WorldWideScience
1

Single Electron Tunneling  

International Nuclear Information System (INIS)

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

2

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)

3

Chemically driven electron tunnelling pumps  

CERN Document Server

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

Goychuk, I

2006-01-01

4

Potential barrier for tunneling electrons in STM [scanning tunneling microscope  

International Nuclear Information System (INIS)

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

5

Electron tunneling across a tunable potential barrier  

International Nuclear Information System (INIS)

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

6

Electron tunneling across a tunable potential barrier  

Energy Technology Data Exchange (ETDEWEB)

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

Mangin, A; Anthore, A; Rocca, M L Della; Boulat, E; Lafarge, P [Universite Paris Diderot-Paris 7, Laboratoire Materiaux et Phenomenes Quantiques CNRS UMR 7162, 10 rue Alice Domon et Leonie Duquet, 75205 Paris (France)], E-mail: anne.anthore@univ-paris-diderot.fr

2009-02-01

7

Silicon Nanocrystal Charging by Hot electron Tunneling  

Science.gov (United States)

Electron charging of silicon nanocrystals is of interest in a myriad of applications of quantum dots. Past work has essentially focused on tunneling of cold electrons through a thin oxide barrier and has illustrated the importance of Coulomb blockade. In this work, we study the injection of hot electrons into and from silicon nanocrystals sandwiched in an oxide dielectric that sheds light into the thermalization processes in the nanocrystal. These hot carriers are generated by Fowler Nordheim (FN) injection or by application of a drain bias in a mosfet. While the former essentially yields carriers of a fixed energy entering the oxide conduction band, the latter approach yields carriers with a spectrum of energies all the way from cold to hot. It is observed that nanocrystals are not charged using hot electrons due to inefficient thermalization in the quantum dot. It is observed however, that warm electrons, those with energies smaller than the oxide barrier height, are very efficient in tunneling into quantum dots. These warm electrons direct tunnel through the oxide with a reduced barrier height and their thermalization in the nanocrystal is observed to be very efficient. Studies with varying nanocrystal sizes and density also show that hot carrier injection with FN tunneling becomes possible at high areal densities of nanocrystals possibly due to improved thermalization facilitated by nanocrystal-nanocrystal coupling. Electron injection of existing electrons out of silicon nanocrystals is facilitated by the Coulomb blockade effect that reduces states accessible to incoming electrons and the inadequate thermalization of hot electrons into the quantum dot.

Muralidhar, R.; Sadd, M.; Steimle, R. F.; Rao, R.; Hradsky, B.; White, B. E., Jr.

2003-03-01

8

Resonance tunneling of electrons interacting with phonons  

International Nuclear Information System (INIS)

The effect of the electron-phonon interaction on the electrons resonance tunneling through the two-barrier nanostructure is studied within the frames of the consecutive quantum-mechanical model. The wave function is derived from the solution of the Schroedinger equation with the correct boundary conditions in the quasi-classical approximation by the electron-phonon interaction. The current, calculated through the wave function, is averaged by the phonon subsystem by means of the Bloch theorem. The analytical expressions for the static and alternating currents of the resonance-tunnel diode with an account of the electron-phonon interaction, formally coinciding with the probability of the Moessbauer effect, are established

9

Spin effects in single-electron tunnelling  

International Nuclear Information System (INIS)

An important consequence of the discovery of giant magnetoresistance in metallic magnetic multilayers is a broad interest in spin-dependent effects in electronic transport through magnetic nanostructures. An example of such systems are tunnel junctions-single-barrier planar junctions or more complex ones. In this review we present and discuss recent theoretical results on electron and spin transport through ferromagnetic mesoscopic junctions including two or more barriers. Such systems are also called ferromagnetic single-electron transistors. We start from the situation when the central part of a device has the form of a magnetic (or nonmagnetic) metallic nanoparticle. Transport characteristics then reveal single-electron charging effects, including the Coulomb staircase, Coulomb blockade, and Coulomb oscillations. Single-electron ferromagnetic transistors based on semiconductor quantum dots and large molecules (especially carbon nanotubes) are also considered. The main emphasis is placed on the spin effects due to spin-dependent tunnelling through the barriers, which gives rise to spin accumulation and tunnel magnetoresistance. Spin effects also occur in the current-voltage characteristics, (differential) conductance, shot noise, and others. Transport characteristics in the two limiting situations of weak and strong coupling are of particular interest. In the former case we distinguish between the sequential tunnelling and cotunnelling regimes. In the strong couplinotunnelling regimes. In the strong coupling regime we concentrate on the Kondo phenomenon, which in the case of transport through quantum dots or molecules leads to an enhanced conductance and to a pronounced zero-bias Kondo peak in the differential conductance. (topical review)

10

Mobile Ventilation as a Tactic Resource at Tunnel Fires  

OpenAIRE

An emergency operation in case of a tunnel fire can easily become a complex operation. The objectives are to save people in danger, save the tunnel and its installations as well as vehicles trapped inside the tunnel and also, if it’s possible and necessary, reduce the effects on the environment. The strategy and the tactics in an emergency operation are very much depending on the specific tunnel, the fire behaviour and the resources from the fire brigade. One of the key factors is to ventil...

Kumm, Mia; Bergqvist, Anders

2008-01-01

11

Electron tunneling in Bi2223 under high pressure  

International Nuclear Information System (INIS)

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

12

Site-directed deep electronic tunneling through a molecular network  

International Nuclear Information System (INIS)

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

13

Electron beam instabilities in gyrotron beam tunnels  

Energy Technology Data Exchange (ETDEWEB)

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

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

1997-10-01

14

Electron tunneling in double quantum dots and rings  

International Nuclear Information System (INIS)

The electron tunneling in double quantum dot (DQD) is studied by changing of inter-dot distance. Localization of an electron is calculated for each level of the whole spectrum of the confinement states of DQD. For identical QDs the tunneling goes consecutively from high energy levels to the ground state. It is changed essentially when the QDs of the system are non-identical. We show that violation of symmetry of the DQD geometry makes it difficult for the tunneling. For double quantum ring (DQR) we demonstrate that the electron states with the same type of rotation symmetry play an important role for tunneling.

15

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

16

Electron tunneling in chemistry chemical reactions over large distances  

CERN Document Server

In Volume 30, an attempt is made to consider comprehensively both theoretical and experimental data that have been obtained to date on electron tunneling reactions involving chemical compounds of various classes, and to discuss the role played by these reactions in different areas of chemistry. The discussion of the above problem is preceded by a review of data on tunneling phenomena in nuclear physics, atomic physics, solid-state physics, as well as on the tunneling effects in chemistry that go beyond the framework of the main subject of this monograph. This review is included to acquaint the reader with the role of tunneling phenomena in physics and chemistry as a whole, to show how diversified the kingdom of tunneling phenomena is, and to see more distinctly the similarities and the differences between electron tunneling in chemical reactions and other tunnel phenomena.

Khairutdinov, RF; Zhadanov, VP

1989-01-01

17

Sub-electron transport in single-electron-tunneling arrays  

Science.gov (United States)

We have analyzed quasi-continuous charge transport in two-dimensional tunnel junction arrays with a special distribution of background charges, providing a complete suppression of Coulomb blockade thresholds of tunneling between any pair of islands. Numerical simulations show that at low currents the dc I-V curve is indeed linear, while the shot noise is strongly suppressed and approaches 1/N of the Schottky value (where N is the array length). Thus both conditions of quasi-continuous transport, formulated earlier by Matsuoka and Likharev (Phys. Rev. B, v57, 15613, 1998), are satisfied. At higher fields the electron-hole pair production begins, and shot noise grows sharply. At higher voltages still, the array enters the "plasma" regime (with nearly balanced number of electrons and holes) and the Fano factor drops to 1/N once again. We have studied the resulting shot noise peak in detail, and concluded that its physics is close to that of critical opalescence.

Kaplan, Daniel; Sverdlov, Viktor; Korotkov, Alexander; Likharev, Konstantin

2002-03-01

18

Tunneling Via Individual Electronic States in Ferromagnetic Nanoparticles  

CERN Document Server

We measure electron tunneling via discrete energy levels in ferromagnetic cobalt particles less than 4 nm in diameter, using non-magnetic electrodes. We see both spin-increasing and decreasing tunneling transitions, but we do not observe the spin degeneracy at small magnetic fields seen previously in non-magnetic materials. Due to magnetic anisotropy, the energy of each tunneling resonance shifts as an applied magnetic field rotates the particle's magnetic moment. The tunneling spectrum is denser than predicted for independent electrons, possibly due to spin-wave excitations.

Guéron, S; Myers, E B; Ralph, D C; Deshmukh, Mandar M.

1999-01-01

19

Human resources handbook [electronic resource].  

International Nuclear Information System (INIS)

Contains documents related to human resources. Initial focus was on making available the rules (Charter, Staff Regulations, Staff Rules, Secretary-General's Bulletins, Administrative Instructions) pertaining to human resources. In addition, Information Circulars and links or references to already existing "Task Tools", such as forms and IMIS desk procedures, are included. Additional "Task Tools" are being placed online as they become available.

20

PATHWAYS - ELECTRON TUNNELING PATHWAYS IN PROTEINS  

Science.gov (United States)

The key to understanding the mechanisms of many important biological processes such as photosynthesis and respiration is a better understanding of the electron transfer processes which take place between metal atoms (and other groups) fixed within large protein molecules. Research is currently focused on the rate of electron transfer and the factors that influence it, such as protein composition and the distance between metal atoms. Current models explain the swift transfer of electrons over considerable distances by postulating bridge-mediated tunneling, or physical tunneling pathways, made up of interacting bonds in the medium around and between donor and acceptor sites. The program PATHWAYS is designed to predict the route along which electrons travel in the transfer processes. The basic strategy of PATHWAYS is to begin by recording each possible path element on a connectivity list, including in each entry which two atoms are connected and what contribution the connection would make to the overall rate if it were included in a pathway. The list begins with the bonded molecular structure (including the backbone sequence and side chain connectivity), and then adds probable hydrogen bond links and through-space contacts. Once this list is completed, the program runs a tree search from the donor to the acceptor site to find the dominant pathways. The speed and efficiency of the computer search offers an improvement over manual techniques. PATHWAYS is written in FORTRAN 77 for execution on DEC VAX series computers running VMS. The program inputs data from four data sets and one structure file. The software was written to input BIOGRAF (old format) structure files based on x-ray crystal structures and outputs ASCII files listing the best pathways and BIOGRAF vector files containing the paths. Relatively minor changes could be made in the input format statements for compatibility with other graphics software. The executable and source code are included with the distribution. The main memory requirement for execution is 2.6 Mb. This program is available in DEC VAX BACKUP format on a 9-track 1600 BPI magnetic tape (standard distribution) or on a TK50 tape cartridge. PATHWAYS was developed in 1988. PATHWAYS is a copyrighted work with all copyright vested in NASA. DEC, VAX, VMS, and TK50 are trademarks of Digital Equipment Corporation. BIOGRAF is a trademark of Molecular Simulations, Inc., Sunnyvale, CA.

Beratan, D. N.

1994-01-01

21

Inelastic electron tunneling spectroscopy of local "spin accumulation" devices  

OpenAIRE

We investigate the origin of purported "spin accumulation" signals observed in local "three-terminal" (3T) measurements of ferromagnet/insulator/n-Si tunnel junctions using inelastic electron tunneling spectroscopy (IETS). Voltage bias and magnetic field dependences of the IET spectra were found to account for the dominant contribution to 3T magnetoresistance signals, thus indicating that it arises from inelastic tunneling through impurities and defects at junction interface...

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

2014-01-01

22

Inelastic electron tunneling spectroscopy of local "spin accumulation" devices  

Science.gov (United States)

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

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

2014-06-01

23

Tunneling of Bloch electrons through a small-size contact  

Science.gov (United States)

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

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

2014-05-01

24

Inelastic electron tunneling spectroscopy of local “spin accumulation” devices  

Energy Technology Data Exchange (ETDEWEB)

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

Tinkey, Holly N.; Li, Pengke; Appelbaum, Ian, E-mail: appelbaum@physics.umd.edu [Department of Physics and CNAM, University of Maryland, College Park, Maryland 20742 (United States)

2014-06-09

25

Inelastic electron tunneling spectroscopy of local “spin accumulation” devices  

International Nuclear Information System (INIS)

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

26

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

27

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

28

Electron-Photon interaction in resonant tunneling diodes  

OpenAIRE

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

29

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

30

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

31

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

32

Attosecond correlation dynamics during electron tunnelling from molecules  

International Nuclear Information System (INIS)

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

33

Single electron pump fabricated with ultrasmall normal tunnel junctions  

International Nuclear Information System (INIS)

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

34

Microwave-induced co-tunneling in single electron tunneling transistors  

DEFF Research Database (Denmark)

The influence of microwaves on the co-tunneling in single electron tunneling transistors has been investigated as function of frequency and power in the temperature range from 150 to 500 mK. All 20 low frequency connections and the RF line were filtered, and the whole cryostat was suspended on rubber bellows. Cross-talk was minimized by using individual coaxial lines between the sample and the room temperature electronics: The co-tunneling experiments were performed at zero DC bias current by measuring the voltage response to a very small amplitude 2 Hz current modulation with the gate voltage fixed at maximum Coulomb blockade. With the microwave signal applied to one side of the transistor, we find that the conductance increases linearly with T-2 and microwave power. (C) 2002 Elsevier Science B.V. All rights reserved.

Ejrnaes, M.; Savolainen, M.

2002-01-01

35

Numerical simulations of electron tunneling currents in water  

CERN Document Server

This paper presents results of numerical simulations of electron tunneling through water that extend our previous calculations on such systems in several ways. First, a tip-substrate configuration is used; second, calculations are carried in the presence of an external potential bias; third, the image potential that reflects the interaction of the electron with the mobile metal electrons is taken into account in the static image approximation. Finally, all-to-all transmission probability calculations are performed in order to get an order-of-magnitude estimate of the current-voltage characteristics of this junction model. The computed currents are within the range of the few available experimental observations on scanning tunneling microscope (STM) currents in water, indicating that our calculation may have taken into account all the important physical attributes of such systems. In addition we examine the effect of the water medium on the spatial distribution of the tunneling flux. We find that while differe...

Galperin, M; Benjamin, I; Galperin, Michael; Nitzan, Abraham; Benjamin, Ilan

2002-01-01

36

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

37

Boltzmann machine neural network devices using single-electron tunnelling  

Science.gov (United States)

We proposed a method of implementing the Boltzmann machine neural network on electronic circuits by making use of the single-electron tunnelling phenomenon. The single-electron circuit shows stochastic behaviour in its operation because of the probabilistic nature of the electron tunnelling phenomenon. It can therefore be successfully used for implementing the stochastic neuron operation of the Boltzmann machine. The authors developed a single-electron neuron circuit that can produce the function required for the Boltzmann machine neuron. A method for constructing Boltzmann machine networks by combining the neuron circuits was also developed. The simulated-annealing operation can be performed easily by regulating an external control voltage for the network circuits. A sample network was designed that solves an instance of a combinatorial optimization problem. Computer simulation demonstrated that, through the simulated-annealing process, the sample network can converge to the global minimum energy state that represents the correct solution to the problem.

Yamada, Takashi; Akazawa, Masamichi; Asai, Tetsuya; Amemiya, Yoshihito

2001-03-01

38

Subelectron transport in single-electron-tunneling arrays  

Science.gov (United States)

We have shown that a special distribution of background charges in islands of single-electron-tunneling arrays can completely suppress its Coulomb blockade and at the same time reduce substantially its shot noise at low applied voltages. In particular the Fano factor F can approach the minimum value Fmin=1/Nopalescence.

Kaplan, Daniel M.; Sverdlov, Victor A.; Likharev, Konstantin K.

2002-05-01

39

Effect of Exchange-type Zero-bias Anomaly on Single Electron Tunnelling of Au Nanoparticles  

OpenAIRE

Using cryogenic scanning tunnelling microscopy and scanning tunnelling spectroscopy we measured single electron tunnelling of isolated Au nanoparticles with 1.4 nm in radius. We observe that a gap {\\Delta}V ~ 2e/C (C is the capacitance of the Au particle) around zero bias in the tunnelling conductance spectrum, followed by a series of discrete single electron tunnelling peaks with voltage widths of EC ~ e/C at both negative and positive bias. Experimental data are well expla...

Xu, Rui; Sun, Yi; Yan, Hui; Yang, Ji-yong; He, Lin; Nie, Jia-cai; Li, Yadong

2011-01-01

40

Single Electron Tunneling at Large Conductance: The Semiclassical Approach  

OpenAIRE

We study the linear conductance of single electron devices showing Coulomb blockade phenomena. Our approach is based on a formally exact path integral representation describing electron tunneling nonperturbatively. The electromagnetic environment of the device is treated in terms of the Caldeira-Leggett model. We obtain the linear conductance from the Kubo formula leading to a formally exact expression which is evaluated in the semiclassical limit. Specifically we consider t...

Goeppert, Georg; Grabert, Hermann

1999-01-01

41

Conductance of the Single Electron Transistor for Arbitrary Tunneling Strength  

OpenAIRE

We study the temperature and gate voltage dependence of the conductance of the single electron transistor focusing on highly conducting devices. Electron tunneling is treated nonperturbatively by means of path integral Monte Carlo techniques and the conductance is determined from the Kubo formula. A regularized singular value decomposition scheme is employed to calculate the conductance from imaginary time simulation data. Our findings are shown to bridge between available a...

Goeppert, Georg; Huepper, Bruno; Grabert, Hermann

2000-01-01

42

Boltzmann machine neuron circuit using single-electron tunneling  

Science.gov (United States)

The inherent stochastic character of single-electron tunneling can be effectively utilized for creating novel electronic circuits having high-level functions. As a sample application, we present a stochastic-response circuit for implementing Boltzmann machine neurons. The circuit consists of a single-electron circuit operating under unstable conditions. It can produce an output of a random 1-0 bit stream with the probability for an output of 1 controlled by an input signal—a task that is difficult for conventional circuits using ordinary electronic devices.

Akazawa, Masamichi; Amemiya, Yoshihito

1997-02-01

43

Attosecond correlation dynamics during electron tunnelling from molecules  

Energy Technology Data Exchange (ETDEWEB)

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

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

2010-08-28

44

Modeling Klein tunneling and caustics of electron waves in graphene  

Science.gov (United States)

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

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

2015-01-01

45

Electronic properties of core-shell nanowire resonant tunneling diodes  

OpenAIRE

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

Zervos, Matthew

2014-01-01

46

Low-frequency noise in single electron tunneling transistor  

OpenAIRE

The noise in current biased aluminium single electron tunneling (SET) transistors has been investigated in the frequency range of 5 mHz < f < 30 Hz. A refined high frequency (HF) shielding including resistive coaxial lines, that prevents spurious electromagnetic radiation and especially high energy photons emitted by the 4.2 K environment from reaching the sample, allows us to study a given background charge configuration for many hours below [approximate] 100 mK. The noise at relatively high...

Tavkhelidze, A. N.; Mygind, Jesper

2006-01-01

47

Simulation of single-electron tunnelling circuits using SPICE:  

OpenAIRE

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

Haar, R.

2004-01-01

48

Many-body effects in magnetic inelastic electron tunneling spectroscopy  

Science.gov (United States)

Magnetic inelastic electron tunneling spectroscopy (IETS) shows sharp increases in conductance when a new conductance channel associated with a change in magnetic structure is open. Typically, the magnetic moment carried by an adsorbate can be changed by collision with a tunneling electron; in this process the spin of the electron can flip or not. A previous one-electron theory [Phys. Rev. Lett.PRLTAO0031-900710.1103/PhysRevLett.103.176601 103, 176601 (2009)] successfully explained both the conductance thresholds and the magnitude of the conductance variation. The elastic spin flip of conduction electrons by a magnetic impurity leads to the well-known Kondo effect. In the present work, we compare the theoretical predictions for inelastic magnetic tunneling obtained with a one-electron approach and with a many-body theory including Kondo-like phenomena. We apply our theories to a singlet-triplet transition model system that contains most of the characteristics revealed in magnetic IETS. We use two self-consistent treatments (noncrossing approximation and self-consistent ladder approximation). We show that, although the one-electron limit is properly recovered, new intrinsic many-body features appear. In particular, sharp peaks appear close to the inelastic thresholds; these are not localized exactly at thresholds and could influence the determination of magnetic structures from IETS experiments. Analysis of the evolution with temperature reveals that these many-body features involve an energy scale different from that of the usual Kondo peaks. Indeed, the many-body features perdure at temperatures much larger than the one given by the Kondo energy scale of the system.

Korytár, Richard; Lorente, Nicolás; Gauyacq, Jean-Pierre

2012-03-01

49

Thin-film chemical sensors based on electron tunneling  

Science.gov (United States)

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.

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

1985-01-01

50

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

51

Long-range electron transfer in biomolecules. Tunneling or hopping?  

Science.gov (United States)

Two competing mechanisms are relevant for long-range electron transfer (ET) in biomolecules: direct electron tunneling between donor (D) and acceptor (A), D ? A, and multistep hopping D ? X ? A, where an electron or an electron hole is transiently localized on intermediate sites X. Which of these mechanisms dominates the ET reaction is determined by the arrangement and electronic properties of the redox centers. For thermal ET, it is shown that single-step tunneling is overcome by hopping when the energy gap E between D and X is smaller than the crossover barrier E(C), E(C) = (?G/2) + (3/4)k(B)T?R(DA), where ?G is the driving force, ? the decay parameter, and R(DA) the donor-acceptor distance. In proteins at T = 300 K, hopping will dominate when E E(C). Thus, one can explore the ET mechanism using three quantities E, ?G, and R(DA). When ?G = 0 and E = 0.5 eV (the difference in redox potentials of D and X is 0.5 V), two-step hopping D ? X ? A will be favored at R(DA) >25 Å. In protein ET chains, the distance between redox cofactors is often smaller than 20 Å, but the gap E between the cofactors and surrounding amino acid residues is larger than 0.5 eV. Therefore, ET in the systems should occur by single-step tunneling D ? A. In the activationless regime (?G ? -?, ? is the reorganization energy) often observed for photoinduced ET, the crossing point energy is determined by E(C) = (2?kT?R(DA))(1/2) - ?. The suggested expressions for the threshold barrier may be useful to predict the ET mechanism in natural and artificial redox systems. PMID:21923189

Voityuk, Alexander A

2011-10-27

52

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

Science.gov (United States)

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

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

1994-01-01

53

Conformational Control of Electron Tunneling in Redox Proteins: Sulfite Oxidase  

Science.gov (United States)

Many redox proteins mediate electron transfer over large (10-25A) distances, with the reaction rate being, in some cases, remarkably sensitive to the protein structure and dynamics (e.g., Science 290, 114-117 (2000)). These properties make redox proteins excellent candidates for molecular electronics applications. Sulfite oxidase (SO) is a molybdenum-containing electron-transfer enzyme that catalyzes the conversion of sulfite to sulfate. The enzyme consists of two domains, one hosting a molybdopterin moiety, which receives an electron from sulfite, and the other hosting a heme, from which electrons travels to cytochrome c. The domains are connected together by a flexible link, which allows for the domains to move relative to each other. This motion is believed to control electron transfer from the molybdopterin to the heme, which is only possible when the enzyme assumes a closed conformation (the two domains are in contact with each other). The only available crystallographic structure of SO (PDB code 1SOX) characterizes an open conformation, when the two domains are separated. Classical molecular dynamics (MD) simulations of the enzyme in solvent, combined with semi-empirical quantum chemistry calculations, were performed to identify possible closed conformations of SO and to investigate the electron transfer rate in these conformations. Steered MD simulations supplemented by analytical modeling were used to characterize kinetics of conformational transitions, particularly opening and closing of the enzyme, which controls the electron tunneling rate.

Balabin, Ilya; Kawatsu, Tsutomu; Beratan, David

2004-03-01

54

Relativistic tunneling picture of electron-positron pair creation  

Science.gov (United States)

The common tunneling picture of electron-positron pair creation in a strong electric field is generalized to pair creation in combined crossed electric and magnetic fields. This enhanced picture, being symmetric for electrons and positrons, is formulated in a gauge-invariant and Lorentz-invariant manner for quasistatic fields. It may be used to infer qualitative features of the pair creation process. In particular, it allows for an intuitive interpretation of how the presence of a magnetic field modifies and, in particular cases, even enhances pair creation. The creation of electrons and positrons from the vacuum may be assisted by an energetic photon, which can also be incorporated into this picture of pair creation.

Wöllert, Anton; Klaiber, Michael; Bauke, Heiko; Keitel, Christoph H.

2015-03-01

55

Scanning electron and tunneling microscopy of palladium-barium emitters  

International Nuclear Information System (INIS)

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

56

Detection of electronic nematicity using scanning tunneling microscopy  

Science.gov (United States)

Electronic nematic phases have been proposed to occur in various correlated electron systems and were recently claimed to have been detected in scanning tunneling microscopy (STM) conductance maps of the pseudogap states of the cuprate high-temperature superconductor Bi2Sr2CaCu2O8+? (Bi-2212). We investigate the influence of anisotropic STM tip structures on such measurements and establish, with a model calculation, the presence of a tunneling interference effect within an STM junction that induces energy-dependent symmetry-breaking features in the conductance maps. We experimentally confirm this phenomenon on different correlated electron systems, including measurements in the pseudogap state of Bi-2212, showing that the apparent nematic behavior of the imaged crystal lattice is likely not due to nematic order but is related to how a realistic STM tip probes the band structure of a material. We further establish that this interference effect can be used as a sensitive probe of changes in the momentum structure of the sample's quasiparticles as a function of energy.

da Silva Neto, Eduardo H.; Aynajian, Pegor; Baumbach, Ryan E.; Bauer, Eric D.; Mydosh, John; Ono, Shimpei; Yazdani, Ali

2013-04-01

57

Scanning electron and tunneling microscopy of palladium barium emitters  

Science.gov (United States)

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

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

2003-06-01

58

High Performance Resonant Tunneling Electronic Circuit with Suitable Resistance Parameters  

OpenAIRE

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 favo...

Hsiao Hsuan Cheng; Yen Chun Lin; Chih Chin Yang

2012-01-01

59

Electron-phonon multiplier with a cascade tunnel NIS junctions and hot electron microcalorimeters  

International Nuclear Information System (INIS)

A device for amplification of weak electric signals produced in a normal or superconducting absorber after absorption of quanta or phonons is proposed. The device consists of a cascade of normal metal-insulator-superconductor (NIS) tunnel junctions in which normal metal plays a role of an electrode and hot electron microcalorimeter. Tunneling through a barrier a particle causes a transfer of an energy ? ? from one microcalorimeter to another and the enhancement of the current through the next NIS junction. The device operates as a solid-state electron multiplier at low temperatures

60

Electron-phonon multiplier involving a cascade of NIS tunnel junctions and hot-electron microcalorimeters  

International Nuclear Information System (INIS)

A device for amplifying weak electric signals arising in a normal- or a superconducting-metal absorber upon the absorption of photons or phonons is proposed. The device consists of a cascade of normal-metal-insulator-superconductor (NIS) tunnel junctions, where the normal metal is used as an electrode and as a hot-electron microcalorimeter. Tunneling through the barrier, a particle transports energy of about ? (energy gap in the superconductor) from one microcalorimeter to another and amplifies the current through the next NIS junction. The device operates as a solid-state electron multiplier at low temperatures

61

Resonant tunneling of interacting electrons in an AC electric field  

International Nuclear Information System (INIS)

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

62

Resonant tunneling of interacting electrons in an AC electric field  

Energy Technology Data Exchange (ETDEWEB)

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

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

2013-11-15

63

Pair tunneling resonance in the single-electron transport regime.  

