WorldWideScience
1

Electron tunneling in chemistry  

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

2

Single Electron Tunneling  

Energy Technology Data Exchange (ETDEWEB)

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

Ruggiero, Steven T.

2005-07-25

3

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

4

Inelastic electron tunneling spectroscopy  

Directory of Open Access Journals (Sweden)

Full Text Available Inelastic Electron Tunneling Spectroscopy (IETS has re-emerged as a premier analytical tool in the understanding of nanoscale and molecular junctions. This review discusses how IETS is used to study molecular transport junctions, and presents an overview of experimental results, the prospects that the technique offers and the challenges it faces.

Mark A. Reed

2008-11-01

5

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)

6

Principles of electron tunneling spectroscopy  

CERN Document Server

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

Wolf, E L

2012-01-01

7

Resonant tunneling of electrons in quantum wires  

International Nuclear Information System (INIS)

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

8

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

9

Electronic tunneling currents at optical frequencies  

Science.gov (United States)

Rectification characteristics of nonsuperconducting metal-barrier-metal junctions as deduced from electronic tunneling theory have been observed experimentally for optical frequency irradiation of the junction.

Faris, S. M.; Fan, B.; Gustafson, T. K.

1975-01-01

10

Tunnel magnetoresistance and interfacial electronic state  

OpenAIRE

We study the relation between tunnel magnetoresistance (TMR) and interfacial electronic states modified by magnetic impurities introduced at the interface of the ferromagnetic tunnel junctions, by making use of the periodic Anderson model and the linear response theory. It is indicated that the TMR ratio is strongly reduced depending on the position of the $d$-levels of impurities, based on reduction in the spin-dependent $s$-electron tunneling in the majority spin state. Th...

Inoue, J.; Itoh, H.

2002-01-01

11

Ac electronic tunneling at optical frequencies  

Science.gov (United States)

Rectification characteristics of non-superconducting metal-barrier-metal junctions deduced from electronic tunneling have been observed experimentally for optical frequency irradiation of the junction. The results provide verification of optical frequency Fermi level modulation and electronic tunneling current modulation.

Faris, S. M.; Fan, B.; Gustafson, T. K.

1974-01-01

12

Electroluminescence from graphene excited by electron tunneling.  

Science.gov (United States)

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

Beams, Ryan; Bharadwaj, Palash; Novotny, Lukas

2014-02-01

13

Hard rock tunneling using pulsed electron beams  

International Nuclear Information System (INIS)

Intense submicrosecond bursts of energetic electrons cause significant pulverization and surface spalling of a variety of rock types, the spall debris generally consisting of sand, dust, and small flakes. If carried out at rapid repetition rate this can lead to a promising technique for increasing the speed and reducing the cost of underground excavation of tunnels, mines, and storage spaces. The conceptual design features of a Pulsed Electron Tunnel Excavator capable of tunneling approximately ten times faster than conventional drill/blast methods were studied. (auth)

14

Interference effects at electron tunneling  

CERN Document Server

Two infinite, two-dimensional, lattice, free fermion systems, initially in different invariant states, are allowed to communicate via two point contacts, through which direct tunneling of fermions takes place. Calculations of the local particle-density and of the local particle-currents distributions, performed in the final stationary state, exhibit neat interference patterns. Their dependence on the interaction details is discussed on examples. The local density and local currents are shown to be correlated.

Angelescu, N; Bundaru, R; Popescu, I

2010-01-01

15

Electron accelerator for tunneling through hard rock  

International Nuclear Information System (INIS)

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

16

Electron transfer: Lower tunnel barriers  

Science.gov (United States)

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

Miller, John R.

2014-10-01

17

Single-electron tunnel junction array  

International Nuclear Information System (INIS)

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

18

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

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

Single-electron tunneling observed with point-contact tunnel junctions  

International Nuclear Information System (INIS)

We have studied the low-temperature tunneling behavior of point-contact junctions with adjustable capacitances in the 10/sup -18/-F range. The tunneling characteristics show clear evidence of single-electron tunneling, induced by a Coulomb blockade, and are in quantitative agreement with theoretical predictions

21

Advanced Undergraduate Laboratory Experiment in Inelastic Electron Tunneling Spectroscopy.  

Science.gov (United States)

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

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

1982-01-01

22

Inelastic electron tunneling spectroscopy of nanoporous gold films  

OpenAIRE

We investigated the localized electronic properties of nanoporous gold films by using an ultra-high vacuum scanning tunneling microscope at low temperature (4.2 K). Second derivative scanning tunneling spectroscopy shows the plasmon peaks of the nanoporous gold films, which are excited by inelastic tunneling electrons. We propose that the nanorod model is appropriate for nanoporous gold studies at the nanometer-scale. These results are supported by a 3D electron tomography a...

Liu, H. W.; Nishitani, R.; Fujita, T.; Li, W.; Zhang, L.; Lang, X. Y.; Richard, P.; Nakayama, K. S.; Chen, X.; Chen, M. W.; Xue, Q. K.

2014-01-01

23

Tunneling Via Individual Electronic States in Ferromagnetic Nanoparticles  

OpenAIRE

We measure electron tunneling via discrete energy levels in ferromagnetic cobalt particles less than 4 nm in diameter, using non-magnetic electrodes. Due to magnetic anisotropy, the energy of each tunneling resonance shifts as an applied magnetic field rotates the particle's magnetic moment. 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. The tunnel...

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

1999-01-01

24

Electron beam instabilities in gyrotron beam tunnels  

International Nuclear Information System (INIS)

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

25

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

26

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

27

Quantum tunneling resonant electron transfer process in Lorentzian plasmas  

Energy Technology Data Exchange (ETDEWEB)

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

Hong, Woo-Pyo [Department of Electronics Engineering, Catholic University of Daegu, Hayang 712-702 (Korea, Republic of); Jung, Young-Dae, E-mail: ydjung@hanyang.ac.kr [Department of Physics, Applied Physics, and Astronomy, Rensselaer Polytechnic Institute, 110 8th Street, Troy, New York 12180-3590 (United States); Department of Applied Physics and Department of Bionanotechnology, Hanyang University, Ansan, Kyunggi-Do 426-791 (Korea, Republic of)

2014-08-15

28

Quantum tunneling and field electron emission theories  

CERN Document Server

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

Liang, Shi-Dong

2013-01-01

29

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

OpenAIRE

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

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

2005-01-01

30

Electron tunneling through atomically flat and ultrathin hexagonal boron nitride  

Science.gov (United States)

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

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

2011-12-01

31

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

32

Agripedia glossary [electronic resource].  

International Nuclear Information System (INIS)

A glossary of terms used in the classes contained within Agripedia, an Internet accessible interactive multimedia instructional resource developed by the University of Kentucky's College of Agriculture.

33

Detection of electronic nematicity using scanning tunneling microscopy  

OpenAIRE

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+x (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 S...

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

2013-01-01

34

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

35

Hard-rock tunneling using pulsed electron beams  

International Nuclear Information System (INIS)

Intense sub-microsecond bursts of energetic electrons cause significant pulverization and surface spalling of a variety of rock types. The spall debris generally consists of sand, dust, and small flakes. If carried out at rapid repetition rate, this technique appears promising for increasing the speed and reducing the cost of underground excavation of tunnels, mines, and storage spaces. The conceptual design features of a pulsed electron tunnel excavator, capable of tunneling approximately ten times faster than conventional drill/blast methods, is presented. (auth)

36

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

OpenAIRE

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

Akkala, Arun Goud

2011-01-01

37

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

38

Wigner time delay for tunneling ionization via the electron propagator  

Science.gov (United States)

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

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

2014-07-01

39

Time-dependent single electron tunneling through a shuttling nanoisland  

Science.gov (United States)

We offer a general approach to the calculation of single electron tunneling spectra and conductance of a shuttle oscillating between two half-metallic leads with fully spin-polarized carriers. In this case the spin-flip processes are completely suppressed and the problem may be solved by means of canonical transformation, where the adiabatic component of the tunnel transparency is found exactly, whereas the nonadiabatic corrections can be taken into account perturbatively. Time-dependent corrections to the tunnel conductance of moving shuttle become noticeable at finite bias in the vicinity of the even/odd occupation boundary at the Coulomb diamond diagram.

Cohen, G.; Fleurov, V.; Kikoin, K.

2009-06-01

40

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

41

Relativistic tunnelling time for electronic wave packets  

International Nuclear Information System (INIS)

We have analyzed the influence of the wave packet size in the relativistic tunnelling time ? and its uncertainty ?? when it traverses a given potential barrier. The analytical expressions obtained for both magnitudes confirm that the size of the incident pulse has a significant effect on the tunnelling process. This effect is greater for short pulses, compared with the length of the barrier. For the evanescent zone, we have derived an analytical expression for ? with a good limit of validity. This expression constitutes a value tool to calculate the relativistic tunnelling time as a function of the incident wave packet with a good limit of validity. Superluminal propagation is found in this region but with a large value of the uncertainty ?? compared with the tunnelling time itself. We can conclude that the probability of superluminal propagation is practically negligible in the evanescent region. In respect to the Klein zone, we have derived an analytical expression for ? that depends on the size of the incident wave packet and the width of the Lorentzian resonance ?r. This equation fits extremely well with our numerical results for Lorentzian resonances near the top of the Klein zone, where the overlap between them is negligible. As in the evanescent case, superluminal propagation is not likely to occur in the Klein region.

42

Relativistic tunnelling time for electronic wave packets  

Energy Technology Data Exchange (ETDEWEB)

We have analyzed the influence of the wave packet size in the relativistic tunnelling time {tau} and its uncertainty {Delta}{tau} when it traverses a given potential barrier. The analytical expressions obtained for both magnitudes confirm that the size of the incident pulse has a significant effect on the tunnelling process. This effect is greater for short pulses, compared with the length of the barrier. For the evanescent zone, we have derived an analytical expression for {tau} with a good limit of validity. This expression constitutes a value tool to calculate the relativistic tunnelling time as a function of the incident wave packet with a good limit of validity. Superluminal propagation is found in this region but with a large value of the uncertainty {Delta}{tau} compared with the tunnelling time itself. We can conclude that the probability of superluminal propagation is practically negligible in the evanescent region. In respect to the Klein zone, we have derived an analytical expression for {tau} that depends on the size of the incident wave packet and the width of the Lorentzian resonance {Gamma}{sub r}. This equation fits extremely well with our numerical results for Lorentzian resonances near the top of the Klein zone, where the overlap between them is negligible. As in the evanescent case, superluminal propagation is not likely to occur in the Klein region.

Del Barco, O [Departamento de Fisica-CIOyN, Universidad de Murcia (Spain); Gasparian, V, E-mail: obn@um.e [Department of Physics, California State University, Bakersfield, CA (United States)

2011-01-07

43

Electron tunneling in lithium-ammonia solutions probed by frequency-dependent electron spin relaxation studies.  

OpenAIRE

Electron transfer or quantum tunneling dynamics for excess or solvated electrons in dilute lithium-ammonia solutions have been studied by pulse electron paramagnetic resonance (EPR) spectroscopy at both X- (9.7 GHz) and W-band (94 GHz) frequencies. The electron spin-lattice (T(1)) and spin-spin (T(2)) relaxation data indicate an extremely fast transfer or quantum tunneling rate of the solvated electron in these solutions which serves to modulate the hyperfine (Fermi-contact) interaction with ...

Maeda, K.; Lodge, Mt; Harmer, J.; Freed, Jh; Edwards, Pp

2012-01-01

44

Spatiotemporal evolution of reaction fronts trigger by tunneling electrons  

International Nuclear Information System (INIS)

Electron-induced reactions by means of STM techniques are performed. Pentaerytritol and explosives are deposited onto a Cu (110) surface. Chemical reactions are trigger by the tunneling electrons and can be detected via a phase modification of the molecular islands attached to the metal surface.

45

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

46

Electron transport through thin film amorphous silicon: A tunneling study  

International Nuclear Information System (INIS)

Electron tunneling through thin films of amorphous silicon (a-Si) is studied. Systematic studies were carried out of the conductance as a function of temperature, bias voltage and barrier thickness. It was found that the localized states in the amorphous silicon barrier, whose formation is due to the structural disorder, can have profound effects on the tunneling characteristics. At low temperatures and small bias (the ohmic regime), the localized states become resonant centers that enhance the tunneling probability greatly. This is marked by a crossover in the dominant tunneling mechanism, from direct tunneling to resonant tunneling as the barrier thickness increases. Increasing temperature or bias voltage enhances inelastic process due to, e.g., electron-phonon interaction. The favored conduction paths in this regime are isolated chains containing localized states that are nearly rectilinearly and equidistantly positioned across the tunnel barrier. Inelastic hopping through these chains gives rise to the voltage and temperature dependence of tunneling conductance which, to the lowest order, is predicted to be proportional to V4/3 and T4/3, respectively, corresponding to chains with two localized states. Convincing experimental evidence, both for the lowest order inelastic effects, and for crossover to higher order hopping channels with larger number of hops, is presented. Moreover, it was found that the threshold for the onset of inelastic effe threshold for the onset of inelastic effects is lowered for thicker barriers. As the barrier thickness and the temperature are further increased, the conductance acquires an asymptotic form which resembles the Mott Variable Range Hopping (VRH) behavior in the bulk limit. The crossover from inelastic hopping through isolated chains to the classical, random-walk-like VRH is discussed

47

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

48

Proximity electron tunneling spectroscopy I. Experiments in Nb  

International Nuclear Information System (INIS)

A quantitative proximity electron tunneling spectroscopy (PETS) id demonstrated for the study of strong coupling superconductors which do not form suitable insulating oxides for conventional McMillan--Rowell tunneling spectroscopy. Proximity junctions of the form C-Al2O3-Al/S are employed, with Al thickness d/sub N/2F(?), electron-phonon coupling constant lambda, and Coulomb pseudopotential ?*. A full discussion of the underlying theory and details of the methods of analysis employed to obtain, in addition, the pair potential of the Al proximity layer are contained in a following paper

49

Using Electronic Resources for Teaching  

Science.gov (United States)

Computers and related electronic resources have come to play a central role in education. Whatever your feelings about what some have called the digital revolution, you must accept that many, perhaps most, of your students are fully immersed in it. At the very simplest level, you will rarely receive a paper or other assignment from a student that has not been written with the help of a computer. Most of your students will have considerable experience with the Internet and will, whether you like it or not, make use of it for much of their academic work. Many of them will be accustomed to using e-mail as a normal form of communication. But it is not just students who find electronic resources valuable. Teachers can benefit from these resources as well, by employing a series of useful tools. We stress the word "useful" because electronic resources complement, but seldom replace, more conventional teaching techniques. Electronic tools can make classes more efficient; lectures more compelling, informative, and varied; reading assignments more extensive, interesting, and accessible; discussions more free ranging and challenging; and students' papers more original and well researched. Only you, however, can judge if these techniques advance your own teaching goals.

2010-06-09

50

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

International Nuclear Information System (INIS)

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

51

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

Energy Technology Data Exchange (ETDEWEB)

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

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

2010-01-01

52

High critical temperature superconductor tunneling spectroscopy using squeezable electron tunneling junctions  

International Nuclear Information System (INIS)

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

53

Study and manipulation of electron tunneling through quantum dots  

Science.gov (United States)

Fermi-Dirac distribution is the fundamental property which governs the electron energy distribution in solids. At finite temperatures, Fermi-Dirac thermal smearing of electron energies limits the operation of many electronic, opto-electronic and spintronic devices. Examples include single electron transistors, quantum dot resonant tunnel diodes for single photon detection, and single electron turnstile devices. To overcome this intrinsic limitation of Fermi-Dirac thermal smearing, these devices have typically been operated at cryogenic temperatures. Room temperature operation of these devices could be realized, however, if the thermal smearing of electron energies could be suppressed. Until now, studies in the fields of electron-tunneling refrigerators and double quantum dot devices have demonstrated limited manipulation/suppression of electron energy distribution, but those have been carried out at cryogenic temperatures. Using a double barrier tunneling junction structure as a model system this research has accomplished the following: * Demonstrated suppression of thermal smearing of electrons at room temperature, without any physical cooling of the system * Demonstrated that cold electrons whose effective temperature as low as ˜45 K can be created at room temperature without any physical cooling * Systematically investigated the phenomenon responsible for suppression in thermal smearing of electron energies * Systematically investigated the cold electron transport in the double barrier tunnel junction structure One of the key achievements of this research was demonstration of effective electron temperature of ˜45K at room temperature without any physical cooling of the system. This was realized by filtering out the thermally excited electrons in a double barrier tunneling junction structure. A discrete energy state of a quantum well, created by band bending of Cr2O3 conduction band, acted as an electron energy filter, effectively suppressing energy distribution of electrons, thereby creating cold electrons (˜45K) at room temperature. This phenomenon of electron energy filtering was observed in double barrier tunnel junction devices fabricated using different quantum dots (˜5.5nm, ˜6.6nm, ˜7nm CdSe and ˜7.8nm CdTe). The full width half maximum peak widths of differential conductance measurements of these devices, which is directly related to the Fermi-Dirac distribution of electrons, were found to be much narrower (˜15meV at room temperature) than theoretically calculated values (˜90meV at room temperature) as a result of suppression of Fermi-Dirac electron energy distribution. A model which takes electron energy filtering into account was used to numerically calculate the full width half maximum peak widths of differential conductance peaks at different temperatures (77K to 295K) and compared to the experimental results. The theoretical calculations are in very good agreement with the experimental results over the entire temperature range explored. Precise placement of quantum dots between the electrodes is one of the major challenges which need to be addressed for a large-scale fabrication of the devices investigated in this study. A nanoparticle placement technique, which is capable of precisely placing single nanoparticles onto desired substrate locations over an entire wafer, was demonstrated. Using this nanoparticle placement technique as a base model, a concept for guided placement of quantum dots/nanoparticles onto the double barrier tunneling junction device structure is presented.

Bhadrachalam, Pradeep Krishna

54

Coulomb blockade of single-electron tunneling, and coherent oscillations in small tunnel junctions  

International Nuclear Information System (INIS)

A microscopic approach to the theory of small, current-biased tunnel junctions is developed. This approach yields a natural account of the ''secondary'' quantization of both the single-electron (quasiparticle) and Cooper-pair (Josephson) current components. The theory shows that the current of the single electrons is blocked by their Coulomb interaction at low temperatures within a considerable range of the junction voltage. As a result of the blockade, coherent oscillations of the voltage can arise even in the absence of Josephson coupling, e. g., for single-electron tunneling (SET) between normal metal electrodes. The most significant features of these ''SET'' oscillations and their coexistence with Bloch oscillations in Josephson junctions are studied in detail. Prospects of experimental verification of the predicted effects and of their possible applications are discussed

55

Interaction between electrons and tunneling levels in metallic glasses  

International Nuclear Information System (INIS)

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

56

Subcycle waveform generation by nonrecolliding tunneling electron wave packets  

Science.gov (United States)

Nonrecolliding tunneling free-state electron wave packets driven by low-frequency ultrashort laser pulses can help synthesize, as we show in this work, extremely short field waveforms lasting a tiny fraction of the field cycle with intensities orders of magnitude higher than the intensities of high-order-harmonic pulses.

Serebryannikov, E. E.; Zheltikov, A. M.

