WorldWideScience
 
 
1

Resonant tunneling of electrons in quantum wires  

International Nuclear Information System (INIS)

[en] We considered resonant electron tunneling in various nanostructures including single wall carbon nanotubes, molecular transistors and quantum wires formed in two-dimensional electron gas. The review starts with a textbook description of resonant tunneling of noninteracting electrons through a double-barrier structure. The effects of electron-electron interaction in sequential and resonant electron tunneling are studied by using Luttinger liquid model of electron transport in quantum wires. The experimental aspects of the problem (fabrication of quantum wires and transport measurements) are also considered. The influence of vibrational and electromechanical effects on resonant electron tunneling in molecular transistors is discussed.

2010-01-01

2

Chemically driven electron tunnelling pumps  

CERN Multimedia

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.

Goychuk, I

2006-01-01

3

Potential barrier for tunneling electrons in STM [scanning tunneling microscope  

International Nuclear Information System (INIS)

[en] The correct interpretation of vacuum-tunneling experiments achieved with the scanning tunneling microscope (STM) makes it necessary to know about the effective potential barrier that an electron leaving the surface sees. A variety of semiclassical and quantum-mechanical approaches are available to calculate the attractive potential between an external charged particle and a semi-infinite polarizable medium, but local effects are not negligible for the distances of interest, and a simple local formalism cannot be applied, either, so it is necessary to include, at the same time, local and non-local correlations effects. Consequently, the determination of this potential barrier is a difficult task and it remains an open problem. Recently some work has been performed going beyond the local density formalism (LDA). The tunneling current in a metal-vacuum-metal junction is very sensitive to the detailed form of the potential barrier between the electrodes, and specially sensitive are the positions of the transmission resonances which occur in the region close to the metal-vacuum interface where the momentum of the electron can be real, so the tunneling electrons can serve as a probe of this surface-interaction. Indeed, the STM has been used to study the distance-voltage characteristics (d-Va) in the constant current mode, and tunneling resonances, that is, peaks in the dJ/dVa curve have been observed in recent experiments, as predicted by Gundlach. Thus, in order to estimate the shape of the potential barrier that electrons feel when they tunnel the vacuum region, the author has carried out theoretical calculations of the dI/dVa-Va characteristics for a W(110) tip on a AU(110) sample. 14 refs., 2 figs

1989-01-01

4

3e tunneling processes in a superconducting single-electron tunneling transistor  

CERN Multimedia

A current due to a tunneling event that involves three times the charge of an electron was observed in the current - voltage characteristics of a superconducting single-electron tunneling transistor. In this tunnel event, a Cooper pair tunnels through one tunnel barrier simultaneously with a quasiparticle that tunnels through a second tunnel barrier which is about 0.5 microns distant from the first tunnel barrier. This current was observed in a bias regime where current flow due to sequential quasiparticle tunneling is forbidden due to the Coulomb blockade.

Hadley, P; Visscher, E H; Lahteenmaki, S; Mooij, J E

1998-01-01

5

Counting electrons with ultrasmall tunnel junctions  

International Nuclear Information System (INIS)

Tunnel junctions with a mesoscopic size scale (less than about 0.1 micrometer) allow electronic devices to be built that can controllably transfer electrons one-by-one. The physical phenomena behind these new devices, the Coulomb blockade, is observable because electronic devices can now be made that are small enough so that movement of a single electron through the device has a large change of energy. I will explain the simple operating principles of this phenomena and show how voltage amplifiers and electron pump devices can then be made. I will also discuss the use of the devices for a fundamental electrical charge standard based on counting electrons.

1993-01-01

6

Resonant tunneling of electrons in quantum wires (Review)  

Science.gov (United States)

We consider resonant electron tunneling in various nanostructures, including single-wall carbon nanotubes, molecular transistors, and quantum wires, formed in two-dimensional electron gas. The review starts with a textbook description of resonant tunneling of noninteracting electrons through a double-barrier structure. The effects of electron-electron interaction in sequential and resonant electron tunneling are studied by using the Luttinger liquid model of electron transport in quantum wires. The experimental aspects of the problem (fabrication of quantum wires and transport measurements) are also considered. The influence of vibrational and electromechanical effects on resonant electron tunneling in molecular transistors is discussed.

Krive, I. V.; Palevski, A.; Shekhter, R. I.; Jonson, M.

2010-02-01

7

Electron tunnelling in glassy media  

International Nuclear Information System (INIS)

The efficiency of electron scavenging by a range of solute molecules in methanol, 2-methyltetrahydrofuran (MTHF) and 10mol dm-3 hydroxide glasses has been investigated by ?-radiolysis at 77K using spectrophotometric detection. The data have been analyzed using the recent theory of Dainton, Pilling and Rice (J.C.S. Faraday II; 71:1311 (1975)), and a satisfactory fit found. The trap depths for the thre systems are estimated to be 1.7eV (methanol), 1.0eV (MTHF) and 0.95eV (aq.hydroxide). A wide variation in the scavenging efficiency is tentatively ascribed to the differing geometries of the scavenger molecules. For MTHF and 10mol dm-3 hydroxide glasses, the efficiency of scavenging is independent of wave-length, suggesting that the width of the electron spectrum is not due to a range of trap depths. (author).

1975-01-01

8

Inelastic electron tunneling spectroscopy for topological insulators.  

UK PubMed Central (United Kingdom)

Inelastic electron tunneling spectroscopy is a powerful spectroscopy that allows one to investigate the nature of local excitations and energy transfer in the system of interest. We study inelastic electron tunneling spectroscopy for topological insulators and investigate the role of inelastic scattering on the Dirac node states on the surface of topological insulators. Local inelastic scattering is shown to significantly modify the Dirac node spectrum. In the weak coupling limit, peaks and steps are induced in second derivative d2I/dV2. In the strong coupling limit, the local negative-U centers are formed at impurity sites, and the Dirac cone structure is fully destroyed locally. At intermediate coupling, resonance peaks emerge. We map out the evolution of the resonance peaks from weak to strong coupling, which interpolate nicely between the two limits. There is a sudden qualitative change of behavior at intermediate coupling, indicating the possible existence of a local quantum phase transition. We also find that, even for a simple local phonon mode, the inherent coupling of spin and orbital degrees in topological insulators leads to the spin-polarized texture in inelastic Friedel oscillations induced by the local mode.

She JH; Fransson J; Bishop AR; Balatsky AV

2013-01-01

9

Inelastic electron tunneling spectroscopy for topological insulators.  

Science.gov (United States)

Inelastic electron tunneling spectroscopy is a powerful spectroscopy that allows one to investigate the nature of local excitations and energy transfer in the system of interest. We study inelastic electron tunneling spectroscopy for topological insulators and investigate the role of inelastic scattering on the Dirac node states on the surface of topological insulators. Local inelastic scattering is shown to significantly modify the Dirac node spectrum. In the weak coupling limit, peaks and steps are induced in second derivative d2I/dV2. In the strong coupling limit, the local negative-U centers are formed at impurity sites, and the Dirac cone structure is fully destroyed locally. At intermediate coupling, resonance peaks emerge. We map out the evolution of the resonance peaks from weak to strong coupling, which interpolate nicely between the two limits. There is a sudden qualitative change of behavior at intermediate coupling, indicating the possible existence of a local quantum phase transition. We also find that, even for a simple local phonon mode, the inherent coupling of spin and orbital degrees in topological insulators leads to the spin-polarized texture in inelastic Friedel oscillations induced by the local mode. PMID:23383930

She, Jian-Huang; Fransson, Jonas; Bishop, A R; Balatsky, Alexander V

2013-01-09

10

Electron beam instabilities in gyrotron beam tunnels  

Energy Technology Data Exchange (ETDEWEB)

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.

Pedrozzi, M.; Alberti, S.; Hogge, J.P.; Tran, M.Q.; Tran, T.M. [Ecole Polytechnique Federale, Lausanne (Switzerland). Centre de Recherche en Physique des Plasma (CRPP)

1997-10-01

11

A single electron tunneling force spectroscopy study of dielectric materials  

Science.gov (United States)

Single electron tunneling force microscopy has been developed over the last decade as a tool to manipulate the occupation and probe the properties of trap states in completely non conducting materials. The technique has been advanced through the efforts of several generations of graduate students in the Clayton Williams research group. Previous graduate students have demonstrated that the single electron tunneling force microscopy technique can repeatably facilitate single electron tunneling between a metallic tip and an electron trap state in a completely non conducting, dielectric material. Also the single electron tunneling force spectroscopy technique has been shown to make these measurements with atomic scale resolution. As solid state device technology rushes toward higher power and increasingly smaller devices single electron tunneling force microscopy is uniquely positioned to identify the properties of trap states in dielectric materials with atomic scale resolution. The main thrust of this work has been concerned with demonstrating a repeatable spectroscopic method which can be used to reliably measure the energy of electron and hole traps due to defect states in dielectric materials. The single electron tunneling force spectroscopy technique was used to make spectroscopic measurements at several places on the surface of silicon dioxide, silicon nitride and hafnium oxide films. The spectra measured were compared to known trap states in both the theoretical and experimental literature. The data show that the density of trap states is not spatially homogeneous, but varies from measurement to measurement. Most of the defect states identified by the single electron tunneling force spectroscopy technique correspond nicely with trap state energies found in either the experimental or theoretical literature. However, several states, not found in the literature, have also been identified by the scanning electron tunneling force spectroscopy technique. Additionally single electron tunneling force spectroscopy has provided evidence of irreversible and reversible tunneling events with irreversible tunneling predominantly near the conduction and valence bands. A noted asymmetry in the amount of irreversible tunneling in favor of trap states near the valence band edge has also been identified. Finally a first demonstration of state creation and characterization by single electron tunneling force spectroscopy in silicon dioxide is discussed.

Winslow, Dustin W.

12

Electronic excitations and the tunneling spectra of metallic nanograins  

CERN Document Server

Tunneling-induced electronic excitations in a metallic nanograin are classified in terms of {em generations}: subspaces of excitations containing a specific number of electron-hole pairs. This yields a hierarchy of populated excited states of the nanograin that strongly depends on (a) the available electronic energy levels; and (b) the ratio between the electronic relaxation rate within the nano-grain and the bottleneck rate for tunneling transitions. To study the response of the electronic energy level structure of the nanograin to the excitations, and its signature in the tunneling spectrum, we propose a microscopic mean-field theory. Two main features emerge when considering an Al nanograin coated with Al oxide: (i) The electronic energy response fluctuates strongly in the presence of disorder, from level to level and excitation to excitation. Such fluctuations produce a dramatic sample dependence of the tunneling spectra. On the other hand, for excitations that are energetically accessible at low applied ...

Narvaez, G A; Kirczenow, George; Narvaez, Gustavo A.

2003-01-01

13

Asymmetric tunable tunneling magnetoresistance in single-electron transistors  

CERN Document Server

We show that the tunneling magnetoresistance (TMR) of a ferromagnetic single-electron transistor in the sequential tunneling regime shows asymmetric Coulomb blockade oscillations as a function of gate voltage if the individual junction-TMRs differ. The relative amplitude of these oscillations grows significantly if the bias voltage is increased, becoming as large as 30% when the bias voltage is comparable to the charging energy of the single-electron transistor. This might be useful for potential applications requiring a tunable TMR.

Pirmann, M; Schön, G

2000-01-01

14

Single electron tunneling near the Coulomb blockade threshold  

Energy Technology Data Exchange (ETDEWEB)

In the vicinity of the Coulomb blockade threshold virtual electron tunneling leads to effective screening of the charge on small metallic junctions. We present a nonperturbative calculation of the junction ground state energy and level splitting close to the edges of the Brillouin zone. We show that the electron tunneling rate can be substantially suppressed due to quantum fluctuations of the charge and the junction current-voltage characteristic becomes nonlinear near the Coulomb gap. We also investigate linear transport properties of a single tunnel junction in the presence of Coulomb effects. ((orig.)).

Zaikin, A.D. [I.E. Tamm Department of Theoretical Physics, P.N. Lebedev Physics Institute, Leninski prospect 53, Moscow 117924 (Russian Federation); Golubev, D.S. [I.E. Tamm Department of Theoretical Physics, P.N. Lebedev Physics Institute, Leninski prospect 53, Moscow 117924 (Russian Federation); Panyukov, S.V. [I.E. Tamm Department of Theoretical Physics, P.N. Lebedev Physics Institute, Leninski prospect 53, Moscow 117924 (Russian Federation)

1994-12-01

15

Single electron tunneling near the Coulomb blockade threshold  

International Nuclear Information System (INIS)

In the vicinity of the Coulomb blockade threshold virtual electron tunneling leads to effective screening of the charge on small metallic junctions. We present a nonperturbative calculation of the junction ground state energy and level splitting close to the edges of the Brillouin zone. We show that the electron tunneling rate can be substantially suppressed due to quantum fluctuations of the charge and the junction current-voltage characteristic becomes nonlinear near the Coulomb gap. We also investigate linear transport properties of a single tunnel junction in the presence of Coulomb effects. ((orig.))

1994-01-01

16

Tunneling time of electrons through a potential barrier  

Energy Technology Data Exchange (ETDEWEB)

The authors investigate the problem of the average time spent by a tunneling electron in the classically forbidden region. They propose a natural method of generalizing the classical transit time concept to the quantum mechanical case and apply it to the problem of tunneling through a one-dimensional potential barrier. Considering the transmitted and reflected particles separately yields complex parameters which represent the tunneling times of reflected and transmitted particles. They investigate the connection of these parameters to the angles of rotation of electron spins in a magnetic field localized in the barrier region.

Baskin, L.M.; Sokolovskii, D.G.

1987-09-01

17

Tunneling spectroscopy on correlated electron systems  

International Nuclear Information System (INIS)

Different current methods for tunneling spectroscopy are discussed. Spectroscopic measurements at low temperatures involving either vacuum tunneling or 'small-junction' tunneling are presented on different systems which show gaps in their density of states. In the Kondo insulators FeSi and CeNiSn, we found gaps 2? of about 100meV and 10meV, respectively. In the heavy fermion materials UPd2Al3 and URu2Si2, we found gaps of about 10meV below the antiferromagnetic ordering when tunneling along the ab planes. No gap was found along the c-axis, so that the normal state of these superconductors appears strongly anisotropic. ((orig.)).

1995-01-01

18

Parity Effect and Tunnel Magnetoresistance of Ferromagnet / Superconductor / Ferromagnet Single-Electron Tunneling Transistors  

CERN Multimedia

We theoretically study the tunnel magnetoresistance(TMR) of ferromagnet / superconductor / ferromagnet single-electron tunneling transistors with a special attention to the parity effect. It is shown that in the plateau region, there is no spin accumulation in the island even at finite bias voltage. However, the information of the injected spin is carried by the excess electron and thus the TMR exists. The spin relaxation rate of the excess electron can be estimated from the TMR. We also show that the TMR increases with decreasing the size of the superconducting island.

Imamura, H; Ebisawa, H; Imamura, Hiroshi; Utsumi, Yasuhiro; Ebisawa, Hiromichi

2002-01-01

19

Inelastic electron tunneling spectroscopy in molecular junctions: Peaks and dips  

CERN Multimedia

We study inelastic electron tunneling through a molecular junction using the non-equilibrium Green function (NEGF) formalism. The effect of the mutual influence between the phonon and the electron subsystems on the electron tunneling process is considered within a general self-consistent scheme. Results of this calculation are compared to those obtained from the simpler Born approximation and the simplest perturbation theory approaches, and some shortcomings of the latter are pointed out. The self-consistent calculation allows also for evaluating other related quantities such as the power loss during electron conduction. Regarding the inelastic spectrum, two types of inelastic contributions are discussed. Features associated with real and virtual energy transfer to phonons are usually observed in the second derivative of the current I with respect to the voltage when plotted against the latter. Signatures of resonant tunneling driven by an intermediate molecular ion appear as peaks in the first derivative d(c...

Galperin, M; Nitzan, A; Galperin, Michael; Ratner, Mark A.; Nitzan, Abraham

2004-01-01

20

Electron-beam-assisted Scanning Tunneling Microscopy Of Insulating Surfaces  

CERN Multimedia

Insulating materials are widely used in electronic devices. Bulk insulators and insulating films pose unique challenges for high resolution study since most commonly used charged particle surface analysis techniques are incompatible with insulating surfaces and materials. A, method of performing scanning tunneling microscopy (STM) on insulating surfaces has been investigated. The method is referred to as electron-beam assisted scanning tunneling microscopy (e-BASTM). It is proposed that by coupling the STM and the scanning electron microscopy (SEM) as one integrated device, that insulating materials may be studied, obtaining both high spatial resolution, and topographic and electronic resolution. The premise of the technique is based on two physical consequences of the interaction of an energetic electron beam (PE) with a material. First, when an electron beam is incident upon a material, low level material electrons are excited into conduction band states. For insulators, with very high secondary electron yi...

Bullock, E T

2000-01-01

 
 
 
 
21

Photon dressed electronic states in topological insulators: tunneling and conductance.  

UK PubMed Central (United Kingdom)

We have obtained analytic results for the surface states of three-dimensional topological insulators in the presence of circularly polarized light. This electron-photon interaction results in an energy gap as well as a novel energy dispersion of the dressed electron-photon states, different from both graphene and the standard two-dimensional electron gas (2DEG). Additionally, we made calculations of the ballistic conductance and Klein tunneling in both two- and three-dimensional topological insulators as well as investigating how these phenomena are affected in the presence of circularly polarized light. We have found a critical energy for an incoming particle, separating two substantially different types of tunneling.

Iurov A; Gumbs G; Roslyak O; Huang D

2013-04-01

22

Sequential Tunneling vs. Electron Correlation in Multiple Photo-ionization  

CERN Document Server

We take advantage of the information provided by use of elliptical polarization in a recent two-electron release time experiment [A.N. Pfeiffer et al., Nature Physics 7, 428 (2011)]. This allows a comparative test of the currently dominant conjectures regarding independent-electron tunneling theory vs. fully electron-correlated classical release theory to describe electron release in strong-field double ionization.

Wang, X; Pfeiffer, A N; Cirelli, C; Keller, U; Eberly, J H

2012-01-01

23

Microwave-induced co-tunneling in single electron tunneling transistors  

DEFF Research Database (Denmark)

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 rubber bellows. Cross-talk was minimized by using individual coaxial lines between the sample and the room temperature electronics: The co-tunneling experiments were performed at zero DC bias current by measuring the voltage response to a very small amplitude 2 Hz current modulation with the gate voltage 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.

Ejrnaes, M.; Savolainen, M.

2002-01-01

24

Electron-Photon interaction in resonant tunneling diodes  

CERN Multimedia

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.

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

1997-01-01

25

Bohmian mechanics and the tunneling time problem for electrons  

International Nuclear Information System (INIS)

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)

1996-08-02

26

High Performance Resonant Tunneling Electronic Circuit with Suitable Resistance Parameters  

Digital Repository Infrastructure Vision for European Research (DRIVER)

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 PVCD...

Chih Chin Yang; Yen Chun Lin; Hsiao Hsuan Cheng

27

ELECTRONIC RESOURCES FOR THE HUMANITIES  

Directory of Open Access Journals (Sweden)

Full Text Available Electronic information resources (EIR) including electronic journals, books, and databases, as well as other different collections of information on the internet either paid or accessed for free withoutany doubt became one of the most important information resources in contemporary research and studies. The point is whether representatives of all fields of sciences use them with equal intensity and effectiveness. There is an opinion, that EIR are more applicable for physical, biomedical and technological sciences and representatives of these sciences are better prepared and use them much more extensively. It is thought that those, who study liberal arts, are technophobial, moreover, representatives of liberal arts themselves maintain that manuscript material is frequently moreimportant than electronic information, that books are primary and not articles.The aim of the article is to overview the peculiarity of representatives of liberal arts and to present an evaluated qualitative and acknowledged register of electronic information resources, which could be useful for representatives of liberal arts, ensure supplying of specific information needs and disseminate information about electronic information resources.To implement this goal the following tasks are solved in the article: problems of typology of electronic information resources are discussed and their original classification scheme presented based on theoretical and practical material; assessment criteria of electronic information resources are analyzed; an annotated list of electronic information resources for representatives of liberal arts is presented.The article may be relevant to the whole community of representatives of liberal arts: researchers, lecturers, students, as well as library specialists and others, interested in electronic information.

Petrauskiene, Zibute

2006-01-01

28

Electron-electron interactions and two-dimensional - two-dimensional tunneling  

CERN Multimedia

We derive and evaluate expressions for the dc tunneling conductance between interacting two-dimensional electron systems at non-zero temperature. The possibility of using the dependence of the tunneling conductance on voltage and temperature to determine the temperature-dependent electron-electron scattering rate at the Fermi energy is discussed. The finite electronic lifetime produced by electron-electron interactions is calculated as a function of temperature for quasiparticles near the Fermi circle. Vertex corrections to the random phase approximation substantially increase the electronic scattering rate. Our results are in an excellent quantitative agreement with experiment.

Jungwirth, T

1996-01-01

29

Optimization of electron cooling by SIN tunnel junctions  

International Nuclear Information System (INIS)

[en] We report on the optimization of electron cooling by SIN tunnel junctions due to the advanced geometry of superconducting electrodes and very effective normal metal traps for more efficient removal of quasiparticles at temperatures from 25 to 500 mK. The maximum decrease in electron temperature of about 200 mK has been observed at bath temperatures 300-350 mK. We used four-junction geometry with Al-AlOx-Cr/Cu tunnel junctions and Au traps. Efficient electron cooling was realized due to the improved geometry of the cooling tunnel junctions (quadrant shape of the superconducting electrode) and optimized Au traps just near the junctions (?0.5 ?m) to reduce reabsorption of quasiparticles after removing them from normal metal. The maximum cooling effect was increased from a temperature drop of d T = -56 mK (ordinary cross geometry) to -130 mK (improved geometry of superconducting electrodes) and to d T = -200 mK (improved geometry of superconducting electrodes and effective Au traps). The heating peak (instead of cooling) near the zero voltage across cooling junctions has been observed in practice for all samples at temperatures below 150 mK. For higher cooling voltages close to the superconducting gap, the heating was converted to cooling with decreased amplitude. The leakage resistance of the tunnel junctions gives a reasonable explanation of the heating peak. The phonon reabsorption due to the recombination of quasiparticles in superconducting electrodes gives an additional improvement in the theoretical fitting but could not explain the heating peak. An anomalous zero-bias resistance peak has been observed for all tested structures. The peak is explained by Coulomb blockade of tunnelling in transistor-type structures with relatively small tunnel junctions. The work on electron cooling is devoted to the development of a cold-electron bolometer (CEB) with capacitive coupling by SIN tunnel junctions to the antenna for sensitive detection in the terahertz region. Direct electron cooling of an absorber plays a crucial role in supersensitive detection in the presence of a realistic background power load

2004-05-01

30

Electron tunneling through ultrathin boron nitride crystalline barriers.  

UK PubMed Central (United Kingdom)

We investigate the electronic properties of ultrathin hexagonal boron nitride (h-BN) crystalline layers with different conducting materials (graphite, graphene, and gold) on either side of the barrier layer. The tunnel current depends exponentially on the number of h-BN atomic layers, down to a monolayer thickness. Conductive atomic force microscopy scans across h-BN terraces of different thickness reveal a high level of uniformity in the tunnel current. Our results demonstrate that atomically thin h-BN acts as a defect-free dielectric with a high breakdown field. It offers great potential for applications in tunnel devices and in field-effect transistors with a high carrier density in the conducting channel.

Britnell L; Gorbachev RV; Jalil R; Belle BD; Schedin F; Katsnelson MI; Eaves L; Morozov SV; Mayorov AS; Peres NM; Neto AH; Leist J; Geim AK; Ponomarenko LA; Novoselov KS

2012-03-01

31

Photon dressed electronic states in topological insulators: tunneling and conductance.  

Science.gov (United States)

We have obtained analytic results for the surface states of three-dimensional topological insulators in the presence of circularly polarized light. This electron-photon interaction results in an energy gap as well as a novel energy dispersion of the dressed electron-photon states, different from both graphene and the standard two-dimensional electron gas (2DEG). Additionally, we made calculations of the ballistic conductance and Klein tunneling in both two- and three-dimensional topological insulators as well as investigating how these phenomena are affected in the presence of circularly polarized light. We have found a critical energy for an incoming particle, separating two substantially different types of tunneling. PMID:23462425

Iurov, Andrii; Gumbs, Godfrey; Roslyak, Oleksiy; Huang, Danhong

2013-03-05

32

The Electronic Banking Resource Center  

Science.gov (United States)

The Electronic Banking Resource Center, provided by an MBA graduate student at Ohio State University, is a one stop resource for information about banking on the Internet. It contains pointers to explanations of various open payment standards; a FAQ on electronic money/Internet payment systems that discusses such issues as challenges of Internet payment systems, electronic cash, credit cards, and checks and the Web, and advice for merchants on the Internet, among others; a page of pointers to examples of Internet financial transactions; and a large page of pointers to banks on the Internet. The Resource Center also contains pointers to other banking related sites. http://www.informatik.uni-trier.de/~damm/Lehre/E-Money/InternetPayment.html

33

Tunneling between two-dimensional electron gases in a weak magnetic field  

CERN Multimedia

We have measured the tunneling between two two-dimensional electron gases (2DEGs) in weak magnetic fields, when the carrier densities of the two electron layers are matched. At zero magnetic field, B=0, the lineshape of the equilibrium tunneling resonance is best fit by a Lorentzian, with a linewidth which is determined by the roughness of the tunnel barrier. For B\

Turner, N; Brown, K M; Linfield, E H; Pepper, M; Ritchie, D A; Jones, G A C; Turner, N; Nicholls, J T; Brown, K M; Linfield, E H; Pepper, M; Ritchie, D A; Jones, G A C

1995-01-01

34

Elementary excitations in double electron layers with tunnel coupling  

International Nuclear Information System (INIS)

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

2003-01-01

35

Sensitivity of electron temperature measurements with the tunnel probe to a fast electron component  

International Nuclear Information System (INIS)

[en] The tunnel probe is a new kind of Langmuir probe for fast dc measurements of ion flux and electron temperature in the tokamak scrape-off layer. The probe is calibrated using two-dimensional kinetic analysis of the ion current distribution on the concave conductors. Though qualitative agreement with classical Langmuir probe measurements was found, the electron temperature given by the tunnel probe is several times lower. One possible explanation might be an overestimation of the electron temperature by the Langmuir probe, due to a non-Maxwellian electron velocity distribution which can be modelled in a first approach as a two-temperature distribution. Hence the possible influence on the tunnel probe of a small population of nonthermal electrons is investigated by means of the two-dimensional kinetic code XOOPIC. It is found that this influence can be seen as the result of two combined physical effects: nonthermal electrons will reach the back plate (BP) and the ion current distribution over tunnel and the BP will change. The resulting dependence on probe bias and parallel ion current density of the TP sensitivity to nonthermal electrons is not reflected in CASTOR measurement results. Thus nonthermal electrons on their own cannot fully explain the discrepancy between Langmuir and tunnel probe measurements

2007-01-01

36

Filtering spin with tunnel-coupled electron wave guides  

CERN Multimedia

Spintronics is an emerging field of semiconductor electronics where the electron's spin is exploited as well as its charge. Operation of spintronic devices requires the ability to create spin-polarized charge carriers in nonmagnetic semiconductors. Using Zeeman splitting of spin states in a magnetic field turns out to be impractical for spin filtering in real applications. More promising approaches employ hybrid structures with metallic or semiconducting magnetic contacts. However, fabrication of these structures poses material-science challenges and may require rather complicated chip design. Achieving spin filtering by means of intrinsic spin-dependent effects in semiconductors is therefore highly desirable. Here we propose a spin-filtering device based on the interplay of the Rashba effect and momentum-resolved tunneling between parallel electron wave guides. Spin-polarized currents are created by applying voltages or small magnetic fields. Switching between opposite spin polarizations is easily achieved. ...

Governale, M; Zülicke, U; Schroll, C

2002-01-01

37

Scanning electron and tunneling microscopy of palladium-barium emitters  

International Nuclear Information System (INIS)

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.

2003-06-15

38

Shadow Bands and Tunneling Magnetoresistance in Itinerant Electron Ferromagnets  

CERN Document Server

In itinerant electron ferromagnets spectral weight is transferred at finite temperatures from quasiparticle peaks located at majority and minority-spin band energies to shadow-band peaks. For a given Bloch wavevector and band index, the majority-spin shadow-band peak is located near the minority-spin quasiparticle energy and the minority-spin shadow-band peak is located near the majority-spin quasiparticle energy. This property can explain much of the temperature dependence seen in the magnetoresistance of magnetic tunnel junctions.

MacDonald, A H; Kasner, M

1998-01-01

39

Coulomb blockade and off-resonance tunneling in small electronic systems  

Science.gov (United States)

The minima of the oscillations of the tunnel conductance through a small electronic system present a rich variety of quantum conduction mechanisms when the charging energy Ec and the electrochemical potential difference eV between the resevoirs compete with the single particle energy level separation ?. We emphasize the strong relation between off-resonance tunneling and elastic co-tunneling in the linear conductance regime while, in the non-linear regime, inelastic co-tunneling has no equivalent for the case of resonant tunneling. We also review the recent experimental results which clearly identify this latter regime and we discuss the intermediate regime, valid for few electron systems, where Ec ? ?.

Glattli, D. C.

1993-06-01

40

Inelastic electron tunneling spectrum from surface magnon and magnetic impurity scatterings in magnetic tunnel junctions  

International Nuclear Information System (INIS)

Analytic expressions for contributions to the inelastic electron tunneling spectrum (IETS) from surface magnon scattering and magnetic impurity scattering are obtained. It is shown that surface magnon scattering alone does not lead to peaks in the IETS. The peaks at small bias often observed in the IETS of magnetic junctions are due to magnetic impurity scattering, in agreement with the traditional model for zero bias anomaly. These impurity resonance peaks can sometimes split due to the impurities magnetic coupling to the electrodes. Measurements of AlO and MgO barrier junctions yield excellent agreement to the theory. The experiment further shows that the magnetic impurities in MgO barriers are strongly coupled to the electrodes but those in AlO barriers are not magnetically coupled to the electrodes.

2010-10-01

 
 
 
 
41

Electron-phonon scattering in molecular electronics: from inelastic electron tunnelling spectroscopy to heating effects  

Energy Technology Data Exchange (ETDEWEB)

In this paper, we investigate dissipation in molecular electronic devices. Dissipation is a crucial quantity which determines the stability and heating of the junction. Moreover, several experimental techniques which use inelastically scattered electrons as probes to investigate the geometry in the junction are becoming fundamental in the field. In order to describe such physical effects, a non-equilibrium Green's function (NEGF) method was implemented to include scattering events between electrons and molecular vibrations in current simulations. It is well known that the final heating of the molecule depends also on the ability of the molecule to relax vibrational quanta into the contact reservoirs. A semi-classical rate equation has been implemented and integrated within the NEGF formalism to include this relaxation. The model is based on two quantities: (i) the rate of emission of phonons in the junction by electron-phonon scattering and (ii) a microscopic approach for the computation of the phonon decay rate, accounting for the dynamical coupling between the vibrational modes localized on the molecule and the contact phonons. The method is applied to investigate inelastic electron tunnelling spectroscopy (IETS) signals in CO molecules on Cu(110) substrates as well as dissipation in C{sub 60} molecules on Cu(110) and Si(100) surfaces. It is found that the mechanisms of energy relaxation are highly mode-specific and depend crucially on the lead electronic structure and junction geometry.

Gagliardi, Alessio; Frauenheim, Thomas; Niehaus, Thomas A [Bremen Center for Computational Materials Science, University of Bremen, D-28359 Bremen (Germany); Romano, Giuseppe; Pecchia, Alessandro; Di Carlo, Aldo [CNR-INFM Department of Electronics Engineering, University of Rome ' Tor Vergata' , Via del Politecnico 1, 00133 Rome (Italy)], E-mail: gagliard@bccms.uni-bremen.de, E-mail: Gagliardi@Ing.uniroma2.it

2008-06-15

42

Electron-phonon scattering in molecular electronics: from inelastic electron tunnelling spectroscopy to heating effects  

International Nuclear Information System (INIS)

In this paper, we investigate dissipation in molecular electronic devices. Dissipation is a crucial quantity which determines the stability and heating of the junction. Moreover, several experimental techniques which use inelastically scattered electrons as probes to investigate the geometry in the junction are becoming fundamental in the field. In order to describe such physical effects, a non-equilibrium Green's function (NEGF) method was implemented to include scattering events between electrons and molecular vibrations in current simulations. It is well known that the final heating of the molecule depends also on the ability of the molecule to relax vibrational quanta into the contact reservoirs. A semi-classical rate equation has been implemented and integrated within the NEGF formalism to include this relaxation. The model is based on two quantities: (i) the rate of emission of phonons in the junction by electron-phonon scattering and (ii) a microscopic approach for the computation of the phonon decay rate, accounting for the dynamical coupling between the vibrational modes localized on the molecule and the contact phonons. The method is applied to investigate inelastic electron tunnelling spectroscopy (IETS) signals in CO molecules on Cu(110) substrates as well as dissipation in C60 molecules on Cu(110) and Si(100) surfaces. It is found that the mechanisms of energy relaxation are highly mode-specific and depend crucially on the lead electronic structure and junction geometry.

2008-01-01

43

Vibration-assisted electron tunneling in C_{140} single-molecule transistors  

CERN Multimedia

We measure electron tunneling in single-molecule transistors made from C_{140}, a molecule with a mass-spring-mass geometry chosen as a model system to study electron-vibration coupling. We observe vibration-assisted tunneling at an energy corresponding to the stretching mode of C_{140}. Molecular modeling provides explanations for why this mode couples more strongly to electron tunneling than the other internal modes of the molecule. We make comparisons between the observed tunneling rates and those expected from the Franck-Condon model.

Pasupathy, A N; Chang, C; Soldatov, A V; Lebedkin, S; Bialczak, R C; Grose, J E; Donev, L A K; Sethna, J P; Ralph, D C; McEuen, P L

2003-01-01

44

Anodic Oxidation of Aluminum by Electron Tunneling through Al/Cadmium-Stearate/Al Structure  

Science.gov (United States)

The conduction of the monolayer Langmuir-Blodgett(LB) film consisting of Cadmium-Stearate(CdSt) may be explained by an electron tunneling process. The tunneling current through the Al/CdSt/Al sample showed a great decrease with time when a constant voltage was applied in air. Such a phenomenon seems to result from the growth of an Al2O3 layer by the anodic oxidation of the aluminum electrode enhanced by the electron tunneling.

Okazaki, Choichiro; Kuniyoshi, Shigekazu; Kudo, Kazuhiro; Tanaka, Kuniaki

1989-11-01

45

High Performance Resonant Tunneling Electronic Circuit with Suitable Resistance Parameters  

Directory of Open Access Journals (Sweden)

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.

Chih Chin Yang; Yen Chun Lin; Hsiao Hsuan Cheng

2012-01-01

46

Managing electronic resources a LITA guide  

CERN Multimedia

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.

Weir, Ryan O

2012-01-01

47

Student attitudes towards electronic information resources  

Directory of Open Access Journals (Sweden)

Full Text Available Students are increasingly expected to use electronic resources while at university. Studies were undertaken to determine the level of use of this type of resource, how students feel about various issues surrounding electronic resources and whether attitudes change dependent upon subject studied. 317 students across three universities completed questionnaires to determine level of use of various electronic information resources; ways in which they felt electronic resources had hindered or improved their academic career; if they perceived themselves capable of using the resources; would the standard of their work suffer without the use of these resources; and the various methods employed to acquire the skills necessary to use the sources. 155 students were questioned as part of a larger study IMPEL2, investigating the Impact on People of Electronic Libraries, supplemented by 162 students, questioned as part of an MA Dissertation, using the same methodology.

Kathryn Ray; Joan Day

1998-01-01

48

Hot-electron transport in 3-terminal devices based on magnetic tunnel junctions  

International Nuclear Information System (INIS)

An original study combining spin polarization with hot-electron transport in a 3-terminal double tunnel junction device is presented. We report for the first time a tunnel magnetoresistance signal for each tunnel barrier in an integrated device made with two different insulating materials. Furthermore, a hot-electron transfer from the emitter to the collector, both magnetic, through the base and both tunnel barriers is presented with an appropriate set of applied voltages. The characteristics of the hot electrons have been successfully modeled theoretically on the basis of experimental tunnel barrier parameters. However, in contrast to the theory, no field dependence of the hot-electron characteristics was measured. Possible origins for this discrepancy are discussed

2002-01-01

49

Hot-electron transport in 3-terminal devices based on magnetic tunnel junctions  

Energy Technology Data Exchange (ETDEWEB)

An original study combining spin polarization with hot-electron transport in a 3-terminal double tunnel junction device is presented. We report for the first time a tunnel magnetoresistance signal for each tunnel barrier in an integrated device made with two different insulating materials. Furthermore, a hot-electron transfer from the emitter to the collector, both magnetic, through the base and both tunnel barriers is presented with an appropriate set of applied voltages. The characteristics of the hot electrons have been successfully modeled theoretically on the basis of experimental tunnel barrier parameters. However, in contrast to the theory, no field dependence of the hot-electron characteristics was measured. Possible origins for this discrepancy are discussed.

Lacour, D.; Jaffres, H.; Rodary, G.; Nguyen Van Dau, F.; Petroff, F. [Centre National de la Recherche Scientifique (CNRS), Unite Mixte de Physique, 91 - Orsay (France); Hehn, M.; Montaigne, F.; Rottlander, P.; Schuhl, A. [Centre National de la Recherche Scientifique (CNRS), Lab. de Physique des Materiaux, UMR 7556, 54 - Nancy (France)

2002-12-01

50

Long-range intervalence electron tunneling through fully saturated systems  

International Nuclear Information System (INIS)

The compounds (?-2,8-dithiadispirol[3.1.3.1]decane)-decaamminediruthenium(II,II) hexafluorophosphate, [(NH3)5RuS2C8H12Ru(NH3)5](PF6)4, and (?-2,10-dithiatrispiro[3.1.1.3.1.1]tridecane)-decaamminediruthenium(II,II) hexafluorophosphate, [(NH3)5RuS2C11H16Ru(NH3)5](PF6)4, were prepared, and upon oxidation, their intervalence properties were measured. The spiro binuclear with three rings had an IT band at 808 nm (epsilon 9 +/- 1 M-1 cm-1) and that with four rings had an IT band at 690 nm (epsilon 2.3 +/- 0.7 M-1 cm-1). This compares with a band at 910 nm (epsilon 43 +/- 2) measured earlier for the two-ring spiro binuclear. The through-bond distances between ruthenium centers range from 11.3 to 17.5 angstrom. The values of the electron tunneling matrix elements were calculated from Hopfield's theory and were found to be 1.7 X 10-2, 6.8 X 10-3, and 3.1 X 10-3 eV for the two-ring, three-ring, and four-ring binuclears, respectively. These correspond to rate constants of 8.0 X 10-7, 4.9 X 10-6, and 3.5 X 10-4 s-1, respectively, for the three binuclears. The results are discussed in terms of long-range tunneling and are compared to results obtained in solid matrices and biological systems

1982-05-05

51

Long-range intervalence electron tunneling through fully saturated systems  

Energy Technology Data Exchange (ETDEWEB)

The compounds (..mu..-2,8-dithiadispirol(3.1.3.1)decane)-decaamminediruthenium(II,II) hexafluorophosphate, ((NH/sub 3/)/sub 5/RuS/sub 2/C/sub 8/H/sub 12/Ru(NH/sub 3/)/sub 5/)(PF/sub 6/)/sub 4/, and (..mu..-2,10-dithiatrispiro(3.1.1.3.1.1)tridecane)-decaamminediruthenium(II,II) hexafluorophosphate, ((NH/sub 3/)/sub 5/RuS/sub 2/C/sub 11/H/sub 16/Ru(NH/sub 3/)/sub 5/)(PF/sub 6/)/sub 4/, were prepared, and upon oxidation, their intervalence properties were measured. The spiro binuclear with three rings had an IT band at 808 nm (epsilon 9 +/- 1 M/sup -1/ cm/sup -1/) and that with four rings had an IT band at 690 nm (epsilon 2.3 +/- 0.7 M/sup -1/ cm/sup -1/). This compares with a band at 910 nm (epsilon 43 +/- 2) measured earlier for the two-ring spiro binuclear. The through-bond distances between ruthenium centers range from 11.3 to 17.5 angstrom. The values of the electron tunneling matrix elements were calculated from Hopfield's theory and were found to be 1.7 X 10/sup -2/, 6.8 X 10/sup -3/, and 3.1 X 10/sup -3/ eV for the two-ring, three-ring, and four-ring binuclears, respectively. These correspond to rate constants of 8.0 X 10/sup -7/, 4.9 X 10/sup -6/, and 3.5 X 10/sup -4/ s/sup -1/, respectively, for the three binuclears. The results are discussed in terms of long-range tunneling and are compared to results obtained in solid matrices and biological systems.

Stein, C.A. (Yeshira Univ., Bronx, NY); Lewis, N.A.; Seitz, G.

