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1

Squeezable electron tunneling junctions  

International Nuclear Information System (INIS)

We report a versatile new technique for constructing electron tunneling junctions with mechanically adjusted artificial barriers. I-V curves are presented for tunneling between Ag electrodes with vacuum, gas, liquid, or solid in the barrier. An energy gap is apparent in the measured I-V curve when tunneling occurs between superconducting Pb electrodes

1983-08-15

2

Squeezable electron tunneling junctions  

Energy Technology Data Exchange (ETDEWEB)

We report a versatile new technique for constructing electron tunneling junctions with mechanically adjusted artificial barriers. I-V curves are presented for tunneling between Ag electrodes with vacuum, gas, liquid, or solid in the barrier. An energy gap is apparent in the measured I-V curve when tunneling occurs between superconducting Pb electrodes.

Moreland, J.; Alexander, S.; Cox, M.; Sonnenfeld, R.; Hansma, P.K.

1983-08-15

3

Resonant tunneling of electrons  

Energy Technology Data Exchange (ETDEWEB)

We propose to use the mechanism of Andreev reflection of quasi-particles to form coherent states inside the resonance well of an N--I--S--I--N tunnel structure (I is an insulator, N is a normal metal, and S is a superconductor). The possibility of resonant tunneling of electrons in such structures is discussed.

Gogadze, G.A.; Dmitrenko, I.M.

1983-11-01

4

Single Electron Tunneling  

Energy Technology Data Exchange (ETDEWEB)

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

Ruggiero, Steven T.

2005-07-25

5

Radiation of tunnel electron  

CERN Document Server

The photorecombination radiation on a neighbor center of an electron ionized in the nonlinear tunneling regime is discussed. In the framework of the active electron model an analytical solution of the problem has been obtained. The analytical solution for distribution of the radiation energy spectrum has been derived both for one and three dimension problems. The optimal parameters of the field and the distance between quantum wells for a process of effective photorecombination with a broad spectrum have been formulated.

Golovinski, P A

2013-01-01

6

Tunneling electron trap  

Energy Technology Data Exchange (ETDEWEB)

The use of the field emission as means of filling the electron traps is proposed. Because of the electron tunneling at the cathode tip, the energy of the emitted electrons is lower than the electrostatic potential of the tip surface by the work function of the tip material. Consequently the electrons are trapped by the electrostatic well without requiring the dynamic trapping. The Brillouin density will be reached readily because the injection on the axis of the cylindrical symmetry dictates that the canonical angular momentum of the electrons vanishes. Furthermore the evaporative cooling due to the electrons escaping from the trap over the potential barrier may be able to cool the trapped electrons to cryogenic temperatures. The interesting regimes of the strongly correlated plasma and the quantum mechanical plasma may be obtained. (author)

Ohkawa, Tihiro

1997-12-01

7

Long-range electron tunneling.  

Science.gov (United States)

Electrons have so little mass that in less than a second they can tunnel through potential energy barriers that are several electron-volts high and several nanometers wide. Electron tunneling is a critical functional element in a broad spectrum of applications, ranging from semiconductor diodes to the photosynthetic and respiratory charge transport chains. Prior to the 1970s, chemists generally believed that reactants had to collide in order to effect a transformation. Experimental demonstrations that electrons can transfer between reactants separated by several nanometers led to a revision of the chemical reaction paradigm. Experimental investigations of electron exchange between redox partners separated by molecular bridges have elucidated many fundamental properties of these reactions, particularly the variation of rate constants with distance. Theoretical work has provided critical insights into the superexchange mechanism of electronic coupling between distant redox centers. Kinetics measurements have shown that electrons can tunnel about 2.5 nm through proteins on biologically relevant time scales. Longer-distance biological charge flow requires multiple electron tunneling steps through chains of redox cofactors. The range of phenomena that depends on long-range electron tunneling continues to expand, providing new challenges for both theory and experiment. PMID:24499470

Winkler, Jay R; Gray, Harry B

2014-02-26

8

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

9

Rapid Measurement of Inelastic Electron Tunneling Spectra.  

Science.gov (United States)

Inelastic electron tunneling spectroscopy is a versatile, high-sensitivity technique for obtaining vibrational spectra of absorbates on oxide surfaces, especially aluminum oxide. The theory and practice of tunneling spectroscopy have been reviewed extensi...

G. J. Gajda W. H. Weinberg

1985-01-01

10

Ponderomotive tunnelling in electron-laser interactions  

International Nuclear Information System (INIS)

We have investigated the electron tunnelling of the ponderomotive potential by using the nonperturbative quantum electrodynamic and a modified Gaussian quantized field Volkov solution. We have shown that the electron can tunnel a ponderomotive potential, which is too wide to tunnel as a static barrier, by absorbing laser photons. The effect is quantized in nature: the tunnelled electron is discrete in both the energy spectra and diffraction patterns as a result of the multiphoton processes. A resonant tunnelling occurs when the ponderomotive energy equals the multiple integer of the laser photon energy. (fast track communication)

2007-07-28

11

Distance metrics for heme protein electron tunneling  

Digital Repository Infrastructure Vision for European Research (DRIVER)

There is no doubt that distance is the principal parameter that sets the order of magnitude for electron-tunneling rates in proteins. However, there continue to be varying ways to measure electron-tunneling distances in proteins. This distance uncertainty blurs the issue of whether the intervening protein medium has been naturally selected to speed or slow any particular electron tunneling reaction. For redox cofactors lacking metals, an edge of the cofactor can be defined that approximates t...

Moser, Christopher C.; Chobot, Sarah E.; Page, Christopher C.; Dutton, P. Leslie

2008-01-01

12

Electroluminescence from graphene excited by electron tunneling.  

Science.gov (United States)

We use low-energy electron tunneling to excite electroluminescence in single layer graphene. Electrons are injected locally using a scanning tunneling microscope and the luminescence is analyzed using a wide-angle optical imaging system. The luminescence can be switched on and off by inverting the tip-sample bias voltage. The observed luminescence is explained in terms of a hot luminescence mechanism. PMID:24407020

Beams, Ryan; Bharadwaj, Palash; Novotny, Lukas

2014-02-01

13

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

CERN Document Server

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

14

Electron tunneling into superconducting ZrN  

Energy Technology Data Exchange (ETDEWEB)

We have prepared tunnel junctions on superconducting ZrN thin films using the natural oxide as a tunnel barrier. In the superconducting density of states we observed the phonon-induced structures due to the acoustic and optical phonons. The tunnel data could be analyzed by the McMillan-Rowell procedure without the need to correct for proximity effects. From the resulting Eliashberg function it was concluded that the optical phonons are coupled slightly more strongly to the electrons than the acoustic phonons.

Geerk, J.; Linker, G.; Smithey, R.

1986-12-29

15

Electron Refrigeration in the Tunneling Approach  

Digital Repository Infrastructure Vision for European Research (DRIVER)

The qualities of electron refrigeration by means of tunnel junctions between superconducting and normal--metal electrodes are studied theoretically. A suitable approximation of the basic expression for the heat current across those tunnel junctions allows the investigation of several features of the device such as its optimal bias voltage, its maximal heat current, its optimal working point, and the maximally gained temperature reduction. Fortunately, the obtained results ca...

Muller, Heinz-olaf; Chao, K. A.

1996-01-01

16

Electron refrigeration in the tunneling approach  

Energy Technology Data Exchange (ETDEWEB)

The performance of electron refrigeration by means of tunnel junctions between superconducting and normal-metal electrodes is studied theoretically. A suitable approximation of the basic expression for the heat current across the tunnel junctions allows the investigation of the main features of the device such as its optimal bias voltage, its maximal heat current, its optimal working point, and the maximal temperature reduction. The theoretical results are compared with those of a recent experiment. {copyright} {ital 1997 American Institute of Physics.}

Mueller, H.; Chao, K.A. [Department of Physics, Norwegian University of Science and Technology, NO-7034 Trondheim (Norway)]|[Department of Theoretical Physics I, Lund University, SE-22362 Lund (Sweden)

1997-07-01

17

Tunnel magnetoresistance on ferromagnetic single-electron transistors with multiple tunnel junction  

International Nuclear Information System (INIS)

Single-electron transistors with ferromagnetic multiple tunnel junctions are studied theoretically. Tunnel magnetoresistance under the Coulomb blockade regime is modulated by the gate voltage and is increased with increasing the number of tunnel junctions. Higher-order tunneling processes, especially for inelastic macroscopic quantum tunneling of charge, play an important role in the enhancement of the tunnel magnetoresistance. This implies that the tunnel magnetoresistance of the ferromagnetic single-electron transistor could be controlled by the gate and drain voltages and the number of the tunnel junctions. [copyright] 2001 American Institute of Physics

2001-06-01

18

Electron tunneling across a tunable potential barrier  

International Nuclear Information System (INIS)

We present an experiment where the elementary quantum electron tunneling process should be affected by an independent gate voltage parameter. We have realized nanotransistors where the source and drain electrodes are created by electromigration inducing a nanometer sized gap acting as a tunnel barrier. The barrier potential shape is in first approximation considered trapezoidal. The application of a voltage to the gate electrode close to the barrier region can in principle affect the barrier shape. Simulations of the source drain tunnel current as a function of the gate voltage predict modulations as large as one hundred percent. The difficulty of observing the predicted behaviour in our samples might be due to the peculiar geometry of the realized tunnel junction.

2009-02-01

19

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

1993-05-01

20

Electron tunneling in respiratory complex I  

Science.gov (United States)

NADH:ubiquinone oxidoreductase (complex I) plays a central role in the respiratory electron transport chain by coupling the transfer of electrons from NADH to ubiquinone to the creation of the proton gradient across the membrane necessary for ATP synthesis. Here the atomistic details of electronic wiring of all Fe/S clusters in complex I are revealed by using the tunneling current theory and computer simulations; both density functional theory and semiempirical electronic structure methods were used to examine antiferromagnetically coupled spin states and corresponding tunneling wave functions. Distinct electron tunneling pathways between neighboring Fe/S clusters are identified; the pathways primarily consist of two cysteine ligands and one additional key residue. Internal water between protein subunits is identified as an essential mediator enhancing the overall electron transfer rate by almost three orders of magnitude to achieve a physiologically significant value. The identified key residues are further characterized by sensitivity of electron transfer rates to their mutations, examined in simulations, and their conservation among complex I homologues. The unusual electronic structure properties of Fe4S4 clusters in complex I explain their remarkable efficiency of electron transfer.

Hayashi, Tomoyuki; Stuchebrukhov, Alexei A.

2010-01-01

 
 
 
 
21

Band Structure Engineering for Electron Tunneling Devices  

Science.gov (United States)

Negative differential resistance devices based on electron tunneling have potential applications in the frequency range above 200 GHz, where conventional field -effect and bipolar transistors have not yet been able to operate. High-speed performance depends primarily on increasing the peak current density and reducing the parasitic resistance. The room temperature peak-to-valley current ratio also must be maximized and the peak voltage should be reduced to reduce the power dissipated in the device. Two-terminal negative differential resistance devices are also stepping stones in the development of three-terminal devices based on coherent electron transport. In the future, these novel devices may offer the prospect of continued downscaling of integrated circuit components to nanometer dimensions, where conventional device concepts apparently fail. We apply standard techniques of molecular beam epitaxy to the growth of novel semiconductor heterostructures for electron tunneling devices. The samples are characterized by current and conductance values, measured as a function of device bias and temperature. The observed electrical characteristics are interpreted in terms of the energy band alignments of the heterojunctions and the energy levels and elastic tunneling current flows predicted by calculations based on a two-band model of the bulk band structures of the constituent materials. Such experiments have yielded nine new results that bear on the development of quantum-effect devices: observation of intervalley coupling at a GaAs/AlAs heterointerface, the crystallographic orientation dependence of the excess valley current in AlAs tunneling barriers, negative differential resistance at room temperature in single tunneling barriers of AlGaSb, the longest coherence distance (24 nm) of any resonant tunneling device (InAs/AlSb) resonant tunneling of holes in GaSb/AlSb quantum wells, interband tunneling in polytype InAs/AlSb/GaSb heterostructures, resonant interband tunneling in this system with low-temperature peak-to-valley current ratios greater than 60:1, substantial negative differential conductance in polytype quantum wells wider than 100 nm, and resonant interband coupling in a single -barrier InAs/GaSb/InAs structure. The achievement of large peak-to-valley ratios in wide InAs quantum wells suggests the possibility of high-speed three-terminal tunneling devices.

Beresford, John Roderic

1990-01-01

22

Electron accelerator for tunneling through hard rock  

International Nuclear Information System (INIS)

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

1975-11-03

23

Electron tunneling spectroscopy of intermediate valence materials  

International Nuclear Information System (INIS)

Electron tunneling spectra of TmSe, SmS, SmB"6 and CePd"3 have been measured using the GaAs Schottky barrier probe tunneling method. TmSe shows an energy gap 2? (FWHM) = 1.2 meV only in the antiferromagnetic phase. In situ pressure-transformed metallic SmS exhibits a gap 2? = 1.7 meV and SmB"6 shows a gap 2? = 2.7 meV, which is independent of magnetic field. For CePd"3 an inelastic excitation is found near +-14 meV, which is absent in YPd"3. An interpretation of the tunneling spectra in terms of quasiparticle excitation energies of bound electron-hole pairs is presented. (Auth.)

1982-01-01

24

Electron tunneling transport theory for molecules  

Science.gov (United States)

Aspects of the theory and applications of electron transport through molecular scale systems are presented. Complex wave-vector Bloch states lay the foundation for understanding quantum tunneling transport through molecules. The complex bandstructure reveals basic information about the intrinsic electron transport properties of molecules that are composed of a repeating sequence of units, including the expected molecule length dependence of the current (beta), an estimate for the alignment of the Fermi level of the metal (the branch point), estimates of molecule conductances, and other quantities. More general and quantitative methods for calculating electron transport characteristics of molecules connected between metallic electrodes are developed using techniques from scattering theory. An analysis is presented of the transport properties of alkanes with particular focus on interpreting results of recent experimental measurements carried out at Arizona State University. Basic issues about alkane conductances, the length dependence of the current, and the alignment of the Fermi level are considered. A double tunnel-junction Coulomb blockade circuit is explored as a possible model for explaining the experimental results. Examples of electron transport phenomena in a variety of other molecular scale systems are analyzed, including current through benzenedithiol, the influence of ring rotation on the conductances of phenyl and phenyl-ethynyl chain molecules, tunneling current through SiO2, and on-off current ratios for molecular transistors. Finally, the question of barrier tunneling times is addressed for electrons and light using the spin clock approach. The results are used to analyze tunneling times through periodic fragments, and a simple connection with complex bandstructures is determined.

Tomfohr, John Karl

25

Interplay of ferroelectricity and single electron tunneling  

Science.gov (United States)

We investigate the interplay of ferroelectricity and quantum electron transport at the nanoscale in the regime of Coulomb blockade. Ferroelectric polarization in this case is no longer the external parameter but should be self-consistently calculated along with electron hopping probabilities leading to physical transport phenomena studied in this paper. These phenomena appear mostly due to effective screening of a grain electric field by ferroelectric environment rather than due to polarization dependent tunneling probabilities. At small bias voltages polarization can be switched by a single excess electron in the grain. In this case transport properties of a single electron transistor exhibit the instability (memory effect).

Fedorov, S. A.; Korolkov, A. E.; Chtchelkatchev, N. M.; Udalov, O. G.; Beloborodov, I. S.

2014-04-01

26

Wind resource accessment in complex terrain by wind tunnel modelling  

Digital Repository Infrastructure Vision for European Research (DRIVER)

To benefit from strong winds, an increasing number of wind turbines are placed in complex terrains. But complex terrains means complex flows and difficult wind resource assessment. This study proposed to use wind tunnel modelling to evaluate the wind in a complex topography. The goal of this study is to evaluate the possibilities of wind resources assessment by wind tunnel modelling and to quantify the important modelling parameters. The lower part of the atmosphere, the atmospheric boundary ...

Conan, Boris

2012-01-01

27

Photocurrent generation in single electron tunneling transistors  

International Nuclear Information System (INIS)

A single electron tunneling transistor (SET) with a non-equilibrium mode population in one of the leads is analysed theoretically. We model transport through a dot coupled to a channel, both formed by gates from the two-dimensional electron gas of a GaAs/AlGaAs heterostructure. The non-equilibrium mode population, which is induced by coherent THz-pumping in the channel, produces empty states below the Fermi level for electrons to tunnel into. A photocurrents arises, which is periodically saw-tooth peaked with respect to the voltage on a central gate. Foe intense THz-field the peaks display plateaus that reflect the energy dependence of the mode population. We also predict a high-gain Vin/Vout transfer characteristic, similar to that of a current biased SET

1999-03-01

28

Interheme electron tunneling in cytochrome c oxidase  

Digital Repository Infrastructure Vision for European Research (DRIVER)

Cytochrome c oxidase (CcO) is the terminal enzyme of the respiratory chain that catalyzes respiratory reduction of dioxygen (O2) to water in all eukaryotes and many aerobic bacteria. CcO, and its homologs among the heme-copper oxidases, has an active site composed of an oxygen-binding heme and a copper center in the vicinity, plus another heme group that donates electrons to this site. In most oxidoreduction enzymes, electron transfer (eT) takes place by quantum-mechanical electron tunneling....

Kaila, Ville R. I.; Johansson, Mikael P.; Sundholm, Dage; Wikstro?m, Ma?rten

2010-01-01

29

Wind Tunnel Management and Resource Optimization: A Systems Modeling Approach  

Science.gov (United States)

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

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

2000-01-01

30

Electron-tunneling pathways in proteins  

Energy Technology Data Exchange (ETDEWEB)

Electron-transfer (ET) reactions are key steps in photosynthisis, respiration, drug metabolism, and many other biochemical processes. The ETs are remarkably fast and proceeded with high specificity. Theoreticians have been intensely interested in long-range protein ET reactions for many years. This perspective paper discusses the tunneling-pathway model for protein ET coupling, giving the example Cytochrome c. Different coupling strength in different pathway families are mentioned and a brief overview of the future of understanding ET reactions is given.

Beratan, D.N. (Univ. of Pittsburgh, PA (United States)); Onuchic, J.N. (Univ. of California, San Diego, La Jolla (United States)); Winkler, J.R.; Gray, H.B. (California Institute of Technology, Pasadena (United States))

1992-12-11

31

Electronic Resource Management Systems  

Directory of Open Access Journals (Sweden)

Full Text Available Computer applications which deal with electronic resource management (ERM are quite a recent development. They have grown out of the need to manage the burgeoning number of electronic resources particularly electronic journals. Typically, in the early years of e-journal acquisition, library staff provided an easy means of accessing these journals by providing an alphabetical list on a web page. Some went as far as categorising the e-journals by subject and then grouping the journals either on a single web page or by using multiple pages. It didn't take long before it was recognised that it would be more efficient to dynamically generate the pages from a database rather than to continually edit the pages manually. Of course, once the descriptive metadata for an electronic journal was held within a database the next logical step was to provide administrative forms whereby that metadata could be manipulated. This in turn led to demands for incorporating more information and more functionality into the developing application.

Mark Ellingsen

2004-09-01

32

Electron tunneling into intermediate-valence materials  

International Nuclear Information System (INIS)

Electron tunneling spectra of TmSe, SmS, SmB"6, and CePd"3 have been measured with the GaAs Schottky-barrier probe tunneling method. Antiferromagnetic TmSe shows an energy gap 2? (full width at half maximum) of 1.2 meV, in situ pressure-transformed metallic SmS exhibits a gap of 1.7 meV, and SmB"6 shows a gap of 2.7 meV, which is independent of magnetic field. For CePd"3 an inelastic excitation is found near +- 14 meV, which is absent in YPd"3

1982-10-04

33

Single-electron tunneling. [Microwave scanning tunneling microscope  

Energy Technology Data Exchange (ETDEWEB)

Pictures using the low-temperature microwave scanning tunneling microscope, have been made of particles and tunneling IV characteristics determined. Strong, sometimes periodic negative differential resistance was observed in small-particle systems. Au and Ag droplets and particles were studied. 4 figs.

Ruggiero, S.T.

1993-01-01

34

Advanced Undergraduate Laboratory Experiment in Inelastic Electron Tunneling Spectroscopy.  

Science.gov (United States)

An advanced undergraduate laboratory experiment in inelastic electron tunneling spectroscopy is described. Tunnel junctions were fabricated, the tunneling spectra of several molecules absorbed on the surface of aluminum oxide measured, and mode assignments made for several of the prominent peaks in spectra using results obtained from optical…

White, H. W.; Graves, R. J.

1982-01-01

35

A novel electron tunneling infrared detector  

Science.gov (United States)

The pneumatic infrared detector, originally developed by Golay in the late 1940s, uses the thermal expansion of one cm(exp 3) of xenon at room temperature to detect the heat deposited by infrared radiation. This detector was limited by thermal fluctuations within a 10 Hz bandwidth, but suffered from long thermal time constants and a fragile structure. Nevertheless, it represents the most sensitive room temperature detector currently available in the long wavelength infrared (LWIR). Fabrication of this type of detector on smaller scales has been limited by the lack of a suitably sensitive transducer. Researchers designed a detector based on this principle, but which is constructed entirely from micromachined silicon, and uses a vacuum tunneling transducer to detect the expansion of the trapped gas. Because this detector is fabricated using micromachining techniques, miniaturization and integration into one and two-dimensional arrays is feasible. The extreme sensitivity of vacuum tunneling to changes in electrode separation will allow a prototype of this detector to operate in the limit of thermal fluctuations over a 10 kHz bandwidth. A calculation of the predicted response and noise of the prototype is presented with the general formalism of thermal detectors. At present, most of the components of the prototype have been fabricated and tested independently. In particular, a characterization of the micromachined electron tunneling transducer has been carried out. The measured noise in the tunnel current is within a decade of the limit imposed by shot noise, and well below the requirements for the operation of an infrared detector with the predicted sensitivity. Assembly and characterization of the prototype infrared detector will be carried out promptly.

Kenny, T. W.; Waltman, S. B.; Reynolds, J. K.; Kaiser, W. J.

1990-01-01

36

Tunneling in the electron box in the nonperturbative regime  

International Nuclear Information System (INIS)

We study charging effects and tunneling in the single electron box. Tunneling mixes different charge states and in the nonperturbative regime the charge in the island may be strongly screened. When charge states are nearly degenerate the screening of the charge is strong even in the weak tunneling regime. Virtual tunneling processes reduce both the level splitting ? and the tunneling strength ?. The charge on the island and the decay rates are calculated. In the strong tunneling regime also nondegenerate states are affected by tunneling. Strong-coupling scaling renormalizes the effective capacitance, a result which we confirm by Monte Carlo simulations. The tunneling strength ? scales to smaller values into the regime where the weak-coupling scaling applies. We propose a two-stage scaling procedure providing the unified picture for the problem. The scaling analysis is also extended to superconducting tunnel junctions with finite subgap conductance. ((orig.))

1994-12-01

37

Electron tunneling in Bi2223 under high pressure  

International Nuclear Information System (INIS)

We have studied the electron tunneling in Bi2223 break junctions under high pressure 0< P<10 kbar. A reproducible pressure influence on the linear conductance background has been found. We observed, that the normalized conductance vs voltage was increased with the pressure. This set of measurements seems to indicate that the linear tunneling conductance may have its explanation in the characteristics of the tunneling barrier namely on the resonant tunneling through the localized states in the insulating barrier

1994-09-03

38

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.

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

2013-01-01

39

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

40

Electron beam instabilities in gyrotron beam tunnels  

International Nuclear Information System (INIS)

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

1997-01-01

 
 
 
 
41

Molecular tips for scanning tunneling microscopy: intermolecular electron tunneling for single-molecule recognition and electronics.  

Science.gov (United States)

This paper reviews the development of molecular tips for scanning tunneling microscopy (STM). Molecular tips offer many advantages: first is their ability to perform chemically selective imaging because of chemical interactions between the sample and the molecular tip, thus improving a major drawback of conventional STM. Rational design of the molecular tip allows sophisticated chemical recognition; e.g., chiral recognition and selective visualization of atomic defects in carbon nanotubes. Another advantage is that they provide a unique method to quantify electron transfer between single molecules. Understanding such electron transfer is mandatory for the realization of molecular electronics. PMID:24420248

Nishino, Tomoaki

2014-01-01

42

Vibrational features in inelastic electron tunneling spectra  

CERN Document Server

A theoretical analysis of inelastic electron tunneling spectroscopy (IETS) experiments conducted on molecular junctions are presented, where the second derivative of the current with respect to voltage is usually plotted as a function of applied bias. Within the nonperturbative computational scheme, adequate for arbitrary parameters of the model, we consider the virtual conduction process in the off-resonance region. Here we study the influence of few crucial factors on the IETS spectra: the strength of the vibronic coupling, the phonon energy, and the device working temperature. It was also shown that weak asymmetry in the IETS signal with respect to bias polarity is obtained as a result of strongly asymmetric connection with the electrodes.

Walczak, K

2007-01-01

43

Vibrational features in inelastic electron tunneling spectra  

International Nuclear Information System (INIS)

A theoretical analysis of inelastic electron tunneling spectroscopy (IETS) experiments conducted on molecular junctions is presented, where the second derivative of the current with respect to voltage is usually plotted as a function of applied bias. Within the nonperturbative computational scheme, adequate for arbitrary parameters of the model, we consider the virtual conduction process in the off-resonance region. Here we study the influence of few crucial factors on the IETS spectra: the strength of the vibronic coupling, the phonon energy, and the device working temperature. It was also shown that weak asymmetry in the IETS signal with respect to bias polarity is obtained as a result of strongly asymmetric connection with the electrodes

2007-03-06

44

Tunneling of Dirac electrons through spatial regions of finite mass  

International Nuclear Information System (INIS)

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

2008-08-13

45

Interheme electron tunneling in cytochrome c oxidase  

Science.gov (United States)

Cytochrome c oxidase (CcO) is the terminal enzyme of the respiratory chain that catalyzes respiratory reduction of dioxygen (O2) to water in all eukaryotes and many aerobic bacteria. CcO, and its homologs among the heme-copper oxidases, has an active site composed of an oxygen-binding heme and a copper center in the vicinity, plus another heme group that donates electrons to this site. In most oxidoreduction enzymes, electron transfer (eT) takes place by quantum-mechanical electron tunneling. Here we show by independent molecular dynamics and quantum-chemical methods that the heme-heme eT in CcO differs from the majority of cases in having an exceptionally low reorganization energy. We show that the rate of interheme eT in CcO may nevertheless be predicted by the Moser-Dutton equation if reinterpreted as the average of the eT rates between all individual atoms of the donor and acceptor weighed by the respective packing densities between them. We argue that this modification may be necessary at short donor/acceptor distances comparable to the donor/acceptor radii.

Kaila, Ville R. I.; Johansson, Mikael P.; Sundholm, Dage; Wikstrom, Marten

2010-01-01

46

Substrate-mediated electron tunneling through molecule-electrode interfaces  

Science.gov (United States)

Electron tunneling properties at the molecule-electrode interfaces formed by coronene molecules adsorbed on Ag(111) and highly oriented pyrolytic graphite surfaces are investigated by scanning tunneling microscopy and first-principles calculations. Experimentally, the coronene molecules display significant variation in the electronic density of states at the molecular centers on different substrates. An analysis of the electronic structures for both systems by first-principles calculations based on density functional theory reveals that substrate dependent molecular image contrast is ascribed to the resonant tunneling process mediated by geometrically different substrates. Possible consequences for electron transport are briefly discussed.

Sun, Jia-Tao; Chen, Lan; Ping Feng, Yuan; Thye Shen Wee, Andrew

2011-10-01

47

Quantum tunneling and field electron emission theories  

CERN Document Server

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

Liang, Shi-Dong

2013-01-01

48

Fundamentals of Electronics Educational Resources  

Science.gov (United States)

This website from UBM Tech provides links to a variety of technical papers, webinars, videos and tutorials pertaining to fundamental electronics. At the top of the page, users will find current spotlight resources.

2013-07-10

49

Tunneling of Bloch electrons through a small-size contact  

Science.gov (United States)

For the first time the tunneling of Bloch waves through a contact of small diameter is studied in the framework of a model of an inhomogeneous tunnel ?-barrier of low transparency. The electron tunneling from bulk-mode states into the surface states localized near the contact interface is considered. An asymptotically exact expression (in the inverse height of the barrier) is derived for the conductance of the system. Prospects for the application of the obtained results to the theory of scanning tunneling microscopy are discussed.

Khotkevych-Sanina, N. V.; Kolesnichenko, Yu. A.

2014-05-01

50

Electron tunneling into superconducting filaments using mechanically adjustable barriers  

International Nuclear Information System (INIS)

A new type of squeezable electron tunneling (SET) junction has been developed for tunneling into superconducting filaments. Stable, mechanically adjustable tunneling barriers between the native surfaces of sputtered Nb films and 30-?m-diam Nb filaments were established in liquid helium at 4 K. The current versus voltage characteristics of these SET junctions were used to determine the superconducting energy gap at the surface of the filaments. Since the filaments were etched from commercial superconducting magnet wire, this type of tunnel junction shows promise as a diagnostic probe of superconducting materials for high-field magnets

1985-07-15

51

Inelastic electron tunneling spectroscopy of local "spin accumulation" devices  

Science.gov (United States)

We investigate the origin of purported "spin accumulation" signals observed in local "three-terminal" (3T) measurements of ferromagnet/insulator/n-Si tunnel junctions using inelastic electron tunneling spectroscopy (IETS). Voltage bias and magnetic field dependences of the IET spectra were found to account for the dominant contribution to 3T magnetoresistance, thus indicating that it arises from inelastic tunneling through impurities and defects at junction interfaces and within the barrier, rather than from spin accumulation due to pure elastic tunneling into bulk Si as has been previously assumed.

Tinkey, Holly N.; Li, Pengke; Appelbaum, Ian

2014-06-01

52

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

2006-12-01

53

Klein tunneling in graphene: optics with massless electrons  

CERN Multimedia

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

Allain, P E

2011-01-01

54

Effective Background Removal Technique for Inelastic Electron Tunneling Spectra.  

Science.gov (United States)

Progress has been made in a number of areas. First, further improvements have been made in the measurement of inelastic electron tunneling spectra. Second, molecular beam scattering has been employed in out continuing investigation of the activated absorp...

G. J. Gajda W. H. Weinberg

1985-01-01

55

Asymmetric tunable tunneling magnetoresistance in single-electron transistors  

International Nuclear Information System (INIS)

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

2000-08-02

56

Time of electron tunneling through a potential barrier  

International Nuclear Information System (INIS)

Problem of mean time of an electron tunnelling in a classically prohibited region is investigated. A natural method for generalizing the classical time-of-flight notion for a quantum-mechanical case is suggested and its application to the tunneling problem through a one-dimensional potential barrier is considered. In separate consideration of passed and reflected particles complex parameters appear which make sense of tunnelling times for passed and reflected particles. Relation of these parameters and angles of electron spin rotation in magnetic field localized in the barrier region was investigated

1987-03-01

57

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

58

Tunneling conductance in a system with strong electron correlation  

Directory of Open Access Journals (Sweden)

Full Text Available We discuss the structure of tunneling conductance, the dI/dV lineshape, observed for a system with strong electron correlation. The structure of the dI/dV lineshape comprises zero-bias peak and two side peaks. We discuss the condition for compressing zero-bias peak and the origin of two side peaks. We explain why the tunneling conductance does not simply reflect the sample density of states in the tunneling experiment for a system with strong electron correlation.

Hong J.

2012-03-01

59

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.))

1994-12-01

60

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 UPd_2Al_3 and URu_2Si_2, 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.))

1995-02-01

 
 
 
 
61

Tunneling spectroscopy on correlated electron systems  

Energy Technology Data Exchange (ETDEWEB)

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{Delta} of about 100meV and 10meV, respectively. In the heavy fermion materials UPd{sub 2}Al{sub 3} and URu{sub 2}Si{sub 2}, 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.)).

