 3-minute rest intervals (LONG). All other RT variables were held constant. The study period lasted 8 weeks with subjects performing 3 total body workouts a week comprised 3 sets of 8-12 repetition maximum (RM) of 7 different exercises per session. Testing was performed prestudy and poststudy for muscle strength (1RM bench press and back squat), muscle endurance (50% 1RM bench press to failure), and muscle thickness of the elbow flexors, triceps brachii, and quadriceps femoris by ultrasound imaging. Maximal strength was significantly greater for both 1RM squat and bench press for LONG compared to SHORT. Muscle thickness was significantly greater for LONG compared to SHORT in the anterior thigh, and a trend for greater increases was noted in the triceps brachii (p = 0.06) as well. Both groups saw significant increases in local upper body muscle endurance with no significant differences noted between groups. This study provides evidence that longer rest periods promote greater increases in muscle strength and hypertrophy in young resistance-trained men.

  9. 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.

  10. 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....

  11. 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.

  12. Enhancement effect of pre-reacted glass on strength of glass-ionomer cement.

    Science.gov (United States)

    Monmaturapoj, Naruporn; Soodsawang, Wiwaporn; Tanodekaew, Siriporn

    2012-02-03

    In this paper, we report on the enhanced strength of glass ionomer cement (GIC) by using the process of pre acid-base reaction and spray drying in glass preparation. The pre acid-base reaction was induced by prior mixing of the glass powder with poly(alkenoic acid). The weight ratios of glass powder to poly(alkenoic acid) were varied to investigate the extent of the pre acid-base reaction of the glass. The effect of the spray drying process which produced spherical glass particles on cement strength was also studied and discussed. The results show that adding 2%-wt of poly(alkenoic acid) liquid in the pre-reacted step improved cement strength. GICs prepared using a mixture of pre-reacted glass with both spherical and irregular powders at 60:40 by weight exhibited the highest compressive strength at 138.64±7.73 MPa. It was concluded that glass ionomer cements containing pre-reacted glass with mixed glass morphology using both spherical and irregular forms are promising as restorative dental materials with improved mechanical properties and handling characteristics.

  13. Psychosocial Strength Enhancing Resilience in Adolescents and Young Adults With Cancer.

    Science.gov (United States)

    Ishibashi, Akiko; Okamura, Jun; Ueda, Reiko; Sunami, Shosuke; Kobayashi, Ryoji; Ogawa, Junko

    2016-01-01

    The purpose of this study was to explore ways of enhancing psychosocial strengths in newly diagnosed and relapsed adolescents and young adults (AYAs) to improve their resilience. A descriptive case study was used. The adolescent resilience model (ARM) and the self-sustaining process model were applied as theories. The data were analyzed using pattern-matching logic. Semistructured interviews were conducted with 18 patients aged 12 to 24 years and discharged within 10 years. We found that the newly diagnosed and the relapsing AYAs developed the 5 strength factors of the ARM during and after treatment. Whether the individuals cultivated a positive attitude and sense of purpose early or late, the AYAs developed resilience eventually. A positive attitude and sense of purpose during the early phase of care may be essential for improving resilience. The AYAs benefited from the support of their parents, friends, and previous experience. Individualized support and social resources may be important to develop these strengths. Further research is needed to develop strengths and improve resilience in newly diagnosed AYAs.

  14. An experimental study on flexural strength enhancement of concrete by means of small steel fibers

    Directory of Open Access Journals (Sweden)

    Abdoullah Namdar

    2013-10-01

    Full Text Available Cost effective improvement of the mechanical performances of structural materials is an important goal in construction industry. To improve the flexural strength of plain concrete so as to reduce construction costs, the addition of fibers to the concrete mixture can be adopted. The addition of small steel fibers with different lengths and proportion have experimentally been analyzed in terms of concrete flexural strength enhancement. The main objectives of the present study are related to the evaluation of the influence of steel fibers design on the increase of concrete flexural characteristics and on the mode of failure. Two types of beams have been investigated. The force level, deflection and time to failure of beams have been measured. The shear crack, flexural crack and intermediate shear-flexural crack have been studied. The steel fiber content controlled crack morphology. Flexural strength and time to failure of fiber reinforce concrete could be further enhanced if, instead of smooth steel fibers, corrugated fibers were used.

  15. Enhancing the adhesion strength of micro electroforming layer by ultrasonic agitation method and the application.

    Science.gov (United States)

    Zhao, Zhong; Du, Liqun; Tao, Yousheng; Li, Qingfeng; Luo, Lei

    2016-11-01

    Micro electroforming is widely used for fabricating micro metal devices in Micro Electro Mechanism System (MEMS). However, there is the problem of poor adhesion strength between micro electroforming layer and substrate. This dramatically influences the dimensional accuracy of the device. To solve this problem, ultrasonic agitation method is applied during the micro electroforming process. To explore the effect of the ultrasonic agitation on the adhesion strength, micro electroforming experiments were carried out under different ultrasonic power (0W, 100W, 150W, 200W, 250W) and different ultrasonic frequencies (0kHz, 40kHz, 80kHz, 120kHz, 200kHz). The effects of the ultrasonic power and the ultrasonic frequency on the micro electroforming process were investigated by polarization method and alternating current (a.c.) impedance method. The adhesion strength between the electroforming layer and the substrate was measured by scratch test. The compressive stress of the electroforming layer was measured by X-ray Diffraction (XRD) method. The crystallite size of the electroforming layer was measured by Transmission Electron Microscopy (TEM) method. The internal contact surface area of the electroforming layer was measured by cyclic voltammetry (CV) method. The experimental results indicate that the ultrasonic agitation can decrease the polarization overpotential and increase the charge transfer process. Generally, the internal contact surface area is increased and the compressive stress is reduced. And then the adhesion strength is enhanced. Due to the different depolarization effects of the ultrasonic power and the ultrasonic frequency, the effects on strengthening the adhesion strength are different. When the ultrasonic agitation is 200W and 40kHz, the effect on strengthening the adhesion strength is the best. In order to prove the effect which the ultrasonic agitation can improve the adhesion strength of the micro devices, micro pillar arrays were fabricated under

  16. Tamarindus indica pectin blend film composition for coating tablets with enhanced adhesive force strength.

    Science.gov (United States)

    Khurana, Rajneet; Singh, Kuldeep; Sapra, Bharti; Tiwary, A K; Rana, Vikas

    2014-02-15

    Tablet coating is the most useful method to improve tablet texture, odour and mask taste. Thus, the present investigation was aimed at developing an industrially acceptable aqueous tablet coating material. The physico-chemical, electrical and SEM investigations ensures that blending of Tamarindus indica (Linn.) pectin (TP) with chitosan gives water resistant film texture. Therefore, CH-TP (60:40) spray coated tablets were prepared. The evaluation of CH-TP coated tablets showed enhanced adhesive force strength (between tablet surface to coat) and negligible cohesive force strength (between two tablets) both evaluated using texture analyzer. The comparison of CH-TP coated tablets with Eudragit coated tablets further supported superiority of the former material. Thus, the findings pointed towards the potential of CH-TP for use as a tablet coating material in food as well as pharmaceutical industry.

  17. High-dose inhaled terbutaline increases muscle strength and enhances maximal sprint performance in trained men

    DEFF Research Database (Denmark)

    Hostrup, Morten; Kalsen, Anders; Bangsbo, Jens

    2014-01-01

    PURPOSE: The purpose of the present study was to investigate the effect of high-dose inhaled terbutaline on muscle strength, maximal sprinting, and time-trial performance in trained men. METHODS: Nine non-asthmatic males with a [Formula: see text] of 58.9 ± 3.1 ml min(-1) kg(-1) (mean ± SEM......) participated in a double-blinded randomized crossover study. After administration of inhaled terbutaline (30 × 0.5 mg) or placebo, subjects' maximal voluntary isometric contraction (MVC) of m.quadriceps was measured. After MVC, subjects performed a 30-s Wingate test. Sixty minutes following the Wingate test...... was not different between treatments (P = 0.236). CONCLUSION: High-dose inhaled terbutaline elicits a systemic response that enhances muscle strength and sprint performance. High-dose terbutaline should therefore continue to be restricted in competitive sport....

  18. Autonomous CaMKII requires further stimulation by Ca2+/calmodulin for enhancing synaptic strength.

    Science.gov (United States)

    Barcomb, Kelsey; Buard, Isabelle; Coultrap, Steven J; Kulbe, Jacqueline R; O'Leary, Heather; Benke, Timothy A; Bayer, K Ulrich

    2014-08-01

    A hallmark feature of Ca(2+)/calmodulin (CaM)-dependent protein kinase II (CaMKII) is generation of autonomous (Ca(2+)-independent) activity by T286 autophosphorylation. Biochemical studies have shown that "autonomous" CaMKII is ∼5-fold further stimulated by Ca(2+)/CaM, but demonstration of a physiological function for such regulation within cells has remained elusive. In this study, CaMKII-induced enhancement of synaptic strength in rat hippocampal neurons required both autonomous activity and further stimulation. Synaptic strength was decreased by CaMKIIα knockdown and rescued by reexpression, but not by mutants impaired for autonomy (T286A) or binding to NMDA-type glutamate receptor subunit 2B (GluN2B; formerly NR2B; I205K). Full rescue was seen with constitutively autonomous mutants (T286D), but only if they could be further stimulated (additional T305/306A mutation), and not with two other mutations that additionally impair Ca(2+)/CaM binding. Compared to rescue with wild-type CaMKII, the CaM-binding-impaired mutants even had reduced synaptic strength. One of these mutants (T305/306D) mimicked an inhibitory autophosphorylation of CaMKII, whereas the other one (Δstim) abolished CaM binding without introducing charged residues. Inhibitory T305/306 autophosphorylation also reduced GluN2B binding, but this effect was independent of reduced Ca(2+)/CaM binding and was not mimicked by T305/306D mutation. Thus, even autonomous CaMKII activity must be further stimulated by Ca(2+)/CaM for enhancement of synaptic strength.

  19. Health enhancing strength training in nonagenarians (STRONG: rationale, design and methods

    Directory of Open Access Journals (Sweden)

    Sanz Natalia

    2009-05-01

    Full Text Available Abstract Background The Health Enhancing Strength Training in Nonagenarians (STRONG is a randomised control trial to assess the effectiveness of an aerobic and strength training program for improving muscle strength, functional capacity and quality of life in nonagenarians. Methods Sixty (51 women nonagenarians (age range: 90–102 years who live in a geriatric nursing home will be randomly assigned to either a usual care (control group (n = 30 or an intervention (training group (n = 30. Participants allocated in the usual care group will receive general physical activity guidelines and participants allocated in the intervention group will also enrol in three weekly non-consecutive individualized training sessions (~45–50 min each during 8 weeks. The exercise program will consist of muscular strength [with a special focus on leg press at 30% (start of the program to 70% 1 repetition maximum (end] and aerobic exercises (cycle-ergometry during 3–5 to 15 minutes at 12–14 points in the rate of perceived exertion scale. Results Results from STRONG will help to better understand the potential of regular physical activity for improving the well-being of the oldest population groups. Conclusion The increase in life expectancy together with the dramatic decrease in birth rates in industrialized countries calls the attention to health care systems and public health policymakers to focus attention on promoting healthy lifestyle in the highest sector of the population pyramid. Our study attempts to improve functional capacity and QOL of nonagenarians by implementing an individualised aerobic and strength training program in a geriatric residential care. Results from STRONG will help to better understand the potential of regular physical activity for improving the well being even in persons aged 90 years or over. Trail Registration ClinicalTrials.gov ID: NCT00848978

  20. 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.

  1. 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.

  2. 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.

  3. Level densities of iron isotopes and lower-energy enhancement of y-strength function

    Energy Technology Data Exchange (ETDEWEB)

    Voinov, A V; Grimes, S M; Agvaanluvsan, U; Algin, E; Belgya, T; Brune, C R; Guttormsen, M; Hornish, M J; Massey, T N; Mitchell, G; Rekstad, J; Schiller, A; Siem, S

    2005-08-30

    The neutron spectrum from the {sup 55}Mn(d,n){sup 56}Fe reaction has been measured at E{sub d} = 7 MeV. The level density of {sup 56}Fe obtained from neutron evaporation spectrum has been compared to the level density from Oslo-type {sup 57}Fe({sup 3}He, a{gamma}){sup 56}Fe experiment [1]. The good agreement supports the recent results [1, 8] including an availability of a low-energy enhancement in the {gamma}-strength function for iron isotopes. The new level density function allowed us to investigate an excitation energy dependence of this enhancement, which is shown to increase with increasing excitation energy.

  4. Aliphatic carboxylic acids and alcohols as efficiency and elution strength enhancers in micellar liquid chromatography.

    Science.gov (United States)

    Boichenko, Alexander P; Berthod, Alain

    2010-09-03

    Micellar liquid chromatography (MLC) uses surfactant solutions as mobile phases with added organic additives to enhance both the elution strength and the chromatographic efficiency. Two aliphatic carboxylic acids (1-butanoic and 1-pentanoic) were used as MLC additives and compared with the two corresponding alcohols (1-butanol, 1-pentanol) in terms of elution strength, efficiency and selectivity. A set of 11 phenol derivatives was used as probe compounds. All micellar mobile phases were prepared with sodium dodecylsulfate (SDS) with concentration ranging from 0.05 to 0.15M and the modifier content within 1.0 and 5.0% (v/v). The elution strength of different mobile phases containing a constant amount of SDS and different amounts of modifiers; and mobile phases containing a constant amount of modifier and different SDS concentration were determined and discussed. The effect of the acid modifiers on efficiency was studied constructing van Deemter plots that showed no minimum within the 0.01-0.7mL/min flow rate range studied. Temperature effects were also studied constructing the classical van't Hoff plots. The slight curvature of the plots in the 25-70 degrees C range may indicate some modification of the surfactant-bonded moiety layer on the stationary phase surface. Since no definitive advantage of the use of aliphatic acids were established compared to their alcohol counterpart, their terrible smell will probably preclude their use as MLC organic modifiers.

  5. Enhancement of shear strength and ductility for reinforced concrete wide beams due to web reinforcement

    Directory of Open Access Journals (Sweden)

    M. Said

    2013-12-01

    Full Text Available The shear behavior of reinforced concrete wide beams was investigated. The experimental program consisted of nine beams of 29 MPa concrete strength tested with a shear span-depth ratio equal to 3.0. One of the tested beams had no web reinforcement as a control specimen. The flexure mode of failure was secured for all of the specimens to allow for shear mode of failure. The key parameters covered in this investigation are the effect of the existence, spacing, amount and yield stress of the vertical stirrups on the shear capacity and ductility of the tested wide beams. The study shows that the contribution of web reinforcement to the shear capacity is significant and directly proportional to the amount and spacing of the shear reinforcement. The increase in the shear capacity ranged from 32% to 132% for the range of the tested beams compared with the control beam. High grade steel was more effective in the contribution of the shear strength of wide beams. Also, test results demonstrate that the shear reinforcement significantly enhances the ductility of the wide beams. In addition, shear resistances at failure recorded in this study are compared to the analytical strengths calculated according to the current Egyptian Code and the available international codes. The current study highlights the need to include the contribution of shear reinforcement in the Egyptian Code requirements for shear capacity of wide beams.

  6. Carbon Nanotube Nanocomposites with Highly Enhanced Strength and Conductivity for Flexible Electric Circuits.

    Science.gov (United States)

    Hwang, Ji-Young; Kim, Han-Sem; Kim, Jeong Hun; Shin, Ueon Sang; Lee, Sang-Hoon

    2015-07-21

    Carbon nanotubes (CNTs) have an important role in nanotechnology due to their unique properties, retaining the inherent material flexibility, superior strength, and electrical conductivity, unless the bottleneck of CNTs persists and the aggregated structure is overcome. Here, we report on the highly enhanced mechanical and electrical properties of the CNT-chitosan nanocomposites through homogeneous dispersion of CNTs into chitosan solution using a high-pressure homogenizer. The optimal condition is a 50% (w/w) chitosan-CNT film, providing about 7 nm thickness of homogeneous chitosan layer on CNTs, a good tensile strength of 51 MPa, high electrical conductivity under 16 Ω/sq, and a stable bending and folding performance. This CNT-chitosan nanocomposite with highly enhanced properties is an amenable material to fabricate structures of various shapes such as films, sensors, and circuits and also enables a simple and cost-effective approach to improve the performance of a device that presents the first flexible and soft electric circuits yet reported using only CNT-chitosan as the conductor.

  7. Strength Training to Enhance Early Recovery after Hematopoietic Stem Cell Transplantation.

    Science.gov (United States)

    Hacker, Eileen Danaher; Collins, Eileen; Park, Chang; Peters, Tara; Patel, Pritesh; Rondelli, Damiano

    2016-12-29

    Intensive cancer treatment followed by hematopoietic stem cell transplantation (HCT) results in moderate to severe fatigue and physical inactivity, leading to diminished functional ability. The purpose of this study was to determine the efficacy of an exercise intervention, strength training to enhance early recovery (STEER), on physical activity, fatigue, muscle strength, functional ability, and quality of life after HCT. This single-blind, randomized clinical trial compared strength training (n = 33) to usual care plus attention control with health education (UC + AC with HE) (n = 34). Subjects were stratified by type of transplantation and age. STEER consisted of a comprehensive program of progressive resistance introduced during hospitalization and continued for 6 weeks after hospital discharge. Fatigue, physical activity, muscle strength, functional ability, and quality of life were assessed before HCT hospital admission and after intervention completion. Data were analyzed using split-plot analysis of variance. Significant time × group interactions effects were noted for fatigue (P = .04). The STEER group reported improvement in fatigue from baseline to after intervention whereas the UC + AC with HE group reported worsened fatigue from baseline to after intervention. Time (P < .001) and group effects (P = .05) were observed for physical activity. Physical activity declined from baseline to 6 weeks after hospitalization. The STEER group was more physically active. Functional ability tests (timed stair climb and timed up and go) resulted in a significant interaction effect (P = .03 and P = .05, respectively). Subjects in the UC + AC with HE group were significantly slower on both tests baseline to after intervention, whereas the STEER group's time remained stable. The STEER group completed both tests faster than the UC + AC with HE group after intervention. Study findings support the use of STEER after intensive cancer treatment and HCT

  8. 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.

  9. Giant piezoelectric response in piezoelectric/dielectric superlattices due to flexoelectric effect

    Science.gov (United States)

    Liu, Chang; Wu, Huaping; Wang, Jie

    2016-11-01

    Flexoelectricity describes the linear response of electrical polarization to a strain gradient, which can be used to enhance the piezoelectric effect of piezoelectric material or realize the piezoelectric effect in nonpiezoelectric materials. Here, we demonstrate from thermodynamics theory that a giant piezoelectric effect exists in piezoelectric/dielectric superlattices due to flexoelectric effect. The apparent piezoelectric coefficient is calculated from the closed-form of analytical expression of the polarization distribution in the piezoelectric/dielectric superlattice subjected to a normal stress, in which the flexoelectric effect is included. It is found that there exists a strong nonlinear coupling between the flexoelectric and piezoelectric effects, which significantly enhances the apparent piezoelectric coefficient in the piezoelectric/dielectric superlattice. For a specific thickness ratio of the piezoelectric and dielectric layers, the enhanced apparent piezoelectric coefficient in the superlattice is ten times larger than that of its pure piezoelectric counterpart. The present work suggests an effective way to obtain giant apparent piezoelectric effect in piezoelectric/dielectric superlattices through flexoelectric effect.

  10. 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...

  11. Spin selector based on periodic diluted-magnetic-semiconductor/nonmagnetic-barrier superlattices

    Directory of Open Access Journals (Sweden)

    Ping-Fan Yang

    2015-07-01

    Full Text Available We propose a spin selector based on periodic diluted-magnetic-semiconductor/nonmagnetic-barrier (DMS/NB superlattices subjected to an external magnetic field. We find that the periodic DMS/NB superlattices can achieve 100% spin filtering over a dramatically broader range of incident energies than the diluted-magnetic-semiconductor/semiconductor (DMS/S case studied previously. And the positions and widths of spin-filtering bands can be manipulated effectively by adjusting the geometric parameters of the system or the strength of external magnetic field. Such a compelling filtering feature stems from the introduction of nonmagnetic barrier and the spin-dependent giant Zeeman effect induced by the external magnetic field. We also find that the external electric field can exert a significant influence on the spin-polarized transport through the DMS/NB superlattices.

  12. Spin selector based on periodic diluted-magnetic-semiconductor/nonmagnetic-barrier superlattices

    Energy Technology Data Exchange (ETDEWEB)

    Yang, Ping-Fan; Guo, Yong, E-mail: guoy66@tsinghua.edu.cn [Department of Physics and State Key Laboratory of Low-Dimensional Quantum Physics, Tsinghua University, Beijing 100084 (China); Collaborative Innovation Center of Quantum Matter, Beijing (China); Zhu, Rui [Department of Physics, South China University of Technology, Guangzhou 510641 (China)

    2015-07-15

    We propose a spin selector based on periodic diluted-magnetic-semiconductor/nonmagnetic-barrier (DMS/NB) superlattices subjected to an external magnetic field. We find that the periodic DMS/NB superlattices can achieve 100% spin filtering over a dramatically broader range of incident energies than the diluted-magnetic-semiconductor/semiconductor (DMS/S) case studied previously. And the positions and widths of spin-filtering bands can be manipulated effectively by adjusting the geometric parameters of the system or the strength of external magnetic field. Such a compelling filtering feature stems from the introduction of nonmagnetic barrier and the spin-dependent giant Zeeman effect induced by the external magnetic field. We also find that the external electric field can exert a significant influence on the spin-polarized transport through the DMS/NB superlattices.

  13. A set of enhanced green fluorescent protein concatemers for quantitative determination of nuclear localization signal strength.

    Science.gov (United States)

    Böhm, Jennifer; Thavaraja, Ramya; Giehler, Susanne; Nalaskowski, Marcus M

    2017-09-15

    Regulated transport of proteins between nucleus and cytoplasm is an important process in the eukaryotic cell. In most cases, active nucleo-cytoplasmic protein transport is mediated by nuclear localization signal (NLS) and/or nuclear export signal (NES) motifs. In this study, we developed a set of vectors expressing enhanced GFP (EGFP) concatemers ranging from 2 to 12 subunits (2xEGFP to 12xEGFP) for analysis of NLS strength. As shown by in gel GFP fluorescence analysis and αGFP Western blotting, EGFP concatemers are expressed as fluorescent full-length proteins in eukaryotic cells. As expected, nuclear localization of concatemeric EGFPs decreases with increasing molecular weight. By oligonucleotide ligation this set of EGFP concatemers can be easily fused to NLS motifs. After determination of intracellular localization of EGFP concatemers alone and fused to different NLS motifs we calculated the size of a hypothetic EGFP concatemer showing a defined distribution of EGFP fluorescence between nucleus and cytoplasm (n/c ratio = 2). Clear differences of the size of the hypothetic EGFP concatemer depending on the fused NLS motif were observed. Therefore, we propose to use the size of this hypothetic concatemer as quantitative indicator for comparing strength of different NLS motifs. Copyright © 2017 Elsevier Inc. All rights reserved.

  14. The Role of Misfit Dislocations in Strength Enhancement of Cu/Ni Microlaminates

    Institute of Scientific and Technical Information of China (English)

    CHENG Dong; YAN Li; YAN Zhi-jun

    2004-01-01

    This paper simulated the nanoindentations of Cu/Ni thin films with 2D Molecular Dynamics Simulations (MDS) and examined the effects of the misfit dislocations on the mechanical properties of the microlaminates. The misfit dislocation network plays an important role in strength enhancement of Cu/Ni microlaminates because of its resistance to glide dislocations. But the strengthening also relies on the wavelength, which is defined as the thickness of adjacent two layers in microlaminates. When the wavelength is less than the critical value λc, the stress concentration caused by the movement of misfit dislocations will make Cu/Ni microlaminates weaken. Also, the critical wavelength should be more than the depth at which the dislocation nucleates in the homogeneous layer.

  15. Nanocomposites biodegradable coating on BOPET films to enhance hot seal strength properties

    Energy Technology Data Exchange (ETDEWEB)

    Barbaro, G., E-mail: giovannibarbaro@email.it; Galdi, M. R., E-mail: mrgaldi@unisa.it; Di Maio, L., E-mail: ldimaio@unisa.it; Incarnato, L., E-mail: lincarnato@unisa.it [Industrial Engineering Department, University of Salerno, Via Giovanni Paolo II 132, 84084 Fisciano (Italy)

    2015-12-17

    The coating technology is a strategic solution to improve the properties of flexible packaging films. Indeed, additional functional layers are often designed and added as coating on the substrate, in order to improve the characteristic of the flexible packaging and to meet the requirements for the desired gas or vapour barrier, for adhesion and sealing, or for improving the film printability, its aesthetics and durability. Moreover, this technology allows to functionalize a polymeric substrate applying materials with different chemistry, rheology, thermal and structural characteristics. BOPET films are widely used for food packaging applications thanks to their good gas barrier and mechanical properties, high transparency and for the excellent printability. In regard to sealing performance, BOPET films show poor sealing properties so they are mostly submitted to lamination processes with polyethylene. Nevertheless, this solution compromises the PET recyclability and influences the gas permeability of the multilayer PET based structures. The aim of this work is to investigate on the effect of nanocomposite biodegradable coatings for BOPET substrates in enhancing the heat sealing strength of eco-compatible PET/PLA films. At this regards, different percentages of Cloisite C30B (0%, 2% and 4%{sub wt/wt}) have been added to PLA by solution intercalation technique and the nanocomposite biodegradable materials produced have been applied on BOPET commercial films by casting. The BOPET coated films have been characterized in order to evaluate the heat sealing strength and the mechanical, gas permeability and surface properties. The results have shown that the addition of nanoclay in PLA coating significantly enhance the hot tack properties of the PET/PLA system produced, while the oxygen and water vapour permeability are slightly increased if compared to pure BOPET films.

  16. Nanocomposites biodegradable coating on BOPET films to enhance hot seal strength properties

    Science.gov (United States)

    Barbaro, G.; Galdi, M. R.; Di Maio, L.; Incarnato, L.

    2015-12-01

    The coating technology is a strategic solution to improve the properties of flexible packaging films. Indeed, additional functional layers are often designed and added as coating on the substrate, in order to improve the characteristic of the flexible packaging and to meet the requirements for the desired gas or vapour barrier, for adhesion and sealing, or for improving the film printability, its aesthetics and durability. Moreover, this technology allows to functionalize a polymeric substrate applying materials with different chemistry, rheology, thermal and structural characteristics. BOPET films are widely used for food packaging applications thanks to their good gas barrier and mechanical properties, high transparency and for the excellent printability. In regard to sealing performance, BOPET films show poor sealing properties so they are mostly submitted to lamination processes with polyethylene. Nevertheless, this solution compromises the PET recyclability and influences the gas permeability of the multilayer PET based structures. The aim of this work is to investigate on the effect of nanocomposite biodegradable coatings for BOPET substrates in enhancing the heat sealing strength of eco-compatible PET/PLA films. At this regards, different percentages of Cloisite C30B (0%, 2% and 4%wt/wt) have been added to PLA by solution intercalation technique and the nanocomposite biodegradable materials produced have been applied on BOPET commercial films by casting. The BOPET coated films have been characterized in order to evaluate the heat sealing strength and the mechanical, gas permeability and surface properties. The results have shown that the addition of nanoclay in PLA coating significantly enhance the hot tack properties of the PET/PLA system produced, while the oxygen and water vapour permeability are slightly increased if compared to pure BOPET films.

  17. Manganite/Cuprate Superlattice as Artificial Reentrant Spin Glass

    KAUST Repository

    Ding, Junfeng

    2016-05-04

    Emerging physical phenomena at the unit-cell-controlled interfaces of transition-metal oxides have attracted lots of interest because of the rich physics and application opportunities. This work reports a reentrant spin glass behavior with strong magnetic memory effect discovered in oxide heterostructures composed of ultrathin manganite La0.7Sr0.3MnO3 (LSMO) and cuprate La2CuO4 (LCO) layers. These heterostructures are featured with enhanced ferromagnetism before entering the spin glass state: a Curie temperature of 246 K is observed in the superlattice with six-unit-cell LSMO layers, while the reference LSMO film with the same thickness shows much weaker magnetism. Furthermore, an insulator-metal transition emerges at the Curie temperature, and below the freezing temperature the superlattices can be considered as a glassy ferromagnetic insulator. These experimental results are closely related to the interfacial spin reconstruction revealed by the first-principles calculations, and the dependence of the reentrant spin glass behavior on the LSMO layer thickness is in line with the general phase diagram of a spin system derived from the infinite-range SK model. The results of this work underscore the manganite/cuprate superlattices as a versatile platform of creating artificial materials with tailored interfacial spin coupling and physical properties. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  18. Pygmy resonance and low-energy enhancement in the $\\gamma$-ray strength functions of Pd~isotopes

    CERN Document Server

    Eriksen, Tomas Kvalheim; Guttormsen, Magne; Görgen, Andreas; Larsen, Ann-Cecilie; Renstrøm, Therese; Ruud, Inger-Eli; Siem, Sunniva; Toft, Heidi Kristine; Tveten, Gry Merete; Wilson, Jonathan

    2014-01-01

    An unexpected enhancement in the $\\gamma$-ray strength function, as compared to the low energy tail of the Giant Dipole Resonance (GDR), has been observed for Sc, Ti, V, Fe and Mo isotopes for $E_\\gamma4$ MeV, which is interpreted as a PDR centered at $E_{\\gamma}\\approx8$ MeV. An enhanced $\\gamma$-ray strength at low energies is also observed for $^{105}$Pd, which is the lightest isotope measured in this work. Further, the results correspond and agree very well with the observations from the Cd isotopes, and support the suggested transitional region for the onset of low-energy enhancement with decreasing mass number. The neutron number dependency of the PDR strength is also evident.

  19. 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.

  20. Enhanced aqueous dissolution of a DNAPL source to characterize the source strength function

    Science.gov (United States)

    Wang, Fang; Annable, Michael D.; Schaefer, Charles E.; Ault, Timothy D.; Cho, Jaehyun; Jawitz, James W.

    2014-11-01

    Simplified analytical solutions, developed as source strength functions (SSFs), are capable of describing the temporal dissolution of nonaqueous phase liquids in groundwater, which is useful for predicting source longevity and can serve as a guide for remedial activities. Here, SSF parameters were estimated by fitting enhanced aqueous dissolution data from a flow cell consisting of three injection and four extraction wells to analytical dissolution models (power law model (PLM) and equilibrium streamtube model (EST)) at a trichloroethene (TCE) contaminated site, Alameda Point, California. Both the PLM and the EST model were able to characterize the observed aqueous TCE dissolution during enhanced water flooding. Additional field activities conducted at the site included soil core collection, a recirculated partitioning tracer test, passive flux meter transects, and push-pull tracer tests. The additional site characterization data were used to independently estimate the observed SSF parameters using information such as the TCE mass, distribution and porous media heterogeneity. The exponential decay model (a subset of the PLM) accurately predicted the enhanced dissolution, likely because the site was significantly aged (most of the mass in the plume rather than in the source zone) or middle stage, and the mass in the source zone could be approximately estimated. The EST tracer-based model, when combined with data from the recirculated partitioning tracer test, soil cores, and the push-pull tracer test, was capable of accurately predicting the observed aqueous dissolution. The mass in the source zone and the fraction of contaminated flowpaths were the most important site characteristics, requiring the greatest accuracy to predict aqueous dissolution. Establishing steady state dissolution was essential to provide a more accurate estimate of the fraction contaminated and high resolution data from soil cores in the source zone were needed to estimate the mass present.

  1. Elevated Nitrogen Deposition Enhances the Net CO2 Sink Strength in Alberta Bogs along a Post-fire Chronosequence

    Science.gov (United States)

    Wieder, R. K.; Vile, M. A.; Albright, C. M.; Scott, K. D.

    2014-12-01

    About 30% of the landscape of northern Alberta, Canada is occupied by peatlands, which persist at the low end range of both mean annual precipitation (moss, was not affected by N addition, suggesting that the overall response of NEE to N addition is the result of enhanced growth of ericaceous shrubs. These findings suggest that while elevated N deposition in the AOSR may enhance the strength of the overall CO2 sink of bogs in the short term, in the longer term, increased shrub growth has the potential to shade Sphagnum mosses, compromising the future bog CO2sink strength across the region.

  2. 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.

  3. Acoustic analogue of electronic BLOCH oscillations and resonant Zener tunneling in ultrasonic superlattices.

    Science.gov (United States)

    Sanchis-Alepuz, Helios; Kosevich, Yuriy A; Sánchez-Dehesa, José

    2007-03-30

    We demonstrate the existence of Bloch oscillations of acoustic fields in sound propagation through a superlattice of water cavities and layers of methyl methacrylate. To obtain the acoustic equivalent of a Wannier-Stark ladder, we employ a set of cavities with different thicknesses. Bloch oscillations are observed as time-resolved oscillations of transmission in a direct analogy to electronic Bloch oscillations in biased semiconductor superlattices. Moreover, for a particular gradient of cavity thicknesses, an overlap of two acoustic minibands occurs, which results in resonant Zener-like transmission enhancement.

  4. 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.

  5. 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.

  6. The issues and tentative solutions for contrast-enhanced magnetic resonance imaging at ultra-high field strength.

    Science.gov (United States)

    Fries, Peter; Morelli, John N; Lux, Francois; Tillement, Olivier; Schneider, Günther; Buecker, Arno

    2014-01-01

    Magnetic resonance imaging (MRI) performed at ultra-high field strengths beyond 3 Tesla (T) has become increasingly prevalent in research and preclinical applications. As such, the inevitable clinical implementation of such systems lies on the horizon. The major benefit of ultra-high field MRI is the markedly increased signal-to-noise ratios achievable, enabling acquisition of MR images with simultaneously greater spatial and temporal resolution. However, at field strengths higher than 3 T, the efficacy of Gd(III)-based contrast agents is diminished due to decreased r1 relaxivity, somewhat limiting imaging of the vasculature and contrast-enhanced imaging of tumors. There have been extensive efforts to design new contrast agents with high r1 relaxivities based on macromolecular compounds or nanoparticles; however, the efficacy of these agents at ultra-high field strengths has not yet been proven. The aim of this review article is to provide an overview of the basic principles of MR contrast enhancement processes and to highlight the main factors influencing relaxivity. In addition, challenges and opportunities for contrast-enhanced MRI at ultra-high field strengths will be explored. Various approaches for the development of effective contrast agent molecules that are suitable for a broad spectrum of applied field strengths will be discussed in the context of the current literature.

  7. Enhanced densification, strength and molecular mechanisms in shock compressed porous silicon

    Science.gov (United States)

    Lane, J. Matthew D.; Vogler, Tracy J.

    2015-06-01

    In most porous materials, void collapse during shock compression couples mechanical energy to thermal energy. Increased temperature drives up pressures and lowers densities in the final Hugoniot states as compared to full-density samples. Some materials, however, exhibit an anomalous enhanced densification in their Hugoniot states when porosity is introduced. We have recently shown that silicon is such a material, and demonstrated a molecular mechanism for the effect using molecular simulation. We will review results from large-scale non-equilibrium molecular dynamics (NEMD) and Hugoniotstat simulations of shock compressed porous silicon, highlighting the mechanism by which porosity produces local shear which nucleate partial phase transition and localized melting at shock pressures below typical thresholds in these materials. Further, we will characterize the stress states and strength of the material as a function of porosity from 5 to 50 percent and with various porosity microstructures. Sandia National Laboratories is a multi program laboratory managed and operated by Sandia Corporation, a wholly owned subsidiary of Lockheed Martin Corporation, for the U.S. Department of Energy's National Nuclear Security Administration under contract DE-AC04-94AL85000.

  8. Enhancing the interaction strength and capacities of hydrogen storage via surface adsorption

    Science.gov (United States)

    Brown, Craig

    2008-03-01

    Storing Hydrogen molecules in porous media based on a physisorption mechanism is one possible approach to reach the US Department of Energy targets for on-board hydrogen storage. Although the storage capacities of metal-organic frameworks (MOFs) have progressed significantly over recent years, some technological obstacles pose challenges for their future improvement. These include the generally low H2 adsorption enthalpy limiting room temperature applications and the lack of understanding of surface packing density hindering the efficient improvement of H2 adsorption uptake. To improve the H2 affinity in MOFs, our previous work has shown that the coordinatively unsaturated metal centers (CUMCs) can greatly enhance the H2 binding strength. Our current study of MOF-74 will be presented, showing that its open Zn^2+ ions bind H2 strongly and are identified as being responsible for the large initial H2 adsorption enthalpy of 8.4 kJ/mol. In all, there are four H2 adsorption sites in MOF-74 identified by neutron powder diffraction. These four hydrogen adsorption sites are closely packed in MOF-74 and form a one dimensional nanoscale tube structure. We also demonstrate an interesting correlation that MOFs with CUMCs generally show larger surface packing densities than that of other MOFs without CUMCs. The implications of this will be addressed.

  9. 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...

  10. 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 ...

  11. 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.

  12. 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.

  13. 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.

  14. 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.

  15. 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.

  16. Negative capacitance in multidomain ferroelectric superlattices

    Science.gov (United States)

    Zubko, Pavlo; Wojdeł, Jacek C.; Hadjimichael, Marios; Fernandez-Pena, Stéphanie; Sené, Anaïs; Luk'Yanchuk, Igor; Triscone, Jean-Marc; Íñiguez, Jorge

    2016-06-01

    The stability of spontaneous electrical polarization in ferroelectrics is fundamental to many of their current applications, which range from the simple electric cigarette lighter to non-volatile random access memories. Research on nanoscale ferroelectrics reveals that their behaviour is profoundly different from that in bulk ferroelectrics, which could lead to new phenomena with potential for future devices. As ferroelectrics become thinner, maintaining a stable polarization becomes increasingly challenging. On the other hand, intentionally destabilizing this polarization can cause the effective electric permittivity of a ferroelectric to become negative, enabling it to behave as a negative capacitance when integrated in a heterostructure. Negative capacitance has been proposed as a way of overcoming fundamental limitations on the power consumption of field-effect transistors. However, experimental demonstrations of this phenomenon remain contentious. The prevalent interpretations based on homogeneous polarization models are difficult to reconcile with the expected strong tendency for domain formation, but the effect of domains on negative capacitance has received little attention. Here we report negative capacitance in a model system of multidomain ferroelectric-dielectric superlattices across a wide range of temperatures, in both the ferroelectric and paraelectric phases. Using a phenomenological model, we show that domain-wall motion not only gives rise to negative permittivity, but can also enhance, rather than limit, its temperature range. Our first-principles-based atomistic simulations provide detailed microscopic insight into the origin of this phenomenon, identifying the dominant contribution of near-interface layers and paving the way for its future exploitation.

  17. Interfacial magnetic coupling in ultrathin all-manganite La0.7Sr0.3MnO3-TbMnO3 superlattices

    KAUST Repository

    Tian, Y. F.

    2014-04-14

    We report the growth and magnetic properties of all-manganite superlattices composed of ultrathin double-exchange ferromagnetic La0.7Sr0.3MnO3 and noncollinear multiferroic TbMnO3 layers. Spontaneous magnetization and hysteresis loops are observed in such superlattices with individual La0.7Sr0.3MnO3 layers as thin as two unit cells, which are accompanied by pronounced exchange bias and enhanced coercivity. Our results indicate substantial interfacial magnetic coupling between spin sublattices in such superlattices, providing a powerful approach towards tailoring the properties of artificial magnetic heterostructures.

  18. 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.

  19. 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.

  20. 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.

