WorldWideScience

Sample records for tunnels electronic resource

  1. Single Electron Tunneling

    International Nuclear Information System (INIS)

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

  2. Tunneling electron trap

    International Nuclear Information System (INIS)

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

  3. Inelastic electron tunneling spectroscopy

    International Nuclear Information System (INIS)

    IETS provides an electronic probe with great sensitivity and resolution for monitoring the vibrational spectra of less-than-monolayer coverages of adsorbed molecular species. Eletronic transitions of large dye molecules and of rare-earth oxides have also been studied by IETS and very recently inelastic electron tunneling has been employed in the design of a tunable light-emitting thin film device. This Proceedings volume provides a comprehensive and up-to-date review of the current state-of-the-art of IETS. A tutorial survey of the techniques and applications of IETS is provided as are discussions of the newest advances in the field. Recent applications of IETS to surface chemistry and catalysis trace substance identification and detection, the study of biological molecules and the study of adhesive materials are included among the papers. Discussions of the IETS theory are also reported. (orig./HT)

  4. Tunnelling hot electron transfer amplifiers

    Science.gov (United States)

    Kircher, C. J.

    1993-10-01

    Significant advances were achieved in tunneling hot electron amplifiers and in the understanding of hot electron transport in the work funded by the contract and carried out by M. Heiblum and his co-workers. The results of this work are described in detail in nine papers that have been published in the open literature. (These papers are listed below as references 1-9 and copies of them are attached.) This report summarizes the principal results. There are three aspects of the work in which the results are particularly noteworthy: the demonstration of the first hot hole tunneling transistor and its use to study hot hole transport in GaAs; the successful fabrication of a hot electron 'THETA' transistor with a pseudomorphic InGaAs base which allowed high transistor gains (beta approx. = 30) to be achieved; and the conception and successful fabrication of a lateral hot electron device and its use to investigate ballistic, hot electron transport in a 2-dimensional electron gas in GaAs.

  5. Interpretation of Electron Tunneling from Uncertainty Principle

    OpenAIRE

    Sarkar, Angik; Bhattacharyya, T K

    2005-01-01

    Beginners studying quantum mechanics are often baffled with electron tunneling.Hence an easy approach for comprehension of the topic is presented here on the basis of uncertainty principle.An estimate of the tunneling time is also derived from the same method.

  6. Many-electron tunneling in atoms

    CERN Document Server

    Zon, B A

    1999-01-01

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

  7. Electron Tunneling in Monolayer and Bilayer Graphene

    OpenAIRE

    WU Di; Chen, Weiqiang; Zhang, Fu-chun

    2008-01-01

    Electron's tunneling through potential barrier in monolayer and bilayer graphene lattices is investigated by using full tight-binding model. Emphasis is placed on the resonance tunneling feature and inter-valley scattering probability. It is shown that normal incidence transmission probabilities for monolayer and bilayer graphene exhibit different properties. Our calculation indicates that valleytronics in graphene systems may be detected, generated and controlled by changin...

  8. Numerical studies of electron tunnelling in liquids

    International Nuclear Information System (INIS)

    The diffusion equation, derived from Fick's second law, with an added exponential sink term to simulate electron tunnelling, is integrated numerically to determine the rate of electron decay at times greater than 1 ps. The effect of a Coulomb interaction with a charged scavenger is examined and the steady-state rate constant shown to approximate closely to that obtained by combining the separate effects of tunnelling and charge-affected diffusion, which can be expressed analytically. Diffusion in the presence of a charge-induced dipole interaction is investigated for the case of scavenging of localised electrons in alkanes. The rate constant is shown to be dominated by random diffusion and tunnelling and the bias induced by the interaction is of little consequence. The sensitivity of the rate constant to changes in the pre-exponential factor in the sink term is shown to be most favourable at short times. (author)

  9. Educating for Electronic Resources

    Science.gov (United States)

    Grogg, Jill E.

