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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

2

Electron-Tunneling Magnetometer  

Science.gov (United States)

Electron-tunneling magnetometer is conceptual solid-state device operating at room temperature, yet offers sensitivity comparable to state-of-art magnetometers such as flux gates, search coils, and optically pumped magnetometers, with greatly reduced volume, power consumption, electronics requirements, and manufacturing cost. Micromachined from silicon wafer, and uses tunneling displacement transducer to detect magnetic forces on cantilever-supported current loop.

Kaiser, William J.; Kenny, Thomas W.; Waltman, Steven B.

1993-01-01

3

Radiation of tunnel electron  

Digital Repository Infrastructure Vision for European Research (DRIVER)

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 photorecombinat...

Golovinski, P. A.; Drobyshev, A. A.

2013-01-01

4

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

5

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

6

Tunneling electron trap  

International Nuclear Information System (INIS)

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)

7

Micromachined electron tunneling infrared sensors  

Science.gov (United States)

The development of an improved Golay cell is reported. This new sensor is constructed entirely from micromachined silicon components. A silicon oxynitride (SiO(x)N(y)) membrane is deflected by the thermal expansion of a small volume of trapped gas. To detect the motion of the membrane, an electron tunneling transducer is used. This sensor detects electrons which tunnel through the classically forbidden barrier between a tip and a surface; the electron current is exponentially dependent on the separation between the tip and the surface. The sensitivity of tunneling transducers constructed was typically better than 10(exp -3) A/square root of Hz. Through use of the electron tunneling transducer, the scaling laws which have prevented the miniaturization of the Golay cell are avoided. This detector potentially offers low cost fabrication, compatibility with silicon readout electronics, and operation without cooling. Most importantly, this detector may offer better sensitivity than any other uncooled infrared sensor, with the exception of the original Golay cell.

Kenny, T. W.; Kaiser, W. J.; Podosek, J. A.; Rockstad, H. K.; Reynolds, J. K.

1993-01-01

8

Principles of electron tunneling spectroscopy  

CERN Document Server

Electron tunnelling spectroscopy as a research tool has strongly advanced understanding of superconductivity. This book explains the physics and instrumentation behind the advances illustrated in beautiful images of atoms, rings of atoms and exotic states in high temperature superconductors, and summarizes the state of knowledge that has resulted.

Wolf, E L

2012-01-01

9

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

10

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

Digital Repository Infrastructure Vision for European Research (DRIVER)

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...

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

1998-01-01

11

Electron tunneling in molecular junctions  

Science.gov (United States)

This thesis describes approximately four years of fundamental research in the field of molecular electronics. Data are obtained on nanoscopic metal---molecule---metal junctions using conducting-probe atomic force microscopy (CP-AFM). The CP-AFM method involves a conductive AFM probe that is brought into contact with a molecular monolayer that has been self-assembled on a conductive substrate. Tunneling currents are measured to describe charge transport through a small number of molecules. While there are many architectures for creating such molecular tunnel junctions, CP-AFM offers a quick and simple route to formation of nanoscale junctions void of pinholes, with the ability to change contact metals, and measure and control junction compression. Four experiments are highlighted in this manuscript as contributions to the field. The first deals with effects of the type of connection between electrode and molecule (i.e., either a chemical bond or a physical contact), electrode work function, and applied bias. The breadth of this experiment focuses on a series of alkanethiol and alkanedithiol monolayers of varying length in order to characterize both the length dependence and the extrapolated contact resistance. These parameters are then used in the context of conventional theory to extract transmission coefficients relating to tunneling transport through different contacts and as the result of different metals. The second experiment focuses on issues of reproducibility in CP-AFM measurements by performing measurements on Au/decanethiol/Au junctions under a variety of experimental conditions. The third experiment focuses on current rectification (asymmetry with applied voltage) of decanethiol junctions in comparison to a perfluorinated analogue (SHC2H4C 8F17). Alkanethiol monolayers are known to create surface dipoles that decrease the work function of the substrate that they are deposited upon. The opposite shift and rectification direction occurs for the perfluorinated analogue, indicating a correlation of the surface dipole and observed asymmetry. Finally, applied load is varied in the fourth experiment similar to nanoindentation. Measurements are performed on alkanethiols other than decanethiol, with various loading rates and maximum applied loads. The data are modeled using conventional contact mechanics to estimate film modulus and plastic deformation.

Engelkes, Vincent Bernard

12

Distance metrics for heme protein electron tunneling.  

Science.gov (United States)

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 the extent in space that includes most of the wavefunction associated with its tunneling electron. Beyond this edge, the wavefunction tails off much more dramatically in space. The conjugated porphyrin ring seems a reasonable edge for the metal-free pheophytins and bacteriopheophytins of photosynthesis. For a metal containing redox cofactor such as heme, an appropriate cofactor edge is more ambiguous. Electron-tunneling distance may be measured from the conjugated heme macrocycle edge or from the metal, which can be up to 4.8 A longer. In a typical protein medium, such a distance difference normally corresponds to a approximately 1000 fold decrease in tunneling rate. To address this ambiguity, we consider both natural heme protein electron transfer and light-activated electron transfer in ruthenated heme proteins. We find that the edge of the conjugated heme macrocycle provides a reliable and useful tunneling distance definition consistent with other biological electron-tunneling reactions. Furthermore, with this distance metric, heme axially- and edge-oriented electron transfers appear similar and equally well described by a simple square barrier tunneling model. This is in contrast to recent reports for metal-to-metal metrics that require exceptionally poor donor/acceptor couplings to explain heme axially-oriented electron transfers. PMID:18471429

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

2008-01-01

13

Many-electron tunneling in atoms  

Digital Repository Infrastructure Vision for European Research (DRIVER)

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

Zon, B. A.

1999-01-01

14

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

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

Role of electronic structure in magnetic tunneling  

Science.gov (United States)

To assess the effect of electronic structure of magnetic electrodes on the magnetoresistance of tunnel junctions (JMR) we made ab initio calculations of the electronic structure of BCC(1 0 0) Fe, and FCC(1 0 0) Co and Ni electrodes. We treat hopping to and propagation in the barrier as adjustable parameters and discuss features of the JMR attributable to the electronic structure of the electrodes.

Wang, Kuising; Zhang, Shufeng; Levy, Peter M.; Szunyogh, Laszlo; Weinberger, Peter

1998-11-01

17

Electron transfer: Lower tunnel barriers  

Science.gov (United States)

A better understanding of electron transfer through molecules could provide the basis for many technological breakthroughs. Now, the rate of electron transfer has been enhanced in a family of molecules by making them more rigid, and this phenomenon may be explained by the loss of electronic energy to vibrations.

Miller, John R.

2014-10-01

18

Scanning tunnelling spectroscopy of electron resonators  

Digital Repository Infrastructure Vision for European Research (DRIVER)

The electronic structure of artificial Mn atom arrays on Ag(111) is characterized in detail with scanning tunnelling spectroscopy and spectroscopic imaging at low temperature. We demonstrate the degree to which variations in geometry may be used to control spatial and spectral distributions of surface state electrons confined within the arrays, how these are influenced by atoms placed within the structure and how the ability to induce spectral features at specific energies m...

Berndt, Richard; Kliewer, Joerg; Crampin, S.

2001-01-01

19

Transient tunneling current of single electron transistors  

CERN Document Server

The transient tunneling current of single electron transistors (SETs) is theoretically investigated. The time-dependent current formula given by Jauho, Wingreen and Meir [Phys. Rev. B 50, 5528 (1994)] is applied to study the temperature effect on the transient current through a single quantum dot embedded into asymmetry barrier. It is found that the tunneling rate ratio significantly influences the feature of transient current. Finally, the oscillation structures on the exponential growth transient current of single hole transistors composed of germanium quantum dots is analyzed.

Kuo, D M T; Lai, W T; Kuo, David M.-T.; Li, Pei-Wen

2005-01-01

20

Micromachined Electron-Tunneling Infrared Detectors  

Science.gov (United States)

Pneumatic/thermal infrared detectors based partly on Golay-cell concept, but smaller and less fragile. Include containers filled with air or other gas trapped behind diaphragms. Infrared radiation heats sensors, causing gas to expand. Resulting deflections of diaphragms measured by displacement sensors based on principle of electron-tunneling transducers of scanning tunneling microscopes. Exceed sensitivity of all other miniature, uncooled infrared sensors presently available. Expected to include low consumption of power, broadband sensitivity, room-temperature operation, and invulnerability to ionizing radiation.

Kenny, Thomas W.; Kaiser, William J.; Waltman, Stephen B.

1993-01-01

 
 
 
 
21

Single-electron tunnel junction array  

International Nuclear Information System (INIS)

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

22

Lowest order in inelastic tunneling approximation: Efficient scheme for simulation of inelastic electron tunneling data  

Digital Repository Infrastructure Vision for European Research (DRIVER)

We have developed an efficient and accurate formalism which allows the simulation at the ab initio level of inelastic electron tunneling spectroscopy data under a scanning tunneling microscope setup. It exploits fully the tunneling regime by carrying out the structural optimization and vibrational mode calculations for surface and tip independently. The most relevant interactions in the inelastic current are identified as the inelastic tunneling terms, which are taken into account up to lowes...

Rossen, E. T. R.; Flipse, C. F. J.; Cerda?, J. I.

2013-01-01

23

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

24

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

25

Water resources sustainability [electronic resource  

International Nuclear Information System (INIS)

Written by a team of leading experts, this resource provides the latest information and thinking on the globally-critical subject of water sustainability and management. The author includes methods for analyzing water resource needs, modeling, supply reliability, irrigation, and optimization.

26

Electronic noise of superconducting tunnel junction detectors  

Energy Technology Data Exchange (ETDEWEB)

The optimal signal to noise ratio for detectors based on superconducting tunnel junctions is calculated and compared for the cases of a detector consisting of one single tunnel junction, as well as of series and of parallel connections of such tunnel junctions. The influence of 1 / f noise and its dependence on the dynamical resistance of tunnel junctions is discussed quantitatively. A single tunnel junction yields the minimum equivalent noise charge. Such a tunnel junction exhibits the best signal to noise ratio if the signal charge is independent of detector size. In case, signal charge increases with detector size, a parallel or a series connection of tunnel junctions would provide the optimum signal to noise ratio. The equivalent noise charge and the respective signal to noise ratio are deduced as functions of tunnel junction parameters such as tunneling time, quasiparticle lifetime, etc. (orig.)

Jochum, J. (Physik Dept. E15, Technische Univ. Muenchen, Garching (Germany)); Kraus, H. (Physik Dept. E15, Technische Univ. Muenchen, Garching (Germany)); Gutsche, M. (Physik Dept. E15, Technische Univ. Muenchen, Garching (Germany)); Kemmather, B. (Physik Dept. E15, Technische Univ. Muenchen, Garching (Germany)); Feilitzsch, F. v. (Physik Dept. E15, Technische Univ. Muenchen, Garching (Germany)); Moessbauer, R.L. (Physik Dept. E15, Technische Univ. Muenchen, Garching (Germany))

1994-01-15

27

Quantum Hall Effect: proposed multi-electron tunneling experiment  

International Nuclear Information System (INIS)

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

28

Quantum tunneling resonant electron transfer process in Lorentzian plasmas  

Science.gov (United States)

The quantum tunneling resonant electron transfer process between a positive ion and a neutral atom collision is investigated in nonthermal generalized Lorentzian plasmas. The result shows that the nonthermal effect enhances the resonant electron transfer cross section in Lorentzian plasmas. It is found that the nonthermal effect on the classical resonant electron transfer cross section is more significant than that on the quantum tunneling resonant charge transfer cross section. It is shown that the nonthermal effect on the resonant electron transfer cross section decreases with an increase of the Debye length. In addition, the nonthermal effect on the quantum tunneling resonant electron transfer cross section decreases with increasing collision energy. The variation of nonthermal and plasma shielding effects on the quantum tunneling resonant electron transfer process is also discussed.

Hong, Woo-Pyo; Jung, Young-Dae

2014-08-01

29

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

30

Tunneling rates in electron transport through double-barrier molecular junctions in a scanning tunneling microscope  

Digital Repository Infrastructure Vision for European Research (DRIVER)

The scanning tunneling microscope enables atomic-scale measurements of electron transport through individual molecules. Copper phthalocyanine and magnesium porphine molecules adsorbed on a thin oxide film grown on the NiAl(110) surface were probed. The single-molecule junctions contained two tunneling barriers, vacuum gap, and oxide film. Differential conductance spectroscopy shows that electron transport occurs via vibronic states of the molecules. The intensity of spectral peaks correspondi...

Nazin, G. V.; Wu, S. W.; Ho, W.

2005-01-01

31

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

32

Electron tunneling into superconducting filaments using mechanically adjustable barriers  

Energy Technology Data Exchange (ETDEWEB)

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-..mu..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.

Moreland, J.; Ekin, J.W.

1985-07-15

33

Influence of electron-electron interactions on pair tunneling through a mesoscopic N-S tunnel junction.  

Science.gov (United States)

At low temperatures and voltages, smaller than the superconducting gap, transport through a normal metal - superconductor (N-S) tunnel barrier is due to tunneling of electrons in pairs. For a mesoscopic N-S tunnel junction, this process is very sensitive to quantum interference effects: pair tunneling is determined by particle-particle diffusion (Cooperon propagation) near the junction (F.W.J. Hekking, Yu.V. Nazarov, Phys. Rev. Lett. 70, 1625 (1993)). On the other hand it is well-known that electron-electron interactions in a disordered metal lead to significant corrections to particle-particle diffusion (Yu.N. Ovchinnikov, Sov. Phys. JETP 37, 366 (1973)). We explore the effect of the interplay between disorder and interactions on the subgap conductivity of a mesoscopic N-S tunnel junction.

Huck, A. K.; Hekking, F. W. J.

1997-03-01

34

Klein tunneling in graphene: optics with massless electrons  

CERN Document Server

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

35

Electron tunnelling through a quantifiable barrier of variable width  

Energy Technology Data Exchange (ETDEWEB)

This is the first study of electron tunnelling through a quantifiable barrier of adjustable width. We find quantitative agreement between the measured and calculated tunnelling probability with no adjustable constants. The tunnel barrier is a thin film of {sup 3}He on Cs{sub 1} which it wets. We excite photoelectrons which have to tunnel through the barrier to escape. The image potential must be included in calculating the barrier and hence the tunnelling current. This has been a debatable point until now. We confirm that an electron has a potential of 1.0 eV in liquid 3He for short times before a bubble forms. We show that the thickness of the {sup 3}He is given by thermodynamics for films of thickness at least down to 3 monolayers.

Wyatt, A F G [School of Physics, University of Exeter, Exeter, EX4 4QL (United Kingdom); Bromberger, H; Klier, J; Leiderer, P; Zech, M [Faculty of Physics, University of Konstanz, Konstanz 78457 (Germany)], E-mail: a.f.g.wyatt@exeter.ac.uk

2009-02-01

36

Observation of electron beam induced chemistry by tunneling spectroscopy  

International Nuclear Information System (INIS)

The technology of tunneling spectroscopy has been developed to allow the observation of in situ electron beam induced chemistry at liquid helium temperatures. In order to demonstrate the technique, we report the irradiation of a monolayer of cyanoacetic acid by a 10 keV electron beam. The formation of lead cyanide upon irradiation at 10 K is observed and is compared with the formation of nickel cyanide from cyanoacetic acid in tunneling junctions

37

Electron-Photon interaction in resonant tunneling diodes  

Digital Repository Infrastructure Vision for European Research (DRIVER)

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 r...

Inarrea, Jesus; Aguado, Ramon; Platero, Gloria

1997-01-01

38

Visualization of electron orbitals in scanning tunneling microscopy  

Science.gov (United States)

Scanning tunneling microscopy (STM) is one of the main techniques for direct visualization of the surface electronic structure and chemical analysis of multi-component surfaces at the atomic scale. This review is focused on the role of the tip orbital structure and tip-surface interaction in STM imaging with picometer spatial resolution. Fabrication of STM probes with well-defined structure and selective visualization of individual electron orbitals in the STM experiments with controlled tunneling gap and probe structure are demonstrated.

Chaika, A. N.

2014-08-01

39

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

40

Tunneling conductance in a system with strong electron correlation  

Digital Repository Infrastructure Vision for European Research (DRIVER)

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

2012-01-01

 
 
 
 
41

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

42

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

43

Electron tunneling through the potential barriers of triangular shape  

International Nuclear Information System (INIS)

In this paper the expression for calculation of coefficient of electron quantum transport through triangular potential barriers is obtained. This expression is based on direct decision of Schroedinger equation by using infinite mathematical rows.The dependencies of coefficient of electron tunneling on electron energy for some triangular potential barriers are calculated

44

Electron tunnelling in planar double junctions with ferromagnetic barriers  

Energy Technology Data Exchange (ETDEWEB)

Electron tunnelling in double junctions with ferromagnetic barriers and nonmagnetic electrodes is analysed in the sequential and coherent limit of electron tunnelling. The free-electron-like one band model is used. The tunnelling current and its spin polarisation, as well as tunnel magnetoresistance (TMR) are determined. The spin accumulation in the central electrode, leading to a nonvanishing TMR effect, is taken into account and analysed in the sequential limit. In the coherent limit the influence of resonant states on the results obtained is analysed. The conditions leading to an enhancement of TMR and negative differential resistance are discussed. The influence of the parameters of the junction on the results obtained is also investigated.

Wilczynski, M. E-mail: wilczyns@if.pw.edu.pl; Barnas, J.; Swirkowicz, R

2003-12-01

45

Polarization control of electron tunneling into ferroelectric surfaces.  

Science.gov (United States)

We demonstrate a highly reproducible control of local electron transport through a ferroelectric oxide via its spontaneous polarization. Electrons are injected from the tip of an atomic force microscope into a thin film of lead-zirconate titanate, Pb(Zr0.2Ti0.8)O3, in the regime of electron tunneling assisted by a high electric field (Fowler-Nordheim tunneling). The tunneling current exhibits a pronounced hysteresis with abrupt switching events that coincide, within experimental resolution, with the local switching of ferroelectric polarization. The large spontaneous polarization of the PZT film results in up to 500-fold amplification of the tunneling current upon ferroelectric switching. The magnitude of the effect is subject to electrostatic control via ferroelectric switching, suggesting possible applications in ultrahigh-density data storage and spintronics. PMID:19520954

Maksymovych, Peter; Jesse, Stephen; Yu, Pu; Ramesh, Ramamoorthy; Baddorf, Arthur P; Kalinin, Sergei V

2009-06-12

46

NEGF simulation of electron transport in resonant tunneling and resonant interband tunneling diodes  

Digital Repository Infrastructure Vision for European Research (DRIVER)

The challenges due to continuous scaling of CMOS has prompted research into alternative structures for future logic devices that are capable of high speed operation with reduced power consumption. One such contender in the emerging devices category, the Resonant tunneling diode (RTD), has attracted considerable interest due to its low voltage operation, THz capabilities and negative differential resistance. RTDs operate on the principle of quantum mechanical tunneling of electrons through a p...

Akkala, Arun Goud

2011-01-01

47

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

CERN Document Server

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

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

2002-01-01

48

Wigner time delay for tunneling ionization via the electron propagator  

Science.gov (United States)

Recent attoclock experiments using the attosecond angular streaking technique enabled the measurement of the tunneling time delay during laser-induced strong-field ionization. One of the theoretical models for the tunneling time delay is the Wigner time delay, which is the asymptotic time difference between the quasiclassical and the Wigner trajectories. The latter is derived from the derivative of the phase of the electron steady-state wave function with respect to energy. Here, we present an alternative method for the calculation of the Wigner trajectory by using the fixed-energy propagator. The developed formalism is applied to the nonrelativistic regime as well as to the relativistic regime of the tunnel-ionization process from a zero-range potential. Finally, it is shown that the Wigner time delay is measurable in the near-threshold-tunneling regime within the current state of the momentum spectroscopy via detecting the induced electron momentum shift in a mixture of two gas species.

Yakaboylu, Enderalp; Klaiber, Michael; Hatsagortsyan, Karen Z.

2014-07-01

49

Electron tunneling infrared sensor module with integrated control circuitry  

Science.gov (United States)

In an integrated electron tunneling sensor, an automatic tunneling control circuit varies a high voltage bias applied to the sensor deflection electrode in response to changes in sensor output to maintain the proper gap between the sensor tip and membrane. The control circuit ensures stable tunneling activity in the presence of large signals and other disturbances to the sensor. Output signals from the module may be derived from the amplified sensor output. The integrated sensor module is particularly well adapted for use in blood glucose measurement and monitoring system.

Boyadzhyan-Sevak, Vardkes V. (Inventor)

2001-01-01

50

Electron tunnelling into amorphous germanium and silicon.  

Science.gov (United States)

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

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

1972-01-01

51

Strong Electron Tunneling through a Small Metallic Grain  

Digital Repository Infrastructure Vision for European Research (DRIVER)

Electron tunneling through mesoscopic metallic grains can be treated perturbatively only provided the tunnel junction conductances are sufficiently small. If it is not the case, fluctuations of the grain charge become strong. As a result (i) contributions of all -- including high energy -- charge states become important and (ii) excited charge states become broadened and essentially overlap. At the same time the grain charge remains discrete and the system conductance $e$-pe...

Golubev, D. S.; Zaikin, A. D.

1996-01-01

52

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

53

Inelastic electron tunneling spectroscopy in molecular junctions: Peaks and dips  

CERN Document Server

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

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

2004-01-01

54

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)

55

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

56

ELECTRONIC RESOURCES FOR THE HUMANITIES  

Digital Repository Infrastructure Vision for European Research (DRIVER)

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 t...

Petrauskiene, Zibute

2006-01-01

57

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

58

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

59

Temperature Dependence of Electron Tunneling between Two Dimensional Electron Gas and Si Quantum Dots  

Science.gov (United States)

Quantum mechanical electron tunneling has potential applications in both science and technology, such as flash memories in modern LSI technologies and electron transport chains in biosystems. Although it is known that one-dimensional quantum electron tunneling lacks temperature dependence, the behavior of electron tunneling between different dimensional systems is still an open question. Here, we investigated the electron tunneling between a two-dimensional electron gas (2DEG) and zero-dimensional Si quantum dots and discovered an unexpected temperature dependence: At high temperature, the gate voltage necessary for electron injection from 2DEG to Si quantum dots becomes markedly small. This unusual tunneling behavior was phenomenologically explained by considering the geometrical matching of wave functions between different dimensional systems. We assumed that electron tunneling would occur within a finite experimental measurement time. Then, the observed electron tunneling is explained only by the contributions of wave packets below the quantum dot with a finite lifetime rather than the ordinary thermal excited states of 2DEG.