  1. Hydrophilic Modification of Multi-Walled Carbon Nanotube for Building Photonic Crystals with Enhanced Color Visibility and Mechanical Strength

    Directory of Open Access Journals (Sweden)

    Feihu Li

    2016-04-01

    Full Text Available Low color visibility and poor mechanical strength of polystyrene (PS photonic crystal films have been the main shortcomings for the potential applications in paints or displays. This paper presents a simple method to fabricate PS/MWCNTs (multi-walled carbon nanotubes composite photonic crystal films with enhanced color visibility and mechanical strength. First, MWCNTs was modified through radical addition reaction by aniline 2,5-double sulfonic acid diazonium salt to generate hydrophilic surface and good water dispersity. Then the MWCNTs dispersion was blended with PS emulsion to form homogeneous PS/MWCNTs emulsion mixtures and fabricate composite films through thermal-assisted method. The obtained films exhibit high color visibility under natural light and improved mechanical strength owing to the light-adsorption property and crosslinking effect of MWCNTs. The utilization of MWCNTs in improving the properties of photonic crystals is significant for various applications, such as in paints and displays.

  2. Enhanced-strength, Thermally-stable, Edge-bonded, Composite Joints Project

    Data.gov (United States)

    National Aeronautics and Space Administration — This project proposes to develop/demonstrate higher strength, low print-through, low mass, discrete core joint design and analysis method for large, lightweight,...

  3. Powder XRD investigations on dotriacontane in mixtures: Phase strength and super lattices

    Indian Academy of Sciences (India)

    P B Shashikanth; P B V Prasad

    2001-04-01

    Powder XRD investigations on dotriacontane-decane and dotriacontane-decanol mixtures are made. Phase strength, phase separation and formation of superlattices are discussed. The role of tunnel-like defects is considered.

  4. 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.

  5. One-Pot Synthesized Polyurethane-Based Nanocomposites Filled by Original Rectorite with Enhanced Strength and Elongation

    Institute of Scientific and Technical Information of China (English)

    ZHANG Fang; XIAO Zhongliang; HUANG Jin; SU Zhongnin; ZHANG Hao; ZHANG Qiaoxin

    2011-01-01

    The unmodified rectorite (REC), a kind of layered silicate, was incorporated into polyurethane (PU) as matrix by the process of one-pot synthesizing polyurethane in situ, and hence produced a series of nanocomposite materials with enhanced strength and elongation. It is worth noting that the nanocomposite containing 2 wt% REC had the maximum elongation (1 449%) and strength (32.66 Mpa) as ca. 2.7- and 1.4-fold over those of neat PU film, respectively. Meanwhile, the unexfoliated agglomerates and exfoliated nanoplatelets of REC co-existed in PU matrix. By virtue of strong interfacial interaction on the surface of REC lamella,the stress facilely transferred to the rigid RECs and hence contributed to the enhancement of strength in spite that the original structure and interaction in the PU matrix were partly cleaved. Moreover, the intertwisting of polymer chains in PU matrix with REC as well as the gliding among the REC lamellae might produce greater strain. Nevertheless, excess unexfoliated REC agglomerates under high loading level inhibited the enhancement of mechanical performances, which verified the key role of exfoliated REC nanoplatelet in improving mechanical performances. As a result, this work submitted a simple method to develop a polyurethane-based nanocomposite with high mechanical performances without any modification of layered silicates and the complicated treatment for exfoliation and dispersion.

  6. 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.

  7. Development of superlattice CrN/NbN coatings for joint replacements deposited by high power impulse magnetron sputtering.

    Science.gov (United States)

    Hovsepian, Papken Ehiasarian; Ehiasarian, Arutiun Papken; Purandare, Yashodhan; Sugumaran, Arunprabhu Arunachalam; Marriott, Tim; Khan, Imran

    2016-09-01

    The demand for reliable coating on medical implants is ever growing. In this research, enhanced performance of medical implants was achieved by a CrN/NbN coating, utilising nanoscale multilayer/superlattice structure. The advantages of the novel high power impulse magnetron sputtering technology, namely, its unique highly ionised plasma, were exploited to deposit dense and strongly adherent coatings on CoCr implants. Transmission electron microscopy analysis revealed coating superlattice structure with bi-layer thickness of 3.5 nm. CrN/NbN deposited on CoCr samples showed exceptionally high adhesion, critical load values of LC2 = 50 N in scratch adhesion tests. Nanoindentation tests showed high hardness of 34 GPa and Young's modulus of 447 GPa. Low coefficient of friction (μ) 0.49 and coating wear coefficient (K C) = 4.94 × 10(-16) m(3) N(-1) m(-1) were recorded in dry sliding tests. Metal ion release studies showed a reduction in Co, Cr and Mo release at physiological and elevated temperatures (70 °C) to almost undetectable levels (<1 ppb). Rotating beam fatigue testing showed a significant increase in fatigue strength from 349 ± 59 MPa (uncoated) to 539 ± 59 MPa (coated). In vitro biological testing has been performed in order to assess the safety of the coating in biological environment; cytotoxicity, genotoxicity and sensitisation testing have been performed, all showing no adverse effects.

  8. 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.

  9. 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.

  10. 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.

  11. 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.

  12. 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.

  13. 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.

  14. An organic donor/acceptor lateral superlattice at the nanoscale.

    Science.gov (United States)

    Otero, Roberto; Ecija, David; Fernandez, Gustavo; Gallego, José María; Sanchez, Luis; Martín, Nazario; Miranda, Rodolfo

    2007-09-01

    A precise control of the nanometer-scale morphology in systems containing mixtures of donor/acceptor molecules is a key factor to improve the efficiency of organic photovoltaic devices. Here we report on a scanning tunneling microscopy study of the first stages of growth of 2-[9-(1,3-dithiol-2-ylidene)anthracen-10(9H)-ylidene]-1,3-dithiole, as electron donor, and phenyl-C61-butyric acid methyl ester, as electron acceptor, on a Au(111) substrate under ultrahigh vacuum conditions. Due to differences in bonding strength with the substrate and different interactions with the Au(111) herringbone surface reconstruction, mixed thin films spontaneously segregate into a lateral superlattice of interdigitated nanoscale stripes with a characteristic width of about 10-20 nm, a morphology that has been predicted to optimize the efficiency of organic solar cells.

  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 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.

  17. 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.

  18. Personality, effective goal-striving, and enhanced well-being: comparing 10 candidate personality strengths.

    Science.gov (United States)

    Sheldon, Kennon M; Jose, Paul E; Kashdan, Todd B; Jarden, Aaron

    2015-04-01

    In a three-wave, year-long, large-sample dataset (N = 755), 10 candidate "personality strengths" (Grit, Gratitude, Curiosity, Savoring, Control Beliefs, Meaning in Life-Presence, Strengths Use, and Engagement, Pleasure, and Meaning-Based Orientations Toward Happiness) were compared as predictors of 6-month increases in goal attainment, and as moderators of goal attainment effects upon boosted subjective well-being (SWB). Seeking internal replication, we tested our models twice, both during T1-T2 and during T2-T3. We also examined whether any Personality × Attainment moderator effects upon change in SWB at T2 still persisted at T3. Grit was the only candidate strength that predicted increased goal attainment from T1 to T2 and from T2 to T3, and Curiosity was the only candidate strength that moderated attainment effects on well-being from T1 to T2 and from T2 to T3. T2 Goal attainment effects on SWB were best sustained at T3 when Meaning Orientation increased from T1 to T2. Implications for identifying keystone constructs in personality (and positive) psychology are discussed.

  19. 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.

  20. Simulational studies of epitaxial semiconductor superlattices: Quantum dynamical phenomena in ac and dc electric fields

    Energy Technology Data Exchange (ETDEWEB)

    Reynolds, Joseph [Iowa State Univ., Ames, IA (United States)

    1997-10-08

    Using high-accuracy numerical methods the author investigates the dynamics of independent electrons in both ideal and realistic superlattices subject to arbitrary ac and/or dc electric fields. For a variety of superlattice potentials, optically excited initial wave packets, and combinations of ac and dc electric fields, he numerically solves the time-dependent Schroedinger equation. In the case of ideal periodic superlattice potentials, he investigates a long list of dynamical phenomena involving multiple miniband transitions and time-dependent electric fields. These include acceleration effects associated with interminiband transitions in strong fields, Zener resonances between minibands, dynamic localization with ac fields, increased single-miniband transport with an auxiliary resonant ac field, and enhanced or suppressed interminiband probability exchange using an auxiliary ac field. For all of the cases studied, the resulting time-dependent wave function is analyzed by projecting the data onto convenient orthonormal bases. This allows a detailed comparison with approximately analytic treatments. In an effort to explain the rapid decay of experimentally measured Bloch oscillation (BO) signals the author incorporates a one-dimensional representation of interface roughness (IR) into their superlattice potential. He shows that as a result of IR, the electron dynamics can be characterized in terms of many discrete, incommensurate frequencies near the Block frequency. Chapters 2, 3, 4 and 5 have been removed from this report and will be processed separately.

  1. 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.

  2. 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)

  3. Designing magnetic superlattices that are composed of single domain nanomagnets

    Directory of Open Access Journals (Sweden)

    Derek M. Forrester

    2014-07-01

    Full Text Available Background: The complex nature of the magnetic interactions between any number of nanosized elements of a magnetic superlattice can be described by the generic behavior that is presented here. The hysteresis characteristics of interacting elliptical nanomagnets are described by a quasi-static method that identifies the critical boundaries between magnetic phases. A full dynamical analysis is conducted in complement to this and the deviations from the quasi-static analysis are highlighted. Each phase is defined by the configuration of the magnetic moments of the chain of single domain nanomagnets and correspondingly the existence of parallel, anti-parallel and canting average magnetization states.Results: We give examples of the phase diagrams in terms of anisotropy and coupling strength for two, three and four magnetic layers. Each phase diagrams character is defined by the shape of the magnetic hysteresis profile for a system in an applied magnetic field. We present the analytical solutions that enable one to define the “phase” boundaries between the emergence of spin-flop, anti-parallel and parallel configurations. The shape of the hysteresis profile is a function of the coupling strength between the nanomagnets and examples are given of how it dictates a systems magnetic response. Many different paths between metastable states can exist and this can lead to instabilities and fluctuations in the magnetization.Conclusion: With these phase diagrams one can find the most stable magnetic configurations against perturbations so as to create magnetic devices. On the other hand, one may require a magnetic system that can easily be switched between phases, and so one can use the information herein to design superlattices of the required shape and character by choosing parameters close to the phase boundaries. This work will be useful when designing future spintronic devices, especially those manipulating the properties of CoFeB compounds.

  4. Infrared Preheating to Enhance Interlayer Strength of Components Printed on the Big Area Additive Manufacturing (BAAM) System

    Energy Technology Data Exchange (ETDEWEB)

    Kishore, Vidya [ORNL; Ajinjeru, Christine [ORNL; Duty, Chad E [ORNL; Nycz, Andrzej [ORNL; Post, Brian K [ORNL; Lindahl, John M [ORNL; Kunc, Vlastimil [ORNL

    2017-01-01

    The Big Area Additive Manufacturing (BAAM) system has the capacity to print structures on the order of several meters at a rate exceeding 50 kg/h, thereby having the potential to significantly impact the production of components in automotive, aerospace and energy sectors. However, a primary issue that limits the functional use of such parts is mechanical anisotropy. The strength of printed parts across successive layers in the build direction (z-direction) is significantly lower than the corresponding in-plane strength (x-y directions). This is largely due to poor bonding between the printed layers as the lower layers cool below the glass transition temperature (Tg) before the next layer is deposited. This work explores the use of infrared heating to increase the surface temperature of the printed layer just prior to deposition of new material to improve the interlayer strength of the components. The material used in this study was acrylonitrile butadiene styrene (ABS) reinforced with 20% chopped carbon fiber by weight. Significant improvements in z-strength were observed for the parts whose surface temperature was increased from below Tg to close to or above Tg using infrared heating. Parameters such as print speed, nozzle diameter and extrusion temperature were also found to impact the heat input required to enhance interlayer adhesion without significantly degrading the polymer and compromising on surface finish.

  5. Type-ii binary superlattices for infrared detector

    Energy Technology Data Exchange (ETDEWEB)

    Razeghi, M.; Mohseni, H. [Northwestern Univ., Evanston (United States); Brown, G. J. [WPAFB, Colombus (United States)

    2001-12-01

    III-V quantum wells and superlattices based on InAs/GaSb/AlSb, and related compounds have attracted many attentions due to their unique band alignments and physical properties. Recently, novel electronic and optoelectronic heterostructures have been proposed from this material system for hundred gigahertz logic circuits, terahertz transistors. RTDs, infrared lasers, and infrared detectors. In this paper we will describe the ongoing research at the Center for Quantum Devices to develop the theory, modeling, growth, characterization, and device fabrication techniques for this material system. We have demonstarted the first uncooled infrared detectors from type-II superlattices. The measured detectivity is more than 1 x 10{sup 8} cmHz{sup 1/2}/W at 10.6 {mu}m at room temperature which is higher than the commercially available uncooled photon detectors at similar wavelength. In paralle, we have demonstraed the first high-performance p-i-n type-II photodiode in the very long wavelength infrared (VLWIR) range operating at T=80K. The devices with cutoff wavelength of 16 mm showed a responsivity of 3.5 A/W at 80 K leading to a detectivity of {approx}1.51x10{sup 10} cmHz{sup 1/2}/W. Similar devices with cutoff wavelengths up to 25 {mu}m was demonstrated at 80 K. To enhance this technology further, we plan to move from quantum wells to quantum wire and quantum dots.

  6. Enhancement of force generated by individual myosin heads in skinned rabbit psoas muscle fibers at low ionic strength.

    Directory of Open Access Journals (Sweden)

    Haruo Sugi

    Full Text Available Although evidence has been presented that, at low ionic strength, myosin heads in relaxed skeletal muscle fibers form linkages with actin filaments, the effect of low ionic strength on contraction characteristics of Ca(2+-activated muscle fibers has not yet been studied in detail. To give information about the mechanism of muscle contraction, we have examined the effect of low ionic strength on the mechanical properties and the contraction characteristics of skinned rabbit psoas muscle fibers in both relaxed and maximally Ca(2+-activated states. By progressively decreasing KCl concentration from 125 mM to 0 mM (corresponding to a decrease in ionic strength μ from 170 mM to 50 mM, relaxed fibers showed changes in mechanical response to sinusoidal length changes and ramp stretches, which are consistent with the idea of actin-myosin linkage formation at low ionic strength. In maximally Ca(2+-activated fibers, on the other hand, the maximum isometric force increased about twofold by reducing KCl concentration from 125 to 0 mM. Unexpectedly, determination of the force-velocity curves indicated that, the maximum unloaded shortening velocity Vmax, remained unchanged at low ionic strength. This finding indicates that the actin-myosin linkages, which has been detected in relaxed fibers at low ionic strength, are broken quickly on Ca(2+ activation, so that the linkages in relaxed fibers no longer provide any internal resistance against fiber shortening. The force-velocity curves, obtained at various levels of steady Ca(2+-activated isometric force, were found to be identical if they are normalized with respect to the maximum isometric force. The MgATPase activity of muscle fibers during isometric force generation was found not to change appreciably at low ionic strength despite the two-fold increase in Ca(2+-activated isometric force. These results can be explained in terms of enhancement of force generated by individual myosin heads, but not by any

  7. Building on Strengths and Addressing Challenges: Enhancing External School Counseling Program Evaluation

    Science.gov (United States)

    Martin, Ian; Rallis, Sharon

    2014-01-01

    This conceptual paper outlines the implications associated with increasing external evaluation within school counseling programs. The authors propose that enhancing external evaluation may help to both strengthen school counseling programs and enhance their legitimacy within increasingly competitive and academically focused school systems. More…

  8. A study on the synthesis and microstructure of WC-TiN superlattice coating

    Energy Technology Data Exchange (ETDEWEB)

    Yoon, J.S.; Myung, H.S.; Han, J.G. [Sung Kyun Kwan Univ., Suwon (Korea). Plasma Appl. Mater. Lab.; Musil, J. [Dept. of Physics, Univ. of West Bohemia (Czech Republic)

    2000-09-01

    WC-TiN superhard coatings are formulated to form a nanoscaled superlattice by separate arc reactive evaporation of Ti and WC. The microstructure of WC-TiN films was identified to be a superlattice of TiN and {beta}-WC{sub 1-x} phases with modulation period ({lambda}) of 5-13 nm and the lattice planes were continuous through the TiN and {beta}-WC{sub 1-x} layers. The residual stress of WC-TiN films was measured to be 7.9 GPa. This high stress was reduced to 2.2 GPa by introducing Ti or Ti-WC interlayers. Ti-WC interlayer also increased the film adhesion strength. In spite of almost the same residual stress of 2.2-2.3 GPa, Ti-WC/WC-TiN film showed a higher adhesion strength of 48.5 N than that of Ti/WC-TiN film. These results are attributed to the low residual stress and higher stiffness of the Ti-WC interlayer than the soft Ti interlayer. The microhardness of Ti-WC/WC-TiN film on cemented carbide was measured to be 40 GPa and the maximum hardness was obtained as the period ({lambda}) was approximately 7 nm. This value is approximately 1.5 times higher than that of the TiN single layer film. Other WC-TiN superlattice coatings with Ti and WC interlayers showed a hardness range of 38-40 GPa. The ratio H{sup 3}/E{sup 2} (plastic deformation resistance) of WC-TiN superlattice films with various interlayers was calculated to be in a range from 0.18 to 0.33. This paper reports the preparation of WC-TiN superlattice coatings on WC-Co and Si substrates using a multi-cathode arc ion-plating system. The microstructures and mechanical properties of WC-TiN superlattice films were investigated, too. (orig.)

  9. Future directions in psychological assessment: combining evidence-based medicine innovations with psychology's historical strengths to enhance utility.

    Science.gov (United States)

    Youngstrom, Eric A

    2013-01-01

    Assessment has been a historical strength of psychology, with sophisticated traditions of measurement, psychometrics, and theoretical underpinnings. However, training, reimbursement, and utilization of psychological assessment have been eroded in many settings. Evidence-based medicine (EBM) offers a different perspective on evaluation that complements traditional strengths of psychological assessment. EBM ties assessment directly to clinical decision making about the individual, uses simplified Bayesian methods explicitly to integrate assessment data, and solicits patient preferences as part of the decision-making process. Combining the EBM perspective with psychological assessment creates a hybrid approach that is more client centered, and it defines a set of applied research topics that are highly clinically relevant. This article offers a sequence of a dozen facets of the revised assessment process, along with examples of corollary research studies. An eclectic integration of EBM and evidence-based assessment generates a powerful hybrid that is likely to have broad applicability within clinical psychology and enhance the utility of psychological assessments.

  10. Characterizing Composition Modulations in InAs/AIAs Short-Period Superlattices

    Energy Technology Data Exchange (ETDEWEB)

    Ahrenkiel, S.P.; Follstaedt, D.M.; Jones, E.D.; Lee, S.R.; Mascarenhas, A.; Millunchick, J. Mirecki; Norman, A.G.; Reno, J.L.; Twesten, R.D.

    1999-04-26

    The formation of quantum wires has much interest due to their novel electronic properties which may lead to enhanced optoelectronic device performance and greater photovoltaic efficiencies. One method of forming these structures is through spontaneous lateral modulation found during the epitaxial growth of III/V alloys. In this paper, we report and summarize our investigations on the formation of lateral moduation in the MBE grown InAlAs/InP(001) system. This system was grown as a short-period superlattice where n-monolayers of InAs are deposited followed by m-Monolayers of AlAs (with n and m~2) and this sequence is repeated to grown a low strain InAlAs ternary alloy on InP(001) that exhibits lateral modulation. Films were grown under a variety of condition (growth temperature, effective alloy composition, superlattice period, and growth rate). These films have been extensively analyzed using X-ray diffraction, atomic force microscopy, and transmission electron microscopy (TEM) and microcharacterization, in addition to photon-based spectroscopes. Here we present results of several microstructural characterizations using a wide range of TEM-based techniques, and compare them to results from the other methods to obtain a unified understanding of composition modulation. Two strong points consistently emerge: 1) The lateral modulation wavelength is insensitive to growth temperature and effective alloy composition, but the strength of the lateral modulation is greatest near an effective alloy composition of In(0.46)Al(0.54)As, which corresponds to a slightly tensile global strain with respect to InP. 2) The composition variation for the strongly modulated films is as much as 0.38 InAs mole fraction. In addition, for these strongly modulated films, the modulation wave is asymmetric showing strongly peaked, narrower InAs-rich regions separated by flat AlAs-rich regions. We discuss these results and their possible implications in addition to detailing the techniques used

  11. SO2-catalyzed steam pretreatment enhances the strength and stability of softwood pellets.

    Science.gov (United States)

    Tooyserkani, Zahra; Kumar, Linoj; Sokhansanj, Shahab; Saddler, Jack; Bi, Xiaotao T; Lim, C Jim; Lau, Anthony; Melin, Staffan

    2013-02-01

    Densification can partially resolve the logistical challenges encountered when large volumes of biomass are required for bioconversion processes to benefit from economies-of-scale. Despite the higher bulk density of pellets, their lower mechanical strength and sensitivity to moisture are still recurring issues hindering long term transportation and storage. In this study, we have evaluated the potential benefits of SO(2)-catalyzed steam treatment to achieve both the needed size reduction prior to pelletization while improving the stability of the produced pellets. This pretreatment substantially reduced the particle size of the woodchips eliminating any further grinding. The treated pellets had a higher density and exhibited a two-time higher mechanical strength compared to untreated pellets. Despite a higher moisture adsorption capacity, treated pellets remained intact even under highly humid conditions. The high heating values, low ash content and good overall carbohydrate recovery of treated pellets indicated their potential suitability for both biochemical and thermochemical applications.

  12. Enhancement of tensile strength of lignocellulosic jute fibers by alkali-steam treatment.

    Science.gov (United States)

    Saha, Prosenjit; Manna, Suvendu; Chowdhury, Sougata Roy; Sen, Ramkrishna; Roy, Debasis; Adhikari, Basudam

    2010-05-01

    The physico-chemical properties of jute fibers treated with alkali (NaOH) solution have been investigated in this study. The treatments were applied under ambient and elevated temperatures and high pressure steaming conditions. To the knowledge of these authors the influence of alkali-steam treatment on the uniaxial tensile strength of natural ligno-cellulosic fibers, such as jute, has not been investigated earlier. The results from this investigation indicate that a 30 min dipping of the fibers in 0.5% alkali solution followed by 30 min alkali-steam treatment leads to an increase in the tensile strength of up to 65%. The increase appears to be due to fiber separation and removal of non-cellulosic materials, which, in turn, resulted in an increased crystallinity.

  13. Early Progressive Strength Training to Enhance Recovery After Fast-Track Total Knee Arthroplasty

    DEFF Research Database (Denmark)

    Jakobsen, Thomas Linding; Kehlet, Henrik; Husted, Henrik

    2014-01-01

    OBJECTIVE: To compare 7 weeks of supervised physical rehabilitation with or without progressive strength training (PST) commenced early after fast-track total knee arthroplasty (TKA) on functional performance. METHODS: In total, 82 patients with a unilateral primary TKA were randomized to 2...... was not superior to 7 weeks of supervised physical rehabilitation without PST in improving functional performance, measured as the maximal walking distance in 6 minutes, at the primary end point 8 weeks after fast-track TKA....

  14. Muscle Strength Enhancement Following Home-Based Virtual Cycling Training in Ambulatory Children with Cerebral Palsy

    Science.gov (United States)

    Chen, Chia-Ling; Hong, Wei-Hsien; Cheng, Hsin-Yi Kathy; Liaw, Mei-Yun; Chung, Chia-Ying; Chen, Chung-Yao

    2012-01-01

    This study is the first well-designed randomized controlled trial to assess the effects of a novel home-based virtual cycling training (hVCT) program for improving muscle strength in children with spastic cerebral palsy (CP). Twenty-eight ambulatory children with spastic CP aged 6-12 years were randomly assigned to an hVCT group (n = 13) or a…

  15. Muscle Strength Enhancement Following Home-Based Virtual Cycling Training in Ambulatory Children with Cerebral Palsy

    Science.gov (United States)

    Chen, Chia-Ling; Hong, Wei-Hsien; Cheng, Hsin-Yi Kathy; Liaw, Mei-Yun; Chung, Chia-Ying; Chen, Chung-Yao

    2012-01-01

    This study is the first well-designed randomized controlled trial to assess the effects of a novel home-based virtual cycling training (hVCT) program for improving muscle strength in children with spastic cerebral palsy (CP). Twenty-eight ambulatory children with spastic CP aged 6-12 years were randomly assigned to an hVCT group (n = 13) or a…

  16. Enhancing the Adhesive Strength of a Plywood Adhesive Developed from Hydrolyzed Specified Risk Materials

    Directory of Open Access Journals (Sweden)

    Birendra B. Adhikari

    2016-08-01

    Full Text Available The current production of wood composites relies mostly on formaldehyde-based adhesives such as urea formaldehyde (UF and phenol formaldehyde (PF resins. As these resins are produced from non-renewable resources, and there are some ongoing issues with possible health hazard due to formaldehyde emission from such products, the purpose of this research was to develop a formaldehyde-free plywood adhesive utilizing waste protein as a renewable feedstock. The feedstock for this work was specified risk material (SRM, which is currently being disposed of either by incineration or by landfilling. In this report, we describe a technology for utilization of SRM for the development of an environmentally friendly plywood adhesive. SRM was thermally hydrolyzed using a Canadian government-approved protocol, and the peptides were recovered from the hydrolyzate. The recovered peptides were chemically crosslinked with polyamidoamine-epichlorohydrin (PAE resin to develop an adhesive system for bonding of plywood specimens. The effects of crosslinking time, peptides/crosslinking agent ratio, and temperature of hot pressing of plywood specimens on the strength of formulated adhesives were investigated. Formulations containing as much as 78% (wt/wt peptides met the ASTM (American Society for Testing and Materials specifications of minimum dry and soaked shear strength requirement for UF resin type adhesives. Under the optimum conditions tested, the peptides–PAE resin-based formulations resulted in plywood specimens having comparable dry as well as soaked shear strength to that of commercial PF resin.

  17. A facile method for preparation superhydrophobic paper with enhanced physical strength and moisture-proofing property.

    Science.gov (United States)

    Li, Hui; Yang, Jin; Li, Pan; Lan, Tianqing; Peng, Lincai

    2017-03-15

    We proposed a green and facile method to fabricate superhydrophobic paper in this study, which is layer-by-layer (LBL) deposition of TiO2 nanoparticles/sodium alginate (ALG) multilayers on paper surface followed by an adsorption treatment of colloidal carnauba wax. The formation of TiO2/ALG multilayers on paper surface was characterized by X-ray photoelectron spectroscopy (XPS), zeta potential measurement, scanning electron microscopy (SEM) and atomic force microscopy (AFM), respectively. The wetting property of modified paper was investigated by water contact angle (WCA) measurement. Moreover, the modified paper tensile strength has been evaluated. The results showed that WCA of paper modified with a wax-treated (TiO2/ALG)3.5 multilayer reached up to 151.5°, and this obtained superhydrophobic paper exhibited improved tensile strength (increased by 4.1% compared to the pristine paper), excellent moisture-proofing property and high strength stability under high relative humidity condition, which might has a great potential for use in the liquid paper packaging and moisture-proof paper packaging.

  18. Asymmetric six-strand core sutures enhance tendon fatigue strength and the optimal asymmetry.

    Science.gov (United States)

    Kozono, N; Okada, T; Takeuchi, N; Hanada, M; Shimoto, T; Iwamoto, Y

    2016-10-01

    Under cyclic loading, we recorded the fatigue strength of a six-strand tendon repair with different symmetry in the lengths of suture purchase in two stumps of 120 dental rolls and in 30 porcine tendons. First, the strengths of the repairs with 1, 2, 3, 4 and 5 mm asymmetry were screened using the dental rolls. The asymmetric core suture repairs were then made with a Kessler repair of equal suture purchase (10 mm) in two tendon stumps, and shifting two other Kessler repairs by 1, 3 or 5 mm, respectively, along the longitudinal axis of the tendon in relation to the first (symmetric) Kessler repair. The core repairs with 3 mm or more asymmetry in suture purchases in two tendon ends showed significantly greater fatigue strength and significantly smaller gaps compared with 1 mm asymmetry in core suture repair. Our results support that asymmetric placement of core sutures in two tendon ends favour resisting gapping at the repair site and 3 mm or more asymmetry is needed to produce such beneficial effects. © The Author(s) 2016.

  19. Enhancement of hydrophobicity and tensile strength of muga silk fiber by radiofrequency Ar plasma discharge

    Science.gov (United States)

    Gogoi, D.; Choudhury, A. J.; Chutia, J.; Pal, A. R.; Dass, N. N.; Devi, D.; Patil, D. S.

    2011-10-01

    The hydrophobicity and tensile strength of muga silk fiber are investigated using radiofrequency (RF) Ar plasma treatment at various RF powers (10-30 W) and treatment times (5-20 min). The Ar plasma is characterized using self-compensated Langmuir and emissive probe. The ion energy is observed to play an important role in determining the tensile strength and hydrophobicity of the plasma treated fibers. The chemical compositions of the fibers are observed to be affected by the increase in RF power rather than treatment time. XPS study reveals that the ions that are impinging on the substrates are mainly responsible for the cleavage of peptide bond and side chain of amino acid groups at the surface of the fibers. The observed properties (tensile strength and hydrophobicity) of the treated fibers are found to be dependent on their variation in atomic concentration and functional composition at the surfaces. All the treated muga fibers exhibit almost similar thermal behavior as compared to the virgin one. At RF power of 10 W and treatment time range of 5-20 min, the treated fibers exhibit properties similar to that of the virgin one. Higher RF power (30 W) and the increase in treatment time deteriorate the properties of the fibers due to incorporation of more surface roughness caused by sufficiently high energetic ion bombardment. The properties of the plasma treated fibers are attempted to correlate with the XPS analysis and their surface morphologies.

  20. Enhancement of hydrophobicity and tensile strength of muga silk fiber by radiofrequency Ar plasma discharge

    Energy Technology Data Exchange (ETDEWEB)

    Gogoi, D.; Choudhury, A.J. [Physical Sciences Division, Institute of Advanced Study in Science and Technology, Paschim Boragaon, Guwahati 781035, Assam (India); Chutia, J., E-mail: joyanti_c@sify.com [Physical Sciences Division, Institute of Advanced Study in Science and Technology, Paschim Boragaon, Guwahati 781035, Assam (India); Pal, A.R.; Dass, N.N. [Physical Sciences Division, Institute of Advanced Study in Science and Technology, Paschim Boragaon, Guwahati 781035, Assam (India); Devi, D. [Life Sciences Division, Institute of Advanced Study in Science and Technology, Paschim Boragaon, Guwahati 781035, Assam (India); Patil, D.S. [Laser and Plasma Technology Division, Bhabha Atomic Research Center, Trombay, Mumbai 400085 (India)

    2011-10-15

    The hydrophobicity and tensile strength of muga silk fiber are investigated using radiofrequency (RF) Ar plasma treatment at various RF powers (10-30 W) and treatment times (5-20 min). The Ar plasma is characterized using self-compensated Langmuir and emissive probe. The ion energy is observed to play an important role in determining the tensile strength and hydrophobicity of the plasma treated fibers. The chemical compositions of the fibers are observed to be affected by the increase in RF power rather than treatment time. XPS study reveals that the ions that are impinging on the substrates are mainly responsible for the cleavage of peptide bond and side chain of amino acid groups at the surface of the fibers. The observed properties (tensile strength and hydrophobicity) of the treated fibers are found to be dependent on their variation in atomic concentration and functional composition at the surfaces. All the treated muga fibers exhibit almost similar thermal behavior as compared to the virgin one. At RF power of 10 W and treatment time range of 5-20 min, the treated fibers exhibit properties similar to that of the virgin one. Higher RF power (30 W) and the increase in treatment time deteriorate the properties of the fibers due to incorporation of more surface roughness caused by sufficiently high energetic ion bombardment. The properties of the plasma treated fibers are attempted to correlate with the XPS analysis and their surface morphologies.

  1. Long-Range Effects on the Pyroelectric Coefficient of Ferroelectric Superlattice

    Institute of Scientific and Technical Information of China (English)

    DONG Wen; YAO Dong-Lai; WU Yin-Zhong; LI Zhen-Ya

    2002-01-01

    Long-range effects on the pyroelectric coefficient of a ferroelectric superlattice consisting of two differentferroelectric materials are investigated based on the transverse Ising model. The effects of the interfacial coupling andthe thickness of one period on the pyroelectric coefficient of the ferroelectric superlattice are studied by taking intoaccount the long-range interaction. It is found that with the increase of the strength of the long-range interaction, thepyroelectric coefficient decreases when the temperature is lower than the phase transition temperature; the number ofthe pyroelectric peaks decreases gradually and the phase transition temperature increases. It is also found that with thedecrease of the interfacial coupling and the thickness of one period, the phase transition temperature and the number ofthe pyroelectric peaks decrease.

  2. Enhanced interfacial strength of carbon nanotube/copper nanocomposites via Ni-coating: Molecular-dynamics insights

    Science.gov (United States)

    Duan, Ke; Li, Li; Hu, Yujin; Wang, Xuelin

    2017-04-01

    The molecular bridging between carbon nanotube (CNT) within the meta matrix is hopeful for enhancing nanocomposite's mechanical performance. One of the main problems for nanocomposites is the inadequate bonding between nonstructural reinforcement and meta matrix. Ni-coating on CNT is an effective method to overcome the drawback of the inadequate strength, but the enhancing mechanism has not well interpreted yet. In this paper, the enhancing mechanism will be interpreted from the molecular-dynamics insights. The pullout process of CNT and Ni-coated CNT against copper matrix is investigated. The effects of geometric parameters, including CNT length and diameter, are taken into considerations and discussed. Results show that the interfacial strength is significantly improved after the Ni-coated CNT, which shows a good agreement with the experimental results available in the open literature. Besides, the sliding mechanism of Ni-coated CNTs against copper matrix is much more like a kind of friction sliding and directly related to the embedded zone. However, the pullout force of the CNT without Ni-coating is nearly proportional to its diameter, but independent of embedded length.

  3. 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.)

  4. Disordered ferroelectricity in the PbTiO3/SrTiO3 superlattice thin film

    Science.gov (United States)

    Kim, Gi-Yeop; Chu, Kanghyun; Sung, Kil-Dong; Lee, Hak-Sung; Kim, Sung-Dae; Song, Kyung; Choi, Taekjib; Lee, Jaichan; Buban, James P.; Yoon, Seog-Young; Kim, Kwang-Ho; Yang, Chan-Ho; Choi, Si-Young

    2017-06-01

    The PbTiO3/SrTiO3 superlattice thin films with a low volume fraction of PbTiO3 have not attracted much interest because they are thought to exhibit only a paraelectric state. In this study, we focus on a superlattice thin film with thin PbTiO3 (PTO) and thick SrTiO3 (STO) layers, wherein the hidden ferroelectricity in the thin PbTiO3 layer is revealed. Atomic scale imaging analysis and electron energy loss spectroscopy reveal the existence of a disordered ferroelectric polarization state without innate tetragonal distortion in the (6PTO/15STO)5 superlattice. The piezoelectric force microscopy analysis confirms that this disordered ferroelectricity can enhance piezoelectric response.

  5. Relationship between Length and Surface-Enhanced Raman Spectroscopy Signal Strength in Metal Nanoparticle Chains: Ideal Models versus Nanofabrication

    Directory of Open Access Journals (Sweden)

    Kristen D. Alexander

    2012-01-01

    Full Text Available We have employed capillary force deposition on ion beam patterned substrates to fabricate chains of 60 nm gold nanospheres ranging in length from 1 to 9 nanoparticles. Measurements of the surface-averaged SERS enhancement factor strength for these chains were then compared to the numerical predictions. The SERS enhancement conformed to theoretical predictions in the case of only a few chains, with the vast majority of chains tested not matching such behavior. Although all of the nanoparticle chains appear identical under electron microscope observation, the extreme sensitivity of the SERS enhancement to nanoscale morphology renders current nanofabrication methods insufficient for consistent production of coupled nanoparticle chains. Notwithstanding this fact, the aggregate data also confirmed that nanoparticle dimers offer a large improvement over the monomer enhancement while conclusively showing that, within the limitations imposed by current state-of-the-art nanofabrication techniques, chains comprising more than two nanoparticles provide only a marginal signal boost over the already considerable dimer enhancement.

  6. Enhancement of strength and stability of nanostructured Ni by small amounts of solutes

    DEFF Research Database (Denmark)

    Zhang, H.W.; Lu, K.; Pippan, R.;

    2011-01-01

    Polycrystalline Ni with a purity of 99.7% (with 0.14% Ti) has been deformed by high-pressure torsion at room temperature to εvM=100. The presence of solute atoms markedly raises both the strength and the thermal stability, showing a flow stress of about 1700MPa and a recrystallization temperature...... of about 500°C. The effect of the solute on dislocation storage during deformation and on the mobility of dislocations and boundaries during annealing are discussed. The strengthening mechanisms and their superposition are also analyzed....

  7. MECHANICAL STRENGTH ENHANCEMENT OF OPEN-CELL ALUMINA FOAMS USING OPTIMUM CONCENTRATION OF DEFLOCCULANT

    Directory of Open Access Journals (Sweden)

    A. Hadi

    2015-06-01

    Full Text Available Open-cell alumina foams were prepared using the appropriate alumina slurry and polyurethane sponge with linear pore density of approximately 14 pores per inch (ppi as a template by the replica method. The rheological studies showed that the optimum solid content for the slurries without deflocculants was 60 wt. %. In order to increase the slurry solid content, Tiron (1,2-dihydroxy-3,5-benzene disulfonic acid disodium salt was used as dispersant. To determine the optimum concentration of dispersant, the viscosity curves of alumina slurries containing different values of Tiron from 0 to 1.2 wt. % (based on dry material weight were studied. The optimum concentration of Tiron obtained for lowest viscosity was 0.8 wt. %. Thus, the solid content in the slurry could be increased from 60 to 66 wt. %. The effect of increase in the slurry solid content and the way it affects the foam structure and the mechanical strength were investigated. Microstructural observations of the foams show a significant reduction in macroscopic and microscopic defects in the foam struts when the slurry solid content is increased. Total porosity of the produced alumina foams prepared using slurries containing 60 and 66 wt. % solid are 83.3 and 80.4 %, respectively, while the compressive strength of the foams has increased from 1.33 to 3.24 MPa.

  8. Effect of normalizing temperature on microstructural stability and mechanical properties of creep strength enhanced ferritic P91 steel

    Energy Technology Data Exchange (ETDEWEB)

    Pandey, C.; Giri, A.; Mahapatra, M.M.

    2016-03-07

    Mechanical properties of creep enhanced ferritic (CSEF) steels is affected by various parameters, the solutionizing temperature is one of them. The present work demonstrates the effect of solutionizing temperature on microstructure and mechanical properties of CSEF P91 steel. Optical metallography (OM) and Scanning electron microscopy (SEM) were carried out to study the microstructure of P91 steel in different heat treatment conditions. In order to determine the precipitates present in microstructure; X-ray analysis was performed. Moreover, the influence of solutionizing temperature on the mechanical properties (strength, hardness and impact toughness) has also been studied. - Highlights: • SEM-EDS analysis of P91 steel precipitates present at grain boundary and grain interior were carried out. • For constant tempering time effect of normalizing temperature on precipitate size, particle-to particle distance, and grain size were carried out. • Effect of normalizing temperature on tensile strength, yield strength, hardness, % elongation and % reduction of area of P91 steel were studied. • For constant tempering time effect of normalizing temperature on room temperature impact toughness of P91 steel were studied. Fracture surface after impact testing were also characterized by using SEM. • Fracture surface after room temperature tensile testing were also characterized by using SEM to study the effect of normalizing temperature on fracture surface.