2014-10-01

57

Electron tunneling through a barrier that depends linearly on time  

International Nuclear Information System (INIS)

We discuss the creation of a negative molecular ion via the decay of a self-captured electron state - the fluctuon - in a nonideal dipole-molecule gas. The creation probability of the negative ion is evaluated in the classical approximation using Green's function methods. We assume that the potential barrier through which the electron tunnels from the potential well of the fluctuon to that of the molecule depends linearly on time

58

Scaling of electronic probability densities in a single-electron tunnelling phenomenon  

International Nuclear Information System (INIS)

We studied electronic tunnelling through a potential barrier between two quantum wells in one- and two-electron systems numerically. We solved a one-dimensional Schroedinger eigenvalue equation by the QL and finite difference methods. We found that taking E-Ec as the control parameter, where E is the strength of the external electric field and Ec is the tunnelling electric field, power laws apply to the tunnelling probability, the first moment and the second moment for both one- and two-electron systems. We carried out a scaling analysis of the electronic tunnelling problem and found that the amount of increase or decrease in the probability density of electron in each quantum well is scaled. We derived the relationship between the scaling exponents, which agreed with the numerical result. We also found that in the case of two-electron systems, the system energy and the information entropy change discontinuously when an electron tunnels, whereas in the case of one-electron systems, they change continuously in the tunnelling electric field. (author)

59

Electron tunneling through ultrathin boron nitride crystalline barriers.  

Science.gov (United States)

We investigate the electronic properties of ultrathin hexagonal boron nitride (h-BN) crystalline layers with different conducting materials (graphite, graphene, and gold) on either side of the barrier layer. The tunnel current depends exponentially on the number of h-BN atomic layers, down to a monolayer thickness. Conductive atomic force microscopy scans across h-BN terraces of different thickness reveal a high level of uniformity in the tunnel current. Our results demonstrate that atomically thin h-BN acts as a defect-free dielectric with a high breakdown field. It offers great potential for applications in tunnel devices and in field-effect transistors with a high carrier density in the conducting channel. PMID:22380756

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

2012-03-14

60

Molecular Light Emission Induced by Inelastic Electron Tunneling  

Science.gov (United States)

Light emission from molecular layers has been induced by inelastically tunneling electrons in a tunneling junction. The fast quenching of molecular emission on metal surfaces was suppressed by use of the "transparent conductor" indium-tin-oxide for the junction electrodes. The emission measurements have been made in squeezable tunneling junctions as small as 10-9 square centimeters, coated with 9-10 dichloro-anthracene layers. At a bias of 2.5 to 3.5 volts, yields of 5000 photons per microcoulomb were observed. Evidence for the molecular origin of the emission is given. This method shows good prospects for use in the imaging of chromophores on surfaces with atomic resolution.

Flaxer, Eli; Sneh, Ofer; Cheshnovsky, Ori

1993-12-01

61

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

International Nuclear Information System (INIS)

An Nb-Sn filament mounted on a flexible glass beam can be broken to form an electron tunneling junction between the fracture elements. Breaking the filament in liquid helium prevents oxidation of the freshly exposed fracture surfaces. A sharp superconducting energy gap in the I-V characteristics measured at 4 K indicates the formation of a high-quality tunneling barrier between the fracture elements. The resistance of the junction can be continuously adjusted by varying the surface bending strain of the beam. An estimated 0.1 nm change in the barrier thickness produces about an order of magnitude change in the resistance over the range from 105 to 108 ?. The exponential character of this dependence shows that the tunnel junction is freely adjustable without intimate contact of the junction elements. ''Break'' junctions made in this way offer a new class of tunneling experiments on freshly exposed surfaces of a fractured sample without the oxide barrier previously required for junction stability. Such experiments provide a simple technique for tunneling to new materials and may eliminate complications that can be encountered during interpretation of data obtained using oxide barriers

62

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

OpenAIRE

Electron transfer or quantum tunneling dynamics for excess or solvated electrons in dilute lithium-ammonia solutions have been studied by pulse electron paramagnetic resonance (EPR) spectroscopy at both X- (9.7 GHz) and W-band (94 GHz) frequencies. The electron spin-lattice (T1) and spin-spin (T2) relaxation data indicate an extremely fast transfer or quantum tunneling rate of the solvated electron in these solutions which serves to modulate the hyperfine (Fermi-contact) interaction with nitr...

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

2012-01-01

63

Inelastic electron tunneling spectroscopy in molecular junctions: peaks and dips.  

Science.gov (United States)

We study inelastic electron tunneling through a molecular junction using the nonequilibrium Green's function formalism. The effect of the mutual influence between the phonon and the electron subsystems on the electron tunneling process is considered within a general self-consistent scheme. Results of this calculation are compared to those obtained from the simpler Born approximation and the simplest perturbation theory approaches, and some shortcomings of the latter are pointed out. The self-consistent calculation allows also for evaluating other related quantities such as the power loss during electron conduction. Regarding the inelastic spectrum, two types of inelastic contributions are discussed. Features associated with real and virtual energy transfer to phonons are usually observed in the second derivative of the current I with respect to the voltage Phi when plotted against Phi. Signatures of resonant tunneling driven by an intermediate molecular ion appear as peaks in the first derivative dI/dPhi and may show phonon sidebands. The dependence of the observed vibrationally induced lineshapes on the junction characteristics, and the linewidth associated with these features are also discussed. PMID:15634159

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

2004-12-15

64

Electron cooling by diffusive normal metal - superconductor tunnel junctions  

OpenAIRE

We investigate heat and charge transport in NN'IS tunnel junctions in the diffusive limit. Here N and S are massive normal and superconducting electrodes (reservoirs), N' is a normal metal strip, and I is an insulator. The flow of electric current in such structures at subgap bias is accompanied by heat transfer from the normal metal into the superconductor, which enables refrigeration of electrons in the normal metal. We show that the two-particle current due to Andreev ref...

Vasenko, A. S.; Bezuglyi, E. V.; Courtois, Herve?; Hekking, F. W. J.

2009-01-01

65

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

66

Inelastic electron tunneling spectroscopy of molecular transport junctions  

Science.gov (United States)

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

Song, Hyunwook; Lee, Takhee; Reed, Mark

2014-05-01

67

Room temperature observation of electron resonant tunneling through InAs/AlAs quantum dots  

OpenAIRE

Molecular beam epitaxy is employed to manufacture self-assembled InAs/AlAs quantum-dot resonant tunneling diodes. Resonant tunneling current is superimposed on the thermal current, and they make up the total electron transport in devices. Steps in current-voltage characteristics and peaks in capacitance-voltage characteristics are explained as electron resonant tunneling via quantum dots at 77K or 300K, and this is the first time that resonant tunneling is observed at room t...

Sun, Jie; Li, Ruoyuan; Zhao, Chang; Yu, Like; Ye, Xiaoling; Xu, Bo; Chen, Yonghai; Wang, Zhanguo

2007-01-01

68

Electronic structure and tunneling resonance spectra of nanoscopic aluminum islands  

CERN Document Server

The electronic structure of nanoscopic oxide-coated aluminum islands is investigated using a tight-binding model that incorporates the geometry, chemistry and disorder of the particle. The oxide coat is found to significantly increase the volume accessible to electrons at the Fermi level. The level statistics agree with random matrix theory predictions. States near the Fermi level show pronounced clustering regardless of disorder. It is suggested that the observed clusters of tunneling resonances may have a more complex origin than if they were solely due to many-body non-equilibrium effects.

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

2002-01-01

69

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

Energy Technology Data Exchange (ETDEWEB)

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

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

2010-06-01

70

Managing electronic resources a LITA guide  

CERN Document Server

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

Weir, Ryan O

2012-01-01

71

Inelastic electron tunneling spectroscopy at local defects in graphene  

CERN Document Server

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

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

2013-01-01

72

Electron tunneling in single layer graphene with an energy gap  

International Nuclear Information System (INIS)

When a single layer graphene is epitaxially grown on silicon carbide, it will exhibit a finite energy gap like a conventional semiconductor, and its energy dispersion is no longer linear in momentum in the low energy regime. In this paper, we have investigated the tunneling characteristics through a two-dimensional barrier in a single layer graphene with an energy gap. It is found that when the electron is at a zero angle of incidence, the transmission probability as a function of incidence energy has a gap. Away from the gap the transmission coefficient oscillates with incidence energy which is analogous to that of a conventional semiconductor. The conductance under zero temperature has a gap. The properties of electron transmission may be useful for developing graphene-based nano-electronics. (condensed matter: electronic structure, electrical, magnetic, and optical properties)

73

Student attitudes towards electronic information resources  

Directory of Open Access Journals (Sweden)

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

Kathryn Ray

1998-01-01

74

(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

75

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

76

Electronic structure and electron-phonon coupling in carbon diamondoids studied by scanning tunneling microscopy  

Science.gov (United States)

Diamondoids are hydrocarbon molecules with diamond-like cage structures. Their structural complexity and chemical bond tunability make them ideal building blocks for creating novel nanostructures. We have used cryogenic scanning tunneling spectroscopy to examine the electronic structure of individual diamondoid molecules on the Au(111) surface. We observed variations in the filled and empty state local density of states for individual 121-tetramer diamondoid molecule. Despite a large HOMO-LUMO gap (? > 5eV) around the Fermi energy, there exists a strong interaction between the tunneling electrons and the diamondoid C-H stretch mode, as revealed by inelastic tunneling spectroscopy (IETS). We further show that the strength of the electron-phonon coupling has a distinct spatial distribution with the dominant inelastic channel localized to a specific region of the diamondoid molecule.

Wang, Yayu; Lu, X. H.; Yamachika, R.; Wachowiak, A.; Kioupakis, E. S.; Louie, S. G.; Crommie, M. F.; Dahl, J. E.; Liu, S. G.; Carlson, R. M. K.

2006-03-01

77

Effects of intermolecular interaction on inelastic electron tunneling spectra  

Science.gov (United States)

We have examined the effects of intermolecular interactions on the inelastic electron tunneling spectroscopy (IETS) of model systems: a pair of benzenethiol or a pair of benzenedithiol sandwiched between gold electrodes. The dependence of the IETS on the mutual position of and distance between the paired molecules has been predicted and discussed in detailed. It is shown that, although in most cases, there are clear spectral fingerprints present which allow identification of the actual structures of the molecules inside the junction. Caution must be exercised since some characteristic lines can disappear at certain symmetries. The importance of theoretical simulation is emphasized.

Kula, Mathias; Luo, Yi

2008-02-01

78

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

79

Crossover in tunneling hops in systems of strongly localized electrons  

International Nuclear Information System (INIS)

Accurate Monte-Carlo simulation data show a consistent crossover in different characters of tunneling hops in two-dimensional systems of strongly localized electrons in the presence of scattering and quantum interference of hopping paths. The results also suggest a negative answer to the question whether there is a two-dimensional sign phase transition. The fractal behaviour observed in the direction perpendicular to the hopping direction is found to be similar to that for eigenstates in one-dimensional localized systems. (author). 16 refs, 6 figs

80

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

81

Phonon and plasmon excitation in inelastic electron tunneling spectroscopy of graphite  

OpenAIRE

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 als...

Vitali, Lucia; Schneider, M. A.; Kern, Klaus; Wirtz, Ludger; Rubio Secades, A?ngel

2003-01-01

82

Two-photon Induced Hot Electron Transfer to a Single Molecule in a Scanning Tunneling Microscope  

OpenAIRE

The junction of a scanning tunneling microscope (STM) operating in the tunneling regime was irradiated with femtosecond laser pulses. A photo-excited hot electron in the STM tip resonantly tunnels into an excited state of a single molecule on the surface, converting it from the neutral to the anion. The electron transfer rate depends quadratically on the incident laser power, suggesting a two-photon excitation process. This nonlinear optical process is further confirmed by t...

Wu, Shiwei; Ho, Wilson

2010-01-01

83

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

Science.gov (United States)

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

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

2014-04-01

84

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

85

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

86

Resonant electron tunneling in a tip-controlled potential landscape  

Science.gov (United States)

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

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

2014-06-01

87

Shapes of leading tunnelling trajectories for single-electron molecular ionization  

CERN Document Server

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

Bondar, Denys I; Ivanov, Misha Yu

2010-01-01

88

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

International Nuclear Information System (INIS)

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

89

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

International Nuclear Information System (INIS)

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

90

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

CERN Document Server

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

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

2005-01-01

91

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 CH3(CH2)nSH:HO(CH2)mSH (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.

2008-01-01

92

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

93

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

94

Electronic and Geometrical Structure of Phthalocyanines on Surfaces : An Electron Spectroscopy and Scanning Tunneling Microscopy Study  

OpenAIRE

Core- and Valence Photoelectron Spectroscopy (PES), X-ray- and Ultraviolet-Visible Absorption Spectroscopy (XAS and UV-Vis), Scanning Tunneling Microscopy (STM) and Density Functional Theory (DFT) calculations are used to study the electronic and geometrical structure of a class of macro-cyclic molecules, Phthalocyanines (Pc), on surfaces. These molecules are widely studied due to their application in many different fields. Multilayer and monolayer coverages of Iron Phthalocyanine (FePc) and ...

A?hlund, John

2007-01-01

95

Binding energy of exciton complexes determined by the tunneling current of single electron transistor under optical pumping  

CERN Document Server

We theoretically study the tunnelling current of a single electron transistor (SET) under optical pumping. It found that holes in the quantum dot(QD) created by optical pumping lead to new channels for the electrons tunnelling from emitter to collector. As a consequence, an electron can tunnel through the QD via additional channels, characterized by the exciton, trion and biexciton states. The binding energy of exciton complexes can be determined by the Coulomb oscillatory tunnelling current.

Kuo, D M T; Kuo, David M T; chang, Yia-chun

2005-01-01

96

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

97

The use of MIM tunnel junctions to investigate kinetic electron excitation in atomic collision cascades  

International Nuclear Information System (INIS)

A novel technique is introduced to investigate the kinetic excitation of electrons in a solid by bombardment with energetic ions. The sample is prepared as a metal-insulator-metal (MIM) tunnel junction which opens the possibility to detect hot electrons with excitation energies well below the vacuum barrier. The excitations produced by the projectile impact onto the top electrode are detected as a tunnel current into the underlying base electrode. By varying the top electrode thickness, the elastic transport of hot electrons towards the tunnel junction can be studied

98

Electron-spin polarization in tunnel junctions with ferromagnetic EuS barriers  

International Nuclear Information System (INIS)

The authors report here spin-polarized tunneling experiments using non-ferromagnetic electrodes and ferromagnetic EuS barriers. Because of the conduction band in EuS splits into spin-up and spin-down subbands when the temperature is below 16.7 K, the Curie temperature of EuS, the tunnel barrier for electrons with different spin directions is different, therefore giving rise to tunnel current polarization. The spin-filter effect, as it may be called, was observed earlier, directly or indirectly, by several groups: Esaki et al. made a tunneling study on junctions having EuS and EuSe barriers; Thompson et al. studied Schottky barrier tunneling between In and doped EuS; Muller et al. and Kisker et al. performed electron field emission experiments on EuS-coated tungsten tips. The field emission experiments gave a maximum polarization of (89 + 7)% for the emitted electrons. Although the previous tunneling studies did not directly show electron polarization, their results were explained by the same spin- filter effect. This work uses the spin-polarized tunneling technique to show directly that tunnel current is indeed polarized and polarization can be as high as 85%

99

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

100

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

101

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

102

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

Energy Technology Data Exchange (ETDEWEB)

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

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

2004-07-01

103

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

International Nuclear Information System (INIS)

The tunnel probe is a new kind of Langmuir probe for use in the tokamak scrape-off layer. 2 dimensional kinetic analysis of the ion current distribution on the concave conductors is used to calibrate the probe for measuring ion flux and electron temperature. Qualitative agreement with classical Langmuir probe measurements is found, but the electron temperature given by the tunnel probe is several times lower. This discrepancy can be caused by secondary electron emission, or the presence of suprathermal electrons. Strong reduction of ion flux and electron temperature fluctuations is observed during electrode biasing. (authors)

104

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

105

Reviewing the Electronic Resources & Libraries Conference  

Science.gov (United States)

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

Tijerina, Bonnie

2008-01-01

106

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

107

First-Principles Simulations of Inelastic Electron Tunneling Spectroscopy of Molecular Electronic Devices  

Science.gov (United States)

A generalized Green's function theory is developed to simulate the inelastic electron tunneling spectroscopy (IETS) of molecular junctions. It has been applied to a realistic molecular junction with an octanedithiolate embedded between two gold contacts in combination with the hybrid density functional theory calculations. The calculated spectra are in excellent agreement with recent experimental results. Strong temperature dependence of the experimental IETS spectra is also reproduced. It is shown that the IETS is extremely sensitive to the intra-molecular conformation and to the molecule-metal contact geometry.

Jiang, Jun; Kula, Mathias; Lu, Wei; Luo, Yi

2005-08-01

108

Photon induced tunneling of electron through a graphene electrostatic barrier  

Energy Technology Data Exchange (ETDEWEB)

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

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

2013-11-14

109

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

110

Coherent oscillations of electrons in tunnel-coupled wells under ultrafast intersubband excitation  

International Nuclear Information System (INIS)

Ultrafast intersubband excitation of electrons in tunnel-coupled wells is studied in respect of its dependence on the structure parameters, the duration of the infrared pump and the detuning frequency. The temporal dependences of the photoinduced carrier concentration and dipole moment are obtained for two cases of transitions: from the single ground state to the tunnel-coupled excited states and from the tunnel-coupled states to the single excited state. The peculiarities of dephasing and population relaxation processes are also taken into account. The nonlinear regime of the response is also considered when the splitting energy between the tunnel-coupled levels is renormalized by the photoexcited electron concentration. The dependences of the period and the amplitude of oscillations on the excitation pulse are presented with a description of the damping of the nonlinear oscillations

111

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

OpenAIRE

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 ...

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

2014-01-01

112

The theory of electro-magnetic radiation of electron transiting through the resonance-tunnel structure  

International Nuclear Information System (INIS)

The quasi-stationary electron states are studied in the three-barrier resonance-tunnel structure which is the basic element of coherent quantum cascade lasers. In the models of rectangular and ?-barrier potentials there is established theory of evolution and collapse of double resonance complexes in a symmetric resonance-tunnel structure. The induced conductivity of nano-system is calculated within the both models. It is shown that the negative induced conductivity of three-barrier resonance-tunnel structure in ?-barrier model is dozens times smaller than more realistic magnitudes obtained within the rectangular potentials model.

113

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

114

Time-dependent single electron tunneling through a shuttling nano-island  

OpenAIRE

We offer a general approach to calculation of single-electron tunneling spectra and conductance of a shuttle oscillating between two half-metallic leads with fully spin polarized carriers. In this case the spin-flip processes are completely suppressed and the problem may be solved by means of canonical transformation, where the adiabatic component of the tunnel transparency is found exactly, whereas the non-adiabatic corrections can be taken into account perturbatively. Time...

Cohen, G.; Fleurov, V.; Kikoin, K.

2009-01-01

115

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

116

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

117

Electronic resource management systems a workflow approach  

CERN Document Server

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

Anderson, Elsa K

2014-01-01

118

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

OpenAIRE

Ethylene glycol in its ground conformation has tunneling transition with the frequency about 7 GHz. This leads to a rather complicated tunneling-rotational spectrum. Because tunneling and rotational energies have different dependence on the electron-to-proton mass ratio $\\mu$, this spectrum is highly sensitive to the possible $\\mu$ variation. We used simple 14 parameter effective Hamiltonian to calculate dimensionless sensitivity coefficients $Q_\\mu$ of the tunneling-rotatio...

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

2014-01-01

119

Free online electronic information resources on applied science and technology  

OpenAIRE

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

Ghosh, T. B.