Science.gov (United States)

We predict a new electron pair tunneling (PT) resonance in nonlinear transport through quantum dots with positive charging energies exceeding the broadening due to thermal and quantum fluctuations. The PT resonance shows up in the single-electron transport (SET) regime as a peak in the derivative of the nonlinear conductance, d(2)I/dV(2), when the electrochemical potential of one electrode matches the average of two subsequent charge addition energies. For a single level quantum dot (Anderson model) we find the analytic peak shape and the dependence on temperature, magnetic field, and junction asymmetry and compare with the inelastic cotunneling peak which is of the same order of magnitude. In experimental transport spectroscopy the PT resonance may be mistaken for a weak SET resonance judging only by the voltage dependence of its position. Our results provide essential clues to avoid such erroneous interpretation. PMID:19905657

Leijnse, M; Wegewijs, M R; Hettler, M H

2009-10-01

64

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

CERN Document Server

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

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

2003-01-01

65

Enhancement of tunneling from a correlated 2D electron system by a many-electron Mossbauer-type recoil in a magnetic field  

OpenAIRE

We consider the effect of electron correlations on tunneling from a 2D electron layer in a magnetic field parallel to the layer. A tunneling electron can exchange its momentum with other electrons, which leads to an exponential increase of the tunneling rate compared to the single-electron approximation. Explicit results are obtained for a Wigner crystal. They provide a qualitative and quantitative explanation of the data on electrons on helium. We also discuss tunneling in ...

Dykman, M. I.; Sharpee, T.; Platzman, P. M.

2000-01-01

66

On the mechanical origin of single electron tunneling feedback effects in suspended carbon nanotubes  

OpenAIRE

In single electron tunneling through clean, suspended carbon nanotube devices at low temperature, distinct switching phenomena have regularly been observed. These can be explained via strong interaction of single electron tunneling and mechanical motion of the nanotube. We present evidence that the switching phenomena are absent if the sample is kept in a viscous medium, additionally supporting this interpretation.

Schmid, D. R.; Stiller, P. L.; Strunk, C.; Hu?ttel, A. K.

2014-01-01

67

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

68

Wrangling Electronic Resources: A Few Good Tools  

Directory of Open Access Journals (Sweden)

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

Brandy Klug

2010-03-01

69

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

Science.gov (United States)

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

Hipps, K. W.; Scudiero, L.

2005-01-01

70

Determination of the tunnel rates through a few-electron quantum dot  

CERN Document Server

We demonstrate how rate equations can be employed to find analytical expressions for the sequential tunneling current through a quantum dot as a function of the tunnel rates, for an arbitrary number of states involved. We apply this method at the one-to-two electron transition where the electron states are known exactly. By comparing the obtained expressions to experimental data, the tunnel rates for six transitions are extracted. We find that these rates depend strongly on the spin and orbital states involved in the tunnel process.

Hanson, R; Di Vincenzo, D P; Vandersypen, L M K; Elzerman, J M; Van Beveren, L H W; Kouwenhoven, L P

2004-01-01

71

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

Energy Technology Data Exchange (ETDEWEB)

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

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

2014-08-21

72

Long-range intervalence electron tunneling through fully saturated systems  

International Nuclear Information System (INIS)

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

73

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

Zervos, Matthew

2014-01-01

74

Electron Tunneling through Pseudomonas aeruginosa Azurins on SAM Gold Electrodes.  

Science.gov (United States)

Robust voltammetric responses were obtained for wild-type and Y72F/H83Q/Q107H/Y108F azurins adsorbed on CH(3)(CH(2))(n)SH:HO(CH(2))(m)SH (n=m=4,6,8,11; n=13,15 m=11) self-assembled monolayer (SAM) gold electrodes in acidic solution (pH 4.6) at high ionic strengths. Electron-transfer (ET) rates do not vary substantially with ionic strength, suggesting that the SAM methyl headgroup binds to azurin by hydrophobic interactions. The voltammetric responses for both proteins at higher pH values (>4.6 to 11) also were strong. A binding model in which the SAM hydroxyl headgroup interacts with the Asn47 carboxamide accounts for the relatively strong coupling to the copper center that can be inferred from the ET rates. Of particular interest is the finding that rate constants for electron tunneling through n = 8, 13 SAMs are higher at pH 11 than those at pH 4.6, possibly owing to enhanced coupling of the SAM to Asn 47 caused by deprotonation of nearby surface residues. PMID:19262679

Yokoyama, Keiko; Leigh, Brian S; Sheng, Yuling; Niki, Katsumi; Nakamura, Nobuhumi; Ohno, Hiroyuki; Winkler, Jay R; Gray, Harry B; Richards, John H

2008-03-01

75

Mechanical modulation of single-electron tunneling through molecular-assembled metallic nanoparticles  

CERN Document Server

We present a microscopic study of single-electron tunneling in nanomechanical double-barrier tunneling junctions formed using a vibrating scanning nanoprobe and a metallic nanoparticle connected to a metallic substrate through a molecular bridge. We analyze the motion of single electrons on and off the nanoparticle through the tunneling current, the displacement current and the charging-induced electrostatic force on the vibrating nanoprobe. We demonstrate the mechanical single-electron turnstile effect by applying the theory to a gold nanoparticle connected to the gold substrate through alkane dithiol molecular bridge and probed by a vibrating platinum tip.

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

2004-01-01

76

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

77

Low-frequency noise in single electron tunneling transistor  

DEFF Research Database (Denmark)

The noise in current biased aluminium single electron tunneling (SET) transistors has been investigated in the frequency range of 5 mHz = 10 Hz, we find the same input charge noise, typically QN = 5 × 10–4 e/Hz1/2 at 10 Hz, with and without the HF shielding. At lower frequencies, the noise is due to charge trapping, and the voltage noise pattern superimposed on the V(Vg) curve (voltage across transistor versus gate voltage) strongly depends on the background charge configuration resulting from the cooling sequence and eventual radio frequency (rf) irradiation.The measured noise spectra which show both 1/f and 1/f1/2 dependencies and saturation for f <100 mHz can be fitted by two-level fluctuators with Debye–Lorentzian spectra and relaxation times of order seconds. In some cases, the positive and negative slopes of the V(Vg) curve have different overlaid noise patterns. For fixed bias on both slopes, we measure the same noise spectrum, and believe that the asymmetric noise is due to dynamic charge trapping near or inside one of the junctions induced when ramping the junction voltage. Dynamic trapping may limit the high frequency applications of the SET transistor. Also reported on are the effects of rf irradiation and the dependence of the SET transistor noise on bias voltage. ©1998 American Institute of Physics.

Tavkhelidze, A.N.; Mygind, Jesper

1998-01-01

78

Integrated NIS electron-tunnelling refrigerator/superconducting bolometer  

International Nuclear Information System (INIS)

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

79

Integrated NIS electron-tunnelling refrigerator/superconducting bolometer  

Energy Technology Data Exchange (ETDEWEB)

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

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

2006-04-15

80

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

CERN Document Server

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

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

2005-01-01

81

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

OpenAIRE

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

C?avar, Elizabeta; Blu?m, Marie-christine; Pivetta, Marina; Patthey, Franc?ois; Chergui, Majed; Schneider, Wolf-dieter

2005-01-01

82

Vertex-corrected tunneling inversion in electron-phonon mediated superconductors: Pb  

International Nuclear Information System (INIS)

The McMillan-Rowell tunneling inversion program, which extracts the electron-phonon spectral function ?2F(?) and the Coulomb pseudopotential ?* from experimental tunneling data, is generalized to include the lowest-order vertex correction. We neglect the momentum dependence of the electron-phonon matrix elements, which is formally equivalent to using a local approximation. The perturbation theory is performed on the imaginary axis and then an exact analytic continuation is employed to produce the tunneling density of states on the real axis. Comparison is made with the experimental data for Pb. We find ? is increased by approximately 1% due to the vertex corrections. copyright 1997 The American Physical Society

83

Phonon and plasmon excitation in inelastic electron tunneling spectroscopy of graphite  

CERN Document Server

The inelastic electron tunneling spectrum (IETS)of highly oriented pyrolitic graphite (HOPG) has been measured with scanning tunneling spectroscopy (STS) at 6K. The observed spectral features are in very good agreement with the vibrational density of states (vDOS) of graphite calculated from first principles. We discuss the enhancement of certain phonon modes by phonon-assisted tunneling in STS based on the restrictions imposed by the electronic structure of graphite. We also demonstrate for the first time the local excitation of surface-plasmons in IETS which are detected at an energy of 40 meV.

Vitali, L; Kern, K; Wirtz, L; Rubio, A

2003-01-01

84

Electronic Resource Management Systems in Practice  

Science.gov (United States)

Electronic resource management (ERM) systems have inundated the library marketplace. Both integrated library systems (ILS) vendors and subscription agents are now offering products and service enhancements that claim to help libraries efficiently manage their electronic resources. Additionally, some homegrown and open-source solutions have emerged…

Grogg, Jill E.

2008-01-01

85

Electron tunneling into Bi thin films under pressure  

International Nuclear Information System (INIS)

We have studied the pressure dependence of the tunneling resistance of tunnel junctions between 300-nm-thick Bi films and 20-nm-thick films of Al deposited at room temperature. Native Al oxide formed by oxygen glow discharge provided the tunnel barrier. The resistance was measured as a function of voltage from 0 to about 1 V. Measurements were made from room temperature to below the superconducting transition temperature of the Al film. The pressure range covered was from 0 to about 8 kbar. The resistance decreases with increasing pressure in a way easily described by simple tunneling theory. In the resistance curves we observe pressure dependence of structure, which has in the past been associated with the pressure dependence of the Bi band structure

86

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

87

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

Energy Technology Data Exchange (ETDEWEB)

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 (H{sub 2}BSTBPP) 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.

Noguchi, Yutaka [Kobe Advanced ICT Research Center, National Institute of Information and Communications Technology, 588-2 Iwaoka, Nishi-ku, Kobe 651-2492 (Japan)], E-mail: y-noguchi@faculty.chiba-u.jp; Ueda, Rieko; Kubota, Tohru; Kamikado, Toshiya; Yokoyama, Shiyoshi [Kobe Advanced ICT Research Center, National Institute of Information and Communications Technology, 588-2 Iwaoka, Nishi-ku, Kobe 651-2492 (Japan); Nagase, Takashi [Osaka Prefecture University, 1-1 Gakuen-cho, Nakaku, Sakai, Osaka 599-8531 (Japan)

2008-03-03

88

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

OpenAIRE

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

Ya Farenyuk, O.; Shvaika, A. M.

2006-01-01

89

Tunneling from a correlated 2D electron system transverse to a magnetic field  

CERN Document Server

We show that, in a magnetic field parallel to the 2D electron layer, strong electron correlations change the rate of tunneling from the layer exponentially. It results in a specific density dependence of the escape rate. The mechanism is a dynamical Mossbauer-type recoil, in which the Hall momentum of the tunneling electron is partly transferred to the whole electron system, depending on the interrelation between the rate of interelectron momentum exchange and the tunneling duration. We also show that, in a certain temperature range, magnetic field can enhance rather than suppress the tunneling rate. The effect is due to the magnetic field induced energy exchange between the in-plane and out-of-plane motion. Magnetic field can also induce switching between intra-well states from which the system tunnels, and a transition from tunneling to thermal activation. Explicit results are obtained for a Wigner crystal. They are in qualitative and quantitative agreement with the relevant experimental data, with no adjus...

Sharpee, T; Platzman, P M

2001-01-01

90

Using electron-tunneling refrigerators to cool electrons, membranes, and sensors  

Science.gov (United States)

Many cryogenic devices require temperatures near 100 mK for optimal performance, such as thin-film, superconducting detectors. Examples include the submillimeter SCUBA camera on the James Clerk Maxwell Telescope, high-resolution X-ray sensors for semiconductor defect analysis, and a planned satellite to search for polarization in the cosmic microwave background. The cost, size, and complexity of refrigerators used to reach 100 mK (dilution and adiabatic demagnetization refrigerators) are significant and alternative technologies are desirable. We demonstrate work on developing a new option for cooling detectors to 100 mK bath temperatures. Solid-state refrigerators based on Normal metal/Insulator/Superconductor (NIS) tunnel junctions can provide cooling from pumped 3He bath temperatures (˜300 mK) to 100 mK. The cooling mechanism is the preferential tunneling of the highest energy (hottest) electrons from the normal metal through the biased tunnel junctions into the superconductor. When NIS refrigerators are combined with a micro-machined membrane, both the electrons and phonons of the membrane can be cooled. We have developed NIS-cooled membranes with both large temperature reductions and large cooling powers. We have shown the first cooling of a bulk material by cooling a neutron transmutation doped (NTD) thermistor. The fabrication of NIS refrigerators can be integrated with existing detector technology. For the first time, we have successfully integrated NIS refrigerators with both mm-wave and X-ray detectors. In particular, we have cooled X-ray detectors by more than 100 mK and have achieved a resolution of <10 eV at 6 keV at a bath temperature 85 mK above the transition temperature of the detector. The use of integrated NIS refrigerators makes the remarkable performance of cryogenic detectors available from 300 mK platforms. We have also performed preliminary work towards building a general-purpose cooling platform for microelectronics devices on separate chips.

Miller, Nathan A.

91

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

92

Direct control of the tunnel splitting in a one-electron double quantum dot  

CERN Document Server

Quasi-static transport measurements are employed on a laterally defined tunnel-coupled double quantum dot. A nearby quantum point contact allows us to track the charge as added to the device. If charged with only up to one electron, the low-energy spectrum of the double quantum dot is characterized by its quantum mechanical interdot tunnel splitting. We directly measure its magnitude by utilizing particular anticrossing features in the stability diagram at finite source-drain bias. By modification of gate voltages defining the confinement potential as well as by variation of a perpendicular magnetic field we demonstrate the tunability of the coherent tunnel coupling.

Huettel, A K; Eberl, K; Kotthaus, J P

2005-01-01

93

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

Energy Technology Data Exchange (ETDEWEB)

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

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

2014-03-03

94

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

International Nuclear Information System (INIS)

Optical excitation of azurin blue copper protein immobilized on indium-tin oxide, in resonance with its ligand-to-metal charge transfer absorption band, resulted in a light-induced current tunnelling within the protein milieu. The related electron transport rate is estimated to be about 105?s?1. A model based on resonant tunnelling through an azurin excited molecular state is proposed. The capability of controlling electron transfer processes through light pulses opens interesting perspectives for implementation of azurin in bio-nano-opto-electronic devices

95

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

96

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

International Nuclear Information System (INIS)

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

97

Reduction of charge trapping and electron tunneling in SIMOX by supplemental implantation of oxygen  

International Nuclear Information System (INIS)

Silicon-on-insulator, SOI, technologies are being aggressively pursued to produce high density, high speed, radiation tolerant electronics. The dielectric isolation of the buried oxide makes it possible to design integrated circuits that greatly minimize single event upset and eliminate dose-rate induced latchup and upset. The reduction of excess-silicon related defects in SIMOX by the supplemental implantation of oxygen has been examined. The supplemental implant is 6% of the oxygen dose used to form the buried oxide, and is followed by a 1,000 C anneal, in contrast to the >1,300 C anneal used to form the buried oxide layer of SIMOX. The defects examined include shallow electron traps, deep hole traps, and silicon clusters. The radiation-induced shallow electron and deep hole trapping are measured by cryogenic detrapping and isothermal annealing techniques. The low-field (3 to 6 MV/cm) electron tunneling is interpreted as due to a two phase mixture of stoichiometric SiO2 and Si clusters a few nm in size. Single and triple SIMOS samples have been examined. All of the defects are reduced by the supplemental oxygen processing. Shallow electron trapping is reduced by an order of magnitude. Because of the larger capture cross section for hole trapping, hole trapping is not reduced as much. The low-field electron tunneling due to Si clusters is also significantly reduced. Both uniform and nonuniform electron tunneling have been observed in SIMOX samples without ve been observed in SIMOX samples without supplement processing. In samples exhibiting only uniform tunneling, electron capture at holes has been observed. The nonuniform tunneling is superimposed upon the uniform tunneling and is characterized by current spiking

98

Bias voltage effect on electron tunneling across a junction with a ferroelectric-ferromagnetic two-phase composite barrier  

Energy Technology Data Exchange (ETDEWEB)

The effect of bias voltage on electron tunneling across a junction with a ferroelectric-ferromagnetic composite barrier is investigated theoretically. Because of the inversion symmetry breaking of the spontaneous ferroelectric polarization, bias voltage dependence of the electron tunneling shows significant differences between the positive bias and the negative one. The differences of spin filtering or tunnel magnetoresistance increase with the increasing absolute value of bias voltage. Such direction preferred electron tunneling is found intimately related with the unusual asymmetry of the electrical potential profile in two-phase composite barrier and provides a unique change to realize rectifying functions in spintronics. - Highlights: Black-Right-Pointing-Pointer Electron tunneling across a ferroelectric-ferromagnetic composite barrier junction. Black-Right-Pointing-Pointer TMR effect is different under the same value but opposite direction bias voltage. Black-Right-Pointing-Pointer This directionality of the electron tunneling enhances with increasing bias voltage.

Wang Jian, E-mail: waugh@163.com [Department of Teaching Affairs, Wuxi City College of Vocational Technology, Wuxi 214153 (China); Ju Sheng; Li, Z.Y. [Department of Physics and Jiangsu Key Laboratory of Thin Films, Soochow University, Suzhou 215006 (China)

2012-03-15

99

Principles of Selection for Electronic Resources.  

Science.gov (United States)

Availability in electronic format of scholarly and scientific literatures and other forms of information has altered challenges faced by library collection managers. Drawing on ideas of the multi-library consortia, which have grown up partly in response to the advent of electronic resources, librarians have devised new criteria and means of…

Metz, Paul

2000-01-01

100

Electron tunnelling phenomena in YPO4?:?Ce,Ln (Ln = Er, Ho, Nd, Dy)  

Science.gov (United States)

Electron tunnelling from an Ln2+-electron trap (Ln = Er, Nd, Ho, Dy) to a Ce4+-recombination centre is investigated experimentally and theoretically in YPO4?:?Ce3+,Ln3+. Low temperature thermoluminescence, fading and isothermal decay measurements for samples with concentrations of Ce and Ln ranging from 0.05 to 5.0% are analysed. We observe a temperature activated tunnelling that depends on type of Ln and concentration. Results are simulated with simple quantum mechanical concepts. The average distance between traps and centres is altered by the Ce and Ln concentrations. The higher the concentration, the higher the electron tunnelling probability which can be attributed to a shorter average Ce4+-Ln2+ distance. As a result, changes in the thermoluminescence characteristics like the fading rates and the isothermal decay curves are observed.

Dobrowolska, Anna; Bos, Adrie J. J.; Dorenbos, Pieter

2014-08-01

101

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

102

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

103

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

DEFF Research Database (Denmark)

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

N. Pfeiffer, Adrian; Cirelli, Claudio

2012-01-01

104

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

Directory of Open Access Journals (Sweden)

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

Madsen Lars B.

2013-03-01

105

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

106

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

International Nuclear Information System (INIS)

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

107

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

CERN Document Server

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

De Parga, A L V; Miranda, R

2000-01-01

108

Zero-bias Anomaly of Tunneling into the Edge of a 2D Electron System  

OpenAIRE

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

Shekhtman, L.; Glazman, L. I.

1995-01-01

109

Phonon-assisted tunneling between singlet states in two-electron quantum dot molecules  

CERN Document Server

We study phonon-assisted electron tunneling in semiconductor quantum dot molecules. In particular, singlet-singlet relaxation in a two-electron doped structure is considered. The influence of Coulomb interaction is discussed via comparison with a single electron system. We find that the relaxation rate reaches similar values in the two cases but the Coulomb interaction shifts the maximum rates towards larger separations between the dots. The difference in electron-phonon interaction between deformation potential and piezoelectric coupling is investigated. We show that the phonon-induced tunneling between two-electron singlet states is a fast process, taking place on the time scales of the order of a few tens of picoseconds.

Grodecka, A; Förstner, J; 10.1103/PhysRevB.78.085302

2009-01-01

110

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

111

Interference effects at tunneling junctions between surface electrons  

Energy Technology Data Exchange (ETDEWEB)

In this paper, we discuss the interference patterns which appear in the local particle-density and particle-current distributions of two infinite 2D lattice systems of free fermions which are allowed to communicate via two tunneling junction points. The two fermion reservoirs are initially in different invariant states, and the particle-density and particle-current distributions are calculated in the final stationary state. The dependence of the interference pattern on the interaction details is discussed in several examples. (paper)

Angelescu, N; Bundaru, M [Institute for Physics and Nuclear Engineering ' H Hulubei' , PO Box MG-6, Bucharest (Romania); Bundaru, R; Popescu, I, E-mail: nangel@theory.nipne.ro, E-mail: bundaru@theory.nipne.ro, E-mail: bundaru@spacescience.ro [Institute for Space Sciences, PO Box MG-23, Bucharest (Romania)

2011-12-09

112

Interference effects at tunneling junctions between surface electrons  

International Nuclear Information System (INIS)

In this paper, we discuss the interference patterns which appear in the local particle-density and particle-current distributions of two infinite 2D lattice systems of free fermions which are allowed to communicate via two tunneling junction points. The two fermion reservoirs are initially in different invariant states, and the particle-density and particle-current distributions are calculated in the final stationary state. The dependence of the interference pattern on the interaction details is discussed in several examples. (paper)

113

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

Science.gov (United States)

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

Lee, Yen-Chi; Lin, Yong-Han; Wu, Jong-Ching; Lin, Juhn-Jong

2014-03-01

114

Electron-magnon coupling and non-linear tunneling transport in ferromagnetic nanoparticles  

CERN Document Server

We present a theory of single-electron tunneling transport through a ferromagnetic nanoparticle in which particle-hole excitations are coupled to spin collective modes. The model employed to describe the interaction between quasiparticles and collective excitations captures the salient features of a recent microscopic study. Our analysis of nonlinear quantum transport in the regime of weak coupling to the external electrodes is based on a rate-equation formalism for the nonequilibrium occupation probability of the nanoparticle many-body states. For strong electron-boson coupling, we find that the tunneling conductance as a function of bias voltage is characterized by a large and dense set of resonances. Their magnetic field dependence in the large-field regime is linear, with slopes of the same sign. Both features are in agreement with recent tunneling experiments.

Michalak, L; Benza, V G

2005-01-01

115

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

116

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

117

Quantum Tunneling Detection of Two-photon and Two-electron Processes  

OpenAIRE

We analyze the operation of a quantum tunneling detector coupled to a coherent conductor. We demonstrate that in a certain energy range the output of the detector is determined by two-photon processes, two-electron processes and the interference of the two. We show how the individual contributions of these processes can be resolved in experiments.

Tobiska, J.; Danon, J.; Snyman, I.; Nazarov, Yu V.

2005-01-01

118

Electronic spectrum and tunnelling properties of multi-wall carbon nanotubes  

CERN Document Server

We develop a general approach to calculations of the electron spectrum of metallic multi-wall carbon nanotubes (MWNT) with arbitrary number of coaxial layers. It is based on the model with singular attractive potential of equidistant conductive cylinders. The knowledge of one-electron spectrum allows to construct the corresponding Green function and then to calculate the entropy and density of states for MWNT. We analyze the tunnelling between the nanotube and normal metal electrode. The possibility of direct determination of one-electron density of states by measurements of the tunnelling conductivity at low temperatures is proved and the necessary restrictions on temperature are formulated. We discuss briefly the conflicting experimental observations of electronic properties of MWNT.

Abrikosov, A A; Varlamov, A A

2004-01-01

119

Pulse radiolysis study of electron tunneling in polar systems at low temperatures  

International Nuclear Information System (INIS)

The decay of captured electrons in alkaline ''glasses'' was studied by impulse radiolysis. The ''glasses'' represented frozen thin plates of NaOH aqueous solutions containing electron acceptors (CrO42-, NO3-, NO2- and Fe(CN)63-). A Y-12 linear accelerator served as the source of electron impulses (approximately 5 MeV). The captured electrons were recorded by a quick-action spectrophotometric apparatus. The decay rate of captured electrons was constant in a wide temperature range (from 77 to 150-180K) and was caused by remote (10-20 A) tunnel transfer of the electron to the acceptor. The kinetics of electron stabilization by environment may be described with account for the process of competitive capture of mobile electrons by environment and acceptor and by subsequent spontaneous decay of captured electrons

120

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)

121

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

OpenAIRE

We present an escape rate theory for current-induced chemical reactions. We use Keldysh nonequilibrium Green's functions to derive a Langevin equation for the reaction coordinate. Due to the out of equilibrium electronic degrees of freedom, the friction, noise, and effective temperature in the Langevin equation depend locally on the reaction coordinate. As an example, we consider the dissociation of diatomic molecules induced by the electronic current from a scanning tunnell...

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

2012-01-01

122

Pair-tunneling resonance in the single-electron transport regime  

OpenAIRE

We predict a new electron pair-tunneling (PT) resonance in non-linear transport through quantum dots with positive charging energies exceeding the broadening due to thermal and quantum fluctuations. The PT resonance shows up in the single-electron transport (SET) regime as a peak in the derivative of the non-linear conductance when the electrochemical potential of one electrode matches the average of two subsequent charge addition energies. For a single level quantum dot (An...

Leijnse, M.; Wegewijs, M. R.; Hettler, M. H.

2009-01-01

123

Dissociation of individual molecules with electrons from the tip of a scanning tunneling microscope.  

Science.gov (United States)

The scanning tunneling microscope (STM) can be used to select a particular adsorbed molecule, probe its electronic structure, dissociate the molecule by using electrons from the STM tip, and then examine the dissociation products. These capabilities are demonstrated for decaborane(14) (B(10)H(14)) molecules adsorbed on a silicon(111)-(7 x 7) surface. In addition to basic studies, such selective dissociation processes can be used in a variety of applications to control surface chemistry on the molecular scale. PMID:17816830

Dujardin, G; Walkup, R E; Avouris, P

1992-03-01

124

Self-excited Oscillations of Charge-Spin Accumulation Due to Single-electron Tunneling  

OpenAIRE

We theoretically study electronic transport through a layer of quantum dots connecting two metallic leads. By the inclusion of an inductor in series with the junction, we show that steady electronic transport in such a system may be unstable with respect to temporal oscillations caused by an interplay between the Coulomb blockade of tunneling and spin accumulation in the dots. When this instability occurs, a new stable regime is reached, where the average spin and charge in ...

Radic, Danko; Kadigrobov, Anatoly M.; Gorelik, Leonid Y.; Shekhter, Robert I.; Jonson, Mats

2010-01-01

125

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)

126

Electron transport simulation in resonant-tunneling GaN/AlGaN heterostructures  

Energy Technology Data Exchange (ETDEWEB)

A numerical method for electron transport calculations in resonant-tunneling GaN/AlGaN heterostructures has been developed on the basis of a self-consistent solution of the Schroedinger and Poisson equations. Dependences of the system's transmission coefficient on the external field and of the peak current on the ratio between the well and barrier widths have been studied for a double-barrier resonant-tunneling diode. For technical applications, the optimal values of the structure's parameters have been found.

Egorkin, V. I., E-mail: egor@qdn.miee.ru; Zhuravlev, M. N. [Moscow State Institute of Electronic Engineering (Technical University) (Russian Federation); Kapaev, V. V. [Russian Academy of Sciences, Lebedev Physical Institute (Russian Federation)

2011-12-15

127

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

128

Inelastic electron tunneling via molecular vibrations in single-molecule transistors.  