  9. Sodium alginate/graphene oxide aerogel with enhanced strength-toughness and its heavy metal adsorption study.

    Science.gov (United States)

    Jiao, Chenlu; Xiong, Jiaqing; Tao, Jin; Xu, Sijun; Zhang, Desuo; Lin, Hong; Chen, Yuyue

    2016-02-01

    Ordered porous sodium alginate/graphene oxide (SAGO) aerogel was fabricated by in situ crosslinking and freeze-drying method. GO, as reinforcing filler, can be easily incorporated with SA matrix by self-assembly via hydrogen bonding interaction. Compared with pure SA aerogel, the as-prepared SAGO exhibited excellent mechanical strength and elasticity, and the compression strength of SAGO can reach up to 324 kPa and remain 249 kPa after five compression cycles when 4 wt% GO was added, which were considered significant improvements. SEM result presents that the addition of GO obviously improves the porous structures of aerogel, which is beneficial for the enhancement of strength-toughness and adsorbability. As a consequence, the adsorption process of SAGO is better described by pseudo-second-order kinetic model and Langmuir isotherm, with maximum monolayer adsorption capacities of 98.0 mg/g for Cu2+ and 267.4 mg/g for Pb2+, which are extremely high adsorption capacities for metal ions and show far more promise for application in sewage treatment.

  10. Enhanced Thermal Performance and Impact Strength of UHMWPE/Recycled-PA6 Blends Synthesized via a Melting Extrusion Route

    Directory of Open Access Journals (Sweden)

    Xiuying Yang

    2016-01-01

    Full Text Available The blends of ultra-high molecular weight polyethylene (UHMWPE and recycled-polyamide 6 (R-PA6 were prepared via a melting extrusion route using high-density polyethylene-graft-maleic anhydride (HDPE-g-MAH as the compatibilizer. The morphologies and distributions of the chemical components of the blends were characterized by scanning electron microscopy and synchrotron Fourier transform infrared microspectroscopy. The effects of R-PA6 content on the Vicat softening temperature (VST, heat distortion temperature (HDT, and impact strength of the blends were studied. Remarkably, in comparison with those of UHMWPE, the VST and HDT of UHMWPE/R-PA6 blends with 44 wt% R-PA6 were increased to 165.1 and 98.4°C, respectively, and the Charpy impact strength and Izod impact strength of the blends were enhanced to 33.9 and 16.2 kJ/m2, respectively. In addition, it was found that the blending system containing 44 wt% R-PA6 and 48 wt% UHMWPE exhibited the best compatibility when it was prepared using 8 wt% HDPE-g-MAH. The distribution of the phases of UHMWPE and R-PA6 was uniform, and no obvious phase separation was observed in the blends.

  11. 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.

  12. Cr concentration dependence of overestimation of long term creep life in strength enhanced high Cr ferritic steels

    Energy Technology Data Exchange (ETDEWEB)

    Maruyama, K., E-mail: maruyama@material.tohoku.ac.j [Graduate School of Environmental Studies, Tohoku University, 6-6-02 Aobayama, Sendai 980-8579 (Japan); Ghassemi Armaki, H.; Chen, R.P.; Yoshimi, K. [Graduate School of Environmental Studies, Tohoku University, 6-6-02 Aobayama, Sendai 980-8579 (Japan); Yoshizawa, M.; Igarashi, M. [Corporate Research and Development Laboratories, Sumitomo Metal Industry, Ltd., 1-8 Fuso-Cho, Amagasaki 660-0891 (Japan)

    2010-06-15

    Creep rupture data and microstructural degradation during aging of high Cr ferritic boiler steels with enhanced creep strength have been studied with special attention to prediction of long term creep rupture life. Tempered lath martensite structure in the high Cr ferritic steels remains unchanged during short term aging, whereas static recovery of the lath martensite structure proceeds when diffusion distance during aging becomes sufficiently long as is the case in long term creep. The static recovery brings about premature failure in long term creep and decreases in apparent activation energy for creep life. The decrease in activation energy is responsible for overestimation of rupture life reported in strength enhanced high Cr ferritic steels. The boundary from a short term region with high activation energy Q{sub H} to a long term region with low activation energy Q{sub L} moves towards longer time with decreasing Cr concentration. The difference in activation energy (Q{sub H} - Q{sub L}) primarily determines the extent of overestimation of rupture life predicted from short term data. In general, the extent of overestimation is less serious at 9%Cr as compared to 12%Cr.

  13. Steam oxidation scale growth and thermal insulation effect on creep life of creep strength enhanced ferritic steels

    Energy Technology Data Exchange (ETDEWEB)

    Masuyama, Fujimitsu; Tokunaga, Tatsuya [Kyushu Inst. of Technology (Japan). Graduate School of Engineering; Takao, Mikito [Kyushu Inst. of Technology (Japan). Graduate School of Engineering; JFE Steel Corporation (Japan); Arakawa, Katsutoshi [Kyushu Inst. of Technology (Japan). Graduate School of Engineering; Kobe Steel Ltd. (Japan)

    2010-07-01

    Creep strength enhanced ferritic steels, such as T91 and T23 are extensively used worldwide for superheater and reheater tubes, not only in advanced power plants but also in plants with conventional steam conditions. However when these steel tubes are used at higher metal temperature, steam oxidation problems are recently experienced resulting in turbine side erosion, and overheating of tubes leading to creep rupture due to scale blockage in tube bends or scale insulation effect due to thick scale, and separation and exfoliation of the scale. In the present study, steam oxidation growth tests of T91, T92, T23 and T22 were conducted to develop steam oxidation growth rate and scale behavior. Then using the steam oxidation growth data measured the metal temperature changes with scale growth were calculated considering the insulation effect of steam oxidation scale. Consequently the creep lives affected by steam oxidation scale growth were predicted as a function of time and temperature increase for creep strength enhanced ferritic steels. (orig.)

  14. Two-phase mixed media dielectric with macro dielectric beads for enhancing resistivity and breakdown strength

    Science.gov (United States)

    Falabella, Steven; Meyer, Glenn A; Tang, Vincent; Guethlein, Gary

    2014-06-10

    A two-phase mixed media insulator having a dielectric fluid filling the interstices between macro-sized dielectric beads packed into a confined volume, so that the packed dielectric beads inhibit electro-hydrodynamically driven current flows of the dielectric liquid and thereby increase the resistivity and breakdown strength of the two-phase insulator over the dielectric liquid alone. In addition, an electrical apparatus incorporates the two-phase mixed media insulator to insulate between electrical components of different electrical potentials. And a method of electrically insulating between electrical components of different electrical potentials fills a confined volume between the electrical components with the two-phase dielectric composite, so that the macro dielectric beads are packed in the confined volume and interstices formed between the macro dielectric beads are filled with the dielectric liquid.

  15. Forecast-Driven Enhancement of Received Signal Strength (RSS-Based Localization Systems

    Directory of Open Access Journals (Sweden)

    Claudio Gallicchio

    2013-10-01

    Full Text Available Real-time user localization in indoor environments is an important issue in ambient assisted living (AAL. In this context, localization based on received signal strength (RSS has received considerable interest in the recent literature, due to its low cost and energy consumption and to its availability on all wireless communication hardware. On the other hand, the RSS-based localization is characterized by a greater error with respect to other technologies. Restricting the problem to localization of AAL users in indoor environments, we demonstrate that forecasting with a little user movement advance (for example, when the user is about to leave a room provides significant benefits to the accuracy of RSS-based localization systems. Specifically, we exploit echo state networks (ESNs fed with RSS measurements and trained to recognize patterns of user’s movements to feed back to the RSS-based localization system.

  16. Enhancing quality of life in older adults: A comparison of muscular strength and power training

    Directory of Open Access Journals (Sweden)

    Marsh Anthony P

    2008-06-01

    Full Text Available Abstract Background Although progressive resistance strength training (ST has been found to improve various measures of physical functioning in older adults, the benefit to quality of life is unclear. Additionally, recent evidence suggests that high velocity power training (PT may be more beneficial for physical functioning than ST, but it is not known whether this type of training impacts quality of life. The purpose of this study was to compare changes in multiple measures of quality of life resulting from ST vs. PT in older adults. A no exercise group was also included as control comparison condition. Methods Forty-five older adults (M age = 74.8 years; SD = 5.7 were randomly assigned to either a PT, b ST, or c control group (no exercise. Measures of self-efficacy (SE, satisfaction with physical function (SPF, and the Satisfaction with Life Scale (SWL were assessed at baseline and following training. The resistance training conditions met 3 times per week for 12 weeks at an intensity of 70% 1 repetition maximum. Results A series of ANCOVA's comparing between group differences in change and controlling for baseline values revealed significant group differences in all three measures: SE (F(2,31 = 9.77; p (2,32 = 3.36; p = .047; SWL (F(2,31 = 4.76; p = .016. Follow up analyses indicated that the PT group reported significantly more change in SE, SPF, and SWL than the control group whereas the ST group reported greater change than the control group only in SE. Conclusion These pilot data indicate that high velocity power training may influence multiple levels of quality of life over and above the benefits gained through traditional strength training.

  17. 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

  18. Enhanced flashover strength in polyethylene nanodielectrics by secondary electron emission modification

    Science.gov (United States)

    Wang, Weiwang; Li, Shengtao; Min, Daomin

    2016-04-01

    This work studies the correlation between secondary electron emission (SEE) characteristics and impulse surface flashover in polyethylene nanodielectrics both theoretically and experimentally, and illustrates the enhancement of flashover voltage in low-density polyethylene (LDPE) through incorporating Al2O3 nanoparticles. SEE characteristics play key roles in surface charging and gas desorption during surface flashover. This work demonstrates that the presence of Al2O3 nanoparticles decreases the SEE coefficient of LDPE and enhances the impact energy at the equilibrium state of surface charging. These changes can be explained by the increase of surface roughness and of surface ionization energy, and the strong interaction between nanoparticles and the polymer dielectric matrix. The surface charge and flashover voltage are calculated according to the secondary electron emission avalanche (SEEA) model, which reveals that the positive surface charges are reduced near the cathode triple point, while the presence of more nanoparticles in high loading samples enhances the gas desorption. Consequently, the surface flashover performance of LDPE/Al2O3 nanodielectrics is improved.

  19. Enhanced flashover strength in polyethylene nanodielectrics by secondary electron emission modification

    Directory of Open Access Journals (Sweden)

    Weiwang Wang

    2016-04-01

    Full Text Available This work studies the correlation between secondary electron emission (SEE characteristics and impulse surface flashover in polyethylene nanodielectrics both theoretically and experimentally, and illustrates the enhancement of flashover voltage in low-density polyethylene (LDPE through incorporating Al2O3 nanoparticles. SEE characteristics play key roles in surface charging and gas desorption during surface flashover. This work demonstrates that the presence of Al2O3 nanoparticles decreases the SEE coefficient of LDPE and enhances the impact energy at the equilibrium state of surface charging. These changes can be explained by the increase of surface roughness and of surface ionization energy, and the strong interaction between nanoparticles and the polymer dielectric matrix. The surface charge and flashover voltage are calculated according to the secondary electron emission avalanche (SEEA model, which reveals that the positive surface charges are reduced near the cathode triple point, while the presence of more nanoparticles in high loading samples enhances the gas desorption. Consequently, the surface flashover performance of LDPE/Al2O3 nanodielectrics is improved.

  20. Enhancing antibacterium and strength of cellulosic paper by coating triclosan-loaded nanofibrillated cellulose (NFC).

    Science.gov (United States)

    Liu, Kai; Chen, Lihui; Huang, Liulian; Ni, Yonghao; Sun, Bo

    2015-03-06

    The nanofibrillated cellulose (NFC) was used as substrates to carry triclosan (TCS), which was then applied as a coating agent for impacting antibacterial property to paper while also improving its strength. The TCS-loaded NFC material was further characterized. UV-vis spectra results showed that a characteristic absorption band at 282 nm was observed, which was attributed to triclosan, confirming its successful loading onto NFC. The antibacterial activity tests indicated that the coated paper exhibited excellent antibacterial activity against Escherichia coli, and the growth inhibition of bacteria (GIB) increased as the loading amount of triclosan coated on paper increased. The GIB can reach 98.7% when the 0.023 g TCS-loaded NFC was coated on paper. Meanwhile, the tensile and tear index of the coated paper increased by 18.0% and 26.4%, respectively compared to the blank paper. Therefore, the triclosan-loaded paper could be potentially used in the medical field. Copyright © 2014 Elsevier Ltd. All rights reserved.

  1. Digital veneering system enhances microtensile bond strength at zirconia core-veneer interface.

    Science.gov (United States)

    Kim, Ki-Yeon; Kwon, Taek-Ka; Kang, Tae-Joo; Yang, Jae-Ho; Lee, Shin-Jae; Yeo, In-Sung

    2014-01-01

    This study investigated the effect of digital veneering system (DVS) on strengthening the bond between a zirconia core and ceramic veneer. Specimens for Groups 1 (negative control), 2 (positive control), 3, and 4 used conventional porcelain veneering technique on untreated, sandblasted, coloring agent-treated, and modifier-treated zirconia cores respectively. Group 5 used DVS, where glass ceramic veneers—produced by computer-aided milling—were fused to zirconia cores. Microtensile bond strengths (MTBS) at the interface were measured. MTBS results of Groups 1 to 5, expressed in mean (standard deviation), were 28.1 (7.3), 27.8 (6.3), 30.0 (10.2), 32.9 (8.1), and 37.8 (8.1) MPa. The DVS group had significantly higher MTBS than the negative and positive controls (pzirconia core and ceramic veneer, indicating that this system could reduce adhesive failure-related complications that frequently occur at the zirconia core-veneer interface.

  2. Solvent-driven symmetry of self-assembled nanocrystal superlattices-A computational study

    KAUST Repository

    Kaushik, Ananth P.

    2012-10-29

    The preference of experimentally realistic sized 4-nm facetted nanocrystals (NCs), emulating Pb chalcogenide quantum dots, to spontaneously choose a crystal habit for NC superlattices (Face Centered Cubic (FCC) vs. Body Centered Cubic (BCC)) is investigated using molecular simulation approaches. Molecular dynamics simulations, using united atom force fields, are conducted to simulate systems comprised of cube-octahedral-shaped NCs covered by alkyl ligands, in the absence and presence of experimentally used solvents, toluene and hexane. System sizes in the 400,000-500,000-atom scale followed for nanoseconds are required for this computationally intensive study. The key questions addressed here concern the thermodynamic stability of the superlattice and its preference of symmetry, as we vary the ligand length of the chains, from 9 to 24 CH2 groups, and the choice of solvent. We find that hexane and toluene are "good" solvents for the NCs, which penetrate the ligand corona all the way to the NC surfaces. We determine the free energy difference between FCC and BCC NC superlattice symmetries to determine the system\\'s preference for either geometry, as the ratio of the length of the ligand to the diameter of the NC is varied. We explain these preferences in terms of different mechanisms in play, whose relative strength determines the overall choice of geometry. © 2012 Wiley Periodicals, Inc.

  3. 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.

  4. PMSE strength during enhanced D region electron densities: Faraday rotation and absorption effects at VHF frequencies

    Science.gov (United States)

    Chau, Jorge L.; Röttger, Jürgen; Rapp, Markus

    2014-10-01

    In this paper we study the effects of absorption and Faraday rotation on measurements of polar mesosphere summer echoes (PMSE). We found that such effects can produce significant reduction of signal-to-noise ratio (SNR) when the D region electron densities (Ne) are enhanced, and VHF radar systems with linearly polarized antennas are used. In particular we study the expected effects during the strong solar proton event (SPE) of July 2000, also known as the Bastille day flare event. During this event, a strong anti-correlation between the PMSE SNR and the D-region Ne was found over three VHF radar sites at high latitudes: Andøya, Kiruna, and Svalbard. This anti-correlation has been explained (a) in terms of transport effects due to strong electric fields associated to the SPE and (b) due to a limited amount of aerosol particles as compared to the amount of D-region electrons. Our calculations using the Ne profiles used by previous researchers explain most, if not all, of the observed SNR reduction in both time (around the SPE peak) and altitude. This systematic effect, particularly the Faraday rotation, should be recognized and tested, and possibly avoided (e.g., using circular polarization), in future observations during the incoming solar maximum period, to contribute to the understanding of PMSE during enhanced D region Ne.

  5. 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.

  6. 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.)

  7. 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

  8. 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.

  9. 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.

  10. 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.

  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. 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.

  13. Enhanced contrast ratio of homogeneously aligned liquid crystal displays by controlling the surface-anchoring strength

    Energy Technology Data Exchange (ETDEWEB)

    Lim, Young Jin; Woo, Chang Woo; Oh, Sang Hoon; Mukherjee, Amrita; Lee, Seung Hee [Department of BIN Fusion Technology and Department of Polymer Nano-Science and Technology, Chonbuk National University, Jeonju, Jeonbuk 561-756 (Korea, Republic of); Baek, Ji Ho; Kim, Kyeong Jin; Yang, Myung Su, E-mail: lsh1@chonbuk.ac.kr [Panel Performance Department, LG Display Co., Ltd., Paju, Gyeonggi-do 413-811 (Korea, Republic of)

    2011-08-17

    The dark state of homogeneously aligned liquid crystal displays (LCDs) associated with the in-plane switching of a LC director depends on their molecular ordering. We propose a new approach to reduce the light leakage in the dark state of homogeneously aligned LCDs. A very small amount of reactive mesogen (RM) is mixed with the LC material and polymerized at room temperature and also at a low temperature (-20 {sup 0}C) to strengthen the surface-anchoring energy. The contrast ratio of the low-temperature cured cell is improved by about 50% over that of the pure LC cell and the room temperature cured RM-mixed LC cell due to an enhanced order parameter.

  14. Adding TiC Nanoparticles to Magnesium Alloy ZK60A for Strength/Ductility Enhancement

    Directory of Open Access Journals (Sweden)

    Muralidharan Paramsothy

    2011-01-01

    Full Text Available ZK60A nanocomposite containing TiC nanoparticles was fabricated using solidification processing followed by hot extrusion. The ZK60A nanocomposite exhibited similar grain size to monolithic ZK60A and significantly reduced presence of intermetallic phase, reasonable TiC nanoparticle distribution, nondominant (0 0 0 2 texture in the longitudinal direction, and 16% lower hardness than monolithic ZK60A. Compared to monolithic ZK60A (in tension, the ZK60A nanocomposite simultaneously exhibited higher 0.2% TYS, UTS, failure strain, and work of fracture (WOF (+13%, +15%, +76%, and +106%, resp.. Also, compared to monolithic ZK60A (in compression, the ZK60A nanocomposite exhibited lower 0.2% CYS (−17% and higher UCS, failure strain, and WOF (+11%, +29%, and +34%, resp.. The beneficial effect of adding TiC nanoparticles on the enhanced tensile and compressive response of ZK60A is investigated in this paper.

  15. 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.

  16. Surface modification of polyester fabrics by atmospheric-pressure air/He plasma for color strength and adhesion enhancement

    Science.gov (United States)

    Zhang, Chunming; Zhao, Meihua; Wang, Libing; Qu, Lijun; Men, Yajing

    2017-04-01

    Surface properties of water-based pigmented inks for ink-jet printed polyester fabrics were modified with atmospheric-pressure air/He plasma to improve the color strength and pigment adhesion of the treated surfaces. The influence of various parameters, including the surface morphology, chemical compositions, surface energy and dynamic contact angles of the control and plasma treated samples was studied. Color strength and edge definition were used to evaluate the ink-jet printing performance of fabrics. The change in pigment adhesion to polyester fibers was analyzed by SEM (scanning electron microscopy). AFM (Atomic force microscope) and XPS (X-ray photoelectron spectroscopy) analyses indicated the increase in surface roughness and the oxygen-containing polar groups(Cdbnd O, Csbnd OH and COOH) reinforced the fixation of pigments on the fiber surface. The result from this study suggested that the improved pigment color yield was clearly affected by alteration of pigment adhesion enhanced by plasma surface modification. Polyester fabrics exhibited better surface property and ink-jet printing performance after the air/He mixture plasma treatment comparing with those after air plasma treatment.

  17. 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.

  18. 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...

  19. 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...

  20. Protein-containing nutrient supplementation following strength training enhances the effect on muscle mass, strength, and bone formation in postmenopausal women

    DEFF Research Database (Denmark)

    Holm, Lars; Olesen, J.L.; Matsumoto, K.

    2008-01-01

    following each training session. At inclusion, each woman was randomly and double-blindedly assigned to a nutrient group or a placebo (control) group. Muscle hypertrophy was evaluated from biopsies, MRI, and dual-energy X-ray absorptiometry (DEXA) scans, and muscle strength was determined in a dynamometer......We evaluated the response of various muscle and bone adaptation parameters with 24 wk of strength training in healthy, early postmenopausal women when a nutrient supplement (protein, carbohydrate, calcium, and vitamin D) or a placebo supplement (a minimum of energy) was ingested immediately....... Bone mineral density (BMD) was measured using DEXA scans, and bone turnover was determined from serum osteocalcin and collagen type I cross-linked carboxyl terminal peptide. The nutrient group improved concentric and isokinetic (60°/s) muscle strength from 6 to 24 wk by 9 ± 3% (P

  1. Protein-containing nutrient supplementation following strength training enhances the effect on muscle mass, strength, and bone formation in postmenopausal women

    DEFF Research Database (Denmark)

    Holm, Lars; Olesen, Jens L; Matsumoto, Keitaro

    2008-01-01

    following each training session. At inclusion, each woman was randomly and double-blindedly assigned to a nutrient group or a placebo (control) group. Muscle hypertrophy was evaluated from biopsies, MRI, and dual-energy X-ray absorptiometry (DEXA) scans, and muscle strength was determined in a dynamometer......We evaluated the response of various muscle and bone adaptation parameters with 24 wk of strength training in healthy, early postmenopausal women when a nutrient supplement (protein, carbohydrate, calcium, and vitamin D) or a placebo supplement (a minimum of energy) was ingested immediately....... Bone mineral density (BMD) was measured using DEXA scans, and bone turnover was determined from serum osteocalcin and collagen type I cross-linked carboxyl terminal peptide. The nutrient group improved concentric and isokinetic (60 degrees /s) muscle strength from 6 to 24 wk by 9 +/- 3% (P

  2. Enhanced superplasticity in an extruded high strength Mg–Gd–Y–Zr alloy with Ag addition

    Energy Technology Data Exchange (ETDEWEB)

    Movahedi-Rad, A. [School of Metallurgical and Materials Engineering, College of Engineering, University of Tehran, Tehran (Iran, Islamic Republic of); Mahmudi, R., E-mail: mahmudi@ut.ac.ir [School of Metallurgical and Materials Engineering, College of Engineering, University of Tehran, Tehran (Iran, Islamic Republic of); Wu, G.H.; Jafari Nodooshan, H.R. [National Engineering Research Center of Light Alloy Net Forming, Shanghai Jiao Tong University, Shanghai 200240 (China)

    2015-03-25

    Highlights: • Addition of 2% Ag to the base alloy refined the microstructure and increased m-value. • Volume fractions of both high angle grain boundaries and particles increased after Ag addition. • Ag-containing alloy had an m-value of 0.51, typical of superplastic materials. • Grain boundary sliding accommodated by lattice diffusion was the dominant deformation mechanism. - Abstract: The effect of 2 wt% Ag addition on the superplastic behavior of an extruded Mg–8.5Gd–2.5Y–0.5Zr (wt%) alloy was investigated by impression testing in the temperature range of 523–598 K. The average sizes of the dynamically recrystallized grains of the Ag-free and Ag-containing alloys were about 8 and 3 μm, respectively. Analysis of electron backscattered diffraction (EBSD) data confirmed the higher fractions of high-angle grain boundaries (HAGBs) in the Ag-containing alloy. The deformation response of this alloy in proper temperature range conforms to regions I, II and III, typical of superplastic deformation behavior. The addition of Ag to the base alloys led to enhanced superplasticity in region II by increasing the strain rate sensitivity (SRS) indices (m-values) from 0.25 to 0.51 and 0.36 to 0.46 at 573 and 598 K, respectively. These high m-values together with the activation energy of 181 kJ/mol suggest that the major mechanism involved in superplastic deformation is grain boundary sliding (GBS) accommodated by lattice diffusion at temperatures above 573 K.

  3. Bending energy penalty enhances the adhesive strength of functional amyloid curli to surfaces.

    Science.gov (United States)

    Zhang, Yao; Wang, Ao; DeBenedictis, Elizabeth P; Keten, Sinan

    2017-09-27

    The functional amyloid curli fiber, a major proteinaceous component of biofilm extracellular matrices, plays an important role in biofilm formation and enterobacteriaceae adhesion. Curli nanofibers exhibit exceptional underwater adhesion to various surfaces, have high rigidity and strong tensile mechanical properties, and thus hold great promise in biomaterials. The mechanisms of how curli fibers strongly attach to surfaces and detach under force remain elusive. To investigate curli fiber adhesion to surfaces, we developed a coarse-grained curli fiber model, in which the protein subunit CsgA (curli specific gene A) self-assembles into the fiber. The coarse-grained model yields physiologically relevant and tunable bending rigidity and persistence length. The force-induced desorption of a single curli fiber is examined using coarse-grained modeling and theoretical analysis. We find that the bending energy penalty arising from high persistence length enhances the resistance of the curli fiber against desorption and thus strengthens the adhesion of the curli fiber to surfaces. The CsgA-surface adhesion energy and the curli fiber bending rigidity both play crucial roles in the resistance of curli fiber against desorption from surfaces. To enable the desorption process, the applied peeling force must overcome both the interfacial adhesion energy and the energy barrier for bending the curli fiber at the peeling front. We show that the energy barrier to desorption increases with the interfacial adhesion energy, however, the bending induced failure of a single curli fiber limits the work of adhesion if the proportion of the CsgA-surface adhesion energy to the CsgA-CsgA cohesive energy becomes large. These results illustrate that the optimal adhesion performance of nanofibers is dictated by the interplay between bending, surface energy and cohesive energy. Our model provides timely insight into enterobacteriaceae adhesion mechanisms as well as future designs of engineered

  4. 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...

  5. 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.

  6. 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.

  7. Understanding the Nature of the Low-energy Enhancement in the Photon Strength Function of 56Fe

    Science.gov (United States)

    Jones, Michael; ANL1564 Collaboration

    2016-09-01

    A recent experiment designed to determine the multipolarity and electric or magnetic character of transitions in the region of the photon strength function (PSF) enhancement in 56Fe was performed at ANL using GRETINA in combination with the Phoswich wall. A beam of 16 MeV protons impinged upon a 1 mg/cm2 56Fe target, inelastically exciting it to high energies. The scattered protons were then measured by the Phoswich wall, providing the entrance excitation energy, while the resulting γ-ray cascades were measured in GRETINA. The PSF can be extracted using two-step cascades from the quasicontiuum to specific low-lying levels by a model independent method first employed in 95Mo. This method is being extended to take advantage of GRETINA as a polarimeter to obtain angular and polarization information in the region of the low-energy enhancement of the PSF. Preliminary results will be discussed. This material is based upon work supported by the U.S. Department of Energy, Office of Science, Office of Nuclear Physics under Contracts No. DE-AC02-05CH11231.

  8. Impact strength and flexural properties enhancement of methacrylate silane treated oil palm mesocarp fiber reinforced biodegradable hybrid composites.

    Science.gov (United States)

    Eng, Chern Chiet; Ibrahim, Nor Azowa; Zainuddin, Norhazlin; Ariffin, Hidayah; Yunus, Wan Md Zin Wan

    2014-01-01

    Natural fiber as reinforcement filler in polymer composites is an attractive approach due to being fully biodegradable and cheap. However, incompatibility between hydrophilic natural fiber and hydrophobic polymer matrix restricts the application. The current studies focus on the effects of incorporation of silane treated OPMF into polylactic acid (PLA)/polycaprolactone (PCL)/nanoclay/OPMF hybrid composites. The composites were prepared by melt blending technique and characterize the composites with Fourier transform infrared spectroscopy (FTIR), thermogravimetric analysis (TGA), and scanning electron microscopy (SEM). FTIR spectra indicated that peak shifting occurs when silane treated OPMF was incorporated into hybrid composites. Based on mechanical properties results, incorporation of silane treated OPMF enhances the mechanical properties of unmodified OPMF hybrid composites with the enhancement of flexural and impact strength being 17.60% and 48.43%, respectively, at 10% fiber loading. TGA thermogram shows that incorporation of silane treated OPMF did not show increment in thermal properties of hybrid composites. SEM micrographs revealed that silane treated OPMF hybrid composites show good fiber/matrix adhesion as fiber is still embedded in the matrix and no cavity is present on the surface. Water absorption test shows that addition of less hydrophilic silane treated OPMF successfully reduces the water uptake of hybrid composites.

  9. Impact Strength and Flexural Properties Enhancement of Methacrylate Silane Treated Oil Palm Mesocarp Fiber Reinforced Biodegradable Hybrid Composites

    Directory of Open Access Journals (Sweden)

    Chern Chiet Eng

    2014-01-01

    Full Text Available Natural fiber as reinforcement filler in polymer composites is an attractive approach due to being fully biodegradable and cheap. However, incompatibility between hydrophilic natural fiber and hydrophobic polymer matrix restricts the application. The current studies focus on the effects of incorporation of silane treated OPMF into polylactic acid (PLA/polycaprolactone (PCL/nanoclay/OPMF hybrid composites. The composites were prepared by melt blending technique and characterize the composites with Fourier transform infrared spectroscopy (FTIR, thermogravimetric analysis (TGA, and scanning electron microscopy (SEM. FTIR spectra indicated that peak shifting occurs when silane treated OPMF was incorporated into hybrid composites. Based on mechanical properties results, incorporation of silane treated OPMF enhances the mechanical properties of unmodified OPMF hybrid composites with the enhancement of flexural and impact strength being 17.60% and 48.43%, respectively, at 10% fiber loading. TGA thermogram shows that incorporation of silane treated OPMF did not show increment in thermal properties of hybrid composites. SEM micrographs revealed that silane treated OPMF hybrid composites show good fiber/matrix adhesion as fiber is still embedded in the matrix and no cavity is present on the surface. Water absorption test shows that addition of less hydrophilic silane treated OPMF successfully reduces the water uptake of hybrid composites.

  10. Effect of microscopic interface asymmetry on optical properties of short-period InAs/GaSb type-II superlattices

    Energy Technology Data Exchange (ETDEWEB)

    Dong, H.M. [Department of Physics, China University of Mining and Technology, Xuzhou 221116 (China); Li, L.L., E-mail: lllihfcas@foxmail.com [Key Laboratory of Materials Physics, Institute of Solid State Physics, Chinese Academy of Sciences, Hefei 230031 (China); Department of Physics and State Key Laboratory of Low-Dimensional Quantum Physics, Tsinghua University, Beijing 100084 (China); Xu, W. [Key Laboratory of Materials Physics, Institute of Solid State Physics, Chinese Academy of Sciences, Hefei 230031 (China); Department of Physics, Yunnan University, Kunming 650091 (China); Han, K. [Department of Physics, China University of Mining and Technology, Xuzhou 221116 (China)

    2015-08-31

    We theoretically investigate the effect of microscopic interface asymmetry (MIA) on the optical properties of short-period InAs/GaSb type-II superlattices (SLs) which can serve for the mid-infrared (mid-IR) detection. To calculate the band structures of such SLs, we use a modified eight-band Kane model which includes the MIA effect. With the band structures, we can evaluate the optical matrix elements and joint density of states for the corresponding SL systems. Based on these obtained results, we employ the Boltzmann equation approach to calculate the optical absorption coefficients for the corresponding SL systems. Theoretical calculations demonstrate that the MIA effect can greatly influence the electronic and optical properties of short-period InAs/GaSb type-II SLs. For the band structures, we find that the MIA effect causes strong interactions between different SL subbands and creates large spin splittings of these subbands. For the optical properties, the MIA effect activates the forbidden optical transition channels for TM polarization, enhances the absorption strength considerably and induces remarkable red-shifts for both transverse electric (TE) and transverse magnetic (TM) polarizations, where TE and TM refer to light polarizations along the in-plane and growth directions of SL structure. Different absorption features for TE and TM polarizations are well manifested by corresponding optical matrix elements. Moreover, in conjunction with recent experiment, we calculate the polarization-dependent absorption spectra for mid-IR InAs/GaSb type-II SLs. Our theoretical results can explain those observed experimentally. The present work sheds the significant importance of MIA effect in short-period InAs/GaSb type-II SLs. - Highlights: • Optical properties of InAs/GaSb superlattices (SLs) are studied theoretically. • The microscopic interface asymmetry (MIA) effect is considered for such SLs. • The MIA effect influences the optical properties of such SLs

  11. 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.

  12. Epitaxial superlattices with titanium nitride as a plasmonic component for optical hyperbolic metamaterials.

    Science.gov (United States)

    Naik, Gururaj V; Saha, Bivas; Liu, Jing; Saber, Sammy M; Stach, Eric A; Irudayaraj, Joseph M K; Sands, Timothy D; Shalaev, Vladimir M; Boltasseva, Alexandra

    2014-05-27

    Titanium nitride (TiN) is a plasmonic material having optical properties resembling gold. Unlike gold, however, TiN is complementary metal oxide semiconductor-compatible, mechanically strong, and thermally stable at higher temperatures. Additionally, TiN exhibits low-index surfaces with surface energies that are lower than those of the noble metals which facilitates the growth of smooth, ultrathin crystalline films. Such films are crucial in constructing low-loss, high-performance plasmonic and metamaterial devices including hyperbolic metamaterials (HMMs). HMMs have been shown to exhibit exotic optical properties, including extremely high broadband photonic densities of states (PDOS), which are useful in quantum plasmonic applications. However, the extent to which the exotic properties of HMMs can be realized has been seriously limited by fabrication constraints and material properties. Here, we address these issues by realizing an epitaxial superlattice as an HMM. The superlattice consists of ultrasmooth layers as thin as 5 nm and exhibits sharp interfaces which are essential for high-quality HMM devices. Our study reveals that such a TiN-based superlattice HMM provides a higher PDOS enhancement than gold- or silver-based HMMs.

  13. Effect of simultaneous application of postural techniques and expiratory muscle strength training on the enhancement of the swallowing function of patients with dysphagia caused by parkinson's disease.

    Science.gov (United States)

    Byeon, Haewon

    2016-06-01

    [Purpose] This study aimed to investigate the effect of simultaneous application of postural techniques and expiratory muscle strength training on the enhancement of the swallowing function of patients with dysphagia caused by Parkinson's disease. [Subjects and Methods] The subjects of this study were 18 patients who received simultaneous application of postural techniques and expiratory muscle strength training and 15 patients who received expiratory muscle strength training only. Postural techniques were conducted in the order of chin tucking, head rotation, head tilting, bending head back, and lying down, while expiratory muscle strength training was conducted at a resistance level of about 70% of the maximal expiratory pressure. Swallowing recovery was assessed by using the Functional Dysphagia Scale based on videofluoroscopic studies. [Results] The mean value obtained in the videofluoroscopic studies for both groups decreased after the treatment. In the postural techniques plus expiratory muscle strength training group, the decrease was significantly greater than that in the expiratory muscle strength training-only group. [Conclusion] The results imply that simultaneous performance of postural techniques and expiratory muscle strength training is more effective than expiratory muscle strength training alone when applied in the swallowing rehabilitation for patients with dysphagia caused by Parkinson's disease.

  14. Helimagnetic order in bulk MnSi and CoSi/MnSi superlattices

    Science.gov (United States)

    Loh, G. C.; Khoo, K. H.; Gan, C. K.

    2017-01-01

    Skyrmions are nanoscopic whirls of spins that reside in chiral magnets. It is only fairly recent that a plethora of applications for these quasiparticles emerges, especially in data storage. On the other hand, spin spirals are the periodic analogs of skyrmions, and are equally imperative in the course of exploration to enhance our understanding of helimagnetism. In this study, a new infrastructure based on the B20 compound, MnSi is propounded as a hosting material for spin spirals; alternating thin layers of CoSi and MnSi in the superlattice form provides a facile way of varying the properties of the spin spirals across a continuum. Using first-principles calculations based on full-potential linearized augmented plane-wave (FLAPW)-based density functional theory (DFT), the spin order of bulk MnSi, MnSi film, and the CoSi/MnSi superlattice is investigated. Spin dispersion plots as a function of propagation vectors show that the spiral size changes in the presence of CoSi - we find that the size of the spiral is reduced in the superlattice with thin CoSi layers (CoSi:MnSi=1:1 thickness ratio), whilst at a larger CoSi:MnSi=2:1 thickness ratio, the material behaves as a ferromagnet. In a similar fashion, the spin moment and orbital occupancy depend significantly on the thickness of the CoSi layers. However, the exchange interaction between Mn atoms appears to be generally impervious to the presence of CoSi. Succinctly, the CoSi/MnSi superlattice could be an excellent functional material in data storage applications.

  15. Effect of subsequent tension and annealing on microstructure evolution and strength enhancement of friction stir welded Mg alloys

    Energy Technology Data Exchange (ETDEWEB)

    Xin, Renlong, E-mail: rlxin@cqu.edu.cn; Sun, Liyun; Liu, Dejia; Zhou, Zheng; Liu, Qing

    2014-04-01

    Friction stir welded (FSW) Mg alloys normally exhibit a lower yield strength compared with the base materials, which is a drawback for their application as structure materials. In this study, subsequent tension along the transverse direction (TD) and then annealing were applied on FSW AZ31 alloys to modify the microstructure and texture in weld zone and to improve the joint strength. The results showed that by subsequent tension ∼4.5% strain along TD and then annealing, the yield strength (YS) could be greatly enhanced for the FSW AZ31 alloys. Specifically the YS was improved from ∼86 to ∼177 MPa by subsequent 4.5% tension and then reduced to ∼156 MPa after annealing. For the initial joint sample, fracture occurred in the stir zone (SZ) side during the transverse tensile test. But after subsequent tension, all the samples fractured in the base materials (BMs) whether subjected to annealing or not. The microstructure and texture evolutions after subsequent tension and annealing were examined by electron backscatter diffraction (EBSD) to understand the underlining mechanisms for the improved mechanical properties. It revealed that a lot of {10−12} extension twins were generated in the SZ side by 4.5% tension along TD, which significantly refined the grains in the SZ side and rotated the grains from soft to hard orientations for the transverse tensile test. Therefore, the formation of {10−12} twin lamellae had significant hardening effects on further transverse tensile tests. Schmid factor (SF) analysis revealed that the texture change by subsequent tension had much more impact on the activation of {10−12} extension twinning than basal slip for the transverse tensile test. This might affect the competition of extension twinning and basal slip and reduce the deformation incompatibility in the SZ side, which was beneficial for the improvement of mechanical properties. Nevertheless the present study showed that it was efficient to improve the YS of FSW Mg

  16. Quasi-ternary nanoparticle superlattices through nanoparticle design

    Energy Technology Data Exchange (ETDEWEB)

    Kortright, Jeffrey; Shevchenko, Elena V.; Kortright, Jeffrey B.; Talapin, Dmitri V.; Aloni, Shaul; Alivisatos, A. Paul

    2007-06-19

    Individual nanoscale building blocks exhibit a wide range of size-dependent properties, since their size can be tuned over known characteristic length scales of bulk materials. In the last several years, the possibility of combining different materials in the form of two and three component nanoparticles (NPs) has been extensively explored. Also multi-component materials can be obtained via self-assembly of NPs from their binary colloidal mixtures. These new nanocrystal solids may possess tunable collective properties that originate from interactions between size and composition controlled building blocks. Exchange coupling between neighboring NPs of magnetically soft and hard materials enhances the magnetic energy product of the nanocomposite material. Randomly mixed solids of small and large semiconducting CdSe NPs revealed enhancement of photoluminescence intensity of large semiconductor particles accompanied by quenching of photoluminescence of the small particles because of long-range resonant transfer of electronic excitations from the more electronically confined small particles to higher excited states of the large particles. Recently, it was demonstrated that binary semiconducting composite materials can show strongly enhanced electronic properties with about 100-fold higher conductance as compared to the sum of individual conductances of single-component films. Creation of highly periodic superlattices is expected not just provide the control of the homogeneity of the sample but also affect their properties. It was shown that silver nanocrystals organized into periodic cubic structures vibrated coherently [20] and demonstrated a change in electronic transport properties.