Sakurai, Yoko; Iwata, Jun-ichi; Muraguchi, Masakazu; Shigeta, Yasuteru; Takada, Yukihiro; Nomura, Shintaro; Endoh, Tetsuo; Saito, Shin-ichi; Shiraishi, Kenji; Ikeda, Mitsuhisa; Makihara, Katsunori; Miyazaki, Seiichi

2010-01-01

60

High critical temperature superconductor tunneling spectroscopy using squeezable electron tunneling junctions  

International Nuclear Information System (INIS)

The authors have performed tunneling spectroscopy measurements on squeezable electron tunneling junctions using Bi-Sr-Ca-Cu-O, Y-Ba-Cu-O, and Nb electrodes in a variety of combinations. A zero-bias conductance peak has been seen repeatedly in the current-voltage (I(V)) and the conductance-voltage (G(V)) characteristics. This paper presents model to explain this conductance peak in terms of quasi-particle tunneling, phase diffusion and a supercurrent. Two additional structures have been seen repeatedly in I(V) and G(V). One of these structures has the characteristics of an energy gap feature. The other structure, which can mimic the gap feature, is explained in terms of the switching to the voltage state of a grain boundary junction that is in series with the SET junction. The dependence of these features upon temperature and the force applied to the junction is examined

 
 
 
 
61

Effect of nonlinear electron-electron interaction on electron tunneling through an asymmetric two-barrier resonance tunnel structure  

International Nuclear Information System (INIS)

The quantum-mechanical theory for the transmission coefficient and the positive and negative conductivities of a monoenergetic electron flux through an open plane asymmetric two-barrier resonance tunnel structure, which can serve as an active element in quantum cascade lasers or quantum cascade detectors, has been developed in the framework of effective-mass and rectangular-potential models. The dependences of the transmission factor and the conductivity in such a structure on the electron energy and the frequency of an electromagnetic field are found. It is shown that the properties of the active conductivity can be used for the experimental evaluation of resonance energies and resonance widths of quasistationary electron states.

62

Isotope effect in reaction of tunnel electron phototransfer  

International Nuclear Information System (INIS)

Anomalous isotope effect of electron tunnel phototransfer from zinc porphyrin (ZnP) on CCl4 in frozen at 77 K glass like ethanol solution is detected: then totally deuterated ZnP is substituted for the normal one the probability of phototransfer increased twofold. In the reaction of dark recombination of ion-radicals formed in the light no isotope effect is observed

63

Interaction between electrons and tunneling levels in metallic glasses  

International Nuclear Information System (INIS)

A simple model in which the conduction electrons of a metallic glass experience a local time-dependent potential due to two-level tunneling states is considered. The model exhibits interesting divergent behavior which is quite different from that predicted by an earlier ''s-d Kondo'' model

64

Bohmian mechanics and the tunneling time problem for electrons  

International Nuclear Information System (INIS)

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

65

Radiation of the Tunnel Electron on Secondary Center of Recombination  

Digital Repository Infrastructure Vision for European Research (DRIVER)

We discuss the photon emission that occurs due to the radiative recombination of an electron on a nearby center after tunneling ionization. The model of an active electron is used, and analytical solution to three-dimensional problem is obtained. The dependence of the photon emission from a distance between centers of ionization and a recombination, and also the electric field orientation are investigated. The formulas for probability of recombination radiation are derived.

Golovinski, P. A.; Drobyshev, A. A.

2013-01-01

66

The Electronic Banking Resource Center  

Science.gov (United States)

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

67

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

68

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

International Nuclear Information System (INIS)

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

69

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

Science.gov (United States)

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

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

2013-04-01

70

Photon dressed electronic states in topological insulators: tunneling and conductance  

International Nuclear Information System (INIS)

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

71

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

72

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

Energy Technology Data Exchange (ETDEWEB)

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.

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

1985-09-15

73

Engineering electron tunneling in natural and artificial proteins  

Science.gov (United States)

Experimental investigation of oxidoreductases has revealed their naturally selected electron tunneling engineering that underlies oxidative and reductive catalysis. This engineering is relatively simple, which allows us to design artificial oxidoreductases from scratch, without the unnecessary complexity found in natural proteins. We have constructed a simple, four ?-helix protein bundle protein framework that can be manipulated to support a range of cofactor and substrate binding, and redox and light driven actions. For example, by controlling water access and mobility, this framework can support hemoglobin-like oxygen transport without anything resembling a globin fold. The same framework provides a clear path to artificial proteins designed to catalyze single or multi electron tunneling coupled to chemistry.

Dutton, P. L.

2011-03-01

74

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

Science.gov (United States)

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

Van Rompuy, T.; Gunn, J. P.; Dejarnac, R.; Stöckel, J.; Van Oost, G.

2007-05-01

75

Electron acceleration and electron-positron pair production by laser in tunnel ionized inhomogeneous plasma  

International Nuclear Information System (INIS)

A high intensity laser short pulse causes rapid tunnel ionization of an inhomogeneous gas. The tunnel ionization of the gas causes a defocusing of the laser pulse. The electron experiences an unequal ponderomotive force due to the trailing and rising part of the laser pulse, hence, gains net energy. The net acquired electron energy is reduced due to the inhomogeneity in gas density. If the accelerated electrons are targeted to a low-Z material nucleus, the electron-positron pair will be created via a trident process

76

Long-Distance Electron Tunneling in Proteins: A New Challenge for Time-Resolved Spectroscopy1  

Science.gov (United States)

Long-distance electron tunneling is a fundamental process which is involved in energy generation in cells. The tunneling occurs between the metal centers in the respiratory enzymes, typically over distances up to 20 or 30 Å. For such distances, the tunneling time—i.e., the time during which an electron passes through the body of the protein molecule from one metal center to another—is of the order of 10 fs. Here the process of electron tunneling in proteins is reviewed, and a possibility of experimental observation of real-time electron tunneling in a single protein molecule is discussed. PMID:25364214

Stuchebrukhov, A. A.

2010-01-01

77

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 Jab(2)>'s. Incorporating the quantum-interference effect into the mean-square interatomic tunneling currents, denoted as Jab(2)>, we could express as a sum of variant Planck's over 2pi(2)Jab(2)>. Drawing the distribution of Jab(2)> on the protein structure, we obtain the Jab(2)> 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 Jab(2)>'s by a combined method of molecular dynamics simulations and quantum chemical calculations. In calculating Jab(2)>, we found that much destructive interference works among the interatomic tunneling currents even after taking the average. We drew the Jab(2)> map by a pipe model where atoms a and b are connected by a pipe with width proportional to the magnitude of Jab(2)>. We found that two groups of Jab(2)>'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

78

Inelastic electron-tunneling study of MgO barriers  

Science.gov (United States)

A detailed study of MgO under a variety of preparation conditions has been carried out by inelastic electron-tunneling spectroscopy on Mg-MgO-Pb junctions. Surface vibrational modes play an important part in the observed spectra. The strong peak at 83 meV can be associated with the excitation of longitudinal-optical surface modes while two smaller maxima at 54 and 69 meV are attributable to a mixture of longitudinal- and transverse-optical surface modes. Some barriers were implanted with low-energy hydrogen ions creating magnesium hydride at the Mg-MgO interface. Hydrogen, either as magnesium hydride or substitutional H- in the MgO lattice, was observed as an intense broad band near 124 meV in the inelastic tunneling spectrum. The catalytic action of water and hydrogen in the oxide growth process and their effect on the barrier height and roughness are also discussed.

Plesiewicz, W.; Adler, J. G.

1986-10-01

79

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.

80

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

 
 
 
 
81

Itinerant Nature of Atom-Magnetization Excitation by Tunneling Electrons  

Science.gov (United States)

We have performed single-atom magnetization curve (SAMC) measurements and inelastic scanning tunneling spectroscopy (ISTS) on individual Fe atoms on a Cu(111) surface. The SAMCs show a broad distribution of magnetic moments with 3.5?B being the mean value. ISTS reveals a magnetization excitation with a lifetime of 200 fsec which decreases by a factor of 2 upon application of a magnetic field of 12 T. The experimental observations are quantitatively explained by the decay of the magnetization excitation into Stoner modes of the itinerant electron system as shown by newly developed theoretical modeling.

Khajetoorians, A. A.; Lounis, S.; Chilian, B.; Costa, A. T.; Zhou, L.; Mills, D. L.; Wiebe, J.; Wiesendanger, R.

2011-01-01

82

Electron-beam-assisted scanning tunneling microscopy of insulating surfaces  

Science.gov (United States)

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 yields, the population of conduction band states could be quite significant. Second, for specific incident primary beam energies, the resulting electron yield will be equal to the incoming beam intensity. These are referred to as the cross over energies (E1 and E2). For a stationary primary beam at E2 the current entering the sample and the current leaving sample are equal so that a state of dynamic equilibrium is quickly reached whereby the charge density distribution local to primary beam, both at the surface and within the material, is fixed. Thus, if the surface of an insulator is illuminated with an energetic electron beam at E2, the surface will be locked to some potential and there will be filled conduction band states. Under these conditions, it may be possible to make STM measurements of material even though it is insulating. That is, from an STM point of view, it may be possible to make an insulator `act' like a conductor. In order to test the principle of e-BASTM, metals, thin insulating films, and bulk insulators have been examined. For metals, as expected, we observe no alteration of the tunneling signal due to the PE beam. However, with SiO 2, there is a significant increase in the tunneling current which can be directly attributed to the PE beam. For Al2O3 and CaF2 it is found that the surfaces are damaged too quickly by the PE beam for this technique to be applied suggesting that e-BASTM may only be suitable for a small class of materials. The STM (not e-BASTM) has been used to electrically stress thin films of SiO2 (native oxide thickness). The stressing is observed to create trapping states which have been connected to stress induced leakage currents (SILC) in metal/SiO2/Si devices. The effect of the stress is observed to depend on the polarization of the applied bias (positive or negative). The trapping site density is observed to reach levels on the order of 1013-1014 traps/cm2 which is about a factor of 10-100 higher than what has been previously been reported.

Bullock, Eugene Thomas

2000-07-01

83

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

Energy Technology Data Exchange (ETDEWEB)

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

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

2008-06-15

84

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

85

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

86

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

87

Electron tunnelling through azurin is mediated by the active site Cu ion  

Science.gov (United States)

Cu- and Zn-azurin chemisorbed on Au(1 1 1) have been comparatively investigated by electrochemical scanning tunnelling microscopy in buffer solution. Cu-azurin shows a marked tunnelling current resonance upon substrate potential at -0.21 V (vs SCE), whereas Zn counterparts do not. These data, discussed in terms of current theories on electron tunnelling through redox adsorbates, demonstrate the role of the electroactive metal ion present in the active site in assisting electron transfer via this metalloprotein.

Alessandrini, Andrea; Gerunda, Mimmo; Canters, G. W.; Verbeet, M. Ph.; Facci, Paolo

2003-07-01

88

Electron tunneling into A15 NbGe  

International Nuclear Information System (INIS)

Electron tunneling studies have been performed on thin films of Nb3Ge prepared by getter sputtering and by e-beam evaporation. The tunneling barriers were formed by natural oxidation and on some junctions by oxidation of a thin Al-overlayer. Detailed studies of the 2nd derivative characteristics showed on high (17.5 K) Tsub(c) films four different peaks located at 8.0, 11.5, 18.3 and 26.0 meV which reflect shoulders or peaks in the Eliashberg function at these energies. On Ge-deficient low (8 K) Tsub(c) films the 8.0 meV peak was found to be absent. The junctions with Al-overlayers showed the slow variation of the normal conducting backround known from Nb films with thin Al-overlayers and exhibited substantial improvement with respect to the deformations in the reduced density of states caused by the proximity effect. (orig.)

89

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

90

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

91

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.

92

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

CERN Document Server

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

93

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)

94

Shapes of leading tunnelling trajectories for single-electron molecular ionization  

CERN Document Server

Based on the geometrical approach to tunnelling by P.D. Hislop and I.M. Sigal [Memoir. AMS 78, No. 399 (1989)], we introduce the concept of a leading tunnelling trajectory. It is then proven that leading tunnelling trajectories for single active electron models of molecular tunnelling ionization (i.e., theories where a molecular potential is modelled by a single-electron multi-centre potential) are linear in the case of short range interactions and ``almost'' linear in the case of long range interactions. The results are presented on both the formal and physically intuitive levels. Physical implications of the proven statements are discussed.

Bondar, Denys I; Ivanov, Misha Yu

2010-01-01

95

Shapes of leading tunnelling trajectories for single-electron molecular ionization  

Energy Technology Data Exchange (ETDEWEB)

Based on the geometrical approach to tunnelling by Hislop and Sigal (1989 Mem. AMS 78 No 399), we introduce the concept of a leading tunnelling trajectory. It is then proven that leading tunnelling trajectories for single-active-electron models of molecular tunnelling ionization (i.e. theories where a molecular potential is modelled by a single-electron multi-centre potential) are linear in the case of short-range interactions and 'almost' linear in the case of long-range interactions. The results are presented on both the formal and physically intuitive levels. Physical implications of the obtained results are discussed.

Bondar, Denys I; Liu Wingki, E-mail: dbondar@princeton.edu, E-mail: wkliu@uwaterloo.ca [Department of Physics and Astronomy, Guelph-Waterloo Physics Institute, University of Waterloo, Waterloo, Ontario N2 L 3G1 (Canada)

2011-07-08

96

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

International Nuclear Information System (INIS)

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

97

Implementing CORAL: An Electronic Resource Management System  

Science.gov (United States)

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

Whitfield, Sharon

2011-01-01

98

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

International Nuclear Information System (INIS)

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

99

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

Energy Technology Data Exchange (ETDEWEB)

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

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

2002-12-01

100

Orbital dependent electron tunneling within the atom superposition approach: Theory and application to W(110)  

Digital Repository Infrastructure Vision for European Research (DRIVER)

We introduce an orbital dependent electron tunneling model and implement it within the atom superposition approach for simulating scanning tunneling microscopy (STM) and spectroscopy (STS). Applying our method, we analyze the convergence and the orbital contributions to the tunneling current and the corrugation of constant current STM images above the W(110) surface. In accordance with a previous study [Heinze et al., Phys. Rev. B 58, 16432 (1998)], we find atomic contrast r...

Palota?s, Krisztia?n; Ma?ndi, Ga?bor; Szunyogh, La?szlo?

2012-01-01

 
 
 
 
101

Electronic properties of core-shell nanowire resonant tunneling diodes  

Science.gov (United States)

The electronic sub-band structure of InAs/InP/InAs/InP/InAs core-shell nanowire resonant tunneling diodes has been investigated in the effective mass approximation by varying the core radius and the thickness of the InP barriers and InAs shells. A top-hat, double-barrier potential profile and optimal energy configuration are obtained for core radii and surface shells >10 nm, InAs middle shells <10 nm, and 5 nm InP barriers. In this case, two sub-bands exist above the Fermi level in the InAs middle shell which belongs to the m?=?0 and m?=?1 ladder of states that have similar wave functions and energies. On the other hand, the lowest m?=?0 sub-band in the core falls below the Fermi level but the m?=?1 states do not contribute to the current transport since they reside energetically well above the Fermi level. We compare the case of GaAs/AlGaAs/GaAs/AlGaAs/GaAs which may conduct current with smaller applied voltages due to the larger effective mass of electrons in GaAs and discuss the need for doping. PMID:25288912

2014-01-01

102

Tunnelling current and emission spectrum of a single electron transistor under optical pumping  

CERN Document Server

Theoretical studies of the tunnelling current and emission spectrum of a single electron transistor (SET) under optical pumping are presented. The calculation is performed via Keldysh Green's function method within the Anderson model with two energy levels. It is found that holes in the quantum dot (QD) created by optical pumping lead to new channels for the electron tunnelling from emitter to collector. As a consequence, an electron can tunnel through the QD via additional channels, characterized by the exciton, trion and biexciton states. It is found that the tunnelling current as a function of the gate voltage displays a series of sharp peaks and the spacing between these peaks can be used to determine the exciton binding energy as well as the electron-electron Coulomb repulsion energy. In addition, we show that the single-photon emission associated with the electron-hole recombination in the exciton complexes formed in the QD can be controlled both electrically and optically.

Kuo, D M T; Kuo, David M.-T.; Chang, Yia-Chung

2005-01-01

103

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

104

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

105

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.)

106

Tunneling measurement of the electron inelastic-scattering rate in a strongly disordered superconductor  

International Nuclear Information System (INIS)

Tunneling measurements show that the inelastic-scattering rate for single-electron excitations in strongly disordered superconducting indium oxide films at T much-lt Tc0 is approximately proportional to T3, rather than to exp(-?/kBT) as expected for electron-electron scattering. A recent theory indicates that electron-phonon scattering may be the explanation

107

Toward low-power electronics: tunneling phenomena in transition metal dichalcogenides.  

Science.gov (United States)

In this article, we explore, experimentally, the impact of band-to-band tunneling on the electronic transport of double-gated WSe2 field-effect transistors (FETs) and Schottky barrier tunneling of holes in back-gated MoS2 FETs. We show that by scaling the flake thickness and the thickness of the gate oxide, the tunneling current can be increased by several orders of magnitude. We also perform numerical calculations based on Landauer formalism and WKB approximation to explain our experimental findings. Based on our simple model, we discuss the impact of band gap and effective mass on the band-to-band tunneling current and evaluate the performance limits for a set of dichalcogenides in the context of tunneling transistors for low-power applications. Our findings suggest that WTe2 is an excellent choice for tunneling field-effect transistors. PMID:24392853

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

2014-02-25

108

ELECTRONIC COMMERCE AND ENTERPRISE RESOURCE PLANNING  

Digital Repository Infrastructure Vision for European Research (DRIVER)

ABSTRACT This thesis focuses on a theoretical definition of two concepts, namely global Enterprise Resource Planning solutions and electronic commerce. Enterprise Resource Planning solutions and electronic commerce nowadays represent some of the most important advantages for a company, as they are time-saving and minimize operating costs. When a company introduces new solutions, it is vital that it chooses the right global solution, considering its needs and ensure the solutions provi...

Brac?ko, Lidija

2010-01-01

109

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

110

Dynamics and Dissipation induced by Single-Electron Tunneling in Carbon Nanotube Nanoelectromechanical Systems  

Digital Repository Infrastructure Vision for European Research (DRIVER)

We demonstrate the effect of single-electron tunneling (SET) through a carbon nanotube quantum dot on its nanomechanical motion. We find that the frequency response and the dissipation of the nanoelectromechanical system (NEMS) to SET strongly depends on the electronic environment of the quantum dot, in particular on the total dot capacitance and the tunnel coupling to the metal contacts. Our findings suggest that one could achieve quality factors of 10$^{6}$ or higher by ch...

Ganzhorn, Marc; Wernsdorfer, Wolfgang

2012-01-01

111

Spin-dependent tunneling in the nearly-free-electron model  

CERN Document Server

Spin-dependent ballistic transport through a tunnel barrier is treated within the one-dimensional nearly-free-electron model. The comparison with free electrons reveals significant effects of band gaps, in particular in the bias dependence. The results are qualitatively explained by the number of incident and transmitted states in the leads. With an extension to ferromagnetic leads the bias dependence of tunnel magneto-resistance is discussed.

Bose, P; Mertig, I; Bose, Peter; Henk, Juergen; Mertig, Ingrid

2006-01-01

112

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.)

113

Distant electron tunneling controlled by external fields in molecular nano structures  

International Nuclear Information System (INIS)

The influence of stochastic, periodic, and magnetic fields on a long-range electron tunneling in donor - bridge - acceptor and electrode - molecular wire - electrode structures is studied theoretically. The description of a bridge-mediated electron tunneling between donor and acceptor groups is shown to be possible via the introduction of effective transfer rates. The principal distinction in the dependence of low-temperature elastic and inelastic tunnel currents mediated by a molecular wire with bridging paramagnetic ions on an applied magnetic field is considered. The appearance of the field-induced inversion and suppression effects is widely discussed

114

Ultralarge area MOS tunnel devices for electron emission  

DEFF Research Database (Denmark)

A comparative analysis of metal-oxide-semiconductor (MOS) capacitors by capacitance-voltage (C-V) and current-voltage (I-V) characteristics has been employed to characterize the thickness variations of the oxide on different length scales. Ultralarge area (1 cm(2)) ultrathin (similar to 5 nm oxide) MOS capacitors have been fabricated to investigate their functionality and the variations in oxide thickness, with the use as future electron emission devices as the goal. I-V characteristics show very low leakage current and excellent agreement to the Fowler-Nordheim expression for the current density. Oxide thicknesses have been extracted by fitting a model based on Fermi-Dirac statistics to the C-V characteristics. By plotting I-V characteristics in a Fowler plot, a measure of the thickness of the oxide can be extracted from the tunnel current. These apparent thicknesses show a high degree of correlation to thicknesses extracted from C-V characteristics on the same MOS capacitors, but are systematically lower invalue. This offset between the thicknesses obtained by C-V characteristics and I-V characteristics is explained by an inherent variation of the oxide thickness. Comparison of MOS capacitors with different oxide areas ranging from 1 cm(2) to 10 mu m(2), using the slope from Fowler-Nordheim plots of the I-V characteristics as a measure of the oxide thickness, points toward two length scales of oxide thickness variations being similar to 1 cm and similar to 10 mu m, respectively.

Thomsen, Lasse BjØrchmar; Nielsen, Gunver

2007-01-01

115

Modulations of electronic tunneling rates through flexible molecular bridges by a dissipative superexchange mechanism  

International Nuclear Information System (INIS)

Long-range coherent electron transfer between a donor and an acceptor is often assisted by intermediate molecular bridge, via the superexchange tunneling mechanism. The effect of electronic-nuclear coupling intensity on the tunneling rate and mechanism is analyzed using a generalized spin-boson model, in which the two level system, representing the donor and the acceptor is coupled to a dissipative nuclear bath only indirectly, via additional N bridge sites. A Langevin-Schroedinger equation, based on a mean field approximation, is applied in order to study the corresponding many-body dynamics, and the results are supported by numerically exact calculations for a single nuclear bridge mode. At zero temperature and when the electron tunneling is slower than the nuclear motion, the main effect of electronic-nuclear coupling is the dissipation of electronic energy at the bridge into nuclear vibrations. At small coupling intensities, the electronic tunneling rate increases due to this dissipative mechanism, but as the coupling intensity increases the tunneling into the acceptor is suppressed and efficient dissipation leads to electronic trapping (solvation) at the bridge. This analysis agrees with numerous experimental and theoretical studies, emphasizing the importance of the nuclear bridge conformation and the bridge flexibility in controlling the electron transfer rate in donor-bridge-acceptor systems

116

Electron and phonon cooling in a superconductor-normal-metal-superconductor tunnel junction.  