2003-01-01

120

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

121

Momentum-dependent multiple gaps in magnesium diboride probed by electron tunnelling spectroscopy  

Science.gov (United States)

The energy gap is the most fundamental property of a superconductor. MgB2, a superconductor discovered in 2001, exhibits two different superconducting gaps caused by the different electron-phonon interactions in two weakly interacting bands. Theoretical calculations predict that the gap values should also vary across the Fermi surface sheets of MgB2. However, until now, no such variation has been observed. It has been suggested that two gap values were sufficient to describe real MgB2 samples. Here we present an electron tunnelling spectroscopy study on MgB2/native oxide/Pb tunnel junctions that clearly shows a distribution of gap values, confirming the importance of the anisotropic electron-phonon interaction. The gap values, and their spreads found from the tunnel junction measurements, provide valuable experimental tests for various theoretical approaches to the multi-band superconductivity in MgB2.

Chen, Ke; Dai, Wenqing; Zhuang, C. G.; Li, Qi; Carabello, Steve; Lambert, Joseph G.; Mlack, Jerome T.; Ramos, Roberto C.; Xi, X. X.

2012-01-01

122

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

Energy Technology Data Exchange (ETDEWEB)

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

Wang, C. [Laser Micro/Nano Fabrication Laboratory, School of Mechanical Engineering, Beijing Institute of Technology, Beijing 100081 (China); Jiang, L., E-mail: jianglan@bit.edu.cn [Laser Micro/Nano Fabrication Laboratory, School of Mechanical Engineering, Beijing Institute of Technology, Beijing 100081 (China); Wang, F.; Li, X.; Yuan, Y.P. [Laser Micro/Nano Fabrication Laboratory, School of Mechanical Engineering, Beijing Institute of Technology, Beijing 100081 (China); Qu, L.T. [Key Laboratory of Cluster Science, Ministry of Education, School of Chemistry, Beijing Institute of Technology, Beijing 100081 (China); Lu, Y.F. [Department of Electrical Engineering, University of Nebraska-Lincoln, Lincoln, NE 68588-0511 (United States)

2012-10-01

123

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

124

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

125

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

126

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

127

HIGH RESOLUTION ELECTRON BEAM INJECTION IN SEMICONDUCTORS USING A SCANNING TUNNELING MICROSCOPE  

OpenAIRE

The tip of a scanning tunneling microscope is used as a source of ultralow-energy electrons to excite luminescence in model AlGaAs/GaAs(001) heterostructures. This beam injection technique has the advantage of providing a nanometer-sized charge generation volume. We demonstrate the application of this technique to determine minority charge carrier transport parameters such as the thermalization length of hot electrons and the diffusion length of minority electrons.

Alvarado, S.; Renaud, Ph; Meier, H.

1991-01-01

128

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

Science.gov (United States)

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

Dolog, Ivan; Mallik, Robert R.; Malz, Dan; Mozynski, Anthony

2004-03-01

129

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

Energy Technology Data Exchange (ETDEWEB)

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

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

2010-11-10

130

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

International Nuclear Information System (INIS)

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

131

Negative differential resistance in electron tunneling in ultrathin films near the two-dimensional limit  

International Nuclear Information System (INIS)

We report on our observation of negative differential resistance (NDR) in electron tunneling conductance in atomic-scale ultrathin Ag films on Si(111) substrates. NDR was observed by scanning tunneling spectroscopy measurements. The tunneling conductance depends on the electronic local density of states (LDOS) of the sample. We show that the sample bias voltage, at which negative differential resistance and peak negative conductance occur, depends on the film thickness. This can be understood from the variation in the LDOS of the Ag films as a function of film thickness down to the two-dimensional limit of one atomic layer. First principles density functional theory calculations have been used to explain the results.

132

Surface morphology and transport properties of Cr nanoparticles in single electron tunneling regime  

Energy Technology Data Exchange (ETDEWEB)

We have carried out an investigation of surface structures of Cr nanoparticles grown on a MgO layer for studying single electron tunneling (SET). Reflection high-energy electron diffraction pattern changes from spotty to streak with decreasing Cr nominal thickness, while Cr forms nano size particles with the size of around 3.5 nm in diameter for all the samples. The double tunnel junctions for the Cr nominal thickness of 0.1 nm show clear Coulomb blockade with the threshold voltage of 50 mV, indicating that this Cr nanoparticle satisfies the condition for the appearance of SET. The relatively large volume of the Cr nanoparticles may be related with the fact that tunnel magnetoresistance due to spin accumulation in Cr nanoparticles is small.

Koda, Tetsunori; Mizuguchi, Masaki; Takanashi, Koki [Institute for Materials Research, Tohoku University, Sendai, 980-8577 (Japan); Mitani, Seiji, E-mail: koda@imr.tohoku.ac.jp [National Institute for Materials Science, Tsukuba, 305-0047 (Japan)

2011-01-01

133

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

134

Do trapped electrons tunnel to scavengers in irradiated alcohol glasses  

International Nuclear Information System (INIS)

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

135

Photon dressed electronic states in topological insulators: Tunneling and conductance  

OpenAIRE

The surface bound electronic states of three-dimensional topological insulators, as well as the edge states in two-dimensional topological insulators, are investigated in the presence of a circularly polarized light. The strong coupling between electrons and photons is found t o give rise to an energy gap as well as a unique energy dispersion of the dressed states, different from both graphene and conventional two-dimensional electron gas (2DEG). The effects of electron-phot...

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

2012-01-01

136

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

Science.gov (United States)

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

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

2012-06-01

137

Effects of Coulomb interaction and tunneling on electron transport in coupled one-dimensional systems from ballistic to diffusive regime  

CERN Document Server

A linear theory of electron transport is developed for a system of two ideal quantum wires, of length L, coupled by tunneling and Coulomb interaction. The interaction of electrons with acoustical phonons is included and the results are valid in both the ballistic and diffusive regime. In the {\\it ballistic} regime, both tunneling and Coulomb drag lead to a {\\it negative} transresistance R_{TR}, while in the {\\it diffusive} regime the tunneling opposes the drag and leads to a {\\it positive} R_{TR}. If L is smaller than the phase-breaking length, the tunneling leads to interference oscillations of the resistance that are damped exponentially with L.

Raichev, O E

1999-01-01

138

Contacting single molecules to metallic electrodes by scanning tunnelling microscope manipulation: model systems for molecular electronics  

International Nuclear Information System (INIS)

The electronic contact between a molecular wire and a metallic electrode will play an important role in future molecular electronics as its properties determine the conductivity of the molecule-metal system. Scanning tunnelling microscopy manipulation reveals various advantages for the investigation of electronic contacts at the atomic scale. In this review, several examples of molecular wire-electrode systems are presented, where single molecules are placed in contact in a controlled way. Changed chemical structures of the molecule and, on the other hand, different shapes and dimensions of electrodes lead to a variety of contact configurations. The contact can be characterized using the additional contribution to the tunnelling current, but also using the influence on the electronic states of the electrode and the molecule. The quality of the contact is discussed in terms of the vertical distance between the molecular wire and the metal atoms and of the chemical composition of the molecular end group

139

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)

140

Assessment of Scanning Tunneling Spectroscopy Modes Inspecting Electron Confinement in Surface-Confined Supramolecular Networks  

OpenAIRE

Scanning tunneling spectroscopy (STS) enables the local, energy-resolved investigation of a samples surface density of states (DOS) by measuring the differential conductance (dI/dV) being approximately proportional to the DOS. It is popular to examine the electronic structure of elementary samples by acquiring dI/dV maps under constant current conditions. Here we demonstrate the intricacy of STS mapping of samples exhibiting a strong corrugation originating from electronic density and local w...

Krenner, Wolfgang; Ku?hne, Dirk; Klappenberger, Florian; Barth, Johannes V.

2013-01-01

141

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

OpenAIRE

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 $eV<\\omega_0$, in which electrons emit and absorb phonons virtually. The process suppresses the resonant amplitude. ...

Ueda, Akiko; Eto, Mikio

2006-01-01

142

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

CERN Document Server

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

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

1998-01-01

143

Electron transport simulation in resonant-tunneling GaN/AlGaN heterostructures  

International Nuclear Information System (INIS)

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 Schrödinger 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.

144

Sequential mechanism of electron transport in the resonant tunneling diode with thick barriers  

International Nuclear Information System (INIS)

A frequency-dependent impedance analysis (0.1-50 GHz) of an InGaAs/InAlAs-based resonant tunneling diode with a 5-nm-wide well and 5-nm-thick barriers showed that the transport mechanism in such a diode is mostly sequential, rather than coherent, which is consistent with estimates. The possibility of determining the coherent and sequential mechanism fractions in the electron transport through the resonant tunneling diode by its frequency dependence on the impedance is discussed

145

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

146

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

Energy Technology Data Exchange (ETDEWEB)

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

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

1982-04-15

147

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

CERN Document Server

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 an application of the general solution of these equations, we consider different kinds of electrical contacts to the double-wire system and calculate the direct resistance, the transresistance, in the presence of tunneling and Coulomb drag, and the tunneling resistance. If L is smaller than the backscattering length l_P, both the tunneling and the drag lead to a negative transresistance, while in the diffusive regime (L >>l_P) the tunneling opposes the drag and leads to a positive transresistance. If L is smaller than the phase-breaking len...

Raichev, O E

2000-01-01

148

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

Science.gov (United States)

We show that electron tunneling from edge states in a two-dimensional topological insulator into a parallel electron waveguide leads to the appearance of spin-polarized current in the waveguide. The spin polarization P can be very close to unity and the electron current passing through the tunnel contact splits in the waveguide into two branches flowing from the contact. The polarization essentially depends on the electron scattering by the contact and the electron-electron interaction in the one-dimensional edge states. The electron-electron interaction is treated within the Luttinger liquid model. The main effect of the interaction stems from the renormalization of the electron velocity, due to which the polarization increases with the interaction strength. Electron scattering by the contact leads to a decrease in P. A specific effect occurs when the bottom of the subbands in the waveguide crosses the Dirac point of the spectrum of edge states when changing the voltage or chemical potential. This leads to changing the direction of the spin current. PMID:22968932

Sukhanov, Aleksei A; Sablikov, Vladimir A

2012-10-10

149

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

CERN Document Server

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

Yakaboylu, Enderalp; Hatsagortsyan, Karen Z

2014-01-01

150

Electronic Resource Management: Functional Integration in Technical Services  

OpenAIRE

Declining usage of print materials along with increasing usage of electronic resources makes it necessary for libraries to reallocate personnel from print management to electronic resources management. Electronic resources management should be the primary focus of technical services units in the early twenty-first century. Print should no longer be treated as the default format, and the work of library staff must be reorganized and reintegrated with librarians and other professionals to refle...

Stachokas, George

2014-01-01

151

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

Scientific Electronic Library Online (English)

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

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

2002-06-01

152

???????? ??? ???????? ?????? ?????? (DNS Tunneling)  

OpenAIRE

?????? ????? ??? ???????????? ???????? ????? ? ????????? ??? ?????? ??????????? ??? ????????? ??????? ??????? ,??? DNS Tunnels ??? ? ????????? ??? ?????????. ?? ?????????? ??????? ??????????? ??? DNS Tunneling. ?? ?????????????? ? ???????? Iodine ??? ?? ?????????? ??? Captive Portal ??? ?? ?...

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

2014-01-01

153

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

Science.gov (United States)

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

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

2002-01-01

154

Electronic structure and tunneling resonance spectra of nanoscopic aluminum islands  

OpenAIRE

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

Narvaez, Gustavo A.; Kirczenow, George

2002-01-01

155

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

OpenAIRE

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 t...

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

2010-01-01

156

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)

157

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

158

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

Science.gov (United States)

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

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

2014-06-01

159

Ultralarge area MOS tunnel devices for electron emission  

OpenAIRE

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 ...

Thomsen, Lasse Bjørchmar; Nielsen, Gunver; Vendelbo, Søren Bastholm; Johansson, Martin; Hansen, Ole; Chorkendorff, Ib

2007-01-01

160

Electronic structure of EuO spin filter tunnel contacts directly on silicon  

International Nuclear Information System (INIS)

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

161

Using Electronic Resources to Support Problem-Based Learning  

Science.gov (United States)

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

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

2012-01-01

162

Image potential of a tunnelling electron moving near two different metals  

International Nuclear Information System (INIS)

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

163

Controlling the Interaction of Electron and Nuclear Spins in a Tunnel-Coupled Quantum Dot  

OpenAIRE

We present a technique for manipulating the nuclear spins and the emission polarization from a single optically active quantum dot. When the quantum dot is tunnel coupled to a Fermi sea, we have discovered a natural cycle in which an electron spin is repeatedly created with resonant optical excitation. The spontaneous emission polarization and the nuclear spin polarization exhibit a bistability. For a sigma(+) pump, the emission switches from sigma(+) to sigma(-) at a partic...

Kloeffel, C.; Dalgarno, P. A.; Urbaszek, B.; Gerardot, B. D.; Brunner, D.; Petroff, P. M.; Loss, D.; Warburton, R. J.

2010-01-01

164

Combined Scanning Force Microscopy and Scanning tunneling spectroscopy of an electronic nanocircuit at very low temperature.  

OpenAIRE

We have developed a combined microscope Atomic Force Microscope (AFM) / Scanning Tunneling Microscope (STM) at very low temperature. This microscope allows the study of the electronic Local Density Of States (LDOS) on current biased nanocircuits. We have developed a nanofabrication process to obtain superconducting wires of niobium (Nb) with 10×300 nm2 section.This process gives on Nb a subnanometric surface roughness. We describe also the method of tip's fabrication which are glued on...

Senzier, Julien

2007-01-01

165

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

OpenAIRE

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

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

2014-01-01

166

Scanning Tunneling Microscopy and Low-Energy Electron Diffraction Studies of Quantum Wires on Si(332)  

OpenAIRE

In this master thesis I have investigated one-dimensional nanostructures, so called quantum wires. The goal was to grow them in situ on a stepped silicon surface and thereafter do several kinds of measurements, like Scanning Tunneling Microscopy, Low-Energy Electron Diffraction and Photoemission. The surface that was used was a Si(332) surface and the metals used in the growth of the quantum wires were gold and silver. After the preparation and measurement of the stepped surface, evaporation ...

Gladh, Jo?rgen

2006-01-01

167

STM based inelastic electron tunneling spectroscopy on NdBa2Cu3O7-?  

International Nuclear Information System (INIS)

Inelastic electron tunneling spectroscopy (IETS) is a very powerful tool to detect collective excitations in conducting materials. Due to inelastic excitation by tunneling electrons, a very weak kink is usually observed in dI/dV curves at the bias voltage corresponding to the excitation energy. In IETS on s wave superconductors, phonon modes (?ph) were observed at energies given by E = ?+ ??ph, where ? is the energy gap. Recently IETS using scanning tunneling spectroscopy (STS) has been used to detect a bosonic mode in Bi2Sr2CaCu2O8+?. In the STS data obtained on NdBa2Cu3O7-? single crystals, we observed peaks in d2I/dV2 curves beyond the coherence peaks from which collective excitation energies of ?23 meV and ? 34 meV have been found for the samples with Tc of 93.5 K and 95.5 K respectively. Band structure calculation shows that there is no structure in the density of state at the observed energies which thus supports the presumption that the observed kinks in dI/dV curves are due to inelastic scattering of electrons

168

Electron transport through cubic InGaN/AlGaN resonant tunneling diodes  

Science.gov (United States)

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

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

2014-12-01

169

Electron Tunneling through Pseudomonas aeruginosa Azurins on SAM Gold Electrodes  

OpenAIRE

Robust voltammetric responses were obtained for wild-type and Y72F/H83Q/Q107H/Y108F azurins adsorbed on CH3(CH2)nSH:HO(CH2)mSH (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) a...

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

2008-01-01

170

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

Energy Technology Data Exchange (ETDEWEB)

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

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

2013-11-25

171

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

172

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

Energy Technology Data Exchange (ETDEWEB)

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.

Kiyama, H., E-mail: kiyama@meso.t.u-tokyo.ac.jp; Fujita, T.; Teraoka, S.; Oiwa, A. [Department of Applied Physics, The University of Tokyo, Tokyo 113-8656 (Japan); Tarucha, S. [Department of Applied Physics, The University of Tokyo, Tokyo 113-8656 (Japan); Center for Emergent Matter Science, RIKEN, Saitama 351-0198 (Japan)

2014-06-30

173

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.

174

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

International Nuclear Information System (INIS)

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

175

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

176

Cryogenic amplifier for fast real-time detection of single-electron tunneling:  

OpenAIRE

The authors employ a cryogenic high electron mobility transistor (HEMT) amplifier to increase the bandwidth of a charge detection setup with a quantum point contact (QPC) charge sensor. The HEMT is operating at 1?K and the circuit has a bandwidth of 1?MHz. The noise contribution of the HEMT at high frequencies is only a few times higher than that of the QPC shot noise. The authors use this setup to monitor single-electron tunneling to and from an adjacent quantum dot. The authors measure ...

Vink, I. T.; Nooitgedagt, T.; Schouten, R. N.; Vandersypen, L. M. K.; Wegscheider, W.

2007-01-01

177

A cryogenic amplifier for fast real-time detection of single-electron tunneling  

OpenAIRE

We employ a cryogenic High Electron Mobility Transistor (HEMT) amplifier to increase the bandwidth of a charge detection setup with a quantum point contact (QPC) charge sensor. The HEMT is operating at 1K and the circuit has a bandwidth of 1 MHz. The noise contribution of the HEMT at high frequencies is only a few times higher than that of the QPC shot noise. We use this setup to monitor single-electron tunneling to and from an adjacent quantum dot and we measure fluctuation...

Vink, I. T.; Nooitgedagt, T.; Schouten, R. N.; Wegscheider, W.; Vandersypen, L. M. K.

2007-01-01

178

Quasistationary electron states and the conductivity of a symmetric three-barrier resonant tunnel structure  

International Nuclear Information System (INIS)

The evolution of spectral parameters (resonance energies and widths) of quasistationary electron states and its dependence on geometrical parameters of a nanosystem have been studied in the framework of the rectangular and ?-like potential barrier models for a symmetric three-barrier resonant tunnel structure (TBRTS). The conductivity of symmetric TBRTS has been determined in the low-electric-field approximation. The maximal magnitudes of conductivity in the model of ?-like potential barriers were found to be ten times as low as that in a more realistic model of rectangular potentials, due to the neglect of the difference between electron effective masses in the wells and barriers.

179

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.

180

Effects of intradot electron electron interaction on the photon-assisted Andreev tunneling through a finite-sized carbon-nanotube system  

Science.gov (United States)

The effects of intradot electron electron interaction on the photon-assisted Andreev tunneling of a superconductor/carbon-nanotube/superconductor system are studied by using nonequilibrium Green's function technique. The inverse supercurrent reflecting the ?-junction transition emerges in the spin-split energy-levels regime polarized by the Coulomb interaction. For the positive tunneling case, the supercurrent reaches its maximum when the spin-degenerate energy-levels are nearest to the Fermi surface. Conversely, for the negative tunneling case, the supercurrent reaches its maximum when two split energy-levels are symmetric with respect of the Fermi surface. The sign and the amplitude of the Andreev tunneling depend distinctly on the energy-level spacing tuned by photon-assisted tunneling. In order to fully understand the transport characteristics, the current-carrying density of states are investigated, which clearly shows the enhancement, suppression or even reversion of the supercurrent.

Zhao, Li-Na; Pan, Hui; Lin, Tsung-Han; Yu, Dapeng

2007-01-01

181

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

182

Ultrafast laser-induced electron emission from multiphoton to optical tunneling  

Science.gov (United States)

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

Pant, M.; Ang, L. K.