Science.gov (United States)

In single-molecule transistors, we observe inelastic cotunneling features that correspond energetically to vibrational excitations of the molecule, as determined by Raman and infrared spectroscopy. This is a form of inelastic electron tunneling spectroscopy of single molecules, with the transistor geometry allowing in situ tuning of the electronic states via a gate electrode. The vibrational features shift and change shape as the electronic levels are tuned near resonance, indicating significant modification of the vibrational states. When the molecule contains an unpaired electron, we also observe vibrational satellite features around the Kondo resonance. PMID:15698003

Yu, L H; Keane, Z K; Ciszek, J W; Cheng, L; Stewart, M P; Tour, J M; Natelson, D

2004-12-31

129

Inelastic electron tunneling via molecular vibrations in single-molecule transistors  

CERN Document Server

In single-molecule transistors, we observe inelastic cotunneling features that correspond energetically to vibrational excitations of the molecule, as determined by Raman and infrared spectroscopy. This is a form of inelastic electron tunneling spectroscopy of single molecules, with the transistor geometry allowing in-situ tuning of the electronic states via a gate electrode. The vibrational features shift and change shape as the electronic levels are tuned near resonance, indicating significant modification of the vibrational states. When the molecule contains an unpaired electron, we also observe vibrational satellite features around the Kondo resonance.

Yu, L H; Ciszek, J W; Cheng, L; Stewart, M P; Tour, J M; Natelson, D

2004-01-01

130

Symmetry-dependent electron-electron interaction in coherent tunnel junctions resolved by measurements of zero-bias anomaly  

Science.gov (United States)

We provide conclusive experimental evidence that zero-bias anomaly in the differential resistance of magnetic tunnel junctions is due to electron-electron interaction (EEI), clarifying a longstanding issue. The magnon effect that caused confusion is now excluded by measuring at low temperatures down to 0.2 K and with reduced ac measurement voltages down to 0.06 mV. The normalized change of conductance is proportional to ln(e V /kBT ) , consistent with the Altshuler-Aronov theory of tunneling that describes the reduction of density of states due to EEI, but inconsistent with magnetic impurity scattering. The slope of the ln(e V /kBT ) dependence is symmetry dependent: the slopes for parallel and antiparallel states are different for coherent tunnel junctions with symmetry filtering, while nearly the same for those without symmetry filtering (amorphous barriers). This observation may be helpful for verifying symmetry-preserved filtering in search of new coherent tunneling junctions, and for probing and separating electron Bloch states of different symmetries in other correlated systems.

Liu, Liang; Niu, Jiasen; Xiang, Li; Wei, Jian; Li, D.-L.; Feng, J.-F.; Han, X.-F.; Zhang, X.-G.; Coey, J. M. D.

2014-11-01

131

A theory of redox-mediated electron tunneling through an electrochemical two-center contact  

International Nuclear Information System (INIS)

The dependences of the tunnel current on the overpotential and bias voltage for a symmetric electrochemical contact involving two redox groups are calculated. The main physical situations involving various combinations of the strengths of the electronic coupling of the redox groups with each other and with the electrodes are considered in detail. The treatment is more rigorous and complete as compared with previous work. In particular, totally adiabatic transitions are discussed and the potential distribution in the tunnel gap is taken into account. It is shown that the system under consideration manifests negative differential resistance and rectification. A new effect is predicted in the current/overpotential dependence, namely the appearance of two maxima. The experimental data of (Tran et al 2006 Faraday Discuss. 131 197) are addressed. It is concluded that they are compatible with the assumption on a strong screening of the electric potential within the tunnel gap

132

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

Scientific Electronic Library Online (English)

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

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

2002-06-01

133

Qualification of electronic components and systems in a LHC Tunnel Radiation Environment  

CERN Document Server

Around 10.200 electronic crates will be installed in the LHC underground areas of which some 4.200 will be connected to the machine control network. Some of the electronic equipment will be housed under the cryostats of the main dipoles inside the tunnel. Other equipment will be placed alongside the tunnel, in the alcoves or in galleries parallel to the machine. In the regular arcs and in the dispersion suppressors areas the expected annual dose is low, i.e. only a few Gy/y. However, preliminary radiation tests showed that electronic equipment fails even at such low dose rates. Since radiation qualification of all tunnel electronics is essential in order to guarantee its reliable operation over the lifetime of the machine, a LHC radiation test facility was commissioned in the North Experimental Area of the SPS accelerator. This paper presents the simulation study concerning the radiation environment of the LHC Radiation Test Facility and gives an overview of the various underground electronic systems as they ...

Rausch, R; Wijnands, Thijs

2002-01-01

134

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

International Nuclear Information System (INIS)

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

135

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

International Nuclear Information System (INIS)

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

136

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

2012-03-01

137

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

138

Single-electron tunneling in InP nanowires  

CERN Document Server

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

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

2003-01-01

139

Electronic coolers based on superconducting tunnel junctions: fundamentals and applications  

OpenAIRE

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

Courtois, Herve?; Hekking, Frank W. J.; Nguyen, Hung Q.; Winkelmann, Clemens

2014-01-01

140

Infrared catastrophe and tunneling into strongly correlated electron systems: Beyond the x-ray edge limit  

CERN Document Server

We develop a nonperturbative method to calculate the electron propagator in low-dimensional and strongly correlated electron systems. The method builds on our earlier work using a Hubbard-Stratonovich transformation to map the tunneling problem to the x-ray edge problem, which accounts for the infrared catastrophe caused by the sudden introduction of a new electron into a conductor during a tunneling event. Here we use a cumulant expansion to include fluctuations about this x-ray edge limit. We find that the dominant effect of electron-electron interaction at low energies is to correct the noninteracting Green's function by a factor exp(-S), where S can be interpreted as the Euclidean action for a density field describing the time-dependent charge distribution of the newly added electron. Initially localized, this charge distribution spreads in time as the electron is accommodated by the host conductor, and during this relaxation process action is accumulated according to classical electrostatics with a scree...

Patton, K R; Patton, Kelly R.; Geller, Michael R.

2005-01-01

141

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 cantly 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

142

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

International Nuclear Information System (INIS)

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

143

Local 2D-2D tunneling in high mobility 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) [1,2] as the influence of the scanning gate is analogous to an STM tip, except at a GaAs/AlGaAs interface instead of a surface. We will discuss the spectroscopic capabilities of the technique, and show preliminary results of measurements on a high mobility 2D electron system.[1] A. Sciambi, M. Pelliccione et al., Appl. Phys. Lett. 97, 132103 (2010).[2] A. Sciambi, M. Pelliccione et al., Phys. Rev. B 84, 085301 (2011).

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

2012-02-01

144

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

145

Quantum discreteness and fundamental 1/f noise in tunnel junctions, nano-composites and other many-electron systems  

OpenAIRE

It is shown, with citing tunnel junction as an example, that mutual interplay of electron quantum transfers in a conducting system can be the fast mechanism for generation fundamental low-frequency flicker conductance fluctuations (1/f noise) without composing Lorentzians. This effect is lost in a theory which neglects the actual discreteness of electron energy levels. The analytical estimates of fluctuations of tunnel conductance are obtained, and the strong 1/f-noise sensi...

Kuzovlev, Yu E.; Medvedev, Yu V.; Grishin, A. M.

2000-01-01

146

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

International Nuclear Information System (INIS)

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

147

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

148

Probing flexible conformations in molecular junctions by inelastic electron tunneling spectroscopy  

Directory of Open Access Journals (Sweden)

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

Mingsen Deng

2015-01-01

149

Probing flexible conformations in molecular junctions by inelastic electron tunneling spectroscopy  

Science.gov (United States)

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

Deng, Mingsen; Ye, Gui; Cai, Shaohong; Sun, Guangyu; Jiang, Jun

2015-01-01

150

Dysprosium disilicide nanostructures on silicon(001) studied by scanning tunneling microscopy and transmission electron microscopy  

International Nuclear Information System (INIS)

The microstructure of self-assembled dysprosium silicide nanostructures on silicon(001) has been studied by scanning tunneling microscopy and transmission electron microscopy. The studies focused on nanostructures that involve multiple atomic layers of the silicide. Cross-sectional high resolution transmission electron microscopy images and fast Fourier transform analysis showed that both hexagonal and orthorhombic/tetragonal silicide phases were present. Both the magnitude and the anisotropy of lattice mismatch between the silicide and the substrate play roles in the morphology and epitaxial growth of the nanostructures formed

151

Quantum chaotic tunneling in graphene systems with electron-electron interactions  

Science.gov (United States)

An outstanding and fundamental problem in contemporary physics is to include and probe the many-body effect in the study of relativistic quantum manifestations of classical chaos. We address this problem using graphene systems described by the Hubbard Hamiltonian in the setting of resonant tunneling. Such a system consists of two symmetric potential wells separated by a potential barrier, and the geometric shape of the whole domain can be chosen to generate integrable or chaotic dynamics in the classical limit. Employing a standard mean-field approach to calculating a large number of eigenenergies and eigenstates, we uncover a class of localized states with near-zero tunneling in the integrable systems. These states are not the edge states typically seen in graphene systems, and as such they are the consequence of many-body interactions. The physical origin of the non-edge-state type of localized states can be understood by the one-dimensional relativistic quantum tunneling dynamics through the solutions of the Dirac equation with appropriate boundary conditions. We demonstrate that, when the geometry of the system is modified to one with chaos, the localized states are effectively removed, implying that in realistic situations where many-body interactions are present, classical chaos is capable of facilitating greatly quantum tunneling. This result, besides its fundamental importance, can be useful for the development of nanoscale devices such as graphene-based resonant-tunneling diodes.

Ying, Lei; Wang, Guanglei; Huang, Liang; Lai, Ying-Cheng

2014-12-01

152

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

153

Prototype spin-dependent tunneling isolators integrated with integrated circuit electronics  

Science.gov (United States)

Low power, fast speed, small size, wide temperature range, and common-mode-noise-rejection capability are some of the attributes of magnetoresistive devices for galvanic isolation over conventional devices such as optical and capacitive devices. We have fabricated prototype galvanic isolators using spin-dependent tunneling materials. The tunnel junctions have been deposited by rf diode sputtering and the Al2O3 barriers are formed by depositing a thin layer of Al, then oxidizing it with oxygen contained plasma. The junctions are then patterned using photolithography techniques to define the pinned and free layers separately. A series of tunnel junctions are connected in a Wheatstone bridge form and are fabricated directly on top of the integrated circuit (IC) electronics that are used to process the signals from the bridge. In its core magnetics design, this digital device simply employs a one-bit memory cell capable of operating at 5 V. The functions of the devices are tested using a function generator, an IC driver chip, a probe station, two dc power supplies, and a high-speed network analyzer. The power consumption for the isolator is device reaches 60 MHz, limited by the design of the electronics.

Wang, Dexin; Tondra, Mark; Nordman, Cathy; Qian, Zhenghong; Daughton, James M.; Lange, Erik; Brownell, David; Tran, Loc; Schuetz, James

2002-05-01

154

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

DEFF Research Database (Denmark)

We present an analytical theory for electron flow through a molecule with several redox levels, enclosed between a pair of metallic electrodes. The levels can be electronic or electronic-vibrational levels. Vibrational energy spacing characterises the latter sets. The levels are further coupled to environmental nuclear motion. Cryogenic temperatures are considered. This implies that thermal activation is disregarded but vibrational relaxation in the molecular charge states is central. The electrochemical potentials of the electrodes are controlled relative to a reference electrode. The electrodes represent the substrate and tip in electrochemical in situ scanning tunnelling microscopy. An equivalent three-electrode configuration represents a molecular single-electron transistor in which the enclosing electrodes constitute source and drain, and the reference electrode the gate. Current-bias voltage relations at fixed electrochemical overpotential or gate voltage, and current-overpotential or current-gate voltage relations at fixed bias voltage are equivalent in the two systems. Due to the activation-less nature of the processes, electron flow between the electrodes through the molecular redox levels can be only achieved when the latter are located between the Fermi levels of the substrate and tip or source and drain electrodes. The redox levels can be brought into this "energy window", either by the overpotential or bias and gate voltages, or by vibrational relaxation of (a) given (set of) redox level(s) subsequent to electron transfer. Several physical mechanisms can be distinguished and distinctive current-overpotential/gate voltage or current-bias voltage relations obtained. These reflect electronic level separation, environmental nuclear reorganisation, and coherent or incoherent multi-electron flow. The models and formalism have bearings on construction of single-molecule devices, illustrated by a short discussion of single-electron tunnelling in semiconductor quantum dots and reported low-temperature single-molecular transistor effects.

Kuznetsov, A.M.; Ulstrup, Jens

2004-01-01

155

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 samnsport 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)

156

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

International Nuclear Information System (INIS)

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

157

Electron-phonon interaction function by numerical analysis of superconducting tunnelling experimental data  

Energy Technology Data Exchange (ETDEWEB)

A new method of numerical analysis is presented which allows the determination of the electron-phonon interaction function ..cap alpha../sup 2/(..omega..)F(..omega..) using the experimental data obtained from a superconducting tunnel junction. This method utilizes the dispersion relation for ..delta..(..omega..) (complex energy gap function) proposed by Galkin, D'yachenko and Svistunov. The method and the hypotheses which allow the numerical solution of the first-kind integral equation derived from the Eliashberg equations are shown and discussed. ..delta..(..omega..) and ..cap alpha../sup 2/(..omega..)F(..omega..) of Pb are obtained by applying this method to the tunnel data of an Al-Al/sub 2/O/sub 3/-Pb (superconducting electrode) junction. The results are discussed with particular reference to the stability and convergence of the method applied.

Burrafato, G.; Mancini, N.A.; Troja, S.O. (Catania Univ. (Italy). Ist. di Fisica; Consiglio Nazionale delle Ricerche, Catania (Italy). Gruppo Nazionale di Struttura della Materia; Centro Siciliano di Fisica Nucleare e Struttura della Materia, Catania (Italy); Centro Universitario di Microscopia Elettronica, Catania (Italy))

158

Electron-Phonon Interaction Function by Numerical Analysis of Superconducting Tunneling Experimental Data  

International Nuclear Information System (INIS)

A new method of numerical analysis is presented which allows the determination of the electron-phonon interaction function ?2(?)F(?) using the experimental data obtained from a superconducting tunnel junction. This method utilizes the dispersion relation for ?(?) (complex energy gap function) proposed by Galkin, D'yachenko and Svistunov. The method and the hypotheses which allow the numerical solution of the first-kind integral equation derived from the Eliashberg equations are shown and discussed. ?(?) and ?2(?)F(?) of Pb are obtained by appling this method to the tunnel data of an Al-Al2O3-Pb (superconducting electrode) junction. The results are discussed with particular reference to the stability and convergence of the method applied

159

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

CERN Document Server

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

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

2014-01-01

160

Resonant tunneling and Fano resonance in quantum dots with electron-phonon interaction  

CERN Document Server

We theoretically study the resonant tunneling and Fano resonance in quantum dots with electron-phonon (e-ph) interaction. We examine the bias-voltage ($V$) dependence of the decoherence, using Keldysh Green function method and perturbation with respect to the e-ph interaction. With optical phonons of energy $\\omega_0$, only the elastic process takes place when $eV\\omega_0$, the inelastic process is possible which is accompanied by real emission of phonons. It results in the dephasing and broadens the resonant width. The bias-voltage dependence of the decoherence cannot be obtained by the canonical transformation method to consider the e-ph interaction if its effect on the tunnel coupling is neglected. With acoustic phonons, the asymmetric shape of the Fano resonance grows like a symmetric one as the bias voltage increases, in qualitative accordance with experimental results.

Ueda, A; Eto, Mikio; Ueda, Akiko

2006-01-01

161

Injection and trapping of tunnel-ionized electrons into laser-produced wakes.  

Science.gov (United States)

A method, which utilizes the large difference in ionization potentials between successive ionization states of trace atoms, for injecting electrons into a laser-driven wakefield is presented. Here a mixture of helium and trace amounts of nitrogen gas was used. Electrons from the K shell of nitrogen were tunnel ionized near the peak of the laser pulse and were injected into and trapped by the wake created by electrons from majority helium atoms and the L shell of nitrogen. The spectrum of the accelerated electrons, the threshold intensity at which trapping occurs, the forward transmitted laser spectrum, and the beam divergence are all consistent with this injection process. The experimental measurements are supported by theory and 3D OSIRIS simulations. PMID:20366604

Pak, A; Marsh, K A; Martins, S F; Lu, W; Mori, W B; Joshi, C

2010-01-15

162

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)

163

Correlation between polarity of magnetoresistance ratio and tunnel resistance in ferromagnetic single-electron transistor with superconductive island  

Science.gov (United States)

We report on the correlation between the polarity of magnetoresitance ratios and the tunnel resistance observed in ferromagnetic single-electron transistors with a superconductive island (FM-SC-FM SETs). Negative magnetoresistance ratios are observed at approximately the superconductive gap voltages, which indicates that an excessive number of spin-polarized quasiparticles accumulated in a superconductive island suppress the superconductive gaps. Since the spin polarization in a superconductor decays with time, the spin injection rate should be high enough to observe the suppression of superconductive gaps. The spin injection rate at a certain bias voltage is inversely proportional to the tunnel resistance; hence, the polarity of magnetoresistance ratio should correlate with the tunnel resistance. We fabricated 26 FM-SC-FM SETs. Samples having tunnel resistances lower than 100 k? exhibited negative magnetoresistance ratios, while samples having tunnel resistances higher than 600 k? exhibited positive magnetoresistance ratios.

Takiguchi, Masashi; Shimada, Hiroshi; Mizugaki, Yoshinao

2014-04-01

164

Estimation of the radiation dose to the electronic equipment inside the B - factory ring tunnel  

International Nuclear Information System (INIS)

The B - factory is a new, future high energy physics project at SLAC that utilizes an existing tunnel to house two accelerator storage rings; a positron ring (4 GeV, called LER) atop an electron ring ( 10 GeV, called HER). Both rings have a circulating current of 3 A, corresponding to a beam particle number of 1.38 x 10 sup 1 sup 4. Interest was expressed to place electronic equipment inside the tunnel for cost reasons. Estimation of the radiation dose that may damage the electronics was therefore made at a few locations. An analytical SHIELD 11 code was used to calculate the dose from high energy photon and neutron radiation resulting from various beam loss scenarios, which include normal stored beam, injection and unusual operations. The EGS4 Monte Carlo code was used to calculate the dose from the synchrotron radiation escaping the vacuum chambers. The synchrotron radiation doses from two different LER designs were studied : a 0.35 cm thick copper wall vacuum chamber and a 1 cm thick aluminum chamber with a copper mask 6 m downstream of the bending magnet to absorb the synchrotron radiation locally. The HER design was a 0.5 cm thick copper chamber. No bending magnet structure shielding was assumed for LER while a C - shape iron bending magnet was used for HER. In addition, the dose from the radiation ( photon, neutron, and synchrotron radiation) scattering back from the concrete tunnel wall was also estimated with albedo method, which was derived from the MORSE runthod, which was derived from the MORSE runs. The results showed that a location between the HER and the floor has a dose level of 3 Gy y sup -1 , which makes it the most suitable location for the electronic equipment with a damage threshold of Gy y sup-1. Other results and discussions will be given. 1 fig; 2 tabs; 2 refs (author)

165

Assessment of field-induced quantum confinement in heterogate germanium electron–hole bilayer tunnel field-effect transistor  

International Nuclear Information System (INIS)

The analysis of quantum mechanical confinement in recent germanium electron–hole bilayer tunnel field-effect transistors has been shown to substantially affect the band-to-band tunneling (BTBT) mechanism between electron and hole inversion layers that constitutes the operating principle of these devices. The vertical electric field that appears across the intrinsic semiconductor to give rise to the bilayer configuration makes the formerly continuous conduction and valence bands become a discrete set of energy subbands, therefore increasing the effective bandgap close to the gates and reducing the BTBT probabilities. In this letter, we present a simulation approach that shows how the inclusion of quantum confinement and the subsequent modification of the band profile results in the appearance of lateral tunneling to the underlap regions that greatly degrades the subthreshold swing of these devices. To overcome this drawback imposed by confinement, we propose an heterogate configuration that proves to suppress this parasitic tunneling and enhances the device performance.

166

Assessment of field-induced quantum confinement in heterogate germanium electron–hole bilayer tunnel field-effect transistor  

Energy Technology Data Exchange (ETDEWEB)

The analysis of quantum mechanical confinement in recent germanium electron–hole bilayer tunnel field-effect transistors has been shown to substantially affect the band-to-band tunneling (BTBT) mechanism between electron and hole inversion layers that constitutes the operating principle of these devices. The vertical electric field that appears across the intrinsic semiconductor to give rise to the bilayer configuration makes the formerly continuous conduction and valence bands become a discrete set of energy subbands, therefore increasing the effective bandgap close to the gates and reducing the BTBT probabilities. In this letter, we present a simulation approach that shows how the inclusion of quantum confinement and the subsequent modification of the band profile results in the appearance of lateral tunneling to the underlap regions that greatly degrades the subthreshold swing of these devices. To overcome this drawback imposed by confinement, we propose an heterogate configuration that proves to suppress this parasitic tunneling and enhances the device performance.

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

2014-08-25

167

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

168

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

169

Light emission induced by tunneling electrons from surface nanostructures observed by novel conductive and transparent probes.  

Science.gov (United States)

We have developed an ultrahigh-vacuum low-temperature scanning tunneling microscope (STM) equipped with a near-field optical detection system using novel conductive and optically transparent probes. Tunneling-electron induced photons generated in a nanometer-scale area just under the STM probe can be collected directly into the core of the optical fiber probe within the optical near-field region. Firstly, optical fiber probes coated with indium-tin-oxide thin film are applied to quantitative analysis of p-type GaAs(110) surface, where a decrease of light emission in photon mapping clearly extracts the existence of Zn accepter atoms located at the sub-surface layers. Secondly, in order to enhance the efficiency for inelastic tunneling excitation of a tip-induced plasmon mode, a STM probe coated with an Ag/ITO dual-layer film has been developed and applied to an Ag(111) surface, where photon mapping with a step resolution has been achieved by near-field detection. PMID:15549699

Fujita, Daisuke; Onishi, Keiko; Niori, Noriko

2004-08-01

170

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

171

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

172

Correlation - Function Analysis of Coupled Electron - Phonon Systems: Signatures of Polaron Tunneling  

International Nuclear Information System (INIS)

Intrinsic 'local textures' are becoming a leitmotiv of complex electronic materials, including high-Tc superconductors. Here we discuss signatures of nonlinear dynamics in the context of small polarons through various correlation functions which measure correlated structural and optical properties of a system. It is shown that energy-resolved correlation functions can be used to probe length and time scales in a unique fashion. These methods are applied to a polaron-tunneling problem which not only serves as a prototype for nonlinear and nonadiabatic behaviour in the presence of coupled electronic and lattice degrees of freedom, but may also be relevant to discraibing aspects of local electronic and structural dynamics in high-Tc superconducting materials. (author)

173

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

CERN Document Server

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

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

2005-01-01

174

A hybrid instrument combining electronic and photonic tunnelling for surface analysis  

International Nuclear Information System (INIS)

A PSTM working in the collection mode and based on an STM probe-sample regulation scheme has been developed. This original hybrid instrument for surface analysis uses apertureless metal-coated chemically etched optical fibres. The use of an electronic tunnelling-based feedback loop significantly reduces tip-sample distance and leads to the collection of a high level near-field optical (NFO) signal. A simple amplified photodiode is thus used to perform optical signal acquisition and to draw electromagnetic field maps of sample surfaces. Experimental results on nanostructured gold surfaces are presented

175

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

176

Transverse Pseudospin Susceptibility and Tunneling Parameters of Double Layer Electron Gas Systems  

CERN Document Server

The subbands of weakly coupled double-layer two dimensional electron gas systems consist of narrowly spaced pairs whose corresponding wavefunctions are symmetric and antisymmetric combinations of isolated layer subband wavefunctions. The energetic spacing within a pair is 2t where t is the interlayer tunneling amplitude. t is an important parameter in modeling these systems and, if interactions could be neglected, it would be proportional to beating frequencies seen in weak-field magnetic oscillations experiments and therefore readily measurable. We point out that interactions alter the beating frequency. We discuss similarities and differences between this effect and exchange-correlation enhanced spin-splitting.

Swierkowski, L

1996-01-01

177

Electron tunneling study of the superconducting proximity effect in Pb--Cd  

Energy Technology Data Exchange (ETDEWEB)

We show that the recent experimental data of Toplicar and Finnemore on the superconducting proximity effect in Pb--Cd thin films can be understood within the McMillan tunneling model by using our new transition temperature (T/sub c/) formula and determining the parameters self-consistently. Agreement between the theoretical and the experimental values of T/sub c/, the gap, and the general shape and the height of the electronic density of state N/sub S/(E) curves is very good. In agreement with experiment, we find no low-energy peak in the density of states.

Mohabir, S.; Nagi, A.D.S.

1979-09-01

178

Transport of electrons in the tunnel of an ion sensitive probe.  

Czech Academy of Sciences Publication Activity Database

Ro?. 53, ?. 1 (2011), 015005-015005. ISSN 0741-3335 R&D Projects: GA AV ?R KJB100430901; GA MŠk 7G09042; GA MŠk LA08048 Institutional research plan: CEZ:AV0Z20430508 Keywords : Tokamak * plasma * katsumata probe * ExB drift * ion temperature * tunnel * electron Subject RIV: BL - Plasma and Gas Discharge Physics Impact factor: 2.425, year: 2011 http://iopscience.iop.org/0741-3335/53/1/015005/pdf/0741-3335_53_1_015005.pdf

Komm, Michael; Adámek, Ji?í; Dejarnac, Renaud; Gunn, J. P.; Pekárek, Z.

2011-01-01

179

Ballistic electron magnetic microscopy: Hot-electron transport studies and magnetic imaging of ferromagnetic multilayer films, nanostructures, and tunnel junctions  

Science.gov (United States)

This dissertation describes the development of a new magnetic imaging technique, ballistic electron magnetic microscopy (BEMM), and its application to thin ferromagnetic films. Using this technique, the magnetic behavior of both continuous and patterned ferromagnetic multilayer films has been studied as a function of applied magnetic field. The typical domain size in these thin films is found to be ˜500--1000 nm, although much smaller magnetic structures are commonly observed. It is demonstrated that the switching of magnetic nanostructures can generally be controlled by applying modest magnetic fields, although occasionally the reversal process is hindered by the formation of 360° domain walls in the interiors of the elements. Thermally assisted domain wall motion is also found to play a role in the magnetization reversal process, particularly in permalloy nanostructures. The hot-electron scattering properties of thin Co and permalloy films have also been studied. Specifically, the inelastic scattering lengths of both majority and minority electrons in Co have been determined as a function of electron energy over the range of 1.0 to 2.0 eV above the Fermi energy. The cumulative spin-filtering effects of spin-dependent tunneling to Co and subsequent transmission across a Co/Cu interface have been measured over this same energy range. Studies on films prepared both by thermal evaporation and sputter deposition have been performed. While the magnetic behavior of the films prepared by the two different deposition methods has been found to be very similar, the details of current transport in films prepared by the two techniques are distinctly different. Electron transport through thin AlOx based magnetic tunnel junctions has also been studied at the nanometer length scale. The effective barrier height of these insulating barriers has been determined to be 1.25 +/- 0.5 eV. The transmission probability of hot electrons through these barriers has also been measured. Tunnel junctions prepared by thermal evaporation and sputter deposition are compared. While the effective barrier height of junctions formed by the two techniques are very similar, the electron transmission probabilities through the two types of barriers are different.

Rippard, William Horrocks

180

Quantum Tunneling  

Science.gov (United States)

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

The Concord Consortium

2011-12-11

181

Electron tunneling into surface states through an inhomogeneous barrier: asymptotically exact solution of the problem and STM theory  

International Nuclear Information System (INIS)

We have found an asymptotically exact solution of the Schrodinger equation for electrons tunneling into surface states through an inhomogeneous barrier of large amplitude. Assuming an elliptic dispersion law for the charge carriers the 'standing wave' pattern in the conductance of the system resulting from the electron scattering by a single defect in the vicinity of the surface is analyzed.