1982-05-05

52

Electron tunnelling and polarity reversal of tungsten-nickel point-contact diodes  

Science.gov (United States)

Tunnelling and rectification characteristics of MIM point contact diodes are interpreted in terms of the different electronic band structures of the two metals at the junction. The experimentally observed polarity reversal is shown to be consistent with the tunnelling mechanism describing the operation of the MIM diode.

Riccius, H. D.; Smith, D. S.

1981-03-01

53

Rates, distances, and energy control of electron tunneling reactions in rigid media  

International Nuclear Information System (INIS)

Electron tunneling leads to transfer of trapped positive, or negative charge tens of angstroms in rigid matrices. Franck-Condon effects give energy specificity to charge transfer and ion recombination, and adds sensitivity to molecular structure, solvation and H/D isotope effects. The specificity is important in photosynthesis and solar energy storage as well as in radiation chemistry. We feel that the question of hopping vs. tunneling is definitely settled in favor of tunneling for intermolecular electron transfer at low temperatures. Hopping cannot yet be conclusively ruled out in reactions of trapped electrons. Hopping is expected to become important in many media near room temperature.

1979-05-19

54

Integrated NIS electron-tunnelling refrigerator/superconducting bolometer  

Energy Technology Data Exchange (ETDEWEB)

We describe progress in the development of a close-packed array of bolometers designed for use in photometric applications at millimeter wavelengths from ground-based telescopes. Each bolometer in the array will use a proximity-effect Transition Edge Sensor (TES) sensing element and each will have integrated Normal-Insulator-Superconductor (NIS) refrigerators to cool the bolometer below the thermal reservoir temperature. The NIS refrigerators and acoustic-phonon-mode-isolated bolometers are fabricated on silicon. The radiation absorbing element is mechanically suspended by four legs, whose dimensions are used to control and optimize the thermal conductance of the bolometer. Using the technology developed at NIST, we fabricate NIS refrigerators at the base of each of the suspension legs. The NIS refrigerators remove hot electrons by quantum-mechanical tunneling and are expected to cool the biased (10pW) bolometers to <170mK while the bolometers are inside a pumped {sup 3}He-cooled cryostat operating at {approx}280mK. This significantly lower temperature at the bolometer allows the detectors to approach background-limited performance despite the simple cryogenic system.

Silverberg, R.F. [NASA/Goddard Space Flight Center, Laboratory for Experimental Cosmology, Greenbelt, MD 20771 (United States)]. E-mail: robert.silverberg@nasa.gov; Benford, D.J. [NASA/Goddard Space Flight Center, Laboratory for Experimental Cosmology, Greenbelt, MD 20771 (United States); Chen, T.C. [Global Science and Technology, Greenbelt, MD 20771 (United States); Chervenak, J. [NASA/Goddard Space Flight Center, Laboratory for Experimental Cosmology, Greenbelt, MD 20771 (United States); Finkbeiner, F. [SSAI, Greenbelt, MD 20771 (United States); Moseley, S.H. [NASA/Goddard Space Flight Center, Laboratory for Experimental Cosmology, Greenbelt, MD 20771 (United States); Duncan, W.D. [National Institute of Standards and Technology (NIST), 325 Broadway, Boulder, CO 80305 (United States); Miller, N.A. [National Institute of Standards and Technology (NIST), 325 Broadway, Boulder, CO 80305 (United States); Schmidt, D.R. [National Institute of Standards and Technology (NIST), 325 Broadway, Boulder, CO 80305 (United States); Ullom, J.N. [National Institute of Standards and Technology (NIST), 325 Broadway, Boulder, CO 80305 (United States)

2006-04-15

55

Integrated NIS electron-tunnelling refrigerator/superconducting bolometer  

International Nuclear Information System (INIS)

[en] We describe progress in the development of a close-packed array of bolometers designed for use in photometric applications at millimeter wavelengths from ground-based telescopes. Each bolometer in the array will use a proximity-effect Transition Edge Sensor (TES) sensing element and each will have integrated Normal-Insulator-Superconductor (NIS) refrigerators to cool the bolometer below the thermal reservoir temperature. The NIS refrigerators and acoustic-phonon-mode-isolated bolometers are fabricated on silicon. The radiation absorbing element is mechanically suspended by four legs, whose dimensions are used to control and optimize the thermal conductance of the bolometer. Using the technology developed at NIST, we fabricate NIS refrigerators at the base of each of the suspension legs. The NIS refrigerators remove hot electrons by quantum-mechanical tunneling and are expected to cool the biased (10pW) bolometers to 3He-cooled cryostat operating at ?280mK. This significantly lower temperature at the bolometer allows the detectors to approach background-limited performance despite the simple cryogenic system

2006-04-15

56

Measurement of pressure distribution in a wind-tunnel experiment using electronic pressure commutators  

Energy Technology Data Exchange (ETDEWEB)

We report on the development of instruments for measuring pressures on the surface of drained aircraft models in wind tunnels at TsAGI. As sensors we used ESP-48 electronic pressure commutators manufactured by PSI (USA).

Vyalkov, A.V.; Zimenkov, E.V.; Abashkin, A.M. [and others

1995-01-01

57

Unipolar Complementary Circuits Using Double Electron Layer Tunneling Tansistors  

Energy Technology Data Exchange (ETDEWEB)

We demonstrate unipolar complementary circuits consisting of a pair of resonant tunneling transistors based on the gate control of 2D-2D interlayer tunneling, where a single transistor - in addition to exhibiting a welldefined negative-differential-resistance can be operated with either positive or negative transconductance. Details of the device operation are analyzed in terms of the quantum capacitance effect and band-bending in a double quantum well structure, and show good agreement with experiment. Application of resonant tunneling complementary logic is discussed by demonstrating complementary static random access memory using two devices connected in series.

Blount, M.A.; Hafich, M.J.; Moon, J.S.; Reno, J.L.; Simmons, J.A.

1998-10-19

58

Measurement of electron temperature fluctuations with tunnel probe in the CASTOR tokamak  

Energy Technology Data Exchange (ETDEWEB)

The tunnel probe is a new kind of Langmuir probe for use in the tokamak scrape-off layer. Two-dimensional kinetic analysis of the ion current distribution on the concave conductors is used to calibrate the probe for making fast de measurements of ion flux and electron temperature. Qualitative agreement with classical Langmuir probe measurements is found, but the electron temperature given by the tunnel probe is several times lower. This discrepancy can be caused by secondary electron emission, or the presence of suprathermal electrons. Strong reduction of ion flux and electron temperature fluctuations is observed during electrode biasing. (orig.)

Gunn, J.P. [Association EURATOM-CEA sur la fusion controlee, Saint Paul Lez Durance (France); Stoeckel, J.; Adamek, J.; Duran, I.; Hron, M.; Panek, R.; Zacek, F. [Inst. of Plasma Physics, Association EURATOM-IPP.CR, Prague (Czech Republic); Van Rompuy, T.; De Beule, P.; Van Oost, G. [Dept. of Applied Physics, Ghent Univ. (Belgium); Balan, P.; Schrittwieser, R. [Inst. for Ion Physics, Univ. of Innsbruck (Austria); Barina, O.; Hrach, R.; Vicher, M. [Charles Univ. in Prague, Faculty of Mathematics and Physics (Czech Republic)

2004-07-01

59

When does an electron exit a tunneling barrier?  

Directory of Open Access Journals (Sweden)

Full Text Available We probe the dynamics of tunnel ionization via high harmonic generation. We characterize the ionization dynamics in helium atoms, and apply our approach to resolve subtle differences in ionization from different orbitals of a CO2 molecule.

Shafir D.; Soifer H.; Bruner B. D.; Dagan M.; Mairesse Y.; Patchkovskii S.; Ivanov M. Yu.; Smirnova O.; Dudovich N.

2013-01-01

60

Effect of the charge of an electron scavenger on the rate of electron tunneling in glasses and liquids  

International Nuclear Information System (INIS)

A theoretical model for electron reactions with ions and molecules (scavengers) in liquids and glasses was developed. To represent quantum mechanical tunneling an exponential sink term was added to Fick's second law. The reaction path was analyzed in terms of encounter pair formation and direct electron tunneling to the scavenger. Analytic expressions for the rate of these processes were obtained by using Gauss's theorem. Electron reactions in glasses are not at steady state and are strongly influenced by the electron trap depth. In liquids, electron reactions rapidly reach the steady state and the rate of reaction is enhanced compared to the predictions of the Smoluchowski theory. The effect of scavenger's charge on the rate of reaction in glasses was considered. As the dominant reaction path between electrons and scavengers is tunneling even in mobile liquids, the Debye correction to the Smoluchowski theory is too large

1975-12-18

 
 
 
 
61

Electron-magnon interaction effect in antiferromagnetic superconductors. Proposal of a tunneling experiment  

Energy Technology Data Exchange (ETDEWEB)

It is shown that in an antiferromagnetic superconductor the electronic density of states is modified to exhibit a deviation from the BCS theory due to the second-order process of the electron-magnon interaction. An electron tunneling experiment is proposed to detect this effect in existing antiferromagnetic superconductors. A close analogy is pointed out between the present electron-magnon system and the electron-phonon system of strong coupling super-conductors.

Machida, K.

1981-07-01

62

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

CERN Multimedia

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.

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

1999-01-01

63

Gate-controlled current and inelastic electron tunneling spectrum of benzene: a self-consistent study.  

UK PubMed Central (United Kingdom)

We use density functional theory based nonequilibrium Green's function to self-consistently study the current through the 1,4-benzenedithiol (BDT). The elastic and inelastic tunneling properties through this Au-BDT-Au molecular junction are simulated, respectively. For the elastic tunneling case, it is found that the current through the tilted molecule can be modulated effectively by the external gate field, which is perpendicular to the phenyl ring. The gate voltage amplification comes from the modulation of the interaction between the electrodes and the molecules in the junctions. For the inelastic case, the electron tunneling scattered by the molecular vibrational modes is considered within the self-consistent Born approximation scheme, and the inelastic electron tunneling spectrum is calculated.

Liang YY; Chen H; Mizuseki H; Kawazoe Y

2011-04-01

64

Characterization of atom and ion-induced 'internal' electron emission by thin film tunnel junctions  

International Nuclear Information System (INIS)

Highly excited charge carriers are released when single or multiply charged ions impinge on metal surfaces. While electron emission into the adjacent vacuum phase is well investigated, one has only limited knowledge about the transport of excited electrons or holes into the bulk of a metal. This shortcoming can be reduced by studying the transport of these excited carriers over buried tunnel barriers in thin film metal-insulator-metal devices. The internal barriers can be tuned by a tunnel voltage which makes the device to a balance for excited electrons and holes. With a simple theoretical model we derive the balance function of different tunnel barriers and show their feasibility for the characterization of particle induced electronic excitations on metal surfaces.

2011-06-01

65

One-dimensional quantum-wire states probed by resonant electron tunneling  

Science.gov (United States)

We have resolved the bound states of a one-dimensional quantum wire by resonant electron tunneling. The atomically precise quantum-confined structure was prepared by cleaved-edge overgrowth in GaAs/AlxGa1-xAs molecular-beam epitaxy. Tunneling proceeded, in a planar geometry, from the edge of a two-dimensional electron source through the bound states of the quantum wire into the edge of a two-dimensional electron drain. The experimental resonance positions, as well as their density dependences, are well reproduced by our self-consistent theoretical calculations.

Dignam, M. M.; Ashoori, R. C.; Stormer, H. L.; Pfeiffer, L. N.; Baldwin, K. W.; West, K. W.

1994-01-01

66

Tunneling properties versus electronic structures in Si/SiO2/Si junctions from first principles  

Science.gov (United States)

Using first-principles calculations, we study tunneling properties and electronic structures of Si(001)/SiO2/Si(001) junctions in a wide energy range covering the local energy gap in the SiO2 regions. We show that the tunneling spectra T(E) as functions of energy E have overall similarity to the projected densities of states (PDOS) at the centers of the SiO2 regions, but T(E) and PDOS have significant difference in their dependencies on the SiO2 thickness. From the energy dependencies of T(E) and PDOS, distinctive energy ranges are recognized in the valence and conduction bands, reflecting the local electronic structures in the SiO2 region induced from the Si regions. From the difference in the SiO2-thickness dependencies of T(E) and PDOS and from eigenchannel analysis, we find that the tunneling wave function inside the SiO2 region decreases with a decay rate which itself decreases as the tunneling distance increases, resulting in a smaller averaged decay rate per length for a thicker SiO2 region. These results provide a rich picture for the SiO2 barrier in the aspects of tunneling and local electronic structures, and a theoretical framework generally applicable to other tunneling barriers.

Ko, Eunjung; Lee, Kwang-Ryeol; Choi, Hyoung Joon

2013-07-01

67

Monte Carlo study of the ion-induced electron current tunneling through a metal-insulator-metal junction  

International Nuclear Information System (INIS)

A Monte Carlo program is developed to investigate the kinetically excited electrons passing through a realistic Ag-Al2O3-Al junction when Ar+ ions impact on the top Ag layer. The program includes excitation of the target electrons (by projectile ions, recoiling target atoms and fast primary electrons) and subsequent transport of these excited electrons from Ag to bottom Al layer of the metal-insulator-metal (MIM) junction. The calculated tunneling electron yield is consistent with the recently reported experimental results. The simulation, however, enables the calculation of partial tunneling electron yields of the electrons excited by the projectile ions, recoil atoms and cascade electrons, the depth distribution of the electron excitation points in the MIM junction and energy distribution of the tunneling electrons. Our calculation showed that the electrons excited by fast cascade electrons are the major contributor to the tunneling electron yield while the direct contribution of projectile ions to tunneling electron yield is evident only at the projectile energies greater than 10 keV. The tunneling electrons have their origin close to the bottom end of the Ag layer and bulk of the tunneling electrons have energies around 2 eV.

2011-06-01

68

Monte Carlo study of the ion-induced electron current tunneling through a metal-insulator-metal junction  

Energy Technology Data Exchange (ETDEWEB)

A Monte Carlo program is developed to investigate the kinetically excited electrons passing through a realistic Ag-Al{sub 2}O{sub 3}-Al junction when Ar{sup +} ions impact on the top Ag layer. The program includes excitation of the target electrons (by projectile ions, recoiling target atoms and fast primary electrons) and subsequent transport of these excited electrons from Ag to bottom Al layer of the metal-insulator-metal (MIM) junction. The calculated tunneling electron yield is consistent with the recently reported experimental results. The simulation, however, enables the calculation of partial tunneling electron yields of the electrons excited by the projectile ions, recoil atoms and cascade electrons, the depth distribution of the electron excitation points in the MIM junction and energy distribution of the tunneling electrons. Our calculation showed that the electrons excited by fast cascade electrons are the major contributor to the tunneling electron yield while the direct contribution of projectile ions to tunneling electron yield is evident only at the projectile energies greater than 10 keV. The tunneling electrons have their origin close to the bottom end of the Ag layer and bulk of the tunneling electrons have energies around 2 eV.

Ullah, S.; Dogar, A.H.; Hussain, S.; Qayyum, A., E-mail: qayyum@pinstech.org.pk

2011-06-01

69

Probing Nanoscale Electronic and Magnetic Interaction with Scanning Tunneling Spectroscopy  

DEFF Research Database (Denmark)

This thesis is concerned with fundamental research into electronic and magnetic interaction on the nanoscale. From small metallic and magnetic islands and layers to single atoms. The research revolves around magnetic interaction probed through the spectroscopic capabilities of the scanning tunneling microscope (STM). Especially at low temperatures the Kondo resonance is used to probe magnetic interaction with ferromagnetic islands and between two atoms. The latter showing a crossover between Kondo screened atoms and antiferromagnetically coupled atoms close to the quantum critical point. This 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 low coverage the silver preferably nucleates on top of the bilayer high cobalt islands compared to directly on the Cu(111) substrate. Furthermore, the silver forms a combination of a reconstruction and a Moire pattern which is investigated with low-energy electron diraction and spectroscopic STM mapping at 6. The heterostructure is found to have very interesting electronic properties. The d-related state from the now buried cobalt island is visible through the silver capping layer, but the silver Moire pattern modulates the spin-polarized cobalt d-related state in amplitude, energy position and width. This is related to the d-band model for catalytic reactions. The largest change is in the amplitude of the state, however the "reversed" structure of cobalt on Ag(111) show similar properties, but with a large shift in energy instead of amplitude. The Kondo eect is used to probe magnetic interaction between the aforementioned silver-capped cobalt islands (and additionally gold-capped cobalt islands) and single cobalt atoms positioned on the Moire pattern. A split Kondo resonance due to the exchange interaction between the island and the atom is observed. In a more technical section of the thesis, it is shown how a gold-coated STM tip will make the tip apex susceptible to a single cobalt atom. The tip is indented either directly in a Au(111) surface or gold akes are picked up from cobalt islands on Cu(111). A change in the local barrier height (work function) of the tip-sample junction indicates that the apex is gold-coated and a single cobalt atom can be pickup up. The cobalt atom attached to the tip displays a Kondo resonance formed between the atom and the tip similar to the resonance displayed when the atom is on the surface with a clean tip. Here, this is used to show how a two-impurity Kondo system consisting of two cobalt atoms, one on the tip and one on the Au(111) sample, is undergoing a continuous crossover from Kondo screened atoms to antiferromagnetically coupled atoms when the atoms are moved from non-interacting to strongly interacting. In the Kondo screened regime, the Kondo temperature is believed to be constant, but the Fano line ii shape changes continuously from a dip to a peak. In the antiferromagnetic regime, inelastic spin-ip excitations reveal a splitting with a continuous increase in energy levels when pushing the atoms further together. This is supported by numerical renormalization group calculations. The crossover between the two regimes is furthermore interesting because it occurs in an area of the phase diagram close to the elusive quantum critical point, where the phase transition line meets absolute zero temperature. This freely positionable Kondo system on the tip represents a novel way to probe magnetic interaction with the possibility to continuously change the position of the probing Kondo system. The experiment is believed to be one of many applications possible and the method opens up for a new eld within STM. We expect that our work has direct impact in other research areas, such as for heavy fermion materials, a class of materials whose properties are governed by the competition between Kondo screening an

Bork, Jakob

2010-01-01

70

Anisotropic magnetic field dependence of many-body enhanced electron tunnelling through a quantum dot  

CERN Document Server

We investigate the effect of an applied magnetic field on resonant tunneling of electrons through the bound states of self-assembled InAs quantum dots (QDs) embedded within an (AlGa)As tunnel barrier. At low temperatures (no more than 2 K), a magnetic field B applied either parallel or perpendicular to the direction of current flow causes a significant enhancement of the tunnel current. For the latter field configuration, we observe a strong angular anisotropy of the enhanced current when B is rotated in the plane of the quantum dot layer. We attribute this behavior to the effect of the lowered symmetry of the QD eigenfunctions on the electron-electron interaction.

Vdovin, E E; Makarovsky, O; Patanè, A; Eaves, L; Henini, M; Mellor, C J; Benedict, K A; Airey, R; Khanin, Yu.N.

2007-01-01

71

Influence of tunneling on electron screening in low energy nuclear reactions in laboratories  

International Nuclear Information System (INIS)

Using a semiclassical mean field theory, we show that the screening potential exhibits a characteristic radial variation in the tunneling region in sharp contrast to the assumption of the constant shift in all previous works. Also, we show that the explicit treatment of the tunneling region gives a larger screening energy than that in the conventional approach, which studies the time evolution only in the classical region and estimates the screening energy from the screening potential at the external classical turning point. This modification becomes important if the electronic state is not a single adiabatic state at the external turning point either by pretunneling transitions of the electronic state or by the symmetry of the system even if there is no essential change with the electronic state in the tunneling region.

2003-01-01

72

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

DEFF Research Database (Denmark)

We present an ellipticity resolved study of momentum distributions arising from strong-field ionization of Helium at constant intensity. 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 the presence of a 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.

N. Pfeiffer, Adrian; Cirelli, Claudio

2012-01-01

73

Monte Carlo study of the ion-induced electron current tunneling through a metal-insulator-metal junction  

International Nuclear Information System (INIS)

A Monte Carlo program was developed to investigate the kinetically excited electrons passing through a realistic Ag-Al/sub 2/O/sub 3/-Al junction when Ar/sup +/ ions impact on the top Ag layer. The program includes excitation of the target electrons (by projectile ions, recoiling target atoms and fast primary electrons) and subsequent transport of these excited electrons from Ag to bottom Al layer of the metal-insulator-metal (MIM) junction. The simulation, however, enables the calculation of partial tunneling electron yields of the electrons excited by the projectile ions, recoil atoms and cascade electrons, the depth distribution of the electron excitation points in the MIM junction and energy distribution of the tunneling electrons. Calculations showed that the electrons excited by fast cascade electrons are the major contributor to the tunneling electron yield while the direct contribution of projectile ions to tunneling electron yield is evident only at the projectile energies greater than 10 keV. The tunneling electrons have their origin close to bottom end of the Ag layer and bulk of the tunneling electrons has energies around 2 eV. (orig./A.B.)

2012-01-01

74

Electron flux during pericyclic reactions in the tunneling limit: Quantum simulation for cyclooctatetraene  

International Nuclear Information System (INIS)

Graphical abstract: In the limit of coherent tunneling, double bond shifting (DBS) of cyclooctatetraene from a reactant (R) to a product (P) is associated with pericyclic electron fluxes from double to single bonds, corresponding to a pincer-motion-type set of arrows in the Lewis structures, each representing a transfer of 0.19 electrons. - Abstract: Pericyclic rearrangement of cyclooctatetraene proceeds from equivalent sets of two reactants to two products. In the ideal limit of coherent tunneling, these reactants and products may tunnel to each other by ring inversions and by double bond shifting (DBS). We derive simple cosinusoidal or sinusoidal time evolutions of the bond-to-bond electron fluxes and yields during DBS, for the tunneling scenario. These overall yields and fluxes may be decomposed into various contributions for electrons in so called pericyclic, other valence, and core orbitals. Pericyclic orbitals are defined as the subset of valence orbitals which describe the changes of Lewis structures during the pericyclic reaction. The quantum dynamical results are compared with the traditional scheme of fluxes of electrons in pericyclic orbitals, as provided by arrows in Lewis structures.

2010-11-10

75

Lateral tunneling through the controlled barrier between edge channels in a two-dimentional electron system  

CERN Document Server

We study the lateral tunneling through the gate-voltage-controlled barrier, which arises as a result of partial elimination of the donor layer of a heterostructure along a fine strip using an atomic force microscope, between edge channels at the depletion-induced edges of a gated two-dimensional electron system. For a sufficiently high barrier a typical current-voltage characteristic is found to be strongly asymmetric and include, apart from a positive tunneling branch, the negative branch that corresponds to the current overflowing the barrier. We establish the barrier height depends linearly on both gate voltage and magnetic field and we describe the data in terms of electron tunneling between the outermost edge channels.

Shashkin, A A; Deviatov, E V; Irmer, B; Haubrich, A G C; Kotthaus, J P; Bichler, M; Wegscheider, W

1999-01-01

76

Energy and Effective Mass Dependence of Electron Tunnelling Through Multiple Quantum barriers in Different Heterostructures  

CERN Document Server

Tunneling of electrons through the barriers in heterostructures has been studied, within unified transfer matrix approach. The effect of barrier width on the transmission coefficient of the electrons has been investigated for different pairs of semi conducting materials that are gaining much importance recently. These pairs include CdS/CdSe, AlGaAs/GaAs and InAs/AlSb. Barrier dimensions have been reduced from 20nm to 5nm to observe the effect of scaling on tunneling properties. Material depended is highlighted for electrons with energy varying from below the barrier height to above it. The electron effective mass inside the barrier and the well are often different. The results show that the coupling effect leads to significant changes on the transmission effect. . The effective-mass dependant transmission coefficient has been plotted with respect to electron energy. The computation is based on the transfer matrix method by using MATLAB.

Gain, Jatindranath; Kundu, Sudakshina

2010-01-01

77

Interfacial polarization and internal electron tunneling effect on dielectric properties of multilayer polymer films  

Science.gov (United States)

Due to large contrasts in dielectric constant and volumetric conductivity, Maxwell-Wagner-Sillars interfacial polarization is observed in poly(vinylidene fluoride) (PVDF) based multilayer films. This interfacial polarization is helpful to enhance the breakdown strength of multilayer films, because they serve as electron traps to prevent hot electron thermal runaway. In this study, the relationship between volumetric resistivity and internal electron tunneling in polysulfone (PSF)/(PVDF) multilayer film is reported. In general, resistivity decreases with decreasing the thickness of the insulating PSF layer. This is attributed to the internal electron tunneling in thin PSF layers. As a result, the electron-hole neutralization via the PSF layer decreases the interfacial polarization in the PVDF layer, resulting in a lower volumetric resistivity.

Tseng, Jung-Kai; Zhou, Zheng; Mackey, Matt; Carr, Joel; Baer, Eric; Zhu, Lei

2013-03-01

78

Electronic properties of graphene: a perspective from scanning tunneling microscopy and magnetotransport.  

UK PubMed Central (United Kingdom)

This review covers recent experimental progress in probing the electronic properties of graphene and how they are influenced by various substrates, by the presence of a magnetic field and by the proximity to a superconductor. The focus is on results obtained using scanning tunneling microscopy, spectroscopy, transport and magnetotransport techniques.

Andrei EY; Li G; Du X

2012-05-01

79

Measurement of Tunneling Conductance of Two-Dimensional Electrons in a Si MOSFET Nanostructure  

Science.gov (United States)

The properties of strongly correlated two-dimensional electrons in semiconductor heterostructure continue to be of a fundamental interest of condensed matter physics [1]. A collection of transport studies have revealed a wealthy of interesting effects in the low-electron density limit, particularly in Si MOSFET structures [2]. In this talk, we present an alternative, tunneling conductance measurement of the 2D electrons in a Si MOSFET nanostructure. In our device, a global gate is used to control the 2D electron density. In addition, a set of small gates, as small as 50nm, forms a lateral tunneling barrier for the measurements. We find that there is a strong correlation between the still puzzling metal-insulator transition observed in transport [2] and our tunneling characteristics. The tunneling conductance is studied under different carrier density and in-plane Magnetic field. The project is supported by the NSF under Grant No. DMR-0804794. [4pt] [1] B. Spivak, S. V. Kravchenko, S. Kivelson, and X.P.A. Gao, Rev. Mod. Phys. 82, 1743 (2010). [2] E. Abrahams, S. V. Kravchenko, M. P. Sarachik, Rev. Mod. Phys. 73, 251 (2001)

Pan, Hong; House, Matthew; Xiao, Ming; Jiang, Hongwen

2011-03-01

80

Tunneling images of a 2D electron system in a quantizing magnetic field  

CERN Document Server

We have applied a scanning probe method, Subsurface Charge Accumulation (SCA) imaging, to resolve the local structure of the interior of a semiconductor two-dimensional electron system (2DES) in a tunneling geometry. Near magnetic fields corresponding to integer Landau level filling, submicron scale spatial structure in the out-of-phase component of the tunneling signal becomes visible. In the images presented here, the structure repeats itself when the filling factor is changed from nu=6 to nu=7. Therefore, we believe the images reflect small modulations in the 2DES density caused by the disorder in the sample.

Maasilta, I J; Kuljanishvili, I; Tessmer, S H; Melloch, M R; Chakraborty, Subhasish

2003-01-01

 
 
 
 
81

Klein tunnelling model of low energy electron field emission from single-layer graphene sheet  

Science.gov (United States)

By considering the effect of Klein tunneling for low energy electrons with linear energy dispersion, a model has been constructed to calculate the amount of emitted line current density from a single-layer graphene sheet, which is vertically aligned inside a dc gap. It is found that the current-voltage scaling obtained from the constructed Klein tunneling model is very different from the traditional field emission model based on the Fowler-Nordheim (FN) law. Under the same geometrical field enhancement factor, our model predicts a much higher emitted current as compared to the FN law at low voltages.

Sun, S.; Ang, L. K.; Shiffler, D.; Luginsland, J. W.

2011-07-01

82

Engineering electron and hole tunneling with asymmetric InAs quantum dot molecules  

CERN Document Server

Most self-assembled quantum dot molecules are intrinsically asymmetric with inequivalent dots resulting from imperfect control of crystal growth. We have grown vertically-aligned pairs of InAs/GaAs quantum dots by molecular beam epitaxy, introducing intentional asymmetry that limits the influence of intrinsic growth fluctuations and allows selective tunneling of electrons or holes. We present a systemic investigation of tunneling energies over a wide range of interdot barrier thickness. The concepts discussed here provide an important tool for the systematic design and characterization of more complicated quantum dot nanostructures.

Bracker, A A S; Doty, M F; Stinaff, E A; Ponomarev, I V; Kim, J C; Whitman, L J; Reinecke, T L; Gammon, D; Bracker, Authors A. S.

2006-01-01

83

Tunneling-induced coherent electron population transfer in an asymmetric quantum well  

CERN Multimedia

We propose an asymmetric double quantum well structure with a common continuum and investigate the effect of resonant tunneling on the control of coherent electron population transfer between the two quantum wells. By numerically solving the motion equations of element moments, the almost complete electron population transfer from initial subband to the target subband could be realized due to the constructive interference via flexibly adjusting the structure parameters.

Cui, Ni; Gong, Shangqing

2009-01-01

84

Single electron tunneling in large scale nanojunction arrays with bisferrocene-nanoparticle hybrids.  

UK PubMed Central (United Kingdom)

We report on the fabrication and single electron tunneling behaviour of large scale arrays of nanogap electrodes bridged by bisferrocene-gold nanoparticle hybrids (BFc-AuNP). Coulomb staircase was observed in the low temperature current-voltage curves measured on the junctions with asymmetric tunnel barriers. On the other hand, junctions with symmetric tunneling barrier exhibited mere nonlinear current voltage characteristics without discrete staircase. The experimental results agreed well with simulations based on the orthodox theory. The junction resistance showed thermally activated conduction behaviour at higher temperature. The overall voltage and temperature dependent results show that the transport behaviour of the large arrays of single particle devices obtained by a facile optical lithography and chemical etching process corresponds with the behaviour of single particle devices fabricated by other techniques like e-beam lithography and mechanical breaking methods.

Karmakar S; Kumar S; Marzo P; Primiceri E; Di Corato R; Rinaldi R; Cozzi PG; Bramanti AP; Maruccio G

2012-04-01

85

Microscopic theory of single-electron tunneling through molecular-assembled metallic nanoparticles  

CERN Multimedia

We present a microscopic theory of single-electron tunneling through metallic nanoparticles connected to the electrodes through molecular bridges. It combines the theory of electron transport through molecular junctions with the description of the charging dynamics on the nanoparticles. We apply the theory to study single-electron tunneling through a gold nanoparticle connected to the gold electrodes through two representative benzene-based molecules. We calculate the background charge on the nanoparticle induced by the charge transfer between the nanoparticle and linker molecules, the capacitance and resistance of molecular junction using a first-principles based Non-Equilibrium Green's Function theory. We demonstrate the variety of transport characteristics that can be achieved through ``engineering'' of the metal-molecule interaction.

Xue, Y; Xue, Yongqiang; Ratner, Mark A.

2003-01-01

86

Inelastic tunneling of electrons through a quantum dot with an embedded single molecular magnet  

Energy Technology Data Exchange (ETDEWEB)

We report a theoretical analysis of electron transport through a quantum dot with an embedded biaxial single-molecule magnet (SMM) based on mapping of the many-body interaction-system onto a one-body problem by means of the non-equilibrium Green function technique. It is found that the conducting current exhibits a stepwise behavior and the nonlinear differential conductance displays additional peaks with variation of the sweeping speed and the magnitude of magnetic field. This observation can be interpreted by the interaction of electron-spin with the SMM and the quantum tunneling of magnetization. The inelastic conductance and the corresponding tunneling processes are investigated with normal as well as ferromagnetic electrodes. In the case of ferromagnetic configuration, the coupling to the SMM leads to an asymmetric tunneling magnetoresistance (TMR), which can be enhanced or suppressed greatly in certain regions. Moreover, a sudden TMR-switch with the variation of magnetic field is observed, which is seen to be caused by the inelastic tunneling.

Chang Bo [Institute of Theoretical Physics and Department of Physics, Shanxi University, Taiyuan, Shanxi 030006 (China); Liang, J.-Q., E-mail: jqliang@sxu.edu.c [Institute of Theoretical Physics and Department of Physics, Shanxi University, Taiyuan, Shanxi 030006 (China)

2010-06-28

87

Tunneling in One-Dimensional non-Luttinger Electron Liquid  

CERN Multimedia

The conductance of a weakly interacting electron gas in the presense of a single scatterer is found at arbitrary strength of the scattering potential. At weak interaction, a simple renormalization group approach can be used instead of the standard bosonization procedure. Our technique allows to take into account the {\\em backscattering\\/} of electrons that leads to a non-Luttinger-liquid behavior of the low-temperature conductance. In the presence of magnetic field, the backscattering may give rise to a peak in differential conductance at bias equal to the Zeeman energy.

Matveev, K A; Glazman, L I; Yue, Dongxiao

1993-01-01

88

Spin-polarized electron tunneling in bcc FeCo/MgO/FeCo(001) magnetic tunnel junctions.  

UK PubMed Central (United Kingdom)

In combining spin- and symmetry-resolved photoemission, magnetotransport measurements and ab initio calculations we detangled the electronic states involved in the electronic transport in Fe(1-x)Co(x)(001)/MgO/Fe(1-x)Co(x)(001) magnetic tunnel junctions. Contrary to previous theoretical predictions, we observe a large reduction in TMR (from 530 to 200% at 20 K) for Co content above 25 atomic% as well as anomalies in the conductance curves. We demonstrate that these unexpected behaviors originate from a minority spin state with ?(1) symmetry that exists below the Fermi level for high Co concentration. Using angle-resolved photoemission, this state is shown to be a two-dimensional state that occurs at both Fe(1-x)Co(x)(001) free surface, and more importantly at the interface with MgO. The combination of this interface state with the peculiar density of empty states due to chemical disorder allows us to describe in details the complex conduction behavior in this system.

Bonell F; Hauet T; Andrieu S; Bertran F; Le Fèvre P; Calmels L; Tejeda A; Montaigne F; Warot-Fonrose B; Belhadji B; Nicolaou A; Taleb-Ibrahimi A

2012-04-01

89

Spin-polarized electron tunneling in bcc FeCo/MgO/FeCo(001) magnetic tunnel junctions.  

Science.gov (United States)

In combining spin- and symmetry-resolved photoemission, magnetotransport measurements and ab initio calculations we detangled the electronic states involved in the electronic transport in Fe(1-x)Co(x)(001)/MgO/Fe(1-x)Co(x)(001) magnetic tunnel junctions. Contrary to previous theoretical predictions, we observe a large reduction in TMR (from 530 to 200% at 20 K) for Co content above 25 atomic% as well as anomalies in the conductance curves. We demonstrate that these unexpected behaviors originate from a minority spin state with ?(1) symmetry that exists below the Fermi level for high Co concentration. Using angle-resolved photoemission, this state is shown to be a two-dimensional state that occurs at both Fe(1-x)Co(x)(001) free surface, and more importantly at the interface with MgO. The combination of this interface state with the peculiar density of empty states due to chemical disorder allows us to describe in details the complex conduction behavior in this system. PMID:22680889

Bonell, F; Hauet, T; Andrieu, S; Bertran, F; Le Fèvre, P; Calmels, L; Tejeda, A; Montaigne, F; Warot-Fonrose, B; Belhadji, B; Nicolaou, A; Taleb-Ibrahimi, A

2012-04-25

90

Tunnel Ionization Dynamics of Bound Systems in Laser Fields: How Long Does It Take for a Bound Electron to Tunnel?  

Science.gov (United States)

A numerical method is developed by which the tunnel ionization dynamics of bound systems in laser fields can be isolated from the total wave function, as given by the time-dependent Schrödinger equation. The analysis of the numerical data for a step function field reveals the following definition for the tunnel time. It is the time it takes the ground state to develop the underbarrier wave function components necessary for reaching the static field ionization rate. This definition is generalized to time varying laser fields. The tunnel time is found to scale with the Keldysh tunnel time. Our Letter establishes the physical meaning of the tunnel time, its relation to the Keldysh tunnel time, and suggests how it can be measured.

McDonald, C. R.; Orlando, G.; Vampa, G.; Brabec, T.

2013-08-01

91

Tunnel ionization dynamics of bound systems in laser fields: how long does it take for a bound electron to tunnel?  

UK PubMed Central (United Kingdom)

A numerical method is developed by which the tunnel ionization dynamics of bound systems in laser fields can be isolated from the total wave function, as given by the time-dependent Schrödinger equation. The analysis of the numerical data for a step function field reveals the following definition for the tunnel time. It is the time it takes the ground state to develop the underbarrier wave function components necessary for reaching the static field ionization rate. This definition is generalized to time varying laser fields. The tunnel time is found to scale with the Keldysh tunnel time. Our Letter establishes the physical meaning of the tunnel time, its relation to the Keldysh tunnel time, and suggests how it can be measured.

McDonald CR; Orlando G; Vampa G; Brabec T

2013-08-01

92

Coulomb repulsion effect in two-electron nonadiabatic tunneling through a one-level redox molecule.  

Science.gov (United States)

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 ( approximately k(B)T) peaks in the limit of strong electron-phonon coupling to the solvent environment. The system also displays current/bias voltage rectification. The differential conductance/bias voltage correlation can have up to four peaks even for a single-level redox molecule. The peak position, height, and width are determined by the oxidized and reduced states of both the ionization and affinity levels of the molecule and depend crucially on the Debye screening of the electric field in the tunneling gap. PMID:19894966

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

2009-10-28

93

Coulomb repulsion effect in two-electron nonadiabatic tunneling through a one-level redox molecule.  

UK PubMed Central (United Kingdom)

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 ( approximately k(B)T) peaks in the limit of strong electron-phonon coupling to the solvent environment. The system also displays current/bias voltage rectification. The differential conductance/bias voltage correlation can have up to four peaks even for a single-level redox molecule. The peak position, height, and width are determined by the oxidized and reduced states of both the ionization and affinity levels of the molecule and depend crucially on the Debye screening of the electric field in the tunneling gap.

Kuznetsov AM; Medvedev IG; Ulstrup J

2009-10-01

94

The weak ? ? ? interaction originated resonant tunneling and fast switching in the carbon based electronic devices  

Directory of Open Access Journals (Sweden)

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 ? ? ? 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.

Jun He; Ke-Qiu Chen; Chang Q. Sun

2012-01-01

95

Out-of-equilibrium catalysis of chemical reactions by electronic tunnel currents.  

Science.gov (United States)

We present an escape rate theory for current-induced chemical reactions. We use Keldysh nonequilibrium Green's functions to derive a Langevin equation for the reaction coordinate. Due to the out of equilibrium electronic degrees of freedom, the friction, noise, and effective temperature in the Langevin equation depend locally on the reaction coordinate. As an example, we consider the dissociation of diatomic molecules induced by the electronic current from a scanning tunnelling microscope tip. In the resonant tunnelling regime, the molecular dissociation involves two processes which are intricately interconnected: a modification of the potential energy barrier and heating of the molecule. The decrease of the molecular barrier (i.e., the current induced catalytic reduction of the barrier) accompanied by the appearance of the effective, reaction-coordinate-dependent temperature is an alternative mechanism for current-induced chemical reactions, which is distinctly different from the usual paradigm of pumping vibrational degrees of freedom. PMID:23574204

Dzhioev, Alan A; Kosov, Daniel S; von Oppen, Felix

2013-04-01

96

Out-of-equilibrium catalysis of chemical reactions by electronic tunnel currents  

Science.gov (United States)

We present an escape rate theory for current-induced chemical reactions. We use Keldysh nonequilibrium Green's functions to derive a Langevin equation for the reaction coordinate. Due to the out of equilibrium electronic degrees of freedom, the friction, noise, and effective temperature in the Langevin equation depend locally on the reaction coordinate. As an example, we consider the dissociation of diatomic molecules induced by the electronic current from a scanning tunnelling microscope tip. In the resonant tunnelling regime, the molecular dissociation involves two processes which are intricately interconnected: a modification of the potential energy barrier and heating of the molecule. The decrease of the molecular barrier (i.e., the current induced catalytic reduction of the barrier) accompanied by the appearance of the effective, reaction-coordinate-dependent temperature is an alternative mechanism for current-induced chemical reactions, which is distinctly different from the usual paradigm of pumping vibrational degrees of freedom.