Science.gov (United States)

We present evidence for the cooling of normal-metal phonons, in addition to the well-known electron cooling, 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 heat transfer that includes the electron-phonon coupling in the normal metal and the Kapitza resistance between the substrate and the metal. It gives a very good fit to the data and enables us to extract an effective phonon temperature in the normal metal. PMID:17678393

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

2007-07-27

117

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

CERN Document Server

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

Patapenka, Andrei

2014-01-01

118

Observation of negative differential resistance and single-electron tunneling in electromigrated break junctions  

International Nuclear Information System (INIS)

We observed a negative differential resistance (NDR) along with single-electron tunneling (SET) in the electron transport of electromigrated break junctions with metal-free tetraphenylporphyrin (H2BSTBPP) at a temperature of 11 K. The NDR strongly depended on the applied gate voltages, and appeared only in the electron tunneling region of the Coulomb diamond. We could explain the mechanism of this new type of electron transport by a model assuming a molecular Coulomb island and local density of states of the source and the drain electrodes

119

Quantum size effect and interlayer electron tunneling in metal-semiconductor superlattices  

International Nuclear Information System (INIS)

A new type of quantum size effect in metal-semiconductor superlattices is predicted. Giant oscillations of the transverse tunnel conductivity arise if size quantization of the electron spectrum in the metal layers takes place. This effect is due to the fact that the probability of metal electron tunneling through a semiconductor layer depends sharply on the electron incidence angle. The oscillations have been found to exist even in disordered systems, provided the electrons in metal layers undergo low-angle scattering on imperfections

120

Hysteresis phenomena in electron tunneling, induced by surface plasmons  

CERN Document Server

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

Kroo, Norbert; Racz, Peter

2013-01-01

 
 
 
 
121

Electron tunneling into 1-2-3 HTSC thin films  

International Nuclear Information System (INIS)

This paper reports on detailed tunneling measurements on thin film planar tunnel junctions of the type RE1Ba2Cu3O7/native oxide/Pb (RE = Y, Eu or Gd). The films were sputter deposited and chemically etched prior to the growth of the native oxide. The structural content of gaplike structure in the I-V characteristic was investigated by taking dl/dV and D3l/dV3 traces. By analysis of the temperature dependence and temperature smearing strong arguments could be provided that all the structures between ±50 mV measured at low temperature are due to density of states effects

122

Electron tunnelling in a double ferromagnetic junction with a magnetic dot as a spacer  

Energy Technology Data Exchange (ETDEWEB)

Electron tunnelling in a double-barrier junction with ferromagnetic external electrodes and a magnetic quantum dot as a spacer is analysed theoretically in the framework of the nonequilibrium Green function technique. The considerations are restricted to spin-conserving tunnelling processes through a quantum dot with a single spin-split discrete level. The Coulomb correlations on the dot are taken into account in terms of the Hubbard Hamiltonian. Transport characteristics, including tunnelling magnetoresistance due to rotation of the magnetic moments of external electrodes, are calculated selfconsistently. (author)

Swirkowicz, R.; Wilczynski, M. [Faculty of Physics, Technical University, Warsaw (Poland); Barnas, J. [Department of Physics, Adam Mickiewicz University, Poznan (Poland) and Institute of Molecular Physics, Polish Academy of Sciences, Poznan (Poland)]. E-mail: barnas@spin.amu.edu.pl

2002-03-04

123

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...

Garci?a-lekue, Aran; Sa?nchez-portal, Daniel; Arnau, Andre?s; Frederiksen, T.

2011-01-01

124

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

Energy Technology Data Exchange (ETDEWEB)

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

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

2011-06-01

125

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.

126

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

Digital Repository Infrastructure Vision for European Research (DRIVER)

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-rotatio...

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

2014-01-01

127

Collection Management and Scholarly Electronic Publishing Resource  

Science.gov (United States)

Last updated April 21st, this Webliography by C.J. Armstrong features linked listings of hundreds of resources on scholarly electronic publishing. The bibliography is divided into five separate sections, covering scholarly electronic publishing in general, licenses and copyrights, authority and digital signatures, preservation and legal deposit, and practical e-publishing. The site is maintained by Information Automation Limited, "a specialist consultancy and research company, operating in the areas of information creation, use and management."

128

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

129

Effects of disorder on electron tunneling through helical edge states  

Science.gov (United States)

A tunnel junction between helical edge states, realized via a constriction in a quantum spin Hall system, can be exploited to steer both charge and spin current into various terminals. We investigate the effects of disorder on the transmission coefficient Tp of the junction by modeling disorder with a randomly varying (complex) tunneling amplitude ?p=|?p|exp[i?p]. We show that, while for a clean junction Tp is only determined by the absolute value |?p| and is independent of the phase ?p, the situation can be quite different in the presence of disorder: phase fluctuations may dramatically affect the energy dependence of Tp of any single sample. Furthermore, analyzing three different models for phase disorder (including correlated ones), we show that not only the amount but also the way the phase ?p fluctuates determines the localization length ?loc and the sample-averaged transmission. Finally, we discuss the physical conditions in which these three models suitably apply to realistic cases.

Sternativo, Pietro; Dolcini, Fabrizio

2014-09-01

130

Herding Cats: Options for Organizing Electronic Resources.  

Science.gov (United States)

Examines strengths and weaknesses of organizational systems developed to organize and access electronic resources available via the Internet. Highlights include library online catalogs; cataloging rules and MARC records; text encoding initiative (TEI) headers; the Internet union catalog; browsing lists; robot-generated indexes; a core data set of…

Vellucci, Sherry L.

1996-01-01

131

Electronic Transport Through EuO Spin Filter Tunnel Junctions  

Digital Repository Infrastructure Vision for European Research (DRIVER)

Epitaxial spin filter tunnel junctions based on the ferromagnetic semiconductor europium monoxide, EuO, are investigated by means of density functional theory. In particular, we focus on the spin transport properties of Cu(100)/EuO(100)/Cu(100) junctions. The dependence of the transmission coefficient and the current-voltage curves on the interface spacing and on the EuO thickness is explained in terms of the EuO density of states and the complex band structure. Furthermore ...

Jutong, Nuttachai; Rungger, Ivan; Schuster, Cosima; Eckern, Ulrich; Sanvito, Stefano; Schwingenschloegl, Udo

2012-01-01

132

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

Science.gov (United States)

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

Hege, Hans-Christian; Manz, Jörn; Marquardt, Falko; Paulus, Beate; Schild, Axel

2010-11-01

133

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 CCL4 in glassy alcoholic matrices at 77 degrees K

134

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

135

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

CERN Document Server

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

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

2007-01-01

136

Atomic excitation during recollision-free ultrafast multi-electron tunnel ionization  

CERN Document Server

Modern intense ultrafast pulsed lasers generate an electric field of sufficient strength to permit tunnel ionization of the valence electrons in atoms. This process is usually treated as a rapid succession of isolated events, in which the states of the remaining electrons are neglected. Such electronic interactions are predicted to be weak, the exception being recollision excitation and ionization caused by linearly-polarized radiation. In contrast, it has recently been suggested that intense field ionization may be accompanied by a two-stage `shake-up' reaction. Here we report a unique combination of experimental techniques that enables us to accurately measure the tunnel ionization probability for argon exposed to 50 femtosecond laser pulses. Most significantly for the current study, this measurement is independent of the optical focal geometry, equivalent to a homogenous electric field. Furthermore, circularly-polarized radiation negates recollision. The present measurements indicate that tunnel ionization...

Bryan, W A; McKenna, J; English, E M L; Suresh, M; Wood, J; Srigengan, B; Turcu, I C E; Smith, J M; Divall, E J; Hooker, C J; Langley, A J; Collier, J L; Williams, I D; Newell, W R; 10.1038/nphys310

2010-01-01

137

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

International Nuclear Information System (INIS)

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

138

Orbital dependent electron tunneling within the atom superposition approach: Theory and application to W(110)  

CERN Document Server

We introduce an orbital dependent electron tunneling model and implement it within the atom superposition approach for simulating scanning tunneling microscopy (STM) and spectroscopy (STS). Applying our computationally efficient method, we analyze the convergence and the orbital contributions to the tunneling current and the corrugation of constant current STM images above the W(110) surface. In accordance with a previous study, we find corrugation reversals depending on the bias voltage and the tip-sample distance. Explaining this effect, we highlight the role of the real space shape of the orbitals involved in the tunneling. Moreover, we calculate corrugation inversion maps considering different tip models, and find two qualitatively different behaviors based on the tip orbital symmetry. From these maps, we predict corrugation reversals for specific tips even at positive bias voltages at enlarged tip-sample distances compared to those at negative bias.

Palotás, Krisztián; Szunyogh, László

2012-01-01

139

Real-time detection of single electron tunneling using a quantum point contact  

CERN Document Server

We observe individual tunnel events of a single electron between a quantum dot and a reservoir, using a nearby quantum point contact (QPC) as a charge meter. The QPC is capacitively coupled to the dot, and the QPC conductance changes by about 1% if the number of electrons on the dot changes by one. The QPC is voltage biased and the current is monitored with an IV-convertor at room temperature. We can resolve tunnel events separated by only 8 $\\mu$s, limited by noise from the IV-convertor. Shot noise in the QPC sets a 25 ns lower bound on the accessible timescales.

Vandersypen, L M K; Schouten, R N; Willems van Beveren, L H; Hanson, R; Kouwenhoven, L P

2004-01-01

140

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

CERN Document Server

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.

Pfeiffer, Adrian N; Landsman, Alexandra S; Smolarski, Mathias; Dimitrovski, Darko; Madsen, Lars B; Keller, Ursula

2011-01-01

 
 
 
 
141

Dissociation of oxygen on Ag(100) induced by inelastic electron tunneling  

Energy Technology Data Exchange (ETDEWEB)

Scanning tunneling microscopy (STM) is used to study the dissociation of molecular oxygen on Ag(100) induced by inelastic electron tunneling (IET) at 5 K. This dissociation is possible above 3.3 V with a yield of (3.63 {+-} 0.47) x 10{sup -9} per electron. Dissociation leads to three different types of hot atom motion: lateral motion, a cannon ball mechanism, and abstractive dissociation. Analysis of the I-t characteristics during dissociation suggests that the dissociation is proceeded by an adsorption site change.

Sprodowski, Carsten; Mehlhorn, Michael; Morgenstern, Karina, E-mail: morgenstern@fkp.uni-hannover.d [Institut fuer Festkoerperphysik, Abteilung ATMOS, Leibniz Universitaet Hannover, Appelstrasse 2, D-30167 Hannover (Germany)

2010-07-07

142

Electron beam damage of chemisorbed surface species: a tunneling spectroscopy study  

International Nuclear Information System (INIS)

Electron beam damage is a problem for low-energy electron diffraction, Auger electron spectroscopy, and electron microscopy. Tunneling spectroscopy has been used to study the damage caused by 30 keV incident electrons on chemisorbed monolayer films of hexanoic acid, 2,4-hexadienoic acid, and benzoic acid. The results on monolayer films are compared to existing work on bulk samples. Damage cross sections are similar to bulk values; molecules with more delocalized electrons are more resistant to damage. In contrast to bulk results, however, little if any conjugation or cross linking is found after irradiation. (Auth.)

143

Fermi-Edge Resonance and Tunneling in Nonequilibrium Electron Gas  

CERN Document Server

Fermi-edge singularity changes in a dramatic way in a nonequilibrium system, acquiring features which reflect the structure of energy distribution. In particular, it splits into several components if the energy distribution exhibits multiple steps. While conventional approaches, such as bosonization, fail to describe the nonequilibrium problem, an exact solution for a generic energy distribution can be obtained with the help of the method of functional determinants. In the case of a split Fermi distribution, while the `open loop' contribution to Green's function has power law singularities, the tunneling density of states profile exhibits broadened peaks centered at Fermi sub-levels.

Abanin, D A

2005-01-01

144

Electron tunneling through superconducting Al/monolayer/Pb junctions  

International Nuclear Information System (INIS)

The current-voltage characteristic of Al/adsorbed monolayer/Pb junctions was measured at 77, 4.2 and 1.8 K at applied voltages from 1 to 3 mV. At 77 K the current changes linearly with voltage whereas at 4.2 and 1.8 K the relationship becomes nonlinear. From the results at 1.8 K an approximate band gap is obtained for Pb equal to 2.6 meV. The observation of a nonlinear current-voltage characteristic at temperatures where Pb becomes superconducting is strong evidence that the observed current through the insulator is a tunneling current. (author)

145

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

International Nuclear Information System (INIS)

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

146

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

Energy Technology Data Exchange (ETDEWEB)

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

Hege, Hans-Christian [Abteilung Visualisierung und Datenanalyse, Zuse-Institut Berlin, Takustr. 9, 14195 Berlin (Germany); Manz, Joern, E-mail: jmanz@chemie.fu-berlin.de [Institut fuer Chemie und Biochemie, Freie Universitaet Berlin, Takustr. 3, 14195 Berlin (Germany); Marquardt, Falko [Abteilung Visualisierung und Datenanalyse, Zuse-Institut Berlin, Takustr. 9, 14195 Berlin (Germany); Institut fuer Mathematik, Freie Universitaet Berlin, Arnimallee 6, 14195 Berlin (Germany); Paulus, Beate; Schild, Axel [Institut fuer Chemie und Biochemie, Freie Universitaet Berlin, Takustr. 3, 14195 Berlin (Germany)

2010-11-10

147

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

International Nuclear Information System (INIS)

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

148

Virtual Scanning Tunneling Microscopy: A local spectroscopic probe of high mobility 2D electron systems  

Science.gov (United States)

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

Pelliccione, Matthew; Bartel, John; Sciambi, Adam; Pfeiffer, Loren; West, Ken; Goldhaber-Gordon, David

2013-03-01

149

Electronic resource management systems a workflow approach  

CERN Document Server

To get to the bottom of a successful approach to Electronic Resource Management (ERM), Anderson interviewed staff at 11 institutions about their ERM implementations. Among her conclusions, presented in this issue of Library Technology Reports, is that grasping the intricacies of your workflow-analyzing each step to reveal the gaps and problems-at the beginning is crucial to selecting and implementing an ERM.

Anderson, Elsa K

2014-01-01

150

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

151

Electron-tunneling studies of the cubic Kondo semiconductors  

International Nuclear Information System (INIS)

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

152

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

International Nuclear Information System (INIS)

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

153

An inelastic electron tunneling spectroscopy study of the adsorption of CO on Rh  

International Nuclear Information System (INIS)

Inelastic Electron Tunneling Spectroscopy of CO adsorbed on alumina supported Rh allows the observation of the low frequency metal carbon vibrational modes (approximately 1000 cm-1) that cannot be seen by Infrared Spectroscopy. The authors present a preliminary attempt to assign the modes observed, using isotopic shifts C16O/C18O. (Auth.)

154

Electron Tunneling Pathway and Role of Adenine in Repair of Damaged DNA by Photolyase  

Science.gov (United States)

Through electron tunneling, photolyase, a photoenzyme, restores damaged DNA into normal bases. Here, we report our systematic characterization and analyses of three electron transfer processes in thymine dimer restoration 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 repairing and for the final electron return to restore the active cofactor and complete the repair photocycle. Significantly, we found that the adenine moiety of the unusual bent cofactor is essential to mediating all electron transfer dynamics through a super-exchange mechanism, leading to a delicate balance of time scales. The active-site structural integrity, unique electron tunneling pathways and the critical role of adenine assure these elementary dynamics in synergy in this complex photorepair machinery to achieve the maximum repair efficiency close to unity. Z. Liu, C. Tan, X. Guo, Y.-T. Kao, J. Li, L. Wang, A. Sancar, and D. Zhong, Proc. Natl. Acad. Sci. USA 108, 14831 (2011) J. Li, Z. Liu, C. Tan, X. Guo, L. Wang, A. Sancar, and D. Zhong, Nature 466, 887 (2010)

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

2012-06-01

155

Atomic scale variation of electron tunneling into a Luttinger liquid ? : High resolution scanning tunneling spectroscopy study on Au/Ge(001)  

Digital Repository Infrastructure Vision for European Research (DRIVER)

Au-induced atomic wires on the Ge(001) surface were recently claimed to be an ideal 1D metal and their tunneling spectra were analyzed as the manifestation of a Tomonaga-Luttinger liquid (TLL) state. We reinvestigate this system for atomically well-ordered areas of the surface with high resolution scanning tunneling microscopy and spectroscopy (STS). The local density-of-states maps do not provide any evidence of a metallic 1D electron channel along the wires. Moreover, the ...

Park, Jewook; Nakatsuji, Kan; Kim, Tae-hwan; Song, Sun Kyu; Komori, Fumio; Yeom, Han Woong

2014-01-01

156

Free online electronic information resources on applied science and technology  

Digital Repository Infrastructure Vision for European Research (DRIVER)

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

Ghosh, T. B.

2003-01-01

157

Electron tunneling study of high-Tsub(c) superconductor La-Sr-Cu-O system  

International Nuclear Information System (INIS)

Electron tunneling experiment on novel superconductor La-Sr-Cu-O system with the transition temperature of about 35K has been carried out by point contact method. The observed electronic density of states is smeared out compared with the BCS one. The energy gap seems to be larger than 3.52kTsub(c) expected by BCS theory. Based on these results, the superconducting properties of the system are discussed. (author)

158

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

International Nuclear Information System (INIS)

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

159

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

CERN Document Server

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

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

2003-01-01

160

Engineering electron and hole tunneling with asymmetric InAs quantum dot molecules  

CERN Document Server

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

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

2006-01-01

 
 
 
 
161

Electron tunneling properties of outer-membrane decaheme cytochromes from Shewanella oneidensis  

Science.gov (United States)

We have characterized the outer-membrane decaheme cytochromes OmcA and MtrC from Shewanella oneidensis MR-1 at the single-molecule level using scanning tunneling microscopy (STM) and tunneling spectroscopy (TS). These cytochrome proteins are of great interest because they are thought to mediate bacterial electron transfer reactions in anoxic waters that control the reductive dissolution of oxide minerals. In our study, to characterize the electron transfer properties of these proteins on a model surface, the purified cytochromes were chemically immobilized as molecular monolayers on Au(111) substrates via a recombinant tetra-cysteine sequence as verified by X-ray photoelectron spectroscopy. Atomic force microscopy images confirm the monolayer films were ˜5-8 nm thick which is consistent with the apparent lateral dimensions of individual cytochrome molecules obtained with STM. Current-voltage TS of single cytochrome molecules revealed that OmcA and MtrC have different abilities to mediate tunneling current despite having otherwise very similar molecular and biochemical properties. These observations suggest that, based on their electron tunneling properties, the two cytochromes could have specific roles during bacterial metal reduction. Additionally, this study establishes single-molecule STM/TS as an effective means for revealing insights into biogeochemical redox processes in the environment.

Wigginton, Nicholas S.; Rosso, Kevin M.; Lower, Brian H.; Shi, Liang; Hochella, Michael F.

2007-02-01

162

Effects of competition for charge capture from the matrix on intermolecular electron-tunneling reactions  

Energy Technology Data Exchange (ETDEWEB)

A general method is presented for correcting for the direct capture of matrix charges by the acceptor in an intermolecular electron-transfer reaction in a rigid medium. The method is based on a two-step electron-tunneling model that takes into account the correlation between matrix charge capture and intermolecular electron transfer. As an experimental test of the method, electron transfer from the anion of cinnamaldehyde to neutral pryomellitic dianhydride was studied in 2-methyltetrahydrofuran glass at 77/sup 0/K. Good agreement between the model and the experimental kinetic results was obtained.

Huddleston, R.K.; Miller, J.R.

1982-04-15

163

Effects of competition for charge capture from the matrix on intermolecular electron-tunneling reactions  

International Nuclear Information System (INIS)

A general method is presented for correcting for the direct capture of matrix charges by the acceptor in an intermolecular electron-transfer reaction in a rigid medium. The method is based on a two-step electron-tunneling model that takes into account the correlation between matrix charge capture and intermolecular electron transfer. As an experimental test of the method, electron transfer from the anion of cinnamaldehyde to neutral pryomellitic dianhydride was studied in 2-methyltetrahydrofuran glass at 770K. Good agreement between the model and the experimental kinetic results was obtained

164

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.

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

2002-06-01

165

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.

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

166

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

167

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

168

Creation of nonlocal spin-entangled electrons via Andreev tunneling, Coulomb blockade and resonant transport  

CERN Document Server

We discuss several scenarios for the creation of nonlocal spin-entangled electrons which provide a source of electronic Einstein-Podolsky-Rosen (EPR) pairs. The central idea is to exploit the spin correlations naturally present in superconductors in form of Cooper pairs. We show that nonlocal spin-entanglement in form of an effective Heisenberg spin interaction is induced between electron spins residing on two quantum dots with no direct coupling between them but each of them being tunnel-coupled to the same superconductor. We then discuss a nonequilibrium setup where mobile and nonlocal spin-entanglement can be created by coherent injection of two electrons in an Andreev tunneling process into two spatially separated quantum dots and subsequently into two Fermi-liquid leads. The current for injecting two spin-entangled electrons into different leads shows a resonance whereas tunneling via the same dot into the same lead is suppressed by the Coulomb blockade effect of the quantum dots. The Aharonov-Bohm oscil...

Recher, P; Recher, Patrik; Loss, Daniel

2002-01-01

169

A Diamond Electron Tunneling Micro-Electromechanical Sensor  

Science.gov (United States)

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

Albin, Sacharia

2000-01-01

170

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

Science.gov (United States)

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

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

2012-04-27

171

Mapping the Electron Transport of Graphene Boundaries Using Scanning Tunneling Potentiometry  

Science.gov (United States)

The symmetry of the graphene honeycomb lattice is a key element for determining many of graphene's unique electronic properties. Topological lattice defects, such as grain boundaries and step edges, break the sublattice symmetry and can affect the electronic properties, especially the transport of graphene. A complete understanding of the physical and electronic properties of defects and boundaries of graphene is needed for future applications. Using a scanning tunneling potentiometry method with a low temperature four-probe scanning tunneling microscope, two-dimensional maps of electrochemical potentials have been measured across individual grain boundaries of graphene films on SiO2, as well as across 1ML to 1ML substrate steps and 1ML to 2ML transitions of graphene on SiC. An Atomic Force Microscope (AFM) is implemented to image the grain boundary that forms between coalesced individual graphene flakes on insulating surfaces where as a Scanning Tunneling Microscopy (STM) is implemented for characterizing the SiC grown graphene samples. Results of the influence that various boundaries have on the electronic transport of graphene will be presented.

Clark, Kendal; Zhang, Xiaoguang; Vlassiouk, Ivan; He, Guowei; Gu, Gong; Feenstra, Randall; Li, An-Ping

2013-03-01

172

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

173

Limitations in cooling electrons using normal-metal-superconductor tunnel junctions.  

Science.gov (United States)

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. First, when the injection rate of electrons exceeds the internal relaxation rate in the metal to be cooled, the electrons do not obey the Fermi-Dirac distribution, and the concept of temperature cannot be applied as such. Second, at low bath temperatures, states within the gap induce anomalous heating and yield a theoretical limit of the achievable minimum temperature. PMID:14995329

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

2004-02-01

174

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

175

Electron tunneling in molecular solids. An orbital overlap model  

International Nuclear Information System (INIS)

The long-range transfer processes (range, R approx. 20-50 A) of excess electrons produced by radiolysis of molecular solids are analyzed in terms of an orbital overlap model. A united atom approximation makes possible the separation of angular and radial factors. The angular dependence is used to treat the effect of the relative orientation of donor and acceptor molecules on the transfer rate; variations of up to a factor of approx. 1000 are predicted. A distinction is drawn between reactions of electrons with scavengers (or transfer between additives), where the significant overlap is localized around donor and acceptor sites, and recombination with a cation produced by the radiolysis, where the overlap is largely spread out over the intervening volume. In the former case, interference due to nodes in the wave functions is significant, while in the latter, various powers of R appear in the preexponential factor. The role of the Franck--Condon principle in determining the effective barrier height is discussed. Electronic interaction is also important in determining transfer rates for different donors and acceptors. 3 figures, 2 tables

176

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.)

177

Scanning tunneling microscopy characterization of the geometric and electronic structure of hydrogen-terminated silicon surfaces  

Science.gov (United States)

Scanning tunneling microscopy (STM) methods are used to characterize hydrogen-terminated Si surfaces prepared by a novel method. The surface preparation method is used to expose the Si-SiO2 interface. STM images directly reveal the topographic structure of the Si-SiO2 interface. The dependence of interface topography on oxide preparation conditions observed by STM is compared to the results of conventional surface characterization methods. Also, the electronic structure of the hydrogen-terminated surface is studied by STM spectroscopy. The near-ideal electronic structure of this surface enables direct tunnel spectroscopy measurements of Schottky barrier phenomena. In addition, this method enables probing of semiconductor subsurface properties by STM.

Kaiser, W. J.; Bell, L. D.; Hecht, M. H.; Grunthaner, F. J.