Aarts, J. [Rijksuniversiteit Leiden (Netherlands). Kamerlingh Onnes Lab.; Volodin, A.P. [Rijksuniversiteit Leiden (Netherlands). Kamerlingh Onnes Lab.

1995-02-01

62

Method of temperature correction for electron tunneling spectrum  

International Nuclear Information System (INIS)

When the effective phonon spectrum is calculated from the electron tunneling spectrum by inversion of the strongly coupled superconducting energy gap equation, the electron density of states must be measured under the condition T?0K. Otherwise the error of the electron density of states and the deviation of effective phonon spectrum from the real one will be very large. In this paper a method is given for correcting this temperature effect, and the above-mentioned difficulty can be overcome. The correct effective phonon spectrum and ? and ?* values can be obtained by this method using electron tunneling spectrum data even measured at T/T/sub c/ = 0.22

1986-01-01

63

Lifetime of two-dimensional electrons measured by tunneling spectroscopy  

CERN Document Server

For electrons tunneling between parallel two-dimensional electron systems, conservation of in-plane momentum produces sharply resonant current-voltage characteristics and provides a uniquely sensitive probe of the underlying electronic spectral functions. We report here the application of this technique to accurate measurements of the temperature dependence of the electron-electron scattering rate in clean two-dimensional systems. Our results are in qualitative agreement with existing calculations.

Murphy, S Q; Pfeiffer, L N; West, K W

1995-01-01

64

Enhancement of tunnel magnetoresistance in ferromagnetic single-electron transistors  

International Nuclear Information System (INIS)

Magnetoresistance of ferromagnetic single-electron transistors (SETs) is known to increase at low temperatures. In this paper, we investigate systematically how the TMR enhancement changes as a function of the tunnel resistance RT using Ni/Co/Ni-SETs. We find the enhancement almost independent of RT as far as RT?30 k?, while it is small for devices with RT?7 k?. These results are not explained by the theories based on the higher-order tunneling

2003-05-01

65

Voltage controlled electron spin dynamics in resonant tunnelling devices  

Science.gov (United States)

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

Galeti, H. V. A.; Brasil, M. J. S. P.; Gobato, Y. Galv ao; Henini, M.

2014-04-01

66

Electron-beam-assisted Scanning Tunneling Microscopy Of Insulating Surfaces  

CERN Document Server

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

67

Simulation of electron tunneling time through a potential barrier  

Energy Technology Data Exchange (ETDEWEB)

Simulated electron tunneling time through a potential barrier is compared with theoretical phase time. For a GaAs/Al{sub 0.3}Ga{sub 0.7}As/GaAs potential barrier with 300 MeV height and 3 nm or 5 nm width, simulations are performed with various average electron energies and momentum deviations. The simulation results become closer to the theoretical phase time as the average electron energy decreases and as the momentum deviation decreases. It is also shown that a barrier, which is due to the peak spectrum shift in the momentum space after tunneling. (author). 12 refs., 5 figs.

Lee, Wook; Lee, Byoung Ho [Seoul National University, Seoul (Korea, Republic of)

1996-01-01

68

Attosecond correlation dynamics during electron tunnelling from molecules  

International Nuclear Information System (INIS)

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

2010-08-28

69

Casimir-like tunneling-induced electronic forces  

CERN Document Server

We study the quantum forces that act between two nearby conductors due to electronic tunneling. We derive an expression for these forces by calculating the flux of momentum arising from the overlap of evanescent electronic fields. Our result is written in terms of the electronic reflection amplitudes of the conductors and it has the same structure as Lifshitz's formula for the electromagnetically mediated Casimir forces. We evaluate the tunneling force between two semiinfinite conductors and between two thin films separated by an insulating gap. We discuss some applications of our results.

Procopio, L M; Mochán, W L; Procopio, Lorenzo M.; Villarreal, Carlos

2005-01-01

70

Casimir-like tunnelling-induced electronic forces  

Energy Technology Data Exchange (ETDEWEB)

We study the quantum forces that act between two nearby conductors due to electronic tunnelling. We derive an expression for these forces by calculating the flux of momentum arising from the overlap of evanescent electronic fields. Our result is written in terms of the electronic reflection amplitudes of the conductors and it has the same structure as Lifshitz's formula for the electromagnetically mediated Casimir forces. We evaluate the tunnelling force between two semiinfinite conductors and between two thin films separated by an insulating gap. We discuss some applications of our results.

Procopio, L M [Centro de Ciencias FIsicas, Universidad Nacional Autonoma de Mexico, Apartado Postal 48-3, 62251 Cuernavaca, Morelos (Mexico); Villarreal, C [Instituto de FIsica, Universidad Nacional Autonoma de Mexico, Apartado Postal 20-364, 01000 Distrito Federal (Mexico); Mochan, W L [Centro de Ciencias FIsicas, Universidad Nacional Autonoma de Mexico, Apartado Postal 48-3, 62251 Cuernavaca, Morelos (Mexico)

2006-05-26

71

Hot electrons in a tunnel structure based on metal nanoclusters  

CERN Document Server

We study the effect of temperature on the tunnel current in a structure based on gold clusters taking into consideration their discrete electronic spectra. We suggest that an overheating of electron subsystem leads to the disappearance of a current gap and gradual smoothing of current--voltage curves that is observed experimentally.

Pogosov, V V; Babich, A V

2006-01-01

72

Single electron pump fabricated with ultrasmall normal tunnel junctions  

International Nuclear Information System (INIS)

We have designed and operated a device through which single electrons can be 'pumped' reversibly. It consists of a linear array of three tunnel junctions voltage biased below the Coulomb gap. Phase shifted ac voltages applied to two gates pump one electron per cycle. (orig.)

1991-02-01

73

Laser induced - tunneling, electron diffraction and molecular orbital imaging  

International Nuclear Information System (INIS)

Full text: Multiphoton ionization in the tunneling limit is similar to tunneling in a scanning tunneling microscope. In both cases an electron wave packet tunnels from a bound (or valence) state to the continuum. I will show that multiphoton ionization provides a route to extend tunneling spectroscopy to the interior of transparent solids. Rotating the laser polarization is the analogue of scanning the STM tip - a means of measuring the crystal symmetry of a solid. In gas phase molecules the momentum spectrum of individual electrons can be measured. I will show that, as we rotate the molecule with respect to the laser polarization, the photoelectron spectrum samples a filter projection of the momentum wave function (the molecular analogue to the band structure) of the ionizing orbital. Some electrons created during multiphoton ionization re-collide with their parent ion. I will show that they diffract, revealing the scattering potential of the ion - the molecular structure. The electron can also interfere with the initial orbital from which it separated, creating attosecond XUV pulses or pulse trains. The amplitude and phase of the radiation contains all information needed to re-construct the image of the orbital (just as a sheared optical interferometer can fully characterize an optical pulse). Strong field methods provide an extensive range of new tools to apply to atomic, molecular and solid-state problems. (author)

2008-07-02

74

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.

Mygind, Jesper

2002-01-01

75

Klein tunneling in graphene: optics with massless electrons  

Science.gov (United States)

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

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

2011-10-01

76

International symposium, tunnelling for water resources and power projects  

Energy Technology Data Exchange (ETDEWEB)

70 papers are presented under 6 sessions: engineering classification of rock mass for tunnelling; planning, investigation and analysis of tunnels; geometric and hydraulic design of tunnels; tunnelling, stabilization and support systems; lining for power tunnels; and monitoring, back analysis and case histories. Includes papers on freeze sunk shafts in the Panji coal district of China, and Dong Feng shaft deformation in the Wu Long Coal mine of Fuxin, China.

1988-01-01

77

Two-step tunnelling of the electron to scavengers  

International Nuclear Information System (INIS)

A formulation is presented of the kinetics of tunnelling of the trapped electron to a solute S1 via a second solute S2, taking into account the spatial distributions of the solutes. The yield of first solute anions was calculated as a function of time and the concentrations of first and second solutes. An interacting finding is that at fixed time and first solute concentration, this yield is almost independent of the second solute concentration. Recent experimental results on selective electron capture are interpreted by the two-step tunnelling model. (author)

1979-01-01

78

Locality of information obtained from proximity-electron-tunneling spectroscopy  

International Nuclear Information System (INIS)

The locality of the information obtained by the technique of proximity-electron tunneling (PETS) is analyzed, with particular attention to the effects on the measured effective-phonon spectrum ?2F(?) of disorder or impurities near the surface of the superconductor electrode. As in conventional tunnel junctions it is determined that the (energy-dependent) electron mean free path determines the maximum depth of the superconductor of which the measured phonon spectrum is characterized. An averaging length L(E) is defined and found to be typically larger in proximity junctions than in conventional junctions. This can make PET results inherently less susceptible than conventional results to surface disorder of the superconductor

1982-02-01

79

Electron-Photon interaction in resonant tunneling diodes  

CERN Document Server

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

80

Hole-electron quantum tunnelling interferences through a molecular junction  

Science.gov (United States)

The Configuration Interaction Elastic Scattering Quantum Chemistry (CI-ESQC) method is used to calculate the many-body electronic transmission coefficient through a molecular junction in a coherent superposition of hole and electron tunnelling processes. Independent hole and electron destructive interferences are still existing and with a net zero of transmission at the interference energy locations. But in the molecule electronic gap, CI-ESQC leads to a destructive interference with a non zero of transmission between hole and electron processes. This explains the non zero of transmission destructive interference recently observed at the Fermi level in the molecule electronic gap.

Portais, Mathilde; Joachim, Christian

2014-01-01

 
 
 
 
81

Inelastic electron tunneling spectroscopy at local defects in graphene  

Digital Repository Infrastructure Vision for European Research (DRIVER)

We address local inelastic scattering from vibrational impurity adsorbed onto graphene and the evolution of the local density of electron states near the impurity from weak to strong coupling regime. For weak coupling the local electronic structure is distorted by inelastic scattering developing peaks/dips and steps. These features should be detectable in the inelastic electron tunneling spectroscopy, $d^2I/dV^2$, using local probing techniques. Inelastic Friedel oscillation...

Fransson, J.; She, J. -h; Pietronero, L.; Balatsky, A. V.

2012-01-01

82

Study of Kondo effect in MgO-based magnetic tunnel junctions by electron tunnelling spectroscopy  

Energy Technology Data Exchange (ETDEWEB)

To investigate the Kondo effect in MgO-based magnetic tunnel junctions (MTJs) electron tunnelling spectroscopy was carried out in Co{sub 60}Fe{sub 20}B{sub 20}/textured MgO(001)/Co{sub 70}Fe{sub 30}magnetic tunnel junctions at temperatures between 2 K and 300 K. The zero-bias anomaly (ZBA) or the logarithmic temperature-dependent peak was observed in dynamic resistance. This behaviour can explain consistently the reduced TMR ratio of MgO-based MTJs compared with the theoretical expectation at low temperature. The properties of ZBAs were also investigated for both single crystal MTJs and the MTJs with the boron-doped top ferromagnetic electrode in order to find out the origin of the Kondo effect.

Bang, D O; Nozaki, T; Suzuki, Y [Graduate School of Engineering Science, Osaka University, Osaka 560-8531 (Japan); Rhie, K [Display and Semiconductor Physics, Korea University, Chochiwon 339-700 (Korea, Republic of); Kim, T-S [Korea Research Institute of Standard and Science, Deajeon 305-340 (Korea, Republic of); Fukushima, A; Yuasa, S [National Institute of Advance Industrial Science and Technology, Tsukuba 305-8568 (Japan); Minamitani, E; Nakanishi, H; Kasai, H, E-mail: bang@spin.mp.es.osaka-u.ac.j [Department of Applied Physics, Osaka University, Suita, Osaka 565-0871 (Japan)

2010-01-01

83

Wrangling Electronic Resources: A Few Good Tools  

Directory of Open Access Journals (Sweden)

Full Text Available There are several freely available tools today that fill the needs of librarians tasked with maintaining electronic resources, that assist with tasks such as editing MARC records and maintaining web sites that contain links to electronic resources. This article gives a tour of a few tools the author has found invaluable as an Electronic Resources Librarian.

Brandy Klug

2010-03-01

84

Molecular Transport Junctions: Propensity Rules for Inelastic Electron Tunneling Spectra  

Digital Repository Infrastructure Vision for European Research (DRIVER)

We develop a series of propensity rules for interpreting Inelastic Electron Tunneling (IET) spectra of single-molecule transport junctions. IETS has no selection rules, such as those seen in optical, infrared and Raman spectra, because IETS features arise not from the field-dipole interaction characterizing these other spectroscopies, but from vibronic modification of the electronic levels. Expansion of the Landauer-Imry formula in Taylor series in molecular normal coordinat...

Troisi, Alessandro; Ratner, Mark A.

2006-01-01

85

Single-electron soliton avalanches in tunnel junction arrays  

CERN Multimedia

Numerical modeling of correlated single-electron tunneling in uniform 2D arrays of small conducting islands separated by tunnel junctions shows the possiblility of soliton-antisoliton avalanches. Though the time duration of any avalanche, and the total charge $\\Delta Q = ne$ transferred across the array during the avalanche, are always finite, in arrays with length $N$ larger than certain critical value $N_c$ and large width $M \\gg f(N)$, the avalanche magnitude $n$ may be exponentially large, resulting in particular in a giant increase of shot noise. Thermal fluctuations and disorder gradually suppress the avalanche effect.

Sverdlov, V A; Korotkov, A N; Likharev, K K; Sverdlov, Viktor A.; Kaplan, Daniel M.; Korotkov, Alexander N.; Likharev, Konstantin K.

2000-01-01

86

Solving rate equations for electron tunneling via discrete quantum states  

CERN Multimedia

We consider the form of the current-voltage curves generated when tunneling spectroscopy is used to measure the energies of individual electronic energy levels in nanometer-scale systems. We point out that the voltage positions of the tunneling resonances can undergo temperature-dependent shifts, leading to errors in spectroscopic measurements that are proportional to temperature. We do this by solving the set of rate equations that can be used to describe electron tunneling via discrete quantum states, for a number of cases important for comparison to experiments, including (1) when just one spin-degenerate level is accessible for transport, (2) when 2 spin-degenerate levels are accessible, with no variation in electron-electron interactions between eigenstates, and (3) when 2 spin-degenerate levels are accessible, but with variations in electron-electron interactions. We also comment on the general case with an arbitrary number of accessible levels. In each case we analyze the voltage-positions, amplitudes,...

Bonet, E; Ralph, D C; Bonet, Edgar; Deshmukh, Mandar M.

2001-01-01

87

Electron tunneling through ultrathin boron nitride crystalline barriers.  

Science.gov (United States)

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. PMID:22380756

Britnell, Liam; Gorbachev, Roman V; Jalil, Rashid; Belle, Branson D; Schedin, Fred; Katsnelson, Mikhail I; Eaves, Laurence; Morozov, Sergey V; Mayorov, Alexander S; Peres, Nuno M R; Neto, Antonio H Castro; Leist, Jon; Geim, Andre K; Ponomarenko, Leonid A; Novoselov, Kostya S

2012-03-14

88

Electron tunneling experiments using Nb-Sn ''break'' junctions  

International Nuclear Information System (INIS)

An Nb-Sn filament mounted on a flexible glass beam can be broken to form an electron tunneling junction between the fracture elements. Breaking the filament in liquid helium prevents oxidation of the freshly exposed fracture surfaces. A sharp superconducting energy gap in the I-V characteristics measured at 4 K indicates the formation of a high-quality tunneling barrier between the fracture elements. The resistance of the junction can be continuously adjusted by varying the surface bending strain of the beam. An estimated 0.1 nm change in the barrier thickness produces about an order of magnitude change in the resistance over the range from 10"5 to 10"8 ?. The exponential character of this dependence shows that the tunnel junction is freely adjustable without intimate contact of the junction elements. ''Break'' junctions made in this way offer a new class of tunneling experiments on freshly exposed surfaces of a fractured sample without the oxide barrier previously required for junction stability. Such experiments provide a simple technique for tunneling to new materials and may eliminate complications that can be encountered during interpretation of data obtained using oxide barriers

1985-11-15

89

Attosecond correlation dynamics during electron tunnelling from molecules  

Energy Technology Data Exchange (ETDEWEB)

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

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

2010-08-28

90

Single electron transistor with programmable tunnelling structure  

International Nuclear Information System (INIS)

A single electron transistor based on the ordered nanodot arrays was reported. The gold nanoparticles self-assembled in the ordered mesoporous silica thin films were used as the Coulomb islands. The Coulomb blockade and Coulomb oscillation are demonstrated at room temperature, and the SIMON simulations are consistent with the experimental results.

2010-11-01

91

Electronic Resonance and Symmetry in Single-Molecule Inelastic Electron Tunneling  

Energy Technology Data Exchange (ETDEWEB)

Inelastic electron tunneling spectroscopy and microscopy with a scanning tunneling microscope revealed two vibrational modes showing a decrease in conductance at {+-}82.0 and {+-}38.3 mV sample bias for single oxygen molecules chemisorbed on the fourfold hollow sites of Ag(110) surface at 13 K. The spatial distribution of the vibrational intensities exhibited {pi}{sub g} -orbital (perpendicular to surface) symmetry of O{sub 2} with the molecular axis along the [001] direction. These results are attributed to resonant inelastic electron tunneling. (c) 2000 The American Physical Society.

Hahn, J. R.; Lee, H. J.; Ho, W.

2000-08-28

92

Limitations in cooling electrons by normal metal - superconductor tunnel junctions  

CERN Document Server

We demonstrate both theoretically and experimentally two limiting factors in cooling electrons using biased tunnel junctions to extract heat from a normal metal into a superconductor. Firstly, when the injection rate of electrons exceeds the internal relaxation rate in the metal to be cooled, the electrons do no more obey the Fermi-Dirac distribution, and the concept of temperature cannot be applied as such. Secondly, at low bath temperatures, states within the gap induce anomalous heating and yield a theoretical limit of the achievable minimum temperature.

Pekola, J P; Savin, A M; Flyktman, J T; Giazotto, F; Hekking, F W J

2004-01-01

93

Observation of adsorbate-induced surface states by elastic electron tunneling spectroscopy  

International Nuclear Information System (INIS)

Electronic structure induced by adsorbates at the interface of Al/AlO/sub x//Au tunnel junctions has been observed by elastic electron tunneling spectroscopy. Strong structures appearing in the tunneling spectra above approx.1 eV after exposure to I, Hg, Bi, and organohalides, have been interpreted in terms of adsorbate-induced surface states. The spectroscopic capabilities of elastic electron tunneling spectroscopy may be useful in the area of chemical detection. In the broader sense, the observation of adsorbate-induced unoccupied electronic states below the vacuum energy, makes elastic electron tunneling spectroscopy a potentially useful technique for the study of surfaces

1985-09-15

94

Observation of adsorbate-induced surface states by elastic electron tunneling spectroscopy  

Science.gov (United States)

Electronic structure induced by adsorbates at the interface of Al/AlOx/Au tunnel junctions has been observed by elastic electron tunneling spectroscopy. Strong structures appearing in the tunneling spectra above approximately 1 eV after exposure to I, Hg, Bi, and organohalides, have been interpreted in terms of adsorbate-induced surface states. The spectroscopic capabilities of elastic electron tunneling spectroscopy may be useful in the area of chemical detection. In the broader sense, the observation of adsorbate-induced unoccupied electronic states below the vacuum energy, makes elastic electron tunneling spectroscopy a potentially useful technique for the study of surfaces.

Leduc, H. G.; Lambe, J.; Thakoor, A. P.; Khanna, S. K.

1985-01-01

95

Electron tunneling through sensitizer wires bound to proteins  

Science.gov (United States)

We report a quantitative theoretical analysis of long-range electron transfer through sensitizer wires bound in the active-site channel of cytochrome P450cam. Each sensitizer wire consists of a substrate group with high binding affinity for the enzyme active site connected to a ruthenium-diimine through a bridging aliphatic or aromatic chain. Experiments have revealed a dramatic dependence of electron transfer rates on the chemical composition of both the bridging group and the substrate. Using combined molecular dynamics simulations and electronic coupling calculations, we show that electron tunneling through perfluorinated aromatic bridges is promoted by enhanced superexchange coupling through virtual reduced states. In contrast, electron flow through aliphatic bridges occurs by hole-mediated superexchange. We have found that a small number of wire conformations with strong donor-acceptor couplings can account for the observed electron tunneling rates for sensitizer wires terminated with either ethylbenzene or adamantane. In these instances, the rate is dependent not only on electronic coupling of the donor and acceptor but also on the nuclear motion of the sensitizer wire, necessitating the calculation of average rates over the course of a molecular dynamics simulation. These calculations along with related recent findings have made it possible to analyze the results of many other sensitizer-wire experiments that in turn point to new directions in our attempts to observe reactive intermediates in the catalytic cycles of P450 and other heme enzymes.

Hartings, Matthew R.; Kurnikov, Igor V.; Dunn, Alexander R.; Winkler, Jay R.; Gray, Harry B.; Ratner, Mark A.

2009-01-01

96

Attosecond correlation dynamics during electron tunnelling from molecules  

Digital Repository Infrastructure Vision for European Research (DRIVER)

Abstract We present analytical theory of strong field ionization of molecules, which takes into account rearrangement of multiple interacting electrons during the ionization process. We show that such rearrangement offers an alternative pathway to the ionization of orbitals more deeply bound than the Highest Occupied Molecular Orbital (HOMO). This pathway is not subject to the full exponential suppression characteristic of the direct tunnel ionization from the deeper orbitals. The departin...

2010-01-01

97

Simulation of single-electron tunnelling circuits using SPICE:  

Digital Repository Infrastructure Vision for European Research (DRIVER)

Single-electron tunnelling (SET) devices have very promising properties, like their extremely low power consumption, their extremely high switching speeds and their extremely small physical dimensions. Since the field of SET devices is far from being fully exploited, and their device properties seem very promising, the motivation for investigating these devices was enlarged. In the literature many SET models and SET circuit simulators can be found. Most of them are based on the orthodox theor...

2004-01-01

98

Managing electronic resources a LITA guide  

CERN Document Server

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

99

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

1998-01-01

100

Electron Tunneling in Lithium Ammonia Solutions Probed by Frequency-Dependent Electron-Spin Relaxation Studies  

Science.gov (United States)

Electron transfer or quantum tunneling dynamics for excess or solvated electrons in dilute lithium-ammonia solutions have been studied by pulse electron paramagnetic resonance (EPR) spectroscopy at both X- (9.7 GHz) and W-band (94 GHz) frequencies. The electron spin-lattice (T1) and spin-spin (T2) relaxation data indicate an extremely fast transfer or quantum tunneling rate of the solvated electron in these solutions which serves to modulate the hyperfine (Fermi-contact) interaction with nitrogen nuclei in the solvation shells of ammonia molecules surrounding the localized, solvated electron. The donor and acceptor states of the solvated electron in these solutions are the initial and final electron solvation sites found before, and after, the transfer or tunneling process. To interpret and model our electron spin relaxation data from the two observation EPR frequencies requires a consideration of a multi-exponential correlation function. The electron transfer or tunneling process that we monitor through the correlation time of the nitrogen Fermi-contact interaction has a time scale of (1–10)×10?12 s over a temperature range 230–290K in our most dilute solution of lithium in ammonia. Two types of electron-solvent interaction mechanisms are proposed to account for our experimental findings. The dominant electron spin relaxation mechanism results from an electron tunneling process characterized by a variable donor-acceptor distance or range (consistent with such a rapidly fluctuating liquid structure) in which the solvent shell that ultimately accepts the transferring electron is formed from random, thermal fluctuations of the liquid structure in, and around, a natural hole or Bjerrum-like defect vacancy in the liquid. Following transfer and capture of the tunneling electron, further solvent-cage relaxation with a timescale of ca. 10?13 s results in a minor contribution to the electron spin relaxation times. This investigation illustrates the great potential of multi-frequency EPR measurements to interrogate the microscopic nature and dynamics of ultra fast electron transfer or quantum-tunneling processes in liquids. Our results also impact on the universal issue of the role of a host solvent (or host matrix, e.g. a semiconductor) in mediating long-range electron transfer processes and we discuss the implications of our results with a range of other materials and systems exhibiting the phenomenon of electron transfer.

Maeda, Kiminori; Lodge, Matthew T.J.; Harmer, Jeffrey; Freed, Jack H.; Edwards, Peter P.

2012-01-01

 
 
 
 
101

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

Science.gov (United States)

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

Nishioka, Hirotaka; Kakitani, Toshiaki

2008-08-14

102

Shifts and Dips in Inelastic Electron Tunneling Spectra Due to the Tunnel Junction Environment.  

Science.gov (United States)

In general, the tunnel junction environment has proved to be surprisingly benign; tunneling spectra of molecules included within tunnel junctions are similar to infrared and Raman spectra of molecules not covered by a metal electrode. Peak shifts have bee...

A. Bayman P. K. Hansma W. C. Kaska

1981-01-01

103

Evidence of strong electron-phonon interaction in superconducting MgB$_2$ from electron tunneling  

Digital Repository Infrastructure Vision for European Research (DRIVER)

We report tunneling measurements of the electron-phonon (e-ph) interaction in superconducting MgB$_2$ using the MgB$_2$-I-Nb junctions, where I stands for insulator. The phonon structure in tunneling density of states in MgB$_2$ clearly indicates strong e-ph coupling for the E$_{2g}$ in-plane boron phonons in a narrow range around 60 meV. The Eliashberg spectral function $\\alpha^2(\\omega)F(\\omega)$ reconstructed from the tunneling data, exhibits significant additional contri...

D Yachenko, A. I.; Tarenkov, V. Yu; Abal Oshev, A. V.; Lewandowski, S. J.

2002-01-01

104

Quantum tunneling transport of electrons in double-barrier heterostructures  

International Nuclear Information System (INIS)

Not only has the miniaturization penetrated the field of micro-electronics to the point that the quantum character of matter has to be reckoned with, but also there is nowadays a new class of semiconductor structures, the operation of which is directly based on quantum mechanical phenomena such as tunneling. These developments are interesting both from the viewpoint of applications and for reasons of theoretical modeling. An important class of these nanostructures is constituted by the heterojunction superlattices having two or more barriers, the shortest of which - the Double-Barrier Resonant-Tunneling (DBRT) diode -has been chosen for a model system in our study. An interesting property of DBRT structures is the negative differential resistance (NDR) in the current-voltage characteristics, making them useful components in amplifiers, mixers and detectors. If the structure parameters are chosen favourably, the charge build-up in the well between the barriers is sufficiently substantial to give cause to a current bistability in the NDR region. In this thesis, a DBRT model is presented, in which the electric current is considered a tunnel current of coherently propagating electron waves between two reservoirs. Varying the external bias voltage, one can tune the resonance energy in the well with respect to the Fermi seas in the reservoirs. The electrostatic feed-back due to the charge displacements in the structure is taken into account in the Hartree approximation. Both the NDR and the bistability are within the domain of this model. (orig.)

1993-01-01

105

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

Energy Technology Data Exchange (ETDEWEB)

A low-temperature scanning tunneling microscope (STM) was used to investigate the adsorption state of a single methyl isocyanide (MeNC) molecule on the Pt(111) surface at 4.7 K. We found that MeNC was resolved as a round-shaped protrusion in the STM image. The STM image of paired MeNC is highly protruded in comparison with that of isolated MeNC due to the charge transfer from Pt to MeNC. Inelastic electron tunneling spectroscopy with the STM system (STM-IETS) was also employed in order to reveal the adsorption state of individual MeNC molecules on Pt(111). The STM-IETS spectrum of MeNC exhibits peaks at 8, 48 and 375 mV. Referring to the vibrational spectra reported previously, we assigned these peaks to the frustrated translation mode, PtC stretching mode and CH{sub 3} stretching mode, respectively. The absence of other vibrational modes could be due to a reduction of the elastic tunneling current.

Katano, Satoshi [Research Institute of Electrical Communication, Tohoku University, 2-1-1 Katahira, Aoba-ku, Sendai 980-8577 (Japan); Kim, Yousoo; Hori, Masafumi; Kawai, Maki [Surface Chemistry Laboratory, RIKEN, 2-1 Hirosawa, Wako, Saitama 351-0198 Japan (Japan); Trenary, Michael, E-mail: maki@riken.j, E-mail: skatano@riec.tohoku.ac.j [Department of Chemistry, University of Illinois at Chicago, 845 West Taylor Street, Chicago, Illinois 60607-7061 (United States)

2010-06-01

106

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

International Nuclear Information System (INIS)

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

2010-06-01

107

Electronic transport properties of magnetic tunnel junctions at high temperatures  

Energy Technology Data Exchange (ETDEWEB)

In this contribution the results of electronic transport measurements on magnetic tunnel junctions (MTJs) at high temperatures are presented. Two types of magnetic tunnel junctions were investigated. First, junctions based on the half-Heusler alloy CoMnSb with a Curie-temperature of about 500 K. And second, CoFeB/MgO/CoFeB junctions, which were characterized in-situ during an annealing process and after a conventional annealing. The evolution of the TMR effect with temperature and bias voltage of the CoMnSb based junctions is discussed as well as the temperature dependence of the TMR effect and the resistance of CoFeB/MgO/CoFeB-junctions.

Meinert, Markus; Schmalhorst, Jan; Ebke, Daniel; Thomas, Andy; Reiss, Guenter [Department of Physics, Bielefeld University (Germany)

2009-07-01

108

Electronic transport properties of magnetic tunnel junctions at high temperatures  

International Nuclear Information System (INIS)

In this contribution the results of electronic transport measurements on magnetic tunnel junctions (MTJs) at high temperatures are presented. Two types of magnetic tunnel junctions were investigated. First, junctions based on the half-Heusler alloy CoMnSb with a Curie-temperature of about 500 K. And second, CoFeB/MgO/CoFeB junctions, which were characterized in-situ during an annealing process and after a conventional annealing. The evolution of the TMR effect with temperature and bias voltage of the CoMnSb based junctions is discussed as well as the temperature dependence of the TMR effect and the resistance of CoFeB/MgO/CoFeB-junctions.

2009-03-22

109

Inelastic electron tunneling spectroscopy at local defects in graphene  

CERN Document Server

We address local inelastic scattering from vibrational impurity adsorbed onto graphene and the evolution of the local density of electron states near the impurity from weak to strong coupling regime. For weak coupling the local electronic structure is distorted by inelastic scattering developing peaks/dips and steps. These features should be detectable in the inelastic electron tunneling spectroscopy, $d^2I/dV^2$, using local probing techniques. Inelastic Friedel oscillations distort the spectral density at energies close to the inelastic mode. In the strong coupling limit, a local negative $U$-center forms in the atoms surrounding the impurity site. For those atoms, the Dirac cone structure is fully destroyed. We further consider the effects of the negative $U$ formation and its evolution from weak to strong coupling. The negative $U$-site effectively acts as local impurity such that sharp resonances appear in the local electronic structure. The main resonances are caused by elastic scattering off the impuri...

Fransson, J; Pietronero, L; Balatsky, A V

2013-01-01

110

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

111

Scanning electron and tunneling microscopy of palladium-barium emitters  

Energy Technology Data Exchange (ETDEWEB)

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

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

2003-06-15

112

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

2008-06-01

113

Metallic single-electron transistor without traditional tunnel barriers  

International Nuclear Information System (INIS)

We report a new type of single-electron transistor (SET) comprising two highly resistive Cr thin-film strips (? 1 ?m long) connecting a 1 ?m-long Al island to two Al outer electrodes. These resistors replace small-area oxide tunnel junctions of traditional SETs. Our transistor with a total asymptotic resistance of 110 k? showed a very sharp Coulomb blockade and reproducible, deep and strictly e-periodic gate modulation in wide ranges of bias currents I and gate voltages Vg. In the Coulomb blockade region (|V| ? about 0.5 mV), we observed a strong suppression of the co-tunneling current allowing appreciable modulation curves V(Vg) to be measured at currents I as low as 100 fA. The noise figure of our SET was found to be similar to that of typical Al/AlOx/Al single-electron transistors, viz. ?Q ? 5 x 10-4e/?Hz at 10 Hz. (5. superconductor-metal-insulator transitions)

2001-10-01

114

Electronic characterization of individual monolayer protected Au clusters by single electron tunneling force spectroscopy  

International Nuclear Information System (INIS)

Gold monolayer protected clusters (MPCs) exhibit strong quantum confinement effects and size dependent electronic, optical and chemical properties. Chemical tuning of these properties can be achieved by established synthesis methods, providing an excellent system for the study of the relationship between chemical and electronic structure. In this paper, the first electronic spectra of individual Au MPCs (Au25) acquired by single electron tunneling force spectroscopy on non-conducting silicon dioxide surfaces are reported. A HOMO-LUMO (highest occupied molecular orbital-lowest unoccupied molecular orbital) energy gap is observed in the Au25 spectra. Hysteretic charging of the particles is also observed while obtaining the energy spectra. The new single electron tunneling measurement methodology is described. A model explaining the measurements supports the existence of mid-HOMO-LUMO gap defect states.

