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Sample records for tunnels electronic resource

  1. Single Electron Tunneling

    Financial support for this project has led to advances in the science of single-electron phenomena. Our group reported the first observation of the so-called ''Coulomb Staircase'', which was produced by tunneling into ultra-small metal particles. This work showed well-defined tunneling voltage steps of width e/C and height e/RC, demonstrating tunneling quantized on the single-electron level. This work was published in a now well-cited Physical Review Letter. Single-electron physics is now a major sub-field of condensed-matter physics, and fundamental work in the area continues to be conducted by tunneling in ultra-small metal particles. In addition, there are now single-electron transistors that add a controlling gate to modulate the charge on ultra-small photolithographically defined capacitive elements. Single-electron transistors are now at the heart of at least one experimental quantum-computer element, and single-electron transistor pumps may soon be used to define fundamental quantities such as the farad (capacitance) and the ampere (current). Novel computer technology based on single-electron quantum dots is also being developed. In related work, our group played the leading role in the explanation of experimental results observed during the initial phases of tunneling experiments with the high-temperature superconductors. When so-called ''multiple-gap'' tunneling was reported, the phenomenon was correctly identified by our group as single-electron tunneling in small grains in the material. The main focus throughout this project has been to explore single electron phenomena both in traditional tunneling formats of the type metal/insulator/particles/insulator/metal and using scanning tunneling microscopy to probe few-particle systems. This has been done under varying conditions of temperature, applied magnetic field, and with different materials systems. These have included metals, semi-metals, and superconductors. Amongst a number of results, we have verified that clusters of down to one, two, and three metal atoms can be identified with single-electron techniques. We have also, extended the regime of single-electron phenomenology through the observation of single-electron effects in metal droplets in the high-conductance regime

  2. Electron tunneling in proteins program.

    Hagras, Muhammad A; Stuchebrukhov, Alexei A

    2016-06-01

    We developed a unique integrated software package (called Electron Tunneling in Proteins Program or ETP) which provides an environment with different capabilities such as tunneling current calculation, semi-empirical quantum mechanical calculation, and molecular modeling simulation for calculation and analysis of electron transfer reactions in proteins. ETP program is developed as a cross-platform client-server program in which all the different calculations are conducted at the server side while only the client terminal displays the resulting calculation outputs in the different supported representations. ETP program is integrated with a set of well-known computational software packages including Gaussian, BALLVIEW, Dowser, pKip, and APBS. In addition, ETP program supports various visualization methods for the tunneling calculation results that assist in a more comprehensive understanding of the tunneling process. © 2016 Wiley Periodicals, Inc. PMID:26990540

  3. Chemically driven electron tunnelling pumps

    Goychuk, I

    2006-01-01

    The simplest mechanism for molecular electron pumps is discussed which is based on nonadiabatic electron tunnelling and nonequilibrium conformational fluctuations. Such fluctuations can be induced, e.g. by random binding of negatively charged ATP molecules to the electron-transferring molecular complex, their subsequent hydrolysis and the products dissociation. The pumping rate can be controlled by the ATP concentration in solution. Depending on the model parameters there may exist a critical ATP concentration for the pump to function. Alternatively, nonequilibrium fluctuations can be induced by externally applied stochastic electric fields. For realistically chosen parameters, the mechanism is shown to be robust and highly efficient.

  4. Many-electron tunneling in atoms

    Zon, B A

    1999-01-01

    A theoretical derivation is given for the formula describing N-electron ionization of atom by a dc field and laser radiation in tunneling regime. Numerical examples are presented for noble gases atoms.

  5. Numerical studies of electron tunnelling in liquids

    The diffusion equation, derived from Fick's second law, with an added exponential sink term to simulate electron tunnelling, is integrated numerically to determine the rate of electron decay at times greater than 1 ps. The effect of a Coulomb interaction with a charged scavenger is examined and the steady-state rate constant shown to approximate closely to that obtained by combining the separate effects of tunnelling and charge-affected diffusion, which can be expressed analytically. Diffusion in the presence of a charge-induced dipole interaction is investigated for the case of scavenging of localised electrons in alkanes. The rate constant is shown to be dominated by random diffusion and tunnelling and the bias induced by the interaction is of little consequence. The sensitivity of the rate constant to changes in the pre-exponential factor in the sink term is shown to be most favourable at short times. (author)

  6. Electron accelerator for tunneling through hard rock

    Earlier work demonstrated that intense sub-microsecond bursts of energetic electrons cause significant pulverization and spalling of a variety of rock types. The spall debris generally consists of sand, dust, and small flakes. If carried out at rapid repetition rate, this can lead to a promising technique for increasing the speed and reducing the cost of underground excavation of tunnels, mines, and storage spaces. The conceptual design features of a Pulsed Electron Tunnel Excavator capable of tunneling approximately ten times faster than conventional drill/blast methods are presented, with primary emphasis on the electron accelerator and only a brief description of the tunneling aspects. Of several candidate types of accelerators, a linear induction accelerator producing electron pulses (5 MV, 5 kA, 1.0 μs = 25 kJ) at a 360 Hz rate was selected for the conceptual example. This provides the required average electron beam power output of 9 MW. The feasibility of such an accelerator is discussed

  7. Single-electron tunnel junction array

    The authors have carried out an analysis of statics and dynamics of uniform one-dimensional arrays of ultrasmall tunnel junctions. The correlated single-electron tunneling in the junctions of the array results in its behavior qualitatively similar to that of the Josephson transmission line. In particular, external electric fields applied to the array edges can inject single-electron-charged solitons into the array interior. Shape of such soliton and character of its interactions with other solitons and the array edges are very similar to those of the Josephson vortices (sine-Gordon solitons) in the Josephson transmission line. Under certain conditions, a coherent motion of the soliton train along the array is possible, resulting in generation of narrowband SET oscillations with frequency f/sub s/ = /e where is the dc current flowing along the array

  8. Superconducting tunnel junctions and their electronic analogues

    Electronic analogues have often been used to investigate the properties of Josephson effect devices. However, they have generally been limited to modelling the adiabatic, resistively-shunted junction theory of the Josephson effects. An electronic analogue has been built which models the theory developed by Werthamer for superconducting tunnel junctions. This analogue, based on a phased-lock loop design, includes high frequency and energy gap effects, nonlinear quasiparticle tunnelling, the Riedel peak, the cosine phi term and the effects of nonzero temperature. The resistivity-shunted junction (RSJ) theory and the Werthamer theory are summarized and a review of existing analogues presented. The design and use and results of an RSJ model analogue are discussed. (author)

  9. Tunneling of electrons through semiconductor superlattices

    C L Roy

    2002-11-01

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

  10. Wind Tunnel Management and Resource Optimization: A Systems Modeling Approach

    Jacobs, Derya, A.; Aasen, Curtis A.

    2000-01-01

    Time, money, and, personnel are becoming increasingly scarce resources within government agencies due to a reduction in funding and the desire to demonstrate responsible economic efficiency. The ability of an organization to plan and schedule resources effectively can provide the necessary leverage to improve productivity, provide continuous support to all projects, and insure flexibility in a rapidly changing environment. Without adequate internal controls the organization is forced to rely on external support, waste precious resources, and risk an inefficient response to change. Management systems must be developed and applied that strive to maximize the utility of existing resources in order to achieve the goal of "faster, cheaper, better". An area of concern within NASA Langley Research Center was the scheduling, planning, and resource management of the Wind Tunnel Enterprise operations. Nine wind tunnels make up the Enterprise. Prior to this research, these wind tunnel groups did not employ a rigorous or standardized management planning system. In addition, each wind tunnel unit operated from a position of autonomy, with little coordination of clients, resources, or project control. For operating and planning purposes, each wind tunnel operating unit must balance inputs from a variety of sources. Although each unit is managed by individual Facility Operations groups, other stakeholders influence wind tunnel operations. These groups include, for example, the various researchers and clients who use the facility, the Facility System Engineering Division (FSED) tasked with wind tunnel repair and upgrade, the Langley Research Center (LaRC) Fabrication (FAB) group which fabricates repair parts and provides test model upkeep, the NASA and LARC Strategic Plans, and unscheduled use of the facilities by important clients. Expanding these influences horizontally through nine wind tunnel operations and vertically along the NASA management structure greatly increases the complexity of developing a model that can be used for successfully implementing a standardized management planning tool. The objective of this study was to implement an Integrated Wind Tunnel Planning System to improve the operations within the aeronautics testing and research group, in particular Wind Tunnel Enterprise. The study included following steps: Conducted literature search and expert discussions (NASA and Old Dominion University faculty), Performed environmental scan of NASA Langley wind tunnel operations as foundation for problem definition. Established operation requirements and evaluation methodologies. Examined windtunnel operations to map out the common characteristics, critical components, and system structure. Reviewed and evaluated various project scheduling and management systems for implementation, Evaluated and implemented "Theory of Constraints (TOC)" project scheduling methodology at NASA Langley wind tunnel operations together with NASA staff.

  11. Site-directed deep electronic tunneling through a molecular network

    Electronic tunneling in a complex molecular network of N(>2) donor/acceptor sites, connected by molecular bridges, is analyzed. The 'deep' tunneling dynamics is formulated using a recursive perturbation expansion, yielding a McConnell-type reduced N-level model Hamiltonian. Applications to models of molecular junctions demonstrate that the donor-bridge contact parameters can be tuned in order to control the tunneling dynamics and particularly to direct the tunneling pathway to either one of the various acceptors

  12. Electron beam instabilities in gyrotron beam tunnels

    Electron beam instabilities occurring in a gyrotron electron beam can induce an energy spread which might significantly deteriorate the gyrotron efficiency. Three types of instabilities are considered to explain the important discrepancy found between the theoretical and experimental efficiency in the case of quasi-optical gyrotrons (QOG): the electron cyclotron maser instability, the Bernstein instability and the Langmuir instability. The low magnetic field gradient in drift tubes of QOG makes that the electron cyclotron maser instability can develop in the drift tube at very low electron beam currents. Experimental measurements show that with a proper choice of absorbing structures in the beam tunnel, this instability can be suppressed. At high beam currents, the electrostatic Bernstein instability can induce a significant energy spread at the entrance of the interaction region. The induced energy spread scales approximately linearly with the electron beam density and for QOG one observes that the beam density is significantly higher than the beam density of an equivalent cylindrical cavity gyrotron. (author) figs., tabs., refs

  13. Quantum Hall Effect: proposed multi-electron tunneling experiment

    Here we propose a tunneling experiment for the fractional and Integral Quantum Hall Effect. It may demonstrate multi-electron tunneling and may provide information about the nature of the macroscopic quantum states of 2D electronic liquid or solid. (author)

  14. Electronic Resources Management : An Update

    Medeiros, Norm

    2005-01-01

    This article reviews the Digital Library Federation’s (DLF) Electronic Resource Management Initiative (ERMI) guidelines, finalized in August 2004. The specifications are reviewed in light of the electronic resource (e-resource) management needs of academic libraries. The piece reflects on comments made by Tim Jewell and Adam Chandler in an earlier “On the Dublin Core Front” column. A review of commercial e-resource management system development is also included.

  15. Tunneling of Dirac electrons through spatial regions of finite mass

    Viana Gomes, J; Peres, N M R [Center of Physics and Department of Physics, University of Minho, P-4710-057, Braga (Portugal)

    2008-08-13

    We study the tunneling of chiral electrons in graphene through a region where the electronic spectrum changes from the usual linear dispersion to a hyperbolic dispersion, due to the presence of a gap. It is shown that, contrary to the tunneling through a potential barrier, the transmission of electrons is, in this case, smaller than one for normal incidence. This mechanism may be useful for designing electronic devices made of graphene.

  16. "Size-Independent" Single-Electron Tunneling.

    Zhao, Jianli; Sun, Shasha; Swartz, Logan; Riechers, Shawn; Hu, Peiguang; Chen, Shaowei; Zheng, Jie; Liu, Gang-Yu

    2015-12-17

    Incorporating single-electron tunneling (SET) of metallic nanoparticles (NPs) into modern electronic devices offers great promise to enable new properties; however, it is technically very challenging due to the necessity to integrate ultrasmall (<10 nm) particles into the devices. The nanosize requirements are intrinsic for NPs to exhibit quantum or SET behaviors, for example, 10 nm or smaller, at room temperature. This work represents the first observation of SET that defies the well-known size restriction. Using polycrystalline Au NPs synthesized via our newly developed solid-state glycine matrices method, a Coulomb Blockade was observed for particles as large as tens of nanometers, and the blockade voltage exhibited little dependence on the size of the NPs. These observations are counterintuitive at first glance. Further investigations reveal that each observed SET arises from the ultrasmall single crystalline grain(s) within the polycrystal NP, which is (are) sufficiently isolated from the nearest neighbor grains. This work demonstrates the concept and feasibility to overcome orthodox spatial confinement requirements to achieve quantum effects. PMID:26618859

  17. Quantum tunneling and field electron emission theories

    Liang, Shi-Dong

    2013-01-01

    Quantum tunneling is an essential issue in quantum physics. Especially, the rapid development of nanotechnology in recent years promises a lot of applications in condensed matter physics, surface science and nanodevices, which are growing interests in fundamental issues, computational techniques and potential applications of quantum tunneling. The book involves two relevant topics. One is quantum tunneling theory in condensed matter physics, including the basic concepts and methods, especially for recent developments in mesoscopic physics and computational formulation. The second part is the f

  18. Electron tunneling through atomically flat and ultrathin hexagonal boron nitride

    Lee, Gwan-Hyoung; Yu, Young-Jun; Lee, Changgu; Dean, Cory; Shepard, Kenneth L.; Kim, Philip; Hone, James

    2011-12-01

    Electron tunneling through atomically flat and ultrathin hexagonal boron nitride (h-BN) on gold-coated mica was investigated using conductive atomic force microscopy. Low-bias direct tunneling was observed in mono-, bi-, and tri-layer h-BN. For all thicknesses, Fowler-Nordheim tunneling (FNT) occurred at high bias, showing an increase of breakdown voltage with thickness. Based on the FNT model, the barrier height for tunneling (3.07 eV) and dielectric strength (7.94 MV/cm) of h-BN are obtained; these values are comparable to those of SiO2.

  19. Klein tunneling in graphene: optics with massless electrons

    Allain, P E

    2011-01-01

    This article provides a pedagogical review on Klein tunneling in graphene, i.e. the peculiar tunneling properties of two-dimensional massless Dirac electrons. We consider two simple situations in detail: a massless Dirac electron incident either on a potential step or on a potential barrier and use elementary quantum wave mechanics to obtain the transmission probability. We emphasize the connection to related phenomena in optics, such as the Snell-Descartes law of refraction, total internal reflection, Fabry-P\\'erot resonances, negative refraction index materials (the so called meta-materials), etc. We also stress that Klein tunneling is not a genuine quantum tunneling effect as it does not necessarily involve passing through a classically forbidden region via evanescent waves. A crucial role in Klein tunneling is played by the conservation of (sublattice) pseudo-spin, which is discussed in detail. A major consequence is the absence of backscattering at normal incidence, of which we give a new shorten proof. ...

  20. Klein tunneling in graphene: optics with massless electrons

    Allain, P. E.; Fuchs, J.N.

    2011-01-01

    This article provides a pedagogical review on Klein tunneling in graphene, i.e. the peculiar tunneling properties of two-dimensional massless Dirac electrons. We consider two simple situations in detail: a massless Dirac electron incident either on a potential step or on a potential barrier and use elementary quantum wave mechanics to obtain the transmission probability. We emphasize the connection to related phenomena in optics, such as the Snell-Descartes law of refraction, total internal r...

  1. Electron-Photon interaction in resonant tunneling diodes

    Inarrea, Jesus; Aguado, Ramon; Platero, Gloria

    1997-01-01

    We develope a model to describe the transmission coefficient and tunneling current in the presence of photon-electron coupling in a resonant diode. Our model takes into account multiphoton processes as well as the transitions between electronic states with different wave numbers. This is crutial to explain the experimental features observed in the tunneling current through a double barrier which cannot be reproduced with more simplified established models. According to our results, what exper...

  2. Scanning tunneling spectroscopy on electron-boson interactions in superconductors

    Schackert, Michael Peter

    2015-01-01

    This work describes the experimental study of electron-boson interactions in superconductors by means of inelastic electron tunneling spectroscopy performed with a scanning tunneling microscope (STM) at temperatures below 1 K. This new approach allows the direct measurement of the Eliashberg function of conventional superconductors as demonstrated on lead (Pb) and niobium (Nb). Preparative experiments on unconventional iron-pnictides are presented in the end.

  3. Internal Electron Tunneling Enabled Ultrasensitive Position/Force Peapod Sensors.

    Tao, Xinyong; Fan, Zheng; Nelson, Bradley J; Dharuman, Gautham; Zhang, Wenkui; Dong, Lixin; Li, Xiaodong

    2015-11-11

    The electron quantum tunneling effect guarantees the ultrahigh spatial resolution of the scanning tunneling microscope (STM), but there have been no other significant applications of this effect after the invention of STM. Here we report the implementation of electron-tunneling-based high sensitivity transducers using a peapod B4C nanowire, where discrete Ni6Si2B nanorods are embedded in the nanowire in a peapod form. The deformation of the nanowire provides a higher order scaling effect between conductivity and deformation strain, thus allowing the potentials of position and force sensing at the picoscale. PMID:26457662

  4. Spin-dependent electron tunneling through magnetic barriers

    An exact solution to the model problem of 2D-electron funneling through magnetic barriers is given with regard for electron is intrinsic magnetic momentum. General requirements to the topology of a magnetic structure that has spin-depended tunneling are clarified. A structure is proposed which is able to filter electrons in the direction of their spin polarization

  5. Electronic thermometry in tunable tunnel junction

    Maksymovych, Petro

    2016-03-15

    A tunable tunnel junction thermometry circuit includes a variable width tunnel junction between a test object and a probe. The junction width is varied and a change in thermovoltage across the junction with respect to the change in distance across the junction is determined. Also, a change in biased current with respect to a change in distance across the junction is determined. A temperature gradient across the junction is determined based on a mathematical relationship between the temperature gradient, the change in thermovoltage with respect to distance and the change in biased current with respect to distance. Thermovoltage may be measured by nullifying a thermoelectric tunneling current with an applied voltage supply level. A piezoelectric actuator may modulate the probe, and thus the junction width, to vary thermovoltage and biased current across the junction. Lock-in amplifiers measure the derivatives of the thermovoltage and biased current modulated by varying junction width.

  6. Parity effects on electron tunnelling through small superconducting islands

    Single-electron tunnelling into small superconducting islands is sensitive to the gap energy of the excitations created in the process and, hence, depends on the electron number parity. At low temperatures, a 2e-periodic, even-odd asymmetric dependence on the applied gate voltage has been observed, turning into an e-periodic behaviour at higher temperature. We explain the crossover and derive I-V characteristics of such systems by studying the dynamics. The rate of tunnelling of a single electron, the odd one, turns out to be crucial. It dominates at low temperature since in this process the excitation energy can be regained, while the competing many-electron processes are exponentially suppressed. Parity effects on single-electron and Cooper-pair tunnelling and the Andreev reflection in superconducting transistors yield rich structures in the I-V characteristics, which compare well with recent experimental findings. (orig.)

  7. Electron tunnelling into amorphous germanium and silicon.

    Smith, C. W.; Clark, A. H.

    1972-01-01

    Measurements of tunnel conductance versus bias, capacitance versus bias, and internal photoemission were made in the systems aluminum-oxide-amorphous germanium and aluminium-oxide-amorphous silicon. A function was extracted which expresses the deviation of these systems from the aluminium-oxide-aluminium system.

  8. Voltage controlled electron spin dynamics in resonant tunnelling devices

    We investigate the electron spin dynamics in a p-type GaAs/AlAs resonant tunnelling device by measuring the time- and polarized-resolved photoluminescence (PL) from the GaAs quantum well under a high magnetic field (15T). The voltage dependence of the PL transients have revealed various tunnelling processes with different time constants that give rise to distinct spin-polarized carriers injected into the double-barrier structure. (paper)

  9. Inelastic electron tunneling spectroscopy of a single nuclear spin

    Delgado Acosta, Fernando; Fernndez Rossier, Joaqun

    2011-01-01

    Detection of a single nuclear spin constitutes an outstanding problem in different fields of physics such as quantum computing or magnetic imaging. Here we show that the energy levels of a single nuclear spin can be measured by means of inelastic electron tunneling spectroscopy (IETS). We consider two different systems, a magnetic adatom probed with scanning tunneling microscopy and a single Bi dopant in a silicon nanotransistor. We find that the hyperfine coupling opens new transport channel...

  10. Thermal electron-tunneling devices as coolers and amplifiers

    Su, Shanhe; Zhang, Yanchao; Chen, Jincan; Shih, Tien-Mo

    2016-01-01

    Nanoscale thermal systems that are associated with a pair of electron reservoirs have been previously studied. In particular, devices that adjust electron tunnels relatively to reservoirs’ chemical potentials enjoy the novelty and the potential. Since only two reservoirs and one tunnel exist, however, designers need external aids to complete a cycle, rendering their models non-spontaneous. Here we design thermal conversion devices that are operated among three electron reservoirs connected by energy-filtering tunnels and also referred to as thermal electron-tunneling devices. They are driven by one of electron reservoirs rather than the external power input, and are equivalent to those coupling systems consisting of forward and reverse Carnot cycles with energy selective electron functions. These previously-unreported electronic devices can be used as coolers and thermal amplifiers and may be called as thermal transistors. The electron and energy fluxes of devices are capable of being manipulated in the same or oppsite directions at our disposal. The proposed model can open a new field in the application of nano-devices. PMID:26893109

  11. Thermal electron-tunneling devices as coolers and amplifiers

    Su, Shanhe; Zhang, Yanchao; Chen, Jincan; Shih, Tien-Mo

    2016-02-01

    Nanoscale thermal systems that are associated with a pair of electron reservoirs have been previously studied. In particular, devices that adjust electron tunnels relatively to reservoirs’ chemical potentials enjoy the novelty and the potential. Since only two reservoirs and one tunnel exist, however, designers need external aids to complete a cycle, rendering their models non-spontaneous. Here we design thermal conversion devices that are operated among three electron reservoirs connected by energy-filtering tunnels and also referred to as thermal electron-tunneling devices. They are driven by one of electron reservoirs rather than the external power input, and are equivalent to those coupling systems consisting of forward and reverse Carnot cycles with energy selective electron functions. These previously-unreported electronic devices can be used as coolers and thermal amplifiers and may be called as thermal transistors. The electron and energy fluxes of devices are capable of being manipulated in the same or oppsite directions at our disposal. The proposed model can open a new field in the application of nano-devices.

  12. Klein tunneling in graphene: optics with massless electrons

    Allain, P. E.; Fuchs, J. N.

    2011-10-01

    This article provides a pedagogical review on Klein tunneling in graphene, i.e. the peculiar tunneling properties of two-dimensional massless Dirac electrons. We consider two simple situations in detail: a massless Dirac electron incident either on a potential step or on a potential barrier and use elementary quantum wave mechanics to obtain the transmission probability. We emphasize the connection to related phenomena in optics, such as the Snell-Descartes law of refraction, total internal reflection, Fabry-Pérot resonances, negative refraction index materials (the so called meta-materials), etc. We also stress that Klein tunneling is not a genuine quantum tunneling effect as it does not necessarily involve passing through a classically forbidden region via evanescent waves. A crucial role in Klein tunneling is played by the conservation of (sublattice) pseudo-spin, which is discussed in detail. A major consequence is the absence of backscattering at normal incidence, of which we give a new shorten proof. The current experimental status is also thoroughly reviewed. The Appendix contains the discussion of a one-dimensional toy model that clearly illustrates the difference in Klein tunneling between mono- and bi-layer graphene.

  13. Electron-Photon interaction in resonant tunneling diodes

    Iarrea, J; Platero, G; Inarrea, Jesus; Aguado, Ramon; Platero, Gloria

    1997-01-01

    We develope a model to describe the transmission coefficient and tunneling current in the presence of photon-electron coupling in a resonant diode. Our model takes into account multiphoton processes as well as the transitions between electronic states with different wave numbers. This is crutial to explain the experimental features observed in the tunneling current through a double barrier which cannot be reproduced with more simplified established models. According to our results, what experiments show in the current density are quantum photon-assisted features coming from multiphoton transitions which are not related with sample heating.

  14. Microwave-induced co-tunneling in single electron tunneling transistors

    Ejrnaes, M.; Savolainen, M.; Manscher, M.; Mygind, Jesper

    2002-01-01

    The influence of microwaves on the co-tunneling in single electron tunneling transistors has been investigated as function of frequency and power in the temperature range from 150 to 500 mK. All 20 low frequency connections and the RF line were filtered, and the whole cryostat was suspended on...... fixed at maximum Coulomb blockade. With the microwave signal applied to one side of the transistor, we find that the conductance increases linearly with T-2 and microwave power. (C) 2002 Elsevier Science B.V. All rights reserved....

  15. Bohmian mechanics and the tunneling time problem for electrons

    The controversial concepts of dwell, transmission, reflection, and arrival times for quantum particles scattered by a potential barrier are discussed for Schroedinger electrons within the framework of Bohm's causal alternative to conventional quantum mechanics. Several other approaches to ''the tunneling time problem'', including the systematic projector approach of Brouard, Sala and Muga, are reviewed from the point of view of Bohmian mechanics. (author)

  16. Electronic structure and tunneling resonance spectra of nanoscopic aluminum islands

    Narvaez, Gustavo A.; Kirczenow, George

    2002-01-01

    The electronic structure of nanoscopic oxide-coated aluminum islands is investigated using a tight-binding model that incorporates the geometry, chemistry and disorder of the particle. The oxide coat is found to significantly increase the volume accessible to electrons at the Fermi level. The level statistics agree with random matrix theory predictions. States near the Fermi level show pronounced clustering regardless of disorder. It is suggested that the observed clusters of tunneling resona...

  17. Electron Tunneling in Self-Assembled Nanocrystal Superlattices

    Black, C. T.

    2000-03-01

    We use high-temperature solution-phase synthesis to produce monodisperse organically-passivated nanocrystals of metals and semiconductors. Through adjustment of synthetic conditions and careful size-selective processing, we precisely tune nanocrystal diameters from 2-10 nm, with variations on the order of a single atomic layer. The uniformity of these nanoparticles allows them to self-organize into two- or three-dimensional arrays when deposited from solution onto a substrate. The resulting solid is a new form of crystalline material, which has monodisperse nanocrystals as its fundamental building-blocks. We use electron tunneling to understand the electrical properties of these nanocrystalline superlattices. At low temperatures, electron transport through the array is strongly influenced by the Coulomb energy for charging the individual nanocrystals. We measure a sharp voltage threshold for the onset of current, below which tunneling is exponentially-suppressed. Current above the threshold voltage scales with a power-law-dependence on applied voltage. Our observations agree well with models for single-electron tunneling in arrays of Coulomb islands. For solids composed of ferromagnetic nanoparticles, the tunneling magnetoresistance is determined by the relative orientations of nanoparticle magnetic moments. We have measured magnetoresistance changes in excess of 10 percent (for magnetic fields less than 0.4 T) in nanocrystalline cobalt films. Our measurement techniques are not limited to studies of magnetic arrays: we also discuss more recent results for nanocrystalline solids composed of narrow-bandgap semiconductor materials, such as PbSe .

  18. Inelastic electron tunneling spectroscopy with a dilution refrigerator based scanning tunneling microscope

    This paper presents the design and operations of a compact cryogenic scanning tunneling microscope system combined with a dilution refrigerator. We obtained a minimum temperature of 260 mK at the sample position. Taking advantage of low-temperature measurement for the spectroscopy, inelastic electron tunneling spectroscopy (IETS) at 4.4 K was demonstrated for the octanethiol molecules in a self-assembled monolayer. The spectrum showed many vibrational features as in the case of a high-resolution electron energy loss spectroscopy. We discuss the resolution of the IET signals focusing on its changes with the modulation voltage and the sample temperature. IETS at 260 mK is also presented with similar quality as in the case of 4.4 K, indicating that the vibration-dumping methods for the operation of the dilution refrigerator described in this paper are adequate

  19. Attosecond correlation dynamics during electron tunnelling from molecules

    Walters, Zachary B; Smirnova, Olga, E-mail: zwalters@gmail.co, E-mail: Olga.Smirnova@mbi-berlin.d [Max-Born-Institut fuer Nichtlineare Optik und Kurzzeitspektroskopie, D-12489 Berlin (Germany)

    2010-08-28

    In this communication, we present an analytical theory of strong-field ionization of molecules, which takes into account the rearrangement of multiple interacting electrons during the ionization process. We show that such rearrangement offers an alternative pathway to the ionization of orbitals more deeply bound than the highest occupied molecular orbital. This pathway is not subject to the full exponential suppression characteristic of direct tunnel ionization from the deeper orbitals. The departing electron produces an 'attosecond correlation pulse' which controls the rearrangement during the tunnelling process. The shape and duration of this pulse are determined by the electronic structure of the relevant states, molecular orientation and laser parameters. (fast track communication)

  20. Modeling Klein tunneling and caustics of electron waves in graphene

    Logemann, R.; Reijnders, K. J. A.; Tudorovskiy, T.; Katsnelson, M. I.; Yuan, Shengjun

    2015-01-01

    We employ the tight-binding propagation method to study Klein tunneling and quantum interference in large graphene systems. With this efficient numerical scheme, we model the propagation of a wave packet through a potential barrier and determine the tunneling probability for different incidence angles. We consider both sharp and smooth potential barriers in n-p-n and n -n' junctions and find good agreement with analytical and semiclassical predictions. When we go outside the Dirac regime, we observe that sharp n -p junctions no longer show Klein tunneling because of intervalley scattering. However, this effect can be suppressed by considering a smooth potential. Klein tunneling holds for potentials changing on the scale much larger than the interatomic distance. When the energies of both the electrons and holes are above the Van Hove singularity, we observe total reflection for both sharp and smooth potential barriers. Furthermore, we consider caustic formation by a two-dimensional Gaussian potential. For sufficiently broad potentials we find a good agreement between the simulated wave density and the classical electron trajectories.

  1. Attosecond control of tunneling ionization and electron trajectories

    Fiess, M; Horvath, B; Wittmann, T; Helml, W; Gagnon, J; Krausz, F; Kienberger, R [Max-Planck-Institute of Quantum Optics, Hans-Kopfermann-Strasse 1, Garching (Germany); Cheng, Y; Zeng, B; Xu, Z [State Key Laboratory of High Field Laser Physics, Shanghai Institute of Optics and Fine Mechanics, Chinese Academy of Sciences, PO Box 800-211, Shanghai 201800 (China); Scrinzi, A, E-mail: markus.fiess@mpq.mpg.de [Ludwig-Maximilians-Universitaet Muenchen, Fakultaet fuer Physik, Theresienstrasse 37, 80333 Muenchen (Germany)

    2011-03-15

    We demonstrate the control of electron tunneling in the high-order harmonic generation process and subsequent positive-energy wavepacket propagation until recollision with the unprecedented precision of about 10 attoseconds. This is accomplished with waveforms synthesized from a few-cycle near-infrared pulse and its second harmonic. The presented attosecond control of few-cycle-driven high harmonics permits the generation of tunable isolated attosecond pulses, opening the prospects for a new class of attosecond pump-probe experiments.

  2. Inelastic electron tunneling spectroscopy of molecular transport junctions

    Song, Hyunwook [Kyung Hee University, Yongin (Korea, Republic of); Lee, Takhee [Seoul National University, Seoul (Korea, Republic of); Reed, Mark [Yale University, New Haven, CT (United States)

    2014-05-15

    Inelastic electron tunneling spectroscopy (IETS) has become a premier analytical tool in the investigation of nano scale and molecular junctions. The IETS spectrum provides invaluable information about the structure, bonding, and orientation of component molecules in the junctions. One of the major advantages of IETS is its sensitivity and resolution at the level of single molecules. This review discusses how IETS is used to study molecular transport junctions and presents an overview of recent experimental studies.

  3. Attosecond control of tunneling ionization and electron trajectories

    We demonstrate the control of electron tunneling in the high-order harmonic generation process and subsequent positive-energy wavepacket propagation until recollision with the unprecedented precision of about 10 attoseconds. This is accomplished with waveforms synthesized from a few-cycle near-infrared pulse and its second harmonic. The presented attosecond control of few-cycle-driven high harmonics permits the generation of tunable isolated attosecond pulses, opening the prospects for a new class of attosecond pump-probe experiments.

  4. Elementary excitations in double electron layers with tunnel coupling

    The new class of the single-particle excitations in the double electron layers with the tunneling coupling between the layers is studied through the method of the light inelastic scattering. The dispersion law and dependence of the energies of the given excitations on the degree of the layers unbalance are measured. The new spectroscopic method for determining the degree of the double layers unbalance is proposed

  5. Electron tunneling study of single crystal BCSCO superconductors

    The single crystal BCSCO superconductors have been investigated by electron tunneling with both point contacts and BCSCO/Sn junctions. A gap parameter of ? = 34meV and 2?/kTc = 8.9 have been obtained. Various dI/dV curves including BCS-like and so-called harmonic structure have been observed. The authors propose to make use of proximity effect and quasiparticle interference to interpret these phenomena

  6. First Principles Study of Electron Tunneling through Ice

    Cucinotta, Clotilde S.

    2012-10-25

    With the aim of understanding electrochemical scanning tunnel microscopy experiments in an aqueous environment, we investigate electron transport through ice in the coherent limit. This is done by using the nonequilibrium Greens functions method, implemented within density functional theory, in the self-interaction corrected local density approximation. In particular, we explore different ice structures and different Au electrode surface orientations. By comparing the decay coefficient for different thicknesses to the ice complex band structure, we find that the electron transport occurs via tunneling with almost one-dimensional character. The slow decay of the current with the ice thickness is largely due to the small effective mass of the conduction electrons. Furthermore, we find that the calculated tunneling decay coefficients at the Fermi energy are not sensitive to the structural details of the junctions and are at the upper end of the experimental range for liquid water. This suggests that linear response transport measurements are not capable of distinguishing between different ordered ice structures. However, we also demonstrate that a finite bias measurement may be capable of sorting polar from nonpolar interfaces due to the asymmetry of the current-voltage curves for polar interfaces. © 2012 American Chemical Society.

  7. Average electron tunneling route of the electron transfer in protein media.

    Nishioka, Hirotaka; Kakitani, Toshiaki

    2008-08-14

    We present a new theoretical method to determine and visualize the average tunneling route of the electron transfer (ET) in protein media. In this, we properly took into account the fluctuation of the tunneling currents and the quantum-interference effect. The route was correlated with the electronic factor in the case of ET by the elastic tunneling mechanism. We expanded by the interatomic tunneling currents 's. Incorporating the quantum-interference effect into the mean-square interatomic tunneling currents, denoted as , we could express as a sum of variant Planck's over 2pi(2). Drawing the distribution of on the protein structure, we obtain the map which visually represents which parts of bonds and spaces most significantly contribute to . We applied this method to the ET from the bacteriopheophytin anion to the primary quinone in the bacterial photosynthetic reaction center of Rhodobacter sphaeroides. We obtained 's by a combined method of molecular dynamics simulations and quantum chemical calculations. In calculating , we found that much destructive interference works among the interatomic tunneling currents even after taking the average. We drew the map by a pipe model where atoms a and b are connected by a pipe with width proportional to the magnitude of . We found that two groups of 's, which are mutually coupled with high correlation in each group, have broad pipes and form the average tunneling routes, called Trp route and Met route. Each of the two average tunneling routes is composed of a few major pathways in the Pathways model which are fused at considerable part to each other. We also analyzed the average tunneling route for the ET by the inelastic tunneling mechanism. PMID:18630851

  8. Scanning tunneling microscopy and inelastic electron tunneling spectroscopy studies of methyl isocyanide adsorbed on Pt(111)

    A low-temperature scanning tunneling microscope (STM) was used to investigate the adsorption state of a single methyl isocyanide (MeNC) molecule on the Pt(111) surface at 4.7 K. We found that MeNC was resolved as a round-shaped protrusion in the STM image. The STM image of paired MeNC is highly protruded in comparison with that of isolated MeNC due to the charge transfer from Pt to MeNC. Inelastic electron tunneling spectroscopy with the STM system (STM-IETS) was also employed in order to reveal the adsorption state of individual MeNC molecules on Pt(111). The STM-IETS spectrum of MeNC exhibits peaks at 8, 48 and 375 mV. Referring to the vibrational spectra reported previously, we assigned these peaks to the frustrated translation mode, PtC stretching mode and CH3 stretching mode, respectively. The absence of other vibrational modes could be due to a reduction of the elastic tunneling current.

  9. Analysis of electron tunneling events with the hidden Markov model

    House, Matthew; Jiang, Hong Wen

    2010-03-01

    The charge fluctuations of a quantum dot in a semiconductor heterostructure can be observed using a charge sensor which observes electrons transiting on and off of the quantum dot in real time. As electrons tunnel onto and off of the quantum dot, the conductance of the charge sensor shows stochastic transitions between two levels in a pattern that is commonly referred to as a random telegraph signal. Information about the quantized states of electrons on the quantum dot can be inferred from measurements of the charge sensor conductance. We have applied the hidden Markov model (HMM) formalism to the problem of extracting information about quantum dot states and transition rates from charge sensor data. HMM theory provides a mathematical approach for inferring the details of a stochastic process from indirect observations. We discuss how this applies to the analysis of charge sensor data in quantum dot experiments. We apply HMMs to simulated and experimental data, and demonstrate its usefulness in extracting the electron transition rates. Data analysis by HMM is much more robust against noise than previous approaches, and has the potential to infer whether tunneling events correspond to the ground state or to excited states of the quantum dot, information which is not directly observable by the charge sensor.

  10. (abstract) A Miniature, High-Sensitivity, Electron-Tunneling Accelerometer

    Gabrielson, Thomas B.; Rockstad, Howard K.; Tang, Tony K.

    1994-01-01

    A prototype low-noise accelerometer has been fabricated with an electron-tunneling transducer. By measuring the tunneling current between an electrode on the proof mass and a feedback-controlled monitor electrode, very small accelerations can be detected with high responsivity. This particular prototype (10x10x1.5 mm) was designed for underwater acoustic measurement from a few hertz to 1 kHz. The measured responsivity below the fundamental device resonance at 100 Hz is roughly 1500 volts per m/s(sup 2) with a measured noise spectral density of 10(sup -6) m/s(sup 2) per root hertz or less between 30 and 300 Hz. The noise floor is controlled primarily by 1/f noise in the tunneling current although the noise floor reaches the theoretical molecular-agitation limit at 100 hertz. The responsivity and directivity of the device were measured in a standard gradient-hydrophone calibrator; the noise floor was determined in a vacuum-ionization chamber assembled from commercial off-the-shelf components; and the detailed dynamics of the proof-mass motion were examined using a heterodyne laser interferometer that was scanned across the surface and synchronously detected with respect to the excitation.

  11. Managing electronic resources a LITA guide

    Weir, Ryan O

    2012-01-01

    Informative, useful, current, Managing Electronic Resources: A LITA Guide shows how to successfully manage time, resources, and relationships with vendors and staff to ensure personal, professional, and institutional success.

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

    Padilla, J. L.; Palomares, A.; Alper, C.; Gámiz, F.; Ionescu, A. M.

    2016-01-01

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

  13. Scanning electron and tunneling microscopy of palladium-barium emitters

    The results of study of metal-alloyed palladium-barium emitters' of modern very high frequency high-powered electronic vacuum tubes by scanning electron microscopy (SEM) and scanning tunneling microscopy/spectroscopy (STM/STS) are presented. Since the Pd/Ba foil surface is fairly smooth and is not oxidized in air STM/STS investigations are carried out in air in normal laboratory environment. SEM and STM images show that the emitter surface has a complex porous structure. The cathode surface study by STS in tunneling gap modulation mode allowed to take a map of phase distribution with various work function values and high lateral resolution. Obtained images demonstrate the presence of three phases on the Pd/Ba emitter surface, viz. barium-oxygen compounds, intermetallic, and palladium. As it is seen from presented STS image the phase with a low work function value (barium oxides) is concentrated along boundaries of the substance inclusions with work function corresponding to the intemetallic compound Pd5Ba. This supports the model of low work function areas obtained via Ba segregation from the intermetallic compound and oxidation. The presented methods may be used in the Pd/Ba cathode manufacturing process for increasing the yield of electronic devices in microwave tube production and optimize the emitters' characteristics

  14. Scanning electron and tunneling microscopy of palladium barium emitters

    Baiburin, V. B.; Volkov, U. P.; Semenov, S. V.; Semenov, A. S.

    2003-06-01

    The results of study of metal-alloyed palladium-barium emitters' of modern very high frequency high-powered electronic vacuum tubes by scanning electron microscopy (SEM) and scanning tunneling microscopy/spectroscopy (STM/STS) are presented. Since the Pd/Ba foil surface is fairly smooth and is not oxidized in air STM/STS investigations are carried out in air in normal laboratory environment. SEM and STM images show that the emitter surface has a complex porous structure. The cathode surface study by STS in tunneling gap modulation mode allowed to take a map of phase distribution with various work function values and high lateral resolution. Obtained images demonstrate the presence of three phases on the Pd/Ba emitter surface, viz. barium-oxygen compounds, intermetallic, and palladium. As it is seen from presented STS image the phase with a low work function value (barium oxides) is concentrated along boundaries of the substance inclusions with work function corresponding to the intemetallic compound Pd 5Ba. This supports the model of low work function areas obtained via Ba segregation from the intermetallic compound and oxidation. The presented methods may be used in the Pd/Ba cathode manufacturing process for increasing the yield of electronic devices in microwave tube production and optimize the emitters' characteristics.

  15. Electronic Spin Tunneling in the Binding of Carbon - to Hemoglobin.

    Gerstman, Bernard Scott

    1981-11-01

    A non-adiabatic quantum tunneling process is investigated as the mechanism for effecting the electronic spin change of the hemoglobin's iron upon the binding of carbon monoxide. As the carbon monoxide approaches there is a spin state change in the Fe('2+) from S = 2 to S = 0. The Born -Oppenheimer approximation can be used to separate the recombination of the CO to the iron in the heme at low temperatures into a nuclear tunneling and an electronic tunneling. Based upon the spin change of the Fe as well as the size of the tunneling matrix element and the energy splitting of the two states in the transition region, we assume the reaction to be a non-adiabatic electronic Landau-Zener state to state tunneling. The tunneling involves a spin change of the Fe and thus a spin-orbit interaction is used as the perturbation that couples the S = 2 and S = 0 manifolds. Since the matrix element for the transition is due to spin-orbit coupling the size of the matrix element can be changed, and hence the tunneling rate, by changing the spin magnetic sublevel of the initially CO unbound Fe. This is accomplished by applying a strong magnetic field of approximately 100 000 gauss which will tend to align the Fe spin at low enough temperature. The L vector will be affected only slightly by the external magnetic field since the Zeeman effect on the orbital levels is much smaller (10('-2)) than that of the internal crystal field of the molecule. Hence the crystal field of the heme determines the L quantization axis in each local heme coordinate system. Thus in a random oriented distribution of hemes frozen in place we expect faster CO recombination for those hemes who have their L vector aligned in the direction of the magnetic field than for those hemes whose L vector is perpendicular to the magnetic field. Hemoglobin has a strong absorption band at 436 nm when CO is bound. This absorption is also orientation dependent for the absorption is predominantly for light polarized in the plane of the dish like heme inside the hemoglobin molecule. We look for an orientation dependence to the recombination rate by looking for a magnetically induced optical dichroism in the sample. The CO molecules that are bound to hemoglobin molecules in a sample are photo-dissociated by an intense laser pulse in the presence of a magnetic field. As the CO molecules recombine with the hemoglobin we monitor the optical dichroism of the sample. The theory behind the magnetic field dependence is investigated in this work. I also describe the experiment carried out to test this theory and present the results which showed a magnetic field dependence to the recombination rate.

  16. Lateral electron tunnelling spectroscopy in etched GaAs/AlGaAs-based nanostructures

    Tunnelling spectroscopy between laterally positioned low-dimensional electron systems is investigated. We demonstrate that a reliable highly transparent tunnelling barrier can be fabricated by means of dynamic ploughing with the tip of an atomic force microscope and wet etching into the surface of a GaAs/AlGaAs heterostructure. This barrier allows to perform a tunnelling spectroscopy with dc bias voltages up to 30 mV. Band edge effects due to tunnel coupling were observed for two-dimensional electron gases (2DEGs) separated by such lateral tunnel barrier. Tunneling spectroscopy of a 2DEG and a laterally adjacent electron waveguide enable to monitor the one-dimensional (1D) density of states. Firstly, a lateral dual electron waveguide with 1D subband spacings of more than 5 meV was implemented showing significant features of 1D mode coupling in tunnelling spectroscopy.

  17. Tunneling electron induced luminescence from porphyrin molecules on monolayer graphene

    Geng, Feng; Kuang, Yanmin; Yu, Yunjie; Liao, Yuan; Zhang, Yao; Zhang, Yang; Dong, Zhenchao, E-mail: zcdong@ustc.edu.cn

    2015-01-15

    Using epitaxially grown graphene on Ru(0001) as a decoupling layer, we investigate the evolution of tunneling electron induced luminescence from different number of layers of porphyrin molecules. Light emission spectra and photon maps, acquired via a combined optical setup with scanning tunneling microscopy (STM), indicate that the electronic decoupling effect of a monolayer (ML) graphene alone is still insufficient for generating molecule-specific emission from both the 1st- and 2nd-layer porphyrin molecules. Nevertheless, interestingly, the plasmonic emission is enhanced for the 1st-layer but suppressed for the 2nd-layer in comparison with the plasmonic emission on the monolayer graphene. Intrinsic intramolecular molecular fluorescence occurs at the 3rd-layer porphyrin. Such molecular thickness is about two MLs thinner than previous reports where molecules were adsorbed directly on metals. These observations suggest that the monolayer graphene does weaken the interaction between molecule and metal substrate and contribute to the reduction of nonradiative decay rates. - Highlights: • Showing molecularly resolved photon maps of graphene and porphyrins on it. • Revealing the influence of spacer thickness on molecular electroluminescence. • Graphene does weaken the interaction between molecules and metal substrate.

  18. Resonant tunneling of interacting electrons in an AC electric field

    Elesin, V. F., E-mail: VFElesin@mephi.ru [National Research Nuclear University MEPhI (Russian Federation)

    2013-11-15

    The problem of the effect of electron-electron interaction on the static and dynamic properties of a double-barrier nanostructure (resonant tunneling diode (RTD)) is studied in terms of a coherent tunneling model, which includes a set of Schrdinger and Poisson equations with open boundary conditions. Explicit analytical expressions are derived for dc and ac potentials and reduced (active and reactive) currents in the quasi-classical approximation over a wide frequency range. These expressions are used to analyze the frequency characteristics of RTD. It is shown that the interaction can radically change the form of these expressions, especially in the case of a hysteretic I-V characteristic. In this case, the active current and the ac potentials can increase sharply at both low and high frequencies. For this increase to occur, it is necessary to meet quantum regime conditions and to choose a proper working point in the I-V characteristic of RTD. The possibility of appearance of specific plasma oscillations, which can improve the high-frequency characteristics of RTD, is predicted. It is found that the active current can be comparable with the resonant dc current of RTD.

  19. Signatures of attosecond electron tunneling dynamics in the evolution of intense few-cycle light pulses

    Serebryannikov, E. E.; Verhoef, A. J.; Mitrofanov, A.; Baltuška, A.; Zheltikov, A. M.

    2009-11-01

    The sensitivity of electron tunneling to the phase of an ionizing light field is shown to manifest itself in detectable features in the spectral and temporal evolution of intense few-cycle light pulses in an ionizing medium. An ultrafast buildup of electron density in the regime of tunneling ionization gives rise to a modulation of a few-cycle field wave form and enhances the short-wavelength part of its spectrum. In a low-pressure gas, the signatures of electron tunneling in the evolution of few-cycle pulses can be isolated from the effects related to atomic nonlinear susceptibilities, giving an access to attosecond electron tunneling dynamics.

  20. Thermoelectric effects in electron chiral tunneling in metallic carbon nanotubes

    Parafilo, A. V.; Ilinskaya, O. A.; Krive, I. V.; Park, Y. W.

    2015-12-01

    Thermoelectric effects in a metallic single-wall carbon nanotube in the presence of long-range electrostatic and pseudomagnetic potentials (produced by strain) are considered. It is shown that for strong scattering potentials (chiral tunneling) a pronounced energy "gap" appears in the energy dependence of electron transmission coefficient. This results in strong violation of Wiedemann-Franz law and in a peak-like behavior of thermopower as a function of chemical potential. The electronic figure-of-merit (ZT) is calculated and shown to be sensitive at low temperatures to nanotube chirality. By tuning chemical potential, ZT can reach high values (ZT?5) that makes specially engineered nanotube-based thermocouple to be a promising nano-device with a high thermoelectric performance.

  1. Implementing CORAL: An Electronic Resource Management System

    Whitfield, Sharon

    2011-01-01

    A 2010 electronic resource management survey conducted by Maria Collins of North Carolina State University and Jill E. Grogg of University of Alabama Libraries found that the top six electronic resources management priorities included workflow management, communications management, license management, statistics management, administrative…

  2. TERMS: Techniques for electronic resources management

    Emery, Jill; Stone, Graham

    2013-01-01

    Librarians and information specialists have been finding ways to manage electronic resources for over a decade now. However, much of this work has been an ad hoc and learn-as-you-go process. The literature on electronic resource management shows this work as being segmented into many different areas of traditional librarian roles within the library. In addition, the literature show how management of these resources has driven the development of various management tools in the market as well a...

  3. High Performance Resonant Tunneling Electronic Circuit with Suitable Resistance Parameters

    Hsiao Hsuan Cheng

    2012-10-01

    Full Text Available Well-defined experimental and simulating single peak to valley current density ratio (PVCDR resonant tunneling electronic circuit (RTEC element is proposed in this research. The variation of passive element value in RTEC structure is explored using simulation method, which obtains the optimum PVCDR values about 66. The simulating peak current density (PCD value is such high as 38 mA. Even though the experimental PCD value is less, but the PVCDR value is as high as 22.5, which value is favorably compared with semiconductor resonant tunneling devices (RTDs in single PVCDR RTEC element. The obvious triple negative differential resistance (NDR is also completed using composition of three suitable single RTEC elements. Also, experimental triple PVCDR RTEC element significantly exhibits three NDR curves with obvious three PVCDR values about 3.4, 3.8, and 6.0, respectively. Both peak voltage (PV value and valley voltage (VV values of experimental triple PVCDR RTEC element is less than 2.8 V, which value is profitable in development of commercial product. Power consumption of triple PVCDR RTEC element is as low as 75.5 ?W, which low power consumption will shrink the difficulty of element packaging in heat dissipation.

  4. Digital Preservation of Electronic Resources

    Ramesh C. Gaur,

    2012-07-01

    Full Text Available Due to huge advances in information communication technologies (ICTs, there has been an astronomicalgrowth of e-resourcese-journals, e-books, online databases and so on; libraries spend phenomenally onacquisition of these e- resources as these are very popularly used by the students and researchers.Unfortunately, this growth is accompanied by many threats. Digital content (of the e- resources is fragile andnot durable. Its accessibility and use by future generations depends on technology which very rapidly evolvesand changes. Hence, ensuring access of e-resources for future generation of users is a big challenge forlibraries. The present paper highlights various problems of digital content and elaborates how digital preservationis more demanding and challenging than preserving print copies of journals. It also gives a birds eye viewof various projects initiated for archiving digital content of scholarly journals.

  5. Spurious signals generated by electron tunneling on large reflector antennas

    Higa, W. H.

    1975-01-01

    Large reflector antennas are currently fabricated by assembling a large number of small light aluminum panels onto a superstructure. A large number of aluminum-to-aluminum joints are inherently exposed to RF radiation on such an antenna. It is shown in this paper that the natural oxide layer on aluminum is of the correct thickness to permit electron tunneling through the Al-Al2O3-Al junctions. The nonlinearity due to the junctions then generates spurious signals when these antennas are used for simultaneous transmission and reception of signals at different frequencies. Moreover, the large number of junctions (rivets) on an antenna can combine to produce serious interference in these diplexed systems.

  6. Electronic Single Molecule Identification of Carbohydrate Isomers by Recognition Tunneling

    Im, JongOne; Liu, Hao; Zhao, Yanan; Sen, Suman; Biswas, Sudipta; Ashcroft, Brian; Borges, Chad; Wang, Xu; Lindsay, Stuart; Zhang, Peiming

    2016-01-01

    Glycans play a central role as mediators in most biological processes, but their structures are complicated by isomerism. Epimers and anomers, regioisomers, and branched sequences contribute to a structural variability that dwarfs those of nucleic acids and proteins, challenging even the most sophisticated analytical tools, such as NMR and mass spectrometry. Here, we introduce an electron tunneling technique that is label-free and can identify carbohydrates at the single-molecule level, offering significant benefits over existing technology. It is capable of analyzing sub-picomole quantities of sample, counting the number of individual molecules in each subset in a population of coexisting isomers, and is quantitative over more than four orders of magnitude of concentration. It resolves epimers not well separated by ion-mobility and can be implemented on a silicon chip. It also provides a readout mechanism for direct single-molecule sequencing of linear oligosaccharides.

  7. Low-frequency noise in single electron tunneling transistor

    Tavkhelidze, A.N.; Mygind, Jesper

    1998-01-01

    The noise in current biased aluminium single electron tunneling (SET) transistors has been investigated in the frequency range of 5 mHz = 10 Hz......, we find the same input charge noise, typically QN = 5 × 10–4 e/Hz1/2 at 10 Hz, with and without the HF shielding. At lower frequencies, the noise is due to charge trapping, and the voltage noise pattern superimposed on the V(Vg) curve (voltage across transistor versus gate voltage) strongly depends...

  8. Characterization of aluminum oxide tunnel barriers by combining transport measurements and transmission electron microscope imaging

    Aref, T.; Averin, A.; van Dijken, Sebastiaan; Ferring, A.; Koberidze, M; Maisi, V. F.; Nguyend, H. Q.; Nieminen, Risto M.; Pekola, Jukka P.; Yao, L. D.

    2014-01-01

    We present two approaches for studying the uniformity of a tunnel barrier. The first approach is based on measuring single-electron and two-electron tunneling in a hybrid single-electron transistor. Our measurements indicate that the effective area of a conduction channel is about one order of magnitude larger than predicted by theoretical calculations. With the second method, transmission electron microscopy, we demonstrate that variations in the barrier thickness are a plausible explanation...

  9. Tunneling electron induced chemisorption of copper phthalocyanine molecules on the Cu(111) surface

    Stock, T.; Nogami, J. [Department of Materials Science and Engineering, University of Toronto, Toronto, Ontario M5S 3E4 (Canada)

    2014-02-17

    The adsorption of up to one monolayer (ML) of copper phthalocyanine (CuPc) molecules on a room temperature Cu(111) surface has been studied using scanning tunneling microscopy (STM). Below 1 ML the molecules are in a fluid state and are highly mobile on the surface. At 1 ML coverage the molecules coalesce into a highly ordered 2D crystal phase. At sub-ML coverages, chemisorption of individual CuPc molecules can be induced through exposure to tunneling electrons at a tunneling bias voltage exceeding a threshold value. This tunneling electron induced effect has been exploited to perform molecular STM lithography.