182

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)

183

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

International Nuclear Information System (INIS)

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

184

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

Science.gov (United States)

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 Å, we adopt a theoretical model that treats nanometer-size features and/or subnanometer-size gaps or spacers by taking into account (i) the limits imposed by atomic size to fulfill the requirements of continuum electrodynamics, (ii) spillage of the nearly free electron cloud into the surrounding vacuum, and (iii) the increased probability of quantum tunneling as objects are placed in close proximity. Our approach also includes the treatment of bound charges, which add crucial, dynamical components to the dielectric constant that are neglected in the conventional hydrodynamic model, especially in the visible and UV ranges, where interband transitions are important. The model attempts to inject into the classical electrodynamic picture a simple, perhaps more realistic description of the metal surface by incorporating a thin patina of free electrons that screens an internal, polarizable medium.

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

2014-07-01

185

Electronic band dispersion of graphene nanoribbons via Fourier-transformed scanning tunneling spectroscopy  

Science.gov (United States)

The electronic structure of atomically precise armchair graphene nanoribbons of width N =7 (7-AGNRs) are investigated by scanning tunneling spectroscopy (STS) on Au(111). We record the standing waves in the local density of states of finite ribbons as a function of sample bias and extract the dispersion relation of frontier electronic states by Fourier transformation. The wave-vector-dependent contributions from these states agree with density functional theory calculations, thus enabling the unambiguous assignment of the states to the valence band, the conduction band, and the next empty band with effective masses of 0.41 ±0.08 me ,0.40 ±0.18 me , and 0.20 ±0.03 me , respectively. By comparing the extracted dispersion relation for the conduction band to corresponding height-dependent tunneling spectra, we find that the conduction band edge can be resolved only at small tip-sample separations and has not been observed before. As a result, we report a band gap of 2.37 ±0.06 eV for 7-AGNRs adsorbed on Au(111).

Söde, Hajo; Talirz, Leopold; Gröning, Oliver; Pignedoli, Carlo Antonio; Berger, Reinhard; Feng, Xinliang; Müllen, Klaus; Fasel, Roman; Ruffieux, Pascal

2015-01-01

186

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

International Nuclear Information System (INIS)

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

187

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

Science.gov (United States)

The electron beam process has proved to be an efficient method for the removal of inorganic pollutants from flue gas. Since it simulates natural processes which occur in the atmospheric photochemistry, it appeared attractive to investigate the potential of the e-beam process to clean off-gases which contain hydrocarbon and inorganic trace components. Such emissions arise from industrial processes and from automobile tunnels. Commercial solvents were vaporized in air and irradiated with energetic electrons (300 keV). CO, CO 2 and aerosol particles were found as products and were determined quantitatively. The aerosol particles can be collected by a gravel bed filter and can be removed by combustion or biological degradation. From experiments and model calculations it was found that the e-beam process is a very economic tool to remove hydrocarbons from large off-gas volumes at initial concentrations of 50-100 mg C/m 3, and that NO x can be removed very efficiently from tunnel off-gas.

Paur, H.-R.; Mätzing, H.

1993-10-01

188

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.

189

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

Science.gov (United States)

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

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

2013-05-23

190

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.

191

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

Science.gov (United States)

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.

Baniassadi, M.; Safdari, M.; Ghazavizadeh, A.; Garmestani, H.; Ahzi, S.; Grácio, J.; Ruch, D.

2011-11-01

192

Time-dependent tunneling of spin-polarized electrons in coupled quantum wells  

International Nuclear Information System (INIS)

We have solved the in-plane momentum-dependent effective-mass nonlinear Schroedinger equation for a spin-polarized electron wave packet in a InAs double quantum well system with an interlayer voltage. Considering a time-dependent Hartree potential, we have calculated the spin-polarized nonlinear electron dynamics between both quantum wells at different in-plane momentum values and applied bias. The spin-splitting caused by the Rashba effect is combined with the level matching between the spin dependent resonant tunneling levels making possible the observed local spin density oscillations which depend on the applied bias value. The filtering efficiency has been studied using time-dependent calculations

193

Time-dependent tunneling of spin-polarized electrons in coupled quantum wells  

Energy Technology Data Exchange (ETDEWEB)

We have solved the in-plane momentum-dependent effective-mass nonlinear Schroedinger equation for a spin-polarized electron wave packet in a InAs double quantum well system with an interlayer voltage. Considering a time-dependent Hartree potential, we have calculated the spin-polarized nonlinear electron dynamics between both quantum wells at different in-plane momentum values and applied bias. The spin-splitting caused by the Rashba effect is combined with the level matching between the spin dependent resonant tunneling levels making possible the observed local spin density oscillations which depend on the applied bias value. The filtering efficiency has been studied using time-dependent calculations.

Cruz, H; Luis, D [Departamento de Fisica Basica, Universidad de La Laguna, 38204 La Laguna, Tenerife (Spain)], E-mail: hcruz@ull.es

2008-02-15

194

A Direct Probe of Electronic Nematic Order; Symmetry Information in Scanning Tunneling Microscope Images  

CERN Document Server

An electronic nematic state spontaneously breaks a point-group symmetry of an underlying lattice. As a result, the nematic-isotropic transition accompanies a Fermi surface distortion. However, the anisotropic nature of the nematic state at a macroscopic scale can be easily wiped out when domains of different orientations of nematic order exist. We suggest that a spatial pattern of local density of states (LDOS) in the presence of a non-magnetic impurity can be a direct probe of the nematic order. We study various patterns of LDOS across the quantum phase transition between the isotropic and nematic phases. Especially the Fourier transformed local density of states (FT-LDOS), which can be deduced from scanning tunneling microscope images, represent a transparent symmetry of an electronic structure. The application of our results to the bilayer ruthenate, Sr$_3$Ru$_2$O$_7$ is also discussed.

Doh, H; Doh, Hyeonjin; Kee, Hae-Young

2007-01-01

195

Conductance enhancement due to interface magnons in electron-beam evaporated MgO magnetic tunnel junctions with CoFeB free layer deposited at different pressure  

Energy Technology Data Exchange (ETDEWEB)

Electron-beam evaporated MgO-based magnetic tunnel junctions have been fabricated with the CoFeB free layer deposited at Ar pressure from 1 to 4?mTorr, and their tunneling process has been studied as a function of temperature and bias voltage. By changing the growth pressure, the junction dynamic conductance dI/dV, inelastic electron tunneling spectrum d{sup 2}I/dV{sup 2}, and tunneling magnetoresistance vary with temperature. Moreover, the low-energy magnon cutoff energy E{sub C} derived from the conductance versus temperature curve agrees with interface magnon energy obtained directly from the inelastic electron tunneling spectrum, which demonstrates that interface magnons are involved in the electron tunneling process, opening an additional conductance channel and thus enhancing the total conductance.

Guo, P.; Yu, G. Q.; Wei, H. X.; Han, X. F., E-mail: jiafengfeng@aphy.iphy.ac.cn, E-mail: xfhan@aphy.iphy.ac.cn [Beijing National Laboratory of Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences, Beijing 100190 (China); Li, D. L.; Feng, J. F., E-mail: jiafengfeng@aphy.iphy.ac.cn, E-mail: xfhan@aphy.iphy.ac.cn [Beijing National Laboratory of Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences, Beijing 100190 (China); CRANN and School of Physics, Trinity College, Dublin 2 (Ireland); Kurt, H. [CRANN and School of Physics, Trinity College, Dublin 2 (Ireland); Department of Engineering Physics, Istanbul Medeniyet University, 34720 Istanbul (Turkey); Chen, J. Y.; Coey, J. M. D. [CRANN and School of Physics, Trinity College, Dublin 2 (Ireland)

2014-10-21

196

Conductance enhancement due to interface magnons in electron-beam evaporated MgO magnetic tunnel junctions with CoFeB free layer deposited at different pressure  

Science.gov (United States)

Electron-beam evaporated MgO-based magnetic tunnel junctions have been fabricated with the CoFeB free layer deposited at Ar pressure from 1 to 4 mTorr, and their tunneling process has been studied as a function of temperature and bias voltage. By changing the growth pressure, the junction dynamic conductance dI/dV, inelastic electron tunneling spectrum d2I/dV2, and tunneling magnetoresistance vary with temperature. Moreover, the low-energy magnon cutoff energy EC derived from the conductance versus temperature curve agrees with interface magnon energy obtained directly from the inelastic electron tunneling spectrum, which demonstrates that interface magnons are involved in the electron tunneling process, opening an additional conductance channel and thus enhancing the total conductance.

Guo, P.; Li, D. L.; Feng, J. F.; Kurt, H.; Yu, G. Q.; Chen, J. Y.; Wei, H. X.; Coey, J. M. D.; Han, X. F.

2014-10-01

197

Application of the many-electron weak-field asymptotic theory of tunneling ionization to atoms  

Science.gov (United States)

The many-electron weak-field asymptotic theory (ME-WFAT) of tunneling ionization [Tolstikhin et al., Phys. Rev. A 89, 013421 (2014), 10.1103/PhysRevA.89.013421] is applied to atoms. The procedure to extract the asymptotic coefficient of a Dyson orbital needed to implement the ME-WFAT from many-electron wave functions given by a linear combination of Slater determinants composed of one-electron orbitals, as is typically the case in practical atomic structure calculations, is discussed. It is shown that in the one-configuration approximation such wave functions enable one to consistently implement the theory and calculate the ionization rate. The effect of relaxation of the ionic orbitals and the dependence of the rate on the total orbital momentum and spin states of the atom and ion are considered. However, wave functions constructed by mixing several electronic configurations, maybe more accurate in some sense, do not have the correct asymptotic behavior required for implementing the ME-WFAT. The theory is illustrated by calculations for atoms of the first three periods with the use of one-electron orbitals obtained by the Hartree-Fock method.

Tolstikhina, Inga Yu.; Morishita, Toru; Tolstikhin, Oleg I.

2014-11-01

198

Electrochemical quantum tunneling for electronic detection and characterization of biological toxins  

Science.gov (United States)

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

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

2012-06-01

199

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

International Nuclear Information System (INIS)

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

200

Insights into channel potentials and electron quasi-Fermi potentials for DG tunnel FETs  

Science.gov (United States)

A detailed investigation carried out, with the help of extensive simulations using the TCAD device simulator Sentaurus, with the aim of achieving an understanding of the effects of variations in gate and drain potentials on the device characteristics of a silicon double-gate tunnel field effect transistor (Si-DG TFET) is reported in this paper. The investigation is mainly aimed at studying electrical properties such as the electric potential, the electron density, and the electron quasi-Fermi potential in a channel. From the simulation results, it is found that the electrical properties in the channel region of the DG TFET are different from those for a DG MOSFET. It is observed that the central channel potential of the DG TFET is not pinned to a fixed potential even after the threshold is passed (as in the case of the DG MOSFET); instead, it initially increases and later on decreases with increasing gate voltage, and this is also the behavior exhibited by the surface potential of the device. However, the drain current always increases with the applied gate voltage. It is also observed that the electron quasi-Fermi potential (eQFP) decreases as the channel potential starts to decrease, and there are hiphops in the channel eQFP for higher applied drain voltages. The channel regime resistance is also observed for higher gate length, which has a great effect on the I–V characteristics of the DG TFET device. These channel regime electrical properties will be very useful for determining the tunneling current; thus these results may have further uses in developing analytical current models.

Menka; Bulusu, Anand; Dasgupta, S.

2015-01-01

201

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)

202

IRENA Resource [electronic resource] : your source for renewable energy information.  

International Nuclear Information System (INIS)

The International Renewable Energy Agency (IRENA) is an intergovernmental organisation that supports countries in their transition to a sustainable energy future, and serves as the principal platform for international cooperation, a centre of excellence, and a repository of policy, technology, resource and financial knowledge on renewable energy.

203

Chemical imaging of latent fingerprints by mass spectrometry based on laser activated electron tunneling.  

Science.gov (United States)

Identification of endogenous and exogenous chemicals contained in latent fingerprints is important for forensic science in order to acquire evidence of criminal identities and contacts with specific chemicals. Mass spectrometry has emerged as a powerful technique for such applications without any derivatization or fluorescent tags. Among these techniques, MALDI (Matrix Assisted Laser Desorption Ionization) provides small beam size but has interferences with MALDI matrix materials, which cause ion suppressions as well as limited spatial resolution resulting from uneven distribution of MALDI matrix crystals with different sizes. LAET (Laser Activated Electron Tunneling) described in this work offers capabilities for chemical imaging through electron-directed soft ionization. A special film of semiconductors has been designed for collection of fingerprints. Nanoparticles of bismuth cobalt zinc oxide were compressed on a conductive metal substrate (Al or Cu sticky tape) under 10 MPa pressure. Resultant uniform thin films provide tight and shining surfaces on which fingers are impressed. Irradiation of ultraviolet laser pulses (355 nm) on the thin film instantly generates photoelectrons that can be captured by adsorbed organic molecules and subsequently cause electron-directed ionization and fragmentation. Imaging of latent fingerprints is achieved by visualization of the spatial distribution of these molecular ions and structural information-rich fragment ions. Atomic electron emission together with finely tuned laser beam size improve spatial resolution. With the LAET technique, imaging analysis not only can identify physical shapes but also reveal endogenous metabolites present in females and males, detect contacts with prohibited substances, and resolve overlapped latent fingerprints. PMID:25647159

Tang, Xuemei; Huang, Lulu; Zhang, Wenyang; Zhong, Hongying

2015-03-01

204

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

205

Bulletin of entomological research [electronic resource].  

International Nuclear Information System (INIS)

A journal covering agricultural entomology, medical and veterinary entomology, biological control, stored products entomology, and natural resource management. Includes taxonomic papers when relevant.

206

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

International Nuclear Information System (INIS)

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

207

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

208

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

209

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.)

210

Theoretical studies of scanning tunneling microsopy and electron transport through nanostructures  

Science.gov (United States)

In this dissertation, we present several studies that employ density functional theory (DFT) to investigate physical principles underlying electron transport in nanostructures. Scanning tunneling microscopy and spectroscopy (STM/STS) experiments have been modeled using DFT calculations within the Tersoff-Hamann approximation, and the conductance and nonlinear I-V characteristics of several molecules have been studied using a method that combines the scattering-state formalism with DFT calculation techniques. We start with an introduction to density functional theory methods in Chapter One, followed by an application of these methods to study changes induced in boron nitride (BN) nanotubes under a transverse electric field in Chapter Two. Our calculations show that sufficiently strong fields can induce significant gap reduction and provide a way of tuning BN nanotube band gaps for applications. It was found that the band gap modulation increases with the nanotube diameter and is nearly independent of chirality. In Chapter Three, we performed DFT calculations to investigate recent scanning tunneling microscopy and spectroscopy (STM/STS) experiments performed on C60 monomers adsorbed on Au(111) and Ag(100) substrates. Our calculations demonstrated that resonances in the STS spectra of C60 on Au(III) and Ag(100) originate from C60 HOMO, LUMO, and LUMO+1 states, and that the STM tip trajectory plays an important role in determining the spatial inhomogeneities of dI/dV images. Continuing the theme of combined STM/DFT studies in Chapter Four, we carried out an investigation of the elastic and inelastic tunneling properties of Gd C82 monomers adsorbed on Ag(100). Measurements show the dominant inelastic channel to be spatially localized in a particular region of the molecule, and calculations indicate that this channel arises from a vibrational cage mode. The observed inelastic tunneling localization is then explained as a consequence of strong localization of the electron-phonon coupling to this mode. To calculate transport properties across non-equilibrium aperiodic systems, we developed a method that combines DFT calculation techniques with the scattering-state formalism in Chapter Five. The semi-infinite nature of the leads is accounted for by using scattering-state wavefunctions to represent electron states and the chemical potential difference between the leads is reproduced by introducing shifts in the bulk-lead Hartree potential corresponding to the applied bias. This scattering-state method was then applied in Chapter Six to investigate a recent negative differential resistance (NDR) measurement, postulated to originate from current carried by a carbon atomic wire bridging carbon nanotube leads. Our calculations show that such junctions exhibit NDR and display clear even-odd behavior in the size of their currents, lending support to the postulate of carbon chain mediated NDR. In Chapter Seven, we applied our scattering-state method to study electron transport across a single hydrogen molecule sandwiched between Pd and Pt contacts. Substituting Pt contacts with Pd is found to result in a dramatic reduction in conductance, consistent with two recent break junction experiments. The computed drop in conductance is explained in terms of a qualitative change in transport behavior between the two systems. (Abstract shortened by UMI.)

Khoo, Khoonghong

211

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

International Nuclear Information System (INIS)

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

212

A study of density measurements in hypersonic helium tunnels using an electron beam fluorescence technique  

Science.gov (United States)

A series of experiments have been conducted at Langley Research Center to determine the feasibility of using electron-beam fluorescence to measure the free-stream static density of gaseous helium flow over a wide range of conditions. These experiments were conducted in the Langley hypersonic helium tunnel facility and its 3-inch prototype. Measurements were made for a range of stagnation pressures and temperatures and produced free-stream number densities of 1.53 x 10 to the 23rd to 1.25 x 10 to the 24th molecules/cu m and static temperatures from 2 K to 80 K. The results showed the collision quenching cross section to be 4.4 x 10 to the -15th sq cm at 1 K and to have a weak temperature dependence of T to the 1/6. With knowledge of these two values, the free-stream number density can be measured quite accurately.

Honaker, W. C.; Hunter, W. W., Jr.; Woods, W. C.

1979-01-01

213

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

Science.gov (United States)

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

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

2013-03-01

214

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

215

Germanium electron–hole bilayer tunnel field-effect transistors with a symmetrically arranged double gate  

Science.gov (United States)

A germanium tunnel field-effect transistor (TFET) with a bias-induced electron–hole bilayer (EHB) with double gates that are symmetrically arranged and independently biased is simulated. The symmetric double gate scheme is feasible, presenting a simple EHB-TFET structure that is practicable for industrial fabrication. According to simulation results, the improvement of on/off current ratio of ?108 is achieved by inserting a lightly-doped drain-source (LDD) region. Also, fin-type EHB-TFETs show an extremely low average sub-threshold swing of 11 mV/decade over 4 decades at VDD = 0.5 V, and thus are suitable for ultra-low power applications.

Jeong, Woo Jin; Kim, Tae Kyun; Moon, Jung Min; Park, Min Gyu; Yoon, Young Gwang; Hwang, Byeong Woon; Choi, Woo Young; Shin, Mincheol; Lee, Seok-Hee

2015-03-01

216

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

Energy Technology Data Exchange (ETDEWEB)

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

2014-10-21

217

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

International Nuclear Information System (INIS)

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.

218

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

219

Resonant Tunnelling and Storage of Electrons in Si Nanocrystals within a-SiNx/nc-Si/a-SiNx Structures  

International Nuclear Information System (INIS)

The a-SiNx/nanocrystalline silicon (nc-Si)/a-SiNx sandwiched structures with asymmetric double-barrier are fabricated in a plasma enhanced chemical vapour deposition (PECVD) system on p-type Si substrates. The nc-Si layer in thickness 5nm is fabricated from a hydrogen-diluted silane gas by the layer-by-layer deposition technique. The thicknesses of tunnel and control SiNx layers are 3nm and 20nm, respectively. Frequency-dependent capacitance spectroscopy is used to study the electron tunnelling and the storage in the sandwiched structures. Distinct frequency-dependent capacitance peaks due to electrons tunnelling into the nc-Si dots and capacitance-voltage (C - V) hysteresis characteristic due to electrons storage in the nc-Si dots are observed with the same sample. Moreover, conductance peaks have also been observed at the same voltage region by conductance-voltage (G - V) measurements. The experimental results demonstrate that electrons can be loaded onto nc-Si dots via resonant tunnelling and can be stored in our a-SiNx/nc-Si/a-SiNx structures

220

Transverse electron momentum distribution in tunneling and over the barrier ionization by laser pulses with varying ellipticity  

CERN Document Server

We study transverse electron momentum distribution (TEMD) in strong field atomic ionization driven by laser pulses with varying ellipticity. We show, both experimentally and theoretically, that the TEMD in the tunneling and over the barrier ionization regimes evolves in a qualitatively different way when the ellipticity parameter describing polarization state of the driving laser pulse increases.

Ivanov, I A; Calvert, J E; Goodall, S; Wang, X; Xu, Han; Palmer, A J; Kielpinski, D; Litvinyuk, I V; Sang, R T

2015-01-01

221

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

222

Photo-catalytic Activities of Plant Hormones on Semiconductor Nanoparticles by Laser-Activated Electron Tunneling and Emitting.  

Science.gov (United States)

Understanding of the dynamic process of laser-induced ultrafast electron tunneling is still very limited. It has been thought that the photo-catalytic reaction of adsorbents on the surface is either dependent on the number of resultant electron-hole pairs where excess energy is lost to the lattice through coupling with phonon modes, or dependent on irradiation photon wavelength. We used UV (355?nm) laser pulses to excite electrons from the valence band to the conduction band of titanium dioxide (TiO2), zinc oxide (ZnO) and bismuth cobalt zinc oxide (Bi2O3)0.07(CoO)0.03(ZnO)0.9 semiconductor nanoparticles with different photo catalytic properties. Photoelectrons are extracted, accelerated in a static electric field and eventually captured by charge deficient atoms of adsorbed organic molecules. A time-of-flight mass spectrometer was used to detect negative molecules and fragment ions generated by un-paired electron directed bond cleavages. We show that the probability of electron tunneling is determined by the strength of the static electric field and intrinsic electron mobility of semiconductors. Photo-catalytic dissociation or polymerization reactions of adsorbents are highly dependent on the kinetic energy of tunneling electrons as well as the strength of laser influx. By using this approach, photo-activities of phytohormones have been investigated. PMID:25749635

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

2015-01-01

223

Photo-catalytic Activities of Plant Hormones on Semiconductor Nanoparticles by Laser-Activated Electron Tunneling and Emitting  

Science.gov (United States)

Understanding of the dynamic process of laser-induced ultrafast electron tunneling is still very limited. It has been thought that the photo-catalytic reaction of adsorbents on the surface is either dependent on the number of resultant electron-hole pairs where excess energy is lost to the lattice through coupling with phonon modes, or dependent on irradiation photon wavelength. We used UV (355 nm) laser pulses to excite electrons from the valence band to the conduction band of titanium dioxide (TiO2), zinc oxide (ZnO) and bismuth cobalt zinc oxide (Bi2O3)0.07(CoO)0.03(ZnO)0.9 semiconductor nanoparticles with different photo catalytic properties. Photoelectrons are extracted, accelerated in a static electric field and eventually captured by charge deficient atoms of adsorbed organic molecules. A time-of-flight mass spectrometer was used to detect negative molecules and fragment ions generated by un-paired electron directed bond cleavages. We show that the probability of electron tunneling is determined by the strength of the static electric field and intrinsic electron mobility of semiconductors. Photo-catalytic dissociation or polymerization reactions of adsorbents are highly dependent on the kinetic energy of tunneling electrons as well as the strength of laser influx. By using this approach, photo-activities of phytohormones have been investigated.

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

2015-03-01

224

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

International Nuclear Information System (INIS)

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

225

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

Science.gov (United States)

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

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

2014-05-27

226

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

OpenAIRE

The non-perturbation theory of electronic dynamic conductivity for open two-barrier resonance tunnel structure is established for the first time within the model of rectangular potentials and different effective masses of electrons in the elements of nano-structure and the wave function linear over the intensity of electromagnetic field. It is proven that the results of the theory of dynamic conductivity, developed earlier in weak signal approximation within the perturbation...

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

2012-01-01

227

Polarity Reversal of Tunnel Magnetoresistance Observed in Lateral Co-Al-Co Single-Electron Transistor  

Science.gov (United States)

Polarity reversal of tunnel magnetoresistance is a unique feature of double-tunnel-junction systems comprising a superconducting (SC) middle electrode sandwiched by two ferromagnetic (FM) outer electrodes. Yang et al. demonstrated a good agreement between experimental and theoretical tunnel magnetoresistance in vertically-stacked FM/SC/FM double tunnel junctions, in which the SC layer was 4.5-nm-thick Al. In this paper, we present the polarity reversal of tunnel magnetoresistance in Co-Al-Co double tunnel junctions, where two Co electrodes are laterally placed with spacing of 570?nm. The tunnel magnetoresistance is negative at the bias voltages near the SC gap voltage, whereas it is positive at higher bias voltages. The results demonstrate that the long spin lifetime in the SC Al electrode enables us to observe the spin accumulation even in the lateral structure.

Takiguchi, Masashi; Sato, Takayuki; Shimada, Hiroshi; Mizugaki, Yoshinao

228

Marine Environment Laboratories Monaco [electronic resource  

International Nuclear Information System (INIS)

A central facility for the collection, synthesis and interpretation of data on marine radioactivity in the world ocean. It stores all available data on marine radioactivity of seawater, sediments and biota. Please note: To access this resource contact the IAEA's Marine Environment Laboratories Monaco.

229

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

230

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 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

231

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.)

232

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

Directory of Open Access Journals (Sweden)

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

O.M. Voitsekhivska

2011-12-01

233

High-resolution microscopy of plasmon field distributions by scanning tunneling luminescence and photoemission electron microscopies  

Science.gov (United States)

The exploitation of plasmon resonances to promote the interaction between conjugated molecules and optical fields motivates intensive research. The objectives are to understand the mechanisms of plasmon-mediated interactions, and to realize molecularly- or atomically-precise metal nanostructures, combining field enhancements and optical antenna effects. In this review paper, we present examples of plasmonic-field mappings based on scanning tunneling microscope (STM)-induced light emission or multiphoton photoemission (PEEM), two techniques among those which offer today's best spatial resolutions for plasmon microscopy. An unfamiliar property of the junction of an STM is its ability to behave as a highly localized source of light. It can be exploited to probe optoelectronic properties, in particular plasmonic fields, with ultimate subnanometer spatial resolution, an advantage balanced by a sometimes delicate deconvolution of local-probe influence. Alternatively, local-probe disadvantages can be overcome by imaging the photoemitted electrons, using well-established electron optics. This allows obtaining two-dimensional intensity maps reflecting the unperturbed distribution of the optical near field. This approach provides full field spectroscopic images with a routine spatial resolution of the order of 20 nm (down to 5 nm with recent aberration corrected instruments).

Douillard, Ludovic; Charra, Fabrice

2012-10-01

234

Using Zapier with Trello for Electronic Resources Troubleshooting Workflow  

OpenAIRE

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

2014-01-01

235

Resource letter EPA-1: Electronic polymers and their applications  

Science.gov (United States)

This Resource Letter provides a guide to the literature on electronic polymers and their potential applications. Journal articles and books are cited for the following topics: (i) theories of the electronic structure and excited states of conjugated polymers, the role of electron-phonon and electron-electron interactions in determining these states, the mechanisms of charge transport, and the insulator-metal transition; (ii) information on the synthesis, structure, and morphology of representative polymers; (iii) results of transport, optical, and magnetic measurements on both conductive and semiconducting/insulating materials; and (iv) solid state device and other applications for conjugated polymers.

Blatchford, J. W.; Epstein, A. J.