2012-07-01

183

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

184

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)

185

Electron magneto-tunneling through single self-assembled InAs quantum dashes  

Science.gov (United States)

We have investigated electron magneto-tunneling through single self-assembled InAs quantum dashes (QDHs) coupled to metal nanogap electrodes. The samples operate as single electron transistors and exhibit clear shell structures, reflecting the anisotropic shape of the QDHs. In high magnetic fields, the samples exhibit strongly orbital-dependent large diamagnetic shifts and large electron g-factors in the range |g| ˜ 3-11. The strong level-to-level fluctuation of the g-factors implies the presence of strong spin-orbit interaction in this system. These properties suggest that InAs QDHs are promising for the manipulation of single-electron orbital/spin states by external electric/magnetic fields.

Shibata, Kenji; Pascher, Nikola; Luukko, Perttu J. J.; Räsänen, Esa; Schnez, Stephan; Ihn, Thomas; Ensslin, Klaus; Hirakawa, Kazuhiko

2014-04-01

186

BBC news style guide [electronic resource].  

International Nuclear Information System (INIS)

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

187

Evaluation Criteria for Electronic Reference Resources Available on the Internet  

Directory of Open Access Journals (Sweden)

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

Reda Mohamed al-Najar

2007-06-01

188

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

Directory of Open Access Journals (Sweden)

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

Micaela Waldman

2003-01-01

189

User Perception of Electronic Resources in the University of Ilorin  

Directory of Open Access Journals (Sweden)

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

BASHORUN

2011-11-01

190

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

191

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

Science.gov (United States)

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

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

2013-12-01

192

Fabrication of tunnel junction-based molecular electronics and spintronics devices  

International Nuclear Information System (INIS)

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

193

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

194

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

195

Proximity effect and hot-electron diffusion in Ag/Al{sub 2}O{sub 3}/Al tunnel junctions  

Energy Technology Data Exchange (ETDEWEB)

We have fabricated Ag/Al{sub 2}O{sub 3}/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.

Netel, H., Jochum, J., Labov, S.E., Mears, C.A., Frank, M. [Physics and Space Technology Directorate, Lawrence Livermore National Lab., CA (United States); Chow, D., Lindeman, M.A., Hiller, L.J. [California Univ., Davis, CA (United States). Dept. of Applied Science

1997-02-18

196

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

197

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

198

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)

199

The Ni(111) surface electrons investigated with low-temperature scanning tunneling spectroscopy  

Science.gov (United States)

The electronic structure of the ferromagnetic Ni(111) surface has been attracting interest for a long time. Despite experimental and theoretical effort, reported values of binding energies, effective masses and number of the surface states and surface resonances differed substantially. Working with a local probe technique reveals relevant contributions from adsorbates and defects. Here we present an extensive scanning tunneling microscopy and spectroscopy investigation at low temperature, employing fourier transform methods for the analysis. The results show a parabolic surface state with an upward dispersion at --165 meV with a surprisingly low effective mass of 0.17 me and a downward dispersing surface resonance at --230 meV. From the decay of the standing wave pattern at step edges electron and hole lifetimes have been determined with values considerably smaller than found on noble metal surfaces. Details of the surface electronic structure have been revealed including an anti-resonance at the Fermi energy.

Braun, Kai-Felix; Flipse, C. F. J.; Rieder, K.-H.

2005-03-01

200

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

International Nuclear Information System (INIS)

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

201

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

Science.gov (United States)

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

Li, Wei; Zhang, Qin; Bijesh, R.; Kirillov, Oleg A.; Liang, Yiran; Levin, Igor; Peng, Lian-Mao; Richter, Curt A.; Liang, Xuelei; Datta, S.; Gundlach, David J.; Nguyen, N. V.

2014-11-01

202

First-Principles Simulations of Inelastic Electron Tunneling Spectroscopyof Molecular Junctions  

CERN Document Server

A generalized Green's function theory is developed to simulate the inelastic electron tunneling spectroscopy (IETS) of molecular junctions. It has been applied to a realistic molecular junction with an octanedithiolate embedded between two gold contacts in combination with the hybrid density functional theory calculations. The calculated spectra are in excellent agreement with recent experimental results. Strong temperature dependence of the experimental IETS spectra is also reproduced. It is shown that the IETS is extremely sensitive to the intra-molecular conformation and to the molecule-metal contact geometry.

Jiang, J; Lu, W; Luo, Y; Jiang, Jun; Kula, Mathias; Lu, Wei; Luo, Yi

2005-01-01

203

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

Directory of Open Access Journals (Sweden)

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

L. Moldovan

2008-05-01

204

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

205

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.

206

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

International Nuclear Information System (INIS)

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

207

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

208

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

209

D-Lib magazine [electronic resource].  

International Nuclear Information System (INIS)

Presents "D-Lib Magazine," a monthly electronic publication related to digital libraries. Includes commentaries and news articles. Offers an archive of back issues and a site search engine. Provides access to working groups, digital library research

210

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

International Nuclear Information System (INIS)

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

211

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

Science.gov (United States)

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

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

2012-07-01

212

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

International Nuclear Information System (INIS)

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

213

IBEX Electronic Resource for Museum Educators  

Science.gov (United States)

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

214

Assessment of scanning tunneling spectroscopy modes inspecting electron confinement in surface-confined supramolecular networks.  

Science.gov (United States)

Scanning tunneling spectroscopy (STS) enables the local, energy-resolved investigation of a samples surface density of states (DOS) by measuring the differential conductance (dI/dV) being approximately proportional to the DOS. It is popular to examine the electronic structure of elementary samples by acquiring dI/dV maps under constant current conditions. Here we demonstrate the intricacy of STS mapping of samples exhibiting a strong corrugation originating from electronic density and local work function changes. The confinement of the Ag(111) surface state by a porous organic network is studied with maps obtained under constant-current (CC) as well as open-feedback-loop (OFL) conditions. We show how the CC maps deviate markedly from the physically more meaningful OFL maps. By applying a renormalization procedure to the OFL data we can mimic the spurious effects of the CC mode and thereby rationalize the physical effects evoking the artefacts in the CC maps. PMID:23503526

Krenner, Wolfgang; Kühne, Dirk; Klappenberger, Florian; Barth, Johannes V

2013-01-01

215

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

Science.gov (United States)

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

Huerkamp, Felix; Krüger, Peter; Pollmann, Johannes

2014-03-01

216

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

International Nuclear Information System (INIS)

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

217

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

International Nuclear Information System (INIS)

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.

218

Electron transport through aluminum oxide tunnel barriers and OPE-based molecular junctions  

Science.gov (United States)

This work presents results of a study of electron transport through aluminum-oxide based tunnel barriers and single-molecule transistors. Both systems have the potential for a dramatic increase of the density and performance of integrated circuits with critical dimensions well below the scaling limits of the conventional semiconductor technology. Studies of these two systems are also united by a common experimental approach - measurement of very small (down to 10 --14 A) currents within a broad temperature range (from 4.2 K to 350 K). Transport properties of (Nb/)Al/AlOx/Nb tunnel barriers have been studied for structures formed by (i) thermal oxidation and (ii) plasma oxidation, before and after their rapid thermal post-annealing at temperatures up to 650°C. The post-annealing results in a substantial increase of the barrier height of the thermally formed aluminum oxide, which (within a broad range of RTA temperatures) may be substantially higher than that of the plasma-grown AlOx barriers. This fact, together with high endurance of annealed barriers under electric stress, may eventually lead to the fabrication of AlOx and SiO2/AlOx layered ("crested") barriers for advanced floating-gate memories. Electron transport through single molecular devices has been studied for structures of three types: (i) co-planar Au electrodes with 5-nm-scale gaps formed by e-beam lithography, (ii) co-planar Au electrodes with 1--2 nm-scale gaps formed by electromigration, and (iii) nanowires crosspoints with vertical gaps of 3 to 5 nm formed by under-etched aluminum oxide layers. Two types of Oligo(Phenylene Ethynylene) based molecules (with or without naphthalene diimide groups working as acceptors), capped with isocyanide terminal groups, have been investigated. For both molecules, nonlinear current-voltage curves with discrete current steps, due to tunneling through one or a few molecules, have been observed, and their dependences on the gate voltage and temperature have been studied in detail. Key Words: electron transport, aluminum oxide, crested barrier, rapid thermal annealing, single-electron transistor, electromigration, molecular junction.

Liu, Xueqing

219

IBEX: An Electronic Resource for Museum Educators  

Science.gov (United States)

This PowerPoint is a resource for museum educators that highlights the major mission information and science background for the Interstellar Boundary Explorer (IBEX) Mission, a Small Explorer Earth-orbiting spacecraft that is designed to map the distant boundary between the solar wind from our Sun and the interstellar medium. This PowerPoint supports a full-length planetarium show about the IBEX mission and the boundary of the Solar System. Each short activity/product helps to build awareness and engagement in the science and engineering aspects of the mission that is reinforced as visitors choose to participate in more activities, including viewing the Show and mission Web site.

Nichols, Michelle

2008-01-01

220

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

221

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

222

Proposed alteration of images of molecular orbitals obtained using a scanning tunnelling microscope as a probe of electron correlation  

OpenAIRE

Scanning tunneling spectroscopy (STS) allows to image single molecules decoupled from the supporting substrate. The obtained images are routinely interpreted as the square moduli of molecular orbitals, dressed by the mean-field electron-electron interaction. Here we demonstrate that the effect of electron correlation beyond mean field qualitatively alters the uncorrelated STS images. Our evidence is based on the ab-initio many-body calculation of STS images of planar molecul...

Toroz, Dimitrios; Rontani, Massimo; Corni, Stefano

2012-01-01

223

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

DEFF Research Database (Denmark)

Theories of in situ scanning tunnelling microscopy (STM) of molecules with redox levels near the substrate and tip Fermi levels point to 'spectroscopic' current-overpotential features. Prominent features require a narrow 'probing tip', i.e. a small bias voltage, eV(bias), compared with the molecular and solvent reorganisation Gibbs energy, E-r. However, a large V-bias is frequently needed for stable imaging. This applies particularly to in situ STM of redox metalloproteins, emerging as a new approach to imaging of biological processes directly in aqueous medium. We provide first an extension of previous theoretical work on in situ STM of redox molecules, to large bias voltages, \\eV(bias)\\ > E-r. Large bias voltages give tunnelling contrasts independent of the overpotential over a broad range, as both the oxidised and reduced redox levels are located within the 'energy tip' between the substrate and tip Fermi levels. STM here involves coherent two-step interfacial electron transfer between the redox level and the enclosing substrate and tip. We have also extended previous experimental in situ STM studies of the blue copper protein Pseudomonas aeruginosa azurin, adsorbed on Au(111), to cover a broad tunnelling current-overpotential range at a constant (large) bias voltage of +0.2 V. The current is found to be constant over a 0.25 V overpotential range, which covers roughly the range where the oxidised and reduced redox levels are located within the energy tip. STM contrast and apparent adsorbate coverage decrease outside this range. This could reflect in part redox processes of azurin, but also tip-induced disassembly of the azurin monolayer.

Zhang, Jingdong; Kuznetsov, A.M.

2003-01-01

224

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

225

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

226

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

227

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

228

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

International Nuclear Information System (INIS)

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

229

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

230

Resonant polaron-assisted tunneling of strongly interacting electrons through a single-level vibrating quantum dot  

Science.gov (United States)

The problem of resonant transport of strongly interacting electrons through a one-dimensional single-level vibrating quantum dot is being considered. In this paper, we generalize the Komnik and Gogolin model [Phys. Rev. Lett.PRLTAO0031-900710.1103/PhysRevLett.90.246403 90, 246403 (2003)] for the single-electron transistor with g=1/2 Luttinger liquid leads to the case of a strong electron-vibron interaction in a quantum dot. The effective transmission coefficient and differential conductance of the system has been derived for the general case of asymmetric tunnel barriers. The main result obtained is that, in the zero-temperature limit, the resonant polaron-assisted tunneling with perfect transmission is possible. This resonant tunneling is of the novel (Andreev-like) type due to a special electron-electron interaction in the leads. As a result, a strong domination of resonant polaron-assisted electron transport at low temperatures has been found. Additional narrowing due to electron-electron interaction in the leads, is roughly the same for all polaron-assisted resonances.

Skorobagatko, Gleb A.

2012-02-01

231

Surface acoustic wave induced electron tunneling from an InGaAs/GaAs wetting layer  

International Nuclear Information System (INIS)

We report on a stroboscopic technique to probe the dynamic modulation controlled by a surface acoustic wave (SAW) of the photoluminescence (PL) of a wetting layer which is formed during the growth of InGaAs/GaAs quantum dots. A short laser pulse (? <100 ps) is actively phase locked to the frequency of the SAW and the relative phase between laser excitation and SAW can be precisely controlled. Thus, we are able to map one complete cycle of the SAW and study the PL quenching and its modulation in the time domain. For low SAW powers the observed modulation with the fundamental period of the SAW arises from different mobilities of electrons and holes. This imbalance leads to different ionization efficiencies in the type-II band gap modulation induced by the SAW. At high SAW power levels, the modulation period doubles which can be readily explained by SAW induced tunneling induced by the vertical piezoelectric field component.

232

Photoisomerization-induced manipulation of single-electron tunneling for novel Si-based optical memory.  

Science.gov (United States)

We demonstrated optical manipulation of single-electron tunneling (SET) by photoisomerization of diarylethene molecules in a metal-insulator-semiconductor (MIS) structure. Stress is placed on the fact that device operation is realized in the practical device configuration of MIS structure and that it is not achieved in structures based on nanogap electrodes and scanning probe techniques. Namely, this is a basic memory device configuration that has the potential for large-scale integration. In our device, the threshold voltage of SET was clearly modulated as a reversible change in the molecular orbital induced by photoisomerization, indicating that diarylethene molecules worked as optically controllable quantum dots. These findings will allow the integration of photonic functionality into current Si-based memory devices, which is a unique feature of organic molecules that is unobtainable with inorganic materials. Our proposed device therefore has enormous potential for providing a breakthrough in Si technology. PMID:24099440

Hayakawa, Ryoma; Higashiguchi, Kenji; Matsuda, Kenji; Chikyow, Toyohiro; Wakayama, Yutaka

2013-11-13

233

Thermal Management Solutions Using Electron Tunneling Through a Nano-Scale Vacuum Gap  

Science.gov (United States)

Requirements for cooling and power consumption in space platforms are subject to significantly greater constraints than the requirements for terrestrial applications. Existing cooling systems incorporate various mechanisms including thermoelectric (Peltier) cooling elements, radiative cooling, and phase-change compressor-based systems. This paper outlines an alternative mechanism currently in development called "thermotunneling". This mechanism exploits electron tunneling across a vacuum gap of ˜10nm to effect a temperature differential with high efficiency. When complete, these devices ("Cool Chips") are expected to offer a compact, lightweight, low maintenance and highly efficient (in excess of 50% of Carnot Efficiency) thermal management solution ideally suited for the needs of aerospace applications. This article was originally published with an incorrect list of authors which is now corrected.

Tavkhelidze, Avto; Taliashvili, Zaza; Bibilashvili, Amiran; Tsakadze, Leri; Jangadze, Larisa; Skhiladze, Givi; Cox, Isaiah W.; Magdych, Jim

2004-02-01

234

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

235

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

236

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

Science.gov (United States)

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

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

2014-11-01

237

Electronic Document Management: A Human Resource Management Case Study  

OpenAIRE

This case study serve as exemplar regarding what can go wrong with the implementation of an electronic document management system. Knowledge agility and knowledge as capital, is outlined against the backdrop of the information society and knowledge economy. The importance of electronic document management and control is sketched thereafter. The literature review is concluded with the impact of human resource management on knowledge agility, which includes references to the learning organisati...

Thomas Groenewald

2004-01-01

238

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.

239

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

240

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

241

Spin Inelastic Electron Tunneling Spectroscopy on Local Magnetic Moment Embedded in Josephson Junction  

OpenAIRE

Recent experimental conductance measurements performed on paramagnetic molecular adsorbates on a superconducting surface, using superconducting scanning tunneling microscopy techniques, are theoretically investigated. For low temperatures, we demonstrate that tunneling current assisted excitations of the local magnetic moment cannot occur for voltage biases smaller than the superconducting gap of the scanning tunneling microscope. The magnetic moment is only excited for volt...

Berggren, P.; Fransson, J.

2014-01-01

242

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

243

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

Science.gov (United States)

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

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

2013-04-10

244

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

245

Electron Tunneling Spectroscopic Measurements on Al-doped MgB2 Thin Films  

Science.gov (United States)

The effect of Al-doping on the electron-phonon coupling in magnesium diboride films was studied by electron tunneling spectroscopy on planar sandwich-type Mg1-xAlxB2-oxide-indium junctions. The superconducting Mg1-xAlxB2 films (0 ? x < 0.5) were prepared in situ by simultaneous sublimation of Mg and sputtering of B and Al. The oxide barrier was either natural or artificial (aluminium oxide). The high junction quality allowed precise measurements of the differential conduction up to high bias-voltages of 120 mV. In the low bias range the small energy gap ?? was measured: it decreased linearly with increasing Al-doping in agreement with the band filling model. The measurements at higher energies revealed the phonon induced features in the electron density of states. Although the spectra were influenced by the proximity effect below ?20meV, they enabled the determination of the effective Eliashberg function ?2F. For the same film compositions ?2F data were obtained theoretically from first principles calculations. The progressive loss of superconductivity with increasing Al doping was reflected in both the experiment and calculations by the evolution of ?2F. The dominating ?-? interband pairing interaction, which contributes most to the superconductivity on the ? sheet, was gradually weakened in correlation with the band structure calculations.

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

246

Discretization of electronic states in large InAsPInP multilevel quantum dots probed by scanning tunneling spectroscopy  

OpenAIRE

The topography and the electronic structure of InAsP/InP quantum dots are probed by crosssectionnal scanning tunneling microscopy and spectroscopy. The study of the local density of states in such large quantumdots con?rms the discrete nature of theelectronic levels whose wavefunctions are measured by di?erential conductivity mapping. Due to their large dimensions, the energy separation between the discrete electronic levels is low, allowing for quantization both in the lateral and growth...

Fain, Bruno; Robert-philip, Isabelle; Beveratos, Alexios; David, Christophe; Wang, Zhao-zhong; Sagnes, Isabelle; Girard, Jean-christophe

2012-01-01

247

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 method, qualitati...

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

2011-01-01

248

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

Science.gov (United States)

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

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

2002-01-01

249

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

Science.gov (United States)

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

Stachokas, George

2009-01-01

250

The effect of thermal annealing on the properties of Al-AlOx-Al single electron tunneling transistors  

CERN Document Server

The effect of thermal annealing on the properties of Al-AlOx-Al single electron tunneling transistors is reported. After treatment of the devices by annealing processes in forming gas atmosphere at different temperatures and for different times, distinct and reproducible changes of their resistance and capacitance values were found. According to the temperature regime, we observed different behaviors as regards the resistance changes, namely the tendency to decrease the resistance by annealing at T = 200 degree C, but to increase the resistance by annealing at T = 400 degree C. We attribute this behavior to changes in the aluminum oxide barriers of the tunnel junctions. The good reproducibility of these effects with respect to the changes observed allows the proper annealing treatment to be used for post-process tuning of tunnel junction parameters. Also, the influence of the annealing treatment on the noise properties of the transistors at low frequency was investigated. In no case did the noise figures in t...

Scherer, H; Zorin, A B; Niemeyer, J C; Weimann, Th.

2001-01-01

251

How does thermal motion of atoms influence rates of bridge-mediated electron transfer reactions? 1. Dynamical modulation of the effective tunneling coupling.  