Dzhioev, Alan A.; Kosov, Daniel S.; von Oppen, Felix

2013-04-01

97

Electronic structure of EuO spin filter tunnel contacts directly on silicon  

International Nuclear Information System (INIS)

We present an electronic structure study of a magnetic oxide/ semiconductor model system, EuO on silicon, which is dedicated for efficient spin injection and spin detection in silicon-based spintronics devices. A combined electronic structure analysis of Eu core levels and valence bands using hard X-ray photoemission spectroscopy was performed to quantify the nearly ideal stoichiometry of EuO ''spin filter'' tunnel barriers directly on silicon, and the absence of silicon oxide at the EuO/Si interface. These results provide evidence for the successful integration of a magnetic oxide tunnel barrier with silicon, paving the way for the future integration of magnetic oxides into functional spintronics devices. Hard X-ray photoemission spectroscopy of an Al/EuO/Si heterostructure probing the buried EuO and EuO/Si interface. (copyright 2011 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

2011-01-01

98

Controlling the Spin Polarization of the Electron Current in a Semimagnetic Resonant-Tunneling Diode  

CERN Document Server

The spin filtering effect of the electron current in a double-barrier resonant-tunneling diode (RTD) consisting of ZnMnSe semimagnetic layers has been studied theoretically. The influence of the distribution of the magnesium ions on the coefficient of the spin polarization of the electron current has been investigated. The dependence of the spin filtering degree of the electron current on the external magnetic field and the bias voltage has been obtained. The effect of the total spin polarization of the electron current has been predicted. This effect is characterized by total suppression of the spin-up component of electron current, that takes place when the Fermi level coincides with the lowest Landau level for spin-up electrons in the RTD semimagnetic emitter.

Beletskii, N N; Borysenko, S A

2004-01-01

99

Titanium Silicide Islands on Atomically Clean Si(100): Identifying Single Electron Tunneling Effects  

CERN Document Server

Titanium silicide islands have been formed by the ultrahigh vacuum deposition of thin films of titanium (< 2 nm) on atomically clean Si(100) substrates followed by annealing to ~800 degrees C. Scanning tunneling microscopy (STM) and scanning tunneling spectroscopy have been performed on these islands to record current-voltage (I-V) curves. Because each island forms a double barrier tunnel junction (DBTJ) structure with the STM tip and the substrate, they would be expected to exhibit single electron tunneling (SET) according to the orthodox model of SET. Some of the islands formed are small enough (diameter < 10 nm) to exhibit SET at room temperature and evidence of SET has been identified in some of the I-V curves recorded from these small islands. Those curves are analyzed within the framework of the orthodox model and are found to be consistent with that model, except for slight discrepancies of the shape of the I-V curves at current steps. However, most islands that were expected to exhibit SET did n...

Tedesco, Joseph L; Nemanich, Robert J; 10.1063/1.3437049

2010-01-01

100

Surface reaction of dialkyl phosphite on alumina and magnesia studied by inelastic electron tunneling spectroscopy  

Energy Technology Data Exchange (ETDEWEB)

Vibrational spectra of dimethyl, diethyl, and diphenyl phosphite on alumina and magnesia surfaces have been measured by inelastic electron tunneling spectroscopy. These dialkyl phosphites (O,O-dialkyl phosphonates) were adsorbed onto Al{sub 2}O{sub 3} and MgO surfaces from anhydrous benzene solutions by using a spin doping method. The tunneling spectra of phosphorous acid (phosphonic acid) on Al{sub 2}O{sub 3} have also been measured for comparison. Phosphorous acid reacts with surface OH groups of Al{sub 2}O{sub 3} by losing its protons and is adsorbed as phosphite anion (phosphonate dianion) onto the surface. Analysis of the tunneling spectra and comparison of the infrared and Raman spectra of the dialkyl phosphites give information about their molecular structures on Al{sub 2}O{sub 3} and MgO and a surface reaction on them. These dialkyl phosphites decompose by a reaction with the surface OH groups on Al{sub 2}O{sub 3} and MgO to give the adsorbed O-alkyl phosphonate monoanions and phosphonate dianion. The similarity of the tunneling spectra of dimethyl phosphite and that of phosphorous acid suggests that dimethyl phosphite decomposes rapidly to give preferentially the adsorbed phosphonate dianion on the surfaces.

Higo, Morihide; Kamata, Satsuo (Kagoshima Univ. (Japan))

1990-11-29

 
 
 
 
101

New method for determining the energy gap of a superconductor using the maximum in differential conductance of electron tunneling spectrum  

Energy Technology Data Exchange (ETDEWEB)

A new method for determining the energy gap of a superconductor using the maximum in the differential conductance curve of electron tunneling spectrum is given in this paper. The V/sub max//kT versus ..delta../kT curve was calculated from tunneling theory. V/sub max/, the voltage of the conductance maximum, can be measured from electron tunneling spectrum. ..delta../kT can be found from this curve, then the energy gap ..delta.. can be calculated. This method is simple, fast and accurate. The accuracy almost approaches that of the curve fitting method.

Li Hong-cheng; Wang Rui-lan; Wang Ping-shu; Guan Wei-yen

1986-02-01

102

Detection and Cloaking of Molecular Objects in Coherent Nanostructures Using Inelastic Electron Tunneling Spectroscopy  

CERN Document Server

We address quantum invisibility in the context of electronics in nanoscale quantum structures. We make use of the freedom of design that quantum corrals provide and show that quantum mechanical objects can be hidden inside the corral, with respect to inelastic electron scattering spectroscopy in combination with scanning tunneling microscopy, and we propose a design strategy. A simple illustration of the invisibility is given in terms of an elliptic quantum corral containing a molecule, with a local vibrational mode, at one of the foci. Our work has implications to quantum information technology and presents new tools for nonlocal quantum detection and distinguishing between different molecules.

Fransson, J; Balatsky, A V; 10.1021/nl903991a

2010-01-01

103

Identification of metal-cage coupling in a single metallofullerene by inelastic electron tunneling spectroscopy  

Science.gov (United States)

We report hybrid density functional theory calculations for inelastic electron tunneling spectroscopy (IETS) of a single metallofullerene Gd@C82. It is found that the metal atom inside the carbon cage can have significant impact on the IETS spectral profiles of the system, by modulating both the vibration and electron density. It is demonstrated that the IETS signals are very sensitive to the changes in the metal position and charge states, so that provide a unique tool for identifying the metal-cage coupling in metallofullerenes.

Jiang, J.; Gao, B.; Hu, Z. P.; Lu, Wei; Wu, Z. Y.; Yang, J. L.; Luo, Y.

2010-06-01

104

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

International Nuclear Information System (INIS)

[en] 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.

2012-09-05

105

Ultrafast laser-induced electron emission from multiphoton to optical tunneling  

Science.gov (United States)

Based on a time-dependent quantum model, a relation between the onset of the optical tunneling regime and the metal work function is determined. In the multiphoton regime, the number of photons required for absorption is reduced from n=3 (at pulse length ?>20 fs) to n=2 (at ?<8 fs) due to the energy uncertainty principle. The phase of the laser is important for optical tunneling, but is only manifest in the multiphoton regime when the number of laser cycles is close to or less than 1. The effect of the field gradient at the tip can be important when the radius of the tip is 40 nm or smaller. The extension of the model to include nonequilibrium electron distribution due to ultrafast laser excitation is discussed. Comparisons with other models and experimental findings are presented.

Pant, M.; Ang, L. K.

2012-07-01

106

Tunneling magnetoresistance and electron spin resonance study on Co-Al-O granular films  

International Nuclear Information System (INIS)

[en] In this work, a series of Co-Al-O granular films were prepared using an Ar-O2 reactive rf sputtering system. The optimal magnetoresistance (MR) ratio of 5.1% at room temperature was found in Co44Al23O33 sample. After annealing at 300 deg. C, MR ratio can be raised to 6.1%. We also measured the spectra of electron spin resonance for this series of samples and found an interesting correlation between the magnitude of MR ratio and the width of absorption field (?H). Our results show that the maximum tunneling magnetoresistance occurs when ?H is the largest, indicating the important role of magnetic microstructure in the mechanism of granular tunneling

2002-01-01

107

Molecular electronics of a single photosystem I reaction center: studies with scanning tunneling microscopy and spectroscopy.  

UK PubMed Central (United Kingdom)

Thylakoids and photosystem I (PSI) reaction centers were imaged by scanning tunneling microscopy. The thylakoids were isolated from spinach chloroplasts, and PSI reaction centers were extracted from thylakoid membranes. Because thylakoids are relatively thick nonconductors, they were sputter-coated with Pd/Au before imaging. PSI photosynthetic centers and chemically platinized PSI were investigated without sputter-coating. They were mounted on flat gold substrates that had been treated with mercaptoacetic acid to help bind the proteins. With tunneling spectroscopy, the PSI centers displayed a semiconductor-like response with a band gap of 1.8 eV. Lightly platinized (platinized for 1 hr) centers displayed diode-like conduction that resulted in dramatic contrast changes between images taken with opposite bias voltages. The electronic properties of this system were stable under long-term storage.

Lee I; Lee JW; Warmack RJ; Allison DP; Greenbaum E

1995-03-01

108

Inelastic electron tunneling spectroscopy of CoFeB/ MgO/ CoFeB based magnetic tunnel junctions in high magnetic fields  

International Nuclear Information System (INIS)

Magnetic tunnel junctions (MTJs) showing a high tunnel magnetoresistance (TMR) are important for the fabrication of MRAM devices when combined with current induced switching. We discuss inelastic electron tunneling spectroscopy (IETS) measurements on CoFeB/MgO/CoFeB magnetic tunnel junctions. The junctions are prepared by means of magnetron sputtering of CoFeB and e-beam evaporation of stoichiometric MgO. Structuring of the multilayer is done using a photolithography process and Argon ion-milling. The IETS measurements are carried out at low temperatures down to 4.2 K, high magnetic fields up to 9 T and in parallel as well as antiparallel electrode configuration in order to distinguish between different kind of excitations such as e.g. magnons and phonons. Furthermore, oxygen vacancies in the MgO barrier are controlled through variation of the sample temperature during e-beam growth to investigate the influences of these vacancies on the tunneling spectra of MTJs.

2010-01-01

109

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

DEFF Research Database (Denmark)

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 environmental nuclear motion. Cryogenic temperatures are considered. This implies that thermal activation is disregarded but vibrational relaxation in the molecular charge states is central. The electrochemical potentials of the electrodes are controlled relative to a reference electrode. The electrodes represent the substrate and tip in electrochemical in situ scanning tunnelling microscopy. An equivalent three-electrode configuration represents a molecular single-electron transistor in which the enclosing electrodes constitute source and drain, and the reference electrode the gate. Current-bias voltage relations at fixed electrochemical overpotential or gate voltage, and current-overpotential or current-gate voltage relations at fixed bias voltage are equivalent in the two systems. Due to the activation-less nature of the processes, electron flow between the electrodes through the molecular redox levels 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 level(s) subsequent to electron transfer. Several physical mechanisms can be distinguished and distinctive current-overpotential/gate voltage or current-bias voltage relations obtained. These reflect electronic level separation, environmental nuclear reorganisation, and coherent or incoherent multi-electron flow. The models and formalism have bearings on construction of single-molecule devices, illustrated by a short discussion of single-electron tunnelling in semiconductor quantum dots and reported low-temperature single-molecular transistor effects.

Kuznetsov, A.M.; Ulstrup, Jens

2004-01-01

110

Application of Airy Function Approach to Model Electron Tunneling in Graphene Nanoribbon-Based P-N Junction Diodes  

Directory of Open Access Journals (Sweden)

Full Text Available Electron transmittance in a graphene nanoribbon (GNR)-based p+-n+ junction is modeled by employing an Airy function approach. An analytical expression of the transmittance is given and electron tunneling currents in the GNR-based p+-n+ junction are also calculated. It is found that the tunneling current obtained by using the Airy function approach is higher than that under the WKB approach for narrow ribbons. For wider ribbons, the calculated tunneling current under the Airy function approach goes to that under the WKB approach. Moreover, curves of tunneling current versus ribbon width have peak currents and the peak current shifts to narrower ribbon as the electric field in the depletion region increases.

Widi Yansen; Mikrajuddin Abdullah; Khairurrijal

2010-01-01

111

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

International Nuclear Information System (INIS)

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

1997-01-01

112

Electron--Vibron Interaction Effects on Scanning Tunneling Microscopy Current through Melamine Adsorbed on Cu(100)  

Science.gov (United States)

Electron transport through the melamine molecule was studied. Melamine molecules adsorbed on a Cu(100) surface were investigated by density functional theory (DFT) calculations with the dynamical matrix method. On the basis of calculation results, a model Hamiltonian for a system composed of scanning tunneling microscope (STM), a melamine molecule, and a Cu surface was proposed, taking into account electron--vibron (electron--molecular vibrations) interactions within the melamine molecule. Then, the electronic current was formulated by the nonequilibrium Green's function (NEGF) method. Results show that current is affected by the electron--vibron interactions defined in the melamine molecule through its controllable structural changes. The rectification and fluctuation of current are triggered by low-energy electron--vibron interactions. Furthermore, the electron--vibron interaction effect is found to be enhanced as temperature increases to where higher-energy vibrons begin to be excited at lower energies. However, current becomes uniform at higher temperatures, which shows an undesired sensitivity. The weakening of the electron--vibron interaction of the out-of-molecular-plane vibrational motion can transfer the melamine molecule in its tautomerization state into a current rectifier. The reduction or induction of the repulsion of lone pairs of consecutive N atoms causes the induction or reduction of the low-energy in-plane vibrational motion, which in turn causes the switching of the I--V characteristics between less stable melamine tautomers.

Sarhan, Abdulla; Sakaue, Mamoru; Nakanishi, Hiroshi; Kasai, Hideaki

2012-10-01

113

Electron tunneling through single self-assembled InAs quantum dots coupled to nanogap electrodes  

Energy Technology Data Exchange (ETDEWEB)

We have investigated electronic properties of self-assembled InAs quantum dots (QDs) grown on GaAs surfaces by using metallic Au and Al leads with narrow gaps. The fabricated junctions with Au nanogap electrodes show single electron tunneling behaviors. When coupling between electrons in the QDs and the electrodes is strong, Kondo effect with relatively high Kondo temperature T{sub K} of 10-15 K is observed. The samples with superconducting (SC) Al electrodes also exhibit clear Coulomb blockade effects. Furthermore, clear suppression in conductance is observed around V{sub SD}=0 V for a voltage range of 4{delta}/e at T=40 mK, where {delta} is the SC energy gap of Al, demonstrating successful fabrication of the SC-QD-SC junction in the self-assembled InAs QD system. (copyright 2008 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

Jung, M. [Institute of Industrial Science, University of Tokyo, Meguro-ku (Japan); Buizert, C. [Department of Applied Physics, University of Tokyo, Hongo (Japan); Oiwa, A. [Department of Applied Physics, University of Tokyo, Hongo (Japan); CREST-JST, Honchou, Kawaguchi, Saitama (Japan); Hirakawa, K.; Machida, T. [Institute of Industrial Science, University of Tokyo, Meguro-ku (Japan); CREST-JST, Honchou, Kawaguchi, Saitama (Japan); Institute for Nano Quantum Information Electronics, University of Tokyo (Japan); Tarucha, S. [Department of Applied Physics, University of Tokyo, Hongo (Japan); CREST-JST, Honchou, Kawaguchi, Saitama (Japan); Institute for Nano Quantum Information Electronics, University of Tokyo (Japan); ICORP Spin Information Project, JST, Atsugi-shi, Kanagawa (Japan); Shibata, K.

2008-07-01

114

Electron tunneling through single self-assembled InAs quantum dots coupled to nanogap electrodes  

International Nuclear Information System (INIS)

We have investigated electronic properties of self-assembled InAs quantum dots (QDs) grown on GaAs surfaces by using metallic Au and Al leads with narrow gaps. The fabricated junctions with Au nanogap electrodes show single electron tunneling behaviors. When coupling between electrons in the QDs and the electrodes is strong, Kondo effect with relatively high Kondo temperature TK of 10-15 K is observed. The samples with superconducting (SC) Al electrodes also exhibit clear Coulomb blockade effects. Furthermore, clear suppression in conductance is observed around VSD=0 V for a voltage range of 4?/e at T=40 mK, where ? is the SC energy gap of Al, demonstrating successful fabrication of the SC-QD-SC junction in the self-assembled InAs QD system. (copyright 2008 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

2008-01-01

115

Fabrication and characterization of single electron tunneling device on Au/SiO2 nanocomposite films.  

UK PubMed Central (United Kingdom)

Amino-functionalized mesoporous silica thin films (AF-MSTFs) have been directly dip-coated on silica wafers by co-condensation of tetraethoxysilane (TEOS) and 3-aminopropyltriethoxysilane (APTES) in the presence of Brij56 (C16H33(OCH2CH2)10OH) under acidic condition. Using the AF-MSTFs as templates, gold nanoparticles (GNPs) are well formed within the mesopores. The transmission electron microscope images and X-ray diffraction patterns demonstrate that the MSTFs are consistent with well ordered mesostructures and the GNPs are well crystallized in the templates. A single electron tunneling device based on self-assembled GNPs of the Au/SiO2 nanocomposite film has been fabricated by using nanolithographic definitions. The device shows Coulomb stair-cases at 77 K. The data are interpreted as single electron tunneling through the GNP which served as a Coulomb island between the source and drain electrodes. The charging energy is estimated to be much larger than the thermal energy at 77 K. The Coulomb island size calculated from the experimental data is -3.8 nm, which is consistent with the size of the GNPs self-assembled in the MSTFs.

Fang J; Qin S; Zhang X; Sun J; Li J; Qin H; Wu D; Fang L; Chang S

2013-02-01

116

Fabrication and characterization of single electron tunneling device on Au/SiO2 nanocomposite films.  

Science.gov (United States)

Amino-functionalized mesoporous silica thin films (AF-MSTFs) have been directly dip-coated on silica wafers by co-condensation of tetraethoxysilane (TEOS) and 3-aminopropyltriethoxysilane (APTES) in the presence of Brij56 (C16H33(OCH2CH2)10OH) under acidic condition. Using the AF-MSTFs as templates, gold nanoparticles (GNPs) are well formed within the mesopores. The transmission electron microscope images and X-ray diffraction patterns demonstrate that the MSTFs are consistent with well ordered mesostructures and the GNPs are well crystallized in the templates. A single electron tunneling device based on self-assembled GNPs of the Au/SiO2 nanocomposite film has been fabricated by using nanolithographic definitions. The device shows Coulomb stair-cases at 77 K. The data are interpreted as single electron tunneling through the GNP which served as a Coulomb island between the source and drain electrodes. The charging energy is estimated to be much larger than the thermal energy at 77 K. The Coulomb island size calculated from the experimental data is -3.8 nm, which is consistent with the size of the GNPs self-assembled in the MSTFs. PMID:23646534

Fang, Jingyue; Qin, Shiqiao; Zhang, Xueao; Sun, Jiandong; Li, Jiadong; Qin, Hua; Wu, Dongming; Fang, Liang; Chang, Shengli

2013-02-01

117

Shot noise of low energy electron field emission due to Klein tunneling  

Science.gov (United States)

This paper investigates the property of shot noise for low energy electron field emission from a single-layer vertically aligned graphene sheet assuming the emission process is due to Klein tunneling. In our model, we use two different methods (relativistic WKB and transfer matrix) to calculate the transmission coefficient and thus obtain the Fano factor (? or suppression of shot noise) as a function of temperature T, Fermi energy Ef, and local electric field F. It is found that a universal maximum value of about ? = 1/3 can be reached at low temperature limit within a certain range of local electric field.

Sun, S.; Ang, L. K.

2012-07-01

118

Electron radiation effect on volt-farad characteristics of MDC-structures with tunnel-thin dielectric  

International Nuclear Information System (INIS)

[en] Effect of electron radiation in the 5-20 keV energy and 3.10-3-3.10-1 Cal/cm2 dose ranges on voltfarad characteristics of MOS structures with tunnel-thin dielectric is investigated. Electron radiation is shown to reproducibly vary the value of built- in charge and density of surface states

1985-01-01

119

Dielectric breakdown and inelastic electron tunneling spectroscopy of top pinned and bottom pinned Co-Fe-B/MgO/Co-Fe-B magnetic tunnel junctions  

International Nuclear Information System (INIS)

We present a detailed investigation into the intrinsic tunnel barrier reliability in Co-Fe-B/MgO/Co-Fe-B magnetic tunnel junctions (MTJ). The intrinsic reliability is measured as the ramped breakdown voltage (Vbd) at room temperature for both positive and negative polarity. The measurements were done for two types of junctions: one set of junctions had exchange biased (pinned) bottom electrodes, one set exchange biased (pinned) top electrodes with an additional artificial ferrimagnet. We found a significant polarity dependence in the dielectric breakdown: top as well as bottom pinned tunnel junctions showed higher breakdown voltage when the top electrode was biased positively compared to negative bias. In contrast to this the differential resistance (dV)/(dI)-V spectra revealed an asymmetry for the top pinned junctions which was reversed in comparison to the bottom pinned system. This indicates that both asymmetries have different origins. Additionally the bottom pinned junctions showed in general slightly lower breakdown voltages and stronger magnon excitation in the inelastic electron tunneling (d2I)/(dV2)-V spectra than the top pinned junctions.Possible reasons for these correlations are discussed.

2009-01-01

120

Dielectric breakdown and inelastic electron tunneling spectroscopy of top pinned and bottom pinned Co-Fe-B/MgO/Co-Fe-B magnetic tunnel junctions  

Energy Technology Data Exchange (ETDEWEB)

We present a detailed investigation into the intrinsic tunnel barrier reliability in Co-Fe-B/MgO/Co-Fe-B magnetic tunnel junctions (MTJ). The intrinsic reliability is measured as the ramped breakdown voltage (V{sub bd}) at room temperature for both positive and negative polarity. The measurements were done for two types of junctions: one set of junctions had exchange biased (pinned) bottom electrodes, one set exchange biased (pinned) top electrodes with an additional artificial ferrimagnet. We found a significant polarity dependence in the dielectric breakdown: top as well as bottom pinned tunnel junctions showed higher breakdown voltage when the top electrode was biased positively compared to negative bias. In contrast to this the differential resistance (dV)/(dI)-V spectra revealed an asymmetry for the top pinned junctions which was reversed in comparison to the bottom pinned system. This indicates that both asymmetries have different origins. Additionally the bottom pinned junctions showed in general slightly lower breakdown voltages and stronger magnon excitation in the inelastic electron tunneling (d{sup 2}I)/(dV{sup 2})-V spectra than the top pinned junctions.Possible reasons for these correlations are discussed.

Khan, Ayaz Arif; Schmalhorst, Jan; Rott, Karsten; Thomas, Andy; Reiss, Guenter [Thin Films and Physics of Nano Structures, Department of Physics, Bielefeld University, P. O. Box 100131, 33501 Bielefeld (Germany)

2009-07-01

 
 
 
 
121

Metadata for long-term preservation of electronic resources  

Directory of Open Access Journals (Sweden)

Full Text Available Metadata provide information about electronic resources and are indispensable for their localization. In the last few years due to the proliferation of digital archives increased attention has been given to metadata for long-term preservation. These metadata provide information important for accessing electronic resources in the future. The paper presents the role and function of metadata for long-term preservation in electronic archives according to the OAIS model.The author gives an overview of important international metadata frameworks and proposes a minimal metadata set for the longterm preservaton of electronic resources.

Alenka Kav?i?-?oli?

2004-01-01

122

Use of electronic information resources in goverment libraries  

Directory of Open Access Journals (Sweden)

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.

Simona Omahen; Maja Žumer

2003-01-01

123

Self-tunnelling oscillations in non-linear quantum mechanics and the electron-transfer problem  

International Nuclear Information System (INIS)

A small quantum system with a non-linear self-consistent potential may display a spontaneous symmetry breaking of the ground state. This simple result, which can be interpreted also as a spontaneous self-localization of the wavefunction, results in the presence of several equivalent ground states, which do not exist simultaneously. There is a virtual degeneracy in the system. The addition of a stochastic perturbation (noise) to such a system provides the possibility of tunnelling among the different equivalent ground states. The tunnelling process can lock itself in into a characteristic frequency related to the dynamics of the system and not contained in the input noise. A self-pulsating quantum system is then generated based on the intrinsic non-linearity of the dynamics and the presence of noise, which is used as a seed. We inquiry into the relevance of these phenomena for electron transfer processes in large biomolecules. By combining non-linearity and noise a controlled transfer rate can be achieved in what is effectively a quantum-switch regulated by external perturbations; a mechanism that could be at work in many electron-transfer processes in proteins.

2004-02-16

124

Electron beam induced purification of dilute off gases from industrial processes and automobile tunnels  

International Nuclear Information System (INIS)

The electron beam process has proved to be an efficient method for the removal of inorganic pollutants from flue gas. Since it simulates natural processes which occur in the atmospheric photochemistry, it appeared attractive to investigate the potential of the e-beam process to clean off-gases which contain hydrocarbon and inorganic trace components. Such emissions arise from industrial processes and from automobile tunnels. Commercial solvents were vaporized in air and irradiated with energetic electrons (300 keV). CO, CO2 and aerosol particles were found as products and were determined quantitatively. The aerosol particles can be collected by a gravel bed filter and can be removed by combustion or biological degradation. From experiments and model calculations it was found that the e-beam process is a very economic tool to remove hydrocarbons from large off-gas volumes at initial concentrations of 50-100 mg C/m3, and that NOx can be removed very efficiently from tunnel off-gas. (author).

1993-01-01

125

Kinetics of tunneling electron transfer between antimorphous defects in optical crystals with mobile cations  

Science.gov (United States)

The experimental data on the transient optical absorption of wide-band-gap optical crystals of lithium borates Li2B4O7, LiB3O5, and Li6Gd(BO3)3 and potassium (KH2PO4 (KDP)) and ammonium (NH4H2PO4 (ADP)) dihydrogen phosphates in the visible and ultraviolet spectral regions are analyzed using the theory of diffusion-controlled tunneling recombination. A nanosecond pulsed radiation action on these crystals is shown to form defect pairs, such as polaron-type hole centers and electron centers based on interstitial cations. The relaxation kinetics of these centers over a wide time range of 10-8-10 s is described by a proposed model of tunneling electron transfer between antimorphous defects in the cation sublattice under the thermally stimulated mobility of recombination partners. The numerical values of the kinetic parameters are determined and the time dependences of the reaction rate constants are calculated for all crystals under study. As a result, the dynamics of change in the optical properties of these crystals under a pulsed radiation action can be simulated.

Ogorodnikov, I. N.; Kiseleva, M. S.

2012-07-01

126

Recovery of nanomolecular electronic states from tunneling spectroscopy: LDOS of low-dimensional phthalocyanine molecular structures on Cu(111)  

Science.gov (United States)

Organic nanomolecules have become one of the most attractive materials for new nanoelectronics devices. Understanding of the electronic density of states around the Fermi energy of low-dimensional molecules is crucial in designing the electronic properties of molecular devices. The low dimensionality of nanomolecules results in new electronic properties owing to their unique symmetry. Scanning tunneling spectroscopy is one of the most effective techniques for studying the electronic states of nanomolecules, particularly near the Fermi energy (±1.5 eV), whereas these molecular electronic states are frequently buried by the tunneling probability background in tunneling spectroscopy, resulting in incorrect determination of the molecular electronic states. Here, we demonstrate how to recover nanomolecular electronic states from dI/dV curves obtained by tunneling spectroscopy. Precise local density of states (LDOS) peaks for low-dimensional nanostructures (monolayer ultrathin films, one-dimensional chains, and single molecules) of phthalocyanine (H2Pc) molecules grown on noble fcc-Cu(111) were obtained.

Yamagishi, Y.; Nakashima, S.; Oiso, K.; Yamada, T. K.

2013-10-01

127

Disentangling electron tunneling and protein dynamics of cytochrome c through a rationally designed surface mutation.  

Science.gov (United States)

Nonexponential distance dependence of the apparent electron-transfer (ET) rate has been reported for a variety of redox proteins immobilized on biocompatible electrodes, thus posing a physicochemical challenge of possible physiological relevance. We have recently proposed that this behavior may arise not only from the structural and dynamical complexity of the redox proteins but also from their interplay with strong electric fields present in the experimental setups and in vivo (J. Am Chem. Soc. 2010, 132, 5769-5778). Therefore, protein dynamics are finely controlled by the energetics of both specific contacts and the interaction between the protein's dipole moment and the interfacial electric fields. In turn, protein dynamics may govern electron-transfer kinetics through reorientation from low to high donor-acceptor electronic coupling orientations. Here we present a combined computational and experimental study of WT cytochrome c and the surface mutant K87C adsorbed on electrodes coated with self-assembled monolayers (SAMs) of varying thickness (i.e., variable strength of the interfacial electric field). Replacement of the positively charged K87 by a neutral amino acid allowed us to disentangle protein dynamics and electron tunneling from the reaction kinetics and to rationalize the anomalous distance dependence in terms of (at least) two populations of distinct average electronic couplings. Thus, it was possible to recover the exponential distance dependence expected from ET theory. These results pave the way for gaining further insight into the parameters that control protein electron transfer. PMID:23611698

Alvarez-Paggi, Damián; Meister, Wiebke; Kuhlmann, Uwe; Weidinger, Inez; Tenger, Katalin; Zimányi, László; Rákhely, Gábor; Hildebrandt, Peter; Murgida, Daniel H

2013-05-09

128

Magnetooscillations of the tunneling current between two-dimensional electron systems  

International Nuclear Information System (INIS)

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.

1995-01-01

129

Imaging surface electronic structure of NiAl(110) using low-temperature scanning tunneling microscopy  

International Nuclear Information System (INIS)

The surface electronic structure of NiAl(110) is examined by means of scanning tunneling microscopy and spectroscopy at a temperature of 4 K. Topography and conductance images for a wide range of bias voltages reveal wavelike patterns around steps and defects. Fourier transforms of conductance images are used to map the surface electronic structure of NiAl(110). We interpret the patterns in the Fourier transforms in terms of surface resonances, and analyze the details of its dispersion relation E(k parallel). A comparison with density-functional-based calculations and photoemission experiments is presented, and alternative explanations for the appearance of structures in Fourier transforms of conductance images are discussed. (orig.)

2001-01-01

130

Imaging surface electronic structure of NiAl(110) using low-temperature scanning tunneling microscopy  

Energy Technology Data Exchange (ETDEWEB)

The surface electronic structure of NiAl(110) is examined by means of scanning tunneling microscopy and spectroscopy at a temperature of 4 K. Topography and conductance images for a wide range of bias voltages reveal wavelike patterns around steps and defects. Fourier transforms of conductance images are used to map the surface electronic structure of NiAl(110). We interpret the patterns in the Fourier transforms in terms of surface resonances, and analyze the details of its dispersion relation E(k {sub parallel}). A comparison with density-functional-based calculations and photoemission experiments is presented, and alternative explanations for the appearance of structures in Fourier transforms of conductance images are discussed. (orig.)

Song, Z.; Pascual, J.I.; Conrad, H.; Horn, K.; Rust, H.P. [Fritz-Haber-Institut der Max-Planck-Gesellschaft, Berlin (Germany)

2001-04-01

131

Single- and two-electron tunneling processes in superconductors with local pairs  

International Nuclear Information System (INIS)

It is shown that the tunnel current flowing from the superconductor with local pairs to the normal metal or a BCS superconductor has two components. One of them is exactly similar to that in the BCS theory; the only distinction consists in a different temperature dependence of the single-electron energy gap, which can be very anisotropic. The other component is related to the transformation of local pairs into band states at the metal boundary. Its voltage dependence permits finding a pair into band states at the metal boundary. Its voltage dependence permits finding a pair gap R along with the single-electron one. The pair concentration ? can be estimated from the asymmetry of the I-V-characteristics of the quasi-particle current in the normal state.

1989-01-01

132

Nonequilibrium theory of a hot-electron bolometer with normal metal-insulator-superconductor tunnel junction  

Energy Technology Data Exchange (ETDEWEB)

The operation of the hot-electron bolometer with normal metal-insulator-superconductor (NIS) tunnel junction as a temperature sensor is analyzed theoretically. The responsivity and the noise equivalent power (NEP) of the bolometer are obtained numerically for typical experimental parameters. Relatively simple approximate analytical expressions for these values are derived. The time constant of the device is also found. We demonstrate that the effect of the electron cooling by the NIS junction, which serves as a thermometer, can improve the sensitivity. This effect is also useful in the presence of the finite background power load. We discuss the effect of the correlation of the shot noise and the heat flow noise in the NIS junction. {copyright} 2001 American Institute of Physics.

Golubev, Dmitri; Kuzmin, Leonid

2001-06-01

133

Nonequilibrium theory of a hot-electron bolometer with normal metal-insulator-superconductor tunnel junction  

International Nuclear Information System (INIS)

[en] The operation of the hot-electron bolometer with normal metal-insulator-superconductor (NIS) tunnel junction as a temperature sensor is analyzed theoretically. The responsivity and the noise equivalent power (NEP) of the bolometer are obtained numerically for typical experimental parameters. Relatively simple approximate analytical expressions for these values are derived. The time constant of the device is also found. We demonstrate that the effect of the electron cooling by the NIS junction, which serves as a thermometer, can improve the sensitivity. This effect is also useful in the presence of the finite background power load. We discuss the effect of the correlation of the shot noise and the heat flow noise in the NIS junction. [copyright] 2001 American Institute of Physics

2001-06-01

134

Resonance tunneling and localized center electron Coulomb pushing on volt-ampere characteristics of NIN-, SIN- and SIS-tunnel structures  

International Nuclear Information System (INIS)

Effect of strong (U?T, eV) coulomb pushing of electrons at the localized states inside dielectrical interlayer on properties of tunnel SIS- SIN- and NIN-structures is studied in ferms of Anderson model. Distribution of the localized states by energy is considered to be uniform one, while in space, both uniform and plane concentrated one, where plane is parallel to the structure boundaries. Nonsymmetry of volt-ampere characteristic is shown to be observed at U?0 in NIN-transitions. The obtained results agree with the experimental data obtained in tunnel SIN-transitions with HTSC electrodes and at investigation into superconductor/semiconductor boundaries. Conclusion is made about the possibility to determine the fields of location of localized states in the interlayer proceeding from the analysis of peculiarities of volt-ampere characteristics of transitions.

1993-01-01

135

Role of Inter-Electron Interaction in the Pseudo-Gap Opening in High $T_{c}$ Tunneling Experiments  

CERN Multimedia

The analysis of tunneling experiments showing the pseudogap type behavior is carried out based on the idea of the renormalization of density of states due to the inter-electron interaction in the Cooper channel (superconducting fluctuations contribution in tunneling current). It is demonstrated that the observed kink of the zero-bias conductance $G(0,T)$ of $YBaCuO/Pb$ junctions in the vicinity of $T_c$ can be explained in terms of fluctuation theory in a quite wide range of temperature above $T_c$, using the values of microscopic parameters of the $YBaCuO$ electron spectrum taken from independent experiments. The approach proposed also permits to explain qualitatively the shape of the tunneling anomalies in $G(V,T)$ and gives a correct estimate for the pseudogap position and amplitude observed in the experiments on $BiSrCaCuO$ junctions.

Cucolo, A M; Varlamov, A A

1999-01-01

136

Electron tunneling characteristics on La[subscript 0.7]Sr[subscript 0.3]MnO[subscript 3] thin-film surfaces at high temperature Electron tunneling characteristics on La0.7Sr0.3MnO3 thin-film surfaces at high temperature  

Digital Repository Infrastructure Vision for European Research (DRIVER)

We report on the electron tunneling characteristics on La0.7Sr0.3MnO3 (LSM) thin-film surfaces up to 580?°C in 10[superscript ?3]?mbar oxygen pressure, using scanning tunneling microscopy/spectroscopy (STM/STS). A thresholdlike drop in the tunneling current was observed at positive bias in STS, whic...

Katsiev, Khabiboulakh; Yildiz, Bilge; Balasubramaniam, Kavaipatti; Salvador, Paul A.

137

Scanning Tunneling and Electronic Microscopy of Diamond Irradiated by High Energy Ions  

International Nuclear Information System (INIS)

The surfaces of boron doped synthetic and natural diamonds have been investigated by scanning tunneling (STM) and electronic microscopy (SEM) before and after irradiation with 40 Ar (25 MeV), 84 Kr (210 MeV), 129 Xe (124 MeV) ions. The structures observed (STM) after irradiation showed craters ranging from 3 nm to 20 nm in diameters, which are deduced to be single ion tracks and multiple hits of ions at the nearest positions of the surface. In the case of argon ion irradiation the surface was very amorphous, but after xenon irradiation one could see parts of surface without amorphism. It can be explained by the influence of high inelastic energy losses. 20 refs., 5 figs

1994-01-01

138

Scanning tunneling microscopy of defects and electronic fluctuations in Cu-doped Bi2Se3  

Science.gov (United States)

We report scanning tunneling microscopy and spectroscopy studies of the topological insulator CuxBi2Se3. We have identified five different atomic-resolution signatures of Cu dopant-related point defects and correlated several of them to density functional theory simulations of the defects. Most interestingly, by investigating the dI/dV images of the known BiSe antisite defects as a function of bias, we show that local electronic structure can vary substantially over a length scale of 30nm, with amplitudes as large as ±50meV. The strong fluctuations appear to be caused by a variety of defects and may have consequences for the topological surface state, as revealed by quasiparticle scattering studies. Correlation of quasiparticle scattering with the various defects indicates that the surface state is robust to backscattering, though detailed analysis shows that some defects are more effective in producing stationary scattering states than others.

Mann, Christopher; West, Damien; Miotkowski, Ireneusz; Chen, Yong; Zhang, Shengbai; Shih, Chih-Kang

2013-03-01

139

Detailed analysis of water structure in a solvent mediated electron tunneling mechanism  

Energy Technology Data Exchange (ETDEWEB)

This work aims at describing the water structure characteristics that influence the electron transfer superexchange mechanism by explicitly calculating the solvent mediated conductance between the donor and acceptor in a generic pair. The method employed here is based on the non-equilibrium Green function formalism for calculating the conductance over solvent trajectories previously determined by molecular dynamics methods. A non-exponential dependence of the conductance is observed with respect to the distance between the donor and the acceptor. Local fluctuations of the solvent structure are responsible for the non-monotonic dependence, mainly due to the formation of solvent bridges that act as a molecular wire connecting the sites. This shortcutting phenomenon is observed for certain ranges of distances between the donor and acceptor in the pair. Charge on the sites strongly affects the local solvent structure and causes qualitative changes in the distance dependence of the tunneling probability.

Negre, Christian F A; Sanchez, Cristian G [Departamento de Matematica y Fisica, Facultad de Ciencias Quimicas, INFIQC, Universidad Nacional de Cordoba, Ciudad Universitaria, Cordoba (Argentina); Jara, Gabriel E; Pierini, Adriana B [Departamento de Quimica Organica, Facultad de Ciencias Quimicas, INFIQC, Universidad Nacional de Cordoba, Ciudad Universitaria, Cordoba (Argentina); Vera, D Mariano A, E-mail: cgsanchez@fcq.unc.edu.ar [Departamento de Quimica, Facultad de Ciencias Exactas, Universidad Nacional de Mar del Plata, Mar del Plata (Argentina)

2011-06-22

140

High resolution electron microscopy observation of different Al-oxide layers in magnetic tunnel junctions  

Energy Technology Data Exchange (ETDEWEB)

Microstructure and morphology of Al-oxide layers in magnetic tunnel junctions (MTJs) were characterized using high resolution electron microscopy (HREM). The MTJs were fabricated using magnetron sputtering. The Al-oxide layers were prepared using four different methods; natural, thermal, and plasma oxidation techniques as well as sputtering from pure alumina. HREM results showed that sputtering conditions, surface roughness of the bottom electrode in the MTJs, and oxidation conditions for the Al-oxide are essential factors affecting the quality of the insulating layer. High sputtering power was required to deposit a relatively smooth layer of pure alumina. Al matrices were observed in Al-oxide with only 24h natural oxidation time. It was found optimum to thermally oxidize an Al-oxide layer between 333 and 473K for 48h. It is more effective and useful to oxidize an Al layer at a slightly higher plasma power rather than using a longer oxidation time in plasma oxidation method. (author)

Yu, Andrew Chak Chung; Miyazaki, Terunobu [Department of Applied Physics, Graduate School of Engineering, Tohoku Univ., Sendai, Miyagi (Japan); Doole, Ron; Petford-Long, Amanda [Department of Materials, Univ. of Oxford, Parks Road, Oxford (United Kingdom)

2001-08-01

 
 
 
 
141

User Perception of Electronic Resources in the University of Ilorin  

Directory of Open Access Journals (Sweden)

Full Text Available This study examined the user perception of the electronic resources by the academic staff of the University of Ilorin. The sample consists of 250 academic staff selected from eight (8) out of the twelve (12) faculties that made up of the university. Data were collected through an electronic resources user perceptional survey (ERUPS). Responses were received from 225 (90%) academic staff of the eight faculties. Analysis revealed frequency of use of electronic resources was low. Reasons alluded to were lack of time because of the time required to focus on teaching; lack of awareness to electronic resources provided by the library; power outage, ineffective communication channels, slow network and inadequate searching skills. The study recommended adequate Information and Communication Technologies (ICT) training for all categories of academic staff and provision of adequate power supply.

BASHORUN; M. Tunji; ISAH Abdulmumin; M.Y ADISA

2011-01-01

142

Freshmen's use of library electronic resources and self-efficacy  

Directory of Open Access Journals (Sweden)

Full Text Available To encourage students use of the library, and in particular of its electronic resources, we need to understand what factors encourage students to seek out information in the library setting. Research has shown that self-efficacy influences academic achievement. This paper looks at the role self-efficacy plays in their search for information and use of the library's electronic resources, by surveying a class of freshmen at Baruch College. Their library and computer use were analyzed and correlated with their self-efficacy scores. Through statistical analysis, we found that use of the library correlated to the students' use of the library's electronic resources. We also found out that students who express an interest in learning about the library's electronic resources will be more likely to have higher self-efficacy.