1996-02-01

236

Single-electron charging effects and implications for tunneling measurements of the high-T/sub c/ superconductors  

International Nuclear Information System (INIS)

The authors present a theory for the dynamics of two voltage-biased, ultra-small-capacitance tunnel junctions connected in series when one or more electrodes are superconducting and experiments performed on parallel arrays of such junctions. Using the semiclassical model, they find that the I-V characteristics display steps and therefore multiple peaks in dI/dV, corresponding to the time-average occupation of the interjunction region by integral numbers of electrons. The voltage at which the first step is located depends on the superconducting gap, ?(T), and the capacitances of the junctions. The spacing between subsequent steps depends solely on the capacitances. They discuss electron tunneling results performed on metal/Al/sub 2/O/sub 3//2-10 nm-diameter metal particles/Al/sub 2/O/sub 3//metal junctions where this multiple-peak structure is observed. They present preliminary tunneling results in junctions employing Pb-particles, where they observe a shift of the peaks when the sample is cooled below T/sub c/ of Pb consistent with theory. Taken together, these results indicate that the multiple-peak structure commonly observed in tunneling data of high-T/sub c/ oxide superconductors can be explained in terms of charging effects in a material with a single superconducting gap. Finally, they discuss possible applications in a new type of transistor element

237

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

238

Biology Resources in the Electronic Age  

CERN Document Server

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

Bazler, Judith

2003-01-01

239

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

DEFF Research Database (Denmark)

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

Medvedev, Igor M.; Kuznetsov, Alexander M.

2009-01-01

240

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

Science.gov (United States)

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

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

2014-03-25

241

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

CERN Document Server

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

Iorsh, Ivan

2015-01-01

242

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

Science.gov (United States)

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

Yang, Zhichao; Zhang, Yuewei; Nath, Digbijoy N.; Khurgin, Jacob B.; Rajan, Siddharth

2015-01-01

243

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

Science.gov (United States)

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

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

2005-01-01

244

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.

245

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

OpenAIRE

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

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

2012-01-01

246

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.

247

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.

248

Scanning tunneling microscopy study of the electron transport properties of self-assembled monolayers of bis-phenyloxazoles  

Science.gov (United States)

The self-assembly and electron transport properties of monothiol-terminated bis-phenyloxazole molecules have been studied by scanning tunneling microscopy and spectroscopy. The molecules were deposited on a clean Au(111) surface from solution and were studied under vacuum. In the as-deposited state, no long-range ordering was present. Upon annealing, however, an ordered monolayer was observed, characterized by well-defined columnar structures. The height of the corrugations was compatible with molecules aligned normal to the surface. This structure is attributed to the orthogonal terphenyl arms in the cruciform species study, which act to inhibit the molecules from assuming a prone position.[1] Scanning tunneling spectroscopy revealed a relatively high conductance, as expected for the conjugated electron system. Threshold features in the I-V characteristics were observed, indicative of resonant tunneling processes. The electronic properties of the molecules will be discussed in the context of the HOMO-LUMO gap deduced from complementary optical absorption data. [1] J. E. Klare et al., JACS 125, 6030 (2003).

Park, Hayn; Lee, Whasil; Klare, Jennifer E.; Nuckolls, Colin; Heinz, Tony F.

2004-03-01

249

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

Science.gov (United States)

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

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

2015-02-01

250

Tunnel Diode Macro-model in the Electronic Circuits Modeling Systems  

Directory of Open Access Journals (Sweden)

Full Text Available Introduction. The circuit simulation programs that are currently in use do not have tunnel diodes macro-models in their standard libraries. So it is important to create and examine a circuit diagram of tunnel diode macro-model, because tunnel diodes are often used for oscillators and amplifiers developing. Theoretical statement. The tunnel diodes macro-models are based on current / voltage characteristics that correspond to the real static characteristics and parameters. The static current/voltage characteristic of the device is defined by coordinates in characteristic points and contains a region of negative dynamic resistance. The suggested circuit diagram of tunnel diode macro-model consists of two parallel circuits. One of them forms so called ?-diode, and the other represents diode with parasitic capacitance. Conclusions. The tunnel diode macro-model was created. A set of equations for parameter computation of micro-models of different types were derived. The oscillator simulation with using created tunnel diode macro-model shows availability of adopted simulating principles.

J. F. Zinkowskiy

2014-12-01

251

Band Shift, Band Filling, and Electron Localization in a Quantum Wire Detected via Tunneling between Parallel Quantum Wires  

Science.gov (United States)

Quantum wires are building blocks of quantum devices, in which the phase of an electron wave function plays a fundamental role. Since electronic correlation in a quantum wire modifies or disturbs the Fermi wave vector of a single particle in a quantum wire, the detection of such correlation effects is an important issue in the field of quantum electronics. We report on the modification of the Fermi wave vector of a biased quantum wire due to the convolution of band filling and interaction-induced band shifting detected via tunneling between parallel quantum wires. We also show that the Fermi wave vector is no longer a good quantum number when the electron density is sufficiently low, which is consistent with the formation of a localized or Wigner-crystal-like state appearing when the electron correlation is dominant over the kinetic energy.

Yamamoto, Michihisa; Tokura, Yasuhiro; Hirayama, Yoshiro; Tarucha, Seigo

2015-03-01

252

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

253

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

International Nuclear Information System (INIS)

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

254

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

Energy Technology Data Exchange (ETDEWEB)

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

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

2010-12-15

255

Giant fullerenes formed on C60 films irradiated with electrons field-emitted from scanning tunneling microscope tips  

International Nuclear Information System (INIS)

It has been found that spherical large clusters of carbon atoms are formed by irradiation of crystalline C60 films grown on Si(1 1 1)-(7 x 7) surfaces with electrons field-emitted from a scanning tunneling microscope probe tip. The size distribution of the clusters deduced from surface profile measurements suggests that the dominant clusters were not necessarily C60n (n = 2-4) expected from the simple fusion of C60 molecules. It was proposed that electronic excitations of C60 molecules caused the fragment and coalescence of the molecules to form the giant fullerenes as in the photo-induced similar effects

256

Electronic transport in single molecule junctions: control of the molecule-electrode coupling through intramolecular tunneling barriers.  

Science.gov (United States)

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 pi-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. PMID:18085806

Danilov, Andrey; Kubatkin, Sergey; Kafanov, Sergey; Hedegård, Per; Stuhr-Hansen, Nicolai; Moth-Poulsen, Kasper; Bjørnholm, Thomas

2008-01-01

257

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

258

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

Directory of Open Access Journals (Sweden)

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

Chung-Yen Yu

2014-10-01

259

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

260

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

OpenAIRE

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

Toroz, Dimitrios; Rontani, Massimo; Corni, Stefano

2011-01-01

261

Suppression of the stochastic fluctuations of suspended nanowires by temperature-induced single-electron tunneling  

OpenAIRE

We theoretically investigate the electromechanical properties of freely suspended nanowires that are in tunneling contact with the tip of a scanning tunneling microscope (STM) and two supporting metallic leads. The aim of our analysis is to characterize the fluctuations of the dynamical variables of the nanowire when a temperature drop is maintained between the STM tip and the leads, which are all assumed to be electrically grounded. By solving a quantum master equation that describes the cou...

Santandrea, Fabio; Gorelik, Leonid Y.; Shekhter, Robert I.; Jonson, Mats

2011-01-01

262

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

International Nuclear Information System (INIS)

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

263

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

Science.gov (United States)

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

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

2013-03-01

264

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

DEFF Research Database (Denmark)

Electronic transport mechanisms in molecular junctions are investigated by a combination of first-principles calculations and current?voltage measurements of several well-characterized structures. We study self-assembled layers of alkanethiols grown on Au(111) and form tunnel junctions by contacting the molecular layers with the tip of a conductive force microscope. Measurements done under low-load conditions permit us to obtain reliable tilt-angle and molecular length dependencies of the low-bias conductance through the alkanethiol layers. The observed dependence on tilt-angle is stronger for the longer molecular chains. Our calculations confirm the observed trends and explain them as a result of two mechanisms, namely, a previously proposed intermolecular tunneling enhancement as well as a hitherto overlooked tilt-dependent molecular gate effect.

Frederiksen, Thomas; Munuera, C.

2009-01-01

265

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

266

Variable temperature scanning tunneling microscopy and spectroscopy: Electronic and physical properties of single and two component thin films  

Science.gov (United States)

A newly acquired, commercial scanning tunneling microscope (STM) designed to work in ultra high vacuum at variable temperatures down to 50 K was used for scanning tunneling microscopy and spectroscopy (STM/STS) studies of organic adsorbates on metal surfaces. Au(111) substrates were prepared by evaporation of gold onto mica. Cobalt(II) phthalocyanine (CoPc), cobalt(II) tetraphenyl porphyrin (CoTPP), and vanadyl(II) phthalocyanine (VOPc) were deposited from vapor onto the substrates to form submonolayer, single and two component thin films. Ultraviolet photoelectron spectroscopy and metal-insulator-sample-metal ' (MISM') tunnel diode spectroscopy were used as complementary techniques to compare ionization potentials and electron affinities. STM constant current images of CoPc/CoTPP mixtures show two compositionally disordered close-packed surface structures. CoPc can also be observed as 1-d chains and single, isolated molecules below 220 K, and these structures cannot be imaged at 294 K (the areas appear noisy) unless the coverage is very close to a full monolayer. This is attributed to surface diffusion of the molecules. Molecular identification is determined by the appearance of the molecules in high resolution images and by orbital mediated tunneling spectroscopy (OMTS). Occupied and unoccupied orbitals are identified by the typical broad peaks observed in dI/dV versus V, and by sharp steps in z versus V. The OMT dependent z(V) curves are unique and this is the first report of such observations. The transient oxidation of the Co dz2 is identified in dI/dV(V) just negative of 0V bias for both molecules. Direct comparison of dz2 OMT detected in constant current images for CoPc and CoTPP reveals a lower Co-Au electron transfer rate for CoTPP, which is attributed to the ˜0.15 nm greater Co-Au distance for CoTPP relative to CoPc. STM/STS of pure VOPc films has previously shown some unusual properties which are not consistent with observations of CoPc or with UPS data. These observations consisted of extraordinarily strong pi*-LUMO mediated tunneling, no observed pi-HOMO mediated tunneling, and anomalous changes in apparent height. Codeposition of VOPc with CoPc for a reference also yielded very unusual results that were not consistent with previous two-component MPc thin film studies.

Barlow, Daniel Edward

2001-07-01

267

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.)

268

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.

269

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

270

Electronic Resources for Selecting and Using Children's Literature.  

Science.gov (United States)

This annotated list of electronic resources suggests materials for selecting and using children's literature. Highlights include children's classics, beginning reader lists, lists by genre and/or grade level, multicultural booklists, annual lists of noted children's literature, children's book awards, extending children's literature, book…

Byerly, Greg; Brodie, Carolyn S.

2001-01-01

271

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

OpenAIRE

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 disc...

Sanna Torma; Pertti Vakkari

2004-01-01

272

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

Science.gov (United States)

Single-molecule electronics, that is, realizing novel electronic functionalities from single (or very few) molecules, holds promise for application in various technologies, including signal processing and sensing. Nanographenes, which are extended polycyclic aromatic hydrocarbons (PAHs), are highly attractive subjects for studies of single-molecule electronics because the electronic properties of their flat conjugated systems can be varied dramatically through synthetic modification of their sizes and topologies. Single nanographenes provide high tunneling currents when adsorbed flat onto conducting substrates, such as graphite. Because of their chemical inertness, nanographenes interact only weakly with these substrates, thereby preventing the need for special epitaxial structure matching. Instead, self-assembly at the interface between a conducting solid, such as the basal plane of graphite, and a nanographene solution generally leads to highly ordered monolayers. Scanning tunneling spectroscopy (STS) allows the current-voltage characteristics to be measured through a single molecule positioned between two electrodes; the key to the success of STS is the ability to position the scanning tunneling microscopy (STM) tip freely with respect to the molecule in all dimensions, that is, both parallel and perpendicular to the surface. In this Account, we report the properties of nanographenes having sizes ranging from 0.7 to 3.1 nm and exhibiting various symmetry, periphery, and substitution types. The size of the aromatic system and the nature of its perimeter are two essential features affecting its HOMO-LUMO gap and charge carrier mobility in the condensed phase. Moreover, the extended pi area of larger substituted PAHs improves the degree of self-ordering, another key requirement for high-performance electronic devices. Self-assembly at the interface between an organic solution and the basal plane of graphite allows deposition of single molecules within the well-defined environment of a molecular monolayer. We have used STM and STS to investigate both the structures and electronic properties of these single molecules in situ. Indeed, we have observed key electronic functions, rectification and current control through single molecules, within a prototypical chemical field-effect transistor at ambient temperature. The combination of nanographenes and STM/STS, with the PAHs self-assembled in oriented molecular mono- or bilayers at the interface between an organic solution and the basal plane of graphite and contacted by the STM tip, is a simple, reliable, and versatile system for developing the fundamental concepts of molecular electronics. Our future targets include fast reversible molecular switches and complex molecular electronic devices coupled together from several single-molecule systems. PMID:18410086

Müllen, Klaus; Rabe, Jürgen P

2008-04-01

273

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.

274

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

Science.gov (United States)

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

Moro-Melgar, Diego; Mateos, Javier; González, Tomás; Vasallo, Beatriz G.

2014-12-01

275

Electron tunneling into the A15 superconductors: Nb3Sn, V3Si, and Nb3Ge  

International Nuclear Information System (INIS)

Oxide-layer tunnel junctions which have outstandingly good quasiparticle (Giaever) and pair (Josephson) tunneling characteristics are described. The superconductive properties such as the energy gap and critical temperature as a function of composition of the A15 films were studied. The junctions on niobium-tin are suitable for quantitative study of the tunneling density of states. From the data, the electron-phonon spectral function which describes the interaction responsible for superconductivity is calculated. It is interesting that as the composition is changed from twenty-five to twenty atomic percent tin, niobium-tin changes from a strong-coupling superconductor with a high critical temperature to a weak-coupling superconductor with a low critical temperature. Another study made possible by the availability of excellent junctions on the A15 superconductors is an examination of their low field behavior. We observe delayed fluxoid entry and the existence of a surface barrier of order one hundred and seventy milliTesla in niobium-tin and vanadium-silicon. These data help explain the potential utility of the A15 superconductors in power transmission line and resonant cavity applications

276

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. PMID:22304032

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

2011-12-01

277

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

CERN Document Server

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

Hassel, J; Seppä, H; Hakonen, P J

2003-01-01

278

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.

2003-01-01

279

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

International Nuclear Information System (INIS)

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

280

Density functional theory based direct comparison of coherent tunneling and electron hopping in redox-active single-molecule junctions  

Science.gov (United States)

To define the conductance of single-molecule junctions with a redox functionality in an electrochemical cell, two conceptually different electron transport mechanisms, namely, coherent tunneling and vibrationally induced hopping, compete with each other, where implicit parameters of the setup such as the length of the molecule and the applied gate voltage decide which mechanism is the dominant one. Although coherent tunneling is most efficiently described within Landauer theory and the common theoretical treatment of electron hopping is based on Marcus theory, both theories are adequate for the processes they describe without introducing accuracy-limiting approximations. For a direct comparison, however, it has to be ensured that the crucial quantities obtained from electronic structure calculations, i.e., the transmission function T (E ) in Landauer theory and the transfer integral V , the reorganization energy ? , and the driving force ? G0 in Marcus theory, are derived from similar grounds, as pointed out by Nitzan and coworkers in a series of publications. In this paper our framework is a single-particle picture, for which we perform density functional theory calculations for the conductance corresponding to both transport mechanisms for junctions with the central molecule containing one, two, or three Ruthenium centers, from which we extrapolate our results in order to define the critical length of the transition point of the two regimes which we identify at 5.76nm for this type of molecular wire. We also discuss trends in the dependence on an electrochemically induced gate potential.

Kastlunger, Georg; Stadler, Robert

2015-03-01

281

Modeling the Effects of Many Valley Electron Scattering on the Current-Voltage Characteristics of Resonant Tunneling Diodes  

Science.gov (United States)

Intervalley scattering of electrons has been experimentally shown to affect the current-voltage characteristics of resonant tunneling diodes. Electron scattering to satellite valleys and subsequent propagation through alternate conduction paths leads to leakage current and hence degrades the region of negative differential resistance. In this thesis, intervalley scattering is examined to study the effects of anisotropic density of states in the first Brillouin zone and then it is incorporated into a quantum kinetic transport model. In quantum kinetic theory the time evolution of a system is expressed in terms of density operators such as the density matrix and the Wigner function. By using the Wigner function, processes of significance to transport in the resonant tunneling diode, such as implementation of time irreversible boundary conditions at the ohmic contacts, ballistic motion of electrons, polar optical phonon scattering, and intervalley deformation potential scattering are incorporated into the quantum kinetic theory. The current-voltage characteristics are then computed as a function of temperature and it is shown that the current-voltage characteristics are sensitive to the value of the optical deformation potential.

Kia, Arash Kojouri

282

Surface state electron dynamics of clean and adsorbate-covered metal surfaces studied with the scanning tunnelling microscope  

Science.gov (United States)

Using low-temperature scanning tunnelling microscopy and spectroscopy we have studied the dynamics of surface state electrons confined to vacancy islands on Ag(1 1 1) and localised at single magnetic and non-magnetic atoms adsorbed on Ag(1 1 1) and Cu(1 1 1). The line width of confined electronic states is found to be only weakly affected by the actual geometry of the vacancy island. A corresponding model shows that lossy boundary scattering is the dominant lifetime-limiting process in the vacancies studied. We present a corrected analysis of the spatial decay of electron interference patterns, leading to a more consistent description of the Ag(1 1 1) surface state lifetime than was previously the case. A scanning tunnelling spectroscopy study of single adsorbed atoms is presented. By means of an extended Newns-Anderson model an observed resonance is interpreted in terms of an adsorbate-induced bound state split off from the bottom of the surface-state band. A preliminary line shape analysis of the bound state indicates that adsorbed atoms can modify the surface-state lifetime.

Kröger, J.; Limot, L.; Jensen, H.; Berndt, R.; Crampin, S.; Pehlke, E.

283

A scanning tunnelling and transmission electron microscopy comparison of the surface structure of evaporated and ion-assisted gold films  

Science.gov (United States)

The surface topography of evaporated and ion-assisted deposited gold films on silica has been studied by scanning tunnelling and transmission electron microscopy. Both techniques demonstrate that the bulk microstructures of the ion-assisted films have lower average dimensions than that of the evaporated films. The STM is used to compare the surface roughness of the evaporated and ion-assisted films. We discuss some of the difficulties in identifying grain sizes and grain boundaries from STM and TEM images of thin films.

Bartlett, R.; Jaeger, H.; Sexton, B. A.; Netterfield, R. P.; Martin, P. J.

1991-03-01

284

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

285

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

OpenAIRE

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

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

2010-01-01

286

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

287

Calculated electronic and transport properties of Fe/GaAs/Fe(001) tunnel junctions.  

Czech Academy of Sciences Publication Activity Database

566-568, ?. 1 (2004), s. 303-308. ISSN 0039-6028 R&D Projects: GA ?R GA202/04/0583 Institutional research plan: CEZ:AV0Z2041904 Keywords : magnetic multilayers * tunnel junctions Subject RIV: BM - Solid Matter Physics ; Magnetism Impact factor: 2.168, year: 2004

Vlaic, P.; Baadji, N.; Alouani, M.; Dreysse, H.; Eriksson, O.; Bengone, O.; Turek, Ilja

288

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

International Nuclear Information System (INIS)

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

289

Comparative study of perturbative methods for computing electron transfer tunneling matrix elements with a nonorthogonal basis set  

Science.gov (United States)

The authors consider the problem of computing tunneling matrix elements for bridge-mediated electron transfer reactions using the Löwdin [J. Math. Phys. 3, 969 (1962); J. Mol. Spectrosc. 13, 326 (1964)] projection-iteration technique with a nonorthogonal basis set. They compare the convergence properties of two different Löwdin projections, one containing the overlap matrix S and the other containing the inverse S-1 in the projected Hamiltonian. It was suggested in the literature that the projected Hamiltonian with S-1 has better convergence properties compared to the projected Hamiltonian with S. The authors test this proposal using a simple analytical model, and ab initio Hartree-Fock calculations on different molecules with several types of basis sets. Their calculations show that, for Gaussian-type basis sets, the projected Hamiltonian containing S has the best convergence properties, especially for diffuse basis sets and in the strong coupling limit. The limit of diffuse basis sets is relevant to tunneling matrix element calculations involving excited states and anionic electron transfer.

Teklos, Antonios; Skourtis, Spiros S.

2006-12-01

290

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

Directory of Open Access Journals (Sweden)

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

Reuter Dirk

2010-01-01

291

Electronic band alignment and electron transport in Cr/BaTiO3/Pt ferroelectric tunnel junctions  

International Nuclear Information System (INIS)

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/BaTiO3(001)/Pt(001) heterostructures. Transport properties of Cr/BaTiO3/Pt junctions with a sub-?m Cr top electrode are interpreted in terms of tunneling electroresistance with resistance changes of a factor of ?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 BaTiO3/Pt (Cr/BaTiO3) interface +0.42(?0.03) eV following downward to upward polarization reversal.

292

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

293

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

OpenAIRE

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

294

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

International Nuclear Information System (INIS)

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

295

Journals, Data and Abstracts Make an Integrated Electronic Resource  

Science.gov (United States)

Astronomy now has an integrated, Web-based information resource for research papers, data and bibliographic information. The major scholarly research journals, a comprehensive abstract service and the astronomical data centers are now linked together to provide an information resource which is not available to most other scientific disciplines. As of January, 1997, the Astrophysical Journal joins the ApJ Letters on the Web. Astronomy and Astrophysics Supplements now has a page image version. Elsevier's electronic journal New Astronomy has recently made its appearance. Over forty percent of the new peer-reviewed, astronomical literature is now available electronically. The main Astronomy and Astrophysics journal, the Astronomical Journal and others will be available by 1998, at which point ninety percent of the literature will be available electronically, a figure not approached by any other scientific discipline. With so many different sources, one of the challenges has been to integrate the on-line, peer-reviewed literature into a resource which serves the astronomical community in a unified and coherent manner. Following the lead of the AAS, the major publishers have chosen to rely upon the NASA-supported Astrophysics Data System (ADS) and the astronomical data centers to provide the means by which the various separate journals can interoperate. The data centers and the ADS have developed unique identification codes for journal articles. By adopting the existing standard "bibcodes" and integrating them into their WWW links, each of the major astronomical journals are able to link to the abstracts of most of the referenced articles. Since the ADS also serves as an on-line repository for page images of the past twenty years of the major astronomical journals, the full text of many of the referenced articles are available, too. The articles in the ADS have recently been linked through their references, both forward and backward in time. With the "bibcode" providing the linking framework, papers in the electronic research journals, data and abstracts will be incorporated into the system in a routine manner. The astronomical community now has an ever-growing, operational integrated information system which fulfills today, the dream of the digital library. It remains to be seen how this electronic resource will affect the progress of research.

Boyce, P.

1996-12-01

296

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.

297

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

298

Electronic-state-controlled reset operation in quantum dot resonant-tunneling single-photon detectors  

Energy Technology Data Exchange (ETDEWEB)

The authors present a systematic study of an introduced reset operation on quantum dot (QD) single photon detectors operating at 77?K. The detectors are based on an AlAs/GaAs/AlAs double-barrier resonant tunneling diode with an adjacent layer of self-assembled InAs QDs. Sensitive single-photon detection in high (dI)/(dV) region with suppressed current fluctuations is achieved. The dynamic detection range is extended up to at least 10{sup 4} photons/s for sensitive imaging applications by keeping the device far from saturation by employing an appropriate reset frequency.

Weng, Q. C.; Zhu, Z. Q. [Key Laboratory of Polar Materials and Devices, Ministry of Education, East China Normal University, Shanghai 200241 (China); An, Z. H., E-mail: anzhenghua@fudan.edu.cn [State Key Laboratory of Surface Physics and Institute of Advanced Materials, Fudan University, Shanghai 200433 (China); Song, J. D.; Choi, W. J. [Center for Opto-Electronic Convergence Systems, Institute of Science and Technology, Seoul 130-650 (Korea, Republic of)

2014-02-03

299

Direct probing of the stacking order and electronic spectrum of rhombohedral trilayer graphene with scanning tunneling microscopy  

Science.gov (United States)

Recently, rhombohedral trilayer graphene (r-TLG) has attracted much attention because of its low-energy flat bands, which are predicted to result in many strongly correlated phenomena. However, there has been a need for more experimental evidence for these flat bands in the r-TLG, since the supporting substrates usually have strong destructive effects on the low-energy band structure of graphene systems. Here, we demonstrate that it is possible to directly probe the stacking order and electronic spectrum of the r-TLG on a graphite surface with scanning tunneling microscopy around a monoatomic step edge of the top graphene layer. The tunneling spectra of the r-TLG exhibit four adjacent peaks, which are generated by the low-energy flat bands, flanking the charge neutrality point. Based on these spectra, the true energy gap and the energy gap at the K point of the r-TLG are determined as about 9 and 23 meV, respectively. The observed features are well reproduced by a low-energy effective Hamiltonian.

Xu, Rui; Yin, Long-Jing; Qiao, Jia-Bin; Bai, Ke-Ke; Nie, Jia-Cai; He, Lin

2015-01-01

300

Analysis of Human Resources Management Strategy in China Electronic Commerce Enterprises  

Science.gov (United States)

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

Shao, Fang

301

Local opening of a large bandgap in metallic single-walled carbon nanotubes induced by tunnel injection of low-energy electrons  

International Nuclear Information System (INIS)

Probing with a tip of scanning tunneling microscopy (STM) of metallic single-walled carbon nanotubes (SWCNT) was found to induce defects in the tubes. The primary defect formation by probing was enhanced with a rate proportional to tunnel-injected electron current above a sample-bias threshold of around +4 V. Scanning tunneling spectroscopic measurements of local density of states revealed that the defects imaged by STM, presumably secondary defects stabilized at the test temperature (95 K), are accompanied by a localized bandgap of 0.7 eV, which may account for the reported metal-semiconductor conversion in SWCNT-based field-effect transistor that is induced by low-energy electron irradiation.

302

Combined scanning tunneling microscopy and high-resolution electron energy loss spectroscopy study on the adsorption state of CO on Ag(001).  

Science.gov (United States)

The adsorption site and vibrational energies of CO on a clean Ag(001) surface were determined using scanning tunneling microscopy, inelastic electron tunneling spectroscopy with a scanning tunneling microscope, and high-resolution electron energy loss spectroscopy. The CO molecules were found to adsorb on the atop site of the Ag(001) surface, which was similar to their adsorption on the Cu(001) surface. The vibrational energy of the CO internal stretching mode was found to be 263 meV, which is only 3 meV less than that of CO in the gas phase. This result indicates that the CO molecules chemisorb very weakly on the Ag(001) surface. PMID:22909144

Arafune, Ryuichi; Shin, Hyung-Joon; Jung, Jaehoon; Minamitani, Emi; Takagi, Noriaki; Kim, Yousoo; Kawai, Maki

2012-09-18

303

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)

304

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.

305

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

Science.gov (United States)

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

DeLoach, Richard; Micol, John R.

2011-01-01

306

Hot-Electron Tunneling sensors for high-resolution x-ray and gamma-ray spectroscopy  

Energy Technology Data Exchange (ETDEWEB)

Over the past 2 years, we have been studying the use of Hot Electron Tunneling sensors for use in high-energy-resolution x-ray and gamma-ray spectrometers. These sensors promise several advantages over existing cryogenic sensors, including simultaneous high count rate and high resolution capability, and relative ease of use. Using simple shadow mask lithography, we verified the basic principles of operation of these devices and discovered new physics in their thermal behavior as a function applied voltage bias. We also began to develop ways to use this new sensor in practical x-ray and gamma-ray detectors based on superconducting absorbers. This requires the use of quasiparticle trapping to concentrate the signal in the sensing elements.

Mears, C.A.; Labov, S.E.; Frank, M.; Netel, H.

1997-02-07

307

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

International Nuclear Information System (INIS)

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

308

Inelastic electron tunnelling spectroscopy—III. A study of the molecular orientation of phthalic, isophthalic and terephthalic acids adsorbed on alumina  

Science.gov (United States)

Inelastic electron tunnelling spectroscopy has been employed to determine the molecular orientation of the three benzene dicarboxylic acids on alumina. All three acids are assigned as coordinating to the alumina via one of their carboxyl groups; the non-adsorbed carboxyl group participating in intermolecular hydrogen bonding with its neighbour.