  10. Dynamics of Managing Electronic Resources: Electronic Resource Management System (ERMS) Initiatives

    John Paul Anbu K.; Sanjay Kataria; Shri Ram,

    2013-01-01

    Even after two decades of digital presence in libraries and proliferation of electronic resources (e-resources) in terms of production, acquisition and usage the management of e-resources remains a cumbersome process. The process involved in the management of e-resources has often overwhelmed the library personnel. The life cycle of e-resources, especially in the academic institutions begin with the discovery and identification of the resource and moves on to the trial access, selecting the s...

  11. Managing Electronic Resources with Open Source Software

    Roën Janyk; Sandra Wong

    2012-01-01

    The Simon Fraser University Library has been a leader in developing open source solutions for libraries for more than a decade.  This session will provide an overview of the complex world of library systems (Link Resolvers, Knowledgebases, Integrated Library Systems, Electronic Resource Management Systems, Discovery Services, Off-campus authentication systems) used by the modern academic library to efficiently manage electronic resources.  The session will present perspectives from ...

  12. Techniques in Electronic Resource Management (TERMS)

    Stone, Graham; Emery, Jill

    2012-01-01

    Two decades after the advent of electronic journals and databases, librarians are still grappling with ways to best manage these resources in conjunction with their print resources. In addition, economic pressures at many institutions of Higher Education are resulting in librarians having to justify their spending on collections and resource management. Furthermore, ebooks are becoming yet another stream of purchasing and management with the added complexity of patron driven acquisitions. All...

  13. Characterization of aluminum oxide tunnel barriers by combining transport measurements and transmission electron microscopy imaging

    Aref, T.; Averin, A.; Nguyend, H. Q.; Pekola, J. P. [Low Temperature Laboratory (OVLL), Aalto University School of Science, P.O. Box 13500, 00076 Aalto (Finland); Dijken, S. van; Yao, L. D. [NanoSpin, Department of Applied Physics, Aalto University School of Science, P.O. Box 15100, FI-00076 Aalto (Finland); Ferring, A. [Kirchhoff-Institute for Physics, Heidelberg University, Im Neuenheimer Feld 227, D-69120 Heidelberg (Germany); Koberidze, M.; Nieminen, R. M. [COMP/Department of Applied Physics, Aalto University School of Science, P.O. Box 11100, FI-00076 Aalto, Espoo (Finland); Maisi, V. F., E-mail: ville.maisi@gmail.com [Low Temperature Laboratory (OVLL), Aalto University School of Science, P.O. Box 13500, 00076 Aalto (Finland); Centre for Metrology and Accreditation (MIKES), P.O. Box 9, 02151 Espoo (Finland)

    2014-08-21

    We present two approaches for studying the uniformity of a tunnel barrier. The first approach is based on measuring single-electron and two-electron tunneling in a hybrid single-electron transistor. Our measurements indicate that the effective area of a conduction channel is about one order of magnitude larger than predicted by theoretical calculations. With the second method, transmission electron microscopy, we demonstrate that variations in the barrier thickness are a plausible explanation for the larger effective area and an enhancement of higher order tunneling processes.

  14. Excitation of plasmonic nanoantennas with nonresonant and resonant electron tunnelling

    Uskov, Alexander V; Protsenko, Igor E; Smetanin, Igor V; Bouhelier, Alexandre

    2016-01-01

    A rigorous theory of photon emission accompanied inelastic tunnelling inside the gap of plasmonic nanoantennas has been developed. The disappointingly low efficiency of the electrical excitation of surface plasmon polaritons in these structures can be increased by orders of magnitude when a resonant tunnelling structure is incorporated inside the gap. Resonant tunnelling assisted surface plasmon emitter may become a key element in future electrically-driven nanoplasmonic circuits.

  15. Electron Tunneling Pathways and Role of Adenine in Repair of Cyclobutane Pyrimidine Dimer by DNA Photolyase

    Liu, Zheyun; Guo, Xunmin; Tan, Chuang; Li, Jiang; Kao, Ya-Ting; Wang, Lijuan; Sancar, Aziz; Zhong, Dongping

    2012-01-01

    Electron tunneling pathways in enzymes are critical to their catalytic efficiency. Through electron tunneling, photolyase, a photoenzyme, splits UV-induced cyclobutane pyrimidine dimer into two normal bases. Here, we report our systematic characterization and analyses of photo-initiated three electron transfer processes and cyclobutane ring splitting by following the entire dynamical evolution during enzymatic repair with femtosecond resolution. We observed the complete dynamics of the reacta...

  16. Electron beam fluorescence measurements in the Boeing hypersonic shock tunnel

    Price, Linwood L.; Williams, W. Dan; Powell, H. M.

    1992-01-01

    The Calspan electron beam fluorescence (EBF) measurement system is described along with the results of measurements made in hypersonic flow. Numerous self-emitting metallic species were identified, many of which may be associated with an aging/erosion process within the B30HST. Because there were only 16 tunnel runs, it was only possible to obtain spectral measurements over a limited range of wavelengths and time sampling periods. Many spectral features of the flow remain uninvestigated. Because flow self-emission is important to all optical diagnostic techniques, it is recommended that additional spectral studies by performed. The three electron beam-excited species that were identified are nitrogen, helium, and nitric oxide. The high metallic radiation background interfered with attempts to obtain the time-wise variation of N2 density and He radiation with the optical fiber/PMT channels. In the case of the N2 density measurements the result of interference was increased uncertainty. Unfortunately, the interference caused the time-wise He measurements to fail completely. It is recommended that the electron beam be modulated to provide discrimination against the background radiation in future N2 density measurements. Careful data reduction produced useful measurements of N2 vibrational temperature, even though the high background from metallic species significantly increased measurement uncertainty. Perhaps the recommended additional spectral studies would reveal N2(+) First Negative System band-pair regions having less background. Detection of the He arrival was easily accomplished with the spectrometer/array detector system. Because of this, it is recommended that this means of detecting He arrival be used in the future. With proper calibrations of the system an He number density could be obtained. Although the flow conditions were out of limits for the run in which the NO spectrum was recorded, the usefulness of the NO spectrum for determination of free-stream rotational temperature was demonstrated and should be exploited in future experiments. Indeed, based on the strong NO signals, it is recommended that lower resolution NO spectra be obtained to provide a measure of NO vibrational temperature in the same manner that the N2 temperature was obtained.

  17. A fullerene molecular tip can detect localized and rectified electron tunneling within a single fullereneporphyrin pair

    Nishino, Tomoaki; Ito, Takashi; Umezawa, Yoshio

    2005-01-01

    A fullerene molecular tip was used to detect electron tunneling from a single porphyrin molecule. Electron tunneling was found to occur locally from an electron-donating moiety of the porphyrin to the fullerene through charge-transfer interaction between them. In addition, electron tunneling within the single fullereneporphyrin pair exhibited rectifying behavior in which electrons can be driven only at the direction from the porphyrin to the fullerene. It is demonstrated that localized elect...

  18. Fluorescence and phosphorescence from individual C$_{60}$ molecules excited by local electron tunneling

    Cavar, E; Pivetta, M; Chergui, M; Schneider, W D; Cavar, Elizabeta \\'; Bl\\"um, Marie-Christine; Pivetta, Marina; Chergui, Majed; Schneider, Wolf-Dieter

    2005-01-01

    Using the highly localized current of electrons tunneling through a double barrier Scanning Tunneling Microscope (STM) junction, we excite luminescence from a selected C$_{60}$ molecule in the surface layer of fullerene nanocrystals grown on an ultrathin NaCl film on Au(111). In the observed luminescence fluorescence and phosphorescence spectra, pure electronic as well as vibronically induced transitions of an individual C$_{60}$ molecule are identified, leading to unambiguous chemical recognition on the single-molecular scale.

  19. Bilayer insulator tunnel barriers for graphene-based vertical hot-electron transistors

    Vaziri, S.; Belete, M.; Dentoni Litta, E.; Smith, A. D.; Lupina, G.; Lemme, M. C.; stling, M.

    2015-07-01

    Vertical graphene-based device concepts that rely on quantum mechanical tunneling are intensely being discussed in the literature for applications in electronics and optoelectronics. In this work, the carrier transport mechanisms in semiconductor-insulator-graphene (SIG) capacitors are investigated with respect to their suitability as electron emitters in vertical graphene base transistors (GBTs). Several dielectric materials as tunnel barriers are compared, including dielectric double layers. Using bilayer dielectrics, we experimentally demonstrate significant improvements in the electron injection current by promoting Fowler-Nordheim tunneling (FNT) and step tunneling (ST) while suppressing defect mediated carrier transport. High injected tunneling current densities approaching 103 A cm-2 (limited by series resistance), and excellent current-voltage nonlinearity and asymmetry are achieved using a 1 nm thick high quality dielectric, thulium silicate (TmSiO), as the first insulator layer, and titanium dioxide (TiO2) as a high electron affinity second layer insulator. We also confirm the feasibility and effectiveness of our approach in a full GBT structure which shows dramatic improvement in the collector on-state current density with respect to the previously reported GBTs. The device design and the fabrication scheme have been selected with future CMOS process compatibility in mind. This work proposes a bilayer tunnel barrier approach as a promising candidate to be used in high performance vertical graphene-based tunneling devices.

  20. Electron tunnelling through single azurin molecules can be on/off switched by voltage pulses

    Baldacchini, Chiara [Biophysics and Nanoscience Centre, DEB-CNISM, Universit della Tuscia, I-01100 Viterbo (Italy); Institute of Agro-Environmental and Forest Biology, CNR, I-05010 Porano (Italy); Kumar, Vivek; Bizzarri, Anna Rita; Cannistraro, Salvatore, E-mail: cannistr@unitus.it [Biophysics and Nanoscience Centre, DEB-CNISM, Universit della Tuscia, I-01100 Viterbo (Italy)

    2015-05-04

    Redox metalloproteins are emerging as promising candidates for future bio-optoelectronic and nano-biomemory devices, and the control of their electron transfer properties through external signals is still a crucial task. Here, we show that a reversible on/off switching of the electron current tunnelling through a single protein can be achieved in azurin protein molecules adsorbed on gold surfaces, by applying appropriate voltage pulses through a scanning tunnelling microscope tip. The observed changes in the hybrid system tunnelling properties are discussed in terms of long-sustained charging of the protein milieu.

  1. Hysteresis phenomena in electron tunneling, induced by surface plasmons

    Kroo, Norbert; Racz, Peter

    2013-01-01

    A high spatial resolution surface plasmon near field scanning tunneling microscope (STM) has been used to study the properties of localized surface plasmons (SPO) in so-called hot spots on a gold surface, where the local electromagnetic field is extremely high. A CW semiconductor laser and a femtosecond Ti:Sa laser were used to excite the plasmons and the SPO excited tunnel current was used as the detector. When scanning the STM from negative to positive bias and reversed, hysteresis in the tunnel signal was found, excluding (or rather minimizing) the role of the presence of a Casimir effect in the process. It was found, however, that a multiple image charge induced double well potential may explain our experimental findings. The stepwise behaviour of the area of the observed hysteresis loops is a new, additional indication of the non-classical properties of the SPOs.

  2. Inelastic Electron Tunneling Spectroscopy in Molecular Electronic Devices from First-Principles

    Ji, Tao

    In this thesis, we present the first-principle calculations of inelastic electron tunneling spectroscopy(IETS) in single molecular break junctions. In a two-probe electrode-molecule-electrode setup, density functional theory(DFT) is used for the construction of the Hamiltonian and the Keldysh non-equilibrium Green's function(NEGF) technique will be employed for determining the electron density in non-equilibrium system conditions. Total energy functional, atomic forces and Hessian matrix can be obtained in the DFT-NEGF formalism and self-consistent Born approximation(SCBA) is used to integrate the molecular vibrations (phonons) into the framework once the phonon spectra and eigenvectors are calculated from the dynamic matrix. Geometry optimization schemes will also be discussed as an indispensable part of the formalism as the equilibrium condition is crucial to correctly calculate the phonon properties of the system. To overcome the numerical difficulties, especially the large computational time demand of the electron-phonon coupling problem, we develop a numerical approximation for the electron self-energy due to phonons and the error is controlled within numerical precision. Besides, a direct IETS second order I-V derivative expression is derived to reduce the error of numerical differentiation under reasonable assumptions. These two approximations greatly reduce the computation requirement and make the calculation feasible within current numerical capability. As the application of the DFT-NEGF-SCBA formalism, we calculate the IETS of the gold-octanedithiol(ODT) molecular junction. The I-V curve, conductance and IETS from ab-inito calculations are compared directly to experiments. A microscopic understanding of the electron-phonon coupling mechanism in the molecular tunneling junctions is explained in this example. In addition, comparisons of the hydrogen-dissociative and hydrogen-non-dissociative ODT junctions as well as the different charge transfer behaviors are presented to show the effects of thiol formation in the ODT molecular junction.

  3. Estimation of potential radiation damage to electronics units in the CLIC tunnel

    Patapenka, Andrei

    2014-01-01

    An electronic unit is required for each CLIC “Two Beam Module”. This study aims to estimate the potential damage due to the prompt radiation to the electronics units installed inside the CLIC Main Linac tunnel. Sets of Monte-Carlo simulations have been done to estimate damage to electronics installed at various locations inside the tunnel. Continuous and point beam losses have been considered for CLIC Main and Drive beams. Lead and iron in combination with a polyethylene layer were investigated as a possible shielding. The upper limits of the estimated quantities are presented for stand alone and shielded electronics.

  4. Negative differential resistance in GaN tunneling hot electron transistors

    Yang, Zhichao; Nath, Digbijoy; Rajan, Siddharth [Department of Electrical and Computer Engineering, The Ohio State University, Columbus, Ohio 43202 (United States)

    2014-11-17

    Room temperature negative differential resistance is demonstrated in a unipolar GaN-based tunneling hot electron transistor. Such a device employs tunnel-injected electrons to vary the electron energy and change the fraction of reflected electrons, and shows repeatable negative differential resistance with a peak to valley current ratio of 7.2. The device was stable when biased in the negative resistance regime and tunable by changing collector bias. Good repeatability and double-sweep characteristics at room temperature show the potential of such device for high frequency oscillators based on quasi-ballistic transport.

  5. Negative differential resistance in GaN tunneling hot electron transistors

    Room temperature negative differential resistance is demonstrated in a unipolar GaN-based tunneling hot electron transistor. Such a device employs tunnel-injected electrons to vary the electron energy and change the fraction of reflected electrons, and shows repeatable negative differential resistance with a peak to valley current ratio of 7.2. The device was stable when biased in the negative resistance regime and tunable by changing collector bias. Good repeatability and double-sweep characteristics at room temperature show the potential of such device for high frequency oscillators based on quasi-ballistic transport

  6. Electronics and electrotechnics in technical management of the Channel tunnel

    Pascal, A.

    1995-07-01

    Power supplies to the Channel Tunnel come from the EDF switchyard at Les Mandarins and that of Seeboard at Sellindge, both of which are normally in service. Power is distributed from 20 kV/400 V sub-stations. The lighting circuits are ranked in order of priority. Tunnel auxiliaries are powered through four 20 kV cables. This supply is transformed in sub-stations to 3.3 kV before feeding the electrical plant. This power supply system benefits from considerable redundancy which should ensure an availability close to 100%. (author). 6 figs., 1 tab.

  7. Characterization of All-Chromium Tunnel Junctions and Single Electron Tunneling Devices Fabricated by Direct-Writing Multilayer Technique

    Scherer, H; Hinze, P; Samwer, B W; Zorin, A B; Niemeyer, J C; Weimann, Th.

    1999-01-01

    We report about the fabrication and analysis of the properties of Cr/CrO_x/Cr tunnel junctions and SET transistors, prepared by different variants of direct-writing multilayer technique. In all cases, the CrO_x tunnel barriers were formed in air under ambient conditions. From the experiments on single junctions, values for the effective barrier height and thickness were derived. For the Cr/CrO_x/Cr SET transistors we achieved minimal junction areas of 17 x 60 nm^2 using a scanning transmission electron microscope for the e-beam exposure on Si_3N_4 membrane substrate. We discuss the electrical performance of the transistor samples as well as their noise behavior.

  8. Electronic Resources and Web Sites: Replacing a Back-end Database with Innovative's Electronic Resource Management

    Tull, Laura

    2013-01-01

    In the fall of 2002, Ohio State University along with the University of Washington, the University of Western Australia, Washington State University, and Glasgow University entered into a development partnership with Innovative Interfaces. The goal was to develop a module to manage electronic resources, integrated into Innovatives Millennium library system. The product, Electronic Resource Management (ERM), became available in 2004 and is based on the work of the Digital Library Federation E...

  9. Dynamics of Managing Electronic Resources: Electronic Resource Management System (ERMS Initiatives

    John Paul Anbu K.

    2013-07-01

    Full Text Available Even after two decades of digital presence in libraries and proliferation of electronic resources (e-resources in terms of production, acquisition and usage the management of e-resources remains a cumbersome process. The process involved in the management of e-resources has often overwhelmed the library personnel. The life cycle of e-resources, especially in the academic institutions begin with the discovery and identification of the resource and moves on to the trial access, selecting the specific resource from the gamut of other resources followed by acquisition of the specific resource into the library realm and then felicitating access to the users and then the follow-up of studying the usage of the resource for further continuation of those resources. In between these processes there is the cumbersome chore of going through the licensing agreements and keeping the records correct. All these processes are time consuming and involve a lot of work. These relentless arrays of work have made librarians to look for systems which can save their time and energy and provide efficient management of e-resources. This paper looks at the origin of the ERMS (E-resource Management Systems and the available ERMS in the library digital landscape.

  10. Dynamics of Managing Electronic Resources: Electronic Resource Management System (ERMS Initiatives

    John Paul Anbu K.

    2013-07-01

    Full Text Available Even after two decades of digital presence in libraries and proliferation of electronic resources (e-resources in terms of production, acquisition and usage the management of e-resources remains a cumbersome process. The process involved in the management of e-resources has often overwhelmed the library personnel. The life cycle of e-resources, especially in the academic institutions begin with the discovery and identification of the resource and moves on to the trial access, selecting the specific resource from the gamut of other resources followed by acquisition of the specific resource into the library realm and then felicitating access to the users and then the follow-up of studying the usage of the resource for further continuation of those resources. In between these processes there is the cumbersome chore of going through the licensing agreements and keeping the records correct. All these processes are time consuming and involve a lot of work. These relentless arrays of work have made librarians to look for systems which can save their time and energy and provide efficient management of e-resources. This paper looks at the origin of the ERMS (E-resource Management Systems and the available ERMS in the library digital landscape.http://dx.doi.org/10.14429/djlit.33.4885

  11. Investigation of electron and hole tunneling through thin silicon dioxide films

    The processes of electrons and holes tunneling through thin silicon dioxide films have been investigated. In parallel with the direct measurement of tunneling current in Si-SiO2-Al structures, an original method, based on the accumulation of charge in Si-SiO2-Si3N4-Al structures, have been used. The current-voltage dependences obtained by two methods for electron tunneling are in agreement and correspond to carrier injection from silicon at a positive voltage on metal according to the Fowler-Nordheim mechanism. The hole tunneling current can be measured only by the charge accumulation method due to a high energy barrier for holes. Possible mechanisms of positive charge accumulation are discussed

  12. Toward Low-Power Electronics: Tunneling Phenomena in Transition Metal Dichalcogenides

    Das, Saptarshi; Prakash, Abhijith; Salazar, Ramon; Appenzeller, Joerg

    2014-01-01

    In this article, we explore, experimentally, the impact of band-to-band tunneling on the electronic transport of double-gated WSe2 field-effect transistors (FETs) and Schottky barrier tunneling of holes in back-gated MoS2 FETs. We show that by scaling the flake thickness and the thickness of the gate oxide, the tunneling current can be increased by several orders of magnitude. We also perform numerical calculations based on Landauer formalism and WKB approximation to explain our experimental ...

  13. Semantic Web and Electronic Information Resources

    Radovanovic, Danica

    2003-01-01

    The usage of electronic resources depends on good possibilities of searching and the Semantic Web concept can be convenient solution for information retrieval (IR). WWW (World Wide Web) enables, with the help of search engines and huge number of available (meta)information, data that can satisfy user's need for information, but only at some extent. At the same time, there are more and more research efforts to increase the efficiency for IR until one gets as much as possible rel...

  14. Detecting hydrogen gas by single electron tunneling based sensors: an image processing and simulation study

    ABBASI, H.; KHAJE, M.; H Sedghi

    2015-01-01

    Abstract. We present a hydrogen sensor based on single electron tunneling at two dimensional (2D) hexagonal closed packed arrays of palladium nano-islands. Parameters of the hexagonal closed packed arrays of palladium nanoparticles were extracted from experimental TEM results by image processing methods. Using SIMON simulator, emergences of the coulomb blockade were inspected by studying Current-Voltage (IV) characteristics of equivalent circuits consisting of palladium islands and tunneling ...

  15. Simulation of inelastic electron tunneling spectroscopy of single molecules with functionalized tips

    García-Lekue, Aran; Sánchez-Portal, Daniel; Arnau, Andrés; Frederiksen, T.

    2011-01-01

    The role of the tip in inelastic electron tunneling spectroscopy (IETS) performed with scanning tunneling microscopes (STM) is theoretically addressed via first-principles simulations of vibrational spectra of single carbon monoxide (CO) molecules adsorbed on Cu(111). We show how chemically functionalized STM tips modify the IETS intensity corresponding to adsorbate modes on the sample side. The underlying propensity rules are explained using symmetry considerations for both the vibrational m...

  16. Ferrocenes on Calcite: Single-electron tunneling detected at room temperature

    Rahe, Philipp; Steele, Ryan; Williams, Clayton

    2014-03-01

    We present the assembly of a functionalized ferrocene derivative on a truly insulating support, namely the calcite (10 1 4) surface, and investigate the transfer of single electrons between the molecules and the conductive tip of an atomic force microscope in the absence of a macroscopic tunneling current. Molecules on insulating surfaces attract currently increasing attention, stimulated by promising applications in the fields of surface functionalization and, especially, in the context of molecular (opto-)electronics. For isolated atoms and single molecules adsorbed on thin insulating films, the manipulation and storage of single charges has been induced by a tunneling current. Our approach, however, is based on single-electron tunneling force microscopy methods combined with Kelvin-probe force microscopy. By using this combination of methods we present the measurement and control of the charge state of the ferrocene molecules by injecting and extracting charge on the order of single electrons.

  17. Excitation of the ligand-to-metal charge transfer band induces electron tunnelling in azurin

    Baldacchini, Chiara [Biophysics and Nanoscience Centre, DEB-CNISM, Universit della Tuscia, I-01100 Viterbo (Italy); Institute of Agro-environmental and Forest Biology, National Research Council, I-05010 Porano (Italy); Bizzarri, Anna Rita; Cannistraro, Salvatore, E-mail: cannistr@unitus.it [Biophysics and Nanoscience Centre, DEB-CNISM, Universit della Tuscia, I-01100 Viterbo (Italy)

    2014-03-03

    Optical excitation of azurin blue copper protein immobilized on indium-tin oxide, in resonance with its ligand-to-metal charge transfer absorption band, resulted in a light-induced current tunnelling within the protein milieu. The related electron transport rate is estimated to be about 10{sup 5}?s{sup ?1}. A model based on resonant tunnelling through an azurin excited molecular state is proposed. The capability of controlling electron transfer processes through light pulses opens interesting perspectives for implementation of azurin in bio-nano-opto-electronic devices.

  18. Imaging Electronic Excitation of NO by Ultrafast Laser Tunneling Ionization

    Endo, Tomoyuki; Matsuda, Akitaka; Fushitani, Mizuho; Yasuike, Tomokazu; Tolstikhin, Oleg I.; Morishita, Toru; Hishikawa, Akiyoshi

    2016-04-01

    Tunneling-ionization imaging of photoexcitation of NO has been demonstrated by using few-cycle near-infrared intense laser pulses (8 fs, 800 nm, 1.1 ×1014 W /cm2 ). The ion image of N+ fragment ions produced by dissociative ionization of NO in the ground state, NO (X2Π ,2 π )→NO+ +e-→N+ +O +e- , exhibits a characteristic momentum distribution peaked at 45° with respect to the laser polarization direction. On the other hand, a broad distribution centered at ˜0 ° appears when the A2Σ+ (3 s σ ) excited state is prepared as the initial state by deep-UV photoexcitation. The observed angular distributions are in good agreement with the corresponding theoretical tunneling ionization yields, showing that the fragment anisotropy reflects changes of the highest-occupied molecular orbital by photoexcitation.

  19. Competing Anisotropy-Tunneling Correlation of the CoFeB/MgO Perpendicular Magnetic Tunnel Junction: An Electronic Approach

    Yang, Chao-Yao; Chang, Shu-Jui; Lee, Min-Han; Shen, Kuei-Hung; Yang, Shan-Yi; Lin, Horng-Ji; Tseng, Yuan-Chieh

    2015-11-01

    We intensively investigate the physical principles regulating the tunneling magneto-resistance (TMR) and perpendicular magnetic anisotropy (PMA) of the CoFeB/MgO magnetic tunnel junction (MTJ) by means of angle-resolved x-ray magnetic spectroscopy. The angle-resolved capability was easily achieved, and it provided greater sensitivity to symmetry-related d-band occupation compared to traditional x-ray spectroscopy. This added degree of freedom successfully solved the unclear mechanism of this MTJ system renowned for controllable PMA and excellent TMR. As a surprising discovery, these two physical characteristics interact in a competing manner because of opposite band-filling preference in space-correlated symmetry of the 3d-orbital. An overlooked but harmful superparamagnetic phase resulting from magnetic inhomogeneity was also observed. This important finding reveals that simultaneously achieving fast switching and a high tunneling efficiency at an ultimate level is improbable for this MTJ system owing to its fundamental limit in physics. We suggest that the development of independent TMR and PMA mechanisms is critical towards a complementary relationship between the two physical characteristics, as well as the realization of superior performance, of this perpendicular MTJ. Furthermore, this study provides an easy approach to evaluate the futurity of any emerging spintronic candidates by electronically examining the relationship between their magnetic anisotropy and transport.

  20. Novel Transport Mechanism for Interacting Electrons in Disordered Systems: Variable-Range Resonant Tunneling

    Baranovskii, S. D.; Shlimak, I. S.

    1998-01-01

    To interpret recent experimental observations of the phononless hopping conduction, we suggest a novel transport mechanism according to which the current-carrying single electrons move via quantum resonant tunneling between localized states brought into resonance by fast electron hops in their environment.

  1. Resonant tunneling through discrete electronic levels of a C60 molecule in the presence of charging effects

    We have conducted tunneling spectroscopy studies for isolated C60 molecules in a double barrier tunnel junction configuration. The tunneling current-voltage (I-V) and dI/dV vs. V spectra of these molecules exhibit rich structures resulting from both resonant tunneling through the discrete levels and single electron charging effects. In particular, we observe degeneracy lifting within the molecular orbitals, probably due to Jahn-Teller effect and local electric fields. Theoretical fits, performed using the 'orthodox' model for single-electron tunneling modified to account for the discrete level spectrum of C60, agree well with our data. (author)

  2. Electron Tunneling Pathways and Role of Adenine in Repair of Cyclobutane Pyrimidine Dimer by DNA Photolyase

    Liu, Zheyun; Guo, Xunmin; Tan, Chuang; Li, Jiang; Kao, Ya-Ting; Wang, Lijuan; Sancar, Aziz; Zhong, Dongping

    2012-01-01

    Electron tunneling pathways in enzymes are critical to their catalytic efficiency. Through electron tunneling, photolyase, a photoenzyme, splits UV-induced cyclobutane pyrimidine dimer into two normal bases. Here, we report our systematic characterization and analyses of photo-initiated three electron transfer processes and cyclobutane ring splitting by following the entire dynamical evolution during enzymatic repair with femtosecond resolution. We observed the complete dynamics of the reactants, all intermediates and final products, and determined their reaction time scales. Using (deoxy)uracil and thymine as dimer substrates, we unambiguously determined the electron tunneling pathways for the forward electron transfer to initiate repair and for the final electron return to restore the active cofactor and complete the catalytic photocycle. Significantly, we found that the adenine moiety of the unusual bent flavin cofactor is essential to mediating all electron-transfer dynamics through a super-exchange mechanism, leading to a delicate balance of time scales. The cyclobutane ring splitting takes tens of picoseconds while electron-transfer dynamics all occur on a longer time scale. The active-site structural integrity, unique electron tunneling pathways and the critical role of adenine assure the synergy of these elementary steps in this complex photorepair machinery to achieve maximum repair efficiency which is close to unity. Finally, we used the Marcus electron-transfer theory to evaluate all three electron transfer processes and thus obtained their reaction driving forces (free energies), reorganization energies, and electronic coupling constants, concluding the forward and futile back electron transfer in the normal region and that the final electron return of the catalytic cycle is in the inverted region. PMID:22533849

  3. Dynamic tunneling force microscopy for characterizing electronic trap states in non-conductive surfaces

    Dynamic tunneling force microscopy (DTFM) is a scanning probe technique for real space mapping and characterization of individual electronic trap states in non-conductive films with atomic scale spatial resolution. The method is based upon the quantum mechanical tunneling of a single electron back and forth between a metallic atomic force microscopy tip and individual trap states in completely non-conducting surface. This single electron shuttling is measured by detecting the electrostatic force induced on the probe tip at the shuttling frequency. In this paper, the physical basis for the DTFM method is unfolded through a physical model and a derivation of the dynamic tunneling signal as a function of several experimental parameters is shown. Experimental data are compared with the theoretical simulations, showing quantitative consistency and verifying the physical model used. The experimental system is described and representative imaging results are shown

  4. Tunneling of electrons via rotor-stator molecular interfaces: combined ab initio and model study

    Petreska, Irina; Pejov, Ljupco; Kocarev, Ljupco

    2015-01-01

    Tunneling of electrons through rotor-stator anthracene aldehyde molecular interfaces is studied with a combined ab initio and model approach. Molecular electronic structure calculated from first principles is utilized to model different shapes of tunneling barriers. Together with a rectangular barrier, we also consider a sinusoidal shape that captures the effects of the molecular internal structure more realistically. Quasiclassical approach with the Simmons' formula for current density is implemented. Special attention is paid on conformational dependence of the tunneling current. Our results confirm that the presence of the side aldehyde group enhances the interesting electronic properties of the pure anthracene molecule, making it a bistable system with geometry dependent transport properties. We also investigate the transition voltage and we show that confirmation dependent field emission could be observed in these molecular interfaces at realistically low voltages. The present study accompanies our previ...

  5. Highly Efficient Midinfrared On-Chip Electrical Generation of Graphene Plasmons by Inelastic Electron Tunneling Excitation

    Ooi, Kelvin J A; Hsieh, Chang Yu; Tan, Dawn T H; Ang, Lay Kee

    2015-01-01

    Inelastic electron tunneling provides a low-energy pathway for the excitation of surface plasmons and light emission. We theoretically investigate tunnel junctions based on metals and graphene. We show that graphene is potentially a highly efficient material for tunneling excitation of plasmons because of its narrow plasmon linewidths, strong emission, and large tunability in the midinfrared wavelength regime. Compared to gold and silver, the enhancement can be up to 10 times for similar wavelengths and up to 5 orders at their respective plasmon operating wavelengths. Tunneling excitation of graphene plasmons promises an efficient technology for on-chip electrical generation and manipulation of plasmons for graphene-based optoelectronics and nanophotonic integrated circuits.

  6. Free online electronic information resources on applied science and technology

    Ghosh, T B.

    2003-01-01

    The paper discusses free online electronic information resources and different means of collection of the resources. The online electronic information resources on Applied Science and Technology are compiled and linked at URL: http://www.geocities.com/ghosh_svrec and described the different free Internet resource like online electronic journals, online electronic books, online databases, organizations, virtual libraries on Applied Science and Technology and special page on earthquake inform...

  7. Probing the longitudinal momentum spread of the electron wave packet at the tunnel exit

    Madsen Lars B.

    2013-03-01

    Full Text Available We present an ellipticity resolved study of momentum distribution arising from strong-field ionization of helium. The influence of the ion potential on the departing electron is considered within a semi-classical model consisting of an initial tunneling step and subsequent classical propagation. We find that the momentum distribution can be explained by including the longitudinal momentum spread of the electron at the exit from the tunnel. Our combined experimental and theoretical study provides an estimate of this momentum spread.

  8. Phase change of tetrahedral amorphous-carbon by low energy electrons in a scanning tunnelling microscope

    Low energy electron-based energy deposition in tetrahedral amorphous-carbon thin films by a scanning tunnelling microscope leads to a local phase change of the carbon. Both the mass density and the electrical resistivity are reduced indicating a graphitization. We expose nano-sized surface areas to field emitted low energy electrons under high vacuum conditions and investigate the temperature and electron energy dependence of the carbon phase change process. Supplementary topography measurements are performed by atomic force microscopy.

  9. On-chip molecular electronic plasmon sources based on self-assembled monolayer tunnel junctions

    Du, Wei; Wang, Tao; Chu, Hong-Son; Wu, Lin; Liu, Rongrong; Sun, Song; Phua, Wee Kee; Wang, Lejia; Tomczak, Nikodem; Nijhuis, Christian A.

    2016-04-01

    Molecular electronic control over plasmons offers a promising route for on-chip integrated molecular plasmonic devices for information processing and computing. To move beyond the currently available technologies and to miniaturize plasmonic devices, molecular electronic plasmon sources are required. Here, we report on-chip molecular electronic plasmon sources consisting of tunnel junctions based on self-assembled monolayers sandwiched between two metallic electrodes that excite localized plasmons, and surface plasmon polaritons, with tunnelling electrons. The plasmons originate from single, diffraction-limited spots within the junctions, follow power-law distributed photon statistics, and have well-defined polarization orientations. The structure of the self-assembled monolayer and the applied bias influence the observed polarization. We also show molecular electronic control of the plasmon intensity by changing the chemical structure of the molecules and by bias-selective excitation of plasmons using molecular diodes.

  10. Electron-tunneling studies of the cubic Kondo semiconductors

    We present the experimental evidence for the energy gap in cubic Ce3Bi4Pt3 and YbB12 single crystals using break-junction tunneling. The well-defined gap values 2?(4.2 K) = 85 20 meV and 220 - 260 meV are obtained for Ce3Bi4Pt3 and YbB12, respectively. The ratio 2?/kBT? for Ce3Bi4Pt3 is evaluated to be approx. = 13 with the susceptibility-maximum temperature T? = 80 K. On the other hand, 2?/kBT? approx. = 37 for YbB12 is much larger than that of Ce3Bi4Pt3 in spite of possessing the similar T? value of 75 K. These results indicate that the characteristic energy for the gap creation in YbB12 is much higher than that in Ce3Bi4Pt3. (author)

  11. Band electron spectrum and thermodynamic properties of the pseudospin-electron model with tunneling splitting of levels

    O.Ya.Farenyuk

    2006-01-01

    Full Text Available The pseudospin-electron model with tunneling splitting of levels is considered. Generalization of dynamic mean-field method for systems with correlated hopping was applied to the investigation of the model. Electron spectra, electron concentrations, average values of pseudospins and grand canonical potential were calculated within the alloy-analogy approximation. Electron spectrum and dependencies of the electron concentrations on chemical potential were obtained. It was shown that in the alloy-analogy approximation, the model possesses the first order phase transition to ferromagnetic state with the change of chemical potential and the second order phase transition with the change of temperature.

  12. Electron-acoustic phonon field induced tunnel scattering

    S.V. Melkonyan

    2015-06-01

    Full Text Available Theory of electron-acoustic single phonon scattering has been reconsidered. It is assumed that the non-degenerate semiconductor has a spherical parabolic band structure. In the basis of the reconsideration there is a phenomenon of the tilting of semiconductor bands by the perturbing potential of an electric field. In this case, electron eigenfunctions are not plane waves or Bloch functions. In low-field regime, the expressions for electron intraband transition probability and scattering time are obtained under elastic collision approximation. Dependencies of scattering time on electron energy and uniform electric field are analyzed. The results of corresponding numerical computations for n-Si at 300 K are presented. It is established that there is no fracture on the curve of electron scattering time on the electron energy dependence.

  13. Local imaging of high mobility two-dimensional electron systems with virtual scanning tunneling microscopy

    Pelliccione, M. [Department of Applied Physics, Stanford University, 348 Via Pueblo Mall, Stanford, California 94305 (United States); Stanford Institute for Materials and Energy Sciences, SLAC National Accelerator Laboratory, 2575 Sand Hill Road, Menlo Park, California 94025 (United States); Department of Physics, University of California, Santa Barbara, Santa Barbara, California 93106 (United States); Bartel, J.; Goldhaber-Gordon, D. [Stanford Institute for Materials and Energy Sciences, SLAC National Accelerator Laboratory, 2575 Sand Hill Road, Menlo Park, California 94025 (United States); Department of Physics, Stanford University, 382 Via Pueblo Mall, Stanford, California 94305 (United States); Sciambi, A. [Department of Applied Physics, Stanford University, 348 Via Pueblo Mall, Stanford, California 94305 (United States); Stanford Institute for Materials and Energy Sciences, SLAC National Accelerator Laboratory, 2575 Sand Hill Road, Menlo Park, California 94025 (United States); Pfeiffer, L. N.; West, K. W. [Department of Electrical Engineering, Princeton University, Princeton, New Jersey 08544 (United States)

    2014-11-03

    Correlated electron states in high mobility two-dimensional electron systems (2DESs), including charge density waves and microemulsion phases intermediate between a Fermi liquid and Wigner crystal, are predicted to exhibit complex local charge order. Existing experimental studies, however, have mainly probed these systems at micron to millimeter scales rather than directly mapping spatial organization. Scanning probes should be well-suited to study the spatial structure of these states, but high mobility 2DESs are found at buried semiconductor interfaces, beyond the reach of conventional scanning tunneling microscopy. Scanning techniques based on electrostatic coupling to the 2DES deliver important insights, but generally with resolution limited by the depth of the 2DES. In this letter, we present our progress in developing a technique called virtual scanning tunneling microscopy that allows local tunneling into a high mobility 2DES. Using a specially designed bilayer GaAs/AlGaAs heterostructure where the tunnel coupling between two separate 2DESs is tunable via electrostatic gating, combined with a scanning gate, we show that the local tunneling can be controlled with sub-250?nm resolution.

  14. Constructing a dental electronic information resource (DEIR).

    Lang, W P

    1994-04-01

    This paper discusses the construction of a dental electronic information resource (DEIR). Development is based on the Internet gopher client/server model. Information is organized in a series of hierarchical menus. A DEIR can be browsed by traversing the menu hierarchy or by performing keyword searches. Searches can result in a menu of found items from across the Internet. Initially, contents of the DEIR will be text files. Electronic copy will be given to an editorial board that will review submissions for conformity to publication standards. A current estimate for electronic storage costs of a DEIR is $1.25/Mb per year. There will be additional costs associated with any purchases of data (e.g. Current Contents), production of data (e.g. development time), and editorial and managerial activities. The DEIR will be accessible from any computer or terminal that can connect to the Internet. Primary user groups will be faculty, staff, and students of dental schools. However, access to the DEIR will be free, and an extensive user community will be encouraged, including practicing dentists, dental associations, public health agencies, and dental insurance companies. PMID:8005714

  15. Subterahertz acoustical pumping of electronic charge in a resonant tunneling device.

    Young, E S K; Akimov, A V; Henini, M; Eaves, L; Kent, A J

    2012-06-01

    We demonstrate that controlled subnanosecond bursts of electronic charge can be transferred through a resonant tunneling diode by successive picosecond acoustic pulses. The effect exploits the nonlinear current-voltage characteristics of the device and its asymmetric response to the compressive and tensile components of the strain pulse. This acoustoelectronic pump opens new possibilities for the control of quantum phenomena in nanostructures. PMID:23003634

  16. Tunnel and pnpn diodes in fast electronics for discrimination and counting devices in nuclear physics

    With a simple apparatus without power supply, the authors measured the rise time of the pulse produced by the fast switching of a tunnel diode. This time was of the order of 0.5 ns. The addition of a source of current made it possible to mount an ultra-fast amplitude-discrimination trigger working at a nanosecond. Problems of power supply and impedance adaptation make this a delicate experiment to perform successfully. It is particularly difficult to get good trigger threshold stability, as this is very sensitive to the supply voltage. At the present stage of the technique, a bi-stable flip-flop utilizing only one tunnel diode does not offer the operational security which would permit its use in nuclear physics. But it is possible to construct bi-stable flip-flops with two tunnel diodes. A system of n tunnel diodes in series, fed by a constant-current generator, presents n potential stable states. It is therefore possible to construct fast scalers of astonishing simplicity. Unfortunately, up until now zeroing has required the use of slower active or passive elements which do not allow full use to be made of the scaler's capacity. Combinations of tunnel diodes make it easy to construct rather complex electronic commutators. To conclude: the difficulty of using tunnel diode circuits lies essentially in problems of power feed and in linking them with other electronic gear. Nevertheless, their very considerable advantages justify intensive study in order to render them simpler to use. With four-layer diodes similar apparatus, but capable of furnishing considerable power, can be constructed. However, they require high voltages to justify their use in electronic tube circuits. (author)

  17. Interference, fluctuation, and alternation of electron tunneling in protein media. 1. Two tunneling routes in photosynthetic reaction center alternate due to thermal fluctuation of protein conformation.

    Nishioka, Hirotaka; Kimura, Akihiro; Yamato, Takahisa; Kawatsu, Tsutomu; Kakitani, Toshiaki

    2005-02-10

    Electron tunneling routes for the electron transfer from the bacteriopheophytin anion to the primary quinone in the bacterial photosynthetic reaction center of Rhodobactor sphaeroides are investigated by a combined method of molecular dynamics simulations for the protein conformation fluctuation and quantum chemical calculations for the electronic states of the donor, acceptor, and protein medium. The analysis of the tunneling route is made by mapping interatomic electron tunneling currents for each protein conformation. We found that there are two dominant routes mainly passing through Trp(M252) (Trp route) or mainly passing through Met(M218) (Met route). Actual electron tunneling pathways alternate between the two routes, depending on the protein conformation which varies with time. When either the Trp route or the Met route dominates, the electron tunneling matrix element /T(DA)/ becomes large. When both the Trp route and the Met route dominate, /T(DA)/ becomes very small due to the destructive interference of the electron tunneling currents between the two routes. We found that a linear relationship exists between the value of /T(DA)/ and the inverse of the degree of destructive interference Q for a wide range of values (ca. 3-10(3) for Q). A similar relationship was also found previously for electron transfer in ruthenium-modified azurins, suggesting that this relationship holds true in general. From these results, we are led to the conclusion that /T(DA)/ cannot exceed a maximum value at Q = 1, even if much variation of /T(DA)/ happens due to the fluctuation of protein conformation. We also conclude that the property of the electron transfer alternates between constructive and destructive interference, due to the fluctuation of protein conformation. It is impossible to keep a system in either constructive or destructive interference because thermal fluctuation of protein conformation takes place. PMID:16851182

  18. Electron-tunneling studies of the cubic Kondo semiconductors

    Ekino, Toshikazu; Fujii, Hironobu [Faculty of Integrated Arts and Sciences, Hiroshima Univ., Higashi-Hiroshima (Japan); Katoh, Ken-ichi; Iga, Fumitoshi; Takabatake, Toshiro [Graduate School of Advanced Science of Matter, Hiroshima Univ., Higashi-Hiroshima (Japan)

    1999-02-28

    We present the experimental evidence for the energy gap in cubic Ce{sub 3}Bi{sub 4}Pt{sub 3} and YbB{sub 12} single crystals using break-junction tunneling. The well-defined gap values 2{delta}(4.2 K) = 85 {+-} 20 meV and 220 - 260 meV are obtained for Ce{sub 3}Bi{sub 4}Pt{sub 3} and YbB{sub 12}, respectively. The ratio 2{delta}/k{sub B}T{sub {chi}} for Ce{sub 3}Bi{sub 4}Pt{sub 3} is evaluated to be approx. = 13 with the susceptibility-maximum temperature T{sub {chi}} = 80 K. On the other hand, 2{delta}/k{sub B}T{sub {chi}} approx. = 37 for YbB{sub 12} is much larger than that of Ce{sub 3}Bi{sub 4}Pt{sub 3} in spite of possessing the similar T{sub {chi}} value of 75 K. These results indicate that the characteristic energy for the gap creation in YbB{sub 12} is much higher than that in Ce{sub 3}Bi{sub 4}Pt{sub 3}. (author)

  19. Nature of Asymmetry in the Vibrational Line Shape of Single-Molecule Inelastic Electron Tunneling Spectroscopy with the STM

    Xu, Chen; Chiang, Chi-lun; Han, Zhumin; Ho, W.

    2016-04-01

    Single molecule vibrational spectroscopy and microscopy was demonstrated in 1998 by inelastic electron tunneling with the scanning tunneling microscope. To date, the discussion of its application has mainly focused on the spatial resolution and the spectral energy and intensity. Here we report on the vibrational line shape for a single carbon monoxide molecule that qualitatively exhibits inversion symmetry when it is transferred from the surface to the tip. The dependence of the line shape on the molecule's asymmetric couplings in the tunnel junction can be understood from theoretical simulation and further validates the mechanisms of inelastic electron tunneling.

  20. Electron-phonon interaction in electronic tunneling: from sequential rate equations to a coherent description

    L.E.F. Foa, Torres; H.M., Pastawski; S. S., Makler.

    2002-06-01

    Full Text Available We discuss the main theoretical approaches for the phonon-assisted tunneling in double barrier resonant tunneling devices and introduce a quantum coherent treatment based on the mapping of the many-body problem into a higher dimensional one-body system. Conditions for a maximized phonon-emission are [...] established.

  1. An innovative display: surface-conduction electron-emitter display based on tunneling effect

    The surface-conduction electron-emitter display (SED) is a newly developed display technology based on tunneling effect by Canon and Toshiba. The working principle of SED is introduced basically, and both multi-scattering model and inertial centrifugal force model are discussed with the purpose of interpreting the behavior of electrons in SED. the situation of various display technologies is briefly reviewed with a comparison between these technologies and SED. (authors)

  2. Infrared catastrophe and tunneling into strongly correlated electron systems: Perturbative x-ray edge limit

    Patton, Kelly R.; Geller, Michael R.

    2005-09-01

    The tunneling density of states exhibits anomalies (cusps, algebraic suppressions, and pseudogaps) at the Fermi energy in a wide variety of low-dimensional and strongly correlated electron systems. We argue that in many cases these spectral anomalies are caused by an infrared catastrophe in the screening response to the sudden introduction of a new electron into the system during a tunneling event. A nonperturbative functional integral method is introduced to account for this effect, making use of methods developed for the x-ray edge singularity problem. The formalism is applicable to lattice or continuum models of any dimensionality, with or without translational invariance. An approximate version of the technique is applied to the 1D electron gas and the 2D Hall fluid, yielding qualitatively correct results.

  3. Probing Nanoscale Electronic and Magnetic Interaction with Scanning Tunneling Spectroscopy

    Bork, Jakob

    is related to research in correlated electron materials such as studies of phase transitions in heavy fermion compounds and magnetic interaction in spintronic research. The capping of cobalt islands on Cu(111) with silver is investigated with STM and photoemission spectroscopy. It is shown that at...

  4. A Diamond Electron Tunneling Micro-Electromechanical Sensor

    Albin, Sacharia

    2000-01-01

    A new pressure sensing device using field emission from diamond coated silicon tips has been developed. A high electric field applied between a nano-tip array and a diaphragm configured as electrodes produces electron emission governed by the Fowler Nordheim equation. The electron emission is very sensitive to the separation between the diaphragm and the tips, which is fixed at an initial spacing and bonded such that a cavity is created between them. Pressure applied to the diaphragm decreases the spacing between the electrodes, thereby increasing the number of electrons emitted. Silicon has been used as a substrate on which arrays of diamond coated sharp tips have been fabricated for electron emission. Also, a diaphragm has been made using wet orientation dependent etching. These two structures were bonded together using epoxy and tested. Current - voltage measurements were made at varying pressures for 1-5 V biasing conditions. The sensitivity was found to be 2.13 mV/V/psi for a 20 x 20 array, which is comparable to that of silicon piezoresistive transducers. Thinner diaphragms as well as alternative methods of bonding are expected to improve the electrical characteristics of the device. This transducer will find applications in many engineering fields for pressure measurement.

  5. Electronic Resource Management System. Vernetzung von Lizenzinformationen

    Michaela Selbach

    2014-12-01

    Full Text Available In den letzten zehn Jahren spielen elektronische Ressourcen im Bereich der Erwerbung eine zunehmend wichtige Rolle: Eindeutig lässt sich hier ein Wandel in den Bibliotheken (fort vom reinen Printbestand zu immer größeren E-Only-Beständen feststellen. Die stetig wachsende Menge an E-Ressourcen und deren Heterogenität stellt Bibliotheken vor die Herausforderung, die E-Ressourcen effizient zu verwalten. Nicht nur Bibliotheken, sondern auch verhandlungsführende Institutionen von Konsortial- und Allianzlizenzen benötigen ein geeignetes Instrument zur Verwaltung von Lizenzinformationen, welches den komplexen Anforderungen moderner E-Ressourcen gerecht wird. Die Deutsche Forschungsgemeinschaft (DFG unterstützt ein Projekt des Hochschulbibliothekszentrums des Landes Nordrhein-Westfalen (hbz, der Universitätsbibliothek Freiburg, der Verbundzentrale des Gemeinsamen Bibliotheksverbundes (GBV und der Universitätsbibliothek Frankfurt, in dem ein bundesweit verfügbares Electronic Ressource Managementsystem (ERMS aufgebaut werden soll. Ein solches ERMS soll auf Basis einer zentralen Knowledge Base eine einheitliche Nutzung von Daten zur Lizenzverwaltung elektronischer Ressourcen auf lokaler, regionaler und nationaler Ebene ermöglichen. Statistische Auswertungen, Rechteverwaltung für alle angeschlossenen Bibliotheken, kooperative Datenpflege sowie ein über standardisierte Schnittstellen geführter Datenaustausch stehen bei der Erarbeitung der Anforderungen ebenso im Fokus wie die Entwicklung eines Daten- und Funktionsmodells. In the last few years the importance of electronic resources in library acquisitions has increased significantly. There has been a shift from mere print holdings to both e- and print combinations and even e-only subscriptions. This shift poses a double challenge for libraries: On the one hand they have to provide their e-resource collections to library users in an appealing way, on the other hand they have to manage these collections efficiently. Not only libraries, but also the negotiators of Alliance and National Licences need a software application which helps them to handle these complex licences efficiently. The project presented in this paper aims at developing a national Electronic Resource Management System (ERMS. It is funded by the German Research Foundation/Deutsche Forschungsgemeinschaft (DFG. The project partners are the North Rhine-Westphalian Library Service Centre (hbz, the University Library Johann Christian Senckenberg Frankfurt, the Head Office of the Gemeinsamer Bibliotheksverbund (GBV and the Freiburg University Library. The projected ERMS  will provide a software system with a central knowledge base which supports a unified overview of licence data with a local, regional and national scope. In the current state of development, the focus is on data and function modelling and on designing concepts for rights management, cooperative data management, implementation of interface standards and the intended services such as statistical analyses.

  6. Techniques for Electronic Resource Management: Crowdsourcing for Best Practices

    Emery, Jill; Stone, Graham

    2013-01-01

    TERMS: Techniques for Electronic Resource Management has been a crowdsourcing experiment to get librarians from Europe and the U.S. to share their best practices and workflows of electronic resource management freely to interested librarians via social media venues such as Facebook, Twitter and Tumblr. You will be participating in the development of the next steps of capturing the best practices of electronic resources management

  7. "Have I Learnt It?" Evaluating Skills for Resource-based Study Using Electronic Resources.

    Macdonald, Janet; Heap, Nick; Mason, Robin

    2001-01-01

    Discussion of electronic information resources and information literacy in higher education focuses on the information handling skills students need and the factors influencing their acquisition in two networked resource-based courses at the United Kingdom Open University. Offers guidelines for course designers incorporating electronic resources.

  8. Hysteresis loops of spin-dependent electronic current in a paramagnetic resonant tunnelling diode

    Nonlinear properties of the spin-dependent electronic transport through a semiconductor resonant tunnelling diode with a paramagnetic quantum well are considered. The spin-dependent WignerPoisson model of the electronic transport and the two-current Motts formula for the independent spin channels are applied to determine the currentvoltage curves of the nanodevice. Two types of the electronic current hysteresis loops are found in the currentvoltage characteristics for both the spin components of the electronic current. The physical interpretation of these two types of the electronic current hysteresis loops is given based on the analysis of the spin-dependent electron densities and the potential energy profiles. The differences between the currentvoltage characteristics for both the spin components of the electronic current allow us to explore the changes of the spin polarization of the current for different electric fields and determine the influence of the electronic current hysteresis on the spin polarization of the current flowing through the paramagnetic resonant tunnelling diode. (paper)

  9. Theoretical model for diffusion controlled reactions of solvated electrons, incorporating a tunnelling mechanism

    The effect on diffusion-controlled reactions, of electron tunnelling from a solvent cavity to a scavenger molecule, is examined. The radial diffusion equation is modified to include a sink term, which varies exponentially with distance from the origin, and thus simulates tunnelling behaviour. An analytical solution is obtained for the steady-state, and applied to diffusion controlled reactions of the solvated electron in media covering a wide range of viscosities. In low viscosity media (eta approximately 10-3kgm-1s-1) reaction can take place at a reactant separation of about two molecular diameters, this distance increases with viscosity, reaching about eight molecular diameters for eta=109(gm-1s-1. The theory is also applied to energy transfer by an exchange mechanism; transfer only begins to take place from distances greater than the encounter distance when the viscosity reaches approximately 105kgm-1s-1. (author)

  10. Electronic effects in scanning tunneling microscopy: Moir pattern on a graphite surface

    Rong, Zhao Y.; Kuiper, Pieter

    1993-12-01

    We observed by scanning tunneling microscopy (STM) a hexagonal superlattice on graphite with a period of 66 . Direct measurement of the angle between lattice vectors confirmed that the superlattice is a Moir pattern caused by a 2.1 rotation of the topmost (0001) plane with respect to the bulk. The STM corrugation of 2.6 is not due to physical buckling, but to differences in electronic structure between AA-stacked, normal AB-stacked, and rhombohedral CAB-stacked graphite. The high tunneling current of AA-stacked regions is in agreement with the high density of states at the Fermi level calculated for AA graphite. The Moir pattern changes, both the amplitude and the shape, with bias voltage. The observation provides a basis for a comparative study of surface electronic structures with different subsurface layer configuration, which is a vital test of our understanding of STM.

  11. Effectiveness Analysis of Electronic Resources at the Hacettepe University

    E. Cosgun; A. Küyük; Karabulut, E; E. Karaagaoglu

    2011-01-01

    It is important to collect and analyze the usage data of electronic databases and periodicals in order to make policies regarding the composition, improvement and more extensive utilization of electronic resources of libraries. The aim of this study is to investigate how efficiently the full text accessible electronic resources of Hacettepe University Libraries are used. For this purpose the usage data obtained from COUNTER Software regarding the electronic databases to which Hacettepe Univer...

  12. Scanning tunnelling microscopy and electronic structure of Mn clusters on Ag(111)

    Kliewer, J.; Berndt, R. [Christian-Albrechts-Universitaet zu Kiel, Institut fuer Experimentelle und Angewandte Physik, Kiel (Germany); Minar, J.; Ebert, H. [University of Munich, Dept. Chemie und Biochemie, Muenchen (Germany)

    2006-01-01

    Small Mn clusters (Mn{sub 1}-Mn{sub 4}) are prepared by manipulation of Mn adatoms on Ag(111) with the tip of a scanning tunnelling microscope. The apparent heights of the clusters are observed to increase monotonously from 1.6 A for a monomer to 2.2 A for a tetramer. Self-consistent calculations of the electronic structure of these clusters are in encouraging agreement with the experimental data. (orig.)