Micaela Waldman

2003-01-01

143

Evaluation Criteria for Electronic Reference Resources Available on the Internet  

Directory of Open Access Journals (Sweden)

Full Text Available Article about evaluation of electronic reference resources available on the internet, it aims at creating a check list for evaluation criteria, the suggested list contains four main categories; technical features, content, media features, and user interface

Reda Mohamed al-Najar

2007-01-01

144

Study of Scanning Tunneling Microscope control electronics. Estudio del Sistema de Control y Estabilidad en el microscopico de efecto tunel  

Energy Technology Data Exchange (ETDEWEB)

A theoretical study of Scanning Tunneling Microscope control electronics is made. The knowledge of its behaviour allows us to determine accurately the region where the unstable operation could effect the measurements, and also to set the optimal working parameters. Each feedback circuitry compound is discussed as well as their mutual interaction. Different working conditions analysis and results are presented. (Author) 12 refs.

Oliva, A.J.; Pancarobo, M.; Denisenko, N.; Aguilar, M.; Rejon, V.; Pea, J.L. (Instituto de Ciencia de Materiales, CSIC, Universidad Autonoma de Madrid, Madrid (Spain))

1994-01-01

145

Influence of doping on the electronic transport in GaSb/InAs(Sb) nanowire tunnel devices  

Digital Repository Infrastructure Vision for European Research (DRIVER)

The effect of various doping profiles on the electronic transport in GaSb/InAs(Sb) nanowire tunnel diodes is investigated. Zn-doping of the GaSb segment increases both the peak current density and the current level in reverse bias. Top-gated diodes exhibit peak current modulation with a threshold vo...

Borg, Mattias; Ek, Martin; Ganjipour, Bahram; Dey, Anil; Dick, Kimberly; Wernersson, Lars-Erik; Thelander, Claes

146

Atomic and electronic structure of the BaTiO3/Fe interface in multiferroic tunnel junctions.  

UK PubMed Central (United Kingdom)

Artificial multiferroic tunnel junctions combining a ferroelectric tunnel barrier of BaTiO(3) with magnetic electrodes display a tunnel magnetoresistance whose intensity can be controlled by the ferroelectric polarization of the barrier. This effect, called tunnel electromagnetoresistance (TEMR), and the corollary magnetoelectric coupling mechanisms at the BaTiO(3)/Fe interface were recently reported through macroscopic techniques. Here, we use advanced spectromicroscopy techniques by means of aberration-corrected scanning transmission electron microscopy (STEM) and electron energy-loss spectroscopy (EELS) to probe locally the nanoscale structural and electronic modifications at the ferroelectric/ferromagnetic interface. Atomically resolved real-space spectroscopic techniques reveal the presence of a single FeO layer between BaTiO(3) and Fe. Based on this accurate description of the studied interface, we propose an atomistic model of the ferroelectric/ferromagnetic interface further validated by comparing experimental and simulated STEM images with atomic resolution. Density functional theory calculations allow us to interpret the electronic and magnetic properties of these interfaces and to understand better their key role in the physics of multiferroics nanostructures.

Bocher L; Gloter A; Crassous A; Garcia V; March K; Zobelli A; Valencia S; Enouz-Vedrenne S; Moya X; Mathur ND; Marthur ND; Deranlot C; Fusil S; Bouzehouane K; Bibes M; Barthélémy A; Colliex C; Stéphan O

2012-01-01

147

Potential electron emission induced by multiply charged ions in thin film tunnel junctions  

International Nuclear Information System (INIS)

Thin film metal-insulator-metal tunnel junctions are used to investigate the electronic excitation process induced by the impact of multiply charged ions onto a metallic surface. Hot charge carriers (electrons and holes) generated by the dissipation of the kinetic and potential energies of the projectiles are detected as an ion induced internal emission current from the bombarded 'top' metal film into the 'bottom' substrate electrode. Results are presented for Arq+ ions with a kinetic impact energy of 1 keV and charge states q=1-8 impinging onto an Ag-AlOx-Al junction. It is shown that the internal emission yield exhibits an approximately linear dependence on the potential energy of the projectile. At low potential energy, a bias voltage applied between the two metal films is found to strongly influence the internal emission current, whereas this influence becomes much weaker with increasing projectile charge state. The results are shown to be qualitatively well described in the framework of a thermodynamical free-electron model.

2008-06-15

148

Tunneling of electrons with conservation of the transverse wave vector in the Au/CaF2/Si(111) system  

Science.gov (United States)

Epitaxial layers of calcium fluoride on silicon(111) have been prepared, in which tunneling transfer of electrons with conservation of the transverse momentum component has been observed. A good agreement between the results of simulation and the experimental data has been achieved. The procedure underlying the calculations has been described in detail. The obtained films are suitable for the use as barrier layers in various solid-state electronic devices.

Vexler, M. I.; Illarionov, Yu. Yu.; Suturin, S. M.; Fedorov, V. V.; Sokolov, N. S.

2010-11-01

149

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

Science.gov (United States)

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 can be controlled, reflected in spectroscopic features when the potential variation brings the redox level to cross the Fermi levels of the substrate and tip. The blue copper protein azurin adsorbs on gold(111) via a surface disulfide group. Well resolved in situ STM images show arrays of molecules on the triangular gold(111) terraces. This points to the feasibility of in situ STM of redox metalloproteins directly in their natural aqueous medium. Each structure also shows a central brighter contrast in the constant current mode, indicative of 2- to 4-fold current enhancement compared with the peripheral parts. This supports the notion of tunneling via the redox level of the copper atom and of in situ STM as a new approach to long-range electron tunneling in metalloproteins. PMID:9990032

Friis, E P; Andersen, J E; Kharkats, Y I; Kuznetsov, A M; Nichols, R J; Zhang, J D; Ulstrup, J

1999-02-16

150

Building an electronic resource collection a practical guide  

CERN Document Server

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.

Lee, Stuart D

2004-01-01

151

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

International Nuclear Information System (INIS)

[en] 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.)

2008-01-01

152

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

Directory of Open Access Journals (Sweden)

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.

M.V. Tkach; Ju.O. Seti; O.M. Voitsekhivska

2011-01-01

153

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

DEFF Research Database (Denmark)

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 chronocoulometry, and density functional theory (DFT) computations. Cys molecules were assembled on single-crystal Au(110) surfaces to form a highly ordered monolayer with a periodic lattice structure of c(2 x 2) in which each unit contains two molecules; this conclusion is confirmed by the results of calculations based on a slab model for the metal surface. The ordered monolayer offers a platform for submolecular scale electronic mapping that is an issue of fundamental interest but remains a challenge in STM imaging science and surface chemistry. Single Cys molecules were mapped as three electronic subunits contributed mainly from three chemical moieties: thiol (-SH), carboxylic (-COOH), and amine (-NH2) groups. The contrastsof the three subunits depend on the environment (e.g., pH), which affects the electronic structure of adsorbed species. From the DFT computations focused on single molecules, rational analysis of the electronic structures is achieved to delineate the main factors that determine electronic contrasts in the STM images. These factors include the molecular orientation, the chemical nature of the elements or groups in the molecule, and the interaction of the elements with the substrate 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, suggesting solvent plays a role during molecular assembly.

Zhang, Jingdong; Chi, Qijin

2009-01-01

154

Correlated sequential tunneling through a double barrier for interacting one-dimensional electrons  

CERN Multimedia

The problem of resonant tunneling through a quantum dot weakly coupled to spinless Tomonaga-Luttinger liquids has been studied. We compute the linear conductance due to sequential tunneling processes upon employing a master equation approach. Besides the previously used lowest-order Golden Rule rates describing uncorrelated sequential tunneling (UST) processes, we systematically include higher-order correlated sequential tunneling (CST) diagrams within the standard Weisskopf-Wigner approximation. We provide estimates for the parameter regions where CST effects can be important. Focusing mainly on the temperature dependence of the peak conductance, we discuss the relation of these findings to previous theoretical and experimental results.

Thorwart, M; Grifoni, M

2004-01-01

155

Biology Resources in the Electronic Age  

CERN Multimedia

How can students, teachers, parents, and librarians be certain that the information a Web site provides is accurate and age appropriate? In this unique book, experienced science educator Judith A. Bazler reviews hundreds of the most reliable biology-related Web sites. Each review discusses the most appropriate grade level of the site, analyzes its accuracy and usefulness, and provides helpful hints for getting the most out of the resource.||The Web is the first place many students look for information. Yet the Web is notoriously unreliable. How can students, teachers, parents, and librarians b

Bazler, Judith

2003-01-01

156

Electronics Learning-Resources on the Web  

Science.gov (United States)

The links on this page are to background information which students taking electronics courses (particularly PHY2003, PHY3128) may find helpful. The descriptors used in the tables are explained at the bottom of the page. Topics include Circuit Analysis and Complex Variables, Techniques and Good Practice, Oscilloscopes, Passive Components, Diodes, Transistors, Op-Amps, Filters, Digital Signal, Processing, Applications and Circuits, Monostables and Astables, and Microcontrollers and PICsSpice: Learning and using Spice

Williams, Charles D.

2013-06-12

157

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

DEFF Research Database (Denmark)

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 rectification. The differential conductance/bias voltage correlation can have up to four peaks even for a single-level redox molecule. The peak position, height, and width are determined by the oxidized and reduced states of both the ionization and affinity levels of the molecule and depend crucially on the Debye screening of the electric field in the tunneling gap. ©2009 American Institute of Physics

Medvedev, Igor M.; Kuznetsov, Alexander M.

2009-01-01

158

Why and How to Measure the Use of Electronic Resources  

Directory of Open Access Journals (Sweden)

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.

Jean Bernon

2008-01-01

159

Access to electronic resources by visually impaired people  

Directory of Open Access Journals (Sweden)

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.

Jenny Craven

2003-01-01

160

Discipline, availability of electronic resources and the use of Finnish National Electronic Library - FinELib  

Directory of Open Access Journals (Sweden)

Full Text Available This study elaborated relations between digital library use by university faculty, users' discipline and the availability of key resources in the Finnish National Electronic Library (FinELib), Finnish national digital library, by using nationwide representative survey data. The results show that the perceived availability of key electronic resources by researchers in FinELib was a stronger predictor of the frequency and purpose of use of its services than users' discipline. Regardless of discipline a good perceived provision of central resources led to a more frequent use of FinELib. The satisfaction with the services did not vary with the discipline, but with the perceived availability of resources.

Sanna Torma; Pertti Vakkari

2004-01-01

 
 
 
 
161

Fine structure in the tunneling spectra of electron-doped cuprates: no coupling to the magnetic resonance mode.  

UK PubMed Central (United Kingdom)

We reanalyze high-resolution scanning tunneling spectra of the electron-doped cuprate Pr(0.88)LaCe(0.12)CuO(4) (T(c) = 24 K). We find that the spectral fine structure below 35 meV is consistent with strong coupling to a bosonic mode at about 16 meV, in quantitative agreement with early tunneling spectra of Nd(1.85)Ce(0.15)CuO(4). Since the energy of the bosonic mode is significantly higher than that (9.5-11 meV) of the magnetic resonancelike mode observed by inelastic neutron scattering, the coupling feature at about 16 meV cannot arise from strong coupling to the magnetic mode. The present work thus demonstrates that the magnetic resonancelike mode cannot be the origin of high-temperature superconductivity in electron-doped cuprates.

Zhao GM

2009-12-01

162

Fine structure in the tunneling spectra of electron-doped cuprates: no coupling to the magnetic resonance mode.  

Science.gov (United States)

We reanalyze high-resolution scanning tunneling spectra of the electron-doped cuprate Pr(0.88)LaCe(0.12)CuO(4) (T(c) = 24 K). We find that the spectral fine structure below 35 meV is consistent with strong coupling to a bosonic mode at about 16 meV, in quantitative agreement with early tunneling spectra of Nd(1.85)Ce(0.15)CuO(4). Since the energy of the bosonic mode is significantly higher than that (9.5-11 meV) of the magnetic resonancelike mode observed by inelastic neutron scattering, the coupling feature at about 16 meV cannot arise from strong coupling to the magnetic mode. The present work thus demonstrates that the magnetic resonancelike mode cannot be the origin of high-temperature superconductivity in electron-doped cuprates. PMID:20366161

Zhao, Guo-meng

2009-12-04

163

Characterization of the asymmetrical barrier potentials in CoFe/AlOx/Co magnetic tunneling junction by electron holography  

International Nuclear Information System (INIS)

Electron holography (EH) in a field emission gun transmission electron microscope has been used to profile the inner potential V0 across CoFe/AlOx/Co magnetic tunneling junctions (MTJs). The spatial dimension of the AlOx barrier layer can be accurately determined from the phase profile at the tunneling junctions. The EH results show unambiguously that the potential jump across the CoFe/AlOx interface is smaller than that across the Co/AlOx interface, which results in asymmetrical barriers in the MTJs. The inner potential difference and the asymmetrical barrier were discussed based on the different oxidation statuses between Co/AlOx and CoFe/AlOx interfaces.

2003-01-01

164

Sequential and co-tunneling behavior in the temperature-dependent thermopower of few-electron quantum dots  

CERN Multimedia

We have studied the temperature dependent thermopower of gate-defined, lateral quantum dots in the Coulomb blockade regime using an electron heating technique. The line shape of the thermopower oscillations depends strongly on the contributing tunneling processes. Between 1.5 K and 40 mK a crossover from a pure sawtooth- to an intermitted sawtooth-like line shape is observed. The latter is attributed to the increasing dominance of cotunneling processes in the Coulomb blockade regime at low temperatures.

Scheibner, R; Borzenko, T; König, M; Reuter, D; Wieck, A D; Buhmann, H; Molenkamp, L W

2006-01-01

165

Some observations on tunnelling of trapped electrons in feldspars and their implications for optical dating  

Science.gov (United States)

Anomalous fading in feldspars is now understood to be caused by the tunnelling of electrons from one defect site to another. Here we present some experimental observations concerning the phenomenon. The fading rates of a variety of feldspar crystals and K-feldspar separates from sediments are reported. It is found that (1) the fading rates of 77 K-feldspar extracts from sediments range from 1 to 10%/decade, with an average value of about 5%/decade, (2) the fading rates of K-feldspars extracted from sediments derived largely from volcanic bedrock are not higher than those from non-volcanic bedrock as is widely thought, (3) the fading rates of 31 individual feldspars range from 1 to 35%/decade, (4) in plagioclase feldspars the fading rate increases with increasing Ca and/or Fe content, (5) the fading rate increases with laboratory radiation dose at large doses, (6) for samples for which the time elapsed since burial is long enough for their luminescence to be in saturation, the fading rate is correlated with the ratio of the field saturation intensity to the laboratory saturation intensity; extrapolation to zero fading rate shows that trap emptying as a result of thermal eviction is not significant, and that the mean thermal lifetime in temperate environments of electrons in traps relevant to dating is ?4 Ma., and (7), different aliquots of a sample can have fading rates that differ by a factor as large as two even if the aliquots contain several thousands of grains, thus it is necessary to ensure when correcting ages for anomalous fading that the fading rate used is that applicable to the aliquots on which the equivalent dose is measured.

Huntley, D. J.; Lian, Olav B.

2006-10-01

166

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

International Nuclear Information System (INIS)

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.

2009-01-01

167

Effect of internal conversion of vibrational quanta in electron tunneling: a scheme for direct experimental observation and current/voltage relationships.  

UK PubMed Central (United Kingdom)

Electron tunneling through bridge molecular groups with a strong coupling to a local quantum vibrational mode is considered. A scheme is suggested for direct experimental observation of the effect of internal conversion of vibrational quanta in inelastic electron tunneling. The effect consists of excitation and re-absorption of vibrational quanta in bridge by tunneling electrons. The tunnel current produced by the absorption of vibrational quanta by the same or another electron can in principle be detected in an experimental setup a scheme of which is suggested. Current/voltage dependences have general spectroscopic features. Possible effects that can take place in the case of additional strong interaction with classical vibrational modes are discussed.

Kuznetsov AM

2006-01-01

168

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

International Nuclear Information System (INIS)

[en] 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 (? = 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.

2012-06-04

169

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

Energy Technology Data Exchange (ETDEWEB)

Highlights: Black-Right-Pointing-Pointer Irradiation of photons with energies more than the band gap generates electron-hole pairs. Black-Right-Pointing-Pointer Electron tunneling probability is dependent on the electron mobility. Black-Right-Pointing-Pointer Tunneling electrons are captured by charge deficient atoms. Black-Right-Pointing-Pointer 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 ({lambda} = 355 nm) with energy more than the band gap of ZnO produces ions that can be detected in negative mode. When TiO{sub 2} 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.

Zhong Hongying, E-mail: hyzhong@mail.ccnu.edu.cn [Key Laboratory of Pesticides and Chemical Biology, Ministry of Education, College of Chemistry, Central China Normal University, Wuhan, Hubei 430079 (China); Fu Jieying; Wang Xiaoli; Zheng Shi [Key Laboratory of Pesticides and Chemical Biology, Ministry of Education, College of Chemistry, Central China Normal University, Wuhan, Hubei 430079 (China)

2012-06-04

170

Impact of phonon-assisted tunneling on electronic conductivity in graphene nanoribbons and oxides ones  

Directory of Open Access Journals (Sweden)

Full Text Available Phonon-assisted tunneling (PhAT) model is applied for explication of temperature-dependent conductivity and I-V characteristics measured by various investigators for graphene nanoribbons and oxides ones. Proposed model describes well not only current dependence on temperature but also the temperature-dependent I-V data using the same set of parameters characterizing material under investigation. The values of active phonons energy and field strength for tunneling are estimated from the fit of current dependence on temperature and I-V/T data with the phonon-assisted tunneling theory.

Povilas Pipinys; Antanas Kiveris

2010-01-01

171

Electronic Transport in Single Molecule Junctions: Control of the Molecule-Electrode Coupling Through Intramolecular Tunneling Barriers  

DEFF Research Database (Denmark)

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. One derivative has additional methylene groups separating the thiols from the delocalized -electron system. The insertion of methylene groups changes the open state conductance by 3-4 orders of magnitude and changes the transport mechanism from a coherent regime with finite zero-bias conductance to sequential tunneling and Coulomb blockade behavior.

Danilov, Andrey; Kubatkin, Sergey

2008-01-01

172

Electronic structures of one-dimensional metal-molecule hybrid chains studied using scanning tunneling microscopy and density functional theory.  

UK PubMed Central (United Kingdom)

The electronic structures of self-assembled hybrid chains comprising Ag atoms and organic molecules were studied using scanning tunneling microscopy (STM) and spectroscopy (STS) in parallel with density functional theory (DFT). Hybrid chains were prepared by catalytic breaking of Br-C bonds in 4,4?-dibromo-p-terphenyl molecules, followed by spontaneous formation of Ag-C bonds on Ag(111). An atomic model was proposed for the observed hybrid chain structures. Four electronic states were resolved using STS measurements, and strong energy dependence was observed in STM images. These results were explained using first-principles calculations based on DFT.

Chung KH; Koo BG; Kim H; Yoon JK; Kim JH; Kwon YK; Kahng SJ

2012-05-01

173

Scanning tunneling spectroscopy study of electric-pulse-induced electronic inhomogeneities in GaTa4Se8  

Science.gov (United States)

We have recently discovered a bulk Electric Pulse Induced Insulator-Metal Transition and possible superconductivity in the cluster Mott Insulator GaTa4Se8 [1]. The transport measurements, conducted on single crystals, are consistent with a two-channel model, which suggests that the electric pulse generates electronic inhomogeneities in the bulk of the samples. Our Scanning Tunneling Microscopy/Spectroscopy experiments indeed confirmed that the observed drop in the electric resistance originates from an electronic phase separation with the coexistence of metallic- like and insulating like domains at the nanometer scale [1]. [1] Vaju et al. Advanced Materials, 20 2760 (2008), Microelectronics engineering in press, (2008)

Dubost, Vincent; Vaju, Cristian; Cren, Tristan; Corraze, Benoit; Debontridder, Francois; Janod, Etienne; Roditchev, Dimitri; Cario, Laurent

2009-03-01

174

Vertical magneto-tunneling through a quantum dot and the density of states of small electronic systems  

CERN Multimedia

One-electron tunneling through a quantum dot with a strong magnetic field in the direction of the current is studied. The linear magneto-conductance is computed for a model parabolic dot with seven electrons in the intermediate states and for different values of the magnetic field. It is shown that the dot density of states at low excitation energies can be extracted from a precise measurement of the conductance at the upper edge of the Coulomb blockade diamond. We parametrized the density of states with a single ``temperature'' parameter (in the so called ``constant temperature approximation''), and found that this parameter depends very weakly on the magnetic field.

González, A; Gonzalez, Augusto; Capote, Roberto

2001-01-01

175

Scanning tunnelling spectroscopy on the local electronic structure of Gd rate at C{sub 82} peapods  

Energy Technology Data Exchange (ETDEWEB)

The electronic structure of Gd rate at C{sub 82} metallofullerene peapods is studied experimentally by using scanning tunnelling microscopy and spectroscopy (STM and STS). The spatial modulation of the nanotube electronic structure induced by Gd rate at C{sub 82} encapsulation has been observed depending on the position along the tube axis. Both STM and STS reveal a 1.2 nm periodicity which is consistent with the intermolecular distance of Gd rate at C{sub 82} inside single-wall carbon nanotubes. (Copyright copyright 2010 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim)

Ohashi, Kazunori; Imazu, Naoki; Kitaura, Ryo; Shinohara, Hisanori [Department of Chemistry and Institute for Advanced Research, Nagoya University, Nagoya 464-8602 (Japan)

2010-12-15

176

Conceptual design of a 100 MW electron beam accelerator module for the National Hypersonic Wind Tunnel Program  

International Nuclear Information System (INIS)

[en] The National Hypersonic Wind Tunnel program requires an unprecedented electron beam source capable of 1-2 MeV at a total average beam power of 100-200 MW for several seconds. Although a 100 MW module is a two-order extrapolation from demonstrated average power levels, the scaling of accelerator components appears reasonable. This paper will present an evaluation of component and system issues involved in the design of a 100 MW electron beam accelerator module with precision beam transport into a high pressure flowing air environment

2001-07-12

177

Scanning tunneling microscopy investigation of electronic properties of cobalt nanoislands supported by Cu-9at.%Al(111)  

Science.gov (United States)

Growth and surface electronic states of Co nanoislands supported by Cu-9 at.%Al(111) are investigated by low temperature scanning tunneling microscopy. Deposition of about 0.25 monolayer of Co atoms causes the formation of flat Co nanoislands with thicknesses ranging from monolayer to triple layer. Scanning tunneling spectroscopy measurements reveal that a Tamm-type surface state exists on the Co islands and its energy varies with the thicknesses and stacking manners. In addition, density functional theory calculations conclude that the surface states of the mono- and bilayer nanoislands mainly originate from the hybridization between Co d bands and sp bands of the substrate and the Co d minority-spin bands, respectively.

Yu, Yinghui; Zhang, Yun; She, Limin; Wu, Ping; Huang, Min; Cao, Gengyu

2013-03-01

178

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

DEFF Research Database (Denmark)

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 contacting the molecular layers with the tip of a conductive force microscope. Measurements done under low-load conditions permit us to obtain reliable tilt-angle and molecular length dependencies of the low-bias conductance through the alkanethiol layers. The observed dependence on tilt-angle is stronger for the longer molecular chains. Our calculations confirm the observed trends and explain them as a result of two mechanisms, namely, a previously proposed intermolecular tunneling enhancement as well as a hitherto overlooked tilt-dependent molecular gate effect.

Frederiksen, Thomas; Munuera, C.

2009-01-01

179

Direct measurement of the maximum tunnel rate in a radio frequency single electron transistor operated as a microwave mixer  

CERN Document Server

By operating the radio frequency single electron transistor (rf-SET) as a mixer we present measurements in which the RC roll-off of the tunnel junctions is observed at high frequencies. Our technique makes use of the non-linear rf-SET transconductance to mix high frequency gate signals and produce difference-frequency components that fall within the bandwidth of the rf-SET. At gate frequencies >15GHz the induced charge on the rf-SET island is altered on time-scales faster than the inverse tunnel rate, preventing mixer operation. We suggest the possibility of utilizing this technique to sense high frequency signals beyond the usual rf-SET bandwidth.

Reilly, D J

2004-01-01

180

Electronic characterization of LaAlO3-SrTiO3 interfaces by scanning tunneling spectroscopy  

International Nuclear Information System (INIS)

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.)

2010-01-01

 
 
 
 
181

Investigation of Si-Au vicinal surfaces using scanning tunnelling microscopy and reflection high-energy electron diffraction.  

Science.gov (United States)

Silicon vicinal surfaces can be successfully used as substrates for the preparation of one-dimensional nanostructures. The quality of the structures prepared may be controlled using scanning tunnelling microscopy, as shown in this work. Additionally, it is possible to obtain valuable information using reflection high-energy electron diffraction. A typical way of employing reflection high-energy electron diffraction is to observe patterns of scattered electrons on a screen. However, it is possible to obtain more detailed information on the arrangement of atoms at the surface if azimuthal plots are collected. Azimuthal plots are measured by recording the intensity of specularly reflected electrons during the rotation of the sample around an axis perpendicular to its surface. So far, only flat surfaces have been examined in such a way. In this work, it is shown that such data, containing interesting features, can also be collected for vicinal surfaces. PMID:17100924

Mazurek, P; Paprocki, K; Mitura, Z

2006-10-01

182

Investigation of Si-Au vicinal surfaces using scanning tunnelling microscopy and reflection high-energy electron diffraction.  

UK PubMed Central (United Kingdom)

Silicon vicinal surfaces can be successfully used as substrates for the preparation of one-dimensional nanostructures. The quality of the structures prepared may be controlled using scanning tunnelling microscopy, as shown in this work. Additionally, it is possible to obtain valuable information using reflection high-energy electron diffraction. A typical way of employing reflection high-energy electron diffraction is to observe patterns of scattered electrons on a screen. However, it is possible to obtain more detailed information on the arrangement of atoms at the surface if azimuthal plots are collected. Azimuthal plots are measured by recording the intensity of specularly reflected electrons during the rotation of the sample around an axis perpendicular to its surface. So far, only flat surfaces have been examined in such a way. In this work, it is shown that such data, containing interesting features, can also be collected for vicinal surfaces.

Mazurek P; Paprocki K; Mitura Z

2006-10-01

183

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

International Nuclear Information System (INIS)

[en] 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.

2013-01-01

184

Nanographenes as active components of single-molecule electronics and how a scanning tunneling microscope puts them to work.  

UK PubMed Central (United Kingdom)

Single-molecule electronics, that is, realizing novel electronic functionalities from single (or very few) molecules, holds promise for application in various technologies, including signal processing and sensing. Nanographenes, which are extended polycyclic aromatic hydrocarbons (PAHs), are highly attractive subjects for studies of single-molecule electronics because the electronic properties of their flat conjugated systems can be varied dramatically through synthetic modification of their sizes and topologies. Single nanographenes provide high tunneling currents when adsorbed flat onto conducting substrates, such as graphite. Because of their chemical inertness, nanographenes interact only weakly with these substrates, thereby preventing the need for special epitaxial structure matching. Instead, self-assembly at the interface between a conducting solid, such as the basal plane of graphite, and a nanographene solution generally leads to highly ordered monolayers. Scanning tunneling spectroscopy (STS) allows the current-voltage characteristics to be measured through a single molecule positioned between two electrodes; the key to the success of STS is the ability to position the scanning tunneling microscopy (STM) tip freely with respect to the molecule in all dimensions, that is, both parallel and perpendicular to the surface. In this Account, we report the properties of nanographenes having sizes ranging from 0.7 to 3.1 nm and exhibiting various symmetry, periphery, and substitution types. The size of the aromatic system and the nature of its perimeter are two essential features affecting its HOMO-LUMO gap and charge carrier mobility in the condensed phase. Moreover, the extended pi area of larger substituted PAHs improves the degree of self-ordering, another key requirement for high-performance electronic devices. Self-assembly at the interface between an organic solution and the basal plane of graphite allows deposition of single molecules within the well-defined environment of a molecular monolayer. We have used STM and STS to investigate both the structures and electronic properties of these single molecules in situ. Indeed, we have observed key electronic functions, rectification and current control through single molecules, within a prototypical chemical field-effect transistor at ambient temperature. The combination of nanographenes and STM/STS, with the PAHs self-assembled in oriented molecular mono- or bilayers at the interface between an organic solution and the basal plane of graphite and contacted by the STM tip, is a simple, reliable, and versatile system for developing the fundamental concepts of molecular electronics. Our future targets include fast reversible molecular switches and complex molecular electronic devices coupled together from several single-molecule systems.

Müllen K; Rabe JP

2008-04-01

185

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

International Nuclear Information System (INIS)

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.

2012-01-01

186

Scanning tunneling spectroscopy  

International Nuclear Information System (INIS)

Scanning tunneling microscopy (STM) provides a means of directly imaging surface topography with atomic scale resolution. Scanning tunneling spectroscopy (STS) usually refers to the image-wise determination of the tunnel current variation with bias voltage for fixed tunnel gap width. Results can be related to the density of filled and empty surface electronic states. The association of energic features with spatially localized features is a unique capability. Other variations of STS are inelastic tunneling imaging and barrier spectroscopic imaging. All these techniques are described and representative examples given to provide a survey of STS.

1988-01-01

187

Proton tunneling in solids  

Energy Technology Data Exchange (ETDEWEB)

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)

Kondo, J.

1998-10-01

188

Analysis of Human Resources Management Strategy in China Electronic Commerce Enterprises  

Science.gov (United States)

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.

Shao, Fang

189

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

Directory of Open Access Journals (Sweden)

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.

M.V. Tkach; Ju.O. Seti; O.M. Voitsekhivska

2012-01-01

190

Characteristics of amine-ended and thiol-ended alkane single-molecule junctions revealed by inelastic electron tunneling spectroscopy.  

UK PubMed Central (United Kingdom)

A combined experimental and theoretical analysis of the charge transport through single-molecule junctions is performed to define the influence of molecular end groups for increasing electrode separation. For both amine-ended and thiol-ended octanes contacted to gold electrodes, we study signatures of chain formation by analyzing kinks in conductance traces, the junction length, and inelastic electron tunneling spectroscopy. The results show that for amine-ended molecular junctions no atomic chains are pulled under stretching, whereas the Au electrodes strongly deform for thiol-ended molecular junctions. This advanced approach hence provides unambiguous evidence that the amine anchors bind only weakly to Au.

Kim Y; Hellmuth TJ; Bürkle M; Pauly F; Scheer E

2011-05-01

191

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

International Nuclear Information System (INIS)

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.

2006-08-04

192

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

Energy Technology Data Exchange (ETDEWEB)

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.

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

193

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

Science.gov (United States)

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: PMID:21711779

Ma, Jing-Min; Zhao, Jia; Zhang, Kai-Cheng; Peng, Ya-Jing; Chi, Feng

2011-03-28

194

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

UK PubMed Central (United Kingdom)

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:

Ma JM; Zhao J; Zhang KC; Peng YJ; Chi F

2011-01-01

195

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

Directory of Open Access Journals (Sweden)

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:

Ma Jing-Min; Zhao Jia; Zhang Kai-Cheng; Peng Ya-Jing; Chi Feng

2011-01-01

196

Surface structure and analysis with scanning probe microscopy and electron tunneling spectroscopy. Final report  

Energy Technology Data Exchange (ETDEWEB)

This report summarizes the results accomplished during the funding period of this grant (June 1, 1995 to May 31, 1998). The projects are (1) room-temperature atomic force microscopy (AFM) studies of NbSe{sub 3} doped with various elements and (2) low-temperature scanning tunneling microscopy (STM) studies of NbSe{sub 3}. In addition, AFM was used to study the surface morphology and defects of GaAs films grown on Ge and Ge/Si substracts.

Hsu, Julia

1998-05-01

197

Observation of squeezing in the electron quantum shot noise of a tunnel junction.  

UK PubMed Central (United Kingdom)

We report the measurement of the fluctuations of the two quadratures of the electromagnetic field generated by a quantum conductor, a dc- and ac-biased tunnel junction placed at very low temperature. We observe that the variance of the fluctuations on one quadrature can go below that of vacuum, i.e., that the radiated field is squeezed. This demonstrates the quantum nature of the radiated electromagnetic field.

Gasse G; Lupien C; Reulet B

2013-09-01

198

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

Directory of Open Access Journals (Sweden)

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.

S. A. Ketabi; N. Shahtahmasebi

2003-01-01

199

Low-temperature scanning tunneling microscopy of ring-like surface electronic structures around Co islands on InAs(110) surfaces.  

Science.gov (United States)

We report on the experimental observation by scanning tunneling microscopy at low temperature of ring-like features that appear around Co metal islands deposited on a clean (110) oriented surface of cleaved p-type InAs crystals. These features are visible in spectroscopic images within a certain range of negative tunneling bias voltages due to the presence of a negative differential conductance in the current-voltage dependence. A theoretical model is introduced, which takes into account non-equilibrium effects in the small tunneling junction area. In the framework of this model the appearance of the ring-like features is explained in terms of interference effects between electrons tunneling directly and indirectly (via a Co island) between the tip and the InAs surface. PMID:19928137

Muzychenko, D A; Schouteden, K; Savinov, S V; Maslova, N S; Panov, V I; Van Haesendonck, C

2009-08-01

200

Temperature dependence of the recombination fluorescence of photoionized indole and N,N,N',N'-tetramethyl-p-phenylenediamine in organic glasses. Consequences of electron tunneling and diffusion  

International Nuclear Information System (INIS)

The recombination fluorescence seen when TMPD is photoionized in methylcyclohexane, 3-methylhexane, and 2-methyltetrahydrofuran glasses and when indole is photoionized in 2-propanol and ethanol glasses has been investigated. The initial intensity and decay rate of the recombination fluorescence decreases as the UV irradiation temperature is increased from temperatures below the glass transition temperature T/sub g/ of the matrix. This is interpreted in terms of electron tunneling to the cation in which the tunneling barrier height or electron trap depth increases slightly (0.05 to 0.2 eV) with increasing irradiation temperature. By considering how the matrix polarity affects the degree of electron trap deepening as well as the electron trap depth relative to the excited singlet level of the solute, we are able to understand the difference in magnitudes and their changes for the initial decay rate and the initial recombination fluorescence. At temperatures 10 to 30 K above T/sub g/, depending on the matrix polarity, diffusive recombination dominates tunneling recombination and produces a peak in the recombination fluorescence unless the electron trap depth has dropped below the excited singlet of the solute. Thus, this type of experiment offers a simple diagnostic for distinguishing tunneling and diffusive recombination of electrons with cations in disordered matrices.

1977-01-01

 
 
 
 
201

Electron tunneling through graphene-based double barriers driven by a periodic potential  

Science.gov (United States)

Photon-assisted charge transport through a double barrier structure under a time periodic field in graphene is studied. Within the framework of the Floquet formalism and using the transfer matrix method, the transmission probabilities for the central band and sidebands are calculated. A critical phase difference between the harmonic potentials at the barriers, which cancels transmission through the inelastic sidebands due to quantum interference is found. This phenomenon could be of help to design graphene based filters and high-frequency radiation detectors. Quenching of resonant tunneling by the harmonic field applied to the barriers or the well is also discussed.

Ojeda-Collado, H. P.; Rodríguez-Castellanos, C.

2013-07-01

202

Electron tunneling experiments on La-substituted Kondo-semiconductor CeRhAs  

Energy Technology Data Exchange (ETDEWEB)

Polycrystalline Ce{sub 1-x}La{sub x}RhAs is investigated by means of break-junction tunneling. On Ce substituted by La (x=0.01), a pronounced hump structure is developed at the bias +/-0.25V with a shallow dip on it. The hump emergence is consistent with a drastic reduction in the resistivity. These facts give direct evidence for the appearance of mid-gap states near the Fermi energy by a small La substitution for Ce in CeRhAs.

Ekino, Toshikazu [Faculty of Integrated Arts and Sciences, Hiroshima University, Higashi-Hiroshima 739-8521 (Japan) and Hiroshima University, Graduate School of Advanced Sciences of Matter, Higashi-Hiroshima 739-8530 (Japan)]. E-mail: ekino@hiroshima-u.ac.jp; Miyaoka, Hiroki [Hiroshima University, Graduate School of Advanced Sciences of Matter, Higashi-Hiroshima 739-8530 (Japan); Sasakawa, Tetsuya [Hiroshima University, Graduate School of Advanced Sciences of Matter, Higashi-Hiroshima 739-8530 (Japan); Takabatake, Toshiro [Hiroshima University, Graduate School of Advanced Sciences of Matter, Higashi-Hiroshima 739-8530 (Japan); Gabovich, Alexander M. [Institute of Physics, National Academy of Sciences, prospekt Nauki 46, 03028, Kiev (Ukraine)

2006-08-15

203

Persistence of strong electron coupling to a narrow boson spectrum in overdoped Bi2Sr2CaCu2O(8+delta) tunneling data.  

UK PubMed Central (United Kingdom)

A d-wave, Eliashberg analysis of break-junction and STM tunneling spectra on Bi2Sr2CaCu2O(8+delta) (Bi2212) reveals that the spectral dip feature is directly linked to strong electronic coupling to a narrow boson spectrum, evidenced by a large peak in alpha2F(omega). The tunneling dip feature remains robust in the overdoped regime of Bi2212 with bulk T(c) values of 56 K-62 K. This is contrary to recent optical conductivity measurements of the self-energy that suggest the narrow boson spectrum disappears in overdoped Bi2212 and therefore cannot be essential for the pairing mechanism. The discrepancy is resolved by considering the way each technique probes the electron self-energy, in particular, the unique sensitivity of tunneling to the off-diagonal or pairing part of the self-energy.

Zasadzinski JF; Ozyuzer L; Coffey LO; Coffey L; Gray KE; Hinks DG; Kendziora C

2006-01-01

204

Persistence of Strong Electron Coupling to a Narrow Boson Spectrum in Overdoped BiSrCaCuO (Bi2212) Tunneling Data  

CERN Multimedia

A d-wave, Eliashberg analysis of break junction and STM tunneling spectra on BiSrCaCuO (Bi2212) reveals that a spectral dip feature is directly linked to strong electronic coupling to a narrow boson spectrum, evidenced by a large peak in the boson spectral weight. The tunneling dip feature remains robust in the overdoped regime of Bi2212 with bulk Tc values of 56 K-62 K. This is contrary to recent optical conductivity measurements of the self-energy that suggest the narrow boson spectrum disappears in overdoped Bi2212 and therefore cannot be essential for the pairing mechanism. The discrepancy is resolved by considering the way each technique probes the electron self-energy, in particular, the unique sensitivity of tunneling to the off-diagonal or pairing part of the self-energy.

Zasadzinski, J F; Coffey, L; Gray, K E; Hinks, D G; Kendziora, C

2005-01-01

205

Persistence of strong electron coupling to a narrow boson spectrum in overdoped Bi2Sr2CaCu2O(8+delta) tunneling data.  

Science.gov (United States)

A d-wave, Eliashberg analysis of break-junction and STM tunneling spectra on Bi2Sr2CaCu2O(8+delta) (Bi2212) reveals that the spectral dip feature is directly linked to strong electronic coupling to a narrow boson spectrum, evidenced by a large peak in alpha2F(omega). The tunneling dip feature remains robust in the overdoped regime of Bi2212 with bulk T(c) values of 56 K-62 K. This is contrary to recent optical conductivity measurements of the self-energy that suggest the narrow boson spectrum disappears in overdoped Bi2212 and therefore cannot be essential for the pairing mechanism. The discrepancy is resolved by considering the way each technique probes the electron self-energy, in particular, the unique sensitivity of tunneling to the off-diagonal or pairing part of the self-energy. PMID:16486501

Zasadzinski, J F; Ozyuzer, L; Coffey, L Ozyuzer L; Coffey, L; Gray, K E; Hinks, D G; Kendziora, C

2006-01-09

206

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

International Nuclear Information System (INIS)

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.

2011-01-01

207

Signatures of Wannier-Stark and surface states in electron tunneling and related phenomena Electron transmission through a tilted band  

CERN Multimedia

Predicted by Wannier in 1960 band states quantization in a constant electric field, $E_n$ = const $\\pm n {\\cal E}$, where $n =0$, 1, 2, ..., and ${\\cal E}$ is proportional to the strength of electric field [this kind of spectrum is commonly referred as the Wannier-Stark ladder (WSL)], implies that the probability of tunneling through a tilted band should have ${\\cal E}$ spaced peaks, at least, under the weak coupling of the band states to the source and drain electrodes. It has been shown, however, (Phys. Rev. B {\\bf 63}, ..., 2001), that the appearance of the canonical WSL is preceded by WSLs with other level spacing, namely, ${\\cal E}_{m'/m}/(1-2m'/m)$, where $m$ and $m'< m/2$ are positive integers specifying certain applied voltage. Here we show that canonical and noncanonical WSLs, in addition to different peak spacing in the transmission spectrum, have other pronouncedly distinctive features. As an example, for the former, the peak and valley tunneling probability decays exponentially with the increas...