Science.gov (United States)

Understanding how thermal nuclear motion affects the electron transfer (ET) reaction rates is essential for describing a broad range of vital biological redox reactions as well as designing molecular electronic devices. Theoretical studies of biological ET reaction rates usually assume a) the superexchange ET regime (virtual bridge electronic states), and b) the Franck-Condon approximation (electronic dephasing slower than the time-dependent Franck-Condon factor decay time). We present the first investigation of the electronic dephasing effects and the first quantitative analysis of the modulation of effective tunneling coupling by nuclear dynamics. Molecular dynamics simulations coupled with extended Huckel-level quantum chemical calculations of the effective electronic coupling were performed for the blue copper ET protein azurin. We discuss effects of the donor-to-acceptor distance, tunneling pathway structure, tunneling energy, temperature, and protein motion on the dynamics of the effective tunneling coupling and the ET reaction rate.

Balabin, Ilya; Skourtis, Spyros; Kawatsu, Tsutomu

2005-03-01

252

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.)

253

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

254

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

Science.gov (United States)

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

White, Marilyn; Sanders, Susan

2009-01-01

255

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

DEFF Research Database (Denmark)

We have used L-Cysteine (Cys) as a model system to study the surface electronic structures of single molecules at the submolecular level in aqueous buffer solution by a combination of electrochemical scanning tunneling microscopy (in situ STM), electrochemistry including voltammetry and chronocoulometry, and density functional theory (DFT) computations. Cys molecules were assembled on single-crystal Au(110) surfaces to form a highly ordered monolayer with a periodic lattice structure of c(2 x 2) in which each unit contains two molecules; this conclusion is confirmed by the results of calculations based on a slab model for the metal surface. The ordered monolayer offers a platform for submolecular scale electronic mapping that is an issue of fundamental interest but remains a challenge in STM imaging science and surface chemistry. Single Cys molecules were mapped as three electronic subunits contributed mainly from three chemical moieties: thiol (-SH), carboxylic (-COOH), and amine (-NH2) groups. The contrastsof the three subunits depend on the environment (e.g., pH), which affects the electronic structure of adsorbed species. From the DFT computations focused on single molecules, rational analysis of the electronic structures is achieved to delineate the main factors that determine electronic contrasts in the STM images. These factors include the molecular orientation, the chemical nature of the elements or groups in the molecule, and the interaction of the elements with the substrate and tip. The computational images recast as constant-current-height profiles show that the most favorable molecular orientation is the adsorption of cysteine as a radical in zwitterionic form located on the bridge between the Au(I 10) atomic rows and with the amine and carboxyl group toward the solution bulk. The correlation between physical location and electronic contrast of the adsorbed molecules was also revealed by the computational data. The present study shows that cysteine packing in the adlayer on Au(110) from the liquid environment is in contrast to that from the ultrahigh-vacuum environment, suggesting solvent plays a role during molecular assembly.

Zhang, Jingdong; Chi, Qijin

2009-01-01

256

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

Science.gov (United States)

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

England, Lenore; Fu, Li

2011-01-01

257

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

OpenAIRE

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

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

2010-01-01

258

Spin-Polarized Vacuum Tunneling:. Correlation of Electronic and Magnetic Properties on the Nanometer Scale  

Science.gov (United States)

The realization of spin-polarized vacuum tunneling is demonstrated for the Gd(0001) surface, which is ideally suited since it exhibits a surface state that is exchange-split into two parts with opposite spin polarization. Both appear as distinct features in the tunneling spectra. The use of ferromagnetic probe tips leads to magnetic-field-dependent asymmetries in the differential tunneling conductivity at bias voltages which correspond to the energies of the spin components. By mapping the asymmetry parameter we can image the magnetic domain structure of the sample. The spin polarization of the differential tunneling conductivity is found to be in excellent agreement with (inverse) photoemission data.

Getzlaff, M.; Bode, M.; Wiesendanger, R.

259

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

260

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

261

Resources  

Science.gov (United States)

... palate - resources Colon cancer - resources Cystic fibrosis - resources Depression - resources Diabetes - resources Digestive disease - resources Drug abuse - resources Eating disorders - resources Elder care - resources Epilepsy - resources Family ...

262

Evaluation of Surface Acidity of Aluminum Oxide Film by Inelastic Electron Tunneling Spectroscopy  

Science.gov (United States)

The surface acidity of aluminum oxide (AlOx) films was evaluated for the first time by inelastic electron tunneling (IET) spectroscopy using the Hammett indicators as probe molecules. The AlOx films were formed by oxidation of the aluminum films by DC glow discharge in oxygen atmosphere, and the indicators with pKa values ranging from -8.2 to +4.8 were used. The indicators, methyl red (MR) with pKa=+4.8 and methyl yellow (MY) with pKa=+3.3 contain the N=N bond and do not have the N-H bond. The IET spectrum of MR showed the peak related to the N-H stretching vibration at 3295 cm-1, while the spectrum of MY did not show the peak. These results indicate that the MR molecule chemisorbs at the N atom on the hydroxyl group acting as the Brønsted acid site and the MY molecule does not chemisorb on the site. Thus, the acid strength of the Brønsted site was determined to be approximately +3.3?q H0(B)?q+4.8.

Mouloudi, Halal El; Takahashi, Haruo; Haji, Hideki; Ooe, Akihiro; Nishikawa, Hiroyuki; Iri, Takeo

2003-04-01

263

Electron tunneling spectroscopy of superconducting A15 V-Ga alloy films  

International Nuclear Information System (INIS)

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

264

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

265

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

Energy Technology Data Exchange (ETDEWEB)

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: Black-Right-Pointing-Pointer Synchrotron enhanced x-ray scanning tunneling microscope (SXSTM) system designed. Black-Right-Pointing-Pointer Unique STM mount design allows angular DOF for tip alignment with x-ray beam. Black-Right-Pointing-Pointer System demonstrates ability to resolve atomic corrugations on HOPG. Black-Right-Pointing-Pointer Studies show chemical sensitivity with STM tip from photocurrent and tunneling. Black-Right-Pointing-Pointer Results show system's ability to study local magnetic (XMCD) properties on Fe films.

Cummings, M.L. [Rice University, Mechanical Engineering and Materials Science Department, Houston, TX 77005 (United States); Center for Nanoscale Materials, Argonne National Laboratory, Argonne, IL 60439 (United States); Chien, T.Y.; Preissner, C. [Advanced Photon Source, Argonne National Laboratory, Argonne, IL 60439 (United States); Madhavan, V. [Boston College, Department of Physics, Chestnut Hill, MA 02467 (United States); Diesing, D. [University of Duisburg-Essen, Faculty for Chemistry, 45141 Essen (Germany); Bode, M. [Center for Nanoscale Materials, Argonne National Laboratory, Argonne, IL 60439 (United States); Freeland, J.W. [Advanced Photon Source, Argonne National Laboratory, Argonne, IL 60439 (United States); Rose, V., E-mail: vrose@anl.gov [Advanced Photon Source, Argonne National Laboratory, Argonne, IL 60439 (United States)

2012-01-15

266

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.

267

Design and simulation of cellular nonlinear networks using single-electron tunneling transistor technology  

Science.gov (United States)

It is currently predicted that semiconductor device scaling will end at the 22-nm device feature size (7 nm physical channel length) according to the International Technology Roadmap for Semiconductors. The main challenge is then to develop innovative technologies that will extend the scaling beyond roadmap projection. Any new technology must be well matched with complementary metal oxide semiconductor (CMOS) technology and scaleable beyond CMOS scaling projections and must provide low-power high-speed signal processing. Nanotechnology will become an appealing option for developing devices for integrated circuits with dimensions and performances well beyond roadmap predictions. Such devices, based on the controllable transfer of charge between dots or 'islands', can take advantage of the quantum mechanical effects, such as tunneling and energy quantization, which would normally occur at the nanometer scale. An outstanding challenge is in arranging such nanodevices in new architectures that can be integrated on a single chip. In particular, locally interconnected architectures are believed to be necessary to alleviate the problems associated with increasing interconnect length and complexity in ultra-dense circuits. The goal of this work is to investigate the use of nanoelectronic structures in cellular non-linear network (CNN) architectures for potential application in future high-density and low-power CMOS-nanodevice hybrid circuits. The operation of the single-electron tunneling (SET) transistor is first reviewed, followed by a discussion of simple CNN linear architectures using a SET inverter topology as the basis for the non-linear transfer characteristics for individual cells to be used in analog processing arrays for image-processing applications. The basic SET CNN cell acts as a summing node that is capacitively coupled to the inputs and outputs of nearest neighbor cells. Monte Carlo simulation results are used to show CNN-like behavior in attempting to realize different functionality, such as connected component detector, shadowing, and NOT function. The speed and signal delay in SET networks are also discussed, and the power consumption of the SET-CNN is estimated and compared to a state-of-the-art CMOS processor.

Gerousis, Costa P.

268

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.

269

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

Science.gov (United States)

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

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

2011-07-01

270

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

OpenAIRE

For many years, library users have used only from the printed media in order to get the information that they have needed. Today with the widespread use of the Web and the addition of electronic information resources to library collections, the use of information in the electronic environment as well as in printed media is started to be used. In time, such types of information resources as, electronic journals, electronic books, electronic encyclopedias, electronic dictionaries and electronic...

P?nar Al; Umut Al

2003-01-01

271

Electron tunneling into the high-T/sub c/ superconductor Y-Ba-Cu-O  

International Nuclear Information System (INIS)

We have made tunneling measurements on junctions made on a polished surface of an Y-Ba-Cu-O pellet with an evaporated Pb layer as counterelectrode. We observe a Zeller-Giaever-like tunneling characteristic with a superconducting energy gap ? = 6 meV. This value is much smaller than the gap seen in point-contact tunneling experiments but is consistent with the gap found from infrared reflectivity measurements. We argue that this difference is due to the different superconducting properties of the surface layer and of the bulk of the material

272

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

Directory of Open Access Journals (Sweden)

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

Antanas Kiveris

2010-10-01

273

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

International Nuclear Information System (INIS)

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

274

Tunable valley polarization by a gate voltage when an electron tunnels through multiple line defects in graphene  

Science.gov (United States)

By means of an appropriate wave function connection condition, we study the electronic structure of a line defect superlattice of graphene with the Dirac equation method. We obtain the analytical dispersion relation, which can simulate well the tight-binding numerical result about the band structure of the superlattice. Then, we generalize this theoretical method to study the electronic transmission through a potential barrier where multiple line defects are periodically patterned. We find that there exists a critical incident angle which restricts the electronic transmission through multiple line defects within a specific incident angle range. The critical angle depends sensitively on the potential barrier height, which can be modulated by a gate voltage. As a result, non-trivial transmissions of K and K? valley electrons are restricted, respectively, in two distinct ranges of the incident angle. Our theoretical result demonstrates that a gate voltage can act as a feasible measure to tune the valley polarization when electrons tunnel through multiple line defects.

Liu, Zhe; Jiang, Liwei; Zheng, Yisong

2015-02-01

275

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

276

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

277

Tunnelling ratchets  

International Nuclear Information System (INIS)

Full text: A ratchet is an asymmetric potential that can be used to induce a particle flow when subjected to external fluctuations, in the absence of macroscopic net forces. When tunnelling contributes to the particle flow in an adiabatically-rocked ratchet, it has been predicted that the current direction will depend on temperature. Here we use quantum confinement to define an electron ratchet in a semiconductor nanostructure. We find that the two contributions to the rocking-induced current tunnelling through, and excitation over, the ratchet's energy barrier - flow in opposite directions. Thus, the net current direction depends on the electron energy distribution at a given temperature. This behaviour demonstrates a fundamental difference between classical and quantum ratchets and implies that tunnelling ratchets may be used as quantum heat pumps. A wave-mechanical model reproduced the temperature-induced current reversal and provides an intuitive explanation

278

Tunnel field-effect transistors as energy-efficient electronic switches.  

Science.gov (United States)

Power dissipation is a fundamental problem for nanoelectronic circuits. Scaling the supply voltage reduces the energy needed for switching, but the field-effect transistors (FETs) in today's integrated circuits require at least 60 mV of gate voltage to increase the current by one order of magnitude at room temperature. Tunnel FETs avoid this limit by using quantum-mechanical band-to-band tunnelling, rather than thermal injection, to inject charge carriers into the device channel. Tunnel FETs based on ultrathin semiconducting films or nanowires could achieve a 100-fold power reduction over complementary metal-oxide-semiconductor (CMOS) transistors, so integrating tunnel FETs with CMOS technology could improve low-power integrated circuits. PMID:22094693

Ionescu, Adrian M; Riel, Heike

2011-11-17

279

A Miniature High-Sensitivity Braodband Accelerometer Based on Electron Tunneling Transducers  

Science.gov (United States)

This paper describes the successful fabrication and demonstration of a new dual-element micromachined silicon tunnel accelerometer that extends the operational bandwidth beyond the resonant frequency of the proof mass.

Rockstad, H.; Kenny, T.; Reynolds, J.; Kaiser, W.; Gabrielson, T.

1993-01-01

280

Electron tunnelling measurement of the energy gap in a La-Sr-Cu-O superconductor  

International Nuclear Information System (INIS)

We have used the break junction technique to determine the energy gap of lanthanum-strontium-copper-oxide, one of the new high critical temperature superconductors. The current-voltage characteristics demonstrated a variety of tunneling behaviours. The best characteristic indicating quasiparticle tunneling between superconducting electrodes implied an energy gap of 7.0 + - 0.1 meV. Derivatives of other characteristics showed weak structure indicating possible energy gaps up to 9 meV. (author)

281

Tunneling-Assisted Acoustic Plasmon-Quasiparticle Excitation Resonances in Coupled Q1D Electron Gases  

OpenAIRE

We show that a weak non-resonant tunneling between two quantum wires leads to splitting of the acoustic plasmon mode at finite wavevector. Two gaps open up in the dipersion of the acoustic plasmon mode when its frequency is close to the frequencies of the quasiparticle excitations. In contrast to the Laudau damping of the collective excitations, these gaps are attributed to tunneling assisted acoustic plasmon-quasiparticle excitation resonances. We predict that such a resona...

Hai, Guo-qiang; Tavares, Marcos R. S.

1999-01-01

282

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

Directory of Open Access Journals (Sweden)

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

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

2011-02-01

283

Interplay of single particle and Josephson Cooper pair tunnelings on the electronic spectra of bilayer cuprate superconductors  

International Nuclear Information System (INIS)

We have investigated the interplay of single particle and Josephson Cooper pair tunnelings on the electronic spectra of optimal and overdoped bilayer cuprate (Bi2Sr2CaCu2O8+x) superconductors using tight binding bilayer Hubbard Hamiltonian within BCS d-wave superconducting state. On the basis of the numerical computation of the spectral function at (?, 0) point of the Brillouin zone, a reduction in bilayer splitting energy is pointed out due to the existence of Josephson Cooper pair tunneling in the superconducting state. We have explained our theoretical analysis of the spectral function in the light of recent angle resolved photoemission spectroscopic (ARPES) measurements on optimal doped bilayer cuprates, where a reduction in the bilayer splitting energy is observed in the superconducting state as compared to normal state

284

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

285

Resonant tunneling of electrons between two-dimensional systems of different densities in a quantizing magnetic field  

International Nuclear Information System (INIS)

The results of experimental investigation of the vertical electron transport in a GaAs/Al0.3Ga0.7As/GaAs single-barrier tunneling heterostructure with a doped barrier are presented. Two-dimensional accumulation layers appear on different sides of the barrier as a result of the ionization of Si donors in the barrier layer. The nonmonotonic shift of the current peak is found in the I-V curve of the tunneling diode in a magnetic field perpendicular to the planes of two-dimensional layers. Such a behavior is shown to be successfully explained in the model of appearing the Coulomb pseudogap and the pinning of the spin-split Landau levels at the Fermi levels of the contacts. In this explanation, it is necessary to assume that the Lande factor is independent of the filling factors of the Landau levels and is g* = 7.5 for both layers

286

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.)

287

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.

288

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

Directory of Open Access Journals (Sweden)

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

Zhong Wenjuan

2014-01-01

289

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

Science.gov (United States)

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 TiO(2) nanoparticles with similar band gap but much lower electron mobility were used, these ions were not observed unless the voltage on the sample plate was increased. The experimental results indicate that laser induced electron tunneling is dependent on the electron mobility and the strength of the electric field. Capture of low energy electrons by charge-deficient atoms of adsorbed organic molecules causes unpaired electron-directed cleavages of chemical bonds in a nonergodic pathway. In positive detection mode, electron tunneling cannot be observed due to the reverse moving direction of electrons. It should be able to expect that laser desorption ionization mass spectrometry is a new technique capable of probing the dynamics of electron tunneling. LAET offers advantages as a new ionization dissociation method for mass spectrometry. PMID:22595432

Zhong, Hongying; Fu, Jieying; Wang, Xiaoli; Zheng, Shi

2012-06-01

290

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

Science.gov (United States)

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

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

2008-01-01

291

Spin inelastic electron tunneling spectroscopy on local magnetic moment embedded in Josephson junction  

Science.gov (United States)

Recent experimental conductance measurements performed on paramagnetic molecular adsorbates on a superconducting surface, using superconducting scanning tunneling microscopy techniques, are theoretically investigated. For low temperatures, we demonstrate that tunneling current assisted excitations of the local magnetic moment cannot occur for voltage biases smaller than the superconducting gap of the scanning tunneling microscope. The magnetic moment is only excited for voltages corresponding to the sum of the superconducting gap and the spin excitation energies. In excellent agreement with experiment, we show that pumping into higher excitations gives additional current signatures by accumulation of density in the lower ones. Using external magnetic fields, we Zeeman-split the possible degeneracy and thereby resolve all excitations comprised in the magnetic moment.

Berggren, P.; Fransson, J.

2014-12-01

292

Dynamic Spin-Polarized Resonant Tunneling in Magnetic Tunnel Junctions  

OpenAIRE

Precisely engineered tunnel junctions exhibit a long sought effect that occurs when the energy of the electron is comparable to the potential energy of the tunneling barrier. The resistance of metal-insulator-metal tunnel junctions oscillates with an applied voltage when electrons that tunnel directly into the barrier's conduction band interfere upon reflection at the classical turning points: the insulator-metal interface, and the dynamic point where the incident electron e...

Miller, Casey W.; Li, Zhi-pan; Schuller, Ivan K.; Dave, R. W.; Slaughter, J. M.; Akerman, Johan

2007-01-01

293

Tunneling between quantum wells  

International Nuclear Information System (INIS)

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

294

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

Science.gov (United States)

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

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

2012-06-01

295

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

296

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

Energy Technology Data Exchange (ETDEWEB)

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

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

2014-01-06

297

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

International Nuclear Information System (INIS)

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

298

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

299

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

300

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

International Nuclear Information System (INIS)

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

301

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

Science.gov (United States)

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

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

2014-10-01

302

TUNNELING FROM QUASI 2D ELECTRONIC STATES INTO CONTINUUM- AND BOUND STATES IN GaAs/GaAlAs-HETEROSTRUCTURES  

OpenAIRE

Oscillatory structure is observed in forward biased dI/dV and d2I/dV2 curves of conventional GaAs/GaAlAs high electron mobility transistor samples at liquid helium temperature using modulation techniques. These oscillations can be explained by Fowler-Nordheim tunneling. From the position of the oscillations the conduction band discontinuity is determined as a function of the aluminum concentration x. For samples having an aluminum concentration between 0.3 and 0.4 a value of ?Eg/?Eg = 0.61 ...

Smoliner, J.; Lassnig, R.; Gornik, E.; Weimann, G.; Ploog, K.

1987-01-01

303

Landau-level spectroscopy of a two-dimensional electron system by tunneling through a quantum dot.  