  13. Exploring structural, electronic, magnetic, and vibrational properties of nanostructures with a scanning tunneling microscope

    Ziegler, Martin

    2009-01-01

    In this thesis spin-resolved and spin-integrated scanning tunneling microscopy (STM) and spectroscopy (STS) are used to explore structural, electronic, magnetic, and vibrational properties of nanostructures on surfaces. STS of the differential conductance is performed at constant current and at constant distance. These modes of operation significantly affect peak positions and line shapes in spectra as well as patterns in spatial maps of the differential conductance. A normalization pr...

  14. Image potential of a tunnelling electron moving near two different metals

    The image potential of a tunnelling electron near two metal surfaces is studied by calculating its self-energy, applying hydrodynamic model for two different metals separated by a narrow vacuum gap. The self-energy is calculated for its motion in every metal and in the vacuum gap between them. The most important limiting cases for the self-energy are also derived. Agreement between our results in corresponding limits with previous ones is shown. (author). 14 refs

  15. On the theory of tunnelling in electron and proton transfer reactions.

    Sen, R. K.; Bockris, J. O.

    1973-01-01

    The concept of tunnelling in the theory of electron and proton transfer reactions has recently been questioned on the ground that the situation is a nonstationary one. It has been suggested that time-dependent perturbation theory should be applied to obtain the quantum mechanical transition probability. We have done this for a square barrier. The result for most reactions is the same as obtained by the WKB approximation.

  16. Electron Tunneling and Hopping Possibilites in RuO2 Thick Films

    Halder, N. C.

    1983-01-01

    It is proposed in this paper that the temperature coefficient of resistivity (TCR) in thick film resistors arises from (i) the usual particle-to-particle conduction, (ii) electron tunneling, and (iii) the phononassisted hopping. Equations for activation energies are derived for the temperature minimum of the resistance with and without hopping. New equations for TCR are suggested. Some extensive calculations of TCR and activation energy have been made for RuO2 thick film resistors, the result...

  17. Electron-positron pair creation by Coulomb and laser fields in the tunneling regime

    Kuchiev, M. Yu.; Robinson, D.J.

    2007-01-01

    Electron-positron pair creation due to combined nuclear Coulomb and strong laser fields is investigated for the tunneling regime. The energy spectra and angular distributions of the pair are found analytically for the first time. The energy spectrum for each lepton exhibits a sharp maximum located well above the threshold for any polarization of the laser field. The angular distributions of leptons depend on the polarization: for the linear polarization both leptons move predominantly along t...

  18. Electron and hole transfer in DNA: the role of tunneling and environment

    Owing to the biological significance of radiation induced DNA damage, electron and hole transfer processes in DNA have attracted considerable interest. Various mechanisms for these processes have been proposed including tunneling and hopping. In our efforts we have investigated electron transfer for DNA in glasses, ices and solids at low temperatures via electron spin resonance (ESR) spectroscopy. Electrons and holes generated by irradiation at 77 K are trapped on DNA and transfer to a randomly interspersed intercalator, mitoxantrone (MX). Monitoring the changes of ESR signals of MX radicals, one electron oxidized guanine (G·+), one-electron reduced cytosine [C(N3)H·], and thymine anion radicals (T·-) with time at 77 K allows for the direct observation of electron and hole transfer. For DNA in aqueous glasses at low temperatures we are able to isolate the tunneling of excess electrons and we report overall distances of travel and the tunneling decay constant, beta. Studies with the duplexes polydAdT·polydAdT and polydIdC·polydIdC randomly intercalated with mitoxantrone (MX) show the excess electron transfer distances to be longer for pdAdT·pdAdT, than for for pdIdC·pdIdC. The beta value for DNA (0.9Angstroms-1) lies intermediate between that for pdAdT·pdAdT (0.75 Angstroms-1) and that for pdIdC·pdIdC (1.4 Angstroms-1). These results suggest that proton transfer from I to C·- forming CH· significantly slows but does not stop electron transfer. Similarly in DNA proton transfer in GC anion radical is not found to prevent electron transfer. Electron and hole transfer processes in frozen solutions (D2O ices) show that electron/hole transfer in polyA·polyU is significantly further than in DNA and transfer distances in polyC·polyG are substantially less than in DNA. These findings confirm our results in aqueous glasses. Our investigations of the effect of hydration, space filling lipid amine cation complexes, and temperature will also be discussed. Our modeling of electron transfer rates and distances of electron transfer in DNA-complexes allow for estimates of the spacing between DNA double stranded helices in each complex. This research was supported by the NIH NCI Grant RO1 CA45424

  19. Local 2D-2D tunneling in high mobility electron systems

    Pelliccione, Matthew; Sciambi, Adam; Bartel, John; Goldhaber-Gordon, David; Pfeiffer, Loren; West, Ken; Lilly, Michael; Bank, Seth; Gossard, Arthur

    2012-02-01

    Many scanning probe techniques have been utilized in recent years to measure local properties of high mobility two-dimensional (2D) electron systems in GaAs. However, most techniques lack the ability to tunnel into the buried 2D system and measure local spectroscopic information. We report scanning gate measurements on a bilayer GaAs/AlGaAs heterostructure that allows for a local modulation of tunneling between two 2D electron layers. We call this technique Virtual Scanning Tunneling Microscopy (VSTM) [1,2] as the influence of the scanning gate is analogous to an STM tip, except at a GaAs/AlGaAs interface instead of a surface. We will discuss the spectroscopic capabilities of the technique, and show preliminary results of measurements on a high mobility 2D electron system.[1] A. Sciambi, M. Pelliccione et al., Appl. Phys. Lett. 97, 132103 (2010).[2] A. Sciambi, M. Pelliccione et al., Phys. Rev. B 84, 085301 (2011).

  20. Online electronic information resources on business management

    Ghosh, T. B.

    2002-01-01

    The paper discusses the Post Graduate Management Institutes in South Gujarat and the problems of their libraries. The author has described the freely available Internet resources on Business management like E-journals, business databases, stock exchanges, management virtual libraries etc. and has also started to compile the links of these free internet resources at URL http://www.geocities.com/ghoshtbin to integrate the resources in a uniform location for the benefit of the Management faculti...

  1. Influence of the image dynamic character and the finite electron screening length on tunneling through thin barriers

    The use of the dielectric formalism to describe the non-adiabatic electronic subsystem properties in heterogeneous structures (dynamic image forces) and their influence on the tunneling processes is briefly discussed

  2. Imaging of Endogenous Metabolites of Plant Leaves by Mass Spectrometry Based on Laser Activated Electron Tunneling

    Huang, Lulu; Tang, Xuemei; Zhang, Wenyang; Jiang, Ruowei; Chen, Disong; Zhang, Juan; Zhong, Hongying

    2016-04-01

    A new mass spectrometric imaging approach based on laser activated electron tunneling (LAET) was described and applied to analysis of endogenous metabolites of plant leaves. LAET is an electron-directed soft ionization technique. Compressed thin films of semiconductor nanoparticles of bismuth cobalt zinc oxide were placed on the sample plate for proof-of-principle demonstration because they can not only absorb ultraviolet laser but also have high electron mobility. Upon laser irradiation, electrons are excited from valence bands to conduction bands. With appropriate kinetic energies, photoexcited electrons can tunnel away from the barrier and eventually be captured by charge deficient atoms present in neutral molecules. Resultant unpaired electron subsequently initiates specific chemical bond cleavage and generates ions that can be detected in negative ion mode of the mass spectrometer. LAET avoids the co-crystallization process of routinely used organic matrix materials with analyzes in MALDI (matrix assisted-laser desorption ionization) analysis. Thus uneven distribution of crystals with different sizes and shapes as well as background peaks in the low mass range resulting from matrix molecules is eliminated. Advantages of LAET imaging technique include not only improved spatial resolution but also photoelectron capture dissociation which produces predictable fragment ions.

  3. Imaging of Endogenous Metabolites of Plant Leaves by Mass Spectrometry Based on Laser Activated Electron Tunneling.

    Huang, Lulu; Tang, Xuemei; Zhang, Wenyang; Jiang, Ruowei; Chen, Disong; Zhang, Juan; Zhong, Hongying

    2016-01-01

    A new mass spectrometric imaging approach based on laser activated electron tunneling (LAET) was described and applied to analysis of endogenous metabolites of plant leaves. LAET is an electron-directed soft ionization technique. Compressed thin films of semiconductor nanoparticles of bismuth cobalt zinc oxide were placed on the sample plate for proof-of-principle demonstration because they can not only absorb ultraviolet laser but also have high electron mobility. Upon laser irradiation, electrons are excited from valence bands to conduction bands. With appropriate kinetic energies, photoexcited electrons can tunnel away from the barrier and eventually be captured by charge deficient atoms present in neutral molecules. Resultant unpaired electron subsequently initiates specific chemical bond cleavage and generates ions that can be detected in negative ion mode of the mass spectrometer. LAET avoids the co-crystallization process of routinely used organic matrix materials with analyzes in MALDI (matrix assisted-laser desorption ionization) analysis. Thus uneven distribution of crystals with different sizes and shapes as well as background peaks in the low mass range resulting from matrix molecules is eliminated. Advantages of LAET imaging technique include not only improved spatial resolution but also photoelectron capture dissociation which produces predictable fragment ions. PMID:27053227

  4. The Role of the Acquisitions Librarian in Electronic Resources Management

    Pomerantz, Sarah B.

    2010-01-01

    With the ongoing shift to electronic formats for library resources, acquisitions librarians, like the rest of the profession, must adapt to the rapidly changing landscape of electronic resources by keeping up with trends and mastering new skills related to digital publishing, technology, and licensing. The author sought to know what roles…

  5. Using Electronic Resources to Support Problem-Based Learning

    Chang, Chen-Chi; Jong, Ay; Huang, Fu-Chang

    2012-01-01

    Students acquire skills in problem solving and critical thinking through the process as well as team work on problem-based learning courses. Many courses have started to involve the online learning environment and integrate these courses with electronic resources. Teachers use electronic resources in their classes. To overcome the problem of the

  6. Using Electronic Resources to Support Problem-Based Learning

    Chang, Chen-Chi; Jong, Ay; Huang, Fu-Chang

    2012-01-01

    Students acquire skills in problem solving and critical thinking through the process as well as team work on problem-based learning courses. Many courses have started to involve the online learning environment and integrate these courses with electronic resources. Teachers use electronic resources in their classes. To overcome the problem of the…

  7. Single- and multiple-electron dynamics in the strong-field tunneling limit

    Evolution of atomic ionization into the strong-field limit offers the opportunity to study the fundamentals of atom-laser interaction. In this study, we report on high precision measurements of the ion and electron distributions from laser-excited helium and neon atoms which reflect the changing continuum dynamics as the ionization process evolves into the pure tunneling regime. The experiments present evidence of both single- and two-electron ionization. These data provide a direct quantitative test of various theories of strong-field ionization. We show that a relatively simple semiclassical model which includes a description of a field-driven electron elastically rescattering from an accurate ion core potential reproduces the measured electron distributions for both atoms. However, using this model to calculate e-2e inelastic rescattering yields cross sections which are incompatible with the measured two-electron ionization. copyright 1998 The American Physical Society

  8. An approach to long-range electron transfer mechanisms in metalloproteins: In situ scanning tunneling microscopy with submolecular resolution

    Friis, Esben P.; Jens E. T. Andersen; Kharkats, Yu. I.; Kuznetsov, A. M.; Nichols, R.J.; Zhang, J.-D.; Ulstrup, Jens

    1999-01-01

    In situ scanning tunneling microscopy (STM) of redox molecules, in aqueous solution, shows interesting analogies and differences compared with interfacial electrochemical electron transfer (ET) and ET in homogeneous solution. This is because the redox level represents a deep indentation in the tunnel barrier, with possible temporary electronic population. Particular perspectives are that both the bias voltage and the overvoltage relative to a reference electrode ca...

  9. Three-Dimensional S-Matrix Simulation of Single-Electron Resonant Tunnelling Through Random Ionised Donor States

    Mizuta, Hiroshi

    1998-01-01

    This paper presents a numerical study of single-electron resonant tunnelling (RT) assisted by a few ionised donors in a laterally-confined resonant tunnelling diode (LCRTD). The 3D multi-mode S-matrix simulation is performed newly introducing the scattering potential of discrete impurities. With a few ionised donors being placed, the calculated energy-dependence of the total transmission rate shows new resonances which are donor-configuration dependent. Visualised electron probability density...

  10. Probing flexible conformations in molecular junctions by inelastic electron tunneling spectroscopy

    Mingsen Deng

    2015-01-01

    Full Text Available The probe of flexible molecular conformation is crucial for the electric application of molecular systems. We have developed a theoretical procedure to analyze the couplings of molecular local vibrations with the electron transportation process, which enables us to evaluate the structural fingerprints of some vibrational modes in the inelastic electron tunneling spectroscopy (IETS. Based on a model molecule of Bis-(4-mercaptophenyl-ether with a flexible center angle, we have revealed and validated a simple mathematical relationship between IETS signals and molecular angles. Our results might open a route to quantitatively measure key geometrical parameters of molecular junctions, which helps to achieve precise control of molecular devices.

  11. Magnetic control of resonant tunneling and Kondo effect in a one-electron double quantum dot

    Schr"oer, D M; Eberl, K; Ludwig, S; Kiselev, M N; Altshuler, B L

    2006-01-01

    We present first transport measurements of the Kondo effect in a double quantum dot charged with only one or two electrons, respectively. For the one electron case we observe a surprising quasi-periodic oscillation of the Kondo conductance as a function of a small perpendicular magnetic field |B| \\lesssim 50mT. We interpret this behavior by means of a fine tuning of the interdot tunnel coupling. Such a magnetic field dependent coupling implies important consequences for applications in quantum information processing.

  12. Probing flexible conformations in molecular junctions by inelastic electron tunneling spectroscopy

    The probe of flexible molecular conformation is crucial for the electric application of molecular systems. We have developed a theoretical procedure to analyze the couplings of molecular local vibrations with the electron transportation process, which enables us to evaluate the structural fingerprints of some vibrational modes in the inelastic electron tunneling spectroscopy (IETS). Based on a model molecule of Bis-(4-mercaptophenyl)-ether with a flexible center angle, we have revealed and validated a simple mathematical relationship between IETS signals and molecular angles. Our results might open a route to quantitatively measure key geometrical parameters of molecular junctions, which helps to achieve precise control of molecular devices

  13. Electrically tunable spin filtering for electron tunneling between spin-resolved quantum Hall edge states and a quantum dot

    Spin filtering with electrically tunable efficiency is achieved for electron tunneling between a quantum dot and spin-resolved quantum Hall edge states by locally gating the two-dimensional electron gas (2DEG) leads near the tunnel junction to the dot. The local gating can change the potential gradient in the 2DEG and consequently the edge state separation. We use this technique to electrically control the ratio of the dot–edge state tunnel coupling between opposite spins and finally increase spin filtering efficiency up to 91%, the highest ever reported, by optimizing the local gating.

  14. Use of electronic information resources in goverment libraries

    Simona Omahen

    2003-01-01

    Full Text Available The article presents the use of electronic information resources in government libraries in Slovenia. It starts with the definition of government libraries and electronic publications. On a selected sample of government libraries, the state of the usage of electronic information resources in government libraries was studied. On the basis of interviews, carried out in five government libraries, it was established that government libraries mostly do not focus on, or even think about, the use of electronic information resources. What they have and use seems self-evident to them.

  15. Effect of ion-milled barriers on electron transport in micrometer-sized tunnel junctions

    We studied the electron transport properties of micrometre-sized all-Al tunnel junctions (TJs) between 2 and 300 K, in which the AlOx layer grown by O2 plasma was moderately Ar-ion-milled prior to top electrode deposition. In contrast to the direct tunnelling in the TJs whose barriers are intact (not ion-milled), the zero-bias conductances and the current–voltage characteristics of the TJs as processed are found to be best described by the fluctuation-induced tunnelling conduction mechanism. This observation indicates the formation of nanoscopic incomplete pinholes in the AlOx layer, owing to large junction–barrier interfacial roughness introduced by the ion-milling process. Topographical features revealed by the cross-sectional transmission electron microscopy imaging of the TJ stack conform to this result. This study is of relevance to cases in which ion-milling techniques are applied in tailoring the TJ properties. (paper)

  16. Revisiting the inelastic electron tunneling spectroscopy of single hydrogen atom adsorbed on the Cu(100) surface

    Inelastic electron tunneling spectroscopy (IETS) of a single hydrogen atom on the Cu(100) surface in a scanning tunneling microscopy (STM) configuration has been investigated by employing the non-equilibrium Green’s function formalism combined with density functional theory. The electron-vibration interaction is treated at the level of lowest order expansion. Our calculations show that the single peak observed in the previous STM-IETS experiments is dominated by the perpendicular mode of the adsorbed H atom, while the parallel one only makes a negligible contribution even when the STM tip is laterally displaced from the top position of the H atom. This propensity of the IETS is deeply rooted in the symmetry of the vibrational modes and the characteristics of the conduction channel of the Cu-H-Cu tunneling junction, which is mainly composed of the 4s and 4pz atomic orbitals of the Cu apex atom and the 1s orbital of the adsorbed H atom. These findings are helpful for deepening our understanding of the propensity rules for IETS and promoting IETS as a more popular spectroscopic tool for molecular devices

  17. Effect of interface geometry on electron tunnelling in Al/Al2O3/Al junctions

    Koberidze, M.; Feshchenko, A. V.; Puska, M. J.; Nieminen, R. M.; Pekola, J. P.

    2016-04-01

    We investigate how different interface geometries of an Al/Al2O3 junction, a common component of modern tunnel devices, affect electron transport through the tunnel barrier. We study six distinct Al/Al2O3 interfaces which differ in stacking sequences of the metal and the oxide surface atoms and the oxide termination. To construct model potential barrier profiles for each examined geometry, we rely on first-principles density-functional theory (DFT) calculations for the barrier heights and the shapes of the interface regions as well as on experimental data for the barrier widths. We show that even tiny variations in the atomic arrangement at the interface cause significant changes in the tunnel barrier parameters and, consequently, in electron transport properties. Especially, we find that variations in the crucial barrier heights and widths can be as large as 2 eV and 5 Å, respectively. Finally, to gain information about the average properties of the measured junction, we fit the conductance calculated within the Wentzel-Kramers-Brillouin approximation to the experimental data and interpret the fit parameters with the help of the DFT results.

  18. Single-electron tunneling by using a two-dimensional Corbino nano-scale disk

    H. Taira

    2015-09-01

    Full Text Available We investigate a single-electron tunneling effect of two-dimensional electron systems formed in the Corbino nano-scale disk. By controlling bias and gate voltages, the transistor using this effect is able to control electrons one by one. The present study focuses on the electronic transmission probability affected by the charging energy in the Corbino-type single-electron transistor. We reformulated the Schrdinger equation for an electron in the Corbino disk in order to consider the effect of the curvature of the disk, taking into account the charging effect on the performance of the Corbino-type single-electron transistor. We formulated the transmission probability of the electron by applying the Wentzel-Kramers-Brillouin (WKB method. The electrons energy in the formula of the transmission probability is then associated to the energy eigenvalue of the Schrdinger equation for an electron in an effective confining potential. We numerically solved the Schrdinger equation to evaluate the transmission probability. Our results show that the transmission probability strongly depends on the charging energy stored in the Corbino disk depending on its size.

  19. Fabrication of metallic single electron transistors featuring plasma enhanced atomic layer deposition of tunnel barriers

    Karbasian, Golnaz

    The continuing increase of the device density in integrated circuits (ICs) gives rise to the high level of power that is dissipated per unit area and consequently a high temperature in the circuits. Since temperature affects the performance and reliability of the circuits, minimization of the energy consumption in logic devices is now the center of attention. According to the International Technology Roadmaps for Semiconductors (ITRS), single electron transistors (SETs) hold the promise of achieving the lowest power of any known logic device, as low as 1x10-18 J per switching event. Moreover, SETs are the most sensitive electrometers to date, and are capable of detecting a fraction of an electron charge. Despite their low power consumption and high sensitivity for charge detection, room temperature operation of these devices is quite challenging mainly due to lithographical constraints in fabricating structures with the required dimensions of less than 10 nm. Silicon based SETs have been reported to operate at room temperature. However, they all suffer from significant variation in batch-to-batch performance, low fabrication yield, and temperature-dependent tunnel barrier height. In this project, we explored the fabrication of SETs featuring metal-insulator-metal (MIM) tunnel junctions. While Si-based SETs suffer from undesirable effect of dopants that result in irregularities in the device behavior, in metal-based SETs the device components (tunnel barrier, island, and the leads) are well-defined. Therefore, metal SETs are potentially more predictable in behavior, making them easier to incorporate into circuits, and easier to check against theoretical models. Here, the proposed fabrication method takes advantage of unique properties of chemical mechanical polishing (CMP) and plasma enhanced atomic layer deposition (PEALD). Chemical mechanical polishing provides a path for tuning the dimensions of the tunnel junctions, surpassing the limits imposed by electron beam lithography and lift-off, while atomic layer deposition provides precise control over the thickness of the tunnel barrier and significantly increases the choices for barrier materials. As described below in detail, the fabrication of ultra-thin (~1nm) tunnel transparent barriers with PEALD is in fact challenging; we demonstrate that in fabrication of SETs with PEALD to form the barrier in the Ni-insulator-Ni tunnel junctions, additional NiO layers are parasitically formed in the Ni layers that form the top and bottom electrodes of the tunnel junctions. The NiO on the bottom electrode is formed due to oxidizing effect of the O 2 plasma used in the PEALD process, while the NiO on the bottom of the top electrode is believed to form during the metal deposition due to oxygen-containing contaminants on the surface of the deposited tunnel barrier. We also show that due to the presence of these surface parasitic layers of NiO, the resistance of Ni-insulator-Ni tunnel junctions is drastically increased. Moreover, the transport mechanism is changed from quantum tunneling through the dielectric barrier to one consistent with the tunnel barrier in series with compound layers of NiO and possibly, NiSixOy. The parasitic component in the tunnel junctions results in conduction freeze-out at low temperatures, deviation of junction parameters from ideal model, and excessive noise in the device. The reduction of NiO to Ni is therefore necessary to restore the metal-insulator-metal structure of the junctions. We have studied forming gas anneal as well as H2 plasma treatment as techniques to reduce the NiO layers that are parasitically formed in the junctions. Using either of these two techniques, we reduced the NiO formed on the island after being covered with the PEALD dielectric and before defining the top source and drain. Later, the NiO formed on the bottom of the source/drain is reduced during a second reducing step after the source/drain are formed on the tunnel barrier. Electrical characterization of SETs that are made with the proposed reducing treatments enable us to study the effect of each reducing process on the properties of the constituent tunnel junctions. In comparison to the junctions annealed twice in forming gas at 400°C, we consistently observed a ~10x higher conductance in devices treated twice with H2 plasma at 300°C. The possible damage to the barrier during the plasma treatment and thermally induced film deformation during the anneal which respectively, is believed to increase and lower the conductance are among the possible cause of this difference. Although both types of treatments were effective in alleviating the effect of the activated components in the junctions, all the devices that were treated by two anneal steps or by two H2 plasma steps (for reducing the top and bottom NiO) show deviations from ideal simulated MIM SET model and suffer from significant random telegraph signal (RTS) noise. However, our results show that by using forming gas anneal for bottom NiO reduction and H2 plasma for the top NiO reduction, one can achieve devices close to ideal MIM SETs with significantly less noise.

  20. Nonlocal and Quantum Tunneling Contributions to Harmonic Generation in Nanostructures: Electron Cloud Screening Effects

    Scalora, Michael; de Ceglia, Domenico; Haus, Joseph W

    2014-01-01

    Our theoretical examination of second and third harmonic generation from metal-based nanostructures predicts that nonlocal and quantum tunneling phenomena can significantly exceed expectations based solely on local, classical electromagnetism. Mindful that the diameter of typical transition metal atoms is approximately 3{\\AA}, we adopt a theoretical model that treats nanometer-size features and/or sub-nanometer size gaps or spacers by taking into account: (i) the limits imposed by atomic size to fulfill the requirements of continuum electrodynamics; (ii) spillage of the nearly-free electron cloud into the surrounding vacuum; and (iii) the increased probability of quantum tunneling as objects are placed in close proximity. Our approach also includes the treatment of bound charges, which add crucial, dynamical components to the dielectric constant that are neglected in the conventional hydrodynamic model, especially in the visible and UV ranges, where interband transitions are important. The model attempts to i...

  1. Mapping the first electronic resonances of a Cu phthalocyanine STM tunnel junction

    Using a low temperature, ultrahigh vacuum scanning tunneling microscope (STM), dI/dV differential conductance maps were recorded at the tunneling resonance energies for a single Cu phthalocyanine molecule adsorbed on an Au(111) surface. We demonstrated that, contrary to the common assumption, such maps are not representative of the molecular orbital spatial expansion, but rather result from their complex superposition captured by the STM tip apex with a superposition weight which generally does not correspond to the native weight used in the standard Slater determinant basis set. Changes in the molecule conformation on the Au(111) surface further obscure the identification between dI/dV conductance maps and the native molecular orbital electronic probability distribution in space.

  2. Tunneling electron induced molecular electroluminescence from individual porphyrin J-aggregates

    We investigate molecular electroluminescence from individual tubular porphyrin J-aggregates on Au(111) by tunneling electron excitations in an ultrahigh-vacuum scanning tunneling microscope (STM). High-resolution STM images suggest a spiral tubular structure for the porphyrin J-aggregate with highly ordered “brickwork”-like arrangements. Such aggregated nanotube is found to behave like a self-decoupled molecular architecture and shows red-shifted electroluminescence characteristics of J-aggregates originated from the delocalized excitons. The positions of the emission peaks are found to shift slightly depending on the excitation sites, which, together with the changes in the observed spectral profiles with vibronic progressions, suggest a limited exciton coherence number within several molecules. The J-aggregate electroluminescence is also found unipolar, occurring only at negative sample voltages, which is presumably related to the junction asymmetry in the context of molecular excitations via the carrier injection mechanism

  3. Tunneling electron induced molecular electroluminescence from individual porphyrin J-aggregates

    Meng, Qiushi; Zhang, Chao; Zhang, Yang, E-mail: zhyangnano@ustc.edu.cn, E-mail: zcdong@ustc.edu.cn; Zhang, Yao; Liao, Yuan; Dong, Zhenchao, E-mail: zhyangnano@ustc.edu.cn, E-mail: zcdong@ustc.edu.cn [Hefei National Laboratory for Physical Sciences at the Microscale and Synergetic Innovation Center of Quantum Information and Quantum Physics, University of Science and Technology of China, Hefei, Anhui 230026 (China)

    2015-07-27

    We investigate molecular electroluminescence from individual tubular porphyrin J-aggregates on Au(111) by tunneling electron excitations in an ultrahigh-vacuum scanning tunneling microscope (STM). High-resolution STM images suggest a spiral tubular structure for the porphyrin J-aggregate with highly ordered “brickwork”-like arrangements. Such aggregated nanotube is found to behave like a self-decoupled molecular architecture and shows red-shifted electroluminescence characteristics of J-aggregates originated from the delocalized excitons. The positions of the emission peaks are found to shift slightly depending on the excitation sites, which, together with the changes in the observed spectral profiles with vibronic progressions, suggest a limited exciton coherence number within several molecules. The J-aggregate electroluminescence is also found unipolar, occurring only at negative sample voltages, which is presumably related to the junction asymmetry in the context of molecular excitations via the carrier injection mechanism.

  4. Single electron tunnelling oscillations in a current-biased Josephson junction

    Searching for single electron tunnelling (SET) oscillations has been done in single ultrasmall Josephson junctions of area S∼0.01 μm2 at low temperatures, T∼50 mK. The current-biased regime of the junctions was achieved by insertion of high-Ohmic metallic resistors with R∼500 kΩ into dc leads and additional tunnel junctions of the same area into the voltage leads. Existence of the SET oscillations was proved by observation of the peaks in the dV/dI curves under irradiation of the junctions by an external RF signal when the critical current was suppressed by a magnetic field. The dc current position of the peaks was proportional to the frequency of the RF signal, following a relation I=±ef in correspondence to predictions of the Orthodox theory. Without magnetic field, clear peaks occurred at I=±2ef, following the Bloch relation. (orig.)

  5. TERMS: Techniques for electronic resource management

    Stone, Graham; Emery, Jill

    2011-01-01

    Graham Stone, University of Huddersfield, and Jill Emery, Portland State University, have set up TERMS, a project looking at each of the stages in the e-resources cycle. They are inviting review and comment on the blog.

  6. Electron-phonon coupling in C{sub 60} as revealed by scanning tunneling spectroscopy

    Franke, Katharina J.; Schulze, Gunnar; Pascual, Jose Ignacio [Freie Universitaet Berlin (Germany); Frederiksen, Thomas; Arnau, Andres [Donostia International Physics Center, Donostia (Spain); Monturet, Sergio [Universite Paul Sabatier, Toulouse (France); Lorente, Nicolas [Centro de Investigaciones en Nanociencia y Nanotecnologia, Bellaterra (Spain)

    2008-07-01

    Electron-phonon coupling is of major importance for charge transport through single molecule tunneling junctions. In most experimental implementations of molecular junctions the electronic coupling of the molecular orbitals with substrate states leads to a significant broadening, thus obscuring electron-phonon coupling effects. Here, we investigate the electronic structure of single C{sub 60} molecules adsorbed on top of a self-assembled pattern of alternating tetraphenyladamantane and C{sub 60}. Scanning tunnelling spectroscopy reveals that these molecules exhibit properties similar to the free molecule, such as a large gap of 3.7 eV and a narrow LUMO resonance of only {approx}60 meV line width. The LUMO resonance is followed by a broad weaker peak at about 240 meV higher energy. By density functional calculations including the Jahn-Teller effect, we show that this broad feature is induced by a complex coupling of the C{sub 60} vibrational eigenmodes with the LUMO resonance.

  7. Atomic-scale mapping of electronic structures across heterointerfaces by cross-sectional scanning tunneling microscopy

    Chiu, Ya-Ping; Huang, Bo-Chao; Shih, Min-Chuan; Huang, Po-Cheng; Chen, Chun-Wei

    2015-09-01

    Interfacial science has received much attention recently based on the development of state-of-the-art analytical tools that can create and manipulate the charge, spin, orbital, and lattice degrees of freedom at interfaces. Motivated by the importance of nanoscale interfacial science that governs device operation, we present a technique to probe the electronic characteristics of heterointerfaces with atomic resolution. In this work, the interfacial characteristics of heteroepitaxial structures are investigated and the fundamental mechanisms that pertain in these systems are elucidated through cross-sectional scanning tunneling microscopy (XSTM). The XSTM technique is employed here to directly observe epitaxial interfacial structures and probe local electronic properties with atomic-level capability. Scanning tunneling microscopy and spectroscopy experiments with atomic precision provide insight into the origin and spatial distribution of electronic properties across heterointerfaces. The first part of this report provides a brief description of the cleavage technique and spectroscopy analysis in XSTM measurements. The second part addresses interfacial electronic structures of several model heterostructures in current condensed matter research using XSTM. Topics to be discussed include high-κ‘s/III-V’s semiconductors, polymer heterojunctions, and complex oxide heterostructures, which are all material systems whose investigation using this technique is expected to benefit the research community. Finally, practical aspects and perspectives of using XSTM in interface science are presented.

  8. Electronic Media: A Motif for Shared Resources.

    Lightner, Stanley L.; Johnson, W. C.

    2000-01-01

    A survey of trade and industrial education supervisors from 10 states determined the degree of use of electronic education methods. Instructors in these states used presentation software and web-based exercises most often; fewer used video, CD-ROM, and distance technologies; 70% had been taught electronic presentation methods in preservice or…

  9. Electron tunneling characteristics of a cubic quantum dot, (PbS)32

    The electron transport properties of the cubic quantum dot, (PbS)32, are investigated. The stability of the quantum dot has been established by recent scanning tunneling microscope experiments [B. Kiran, A. K. Kandalam, R. Rallabandi, P. Koirala, X. Li, X. Tang, Y. Wang, H. Fairbrother, G. Gantefoer, and K. Bowen, J. Chem. Phys. 136(2), 024317 (2012)]. In spite of the noticeable energy band gap (∼2 eV), a relatively high tunneling current for (PbS)32 is predicted affirming the observed bright images for (PbS)32. The calculated I-V characteristics of (PbS)32 are predicted to be substrate-dependent; (PbS)32 on the Au (001) exhibits the molecular diode-like behavior and the unusual negative differential resistance effect, though this is not the case with (PbS)32 on the Au (110). Appearance of the conduction channels associated with the hybridized states of quantum dot and substrate together with their asymmetric distribution at the Fermi level seem to determine the tunneling characteristics of the system

  10. Fabrication of tunnel junction-based molecular electronics and spintronics devices

    Tunnel junction-based molecular devices (TJMDs) are highly promising for realizing futuristic electronics and spintronics devices for advanced logic and memory operations. Under this approach, ∼2.5 nm molecular device elements bridge across the ∼2-nm thick insulator of a tunnel junction along the exposed side edge(s). This paper details the efforts and insights for producing a variety of TJMDs by resolving multiple device fabrication and characterization issues. This study specifically discusses (i) compatibility between tunnel junction test bed and molecular solutions, (ii) optimization of the exposed side edge profile and insulator thickness for enhancing the probability of molecular bridging, (iii) effect of fabrication process-induced mechanical stresses, and (iv) minimizing electrical bias-induced instability after the device fabrication. This research will benefit other researchers interested in producing TJMDs efficiently. TJMD approach offers an open platform to test virtually any combination of magnetic and nonmagnetic electrodes, and promising molecules such as single molecular magnets, porphyrin, DNA, and molecular complexes.

  11. Fabrication of tunnel junction-based molecular electronics and spintronics devices

    Tyagi, Pawan, E-mail: ptyagi@udc.edu [University of the District of Columbia, Department of Civil and Mechanical Engineering (United States)

    2012-10-15

    Tunnel junction-based molecular devices (TJMDs) are highly promising for realizing futuristic electronics and spintronics devices for advanced logic and memory operations. Under this approach, {approx}2.5 nm molecular device elements bridge across the {approx}2-nm thick insulator of a tunnel junction along the exposed side edge(s). This paper details the efforts and insights for producing a variety of TJMDs by resolving multiple device fabrication and characterization issues. This study specifically discusses (i) compatibility between tunnel junction test bed and molecular solutions, (ii) optimization of the exposed side edge profile and insulator thickness for enhancing the probability of molecular bridging, (iii) effect of fabrication process-induced mechanical stresses, and (iv) minimizing electrical bias-induced instability after the device fabrication. This research will benefit other researchers interested in producing TJMDs efficiently. TJMD approach offers an open platform to test virtually any combination of magnetic and nonmagnetic electrodes, and promising molecules such as single molecular magnets, porphyrin, DNA, and molecular complexes.

  12. Single electron turnstile and pump devices using long arrays of small tunnel junctions

    We have investigated, both experimentally and numerically, single electron tunneling devices of interest for current standard applications. The devices consist of long arrays of small tunnel junctions with gate electrodes capacitively coupled to electrodes inside the arrays. Experiments on arrays of 25 small aluminum tunnel junctions with a single gate electrode capacitively coupled to the center of the array (an ''array turnstile'') have been performed at temperatures down to 40 mK. We observe sharp steps in the I-V characteristics at currents I = ef when an rf-signal of frequency f is applied to the gate electrode. The sharp steps can be obtained even without any compensation for background charge. Numerical simulations of a similar device (an ''array pump'') are also presented. This device consists of an array with two gate electrodes where two rf signals with a phase shift of 90deg may be applied. The size of the voltage steps in the I-V characteristics are investigated as a funtion of several parameters. For instance, the dependence of electrode capacitance, number of junctions, and background charge is investigated. (orig.)

  13. Improving Electronic Resources through Holistic Budgeting

    Kusik, James P.; Vargas, Mark A.

    2009-01-01

    To establish a more direct link between its collections and the educational goals of Saint Xavier University, the Byrne Memorial Library has adopted a "holistic" approach to collection development. This article examines how traditional budget practices influenced the library's selection of resources and describes how holistic collection…

  14. Electronic structure of nanoscale iron oxide particles measured by scanning tunneling and photoelectron spectroscopies

    Preisinger, M; Rudolf, T; Horn, S; Strongin, D R

    2005-01-01

    We have investigated the electronic structure of nano-sized iron oxide by scanning tunnelling microscopy (STM) and spectroscopy (STS) as well as by photoelectron spectroscopy. Nano particles were produced by thermal treatment of Ferritin molecules containing a self-assembled core of iron oxide. Depending on the thermal treatment we were able to prepare different phases of iron oxide nanoparticles resembling gamma-Fe2O3, alpha-Fe2O3, and a phase which apparently contains both gamma-Fe2O3 and alpha-Fe2O3. Changes to the electronic structure of these materials were studied under reducing conditions. We show that the surface band gap of the electronic excitation spectrum can differ from that of bulk material and is dominated by surface effects.

  15. Submolecular Electronic Mapping of Single Cysteine Molecules by in Situ Scanning Tunneling Imaging

    Zhang, Jingdong; Chi, Qijin; Nazmutdinov, R. R.; Zinkicheva, T. T.; Bronshtein, M. D.

    2009-01-01

    We have used L-Cysteine (Cys) as a model system to study the surface electronic structures of single molecules at the submolecular level in aqueous buffer solution by a combination of electrochemical scanning tunneling microscopy (in situ STM), electrochemistry including voltammetry and chronocou......We have used L-Cysteine (Cys) as a model system to study the surface electronic structures of single molecules at the submolecular level in aqueous buffer solution by a combination of electrochemical scanning tunneling microscopy (in situ STM), electrochemistry including voltammetry and...... tip. The computational images recast as constant-current-height profiles show that the most favorable molecular orientation is the adsorption of cysteine as a radical in zwitterionic form located on the bridge between the Au(I 10) atomic rows and with the amine and carboxyl group toward the solution...... bulk. The correlation between physical location and electronic contrast of the adsorbed molecules was also revealed by the computational data. The present study shows that cysteine packing in the adlayer on Au(110) from the liquid environment is in contrast to that from the ultrahigh-vacuum environment...

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

    We report experimental methods to ascertain a complete energy band alignment of a broken-gap tunnel field-effect transistor based on an InAs/GaSb hetero-junction. By using graphene as an optically transparent electrode, both the electron and hole barrier heights at the InAs/GaSb interface can be quantified. For a Al2O3/InAs/GaSb layer structure, the barrier height from the top of the InAs and GaSb valence bands to the bottom of the Al2O3 conduction band is inferred from electron emission whereas hole emissions reveal the barrier height from the top of the Al2O3 valence band to the bottom of the InAs and GaSb conduction bands. Subsequently, the offset parameter at the broken gap InAs/GaSb interface is extracted and thus can be used to facilitate the development of predicted models of electron quantum tunneling efficiency and transistor performance

  17. Electronic structure of nanoscale iron oxide particles measured by scanning tunneling and photoelectron spectroscopies

    Preisinger, M.; Krispin, M.; Rudolf, T; Horn, S.; Strongin, D. R.

    2005-01-01

    We have investigated the electronic structure of nano-sized iron oxide by scanning tunnelling microscopy (STM) and spectroscopy (STS) as well as by photoelectron spectroscopy. Nano particles were produced by thermal treatment of Ferritin molecules containing a self-assembled core of iron oxide. Depending on the thermal treatment we were able to prepare different phases of iron oxide nanoparticles resembling gamma-Fe2O3, alpha-Fe2O3, and a phase which apparently contains both gamma-Fe2O3 and a...

  18. Consecutive Charging of a Molecule-on-Insulator Ensemble Using Single Electron Tunnelling Methods.

    Rahe, Philipp; Steele, Ryan P; Williams, Clayton C

    2016-02-10

    We present the local charge state modification at room temperature of small insulator-supported molecular ensembles formed by 1,1'-ferrocenedicarboxylic acid on calcite. Single electron tunnelling between the conducting tip of a noncontact atomic force microscope (NC-AFM) and the molecular islands is observed. By joining NC-AFM with Kelvin probe force microscopy, successive charge build-up in the sample is observed from consecutive experiments. Charge transfer within the islands and structural relaxation of the adsorbate/surface system is suggested by the experimental data. PMID:26713686

  19. In situ scanning tunnelling microscopy of redox molecules. Coherent electron transfer at large bias voltages

    Zhang, Jingdong; Kuznetsov, A.M.; Ulstrup, Jens

    2003-01-01

    Theories of in situ scanning tunnelling microscopy (STM) of molecules with redox levels near the substrate and tip Fermi levels point to 'spectroscopic' current-overpotential features. Prominent features require a narrow 'probing tip', i.e. a small bias voltage, eV(bias), compared with the...... substrate and tip Fermi levels. STM here involves coherent two-step interfacial electron transfer between the redox level and the enclosing substrate and tip. We have also extended previous experimental in situ STM studies of the blue copper protein Pseudomonas aeruginosa azurin, adsorbed on Au(111), to...

  20. Electron tunneling into superconducting indium and lead films containing the magnetic impurity manganese

    Tunneling measurements of quench-condensed In-Mn and Pb-Mn alloy films were made. The results were compared with Shiba's theory of superconductors containing magnetic impurities. The localized excited impurity states predicted by Shiba's theory were observed in both alloys. In addition to s-wave scattering, it was necessary to include p- and d-wave scattering of the conduction electrons in the theory in order to explain the experimental data. Partial agreement between the theory and the experimental data was obtained using phase shifts from band calculations by A.B. Kunz. The results on In-Mn also agree with thermal conductivity data

  1. A low temperature scanning tunneling microscope for electronic and force spectroscopy

    In this article, we describe and test a novel way to extend a low temperature scanning tunneling microscope with the capability to measure forces. The tuning fork that we use for this is optimized to have a high quality factor and frequency resolution. Moreover, as this technique is fully compatible with the use of bulk tips, it is possible to combine the force measurements with the use of superconductive or magnetic tips, advantageous for electronic spectroscopy. It also allows us to calibrate both the amplitude and the spring constant of the tuning fork easily, in situ and with high precision

  2. Proximity effect and hot-electron diffusion in Ag/Al2O3/Al tunnel junctions

    We have fabricated Ag/Al2O3/Al tunnel junctions on Si substrates using a new process. This process was developed to fabricate superconducting tunnel junctions (STJs) on the surface of a superconductor. These junctions allow us to study the proximity effect of a superconducting Al film on a normal metal trapping layer. In addition, these devices allow us to measure the hot-electron diffusion constant using a single junction. Lastly these devices will help us optimize the design and fabrication of tunnel junctions on the surface of high-Z, ultra-pure superconducting crystals. 5 refs., 8 figs

  3. Euler European Libraries and Electronic Resources in Mathematical Sciences

    The Euler Project. Karlsruhe

    The European Libraries and Electronic Resources (EULER) Project in Mathematical Sciences provides the EulerService site for searching out "mathematical resources such as books, pre-prints, web-pages, abstracts, proceedings, serials, technical reports preprints) and NetLab (for Internet resources), this outstanding engine is capable of simple, full, and refined searches. It also offers a browse option, which responds to entries in the author, keyword, and title fields. Further information about the Project is provided at the EULER homepage.

  4. Access to electronic resources by visually impaired people

    Jenny Craven

    2003-01-01

    Research into access to electronic resources by visually impaired people undertaken by the Centre for Research in Library and Information Management has not only explored the accessibility of websites and levels of awareness in providing websites that adhere to design for all principles, but has sought to enhance understanding of information seeking behaviour of blind and visually impaired people when using digital resources.

  5. Opto-electronic studies of semiconductor tunnelling structures and quantum wells

    This thesis describes optical and electrical studies of two groups of low dimensional semiconductor structures. The majority of the work concerns an optical study of electron populations (n1,n2) in the ground (E1) and first excited (E2) states of the quantum well (QW) regions of various GaAs-AlGaAs double and triple barrier resonant tunnelling structures (DBRTS and TBRTS respectively). The relative populations of the E2 and E1 confined states are determined from analysis of the photoluminescence (PL) intensities. When the structures are biased for tunnelling into the E2 state, rate equation analysis shows that n2/n1 is approximately equal to τi/τ1, where τi is the E2-E1 intersubband scattering time and τ1 is the tunnelling-out time from E1. The relative electron populations are thus expected to be a sensitive function of the QW and collector barrier widths. The second group of structures studied in this thesis consists of a series of shallow GaAs-AlyGa1-yAs multi-quantum well structures, with aluminium concentrations of 1 to 4.5%. The 1s-2s exciton energy separation is measured from PL excitation (PLE) experiments and is combined with a small correction for the 2s binding energy to give an accurate determination of the exciton binding energy (Ex). It is found that even in these very shallow QW structures there is a marked enhancement in the value of Ex over that in 3D GaAs

  6. Resonant tunneling assisted propagation and amplification of plasmons in high electron mobility transistors

    A rigorous theoretical and computational model is developed for the plasma-wave propagation in high electron mobility transistor structures with electron injection from a resonant tunneling diode at the gate. We discuss the conditions in which low-loss and sustainable plasmon modes can be supported in such structures. The developed analytical model is used to derive the dispersion relation for these plasmon-modes. A non-linear full-wave-hydrodynamic numerical solver is also developed using a finite difference time domain algorithm. The developed analytical solutions are validated via the numerical solution. We also verify previous observations that were based on a simplified transmission line model. It is shown that at high levels of negative differential conductance, plasmon amplification is indeed possible. The proposed rigorous models can enable accurate design and optimization of practical resonant tunnel diode-based plasma-wave devices for terahertz sources, mixers, and detectors, by allowing a precise representation of their coupling when integrated with other electromagnetic structures

  7. Nonlocal and quantum-tunneling contributions to harmonic generation in nanostructures: Electron-cloud-screening effects

    Scalora, Michael; Vincenti, Maria Antonietta; de Ceglia, Domenico; Haus, Joseph W.

    2014-07-01

    Our theoretical examination of second- and third-harmonic generation from metal-based nanostructures predicts that nonlocal and quantum-tunneling phenomena can significantly exceed expectations based solely on local, classical electromagnetism. Mindful that the diameter of typical transition-metal atoms is approximately 3 , we adopt a theoretical model that treats nanometer-size features and/or subnanometer-size gaps or spacers by taking into account (i) the limits imposed by atomic size to fulfill the requirements of continuum electrodynamics, (ii) spillage of the nearly free electron cloud into the surrounding vacuum, and (iii) the increased probability of quantum tunneling as objects are placed in close proximity. Our approach also includes the treatment of bound charges, which add crucial, dynamical components to the dielectric constant that are neglected in the conventional hydrodynamic model, especially in the visible and UV ranges, where interband transitions are important. The model attempts to inject into the classical electrodynamic picture a simple, perhaps more realistic description of the metal surface by incorporating a thin patina of free electrons that screens an internal, polarizable medium.

  8. Resonant tunneling assisted propagation and amplification of plasmons in high electron mobility transistors

    Bhardwaj, Shubhendu; Sensale-Rodriguez, Berardi; Xing, Huili Grace; Rajan, Siddharth; Volakis, John L.

    2016-01-01

    A rigorous theoretical and computational model is developed for the plasma-wave propagation in high electron mobility transistor structures with electron injection from a resonant tunneling diode at the gate. We discuss the conditions in which low-loss and sustainable plasmon modes can be supported in such structures. The developed analytical model is used to derive the dispersion relation for these plasmon-modes. A non-linear full-wave-hydrodynamic numerical solver is also developed using a finite difference time domain algorithm. The developed analytical solutions are validated via the numerical solution. We also verify previous observations that were based on a simplified transmission line model. It is shown that at high levels of negative differential conductance, plasmon amplification is indeed possible. The proposed rigorous models can enable accurate design and optimization of practical resonant tunnel diode-based plasma-wave devices for terahertz sources, mixers, and detectors, by allowing a precise representation of their coupling when integrated with other electromagnetic structures.

  9. Superluminescence from an optically pumped molecular tunneling junction by injection of plasmon induced hot electrons

    Kai Braun

    2015-05-01

    Full Text Available Here, we demonstrate a bias-driven superluminescent point light-source based on an optically pumped molecular junction (gold substrate/self-assembled molecular monolayer/gold tip of a scanning tunneling microscope, operating at ambient conditions and providing almost three orders of magnitude higher electron-to-photon conversion efficiency than electroluminescence induced by inelastic tunneling without optical pumping. A positive, steadily increasing bias voltage induces a step-like rise of the Stokes shifted optical signal emitted from the junction. This emission is strongly attenuated by reversing the applied bias voltage. At high bias voltage, the emission intensity depends non-linearly on the optical pump power. The enhanced emission can be modelled by rate equations taking into account hole injection from the tip (anode into the highest occupied orbital of the closest substrate-bound molecule (lower level and radiative recombination with an electron from above the Fermi level (upper level, hence feeding photons back by stimulated emission resonant with the gap mode. The system reflects many essential features of a superluminescent light emitting diode.

  10. Resonant tunneling of 1-dimensional electrons across an array of 3-dimensionally confined potential wells

    Allee, D. R.; Chou, S. Y.; Harris, J. S.; Pease, R. F. W.

    A lateral resonant tunneling field effect transistor has been fabricated with a gate electrode in the form of a railway such that the two rails form a lateral double barrier potential at the GaAs/AlGaAs interface. The ties confine the electrons in the third dimension forming an array of potential boxes or three dimensionally confined potential wells. The width of the ties and rails is 50nm; the spacings between the ties and between the two rails are 230nm and 150nm respectively. The ties are 750nm long and extend beyond the the two rails forming one dimensional wires on either side. Conductance oscillations are observed in the drain current at 4.2K as the gate voltage is scanned. Comparison with devices with a solid gate, and with a monorail gate with ties fabricated on the same wafer suggest that these conductance oscillations are electron resonant tunneling from one dimensional wires through the quasi-bound states of the three dimensionally confined potential wells. Comparison with a device with a two rail gate without ties (previously published) indicates that additional confinement due to the ties enhances the strength of the conductance oscillations.

  11. Proton coupled electron transfer tunneling reactions in WO3 and MoO3 nanostructured films

    Gavrilyuk, A. I.

    2007-12-01

    WO3 and MoO3 are famous hydrogenphilics, hydrogen loving materials, capable of performing various functions concerning atomic hydrogen. They are active catalysts in photochemical reactions connected with detachment of hydrogen atoms, being, at the same time, capable of accomodating great quantities of the detached hydrogen atoms, and transporting them to other functional materials via employment of various heterostructures. It was shown that tunneling proton-coupled electron transfer is the mechanism of the photochemical hydrogen abstraction reaction on the surface of highly disordered nanostructured WO3 and MoO3 thin films. Specially selected hydrogen donor molecules were adsorbed on the oxide surface bonding via donor-acceptor and hydrogen bonds which yield a decrease in the energy barrier for the hydrogen transfer from the adsorbed hydrogen donor molecule to the oxide surface. The very rough and heterogeneous film surface yields space fluctuations of the energy barrier parameters whereas intermolecular vibrations yield time fluctuations; the fluctuative barrier preparation being responsible for the tunneling photo-stimulated proton-coupled electron transfer.

  12. Building an electronic resource collection a practical guide

    Lee, Stuart D

    2004-01-01

    This practical book guides information professionals step-by-step through building and managing an electronic resource collection. It outlines the range of electronic products currently available in abstracting and indexing, bibliographic, and other services and then describes how to effectively select, evaluate and purchase them.

  13. Characterization of GaSb-based heterostructures by scanning electron microscope cathodoluminescence and scanning tunnelling microscope

    Storgards, J [Departamento de FIsica de Materiales, Facultad de Ciencias FIsicas, Universidad Complutense de Madrid, 28040 Madrid (Spain); Mendez, B [Departamento de FIsica de Materiales, Facultad de Ciencias FIsicas, Universidad Complutense de Madrid, 28040 Madrid (Spain); Piqueras, J [Departamento de FIsica de Materiales, Facultad de Ciencias FIsicas, Universidad Complutense de Madrid, 28040 Madrid (Spain); Chenot, M [Fraunhofer Institute for Solar Energy Systems, 79110 Freiburg (Germany); Dimroth, F [Fraunhofer Institute for Solar Energy Systems, 79110 Freiburg (Germany); Bett, A W [Fraunhofer Institute for Solar Energy Systems, 79110 Freiburg (Germany)

    2004-01-21

    The luminescence of GaSb and AlGaSb layers grown on GaAs substrates by metal organic vapour phase epitaxy has been studied by means of cathodoluminescence (CL) using a scanning electron microscope. CL plane-view analysis reveals a distribution of defects, as misfit dislocations, in some of the structures. The luminescence bands observed in the GaSb layers are related to near band edge recombination and to an excess of Ga. In the case of AlGaSb/GaSb heterostructure emission bands related to the ternary compound and to donor-acceptor recombination are detected. In addition, with the aid of a scanning tunnelling microscope (STM), local electronic properties, such as conductance and surface energy gap, were studied in sample cross-sections. The results obtained from imaging and spectroscopy modes of STM enabled us to image the single AlGaSb layer.