Lewis, D. M.; Field, B. O.

309

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

310

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

Energy Technology Data Exchange (ETDEWEB)

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

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

2012-02-01

311

Superconducting Tunnel Junction Refrigerators for Sub-Kelvin Cooling of Electrons, Phonons, and Arbitrary, User-Supplied Payloads  

Science.gov (United States)

Modern science often requires measurements at sub-Kelvin temperatures. Temperatures of 300 mK can be reached by using liquid 3He, but reaching lower temperatures requires the use of adiabatic demagnetization and dilution refrigerators which are complex, large, and costly. Normal-metalInsulatorSuperconductor (NIS) tunnel junctions provide an alternative refrigeration method that is simple to use, compact, and provides continuous cooling power that has the potential to expand the accessibility of these sub-Kelvin temperatures. When properly biased, the electron system in the normal metal of an NIS junction is cooled since the hottest electrons preferentially tunnel from the normal metal to the superconductor, transferring heat in the process. When the normal metal is extended onto a thermally isolated membrane, the cold electrons cool the phonons in the membrane through electron-phonon coupling. In previous work, NIS junctions have been used to cool detectors and bulk objects that were integrated with the membrane, but could not be considered a general-purpose refrigerator since they could not cool arbitrary objects. The goal of this work has been to demonstrate a general-purpose NIS refrigerator to which a user can attach arbitrary bulk objects. First, we discuss NIS refrigeration and then develop a model to predict phonon cooling. We fabricated and tested NIS refrigerators capable of cooling bulk objects and used the model to explain the results. The devices were able to cool phonons from 300 mK to 154 mK with 100 pW of cooling power at 200 mK. With these devices, we were able to cool a 2 cm3 piece of copper from 290 mK to 256 mK with 700 pW of cooling power at 290 mK. This demonstration marks the emergence of NIS refrigerators as a true, general-purpose refrigerator since users can attach arbitrary objects. Measurements of Andreev reflections in the devices and next-generation refrigerators that cool electrons from 100 mK to below 50 mK are also presented.

Lowell, Peter Joseph

312

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

Science.gov (United States)

Short chains containing a series of metal-molecule-nanoparticle nanojunctions are a nano-material system with the potential to give electrical signatures close to those from single molecule experiments while enabling us to build portable devices on a chip. Inelastic electron tunnelling spectroscopy (IETS) measurements provide one of the most characteristic electrical signals of single and few molecules. In interlinked molecule-nanoparticle (NP) chains containing typically 5-7 molecules in a chain, the spectrum is expected to be a superposition of the vibrational signatures of individual molecules. We have established a stable and reproducible molecule-AuNP multi-junction by placing a few 1,8-octanedithiol (ODT) molecules onto a versatile and portable nanoparticle-nanoelectrode platform and measured for the first time vibrational molecular signatures at complex and coupled few-molecule-NP junctions. From quantum transport calculations, we model the IETS spectra and identify vibrational modes as well as the number of molecules contributing to the electron transport in the measured spectra.Short chains containing a series of metal-molecule-nanoparticle nanojunctions are a nano-material system with the potential to give electrical signatures close to those from single molecule experiments while enabling us to build portable devices on a chip. Inelastic electron tunnelling spectroscopy (IETS) measurements provide one of the most characteristic electrical signals of single and few molecules. In interlinked molecule-nanoparticle (NP) chains containing typically 5-7 molecules in a chain, the spectrum is expected to be a superposition of the vibrational signatures of individual molecules. We have established a stable and reproducible molecule-AuNP multi-junction by placing a few 1,8-octanedithiol (ODT) molecules onto a versatile and portable nanoparticle-nanoelectrode platform and measured for the first time vibrational molecular signatures at complex and coupled few-molecule-NP junctions. From quantum transport calculations, we model the IETS spectra and identify vibrational modes as well as the number of molecules contributing to the electron transport in the measured spectra. Electronic supplementary information (ESI) available: Methods and materials. Details of the ab initio calculation of molecular vibrations and inelastic spectra of ODT between two Au electrodes. A model of carrier transport through the molecular junctions. See DOI: 10.1039/c3nr00505d

Jafri, S. H. M.; Löfås, H.; Fransson, J.; Blom, T.; Grigoriev, A.; Wallner, A.; Ahuja, R.; Ottosson, H.; Leifer, K.

2013-05-01

313

Electronic Document Management: A Human Resource Management Case Study  

Directory of Open Access Journals (Sweden)

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

Thomas Groenewald

2004-11-01

314

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

International Nuclear Information System (INIS)

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

315

An entropic quantum drift-diffusion model for electron transport in resonant tunneling diodes  

International Nuclear Information System (INIS)

We present an entropic quantum drift-diffusion model (eQDD) and show how it can be derived on a bounded domain as the diffusive approximation of the Quantum Liouville equation with a quantum BGK operator. Some links between this model and other existing models are exhibited, especially with the density gradient (DG) model and the Schroedinger-Poisson drift-diffusion model (SPDD). Then a finite difference scheme is proposed to discretize the eQDD model coupled to the Poisson equation and we show how this scheme can be slightly modified to discretize the other models. Numerical results show that the properties listed for the eQDD model are checked, as well as the model captures important features concerning the modeling of a resonant tunneling diode. To finish, some comparisons between the models stated above are realized

316

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

OpenAIRE

The Hamiltonian of electrons interacting with interface phonons in three-barrier resonant tunneling structure is established using the first principles within the models of effective mass and polarization continuum. Using the Green's functions method, the temperature shifts and decay rates of operating electron states are calculated depending on geometric design of three-barrier nano-structure GaAs/AlxGa1-xAs which is an active region of quantum cascade detector. It is established that indepe...

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

2014-01-01

317

Non-Equilibrium Green's Function Calculation for Electron Transport through Magnetic Tunnel Junction  

OpenAIRE

In this paper non-equilibrium Green's function method –dependent electron transport through non magnetic layer (insulator ) has been studied in one dimension .electron transport in multi-layer (magnetic/non magnetic/ magnetic)layers is studied as quantum .the result show increasing the binding strength of the electrical insulator transition probability density case , the electron density , broad levels of disruption increases. Broad band connection increases the levels of di...

Sara Nobakht; Adeleh Vatan-Khahan

2014-01-01

318

Electron transport in Coulomb- and tunnel-coupled one-dimensional systems  

OpenAIRE

We develop a linear theory of electron transport for a system of two identical quantum wires in a wide range of the wire length L, unifying both the ballistic and diffusive transport regimes. The microscopic model, involving the interaction of electrons with each other and with bulk acoustical phonons allows a reduction of the quantum kinetic equation to a set of coupled equations for the local chemical potentials for forward- and backward-moving electrons in the wires. As a...

Raichev, O. E.; Vasilopoulos, P.

2000-01-01

319

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

Energy Technology Data Exchange (ETDEWEB)

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

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

2001-06-15

320

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

321

Resonator design for surface electron lifetime studies using scanning tunneling spectroscopy  

CERN Document Server

We derive expressions for the lossy boundary-scattering contribution to the linewidth of surface electronic states confined with atomic corrals and island resonators. Correcting experimentally measured linewidths for these contributions along with thermal and intrumental broadening enables intrinsic many-body lifetimes due to electron-electron and electron-phonon scattering to be determined. In small resonators lossy-scattering dominates linewidths whilst different scaling of widths and separations cause levels to merge in large resonators. Our results enable the design of resonators suitable for lifetime studies.

Crampin, S; Kröger, J; Limot, L; Berndt, R

2005-01-01

322

Using a superconducting tunnel junction detector to measure the secondary electron emission efficiency for a microchannel plate detector bombarded by large molecular ions  

Science.gov (United States)

An energy-sensitive superconducting tunnel junction (STJ) detector was used to measure the secondary electron emission efficiency, epsilon(e), for a microchannel plate (MCP) detector bombarded by large (up to 66 kDa), slow moving (secondary electron yield was calculated from the secondary electron emission efficiency and found to scale linearly with the mass of the impinging molecular ion and to about the fourth power of ion velocity. Secondary electrons were observed for primary ion impacts >5 km/s, regardless of mass, and no evidence of a velocity (detection) threshold was observed. Copyright 2000 John Wiley & Sons, Ltd. PMID:11006596

Westmacott; Frank; Labov; Benner

2000-01-01

323

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

324

Non-Equilibrium Green's Function Calculation for Electron Transport through Magnetic Tunnel Junction  

Directory of Open Access Journals (Sweden)

Full Text Available In this paper non-equilibrium Green's function method –dependent electron transport through non magnetic layer (insulator has been studied in one dimension .electron transport in multi-layer (magnetic/non magnetic/ magneticlayers is studied as quantum .the result show increasing the binding strength of the electrical insulator transition probability density case , the electron density , broad levels of disruption increases. Broad band connection increases the levels of disruption to electrical insulation and show non- conductive insulating state to semiconductor stat and even conductor

Sara Nobakht

2014-06-01

325

Electronic phase diagram of NaFe1?xCoxAs investigated by scanning tunneling microscopy  

International Nuclear Information System (INIS)

Our recent scanning tunneling microscopy (STM) studies of the NaFe1?xCoxAs phase diagram over a wide range of dopings and temperatures are reviewed. Similar to the high-Tc cuprates, the iron-based superconductors lie in close proximity to a magnetically ordered phase. Therefore, it is widely believed that magnetic interactions or fluctuations play an important role in triggering their Cooper pairings. Among the key issues regarding the electronic phase diagram are the properties of the parent spin density wave (SDW) phase and the superconducting (SC) phase, as well as the interplay between them. The NaFe1?xCoxAs is an ideal system for resolving these issues due to its rich electronic phases and the charge-neutral cleaved surface. In our recent work, we directly observed the SDW gap in the parent state, and it exhibits unconventional features that are incompatible with the simple Fermi surface nesting picture. The optimally doped sample has a single SC gap, but in the underdoped regime we directly viewed the microscopic coexistence of the SDW and SC orders, which compete with each other. In the overdoped regime we observed a novel pseudogap-like feature that coexists with superconductivity in the ground state, persists well into the normal state, and shows great spatial variations. The rich electronic structures across the phase diagram of NaFe1?xCoxAs revealed here shed important new light for defining microscopic models of the iron-based superconductors. In particular, we argue that both the itinerant electrons and local moments should be considered on an equal footing in a realistic model. (topical review - iron-based high temperature superconductors)

326

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

DEFF Research Database (Denmark)

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

Chi, Qijin; Farver, O

2005-01-01

327

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

328

Electronic transport through EuO spin-filter tunnel junctions  

KAUST Repository

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

329

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

330

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

OpenAIRE

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

331

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

Science.gov (United States)

Analytical models describing the temperature dependence of the deep tunneling rate, useful for proton, hydrogen, or hydride transfer in proteins, are developed and compared. Electronically adiabatic and non-adiabatic expressions are presented where the donor-acceptor (D-A) motion is treated either as a quantized vibration or as a classical "gating" distribution. We stress the importance of fitting experimental data on an absolute scale in the electronically adiabatic limit, which normally applies to these reactions, and find that vibrationally enhanced deep tunneling takes place on sub-ns timescales at room temperature for typical H-bonding distances. As noted previously, a small room temperature kinetic isotope effect (KIE) does not eliminate deep tunneling as a major transport channel. The quantum approach focuses on the vibrational sub-space composed of the D-A and hydrogen atom motions, where hydrogen bonding and protein restoring forces quantize the D-A vibration. A Duschinsky rotation is mandated between the normal modes of the reactant and product states and the rotation angle depends on the tunneling particle mass. This tunnel-mass dependent rotation contributes substantially to the KIE and its temperature dependence. The effect of the Duschinsky rotation is solved exactly to find the rate in the electronically non-adiabatic limit and compared to the Born-Oppenheimer (B-O) approximation approach. The B-O approximation is employed to find the rate in the electronically adiabatic limit, where we explore both harmonic and quartic double-well potentials for the hydrogen atom bound states. Both the electronically adiabatic and non-adiabatic rates are found to diverge at high temperature unless the proton coupling includes the often neglected quadratic term in the D-A displacement from equilibrium. A new expression is presented for the electronically adiabatic tunnel rate in the classical limit for D-A motion that should be useful to experimentalists working near room temperature. This expression also holds when a broad protein conformational distribution of D-A equilibrium distances dominates the spread of the D-A vibrational wavefunction. PMID:25796225

Benabbas, Abdelkrim; Salna, Bridget; Sage, J Timothy; Champion, Paul M

2015-03-21

332

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

Science.gov (United States)

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

Benabbas, Abdelkrim; Salna, Bridget; Sage, J. Timothy; Champion, Paul M.

2015-03-01

333

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

International Nuclear Information System (INIS)

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

334

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

335

Electronic Non-Resonant Tunneling through Diaminoacenes: A First-Principles Investigation  

International Nuclear Information System (INIS)

The electron transport through diaminoacenes sandwiched between two Au electrodes is simulated by using a first-principles analysis. The nonlinear current-voltage characteristic is observed. Effects of the ring number and positions of amine groups on equilibrium transport properties are found. For 1,4 series, the greater the number of the rings, the stronger the transmission spectrum near the Fermi energy. For 2,6 series, the larger the number of the rings, the weaker the transmission spectrum near the Fermi energy. This is helpful for understanding the recently reported results on conductance measurements using amines. (condensed matter: electronic structure, electrical, magnetic, and optical properties)

336

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

CERN Document Server

We investigated electron emissions in strong field enhanced ionization of asymmetric diatomic molecules by quantum calculations. It is demonstrated that the widely-used intuitive physical pic- ture, i.e., electron wave packet direct ionization from the up-field site (DIU), is incomplete. Besides DIU, we find another two new ionization channels, the field-induced excitation with subsequent ionization from the down-field site (ESID), and the up-field site (ESIU). The contributions from these channels depend on the molecular asymmetry and internuclear distance. Our work provides a more comprehensive physical picture for the long-standing issue about enhanced ionization of diatomic molecules.

Huang, Cheng; Zhou, Yueming; Zhang, Qingbin; Liu, Kunlong; Lu, Peixiang

2014-01-01

337

Tunneling site of electrons in strong-field-enhanced ionization of molecules  

Science.gov (United States)

We investigated electron emissions in strong-field-enhanced ionization of asymmetric diatomic molecules by quantum calculations. It is demonstrated that the widely used intuitive physical picture, i.e., electron wave-packet direct ionization from the up-field site (DIU), is incomplete. Besides DIU, we find another two ionization channels: the field-induced excitation with subsequent ionization from the down-field site and that from the up-field site. The contributions from these channels depend on the molecular asymmetry and internuclear distance. Our work provides a more comprehensive physical picture for the long-standing issue about enhanced ionization of diatomic molecules.

Huang, Cheng; Lan, Pengfei; Zhou, Yueming; Zhang, Qingbin; Liu, Kunlong; Lu, Peixiang

2014-10-01

338

An inexpensive up-gradation of scanning tunneling microscope for ballistic electron emission microscopy and spectroscopy  

Science.gov (United States)

Ballistic electron emission microscopy (BEEM) and Ballistic electron emission spectroscopy (BEES) have become highly useful tools for studying the transport property of electrons and holes across metals, metal-semiconductor interfaces and in semiconductors. Although the techniques are developed, but there is hardly any detailed description of experimental set-ups in this regard. We have carried out an inexpensive upgradation of commercial STM (model STM635 of RHK Technologies) for BEEM and BEES studies on metal-semiconductor interfaces. Along with the associated electronics and a suitable sample holder, we have also developed a technique to produce high quality STM tips necessary for these studies. We have carried out BEEM studies on gold-silicon interface and the results are in conformity with those reported earlier. The minimum threshold of obtaining ballistic current is found to be 0.7 V for Au-n-Si interface whereas it may rise up to 4 V if a layer of oxide is permitted to grow on silicon before deposition of gold film. In the case of a 100 Å gold film over n-Si(100), the BEEM current is more intense at the grain boundaries and relatively less over the grains of greater heights.

Gangopadhyay, S.; Kar, A. K.; Ray, S. K.; Mathur, B. K.

2000-02-01

339

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

340

Tarsal Tunnel Syndrome  

Science.gov (United States)

... Conditions » Tarsal Tunnel Syndrome Text Size Print Bookmark Tarsal Tunnel Syndrome What Is the Tarsal Tunnel? The tarsal tunnel ... the focus of tarsal tunnel syndrome. What Is Tarsal Tunnel Syndrome? Tarsal tunnel syndrome is a compression, or squeezing, ...

341

Compact device for cleaning scanner-mounted scanning tunneling microscope tips using electron bombardment  

Science.gov (United States)

Most scanning probe techniques rely on the assumption that both sample and tip are free from adsorbates, residues, and oxide not deposited intentionally. Getting a clean sample surface can be readily accomplished by applying ion sputtering and subsequent annealing, whereas finding an adequate treatment for tips is much more complicated. The method of choice would effectively desorb undesired compounds without reducing the sharpness or the general geometry of the tip. Several devices which employ accelerated electrons to achieve this are described in the literature. To minimize both the effort to implement this technique in a UHV chamber and the overall duration of the cleaning procedure, we constructed a compact electron source fitted into a sample holder, which can be operated in a standard Omicron variable-temperature (VT)-STM while the tip stays in place. This way a maximum of compatibility with existing systems is achieved and short turnaround times are possible for tip cleaning.

Hellmann, D.; Worbes, L.; Kittel, A.

2011-08-01

342

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

International Nuclear Information System (INIS)

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

343

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

International Nuclear Information System (INIS)

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.

344

Fabrication of Sub-Micron Size Al-AlOx-Al Tunnel Junction using Electron-Beam Lithography and Double-Angle Shadow Evaporation Technique  

International Nuclear Information System (INIS)

We report our development of the fabrication process of sub-micron scale Al-AlOx-Al tunnel junction by using electron-beam lithography and double-angle shadow evaporation technique. We used double-layer resist to construct a suspended bridge structure, and double-angle electron-beam evaporation to form a sub-micron scale overlapped junction. We adopted an e-beam insensitive resist as a bottom sacrificing layer. Tunnel barrier was formed by oxidation of the bottom aluminum layer between the bottom and top electrode deposition, which was done in a separate load-lock chamber. The junction resistance is designed and controlled to be 50 ?to match the impedance of the transmission line. The junctions will be used in the broadband shot noise thermometry experiment, which will serve as a link between the electrical unit and the thermodynamic unit.

345

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

346

Availability And Use Of Electronic Resources In Spspm Libraries: A Study  

OpenAIRE

This research paper describes availability and use of electronic resource by faculty members of SPSPM libraries. Now a day's e - resources are growing tremendously in the world and demands of the same are also increasing day by day from users.

Kamble M.G; Ghante P. B.

2012-01-01

347

Scanning tunneling microscopy studies of an electron-doped high-Tc superconductor, praseodymium lanthanum cerium copper oxide  

Science.gov (United States)

It has been more than two decades since the first high temperature superconductor was discovered. In this time there has been tremendous progress in understanding these materials both theoretically and experimentally. Some important questions however remain to be answered; one of them is the temperature dependence of the superconducting gap which is in turn tied to question of the origin of the pseudogap and its connection with superconductivity. In this thesis, we present detailed Scanning Tunneling Microscopy (STM) spectroscopic studies of an electron doped superconductor, Pr0.88LaCe 0.12CuO4-delta (PLCCO). The electron doped compounds form an interesting venue for STM studies for many reasons. In the hole-doped materials, especially in the underdoped side of the phase diagram, there is mounting evidence of a second gap that survives to high temperatures (high temperature pseudogap) that may have a different origin from superconductivity. This complicates studies of the temperature dependence of the superconducting gap in these materials. In PLCCO however, there is little evidence for a high temperature pseudogap potentially allowing us to address the question of the temperature evolution of the superconducting gap without the complication of a second gap. Secondly, the low Tc of the optimally doped materials makes it easily accessible to temperature dependent STM studies. Finally, while hole-doped materials have been extensively studied by scanning tunneling microscopy (STM), there have been no detailed STM spectroscopic studies on the electron doped compounds. In the first part of the thesis, we investigate the effect of temperature on the superconducting gap of optimally doped PLCCO with Tc = 24K. STM spectroscopy data is analyzed to obtain the gap as a function of temperature from 5K to 35K. The gap is parameterized with a d-wave form and the STM spectra are fit at each temperature to extract the gap value. A plot of this gap value as a function of temperature shows clear deviations from what is expected from BCS theory. We find that similar to the hole-doped superconductors a fraction of the surface still shows a gap above Tc. The implications of our finding to the pseudogap phase are discussed. In the second part of the thesis, STM spectra are analyzed to determine the effect of impurities or vacancies on the local density of states. Electron doped superconductors require a post-annealing process to induce superconductivity. It is claimed that Cu vacancies in the CuO2 planes which suppress superconductivity are healed by this process. This implies that for the same doping, a sample with higher Tc should have fewer impurities compared to a sample with lower Tc. We studied two PLCCO samples with 12% Ce doping; one with higher Tc (24K) and the other with lower T c (21K). Through quasiparticle scattering study we find that there are more impurities in 21K samples than 24K sample, consistent with the picture of Cu vacancies in as grown samples. Finally, we present a discussion of the bosonic modes observed in the STM spectra and their connection to the spin excitations measured by neutron scattering.

Kunwar, Shankar

348

Resources  

Science.gov (United States)

... Diabetes - resources Digestive disease - resources Drug abuse - resources Eating disorders - resources Elder care - resources Epilepsy - resources Family troubles - resources Gastrointestinal disorders - resources Hearing impairment - resources ...

349

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

350

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

OpenAIRE

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; Courtois, Herve?

2007-01-01

351

Visualizing the Pt Doping Effect on Surface and Electronic Structure in Ir1-xPtxTe2 by Scanning Tunneling Microscopy and Spectroscopy  

Science.gov (United States)

We report on the Pt doping effect on surface and electronic structure in Ir1-xPtxTe2 by scanning tunneling microscopy (STM) and spectroscopy (STS). The surface prepared by cleavage at 4.2 K shows a triangular lattice of topmost Te atoms. The compounds that undergo structural transition have supermodulation with a fixed wave vector q = 2?/5am (where am is the lattice constant in the monoclinic phase) despite the different Pt concentrations. The superconducting compounds show patch structures. The surface of the compound that exhibits neither the superconductivity nor the structural transition shows no superstructure. In all doped samples, the dopant is observed as a dark spot in STM images. The tunneling spectra near the dopant show the change in the local density of state at approximately -200 mV. Such microscopic effects of the dopant give us the keys for establishing a microscopic model of this material.

Fujisawa, Yuita; Machida, Tadashi; Igarashi, Kei; Kaneko, Akihiro; Mochiku, Takashi; Ooi, Shuuichi; Tachiki, Minoru; Komori, Kazunori; Hirata, Kazuto; Sakata, Hideaki

2015-04-01

352

Scanning tunneling microscopy study of morphology and electronic properties in (K0.7Na0.3)Fe2?ySe2 single crystal  

International Nuclear Information System (INIS)

We investigated the microstructure of the iron selenide superconductor (K0.7Na0.3)Fe2?ySe2 with a Tc?=?32?K and a near 100% Meissner screening volume fraction. Topography and electron transport properties were studied using electron microscopy and ultra-high vacuum scanning tunneling microscopy (STM) techniques. Room temperature STM measurements reliably identify spatial variations of the local electronic properties of this material. The studied crystals consist of continuous regions with significantly different shapes of current-voltage curves reflecting different electronic transport properties of these regions. Fitting of the local current-voltage curves with the Simmons model for metal-dielectric-metal structure confirmed a phase separation in the sample to a metal and semiconducting phases. The observed regions have dimensions in the range of several tenths of a micrometer and indicate a phase separation in the sample.

353

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

354

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

355

Renormalization of resonant tunneling in MOSFETs  

CERN Document Server

We study tunneling between a localized defect state and a conduction band in the presence of strong electron-electron and electron-phonons interactions. We derive the tunneling rate as a function of the position of the defect energy level relative to the Fermi energy of conduction electrons. We argue that our results can explain the large tunneling timescales observed in experiments on random telegraph signals in ${\\rm Si}$ metal-oxide-semiconductor field effect transistors.

Mozyrsky, D; Shnirman, A; Hastings, M B

2003-01-01

356

Sistema internacional sobre contaminates y residuos en alimentos [electronic resource  

International Nuclear Information System (INIS)

ISICRA the Spanish version of INFOCRIS provided an ideal Internet tool to improve awareness of successful case studies. SICRA uses a common set of Divisional resources to address issues from production to consumption.

357

DIR-SIT search form (36 facilities) [electronic resource  

International Nuclear Information System (INIS)

The Sterile Insect Mass Rearing Facilities Directory is being developed with the objective of aiding the retrieval of information on all mass rearing facilities of sterile pest insects, ticks and mites. DIR-SIT is part of IDIDAS resources.

358

Programmable ferroelectric tunnel memristor  

OpenAIRE

We report an analogously programmable memristor based on genuine electronic resistive switching combining ferroelectric switching and electron tunneling. The tunnel current through an 8 unit cell thick epitaxial Pb(Zr[0.2]Ti[0.8])O[3] film sandwiched between La[0.7]Sr[0.3]MnO[3] and cobalt electrodes obeys the Kolmogorov-Avrami-Ishibashi model for bidimensional growth with a characteristic switching time in the order of 10^-7 seconds. The analytical description of switching kinetics allows us...

AndyQuindeau

2014-01-01

359

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)

360

Electron tunneling through barriers of adjustable width : Role of the image potential and the wetting behavior of Cs by He  

OpenAIRE

Photocurrents from cesium, flowing through gaseous 3He or 4He and also through thin liquid helium films, are investigated as a function of the chemical potential of helium at T=1.33 K. At low pressures, the two isotopes behave similarly as the photocurrent is governed by scattering by the gas. At higher pressures, a film of 3He grows on the Cs and forms a tunnel barrier; but for 4He, the film is too thin to form a tunnel barrier below liquid-vapor coexistence. This is because 4He does not wet...

Zech, Martin; Bromberger, Hubertus; Klier, Ju?rgen; Leiderer, Paul; Wyatt, Adrian F. G.

2008-01-01

361

Electronic Resources and the Education of History Professionals  

Science.gov (United States)

The transforming effects of the tremendous advances in technology that have reshaped the economy and many other elements of American society have had an equally profound impact on historical agencies. The personal computer, the Internet, and associated electronic communications developments have already transformed the museum and historical agency…

Mulligan, William H., Jr.

2001-01-01

362

Growing an Electronic Library: Resources, Utility, Marketing and Politics.  

Science.gov (United States)

Describes the development of the ResIDe Electronic Library at the University of the West of England, Bristol. Analyzes potential of the system to increase economy, efficiency and effectiveness in library services and relates it to how the needs of sponsors and students can be met. (Author/LRW)

Dugdale, David; Dugdale, Christine

2000-01-01

363

Multibarrier tunneling  

OpenAIRE

We study the tunneling through an arbitrary number of finite rectangular opaque barriers and generalize earlier results by showing that the total tunneling phase time depends neither on the barrier thickness nor on the inter-barrier separation. We also predict two novel peculiar features of the system considered, namely the independence of the transit time (for non resonant tunneling) and the resonant frequency on the number of barriers crossed, which can be directly tested ...

Esposito, S.

2002-01-01

364

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)

365

Electroresistance effects in ferroelectric tunnel barriers  

OpenAIRE

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

366

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

367

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.