1988-01-01

178

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

179

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

CERN Document Server

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

Beletskii, N N; Borysenko, S A

2004-01-01

180

The radiation field measurement in the 200 MeV electron linac tunnel  

International Nuclear Information System (INIS)

To measure the radiation level in tunnel during a Linac running period can provide important data to improve the machine, forcast the lives of electronic devices and other materials, and can exploit the radiation field as well. The properties of the radiation field around Linac are introduced, the measurement of the radiation level with alanine dosemeter and ESR method, the result of the measurement is analysed

 
 
 
 
181

Tunneling transport through multi-electrons states in coupled quantum dots with Coulomb correlations  

Science.gov (United States)

We investigated the peculiarities of non-equilibrium charge configurations in the system of two strongly coupled quantum dots (QDs) weakly connected to the reservoirs in the presence of Coulomb correlations. We revealed that total electron occupation demonstrates in some cases significant decreasing with increasing of applied bias - contrary to the situation when Coulomb correlations are absent and found well pronounced ranges of system parameters where negative tunneling conductivity appears due to the Coulomb correlations.

Mantsevich, V. N.; Maslova, N. S.; Arseyev, P. I.

2014-12-01

182

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

International Nuclear Information System (INIS)

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

183

Thin-film chemical sensors based on electron tunneling: Final report  

Energy Technology Data Exchange (ETDEWEB)

The physical mechanisms underlying a novel chemical sensor based on electron tunneling in metal-insulator-metal (MIM) tunnel junctions were studied. Chemical sensors based on electron tunneling were shown to be sensitive to a variety of substances that include iodine, mercury, bismuth, ethylenedibromide, and ethylenedichloride. A sensitivity of 13 parts per billion of iodine dissolved in hexane was demonstrated. The physical mechanisms involved in the chemical sensitivity of these devices were determined to be the chemical alteration of the surface electronic structure of the top metal electrode in the MIM structure. In addition, electroreflectance spectroscopy (ERS) was studied as a complementary surface-sensitive technique. ERS was shown to be sensitive to both iodine and mercury. Electrolyte electroreflectance and solid-state MIM electroreflectance revealed qualitatively the same chemical response. A modified thin-film structure was also studied in which a chemically active layer was introduced at the top Metal-Insulator interface of the MIM devices. Cobalt phthalocyanine was used for the chemically active layer in this study. Devices modified in this way were shown to be sensitive to iodine and nitrogen dioxide. The chemical sensitivity of the modified structure was due to conductance changes in the active layer. 32 refs., 24 figs.

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

1985-11-15

184

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

CERN Document Server

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

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

2010-01-01

185

Electron transport through cubic InGaN/AlGaN resonant tunneling diodes  

Science.gov (United States)

We theoretically study the electron transport through a resonant tunneling diode (RTD) based on strained AlxGa1-xN/In0.1Ga0.9N/AlxGa1-xN quantum wells embedded in relaxed n- Al0.15Ga0.85N/strained In0.1Ga0.9N emitter and collector. The aluminum composition in both injector and collector contacts is taken relatively weak; this does not preclude achieving a wide band offset at the border of the pre-confinement wells. The epilayers are assumed with a cubic crystal structure to reduce spontaneous and piezoelectric polarization effects. The resonant tunneling and the thermally activated transfer through the barriers are the two mechanisms of transport taken into account in the calculations based on the Schrödinger, Poisson and kinetic equations resolved self-consistently. Using the transfer matrix formalism, we have analyzed the influence of the double barrier height on the resonant current. With an Al composition in the barriers varying between 30% and 50%, we have found that resonant tunneling dominates over the transport mediated by the thermally activated charge transfer for low applied voltages. It is also found that the designed n-type InGaN/AlGaN RTD with 30% of Al composition in the barriers is a potential candidate for achieving a resonant tunneling diode.

Yahyaoui, N.; Sfina, N.; Nasrallah, S. Abdi-Ben; Lazzari, J.-L.; Said, M.

2014-12-01

186

Electron tunneling into Nb3Sn, Nb3Ge, and Nb3Al  

International Nuclear Information System (INIS)

We have prepared high-quality tunnel junctions on thin films of Nb3Sn, Nb3Ge, and Nb3Al with artificial tunnel barriers of Al oxide and AlZr oxide. The Nb3Sn/AlZr-oxide/Pb tunnel junctions prepared on Sn-deficient material showed no measurable proximity effect. Whereas the tunnel spectra of Sn-deficient A15 NbSn could be satisfactorily analyzed by the standard Rowell-McMillan inversion procedure, the reduced density of states of the stoichiometric samples exhibited characteristic deformations in the form of an overswing at energies far above the highest phonon energy. These deformations can be fitted by proximity analysis, but it is shown that they can also be referred to the influence of an electronic density of states which is strongly structured in the range of phonon energies near the Fermi level. A very similar behavior is found for Nb3Ge and to a smaller extent for Nb3Al

187

Electron tunneling spectroscopy study of electrically active traps in AlGaN/GaN high electron mobility transistors  

International Nuclear Information System (INIS)

We investigate the energy levels of electron traps in AlGaN/GaN high electron mobility transistors by the use of electron tunneling spectroscopy. Detailed analysis of a typical spectrum, obtained in a wide gate bias range and with both bias polarities, suggests the existence of electron traps both in the bulk of AlGaN and at the AlGaN/GaN interface. The energy levels of the electron traps have been determined to lie within a 0.5?eV band below the conduction band minimum of AlGaN, and there is strong evidence suggesting that these traps contribute to Frenkel-Poole conduction through the AlGaN barrier

188

Electron tunneling spectroscopy study of electrically active traps in AlGaN/GaN high electron mobility transistors  

Energy Technology Data Exchange (ETDEWEB)

We investigate the energy levels of electron traps in AlGaN/GaN high electron mobility transistors by the use of electron tunneling spectroscopy. Detailed analysis of a typical spectrum, obtained in a wide gate bias range and with both bias polarities, suggests the existence of electron traps both in the bulk of AlGaN and at the AlGaN/GaN interface. The energy levels of the electron traps have been determined to lie within a 0.5?eV band below the conduction band minimum of AlGaN, and there is strong evidence suggesting that these traps contribute to Frenkel-Poole conduction through the AlGaN barrier.

Yang, Jie, E-mail: jie.yang@yale.edu; Cui, Sharon; Ma, T. P. [Department of Electrical Engineering, Yale University, New Haven, Connecticut 06520 (United States); Hung, Ting-Hsiang; Nath, Digbijoy; Krishnamoorthy, Sriram; Rajan, Siddharth [Department of Electrical and Computer Engineering, Ohio State University, Columbus, Ohio 43210 (United States)

2013-11-25

189

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

190

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.

191

Zener Tunneling Between Landau Orbits in a High-Mobility Two-Dimensional Electron Gas  

Science.gov (United States)

Magnetotransport in a laterally confined two-dimensional electron gas (2DEG) can exhibit modified scattering channels owing to a tilted Hall potential. Transitions of electrons between Landau levels with shifted guiding centers can be accomplished through a Zener tunneling mechanism, and make a significant contribution to the magnetoresistance. A remarkable oscillation effect in weak field magnetoresistance has been observed in high-mobility 2DEGs in GaAs -Al Ga 0.3As 0.7 heterostructures, and can be well explained by the Zener mechanism.

Yang, C. L.; Zhang, J.; Du, R. R.; Simmons, J. A.; Reno, J. L.

2002-07-01

192

Zener Tunneling Between Landau Orbits in a High-Mobility Two-Dimensional Electron Gas  

CERN Document Server

Magnetotransport in a laterally confined two-dimensional electron gas (2DEG) can exhibit modified scattering channels owing to a tilted Hall potential. Transitions of electrons between Landau levels with shifted guiding centers can be accomplished through a Zener tunneling mechanism, and make a significant contribution to the magnetoresistance. A remarkable oscillation effect in weak field magnetoresistance has been observed in high-mobility 2DEGs in GaAs-AlGa$_{0.3}$As$_{0.7}$ heterostructures, and can be well explained by the Zener mechanism.

Yang, C L; Du, R R; Simmons, J A; Reno, J L

2002-01-01

193

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

194

Influence of the competition between electron and hole channels of tunneling on the intrinsic resolution of STJ detectors  

International Nuclear Information System (INIS)

The effect of competition between electron and hole channels of tunneling on the quasiparticle multitunneling in STJ-detectors is considered. The formulae for the mean value, the variance and the relative variance of the detector signal for general case ?1 ? ?2 are given. For a symmetric junction the tunneling rates and the probabilities of quasiparticle tunneling as an electron and as a hole, the mean value of the transferred charge and the noise G-factor were calculated as a function of the junction bias voltage. The results of the calculations demonstrate the considerable effect of the competition between the electron and the hole channels of tunneling on the signal and the energy resolution at the bias voltages that satisfy the condition Vb ? |?1 ? ?2|/e + kBT.

195

Influence of the competition between electron and hole channels of tunneling on the intrinsic resolution of STJ detectors  

Energy Technology Data Exchange (ETDEWEB)

The effect of competition between electron and hole channels of tunneling on the quasiparticle multitunneling in STJ-detectors is considered. The formulae for the mean value, the variance and the relative variance of the detector signal for general case {Delta}{sub 1} {ne} {Delta}{sub 2} are given. For a symmetric junction the tunneling rates and the probabilities of quasiparticle tunneling as an electron and as a hole, the mean value of the transferred charge and the noise G-factor were calculated as a function of the junction bias voltage. The results of the calculations demonstrate the considerable effect of the competition between the electron and the hole channels of tunneling on the signal and the energy resolution at the bias voltages that satisfy the condition V{sub b} Less-Than-Or-Slanted-Equal-To |{Delta}{sub 1} - {Delta}{sub 2}|/e + k{sub B}T.

Samedov, V.V., E-mail: v-samedov@yandex.ru [National Research Nuclear University, Moscow Engineering Physics Institute, Kashirskoye Shosse 31, 115409 Moscow (Russian Federation); Andrianov, V.A., E-mail: andrva22@mail.ru [Lomonosov Moscow State University, Skobeltsyn Institute of Nuclear Physics, GSP-1, 119991 Moscow (Russian Federation)

2012-02-15

196

Influence of the competition between electron and hole channels of tunneling on the intrinsic resolution of STJ detectors  

Science.gov (United States)

The effect of competition between electron and hole channels of tunneling on the quasiparticle multitunneling in STJ-detectors is considered. The formulae for the mean value, the variance and the relative variance of the detector signal for general case ?1 ? ?2 are given. For a symmetric junction the tunneling rates and the probabilities of quasiparticle tunneling as an electron and as a hole, the mean value of the transferred charge and the noise G-factor were calculated as a function of the junction bias voltage. The results of the calculations demonstrate the considerable effect of the competition between the electron and the hole channels of tunneling on the signal and the energy resolution at the bias voltages that satisfy the condition V b ? | ?1 - ?2|/ e + k BT .

Samedov, V. V.; Andrianov, V. A.

2012-02-01

197

Studies of electron tunnelling low-dimensional GaAs/(AlGa)As heterostructures  

International Nuclear Information System (INIS)

Low-dimensional electron systems can be created in artificially-constructed semiconductor structures. The additional quantum confinement in one, two or three dimensions can be introduced through a variety of methods. The quantum tunnelling behaviour of such electrons in these systems is the subject of study in this thesis. Chapter 3 describes experiments on small double-barrier resonant tunnelling devices, containing Si doping in the centre plane of their GaAs quantum wells. For the first time, a systematic study is made of the amplitude and voltage period of the fluctuations in the differential conductance of these devices. The fluctuations arise from the passage of 0D tunnelling channels through the emitter chemical potential as the bias is swept. The density of dopants, the temperature, and the device area were all variables in these studies. Good agreement is found with the theory, which is now over ten years old. Chapter 4 presents a study of resonant tunnelling transport of electrons through the 0D states associated with self-assembled InAs islands, grown by the Stranski-Krastanow growth mode. The fluctuations in the electrical conductance of the device are investigated. The increase in the root-mean-square amplitude of the fluctuations with voltage is taken as evidence that the distribution of bound levels has its median well above the chemical potential at equilibrium. Chapters 5 and 6 contain results from in-plane transport measurements on mesoscopic wire samples, fabricated from a double quantum well structure and a wide single quantum well structure, respectively, with a magnetic field applied parallel to the plane of the grown layers. All samples studied contain parallel 2D electron gases, bound a finite distance apart, separated by a tunnel barrier. As the in-plane magnetic field is swept, we observe a resistance resonance, universal conductance fluctuations, an enhanced high-field feature (qualitatively different to that seen in macroscopic Hall bars), and a marked quenching of the conductance fluctuations when the Fermi surface is broken into two separate parts in k-space. Comparisons are made between the appearances of these features in the two fundamental in-plane field/current orientations. The effect of increasing temperature is also studied. (author)

198

Tunneling Characteristics of an Electron-Hole Trilayer under an In-plane Magnetic Field  

CERN Document Server

We have studied the tunneling properties of GaSb/AlSb/InAs/AlSb/GaSb heterostructures, in which electrons and holes accumulate in the InAs and GaSb regions respectively, under a magnetic field parallel to the interfaces. The low-temperature (T = 4.2K), zero-bias magnetoconductance has shown a behavior with field that evidences the two-dimensional character of both electrons and holes and that has allowed us to determine the hole density and the electron-hole separation. The observed field dependence of the current-voltage characteristics is explained by the relative change in parallel momentum of electrons and holes induced by the field.

Lin, Y; Abanov, A G

2002-01-01

199

A density-functional theory study of tip electronic structures in scanning tunneling microscopy  

International Nuclear Information System (INIS)

In this work, we report a detailed analysis of the atomic and electronic structures of transition metal scanning tunneling microscopy tips: Rh, Pd, W, Ir, and Pt pyramidal models, and transition metal (TM) atom tips supported on the W surface, by means of ab initio density-functional theory methods. The d electrons of the apex atoms of the TM tips (Rh, Pd, W, Ir, and Pt tetrahedral structures) show different behaviors near the Fermi level and, especially for the W tip, dz2 states are shown to be predominant near the Fermi level. The electronic structures of larger pyramidal TM tip structures with a single apex atom are also reported. Their obtained density of states are thoroughly discussed in terms of the different d-electron occupations of the TM tips. (paper)

200

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.

 
 
 
 
201

Weak-field asymptotic theory of tunneling ionization in many-electron atomic and molecular systems  

Science.gov (United States)

The weak-field asymptotic theory of tunneling ionization in an external static uniform electric field [Tolstikhin et al., Phys. Rev. A 84, 053423 (2011), 10.1103/PhysRevA.84.053423] is extended to many-electron atomic and molecular systems treated in the frozen-nuclei approximation. The leading-order term in the asymptotic expansion of the ionization rate ? in the value of the field F for F ?0 is obtained. The resulting formulas express ? in terms of properties of the unperturbed system. The most essential difference from the one-electron case, through which the many-electron character of the present theory reveals itself, is that the structure factor for a given ionization channel, defining the dependence of the ionization rate into this channel on the orientation of the system with respect to the field, is determined by the corresponding Dyson orbital. The theory is illustrated by calculations for several few-electron systems. The asymptotic results are compared with accurate fully correlated calculations of tunneling ionization rates available in the literature.

Tolstikhin, Oleg I.; Madsen, Lars Bojer; Morishita, Toru

2014-01-01

202

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)

203

What Faculty Think: A Survey on Electronic Resources  

Science.gov (United States)

In the fall of 2007, ebrary surveyed 906 faculty from around the world, asking them how they used electronic resources. This article, focusing on the responses of faculty to a few survey questions, finds some expected and surprising attitudes that faculty have about electronic resources for their own and students' research. (Contains 2 notes.)

Jackson, Millie

2008-01-01

204

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

205

Using Electronic Resources to Support Problem-Based Learning  

Science.gov (United States)

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

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

2012-01-01

206

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

International Nuclear Information System (INIS)

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

207

Fabrication of tunnel junction-based molecular electronics and spintronics devices  

International Nuclear Information System (INIS)

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

208

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

Energy Technology Data Exchange (ETDEWEB)

The electron transport properties of the cubic quantum dot, (PbS){sub 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){sub 32} is predicted affirming the observed bright images for (PbS){sub 32}. The calculated I-V characteristics of (PbS){sub 32} are predicted to be substrate-dependent; (PbS){sub 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){sub 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., E-mail: sanjeevg@mtu.edu, E-mail: haiying.he@valpo.edu; Banyai, Douglas; Pandey, Ravindra [Department of Physics, Michigan Technological University, Houghton, Michigan 49931 (United States); He, Haiying, E-mail: sanjeevg@mtu.edu, E-mail: haiying.he@valpo.edu [Department of Physics and Astronomy, Valparaiso University, Valparaiso, Indiana 46383 (United States); Kandalam, Anil K. [Department of Physics, West Chester University of Pennsylvania, West Chester, Pennsylvania 19383 (United States)

2013-12-28

209

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

210

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

211

Electronic Properties of Added Rows on TiO2(110) Surface Observed by Scanning Tunneling Spectroscopy  

Science.gov (United States)

The electronic properties of added rows on TiO2(110) surface have been studied in real space with atomic resolution by scanning tunneling spectroscopy. It is found that no vacant Ti 3d state is observed near the Fermi level in the tunneling spectra, and accordingly the tunneling conductance is lowest at the added row sites. On the other hand, a peak of vacant states appears at 1.2 eV above the Fermi level in the spectra obtained at a hill by which an added row is terminated.

Sakai, Yoshiyuki; Ehara, Shaw

2000-11-01

212

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

213

Eu2 + ? Sm3 + electron transfer by tunneling in MgS:Eu,Sm  

International Nuclear Information System (INIS)

Exposure of MgS:Eu,Sm (bank gap - 5.4 eV) to UV radiation caused a band to band transition. Some of these electrons from the conduction band are captured by Sm3 + ions forming Sm2 + ions. When optically stimulated by a Nd:YAG laser, the trapped electrons at Sm3 + ions recombine with he holes trapped at Eu2 + ions resulting in the characteristic Eu2 + board emission. However, optically stimulated luminescence is also observed subsequent to exciting the sample with 480 nm light which corresponds to the Eu2 + absorption involving a 8S11/2 (4f) arrow 2T2g (5d) transition. Since the 2T2g state of Eu2 + lies below the 2Eg state in Oh symmetry, this result strongly suggests that the electrons tunnel from the t2g level of the Eu2 + ions to the Sm3 + ions

214

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. PMID:22681092

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

2012-05-01

215

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

International Nuclear Information System (INIS)

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

216

Scanning Tunneling Microscopy Studies of Layered Correlated Electron Systems: Transition Metal Dichalcogenides and Iridates  

Science.gov (United States)

Strongly correlated electron problems, including high temperature superconductivity, colossal magneto-resistivity, charge-density wave, heavy fermion phenomena, etc., have been major research focuses in condensed-matter physics for the past several decades. Involvements of and competitions between different degrees of freedom and energy scales present considerable difficulties for understanding these problems. In this thesis, I have used home-built variable-temperature high resolution (spatial and energy) spectroscopic imaging scanning tunneling microscopes (SI-STM) to study the topography and the local single-particle tunneling spectroscopy in a family of two-dimensional charge-density wave (2D-CDW) materials (TaSe 2, TaS2, and NbSe2) and in a newly discovered 5d Mott insulator Sr2IrO4 with strong spin-orbit coupling. In the 2D-CDW materials, we have shown the strong lattice distortion and weak electron modulation accompanying CDW transition, directly opposite to Peierls mechanism. We have also discovered that the 2D-CDW transitions in TaSe 2 and TaS2 show involvement of the orbital degree of freedom, shedding light on a long standing puzzle with their electrical resistivity anomalies. In the novel 5d Mott insulator Sr2IrO4 we have found a large insulating gap of 620 meV, indicating a stronger-than-expected correlation effect for a 5d electron system.

Dai, Jixia

217

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

218

Electronic properties of (Zn,CoO systems probed by scanning tunnelling spectroscopy  

Directory of Open Access Journals (Sweden)

Full Text Available The aim of this paper is to gain insight into theelectronic properties of (Zn,CoO system - a widebandgap Diluted Magnetic Semiconductors (DMSshowing room temperature (RT ferromagnetism undern-type doping conditions. On the experimental side, ultrahigh-vacuum scanning tunnelling microscopy andspectroscopy (STM and STS at variable temperature (Tare used to probe the local electronic structure of thesystem. It is presented the map of the local density ofstates (LDOS of polar ZnO surfaces. Then, it is possibleto decorate (incorporate Co atoms onto (into thesemiconductor.

L. Moldovan

2008-05-01

219

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

220

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

International Nuclear Information System (INIS)

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 direction of the Cu substrate, resulting in long range distortion. A large insulator-like band gap of ? 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.

 
 
 
 
221

Scanning tunnel microscopic image of tungsten (100) and (110) real surfaces and nature of conduction electron reflection  

International Nuclear Information System (INIS)

The electrically polished (100) and (110) surfaces of tungsten are studied with the aid of a scanning tunnel microscope at atmospheric pressure. The (110) surface consists of a large number of atomically plane terraces whereas the (100) surface is faceted. The scanning tunnel microscope data can explain such results of experiments on transverse electron focussing as the strong dependence of the probability for specular reflection of conduction electrons scattered by the (100) surface on the electron de Broglie wavelength and the absence of a dependence of the probability for specular reflection on the wavelength for the (110) surface

222

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

Energy Technology Data Exchange (ETDEWEB)

The experimental data on the transient optical absorption of wide-band-gap optical crystals of lithium borates Li{sub 2}B{sub 4}O{sub 7}, LiB{sub 3}O{sub 5}, and Li{sub 6}Gd(BO{sub 3}){sub 3} and potassium (KH{sub 2}PO{sub 4} (KDP)) and ammonium (NH{sub 4}H{sub 2}PO{sub 4} (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{sup -8}-10 s is described by a proposed model of tunneling electron transfer between antimorphous defects in the cation sublattice under the thermally stimulated mobility of recombination partners. The numerical values of the kinetic parameters are determined and the time dependences of the reaction rate constants are calculated for all crystals under study. As a result, the dynamics of change in the optical properties of these crystals under a pulsed radiation action can be simulated.

Ogorodnikov, I. N., E-mail: igor.ogorodnikov@bk.ru; Kiseleva, M. S. [Ural Federal University (Russian Federation)

2012-07-15

223

Improved model for the stress-induced leakage current in thin silicon dioxide based on conduction-band electron and valence-band electron tunneling  

Science.gov (United States)

This article presents a detailed investigation on the stress-induced leakage current (SILC) conduction mechanism via conduction-band electron (CBE) and valence-band electron (VBE) tunneling in thin oxides. An improved SILC model that is able to reproduce the experimental SILC over a wide range of oxide fields, and yet give a realistic level of extracted neutral trap concentration, is proposed. Calculations performed with the improved SILC model suggest that SILC conduction via neutral traps is accompanied by energy relaxation (i.e., an inelastic mechanism), irrespective of the origin (i.e., whether CBE or VBE) of the tunneling species. For both CBE and VBE tunneling, inelastic tunneling with energy relaxation (Erelax) of 1.5 and 0.8 eV, was found to fit the experimental measurements well. These values of Erelax agree with those reported in the literature.

Chim, W. K.; Lim, P. S.