  14. Characterization of GaSb-based heterostructures by scanning electron microscope cathodoluminescence and scanning tunnelling microscope

    The luminescence of GaSb and AlGaSb layers grown on GaAs substrates by metal organic vapour phase epitaxy has been studied by means of cathodoluminescence (CL) using a scanning electron microscope. CL plane-view analysis reveals a distribution of defects, as misfit dislocations, in some of the structures. The luminescence bands observed in the GaSb layers are related to near band edge recombination and to an excess of Ga. In the case of AlGaSb/GaSb heterostructure emission bands related to the ternary compound and to donor-acceptor recombination are detected. In addition, with the aid of a scanning tunnelling microscope (STM), local electronic properties, such as conductance and surface energy gap, were studied in sample cross-sections. The results obtained from imaging and spectroscopy modes of STM enabled us to image the single AlGaSb layer

  15. Magnetooscillations of the tunneling current between two-dimensional electron systems

    We calculate electric current caused by electron tunnelling between two-dimensional layers in the magnetic field applied perpendicular to the layers. An elastic scattering of the electrons is taken into account. Analytical results are obtained for two regimes: i) small magnetic field, when the Landau quantization is suppressed by the scattering and the oscillatory part of the current shows nearly harmonic behaviour; ii) high magnetic field, when the Landau levels are well-defined and the conductivity shows series of sharp peaks corresponding to resonant magnetotunneling. In the last case, we used two alternative approaches: self-consistent Born approximation and path integral method, and compared obtained results. (author). 12 refs, 3 figs

  16. Inelastic electron tunneling through degenerate and nondegenerate ground state polymeric junctions

    Highlights: • Current–voltage characteristics of two polymeric junctions are studied. • Current is reduced in phonon assistant tunneling regime. • Behavior of current is independent of temperature. • Elastic energy changes current drastically. - Abstract: The inelastic electron transport properties through two polymeric (trans-polyacetylene and polythiophene) molecular junctions are studied using Keldysh nonequilibrium Green function formalism. The Hamiltonian of the polymers is described via Su–Schrieffer–Heeger model and the metallic electrodes are modeled by the wide-band approximation. Results show that the step-like behavior of the current–voltage characteristics is deformed in presence of strong electron–phonon interaction. Also, the magnitude of current is slightly decreased in the phonon assistant electron transport regime. In addition, it is observed that the I–V curves are independent of temperature

  17. Equilibrium and space-charge wave analysis of electron beams in conducting and absorbing gyrotron beam tunnels

    The fluid equations for an electron beam are used to calculate the equilibrium velocity and density profiles, limiting current and space-charge wave properties of an annular beam undergoing magnetic compression in a gyrotron beam tunnel. Both non-relativistic and relativistic equations are derived. The beam tunnel may have a conventional smooth wall or an absorbing dielectric-loaded wall. Small values of magnetic compression are seen to have a large effect on the profiles and the current limit of a given tunnel. Common dielectric-loaded tunnels are also seen to reduce the limiting current by 5-20%. Limiting current data for a wide range of beam parameters are shown. The dispersion relation for a convective instability arising from the gradient in the equilibrium potential depression profiles is derived using the linearized fluid equations. The growth rate is seen to increase for increasing current and pitch angle, and for increasing wall effects of an absorbing tunnel. The average growth rate is calculated for a typical gyrotron beam and beam tunnel as well as for a beam entering an interaction cavity. Growth rates for all values of kz are seen to decrese for a conventional conducting beam tunnel in a constant magnetic field. (author) 13 figs., refs

  18. Single-molecule electronics: Cooling individual vibrational modes by the tunneling current.

    Lykkebo, Jacob; Romano, Giuseppe; Gagliardi, Alessio; Pecchia, Alessandro; Solomon, Gemma C

    2016-03-21

    Electronic devices composed of single molecules constitute the ultimate limit in the continued downscaling of electronic components. A key challenge for single-molecule electronics is to control the temperature of these junctions. Controlling heating and cooling effects in individual vibrational modes can, in principle, be utilized to increase stability of single-molecule junctions under bias, to pump energy into particular vibrational modes to perform current-induced reactions, or to increase the resolution in inelastic electron tunneling spectroscopy by controlling the life-times of phonons in a molecule by suppressing absorption and external dissipation processes. Under bias the current and the molecule exchange energy, which typically results in heating of the molecule. However, the opposite process is also possible, where energy is extracted from the molecule by the tunneling current. Designing a molecular "heat sink" where a particular vibrational mode funnels heat out of the molecule and into the leads would be very desirable. It is even possible to imagine how the vibrational energy of the other vibrational modes could be funneled into the "cooling mode," given the right molecular design. Previous efforts to understand heating and cooling mechanisms in single molecule junctions have primarily been concerned with small models, where it is unclear which molecular systems they correspond to. In this paper, our focus is on suppressing heating and obtaining current-induced cooling in certain vibrational modes. Strategies for cooling vibrational modes in single-molecule junctions are presented, together with atomistic calculations based on those strategies. Cooling and reduced heating are observed for two different cooling schemes in calculations of atomistic single-molecule junctions. PMID:27004879

  19. Two-photon-induced hot-electron transfer to a single molecule in a scanning tunneling microscope

    The junction of a scanning tunneling microscope (STM) operating in the tunneling regime was irradiated with femtosecond laser pulses. A photoexcited hot electron in the STM tip resonantly tunnels into an excited state of a single molecule on the surface, converting it from the neutral to the anion. The electron-transfer rate depends quadratically on the incident laser power, suggesting a two-photon excitation process. This nonlinear optical process is further confirmed by the polarization measurement. Spatial dependence of the electron-transfer rate exhibits atomic-scale variations. A two-pulse correlation experiment reveals the ultrafast dynamic nature of photoinduced charging process in the STM junction. Results from these experiments are important for understanding photoinduced interfacial charge transfer in many nanoscale inorganic-organic structures.

  20. Resonant electron tunneling in single quantum well heterostructure junction of electrodeposited metal semiconductor nanostructures using nuclear track filters

    We report on resonant electron tunneling through a Cu-Se heterostructure junction grown electrochemically in the submicron size pores (0.8 ?m) of a nuclear track filter (Polycarbonate). The prominent feature of negative differential resistance (NDR) has been observed in the current-voltage (I-V) characteristic of the so-fabricated array of resonant tunneling diodes (RTDs) even at room temperature, along with a significant peak to valley current ratio (2.5) of the resonance. Tunneling structures of the nanofabricated RTDs around zero bias are also observed at room temperature. Our results show that the low cost and relatively easy electrodeposition method can be a very effective way to prepare resonant quantum tunneling devices, using the pores of nuclear track filters

  1. Sensitivity of Tunneling-Rotational Transitions in Ethylene Glycol to Variation of Electron-to-Proton Mass Ratio

    Viatkina, A V

    2014-01-01

    Ethylene glycol in its ground conformation has tunneling transition with the frequency about 7 GHz. This leads to a rather complicated tunneling-rotational spectrum. Because tunneling and rotational energies have different dependence on the electron-to-proton mass ratio $\\mu$, this spectrum is highly sensitive to the possible $\\mu$ variation. We used simple 14 parameter effective Hamiltonian to calculate dimensionless sensitivity coefficients $Q_\\mu$ of the tunneling-rotational transitions and found that they lie in the range from $-17$ to $+18$. Ethylene glycol has been detected in the interstellar medium. All this makes it one of the most sensitive probes of $\\mu$ variation at the large space and time scales.

  2. Electron tunnelling through a self-similar fractal potential on the generalized Cantor set

    A proper formalism developed earlier to study electron tunnelling through a self-similar fractal potential (SSFP) posed on the Cantor set is extended here to describe the SSFP whose levels consist of N fractals of the next level. We have derived a functional equation for the transfer matrix of this potential and found three different solutions. Two of them correspond to SSFP barriers and SSFP wells whose power may be arbitrary. The third one relates to the only SSFP barrier whose power has a definite value. These solutions show that SSFPs, in the general case, are approximately scale invariant in the long- and short-wave regions, and only the limiting SSFP whose fractal dimension is equal to unity should be strictly scale invariant. We have shown that except for the limiting case the tunnelling parameters of SSFPs, with the same fractal dimension depend on N. In addition, we have established a link between the solutions of the functional equation and the power of SSFPs. (author)

  3. Why and How to Measure the Use of Electronic Resources

    Jean Bernon

    2008-11-01

    Full Text Available A complete overview of library activity implies a complete and reliable measurement of the use of both electronic resources and printed materials. This measurement is based on three sets of definitions: document types, use types and user types. There is a common model of definitions for printed materials, but a lot of questions and technical issues remain for electronic resources. In 2006 a French national working group studied these questions. It relied on the COUNTER standard, but found it insufficient and pointed out the need for local tools such as web markers and deep analysis of proxy logs. Within the French national consortium COUPERIN, a new working group is testing ERMS, SUSHI standards, Shibboleth authentication, along with COUNTER standards, to improve the counting of the electronic resources use. At this stage this counting is insufficient and its improvement will be a European challenge for the future.

  4. Access to electronic resources by visually impaired people

    Jenny Craven

    2003-01-01

    Full Text Available Research into access to electronic resources by visually impaired people undertaken by the Centre for Research in Library and Information Management has not only explored the accessibility of websites and levels of awareness in providing websites that adhere to design for all principles, but has sought to enhance understanding of information seeking behaviour of blind and visually impaired people when using digital resources.

  5. The Study of Analytical Model of Library Electronic Resources Usage-A Case of Medical Electronic Resources

    Chung-Yen Yu

    2014-10-01

    Full Text Available With the advents of internet, the importance of electronic resources is growing. Due to the increasing expensiveness of electronic resources, university libraries normally received budgets from parent institutions annually. They necessarily applied effective and systematic methods for decision making in electronic resources purchase or re-subscription. However, there are some difficulties in practices: First of all, libraries are unable to receive user records; second, the COUNTER statistics does not include details about users and their affiliation. As a result, one cannot conduct advanced user analysis based on the usage of users, institutions, and departments. To overcome the difficulties, this study presents a feasible model to analyze electronic resource usage effectively and flexibly. We set up a proxy server to collect actual usage raw data. By analyzing items in internet browsing records, associated with original library automatic system, this study aims at exploring how to use effective ways to analyze big data of website log data. We also propose the process of how original data to be transformed, cleared, integrated, and demonstrated. This study adopted a medical university library and its subscription of medical electronic resources as a case. Our data analysis includes (1 year of subscription,(2 title of journal, (3 affiliation, (4 subjects, and (5 specific journal requirements, etc. The findings of the study are contributed to obtain further understanding in policy making and user behavior analysis. The integrated data provides multiple applications in informatics research, information behavior, bibliomining, presenting diverse views and extended issues for further discussion.

  6. Practical guide to electronic resources in the humanities

    Dubnjakovic, Ana

    2010-01-01

    From full-text article databases to digitized collections of primary source materials, newly emerging electronic resources have radically impacted how research in the humanities is conducted and discovered. This book, covering high-quality, up-to-date electronic resources for the humanities, is an easy-to-use annotated guide for the librarian, student, and scholar alike. It covers online databases, indexes, archives, and many other critical tools in key humanities disciplines including philosophy, religion, languages and literature, and performing and visual arts. Succinct overviews of key eme

  7. A New XOR Structure Based on Resonant-Tunneling High Electron Mobility Transistor

    Mohammad Javad Sharifi

    2009-01-01

    Full Text Available A new structure for an exclusive-OR (XOR gate based on the resonant-tunneling high electron mobility transistor (RTHEMT is introduced which comprises only an RTHEMT and two FETs. Calculations are done by utilizing a new subcircuit model for simulating the RTHEMT in the SPICE simulator. Details of the design, input, and output values and margins, delay of each transition, maximum operating frequency, static and dynamic power dissipations of the new structure are discussed and calculated and the performance is compared with other XOR gates which confirm that the presented structure has a high performance. Furthermore, to the best of authors' knowledge, it has the least component count in comparison to the existing structures.

  8. The study of optimal conditions of electrochemical etching of tunnel electron microscopy tungsten tips

    We present the experimental results obtained during the study made in the electrochemical etching of tunneling electron microscopy tungsten tips. The experiments was made using DC and two usual electrolytes: KOH and NaOH. For the tip preparation we used a electrochemical cell with stainless steel cathode and the tungsten wire as anode. the electrodes was introduced in a glass recipient containing the electrolytic solution. We study the effects of applied voltage, polish time, tip length and electrolyte concentration as process relevant parameters. The best condition for tip preparation was obtained with a metallurgical microscope and with a SEM.EDX and Auger analysis was made. The results shown the better tips was made with KOH as electrolyte with a limited concentration range (2-4 normal) and applied voltage (2-6 volts) (Author) 20 refs

  9. Probing the local environment of a single OPE3 molecule using inelastic tunneling electron spectroscopy

    Riccardo Frisenda

    2015-12-01

    Full Text Available We study single-molecule oligo(phenylene ethynylenedithiol junctions by means of inelastic electron tunneling spectroscopy (IETS. The molecule is contacted with gold nano-electrodes formed with the mechanically controllable break junction technique. We record the IETS spectrum of the molecule from direct current measurements, both as a function of time and electrode separation. We find that for fixed electrode separation the molecule switches between various configurations, which are characterized by different IETS spectra. Similar variations in the IETS signal are observed during atomic rearrangements upon stretching of the molecular junction. Using quantum chemistry calculations, we identity some of the vibrational modes which constitute a chemical fingerprint of the molecule. In addition, changes can be attributed to rearrangements of the local molecular environment, in particular at the moleculeelectrode interface. This study shows the importance of taking into account the interaction with the electrodes when describing inelastic contributions to transport through single-molecule junctions.

  10. Detection of post-translational modifications in single peptides using electron tunnelling currents

    Ohshiro, Takahito; Tsutsui, Makusu; Yokota, Kazumichi; Furuhashi, Masayuki; Taniguchi, Masateru; Kawai, Tomoji

    2014-10-01

    Post-translational modifications alter the properties of proteins through the cleavage of peptide bonds or the addition of a modifying group to one or more amino acids. These modifications allow proteins to perform their primary biological functions, but single-protein studies of post-translational modifications have been hindered by a lack of suitable analysis methods. Here, we show that single amino acids can be identified using electron tunnelling currents measured as the individual molecules pass through a nanoscale gap between electrodes. We identify 12 different amino acids and the post-translational modification phosphotyrosine, which is involved in the process that switches enzymes on and off. Furthermore, we show that the conductance measurements can be used to partially sequence peptides of an epidermal growth factor receptor substrate, and can discriminate a peptide from its phosphorylated variant.

  11. Electron-positron pair creation by Coulomb and laser fields in the tunneling regime

    Electron-positron pair creation due to combined nuclear Coulomb and strong laser fields is investigated for the tunneling regime. The energy spectra and angular distributions of the pair are found analytically. The energy spectrum for each lepton exhibits a sharp maximum located well above the threshold for any polarization of the laser field. The angular distributions of leptons depend on the polarization: for linear polarization, both leptons move predominantly along the laser beam direction; for circular polarization, leptons are emitted in a thin-walled cone centered on the laser beam. The spectral and angular distributions found are governed by the intensity and frequency of the field, and the frequency-independent total pair creation rates comply with the previously known results. A method of calculation--the vicinal approximation--that uses the fact that the pair production takes place in the close vicinity of the nucleus is suggested

  12. Electron tunneling into superconducting indium and lead films containing the magnetic impurity manganese

    Tsang, Juine Kai

    1980-01-01

    Tunneling measurements of quench-condensed In-Mn and Pb-Mn alloy films were made. The results were compared with Shiba's theory of superconductors containing magnetic impurities. The localized excited impurity states predicted by Shiba's theory were observed in both alloys. In addition to s-wave scattering, it was necessary to include p- and d-wave scattering of the conduction electrons in the theory in order to explain the experimental data. Partial agreement between the theory and the experimental data was obtained using phase shifts from band calculations by A.B. Kunz. The results on In-Mn also agree with thermal conductivity data.

  13. Calculating electronic tunnel currents in networks of disordered irregularly shaped nanoparticles by mapping networks to arrays of parallel nonlinear resistors

    Aghili Yajadda, Mir Massoud [CSIRO Manufacturing Flagship, P.O. Box 218, Lindfield NSW 2070 (Australia)

    2014-10-21

    We have shown both theoretically and experimentally that tunnel currents in networks of disordered irregularly shaped nanoparticles (NPs) can be calculated by considering the networks as arrays of parallel nonlinear resistors. Each resistor is described by a one-dimensional or a two-dimensional array of equal size nanoparticles that the tunnel junction gaps between nanoparticles in each resistor is assumed to be equal. The number of tunnel junctions between two contact electrodes and the tunnel junction gaps between nanoparticles are found to be functions of Coulomb blockade energies. In addition, the tunnel barriers between nanoparticles were considered to be tilted at high voltages. Furthermore, the role of thermal expansion coefficient of the tunnel junction gaps on the tunnel current is taken into account. The model calculations fit very well to the experimental data of a network of disordered gold nanoparticles, a forest of multi-wall carbon nanotubes, and a network of few-layer graphene nanoplates over a wide temperature range (5-300 K) at low and high DC bias voltages (0.001 mV50 V). Our investigations indicate, although electron cotunneling in networks of disordered irregularly shaped NPs may occur, non-Arrhenius behavior at low temperatures cannot be described by the cotunneling model due to size distribution in the networks and irregular shape of nanoparticles. Non-Arrhenius behavior of the samples at zero bias voltage limit was attributed to the disorder in the samples. Unlike the electron cotunneling model, we found that the crossover from Arrhenius to non-Arrhenius behavior occurs at two temperatures, one at a high temperature and the other at a low temperature.

  14. Calculating electronic tunnel currents in networks of disordered irregularly shaped nanoparticles by mapping networks to arrays of parallel nonlinear resistors

    We have shown both theoretically and experimentally that tunnel currents in networks of disordered irregularly shaped nanoparticles (NPs) can be calculated by considering the networks as arrays of parallel nonlinear resistors. Each resistor is described by a one-dimensional or a two-dimensional array of equal size nanoparticles that the tunnel junction gaps between nanoparticles in each resistor is assumed to be equal. The number of tunnel junctions between two contact electrodes and the tunnel junction gaps between nanoparticles are found to be functions of Coulomb blockade energies. In addition, the tunnel barriers between nanoparticles were considered to be tilted at high voltages. Furthermore, the role of thermal expansion coefficient of the tunnel junction gaps on the tunnel current is taken into account. The model calculations fit very well to the experimental data of a network of disordered gold nanoparticles, a forest of multi-wall carbon nanotubes, and a network of few-layer graphene nanoplates over a wide temperature range (5-300 K) at low and high DC bias voltages (0.001 mV–50 V). Our investigations indicate, although electron cotunneling in networks of disordered irregularly shaped NPs may occur, non-Arrhenius behavior at low temperatures cannot be described by the cotunneling model due to size distribution in the networks and irregular shape of nanoparticles. Non-Arrhenius behavior of the samples at zero bias voltage limit was attributed to the disorder in the samples. Unlike the electron cotunneling model, we found that the crossover from Arrhenius to non-Arrhenius behavior occurs at two temperatures, one at a high temperature and the other at a low temperature.

  15. Electron Tunneling Spectroscopic Measurements on Al-doped MgB2 Thin Films

    Zaitsev, A. G.; Schneider, R.; de la Pe-a-Seaman, O.; de Coss, R.; Heid, R.; Bohnen, K.-P.; Geerk, J.

    The effect of Al-doping on the electron-phonon coupling in magnesium diboride films was studied by electron tunneling spectroscopy on planar sandwich-type Mg1-xAlxB2-oxide-indium junctions. The superconducting Mg1-xAlxB2 films (0 ≤ x aluminium oxide). The high junction quality allowed precise measurements of the differential conduction up to high bias-voltages of 120 mV. In the low bias range the small energy gap Δπ was measured: it decreased linearly with increasing Al-doping in agreement with the band filling model. The measurements at higher energies revealed the phonon induced features in the electron density of states. Although the spectra were influenced by the proximity effect below ∼20meV, they enabled the determination of the effective Eliashberg function α2F. For the same film compositions α2F data were obtained theoretically from first principles calculations. The progressive loss of superconductivity with increasing Al doping was reflected in both the experiment and calculations by the evolution of α2F. The dominating π-σ interband pairing interaction, which contributes most to the superconductivity on the π sheet, was gradually weakened in correlation with the band structure calculations.

  16. Giant tunneling piezoresistance of composite elastomers with interlocked microdome arrays for ultrasensitive and multimodal electronic skins.

    Park, Jonghwa; Lee, Youngoh; Hong, Jaehyung; Ha, Minjeong; Jung, Young-Do; Lim, Hyuneui; Kim, Sung Youb; Ko, Hyunhyub

    2014-05-27

    The development of flexible electronic skins with high sensitivities and multimodal sensing capabilities is of great interest for applications ranging from human healthcare monitoring to robotic skins to prosthetic limbs. Although piezoresistive composite elastomers have shown great promise in this area of research, typically poor sensitivities and low response times, as well as signal drifts with temperature, have prevented further development of these materials in electronic skin applications. Here, we introduce and demonstrate a design of flexible electronic skins based on composite elastomer films that contain interlocked microdome arrays and display giant tunneling piezoresistance. Our design substantially increases the change in contact area upon loading and enables an extreme resistance-switching behavior (ROFF/RON of ∼10(5)). This translates into high sensitivity to pressure (-15.1 kPa(-1), ∼0.2 Pa minimum detection) and rapid response/relaxation times (∼0.04 s), with a minimal dependence on temperature variation. We show that our sensors can sensitively monitor human breathing flows and voice vibrations, highlighting their potential use in wearable human-health monitoring systems. PMID:24592988

  17. The cosmo-nucleonic ultra-relativistic quantum electronic tunnelling (URQET) as EM-Signals of QGP

    The physical reality of nucleonic matters had been endeavoured as a process of super-relativistic cosmo-nucleonic quantum electronic tunnelling, coupling the two. The theory will be beneficial in disclosing the ways to regulate the nuclear synthesis, fusion, fission, solar flares and the cosmic events

  18. Exploring the Tilt-Angle Dependence of electron tunneling across Molecular junction of Self-Assembled Alkanethiols

    Frederiksen, Thomas; Munuera, C.; Ocal, C.; Brandbyge, Mads; Paulsson, Magnus; Sanchez-Portal, D.; Arnau, A.

    2009-01-01

    Electronic transport mechanisms in molecular junctions are investigated by a combination of first-principles calculations and current−voltage measurements of several well-characterized structures. We study self-assembled layers of alkanethiols grown on Au(111) and form tunnel junctions by contact...

  19. A Pioneering Spirit: Using Administrative Metadata to Manage Electronic Resources

    Medeiros, Norm

    2003-01-01

    This article describes administrative metadata, and its use in managing electronic resources. The focus of the article is an interview with Tim Jewell, Head of Collection Management Services at the University of Washington and Adam Chandler, Information Technology Librarian at Cornell University.

  20. Electronic Commerce Resource Centers. An Industry--University Partnership.

    Gulledge, Thomas R.; Sommer, Rainer; Tarimcilar, M. Murat

    1999-01-01

    Electronic Commerce Resource Centers focus on transferring emerging technologies to small businesses through university/industry partnerships. Successful implementation hinges on a strategic operating plan, creation of measurable value for customers, investment in customer-targeted training, and measurement of performance outputs. (SK)

  1. Providing Access to Electronic Information Resources in Further Education

    Banwell, Linda; Ray, Kathryn; Coulson, Graham; Urquhart, Christine; Lonsdale, Ray; Armstrong, Chris; Thomas, Rhian; Spink, Sin; Yeoman, Alison; Fenton, Roger; Rowley, Jennifer

    2004-01-01

    This article aims to provide a baseline for future studies on the provision and support for the use of digital or electronic information services (EIS) in further education. The analysis presented is based on a multi-level model of access, which encompasses access to and availability of information and communication technology (ICT) resources,…

  2. Coulomb Repulsion Effect in Two-electron Non-adiabatic Tunneling through a One-level redox Molecule

    Medvedev, Igor M.; Kuznetsov, Alexander M.; Ulstrup, Jens

    2009-01-01

    We investigated Coulomb repulsion effects in nonadiabatic (diabatic) two-electron tunneling through a redox molecule with a single electronic level in a symmetric electrochemical contact under ambient conditions, i.e., room temperature and condensed matter environment. The electrochemical contact...... is representative of electrochemical scanning tunneling microscopy or a pair of electrochemical nanoscale electrodes. The two-electron transfer molecular system also represents redox molecules with three electrochemically accessible oxidation states, rather than only two states such as...... comprehensively studied. It is shown that depending on the effective Coulomb repulsion energy, the current/overpotential relation at fixed bias voltage shows two narrow (~kBT) peaks in the limit of strong electron-phonon coupling to the solvent environment. The system also displays current/bias voltage...

  3. Non-exponential tunneling and control of microwave absorption lineshapes via Fano resonance for electrons on Helium

    Duki, Solomon; Mathur, Harsh

    2008-01-01

    We consider the application of a small in-plane magnetic field to electrons on a helium surface in a perpendicular magnetic field. Certain states that were bound to the helium surface then dissolve into the continuum turning into long-lived resonances. As a result microwave absorption lines acquire an asymmetric Fano lineshape that is tunable by varying the microwave polarisation or the in-plane magnetic field. Electrons trapped in a formerly bound state will tunnel off the surface of helium;...

  4. Comment on 'electron-hole bilayer tunnel field-effect transistors with a symmetrically arranged double gale'

    Padilla de la Torre, José Luis; Alper, Cem; Gámiz, Francisco; Ionescu, Mihai Adrian

    2015-01-01

    In this comment we demonstrate that the inclusion of field--induced quantum confinement effects through appropriate discretization of conduction and valence bands refutes the suitability of a germanium electron--hole bilayer tunnel field-effect transistor with symmetrically arranged gates (W J Jeong et al. 2015, Semiconductor Science and Technology, 30-035021). Delayed alignment of first electron and hole energy subbands in the central gated intrinsic channel region makes the onset of vertica...

  5. Evaluating the appropriateness of electronic information resources for learning

    Nolan, Nathanial S.

    2016-01-01

    Objectives Current US medical students have begun to rely on electronic information repositoriessuch as UpToDate, AccessMedicine, and Wikipediafor their pre-clerkship medical education. However, it is unclear whether these resources are appropriate for this level of learning due to factors involving information quality, level of evidence, and the requisite knowledgebase. This study evaluated appropriateness of electronic information resources from a novel perspective: amount of mental effort learners invest in interactions with these resources and effects of the experienced mental effort on learning. Methods Eighteen first-year medical students read about three unstudied diseases in the above-mentioned resources (a total of fifty-four observations). Their eye movement characteristics (i.e., fixation duration, fixation count, visit duration, and task-evoked pupillary response) were recorded and used as psychophysiological indicators of the experienced mental effort. Post reading, students' learning was assessed with multiple-choice tests. Eye metrics and test results constituted quantitative data analyzed according to the repeated Latin square design. Students' perceptions of interacting with the information resources were also collected. Participants' feedback during semi-structured interviews constituted qualitative data and was reviewed, transcribed, and open coded for emergent themes. Results Compared to AccessMedicine and Wikipedia, UpToDate was associated with significantly higher values of eye metrics, suggesting learners experienced higher mental effort. No statistically significant difference between the amount of mental effort and learning outcomes was found. More so, descriptive statistical analysis of the knowledge test scores suggested similar levels of learning regardless of the information resource used. Conclusions Judging by the learning outcomes, all three information resources were found appropriate for learning. UpToDate, however, when used alone, may be less appropriate for first-year medical students' learning as it does not fully address their information needs and is more demanding in terms of cognitive resources invested. PMID:26807049

  6. Insights into Solid-State Electron Transport through Proteins from Inelastic Tunneling Spectroscopy: The Case of Azurin.

    Yu, Xi; Lovrincic, Robert; Sepunaru, Lior; Li, Wenjie; Vilan, Ayelet; Pecht, Israel; Sheves, Mordechai; Cahen, David

    2015-10-27

    Surprisingly efficient solid-state electron transport has recently been demonstrated through "dry" proteins (with only structural, tightly bound H2O left), suggesting proteins as promising candidates for molecular (bio)electronics. Using inelastic electron tunneling spectroscopy (IETS), we explored electron-phonon interaction in metal/protein/metal junctions, to help understand solid-state electronic transport across the redox protein azurin. To that end an oriented azurin monolayer on Au is contacted by soft Au electrodes. Characteristic vibrational modes of amide and amino acid side groups as well as of the azurin-electrode contact were observed, revealing the azurin native conformation in the junction and the critical role of side groups in the charge transport. The lack of abrupt changes in the conductance and the line shape of IETS point to far off-resonance tunneling as the dominant transport mechanism across azurin, in line with previously reported (and herein confirmed) azurin junctions. The inelastic current and hence electron-phonon interaction appear to be rather weak and comparable in magnitude with the inelastic fraction of tunneling current via alkyl chains, which may reflect the known structural rigidity of azurin. PMID:26381112

  7. Single-dot spectroscopy via elastic single-electron tunneling through a pair of coupled quantum dots

    Ota, T; Stopa, M; Hatano, T; Tarucha, S; Song, H Z; Nakata, Y; Miyazawa, T; Ohshima, T; Yokoyama, N

    2004-01-01

    We study the electronic structure of a single self-assembled InAs quantum dot by probing elastic single-electron tunneling through a single pair of weakly coupled dots. In the region below pinch-off voltage, the non-linear threshold voltage behavior provides electronic addition energies exactly as the linear, Coulomb blockade oscillation does. By analyzing it, we identify the s and p shell addition spectrum for up to six electrons in the single InAs dot, i.e. one of the coupled dots. The evolution of shell addition spectrum with magnetic field provides Fock-Darwin spectra of s and p shell.

  8. Increasing the efficiency of a silicon tunnel MIS injector of hot electrons by using high-K oxides

    Vexler, M. I.

    2015-09-01

    It is demonstrated theoretically that replacing silicon dioxide in a metal-insulator-semiconductor (MIS) structure with a double-layer insulator HfO2(ZrO2)/SiO2 must lead to a decrease in the relative contribution of electrons with comparatively low energies to the total tunneling current. As a consequence, a suppression of the current component associated with the charge transport into the valence band of Si or from it is predicted for many regimes, especially of the low-energy part of this component. This effect can improve the efficiency of injection devices, such as a transistor with a tunnel MIS emitter or a resonant-tunneling diode based on a heavily doped MIS structure.

  9. Quantum tunnelling and classical above-barrier transitions in electron detachment from negative ions by negatively charged projectiles

    A simple model of electron detachment from negative ions by negatively charged projectile impact is developed as a combination of quantum tunnelling and classical field ionization. While the tunnelling theory has been discussed previously by Smirnov and Chibisov, we have substantially amended Solovevs classical model for above-barrier transition. As the most important modification we introduce the concept of decay rate for the classical ensemble related to the quantumstate and evaluate the rate in terms of the simple free-fall atomic model. The present theory compares very well with recent experiments while the isolated application of the tunnelling model and of the classical model yields results that are a factor of two too large and too small, respectively. (author)

  10. Grain boundary tunnel spectroscopy of the electron-doped cuprate superconductor La2-xCexCuO4

    The electron doped superconductor La2-xCexCuO4 (LCCO) has been investigated by electric transport measurements at low temperatures T down to 5 K and high magnetic fields up to 16 T. For this purpose LCCO thin film tunnel junctions have been prepared on bicrystal substrates by molecular beam epitaxy and micro structuring. The samples were characterised by measuring the thin film resistivity and the tunnel conductance of quasi particles across the grain boundary. By these measurements an unconventional symmetry of the order parameter could be revealed for La2-xCexCuO4. Furthermore it was shown, that the tunnel conductance can be used as a probe for the upper critical field Bc2(T). By using this method a value of Bc2∝24 T has been found for La2-xCexCuO4, a value roughly three times bigger than previously known. By this observation it was shown that the superconducting phase covers a larger region in the B-T-phase diagram. In addition it was concluded, that the pseudogap phase in La2-xCexCuO4 is either not existent at all or covers only a small temperature region. Besides quasiparticle tunneling also the tunneling of Cooper pairs in small magnetic fields has been investigated. It was shown that the critical current across the grain boundary depends on the supplier of the bicrystal substrate. (orig.)

  11. Non-perturbation theory of electronic dynamic conductivity for two-barrier resonance tunnel nano-structure

    O.M. Voitsekhivska

    2011-12-01

    Full Text Available The non-perturbation theory of electronic dynamic conductivity for open two-barrier resonance tunnel structure is established for the first time within the model of rectangular potentials and different effective masses of electrons in the elements of nano-structure and the wave function linear over the intensity of electromagnetic field. It is proven that the results of the theory of dynamic conductivity, developed earlier in weak signal approximation within the perturbation method, qualitatively and quantitatively correlate with the obtained results. The advantage of non-perturbation theory is that it can be extended to the case of electronic currents interacting with strong electromagnetic fields in open multi-shell resonance tunnel nano-structures, as active elements of quantum cascade lasers and detectors.

  12. E-Resources Management: How We Positioned Our Organization to Implement an Electronic Resources Management System

    White, Marilyn; Sanders, Susan

    2009-01-01

    The Information Services Division (ISD) of the National Institute of Standards and Technology (NIST) positioned itself to successfully implement an electronic resources management system. This article highlights the ISD's unique ability to "team" across the organization to realize a common goal, develop leadership qualities in support of…

  13. Analysis of electron direct tunneling current through very-thin gate oxides in MOS capacitors with the parallel-perpendicular kinetic energy components and anisotropic masses

    Fatimah Arofiati, Noor; Mikrajuddin, Abdullah; , Sukirno; , Khairurrijal.

    2010-12-01

    Full Text Available An electron direct tunneling current model of n+- poly - Si/SiO2/p - Si(100) metal-oxide-semiconductor (MOS) capacitors has been developed by considering a parallel-perpendicular kinetic energy coupling, which is represented by the gate electron phase velocity, and anisotropic masses under a parabol [...] ic E-k dispersion relationship. The electron effective mass in the oxide and the electron phase velocity in the n+ poly-Si gate are the only two fitting parameters to compare calculated tunneling currents to measured ones. It was obtained that the calculated tunneling currents fit well to the measured ones. The electron effective mass in the oxide layer tends to increase with decreasing the oxide thickness. In addition, the gate electron velocity is a constant of 1x10(5)m/s. Moreover, the theoretical model offers a simple treatment and an accurate result in obtaining the tunneling current.

  14. Room temperature observation of size dependent single electron tunneling in a sub-2 nm size tunable Pt nanoparticle embedded metaloxidesemiconductor structure

    In this paper we report size dependent single electron tunneling behavior at room temperature in a metaloxidesemiconductor structure with uniformly sized Pt nanoparticles embedded in an Al2O3 dielectric. The sub-2 nm size Pt nanoparticles sandwiched between the Al2O3 layers are deposited by a unique tilted target sputter deposition technique which produces metal nanoparticles as small as 0.5 nm with narrow size distributions at room temperature. The charging behavior of these nanoparticles shows clear single electron tunneling peaks due to the Coulomb blockade effect. Moreover, the average single electron addition energy and height of the single electron tunneling current strongly depend on the size of the Pt nanoparticle. These controllable single electron tunneling behaviors suggest a new route for fabrication of single electron devices.

  15. An electronic approach to evaluating healthcare Web resources.

    Hodson-Carlton, K; Dorner, J L

    1999-01-01

    Information literacy skills, which include the ability to evaluate electronic healthcare sites, are critical to the decision-making responsibilities of students and professionals. The authors describe the experiences of nursing and library services faculty in the development and implementation of a Web-delivered module for the evaluation of healthcare Web resources. A range of electronic tools was used for both the collaborative creation of the module as well as the instructional delivery of the content. Evaluation of the module revealed its usefulness to the students and the potential of the collaborative development model for other content areas. PMID:10795251

  16. Public libraries and the consortium purchase of electronic resources

    Ball, David

    2003-01-01

    This paper embodies research on the purchasing of electronic resources by public libraries. It sought to identify what works well and what is problematic with respect to the management of commercial products. Views were also sought on future development, and how procurement could best be managed. The main concerns identified were the lack of a national dimension and strategy, and of expertise in individual authorities and consortia, particularly with licences. Purchasers were felt to be r...

  17. The weak π − π interaction originated resonant tunneling and fast switching in the carbon based electronic devices

    Jun He

    2012-03-01

    Full Text Available By means of the nonequilibrium Green's functions and the density functional theory, we have investigated the electronic transport properties of C60 based electronic device with different intermolecular interactions. It is found that the electronic transport properties vary with the types of the interaction between two C60 molecules. A fast electrical switching behavior based on negative differential resistance has been found when two molecules are coupled by the weak π − π interaction. Compared to the solid bonding, the weak interaction is found to induce resonant tunneling, which is responsible for the fast response to the applied electric field and hence the velocity of switching.

  18. Electronic Resources and Mission Creep: Reorganizing the Library for the Twenty-First Century

    Stachokas, George

    2009-01-01

    The position of electronic resources librarian was created to serve as a specialist in the negotiation of license agreements for electronic resources, but mission creep has added more functions to the routine work of electronic resources such as cataloging, gathering information for collection development, and technical support. As electronic

  19. Characterization and Properties of Oligothiophenes Using Scanning Tunneling Microscopy for Possible Use in Organic Electronics

    A scanning tunneling microscopy study has been made on a group of alkyl-substituted oligothiophenes. The self-assembled monolayers of this type of semi-conducting oligomers on graphite were observed and characterized. To control the self-assembly, it is important to first understand the forces that drive the spontaneous ordering of molecules at interfaces. For the identification of the forces, several substituted oligothiophenes were examined: carboxylic acid groups, methyl ester carboxylic acid, and iodine atoms at one end and benzyl esters at the other end of the oligomers this is in addition to the non-functionalized oligothiophehens, Self-assembled monolayers of these molecules were then examined by STM. A detailed analysis of the driving forces and parameters controlling the formation of the self-assembled 2- D crystal monolayers was carried out by performing modeling of the experimental observations. The theoretical calculations gave us a conclusive insight into the intermolecular interactions, which lead to the observed conformation of molecules on the surface. An attempt to react two iodinated oligomers on the surface after the formation of the monolayer has been done; a topochemical reaction studies using UV/Vis light irradiation has been preceded. The targeted reaction was achieved. This can be considered as a great step towards the formation of nano-wires and other organic electronic devices. The applicability of the above method of force-driven self organisation in different patterns was examined as template for building donor-nano structures for electronic devices. It was necessary to examine the stability of the formed templates in air. The monolayers were left to dry and STM images were taken; C60 was then added to the monolayer, and the complexation of the C60 (as acceptor) with the formed monolayer template was examined.

  20. Electronic Resources Evaluation Central: Using Off-the-Shelf Software, Web 2.0 Tools, and LibGuides to Manage an Electronic Resources Evaluation Process

    England, Lenore; Fu, Li

    2011-01-01

    A critical part of electronic resources management, the electronic resources evaluation process is multi-faceted and includes a seemingly endless range of resources and tools involving numerous library staff. A solution is to build a Web site to bring all of the components together that can be implemented quickly and result in an organizational…

  1. Single molecule dissociation by tunneling electrons in NO-Co-Porphyrin complex on Au(111): A novel mechanics revealed by scanning tunneling spectroscopy and first-principles thermodynamic simulation

    Chang, Yunhee; Kim, Howon; Lee, Eui-Sup; Jang, Won-Jun; Kim, Yong-Hyun; Kahng, Se-Jong

    2015-03-01

    To microscopically understand the mechanisms of electron-induced NO dissociations, we performed first-principles density-functional theory (DFT) calculations for NO-CoTPP on Au(111). We explain the scanning tunneling microscopy (STM) results that the dissociations of NO were induced by both positive and negative voltage pulses with threshold voltages, +0.68 V and 0.74 V, respectively, at 0.1 nA tunneling current, showing power law relations between tunneling current and dissociation yield. To evaluate first-principles thermodynamics of the NO dissociation, we considered not only adsorption-desorption energetics, zero-point energy, and vibrational free energy at experiment temperature from first-principles, but also the chemical potential of NO gas at the cryogenic ultra-high vacuum condition. Using first-principles thermodynamics for the NO dissociation, we argue that the dissociations are induced with inelastic electron tunneling through molecular orbital resonances.

  2. 2-dimensional hyperbolic medium for electrons and photons based on the array of tunnel-coupled graphene nanoribbons

    Iorsh, Ivan

    2015-01-01

    We study the electronic band structure and optical conductivity of an array of tunnel-coupled array of graphene nanoribbons. We show that due to the coupling of electronic edge states for the zigzag nanoribbon structure, the Fermi surface can become a hyperbola similarly to the case of the layered metal-dielectric structures, where the hyperbolic isofrequency contours originate from the coupling of localized surface plasmon polaritons. Moreover, we show that for both types of the ribbon edge, the optical response of the structure can be characterized by a uniaxial conductivity tensor, having principal components of the different signs. Therefore, the tunnel-coupled nanoribbon array can be regarded as a tunable hyperbolic metasurface.

  3. Combining scanning tunneling microscopy and synchrotron radiation for high-resolution imaging and spectroscopy with chemical, electronic, and magnetic contrast

    The combination of high-brilliance synchrotron radiation with scanning tunneling microscopy opens the path to high-resolution imaging with chemical, electronic, and magnetic contrast. Here, the design and experimental results of an in-situ synchrotron enhanced x-ray scanning tunneling microscope (SXSTM) system are presented. The system is designed to allow monochromatic synchrotron radiation to enter the chamber, illuminating the sample with x-ray radiation, while an insulator-coated tip (metallic tip apex open for tunneling, electron collection) is scanned over the surface. A unique feature of the SXSTM is the STM mount assembly, designed with a two free-flex pivot, providing an angular degree of freedom for the alignment of the tip and sample with respect to the incoming x-ray beam. The system designed successfully demonstrates the ability to resolve atomic-scale corrugations. In addition, experiments with synchrotron x-ray radiation validate the SXSTM system as an accurate analysis technique for the study of local magnetic and chemical properties on sample surfaces. The SXSTM system's capabilities have the potential to broaden and deepen the general understanding of surface phenomena by adding elemental contrast to the high-resolution of STM. -- Highlights: ► Synchrotron enhanced x-ray scanning tunneling microscope (SXSTM) system designed. ► Unique STM mount design allows angular DOF for tip alignment with x-ray beam. ► System demonstrates ability to resolve atomic corrugations on HOPG. ► Studies show chemical sensitivity with STM tip from photocurrent and tunneling. ► Results show system's ability to study local magnetic (XMCD) properties on Fe films.

  4. Tunneling spectroscopy on grain boundary junctions in electron-doped high-temperature superconductors

    Some methods are developed anf presented, by means of which from experimental tunnel spectra, especially on symmetric SIS contacts, informations about the properties of electrodes and tunnel barriers can be obtained. Especially a procedure for the numerical unfolding of symmetric SIS spectra is proposed. Furthermore a series of models is summarized, which can explain the linear background conductivity observed in many spectra on high-temperature superconductors. The results of resistance measurements on film bridges are presented. Especially different methods for the determination of Hc2(T) respectively Hc2(0) are presented and applied to the experimental data. Finally the results of the tunnel-spectroscopy measurements are shown

  5. Is spin transport through molecules really occurring in organic spin valves? A combined magnetoresistance and inelastic electron tunnelling spectroscopy study

    Galbiati, Marta; Tatay, Sergio; Delprat, Sophie; Khanh, Hung Le; Deranlot, Cyrile; Collin, Sophie; Seneor, Pierre, E-mail: pierre.seneor@thalesgroup.com; Mattana, Richard, E-mail: richard.mattana@thalesgroup.com; Petroff, Frédéric [Unité Mixte de Physique CNRS/Thales, 1 Av. A. Fresnel, 91767 Palaiseau, France and Université Paris-Sud, 91405 Orsay (France); Servet, Bernard [Thales Research and Technology, 1 Av. A. Fresnel, 91767 Palaiseau (France)

    2015-02-23

    Molecular and organic spintronics is an emerging research field which combines the versatility of chemistry with the non-volatility of spintronics. Organic materials have already proved their potential as tunnel barriers (TBs) or spacers in spintronics devices showing sizable spin valve like magnetoresistance effects. In the last years, a large effort has been focused on the optimization of these organic spintronics devices. Insertion of a thin inorganic tunnel barrier (Al{sub 2}O{sub 3} or MgO) at the bottom ferromagnetic metal (FM)/organic interface seems to improve the spin transport efficiency. However, during the top FM electrode deposition, metal atoms are prone to diffuse through the organic layer and potentially short-circuit it. This may lead to the formation of a working but undesired FM/TB/FM magnetic tunnel junction where the organic plays no role. Indeed, establishing a protocol to demonstrate the effective spin dependent transport through the organic layer remains a key issue. Here, we focus on Co/Al{sub 2}O{sub 3}/Alq{sub 3}/Co junctions and show that combining magnetoresistance and inelastic electron tunnelling spectroscopy measurements one can sort out working “organic” and short-circuited junctions fabricated on the same wafer.

  6. Is spin transport through molecules really occurring in organic spin valves? A combined magnetoresistance and inelastic electron tunnelling spectroscopy study

    Galbiati, Marta; Tatay, Sergio; Delprat, Sophie; Khanh, Hung Le; Servet, Bernard; Deranlot, Cyrile; Collin, Sophie; Seneor, Pierre; Mattana, Richard; Petroff, Frdric

    2015-02-01

    Molecular and organic spintronics is an emerging research field which combines the versatility of chemistry with the non-volatility of spintronics. Organic materials have already proved their potential as tunnel barriers (TBs) or spacers in spintronics devices showing sizable spin valve like magnetoresistance effects. In the last years, a large effort has been focused on the optimization of these organic spintronics devices. Insertion of a thin inorganic tunnel barrier (Al2O3 or MgO) at the bottom ferromagnetic metal (FM)/organic interface seems to improve the spin transport efficiency. However, during the top FM electrode deposition, metal atoms are prone to diffuse through the organic layer and potentially short-circuit it. This may lead to the formation of a working but undesired FM/TB/FM magnetic tunnel junction where the organic plays no role. Indeed, establishing a protocol to demonstrate the effective spin dependent transport through the organic layer remains a key issue. Here, we focus on Co/Al2O3/Alq3/Co junctions and show that combining magnetoresistance and inelastic electron tunnelling spectroscopy measurements one can sort out working "organic" and short-circuited junctions fabricated on the same wafer.

  7. Search for Spin Filtering By Electron Tunneling Through Ferromagnetic EuS Barriers in Pbs

    Figielski, T.; Morawski, A.; Wosinski, T.; Wrotek, S.; Makosa, A.; Lusakowska, E.; Story, T.; Sipatov, A. Yu.; Szczerbakow, A.; Grasza, K.; Curreri, Peter A. (Technical Monitor)

    2002-01-01

    Perpendicular transport through single- and double-barrier heterostructures consisting of ferromagnetic EuS layers embedded into PbS matrix was investigated. Manifestations of both resonant tunneling and spin filtering through EuS barrier have been observed.

  8. Visualizing electron correlation by means of ab-initio scanning tunneling spectroscopy images of single molecules

    Toroz, Dimitrios; Rontani, Massimo; Corni, Stefano

    2011-01-01

    Scanning tunneling microscopy (STM) has been a fundamental tool to characterize many-body effects in condensed matter systems, from extended solids to quantum dots. STM of molecules decoupled from the supporting conductive substrate has the potential to extend STM characterization of many body effects to the molecular world as well. In this article, we describe a many-body tunneling theory for molecules decoupled from the STM substrate, and we report on the use of standard quantum chemical me...

  9. Magneto-tunnelling spectroscopy of chiral two-dimensional electron systems

    Pratley, L; Zuelicke, U.

    2013-01-01

    We present a theoretical study of momentum-resolved tunneling between parallel two-dimensional conductors whose charge carriers have a (pseudo-)spin-1/2 degree of freedom that is strongly coupled to their linear orbital momentum. Specific examples are single and bilayer graphene as well as single-layer molybdenum disulphide. Resonant behavior of the differential tunneling conductance exhibited as a function of an in-plane magnetic field and bias voltage is found to be strongly affected by the...

  10. Analysis of Human Resources Management Strategy in China Electronic Commerce Enterprises

    Shao, Fang

    The paper discussed electronic-commerce's influence on enterprise human resources management, proposed and proved the human resources management strategy which electronic commerce enterprise should adopt from recruitment strategy to training strategy, keeping talent strategy and other ways.

  11. Scanning-Tunneling Microscope Imaging of Single-Electron Solitons in a Material with Incommensurate Charge-Density Waves

    Brazovskii, Serguei; Brun, Christophe; Wang, Zhao-Zhong; Monceau, Pierre

    2012-03-01

    We report on scanning-tunneling microscopy experiments in a charge-density wave (CDW) system allowing visually capturing and studying in detail the individual solitons corresponding to the self-trapping of just one electron. This Amplitude Soliton is marked by vanishing of the CDW amplitude and by the ? shift of its phase. It might be the realization of the spinonthe long-sought particle (along with the holon) in the study of science of strongly correlated electronic systems. As a distinct feature we also observe one-dimensional Friedel oscillations superimposed on the CDW which develop independently of solitons.

  12. Measurement of laser activated electron tunneling from semiconductor zinc oxide to adsorbed organic molecules by a matrix assisted laser desorption ionization mass spectrometer

    Highlights: ► Irradiation of photons with energies more than the band gap generates electron–hole pairs. ► Electron tunneling probability is dependent on the electron mobility. ► Tunneling electrons are captured by charge deficient atoms. ► Unpaired electrons induce cleavages of chemical bonds. - Abstract: Measurement of light induced heterogeneous electron transfer is important for understanding of fundamental processes involved in chemistry, physics and biology, which is still challenging by current techniques. Laser activated electron tunneling (LAET) from semiconductor metal oxides was observed and characterized by a MALDI (matrix assisted laser desorption ionization) mass spectrometer in this work. Nanoparticles of ZnO were placed on a MALDI sample plate. Free fatty acids and derivatives were used as models of organic compounds and directly deposited on the surface of ZnO nanoparticles. Irradiation of UV laser (λ = 355 nm) with energy more than the band gap of ZnO produces ions that can be detected in negative mode. When TiO2 nanoparticles with similar band gap but much lower electron mobility were used, these ions were not observed unless the voltage on the sample plate was increased. The experimental results indicate that laser induced electron tunneling is dependent on the electron mobility and the strength of the electric field. Capture of low energy electrons by charge-deficient atoms of adsorbed organic molecules causes unpaired electron-directed cleavages of chemical bonds in a nonergodic pathway. In positive detection mode, electron tunneling cannot be observed due to the reverse moving direction of electrons. It should be able to expect that laser desorption ionization mass spectrometry is a new technique capable of probing the dynamics of electron tunneling. LAET offers advantages as a new ionization dissociation method for mass spectrometry.

  13. Atomic scale imaging and characterization of electronic defect states in dielectric thin film materials using dynamic tunneling force microscopy

    Wang, Ruiyao

    Dynamic Tunneling Force Microscopy (DTFM) is an Atomic Force Microscopy (AFM) technique used for imaging and characterizing trap states on nonconducting surfaces. In this thesis, DTFM images are acquired under Kelvin Probe Force Microscopy (KPFM) feedback and height feedback control. Simultaneous acquisition of DTFM, surface potential, and topographic images is realized, and correlation between trap states, surface potential, and surface topography can be extracted. The methodology for obtaining three-dimensional location and energy of individual atomic scale electronic trap states is described. The energy and depth of states accessible by a DTFM experiment are calculated using tunneling and electrostatic models. The DTFM signal amplitude is derived using a one-dimensional electrostatic model. Comparison between simulated DTFM signal and experimental results show a good consistency, verifying the single electron tunneling model. DTFM is demonstrated on interlayer dielectric materials. Density, spatial distribution, energy, and depth distribution of trap states in these materials are measured by DTFM. An atomic scale study of electrical stressing effects using the DTFM method is performed showing both state appearance and disappearance after electrical stressing.

  14. Effects of Electronic Information Resources Skills Training for Lecturers on Pedagogical Practices and Research Productivity

    Bhukuvhani, Crispen; Chiparausha, Blessing; Zuvalinyenga, Dorcas

    2012-01-01

    Lecturers use various electronic resources at different frequencies. The university library's information literacy skills workshops and seminars are the main sources of knowledge of accessing electronic resources. The use of electronic resources can be said to have positively affected lecturers' pedagogical practices and their work in general. The…

  15. Electronic Resources and Mission Creep: Reorganizing the Library for the Twenty-First Century

    Stachokas, George

    2009-01-01

    The position of electronic resources librarian was created to serve as a specialist in the negotiation of license agreements for electronic resources, but mission creep has added more functions to the routine work of electronic resources such as cataloging, gathering information for collection development, and technical support. As electronic…

  16. Correlations between the final momenta of electrons and their initial phase-space distribution in the process of tunnel ionization

    Ayadi, Viktor; Dombi, Peter; Tokesi, Karoly

    2016-01-01

    We present both full quantum mechanical and semiclassical calculations of above threshold ionization (ATI) of a hydrogen atom in the tunneling regime by a few-cycle linearly polarized infrared laser pulse. As a quantum treatment, we applied the direct integration of the time dependent Schr\\"odinger equation (TDSE). In the semiclassical approximation (SCA), it is assumed that wavepacket propagation in the post-tunneling process can be well described within the classical framework. With these two methods, we analyze the similarities and deviations for ionization of the hydrogen atom. We found that the 3 dimensional semiclassical method can describe reasonably well the momentum correlation pattern of the ATI peaks. We also show good agreement between the results obtained by TDSE method and the semi-classical method. Furthermore, with the semiclassical approximation we clearly identify and separate the regions in momentum distributions of the ejected electrons according to initial conditions. We illustrate the co...

  17. Electron transport in a ferromagnetic/normal/ferromagnetic tunnel junction based on the surface of a topological insulator

    Yuan, Jianhui; Zhang, Yan; Zhang, Jianjun; Cheng, Ze

    2013-02-01

    We theoretically study the electron transport properties in a ferromagnetic/normal/ferromagnetic tunnel junction, which is deposited on the top of a topological surface. The conductance at the parallel (P) configuration can be much bigger than that at the antiparallel (AP) configuration. Compared P with AP configuration, there exists a shift of phase which can be tuned by gate voltage. We find that the exchange field weakly affects the conductance of carriers for P configuration but can dramatically suppress the conductance of carriers for AP configuration. This controllable electron transport implies anomalous magnetoresistance in this topological spin valve, which may contribute to the development of spintronics. In addition, there shows an existence of Fabry-Perot-like electron interference in our model based on the topological insulator, which does not appear in the same model based on the two dimensional electron gas.

  18. Electronic characterization of LaAlO3-SrTiO3 interfaces by scanning tunneling spectroscopy

    When LaAlO3 is epitaxially grown on TiO2-terminated SrTiO3, an electrically conducting interface is generated. In this respect, the physical properties of the interface differ substantially from those of both LaAlO3 and SrTiO3, which are electrically insulating in bulk form. This dissertation looks into the question of the microscopic structure of the conducting two-dimensional interface electron system. Comparing the electronic density of states of LaAlO3-SrTiO3 interfaces measured by scanning tunneling spectroscopy with results of density functional theory, the interface electron system is found to be substantially coined by the hosting transition metal lattices. The comparison yields a detailed picture of the microscopic structure of the interface electron system. (orig.)

  19. Pulse radiolysis study of electron tunneling in an 8 M NaOH glass between 4 and 100 K

    Pulse radiolysis experiments have been performed in an 8 M NaOH glass between 4 and 100 K and in the time range 10-6 to 10 s. The spur radius was estimated from the decay of the trapped electrons on the red side of the absorption maximum. The spur radius was about 4 nm at 80 K and increased to about 6 nm at 10 K. We studied the decay of trapped electrons in the presence of the following electron scavengers: CrO2-4, Fe(CN)3-6, and NO-2. No temperature dependence was found between 10 and 100 K. To explain the results distance-dependent and/or time-dependent Franck--Condon factors have been introduced. We show that in the time range studied it is not possible to distinguish between direct tunneling and trap-to-trap tunneling. Dry electron scavenging efficiencies and encounter pair formation are expressed in S37. For CrO2-4, Fe(CN)3-6, and NO-2 we found that S37 was 45, 130, and 300 M, respectively

  20. Construction of a four tip scanning tunneling microscope/scanning electron microscope combination and conductivity measurements of silicide nanowires

    In this work the combination of a four-tip scanning tunneling microscope with a scanning electron microscope is presented. By means of this apparatus it is possible to perform the conductivity measurements on the in-situ prepared nanostructures in ultra-high vacuum. With the aid of a scanning electron microscope (SEM), it becomes possible to position the tunneling tips of the four-tip scanning tunneling microscope (STM), so that an arrangement for a four-point probe measurement on nanostructures can be obtained. The STM head was built according to the novel coaxial Beetle concept. This concept allows on the one hand, a very compact arrangement of the components of the STM and on the other hand, the new-built STM head has a good mechanical stability, in order to achieve atomic resolution with all four STM units. The atomic resolution of the STM units was confirmed by scanning a Si(111)-7 x 7 surface. The thermal drift during the STM operation, as well as the resonant frequencies of the mechanical structure of the STM head, were determined. The scanning electron microscope allows the precise and safe navigation of the tunneling tips on the sample surface. Multi tip spectroscopy with up to four STM units can be performed synchronously. To demonstrate the capabilities of the new-built apparatus the conductivity measurements were carried out on metallic yttrium silicide nanowires. The nanowires were prepared by the in-situ deposition of yttrium on a heated Si(110) sample surface. Current-voltage curves were recorded on the nanowires and on the wetting layer in-between. The curves indicate an existence of the Schottky barrier between the yttrium silicide nanowires and the silicon bulk. By means of the two-tip measurements with a gate, the insulating property of the Schottky barrier has been confirmed. Using this Schottky barrier, it is possible to limit the current to the nanowire and to prevent it from flowing through the silicon bulk. A four-tip resistance measurement with a gate has provided the resistance of the nanowire. From the dimensions of the nanowire the resistivity was calculated. The obtained resistivity was found to be in agreement with literature values. In addition, the contact resistances of the tunneling tips on the silicide nanowires were determined.