  17. Influence of tension-twisting deformations and defects on optical and electrical properties of B, N doped carbon nanotube superlattices

    Science.gov (United States)

    Guili, Liu; Yan, Jiang; Yuanyuan, Song; Shuang, Zhou; Tianshuang, Wang

    2016-06-01

    As the era of nanoelectronics is dawning, CNT (carbon nanotube), a one-dimensional nano material with outstanding properties and performances, has aroused wide attention. In order to study its optical and electrical properties, this paper has researched the influence of tension-twisting deformation, defects, and mixed type on the electronic structure and optical properties of the armchair carbon nanotube superlattices doped cyclic alternately with B and N by using the first-principle method. Our findings show that if tension-twisting deformation is conducted, then the geometric structure, bond length, binding energy, band gap and optical properties of B, N doped carbon nanotube superlattices with defects and mixed type will be influenced. As the degree of exerted tension-twisting deformation increases, B, N doped carbon nanotube superlattices become less stable, and B, N doped carbon nanotube superlattices with defects are more stable than that with exerted tension-twisting deformations. Proper tension-twisting deformation can adjust the energy gap of the system; defects can only reduce the energy gap, enhancing the system metallicity; while the mixed type of 5% tension, twisting angle of 15° and atomic defects will significantly increase the energy gap of the system. From the perspective of optical properties, doped carbon nanotubes may transform the system from metallicity into semi-conductivity. Project supported by the National Natural Science Foundation of China (No. 51371049) and the Natural Science Foundation of Liaoning Province (No. 20102173).

  18. Investigation of the vertical electrical transport in a-Si:H/nc-Si:H superlattice thin films.

    Science.gov (United States)

    Das, Debajyoti; Kar, Debjit

    2015-07-14

    Tuning the size of silicon nano-crystallites (Si-ncs) has been realized simply by controlling the thickness of the nc-Si:H sub-layer (tnc) in the a-Si:H/nc-Si:H superlattice thin films grown by low temperature plasma processing in PE-CVD. The vertical electrical transport phenomena accomplished in superlattice films have been investigated in order to identify their effective utilization in practical device configuration. The reduced size of the Si-ncs at thinner tnc and the associated band gap widening due to quantum confinement effects generates the Coulomb potential barrier at the a-Si/nc-Si interface which in turn obstructs the transport of charge carriers to the allowed energy states in Si-ncs, leading to the Poole-Frenkel tunneling as the prevailing charge transport mechanism in force. The advantages of the conduction process governed by the Poole-Frenkel mechanism are two-fold. The lower barrier height caused by the a-Si:H sub-layer in the superlattice than the silicon oxide sub-layer in conventional structures enhances the conduction current. Moreover, increasing trapped charges in the a-Si:H sub-layer can arbitrarily increase the current conduction. Accordingly, a-Si:H/nc-Si:H superlattice structures could provide superior electrical transport in stacked layer devices e.g., multi-junction all silicon solar cells.

  19. Nonlinear THz response of metallic armchair graphene nanoribbon superlattices

    Science.gov (United States)

    Wang, Yichao; Andersen, David R.

    2016-11-01

    We study the third order THz nonlinear response of metallic armchair graphene nanoribbon superlattices in the presence of an elliptically-polarized excitation field using the time dependent perturbation theory. For a one-dimensional Kronig-Penney potential of infinite length, the nonlinear response can be described perturbatively by a low energy \\mathbf{k}\\centerdot \\mathbf{p} N-photon coupling model. Remarkably, as shown by Burset et al the energy dispersion of the metallic band in the direction parallel to the superlattice wavevector is independent of the applied superlattice potential while the energy dispersion in the direction perpendicular to the superlattice wavevector depends strongly on the superlattice parameters. As a result, we predict novel behavior for the nonlinear response of single layer metallic acGNR superlattices to an applied elliptically-polarized electric field. Our work shows that the superlattice potential, periodicity, Fermi level, excitation field polarization state, and temperature all play a significant role in the resulting THz nonlinear conductances.

  20. Transfer Matrix for Fibonacci Dielectric Superlattice

    Institute of Scientific and Technical Information of China (English)

    蔡祥宝

    2001-01-01

    The transfer matrices, which transfer the amplitudes of the electric fields of second- and third-harmonic waves from one side of the interface to the other, are defined for layers joined coherently, and the total transfer matrices for several sequential interfaces can be simply obtained by multiplication of the matrices. Using the transfer matrix method, the interacting processes of second- and third-harmonic waves in a one-dimensional finite Fibonacci dielectric superlattice are investigated. Applying the numerical procedure described in this letter, the dependence of the second- and third-harmonic fields on sample thickness is obtained. The numerical results agree with the quasi-phase-matching theory.

  1. 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

  2. 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.

  3. Atom probe tomography and transmission electron microscopy of a Mg-doped AlGaN/GaN superlattice

    Energy Technology Data Exchange (ETDEWEB)

    Bennett, S.E., E-mail: sb534@cam.ac.uk [Department of Materials Science and Metallurgy, University of Cambridge, Pembroke Street, Cambridge CB2 3QZ (United Kingdom); Ulfig, R.M.; Clifton, P.H. [Imago Scientific Instruments Corporation, 5500 Nobel Drive, Madison, WI 53711 (United States); Kappers, M.J.; Barnard, J.S.; Humphreys, C.J.; Oliver, R.A. [Department of Materials Science and Metallurgy, University of Cambridge, Pembroke Street, Cambridge CB2 3QZ (United Kingdom)

    2011-02-15

    The electronic characteristics of semiconductor-based devices are greatly affected by the local dopant atom distribution. In Mg-doped GaN, the clustering of dopants at structural defects has been widely reported, and can significantly affect p-type conductivity. We have studied a Mg-doped AlGaN/GaN superlattice using transmission electron microscopy (TEM) and atom probe tomography (APT). Pyramidal inversion domains were observed in the TEM and the compositional variations of the dopant atoms associated with those defects have been studied using APT. Rarely has APT been used to assess the compositional variations present due to structural defects in semiconductors. Here, TEM and APT are used in a complementary fashion, and the strengths and weaknesses of the two techniques are compared. -- Research Highlights: {yields} Mg-rich regions of approximately 5 nm in size were revealed in Mg-doped AlGaN/GaN superlattices using atom probe tomography (APT). {yields} Transmission electron microscopy (TEM) of the superlattice sample showed pyramidal inversion domains, concluded to be the same Mg-rich features observed by APT. {yields} The information gained from both the 3D APT study and the 2D TEM characterisation was then compared to determine the strengths and weaknesses of each technique in analysing nanoscale features in nitride materials.

  4. 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.

  5. Influence of Deviation on Optical Transmission through Aperiodic Superlattices

    Institute of Scientific and Technical Information of China (English)

    YIN Hai-Long; YANG Xiang-Bo; LAN Sheng; HU Wei

    2007-01-01

    We propose a deviation model and study the influences of the relative error and sensitivity of a machine on the transmission coefficients (TCs) of Fibonacci superlattices. It is found that for a system with fewer layers, the influence of deviation can be ignored. When superlattices become more complicated, they may be fabricated by a machine with suitable relative error and possess the designed value of TC. However, when the number of system layers exceeds some critical value, superlattices should be manufactured only by precise machines. The influence of the sensitivity is also discussed.

  6. 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.

  7. 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

  8. Raman fingerprint of aligned graphene/h-BN superlattices.

    Science.gov (United States)

    Eckmann, Axel; Park, Jaesung; Yang, Huafeng; Elias, Daniel; Mayorov, Alexander S; Yu, Geliang; Jalil, Rashid; Novoselov, Kostya S; Gorbachev, Roman V; Lazzeri, Michele; Geim, Andre K; Casiraghi, Cinzia

    2013-11-13

    Graphene placed on hexagonal-boron nitride (h-BN) experiences a superlattice (Moiré) potential, which leads to a strong reconstruction of graphene's electronic spectrum with new Dirac points emerging at sub-eV energies. Here we study the effect of such superlattices on graphene's Raman spectrum. In particular, the 2D Raman peak is found to be exquisitely sensitive to the misalignment between graphene and h-BN lattices, probably due to the presence of a strain distribution with the same periodicity of the Moiré potential. This feature can be used to identify graphene superlattices with a misalignment angle smaller than 2°.

  9. 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.

  10. Ge/SiGe superlattices for nanostructured thermoelectric modules

    Energy Technology Data Exchange (ETDEWEB)

    Chrastina, D., E-mail: daniel@chrastina.net [L-NESS Politecnico di Milano, Polo di Como, via Anzani 42, 22100 Como (Italy); Cecchi, S. [L-NESS Politecnico di Milano, Polo di Como, via Anzani 42, 22100 Como (Italy); Hague, J.P. [Department of Physical Sciences, The Open University, Walton Hall, Milton Keynes, MK7 6AA (United Kingdom); Frigerio, J. [L-NESS Politecnico di Milano, Polo di Como, via Anzani 42, 22100 Como (Italy); Samarelli, A.; Ferre–Llin, L.; Paul, D.J. [School of Engineering, University of Glasgow, Oakfield Avenue, Glasgow, G12 8LT (United Kingdom); Müller, E. [Electron Microscopy ETH Zurich (EMEZ), ETH-Zürich, CH-8093 (Switzerland); Etzelstorfer, T.; Stangl, J. [Institut für Halbleiter und Festkörperphysik, Universität Linz, A-4040 Linz (Austria); Isella, G. [L-NESS Politecnico di Milano, Polo di Como, via Anzani 42, 22100 Como (Italy)

    2013-09-30

    Thermoelectrics are presently used in a number of applications for both turning heat into electricity and also for using electricity to produce cooling. Mature Si/SiGe and Ge/SiGe heteroepitaxial growth technology would allow highly efficient thermoelectric materials to be engineered, which would be compatible and integrable with complementary metal oxide silicon micropower circuits used in autonomous systems. A high thermoelectric figure of merit requires that electrical conductivity be maintained while thermal conductivity is reduced; thermoelectric figures of merit can be improved with respect to bulk thermoelectric materials by fabricating low-dimensional structures which enhance the density of states near the Fermi level and through phonon scattering at heterointerfaces. We have grown and characterized Ge-rich Ge/SiGe/Si superlattices for nanofabricated thermoelectric generators. Low-energy plasma-enhanced chemical vapor deposition has been used to obtain nanoscale-heterostructured material which is several microns thick. Crystal quality and strain control have been investigated by means of high resolution X-ray diffraction. High-resolution transmission electron microscopy images confirm the material and interface quality. Electrical conductivity has been characterized by the mobility spectrum technique. - Highlights: ► High-quality Ge/SiGe multiple quantum wells for thermoelectric applications ► Mobility spectra of systems featuring a large number of parallel conduction channels ► Competitive thermoelectric properties measured in single devices.

  11. 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.

  12. Theoretical investigation of InAs/GaSb type-II pin superlattice infrared detector in the mid wavelength infrared range

    Science.gov (United States)

    Kaya, U.; Hostut, M.; Kilic, A.; Sakiroglu, S.; Sokmen, I.; Ergun, Y.; Aydinli, A.

    2013-02-01

    In this study, we present the theoretical investigation of type-II InAs/GaSb superlattice p-i-n detector. Kronig-Penney and envelope function approximation is used to calculate band gap energy and superlattice minibands. Variational method is also used to calculate exciton binding energies. Our results show that carriers overlap increases at GaSb/InAs interface on the higher energy side while it decreases at InAs/GaSb interface on the lower energy side with increasing reverse bias due to shifting the hole wavefunction toward to the GaSb/InAs interface decisively. Binding energies increase with increasing electric field due to overall overlap of electron and hole wave functions at the both interfaces in contrast with type I superlattices. This predicts that optical absorption is enhanced with increasing electric field.

  13. Superior Properties of Energetically Stable La2/3Sr1/3MnO3/Tetragonal BiFeO3 Multiferroic Superlattices

    KAUST Repository

    Feng, Nan

    2015-04-30

    The superlattice of energetically stable La2/3Sr1/3MnO3 and tetragonal BiFeO3 is investigated by means of density functional theory. The superlattice as a whole exhibits a half-metallic character, as is desired for spintronic devices. The interfacial electronic states and exchange coupling are analyzed in details. We demonstrate that the interfacial O atoms play a key role in controlling the coupling. The higher ferroelectricity of tetragonal BiFeO3 and stronger response to the magnetic moment in La2/3Sr1/3MnO3/BiFeO3 superlattice show a strongly enhanced electric control of the magnetism as compared to the rhombohedral one. Therefore, it is particularly practical interest in the magnetoelectric controlled spintronic devices.

  14. Optimum thickness of soft magnetic phase in FePt/FeCo permanent magnet superlattices with high energy product and large magnetic anisotropy energy

    Directory of Open Access Journals (Sweden)

    Sandeep Kumar Jain

    2016-02-01

    Full Text Available Ab initio calculations on hard/soft (FePtm/(FeCon, (m = 4, 6, 8 and n = 2-2m magnetic superlattices show that the B2 type FeCo layers become anisotropic with varying interlayer spacing and enhanced magnetic moments. The average magnetic moment in superlattices is higher than in bulk FePt, resulting in high maximum energy product for (FePt4/(FeCo8 which is nearly double the calculated value for bulk FePt. The calculation of the magnetic anisotropy energy shows that the optimal thickness of the soft magnetic phase for good permanent magnet behaviour of the superlattice is less than ∼2 nm.

  15. 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

  16. Quantum Transport: The Link between Standard Approaches in Superlattices

    DEFF Research Database (Denmark)

    Wacker, Andreas; Jauho, Antti-Pekka

    1998-01-01

    Theories describing electrical transport in semiconductor superlattices can essentially be divided in three disjoint categories: (i) transport in a miniband; (ii) hopping between Wannier-Stark ladders; and (iii) sequential tunneling. We present a quantum transport model, based on nonequilibrium...

  17. The soliton properties of dipole domains in superlattices

    Institute of Scientific and Technical Information of China (English)

    张启义; 田强

    2002-01-01

    The formation and propagation of dipole domains in superlattices are studied both by the modified discrete driftmodel and by the nonlinear Schrodinger equation. The spatiotemporal distribution of the electric field and electrondensity are presented. The numerical results are compared with the soliton solutions of the nonlinear Schrodingerequation and analysed. It is shown that the numerical solutions agree with the soliton solutions of the nonlinearSchrodinger equation. The dipole electric-field domains in semiconductor superlattices have the properties of solitons.

  18. 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

  19. Experimental evidence of delocalized states in random dimer superlattices

    OpenAIRE

    Bellani, V.; Díez, E.; Hey, R.; Toni, L.; Tarricone, L.; Parravicini, G.B.; Domínguez-Adame Acosta, Francisco; Gómez-Alcalá, R.

    1999-01-01

    We study the electronic properties of GaAs-AlGaAs superlattices with intentional correlated disorder by means of photoluminescence and vertical dc resistance. The results are compared to those obtained in ordered and uncorrelated disordered superlattices. We report the first experimental evidence that spatial correlations inhibit localization of states in disordered low-dimensional systems, as our previous theoretical calculations suggested, in contrast to the earlier belief that all eigensta...

  20. Developmental Model Using Gestalt-Play versus Cognitive-Verbal Group with Chinese Adolescents: Effects on Strengths and Adjustment Enhancement

    Science.gov (United States)

    Shen, Yih-Jiun

    2007-01-01

    This study compared the effectiveness of short-term developmental group counseling applying Gestalt-play versus cognitive-verbal approaches with Taiwanese adolescents. On a measure of behavioral and emotional strengths, teachers reported significant changes in students' overall behavioral and emotional strengths measured via total scores. Specific…

  1. Developmental Model Using Gestalt-Play versus Cognitive-Verbal Group with Chinese Adolescents: Effects on Strengths and Adjustment Enhancement

    Science.gov (United States)

    Shen, Yih-Jiun

    2007-01-01

    This study compared the effectiveness of short-term developmental group counseling applying Gestalt-play versus cognitive-verbal approaches with Taiwanese adolescents. On a measure of behavioral and emotional strengths, teachers reported significant changes in students' overall behavioral and emotional strengths measured via total scores. Specific…

  2. 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.

  3. 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.

  4. 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.

  5. Magnetocaloric properties of Co/Cr superlattices

    Science.gov (United States)

    Mukherjee, Tathagata; Skomski, Ralph; Sellmyer, David; Binek, Christian

    2010-03-01

    Nanostructured materials aiming on refrigeration applications are experimentally realized by molecular beam epitaxial (MBE) growth of Co/Cr superlattices using mean-field theoretical concepts as guiding principles.footnotetextT. Mukherjee, S. Sahoo, R. Skomski, D. J. Sellmyer, and Ch. Binek, Phys. Rev. B 79, 144406-1-9 (2009). Magnetocaloric properties are deduced from measurements of the temperature and field dependence of the magnetization of our samples. More generally, the potential of artificial antiferromagnets for near room-temperature refrigeration is explored. The effects of intra-plane and inter-plane exchange interactions on the magnetic phase diagram in Ising-type model systems are revisited in mean-field considerations with special emphasis on tailoring magnetocaloric properties. The experimental results are discussed in light of our theoretical findings, and extrapolations for future improved nanostructures are provided. Financial support by NRI, and NSF through EPSCoR, Career DMR-0547887, and MRSEC.

  6. Magnetic Field in Superlattices Semiconductors of Crystals

    Directory of Open Access Journals (Sweden)

    Luciano Nascimento

    2015-05-01

    Full Text Available In this work we present a study on the super-semiconductor networks, using the Kronig-Penney model for the effective mass approximation, and then the calculations for the application of the magnetic field perpendicular and parallel to the layers of super lattices crystals. The magnetic field applied parallel to the layers, was used to adjust the resonance of a higher energy subband of a well by thermal excitation with a lower energy subband of the adjacent well, increasing energy levels in its tunneling rate. We use the formalism of Schrödinger equation of quantum mechanics. Introducing the calculations in a systematic way in superlattices for each semiconductor quantum well to assess their energy spectrum systematically studied.

  7. Development of Strained-Layer Superlattice (SLS) IR Detector Camera Project

    Data.gov (United States)

    National Aeronautics and Space Administration — Strained Layer Superlattice (SLS) detectors are a new class of detectors.   In our FY12 IRAD “Strained Layer Superlattice Infrared Detector Array...

  8. Wildfire Prevention and Suppression plans enhancing: a first overview on strength and weakness in Italian stakeholders experiences and perception.

    Science.gov (United States)

    Bonora, Laura; Conese, Claudio; Barbati, Anna

    2014-05-01

    Fires and wildfires represent an element of vulnerability for forests, considering that have now reached a level beyond which further burning would seriously endanger the ecosystem services and their sustainable management. It is fundamental to support fire-fighting Centres by giving them tools, useful to faces future trends; in this sense the first step is to examine technical and operative procedures to evaluate their strong and weak aspects, in collaboration with personnel responsible of risk management, suppression coordination and patrol responsible of direct attack. The aims this work is to identify present elements of strength ad problematic aspects to tuning the wildfire suppression actions to future changes; this is a crucial challenge both for policy and territory planners and managers. Historical investigation lines on forest fire covered the basilar and fundamental dynamics which understanding was necessary to confine and fight the wildfire phenomenon. At the present all the competences, knowledge and connections acquired are translating and including in the Plans, sharing innovative strategies -with the "direct involved actors"- trying to decrease the fire trend. Stakeholders underlined that collaboration between research and territorial Institutions are producing positive results, showing the conceptual rightness and the well-run of the in-progress implementations. The Italian framework of wildfire prevention plans is very peculiar because the Plans related to prevention and active intervention procedure are coincident. Normative, procedural, economic and logistic aspects are considered and handled in the same general document; each year the local structures, designed by the Regions, have in charge the draft of the operative plan, defining and managing the means and patrols distribution and turnover. In the present work 3 Italian Regions (Tuscany, Puglia and Sardinia, with different territorial and vegetation characteristics and affected by different

  9. Effects of crossed electric and magnetic fields on the interband optical absorption spectra of variably spaced semiconductor superlattices

    Science.gov (United States)

    Zuleta, J. N.; Reyes-Gómez, E.

    2016-05-01

    The interband optical absorption spectra of a GaAs-Ga1-xAlxAs variably spaced semiconductor superlattice under crossed in-plane magnetic and growth-direction applied electric fields are theoretically investigated. The electronic structure, transition strengths and interband absorption coefficients are analyzed within the weak and strong magnetic-field regimes. A dramatic quenching of the absorption coefficient is observed, in the weak magnetic-field regime, as the applied electric field is increased, in good agreement with previous experimental measurements performed in a similar system under growth-direction applied electric fields. A decrease of the resonant tunneling in the superlattice is also theoretically obtained in the strong magnetic-field regime. Moreover, in this case, we found an interband absorption coefficient weakly dependent on the applied electric field. Present theoretical results suggest that an in-plane magnetic field may be used to tune the optical properties of variably spaced semiconductor superlattices, with possible future applications in solar cells and magneto-optical devices.

  10. Attitude Strength.

    Science.gov (United States)

    Howe, Lauren C; Krosnick, Jon A

    2017-01-03

    Attitude strength has been the focus of a huge volume of research in psychology and related sciences for decades. The insights offered by this literature have tremendous value for understanding attitude functioning and structure and for the effective application of the attitude concept in applied settings. This is the first Annual Review of Psychology article on the topic, and it offers a review of theory and evidence regarding one of the most researched strength-related attitude features: attitude importance. Personal importance is attached to an attitude when the attitude is perceived to be relevant to self-interest, social identification with reference groups or reference individuals, and values. Attaching personal importance to an attitude causes crystallizing of attitudes (via enhanced resistance to change), effortful gathering and processing of relevant information, accumulation of a large store of well-organized relevant information in long-term memory, enhanced attitude extremity and accessibility, enhanced attitude impact on the regulation of interpersonal attraction, energizing of emotional reactions, and enhanced impact of attitudes on behavioral intentions and action. Thus, important attitudes are real and consequential psychological forces, and their study offers opportunities for addressing behavioral change.

  11. Crossover from Incoherent to Coherent Phonon Scattering in Epitaxial Oxide Superlattices

    Science.gov (United States)

    2013-12-08

    of the superlattices. Figure 3a shows a high-resolution, short-angular-range θ–2θ X - ray diffraction (XRD) scan of a (STO)6/(CTO)6 superlattice...function of interface density. We do so by synthesizing superlattices of electrically insulating perovskite oxides 1. REPORT DATE (DD-MM-YYYY) 4. TITLE...synthesizing superlattices of electrically insulating perovskite oxides and systematically varying the interface density, with unit-cell precision, using two

  12. Evaluation of strength-enhancing factors of a ductile binder in direct compression of sodium bicarbonate and calcium carbonate powders.

    Science.gov (United States)

    Mattsson, S; Nyström, C

    2000-03-01

    This study evaluated the effectiveness of a ductile binder in direct compression of sodium bicarbonate and calcium carbonate powders. Properties associated with both the binder and the compound were studied. The addition of binder materials, such as polyethylene glycols (PEGs) of differing molecular weights or microcrystalline cellulose, generally resulted in an increase in the axial tensile strength of the corresponding compacts. The increase in tablet strength was generally greater with the PEGs than with microcrystalline cellulose. The results indicate that the improvement in tablet strength caused by the binder is dependent on properties of both the binder and the compound. By utilising different methods it was established that the fracture during tablet strength testing mainly occurred around the compound particles. As a consequence of this, it appears that the ability of the binder to fill the voids between the compound particles is a determinative factor for increasing tablet strength. The binder appeared to have less effect when added to compounds that fragmented during compaction. Characteristics of the binder resulting in the greatest decrease in porosity, and thus the greatest increase in the tensile strength of the compound, included a high degree of plastic deformation with a limited elastic component and a small particle size. Obviously, the amount of binder added to the mixture also affected the results.

  13. First-principles and molecular dynamics study of thermoelectric transport properties of N-type silicon-based superlattice-nanocrystalline heterostructures

    Science.gov (United States)

    Zhou, Yanguang; Gong, Xiaojing; Xu, Ben; Hu, Ming

    2017-08-01

    Electrical and thermal transport in silicon germanium superlattice nanostructures has received extensive attention from scientists for understanding carrier properties at the nanoscale, and the figure-of-merit (ZT) reported in such structures has inspired engineers to develop cost-effective waste heat recovery systems. In this paper, the thermoelectric transport properties of the silicon-based superlattice- and anti-superlattice-nanocrystalline heterostructures are systematically studied by first-principles and molecular dynamics simulations combined with the Boltzmann transport theory. The thermal conductivity, which is thought to be the essential bottleneck for bulk crystalline Si to gain a high ZT value, of such structures is found to be reduced by two orders of magnitude and reaches a level far below the amorphous limit of Si. This is achieved due to the extremely strong phonon-boundary scattering at both grain boundaries and Si-Ge interfaces, which will lead to the phonon mean free path being much smaller than the grain size (Casmir limit): for instance, the dominant phonons are in range of 0.5 to 3 nm for the heterostructures with a grain size of around 8 nm. Meanwhile, the power factor can be preserved at the level comparable to bulk crystalline because of the quantum confinement effect, which resulted from the conduction band minima converge, reduction of band gap, and the short mean free path of carriers. As a result, the ZT of such superlattice based nanomembranes can reach around 0.3 at room temperature, which is two orders of magnitude higher than the bulk crystalline case. The corresponding bulk superlattice-nanocrystalline heterostructures possess a ZT value of 0.5 at room temperature, which is superior to all other bulk silicon-based thermoelectrics. Our results here show that nanostructuring the superlattice structure can further decrease the thermal conductivity while keeping the electrical transport properties at the bulk comparable level, and

  14. Conservation Research and Development/ New Ultra-Low Carbon High Strength Steels with Improved Bake Hardenability for Enhanced Stretch Formability and Dent Resistance

    Energy Technology Data Exchange (ETDEWEB)

    Anthony J. DeArdo; C. Isaac Garcia

    2003-12-15

    Conservation Research and Development/New Ultra-Low Carbon High Strength Steels with Improved Bake Hardenability for Enhanced Stretch Formability and Dent Resistance. The experimental work can be divided into four phases. In each phase, the materials were received or designed, processed and tested, to evaluate the BH increment or response, as a function of compositions and processing conditions. Microstructural characterization by various techniques was performed in order to gain insights into the mechanisms of flow stress increment by bake hardening.

  15. Quantum Dot Superlattice Enabled Rational Design in Optoelectronics and Hydrogen Generation

    Science.gov (United States)

    2014-11-25

    Final 3. DATES COVERED (From - To) 22-April-2013 to 21-April-2014 4. TITLE AND SUBTITLE Quantum Dot Superlattice Enabled Rational Design...15. SUBJECT TERMS Quantum Dots , Optoelectronic Applications, Charge Transfer, Superlattices, Density Functional Theory, Coupling...FA2386-13-1-4074 “ Quantum Dot Superlattice Enabled Rational Design in Optoelectronics and Hydrogen Generation” April 21, 2014 PI and Co-PI

  16. 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.

  17. Raman spectra and magnetization of all-ferromagnetic superlattices grown on (110) oriented SrTiO{sub 3}

    Energy Technology Data Exchange (ETDEWEB)

    Behera, B. C.; Ravindra, A. V.; Padhan, P. [Department of Physics, Indian Institute of Technology Madras, Chennai 600036 (India); Prellier, W. [Laboratoire CRISMAT, CNRS UMR 6508, ENSICAEN, 6 Bd du Marehal Juin, F-14050 Caen Cedex (France)

    2014-03-03

    Superlattices consist of two ferromagnets La{sub 0.7}Sr{sub 0.3}MnO{sub 3} (LSMO) and SrRuO{sub 3} (SRO) were grown in (110)-orientation on SrTiO{sub 3} (STO) substrates. The x-ray diffraction and Raman spectra of these superlattices show the presence of in-plane compressive strain and orthorhombic structure of less than 4 u.c. thick LSMO spacer, respectively. Magnetic measurements reveal several features including reduced magnetization, enhanced coercivity, antiferromagnetic coupling, and switching from antiferromagnetic to ferromagnetic coupling with magnetic field orientations. These magnetic properties are explained by the observed orthorhombic structure of spacer LSMO in Raman scattering which occurs due to the modification in the stereochemistry of Mn at the interfaces of SRO and LSMO.

  18. Effect of traditional resistance and power training using rated perceived exertion for enhancement of muscle strength, power, and functional performance.

    Science.gov (United States)

    Tiggemann, Carlos Leandro; Dias, Caroline Pieta; Radaelli, Regis; Massa, Jéssica Cassales; Bortoluzzi, Rafael; Schoenell, Maira Cristina Wolf; Noll, Matias; Alberton, Cristine Lima; Kruel, Luiz Fernando Martins

    2016-04-01

    The present study compared the effects of 12 weeks of traditional resistance training and power training using rated perceived exertion (RPE) to determine training intensity on improvements in strength, muscle power, and ability to perform functional task in older women. Thirty healthy elderly women (60-75 years) were randomly assigned to traditional resistance training group (TRT; n = 15) or power training group (PT; n = 15). Participants trained twice a week for 12 weeks using six exercises. The training protocol was designed to ascertain that participants exercised at an RPE of 13-18 (on a 6-20 scale). Maximal dynamic strength, muscle power, and functional performance of lower limb muscles were assessed. Maximal dynamic strength muscle strength leg press (≈58 %) and knee extension (≈20 %) increased significantly (p training. Muscle power also increased with training (≈27 %; p training period (≈13 %; p strength, muscle power, and functional performance of lower limbs in elderly women.

  19. Protein fouling in carbon nanotubes enhanced ultrafiltration membrane: Fouling mechanism as a function of pH and ionic strength

    KAUST Repository

    Lee, Jieun

    2016-11-04

    The protein fouling behavior was investigated in the filtration of the multiwall carbon nanotube (MWCNT) composite membrane and commercial polyethersulfone ultrafiltration (PES-UF) membrane. The effect of solution chemistry such as pH and ionic strength on the protein fouling mechanism was systematically examined using filtration model such as complete pore blocking, intermediate pore blocking and cake layer formation. The results showed that the initial permeate flux pattern and fouling behavior of the MWCNT composite membrane were significantly influenced by pH and ionic strength while the effect of PES-UF membrane on flux was minimal. In a lysozyme (Lys) filtration, the severe pore blocking in the MWCNT membrane was made by the combined effect of intra-foulant interaction (Lys-Lys) and electrostatic repulsion between the membrane surface and the foulant at pH 4.7 and 10.4, and increasing ionic strength where the foulant-foulant interaction and membrane-fouling interaction were weak. In a bovine serum albumin (BSA) filtration, severe pore blocking was reduced by less deposition via the electrostatic interaction between the membrane and foulant at pH 4.7 and 10.4 and increasing ionic strength, at which the interaction between the membrane and BSA became weak. For binary mixture filtration, the protein fouling mechanism was more dominantly affected by foulant-foulant interaction (Lys-BSA, Lys-Lys, and BSA-BSA) at pH 7.0 and increase in ionic strength. This research demonstrates that MWCNT membrane fouling can be alleviated by changing pH condition and ionic strength based on the foulant-foulant interaction and the electrostatic interaction between the membrane and foulant.

  20. 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.

  1. 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.

  2. Quasi-Dirac points in one-dimensional graphene superlattices

    Energy Technology Data Exchange (ETDEWEB)

    Chen, C.H.; Tseng, P.; Hsueh, W.J., E-mail: hsuehwj@ntu.edu.tw

    2016-08-26

    Quasi-Dirac points (QDPs) with energy different from the traditional Dirac points (TDPs) have been found for the first time in one-dimensional graphene superlattices. The angular-averaged conductance reaches a minimum value at the QDPs, at which the Fano factor approaches 1/3. Surprisingly, the minimum conductance at these QDPs may be lower than that at the TDPs under certain conditions. This is remarkable as the minimum conductance attainable in graphene superlattices was believed to appear at TDPs. - Highlights: • Quasi-Dirac points (QDPs) are found for the first time in one-dimensional graphene superlattices. • The QDP is different from the traditional Dirac points (TDPs) in graphene superlattices. • The angular-averaged conductance reaches a minimum value at the QDPs, at which the Fano factor approaches 1/3. • The minimum conductance at these QDPs may be lower than that at the TDPs under certain conditions. • The minimum conductance attainable in graphene superlattices was believed to appear at TDPs.

  3. Newly developed Ti-Nb-Zr-Ta-Si-Fe biomedical beta titanium alloys with increased strength and enhanced biocompatibility.

    Science.gov (United States)

    Kopova, Ivana; Stráský, Josef; Harcuba, Petr; Landa, Michal; Janeček, Miloš; Bačákova, Lucie

    2016-03-01

    Beta titanium alloys are promising materials for load-bearing orthopaedic implants due to their excellent corrosion resistance and biocompatibility, low elastic modulus and moderate strength. Metastable beta-Ti alloys can be hardened via precipitation of the alpha phase; however, this has an adverse effect on the elastic modulus. Small amounts of Fe (0-2 wt.%) and Si (0-1 wt.%) were added to Ti-35Nb-7Zr-6Ta (TNZT) biocompatible alloy to increase its strength in beta solution treated condition. Fe and Si additions were shown to cause a significant increase in tensile strength and also in the elastic modulus (from 65 GPa to 85 GPa). However, the elastic modulus of TNZT alloy with Fe and Si additions is still much lower than that of widely used Ti-6Al-4V alloy (115 GPa), and thus closer to that of the bone (10-30 GPa). Si decreases the elongation to failure, whereas Fe increases the uniform elongation thanks to increased work hardening. Primary human osteoblasts cultivated for 21 days on TNZT with 0.5Si+2Fe (wt.%) reached a significantly higher cell population density and significantly higher collagen I production than cells cultured on the standard Ti-6Al-4V alloy. In conclusion, the Ti-35Nb-7Zr-6Ta-2Fe-0.5Si alloy proves to be the best combination of elastic modulus, strength and also biological properties, which makes it a viable candidate for use in load-bearing implants.

  4. Preparation of microfibrillated cellulose/chitosan-benzalkonium chloride biocomposite for enhancing antibacterium and strength of sodium alginate films.

    Science.gov (United States)

    Liu, Kai; Lin, Xinxing; Chen, Lihui; Huang, Liulian; Cao, Shilin; Wang, Huangwei

    2013-07-03

    The nonantibacterial and low strength properties of sodium alginate films negatively impact their application for food packaging. In order to improve these properties, a novel chitosan-benzalkonium chloride (C-BC) complex was prepared by ionic gelation using tripolyphosphate (TPP) as a coagulant, and a biocomposite obtained through the adsorption of C-BC complex on microfibrillated cellulose, MFC/C-BC, was then incorporated into a sodium alginate film. The TEM image showed that the C-BC nanoparticles were spherical in shape with a diameter of about 30 nm, and the adsorption equilibrium time of these nanoparticles on the surface of MFC was estimated to be 6 min under the driving forces of hydrogen bonds and electrostatic interactions. According to the disc diffusion method, the MFC/C-BC biocomposite-incorporated sodium alginate film exhibited remarkable antibacterial activity against Staphylococcus aureus and certain antibacterial activity against Escherichia coli . The strength tests indicated that the tensile strength of the composite sodium alginate film increased about 225% when the loading of MFC/C-BC biocomposite was 10 wt %. These results suggested that the MFC/C-BC biocomposite-incorporated sodium alginate film with excellent antibacterial and strength properties would be a promising material for food packaging, and the MFC/C-BC may also be a potential multifunctional biocomposite for other biodegradable materials.

  5. Prior sprint cycling did not enhance training adaptation, but resting salivary hormones were related to workout power and strength.

    Science.gov (United States)

    Crewther, Blair T; Lowe, Tim; Weatherby, Robert P; Gill, Nicholas

    2009-04-01

    This study examined the effect of cycle sprints as a potentiating stimulus for power and strength adaptation in semi-elite athletes. Eighteen rugby players were assigned into training groups that completed either a 40-s cycle sprint (T(SPRINT)) or rested (T(CONTROL)) before each workout (n = 6-8) of a 4-week programme. Squat jump (SJ) peak power (PP) and mean power (MP), and box squat (BS) one repetition maximum (1RM) strength were assessed every workout. Saliva was collected across each workout and assayed for testosterone (Sal-T) and cortisol (Sal-C). The T(SPRINT) and T(CONTROL) groups both showed significant improvements in SJ PP (8.2 +/- 2.9 vs. 11.9 +/- 3.6%), SJ MP (11.8 +/- 2.6 vs. 18.6 +/- 4.8%) and BS 1RM (20.5 +/- 2.6 vs. 23.2 +/- 1.3%), respectively. However, there were no group differences in training adaptation, workout performance or the workout hormonal responses. As a combined group (all players), significant relationships were demonstrated between resting Sal-T and/or Sal-C concentrations and absolute SJ power (r = 0.20-0.30) and BS strength (r = 0.36-0.44) across all workouts. For individual players, the respective relationships with SJ power (r = 0.22-0.42) and BS strength (r = 0.41-0.49) were, on average, found to be stronger. In conclusion, leg workouts performed with or without prior cycle sprints can produce similar power and strength improvements in semi-elite rugby players. Resting salivary hormone concentrations appear important for workout performance, especially for individuals, thereby potentially moderating training adaptation.

  6. Enhancement of delamination strength in Cu-stabilized coated conductor tapes through additional treatments under transverse tension at room temperature

    Energy Technology Data Exchange (ETDEWEB)

    Shin, Hyung Seop; Bautista, Zhierwinjay [Andong National University, Andong (Korea, Republic of); Moon, Seung Hyun; Lee, Jae Hun; Mean, Byoung Jean [SuNAM Co Ltd., Anseong (Korea, Republic of)

    2017-06-15

    In superconducting coil applications particularly in wet wound coils, coated conductor (CC) tapes are subjected to different type of stresses that could affect its electromechanical transport property. These include hoop stress acting along the length of the CC tape and the Lorentz force acting perpendicular to the CC tape’s surface. Since the latter is commonly associated with the delamination problem of multi-layered REBCO CC tapes, more understanding and attention on the delamination phenomena induced in the case of coil applications are needed. Difference on the coefficient of thermal expansion (CTE) of each constituent layer of the CC tape, the bobbin, and the impregnating materials is the main causes of delamination in CC tapes when subjected to thermal and mechanical cycling. In the design of degradation-free superconducting coils, therefore, characterization of the delamination behaviors including mechanism and strength in the multi-layered REBCO CC tapes becomes a critical issue. Various trials to increase the delamination strength by improving interface characteristics at interlayers have been performed. In this study, in order to investigate the influences of laser cleaning and Ag annealing treated at the substrate side surface, transverse tensile tests were conducted under different sample configurations using 4.5mm x 8 mm upper anvil. The mechanical delamination strength of differently processed CC samples was examined at room temperature (RT). As a result, the Sample 1 with the additional laser cleaning and Ag annealing processes and the Sample 2 with additional Ag annealing process only showed higher mechanical delamination strength as compared to the Sample 3 without such additional treatments. Sample 3 showed quite different behavior when the loading direction is to the substrate side where the delamination strength much lower as compared to other cases.

  7. Aquatic Therapy Improves Outcomes for Subacute Stroke Patients by Enhancing Muscular Strength of Paretic Lower Limbs Without Increasing Spasticity: A Randomized Controlled Trial.

    Science.gov (United States)

    Zhang, Yue; Wang, Yi-Zhao; Huang, Li-Ping; Bai, Bei; Zhou, Shi; Yin, Miao-Miao; Zhao, Hua; Zhou, Xiao-Na; Wang, Hong-Tu

    2016-11-01

    The aim of this study was to evaluate the effects of an aquatic exercise program designed to enhance muscular strength in paretic lower limbs in subacute stroke patients. Thirty-six subacute stroke patients were randomly divided to a conventional or an aquatic group (n = 18 each). Outcome measures were assessed at baseline and after 8 wks of training. For the paretic lower limbs, maximum isometric voluntary contraction strength of the rectus femoris and biceps femoris caput longus and the tibialis anterior and lateral gastrocnemius was measured. Cocontraction ratios during knee extension and flexion and ankle dorsiflexion and plantarflexion were calculated respectively. In addition, Modified Ashworth Scale, Functional Ambulation Category, and Barthel Index were assessed. Compared with the conventional intervention, the aquatic intervention resulted in significantly higher knee extension (P = 0.002) and ankle plantarflexion torque (P = 0.002), accompanied with a significantly lower knee extension cocontraction ratio in the paretic limb (P = 0.000). Functional Ambulation Category (P = 0.009) and Barthel Index (P = 0.024) were greater in aquatic group than conventional group posttreatment. Modified Ashworth Scale scores did not show any differences between groups. Aquatic exercise enhanced muscle strength in paretic lower limbs and improved muscle cocontraction without increasing spasticity in subacute stroke patients.