2002-02-01

224

An extended model of electrons: experimental evidence from high-resolution scanning tunneling microscopy  

International Nuclear Information System (INIS)

In a recent paper we introduced a model of extended electrons, which is fully compatible with quantum mechanics in the formulation of Schrödinger. However, it contradicts the current interpretation of electrons as point-particles. Here, we show by a statistical analysis of high-resolution scanning tunneling microscopy (STM) experiments, that the interpretation of electrons as point particles and, consequently, the interpretation of the density of electron charge as a statistical quantity will lead to a conflict with the Heisenberg uncertainty principle. Given the precision in these experiments we find that the uncertainty principle would be violated by close to two orders of magnitude, if this interpretation were correct. We are thus forced to conclude that the density of electron charge is a physically real, i.e. in principle precisely measurable quantity, as derived in a recent paper. Experimental evidence to the contrary, in particular high-energy scattering experiments, is briefly discussed. The finding is expected to have wide implications in condensed matter physics, chemistry, and biology, scientific disciplines which are based on the properties and interactions of electrons.

225

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

International Nuclear Information System (INIS)

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

226

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

227

Irradiation-induced electron tunnelling and small-polaron hopping in single-crystalline YIG  

International Nuclear Information System (INIS)

In electron (e-)-irradiated (>1023 e-m-2) single crystalline yttrium-ion Garnet (YIG), after moderate annealing, low-temperature (T 3O4) below the Verwey transition (TV ? 125 K). Our analysis shows that this similarity is the result of corresponding relaxation mechanisms in both systems, i.e. electron tunnelling and small-polaron hopping. Deeper insights into these mechanisms are obtained from a thorough inspection of these spectra and their physical preconditions in the two, a-priori, completely different ferrimagnetic systems: (i) semiconductor, transformed into a quasi-insulating state due to long-range ionic ordering at low-temperatures (Fe3O4) and (ii) insulator, brought into a state of low resistivity due to radiation-induced perturbations of the charge equilibrium (YIG). (orig.)

228

Incorporation of electron tunnelling phenomenon into 3D Monte Carlo simulation of electrical percolation in graphite nanoplatelet composites  

International Nuclear Information System (INIS)

The percolation threshold problem in insulating polymers filled with exfoliated conductive graphite nanoplatelets (GNPs) is re-examined in this 3D Monte Carlo simulation study. GNPs are modelled as solid discs wrapped by electrically conductive layers of certain thickness which represent half of the electron tunnelling distance. Two scenarios of 'impenetrable' and 'penetrable' GNPs are implemented in the simulations. The percolation thresholds for both scenarios are plotted versus the electron tunnelling distance for various GNP thicknesses. The assumption of successful dispersion and exfoliation, and the incorporation of the electron tunnelling phenomenon in the impenetrable simulations suggest that the simulated percolation thresholds are lower bounds for any experimental study. Finally, the simulation results are discussed and compared with other experimental studies.

229

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

230

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

International Nuclear Information System (INIS)

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

231

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

232

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

233

BBC news style guide [electronic resource].  

International Nuclear Information System (INIS)

Representing some of BBC's accumulated wisdom surrounding the use of English in written and spoken communications, this guide was written for BBC journalists but is a valuable resource for anyone who wants to write well.

234

Using Zapier with Trello for Electronic Resources Troubleshooting Workflow  

Directory of Open Access Journals (Sweden)

Full Text Available Troubleshooting access problems is an important part of the electronic resources management workflow. This article discusses an opportunity to streamline and track troubleshooting using two web-based services: Trello and Zapier.

Meghan Finch

2014-10-01

235

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

236

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

Directory of Open Access Journals (Sweden)

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

Micaela Waldman

2003-01-01

237

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

238

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

International Nuclear Information System (INIS)

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

239

Ultrafast Electron Emission and Molecular Dynamics in a Scanning Tunneling Microscope  

Science.gov (United States)

In pursuit of measurements at the limits of space and time relevant to chemistry, we have developed the cross-polarized double beat (CPDB) method. This method employs phase modulation in a Mach-Zehnder type interferometer to enable signal modulation without intensity modulation of the incident light. The method is applied to a scanning tunneling microscope (STM) tip, where the ultrafast induced electron emission properties are measured. The mechanism of electron emission is found to be the result of a nonlinear excitation of the surface plasmon, followed by a Fowler-Nordheim type field emission. This is determined through analysis of the dependence of the current on laser power, incident polarization, and delay time (in a pump-probe type measurement). We have also discovered latent time information in traditional STM measurements on Zinc(II) Etioporphyrin. The Jahn-Teller active electron of the anion couples the vibrational and electronic densities, allowing complete reconstruction of its vibrational superposition from the topography and electroluminescent spectrum. ZnEtio- also undergoes a spin flip transition which allows it to be used as a tunable molecular switch.

Perdue, Shawn Michael

240

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)

 
 
 
 
241

Contribution of the metal/SiO2 interface potential to photoinduced switching in molecular single-electron tunneling junctions  

International Nuclear Information System (INIS)

Photoinduced switching of the Coulomb staircase in molecular single-electron tunneling junctions was previously observed. These junctions consisted of evaporated SiO2 insulator (?5 nm), with tetrakis-3,5-di-t-butylphenyl-porphyrin (H2-TBPP) molecules as Coulomb islands, sandwiched between top and bottom electrodes. The reversible response and the relaxation time of the photoinduced switching suggest that this phenomenon depends on the properties of the metal/SiO2 interface rather than those of the H2-TBPP molecule or SiO2 tunneling layer. We analyzed the photoinduced switching according to the theory of single-electron tunneling taking into account the discrete molecular energy states and the metal/SiO2 interfacial electrostatic phenomena. We conclude that the main contributor to the photoinduced shift was the electrostatic potential formed through the space-charge exchange at the metal/SiO2 interface

242

Electronic neural network for dynamic resource allocation  

Science.gov (United States)

A VLSI implementable neural network architecture for dynamic assignment is presented. The resource allocation problems involve assigning members of one set (e.g. resources) to those of another (e.g. consumers) such that the global 'cost' of the associations is minimized. The network consists of a matrix of sigmoidal processing elements (neurons), where the rows of the matrix represent resources and columns represent consumers. Unlike previous neural implementations, however, association costs are applied directly to the neurons, reducing connectivity of the network to VLSI-compatible 0 (number of neurons). Each row (and column) has an additional neuron associated with it to independently oversee activations of all the neurons in each row (and each column), providing a programmable 'k-winner-take-all' function. This function simultaneously enforces blocking (excitatory/inhibitory) constraints during convergence to control the number of active elements in each row and column within desired boundary conditions. Simulations show that the network, when implemented in fully parallel VLSI hardware, offers optimal (or near-optimal) solutions within only a fraction of a millisecond, for problems up to 128 resources and 128 consumers, orders of magnitude faster than conventional computing or heuristic search methods.

Thakoor, A. P.; Eberhardt, S. P.; Daud, T.

1991-01-01

243

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

Energy Technology Data Exchange (ETDEWEB)

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.

Tsang, Juine Kai

1980-01-01

244

An XPS investigation of alumina thin films utilized in inelastic electron tunneling spectroscopy  

International Nuclear Information System (INIS)

X-ray photoelectron spectroscopy (XPS) has been applied to characterize a number of different aluminium oxide (alumina) thin films utilized in inelastic electron tunneling spectrocopy (IETS). Since IETS has been found to be an effective means for obtaining vibrational information on catalytic systems, reliable means of clarifying the exact relationship between the IET thin film model catalysts and high surface area commercial aluminas are of considerable importance. XPS data might profitably provide such a means of comparison, although sufficiently reliable XPS data for commercial samples are not currently available. The various thin film aluminas are characterized as to their chemical nature, chemical state distributions, and relative oxygen-to-alumina concentration ratios by analysis of peak positions, peak widths and peak intensities, respectively. Moreover, effects due to heating and halogenating the surface have been investigated independently, since these are commonly utilized to enhance the catalytic behavior of commercial aluminas. (orig.)

245

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

246

Excitation of bond-alternating spin-1/2 Heisenberg chains by tunnelling electrons.  

Science.gov (United States)

Inelastic electron tunneling spectra (IETS) are evaluated for spin-1/2 Heisenberg chains showing different phases of their spin ordering. The spin ordering is controlled by the value of the two different Heisenberg couplings on the two sides of each of the chain's atoms (bond-alternating chains). The perfect anti-ferromagnetic phase, i.e. a unique exchange coupling, marks a topological quantum phase transition (TQPT) of the bond-alternating chain. Our calculations show that the TQPT is recognizable in the excited states of the chain and hence that IETS is in principle capable of discriminating the phases. We show that perfectly symmetric chains, such as closed rings mimicking infinite chains, yield the same spectra on both sides of the TQPT and IETS cannot reveal the nature of the spin phase. However, for finite size open chains, both sides of the TQPT are associated with different IETS spectra, especially on the edge atoms, thus outlining the transition. PMID:25212245

Gauyacq, J-P; Lorente, N

2014-10-01

247

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

Science.gov (United States)

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

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

2014-10-01

248

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.

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

249

Sub-50-mK Electronic Cooling with Large-Area Superconducting Tunnel Junctions  

Science.gov (United States)

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 aluminum-based coolers that are equipped with a suspended normal metal and an efficient quasiparticle drain. At intermediate temperatures, the phonon bath of the suspended normal metal is cooled. By adjusting the junction transparency, we control the injection current and, thus, the temperature of the superconducting lead at the optimum cooling point. The best device shows remarkable cooling from 150 mK down to about 30 mK, a factor of 5 in temperature at a power of 40 pW. We discuss heat transport in our device and the reasons for cooling saturation at the low-temperature end.

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

2014-11-01

250

Excitation of bond-alternating spin-1/2 Heisenberg chains by tunnelling electrons  

Science.gov (United States)

Inelastic electron tunneling spectra (IETS) are evaluated for spin-1/2 Heisenberg chains showing different phases of their spin ordering. The spin ordering is controlled by the value of the two different Heisenberg couplings on the two sides of each of the chain's atoms (bond-alternating chains). The perfect anti-ferromagnetic phase, i.e. a unique exchange coupling, marks a topological quantum phase transition (TQPT) of the bond-alternating chain. Our calculations show that the TQPT is recognizable in the excited states of the chain and hence that IETS is in principle capable of discriminating the phases. We show that perfectly symmetric chains, such as closed rings mimicking infinite chains, yield the same spectra on both sides of the TQPT and IETS cannot reveal the nature of the spin phase. However, for finite size open chains, both sides of the TQPT are associated with different IETS spectra, especially on the edge atoms, thus outlining the transition.

Gauyacq, J.-P.; Lorente, N.

2014-10-01

251

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

Directory of Open Access Journals (Sweden)

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

Mohammad Javad Sharifi

2009-01-01

252

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

253

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

Science.gov (United States)

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

Aghili Yajadda, Mir Massoud

2014-10-01

254

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

255

IBEX Electronic Resource for Museum Educators  

Science.gov (United States)

This material is a comprehensive educational resource for informal educators highlighting the major mission information and science background for the Interstellar Boundary Explorer mission, a Small Explorer Earth-orbiting spacecraft that is designed to map the distant boundary between the solar wind from our Sun and the interstellar medium. New for 2012, this material also includes a comprehensive overview of all of the science results released through mid-2011 and information about the IBEX satellite's orbital change in June 2011. All of this material can be modified to use with informal education audiences, including museum and planetarium visitors, afterâschool clubs, and others. It is available as PDF .zip file and as a PowerPoint .zip file. The PowerPoint .zip file contains the newlyârevised PowerPoint resource and its associated movie clips. The PDF .zip file contains a PDF version of the newly-revised PowerPoint resource, a PDF version of the Notes section for each of the slides, and the movie clips. Because movie clips cannot be embedded into the PDF slides, each movie clip file name contains its associated slide number so users can play the movie clip alongside the slide.

256

Electron-tunneling modulation in percolating network of graphene quantum dots: fabrication, phenomenological understanding, and humidity/pressure sensing applications.  

Science.gov (United States)

The two-dimensional (2D) electron cloud, flexible carbon-carbon bonds, chemical modifiability, and size-dependent quantum-confinement and capacitance makes graphene nanostructures (GN) a widely tunable material for electronics. Here we report the oxidation-led edge-roughening and cleavage of long graphene nanoribbons (GNRs) (150 nm wide) synthesized via nanotomy (nanoscale cutting) of graphite (with 2 nm edged diamond knife) to produce graphene quantum dots (GQD). These GQDs (~100-200 nm) selectively interfaced with polyelectrolyte microfiber (diameter = 2-20 ?m) form an electrically percolating-network exhibiting a characteristic Coulomb blockade signature with a dry tunneling distance of 0.58 nm and conduction activation energy of 3 meV. We implement this construct to demonstrate the functioning of humidity and pressure sensors and outline their governing model. Here, a 0.36 nm decrease in the average tunneling-barrier-width between GQDs (tunneling barrier = 5.11 eV) increases the conductivity of the device by 43-fold. These devices leverage the modulation in electron tunneling distances caused by pressure and humidity induced water transport across the hygroscopic polymer microfiber (Henry's constant = 0.215 Torr(-1)). This is the foremost example of GQD-based electronic sensors. We envision that this polymer-interfaced GQD percolating network will evolve a new class of sensors leveraging the low mass, low capacitance, high conductivity, and high sensitivity of GQD and the interfacial or dielectric properties of the polymer fiber. PMID:23506081

Sreeprasad, T S; Rodriguez, Alfredo Alexander; Colston, Jonathan; Graham, Augustus; Shishkin, Evgeniy; Pallem, Vasanta; Berry, Vikas

2013-04-10

257

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

Science.gov (United States)

Artificial multiferroic tunnel junctions combining a ferroelectric tunnel barrier of BaTiO(3) with magnetic electrodes display a tunnel magnetoresistance whose intensity can be controlled by the ferroelectric polarization of the barrier. This effect, called tunnel electromagnetoresistance (TEMR), and the corollary magnetoelectric coupling mechanisms at the BaTiO(3)/Fe interface were recently reported through macroscopic techniques. Here, we use advanced spectromicroscopy techniques by means of aberration-corrected scanning transmission electron microscopy (STEM) and electron energy-loss spectroscopy (EELS) to probe locally the nanoscale structural and electronic modifications at the ferroelectric/ferromagnetic interface. Atomically resolved real-space spectroscopic techniques reveal the presence of a single FeO layer between BaTiO(3) and Fe. Based on this accurate description of the studied interface, we propose an atomistic model of the ferroelectric/ferromagnetic interface further validated by comparing experimental and simulated STEM images with atomic resolution. Density functional theory calculations allow us to interpret the electronic and magnetic properties of these interfaces and to understand better their key role in the physics of multiferroics nanostructures. PMID:22191458

Bocher, Laura; Gloter, Alexandre; Crassous, Arnaud; Garcia, Vincent; March, Katia; Zobelli, Alberto; Valencia, Sergio; Enouz-Vedrenne, Shaïma; Moya, Xavier; Mathur, Neil D; Marthur, Neil D; Deranlot, Cyrile; Fusil, Stéphane; Bouzehouane, Karim; Bibes, Manuel; Barthélémy, Agnès; Colliex, Christian; Stéphan, Odile

2012-01-11

258

Low-temperature scanning tunneling microscopy and transport measurements on adsorbate-induced two-dimensional electron systems  

Energy Technology Data Exchange (ETDEWEB)

We have performed not only magnetotransport measurements on two-dimensional electron systems (2DESs) formed at the cleaved surfaces of p-InAs but also observations of the surface morphology of the adsorbate atoms, which induced the 2DES at the surfaces of narrow band-gap semiconductors, with use of a scanning tunneling microscopy. The electron density of the 2DESs is compared to the atomic density of the isolated Ag adatoms on InAs surfaces.

Masutomi, Ryuichi; Triyama, Naotaka; Okamoto, Tohru [Department of Physics, University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-0033 (Japan)

2013-12-04

259

Antenna-Coupled Superconducting Tunnel Junctions with Single-Electron Transistor Readout for Detection of Sub-mm Radiation  

Science.gov (United States)

Antenna-coupled superconducting tunnel junction detectors have the potential for photon-counting sensitivity at sub-mm wavelengths. The device consists of an antenna structure to couple radiation into a small superconducting volume and cause quasiparticle excitations, and a single-electron transistor to measure currents through tunnel junction contacts to the absorber volume. We will describe optimization of device parameters, and recent results on fabrication techniques for producing devices with high yield for detector arrays. We will also present modeling of expected saturation power levels, antenna coupling, and rf multiplexing schemes.

Stevenson, T. R.; Hsieh, W.-T.; Li, M. J.; Stahle, C. M.; Wollack, E. J.; Schoelkopf, R. J.; Teufel, J.; Krebs, Carolyn (Technical Monitor)

2002-01-01

260

E-print network [electronic resource].  

International Nuclear Information System (INIS)

Provides access to scholarly and professional works electronically produced and shared by researchers with the intent of communicating research findings to colleagues. Contains e-prints in basic and applied sciences, primarily in physics but also including subject areas such as chemistry, biology and life sciences, materials science, nuclear sciences and engineering, energy research, computer and information technologies, and other disciplines of interest to the U.S. Department of Energy.

 
 
 
 
261

I Studies of Chemical Splittings, Triplet Levels and Tunneling States at Electronic Defects in Silicon.  

Science.gov (United States)

Infrared spectroscopy, combined with temperature dependence, magnetic field and uniaxial stress, has been used to study a variety of modifications to the hydrogen model for donors and acceptors in semiconductors. These are spin-triplet levels for double donors, tunneling or rotational motion for molecular acceptors, a novel chemical -splitting scheme for a hydrogen-related donor, and a dependence of level lifetimes on chemical-splitting magnitude. The significance of many-body interactions for double donors has been demonstrated by the observation of weak absorption lines, not predicted by the hydrogen model, in the spectra of selenium and telurium in silicon. Zeeman splitting, interpreted by the theory of Lande g-factors, confirms their identification as transitions to spin-triplet terms. In addition, as a test of our analysis, Zeeman spectroscopy of the singly-ionized double-donors is studied. To investigate the influence of the nuclear degrees of freedom on the electronic spectrum, the temperature - and stress-dependences of the electronic 2p^ ' line for the acceptors (Li,Be), (D,Be) and (H,Be) in silicon have been measured. The results demonstrate that the (Li,Be) center has a fixed -orientation with a ground level split by local distortion and that the (D,Be) and (H,Be) centers undergo either tunneling or hindered -rotor motion between equivalent equilibrium orientations. The temperature-dependent infrared spectra of a new hydrogen-activated donor in silicon reveals three low-lying energy levels with degeneracies in the ratio 1:2:2. No isotope effect is observed when hydrogen is replaced by deuterium, so any model must be based on electronic degrees of freedom. Our observations are consistent with a D_{rm 3d} interstitial site for monatomic hydrogen whose level structure arises from an "inverted" valley-orbit interaction. Laser saturation has been used to prove a transition of the deep-donor Se in AlSb. The intensity dependence of the absorptivity is explained by a two-photon process. We find an excited-state lifetime which is about three orders of magnitude smaller than that for shallow donors in III -V compounds.

Peale, Robert Edwin

262

Interfacial Electronic and Magnetic Coupling in Organic-metal System Studied by Scanning Tunneling Microscopy  

Science.gov (United States)

Organic materials have drawn much attention in spintronics studies because of their tunable properties by functional groups and potential to achieve molecular magnets. An important factor influencing these properties is the interfacial effect. In organic-metal systems, different interfaces lead to strong modulation of electronic structures and even magnetic behaviors like spin coupling. In our study, Mn-phthalocyanine (MnPc) deposited on Cu(111) surface have been measured by scanning tunneling microscopy (STM) and spectroscopy (STS) at 4.5 K. With different deposition amount, MnPc are adsorbed as isolated molecules or in an ordered assembled structure. From STS curves, assembled MnPc possess a broadened state near the onset of Cu(111) surface state comparing to islolated ones. According to ab initio calculation, distance between the central Mn atom and the substrate in assembled molecules is reduced due to intermolecular interaction and affects the electronic structures. Magnetic behaviors of MnPc on ferromagnetic metal substrate are further investigated by spin-polarized STM (SP-STM). Spin contrast of isolated molecules on Co nanoislands on Cu(111) is found near the Fermi level in STS maps, which is considered to be ferromagnetic coupling between MnPc and Co islands.

Chu, Yu-Hsun; Hsu, C. H.; Hsu, P. J.; Hsieh, W. J.; Lu, C. I.; Chen, S. W.; Butler, C. J.; Kaun, Chao-Cheng; Lin, Minn-Tsong

2012-02-01

263

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

International Nuclear Information System (INIS)

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

264

Why and How to Measure the Use of Electronic Resources  

Directory of Open Access Journals (Sweden)

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

Jean Bernon

2008-11-01

265

Influence of electron tunneling barriers on the performance of InGaN-GaN ultraviolet light-emitting diodes  

Energy Technology Data Exchange (ETDEWEB)

InGaN-GaN multiple quantum well (MQW) ultraviolet (UV) light-emitting diodes (LEDs) with and without n-AlGaN electron tunneling barriers (ETBs), grown on sapphire substrates by metal organic chemical vapor deposition (MOCVD), are characterized by comparison with device simulation results. Compared with a conventional LED without the ETB, one of the proposed LEDs with the optimized ETB shows an 11% increase in normalized photodiode (PD) currents. We contribute this improvement to the reduced number of hot electron overflowing to the p-side from MQW by low-energy electron tunneling, which is consistent with the simulation results regarding the carrier distributions. (copyright 2004 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

Kim, K.C.; Choi, Y.C.; Kim, D.H.; Kim, T.G. [Dept. of Electronic Materials Engineering, KwangWoon University, 447-1, Wolgye1-dong, Nowon-gu, Seoul 139-701 (Korea); Yoon, S.H.; Sone, C.S.; Park, Y.J. [Photonics Lab., Samsung Advanced Institute of Technology, San 14-1, Nongseo-ri, Giheung-eup, Yongin-si, Gyeonggi-do 449-901 (Korea)

2004-09-01

266

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

267

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

268

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

269

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

Digital Repository Infrastructure Vision for European Research (DRIVER)

Titanium silicide islands have been formed by the ultrahigh vacuum deposition of thin films of titanium (< 2 nm) on atomically clean Si(100) substrates followed by annealing to ~800 degrees C. Scanning tunneling microscopy (STM) and scanning tunneling spectroscopy have been performed on these islands to record current-voltage (I-V) curves. Because each island forms a double barrier tunnel junction (DBTJ) structure with the STM tip and the substrate, they would be expected to...

Tedesco, Joseph L.; Rowe, J. E.; Nemanich, Robert J.

2010-01-01

270

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

271

The role of tunnel junction resistances and defects on electron transport mechanism in networks of two-dimensional disordered conductors  

Science.gov (United States)

The effect of tunnel junction resistances on the electronic property and the magneto-resistance of few-layer graphene sheet networks is investigated. By decreasing the tunnel junction resistances, transition from strong localization to weak localization occurs and magneto-resistance changes from positive to negative. It is shown that the positive magneto-resistance is due to Zeeman splitting of the electronic states at the Fermi level as it changes with the bias voltage. As the tunnel junction resistances decrease, the network resistance is well described by 2D weak localization model. Sensitivity of the magneto-resistance to the bias voltage becomes negligible and diminishes with increasing temperature. It is shown 2D weak localization effect mainly occurs inside of the few-layer graphene sheets and the minimum temperature of 5 K in our experiments is not sufficiently low to allow us to observe 2D weak localization effect of the networks as it occurs in 2D disordered metal films. Furthermore, defects inside the few-layer graphene sheets have negligible effect on the resistance of the networks which have small tunnel junction resistances between few-layer graphene sheets.

Yajadda, M. M. A.; Kumar, S.; Ostrikov, K.