368

Canadian tunnelling, 1989. Tunnelling canadien, 1989  

Energy Technology Data Exchange (ETDEWEB)

A compilation is presented of papers on various aspects of Canadian tunneling research and experience. Papers are included from a tunnelling conference held in Toronto in 1989 as well as original papers from around the world. Topics of papers include hydroelectric power tunnels, railway tunnel construction and design, design and performance of vertical shafts, microcomputer techniques in geologic mapping, tunnels in swelling rock, tunnel instrumentation analysis, road tunnels, ventilation systems, use of tunnel boring machines, drilling equipment used for underground structures, construction of drainage adits, the New Austrian Tunnelling Method, tunnel construction management, and cooling water tunnels for nuclear power plants. Separate abstracts have been prepared for 2 papers from this compilation.

Eisenstein, Z. (ed.)

1989-01-01

369

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

370

The LEP tunnel  

CERN Multimedia

The LEP collider, which ran from 1989 to 2000. Electrons and positrons were accelerated through these magnets until they were travelling at almost the speed of light before colliding in the centre of one of the four detectors. The huge circumference of the ring means that the curvature is very small and so the tunnel looks rather straight.

Patrice Loiez

1991-01-01

371

Electronic textbooks as a professional resource after dental school.  

Science.gov (United States)

In two previous studies of dental students' attitudes about the VitalSource Bookshelf, a digital library of dental textbooks, students expressed negative opinions about owning and reading electronic textbooks. With the assumption that dentists would find the digital textbooks useful for patient care, the authors surveyed recent graduates to determine if their attitude toward the VitalSource Bookshelf had changed. A brief survey was sent to 119 alumni from the classes of 2009 and 2010 of one U.S. dental school. Forty-seven (39.5 percent) completed the questionnaire. Eighteen respondents (48.3 percent) reported using the e-textbooks often or sometimes. The twenty-nine dentists who said they have not used the collection since graduation reported preferring print books or other online sources or having technical problems when downloading the books to a new computer. Only five respondents selected the VitalSource Bookshelf as a preferred source of professional information. Most of the respondents reported preferring to consult colleagues (37.8 percent), the Internet (20 percent), or hardcopy books (17.8 percent) for information. When asked in an open-ended question to state their opinion of the Bookshelf, nineteen (42.2 percent) responded positively, but almost one-third of these only liked the search feature. Six respondents reported that they never use the program. Twenty-two said they have had technical problems with the Bookshelf, including fifteen who have not been able to install it on a new computer. Many of them said they have not followed up with either the dental school or VitalSource support services to overcome this problem. Our study suggests that dentists, similar to dental students, dislike reading electronic textbooks, even with the advantage of searching a topic across more than sixty dental titles. PMID:22550109

Bates, Michael L; Strother, Elizabeth A; Brunet, Darlene P; Gallo, John R

2012-05-01

372

Generation of single-frequency coherent transition radiation by a prebunched electron beam traversing a vacuum beam tunnel in a periodic medium  

International Nuclear Information System (INIS)

A classical Maxwell equation longitudinal boundary value problem analysis of a prebunched ac electron beam traversing a vacuum tunnel in a periodic layered dielectric medium is used to calculate the single-frequency coherent transition radiation power generated per unit length. For low voltage electron beams in the kilovolt range, only transition radiation is produced, the Cerenkov effect being below threshold. A numerical example indicates that power levels of the order of milliwatts per centimeter can be produced in the 35 GHz range with 3-10 keV beams. An interesting aspect of transition versus Cerenkov radiation is that the transition 'cone' of radiation is in the backward direction of the charge beam

373

Hybridization effects on the out-of-plane electron tunneling properties of monolayers: is h-BN more conductive than graphene?  

Science.gov (United States)

Electron transport properties through multilayers of hexagonal boron nitride (h-BN) sandwiched between gold electrodes is investigated by density functional theory together with the non-equilibrium Green’s function method. The calculated results find that despite graphene being a gapless semimetal and h-BN two-dimensional layer being an insulator, the transmission function perpendicular to the atomic layer plane in both systems is nearly identical. The out-of-plane tunnel current is found to be strongly dependent on the interaction at the interface of the device. As a consequence, single layer h-BN coupled with atomically flat weakly interacting metals such as gold may not work as a good dielectric material, but the absence of sharp resonances would probably lead to more stable out-of-plane electronic transport properties compared to graphene.

Zhong, Xiaoliang; Amorim, Rodrigo G.; Rocha, Alexandre R.; Pandey, Ravindra

2014-08-01

374

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

Directory of Open Access Journals (Sweden)

Full Text Available The Hamiltonian of electrons interacting with interface phonons in three-barrier resonant tunneling structure is established using the first principles within the models of effective mass and polarization continuum. Using the Green's functions method, the temperature shifts and decay rates of operating electron states are calculated depending on geometric design of three-barrier nano-structure GaAs/AlxGa1-xAs which is an active region of quantum cascade detector. It is established that independently of the temperature, the energy of quantum transition during the process of electromagnetic field absorption is a nonlinear weakly varying function of the position of the inner barrier with respect to the outer barriers of the structure.

M.V. Tkach

2014-06-01

375

Structure of epitaxial thin TiOx films on W(110) as studied by low energy electron diffraction and scanning tunneling microscopy  

International Nuclear Information System (INIS)

We have studied the growth and structure of thin TiOx films on W(110) using Auger electron spectroscopy, low energy electron diffraction (LEED), and scanning tunneling microscopy (STM). The procedure used to grow these films includes the deposition of Ti metal onto the W(110) surface followed by a saturation oxygen exposure. LEED and STM reveal that several different ordered TiOx film structures can result depending upon the initial amount of Ti deposited and the final annealing temperature. Specifically, the oxidation and anneal to 1350 K of a one monolayer (ML) film of Ti resulted in the formation of a strained ML structure that has a distorted hexagonal lattice and long-range order as observed by LEED and STM. The epitaxial relationship of this 1 ML TiOx structure with the W(110) substrate is found to occur with a Nishiyama endash Wassermann orientation. copyright 1996 American Vacuum Society

376

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

377

Deconvolution of the electronic density of states of tip and sample from scanning tunneling spectroscopy data: Proof of principle  

Science.gov (United States)

It is demonstrated that deconvolution of the density of states (DOS) of tip and sample from scanning tunneling spectroscopy data is possible within the framework of a one-dimensional Wentzel-Kramers-Brillouin approximation if additional information such as data sets taken at two sufficiently different tip-sample separations is provided. The basic concept is to convert the underlying integral equation for the tunneling current by differentiation with respect to the sample bias (first set) and, in addition, with respect to the tip-sample separation (second set) into two sets of Volterra integral equations of the second kind with two equations for the tip and another two for the sample DOS. Though these integro-differential equations can in principle be solved numerically employing the Neumann approximation scheme, it turns out in practice that suitable iteration schemes have to be found to guarantee stable solutions. Employing tunneling data taken at two sufficiently different tip-sample separations, it is demonstrated that iterating suitably through the system of equations results in a recovery and deconvolution of the tip and sample DOS. The underlying formalism is derived, examples are given and limitations discussed. Finally, we apply an adapted procedure to experimental data obtained on Nb(110) and compare the deconvolved sample DOS with density-functional theory data.

Koslowski, B.; Pfeifer, H.; Ziemann, P.

2009-10-01

378

Scanning Tunneling Microscopy  

Science.gov (United States)

Use a virtual scanning tunneling microscope (STM) to observe electron behavior in an atomic-scale world. Walk through the principles of this technology step-by-step. First learn how the STM works. Then try it yourself! Use a virtual STM to manipulate individual atoms by scanning for, picking up, and moving electrons. Finally, explore the advantages and disadvantages of the two modes of an STM: the constant-height mode and the constant-current mode.

The Concord Consortium

2011-12-11

379

Tunnel-City 1985. Contributions  

Energy Technology Data Exchange (ETDEWEB)

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

1985-01-01

380

Tunneling spectroscopy of a ballistic quantum wire  

Science.gov (United States)

We implement a tunneling-spectroscopy experiment on a ballistic quantum wire by modifying the split-gate method to realize a wire in which an external reservoir can be used to inject tunneling electrons into its interior. We observe a number of features in the tunnel signal of these structures, including a pronounced response associated with the one-dimensional density of states of the wire, as well as signatures of coherent interference of the injected electrons, and dephasing introduced by tunneling of electrons between the wire and the external reservoir.

Ramamoorthy, A.; Mourokh, L.; Reno, J. L.; Bird, J. P.

2008-07-01

381

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

International Nuclear Information System (INIS)

The influence of crystal defects on the phonon spectra was studied for fcc lead using superconducting tunneling spectroscopy. The theory predicts low frequency modes for the vibrational states of interstitials in (100) dumbbell configuration. Low temperature irradiation of superconducting point contacts with fast ions (point contact thickness small compared to the average ion range) showed radiation-induced structures in the low-energy part of the Eliashberg function for lead. These resonant modes are reduced by annealing at 18.5 K; they are attributed to small interstitial clusters. The radiation-induced structures are completely removed by room temperature annealing. (orig.)

382

Visualization of the effect of structural supermodulation on electronic structure in IrTe$_{2}$ by scanning tunneling spectroscopy  

OpenAIRE

We report on the scanning tunneling spectroscopy experiments on single crystals of IrTe$_{2}$. A structural supermodulation and a local density-of-states (LDOS) modulation with a wave vector of $q$ = 1/5$\\times$$2\\pi /a_{0}$ ($a_{0}$ is the lattice constant in the $ab$-plane) have been observed at 4.2K where the sample is in the monoclinic phase. %We cannot find an energy gap emerging reproducibly.% on the region where the supermodulation resides. As synchronized with the su...

Machida, T.; Fujisawa, Y.; Igarashi, K.; Kaneko, A.; Ooi, S.; Mochiku, T.; Tachiki, M.; Komori, K.; Hirata, K.; Sakata, H.

2013-01-01

383

Resonant Structures in the Low-Energy Electron Continuum for Single Ionization of Atoms in the Tunneling Regime  

OpenAIRE

We present results of high-resolution experiments on single ionization of He, Ne and Ar by ultra-short (25 fs, 6 fs) 795 nm laser pulses at intensities 0.15-2.0x10^15 W/cm^2. We show that the ATI-like pattern can survive deep in the tunneling regime and that the atomic structure plays an important role in the formation of the low-energy photoelectron spectra even at high intensities. The absence of ponderomotive shifts, the splitting of the peaks and their degeneration for f...

Rudenko, A.; Zrost, K.; Schro?ter, C. D.; Jesus, V. L. B.; Feuerstein, B.; Moshammer, R.; Ullrich, J.

2004-01-01

384

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

International Nuclear Information System (INIS)

We have used electron-tunneling measurements to determine the density of states of quench-condensed thin films of In-Cr, Zn-Mn, and Al-Mn, and of annealed thin films of Zn-Mn. The results on In-Cr and Zn-Mn were compared with Shiba's theory for magentic atoms in superconductors. We observed the localized band of states predicted to form in the energy gap of such alloys, though the observed band was broader than that predicted. The annealed samples of Zn-Mn showed a narrower band than did the quench-condensed samples. Reasonable agreement with Shiba's theory was found if s, p, and d wave scattering were included. The results on Al-Mn were compared with Salomaa and Nieminen's theory for nonmagnetic resonant-state atoms in superconductors. The predicted band of states was not observed. Our measurements indicate that Mn in quench-condensed Al is nonmagnetic. Any resonant states which do exist in the superconducting alloy are too broad to be seen in our tunneling measurement

385

Stability Tunnel  

Science.gov (United States)

Engineers operate the controls of the Stability Tunnel: Plans for a new tunnel to study stability problems began in the late thirties. The Stability Tunnel was authorized in 1939 and began operations in June 1941. The installation was completed in December that year with the completion of a new 10,000 Horsepower Diesel-electric generating plant. It was a single return, closed jet tunnel with a 6-foot square test section. The tunnel was disassembled and shipped to Virginia Polytechnic Institute and State University in 1958. The tunnel had two separate test sections: one for curved flow, the other for rolling flow. 'The facility...simulates the motion of the aircraft in curved or rolling flight. This is done by actually curving or rolling the airstream as it passes over the model and at the same time providing the proper velocity distribution.' (From AIAA-80-0309) >From Alan Pope, Wind-Tunnel Testing: 'The only tunnel directly designed for dynamic stability work is located at the Langley Field branch of the NACA. Its most vital feature is its ability to subject the models to curving air streams that simulate those actually encountered when an airplane rolls, pitches, or yaws. the rotating airstream for simulating roll is produced by a motor-driven paddle just ahead of the test section. Curved air of properly varying velocity for simulating pitch and yaw is produced by a combination of a curved test section and velocity screens. The proper use of this apparatus makes possible the determination of the stability derivatives.' (pp. 13-14)

1943-01-01

386

Insights into electron tunneling across hydrogen-bonded base-pairs in complete molecular circuits for single-stranded DNA sequencing  

International Nuclear Information System (INIS)

We report a first-principles study of electron ballistic transport through a molecular junction containing deoxycytidine-monophosphate (dCMP) connected to metal electrodes. A guanidinium ion and guanine nucleobase are tethered to gold electrodes on opposite sides to form hydrogen bonds with the dCMP molecule providing an electric circuit. The circuit mimics a component of a potential device for sequencing unmodified single-stranded DNA. The molecular conductance is obtained from DFT Green's function scattering methods and is compared to estimates from the electron tunneling decay constant obtained from the complex band structure. The result is that a complete molecular dCMP circuit of 'linker((CH2)2)-guanidinium-phosphate-deoxyribose-cytosine-guanine' has a very low conductance (of the order of fS) while the hydrogen-bonded guanine-cytosine base-pair has a moderate conductance (of the order of tens to hundreds of nS). Thus, while the transverse electron transfer through base-pairing is moderately conductive, electron transfer through a complete molecular dCMP circuit is not. The gold Fermi level is found to be aligned very close to the HOMO for both the guanine-cytosine base-pair and the complete molecular dCMP circuit. Results for two different plausible geometries of the hydrogen-bonded dCMP molecule reveal that the conductance varies from fS for an extended structure to pS for a slightly compressed structure.ucture.

387

Coherent tunneling and giant tunneling magnetoresistance in Co2FeAl/MgO/CoFe magnetic tunneling junctions  

Science.gov (United States)

Spin-dependent coherent tunneling has been experimentally observed in high-quality sputtered-deposited Co2FeAl/MgO/CoFe epitaxial magnetic tunneling junctions (MTJs). Consequently, the microfabricated MTJs manifest a very large tunnel magnetoresistance (TMR) at room temperature and an unexpectedly TMR oscillation as a function of MgO barrier thickness. First-principles electronic band calculations confirm the pronounced coherent tunneling effect and are in good agreement with the experimental data. The present work demonstrates the importance of coherent tunneling for large TMR with Heusler alloys

Wang, Wenhong; Liu, Enke; Kodzuka, Masaya; Sukegawa, Hiroaki; Wojcik, Marec; Jedryka, Eva; Wu, G. H.; Inomata, Koichiro; Mitani, Seiji; Hono, Kazuhiro

2010-04-01

388

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

OpenAIRE

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

389

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

390

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

International Nuclear Information System (INIS)

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

391

Vibrational Coherences in Nano-Elastic Tunneling  

OpenAIRE

Charging a nano-scale oscillator by single electron tunneling leads to an effective double-well potential due to image charges. We combine exact numerical diagonalizations with generalized Master equations and show that the resulting quantum tunneling of the mechanical degree of freedom can be visualized in the electronic current noise spectrum.

Hu?bener, Hannes; Brandes, Tobias

2007-01-01

392

Quantum Tunnelling to the Origin and Evolution of Life  

OpenAIRE

Quantum tunnelling is a phenomenon which becomes relevant at the nanoscale and below. It is a paradox from the classical point of view as it enables elementary particles and atoms to permeate an energetic barrier without the need for sufficient energy to overcome it. Tunnelling might seem to be an exotic process only important for special physical effects and applications such as the Tunnel Diode, Scanning Tunnelling Microscopy (electron tunnelling) or Near-field Optical Microscopy operating ...

Trixler, Frank

2013-01-01

393

Signatures of electron-magnon interaction in charge and spin currents through magnetic tunnel junctions: A nonequilibrium many-body perturbation theory approach  

Science.gov (United States)

We develop a numerically exact scheme for resumming certain classes of Feynman diagrams in the self-consistent perturbative expansion for the electron and magnon self-energies in the nonequilibrium Green function formalism applied to a coupled electron-magnon (e-m) system driven out of equilibrium by the applied finite bias voltage. Our scheme operates with the electronic and magnonic GFs and the corresponding self-energies viewed as matrices in the Keldysh space, rather than conventionally extracting their retarded and lesser components, which greatly simplifies translation of diagrams into compact mathematical expressions and their computational implementation. This is employed to understand the effect of inelastic e-m scattering on charge and spin current vs bias voltage Vb in F/I/F (F-ferromagnet; I-insulating barrier) magnetic tunnel junctions (MTJs), which are modeled on a quasi-one-dimensional (quasi-1D) tight-binding lattice for the electronic subsystem and quasi-1D Heisenberg model for the magnonic subsystem. For this purpose, we evaluate the Fock diagram for the electronic self-energy and the electron-hole polarization bubble diagram for the magnonic self-energy. The respective electronic and magnonic GF lines within these diagrams are the fully interacting ones, thereby requiring to solve the ensuing coupled system of nonlinear integral equations self-consistently. Despite using the quasi-1D model and treating e-m interaction in many-body fashion only within a small active region consisting of few lattice sites around the F/I interface, our analysis captures essential features of the so-called zero-bias anomaly observed [V. Drewello, J. Schmalhorst, A. Thomas, and G. Reiss, Phys. Rev. B 77, 014440 (2008), 10.1103/PhysRevB.77.014440] in both MgO- and AlOx-based realistic 3D MTJs where the second derivative d2I /dVb2 (i.e., inelastic electron tunneling spectrum) of charge current exhibits sharp peaks of opposite sign on either side Vb=0. We show that this is closely related to a substantially modified magnonic density of states (DOS) after the e-m interaction is turned on—the magnonic bandwidth over which DOS is nonzero becomes broadened, thereby making e-m scattering at arbitrary small bias voltage possible, while DOS also acquires peaks (on the top of a continuous background) signifying the formation of quasibound states of magnons dressed by the cloud of electron-hole pair excitations. We also demonstrate that the sum of electronic spin currents in all of the semi-infinite leads attached to the active region quantifies the loss of spin angular momentum carried away from the active region by the magnonic spin current.

Mahfouzi, Farzad; Nikoli?, Branislav K.

2014-07-01

394

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

Science.gov (United States)

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

Koehn, Shona L.; Hawamdeh, Suliman

2010-01-01

395

Implementation of an Electronic Resource Assessment System in an Academic Library  

Science.gov (United States)

Purpose: The purpose of this paper is to provide a library with useful information about selection criteria for an electronic resource assessment system and practical assistance on how to implement efficiently such a system. Design/methodology/approach: The paper is based on literature review, desk research, and implementation experience.…

Xu, Fei

2010-01-01

396

Programmable ferroelectric tunnel memristor  

Science.gov (United States)

We report an analogously programmable memristor based on genuine electronic resistive switching combining ferroelectric switching and electron tunneling. The tunnel current through an 8 unit cell thick epitaxial Pb(Zr[0.2]Ti[0.8])O[3] film sandwiched between La[0.7]Sr[0.3]MnO[3] and cobalt electrodes obeys the Kolmogorov-Avrami-Ishibashi model for bidimensional growth with a characteristic switching time in the order of 10^-7 seconds. The analytical description of switching kinetics allows us to develop a characteristic transfer function that has only one parameter viz. the characteristic switching time and fully predicts the resistive states of this type of memristor.

Quindeau, Andy; Hesse, Dietrich; Alexe, Marin

2014-02-01

397

Programmable ferroelectric tunnel memristor  

Directory of Open Access Journals (Sweden)

Full Text Available We report an analogously programmable memristor based on genuine electronic resistive switching combining ferroelectric switching and electron tunneling. The tunnel current through an 8 unit cell thick epitaxial Pb(Zr[0.2]Ti[0.8]O[3] film sandwiched between La[0.7]Sr[0.3]MnO[3] and cobalt electrodes obeys the Kolmogorov-Avrami-Ishibashi model for bidimensional growth with a characteristic switching time in the order of 10^-7 seconds. The analytical description of switching kinetics allows us to develop a characteristic transfer function that has only one parameter viz. the characteristic switching time and fully predicts the resistive states of this type of memristor.

AndyQuindeau

2014-02-01

398

Wind Tunnel  

Science.gov (United States)

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

Lawrence Hall of Science

2009-01-01

399

Soliton Tunneling Transistor  

OpenAIRE

We report on a macroscopic version of the single-electron transistor (SET), which we call the soliton tunneling transistor (STT). The STT, consists of a gate capacitor coupled to a NbSe$_{3}$ crystal with a charge density wave (CDW). The current-voltage characteristic of an STT is periodically modulated by the gate voltage, as in the SET,except that the periodicity corresponds to a macroscopic displacement charge. These results appear to be consistent with time- correlated q...

Miller, Jr; Cardenas, G.; Garcia, A.; More, W.; Beckwith, A. W.; Mccarten, J. P.

2001-01-01

400

Origin of tunneling spin polarization  

International Nuclear Information System (INIS)

Full text: The relationship of the spin polarization of current tunneling from a ferromagnetic material through a tunnel barrier to its magnetization is of considerable current interest, particularly with regard to the development of magnetic tunnel junctions with high tunneling magnetoresistance suitable for magnetic memory and sensor applications 1. The tunneling spin polarization (TSP) can be directly measured using superconducting tunneling spectroscopy (STS) or inferred from measurements of tunneling magnetoresistance (TMR). The TSP depends not only on the ferromagnetic material but also on the tunneling barrier. Using crystalline (100) oriented MgO tunnel barriers and bcc CoFe electrodes, TSP values exceeding 85% are found from STS studies at 0.25 K with TMR values greater than 300% at 5K2. The same ferromagnetic electrodes using conventional amorphous alumina tunnel barriers exhibit TSP values of only ?50%. In these cases the sign of TSP is positive corresponding to the preferential tunneling of majority spin electrons. However, using magnetic electrodes formed from the ferrimagnetic rare-earth transition-metal alloys, such as Co-Gd, we show that the sign of the TSP and TMR can be either positive or negative depending on the composition of the alloy and temperature. For alloys of Co and Fe with Pt and Pd we show that the TSP is strongly influenced by bonding at the tunnel barrier/ ferromagnetic electrode interface. In particular, we compare resultsrface. In particular, we compare results for CoPt alloys with AlN and Al2O3 tunnel barriers. For AlN barriers the TSP decreases linearly with increasing Pt content whereas for Al2O3 tunnel barriers the TSP has only a weak dependence on Pt content for up to ?50 atomic % Pt. These results can be understood as a consequence of stronger Co - oxygen bonds as compared to Pt - oxygen bonds. References: 1. S. S. P. Parkin, X. Jiang, C. Kaiser, et al., Proc. IEEE 91, 661 (2003). 2 . S. P. Parkin, C. Kaiser, A. Panchula, et al., Nature Mater. 3, 862 (2004)

401

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

Science.gov (United States)

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

Shizu, Katsuyuki; Sato, Tohru; Tanaka, Kazuyoshi

2010-10-01

402

Enhancing metal-insulator-insulator-metal tunnel diodes via defect enhanced direct tunneling  

Science.gov (United States)

Metal-insulator-insulator-metal tunnel diodes with dissimilar work function electrodes and nanolaminate Al2O3-Ta2O5 bilayer tunnel barriers deposited by atomic layer deposition are investigated. This combination of high and low electron affinity insulators, each with different dominant conduction mechanisms (tunneling and Frenkel-Poole emission), results in improved low voltage asymmetry and non-linearity of current versus voltage behavior. These improvements are due to defect enhanced direct tunneling in which electrons transport across the Ta2O5 via defect based conduction before tunneling directly through the Al2O3, effectively narrowing the tunnel barrier. Conduction through the device is dominated by tunneling, and operation is relatively insensitive to temperature.

Alimardani, Nasir; Conley, John F.

2014-08-01

403

Enhancing metal-insulator-insulator-metal tunnel diodes via defect enhanced direct tunneling  

International Nuclear Information System (INIS)

Metal-insulator-insulator-metal tunnel diodes with dissimilar work function electrodes and nanolaminate Al2O3-Ta2O5 bilayer tunnel barriers deposited by atomic layer deposition are investigated. This combination of high and low electron affinity insulators, each with different dominant conduction mechanisms (tunneling and Frenkel-Poole emission), results in improved low voltage asymmetry and non-linearity of current versus voltage behavior. These improvements are due to defect enhanced direct tunneling in which electrons transport across the Ta2O5 via defect based conduction before tunneling directly through the Al2O3, effectively narrowing the tunnel barrier. Conduction through the device is dominated by tunneling, and operation is relatively insensitive to temperature.

404

Enhancing metal-insulator-insulator-metal tunnel diodes via defect enhanced direct tunneling  

Energy Technology Data Exchange (ETDEWEB)

Metal-insulator-insulator-metal tunnel diodes with dissimilar work function electrodes and nanolaminate Al{sub 2}O{sub 3}-Ta{sub 2}O{sub 5} bilayer tunnel barriers deposited by atomic layer deposition are investigated. This combination of high and low electron affinity insulators, each with different dominant conduction mechanisms (tunneling and Frenkel-Poole emission), results in improved low voltage asymmetry and non-linearity of current versus voltage behavior. These improvements are due to defect enhanced direct tunneling in which electrons transport across the Ta{sub 2}O{sub 5} via defect based conduction before tunneling directly through the Al{sub 2}O{sub 3}, effectively narrowing the tunnel barrier. Conduction through the device is dominated by tunneling, and operation is relatively insensitive to temperature.

Alimardani, Nasir; Conley, John F., E-mail: jconley@eecs.oregonstate.edu [School of Electrical Engineering and Computer Science, Oregon State University, Corvallis, Oregon 97331 (United States)

2014-08-25

405

Tunneling spectroscopy of novel superconductors  

International Nuclear Information System (INIS)

Recent discoveries of exciting new superconductors have led to further exciting speculations about novel mechanisms and/or pairing. Tunneling spectroscopy can again play an important role in establishing the applicability of these ideas to specific superconductors. In addition to the traditional role of verifying in detail the electron-phonon coupling through ?2F, in many cases the magnitude of the gap compared to the BCS prediction or the crystalline gap anisotropy can reveal direct information about novel mechanisms and/or pairing. Since many of these new materials have only been available as bulk samples, or bulk single-crystal studies are desired, the technique of vacuum tunneling spectroscopy, pioneered by Poppe (1981) for superconductors, is most appropriate. However, thick, nonconducting surface layers are often found which prevent true vacuum tunneling. For these samples, mechanical contact of the tunneling tip is required to break through the surface layer to the superconductor below. The resulting point-contact tunneling can, however, emulate many of the results of true tunneling through a vacuum or insulator. In this paper, they shall briefly review relevant tunneling techniques and some recent experiments on magnetic, organic, heavy fermion and high-T/sub c/ oxide superconductors. Connections are made to theoretical ideas, especially regarding novel mechanisms and/or pairing

406

Suppression of tunneling into multiwall carbon nanotubes.  

OpenAIRE

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

Bachtold, A.; Jonge, M.; Grove-rasmussen, K.; Mceuen, P. L.; Buitelaar, M.; Scho?nenberger, C.

2001-01-01

407

On superluminal tunneling [review article  

Science.gov (United States)

Photonic tunneling is currently of theoretical and applied interest. In a previous review, faster-than-light (i.e. superluminal) photonic tunneling was discussed (Progr. Quantum Electron. 21 (1997) 81). Recently, superluminal photonic pulse transmission and reflection have been measured at microwave and infrared frequencies. It seems clear that superluminal photonic and electronic devices will become a reality in the near future. In the present report, we introduce new experimental and theoretical data on superluminal tunneling and reflection. Data of reflection by barriers have evidenced the nonlocal nature of tunneling. Asymmetric barriers have revealed a strange asymmetric reflection behavior in time. The principle of causality is not violated by a superluminal speed even though the time duration between cause and effect can be shortened compared with a luminal interaction exchange. An empirical relationship independent of the barrier system is found for the photonic tunneling time. This relation seems to be universal for all kind of tunneling processes in the case of single opaque barriers. We show that the superluminal velocity can be applied to speed up photonic modulation and transmission as well as to improve microelectronic devices.