  8. Magnetic and electronic properties of hard|soft magnetic interface in (YCo{sub 5}|Co){sub [0001]} and (YFe{sub 5}|Co){sub [0001]} superlattices

    Energy Technology Data Exchange (ETDEWEB)

    Chandrasekaran, S. Selva [CSIR-Central Electrochemical Research Institute, Karaikudi 630003, Tamil Nadu (India); Academy of Scientific and Innovative Research, CSIR-Central Electrochemical Research Institute, Karaikudi 630003, Tamil Nadu (India); Ponnaiah, M. Rama [CSIR-Central Electrochemical Research Institute, Karaikudi 630003, Tamil Nadu (India); Murugan, P. [CSIR-Central Electrochemical Research Institute, Karaikudi 630003, Tamil Nadu (India); Academy of Scientific and Innovative Research, CSIR-Central Electrochemical Research Institute, Karaikudi 630003, Tamil Nadu (India); Saravanan, P. [Defence Metallurgical Research Laboratory, Hyderabad 500058 (India)

    2016-11-15

    The physics of interface between the hard- and soft-magnetic phases play an important role in determining the performance of exchange-coupled multilayers towards development of high-energy permanent magnets. Herein, we employed first principles calculations to understand the magnetic and electronic properties of exchange-coupled hard and soft magnetic superlattices of (YCo{sub 5}|Co){sub [0001]} and (YFe{sub 5}|Co){sub [0001]}. The calculated spin moment and exchange-coupling parameter for the (YFe{sub 5}|Co){sub [0001]} superlattice are found to be higher than that of the (YCo{sub 5}|Co){sub [0001]}. The results of present study suggest that the (YFe{sub 5}|Co){sub [0001]} superlattice can be used as exchange-coupled magnet with enhanced magnetic performance. - Highlights: • Understanding the properties of interface between hard- and soft-magnetic phases. • The properties of superlattices of (YCo{sub 5}|Co){sub [0001]} and (YFe{sub 5}|Co){sub [0001]} were studied. • The enhancement of spin moment and exchange-coupling in superlattices are observed.

  9. 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.

  10. 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.

  11. Rabi Oscillations in Realistic Superlattice with Finite Bloch Bands

    Institute of Scientific and Technical Information of China (English)

    FAN Wen-Bin; ZHANG Ping; LUO Ying; ZHAO Xian-Geng

    2001-01-01

    We investigate the dynamical processes taking place in nanodevices by high-frequency dc-ac fields. We found that Rabi oscillations between minibands are clearly identified under theoretical resonant conditions derived by an ideal two-band superlattice model, the resonant conditions have broadened, and the amount of broadening is about four times of the Rabi oscillation frequency. We also want to elucidate the role of different mechanisms that could lead to loss of quantum coherence. Our results show how the dephasing effects of disorder of interface roughness and doping fluctuation that after some periods destroy coherent oscillations, such as Rabi oscillations,can be reduced dramatically if we apply a bias static electric field to the superlattice system. The doping fluctuation dephasing effect is much stronger than that of interface roughness in the coherent process of realistic superlattices.

  12. 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.

  13. Electronic states of InSe/GaSe superlattice

    Science.gov (United States)

    Erkoç, Ş.; Allahverdi, K.; Ibrahim, Z.

    1994-06-01

    Analysis of recent publications revealed an increasing interest in epitaxial growth of InSe/GaSe superlattice. Within the effective mass theory we carried out self-consistent calculations of the confined and itinerant electronic states, potential profile and charge density distribution of InSe/GaSe superlattice, where the InSe layers are the well and the GaSe layers the barrier. Calculations were performed for three types of doping: uniform, modulated in the well, and modulated in the barrier. It has been found that the Coulomb interaction in the well and barrier forces the formation of localized states in the barrier region. The possibility of an insulator-metal transition in InSe/GaSe superlattice is predicted for modulation doping in the barrier and for a doping level n = 10 19cm-3. A decrease of the barrier height has been found for modulation doping in the well.

  14. Enhanced electric polarization and breakdown strength in the all-organic sandwich-structured poly(vinylidene fluoride-based dielectric film for high energy density capacitor

    Directory of Open Access Journals (Sweden)

    Yue Zhang

    2017-07-01

    Full Text Available It is essential to develop the dielectric energy storage capacitor for the modern electrical and electronic equipment. Here, the all-organic sandwich-structured composite with superior breakdown strength and delayed saturation polarization is presented. Furthermore, the energy storage characteristics of the composite are enhanced by the poly(vinylidene fluoride-trifluoroethylene-chlorofluoroethylene fiber and the redistribution of local electric field. The dielectric permittivity of composite increases to ∼16, and the discharged energy density is high to ∼8.7 J/cm3 at 360 kV/mm, and the breakdown strength is up to ∼408 kV/mm. The excellent performance of the composite broadens the application in the field of power electronics industry.

  15. Electric and magnetic superlattices in trilayer graphene

    Science.gov (United States)

    Uddin, Salah; Chan, K. S.

    2016-01-01

    The properties of one dimensional Kronig-Penney type of periodic electric and vector potential on ABC-trilayer graphene superlattices are investigated. The energy spectra obtained with periodic vector potentials shows the emergence of extra Dirac points in the energy spectrum with finite energies. For identical barrier and well widths, the original as well as the extra Dirac points are located in the ky = 0 plane. An asymmetry between the barrier and well widths causes a shift in the extra Dirac points away from the ky = 0 plane. Extra Dirac points having same electron hole crossing energy as that of the original Dirac point as well as finite energy Dirac points are generated in the energy spectrum when periodic electric potential is applied to the system. By applying electric and vector potential together, the symmetry of the energy spectrum about the Fermi level is broken. A tunable band gap is induced in the energy spectrum by applying both electric and vector potential simultaneously with different barrier and well widths.

  16. Carboxyl functionalization of carbon fibers via aryl diazonium reaction in molten urea to enhance interfacial shear strength

    Science.gov (United States)

    Wang, Yuwei; Meng, Linghui; Fan, Liquan; Wu, Guangshun; Ma, Lichun; Zhao, Min; Huang, Yudong

    2016-01-01

    Using molten urea as the solvent, carbon fibers were functionalized with carboxylic acid groups via aryl diazonium reaction in 15 min to improve their interfacial bonding with epoxy resin. The surface functionalization was quantified by X-ray photoelectron spectroscopy, which showed that the relative surface coverage of carboxylic acid groups increased from an initial percentage of 3.17-10.41%. Mechanical property test results indicated that the aryl diazonium reaction in this paper could improve the interfacial shear strength by 66%. Meanwhile, the technique did not adopt any pre-oxidation step to produce functional groups prior to grafting and was shown to maintain the tensile strength of the fibers. This methodology provided a rapid, facile and economically viable route to produce covalently functionalized carbon fibers in large quantities with an eco-friendly method.

  17. Long—Range Effects on the Pyroelectric Coefficient of Ferroelectric Superlattice

    Institute of Scientific and Technical Information of China (English)

    DONGWen; WUYin-Zhong; 等

    2002-01-01

    Long-range effects on the pyroelectric coefficient of a ferroelectric superlattice consisting of two different ferroelectric materials are investigated based on the transverse Ising model.The effects of the interfacial coupling and the thickness of one period on the pyroelectric coefficient of the ferroelectric superlattics are studied by taking into account the long-range interaction.It is found that with the increase of the strength of the long-range interaction,the pyroelectric coefficient decreases when the temperature is lower than the phase transition temperature;the mumber of the pyroelectric peaks decreases gradually and the phase transition temperature increases,It is also found that with the decrease of the interfacial coupling and the thickness of one period.the phase transition temperature and the number of the pyroelectric peaks decrease.

  18. Amorphous sub-nanometre Tb-doped SiO(x)N(y)/SiO2 superlattices for optoelectronics.

    Science.gov (United States)

    Ramírez, Joan Manel; Wojcik, Jacek; Berencén, Yonder; Ruiz-Caridad, Alícia; Estradé, Sònia; Peiró, Francesca; Mascher, Peter; Garrido, Blas

    2015-02-27

    Amorphous sub-nanometre Tb-doped SiOxNy/SiO2 superlattices were fabricated by means of alternating deposition of 0.7 nm thick Tb-doped SiOxNy layers and of 0.9 nm thick SiO2 barrier layers in an electron-cyclotron-resonance plasma enhanced chemical vapour deposition system with in situ Tb-doping capability. High resolution transmission electron microscopy images showed a well-preserved superlattice morphology after annealing at a high temperature of 1000 °C. In addition, transparent indium tin oxide (ITO) electrodes were deposited by electron beam evaporation using a shadow mask approach to allow for the optoelectronic characterization of superlattices. Tb(3+) luminescent spectral features were obtained using three different excitation sources: UV laser excitation (photoluminescence (PL)), under a bias voltage (electroluminescence (EL)) and under a highly energetic electron beam (cathodoluminescence (CL)). All techniques displayed Tb(3+) inner transitions belonging to (5)D4 levels except for the CL spectrum, in which (5)D3 transition levels were also observed. Two competing mechanisms were proposed to explain the spectral differences observed between PL (or EL) and CL excitation: the population rate of the (5)D3 state and the non-radiative relaxation rate of the (5)D3-(5)D4 transition due to a resonant OH-mode. Moreover, the large number of interfaces (trapping sites) that electrons have to get through was identified as the main reason for observing a bulk-limited charge transport mechanism governed by Poole-Frenkel conduction in the J-V characteristic. Finally, a linear EL-J dependence was measured, with independent spectral shape and an EL onset voltage as low as 6.7 V. These amorphous sub-nanometre superlattices are meant to provide low-cost solutions in different areas including sensing, photovoltaics or photonics.

  19. Amorphous sub-nanometre Tb-doped SiOxNy/SiO2 superlattices for optoelectronics

    Science.gov (United States)

    Ramírez, Joan Manel; Wojcik, Jacek; Berencén, Yonder; Ruiz-Caridad, Alícia; Estradé, Sònia; Peiró, Francesca; Mascher, Peter; Garrido, Blas

    2015-02-01

    Amorphous sub-nanometre Tb-doped SiOxNy/SiO2 superlattices were fabricated by means of alternating deposition of 0.7 nm thick Tb-doped SiOxNy layers and of 0.9 nm thick SiO2 barrier layers in an electron-cyclotron-resonance plasma enhanced chemical vapour deposition system with in situ Tb-doping capability. High resolution transmission electron microscopy images showed a well-preserved superlattice morphology after annealing at a high temperature of 1000 °C. In addition, transparent indium tin oxide (ITO) electrodes were deposited by electron beam evaporation using a shadow mask approach to allow for the optoelectronic characterization of superlattices. Tb3+ luminescent spectral features were obtained using three different excitation sources: UV laser excitation (photoluminescence (PL)), under a bias voltage (electroluminescence (EL)) and under a highly energetic electron beam (cathodoluminescence (CL)). All techniques displayed Tb3+ inner transitions belonging to 5D4 levels except for the CL spectrum, in which 5D3 transition levels were also observed. Two competing mechanisms were proposed to explain the spectral differences observed between PL (or EL) and CL excitation: the population rate of the 5D3 state and the non-radiative relaxation rate of the 5D3-5D4 transition due to a resonant OH-mode. Moreover, the large number of interfaces (trapping sites) that electrons have to get through was identified as the main reason for observing a bulk-limited charge transport mechanism governed by Poole-Frenkel conduction in the J-V characteristic. Finally, a linear EL-J dependence was measured, with independent spectral shape and an EL onset voltage as low as 6.7 V. These amorphous sub-nanometre superlattices are meant to provide low-cost solutions in different areas including sensing, photovoltaics or photonics.

  20. Enhanced muscle strength with carbohydrate supplement two hours before open cholecystectomy: a randomized, double-blind study.

    Science.gov (United States)

    Gava, Marcella Giovana; Castro-Barcellos, Heloísa Michelon; Caporossi, Cervantes; Aguilar-Nascimento, José Eduardo de

    2016-02-01

    to investigate the effects of preoperative fasting abbreviation with oral supplementation with carbohydrate in the evolution of grip strength in patients undergoing cholecystectomy by laparotomy. we conducted a clinical, randomizeddouble blind study with adult female patients, aged 18-60 years. Patients were divided into two groups: Control Group, with fasting prescription 6-8h until the time of operation; and Intervention Group, which received prescription of fasting for solids 6-8h before surgery, but ingested an oral supplement containing 12.5% carbohydrate, six (400ml) and two (200ml) hours before theprocedure. The handgrip strength was measured in both hands in both groups, at patient's admission (6h before surgery), the immediate pre-operative time (1h before surgery) and 12-18h postoperatively. we analyzed 27 patients, 14 in the intervention group and 13 in the control group. There was no mortality. The handgrip strength (mean [standard deviation]) was significantly higher in the intervention group in the three periods studied, in at least one hand: preoperatively in the dominant hand (27.8 [2.6] vs 24.1 [3.7] kg; p=0.04), in the immediate preoperative in both hands, and postoperatively in the non-dominant hand (28.5 [3.0] vs 21.3 [5.9] kg; p=0.01). the abbreviation of preoperative fasting to two hours with drink containing carbohydrate improves muscle function in the perioperative period.

  1. Enhanced muscle strength with carbohydrate supplement two hours before open cholecystectomy: a randomized, double-blind study

    Directory of Open Access Journals (Sweden)

    Marcella Giovana Gava

    Full Text Available Objective: to investigate the effects of preoperative fasting abbreviation with oral supplementation with carbohydrate in the evolution of grip strength in patients undergoing cholecystectomy by laparotomy. Methods : we conducted a clinical, randomizeddouble blind study with adult female patients, aged 18-60 years. Patients were divided into two groups: Control Group, with fasting prescription 6-8h until the time of operation; and Intervention Group, which received prescription of fasting for solids 6-8h before surgery, but ingested an oral supplement containing 12.5% carbohydrate, six (400ml and two (200ml hours before theprocedure. The handgrip strength was measured in both hands in both groups, at patient's admission (6h before surgery, the immediate pre-operative time (1h before surgery and 12-18h postoperatively. Results : we analyzed 27 patients, 14 in the intervention group and 13 in the control group. There was no mortality. The handgrip strength (mean [standard deviation] was significantly higher in the intervention group in the three periods studied, in at least one hand: preoperatively in the dominant hand (27.8 [2.6] vs 24.1 [3.7] kg; p=0.04, in the immediate preoperative in both hands, and postoperatively in the non-dominant hand (28.5 [3.0] vs 21.3 [5.9] kg; p=0.01. Conclusion : the abbreviation of preoperative fasting to two hours with drink containing carbohydrate improves muscle function in the perioperative period.

  2. Relationships between pre-sunset electrojet strength, pre-reversal enhancement and equatorial spread-F onset

    Directory of Open Access Journals (Sweden)

    J. Uemoto

    2010-02-01

    Full Text Available The virtual height of the bottom side F-region (h'F and equatorial spread-F (ESF onsets at Chumphon (10.7° N, 99.4° E; 3.3° N magnetic latitude were compared with the behaviour of equatorial electrojet (EEJ ground strength at Phuket (8.1° N, 98.3° E; 0.1° N magnetic latitude during the period from November 2007 to October 2008. Increase in the F-layer height and ESF onsets during the evening hours were well connected with the EEJ ground strength before sunset, namely, both the height increase and ESF onsets were suppressed when the integrated EEJ ground strength for the period from 1 to 2 h prior to sunset was negative. The finding suggests observationally that the pre-sunset E-region dynamo current and/or electric field are related to the F-region dynamics and ESF onsets around sunset.

  3. Raman-induced Spin-Orbit Coupling in Optical Superlattices

    Science.gov (United States)

    Li, Junru; Huang, Wujie; Shteynas, Boris; Burchesky, Sean; Top, Furkan; Jamison, Alan; Ketterle, Wolfgang

    2016-05-01

    We demonstrate a new scheme for spin-orbit coupling (SOC) of ultracold atoms. Instead of internal (hyperfine) states, two lowest bands in an optical superlattice were used as pseudospins. A Raman process was implemented to provide coupling between pseudospin and momentum. With single internal state and far-detuned beams used, our new scheme will allow convenient generalisation to a wide range of atoms. Pseudospin interaction is tuneable by controlling the superlattice, allowing us to study many-body phenomena in SOC systems such as the stripe phase.

  4. 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.

  5. The solition properties of dipole domains in superlattices

    Institute of Scientific and Technical Information of China (English)

    张启义; 田强

    2002-01-01

    The formation and propagation of dipole domains in superlattices are studied both by the modified discrete drift model and by the nonlinear schroedinger equation,the spatiotemporal distribution of the electric field and electron density are presented.The numerical results are compared with the soliton solutions of the nonlinear Schroedinger equation and analysed.It is shown that the numerical solutions agree with the soliton solutions of the nonlinear Schroedinger equation.The dipole electric-field domains in semiconductor superlattices have the properties of solitons.

  6. 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.

  7. 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.

  8. 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.

  9. 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

    2014-01-20

    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.

  10. Ultra-low Thermal Conductivity in Si/Ge Hierarchical Superlattice Nanowire.

    Science.gov (United States)

    Mu, Xin; Wang, Lili; Yang, Xueming; Zhang, Pu; To, Albert C; Luo, Tengfei

    2015-11-16

    Due to interfacial phonon scattering and nanoscale size effect, silicon/germanium (Si/Ge) superlattice nanowire (SNW) can have very low thermal conductivity, which is very attractive for thermoelectrics. In this paper, we demonstrate using molecular dynamics simulations that the already low thermal conductivity of Si/Ge SNW can be further reduced by introducing hierarchical structure to form Si/Ge hierarchical superlattice nanowire (H-SNW). The structural hierarchy introduces defects to disrupt the periodicity of regular SNW and scatters coherent phonons, which are the key contributors to thermal transport in regular SNW. Our simulation results show that periodically arranged defects in Si/Ge H-SNW lead to a ~38% reduction of the already low thermal conductivity of regular Si/Ge SNW. By randomizing the arrangement of defects and imposing additional surface complexities to enhance phonon scattering, further reduction in thermal conductivity can be achieved. Compared to pure Si nanowire, the thermal conductivity reduction of Si/Ge H-SNW can be as large as ~95%. It is concluded that the hierarchical structuring is an effective way of reducing thermal conductivity significantly in SNW, which can be a promising path for improving the efficiency of Si/Ge-based SNW thermoelectrics.

  11. Strain-balanced type-II superlattices for efficient multi-junction solar cells.

    Science.gov (United States)

    Gonzalo, A; Utrilla, A D; Reyes, D F; Braza, V; Llorens, J M; Fuertes Marrón, D; Alén, B; Ben, T; González, D; Guzman, A; Hierro, A; Ulloa, J M

    2017-06-21

    Multi-junction solar cells made by assembling semiconductor materials with different bandgap energies have hold the record conversion efficiencies for many years and are currently approaching 50%. Theoretical efficiency limits make use of optimum designs with the right lattice constant-bandgap energy combination, which requires a 1.0-1.15 eV material lattice-matched to GaAs/Ge. Nevertheless, the lack of suitable semiconductor materials is hindering the achievement of the predicted efficiencies, since the only candidates were up to now complex quaternary and quinary alloys with inherent epitaxial growth problems that degrade carrier dynamics. Here we show how the use of strain-balanced GaAsSb/GaAsN superlattices might solve this problem. We demonstrate that the spatial separation of Sb and N atoms avoids the ubiquitous growth problems and improves crystal quality. Moreover, these new structures allow for additional control of the effective bandgap through the period thickness and provide a type-II band alignment with long carrier lifetimes. All this leads to a strong enhancement of the external quantum efficiency under photovoltaic conditions with respect to bulk layers of equivalent thickness. Our results show that GaAsSb/GaAsN superlattices with short periods are the ideal (pseudo)material to be integrated in new GaAs/Ge-based multi-junction solar cells that could approach the theoretical efficiency limit.

  12. Enhanced mechanical strength and biocompatibility of electrospun polycaprolactone-gelatin scaffold with surface deposited nano-hydroxyapatite

    Energy Technology Data Exchange (ETDEWEB)

    Jaiswal, A.K. [Department of Biosciences and Bioengineering, Indian Institute of Technology Bombay, Powai, Mumbai, 400076 (India); Chhabra, H. [Department of Chemical Engineering, Indian Institute of Technology Bombay, Powai, Mumbai, 400076 (India); Soni, V.P. [Department of Biosciences and Bioengineering, Indian Institute of Technology Bombay, Powai, Mumbai, 400076 (India); Bellare, J.R., E-mail: jb@iitb.ac.in [Department of Chemical Engineering, Indian Institute of Technology Bombay, Powai, Mumbai, 400076 (India)

    2013-05-01

    In this study for the first time, we compared physico-chemical and biological properties of polycaprolactone-gelatin-hydroxyapatite scaffolds of two types: one in which the nano-hydroxyapatite (n-HA) was deposited on the surface of electrospun polycaprolactone-gelatin (PCG) fibers via alternate soaking process (PCG-HA{sub AS}) and other in which hydroxyapatite (HA) powders were blended in electrospinning solution of PCG (PCG-HA{sub B}). The microstructure of fibers was examined by scanning electron microscopy (SEM) and transmission electron microscopy (TEM) which showed n-HA particles on the surface of the PCG-HA{sub AS} scaffold and embedded HA particles in the interior of the PCG-HA{sub B} fibers. PCG-HA{sub AS} fibers exhibited the better Young's moduli and tensile strength as compared to PCG-HA{sub B} fibers. Biological properties such as cell proliferation, cell attachment and alkaline phosphatase activity (ALP) were determined by growing human osteosarcoma cells (MG-63) over the scaffolds. Cell proliferation and confocal results clearly indicated that the presence of hydroxyapatite on the surface of the PCG-HA{sub AS} scaffold promoted better cellular adhesion and proliferation as compared to PCG-HA{sub B} scaffold. ALP activity was also observed better in alternate soaked PCG scaffold as compared to PCG-HA{sub B} scaffold. Mechanical strength and biological properties clearly demonstrate that surface deposited HA scaffold prepared by alternate soaking method may find application in bone tissue engineering. - Highlights: ► PCG-HA scaffold was prepared by two methods: blending and by alternate soaking. ► Uniform n-HA was found at the nanofiber surface with the alternate soaking method. ► PCG-HA{sub AS} scaffold showed better mechanical strength compared to PCG-HA{sub B} fibers. ► Cell adhesion, proliferation and ALP activity were also better in PCG-HA{sub AS}.

  13. Synergic Adsorption–Biodegradation by an Advanced Carrier for Enhanced Removal of High-Strength Nitrogen and Refractory Organics

    KAUST Repository

    Ahmad, Muhammad

    2017-03-29

    Coking wastewater contains not only high-strength nitrogen but also toxic biorefractory organics. This study presents simultaneous removal of high-strength quinoline, carbon, and ammonium in coking wastewater by immobilized bacterial communities composed of a heterotrophic strain Pseudomonas sp. QG6 (hereafter referred as QG6), ammonia-oxidizing bacteria (AOB), and anaerobic ammonium oxidation bacteria (anammox). The bacterial immobilization was implemented with the help of a self-designed porous cubic carrier that created structured microenvironments including an inner layer adapted for anaerobic bacteria, a middle layer suitable for coaggregation of certain aerobic and anaerobic bacteria, and an outer layer for heterotrophic bacteria. By coating functional polyurethane foam (FPUF) with iron oxide nanoparticles (IONPs), the biocarrier (IONPs-FPUF) could provide a good outer-layer barrier for absorption and selective treatment of aromatic compounds by QG6, offer a conducive environment for anammox in the inner layer, and provide a mutualistic environment for AOB in the middle layer. Consequently, simultaneous nitrification and denitrification were reached with the significant removal of up to 322 mg L (98%) NH, 311 mg L (99%) NO, and 633 mg L (97%) total nitrogen (8 mg L averaged NO concentration was recorded in the effluent), accompanied by an efficient removal of chemical oxygen demand by 3286 mg L (98%) and 350 mg L (100%) quinoline. This study provides an alternative way to promote synergic adsorption and biodegradation with the help of a modified biocarrier that has great potential for treatment of wastewater containing high-strength carbon, toxic organic pollutants, and nitrogen.

  14. Grafting Carbon Nanotubes on Glass Fiber by Dip Coating Technique to Enhance Tensile and Interfacial Shear Strength

    Directory of Open Access Journals (Sweden)

    Bahador Dastorian Jamnani

    2015-01-01

    Full Text Available The effects of noncovalent bonding and mechanical interlocking of carbon nanotubes (CNT coating on tensile and interfacial strength of glass fiber were investigated. CNT were coated over glass fiber by a simple dip coating method. Acid treated CNT were suspended in isopropanol solution containing Nafion as binding agent. To achieve uniform distribution of CNT over the glass fiber, an optimized dispersion process was developed by two parameters: CNT concentration and soaking time. CNT concentration was varied from 0.4 to 2 mg/mL and soaking time was varied from 1 to 180 min. The provided micrographs demonstrated appropriate coating of CNT on glass fiber by use of CNT-Nafion mixture. The effects of CNT concentration and soaking time on coating layer were studied by performing single fiber tensile test and pull-out test. The obtained results showed that the optimum CNT concentration and soaking time were 1 mg/mL and 60 min, respectively, which led to significant improvement of tensile strength and interfacial shear stress. It was found that, at other concentrations and soaking times, CNT agglomeration or acutely curly tubes appeared over the fiber surface which caused a reduction of nanotubes interaction on the glass fiber.

  15. Enhancement of Impact Toughness by Delamination Fracture in a Low-Alloy High-Strength Steel with Al Alloying

    Science.gov (United States)

    Sun, Junjie; Jiang, Tao; Liu, Hongji; Guo, Shengwu; Liu, Yongning

    2016-09-01

    The effect of delamination toughening of martensitic steel was investigated both at room and low temperatures [253 K and 233 K (-20 °C and -40 °C)]. Two low-alloy martensitic steels with and without Al alloying were both prepared. Layered structure with white band and black matrix was observed in Al alloyed steel, while a homogeneous microstructure was displayed in the steel without Al. Both steels achieved high strength (tensile strength over 1600 MPa) and good ductility (elongation over 11 pct), but they displayed stark contrasts on impact fracture mode and Charpy impact energy. Delamination fracture occurred in Al alloyed steel and the impact energies were significantly increased both at room temperature (from 75 to 138 J, i.e., nearly improved up to 2 times) and low temperatures [from 47.9 to 71.3 J at 233 K (-40 °C)] compared with the one without Al. Alloying with Al promotes the segregation of Cr, Mn, Si and C elements to form a network structure, which is martensite with higher carbon content and higher hardness than that of the matrix. And this network structure evolved into a band structure during the hot rolling process. The difference of yield stress between the band structure and the matrix gives rise to a delamination fracture during the impact test, which increases the toughness greatly.

  16. Synergistic effects of chitosan-guanidine complexes on enhancing antimicrobial activity and wet-strength of paper.

    Science.gov (United States)

    Sun, Shengling; An, Qiaozhi; Li, Xu; Qian, Liying; He, Beihai; Xiao, Huining

    2010-07-01

    Chitosan-guanidine complexes were prepared by reacting chitosan and polyhexamethylene guanidine hydrochloride or crosslinked polyhexamethylene guanidine hydrochloride in the presence of sodium tripolyphosphate as a crosslinking agent. The complexes, used as functional additives for paper, synergistically improved wet-strength and antimicrobial activities. In comparison with the control sample, the wet/dry strength ratio of hand-sheets treated with the complexes was increased from 2.65% up to 23.3%. The MIC values of the chitosan-PHGH and chitosan-PHGHE complexes against Escherichia coli were 15.6 and 31.2 microg mL(-1), respectively, thus demonstrating excellent antimicrobial activity. Hand-sheets treated with the complexes exhibited antibacterial activity against E. coli and Staphylococcus aureus. The release of the guanidine polymers included in the complexes was dynamically monitored using UV and the results showed the amount released exceeded 80%. Atomic force microscopy images indicated that the antimicrobial mechanism of the complexes was likely due to membrane damage. Copyright (c) 2010 Elsevier Ltd. All rights reserved.

  17. Enhanced Corticospinal Excitability and Volitional Drive in Response to Shortening and Lengthening Strength Training and Changes Following Detraining

    Science.gov (United States)

    Tallent, Jamie; Goodall, Stuart; Gibbon, Karl C.; Hortobágyi, Tibor; Howatson, Glyn

    2017-01-01

    There is a limited understanding of the neurological adaptations responsible for changes in strength following shortening and lengthening resistance training and subsequent detraining. The aim of the study was to investigate differences in corticospinal and spinal responses to resistance training of the tibialis anterior muscle between shortening or lengthening muscle contractions for 4 weeks and after 2 weeks of detraining. Thirty-one untrained individuals were assigned to either shortening or lengthening isokinetic resistance training (4 weeks, 3 days/weeks) or a non-training control group. Transcranial magnetic stimulation and peripheral nerve stimulation (PNS) were used to assess corticospinal and spinal changes, respectively, at pre-, mid-, post-resistance training and post detraining. Greater increases changes (P MVC were found from the respective muscle contraction training. Motor evoked potentials (expressed relative to background EMG) significantly increased in lengthening resistance training group under contraction intensities ranging from 25 to 80% of the shortening and lengthening contraction intensity (P MVC and V-wave did not change (P > 0.05), although MEP amplitude decreased during the detraining period (P < 0.01). No changes in H-reflex were found pre to post resistance training or post detraining. Modulation in V-wave appeared to be contraction specific, whereby greatest increases occurred following lengthening resistance training. Strength and volitional drive is maintained following 2 weeks detraining, however corticospinal excitability appears to decrease when the training stimulus is withdrawn. PMID:28223941

  18. Enhancement of Impact Toughness by Delamination Fracture in a Low-Alloy High-Strength Steel with Al Alloying

    Science.gov (United States)

    Sun, Junjie; Jiang, Tao; Liu, Hongji; Guo, Shengwu; Liu, Yongning

    2016-12-01

    The effect of delamination toughening of martensitic steel was investigated both at room and low temperatures [253 K and 233 K (-20 °C and -40 °C)]. Two low-alloy martensitic steels with and without Al alloying were both prepared. Layered structure with white band and black matrix was observed in Al alloyed steel, while a homogeneous microstructure was displayed in the steel without Al. Both steels achieved high strength (tensile strength over 1600 MPa) and good ductility (elongation over 11 pct), but they displayed stark contrasts on impact fracture mode and Charpy impact energy. Delamination fracture occurred in Al alloyed steel and the impact energies were significantly increased both at room temperature (from 75 to 138 J, i.e., nearly improved up to 2 times) and low temperatures [from 47.9 to 71.3 J at 233 K (-40 °C)] compared with the one without Al. Alloying with Al promotes the segregation of Cr, Mn, Si and C elements to form a network structure, which is martensite with higher carbon content and higher hardness than that of the matrix. And this network structure evolved into a band structure during the hot rolling process. The difference of yield stress between the band structure and the matrix gives rise to a delamination fracture during the impact test, which increases the toughness greatly.

  19. Statistical properties of warm nuclei: Investigating the low-energy enhancement in the $\\gamma$- strength function of neutron-rich nuclei

    CERN Multimedia

    We propose to start a program to study the $\\gamma$-ray strength function of neutron rich nuclei in inverse kinematics with radioactive beams at HIE-ISOLDE. An unexpected increase in the $\\gamma$-strength function at low energy has been observed in several stable nuclei using the Oslo method. This year these results were confirmed with a different experimental technique and model independent analysis developed by iThemba/Livermore. If this enhancement of the $\\gamma$-strength function is also present in neutron-rich nuclei, it will strongly affect the neutron capture cross sections, which are important input in stellar models of synthesis of heavier elements in stars. We propose to start with an experiment using a $^{66}$Ni beam of 5.5 MeV /u, where the data will be analyzed using both methods independently, and we are sure to get enough statistics, before moving to more neutron-rich nuclei. When/if neutron-rich Ti, Fe or Mo beams will be available at ISOLDE, we will submit additional proposals.

  20. 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.

  1. 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.

  2. Superlattice conductivity sign change induced by intense electromagnetic radiation

    Science.gov (United States)

    Kryuchkov, S. V.; Kukhar', E. I.; Ionkina, E. S.

    2016-07-01

    The current density in a superlattice exposed to a quantizing electric field and the terahertz field has been calculated. The calculations have been carried out taking into account inelastic scattering of charge carriers by phonons. The possibility of an absolute negative conductivity, i.e., the emergence of electric current opposing the direction of the quantizing electric field, has been demonstrated.

  3. Strong impact of impurity bands on domain formation in superlattices

    DEFF Research Database (Denmark)

    Wacker, Andreas; Jauho, Antti-Pekka

    1998-01-01

    The formation of electric field domains in doped semiconductor superlattices is described within a microscopic model. Due to the presence of impurity bands in low-doped samples the current-voltage characteristic is essentially different compared to medium-doped samples. (C) 1998 Published by Else...

  4. 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...

  5. 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...

  6. 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...

  7. Bypassing of a barrier by dissociated and superlattice dislocations

    DEFF Research Database (Denmark)

    Bhushan, Karihaloo

    1975-01-01

    Very simple procedures are used to calculate the upper and lower bounds for the applied stress required for the leading extended (superlattice) dislocation in a group of n coplanar screw dislocations of like sign with Burgers vector b to bypass a noncoplanar perfect screw dislocation with Burgers...... vector mb (m...

  8. Type-II superlattice photodiodes: an alternative for VLWIR detection

    Science.gov (United States)

    Brown, Gail J.; Houston, Shanee; Szmulowicz, Frank; Mahalingam, Krishnamur; Haugan, Heather; Wei, Yajun; Gin, Aaron; Razeghi, Manijeh

    2003-09-01

    In the very long wavelength infrared (VLWIR) band, λ>14 microns, the detector materials are currently limited to extrinsic semiconductors. These extrinsic materials can be either heavily doped bulk semiconductor, like silicon or germanium, or a doped quantum well heterostructure. An alternative choice that provides the opportunity for higher temperature operation for VLWIR sensing is an intrinsic material based on a type-II InAs/Ga(In)Sb superlattice. There are many possible designs for these superlattices which will produce the same narrow band gap by adjusting individual layer thicknesses, indium content or substrate orientation. The infrared properties of various compositions and designs of these type-II superlattices have been studied. In the past few years, excellent results have been obtained on photoconductive and photodiode samples designed for infrared detection beyond 15 microns. An overview of the status of this material system will be presented. In addition, the latest experimental results for superlattice photodiodes with cut-off wavelengths as long as 30 microns will be covered.

  9. 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.

  10. Hot electrons in superlattices: quantum transport versus Boltzmann equation

    DEFF Research Database (Denmark)

    Wacker, Andreas; Jauho, Antti-Pekka; Rott, S.;

    1999-01-01

    A self-consistent solution of the transport equation is presented for semiconductor superlattices within different approaches: (i) a full quantum transport model based on nonequilibrium Green functions, (ii) the semiclassical Boltzmann equation for electrons in a miniband, and (iii) Boltzmann...

  11. Influence of field strength, coil type and image resolution on assessment of synovitis by unenhanced MRI - a comparison with contrast-enhanced MRI

    Energy Technology Data Exchange (ETDEWEB)

    Eshed, Iris [The Sheba Medical Center, Department of Diagnostic Imaging, Tel Hashomer (Israel); Tel Aviv University, Sackler School of Medicine, Tel Aviv (Israel); Krabbe, Simon; Axelsen, Mette; Pedersen, Susanne Juhl [Copenhagen University Hospital Glostrup, Copenhagen Center for Arthritis Research, Center for Rheumatology and Spine Diseases, Copenhagen (Denmark); Oestergaard, Mikkel [Copenhagen University Hospital Glostrup, Copenhagen Center for Arthritis Research, Center for Rheumatology and Spine Diseases, Copenhagen (Denmark); Copenhagen University Hospital Gentofte, Department of Rheumatology/C, Copenhagen (Denmark); Boeyesen, Pernille [Diakonhjemmet Hospital, Department of Rheumatology, Oslo (Norway); Moeller, Jakob M. [Copenhagen University Hospital at Herlev, Department of Radiology, Copenhagen (Denmark); Therkildsen, Flemming [Metropolitan University College, Copenhagen (Denmark); Madsen, Ole Rintek [Copenhagen University Hospital Gentofte, Department of Rheumatology/C, Copenhagen (Denmark)

    2015-04-01

    To explore if the reliability of synovitis assessment by unenhanced MRI is influenced by different MRI field-strengths, coil types and image resolutions in RA patients. Forty-one RA patients and 12 healthy controls underwent hand MRI (wrist and 2{sup nd}-5{sup th} metacarpophalangeal joints) at 4 different field-strengths (0.23 T/0.6 T/1.5 T/3.0 T) on the same day. Seven protocols using a STIR sequence with different field-strengths, coils (flex coils/dedicated phased-array extremity coils) and resolution were applied and scored blindly for synovitis (OMERACT-RAMRIS method). A 1.5 T post-contrast T1-weighted sequence was used as gold standard reference. Fair-good agreement (ICC=0.38-0.72) between the standard reference and the different STIR protocols (best agreement with extremity coil and small voxel size at 1.5 T). The accuracy for presence/absence of synovitis was very high per person (0.80-1.0), and moderate-high per joint (0.63-0.85), whereas exact agreements on scores were moderate (0.50-0.66). The intrareader agreement (15 patients and 3 controls) on presence/absence of synovitis was very high (0.87-1.0). Unenhanced MRI using STIR sequence is only moderately reliable for assessing hand synovitis in RA, when contrast-enhanced MRI is considered the gold standard reference. Contrast injection, field strength and coil type influence synovitis assessment, and should be considered before performing MRI in clinical trials and practice. (orig.)

  12. Designing Optical Properties in DNA-Programmed Nanoparticle Superlattices

    Science.gov (United States)

    Ross, Michael Brendan

    A grand challenge of modern science has been the ability to predict and design the properties of new materials. This approach to the a priori design of materials presents a number of challenges including: predictable properties of the material building blocks, a programmable means for arranging such building blocks into well understood architectures, and robust models that can predict the properties of these new materials. In this dissertation, we present a series of studies that describe how optical properties in DNA-programmed nanoparticle superlattices can be predicted prior to their synthesis. The first chapter provides a history and introduction to the study of metal nanoparticle arrays. Chapter 2 surveys and compares several geometric models and electrodynamics simulations with the measured optical properties of DNA-nanoparticle superlattices. Chapter 3 describes silver nanoparticle superlattices (rather than gold) and identifies their promise as plasmonic metamaterials. In chapter 4, the concept of plasmonic metallurgy is introduced, whereby it is demonstrated that concepts from materials science and metallurgy can be applied to the optical properties of mixed metallic plasmonic materials, unveiling rich and tunable optical properties such as color and asymmetric reflectivity. Chapter 5 presents a comprehensive theoretical exploration of anisotropy (non-spherical) in nanoparticle superlattice architectures. The role of anisotropy is discussed both on the nanoscale, where several desirable metamaterial properties can be tuned from the ultraviolet to near-infrared, and on the mesoscale, where the size and shape of a superlattice is demonstrated to have a pronounced effect on the observed far-field optical properties. Chapter 6 builds upon those theoretical data presented in chapter 5, including the experimental realization of size and shape dependent properties in DNA-programmed superlattices. Specifically, nanoparticle spacing is explored as a parameter that

  13. Intelligent Physical Exercise Training proves effective in enhancing muscle strength and reducing musculoskeletal pain in a workplace setting

    DEFF Research Database (Denmark)

    Dalager, Tina; Justesen, Just Bendix; Sjøgaard, Gisela

    Background: Physical exercise training interventions at the workplace may cause health benefits but not all employees may benefit from the same program despite having the same occupational exposure. The present aim was to individually tailor Intelligent Physical Exercise Training (IPET) for office...... workers based on health checks and to assess the effect on musculoskeletal health (Sjøgaard G et al. BMC Public Health 2014, 14:652). Methods: Office workers were at each of 6 companies randomized 1:1 to a training group, TG (N=194) or a reference group, REF (N=195). TG received one-hour supervised high...... balance. In total 32 individual training programs were developed but 9 of those covered more than 85 % of the participants’ needs, most of which included neck/shoulder strength training and cardio training. Trial registration was in ClinicalTrials.gov, number: NCT01366950. Results: There were no baseline...