Science.gov (United States)

A single InAs self-assembled quantum dot is incorporated in the barrier of a tunnel diode and used as a spectroscopic probe of an adjacent two-dimensional electron system from the Fermi energy to the subband edge. We obtain quantitative information about the energy dependence of the quasiparticle lifetime. For magnetic field B, applied parallel to the current, we observe peaks in the current-voltage characteristics I(V) corresponding to the formation of Landau levels. Close to filling factor nu=1 we observe directly the exchange enhancement of the Lande g factor. PMID:11017358

Main, P C; Thornton, A S; Hill, R J; Stoddart, S T; Ihn, T; Eaves, L; Benedict, K A; Henini, M

2000-01-24

304

Giant tunneling magnetoresistance with electron beam evaporated MgO barrier and CoFeB electrodes  

OpenAIRE

Electron-beam (EB) evaporated MgO grows with (001) texture on amorphous CoFeB when the deposition rate is kept below 5 pm/s. Magnetic tunnel junctions (MTJs) fabricated using this method exhibit similar to 240% magnetoresistance at room temperature for a 2.5 nm thick EB-MgO barrier, which is similar to the value for a radio frequency (rf) sputtered barrier with the same junction geometry. The average barrier height of the EB-MgO is 0.48 eV, which is higher than previously reported values for ...

Kurt, Huseyin; Coey, John Michael David

2010-01-01

305

Magnetic transitions induced by tunneling electrons in individual adsorbed M-phthalocyanine molecules (M=Fe and Co)  

OpenAIRE

We report on a theoretical study of magnetic transitions induced by tunneling electrons in individual adsorbed M-Phthalocyanine (M-Pc) molecules where M is a metal atom: Fe-Pc on a Cu(110)(2×1)-O surface and Co-Pc layers on Pb(111) islands. The magnetic transitions correspond to the change in 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 density-functional-theory-t...

Gauyacq, J. P.; Novaes, Frederico D.; Lorente, N.

2010-01-01

306

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

307

Strained silicon based complementary tunnel-FETs: Steep slope switches for energy efficient electronics  

Science.gov (United States)

Electrical characteristics of silicon nanowire tunnel field effect transistors (TFETs) are presented and benchmarked versus other concepts. Particular emphasis is placed on the band to band tunneling (BTBT) junctions, the functional core of the device. Dopant segregation from ion implanted ultrathin silicide contacts is proved as a viable method to achieve steep tunneling junctions. This reduces defect generation by direct implantation into the junction and thus minimizes the risk of trap assisted tunneling. The method is applied to strained silicon, specifically to nanowire array transistors, enabling the realization of n-type and p-type TFETs with fairly high currents and complementary TFET inverters with sharp transitions and good static gain, even at very low drain voltages of VDD = 0.2 V. These achievements suggest a considerable potential of TFETs for ultralow power applications. Gate-all-around Si nanowire array p-type TFETs have been fabricated to demonstrate the impact of electrostatic control on the device performance. A high on-current of 78 ?A/?m at VD = VG = 1.1 V is obtained.

Knoll, L.; Richter, S.; Nichau, A.; Trellenkamp, S.; Schäfer, A.; Wirths, S.; Blaeser, S.; Buca, D.; Bourdelle, K. K.; Zhao, Q.-T.; Mantl, S.

2014-08-01

308

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

309

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

310

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

OpenAIRE

Many university libraries now utilize an Electronic Resource Management (ERM) system to assist with operations related to electronic resources. An ERM is a relational database containing information such as suppliers, costs, holdings, and renewal dates for electronic resources, both at the database and title levels. While commercial ERM products are widely available, some institutions are custom building their own ERM in- house. This article describes how York University in Toronto, Canada, d...

Aaron August Lupton; Marcia Kay Salmon

2012-01-01

311

Proton tunneling in solids  

International Nuclear Information System (INIS)

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)

312

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

313

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

International Nuclear Information System (INIS)

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

314

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

International Nuclear Information System (INIS)

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

315

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.

316

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

317

Influence of polarization-induced electric fields on coherent electron tunneling in AlN/GaN coupled double quantum wells  

Science.gov (United States)

The influence of polarization-induced electric fields on the coherent electron tunneling probability in AlN/GaN coupled double quantum wells (CDQWs) has been performed by solving Schrödinger and Poisson equations self-consistently. It is found that when the first excited state (E2) and the second excited state (E3) resonate in AlN/GaN CDQWs, the coherent electron tunneling probability is 16 times higher than that in AlN/GaN single quantum well, which is attributed to the Fabry-Perot quantum interference mechanism in AlN/GaN CDQWs. However, the coherent electron tunneling probability decreases rapidly with the polarization-induced electric fields increasing, which is attributed to the resonance between the E2 and E3 subbands weakening with the polarization-induced electric fields increasing in AlN/GaN CDQWs.

Cen, L. B.; Shen, B.; Huang, C. C.; Xu, F. J.; Qin, Z. X.; Zhang, G. Y.; Chen, X. S.; Lu, W.

2010-12-01

318

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

Directory of Open Access Journals (Sweden)

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

Ma Jing-Min

2011-01-01

319

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

Science.gov (United States)

We report the measurement of the fluctuations of the two quadratures of the electromagnetic field generated by a quantum conductor, a dc- and ac-biased tunnel junction placed at very low temperature. We observe that the variance of the fluctuations on one quadrature can go below that of vacuum, i.e., that the radiated field is squeezed. This demonstrates the quantum nature of the radiated electromagnetic field. PMID:24116798

Gasse, Gabriel; Lupien, Christian; Reulet, Bertrand

2013-09-27

320

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

321

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

OpenAIRE

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

Mu?llegger, Stefan; Tebi, Stefano; Das, Amal K.; Scho?fberger, Wolfgang; Faschinger, Felix; Koch, Reinhold

2014-01-01

322

Single electron tunneling as a possible conduction mechanism in diamond like carbon film  

OpenAIRE

Nonlinear current voltage characteristics and in some cases also step like characteristics were observed in diamond like carbon films. We suggest that the transport mechanism is tunneling between conducting nanoparticles in the films and the observation of step like structures is a manifestation of Coulomb blockade found for the first time in these films. We point out that the origin of similar current voltage characteristics observed in other carbon structures can be also C...

Tinchev, S. S.; Alexandrova, S.; Valcheva, E.

2008-01-01

323

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

Scientific Electronic Library Online (English)

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

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

2010-12-01

324

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

325

Tunable valley polarization by a gate voltage when an electron tunnels through multiple line defects in graphene.  

Science.gov (United States)

By means of an appropriate wave function connection condition, we study the electronic structure of a line defect superlattice of graphene with the Dirac equation method. We obtain the analytical dispersion relation, which can simulate well the tight-binding numerical result about the band structure of the superlattice. Then, we generalize this theoretical method to study the electronic transmission through a potential barrier where multiple line defects are periodically patterned. We find that there exists a critical incident angle which restricts the electronic transmission through multiple line defects within a specific incident angle range. The critical angle depends sensitively on the potential barrier height, which can be modulated by a gate voltage. As a result, non-trivial transmissions of K and K' valley electrons are restricted, respectively, in two distinct ranges of the incident angle. Our theoretical result demonstrates that a gate voltage can act as a feasible measure to tune the valley polarization when electrons tunnel through multiple line defects. PMID:25564496

Liu, Zhe; Jiang, Liwei; Zheng, Yisong

2015-02-01

326

Use and Users of Electronic Library Resources: An Overview and Analysis of Recent Research Studies  

Science.gov (United States)

This Council on Library and Information Resources (CLIR) report summarizes and analyzes more than 200 recent research publications that focus on the use of electronic library resources (digital libraries and digital resources) and were published between 1995 and 2003. Eight major ongoing studies (each with multiple publications) are identified as…

Tenopir, Carol

2003-01-01

327

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

328

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

329

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

330

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

331

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

Science.gov (United States)

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

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

2014-09-01

332

Combined action of the bound-electron nonlinearity and the tunnel-ionization current in low-order harmonic generation in noble gases  

CERN Document Server

We study numerically low-order harmonic generation in noble gases pumped by intense femtosecond laser pulses in the tunneling ionization regime. We analyze the influence of the phase-mismatching on this process, caused by the generated plasma, and study in dependence on the pump intensity the origin of harmonic generation arising either from the bound-electron nonlinearity or the tunnel-ionization current. It is shown that in argon the optimum pump intensity of about 100 TW/cm$^2$ leads to the maximum efficiency, where the main contribution to low-order harmonics originates from the bound-electron third and fifth order susceptibilities, while for intensities higher than 300 TW/cm$^2$ the tunnel-ionization current plays the dominant role. Besides, we predict that VUV pulses at 133 nm can be generated with relatively high efficiency of about $1.5\\times10^{-3}$ by 400 nm pump pulses.

Sapaev, U; Herrmann, J

2013-01-01

333

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)

334

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

CERN Document Server

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

Onipko, A; Onipko, Alexander; Malysheva, Lyuba

2001-01-01

335

Inelastic electron tunnelling spectroscopy—IV. A study of the formation of formic acid from atmospheric carbon dioxide and water within an Al—Aloxide—Pb tunnelling junction  

Science.gov (United States)

Considerable confusion exists in the literature regarding the interpretation of peaks in the spectra of aluminium—aluminium oxide—lead tunnelling junctions doped with either water or water vapour. These peaks, which appear in the CH bend and stretch regions, have been variously assigned as trace organic impurities or as formic acid chemically produced within the tunnelling junction by a reaction between atmospheric carbon dioxide and the water dopant. The present work attempts to resolve this ambiguity by producing formic acid tunnelling spectra and comparing these with spectra produced from triply distilled water doped junctions. These spectra, which fingerprint exactly, have been assigned. Potential organic impurities in the water have been investigated by high resolution mass spectroscopy. The tunnelling spectrum of a junction electrode penetration doped with a suspension of calcium oxide in water has been produced and is assigned as calcium carbonate. It is suggested that a reaction takes place between calcium hydroxide and carbon dioxide adsorbed on the surface of the alumina to produce calcium carbonate. It is concluded that formic acid is produced within tunnelling junctions by a reaction between atmospheric carbon dioxide and water on the alumina surface.

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

1985-01-01

336

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

Science.gov (United States)

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

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

1950-01-01

337

Enhanced Performance of ZnO Piezotronic Pressure Sensor through Electron-Tunneling Modulation of MgO Nanolayer.  

Science.gov (United States)

Piezoelectric materials can be applied into electromechanical conversion and attract extensive attention with potential applications in various sensors. Here, we present two types of piezotronic pressure sensors based on ZnO nanoarrays. By introducing an insulating MgO (i-MgO) nanolayer, the "on/off" current ratio of the sensor is significantly improved up to 10(5). Furthermore, the sensor shows a high sensitivity of 7.1 × 10(4) gf(-1), a fast response time of 128 ms. The excellent properties are attributed to the combination of piezoelectric effect of ZnO nanoarrays and electron-tunneling modulation of MgO nanolayer, and the reversible potential barrier height controlled by piezoelectric potential. We further investigate the service behavior of the sensor, which can detect force varying from 3.2 to 27.2 gf. Our research provides a promising approach to boost the performance of nanodevices. PMID:25559586

Liao, Xinqin; Yan, Xiaoqin; Lin, Pei; Lu, Shengnan; Tian, Yuan; Zhang, Yue

2015-01-28

338

Tunneling of Conduction Band Electrons Driven by a Laser Field in a Double Quantum dot: An Open Systems Approach  

Science.gov (United States)

In this paper, we investigate tunneling of conduction band electrons in a system of an asymmetric double quantum dot which interacts with an environment. First we consider the case in which the system only interacts with the environment and demonstrate that as time goes to infinity they both reach an equilibrium, which is expected, and there is always a maximum and minimum for the populations of the states of the system. Then we investigate the case in which an external resonant optical pulse (a laser) is applied to the system interacting with the environment. However, in this case for different intensities we have different populations of the states in equilibrium and as the intensity of the laser gets stronger, the populations of the states in equilibrium approach the same constant.

Ahmadi, B.; Salimi, S.; Khorashad, A. S.

2015-01-01

339

Model of electron tunneling coupled to torsional vibrations: Exact solution and study of performance of approximation methods  

Science.gov (United States)

A two dimensional model for the electron interaction with molecular vibrations in molecular junctions is proposed. Alternatively the model can be applied to tunneling through a cylindrical nano-structure. The transmission function is calculated accurately numerically. The exact results are then compared with various approximations: (1) completely frozen vibrations for very light molecule, (2) Chase approximation for very heavy molecule, and (3) discrete-state-in-continuum model in resonant regime. The validity of these approximations is discussed in terms of the characteristic time-scales and coupling strengths. The excitation of the vibrational degree of freedom and the emergence of prominent threshold structures in the strong coupling regime are discussed in more details.

Gráf, Lukáš; ?ížek, Martin

2014-09-01

340

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

341

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

International Nuclear Information System (INIS)

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

342

Investigation of the chemical nature of two-dimensional polymerized octadecyltrimethoxysilane Langmuir films by inelastic electron tunneling spectroscopy  

Science.gov (United States)

High resolution vibrational spectra of Langmuir films of octadecyltrimethoxysilane (C18TMS) have been obtained by Inelastic Electron Tunneling Spectroscopy (IETS) in order to identify chemical modifications of C18TMS occurring at the air-water interface when the pH of the subphase is changed. The Langmuir films have been transferred onto an aluminum electrode by the Langmuir-Schaefer technique at three different acidic pH: 1.3, 3.3, and 3.8. The former was expected to promote the formation of polysiloxane polymers, while the latter was presumed to considerably slow down the condensation reaction, although the hydrolysis is effective. These assumptions found a direct proof in the vibrational fingerprint of C18TMS. Finally, we show that IETS is the most appropriate technique for the vibrational study of such films.

Brousseau, J.-L.; Vidon, S.; Leblanc, R. M.

1998-05-01

343

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

CERN Document Server

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

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

1998-01-01

344

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

345

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

Science.gov (United States)

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

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

2014-11-01

346

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

International Nuclear Information System (INIS)

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

347

Observation of the low-temperature peak in the interlayer tunneling conductance in bilayer electron systems in the absence of the magnetic field  

International Nuclear Information System (INIS)

A high narrow peak in the interlayer differential tunnel conductance has been observed in heterostructures with two closely located electron layers at low temperatures. Analysis of the experimental results suggests that this peak is due to the interlayer phase coherence, which appears in the system under investigation owing to the Bose condensation of indirect excitons, i.e., pairs of electrons and holes from different layers in the absence of the magnetic field

348

A single-electron tunneling reset-set flip-flop  

International Nuclear Information System (INIS)

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

349

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

Science.gov (United States)

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

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

2013-11-01

350

Electronic disorder of P- and B-doped Si at the metal–insulator transition investigated by scanning tunnelling microscopy and electronic transport  

International Nuclear Information System (INIS)

The (111)-2 × 1 surface of in situ cleaved heavily P- or B-doped Si is investigated by scanning tunnelling microscopy and spectroscopy at room temperature and at low temperature. P atoms have been identified on different sites of the Si(111)-2 × 1 surface by their characteristic voltage-dependent contrast for positive as well as negative buckling of the ?-bonded chains. The distributions of dopants per surface area and of nearest-neighbour distances are found to be in agreement with a random arrangement of dopants in Si up to doping levels well above the metal–insulator transition. In addition, P atoms have been identified by their depth-dependent contrast down to the third layer beneath the surface with a volume density in agreement with the bulk doping density. The random electronic disorder supports the view of an Anderson transition driven by disorder close to the critical concentration or critical uniaxial stress. (paper)

351

Tunneling spectroscopy on an electron-doped Pr1-xLaCexCuO4 with x = 0.11  

International Nuclear Information System (INIS)

We present point contact tunneling conductances measured on single crystals of an electron-doped cuprate, Pr0.89LaCe0.11CuO4 (PLCCO) with Tc?26K, which is nearly optimally-doped regime. The tunneling conductances on PLCCO measured at 4.2K exhibit reproducible superconducting gap peaks at ?6.09 ± 0.47mV on the V-shaped background conductance, where the subgap-shape is cusplike, and the model with the nonmonotonic d-wave energy gap is in good agreement with the experimental tunneling conductance for PLCCO. Furthermore we observed a fine structure beyond the gap peak, which would reflect a bosonic mode for pairing, such like phonon for conventional superconductors.

352

Fabrication of electron tunneling junctions on Nb3Ge and ErRh4B4 using artificial barriers of rare earth oxides  

International Nuclear Information System (INIS)

Electron tunneling junctions have been prepared on Nb3Ge and ErRh4B4 using artificial barriers of thin oxidized films of sputtered rare earth metals. The junction fabrication technique is simple and fast, and has been used to produce Josephson junctions on Nb and ErRh4B4 which have observed to thermally cycle. Although the process was not optimized in the case of Nb3Ge, it showed promise of eliminating the problems that have in the past prevented quantitative tunneling studies of this compound. Single particle and pair tunneling investigations of the re-entrant superconductor ErRh4B4 suggest that a magnetic structure of semi-macroscopic size can coexist with superconductivity at temperatures near the re-entrant transition temperature

353

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)

354

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

355

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

International Nuclear Information System (INIS)

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

356

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

357

On the recollision-free excitation of krypton during ultrafast multi-electron tunnel ionization  

International Nuclear Information System (INIS)

The probability of multiple ionization of krypton by 50 femtosecond circularly polarized laser pulses, independent of the optical focal geometry, has been obtained for the first time. The excellent agreement over the intensity range 100 TW cm-2 to 100 PW cm-2 with the recent predictions of Kornev et al (2003 Phys. Rev. A 68 043414) provides the first experimental confirmation that non-recollisional electronic excitation can occur in strong-field ionization. This is particularly true for higher stages of ionization, when the laser intensity exceeds 10 PW cm-2 as the energetic departure of the ionized electron(s) diabatically distorts the wavefunctions of the bound electrons. By scaling the probability of ionization by the focal volume, we discuss why this mechanism was not apparent in previous studies

358

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

359

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

360

Experimental test of the competition correction for charge capture from the matrix in intermolecular electron tunneling reactions  

International Nuclear Information System (INIS)

Further experimental tests have been made of a previously presented method to correct for competition for charge capture from the matrix in intermolecular electron transfer (ET) reactions in rigid media. The method is based on a two-step tunneling model which takes into account the correlation between matrix charge capture and intermolecular electron transfer. The goal is to obtain reliable intermolecular ET rates as a function of distance from measurements on rigid solutions containing two randomly distributed solutes. The method should yield the same rate vs. distance function for different donor solute concentrations. Good agreement was obtained by applying the competition correction to pulse radioloysis data for the reaction of the biphenyl anion with 2-methyl-1,4-naphthoquinone in 2-methyltetrahydrofuran (MTHF) at 77 K for donor:acceptor solute concentration ratios of 20:1 to 2:1. Worse agreement was obtained for the reaction of the biphenyl anion with phenanthrene in MTHF, in which case the reaction is slow, and its energetics are substantially influenced by solvation. For such slow reactions, accurate measurements of intermolecular ET rates require donor:acceptor solute concentration ratios so that the donor solute captures most of the matrix charges. Some biphenyl cations are produced by direct ionizations and are stable in frozen MTHF. 14 references, 4 figures, 1 table

361

Electron tunneling effects on radiative recombination in modulation n-doped ZnSe/BeTe type-II quantum wells  

International Nuclear Information System (INIS)

We have studied the cyclotron-resonance absorption and photoluminescence properties of the modulation n-doped ZnSe/BeTe/ZnSe type-II quantum wells. It is shown that only the doped sample shows electron cyclotron-resonance absorption. Also, the undoped sample shows two distinctive peaks in the spatially indirect photoluminescence spectra, and the doped one shows only one peak. The results reveal that the high concentration electrons accumulated in ZnSe quantum well layers from n-doped layers can tunnel through BeTe barrier from one well layer to the other. The electron concentration difference between these two well layers originating from the tunneling results in a new additional electric field, and can cancel out a built-in electric field as observed in the undoped structures

362

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

363

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.