2010-07-23

115

Electronic characterization of individual monolayer protected Au clusters by single electron tunneling force spectroscopy  

Energy Technology Data Exchange (ETDEWEB)

Gold monolayer protected clusters (MPCs) exhibit strong quantum confinement effects and size dependent electronic, optical and chemical properties. Chemical tuning of these properties can be achieved by established synthesis methods, providing an excellent system for the study of the relationship between chemical and electronic structure. In this paper, the first electronic spectra of individual Au MPCs (Au{sub 25}) acquired by single electron tunneling force spectroscopy on non-conducting silicon dioxide surfaces are reported. A HOMO-LUMO (highest occupied molecular orbital-lowest unoccupied molecular orbital) energy gap is observed in the Au{sub 25} spectra. Hysteretic charging of the particles is also observed while obtaining the energy spectra. The new single electron tunneling measurement methodology is described. A model explaining the measurements supports the existence of mid-HOMO-LUMO gap defect states.

Zheng, N; Johnson, J P; Williams, C C [Department of Physics, University of Utah, Salt Lake City, UT 84112 (United States); Wang, G, E-mail: clayton@physics.utah.edu [Department of Chemistry, George State University, Atlanta, GA 30302 (United States)

2010-07-23

116

Inelastic electron tunneling spectroscopy at local defects in graphene  

Science.gov (United States)

We address local inelastic scattering from the vibrational impurity adsorbed onto graphene and the evolution of the local density of electron states near the impurity from a weak to strong coupling regime. For weak coupling the local electronic structure is distorted by inelastic scattering developing peaks or dips and steps. These features should be detectable in the inelastic electron tunneling spectroscopy d2I/dV2 using local probing techniques. Inelastic Friedel oscillations distort the spectral density at energies close to the inelastic mode. In the strong coupling limit, a local negative U center forms in the atoms surrounding the impurity site. For those atoms, the Dirac cone structure is fully destroyed, that is, the linear energy dispersion as well as the V-shaped local density of electron states is completely destroyed. We further consider the effects of the negative U formation and its evolution from weak to strong coupling. The negative U site effectively acts as a local impurity such that sharp resonances appear in the local electronic structure. The main resonances are caused by elastic scattering off the impurity site, and the features are dressed by the presence of vibrationally activated side resonances. Going from weak to strong coupling, changes the local electronic structure from being Dirac-cone-like including midgap states, to a fully destroyed Dirac cone with only the impurity resonances remaining.

Fransson, J.; She, J.-H.; Pietronero, L.; Balatsky, A. V.

2013-06-01

117

Molecular Transport Junctions: Propensity Rules for Inelastic Electron Tunneling Spectra  

CERN Document Server

We develop a series of propensity rules for interpreting Inelastic Electron Tunneling (IET) spectra of single-molecule transport junctions. IETS has no selection rules, such as those seen in optical, infrared and Raman spectra, because IETS features arise not from the field-dipole interaction characterizing these other spectroscopies, but from vibronic modification of the electronic levels. Expansion of the Landauer-Imry formula in Taylor series in molecular normal coordinates gives a convenient, accurate perturbation-type formula for calculating both frequency and intensity of the IETS spectrum. Expansion in a Dyson-like form permits derivation of propensity rules, both symmetry-based and pathway-deduced, allowing correlation of structure and coupling geometry with the IETS spectrum. These propensity rules work very well for the calculated spectrum of four typical molecular bridges.

Troisi, A; Troisi, Alessandro; Ratner, Mark A.

2006-01-01

118

Metallic single-electron transistor without traditional tunnel barriers  

CERN Document Server

We report on a new type of single-electron transistor (SET) comprising two highly resistive Cr thin-film strips (~ 1um long) connecting a 1 um-long Al island to two Al outer electrodes. These resistors replace small-area oxide tunnel junctions of traditional SETs. Our transistor with a total asymptotic resistance of 110 kOhm showed a very sharp Coulomb blockade and reproducible, deep and strictly e-periodic gate modulation in wide ranges of bias currents I and gate voltages V_g. In the Coulomb blockade region (|V| < 0.5 mV), we observed a strong suppression of the cotunneling current allowing appreciable modulation curves V-V_g to be measured at currents I as low as 100 fA. The noise figure of our SET was found to be similar to that of typical Al/AlOx/Al single-electron transistors.

Krupenin, V A; Presnov, D E; Savvateev, M N; Niemeyer, J C

2000-01-01

119

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

120

Inelastic electron tunneling spectroscopy: A route to the identification of the tip-apex structure  

Digital Repository Infrastructure Vision for European Research (DRIVER)

The vibrational spectrum of a tunneling junction on a clean Cu(111) surface has been characterized by vibrational density of states calculations and inelastic electron tunneling spectroscopy technique. We demonstrate that the achieved spectrum consists not only of vibrational modes excited by the tunneling electrons on the clean surface but also of modes characteristic of the structure of the tip apex. This allows to identify unequivocally the atomic structure of the tip, which is still the l...

Vitali, Lucia; Borisova, S. D.; Rusina, G. G.; Chulkov, Eugene V.; Kern, Klaus

2010-01-01

 
 
 
 
121

Resource Letter: TE-1: Teaching electronics  

Science.gov (United States)

This Resource Letter examines the evolution, roles, and content of courses in electronics in the undergraduate physics curriculum, and provides a guide to resources for faculty teaching such courses. It concludes with a brief section addressing problems of electromagnetic interference in electronic systems, and provides an introduction to the literature and practice of electromagnetic compatibility. I have included textbooks, reference books, articles, collections of laboratory experiments and projects, sources of equipment and parts, software packages, videos, and websites.

Henry, Dennis C.

2002-01-01

122

Managing Electronic Resources with Open Source Software  

Digital Repository Infrastructure Vision for European Research (DRIVER)

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

Roën Janyk; Sandra Wong

2012-01-01

123

Manipulating photon emission efficiency with local electronic states in a tunneling gap.  

Science.gov (United States)

We demonstrate manipulation of photon emission efficiency in a tunneling gap by tuning the rates of elastic and inelastic electron tunneling processes with local electronic states. The artificial local electronic states are created by a scanning tunneling microscope tip on a CuN nanoisland grown on a Cu(100) surface at cryogenic temperature. These local electronic states can either enhance or suppress the excitation of tip-induced surface plasmon modes at specific bias voltages, and thus the induced photon emission rates. A theoretical model quantitatively analyzing inelastic and elastic tunneling processes associated with characteristic electronic states shows good agreement with experiments. We also show that tip-induced photon emission measurement can be used for probing the electronic states in the tunneling gap. PMID:24718199

Chen, Peng; Wang, Weihua; Lin, Nian; Du, Shengwang

2014-04-01

124

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.

Hsiao Hsuan Cheng

2012-10-01

125

Evidence of strong electron-phonon interaction in superconducting MgB$_2$ from electron tunneling  

CERN Multimedia

We report tunneling measurements of the electron-phonon (e-ph) interaction in superconducting MgB$_2$ using the MgB$_2$-I-Nb junctions, where I stands for insulator. The phonon structure in tunneling density of states in MgB$_2$ clearly indicates strong e-ph coupling for the E$_{2g}$ in-plane boron phonons in a narrow range around 60 meV. The Eliashberg spectral function $\\alpha^2(\\omega)F(\\omega)$ reconstructed from the tunneling data, exhibits significant additional contribution into e-ph interaction from other vibrations such as acoustic ($\\sim 38$ meV) and optical ($\\sim 90$ meV) bands. Our results are in reasonable agreement with neutron scattering experiments, and also to some data of Raman and infrared spectroscopy.

Dyachenko, A T; Abalioshev, A V; Lewandowski, S J

2002-01-01

126

Thermally stimulated tunneling of electrons from deep traps: a new phenomenon  

International Nuclear Information System (INIS)

A new phenomenon of electron tunneling is reported. During the phosphorescence decay of MgO:Li:Eu 10"-"3 at 480 K it was observed that the electrons from 550K trapping group tunnel into shallow traps. This tunneling is evident from the peak in the decay curve. It is observed that the location of the peak depends on the ambient temperature, dose of excitation and thermal/ excitation history of the sample. It is observed that the charge nature of the trapping groups also determines the possibility of electron tunneling. Thermal stimulation is required in the form of a higher ambient temperature. It is shown that this type of tunneling is different from those known at present, namely the tunneling due to infrared and electric or magnetic field stimulation. (author)

1985-10-01

127

Resonant electron tunneling in a tip-controlled potential landscape  

Science.gov (United States)

By placing the biased tip of an atomic force microscope at a specific position above a semiconductor surface we can locally shape the potential landscape. Inducing a local repulsive potential in a two-dimensional electron gas near a quantum point contact, one obtains a potential minimum which exhibits a remarkable behavior in transport experiments at high magnetic fields and low temperatures. In such an experiment, we observe distinct and reproducible oscillations in the measured conductance as a function of magnetic field, voltages, and tip position. They follow a systematic behavior consistent with a resonant tunneling mechanism. From the periodicity in the magnetic field we can find the characteristic width of this minimum to be of the order of 100 nm. Surprisingly, this value remains almost the same for different values of the bulk filling factors, although the tip position has to be adjusted by distances of the order of one micron.

Pascher, Nikola; Timpu, Flavia; Rössler, Clemens; Ihn, Thomas; Ensslin, Klaus; Reichl, Christian; Wegscheider, Werner

2014-06-01

128

Electronic transport through EuO spin filter tunnel junctions  

International Nuclear Information System (INIS)

Spin filter tunnel junctions based on europium monoxide (EuO), a ferromagnetic semiconductor, are investigated by means of density functional theory. In particular, the spin transport of Cu/EuO/Cu junctions is investigated by using the self-consistent ab-initio electron transport code SMEAGOL. The dependence of the transmission coefficient on the interface spacing and on the EuO thickness is studied, and explained in terms of the density of states and the complex band structure of EuO. Our calculation indicates that EuO epitaxially grown on Cu can act as a perfect spin filter, with polarization close to 100%, which is related mainly to the Eu-4f states. The transmission coefficient is sensitive to the interface spacing, since this spacing determines the charge transfer between EuO and the Cu leads.

2012-03-25

129

Electronic transport through EuO spin filter tunnel junctions  

Energy Technology Data Exchange (ETDEWEB)

Spin filter tunnel junctions based on europium monoxide (EuO), a ferromagnetic semiconductor, are investigated by means of density functional theory. In particular, the spin transport of Cu/EuO/Cu junctions is investigated by using the self-consistent ab-initio electron transport code SMEAGOL. The dependence of the transmission coefficient on the interface spacing and on the EuO thickness is studied, and explained in terms of the density of states and the complex band structure of EuO. Our calculation indicates that EuO epitaxially grown on Cu can act as a perfect spin filter, with polarization close to 100%, which is related mainly to the Eu-4f states. The transmission coefficient is sensitive to the interface spacing, since this spacing determines the charge transfer between EuO and the Cu leads.

Jutong, Nuttachai; Eckern, Ulrich [Institut fuer Physik, Universitaet Augsburg, 86135 Augsburg (Germany); Rungger, Ivan; Sanvito, Stefano [School of Physics and CRANN, Trinity College Dublin, Dublin (Ireland); Schwingenschloegl, Udo [KAUST, PSE Division, Thuwal 23955-6900, Kingdom of Saudi Arabia (Saudi Arabia)

2012-07-01

130

Spurious signals generated by electron tunneling on large reflector antennas  

Science.gov (United States)

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

Higa, W. H.

1975-01-01

131

Electron Tunneling, a Quantum Probe for the Quantum World of Nanotechnology  

Science.gov (United States)

A quantum-mechanical probe is essential to study the quantum world, which is provided by electron tunneling. A spectroscopic mapping to image the electron-transport pathways on a sub-molecular scale is used.

Hipps, K. W.; Scudiero, L.

2005-01-01

132

Computer simulation of decay of trapped electrons in glassy matrices by tunnelling to scavenger molecules  

International Nuclear Information System (INIS)

The kinetics of decay of trapped electrons via tunnelling to acceptor molecules in a glassy matrix was computed by the method of stochastic simulation. The kinetic curves of electron decay were obtained for different concentrations of electron acceptor in the matrix. The results of the simulation are compared with the corresponding results calculated on the basis of certain kinetic models of the electron tunnelling in low-temperature glasses. (author)

1986-10-01

133

Shifts and dips in inelastic-electron-tunneling spectra due to the tunnel-junction environment  

International Nuclear Information System (INIS)

In general, the tunnel-junction environment has proved to be surprisingly benign; tunneling spectra of molecules included within tunnel junctions are similar to infrared and Raman spectra of molecules not covered by a metal electrode. Peak shifts have been typically less than the linewidth of the peaks, and peaks intensities have been comparable to infrared and Raman intensities. Here we report a different situation for tunnel junctions containing molecules adsorbed on metal particles. Specifically, we find that different-top-metal electrodes give different tunneling spectra for CO on alumina-supported iron and rhodium particles. Though metals with similar atomic radii give similar spectra, metals with dissimilar atomic radii can give qualitatively different spectra. We also find anomalies concerning intensities. Specifically, for methyl isocyanide adsorbed on alumina-supported rhodium particles, the strongest peak in the infrared spectrum, the --NequivalentC stretching mode, appears as a dip in the tunneling spectrum

1981-09-01

134

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

Science.gov (United States)

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

Stock, T.; Nogami, J.

2014-02-01

135

Tunneling Rates of Electron Pumping in the R-SINIS Transistor  

Science.gov (United States)

We consider the influence of the electromagnetic fluctuations on the transport properties of a hybrid single electron transistor, consisting of superconducting electrodes and a normal-metal island, when operated as a turnstile. We derive the analytic expressions for the rates near the thresholds of single electron tunneling, Andreev reflection, and Cooper-pair-electron cotunneling processes. These results show that the dissipative on-chip impedance suppresses the rates of the undesirable higher-order tunneling processes much stronger than the single electron tunneling which can therefore be utilized to increase the accuracy of such a device in quantum metrological applications.

Bubanja, Vladimir

2014-05-01

136

Direct evidence of electron tunneling in the ionization of sputtered atoms  

International Nuclear Information System (INIS)

Direct evidence has been obtained for electron tunneling between sputtered Cs"+ ions and the solid surfaces from which they originate. Strong neutralization of the Cs"+ ions is observed whenever the tunneling channel is opened by changing the surface work function so that a crossing of the Fermi level by the Cs 6s level occurs. A tunneling model which takes the spatial dependences of the position and the width of the atomic level into account explains the data successfully

1059-01-00

137

On the multi-step tunneling model for electron scavenging in low-temperature glasses  

International Nuclear Information System (INIS)

A detailed analysis is given of the Hammill-Funabashi(HF) model for electron scavenging in low-temperature glasses. It is concluded that contrary to their assertion, HF model is based upon the tunneling mechanism. It is also shown that although HF model can be regarded as a multi-step tunneling model, it is not correct even as such. A correct formulation of the multi-step tunneling mode is presented. (author)

1981-01-01

138

Intervortex quasiparticle tunneling and electronic structure of multi-vortex configurations in type-II superconductors  

International Nuclear Information System (INIS)

The electronic spectrum of multivortex configurations in type-II superconductors is studied taking account of the effect of quasiparticle tunneling between the vortex cores. The tunneling is responsible for the formation of strongly coupled quasiparticle states for intervortex distances. Analyzing the resulting spectra of vortex clusters bonded by the quasiparticle tunneling it is found that this spectrum transformation results in the oscillatory behavior of the density of states at the Fermi level

2006-06-01

139

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

Digital Repository Infrastructure Vision for European Research (DRIVER)

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

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

2012-01-01

140

Donor-bridge-acceptor energetics determine the distance dependence of electron tunneling in DNA  

Digital Repository Infrastructure Vision for European Research (DRIVER)

Electron transfer (ET) processes in DNA are of current interest because of their involvement in oxidative strand cleavage reactions and their relevance to the development of molecular electronics. Two mechanisms have been identified for ET in DNA, a single-step tunneling process and a multistep charge-hopping process. The dynamics of tunneling reactions depend on both the distance between the electron donor and acceptor and the nature of the molecular bridge separating the donor and acceptor....

2002-01-01

 
 
 
 
141

Electron and phonon Cooling in a Superconductor - Normal Metal - Superconductor Tunnel Junction  

Digital Repository Infrastructure Vision for European Research (DRIVER)

We present evidence for the cooling of normal metal phonons by electron tunneling in a Superconductor - Normal metal - Superconductor tunnel junction. The normal metal electron temperature is extracted by comparing the device current-voltage characteristics to the theoretical prediction. We use a quantitative model for the phonon cooling that includes the electron-phonon coupling in the normal metal and the Kapitza resistance between the substrate and the metal. It gives an ...

Rajauria, Sukumar; Luo, P. S.; Fournier, T.; Hekking, F. W. J.; Courtois, H.; Pannetier, B.

2006-01-01

142

Atomic and electronic structure in collapsed carbon nanotubes evidenced by scanning tunneling microscopy  

Digital Repository Infrastructure Vision for European Research (DRIVER)

The electronic behavior of a radially collapsed armchair carbon nanotube encountered by scanning tunneling microscopy experiments is presented in a study that probes the electronic changes directly associated with the atomically resolved structural perturbations. The finite density of states obtained through scanning tunneling spectroscopy at the Fermi energy when the interspacing of the flattened faces does not allow for bond formation suggests that the electronic properties are slightly ...

2007-01-01

143

Inelastic electron tunneling spectroscopy of single-molecule junctions using a mechanically controllable break junction  

International Nuclear Information System (INIS)

We report the use of electrical measurements to identify simultaneously the number and type of organic molecules within metal-molecule-metal junctions. Our strategy combines analyses of single-molecule conductance and inelastic electron tunneling spectra, exploiting a nanofabricated mechanically controllable break junction. We found that the peak linewidth of the inelastic electron tunneling spectrum decreased as the modulation voltage and temperature decreased, and that the selection rule for inelastic electron tunneling spectroscopy agrees with that for Raman spectroscopy. Furthermore, the differential conductance curve of the single-molecule junction suggests that it has asymmetrical electrode-molecule coupling.

2009-10-28

144

Refrigerator based on the Coulomb barrier for single-electron tunneling  

Science.gov (United States)

We propose a remarkably simple electronic refrigerator based on the Coulomb barrier for single-electron tunneling. A fully normal single-electron transistor is voltage V biased at a gate position such that tunneling through one of the junctions costs an energy of about kBT?eV,EC, where T is the temperature and EC is the transistor charging energy. The tunneling in the junction with positive energy cost cools both leads attached to it. Immediate practical realizations of such a refrigerator make use of Andreev mirrors which suppress heat current while maintaining full electric contact.

Pekola, Jukka P.; Koski, Jonne V.; Averin, Dmitri V.

2014-02-01

145

Refrigerator based on the Coulomb barrier for single-electron tunneling  

Digital Repository Infrastructure Vision for European Research (DRIVER)

We propose a remarkably simple electronic refrigerator based on the Coulomb barrier for single-electron tunneling. A fully normal single-electron transistor is voltage V biased at a gate position such that tunneling through one of the junctions costs an energy of about k(B)T << eV, E-C, where T is the temperature and E-C is the transistor charging energy. The tunneling in the junction with positive energy cost cools both leads attached to it. Immediate practical realizations of such a refrige...

2014-01-01

146

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

International Nuclear Information System (INIS)

Electron tunneling leads to the transfer of trapped positive or negative charges by tens of angstrom in rigid matrices. Electron tunneling reactions occur after the radiolysis of a rigid inert matrix containing two added solutes. The ''initial'' species, the matrix, trapped electrons and trapped positive charges of ''holes'', can each react with either solute, and both negative and positive charges can be transferred from one solute to another. These reactions occur by long range tunneling. Trapped electrons can react with radiation-produced free radicals, and ion recombination can occur between all possible pairs of + and - species. Franck-Condon effects give energy specificity to charge transfer and ion recombination, and add sensitivity to molecular structure, solvation and H/D isotope effects. The specificity is important in photosynthesis and solar energy storage as well as radiation chemistry. Hopping versus tunneling seemed to be settled in favor of tunneling for intermolecular electron transfer at low temperature. Hopping is expected to become important in many media near room temperature, and thus cannot be conclusively ruled out in the reactions of trapped electrons. The tunneling effect in liquids is usually small, leading only to the increase of a few angstrom in reaction radius in low viscosity liquids, but tunneling effects can be quite important in overcoming steric hindrance or Coulomb repulsion. (Yamashita, S.)

1979-05-19

147

Characterization of hot electron transmission tunneling through the gap potential in scanning hot electron microscopy  

Science.gov (United States)

With the emitter/gap-potential/tip structure, we have studied the hot electron (HE) transmission properties used in scanning hot electron microscopy (SHEM). The rational and practical gap potential profile between two electrodes has been constructed based on the electrostatic image force and the jellium model. The transmission probability calculated using the constructed potential profile in this paper differs from that using conventional profiles appreciably. Dependencies of the transmission probability on the gap separation, HE energy, and the tunnel voltage have been made clear.

Zhang, B. Y.; Furuya, K.

2001-05-01

148

The use of tunnel diodes in impulsion electronics  

International Nuclear Information System (INIS)

The purpose of the paper is to describe the performance limits which can be expected with basic pulse systems using tunnel diodes. The first part of the paper studies the response of a tunnel diode to a current step, and to a square-wave current. The second part, as an illustration, describes some actual systems and their performance. (author)

1962-04-01

149

Reviewing the Electronic Resources & Libraries Conference  

Science.gov (United States)

The third Electronic Resources & Libraries (ER&L) conference gathered at Georgia Institute of Technology's Global Learning and Conference Center in Atlanta, Georgia, March 18-21, 2008. Over 360 attendees, from six countries and from 80% of the United States, represented their libraries and organizations resulting in a diverse and informative…

Tijerina, Bonnie

2008-01-01

150

Tunneling  

Science.gov (United States)

This web page illustrates the tunneling of a quantum wavepacket through potential barriers. Movies show the time-dependent properties of wavepackets interacting with various potential barriers and wells are shown. Issues related to energy and barrier width are considered, along with comparison to scattering by a potential well.

Michielsen, Kristel; De Raedt, Hans

2004-03-16

151

Integrated NIS electron-tunnelling refrigerator/superconducting bolometer  

International Nuclear Information System (INIS)

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

152

Self-consistent coupling between driven electron tunneling and electromagnetic propagation at terahertz frequencies  

Digital Repository Infrastructure Vision for European Research (DRIVER)

An accurate procedure for coupling (time-dependent) driven electron tunneling and electromagnetic propagation at terahertz frequencies cannot be developed neither with equivalent electric-circuit approximations nor using standard electromagnetic solvers. Alternatively, in this work, a full-physical time-dependent self-consistent algorithm for such coupling is presented. In order to demonstrate the numerical viability of the algorithm and to show the great interest of driven electron tunneling...

2008-01-01

153

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

CERN Document Server

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

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

2005-01-01

154

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. 2 dimensional kinetic analysis of the ion current distribution on the concave conductors is used to calibrate the probe for measuring 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. (authors)

Gunn, J.P. [Association Euratom-CEA Cadarache, 13 - Saint-Paul-lez-Durance (France). Dept. de Recherches sur la Fusion Controlee; Stoeckel, J.; Adamek, J.; Duran, I.; Hron, M.; Panek, R.; Zacek, F. [Association Euratom-IPP.CR, Institute of Plasma Physics, Prague (Czech Republic); Barina, O.; Hrach, R.; Vicher, M. [Charles University in Prague, Faculty of Mathematics and Physics (Czech Republic); Van Rompuy, T.; Beuele, P. de; Van Oost, G. [Ghent Univ., Dept. of Applied Physics (Belgium); Balan, P.; Schrittweiser, R. [Innsbruck Univ., Inst. for Ion Physics (Austria)

2003-07-01

155

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

International Nuclear Information System (INIS)

The tunnel probe is a new kind of Langmuir probe for use in the tokamak scrape-off layer. 2 dimensional kinetic analysis of the ion current distribution on the concave conductors is used to calibrate the probe for measuring 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. (authors)

2003-10-01

156

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

International Nuclear Information System (INIS)

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.)

2003-10-11

157

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

Digital Repository Infrastructure Vision for European Research (DRIVER)

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

Tull, Laura

2013-01-01

158

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.

Ivanov M. Yu.

2013-03-01

159

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

Digital Repository Infrastructure Vision for European Research (DRIVER)

The pseudospin-electron model with tunneling splitting of levels is considered. Generalization of dynamic mean-field method for systems with correlated hopping was applied to the investigation of the model. Electron spectra, electron concentrations, average values of pseudospins and grand canonical potential were calculated within the alloy-analogy approximation. Electron spectrum and dependencies of the electron concentrations on chemical potential were obtained. It was shown that in the all...

2006-01-01

160

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

Science.gov (United States)

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

Ji, Tao

 
 
 
 
161

Photon induced tunneling of electron through a graphene electrostatic barrier  

Energy Technology Data Exchange (ETDEWEB)

The influence of an external intense laser field on the tunneling transport (ballistic) of the Dirac fermions through a monolayer graphene electrostatic barrier is studied in the framework of the Floquet approach for a continuous wave, linearly polarized, monochromatic laser. The Klein tunneling is shown to be suppressed by the irradiation of a strong laser field, arising due to breaking of chiral symmetry. The symmetric nature of the field free angular transmission spectrum around the normal to the well-barrier interface is destroyed due to the additional coupling between the pseudo-spin and the time dependent vector potential. The energy distribution of the tunneling spectrum displays Fano resonance which is absent for a laser assisted conventional electrostatic barrier but similar to the case of quantum well structures, providing an optical tool to identify field free quasi bound states inside the graphene nanostructures.

Biswas, R. [Department of Physics, P.K. College, Contai, Purba Medinipur, West Bengal 721401 (India); Sinha, C. [Department of Theoretical Physics, Indian Association for the Cultivation of Science, Jadavpur, Kolkata 700032 (India)

2013-11-14

162

Photon induced tunneling of electron through a graphene electrostatic barrier  

International Nuclear Information System (INIS)

The influence of an external intense laser field on the tunneling transport (ballistic) of the Dirac fermions through a monolayer graphene electrostatic barrier is studied in the framework of the Floquet approach for a continuous wave, linearly polarized, monochromatic laser. The Klein tunneling is shown to be suppressed by the irradiation of a strong laser field, arising due to breaking of chiral symmetry. The symmetric nature of the field free angular transmission spectrum around the normal to the well-barrier interface is destroyed due to the additional coupling between the pseudo-spin and the time dependent vector potential. The energy distribution of the tunneling spectrum displays Fano resonance which is absent for a laser assisted conventional electrostatic barrier but similar to the case of quantum well structures, providing an optical tool to identify field free quasi bound states inside the graphene nanostructures

2013-11-14

163

Photon induced tunneling of electron through a graphene electrostatic barrier  

Science.gov (United States)

The influence of an external intense laser field on the tunneling transport (ballistic) of the Dirac fermions through a monolayer graphene electrostatic barrier is studied in the framework of the Floquet approach for a continuous wave, linearly polarized, monochromatic laser. The Klein tunneling is shown to be suppressed by the irradiation of a strong laser field, arising due to breaking of chiral symmetry. The symmetric nature of the field free angular transmission spectrum around the normal to the well-barrier interface is destroyed due to the additional coupling between the pseudo-spin and the time dependent vector potential. The energy distribution of the tunneling spectrum displays Fano resonance which is absent for a laser assisted conventional electrostatic barrier but similar to the case of quantum well structures, providing an optical tool to identify field free quasi bound states inside the graphene nanostructures.

Biswas, R.; Sinha, C.

2013-11-01

164

Electronics and electrotechnics in technical management of the Channel tunnel  

Energy Technology Data Exchange (ETDEWEB)

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

Pascal, A.

1995-07-01

165

Voltage-dependence of magnetoresistance in ferromagnetic tunneling junctions: a rigorous free electron model study  

CERN Multimedia

Spin-dependent tunneling current and tunneling magnetoresistance (MR) of ferromagnetic tunneling junctions have been calculated within the free electron model by solving rigorously the 3D Schroedinger equation for different bias voltages and barrier widths. It is found that in general, the MR would decrease with voltage and become negative at some large voltages, a trend in agreement with both earlier and recent experiments. Also, it is revealed that for certain barrier widths, the MR would oscillate with bias voltage, a prediction to be confirmed by experiments.

Liu, S S

2000-01-01

166

Identifying configuration and orientation of adsorbed molecules by inelastic electron tunneling spectra.  

Science.gov (United States)

Scanning tunneling microscopy (STM) topographical images and inelastic electron tunneling spectra (IETS) of a cis-2-butene molecule adsorbed on a Pd(110) surface have been simulated by first-principles calculations. Calculations have eliminated the ambiguity between the STM image and the adsorption orientation caused by the symmetry of the system and local chemical environment. A combination of STM images and IETS spectra has been shown to be particularly useful in determining the configuration of the molecule on the surface. PMID:20707581

Ren, Hao; Yang, Jinlong; Luo, Yi

2010-08-14

167

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

Digital Repository Infrastructure Vision for European Research (DRIVER)

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

2011-01-01

168

Strong-Field Tunneling from a Coherent Superposition of Electronic States  

Science.gov (United States)

Laser-induced tunnel ionization from a coherent superposition of electronic states in Ar+ is studied in a kinematically complete experiment. Within a pump-probe scheme a spin-orbit wave packet is launched through the first ionization step from the neutral species. The multielectron coherent wave packet is probed as a function of time by the second pulse which ionizes the system to Ar++. By measuring delay-dependent electron momentum distributions we directly image the evolution of the nonstationary multielectron wave function. Comparing the results with simulations we test common assumptions about electron momentum distributions and the tunneling process itself.

Fechner, Lutz; Camus, Nicolas; Ullrich, Joachim; Pfeifer, Thomas; Moshammer, Robert

2014-05-01

169

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

170

Making sense of the electronic resource marketplace: trends in health-related electronic resources.  

Digital Repository Infrastructure Vision for European Research (DRIVER)

Changes in the practice of medicine and technological developments offer librarians unprecedented opportunities to select and organize electronic resources, use the Web to deliver content throughout the organization, and improve knowledge at the point of need. The confusing array of available products, access routes, and pricing plans makes it difficult to anticipate the needs of users, identify the top resources, budget effectively, make sound collection management decisions, and organize th...

Blansit, B. D.; Connor, E.