Nimtz, Günter

408

Time dependent characteristics of electron tunnelling processes in H-, O- and F- formation on Ag(1 1 1)  

International Nuclear Information System (INIS)

Results of a study of electron transfer processes in the interaction of hydrogen, oxygen and fluorine with Ag(1 1 1) are reported for a wide range of interaction times. We observe that for long interaction times, the yield of H-, resulting from resonant electron exchange, is much larger than what would be expected for a jellium like metal surface with a similar work function. For short interaction times on the other hand, the yields follow the trend for jellium like surfaces. These results confirm the predictions of the theoretical work using a wave packet propagation method (Phys. Rev. Lett. 80 (1998) 1996) on electron transfer on surfaces with L band gap. In the case of O- and F- significant effects were not observed

409

Tunneling and Resonant Conductance in One-Dimensional Molecular Structures  

CERN Document Server

We present a theory of tunneling and resonant transitions in one-dimensional molecular systems which is based on Green's function theory of electron sub-barrier scattering off the structural units (or functional groups) of a molecular chain. We show that the many-electron effects are of paramount importance in electron transport and they are effectively treated using a formalism of sub-barrier scattering operators. The method which calculates the total scattering amplitude of the bridge molecule not only predicts the enhancement of the amplitude of tunneling transitions in course of tunneling electron transfer through one-dimensional molecular structures but also allows us to interpret conductance mechanisms by calculating the bound energy spectrum of the tunneling electron, the energies being obtained as poles of the total scattering amplitude of the bridge molecule. We found that the resonant tunneling via bound states of the tunneling electron is the major mechanism of electron conductivity in relatively l...

Oleynik, I I; Posvyanskii, V S

2005-01-01

410

Medical Image Resource Center–making electronic teaching files from PACS  

OpenAIRE

A picture archive and communications system (PACS) is a rich source of images and data suitable for creating electronic teaching files (ETF). However, the potential for PACS to support nonclinical applications has not been fully realized: at present there is no mechanism for PACS to identify and store teaching files; neither is there a standardized method for sharing such teaching images. The Medical Image Resource Center (MIRC) is a new central image repository that defines standards for dat...

Tchoyoson Lim, C. C.; Yang, Guo Liang; Nowinski, Wieslaw L.; Hui, Francis

2003-01-01

411

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

Scientific Electronic Library Online (English)

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

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

2012-09-01

412

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

International Nuclear Information System (INIS)

Fundamental understanding of interfacial electron transfer (ET) among electrolyte/DNA/solid-surface will facilitate the design for electrical detection of DNA molecules. In this report, the electron transfer characteristics of synthetic DNA (sequence from pathogenic Cryptosporidium parvum) self-assembled on a gold surface was electrochemically studied. The effects of immobilization order on the interface ET related parameters such as diffusion coefficient (D0), surface coverage (?R), and monolayer thickness (di) were determined by cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). DNA surface density (?DNA) was determined by the integration of the charge of the electro-oxidation current peaks during the initial cyclic voltammetry scans. It was found that the DNA surface densities at different modifications followed the order: ?DNA (dsS-DNA/Au) > ?DNA (MCH/dsS-DNA/Au) > ?DNA (dsS-DNA/MCH/Au). It was also revealed that the electro-oxidation of the DNA modified gold surface would involve the oxidation of nucleotides (guanine and adenine) with a 5.51 electron transfer mechanism and the oxidative desorption of DNA and MCH molecules by a 3 electron transfer mechanism. STM topography and current image analysis indicated that the surface conductivity after each surface modification followed the order: dsS-DNA/Au < MCH/dsS-DNA/Au < oxidized MCH/dsS-DNA/Au < Hoechst/oxidizedzed MCH/dsS-DNA/Au < Hoechst/oxidized MCH/dsS-DNA/Au. The results from this study suggested a combination of variations in immobilization order may provide an alternative approach for the optimization of DNA hybridization and the further development for electrical detection of DNA.

413

Visualizing the Interplay of Structural and Electronic Disorders in High-Temperature Superconductors Using Scanning Tunneling Microscopy  

OpenAIRE

The discovery of high-\\(T_c\\) superconductivity in 1986 generated tremendous excitement. However, despite over 25 years of intense research efforts, many properties of these complex materials are still poorly understood. For example, the cuprate phase diagram is dominated by a mysterious "pseudogap" state, a depletion in the Fermi level density of states which persists above the superconducting critical temperature \\(T_c\\). Furthermore, these materials are typically electronically inhomogeneo...

Zeljkovic, Ilija

2013-01-01

414

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

Directory of Open Access Journals (Sweden)

Full Text Available Abstract Si and Ge growth on the stripe-patterned Si (001 substrates is studied using in situ reflection high-energy electron diffraction (RHEED and scanning tunneling microscopy (STM. During Si buffer growth, the evolution of RHEED patterns reveals a rapid change of the stripe morphology from a multifaceted “U” to a single-faceted “V” geometry with {119} sidewall facets. This allows to control the pattern morphology and to stop Si buffer growth once a well-defined stripe geometry is formed. Subsequent Ge growth on “V”-shaped stripes was performed at two different temperatures of 520 and 600°C. At low temperature of 520°C, pronounced sidewall ripples are formed at a critical coverage of 4.1 monolayers as revealed by the appearance of splitted diffraction streaks in RHEED. At 600°C, the ripple onset is shifted toward higher coverages, and at 5.2 monolayers dome islands are formed at the bottom of the stripes. These observations are in excellent agreement with STM images recorded at different Ge coverages. Therefore, RHEED is an efficient tool for in situ control of the growth process on stripe-patterned substrate templates. The comparison of the results obtained at different temperature reveals the importance of kinetics on the island formation process on patterned substrates.

Sanduijav B

2010-01-01

415

Field emission properties originated from 2D electronics gas successively tunneling for 1D heterostructures of ZnO nanobelts decorated with In2O3 nanoteeth  

International Nuclear Information System (INIS)

ZnO–In2O3 one-dimensional (1D) nanosized heterostructures constructed by ZnO belts and In2O3 tooth-like particles were self-assembled on single crystal silicon substrate using thermal chemical vapor transport and condensation without being aided by any metal catalyst. The morphology, structure, and composition of the as-synthesized 1D heterostructures were analyzed in detail. The widths of the ZnO nanobelts ranged from several tens of nanometers to one micrometer, and the lengths ranged from several tens to one hundred of micrometers. In2O3 tooth-like nanoparticles with sizes of about 50–100 nm were found grown at two edges of ZnO nanobelts. ZnO nanobelts grew along [101bar 0] direction, whereas In2O3 nanoteeth grew along [311bar], [31bar 1], [3bar 1bar 1], and [3bar 11bar] directions so as to form rhombus-shaped structures. The growth mechanism of the nanosized heterostructures was discussed on the basis of the vapor–solid process and polar surface effect of ZnO nanobelts. Field emission characteristics of the as-prepared heterostructures were measured and explained by energy band theory of heterostructure in detail. It is important to note that the 2D electronics gas (2DEG) was formed between the ZnO energy band bending down and the interface of the heterostructure. The successive tunneling of 2DEG that took place from ZnO to In2O3 and then from InO3 and then from In2O3 to vacuum was the main reason resulting in electronics emission for the nanosized heterostructures in the process of field emission.

416

Effect of surface treatment on the ?-WO3(001) surface: A comprehensive study of oxidation and reduction by scanning tunneling microscopy and low-energy electron diffraction  

International Nuclear Information System (INIS)

The structure of the (001) surface of monoclinic ?-WO3 was characterized using scanning tunneling microscopy (STM), Auger electron spectroscopy (AES), and low-energy electron diffraction (LEED). The surface structure depended strongly on preparation conditions. Oxidizing by heating in O2 removed carbonaceous impurities and resulted in large atomically rough terraces. Subsequent heating in lower O2 pressures led to metastable superstructures and c(2x2) terraces. Continued heating progressively reduced the surface, resulting in a series of reconstructions. Each could be explained in terms of ordered oxygen vacancies. First, regions of a c(2x2) reconstruction grew. This structure corresponds to a WO2 plane in which half the W6+ sites are covered by terminal O. Since all the W atoms are in a 6+ oxidation state, this surface is considered 'fully oxidized'. Certain STM images of the c(2x2) terraces revealed a pseudo-primitive-(2x2) periodicity that can be related to the monoclinic distortion from cubic symmetry. It is shown that the distortion is always present but the ability to detect it depends on the tip. The distortion also caused twinning that lead to spot splitting in LEED patterns. The splitting disappeared on heating to 785 K when the bulk converted to orthorhombic symmetry. Continued reduction produced areas with (2x2), (6x2), and c(4x2) periodicities. These reconstructions are formed when further terminal O tions are formed when further terminal O is removed, and half the total W sites are reduced to W5+. Sputtering and ultrahigh vacuum annealing also reduced the surface, ultimately leading to 'fully reduced' (1x1) terraces with no terminal oxygen and only W5+ surface cations. These structural transformations were reversible: at any stage during reduction, heating in ?10-4 Torr of O2 reoxidized the surface, regenerating the original rough morphology

417

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

Directory of Open Access Journals (Sweden)

Full Text Available Large quantities of waste electronic devices (e-waste at their end-of-life, generated internally or imported illegally from developed countries, are currently being managed in the developing countries, through low-end means such as crude backyard recycling and disposal at unlined landfills or open dumps. The extension of the lifespan of electronic devices through reuse options such as repair, reconditioning and remanufacturing should be a priority in the management of electronic waste in developing countries considering the near absence of state-of-the-art recycling facilities in these countries. Life extension through product and component reuse is especially critical to electronic products because in recent years, electronics have increased in technological complexity, with new product innovations and ever shortening product life expectancy. For many products, environmentalists assume that reuse is environmentally beneficial because it replaces the manufacturing and purchase of new goods. However, on the contrary, manufacturers may oppose this type of reuse for the same reason. There is an urgent need to control the trans-boundary movement of electronic scrap especially to countries without established recycling facilities. Importations of secondhand electronics make such devices available to those who cannot afford new products. However, an international method of testing and certification is needed to ensure that exported secondhand devices are functional. Establishment of formal recycling facilities for e-waste in the developing countries will ensure resource reutilization with both economical and ecological gains. This study reviews options available in working towards eco-efficient management of e-waste in developing countries in the light of the present low-end management practices.

Innocent Chidi Nnorom

2007-01-01

418

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

Science.gov (United States)

Large quantities of waste electronic devices (e-waste) at their end-of-life, generated internally or imported illegally from developed countries, are currently being managed in the developing countries, through low-end means such as crude backyard recycling and disposal at unlined landfills or open dumps. The extension of the lifespan of electronic devices through reuse options such as repair, reconditioning and remanufacturing should be a priority in the management of electronic waste in developing countries considering the near absence of state-of-the-art recycling facilities in these countries. Life extension through product and component reuse is especially critical to electronic products because in recent years, electronics have increased in technological complexity, with new product innovations and ever shortening product life expectancy. For many products, environmentalists assume that reuse is environmentally beneficial because it replaces the manufacturing and purchase of new goods. However, on the contrary, manufacturers may oppose this type of reuse for the same reason. There is an urgent need to control the trans-boundary movement of electronic scrap especially to countries without established recycling facilities. Importations of secondhand electronics make such devices available to those who cannot afford new products. However, an international method of testing and certification is needed to ensure that exported secondhand devices are functional. Establishment of formal recycling facilities for e-waste in the developing countries will ensure resource reutilization with both economical and ecological gains. This study reviews options available in working towards eco-efficient management of e-waste in developing countries in the light of the present low-end management practices.

Chidi Nnorom, Innocent; Osibanjo, Oladele; Onyedikachi Nnorom, Stanley

419

QUANTUM TUNNELLING AND MAGNETIZATION DYNAMICS IN LOW DIMENSIONAL SYSTEMS  

Directory of Open Access Journals (Sweden)

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

ANDREA CORNIA

2011-12-01

420

Investigation into scanning tunnelling luminescence microscopy  

CERN Document Server

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

Manson-Smith, S K

2001-01-01

421

Carpal Tunnel Release  

Medline Plus

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

422

Carpal Tunnel Surgery  

Medline Plus

Full Text Available ... crease. The scar almost disappears. This procedure is known as the Open Carpal Tunnel Release because you ... cedure to release the carpal tunnel, and that’s known as the endoscopic carpal tunnel release. In that ...

423

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

International Nuclear Information System (INIS)

A theory of evolution and collapse of resonance pairs due to variations in inner barrier strength (thickness) is developed by using the model of effective masses and symmetric rectangular potential barriers for an electron in the plane three-barrier structure. The analytical and numerical calculations of spectral parameters (resonance energy and width) are performed with the use of transparent coefficient and probability distribution function within the transfer matrix and scattering S-matrix. It is shown that the collapse of resonance energies and widths of all quasi-stationary states in the symmetric three-barrier structure happens almost at the same values of inner barrier width, which are somewhat larger than the sum of outer thicknesses. It is found that the ?-model as compared to the rectangular barrier one, gives much higher values of resonance energies (by the order of percents) and resonance widths (almost twice).

424

Increase resource power electronics module on the physics of failure method  

Directory of Open Access Journals (Sweden)

Full Text Available A new approach to improving resource devices for power electronics. The numerical analysis of non-uniform temperature field of power semiconductor devices. A comparison of the intensities of the failure of a power unit with the real thermal regime of the device under conditions of natural convection and obtained by using statistical data analysis. The integrated assessment of reliability based on the methods of physics failures. The necessity of taking into account the actual non-stationary temperature fields to improve the reliability of the forecast operating life of power semiconductor devices.

Kravchenko Evgeny V.

2014-01-01

425

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

Directory of Open Access Journals (Sweden)

Full Text Available ??????????????????????????????????????????E-Metrics?COUNTER??????????????COUNTER????????????????????????????????COUNTER???????????????????????????????????????????????This study will be initiated from the controversies derived from generating electronic resource statistics, by way of literature review to recognize the solutions proposed by libraries, and further on to look into the development and the intention of E-Metrics and COUNTER projects, and lastly to proceed a comprehensive analysis of the reports from publishers under the standard format regulated by COUNTER. Through this study we expect to clarify and define the capabilities and limitations of COUNTER, and with which we hope to provide librarians a reliable standard to follow while generating statistics, and for publishers a referable criterion while selecting log files.

Hui-Hsin Yeh

2006-06-01

426

Attoclock elicits physics of laser-induced tunnel ionization  

CERN Document Server

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

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

2011-01-01

427

The Internet: A Resource in the Teaching of Economics and Beyond. [and] Promoting Interaction and Teamwork with Electronic Mail.  

Science.gov (United States)

Boldt et al. describe economic resources available on the Internet and illustrate ways to integrate the information into introductory courses. Baker shows how to use electronic mail to expand student-teacher involvement and group interaction/teamwork. (SK)

Boldt, David J.; And Others

1994-01-01

428

Two vertically coupled quantum rings with tunneling  

Scientific Electronic Library Online (English)

Full Text Available We study the effect of tunneling on the electronic structure of two vertically coupled quantum rings within the spin density functional theory. The ground state configurations of the coupled rings are obtained for a system with 10 electrons as a function of the ring radius and the inter-ring distanc [...] e. For small ring radius, our results recover those of coupled quantum dots. For large ring radius, new ground state configurations are found in the strong tunneling regime.

L. K., Castelano; G.-Q., Hai; B., Partoens; F. M., Peeters.

2006-09-01

429

Proton nuclear magnetic resonance studies of hydrogen diffusion and electron tunneling in Ni-Nb-Zr-H glassy alloys  

Energy Technology Data Exchange (ETDEWEB)

Using the Fourier transform of the echo envelope, the proton line shapes, spin-lattice relaxation time, and spin-spin relaxation time have been measured in a (Ni{sub 0.36}Nb{sub 0.24}Zr{sub 0.40}){sub 90}H{sub 10} glassy alloy at 1.83 T ({approx}78 MHz) and at temperatures between 1.8 and 300 K. First, the spectral line width decreases abruptly between 1.8 and 2.1 K. Next, it remains almost constant at 13 kHz up to {approx}150 K. Finally, the line width decreases as the temperature increases from {approx}150 to 300 K. The initial decrease in the spectral line width is ascribed to the distribution of the external field, which is caused by the penetration of vortices in the superconducting state. The subsequent leveling off in the spectral line width is ascribed to the dipole-dipole interaction between protons when hydrogen atoms are trapped into vacancies among the Zr-centered icosahedral Zr{sub 5}Ni{sub 5}Nb{sub 3} clusters. The final decrease in the spectral line width is ascribed to the motional narrowing of the width that is caused by the movement of hydrogen atoms. The temperature dependences of the spin-lattice and spin-spin relaxation time showed that at temperature above 150 K and the activation energy of 8.7 kJ/mol allowed the hydrogen atoms to migrate among the clusters. The distance between the hydrogen atoms is estimated to be 2.75 A. Hydrogen occupancies among clusters in the (Ni{sub 0.36}Nb{sub 0.24}Zr{sub 0.40}){sub 90}H{sub 10} glassy alloy play an important role in the diffusion behavior and in the electronic properties of this alloy.

Niki, Haruo; Okuda, Hiroyuki; Oshiro, Morihito; Yogi, Mamoru [Department of Physics, Faculty of Science, University of the Ryukyus, Nishihara, Okinawa 903-0213 (Japan); Seki, Ichiro; Fukuhara, Mikio [Institute for Materials Research, Tohoku University, Sendai 980-8577 (Japan)

2012-06-15

430

Proton nuclear magnetic resonance studies of hydrogen diffusion and electron tunneling in Ni-Nb-Zr-H glassy alloys  

International Nuclear Information System (INIS)

Using the Fourier transform of the echo envelope, the proton line shapes, spin-lattice relaxation time, and spin-spin relaxation time have been measured in a (Ni0.36Nb0.24Zr0.40)90H10 glassy alloy at 1.83 T (?78 MHz) and at temperatures between 1.8 and 300 K. First, the spectral line width decreases abruptly between 1.8 and 2.1 K. Next, it remains almost constant at 13 kHz up to ?150 K. Finally, the line width decreases as the temperature increases from ?150 to 300 K. The initial decrease in the spectral line width is ascribed to the distribution of the external field, which is caused by the penetration of vortices in the superconducting state. The subsequent leveling off in the spectral line width is ascribed to the dipole-dipole interaction between protons when hydrogen atoms are trapped into vacancies among the Zr-centered icosahedral Zr5Ni5Nb3 clusters. The final decrease in the spectral line width is ascribed to the motional narrowing of the width that is caused by the movement of hydrogen atoms. The temperature dependences of the spin-lattice and spin-spin relaxation time showed that at temperature above 150 K and the activation energy of 8.7 kJ/mol allowed the hydrogen atoms to migrate among the clusters. The distance between the hydrogen atoms is estimated to be 2.75 Å. Hydrogen occupancies among clusters in the (Ni0.36Nb0.24Zr0.40)0.24Zr0.40)90H10 glassy alloy play an important role in the diffusion behavior and in the electronic properties of this alloy.

431

Demonstration of an amorphous carbon tunnel diode  

OpenAIRE

Negative differential conductance in metal/amorphous nitrogenated carbon (a-CNx)/Si structures is demonstrated at room temperature. These metal-insulator-semiconductor tunnel diodes are fabricated by optimizing the tunnel barrier at the a-CNx/Si junction through the control of the band gap and nitrogen doping level in carbon where this a-C layer acts as a semi-insulator. A small electron tunneling effective mass of about 0.06 times the free electron mass, a coherence length of similar to 10 n...

Bhattacharyya, S.; Silva, Srp

2007-01-01

432

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

International Nuclear Information System (INIS)

Highlights: ? End-of-life electrical and electronic equipment (EEE) as secondary metal resources. ? The content and the total amount of metals in specific equipment are both important. ? We categorized 21 EEE types from contents and total amounts of various metals. ? Important equipment types as secondary resources were listed for each metal kind. ? Collectability and possible collection systems of various EEE types were discussed. - Abstract: End-of-life electrical and electronic equipment (EEE) has recently received attention as a secondary source of metals. This study examined characteristics of end-of-life EEE as secondary metal resources to consider efficient collection and metal recovery systems according to the specific metals and types of EEE. We constructed an analogy between natural resource development and metal recovery from end-of-life EEE and found that metal content and total annual amount of metal contained in each type of end-of-life EEE should be considered in secondary resource development, as well as the collectability of the end-of-life products. We then categorized 21 EEE types into five groups and discussed their potential as secondary metal resources. Refrigerators, washing machines, air conditioners, and CRT TVs were evaluated as the most important sources of common metals, and personal computers, mobile phones, and video games were evaluated as the most important sources of precious metals. Several types of small digital equipment wpes of small digital equipment were also identified as important sources of precious metals; however, mid-size information and communication technology (ICT) equipment (e.g., printers and fax machines) and audio/video equipment were shown to be more important as a source of a variety of less common metals. The physical collectability of each type of EEE was roughly characterized by unit size and number of end-of-life products generated annually. Current collection systems in Japan were examined and potentially appropriate collection methods were suggested for equipment types that currently have no specific collection systems in Japan, particularly for video games, notebook computers, and mid-size ICT and audio/video equipment.

433

Laser tunneling from aligned molecules  

CERN Document Server

We study multi-photon ionization from N_2, O_2 and benzene using circularly polarized light. By examining molecular frame photo-electron angular distributions, we illustrate how multi-photon ionization acts a momentum-selective probe of the local electron density in the Dyson orbitals for these molecules. We find good agreement with calculations based on a tunneling model and including saturation effects.

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

2013-01-01

434

Electronic characterization of LaAlO{sub 3}-SrTiO{sub 3} interfaces by scanning tunneling spectroscopy; Elektronische Charakterisierung von LaAlO{sub 3}-SrTiO{sub 3}-Grenzflaechen mittels Rastertunnelspektroskopie  

Energy Technology Data Exchange (ETDEWEB)

When LaAlO{sub 3} is epitaxially grown on TiO{sub 2}-terminated SrTiO{sub 3}, an electrically conducting interface is generated. In this respect, the physical properties of the interface differ substantially from those of both LaAlO{sub 3} and SrTiO{sub 3}, which are electrically insulating in bulk form. This dissertation looks into the question of the microscopic structure of the conducting two-dimensional interface electron system. Comparing the electronic density of states of LaAlO{sub 3}-SrTiO{sub 3} interfaces measured by scanning tunneling spectroscopy with results of density functional theory, the interface electron system is found to be substantially coined by the hosting transition metal lattices. The comparison yields a detailed picture of the microscopic structure of the interface electron system. (orig.)

Breitschaft, Martin

2010-10-22

435

Scanning tunneling microscopy study of morphology and electronic properties in (K{sub 0.7}Na{sub 0.3})Fe{sub 2?y}Se{sub 2} single crystal  

Energy Technology Data Exchange (ETDEWEB)

We investigated the microstructure of the iron selenide superconductor (K{sub 0.7}Na{sub 0.3})Fe{sub 2?y}Se{sub 2} with a T{sub c}?=?32?K and a near 100% Meissner screening volume fraction. Topography and electron transport properties were studied using electron microscopy and ultra-high vacuum scanning tunneling microscopy (STM) techniques. Room temperature STM measurements reliably identify spatial variations of the local electronic properties of this material. The studied crystals consist of continuous regions with significantly different shapes of current-voltage curves reflecting different electronic transport properties of these regions. Fitting of the local current-voltage curves with the Simmons model for metal-dielectric-metal structure confirmed a phase separation in the sample to a metal and semiconducting phases. The observed regions have dimensions in the range of several tenths of a micrometer and indicate a phase separation in the sample.

Trifonov, A. S., E-mail: trifonov.artem@phys.msu.ru; Presnov, D. E. [Skobeltsyn Institute of Nuclear Physics, Lomonosov Moscow State University, 1(2), Leninskie Gory, GSP-1, Moscow 119991 (Russian Federation); Low Temperature Physics and Superconductivity Department, Physics Faculty, Lomonosov Moscow State University, 119991 Moscow (Russian Federation); Ovchenkov, Y. A. [Low Temperature Physics and Superconductivity Department, Physics Faculty, Lomonosov Moscow State University, 119991 Moscow (Russian Federation); Belosludov, R. [Institute for Materials Research, Tohoku University, 980-8577 Sendai (Japan); Boltalin, A. I.; Liu, M.; Morozov, I. V. [Department of Chemistry, Lomonosov Moscow State University, 119991 Moscow (Russian Federation); Nejo, H. [National Institute for Material Science, Tsukuba 305-0047 (Japan); Vasiliev, A. N. [Low Temperature Physics and Superconductivity Department, Physics Faculty, Lomonosov Moscow State University, 119991 Moscow (Russian Federation); Theoretical Physics and Applied Mathematics Department, Institute of Physics and Technology, Ural Federal University, Ekaterinburg 620002 (Russian Federation); National University of Science and Technology ' MISiS' , Moscow 119049 (Russian Federation)

2014-07-28

436

Construction of a four tip scanning tunneling microscope/scanning electron microscope combination and conductivity measurements of silicide nanowires; Aufbau einer Vierspitzen-Rastertunnelmikroskop/Rasterelektronenmikroskop-Kombination und Leitfaehigkeitsmessungen an Silizid Nanodraehten  

Energy Technology Data Exchange (ETDEWEB)

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

Zubkov, Evgeniy

2013-09-01

437

Improved Design of Beam Tunnel for 42 GHz Gyrotron  

Science.gov (United States)

In gyrotron, there is the chance of generation and excitation of unwanted RF modes (parasite oscillations). These modes may interact with electron beam and consequently degrade the beam quality. This paper presents the improved design of the beam tunnel to reduce the parasite oscillations and the effect of beam tunnel geometry on the electron beam parameters. The design optimization of the beam tunnel has been done with the help of 3-D simulation software CST-Microwave Studio and the effect of beam tunnel geometry on the electron beam parameters has been analyzed by EGUN code.

Singh, Udaybir; Kumar, Nitin; Purohit, L. P.; Sinha, A. K.

2011-04-01

438

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

Science.gov (United States)

End-of-life electrical and electronic equipment (EEE) has recently received attention as a secondary source of metals. This study examined characteristics of end-of-life EEE as secondary metal resources to consider efficient collection and metal recovery systems according to the specific metals and types of EEE. We constructed an analogy between natural resource development and metal recovery from end-of-life EEE and found that metal content and total annual amount of metal contained in each type of end-of-life EEE should be considered in secondary resource development, as well as the collectability of the end-of-life products. We then categorized 21 EEE types into five groups and discussed their potential as secondary metal resources. Refrigerators, washing machines, air conditioners, and CRT TVs were evaluated as the most important sources of common metals, and personal computers, mobile phones, and video games were evaluated as the most important sources of precious metals. Several types of small digital equipment were also identified as important sources of precious metals; however, mid-size information and communication technology (ICT) equipment (e.g., printers and fax machines) and audio/video equipment were shown to be more important as a source of a variety of less common metals. The physical collectability of each type of EEE was roughly characterized by unit size and number of end-of-life products generated annually. Current collection systems in Japan were examined and potentially appropriate collection methods were suggested for equipment types that currently have no specific collection systems in Japan, particularly for video games, notebook computers, and mid-size ICT and audio/video equipment. PMID:21683566

Oguchi, Masahiro; Murakami, Shinsuke; Sakanakura, Hirofumi; Kida, Akiko; Kameya, Takashi

2011-01-01