    2008-01-01

    While mission statements for various libraries and information centers necessarily vary, all librarians face "two very pressing charges: make voluminous numbers of electronic resources as visible as possible in a landscape of multiple access points and simultaneously manage all the technology, tasks, and data necessary to facilitate such…

  10. The AAS electronic resource

    Science.gov (United States)

    Boyce, Peter B.; Biemesderfer, Chris; Owens, Evan

    Recent experience is helping to sharpen our understanding of how the electronic world differs from the centuries-old, paper-based communication methods. The electronic future is highly interlinked, with all different types of information being included in the web of available resources. The enhanced ability to interchange information electronically improves the effectiveness of communication. At this time the author community does not make full use of the new capabilities. Most astronomers writing for electronic distribution have been slow to adopt new styles of presentation which exploit the new capabilities inherent in the electronic environment. By working together and sharing the burden, the community's resources can be multiplied. A coordinated distributed effort can yield a much more valuable product than any single person or group. Long term archiving and site maintenance are important responsibilities for publishers of electronic scholarly information. Ensuring access to electronic information into the foreseeable future takes planning from the beginning, and requires cooperation between the publishers, libraries, and other scholarly institutions.

  11. 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

  12. Tunneling of electrons through semiconductor superlattices

    Indian Academy of Sciences (India)

    C L Roy

    2002-11-01

    The purpose of the present paper is to report a study of tunneling of electrons through semiconductor superlattices (SSL); specially, we have analysed diverse features of transmission coefficient of SSL. The SSL we have considered is Ga0.7Al0.3As–GaAs which has been drawing considerable attention during the recent past on account of some typical features of its band structure. We have indicated how our results would help fabrication of ultra high speed devices.

  13. Wind Tunnel Management and Resource Optimization: A Systems Modeling Approach

    Science.gov (United States)

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

    2000-01-01

    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.

  14. Electronic Resource Management Systems

    Directory of Open Access Journals (Sweden)

    Mark Ellingsen

    2004-10-01

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

  15. Single-electron tunneling. [Microwave scanning tunneling microscope

    Energy Technology Data Exchange (ETDEWEB)

    Ruggiero, S.T.

    1993-01-01

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

  16. Site-directed deep electronic tunneling through a molecular network

    International Nuclear Information System (INIS)

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

  17. Electronic Resource Management and Design

    Science.gov (United States)

    Abrams, Kimberly R.

    2015-01-01

    We have now reached a tipping point at which electronic resources comprise more than half of academic library budgets. Because of the increasing work associated with the ever-increasing number of e-resources, there is a trend to distribute work throughout the library even in the presence of an electronic resources department. In 2013, the author…

  18. Electron tunneling in chemistry chemical reactions over large distances

    CERN Document Server

    Khairutdinov, RF; Zhadanov, VP

    1989-01-01

    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.

  19. Quantum Hall Effect: proposed multi-electron tunneling experiment

    International Nuclear Information System (INIS)

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

  20. Tunneling of Dirac electrons through spatial regions of finite mass

    Energy Technology Data Exchange (ETDEWEB)

    Viana Gomes, J; Peres, N M R [Center of Physics and Department of Physics, University of Minho, P-4710-057, Braga (Portugal)

    2008-08-13

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

  1. Quantum tunneling and field electron emission theories

    CERN Document Server

    Liang, Shi-Dong

    2013-01-01

    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

  2. Quantum tunneling resonant electron transfer process in Lorentzian plasmas

    International Nuclear Information System (INIS)

    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

  3. Single-electron tunneling. Technical progress report

    Energy Technology Data Exchange (ETDEWEB)

    Ruggiero, S.T.

    1993-05-01

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

  4. Electron tunneling through atomically flat and ultrathin hexagonal boron nitride

    Science.gov (United States)

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

    2011-12-01

    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.

  5. Microwave-induced co-tunneling in single electron tunneling transistors

    DEFF Research Database (Denmark)

    Ejrnaes, M.; Savolainen, M.; Manscher, M.; Mygind, Jesper

    2002-01-01

    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 me...