1999-01-01

171

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

172

Darwin at the molecular scale: selection and variance in electron tunnelling proteins including cytochrome c oxidase  

Science.gov (United States)

Biological electron transfer is designed to connect catalytic clusters by chains of redox cofactors. A review of the characterized natural redox proteins with a critical eye for molecular scale measurement of variation and selection related to physiological function shows no statistically significant differences in the protein medium lying between cofactors engaged in physiologically beneficial or detrimental electron transfer. Instead, control of electron tunnelling over long distances relies overwhelmingly on less than 14?? spacing between the cofactors in a chain. Near catalytic clusters, shorter distances (commonly less than 7??) appear to be selected to generate tunnelling frequencies sufficiently high to scale the barriers of multi-electron, bond-forming/-breaking catalysis at physiological rates. We illustrate this behaviour in a tunnelling network analysis of cytochrome c oxidase. In order to surmount the large, thermally activated, adiabatic barriers in the 5–10?kcal?mol?1 range expected for H+ motion and O2 reduction at the binuclear centre of oxidase on the 103–105?s?1 time-scale of respiration, electron access with a tunnelling frequency of 109 or 1010?s?1 is required. This is provided by selecting closely placed redox centres, such as haem a (6.9??) or tyrosine (4.9??). A corollary is that more distantly placed redox centres, such as CuA, cannot rapidly scale the catalytic site barrier, but must send their electrons through more closely placed centres, avoiding direct short circuits that might circumvent proton pumping coupled to haems a to a3 electron transfer. The selection of distances and energetic barriers directs electron transfer from CuA to haem a rather than a3, without any need for delicate engineering of the protein medium to ‘hard wire’ electron transfer. Indeed, an examination of a large number of oxidoreductases provides no evidence of such naturally selected wiring of electron tunnelling pathways.

Moser, Christopher C; Page, Christopher C; Dutton, P. Leslie

2006-01-01

173

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

Science.gov (United States)

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

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

2012-01-01

174

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

Energy Technology Data Exchange (ETDEWEB)

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 (T approx. less than 200/sup 0/K).

Miller, John R.; Beitz, James V.

1979-01-01

175

Influence of Coulomb and proximity effects on electron tunneling through normal metal-superconductor interfaces  

International Nuclear Information System (INIS)

We develop a microscopic description of single and double electron tunneling through normal metal - superconductor interfaces in the presence of proximity and charging effects. In both ballistic and diffusive limits we derive the effective action for the system and show that its behavior can essentially depend on the physical boundary conditions in both normal and superconducting electrodes far from the tunnel barrier. We study quantum fluctuations of the charge at the NS interface due to virtual Andreev reflection which can substantially modify the Coulomb blockade for double electron tunneling. We also investigate the charge transfer through mesoscopic NS interfaces and NSN transistors in the presence of Coulomb effects for various physical situations. We describe a novel charge transfer mechanism in NSN structures - double electron cotunneling - and show that this mechanism can play an important role in the limit of relatively small external voltages. The results of our theory agree well with available experimental data. ((orig.))

1994-12-01

176

Possibility of the determination of tunneling parameters from experimental data on photoinduced electron transfer  

International Nuclear Information System (INIS)

The author proposes a simple method for determining the parameters (a and v) in the expression for the dependence of the tunneling probability (w) on the distance (r) between reactants (w=v exp (-2r/a)) for reactions involving tunneling electron transfer from electronically excited donor molecules to acceptor additions from experimental data on the photogeneration of radical ions. The method presented is based on the study of the dependence of the concentration of the unionized donor particles on the irradiation time. The method has been used to determine the tunneling parameters for photoinduced electron transfer from zinc and magnesium porphyrins to CCL_4 in glassy alcoholic matrices at 77 degrees K

1986-03-01

177

Tuning the electron transport at single donors in zinc oxide with a scanning tunnelling microscope  

Science.gov (United States)

In devices like the single-electron transistor the detailed transport properties of a nanostructure can be measured by tuning its energy levels with a gate voltage. The scanning tunnelling microscope in contrast usually lacks such a gate electrode. Here we demonstrate tuning of the levels of a donor in a scanning tunnelling microscope without a third electrode. The potential and the position of the tip are used to locally control band bending. Conductance maps in this parameter space reveal Coulomb diamonds known from three-terminal data from single-electron transistors and provide information on charging transitions, binding energies and vibrational excitations. The analogy to single-electron transistor data suggests a new way of extracting these key quantities without making any assumptions about the unknown shape of the scanning tunnelling microscope tip.

Zheng, Hao; Weismann, Alexander; Berndt, Richard

2014-01-01

178

Estimation of the acceleration ability for electrons in SiO2 and the tunneling effect  

International Nuclear Information System (INIS)

Silicon dioxide (SiO2) plays an important role in layered optimization scheme and solid-state cathodoluminescence (SSCL). Initially, it was believed that the SiO2 layer would (i) generate extra interface states contributing to a number of primary electrons available for exciting the luminescent centers, and/or (ii) act as acceleration layer resulted in gaining high energy for those electrons that would tunnel into the luminescent layer to excite luminescent centers. Based on the brightness vs. voltage (B-V) measurements, we deem that the latter case, i.e. acceleration and tunneling, is the dominant mechanism. A detailed discussion in terms of electrons acceleration and tunneling as the main contributions to the enhancement of brightness is presented

2006-03-01

179

FORMATION AND USE OF ELECTRONIC INFORMATION SCIENTIFIC AND EDUCATIONAL RESOURCES ?????????? ? ???????????? ????????????? ??????????? ???????-???????? ????????  

Digital Repository Infrastructure Vision for European Research (DRIVER)

The article presents the results of a study of one of the components of typical scientific electronic libraries – electronic information resources. The structure of electronic scientific information and educational resources allocated to their structure. The distribution of electronic information resources for the essential attributes: their properties, typology, for the creation, formation and storage technology. Based on the fact that the most promising way of information support of s...

????????, ?. ?.

2010-01-01

180

Transient localized electron dynamics simulation during femtosecond laser tunnel ionization of diamond  

International Nuclear Information System (INIS)

Highlights: ? A first-principles calculation of nonlinear electron–photon interactions when tunnel ionization dominates is presented. ? TDDFT is applied for the description of transient localized electrons dynamics. ? The relationships among average absorbed energy, Keldysh parameter and laser intensity are revealed. -- Abstract: A real-time and real-space time-dependent density-functional theory (TDDFT) is applied to simulate the nonlinear electron–photon interactions during femtosecond laser processing of diamond when tunnel ionization dominates. The transient localized electron dynamics including the electron excitation, energy absorption and electron density evolution are described in this Letter. In addition, the relationships among average absorbed energy, Keldysh parameter and laser intensity are revealed when the laser frequency is fixed.

2012-10-01

 
 
 
 
181

Quantum Tunneling Activity  

Science.gov (United States)

This resource provides an introductory activity on the basics of quantum tunneling. As the activity states, "Real-world examples are given to demonstrate the importance of this effect to modern technologies." The activity covers concepts such as crossing a barrier both at the macroscopic and microscopic scale, tunneling leakage in computer chips, tunnel injection and release in flash memory and DNA sequencing. This module allows students to test their knowledge as they go. The other educational modules in this series can be found here. Instructors and students are encouraged to sign up with the Electron Technologies site here before starting to use these materials.

2012-03-09

182

Potential barriers for electron tunnelling in low-temperature aqueous glasses (comparison of the computer simulation model with experiments)  

Energy Technology Data Exchange (ETDEWEB)

The experimental kinetic data on the trapped electron decay in 6 M NaOH aqueous glass doped with electron scavengers were analysed. The electron decay curves obtained by the computer simulation under assumption of the simple tunnelling mechanism of the electron transfer were fitted to the experimental decays. It was found that for a group of scavengers the optimization procedure works well and gives the average barrier height for electron tunnelling between 1.26 and 1.42 eV. There is however a numerous group of scavengers for which the simple tunnelling mechanism does not provide adequate simulated kinetics of the trapped electron decay. (author).

Feret, B.; Bartczak, W.M.; Kroh, J. (Politechnika Lodzka, Lodz (Poland). Katedra Chemii Radiacyjnej)

1991-01-01

183

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

184

Electron tunnelling in 1:1 ethylene glycol - water glasses at 77 K  

International Nuclear Information System (INIS)

The influence of the scavenger concentration on the optical density of electrons trapped in 1:1 ethylene glycol-water and 8 M NaOH glasses has been studied at 77 K. The results are interpreted in terms of tunnelling and dry electron scavenging. The values of ''inefficiency factors'' F characterizing the rate of tunnelling are evaluated. Samples were irradiated by ?-Co-60 rays with doses of 0.125 to 0.5 Mrad. The absorption spectra were recorded spectrophotometrically. ?-irradiated at 77 K glassy 50% EG shows a blue absorption band of esub(t)sup(-) with a maximum at 585 nm. (T.I.)

1977-05-20

185

Zero-bias anomaly of tunneling into the edge of a 2D electron system  

CERN Document Server

We investigate the electron tunneling into the edge of a clean weakly interacting two-dimensional electron gas. It is shown that the corresponding differential conductance G(V) has a cusp at zero bias, and is characterized by a universal slope |dG/dV| at V=0. This singularity originates from the electron scattering on the Friedel oscillation caused by the boundary of the system.

Shekhtman, L I

1995-01-01

186

Detecting Electronic States at Stacking Faults in Magnetic Thin Films by Tunneling Spectroscopy  

CERN Document Server

Co islands grown on Cu(111) with a stacking fault at the interface present a conductance in the empty electronic states larger than the Co islands that follow the stacking sequence of the Cu substrate. Electrons can be more easily injected into these faulted interfaces, providing a way to enhance transmission in future spintronic devices. The electronic states associated to the stacking fault are visualized by tunneling spectroscopy and its origin is identified by band structure calculations.

De Parga, A L V; Miranda, R

2000-01-01

187

Detecting Electronic States at Stacking Faults in Magnetic Thin Films by Tunneling Spectroscopy  

Digital Repository Infrastructure Vision for European Research (DRIVER)

Co islands grown on Cu(111) with a stacking fault at the interface present a conductance in the empty electronic states larger than the Co islands that follow the stacking sequence of the Cu substrate. Electrons can be more easily injected into these faulted interfaces, providing a way to enhance transmission in future spintronic devices. The electronic states associated to the stacking fault are visualized by tunneling spectroscopy and its origin is identified by band struc...

Parga, A. L. Vazquez; Garcia-vidal, F. J.; Miranda, R.

2000-01-01

188

Spectroscopic, topological, and electronic characterization of ultrathin a-CdTe:O tunnel barriers  

International Nuclear Information System (INIS)

Ultrathin oxygenated amorphous CdTe (a-CdTe:O) films are prepared by rf sputtering of CdTe in a background of argon or argon/nitrogen/oxygen mixtures. Atomic force microscopy (AFM) is used to characterize the films and shows that they have an island structure typical of most sputtered thin films. However, when sufficiently low powers and deposition rates are employed during sputtering, the resulting films are remarkably smooth and sufficiently thin for use as barrier layers in inelastic electron tunneling (IET) junctions. Four terminal current-voltage data are recorded for Al/a-CdTe:O/Pb tunnel junctions and conductance-voltage curves are derived numerically. WKB fits to the conductance-voltage curves are obtained using a two-component trapezoidal plus square (TRAPSQR) model barrier potential to determine values for the tunnel barrier parameters (height, shape, and width); these parameters are consistent with AFM topological measurements and values from similar devices reported in the literature. IET spectra are presented which confirm that electrons tunnel through ultrathin regions of the a-CdTe:O films, which contain aluminum oxide subregions in a manner consistent with the TRAPSQR barrier model. Because tunneling occurs predominantly through these ultrathin regions, IET spectroscopic data obtained are representative of states at, or within a few tenths of nanometers from, the surface and confirm that the a-CdTe:O surface stoichiometry is very sensitive to changes in the argon/oxygen/nitrogen concentration ratios during film growth. Full IET spectra, current-voltage, and conductance-voltage data are presented together with tunnel barrier parameters derived from (WKB) fits to the data. The results presented here indicate that inelastic electron tunneling spectroscopy is a useful tool for characterizing the surface states of a-CdTe:O and possibly other photovoltaic materials

2004-03-15

189

Charge transport and photon-assisted tunneling in the NSN single-electron transistor  

International Nuclear Information System (INIS)

We present extensive experimental data concerning charge transport and photon-assisted tunneling in the NSN single-electron transistor. At subgap bias voltages and low temperatures, the current through this system arises from a combination of Andreev reflection and single-electron tunneling. The experimental data clearly show the Coulomb blockade of Andreev reflection, as well as the ''trapping'' of quasiparticles on the superconducting island. The voltage thresholds for Andreev reflection and single-electron tunneling as well as the dependence of the Andreev current on the gate charge Q_0 are in excellent agreement with theory. The magnitude of the Andreev current agrees well with theory in which the probability of Andreev reflection is greatly enhanced by phase-coherent multiple scattering. When the sample is exposed to small amounts of microwave radiation, electron transport is modified dramatically and several additional features appear in the experimental data. These new features are well described by including the effects of photon-assisted tunneling which greatly increases the rates of energetically unfavorable single-electron transitions. Finally, we discuss why the SET transistor with a superconducting island is such a sensitive microwave detector and present an estimate of its ultimate sensitivity. ((orig.))

1994-12-01

190

Scanning tunneling spectrum of electrons confined in a rectangular quantum corral  

International Nuclear Information System (INIS)

We obtained the scanning tunneling spectrum (STS) of an electron confined in a rectangular quantum corral by considering the electron to be in a quasi-stationary state. Because of non-hermiticity of the Hamiltonian, the electron has a complex eigenenergy. The imaginary part gives the peak width coming mainly from the electron tunneling through a corral barrier. Our STS is consistent with the experimental spectrum that had been measured for electrons confined in a rectangular quantum corral. We obtained peak widths against energy levels and components of the STS which are constructed with quasi-stationary eigenstates. It is shown that normalization of a wavefunction by considering its time evolution is decisive in obtaining the proper STS. Moreover, we specified the position dependence of STS in relation to the image of the surface local density of states.

2009-06-03

191

Do trapped electrons tunnel to scavengers in irradiated alcohol glasses  

International Nuclear Information System (INIS)

It is suggested that electrons trapped in irradiated 95% alcohol glasses (+5%H2O) do not react with the scavenger molecules and probably recombine with geminate cations. The scavenging has been interpreted in terms of dry electron reaction. (Auth.)

1977-05-01

192

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

Directory of Open Access Journals (Sweden)

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

O.Ya.Farenyuk

2006-01-01

193

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

Science.gov (United States)

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

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

2012-06-01

194

Effect of electron topological transitions on sound absorption and tunnel structure properties  

International Nuclear Information System (INIS)

Some features of sound absorption near the electron topological transitions (ETT) in metals are analyzed in terms of the microscopic approach by the temperature diagramm technique. The changes in the electrophysical characteristics of tunnelling structures subject to ETT are also considered. Comparison is made with the available experimental results. 25 refs.; 7 figs

1988-01-01

195

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

Science.gov (United States)

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

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

2005-02-10

196

Selecting the tip electron orbital for scanning tunneling microscopy imaging with sub-ångström lateral resolution  

Digital Repository Infrastructure Vision for European Research (DRIVER)

We report on scanning tunneling microscopy (STM) studies performed with single crystalline W[001] tips on a graphite(0001) surface. Results of distance-dependent STM experiments with sub-ångström lateral resolution and density functional theory electronic structure calculations show how to controllably select one of the tip electron orbitals for high-resolution STM imaging. This is confirmed by experimental images reproducing the shape of the 5dxz,yz and 5dx2 ? y2 tungsten atomic orbitals...

Shvets, Igor; Bozhko, Sergey; Krasnikov, Sergey; Lubben, Olaf

2010-01-01

197

LETTER TO THE EDITOR: Hot electrons in the tunnelling ionization of atoms  

Science.gov (United States)

A compact analytical generalization of the Landau - Dykhne approach is derived that includes rescattering of electrons in the tunnelling ionization of atoms. It is used for calculations of electron energy spectra in the high-energy region. Most of the essential features of recent measurements are reproduced analytically, that is, the onset, the extent and the relative height of the plateau. Coulomb correction is taken into account in the calculations.

Smirnov, M. B.; Krainov, V. P.

1998-06-01

198

Insight into action spectroscopy for single molecule motion and reactions through inelastic electron tunneling.  

Science.gov (United States)

We propose a versatile formula that describes action spectra for vibrationally mediated reactions of single molecules with a scanning tunneling microscope. Spectral fitting of the formula to CO hopping and the configurational change of the cis-2-butene molecule on Pd(110) enables us to determine the vibrational energy, reaction order, and transition rate associated with anharmonic coupling between the modes excited by tunneling electrons and the reaction-coordinate modes. The formula proposed here is general and easy to apply to any vibrationally mediated motion and reaction of single molecules. PMID:20868059

Motobayashi, Kenta; Kim, Yousoo; Ueba, Hiromu; Kawai, Maki

2010-08-13

199

DNA - Nanoelectronics Realization of a Single Electron Tunneling Transistor and a Quantum Bit Element  

CERN Document Server

Based on the understanding that chemical bonds can act as tunnel junctions in the Coulomb blockade regime, and on the technical ability to coat a DNA strand with metal, we suggest that DNA can be used to built logical devices. We discuss two explicit examples: a Single Electron Tunneling Transistor (SET) and a Quantum Bit Element. These devices would be literally in the nano-meter scale and would be able to operate at room temperature. In addition they would be identical to each other, highly stable and would have a self assembly property.

Ben-Jacob, E; Caspi, S; Ben-Jacob, Eshel; Hermon, Ziv; Caspi, Shay

1998-01-01

200

Estimation of oxidation states of AlOx barriers in a tunneling junction by inelastic electron tunneling spectroscopy  

International Nuclear Information System (INIS)

Co/AlOx/Co with AlOx barriers of various oxidation states were fabricated and investigated using inelastic electron tunneling (IET) spectroscopy and X-ray photoelectron spectroscopy (XPS). XPS revealed that AlOx oxidized for 8 h contained an inhomogeneous distribution of metallic Al, whereas AlOx oxidized for 24 h contained a homogeneous distribution. The inhomogeneous and homogeneous distributions of metallic Al corresponded to asymmetric and symmetric IET spectra, respectively. These junctions showed peaks at ± 0.03 V. AlOx oxidized for 168 h contained no metallic Al, and this junction had no peaks, suggesting that peaks at ± 0.03 V originate from metallic Al.

2009-07-31

 
 
 
 
201

2D model for electron nonstationary tunneling through a double barrier and quantum control  

International Nuclear Information System (INIS)

Passing of an electron package through two-dimensional double barrier is studied. The wave package can be created by super short laser impulse, exciting localized electron of impurity center in the conductivity zone. The well, to which electron is tunneled the electron having potential of cylindrical symmetry, was considered. Programmable optics permits localization of the wave package in a chosen point of the well at a present moment of time. The effect of package localization occurs along with iridescent scattering, which is a well-known quantum-mechanical (as well as optical) phenomenon

2000-01-01

202

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

Scientific Electronic Library Online (English)

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

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

203

Electron tunneling from electronically excited states of isolated bisdisulizole-derived trianion chromophores following UV absorption.  

Science.gov (United States)

Photoelectron spectra of isolated [M-BDSZ](3-) (BDSZ = bisdisulizole, M = H, Li, Na, K, Cs) triply charged anions exhibit a dominant constant electron kinetic energy (KE) detachment feature, independent of detachment wavelengths over a wide UV range. Photoelectron imaging spectroscopy shows that this constant KE feature displays an angular distribution consistent with delayed rather than direct electron emission. Time-resolved pump-probe (388 nm/775 nm) two-colour photoelectron spectroscopy reveals that the constant KE feature results from two simultaneously populated excited states, which decay at different rates. The faster of the two rates is essentially the same for all the [M-BDSZ](3-) species, regardless of M. The slower process is associated with lifetimes ranging from several picoseconds to tens of picoseconds. The lighter the alkali cation is, the longer the lifetime of this state. Quantum chemical calculations indicate that the two decaying states are in fact the two lowest singlet excited states of the trianions. Each of the two corresponding photoexcitations is associated with significant charge transfer. However, electron density is transferred from different ends of the roughly chain-like molecule to its aromatic center. The energy (and therefore the decay rate) of the longer-lived excited state is found to be influenced by polarization effects due to the proximal alkali cation complexed to that end of the molecule. Systematic M-dependent geometry changes, mainly due to the size of the alkali cation, lead to M-dependent shifts in transition energies. At the constant pump wavelength this leads to different amounts of vibrational energy in the respective excited state, contributing to the variations in decay rates. The current experiments and calculations confirm excited state electron tunneling detachment (ESETD) to be the mechanism responsible for the observed constant KE feature. The ESETD phenomenon may be quite common for isolated multiply charged anions, which are strong fluorophores in the condensed phase - making ESETD useful for studies of the transient response of such species after electronic excitation. PMID:23549163

Winghart, Marc-Oliver; Yang, Ji-Ping; Kühn, Michael; Unterreiner, Andreas-Neil; Wolf, Thomas J A; Dau, Phuong D; Liu, Hong-Tao; Huang, Dao-Ling; Klopper, Wim; Wang, Lai-Sheng; Kappes, Manfred M

2013-05-14

204

Intervortex quasiparticle tunneling and electronic structure of multi-vortex configurations in type-II superconductors  

CERN Document Server

The electronic spectrum of multi-vortex configurations in type-II superconductors is studied taking account of the effect of quasiparticle tunneling between the vortex cores. The tunneling is responsible for the formation of strongly coupled quasiparticle states for intervortex distances $atunneling we find a transition from a set of degenerate Caroli - de Gennes - Matricon branches to anomalous branches similar to the ones in multi-quanta giant vortices. This spectrum transformation results in the oscillatory behavior of the density of states at the Fermi level as a function of $a$ and could be observed in mesoscopic superconductors and disordered flux line arrays in the bulk systems.

Melnikov, A S

2006-01-01

205

The Wigner time delay for laser induced tunnel-ionization via the electron propagator  

CERN Document Server

Recent attoclock experiments using the attsecond angular streaking technique enabled the measurement of the tunneling time delay during laser induced strong field ionization. Theoretically the tunneling time delay is commonly modelled by the Wigner time delay concept which is derived from the derivative of the electron wave function phase with respect to energy. Here, we present an alternative method for the calculation of the Wigner time delay by using the fixed energy propagator. The developed formalism is applied to the nonrelativistic as well as to the relativistic regime of the tunnel-ionization process from a zero-range potential, where in the latter regime the propagator can be given by means of the proper-time method.

Yakaboylu, Enderalp; Hatsagortsyan, Karen Z

2014-01-01

206

Local interlayer tunneling between two-dimensional electron systems in the ballistic regime  

Science.gov (United States)

We study a theoretical model of virtual scanning tunneling microscopy (VSTM) [A. Sciambi, M. Pelliccione, M. Lilly, S. Bank, A. Gossard, L. Pfeiffer, K. West, and D. Goldhaber-Gordon, arXiv:1008.0668 (unpublished); A. Sciambi, M. Pelliccione, S. R. Bank, A. C. Gossard, and D. Goldhaber-Gordon, Appl. Phys. Lett. 97, 132103 (2010)10.1063/1.3492440]: a proposed application of interlayer tunneling in a bilayer system to locally probe a two-dimensional electron system (2DES) in a semiconductor heterostructure. We consider tunneling for the case where transport in the 2DESs is ballistic and show that the zero-bias anomaly is suppressed by extremely efficient screening. Since such an anomaly would complicate the interpretation of data from VSTM, this result is encouraging for efforts to implement such a microscopy technique.

Luna, Katherine; Kim, Eun-Ah; Oreto, Paul; Kivelson, Steven A.; Goldhaber-Gordon, David

2010-12-01

207

Spin current in an electron waveguide tunnel-coupled to a topological insulator  

International Nuclear Information System (INIS)

We show that electron tunneling from edge states in a two-dimensional topological insulator into a parallel electron waveguide leads to the appearance of spin-polarized current in the waveguide. The spin polarization P can be very close to unity and the electron current passing through the tunnel contact splits in the waveguide into two branches flowing from the contact. The polarization essentially depends on the electron scattering by the contact and the electron-electron interaction in the one-dimensional edge states. The electron-electron interaction is treated within the Luttinger liquid model. The main effect of the interaction stems from the renormalization of the electron velocity, due to which the polarization increases with the interaction strength. Electron scattering by the contact leads to a decrease in P. A specific effect occurs when the bottom of the subbands in the waveguide crosses the Dirac point of the spectrum of edge states when changing the voltage or chemical potential. This leads to changing the direction of the spin current.

2012-10-10

208

Formation of hot electrons in noble gases by intense-field ionization: A quasistatic tunneling, independent-electron model  

International Nuclear Information System (INIS)

Recent experiments by Mohideen et al. [Phys. Rev. Lett. 71, 509 (1993)] demonstrated that more hot electrons result from high-intensity above-threshold ionization of atoms than had been predicted by existing models. In this paper we explain most of the discrepancy between the theory and experimental data on the basis of a quasistatic tunneling independent-electron (QTIE) model, formulated using a simple set of rate equations with quasistatic expressions for ionization probabilities. Because of the efficiency of the QTIE approach, one can easily perform calculations of strong-field ionization for many-electron atoms. We demonstrate the properties of tunneling ionization in applications to He, Ne, Ar, Kr, and Xe

1995-02-01

209

Fabrication of Tunnel Junctions For Direct Detector Arrays With Single-Electron Transistor Readout Using Electron-Beam Lithography  

Science.gov (United States)

This paper will describe the fabrication of small aluminum tunnel junctions for applications in astronomy. Antenna-coupled superconducting tunnel junctions with integrated single-electron transistor readout have the potential for photon-counting sensitivity at sub-millimeter wavelengths. The junctions for the detector and single-electron transistor can be made with electron-beam lithography and a standard self-aligned double-angle deposition process. However, high yield and uniformity of the junctions is required for large-format detector arrays. This paper will describe how measurement and modification of the sensitivity ratio in the resist bilayer was used to greatly improve the reliability of forming devices with uniform, sub-micron size, low-leakage junctions.

Stevenson, T. R.; Hsieh, W.-T.; Li, M. J.; Stahle, C. M.; Rhee, K. W.; Teufel, J.; Schoelkopf, R. J.

2002-01-01

210

You Have "How Many" Spreadsheets? Rethinking Electronic Resource Management  

Science.gov (United States)

As libraries face a veritable explosion of electronic resources and as the interconnectedness of print and online resources becomes increasingly complicated, many librarians are challenged to find efficient and cost-friendly ways to manage these resources. In this article, the authors describe how a team of people from various library departments…

Rux, Erika; Borchert, Theresa

2010-01-01

211

An adhesive study by electron tunnelling: Ethyl ?-cyanoacrylate adsorbed on an oxidized aluminium surface  

Science.gov (United States)

The interfacial properties of an adhesive system, ethyl ?-cyanoacrylate/aluminium, are investigated by the adsorption of a thin adhesive layer upon the Al oxide insulator of an Al?Pb tunnel junction. Such junctions exhibit electrical properties determined in part by the physical and chemical nature of the adsorbed layer. Inelastic electron tunnelling spectra, and resistance and capacitance data are presented which indicate that exposure of the oxide to pure adhesive vapour produces an inhomogeneous adsorbed layer, which increases in overall thickness with increasing vapour exposure time. By retarding vapour polymerization, a more uniform layer is adsorbed, whose thickness is less strongly dependent on exposure time. Tunnelling spectra agree well with those obtained using bulk i.r. spectroscopy (which are also presented here), allowing IET vibrational mode assignments to be inferred. Shifts in C?O and C?O-stretching frequencies are observed in the tunnelling spectrum of the uniform layer which have been attributed by other workers using a reflectance i.r. technique to adhesive hydrogen bonding at the oxide surface. The absence of C?C and ?CH 2 modes in the tunnelling spectra is indicative of cyanoacrylate polymerization at the monomolecular level. A chemical model of the interface based on this, and on peak intensity data, is presented.

Reynolds, S.; Oxley, D. P.; Pritchard, R. G.

212

Inelastic electron tunneling spectroscopy of gold-benzenedithiol-gold junctions: accurate determination of molecular conformation.  

Science.gov (United States)

The gold-benzenedithiol-gold junction is the classic prototype of molecular electronics. However, even with the similar experimental setup, it has been difficult to reproduce the measured results because of the lack of basic information about the molecular confirmation inside the junction. We have performed systematic first principles study on the inelastic electron tunneling spectroscopy of this classic junction. By comparing the calculated spectra with four different experimental results, the most possible conformations of the molecule under different experimental conditions have been successfully determined. The relationship between the contact configuration and the resulted spectra is revealed. It demonstrates again that one should always combine the theoretical and experimental inelastic electron tunneling spectra to determine the molecular conformation in a junction. Our simulations have also suggested that in terms of the reproducibility and stability, the electromigrated nanogap technique is much better than the mechanically controllable break junction technique. PMID:21309567

Lin, Li-Li; Wang, Chuan-Kui; Luo, Yi

2011-03-22

213

The Role of the Acquisitions Librarian in Electronic Resources Management  

Science.gov (United States)

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

Pomerantz, Sarah B.

2010-01-01

214

Anomalous tunneling of dressed Dirac electrons through potential barrier  

Science.gov (United States)

It has been shown that when a potential barrier is placed on a layer of graphene, electrons incident on the barrier head-on can be transmitted without any reflection, regardless of how high the barrier is made to become. This anomalous scattering has also been investigated in the case of bilayer graphene. The energy gap between the valence and conduction bands for bilayer graphene leads to perfect reflection for head-on collisions for all barrier heights. We report on results for reflection and transmission coefficients for dressed Dirac electrons when circularly polarized light is applied to graphene and an energy gap in the energy bands is opened up. Since this gap depends on the frequency and intensity, we investigate how the electron and hole scattering off a fixed barrier is modified by varying the energy gap produced by light. We also present results for the transmission for the perpendicular incidentce. Both numerical and analytical results are obtained.

Iurov, Andrii; Roslyak, Oleksiy; Gumbs, Godfrey

2011-03-01

215

Advanced electron microscopy of novel ferromagnetic materials and ferromagnet/oxide interfaces in magnetic tunnel junctions  

Science.gov (United States)

We have studied novel ferromagnetic (FM) materials and FM electrode/tunnel barrier interfaces in magnetic tunnel junctions (MTJs) by advanced electron microscopy including scanning transmission electron microscopy (HRSTEM) and electron energy loss spectroscopy (EELS). MTJs are one of the prototypical spintronic devices, with applications in magnetic random access memory, sensors and read heads. The performance of MTJs depends on several factors, including the FM electrodes and the FM/tunnel barrier interfaces. Therefore, to realize the high performance of MTJs, we first need high quality ferromagnetic electrodes with high spin polarization. High-quality Fe3O4 and Fe4N electrodes with theoretically predicted -100% spin polarization were fabricated by various methods and investigated by HRSTEM and STEM EELS. The Fe3O4 and Fe4N thin films have low defect density and good crystallinity, but when integrated as electrodes in a MTJ, problems emerged. In a Fe4N/AlOx/Fe MTJ, the magnetoresistance was negative, but relatively small, due to a defective Fe 3O4 reaction layer formed at the Fe4N/tunnel barrier interface revealed by HRSTEM and EELS. The interfacial reaction layer was thin and discontinuous which made direct imaging difficult. Therefore, STEM EELS was used to map out the reaction layer. A Fe3O4 reaction layer was also found in a nominally symmetric CoFe/AlOx/CoFe MTJs after annealing, which also exhibited inverse TMR and a non-symmetric bias dependence. We also investigated the MTJs with the Heusler alloy Co2MnSi as one or both electrode and crystalline MgO as the tunnel barrier, which exhibit quite high TMR due to coherent tunneling. We showed that the Co2MnSi/MgO interface in these junctions is dominated by a configuration of a pure Mn plane bonded across the interface to O. This was the first observation of that interface termination. HRSTEM images also show that the fraction of MnMn/O interface termination increases with increasing Mn concentration in the CMS electrode. With the help of electron microscopy, we have found methods to increase the TMR of MTJs with half metallic materials as electrodes including Fe3O4 and Co2MnSi. We believe that the potential of half metallic materials will be realized with the development of new materials and new design of FM/tunnel barrier interfaces.

Shi, Fengyuan

216

The impact of subject-specific electronic resources on the research process using ERIC (Education Resources Information Center) and SciFinder Scholar electronic resources as exemplars.  

Digital Repository Infrastructure Vision for European Research (DRIVER)

As part of a UK wide study attempting to assess the impact libraries have on the work and study of their members, Edinburgh University Library (EUL) decided to “measure the impact of subject-specific electronic resources on the research process”, using the ERIC (Education Resources Information Center) and SciFinder Scholar electronic resources as exemplars.