Onipko, A; Onipko, Alexander; Malysheva, Lyuba

2001-01-01

208

Electronic Document Management: A Human Resource Management Case Study  

Directory of Open Access Journals (Sweden)

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.

Thomas Groenewald

2004-01-01

209

Pendant unit effect on electron tunneling in U-shaped molecules  

International Nuclear Information System (INIS)

The electron transfer reactions of three U-shaped donor-bridge-acceptor molecules with different pendant groups have been studied in different solvents as a function of temperature. Analysis of the electron transfer kinetics in nonpolar and weakly polar solvents provides experimental reaction Gibbs energies that are used to parameterize a molecular solvation model. This solvation model is then used to predict energetic parameters in the electron transfer rate constant expression and allow the electronic coupling between the electron donor and electron acceptor groups to be determined from the rate data. The U-shaped molecules differ by alkylation of the aromatic pendant group, which lies in the 'line-of-sight' between the donor and acceptor groups. The findings show that the electronic coupling through the pendant group is similar for these molecules.

2006-05-09

210

Excess electrons scavenging in n-dodecane solution: The role of tunneling of electron from its localized state to acceptor  

International Nuclear Information System (INIS)

The quenching of delayed radiofluorescence of n-dodecane solutions of N,N,N',N'-tetramethyl-1,4-phenylenediamine by both electron acceptors and electric field was studied. The values of excess electron mobility and rate constants of electron scavenging by different acceptors were determined over the temperature range of 265-343 K. The data were analyzed with the theory of diffusion-controlled reactions with distant transfer of electron to an acceptor. Evidence was obtained that no enthalpy and entropy of activation were needed for the electron scavenging.

2008-01-01

211

Temperature-independent electron tunneling injection in tris (8-hydroxyquinoline) aluminum thin film from high-work-function gold electrode  

International Nuclear Information System (INIS)

We fabricated electron-only tris (8-hydroxyquinoline) aluminum (Alq3) single-layer devices with a device structure of glass substrate/MgAg anode (100 nm)/Alq3 layer (100 nm)/metal cathode (100 nm), and systematically varied the work functions (WF) of the metal cathodes from WF = - 1.9 (Cs) to - 2.9 (Ca), - 3.8 (Mg), - 4.4 (Al), - 4.6 (Ag), and - 5.2 eV (Au) to investigate how electron injection barriers at the cathode/Alq3 interfaces influence their current density-voltage (J-V) characteristics. We found that current densities at a certain driving voltage decrease and the temperature dependence of J-V characteristics of the devices gradually becomes weaker as the work functions of the metal cathodes are decreased. The device with the highest-work-function Au cathode exhibited virtually temperature-independent J-V characteristics, suggesting that a current flow mechanism of this device is mainly controlled by electron tunneling injection at the Au/Alq3 interface.

2008-06-02

212

Temperature-independent electron tunneling injection in tris (8-hydroxyquinoline) aluminum thin film from high-work-function gold electrode  

Energy Technology Data Exchange (ETDEWEB)

We fabricated electron-only tris (8-hydroxyquinoline) aluminum (Alq{sub 3}) single-layer devices with a device structure of glass substrate/MgAg anode (100 nm)/Alq{sub 3} layer (100 nm)/metal cathode (100 nm), and systematically varied the work functions (WF) of the metal cathodes from WF = - 1.9 (Cs) to - 2.9 (Ca), - 3.8 (Mg), - 4.4 (Al), - 4.6 (Ag), and - 5.2 eV (Au) to investigate how electron injection barriers at the cathode/Alq{sub 3} interfaces influence their current density-voltage (J-V) characteristics. We found that current densities at a certain driving voltage decrease and the temperature dependence of J-V characteristics of the devices gradually becomes weaker as the work functions of the metal cathodes are decreased. The device with the highest-work-function Au cathode exhibited virtually temperature-independent J-V characteristics, suggesting that a current flow mechanism of this device is mainly controlled by electron tunneling injection at the Au/Alq{sub 3} interface.

Matsushima, Toshinori [Core Research for Evolutional Science and Technology Program, Japan Science and Technology Agency, 1-32-12 Higashi, Shibuya, Tokyo 150-0011 (Japan); Adachi, Chihaya [Core Research for Evolutional Science and Technology Program, Japan Science and Technology Agency, 1-32-12 Higashi, Shibuya, Tokyo 150-0011 (Japan); Center for Future Chemistry, Kyushu University, 744 Motooka, Nishi, Fukuoka 819-0395 (Japan)], E-mail: adachi@cstf.kyushu-u.ac.jp

2008-06-02

213

Voltage Dependence of Spin Polarized Tunneling  

CERN Multimedia

A mesoscopic spin valve is used to determine the effective spin polarization of electrons tunneling from and into ferromagnetic transition metals at finite voltages. The tunneling spin polarization from the ferromagnet (FM) slowly decreases with bias, but drops faster and even inverts with voltage when electrons tunnel into it. A bias-dependent free electron model shows that in the former case electrons originate near the Fermi level of the FM with large polarization whereas in the latter, electrons tunnel into hot electron states for which the polarization is significantly reduced. The change in sign is ascribed to the detailed matching of the electron wave function through the tunnel barrier.

Valenzuela, S O; Marcus, C M; Narayanamurti, V; Tinkham, M

2004-01-01

214

Spatial delocalization and perfect tunneling of matter waves: electron perfect lens.  

UK PubMed Central (United Kingdom)

It is theoretically demonstrated that electron states in semiconductors or graphene can be perfectly transmitted through a complementary material with dual properties, independent of the angle of incidence. It is shown that such complementary material may also provide a strong spatial delocalization of bounded electronic states, changing dramatically the confinement of the wave function, and acting effectively as a lens for the probability wave. The results are the electron analogue of a perfect lens for electromagnetic waves proposed in an earlier work.

Silveirinha MG; Engheta N

2013-05-01

215

Single-electron tunneling in highly doped silicon nanowires in a dual-gate configuration  

International Nuclear Information System (INIS)

[en] Lateral patterning of highly doped silicon-on-insulator films allows us to observe conductance oscillations due to single-electron charging effects. In our devices, silicon nanostructures are embedded into a metal - oxide - silicon configuration. The single-electron effects can be tuned both by an in-plane sidegate, as well as by a metallic topgate, a technology which is compatible with large-scale integration of single-electron devices with dimensions down to 10 nm. We compare the influence of different gating electrodes, important for ultralarge scale integration, on the electron islands. [copyright] 2001 American Institute of Physics

2001-06-15

216

Single-electron tunneling in highly doped silicon nanowires in a dual-gate configuration  

Energy Technology Data Exchange (ETDEWEB)

Lateral patterning of highly doped silicon-on-insulator films allows us to observe conductance oscillations due to single-electron charging effects. In our devices, silicon nanostructures are embedded into a metal{endash}oxide{endash}silicon configuration. The single-electron effects can be tuned both by an in-plane sidegate, as well as by a metallic topgate, a technology which is compatible with large-scale integration of single-electron devices with dimensions down to 10 nm. We compare the influence of different gating electrodes, important for ultralarge scale integration, on the electron islands. {copyright} 2001 American Institute of Physics.

Tilke, A.; Blick, R. H.; Lorenz, H.; Kotthaus, J. P.

2001-06-15

217

The determination of the electron-phonon interaction from tunneling data in the two-band superconductor MgB2  

CERN Multimedia

We calculate the tunneling density of states (DOS) of MgB2 for different tunneling directions, by directly solving the real-axis, two-band Eliashberg equations (EE). Then we show that the numeric inversion of the standard single-band EE, if applied to the DOS of the two-band superconductor MgB2, may lead to wrong estimates of the strength of certain phonon branches (e.g. the E_2g) in the extracted electron-phonon spectral function alpha^(2)F(omega). The fine structures produced by the two-band interaction turn out to be clearly observable only for tunneling along the ab planes in high-quality single crystals. The results are compared to recent experimental data.

Daghero, D; Ummarino, G A; Dolgov, O V; Kortus, J; Golubov, A A; Shulga, S V

2004-01-01

218

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

Science.gov (United States)

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-biological environment, suitable for detailed observations of long-range protein interfacial ET at the nanoscale and single-molecule levels. Because azurin is located at clearly identifiable fixed sites in well controlled orientation, the ET configuration parallels biological ET. The ET is nonadiabatic, and the rate constants display tunneling features with distance-decay factors of 0.83 and 0.91 A(-1) in H(2)O and D(2)O, respectively. Redox-gated tunneling resonance is observed in situ at the single-molecule level by using electrochemical scanning tunneling microscopy, exhibiting an asymmetric dependence on the redox potential. Maximum resonance appears around the equilibrium redox potential of azurin with an on/off current ratio of approximately 9. Simulation analyses, based on a two-step interfacial ET model for the scanning tunneling microscopy redox process, were performed and provide quantitative information for rational understanding of the ET mechanism. PMID:16260751

Chi, Qijin; Farver, Ole; Ulstrup, Jens

2005-10-31

219

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

UK PubMed Central (United Kingdom)

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-biological environment, suitable for detailed observations of long-range protein interfacial ET at the nanoscale and single-molecule levels. Because azurin is located at clearly identifiable fixed sites in well controlled orientation, the ET configuration parallels biological ET. The ET is nonadiabatic, and the rate constants display tunneling features with distance-decay factors of 0.83 and 0.91 A(-1) in H(2)O and D(2)O, respectively. Redox-gated tunneling resonance is observed in situ at the single-molecule level by using electrochemical scanning tunneling microscopy, exhibiting an asymmetric dependence on the redox potential. Maximum resonance appears around the equilibrium redox potential of azurin with an on/off current ratio of approximately 9. Simulation analyses, based on a two-step interfacial ET model for the scanning tunneling microscopy redox process, were performed and provide quantitative information for rational understanding of the ET mechanism.

Chi Q; Farver O; Ulstrup J

2005-11-01

220

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

DEFF Research Database (Denmark)

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-biological environment, suitable for detailed observations of long-range protein interfacial ET at the nanoscale and single-molecule levels. Because azurin is located at clearly identifiable fixed sites in well controlled orientation, the ET configuration parallels biological ET. The ET is nonadiabatic, and the rate constants display tunneling features with distance-decay factors of 0.83 and 0.91 angstrom(-1) in H2O and D2O, respectively. Redox-gated tunneling resonance is observed in situ at the single-molecule level by using electrochemical scanning tunneling microscopy, exhibiting an asymmetric dependence on the redox potential. Maximum resonance appears around the equilibrium redox potential of azurin with an on/off current ratio of approximate to 9. Simulation analyses, based on a two-step interfacial ET model for the scanning tunneling microscopy redox process, were performed and provide quantitative information for rational understanding of the ET mechanism

Chi, Qijin; Farver, O

2005-01-01

 
 
 
 
221

Effect of electron overheating on the tunneling current of a molecular transistor  

Science.gov (United States)

The effect of overheating of the electron subsystem on the Coulomb blockade in a structure (molecular transistor) based on a metal cluster containing a finite number of atoms has been theoretically studied. The electron energy spectrum in such quantum grains of cylindrical and spherical shape has been calculated. An increase in the electron subsystem temperature in the cluster leads to vanishing of the current gap and pronounced smoothening of the quantum and Coulomb steps on the current-voltage characteristic of the structure, in agreement with experimental observations.

Pogosov, V. V.; Vasyutin, E. V.; Babich, A. V.

2007-09-01

222

Identification of vibrational signatures from short chains of interlinked molecule-nanoparticle junctions obtained by inelastic electron tunnelling spectroscopy.  

UK PubMed Central (United Kingdom)

Short chains containing a series of metal-molecule-nanoparticle nanojunctions are a nano-material system with the potential to give electrical signatures close to those from single molecule experiments while enabling us to build portable devices on a chip. Inelastic electron tunnelling spectroscopy (IETS) measurements provide one of the most characteristic electrical signals of single and few molecules. In interlinked molecule-nanoparticle (NP) chains containing typically 5-7 molecules in a chain, the spectrum is expected to be a superposition of the vibrational signatures of individual molecules. We have established a stable and reproducible molecule-AuNP multi-junction by placing a few 1,8-octanedithiol (ODT) molecules onto a versatile and portable nanoparticle-nanoelectrode platform and measured for the first time vibrational molecular signatures at complex and coupled few-molecule-NP junctions. From quantum transport calculations, we model the IETS spectra and identify vibrational modes as well as the number of molecules contributing to the electron transport in the measured spectra.

Jafri SH; Löfås H; Fransson J; Blom T; Grigoriev A; Wallner A; Ahuja R; Ottosson H; Leifer K

2013-06-01

223

Molecular clusters as building blocks for nanoelectronics: the first demonstration of a cluster single-electron tunnelling transistor at room temperature  

Science.gov (United States)

This work is the result of coherent effort of a multi-disciplinary research team working for a considerable number of years in the former USSR in the area of nanocluster molecular electronics. For the first time the successful demonstration of a single-electron tunnelling transistor working reliably at room temperature and based on a single molecular metallorganic cluster is presented. A broad spectrum of different molecular clusters was investigated. Our group has developed a complete cycle of custom-designed molecular cluster manufacturing, deposition, characterization and modification of nanoelectronic devices based on a single molecular cluster. It was shown that the atomic and electronic structure of nanoclusters containing from 3 up to 23 metal atoms had no crucial importance for the transistor fabrication. At the same time extensive research into characteristics of nanoelectronic devices based on single molecular clusters and their tunnelling properties is summarized.

Gubin, S. P.; Gulayev, Yu V.; Khomutov, G. B.; Kislov, V. V.; Kolesov, V. V.; Soldatov, E. S.; Sulaimankulov, K. S.; Trifonov, A. S.

2002-04-01

224

Experimental investigation of the possibilities of the optical tunnelling of electron from a metal surface induced by strong CO2 laser pulses  

International Nuclear Information System (INIS)

According to the fundamental laws of the intense field QED, the general processes governing the laser-induced electron emission from atoms or solids traditionally may be interpreted as two complementary limiting interaction processes of the same phenomenon. The first is the multiphoton type process, when the electron interacts only with several well determined small number of photons (quantum limit), the second is the tunnelling type, when the number of the interacting photons is increasingly high (classical limit). While practically all research activity was concentrated both theoretically and experimentally to the multiphoton questions, less attention was paid to the tunnelling case, in spite of the fact that the early beginning of the intense field QED started with the pronunciation of this latter. After a short summarizing formulation of the topics, we describe several experiments performed by use at the Laval University for the study of the laser induced tunnelling. The surface photoeffect of gold proved to be a good experimental tool for these studies giving complementary results to the experiments carried out by use for the tunnel ionization of gas atoms. 36 references, 9 figures

1984-01-01

225

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

Science.gov (United States)

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…

Hulseberg, Anna; Monson, Sarah

2009-01-01

226

Using Google Calendar as an Email Alert System for Electronic Resource Renewals  

Directory of Open Access Journals (Sweden)

Full Text Available This article describes an innovative and simple way for libraries to generate email reminders for the renewal and payment of electronic resources using Google Calendar. The advantages of using Google Calendar include cost (it’s free) and ease of use. Setting up an email alert system using Google Calendar enables librarians to track and manage their electronic resources more effectively.

Steven Shapiro

2010-01-01

227

eFG: an electronic resource for Fusarium graminearum.  

Science.gov (United States)

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

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

2013-06-22

228

Tunneling in mesoscopic junctions  

CERN Document Server

We have applied the Numerical Renormalization Group method to study a mesoscopic system consisting of two samples of metal separated by an insulating barrier, with nanometer dimensions, which allows the tunnelling of a single electron from one to the other side of the junction. The junction is represented by a generalized orthodox model, taking into account the electronic scattering interaction due the hole and the tunnelling electrons, localized in the source and in the drain electrode, respectively. We have calculated the static properties (charge transference, charge average, quadractic charge average and specific heat) and the electric conductivity of the junction, for the model parameters given by the tunneling matrices element, the barrier energy and by the electronic scattering potentials acting on the electrons of the left(right) electrode.

Frota, H O

2004-01-01

229

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

Energy Technology Data Exchange (ETDEWEB)

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 {ital American} {ital Institute} {ital of} {ital Physics}.

Lubell, M.S. [Department of Physics, City College of CUNY, New York, New York 10031 (United States)

1995-09-20

230

Nanoscale magnetic characterization of tunneling magnetoresistance spin valve head by electron holography.  

UK PubMed Central (United Kingdom)

Nanostructured magnetic materials play an important role in increasing miniaturized devices. For the studies of their magnetic properties and behaviors, nanoscale imaging of magnetic field is indispensible. Here, using electron holography, the magnetization distribution of a TMR spin valve head of commercial design is investigated without and with a magnetic field applied. Characterized is the magnetic flux distribution in complex hetero-nanostructures by averaging the phase images and separating their component magnetic vectors and electric potentials. The magnetic flux densities of the NiFe (shield and 5 nm-free layers) and the CoPt (20 nm-bias layer) are estimated to be 1.0 T and 0.9 T, respectively. The changes in the magnetization distribution of the shield, bias, and free layers are visualized in situ for an applied field of 14 kOe. This study demonstrates the promise of electron holography for characterizing the magnetic properties of hetero-interfaces, nanostructures, and catalysts.

Park HS; Hirata K; Yanagisawa K; Ishida Y; Matsuda T; Shindo D; Tonomura A

2012-12-01

231

Electron tunneling in very low energy C sub 6 sub 0 -surface collisions Probing normal and tangential exit velocity effects  

CERN Document Server

Normal and tangential exit velocity effects were studied for negative ion formation in collisions of very low energy (E sub 0 =10-40 eV) neutral C sub 6 sub 0 molecular beams with a conducting surface. The normal and tangential velocity components of the scattered C sub 6 sub 0 sup - were (1.3-5.6)x10 sup - sup 4 a.u. and (0.8-3.1)x10 sup - sup 4 a.u. correspondingly. The average vibrational energy per C sub 6 sub 0 molecule was kept nearly constant for all E sub 0 values. The C sub 6 sub 0 sup - yield was found to decrease exponentially with the inverse of the normal velocity component for both near normal and near grazing incidence angles. Practically the same slope, within experimental uncertainty, was extracted from the semilog yield plots showing that tangential velocity effects are negligible. The distance dependent electron tunneling rates from C sub 6 sub 0 sup - to the conducting surface were calculated and the results were used in order to derive a characteristic distance for ion formation.

Bekkerman, A; Kolodney, E

2002-01-01

232

Cross-sectional scanning tunneling microscopy across a metal-semiconductor interface - structural and electronic properties on the atomic scale  

Energy Technology Data Exchange (ETDEWEB)

Understanding the formation of Schottky barriers has been a major theme of surface science for more than half a century. However, the various mechanisms that determine the barrier height are still subject to discussion. To a large part this is due to the lack of appropriate experimental techniques with atomic resolution and the difficulties associated with preparing well-defined epitaxial interfaces. We report scanning tunnelling spectroscopy (STS) across a cleaved epitaxial GaAs(110)/Fe interface. It provides information on the structural as well as the electronic properties of the heterointerface on the atomic scale. Furthermore, in combination with 3D simulations of the tip induced band bending we are able to quantify both the local Schottky barrier height and the influence of single dopant atoms on the electrostatic potential landscape representing the space charge layer in the semiconductor. Our experimental data are discussed in the context of existing theoretical models for Schottky barrier formation, like the advanced unified defect model or the metal-induced gap states model.

Winking, Lars; Wenderoth, Martin; Ifflaender, Tim; Druga, Thomas; Ulbrich, Rainer G. [IV. Physikalisches Institut, Georg-August-Universitaet, Goettingen (Germany)

2009-07-01

233

Ionization and displacement damage irradiation studies of quantum devices: Resonant tunneling diodes and two-dimensional electron gas transistors  

International Nuclear Information System (INIS)

The radiation tolerance of two quantum devices, InP-based resonant tunneling diodes (RTD) and GaAs based two-dimensional electron gas transistors (2-DEGT), was investigated with ionizing and displacement damage radiation. The RTDs were subject to a maximum total gamma dose of 1 Mrad(InP), 55 MeV protons to a fluence of 3.5x1011 cm-2, high energy neutrons to a fluence of 5x1010 cm-2 and heavy ions with a maximum LET (InP) of 23.6 MeV-cm2/mg to a fluence of 1x107 cm-2. Using the peak-to-valley current ratios as the figure of merit, no radiation effects were detected on the RTDs measured under these circumstances. The 2-DEGTs were irradiated to a total gamma dose of 50 krad(GaAs) and 55 MeV protons to a fluence of 5x1010 cm-2. Under gamma irradiation, a reduction in transconductance was observed, while the proton irradiated devices show an enhancement in the transconductance. The magnitude of these effects was proportional to gamma dose and proton fluence respectively. The effects are transient. For the gamma exposure, the tested 2-DEGTs almost completely recovered their pre-radiation performance. However, the proton-irradiated devices only recovered about half-way to their pre-irradiated characteristics. The transient times were on order of hours and may indicate annealing effects

1999-01-01

234

Characterization of the asymmetrical barrier potentials in CoFe/AlO{sub x}/Co magnetic tunneling junction by electron holography  

Energy Technology Data Exchange (ETDEWEB)

Electron holography (EH) in a field emission gun transmission electron microscope has been used to profile the inner potential V{sub 0} across CoFe/AlO{sub x}/Co magnetic tunneling junctions (MTJs). The spatial dimension of the AlO{sub x} barrier layer can be accurately determined from the phase profile at the tunneling junctions. The EH results show unambiguously that the potential jump across the CoFe/AlO{sub x} interface is smaller than that across the Co/AlO{sub x} interface, which results in asymmetrical barriers in the MTJs. The inner potential difference and the asymmetrical barrier were discussed based on the different oxidation statuses between Co/AlO{sub x} and CoFe/AlO{sub x} interfaces.

Xu, Q.Y. E-mail: xuqingyu@blem.ac.cn; Wang, Y.G.; Zhang, Z.; You, B.; Du, J.; Hu, A

2003-07-01

235

Tunneling works. Tunnel koji  

Energy Technology Data Exchange (ETDEWEB)

A mountain tunneling method for rock-beds used to be applied mainly to construction works in the mountains under few restrictions by environmental problems. However, construction works near residential sreas have been increasing. There are such enviromental problems due to tunneling works as vibration, noise, lowering of ground-water level, and influences on other structures. This report mainly describes the measurement examples of vibration and noise accompanied with blasting and the effects of the measures to lessen such influences. When the tunneling works for the railroad was carried out on the natural ground mainly composed of basalt, vibration of the test blasting was measured at three stations with piezoelectric accelerometers. Then, ordinary blasting, mutistage blasting, and ABM blasting methods were used properly besed on the above results, and only a few complaints were made. In the different works, normal noise and low-frequency sound were mesured at 22 stations around the pit mouth. As countermeasures for noise, sound-proof sheets, walls, and single and double doors were installed and foundto be effective. 1 ref., 6 figs., 1 tab.

Higo, M. (Hazam Gumi, Ltd., Tokyo (Japan))

1991-10-25

236

Periodic faceting on TaC(110): Observations using high-resolution low-energy electron diffraction and scanning tunneling microscopy  

International Nuclear Information System (INIS)

Unidirectional alternating (100)-(010) faceting has been observed for the clean TaC(110) surface using both high-resolution low-energy electron diffraction and scanning tunneling microscopy. Facets propagate periodically along the [1 bar 10] direction and form a ridge-and-valley grating, characterized by an average periodicity of ?6 lattice spacings in the [1 bar 10] direction, where (110) terraces are completely absent. This faceted surface is shown to be an energetically favored structure.

1993-01-01

237

Dispersion of a layered electron gas with nearest neighbour-tunneling  

International Nuclear Information System (INIS)

The dispersion of the first plasmon band is calculated within the Random Phase Approximation for a superlattice of two-dimensional electron-gases, mutually interacting, and with nearest neighbour hopping between the planes. It is further shown that the deviations of this dispersion from the one in systems with zero interplane motion are very small in commonly realized experimental situations and that they are expected to be observable only in samples with plane distances of 100A and less. (author). 15 refs, 3 figs, 1 tab.

1988-01-01

238

Three-body scattering problem and two-electron tunneling in molecular wires  

CERN Document Server

We solve the Lippmann-Schwinger equation describing elastic scattering of preformed pairs (e.g. bipolarons) off a short-range scattering center and find the two-particle transmission through a thin potential barrier. While the pair transmission is smaller than the single-electron transmission in the strong-coupling limit, it is remarkably larger in the weak coupling limit. We also calculate current-voltage characteristics of a molecule - barrier - molecule junction. They show unusual temperature and voltage behavior which are experimentally verifiable at low temperatures.

Alexandrov, A S; Kornilovitch, P E

2001-01-01

239

Nanoscale magnetic characterization of tunneling magnetoresistance spin valve head by electron holography.  

Science.gov (United States)

Nanostructured magnetic materials play an important role in increasing miniaturized devices. For the studies of their magnetic properties and behaviors, nanoscale imaging of magnetic field is indispensible. Here, using electron holography, the magnetization distribution of a TMR spin valve head of commercial design is investigated without and with a magnetic field applied. Characterized is the magnetic flux distribution in complex hetero-nanostructures by averaging the phase images and separating their component magnetic vectors and electric potentials. The magnetic flux densities of the NiFe (shield and 5 nm-free layers) and the CoPt (20 nm-bias layer) are estimated to be 1.0 T and 0.9 T, respectively. The changes in the magnetization distribution of the shield, bias, and free layers are visualized in situ for an applied field of 14 kOe. This study demonstrates the promise of electron holography for characterizing the magnetic properties of hetero-interfaces, nanostructures, and catalysts. PMID:22887895

Park, Hyun Soon; Hirata, Kei; Yanagisawa, Keiichi; Ishida, Yoichi; Matsuda, Tsuyoshi; Shindo, Daisuke; Tonomura, Akira

2012-08-09

240

21 October 2008 - LHC Inauguration - Deputy Minister for Environment, Physical Planning and Public Works T. Xanthopulos welcomed by CERN Director-General R. Aymar, visiting the ATLAS cavern and LHC tunnel and signing the electronic guest book with E. Tsesmelis.  

CERN Multimedia

21 October 2008 - LHC Inauguration - Deputy Minister for Environment, Physical Planning and Public Works T. Xanthopulos welcomed by CERN Director-General R. Aymar, visiting the ATLAS cavern and LHC tunnel and signing the electronic guest book with E. Tsesmelis.

CERN Photo Service

2008-01-01

 
 
 
 
241

Probing the tunneling site of electrons in strong field enhanced ionization of molecules  

CERN Document Server

Molecules show a much increased multiple ionization rate in a strong laser field as compared to atoms of similar ionization energy. A widely accepted model attributes this to the action of the joint fields of the adjacent ionic core and the laser on its neighbor inside the same molecule. The underlying physical picture for the enhanced ionization is that the up-field atom that gets ionized. However, this is still debated and remains unproven. Here we report an experimental verification of this long-standing prediction. This is accomplished by probing the two-site double ionization of ArXe, where the instantaneous field direction at the moment of electron release and the emission direction of the correlated ionizing center are measured by detecting the recoil sum- and relative-momenta of the fragment ions. Our results unambiguously prove the intuitive picture of the enhanced multielectron dissociative ionization of molecules and clarify a long-standing controversy.

Wu, J; Schmidt, L Ph H; Kunitski, M; Voss, S; Sann, H; Kim, H; Jahnke, T; Czasch, A; Dörner, R

2013-01-01

242

Dynamics of a nano-scale rotor driven by single-electron tunneling  

CERN Multimedia

We investigate theoretically the dynamics and the charge transport properties of a rod-shaped nano-scale rotor, which is driven by a similar mechanism as the nanomechanical single-electron transistor (NEMSET). We show that a static electric potential gradient can lead to self-excitation of oscillatory or continuous rotational motion. The relevant parameters of the device are identified and the dependence of the dynamics on these parameters is studied. We further discuss how the dynamics is related to the measured current through the device. Notably, in the oscillatory regime, we find a negative differential conductance. The current-voltage characteristics can be used to infer details of the surrounding environment which is responsible for damping.

Croy, A

2012-01-01

243

Direct, coherent and incoherent intermediate state tunneling and scanning tunnel microscopy (STM)  

International Nuclear Information System (INIS)

Theory and experiment in tunneling are still qualitative in nature, which hold true also for the latest developments in direct-, resonant-, coherent- and incoherent-tunneling. Those tunnel processes have recently branched out of the field of ''solid state tunnel junctions'' into the fields of scanning tunnel microscopy (STM), single electron tunneling (SET) and semiconducting resonant tunnel structures (RTS). All these fields have promoted the understanding of tunneling in different ways reaching from the effect of coherence, of incoherence and of charging in tunneling, to spin flip or inelastic effects. STM allows not only the accurate measurements of the tunnel current and its voltage dependence but, more importantly, the easy quantification via the (quantum) tunnel channel conductance and the distance dependence. This new degree of freedom entering exponentially the tunnel current allows an unique identification of individual tunnel channels and their quantification. In STM measurements large tunnel currents are observed for large distances d > 1 nm explainable by intermediate state tunneling. Direct tunneling with its reduced tunnel time and reduced off-site Coulomb charging bridges distances below 1 nm, only. The effective charge transfer process with its larger off-site and on-site charging at intermediate states dominates tunnel transfer in STM, biology and chemistry over distances in the nm-range. Intermediates state tunneling becomes variable range hopping conduction for distances larger than d > 2 nm, for larger densities of intermediate states n1(?) and for larger temperatures T or voltages U, still allowing high resolution imaging.

1997-01-01

244

Effect of quantum tunneling on single strand breaks in a modeled gas phase cytidine nucleotide induced by low energy electron: A theoretical approach  

Science.gov (United States)

Effect of quantum mechanical tunneling on single strand breaks induced by low energy electron (LEE) has been investigated in a modeled gas phase system, 2'-deoxycytidine-3'-monophosphate (3'-dCMPH). The potential energy curves for the sugar-phosphate C-O (3' C-O) bond cleavage have been generated using second order Møller-Plesset perturbation theory at the 6-31+G(d) accuracy level. Results from the electronic structure theory calculations in conjunction with our time dependent calculations for the 3' C-O bond rupture in 3'-dCMPH using local complex potential based time dependent wave packet approach show significant quantum tunneling of the 3' C-O bond from the bound vibrational states above 1 eV of the anionic potential energy curve. A comparison of the fragmentation profile with that of our earlier gas phase investigations based on Hartree-Fock and density functional theory - Becke, 3-parameter, Lee-Yang-Parr methods with 6-31+G(d) basis set is also provided. Further, inspection of the singly occupied molecular orbitals generated at different 3' C-O bond lengths clearly indicates the electron transfer from the low lying base-?* shape resonance state to the phosphate P = O ?* orbital of the DNA backbone during the strand breaks. The decisive step during LEE induced strand breaks follows via ``charge induced dissociation'' (CID) for the metastable anion formed below 1 eV, whereas quantum mechanical tunnel-ing is out-weighted the CID mechanism for the LEE above 1 eV.

Bhaskaran, Renjith; Sarma, Manabendra

2013-07-01

245

Tunneling recombination luminescence of glassy polyethylene adipate ?-irradiated at low temperature and effect of electron scavengers  

International Nuclear Information System (INIS)

[en] The isothermal luminescence (ITL) from glassy polyethylene adipate (PEA) ?-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 + ?t)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)

1985-01-01

246

Ionization and displacement damage irradiation studies of quantum devices: Resonant tunneling diodes and two-dimensional electron gas transistors  

Energy Technology Data Exchange (ETDEWEB)

The radiation tolerance of two quantum devices, InP-based resonant tunneling diodes (RTD) and GaAs based two-dimensional electron gas transistors (2-DEGT), was investigated with ionizing and displacement damage radiation. The RTDs were subject to a maximum total gamma dose of 1 Mrad(InP), 55 MeV protons to a fluence of 3.5x10{sup 11} cm{sup {minus}2}, high energy neutrons to a fluence of 5x10{sup 10} cm{sup {minus}2} and heavy ions with a maximum LET (InP) of 23.6 MeV-cm{sup 2}/mg to a fluence of 1x10{sup 7} cm{sup {minus}2}. Using the peak-to-valley current ratios as the figure of merit, no radiation effects were detected on the RTDs measured under these circumstances. The 2-DEGTs were irradiated to a total gamma dose of 50 krad(GaAs) and 55 MeV protons to a fluence of 5x10{sup 10} cm{sup {minus}2}. Under gamma irradiation, a reduction in transconductance was observed, while the proton irradiated devices show an enhancement in the transconductance. The magnitude of these effects was proportional to gamma dose and proton fluence respectively. The effects are transient. For the gamma exposure, the tested 2-DEGTs almost completely recovered their pre-radiation performance. However, the proton-irradiated devices only recovered about half-way to their pre-irradiated characteristics. The transient times were on order of hours and may indicate annealing effects.

Wilkins, R.; Shojah-Ardalan, S.; Kirk, W.P. [and others

1999-12-01

247

Use and Search Pattern of Electronic Resources in Five Autonomous Engineering Colleges (Bengaluru)  

Directory of Open Access Journals (Sweden)

Full Text Available Purpose: This study evaluates the use of electronic resources among the faculty in five autonomous Engineering Colleges in Bengaluru. It evaluates the purpose,benefits, preference of web browsers, search engines, file formats, problem faced,and search patterns as the key parameters. It highlights some problems,constraints and forward suggestions for better use of electronic resources.Methodology/Approach: The structured questionnaire is used for data collection besides personal interview and observation to add clarity.Findings: The study assesses the faculty awareness and use of electronic resources in their academic and research needs. Besides, familiarity about search patterns for effective retrieval.Research Limitations: The study is limited to the faculty of the Autonomous Engineering Colleges affiliated to Visvesvaraya Technological University (VTU) in Bengaluru Region of Karnataka State, India.Keywords: e-resources; search pattern; e-resource use; Autonomous Engineering Colleges.Paper Type: Survey cum Research

G. Kiran Kumar; Mallinath Kumbar

2012-01-01

248

Scanning tunneling microscopy and spectroscopy studies of the surface structure and electronic properties of single-crystal Tl-Ba-Ca-Cu-O superconductors  

International Nuclear Information System (INIS)

[en] The use of scanning tunneling microscopy (STM) and scanning tunneling spectroscopy (STS) to characterize the surface structure and electronic properties of Tl2Ba2CaCu2O8 and Tl2Ba2Ca2Cu3O10 single crystals is described in this paper. Atomic resolution STM images show that 90%-95% of the surface has a near-trigonal structure with a = b = 0.24 nm and an a-b angle of 65 degree. The remaining 5%-10% of the surface consists of a new orthorhombic structure with a = b = 0.40 nm. Spatially resolved STS measurements further demonstrate that regions with the 0.24 nm period structure are metallic, while areas with the 0.40 nm period structure are semiconducting

1991-01-01

249

User Perception of Electronic Resources in the University of Ilorin, Nigeria (UNILORIN)  

Directory of Open Access Journals (Sweden)

Full Text Available This study examined the user perception of the electronic resources by the academic staff of the University of Ilorin. The sample consists of 250 academic staff selected from eight (8) out of the twelve (12) faculties that made up of the university. Data were collected through an electronic resources user perceptional survey (ERUPS). Responses were received from 225 (90%) academic staff of the eight faculties. Analysis revealed frequency of use of electronic resources was low. Reasons alluded to were lack of time because of the time required to focus on teaching; lack of awareness to electronic resources provided by the library; power outage, ineffective communication channels, slow network and inadequate searching skills. The study recommended adequate Information and Communication Technologies (ICT) training for all categories of academic staff and provision of adequate power supply.

BASHORUN; M. Tunji; ISAH Abdulmumin; M.Y ADISA

2011-01-01

250

?????????????????????? A Study of Demands Analysis and Marketing Strategy of Electronic Resources in University Library  

Directory of Open Access Journals (Sweden)

Full Text Available ?????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????/??????????????????????????????????????????????????The emergence of electronic resources has made new breakthrough in knowledge carriers because of their ease of use, instant availability, and the characteristic of no time and space constraints. For public libraries to achieve maximum efficiency in its electronic resources, it is necessary to seek the most effective marketing strategies. Therefore, the marketing concept of the electronic resources should be reader oriented, such as respecting and understanding library user’s information needs. Libraries also need to utilize various media and techniques to market the electronic resources, so that more comprehensive services and experiences can be provided to readers. The purpose of this study is to investigate library user’s needs and promotion strategies of electronic resources in order to identify the most effective ways of marketing. This study focuses on the students of the four colleges (College of Business, College of Tourism, College of Information, and College of Humanities and Social Science) in Kainan University as subjects in the survey questionnaire. It uses the Gap Analysis Model as the main analytical tool to examine cases in which readers/ students show real demands to electronic resources. The study concludes with promotion and marketing strategies with regards to service offerings for the university libraries.

Huang-Yu Liu; Jung-Huei Shu

2008-01-01

251

Impact of adsorbed organic monolayers on vacuum electron tunneling contributions to electrical resistance at an asperity contact  

Science.gov (United States)

Electrical Contact Resistance measurements are reported for RF MEMS switches situated within an ultrahigh vacuum system equipped with in situ oxygen plasma cleaning capabilities. Measurements were preformed on Au/Au permanently adhered switches, and functioning Au/RuO2 switches in the presence and absence of adsorbed monolayers of pentane and dodecane. The data are analyzed to explore how adsorbed molecules in regions close to the contact may impact vacuum tunneling contributions to the experimentally measured resistance: (1) The resistance associated with direct contact in parallel with a vacuum tunneling path, which upon uptake of the monolayer is replaced by the molecular resistance, and (2) A series connection of the direct contact resistance with the molecular layer after adsorption occurs, with the vacuum tunneling path assumed to be negligible. The results favor scenario (1), whereby uptake of the molecular layer effectively shuts down the vacuum tunneling path, which in this case is effectively ˜30 Ohms in the absence of an adsorbed film. The methods constitute a new and original approach to documenting vacuum tunneling levels in regions of close proximity. Funding agencies: NSF, AFOSR MURI, DARPA. [4pt] [1] D. Berman, M. Walker, C. Nordquist, J. Krim, J. Appl. Phys., in press

Berman, Diana; Walker, Matthew; Krim, Jacqueline

2012-02-01

252

Electronic Document Management: A Human Resource Management Case Study  

Digital Repository Infrastructure Vision for European Research (DRIVER)

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 mana...

Thomas Groenewald

253

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

Science.gov (United States)

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.

Ienaga, K.; Yokota, T.; Nakashima, N.; Inagaki, Y.; Kawae, T.; Tsujii, H.

2012-12-01

254

Time resolved control of electron tunnelling times and single-shot spin readout in a quantum dot  

Science.gov (United States)

We are pursuing a capability to perform time resolved manipulations of single spins in quantum dot circuits involving more than two quantum dots. In this paper, we demonstrate full counting statistics as well as averaging techniques used to calibrate the tunnel barriers. We make use of this to implement the Delft protocol [1] for single shot single spin readout in a device designed to form a triple quantum dot potential. We are able to tune the tunnelling times over around three orders of magnitude. We obtain a spin relaxation time of 300?s at 10 T.

Gaudreau, L.; Kam, A.; Kycia, J. B.; Studenikin, S. A.; Granger, G.; Mason, J. D.; Zawadzki, P.; Sachrajda, A. S.

2010-02-01

255

Using Electronic Repositories as a Student Resource for MSE Applications  

Science.gov (United States)

In the majority of engineering disciplines, MSE provides resources and applications with many other areas of engineering, e.g., design, structures, mechanics, and manufacturing. For the students to transfer and implement their MSE knowledge, they must have easy access to all their information. The eportfolio is a repository of the students entire academic MSE content and provides a wealth of knowledge applicable to all engineering disciplines. This repository combines not only lecture and textbook material, but also every assignment (in assessed format), all quizzes (with answers) laboratory activities (in audiovisual format), student oral presentations (podcast), and lectures in asynchronous format. This allows all of the data and information accumulated by students throughout their varying MSE course collected in one place, and is able to act as a quick resource and information kit for future use as the eportfolio is quickly accessed. Student and graduate responses have been positive especially for those in the workforce who require immediate and correct information.

Blicblau, Aaron

2009-09-22

256

Tunneling behaviors of photogenerated electrons in In{sub 0.15}Ga{sub 0.85}As/GaAs quantum well photoelectrodes  

Energy Technology Data Exchange (ETDEWEB)

The photovoltaic spectral features and the behaviors of photocurrent versus the electrode potential for near surface In{sub 0.15}Ga{sub 0.85}As/GaAs quantum well electrodes have been investigated in nonaqueous solutions of ferrocene and acetylferrocene. The photovoltaic spectrum shows a sharp structure that reflects confined state-to-state exciton transition in the quantum well. Deep dips are observed in the photocurrent versus the electrode potential curves in both electrolytes at the different electrode potentials under the illumination of exciton resonance wavelength. These dips are qualitatively explained by considering the interfacial tunneling transfer of photogenerated electron within the quantum well.