  6. Klein tunneling in graphene: optics with massless electrons

    CERN Document Server

    Allain, P E

    2011-01-01

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

  7. Electron-Photon interaction in resonant tunneling diodes

    OpenAIRE

    Inarrea, Jesus; Aguado, Ramon; Platero, Gloria

    1997-01-01

    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...

  8. Scanning tunneling spectroscopy on electron-boson interactions in superconductors

    CERN Document Server

    Schackert, Michael Peter

    2015-01-01

    This work describes the experimental study of electron-boson interactions in superconductors by means of inelastic electron tunneling spectroscopy performed with a scanning tunneling microscope (STM) at temperatures below 1 K. This new approach allows the direct measurement of the Eliashberg function of conventional superconductors as demonstrated on lead (Pb) and niobium (Nb). Preparative experiments on unconventional iron-pnictides are presented in the end.

  9. Time of electron tunneling through a potential barrier

    International Nuclear Information System (INIS)

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

  10. ELECTRONIC RESOURCES FOR THE HUMANITIES

    Directory of Open Access Journals (Sweden)

    Petrauskiene, Zibute

    2006-12-01

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

  11. Spin-dependent electron tunneling through magnetic barriers

    International Nuclear Information System (INIS)

    An exact solution to the model problem of 2D-electron funneling through magnetic barriers is given with regard for electron is intrinsic magnetic momentum. General requirements to the topology of a magnetic structure that has spin-depended tunneling are clarified. A structure is proposed which is able to filter electrons in the direction of their spin polarization

  12. Electronic thermometry in tunable tunnel junction

    Energy Technology Data Exchange (ETDEWEB)

    Maksymovych, Petro

    2016-03-15

    A tunable tunnel junction thermometry circuit includes a variable width tunnel junction between a test object and a probe. The junction width is varied and a change in thermovoltage across the junction with respect to the change in distance across the junction is determined. Also, a change in biased current with respect to a change in distance across the junction is determined. A temperature gradient across the junction is determined based on a mathematical relationship between the temperature gradient, the change in thermovoltage with respect to distance and the change in biased current with respect to distance. Thermovoltage may be measured by nullifying a thermoelectric tunneling current with an applied voltage supply level. A piezoelectric actuator may modulate the probe, and thus the junction width, to vary thermovoltage and biased current across the junction. Lock-in amplifiers measure the derivatives of the thermovoltage and biased current modulated by varying junction width.

  13. Parity effects on electron tunnelling through small superconducting islands

    International Nuclear Information System (INIS)

    Single-electron tunnelling into small superconducting islands is sensitive to the gap energy of the excitations created in the process and, hence, depends on the electron number parity. At low temperatures, a 2e-periodic, even-odd asymmetric dependence on the applied gate voltage has been observed, turning into an e-periodic behaviour at higher temperature. We explain the crossover and derive I-V characteristics of such systems by studying the dynamics. The rate of tunnelling of a single electron, the odd one, turns out to be crucial. It dominates at low temperature since in this process the excitation energy can be regained, while the competing many-electron processes are exponentially suppressed. Parity effects on single-electron and Cooper-pair tunnelling and the Andreev reflection in superconducting transistors yield rich structures in the I-V characteristics, which compare well with recent experimental findings. (orig.)

  14. Electron tunnelling into amorphous germanium and silicon.

    Science.gov (United States)

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

    1972-01-01

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

  15. Wigner time delay for tunneling ionization via the electron propagator

    Science.gov (United States)

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

    2014-07-01

    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.