Love-rodgers, Christine; Stewart, Rowena

2006-01-01

217

Electron mobility variance in the presence of an electric field: Electron-phonon field-induced tunnel scattering  

Energy Technology Data Exchange (ETDEWEB)

The problem of electron mobility variance is discussed. It is established that in equilibrium semiconductors the mobility variance is infinite. It is revealed that the cause of the mobility variance infinity is the threshold of phonon emission. The electron-phonon interaction theory in the presence of an electric field is developed. A new mechanism of electron scattering, called electron-phonon field-induced tunnel (FIT) scattering, is observed. The effect of the electron-phonon FIT scattering is explained in terms of penetration of the electron wave function into the semiconductor band gap in the presence of an electric field. New and more general expressions for the electron-non-polar optical phonon scattering probability and relaxation time are obtained. The results show that FIT transitions have principle meaning for the mobility fluctuation theory: mobility variance becomes finite.

Melkonyan, S.V., E-mail: smelkonyan@ysu.am [Department of Physics of Semiconductors and Microelectronics, Yerevan State University, 1 Alex Manoogian Str., Yerevan 0025 (Armenia)

2012-12-15

218

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

219

Intensity analysis of inelastic tunneling due to excitation of electronic transitions in rare-earth oxides  

Science.gov (United States)

The electronic transitions 5I8?5I7 of Ho3+ and 4I15/2?4I13/2 of Er3+ ions have been previously observed by inelastic tunneling spectroscopy at 645 and 811 meV, respectively [A. Adane et al., Solid State Commun. 16, 1071 (1975)]. In this paper we present an analysis of the intensity of the observed structures in order to understand why the oscillator strengths obtained (fn0>10-5) are 10 times greater than those measured optically. We consider two interactions which might explain the phenomenon. The first arises from the mixing of 4fN and 4fN-15d configurations by the electric field in the tunnel junction. The second is due to the electric quadrupole interaction between the tunneling electron and the rare-earth ion. The latter seems to be more important and emphasizes the difference between the selection rules of tunneling and optical spectroscopies.

Adane, A.; Klein, J.; Leger, A.; Belin, M.; Defourneau, D.

1984-04-01

220

Tunneling between parallel two-dimensional electron liquids.  

Czech Academy of Sciences Publication Activity Database

. 361/362, - (1996), s. 167-170. ISSN 0039-6028.[International Conference on the Electronic Properties of Two Dimensional Systems /11./. Nottingham, 07.08.1995-11.08.1995]Grant CEP: GA ?R GA202/94/1278Grant ostatní: INT(XX) 9106888Impakt faktor: 2.783, rok: 1996

Jungwirth, Tomáš; MacDonald, A. H.

 
 
 
 
221

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

2012-02-01

222

Tunnelling through diamond-like carbon nanofilms deposited by electron-beam-induced deposition  

International Nuclear Information System (INIS)

The tunnelling properties in metal/diamond-like carbon (DLC)/semiconductor junctions and structural characteristics of thin DLC films produced using different electron beam conditions were studied. We show that under the same electron dose conditions, thicker DLC films were obtained using lower accelerating voltages (2 kV) than when using higher accelerating voltage (20 kV). However, under the settings used the thicker films showed worse insulating performance than the thinner films. We attribute this effect to the variation of tunnelling barrier height in DLC deposited using different accelerating voltages. DLC films with a tunnelling barrier height of up to 3.12 eV were obtained using a 20 kV electron-beam, while only 0.73 eV was achieved for 2 kV DLC films. The X-ray photoemission spectra of the C 1s core level in these films reveal components at 284.4 ± 0.1 eV and 285 ± 0.1 eV, which were identified as the sp2 and sp3 hybrid forms of carbon. The sp3/sp2 concentration ratio increased with increasing electron beam accelerating voltage. We show how this effect is responsible for the barrier height variation.

2009-10-30

223

Sensitivity of tunneling-rotational transitions in ethylene glycol to variation of electron-to-proton mass ratio  

Science.gov (United States)

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

Viatkina, A. V.; Kozlov, M. G.

2014-06-01

224

Single-electron tunneling in InP nanowires  

CERN Document Server

We report on the fabrication and electrical characterization of field-effect devices based on wire-shaped InP crystals grown from Au catalyst particles by a vapor-liquid-solid process. Our InP wires are n-type doped with diameters in the 40-55 nm range and lengths of several microns. After being deposited on an oxidized Si substrate, wires are contacted individually via e-beam fabricated Ti/Al electrodes. We obtain contact resistances as low as ~10 kOhm, with minor temperature dependence. The distance between the electrodes varies between 0.2 and 2 micron. The electron density in the wires is changed with a back gate. Low-temperature transport measurements show Coulomb-blockade behavior with single-electron charging energies of ~1 meV. We also demonstrate energy quantization resulting from the confinement in the wire.

De Franceschi, S; Bakkers, E P A M; Feiner, L F; Gurevich, L A; Kouwenhoven, Leo P

2003-01-01

225

Metadata for long-term preservation of electronic resources  

Digital Repository Infrastructure Vision for European Research (DRIVER)

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 overvie...

2004-01-01

226

Electronic Coolers Based on Superconducting Tunnel Junctions: Fundamentals and Applications  

Science.gov (United States)

Thermo-electric transport at the nano-scale is a rapidly developing topic, in particular in superconductor-based hybrid devices. In this review paper, we first discuss the fundamental principles of electronic cooling in mesoscopic superconducting hybrid structures, the related limitations and applications. We review recent work performed in Grenoble on the effects of Andreev reflection, photonic heat transport, phonon cooling, as well as on an innovative fabrication technique for powerful coolers.

Courtois, H.; Hekking, F. W. J.; Nguyen, H. Q.; Winkelmann, C. B.

2014-02-01

227

Spin-flip inelastic electron tunneling spectroscopy in atomic chains  

Digital Repository Infrastructure Vision for European Research (DRIVER)

We present a theoretical study of the spin transport properties of monoatomic magnetic chains with a focus on the spectroscopical features of the I - V curve associated with spin-flip processes. Our calculations are based on the s-d model for magnetism with the electron transport treated at the level of the nonequilibrium Green's function formalism. Inelastic spin-flip scattering processes are introduced perturbatively via the first Born approximation, and an expression for the associated sel...

2011-01-01

228

Electronic Coolers Based on Superconducting Tunnel Junctions: Fundamentals and Applications  

Science.gov (United States)

Thermo-electric transport at the nano-scale is a rapidly developing topic, in particular in superconductor-based hybrid devices. In this review paper, we first discuss the fundamental principles of electronic cooling in mesoscopic superconducting hybrid structures, the related limitations and applications. We review recent work performed in Grenoble on the effects of Andreev reflection, photonic heat transport, phonon cooling, as well as on an innovative fabrication technique for powerful coolers.

Courtois, H.; Hekking, F. W. J.; Nguyen, H. Q.; Winkelmann, C. B.

2014-06-01

229

Elastic and Inelastic Electron Tunneling in Molecular Devices  

Digital Repository Infrastructure Vision for European Research (DRIVER)

A theoretical framework for calculating electron transport through molecular junctions is presented. It is based on scattering theory using a Green's function formalism. The model can take both elastic and inelastic scattering into account and treats chemical and physical bonds on equal footing. It is shown that it is quite reliable with respect to the choice of functional and basis set. Applications concerning both elastic and inelastic transport are presented, though the emphasis is on the ...

Kula, Mathias

2006-01-01

230

Quantum coherence of bulk electrons on metals revealed by scanning tunneling spectroscopy  

Science.gov (United States)

The quantum dynamics of electrons in bulk states is investigated by scanning tunneling microscopy and spectroscopy on a Ag(100) surface. By measuring conductance maps above a threshold voltage, we observe standing waves at step edges and defects. We interpret these to originate from electrons in a bulk band edge at the ? point. From the spatially decaying waves, the wave vector and the quantum coherence parameters—coherence length, lifetime, and linewidth—are determined as a function of energy. We measure a coherence length of about 5-7 Å, which is order of magnitudes lower than typically observed for surface or image-potential states. The energy of the band edge is extracted from the dispersion relation and agrees with the peak measured in scanning tunneling spectra at 1.9 eV above the Fermi energy. Theoretical calculations confirm the nature of the state elucidating the experimental findings.

Ohmann, Robin; Toher, Cormac; Meyer, Jörg; Nickel, Anja; Moresco, Francesca; Cuniberti, Gianaurelio

2014-05-01

231

Intensity and line-shape measurements in inelastic electron tunneling spectroscopy  

International Nuclear Information System (INIS)

Two techniques for removing the background in inelastic electron tunneling spectroscopy (IETS) have been examined in detail. The first of these uses a polynomial least-squares routine to fit a smooth curve to the data on either side of the IETS peak, while the second relies on differential inelastic electron tunneling spectroscopy (DIETS) to subtract one spectrum from another in order to remove some unwanted IETS peaks. Both procedures were applied to spectra obtained from Al-Pb junctions with the lead normal and superconducting. One finds that it is easier to determine the background when the normal rather than superconducting lead is used, as the superconducting line shape has a broad undershoot. The intensity results shown here indicate that failure to consider the undershoot may result in errors as large as 30%. A comparison of theoretical and experimental line shapes is made for data with both normal and superconducting electrodes

1978-01-01

232

Electronic structure of EuO spin filter tunnel contacts directly on silicon  

Energy Technology Data Exchange (ETDEWEB)

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.)

Caspers, C.; Mueller, M. [Peter Gruenberg Institut (PGI-6), Forschungszentrum Juelich, 52425 Juelich (Germany); JARA Juelich-Aachen Research Alliance, Forschungszentrum Juelich, 52425 Juelich (Germany); Gray, A.X.; Fadley, C.S. [Department of Physics, University of California, Davis, California (United States); Materials Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, California (United States); Kaiser, A.M. [Peter Gruenberg Institut (PGI-6), Forschungszentrum Juelich, 52425 Juelich (Germany); Department of Physics, University of California, Davis, California (United States); Materials Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, California (United States); Gloskovskii, A. [Institut fuer Analytische und Anorganische Chemie, Johannes Gutenberg-Universitaet, 55128 Mainz (Germany); Drube, W. [DESY Photon Science, Deutsches Elektronen-Synchrotron, 22603 Hamburg (Germany); Schneider, C.M. [Peter Gruenberg Institut (PGI-6), Forschungszentrum Juelich, 52425 Juelich (Germany); JARA Juelich-Aachen Research Alliance, Forschungszentrum Juelich, 52425 Juelich (Germany); Fakultaet fuer Physik and Center for Nanointegration Duisburg-Essen (CeNIDE), 47048 Duisburg (Germany)

2011-12-15

233

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.)

2011-12-01

234

Role of tunnelling in reactions of electron transfer in initial stages of radiolysis of condensed media  

International Nuclear Information System (INIS)

It is shown that the efficiency, of an acceptor in reducing the yield of esub(sol)sup(-) is proportional to tausub(s), the electron solvation time. This result suggests that the reactive precursor of esub(sol)sup(-) taking part in chemical reactions under conditions of picosecond pulse radiolysis is the electron with underformed solvation shell. The electron transfer from shallow trap to acceptor proceeds by tunnelling as in the case of fully solvated state. The similarity of decay kinetics of solvating electron and that trapped at low temperatures is due to this circumstance. The equations for decay kinetics of trapped electron including trap-to-trap diffusion is obtained. It has been shown that linear decrease of H-atom concentration at low temperatures with square root of time is related to uneffective electron transfer from donor to acceptor

1977-01-01

235

Scanning tunnelling vibrational spectroscopy of single surface complexes and detection of single electron spins  

International Nuclear Information System (INIS)

New spectroscopic techniques employing the scanning tunnelling microscope are considered. The new methods allow measurements of the vibrational spectra of single surface complexes, determination of the nonequilibrium distributions of such complexes over vibrational levels, studies on the kinetics of vibrational transitions, determination of vibrational relaxation parameters, detection of single surface electron spins and studies on the dynamics of fast surface migration of species. The physical grounds and possible applications of the methods in chemical research are also discussed. The bibliography includes 80 references.

2001-08-31

236

Electronic conduction and tunneling in Ta-oxide and Sn-oxide thick films  

International Nuclear Information System (INIS)

Electrical resistivity and its temperature coefficient are measured for a large number of Ta-oxide and Sn-oxide thick films in the temperature range 80 to 400 K. These results, along with the measurement of other physical properties, are used to explain the behavior of electronic conduction in these metal oxide thick films. From this study, the importance of tunneling and hopping in these thick films is ascertained. (author)

1987-04-16

237

Sub-50 mK electronic cooling with large-area superconducting tunnel junctions  

Digital Repository Infrastructure Vision for European Research (DRIVER)

In electronic cooling with superconducting tunnel junctions, the cooling power is counterbalanced by the interaction with phonons and by the heat flow from the overheated leads. We study aluminium-based coolers that are equipped with a suspended normal metal and an efficient quasi-particle drain. At intermediate temperatures, the phonon bath of the suspended normal metal is cooled. At lower temperatures, by adjusting the junction transparency, we control the injection curren...

Nguyen, H. Q.; Meschke, M.; Courtois, H.; Pekola, J. P.

2014-01-01

238

Magnetic field enhanced resonant tunneling in a silicon nanowire single-electron-transistor.  

Science.gov (United States)

We report fabrication, measurement and simulation of silicon single-electron-transistors made on silicon-on-insulator wafers. At T-2 K, these devices showed clear Coulomb blockade structures. An external perpendicular magnetic field was found to enhance the resonant tunneling peak and was used to predict the presence of two laterally coupled quantum dots in the narrow constriction between the source-drain electrodes. The proposed model and measured experimental data were consistently explained using numerical simulations. PMID:22755082

Aravind, K; Lin, M C; Ho, I L; Wu, C S; Kuo, Watson; Kuan, C H; Chang-Liao, K S; Chen, C D

2012-03-01

239

Single-electron charging phenomena in silicon nanopillars with and without silicon nitride tunnel barriers  

Science.gov (United States)

Electron transport in silicon nanopillars has been studied for pillars with zero, one, or two silicon nitride barrier layers of 2 nm thickness. Evidence of Coulomb blockade is presented and the role of the silicon nitride layers is discussed. Wide zero current regions are observed for some devices with two silicon nitride tunnel barriers and these are attributed to the formation of fully depleted quantum dots.

Pooley, D. M.; Ahmed, H.; Mizuta, H.; Nakazato, K.

2001-11-01

240

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

Science.gov (United States)

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

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

1973-01-01

 
 
 
 
241

Scanning tunnelling spectroscopy of quantized electron accumulation at InxGa1-xN surfaces  

International Nuclear Information System (INIS)

Electron tunnelling spectroscopy has been used to investigate quantized levels in electron accumulation layers at InGaN surfaces. The tunnelling spectra exhibit a plateau in the normalized conductance which widens with increasing Ga-content, corresponding to the band gap of InGaN. The measured InxGa1-xN band gaps (between ?0.65 eV for x=1 and 1.8 eV for x=0.43) are consistent with the band gaps determined by previous optical absorption and cathodoluminescence spectroscopy. Additional structures in the spectra reflect the two-dimensional electronic subbands in the surface quantum well. The subband energies depend on Ga-content, bulk doping level and the resultant shape of the surface potential well. The tunnelling spectra are compared with calculations of the potential well, the charge-profile and the subband energies. (copyright 2006 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

2006-01-01

242

Massive Dirac electron tunneling through a time-periodic potential in single layer graphene  

International Nuclear Information System (INIS)

We explore the transmission through a time-periodic potential barriers in single layer graphene with an induced energy gap in this work. The analytical solutions of the transmission probabilities for the central band and the first sidebands are obtained. The transmission probabilities as the function of the induced energy gap and the incidence electron energy are discussed. We also investigate how critical angles change as the induced energy gap and incidence electron energy. The study of transmission properties will benefit applications in graphene-based nano-electronics. -- Highlights: ? The tunneling of massive electrons through a harmonically driven potential barrier. ? Analytical solutions of transmission probabilities for the first sidebands. ? Adjusting energy gap and incidence energy will optimize transmission probabilities. ? Incidence critical angles change as energy gap and incidence electron energy.

2011-10-31

243

Conceptual design for an electron-beam heated hypersonic wind tunnel  

Energy Technology Data Exchange (ETDEWEB)

There is a need for hypersonic wind-tunnel testing at about mach 10 and above using natural air and simulating temperatures and pressures which are prototypic of flight at 50 km altitude or below. With traditional wind-tunnel techniques, gas cooling during expansion results in exit temperatures which are too low. Miles, et al., have proposed overcoming this difficulty by heating the air with a laser beam as it expands in the wind-tunnel nozzle. This report discusses an alternative option of using a high-power electron beam to heat the air as it expands. In the e-beam heating concept, the electron beam is injected into the wind-tunnel nozzle near the exit and then is guided upstream toward the nozzle throat by a strong axial magnetic field. The beam deposits most of its power in the dense air near the throat where the expansion rate is greatest. A conceptual design is presented for a large-scale system which achieves Mach 14 for 0.1 seconds with an exit diameter of 2.8 meters. It requires 450 MW of electron beam power (5 MeV at 90 A). The guiding field is 500 G for most of the transport length and increases to 100 kG near the throat to converge the beam to a 1.0-cm diameter. The beam generator is a DC accelerator using a Marx bank (of capacitors) and a diode stack with a hot cathode. 14 refs. 38 figs., 9 tabs.

Lipinski, R.J.; Kensek, R.P.

1997-07-01

244

Tunnel rates and quantum spillage in single-electron pumps at high magnetic fields  

CERN Document Server

We study the effect of perpendicular magnetic fields on a single-electron system with a strongly time-dependent electrostatic potential. Continuous improvements to the current quantization in these electron pumps are revealed by high-resolution measurements. Simulations show that the sensitivity of tunnel rates to the barrier potential is enhanced, stabilizing particular charge states. Nonadiabatic excitations are also suppressed due to a reduced sensitivity of the Fock-Darwin states to electrostatic potential. The combination of these effects leads to significantly more accurate current quantization.

Fletcher, J D; Giblin, S P; Park, Sunghun; Sim, H -S; See, P; Janssen, T J B M; Griffiths, J P; Jones, G A C; Beere, H E; Ritchie, D A

2011-01-01

245

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

2007-06-01

246

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

2011-11-01

247

Negative differential resistance at sequential single-electron tunnelling through atoms and molecules  

International Nuclear Information System (INIS)

We have carried out calculations of electron transport in single-electron transistors using single atoms or small molecules as single-electron islands. The theory is based on a combination of (i) the general theory of the sequential single-electron transport through objects with a quantized energy spectrum, developed by Averin and Korotkov, (ii) the ab initio calculation of molecular orbitals and energy spectra within the density functional theory framework (using the NRLMOL software package), and (iii) Bardeen's approximation for the rate of tunnelling due to wavefunction overlap. The results show, in particular, that dc I-V curves of molecular-scale single-electron transistors typically have extended branches with negative differential resistance. This effect is due to the enhancement of one of the two tunnelling barriers of the transistor by the source-drain electric field, and apparently has already been observed experimentally by at least two groups. In conclusion, the possibility of using this effect for increasing the density and performance of hybrid semiconductor/nanodevice integrated circuits is discussed in brief

2007-10-24

248

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

249

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

International Nuclear Information System (INIS)

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

250

Electron tunneling into intermediate-valence materials. [CePd/sub 3/  

Energy Technology Data Exchange (ETDEWEB)

Electron tunneling spectra of TmSe, SmS, SmB/sub 6/, and CePd/sub 3/ have been measured with the GaAs Schottky-barrier probe tunneling method. Antiferromagnetic TmSe shows an energy gap 2..delta.. (full width at half maximum) of 1.2 meV, in situ pressure-transformed metallic SmS exhibits a gap of 1.7 meV, and SmB/sub 6/ shows a gap of 2.7 meV, which is independent of magnetic field. For CePd/sub 3/ an inelastic excitation is found near +- 14 meV, which is absent in YPd/sub 3/.

Guentherodt, G.; Thompson, W.A.; Holtzberg, F.; Fisk, Z.

1982-10-04

251

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

CERN Multimedia

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

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

2014-01-01

252

Injection and Trapping of Tunnel-Ionized Electrons into Laser-Produced Wakes  

International Nuclear Information System (INIS)

A method, which utilizes the large difference in ionization potentials between successive ionization states of trace atoms, for injecting electrons into a laser-driven wakefield is presented. Here a mixture of helium and trace amounts of nitrogen gas was used. Electrons from the K shell of nitrogen were tunnel ionized near the peak of the laser pulse and were injected into and trapped by the wake created by electrons from majority helium atoms and the L shell of nitrogen. The spectrum of the accelerated electrons, the threshold intensity at which trapping occurs, the forward transmitted laser spectrum, and the beam divergence are all consistent with this injection process. The experimental measurements are supported by theory and 3D OSIRIS simulations.

2010-01-15

253

Characteristics of silicon-on-insulator single-electron transistors with electrically induced tunnel barriers  

International Nuclear Information System (INIS)

Single-electron transistors with a side gate structure were fabricated on SOI (silicon-on-insulator) substrate. The silicon channel in which electrons could be transported was defined by electron-beam lithography, and the channel was wrapped by two side gates which could control the electrically induced tunnel barrier. The electrical characteristics of the fabricated device were measured at 4.2 K. The measured characteristics showed a larger current oscillation period and amplitude than those estimated from the structural parameters. Also, the current contour plot showed irregular Coulomb diamonds with different sizes. These characteristics are the result of multi-dot formation. A Monte-Carlo simulation verified that these multi-dot characteristics result from unintentional quantum dots due to the irregularity of electron-beam lithography

2002-01-01

254

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.

2010-03-21

255

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

Energy Technology Data Exchange (ETDEWEB)

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.

Walter, Marvin; Zbarskyy, Vladyslav; Muenzenberg, Markus [I. Phys. Inst., Georg-August-Universitaet Goettingen, 37077 Goettingen (Germany); Seibt, Michael [IV. Phys. Inst., Georg-August-Universitaet Goettingen, 37077 Goettingen (Germany); Drewello, Volker; Schaefers, Markus; Reiss, Guenter; Thomas, Andy [Bielefeld University, Physics Department, 33501 Bielefeld (Germany)

2010-07-01

256

Rashba spin-orbit effect on dwell time of electrons tunneling through semiconductor barrier  

International Nuclear Information System (INIS)

A study on characteristics of electrons tunneling through semiconductor barrier is evaluated, in which we take into account the effects of Rashba spin-orbit interaction. Our numerical results show that Rashba spin-orbit effect originating from the inversion asymmetry can give rise to the spin polarization. The spin polarization does not increase linearly but shows obvious resonant features as the strength of Rashba spin-orbit coupling increases, and the amplitudes of spin polarization can reach the highest around the first resonant energy level. Furthermore, it is found that electrons with different spin orientations will spend quite different time through the same heterostructures. The difference of the dwell time between spin-up and spin-down electrons arise from the Rashba spin-orbit coupling. And it is also found that the dwell time will reach its maximum at the first resonant energy level. It can be concluded that, in the time domain, the tunneling processes of the spin-up and spin-down electrons can be separated by modulating the strength of Rashba spin-orbit coupling. Study results indicate that Rashba spin-orbit effect can cause a nature spin filter mechanism in the time domain

2008-03-17

257

Rashba spin-orbit effect on dwell time of electrons tunneling through semiconductor barrier  

Energy Technology Data Exchange (ETDEWEB)

A study on characteristics of electrons tunneling through semiconductor barrier is evaluated, in which we take into account the effects of Rashba spin-orbit interaction. Our numerical results show that Rashba spin-orbit effect originating from the inversion asymmetry can give rise to the spin polarization. The spin polarization does not increase linearly but shows obvious resonant features as the strength of Rashba spin-orbit coupling increases, and the amplitudes of spin polarization can reach the highest around the first resonant energy level. Furthermore, it is found that electrons with different spin orientations will spend quite different time through the same heterostructures. The difference of the dwell time between spin-up and spin-down electrons arise from the Rashba spin-orbit coupling. And it is also found that the dwell time will reach its maximum at the first resonant energy level. It can be concluded that, in the time domain, the tunneling processes of the spin-up and spin-down electrons can be separated by modulating the strength of Rashba spin-orbit coupling. Study results indicate that Rashba spin-orbit effect can cause a nature spin filter mechanism in the time domain.

Zhang Yingtao [College of Physics, Hebei Normal University, Shijiazhuang 050016 (China)], E-mail: zhangyt@mail.hebtu.edu.cn; Li Youcheng [College of Physics, Hebei Normal University, Shijiazhuang 050016 (China)

2008-03-17

258

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

259

Electron-tunneling studies of electron-phonon renormalization effects in indium  

International Nuclear Information System (INIS)

Tunneling spectra produced by thick In films (approx.5-40 ?m) backed by Al contain strong, damped oscillations due to Andreev scattering. Spectra are classifiable as simple, beat-modulated, or complex. Complex spectra are rare and difficult to interpret. Beam-modulated spectra are more common (approx.25%), and simple spectra are the most common. Modulated spectra are attributed to tunneling from two specific patches on the In Fermi surface. All simple spectra are attributed to just one of these patches. The known occurrence of two In fiber textures is probably responsible for this situation. The author's view requires all modulated spectra to yield the same two velocities. It also requires all simple spectra to yield the same velocity, and that this value be degenerate with one of the others. These conditions were found to be satisfied. Results justify analysis of a representative simple spectrum to obtain the complex renormalization, Z(E)

1985-01-01

260

Fabrication of tunnel junction-based molecular electronics and spintronics devices  

Energy Technology Data Exchange (ETDEWEB)

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

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

2012-10-15

 
 
 
 
261

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

Science.gov (United States)

The electron transport properties of the cubic quantum dot, (PbS)32, are investigated. The stability of the quantum dot has been established by recent scanning tunneling microscope experiments [B. Kiran, A. K. Kandalam, R. Rallabandi, P. Koirala, X. Li, X. Tang, Y. Wang, H. Fairbrother, G. Gantefoer, and K. Bowen, J. Chem. Phys. 136(2), 024317 (2012)]. In spite of the noticeable energy band gap (~2 eV), a relatively high tunneling current for (PbS)32 is predicted affirming the observed bright images for (PbS)32. The calculated I-V characteristics of (PbS)32 are predicted to be substrate-dependent; (PbS)32 on the Au (001) exhibits the molecular diode-like behavior and the unusual negative differential resistance effect, though this is not the case with (PbS)32 on the Au (110). Appearance of the conduction channels associated with the hybridized states of quantum dot and substrate together with their asymmetric distribution at the Fermi level seem to determine the tunneling characteristics of the system. PMID:24387370

Gupta, Sanjeev K; He, Haiying; Banyai, Douglas; Kandalam, Anil K; Pandey, Ravindra

2013-12-28

262

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

Science.gov (United States)

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

Gupta, Sanjeev K.; He, Haiying; Banyai, Douglas; Kandalam, Anil K.; Pandey, Ravindra

2013-12-01

263

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

2010-02-01

264

Electrical control of interdot electron tunneling in a double InGaAs quantum-dot nanostructure.  

Science.gov (United States)

We employ ultrafast pump-probe spectroscopy to directly monitor electron tunneling between discrete orbital states in a pair of spatially separated quantum dots. Immediately after excitation, several peaks are observed in the pump-probe spectrum due to Coulomb interactions between the photogenerated charge carriers. By tuning the relative energy of the orbital states in the two dots and monitoring the temporal evolution of the pump-probe spectra the electron and hole tunneling times are separately measured and resonant tunneling between the two dots is shown to be mediated both by elastic and inelastic processes. Ultrafast (tunneling is shown to occur over a surprisingly wide bandwidth, up to ?8??meV, reflecting the spectrum of exciton-acoustic phonon coupling in the system. PMID:23003087

Müller, K; Bechtold, A; Ruppert, C; Zecherle, M; Reithmaier, G; Bichler, M; Krenner, H J; Abstreiter, G; Holleitner, A W; Villas-Boas, J M; Betz, M; Finley, J J

2012-05-11

265

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

1996-08-25

266

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

267

Tunneling and relaxation of single quasiparticles in a normal-superconductor-normal single-electron transistor  

Science.gov (United States)

We investigate the properties of a hybrid single-electron transistor, involving a small superconducting island sandwiched between normal metal leads, which is driven by dc plus ac voltages. In order to describe its properties we derive from the microscopic theory a set of coupled equations. They consist of a master equation for the probability to find excess charges on the island, with rates depending on the distribution of nonequilibrium quasiparticles. Their dynamics follows from a kinetic equation which accounts for the excitation by single-electron tunneling as well as the relaxation and eventual recombination due to the interaction with phonons. Our low-temperature results compare well with recent experimental findings obtained for ac-driven hybrid single-electron turnstiles.

Heimes, Andreas; Maisi, Ville F.; Golubev, Dmitri S.; Marthaler, Michael; Schön, Gerd; Pekola, Jukka P.

2014-01-01

268

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

CERN Document Server

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

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

2005-01-01

269

Local Electronic Structure and Fano Interference in Tunneling into a Kondo Hole System  

Science.gov (United States)

Motivated by the recent success of local electron tunneling into heavy-fermion materials, we study the local electronic structure around a single Kondo hole in an Anderson lattice model and the Fano interference pattern relevant to STM experiments. Within the Gutzwiller method, we find that an intragap bound state exists in the heavy Fermi liquid regime. The energy position of the intragap bound state is dependent on the on-site potential scattering strength in the conduction and f-orbital channels. Within the same method, we derive a new dI/dV formulation, which includes explicitly the renormalization effect due to the f-electron correlation. It is found that the Fano interference gives asymmetric coherent peaks separated by the hybridization gap. The intragap peak structure has a Lorenzian shape, and the corresponding dI/dV intensity depends on the energy location of the bound state.

Zhu, Jian-Xin; Julien, Jean-Pierre; Dubi, Y.; Balatsky, A. V.

2012-05-01

270

Electronic Signatures of all Four DNA Nucleosides in a Tunneling Gap  

Science.gov (United States)

Nucleosides diffusing through a 2 nm electron-tunneling junction generate current spikes of sub-millisecond duration with a broad distribution of peak currents. This distribution narrows 10-fold when one of the electrodes is functionalized with a reagent that traps nucleosides in a specific orientation with hydrogen bonds. Functionalizing the second electrode reduces contact resistance to the nucleosides, allowing them to be identified via their peak currents according to deoxyadenosine > deoxycytidine > deoxyguanosine > thymidine, in agreement with the order predicted by a density functional calculation.

2010-01-01

271

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

International Nuclear Information System (INIS)

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

1980-01-01

272

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

273

Developing an Electronic Resource Management System: Verde from Ex Libris  

Directory of Open Access Journals (Sweden)

Full Text Available Rapid growth in the number of electronic resources and the complexity of managing e-collections has posed new challenges for libraries and hence requires the development of new tools. To meet this need, Ex Libris is developing a new product, an electronic resource management (ERM system. The development process began in 2002 and has benefited from the company's 25 years of experience in providing libraries with various products - an integrated library system, digital asset management system, library portal, and link server. Working with an international focus group and development partners and interacting with the Digital Library Federation's Electronic Resource Management Initiative (DLF ERMI committee, Ex Libris explored the various aspects of the e-resource life cycle. As a result, the Ex Libris ERM system was designed to address the issues raised through this collaboration and the DLF requirements. The interface of the system represents all of its components; it includes navigation options and facilitates workflows that support the various activities that librarians perform when dealing with electronic resources. This paper describes the development process of the Ex Libris ERM system. The emphasis is on the particular functionality required for managing e-resources and the ways in which existing systems in the library arena can handle specific tasks.