Liu, Y.; Xiao, X.R.; Zeng, Y.P.; Pan, D.

1999-11-25

257

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

Energy Technology Data Exchange (ETDEWEB)

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.

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

2000-02-09

258

A theory of single-electron non-adiabatic tunneling through a small metal nanoparticle with due account of the strong interaction of valence electrons with phonons of the condensed matter environment.  

UK PubMed Central (United Kingdom)

A theory of electrochemical behavior of small metal nanoparticles (NPs) which is governed both by the charging effect and the effect of the solvent reorganization on the dynamic of the electron transfer (ET) is considered under ambient conditions. The exact expression for the rate constant of ET from an electrode to NP which is valid for all values of the reorganization free energy E(r), bias voltage, and overpotential is obtained in the non-adiabatic limit. The tunnel current/overpotential relations are studied and calculated for different values of the bias voltage and E(r). The effect of E(r) on the full width at half maximum of the charging peaks is investigated at different values of the bias voltage. The differential conductance/bias voltage and the tunnel current/bias voltage dependencies are also studied and calculated. It is shown that, at room temperature, the pronounced Coulomb blockade oscillations in the differential conductance/bias voltage curves and the noticeable Coulomb staircase in the tunnel current/bias voltage relations are observed only at rather small values of E(r) in the case of the strongly asymmetric tunneling contacts.

Medvedev IG

2011-11-01

259

A theory of single-electron non-adiabatic tunneling through a small metal nanoparticle with due account of the strong interaction of valence electrons with phonons of the condensed matter environment.  

Science.gov (United States)

A theory of electrochemical behavior of small metal nanoparticles (NPs) which is governed both by the charging effect and the effect of the solvent reorganization on the dynamic of the electron transfer (ET) is considered under ambient conditions. The exact expression for the rate constant of ET from an electrode to NP which is valid for all values of the reorganization free energy E(r), bias voltage, and overpotential is obtained in the non-adiabatic limit. The tunnel current/overpotential relations are studied and calculated for different values of the bias voltage and E(r). The effect of E(r) on the full width at half maximum of the charging peaks is investigated at different values of the bias voltage. The differential conductance/bias voltage and the tunnel current/bias voltage dependencies are also studied and calculated. It is shown that, at room temperature, the pronounced Coulomb blockade oscillations in the differential conductance/bias voltage curves and the noticeable Coulomb staircase in the tunnel current/bias voltage relations are observed only at rather small values of E(r) in the case of the strongly asymmetric tunneling contacts. PMID:22070315

Medvedev, Igor G

2011-11-01

260

Tunnel-City 1985. Contributions  

Energy Technology Data Exchange (ETDEWEB)

Seventy-four papers were published, the majority of which deals with construction of urban underground transport systems. Tunneling projects carried out in the city of Prague for the construction of the Prague metro are discussed in numerous papers; individual papers also concern construction of metro systems in a number of cities. Railway tunnel and road tunnel projects in urban areas are also given particular attention. Further topics include tunnel construction for district heating systems, sewage tunnels, the construction of a proton-electron accelerater ring in Hamburg, pedestrian subways, seasonal heat storage in rock in Lulea, Sweden. Methods of ground control during tunneling and explosive fracturing, rock freezing, shield tunneling systems, tunnel liners, grouting techniques and tunneling machines used are also discussed. Papers are in English, French or in Russian. In addition to the proceedings, a volume of abstracts of the reports was published in three languages along with a volume containing a summary of papers held under each of three main topics.

1985-01-01

 
 
 
 
261

Electronic dipole moment and tunneling state of hydrogen atom in hydrogen-bond materials revealed by neutron and X-ray structure analyses  

International Nuclear Information System (INIS)

The isolated hydrogen-bonded materials, 5-methyl-9-hydroxyphenalenone (MeHPLN) and 5-bromo-9-hydroxyphenalenone (Br-HPLN), were studied by means of X-ray and neutron diffraction methods. It was found that the position of the nucleus of the hydrogen atom in the hydrogen-bond region does not agree with the center of mass of the electron cloud of the hydrogen atom. This leads to a local electronic dipole moment in the hydrogen-bond region. Using the experimentally obtained dipole moment, phase transition temperatures for MeHPLN and BrHPLN were calculated based on a tunneling model. Result shows good agreement with the ones obtained by a dielectric measurement. (author)

2007-01-01

262

Decay of trapped electrons by tunnelling to scavenger molecules in the systems with dispersion of energy of the trapping sites. A computer simulation study  

International Nuclear Information System (INIS)

The kinetics of decay of trapped electrons via tunnelling to acceptor molecules in a glassy matrix was calculated by the method of stochastic simulation for the systems with statistical distribution of energy of the trapping sites. The kinetic curves of electron decay were calculated for different distributions of the barrier height and for the uniform distribution of the frequency factor. It is shown that while the scatter in the frequency factor does not markedly affect the shape of the kinetic curves, certain asymmetric distributions of the barrier height can cause large deviations from the previous calculations and lead to the so called ''flatness'' effect. However, the parameters of the barrier height distribution cannot be extracted from the experimental decays. (author)

1991-01-01

263

Electronic effect of lead substitution in single-crystal Bi(Pb)-Sr-Ca-Cu-O superconductors determined by scanning tunneling microscopy  

International Nuclear Information System (INIS)

Scanning tunneling microscopy has been used to characterize directly the surface electronic structure of a series of single-crystal PbxBi2-xSr2CaCu2O8 superconductors. High-resolution spectroscopic measurements show that within ±0.5 eV of the Fermi level the Bi(Pb)-O electronic structure is independent of the Pb concentration (x?0.7). Extended spectroscopic measurements demonstrate that the density of unfilled states at +1 eV systematically decrease as the concentration of Pb increases, although the filled states between 0 and -2 eV are essentially independent of the concentration of Pb. In addition, analysis of the differential conductivity indicates that the surface conductivity varies from weakly metallic to semiconducting as the tip-surface separation increases

1990-07-01

264

Kinetics of electron tunneling transfer in KH2PO4 and NH4H2PO4 crystals with hydrogen bonds  

Science.gov (United States)

A model of electron transfer by tunneling between trapped electron and hole centers in crystals with hydrogen bonds under the conditions of thermostimulated mobility of one carrier type in the recombination process has been developed. The proposed model describes all features in the kinetics of induced optical density relaxation observed in nonlinear optical crystals of KH2PO4 (KDP) and NH4H2PO4 (ADP) on a wide temporal scale (10-8-10 s) under pulsed irradiation. The results of model calculations have been compared with experimental data on the photoinduced transient optical absorption (TOA) in KDP and ADP crystals in the visible and UV ranges. The nature of the radiation-induced defects, which account for the TOA, and the dependence of the TOA decay kinetics on the temperature, excitation power, and other experimental conditions have been considered.

Ogorodnikov, I. N.; Kiseleva, M. S.

2012-02-01

265

Enhancement of electronic inhomogeneities due to out-of-plane disorder in Bi_2Sr_2CuO_{6+delta} superconductors observed by scanning tunneling spectroscopy  

CERN Document Server

Nanoscale electronic inhomogeneity in optimally doped single-layer Bi_2Sr_{1.6}L_{0.4}CuO_{6+delta}, (L-Bi2201, L=La and Gd) as well as bilayer Bi_2Sr_2CaCu_2O_{8+delta} (Bi2212), superconductors has been investigated by the low-temperature scanning-tunneling-microscopy and spectroscopy. The inhomogeneous gap structures are observed above and below Tc on Gd-Bi2201. Increasing the out-of-plane disorder which is controlled by mismatch of the ionic radius between Sr and Ln results in the enhancement of pseudogap region with suppressed coherence peaks in the conductance spectrum, making the gap average larger and the gap distribution wider. The degree of electronic inhomogeneity measured by the distribution width of the gap amplitude is shown to have a correlation with Tc in optimally doped Bi2201 and Bi2212.

Sugimoto, A; Eisaki, H; Kashiwaya, H; Tsuchiura, H; Tanaka, Y; Fujita, K; Uchida, S I

2006-01-01

266

Disseminating Context-Specific Access to Online Knowledge Resources within Electronic Health Record Systems.  

UK PubMed Central (United Kingdom)

Clinicians' patient care information needs are frequent and largely unmet. Online knowledge resources are available that can help clinicians meet these information needs. Yet, significant barriers limit the use of these resources within the clinical workflow. Infobuttons are clinical decision support tools that use the clinical context (e.g., institution, user, patient) within electronic health record (EHR) systems to anticipate clinicians' questions and provide automated links to relevant information in knowledge resources. This paper describes OpenInfobutton (www.openinfobutton.org): a standards-based, open source Web service that was designed to disseminate infobutton capabilities in multiple EHR systems and healthcare organizations. OpenInfobutton has been successfully integrated with 38 knowledge resources at 5 large healthcare organizations in the United States. We describe the OpenInfobutton architecture, knowledge resource integration, and experiences at five large healthcare organizations.

Del Fiol G; Curtis C; Cimino JJ; Iskander A; Kalluri AS; Jing X; Hulse NC; Long J; Overby CL; Schardt C; Douglas DM

2013-01-01

267

Origin of the electron-hole asymmetry in the scanning tunneling spectrum of the high-temperature Bi2Sr2CaCu2O8+delta superconductor.  

Science.gov (United States)

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

Nieminen, Jouko; Lin, Hsin; Markiewicz, R S; Bansil, A

2009-01-21

268

Origin of the electron-hole asymmetry in the scanning tunneling spectrum of the high-temperature Bi2Sr2CaCu2O8+delta superconductor.  

UK PubMed Central (United Kingdom)

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.

Nieminen J; Lin H; Markiewicz RS; Bansil A

2009-01-01

269

Eavesdropping on Electronic Guidebooks Observing Learning Resources in Shared Listening Environments  

CERN Document Server

We describe an electronic guidebook, Sotto Voce, that enables visitors to share audio information by eavesdropping on each other's guidebook activity. We have conducted three studies of visitors using electronic guidebooks in a historic house: one study with open air audio played through speakers and two studies with eavesdropped audio. An analysis of visitor interaction in these studies suggests that eavesdropped audio provides more social and interactive learning resources than open air audio played through speakers.

Woodruff, A; Grinter, R E; Hurst, A; Szymanski, M H; Thornton, J D; Woodruff, Allison; Aoki, Paul M.; Grinter, Rebecca E.; Hurst, Amy; Szymanski, Margaret H.; Thornton, James D.

2002-01-01

270

Tunneling through nanographene stacks  

Science.gov (United States)

We present a scanning tunneling microscopy (STM) and spectroscopy (STS) study of a nanographene, hexa-peri-hexabenzocoronene (HBC), in different stacked geometries, covalently bound in cyclophanes or physisorbed in double layers consisting either of HBCs only or of a mixture of HBC and an alkylated disk-type electron acceptor, coronenediimide. Tunneling bias-dependent STM and STS at the solid-liquid interface reveal that the lateral offset between the stacked molecules strongly influences the electron transport through the stacks, which is attributed to different highest occupied and lowest unoccupied molecular orbital splittings in the stacks. The results imply that the control over the stacking in nanographene multilayers or columns can be used to control their electron transport properties.

Jäckel, F.; Watson, M. D.; Müllen, K.; Rabe, J. P.

2006-01-01

271

Tunneling into high-Tc superconductors: methods of fabricating tunnel junctions  

International Nuclear Information System (INIS)

[en] In the preprint we shell review some experimental results on electron tunneling into high-Tc superconductors. Pros and cons of various methods of fabricating the tunnel junctions with metal oxide compound as a base electrode are discussed. The data obtained by different groups are examined in terms of the tunneling criterion. 66 refs.; 13 figs

1990-01-01

272

Superconducting electron tunneling as detection method for low frequency resonant vibration modes of interstitials in fcc lead  

International Nuclear Information System (INIS)

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.).

1981-01-01

273

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

Digital Repository Infrastructure Vision for European Research (DRIVER)

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 stud...

Romanov Kalle; Aarnio Matti

274

Electron-tunneling study of superconductors doped with magnetic atoms and nonmagnetic resonant-state atoms: indium-chromium, zinc-manganese, and aluminum-manganese  

International Nuclear Information System (INIS)

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

1983-01-01

275

Operation of resonant-tunnelling oscillators beyond tunnel lifetime limit  

Science.gov (United States)

The tunnel lifetime of the electrons in the quantum well of a resonant-tunnelling diode (RTD) is usually assumed to be imposing an inherent fundamental limitation on the operating frequencies of RTD oscillators. Here, we experimentally demonstrate that one can overcome the limitation by heavy doping of the RTD collector. We present RTD oscillators with the fundamental oscillation frequency up to a factor of 3 above the tunnel lifetime limitation. Our results indicate that the inherent frequency limitations of RTDs should lie far above the state-of-the-art frequency of the contemporary RTD oscillators.

Feiginov, M.; Sydlo, C.; Cojocari, O.; Meissner, P.

2011-05-01

276

Anisotropic scattering of Bi(111) surface state electrons at a point defect visualized by low temperature scanning tunneling microscopy and spectroscopy  

Energy Technology Data Exchange (ETDEWEB)

The semimetal bismuth (Bi) has recently attracted a lot of attention due to its interesting transport properties. The metallic surface states which occur on various of its surfaces underlie a large spin orbit splitting. We use scanning tunneling microscopy to analyze the lateral variation in the local density of states in the vicinity of a point defect on a Bi(111)-surface. The observed pattern in the dI/dV-images visualizes the scattering of surface state electrons. At energies close to the Fermi level, the pattern is highly anisotropic and shows a threefold symmetry. Using the calculated Fermi surface of Bi(111) the scattering processes are ascribed to spin-conserving transitions between two spin orbit split surface states. The scattering pattern can be simulated by the superposition of three monochromatic waves where the phase with respect to the scattering center has a significant impact on the appearance and the symmetry of the pattern.

Cottin, Maren; Bobisch, Christian; Schaffert, Johannes; Sonntag, Andreas; Jnawali, Giriraj; Moeller, Rolf [Faculty of Physics, Center for Nanointegration Duisburg-Essen, University of Duisburg-Essen, 47048 Duisburg (Germany); Bihlmayer, Gustav [Institut fuer Festkoerperforschung and Institute for Advanced Simulation, Forschungszentrum Juelich, 52425 Juelich (Germany)

2011-07-01

277

Local electronic transport in La0.7Sr0.3MnO3 thin films studied by scanning tunneling potentiometry  

International Nuclear Information System (INIS)

We have used a scanning tunneling microscope in potentiometry mode to investigate the local electric potential distribution in current carrying epitaxial La0.7Sr0.3MnO3 thin films, with magnetotransport properties similar to the ones of single crystals. Scans imaging simultaneously the surface topography and the potential distribution have been obtained with an unprecedented resolution. In textured La0.7Sr0.3MnO3/MgO, sharp potential steps coincide with some of the grain boundaries, whereas other grains are electrically well connected. The precise nature of the local electronic transport, the percolation of the current through the grain network, and the existence of phase separated insulating domains are then discussed.

2000-10-01

278

Single crystal studies and electron tunneling of (La/sub 1-x/M/sub x/)2CuO/sub 4-?/ (M=Ba and Sr)  

International Nuclear Information System (INIS)

It is not easy to clarify what differences induce the large difference of the T/sub c/ values between the present high-T/sub c/ oxides and other conductive oxides. In order to extract certain information, it seemed necessary to study the detailed physical properties of the high-T/sub c/ oxides. Therefore, single crystals of these oxides were prepared. For (La/sub 1-x/M/sub x/)2CuO/sub 4-?/ M = (Sr and Ba), single crystals were obtained which exhibited superconductivity and studied various physical properties were studied using these crystals. As another important technique to extract the information on the unusually high-T/sub c/ superconductors, the electron tunneling where the superconducting energy gap can directly be observed. The present paper reports results from these experimental studies.

1987-01-01

279

Wind Tunnel  

Science.gov (United States)

Scientists use enormous wind tunnels to test the design of planes, helicopters, even the Space Shuttle. In this simulation activity, learners create a miniature wind tunnel test by blowing air with a fan or blow dryer through a large tube, then flying paper airplanes, helicopters and other folded paper models in the "wind." Unless the source of the air is a fan that stands on its own, for example, more than one person will be needed to do the activity.This activity can be combined with the Helicopter Twirl, Parachute Drop and Boomerang activities, also found on the Lawrence Hall of Science Kids Site.

Science, Lawrence H.

2009-01-01

280

Tunneling spectroscopy studies of aluminum oxide tunnel barrier layers  

CERN Multimedia

We report scanning tunneling microscopy and ballistic electron emission microscopy studies of the electronic states of the uncovered and chemisorbed-oxygen covered surface of AlOx tunnel barrier layers. These states change when chemisorbed oxygen ions are moved into the oxide by either flood gun electron bombardment or by thermal annealing. The former, if sufficiently energetic, results in locally well defined conduction band onsets at ~1 V, while the latter results in a progressively higher local conduction band onset, exceeding 2.3 V for 500 and 600 C thermal anneals.

Mather, P G; Tan, E; Read, J C; Buhrman, R A

2005-01-01

 
 
 
 
281

Tunneling conductance in gapped graphene-based normal metal-insulator-superconductor junctions: Case of massive Dirac electrons  

International Nuclear Information System (INIS)

[en] We study the quantum transport property in a gapped graphene-based normal metal-insulator-superconductor junctions (NG/IG/SG), in the limit of a thin barrier. The charged fermions in NG/IG/SG structure are treated as massive relativistic particles. Based on Andreev and normal reflections in normal-superconductor graphene-based junction and BTK formalism, the tunneling conductance's in terms of some different electrostatic superconductor, U0 and barrier, V0 potential are obtained. Using the experimental based values of the Fermi energy in the NG and SG (EFN and EFN + U0, respectively), energy gap in graphene (2mvF2) and superconducting order parameter, ?, it is shown that the conductance spectra of such system represent a new behavior, i.e. if we take |EFN-mvF2|?0, it becomes as a step function of V0. This behavior of charge transportation can be considered as a nano switch.

2010-12-01

282

Observation of diffusion and tunneling recombination of dye-photoinjected electrons in ultrathin TiO2 layers by surface photovoltage transients.  

Science.gov (United States)

Surface photovoltage transients were used to monitor both the short time dynamics (>10 ns) and the spatial distribution of electrons photoinjected in thin (2-20 nm) TiO2 layers from dye molecules adsorbed at the surface. At low temperatures (100-250 K), the dynamics are governed exclusively by spatially dependent tunneling recombination, with a rate that varies with the distance from the surface x as exp(-2x/a), and an initial exponential distribution of photoinjected electrons, n0 exp(-x/b). This model is confirmed by the observation of power law decay in time t(-a/2b) with a ratio a/b = 0.28 +/- 0.04. The stability of cis-di(isothiocyanato)-N-bis(2,2'-bipyridine-4,4'-dicarboxy) ruthenium(II) (N3) dye molecules on TiO2 during treatment in a vacuum at high temperatures was proven. For high temperatures (250-540 K), the thickness dependence of the decays indicates that the dynamics of surface recombination are retarded by the diffusion of electrons toward the interior of the film. The implications for thin layer coating in dye-sensitized solar cells are discussed. PMID:16852891

Mora-Seró, Ivan; Dittrich, Thomas; Belaidi, Abdelhak; Garcia-Belmonte, Germà; Bisquert, Juan

2005-08-11

283

Observation of diffusion and tunneling recombination of dye-photoinjected electrons in ultrathin TiO2 layers by surface photovoltage transients.  

UK PubMed Central (United Kingdom)

Surface photovoltage transients were used to monitor both the short time dynamics (>10 ns) and the spatial distribution of electrons photoinjected in thin (2-20 nm) TiO2 layers from dye molecules adsorbed at the surface. At low temperatures (100-250 K), the dynamics are governed exclusively by spatially dependent tunneling recombination, with a rate that varies with the distance from the surface x as exp(-2x/a), and an initial exponential distribution of photoinjected electrons, n0 exp(-x/b). This model is confirmed by the observation of power law decay in time t(-a/2b) with a ratio a/b = 0.28 +/- 0.04. The stability of cis-di(isothiocyanato)-N-bis(2,2'-bipyridine-4,4'-dicarboxy) ruthenium(II) (N3) dye molecules on TiO2 during treatment in a vacuum at high temperatures was proven. For high temperatures (250-540 K), the thickness dependence of the decays indicates that the dynamics of surface recombination are retarded by the diffusion of electrons toward the interior of the film. The implications for thin layer coating in dye-sensitized solar cells are discussed.

Mora-Seró I; Dittrich T; Belaidi A; Garcia-Belmonte G; Bisquert J

2005-08-01

284

Recent advances in photoelectrochemistry. Part 4. Redox molecular quantum electron tunnelling device; Saikin no hikari denki kagaku. 4. Yuki redokkusu kei wo mochiiru ryoshi tonneru denshi debaisu  

Energy Technology Data Exchange (ETDEWEB)

The outline of the study on organic redox device is given which can restructure high quantum function of organism artificially. The important problems for the realization and controlling of electron movement in a molecular scale field are the control of redox potential difference among functional molecule groups and the orientation and distances between molecules. To verify whether the mechanism of the fundamental movement of a molecular element model can be made artificially, the elemental process of the movement of photoelectron in artificial molecular structure having flavin and porphyrin as an electron transfer functional group is analyzed by picosecond laser spectrometry. Even in the artificial molecule structure, it is verified that electron movement between flavin and porphyrin is an ultrahigh speed process predicated by the quantum tunneling structure. Photoelectric properties are investigated using molecular film heterojunction (MHJ) of aluminium-porphyrin LB film-flavin LB film-aluminium type, and dynamic mechanism of elemental process of photoelectron movement in MHJ is analyzed. 13 refs., 5 figs.

Isoda, S. [Mitsubishi Electric Corp., Amagasaki, Hyogo (Japan). Central Research Lab.

1995-01-05

285

Tunnelling `97  

Energy Technology Data Exchange (ETDEWEB)

Papers are presented under the following headings: design and construction; tunnel advance methods; geotechnical topics; products and techniques; health, safety and risk assessment; case histories; Heathrow express project; Jubilee line extension project; and environmental topics. One paper on cablebolt reinforcement in coal mines has been abstracted separately.

NONE

1997-12-31

286

Coulomb Drag in Systems with Tunneling Bridges  

CERN Multimedia

We study the Coulomb drag effect in double layer electronic systems with local tunneling links. The possibility of tunneling between the layers leads to a pronounced exchange contribution to the transconductance, which is negative and non--vanishing at zero temperature. The diffusive motion of the electrons inside each layer in interplay with the electron--electron interaction cause a distinguishable singular temperature dependence of the transconductance at low temperatures.

Oreg, Y; Oreg, Yuval; Kamenev, Alex

1998-01-01

287

Ferroelectric tunnel memristor.  

UK PubMed Central (United Kingdom)

Strong interest in resistive switching phenomena is driven by a possibility to develop electronic devices with novel functional properties not available in conventional systems. Bistable resistive devices are characterized by two resistance states that can be switched by an external voltage. Recently, memristors-electric circuit elements with continuously tunable resistive behavior-have emerged as a new paradigm for nonvolatile memories and adaptive electronic circuit elements. Employment of memristors can radically enhance the computational power and energy efficiency of electronic systems. Most of the existing memristor prototypes involve transition metal oxide resistive layers where conductive filaments formation and/or the interface contact resistance control the memristive behavior. In this paper, we demonstrate a new type of memristor that is based on a ferroelectric tunnel junction, where the tunneling conductance can be tuned in an analogous manner by several orders of magnitude by both the amplitude and the duration of the applied voltage. The ferroelectric tunnel memristors exhibit a reversible hysteretic nonvolatile resistive switching with a resistance ratio of up to 10(5) % at room temperature. The observed memristive behavior is attributed to the field-induced charge redistribution at the ferroelectric/electrode interface, resulting in the modulation of the interface barrier height.

Kim DJ; Lu H; Ryu S; Bark CW; Eom CB; Tsymbal EY; Gruverman A

2012-11-01

288

Evidence of hole-electron quasiparticle interference in ErSi2 semimetal by Fourier-transform scanning tunneling spectroscopy.  

UK PubMed Central (United Kingdom)

The semimetallic ErSi2 layer grown on Si(111) substrates provides an ideally confined 2D electron and hole gas that reflects in complex standing wave pattern at 77 K. The quasiparticles exist in a wide energy range from -800 to 300 meV without mixing with silicon bulk excitations. By comparing high resolution Fourier transform of dI/dV maps, with joint density of states calculations, we are able to determine the 2D band structure. We also clearly demonstrate that hole-hole and hole-electron quantum interferences dominate over electron-electron ones.

Vonau F; Aubel D; Gewinner G; Zabrocki S; Peruchetti JC; Bolmont D; Simon L

2005-10-01

289

Evidence of hole-electron quasiparticle interference in ErSi2 semimetal by Fourier-transform scanning tunneling spectroscopy.  

Science.gov (United States)

The semimetallic ErSi2 layer grown on Si(111) substrates provides an ideally confined 2D electron and hole gas that reflects in complex standing wave pattern at 77 K. The quasiparticles exist in a wide energy range from -800 to 300 meV without mixing with silicon bulk excitations. By comparing high resolution Fourier transform of dI/dV maps, with joint density of states calculations, we are able to determine the 2D band structure. We also clearly demonstrate that hole-hole and hole-electron quantum interferences dominate over electron-electron ones. PMID:16383855

Vonau, F; Aubel, D; Gewinner, G; Zabrocki, S; Peruchetti, J C; Bolmont, D; Simon, L

2005-10-20

290

Bibliotecas digitales: recursos bibliográficos electrónicos en educación básica Digital Libraries: Electronic Bibliographic Resources on Basic Education  

Directory of Open Access Journals (Sweden)

Full Text Available Estudiar recursos bibliográficos en formato electrónico para la educación básica implica reflexionar sobre mecanismos de búsqueda que atiendan las necesidades de los pequeños usuarios. A través de los trabajos realizados en el proyecto de investigación educativa «Bibliotecas digitales», se puso en evidencia que los acervos explorados, manejan un lenguaje para un nivel de educación superior. Ante esta problemática, se planteó la siguiente pregunta de investigación: ¿Cuáles son los criterios de clasificación de los recursos bibliográficos electrónicos para la educación básica? Se propuso una investigación no experimental, con una muestra de estudio no probabilística de casos tipo, integrada por 250 recursos que ofrecen los diez acervos bibliográficos seleccionados en base a un estudio exploratorio previamente realizado. Para el análisis, se valoraron los siguientes recursos: accesibilidad, eje curricular al que está dirigido, formato y aspectos pedagógicos, funcionales, tecnológicos y estéticos. Los resultados muestran una media de 3.76, la cual indica que los acervos bibliográficos ofrecen recursos de calidad, aunque es necesario trabajar en los aspectos pedagógicos y funcionales. Clasificar recursos electrónicos para educación básica requiere considerar necesidades pedagógicas, entorno gráfico, tecnológico y sobre todo, la forma dinámica y cambiante de cómo se concibe la información. Esto corrobora la necesidad de establecer un conjunto de indicadores que permita a los docentes seleccionar recursos electrónicos en relación a los ejes curriculares de la educación básica.Studying electronic bibliographic resources for basic education involves thinking about search mechanisms that meet the needs of young users. Through the investigation carried out during the educational research project «Digital libraries», it became evident that the collections explored use a language better suited to higher education. Faced with this problem, the following question arose: What are the criteria for classifying electronic bibliographic resources for basic education? The proposed investigation was non-experimental, with a non-probabilistic sample of case studies; the sample comprised 250 resources from 10 bibliographic collections. The analysis assessed resources according to: accessibility, the curricular axis to which it is addressed, and format; pedagogical, functional, technological and aesthetic aspects. The results show a mean of 3.76, which indicates that the bibliographic collections provide quality resources, although it is necessary to improve educational and functional aspects. Classifying electronic resources for basic education requires the consideration of pedagogical needs, graphical and technological qualities and, especially, the dynamic way in which information is conceived nowadays. This confirms the need to establish a set of indicators that enable teachers to select electronic resources based on basic education curricular axes.

Marcela Georgina López Zermeño

2012-01-01

291

Los recursos educativos electrónicos: perspectivas y herramientas de evaluación/ Electronic educational resources: perspectives and evaluation tools  

Scientific Electronic Library Online (English)

Full Text Available Abstract in spanish Los recursos electrónicos con fines educativos están cada vez más presentes en los procesos de enseñanza-aprendizaje actuales, y por tanto, en las colecciones digitales de las bibliotecas. Ante su proliferación y heterogeneidad cada vez mayor se ha planteado como una necesidad para la comunidad universitaria definirlos y establecer un conjunto de criterios claros y relevantes de evaluación que permitan determinar la calidad de los mismos. En este trabajo se analizan (more) las principales definiciones sobre recursos educativos electrónicos de cara a su acotación, se revisan las diferentes perspectivas para la evaluación de su calidad a través de la literatura científica, y se revisan las principales herramientas utilizadas para valorarlos. Finalmente, se presenta EVALUAREED, un instrumento diseñado para analizar y medir la calidad de los mismos, enfocado para ser utilizado por la comunidad universitaria, incluidas las bibliotecas. Abstract in english Electronic resources for education are increasingly present in the teaching-learning processes and in the digital library collections. Because of the proliferation and variety of educational resources, the educational community needs to define and establish a set of clear and relevant assessment to determine their quality. This paper reviews the main definitions of electronic educational resources as well as different perspectives to the assessment of their quality throug (more) h the scientific literature, and the main tools used to value them. Finally, it describes EVALUAREED, an instrument designed to analyze and measure the quality of these resources used by universitary community included the libraries.

Pinto, Maria; Gomez-Camarero, Carmen; Fernández-Ramos, Andrés

2012-09-01

292

Tunneling conductance in gapped graphene-based normal metal-insulator-superconductor junctions: Case of massive Dirac electrons  

Energy Technology Data Exchange (ETDEWEB)

We study the quantum transport property in a gapped graphene-based normal metal-insulator-superconductor junctions (NG/IG/SG), in the limit of a thin barrier. The charged fermions in NG/IG/SG structure are treated as massive relativistic particles. Based on Andreev and normal reflections in normal-superconductor graphene-based junction and BTK formalism, the tunneling conductance's in terms of some different electrostatic superconductor, U{sub 0} and barrier, V{sub 0} potential are obtained. Using the experimental based values of the Fermi energy in the NG and SG (E{sub FN} and E{sub FN} + U{sub 0}, respectively), energy gap in graphene (2mv{sub F}{sup 2}) and superconducting order parameter, {Delta}, it is shown that the conductance spectra of such system represent a new behavior, i.e. if we take |E{sub FN}-mv{sub F}{sup 2}|{yields}0, it becomes as a step function of V{sub 0}. This behavior of charge transportation can be considered as a nano switch.

Goudarzi, H., E-mail: h.goudarzi@urmia.ac.i [Department of Physics, Faculty of Science, Urmia University, P.O. Box 165, Urmia (Iran, Islamic Republic of); Sedghi, H.; Khezerlou, M.; Mabhouti, Kh. [Department of Physics, Faculty of Science, Urmia University, P.O. Box 165, Urmia (Iran, Islamic Republic of)

2010-12-01

293

SIN and SIS tunneling in cuprates  

CERN Multimedia

We calculate the SIN and SIS tunneling conductances for the spin-fermion model. We argue that at strong spin-fermion coupling, relevant to cuprates, both conductances have dip features near the threshold frequencies when a tunneling electron begin emitting propagating spin excitation. We argue that the resonance spin frequency measured in neutron scattering can be inferred from the tunneling data by analyzing the derivatives of SIN and SIS conductances.

Abanov, A G; Chubukov, Andrey V.

2000-01-01

294

High-Resolution Scanning Tunneling Spectroscopy of Vortex Cores in Inhomogeneous Electronic States of Bi2Sr2CaCu2Ox  

Science.gov (United States)

We studied electronic states in vortex cores of slightly overdoped Bi2Sr2CaCu2Ox by scanning tunneling spectroscopy. We have found that they have stripe structures with a 4a0 width extending along the Cu--O bond directions. Vortex core states are observed as two peaks at particle--hole symmetric positions in the energy gap. Along a stripe, the peak positions of vortex core states are constant and not influenced by the spatial variation of the energy gap ?. Outer stripes have a larger energy than inner stripes. A mazelike pattern in the electronic states at E = ±? has been observed all over the surface both inside and outside the vortex core. The orientation of stripes of vortex core states was found to be related to the mazelike pattern in the vortex core region. A short-range order of the mazelike pattern spatially coexists with the superconductivity and locally breaks the symmetry of the two Cu--O bond directions. We propose that the vortex core bound states are formed by Bogoliubov quasiparticles owing to the depairing of Cooper pairs and have a local C2 symmetry influenced by the short-range order of the mazelike pattern.

Yoshizawa, Shunsuke; Koseki, Taiji; Matsuba, Ken; Mochiku, Takashi; Hirata, Kazuto; Nishida, Nobuhiko

2013-08-01

295

Inelastic electron tunneling spectra and vibronic coupling density analysis of 2,5-dimercapto-1,3,4-thiadiazole and tetrathiafulvalene dithiol.  

UK PubMed Central (United Kingdom)

We calculate inelastic electron tunneling (IET) spectra for 2,5-dimercapto-1,3,4-thiadiazole (DMcT) and tetrathiafulvalene dithiol (TTF-DT) sandwiched between two gold electrodes using non-equilibrium Green's function (NEGF) theory. The calculated peak positions are in reasonable agreement with the experimental data. We also calculate IET spectrum for thiophene dithiol (Th-DT) sandwiched between two gold electrodes and compare it with that for the Au/DMcT/Au junction. Th-DT and DMcT can be distinguished using the IET spectroscopy by the peak of the C-C stretching mode. The peak intensity in the IET spectra is analyzed using vibronic coupling density (VCD) analysis. For the Au/DMcT/Au junction, large distribution of electron-density difference ??(HOMO) on the C-N bond is responsible for the intense peak of the C-N stretching mode; on the other hand, for Au/TTF-DT/Au junction, large distribution of ??(HOMO) on the central C=C bond is responsible for the intense peak of the C=C stretching modes.

Shizu K; Sato T; Tanaka K

2010-10-01

296

Inelastic electron tunneling spectra and vibronic coupling density analysis of 2,5-dimercapto-1,3,4-thiadiazole and tetrathiafulvalene dithiol.  

Science.gov (United States)

We calculate inelastic electron tunneling (IET) spectra for 2,5-dimercapto-1,3,4-thiadiazole (DMcT) and tetrathiafulvalene dithiol (TTF-DT) sandwiched between two gold electrodes using non-equilibrium Green's function (NEGF) theory. The calculated peak positions are in reasonable agreement with the experimental data. We also calculate IET spectrum for thiophene dithiol (Th-DT) sandwiched between two gold electrodes and compare it with that for the Au/DMcT/Au junction. Th-DT and DMcT can be distinguished using the IET spectroscopy by the peak of the C-C stretching mode. The peak intensity in the IET spectra is analyzed using vibronic coupling density (VCD) analysis. For the Au/DMcT/Au junction, large distribution of electron-density difference ??(HOMO) on the C-N bond is responsible for the intense peak of the C-N stretching mode; on the other hand, for Au/TTF-DT/Au junction, large distribution of ??(HOMO) on the central C=C bond is responsible for the intense peak of the C=C stretching modes. PMID:20714648

Shizu, Katsuyuki; Sato, Tohru; Tanaka, Kazuyoshi

2010-08-11

297

Immobilization, hybridization, and oxidation of synthetic DNA on gold surface: Electron transfer investigated by electrochemistry and scanning tunneling microscopy  

International Nuclear Information System (INIS)

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

2009-06-08

298

Carpal Tunnel Release  

Medline Plus

Full Text Available ... typically associated with carpal tunnel syndrome, but we'd like to point out today that carpal tunnel ... so all keyboard users are not somebody who'd develop carpal tunnel syndrome, and just because you' ...

299

Carpal Tunnel Syndrome  

Science.gov (United States)

... arm. Just a passing cramp? It could be carpal tunnel syndrome. The carpal tunnel is a narrow passageway of ... Women are three times more likely to have carpal tunnel syndrome than men. Early diagnosis and treatment are important ...

300

Resonant photon-assisted tunneling through a double quantum dot an electron pump from spatial Rabi oscillations  

CERN Document Server

The time average of the fully nonlinear current through a double quantum dot, subject to an arbitrary combination of ac and dc voltages is calculated exactly using the Keldysh nonequilibrium Green function technique. When driven on resonance, the system functions as an efficient electron pump due to Rabi oscillation between the dots. The pumping current is maximum when the coupling to the leads equals the Rabi frequency.

Stafford, C A; Stafford, Charles A; Wingreen, Ned S

1996-01-01

 
 
 
 
301

Immobilization, hybridization, and oxidation of synthetic DNA on gold surface: Electron transfer investigated by electrochemistry and scanning tunneling microscopy  

Energy Technology Data Exchange (ETDEWEB)

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.

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

302

Review of material recovery from used electric and electronic equipment-alternative options for resource conservation.  

UK PubMed Central (United Kingdom)

For waste from electric and electronic equipment, the WEEE Directive stipulates the separate collection of electric and electronic waste. As to new electric and electronic devices, the Restriction of Hazardous Substances (RoHS) Directive bans the use of certain chemicals dangerous for man and environment. From the implementation of the WEEE directive, many unsolved problems have been documented: poor collection success, emission of dangerous substances during collection and recycling, irretrievable loss of valuable metals among others. As to RoHS, data from the literature show a satisfying success. The problems identified in the process can be reduced to some basic dilemmas at the borders between waste management, product policy and chemical safety. The objectives of the WEEE Directive and the specific targets for use and recycling of appliances are not consistent. There is no focus on scarce resources. Extended producer responsibility is not sufficient to guarantee sustainable waste management. Waste management reaches its limits due to problems of implementation but also due to physical laws. A holistic approach is necessary looking at all branch points and sinks in the stream of used products and waste from electric and electronic equipment. This may be done with respect to the general rules for sustainable management of material streams covering the three dimensions of sustainable policy. The relationships between the players in the field of electric and electronic devices have to be taken into account. Most of the problems identified in the implementation process will not be solved by the current amendment of the WEEE Directive.

Friege H

2012-09-01

303

Tunneling between Two Quantum Hall Droplets  

CERN Document Server

We report on tunneling experiment between two quantum Hall droplets separated by a nearly ideal tunnel barrier. The device is produced by cleaved edge overgrowth that laterally juxtaposes two two-dimensional electron systems across a high quality semiconductor barrier. The dramatic evolution of the tunneling characteristics is consistent with the magnetic field-dependent tunneling between the coupled edge states of the quantum Hall droplets. We identify a series of quantum critical points between successive strong and weak tunneling regimes that are reminiscent of the plateau-transitions in quantum Hall effect. Scaling analysis shows that the conductance near the critical magnetic fields $B_{c}$ is a function of a single scaling argument $|B-B_{c}|T^{-\\kappa}$, where the exponent $\\kappa = 0.42$. This puzzling resemblance to a quantum Hall-insulator transition points to the significance of interedge correlation in the lateral tunneling of quantum Hall droplets.

Yang, I; Pfeiffer, L N; Baldwin, K; West, K; Yang, Inseok; Kang, Woowon; Pfeiffer, Loren; Baldwin, Kirk; West, Ken

2004-01-01

304

Investigation into scanning tunnelling luminescence microscopy  

CERN Multimedia

This work reports on the development of a scanning tunnelling luminescence (STL) microscope and its application to the study of Ill-nitride semiconductor materials used in the production of light emitting devices. STL microscopy is a technique which uses the high resolution topographic imaging capabilities of the scanning tunnelling microscope (STM) to generate high resolution luminescence images. The STM tunnelling current acts as a highly localised source of electrons (or holes) which generates luminescence in certain materials. Light generated at the STM tunnelling junction is collected concurrently with the height variation of the tunnelling probe as it is scanned across a sample surface, producing simultaneous topographic and luminescence images. Due to the very localised excitation source, high resolution luminescence images can be obtained. Spectroscopic resolution can be obtained by using filters. Additionally, the variation of luminescence intensity with tunnel current and with bias voltage can provi...

Manson-Smith, S K

2001-01-01

305

In situ Control of Si/Ge Growth on Stripe-Patterned Substrates Using Reflection High-Energy Electron Diffraction and Scanning Tunneling Microscopy  

Science.gov (United States)

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.

Sanduijav, B.; Matei, D. G.; Springholz, G.

2010-12-01

306

In situ Control of Si/Ge Growth on Stripe-Patterned Substrates Using Reflection High-Energy Electron Diffraction and Scanning Tunneling Microscopy.  

UK PubMed Central (United Kingdom)

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.

Sanduijav B; Matei DG; Springholz G

2010-01-01

307

In situ Control of Si/Ge Growth on Stripe-Patterned Substrates Using Reflection High-Energy Electron Diffraction and Scanning Tunneling Microscopy  

Directory of Open Access Journals (Sweden)

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.

Sanduijav B; Matei DG; Springholz G

2010-01-01

308

The structures and dynamics of atomic and molecular adsorbates on metal surfaces by scanning tunneling microscopy and low energy electron diffraction  

Energy Technology Data Exchange (ETDEWEB)

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.