  1. Control of Coulomb blockade in a mesoscopic Josephson junction using single electron tunneling

    Hassel, J; Seppä, H; Hakonen, P J

    2003-01-01

    We study a circuit where a mesoscopic Josephson junction (JJ) is embedded in an environment consisting of a large bias resistor and a normal metal - superconductor tunnel junction (NIS). The effective Coulomb blockade of the JJ can be controlled by the tunneling current through the NIS junction leading to transistor-like characteristics. We show using phase correlation theory and numerical simulations that substantial current gain with low current resolution (< 0.1 fA) and noise temperature (< 0.1 K) can be achieved. Good agreement between our numerical simulations and experimental results is obtained.

  2. Electronic Document Management: A Human Resource Management Case Study

    Thomas Groenewald

    2004-11-01

    Full Text Available This case study serve as exemplar regarding what can go wrong with the implementation of an electronic document management system. Knowledge agility and knowledge as capital, is outlined against the backdrop of the information society and knowledge economy. The importance of electronic document management and control is sketched thereafter. The literature review is concluded with the impact of human resource management on knowledge agility, which includes references to the learning organisation and complexity theory. The intervention methodology, comprising three phases, follows next. The results of the three phases are presented thereafter. Partial success has been achieved with improving the human efficacy of electronic document management, however the client opted to discontinue the system in use. Opsomming Die gevalle studie dien as voorbeeld van wat kan verkeerd loop met die implementering van n elektroniese dokumentbestuur sisteem. Teen die agtergrond van die inligtingsgemeenskap en kennishuishouding word kennissoepelheid en kennis as kapitaal bespreek. Die literatuurstudie word afgesluit met die inpak van menslikehulpbronbestuur op kennissoepelheid, wat ook die verwysings na die leerorganisasie en kompleksietydsteorie insluit. Die metodologie van die intervensie, wat uit drie fases bestaan, volg daarna. Die resultate van die drie fases word vervolgens aangebied. Slegs gedeelte welslae is behaal met die verbetering van die menslike doeltreffendheid ten opsigte van elektroniese dokumentbestuur. Die klient besluit egter om nie voort te gaan om die huidige sisteem te gebruik nie.

  3. Electronic Document Management: A Human Resource Management Case Study

    Thomas Groenewald

    2004-11-01

    Full Text Available This case study serve as exemplar regarding what can go wrong with the implementation of an electronic document management system. Knowledge agility and knowledge as capital, is outlined against the backdrop of the information society and knowledge economy. The importance of electronic document management and control is sketched thereafter. The literature review is concluded with the impact of human resource management on knowledge agility, which includes references to the learning organisation and complexity theory. The intervention methodology, comprising three phases, follows next. The results of the three phases are presented thereafter. Partial success has been achieved with improving the human efficacy of electronic document management, however the client opted to discontinue the system in use. Opsomming Die gevalle studie dien as voorbeeld van wat kan verkeerd loop met die implementering van ’n elektroniese dokumentbestuur sisteem. Teen die agtergrond van die inligtingsgemeenskap en kennishuishouding word kennissoepelheid en kennis as kapitaal bespreek. Die literatuurstudie word afgesluit met die inpak van menslikehulpbronbestuur op kennissoepelheid, wat ook die verwysings na die leerorganisasie en kompleksietydsteorie insluit. Die metodologie van die intervensie, wat uit drie fases bestaan, volg daarna. Die resultate van die drie fases word vervolgens aangebied. Slegs gedeelte welslae is behaal met die verbetering van die menslike doeltreffendheid ten opsigte van elektroniese dokumentbestuur. Die klient besluit egter om nie voort te gaan om die huidige sisteem te gebruik nie.

  4. Revealing energy level structure of individual quantum dots by tunneling rate measured by single-electron sensitive electrostatic force spectroscopy.

    Roy-Gobeil, Antoine; Miyahara, Yoichi; Grutter, Peter

    2015-04-01

    We present theoretical and experimental studies of the effect of the density of states of a quantum dot (QD) on the rate of single-electron tunneling that can be directly measured by electrostatic force microscopy (e-EFM) experiments. In e-EFM, the motion of a biased atomic force microscope cantilever tip modulates the charge state of a QD in the Coulomb blockade regime. The charge dynamics of the dot, which is detected through its back-action on the capacitavely coupled cantilever, depends on the tunneling rate of the QD to a back-electrode. The density of states of the QD can therefore be measured through its effect on the energy dependence of tunneling rate. We present experimental data on individual 5 nm colloidal gold nanoparticles that exhibit a near continuous density of state at 77 K. In contrast, our analysis of already published data on self-assembled InAs QDs at 4 K clearly reveals discrete degenerate energy levels. PMID:25761141

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

    In this paper, the electronic transport characteristics of Fe/trans-polyacetylene/Fe magnetic tunnel junctions (MTJs) are investigated using multi-band tight-binding calculations within the framework of nonequilibrium Green function theory. A CH2 radical is added to different positions on the polymer chain and its effects on the tunnelling magnetoresistance of the MTJ are studied. The ferromagnetic electrodes are assumed to be single-band and their tight-binding parameters are chosen in such a way as to simulate the ab initio density functional calculations of the band structure of bcc-Fe along its [001] crystallographic direction. In building the Hamiltonian of the trans-polyacetylene (t-PA) chain, we have assumed an s orbital on the H atoms and one s and three p(px,py,pz) orbitals on the C atoms, and the dimerization effects are taken into account. It is found that moving the radical out of the centre of the polymer chain enhances the tunnelling magnetoresistance of the MTJ.

  6. Harnessing electronic information resources through prospective consortia approach: a national necessity

    Vasishta, Seema; Dhingra, Navjyoti

    2007-01-01

    Earlier information resources were considered physical entities but now these have evolved from traditional print documents to electronically stored information resources. In this time of lessening finances, myriad forms of resources and rising expectations of user community, libraries face many challenges to operate competently. The demand to provide more electronic information resources often results in a need to find creative ways to get the most out of our limited financial resources. Pre...

  7. Effect of tunnel injection through the Schottky gate on the static and noise behavior of GaInAs/AlInAs high electron mobility transistor

    Moro-Melgar, Diego, E-mail: diego.moro-melgar@obspm.fr [Observatoire de Paris, LERMA, 77 avenue Denfert Rochereau 75014 Paris (France); Mateos, Javier, E-mail: javierm@usal.es; Gonzlez, Toms, E-mail: tomasg@usal.es; Vasallo, Beatriz G., E-mail: bgvasallo@usal.es [Departamento de Fsica Aplicada, Universidad de Salamanca, Plaza de la Merced s/n, 37008 Salamanca (Spain)

    2014-12-21

    By using a Monte Carlo simulator, the influence of the tunnel injection through the Schottky contact at the gate electrode of a GaInAs/AlInAs High Electron Mobility Transistor (HEMT) has been studied in terms of the static and noise performance. The method used to characterize the quantum tunnel current has been the Wentzel-Kramers-Brillouin (WKB) approach. The possibility of taking into account the influence of the image charge effect in the potential barrier height has been included as well. Regarding the static behavior, tunnel injection leads to a decrease in the drain current I{sub D} due to an enhancement of the potential barrier controlling the carrier transport through the channel. However, the pinch-off is degraded due to the tunneling current. Regarding the noise behavior, since the fluctuations in the potential barrier height caused by the tunnel-injected electrons are strongly coupled with the drain current fluctuations, a significant increase in the drain-current noise takes place, even when the tunnel effect is hardly noticeable in the static I-V characteristics, fact that must be taken into account when designing scaled HEMT for low-noise applications. In addition, tunnel injection leads to the appearance of full shot noise in the gate current.

  8. Effect of tunnel injection through the Schottky gate on the static and noise behavior of GaInAs/AlInAs high electron mobility transistor

    By using a Monte Carlo simulator, the influence of the tunnel injection through the Schottky contact at the gate electrode of a GaInAs/AlInAs High Electron Mobility Transistor (HEMT) has been studied in terms of the static and noise performance. The method used to characterize the quantum tunnel current has been the Wentzel-Kramers-Brillouin (WKB) approach. The possibility of taking into account the influence of the image charge effect in the potential barrier height has been included as well. Regarding the static behavior, tunnel injection leads to a decrease in the drain current ID due to an enhancement of the potential barrier controlling the carrier transport through the channel. However, the pinch-off is degraded due to the tunneling current. Regarding the noise behavior, since the fluctuations in the potential barrier height caused by the tunnel-injected electrons are strongly coupled with the drain current fluctuations, a significant increase in the drain-current noise takes place, even when the tunnel effect is hardly noticeable in the static I-V characteristics, fact that must be taken into account when designing scaled HEMT for low-noise applications. In addition, tunnel injection leads to the appearance of full shot noise in the gate current

  9. Conceptual Design of a 50-100 MW Electron Beam Accelerator System for the National Hypersonic Wind Tunnel Program

    The National Hypersonic Wind Tunnel program requires an unprecedented electron beam source capable of 1--2 MeV at a beam power level of 50--100 MW. Direct-current electron accelerator technology can readily generate high average power beams to approximately 5 MeV at output efficiencies greater than 90%. However, due to the nature of research and industrial applications, there has never been a requirement for a single module with an output power exceeding approximately 500 kW. Although a 50--100 MW module is a two-order extrapolation from demonstrated power levels, the scaling of accelerator components appears reasonable. This paper presents an evaluation of component and system issues involved in the design of a 50--100 MW electron beam accelerator system with precision beam transport into a high pressure flowing air environment

  10. Conceptual Design of a 50--100 MW Electron Beam Accelerator System for the National Hypersonic Wind Tunnel Program

    SCHNEIDER,LARRY X.

    2000-06-01

    The National Hypersonic Wind Tunnel program requires an unprecedented electron beam source capable of 1--2 MeV at a beam power level of 50--100 MW. Direct-current electron accelerator technology can readily generate high average power beams to approximately 5 MeV at output efficiencies greater than 90%. However, due to the nature of research and industrial applications, there has never been a requirement for a single module with an output power exceeding approximately 500 kW. Although a 50--100 MW module is a two-order extrapolation from demonstrated power levels, the scaling of accelerator components appears reasonable. This paper presents an evaluation of component and system issues involved in the design of a 50--100 MW electron beam accelerator system with precision beam transport into a high pressure flowing air environment.

  11. Shaping a time-dependent excitation to control the electron distribution function: noise minimization in a tunnel junction

    Gabelli, Julien; Reulet, Bertrand

    2012-01-01

    We report measurements of shot noise in a tunnel junction under bi-harmonic illumination, Vac(t) = Vac1 cos(2\\pi ft) + Vac2 cos(4\\pi ft+ \\phi). The experiment is performed in the quantum regime, hf >> k_BT at low temperature T = 70 mK and high frequency f = 10 GHz. From the measurement of noise at low frequency, we show that we can infer and control the non-equilibrium electronic distribution function by adjusting the amplitudes and phase of the excitation, thus modeling its shape. In particu...

  12. Investigation of inelastic electron tunneling spectra of metal-molecule-metal junctions fabricated using direct metal transfer method

    We measured the inelastic electron tunneling spectroscopy (IETS) characteristics of metal-molecule-metal junctions made with alkanethiolate self-assembled monolayers. The molecular junctions were fabricated using a direct metal transfer method, which we previously reported for high-yield metal-molecule-metal junctions. The measured IETS data could be assigned to molecular vibration modes that were determined by the chemical structure of the molecules. We also observed discrepancies and device-to-device variations in the IETS data that possibly originate from defects in the molecular junctions and insulating walls introduced during the fabrication process and from the junction structure

  13. InAs nanowire with epitaxial aluminium as a single-electron transistor with fixed tunnel barriers

    Taupin, Mathieu; Krogstrup, Peter; Nguyen, Hung Q.; Mannila, Elsa; Albrecht, Sven M.; Nygård, Jesper; Marcus, Charles M.; Pekola, Jukka P.

    2016-01-01

    We report on fabrication of a single-electron transistor using InAs nanowires with epitaxial aluminium with fixed tunnel barriers made of aluminium oxide. The device exhibits a hard superconducting gap induced by the proximized aluminium cover shell and it behaves as its metallic counterpart. We confirm that unwanted extra quantum dots can appear at the surface of the nanowire, but can be prevented either by covering the nanowire with aluminium, or by inserting a layer of GaAs between the InA...

  14. Quasi-stationary states of electrons interacting with strong electromagnetic field in two-barrier resonance tunnel nano-structure

    M.V. Tkach

    2012-10-01

    Full Text Available An exact solution of non-stationary Schrodinger equation is obtained for a one-dimensional movement of electrons in an electromagnetic field with arbitrary intensity and frequency. Using it, the permeability coefficient is calculated for a two-barrier resonance tunnel nano-structure placed into a high-frequency electromagnetic field. It is shown that a nano-structure contains quasi-stationary states the spectrum of which consists of the main and satellite energies. The properties of resonance and non-resonance channels of permeability are displayed.

  15. On the valve nature of a monolayer of aligned molecular magnets in tunneling spin-polarized electrons: Towards organic molecular spintronics

    We form a monolayer of magnetic organic molecules and immobilize their moments pointing either upwards or downwards with respect to the substrate through an electrostatic-binding process. Such a monolayer is probed with a scanning tunneling microscope tip, which is also magnetized with the magnetization vector pointing towards (or away from) apex of the tip. From spin-polarized tunneling current, we show that the current was higher when magnetization vectors of the tip and molecules were parallel as compared to that when they were anti-parallel. We show that for tunneling of spin-polarized electrons, aligned organic molecular magnets can act as a valve

  16. Assessing Ongoing Electronic Resource Purchases: Linking Tools to Synchronize Staff Workflows

    Carroll, Jeffrey D.; Major, Colleen; O'Neal, Nada; Tofanelli, John

    2012-01-01

    Ongoing electronic resource purchases represent a substantial proportion of collections budgets. Recognizing the necessity of systematic ongoing assessment with full selector engagement, Columbia University Libraries appointed an Electronic Resources Assessment Working Group to promote the inclusion of such resources within our current culture of…

  17. Electron transport across capped Au nanoclusters adsorbed in different configurations on highly oriented pyrolytic graphite substrate using scanning tunneling microscopy / spectroscopy

    Singh, Poonam; Dharmadhikari, C V [Centre for Advanced Studies in Materials Science and Solid State Physics, Department of Physics, University of Pune, Pune 411007 (India)

    2007-04-15

    Comparison of electron transport across dodecanethiol capped Au nanoclusters adsorbed in different locations viz. in an agglomeration, on isolated particle either on the terrace or at the step edge of highly oriented pyrolytic graphite using scanning tunneling microscopy / spectroscopy is carried out. Current-distance measurements on these different locations shows different regimes suggesting different mechanisms for electron transport. Current-voltage measurements at these locations have been carried out and the results are discussed in the light of orthodox theory for electron transport in double-barrier tunnel junction.

  18. Electronic band alignment and electron transport in Cr/BaTiO{sub 3}/Pt ferroelectric tunnel junctions

    Zenkevich, A. [NRNU ' Moscow Engineering Physics Institute,' 115409 Moscow (Russian Federation); Moscow Institute of Physics and Technology, Dolgoprudny, Moscow Region (Russian Federation); Minnekaev, M.; Matveyev, Yu.; Lebedinskii, Yu. [NRNU ' Moscow Engineering Physics Institute,' 115409 Moscow (Russian Federation); Bulakh, K.; Chouprik, A.; Baturin, A. [Moscow Institute of Physics and Technology, Dolgoprudny, Moscow Region (Russian Federation); Maksimova, K. [Immanuel Kant Baltic Federal University, 236041 Kaliningrad (Russian Federation); Thiess, S.; Drube, W. [Deutsches Elektronen-Synchrotron DESY, D-22603 Hamburg (Germany)

    2013-02-11

    Electroresistance in ferroelectric tunnel junctions is controlled by changes in the electrostatic potential profile across the junction upon polarization reversal of the ultrathin ferroelectric barrier layer. Here, hard X-ray photoemission spectroscopy is used to reconstruct the electric potential barrier profile in as-grown Cr/BaTiO{sub 3}(001)/Pt(001) heterostructures. Transport properties of Cr/BaTiO{sub 3}/Pt junctions with a sub-{mu}m Cr top electrode are interpreted in terms of tunneling electroresistance with resistance changes of a factor of {approx}30 upon polarization reversal. By fitting the I-V characteristics with the model employing an experimentally determined electric potential barrier we derive the step height changes at the BaTiO{sub 3}/Pt (Cr/BaTiO{sub 3}) interface +0.42(-0.03) eV following downward to upward polarization reversal.

  19. Electronic picture of spin-polarized tunneling with a Cr tip

    We use spin-resolved scanning tunneling spectroscopy with a Cr-covered W-tip to investigate the magnetic switching of single Co islands on Cu(111) in polar magnetic fields. The observed hysteretic curve resembles a shape which is well known from so-called butterfly curves of tunneling magnetoresistance measurements. This indicates that not only the Co-island but also the Cr-tip changes its spin orientation in response to the applied magnetic field. For the interpretation of the experimental observations, we perform ab initio calculations by means of the Korringa-Kohn-Rostoker Green's function method. The calculations demonstrate that the Cr-tip is not a perfect antiferromagnet and has an uncompensated magnetic moment which changes its spin orientation continuously due to the applied magnetic field.

  20. Spatially resolved electron tunneling spectroscopy on single crystalline Rb3C60

    A Rb3C60 single crystal (Tc=30.5 K) is investigated in the superconducting state at 2.8 K by scanning tunneling microscopy and scanning tunneling spectroscopy (STS). STS data reveals a spatial variation of the superconducting energy gap Δ on a scale of 50 nm (Δ=2.6 endash 5.2 meV; 2Δ/kBTc=2.0 endash 4.0). This behavior is attributed to varying stoichiometry on the sample surface. An investigation of a Rb3C60 facet shows that I(V) characteristics even vary on molecular scale. I(V) curves acquired between fullerene molecules exhibit a nonvanishing slope at zero bias whereas I(V) characteristics measured above molecules exhibit vanishing slope at zero bias. copyright 1996 American Vacuum Society

  1. Quantum interference effect in electron tunneling through a quantum-dot-ring spin valve

    Ma Jing-Min

    2011-01-01

    Full Text Available Abstract Spin-dependent transport through a quantum-dot (QD ring coupled to ferromagnetic leads with noncollinear magnetizations is studied theoretically. Tunneling current, current spin polarization and tunnel magnetoresistance (TMR as functions of the bias voltage and the direct coupling strength between the two leads are analyzed by the nonequilibrium Green's function technique. It is shown that the magnitudes of these quantities are sensitive to the relative angle between the leads' magnetic moments and the quantum interference effect originated from the inter-lead coupling. We pay particular attention on the Coulomb blockade regime and find the relative current magnitudes of different magnetization angles can be reversed by tuning the inter-lead coupling strength, resulting in sign change of the TMR. For large enough inter-lead coupling strength, the current spin polarizations for parallel and antiparallel magnetic configurations will approach to unit and zero, respectively. PACS numbers:

  2. Nuclear and electronic resonance spectroscopy of single molecules by radio-frequency scanning tunnelling microscopy

    Müllegger, Stefan; Tebi, Stefano; Das, Amal K.; Schöfberger, Wolfgang; Faschinger, Felix; Koch, Reinhold

    2014-01-01

    The ongoing miniaturization in nanoscience and -technology challenges the sensitivity and selectivity of experimental analysis methods to the ultimate level of single atoms and molecules. A promising new approach, addressed here, focuses on the combination of two well-established complementary techniques that have proven to be very successful in their own fields: (i) low-temperature scanning tunneling microscopy (STM), offering high spatial resolution for imaging and spectroscopy together wit...

  3. Plane-wave based electron tunneling through field emission resonance states

    Garca-Lekue, Aran; Snchez-Portal, Daniel; Arnau, Andrs; Wang, L W

    2013-01-01

    Field emission resonances (FERs) on Cu(100) surface are investigated by means of tunneling regime simulations performed with a plane-wave based transport calculation method. FERs are located near the surface and decay into the vacuum, and their accurate simulation requires a faithful description of vacuum states. This type of simulations is thus not possible using the popular transport methods based on atom-centered localized basis sets and the use of plane waves becomes important. We introdu...

  4. Ferroelectric tunnel junctions

    Rodriguez Contreras, J.

    2004-01-01

    Ferroelectricity and quantum-mechanical electron tunneling are well-known physical phenomena that have been studied for as long as a century. During this long period, scientific research has been restricted either to ferroelectricity or to electron tunneling. Never before have these subjects been combined into a new phenomenon based on their interaction. Within this work, I present the novel concept of a ferroelectric tunnel junction, where the term ferroelectric refers to a property of the b...

  5. Time-dependent exchange and tunneling: detection at the same place of two electrons emitted simultaneously from different sources.

    Marian, D; Colomés, E; Oriols, X

    2015-06-24

    Two-particle scattering probabilities in tunneling scenarios with exchange interaction are analyzed with quasi-particle wave packets. Two initial one-particle wave packets (with opposite central momentums) are spatially localized at each side of a barrier. After impinging upon a tunneling barrier, each wave packet splits into transmitted and reflected components. When the initial two-particle anti-symmetrical state is defined as a Slater determinant of any type of (normalizable) one-particle wave packet, it is shown that the probability of detecting two (identically injected) electrons at the same side of the barrier is different from zero in very common (single or double barrier) scenarios. In some particular scenarios, the transmitted and reflected components become orthogonal and the mentioned probabilities reproduce those values associated to distinguishable particles. These unexpected non-zero probabilities are still present when non-separable Coulomb interaction or non-symmetrical potentials are considered. On the other hand, for initial wave packets close to Hamiltonian eigenstates, the usual zero two-particle probability for electrons at the same side of the barrier found in the literature is recovered. The generalization to many-particle scattering probabilities with quasi-particle wave packets for low and high phase-space density are also analyzed. The far-reaching consequences of these non-zero probabilities in the accurate evaluation of quantum noise in mesoscopic systems are briefly indicated. PMID:26030519

  6. An array of cold-electron bolometers with SIN tunnel junctions and JFET readout for cosmology instruments

    Kuzmin, L [Chalmers University of Technology, S-41296 Gothenburg (Sweden)], E-mail: leonid.kuzmin@mc2.chalmers.se

    2008-02-01

    A novel concept of the parallel/series array of Cold-Electron Bolometers (CEB) with Superconductor-Insulator-Normal (SIN) Tunnel Junctions has been proposed. The concept was developed specially for matching the CEB with JFET amplifier at conditions of high optical power load. The CEB is a planar antenna-coupled superconducting detector with high sensitivity. For combination of effective HF operation and low noise properties the current-biased CEBs are connected in series for DC and in parallel for HF signal. A signal is concentrated from an antenna to the absorber through the capacitance of the tunnel junctions and through additional capacitance for coupling of superconducting islands. Using array of CEBs the applications can be considerably extended to higher power load by distributing the power between N CEBs and decreasing the electron temperature. Due to increased responsivity the noise matching is so effective that photon NEP could be easily achieved at 300 mK with a room temperature JFET for wide range of optical power loads. The concept of the CEB array has been developed for the BOOMERanG balloon telescope and other Cosmology instruments.

  7. Design of a novel on-chip electronic refrigerator based on a normal-insulator-superconductor tunnel junction

    We present a design for a novel electronic refrigerator having a base temperature of about 18 mK when operating from a bath temperature as high as 1.5 K. This all-electronic refrigerator is a factor of 104 smaller and lighter than dilution and adiabatic demagnetization refrigerators, and is compatible with conventional photolithographic fabrication. The refrigerator, based on the unique thermal transport properties of a normal-insulator-superconductor (NIS) tunnel function, preferentially removes electrons whose energy is higher than the Fermi energy from a normal metal. Electrons with an average energy equal to the Fermi energy are returned to the metal by a superconductor contact. Consequently, high energy thermal excitations are removed from the normal metal, thus cooling the electrons. In our configuration, the junction is deposited on a Si3N4 membrane of submicron thickness that thermally isolates the normal electrode from the bath. As a result, both electrons and phonons in the metal are cooled below the bath temperature. We calculate a cooling power of 2 nW at 100 mK, and a base temperature of 18 mK for a refrigerator area of about 100X100μm2. Using 105 such refrigerator circuits, the cooling power can be increased to 200 μW

  8. Direct observation of electron emission from the grain boundaries of chemical vapour deposition diamond films by tunneling atomic force microscopy

    The emission of electrons from diamond in vacuum occurs readily as a result of the negative electron affinity of the hydrogenated surface due to features with nanoscale dimensions, which can concentrate electric fields high enough to induce electron emission from them. Electrons can be emitted as a result of an applied electric field (field emission) with possible uses in displays or cold-cathode devices. Alternatively, electrons can be emitted simply by heating the diamond in vacuum to temperatures as low as 350?C (thermionic emission), and this may find applications in solar energy generation or energy harvesting devices. Electron emission studies usually use doped polycrystalline diamond films deposited onto Si or metallic substrates by chemical vapor deposition, and these films have a rough, faceted morphology on the micron or nanometer scale. Electron emission is often improved by patterning the diamond surface into sharp points or needles, the idea being that the field lines concentrate at the points lowering the barrier for electron emission. However, there is little direct evidence that electrons are emitted from these sharp tips. The few reports in the literature that have studied the emission sites suggested that emission came from the grain boundaries and not the protruding regions. We now present direct observation of the emission sites over a large area of polycrystalline diamond using tunneling atomic force microscopy. We confirm that the emission current comes mostly from the grain boundaries, which is consistent with a model for emission in which the non-diamond phase is the source of electrons with a threshold that is determined by the surrounding hydrogenated diamond surface

  9. The calculation of the conductance and electron tunneling characteristic time from metal-molecule contact in a molecular wire

    S. A. Ketabi

    2003-12-01

    Full Text Available In this paper, on the basis of tight-binding model and a generalized Green- function method as well as Lanczos algorithm procedure, the effects of the metal-molecule coupling(MMC strength on the electronic transmission through a metal-single molecule-metal(MMM system is investigated. Using the Landauer formalism we study some of the significant conductance properties of this system as a molecular wire. Our results show that with the increase of the length of the molecule, the conductance of the molecular wire decreases exponentially. With trans-polyacetylene (trans-PA as the molecule, we calculate a characteristic time for electron transmission through the MMM system. This time scale measures the delay caused by tunneling through the MMC. Our calculations show that the conductance is sensitive to the MMC strength. The focus is on the significant relationship between this time scale and the strength of the metal-molecule(trans-PA coupling.

  10. Proton tunneling in solids

    Kondo, J.

    1998-10-01

    The tunneling rate of the proton and its isotopes between interstitial sites in solids is studied theoretically. The phonons and/or the electrons in the solid have two effects on the tunneling phenomenon. First, they suppress the transfer integral between two neighbouring states. Second, they give rise to a finite lifetime of the proton state. Usually the second effect is large and the tunneling probability per unit time (tunneling rate) can be defined. In some cases, however, a coherent tunneling is expected and actually observed. (author)

  11. Elektronik Bilgi Kaynaklar?n?n Seimi / Selection of Electronic Information Resources

    P?nar Al

    2003-04-01

    Full Text Available For many years, library users have used only from the printed media in order to get the information that they have needed. Today with the widespread use of the Web and the addition of electronic information resources to library collections, the use of information in the electronic environment as well as in printed media is started to be used. In time, such types of information resources as, electronic journals, electronic books, electronic encyclopedias, electronic dictionaries and electronic theses have been added to library collections. In this study, selection criteria that can be used for electronic information resources are discussed and suggestions are provided for libraries that try to select electronic information resources for their collections.

  12. Comparison of Resource Requirements for a Wind Tunnel Test Designed with Conventional vs. Modern Design of Experiments Methods

    DeLoach, Richard; Micol, John R.

    2011-01-01

    The factors that determine data volume requirements in a typical wind tunnel test are identified. It is suggested that productivity in wind tunnel testing can be enhanced by managing the inference error risk associated with evaluating residuals in a response surface modeling experiment. The relationship between minimum data volume requirements and the factors upon which they depend is described and certain simplifications to this relationship are realized when specific model adequacy criteria are adopted. The question of response model residual evaluation is treated and certain practical aspects of response surface modeling are considered, including inference subspace truncation. A wind tunnel test plan developed by using the Modern Design of Experiments illustrates the advantages of an early estimate of data volume requirements. Comparisons are made with a representative One Factor At a Time (OFAT) wind tunnel test matrix developed to evaluate a surface to air missile.

  13. A Two-Dimensional Electron Gas as a Sensitive Detector for Time-Resolved Tunneling Measurements on Self-Assembled Quantum Dots

    Reuter Dirk

    2010-01-01

    Full Text Available Abstract A two-dimensional electron gas (2DEG situated nearby a single layer of self-assembled quantum dots (QDs in an inverted high electron mobility transistor (HEMT structure is used as a detector for time-resolved tunneling measurements. We demonstrate a strong influence of charged QDs on the conductance of the 2DEG which allows us to probe the tunneling dynamics between the 2DEG and the QDs time resolved. Measurements of hysteresis curves with different sweep times and real-time conductance measurements in combination with an boxcar-like evaluation method enables us to unambiguously identify the transients as tunneling events between the s- and p-electron QD states and the 2DEG and rule out defect-related transients.

  14. Internal electron emission detected in metal-insulator-metal thin film tunnel devices bombarded with keV cluster projectiles

    The electronic excitation of a solid surface bombarded by energetic ions manifests in the production of hot electrons, which can be either emitted from the surface (''kinetic electron emission'') or remain within the solid. We use Metal-Insulator-Metal (MIM) tunneling junctions to detect and investigate hot charge carriers (electrons and holes) produced during bombardment of a metal surface with keV rare gas (Ar+) ions. The sample consists of a top metal film of about 20 nm thickness (the actual bombarded target surface), an underlying thin (2-3 nm) oxide film deposited and another metal electrode underneath. With such a device, excitations below the vacuum level can be detected as an internal electron emission current between the two metal electrodes. By combining the information obtained from external and internal emission, it is possible to gain information regarding the depth distribution of the generated excitation as well as the transport mechanism distributing the excitation away from its initial point of generation. We demonstrate this by varying the impact angle of the projectile ion beam. It is found that external and internal emission currents vary exactly in opposite direction when going from normal to oblique incidence.

  15. eFG: an electronic resource for Fusarium graminearum.

    Liu, Xiaoping; Zhang, Xiaodong; Tang, Wei-Hua; Chen, Luonan; Zhao, Xing-Ming

    2013-01-01

    Fusarium graminearum is a plant pathogen, which causes crop diseases and further leads to huge economic damage worldwide in past decades. Recently, the accumulation of different types of molecular data provides insights into the pathogenic mechanism of F. graminearum, and might help develop efficient strategies to combat this destructive fungus. Unfortunately, most available molecular data related to F. graminearum are distributed in various media, where each single source only provides limited information on the complex biological systems of the fungus. In this work, we present a comprehensive database, namely eFG (Electronic resource for Fusarium graminearum), to the community for further understanding this destructive pathogen. In particular, a large amount of functional genomics data generated by our group is deposited in eFG, including protein subcellular localizations, protein-protein interactions and orthologous genes in other model organisms. This valuable knowledge can not only help to disclose the molecular underpinnings of pathogenesis of the destructive fungus F. graminearum but also help the community to develop efficient strategies to combat this pathogen. To our best knowledge, eFG is the most comprehensive functional genomics database for F. graminearum until now. The eFG database is freely accessible at http://csb.shu.edu.cn/efg/ with a user-friendly and interactive interface, and all data can be downloaded freely. DATABASE URL: http://csb.shu.edu.cn/efg/ PMID:23798489

  16. Electronic Safety Resource Tools -- Supporting Hydrogen and Fuel Cell Commercialization

    Barilo, Nick F.

    2014-09-29

    The Pacific Northwest National Laboratory (PNNL) Hydrogen Safety Program conducted a planning session in Los Angeles, CA on April 1, 2014 to consider what electronic safety tools would benefit the next phase of hydrogen and fuel cell commercialization. A diverse, 20-person team led by an experienced facilitator considered the question as it applied to the eight most relevant user groups. The results and subsequent evaluation activities revealed several possible resource tools that could greatly benefit users. The tool identified as having the greatest potential for impact is a hydrogen safety portal, which can be the central location for integrating and disseminating safety information (including most of the tools identified in this report). Such a tool can provide credible and reliable information from a trustworthy source. Other impactful tools identified include a codes and standards wizard to guide users through a series of questions relating to application and specific features of the requirements; a scenario-based virtual reality training for first responders; peer networking tools to bring users from focused groups together to discuss and collaborate on hydrogen safety issues; and a focused tool for training inspectors. Table ES.1 provides results of the planning session, including proposed new tools and changes to existing tools.

  17. Controlling user access to electronic resources without password

    Smith, Fred Hewitt

    2015-06-16

    Described herein are devices and techniques for remotely controlling user access to a restricted computer resource. The process includes pre-determining an association of the restricted computer resource and computer-resource-proximal environmental information. Indicia of user-proximal environmental information are received from a user requesting access to the restricted computer resource. Received indicia of user-proximal environmental information are compared to associated computer-resource-proximal environmental information. User access to the restricted computer resource is selectively granted responsive to a favorable comparison in which the user-proximal environmental information is sufficiently similar to the computer-resource proximal environmental information. In at least some embodiments, the process further includes comparing user-supplied biometric measure and comparing it with a predetermined association of at least one biometric measure of an authorized user. Access to the restricted computer resource is granted in response to a favorable comparison.

  18. Electron immigration from shallow traps to deep traps by tunnel mechanism on Seydisehir aluminas

    In this study, the fading mechanism of Seydisehir alumina in Turkey, which is considered to be used for radiation dosimetric purposes, was investigated. The materials were first exposed to beta radiation and then stored in dark and dry ambient conditions at room temperature (RT) at previously desired storage periods. It was observed that the glow curve of Seydisehir alumina consists of four glow peaks between RT and 400 deg. C. The glow peaks (peaks 1, 2 and 3) between room temperature and 250 deg. C possessed very high levels of anomalous fading. However, the intensity of new glow peak at around 378 deg. C is highly increased with time. As a result of the experimental studies, it was concluded that the reason behind anomalous fading can be explained by means of tunneling (quantum tunneling) mechanism. - Highlights: → Fading mechanism of Turkish Seydisehir alumina was investigated. → Materials were exposed to beta radiation and stored under special conditions. → Glow curve was obtained and changes have been observed.

  19. Negative refractive index electron `optics', pseudospintronics and chiral tunneling in graphene pn junction -- beating the Landauer switching limit?

    Sajjad, Redwan; Pan, Chenyun; Naeemi, Azad; Ghosh, Avik

    2013-03-01

    We use atomistic quantum kinetic calculations to demonstrate how graphene PN junctions can switch with high ON currents, low OFF currents, steep gate transfer characteristics and unipolar rectification. The physics of such unconventional switching relies on (a) field-engineering with patterned gates to create a transmission gap, by sequential filtering of all propagating modes, and (b) using tilted junctions to suppress Klein tunneling under appropriate gate biasing, making that transmission gap gate tunable. The doping ratio of the junction dictates the energy range over which the tilt angle exceeds the critical angle for transmission, generating thereby a gate tunable transmission gap that enables switching at voltages less than the Landauer-Shannon thermal limit. The underlying physics involves a combination of `electron optics' driven by Snell's law, negative index metamaterial with a PN junction, and pseudospin driven chiral tunneling, for which we also present experimental verification. [Sajjad et al, APL 99, 123101 (2011); Sajjad et al, PRB 86, 155412 (2012)]. Authors acknowledge financial grant from NRI-INDEX

  20. Electronic and Magnetic Properties of Surface-Supported Hydrocarbon Radicals Studied by Low-Temperature Scanning Tunneling Microscopy

    Full text: The competition between screening of local spins and magnetic interactions of neighbouring spins determines many of the electronic and magnetic properties of dilute magnetic systems. We report on low-temperature scanning tunneling microscopy (STM) and spectroscopy (STS) experiments performed on linear chains of surface-supported hydrocarbon spin-1/2 radicals. The spin chains are prepared by self-assembly of the stable sp magnetic radicals a,g-bisdiphenylene-b-phenylallyl (BDPA) on a single-crystal metal surface under ultrahigh vacuum conditions. Below about 50 K the chains exhibit many of the characteristic properties of the Kondo effect observed by STM-based electron transport experiments at the atomic scale. We find strong evidence for a parallel alignment of neighbouring spins within the chains mediated by the electron gas of the supporting metal substrate. Spectroscopic imaging of radical chains reveals extended two-dimensional Kondo patterns. They span several nm2 across the substrate area even into regions of the pristine Au substrate, indicating the involvement of surface-state electrons from the substrate. The single adsorbed radicals exhibit a handedness as revealed by topographic STM imaging at the single-molecule level, which leads to an enantio-selective chain growth and the formation of structurally different domains of neighboring radical chains. (author)

  1. Single-Nanoparticle Collision Events: Tunneling Electron Transfer on a Titanium Dioxide Passivated n-Silicon Electrode.

    Ahn, Hyun S; Bard, Allen J

    2015-11-01

    Single-nanoparticle collisions were observed on an n-type silicon electrode (600??m diameter) passivated by a thin layer of amorphous TiO2, where the current steps occurred by tunneling electron transfer. The observed collision frequency was in reasonable agreement with that predicted from theory. The isolated electrode, after a collision experiment, with a Pt/TiO2/n-Si architecture was shown to retain the photoelectrochemical properties of n-Si without photocorrosion or current decay. The Pt/TiO2/n-Si electrode produced 19?mA?cm(-2) of photocurrent density under 100?mW?cm(-2) irradiation from a xenon lamp during oxygen evolution without current fading for over 12?h. PMID:26377039

  2. Preliminary Performance Data on Westinghouse Electronic Power Regulator Operating on J34-WE-32 Turbojet Engine in Altitude Wind Tunnel

    Ketchum, James R.; Blivas, Darnold; Pack, George J.

    1950-01-01

    The behavior of the Westinghouse electronic power regulator operating on a J34-WE-32 turbojet engine was investigated in the NACA Lewis altitude wind tunnel at the request of the Bureau of Aeronautics, Department of the Navy. The object of the program was to determine the, steady-state stability and transient characteristics of the engine under control at various altitudes and ram pressure ratios, without afterburning. Recordings of the response of the following parameters to step changes in power lever position throughout the available operating range of the engine were obtained; ram pressure ratio, compressor-discharge pressure, exhaust-nozzle area, engine speed, turbine-outlet temperature, fuel-valve position, jet thrust, air flow, turbine-discharge pressure, fuel flow, throttle position, and boost-pump pressure. Representative preliminary data showing the actual time response of these variables are presented. These data are presented in the form of reproductions of oscillographic traces.

  3. Determination of carbide structures on an Mo(110) surface by scanning tunneling microscopy and low energy electron diffraction

    Yu, De-Wei; Wu, Yi-Hsueh; Lin, Rong-Bin; Lo, Rong-Li

    2008-04-01

    Surface properties of transition metals can be modified considerably by forming carbide overlayers. In this study we fabricated molybdenum carbide overlayers by carburizing the Mo(110) surface with ethylene (C2H4) and successfully determined their real space structures by using low energy electron diffraction (LEED) and scanning tunneling microscopy (STM). With various carburization recipes, three carbon-terminated structures {\\scriptsize \\bigl (\\matrix {5 & 0 \\cr {-2} & 6 }\\bigr)} , (12 4)-2C, and (4 4) of coverages 1/30,1/24, and 1/16 monolayer (ML) were formed on the surface, respectively. Since the carbide overlayers were formed at high temperatures, inward diffusion of carbon atoms played a key role in structure formation.

  4. Determination of carbide structures on an Mo(110) surface by scanning tunneling microscopy and low energy electron diffraction

    Surface properties of transition metals can be modified considerably by forming carbide overlayers. In this study we fabricated molybdenum carbide overlayers by carburizing the Mo(110) surface with ethylene (C2H4) and successfully determined their real space structures by using low energy electron diffraction (LEED) and scanning tunneling microscopy (STM). With various carburization recipes, three carbon-terminated structures ((5)/-2/(0)/6), (12 x 4)-2C, and (4 x 4) of coverages 1/30,1/24, and 1/16 monolayer (ML) were formed on the surface, respectively. Since the carbide overlayers were formed at high temperatures, inward diffusion of carbon atoms played a key role in structure formation

  5. Investigation of Gd3N@C2n (40 < n < 44) family by Raman and inelastic electron tunneling spectroscopy

    Burke, Brian G; Williams, Keith A; Ge, Jiechao; Shu, Chunying; Fu, Wujun; Dorn, Harry C; Kushmerick, James G; Puretzky, Alexander A; Geohegan, David B

    2009-01-01

    The structure and vibrational spectrum of Gd3N@C80 is studied through Raman and inelastic electron tunneling spectroscopy (IETS) as well as density functional theory (DFT) and universal force field (UFF) calculations. Hindered rotations, shown by both theory and experiment, indicate the formation of a Gd3N-C80 bond which reduces the ideal icosahedral symmetry of the C80 cage. The vibrational modes involving the movement of the encapsulated species are a fingerprint of the interaction between the fullerene cage and the core complex. We present Raman data for the Gd3N@C2n (40 < n < 44) family as well as Y3N@C80, Lu3N@C80, and Y3N@C88 for comparison. Conductance measurements have been performed on Gd3N@C80 and reveal a Kondo effect similar to that observed in C60.

  6. What Do Libraries Really Do with Electronic Resources? The Practice in 2003

    Shorten, Jay

    2005-01-01

    One hundred fourteen academic libraries in the United States and Canada are surveyed for the organization of electronic resources within their home page and their cataloguing practice. The majority provide access to databases, electronic resources, subject guides, ready reference, and their own catalogue both on their home page and within their

  7. Developing Humanities Collections in the Digital Age: Exploring Humanities Faculty Engagement with Electronic and Print Resources

    Kachaluba, Sarah Buck; Brady, Jessica Evans; Critten, Jessica

    2014-01-01

    This article is based on quantitative and qualitative research examining humanities scholars' understandings of the advantages and disadvantages of print versus electronic information resources. It explores how humanities' faculty members at Florida State University (FSU) use print and electronic resources, as well as how they perceive these…

  8. Electronic resource management practical perspectives in a new technical services model

    Elguindi, Anne

    2012-01-01

    A significant shift is taking place in libraries, with the purchase of e-resources accounting for the bulk of materials spending. Electronic Resource Management makes the case that technical services workflows need to make a corresponding shift toward e-centric models and highlights the increasing variety of e-formats that are forcing new developments in the field.Six chapters cover key topics, including: technical services models, both past and emerging; staffing and workflow in electronic resource management; implementation and transformation of electronic resource management systems; the ro

  9. The Relevancy of Graduate Curriculum to Human Resource Professionals' Electronic Communication.

    Hoell, Robert C.; Henry, Gordon O.

    2003-01-01

    Electronic communications of human resource professionals and the content of 23 university human resource management courses were categorized using the Human Resource Certification Institute's body of knowledge. Differences between proportion of topics discussed and topics covered in curricula suggest some topics are over- or undertaught.…

  10. Strategic Planning for Electronic Resources Management: A Case Study at Gustavus Adolphus College

    Hulseberg, Anna; Monson, Sarah

    2009-01-01

    Electronic resources, the tools we use to manage them, and the needs and expectations of our users are constantly evolving; at the same time, the roles, responsibilities, and workflow of the library staff who manage e-resources are also in flux. Recognizing a need to be more intentional and proactive about how we manage e-resources, the…

  11. Experimental demonstration of single electron transistors featuring SiO2 plasma-enhanced atomic layer deposition in Ni-SiO2-Ni tunnel junctions

    The authors report the use of plasma-enhanced atomic layer deposition (PEALD) to fabricate single-electron transistors (SETs) featuring ultrathin (≈1 nm) tunnel-transparent SiO2 in Ni-SiO2-Ni tunnel junctions. They show that, as a result of the O2 plasma steps in PEALD of SiO2, the top surface of the underlying Ni electrode is oxidized. Additionally, the bottom surface of the upper Ni layer is also oxidized where it is in contact with the deposited SiO2, most likely as a result of oxygen-containing species on the surface of the SiO2. Due to the presence of these surface parasitic layers of NiO, which exhibit features typical of thermally activated transport, the resistance of Ni-SiO2-Ni tunnel junctions is drastically increased. Moreover, the transport mechanism is changed from quantum tunneling through the dielectric barrier to one consistent with thermally activated resistors in series with tunnel junctions. The reduction of NiO to Ni is therefore required to restore the metal-insulator-metal (MIM) structure of the junctions. Rapid thermal annealing in a forming gas ambient at elevated temperatures is presented as a technique to reduce both parasitic oxide layers. This method is of great interest for devices that rely on MIM tunnel junctions with ultrathin barriers. Using this technique, the authors successfully fabricated MIM SETs with minimal trace of parasitic NiO component. They demonstrate that the properties of the tunnel barrier in nanoscale tunnel junctions (with <10−15 m2 in area) can be evaluated by electrical characterization of SETs

  12. Controlled assembly and single electron charging of monolayer protected Au144 clusters: an electrochemistry and scanning tunneling spectroscopy study

    Bodappa, Nataraju; Fluch, Ulrike; Fu, Yongchun; Mayor, Marcel; Moreno-Garca, Pavel; Siegenthaler, Hans; Wandlowski, Thomas

    2014-11-01

    Single gold particles may serve as room temperature single electron memory units because of their size dependent electronic level spacing. Here, we present a proof-of-concept study by electrochemically controlled scanning probe experiments performed on tailor-made Au particles of narrow dispersity. In particular, the charge transport characteristics through chemically synthesized hexane-1-thiol and 4-pyridylbenzene-1-thiol mixed monolayer protected Au144 clusters (MPCs) by differential pulse voltammetry (DPV) and electrochemical scanning tunneling spectroscopy (EC-STS) are reported. The pyridyl groups exposed by the Au-MPCs enable their immobilization on Pt(111) substrates. By varying the humidity during their deposition, samples coated by stacks of compact monolayers of Au-MPCs or decorated with individual, laterally separated Au-MPCs are obtained. DPV experiments with stacked monolayers of Au144-MPCs and EC-STS experiments with laterally separated individual Au144-MPCs are performed both in aqueous and ionic liquid electrolytes. Lower capacitance values were observed for individual clusters compared to ensemble clusters. This trend remains the same irrespective of the composition of the electrolyte surrounding the Au144-MPC. However, the resolution of the energy level spacing of the single clusters is strongly affected by the proximity of neighboring particles.Single gold particles may serve as room temperature single electron memory units because of their size dependent electronic level spacing. Here, we present a proof-of-concept study by electrochemically controlled scanning probe experiments performed on tailor-made Au particles of narrow dispersity. In particular, the charge transport characteristics through chemically synthesized hexane-1-thiol and 4-pyridylbenzene-1-thiol mixed monolayer protected Au144 clusters (MPCs) by differential pulse voltammetry (DPV) and electrochemical scanning tunneling spectroscopy (EC-STS) are reported. The pyridyl groups exposed by the Au-MPCs enable their immobilization on Pt(111) substrates. By varying the humidity during their deposition, samples coated by stacks of compact monolayers of Au-MPCs or decorated with individual, laterally separated Au-MPCs are obtained. DPV experiments with stacked monolayers of Au144-MPCs and EC-STS experiments with laterally separated individual Au144-MPCs are performed both in aqueous and ionic liquid electrolytes. Lower capacitance values were observed for individual clusters compared to ensemble clusters. This trend remains the same irrespective of the composition of the electrolyte surrounding the Au144-MPC. However, the resolution of the energy level spacing of the single clusters is strongly affected by the proximity of neighboring particles. Electronic supplementary information (ESI) available. See DOI: 10.1039/c4nr03793f

  13. Resistivity of thin gold films on mica induced by electron-surface scattering: Application of quantitative scanning tunneling microscopy

    Robles, Marcelo E. [Departamento de Ciencias de la Construccion, FCCyOT, Universidad Tecnologica Metropolitana, Dieciocho 390, Santiago 8330526 (Chile); Gonzalez-Fuentes, Claudio A.; Henriquez, Ricardo [Departamento de Fisica, Facultad de Ciencias Fisicas y Matematicas, Universidad de Chile, Blanco Encalada 2008, Casilla 487-3, Santiago 8370449 (Chile); Kremer, German [Departamento de Fisica, Facultad de Ciencias, Universidad de Chile, Las Palmeras 3425, Santiago 7800024 (Chile); Moraga, Luis; Oyarzun, Simon; Suarez, Marco Antonio; Flores, Marcos [Departamento de Fisica, Facultad de Ciencias Fisicas y Matematicas, Universidad de Chile, Blanco Encalada 2008, Casilla 487-3, Santiago 8370449 (Chile); Munoz, Raul C., E-mail: ramunoz@ing.uchile.cl [Departamento de Fisica, Facultad de Ciencias Fisicas y Matematicas, Universidad de Chile, Blanco Encalada 2008, Casilla 487-3, Santiago 8370449 (Chile)

    2012-02-01

    We report a comparison between the resistivity measured on thin gold films deposited on mica, with predictions based upon classical theories of size effects (Drude's, Sondheimer's and Calecki's), as well as predictions based upon quantum theories of electron-surface scattering (the modified theory of Sheng, Xing and Wang, the theory of Tesanovic, Jaric and Maekawa, and that of Trivedi and Aschroft). From topographic images of the surface recorded with a Scanning Tunneling Microscope, we determined the rms roughness amplitude, {delta} and the lateral correlation length, {xi} corresponding to a Gaussian representation of the average height-height autocorrelation function, describing the roughness of each sample in the scale of length set by the Fermi wave length. Using ({delta}, {xi}) as input data, we present a rigorous comparison between resistivity data and predictions based upon the theory of Calecki as well as quantum theoretical predictions without adjustable parameters. The resistivity was measured on gold films of different thickness evaporated onto mica substrates, between 4 K and 300 K. The resistivity data covers the range 0.1 < x(T) < 6.8, for 4 K < T < 300 K, where x(T) is the ratio between film thickness and electron mean free path in the bulk at temperature T. We experimentally identify electron-surface and electron-phonon scattering as the microscopic electron scattering mechanisms giving rise to the macroscopic resistivity. The different theories are all capable of estimating the thin film resistivity to an accuracy better than 10%; however the mean free path and the resistivity characterizing the bulk turn out to depend on film thickness. Surprisingly, only the Sondheimer theory and its quantum version, the modified theory of Sheng, Xing and Wang, predict and increase in resistivity induced by size effects that seems consistent with published galvanomagnetic phenomena also arising from electron-surface scattering measured at low temperatures.

  14. Resistivity of thin gold films on mica induced by electron-surface scattering: Application of quantitative scanning tunneling microscopy

    We report a comparison between the resistivity measured on thin gold films deposited on mica, with predictions based upon classical theories of size effects (Drude's, Sondheimer's and Calecki's), as well as predictions based upon quantum theories of electron-surface scattering (the modified theory of Sheng, Xing and Wang, the theory of Tesanovic, Jaric and Maekawa, and that of Trivedi and Aschroft). From topographic images of the surface recorded with a Scanning Tunneling Microscope, we determined the rms roughness amplitude, δ and the lateral correlation length, ξ corresponding to a Gaussian representation of the average height-height autocorrelation function, describing the roughness of each sample in the scale of length set by the Fermi wave length. Using (δ, ξ) as input data, we present a rigorous comparison between resistivity data and predictions based upon the theory of Calecki as well as quantum theoretical predictions without adjustable parameters. The resistivity was measured on gold films of different thickness evaporated onto mica substrates, between 4 K and 300 K. The resistivity data covers the range 0.1 < x(T) < 6.8, for 4 K < T < 300 K, where x(T) is the ratio between film thickness and electron mean free path in the bulk at temperature T. We experimentally identify electron-surface and electron-phonon scattering as the microscopic electron scattering mechanisms giving rise to the macroscopic resistivity. The different theories are all capable of estimating the thin film resistivity to an accuracy better than 10%; however the mean free path and the resistivity characterizing the bulk turn out to depend on film thickness. Surprisingly, only the Sondheimer theory and its quantum version, the modified theory of Sheng, Xing and Wang, predict and increase in resistivity induced by size effects that seems consistent with published galvanomagnetic phenomena also arising from electron-surface scattering measured at low temperatures.

  15. Cataloguing the Chameleon: A Guide to Electronic Resources

    Cox, Joseph P.; Dekker, Jennifer

    1999-01-01

    This manual was created to bridge the gap in guidelines for describing internet resources during the long period when AACR2 was updating its rules for cataloguing. Librarians needed interim procedures and Cataloguing the Chameleon was a set of guidelines recommended by the Cataloguing Internet Resources Project based at the University of Toronto's Faculty of Information Studies.

  16. Interaction-dependent photon-assisted tunneling in optical lattices: a quantum simulator of strongly-correlated electrons and dynamical Gauge fields

    Bermudez, Alejandro; Porras, Diego

    2015-10-01

    We introduce a scheme that combines photon-assisted tunneling (PAT) by a moving optical lattice with strong Hubbard interactions, and allows for the quantum simulation of paradigmatic quantum many-body models. We show that, in a certain regime, this quantum simulator yields an effective Hubbard Hamiltonian with tunable bond-charge interactions, a model studied in the context of strongly-correlated electrons. In a different regime, we show how to exploit a correlated destruction of tunneling to explore Nagaoka ferromagnetism at finite Hubbard repulsion. By changing the photon-assisted tunneling parameters, we can also obtain a t-J model with independently controllable tunneling t, super-exchange interaction J, and even a Heisenberg-Ising anisotropy. Hence, the full phase diagram of this paradigmatic model becomes accessible to cold-atom experiments, departing from the region t\\gg J allowed by standard single-band Hubbard Hamiltonians in the strong-repulsion limit. We finally show that, by generalizing the PAT scheme, the quantum simulator yields models of dynamical Gauge fields, where atoms of a given electronic state dress the tunneling of the atoms with a different internal state, leading to Peierls phases that mimic a dynamical magnetic field.

  17. "Not" a One-Size-Fits-All Solution: Lessons Learned from Implementing an Electronic Resources Management System in Three Days

    Pan, Denise

    2009-01-01

    Auraria Library purchased Innovative Interfaces, Inc.'s Millennium Electronic Resources Management (ERM) to manage data about acquisitions, licensing, troubleshooting, and usage statistics of electronic resources. After 3 days of implementation, the software vendor enabled resources records to display. As a result, the electronic resources team…

  18. Assessment of pseudo-bilayer structures in the heterogate germanium electron-hole bilayer tunnel field-effect transistor

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

    2015-06-29

    We investigate the effect of pseudo-bilayer configurations at low operating voltages (≤0.5 V) in the heterogate germanium electron-hole bilayer tunnel field-effect transistor (HG-EHBTFET) compared to the traditional bilayer structures of EHBTFETs arising from semiclassical simulations where the inversion layers for electrons and holes featured very symmetric profiles with similar concentration levels at the ON-state. Pseudo-bilayer layouts are attained by inducing a certain asymmetry between the top and the bottom gates so that even though the hole inversion layer is formed at the bottom of the channel, the top gate voltage remains below the required value to trigger the formation of the inversion layer for electrons. Resulting benefits from this setup are improved electrostatic control on the channel, enhanced gate-to-gate efficiency, and higher I{sub ON} levels. Furthermore, pseudo-bilayer configurations alleviate the difficulties derived from confining very high opposite carrier concentrations in very thin structures.