  14. Effect of post-annealing temperatures on thin-film transistors with ZnO/Al{sub 2}O{sub 3} superlattice channels

    Energy Technology Data Exchange (ETDEWEB)

    Ahn, Cheol Hyoun; Kim, So Hee; Kim, Ye Kyun [School of Advanced Materials Science and Engineering, Sungkyunkwan University, 2066 Seobu-ro, Jangan-gu, Suwon, Gyeonggi-do (Korea, Republic of); Lee, Ho Seong [School of Materials Science and Engineering, Kyungpook National University, 1370 Sankyuk-dong, Buk-gu, Daegu 702-701 (Korea, Republic of); Cho, Hyung Koun, E-mail: chohk@skku.edu [School of Advanced Materials Science and Engineering, Sungkyunkwan University, 2066 Seobu-ro, Jangan-gu, Suwon, Gyeonggi-do (Korea, Republic of)

    2015-06-01

    Oxide-based thin-film transistors (TFTs) were fabricated using ZnO/Al{sub 2}O{sub 3} superlattice channels deposited by atomic layer deposition. Here, a post-annealing treatment was performed at various temperatures (200–550 °C) and the properties of the oxide TFTs were evaluated. An annealing temperature up to 250 °C showed enhanced TFT performance, while further increases in the annealing temperature resulted in an abruptly invisible switching property due to the high conductivity of the channel layers. With respect to annealing temperature, increased electrical conductivity in the superlattice films was attributed to the increase of conducting crystalline layers due to the inter-diffusion behavior between the ZnO and Al{sub 2}O{sub 3} layers. The formation of the conducting layer was related to substitution by Al{sup 3+} ions into Zn{sup 2+} sites in the inter-diffusion region. The ZnO/Al{sub 2}O{sub 3} superlattice TFT with the best field effect mobility, 30.2 cm{sup 2}/Vs, was observed for an annealing temperature of 250 °C. - Highlights: • Thin-film transistors (TFTs) of ZnO/Al{sub 2}O{sub 3} superlattice channel were studied. • Effect of annealing temperature of the TFTs was investigated. • Electrical properties of superlattice TFTs were tuned by post-annealing. • Increased conductivity was attributed to the interdiffusion within channels. • Annealing temperature affected microstructure and electrical properties.

  15. Powder XRD studies on -C28H58 : -CH2+2 ( = 10, 12, 14, 16, 18) hydrocarbon mixtures: Phase strength analysis

    Indian Academy of Sciences (India)

    P B V Prasad; P B Shashikanth; P Neelima

    2006-06-01

    Powder XRD investigations were made on mixtures of title compounds and strength of monoclinic, orthorhombic and super-lattice phases were evaluated. Interpretations were made in terms of the influence of tunnel-like defects (TLIDs) and a linear relationship was noticed between the strength of orthorhombic phase and 〈$\\ell$TLID 〉.

  16. Dose Reduction in Contrast-Enhanced Cervical MR Angiography: Field Strength Dependency of Vascular Signal Intensity, Contrast Administration, and Arteriographic Quality.

    Science.gov (United States)

    Dehkharghani, Seena; Qiu, Deqiang; Albin, Lauren S; Saindane, Amit M

    2015-06-01

    Cervical contrast-enhanced MR angiography (MRA) has proven accurate and superior to noncontrast alternatives. We proposed the systematic investigation of dose reduction in contrast-enhanced MRA, hypothesizing heightened tolerance at 3 T vs 1.5 T. Quantitative and qualitative features were compared between full-dose and 50%-reduced dose examinations at 1.5 T and 3 T. One hundred eight cervical contrast-enhanced MRA examinations were reviewed for qualitative and quantitative (signal-to-noise ratio [SNR] and contrast-to-noise ratio [CNR]) features across four dose-field strength combinations: 1.5 T, 0.05 mmol/kg; 3 T, 0.05 mmol/kg; 1.5 T, 0.1 mmol/kg; and 3 T, 0.1 mmol/kg. Quantitative features were evaluated among the following segments: aortic arch, common carotid arteries, common carotid bifurcations, and cervical internal carotid arteries. A qualitative visual rating scale was applied for the same segments as well as to the vertebral arteries along their proximal (V1), intraforaminal (V2), and distal extraforaminal (V3) courses. Significant between-group differences were reported at p contrast-enhanced MRA is feasible at 3 T without significant compromise in arteriographic quality in most segments. Particularly at 3 T, arteriography is quantitatively and qualitatively robust and may be advisable in high-risk patients.

  17. 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

  18. Resonance Raman Scattering Studies of Gallium - - Aluminum-Arsenide Superlattices.

    Science.gov (United States)

    Gant, Thomas Andrew

    We have made resonance Raman scattering studies of folded LA phonons and quantized LO phonons in several GaAs-AlAs superlattices. The motivation for this work was to study the electronic structure and the electron -phonon interaction in these structures. The samples were not intentionally doped. The Raman spectra of optic phonons were usually taken at a temperature of 10 K or less. The folded acoustic phonon work was taken at temperatures ranging from 200-300 K in order to enhance the scattering by the thermal factor. Two samples in particular have received very close attention: sample 2292 (50 A GaAs- 20 A AlAs) and sample 3250 (20 A GaAs- 50 A AlAs). In sample 2292 we have made resonance studies of the folded LA phonons and the GaAs -like confined LO_2 mode near the second heavy hole exciton. The results on the folded acoustic phonons show a very strong resonance enhancement for the second order folded phonons, but very little for the first order. An interference between two different scattering channels (the n = 1 light hole and the n = 2 heavy hole subbands) seems to be responsible for this effect. The resonance profile for the LO_2 confined optic phonon in sample 2292 shows 4 peaks in the region from 1.8 eV to 2.05 eV. We have studied the dependence of this resonance profile on the power density. A higher power density was achieved by using the same laser power with a tighter focus. At the higher power density the peak at 1.93 eV (formerly the strongest peak present) vanished. This "bleaching" effect is related to screening due to the higher carrier density. In sample 3250 we have studied the polarization dependence of the resonance profiles of four peaks (LO _2, LO_4, LO_6, and an interface mode) near the lowest direct gap. The A_1 symmetry confined LO modes are seen in both polarized and depolarized geometries, in violation of the usual selection rule (polarized). A mechanism is proposed to explain this result, which has been previously observed by other

  19. Enhancement and Prediction of Adhesion Strength of Copper Cold Spray Coatings on Steel Substrates for Nuclear Fuel Repository

    Science.gov (United States)

    Fernández, R.; MacDonald, D.; Nastić, A.; Jodoin, B.; Tieu, A.; Vijay, M.

    2016-12-01

    Thick copper coatings have been envisioned as corrosion protection barriers for steel containers used in repositories for nuclear waste fuel bundles. Due to its high deposition rate and low oxidation levels, cold spray is considered as an option to produce these coatings as an alternative to traditional machining processes to create corrosion protective sleeves. Previous investigations on the deposition of thick cold spray copper coatings using only nitrogen as process gas on carbon steel substrates have continuously resulted in coating delamination. The current work demonstrates the possibility of using an innovative surface preparation process, forced pulsed waterjet, to induce a complex substrate surface morphology that serves as anchoring points for the copper particles to mechanically adhere to the substrate. The results of this work show that, through the use of this surface preparation method, adhesion strength can be drastically increased, and thick copper coatings can be deposited using nitrogen. Through finite element analysis, it was shown that it is likely that the bonding created is purely mechanical, explaining the lack of adhesion when conventional substrate preparation methods are used and why helium is usually required as process gas.

  20. Formation of a bimodal structure in ultrafine Ti–Fe–Nb alloys with high-strength and enhanced ductility

    Energy Technology Data Exchange (ETDEWEB)

    Cao, G.H., E-mail: ghcao@shu.edu.cn [Department of Materials Engineering, Shanghai Key Laboratory of Modern Metallurgy and Materials Processing, Shanghai University, 149 Yanchang Road, Shanghai 200072 (China); Peng, Y.F.; Liu, N.; Li, X.; Lei, Z.S.; Ren, Z.M. [Department of Materials Engineering, Shanghai Key Laboratory of Modern Metallurgy and Materials Processing, Shanghai University, 149 Yanchang Road, Shanghai 200072 (China); Gerthsen, D. [Laboratorium für Elektronenmikroskopie, Karlsruher Institut für Technologie, D-76128 Karlsruhe (Germany); Russell, A.M. [Division of Materials Science and Engineering, Ames Laboratory of the U.S.D.O.E., Ames, IA 50011-3020 (United States); Department of Materials Science and Engineering, Iowa State University, Ames, IA 50011-2300 (United States)

    2014-07-15

    Bulk (Ti{sub 70.5}Fe{sub 29.5}){sub 100−x}Nb{sub x} (x=0, 3, 5 and 7 at%) alloys were prepared by cold crucible levitation melting, and their mechanical properties were tested in compression at room temperature. A (Ti{sub 70.5}Fe{sub 29.5}){sub 97}Nb{sub 3} alloy specimen in compression exhibited an ultimate compressive strength of 2.53 GPa and a compressive plastic strain of 15%. Electron microscope observations indicated that lamellar structures present in the eutectic Ti{sub 70.5}Fe{sub 29.5} alloy could be modified by the addition of Nb to obtain a bimodal structure. The improvement of the mechanical properties is attributed to two factors: (1) the bimodal phase size distribution with micrometer-sized primary β-Ti dendrites embedded inside a matrix of refined ultrafine eutectics (β-Ti+TiFe), and (2) the larger lattice mismatches between the β-Ti and TiFe phases in Nb-modified eutectic Ti–Fe alloys that introduce coherency strain at the interface. The orientation relationship of A2 β-Ti with B2 TiFe in binary and Nb-modified Ti–Fe alloys is TiFe (110)[001] || β-Ti (110)[001].

  1. Acute caffeine ingestion enhances strength performance and reduces perceived exertion and muscle pain perception during resistance exercise.

    Science.gov (United States)

    Duncan, Michael J; Stanley, Michelle; Parkhouse, Natalie; Cook, Kathryn; Smith, Mike

    2013-01-01

    The efficacy of caffeine ingestion in enhancing aerobic performance is well established. However, despite suggestions that caffeine may enhance resistance exercise performance, research is equivocal on the effect of acute caffeine ingestion on resistance exercise performance. It has also been suggested that dampened perception of perceived exertion and pain perception might be an explanation for any possible enhancement of resistance exercise performance due to caffeine ingestion. Therefore, the aim of this study was to examine the acute effect of caffeine ingestion on repetitions to failure, rating of perceived exertion (RPE) and muscle pain perception during resistance exercise to failure. Eleven resistance trained individuals (9 males, 2 females, mean age±SD=26.4±6.4 years), took part in this double-blind, randomised cross-over experimental study whereby they ingested a caffeinated (5 mg kg(-1)) or placebo solution 60 minutes before completing a bout of resistance exercise. Experimental conditions were separated by at least 48 hours. Resistance exercise sessions consisted of bench press, deadlift, prone row and back squat exercise to failure at an intensity of 60% 1 repetition maximum. Results indicated that participants completed significantly greater repetitions to failure, irrespective of exercise, in the presence of caffeine (p=0.0001). Mean±S.D of repetitions to failure was 19.6±3.7 and 18.5±4.1 in caffeine and placebo conditions, respectively. There were no differences in peak heart rate or peak blood lactate values across conditions (both p >0.05). RPE was significantly lower in the caffeine compared to the placebo condition (p=0.03) and was significantly higher during lower body exercises compared to upper body exercises irrespective of substance ingested (p=0.0001). For muscle pain perception, a significant condition by exercise interaction (p=0.027) revealed that muscle pain perception was lower in the caffeine condition, irrespective of exercise

  2. Piezoelectrics by Design: A Route through Short-period Perovskite Superlattices

    CERN Document Server

    Das, Hena; Saha-Dasgupta, T

    2010-01-01

    Using first-principles density functional theory, we study piezoelectricity in short-period superlattices made with combination of ferroelectric and paraelectric components and exhibiting polar discontinuities. We show that piezoelectric response of such a superlattice can be tuned both in terms of sign and magnitude with a choice of its components. As these superlattices with nonswitchable polarization do not undergo ferroelectric transitions, we predict them to exhibit a robust piezoelectric response with weaker temperature dependence compared to their bulk counterparts.

  3. Calculation of Elastic Constants of Ag/Pd Superlattice Thin Films by Molecular Dynamics with Many-Body Potentials

    Institute of Scientific and Technical Information of China (English)

    GAO Ning; LAI Wen-Sheng

    2006-01-01

    @@ The calculation of elastic constants of Ag/Pd superlattice thin films by molecular dynamics simulations with many-body potentials is presented. It reveals that the elastic constants C11 and C55 increase with decreasing modulation wavelength A of the films, which is consistent with experiments. However, the change of C11 and C55 with A is found to be around the values determined by a rule of mixture using bulk elastic constants of metals.No supermodulus effect is observed and it is due to cancellation between enhanced and reduced contributions to elastic constants from Ag and Pd layers subjected to compressive and tensile strains, respectively.

  4. Enhancement of the performance of a combined microalgae-activated sludge system for the treatment of high strength molasses wastewater.

    Science.gov (United States)

    Tsioptsias, Costas; Lionta, Gesthimani; Deligiannis, Andreas; Samaras, Petros

    2016-12-01

    The treatment of molasses wastewater, by a combined microalgae-activated sludge process, for the simultaneous organics and total nitrogen reduction, was examined. Further enhancement of the performance of the combined process was accomplished, by means of biofilm carriers or electrocoagulation. A LED light tube was immersed into the reactor tank aiming to enhance the growth of photosynthetic microalgae, while in a similar unit, biofilm carriers were added to the system, representing a moving bed bioreactor. Exposure of the activated sludge biocommunity to light source, resulted in the growth of microalgae and photoreactors exhibited higher removal rates of total nitrogen and nitrates. However, operation at longer times resulted in low effluent quality due to the presence of microalgae cells as a result of high growth rates, and potential light shading effect. Nevertheless, the moving bed system was more beneficial than the single photoreactor, as biofilm carriers provided a self cleaning capacity of the light source, reducing the effect of microalgae deposition. Advanced treatment of the biological effluents, by electrocoagulation, increased even more the process efficiency: the combined photobioreactor and electrocoagulation process resulted in about 78% COD removal and more than 35% total nitrogen removal in the effluent, where nitrates represented almost the single form of total nitrogen. Copyright © 2016 Elsevier Ltd. All rights reserved.

  5. Laser molecular-beam epitaxy and second-order optical nonlinearity of BaTiO3/SrTiO3 superlattices

    Institute of Scientific and Technical Information of China (English)

    2000-01-01

    A series of c-axis oriented BaTiO3/SrTiO3 superlattices with the atomic-scale precision were epitaxially grown on single-crystal SrTiO3 (100) substrates using laser molecular-beam epitaxy (LMBE). A periodic modulation of the intensity of reflection high-energy electron diffraction (RHEED) in BaTiO3 and SrTiO3 layers was observed and attributed to the lattice-misfit-induced periodic variation of the terrace density in film surface. The relationship between the second-order nonlinear optical susceptibilities and the superlattice structure was systematically studied. The experimental and theoretical fitting results indicate that the second-order nonlinear optical susceptibilities of BaTiO3/SrTiO3 superlattices were greatly enhanced with the maximum value being more than one order of magnitude larger than that of bulk BaTiO3 crystal. The mechanism of the enhancement of the second-order optical nonlinearity was discussed by taking into account the stress-induced lattice distortion and polarization enhancement.

  6. 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.

  7. A GaAssolarAlAs superlattice autocorrelator for picosecond THz radiation pulses

    Science.gov (United States)

    Winnerl, S.; Pesahl, S.; Schomburg, E.; Grenzer, J.; Renk, K. F.; Pellemans, H. P. M.; van der Meer, A. F. G.; Pavel'ev, D. G.; Koschurinov, Yu.; Ignatov, A. A.; Melzer, B.; Ustinov, V.; Ivanov, S.; Kop'ev, P. S.

    1999-01-01

    We report on a GaAs/AlAs, wide-miniband, superlattice autocorrelator for picosecond THz radiation pulses (operated at room temperature); the autocorrelator is based on the THz radiation-induced reduction of current through the superlattice. THz radiation (frequency 7.2 THz) from the FELIX (free-electron laser for infrared experiments) was coupled into the superlattice with an antenna system. We measured the current reduction for two time-delayed pulses and found that the signal decreased when the time delay was smaller than the pulse duration. With this superlattice autocorrelator we were able to resolve laser pulses that had a duration of a few picoseconds.

  8. Quasiperiodic AlGaAs superlattices for neuromorphic networks and nonlinear control systems

    Energy Technology Data Exchange (ETDEWEB)

    Malyshev, K. V., E-mail: malyshev@bmstu.ru [Electronics and Laser Technology Department, Bauman Moscow State Technical University, Moscow 105005 (Russian Federation)

    2015-01-28

    The application of quasiperiodic AlGaAs superlattices as a nonlinear element of the FitzHugh–Nagumo neuromorphic network is proposed and theoretically investigated on the example of Fibonacci and figurate superlattices. The sequences of symbols for the figurate superlattices were produced by decomposition of the Fibonacci superlattices' symbolic sequences. A length of each segment of the decomposition was equal to the corresponding figurate number. It is shown that a nonlinear network based upon Fibonacci and figurate superlattices provides better parallel filtration of a half-tone picture; then, a network based upon traditional diodes which have cubic voltage-current characteristics. It was found that the figurate superlattice F{sup 0}{sub 11}(1) as a nonlinear network's element provides the filtration error almost twice less than the conventional “cubic” diode. These advantages are explained by a wavelike shape of the decreasing part of the quasiperiodic superlattice's voltage-current characteristic, which leads to multistability of the network's cell. This multistability promises new interesting nonlinear dynamical phenomena. A variety of wavy forms of voltage-current characteristics opens up new interesting possibilities for quasiperiodic superlattices and especially for figurate superlattices in many areas—from nervous system modeling to nonlinear control systems development.

  9. Quasi free-standing silicene in a superlattice with hexagonal boron nitride

    KAUST Repository

    Kaloni, T. P.

    2013-11-12

    We study a superlattice of silicene and hexagonal boron nitride by first principles calculations and demonstrate that the interaction between the layers of the superlattice is very small. As a consequence, quasi free-standing silicene is realized in this superlattice. In particular, the Dirac cone of silicene is preserved. Due to the wide band gap of hexagonal boron nitride, the superlattice realizes the characteristic physical phenomena of free-standing silicene. In particular, we address by model calculations the combined effect of the intrinsic spin-orbit coupling and an external electric field, which induces a transition from a semimetal to a topological insulator and further to a band insulator.

  10. Feshbach shape resonance for high Tc pairing in superlattices of quantum stripes and quantum wells

    Directory of Open Access Journals (Sweden)

    A Bianconi

    2006-09-01

    Full Text Available   The Feshbach shape resonances in the interband pairing in superconducting superlattices of quantum wells or quantum stripes is shown to provide the mechanism for high Tc superconductivity. This mechanism provides the Tc amplification driven by the architecture of material: superlattices of quantum wells (intercalated graphite or diborides and superlattices of quantum stripes (doped high Tc cuprate perovskites where the chemical potential is tuned to a Van Hove-Lifshitz singularity (vHs in the electronic energy spectrum of the superlattice associated with the change of the Fermi surface dimensionality in one of the subbands.

  11. Quasiperiodic AlGaAs superlattices for neuromorphic networks and nonlinear control systems

    Science.gov (United States)

    Malyshev, K. V.

    2015-01-01

    The application of quasiperiodic AlGaAs superlattices as a nonlinear element of the FitzHugh-Nagumo neuromorphic network is proposed and theoretically investigated on the example of Fibonacci and figurate superlattices. The sequences of symbols for the figurate superlattices were produced by decomposition of the Fibonacci superlattices' symbolic sequences. A length of each segment of the decomposition was equal to the corresponding figurate number. It is shown that a nonlinear network based upon Fibonacci and figurate superlattices provides better parallel filtration of a half-tone picture; then, a network based upon traditional diodes which have cubic voltage-current characteristics. It was found that the figurate superlattice F011(1) as a nonlinear network's element provides the filtration error almost twice less than the conventional "cubic" diode. These advantages are explained by a wavelike shape of the decreasing part of the quasiperiodic superlattice's voltage-current characteristic, which leads to multistability of the network's cell. This multistability promises new interesting nonlinear dynamical phenomena. A variety of wavy forms of voltage-current characteristics opens up new interesting possibilities for quasiperiodic superlattices and especially for figurate superlattices in many areas—from nervous system modeling to nonlinear control systems development.

  12. High Coefficient of Performance HgCdTe And Metallic Superlattice-Based Thermoelectric Coolers Project

    Data.gov (United States)

    National Aeronautics and Space Administration — We propose the development of nanoscale superlattices (SLs) as the active elements of high efficiency thermoelectric coolers. Recent models predict that the...

  13. Lattice relaxation and ferromagnetic character of (LaVO3)m/SrVO3superlattices

    Science.gov (United States)

    Schuster, Cosima; Lüders, Ulrike; Frésard, Raymond; Schwingenschlögl, Udo

    2013-08-01

    The experimental observation that vanadate superlattices (LaVO3)m/SrVO3 show ferromagnetism up to room temperature (Lüders U. et al., Phys. Rev. B, 80 (2009) 241102(R)) is investigated by means of density functional theory, and the band structure for m = 5 and 6 is calculated. A buckling of the interface VO2 layers is found in both cases, but subtle differences in bond length lead to very different properties for even and odd values of m: in the even case, the two interface VO2 layers effectively decouple from the adjacent LaO layers due to a strong bond length enhancement. This results into a local inversion of the orbital occupancy and to the confinement of the charge carriers. In the odd case, the amplitude of the bond length variation is smaller, so that the charge carriers spill into the deeper-lying VO2 layers, and spin-polarised interfaces are obtained.

  14. Fingolimod Hydrochloride Gel for Dermatological Applications: Optimization of Formulation Strength and Effect of Colloidal Oatmeal (Aveeno®) as Penetration Enhancer.

    Science.gov (United States)

    Tamakuwala, M; Stagni, G

    2016-08-01

    Fingolimod (FNGL) is an immune-modulatory agent prescribed for relapsing forms of multiple sclerosis. Because of its mechanism of action, FNGL is potentially a treatment for chronic, non-curable T-lymphocyte-driven inflammatory skin diseases (TLDISD) such as psoriasis and atopic dermatitis. Since severe side effects limit the systemic administration of FNGL, the objective of this study is to develop a hydroxypropyl cellulose (2%) FNGL gel for dermatological applications. First, the effect of FNGL strength (0.05%, 0.10%, 0.50%, and 1.00%) on skin permeability and retention was investigated. We carried out several permeation studies with vertical Franz diffusion cells and (i) cellulose or (ii) excised dorsal porcine ear skin (EDPES) as membrane. We also quantified FNGL in the stratum corneum and in dermis with the tape-stripping method. Permeability parameters as well as the amount retained in skin increased significantly (p oatmeal (0%, 1%, 3%, 6%, and 10%) on FNGL in vitro permeability and skin retention. Colloidal oatmeal has beneficial dermatological properties for TLDISD and may complement FNGL activity. Permeability increased significantly (p oatmeal at the 6% and 10% strength with an enhancement ratio of 3.5 and 2.4, respectively, whereas the amount retained in the skin decreased significantly (p < 0.001) compared to the base gel. In conclusion, the 0.50% FNGL(.)HCL gel with 6% Aveeno® has very promising permeability characteristics for delivery of FNGL to the skin.

  15. 提高军用手持机续航能力设计%The Design of Enhancing the Endurance Strength of the Personal Digital Assistant for Military

    Institute of Scientific and Technical Information of China (English)

    刘彩霞

    2014-01-01

    The endurance strength of the power supply is one of the key targets for the design of the Personal Digital Assistant(PDA) for military. It directly concerns whether a PDA is available. In the instance of our finite electric capacity of batteries, the key of enhancing endurance strength of a PDA for military is to design of low-power PDA hardware platform which focus CPU selection, LCD selection, power chipset choice and the design of supply circuits, to use the technique of the dynamic power management, and to optimize software to the best of our ability, and so on.%电源续航能力是军用手持机设计的关键指标之一,它直接关系到一款手持机是否可用。在电池容量一定的情况下,提高军用手持机续航能力的关键是:设计低功耗硬件平台,重点考虑CPU选型、彩色屏幕选择、电源芯片选择和供电电路设计;采用动态电源管理技术;最大限度优化软件等。

  16. Enhanced micro-vibration sensitive high-damping capacity and mechanical strength achieved in Al matrix composites reinforced with garnet-like lithium electrolyte

    Science.gov (United States)

    Wang, Xian-Ping; Zhang, Yi; Xia, Yu; Jiang, Wei-Bing; Liu, Hui; Liu, Wang; Gao, Yun-Xia; Zhang, Tao; Fang, Qian-Feng

    2016-12-01

    A novel micro-vibration sensitive-type high-damping Al matrix composites reinforced with Li7-xLa3Zr2-xNbxO12 (LLZNO, x = 0.25) was designed and prepared using an advanced spark plasma sintering (SPS) technique. The damping capacity and mechanical properties of LLZNO/Al composites (LLZNO content: 0-40 wt.%) were found to be greatly improved by the LLZNO addition. The maximum damping capacity and the ultimate tensile strength (UTS) of LLZNO/Al composite can be respectively up to 0.033 and 101.2 MPa in the case of 20 wt.% LLZNO addition. The enhancement of damping and mechanical properties of the composites was ascribed to the intrinsic high-damping capacity and strengthening effects of hard LLZNO particulate. This investigation provides a new insight to sensitively suppress micro-vibration of payloads in the aerospace environment.

  17. Strength Enhancement of Car Front Bumper for Slow Speed Impact by FEA Method as per IIHS Regulation

    Science.gov (United States)

    Sonawane, Chandrakant Rameshchandra; Shelar, Ajit Lavaji

    2017-05-01

    Low speed collisions happen significantly due to on road slow moving heavy traffic as well as during parking of vehicles. The bumpers are provided in front and back side of a vehicle has two main purposes: first is to absorb the energy generated during these kinds of slow speed impacts and secondly to protect the expensive parts like main engine parts, radiators and connected engine cooling mechanism, headlights, taillights, etc, by slowing down the vehicles. The problem often in various cars bumper is that they doesn't line-up vertically during low speed impact and leads to damage of various parts which are costly to repair. Many a times bumper design does not have sufficient capacity to absorb the energy generated during these impact. Guideline by International Institute Highway Safety (IIHS) regulation provides useful insight for such low speed impact study. In this paper, slow speed impact test were conducted as per IIHS regulation in three positions namely central impact, left hand corner impact and right hand corner impact. Parameters including bumper material, shape, thickness and impact condition are analyzed using fine element analysis (FEA) to enhance crashworthiness design in low speed impact. Then the vehicle front structure has been modified suitably. It has been observed that lining up the front metal bumper with suitable stiffness provides the best result which ultimately reduces the damage to the vehicle parts.

  18. The first-principles study of ferroelectric behaviours of PbTiO3/SrTiO3 and BaTiO3/SrTiO3 superlattices

    Institute of Scientific and Technical Information of China (English)

    Zhu Zhen-Ye; Wang Biao; Wang Hai; Zheng Yue; Li Qing-Kun

    2007-01-01

    We have performed the first-principles calculation to investigate the origins of ferroelectricities and different polarization behaviours of superlattices BaTiO3/SrTiO3 and PbTiO3/SrTiO3- The density of state (DOS) and electronic charge profiles show that there are strong hybridizations between atoms Ti and O and between atoms Pb and O which play very important roles in producing the ferroelectricities of superlattices BaTiO3/rTiO3 and PbTiO3/SrTiO3. Owing to the decline of internal electric field in SrTiO3 (ST) layer, the tetragonality and polarizations of superlattices decrease with increasing the fraction of SrTiO3 in the superlattices. We find that the polarization of PbTiO3/SrTiO3 is largerthan that of BaTiO3/SrTiO3 at the same ratio of components, because the polarization mismatch between PbTiO3 and SrTiO3 is larger than that between BaTiO3 and SrTiO3. The polarization and tetragonality are enhanced with respect to those of bulk tetragonal BaTiO3 in the superlattices BaTiO3/SrTiO3, while the polarization and tetragonality are reduced with respect to those of bulk tetragonal PbTiO3 in superlattices PbTiO3/SrTiO3.

  19. 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.

  20. 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.

  1. 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.

  2. Measuring spin correlations in optical lattices using superlattice potentials

    DEFF Research Database (Denmark)

    Pedersen, Kim Georg Lind; Andersen, Brian Møller; Bruun, Georg Morten;

    2011-01-01

    We suggest two experimental methods for probing both short- and long-range spin correlations of atoms in optical lattices using superlattice potentials. The first method involves an adiabatic doubling of the periodicity of the underlying lattice to probe neighboring singlet (triplet) correlations...... for fermions (bosons) by the occupation of the resulting vibrational ground state. The second method utilizes a time-dependent superlattice potential to generate spin-dependent transport by any number of prescribed lattice sites, and probes correlations by the resulting number of doubly occupied sites....... For experimentally relevant parameters, we demonstrate how both methods yield large signatures of antiferromagnetic correlations of strongly repulsive fermionic atoms in a single shot of the experiment. Lastly, we show how this method may also be applied to probe d-wave pairing, a possible ground-state candidate...

  3. 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.

  4. 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.

  5. Coupled bloch-phonon oscillations in semiconductor superlattices

    Science.gov (United States)

    Dekorsy; Bartels; Kurz; Kohler; Hey; Ploog

    2000-07-31

    We investigate coherent Bloch oscillations in GaAs/AlxGa1-xAs superlattices with electronic miniband widths larger than the optical phonon energy. In these superlattices the Bloch frequency can be tuned into resonance with the optical phonon. Close to resonance a direct coupling of Bloch oscillations to LO phonons is observed which gives rise to the coherent excitation of LO phonons. The density necessary for driving coherent LO phonons via Bloch oscillations is about 2 orders of magnitude smaller than the density necessary to drive coherent LO phonons in bulk GaAs. The experimental observations are confirmed by the theoretical description of this phenomenon [A.W. Ghosh et al., Phys. Rev. Lett. 85, 1084 (2000)].

  6. 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.)

  7. 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)

  8. 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.

  9. Optical properties of InAsBi and optimal designs of lattice-matched and strain-balanced III-V semiconductor superlattices

    Science.gov (United States)

    Webster, P. T.; Shalindar, A. J.; Riordan, N. A.; Gogineni, C.; Liang, H.; Sharma, A. R.; Johnson, S. R.

    2016-06-01

    The optical properties of bulk InAs0.936Bi0.064 grown by molecular beam epitaxy on a (100)-oriented GaSb substrate are measured using spectroscopic ellipsometry. The index of refraction and absorption coefficient are measured over photon energies ranging from 44 meV to 4.4 eV and are used to identify the room temperature bandgap energy of bulk InAs0.936Bi0.064 as 60.6 meV. The bandgap of InAsBi is expressed as a function of Bi mole fraction using the band anticrossing model and a characteristic coupling strength of 1.529 eV between the Bi impurity state and the InAs valence band. These results are programmed into a software tool that calculates the miniband structure of semiconductor superlattices and identifies optimal designs in terms of maximizing the electron-hole wavefunction overlap as a function of transition energy. These functionalities are demonstrated by mapping the design spaces of lattice-matched GaSb/InAs0.911Sb0.089 and GaSb/InAs0.932Bi0.068 and strain-balanced InAs/InAsSb, InAs/GaInSb, and InAs/InAsBi superlattices on GaSb. The absorption properties of each of these material systems are directly compared by relating the wavefunction overlap square to the absorption coefficient of each optimized design. Optimal design criteria are provided for key detector wavelengths for each superlattice system. The optimal design mid-wave infrared InAs/InAsSb superlattice is grown using molecular beam epitaxy, and its optical properties are evaluated using spectroscopic ellipsometry and photoluminescence spectroscopy.

  10. Heterogenous Material Integration and Band Engineering With Type II Superlattice

    Science.gov (United States)

    2015-10-26

    of chemical vapor deposited graphene transferred to SiO2 . Appl. Phys. Lett. 99, 122108 (2011). 113 Ferrari, A. C. Raman spectroscopy of graphene ...extrinsic performance limits of graphene devices on SiO2 . Nat. Nanotechnol. 3, 206-209 (2008). 130 Fang, T., Konar, A., Xing, H. & Jena, D. Mobility...AlSb strained layer superlattices. 15. SUBJECT TERMS crystal growth, characterization, semiconductor fabrication, infrared detectors, graphene

  11. 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)

  12. Enhanced ozone strongly reduces carbon sink strength of adult beech (Fagus sylvatica) - Resume from the free-air fumigation study at Kranzberg Forest

    Energy Technology Data Exchange (ETDEWEB)

    Matyssek, R., E-mail: matyssek@wzw.tum.d [Ecophysiology of Plants, Technische Universitaet Muenchen, Hans-Carl-von-Carlowitz-Platz 2, D-85354 Freising (Germany); Wieser, G. [Dept. Alpine Timberline Ecophysiology, Federal Office and Research Centre for Forests, Rennweg 1, A-6020 Innsbruck (Austria); Ceulemans, R. [Dept. of Biology, University of Antwerp, Universiteitsplein 1, B-2610 Wilrijk (Belgium); Rennenberg, H. [Tree Physiology, Institute of Forest Botany and Tree Physiology, University of Freiburg, Georges-Koehler-Allee 53, D-79110 Freiburg (Germany); Pretzsch, H. [Forest Growth and Yield Sciences, Technische Universitaet Muenchen, Hans-Carl-von-Carlowitz-Platz 2, D-85354 Freising (Germany); Haberer, K. [Tree Physiology, Institute of Forest Botany and Tree Physiology, University of Freiburg, Georges-Koehler-Allee 53, D-79110 Freiburg (Germany); Loew, M.; Nunn, A.J. [Ecophysiology of Plants, Technische Universitaet Muenchen, Hans-Carl-von-Carlowitz-Platz 2, D-85354 Freising (Germany); Werner, H. [Ecoclimatology (formerly: Bioclimatology and Air Pollution Research), Hans-Carl-von-Carlowitz-Platz 2, D-85354 Freising (Germany); Wipfler, P. [Forest Growth and Yield Sciences, Technische Universitaet Muenchen, Hans-Carl-von-Carlowitz-Platz 2, D-85354 Freising (Germany); Osswald, W. [Phytopathology of Woody Plants, Technische Universitaet Muenchen, Hans-Carl-von-Carlowitz-Platz 2, D-85354 Freising (Germany); Nikolova, P. [Ecophysiology of Plants, Technische Universitaet Muenchen, Hans-Carl-von-Carlowitz-Platz 2, D-85354 Freising (Germany); Hanke, D.E. [Dept. Plant Sciences, University of Cambridge, Downing Street, Cambridge CB2 3EA (United Kingdom); Kraigher, H. [Slovenian Forestry Institute, Forest Biology, Ecology and Technology, Vecna pot 2, 1000 Ljubljana (Slovenia); Tausz, M. [Dept. of Forest and Ecosystem Science, Melbourne School of Land and Environment, Water Street, Creswick Vic 3363 (Australia)

    2010-08-15

    Ground-level ozone (O{sub 3}) has gained awareness as an agent of climate change. In this respect, key results are comprehended from a unique 8-year free-air O{sub 3}-fumigation experiment, conducted on adult beech (Fagus sylvatica) at Kranzberg Forest (Germany). A novel canopy O{sub 3} exposure methodology was employed that allowed whole-tree assessment in situ under twice-ambient O{sub 3} levels. Elevated O{sub 3} significantly weakened the C sink strength of the tree-soil system as evidenced by lowered photosynthesis and 44% reduction in whole-stem growth, but increased soil respiration. Associated effects in leaves and roots at the gene, cell and organ level varied from year to year, with drought being a crucial determinant of O{sub 3} responsiveness. Regarding adult individuals of a late-successional tree species, empirical proof is provided first time in relation to recent modelling predictions that enhanced ground-level O{sub 3} can substantially mitigate the C sequestration of forests in view of climate change. - Empirical proof corroborates substantial mitigation of carbon sequestration in the tree-soil system of a forest site under enhanced O{sub 3} impact for adult beech.

  13. Enhancement of the performance of an anaerobic sequencing batch reactor treating low-strength wastewater through implementation of a variable stirring rate program

    Energy Technology Data Exchange (ETDEWEB)

    Rodrigues, J.A.D.; Pinto, A.G.; Ratusznei, S.M.; Gedraite, R. [Instituto Maua de Tecnologia (IMT), Sao Caetano do Sul, SP (Brazil). Escola de Engenharia. Dept. de Engenharia Quimica e de Alimentos]. E-mail: rodrigues@maua.br; Zaiat, M. [Sao Paulo Univ., Sao Carlos, SP (Brazil). Escola de Engenharia. Dept. de Hidraulica e Saneamento

    2004-09-01

    This work focuses on enhancement of the performance of an anaerobic sequencing batch reactor with a six-vertical-blade-disk-turbine impeller, containing granulated biomass treating low-strength synthetic wastewater, through a study of the feasibility of implementing a variable stirring rate program. The reactor was operated at 30 deg C and a six-hour cycle was used to treat approximately 2.0 L of the synthetic substrate with a chemical oxygen demand (COD) of nearly 500 mg/L. Two different stirring rate program were implemented: a constant rate of 50 rpm and a variable rate consisting of 75 rpm for one hour, 50 rpm for four hours and 25 rpm for 0.5 hour. The last 0.5 hour of the cycle was used for the settling step. In both cases, a very short start-up period and unfiltered and filtered substrate removal efficiencies of 81% and 88%, respectively, were attained. However, use of the variable stirring rate enhanced efficiency of the reactor dynamics without impairing biomass morphology, thus resulting in a reduction in the total cycle time and a possible decrease in energy consumption. Additionally, a simplified model of the anaerobic metabolic activity, using apparent kinetic parameters, was proposed as a consecutive first-order kinetic model with substrate and total volatile acid residual concentrations in order to analyze how the variable stirring rate affects reactor performance. (author)

  14. Integrating microbial fuel cells with anaerobic acidification and forward osmosis membrane for enhancing bio-electricity and water recovery from low-strength wastewater.

    Science.gov (United States)

    Liu, Jinmeng; Wang, Xinhua; Wang, Zhiwei; Lu, Yuqin; Li, Xiufen; Ren, Yueping

    2017-03-01

    Microbial fuel cells (MFCs) and forward osmosis (FO) are two emerging technologies with great potential for energy-efficient wastewater treatment. In this study, anaerobic acidification and FO membrane were simultaneously integrated into an air-cathode MFC (AAFO-MFC) for enhancing bio-electricity and water recovery from low-strength wastewater. During a long-term operation of approximately 40 days, the AAFO-MFC system achieved a continuous and relatively stable power generation, and the maximum power density reached 4.38 W/m(3). The higher bio-electricity production in the AAFO-MFC system was mainly due to the accumulation of ethanol resulted from anaerobic acidification process and the rejection of FO membrane. In addition, a proper salinity environment in the system controlled by the addition of MF membrane enhanced the electricity production. Furthermore, the AAFO-MFC system produced a high quality effluent, with the removal rates of organic matters and total phosphorus of more than 97%. However, the nitrogen removal was limited for the lower rejection of FO membrane. The combined biofouling and inorganic fouling were responsible for the lower water flux of FO membrane, and the Desulfuromonas sp. utilized the ethanol for bio-electricity production was observed in the anode. These results substantially improve the prospects for simultaneous wastewater treatment and energy recovery, and further studies are needed to optimize the system integration and operating parameters. Copyright © 2016 Elsevier Ltd. All rights reserved.