Yoon, Hyungsuk Alexander

1996-12-01

309

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  

CERN Document Server

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.

Lu, Z H; Khangura, R S; Zgierski, M Z; Ritchie, D; Zgierski, Marek Z.; Ritchie, Douglas

2004-01-01

310

QUANTUM TUNNELLING AND MAGNETIZATION DYNAMICS IN LOW DIMENSIONAL SYSTEMS  

Directory of Open Access Journals (Sweden)

Full Text Available Quantum mechanics allows a system to overcome a classically-unsurmountable energy barrier through a mechanism called Quantum Tunnelling (QT). Although pertaining to the quantum domain, QT is the cause of important physical phenomena that can be detected at the macroscopic scale. Some of them have led to breakthrough applications in electronics (tunnel junctions) and imaging (scanning tunnelling microscope).

ANDREA CORNIA

2011-01-01

311

A preliminary categorization of end-of-life electrical and electronic equipment as secondary metal resources  

International Nuclear Information System (INIS)

[en] 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.

2011-01-01

312

??????????COUNTER???????? Statistical Problems of Electronic Resources and the Development and Application of COUNTER Project  

Directory of Open Access Journals (Sweden)

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.

Hui-Hsin Yeh

2006-01-01

313

Achieving Resource Conservation in Electronic Waste Management: A Review of Options Available to Developing Countries  

Directory of Open Access Journals (Sweden)

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.

Innocent Chidi Nnorom; Oladele Osibanjo; Stanley Onyedikachi Nnorom

2007-01-01

314

The effects of Dresselhaus and Rashba spin-orbit interactions on the electron tunneling in a non-magnetic heterostructure  

Energy Technology Data Exchange (ETDEWEB)

We theoretically investigate the electron transport properties in a non-magnetic heterostructure with both Dresselhaus and Rashba spin-orbit interactions. The detailed-numerical results show that (1) the large spin polarization can be achieved due to Dresselhaus and Rashba spin-orbit couplings induced splitting of the resonant level, although the magnetic field is zero in such a structure, (2) the Rashba spin-orbit coupling plays a greater role on the spin polarization than the Dresselhaus spin-orbit interaction does, and (3) the transmission probability and the spin polarization both periodically change with the increase of the well width.

Lu Jianduo, E-mail: l_j316@163.com [Department of Applied Physics, Wuhan University of Science and Technology, Wuhan 430081 (China) and Hubei Province Key Laboratory of Systems Science in Metallurgical Process, Wuhan University of Science and Technology, Wuhan 430081 (China); Li Jianwen [Department of Physics, Nanchang Institute of Technology, Nanchang 330099 (China)

2010-04-01

315

Revealing the atomic surface structure of the (100) Y-Al-Ni-Co approximant by low-energy electron diffraction and scanning tunneling microscopy  

Science.gov (United States)

In this paper we present an investigation of the (100) Y-Al75.8Ni2.1Co22.1 surface, which is structurally and chemically related to the (10000) twofold symmetric surface of the decagonal Al-Ni-Co quasicrystal. The atomic surface structure was probed by low-energy electron diffraction (LEED) and by scanning tunneling microscopy (STM), revealing three different surface terminations and three different types of surface reconstructions. All three terminations were successfully assigned to the densest bulk layers and the origin of the surface reconstructions revealed by LEED could be identified locally by STM. The (100) Y-Al-Ni-Co surface shares with the related (10000) d-AlNiCo quasicrystal surface the strong tendency of reconstruction, which in the former case is occurring along the b axis and in the later along the periodic [00001] direction. Gaining a theoretical understanding of the reconstructions of the (100) Y-Al-Ni-Co surface might therefore help to understand the stability of bulk and surface atomic structures in decagonal quasicrystals. Furthermore, due to the strong relation to the quasicrystalline (10000) d-AlNiCo surface, the crystalline (100) Y-Al75.8Ni2.1Co22.1 surface is now a very promising candidate to study directional anisotropies in epitaxial thin film growth, friction, or the electronic structure, with the advantage of representing a much simpler structure (32 atoms/unit cell) which can be theoretically addressed with less effort compared to its quasicrystalline counter part.

Mäder, R.; Widmer, R.; Bauer, B.; Gille, P.; Gröning, P.; Steurer, W.; Gröning, O.

2010-02-01

316

Coherent and phonon-assisted tunnelling in asymmetric double barrier resonant tunnelling structures  

International Nuclear Information System (INIS)

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

1998-12-08

317

Behavioral response of termites to tunnel surface irregularity.  

Science.gov (United States)

Subterranean termites construct underground tunnels, tens to hundreds of meters in length, in order to search for and transport resources. Diverse soil conditions surrounding the tunnels, such as soil pores and differing moisture concentrations, may cause different sized- and shaped-irregularities in the tunnels. To understand how individual termites respond to the irregularities, the present study monitored the movement of termites, Coptotermes formosanus Shiraki, in artificially excavated tunnels with rectangular irregularities of varying sizes in two-dimensional sand substrates. Termites tunneled at some of the irregularities and not at the others. The tunneling or non-tunneling behavior resulted from four different responses. The non-tunneling response may result from a behavioral adaptation that allows termites to avoid wasting energy that may be used in foraging. PMID:18359581

Lee, S-H; Bardunias, P; Su, N-Y; Yang, R-L

2008-02-19

318

Evolution and collapse of electron quasi-stationary states in plane symmetric three-barrier resonance-tunnel structures  

International Nuclear Information System (INIS)

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 ?-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).

2009-01-01

319

Reducing Clinical Trial Monitoring Resource Allocation and Costs Through Remote Access to Electronic Medical Records  

Science.gov (United States)

Purpose: With electronic medical records (eMRs), the option now exists for clinical trial monitors to perform source data verification (SDV) remotely. We report on a feasibility study of remote access to eMRs for SDV and the potential advantages of such a process in terms of resource allocation and cost. Methods: The Clinical Trials Unit at the Peter MacCallum Cancer Centre, in collaboration with Novartis Pharmaceuticals Australia, conducted a 6-month feasibility study of remote SDV. A Novartis monitor was granted dedicated software and restricted remote access to the eMR portal of the cancer center, thereby providing an avenue through which perform SDV. Results: Six monitoring visits were conducted during the study period, four of which were performed remotely. The ability to conduct two thirds of the monitoring visits remotely in this complex phase III study resulted in an overall cost saving to Novartis. Similarly, remote monitoring eased the strain on internal resources, particularly monitoring space and hospital computer terminal access, at the cancer center. Conclusion: Remote access to patient eMRs for SDV is feasible and is potentially an avenue through which resources can be more efficiently used. Although this feasibility study involved limited numbers, there is no limit to scaling these processes to any number of patients enrolled onto large clinical trials.

Uren, Shannon C.; Kirkman, Mitchell B.; Dalton, Brad S.; Zalcberg, John R.

2013-01-01

320

Reducing clinical trial monitoring resource allocation and costs through remote access to electronic medical records.  

UK PubMed Central (United Kingdom)

PURPOSE: With electronic medical records (eMRs), the option now exists for clinical trial monitors to perform source data verification (SDV) remotely. We report on a feasibility study of remote access to eMRs for SDV and the potential advantages of such a process in terms of resource allocation and cost. METHODS: The Clinical Trials Unit at the Peter MacCallum Cancer Centre, in collaboration with Novartis Pharmaceuticals Australia, conducted a 6-month feasibility study of remote SDV. A Novartis monitor was granted dedicated software and restricted remote access to the eMR portal of the cancer center, thereby providing an avenue through which perform SDV. RESULTS: Six monitoring visits were conducted during the study period, four of which were performed remotely. The ability to conduct two thirds of the monitoring visits remotely in this complex phase III study resulted in an overall cost saving to Novartis. Similarly, remote monitoring eased the strain on internal resources, particularly monitoring space and hospital computer terminal access, at the cancer center. CONCLUSION: Remote access to patient eMRs for SDV is feasible and is potentially an avenue through which resources can be more efficiently used. Although this feasibility study involved limited numbers, there is no limit to scaling these processes to any number of patients enrolled onto large clinical trials.

Uren SC; Kirkman MB; Dalton BS; Zalcberg JR

2013-01-01

 
 
 
 
321

Realizing a Four-Step Molecular Switch in Scanning Tunneling Microscope Manipulation of Single Chlorophyll-a Molecules  

CERN Document Server

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.

Iancu, V; Iancu, Violeta; Hla, Saw-Wai

2006-01-01

322

Tunnelling machine  

Energy Technology Data Exchange (ETDEWEB)

A tunnelling machine has a swing unit (31) that is swingable about a horizontal axis (I). The swing unit has a head (50) that rotates about an axis (II) that is transverse to said horizontal axis and passes the horizontal at a distance below the horizontal axis. The head is equipped with a plurality of disc-cutters (53-58, 63) that are arranged to have their cutting edges on an imaginary sphere with a radius of about the same length as the swing radius. Upon simultaneous upward swinging of the swing unit and rotation of the head, the cutters cut both when on the leading side of the head and when on the trailing side. No cutting occurs during the return swing stroke. When the swing unit has been returned, the machine is advanced a step which is somewhat larger than the distance between the two axes, and another upward cutting stroke can be effected.

Dick, H.

1980-11-11

323

Quantum Tunneling  

CERN Multimedia

This article is a slightly expanded version of the talk I delivered at the Special Plenary Session of the 46-th Annual Meeting of the Israel Physical Society (Technion, Haifa, May 11, 2000) dedicated to Misha Marinov. In the first part I briefly discuss quantum tunneling, a topic which Misha cherished and to which he was repeatedly returning through his career. My task was to show that Misha's work had been deeply woven in the fabric of today's theory. The second part is an attempt to highlight one of many facets of Misha's human portrait. In the 1980's, being a refusenik in Moscow, he volunteered to teach physics under unusual circumstances. I present recollections of people who were involved in this activity.

Shifman, M

2002-01-01

324

Attoclock elicits physics of laser-induced tunnel ionization  

CERN Multimedia

Tunneling of particles through a classically forbidden region is a truly quantum mechanical effect influencing the atomic and molecular building blocks of matter. Tunneling is typically assumed to play a central role in the interaction of matter with intense laser pulses and in time-resolved measurements on the attosecond timescale of electronic motion. Here we perform laser tunnel ionization experiments on atomic helium and argon with attosecond time resolution. We show by comparing the helium and argon results that a tunneling model correctly describes the data assuming instantaneous tunneling delay time. However tunneling occurs through a potential barrier that is modified by all of the remaining electrons and from a state that is shifted in energy by the external field. The resulting modified force term influences the dynamics of the tunneled electron, changes important physical parameters and hence needs to be accounted for in attosecond measurement techniques. The multielectron effects identified here a...

Pfeiffer, Adrian N; Smolarski, Mathias; Dimitrovski, Darko; Abu-samha, Mahmoud; Madsen, Lars Bojer; Keller, Ursula

2011-01-01

325

Use of Electronic Information Resources and Research Output by Academic Staff in Private Universities in Ogun State, Nigeria  

Directory of Open Access Journals (Sweden)

Full Text Available 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 structured questionnaire. 225 copies of the questionnaire were administered at Babcock University and 144 were retrieved. 88 at Crescent University and 80 were retrieved, while 215 at the Redeemers’ University and 130 were retrieved. The research looked at the extent with which electronic information resources were used in the private universities in Ogun State, using the three universities as sample. A total of 528 copies of the questionnaire were distributed to the respondents at the three universities and a valid number of 354 (66%) questionnaires were retrieved and analyzed. The questionnaire was designed using nominal and likert scales. The study revealed that most of the academic staff from the three private universities knew and used electronic information resources for their research work as shown on Tables 5, 6, 7 and 8. Findings from Tables 8 and 9 indicate that most of respondents from the three private universities have published their articles and presented papers with the use of electronic information resources. The study also revealed on Table 6 that effective use of electronic information resources contribute to the academics’ research output hence 329 (92.9%) of the total respondents supported that view. It is imperative to state here that lack of personal computer and erratic power supply among others are major constraints that inhibit use of electronic information resources in the three private universities which invariably affects their research output. The researchers recommended that private universities in Nigeria expedite action in the area of improving access to electronic information resources through provision of subsidized computers and improved electricity supply in their various universities. Moreso, academic staff are advised to acquire computer skills, learn and relearn to navigate and utilize the vast available electronic information resources on the internet to achieve better research output.Key words: Electronic information resources; Research output; Academics; Information access; Information skill; ICT; Electronic journal; Private university; Ogun state

Saturday U. Omeluzor; Ezinwayi Madukoma; Itunu Bamidele; Susan U. Ogbuiyi

2012-01-01

326

Carpal Tunnel Release  

Medline Plus

Full Text Available ... Hospital in Hartford, Connecticut, see surgery to correct carpal tunnel syndrome. When the median nerve in the carpal tunnel ... a carpal tunnel release on a patient with carpal tunnel syndrome. I'm Dr. Kevin Burton, and I'll ...

327

Resonant tunneling and Coulomb oscillations  

CERN Multimedia

The influence of quantum fluctuations on electron transport through small metallic islands with Coulomb blockade effects is studied beyond the perturbative regime. In tunnel junctions with low resistance higher order coherent processes and ``inelastic resonant tunneling'' become important. We present a path integral real-time description, which allows a systematic diagrammatic classification of these processes. Quantum fluctuations renormalize system parameters and lead to finite lifetime broadening. Both effects are observable in the gate voltage dependence of the nonlinear conductance. The finite bias voltage introduces an energy scale up to which quantum fluctuations are probed. It can be larger than the temperature, which makes quantum effects experimentally observable above thermal fluctuations.

König, J; Schön, G; Konig, Jurgen; Schoeller, Herbert; Schon, Gerd

1995-01-01

328

Laser tunneling from aligned molecules  

CERN Multimedia

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.

Smeenk, C T L; Sokolov, A V; Spanner, M; Lee, K F; Staudte, A; Villeneuve, D M; Corkum, P B

2013-01-01

329

Practical tunnel construction  

CERN Multimedia

The only modern guide to all aspects of practical tunnel construction Practical Tunnel Construction fills a void in the literature for a practical guide to tunnel construction. By taking the reader through a brief introduction and history to a comprehensive discussion of how the geological factors affect tunneling, the author covers the stages and technology that are common today without using complex equations. Written for the individual who does not have an extensive background in tunneling but who has to make tunneling decisions, the various tunneling methods are disc

Hemphill, Gary B

2012-01-01

330

Review of material recovery from used electric and electronic equipment-alternative options for resource conservation.  

Science.gov (United States)

For waste from electric and electronic equipment, the WEEE Directive stipulates the separate collection of electric and electronic waste. As to new electric and electronic devices, the Restriction of Hazardous Substances (RoHS) Directive bans the use of certain chemicals dangerous for man and environment. From the implementation of the WEEE directive, many unsolved problems have been documented: poor collection success, emission of dangerous substances during collection and recycling, irretrievable loss of valuable metals among others. As to RoHS, data from the literature show a satisfying success. The problems identified in the process can be reduced to some basic dilemmas at the borders between waste management, product policy and chemical safety. The objectives of the WEEE Directive and the specific targets for use and recycling of appliances are not consistent. There is no focus on scarce resources. Extended producer responsibility is not sufficient to guarantee sustainable waste management. Waste management reaches its limits due to problems of implementation but also due to physical laws. A holistic approach is necessary looking at all branch points and sinks in the stream of used products and waste from electric and electronic equipment. This may be done with respect to the general rules for sustainable management of material streams covering the three dimensions of sustainable policy. The relationships between the players in the field of electric and electronic devices have to be taken into account. Most of the problems identified in the implementation process will not be solved by the current amendment of the WEEE Directive. PMID:22993131

Friege, Henning

2012-09-01

331

Spin-polarized tunneling in MgO-based tunnel junctions with superconducting electrodes  

Digital Repository Infrastructure Vision for European Research (DRIVER)

We prepared magnetic tunnel junctions with one ferromagnetic and one superconducting Al–Si electrode. Pure cobalt electrodes were compared with a Co–Fe–B alloy and the Heusler compound Co[subscript 2]FeAl. The polarization of the tunneling electrons was determined using the Maki–Fulde model and is d...

Schebaum, Oliver; Fabretti, Savio; Moodera, Jagadeesh S.; Thomas, Andy

332

????????Marketing of Electronic Information Resources: A Case of The J.D. Rockefeller Research Library, Egerton University?Nerisa Kamar  

Directory of Open Access Journals (Sweden)

Full Text Available This paper gives a brief overview of electronic information resources and services offered by The J.D. Rockefeller Research Library at Egerton University and the marketing of these resources. The paper examines the various reasons for marketing electronic information resources, with emphasis on the various, and illustrates marketing strategies used by J.D Rockefeller Research library towards effective utilization of the available resources in supporting research, teaching and learning. These strategies include use of posters, notices, brochures, telephone calls, Current Awareness Services (CAS), workshops and seminars, and decentralization of services, among others. It concludes with a discussion of cost effective use of these strategies in research and teaching.???89-93

? Nerisa Kamar?

2008-01-01

333

Electronic tracking of human resource skills and knowledge, just in time training, manageable due diligence  

Energy Technology Data Exchange (ETDEWEB)

KeySpan Energy Canada is in the process of obtaining recognition of various occupational profiles including pipeline operators, inspectors, and field and plant operators from various certifying organizations. The process of allowing individuals to obtain certification is recognized by Canadian Technology Human Resources Board as a step towards national standards for technologists and technicians. Proven competency is a must for workers in todays oil industry in response to increasingly stringent government safety regulations, environmental concerns and high public scrutiny. Quick Test international Inc. has developed a management tool in collaboration with end users at KeySpan Energy Canada. It is an electronic, Internet based competency tool for tracking personal competencies and maintaining continued competency. Response to the tool has been favourable. 2 refs., 4 figs.

Kolodziej, M.A. [Quick Test International Inc., (Canada). Canadian Technology Human Resource Board; Baker, O. [KeySpan Energy Canada, Calgary, AB (Canada)

2001-06-01

334

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  

Energy Technology Data Exchange (ETDEWEB)

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.)

Breitschaft, Martin

2010-10-22

335

Tunneling Current through Ultrathin Silicon Dioxide Films under Light Exposure  

Science.gov (United States)

Tunneling current through ultrathin silicon dioxide films with a thickness of approximately 3.1 nm, formed on n-Si (100) by controlling preoxide growth during heating, is examined using Al/oxide/n-Si structures. Electron tunneling current through the oxide from n-Si to Al is decreased and the dielectric breakdown voltage is increased by the preoxide growth control. Electron tunneling current from Al to n-Si is increased by light exposure. The increase in electron tunneling current can be explained by the increase in oxide voltage with an inversion layer formed by photoexcitation.

Morita, Satoru; Shinozaki, Akihito; Morita, Yuuki; Nishimura, Kazuo; Okazaki, Tatsuya; Urabe, Shinichi; Morita, Mizuho

2004-11-01

336

STM tunneling spectroscopy on high Tc superconductors  

International Nuclear Information System (INIS)

[en] STM tunneling spectroscopy has been performed on the bulk single crystals of BiSrCaCuO (BSCCO) and the epitaxial thin films of YBaCuO (YBCO) at cryogenic temperatures. The STM images and tunneling spectra observed on the (001) surfaces can be classified into three cases; (1) Atomic image is visible. However, the tunneling spectrum shows semiconducting or smeared superconducting gap structures, depending on the tip-sample distance. (2) Clear atomic image can be obtained. But, the tunneling spectrum shows flat bottom region with quite low zero bias conductance. (3) Tunneling spectra demonstrate gapless behavior, independent of the tip-sample separation. These observations support the quasi-2D electronic picture in which s-wave like 2D superconducting layers are coupled with each other through the Josephson effect

1995-01-01

337

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  

Energy Technology Data Exchange (ETDEWEB)

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.

Zubkov, Evgeniy

2013-09-01

338

Tunneling spectroscopy on grain boundary junctions in electron-doped high-temperature superconductors; Tunnelspektroskopie an Korngrenzenkontakten aus elektronendotierten Hochtemperatur-Supraleitern  

Energy Technology Data Exchange (ETDEWEB)

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.

Welter, B.

2007-12-07

339

The Impact of Electronic Banking on Human Resources Performance in the Nigerian Banking Industry  

Directory of Open Access Journals (Sweden)

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.

Ojokuku, R. M.; Sajuyigbe, A. S.

2012-01-01

340

Observation of Unitary Conductance for Resonant Tunneling with Dissipation  

International Nuclear Information System (INIS)

We investigate tunneling through a resonant level formed in a carbon nanotube quantum dot contacted by resistive metal wires. These contacts create a dissipative environment for the electrons tunneling across the nanotube, thus suppressing the tunneling rate. We study the shape of the resonant peak in the nanotube conductance, with the expectation that the peak width and height, both dependent on the tunneling rate, will be suppressed. Instead, we find that the behavior crucially depends on the ratio of the tunneling rates from the resonant level to the two contacts. We discuss the implication of our findings for a boundary quantum phase transition in this system.

2012-12-17

 
 
 
 
341

Tunneling and resonant conductance in one-dimensional molecular structures  

Energy Technology Data Exchange (ETDEWEB)

We present a theory of tunneling and resonant transitions in one-dimensional molecular systems which is based on Green's function theory of electron sub-barrier scattering off the structural units (or functional groups) of a molecular chain. We show that the many-electron effects are of paramount importance in electron transport and they are effectively treated using a formalism of sub-barrier scattering operators. The method which calculates the total scattering amplitude of the bridge molecule not only predicts the enhancement of the amplitude of tunneling transitions in course of tunneling electron transfer through onedimensional molecular structures but also allows us to interpret conductance mechanisms by calculating the bound energy spectrum of the tunneling electron, the energies being obtained as poles of the total scattering amplitude of the bridge molecule. We found that the resonant tunneling via bound states of the tunneling electron is the major mechanism of electron conductivity in relatively long organic molecules. The sub-barrier scattering technique naturally includes a description of tunneling in applied electric fields which allows us to calculate I-V curves at finite bias. The developed theory is applied to explain experimental findings such as bridge effect due to tunneling through organic molecules, and threshold versus Ohmic behavior of the conductance due to resonant electron transfer.

Kozhushner, M.A. [Institute of Chemical Physics RAS, Moscow (Russian Federation)], E-mail: kozhush@center.chph.ras.ru; Posvyanskii, V.S. [Institute of Chemical Physics RAS, Moscow (Russian Federation); Oleynik, I.I. [Department of Physics, University of South Florida, Tampa FL (United States)

2005-12-07

342

Tunneling and resonant conductance in one-dimensional molecular structures  

International Nuclear Information System (INIS)

We present a theory of tunneling and resonant transitions in one-dimensional molecular systems which is based on Green's function theory of electron sub-barrier scattering off the structural units (or functional groups) of a molecular chain. We show that the many-electron effects are of paramount importance in electron transport and they are effectively treated using a formalism of sub-barrier scattering operators. The method which calculates the total scattering amplitude of the bridge molecule not only predicts the enhancement of the amplitude of tunneling transitions in course of tunneling electron transfer through onedimensional molecular structures but also allows us to interpret conductance mechanisms by calculating the bound energy spectrum of the tunneling electron, the energies being obtained as poles of the total scattering amplitude of the bridge molecule. We found that the resonant tunneling via bound states of the tunneling electron is the major mechanism of electron conductivity in relatively long organic molecules. The sub-barrier scattering technique naturally includes a description of tunneling in applied electric fields which allows us to calculate I-V curves at finite bias. The developed theory is applied to explain experimental findings such as bridge effect due to tunneling through organic molecules, and threshold versus Ohmic behavior of the conductance due to resonant electron transfer.

2005-12-07

343

The growth of epitaxial iron oxides on platinum (111) as studied by X-ray photoelectron diffraction, scanning tunneling microscopy, and low energy electron diffraction  

Energy Technology Data Exchange (ETDEWEB)

Three complementary surface structure probes, x-ray photoelectron diffraction (XPD), scanning tunneling microscopy (STM), and low-energy electron diffraction (LEED) have been combined in a single instrument. This experimental system has been utilized to study the structure and growth mechanisms of iron oxide films on Pt(111); these films were formed by first depositing a single overlayer of Fe with a certain coverage in monolayers (ML`s), and then thermally oxidizing it in an oxygen atmosphere. For films up to {approximately}1 ML in thickness, a bilayer of Fe and O similar to those in FeO(111) is found to form. In agreement with prior studies, STM and LEED show this to be an incommensurate oxide film forming a lateral superlattice with short- and long-range periodicities of {approximately}3.1 {Angstrom} and {approximately}26.0 {Angstrom}. XPD in addition shows a topmost oxygen layer to be relaxed inward by -0.6 {Angstrom} compared to bulk FeO(111), and these are new structural conclusions. The oxygen stacking in the FeO(111) bilayer is dominated by one of two possible binding sites. For thicker iron oxide films from 1.25 ML to 3.0 ML, the growth mode is essentially Stranski-Krastanov: iron oxide islands form on top of the FeO(111) bilayer mentioned above. For iron oxide films of 3.0 ML thickness, x-ray photoelectron spectroscopy (XPS) yields an Fe 2p{sub 3/2} binding energy and an Fe:O stoichiometry consistent with the presence of Fe{sub 3}O{sub 4}. Our XPD data further prove this overlayer to be Fe{sub 3}O{sub 4}(111)-magnetite in two almost equally populated domains with a 180{degrees} rotation between them. The structural parameters for this Fe{sub 3}O{sub 4} overlayer generally agree with those of a previous LEED study, except that we find a significant difference in the first Fe-O interplanar spacing. This work demonstrates the considerable benefits to be derived by using this set of complementary surface structure probes in such epitaxial growth studies.

Kim, Y.J.

1995-05-01

344

Coherent resonant tunneling in AC fields  

CERN Document Server

We have analyzed the tunneling transmission probability and electronic current density through resonant heterostructures in the presence of an external electromagnetic field. In this work, we compare two different models for a double barrier : In the first case the effect of the external field is taken into account by spatially dependent AC voltages and in the second one the electromagnetic field is described in terms of a photon field that irradiates homogeneously the whole sample. While in the first description the tunneling takes place mainly through photo sidebands in the case of homogeneous illumination the main effective tunneling channels correspond to the coupling between different electronic states due to photon absorption and emission. The difference of tunneling mechanisms between these configurations is strongly reflected in the transmission and current density which present very different features in both cases.\\\\ In order to analyze these effects we have obtained, within the Transfer Hamiltonian...

Aguado, R

1996-01-01

345

Carpal Tunnel Release  

Medline Plus

Full Text Available ... quickly. In the immed-- sorry, in the intermediate stages of carpal tunnel syndrome, the nerve starts to ... rule out the diagnosis. So back to treatment stages. Early on, the carpal tunnel syndrome is potentially ...

346

Carpal Tunnel Release  

Medline Plus

Full Text Available ... on a patient with carpal tunnel syndrome. I'm Dr. Kevin Burton, and I'll be joined ... the causes of carpal tunnel syndrome? And I'm going to actually defer on that question because ...

347

Carpal Tunnel Release  

Medline Plus

Full Text Available ... tendons, if those become swollen, that will put pressure on that nerve as it's crossing at the ... on in carpal tunnel syndrome, there is increased pressure in the carpal tunnel which causes some decreased ...

348

Nonlinear resonant tunnelling through double barrier structures  

CERN Document Server

We study resonant tunnelling through double-barrier structures under an applied bias voltage, in which nonlinearities due to self-interaction of electrons in the barrier regions are included. As an approximation, we concern ourselves with thin barriers simulated by \\delta-function potentials. This approximation allows for an analytical expression of the transmission probability through the structure. We show that the typical peaks due to resonant tunneling decrease and broaden as nonlinearity increases. The main conclusion is that nonlinear effects degrade the peak-to-valley ratio but improve the maximum operation frequency of the resonant tunnelling devices.

Diez, E; Sánchez, A; Diez, Enrique; Dominguez-Adame, Francisco; Sanchez, Angel

1994-01-01

349

Transmission Electron Microscopy evidence of the growth of a magnetite layer acting as a spin filter in CoFe/Al2O3/CoFe magnetic tunnel junctions  

International Nuclear Information System (INIS)

Magnetic tunnel junctions (MTJs) in which an iron oxide was deposited between the Al2O3 barrier and the pinned CoFe electrode were shown to exhibit a large tunneling magnetoresistance (TMR) value of 39% after annealing at 380 deg. C. Local transmission electron microscopy (TEM) analyses were performed on the MTJs before and after the thermal treatments. In the as-deposited state, the high-resolution transmission electron microscopy (HRTEM) and the electron-energy-loss spectroscopy (EELS) demonstrate that the pure Fe exists at the Al2O3 interface, followed by the half-metallic ferromagnetic compound Fe3O4 that is formed when oxidizing the Fe layer. Similar structural studies show that the 380 deg. C annealing achieves the oxidation of the iron into an extra Fe3O4 layer, now in contact with the Al2O3 barrier that leads to the high TMR values. These local TEM studies indicate that further annealing at higher temperature (400 deg. C) induces the oxidation of the pinned CoFe electrode and the diffusion of Mn in the whole junction, resulting in a large decrease of the TMR.

2004-09-15

350

Challenges of Providing Bibliographic Access to Remote Electronic Resources in National Bibliographies: Problems and Solutions--An Overview.  

Science.gov (United States)

The proliferation of online resources has resulted in creating and accentuating challenges for national bibliographic agencies throughout the world. Through strategic planning and innovative approaches, providers of national bibliographies are seeking to realize bibliographic control of remote electronic material. For success, they will need to…

Byrum, John D., Jr.

351

Mechanised shield tunnelling  

CERN Document Server

Mechanised shield tunnelling has developed considerably since the publication of the first edition of this book. Challenging tunnel projects under difficult conditions demand innovative solutions, which has led to constant further development and innovation in process technology, constructions operations and the machines and materials used.The book collects the latest state of technology in mechanised shield tunnelling. It describes the basics of mechanised tunnelling technology and the various types of machines and gives calculation methods and constructural advice. Further chapters cover

Maidl, Bernhard; Maidl, Ulrich; Wehrmeyer, Gerhard; Sturge, David S

2013-01-01

352

Tunnels in digital objects  

CERN Multimedia

An important concept in digital geometry for computer imagery is that of tunnel. In this paper we obtain a formula for the number of tunnels as a function of the number of the object vertices, pixels, holes, connected components, and 2x2 grid squares. It can be used to test for tunnel-freedom a digital object, in particular a digital curve.

Brimkov, V

2005-01-01

353

Carpal Tunnel Surgery  

Medline Plus

Full Text Available ... which is carried out for the condition of carpal tunnel syndrome. Carpal Tunnel Syndrome is a neuropathy where the median nerve gets ... affecting function of the hand. The surgery for carpal tunnel syndrome consists of a release of the transverse carpal ...

354

Static and dynamic aspects of spin tunnelling in crystalline magnetic tunnel junctions  

International Nuclear Information System (INIS)

Single-crystal magnetic tunnel junctions employing bcc (100) Fe electrodes and MgO(100) insulating barrier are elaborated by molecular beam epitaxy. The magneto-transport properties are investigated in two extreme regimes. First, for extremely small MgO thickness, we show that the equilibrium tunnel transport in Fe/MgO/Fe systems leads to antiferromagnetic interactions, mediated by the tunnelling of the minority spin interfacial resonance state. Second, for large MgO barrier thickness, the tunnel transport validates specific spin filtering effects in terms of symmetry of the electronic Bloch function and symmetry-dependent wavefunction attenuation in the single-crystal barrier. Within this framework, we present giant tunnel magnetoresistive effects at room temperature (125-160%). Moreover, we illustrate that the interfacial chemical and electronic structure plays a crucial role in the spin filtering. We point out imperfect filtering effects and a strong implication of the minority surface state of Fe on the low voltage variation of tunnel magnetoresistance. The insertion of carbon impurities at the Fe/MgO interface changes radically the voltage response of the tunnel magnetoresistance and activates a resonant tunnelling mechanism via the interfacial resonance state.

2006-01-25

355

Tunneling Time in Ultrafast Science is Real and Probabilistic  

CERN Multimedia

We compare the main competing theories of tunneling time against experimental measurements using the attoclock in strong laser field ionization of helium atoms. Refined attoclock measurements reveal a real and not instantaneous tunneling delay time over a large intensity regime, using two different experimental apparatus. Only two of the theoretical predictions are compatible within our experimental error: the Larmor time, and the probability distribution of tunneling times constructed using a Feynman Path Integral (FPI) formulation. The latter better matches the observed qualitative change in tunneling time over a wide intensity range, and predicts a broad tunneling time distribution with a long tail. The implication of such a probability distribution of tunneling times, as opposed to a distinct tunneling time, challenges how valence electron dynamics are currently reconstructed in attosecond science. It means that one must account for a significant uncertainty as to when the hole dynamics begin to evolve.

Landsman, Alexandra; Maurer, Jochen; Boge, Robert; Ludwig, André; Heuser, Sebastian; Cirelli, Claudio; Gallmann, Lukas; Keller, Ursula

2013-01-01

356

Relationship between crystal chemistry and the local structure and electronic properties of Tl sub 2 Ba sub 2 Ca sub 2 Cu sub 3 O sub 10 superconductors determined by scanning tunneling microscopy and  

Energy Technology Data Exchange (ETDEWEB)

Scanning tunneling microscopy (STM) and scanning tunneling spectroscopy (STS) have been used to characterize the local structure and electronic properties of Tl{sub 2}Ba{sub 2}Ca{sub 2}Cu{sub 3}O{sub 10} single crystals prepared from 4:1:3:6 and 4:1:3:10 stoichiometry melts. Magnetic-susceptibility, resistivity, x-ray-fluorescence, and x-ray-diffraction measurements indicate that samples prepared from the 4:1:3:6 melts (type 1) have a chemical inhomogeneity, while crystals obtained from the 4:1:3:10 melts (type 2) are high quality. STM studies of the type-1 crystals demonstrate that the inhomogeneities can be associated with distortions in the TlO layer atomic structure. STS measurements on the distorted TlO layer of the type-1 samples have shown that this layer is also metallic. STM and STS investigations of the type-2 samples have shown, however, that the TlO layer in these crystals is tetragonal and semiconducting. In addition, a superstructure that is localized over small regions of the TlO surface has been characterized in the type-1 crystals. These results demonstrate that single crystals of the same average structure and composition can exhibit substantial differences in the local-structure electronic states and superconducting properties.

Zhang, Z.; Chen, C.; Lieber, C.M. (Department of Chemistry and Division of Applied Sciences, Harvard University, Cambridge, Massachusetts 02138 (United States)); Morosin, B.; Ginley, D.S.; Venturini, E.L. (Sandia National Laboratories, Albuquerque, New Mexico 87185 (United States))

1992-01-01

357

Resonant tunnelling through zero dimensional quantum dots  

Energy Technology Data Exchange (ETDEWEB)

When InAs is grown above GaAs or AlAs, a lattice mismatch between the two layers causes strain fields to develop. Above a critical thickness, these strain fields cause the InAs to form islands or dots. The dots are typically 10nm in diameter, and 4nm high. As the dimensions of the dots are below the typical electron wavelength, zero dimensional states are formed. In this thesis quantum dots are grown within an AlAs tunnel barrier. When a bias is applied between the top and bottom contacts of the device, resonant tunnelling is observed of electrons from the two dimensional electron gas formed in front of the AlAs tunnel barrier, through individual InAs quantum dots, despite the presence of several million dots within a typical sample. By measuring the tunnel current through a dot as a function of the applied bias, information can be gained as to the properties of the dot itself, and the electron gas from which tunnelling occurs. Conventional magneto-transport measurements are sensitive only to effects at the Fermi energy of the electron emitter gas. Due to the zero-dimensionality of the quantum dots, a single dot can be used as a spectroscopic probe of the occupied density of states of an electron gas at all energies between the Fermi energy and the subband edge, in a manner not available to any other measurement technique. Further, many body effects cause an enhancement of the tunnel current when the dot ground state is resonant with the Fermi energy of the two dimensional electron gas. The ground state of the quantum dot can also therefore be used to study many body processes at the Fermi level. (author)

Thornton, A.S.G

1998-11-01

358

Tunneling spectroscopy using carbon nanotubes quantum dots  

Science.gov (United States)

Tunneling spectroscopy is an important measurement technique, encompassing, for example, planar tunneling, scanning tunneling microscopy and superconducting tunnel probes. Here, we demonstrate that carbon nanotube quantum dots (QDs) can be used as tunneling probes. The sharp features in the density of states of the QDs in the Coulomb blockade regime can map out the density of states and the energy distribution function of the system to be studied. We present preliminary data showing tunneling from a carbon nanotube quantum dot into mesoscopic metal wires that have been driven out of equilibrium by a bias voltage. Previous measurements of these systems using superconducting probes [1-2] showed that the electron energy distribution functions and electron interactions can be determined. With the present measurements, the use of a QD instead of a superconductor allows us to probe at significantly higher temperatures and biases. [4pt] [1] H. Pothier, S. Gueron, Norman O. Birge, D. Esteve, and M. H. Devoret, Phys Rev Lett 79, 3490 (1997) [0pt] [2] Yung-fu Chen, Travis Dirks, Gassem Al-Zoubi, Norman O. Birge, and Nadya Mason, Phys Rev Lett 102, 036804 (2009)

Li, Yanjing; Mason, Nadya

2011-03-01

359

Systematically assessing the situational relevance of electronic knowledge resources: a mixed methods study.  

UK PubMed Central (United Kingdom)

UNLABELLED: Electronic Knowledge Resources (EKRs) are increasingly used by physicians, but their situational relevance has not been systematically examined. OBJECTIVE: Systematically scrutinize the situational relevance of EKR-derived information items in and outside clinical settings. BACKGROUND: Physicians use EKRs to accomplish four cognitive objectives (C1-4), and three organizational objectives (O1-3): (C1) Answer questions/solve problems/support decision-making in a clinical context; (C2) fulfill educational-research objectives; (C3) search for personal interest or curiosity; (C4) overcome limits of human memory; (O1) share information with patients, families, or caregivers; (O2) exchange information with other health professionals; (O3) plan-manage-monitor tasks with other health professionals. METHODS: Longitudinal mixed methods multiple case study: Cases were 17 residents' critical searches for information, using a commercial EKR, during a 2-month block of family practice. Usage data were automatically recorded. Each "opened" item of information was linked to an impact assessment questionnaire, and 1,981 evaluations of items were documented. Interviews with residents were guided by log files, which tracked use and impact of EKR-derived information items. Thematic analysis identified 156 critical searches linked to 877 information items. For each case, qualitative data were assigned to one of the seven proposed objectives. RESULTS: Residents achieved their search objectives in 85.9% of cases (situational relevance). Additional sources of information were sought in 52.6% of cases. Results support the seven proposed objectives, levels of comparative relevance (less, equally, more), and levels of stimulation of learning and knowledge (individual, organizational). CONCLUSION: Our method of systematic assessment may contribute to user-based evaluation of EKRs.

Pluye P; Grad RM; Mysore N; Knaapen L; Johnson-Lafleur J; Dawes M

2007-09-01

360

Human resource requirements for quality-assured electronic data capture of the tuberculosis case register  

Directory of Open Access Journals (Sweden)

Full Text Available Abstract Background The tuberculosis case register is the data source for the reports submitted by basic management units to the national tuberculosis program. Our objective was to measure the data entry time required to complete and double-enter one record, and to estimate the time for the correction of errors in the captured information from tuberculosis case registers in Cambodia and Viet Nam. This should assist in quantifying the additional requirements in human resources for national programs moving towards electronic recording and reporting. Methods Data from a representative sample of tuberculosis case registers from Cambodia and Viet Nam were double-entered and discordances resolved by rechecking the original case register. Computer-generated data entry time recorded the time elapsed between opening of a new record and saving it to disk. Results The dataset comprised 22,732 double-entered records of 11,366 patients (37.1% from Cambodia and 62.9% from Viet Nam). The mean data entry times per record were 97.5 (95% CI: 96.2-98.8) and 66.2 (95% CI: 59.5-73.0) seconds with medians of 90 and 31 s respectively in Cambodia and in Viet Nam. The percentage of records with an error was 6.0% and 39.0% respectively in Cambodia and Viet Nam. Data entry time was inversely associated with error frequency. We estimate that approximately 118-person-hours were required to produce 1,000 validated records. Conclusions This study quantifies differences between two countries for data entry time for the tuberculosis case register and frequencies of data entry errors and suggests that higher data entry speed is partially offset by requiring revisiting more records for corrections.

Hoa Nguyen B; Sokun Chay; Wei Chen; Lauritsen Jens M; Rieder Hans L

2012-01-01

 
 
 
 
361

Human resource requirements for quality-assured electronic data capture of the tuberculosis case register.  