  19. Assessment of pseudo-bilayer structures in the heterogate germanium electron-hole bilayer tunnel field-effect transistor

    We investigate the effect of pseudo-bilayer configurations at low operating voltages (≤0.5 V) in the heterogate germanium electron-hole bilayer tunnel field-effect transistor (HG-EHBTFET) compared to the traditional bilayer structures of EHBTFETs arising from semiclassical simulations where the inversion layers for electrons and holes featured very symmetric profiles with similar concentration levels at the ON-state. Pseudo-bilayer layouts are attained by inducing a certain asymmetry between the top and the bottom gates so that even though the hole inversion layer is formed at the bottom of the channel, the top gate voltage remains below the required value to trigger the formation of the inversion layer for electrons. Resulting benefits from this setup are improved electrostatic control on the channel, enhanced gate-to-gate efficiency, and higher ION levels. Furthermore, pseudo-bilayer configurations alleviate the difficulties derived from confining very high opposite carrier concentrations in very thin structures

  20. Long-range protein electron transfer observed at the single-molecule level: In situ mapping of redox-gated tunneling resonance

    Chi, Qijin; Farver, O; Ulstrup, Jens

    2005-01-01

    A biomimetic long-range electron transfer (ET) system consisting of the blue copper protein azurin, a tunneling barrier bridge, and a gold single-crystal electrode was designed on the basis of molecular wiring self-assembly principles. This system is sufficiently stable and sensitive in a quasi...

  1. Electron tunneling studies of spin-flip scattering with native and artificial rare-earth barriers

    Both artificial and native rare earth (RE) tunnel barriers have been successfully fabricated. Artificial barriers are of the form M-REOx-M (M = Al, Pb, PbBi; RE = Ho, Dy, Gd, Lu), and native barriers are of the form RE-REOx-s (S = Pb, PbBi; RE = Dy, Ho). Artificial barriers are formed by oxidizing a thin (5-20 angstrom) film of evaporated RE. Current-Voltage characteristics (I-V) produced by Al-REOx-Al junctions shown substantial gap depression and gap smearing for magnetic rare earths (Ho, Dy, Gd). Using the Abrikosov-Gorkov (AG) theory of spin-flip scattering, we have successfully fit gap-depressed I-V's. Since the actual experimental temperature (T = 0.93 degree K) corresponds to a high reduced temperature (T/Tc) for Al, the AG predicted temperature dependence of the pair potential was necessary to obtain good fits. Our tunneling experiments utilize a variety of fabrication geometries. Our results do not support the view that contact between Al and the REOx barrier is responsible for gap depression. Instead, they indicate that gap depression is caused by inter-diffusion of Al and RE at the metal-metal interface. Native Dy barriers have been fabricated in-situ using a wet-oxygen ambient. The presence of water was found to be crucial for the formation of low leakage (0.6%) barriers. PbBi counter-electrodes show no sign-of-gap depression, despite clean contact with the DyOx barriers. Barrier characteristics for native RE barriers are quite different from those of artificial RE barriers. Native RE dV/dI's are quite symmetric corresponding to rectangular (flat) WKB barriers. The average height and width are 1.02 eV and 27.8 A, respectively. IETS has been performed for both HoOx and DyOx barriers. We report new quantitative results for barrier phonons in both HoOx and DyOx

  2. Tunneling and migration of the dumbbell defect in electron irradiated aluminum-zinc alloys

    Ultrasonic attenuation and velocity measurements have been made on irradiated Al-Zn alloys (Zn concentrations of .01%, .1%, and .5% atomic). They provide strong evidence for a tunneling relaxation of the predominant mixed dumbbell defect at low temperatures and for mixed dumbbell migration at the Stage II anneal temperature. The effect of an internal strain varying with the zinc concentration of the measured decrement and modulus change is striking. Evaluated in the framework of a six level system, this reveals the simultaneous action of resonance and non-classical relaxation processes. Using Fe as a probe atom, it is shown that mixed dumbbell dissociation is in an insignificant component of the annealing of this defect. The decrease of the annealing temperature at higher zinc concentrations provides evidence that the mixed dumbbell migrates as a unit during annealing. The energies associated with dumbbell migration and interstitial escape are derived. Further evidence for the migration mechanism is obtained from successive irradiation and annealing measurements on the Al-Zn .01% alloy, and from a comparison of these results with published radiation damage rate measurements of dilute Al-Zn alloys

  3. Electronic transport through EuO spin-filter tunnel junctions

    Jutong, Nuttachai

    2012-11-12

    Epitaxial spin-filter tunnel junctions based on the ferromagnetic semiconductor europium monoxide (EuO) are investigated by means of density functional theory. In particular, we focus on the spin transport properties of Cu(100)/EuO(100)/Cu(100) junctions. The dependence of the transmission coefficient and the current-voltage curves on the interface spacing and EuO thickness is explained in terms of the EuO density of states and the complex band structure. Furthermore, we also discuss the relation between the spin transport properties and the Cu-EuO interface geometry. The level alignment of the junction is sensitively affected by the interface spacing, since this determines the charge transfer between EuO and the Cu electrodes. Our calculations indicate that EuO epitaxially grown on Cu can act as a perfect spin filter, with a spin polarization of the current close to 100%, and with both the Eu-5d conduction-band and the Eu-4f valence-band states contributing to the coherent transport. For epitaxial EuO on Cu, a symmetry filtering is observed, with the Δ1 states dominating the transmission. This leads to a transport gap larger than the fundamental EuO band gap. Importantly, the high spin polarization of the current is preserved up to large bias voltages.

  4. Single-molecule electron tunnelling through multiple redox levels with environmental relaxation

    Kuznetsov, A.M.; Ulstrup, Jens

    We present an analytical theory for electron flow through a molecule with several redox levels, enclosed between a pair of metallic electrodes. The levels can be electronic or electronic-vibrational levels. Vibrational energy spacing characterises the latter sets. The levels are further coupled to...... can be only achieved when the latter are located between the Fermi levels of the substrate and tip or source and drain electrodes. The redox levels can be brought into this "energy window", either by the overpotential or bias and gate voltages, or by vibrational relaxation of (a) given (set of) redox...

  5. The effect of interface phonons on operating electron states in three-barrier resonant tunneling structure as an active region of quantum cascade detector

    M.V. Tkach; Ju.O.Seti; Grynyshyn, Y. B.; O.M. Voitsekhivska

    2014-01-01

    The Hamiltonian of electrons interacting with interface phonons in three-barrier resonant tunneling structure is established using the first principles within the models of effective mass and polarization continuum. Using the Green's functions method, the temperature shifts and decay rates of operating electron states are calculated depending on geometric design of three-barrier nano-structure GaAs/Al$_{x}$Ga$_{1-x}$As which is an active region of quantum cascade detector. It is established t...

  6. Electrical injection and detection of spin-polarized electrons in silicon through an Fe_3Si/Si Schottky tunnel barrier

    Ando, Y.; Hamaya, K.; Kasahara, K.; Kishi, Y; Ueda, K; Sawano, K.; Sadoh, T.; Miyao, M

    2009-01-01

    We demonstrate electrical injection and detection of spin-polarized electrons in silicon (Si) using epitaxially grown Fe_3Si/Si Schottky-tunnel-barrier contacts. By an insertion of a delta-doped n^+-Si layer (~ 10^19 cm^-3) near the interface between a ferromagnetic Fe_3Si/Si contact and a Si channel (~ 10^15 cm^-3), we achieve a marked enhancement in the tunnel conductance for reverse-bias characteristics of the Fe_3Si/Si Schottky diodes. Using laterally fabricated four-probe geometries with...

  7. Resonant tunneling of polarized electrons through nonmagnetic III-V semiconductor multiple barriers

    C. Moyss, Arajo; A. Ferreira da, Silva; E. A. de Andrada e, Silva.

    2002-06-01

    Full Text Available The quantum transport of spin-polarized electrons across nonmagnetic III-V semiconductor multiple barriers is considered theoretically. We have calculated the spin dependent transmission coeficient, for conducting electrons transversing lattice-matched In0. 53Ga0. 47As/GaAs0. 5Sb0: /In0. 53Ga0. 47As [...] / InP/In0. 53Ga0. 47As nanostructures with different numbers of asymmetric double barriers, as a function of electron energy and angle of incidence. Spin-orbit split resonances, due to the Rashba term, are observed. The envelope function approximation and the Kane k p model for the bulk are used. For an unpolarized incident beam of electrons, we also obtain the spin polarization of the transmitted beam. The formation of spin dependent minibands of energy with nonzero transmission is observed.

  8. Intra-cavity photon-assisted tunneling collector-base voltage-mediated electron-hole spontaneous-stimulated recombination transistor laser

    Feng, M.; Qiu, Junyi; Wang, C. Y.; Holonyak, N.

    2016-02-01

    Optical absorption in a p-n junction diode for a direct-gap semiconductor can be enhanced by photon-assisted tunneling in the presence of a static or dynamic electrical field. In the transistor laser, the coherent photons generated at the base quantum-well interact with the collector field and "assist" optical cavity electron tunneling from the valence band of the base to the conduction band states of the collector. In the present work, we study the cavity coherent photon intensity effect on intra-cavity photon-assisted tunneling (ICPAT) in the transistor laser and realize photon-field enhanced optical absorption. This ICPAT in a transistor laser is the unique property of voltage (field) modulation and the basis for ultrahigh speed direct laser modulation and switching.

  9. Identifying highly conducting Au–C links through inelastic electron tunneling spectroscopy

    Foti, G.; Vázquez, Héctor; Sanchez-Portal, D.; Arnau, A.; Frederiksen, T.

    2014-01-01

    Roč. 118, OCT (2014), s. 27106-27112. ISSN 1932-7447 Institutional support: RVO:68378271 Keywords : molecular electronics * alkanes * tin -functionalization * anchoring groups * vibrational spectroscopy Subject RIV: CF - Physical ; Theoretical Chemistry Impact factor: 4.772, year: 2014

  10. Collection Development of Electronic Information Resources in Turkish University Libraries

    Tonta, Yaşar

    2001-01-01

    The number of information sources available through both printed and electronic media are ever increasing. Even libraries with sizable collection development budgets are having difficulties in coping with this increase. Yet with the development of new technologies, the possibilities of innovative interlibrary cooperation projects emerge: libraries combining their efforts through various consortia are trying to get access to electronic information sources more economically. In this paper, we b...

  11. Electron tunneling between two electrodes mediated by a molecular wire containing a redox center

    Graphical abstract: We present a model for a molecular wire containing a redox center and suspended in an electrolyte solution. Current potential curves can contain plateaus and negative differential resistances. - Abstract: We derive an explicit expression for the quantum conductivity of a molecular wire containing a redox center, which is embedded in an electrochemical environment. The redox center interacts with the solvent, and the average over the solvent configurations is performed numerically. Explicit calculations have been performed for a chain of three atoms. When the redox center interacts strongly with neighboring electronic levels, the current-potential curves show interesting features like rectification, current plateaus and negative differential resistance. Electronic spectroscopy of intermediate states can be performed at constant small bias by varying the electrochemical potential of the wire.

  12. Is there light at the end of the two-electron tunnel?

    Since the earliest days of quantum mechanics, the theoretical description of the two-electron system has remained one of the most vexing problems in atomic physics. The last four years have witnessed serious theoretical and experimental challenges to the orthodox characterization of the discrete spectrum of doubly excited states and the process of double escape in the near-threshold continuum. Intense photon beams in the far-uv and x-ray regimes, now being produced at the newly commissioned Advanced Light Source at Lawrence Berkeley Laboratory, provide unprecedented opportunities for advancing our knowledge of the behavior of two-electron atomic systems. The status of the field and Chris Bottcher's poignant role in promoting new experimental ventures will be reviewed. copyright 1995 American Institute of Physics

  13. Strong overtones modes in inelastic electron tunneling spectroscopy with cross-conjugated molecules

    Jørgensen, Jacob Lykkebo; Gagliardi, Alessio; Pecchia, Alessandro; Solomon, Gemma C.

    2013-01-01

    Cross-conjugated molecules are known to exhibit destructive quantum interference, a property that has recently received considerable attention in single-molecule electronics. Destructive quantum interference can be understood as an antiresonance in the elastic transmission near the Fermi energy and...... leading to suppressed levels of elastic current. In most theoretical studies, only the elastic contributions to the current are taken into account. In this paper, we study the inelastic contributions to the current in cross-conjugated molecules and find that while the inelastic contribution to the current...... is larger than for molecules without interference, the overall behavior of the molecule is still dominated by the quantum interference feature. Second, an ongoing challenge for single molecule electronics is understanding and controlling the local geometry at the molecule-surface interface. With this...

  14. Low energy anomalies in electron tunneling through strongly asymmetric Majorana nanowire

    Shkop, A. D.; Parafilo, A. V.; Krive, I. V.; Shekhter, R.I.

    2016-01-01

    Electron transport through Majorana nanowire with strongly asymmetric couplings to normal metal leads is considered. In three terminal geometry (electrically grounded nanowire) it is shown that the presence of unbiased electrode restores zero-bias anomaly even for strong Majorana energy splitting. For effectively two-terminal geometry we show that electrical current through asymmetric Majorana junction is qualitatively different from the analogous current through a resonant (Breit-Wigner) level.

  15. Deep proton tunneling in the electronically adiabatic and non-adiabatic limits: Comparison of the quantum and classical treatment of donor-acceptor motion in a protein environment

    Benabbas, Abdelkrim; Salna, Bridget; Sage, J. Timothy; Champion, Paul M., E-mail: champ@neu.edu [Department of Physics and Center for Interdisciplinary Research on Complex Systems,Northeastern University, Boston, Massachusetts 02115 (United States)

    2015-03-21

    Analytical models describing the temperature dependence of the deep tunneling rate, useful for proton, hydrogen, or hydride transfer in proteins, are developed and compared. Electronically adiabatic and non-adiabatic expressions are presented where the donor-acceptor (D-A) motion is treated either as a quantized vibration or as a classical “gating” distribution. We stress the importance of fitting experimental data on an absolute scale in the electronically adiabatic limit, which normally applies to these reactions, and find that vibrationally enhanced deep tunneling takes place on sub-ns timescales at room temperature for typical H-bonding distances. As noted previously, a small room temperature kinetic isotope effect (KIE) does not eliminate deep tunneling as a major transport channel. The quantum approach focuses on the vibrational sub-space composed of the D-A and hydrogen atom motions, where hydrogen bonding and protein restoring forces quantize the D-A vibration. A Duschinsky rotation is mandated between the normal modes of the reactant and product states and the rotation angle depends on the tunneling particle mass. This tunnel-mass dependent rotation contributes substantially to the KIE and its temperature dependence. The effect of the Duschinsky rotation is solved exactly to find the rate in the electronically non-adiabatic limit and compared to the Born-Oppenheimer (B-O) approximation approach. The B-O approximation is employed to find the rate in the electronically adiabatic limit, where we explore both harmonic and quartic double-well potentials for the hydrogen atom bound states. Both the electronically adiabatic and non-adiabatic rates are found to diverge at high temperature unless the proton coupling includes the often neglected quadratic term in the D-A displacement from equilibrium. A new expression is presented for the electronically adiabatic tunnel rate in the classical limit for D-A motion that should be useful to experimentalists working near room temperature. This expression also holds when a broad protein conformational distribution of D-A equilibrium distances dominates the spread of the D-A vibrational wavefunction.

  16. Electronic Engineering Library In Sweden: A Quality Assessed Internet Resource from the Swedish Technological University Libraries

    Lager, Gunnar; Nordlander, Marianne

    2012-01-01

    A status report of the plans and issues under discussion in creating this cooperative electronic national resource to support engineering education in Sweden. An opportunity to preview what is currently under construction for the EELS.

  17. Utilization of bio-resources by low energy electron beam

    Utilization of bio-resources by radiation has been investigated for recycling the natural resources and reducing the environmental pollution. Polysaccharides such as chitosan and sodium alginate were easily degraded by irradiation and induced various kinds of biological activities, i.g. anti-microbial activity, promotion of plant growth, suppression of heavy metal stress, phytoalexins induction. Radiation degraded chitosan was effective to enhance the growth of plants in tissue culture. It was demonstrated that the liquid sample irradiation system using low energy EB was effective for the preparation of degraded polysaccharides. Methylcellulose (MC) can be crosslinked under certain radiation condition as same as carboxymethylcellulose (CMC) and produced the biodegradable hydrogel for medical and agricultural use. Treatment of soybean seeds by low energy EB enhanced the growth and the number of rhizobia on the root. (author)

  18. NRC Clients' Perceptions of Electronic Resources and Use of CISTI's Virtual Library.

    Belzile, Sylvie; Kneale, Jean; Young, Ian; Summers, Randy; Colbourne, David

    1999-01-01

    Discusses a study of use of the Web-based virtual library at CISTI (Canada Institute for Scientific and Technical Information) by NRC (National Research Council of Canada). Results indicate that NRC staff is favorably inclined toward electronic resources and that a positive correlation exists between use of digital resources and perception and

  19. An Evaluation of Electronic Product Design Education Using Hypermedia-Resourced Learning Environments

    Page, Tom; Thorsteinsson, Gisli

    2006-01-01

    The work outlined here provides a comprehensive report and formative observations of the development and implementation of hypermedia resources for learning and teaching used in conjunction with a managed learning environment (MLE). These resources are used to enhance teaching and learning of an electronics module in product design at final year

  20. Spin-flip induction of Fano resonance upon electron tunneling through atomic-scale spin structures

    The inclusion of inelastic spin-dependent electron scatterings by the potential profiles of a single magnetic impurity and a spin dimer is shown to induce resonance features due to the Fano effect in the transport characteristics of such atomic-scale spin structures. The spin-flip processes leading to a configuration interaction of the system’s states play a fundamental role for the realization of Fano resonance and antiresonance. It has been established that applying an external magnetic field and a gate electric field allows the conductive properties of spin structures to be changed radically through the Fano resonance mechanism.

  1. Electron beam pasteurised oil palm waste: a potential feed resource

    Pasteurization of oil palm empty fruit bunch (EFB) was performed using electron beam single sided irradiation. The dose profiles of oil palm EFB samples for different thickness in both directions X and Y were established. The results showed the usual characteristics dose uniformity as sample thickness decreased. The mean average absorbed dose on both sides at the surface and bottom of the samples for different thickness samples lead to establishing depth dose curve. Based on depth dose curve and operation conditions of electron beam machine, the process throughput for pasteurized oil palm EFB were estimated. (Author)

  2. Final Scientific/Technical Report: Electronics for Large Superconducting Tunnel Junction Detector Arrays for Synchrotron Soft X-ray Research

    Warburton, William K

    2009-03-06

    Superconducting tunnel junction (STJ) detectors offer a an approach to detecting soft x-rays with energy resolutions 4-5 times better and at rates 10 faster than traditions semiconductor detectors. To make such detectors feasible, however, then need to be deployed in large arrays of order 1000 detectors, which in turn implies that their processing electronics must be compact, fully computer controlled, and low cost per channel while still delivering ultra-low noise performance so as to not degrade the STJ's performance. We report on our progress in designing a compact, low cost preamplifier intended for this application. In particular, we were able to produce a prototype preamplifier of 2 sq-cm area and a parts cost of less than $30 that matched the energy resolution of the best conventional system to date and demonstrated its ability to acquire an STJ I-V curve under computer control, the critical step for determining and setting the detectors' operating points under software control.

  3. Field emission spectroscopy evidence for dual-barrier electron tunnelling in nanographite

    Bandurin, D. A.; Kleshch, V. I. [Department of Physics, M.V. Lomonosov Moscow State University, Moscow 119991 (Russian Federation); Mingels, S.; Ltzenkirchen-Hecht, D.; Mller, G. [FB C Physics Department, University of Wuppertal, 42119 Wuppertal (Germany); Obraztsov, A. N., E-mail: obraz@polly.phys.msu.ru [Department of Physics, M.V. Lomonosov Moscow State University, Moscow 119991 (Russian Federation); Department of Physics and Mathematics, University of Eastern Finland, Joensuu 80101 (Finland)

    2015-06-08

    Nanocarbon films with upstanding flake-like graphite crystallites of nanometre thickness were fabricated by carbon condensation from a methanehydrogen gas mixture activated by a direct-current discharge. The nanographite (NG) crystallites are composed of a few graphene layers. The adjacent atomic layers are connected partially at the edges of the crystallites to form strongly curved graphene structures. The extraordinary field emission (FE) properties were revealed for the NG films with an average current density of a few mA/cm{sup 2}, reproducibly obtained at a macroscopic applied field of about 1?V/?m. The integral FE currentvoltage curves and electron spectra (FEES) of NG cathodes with multiple emitters were measured in a triode configuration. Most remarkably, above a threshold field, two peaks were revealed in FEES with different field-dependent shifts to lower energies. This behaviour evidences electron emission through a dual potential barrier, corresponding to carboncarbon heterostructure formed as a result of the graphene bending.

  4. Current gain in sub-10 nm base GaN tunneling hot electron transistors with AlN emitter barrier

    Yang, Zhichao, E-mail: zcyang.phys@gmail.com; Zhang, Yuewei; Nath, Digbijoy N.; Rajan, Siddharth [Department of Electrical and Computer Engineering, The Ohio State University, Columbus, Ohio 43210 (United States); Khurgin, Jacob B. [Department of Electrical and Computer Engineering, The Johns Hopkins University, Baltimore, Maryland 21218 (United States)

    2015-01-19

    We report on Gallium Nitride-based tunneling hot electron transistor amplifier with common-emitter current gain greater than 1. Small signal current gain up to 5 and dc current gain of 1.3 were attained in common-emitter configuration with collector current density in excess of 50 kA/cm{sup 2}. The use of a combination of 1 nm GaN/3 nm AlN layers as an emitter tunneling barrier was found to improve the energy collimation of the injected electrons. These results represent demonstration of unipolar vertical transistors in the III-nitride system that can potentially lead to higher frequency and power microwave devices.

  5. Numerical modelling of emission of a two-level atom near a metal nanoparticle with account for tunnelling of an electron from an atom into a particle

    Fedorovich, S. V.; Protsenko, I. E.

    2016-01-01

    We report the results of numerical modelling of emission of a two-level atom near a metal nanoparticle under resonant interaction of light with plasmon modes of the particle. Calculations have been performed for different polarisations of light by a dipole approximation method and a complex multipole method. Depending on the distance between a particle and an atom, the contribution of the nonradiative process of electron tunnelling from a two-level atom into a particle, which is calculated using the quasi-classical approximation, has been taken into account and assessed. We have studied spherical gold and silver particles of different diameters (10 100 nm). The rates of electron tunnelling and of spontaneous decay of the excited atomic state are found. The results can be used to develop nanoscale plasmonic emitters, lasers and photodetectors.

  6. Current gain in sub-10 nm base GaN tunneling hot electron transistors with AlN emitter barrier

    We report on Gallium Nitride-based tunneling hot electron transistor amplifier with common-emitter current gain greater than 1. Small signal current gain up to 5 and dc current gain of 1.3 were attained in common-emitter configuration with collector current density in excess of 50 kA/cm2. The use of a combination of 1 nm GaN/3 nm AlN layers as an emitter tunneling barrier was found to improve the energy collimation of the injected electrons. These results represent demonstration of unipolar vertical transistors in the III-nitride system that can potentially lead to higher frequency and power microwave devices

  7. Electronic Information Resources in Undergraduate Education: An Exploratory Study of Opportunities for Student Learning and Independence.

    McDowell, Liz

    2002-01-01

    This qualitative interview-based study examines lecturer perspectives on the roles of electronic information resources in undergraduate education. Highlights include electronic academic libraries; changes toward more constructivist approaches to learning; information quality on the Web; plagiarism; information use; information literacy; and…

  8. Where Do Electronic Books Fit in the College Research Arsenal of Resources?

    Barbier, Patricia

    2007-01-01

    Student use of electronic books has become an accepted supplement to traditional resources. Student use and satisfaction was monitored through an online course discussion board. Increased use of electronic books indicate this service is an accepted supplement to the print book collection.

  9. Using the Internet Gopher Protocol to link a computerized patient record and distributed electronic resources.

    Hales, J. W.; Low, R. C.; Fitzpatrick, K T

    1993-01-01

    At Duke University Medical Center, we are developing a prototype clinical application for automated patient care plans with integrated links to electronic documents and other electronic resources. These links are implemented using the Internet Gopher Protocol, an emerging standard for distributed document search and retrieval. Use of this protocol permits storage of electronic documents in an open, nonproprietary manner. This paper discusses the architecture of the link mechanism and presents...

  10. Investigations on the electronic surface properties of the stoichiometric superconductor LiFeAs using scanning tunneling microscopy and spectroscopy

    This work presents scanning tunneling microscopy and spectroscopy investigations on the stoichiometric superconductor lithium iron arsenide (LiFeAs). To reveal the electronic properties, measurements on defect-free surfaces as well as near defects have been performed. The former shows a shift of atomic position with respect to the applied bias voltage. Furthermore, temperature dependent spectroscopic measurements indicate the coupling of quasiparticles in the vicinity of the superconducting coherence peaks. LiFeAs surfaces influenced by atomic defects show a spacial variation of the superconducting gap. The defects can be characterized by their symmetry and thus can be assigned to a position in the atomic lattice. Detailed spectroscopic investigations of defects reveal their influence on the quasiparticle density of states. In particular, Fe-defects show a small effect on the superconductivity while As-defects strongly disturb the superconducting gap. Measurements in magnetic field have been performed for the determination of the Ginzburg-Landau coherence length ξGL. For this purpose, a suitable fit-function has been developed in this work. This function allows to fit the differential conductance of a magnetic vortex at EF. The fit results in a coherence length of ξGL = 3,9 nm which corresponds to an upper critical field of 21 Tesla. Besides measurements on a single vortex, investigation on the vortex lattice have been performed. The vortex lattice constant follows thereby the predicted behavior of a trigonal vortex lattice. However, for magnetic fields larger than 6 Tesla an increasing lattice disorder sets in, presumably due to vortex-vortex-interactions.

  11. Effect of Defects Buried in Pentacene/Alkanethiol Self-Assembled Monolayer/Au Film on Its Electronic Properties Visualized by Scanning Tunneling Microscopy/Spectroscopy

    Terada, Yasuhiko; Takeuchi, Noriaki; Yoshida, Shoji; Taninaka, Atsushi; Takeuchi, Osamu; Shigekawa, Hidemi

    2010-08-01

    We have used scanning tunneling microscopy/spectroscopy to visualize the spatial correlation between buried structural defects and observed electronic properties in organic device structures. As a typical structure of an organic field-effect transistor, we have prepared pentacene/alkanethiol self-assembled monolayer (SAM)/Au samples with or without defects associated with a gap state at the molecule/Au interface. The effect of the defects, which were hidden behind the pentacene overlayers, on the electronic properties of the SAM was clearly observed. The method used in this study has potential for evaluating the nanoscale correlation between electrical properties and hidden defects inside organic devices.

  12. Energy Dependent Tunneling in a Quantum Dot

    MacLean, K; Amasha, S.; Radu, Iuliana P.; Zumbuhl, D. M.; Kastner, M. A.; Hanson, M. P.; Gossard, A. C.

    2006-01-01

    We present measurements of the rates for an electron to tunnel on and off a quantum dot, obtained using a quantum point contact charge sensor. The tunnel rates show exponential dependence on drain-source bias and plunger gate voltages. The tunneling process is shown to be elastic, and a model describing tunneling in terms of the dot energy relative to the height of the tunnel barrier quantitatively describes the measurements.

  13. The National Site Licensing of Electronic Resources: An Institutional Perspective

    Xiaohua Zhu

    2011-06-01

    Full Text Available While academic libraries in most countries are struggling to negotiate with publishers and vendors individually or collaboratively via consortia, a few countries have experimented with a different model, national site licensing (NSL. Because NSL often involves government and large-scale collaboration, it has the potential to solve many problems in the complex licensing world. However, not many nations have adopted it. This study uses historical research approach and the comparative case study research method to explore the seemingly low level of adoption. The cases include the Canadian National Site Licensing Project (CNSLP, the United Kingdom’s National Electronic Site Licensing Initiative (NESLI, and the United States, which has not adopted NSL. The theoretical framework guiding the research design and data collection is W. Richard Scott’s institutional theory, which utilizes three supporting pillars—regulative, normative, and cultural-cognitive—to analyze institutional processes. In this study, the regulative pillar and the normative pillar of NSL adoption— an institutional construction and change—are examined. Data were collected from monographs, research articles, government documents, and relevant websites. Based on the analysis of these cases, a preliminary model is proposed for the adoption of NSL. The factors that support a country’s adoption of NSL include the need for new institutions, a centralized educational policy-making system and funding system, supportive political trends, and the tradition of cooperation. The factors that may prevent a country from adopting NSL include decentralized educational policy and funding, diversity and the large number of institutions, the concern for the “Big Deal,” and the concern for monopoly.

  14. Connecting knowledge resources to the veterinary electronic health record: opportunities for learning at point of care.

    Alpi, Kristine M; Burnett, Heidi A; Bryant, Sheila J; Anderson, Katherine M

    2011-01-01

    Electronic health records (EHRs) provide clinical learning opportunities through quick and contextual linkage of patient signalment, symptom, and diagnosis data with knowledge resources covering tests, drugs, conditions, procedures, and client instructions. This paper introduces the EHR standards for linkage and the partners-practitioners, content publishers, and software developers-necessary to leverage this possibility in veterinary medicine. The efforts of the American Animal Hospital Association (AAHA) Electronic Health Records Task Force to partner with veterinary practice management systems to improve the use of controlled vocabulary is a first step in the development of standards for sharing knowledge at the point of care. The Veterinary Medical Libraries Section (VMLS) of the Medical Library Association's Task Force on Connecting the Veterinary Health Record to Information Resources compiled a list of resources of potential use at point of care. Resource details were drawn from product Web sites and organized by a metric used to evaluate medical point-of-care resources. Additional information was gathered from questions sent by e-mail and follow-up interviews with two practitioners, a hospital network, two software developers, and three publishers. Veterinarians with electronic records use a variety of information resources that are not linked to their software. Systems lack the infrastructure to use the Infobutton standard that has been gaining popularity in human EHRs. While some veterinary knowledge resources are digital, publisher sites and responses do not indicate a Web-based linkage of veterinary resources with EHRs. In order to facilitate lifelong learning and evidence-based practice, veterinarians and educators of future practitioners must demonstrate to veterinary practice software developers and publishers a clinically-based need to connect knowledge resources to veterinary EHRs. PMID:22023919

  15. A survey of the use of electronic scientific information resources among medical and dental students

    Aarnio Matti

    2006-05-01

    Full Text Available Abstract Background To evaluate medical and dental students' utilization of electronic information resources. Methods A web survey sent to 837 students (49.9% responded. Results Twenty-four per cent of medical students and ninteen per cent of dental students searched MEDLINE 2+ times/month for study purposes, and thiry-two per cent and twenty-four per cent respectively for research. Full-text articles were used 2+ times/month by thirty-three per cent of medical and ten per cent of dental students. Twelve per cent of respondents never utilized either MEDLINE or full-text articles. In multivariate models, the information-searching skills among students were significantly associated with use of MEDLINE and full-text articles. Conclusion Use of electronic resources differs among students. Forty percent were non-users of full-text articles. Information-searching skills are correlated with the use of electronic resources, but the level of basic PC skills plays not a major role in using these resources. The student data shows that adequate training in information-searching skills will increase the use of electronic information resources.

  16. Improving access to information – defining core electronic resources for research and wellbeing

    Kristiina Hormia-Poutanen

    2007-11-01

    Full Text Available Research and innovation are listed as the key success factors for the future development of Finnish prosperity and the Finnish economy. The Finnish libraries have developed a scenario to support this vision. University, polytechnic and research institute libraries as well as public libraries have defined the core electronic resources necessary to improve access to information in Finland. The primary aim of this work has been to provide information and justification for central funding for electronic resources to support the national goals. The secondary aim is to help with the reallocation of existing central funds to better support access to information.

  17. Considering Point-of-Care Electronic Medical Resources in Lieu of Traditional Textbooks for Medical Education.

    Hale, LaDonna S; Wallace, Michelle M; Adams, Courtney R; Kaufman, Michelle L; Snyder, Courtney L

    2015-09-01

    Selecting resources to support didactic courses is a critical decision, and the advantages and disadvantages must be carefully considered. During clinical rotations, students not only need to possess strong background knowledge but also are expected to be proficient with the same evidence-based POC resources used by clinicians. Students place high value on real world learning and therefore may place more value on POC resources that they know practicing clinicians use as compared with medical textbooks. The condensed nature of PA education requires students to develop background knowledge and information literacy skills over a short period. One way to build that knowledge and those skills simultaneously is to use POC resources in lieu of traditional medical textbooks during didactic training. Electronic POC resources offer several advantages over traditional textbooks and should be considered as viable options in PA education. PMID:26309211

  18. Electron tunneling measurements in atomic scale gap filled with liquid 4He below 4.2K

    We report the tunneling spectroscopy investigation in an atomic scale gap filled with liquid 4He using mechanically controllable break junction (MCBJ) technique. In order to assure the filling of liquid 4He into the gap, we construct a cryostat with an inner chamber for the tunneling spectroscopy inside the vacuum jacket of the liquid 4He bath. MCBJ apparatus is installed in the inner chamber with a flexible bellows. After filling inner chamber with liquid 4He below 4.2 K, Au electrical electrodes were stretched by the mechanical force generated by a piezo device. We observed the increase of the tunnel conductance through liquid 4He compared to that in the vacuum environment.

  19. A virtual detector approach to tunnel ionization and tunneling times

    Teeny, Nicolas; Bauke, Heiko

    2016-01-01

    Tunneling times in atomic ionization is studied theoretically by a virtual detector approach. A virtual detector is a hypothetical device that allows to monitor the wave-function's density with spatial and temporal resolution during the ionization process. With this theoretical approach, it becomes possible to define unique moments when the electron enters and leaves with highest probability the classically forbidden region from first principles and a tunneling time can be specified unambiguously. It is shown that neither the moment when the electron enters the tunneling barrier nor when it leaves the tunneling barrier coincide with the moment when the external electric field reaches its maximum. Under the tunneling barrier as well as at the exit the electron has a nonzero velocity in electric field direction. This nonzero exit velocity has to be incorporated when the free motion of the electron is modeled by classical equations of motion.

  20. Tombs, tunnels, and terraces a cultural resources survey of a former ammunition supply point in Okinawa, Japan

    Verhaaren, B. T.; Levenson, J. B.; Komine, G.

    2000-02-09

    U.S. forces serving at military bases on foreign soil are obligated to act as good stewards of the cultural and natural resources under their control. However, cultural resources management presents special challenges at U.S. bases in other countries where cultural properties laws differ in emphasis and detail from those in the United States and issues of land ownership and occupancy are not always clear. Where status of forces agreements (SOFAs) exist, environmental governing standards bridge the gap between U.S. and host nation cultural priorities. In Japan, the Department of Defense Japan Environmental Governing Standards (JEGS) fill this function. Under Criteria 12-4.2 and 12-4.3 of the JEGS, U.S. Forces Japan commit themselves to inventory and protect cultural properties found on the lands they control or use. Cultural properties include archaeological sites, tombs, historic buildings, and shrines. Natural monuments, such as landscape features or plant and animal species, may also be designated as cultural properties. As part of this commitment, in February 1999 a cultural resources inventory was conducted in Area 1, part of Kadena Air Base (AB), Okinawa, Japan. Area 1, the former U.S. army Ammunition Supply Point 1, is currently used primarily for training exercises and recreational paint ball.

  1. Dealing with diversity: hybrid libraries and the Distributed National Electronic Resource

    Rusbridge, Chris

    2000-01-01

    Over the past 5 years or so the Joint Information Systems Committee (JISC) working on behalf of UK Higher Education has sponsored a series of initiatives in the field of electronic information. The main aim of the paper is to illustrate how this has led through successive refinements via the idea of the hybrid library to the Distributed National Electronic Resource (the DNER). Some links with related work in Australia are mentioned.

  2. Optical Detection of Tunneling Ionization

    Verhoef, Aart J.; Mitrofanov, Alexander V.; Serebryannikov, Evgenii E.; Kartashov, Daniil V.; Zheltikov, Aleksei M.; Baltuška, Andrius

    2010-04-01

    We have experimentally detected optical harmonics that are generated due to a tunneling-ionization-induced modulation of the electron density. The optical signature of electron tunneling can be isolated from concomitant optical responses by using a noncollinear pump-probe setup. Whereas previously demonstrated tools for attosecond metrology of gases, plasmas, and surfaces rely on direct detection of charged particles, detection of the background-free time-resolved optical signal, which uniquely originates from electron tunneling, offers an interesting alternative that is especially suited for systems in which free electrons cannot be directly measured.

  3. Optical Detection of Tunneling Ionization

    We have experimentally detected optical harmonics that are generated due to a tunneling-ionization-induced modulation of the electron density. The optical signature of electron tunneling can be isolated from concomitant optical responses by using a noncollinear pump-probe setup. Whereas previously demonstrated tools for attosecond metrology of gases, plasmas, and surfaces rely on direct detection of charged particles, detection of the background-free time-resolved optical signal, which uniquely originates from electron tunneling, offers an interesting alternative that is especially suited for systems in which free electrons cannot be directly measured.

  4. Cost-Benefit Analysis of Electronic Information Resources: An Evaluation of the Middle East Technical University Library

    Batı, Hacer

    2006-01-01

    In recent years there has been a rapid transition from print to electronic resources. Significant amount of library budgets are allocated for licensing electronic resources. Identifying and analyzing the benefits and costs of this new trend is therefore important for academic libraries. In this presentation experiences of METU (Middle East Technical University) Library on licensing and usage of electronic resources is evaluated by providing a cost-benefit analysis based on the cost and ...

  5. Tunneling in Fractional Quantum Hall line junctions

    Aranzana, Manuel; Regnault, Nicolas; Jolicoeur, Thierry

    2005-01-01

    We study the tunneling current between two counterpropagating edge modes described by chiral Luttinger liquids when the tunneling takes place along an extended region. We compute this current perturbatively by using a tunnel Hamiltonian. Our results apply to the case of a pair of different two-dimensional electron gases in the fractional quantum Hall regime separated by a barrier, e. g. electron tunneling. We also discuss the case of strong interactions between the edges, leading to nonuniver...

  6. Specific Features of Development of Electronic Information and Education Resources for the Distant Learning Systems ??????????? ???????? ??????????? ?????????????-??????????????? ???????? ??? ?????? ?????????????? ????????

    Sergienko Yelena A.

    2012-07-01

    Full Text Available The article is analyzed the features of distance learning and forms of its realization, is devoted to research existing technologies and tools of distance learning, as well as their possible applications in modern education system. Presents the potential for electronic information-educational resources for distance education systems.? ?????? ???????? ?????? ???????????? ?????????????? ???????? ? ???? ??? ??????????. ??????????? ?????????? ? ???????? ?????????????? ????????, ? ????? ??????????? ?? ?????????? ? ??????????? ??????? ???????????. ???????????? ??????????? ???????? ??????????? ?????????????- ??????????????? ???????? ??? ?????? ?????????????? ???????????.

  7. The Acquisition and Management of Electronic Resources: Can Use Justify Cost?

    Koehn, Shona L.; Hawamdeh, Suliman

    2010-01-01

    As library collections increasingly become digital, libraries are faced with many challenges regarding the acquisition and management of electronic resources. Some of these challenges include copyright and fair use, the first-sale doctrine, licensing versus ownership, digital preservation, long-term archiving, and, most important, the issue of…

  8. Use of Electronic Information Resources among Research Scholars in the Islamia University of Bahawalpur, Pakistan

    Amjad, Anam; Ahmed, Shamshad; Bin Naeem, Salman

    2013-01-01

    This study examined the use of electronic resources among academic scholars of The Islamia University of Bahawalpur (IUB), Punjab, Pakistan. A quantitative survey was found most convenient and useful for this study. The total population of the study was 169 research students in IUB. The response rate was 79% and 133 utilizable responses were coded…

  9. A Mid-infrared Digital Electronic Camera System for Assessing Natural Resources

    Water strongly absorbs mid-infrared (1300-2500 nm) radiation, resulting in this region of the spectrum being sensitive to the water content within features. Little information is available on using an electronic digital camera filtered to this region of the spectrum to assess natural resources. Th...

  10. A Survey of the Use of Electronic Resources at Seven Universities in Wuhan, China

    Zhang, Liyi; Ye, Pinghao; Liu, Qihua

    2011-01-01

    Purpose: The purpose of this paper is to report on users' information behaviour in China, a topic which has not been researched extensively. The aim is to help producers and providers collect and develop more electronic resources. Design/methodology/approach: The study investigates users' information behaviour at seven "211 Project" universities…

  11. What Do Community College Libraries Do with Electronic Resources? The Practice in 2003

    Shorten, Jay

    2004-01-01

    One hundred fourteen community college libraries in the United States and Canada are surveyed for the organization of electronic resources within their home page and their cataloguing practice. The majority provide access to databases, ready reference, and their own catalogue both on their home page and within their web site. They do not usually

  12. Attosecond tunnelling interferometry

    Pedatzur, O.; Orenstein, G.; Serbinenko, V.; Soifer, H.; Bruner, B. D.; Uzan, A. J.; Brambila, D. S.; Harvey, A. G.; Torlina, L.; Morales, F.; Smirnova, O.; Dudovich, N.

    2015-10-01

    Attosecond physics offers new insights into ultrafast quantum phenomena involving electron dynamics on the fastest measurable timescales. The rapid progress in this field enables us to re-visit one of the most fundamental strong-field phenomena: field-induced tunnel ionization. In this work, we employ high-harmonic generation to probe the electron wavefunction during field-induced tunnelling through a potential barrier. By using a combination of strong and weak driving laser fields, we modulate the atomic potential barrier on optical subcycle timescales. This induces a temporal interferometer between attosecond bursts originating from consecutive laser half-cycles. Our study provides direct insight into the basic properties of field-induced tunnelling, following the evolution of the electronic wavefunction within a temporal window of approximately 200 attoseconds.

  13. Transmission electron microscopy and ferromagnetic resonance investigations of tunnel magnetic junctions using Co2MnGe Heusler alloys as magnetic electrodes

    High resolution transmission electron microscopy, nano-beam electronic diffraction, energy dispersive X-rays scanning spectroscopy, vibrating sample magnetometry (VSM) and ferromagnetic resonance (FMR) techniques are used in view of comparing (static and dynamic) magnetic and structural properties of Co2MnGe(13 nm)/Al2O3(3 nm)/Co(13 nm) tunnel magnetic junctions (TMJs), deposited on various single crystalline substrates (a-plane sapphire, MgO(100) and Si(111)). They allow for providing a correlation between these magnetic properties and the fine structure investigated at atomic scale. The Al2O3 tunnel barrier is always amorphous and contains a large concentration of Co atoms, which, however, is significantly reduced when using a sapphire substrate. The Co layer is polycrystalline and shows larger grains for films grown on a sapphire substrate. The VSM investigation reveals in-plane anisotropy only for samples grown on a sapphire substrate. The FMR spectra of the TMJs are compared to the obtained ones with a single Co and Co2MnGe films of identical thickness deposited on a sapphire substrate. As expected, two distinct modes are detected in the TMJs while only one mode is observed in each single film. For the TMJ grown on a sapphire substrate, the FMR behavior does not significantly differ from the superposition of the individual spectra of the single films, allowing for a conclusion that the exchange coupling between the two magnetic layers is too small to give rise to observable shifts. For TMJs grown on a Si or on a MgO substrate, the resonance spectra reveal one mode which is nearly identical to the obtained one in the single Co film, while the other observed resonance shows a considerably smaller intensity and cannot be described using the magnetic parameters appropriate to the single Co2MnGe film. The large Co concentration in the Al2O3 interlayer prevents for a simple interpretation of the observed spectra when using Si or MgO substrates. - Highlights: • Tunnel magnetic junctions have been grown on different substrates. • Their nanoscale structure has been studied and compared to the magnetic properties. • Inter-diffusion to the tunnel barrier has been observed. • Differences between tunnel junctions have a direct impact on magnetic properties

  14. Transmission electron microscopy and ferromagnetic resonance investigations of tunnel magnetic junctions using Co{sub 2}MnGe Heusler alloys as magnetic electrodes

    Belmeguenai, M., E-mail: belmeguenai.mohamed@univ-paris13.fr [LSPM (CNRS-UPR 3407), Université Paris 13, 99 avenue Jean-Baptiste Clément, 93430 Villetaneuse (France); Genevois, C. [Groupe de Physique des Matériaux, UMR CNRS 6634, Site Universitaire du Madrillet, BP12, 76801 Saint Etienne du Rouvray cedex (France); Zighem, F.; Roussigné, Y.; Chérif, S.M. [LSPM (CNRS-UPR 3407), Université Paris 13, 99 avenue Jean-Baptiste Clément, 93430 Villetaneuse (France); Westerholt, K. [Institut für Experimentelle Physik, Ruhr-Universität Bochum, 44780 Bochum (Germany); El Bahoui, A.; Fnidiki, A. [Groupe de Physique des Matériaux, UMR CNRS 6634, Site Universitaire du Madrillet, BP12, 76801 Saint Etienne du Rouvray cedex (France); Moch, P. [LSPM (CNRS-UPR 3407), Université Paris 13, 99 avenue Jean-Baptiste Clément, 93430 Villetaneuse (France)

    2014-01-31

    High resolution transmission electron microscopy, nano-beam electronic diffraction, energy dispersive X-rays scanning spectroscopy, vibrating sample magnetometry (VSM) and ferromagnetic resonance (FMR) techniques are used in view of comparing (static and dynamic) magnetic and structural properties of Co{sub 2}MnGe(13 nm)/Al{sub 2}O{sub 3}(3 nm)/Co(13 nm) tunnel magnetic junctions (TMJs), deposited on various single crystalline substrates (a-plane sapphire, MgO(100) and Si(111)). They allow for providing a correlation between these magnetic properties and the fine structure investigated at atomic scale. The Al{sub 2}O{sub 3} tunnel barrier is always amorphous and contains a large concentration of Co atoms, which, however, is significantly reduced when using a sapphire substrate. The Co layer is polycrystalline and shows larger grains for films grown on a sapphire substrate. The VSM investigation reveals in-plane anisotropy only for samples grown on a sapphire substrate. The FMR spectra of the TMJs are compared to the obtained ones with a single Co and Co{sub 2}MnGe films of identical thickness deposited on a sapphire substrate. As expected, two distinct modes are detected in the TMJs while only one mode is observed in each single film. For the TMJ grown on a sapphire substrate, the FMR behavior does not significantly differ from the superposition of the individual spectra of the single films, allowing for a conclusion that the exchange coupling between the two magnetic layers is too small to give rise to observable shifts. For TMJs grown on a Si or on a MgO substrate, the resonance spectra reveal one mode which is nearly identical to the obtained one in the single Co film, while the other observed resonance shows a considerably smaller intensity and cannot be described using the magnetic parameters appropriate to the single Co{sub 2}MnGe film. The large Co concentration in the Al{sub 2}O{sub 3} interlayer prevents for a simple interpretation of the observed spectra when using Si or MgO substrates. - Highlights: • Tunnel magnetic junctions have been grown on different substrates. • Their nanoscale structure has been studied and compared to the magnetic properties. • Inter-diffusion to the tunnel barrier has been observed. • Differences between tunnel junctions have a direct impact on magnetic properties.

  15. Transmission electron microscopy and ferromagnetic resonance investigations of tunnel magnetic junctions using Co2MnGe Heusler alloy as magnetic electrodes

    Belmeguenai, M.; Genevois, C.; ZIGHEM, F; Roussigné, Y; Chérif, S-M.; Westerholt, K.; Bahoui, A. El; Fnidiki, A.; MOCH, P

    2013-01-01

    HRTEM, nano-beam electronic diffraction, energy dispersive X-rays scanning spectroscopy, Vibrating Sample Magnetometry (VSM) and FerroMagnetic Resonance (FMR) techniques are used in view of comparing (static and dynamic) magnetic and structural properties of Co2MnGe (13 nm)/Al2O3 (3 nm)/Co (13 nm) tunnel magnetic junctions (TMJ), deposited on various single crystalline substrates (a-plane sapphire, MgO(100) and Si(111)). They allow for providing a correlation between these magnetic properties...

  16. Generation-recombination and trap-assisted tunneling in long wavelength infrared minority electron unipolar photodetectors based on InAs/GaSb superlattice

    A long wavelength infrared minority electron unipolar photodetector based on InAs/GaSb type-II superlattices is demonstrated. At 77?K, a dark current of 3??10?5?A/cm2 and a differential resistance-area of 3700??.cm2 are achieved at the turn-on bias, with a 50%-cutoff of 10.0??m and a specific detectivity of 6.2??1011?Jones. The dark current is fitted as a function of bias and temperature using a model combining generation-recombination and trap-assisted tunneling. Good agreement was observed between the theory and the experimental dark current

  17. Identifying and evaluating electronic learning resources for use in adult-gerontology nurse practitioner education.

    Thompson, Hilaire J; Belza, Basia; Baker, Margaret; Christianson, Phyllis; Doorenbos, Ardith; Nguyen, Huong

    2014-01-01

    Enhancing existing curricula to meet newly published adult-gerontology advanced practice registered nurse (APRN) competencies in an efficient manner presents a challenge to nurse educators. Incorporating shared, published electronic learning resources (ELRs) in existing or new courses may be appropriate in order to assist students in achieving competencies. The purposes of this project were to (a) identify relevant available ELR for use in enhancing geriatric APRN education and (b) to evaluate the educational utility of identified ELRs based on established criteria. A multilevel search strategy was used. Two independent team members reviewed identified ELR against established criteria to ensure utility. Only resources meeting all criteria were retained. Resources were found for each of the competency areas and included formats such as podcasts, Web casts, case studies, and teaching videos. In many cases, resources were identified using supplemental strategies and not through traditional search or search of existing geriatric repositories. Resources identified have been useful to advanced practice educators in improving lecture and seminar content in a particular topic area and providing students and preceptors with additional self-learning resources. Addressing sustainability within geriatric APRN education is critical for sharing of best practices among educators and for sustainability of teaching and related resources. PMID:24720944

  18. CEBAF: Injector tunnel in action

    On 28 October, a 100 kV DC electron beam was generated in the injector tunnel at the Continuous Electron Beam Accelerator Facility (CEBAF) being constructed at Newport News, Virginia. In this first tunnel operation, the beam was transported from the electron gun via the room-temperature section to the injector's first superconducting section (5 MeV). The gun and beam steering subsystems behaved as designed, under control from the main control centre

  19. Simulation of electron transmittance and tunnel current in n{sup +} Poly-Si/HfSiO{sub x}N/Trap/SiO{sub 2}/Si(100) capacitors using analytical and numerical approaches

    Noor, Fatimah A., E-mail: fatimah@fi.itb.ac.id; Iskandar, Ferry; Abdullah, Mikrajuddin; Khairurrijal [Physics of Electronic Materials Research Division Faculty of Mathematics and Natural Sciences, Institut Teknologi Bandung Jalan Ganesa 10, Bandung 40132 (Indonesia)

    2015-04-16

    In this paper, we discuss the electron transmittance and tunneling current in high-k-based-MOS capacitors with trapping charge by including the off-diagonal effective-mass tensor elements and the effect of coupling between transverse and longitudinal energies represented by an electron velocity in the gate. The HfSiO{sub x}N/SiO{sub 2} dual ultrathin layer is used as the gate oxide in an n{sup +} poly- Si/oxide/Si capacitor to replace SiO{sub 2}. The main problem of using HfSiO{sub x}N is the charge trapping formed at the HfSiO{sub x}N/SiO{sub 2} interface that can influence the performance of the device. Therefore, it is important to develop a model taking into account the presence of electron traps at the HfSiO{sub x}N/SiO{sub 2} interface in the electron transmittance and tunneling current. The transmittance and tunneling current in n{sup +} poly- Si/HfSiO{sub x}N/trap/SiO2/Si(100) capacitors are calculated by using Airy wavefunctions and a transfer matrix method (TMM) as analytical and numerical approaches, respectively. The transmittance and tunneling current obtained from the Airy wavefunction are compared to those computed by the TMM. The effects of the electron velocity on the transmittance and tunneling current are also discussed.

  20. Effect of the density of the electronic states at the valence orbital of the bridge redox molecule on the dependence of the tunnel current on the overvoltage in the case of fully adiabatic electron transition

    Effect of the density of the electronic states at the valence orbital of the bridge redox molecule on the dependence of the tunnel current on the overvoltage and on the width at half maximum of the current-overvoltage curve is studied. A number of the approximate expressions for the density of states, the tunnel current and the width are obtained in the fully adiabatic limit for different particular cases. It is shown that at small values of the coupling of the electronic levels of the electrodes with the valence orbital of the redox molecule and the small values of the bias voltage two regions of the reorganization Gibbs energy exist with different dependence of the width on the reorganization Gibbs energy. The results of calculations of the density of states, the tunnel current and the width are presented and used for the interpretation of the experimental data [N.G. Tao, Phys. Rev. Lett. 76 (1996) 4066, I. Visoly-Fisher, K. Daie, Y. Terazono, C. Herrero, F. Fungo, L. Otero, E. Durantini, J.J. Silber, L. Sereno, D. Gust, T.A. Moore, A.L. Moore, S.M. Lindsay, PNAS 103 (2006) 8686

  1. Semiclassical description of resonant tunneling

    A semiclassical formula is calculated for the tunneling current of electrons trapped in a potential well which can tunnel into and across a wide quantum well. The tunneling current is measured at the second interface of this well and the calculations idealized an experimental situation where a strong magnetic field tilted with respect to an electric field was used. It is shown that the contribution to the tunneling current, due to trajectories which begin at the first interface and end on the second, is dominant for periodic orbits which hit both walls of the quantum well. (author)

  2. Semiclassical description of resonant tunneling

    Bogomolny, E.B.; Rouben, D.C.

    1996-12-31

    A semiclassical formula is calculated for the tunneling current of electrons trapped in a potential well which can tunnel into and across a wide quantum well. The tunneling current is measured at the second interface of this well and the calculations idealized an experimental situation where a strong magnetic field tilted with respect to an electric field was used. It is shown that the contribution to the tunneling current, due to trajectories which begin at the first interface and end on the second, is dominant for periodic orbits which hit both walls of the quantum well. (author). 21 refs.

  3. Progress Towards High-Sensitivity Arrays of Detectors of Sub-mm Radiation using Superconducting Tunnel Junctions with Radio-Frequency Single-Electron Transistors

    Stevenson, T. R.; Hsieh, W.-T.; Li, M. J.; Stahle, C. M.; Wollack, E. J.; Schoelkopf, R. J.; Krebs, Carolyn (Technical Monitor)

    2002-01-01

    The science drivers for the SPIRIT/SPECS missions demand sensitive, fast, compact, low-power, large-format detector arrays for high resolution imaging and spectroscopy in the far infrared and submillimeter. Detector arrays with 10,000 pixels and sensitivity less than 10(exp 20)-20 W/Hz(exp 20)0.5 are needed. Antenna-coupled superconducting tunnel junction detectors with integrated rf single-electron transistor readout amplifiers have the potential for achieving this high level of sensitivity, and can take advantage of an rf multiplexing technique when forming arrays. The device consists of an antenna structure to couple radiation into a small superconducting volume and cause quasiparticle excitations, and a single-electron transistor to measure currents through tunnel junction contacts to the absorber volume. We will describe optimization of device parameters, and recent results on fabrication techniques for producing devices with high yield for detector arrays. We will also present modeling of expected saturation power levels, antenna coupling, and rf multiplexing schemes.

  4. Progress Towards High-Sensitivity Arrays of Detectors of Sub-mm Radiation Using Superconducting Tunnel Junctions with Integrated Radio Frequency Single-Electron Transistors

    Stevenson, T. R.; Hsieh, W.-T.; Li, M. J.; Prober, D. E.; Rhee, K. W.; Schoelkopf, R. J.; Stahle, C. M.; Teufel, J.; Wollack, E. J.