364

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

Directory of Open Access Journals (Sweden)

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

BASHORUN

2011-11-01

365

A comparative analysis of the use of electronic resources by undergraduate students at two Kenyan universities  

OpenAIRE

This article compares the information and communication technology (ICT) infrastructures, the levels of access, and the electronic resources usage patterns at two academic libraries in Kenya. The focus is on the use by undergraduate students at the private University of Eastern Africa, Baraton (UEAB) and the public Kenyatta University (KU) of electronic resources to support formal and informal learning. The article also briefly explores the perceptions of library managers with regard to teach...

Ingutia-oyieke, Lilian; Dick, Archie L.

2010-01-01

366

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

OpenAIRE

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

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

2012-01-01

367

Managing Selection for Electronic Resources: Kent State University Develops a New System to Automate Selection  

Science.gov (United States)

Kent State University has developed a centralized system that manages the communication and work related to the review and selection of commercially available electronic resources. It is an automated system that tracks the review process, provides selectors with price and trial information, and compiles reviewers' feedback about the resource. It…

Downey, Kay

2012-01-01

368

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

Directory of Open Access Journals (Sweden)

Full Text Available 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

2012-10-01

369

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

370

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

371

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)

372

The Fano effect under tunneling of a spin-polarized electron through a single magnetic impurity  

International Nuclear Information System (INIS)

The calculation of single magnetic impurity transport characteristics has showed that presence of different effective channels for electron transmission results the Fano effect. It was noticed the external magnetic field and gate voltage allow to control of conducting properties which are specified by the configuration interaction between states of the system.

373

Pesticides and electronic resources for health care providers.  

Science.gov (United States)

Agricultural workers are at higher risk of occupational injuries, including pesticide exposures. There is general agreement that the training of health care providers to recognize and manage such exposures is limited and in need of improvement. While the Internet presents opportunities for health care providers to access information and continue their medical education, it can be difficult to identify relevant resources in a timely manner. This case report presents a realistic scenario of a suspected pesticide exposure among symptomatic agricultural workers. The discussion that follows presents Web-based resources that health care providers can rely upon in recognizing, managing, and preventing pesticide-related illness. PMID:15927917

Sudakin, Daniel L

2005-01-01

374

Tunneling in the representation of scattering states  

Energy Technology Data Exchange (ETDEWEB)

A new gauge-invariant many-electron approach is given to the problem of tunneling in condensed systems, based on a Hamiltonian in the representation of scattering states for tunnel junctions with arbitrary strength of coupling. The kinetic equation for the electron density matrix is derived; collision integrals for the cases of electron-electron, electron-phonon, and electron-impurity interactions are found. The noise properties of tunnel contacts of normal metals are analysed. (orig.).

Valeev, V.G. (Sektion Physik, Karl-Marx-Univ., Leipzig (Germany))

1992-02-01

375

Resource Sharing in the Electronic Era: Potentials and Paradoxes.  

Science.gov (United States)

Discusses library resource sharing. Highlights include access to information, document delivery, interlibrary loan, and the social, economic, and technological complexities of new mechanisms; and traditional roles of libraries that provide both opportunities for cooperation and paradoxes for the continuation of selection, archiving, and…

Dannelly, Gay N.

1995-01-01

376

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

International Nuclear Information System (INIS)

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

377

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

Energy Technology Data Exchange (ETDEWEB)

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.

Cruz, A.V.B.; Mishra, A.K. [Institute of Mathematical Sciences, CIT Campus, Chennai 600 113 (India); Schmickler, W., E-mail: Wolfgang.Schmickler@chemie.uni-ulm.de [Institute of Theoretical Chemistry, Ulm University, D89069 Ulm (Germany)

2010-05-25

378

Inelastic tunnel transport of electrons through an anisotropic magnetic structure in an external magnetic field  

Science.gov (United States)

Quantum transport of electrons through a magnetic impurity located in an external magnetic field and affected by a substrate is considered using the Keldysh diagram technique for the Fermi and Hubbard operators. It is shown that in a strongly nonequilibrium state induced by multiple reflections of electrons from the impurity, the current-voltage ( I-V) characteristic of the system contains segments with a negative conductivity. This effect can be controlled by varying the anisotropy parameter of the impurity center as well as the parameters of coupling between the magnetic impurity and metal contacts. The application of the magnetic field is accompanied by an increase in the number of Coulomb steps in the I-V curve of the impurity. The effect of appreciable magnetoresistance appears in this case. We demonstrate the possibility of switching between magnetic impurity states with different total spin projection values in the regime of asymmetric coupling of this impurity with the contacts.

Val'kov, V. V.; Aksenov, S. V.; Ulanov, E. A.

2014-07-01

379

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

OpenAIRE

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

Alexandrov, A. S.; Bratkovsky, A. M.; Kornilovitch, P. E.

2001-01-01

380

Surge current and electron swarm tunnel tests of thermal blanket and ground strap materials  

Science.gov (United States)

The results are described of a series of current conduction tests with a thermal control blanket to which grounding straps have been attached. The material and the ground strap attachment procedure are described. The current conduction tests consisted of a surge current examination of the ground strap and a dilute flow, energetic electron deposition and transport through the bulk of the insulating film of this thermal blanket material. Both of these test procedures were used previously with thermal control blanket materials.

Hoffmaster, D. K.; Inouye, G. T.; Sellen, J. M., Jr.

1977-01-01

381

The Dwell Time of Electron Tunneling Through a Double Barrier in the Presence of Rashba SOI  

International Nuclear Information System (INIS)

Some aspects related to the influence of the Rashba spin-orbit interaction (SOI) on the dwell time spent by the electrons in an asymmetric double barrier are analyzed. It is revealed that in the presence of the Rashba SOI, a difference between the dwell times associated to the spin-up and spin-down species can be obtained. This opens the way to a spin filtration in the time domain.

382

Electronic coupling in self-assembled nanocrystal arrays, a scanning tunneling microscopy study  

OpenAIRE

Colloidal semiconductor nanocrystals (NCs) are one the most actively studied components of modern nanoscience. The high degree of control over their size and shape makes it possible to accurately tune their opto-electronic properties through quantum confinement. Colloidal nanocrystals can serve as building blocks for more complex architectures. Formation of binary superlattices is a particularly important development in this field as it opens up new avenues towards nanostructured metamaterial...

Overgaag, K.

2008-01-01

383

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

384

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.

385

Analyzing multiple encounter as a possible origin of electron spin resonance signals in scanning tunneling microscopy on Si(111) featuring C and O defects  

Science.gov (United States)

The Si(111)7 × 7 surface exposed to 0.1 L of O2 and the carbonized Si(111) surface are investigated by electron spin resonance scanning tunneling microscopy (ESR-STM) using frequency sweeps and magnetic field sweeps. Only after oxidizing the clean Si(111)7 × 7 or by using the carbonized Si(111), spatially averaged ESR-STM spectra exhibit several peaks and dips around the frequencies corresponding to g = 2. The energy difference between these features is close to the known hyperfine splitting of A ? 9 MHz for vacancies in SiC interacting with next-nearest neighbor 29Si. Such spectra with peaks and dips can be qualitatively reproduced by introducing a primary encounter of the lead electrons with the localized spin correlating the two spins which afterwards evolve in different local hyperfine fields, thus, developing a relative spin angle prior to tunneling.

Manassen, Y.; Averbukh, M.; Morgenstern, M.

2014-05-01

386

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

CERN Document Server

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

Bekkerman, A; Kolodney, E

2002-01-01

387

Nonlinear Metal-Insulator-Metal (MIM) Nanoplasmonic Waveguides Based on Electron Tunneling for Optical Rectification and Frequency Generation  

Science.gov (United States)

Metal-Insulator-Metal (MIM) electron tunneling diodes have recently emerged as an attractive alternative to semiconductor photodiodes for THz and optical detection due to their fast response time and relative ease of fabrication. However, current antenna-coupled MIM diode detectors are still limited by poor responsivity and low detection bandwidth due to impedance mismatch between the diode and antenna, large RC time constant of lumped MIM junctions, and narrow bandwidth of traditional antenna designs. In this thesis we address these issues by considering traveling-wave MIM detector designs which exhibit enhanced responsivity and low impedance that can be more easily matched to planar antennas. We also propose new antenna geometries based on surface modification of traditional bowtie antennas that are capable of receiving ultra-wideband THz signals. The concept of traveling-wave MIM detectors is then extended to the investigation of nonlinear MIM nanoplasmonic waveguides for on-chip single-cycle THz pulse generation, frequency conversion, as well as plasmonic switching and modulation.

Lei, Xiaoqin

388

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

389

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

Energy Technology Data Exchange (ETDEWEB)

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

Warburton, William K

2009-03-06

390

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, ...

391

Dispersion of a layered electron gas with nearest neighbour-tunneling  

International Nuclear Information System (INIS)

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

392

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

Energy Technology Data Exchange (ETDEWEB)

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

Val' kov, V. V., E-mail: vvv@iph.krasn.ru; Aksenov, S. V., E-mail: asv86@iph.krasn.ru [Russian Academy of Sciences, Siberian Branch, Kirensky Institute of Physics (Russian Federation); Ulanov, E. A. [Siberian State Aerospace University (Russian Federation)

2013-05-15

393

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

OpenAIRE

The luminescence of GaSb and AlGaSb layers grown on GaAs substrates by metal organic vapour phase epitaxy has been studied by means of cathodoluminescence (CL) rising a scanning electron microscope. CL plane-view analysis reveals a distribution of defects, as misfit dislocations, in some of the structures. The luminescence bands observed in the GaSb layers are related to near band edge recombination and to an excess of Ga. In the case of AlGaSb/GaSb heterostructure emission bands related to t...

Storgardsstorgards, J.; Me?ndez Marti?n, Bianchi; Piqueras Noriega, Javier; Storgards, M.; Dimroth, F.; Bett, A. W.

2004-01-01

394

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

International Nuclear Information System (INIS)

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

395

Electron-vibration interaction in single-molecule junctions: from contact to tunneling regimes.  

Science.gov (United States)

Point contact spectroscopy on a H(2)O molecule bridging Pt electrodes reveals a clear crossover between enhancement and reduction of the conductance due to electron-vibration interaction. As single-channel models predict such a crossover at a transmission probability of tau=0.5, we used shot noise measurements to analyze the transmission and observed at least two channels across the junction where the dominant channel has a tau=0.51 +/- 0.01 transmission probability at the crossover conductance, which is consistent with the predictions for single-channel models. PMID:18518474

Tal, O; Krieger, M; Leerink, B; van Ruitenbeek, J M

2008-05-16

396

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

OpenAIRE

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

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

1993-01-01

397

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

CERN Multimedia

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

CERN Photo Service

2008-01-01

398

Decay of H2- anions in solid parahydrogen by quantum tunneling: observations of electron bubbles  

International Nuclear Information System (INIS)

Decay mechanism of H2- anions produced by ?-ray or X-ray radiolysis of solid para-H2 (p-H2) has been studied using high-resolution ESR spectroscopy in the temperature range between 2.7-6.6 K. The results can be summarized as follows; First, the decay rate constant of the H2- anion is not proportional to initial yields of reactive species such as H radical and cation but proportional to concentrations of HD and D2 impurities in p-H2. Second, ESR spectra assigned as electron bubbles were observed in solid p-H2 containing large amount of HD or D2 (11 mol %), while they were not observed in pure solid p-H2. Third, the decay rate constant of the H2- anion increases with the decrease in temperature between 2.7-5 K, while it decreases with the decrease between 5-6.6 K. Fourth, the decay of the H2- anion is suppressed by addition of ortho-H2 (o-H2) impurity. The first and second results suggest that the H2- anion reacts with the HD or D2 molecule to produce the electron bubble. The third and fourth results are interpreted in terms of two-phonon scattering quantum diffusion and thermally activated diffusion below and above 5 K, respectively. (author)

399

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)

400

Energy Dependent Tunneling in a Quantum Dot  

CERN Document Server

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

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

2006-01-01

401

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

Science.gov (United States)

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

Bhaskaran, Renjith; Sarma, Manabendra

2013-07-01

402

Electronic information resource use: implications for teaching and library staff  

Directory of Open Access Journals (Sweden)

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

Roger Ottewill

1997-12-01

403

Tunneling Processes in Optically Excited Quantum Dots  

International Nuclear Information System (INIS)

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

404

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

OpenAIRE

This paper gives a brief overview of electronic information resources and services offered by The J.D. Rockefeller Research Library at Egerton University and the marketing of these resources. The paper examines the various reasons for marketing electronic information resources, with emphasis on the various, and illustrates marketing strategies used by J.D Rockefeller Research library towards effective utilization of the available resources in supporting research, teaching and learnin...

Nerisa Kamar

2008-01-01

405

Resonant electronic states and I-V curves of Fe/MgO/Fe(100) tunnel junctions  

OpenAIRE

The bias dependence of the tunnel magnetoresistance (TMR) of Fe/MgO/Fe tunnel junctions is investigated theoretically with a fully self-consistent scheme that combines the non-equilibrium Green's functions method with density functional theory. At voltages smaller than 20 mVolt the I-V characteristics and the TMR are dominated by resonant transport through narrow interface states in the minority spin-band. In the parallel configuration this contribution is quenched by a volt...

Rungger, Ivan; Mryasov, Oleg N.; Sanvito, Stefano

2008-01-01

406

Optical Detection of Tunneling Ionization  

International Nuclear Information System (INIS)

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

407

Resonance tunneling spectroscopy of heteropoly compounds  

International Nuclear Information System (INIS)

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

408

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.

409

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

410

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

411

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

Energy Technology Data Exchange (ETDEWEB)

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

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

2000-02-09

412

Accommodating Consortia within Electronic Resource Management Systems: Extending the ERMI Specifications  

OpenAIRE

This article discusses the needs of library consortia with respect to electronic resource management systems. The paper notes areas where the ERMI data dictionary fails to accommodate groups of libraries that by choice or necessity share an ERMS. The article documents areas where extension of the ERMI specifications is warranted in order to support library consortia.

Medeiros, Norm

2006-01-01

413

The National Site Licensing of Electronic Resources: An Institutional Perspective  

Directory of Open Access Journals (Sweden)

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

Xiaohua Zhu

2011-06-01

414

Strong enhancement of the tunneling magnetoresistance by electron filtering in an Fe/MgO/Fe/GaAs(001) junction  

OpenAIRE

Calculations of the tunneling magnetoresistance (TMR) of an epitaxial Fe/MgO/Fe tunneling junction attached to an n-type GaAs lead, under positive gate voltage, are presented. It is shown that for realistic GaAs carrier densities the TMR of this composite system can be more than 2 orders of magnitude higher than that of a conventional Fe/MgO/Fe junction. Furthermore, the high TMR is achieved with modest MgO thicknesses and is very robust to disorder at the Fe/GaAs interface and within ...

Aute?s, G.; Mathon, J.; Umerski, A.

2010-01-01

415

Theory of Electron Transport in Scanning Tunneling Microscopy and Applications to the Simulation of Images of Metal Surfaces and Adsorbed Molecules.  

Science.gov (United States)

Scanning Tunneling Microscopy (STM) has revealed the possibility of imaging bare metal surfaces and molecules adsorbed on a metal substrate with atomic resolution. Yet, the mechanism of contrast responsible for the observed features is not completely understood in the context of former theories of STM. Clarification of this issue is of central importance to the experimentalist both to interpret data and to determine the optimal imaging conditions of specific samples. We have developed a theoretical framework suitable to describe the STM current between the probe and either a bare or an adsorbate-covered metal surface. We model the Scanning Tunneling Microscope as a problem of quantum mechanical electron transport in a system made of the tip, the substrate and the molecule, that exchanges electrons with two reservoirs. We derive the tunneling current and other STM observables in terms of electron probability propagators that depend upon the microscopic interactions between the states of the system, as well as on bath interactions. This approach overcomes the limitations of perturbative theories and allows the inclusion of temperature and dissipative effects in the calculation of the current. The widely adopted Transfer Hamiltonian theory can be recovered as a particular case. Within this framework, we use simple Hamiltonian models and simple transport theories (Master Equation, Stochastic Liouville Equation) to rationalize the factors that determine the contrast in STM images, and we find interesting and sometimes counter-intuitive results. In particular, we show how the STM current can increase due to the presence of adsorbed molecules on a metal surface. Also the possibility of building simple electric circuits at atomic level is investigated. Finally we present a computational method to simulate STM images with Extended Huckel Hamiltonian and Stochastic Liouville Equation within our framework. We apply it to cluster models of the STM system to reproduce experimental STM images of metal surfaces and adsorbed molecules on metals.

Biscarini, Fabio

416

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

417

Generation-recombination and trap-assisted tunneling in long wavelength infrared minority electron unipolar photodetectors based on InAs/GaSb superlattice  

International Nuclear Information System (INIS)

A long wavelength infrared minority electron unipolar photodetector based on InAs/GaSb type-II superlattices is demonstrated. At 77?K, a dark current of 3?×?10?5?A/cm2 and a differential resistance-area of 3700??.cm2 are achieved at the turn-on bias, with a 50%-cutoff of 10.0??m and a specific detectivity of 6.2?×?1011?Jones. The dark current is fitted as a function of bias and temperature using a model combining generation-recombination and trap-assisted tunneling. Good agreement was observed between the theory and the experimental dark current

418

Transmission electron microscopy and ferromagnetic resonance investigations of tunnel magnetic junctions using Co2MnGe Heusler alloy as magnetic electrodes  

OpenAIRE

HRTEM, nano-beam electronic diffraction, energy dispersive X-rays scanning spectroscopy, Vibrating Sample Magnetometry (VSM) and FerroMagnetic Resonance (FMR) techniques are used in view of comparing (static and dynamic) magnetic and structural properties of Co2MnGe (13 nm)/Al2O3 (3 nm)/Co (13 nm) tunnel magnetic junctions (TMJ), deposited on various single crystalline substrates (a-plane sapphire, MgO(100) and Si(111)). They allow for providing a correlation between these m...

Belmeguenai, M.; Genevois, C.; Zighem, F.; Roussigne?, Y.; Che?rif, S-m; Westerholt, K.; Bahoui, A. El; Fnidiki, A.; Moch, P.

2013-01-01

419

Influence of Rashba spin-orbit interaction on the transmission and the dwell time of the electron tunneling through a multiple quantum well structure  

Energy Technology Data Exchange (ETDEWEB)

In this paper we propose a model for computing the transmission coefficient and the dwell time of the electron tunneling through a multiple quantum well structure with Rashba spin-orbit interaction and with an external and constant electric field, using the transfer matrix formalism with piecewise constant potentials. The results indicate a difference between the transmission coefficients and the dwell times for spin-up and spin-down orientations. This difference can be modified by varying the electric field and the number of the barriers and wells, this opening the way to create a spin filtering in the time domain.