  16. Giant tunnel-electron injection in nitrogen-doped graphene

    DEFF Research Database (Denmark)

    Lagoute, Jerome; Joucken, Frederic; Repain, Vincent; Tison, Yann; Chacon, Cyril; Bellec, Amandine; Girard, Yann; Sporken, Robert; Conrad, Edward H.; Ducastelle, Francois; Palsgaard, Mattias Lau Nøhr; Andersen, Nick Papior; Brandbyge, Mads; Rousset, Sylvie

    2015-01-01

    Scanning tunneling microscopy experiments have been performed to measure the local electron injection in nitrogen-doped graphene on SiC(000) and were successfully compared to ab initio calculations. In graphene, a gaplike feature is measured around the Fermi level due to a phonon-mediated tunneling channel. At nitrogen sites, this feature vanishes due to an increase of the elastic channel that is allowed because of symmetry breaking induced by the nitrogen atoms. A large conductance enhancement ...

  17. Inelastic electron tunneling spectroscopy of a single nuclear spin

    OpenAIRE

    Delgado Acosta, Fernando; Fernández Rossier, Joaquín

    2011-01-01

    Detection of a single nuclear spin constitutes an outstanding problem in different fields of physics such as quantum computing or magnetic imaging. Here we show that the energy levels of a single nuclear spin can be measured by means of inelastic electron tunneling spectroscopy (IETS). We consider two different systems, a magnetic adatom probed with scanning tunneling microscopy and a single Bi dopant in a silicon nanotransistor. We find that the hyperfine coupling opens new transport channel...

  18. Voltage controlled electron spin dynamics in resonant tunnelling devices

    International Nuclear Information System (INIS)

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

  19. Attosecond correlation dynamics during electron tunnelling from molecules

    International Nuclear Information System (INIS)

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

  20. Thermal electron-tunneling devices as coolers and amplifiers

    Science.gov (United States)

    Su, Shanhe; Zhang, Yanchao; Chen, Jincan; Shih, Tien-Mo

    2016-01-01

    Nanoscale thermal systems that are associated with a pair of electron reservoirs have been previously studied. In particular, devices that adjust electron tunnels relatively to reservoirs’ chemical potentials enjoy the novelty and the potential. Since only two reservoirs and one tunnel exist, however, designers need external aids to complete a cycle, rendering their models non-spontaneous. Here we design thermal conversion devices that are operated among three electron reservoirs connected by energy-filtering tunnels and also referred to as thermal electron-tunneling devices. They are driven by one of electron reservoirs rather than the external power input, and are equivalent to those coupling systems consisting of forward and reverse Carnot cycles with energy selective electron functions. These previously-unreported electronic devices can be used as coolers and thermal amplifiers and may be called as thermal transistors. The electron and energy fluxes of devices are capable of being manipulated in the same or oppsite directions at our disposal. The proposed model can open a new field in the application of nano-devices. PMID:26893109

  1. Thermal electron-tunneling devices as coolers and amplifiers

    Science.gov (United States)

    Su, Shanhe; Zhang, Yanchao; Chen, Jincan; Shih, Tien-Mo

    2016-02-01

    Nanoscale thermal systems that are associated with a pair of electron reservoirs have been previously studied. In particular, devices that adjust electron tunnels relatively to reservoirs’ chemical potentials enjoy the novelty and the potential. Since only two reservoirs and one tunnel exist, however, designers need external aids to complete a cycle, rendering their models non-spontaneous. Here we design thermal conversion devices that are operated among three electron reservoirs connected by energy-filtering tunnels and also referred to as thermal electron-tunneling devices. They are driven by one of electron reservoirs rather than the external power input, and are equivalent to those coupling systems consisting of forward and reverse Carnot cycles with energy selective electron functions. These previously-unreported electronic devices can be used as coolers and thermal amplifiers and may be called as thermal transistors. The electron and energy fluxes of devices are capable of being manipulated in the same or oppsite directions at our disposal. The proposed model can open a new field in the application of nano-devices.

  2. Microwave-induced co-tunneling in single electron tunneling transistors

    DEFF Research Database (Denmark)

    Ejrnaes, M.; Savolainen, M.

    2002-01-01

    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.

  3. Klein tunneling in graphene: optics with massless electrons

    Science.gov (United States)

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

    2011-10-01

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

  4. Observation of interdot tunneling process of spin-polarized electrons

    Science.gov (United States)

    Tackeuchi, A.; Nakata, Y.; Sasou, R.; Mase, K.; Kuroda, T.; Yokoyama, N.