    2004-01-01

    For high resolution imaging and spectroscopy in the FIR and submillimeter, space observatories will demand sensitive, fast, compact, low-power detector arrays with 104 pixels and sensitivity less than 10(exp -20) W/Hz(sup 0.5). Antenna-coupled superconducting tunnel junctions with integrated rf single-electron transistor readout amplifiers have the potential for achieving this high level of sensitivity, and can take advantage of an rf multiplexing technique. The device consists of an antenna to couple radiation into a small superconducting volume and cause quasiparticle excitations, and a single-electron transistor to measure current through junctions contacting the absorber. We describe optimization of device parameters, and results on fabrication techniques for producing devices with high yield for detector arrays. We also present modeling of expected saturation power levels, antenna coupling, and rf multiplexing schemes.

  5. The effect of interface phonons on operating electron states in three-barrier resonant tunneling structure as an active region of quantum cascade detector

    M.V. Tkach

    2014-06-01

    Full Text Available The Hamiltonian of electrons interacting with interface phonons in three-barrier resonant tunneling structure is established using the first principles within the models of effective mass and polarization continuum. Using the Green's functions method, the temperature shifts and decay rates of operating electron states are calculated depending on geometric design of three-barrier nano-structure GaAs/AlxGa1-xAs which is an active region of quantum cascade detector. It is established that independently of the temperature, the energy of quantum transition during the process of electromagnetic field absorption is a nonlinear weakly varying function of the position of the inner barrier with respect to the outer barriers of the structure.

  6. Carpal tunnel release

    Carpal tunnel release is surgery to treat carpal tunnel syndrome . Carpal tunnel syndrome is pain and weakness in the hand that ... the problem is carpal tunnel syndrome, carpal tunnel release surgery may be recommended. If the muscles in ...

  7. Direct measurement of sub-10 nm-level lateral distribution in tunneling-electron luminescence intensity on a cross-sectional 50-nm-thick AlAs layer by using a conductive transparent tip

    Tunneling-electron luminescence (TL) from nanometer-sized regions can be effectively collected with a conductive transparent (CT) tip that injects tunneling electrons and simultaneously collects luminescence. By using the CT tip, the lateral distribution of TL intensities has been directly measured on a cleaved 50-nm-thick AlAs layer in AlAs/GaAs multiple quantum wells. The TL intensity distribution measured on the AlAs layer agree fairly well with the sum of the exponential decay functions from each GaAs/AlAs interface with a decay length of 8 nm with an accuracy as high as a one-pixel interval of 3 nm. This decay length is close to the thermalization length of tunneling electrons in the AlAs layer. [copyright] 2001 American Institute of Physics

  8. Direct Observation of Second Order Atom Tunnelling

    Foelling, S; Cheinet, P; Feld, M; Saers, R; Widera, A; Mller, T; Bloch, I

    2008-01-01

    Tunnelling of material particles through a classically impenetrable barrier constitutes one of the hallmark effects of quantum physics. When interactions between the particles compete with their mobility through a tunnel junction, intriguing novel dynamical behaviour can arise where particles do not tunnel independently. In single-electron or Bloch transistors, for example, the tunnelling of an electron or Cooper pair can be enabled or suppressed by the presence of a second charge carrier due to Coulomb blockade. Here we report on the first direct and time-resolved observation of correlated tunnelling of two interacting atoms through a barrier in a double well potential. We show that for weak interactions between the atoms and dominating tunnel coupling, individual atoms can tunnel independently, similar to the case in a normal Josephson junction. With strong repulsive interactions present, two atoms located on one side of the barrier cannot separate, but are observed to tunnel together as a pair in a second ...

  9. Origin of the electron-hole asymmetry in the scanning tunneling spectrum of the high-temperature Bi2Sr2CaCu2O8+delta superconductor.

    Nieminen, Jouko; Lin, Hsin; Markiewicz, R S; Bansil, A

    2009-01-23

    We have developed a material specific theoretical framework for modeling scanning tunneling spectroscopy (STS) of high-temperature superconducting materials in the normal as well as the superconducting state. Results for Bi2Sr2CaCu2O8+delta (Bi2212) show clearly that the tunneling process strongly modifies the STS spectrum from the local density of states of the dx2-y2 orbital of Cu. The dominant tunneling channel to the surface Bi involves the dx2-y2 orbitals of the four neighboring Cu atoms. In accord with experimental observations, the computed spectrum displays a remarkable asymmetry between the processes of electron injection and extraction, which arises from contributions of Cu dz2 and other orbitals to the tunneling current. PMID:19257381

  10. Electronic Human Resource Management (e-HRM) of Hotel Business in Phuket

    Kitimaporn Choochote; Kitsiri Chochiang

    2015-01-01

    This research aims to study the pattern of the electronic human resources management (e-HRM) of the hotel business in Phuket. The study is conducted with the implementation of field data and in-depth interview of hotels’ HR managers. In consequence, the study reveals that the hotel business has applied the use of the e-HRM varying in job recruitment (15 percent), employee engagement (55 percent), organizational file structure (10 percent), idea and creativity exchanges (38 percent) and assess...

  11. Increase resource power electronics module on the physics of failure method

    Kravchenko Evgeny V.; Kuznetsov Geniy V.

    2014-01-01

    A new approach to improving resource devices for power electronics. The numerical analysis of non-uniform temperature field of power semiconductor devices. A comparison of the intensities of the failure of a power unit with the real thermal regime of the device under conditions of natural convection and obtained by using statistical data analysis. The integrated assessment of reliability based on the methods of physics failures. The necessity of taking into account the actual non-stationary t...

  12. PROJECT VERITY: virtual and Electronic Resources for Information Skills Training for Young People

    Παπάζογλου, Αλεξάνδρα

    1999-01-01

    Introduces VERITY (Virtual and Electronic Resources for Information Skills Training for Young People) and its Virtual Librarian to help young people with their information seeking process. VERITY, funded by the Libraries sector under the European Union's Telematics Applications Programme, aims to explore new ways of providing virtual library services that are creative, stimulating and educational for young people in the 13-19 age group. It will be developed in parallel in five languages (Engl...

  13. ENABLING CLOSED RESOURCE LOOPS IN ELECTRONICS: UNDERSTANDING CONSUMER DISPOSAL BEHAVIOUR USING INSIGHTS FROM DIFFUSION MODELS

    Sinha Khetriwal, Deepali; First, Ivana

    2012-01-01

    The paper explores consumer disposal behaviour, especially in the context of durable electronic products. The purpose of the research is to understand why, how and when consumers dispose of their durable products. The research aims to provide policy makers, waste managers and product marketers new insights on consumer disposal behaviour that will help improve policy, encourage better resource management and incentivise product designs that maximise environmental and social benefits. We apply ...

  14. The scanning tunneling microscope

    A newly conceived microscope, based on a pure quantum phenomenon, is an ideal tool to study atom by atom the topography and properties of surfaces. Applications are presented: surface ''reconstruction'' of silicon, lamellar compound study, etc... Spectroscopy by tunnel effect will bring important information on electronic properties; it is presented with an application on silicon

  15. The LEP tunnel

    Patrice Loiez

    1991-01-01

    The LEP collider, which ran from 1989 to 2000. Electrons and positrons were accelerated through these magnets until they were travelling at almost the speed of light before colliding in the centre of one of the four detectors. The huge circumference of the ring means that the curvature is very small and so the tunnel looks rather straight.

  16. Tunnel electroresistance through organic ferroelectrics.

    Tian, B B; Wang, J L; Fusil, S; Liu, Y; Zhao, X L; Sun, S; Shen, H; Lin, T; Sun, J L; Duan, C G; Bibes, M; Barthélémy, A; Dkhil, B; Garcia, V; Meng, X J; Chu, J H

    2016-01-01

    Organic electronics is emerging for large-area applications such as photovoltaic cells, rollable displays or electronic paper. Its future development and integration will require a simple, low-power organic memory, that can be written, erased and readout electrically. Here we demonstrate a non-volatile memory in which the ferroelectric polarisation state of an organic tunnel barrier encodes the stored information and sets the readout tunnel current. We use high-sensitivity piezoresponse force microscopy to show that films as thin as one or two layers of ferroelectric poly(vinylidene fluoride) remain switchable with low voltages. Submicron junctions based on these films display tunnel electroresistance reaching 1,000% at room temperature that is driven by ferroelectric switching and explained by electrostatic effects in a direct tunnelling regime. Our findings provide a path to develop low-cost, large-scale arrays of organic ferroelectric tunnel junctions on silicon or flexible substrates. PMID:27143121

  17. Superconducting electron tunneling as detection method for low frequency resonant vibration modes of interstitials in fcc lead

    The influence of crystal defects on the phonon spectra was studied for fcc lead using superconducting tunneling spectroscopy. The theory predicts low frequency modes for the vibrational states of interstitials in (100) dumbbell configuration. Low temperature irradiation of superconducting point contacts with fast ions (point contact thickness small compared to the average ion range) showed radiation-induced structures in the low-energy part of the Eliashberg function for lead. These resonant modes are reduced by annealing at 18.5 K; they are attributed to small interstitial clusters. The radiation-induced structures are completely removed by room temperature annealing. (orig.)

  18. Computational multiqubit tunnelling in programmable quantum annealers

    Boixo, Sergio; Smelyanskiy, Vadim N.; Shabani, Alireza; Isakov, Sergei V.; Dykman, Mark; Denchev, Vasil S.; Amin, Mohammad H.; Smirnov, Anatoly Yu; Mohseni, Masoud; Neven, Hartmut

    2016-01-01

    Quantum tunnelling is a phenomenon in which a quantum state traverses energy barriers higher than the energy of the state itself. Quantum tunnelling has been hypothesized as an advantageous physical resource for optimization in quantum annealing. However, computational multiqubit tunnelling has not yet been observed, and a theory of co-tunnelling under high- and low-frequency noises is lacking. Here we show that 8-qubit tunnelling plays a computational role in a currently available programmable quantum annealer. We devise a probe for tunnelling, a computational primitive where classical paths are trapped in a false minimum. In support of the design of quantum annealers we develop a nonperturbative theory of open quantum dynamics under realistic noise characteristics. This theory accurately predicts the rate of many-body dissipative quantum tunnelling subject to the polaron effect. Furthermore, we experimentally demonstrate that quantum tunnelling outperforms thermal hopping along classical paths for problems with up to 200 qubits containing the computational primitive.

  19. Computational multiqubit tunnelling in programmable quantum annealers.

    Boixo, Sergio; Smelyanskiy, Vadim N; Shabani, Alireza; Isakov, Sergei V; Dykman, Mark; Denchev, Vasil S; Amin, Mohammad H; Smirnov, Anatoly Yu; Mohseni, Masoud; Neven, Hartmut

    2016-01-01

    Quantum tunnelling is a phenomenon in which a quantum state traverses energy barriers higher than the energy of the state itself. Quantum tunnelling has been hypothesized as an advantageous physical resource for optimization in quantum annealing. However, computational multiqubit tunnelling has not yet been observed, and a theory of co-tunnelling under high- and low-frequency noises is lacking. Here we show that 8-qubit tunnelling plays a computational role in a currently available programmable quantum annealer. We devise a probe for tunnelling, a computational primitive where classical paths are trapped in a false minimum. In support of the design of quantum annealers we develop a nonperturbative theory of open quantum dynamics under realistic noise characteristics. This theory accurately predicts the rate of many-body dissipative quantum tunnelling subject to the polaron effect. Furthermore, we experimentally demonstrate that quantum tunnelling outperforms thermal hopping along classical paths for problems with up to 200 qubits containing the computational primitive. PMID:26739797

  20. Design and Analysis of CMOS-Compatible III-V Compound Electron-Hole Bilayer Tunneling Field-Effect Transistor for Ultra-Low-Power Applications.

    Kim, Sung Yoon; Seo, Jae Hwa; Yoon, Young Jun; Lee, Ho-Young; Lee, Seong Min; Cho, Seongjae; Kang, In Man

    2015-10-01

    In this work, we design and analyze complementary metal-oxide-semiconductor (CMOS)-compatible III-V compound electron-hole bilayer (EHB) tunneling field-effect transistors (TFETs) by using two-dimensional (2D) technology computer-aided design (TCAD) simulations. A recently proposed EHB TFET exploits a bias-induced band-to-band tunneling (BTBT) across the electron-hole bilayer by an electric field from the top and bottom gates. This is in contrast to conventional planar p(+)-p(-)-n TFETs, which utilize BTBT across the source-to-channel junction. We applied III-V compound semiconductor materials to the EHB TFETs in order to enhance the current drivability and switching performance. Devices based on various compound semiconductor materials have been designed and analyzed in terms of their primary DC characteristics. In addition, the operational principles were validated by close examination of the electron concentrations and energy-band diagrams under various operation conditions. The simulation results of the optimally designed In0.533Ga0.47As EHB TFET show outstanding performance, with an on-state current (Ion) of 249.5 ?A/?m, subthreshold swing (S) of 11.4 mV/dec, and threshold voltage (Vth) of 50 mV at VDS = 0.5 V. Based on the DC-optimized InGaAs EHB TFET, the CMOS inverter circuit was simulated in views of static and dynamic behaviors of the p-channel device with exchanges between top and bottom gates or between source and drain electrodes maintaining the device structure. PMID:26726356

  1. Potential resource and toxicity impacts from metals in waste electronic devices.

    Woo, Seung H; Lee, Dae Sung; Lim, Seong-Rin

    2016-04-01

    As a result of the continuous release of new electronic devices, existing electronic devices are quickly made obsolete and rapidly become electronic waste (e-waste). Because e-waste contains a variety of metals, information about those metals with the potential for substantial environmental impact should be provided to manufacturers, recyclers, and disposers to proactively reduce this impact. This study assesses the resource and toxicity (i.e., cancer, noncancer, and ecotoxicity) potentials of various heavy metals commonly found in e-waste from laptop computers, liquid-crystal display (LCD) monitors, LCD TVs, plasma TVs, color cathode ray tube (CRT) TVs, and cell phones and then evaluates such potentials using life cycle impact-based methods. Resource potentials derive primarily from Cu, Sb, Ag, and Pb. Toxicity potentials derive primarily from Pb, Ni, and Hg for cancer toxicity; from Pb, Hg, Zn, and As for noncancer toxicity; and from Cu, Pb, Hg, and Zn for ecotoxicity. Therefore, managing these heavy metals should be a high priority in the design, recycling, and disposal stages of electronic devices. Integr Environ Assess Manag 2016;12:364-370. © 2015 SETAC. PMID:27017840

  2. Pressure measurement method using electronically scanner pressure sensor (ESP) installed in a gust wind tunnel; Denshishiki sosa taten atsuryoku sensor (ESP) wo mochiita toppu fudo atsuryoku keisoku system

    Fujita, T.; Iwasaki, A.; Ito, F.; Fujieda, H. [National Aerospace Laboratory, Tokyo (Japan)

    1991-07-01

    Electronically scanner pressure sensors (ESP) were installed at various data acquisition locations in a gust wind tunnel and the system using ESP was developed in order to obtain pressure measurements at high speeds. It was feared that changes in the environmental conditions, particularly flow temperature, resulted in the sensors displaying a span and zero shift, thus making it difficult to use them in a long run wind tunnel tests. In order to solve these problems, a calibration method with known monitoring pressures was developed, experiments were subsequently performed, and a method was established which assured they maintain their required measurement accuracy. In the case of a short take-off and landing (STOL) aircraft semi-span model, the time required for wake measurements was reduced by about 92 %, namely the test took only 1 h versus 1.5 days using the previous method. Establishment of the ESP system for high speed pressure measurements and preparations of equipment including a renewal of the data processing computer enabled the real time processing and displaying of flow fields, and enhanced reliability and efficiency of pressure measurements. 9 refs., 28 figs., 20 tabs.

  3. Single-electron tunneling in a single PbS nanocrystal nucleated on 11-mercaptoundecanoic acid self-assembled monolayer at room temperature

    Nanometer-sized PbS particles in the size of about 3 nm produced by exposing a self-assembled monolayer of 11-mercaptoundecanoic acid salts on gold (111) substrate in a H2S atmosphere were studied by scanning tunneling microscopy (STM) and high-resolution transmission electron microscopy at room temperature in air. The stability of thus-obtained PbS nanoparticles makes STM imaging possible and repeatable scans of the semiconductor nanoparticles were performed. The current-voltage (I--V) characteristics of a single PbS nanoparticle exhibited clearly Coulomb blockade and Coulomb staircase. Furthermore, by varying the gap between a STM tip and the PbS nanoparticle, we also verified the dependence of staircase width on the change of the gap in the local I--V characteristics on the same PbS nanoparticle. The phenomena can be well described by a semi-classical double-barrier tunneling model. copyright 2001 American Institute of Physics

  4. Electron-tunneling study of superconductors doped with magnetic atoms and nonmagnetic resonant-state atoms: indium-chromium, zinc-manganese, and aluminum-manganese

    We have used electron-tunneling measurements to determine the density of states of quench-condensed thin films of In-Cr, Zn-Mn, and Al-Mn, and of annealed thin films of Zn-Mn. The results on In-Cr and Zn-Mn were compared with Shiba's theory for magentic atoms in superconductors. We observed the localized band of states predicted to form in the energy gap of such alloys, though the observed band was broader than that predicted. The annealed samples of Zn-Mn showed a narrower band than did the quench-condensed samples. Reasonable agreement with Shiba's theory was found if s, p, and d wave scattering were included. The results on Al-Mn were compared with Salomaa and Nieminen's theory for nonmagnetic resonant-state atoms in superconductors. The predicted band of states was not observed. Our measurements indicate that Mn in quench-condensed Al is nonmagnetic. Any resonant states which do exist in the superconducting alloy are too broad to be seen in our tunneling measurement

  5. Postgraduate medical students’ acceptance and understanding of scientific information databases and electronic resources

    Azami, Mohammad; Khajouei, Reza; Rakhshani, Safiyeh

    2016-01-01

    Introduction The significance and validity of web-based scientific databases are increasing dramatically in the scientific community. Moreover, a great number of students use these resources without having sufficient and accurate knowledge and understanding. In order for students to use these databases and electronic resources optimally, identifying the factors that affect the understanding and acceptance of these resources seems necessary. The aim of this study was to determine postgraduate medical students’ acceptance and understanding of these resources. Methods This cross-sectional study was conducted on 311 postgraduate medical students from Kerman University of Medical Science (KMU) in 2013. Data were collected using a researcher-made questionnaire, and the data were analyzed using SPSS. In order to design the model (i.e., the interaction between study variables and to determine the relationships between them in an integrated pattern), LISREL version 8.7 and a structural equation model were used. Descriptive statistics and t-tests also were used in data analysis. Results The results showed that the average components of the perception of usefulness, perception of ease of use, attitude towards use, decision to use, using to perform duties, and using to increase knowledge were 4.31, 4.14, 4.24, 16.27, 20.85, and 16.13 respectively. Accordingly, the average of all these indicators was significantly higher than the assumed amount (p easy to use, the more they are used. Therefore, designers of databases and electronic resources can design systems that are both useful and easy to learn by considering the components of the research model. PMID:27123213

  6. Equipment concept design and development plans for microgravity science and applications research on space station: Combustion tunnel, laser diagnostic system, advanced modular furnace, integrated electronics laboratory

    Uhran, M. L.; Youngblood, W. W.; Georgekutty, T.; Fiske, M. R.; Wear, W. O.

    1986-01-01

    Taking advantage of the microgravity environment of space NASA has initiated the preliminary design of a permanently manned space station that will support technological advances in process science and stimulate the development of new and improved materials having applications across the commercial spectrum. Previous studies have been performed to define from the researcher's perspective, the requirements for laboratory equipment to accommodate microgravity experiments on the space station. Functional requirements for the identified experimental apparatus and support equipment were determined. From these hardware requirements, several items were selected for concept designs and subsequent formulation of development plans. This report documents the concept designs and development plans for two items of experiment apparatus - the Combustion Tunnel and the Advanced Modular Furnace, and two items of support equipment the Laser Diagnostic System and the Integrated Electronics Laboratory. For each concept design, key technology developments were identified that are required to enable or enhance the development of the respective hardware.

  7. Integrating electronic information resources for NHS Glasgow staff at the point of need: a model of interlibrary collaboration and resource sharing.

    Davies, S; Wales, A

    2001-12-01

    The Glasgow NHS Libraries Consortium has harnessed the political imperative of collaboration and the capability of electronic information resources to address inequalities in access to the knowledge base across NHS Glasgow. They have negotiated consortium arrangements to an extensive range of electronic databases and journals which no single Glasgow NHS library could afford independently. A Project Officer was appointed to undertake the administration, technical work and promotion required to build a Web-based electronic library to deliver resources to all NHS Glasgow staff on an equitable basis. Close partnership with online content providers enabled the Project Officer to find solutions to problems caused by authentication systems and license restrictions. These efforts have culminated in the production of a fully integrated virtual library--the NHS Glasgow e-Library--delivering 11 major electronic databases, 440 full-text electronic journals, 48 electronic textbooks and over 5000 journal contents pages. The NHS Glasgow e-Library is without precedent within the NHS in terms of its wealth of resources, and it provides a model for Scotland-wide access to the knowledge base. The sustainability and transferability of the resource is dependent on a number of key areas-maintenance, user training, evaluation, IT infrastructure and ongoing collaboration and unification. Ongoing research will monitor how far the NHS Glasgow e-Library has strengthened the connection between research evidence and clinical practice. PMID:11791863

  8. Resonant Tunneling Spin Pump

    Ting, David Z.

    2007-01-01

    The resonant tunneling spin pump is a proposed semiconductor device that would generate spin-polarized electron currents. The resonant tunneling spin pump would be a purely electrical device in the sense that it would not contain any magnetic material and would not rely on an applied magnetic field. Also, unlike prior sources of spin-polarized electron currents, the proposed device would not depend on a source of circularly polarized light. The proposed semiconductor electron-spin filters would exploit the Rashba effect, which can induce energy splitting in what would otherwise be degenerate quantum states, caused by a spin-orbit interaction in conjunction with a structural-inversion asymmetry in the presence of interfacial electric fields in a semiconductor heterostructure. The magnitude of the energy split is proportional to the electron wave number. Theoretical studies have suggested the possibility of devices in which electron energy states would be split by the Rashba effect and spin-polarized currents would be extracted by resonant quantum-mechanical tunneling.

  9. Temperature dependent electron delocalization in CdSe/CdS type-I core-shell systems: An insight from scanning tunneling spectroscopy

    Kundu, Biswajit; Chakrabarti, Sudipto; Pal, Amlan J.

    2016-03-01

    Core-shell nanocrystals having a type-I band-alignment confine charge carriers to the core. In this work, we choose CdSe/CdS core-shell nano-heterostructures that evidence confinement of holes only. Such a selective confinement occurs in the core-shell nanocrystals due to a low energy-offset of conduction band (CB) edges resulting in delocalization of electrons and thus a decrease in the conduction band-edge. Since the delocalization occurs through a thermal assistance, we study temperature dependence of selective delocalization process through scanning tunneling spectroscopy. From the density of states (DOS), we observe that the electrons are confined to the core at low temperatures. Above a certain temperature, they become delocalized up to the shell leading to a decrease in the CB of the core-shell system due to widening of quantum confinement effect. With holes remaining confined to the core due to a large offset in the valence band (VB), we record the topography of the core-shell nanocrystals by probing their CB and VB edges separately. The topographies recorded at different temperatures representing wave-functions of electrons and holes corresponded to the results obtained from the DOS spectra. The results evidence temperature-dependent wave-function delocalization of one-type of carriers up to the shell layer in core-shell nano-heterostructures.

  10. Achieving Resource Conservation in Electronic Waste Management: A Review of Options Available to Developing Countries

    Innocent Chidi Nnorom

    2007-01-01

    Full Text Available Large quantities of waste electronic devices (e-waste at their end-of-life, generated internally or imported illegally from developed countries, are currently being managed in the developing countries, through low-end means such as crude backyard recycling and disposal at unlined landfills or open dumps. The extension of the lifespan of electronic devices through reuse options such as repair, reconditioning and remanufacturing should be a priority in the management of electronic waste in developing countries considering the near absence of state-of-the-art recycling facilities in these countries. Life extension through product and component reuse is especially critical to electronic products because in recent years, electronics have increased in technological complexity, with new product innovations and ever shortening product life expectancy. For many products, environmentalists assume that reuse is environmentally beneficial because it replaces the manufacturing and purchase of new goods. However, on the contrary, manufacturers may oppose this type of reuse for the same reason. There is an urgent need to control the trans-boundary movement of electronic scrap especially to countries without established recycling facilities. Importations of secondhand electronics make such devices available to those who cannot afford new products. However, an international method of testing and certification is needed to ensure that exported secondhand devices are functional. Establishment of formal recycling facilities for e-waste in the developing countries will ensure resource reutilization with both economical and ecological gains. This study reviews options available in working towards eco-efficient management of e-waste in developing countries in the light of the present low-end management practices.

  11. Increase resource power electronics module on the physics of failure method

    Kravchenko Evgeny V.

    2014-01-01

    Full Text Available A new approach to improving resource devices for power electronics. The numerical analysis of non-uniform temperature field of power semiconductor devices. A comparison of the intensities of the failure of a power unit with the real thermal regime of the device under conditions of natural convection and obtained by using statistical data analysis. The integrated assessment of reliability based on the methods of physics failures. The necessity of taking into account the actual non-stationary temperature fields to improve the reliability of the forecast operating life of power semiconductor devices.

  12. Aufwand und Nutzen des Electronic Resource Management Systems RMS an der UB Kassel

    Tobias Pohlmann

    2016-01-01

    Die Verwaltung elektronischer Ressourcen stellt für Bibliotheken eine wichtige und zugleich nicht einfache Aufgabe dar. Sie müssen den Überblick behalten über heterogene Informationen, die sich mit herkömmlichen Bibliothekssystemen nur bedingt abbilden lassen. Die UB Kassel verwendet daher seit August 2014 das webbasierte Electronic Resource Management System RMS von SemperTool. Dieser Beitrag stellt die Funktionalitäten des Systems vor und schätzt den erforderlichen Arbeitsaufwand ab, ...

  13. ??????????COUNTER???????? Statistical Problems of Electronic Resources and the Development and Application of COUNTER Project

    Hui-Hsin Yeh

    2006-06-01

    Full Text Available ??????????????????????????????????????????E-Metrics?COUNTER??????????????COUNTER????????????????????????????????COUNTER???????????????????????????????????????????????This study will be initiated from the controversies derived from generating electronic resource statistics, by way of literature review to recognize the solutions proposed by libraries, and further on to look into the development and the intention of E-Metrics and COUNTER projects, and lastly to proceed a comprehensive analysis of the reports from publishers under the standard format regulated by COUNTER. Through this study we expect to clarify and define the capabilities and limitations of COUNTER, and with which we hope to provide librarians a reliable standard to follow while generating statistics, and for publishers a referable criterion while selecting log files.

  14. AWARENESS AND USE OF ELECTRONIC INFORMATION RESOURCES IN DEGREE COLLEGES OF KODAGU DISTRICT.

    Muthamma A.R

    2015-07-01

    Full Text Available A study with a view to survey awareness and use of electronic information resources by social science research scholar and the library professionals, a random sampling techniques were used. About 200 questionnaire were distributed for data collection 180 filled questionnaire was received giving a responds rate of 90%.Simple frequency counting and percentage were used in reporting and finding. The paper suggests for an improvement in the access facilities with high internet speed and subscription to more eresources by the academic college Libraries in Kodagu.

  15. A preliminary categorization of end-of-life electrical and electronic equipment as secondary metal resources

    Highlights: → End-of-life electrical and electronic equipment (EEE) as secondary metal resources. → The content and the total amount of metals in specific equipment are both important. → We categorized 21 EEE types from contents and total amounts of various metals. → Important equipment types as secondary resources were listed for each metal kind. → Collectability and possible collection systems of various EEE types were discussed. - Abstract: End-of-life electrical and electronic equipment (EEE) has recently received attention as a secondary source of metals. This study examined characteristics of end-of-life EEE as secondary metal resources to consider efficient collection and metal recovery systems according to the specific metals and types of EEE. We constructed an analogy between natural resource development and metal recovery from end-of-life EEE and found that metal content and total annual amount of metal contained in each type of end-of-life EEE should be considered in secondary resource development, as well as the collectability of the end-of-life products. We then categorized 21 EEE types into five groups and discussed their potential as secondary metal resources. Refrigerators, washing machines, air conditioners, and CRT TVs were evaluated as the most important sources of common metals, and personal computers, mobile phones, and video games were evaluated as the most important sources of precious metals. Several types of small digital equipment were also identified as important sources of precious metals; however, mid-size information and communication technology (ICT) equipment (e.g., printers and fax machines) and audio/video equipment were shown to be more important as a source of a variety of less common metals. The physical collectability of each type of EEE was roughly characterized by unit size and number of end-of-life products generated annually. Current collection systems in Japan were examined and potentially appropriate collection methods were suggested for equipment types that currently have no specific collection systems in Japan, particularly for video games, notebook computers, and mid-size ICT and audio/video equipment.

  16. Spin-polarized electron tunneling across a Si delta-doped GaMnAs/n-GaAs interface

    Andresen, S.E.; Sørensen, B.S.; Lindelof, P.E.; Sadowski, J.; Guertler, C.M.; Bland, J.A.C.; Rasmussen, Finn Berg

    2003-01-01

    Spin-polarized electron coupling across a Si delta-doped GaMnAs/n-GaAs interface was investigated. The injection of spin-polarized electrons was detected as circular polarized emission from a GaInAs/GaAs quantum well light emitting diode. The angular momentum selection rules were simplified by th...

  17. Signatures of electron-magnon interaction in charge and spin currents through magnetic tunnel junctions: A nonequilibrium many-body perturbation theory approach

    Mahfouzi, Farzad; Nikoli?, Branislav K.

    2014-07-01

    We develop a numerically exact scheme for resumming certain classes of Feynman diagrams in the self-consistent perturbative expansion for the electron and magnon self-energies in the nonequilibrium Green function formalism applied to a coupled electron-magnon (e-m) system driven out of equilibrium by the applied finite bias voltage. Our scheme operates with the electronic and magnonic GFs and the corresponding self-energies viewed as matrices in the Keldysh space, rather than conventionally extracting their retarded and lesser components, which greatly simplifies translation of diagrams into compact mathematical expressions and their computational implementation. This is employed to understand the effect of inelastic e-m scattering on charge and spin current vs bias voltage Vb in F/I/F (F-ferromagnet; I-insulating barrier) magnetic tunnel junctions (MTJs), which are modeled on a quasi-one-dimensional (quasi-1D) tight-binding lattice for the electronic subsystem and quasi-1D Heisenberg model for the magnonic subsystem. For this purpose, we evaluate the Fock diagram for the electronic self-energy and the electron-hole polarization bubble diagram for the magnonic self-energy. The respective electronic and magnonic GF lines within these diagrams are the fully interacting ones, thereby requiring to solve the ensuing coupled system of nonlinear integral equations self-consistently. Despite using the quasi-1D model and treating e-m interaction in many-body fashion only within a small active region consisting of few lattice sites around the F/I interface, our analysis captures essential features of the so-called zero-bias anomaly observed [V. Drewello, J. Schmalhorst, A. Thomas, and G. Reiss, Phys. Rev. B 77, 014440 (2008), 10.1103/PhysRevB.77.014440] in both MgO- and AlOx-based realistic 3D MTJs where the second derivative d2I /dVb2 (i.e., inelastic electron tunneling spectrum) of charge current exhibits sharp peaks of opposite sign on either side Vb=0. We show that this is closely related to a substantially modified magnonic density of states (DOS) after the e-m interaction is turned onthe magnonic bandwidth over which DOS is nonzero becomes broadened, thereby making e-m scattering at arbitrary small bias voltage possible, while DOS also acquires peaks (on the top of a continuous background) signifying the formation of quasibound states of magnons dressed by the cloud of electron-hole pair excitations. We also demonstrate that the sum of electronic spin currents in all of the semi-infinite leads attached to the active region quantifies the loss of spin angular momentum carried away from the active region by the magnonic spin current.

  18. Assessment of accepting rate of Electronic Information Resources (EIR by Iranian Knowledge and Information Science faculty members

    Afshin Hamdipour

    2014-12-01

    Full Text Available Electronic information resources (EIR play an important role in the process of education and research. The aim of this study was to analyze the status of adoption of electronic information resources (EIR by Iranian Knowledge and Information Science (KIS faculty members. This applied- descriptive survey was carried out on Iranian KIS Faculty Members in 2012. The number of participants was determined based on the Cochran's sample size table. Of the 170 Faculty Members, 122 individuals were randomly selected. Data collection tool was an Electronic questionnaire, and its validity was confirmed by professionals. The reliability of the questionnaire was verified after a pilot study. By using IBM SPSS 20 software and through exploratory factor analysis, descriptive statistics, and inferential tests the data were analyzed. Results showed that, there is significant difference between the mean of adoption rate of electronic information resources (EIR by people with different levels of education. In addition, the Pearson correlation coefficient showed a significant relationship between mean of adoption rate and the faculty’s teaching experience and age. The results of Kolmogorov-Smirnoff test showed that the curve of adoption rate of electronic information resources among the sample is normal, and thus, the adoption rate of resources over time, is S-shaped. Ultimately, this study confirmed The Rogers’ Diffusion of Innovation Theory (2003 in context of Adaptor categories of electronic information resources (EIR, and S-shaped curve, among faculty members in departments of knowledge and Information science in Iran.

  19. Tunnel magnetoresistance in magnetic tunnel junctions with embedded nanoparticles

    Useinov, Arthur; Ye, Lin-Xiu; Wu, Te-Ho; Lai, Chih-Huang

    2015-01-01

    In this paper, we attempt the theoretical modeling of the magnetic tunnel junctions with embedded magnetic and nonmagnetic nanoparticles (NPs). A few abnormal tunnel magnetoresistance (TMR) effects, observed in related experiments, can be easily simulated within our model: we found, that the suppressed TMR magnitudes and the TMR sign-reversing effect at small voltages are related to the electron momentum states of the NP located inside the insulating layer. All these TMR behaviors can be explained within the tunneling model, where NP is simulated as a quantum well (QW). The coherent (direct) double barrier tunneling is dominating over the single barrier one. The origin of the TMR suppression is the quantized angle transparency for spin polarized electrons being in one of the lowest QW states. The phenomenon was classified as the quantized conductance regime due to restricted geometry.

  20. Spin-dependent tunneling with Coulomb blockade

    Schelp, L. F.; Fert, A.; Fettar, F.; Holody, P.; Lee, S. F.; Maurice, J. L.; Petroff, F.; Vaurès, A.

    1997-09-01

    We have fabricated Co/Al2O3/Co tunnel junctions in which the Al2O3 layer includes a unique layer of small and disconnected cobalt clusters, with a typical mean diameter ranging from 2.0 to 4.0 nm. We observe spin-dependent tunneling properties with, below about 50 K, typical Coulomb-blockade effects induced by intermediate electron tunneling into cobalt clusters. The tunnel magnetoresistance ratio is approximately the same in the Coulomb-blockade regime (low-temperature range with very high tunnel resistance) and in the room-temperature regime without Coulomb blockade. It also depends weakly on the applied voltage.

  1. Observation of vortices and hidden pseudogap from scanning tunneling spectroscopic studies of the electron-doped cuprate superconductor Sr0.9La0.1CuO2

    Teague, M. L.; Beyer, A. D.; Grinolds, M. S.; Lee, S. I.; Yeh, N.-C.

    2009-01-01

    We present the first demonstration of vortices in an electron-type cuprate superconductor, the highest Tc(=43 K) electron-type cuprate Sr0.9La0.1CuO2. Our spatially resolved quasiparticle tunneling spectra reveal a hidden low-energy pseudogap inside the vortex core and unconventional spectral evolution with temperature and magnetic field. These results cannot be easily explained by the scenario of pure superconductivity in the ground state of high-Tc superconductivity.

  2. Transmission electron microscopy and ferromagnetic resonance investigations of tunnel magnetic junctions using Co2MnGe Heusler alloys as magnetic electrodes

    Belmeguenai, M.; Genevois, C.; Zighem, F.; Roussigné, Y.; Chérif, S. M.; Westerholt, K.; El Bahoui, A.; Fnidiki, A.; Moch, P.

    2014-01-01

    HRTEM, nano-beam electronic diffraction, energy dispersive X-rays scanning spectroscopy, Vibrating Sample Magnetometry (VSM) and FerroMagnetic Resonance (FMR) techniques are used in view of comparing (static and dynamic) magnetic and structural properties of Co2MnGe (13 nm)/Al2O3 (3 nm)/Co (13 nm) tunnel magnetic junctions (TMJ), deposited on various single crystalline substrates (a-plane sapphire, MgO(100) and Si(111)). They allow for providing a correlation between these magnetic properties and the fine structure investigated at atomic scale. The Al2O3 tunnel barrier is always amorphous and contains a large concentration of Co atoms, which, however, is significantly reduced when using a sapphire substrate. The Co layer is polycrystalline and shows larger grains for films grown on a sapphire substrate. The VSM investigation reveals in-plane anisotropy only for samples grown on a sapphire substrate. The FMR spectra of the TMJs are compared to the obtained ones with a single Co and Co2MnGe films of identical thickness deposited on a sapphire substrate. As expected, two distinct modes are detected in the TMJs while only one mode is observed in each single film. For the TMJ grown on a sapphire substrate the FMR behavior does not significantly differ from the superposition of the individual spectra of the single films, allowing for concluding that the exchange coupling between the two magnetic layers is too small to give rise to observable shifts. For TMJs grown on a Si or on a MgO substrate the resonance spectra reveal one mode which is nearly identical to the obtained one in the single Co film, while the other observed resonance shows a considerably smaller intensity and cannot be described using the magnetic parameters appropriate to the single Co2MnGe film.

  3. Climatic wind tunnel for wind engineering tasks

    Kuznetsov, Sergeii; Pospíšil, Stanislav; Král, Radomil

    2015-01-01

    Roč. 112, 2-B (2015), s. 303-316. ISSN 1897-628X R&D Projects: GA ČR(CZ) GA14-12892S Keywords : climatic tunnel * wind tunnel * atmospheric boundary layer * flow resistance * wind tunnel contraction Subject RIV: JM - Building Engineering https://suw.biblos.pk.edu.pl/resources/i5/i6/i6/i7/i6/r56676/KuznetsovS_ClimaticWind.pdf

  4. Programmable ferroelectric tunnel memristor

    AndyQuindeau

    2014-02-01

    Full Text Available We report an analogously programmable memristor based on genuine electronic resistive switching combining ferroelectric switching and electron tunneling. The tunnel current through an 8 unit cell thick epitaxial Pb(Zr[0.2]Ti[0.8]O[3] film sandwiched between La[0.7]Sr[0.3]MnO[3] and cobalt electrodes obeys the Kolmogorov-Avrami-Ishibashi model for bidimensional growth with a characteristic switching time in the order of 10^-7 seconds. The analytical description of switching kinetics allows us to develop a characteristic transfer function that has only one parameter viz. the characteristic switching time and fully predicts the resistive states of this type of memristor.

  5. Magneto-transport characteristics of electron-doped Ca0.85Sm0.15MnO3 manganite: Hopping and tunneling

    Hossain Khan, Momin; Pal, Sudipta

    2015-11-01

    In this work we have reported the temperature and magnetic field dependence of resistivity and magnetoresistance in electron-doped polycrystalline Ca0.85Sm0.15MnO3 (CSMO). It shows a robust semiconducting behavior down to the lowest temperature (5 K) of investigation. High-T resistivity of the present sample follows small polaron hopping (SPH) conduction mechanism. The variable range hopping (VRH) model has been found to fit low-T resistivity data. Intermediate-temperature ρ(T) data has been explained using a parallel combination of SPH and 3D-VRH model. The resistivity shows strong dependence on the magnetic field-temperature history. Magnetoresistance (MR) of the sample shows strong irreversibility with respect to sweeping of the field between the highest positive and negative values. Low-ρ state of the envelope curve in MR indicates a manifestation of kinetic arrest of the electronic phase on application of magnetic field. We demonstrates that the sizable MR at low fields dominated by spin-polarized tunneling between the adjacent grains.

  6. Relationship between Human Resources Management Practices, Transformational Leadership, and Knowledge Sharing on Innovation in Iranian Electronic Industry

    Mahmoud Manafi; Indra Devi Subramaniam

    2015-01-01

    Electronic industry needs innovation to survive, and also to compete internationally. This study examines factors that can enhance technical innovation of companies in the electronic industry of Iran. The main purpose of this study is to examine the relationship between human resource management practices, transformational leadership, knowledge sharing, and innovation of the large and major electronic companies.More specifically, the research attempts to examine whether knowledge sharing medi...

  7. Usage of Electronic Resources at Dr T.P.M. Library, Madurai Kamaraj University: A Case Study

    S. Thanuskodi

    2011-11-01

    Full Text Available Information technology (IT has thrown a new challenge to the libraries. The technology has shown a great impact on the services of the libraries. Libraries use IT for better services and satisfying diverse user needs. Libraries have transformed into digital and virtual libraries where books, journals, and magazines have changed into e-books, e-journals, and e-zines. This has increased the global dissemination of information. Electronic resources (e-resources are easily accessible in the remote areas. The e-resources solve storage problems and control the flood of information. Print sources are being digitised. There is a great need to study the use of e-resources and investigate the factors that are a hindrance to their use. The present study is an attempt to examine the usage of electronic resources at Dr T.P.M. Library, Madurai Kamaraj University. Study revealed that MPhil students respondents took the first position in their overall methods of searching e-resources, postgraduate student respondents the second position, PhD Scholar respondents the last position. The study confirmed that respondents were aware of the e-resources and various types of e-resources, e-database, and e-journals. The study recommended the improvement in the access facilities with high internet speed and subscription to more e-resources at Dr T.P.M. Library, Madurai Kamaraj University.

  8. Electronic Transport in Single Molecule Junctions: Control of the Molecule-Electrode Coupling Through Intramolecular Tunneling Barriers

    Danilov, Andrey; Kubatkin, Sergey; Kafanov, Sergey; Hedegård, Per; Stuhr-Hansen, Nicolai; Moth-Poulsen, Kasper; Bjørnholm, Thomas

    2008-01-01

    We report on single molecule electron transport measurements of two oligophenylenevinylene (OPV3) derivatives placed in a nanogap between gold (Au) or lead (Pb) electrodes in a field effect transistor device. Both derivatives contain thiol end groups that allow chemical binding to the electrodes....

  9. New insights into the mechanism of electron transfer within flavohemoglobins: tunnelling pathways, packing density, thermodynamic and kinetic analyses

    El Hammi, E.; Houée-Lévin, Ch.; Řezáč, Jan; Lévy, B.; Demachy, I.; Baciou, L.; de la Lande, A.

    2012-01-01

    Roč. 14, č. 40 (2012), s. 13872-13880. ISSN 1463-9076 Institutional research plan: CEZ:AV0Z40550506 Keywords : metalloenzymes * flavohemoglobin * electron transfer * monooxygenase Subject RIV: CF - Physical ; Theoretical Chemistry Impact factor: 3.829, year: 2012

  10. Spinoff from Wind Tunnel Technology

    1985-01-01

    Douglas Juanarena, a former NASA Langley instrument design engineer, found a solution to the problem of long, repetitive tunnel runs needed to measure airflow pressures. Electronically scanned pressure (ESP) replaced mechanical systems with electronic sensors. Juanarena licensed the NASA-patented technology and now manufactures ESP modules for research centers, aerospace companies, etc.

  11. Immobilization, hybridization, and oxidation of synthetic DNA on gold surface: Electron transfer investigated by electrochemistry and scanning tunneling microscopy

    McEwen, Gerald D.; Chen Fan [Biological Engineering Program, Department of Biological and Irrigation Engineering, Utah State University, 4105 Old Main Hill, Logan, UT 84322-4105 (United States); Zhou Anhong, E-mail: Anhong.Zhou@usu.edu [Biological Engineering Program, Department of Biological and Irrigation Engineering, Utah State University, 4105 Old Main Hill, Logan, UT 84322-4105 (United States)

    2009-06-08

    Fundamental understanding of interfacial electron transfer (ET) among electrolyte/DNA/solid-surface will facilitate the design for electrical detection of DNA molecules. In this report, the electron transfer characteristics of synthetic DNA (sequence from pathogenic Cryptosporidium parvum) self-assembled on a gold surface was electrochemically studied. The effects of immobilization order on the interface ET related parameters such as diffusion coefficient (D{sub 0}), surface coverage ({theta}{sub R}), and monolayer thickness (d{sub i}) were determined by cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). DNA surface density ({Gamma}{sub DNA}) was determined by the integration of the charge of the electro-oxidation current peaks during the initial cyclic voltammetry scans. It was found that the DNA surface densities at different modifications followed the order: {Gamma}{sub DNA} (dsS-DNA/Au) > {Gamma}{sub DNA} (MCH/dsS-DNA/Au) > {Gamma}{sub DNA} (dsS-DNA/MCH/Au). It was also revealed that the electro-oxidation of the DNA modified gold surface would involve the oxidation of nucleotides (guanine and adenine) with a 5.51 electron transfer mechanism and the oxidative desorption of DNA and MCH molecules by a 3 electron transfer mechanism. STM topography and current image analysis indicated that the surface conductivity after each surface modification followed the order: dsS-DNA/Au < MCH/dsS-DNA/Au < oxidized MCH/dsS-DNA/Au < Hoechst/oxidized MCH/dsS-DNA/Au. The results from this study suggested a combination of variations in immobilization order may provide an alternative approach for the optimization of DNA hybridization and the further development for electrical detection of DNA.

  12. Immobilization, hybridization, and oxidation of synthetic DNA on gold surface: Electron transfer investigated by electrochemistry and scanning tunneling microscopy

    Fundamental understanding of interfacial electron transfer (ET) among electrolyte/DNA/solid-surface will facilitate the design for electrical detection of DNA molecules. In this report, the electron transfer characteristics of synthetic DNA (sequence from pathogenic Cryptosporidium parvum) self-assembled on a gold surface was electrochemically studied. The effects of immobilization order on the interface ET related parameters such as diffusion coefficient (D0), surface coverage (?R), and monolayer thickness (di) were determined by cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). DNA surface density (?DNA) was determined by the integration of the charge of the electro-oxidation current peaks during the initial cyclic voltammetry scans. It was found that the DNA surface densities at different modifications followed the order: ?DNA (dsS-DNA/Au) > ?DNA (MCH/dsS-DNA/Au) > ?DNA (dsS-DNA/MCH/Au). It was also revealed that the electro-oxidation of the DNA modified gold surface would involve the oxidation of nucleotides (guanine and adenine) with a 5.51 electron transfer mechanism and the oxidative desorption of DNA and MCH molecules by a 3 electron transfer mechanism. STM topography and current image analysis indicated that the surface conductivity after each surface modification followed the order: dsS-DNA/Au < MCH/dsS-DNA/Au < oxidized MCH/dsS-DNA/Au < Hoechst/oxidized MCH/dsS-DNA/Au. The results from this study suggested a combination of variations in immobilization order may provide an alternative approach for the optimization of DNA hybridization and the further development for electrical detection of DNA.

  13. Electronic Human Resource Management (e-HRM of Hotel Business in Phuket

    Kitimaporn Choochote

    2015-04-01

    Full Text Available This research aims to study the pattern of the electronic human resources management (e-HRM of the hotel business in Phuket. The study is conducted with the implementation of field data and in-depth interview of hotels’ HR managers. In consequence, the study reveals that the hotel business has applied the use of the e-HRM varying in job recruitment (15 percent, employee engagement (55 percent, organizational file structure (10 percent, idea and creativity exchanges (38 percent and assessment system (6 percent. However, considered as 100 percent, the hotel business has not prepared to apply the use of the e-HRM in salary system, learning and training program, welfare allocation and career development.

  14. Factors Influencing Students' Use of Electronic Resources and their Opinions About this Use: The Case of Students at An-Najah National University

    Wajeeh M. Daher

    2010-12-01

    Full Text Available Electronic resources are becoming an integral part of the modern life and of the educational scene, especially the high education scene. In this research we wanted to verify what influences first degree university students' use of electronic resources and their opinions regarding this use. Collecting data from 202 students and analyzing it using SPSS, we found that more than one half of the participants had high level of electronic media use and more than one third had moderate level of electronic media use. These levels of use indicate the students' awareness of the role and benefits of electronic media use. Regarding the factors that influence the students' se of electronic resources we found that the student's use of electronic resources had significant strong positive relationships with the provision of electronic resources by the academic institution. It had significant moderate positive relationships with the resources characteristics and the course requirement, and had significant weak relationships with the instructor's support and the student's characteristics. We explained these relationships as resulting from the influence of the surrounding community. Regarding the students' opinions about the use of electronic resources, we found that the student's opinion of electronic resources has significant strong positive relationships with student's use of electronic resources, level of this use, the academic institution available facilities, student's characteristics and resources characteristics. It does not have significant relationships with the instructor's support or the course requirement. We explained these relationships depending on activity theory and its integration with ecological psychology.

  15. Caring for children and adolescents with epilepsy: creating an innovative electronic educational resource.

    Connolly, Anne M; Slade, Rob; Uppal, Preena; Bye, Ann M E

    2014-10-01

    The majority of children and adolescents with epilepsy are managed in the community setting by general paediatricians. However, there is a paucity of practical, relevant information and standardised management documents assisting paediatricians. In the era of sub-specialisation, an electronic educational resource developed by specialists in epilepsy and paediatrics enhances the interface between tertiary and secondary/primary care. We aimed to create a website (www.pennsw.com.au) designed to optimise the care of all children and adolescents living with epilepsy and to assess its clinical usefulness. The site provides clinicians and families an aligned resource, including key information on epilepsy syndromes, medication usage and adverse effects, safety (sleep deprivation, water sports), driving, pregnancy, psychosocial impact of epilepsy and coping skills. General paediatricians and carers completed a questionnaire, utilising rating scales and open ended questions, to evaluate design, content and clinical usefulness. Forty-nine general paediatricians with a median 12 years of paediatric practice participated. Thirty-two carers participated. Epilepsy syndrome was focal in 59% of the children and generalised in 41%. The majority of participants (paediatricians: 84-100%, families: 69-100%) rated the website as well designed, practical, informative and clinically useful. General paediatricians considered the "Medication" pages and "Epilepsy Management Documents" as practically useful. Carers recorded the "Family Resources", seizure recording documents, the support information on mental health, and the "Coping with Epilepsy" segment as most informative. General paediatricians and carers highly valued the website, reflected by 120,000 page views in 12 months since its launch. PMID:24906210

  16. Tunneling spectroscopy of novel superconductors

    Recent discoveries of exciting new superconductors have led to further exciting speculations about novel mechanisms and/or pairing. Tunneling spectroscopy can again play an important role in establishing the applicability of these ideas to specific superconductors. In addition to the traditional role of verifying in detail the electron-phonon coupling through ?2F, in many cases the magnitude of the gap compared to the BCS prediction or the crystalline gap anisotropy can reveal direct information about novel mechanisms and/or pairing. Since many of these new materials have only been available as bulk samples, or bulk single-crystal studies are desired, the technique of vacuum tunneling spectroscopy, pioneered by Poppe (1981) for superconductors, is most appropriate. However, thick, nonconducting surface layers are often found which prevent true vacuum tunneling. For these samples, mechanical contact of the tunneling tip is required to break through the surface layer to the superconductor below. The resulting point-contact tunneling can, however, emulate many of the results of true tunneling through a vacuum or insulator. In this paper, they shall briefly review relevant tunneling techniques and some recent experiments on magnetic, organic, heavy fermion and high-T/sub c/ oxide superconductors. Connections are made to theoretical ideas, especially regarding novel mechanisms and/or pairing

  17. Micromachined Tunneling Displacement Transducers for Physical Sensors

    Kenny, T. W.; Kaiser, W. J.; Podosek, J. A.; Rockstad, H. K.; Reynolds, J. K.; Vote, E. C.

    1993-01-01

    We have designed and constructed a series of tunneling sensors which take advantage of the extreme position sensitivity of electron tunneling. In these sensors, a tunneling displacement transducer, based on scanning tunneling microscopy principles, is used to detect the signal-induced motion of a sensor element. Through the use of high-resonant frequency mechanical elements for the transducer, sensors may be constructed which offer wide bandwidth, and are robust and easily operated. Silicon micromachining may be used to fabricate the transducer elements, allowing integration of sensor and control electronics. Examples of tunneling accelerometers and infrared detectors will be discussed. In each case, the use of the tunneling transducer allows miniaturization of the sensor as well as enhancement of the sensor performance.

  18. Classical Tunneling

    Cohn, A G; Rabinowitz, Mario

    2003-01-01

    A classical representation of an extended body over barriers of height greater than the energy of the incident body is shown to have many features in common with quantum tunneling as the center-of-mass literally goes through the barrier. It is even classically possible to penetrate any finite barrier with a body of arbitrarily low energy if the body is sufficiently long. A distribution of body lengths around the de Broglie wavelength leads to reasonable agreement with the quantum transmission coefficient.

  19. Classical Tunneling

    Cohn, Arthur; Rabinowitz, Mario

    2003-01-01

    A classical representation of an extended body over barriers of height greater than the energy of the incident body is shown to have many features in common with quantum tunneling as the center-of-mass literally goes through the barrier. It is even classically possible to penetrate any finite barrier with a body of arbitrarily low energy if the body is sufficiently long. A distribution of body lengths around the de Broglie wavelength leads to reasonable agreement with the quantum transmission...

  20. In situ Control of Si/Ge Growth on Stripe-Patterned Substrates Using Reflection High-Energy Electron Diffraction and Scanning Tunneling Microscopy

    Sanduijav B

    2010-01-01

    Full Text Available Abstract Si and Ge growth on the stripe-patterned Si (001 substrates is studied using in situ reflection high-energy electron diffraction (RHEED and scanning tunneling microscopy (STM. During Si buffer growth, the evolution of RHEED patterns reveals a rapid change of the stripe morphology from a multifaceted “U” to a single-faceted “V” geometry with {119} sidewall facets. This allows to control the pattern morphology and to stop Si buffer growth once a well-defined stripe geometry is formed. Subsequent Ge growth on “V”-shaped stripes was performed at two different temperatures of 520 and 600°C. At low temperature of 520°C, pronounced sidewall ripples are formed at a critical coverage of 4.1 monolayers as revealed by the appearance of splitted diffraction streaks in RHEED. At 600°C, the ripple onset is shifted toward higher coverages, and at 5.2 monolayers dome islands are formed at the bottom of the stripes. These observations are in excellent agreement with STM images recorded at different Ge coverages. Therefore, RHEED is an efficient tool for in situ control of the growth process on stripe-patterned substrate templates. The comparison of the results obtained at different temperature reveals the importance of kinetics on the island formation process on patterned substrates.

  1. The structures and dynamics of atomic and molecular adsorbates on metal surfaces by scanning tunneling microscopy and low energy electron diffraction

    Yoon, Hyungsuk Alexander

    1996-12-01

    Studies of surface structure and dynamics of atoms and molecules on metal surfaces are presented. My research has focused on understanding the nature of adsorbate-adsorbate and adsorbate-substrate interactions through surface studies of coverage dependency and coadsorption using both scanning tunneling microscopy (STM) and low energy electron diffraction (LEED). The effect of adsorbate coverage on the surface structures of sulfur on Pt(111) and Rh(111) was examined. On Pt(111), sulfur forms p(2x2) at 0.25 ML of sulfur, which transforms into a more compressed ({radical}3x{radical}3)R30{degrees} at 0.33 ML. On both structures, it was found that sulfur adsorbs only in fcc sites. When the coverage of sulfur exceeds 0.33 ML, it formed more complex c({radical}3x7)rect structure with 3 sulfur atoms per unit cell. In this structure, two different adsorption sites for sulfur atoms were observed - two on fcc sites and one on hcp site within the unit cell.