Tamar Sadeh

2004-09-01

274

Geometric and electronic structure of passive CuN monolayer on Cu(111) : a scanning tunneling microscopy and spectroscopy study  

Energy Technology Data Exchange (ETDEWEB)

An insulating CuN monolayer was grown on a Cu(111) surface; subsequently, the dynamic growth process, the reconstructed geometric structure and the electronic structure were studied using scanning tunneling microscopy. Confirmation of the atomic model of the pseudo-(100) layer, proposed by Higgs et al. and Driver et al. was made. In addition, we observed a small misalignment of the super cell away from the <110> direction of the Cu substrate, resulting in long range distortion. A large insulator-like band gap of {approx} 3.3 eV was measured through the CuN surface. The CuN monolayer can be used as a model surface on which the electronic structure of an atom or a molecule is explored by scanning tunneling microscopy. This electronic structure can not be perturbed by the metallic substrate, despite the tunneling of electrons through the surface layer.

Baek, Hongwoo; Jeon, Sangjun; Seo, Jungpil; Kuk, Young [Seoul National University, Seoul (Korea, Republic of); Seo, Jungpil [Princeton University, Princeton, NJ (United States)

2010-02-15

275

Tunneling Hamiltonian  

Digital Repository Infrastructure Vision for European Research (DRIVER)

For the description of the transport of electrons across a quantum dot, which is tunnel coupled to leads at different chemical potentials, it is usual to assume that the total Hamiltonian of the composite system of the leads and the quantum dot is the sum of three contributions: That of the leads (noninteracting electrons), that of the quantum dot and a third one, the "tunneling Hamiltonian", which reflects the possibility that electrons can move from the leads to the quantu...

Kern, Johannes

2013-01-01

276

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

277

Quantum Tunneling  

Science.gov (United States)

Delve into a microscopic world working with models that show how electron waves can tunnel through certain types of barriers. Learn about the novel devices and apparatuses that have been invented using this concept. Discover how tunneling makes it possible for computers to run faster and for scientists to look more deeply into the microscopic world.

Consortium, The C.

2011-12-11

278

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.

2009-03-22

279

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

International Nuclear Information System (INIS)

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.

2012-07-01

280

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

2004-01-01

 
 
 
 
281

Portrait of a potential barrier: electron tunneling at metal-organic interfaces  

Energy Technology Data Exchange (ETDEWEB)

Organic semiconductors constitute the basis of a fast developing microelectronics and are successfully making the first steps towards high performance nanoscale devices. Further improvements and the design of new molecular-based electronic circuits require a better understanding of the charge transport and injection mechanisms. At present, one of the major constrains is given by the electron potential barrier forming at the molecule-metal interface. Here, by means of a low temperature scanning tunneling microscope (STM), we visualize this metal-molecule interface on a local scale. We found that the molecular interaction with the substrate leads to the formation of a potential barrier which is non-uniform across the molecule. This reflects the relation between the chemical composition and the interaction with the metal surface.

Vitali, Lucia; Ohmann, Robin; Kern, Klaus [Max-Planck Institute for Solid State Research, Stuttgart (Germany); Levita, Giacomo [INFM Democritos, University of Trieste (Italy); Comisso, Alessio; Vita, Alessandro de [Physics Department, Kings College, London (United Kingdom)

2009-07-01

282

Quantum electron tunneling in flavin-porphyrin hetero-type Langmuir-Blodgett films  

International Nuclear Information System (INIS)

Photo-induced electron transfer in flavin-porphyrin hetero-type Langmuir-Blodgett (LB) films and its temperature dependence were investigated by means of the photocurrent measurements and the transient fluorometry. From 10 K to room temperature, transient photocurrent in sub-nanosecond time region was found to be independent of the temperature for a metal-insulator-metal device composed of the hetero-type LB films with a flavin-porphyrin molecular heterojunction (MHJ). This transient photocurrent was attributed to the charge separation (CS) process from the photo-excited flavin to the porphyryin at the MHJ on the basis of the temperature dependence of the fluorescence decay profiles of the excited flavin. By integrating these results with UV-visible absorption spectra, it was deduced that the fast temperature-independent CS process at the flavin-porphyrin MHJ was mainly due to the quantum electron tunneling regulated by high-frequency quantum modes of intramolecular vibrations

2004-11-01

283

Detection of Dielectric Trap States in Hafnium Oxide By Single Electron Tunneling Force Spectroscopy  

Science.gov (United States)

Atomic scale detection and imaging of electronic trap states in dielectric films has recently been demonstrated.ootnotetextJ.P. Johnson et al, Nanotechnology 20 (2009) 055701 Standard methods typically provide characterization over a much larger scale. Single Electron Tunneling Force Spectroscopy has been employed to measure the energy levels of trap states in HfO2 with sub-nanometer spatial resolution. Analysis of individual spectra obtained at different locations shows variation in the density of defect states. When multiple spectra taken from 40 different locations are averaged, a broad peak 0.3 eV below the conduction band is observed, which agrees with data obtained over large areas by standard measurements.ootnotetextG. Ribes et al, IEEE Trans. Dev. Mat. Reliability 6, 132 (2006). Additional peaks, not seen by the standard methods, are also observed. The method will be described and the data discussed.

Winslow, Dustin; Johnson, Jon; Williams, Clayton

2011-03-01

284

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

285

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

International Nuclear Information System (INIS)

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

286

Investigation of electron transmission through Co/C/Co magnetic tunnel junctions  

Science.gov (United States)

We investigate transmission properties of electrons at the interfaces of cobalt-diamond hybrid systems. To this end, we employ a Green's function method based on spin-polarized density-functional theory calculations using a Gaussian orbital representation of the wave functions. The considered open systems are magnetic tunnel junctions consisting of semi-infinite hcp cobalt leads and n layers of carbon atoms stacked in (111) direction. These systems are characterized by a very small lattice mismatch of their constituents. We have identified three types of states that give rise to an almost complete transmission. The transmission for minority electrons is considerably suppressed at the Fermi level in most parts of the interface Brillouin zone.

Huerkamp, Felix; Krüger, Peter; Pollmann, Johannes

2014-03-01

287

Tunneling and Raman spectroscopies of the electron-doped high-temperature superconductors  

Science.gov (United States)

This thesis consists of spectroscopic studies of the electron-doped high temperature cuprate superconductors Pr2-xCe xCuO4-delta (PCCO) and Nd 2-xCexCuO 4-delta (NCCO). Point contact and high barrier tunneling spectroscopies were employed to study the evolution of the superconducting gap (Delta) with cerium doping. Point contact spectroscopy of low barrier junctions reveals that the gap changes from d-wave in under-doped PCCO to a nodeless gap in over-doped PCCO. This transition in pairing symmetry occurs just above optimal doping. High barrier tunnel junctions were prepared on optimally doped PCCO and NCCO crystals for tunneling into the ab-planes. The spectra are not consistent with either a clean s-wave gap or a clean monotonic dx2-y2 gap, and can be explained by a non-monotonic d-wave gap. A normal state gap near zero voltage bias is observed in the tunneling spectra for dopings between x = 0.13 and x = 0.19 when superconductivity is suppressed by magnetic fields larger than the upper critical fields ( Hc2). The normal state gap appears to coexist with the superconducting gap. The normal state gap vanishes at a temperature close to the superconducting transition temperature for optimally doped samples. Raman spectroscopy was employed to systematically study the electronic properties of PCCO and NCCO crystals and films across the superconducting phase diagram. Polarization and doping dependence of the 2Delta coherence peaks in the superconducting state show a change in the superconducting gap from non-monotonic d-wave at optimal doping to either a dirty d-wave or a dirty s-wave in the over-doped samples. By analyzing coherence effects, we find that all coherent carriers in the non-superconducting state condense to form the superfluid. Carriers that are doped beyond optimal doping are incoherent and do not contribute to the coherent Raman response in the normal and superconducting states. We systematically studied the effects of temperature and magnetic field on the coherence peaks in the Raman spectra for various dopings. Compared to the optimally doped crystals, Hc2 decreases by more than an order of magnitude in the most over-doped crystal. The implications of these observations are discussed.

Qazilbash, Muhammad Mumtaz

288

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

CERN Document Server

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

Viatkina, A V

2014-01-01

289

Point-contact electron tunneling into the high-T/sub c/ superconductor Y-Ba-Cu-O  

International Nuclear Information System (INIS)

We report results of a study of electron tunneling into bulk samples of the new high-T/sub c/ superconductor Y-Ba-Cu-O using point-contact tunneling. Based on a superconductive tunneling interpretation, the results show exceptionally large energy gaps in these materials (roughly 2? = 100 meV), implying 2?/k/sub C/T/sub c/--13. Similar values were found previously by us for La-Sr-Cu-O. We also see Structure in the I-V curves similar to that seen in La-Sr-Cu-O. On the basis of the asymmetries observed in the I-V characteristics, we believe that the natural tunneling barrier on this material is of the Schottky type

1987-06-01

290

A study of inelastic electron-phonon interactions on tunneling magnetoresistance of a nano-scale device  

International Nuclear Information System (INIS)

In this research, we have studied the effect of inelastic electron-phonon interactions on current-voltage characteristic and tunneling magnetoresistance of a polythiophene molecule that is sandwiched between two cobalt electrodes using modified Green's function method as proposed by Walczak. The molecule is described with a modified Su-Schrieffer-Heeger Hamiltonian. The ground state of the molecule is obtained by Hellman-Feynman theorem. Electrodes are described in the wide-band approximation and spin-flip is neglected during conduction. Our calculation results show that with increase in voltage the currents increase and tunneling magnetoresistance decreases. Change in tunneling magnetoresistance due to inelastic interactions is limited in a small bias voltage interval and can be neglected in the other bias voltages. -- Research Highlights: ?We investigate the effect of inelastic interaction on transport properties. ?Due to inelastic interactions tunneling magnetoresistance decreases. ?Decrease in TMR is restricted in a small voltage interval.

2011-02-01

291

A study of inelastic electron-phonon interactions on tunneling magnetoresistance of a nano-scale device  

Energy Technology Data Exchange (ETDEWEB)

In this research, we have studied the effect of inelastic electron-phonon interactions on current-voltage characteristic and tunneling magnetoresistance of a polythiophene molecule that is sandwiched between two cobalt electrodes using modified Green's function method as proposed by Walczak. The molecule is described with a modified Su-Schrieffer-Heeger Hamiltonian. The ground state of the molecule is obtained by Hellman-Feynman theorem. Electrodes are described in the wide-band approximation and spin-flip is neglected during conduction. Our calculation results show that with increase in voltage the currents increase and tunneling magnetoresistance decreases. Change in tunneling magnetoresistance due to inelastic interactions is limited in a small bias voltage interval and can be neglected in the other bias voltages. -- Research Highlights: {yields}We investigate the effect of inelastic interaction on transport properties. {yields}Due to inelastic interactions tunneling magnetoresistance decreases. {yields}Decrease in TMR is restricted in a small voltage interval.

Modarresi, M., E-mail: mo_mo226@stu-mail.um.ac.i [Department of Physics, Ferdowsi University of Mashhad, Mashhad (Iran, Islamic Republic of); Roknabadi, M.R.; Shahtahmasbi, N.; Vahedi Fakhrabad, D.; Arabshahi, H. [Department of Physics, Ferdowsi University of Mashhad, Mashhad (Iran, Islamic Republic of)

2011-02-01

292

Electronic structure properties of the In(Ga)As/GaAs quantum dot–quantum well tunnel-injection system  

International Nuclear Information System (INIS)

We report on the electronic properties of GaAs-substrate-based structures designed as a tunnel-injection system composed of self-assembled InAs quantum dots and an In0.3Ga0.7As quantum well separated by a GaAs barrier. We have performed photoluminescence and photoreflectance measurements which have allowed the determination of the optical transitions in the QW–QD tunnel structure and its respective references with just quantum dots or a quantum well. The effective mass calculations of the band structure dependence on the tunnelling barrier thickness have shown that in spite of an expected significant tunnelling between both parts of the system, its strong asymmetry and the strain distribution cause that the quantum-mechanical-coupling-induced energy shift of the optical transitions is almost negligible for the lowest energy states and weakly sensitive to the width of the barrier, which finds confirmation in the existing experimental data

2009-08-01

293

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 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 organisati...

Thomas Groenewald

2004-01-01

294

Electrochemical quantum tunneling for electronic detection and characterization of biological toxins  

Science.gov (United States)

This paper introduces a label-free, electronic biomolecular sensing platform for the detection and characterization of trace amounts of biological toxins within a complex background matrix. The mechanism for signal transduction is the electrostatic coupling of molecule bond vibrations to charge transport across an insulated electrode-electrolyte interface. The current resulting from the interface charge flow has long been regarded as an experimental artifact of little interest in the development of traditional charge based biosensors like the ISFET, and has been referred to in the literature as a "leakage current". However, we demonstrate by experimental measurements and theoretical modeling that this current has a component that arises from the rate-limiting transition of a quantum mechanical electronic relaxation event, wherein the electronic tunneling process between a hydrated proton in the electrolyte and the metallic electrode is closely coupled to the bond vibrations of molecular species in the electrolyte. Different strategies to minimize the effect of quantum decoherence in the quantized exchange of energy between the molecular vibrations and electron energy will be discussed, as well as the experimental implications of such strategies. Since the mechanism for the transduction of chemical information is purely electronic and does not require labels or tags or optical transduction, the proposed platform is scalable. Furthermore, it can achieve the chemical specificity typically associated with traditional micro-array or mass spectrometry-based platforms that are used currently to analyze complex biological fluids for trace levels of toxins or pathogen markers.

Gupta, Chaitanya; Walker, Ross M.; Gharpuray, Rishi; Shulaker, Max M.; Zhang, Zhiyong; Javanmard, Mehdi; Davis, Ronald W.; Murmann, Boris; Howe, Roger T.

2012-05-01

295

Enhancing the use of electronic resources on a university library's website : herding electronic resources into subject groupings  

Digital Repository Infrastructure Vision for European Research (DRIVER)

The integration of five separate websites from the campus libraries at Texas A&M University in 2002 resulted in the creation of a unified listing of all electronic resources, with well over 20,000 entries. This was the first time we were able to provide library users with a single, comprehensive list of electronic resources. But it quickly became clear that it was not very usable. In June 2002 the University Libraries Web Implementation Team (WIT) identified a diverse group of library staff t...

Carrigan, Esther; Sewell, Robin; Wilson, Mary Dabney; Highsmith, Anne L.

2005-01-01

296

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

International Nuclear Information System (INIS)

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

2012-02-01

297

The Titan Wind Tunnel: a resource in the NASA Ames Planetary Aeolian Laboratory  

Science.gov (United States)

The Titan Wind Tunnel in the NASA Ames Research Center is now available to simulate the kinematic viscosity and wind speeds of the Titan near-surface atmosphere. Early results indicate that threshold wind speeds may differ from previous (terrestrial) models.

Burr, D. M.; Bridges, N.; Marshall, J.; Smith, J. K.; White, B.; Williams, D. A.

2013-09-01

298

Initial distribution and tunneling recombination of cation-electron pairs in irradiated rigid materials as studied by ITL measurement  

International Nuclear Information System (INIS)

Time dependence of the intensity of isothermal luminescence (ITL) from polyethylene terephthalate and polyethylene adipate irradiated at low temperature was observed over a long period of time after irradiation. The ITL decay obeys a law I(t) = I0/(1 + ?t)sup(m) as a function of time t. All of the parameters, I0, ? and m, depend on irradiation time and/or dose rate under which they were irradiated. The ITL process can be interpreted as due to recombination of the cation-electron pair through electron tunneling to cation. The distribution of the separation distances of cation-electron pairs can be obtained by Laplace inverse transformation of the ITL decay function based on an electron tunneling model. The distribution of cation-electron pairs is discussed for different irradiation condition. (author)

1983-01-01

299

Determination of electron-transfer rate constants from data on tunneling to randomly distributed acceptors in a rigid medium  

International Nuclear Information System (INIS)

The problem of analyzing data for an electron-transfer reaction in rigid solution to obtain the rate constant as a function of distance is considered in detail. Effects due to the distribution of donor-acceptor separations and the finite volumes of the individual molecules are explicitly included. Calculations are presented which show that the assumptions of a previously presented tunneling model are essentially correct; reactions with non-nearest-neighbor acceptors are, in general, unimportant, and the concept of a mean-time-dependent reaction radius for tunneling is valid, in spite of the fact that the electron transfer is occurring simultaneously over a range of distances. The earlier tunneling model is modified by making a more careful choice of the reaction radius, and it is shown that the modified model yields accurate rate constants. Convenient procedures for correcting the volume occupied by acceptor molecules and for the fact that a donor cannot be arbitrarily close to an acceptor are presented

1982-01-21

300

Electron self-exchange in azurin : calculation of the superexchange electron tunneling rate  

DEFF Research Database (Denmark)

Electronic coupling between the copper atoms in an azurin dimer has been calculated in this conformationally well-defined system by using many-electronic wave functions. When one of the two water molecules forming intermolecular hydrogen bonds between the copper-ligating His-117 of the two azurins is removed, the calculated coupling element is reduced from 2.5 x 10(-6) to 1.1 x 10(-7) eV (1 eV = 1.602 x 10(-19) J). Also, the effects of the relative orientations of the two water molecules have been analyzed. The results show that water molecules may play an important role as switches for biological electron transfer. The rate of electron self-exchange between two azurins has been calculated, and the result is in very good agreement with the rate found experimentally.

Mikkelsen, K V; Skov, L K

1993-01-01

 
 
 
 
301

Nanostructural and local electronic properties of Fe/W(110) correlated by scanning tunneling spectroscopy  

Energy Technology Data Exchange (ETDEWEB)

Epitaxial Fe(110) films grown on W(110) substrates exhibit, up to the second pseudomorphic monolayer, a peak in {ital dI}/{ital dU} spectra at 0.2 eV above the Fermi level as measured by scanning tunneling spectroscopy (STS). It is shown directly by STS on nanometer-scale wedges of Fe/W(110) that the density of empty states is diminished wherever the stressed Fe film begins to relax. The change in local differential conductivity can therefore be explained by a stress-induced change of electronic structure for the first two monolayers due to the large misfit between film and substrate. {copyright} {ital 1996 The American Physical Society.}

Bode, M.; Pascal, R.; Dreyer, M.; Wiesendanger, R. [Institute of Applied Physics and Microstructure Research Center, University of Hamburg, Jungiusstrasse 11, D-20355 Hamburg (Germany)

1996-09-01

302

The InP - SiO2 interface: Electron tunneling into oxide traps  

International Nuclear Information System (INIS)

Indium Phosphide is an attractive material for high-speed devices. Though many successful devices have been built and demonstrated, InP MISFET's still suffer from drain current drift. From the data current drift measurements, the shift in the threshold voltage ?V was computed for different times. It was found that a linear relationship exists between ??V and log(t). When a positive bias-stress was applied to the gate of an MIS capacitor for a time t, the C-V cure shifted by an amount ?V and again, a linear relationship was observed between ??V and log(t). This was verified on four different gate insulators: pyrolytic SiO2 at 3200C and 3600C, plasma oxide at 3000C and photo CVD oxide at 2250C. These results can only be explained by a model in which electrons tunnel from the substrate into oxide traps

1985-01-01

303

Long-range electron tunnelling in oligo-porphyrin molecular wires.  

Science.gov (United States)

Short chains of porphyrin molecules can mediate electron transport over distances as long as 5-10 nm with low attenuation. This means that porphyrin-based molecular wires could be useful in nanoelectronic and photovoltaic devices, but the mechanisms responsible for charge transport in single oligo-porphyrin wires have not yet been established. Here, based on electrical measurements of single-molecule junctions, we show that the conductance of the oligo-porphyrin wires has a strong dependence on temperature, and a weak dependence on the length of the wire. Although it is widely accepted that such behaviour is a signature of a thermally assisted incoherent (hopping) mechanism, density functional theory calculations and an accompanying analytical model strongly suggest that the observed temperature and length dependence is consistent with phase-coherent tunnelling through the whole molecular junction. PMID:21804555

Sedghi, Gita; García-Suárez, Víctor M; Esdaile, Louisa J; Anderson, Harry L; Lambert, Colin J; Martín, Santiago; Bethell, Donald; Higgins, Simon J; Elliott, Martin; Bennett, Neil; Macdonald, J Emyr; Nichols, Richard J

2011-08-01

304

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

International Nuclear Information System (INIS)

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

2007-07-01

305

Direct observation of adsorption-induced electronic states by low-temperature scanning tunneling microscopy  

International Nuclear Information System (INIS)

We have studied local density states of cobalt-phthalocyanine (CoPc) molecules on a Cu (1 0 0) surface by low-temperature scanning tunneling microscopy. Differential conductance (dI/dV) spectra of CoPc molecules had two peaks at 0.45 eV below and 0.1 eV above the Fermi level (E F). The dI/dV image revealed that Co atoms had large contribution to the state around 0.45 eV. The peak at 0.1 eV above E F was assigned to the states induced by the adsorption of molecules on surfaces. The porphyrin part of the CoPc molecules was found to contribute to this state. The lowest unoccupied molecular orbital was thought to hybridize with the electronic states of Cu (1 0 0) to generate the adsorption-induced state

2005-11-01

306

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

CERN Document Server

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

Kuchiev, M Yu

2007-01-01

307

Normal-metal hot-electron microbolometer with on-chip protection by tunnel junctions  

International Nuclear Information System (INIS)

We describe recent developments in a fully on-chip integrated antenna-coupled bolometer for astrophysical applications at millimetre and submillimetre wavelengths. We have developed a normal-metal hot-electron microbolometer with Andreev mirrors for thermal protection of the absorber and the coupling to the antenna. In previous experiments we could not operate the sensor at temperatures below 300 mK presumably because of the high external noise load. Our latest results with the absorber protected by tunnel junctions show how this problem can be solved experimentally. We have achieved noise performance mostly limited by the amplifier, which corresponds to expected detector NEP on the order of 1.5x10-17 W Hz1/2 at 100 mK. (author)

1999-11-01

308

Normal-metal hot-electron microbolometer with on-chip protection by tunnel junctions  

Energy Technology Data Exchange (ETDEWEB)

We describe recent developments in a fully on-chip integrated antenna-coupled bolometer for astrophysical applications at millimetre and submillimetre wavelengths. We have developed a normal-metal hot-electron microbolometer with Andreev mirrors for thermal protection of the absorber and the coupling to the antenna. In previous experiments we could not operate the sensor at temperatures below 300 mK presumably because of the high external noise load. Our latest results with the absorber protected by tunnel junctions show how this problem can be solved experimentally. We have achieved noise performancemostly limited by the amplifier, which corresponds to expected detector NEP on the order of 1.5x10{sup -17} W Hz{sup 1/2} at 100 mK. (author)

Chouvaev, D.; Kuzmin, L.; Tarasov, M. [Department of Microelectronics and Nanoscience, Chalmers University of Technology, S-412 96 Gothenburg (Sweden)

1999-11-01

309

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

Science.gov (United States)

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.; Jara, Gabriel E.; Vera, D. Mariano A.; Pierini, Adriana B.; Sánchez, Cristián G.

2011-06-01

310

Electronic states of Fe atoms and chains on InAs(110) from scanning tunneling spectroscopy  

Science.gov (United States)

The local density of states (DOS) on and around Fe single atoms and Fe chains deposited on the n-InAs(110) surface is studied by scanning tunneling spectroscopy at T?6K . The single atom shows two characteristic states in the filled as well as in the empty DOS which are attributed to an In-related and an Fe-related state. For chains longer than two atoms oriented along the [11¯0] direction, the In-related state results in a uniform state, while the Fe-related state splits up into an end state and inner states. The end state has a lower energy in the filled as well as in the empty DOS. Chains oriented along the [001] direction show an electronic structure which varies continuously along their axis, suggesting a position-dependent hybridization of each atom to the substrate.

Matsui, T.; Meyer, Chr.; Sacharow, L.; Wiebe, J.; Wiesendanger, R.

2007-04-01

311

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

312

Nanostructural and local electronic properties of Fe/W(110) correlated by scanning tunneling spectroscopy  

International Nuclear Information System (INIS)

Epitaxial Fe(110) films grown on W(110) substrates exhibit, up to the second pseudomorphic monolayer, a peak in dI/dU spectra at 0.2 eV above the Fermi level as measured by scanning tunneling spectroscopy (STS). It is shown directly by STS on nanometer-scale wedges of Fe/W(110) that the density of empty states is diminished wherever the stressed Fe film begins to relax. The change in local differential conductivity can therefore be explained by a stress-induced change of electronic structure for the first two monolayers due to the large misfit between film and substrate. copyright 1996 The American Physical Society

1996-09-01

313

Inelastic electron tunneling study of UV radiation damage in surface adsorbed nucleotides  

International Nuclear Information System (INIS)

Ultraviolet radiation damage to nucleotides has been studied using inelastic electron tunneling (IETS) to monitor the direct bond damage as reflected in the vibrational mode intensity. The damage rate is found to be directly correlated to the resonance energy per ? electron of the purine or pyrimidine base residue. Low lying ring modes are damaged most rapidly while modes associated with CH components are less rapidly damaged. The mononucleotides are damaged more rapidly than the corresponding bases, but no cleaving of the glycodidic bond between the base and sugar is observed. In the case of the purine base nucleotides double bond structure develops during UV exposure and is attributed to the more complex damage sequence of the base ring. The nucleotides are adsorbed on the alumina barrier of an Al--AlO/sub x/--Pb tunnel junction and the PO-2 group interacts with the surface. The majority of the other vibrational modes are unperturbed and indicate that the sugar and base rings form a complex on the surface of relatively fixed orientation. The IETS spectra of all nucleotides indicate a similar surface adsorption and this is not influenced by variation of the substrate temperature as is the case for molecules with a less constrained surface orientation. This unique surface configuration is discussed along with comparison to other molecules where temperature effects on the IETS spectrum are strong. Preliminary results of UV damage to polynucleotides and polypeptides is also reported. The role of the alumina surface structure and interaction with respect to the different types of molecules is also discussed

1980-09-01

314

Temperature impact on the Lorentzian noise induced by electron valence-band tunneling in partially depleted SOI p-MOSFETs  

Science.gov (United States)

In partially depleted (PD) silicon-on-insulator (SOI) MOSFETs with thin gate oxides, a particular effect named linear kink effect (LKE) occurs, which is due to the fact that the body potential is strongly affected by majority carriers injected in the body by the electron valence-band (EVB) tunneling through the ultra-thin gate oxide. This unexpected phenomenon induces a second peak in the transconductance gm curve and an excess Lorentzian noise in the low-frequency noise spectrum. A model based on RC filtered shot noise due to the EVB tunneling current and the forward current of the source-body junction was recently proposed at room temperature. In this work, the focus is on the temperature impact on the Lorentzian noise induced by valence-band electron tunneling in partially depleted SOI p-MOSFETs. For the first time, a Lorentzian noise filtered by the same RC network as the shot noise of the EVB tunneling current has been observed in the LKE operation at low temperature. It seems that the EVB tunneling current can also accompany an excess Lorentzian noise due to traps localized at the Si/gate oxide interface. A simple extension of the model developed by Lukyanchikova et al. is proposed and validated by experimental results from room temperature down to 80 K.

Guo, W.; Cretu, B.; Routoure, J.-M.; Carin, R.; Simoen, E.; Claeys, C.

2007-09-01

315

Extraction of the Eliashberg electron-phonon interaction function from tunneling data. The method and the program  

CERN Document Server

Mathematical correct method for extraction of the complex superconducting energy gap parameter and electron- phonon interaction function from the tunnel density of states is presented. The computer program is shown to be robust against imperfections in experimental data and is widely used to investigate conventional (low Tc) as well as high- temperature superconductors.

Dyachenko, A I

2003-01-01

316

Effect of zero anomalies in the electron state density of electrodes on the spectrum of inelastic tunneling  

International Nuclear Information System (INIS)

It is shown that the minimum in the electron density of one of the electrodes located near the Fermi surface shifting the peaks in the spectrum of the inelastic tunneling to the side of high stresses. It is established that the shift value depends on the value of the correlation parameter and it grows with the increase in the temperature

2003-11-01

317

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

Science.gov (United States)

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

Stachokas, George

2009-01-01

318

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

Science.gov (United States)

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

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

2014-05-27

319

Scanning tunneling microscopy study of polymerized carbon nanobells: Electronic effect and evidence of nitrogen incorporation  

Science.gov (United States)

Polymerized carbon nanobells has been grown by inducing nitrogen in the microwave plasma assisted chemical vapor deposition of carbon nanotubes. The nanobells consist of several tens of graphite layers with one end closed and the other open, and show characteristic field emission behavior with a turn-on field as low as 0.8 V/ mm. In this study, scanning tunneling microscopy/spectroscopy (STM/STS) is used to correlate the unique structure and field emission behavior and to confirm the previously proposed sidewall emission mechanism of the polymerized nanobells. Great contrast modulation along the axis of the tubes is revealed, while atomic-resolution STM images indicate that the bell surface is a nearly perfect carbon network. As enhanced local density of states is observed only on the nanobells, the corrugated morphology is of electronic nature. We discuss the enhanced localized states in terms of the pentagon defects, dangling bonds and enhanced interlayer coupling due to presence of nitrogen. Nitrogen-induced electronic states lies 0.3eV below the Fermi level, which can be used to explain the observed electron field emission behavior.

Sun, Hai-Lin; Jia, Jin-Feng; Shen, Quan-Tong; Zhong, Ding-Yong; Sun, Mu; Xue, Qi-Kun; Wang, En-Ge

2003-03-01

320

Low Yield of Near-Zero-Momentum Electrons and Partial Atomic Stabilization in Strong-Field Tunneling Ionization  

Science.gov (United States)

We measure photoelectron angular distributions of single ionization of krypton and xenon atoms by laser pulses at 1320 nm, 0.2-1.0×1014W/cm2, and observe that the yield of near-zero-momentum electrons in the strong-field tunneling ionization regime is significantly suppressed. Semiclassical simulations indicate that this local ionization suppression effect can be attributed to a fraction of the tunneled electrons that are released in a certain window of the initial field phase and transverse velocity are ejected into Rydberg elliptical orbits with a frequency much smaller than that of the laser; i.e., the corresponding atoms are stabilized. These electrons with high-lying atomic orbits are thus prevented from ionization, resulting in the substantially reduced near-zero-momentum electron yield. The refined transition between the Rydberg states of the stabilized atoms has implication on the THz radiation from gas targets in strong laser fields.

Liu, Hong; Liu, Yunquan; Fu, Libin; Xin, Guoguo; Ye, Difa; Liu, Jie; He, X. T.; Yang, Yudong; Liu, Xianrong; Deng, Yongkai; Wu, Chengyin; Gong, Qihuang

2012-08-01

 
 
 
 
321

Chiral-like tunneling of electrons in two-dimensional semiconductors with Rashba spin-orbit coupling.  

Science.gov (United States)

The unusual tunneling effects of massless chiral fermions (mCF) and massive chiral fermions (MCF) in a single layer graphene and bilayer graphene represent some of the most bizarre quantum transport phenomena in condensed matter system. Here we show that in a two-dimensional semiconductor with Rashba spin-orbit coupling (R2DEG), the real-spin chiral-like tunneling of electrons at normal incidence simultaneously exhibits features of mCF and MCF. The parabolic branch of opposite spin in R2DEG crosses at a Dirac-like point and has a band turning point. These features generate transport properties not found in usual two-dimensional electron gas. Albeit its ? Berry phase, electron backscattering is present in R2DEG. An electron mimics mCF if its energy is in the vicinity of the subband crossing point or it mimics MCF if its energy is near the subband minima. PMID:24445394

Ang, Yee Sin; Ma, Zhongshui; Zhang, C

2014-01-01

322

Chiral-like tunneling of electrons in two-dimensional semiconductors with Rashba spin-orbit coupling  

Science.gov (United States)

The unusual tunneling effects of massless chiral fermions (mCF) and massive chiral fermions (MCF) in a single layer graphene and bilayer graphene represent some of the most bizarre quantum transport phenomena in condensed matter system. Here we show that in a two-dimensional semiconductor with Rashba spin-orbit coupling (R2DEG), the real-spin chiral-like tunneling of electrons at normal incidence simultaneously exhibits features of mCF and MCF. The parabolic branch of opposite spin in R2DEG crosses at a Dirac-like point and has a band turning point. These features generate transport properties not found in usual two-dimensional electron gas. Albeit its ? Berry phase, electron backscattering is present in R2DEG. An electron mimics mCF if its energy is in the vicinity of the subband crossing point or it mimics MCF if its energy is near the subband minima.