2014-11-01

272

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

DEFF Research Database (Denmark)

We investigated Coulomb repulsion effects in nonadiabatic (diabatic) two-electron tunneling through a redox molecule with a single electronic level in a symmetric electrochemical contact under ambient conditions, i.e., room temperature and condensed matter environment. The electrochemical contact is representative of electrochemical scanning tunneling microscopy or a pair of electrochemical nanoscale electrodes. The two-electron transfer molecular system also represents redox molecules with three electrochemically accessible oxidation states, rather than only two states such as comprehensively studied. It is shown that depending on the effective Coulomb repulsion energy, the current/overpotential relation at fixed bias voltage shows two narrow (~kBT) peaks in the limit of strong electron-phonon coupling to the solvent environment. The system also displays current/bias voltage rectification. The differential conductance/bias voltage correlation can have up to four peaks even for a single-level redox molecule. The peak position, height, and width are determined by the oxidized and reduced states of both the ionization and affinity levels of the molecule and depend crucially on the Debye screening of the electric field in the tunneling gap. ©2009 American Institute of Physics

Ulstrup, Jens

2009-01-01

273

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

Science.gov (United States)

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

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

1999-01-01

274

Providing Access to Electronic Information Resources in Further Education  

Science.gov (United States)

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

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

2004-01-01

275

Electron tunneling spectroscopy of superconducting A15 V-Ga alloy films  

International Nuclear Information System (INIS)

The results of a tunneling study of the high-T/sub c/, A15 superconductor V3Ga are presented. The superconducting electron-phonon interaction spectral function ?2F(?) is obtained for a set of samples with compositions spanning stoichiometry. These results are of particular interest since V3Ga is unusual among the high-T/sub c/, A15 superconductors in that single-phase material can be formed on either side of stoichiometry. The results demonstrate that increased weight of ?2F(?) (or so-called mode softening) occurs at low energies as stoichiometry is approached either from above or below. Concomitantly ?/sub log/ is found to show a minimum at stoichiometry. Interestingly, although T/sub c/ is a symmetric function of composition around stoichiometry, ?/sub log/ is asymmetric. Hence, some other factor beyond mode softening is playing a significant factor in the systematics of the high T/sub c/'s exhibited by this superconductor as a function of composition

276

Study of the corrosion of aluminum by CCl4 using inelastic electron tunneling spectroscopy  

Science.gov (United States)

Inelastic electron tunneling spectroscopy (IETS) has been used to determine the molecular species which occur on an aluminum oxide surface during metallic corrosion by carbon tetrachloride. IETS spectra were obtained for CCl4 adsorbed on aluminum oxide and the observed vibration modes were assigned by comparison with infrared and Raman frequencies. Modes were observed which could be associated with the molecular species CCl4, AlCl, AlCl2, AlCl3, .CCl3, C2Cl6, and the complex CCl+3[AlCl4]-. These species are those in the reaction sequence proposed by Stern and Uhlig for the corrosion of aluminum by CCl4. The results do not provide information on whether the reaction is chemical or electrochemical in nature. The fact that no modes were observed which would reflect oxygen-carbon bonding, and the presence of a large number of aluminum-chlorine modes suggest that the corrosion mechanism is by reaction of the solvent with exposed aluminum atoms.

Ellialtiog~Lu, R. M.; White, H. W.; Godwin, L. M.; Wolfram, T.

1980-05-01

277

Tunneling current bistability of correlated 2D electron-hole layers  

Science.gov (United States)

We study the low-temperature vertical tunneling current (TC) of a system of coupled 2D electron and hole gases (2DEG, 2DHG) of equal density realized in a single-barrier GaAs/AlAs/GaAs p-i-n heterostructure under conditions of forward bias. The density can be tuned by external voltage and the in-plane inter-particle distance can be made comparable to the layer separation (25 nm), the GaAs Bohr radius (12 nm), and the magnetic length for a perpendicular magnetic field B=10 T. We observe a discontinuous bistability in the I- V characteristic at T ? 300 mK, which has been never observed in n-type structures, and which is strongly enhanced for B=10 T. Out of the bistability, the current at fixed external voltage is observed to be exactly periodic in the inverse magnetic field for the high current states (HCS), while the 1/ B oscillations of the low current states (LCS) are clearly phase shifted. The transition is found to be discontinuous both in the phase and in the period (i.e. density) in the region of bistability. We interpret the bistability as a phase transition between states of inter-layer correlated exciton-like states (LCS) and the two uncoupled free-carrier 2DEG and 2DHG (HCS) in our bilayer system.

Parlangeli, A.; Christianen, P. C. M.; Geim, A. K.; Maan, J. C.; Eaves, L.; Main, P. C.; Henini, M.

1998-12-01

278

?- X electron transfer in type II tunneling bi-quantum wells  

Science.gov (United States)

We have studied the energy band structure and the ?- X carrier transfer mechanism for type II tunneling bi-quantum wells consisting of GaAs wells, AlGaAs barriers of different thicknesses, and AlAs layers by cw and time-resolved photoluminescence measurements. The cw photoluminescence spectra of the indirect recombination of X electrons in the 7.1 nm thick AlAs layers with ? holes in the 2.8 nm thick GaAs wells show weak zero-phonon lines indicating that the AlAs confined states at Xxy are lower than those at Yz. Time-resolved photoluminescence reveals that the carrier transfer time depends stronger on temperature for thicker AlGaAs barriers. Two scattering mechanisms, temperature-dependent phonon scattering and the temperature-independent interface scattering, are probably involved in the carrier transfer, the latter becoming smaller with increasing AlGaAs barrier thickness. Our results are compared with those obtained for similar type II GaAs/AlAs superlattices.

Tackeuchi, Atsushi; Strauß, Uwe; Rühle, Wolfgang W.; Inata, Tsuguo; Muto, Shunichi

1994-06-01

279

Structural characterization of interfaces in epitaxial Fe/MgO/Fe magnetic tunnel junctions by transmission electron microscopy  

International Nuclear Information System (INIS)

We present a detailed structural characterization of the interfaces in Fe/MgO/Fe layers grown by molecular-beam epitaxy using aberration-corrected transmission electron microscopy (TEM), scanning TEM, and electron energy-loss spectroscopy. When fabricated into magnetic tunnel junctions, these epitaxial devices exhibit large tunnel magnetoresistance ratios (e.g., 318% at 10 K), though still considerably lower than the values predicted theoretically. The reason for this discrepancy is being debated and has been attributed to the structure of, and defects at the interface, namely, the relative position of the atoms, interface oxidation, strain, and structural asymmetry of the interfaces. In this structural study, we observed that Fe is bound to O at the interfaces. The interfaces are semicoherent and mostly sharp with a minor degree of oxidation. A comparison of the two interfaces shows that the top MgO/Fe interface is rougher.

280

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.

 
 
 
 
281

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.

282

Electron heating by photon-assisted tunneling in niobium terahertz mixers with integrated niobium titanium nitride striplines  

Science.gov (United States)

We describe the gap voltage depression and current-voltage (I-V) characteristics in pumped niobium superconductor-insulator-superconductor junction with niobium titanium nitride tuning stripline by introducing an electron heating power contribution resulting from the photon-assisted tunneling process. Theoretical fits using the extended Tien-Gordon theory are obtained that reproduce the most salient features of the pumped I-V characteristics.

Leone, B.; Gao, J. R.; Klapwijk, T. M.; Jackson, B. D.; Laauwen, W. M.; de Lange, G.

2001-03-01

283

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

CERN Document Server

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

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

2006-01-01

284

ASIL Guide to Electronic Resources for International Law  

Science.gov (United States)

The study and practice of international law can be a tough area to get a handle on, and with numerous online resources available for both areas, it can be difficult to separate the wheat from the chaff. Since 1997, The American Society of International Law (ASIL) has been continuously updating and revising their Guide to Electronic Resources for International Law, under the able direction of Marci Hoffman and Jill Watson. Within each of its eight primary sections, users can read about various high-quality online resources for each topical area (such as international organizations and human rights), and then read brief summaries of what each online resource features in terms of its content and scope. As might be expected, the site also contains information on relevant and helpful weblogs that deal with international law.

Hoffman, Marci.; Watson, Jill M.

2003-01-01

285

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

286

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

International Nuclear Information System (INIS)

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

287

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

Energy Technology Data Exchange (ETDEWEB)

Highlights: Black-Right-Pointing-Pointer Irradiation of photons with energies more than the band gap generates electron-hole pairs. Black-Right-Pointing-Pointer Electron tunneling probability is dependent on the electron mobility. Black-Right-Pointing-Pointer Tunneling electrons are captured by charge deficient atoms. Black-Right-Pointing-Pointer Unpaired electrons induce cleavages of chemical bonds. - Abstract: Measurement of light induced heterogeneous electron transfer is important for understanding of fundamental processes involved in chemistry, physics and biology, which is still challenging by current techniques. Laser activated electron tunneling (LAET) from semiconductor metal oxides was observed and characterized by a MALDI (matrix assisted laser desorption ionization) mass spectrometer in this work. Nanoparticles of ZnO were placed on a MALDI sample plate. Free fatty acids and derivatives were used as models of organic compounds and directly deposited on the surface of ZnO nanoparticles. Irradiation of UV laser ({lambda} = 355 nm) with energy more than the band gap of ZnO produces ions that can be detected in negative mode. When TiO{sub 2} nanoparticles with similar band gap but much lower electron mobility were used, these ions were not observed unless the voltage on the sample plate was increased. The experimental results indicate that laser induced electron tunneling is dependent on the electron mobility and the strength of the electric field. Capture of low energy electrons by charge-deficient atoms of adsorbed organic molecules causes unpaired electron-directed cleavages of chemical bonds in a nonergodic pathway. In positive detection mode, electron tunneling cannot be observed due to the reverse moving direction of electrons. It should be able to expect that laser desorption ionization mass spectrometry is a new technique capable of probing the dynamics of electron tunneling. LAET offers advantages as a new ionization dissociation method for mass spectrometry.

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

2012-06-04

288

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

289

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

290

Optical switching of single-electron tunneling in SiO2/molecule/SiO2 multilayer on Si(100)  

International Nuclear Information System (INIS)

Porphyrin-based molecules inserted into the oxide layer of a metal-oxide-semiconductor structure served as Coulomb islands. A Coulomb staircase originating from the single-electron tunneling was observed in a current-voltage curve. We found that light irradiation induced a shift in the Coulomb staircase. This shift was reversible; the shifted Coulomb staircase returned to its original position when the light irradiation was turned off. We thus demonstrated optical switching of a tunneling current. This result indicates that the molecular Coulomb islands have the potential to provide a range of optical functionality in single-electron tunneling devices

291

Optical switching of single-electron tunneling in SiO2/molecule/SiO2 multilayer on Si (100)  

Science.gov (United States)

Porphyrin-based molecules inserted into the oxide layer of a metal-oxide-semiconductor structure served as Coulomb islands. A Coulomb staircase originating from the single-electron tunneling was observed in a current-voltage curve. We found that light irradiation induced a shift in the Coulomb staircase. This shift was reversible; the shifted Coulomb staircase returned to its original position when the light irradiation was turned off. We thus demonstrated optical switching of a tunneling current. This result indicates that the molecular Coulomb islands have the potential to provide a range of optical functionality in single-electron tunneling devices.

Wakayama, Y.; Ogawa, K.; Kubota, T.; Suzuki, H.; Kamikado, T.; Mashiko, S.

2004-07-01

292

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

DEFF Research Database (Denmark)

We report on single molecule electron transport measurements of two oligophenylenevinylene (OPV3) derivatives placed in a nanogap between gold (Au) or lead (Pb) electrodes in a field effect transistor device. Both derivatives contain thiol end groups that allow chemical binding to the electrodes. One derivative has additional methylene groups separating the thiols from the delocalized -electron system. The insertion of methylene groups changes the open state conductance by 3-4 orders of magnitude and changes the transport mechanism from a coherent regime with finite zero-bias conductance to sequential tunneling and Coulomb blockade behavior.

Danilov, Andrey; Kubatkin, Sergey

2008-01-01

293

Antiresonance of electron tunneling through a four-quantum-dot ring with two side-coupled quantum dots  

International Nuclear Information System (INIS)

Making use of the equation of motion method and Keldysh Green function technique, we obtain the current formula for a two-terminal four-quantum-dot-ring with two side-coupled quantum dots under a DC bias voltage. Antiresonance and resonance of electron tunneling is studied by numerical calculations. Only when the quantum dots in the ring has the same single electron energy level with that of the side-coupled quantum dots, i.e. ?i0=?0 and both side-coupling are turned on at the same time, the antiresonance appear exactly at ?0

294

Influence of temperature gradients on tunnel junction thermometry below 1 K: cooling and electron-phonon coupling  

CERN Document Server

We have studied thermal gradients in thin Cu and AlMn wires, both experimentally and theoretically. In the experiments, the wires were Joule heated non-uniformly at sub-Kelvin temperatures, and the resulting temperature gradients were measured using normal metal-insulator-superconducting tunnel junctions. The data clearly shows that even in reasonably well conducting thin wires with a short ($\\sim 10 \\mu$m) non-heated portion, significant temperature differences can form. In most cases, the measurements agree well with a model which includes electron-phonon interaction and electronic thermal conductivity by the Wiedemann-Franz law.

Karvonen, J T; Maasilta, I J

2006-01-01

295

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

296

Electron transfer processes in scanning tunneling spectroscopy through small supported particles  

Energy Technology Data Exchange (ETDEWEB)

Mechanism of the staircase like I-V curve observed recently in scanning tunneling spectroscopy (STS) of a metal fine particle supported on an oxide covered substrate is clarified based on theoretical simulations. It is discussed how the step structures are influenced by the coupling of the fine particle charge to the remaining degrees of freedom, such as induced charge in the surrounding medium. Relation between the characteristic features of single eletron tunneling (SET) and the STS of microclusters is discussed. (orig.).

Tsukada, M. (Tokyo Univ. (Japan). Dept. of Physics)

1991-01-01

297

Electron transfer processes in scanning tunneling spectroscopy through small supported particles  

International Nuclear Information System (INIS)

Mechanism of the staircase like I-V curve observed recently in scanning tunneling spectroscopy (STS) of a metal fine particle supported on an oxide covered substrate is clarified based on theoretical simulations. It is discussed how the step structures are influenced by the coupling of the fine particle charge to the remaining degrees of freedom, such as induced charge in the surrounding medium. Relation between the characteristic features of single eletron tunneling (SET) and the STS of microclusters is discussed. (orig.)

298

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

Science.gov (United States)

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

White, Marilyn; Sanders, Susan

2009-01-01

299

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

300

Tunnel effect  

International Nuclear Information System (INIS)

It is shown that a large number of phenomena have been explained by the tunnel effect, in microscopic physics (field emission, ? radioactivity) and in solid state physics (semiconductors and superconductors). New applications appear everyday as in electronics and in the study of matter

 
 
 
 
301

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

302

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

CERN Document Server

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

Reilly, D J

2004-01-01

303

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.)

304

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 n 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.

305

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.

306

Charge recombination via intercolumnar electron tunneling through the lipid-like mantle of discotic hexa-alkyl-hexa-peri-hexabenzocoronenes.  

Science.gov (United States)

The recombination of the mobile charge carriers formed in pulse-ionized hexa-alkyl-substituted hexa-peri-hexabenzocoronenes occurs mainly via intercolumnar electron tunneling through the intervening hydrocarbon mantle. This is evidenced as a dramatic increase in the time scale of the decay of the radiation-induced conductivity from a few hundred nanoseconds to close to a millisecond as the peripheral alkyl substituents increase in size from 8 to 24 carbon atoms with corresponding disk diameters, D, from 23.4 to 36.6 A. The decay kinetics are a function only of the total number of peripheral carbon atoms with no evidence for specific effects of chain branching. The 1/e decay time, tau(e), increases exponentially with D according to tau(e) = tau(e)(0) exp(betaD) with tau(e)(0) = 48 fs and beta = 0.63 A(-1). Taking into account the tilted columnar configuration of the molecules in the solid phase leads to a beta value of ca. 0.8 A(-1) for the distance dependence of intercolumnar electron tunneling. In contrast to the orders of magnitude changes in the time scale for intercolumnar charge recombination, the intracolumnar charge hopping times vary by only a factor of 4, between 40 and 160 fs, with no systematic dependence on the nature of the alkyl substituents. On the basis of the results, the time scale estimated for electron tunneling across a 40 A thick lipid membrane is estimated to be close to 1 ms. PMID:16218620

Warman, John M; Piris, Jorge; Pisula, Wojciech; Kastler, Marcel; Wasserfallen, Daniel; Müllen, Klaus

2005-10-19

307

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

International Nuclear Information System (INIS)

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

308

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

Energy Technology Data Exchange (ETDEWEB)

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

Chakrabarti, Sudipto; Pal, Amlan J., E-mail: sspajp@iacs.res.in [Department of Solid State Physics, Indian Association for the Cultivation of Science, Jadavpur, Kolkata 700032 (India)

2014-01-06

309

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

310

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

Energy Technology Data Exchange (ETDEWEB)

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

SCHNEIDER,LARRY X.

2000-06-01

311

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

312

Role of Intermolecular Separation in Nanoscale Patterning C60 Films by Local Injection of Electrons from Scanning Tunneling Microscope Tip  

Science.gov (United States)

A systematic study on the polymerization and decomposition of C60 molecules induced by electron injection from scanning tunneling microscope (STM) tips has revealed that increasing intermolecular separation in the lateral directions with respect to the surface reduces both polymerization and decomposition reaction efficiencies and suppresses the spreading effect of polymerization from the electron injection point, down to ˜2 nm under a good condition. This is understood by considering that the wider lateral intermolecular separation and hence the smaller intermolecular spacing vertical to the surface lead to a suppression of electron spreading parallel to the surface but its enhancement normal to the surface, resulting in the small localization of molecular reactions on the surface.

Nakamura, Yoshiaki; Mera, Yutaka; Maeda, Koji

2005-10-01

313

Site-dependent electronic structures of a single molecule on a metal surface studied by scanning tunneling microscopy and spectroscopy  

Science.gov (United States)

Single-molecule observation of the electronic structures of para-cyanobenzoate (pCB) adsorbed on Cu(1 1 0) has been performed using scanning tunneling microscopy (STM) and spectroscopy (STS). We found that pCB has two types of the adsorption site on Cu(1 1 0); i.e., two oxygen atoms of pCB are bridged between adjacent Cu atoms at the short- or long-bridge sites. STS and STS mapping revealed that the pCB adsorbed at the short-bridge site has a resonant peak at 2.0 V above the Fermi level, which is assigned to the lowest unoccupied molecular orbital (LUMO) of pCB. However, the LUMO state is shifted toward lower voltage (1.2 V) when the pCB molecule is adsorbed at the long-bridge site. The energy levels of the LUMO state, depending on the adsorption site of pCB, can thus be ascribed to the degree of the electronic interaction between pCB and the Cu substrate. The site transformation of pCB induced by the injection of tunneling electrons from the STM tip has also been presented.

Katano, Satoshi; Hori, Masafumi; Kim, Yousoo; Kawai, Maki

2014-10-01

314

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

315

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

Digital Repository Infrastructure Vision for European Research (DRIVER)

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...

P?nar Al; Umut Al

2003-01-01

316

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

317

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

318

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

Energy Technology Data Exchange (ETDEWEB)

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

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

2013-02-11

319

Electronic picture of spin-polarized tunneling with a Cr tip  

International Nuclear Information System (INIS)

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.

320

Strongly confined tunnel-coupled one-dimensional electron systems from an asymmetric double quantum well  

Science.gov (United States)

Vertically stacked quantum point contacts (QPCs) are prepared by atomic force microscope (AFM) lithography from an asymmetric GaAs/AlGaAs double quantum well (DQW) heterostructure. Top- and back-gate voltages are used to tune the tunnel-coupled QPCs, and back-gate bias cooling is employed to investigate coupled and decoupled one-dimensional (1D) modes. Parity dependent mode coupling is invoked by the particular asymmetry in the vertical DQW confinement.

Buchholz, S. S.; Fischer, S. F.; Kunze, U.; Schuh, D.; Abstreiter, G.

2008-03-01

 
 
 
 
321

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

Digital Repository Infrastructure Vision for European Research (DRIVER)

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 impo...

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

2014-01-01

322

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

323

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

International Nuclear Information System (INIS)

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

324

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

Energy Technology Data Exchange (ETDEWEB)

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 [School of Chemistry, University of Bristol, Cantock' s Close, Bristol BS8 1TS (United Kingdom); Department of Physics, Birla Institute of Technology, Mesra, Ranchi 835215 (India); Harniman, Robert; May, Paul W., E-mail: paul.may@bristol.ac.uk [School of Chemistry, University of Bristol, Cantock' s Close, Bristol BS8 1TS (United Kingdom); Barhai, P. K. [Department of Physics, Birla Institute of Technology, Mesra, Ranchi 835215 (India)

2014-04-28

325

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

326

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

327

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.

328

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.

2010-12-01

329

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

Energy Technology Data Exchange (ETDEWEB)

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.

Marpe, Mario; Heuser, Christian; Wucher, Andreas [Fakultaet fuer Physik, Universitaet Duisburg-Essen, D-47048 Duisburg (Germany); Diesing, Detlef [Fakultaet fuer Chemie, Universitaet Duisburg-Essen, D-45117 Essen (Germany)

2011-07-01

330

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.

331

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

Science.gov (United States)

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

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

2012-01-01

332

Electron tunneling experiments on La-substituted Kondo-semiconductor CeRhAs  

International Nuclear Information System (INIS)

Polycrystalline Ce1-xLaxRhAs is investigated by means of break-junction tunneling. On Ce substituted by La (x=0.01), a pronounced hump structure is developed at the bias +/-0.25V with a shallow dip on it. The hump emergence is consistent with a drastic reduction in the resistivity. These facts give direct evidence for the appearance of mid-gap states near the Fermi energy by a small La substitution for Ce in CeRhAs

333

Electron tunneling experiments on La-substituted Kondo-semiconductor CeRhAs  

Energy Technology Data Exchange (ETDEWEB)

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

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

2006-08-15

334

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 ? system only, and consequently, in the vicinity of the interference feature, the transmission channels of the ? system and the ? 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

335

Preferential antiferromagnetic coupling of vacancies in graphene on SiO2: Electron spin resonance and scanning tunneling spectroscopy  

Science.gov (United States)

Monolayer graphene grown by chemical vapor deposition and transferred to SiO2 is used to introduce vacancies by Ar+ ion bombardment at a kinetic energy of 50 eV. The density of defects visible in scanning tunneling microscopy is considerably lower than the ion fluence, implying that most of the defects are single vacancies as expected from the low ion energy. The vacancies are characterized by scanning tunneling spectroscopy on graphene and highly oriented pyrolytic graphite (HOPG). A peak close to the Dirac point is found within the local density of states of the vacancies similar to the peak found previously for vacancies on HOPG. The peak persists after air exposure up to 180 min, such that electron spin resonance (ESR) at 9.6 GHz can probe the vacancies exhibiting such a peak. After an ion flux of 10/nm2, we find an ESR signal corresponding to a g factor of 2.001-2.003 and a spin density of 1-2spins/nm2. The peak width is as small as 0.17 mT indicating exchange narrowing. Consistently, the temperature-dependent measurements reveal antiferromagnetic correlations with a Curie-Weiss temperature of -10 K. Thus, the vacancies preferentially couple antiferromagnetically, ruling out a ferromagnetic graphene monolayer at ion induced spin densities of 1-2nm2.