  2. Lateral ordering of PTCDA on the clean and the oxygen pre-covered Cu(100 surface investigated by scanning tunneling microscopy and low energy electron diffraction

    Stefan Gärtner

    2014-09-01

    Full Text Available We have investigated the adsorption of perylene-3,4,9,10-tetracarboxylic acid dianhydride (PTCDA on the clean and on the oxygen pre-covered Cu(100 surface [referred to as (√2 × 2√2R45° – 2O/Cu(100] by scanning tunneling microscopy (STM and low energy electron diffraction (LEED. Our results confirm the (4√2 × 5√2R45° superstructure of PTCDA/Cu(100 reported by A. Schmidt et al. [J. Phys. Chem. 1995, 99,11770–11779]. However, contrary to Schmidt et al., we have no indication for a dissociation of the PTCDA upon adsorption, and we propose a detailed structure model with two intact PTCDA molecules within the unit cell. Domains of high lateral order are obtained, if the deposition is performed at 400 K. For deposition at room temperature, a significant density of nucleation defects is found pointing to a strong interaction of PTCDA with Cu(100. Quite differently, after preadsorption of oxygen and formation of the (√2 × 2√2R45° – 2O/Cu(100 superstructure on Cu(100, PTCDA forms an incommensurate monolayer with a structure that corresponds well to that of PTCDA bulk lattice planes.

  3. Plastics disassembly versus bulk recycling: engineering design for end-of-life electronics resource recovery.

    Rios, Pedro; Stuart, Julie Ann; Grant, Ed

    2003-12-01

    Annual plastic flows through the business and consumer electronics manufacturing supply chain include nearly 3 billion lb of high-value engineering plastics derived from petroleum. The recovery of resource value from this stream presents critical challenges in areas of materials identification and recycling process design that demand new green engineering technologies applied together with life cycle assessment and ecological supply chain analysis to create viable plastics-to-plastics supply cycles. The sustainable recovery of potentially high-value engineering plastics streams requires that recyclers either avoid mixing plastic parts or purify later by separating smaller plastic pieces created in volume reduction (shredding) steps. Identification and separation constitute significant barriers in the plastics-to-plastics recycling value proposition. In the present work, we develop a model that accepts randomly arriving electronic products to study scenarios by which a recycler might identify and separate high-value engineering plastics as well as metals. Using discrete eventsimulation,we compare current mixed plastics recovery with spectrochemical plastic resin identification and subsequent sorting. Our results show that limited disassembly with whole-part identification can produce substantial yields in separated streams of recovered engineering thermoplastics. We find that disassembly with identification does not constitute a bottleneck, but rather, with relatively few workers, can be configured to pull the process and thus decrease maximum staging space requirements. PMID:14700333

  4. The Impact of Electronic Banking on Human Resources Performance in the Nigerian Banking Industry

    Ojokuku, R. M.

    2012-08-01

    Full Text Available The survey examined the impact of electronic banking on Human Resource (HR performance in the Nigerian banking industry, using First Bank Plc as a case study. The objective was to determine how the introduction of e-Banking has impacted on the efficiency and effectiveness of service delivery by the bank's personnel and on bank-customers relationship and customer satisfaction. Structured questionnaire was used with the aid of personal interview to collect data from thirty five respondents randomly sampled from five purposively selected branches of First Bank Plc. Chi-square test was applied for data analysis. Result showed among other things that introduction of electronic banking has impacted positively on the bank's HR performance, in terms of improved efficiency and effectiveness of service delivery by bank personnel. Bank-customer relationship and customers satisfaction was also found to have been greatly enhanced. Hence, Government should lower the tariff on information technology-aided tools and equipment imported and possibly subsidized the cost.

  5. The electronic encapsulation of knowledge in hydraulics, hydrology and water resources

    Abbott, Michael B.

    The rapidly developing practice of encapsulating knowledge in electronic media is shown to lead necessarily to the restructuring of the knowledge itself. The consequences of this for hydraulics, hydrology and more general water-resources management are investigated in particular relation to current process-simulation, real-time control and advice-serving systems. The generic properties of the electronic knowledge encapsulator are described, and attention is drawn to the manner in which knowledge 'goes into hiding' through encapsulation. This property is traced in the simple situations of pure mathesis and in the more complex situations of taxinomia using one example each from hydraulics and hydrology. The consequences for systems architectures are explained, pointing to the need for multi-agent architectures for ecological modelling and for more general hydroinformatics systems also. The relevance of these developments is indicated by reference to ongoing projects in which they are currently being realised. In conclusion, some more general epistemological aspects are considered within the same context. As this contribution is so much concerned with the processes of signification and communication, it has been partly shaped by the theory of semiotics, as popularised by Eco ( A Theory of Semiotics, Indiana University, Bloomington, 1977).

  6. A study of lawyers’ information behaviour leading to the development of two methods for evaluating electronic resources

    Makri, S

    2009-01-01

    In this thesis we examine the information behaviour displayed by a broad cross-section of academic and practicing lawyers and feed our findings into the development of the Information Behaviour (IB) methods - two novel methods for evaluating the functionality and usability of electronic resources. We captured lawyers’ information behaviour by conducting naturalistic observations, where we asked participants to think aloud whilst using existing resources to ‘find information required for t...

  7. Enhancement of tunnel magnetoresistance in magnetic tunnel junction by a superlattice barrier

    Chen, C. H.; Hsueh, W. J., E-mail: hsuehwj@ntu.edu.tw [Nanomagnetism Group, Department of Engineering Science and Ocean Engineering, National Taiwan University, 1, Sec. 4, Roosevelt Road, Taipei 10660, Taiwan (China)

    2014-01-27

    Tunnel magnetoresistance of magnetic tunnel junction improved by a superlattice barrier composed of alternate layers of a nonmagnetic metal and an insulator is proposed. The forbidden band of the superlattice is used to predict the low transmission range in the superlattice barrier. By forbidding electron transport in the anti-parallel configuration, the tunnel magnetoresistance is enhanced in the superlattice junction. The results show that the tunnel magnetoresistance ratio for a superlattice magnetic tunnel junction is greater than that for traditional single or double barrier junctions.

  8. Study of the influence of different dopings on the electronic structure of deposed single fullerenes by means of scanning tunnel spectroscopy

    In this PhD thesis the scanning tunneling microscope is used to perform topographic and spectroscopic investigations on various fullerenes (C60, Ce rate at C60, Ce rate at C50, Ce rate at C44, Ce rate at C36, La rate at C44, La rate at C60, Y rate at C60, and C59N). C60 and the endohedral doped fullerenes have been produced in a laser vaporization source and have been mass-selected prior to soft-landing onto a highly oriented pyrolytic graphite. (C59N)2-powder has been evaporated in situ. After localising the deposited fullerenes onto the substrate surface using topographic measurements, spectroscopic investigations has been performed locally on the individual fullerenes. The results of these investigations demonstrated a dramatic change of the electronic structure depending on the doping and geometric structure of the fullerenes. Specifically the gap of all the endohedral doped fullerenes is smaller than the gap of pure C60. In detail, all cerium-doped fullerenes possess semiconducting properties with an increasing gap for decreasing cage size. No gap has been detected for La rate at C60 und Y rate at C60. Thus, these fullerenes exhibit metallic behaviour. For endohedral doped fullerenes there is only a weak interaction with the substrate. The interaction effect on the electronic structure is negligible in comparison with the effect of endohedral doping. The gap of the heterofullerene C59N is large in comparison with the gap of the endohedral doped fullerenes but less than the gap of pure C60. Furthermore, there is a strong interaction between the heterofullerene and the graphit substrate. (orig.)

  9. Evolution and collapse of electron quasi-stationary states in plane symmetric three-barrier resonance-tunnel structures

    A theory of evolution and collapse of resonance pairs due to variations in inner barrier strength (thickness) is developed by using the model of effective masses and symmetric rectangular potential barriers for an electron in the plane three-barrier structure. The analytical and numerical calculations of spectral parameters (resonance energy and width) are performed with the use of transparent coefficient and probability distribution function within the transfer matrix and scattering S-matrix. It is shown that the collapse of resonance energies and widths of all quasi-stationary states in the symmetric three-barrier structure happens almost at the same values of inner barrier width, which are somewhat larger than the sum of outer thicknesses. It is found that the δ-model as compared to the rectangular barrier one, gives much higher values of resonance energies (by the order of percents) and resonance widths (almost twice).

  10. Molecular electronics exploiting sharp structure in the electrode density-of-states. Negative differential resistance and Resonant Tunneling in a poled molecular layer on Al/LiF electrodes

    Lu, Z H; Khangura, R S; Zgierski, M Z; Ritchie, D; Zgierski, Marek Z.; Ritchie, Douglas

    2004-01-01

    Density-functional calculations are used to clarify the role of an ultrathin LiF layer on Al electrodes used in molecular electronics. The LiF layer creates a sharp density of states (DOS), as in a scanning-tunneling microscope (STM) tip. The sharp DOS, coupled with the DOS of the molecule leads to negative differential resistance (NDR). Electron transfer between oriented molecules occurs via resonant tunneling. The I-V characteristic for a thin-film of tris (8-hydroxyquinoline)- aluminum (AlQ) molecules, oriented using electric-field poling, and sandwiched between two Al/LiF electrodes is in excellent agreement with theory. This molecular device presents a new paradigm for a convenient, robust, inexpensive alternative to STM or mechanical break-junction structures.

  11. Andreev reflection and Klein tunneling in graphene

    Beenakker, C.W.J.

    2007-01-01

    This is a colloquium-style introduction to two electronic processes in a carbon monolayer (graphene), each having an analogue in relativistic quantum mechanics. Both processes couple electron-like and hole-like states, through the action of either a superconducting pair potential or an electrostatic potential. The first process, Andreev reflection, is the electron-to-hole conversion at the interface with a superconductor. The second process, Klein tunneling, is the tunneling through a p-n jun...

  12. Tunneling recombination luminescence of glassy polyethylene adipate γ-irradiated at low temperature and effect of electron scavengers

    The isothermal luminescence (ITL) from glassy polyethylene adipate (PEA) γ-irradiated at 77 K was observed over a long period of time, together with effect of the electron scavengers on it. The decay behavior of ITL is similar to that of polyethylene terephthalate or polycrystalline PEA obtained previously, so that the decay obeys the decay function I(t) = I0/(1 + αt)sup(m). The detailed discussion on the parameters included in the decay function is given. Differences in the parameters between different materials or different physical states are found not to be very large, except the parameter I0. Addition of biphenyl into PEA enhances considerably the intensity of ITL and causes the luminescence center to exchange from the ester cation into the biphenyl cation. In the biphenyl doped PEA, the possibility of the triplet-triplet energy transfer from the excited ester group to the biphenyl and the positive charge transfer from the ester cation to the biphenyl are shown. (author)

  13. Carpal Tunnel Surgery

    Full Text Available ... carried out for the condition of carpal tunnel syndrome. Carpal Tunnel Syndrome is a neuropathy where the median nerve gets ... of the hand. The surgery for carpal tunnel syndrome consists of a release of the transverse carpal ...

  14. Time, tunneling and turbulence

    Azbel' , M Ya [School of Physics and Astronomy, Tel Aviv University (Israel)

    1998-06-30

    This paper considers tunneling traversal time; tunneling through an alternating potential, its enhancement and its fractal (Hofstadter butterfly) and chaotic resonances; and Hartree liquid resonance tunneling and its (specifically quantum) instability and turbulence. (special issue)

  15. Tunneling magnetoresistance in ferromagnetic junctions: bias dependence

    Electron tunneling between two ferromagnetic electrodes across an insulating barrier is analysed theoretically and experimentally. The barrier is either uniform or it includes a layer of small magnetic metallic particles. Particular attention is paid to the origin of the tunneling magnetoresistance and its bias dependence, as well as to the effects due to Coulomb blockade. (author)

  16. True Serials: A True Solution for Electronic Resource Management Needs in a Medium-Size Academic Library

    Milczarski, Vivian; Garofalo, Denise A.

    2011-01-01

    A desire for more functionality seemed to clash with the fiscal reality of limited funds, but after investigating alternatives, Mount Saint Mary College was able to provide its faculty and students with a more useful and function-rich electronic resource management through a move to a hosted open source service. (Contains 8 figures.)

  17. Tunneling technologies for the collider ring tunnels

    The Texas site chosen for the Superconducting Super Collider has been studied, and it has been determined that proven, conventional technology and accepted engineering practice are suitable for constructing the collider tunnels. The Texas National Research Laboratory Commission report recommended that two types of tunneling machines be used for construction of the tunnels: a conventional hard rock tunnel boring machine (TBM) for the Austin chalk and a double shielded, rotary TBM for the Taylor marl. Since the tunneling machines usually set the pace for the project, efficient planning, operation, and coordination of the tunneling system components will be critical to the schedule and cost of the project. During design, tunneling rate prediction should be refined by focusing on the development of an effective tunneling system and evaluating its capacity to meet or exceed the required schedules. 8 refs., 13 figs

  18. Self-assembled monolayers of radical molecules physisorbed on HOPG(0 0 0 1) substrate studied by scanning tunnelling microscopy and electron paramagnetic resonance techniques

    In this paper, we present a combined STM and EPR study on the adsorption and self-organization of monolayers formed from 2-(14-Carboxytetradecyl)-2-ethyl-4,4-dimethyl-3-oxazolidinyloxy (16DS) and 4',4'-Dimethylspiro(5α-cholestane-3,2'-oxazolidin)-3'-yloxy (CSL) adsorbed on a highly oriented pyrolitic graphite HOPG(0 0 0 1) substrate. Both 16DS and CSL molecules are persistent free radicals containing a paramagnetic doxyl group. The STM measurements of 16DS on HOPG(0 0 0 1) were performed at the liquid-solid interface while the studies of CSL on HOPG(0 0 0 1) were carried out under ultrahigh vacuum conditions. It was found that the 16DS molecules on the HOPG(0 0 0 1) surface form a highly-ordered monolayer with a domain structure. The high-resolution STM images show structural details of 16DS molecules on HOPG(0 0 0 1) revealing the paramagnetic doxyl group. In contrast, CSL molecules on HOPG(0 0 0 1) form a well-ordered monolayer without domain structure. The EPR results indicate that both compounds deposited on HOPG(0 0 0 1) substrate are not reduced and retain their paramagnetic character. We believe that the molecular systems described can be used in single spin detection experiments using an electron spin noise-scanning tunnelling microscopy (ESN-STM) technique. In particular, the possibility of obtaining contrast spin signals from the paramagnetic and diamagnetic parts of molecules increases the significance of our results.

  19. Comparison of electron transmittances and tunneling currents in an anisotropic TiNx/HfO2/SiO2/p-Si(100) metal-oxide-semiconductor (MOS) capacitor calculated using exponential- and Airy-wavefunction approaches and a transfer matrix method

    Analytical expressions of electron transmittance and tunneling current in an anisotropic TiNx/HfO2/SiO2/p-Si(100) metal-oxide-semiconductor (MOS) capacitor were derived by considering the coupling of transverse and longitudinal energies of an electron. Exponential and Airy wavefunctions were utilized to obtain the electron transmittance and the electron tunneling current. A transfer matrix method, as a numerical approach, was used as a benchmark to assess the analytical approaches. It was found that there is a similarity in the transmittances calculated among exponential- and Airy-wavefunction approaches and the TMM at low electron energies. However, for high energies, only the transmittance calculated by using the Airy-wavefunction approach is the same as that evaluated by the TMM. It was also found that only the tunneling currents calculated by using the Airy-wavefunction approach are the same as those obtained under the TMM for all range of oxide voltages. Therefore, a better analytical description for the tunneling phenomenon in the MOS capacitor is given by the Airy-wavefunction approach. Moreover, the tunneling current density decreases as the titanium concentration of the TiNx metal gate increases because the electron effective mass of TiNx decreases with increasing nitrogen concentration. In addition, the mass anisotropy cannot be neglected because the tunneling currents obtained under the isotropic and anisotropic masses are very different. (semiconductor devices)

  20. Coherent and phonon-assisted tunnelling in asymmetric double barrier resonant tunnelling structures

    We present a theory for calculating the phonon-assisted tunnelling current in asymmetric double barrier resonant tunnelling structures (DBRTS), in which all of the phonon modes including the interface modes and the confined bulk-like LO phonons and the conduction band nonparabolicity are considered. An important physical picture about coherent and phonon-assisted tunnelling is given. The coherent tunnelling current can be directly determined by both the width of the resonant level and the peak value of the transmission coefficient at the resonant level. The phonon-assisted tunnelling current mainly comes from electron interaction with higher frequency interface phonons (especially the interface phonons localised at either interface of the left barrier). Phonon-assisted tunnelling makes a significant contribution to the valley current. The subband nonparabolicity strongly influences on electron-phonon scattering and current-to-voltage characteristics. A specially designed asymmetric DBRTS may have an improved performance over the symmetric DBRTS. Copyright (2000) CSIRO Australia

  1. Electronic Phase Separation in Pr1x(Ca, Sr)xMnO3δ and Tunneling Magnetoresistance in Sr2FeMoO6

    In this work, we approach two aspects of the physics of magnetic perovskites presenting colossal magnetoresistance (CMR). Firstly, we go deeply into the phase separation (PS) between the ferromagnetic (FM) metallic state and the antiferro-magnetic (AFM) charge ordered (CO) insulating state, in manganites of the type Pr1x(Ca,Sr)xMnO3δ. Secondly, and more briefly, we analyze the problem of the influence of the grain boundary insulating barriers on the tunneling magnetoresistance in the Sr2FeMoO6 double perovskite.The use of different measurement techniques allowed us to make a complete characterization of the PS state in the compounds Pr0.65Ca0.35-ySryMnO3 for 0≤ y ≤ 0.20, Pr0.5Sr0.5-zCazMnO3 for z = 0, 0.1 and 0.2 and Pr1-xCax-0.3Sr0.3MnO3 (0.46≤ x ≤ 0.54), that were prepared in our laboratory.The structural studies of these materials were performed at room temperature by means of X-ray diffraction. At low temperatures, the phase coexistence was observed by global magnetic techniques, as SQUID magnetometry and neutron diffraction, as well as measurements sensitive to the local magnetic environment, as electron spin resonance (ESR).The electrical characterization, performed through resistivity and thermoelectric power (Seebeck effect) measurements, allowed us to elucidate the characteristics of the metal-insulator transitions, which are directly related to the magnetic properties of the PS state. In Pr0.65Ca0.35-ySryMnO3 compound we studied the effects of the average ionic radius of the A site of the perovskite (A> ) keeping constant the carrier concentration (x = 0.35). This material presents an evolution from a CO insulating phase for small A> (y =0), towards the FM metallic phase for large A> (y = 0.20). In the intermediate region, where a first order metal-insulator transition occurs, the strong competition between both phases induces the PS state in a wide temperature range. In order to quantify this coexistence, we obtained the FM phase fraction (X) as a function of temperature from the magnetization data. The effects of the disorder on the first-order metal-insulator transition is one of the proposed mechanisms for the phase coexistence. Magnetization curves as a function of magnetic field (H) in the PS state show the existence of two dynamic regimes separated by the field Hc, which is interpreted as a critical field for the depinning of domain walls. From the analysis of the thermally activated susceptibility at H c, we estimate the size of the FM clusters as ∼130nm, in agreement with the characteristic sizes observed by electron microscopy. The percolative analysis of the conductivity, σ ∼ (X - Xc)p, indicates that the critical percolation threshold is Xc ≅ 15.5%, in good agreement with the expected values in three-dimensional systems. On the other hand, the obtained critical exponent p ∼ 1, is lower than the expected value for these systems (p3D ∼ 2). This could be related to geometrical effects of the ferromagnetic domains or to the presence of a third two-dimensional phase that we observe in the neutron diffraction experiments. The magnetoresistance also presents very different properties for the samples with a percolated FM phase. As a result of this, to obtain the largest values of CMR it is convenient to prepare samples with a FM phase fraction as close as possible to the critical percolation threshold. In the Pr0.5Ca0.2Sr0.3MnO3-δ (δ = 0 and 0.01) we studied the effects of the oxygen vacancies on the phase separation. We showed the the vacancies located in the AFM volume generate a local FM polarization in their vicinity, within a radius of ∼ 1nm. At the same time, this favors the percolation of the metallic phase, inducing a decrease of the resistivity. However, the effect of the vacancies is negligible as compared to the PS already present in the stoichiometric compound. This observation rules out the oxygen vacancies as the root of the origin of the PS phenomenon. Finally, in the ordered double perovskite Sr2FeMoO6 the studies were mainly oriented to the magnetotransport properties. In this material we have analyzed the influence of the oxidation of the grain boundaries (gb) on the tunneling magnetoresistance (TMR), which is observed in ferromagnetic perovskites at low magnetic fields. We showed that the oxidation of the gb induces the formation of SrMoO4 impurities that reinforce the intergranular insulating barriers, producing an increase of resistivity and notably improving the TMR without affecting the magnetism.By other way, we found the the effects of the Fe/Mo disorder are important for the TMR only when the gb barriers are small. However, when the gb resistance increases due to the oxidation, the intergranular barriers dominate and determine the value of the tunneling magnetoresistance

  2. Use and Cost of Electronic Resources in Central Library of Ferdowsi University Based on E-metrics

    Mohammad Reza Davarpanah

    2012-07-01

    Full Text Available The purpose of this study was to investigate the usage of electronic journals in Ferdowsi University, Iran based on e-metrics. The paper also aimed to emphasize the analysis of cost-benefit and the correlation between the journal impact factors and the usage data. In this study experiences of Ferdowsi University library on licensing and usage of electronic resources was evaluated by providing a cost-benefit analysis based on the cost and usage statistics of electronic resources. Vendor-provided data were also compared with local usage data. The usage data were collected by tracking web-based access locally, and by collecting vender-provided usage data. The data sources were one-year of vendor-supplied e-resource usage data such as Ebsco, Elsevier, Proquest, Emerald, Oxford and Springer and local usage data collected from the Ferdowsi university web server. The study found that actual usage values differ for vendor-provided data and local usage data. Elsevier has got the highest usage degree in searches, sessions and downloads. Statistics also showed that a small number of journals satisfy significant amount of use while the majority of journals were used less frequent and some were never used at all. The users preferred the PDF rather than HTML format. The data in subject profile suggested that the provided e-resources were best suited to certain subjects. There was no correlation between IF and electronic journal use. Monitoring the usage of e-resources gained increasing importance for acquisition policy and budget decisions. The article provided information about local metrics for the six surveyed vendors/publishers, e.g. usage trends, requests per package, cost per use as related to the scientific specialty of the university.

  3. Electronic characterization of LaAlO{sub 3}-SrTiO{sub 3} interfaces by scanning tunneling spectroscopy; Elektronische Charakterisierung von LaAlO{sub 3}-SrTiO{sub 3}-Grenzflaechen mittels Rastertunnelspektroskopie

    Breitschaft, Martin

    2010-10-22

    When LaAlO{sub 3} is epitaxially grown on TiO{sub 2}-terminated SrTiO{sub 3}, an electrically conducting interface is generated. In this respect, the physical properties of the interface differ substantially from those of both LaAlO{sub 3} and SrTiO{sub 3}, which are electrically insulating in bulk form. This dissertation looks into the question of the microscopic structure of the conducting two-dimensional interface electron system. Comparing the electronic density of states of LaAlO{sub 3}-SrTiO{sub 3} interfaces measured by scanning tunneling spectroscopy with results of density functional theory, the interface electron system is found to be substantially coined by the hosting transition metal lattices. The comparison yields a detailed picture of the microscopic structure of the interface electron system. (orig.)

  4. Atomic and Molecular Manipulation with a Scanning Tunneling Microscope

    Sperl, Alexander

    2011-01-01

    In this thesis structural, electronic, chemical properties and dynamic processes of adsorbed nanostructures on metal surfaces are investigated with a low-temperature scanning tunneling microscope (STM).

  5. Two vertically coupled quantum rings with tunneling

    L. K., Castelano; G.-Q., Hai; B., Partoens; F. M., Peeters.

    2006-09-01

    Full Text Available We study the effect of tunneling on the electronic structure of two vertically coupled quantum rings within the spin density functional theory. The ground state configurations of the coupled rings are obtained for a system with 10 electrons as a function of the ring radius and the inter-ring distanc [...] e. For small ring radius, our results recover those of coupled quantum dots. For large ring radius, new ground state configurations are found in the strong tunneling regime.

  6. Superpoissonian shot noise in organic magnetic tunnel junctions

    Organic molecules have recently revolutionized ways to create new spintronic devices. Despite intense studies, the statistics of tunneling electrons through organic barriers remains unclear. Here, we investigate conductance and shot noise in magnetic tunnel junctions with 3,4,9,10-perylene-teracarboxylic dianhydride (PTCDA) barriers a few nm thick. For junctions in the electron tunneling regime, with magnetoresistance ratios between 10% and 40%, we observe superpoissonian shot noise. The Fano factor exceeds in 1.52 times the maximum values reported for magnetic tunnel junctions with inorganic barriers, indicating spin dependent bunching in tunneling. We explain our main findings in terms of a model which includes tunneling through a two level (or multilevel) system, originated from interfacial bonds of the PTCDA molecules. Our results suggest that interfaces play an important role in the control of shot noise when electrons tunnel through organic barriers

  7. Superpoissonian shot noise in organic magnetic tunnel junctions

    Cascales, Juan Pedro; Martinez, Isidoro; Aliev, Farkhad G., E-mail: farkhad.aliev@uam.es [Dpto. Fisica Materia Condensada C3, Instituto Nicolas Cabrera (INC), Condensed Matter Physics Institute (IFIMAC), Universidad Autonoma de Madrid, Madrid 28049 (Spain); Hong, Jhen-Yong; Lin, Minn-Tsong, E-mail: mtlin@phys.ntu.edu.tw [Department of Physics, National Taiwan University, Taipei 10617, Taiwan and Institute of Atomic and Molecular Sciences, Academia Sinica, Taipei 10617, Taiwan (China); Szczepański, Tomasz; Dugaev, Vitalii K. [Department of Physics, Rzeszów University of Technology, al. Powstańców Warszawy 6, 35-959 Rzeszów (Poland); Barnaś, Józef [Faculty of Physics, Adam Mickiewicz University, ul. Umultowska 85, 61-614 Poznań, Poland and Institute of Molecular Physics, Polish Academy of Sciences, ul. Smoluchowskiego 17, 60-179 Poznań (Poland)

    2014-12-08

    Organic molecules have recently revolutionized ways to create new spintronic devices. Despite intense studies, the statistics of tunneling electrons through organic barriers remains unclear. Here, we investigate conductance and shot noise in magnetic tunnel junctions with 3,4,9,10-perylene-teracarboxylic dianhydride (PTCDA) barriers a few nm thick. For junctions in the electron tunneling regime, with magnetoresistance ratios between 10% and 40%, we observe superpoissonian shot noise. The Fano factor exceeds in 1.5–2 times the maximum values reported for magnetic tunnel junctions with inorganic barriers, indicating spin dependent bunching in tunneling. We explain our main findings in terms of a model which includes tunneling through a two level (or multilevel) system, originated from interfacial bonds of the PTCDA molecules. Our results suggest that interfaces play an important role in the control of shot noise when electrons tunnel through organic barriers.

  8. Tunneling spectroscopy on grain boundary junctions in electron-doped high-temperature superconductors; Tunnelspektroskopie an Korngrenzenkontakten aus elektronendotierten Hochtemperatur-Supraleitern

    Welter, B.

    2007-12-07

    Some methods are developed anf presented, by means of which from experimental tunnel spectra, especially on symmetric SIS contacts, informations about the properties of electrodes and tunnel barriers can be obtained. Especially a procedure for the numerical unfolding of symmetric SIS spectra is proposed. Furthermore a series of models is summarized, which can explain the linear background conductivity observed in many spectra on high-temperature superconductors. The results of resistance measurements on film bridges are presented. Especially different methods for the determination of H{sub c2}(T) respectively H{sub c2}(0) are presented and applied to the experimental data. Finally the results of the tunnel-spectroscopy measurements are shown.

  9. Laser tunneling from aligned molecules

    Smeenk, C T L; Sokolov, A V; Spanner, M; Lee, K F; Staudte, A; Villeneuve, D M; Corkum, P B

    2013-01-01

    We study multi-photon ionization from N_2, O_2 and benzene using circularly polarized light. By examining molecular frame photo-electron angular distributions, we illustrate how multi-photon ionization acts a momentum-selective probe of the local electron density in the Dyson orbitals for these molecules. We find good agreement with calculations based on a tunneling model and including saturation effects.

  10. Construction of a four tip scanning tunneling microscope/scanning electron microscope combination and conductivity measurements of silicide nanowires; Aufbau einer Vierspitzen-Rastertunnelmikroskop/Rasterelektronenmikroskop-Kombination und Leitfaehigkeitsmessungen an Silizid Nanodraehten

    Zubkov, Evgeniy

    2013-09-01

    In this work the combination of a four-tip scanning tunneling microscope with a scanning electron microscope is presented. By means of this apparatus it is possible to perform the conductivity measurements on the in-situ prepared nanostructures in ultra-high vacuum. With the aid of a scanning electron microscope (SEM), it becomes possible to position the tunneling tips of the four-tip scanning tunneling microscope (STM), so that an arrangement for a four-point probe measurement on nanostructures can be obtained. The STM head was built according to the novel coaxial Beetle concept. This concept allows on the one hand, a very compact arrangement of the components of the STM and on the other hand, the new-built STM head has a good mechanical stability, in order to achieve atomic resolution with all four STM units. The atomic resolution of the STM units was confirmed by scanning a Si(111)-7 x 7 surface. The thermal drift during the STM operation, as well as the resonant frequencies of the mechanical structure of the STM head, were determined. The scanning electron microscope allows the precise and safe navigation of the tunneling tips on the sample surface. Multi tip spectroscopy with up to four STM units can be performed synchronously. To demonstrate the capabilities of the new-built apparatus the conductivity measurements were carried out on metallic yttrium silicide nanowires. The nanowires were prepared by the in-situ deposition of yttrium on a heated Si(110) sample surface. Current-voltage curves were recorded on the nanowires and on the wetting layer in-between. The curves indicate an existence of the Schottky barrier between the yttrium silicide nanowires and the silicon bulk. By means of the two-tip measurements with a gate, the insulating property of the Schottky barrier has been confirmed. Using this Schottky barrier, it is possible to limit the current to the nanowire and to prevent it from flowing through the silicon bulk. A four-tip resistance measurement with a gate has provided the resistance of the nanowire. From the dimensions of the nanowire the resistivity was calculated. The obtained resistivity was found to be in agreement with literature values. In addition, the contact resistances of the tunneling tips on the silicide nanowires were determined.

  11. Realizing a Four-Step Molecular Switch in Scanning Tunneling Microscope Manipulation of Single Chlorophyll-a Molecules

    Iancu, V; Iancu, Violeta; Hla, Saw-Wai

    2006-01-01

    Single chlorophyll-a molecules, a vital resource for the sustenance of life on Earth, have been investigated by using scanning-tunneling-microscope manipulation and spectroscopy on a gold substrate at 4.6 K. The chlorophyll-a binds on Au(111) via its porphyrin unit while the phytyl-chain is elevated from the surface by a support of four CH3 groups. By injecting tunneling electrons from the STM-tip, we are able to bend the phytyl-chain, which enable switching of four molecular conformations in a controlled manner. Statistical analyses and structural calculations reveal that all reversible switching mechanisms are initiated by a single tunnelling-electron energy-transfer process, which induces bond rotation within the phytyl-chain.

  12. Integration and interoperability accessing electronic information resources in science and technology the proposal of Brazilian Digital Library

    Marcondes, C H; Marcondes, Carlos H.; Sayao, Luis Fernando

    2002-01-01

    This paper describes technological and methodological options to achieve interoperability in accessing electronic information resources, available in Internet, in the scope of Brazilian Digital Library in Science and Technology Project - BDL, developed by Brazilian Institute for Scientific and Technical Information - IBICT. It stresses the impact of the Web in the publishing and communication processes in science and technology and also in the information systems and libraries. The work points out the two major objectives of the BDL Project: facilitates electronic publishing of different full text materials such as theses, journal articles, conference papers,grey literature - by Brazilian scientific community, so amplifying their nationally and internationally visibility; and achieving, through a unified gateway, thus avoiding a user to navigate and query across different information resources individually. The work explains technological options and standards that will assure interoperability in this context...

  13. Theory of tunneling in semiconductor heterostructures

    Advances in material growth technology and ultrafast spectroscopic techniques have stimulated a great deal of investigation into the static and dynamic aspects of tunneling in semiconductor heterostructures. The existing theory of tunneling in solids is inadequate to model such tunneling processes in all their complexity. In this thesis, a new theoretical formalism is developed wherein tunneling properties are determined by studying the time evolution of localized wavepackets. Their time evolution is determined by a direct numerical solution of the time-dependent Schroedinger equation, using a unitary approximation of the evolution operator. The procedure is applicable to any multi-band representation of electronic states in heterostructures. It fully retains the band mixing aspects and symmetries of the underlying basis states. It is well suited to study the dynamics of tunneling in the presence of space and time-dependent electric field profiles. This technique was applied to investigate resonant tunneling of holes between localized states in coupled quantum wells, employing the Luttinger representation for degenerate valence bands. An issue of some controversy in reports of experiments on this structure was the role of heavy hole (HH)-light hole (LH) coupling in resonances induced by an external electric field. It was found that tunneling between HH and LH states is suppressed only for zero in-plane wavevector, and is quite rapid otherwise. But this coherent tunneling may be observed experimentally only in the presence of an appropriate relaxation mechanism, which could vary between experiments. The formalism was applied to explore the role of ?-point and X-point states in electron tunneling through indirect bandgap AlxGa1-xAs barriers, employing the tight-binding representation for electronic states. The tunneling lifetime was found to depend exponentially on barrier thickness

  14. Challenges in the implementation of an electronic surveillance system in a resource-limited setting: Alerta, in Peru

    Soto Giselle

    2008-11-01

    Full Text Available Abstract Background Infectious disease surveillance is a primary public health function in resource-limited settings. In 2003, an electronic disease surveillance system (Alerta was established in the Peruvian Navy with support from the U.S. Naval Medical Research Center Detachment (NMRCD. Many challenges arose during the implementation process, and a variety of solutions were applied. The purpose of this paper is to identify and discuss these issues. Methods This is a retrospective description of the Alerta implementation. After a thoughtful evaluation according to the Centers for Disease Control and Prevention (CDC guidelines, the main challenges to implementation were identified and solutions were devised in the context of a resource-limited setting, Peru. Results After four years of operation, we have identified a number of challenges in implementing and operating this electronic disease surveillance system. These can be divided into the following categories: (1 issues with personnel and stakeholders; (2 issues with resources in a developing setting; (3 issues with processes involved in the collection of data and operation of the system; and (4 issues with organization at the central hub. Some of the challenges are unique to resource-limited settings, but many are applicable for any surveillance system. For each of these challenges, we developed feasible solutions that are discussed. Conclusion There are many challenges to overcome when implementing an electronic disease surveillance system, not only related to technology issues. A comprehensive approach is required for success, including: technical support, personnel management, effective training, and cultural sensitivity in order to assure the effective deployment of an electronic disease surveillance system.

  15. The Mouse Tumor Biology Database (MTB): A Central Electronic Resource for Locating and Integrating Mouse Tumor Pathology Data

    Begley, D A; Krupke, D M; Neuhauser, S. B.; Richardson, J. E.; Bult, C. J.; Eppig, J T; Sundberg, J. P.

    2011-01-01

    The Mouse Tumor Biology Database (MTB) is designed to provide an electronic data storage, search, and analysis system for information on mouse models of human cancer. MTB includes data on tumor frequency and latency, strain, germ line and somatic genetics, pathologic notations, and photomicrographs. MTB collects data from the primary literature, other public databases, and direct submissions from the scientific community. MTB is a community resource that provides integrated access to mouse tu...

  16. Use of Electronic Information Resources and Research Output by Academic Staff in Private Universities in Ogun State, Nigeria

    Itunu Bamidele; Ezinwayi Madukoma; Saturday U. Omeluzor; Susan U. Ogbuiyi

    2012-01-01

    The study examined the use of electronic information resources and research output by academic staff in private universities in Ogun state, Nigeria. Three private universities were selected out of the nine private universities in Ogun state. These universities are Crescent University, Abeokuta, Babcock University, Ilishan-Remo, and Redeemers University, Mowe, all in Ogun State, Nigeria. Purposive sampling method was used to investigate respondents. The instrument used for data collection was...

  17. Tracking the Flow of Resources in Electronic Waste - The Case of End-of-Life Computer Hard Disk Drives.

    Habib, Komal; Parajuly, Keshav; Wenzel, Henrik

    2015-10-20

    Recovery of resources, in particular, metals, from waste flows is widely seen as a prioritized option to reduce their potential supply constraints in the future. The current waste electrical and electronic equipment (WEEE) treatment system is more focused on bulk metals, where the recycling rate of specialty metals, such as rare earths, is negligible compared to their increasing use in modern products, such as electronics. This study investigates the challenges in recovering these resources in the existing WEEE treatment system. It is illustrated by following the material flows of resources in a conventional WEEE treatment plant in Denmark. Computer hard disk drives (HDDs) containing neodymium-iron-boron (NdFeB) magnets were selected as the case product for this experiment. The resulting output fractions were tracked until their final treatment in order to estimate the recovery potential of rare earth elements (REEs) and other resources contained in HDDs. The results further show that out of the 244 kg of HDDs treated, 212 kg comprising mainly of aluminum and steel can be finally recovered from the metallurgic process. The results further demonstrate the complete loss of REEs in the existing shredding-based WEEE treatment processes. Dismantling and separate processing of NdFeB magnets from their end-use products can be a more preferred option over shredding. However, it remains a technological and logistic challenge for the existing system. PMID:26351732

  18. Homoepitaxial graphene tunnel barriers for spin transport

    Friedman, Adam L.; van't Erve, Olaf M. J.; Robinson, Jeremy T.; Whitener, Keith E.; Jonker, Berend T.

    2016-05-01

    Tunnel barriers are key elements for both charge-and spin-based electronics, offering devices with reduced power consumption and new paradigms for information processing. Such devices require mating dissimilar materials, raising issues of heteroepitaxy, interface stability, and electronic states that severely complicate fabrication and compromise performance. Graphene is the perfect tunnel barrier. It is an insulator out-of-plane, possesses a defect-free, linear habit, and is impervious to interdiffusion. Nonetheless, true tunneling between two stacked graphene layers is not possible in environmental conditions usable for electronics applications. However, two stacked graphene layers can be decoupled using chemical functionalization. Here, we demonstrate that hydrogenation or fluorination of graphene can be used to create a tunnel barrier. We demonstrate successful tunneling by measuring non-linear IV curves and a weakly temperature dependent zero-bias resistance. We demonstrate lateral transport of spin currents in non-local spin-valve structures, and determine spin lifetimes with the non-local Hanle effect. We compare the results for hydrogenated and fluorinated tunnel and we discuss the possibility that ferromagnetic moments in the hydrogenated graphene tunnel barrier affect the spin transport of our devices.

  19. Cryogenic wind tunnels. II

    Kilgore, Robert A.

    1987-01-01

    The application of the cryogenic concept to various types of tunnels including Ludwieg tube tunnel, Evans clean tunnel, blowdown, induced-flow, and continuous-flow fan-driven tunnels is discussed. Benefits related to construction and operating costs are covered, along with benefits related to new testing capabilities. It is noted that cooling the test gas to very low temperatures increases Reynolds number by more than a factor of seven. From the energy standpoint, ambient-temperature fan-driven closed-return tunnels are considered to be the most efficient type of tunnel, while a large reduction in the required tunnel stagnation pressure can be achieved through cryogenic operation. Operating envelopes for three modes of operation for a cryogenic transonic pressure tunnel with a 2.5 by 2.5 test section are outlined. A computer program for calculating flow parameters and power requirements for wind tunnels with operating temperatures from saturation to above ambient is highlighted.

  20. Interface effects in spin-dependent tunneling

    Tsymbal, E Y; Velev, J P; Jaswal, S S; Van Schilfgaarde, M; Oleynik, I I; Stewart, D A

    2005-01-01

    In the past few years the phenomenon of spin dependent tunneling (SDT) in magnetic tunnel junctions (MTJs) has aroused enormous interest and has developed into a vigorous field of research. The large tunneling magnetoresistance (TMR) observed in MTJs garnered much attention due to possible application in random access memories and magnetic field sensors. This led to a number of fundamental questions regarding the phenomenon of SDT. One such question is the role of interfaces in MTJs and their effect on the spin polarization of the tunneling current and TMR. In this paper we consider different models which suggest that the spin polarization is primarily determined by the electronic and atomic structure of the ferromagnet/insulator interfaces rather than by their bulk properties. First, we consider a simple tight-binding model which demonstrates that the existence of interface states and their contribution to the tunneling current depend on the degree of hybridization between the orbitals on metal and insulator...

  1. Building and Managing Electronic Resources in Digital Era in India with Special Reference to IUCAA and NIV, Pune: A Comparative Case Study

    Sahu, H. K.; Singh, S. N.

    2015-04-01

    This paper discusses and presents a comparative case study of two libraries in Pune, India, Inter-University Centre for Astronomy and Astrophysics and Information Centre and Library of National Institute of Virology (Indian Council of Medical Research). It compares how both libraries have managed their e-resource collections, including acquisitions, subscriptions, and consortia arrangements, while also developing a collection of their own resources, including pre-prints and publications, video lectures, and other materials in an institutional repository. This study illustrates how difficult it is to manage electronic resources in a developing country like India, even though electronic resources are used more than print resources. Electronic resource management can be daunting, but with a systematic approach, various problems can be solved, and use of the materials will be enhanced.

  2. Vibration-assisted tunneling through competing molecular states

    Nowack, Katja C.; Wegewijs, Maarten R.

    2005-01-01

    We calculate the non-linear tunneling current through a molecule with two electron-accepting orbitals which interact with an intramolecular vibration. We investigate the interplay between Coulomb blockade and non-equilibrium vibration-assisted tunneling under the following assumptions: (i) The Coulomb charging effect restricts the number of extra electrons to one. (ii) The orbitals are non-degenerate and couple asymmetrically to the vibration. (iii) The tunneling induces a non-equilibrium vib...

  3. The level of the usage of the human resource information system and electronic recruitment in Croatian companies

    Snježana Pivac

    2014-12-01

    Full Text Available Performing business according to contemporary requirements influences companies for continuous usage of modern managerial tools, such as a human resource information system (HRIS and electronic recruitment (ER. Human resources have been recognised as curtail resources and the main source of a competitive advantage in creation of successful business performance. In order to attract and select the top employees, companies use quality information software for attracting internal ones, and electronic recruitment for attracting the best possible external candidates. The main aim of this paper is to research the level of the usage of HRIS and ER within medium-size and large Croatian companies. Moreover, the additional aim of this paper is to evaluate the relationship among the usage of these modern managerial tools and the overall success of human resource management within these companies. For the purpose of this paper, primary and secondary research has been conducted in order to reveal the level of the usage of HRIS and ER as well as the overall success of human resource management in Croatian companies. The companies’ classification (HRIS and ER is done by using the non-hierarchical k-means cluster method as well as the nonparametric Kruskal Wallis test. Further, the companies are ranked by the multicriteria PROMETHEE method. Relevant nonparametric tests are used for testing the overall companies’ HRM. Finally, binary logistic regression is estimated, relating binary variable HRM and HRIS development. After detailed research, it can be concluded that large Croatian companies apply HRIS in majority (with a positive relation to HRM performance, but still require certain degrees of its development.

  4. Gravitational Tunneling Radiation

    Rabinowitz, M

    1999-01-01

    The isolated black hole radiation of both Hawking and Zel'dovich are idealized abstractions as there is always another body to distort the potential. This is considered with respect to both gravitational tunneling, and black hole "no-hair" theorems. The effects of a second body are to lower the gravitational barrier of a black hole and to give the barrier a finite rather than infinite width so tha a particle can escape by tunneling (as in field emission) or over the top of the lowered barrier (as in Schottky emission). Thus radiation may be emitted from black holes in a process differing from that of Hawking radiation, P SH, which has been undetected for over 24 years. The radiated power from a black hole derived here is PR e ^2__ PSH, where e ^2__ is he ransmission probability for radiation through the barrier. This is similar to electric field emission of electrons from a metal in that the emission can in principle be modulated and beamed. The temperature and entropy of black holes are reexamined. Miniscule...

  5. Icing Research Tunnel

    Chennault, Jonathan

    2004-01-01

    The Icing Research Tunnel in Building 11 at the NASA Glenn Research Center is committed to researching the effects of in flight icing on aircraft and testing ways to stop the formation of hazardous icing conditions on planes. During this summer, I worked here with Richard DelRosa, the lead engineer for this area. address one of the major concerns of aviation: icing conditions. During the war, many planes crashed (especially supply planes going over the.Himalayas) because ice built up in their wings and clogged the engines. To this day, it remains the largest ice tunnel in the world, with a test section that measures 6 feet high, 9 feet long, and 20 feet wide. It can simulate airspeeds from 50 to 300 miles per hour at temperatures as low as -50 Fahrenheit. Using these capabilities, IRT can simulate actual conditions at high altitudes. The first thing I did was creating a cross reference in Microsoft Excel. It lists commands for the DPU units that control the pressure and temperature variations in the tunnel, as well as the type of command (keyboard, multiplier, divide, etc). The cross reference also contains the algorithm for every command, and which page it is listed in on the control sheet (visual Auto-CAD graphs, which I helped to make). I actually spent most of the time on the computer using Auto-CAD. I drew a diagram of the entire icing tunnel and then drew diagrams of its various parts. Between my mentor and me, we have drawings of every part of it, from the spray bars to the thermocouples, power cabinets, input-output connectors for power systems, and layouts of various other machines. I was also responsible for drawing schematics for the Escort system (which controls the spray bars), the power system, DPUs, and other electrical systems. In my spare time, I am attempting to build and program the "toddler". Toddler is a walking robot that I have to program in PBASIC language. When complete, it should be able to walk on level terrain while avoiding obstacles in real-time. It features an infrared detector that can keep it from falling over edges, as well as follow or avoid a light source. The toddler is giving me a much better understanding of the basics of electronic circuitry and computer programming.

  6. Print and Electronic Resources: Usage Statistics at Guru Gobind Singh Indraprastha University Library

    Kapoor, Kanta

    2010-01-01

    Purpose: The purpose of this paper is to quantify the use of electronic journals in comparison with the print collections in the Guru Gobind Singh Indraprastha University Library. Design/methodology/approach: A detailed analysis was made of the use of lending services, the Xerox facility and usage of electronic journals such as Science Direct,

  7. Transonic Dynamics Tunnel (TDT)

    Federal Laboratory Consortium — The Transonic Dynamics Tunnel (TDT) is a continuous flow wind-tunnel facility capable of speeds up to Mach 1.2 at stagnation pressures up to one atmosphere. The TDT...

  8. Quantum theory of tunneling

    Razavy, Mohsen

    2014-01-01

    In this revised and expanded edition, in addition to a comprehensible introduction to the theoretical foundations of quantum tunneling based on different methods of formulating and solving tunneling problems, different semiclassical approximations for multidimensional systems are presented. Particular attention is given to the tunneling of composite systems, with examples taken from molecular tunneling and also from nuclear reactions. The interesting and puzzling features of tunneling times are given extensive coverage, and the possibility of measurement of these times with quantum clocks are critically examined. In addition by considering the analogy between evanescent waves in waveguides and in quantum tunneling, the times related to electromagnetic wave propagation have been used to explain certain aspects of quantum tunneling times. These topics are treated in both non-relativistic as well as relativistic regimes. Finally, a large number of examples of tunneling in atomic, molecular, condensed matter and ...

  9. Hypersonic Tunnel Facility (HTF)

    Federal Laboratory Consortium — The Hypersonic Tunnel Facility (HTF) is a blow-down, non-vitiated (clean air) free-jet wind tunnel capable of testing large-scale, propulsion systems at Mach 5, 6,...

  10. Carpal tunnel syndrome

    Median nerve dysfunction; Median nerve entrapment ... Calandruccio JH. Carpal tunnel syndrome, ulnar tunnel syndrome, and stenosing tenosynovitis. In: Canale ST, Beaty JH, eds. Campbell's Operative Orthopaedics . 12th ed. Philadelphia, PA: Elsevier Mosby; 2013: ...

  11. Light emission in tunneling processes

    We introduce a new method for mapping and analyzing (with atomic resolution) molecules adsorbed on surfaces. This method relies on the detection of fluorescence from molecules, electronically excited by inelastic tunneling in STM. It may combines the excellent spatial resolution of STM together with the specificity of fluorescence as an analytical tool. We propose to overcome this problem by choosing 'transparent conductors' (such as Indium Tin Oxides-lTO) as the STM substrate. ITO, characterized by a large optical gap, will not quench electronically excited molecules. We have tested our idea to enhance the quantum efficiency of molecular emission on surfaces by using transparent conductors in the tunneling junction. We have constructed large area tunnel-junctions by using the squeezable tunnel-Junction technique. The principle of this technique is to squeeze together smooth flat surfaces separated by a thin spacer. By applying a controlled force, junctions with surface area of thousands of square angstroms are made. We have recorded light emission from bare tunneling surfaces and from surfaces coated with molecules (DCA, DCM and COUMARINE), as a function of the bias voltage in the range of 0-5 volts. Typical tunneling currents are 50 nano ampere. Our main findings are: The bare ITO surface emits light at biasing voltages larger than 4.0 eV which corresponds to electron-hole excitation over the optical gap of ITO. ITO surfaces coated with chromophore molecules have shown enhanced light emission at a voltage bias which corresponds to the allowed excitations energies in the chromophore. A voltage bias of 2-5 V yielded light emission of 5 * 103 photon/μC. The corresponding metallic surfaces, bare or coated with a chromophore did not show any emission. In order to test the possibility of using this effect for imaging purposes we have replaced one electrode of junction with an ITO coated glass tip of 180 μm radius. such a tip yield an upper limit of tunneling area of 0.3 μm diameter. (author) 35 refs

  12. Structural comparison between MgO/Fe(0 0 1) and MgO/Fe(0 0 1)–p(1 × 1)O interfaces for magnetic tunneling junctions: An Auger electron diffraction study

    Magnetic tunnel junctions based on MgO(0 0 1) barriers and ferromagnetic electrodes, such as Fe/MgO/Fe, represent a very popular and widely investigated subject in the field of spin-electronics because of the large values of magnetoresistance shown by these systems. In this paper, the structural properties of MgO thin films grown onto Fe(0 0 1) and MgO/Fe(0 0 1)–p(1 × 1)O surfaces, with MgO thickness ranging from 2 to 14 equivalent monolayers, have been investigated by means of Auger electron diffraction. The structural order and the crystal quality of the MgO films result practically independent from the template, the latter being either the clean Fe(0 0 1) surface or the oxidized Fe(0 0 1)–p(1 × 1)O one. This is confirmed by numerical simulations, showing that, apart from the first two MgO layers close to the interface, the structure is unaffected by the choice of the starting surface. By a structural point of view, we can conclude that Fe(0 0 1)–p(1 × 1)O is a good candidate for the role of bottom electrode for the realization of MgO-based magnetic tunnelling junctions, also considering its higher chemical stability and reproducibility if compared to the clean Fe(0 0 1) surface.

  13. Major SSC tunneling begins

    In Texas, work has been completed on the first on the Superconducting Supercollider's major shafts. Now a boring machine has started driving the fifty-four mile elliptical accelerator tunnel. To date, contracts let for the tunnel have come in far below preliminary estimates. Five of the main fourteen foot diameter tunnel contracts have been awarded for a total of 107.4 million dollars, about forty million dollars below estimates. These contracts represent %60 percent of the total tunneling project

  14. MendelWeb: An Electronic Science/Math/History Resource for the WWW.

    Blumberg, Roger B.

    This paper describes a hypermedia resource, called MendelWeb that integrates elementary biology, discrete mathematics, and the history of science. MendelWeb is constructed from Gregor Menders 1865 paper, "Experiments in Plant Hybridization". An English translation of Mendel's paper, which is considered to mark the birth of classical and…

  15. QR Codes as Finding Aides: Linking Electronic and Print Library Resources

    Kane, Danielle; Schneidewind, Jeff

    2011-01-01

    As part of a focused, methodical, and evaluative approach to emerging technologies, QR codes are one of many new technologies being used by the UC Irvine Libraries. QR codes provide simple connections between print and virtual resources. In summer 2010, a small task force began to investigate how QR codes could be used to provide information and…

  16. Quantization of Time in Dynamic Barrier Tunnelling

    Davison, Sydney G.; Davison, Timothy S.

    2016-01-01

    In the B\\"uttiker-Landauer perturbation approach to electron tunnelling, through a time-modulated rectilinear potential barrier, the Tien-Gordon identity was invoked, together with its infinite energy spectrum. Here, an exact treatment is presented which is based on the temporal wave-function matching procedure, that led to a finite energy spectrum. In seeking the condition governing the time evolution of the tunnelling process, the Euler formula provided the crucial ingredient for time quant...

  17. The Mouse Tumor Biology Database (MTB): A Central Electronic Resource for Locating and Integrating Mouse Tumor Pathology Data

    Begley, D. A.; Krupke, D. M.; Neuhauser, S. B.; Richardson, J. E.; Bult, C. J.; Eppig, J. T.; Sundberg, J. P.

    2011-01-01

    The Mouse Tumor Biology Database (MTB) is designed to provide an electronic data storage, search, and analysis system for information on mouse models of human cancer. MTB includes data on tumor frequency and latency, strain, germ line and somatic genetics, pathologic notations, and photomicrographs. MTB collects data from the primary literature, other public databases, and direct submissions from the scientific community. MTB is a community resource that provides integrated access to mouse tumor data from different scientific research areas and facilitates integration of molecular, genetic, and pathologic data. Current status of MTB, search capabilities, data types, and future enhancements are detailed in this article. PMID:21282667

  18. Searching Electronic Resources on Internet : Tools for Researchers And Library Professional

    Lokhande, Rahul

    2010-01-01

    In this Internet Era Libraries & Information Centers increasingly being called upon to provide more relevant, up-to-date and timely information to a wide range of users. To satisfy the varied needs, they require availability and accessibility to a variety of information resources and formats ( such as digital, full text, sound, graphics, images, multimedia & hypertext as well as printed documents). To cope with the new technology library professionals and the researchers should developed hims...

  19. Observation of nuclear gamma resonance with superconducting tunnel junction detectors

    M. G. Kozin

    2016-02-01

    Full Text Available Nb-based superconducting tunnel junction detectors have been used for the registration of electrons following a nuclear gamma resonance (Mössbauer effect. Electrons were produced by a RhFe scatterer under irradiation by the 57Co(Rh Mössbauer source. This observation demonstrates the role which can be played by superconducting tunnel junction detectors in the field of conversion electron Mössbauer spectroscopy and other types of electron spectroscopy.

  20. Power solutions for emergency lighting of tunnels, underpasses and ecoduct

    Mišák, Stanislav; Šnobl, Jaroslav; Dostál, František

    2011-01-01

    In this paper, once of possibilities of an independent power supply emergency lighting of tunnels. Power should be provide by a combination of renewable resource (photovoltaic panels, wind power). This paper aims to estimate the investment costs of such a project and compare them with commonly used UPS (genset). Concrete concept for a hybrid system will be implemented for Klimkovice tunnel.