Ang, Yee Sin; Ma, Zhongshui; Zhang, C.

2014-01-01

323

Universal Time Tunneling  

CERN Multimedia

How much time does a tunneling wave packet spent in traversing a barrier? Quantum mechanical calculations result in zero time inside a barrier . In the nineties analogous tunneling experiments with microwaves were carried out. The results agreed with quantum mechanical calculations. Electron tunneling time is hard to measure being extremely short and parasitic effects due to the electric charge of electrons may be dominant. However, quite recently the atomic ionization tunneling time has been measured. Experimental data of photonic, phononic, and electronic tunneling time is available now and will be presented. It appears that the tunneling time is a universal property independent of the field in question.

Nimtz, Guenter

2009-01-01

324

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

Science.gov (United States)

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

England, Lenore; Fu, Li

2011-01-01

325

Universal Linear Density of States for Tunneling into the Two-Dimensional Electron Gas in a Magnetic field  

CERN Document Server

A new technique permits high fidelity measurement of the tunneling density of states (TDOS) of the two-dimensional electron gas. The obtained TDOS contains no distortions arising from low 2D in-plane conductivity and includes the contribution from localized tunneling sites. In a perpendicular magnetic field, a pseudogap develops in the TDOS at the Fermi level. Improved sensitivity enables resolution of a linear dependence of the TDOS on energy near the Fermi energy. The slopes of this linear gap are strongly field dependent. The data are suggestive of a new model of the gap at low energies.

Chan, H B; Ashoori, R C; Melloch, M L

1997-01-01

326

An electronic approach to evaluating healthcare Web resources.  

Science.gov (United States)

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

Hodson-Carlton, K; Dorner, J L

1999-01-01

327

Open Source Electronic Resource Management System: A Collaborative Implementation  

Digital Repository Infrastructure Vision for European Research (DRIVER)

Librarians and strategists at Simon Fraser University (SFU) have collaborated with a team of middle-sized libraries to expand the open-source CUFTS Researcher suite of tools to include an Electronic Resources Management (ERM) system. This paper focuses on: the development and implementation of the CUFTS ERM; interoperability between CUFTS ERM and integrated library systems (Millennium); impact of the ERM on acquisitions, serials, and collections workflows and staffing at SFU Library and the U...

Taylor, Donald; Dodd, Frances; Murphy, James

2010-01-01

328

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

CERN Multimedia

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

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

2004-01-01

329

High-temperature superconductors studied by electron tunneling and surface analysis techniques  

International Nuclear Information System (INIS)

Part I focuses on the study of superconductivity of Bi2Sr2CaCu2O8 by a conventional planar tunneling method. The tunnel junctions were made on cleaved ab planes of Bi2Sr2CaCu2O8 single crystals with Pb counterelectrodes. A second gap inside the main gap has been observed for fresh junctions. The inner gap ?i (T) is BCS-like, the outer gap ?(T) is not BCS-like. The fitted outer gap ?(0) = 26 meV, or 2?(0)/kTc = 6.7. Tunneling conductances G(V,T) near Tc reveal a broadening ?(T) such that ?(Tc) ? ?(Tc) ? 2kTc. G(V,T > Tc) has a minimum at V = 0, suggestive of known c-direction localization. G(V,T) also reveals the expected fluctuation superconductivity above Tc. In part II, the author concentrates on the studies of Bi2Sr2CaCu2O8 surfaces, Ag adatoms, and iodine intercalation with UHV, STM, AES, and XPS. Bi2Sr2CaCu2O8 crystals were cleaved in situ and examined by AES. The Bi atomic structure and b-axis superstructure were observed by the STM. The DOS measured by the STM shows a weakly metallic property of the BiO layer. STM topography of Ag adatoms on the BSCCO surface revealed that the Ag atoms form clusters. Iodine was used to intercalate the Bi2Sr2CaCu2O8 compound to form stage-1 IBi2Sr2CaCu2Oy. The XPS spectrum confirms that iodine is bonded in the crystal. The iodine 3d5.2 and 3d3/2 core level XPS peaks indicate that iodine is in the I- oxidation state. The O 1s peak was broadened and shifted about 0.8 eV toward higher binding energy, consistent with electrons transferring to the iodine intercalated between the oxygen atoms in the Bi-O bilayers. The Bi 4f and Cu 2p3/2 peaks exhibit relatively small shifts toward lower binding energy

1993-01-01

330

Electron-tunneling studies of thin films of high-T/sub c/ superconducting La-Sr-Cu-O  

International Nuclear Information System (INIS)

We report results of the study of electron tunneling into thin films of the new high-T/sub c/ superconductor La-Sr-Cu-O. Both sandwich-type tunneling with a Pb counterelectrode and point-contact tunneling have been successfully achieved. The results show exceptionally large energy gaps in these materials (roughly 20, 30, and possibly even 60 mV), larger than previously obtained on bulk sintered powders. We interpret these results as due to large anisotropy in this material or due to the presence of a a very high-T/sub c/ layer near the surface of the films. The method of preparation of this new superconductor in thin film form is also discussed

1987-05-01

331

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.

O.M. Voitsekhivska

2011-12-01

332

Energy and angular distribution of relativistic electrons in the tunnelling ionization of atoms by circularly polarized light  

Science.gov (United States)

Simple analytic expressions are obtained for relativistic electron energies and angular distributions produced in tunnelling ionization of atoms by intense laser radiation. Circularly polarized radiation is considered, using the Landau-Dykhne approach. Major differences have been found as compared with the previously investigated case of linearly polarized laser radiation: a circularly polarized intense field produces mainly relativistic electrons, while a linearly polarized intense field produces mainly non-relativistic electrons. In the limit of a weak field we obtain well known expressions for the non-relativistic energy spectrum and angular distribution of ejected electrons in the tunnelling ionization of atoms. (Limited, of course, to the case where the so-called Keldysh parameter corresponds to the tunnelling regime of ionization.) Simple expressions have been found for: (1) the angle between the direction at which most of the relativistic electrons are ejected and the plane of polarization of the laser radiation; (2) the energy spectrum at this angle; (3) the width of the energy spectrum and the position of its maximum; (4) the angular distribution near this angle and the width of this distribution. Our simple purely analytical results for energy and angular distributions are in agreement with the numerical derivations of Reiss based on the strong field approximation.

Krainov, V. P.

1999-03-01

333

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

334

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

CERN Document Server

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

335

Theory of the tunneling resonances of the bilayer electron systems in strong magnetic field  

Science.gov (United States)

We develop a theory for the anomalous interlayer conductance peaks observed in bilayer electron systems at ?=1 [1].Our model shows that the size of the peak at zero bias decreases rapidly with increasing in-plane magnetic field, but its location is unchanged. The I(V) characteristic is linear at small voltages, in agreement with experimental observations [1]. In addition we make quantitative predictions for how the inter-layer conductance peaks vary in position with in-plane magnetic field at high voltages. In this work we propose an approach based on a damped Landau-Lifshitz equation for the pseudospin order parameter. Our model differs from other approaches in the types of dissipation included and how interlayer current is calculated. These differences permit allow the model to capture previously unexplained features of the interlayer tunneling spectrum in low and high bias voltages. Furthermore, we argue the low voltage state is different from the Josephson effect, and therefore argue against possibility of the Josephson effect [2]. Ref: [1] Spielman et al. PRL, 84, 5808, (2000), ibid.87, 036803 (2001). [2] M. Abolfath, R. Khomeriki, K. Mullen, cond-mat/0208236.

Abolfath, Ramin; Khomeriki, Ramaz; Mullen, Kieran

2003-03-01

336

Integrated Electron-tunneling Refrigerator and TES Bolometer for Millimeter Wave Astronomy  

Science.gov (United States)

We describe progress in the development of a close-packed array of bolometers intended for use in photometric applications at millimeter wavelengths from ground- based telescopes. Each bolometer in the may uses 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 ambient bath 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 (approx.10 pW) bolometers to <170 mK while the bolometers are inside a pumped 3He-cooled cryostat operating at approx.280 mK. This significantly lower temperature at the bolometer allows the detectors to approach background-limited performance despite the simple cryogenic system.

Silverberg, R. F.; Benford, D. J.; Chen, T. C.; Chervenak, J.; Finkbeiner, F.; Moseley, S. H.; Duncan, W.; Miller, N.; Schmidt, D.; Ullom, J.

2005-01-01

337

Inelastic electron tunnelling in saturated molecules with different functional groups: correlations and symmetry considerations from a computational study  

International Nuclear Information System (INIS)

The inelastic electron tunnelling (IET) spectra of a series of molecules with the commonest functional groups are evaluated computationally. It is found that ether, secondary amine and thioether groups do not leave any characteristic signatures on the IET spectrum (in comparison with simple alkanes) and they cannot be used as 'tracers' for the tunnelling path of the electron. In contrast, carbonyl and ester groups modify the appearance of the IET spectrum considerably. The series of computations was also used to validate, for the case of saturated molecules, the propensity rules for IET spectroscopy proposed in the literature. It is found that totally symmetric vibrations give the largest contribution to the spectrum and that there is no correlation between IET and infrared or Raman absorption intensities

2008-09-17

338

Sensitizers in inelastic electron tunneling spectroscopy: a first-principles study of functional aromatics on Cu(111).  

Science.gov (United States)

Low sensitivity is a key problem in inelastic electron tunneling spectroscopy (IETS) with the scanning tunneling microscope. Using first-principles simulations, we predict different means to tune the IETS sensitivity of symmetrical functional aromatics on a Cu(111) surface. We show how the IET-spectra of phenyl-NO? compounds can be greatly enhanced as compared to pristine phenyl. More precisely, the NO? substituent qualifies as a sensitizer of low-frequency wagging modes, but also as a quencher of high-frequency stretching modes. At variance, the CO? substituent is found to suppress the whole IET-activity. The head-up (non-anchoring) and head-down (anchoring) configurations of the functional group lead to minor changes in the signals, nevertheless allowing access to discriminate configurational features. It is shown how to disentangle the electronic and steric effects of the substituent in the STM junction. PMID:22797417

Burema, S R; Bocquet, M-L

2012-08-10

339

Reversible achiral-to-chiral switching of single Mn--phthalocyanine molecules by thermal hydrogenation and inelastic electron tunneling dehydrogenation.  

Science.gov (United States)

Induction of chirality in planar adsorbates by hydrogenation of phthalocyanine molecules on a gold surface is demonstrated. This process merely lowers the molecular symmetry from 4- to 2-fold, but also breaks the mirror symmetry of the entire adsorbate complex (molecule and surface), thus rendering it chiral without any realignment at the surface. Repositioning of single molecules by manipulation with the scanning tunneling microscope (STM) causes interconversion of enantiomers. Dehydrogenation of the adsorbate by means of inelastic electron tunneling restores the mirror symmetry of the adsorbate complex. STM as well as density functional theory (DFT) calculations show that chirality is actually imprinted into the electronic molecular system by the surface, i.e., the lowest unoccupied orbital is devoid of mirror symmetry. PMID:24484418

Yang, Kai; Liu, Liwei; Zhang, Lizhi; Xiao, Wende; Fei, Xiangmin; Chen, Hui; Du, Shixuan; Ernst, Karl-Heinz; Gao, Hong-Jun

2014-03-25

340

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

International Nuclear Information System (INIS)

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

2012-01-01

 
 
 
 
341

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

342

Role of the thermoactivated and tunnel electron relaxations of radiation defects in initiation of isothermal exoemission current  

International Nuclear Information System (INIS)

In this paper aimed at the determination of the role of thermoactivated and tunnel electron-hole recombinations of radiation defects in the appearance of the isothermal exoelectron emission (EEE) current, we carry out the calculation of a value of the isothermal EEE current and make its comparison with the experimental curves of the EEE decay, at various ses of the ultraviolet irradiation of the CsBr alkaline-halide crystals

2005-05-01

343

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

Digital Repository Infrastructure Vision for European Research (DRIVER)

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 prope...

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

2012-01-01

344

COLLECTIONS OF ELECTRONIC INFORMATION RESOURCES AND THEIR METADESCRIPTIONS AS COMPONENTS OF SCIENTIFIC ELECTRONIC LIBRARY ???????? ??????????? ????????????? ???????? ? ?? ????????? ?? ?????????? ???????? ??????????? ?????????  

Directory of Open Access Journals (Sweden)

Full Text Available The article presents the results of scientific research components of digital libraries, the main ones being the collection of electronic scientific information resources. An important specific characteristics of collections of scientific information resources, resources of their formation, structure collections, methods of their organization, technology creation, support and use of scientific collections, the role and function of metadata in collections and metadata management technology are represented. On the stage of planning and introduction of scientific e-libraries there can be used results of researches presented in the article, namely: chart of forming of collections of scientific informative resources; stages of planning and development of metadescriptions, and similarly the use of standard the Dublin kernel, creation of metadescriptions.? ?????? ?????? ?????????? ??????????? ????????? ???????? ??????????? ?????????, ????????? ? ???? ? ???????? ???????? ??????????? ????????????? ????????. ???????? ???????????? ?????????? ??????????? ???????? ???????? ????????????? ????????, ??????? ?? ??????????, ????????? ????????, ?????? ?? ??????????????, ?????????? ?????????, ???????????? ????????? ?? ???????????? ???????? ????????; ???? ? ??????? ????????? ? ????????? ? ?????????? ?????????? ??????????. ?? ????? ???????????? ? ???????????? ???????? ??????????? ????????? ?????? ???? ??????????? ?????????? ???????????, ????????? ? ??????, ? ????: ????? ?????????? ???????? ???????? ????????????? ????????; ????? ???????????? ? ???????? ?????????? ? ???????????? ????????? ?????????? ????, ????????? ??????????.

?.?. ????????

2011-02-01

345

Recognition tunneling  

Energy Technology Data Exchange (ETDEWEB)

Single molecules in a tunnel junction can now be interrogated reliably using chemically functionalized electrodes. Monitoring stochastic bonding fluctuations between a ligand bound to one electrode and its target bound to a second electrode ('tethered molecule-pair' configuration) gives insight into the nature of the intermolecular bonding at a single molecule-pair level, and defines the requirements for reproducible tunneling data. Simulations show that there is an instability in the tunnel gap at large currents, and this results in a multiplicity of contacts with a corresponding spread in the measured currents. At small currents (i.e. large gaps) the gap is stable, and functionalizing a pair of electrodes with recognition reagents (the 'free-analyte' configuration) can generate a distinct tunneling signal when an analyte molecule is trapped in the gap. This opens up a new interface between chemistry and electronics with immediate implications for rapid sequencing of single DNA molecules. (topical review)

Lindsay, Stuart; He Jin; Zhang Peiming; Chang Shuai; Huang Shuo [Biodesign Institute, Arizona State University, Tempe, AZ 85287 (United States); Sankey, Otto [Department of Physics, Arizona State University, Tempe, AZ 85287 (United States); Hapala, Prokop; Jelinek, Pavel [Institute of Physics, Academy of Sciences of the Czech Republic, Cukrovarnicka 10, 1862 53, Prague (Czech Republic)

2010-07-02

346

Recognition Tunneling  

Science.gov (United States)

Single molecules in a tunnel junction can now be interrogated reliably using chemically-functionalized electrodes. Monitoring stochastic bonding fluctuations between a ligand bound to one electrode and its target bound to a second electrode (“tethered molecule-pair” configuration) gives insight into the nature of the intermolecular bonding at a single molecule-pair level, and defines the requirements for reproducible tunneling data. Simulations show that there is an instability in the tunnel gap at large currents, and this results in a multiplicity of contacts with a corresponding spread in the measured currents. At small currents (i.e. large gaps) the gap is stable, and functionalizing a pair of electrodes with recognition reagents (the “free analyte” configuration) can generate a distinct tunneling signal when an analyte molecule is trapped in the gap. This opens up a new interface between chemistry and electronics with immediate implications for rapid sequencing of single DNA molecules.

Lindsay, Stuart; He, Jin; Sankey, Otto; Hapala, Prokop; Jelinek, Pavel; Zhang, Peiming; Chang, Shuai; Huang, Shuo

2010-01-01

347

Scanning tunnelling spectroscopy of atomic clusters deposited on oxidized silicon surfaces: induced surface dipole and resonant electron injection  

International Nuclear Information System (INIS)

We investigated the tunnelling conductance of atomic clusters (C60, Si6Hx, AsSi2Hx) deposited on oxidized p-type Si(100) surfaces using scanning tunnelling microscopy where the metal probe/vacuum barrier/cluster/oxide/silicon structures form an asymmetric double-barrier tunnel (ADBT) nanoscale junction. Atomic clusters were assembled onto ultra-thin (?0.3 nm) silicon oxide by either C60 sublimation or ion beam deposition of Si-clusters generated in an ion trap. Electron transfer to the clusters induced surface dipole and reduced junction current under reverse biasing conditions (negatively biased substrate) depending on cluster structure and composition, where the AsSi2Hx clusters created the strongest dipole. Conductance enhancement was observed for forward bias originating in resonance-like electron injection through the unoccupied orbital of the clusters, which was spatially localized within ?1 deg. nm diameter for C60. The resonance peak positions and the weak surface dipole indicated that the orbital energies of C60 and Si6Hx were beyond the forbidden energy gap of Si and shifted with respect to the silicon Fermi energy for heavily doped substrates. In contrast, the orbital energy of doped AsSi2Hx clusters was below the silicon Fermi level. These results demonstrate that the ADBT junction configuration reveals electronic coupling of the clusters to the semiconductor surfaces

2003-10-29

348

Valence-band electron-tunneling measurement of the gate work function: Application to the high-?/polycrystalline-silicon interface  

Science.gov (United States)

A technique is demonstrated to measure the band alignment between the silicon substrate and the gate electrode using the valence-band electron tunneling (VBET). When an n-channel metal-oxide-semiconductor field-effect transistor is biased in inversion the valence-band electron from the Si substrate can tunnel into the gate [A. Shanware, J. Shiely, H. Massoud, E. Vogel, K. Henson, A. Srivastava, C. Osburn, J. Hauser, and J. Wortman, Tech. Dig.-Int. Electron Devices Meet.1999, 815], depending on the overlapping of the density of states in the Si valence band and the gate. This technique is suitable to measure the band alignment between the silicon substrate and the gate electrode with any given gate dielectric, provided that both the gate and substrate leakages are dominated by direct tunneling. This technique has been applied to study the SiO2/polycrystalline-silicon (poly-Si) interface behavior in the presence of submonolayer traces of HfO2. The general applicability of VBET to arbitrary gate stacks is finally demonstrated with the HfSiON/poly-Si case.

Pantisano, Luigi; Afanas'ev, Valeri; Pourtois, Geoffrey; Chen, P. J.

2005-09-01

349

Electron tunneling spectroscopy of SmB6 studied by in situ nano-break-junction method.  

Science.gov (United States)

Tunneling spectra of intermediate-valence semiconductor SmB6 are reported for in-situ break junctions, being able to make nano-scale planar tunnel junctions. The electron tunneling using break junction method is a powerful probe of the intrinsic energy gap. The investigated tunneling conductance dI/dV curves are mostly reproducible and symmetric with respect to the applied voltage. Two kinds of characteristic energy gaps are observed at 2E(d) = 20 mV and 2E(a) = 9 mV, which coincides well with those previously studied by point-contact spectroscopy and the activation energy fitted by our electrical resistivity data. The positions of the gap structures are independent of the zero-bias conductance, implying no additional voltage drop induced by the break junctions. The small anomaly at the activation energy 2E(a) indicates a relatively low density of in-gap states. Furthermore, the results of magnetic properties reveal the ratio of Sm2+:Sm3+ = 3.7:6.3 and the antiferromagnetic nature at high temperature. PMID:22121717

Lee, Hyun-Won; Lee, Kyujoon; Choo, Seongmin; Jo, Nahyun; Jung, Myung-Hwa

2011-07-01

350

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.

Antanas Kiveris

2010-10-01

351

Spin-dependent single-electron-tunneling effects in epitaxial Fe nanoparticles  

Science.gov (United States)

Fe/MgO/Fe nanoparticles/MgO/Co double tunnel junctions were prepared by molecular beam epitaxy for current-perpendicular-to-plane transport measurements on submicrometer-sized pillars. Microstructural observations indicate that the samples exhibit a fully epitaxial layered structure with sharp and flat interfaces including well-defined separated Fe nanoparticles between the barriers. The introduction of asymmetric MgO tunnel barriers, i.e., with different thicknesses, in the double junction leads to a clear observation of Coulomb staircase and associated tunnel magnetoresistance oscillations. An estimation of the capacitance of the system indicates that these transport phenomena are due to charging effects of the magnetic particles.

Ernult, F.; Yamane, K.; Mitani, S.; Yakushiji, K.; Takanashi, K.; Takahashi, Y. K.; Hono, K.

2004-04-01

352

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

International Nuclear Information System (INIS)

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

2007-01-01

353

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

Digital Repository Infrastructure Vision for European Research (DRIVER)

Abstract A two-dimensional electron gas (2DEG) situated nearby a single layer of self-assembled quantum dots (QDs) in an inverted high electron mobility transistor (HEMT) structure is used as a detector for time-resolved tunneling measurements. We demonstrate a strong influence of charged QDs on the conductance of the 2DEG which allows us to probe the tunneling dynamics between the 2DEG and the QDs time resolved. Measurements of hysteresis curves with different sweep times and real-...

2010-01-01

354

Research on the Construction and Management of Electronic Resources in PDA Mode  

Directory of Open Access Journals (Sweden)

Full Text Available PDA Patron Driven Acquisitions (PDA is literature resources construction mode dominating by user, it is approved by the user because of getting real-time and purchasing user needs. In this mode, the construction of electronic resources tends to get the required resources at this moment. The librarians face more challenge that how to coordinate the permanent preservation and used in real-time on the construction and management of library electronic resources. The article try to put forward some tactics of electronic resources reasonable construction and standardized management from allocation of funds, adjustment of the resource type, performance evaluation of electronic resources, improving electronic resources management system, building institutional repository, analyzing and mining user data and other aspects.

Zhong Wenjuan

2014-01-01

355

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

International Nuclear Information System (INIS)

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

356

Optical detection of hot-electron spin injection into GaAs from a magnetic tunnel transistor source.  

Science.gov (United States)

Injection of spin-polarized hot-electron current from a magnetic tunnel transistor into GaAs is demonstrated by the observation of polarized light emission from a GaAs/In(0.2)Ga(0.8)As multiple quantum well light-emitting diode. Electroluminescence from the quantum wells shows a polarization of approximately 10% after subtraction of a linear background polarization. The polarization shows a strong dependence on the bias voltage across the diode, which may originate from changes in the electron spin relaxation rate in the quantum wells under varying bias conditions. PMID:12857153

Jiang, X; Wang, R; van Dijken, S; Shelby, R; Macfarlane, R; Solomon, G S; Harris, J; Parkin, S S P

2003-06-27

357

Chemical reactions and electronic functions of carbon cluster arrays studied by scanning tunneling spectroscopy and high-resolution electron energy loss spectroscopy  

International Nuclear Information System (INIS)

Novel nanometer scale structures have been produced by thermal heating or laser irradiation on the surface of single- and multi-layers of C60 and C84 on Si. These structures were examined by combined measurements of scanning tunneling spectroscopy and high resolution electron energy loss spectroscopy. The results show specific chemical reactions of substrate with carbon clusters having single- and double-bonded network, Covalent bonds are formed in some of these chemical reactions. (author)

1997-07-15

358

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

Science.gov (United States)

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

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

2013-03-01

359

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

360

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

Science.gov (United States)

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

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

2013-02-01

 
 
 
 
361

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

362

Tunneling Violates Special Relativity  

Digital Repository Infrastructure Vision for European Research (DRIVER)

Experiments with evanescent modes and tunneling particles have shown that i) their signal velocity may be faster than light, ii) they are described by virtual particles, iii) they are nonlocal and act at a distance, iv) experimental tunneling data of phonons, photons, and electrons display a universal scattering time at the tunneling barrier front, and v) the properties of evanescent, i.e. tunneling modes is not compatible with the special theory of relativity.

Nimtz, Guenter

2010-01-01

363

Tunneling between Luttinger liquids  

Energy Technology Data Exchange (ETDEWEB)

The exact solution of the one-dimensional Hubbard model (for repulsive and attractive U) is used to calculate the tunneling rates of single electrons and Cooper pairs between two quantum wires. The critical exponents for the tunneling at small frequencies and low temperatures is obtained by means of the mesoscopic energy spectrum and conformal field theory. The situations of crossing wires, tunneling at a boundary, and resonant tunneling (through a bound state) are considered.

Schlottmann, P.

2001-05-15

364

Light controlled photon tunneling  

CERN Document Server

Recent measurements of photon tunneling through individual subwavelength pinholes in a gold film covered with a layer of polydiacetylene (Phys. Rev. Letters 88, 187402 (2002)) provided strong indication of "photon blockade" effect similar to Coulomb blockade phenomenon observed in single-electron tunneling experiments. Here we report first observation of photon tunneling been blocked (gated) by light at a different wavelength. This observation suggests possibility of building new class of photon tunneling gating devices for all-optical signal processing.

Smolyaninov, I I; Davis, C C

2002-01-01

365

Single-photon tunneling  

CERN Document Server

Strong evidence of a single-photon tunneling effect, a direct analog of single-electron tunneling, has been obtained in the measurements of light tunneling through individual subwavelength pinholes in a thick gold film covered with a layer of polydiacetylene. The transmission of some pinholes reached saturation because of the optical nonlinearity of polydiacetylene at a very low light intensity of a few thousands photons per second. This result is explained theoretically in terms of "photon blockade", similar to the Coulomb blockade phenomenon observed in single-electron tunneling experiments. The single-photon tunneling effect may find many applications in the emerging fields of quantum communication and information processing.

Smolyaninov, I I; Gungor, A; Davis, C C

2001-01-01

366

TENDENCIES OF CREATION AND USE OF ELECTRONIC INFORMATIION RESOURCES AND SERVICES ????????? ????????? ? ???????????? ??????????? ????????????? ???????? ? ????????  

Digital Repository Infrastructure Vision for European Research (DRIVER)

In the article there are considered the most essential tendencies of creation and use of electronic information resources and services in the field of information providing of science and education, namely: modern libraries, publishing houses, control system by information resources.? ?????? ?????????? ???????? ??????? ????????? ????????? ?? ???????????? ??????????? ????????????? ???????? ? ?...

????, ?. ?.; ???????, ?. ?.

2010-01-01

367

Core-electron tunneling in diatomics interacting with intense ultrashort-pulsed XUV and X-ray radiation: Theoretical studies  

International Nuclear Information System (INIS)

Research highlights: ? Intense X-ray and XUV laser fields may induce novel resonant effects in molecules. ? Core-hole localization phenomena influence molecular scattering and photoionization. ? We conducted numerical studies of core-hole localization dynamics in a diatomic ion. ? Localization dynamics can be controlled by the field parameters. ? Intense fields can lead to coherent suppression of inter-well core-hole tunneling. - Abstract: New X-ray free-electron and HHG lasers producing ultra-short pulses of intense XUV/X-ray radiation present a unique opportunity for developing novel techniques which would allow to trace the time evolution of the electronic density in molecular systems and identify signatures of core-electron transitions during the probe pulse. The intensity of XFEL emission is sufficient to influence the field-induced bound-state tunneling of core hole states generated by one-photon ionization. Since molecular imaging experiments at atomic resolution are sensitive to the core-electron density in the target, any density modification has potential implications for the single-shot imaging experiments utilizing femtosecond X-ray pulses. In this work, we discuss the effects of field-induced core-hole transport on X-ray scattering properties in molecular systems. As an example, we consider inter-well tunneling of a core electronic density through the Coulomb barrier between nuclei in a single-electron dicarbon ion under influence of an intense XUV laser field. We employ a simple numerical two-state model which is further corroborated by a numerical solution of the time-dependent three-dimensional Schroedinger equation. Our calculations show pronounced coherent suppression of core-hole delocalization dynamics by very intense XUV laser fields. The laser field parameters determining core-hole tunneling times are scalable for the higher intensity/shorter wavelength regimes. Finally, we discuss the implications of this study for the reconstruction of molecular structures by analysis of scattering data in single-shot XFEL experiments.

2011-04-01

368

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

International Nuclear Information System (INIS)

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

369

Elektronik Bilgi Kaynaklar?n?n Seçimi / Selection of Electronic Information Resources  

Directory of Open Access Journals (Sweden)

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

P?nar Al

2003-04-01

370

Electron tunneling measurements in LaSrCuO and YBaCuO  

International Nuclear Information System (INIS)

The authors analyze the break junction technique, whereby vacuum tunneling occurs within the fracture of a bulk sample to study the LaSrCuO and YBaCuO perovskite superconductors. Structure in the current-versus-voltage characteristics is reminiscent of previous quasiparticle curves obtained for BCS superconducting materials. Some curves have anomalous qualities, including large dips in the junction conductance with increasing voltage just above a well defined tunneling gap edge, linearly increasing junction conductance with applied bias, features occurring near 1, 3, 5 voltage intervals

1987-01-01

371

A theoretical rationalization of a total inelastic electron tunneling spectrum: the comparative cases of formate and benzoate on Cu(111).  

Science.gov (United States)

Inelastic electron tunneling spectroscopy (IETS) performed with the scanning tunneling microscope (STM) has been deemed as the ultimate tool for identifying chemicals at the atomic scale. However, direct IETS-based chemical analysis remains difficult due to the selection rules that await a definite understanding. We present IETS simulations of single formate and benzoate species adsorbed in the same upright bridge geometry on a (111)-cleaved Cu surface. In agreement with measurements on a related substrate, the simulated IET-spectra of formate/Cu(111) clearly resolve one intense C-H stretching mode whatever the tip position in the vicinity of the molecular fragment. At variance, benzoate/Cu(111) has no detectable IET signal. The dissimilar IETS responses of chemically related molecules--formate and benzoate adsorbates--permit us to unveil another factor that complements the selection rules, namely the degree of the vacuum extension of the tunneling active states perturbed by the vibrations. As a consequence, the lack of a topmost dangling bond orbital is entirely detrimental for STM-based inelastic spectroscopy but not for STM elastic imaging. PMID:22755587

Burema, S R; Lorente, N; Bocquet, M-L

2012-06-28

372

Electronic properties of conductive pili of the metal-reducing bacterium Geobacter sulfurreducens probed by scanning tunneling microscopy  

Science.gov (United States)

The metal-reducing bacterium Geobacter sulfurreducens produces conductive protein appendages known as “pilus nanowires” to transfer electrons to metal oxides and to other cells. These processes can be harnessed for the bioremediation of toxic metals and the generation of electricity in bioelectrochemical cells. Key to these applications is a detailed understanding of how these nanostructures conduct electrons. However, to the best of our knowledge, their mechanism of electron transport is not known. We used the capability of scanning tunneling microscopy (STM) to probe conductive materials with higher spatial resolution than other scanning probe methods to gain insights into the transversal electronic behavior of native, cell-anchored pili. Despite the presence of insulating cellular components, the STM topography resolved electronic molecular substructures with periodicities similar to those reported for the pilus shaft. STM spectroscopy revealed electronic states near the Fermi level, consistent with a conducting material, but did not reveal electronic states expected for cytochromes. Furthermore, the transversal conductance was asymmetric, as previously reported for assemblies of helical peptides. Our results thus indicate that the Geobacter pilus shaft has an intrinsic electronic structure that could play a role in charge transport.

Veazey, Joshua P.; Reguera, Gemma; Tessmer, Stuart H.