Just, S.; Zimmermann, S.; Kataev, V.; Büchner, B.; Pratzer, M.; Morgenstern, M.

2014-09-01

336

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

337

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

International Nuclear Information System (INIS)

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

338

Modeling of Electronic Transport in Scanning Tunneling Microscope Tip-Carbon Nanotube Systems  

Science.gov (United States)

A model is proposed for two observed current-voltage (I-V) patterns in a recent experiment with a scanning tunneling microscope tip and a carbon nanotube. We claim that there are two mechanical contact modes for a tip (metal) -nanotube (semiconductor) junction (1) with or (2) without a tiny vacuum gap (0.1 - 0.2 nm). With the tip grounded, the tunneling case in (1) would produce large dI/dV with V > 0, small dI/dV with V < 0, and I = 0 near V = 0 for an either n- or p-nanotube; the Schottky mechanism in (2) would result in I does not equal 0 only with V < 0 for an n-nanotube, and the bias polarities would be reversed for a p-nanotube. The two observed I-V patterns are thus entirely explained by a tip-nanotube contact of the two types, where the nanotube must be n-type.

Yamada, Toshishige; Kwak, Dochan (Technical Monitor)

2000-01-01

339

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.

340

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

International Nuclear Information System (INIS)

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

 
 
 
 
341

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

342

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

343

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

Energy Technology Data Exchange (ETDEWEB)

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 eld 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 ngerprint 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 [University of Virginia, Charlottesville; Chan, Jack [University of Virginia, Charlottesville; Williams, Keith A [University of Virginia, Charlottesville; Ge, Jiechao [Virginia Polytechnic Institute and State University (Virginia Tech); Shu, Chunying [Virginia Polytechnic Institute and State University (Virginia Tech); Fu, Wujun [Virginia Polytechnic Institute and State University (Virginia Tech); Dorn, Harry C [Virginia Polytechnic Institute and State University (Virginia Tech); Kushmerick, James G [National Institute of Standards and Technology (NIST), Gaithersburg, MD; Puretzky, Alexander A [ORNL; Geohegan, David B [ORNL

2010-01-01

344

Electron tunnelling into superconducting filaments: depth profiling the energy gap of NbTi filaments from magnet wires  

International Nuclear Information System (INIS)

Squeezable electron tunneling (SET) junctions consisting of superconducting NbTi filaments (extracted from magnet wires) and sputtered Nb thinfilm counter electrodes were used to determine the energy gap at the surface of the filaments. The current versus voltage curves of junctions immersed in liquid helium at 4 K were measured for a series of filaments taken from the same wire. Each filament had been etched to remove a surface layer of varying thickness so that the energy gap could be determined as a function of depth into the surface of an ''average'' filament. It was found that some manufacturing processes yield filaments having surface layers with reduced energy gaps of 0.4 meV compared to measured interior bulk values ranging from 1.2 to 1.3 meV

345

Cost-benefit analysis of electronic information resources: an evaluation on Middle East Technical University Library.  

Digital Repository Infrastructure Vision for European Research (DRIVER)

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

Bati, Hacer

2006-01-01

346

Pendant unit effect on electron tunneling in U-shaped molecules  

International Nuclear Information System (INIS)

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

347

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.

348

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

International Nuclear Information System (INIS)

Ultrasonic attenuation and velocity measurements on irradiated Al-Zn alloys (0.01, 0.1, and 0.5 at %) indicate a tunneling relaxation of the predominant mixed dumbbell defect at low temperatures, and mixed dumbbell migration at the Stage II anneal temperature. The effect of an internal strain varying with the zinc concentration on the measured decrement and modulus change is striking. Evaluated in the framework of a six-level system, this reveals the simultaneous action of resonance and nonclassical relaxation processes. Using Fe as a probe atom, it is shown that mixed dumbbell dissociation is in an insignificant component of the annealing of this defect. The decrease of the annealing temperature at higher zinc concentrations provides evidence that the mixed dumbbell migrates as a unit during annealing. The energies associated with dumbbell migration and interstitial escape are derived. Further evidence for the migration mechanism is obtained from successive irradiation and annealing

349

Molecular fluorescence from H2TBP porphyrin film on Ag substrate excited by tunneling electrons  

International Nuclear Information System (INIS)

Molecular fluorescence from H2TBP porphyrin (H2TBPP) films on Ag substrate is excited by a scanning tunneling microscope (STM) at ambient conditions. The molecular films are prepared by spin-casting method. The thickness of films can be controlled by the times of dropping H2TBPP solution. Molecular fluorescence of as-above prepared H2TBPP films with 4-14 nm thickness at both polarities of applied bias voltage are well defined in good matching with its photoluminescence spectrum, which suggests the same decay channel associated with the HOMO-LUMO radiative transitions similar to H2TBPP/Au. The thickness dependence of light emission intensity of molecular fluorescence has been studied. The results show that for thicker film, molecular fluoresceence tends to be much stronger due to the effective decoupling of the emitter from the metal substrate

350

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 the base surface accumulation layer, and (2) interface trap assisted tunneling in the gate/drain overlap region. The second theory gives better correlation, which is further supported by the DCIV peaks originated from interface traps in the gate/drain overlap region.

Cai, Jin

2000-10-01

351

Combined Scanning Electron and Multi-tip Scanning Tunneling Microscopy as a Method for Charge Transport Measurements at the Nanometer Range  

Digital Repository Infrastructure Vision for European Research (DRIVER)

In dieser Arbeit werden Ladungstransportmessungen im Nanometerbereich unter Ultrahochvakuum-Bedingungen präsentiert. Für diese Messungen ist eine Kombinationsapparatur aus Rasterelektronenmikroskop (engl. Scanning Electron Microscope, SEM) und Rastertunnelmikroskop (engl. Scanning Tunneling Microscope, STM) benutzt worden. Um neben vertikalen auch laterale Transportmessungen durchführen zu können, ist ein 2-Spitzen-STM entwickelt worden, welches in dieser Arbeit vorgestellt wird. Das Desi...

Jaschinsky, Philipp

2007-01-01

352

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

International Nuclear Information System (INIS)

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

353

A single-electron tunneling reset-set flip-flop  

Energy Technology Data Exchange (ETDEWEB)

In this paper, a new Reset-Set flip-flop fully implemented with single-electron devices is proposed. Its topology derived from NAND gates and was validated at room temperature by simulation. Furthermore, a comparison between the proposed single-electron device and MOS devices in terms of power consumption and occupied area is presented.

Alencar, Bianca M. S. M. de; Guimarães, Janaina G. [Department of Electrical Engineering, University of Brasilia, Campus Universitário Darcy Ribeiro, Asa Norte, P.O. Box 4386, Brasilia-DF, 70919-970 (Brazil)

2014-05-15

354

Resources  

Science.gov (United States)

... resources Child abuse - resources Chronic fatigue syndrome - resources Chronic pain - resources Cleft palate - resources Colon cancer - resources Cystic fibrosis - resources Depression - resources Diabetes - resources Digestive disease - resources Drug abuse - ...

355

Systematic modulation of quantum (electron) tunneling behavior by atomic layer deposition on nanoparticulate SnO2 and TiO2 photoanodes.  

Science.gov (United States)

Ultrathin films of TiO2, ZrO2, and Al2O3 were conformally created on SnO2 and TiO2 photoelectrodes via atomic layer deposition (ALD) to examine their influence upon electron transfer (ET) from the electrodes to a representative molecular receptor, I3(-). Films thicker than 2 Å engender an exponential decrease in ET time with increasing film thickness, consistent with tunneling theory. Increasing the height of the barrier, as measured by the energy difference between the transferring electron and the bottom of the conduction band of the barrier material, results in steeper exponential drops in tunneling rate or probability. The variations are quantitatively consistent with a simple model of quantum tunneling of electrons through square barriers (i.e., barriers of individually uniform energy height) that are characterized by individually uniform physical thickness. The findings demonstrate that ALD is a remarkably uniform and precise method for modifying electrode surfaces and imply that standard tunneling theory can be used as a quantitative guide to intentionally and predictively modulating rates of ET between molecules and electrodes. PMID:24148005

Prasittichai, Chaiya; Avila, Jason R; Farha, Omar K; Hupp, Joseph T

2013-11-01

356

Electronic Safety Resource Tools – Supporting Hydrogen and Fuel Cell Commercialization  

Energy Technology Data Exchange (ETDEWEB)

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

Barilo, Nick F.

2014-09-29

357

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

International Nuclear Information System (INIS)

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

358

Electronic transport through EuO spin-filter tunnel junctions  

Epitaxial spin-filter tunnel junctions based on the ferromagnetic semiconductor europium monoxide (EuO) are investigated by means of density functional theory. In particular, we focus on the spin transport properties of Cu(100)/EuO(100)/Cu(100) junctions. The dependence of the transmission coefficient and the current-voltage curves on the interface spacing and EuO thickness is explained in terms of the EuO density of states and the complex band structure. Furthermore, we also discuss the relation between the spin transport properties and the Cu-EuO interface geometry. The level alignment of the junction is sensitively affected by the interface spacing, since this determines the charge transfer between EuO and the Cu electrodes. Our calculations indicate that EuO epitaxially grown on Cu can act as a perfect spin filter, with a spin polarization of the current close to 100%, and with both the Eu-5d conduction-band and the Eu-4f valence-band states contributing to the coherent transport. For epitaxial EuO on Cu, a symmetry filtering is observed, with the ?1 states dominating the transmission. This leads to a transport gap larger than the fundamental EuO band gap. Importantly, the high spin polarization of the current is preserved up to large bias voltages.

Jutong, Nuttachai

2012-11-12

359

Electronic transport through EuO spin-filter tunnel junctions  

Science.gov (United States)

Epitaxial spin-filter tunnel junctions based on the ferromagnetic semiconductor europium monoxide (EuO) are investigated by means of density functional theory. In particular, we focus on the spin transport properties of Cu(100)/EuO(100)/Cu(100) junctions. The dependence of the transmission coefficient and the current-voltage curves on the interface spacing and EuO thickness is explained in terms of the EuO density of states and the complex band structure. Furthermore, we also discuss the relation between the spin transport properties and the Cu-EuO interface geometry. The level alignment of the junction is sensitively affected by the interface spacing, since this determines the charge transfer between EuO and the Cu electrodes. Our calculations indicate that EuO epitaxially grown on Cu can act as a perfect spin filter, with a spin polarization of the current close to 100%, and with both the Eu-5d conduction-band and the Eu-4f valence-band states contributing to the coherent transport. For epitaxial EuO on Cu, a symmetry filtering is observed, with the ?1 states dominating the transmission. This leads to a transport gap larger than the fundamental EuO band gap. Importantly, the high spin polarization of the current is preserved up to large bias voltages.

Jutong, Nuttachai; Rungger, Ivan; Schuster, Cosima; Eckern, Ulrich; Sanvito, Stefano; Schwingenschlögl, Udo

2012-11-01

360

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

Scientific Electronic Library Online (English)

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

C. Moysés, Araújo; A. Ferreira da, Silva; E. A. de Andrada e, Silva.

2002-06-01

 
 
 
 
361

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

Scientific Electronic Library Online (English)

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

C. Moysés, Araújo; A. Ferreira da, Silva; E. A. de Andrada e, Silva.

362

Spin-dependent electron grating effect from helical magnetization in multiferroic tunnel junctions  

Digital Repository Infrastructure Vision for European Research (DRIVER)

In multiferroic oxides with a transverse helical magnetic order, the magnetization exchange coupling is sinusoidally space-dependent. We theoretically investigate the spin-dependent electron grating effect in normal-metal/helical-multiferroic/ferromagnettic heterojunctions. The spin wave vector of the spiral can be added or subtracted from the electron spacial wave vector inducing spin-conserved and spin-flipped diffracted transmission and reflection. The predicted grating e...

Zhu, Rui

2012-01-01

363

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

Science.gov (United States)

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

Pan, Denise

2009-01-01

364

Planar electron-tunneling Si/Si0.7Ge0.3 triple-barrier resonant tunneling diode formed on undoped strain-relaxed buffer with flat surface  

Science.gov (United States)

We demonstrated a planar electron-tunneling Si/Si0.7Ge0.3 triple-barrier (TB) resonant tunneling diode (RTD) formed via a channel layer on an undoped strain-relaxed quadruple-Si1-xGex-layer (QL) buffer. Compared with a conventional vertical Si/Si0.7Ge0.3 TB RTD formed on a heavily doped QL buffer, the dislocation density is low, the surface is flat, and the resonance current density is much larger. These observations, together with analyses of current-voltage (I-V) curve fitting to the physics-based analytical expression, suggest that the enhanced I-V characteristics in the planar RTD are related to decreases in the number of crystalline defect states and the structural and potential fluctuations.

Okubo, Takafumi; Tsukamoto, Takahiro; Suda, Yoshiyuki

2014-03-01

365

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

366

Checklist Manifesto for Electronic Resources: Getting Ready for the Fiscal Year and Beyond  

Science.gov (United States)

Organization of electronic resources workflow is critical in the increasingly complicated and complex world of library management. A simple organizational tool that can be readily applied to electronic resources management (ERM) is the use of checklists. Based on the principles discussed in The Checklist Manifesto: How to Get Things Right, the…

England, Lenore; Fu, Li; Miller, Stephen

2011-01-01

367

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

Science.gov (United States)

Single gold particles may serve as room temperature single electron memory units because of their size dependent electronic level spacing. Here, we present a proof-of-concept study by electrochemically controlled scanning probe experiments performed on tailor-made Au particles of narrow dispersity. In particular, the charge transport characteristics through chemically synthesized hexane-1-thiol and 4-pyridylbenzene-1-thiol mixed monolayer protected Au144 clusters (MPCs) by differential pulse voltammetry (DPV) and electrochemical scanning tunneling spectroscopy (EC-STS) are reported. The pyridyl groups exposed by the Au-MPCs enable their immobilization on Pt(111) substrates. By varying the humidity during their deposition, samples coated by stacks of compact monolayers of Au-MPCs or decorated with individual, laterally separated Au-MPCs are obtained. DPV experiments with stacked monolayers of Au144-MPCs and EC-STS experiments with laterally separated individual Au144-MPCs are performed both in aqueous and ionic liquid electrolytes. Lower capacitance values were observed for individual clusters compared to ensemble clusters. This trend remains the same irrespective of the composition of the electrolyte surrounding the Au144-MPC. However, the resolution of the energy level spacing of the single clusters is strongly affected by the proximity of neighboring particles. PMID:25372883

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

2014-12-21

368

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

369

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

370

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

371

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

DEFF Research Database (Denmark)

A biomimetic long-range electron transfer (ET) system consisting of the blue copper protein azurin, a tunneling barrier bridge, and a gold single-crystal electrode was designed on the basis of molecular wiring self-assembly principles. This system is sufficiently stable and sensitive in a quasi-biological environment, suitable for detailed observations of long-range protein interfacial ET at the nanoscale and single-molecule levels. Because azurin is located at clearly identifiable fixed sites in well controlled orientation, the ET configuration parallels biological ET. The ET is nonadiabatic, and the rate constants display tunneling features with distance-decay factors of 0.83 and 0.91 angstrom(-1) in H2O and D2O, respectively. Redox-gated tunneling resonance is observed in situ at the single-molecule level by using electrochemical scanning tunneling microscopy, exhibiting an asymmetric dependence on the redox potential. Maximum resonance appears around the equilibrium redox potential of azurin with an on/off current ratio of approximate to 9. Simulation analyses, based on a two-step interfacial ET model for the scanning tunneling microscopy redox process, were performed and provide quantitative information for rational understanding of the ET mechanism

Chi, Qijin; Ulstrup, Jens

2005-01-01

372

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

DEFF Research Database (Denmark)

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

Chi, Qijin; Farver, Ole

2005-01-01

373

????????????????????--?????????????? | 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

374

Observation of a two-dimensional electron gas at the surface of annealed SrTiO3 single crystals by scanning tunneling spectroscopy  

Science.gov (United States)

An extensive surface characterization of hydrofluoric acid (HF) etched and annealed SrTiO3 single crystals, vacuum-annealed below 300 ?C, reveals the formation of a two-dimensional electron gas (2DEG). A joint scanning tunneling spectroscopy and low-energy electron diffraction analysis allows us to associate the surface metallic state (characterized by the presence of a nonzero density of states close to the Fermi level) with the low-temperature-annealed highly ordered 1×1 reconstructed SrTiO3 surface hosting two-dimensional carriers. Meanwhile, a gap opens in the tunneling spectrum of 2×1 reconstructed, high-temperature-annealed surfaces. X-ray photoemission spectroscopy shows that the metallic state is associated with the surface formation of Ti3+. Recently published photoemission data demonstrated the formation of a 2DEG on the surface of cleaved SrTiO3, while scanning tunneling spectroscopy on crystals heated at high temperature revealed gaplike features: Our results can help reconcile this seemingly contradicting phenomenology observed so far by scanning tunneling spectroscopy and photoemission spectroscopy.

Di Capua, R.; Radovic, M.; De Luca, G. M.; Maggio-Aprile, I.; Miletto Granozio, F.; Plumb, N. C.; Ristic, Z.; Scotti di Uccio, U.; Vaglio, R.; Salluzzo, M.

2012-10-01

375

Nonequilibrium DC and photon-assisted interlayer tunneling in a bi-layer tunneling structure  

Science.gov (United States)

We study nonequilibrium DC and photon-assisted tunneling (PAT) of electrons between two weakly tunnel-coupled biased electron layers. The PAT current is related to the DC current. The line shape of the PAT current is studied as a function of the bias energy and the temperature. The contributions from the intrinsic screened electron-phonon and electron-electron scattering to the widths of the tunneling spectra are examined. Calculated DC tunneling current is compared with recent data.

Lyo, S. K.; Simmons, J. A.

2002-03-01

376

Magneto-tunnelling spectroscopy for spatial mapping of orbital wavefunctions of the ground and excited electronic states in self-assembled quantum dots  

Energy Technology Data Exchange (ETDEWEB)

We present an experimental study of electron wavefunctions in InAs/GaAs self-assembled quantum dots (QDs). Magneto-tunnelling spectroscopy is employed as a non-invasive probe to produce two-dimensional images of the probability density of an electron confined in a quantum dot. The images reveal clearly the elliptical symmetry of the ground state and the characteristic lobes of the higher energy states of the dots. We use the technique to compare the symmetry properties of the electron wavefunctions in QDs grown on (100)- and (311)B-oriented GaAs substrates. (orig.)

Levin, A.; Vdovin, E.E.; Patane, A.; Eaves, L.; Main, P.C.; Dubrovskii, Yu.V.; Henini, M. [Nnottingham Univ. (United Kingdom). School of Physics and Astronomy; Khanin, Yu.N. [Rossijskaya Akademiya Nauk, Chernogolovka (Russian Federation). Inst. of Microelectronics Technology; Hill, G. [Sheffield Univ. (United Kingdom). Dept. of Electronic and Electrical Engineering

2001-04-01

377

Tunneling of Dirac electrons through one-dimensional potentials in graphene: a T-matrix approach.  

Science.gov (United States)

The standard T-matrix method can be effectively used for studying the dynamics of Dirac electrons under one-dimensional potentials in graphene. The transmission probability expressed in terms of T-matrices and the corresponding ballistic current are derived for any smooth one-dimensional potential, taking into account the chirality of Dirac massless carriers. Numerical calculations are illustrated for the potential approximately describing graphene n-p junctions. PMID:21715801

Chau Nguyen, H; Lien Nguyen, V

2009-01-28

378

Spin-polarized tunneling as a probe of the electronic properties of Ga1-xMnxAs heterostructures  

Science.gov (United States)

We present magnetic and tunnel transport properties of (Ga,Mn)As/(In,Ga)As/(Ga,Mn)As structure before and after adequate annealing procedure. The conjugate increase of magnetization and tunnel magnetoresistance obtained after annealing is shown to be associated with the increase of both exchange energy ?exch and hole concentration by reduction of the Mn interstitial atom in the top magnetic electrode. Through a 6×6 band k•p model, we established general phase diagrams of tunneling magnetoresistance (TMR) and tunneling anisotropic magnetoresistance (TAMR) vs (Ga,Mn)As Fermi energy (EF) and spin-splitting parameter (BG) . This allows us to give a rough estimation of the exchange energy ?exch=6BG?-120meV and hole concentration of the order of p=1×1020cm-3 for (Ga,Mn)As and beyond gives the general trend of TMR and TAMR vs the selected hole band involved in the tunneling transport.

Elsen, M.; Jaffrès, H.; Mattana, R.; Thevenard, L.; Lemaitre, A.; George, J.-M.

2007-10-01

379

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

International Nuclear Information System (INIS)

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

380

Tarsal Tunnel Syndrome  

Science.gov (United States)

... Tarsal Tunnel Syndrome Text Size Print Bookmark Tarsal Tunnel Syndrome What Is the Tarsal Tunnel? The tarsal tunnel is a narrow space that ... focus of tarsal tunnel syndrome. What Is Tarsal Tunnel Syndrome? Tarsal tunnel syndrome is a compression, or ...

 
 
 
 
381

Nanoscale probing of electronic band gap and topography of VO2 thin film surfaces by scanning tunneling microscopy  

Science.gov (United States)

The metal-insulator transition (MIT) in vanadium dioxide in the vicinity of room temperature makes it one of the most interesting materials for novel switching device applications. It is therefore essential to have a fundamental understanding of the VO2 surface when it is incorporated into multilayer structures or nanodevices. This study focuses on the surface modification of VO2 in response to the thermal treatment during phase transition. Vacuum annealing at temperatures in the vicinity of the MIT triggers a partial reduction in the surface, and thus initiates a chemical phase transition. Scanning tunneling microscopy and spectroscopy are used to investigate the electronic properties and surface structure of the VO2 thin film on (0001) sapphire substrates. Band gap maps with a high spatial resolution and single point spectroscopy I-V curves are measured as the sample is cycled through the MIT, and thus provide a direct observation of the surface phase transition at the nanoscale. The VO2 surface exhibits a homogeneous insulating behavior with a typical band gap of ˜0.5 eV at room temperature, and the surface becomes more metallic and spatially inhomogeneous in conductivity during MIT, and wide range of surface oxides can be identified. The surface still remains partially metallic after cooling down from a long period anneal, and such irreversible surface electrical change is attributed to the loss of oxygen. The location of metallic islands after thermal cycling is strongly coupled to the topography of the film, and relaxation processes and continued modification of the spatial distribution of the metallic regions are recognized on a longer timescale. The impact of film morphology, strain, surface chemistry, and structural phase transition on the electronic characteristics of VO2 surfaces are discussed.

Yin, W.; Wolf, S.; Ko, C.; Ramanathan, S.; Reinke, P.

2011-01-01

382

Electronic energy levels, wavefunctions and potential landscape of nanostructures probed by magneto-tunnelling spectroscopy  

International Nuclear Information System (INIS)

We create electrostatically induced quantum dots by thermal diffusion of interstitial Mn out of a p-type (GaMn)As layer into the vicinity of a GaAs quantum well. This leads to the formation of deep, approximately circular and strongly confined dot-like potential minima in a large mesa diode structure. The minima are formed without need for advanced lithography or electrostatic gating. Using fields of up to 30 T, magnetotunnelling spectroscopy of an individual dot reveals the symmetry of the electronic eigenfunctions and, for the approximately circular dots, a rich spectrum of Fock-Darwin-like states with an orbital angular momentum component |lz| ranging from 0 up to 11. We find that a small fraction of the dots has elongated potential minima, giving rise to quenching of the orbital angular momentum of the electronic eigenstates. By developing a model to describe the diffusion of the Mn interstitial ions, we determine the electrostatic potential landscape in the quantum well and hence the distribution of dot shapes and sizes. This is in a good agreement with our experimental data.