    2001-05-01

    We have directly observed the spin-polarized electron tunneling process between double quantum dots (QDs) using spin-dependent time-resolved photoluminescence measurements. The spin relaxation times in isolated In 0.9Al 0.1As Stranski-Krastanow (SK)-mode QDs and InAs SK-mode QDs were measured as 1.3 and 1.2 ns, respectively. The fact that these times are longer than those of quantum wells indicates that the spin relaxation rate is suppressed in QDs by the increased zero dimensionality. The measurement of tunneling between double QDs which consist of In 0.9Al 0.1As QDs and InAs QDs indicates that the spin relaxation time is not affected by the tunneling process. The spin-polarized carriers were found to tunnel from one dot to another dot while retaining spin polarization.

  5. Electron-Photon interaction in resonant tunneling diodes

    CERN Document Server

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

    1997-01-01

    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.

  6. Microwave-induced co-tunneling in single electron tunneling transistors

    DEFF Research Database (Denmark)

    Ejrnaes, M.; Savolainen, M.; Manscher, M.; Mygind, Jesper

    2002-01-01

    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...

  7. Giant tunnel-electron injection in nitrogen-doped graphene

    DEFF Research Database (Denmark)

    Lagoute, Jerome; Joucken, Frederic

    2015-01-01

    Scanning tunneling microscopy experiments have been performed to measure the local electron injection in nitrogen-doped graphene on SiC(000) and were successfully compared to ab initio calculations. In graphene, a gaplike feature is measured around the Fermi level due to a phonon-mediated tunneling channel. At nitrogen sites, this feature vanishes due to an increase of the elastic channel that is allowed because of symmetry breaking induced by the nitrogen atoms. A large conductance enhancement by a factor of up to 500 was measured at the Fermi level by comparing local spectroscopy at nitrogen sites and at carbon sites. Nitrogen doping can therefore be proposed as a way to improve tunnel-electron injection in graphene.

  8. Giant tunnel-electron injection in nitrogen-doped graphene

    Science.gov (United States)

    Lagoute, Jérôme; Joucken, Frédéric; Repain, Vincent; Tison, Yann; Chacon, Cyril; Bellec, Amandine; Girard, Yann; Sporken, Robert; Conrad, Edward H.; Ducastelle, François; Palsgaard, Mattias; Andersen, Nick Papior; Brandbyge, Mads; Rousset, Sylvie

    2015-03-01

    Scanning tunneling microscopy experiments have been performed to measure the local electron injection in nitrogen-doped graphene on SiC(000 1 ¯) and were successfully compared to ab initio calculations. In graphene, a gaplike feature is measured around the Fermi level due to a phonon-mediated tunneling channel. At nitrogen sites, this feature vanishes due to an increase of the elastic channel that is allowed because of symmetry breaking induced by the nitrogen atoms. A large conductance enhancement by a factor of up to 500 was measured at the Fermi level by comparing local spectroscopy at nitrogen sites and at carbon sites. Nitrogen doping can therefore be proposed as a way to improve tunnel-electron injection in graphene.

  9. Student attitudes towards electronic information resources

    OpenAIRE

    Kathryn Ray; Joan Day

    1998-01-01

    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 impr...

  10. 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

  11. Electronic structure and tunneling resonance spectra of nanoscopic aluminum islands

    OpenAIRE

    Narvaez, Gustavo A.; Kirczenow, George

    2002-01-01

    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 resona...