UK PubMed Central (United Kingdom)

BACKGROUND: The tuberculosis case register is the data source for the reports submitted by basic management units to the national tuberculosis program. Our objective was to measure the data entry time required to complete and double-enter one record, and to estimate the time for the correction of errors in the captured information from tuberculosis case registers in Cambodia and Viet Nam. This should assist in quantifying the additional requirements in human resources for national programs moving towards electronic recording and reporting. METHODS: Data from a representative sample of tuberculosis case registers from Cambodia and Viet Nam were double-entered and discordances resolved by rechecking the original case register. Computer-generated data entry time recorded the time elapsed between opening of a new record and saving it to disk. RESULTS: The dataset comprised 22,732 double-entered records of 11,366 patients (37.1% from Cambodia and 62.9% from Viet Nam). The mean data entry times per record were 97.5 (95% CI: 96.2-98.8) and 66.2 (95% CI: 59.5-73.0) seconds with medians of 90 and 31 s respectively in Cambodia and in Viet Nam. The percentage of records with an error was 6.0% and 39.0% respectively in Cambodia and Viet Nam. Data entry time was inversely associated with error frequency. We estimate that approximately 118-person-hours were required to produce 1,000 validated records. CONCLUSIONS: This study quantifies differences between two countries for data entry time for the tuberculosis case register and frequencies of data entry errors and suggests that higher data entry speed is partially offset by requiring revisiting more records for corrections.

Hoa NB; Sokun C; Wei C; Lauritsen JM; Rieder HL

2012-01-01

362

Integration and interoperability accessing electronic information resources in science and technology the proposal of Brazilian Digital Library  

CERN Multimedia

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...

Marcondes, C H; Marcondes, Carlos H.; Sayao, Luis Fernando

2002-01-01

363

??????????????????????????????? | Study of the Electronic Resources Usage Statistics Standards and Guidelines/ Hsueh-Hua Chen;Chia-Chen Hsu;Ya-Chi Chu  

Directory of Open Access Journals (Sweden)

Full Text Available ????????????????????????????????????????????????????????????????????? ???????????????????????????????????????????????????????????????????????? ?????????????????????????????????????????????????????????????????????? ISO 2789? ICOLC Guidelines??ANSI/NISO Z39.7?CNS13151?ARL E-Metrlcs?E-Measures Project???Project COUNTER??Recently, due to the advances of information technology, electronic resources are gradually replacing print resources as the largest consumer of library acquisition budgets. Logically, libraries want to evaluate the usage of electronic resources and incorporate the results into their decision making regarding electronic resource acquisition. Over these years, there is a general awareness among libraries to develop statistics standards and guidelines for library electronic resources usage. In this paper, literature review and content analysis methods are used to compare several library statistics standards, including: ISO 2789 ?ICOLC Guidelines?ANSI/NISO Z39.7?CNS13151?ARL E-Metrics?E-Measures Project?and Project COUNTER etc.???89-102

??????????? ?

2007-01-01

364

Challenges in the implementation of an electronic surveillance system in a resource-limited setting: Alerta, in Peru  

Directory of Open Access Journals (Sweden)

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.

Soto Giselle; Araujo-Castillo Roger V; Neyra Joan; Fernandez Miguel; Leturia Carlos; Mundaca Carmen C; Blazes David L

2008-01-01

365

Spin-polarized tunneling in MgO-based tunnel junctions with superconducting electrodes  

International Nuclear Information System (INIS)

We prepared magnetic tunnel junctions with one ferromagnetic and one superconducting Al-Si electrode. Pure cobalt electrodes were compared with a Co-Fe-B alloy and the Heusler compound Co2FeAl. The polarization of the tunneling electrons was determined using the Maki-Fulde model and is discussed along with the spin-orbit scattering and the total pair-breaking parameters. The junctions were post-annealed at different temperatures to investigate the symmetry filtering mechanism responsible for the giant tunneling magnetoresistance ratios in Co-Fe-B/MgO/Co-Fe-B junctions. (paper)

2012-01-01

366

Scanning Tunneling Spectroscopic Studies of Cuprate Superconductors  

CERN Document Server

Quasiparticle tunneling spectra of both hole-doped (p-type) and electron-doped (n-type) cuprates are studied using a low-temperature scanning tunneling microscope. The results reveal that neither the pairing symmetry nor the pseudogap phenomenon is universal among all cuprates, and that the response of n-type cuprates to quantum impurities is drastically different from that of the p-type cuprates. The only ubiquitous features among all cuprates appear to be the strong electronic correlation and the nearest-neighbor antiferromagnetic Cu^{2+}-Cu^{2+} coupling in the CuO_2 planes.

Yeh, N C; Vásquez, R P; Jung, C U; Lee, S I; Yoshida, K; Tajima, S

2002-01-01

367

Momentum transfers in correlation-assisted tunnelling  

CERN Document Server

We consider correlation-assisted tunnel ionization of a small molecule by an intense low-frequency laser pulse. In this mechanism, the departing electron excites the state of the ion via a Coulomb interaction. We show that the angular distribution for this process has significant qualitative differences compared to direct tunnelling of an electron from a deeper orbital. These differences could be used to distinguish the two contributions, and give rise to interference effects when the contributions are comparable. The saddle-point approximation is also shown to require special attention in this geometric analysis.

Pisanty, Emilio

2013-01-01

368

Electronic Phase Separation in Pr1x(Ca, Sr)xMnO3? and Tunneling Magnetoresistance in Sr2FeMoO6  

International Nuclear Information System (INIS)

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)xMnO3?. 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, ? ? (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-? (? = 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 properti

2003-01-01

369

A tunnel boring machine  

Energy Technology Data Exchange (ETDEWEB)

Telescopic tunnel boring machine including a front shield and a rear shield with a cutting head at the forward end of the front shield. Rearwardly extending shutters can be moved out hydraulically by auxiliary cylinders from the rear end of the rear shield to bridge the gap between this rear end and tunnel lining elements. Additionally expandable cuffs may be provided on the front and rear shields respectively behind the cutting head and radial tunnel wall grippers.

Ince, G.R.

1988-06-29

370

Recurrent carpal tunnel syndrome.  

Science.gov (United States)

Carpal tunnel release is a common procedure with a high rate of alleviating the patient's symptoms. The incidence of recurrent or persistent carpal tunnel syndrome is rare, although likely underestimated. Complaints of worsening numbness, tingling, or weakness should alert the physician to possible nerve injury and need for early exploration. The overall results of revision carpal tunnel procedures are less successful than primary surgery; however, surgery should be performed when indicated, as it may alleviate or improve symptoms. PMID:23895723

Mosier, Brian A; Hughes, Thomas B

2013-06-27

371

Recurrent carpal tunnel syndrome.  

UK PubMed Central (United Kingdom)

Carpal tunnel release is a common procedure with a high rate of alleviating the patient's symptoms. The incidence of recurrent or persistent carpal tunnel syndrome is rare, although likely underestimated. Complaints of worsening numbness, tingling, or weakness should alert the physician to possible nerve injury and need for early exploration. The overall results of revision carpal tunnel procedures are less successful than primary surgery; however, surgery should be performed when indicated, as it may alleviate or improve symptoms.

Mosier BA; Hughes TB

2013-08-01

372

Resonance Enhanced Tunneling  

CERN Multimedia

Time evolution of tunneling in thermal medium is examined using the real-time semiclassical formalism previously developed. Effect of anharmonic terms in the potential well is shown to give a new mechanism of resonance enhanced tunneling. If the friction from environment is small enough, this mechanism may give a very large enhancement for the tunneling rate. The case of the asymmetric wine bottle potential is worked out in detail.

Matsumoto, S; Matsumoto, Sh.

2000-01-01

373

Tunnel closure calculations  

Energy Technology Data Exchange (ETDEWEB)

When a deeply penetrating munition explodes above the roof of a tunnel, the amount of rubble that falls inside the tunnel is primarily a function of three parameters: first the cube-root scaled distance from the center of the explosive to the roof of the tunnel. Second the material properties of the rock around the tunnel, and in particular the shear strength of that rock, its RQD (Rock Quality Designator), and the extent and orientation of joints. And third the ratio of the tunnel diameter to the standoff distance (distance between the center of explosive and the tunnel roof). The authors have used CALE, a well-established 2-D hydrodynamic computer code, to calculate the amount of rubble that falls inside a tunnel as a function of standoff distance for two different tunnel diameters. In particular they calculated three of the tunnel collapse experiments conducted in an iron ore mine near Kirkeness, Norway in the summer of 1994. The failure model that they used in their calculations combines an equivalent plastic strain criterion with a maximum tensile strength criterion and can be calibrated for different rocks using cratering data as well as laboratory experiments. These calculations are intended to test and improve the understanding of both the Norway Experiments and the ACE (Array of conventional Explosive) phenomenology.

Moran, B.; Attia, A.

1995-07-01

374

Carpal tunnel syndrome  

International Nuclear Information System (INIS)

[en] This paper evaluates the normal anatomy and pathologic changes of the carpal tunnel with MR imaging and establishes diagnostic criteria for carpal tunnel syndrome (CTS) in a prospective study. Twenty-one normal volunteers and 84 patients with CTS were examined (1.5T, spin-echo sequences: 500/15 and 2,280/15-90). The measurements presented in the results section were done at three levels: (1) distal radius, (2) pisiform bone (point of entry into the carpal tunnel), and (3) hamate bone (narrowest segment of the carpal tunnel). The median nerve was well delimited in all volunteers and in 73 (87%) patients

1990-01-01

375

Anterior Tarsal Tunnel Syndrome  

Directory of Open Access Journals (Sweden)

Full Text Available The anterior tarsal tunnel syndrome is an entrapment neuropathy which is formed by the sticking of the deep peroneal nerve in the anterior tarsal tunnel with its roof formed by inferior extansor retinakulum and its baseformed by the fascia of naviculer and talus bones. The anterior tarsal tunnel syndrome is an uncommon entrapment neuropathy. This might be due to an unrecognizing of this syndrome rather than rarity. We reported a case of anterior tarsal tunnel syndrome who is operated and followed in our clinic.

Muslum GUNES; Murat GUNAL; Omur GUNALDI; Bekir TUGCU; Metehan ESEOGLU; Utku ADILAY

2006-01-01

376

Scanning tunneling microscopy of hexagonal BN grown on graphite  

Energy Technology Data Exchange (ETDEWEB)

The microscopic surface topography of thin BN{sub {ital x}} films grown on graphite by electron cyclotron resonance plasma chemical vapor deposition have been imaged with scanning tunneling microscopy in air. The scanning tunneling microscope has generated images of hexagonal BN with atomic resolution.

Fukumoto, H.; Hamada, T. (Department of Electrical Engineering, Hiroshima University, Higashihiroshima 724, Japan (JP)); Endo, T. (Hiroshima Denki Institute of Technology, Hiroshima 739-03, Japan (JP)); Osaka, Y. (Department of Electrical Engineering, Hiroshima University, Higashihiroshima 724, Japan (JP))

1991-06-15

377

Suppression of tunneling into multi-wall carbon nanotubes  

CERN Multimedia

We have studied tunneling of electrons into multi-wall carbon nanotubes. Nanotube/electrode interfaces with low transparency as well as nanotube/nanotube junctions created with atomic force microscope manipulation have been used. The tunneling conductance goes to zero as the temperature and bias are reduced, and the functional form is consistent with a power law suppression of tunneling as a function of energy. The exponent depends upon sample geometry. The relationship between these results and theories for tunneling into ballistic and disordered metals is discussed.

Bachtold, A; Grove-Rasmussen, K; McEuen, P L; Buitelaar, M R; Schönenberger, C

2000-01-01

378

Development of a magnetic tunnel transistor based on a double tunnel junction  

International Nuclear Information System (INIS)

We report on the latest development of a new type of magnetic tunnel transistor (MTT) using a ferromagnetic base layer and two magnetic tunnel junctions (MTJ). The principle of the device is based on the transport of a spin-polarized hot electron current which can be manipulated under an appropriate voltage biasing scheme using three terminals. The first MTJ is used as an emitter of hot electrons into the base. The second MTJ and the base play the role of a spin-dependent filter. Transport measurements have been carried out, showing the creation of hot electrons and a collected magnetocurrent (MC) signal.

2005-01-01

379

Development of a magnetic tunnel transistor based on a double tunnel junction  

Energy Technology Data Exchange (ETDEWEB)

We report on the latest development of a new type of magnetic tunnel transistor (MTT) using a ferromagnetic base layer and two magnetic tunnel junctions (MTJ). The principle of the device is based on the transport of a spin-polarized hot electron current which can be manipulated under an appropriate voltage biasing scheme using three terminals. The first MTJ is used as an emitter of hot electrons into the base. The second MTJ and the base play the role of a spin-dependent filter. Transport measurements have been carried out, showing the creation of hot electrons and a collected magnetocurrent (MC) signal.

Rodary, G. [Unite Mixte de Physique CNRS-Thales, Domaine de Corbeville, 91404 Orsay, Cedex (France); Hehn, M. [Laboratoire de Physique des Materiaux UMR CNRS 7556, BP239, 54506 Vandoeuvre-les-Nancy (France); Dimopoulos, T. [Corporate Technology CT MM1, Siemens AG, 91052 Erlangen (Germany); Lacour, D. [Unite Mixte de Physique CNRS-Thales, Domaine de Corbeville, 91404 Orsay, Cedex (France); Laboratoire de Physique des Materiaux UMR CNRS 7556, BP239, 54506 Vandoeuvre-les-Nancy (France); Bangert, J. [Corporate Technology CT MM1, Siemens AG, 91052 Erlangen (Germany); Jaffres, H. [Unite Mixte de Physique CNRS-Thales, Domaine de Corbeville, 91404 Orsay, Cedex (France); Montaigne, F. [Laboratoire de Physique des Materiaux UMR CNRS 7556, BP239, 54506 Vandoeuvre-les-Nancy (France); Van Dau, F. Nguyen [Unite Mixte de Physique CNRS-Thales, Domaine de Corbeville, 91404 Orsay, Cedex (France)]. E-mail: frederic.vandau@thalesgroup.com; Petroff, F. [Unite Mixte de Physique CNRS-Thales, Domaine de Corbeville, 91404 Orsay, Cedex (France); Schuhl, A. [Laboratoire de Physique des Materiaux UMR CNRS 7556, BP239, 54506 Vandoeuvre-les-Nancy (France); Wecker, J. [Corporate Technology CT MM1, Siemens AG, 91052 Erlangen (Germany)

2005-04-15

380

Spin tunnelling phenomena in single-crystal magnetic tunnel junction systems  

International Nuclear Information System (INIS)

A brief theoretical review points out the specific aspects of electronic transport in single-crystal magnetic tunnel junctions employing bcc(100) Fe electrodes and a MgO(100) insulating barrier. The theoretical predictions are compared to the experimental reality in both equilibrium and out-of-equilibrium regimes. For extremely small MgO thickness, we illustrate that the equilibrium tunnel transport in Fe/MgO/Fe systems leads to antiferromagnetic interactions. Artificial antiferromagnetic systems based on coupling by spin polarized tunnelling have been elaborated and studied. In the out-of-equilibrium regime and for large MgO barrier thickness, the tunnel transport validates specific spin filtering effects in terms of symmetry of the electronic Bloch function and symmetry-dependent wavefunction attenuation in the single-crystal barrier. Within this framework, we explain the experimental giant tunnel magnetoresistive effects at room temperature, up to 180%, measured in our simple or double barrier tunnel junction systems. Moreover, we illustrate that the magneto-transport properties of the junctions may be skilfully engineered by adjusting the interfacial chemical and electronic structure.

2007-04-23

 
 
 
 
381

Chiral Tunneling in a Twisted Graphene Bilayer  

Science.gov (United States)

The perfect transmission in a graphene monolayer and the perfect reflection in a Bernal graphene bilayer for electrons incident in the normal direction of a potential barrier are viewed as two incarnations of the Klein paradox. Here we show a new and unique incarnation of the Klein paradox. Owing to the different chiralities of the quasiparticles involved, the chiral fermions in a twisted graphene bilayer show an adjustable probability of chiral tunneling for normal incidence: they can be changed from perfect tunneling to partial or perfect reflection, or vice versa, by controlling either the height of the barrier or the incident energy. As well as addressing basic physics about how the chiral fermions with different chiralities tunnel through a barrier, our results provide a facile route to tune the electronic properties of the twisted graphene bilayer.

He, Wen-Yu; Chu, Zhao-Dong; He, Lin

2013-08-01

382

Tunneling magnetothermopower in magnetic tunnel junction nanopillars.  

UK PubMed Central (United Kingdom)

We study tunneling magnetothermopower (TMTP) in CoFeB/MgO/CoFeB magnetic tunnel junction nanopillars. Thermal gradients across the junctions are generated by an electric heater line. Thermopower voltages up to a few tens of ?V between the top and bottom contact of the nanopillars are measured which scale linearly with the applied heating power and hence the thermal gradient. The thermopower signal varies by up to 10???V upon reversal of the relative magnetic configuration of the two CoFeB layers from parallel to antiparallel. This signal change corresponds to a large spin-dependent Seebeck coefficient of the order of 100???V/K and a large TMTP change of the tunnel junction of up to 90%.

Liebing N; Serrano-Guisan S; Rott K; Reiss G; Langer J; Ocker B; Schumacher HW

2011-10-01

383

Surface structural and electronic properties of cleaved single crystals of Bi2.15Sr1.7CaCu2O8+? compounds: A scanning tunneling microscopy study  

International Nuclear Information System (INIS)

Scanning tunneling microscopy is used to study the surface structural and electronic properties of cleaved single crystals of Bi2.15Sr1.7CaCu2O8+? Images with atomic resolution reveal atomic chains with sinusoidal modulations running along the perovskite cell axis with a periodicity of 9 to 10 unit cells. These atomic chains stack along the b direction with a translational vector of one unit, resulting in an incommensurate periodicity of about 4.75 units along the a direction. In contrast to other reports, no evidence of ''missing Bi-atom rows'' is found. Spectroscopic studies show zero density of states at the Fermi level, implying that the surface Bi-O layer is nonmetallic.

1989-01-01

384

Introduction to tunnel construction  

CERN Multimedia

Tunnelling is one of the most fascinating disciplines within civil engineering and provides a robust solution to a variety of engineering challenges. This book covers a range of areas which you need to know in order to embark upon a career in the exciting field of tunnelling.

Chapman, David; Stärk, Alfred

2010-01-01

385

Wind Tunnel Testing  

Science.gov (United States)

In this activity, learners explore how wind tunnels provide feedback to engineers about the performance and durability of products such as planes, cars, and buildings. Learners work in teams to build their own model of a car, using simple materials, and test their designs in a classroom wind tunnel set up.

Ieee

2013-07-08

386

Frame Stability of Tunnel?Structured Cryptomelane Nanofibers: The Role of Tunnel Cations  

DEFF Research Database (Denmark)

The role of tunnel K+ ions on the growth and stability of tunnel?structured cryptomelane?type MnO2 nanofibers (denoted as cryptomelane nanofibers hereafter) has been discussed by means of X?ray diffraction and electron microscopy. Cryptomelane nanofibers with typical diameters of 20–80 nm and lengths of 1–6 ?m have been synthesized by means of a simple hydrothermal reaction of KMnO4 and MnSO4 aqueous solutions at 140 °C. The growth of cryptomelane nanofibers under hydrothermal conditions follows a dissolution–recrystallization process and involves a morphological transformation from a layered precursor to the tunnel?structured cryptomelane, in which the K+ ions play important roles in templating and stabilizing the tunneled framework. The presence of tunnel K+ ions also enhances the frame stability of the cryptomelane nanofibers at elevated temperatures. The formation of a layered KxMn2O4 (x ? 0.26) with a hexagonal phase structure has been observed at about 900 °C. The transformation from tunneled cryptomelane to layered KxMn2O4 also follows the dissolution–recrystallization growth mechanism, in which the diffusion of K+ ions at high temperatures represents a critical process. The topological correlation between the tunneled and layered MnO2 materials might provide useful information for the synthesis of MnO2 nanomaterials with controlled microstructures for different applications.

Gao, Tao; Norby, Poul

2013-01-01

387

Magnetic tunnel junctions with impurities  

CERN Document Server

The influence of impurities, embedded into the isolating spacer (I) between two ferromagnetic electrodes (F), on the I-V curve and tunnel magnetoresistance (TMR), is theoretically investigated. It is shown, that the current and TMR are strongly enhanced in the vicinity of the impurity under the condition that the energy of the electron's bound state on the impurity is close to the Fermi energy. If the position of the impurity inside the barrier is asymmetric, e.g. closer to the one of the interfaces F/I the I-V curve exhibits quasidiode behavior.

Kanjouri, F; Dieny, B; Strelkov, N; Vedyayev, A

2004-01-01

388

Features of tunneling in small-area contacts  

International Nuclear Information System (INIS)

The possibility of manifesting the cross-sectional constituent quantization of the electron wave vector in the tunneling contacts of the small-area dimensions is considered. It is shown that in the case, when the Fermi energy of one of the tunneling electrodes is low (the order of 1 eV) and one of its cross-sectional dimensions is small (the order of several hundred angstroms), the quantization of the cross-sectional constituent of the tunneling electrons wave vector becomes well noticeable on the general background of the differential tunneling conductivity dependence on the voltage. It is noted that the possibility of manifesting the standing waves in the tunneling contacts should be accounted for studying the spectroscopic-quasi-particle excitation

2003-01-01

389

Characteristics of high-transmission-probability tunnel junctions for use as particle detectors  

International Nuclear Information System (INIS)

Interest in the problem of the galactic dark matter has stimulated development of particle detectors sensitive to very low energies. Superconducting tunnel junctions may be useful in such detectors. We describe here superconducting tunnel junctions with thin barriers which may be suitable for this purpose. We present I-V characteristics and data on the temperature dependence of the subgap tunneling current. We also present some scanning-electron-microscope observations of the thin films of the tunnel junctions

1988-01-01

390

Dissymmetrical tunnelling in heavy fermion metals  

CERN Document Server

A tunnelling conductivity between a heavy fermion metal and a simple metallic point is considered. We show that at low temperatures this conductivity can be noticeably dissymmetrical with respect to the change of voltage bias. The dissymmetry can be observed in experiments on the heavy fermion metals whose electronic system has undergone the fermion condensation quantum phase transition.

Shaginyan, V R

2005-01-01

391

New directions in scanning-tunneling microscopy  

International Nuclear Information System (INIS)

The tunneling of electrons in scanning-tunneling microscopy (STM) has permitted imaging of the electronic distribution about individual atoms on surfaces. The need for use of conducting surfaces in STM limits its applicability, and new forms of scanning microscopy have emerged as a result of interest in poorly conducting samples. Atomic force microscopy has demonstrated that the force between a surface and a probe tip can be used to image selected materials. Now being developed are magnetic probe STM's and photon tunneling microscopes in which the probe is a sharpened optical fiber. Also of great interest presently is the measurement of differential conductance of surfaces using electron STM's. This method supplies spectral information and contrast enhancement in images. At present there remains much theoretical work to be carried out in order to better characterize related data on inelastic electron tunneling, and valuable insight may be gained from data being gathered on the local work function of materials. As matters stand today, the key problems lie in determining tip and contamination effects, preparation of samples, and understanding conductivity mechanisms in very thin materials on conducting substrates. Resolution of these problems and introduction of new forms of scanning microscopy may permit novel and important applications in biology as well as surface science

1989-01-01

392

Assigning Complex Vibration-Tunneling Spectra Using Franck-Condon Fingerprints  

Science.gov (United States)

We propose Franck-Condon fingerprinting as a method to assign complex vibration-tunneling spectra. The ˜{B} electronic excited state of Thiophosgene (SCCl_{2}) is our prototype case. Assignment of its spectrum has proven to be difficult because large tunneling splittings and near-degenerate vibrational frequencies. The dispersed fluorescence spectrum of each unkown vibration-tunneling state reveals its wavefunction character onto the known SCCl_{2} vibrational progressions in the ground states. This Franck-Condon fingerprint allows us to assign several vibration-tunneling states of SCCl_{2} in the ˜{B} electronic excited state. These assigned transitions could be fitted by an effective vibration-tunneling Hamiltonian within measurement uncertainty.

Berrios, Eduardo; Sundaradevan, Praveen; Gruebele, Martin

2013-06-01

393

Scanning Tunneling Microscopy Investigations of Metal Dichalcogenide Materials.  

Science.gov (United States)

Scanning tunneling microscopy (STM) and atomic force microscopy (AFM) have been used to characterize the atomic level structure of electronic properties, reactivity and wear of metal dichalcogenide materials that are or have potential as solid state lubri...

C. M. Lieber

1993-01-01

394

Print and Electronic Resources: Usage Statistics at Guru Gobind Singh Indraprastha University Library  

Science.gov (United States)

|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,…

Kapoor, Kanta

2010-01-01

395

Ultrafast scanning tunneling microscopy  

Energy Technology Data Exchange (ETDEWEB)

I have developed an ultrafast scanning tunneling microscope (USTM) based on uniting stroboscopic methods of ultrafast optics and scanned probe microscopy to obtain nanometer spatial resolution and sub-picosecond temporal resolution. USTM increases the achievable time resolution of a STM by more than 6 orders of magnitude; this should enable exploration of mesoscopic and nanometer size systems on time scales corresponding to the period or decay of fundamental excitations. USTM consists of a photoconductive switch with subpicosecond response time in series with the tip of a STM. An optical pulse from a modelocked laser activates the switch to create a gate for the tunneling current, while a second laser pulse on the sample initiates a dynamic process which affects the tunneling current. By sending a large sequence of identical pulse pairs and measuring the average tunnel current as a function of the relative time delay between the pulses in each pair, one can map the time evolution of the surface process. USTM was used to measure the broadband response of the STM`s atomic size tunnel barrier in frequencies from tens to hundreds of GHz. The USTM signal amplitude decays linearly with the tunnel junction conductance, so the spatial resolution of the time-resolved signal is comparable to that of a conventional STM. Geometrical capacitance of the junction does not appear to play an important role in the measurement, but a capacitive effect intimately related to tunneling contributes to the measured signals and may limit the ultimate resolution of the USTM.

Botkin, D.A. [California Univ., Berkeley, CA (United States). Dept. of Physics]|[Lawrence Berkeley Lab., CA (United States)

1995-09-01

396

Full counting statistics of Andreev tunneling  

CERN Multimedia

The full counting statistics (FCS) of charge transfer in nano-electronic circuits provides information about fundamental tunneling processes. FCS is not limited to normal-state conductors, but may equally well describe charge fluctuations in superconducting structures. Nevertheless, despite considerable theoretical interest in the FCS of superconductors, experiments have so far been restricted to normal-state electrons. Here we measure the FCS of Andreev events in which Cooper pairs are either produced from electrons that are reflected as holes at a superconductor/normal-state interface or annihilated in the reverse process. Surprisingly, the FCS consists of quiet periods with no Andreev processes, interrupted by the tunneling of a single electron that triggers an avalanche of Andreev events giving rise to strongly super-Poissonian distributions. Our experiment is important for quantum metrological applications and for entanglement generation using Cooper pair splitters.

Maisi, V F; Flindt, C; Pekola, J P

2013-01-01

397

Tunnel magnetoresistance in alumina, magnesia and composite tunnel barrier magnetic tunnel junctions  

International Nuclear Information System (INIS)

Using magnetron sputtering, we have prepared Co-Fe-B/tunnel barrier/Co-Fe-B magnetic tunnel junctions with tunnel barriers consisting of alumina, magnesia, and magnesia-alumina bilayer systems. The highest tunnel magnetoresistance ratios we found were 73% for alumina and 323% for magnesia-based tunnel junctions. Additionally, tunnel junctions with a unified layer stack were prepared for the three different barriers. In these systems, the tunnel magnetoresistance ratios at optimum annealing temperatures were found to be 65% for alumina, 173% for magnesia, and 78% for the composite tunnel barriers. The similar tunnel magnetoresistance ratios of the tunnel junctions containing alumina provide evidence that coherent tunneling is suppressed by the alumina layer in the composite tunnel barrier. - Research highlights: ? Transport properties of Co-Fe-B/tunnel barrier/Co-Fe-B magnetic tunnel junctions. ? Tunnel barrier consists of MgO, Al-Ox, or MgO/Al-Ox bilayer systems. ? Limitation of TMR-ratio in composite barrier tunnel junctions to Al-Ox values. ? Limitation indicates that Al-Ox layer is causing incoherent tunneling.

2011-01-01

398

Subgap conductivity of a superconductor--normal-metal tunnel interface  

Energy Technology Data Exchange (ETDEWEB)

At low temperatures, the transport through a superconductor--normal-metal tunnel interface is due to tunneling of electrons in pairs. We show that the rate for this process is often determined by the interference of the electron waves on a space scale determined by the coherence length. Therefore, the subgap current strongly depends on the layout of the electrodes within this space scale. The approach developed allows us to evaluate the subgap current for different layouts of interest.

Hekking, F.W.J.; Nazarov, Y.V. [Institut fuer Theoretische Festkoerperphysik, Universitaet Karlsruhe, Postfach 6980, 7500 Karlsruhe (Germany)

1994-03-01

399

Time dependent quantum tunnelling  

International Nuclear Information System (INIS)

This paper discusses tunnelling in terms of time evolution. Two cases are considered. The case where the barrier is a parabolic repulsive hump. Particles projected on one side of the barrier at regular intervals produce a time-dependent tunnelling current on the other side. A formulation for this current is given in terms the particle's initial conditions. Initially the current increases with each particle entry, but as time proceeds a saturation state is reached. It appears that the two-space-time Hamilton's momentum is responsible for the tunnelling process. An approximate propagator for a particle in a double well represented by a quartic potential is given.

1989-01-01

400

Macroscopic Quantum Tunneling  

Directory of Open Access Journals (Sweden)

Full Text Available In this work, a mechanism of macroscopic quantum tunneling is studied, which shows this sort of phenomena may exist even in the bio-field system. The relevant Davydov solitons fields and the Feynman digraph have been constructed based on the nonlinear Green function theory, which allows one to get a synchronous resonance model to explain the macroscopic quantum tunneling, such as in double potential wells system. Furthermore, the functional of quantum information density can also be applied to drive the object into a type of soliton structure of quantum information density, which allows the system to possess property of the macroscopic quantum tunneling.

Qiao Bi; Kongzhi Song

2013-01-01

 
 
 
 
401

Hardrock tunnel boring machines  

CERN Multimedia

This book covers the fundamentals of tunneling machine technology: drilling, tunneling, waste removal and securing. It treats methods of rock classification for the machinery concerned as well as legal issues, using numerous example projects to reflect the state of technology, as well as problematic cases and solutions. The work is structured such that readers are led from the basics via the main functional elements of tunneling machinery to the different types of machine, together with their areas of application and equipment. The result is an overview of current developments.Close cooper

Maidl, Bernhard; Ritz, Willy; Herrenknecht, Martin; Sturge, David S

2008-01-01

402

The Shadow Uniform Resource Locator: Standardizing Citations of Electronically Published Materials  

Digital Repository Infrastructure Vision for European Research (DRIVER)

Citation of scientific materials published on the Internet is often cumbersome because of unwieldy uniform resource locators (URLs). The authors describe a format for URLs that simplifies citation of scholarly materials. Its use depends on a simple HTML device, the “refresh page.” Uniform citati...

DiCarlo, Joseph V.; Pastor, Xavier; Markovitz, Barry P.

403

Impurity-assisted tunneling in graphene  

CERN Document Server

We demonstrate that a single potential impurity can drastically increase the electric conductance of an ideal strip of graphene. The phenomenon is attributed to the impurity-assisted resonant tunneling of massless Dirac fermions and may be favorably employed in graphene-based electronics. In particular a ribbon of undoped graphene prepared in a resonant state can serve as highly sensitive charge detector. Finally we argue that the impurity-assisted tunneling is a likely source of the experimentally observed enhancement of the minimal conductivity in graphene above the value predicted for clean samples.

Titov, M

2006-01-01

404

Quantum Tunnelling to the Origin and Evolution of Life  

Science.gov (United States)

Quantum tunnelling is a phenomenon which becomes relevant at the nanoscale and below. It is a paradox from the classical point of view as it enables elementary particles and atoms to permeate an energetic barrier without the need for sufficient energy to overcome it. Tunnelling might seem to be an exotic process only important for special physical effects and applications such as the Tunnel Diode, Scanning Tunnelling Microscopy (electron tunnelling) or Near-field Optical Microscopy operating in photon tunnelling mode. However, this review demonstrates that tunnelling can do far more, being of vital importance for life: physical and chemical processes which are crucial in theories about the origin and evolution of life can be traced directly back to the effects of quantum tunnelling. These processes include the chemical evolution in stellar interiors and within the cold interstellar medium, prebiotic chemistry in the atmosphere and subsurface of planetary bodies, planetary habitability via insolation and geothermal heat as well as the function of biomolecular nanomachines. This review shows that quantum tunnelling has many highly important implications to the field of molecular and biological evolution, prebiotic chemistry and astrobiology.

Trixler, Frank

2013-01-01

405

Quantum Tunnelling to the Origin and Evolution of Life.  

UK PubMed Central (United Kingdom)

Quantum tunnelling is a phenomenon which becomes relevant at the nanoscale and below. It is a paradox from the classical point of view as it enables elementary particles and atoms to permeate an energetic barrier without the need for sufficient energy to overcome it. Tunnelling might seem to be an exotic process only important for special physical effects and applications such as the Tunnel Diode, Scanning Tunnelling Microscopy (electron tunnelling) or Near-field Optical Microscopy operating in photon tunnelling mode. However, this review demonstrates that tunnelling can do far more, being of vital importance for life: physical and chemical processes which are crucial in theories about the origin and evolution of life can be traced directly back to the effects of quantum tunnelling. These processes include the chemical evolution in stellar interiors and within the cold interstellar medium, prebiotic chemistry in the atmosphere and subsurface of planetary bodies, planetary habitability via insolation and geothermal heat as well as the function of biomolecular nanomachines. This review shows that quantum tunnelling has many highly important implications to the field of molecular and biological evolution, prebiotic chemistry and astrobiology.

Trixler F

2013-08-01

406

Revealing the quantum regime in tunnelling plasmonics.  

Science.gov (United States)

When two metal nanostructures are placed nanometres apart, their optically driven free electrons couple electrically across the gap. The resulting plasmons have enhanced optical fields of a specific colour tightly confined inside the gap. Many emerging nanophotonic technologies depend on the careful control of this plasmonic coupling, including optical nanoantennas for high-sensitivity chemical and biological sensors, nanoscale control of active devices, and improved photovoltaic devices. But for subnanometre gaps, coherent quantum tunnelling becomes possible and the system enters a regime of extreme non-locality in which previous classical treatments fail. Electron correlations across the gap that are driven by quantum tunnelling require a new description of non-local transport, which is crucial in nanoscale optoelectronics and single-molecule electronics. Here, by simultaneously measuring both the electrical and optical properties of two gold nanostructures with controllable subnanometre separation, we reveal the quantum regime of tunnelling plasmonics in unprecedented detail. All observed phenomena are in good agreement with recent quantum-based models of plasmonic systems, which eliminate the singularities predicted by classical theories. These findings imply that tunnelling establishes a quantum limit for plasmonic field confinement of about 10(-8)?(3) for visible light (of wavelength ?). Our work thus prompts new theoretical and experimental investigations into quantum-domain plasmonic systems, and will affect the future of nanoplasmonic device engineering and nanoscale photochemistry. PMID:23135399

Savage, Kevin J; Hawkeye, Matthew M; Esteban, Rubén; Borisov, Andrei G; Aizpurua, Javier; Baumberg, Jeremy J

2012-11-07

407

Cysteine adsorption on the Au(111) surface and the electron transfer in configuration of a scanning tunneling microscope: A quantum-chemical approach  

DEFF Research Database (Denmark)

Adsorption of two forms, molecule and radical, of amino acid L-cysteine (Cys) on the Au-12 cluster that simulates the (111) face of single-crystal gold is studied in the framework of the density functional theory. Effects of solvation of adsorbed Cys particles and lateral interaction in a monolayer are analyzed. The simulation predicts a commensurate adsorption energetics of the molecule and radical, with a difference between the "on-top," "hollow," and "bridge" positions. An analysis of lateral electrostatic interactions points to the stability of a cluster comprising six Cys particles, which conforms to the size of a fragment observed experimentally. Adsorption calculations are used to build three-dimensional isosurfaces (STM images), where the tungsten needle of the scanning tunneling microscope is simulated by a tungsten atom or by small clusters. The calculated images are sensitive to both the Cys shape and the orientation of adsorbed Cys particles. Calculation results are compared with fresh in situ submolecular-resolution STM data. Simulated images (with commensurate contributions made by sulfur atom and amino group) built for Cys radical adsorbed in the "on-top" position give best conformance to experiment.

Nazmutdinov, R.R.; Manyurov, I.R.

2007-01-01

408

Carpal Tunnel Release  

Medline Plus

Full Text Available ... compression test. Again, we're looking for the similar re-creation of symptoms with numbness and tingling ... C-6 problems can imitate or produce symptoms similar to carpal tunnel in a patient who actually ...

409

Carpal Tunnel Release  

Medline Plus

Full Text Available ... up towards the forearm. Down on the distal end of the wound, we're going to localize ... of the way. Once we localize the distal end of the carpal tunnel ligament which is right ...

410

Carpal Tunnel Release  

Medline Plus

Full Text Available ... first off, carpal tunnel syndrome is a compressive neuropathy, which just means that the nerve is being ... wound, we're going to localize the ulnar neurovascular bundle, which is the ulnar nerve and artery. ...

411

Carpal Tunnel Release  

Medline Plus

Full Text Available ... try to alleviate carpal tunnel syndrome is to limit repetitive activities, especially the ones that tend to ... this tenosynovium because it's quite inflamed and also limits digital motion. And that gives us a good ...

412

Soviet Tunneling Rockets.  

Science.gov (United States)

An operational tunneling rocket is described which has been developed by a Soviet army officer. The information is mainly from one article in a semipopular journal, and hence is largely descriptive without giving precise performance data on the rocket. Pr...

S. G. Hibben

1973-01-01

413

Carpal Tunnel Release  

Medline Plus

Full Text Available ... the viewing audience later in the webcast. To send us your questions at any time, click the ... percentage of patients. Some surgeons do choose to send every patient that they perform a carpal tunnel ...

414

Carpal Tunnel Release  

Medline Plus

Full Text Available ... ll go over some of the exam findings relative to her carpal tunnel diagnosis later. Today we' ... a general anesthetic for specifical-- specific technical reasons relative to accomplishing this today; most of the time, ...

415

Carpal Tunnel Surgery  

Medline Plus

Full Text Available ... the tunnel pass the tendons and the nerv es. So, right beneath this ligament is going to ... ligament has been incised in its entirety. Ther e is a very important branch of this nerve, ...

416

INCAS TRISONIC WIND TUNNEL  

Directory of Open Access Journals (Sweden)

Full Text Available The 1.2 m x 1.2 m Trisonic Blowdown Wind Tunnel is the largest of the experimental facilities at the National Institute for Aerospace Research - I.N.C.A.S. "Elie Carafoli", Bucharest, Romania. The tunnel has been designed by the Canadian company DSMA (now AIOLOS) and since its commissioning in 1978 has performed high speed aerodynamic tests for more than 120 projects of aircraft, missiles and other objects among which the twin jet fighter IAR-93, the jet trainer IAR-99, the MIG-21 Lancer, the Polish jet fighter YRYDA and others. In the last years the wind tunnel has been used mostly for experimental research in European projects such as UFAST. The high flow quality parameters and the wide range of testing capabilities ensure the competitivity of the tunnel at an international level.

Florin MUNTEANU

2009-01-01

417

Carpal Tunnel Release  

Medline Plus

Full Text Available ... ll start here with an incision of the skin. And we use a small retractor called a ... re tunneling with the retractor up into the skin beyond the area where the incision is made ...

418

Josephson scanning tunneling microscopy  

CERN Document Server

We propose a set of scanning tunneling microscopy experiments in which the surface of superconductor is scanned by a superconducting tip. Potential capabilities of such experimental setup are discussed. Most important anticipated results of such an experiment include the position-resolved measurement of the superconducting order parameter and the possibility to determine the nature of the secondary component of the order parameter at the surface. The theoretical description based on the tunneling Hamiltonian formalism is presented.

Smakov, J; Balatsky, A V; Smakov, Jurij; Martin, Ivar; Balatsky, Alexander V.

2000-01-01

419

Preference and Use of Electronic Information and Resources by Blind/Visually Impaired in NCR Libraries in India  

Directory of Open Access Journals (Sweden)

Full Text Available This paper aims to determine the preference and use of electronic information and resources by blind/visually impaired users in the leading National Capital Region (NCR) libraries of India. Survey methodology has been used as the basic research tool for data collection with the help of questionnaires. The 125 in total users surveyed in all the five libraries were selected randomly on the basis of willingness of the users with experience of working in digital environments to participate in the survey. The survey results were tabulated and analyzed with descriptive statistics methods using Excel software and 'Stata version 11'. The findings reveal that ICT have a positive impact in the lives of people with disabilities as it helps them to work independently and increases the level of confidence among them. The Internet is the most preferred medium of access to information among the majority of blind/visually impaired users. The 'Complexity of content available on the net' is found as the major challenge faced during Internet use by blind users of NCR libraries. 'Audio books on CDs/DVDs and DAISY books' are the most preferred electronic resources among the majority of blind/visually impaired users. This study will help the library professionals and organizations/institutions serving people with disabil