2011-12-01

373

Electron-tunneling studies on CeCoIn{sub 5} heavy-fermion thin films and microstructures  

Energy Technology Data Exchange (ETDEWEB)

In many cases, the availability of high-quality thin films of a material under study allows to gain valuable physical insight into its properties. For example, when thin films are available, planar tunneling spectroscopy or quantum mechanical interferometry techniques can be used to probe the electronic properties in a very direct way. In this work, we study the rich but poorly understood electronic properties of the heavy-fermion compound CeCoIn{sub 5}. Numerous attempts to grow homogeneous CeCoIn{sub 5} thin films of the desired quality have not been successful. Our work therefore pursuits two goals: (1) to improve the CeCoIn{sub 5} thin film quality using the molecular beam epitaxy and (2) to investigate the low-temperature electronic properties of the CeCoIn{sub 5} thin films using direct probing methods.

Foyevtsov, Oleksandr

2012-06-12

374

Low-temperature scanning tunneling spectroscopy study of two-dimensional electron systems confined in semiconductor heterostructures  

International Nuclear Information System (INIS)

Low-temperature scanning tunneling spectroscopy under ultra-high vacuum was employed to investigate the two-dimensional electron system at the epitaxial surface of Sidoped In0.53Ga0.47As/In0.52Al0.48As(111)A quantum-well structures. The electron density in the near-surface region of the quantum well could be controlled through modulation doping. Spectra of the electronic local density of states in the conduction band showed a clear step-like energy dependence that reveals the subband states. In spectra acquired at some areas of nanometer size, peaks were observed near subband minima, indicating the existence of bound states

2007-04-01

375

Resonant tunneling and persistent current of a non-interacting and weakly interacting one-dimensional electron gas  

International Nuclear Information System (INIS)

The persistent current for a one-dimensional ring with two tunneling barriers is considered in the limit of weakly interacting electrons. In addition to small off-resonance current, there are two kinds of resonant behaviour; (i) a current independent of the barrier transparency (true resonance) and (ii) a current analogous to the one for a ring with only single barrier (''semi''-resonance). For a given barrier transparency the realization of this or that type of resonant behaviour depends both on the geometrical factor (the ratio of interbarrier distance to a ring circumference) and on the strength of electron-electron interaction. It is shown that repulsive interaction favours the ''semi''-resonance behaviour. For a small barrier transparency the ''semi''-resonance peaks are easily washed out by temperature whereas the true resonance peaks survive. (author). 22 refs, 2 figs

1997-01-01

376

Imaging the electron-boson coupling in superconducting FeSe films using a scanning tunneling microscope.  

Science.gov (United States)

Scanning tunneling spectroscopy has been used to reveal signatures of a bosonic mode in the local quasiparticle density of states of superconducting FeSe films. The mode appears below Tc as a "dip-hump" feature at energy ??4.7kBTc beyond the superconducting gap ?. Spectra on strained regions of the FeSe films reveal simultaneous decreases in ? and ?. This contrasts with all previous reports on other high-Tc superconductors, where ? locally anticorrelates with ?. A local strong coupling model is found to reconcile the discrepancy well, and to provide a unified picture of the electron-boson coupling in unconventional superconductors. PMID:24580624

Song, Can-Li; Wang, Yi-Lin; Jiang, Ye-Ping; Li, Zhi; Wang, Lili; He, Ke; Chen, Xi; Hoffman, Jennifer E; Ma, Xu-Cun; Xue, Qi-Kun

2014-02-01

377

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

2012-10-01

378

Magnetic transitions induced by tunnelling electrons in individual adsorbed M-Phthalocyanine molecules (M $\\equiv$ Fe, Co)  

Digital Repository Infrastructure Vision for European Research (DRIVER)

We report on a theoretical study of magnetic transitions induced by tunnelling electrons in individual adsorbed M-Phthalocyanine (M-Pc) molecules where M is a metal atom: Fe-Pc on a Cu(110)(2$\\times$1)-O surface and Co-Pc layers on Pb(111) islands. The magnetic transitions correspond to the change of orientation of the spin angular momentum of the metal ion with respect to the surroundings and possibly an applied magnetic field. The adsorbed Fe-Pc system is studied with a De...

Gauyacq, Jean-pierre; Novaes, Frederico D.; Lorente, Nicola?s

2010-01-01

379

Tunneling between quantum wells  

International Nuclear Information System (INIS)

Tunneling transfer in various GaAs/Al0.35Ga0.65As asymmetric double quantum well structures is studied by time-resolved photoluminescence measurements in the pico and femtosecond regime. A large variety of electron and hole resonances is detected when electric fields of both signs are externally applied. The ground state resonance shifts, when the electrons tunnel in the reverse direction, revealing the importance of excitonic effects. Longitudinal optical phonon assisted tunneling plays a minor role for narrow quantum wells in comparison to impurity or interface roughness assisted transfer. Resonant electron tunneling times depend exponentially on the square root of integrated tunneling barrier height and are an order of magnitude faster than resonant hole tunneling times. The n = 2 to n = 1 electronic intersubband scattering time in a 10 nm quantum well is determined to be 550 fs measuring the transfer time through a thin barrier

1992-03-23

380

Tunneling transmission coefficients for electrons through (100) GaAs--Ga/sub 1-x/Al/sub x/As--GaAs heterostructures  

International Nuclear Information System (INIS)

We present calculations of tunneling transmission coefficients for electrons through (100) GaAs-Ga/sub 1-x/Al/sub x/As--GaAs heterostructures. The calculations were performed using the empirical tight binding approximation. For sufficiently thick alloy regions, the tunneling probability is an exponential which decays with alloy thickness multiplied by a prefactor which is independent of alloy thickness. We have investigated the dependence of the tunneling prefactors on incident electron wavevector and alloy composition x. For the prefactors, we find a strong dependence on the incident electron wavevector component, normal to the interfaces and the alloy composition x, and a weak dependence on the incident electron wavevector component parallel to the interface for the energy range of interest

1980-01-01

 
 
 
 
381

Ferroelectric Tunnel Junctions  

Digital Repository Infrastructure Vision for European Research (DRIVER)

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

2003-01-01

382

Universal Time Tunneling  

Digital Repository Infrastructure Vision for European Research (DRIVER)

How much time does a tunneling wave packet spent in traversing a barrier? Quantum mechanical calculations result in zero time inside a barrier . In the nineties analogous tunneling experiments with microwaves were carried out. The results agreed with quantum mechanical calculations. Electron tunneling time is hard to measure being extremely short and parasitic effects due to the electric charge of electrons may be dominant. However, quite recently the atomic ionization tunne...

Nimtz, Guenter

2009-01-01

383

Trapped-electron capture by steroid molecules with two distinct, reactive groups. A test of the long-range tunneling mechanism  

International Nuclear Information System (INIS)

A quantitative test of the tunneling mechanism for trapped-electron scavenging in low-temperature glasses is described. Kinetics of reactions of trapped electrons with steroid molecules having two electron accepting groups rigidly held approx. 10 A apart were studied in organic glasses at 77 K. A model for trapped-electron scavenging by such difunctional molecules, based on the long-range tunneling mechanism, is presented. The model predicts that a difunctional molecule can be a considerably less effective electron acceptor than two independent monofunctional molecules when the separation between the two reactive groups is a substantial fraction of the tunneling distances. The experimental results show that the tunneling model does, in fact, quantitatively predict the kinetics for the reaction of e/sub t/"- with difunctional steroids from two pieces of information: (1) the measured kinetics for reaction with monofunctional model compounds and (2) the known distance between the two reactive functional groups. An alternative hopping model might plausibly provide a parametric fit to the data but cannot make a definite prediction. The results provide strong evidence for the long-range tunneling mechanism

1981-07-23

384

Calculations of the radiation doses to the electronic equipment and magnet coil insulation in the PEP-II tunnel  

Science.gov (United States)

The PEP-II collaboration is a new physics project at SLAC that utilizes an existing tunnel to house two accelerator storage rings; a low-energy positron ring (4 GeV, called the LER) atop a high-energy electron ring (10 GeV, called the HER). Both rings are being designed to permit a high circulating current of 3 A, corresponding to a beam particle number of 1.38 × 10 14. Dose calculations were made to estimate the potential for radiation damages to the electronics and magnet coil insulation in the arc section of the tunnel. An analytical code, SHIELD11, was used to calculate the dose from photon and neutron radiations resulting from beam losses in various modes of operation. Several EGS4 Monte Carlo user codes were developed to calculate the dose from the synchrotron radiation escaping the vacuum chamber in stored beam mode. Two different LER vacuum chamber designs were studied: a 0.35-cm-thick copper wall chamber and a 1-cm-thick aluminum wall chamber with a copper absorber 6 m downstream of every dipole to absorb the synchrotron radiation in a local spot. The HER has a 0.5-cm-thick copper vacuum chamber. Shielding from the 5.4-m-long, C-shaped iron bending magnet for the HER was considered for the beam radiation, while no other structural shielding was assumed for the LER. Furthermore, the dose from all radiations scattering back from the tunnel concrete wall were also estimated using the albedo method or the MORSE code. The results of the dose estimations are presented.

Liu, J. C.; Mao, S.; Nelson, W. R.; Kase, K. R.; Ipe, N. E.

1995-02-01

385

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

Science.gov (United States)

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

Hoell, Robert C.; Henry, Gordon O.

2003-01-01

386

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

387

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

388

Electronic resource management practical perspectives in a new technical services model  

CERN Document Server

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

Elguindi, Anne

2012-01-01

389

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

390

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

2011-01-01

391

Rotation of a Single Acetylene Molecule on Cu(001) by Tunneling Electrons in STM  

Science.gov (United States)

We study the elementary processes behind one of the pioneering works on scanning tunneling microscope controlled reactions of single molecules [Stipe et al., Phys. Rev. Lett. 81, 1263 (1998)]. Using the Keldysh-Green function approach for the vibrational generation rate in combination with density functional theory calculations to obtain realistic parameters we reproduce the experimental rotation rate of an acetylene molecule on a Cu(100) surface as a function of bias voltage and tunneling current. This combined approach allows us to identify the reaction coordinate mode of the acetylene rotation and its anharmonic coupling with the C-H stretch mode. We show that three different elementary processes, the excitation of C-H stretch, the overtone ladder climbing of the hindered rotational mode, and the combination band excitation together explain the rotation of the acetylene molecule on Cu(100).

Shchadilova, Yulia E.; Tikhodeev, Sergei G.; Paulsson, Magnus; Ueba, Hiromu

2013-11-01

392

Electronic picture of spin-polarized tunneling with a Cr tip  

Energy Technology Data Exchange (ETDEWEB)

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

Czerner, Michael, E-mail: michael.czerner@physik.uni-halle.d [Martin-Luther-Universitaet Halle, D-06099 Halle (Germany); Rodary, Guillemin; Wedekind, Sebastian [Max-Planck-Institut fuer Mikrostrukturphysik, D-06120 Halle (Germany); Fedorov, Dmitry V. [Martin-Luther-Universitaet Halle, D-06099 Halle (Germany); Sander, Dirk [Max-Planck-Institut fuer Mikrostrukturphysik, D-06120 Halle (Germany); Mertig, Ingrid [Martin-Luther-Universitaet Halle, D-06099 Halle (Germany); Kirschner, Juergen [Max-Planck-Institut fuer Mikrostrukturphysik, D-06120 Halle (Germany)

2010-05-15

393

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

Science.gov (United States)

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

Chatterjee, Vijay; Harniman, Robert; May, Paul W.; Barhai, P. K.

2014-04-01

394

Tunneling Spectroscopy on Grain Boundary Junctions in Electron-Doped High-Temperature Superconductors  

Digital Repository Infrastructure Vision for European Research (DRIVER)

Tunneling spectroscopy on grain boundary junctions and resistivity measurements on thin films of n-doped high temperature superconductors (HTC) with different dopings are used to investigate the n-doped side of the phase diagram for HTC. In terms of data analysis, a recursive devonvolution method for spectra on symmetrical contacts is proposed. The experimental spectra of all superconducting contacts don't show any sign of Andreev bound states, irrespective of the n-doping. The pseudogap in s...

2008-01-01

395

Electronic structure of single DNA molecules resolved by transverse scanning tunnelling spectroscopy.  

Science.gov (United States)

Attempts to resolve the energy-level structure of single DNA molecules by scanning tunnelling spectroscopy span over the past two decades, owing to the unique ability of this technique to probe the local density of states of objects deposited on a surface. Nevertheless, success was hindered by extreme technical difficulties in stable deposition and reproducibility. Here, by using scanning tunnelling spectroscopy at cryogenic temperature, we disclose the energy spectrum of poly(G)-poly(C) DNA molecules deposited on gold. The tunnelling current-voltage (I-V) characteristics and their derivative (dI/dV-V) curves at 78 K exhibit a clear gap and a peak structure around the gap. Limited fluctuations in the I-V curves are observed and statistically characterized. By means of ab initio density functional theory calculations, the character of the observed peaks is generally assigned to groups of orbitals originating from the different molecular components, namely the nucleobases, the backbone and the counterions. PMID:18037894

Shapir, Errez; Cohen, Hezy; Calzolari, Arrigo; Cavazzoni, Carlo; Ryndyk, Dmitry A; Cuniberti, Gianaurelio; Kotlyar, Alexander; Di Felice, Rosa; Porath, Danny

2008-01-01

396

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

2003-12-01

397

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

Directory of Open Access Journals (Sweden)

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

Reuter Dirk

2010-01-01

398

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

Scientific Electronic Library Online (English)

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

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

399

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

International Nuclear Information System (INIS)

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

2011-03-13

400

New insights into the mechanism of electron transfer within flavohemoglobins: tunnelling pathways, packing density, thermodynamic and kinetic analyses.  

Science.gov (United States)

Flavohemoglobins (FlavoHb) are metalloenzymes catalyzing the reaction of nitric oxide dioxygenation. The iron cation of the heme group needs to be preliminarily reduced to the ferrous state to be catalytically competent. This reduction is triggered by a flavin adenine dinucleotide (FAD) prosthetic group which is localized in a distinct domain of the protein. In this paper we obtain new insights into the internal long range electron transfer (over ca. 12 Å) using a combination of experimental and computational approaches. Employing a time-resolved pulse radiolysis technique we report the first direct measurement of the FADH?? HemeFe(III) electron transfer rate. A rate constant of (6.8 ± 0.5) × 10(3) s(-1) is found. A large panel of computational approaches are used to provide the first estimation of the thermodynamic characteristics of the internal electron transfer step within flavoHb: both the driving force and the reorganization energy are estimated as a function of the protonated state of the flavin semi-quinone. We also report an analysis of the electron pathways involved in the tunnelling of the electron through the aqueous interface between the globin and the flavin domains. PMID:22948361

El Hammi, Emna; Houée-Lévin, Chantal; ?ezá?, Jan; Lévy, Bernard; Demachy, Isabelle; Baciou, Laura; de la Lande, Aurélien

2012-10-28

 
 
 
 
401

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

Digital Repository Infrastructure Vision for European Research (DRIVER)

A two-dimensional electron gas (2DEG) situated nearby a single layer of self-assembled quantum dots (QDs) in an inverted high electron mobility transistor (HEMT) structure is used as a detector for time-resolved tunneling measurements. We demonstrate a strong influence of charged QDs on the conductance of the 2DEG which allows us to probe the tunneling dynamics between the 2DEG and the QDs time resolved. Measurements of hysteresis curves with different sweep times and real-time conductance me...

2010-01-01

402

????????????????????--?????????????? | Electronic Resource Sharing of Public Libraries in Taiwan  

Directory of Open Access Journals (Sweden)

Full Text Available

???85-97

?????????????????????88???????????????????????????????????????????????????????????????????????www???????????????????????????????????????????????????????????????

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

The Project of Electronic Resource Sharing of Public Libraries in Taiwan was subsidized by Ministry of Education and carried out by National Taichung Library. The Project started in January of 1999. Its purposes are to establish an electronic database system through WWW for all the public libraries in Taiwan to provide the public to use, and to form a public library cooperation mechanism to foster resource sharing among the libraries.

This paper introduces the brief history, current status, and achievement o

??? Li-Hsiang Lai

2001-04-01

403

The Superluminal Tunneling Story  

CERN Document Server

Since 1992 experimental evidence of superluminal (faster than light, FTL) signals are causing much excitement in the physical community and in the media. Superluminal signal velocity and zero time tunneling was first observed in an analog tunneling experiment with microwaves. Recently, the conjectured zero time of electron was claimed to be observed in ionizing helium. The FTL signal velocity was reproduced with infrared light and with various tunneling barriers in several laboratories worldwide. Remarkable, it was shown that the tunneling time is a universal quantity for elastic and for electromagnetic fields. Many theoretical physicists predicted this FTL nature of the tunneling process. However, even with this background many members of the physics community did not accept the superluminal signal velocity interpretation of the experimental results and they also ignored the universal tunneling time. The predicted and measured zero tunneling time was taken as a fantastic nonsense. A brief explanation of the ...

Aichmann, Horst

2013-01-01

404

Strong overtones modes in inelastic electron tunneling spectroscopy with cross-conjugated molecules : a prediction from theory  

DEFF Research Database (Denmark)

Cross-conjugated molecules are known to exhibit destructive quantum interference, a property that has recently received considerable attention in single-molecule electronics. Destructive quantum interference can be understood as an antiresonance in the elastic transmission near the Fermi energy and leading to suppressed levels of elastic current. In most theoretical studies, only the elastic contributions to the current are taken into account. In this paper, we study the inelastic contributions to the current in cross-conjugated molecules and find that while the inelastic contribution to the current is larger than for molecules without interference, the overall behavior of the molecule is still dominated by the quantum interference feature. Second, an ongoing challenge for single molecule electronics is understanding and controlling the local geometry at the molecule-surface interface. With this in mind, we investigate a spectroscopic method capable of providing insight into these junctions for cross-conjugated molecules: inelastic electron tunneling spectroscopy (IETS). IETS has the advantage that the molecule interface is probed directly by the tunneling current. Previously, it has been thought that overtones are not observable in IETS. Here, overtones are predicted to be strong and, in some cases, the dominant spectroscopic features. We study the origin of the overtones and find that the interference features in these molecules are the key ingredient. The interference feature is a property of the transmission channels of the Ï? system only, and consequently, in the vicinity of the interference feature, the transmission channels of the Ï? system and the Ï? system become equally transmissive. This allows for scattering between the different transmission channels, which serves as a pathway to bypass the interference feature. A simple model calculation is able to reproduce the results obtained from atomistic calculations, and we use this to interpret these findings.

Jørgensen, Jacob Lykkebo; Gagliardi, Alessio

2013-01-01

405

Physisorption versus chemisorption in inelastic electron tunneling spectroscopy: Mode position, intensity, and spatial distribution  

Science.gov (United States)

Local vibrational spectra of meta-dichlorobenzene molecules adsorbed on different parts of the Au(111) reconstruction are investigated using a low-temperature scanning tunneling microscope. The spectra show substantial variations on subnanometer length scale. While for the molecule physisorbed on either the hcp or the fcc domain of the reconstruction only low-energy modes are beyond the detection limit, higher-energy modes are observed for the molecule chemisorbed at the elbow site. The different adsorption strengths of the molecules manifest themselves in an energy shift of the modes. These shifts are used to identify through which part the molecule is bonded to the surface.

Gawronski, Heiko; Morgenstern, Karina

2014-03-01

406

Electronic properties of Al-SiO2-(n or p) Si MIS tunnel diodes  

Digital Repository Infrastructure Vision for European Research (DRIVER)

Automatic measurements I-V, C/G(V, ?) are used to study the electrical properties of a great number of aluminum-SiO 2-n or p type silicon MIS tunnel diodes with an oxide thickness of 30 Å prepared by two technologies of oxidation, low pressure chemical vapour deposition (LPCVD) and low oxygen pressure (LPO2). A comparison between the I-V and C-V characteristics on n and p substrate is presented as well as a dispersion study of I-V characteristics. The modelling of I-V characteristics has be...

Vuillod, J.; Pananakakis, G.

1985-01-01

407

Tunneling Spectroscopy of the Electron-Doped Cuprate Superconductor Pr2-xCexCuO4  

Science.gov (United States)

The properties of electron(n)-doped cuprate superconductors show significant deviations from those of their hold(p)-doped counterparts. Experiments prior to 2000 suggested an s-wave pairing symmetry as opposed to a d-wave pairing symmetry in hole-doped cuprates. Recent experiments have suggested that n-doped cuprates have a d-wave pairing symmetry. However, tunneling spectroscopy of these materials have not revealed a zero bias conductance peak (ZBCP), which is a classic signature of d-wave symmetry. We present the first tunneling spectroscopy data on n-doped Pr2-xCexCuO4 (PCCO) using point contact junctions which show a systematic evolution of the ZBCP. This method of junction fabrication is important as it allows the barrier strength between the normal and the superconducting electrodes to be varied. We show that this is essential to observing the ZBCP. The n-doped cuprates have a low Tc (~25 K) and Hc2 (~10 T). The low Hc2 enables us to obtain the normal state in PCCO at low temperatures. We have used this to probe the density of states in the normal state of PCCO. We observe an anomalous gap even in the normal state.1 This normal state gap (NSG) becomes smaller on the over-doped side. We discuss the behavior of this NSG in the context of the pseudogap which has been observed in hole-doped cuprates.

Biswas, A.; Fournier, P.; Smolyaninova, V. N.; Balci, H.; Higgins, J. S.; Budhani, A. R. C.; Greene, R. L.

2002-07-01

408

Tunneling conductance in a gapped graphene-based superconducting structure: Case of massive Dirac electrons  

International Nuclear Information System (INIS)

The tunneling conductance in a NG/SG graphene junction in which the graphene was grown on a SiC substrate is simulated. The carriers in the normal graphene (NG) and the superconducting graphene (SG) are treated as massive relativistic particles. It is assumed that the Fermi energy in the NG and SG are EFN?400 meV and EFS?400 meV+U, respectively. Here U is the electrostatic potential from the superconducting gate electrode. It is seen that the Klein tunneling disappears in the case where a gap exist in the energy spectrum. As U??, the zero bias normalized conductance becomes persistent at a minimal value of G/G0?1.2. The normalized conductance G/G0 is found to depend linearly on U with constant slope of ?=2/(EFN-mvF2)?7.4, where 2mvF2 is the size of the gap ? opening up in the energy spectrum of the graphene grown on the SiC substrate. It is found that G/G0?2+?U for potentials in the range -270 meV0?2?(U). This last behavior indicates that a NG/SG junction made with gapped graphene could be used as a nano switch having excellent characteristics.

2009-09-14

409

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

CERN Document Server

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

410

CREATION OF ELECTRONIC RESOURCES IN STATE SCIENTIFIC AND PEDAGOGICAL LIBRARY BY V.A.SUHOMLINSKIY ?????????? ??????????? ???????? ? ????????? ???????-???????????? ?????????? ??????? ????? ?. ?. ??????????????  

Directory of Open Access Journals (Sweden)

Full Text Available The main directions of development of the work of SSPL of Ukraine by V.A. Suhomlinskiy on creation of electronic information resources on psychology-pedagogical questions: the electronic directory, the database, the electronic library are considered in the article.?????????? ??????? ??????? ?????? ???? ??????? ??. ?. ?. ?????????????? ?? ????????? ??????????? ????????????? ???????? ?? ?????????-???????????? ??????: ??????????? ???????, ???? ?????, ?????????? ??????????

?.?. ?????????

2010-08-01

411

The Superluminal Tunneling Story  

Digital Repository Infrastructure Vision for European Research (DRIVER)

Since 1992 experimental evidence of superluminal (faster than light, FTL) signals are causing much excitement in the physical community and in the media. Superluminal signal velocity and zero time tunneling was first observed in an analog tunneling experiment with microwaves. Recently, the conjectured zero time of electron was claimed to be observed in ionizing helium. The FTL signal velocity was reproduced with infrared light and with various tunneling barriers in several l...

Aichmann, Horst; Nimtz, Gu?nter

2013-01-01

412

Tunneling in Nanoscale Devices  

Digital Repository Infrastructure Vision for European Research (DRIVER)

Theoretical treatments of tunneling in electronic devices are often based on one-dimensional (1D) approximations. Here we show that for many nanoscale devices, such as widely studied semiconductor gate-defined quantum dots, 1D approximations yield an incorrect functional dependence on the tunneling parameters (e.g., lead width and barrier length) and an incorrect magnitude for the transport conductance. Remarkably, the physics of tunneling in 2D or 3D also yields transport b...

Friesen, Mark; Simmons, M. Y.; Eriksson, M. A.

2013-01-01

413

Single-photon tunneling  

Digital Repository Infrastructure Vision for European Research (DRIVER)

Strong evidence of a single-photon tunneling effect, a direct analog of single-electron tunneling, has been obtained in the measurements of light tunneling through individual subwavelength pinholes in a thick gold film covered with a layer of polydiacetylene. The transmission of some pinholes reached saturation because of the optical nonlinearity of polydiacetylene at a very low light intensity of a few thousands photons per second. This result is explained theoretically in ...

Smolyaninov, I. I.; Zayats, A. V.; Gungor, A.; Davis, C. C.

2001-01-01

414

Light controlled photon tunneling  

Digital Repository Infrastructure Vision for European Research (DRIVER)

Recent measurements of photon tunneling through individual subwavelength pinholes in a gold film covered with a layer of polydiacetylene (Phys. Rev. Letters 88, 187402 (2002)) provided strong indication of "photon blockade" effect similar to Coulomb blockade phenomenon observed in single-electron tunneling experiments. Here we report first observation of photon tunneling been blocked (gated) by light at a different wavelength. This observation suggests possibility of buildin...

Smolyaninov, I. I.; Zayats, A. V.; Davis, C. C.

2002-01-01

415

Josephson tunneling and nanosystems  

Digital Repository Infrastructure Vision for European Research (DRIVER)

Josephson tunneling between nanoclusters is analyzed. The discrete nature of the electronic energy spectra, including their shell ordering, is explicitly taken into account. The treatment considers the two distinct cases of resonant and non-resonant tunneling. It is demonstrated that the current density greatly exceeds the value discussed in the conventional theory. Nanoparticles are shown to be promising building blocks for nanomaterials-based tunneling networks.

Ovchinnikov, Yurii; Kresin, Vladimir

2010-01-01

416

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

2007-11-06

417

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

Science.gov (United States)

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

Burke, Brian; Chan, Jack; Williams, Keith; Ge, Jiechao; Shu, Chunying; Fu, Wujun; Dorn, Harry; Kushmerick, James; Puretzky, Alexander; Geohegan, David

2010-03-01

418

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

Science.gov (United States)

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

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

2010-03-01

419

Nanolithography by non-contact AFM induced local oxidation Fabrication of tunneling barriers suitable for single electron devices  

CERN Document Server

We study local oxidation induced by dynamic atomic force microscopy (AFM), commonly called TappingMode AFM. This minimizes the field induced forces, which cause the tip to blunt, and enables us to use very fine tips. We are able to fabricate Ti/TiOx line grids with 18 nm period and well defined isolating barriers as small as 15 nm. These junctions show a non-linear current-voltage characteristic and an exponential dependence of the conductance on the oxide width, indicating tunneling as the dominant conduction mechanism. From the conductance - barrier width dependence we derive a barrier height of 178 meV. Numerical calculations of the lateral field distribution for different tip geometries allow to design the optimum tip for the most localised electric field. The electron-beam-deposition (EBD) technique makes it possible to actually produce tips of the desired geometry.

Irmer, B; Lorenz, H; Kotthaus, J P

1998-01-01

420

Electronic properties of nanoporous TiO{sub 2} films investigated in real space by means of scanning tunnelling spectroscopy  

Energy Technology Data Exchange (ETDEWEB)

Nanoporous TiO{sub 2} films with a thickness between 100 nm and 8 {mu}m were studied by scanning tunnelling spectroscopy. The bias voltage of significantly increased differential conductivity, indicating the conduction and valence bands, was found to be strongly dependent on layer thickness and the underlying substrate material. This effect is traced back to the high resistivity of the oxide films and the formation of Schottky barriers at the TiO{sub 2}-substrate contact. All films showed a strong hysteresis as a function of sweep direction of the bias voltage pointing towards the existence of a high number of localized electronic trap states. This effect is getting even more pronounced upon sample ageing. Laterally resolved measurements show that the major part of the surface exhibits similar I(V) characteristics with minor deviations, while smaller areas with significantly different response are identified. These areas are comparable in size to the individual crystals the material is composed of.

Jacobsen, Volker [Max Planck Institute for Polymer Research, D-55021 Mainz (Germany); Duerr, Michael [Materials Science Laboratory, Sony Deutschland GmbH, D-70327 Stuttgart (Germany)]. E-mail: duerr@sony.de; Wendling, Bettina [Max Planck Institute for Polymer Research, D-55021 Mainz (Germany); Yasuda, Akio [Materials Science Laboratory, Sony Deutschland GmbH, D-70327 Stuttgart (Germany); Nelles, Gabriele [Materials Science Laboratory, Sony Deutschland GmbH, D-70327 Stuttgart (Germany); Knoll, Wolfgang [Max Planck Institute for Polymer Research, D-55021 Mainz (Germany); Kreiter, Maximilian [Max Planck Institute for Polymer Research, D-55021 Mainz (Germany)]. E-mail: kreiter@mpip-mainz.mpg.de

2006-03-15

 
 
 
 
421

Electronic properties of nanoporous TiO2 films investigated in real space by means of scanning tunnelling spectroscopy  

International Nuclear Information System (INIS)

Nanoporous TiO2 films with a thickness between 100 nm and 8 ?m were studied by scanning tunnelling spectroscopy. The bias voltage of significantly increased differential conductivity, indicating the conduction and valence bands, was found to be strongly dependent on layer thickness and the underlying substrate material. This effect is traced back to the high resistivity of the oxide films and the formation of Schottky barriers at the TiO2-substrate contact. All films showed a strong hysteresis as a function of sweep direction of the bias voltage pointing towards the existence of a high number of localized electronic trap states. This effect is getting even more pronounced upon sample ageing. Laterally resolved measurements show that the major part of the surface exhibits similar I(V) characteristics with minor deviations, while smaller areas with significantly different response are identified. These areas are comparable in size to the individual crystals the material is composed of

2006-03-15

422

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

CERN Document Server

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

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

2009-01-01

423

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

International Nuclear Information System (INIS)

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

2012-02-01

424

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

Energy Technology Data Exchange (ETDEWEB)

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

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

2012-02-01

425

Theory and experiments of electron-hole recombination at silicon/silicon dioxide interface traps and tunneling in thin oxide MOS transistors  

Science.gov (United States)

Surface recombination and channel have dominated the electrical characteristics, performance and reliability of p/n junction diodes and transistors. This dissertation uses a sensitive direct-current current voltage (DCIV) method to measure base terminal currents (IB) modulated by the gate bias (VGB) and forward p/n junction bias (VPN) in a MOS transistor (MOST). Base terminal currents originate from electron-hole recombination at Si/SiO2 interface traps. Fundamental theories which relate DCIV characteristics to device and material parameters are presented. Three theory-based applications are demonstrated on both the unstressed as well as hot-carrier-stressed MOSTs: (1) determination of interface trap density and energy levels, (2) spatial profile of interface traps in the drain/base junction-space-charge region and in the channel region, and (3) determination of gate oxide thickness and impurity doping concentrations. The results show that interface trap energy levels are discrete, which is consistent with those from silicon dangling bonds; in unstressed MOS transistors interface trap density in the channel region rises sharply toward source and drain, and after channel-hot-carrier stress, interface trap density increases mostly in the junction space-charge region. As the gate oxide thins below 3 nm, the gate oxide leakage current via quantum mechanical tunneling becomes significant. A gate oxide tunneling theory which refined the traditional WKB tunneling probability is developed for modeling tunneling currents at low electric fields through a trapezoidal SiO2 barrier. Correlation with experimental data on thin oxide MOSTs reveals two new results: (1) hole tunneling dominates over electron tunneling in p+gate p-channel MOSTs, and (2) the small gate/drain overlap region passes higher tunneling currents than the channel region under depletion to flatband gate voltages. The good theory-experimental correlation enables the extraction of impurity doping concentrations, which complements the DCIV method. Two fundamental theories of interband tunneling are developed to correlate with the VGB dependence of drain/base p/n junction currents: (1) direct tunneling at the drain/base junction perimeter with and without the quantization effects in