Baltateanu, D.M., E-mail: bdmarcel@yahoo.com

2013-12-01

420

Influence of Rashba spin-orbit interaction on the transmission and the dwell time of the electron tunneling through a multiple quantum well structure  

International Nuclear Information System (INIS)

In this paper we propose a model for computing the transmission coefficient and the dwell time of the electron tunneling through a multiple quantum well structure with Rashba spin-orbit interaction and with an external and constant electric field, using the transfer matrix formalism with piecewise constant potentials. The results indicate a difference between the transmission coefficients and the dwell times for spin-up and spin-down orientations. This difference can be modified by varying the electric field and the number of the barriers and wells, this opening the way to create a spin filtering in the time domain

421

Bit by Bit: A Series of Trends, Tools, and Initiatives Are Aimed at Improving Electronic Resource Management  

Science.gov (United States)

Electronic resources are more prominent than ever in library collections, yet they resist easy management. A range of tools and cooperative efforts are emerging to improve the management and evaluation of electronic resources. Initiatives are underway to standardize and automate the harvesting of usage statistics and e-journal title and holdings…

Webster, Peter

2006-01-01

422

Quantum noise in ac-driven resonant-tunneling double barrier structures: Photon-assisted tunneling vs. electron anti-bunching  

OpenAIRE

We study the quantum noise of electronic current in a double barrier system with a single resonant level. In the framework of the Landauer formalism we treat the double barrier as a quantum coherent scattering region that can exchange photons with a coupled electric field, e.g. a laser beam or a periodic ac-bias voltage. As a consequence of the manyfold parameters that are involved in this system, a complicated step-like structure arises in the non-symmetrized current-curren...

Hammer, Jan; Belzig, Wolfgang

2011-01-01

423

Quantum size effects on spin-tunneling time in a magnetic resonant tunneling diode  

OpenAIRE

We study theoretically the quantum size effects of a magnetic resonant tunneling diode (RTD) with a (Zn,Mn)Se dilute magnetic semiconductor layer on the spin-tunneling time and the spin polarization of the electrons. The results show that the spin-tunneling times may oscillate and a great difference between the tunneling time of the electrons with opposite spin directions can be obtained depending on the system parameters. We also study the effect of structural asymmetry whi...

Saffarzadeh, Alireza; Daqiq, Reza

2009-01-01

424

Use and Cost of Electronic Resources in Central Library of Ferdowsi University Based on E-metrics  

OpenAIRE

The purpose of this study was to investigate the usage of electronic journals in Ferdowsi University, Iran based on e-metrics. The paper also aimed to emphasize the analysis of cost-benefit and the correlation between the journal impact factors and the usage data. In this study experiences of Ferdowsi University library on licensing and usage of electronic resources was evaluated by providing a cost-benefit analysis based on the cost and usage statistics of electronic resources. Vendor-provid...

Mohammad Reza Davarpanah; Nayereh Dadkhah

2012-01-01

425

Progress Towards High-Sensitivity Arrays of Detectors of Sub-mm Radiation using Superconducting Tunnel Junctions with Radio-Frequency Single-Electron Transistors  

Science.gov (United States)

The science drivers for the SPIRIT/SPECS missions demand sensitive, fast, compact, low-power, large-format detector arrays for high resolution imaging and spectroscopy in the far infrared and submillimeter. Detector arrays with 10,000 pixels and sensitivity less than 10(exp 20)-20 W/Hz(exp 20)0.5 are needed. Antenna-coupled superconducting tunnel junction detectors with integrated rf single-electron transistor readout amplifiers have the potential for achieving this high level of sensitivity, and can take advantage of an rf multiplexing technique when forming arrays. The device consists of an antenna structure to couple radiation into a small superconducting volume and cause quasiparticle excitations, and a single-electron transistor to measure currents through tunnel junction contacts to the absorber volume. We will describe optimization of device parameters, and recent results on fabrication techniques for producing devices with high yield for detector arrays. We will also present modeling of expected saturation power levels, antenna coupling, and rf multiplexing schemes.

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

2002-01-01

426

Resonant tunneling of electrons through single self-assembled InAs quantum dot at room temperature studied with conductive AFM tip  

International Nuclear Information System (INIS)

Resonant tunneling of electrons through a quantum level in a self-assembled InAs quantum dot (QD) has been measured by conductive atomic force microscopy (AFM) at room temperature. InAs QDs are embedded in a 3.4 nm-thick AlAs layer, and capped with 8.3 nm-thick GaAs layer on which surface InAs QDs are deposited as nano-scale electrodes. Bringing the conductive AFM tip on the surface InAs QD which should be vertically aligned with a buried QD, a bias voltage is applied to the sample, and a current flowing via the buried QD is measured. Negative differential resistance attributed to electron resonant tunnelling through a quantized energy level in the buried QD is observed in the current-voltage characteristics. The voltage loss by nano-scale electrode and the dependence of resonance voltage on the size of the surface QD-electrodes are discussed. (copyright 2008 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

427

Attoclock reveals geometry for laser-induced tunneling  

OpenAIRE

Tunneling plays a central role in the interaction of matter with intense laser pulses, and also in time-resolved measurements on the attosecond timescale. A strong laser field influences the binding potential of an electron in an atom so strongly, that a potential barrier is created which enables the electron to be liberated through tunneling. An important aspect of the tunneling is the geometry of the tunneling current flow. Here we provide experimental access to the tunnel...

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

2011-01-01

428

Tunneling into a Luttinger liquid revisited.  

Science.gov (United States)

We study how electron-electron interactions renormalize tunneling into a Luttinger liquid beyond the lowest order of perturbation in the tunneling amplitude. We find that the conventional fixed point has a finite basin of attraction only in the point contact model, but a finite size of the contact makes it generically unstable to the tunneling-induced breakup of the liquid into two independent parts. In the course of renormalization to the nonperturbative-in-tunneling fixed point, the tunneling conductance may show a nonmonotonic behavior with temperature or bias voltage. PMID:21231690

Aristov, D N; Dmitriev, A P; Gornyi, I V; Kachorovskii, V Yu; Polyakov, D G; Wölfle, P

2010-12-31

429

Progress Towards High-Sensitivity Arrays of Detectors of Sub-mm Radiation Using Superconducting Tunnel Junctions with Integrated Radio Frequency Single-Electron Transistors  

Science.gov (United States)

For high resolution imaging and spectroscopy in the FIR and submillimeter, space observatories will demand sensitive, fast, compact, low-power detector arrays with 104 pixels and sensitivity less than 10(exp -20) W/Hz(sup 0.5). Antenna-coupled superconducting tunnel junctions with integrated rf single-electron transistor readout amplifiers have the potential for achieving this high level of sensitivity, and can take advantage of an rf multiplexing technique. The device consists of an antenna to couple radiation into a small superconducting volume and cause quasiparticle excitations, and a single-electron transistor to measure current through junctions contacting the absorber. We describe optimization of device parameters, and results on fabrication techniques for producing devices with high yield for detector arrays. We also present modeling of expected saturation power levels, antenna coupling, and rf multiplexing schemes.

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

2004-01-01

430

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

431

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

432

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

433

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

434

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

Scientific Electronic Library Online (English)

Full Text Available SciELO Brazil | Language: Spanish Abstract in spanish Los recursos electrónicos con fines educativos están cada vez más presentes en los procesos de enseñanza-aprendizaje actuales, y por tanto, en las colecciones digitales de las bibliotecas. Ante su proliferación y heterogeneidad cada vez mayor se ha planteado como una necesidad para la comunidad 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

435

Coulomb Blockade without Tunnel Junctions  

OpenAIRE

We find that tunnel junctions are not needed to provide single electron effects in a metallic island. Eventually the tunnel junction may be replaced by an arbitrary scatterer. It is important that even a {\\it diffusive} scatterer provides a sufficient isolation for single electron effects to persist. To formulate this in exact terms, we derive and analyze the effective action that describes an arbitrary scatterer. We also consider the fluctuations of the effective charging e...

Nazarov, Y. V.

1998-01-01

436

Inelastic tunneling through mesoscopic structures  

OpenAIRE

Our objective is to study resonant tunneling of an electron in the presence of inelastic scattering by optical phonons. Using a recently developed technique, based on exact mapping of a many-body problem onto a one-body problem, we compute transmission through a single site at finite temperatures. We also compute current through a single site at finite temperatures and an arbitrary strength of the potential drop over the tunneling region. Transmission vs. incident electron e...

Haule, K.; Bonca, J.

1998-01-01

437

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

438

Tunneling properties of ultra-thin SiO2 barriers: a first-principles study  

Science.gov (United States)

We performed first-principles simulations of the electron tunneling through ultra-thin SiO2 barriers in Si(100)/SiO2/Si(100) structures. The atomic structures of the Si/SiO2 interfaces are generated by considering various silicon suboxide states observed in photoemission studies. For comparison, we also consider sharp Si/SiO2 interfaces with dangling bonds. For each atomic structure, the tunneling conductance is calculated by a first-principles scattering-state method based on the ab-initio pseudopotentials and the density functional theory within the local density approximation. As a result we obtained the dependence of the tunneling probabilities on the oxide thickness and on the interfacial structures. Effects of the dangling bonds on the tunneling probabilities will also be discussed. Computational resource for this work is provided by KISTI under the 8th Strategic Supercomputing Support Program.

Ko, Eunjung; Choi, Hyoung Joon

2008-03-01

439

Resonant tunneling and charge fluctuations in mesoscopic tunnel junctions  

International Nuclear Information System (INIS)

Quantum fluctuations in mesoscopic tunnel junctions are studied in the presence of high charging energies. The processes of sequential tunneling, electron cotunneling and resonant tunneling are analysed within a new nonperturbative resummation technique. The current and the average charge are shown to be related to the spectral density describing the charge excitations of the single electron transistor. An energy-dependent finite lifetime is obtained which leads to the theory of inelastic electron cotunneling and gives important corrections to the classical result for strong tunneling and finite temperatures. An additional energy renormalization leads to a logarithmic temperature dependence of the renormalized system parameters. Several formulas for the line shape of the conductance oscillations are presented which show the possibility to observe experimentally quantum fluctuation effects at realistic temperatures. ((orig.))

440

Semisimple tunnels  

CERN Document Server

A knot in the 3-sphere in (1,1)-position (that is, in 1-bridge position with respect to a Heegaard torus) can be described by an element of the braid group of two points in the torus. Our main results tell how to translate between a braid group element and the sequence of slope invariants of the upper tunnel (or lower tunnel) associated to the corresponding (1,1)-position. This enables us to calculate the slope invariants of the four tunnels of the (-2,3,7)-pretzel knot, and to verify previous calculations of the slope invariants for all tunnels of 2-bridge knots and (1,1)-tunnels of torus knots. We also characterize a class of (1,1)-positions that we call toroidal, in terms of the slope invariants of the associated upper tunnel. Finally, we develop a general algorithm to calculate the slope invariants of the associated tunnels, given a braid description. We have implemented the algorithm and other results as software, and we give some sample computations.

Cho, Sangbum

2010-01-01

441

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

442

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)

Electron tunneling measurements were used 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 magnetic atoms in superconductors. The localized band of states predicted to form in the energy gap of such alloys was observed, 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. The 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 tunneling measurement

443

Tunnel magnetoresistance in double spin filter junctions  

OpenAIRE

We consider a new type of magnetic tunnel junction, which consists of two ferromagnetic tunnel barriers acting as spin filters (SFs), separated by a nonmagnetic metal (NM) layer. Using the transfer matrix method and the free-electron approximation, the dependence of the tunnel magnetoresistance (TMR) on the thickness of the central NM layer, bias voltage and temperature in the double SF junction are studied theoretically. It is shown that the TMR and electron-spin polarizati...

Saffarzadeh, Alireza

2003-01-01

444

Resonant Tunneling Spin Pump  

Science.gov (United States)

The resonant tunneling spin pump is a proposed semiconductor device that would generate spin-polarized electron currents. The resonant tunneling spin pump would be a purely electrical device in the sense that it would not contain any magnetic material and would not rely on an applied magnetic field. Also, unlike prior sources of spin-polarized electron currents, the proposed device would not depend on a source of circularly polarized light. The proposed semiconductor electron-spin filters would exploit the Rashba effect, which can induce energy splitting in what would otherwise be degenerate quantum states, caused by a spin-orbit interaction in conjunction with a structural-inversion asymmetry in the presence of interfacial electric fields in a semiconductor heterostructure. The magnitude of the energy split is proportional to the electron wave number. Theoretical studies have suggested the possibility of devices in which electron energy states would be split by the Rashba effect and spin-polarized currents would be extracted by resonant quantum-mechanical tunneling.

Ting, David Z.

2007-01-01

445

Impact of Knowledge Resources Linked to an Electronic Health Record on Frequency of Unnecessary Tests and Treatments  

Science.gov (United States)

Introduction: Electronic knowledge resources have the potential to rapidly provide answers to clinicians' questions. We sought to determine clinicians' reasons for searching these resources, the rate of finding relevant information, and the perceived clinical impact of the information they retrieved. Methods: We asked general internists, family…

Goodman, Kenneth; Grad, Roland; Pluye, Pierre; Nowacki, Amy; Hickner, John

2012-01-01

446

Teachers' Link to Electronic Resources in the Library Media Center: A Local Study of Awareness, Knowledge, and Influence  

Science.gov (United States)

High school students often use online databases and the Internet in the school library media center (SLMC) to complete teachers' assignments. This case study used a survey to assess teachers' awareness of electronic resources, and to determine whether their directions influence student use of these resources in the SLMC. Participants were teachers…

Williams, Teresa D.; Grimble, Bonnie J.; Irwin, Marilyn

2004-01-01

447

Tunnelling barrier structure of Nb/Pb and Nb/(Pb-In) thin film Josephson junctions studied by Auger electron spectroscopy and X-ray photoelectron spectroscopy analysis  

International Nuclear Information System (INIS)

The structure of the insulant barrier of Nb/Pb and Nb/(Pb-In) thin film Josephson tunnel junctions is studied in detail by Auger electron spectroscopy and X-ray photoelectron spectroscopy analysis. The properties of these two types of junction are strictly related to the thin (2-3 nm) oxide acting as a barrier between the superconducting electrodes. Two oxides were found in each barrier: Nb2O5 and PbO in the Nb/Pb junction and Nb2O5 and In2O3 in the Nb/(Pb-In) junction. In addition, the present analysis shows a change with time of the PbO in contact with Nb2O5: this result is correlated with junction aging. Finally, a comparison in terms of the stability of the two junctions is made: Nb/(Pb-In) devices seem to display a more stable behaviour with time. (Auth.)

448

Generation-recombination and trap-assisted tunneling in long wavelength infrared minority electron unipolar photodetectors based on InAs/GaSb superlattice  

Energy Technology Data Exchange (ETDEWEB)

A long wavelength infrared minority electron unipolar photodetector based on InAs/GaSb type-II superlattices is demonstrated. At 77?K, a dark current of 3?×?10{sup ?5}?A/cm{sup 2} and a differential resistance-area of 3700??.cm{sup 2} are achieved at the turn-on bias, with a 50%-cutoff of 10.0??m and a specific detectivity of 6.2?×?10{sup 11}?Jones. The dark current is fitted as a function of bias and temperature using a model combining generation-recombination and trap-assisted tunneling. Good agreement was observed between the theory and the experimental dark current.

Callewaert, F.; Hoang, A. M.; Razeghi, M., E-mail: razeghi@eecs.northwestern.edu [Department of Electrical Engineering and Computer Science, Center for Quantum Devices, Northwestern University, Evanston, Illinois 60208 (United States)

2014-02-03

449

The method of S-matrix in the theory of resonance energies and widths for quasistationary states of an electron in asymmetric two-barrier resonance-tunnel structures  

International Nuclear Information System (INIS)

By the methods of transfer- and S-matrices, we executed the analytic and numerical calculations of resonance energies and widths of quasistationary states of an electron in a plane two-barrier resonance tunnel nanostructure with asymmetric rectangular (with different effective masses in barriers and wells) and ?-like potential barriers

450

Atomic Layer Deposition of Tunnel Barriers for Superconducting Tunnel Junctions  

Science.gov (United States)

We demonstrate a technique for creating high quality, large area tunnel junction barriers for normal-insulating-superconducting or superconducting-insulating-superconducting tunnel junctions. We use atomic layer deposition and an aluminum wetting layer to form a nanometer scale insulating barrier on gold films. Electronic transport measurements confirm that single-particle electron tunneling is the dominant transport mechanism, and the measured current-voltage curves demonstrate the viability of using these devices as self-calibrated, low temperature thermometers with a wide range of tunable parameters. This work represents a promising first step for superconducting technologies with deposited tunnel junction barriers. The potential for fabricating high performance junction refrigerators is also highlighted.

Moyerman, Stephanie M.; Feng, Guangyuan; Krayer, Lisa; Stebor, Nathan; Keating, Brian G.

2014-08-01

451

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

International Nuclear Information System (INIS)

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

452

Tunneling electron induced photon emission from monolayered H 2TBP porphyrin molecules on Cu( 1 0 0 )  

Science.gov (United States)

Positioning of a clean scanning tunneling microscope tip above a monolayer of free-base porphyrin (H 2TBPP) molecules on Cu(1 0 0) is found to induce merely plasmon-mediated emission with molecular fluorescence completely quenched. The molecule acts as a spacer to increase the tip-metal substrate distance to make spectra blue-shifted. Additional broad emissions at low energies may be associated with the molecules either adsorbed onto the tip apex or on the second monolayer and might suggest the involvement of modified molecular fluorescence. In both cases, the energy transfer from molecular excited states to the metal substrate is overwhelmingly dominant, leading to enhanced plasmon-mediated emission.

Dong, Z.-C.; Trifonov, A. S.; Guo, X.-L.; Amemiya, K.; Yokoyama, S.; Kamikado, T.; Yamada, T.; Mashiko, S.; Okamoto, T.

2003-06-01

453

Semanti?ki veb i elektronski izvori informacija-SEMANTIC WEB AND ELECTRONIC INFORMATION RESOURCES  

OpenAIRE

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

Radovanovic, Danica

2003-01-01

454

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

455

Energy-dependent tunneling in a quantum dot.  

Science.gov (United States)

We present measurements of the rates for an electron to tunnel on and off a quantum dot, obtained using a quantum point contact charge sensor. The tunnel rates show exponential dependence on drain-source bias and plunger gate voltages. The tunneling process is shown to be elastic, and a model describing tunneling in terms of the dot energy relative to the height of the tunnel barrier quantitatively describes the measurements. PMID:17358709

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

2007-01-19

456

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

457

Tunneling spectroscopy studies of aluminum oxide tunnel barrier layers  

CERN Document Server

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

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

2005-01-01

458

Resonant Tunneling and Coulomb Oscillations  

OpenAIRE

The influence of quantum fluctuations on electron transport through small metallic islands with Coulomb blockade effects is studied beyond the perturbative regime. In tunnel junctions with low resistance higher order coherent processes and ``inelastic resonant tunneling'' become important. We present a path integral real-time description, which allows a systematic diagrammatic classification of these processes. Quantum fluctuations renormalize system parameters and lead to f...

Koenig, Ju?rgen; Schoeller, Herbert; Schoen, Gerd

1995-01-01

459

Factors Influencing Students' Use of Electronic Resources and their Opinions About this Use: The Case of Students at An-Najah National University  

Directory of Open Access Journals (Sweden)

Full Text Available Electronic resources are becoming an integral part of the modern life and of the educational scene, especially the high education scene. In this research we wanted to verify what influences first degree university students' use of electronic resources and their opinions regarding this use. Collecting data from 202 students and analyzing it using SPSS, we found that more than one half of the participants had high level of electronic media use and more than one third had moderate level of electronic media use. These levels of use indicate the students' awareness of the role and benefits of electronic media use. Regarding the factors that influence the students' se of electronic resources we found that the student's use of electronic resources had significant strong positive relationships with the provision of electronic resources by the academic institution. It had significant moderate positive relationships with the