  15. Transparent conducting oxides: a δ-doped superlattice approach.

    Science.gov (United States)

    Cooper, Valentino R; Seo, Sung S Ambrose; Lee, Suyoun; Kim, Jun Sung; Choi, Woo Seok; Okamoto, Satoshi; Lee, Ho Nyung

    2014-08-11

    Metallic states appearing at interfaces between dissimilar insulating oxides exhibit intriguing phenomena such as superconductivity and magnetism. Despite tremendous progress in understanding their origins, very little is known about how to control the conduction pathways and the distribution of charge carriers. Using optical spectroscopic measurements and density-functional theory (DFT) simulations, we examine the effect of SrTiO3 (STO) spacer layer thickness on the optical transparency and carrier distribution in La δ-doped STO superlattices. We experimentally observe that these metallic superlattices remain highly transparent to visible light; a direct consequence of the appropriately large gap between the O 2p and Ti 3d states. In superlattices with relatively thin STO layers, we predict that three-dimensional conduction would occur due to appreciable overlap of quantum mechanical wavefunctions between neighboring δ-doped layers. These results highlight the potential for using oxide heterostructures in optoelectronic devices by providing a unique route for creating novel transparent conducting oxides.

  16. 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.

  17. 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.

  18. 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)].

  19. Bose-Hubbard model on a checkerboard superlattice

    Science.gov (United States)

    Iskin, Menderes

    2011-05-01

    We study the ground-state phases of the Bose-Hubbard model on a checkerboard superlattice in two dimensions, including the superfluid phase and the Mott and charge-density-wave insulators. First, we discuss the single-particle Hofstadter problem, and show that the presence of a checkerboard superlattice gives rise to a magnetic flux-independent energy gap in the excitation spectrum. Then, we consider the many-particle problem, and derive an analytical mean-field expression for the superfluid-Mott and superfluid-charge-density-wave insulator phase transition boundaries. Finally, since the phase diagram of the Bose-Hubbard model on a checkerboard superlattice is in many ways similar to that of the extended Bose-Hubbard model, we comment on the effects of magnetic field on the latter model, and derive an analytical mean-field expression for the superfluid-insulator phase transition boundaries as well. This work is supported by Marie Curie International Reintegration Grant (FP7-PEOPLE-IRG-2010-268239).

  20. 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.

  1. 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.

  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. 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. 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.

  5. Spin Filtering in a Nanowire Superlattice by Dresselhause Spin-Orbit Coupling

    Institute of Scientific and Technical Information of China (English)

    Samad Javidan

    2011-01-01

    @@ An InAs/GaSb nanowire Superlattice using GaAs for the impure layers is proposed.Dresselhaus spin-orbit coupling eliminates spin degeneracy, induces one miniband in the superlattices to split into two minibands and leads to complete spin polarization and excellent filtering by optimizing the well and barrier widths and GaAs layer distances.

  6. Quantum dynamical phenomena of independent electrons in semiconductor superlattices subject to a uniform electric field

    Energy Technology Data Exchange (ETDEWEB)

    Bouchard, A.M.

    1994-07-27

    This report discusses the following topics: Bloch oscillations and other dynamical phenomena of electrons in semiconductor superlattices; solvable dynamical model of an electron in a one-dimensional aperiodic lattice subject to a uniform electric field; and quantum dynamical phenomena of electrons in aperiodic semiconductor superlattices.

  7. Terahertz radiation induced chaotic electron transport in semiconductor superlattices with a tilted magnetic field

    Energy Technology Data Exchange (ETDEWEB)

    Wang, C., E-mail: cwang@mail.sim.ac.cn; Wang, F.; Cao, J. C., E-mail: jccao@mail.sim.ac.cn [Key Laboratory of Terahertz Solid-State Technology, Shanghai Institute of Microsystem and Information Technology, Chinese Academy of Sciences, 865 Changning Road, Shanghai 200050 (China)

    2014-09-01

    Chaotic electron transport in semiconductor superlattice induced by terahertz electric field that is superimposed on a dc electric field along the superlattice axis are studied using the semiclassical motion equations including the effect of dissipation. A magnetic field that is tilted relative to the superlattice axis is also applied to the system. Numerical simulation shows that electrons in superlattice miniband exhibit complicate nonlinear oscillating modes with the influence of terahertz radiation. Transitions between frequency-locking and chaos via pattern forming bifurcations are observed with the varying of terahertz amplitude. It is found that the chaotic regions gradually contract as the dissipation increases. We attribute the appearance of complicate nonlinear oscillation in superlattice to the interaction between terahertz radiation and internal cooperative oscillating mode relative to Bloch oscillation and cyclotron oscillation.

  8. 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.

  9. Theory of Semiconducting Superlattices and Microstructures

    Science.gov (United States)

    1992-03-01

    appear 1-n >X I 13 (a)= the den-sity of,:pho-rn states, although the strength of the Z Rama spctum mode cais be quite dzfferiit in the Raman and...discussions about their the on-site nudel. measurements. 556 EXPLANATION OF THE ANOMALOUS RAMA SPECTRA OF (GaSb) 1 x GeX Vcl. 56, No. 7 REFERENCES (1) J. E...calcula. Trchnol. AS. 2051 (19671𔃽. K. Furdyna. J. AppI.l’. 53. 7637 (19S2). tions, rathiertman it. termsofsp-d transitions ord-de.% cita - "’.N.e0

  10. Benzothiazoles with tunable electron-withdrawing strength and reverse polarity: a route to triphenylamine-based chromophores with enhanced two-photon absorption.

    Science.gov (United States)

    Hrobárik, Peter; Hrobáriková, Veronika; Sigmundová, Ivica; Zahradník, Pavol; Fakis, Mihalis; Polyzos, Ioannis; Persephonis, Peter

    2011-11-01

    A series of dipolar and octupolar triphenylamine-derived dyes containing a benzothiazole positioned in the matched or mismatched fashion have been designed and synthesized via palladium-catalyzed Sonogashira cross-coupling reactions. Linear and nonlinear optical properties of the designed molecules were tuned by an additional electron-withdrawing group (EWG) and by changing the relative positions of the donor and acceptor substituents on the heterocyclic ring. This allowed us to examine the effect of positional isomerism and extend the structure-property relationships useful in the engineering of novel heteroaromatic-based systems with enhanced two-photon absorption (TPA). The TPA cross-sections (δ(TPA)) in the target compounds dramatically increased with the branching of the triphenylamine core and with the strength of the auxiliary acceptor. In addition, a change from the commonly used polarity in push-pull benzothiazoles to a reverse one has been revealed as a particularly useful strategy (regioisomeric control) for enhancing TPA cross-sections and shifting the absorption and emission maxima to longer wavelengths. The maximum TPA cross-sections of the star-shaped three-branched triphenylamines are ∼500-2300 GM in the near-infrared region (740-810 nm); thereby the molecular weight normalized δ(TPA)/MW values of the best performing dyes within the series (2.0-2.4 GM·g(-1)·mol) are comparable to those of the most efficient TPA chromophores reported to date. The large TPA cross-sections combined with high emission quantum yields and large Stokes shifts make these compounds excellent candidates for various TPA applications, including two-photon fluorescence microscopy.

  11. Mg dopant distribution in an AlGaN/GaN p-type superlattice assessed using atom probe tomography, TEM and SIMS

    Energy Technology Data Exchange (ETDEWEB)

    Bennett, S E; Kappers, M J; Barnard, J S; Humphreys, C J; Oliver, R A [Department of Materials Science and Metallurgy, University of Cambridge, Pembroke St., Cambridge, CB2 3QZ (United Kingdom); Clifton, P H; Ulfig, R M, E-mail: sb534@cam.ac.u [Imago Scientific Instruments Corporation, 5500 Nobel Drive, Madison, WI, 53711 (United States)

    2010-02-01

    P-type conducting layers are critical in GaN-based devices such as LEDs and laser diodes. Such layers are often produced by doping GaN with Mg, but the hole concentration can be enhanced using AlGaN/GaN p-type superlattices by exploiting the built-in polarisation fields. A Mg-doped AlGaN/GaN superlattice was studied using SIMS. Although the AlGaN and GaN were nominally doped to the same level, the SIMS data suggested a difference in doping density between the two materials. Atom probe tomography was then used to investigate the Mg distribution. The superlattice repeats were clearly visible, as expected and, in addition, significant Mg clustering was observed in both the GaN and AlGaN layers. There were many more Mg clusters in the AlGaN layers than the GaN layers, accounting for the difference in doping density suggested by SIMS. To evaluate the structural accuracy of the atom probe reconstruction, layer thicknesses from the atom probe were compared with STEM images. Finally, future work is proposed to investigate the Mg clusters in the TEM.

  12. Simultaneous enhancement in mechanical strength, electrical conductivity, and electromagnetic shielding properties in PVDF-ABS blends containing PMMA wrapped multiwall carbon nanotubes.

    Science.gov (United States)

    Kar, Goutam Prasanna; Biswas, Sourav; Bose, Suryasarathi

    2015-06-14

    A unique approach was adopted to drive the multiwall carbon nanotubes (MWNTs) to the interface of immiscible PVDF-ABS blends by wrapping the nanotubes with a mutually miscible homopolymer (PMMA). A tailor made interface with an improved stress transfer was achieved in the blends with PMMA wrapped MWNTs. This manifested in an impressive 108% increment in the tensile strength and 48% increment in the Young's modulus with 3 wt% PMMA wrapped MWNTs in striking contrast to the neat blends. As the PMMA wrapped MWNTs localized at the interface of PVDF-ABS blends, the electrical conductivity could be tuned with respect to only MWNTs, which were selectively localized in the PVDF phase, driven by thermodynamics. The electromagnetic shielding properties were assessed using a vector network analyser in a broad range of frequency, X-band (8-12 GHz) and Ku-band (12-18 GHz). Interestingly, enhanced EM shielding was achieved by this unique approach. The blends with only MWNTs shielded the EM waves mostly by reflection however, the blends with PMMA wrapped MWNTs (3 wt%) shielded mostly by absorption (62%). This study opens new avenues in designing materials, which show simultaneous improvement in mechanical, electrical conductivity and EM shielding properties.

  13. Enhanced ozone strongly reduces carbon sink strength of adult beech (Fagus sylvatica)--resume from the free-air fumigation study at Kranzberg Forest.

    Science.gov (United States)

    Matyssek, R; Wieser, G; Ceulemans, R; Rennenberg, H; Pretzsch, H; Haberer, K; Löw, M; Nunn, A J; Werner, H; Wipfler, P; Osswald, W; Nikolova, P; Hanke, D E; Kraigher, H; Tausz, M; Bahnweg, G; Kitao, M; Dieler, J; Sandermann, H; Herbinger, K; Grebenc, T; Blumenröther, M; Deckmyn, G; Grams, T E E; Heerdt, C; Leuchner, M; Fabian, P; Häberle, K-H

    2010-08-01

    Ground-level ozone (O(3)) has gained awareness as an agent of climate change. In this respect, key results are comprehended from a unique 8-year free-air O(3)-fumigation experiment, conducted on adult beech (Fagus sylvatica) at Kranzberg Forest (Germany). A novel canopy O(3) exposure methodology was employed that allowed whole-tree assessment in situ under twice-ambient O(3) levels. Elevated O(3) significantly weakened the C sink strength of the tree-soil system as evidenced by lowered photosynthesis and 44% reduction in whole-stem growth, but increased soil respiration. Associated effects in leaves and roots at the gene, cell and organ level varied from year to year, with drought being a crucial determinant of O(3) responsiveness. Regarding adult individuals of a late-successional tree species, empirical proof is provided first time in relation to recent modelling predictions that enhanced ground-level O(3) can substantially mitigate the C sequestration of forests in view of climate change.

  14. Thermoelectric properties of In-rich InGaN and InN/InGaN superlattices

    Directory of Open Access Journals (Sweden)

    James (Zi-Jian Ju

    2016-04-01

    Full Text Available The thermoelectric properties of n-type InGaN alloys with high In-content and InN/InGaN thin film superlattices (SL grown by molecular beam epitaxy are investigated. Room-temperature measurements of the thermoelectric properties reveal that an increasing Ga-content in ternary InGaN alloys (0 < x(Ga < 0.2 yields a more than 10-fold reduction in thermal conductivity (κ without deteriorating electrical conductivity (σ, while the Seebeck coefficient (S increases slightly due to a widening band gap compared to binary InN. Employing InN/InGaN SLs (x(Ga = 0.1 with different periods, we demonstrate that confinement effects strongly enhance electron mobility with values as high as ∼820 cm2/V s at an electron density ne of ∼5×1019 cm−3, leading to an exceptionally high σ of ∼5400 (Ωcm−1. Simultaneously, in very short-period SL structures S becomes decoupled from ne, κ is further reduced below the alloy limit (κ < 9 W/m-K, and the power factor increases to 2.5×10−4 W/m-K2 by more than a factor of 5 as compared to In-rich InGaN alloys. These findings demonstrate that quantum confinement in group-III nitride-based superlattices facilitates improvements of thermoelectric properties over bulk-like ternary nitride alloys.

  15. Dynamics of alkyl chains in monolayer protected metal clusters and their superlattices

    Energy Technology Data Exchange (ETDEWEB)

    Mukhopadhyay, R [Solid State Physics Division, BARC, Mumbai 400085 (India); Mitra, S [Solid State Physics Division, BARC, Mumbai 400085 (India); Johnson, M [Institute Lau-Langevin, BP156, F-38042, Grenoble, Cedex 9 (France); Pradeep, T [Department of Chemistry and SAIF, IITm, Chennai 600 036 (India)

    2007-12-15

    Alkyl chains dynamics in monolayer protected metal cluster (MPC) systems of gold and silver have been studied by the quasielastic neutron scattering (QENS) technique. Isolated MPCs investigated are 6, 12 and 18 carbon n-alkyl chain thiolate protected 4 nm diameter gold clusters while the superlattices are their silver analogues. Evolution of dynamics with temperature is found to be very different in the isolated clusters and their superlattices. While continuous evolution of the dynamics of the monolayer was observed in isolated MPCs, it is abrupt in superlattice systems and occurs at a temperature consistent with the superlattice melting detected in calorimetry measurements. A model where the chain undergoes uniaxial rotational diffusion with additional body axis fluctuation was found to describe the data consistently. For the superlattice systems, the chains are found to be held by strong inter-chain interactions below the superlattice melting. The data from the planar silver thiolate systems show similar behavior like the superlattice systems, consistent with the calorimetric data.

  16. 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.

  17. Progress in MBE grown type-II superlattice photodiodes

    Science.gov (United States)

    Hill, Cory J.; Li, Jian V.; Mumolo, Jason M.; Gunapala, Sarath D.

    2006-01-01

    We report on the status of GaSb/InAs type-II superlattice diodes grown and fabricated at the Jet Propulsion Laboratory designed for infrared absorption in the 8-12(mu)m range. Recent devices have produced detectivities as high as 8x10 to the tenth power Jones with a differential resistance-area product greater than 6 Ohmcm(sup 2) at 80K with a long wavelength cutoff of approximately 12(mu)m. The measured quantum efficiency of these front-side illuminated devices is close to 30% in the 10-11(mu)m range without antireflection coatings.

  18. Theory of the Fermi-level energy in semiconductor superlattices

    Energy Technology Data Exchange (ETDEWEB)

    Luscombe, J.H. (Central Research Laboratories, Texas Instruments Incorporated, Dallas, Texas (USA)); Aggarwal, R. (Central Research Laboratories, Texas Instruments Incorporated, Dallas, Texas (USA) Department of Electrical Engineering and Computer Science, Massachusetts Institute of Technology, Cambridge, Massachusetts (USA)); Reed, M.A. (Central Research Laboratories, Texas Instruments Incorporated, Dallas, Texas (USA) Department of Electrical Engineering, Yale University, New Haven, Connecticut (USA)); Frensley, W.R. (Central Research Laboratories, Texas Instruments Incorporated, Dallas, Texas (USA) Department of Electrical Engineering, University of Texas at Dallas, Richardson, Texas (USA)); Luban, M. (Iowa Univ., Iowa City, IA (USA). Dept. of Physics and Astronomy Ames Lab., IA (USA))

    1991-09-15

    A theoretical study of the properties of the Fermi level in semiconductor superlattices (SL's) is made which is based upon the carrier occupation of the minibands in thermal equilibrium. We find, for a fixed carrier density and temperature, that the SL Fermi level can differ significantly from that obtained using commonly employed three-dimensional approximations, depending upon the relative spacings and widths of the minibands, with the SL Fermi level being higher than the corresponding bulk value. We find that the SL Fermi level is a sensitive function of the relative widths of the quantum wells and barriers.

  19. The DUV Stability of Superlattice-Doped CMOS Detector Arrays

    Science.gov (United States)

    Hoenk, M. E.; Carver, A. G.; Jones, T.; Dickie, M.; Cheng, P.; Greer, H. F.; Nikzad, S.; Sgro, J.; Tsur, S.

    2013-01-01

    JPL and Alacron have recently developed a high performance, DUV camera with a superlattice doped CMOS imaging detector. Supperlattice doped detectors achieve nearly 100% internal quantum efficiency in the deep and far ultraviolet, and a single layer, Al2O3 antireflection coating enables 64% external quantum efficiency at 263nm. In lifetime tests performed at Applied Materials using 263 nm pulsed, solid state and 193 nm pulsed excimer laser, the quantum efficiency and dark current of the JPL/Alacron camera remained stable to better than 1% precision during long-term exposure to several billion laser pulses, with no measurable degradation, no blooming and no image memory at 1000 fps.

  20. Electronic Bloch oscillation in bilayer graphene gradient superlattices

    Energy Technology Data Exchange (ETDEWEB)

    Cheng, Hemeng; Li, Changan; Song, Yun [Department of Physics, Beijing Normal University, Beijing 100875 (China); Ma, Tianxing, E-mail: txma@bnu.edu.cn [Department of Physics, Beijing Normal University, Beijing 100875 (China); Beijing Computational Science Research Center, Beijing 100084 (China); Wang, Li-Gang, E-mail: sxwlg@yahoo.com [Department of Physics, Zhejiang University, Hangzhou 310027 (China); Lin, Hai-Qing [Beijing Computational Science Research Center, Beijing 100084 (China)

    2014-08-18

    We investigate the electronic Bloch oscillation in bilayer graphene gradient superlattices using transfer matrix method. By introducing two kinds of gradient potentials of square barriers along electrons propagation direction, we find that Bloch oscillations up to terahertz can occur. Wannier-Stark ladders, as the counterpart of Bloch oscillation, are obtained as a series of equidistant transmission peaks, and the localization of the electronic wave function is also signature of Bloch oscillation. Furthermore, the period of Bloch oscillation decreases linearly with increasing gradient of barrier potentials.

  1. 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.}

  2. Strength Training

    Science.gov (United States)

    ... strengthens your heart and lungs. When you strength train with weights, you're using your muscles to ... see there are lots of different ways to train with weights. Try a few good basic routines ...

  3. Strength Training

    Science.gov (United States)

    ... en español Entrenamiento de la fuerza muscular Strength training is a vital part of a balanced exercise routine that includes aerobic activity and flexibility exercises. Regular aerobic exercise, such as running or ...

  4. Elastic superlattices with simultaneously negative effective mass density and shear modulus

    Science.gov (United States)

    Solís-Mora, I. S.; Palomino-Ovando, M. A.; Pérez-Rodríguez, F.

    2013-03-01

    We investigate the vibrational properties of superlattices with layers of rubber and polyurethane foam, which can be either conventional or auxetic. Phononic dispersion calculations show a second pass band for transverse modes inside the lowest band gap of the longitudinal modes. In such a band, the superlattices behave as a double-negative elastic metamaterial since the effective dynamic mass density and shear modulus are both negative. The pass band is associated to a Fabry-Perot resonance band which turns out to be very narrow as a consequence of the high contrast between the acoustic impedances of the superlattice components.

  5. Physical properties of ferroelectric superlattice A3/B3 system in electric field

    Institute of Scientific and Technical Information of China (English)

    Jiang Wei; Lo Veng-Cheong; Bai Bao-Dong

    2005-01-01

    Based on the differential operator technique, a transverse Ising model (TIM) in the effective-field theory is developed to study the physical properties of a ferroelectric superlattice A3/B3 system. The effects of an external electric field on the polarization, susceptibility and pyroelectric coefficient of the ferroelectric superlattice A3/B3 system are discussed in detail. The susceptibility of the ferroelectric superlattice A3/B3 system decreases with the increase of the electric field, implying that the polarization is weak.

  6. 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.

  7. 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...

  8. Effect of the degree of disorder on electronic and optical properties in random superlattices

    Science.gov (United States)

    Wang, E. G.; Su, W. P.; Ting, C. S.

    1994-01-01

    A three-dimensional tight-binding calculation is developed and used to study disorder effects in a realistic random superlattice. With increasing disorder, a tendency of possible indirect-direct band-gap transition is suggested. Direct evidence of mobility edges between localized and extended states in three-dimensional random systems is given. As system disorder increases, the optical absorption intensities increase dramatically from five to forty-five times stronger than the ordered (GaAs)(sub 1)/(AlAs)(sub 1) superlattice. It is believed that the degree of disorder significantly affects electronic and optical properties of GaAs/AlAs random superlattices.

  9. 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.

  10. 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.

  11. 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.

  12. 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.

  13. 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.

  14. Commensurability oscillations in a two-dimensional lateral superlattice

    Science.gov (United States)

    Davies, John; Long, Andrew; Grant, David; Chowdhury, Suja

    2000-03-01

    We have calculated and measured conduction in a two-dimensional electron gas subject to a weak two-dimensional periodic potential and a normal magnetic field. Simulations with a potential Vx \\cos(2π x/a) + Vy \\cos(2π y/a) show the usual commensurability oscillations in ρ_xx(B) with Vx alone. The introduction of Vy suppresses these oscillations, rather than introducing the additional oscillations in ρ_yy(B) expected from previous perturbation theories. We explain this in terms of drift of the guiding center of cyclotron motion along contours of an effective potential: open orbits of the guiding center contribute to conduction but closed orbits do not. All orbits are closed in a symmetric superlattice with |V_x| = |V_y| and commensurability oscillations are therefore quenched. Experiments on etched superlattices confirm this picture. Conventional lattice-matched samples give a symmetric potential and weak oscillations; the symmetry is broken by the piezoelectric effect in stressed samples, leading to strong oscillations. Periodic modulation of the magnetic field can be treated in the same way, which explains previous experimental results.

  15. Magnetic domain wall energy in Ni/Co superlattices

    Energy Technology Data Exchange (ETDEWEB)

    Toyoki, Kentaro; Nishimura, Takashi; Harimoto, Shotaro; Shiratsuchi, Yu, E-mail: shiratsuchi@mat.eng.osaka-u.ac.jp; Nakatani, Ryoichi

    2014-12-15

    The magnetic domain wall energy density σ{sub W} of a Ni/Co superlattice possessing perpendicular magnetic anisotropy was determined using the magnetic domain theory derived by Kooy and Enz (1960). To determine σ{sub W}, we obtained the saturation magnetization, magnetic domain period, and perpendicular magnetic anisotropy energy by individual measurements. Using the magnetic domain period and the ferromagnetic layer thickness, we first determined the dipolar length. The estimated dipolar length was about 15–25 nm, which is in good agreement with the change in the magnetization curve with the ferromagnetic layer thickness. By using the dipolar length and saturation magnetization, the σ{sub W} was calculated to be 4–7 erg/cm{sup 2}. - Highlights: • Magnetic domain wall energy of a Ni/Co superlattice was determined experimentally. • The magnetic domain wall energy was estimated to be 4–8 erg/cm{sup 2}. • Using estimated value, the magnetization curves were reproduced well. • The estimated value is reasonable compared with the other ferromagnetic materials.

  16. Artificially engineered Heusler ferrimagnetic superlattice exhibiting perpendicular magnetic anisotropy

    Science.gov (United States)

    Ma, Q. L.; Zhang, X. M.; Miyazaki, T.; Mizukami, S.

    2015-01-01

    To extend density limits in magnetic recording industry, two separate strategies were developed to build the storage bit in last decade, introduction of perpendicular magnetic anisotropy (PMA) and adoption of ferrimagnetism/antiferromagnetism. Meanwhile, these properties significantly improve device performance, such as reducing spin-transfer torque energy consumption and decreasing signal-amplitude-loss. However, materials combining PMA and antiferromagnetism rather than transition-metal/rare-earth system were rarely developed. Here, we develop a new type of ferrimagnetic superlattice exhibiting PMA based on abundant Heusler alloy families. The superlattice is formed by [MnGa/Co2FeAl] unit with their magnetizations antiparallel aligned. The effective anisotropy (Kueff) over 6 Merg/cm3 is obtained, and the SL can be easily built on various substrates with flexible lattice constants. The coercive force, saturation magnetization and Kueff of SLs are highly controllable by varying the thickness of MnGa and Co2FeAl layers. The SLs will supply a new choice for magnetic recording and spintronics memory application such as magnetic random access memory.

  17. 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.

  18. 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.

  19. Artificially engineered Heusler ferrimagnetic superlattice exhibiting perpendicular magnetic anisotropy.

    Science.gov (United States)

    Ma, Q L; Zhang, X M; Miyazaki, T; Mizukami, S

    2015-01-19

    To extend density limits in magnetic recording industry, two separate strategies were developed to build the storage bit in last decade, introduction of perpendicular magnetic anisotropy (PMA) and adoption of ferrimagnetism/antiferromagnetism. Meanwhile, these properties significantly improve device performance, such as reducing spin-transfer torque energy consumption and decreasing signal-amplitude-loss. However, materials combining PMA and antiferromagnetism rather than transition-metal/rare-earth system were rarely developed. Here, we develop a new type of ferrimagnetic superlattice exhibiting PMA based on abundant Heusler alloy families. The superlattice is formed by [MnGa/Co2FeAl] unit with their magnetizations antiparallel aligned. The effective anisotropy (K(u)(eff)) over 6 Merg/cm(3) is obtained, and the SL can be easily built on various substrates with flexible lattice constants. The coercive force, saturation magnetization and K(u)(eff) of SLs are highly controllable by varying the thickness of MnGa and Co2FeAl layers. The SLs will supply a new choice for magnetic recording and spintronics memory application such as magnetic random access memory.

  20. VC/TiC超晶格薄膜的微结构及超硬效应%Microstructure and superhardness effect of VC/TiC superlattice films

    Institute of Scientific and Technical Information of China (English)

    董学超; 岳建岭; 王恩青; 李淼磊; 李戈扬

    2015-01-01

    Vanadium carbide/titanium carbide (VC/TiC) superlattice films were synthesized by magnetron sputtering method. The effects of modulation period on the microstructure evolution and mechanical properties were investigated by EDXA, XRD, HRTEM and nano-indentation. The results reveal that the VC/TiC superlattice films form an epitaxial structure when their modulation period is less than a critical value, accompanied with a remarkable increase in hardness. Further increasing the modulation period, the hardness of superlattices decreases slowly to the rule-of-mixture value due to the destruction of epitaxial structures. The XRD results reveal that three-directional strains are generated in superlattices when the epitaxial structure is formed, which may change the modulus of constituent layers. This may explain the remarkable hardness enhancement of VC/TiC superlattices.%采用磁控溅射工艺制备VC/TiC超晶格薄膜,并采用EDXA、XRD、HRTEM和纳米力学探针研究调制周期对超晶格薄膜的微结构和力学性能的影响。研究结果表明,当超晶格薄膜的调制周期低于临界厚度时,制备的VC/TiC超晶格薄膜能够形成共格生长结构,并获得硬度显著提高的超硬效应。然而,随着调制周期的进一步增大,超晶格薄膜的共格结构遭到破坏,导致薄膜的硬度逐渐降低,并最终趋于其组元的混合平均值。XRD结果表明,当形成共格生长结构时,超晶格薄膜内部将产生共格协调应变,从而改变不同调制层的弹性模量,这也是VC/TiC超晶格薄膜能够获得超硬效应的重要原因。

  1. Controlling Nanocrystal Superlattice Symmetry and Shape-Anisotropic Interactions through Variable Ligand Surface Coverage

    KAUST Repository

    Choi, Joshua J.

    2011-03-09

    The assembly of colloidal nanocrystals (NCs) into superstructures with long-range translational and orientational order is sensitive to the molecular interactions between ligands bound to the NC surface. We illustrate how ligand coverage on colloidal PbS NCs can be exploited as a tunable parameter to direct the self-assembly of superlattices with predefined symmetry. We show that PbS NCs with dense ligand coverage assemble into face-centered cubic (fcc) superlattices whereas NCs with sparse ligand coverage assemble into body-centered cubic (bcc) superlattices which also exhibit orientational ordering of NCs in their lattice sites. Surface chemistry characterization combined with density functional theory calculations suggest that the loss of ligands occurs preferentially on {100} than on reconstructed {111} NC facets. The resulting anisotropic ligand distribution amplifies the role of NC shape in the assembly and leads to the formation of superlattices with translational and orientational order. © 2011 American Chemical Society.

  2. 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.

  3. 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...

  4. 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...

  5. High Electric Field Quantum Transport: Submillimeter Wave AC Stark Localization in Vertical and Lateral Superlattices.

    Science.gov (United States)

    2007-11-02

    superlattices. These experiments have opened the arena of photon assisted transport to semiconductor devices and paved the way for future teraherz: electronics based on quantum transport in semiconductor nanostructures.

  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. Huge spin-transfer torque in a magnetic tunnel junction by a superlattice barrier

    Science.gov (United States)

    Chen, C. H.; Tseng, P.; Ko, C. W.; Hsueh, W. J.

    2017-09-01

    Huge spin-transfer torque (STT) in a magnetic tunnel junction (MTJ) achieved by superlattice barrier composed of alternate layers of a nonmagnetic metal and an insulator is proposed. The magnitude of the STT depends on the number of cells in the superlattice barrier and the nonmagnetic metal layer's thickness. The result shows that the STT of the novel superlattice-barrier MTJ can reach values up to four orders of magnitude greater than those of traditional single-barrier stacks based on three cells superlattice by designing the nonmagnetic metal layer's thickness. In addition, the spin-transfer torque of the proposed MTJ can also be thousands of magnitude greater than those of traditional double-barrier MTJs.

  8. Harmonic hexagonal superlattice pattern in a dielectric barrier discharge at atmospheric pressure

    Institute of Scientific and Technical Information of China (English)

    DONG LiFang; XIE WeiXia; ZHAO HaiTao; FAN WeiLi

    2009-01-01

    We report a harmonic hexagonal superlattice pattern in a dielectric barrier discharge in air/argon mixture at atmospheric pressure.The bifurcation scenario of harmonic hexagonal superlattice pattern with the applied voltage increasing is given.The phase diagram of the pattern types as a function of the applied voltage and the air-concentration is obtained.The hysteresis of pattern transitions at the upward and downward stage of the applied voltage is observed.The correlation measurements indicate that harmonic hexagonal superlattice pattern is an interleaving of two different transient sublattices.The spatial power spectrum demonstrates that harmonic hexagonal superlattice pattern has two separate wave vectors.Both small wave vector qh and big wave vector Kh,belong to the harmonic mode,and they obey a triad resonant interaction q1h + q2h,=Kh.

  9. 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.

  10. Interwell and intrawell magnetoexcitons in GaAs/AlGaAs superlattices

    DEFF Research Database (Denmark)

    Timofeev, V. B.; Filin, A. I.; Tartakovskii, A. I.

    1997-01-01

    The formation of spatially indirect (interwell) excitons in superlattices (SLs) with different barrier widths (different tunneling coupling) is experimentally investigated in a strong enough magnetic field with the use of photoluminescence (PL), photoluminescence excitation (PLE), reflectance spec...

  11. 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.

  12. 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...

  13. Mechanical properties of ground state structures in substitutional ordered alloys: High strength, high ductility and high thermal stability

    Energy Technology Data Exchange (ETDEWEB)

    Tawancy, H.M., E-mail: tawancy@kfupm.edu.sa [Center for Engineering Research, Research Institute, King Fahd University of Petroleum and Minerals, KFUPM Box 1639, Dhahran 31261 (Saudi Arabia); Aboelfotoh, M.O., E-mail: oaboelfotoh@gmail.com [Department of Materials Science and Engineering, North Carolina State University, Raleigh, NC 27606 (United States)

    2014-05-01

    We have studied the effect of atom arrangements in the ground state structures of substitutional ordered alloys on their mechanical properties using nickel–molybdenum-based alloys as model systems. Three alloys with nominal compositions of Ni–19.43 at% Mo, Ni–18.53 at% Mo–15.21 at% Cr and Ni–18.72 at% Mo–6.14 at% Nb are included in the study. In agreement with theoretical predictions, the closely related Pt{sub 2}Mo-type, DO{sub 22} and D1{sub a} superlattices with similar energies are identified by electron diffraction of ground state structures, which can directly be derived from the parent disordered fcc structure by minor atom rearrangements on {420}{sub fcc} planes. The three superlattices are observed to coexist during the disorder–order transformation at 700 °C with the most stable superlattice being determined by the exact chemical composition. Although most of the slip systems in the parent disordered fcc structure are suppressed, many of the twinning systems remain operative in the superlattices favoring deformation by twinning, which leads to considerable strengthening while maintaining high ductility levels. Both the Pt{sub 2}Mo-type and DO{sub 22} superlattices are distinguished by high strength and high ductility due to their nanoscale microstructures, which have high thermal stability. However, the D1{sub a} superlattice is found to exhibit poor thermal stability leading to considerable loss of ductility, which has been correlated with self-induced recrystallization by migration of grain boundaries.

  14. 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

  15. Transport in weakly-coupled superlattices: A quantitative approach for photon-assisted tunneling

    DEFF Research Database (Denmark)

    Wacker, Andreas; Jauho, Antti-Pekka

    1997-01-01

    Photon-assisted tunneling is studied in weakly-coupled semiconductor superlattices under THz irradiation. Using a microscopic transport model we find excellent quantitative agreement with experimental data for two different samples without using any fitting parameters.......Photon-assisted tunneling is studied in weakly-coupled semiconductor superlattices under THz irradiation. Using a microscopic transport model we find excellent quantitative agreement with experimental data for two different samples without using any fitting parameters....

  16. 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.

  17. 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.

  18. 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)

  19. Supersolid Phase in One-Dimensional Hard-Core Boson Hubbard Model with a Superlattice Potential

    Institute of Scientific and Technical Information of China (English)

    GUO Huai-Ming; LIANG Ying

    2008-01-01

    The ground state of the one-dimensional hard-core boson Hubbard model with a superlattice potential is studied by quantum Monte Carlo methods. We demonstrate that besides the CDW phase and the Mort insulator phase, the supersolid phase emerges due to the presence of the superlattice potential, which reflects the competition with the hopping term. We also study the densities of sublattices and have a clear idea about the distribution of the bosons on the lattice.

  20. 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).

  1. Controlling Chaos Probability of a Bose-Einstein Condensate in a Weak Optical Superlattice

    Institute of Scientific and Technical Information of China (English)

    XU Jun; LUO Xiao-Bing

    2009-01-01

    @@ The spatial chaos probability of a Bose-Einstein condensate perturbed by a weak optical superlattice is studied. It is demonstrated that the spatial chaotic solution appears with a certain probability in a given parameter region under a random boundary condition. The effects of the lattice depths and wave vectors on the chaos probability are illustrated, and different regions associated with different chaos probabilities are found. This suggests a feasible scheme for suppressing and strengthening chaos by adjusting the optical superlattice experimentally.

  2. 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.

  3. Minority Carrier Lifetime in Beryllium-Doped InAs/InAsSb Strained Layer Superlattices

    Science.gov (United States)

    2014-06-03

    SECURITY CLASSIFICATION OF: Minority carrier lifetimes in undoped and Beryllium -doped Type-2 Ga-free, InAs/InAsSb strained layer superlattices (SLS) with...is unlimited. Minority Carrier Lifetime in Beryllium -Doped InAs/InAsSb Strained Layer Superlattices The views, opinions and/or findings contained in...Brook University W-5510 Melville Library West Sayville, NY 11796 -3362 1 ABSTRACT Minority Carrier Lifetime in Beryllium -Doped InAs/InAsSb Strained

  4. 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.

  5. Molecular dynamics study of the lattice thermal conductivity of Kr/Ar superlattice nanowires

    Energy Technology Data Exchange (ETDEWEB)

    Chen Yunfei; Li Deyu; Yang Juekuan; Wu Yonghua; Lukes, J.R.; Majumdar, Arun

    2004-06-15

    The nonequilibrium molecular dynamics (NEMD) method has been used to calculate the lattice thermal conductivities of Ar and Kr/Ar nanostructures in order to study the effects of interface scattering, boundary scattering, and elastic strain on lattice thermal conductivity. Results show that interface scattering poses significant resistance to phonon transport in superlattices and superlattice nanowires. The thermal conductivity of the Kr/Ar superlattice nanowire is only about ((1)/(3)) of that for pure Ar nanowires with the same cross-sectional area and total length due to the additional interfacial thermal resistance. It is found that nanowire boundary scattering provides significant resistance to phonon transport. As the cross-sectional area increases, the nanowire boundary scattering decreases, which leads to increased nanowire thermal conductivity. The ratio of the interfacial thermal resistance to the total effective thermal resistance increases from 30% for the superlattice nanowire to 42% for the superlattice film. Period length is another important factor affecting the effective thermal conductivity of the nanostructures. Increasing the period length will lead to increased acoustic mismatch between the adjacent layers, and hence increased interfacial thermal resistance. However, if the total length of the superlattice nanowire is fixed, reducing the period length will lead to decreased effective thermal conductivity due to the increased number of interfaces. Finally, it is found that the interfacial thermal resistance decreases as the reference temperature increases, which might be due to the inelastic interface scattering.

  6. Transport in semiconductor nanowire superlattices described by coupled quantum mechanical and kinetic models.

    Science.gov (United States)

    Alvaro, M; Bonilla, L L; Carretero, M; Melnik, R V N; Prabhakar, S

    2013-08-21

    In this paper we develop a kinetic model for the analysis of semiconductor superlattices, accounting for quantum effects. The model consists of a Boltzmann-Poisson type system of equations with simplified Bhatnagar-Gross-Krook collisions, obtained from the general time-dependent Schrödinger-Poisson model using Wigner functions. This system for superlattice transport is supplemented by the quantum mechanical part of the model based on the Ben-Daniel-Duke form of the Schrödinger equation for a cylindrical superlattice of finite radius. The resulting energy spectrum is used to characterize the Fermi-Dirac distribution that appears in the Bhatnagar-Gross-Krook collision, thereby coupling the quantum mechanical and kinetic parts of the model. The kinetic model uses the dispersion relation obtained by the generalized Kronig-Penney method, and allows us to estimate radii of quantum wire superlattices that have the same miniband widths as in experiments. It also allows us to determine more accurately the time-dependent characteristics of superlattices, in particular their current density. Results, for several experimentally grown superlattices, are discussed in the context of self-sustained coherent oscillations of the current density which are important in an increasing range of current and potential applications.

  7. 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.

  8. 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...

  9. Demonstration of long minority carrier lifetimes in very narrow bandgap ternary InAs/GaInSb superlattices

    Science.gov (United States)

    Haugan, H. J.; Brown, G. J.; Olson, B. V.; Kadlec, E. A.; Kim, J. K.; Shaner, E. A.