383

Dynamics of Tunneling Centers in Metallic Systems  

Digital Repository Infrastructure Vision for European Research (DRIVER)

Dynamics of tunneling centers (TC) in metallic systems is studied, using the technique of bosonization. The interaction of the TC with the conduction electrons of the metal involves two processes, namely, the screening of the TC by electrons, and the so-called electron assisted tunneling. The presence of the latter process leads to a different form of the renormalized tunneling frequency of the TC, and the tunneling motion is damped with a temperature dependent relaxation ra...

Qureshi, Tabish

1994-01-01

384

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

Science.gov (United States)

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

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

2012-10-01

385

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

CERN Document Server

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

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

2013-01-01

386

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

CERN Multimedia

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

CERN Photo Service

2008-01-01

387

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

Directory of Open Access Journals (Sweden)

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

BASHORUN

2011-11-01

388

Evaluating Electronic Resources: Personal Development Planning Resources at the Open University, a Case Study  

Science.gov (United States)

This paper discusses the evaluation of Web-based tools to support Personal Development Planning (PDP) in order to illustrate issues associated with the introduction and assessment of the effectiveness of online resources. The aims of the evaluation were based on concerns about the very complex situation that offering online resources including PDP…

Jelfs, Anne; Kelly, Patrick

2007-01-01

389

Improving Electronic Resources Management (ERM): Critical Work Flow and Operations Solutions  

Digital Repository Infrastructure Vision for European Research (DRIVER)

Organization of electronic resources work flow and operations are critical in the increasingly complex world of library management. The way in which this management process is structured differs according to the type of library and organizational structure within. A common goal, though, is strategically sustaining access and availability to electronic resources over time and the effective management of the library staff that maintains them. In this joint session, librarians from George Mason ...

Appleton, Betsy; Regan, Shannon; England, Lenore; Fu, Li

2012-01-01

390

Combined scanning force microscopy and scanning tunneling spectroscopy of an electronic nano-circuit at very low temperature  

Digital Repository Infrastructure Vision for European Research (DRIVER)

We demonstrate the combination of scanning force microscopy and scanning tunneling spectroscopy in a local probe microscope operating at very low temperature (60 mK). This local probe uses a quartz tuning fork ensuring high tunnel junction stability. We performed the spatially-resolved spectroscopic study of a superconducting nano-circuit patterned on an insulating substrate. Significant deviations from the BCS prediction are observed.

Senzier, Julien; Luo, Pengshun S.; Courtois, Herv

2006-01-01

391

Tunnel Through!  

Science.gov (United States)

Students apply their knowledge about mountains and rocks to transportation engineering, with the task of developing a model mountain tunnel that simulates the principles behind real-life engineering design. Student teams design and create model tunnels through a clay mountain, working within design constraints and testing for success; the tunnels must meet specific design requirements and withstand a certain load.

Integrated Teaching And Learning Program

392

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

Directory of Open Access Journals (Sweden)

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

Huang-Yu Liu

2008-03-01

393

ODLIS : Online Dictionary for Library and Information Science [electronic resource].  

International Nuclear Information System (INIS)

A hypertext reference resource for library and information science professionals, university students and faculty, and users of all types of libraries. Includes not only the terminology of the various specializations within library science and information studies but also the vocabulary of publishing, printing, binding, the book trade, graphic arts, book history, literature, bibliography, telecommunications, and computer science.

394

Tunneling Processes in Optically Excited Quantum Dots  

International Nuclear Information System (INIS)

The single-electron tunneling processes in optically excited coupled quantum dots can be divided into two parts: the electron and the hole parts, which are analytically obtained in the framework of the Keldysh formalism. The tunneling process is selective tunneling, which results in dark tunneling states. The tunneling currents are co-determined by the resonance energies and probability distributions of the particular quantum channels defined by the electron-hole complex resonant states. (condensed matter: electronic structure, electrical, magnetic, and optical properties)

395

Bi-Sr-Ca-Cu-O thin-film energy gap as a function of temperature and force applied to squeezable-electron-tunneling junctions  

International Nuclear Information System (INIS)

Tunneling-spectroscopy measurements have been performed on Bi-Sr-Ca-Cu-O squeezable-electron-tunneling (SET) junctions. Two distinct features have been seen in the current-voltage [I(V)] and conductance-voltage [G(V)] characteristics. One of these features has the appearance of an energy-gap signature, while the other may be due to switching to the voltage state of a grain-boundary junction that is in series with the SET junction. The latter feature can mimic the energy-gap signature in I(V) and G(V) characteristics. These two features respond very differently to changes in temperature and the force applied to the SET junctions

396

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

Science.gov (United States)

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

Barbier, Patricia

2007-01-01

397

Utilization of bio-resources by low energy electron beam  

International Nuclear Information System (INIS)

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

398

Resonance tunneling spectroscopy of heteropoly compounds  

Science.gov (United States)

The electron tunneling spectra of phosphomolybdic and phosphomolybdovanadic acids have been measured using a scanning tunneling microscope. A new mechanism of negative differential resistance (NDR) formation in tunneling nanocontacts is established, which is general for all systems featuring the Wannier-Stark localization effect. A two-center inelastic resonance tunneling model is constructed, which allows the values of both electron and vibrational energy parameters to be determined from the measured spectra.

Dalidchik, F. I.; Budanov, B. A.; Kolchenko, N. N.; Balashov, E. M.; Kovalevskii, S. A.

2012-12-01

399

Tunneling in Fractional Quantum Hall line junctions  

Digital Repository Infrastructure Vision for European Research (DRIVER)

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

Aranzana, Manuel; Regnault, Nicolas; Jolicoeur, Thierry

2005-01-01

400

The role of the university library for an efficient use of the electronic resources  

Directory of Open Access Journals (Sweden)

Full Text Available By means of the topic approached in the present paper we would like to highlight the crucial role of the university library for a better access to the electronic resources, from the perspective of the new information and communication technologies. In this context, we shall try to identify the factors leading to the need to use electronic resources, we shall analyze the role played by the university library in increasing the efficiency of the access to this type of resources (implicitly, instructing the users, we shall suggest ways of collaboration between academics and librarians etc. From a managerial perspective, we shall analyze a few important aspects that one needs to consider when making the decision of buying or not an electronic resource: selection, type of acquisition, legality, monitoring the usefulness etc.

Agnes Erich

2013-01-01

 
 
 
 
401

Electron beam pasteurised oil palm waste: a potential feed resource  

International Nuclear Information System (INIS)

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

402

Electronic information resource use: implications for teaching and library staff  

Directory of Open Access Journals (Sweden)

Full Text Available Within institutions of higher education, teaching staff and library-based information specialists have tended to occupy separate worlds. Although there has been some contact, in the main this has been partial and intermittent. For first-year students, one consequence of this state of affairs has been the absence of a systematic and co-ordinated strategy for enabling them to acquire, practise and develop information-gathering skills. Teaching staff have seen their role in this respect mainly in terms of issuing students with reading lists containing a mix of books and journal articles, and underlying this approach is the expectation that information specialists will be on hand to provide whatever additional help is needed to access these resources, for example through the provision of introductory talks and one-to-one support sessions. Relatively few teaching staff have incorporated library exercises into their teaching and assessment, or adopted a more creative approach to information gathering by students, such as helping them use bibliographic and other aids to prepare personalized reading lists. Consequently, when students have been required to do this at later stages of their studies, especially in the context of preparing a dissertation, they have not been adequately prepared, and often find it extremely difficult to access and evaluate information resources effectively.

Roger Ottewill

1997-12-01

403

We're All in This Together: Library Faculty and Staff and Their Reporting of Electronic Resource Problems  

Science.gov (United States)

Libraries continue to shift budgets toward obtaining more electronic resources. Electronic resources can develop problems at any time when a library offers access. Staff collaboration is vital in ensuring availability to those resources. Partnering with areas in the library that work most closely with patrons can help share the load of the…

Foster, Anita; Williams, Sarah C.

2010-01-01

404

Influence of inter cell resonant tunneling on the out-of-plane electronic transport behavior in layered high {T}c cuprates  

Science.gov (United States)

The influence of inter unit cell resonant tunneling between the copper-oxygen planes on the c-axis electronic conductivity (?c) in normal state of optimal doped bilayer high Tc cuprates like Bi2Sr2CaCu2O8+x is investigated using extended Hubbard Hamiltonian including resonant tunneling term (T12) between the planes in two adjoining cells. The expression for the out-of-plane (c-axis) conductivity is calculated within Kubo formalism and single particle Green's function by employing Green's function equations of motion technique within meanfield approximation. On the basis of numerical computation, it is pointed out that the renormalized c-axis conductivity (tilde {?}c) increases exponentially with the increment in inter cell resonant tunneling. The effect of T12 on renormalized c-axis conductivity is found to be prominent at low temperatures as compared to temperatures above room temperature ( 300 °K). The Coulomb correlation suppresses the variation of renormalized c-axis conductivity with temperature, while renormalized c-axis conductivity increases on increasing carrier concentration. These theoretical results are viewed in terms of existing c-axis transport measurements.

Tewari, B. S.; Dhyani, A.; Ajay, .

2008-11-01

405

Simulation of stress-induced leakage current in silicon dioxides: A modified trap-assisted tunneling model considering Gaussian-distributed traps and electron energy loss  

International Nuclear Information System (INIS)

In this article, a modified generalized trap-assisted tunneling model (GTAT) is proposed to explain the excessive currents occurring at low electric fields during stressing (stress-induced leakage current, SILC). Parameters such as trap energy level, Gaussian-distributed traps, and energy loss (when electrons tunnel through an oxide) are all included in this model. The trap energy levels relative to the effective Fowler - Nordheim tunneling barriers (?B) are classified into either shallow traps or deep traps. Quantitative analyses of the effects of oxide thickness, trap energy levels, trap concentrations, and energy losses on SILC are performed. Examples relating to the SILC of thermal oxides are shown to validate the suitability of our GTAT model. Good agreement between experimental data and the simulated current - voltage curves using this model is obtained for various SILC phenomena. The extracted trap energy levels exist between 1.5 and 2.0 eV for shallow traps and at 3.2 eV for deep traps, while trap concentrations are in the range of 1018 - 1020cm-3 depending on various stress conditions. The energy level of induced traps and trap concentration can be easily derived from this model without the need for other complicated measurements. This model is demonstrated to be an accurate and reliable SILC model for investigating ultrathin gate oxide devices in integrated circuits of future generations. [copyright] 2001 American Institute of Physics

406

Simulation of stress-induced leakage current in silicon dioxides: A modified trap-assisted tunneling model considering Gaussian-distributed traps and electron energy loss  

Science.gov (United States)

In this article, a modified generalized trap-assisted tunneling model (GTAT) is proposed to explain the excessive currents occurring at low electric fields during stressing (stress-induced leakage current, SILC). Parameters such as trap energy level, Gaussian-distributed traps, and energy loss (when electrons tunnel through an oxide) are all included in this model. The trap energy levels relative to the effective Fowler-Nordheim tunneling barriers (?B) are classified into either shallow traps or deep traps. Quantitative analyses of the effects of oxide thickness, trap energy levels, trap concentrations, and energy losses on SILC are performed. Examples relating to the SILC of thermal oxides are shown to validate the suitability of our GTAT model. Good agreement between experimental data and the simulated current-voltage curves using this model is obtained for various SILC phenomena. The extracted trap energy levels exist between 1.5 and 2.0 eV for shallow traps and at 3.2 eV for deep traps, while trap concentrations are in the range of 1018-1020 cm-3 depending on various stress conditions. The energy level of induced traps and trap concentration can be easily derived from this model without the need for other complicated measurements. This model is demonstrated to be an accurate and reliable SILC model for investigating ultrathin gate oxide devices in integrated circuits of future generations.

Chang, Wai Jyh; Houng, Mau Phon; Wang, Yeong Her

2001-06-01

407

Simulation of stress-induced leakage current in silicon dioxides: A modified trap-assisted tunneling model considering Gaussian-distributed traps and electron energy loss  

Energy Technology Data Exchange (ETDEWEB)

In this article, a modified generalized trap-assisted tunneling model (GTAT) is proposed to explain the excessive currents occurring at low electric fields during stressing (stress-induced leakage current, SILC). Parameters such as trap energy level, Gaussian-distributed traps, and energy loss (when electrons tunnel through an oxide) are all included in this model. The trap energy levels relative to the effective Fowler{endash}Nordheim tunneling barriers ({Phi}{sub B}) are classified into either shallow traps or deep traps. Quantitative analyses of the effects of oxide thickness, trap energy levels, trap concentrations, and energy losses on SILC are performed. Examples relating to the SILC of thermal oxides are shown to validate the suitability of our GTAT model. Good agreement between experimental data and the simulated current{endash}voltage curves using this model is obtained for various SILC phenomena. The extracted trap energy levels exist between 1.5 and 2.0 eV for shallow traps and at 3.2 eV for deep traps, while trap concentrations are in the range of 10{sup 18}{endash}10{sup 20}cm{sup {minus}3} depending on various stress conditions. The energy level of induced traps and trap concentration can be easily derived from this model without the need for other complicated measurements. This model is demonstrated to be an accurate and reliable SILC model for investigating ultrathin gate oxide devices in integrated circuits of future generations. {copyright} 2001 American Institute of Physics.

Chang, Wai Jyh; Houng, Mau Phon; Wang, Yeong Her

2001-06-01

408

MULER: Building an Electronic Resource Management (ERM Solution at York University  

Directory of Open Access Journals (Sweden)

Full Text Available Many university libraries now utilize an Electronic Resource Management (ERM system to assist with operations related to electronic resources. An ERM is a relational database containing information such as suppliers, costs, holdings, and renewal dates for electronic resources, both at the database and title levels. While commercial ERM products are widely available, some institutions are custom building their own ERM in- house. This article describes how York University in Toronto, Canada, did just that by building a system called Managing University Library Electronic Resources (MULER. The article details the background and history of how electronic resources were managed pre-MULER; why a new ERM was needed; the planning process; the current and innovative functions of MULER, including integration of MULER data into York University Libraries search and discovery layer, Vufind; subject tagging in MULER; new functions to be added; and lessons learned from the project. Positive and negative implications of choosing an in-house project over paying for a commercial product are also discussed.

Aaron August Lupton

2012-01-01

409

Imaging of electronic defect states in SiO2 and HfSiOx films with sub-nanometer spatial resolution by two-way Single Electron Tunneling Force Mircroscopy  

Science.gov (United States)

Electronic defects in dielectric materials are currently in sharp focus, for nano-technology and quantum information processing. A novel technique has been developed for imaging these states with sub-nanometer spatial resolution. It can be applied to completely non-conducting dielectric films, in contrast to the STM. The method is based on force detected single electron tunneling events to and from the defect states [1-3]. The exponential dependence of the tunneling rate on tip-sample gap provides the same spatial resolution as STM. An oscillating AFM tip is scanned at constant height above the sample surface. A voltage waveform, synchronous with the tip motion is applied. When the tip is above an accessible state, individual electrons shuttle between tip and state with the applied voltage (300 Hz). The two-way tunneling causes a detectable change in tip resonance. Images of SiO2 and HfSiOx films show a repeatable, random array of individual ``point-like'' defect states, some with sub-nanometer width. Spectroscopic measurements of the defect energy are also performed by this approach. The new method and an analysis of the defects in SiO2 and HfSiOx will be presented. [1] E Bussman et al., Appl. Phys. Lett. 85, 2538 (2004) [2] E Bussman and CC Williams, Appl. Phys. Lett. 88, 263108 (2006) [3] E Bussman et al., Nano Lett. 6, 2577 (2006)

Johnson, J. P.; Zheng, N.; Williams, C. C.

2007-03-01

410

Electronic and structural effects of oxygen doping in Bi2Sr2CaCu2Ox superconductors characterized by tunneling microscopy  

International Nuclear Information System (INIS)

Scanning tunneling microscopy has been used to characterize the electronic and structural effects of oxygen doping in Bi2Sr2CaCu2Ox materials. Bias-voltage-dependent images of oxygen-deficient nonsuperconducting crystals show that reversible oxygen loss leads to nonperiodic variations in the electronic states near the Fermi level (±300 mV). Variations in the electronic states near the Fermi level are not observed, however, in images of superconducting samples. In addition, high-resolution images of the BiO layer of oxygen-deficient samples do not exhibit vacancies or strongly perturbed sites, but rather appear similar to images of the BiO layer of superconducting crystals. These data indicate that suppression of Tc in Bi2Sr2CaCu2Ox may not be due to oxygen loss from the BiO layer

411

Structure determination of the Si3N4/Si(111)- (8 x 8) surface: a combined study of Kikuchi electron holography, scanning tunneling microscopy, and ab initio calculations.  

Science.gov (United States)

A comprehensive atomic model for the reconstructed surface of Si3N4 thin layer grown on Si(111) is presented. Kikuchi electron holography images clearly show the existence of adatoms on the Si3N4(0001)/Si(111)-(8x8) surface. Compared with the ab initio calculations, more than 30 symmetry-inequivalent atomic pairs in the outmost layers are successfully identified. Scanning tunneling microscopy (STM) images show diamond-shaped unit cells and nine adatoms in each cell. High-resolution STM images reveal extra features and are in good agreement with the partial charge density distribution obtained from total-energy calculations. PMID:11290047

Ahn, H; Wu, C L; Gwo, S; Wei, C M; Chou, Y C

2001-03-26

412

Strategic pricing, resource allocation and infrastructure in electronic commerce  

Digital Repository Infrastructure Vision for European Research (DRIVER)

In this thesis we identify and obtain structural results for two different problems that are motivated by electronic commerce infrastructure and bundling of information goods. Strategic implications of implementing a priority pricing scheme in an ATM-like network owned by a single firm is the subject of the first study. Network structure consists of a single link modeled as an Mx/D/1 queue with non-preemptive head-of-the-line priority service. The network manager's motive is to maximize th...

Tomak, Kerem

1999-01-01

413

IEEE Nuclear and Plasma Sciences Society [electronic resource].  

International Nuclear Information System (INIS)

Features the Nuclear and Plasma Sciences Society, a professional group on nuclear science within the Institute of Electrical and Electronics Engineers, formed in 1949. The NPSS is composed of nine technical committees with a common interest in advancing nuclear and plasma sciences and engineering, including instrumentation, detection and measurement, particle accelerators, reactor systems, effects of radiation on materials and components, and applications. Its website provides information on the history of the society, lists its meetings and conferences, links to NPSS and IEEE publications and newsletters.

414

The course Electronic resources in libraries: Paris, 13–30 November 2006  

Directory of Open Access Journals (Sweden)

Full Text Available The course Electronic resources in libraries carried out by the Bibliothque nationale de France and Biblioth?que publique d’information within the scope of the programme Courants du monde in November 2006 is presented in the article. The course programme was composed in such a way as to enable the participants to become familiar with all the aspects of selection, digitization, use and preservation of electronic resources in libraries. It was conducted in the form of lectures, the most interesting of which are presented in the article, and visits connected with the lecture topics. The participants were systematically familiarized with electronic resources and were able to compare the circumstances prevailing at their home institutions among themselves.

Mojca Kotar

2007-01-01

415

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

Energy Technology Data Exchange (ETDEWEB)

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

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

2000-02-09

416

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

Directory of Open Access Journals (Sweden)

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

Aarnio Matti

2006-05-01

417

Electroresistance effects in ferroelectric tunnel barriers  

Digital Repository Infrastructure Vision for European Research (DRIVER)

Electron transport through fully depleted ferroelectric tunnel barriers sandwiched between two metal electrodes and its dependence on ferroelectric polarization direction are investigated. The model assumes a polarization direction dependent ferroelectric barrier. The transport mechanisms, including direct tunneling, Fowler-Nordheim tunneling and thermionic injection, are considered in the calculation of the electroresistance as a function of ferroelectric barrier properties...

Pantel, Daniel; Alexe, Marin

2010-01-01

418

Effect of the density of the electronic states at the valence orbital of the bridge redox molecule on the dependence of the tunnel current on the overvoltage in the case of fully adiabatic electron transition  

International Nuclear Information System (INIS)

Effect of the density of the electronic states at the valence orbital of the bridge redox molecule on the dependence of the tunnel current on the overvoltage and on the width at half maximum of the current-overvoltage curve is studied. A number of the approximate expressions for the density of states, the tunnel current and the width are obtained in the fully adiabatic limit for different particular cases. It is shown that at small values of the coupling of the electronic levels of the electrodes with the valence orbital of the redox molecule and the small values of the bias voltage two regions of the reorganization Gibbs energy exist with different dependence of the width on the reorganization Gibbs energy. The results of calculations of the density of states, the tunnel current and the width are presented and used for the interpretation of the experimental data [N.G. Tao, Phys. Rev. Lett. 76 (1996) 4066, I. Visoly-Fisher, K. Daie, Y. Terazono, C. Herrero, F. Fungo, L. Otero, E. Durantini, J.J. Silber, L. Sereno, D. Gust, T.A. Moore, A.L. Moore, S.M. Lindsay, PNAS 103 (2006) 8686

419

Direct Observation of Second Order Atom Tunnelling  

CERN Document Server

Tunnelling of material particles through a classically impenetrable barrier constitutes one of the hallmark effects of quantum physics. When interactions between the particles compete with their mobility through a tunnel junction, intriguing novel dynamical behaviour can arise where particles do not tunnel independently. In single-electron or Bloch transistors, for example, the tunnelling of an electron or Cooper pair can be enabled or suppressed by the presence of a second charge carrier due to Coulomb blockade. Here we report on the first direct and time-resolved observation of correlated tunnelling of two interacting atoms through a barrier in a double well potential. We show that for weak interactions between the atoms and dominating tunnel coupling, individual atoms can tunnel independently, similar to the case in a normal Josephson junction. With strong repulsive interactions present, two atoms located on one side of the barrier cannot separate, but are observed to tunnel together as a pair in a second ...

Foelling, S; Cheinet, P; Feld, M; Saers, R; Widera, A; Müller, T; Bloch, I

2008-01-01

420

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

Digital Repository Infrastructure Vision for European Research (DRIVER)

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

Rusbridge, Chris

2000-01-01

 
 
 
 
421

Carpal tunnel release  

Science.gov (United States)

Carpal tunnel release is surgery to treat carpal tunnel syndrome . Carpal tunnel syndrome is pain and weakness in the ... the test shows that the problem is carpal tunnel syndrome, carpal tunnel release surgery may be recommended. If the ...

422

Transmission electron microscopy of Co2(Cr1- x Fe x )Al sputtered films and their magnetic tunneling junctions  

International Nuclear Information System (INIS)

The microstructures of Co2FeAl and Co2(Cr0.4Fe0.6)Al sputtered films and of their magnetic tunnel junctions (MTJs) have been investigated to discuss the possible reasons for an unexpectedly low tunneling magnetoresistance (TMR). The structure of the Co2FeAl film changed from B2 to L21 with increasing substrate temperature, while that of the Co2(Cr0.4Fe0.6)Al film remained B2 up to 500 deg. C. The thermodynamically predicted phase separation was not observed in the films. The low TMR values obtained from the MTJs using the Co2FeAl and Co2(Cr0.4Fe0.6)Al films are attributed to the low-spin polarization expected from the low degree of order in these films. The TMR values depend sensitively on the interfacial structure of the tunnel junctions when the degree of order of the film is low