    2015-09-01

    Minority carrier lifetimes in very long wavelength infrared (VLWIR) InAs/GaInSb superlattices (SLs) are reported using time-resolved microwave reflectance measurements. A strain-balanced ternary SL absorber layer of 47.0 Å InAs/21.5 Å Ga0.75In0.25Sb, corresponding to a bandgap of ˜50 meV, is found to have a minority carrier lifetime of 140 ± 20 ns at ˜18 K. This lifetime is extraordinarily long, when compared to lifetime values previously reported for other VLWIR SL detector materials. This enhancement is attributed to the strain-engineered ternary design, which offers a variety of epitaxial advantages and ultimately leads to a reduction of defect-mediated recombination centers.

  10. Perspectives from ab-initio and tight-binding: Applications to transition metal compounds and superlattices

    Science.gov (United States)

    Venkataraman, Vijay Shankar

    The experimental and theoretical study of transition metal compounds have occupied condensed matter physicists for the best part of the last century. The rich variety of physical behaviour exhibited by these compounds owes its origin to the subtle balance of the energy scales at play for the d orbitals. In this thesis, we study three different systems comprised of transition metal atoms from the third, the fourth, and the fifth group of the periodic table using a combination of ab-initio density functional theory (DFT) computations and effective tight-binding models for the electronic properties. We first consider the electronic properties of artificially fabricated perovskite superlattices of the form [(SrIrO3)m / SrTiO3] with integer m denoting the number of layers of SrIrO3. After discussing the results of experiments undertaken by our collaborators, we present the results of our DFT calculations and build tight-binding models for the m = 1 and m = 2 superlattices. The active ingredient is found to be the 5d orbitals with significant spin-orbit coupling. We then study the energies of magnetic ground states within DFT and compare and contrast our results with those obtained for the bulk Ruddlesden-Popper iridates. Together with experimental measurements, our results suggest that these superlattices are an exciting venue to probe the magnetism and metal-insulator transitions that occur from the intricate balance of the spin-orbit coupling and electron interactions, as has been reported for their bulk counterparts. Next, we consider alpha-RuCl3, a honeycomb lattice compound. We first show using DFT calculations in conjunction with experiments performed by our collaborators, how spin-orbit coupling in the 4d orbitals of Ru is essential to understand the insulating state realized in this compound. Then, in the latter half of the chapter, we study the magnetic ground states of a two-dimensional analogue of alpha-RuCl3 in weak and strong-coupling regimes obtained from

  11. 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.

  12. Strain Engineering of the Band Gap of HgTe Quantum Wells Using Superlattice Virtual Substrates

    Science.gov (United States)

    Leubner, Philipp; Lunczer, Lukas; Brüne, Christoph; Buhmann, Hartmut; Molenkamp, Laurens W.

    2016-08-01

    The HgTe quantum well (QW) is a well-characterized two-dimensional topological insulator (2D TI). Its band gap is relatively small (typically on the order of 10 meV), which restricts the observation of purely topological conductance to low temperatures. Here, we utilize the strain dependence of the band structure of HgTe QWs to address this limitation. We use CdTe-Cd 0.5Zn0.5Te strained-layer superlattices on GaAs as virtual substrates with adjustable lattice constant to control the strain of the QW. We present magnetotransport measurements, which demonstrate a transition from a semimetallic to a 2D-TI regime in wide QWs, when the strain is changed from tensile to compressive. Most notably, we demonstrate a much enhanced energy gap of 55 meV in heavily compressively strained QWs. This value exceeds the highest possible gap on common II-VI substrates by a factor of 2-3, and extends the regime where the topological conductance prevails to much higher temperatures.

  13. Lattice relaxation and ferromagnetic character of (LaVO3)m/SrVO3 superlattices

    KAUST Repository

    Schuster, Cosima B.

    2013-08-01

    The experimental observation that vanadate superlattices (LaVO 3)m/SrVO3 show ferromagnetism up to room temperature (Lüders U. et al., Phys. Rev. B, 80 (2009) 241102(R)) is investigated by means of density functional theory, and the band structure for m = 5 and 6 is calculated. A buckling of the interface VO2 layers is found in both cases, but subtle differences in bond length lead to very different properties for even and odd values of m: in the even case, the two interface VO2 layers effectively decouple from the adjacent LaO layers due to a strong bond length enhancement. This results into a local inversion of the orbital occupancy and to the confinement of the charge carriers. In the odd case, the amplitude of the bond length variation is smaller, so that the charge carriers spill into the deeper-lying VO2 layers, and spin-polarised interfaces are obtained. © Copyright EPLA, 2013.

  14. 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.

  15. 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.

  16. Dynamical Axion Field in a Magnetic Topological Insulator Superlattice

    Science.gov (United States)

    Wang, Jing; Lian, Biao; Zhang, Shou-Cheng

    We propose that the dynamical axion field can be realized in a magnetic topological insulator superlattice or a topological paramagnetic insulator. The magnetic fluctuations of these systems produce a pseudoscalar field which has an axionic coupling to the electromagnetic field, and thus it gives a condensed-matter realization of the axion electrodynamics. Compared to the previously proposed dynamical axion materials where a long range antiferromagnetic order is required, the systems proposed here have the advantage that only an uniform magnetization or a paramagnetic state is needed for the dynamic axion. We further propose several experiments to detect such a dynamical axion field. This work is supported by the US Department of Energy, Office of Basic Energy Sciences, Division of Materials Sciences and Engineering, under Contract No. DE-AC02-76SF00515.

  17. Kinetics of electron transfer from photoexcited superlattice electrodes

    Energy Technology Data Exchange (ETDEWEB)

    Nozik, A.J.; Turner, J.A.; Peterson, M.W.

    1988-05-05

    A kinetic model has been developed that quantitatively describes electron transfer from photoexcited superlattice electrodes into liquid solutions. The model permits electron transfer from all quantum levels as well as from surface states; it also takes into account recombination in the bulk, space charge layer, and surfaces states, and band-edge movement. The model calculations define the values of the rate constants for heterogeneous electron transfer and hot electron thermalization among the various energy levels in the supperlattice quantum wells that are necessary to achieve hot electron transfer from excited quantum states. The question of whether hot electron transfer is manifested by a dependence of the photocurrent action spectra on acceptor redox potential is examined in detail.

  18. Plasmon modes of a massive Dirac plasma, and their superlattices

    Science.gov (United States)

    Sachdeva, Rashi; Thakur, Anmol; Vignale, Giovanni; Agarwal, Amit

    2015-05-01

    We explore the collective density oscillations of a collection of charged massive Dirac particles, in one, two, and three dimensions, and their one-dimensional (1D) superlattice. We calculate the long-wavelength limit of the dynamical polarization function analytically, and use the random phase approximation to obtain the plasmon dispersion. The density dependence of the long-wavelength plasmon frequency in massive Dirac systems is found to be different compared to systems with parabolic and gapless Dirac dispersion. We also calculate the long-wavelength plasmon dispersion of a 1D metamaterial made from 1D and 2D massive Dirac plasma. Our analytical results will be useful for exploring the use of massive Dirac materials as electrostatically tunable plasmonic metamaterials and can be experimentally verified by infrared spectroscopy, as in the case of graphene [L. Ju et al., Nat. Nanotechnol. 6, 630 (2011), 10.1038/nnano.2011.146].

  19. Electronic and magnetic properties of zincblende half-metal superlattices

    Energy Technology Data Exchange (ETDEWEB)

    Fong, C Y; Qian, M C; Pask, J; Yang, L H; Dag, S

    2003-11-05

    Zincblende half-metallic compounds such as CrAs, with large magnetic moments and high Curie temperatures, are promising materials for spintronic applications. They explore layered materials, consisting of alternating layers of zincblende half-metals, by first principles calculations, and find that superlattices of (CrAs){sub 1}(MnAs){sub 1} and (CrAs){sub 2}(MnAs){sub 2} are half-metallic with magnetic moments of 7.0{mu}{sub B} and 14.0{mu}{sub B} per unit cell, respectively. They discuss the nature of the bonding and half-metallicity in these materials and, based on the understanding acquired, develop a simple expression for the magnetic moment in such materials. They explore the range of lattice constants over which half-metallicity is manifested, and suggest corresponding substrates for growth in thin film form.

  20. Optical Studies on Antimonide Superlattice Infrared Detector Material

    Science.gov (United States)

    Hoglund, Linda; Soibel, Alexander; Hill, Cory J.; Ting, David Z.; Khoshakhlagh, Arezou; Liao, Anna; Keo, Sam; Lee, Michael C.; Nguyen, Jean; Mumolo, Jason M.; hide

    2010-01-01

    In this study the material quality and optical properties of type II InAs/GaSb superlattices are investigated using transmission and photoluminescence (PL) spectroscopy. The influence of the material quality on the intensity of the luminescence and on the electrical properties of the detectors is studied and a good correlation between the photodetector current-voltage (IV) characteristics and the PL intensity is observed. Studies of the temperature dependence of the PL reveal that Shockley-Read-Hall processes are limiting the minority carrier lifetime in both the mid-IR wavelength and the long-IR wavelength detector material studied. These results demonstrate that PL spectroscopy is a valuable tool for optimization of infrared detectors.

  1. 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.

  2. 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.

  3. 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.

  4. 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.

  5. 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.

  6. A Study on the Combined Treatment of Cryorolling, Short-Annealing, and Aging for the Development of Ultrafine-Grained Al 6063 Alloy with Enhanced Strength and Ductility

    Science.gov (United States)

    Panigrahi, Sushanta Kumar; Jayaganthan, R.

    2010-10-01

    High-strength ultrafine-grained (UFG) metals and alloys often show a reduced tensile ductility when compared with their coarse-grained counterparts. The earlier attempts in trying to improve their ductility usually have led to sacrificing its strength. Optimized process conditions are proposed to achieve both high strength and high ductility in the Al 6063 alloy in the current work. It involves solution treatment of the Al 6063 alloy to dissolve the second-phase particles, cryorolling (CR) to produce a high density of dislocations, short annealing (SA) treatment to recrystallize partially the microstructure without affecting the age-hardening effect, and finally aging treatment to generate highly dispersed nano precipitates. The solution treatment prior to CR combined with post-CR SA at 428 K (155 °C) for 5 minutes followed by aging treatment at 398 K (125 °C) for 12 hours are the optimum processing conditions to obtain the UFG microstructure with improved tensile strength (286 MPa) and good tensile ductility (14 pct) in the Al 6063 alloy. It is observed that the accumulation of dislocations and the formation of nanosized precipitates are responsible for improving the strength, whereas both a low dislocation density and a high density of nanosized precipitates contribute to the improvement in ductility of the CR Al 6063 alloy subjected to an optimized treatment of short annealing and aging.

  7. Bonding strength of resin cement to silicate glass ceramics for dental CAD/CAM systems is enhanced by combination treatment of the bonding surface.

    Science.gov (United States)

    Shimakura, Yusuke; Hotta, Yasuhiro; Fujishima, Akihiro; Kunii, Jun; Miyazaki, Takashi; Kawawa, Tadaharu

    2007-09-01

    To increase the bond strength of CAD/CAM-fabricated, leucite-reinforced glass ceramics with a resin cement, the effects of the following were investigated: surface modification by tribochemical (TBC) treatment, followed by combined application of a silane coupling agent and a functional monomer as a primer. Bond strength was evaluated by a shear bond test. It was found that a silane coupling agent was useful for all the surfaces, particularly for the TBC-treated surface. This was because of the presence of a silica layer on the modified surface. The combination of a silane coupling agent and a functional monomer on the TBC surface allowed marked improvement in bonding, whereby the bonding endured 20,000 cycles of thermal cycling. Therefore, TBC treatment in combination with a silane coupling agent and a functional monomer as a primer substantially increased the bond strength of CAD/CAM-fabricated glass ceramics with resin cement, if the treatment conditions were appropriate.

  8. High-density carbon nanotube wet-laid buckypapers with enhanced strength and conductivity using a high-pressure homogenization process

    Energy Technology Data Exchange (ETDEWEB)

    Choi, Jun; Jang, Si Hoon; Park, No Hyung; Jeong, Won Young; Lim, Dae Young [Human and Culture Convergence Technology Group, Korea Institute of Industrial Technology (KITECH), Ansan (Korea, Republic of); Oh, Jun Young; Yang, Seung Jae [Dept. of Applied Organic Materials Engineering, Inha University, Incheon (Korea, Republic of)

    2017-04-15

    In this work, we prepared homogeneously dispersed carbon nanotubes in water using a high-pressure homogenizer, while high-density carbon nanotube buckypapers were prepared by wet-laid process. The strength and conductivity of the buckypaper were increased dramatically after the high-pressure homogenization because of the increased density and uniformity of the paper. In addition, the buckypapers containing various additives and treated with SOCl{sub 2} exhibited further increase of strength and conductivity resulting from the binding and the p-type doping effect. The buckypapers with high electrical conductivity exhibited superior electromagnetic interference shielding effectiveness that could be applied for structural shielding materials.

  9. 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

  10. Enhancement of temporal coherence via time-periodic coupling strength in a scale-free network of stochastic Hodgkin-Huxley neurons

    Science.gov (United States)

    Yilmaz, Ergin; Baysal, Veli; Ozer, Mahmut

    2015-08-01

    We investigate the effects of time-periodic coupling strength on the temporal coherence or firing regularity of a scale-free network consisting of stochastic Hodgkin-Huxley (H-H) neurons. The temporal coherence exhibits a resonance-like behavior depending on the cell size or the channel noise intensity. The best temporal coherence requires an optimal channel noise intensity, and this coherence can be significantly increased by time-periodic coupling strength when its frequency matches the integer multiples of the intrinsic subthreshold oscillation frequency of H-H neuron. Particularly, we find the multiple-coherence resonance depending on frequency of time-periodic coupling strength at the optimal noise intensity. We also obtain a resonance-like dependence of temporal coherence on the amplitude of time-periodic coupling strength. Additionally, we investigate the effects of average degree on the temporal coherence and find that the temporal coherence exhibits a resonance-like behavior with respect to the network average degree, indicating that the best regularity requires an optimal average degree.

  11. Dispersion relation for localized magnetic polaritons propagating at the junction of two ferromagnetic/ non-magnetic superlattices

    Indian Academy of Sciences (India)

    R T Tagiyeva

    2004-09-01

    Localized magnetic polaritons are investigated in the systems consisting of two magnetic superlattices, coupled by a ferromagnetic contact layer. The general dispersion relation for localized magnetic polaritons are derived in the framework of the electromagnetic wave theory in the Voigt geometry by the `transfer' matrix method. The numerical calculations were carried out for different parameters of the superlattices and contact layer and then discussed.

  12. 100-Period InGaAsP/InGaP Superlattice Solar Cell with Sub-Bandgap Quantum Efficiency Approaching 80%

    Energy Technology Data Exchange (ETDEWEB)

    Steiner, Myles A [National Renewable Energy Laboratory (NREL), Golden, CO (United States); Sayed, Islam [National Renewable Energy Laboratory (NREL), Golden, CO (United States); Jain, Nikhil [National Renewable Energy Laboratory (NREL), Golden, CO (United States); Geisz, John F [National Renewable Energy Laboratory (NREL), Golden, CO (United States); Bedair, S. M. [North Carolina State University

    2017-08-25

    InGaAsP/InGaP quantum well (QW) structures are promising materials for next generation photovoltaic devices because of their tunable bandgap (1.50-1.80 eV) and being aluminum-free. However, the strain-balance limitations have previously limited light absorption in the QW region and constrained the external quantum efficiency (EQE) values beyond the In0.49Ga0.51P band-edge to less than 25%. In this work, we show that implementing a hundred period lattice matched InGaAsP/InGaP superlattice solar cell with more than 65% absorbing InGaAsP well resulted in more than 2x improvement in EQE values than previously reported strain balanced approaches. In addition, processing the devices with a rear optical reflector resulted in strong Fabry-Perot resonance oscillations and the EQE values were highly improved in the vicinity of these peaks, resulting in a short circuit current improvement of 10% relative to devices with a rear optical filter. These enhancements have resulted in an InGaAsP/InGaP superlattice solar cell with improved peak sub-bandgap EQE values exceeding 75% at 700 nm, an improvement in the short circuit current of 26% relative to standard InGaP devices, and an enhanced bandgap-voltage offset (Woc) of 0.4 V.

  13. 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.

  14. 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.

  15. 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.

  16. Energy landscape of self-assembled superlattices of PbSe nanocrystals.

    Science.gov (United States)

    Quan, Zewei; Wu, Di; Zhu, Jinlong; Evers, Wiel H; Boncella, James M; Siebbeles, Laurens D A; Wang, Zhongwu; Navrotsky, Alexandra; Xu, Hongwu

    2014-06-24

    Self-assembly of nanocrystals (NCs) into superlattices is an intriguing multiscale phenomenon that may lead to materials with novel collective properties, in addition to the unique properties of individual NCs compared with their bulk counterparts. By using different dispersion solvents, we synthesized three types of PbSe NC superlattices--body-centered cubic (bcc), body-centered tetragonal (bct), and face-centered cubic (fcc)--as confirmed by synchrotron small-angle X-ray scattering. Solution calorimetric measurements in hexane show that the enthalpy of formation of the superlattice from dispersed NCs is on the order of -2 kJ/mol. The calorimetric measurements reveal that the bcc superlattice is the energetically most stable polymorph, with the bct being 0.32 and the fcc 0.55 kJ/mol higher in enthalpy. This stability sequence is consistent with the decreased packing efficiency of PbSe NCs from bcc (17.2%) to bct (16.0%) and to fcc (15.2%). The small enthalpy differences among the three polymorphs confirm a closely spaced energy landscape and explain the ease of formation of different NC superlattices at slightly different synthesis conditions.

  17. 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.

  18. Iron supplementation prevents a decline in iron stores and enhances strength performance in elite female volleyball players during the competitive season.

    Science.gov (United States)

    Mielgo-Ayuso, Juan; Zourdos, Michael C; Calleja-González, Julio; Urdampilleta, Aritz; Ostojic, Sergej

    2015-06-01

    The primary aim of this study was to examine the effects of 11 weeks of iron supplementation on hematological and strength markers in elite female volleyball players. Twenty-two volleyball players (aged 27.0 ± 5.6 years) from 2 Spanish First National League teams participated and were counterbalanced into 1 of 2 groups based upon iron status: (i) control group (CG, n = 11); or (ii) iron treatment group (ITG, n = 11), which received 325 mg/day of ferrous sulphate daily. Subjects performed their team's regimen of training or match play every day. Both groups were tested for hematological and strength levels at 2 points: (i) baseline (T0, before preseason) and (ii) 11 weeks later (T11, post-testing). Hematological parameters were serum iron (sFe), serum ferritin (FER), transferrin saturation index (TSI), and hemoglobin (Hb); strength assessments were bench press, military press, half-squat, power clean, clean and jerk, and pull-over. CG experienced a significant decrease (p 0.05). Consequently, in ITG all hematological parameters were significantly greater (p volleyball players during the competitive season.

  19. (InAs)1/(GaSb)1超晶格原子链的第一原理研究%First-principles study of(InAs)1/(GaSb)1 superlattice atomic chains

    Institute of Scientific and Technical Information of China (English)

    孙伟峰

    2012-01-01

    利用第一原理平面波赝势法,对(InAs)1/(GaSb)1超晶格原子链的原子结构、力学特性、电子能带结构、声子结构和光学特性进行研究,并结合密度泛函理论数值原子轨道赝势法和非平衡格林函数法计算量子输运特性.与二维层结构的(InAs)1/(GaSb)1超晶格相比,(InAs)1/(GaSb)1超晶格原子链的能带结构有明显不同,在某些情况下表现为金属能带特性.对理想条件下(InAs)1/(GaSb)1超晶格原子链的力学强度计算表明,该结构可承受的应变高达ε=0.19.通过对声子结构的完整布里渊区分析,研究了(InAs)1/(GaSb)1超晶格原子链的结构稳定性.对两端接触电极为Al纳米线的InAs/GaSb超晶格原子链的电子输运特性计算表明,电导随链长和应变的改变而发生非单调变化.光吸收谱的计算结果表现出在红外波段具有陡峭吸收边,截止波长随超晶格原子链的结构而变化.预计InAs/GaSb超晶格原子链可应用于红外光电子纳米器件,通过改变超晶格原子链的结构来调节光电响应波段.%The atomic structure,the mechanical properties,the electronic band structure,and the phonon structure of(InAs)1/(GaSb)1 superlattice atomic chain are investigated by first-principles pseudopotential plane wave method,and the quantum transport properties are also calculated by the density functional theory numerical atomic orbit pseudopotential method in combination with nonequilibrium Green’s function formalism.Compared with two-dimensional layer structural(InAs)1/(GaSb)1 superlattice,the(InAs)1/(GaSb)1 superlattice atomic chains have obviously different band structures,and represent metal energy band characteristics in certain conditions. The calculated mechanical strength of(InAs)1/(GaSb)1 superlattice atomic chains indicates that such structures can sustain the strain as high asε= 0.19.The structural stability of

  20. Crossover from incoherent to coherent phonon scattering in epitaxial oxide superlattices

    Science.gov (United States)

    Ravichandran, Jayakanth; Yadav, Ajay K.; Cheaito, Ramez; Rossen, Pim B.; Soukiassian, Arsen; Suresha, S. J.; Duda, John C.; Foley, Brian M.; Lee, Che-Hui; Zhu, Ye; Lichtenberger, Arthur W.; Moore, Joel E.; Muller, David A.; Schlom, Darrell G.; Hopkins, Patrick E.; Majumdar, Arun; Ramesh, Ramamoorthy; Zurbuchen, Mark A.

    2014-02-01

    Elementary particles such as electrons or photons are frequent subjects of wave-nature-driven investigations, unlike collective excitations such as phonons. The demonstration of wave-particle crossover, in terms of macroscopic properties, is crucial to the understanding and application of the wave behaviour of matter. We present an unambiguous demonstration of the theoretically predicted crossover from diffuse (particle-like) to specular (wave-like) phonon scattering in epitaxial oxide superlattices, manifested by a minimum in lattice thermal conductivity as a function of interface density. We do so by synthesizing superlattices of electrically insulating perovskite oxides and systematically varying the interface density, with unit-cell precision, using two different epitaxial-growth techniques. These observations open up opportunities for studies on the wave nature of phonons, particularly phonon interference effects, using oxide superlattices as model systems, with extensive applications in thermoelectrics and thermal management.

  1. 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.

  2. The Tip-Induced Twisted Bilayer Graphene Superlattice on HOPG: Capillary Attraction Effect

    CERN Document Server

    Yin, Long Jing; Feng, Ke Ke; Dou, Rui-Fen; Nie, Jia-Cai

    2014-01-01

    We use the tip of the scanning tunneling microscope (STM) to manipulate single weakly bound nanometer-sized sheets on the the highly oriented pyrolytic graphite (HOPG) surface through artifically increasing the tip and sample interaction in humid environment. By this means it is possible to tear apart a graphite sheet againt a step and fold this part onto the HOPG surface and thus generate the gaphene superlattices with hexagonal symmetry. The tip and sample surface interactions, including the van der Waals force, eletrostatic force and capillary attraction force originating from the Laplace pressure due to the formation of a highly curved fluid meniscus connecting the tip and sample, are discussed in details to understand the fromation mechnism of graphen superlattice induced by the STM tip. Especially, the capillary force is the key role in manipulating the graphite surface sheet in the hunmidity condition. Our approach may provides a simple and feasible route to prepare the controllable superlattices and g...

  3. 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}{\

  4. Bulk elastic waves with unidirectional backscattering-immune topological states in a time-dependent superlattice

    Energy Technology Data Exchange (ETDEWEB)

    Swinteck, N., E-mail: swinteck@email.arizona.edu; Matsuo, S.; Runge, K.; Lucas, P.; Deymier, P. A. [Department of Materials Science and Engineering, University of Arizona, Tucson, Arizona 85721 (United States); Vasseur, J. O. [Institut d' Electronique, de Micro-électronique et de Nanotechnologie, UMR CNRS 8520, Cité Scientifique, 59652 Villeneuve d' Ascq Cedex (France)

    2015-08-14

    Recent progress in electronic and electromagnetic topological insulators has led to the demonstration of one way propagation of electron and photon edge states and the possibility of immunity to backscattering by edge defects. Unfortunately, such topologically protected propagation of waves in the bulk of a material has not been observed. We show, in the case of sound/elastic waves, that bulk waves with unidirectional backscattering-immune topological states can be observed in a time-dependent elastic superlattice. The superlattice is realized via spatial and temporal modulation of the stiffness of an elastic material. Bulk elastic waves in this superlattice are supported by a manifold in momentum space with the topology of a single twist Möbius strip. Our results demonstrate the possibility of attaining one way transport and immunity to scattering of bulk elastic waves.

  5. Lattice Thermal Conductivity of Superlattices from an Adiabatic Bond Charge Model

    Science.gov (United States)

    Ward, Alistair; Broido, David

    2007-03-01

    The adiabatic bond charge model (ABCM) has successfully rendered phonon dispersions of a host of bulk semiconductors [1,2] and has also been used to calculate the phonon dispersions in quantum well superlattices [3]. We have developed an ABCM for superlattices and combined it with a symmetry-based representation of the anharmonic interatomic forces to calculate the lattice thermal conductivity of short-period superlattices, using an iterative solution to the Boltzmann-Peierls equation [4]. We compare our ABCM results with those obtained from some commonly used models for the interatomic forces in semiconductors to assess the importance of accurate descriptions of the phonon dispersions in thermal conductivity calculations. [1] W. Weber, Physical Review B 15, 4789 (1977). [2] K. C. Rustagi and W. Weber, Solid State Communications 18, 673 (1976). [3] S. K. Yip and Y. C. Chang, Physical Review B 30 7037 (1984). [4] D. A. Broido, A. Ward, and N. Mingo, Physical Review B 72, 014308 (2005).

  6. 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.

  7. Nanoscale form dictates mesoscale function in plasmonic DNA–nanoparticle superlattices

    Energy Technology Data Exchange (ETDEWEB)

    Ross, Michael B.; Ku, Jessie C.; Vaccarezza, Victoria M.; Schatz, George C.; Mirkin , Chad A. (NWU)

    2016-06-15

    The nanoscale manipulation of matter allows properties to be created in a material that would be difficult or even impossible to achieve in the bulk state. Progress towards such functional nanoscale architectures requires the development of methods to precisely locate nanoscale objects in three dimensions and for the formation of rigorous structure–function relationships across multiple size regimes (beginning from the nanoscale). Here, we use DNA as a programmable ligand to show that two- and three-dimensional mesoscale superlattice crystals with precisely engineered optical properties can be assembled from the bottom up. The superlattices can transition from exhibiting the properties of the constituent plasmonic nanoparticles to adopting the photonic properties defined by the mesoscale crystal (here a rhombic dodecahedron) by controlling the spacing between the gold nanoparticle building blocks. Furthermore, we develop a generally applicable theoretical framework that illustrates how crystal habit can be a design consideration for controlling far-field extinction and light confinement in plasmonic metamaterial superlattices.

  8. 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.

  9. Effect of roughness on perpendicular magnetic anisotropy in (Co90Fe10/Pt)n superlattices

    Science.gov (United States)

    Qiu, Jinjun; Meng, Zhaoliang; Yang, Yi; Ying, Ji Feng; Yap, Qi Jia; Han, Guchang

    2016-05-01

    Superlattice [Co90Fe10(0.21)/Pt(0.23)]n (unit in nm) with the repeat cycles n ranging from 3 to 30 were studied. Both effective anisotropy (Keff) and PMA constant (KU) reached a maximum at n=8. When the 3 nm Pt underlayer was deposited at low energy condition, the Keff and KU of (CoFe/Pt)8 are 4.0 and 6.1 Merg/cc, respectively. On the other hand, the Keff and KU increased to 6.8 and 9.7 Merg/cc, respectively, when the Pt underlayer deposited at high energy condition. As the n increases, the surface roughness monotonously increases and d111 inside the superlattice layers increase and relax from bottom to top part. The interface roughness and relaxation in superlattice reduce the PMA considerably.

  10. Effect of roughness on perpendicular magnetic anisotropy in (Co90Fe10/Ptn superlattices

    Directory of Open Access Journals (Sweden)

    Jinjun Qiu

    2016-05-01

    Full Text Available Superlattice [Co90Fe10(0.21/Pt(0.23]n (unit in nm with the repeat cycles n ranging from 3 to 30 were studied. Both effective anisotropy (Keff and PMA constant (KU reached a maximum at n=8. When the 3 nm Pt underlayer was deposited at low energy condition, the Keff and KU of (CoFe/Pt8 are 4.0 and 6.1 Merg/cc, respectively. On the other hand, the Keff and KU increased to 6.8 and 9.7 Merg/cc, respectively, when the Pt underlayer deposited at high energy condition. As the n increases, the surface roughness monotonously increases and d111 inside the superlattice layers increase and relax from bottom to top part. The interface roughness and relaxation in superlattice reduce the PMA considerably.

  11. Influence of field strength, coil type and image resolution on assessment of synovitis by unenhanced MRI--a comparison with contrast-enhanced MRI

    DEFF Research Database (Denmark)

    Eshed, Iris; Krabbe, Simon; Østergaard, Mikkel

    2015-01-01

    OBJECTIVES: To explore if the reliability of synovitis assessment by unenhanced MRI is influenced by different MRI field-strengths, coil types and image resolutions in RA patients. METHODS: Forty-one RA patients and 12 healthy controls underwent hand MRI (wrist and 2(nd)--5(th) metacarpophalangeal...... was very high per person (0.80--1.0), and moderate-high per joint (0.63--0.85), whereas exact agreements on scores were moderate (0.50--0.66). The intrareader agreement (15 patients and 3 controls) on presence/absence of synovitis was very high (0.87--1.0). CONCLUSIONS: Unenhanced MRI using STIR sequence...

  12. Modeling functional piezoelectricity in perovskite superlattices with competing instabilities

    Science.gov (United States)

    Swartz, Charles; Wu, Xifan

    2012-02-01

    Multi-component Perovskite Superlattices (SLs) of the form ABO3, provide a very promising avenue for the design of materials with multifunctional properties. Furthermore the interfaces of such multi-component SLs are home to competing anti-ferrodistortive and ferroelectric instabilities which can produce unexpected functionalities. However, at present first principles calculations exceeding more than 10 units cells, are particularly costly as they scale with the valence electrons as N^3. We present a first-principles modeling technique that allows us to accurately model the piezoelectric strains of paraelectric/ferroelectric SLs, BaTiO3/CaTiO3 and PbTiO3/SrTiO3, under a fixed displacement field. The model is based on a maximally localized wannier center layer polarization technique, as well as a truncated cluster expansion, that makes use of the fact that such PE/FE SLs have been shown to have highly localized ionic and electronic interface effects. The prediction of the piezoelectricity for a SL of an arbitrary stacking sequence will be demonstrated. We also use our model to conduct a systemic study of the interface effects on piezoelectric response in the above SLs paying special attention to a strong non-linear effect observed in Bulk SrTiO3.

  13. ``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.

  14. Artificial charge-modulationin atomic-scale perovskite titanate superlattices.

    Science.gov (United States)

    Ohtomo, A; Muller, D A; Grazul, J L; Hwang, H Y

    2002-09-26

    The nature and length scales of charge screening in complex oxides are fundamental to a wide range of systems, spanning ceramic voltage-dependent resistors (varistors), oxide tunnel junctions and charge ordering in mixed-valence compounds. There are wide variations in the degree of charge disproportionation, length scale, and orientation in the mixed-valence compounds: these have been the subject of intense theoretical study, but little is known about the microscopic electronic structure. Here we have fabricated an idealized structure to examine these issues by growing atomically abrupt layers of LaTi(3+)O(3) embedded in SrTi(4+)O(3). Using an atomic-scale electron beam, we have observed the spatial distribution of the extra electron on the titanium sites. This distribution results in metallic conductivity, even though the superlattice structure is based on two insulators. Despite the chemical abruptness of the interfaces, we find that a minimum thickness of five LaTiO(3) layers is required for the centre titanium site to recover bulk-like electronic properties. This represents a framework within which the short-length-scale electronic response can be probed and incorporated in thin-film oxide heterostructures.

  15. Thiol passivation of MWIR type II superlattice photodetectors

    Science.gov (United States)

    Salihoglu, O.; Muti, A.; Aydinli, A.

    2013-06-01

    Poor passivation on photodetectors can result in catastrophic failure of the device. Abrupt termination of mesa side walls during pixel definition generates dangling bonds that lead to inversion layers and surface traps leading to surface leakage currents that short circuit diode action. Good passivation, therefore, is critical in the fabrication of high performance devices. Silicondioxide has been the main stay of passivation for commercial photodetectors, deposited at high temperatures and high RF powers using plasma deposition techniques. In photodetectors based on III-V compounds, sulphur passivation has been shown to replace oxygen and saturate the dangling bonds. Despite its effectiveness, it degrades over time. More effort is required to create passivation layers which eliminate surface leakage current. In this work, we propose the use of sulphur based octadecanethiol (ODT), CH3(CH2)17SH, as a passivation layer for the InAs/GaSb superlattice photodetectors that acts as a self assembled monolayer (SAM). ODT SAMs consist of a chain of 18 carbon atoms with a sulphur atom at its head. ODT Thiol coating is a simple process that consist of dipping the sample into the solution for a prescribed time. Excellent electrical performance of diodes tested confirm the effectiveness of the sulphur head stabilized by the intermolecular interaction due to van der Walls forces between the long chains of ODT SAM which results in highly stable ultrathin hydrocarbon layers without long term degradation.

  16. One-way electromagnetic waveguide using multiferroic Fibonacci superlattices

    Science.gov (United States)

    Tang, Zhenghua; Lei, Dajun; Huang, Jianquan; Jin, Gui; Qiu, Feng; Yan, Wenyan

    2015-12-01

    The multiferroic Fibonacci superlattices (MFSs) are composed of single-phase multiferroic domains with polarization and magnetization according to the rule of Fibonacci sequence. We propose to construct a one-way electromagnetic waveguide by the MFSs. The forbidden band structures of the MFSs for the forward and backward electromagnetic waves are not completely overlapped, and an obvious translation between them occurs around the fixed point ω bar = 1 with broken time-reversal and space inversion symmetries (TRSIS), which indicates the existence of one-way electromagnetic modes in the MFSs. Transmission spectrum is utilized to present this property and to indicate further one-way electromagnetic modes lying within the polaritonic band gap. The maximum forbidden bandwidth (divided by midgap frequency) of 5.4% for the backward electromagnetic wave (BEW) is found, in which the forward electromagnetic wave (FEW) can pass. The functions of one-way propagation modes and polaritonic band gap integrated into the MFSs can miniaturize the one-way photonic devices. The properties can also be applied to construct compact microwave isolators.

  17. Topological hierarchy matters — topological matters with superlattices of defects

    Science.gov (United States)

    He, Jing; Kou, Su-Peng

    2016-11-01

    Topological insulators/superconductors are new states of quantum matter with metallic edge/surface states. In this paper, we review the defects effect in these topological states and study new types of topological matters — topological hierarchy matters. We find that both topological defects (quantized vortices) and non topological defects (vacancies) can induce topological mid-gap states in the topological hierarchy matters after considering the superlattice of defects. These topological mid-gap states have nontrivial topological properties, including the nonzero Chern number and the gapless edge states. Effective tight-binding models are obtained to describe the topological mid-gap states in the topological hierarchy matters. Project supported by the National Basic Research Program of China (Grant Nos. 2011CB921803 and 2012CB921704), the National Natural Science Foundation of China (Grant Nos. 11174035, 11474025, 11404090, and 11674026), the Natural Science Foundation of Hebei Province, China (Grant No. A2015205189), the Hebei Education Department Natural Science Foundation, China (Grant No. QN2014022), and the Specialized Research Fund for the Doctoral Program of Higher Education, China.

  18. Study of Crystals Semiconductors in Superlattices via Quantum Mechanics

    Directory of Open Access Journals (Sweden)

    *1A. L. C. L. Jamshidi

    2013-12-01

    Full Text Available This work analyzes, from the effects related to the processes of transportation of carrier and the changes in the electronic structure of semiconductors materials due to the presence of defects and disorders in the crystalline net. These defects are located in specific areas of the material and either interact or remain inert. In general, they are described by local wave functions. The study of superlattices of semiconductor crystal considers important parameters such as disorder effects in crystals and the alternate periodic growth of the layer of two semiconductors with different gaps and minigaps energies. The quantum mechanical calculations are applied for determining the physical properties of the semiconductors crystals. This study encompasses the effects of defects and the crystalline disorders evaluation by quantum mechanics. Further, it is discuss the presence of defects in the periodic, quasiperiodic and disordered arrangements. The theoretical approach use to understand the mechanism and the results of experimental techniques in which are characterized the current and optic transportation of a semiconductor crystal.

  19. Angle-dependent bandgap engineering in gated graphene superlattices

    Energy Technology Data Exchange (ETDEWEB)

    García-Cervantes, H.; Sotolongo-Costa, O. [Centro de Investigación en Ciencias, IICBA, Universidad Autónoma del Estado de Morelos, Av. Universidad 1001, Col. Chamilpa, 62209 Cuernavaca, Morelos, México (Mexico); Gaggero-Sager, L. M. [CIICAp, IICBA, Universidad Autónoma del Estado de Morelos, Av. Universidad 1001, Col. Chamilpa, 62209 Cuernavaca, Morelos, México (Mexico); Naumis, G. G. [Instituto Física, Depto. de Física-Química, Universidad Nacional Autónoma de México (UNAM). Apdo. Postal 20-364, 01000, México D.F., México (Mexico); Rodríguez-Vargas, I., E-mail: isaac@fisica.uaz.edu.mx [Centro de Investigación en Ciencias, IICBA, Universidad Autónoma del Estado de Morelos, Av. Universidad 1001, Col. Chamilpa, 62209 Cuernavaca, Morelos, México (Mexico); Unidad Académica de Física, Universidad Autónoma de Zacatecas, Calzada Solidaridad Esquina Con Paseo La Bufa S/N, 98060 Zacatecas, Zac., México (Mexico)

    2016-03-15

    Graphene Superlattices (GSs) have attracted a lot of attention due to its peculiar properties as well as its possible technological implications. Among these characteristics we can mention: the extra Dirac points in the dispersion relation and the highly anisotropic propagation of the charge carriers. However, despite the intense research that is carried out in GSs, so far there is no report about the angular dependence of the Transmission Gap (TG) in GSs. Here, we report the dependence of TG as a function of the angle of the incident Dirac electrons in a rather simple Electrostatic GS (EGS). Our results show that the angular dependence of the TG is intricate, since for moderated angles the dependence is parabolic, while for large angles an exponential dependence is registered. We also find that the TG can be modulated from meV to eV, by changing the structural parameters of the GS. These characteristics open the possibility for an angle-dependent bandgap engineering in graphene.

  20. Hetero-engineering infrared detectors with type-II superlattices

    Science.gov (United States)

    Tian, Z.-B.; DeCuir, E. A.; Gautam, N.; Krishna, S.; Wijewarnasuriya, P. S.; Pattison, J. W.; Dhar, N.; Welser, R. E.; Sood, A. K.

    2013-09-01

    InAs/GaSb type-II superlattices (T2-SLs) are of great interest as they provide a lot of band engineering flexibility. A wide variety of unipolar barrier structures have been investigated with this material system. In this report, we will present our recent work on the development of low noise long-wave infrared (LWIR) InAs/GaSb T2-SLs photodetectors. By adopting a so-called pBiBn design, the dark current of LWIR photodetectors is greatly suppressed. The LWIR pBiBn device has demonstrated a dark current density as low as 1.42×10-5 A/cm2 at -60 mV, and R0A of 5365 Ωcm2 at 76 K. A peak detectivity at 7.8 μm of 7.7×1011 cmHz1/2W-1 is obtained at 76 K. Further effort to reduce the operating bias is also reported. By refining the energy-band alignment, a 2-μm-thick LWIR pBiBn device has demonstrated a single pass (no AR coating) quantum efficiency of 20% at 10 μm under zero-bias at 77 K. We have recently extended our efforts to further reduce the dark current by using an interband cascade (IC) photodetector structure. Some further details about the device operation and results will be discussed.