  12. Solving rate equations for electron tunneling via discrete quantum states

    CERN Document Server

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

    2001-01-01

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

  13. Hot electron spectroscopy studies of indirect tunnel barriers

    International Nuclear Information System (INIS)

    The main goal of this thesis is to gain an understanding of electron transport through indirect AlAs potential barriers. This has been achieved by incorporating them as emitter barriers in a three-terminal Tunnelling Hot Electron Transfer Amplifier (THETA) device. Hot Electron spectroscopy was performed downstream of these barriers to measure the actual energy distribution of electrons which have passed through them. Hot electron spectroscopy of a 15nm indirect AlAs emitter barrier transistor reveals that only about 1% of the tunnelling electrons are collected close to their injection energy in contrast to an otherwise identical structure with a nominally direct Al0.5Ga0.5As emitter barrier where the fraction is 30%. Moreover three or four peaks could be clearly resolved in the broad background of scattered electrons in the device with the AlAs barrier. Measurements on AlAs barrier transistor under hydrostatic pressure show clear evidence for the real space transfer of electrons from the emitter electrode into X-point states in the barrier adjacent to the emitter Fermi band. A detailed analysis reveals that the transferred electrons relax down through the ladder of X-point subbands before being re-emitted into the base layer at the well defined but lower energies of the longitudinal subbands. (author)

  14. Modeling Klein tunneling and caustics of electron waves in graphene

    Science.gov (United States)

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

    2015-01-01

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

  15. Wrangling Electronic Resources: A Few Good Tools

    OpenAIRE

    Brandy Klug

    2010-01-01

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

  16. Electronic Resources: A Wolf in Sheep's Clothing?

    Science.gov (United States)

    Schaffner, Bradley L.

    2001-01-01

    Examines the impact of electronic technology on libraries and scholarship. Focuses on some of the challenges of using electronic resources in research libraries, which include cost of acquiring electronic formats and the effect such expenditures have on other library services and collection development practices. Explores how electronic resources…

  17. Low-frequency noise in single electron tunneling transistor

    DEFF Research Database (Denmark)

    Tavkhelidze, A.N.; Mygind, Jesper

    1998-01-01

    The noise in current biased aluminium single electron tunneling (SET) transistors has been investigated in the frequency range of 5 mHz

  18. Elementary excitations in double electron layers with tunnel coupling

    International Nuclear Information System (INIS)

    The new class of the single-particle excitations in the double electron layers with the tunneling coupling between the layers is studied through the method of the light inelastic scattering. The dispersion law and dependence of the energies of the given excitations on the degree of the layers unbalance are measured. The new spectroscopic method for determining the degree of the double layers unbalance is proposed

  19. Inelastic electron tunneling spectroscopy of molecular transport junctions

    Energy Technology Data Exchange (ETDEWEB)

    Song, Hyunwook [Kyung Hee University, Yongin (Korea, Republic of); Lee, Takhee [Seoul National University, Seoul (Korea, Republic of); Reed, Mark [Yale University, New Haven, CT (United States)

    2014-05-15

    Inelastic electron tunneling spectroscopy (IETS) has become a premier analytical tool in the investigation of nano scale 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.

  20. Electron tunneling study of single crystal BCSCO superconductors

    International Nuclear Information System (INIS)

    The single crystal BCSCO superconductors have been investigated by electron tunneling with both point contacts and BCSCO/Sn junctions. A gap parameter of ? = 34meV and 2?/kTc = 8.9 have been obtained. Various dI/dV curves including BCS-like and so-called harmonic structure have been observed. The authors propose to make use of proximity effect and quasiparticle interference to interpret these phenomena

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

    Science.gov (United States)

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

    2007-05-01

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

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

    Energy Technology Data Exchange (ETDEWEB)

    Rompuy, T Van [Department of Applied Physics, Ghent University, Rozier 44, Ghent B-9000 (Belgium); Gunn, J P [Association CEA-EURATOM sur la fusion controlee, Saint Paul Lez Durance F-13108 (France); Dejarnac, R [Institute of Plasma Physics, Association EURATOM-IPP.CR, Za Slovankou 3, 18200 Prague 8 (Czech Republic); Stoeckel, J [Institute of Plasma Physics, Association EURATOM-IPP.CR, Za Slovankou 3, 18200 Prague 8 (Czech Republic); Oost, G Van [Department of Applied Physics, Ghent University, Rozier 44, Ghent B-9000 (Belgium)

    2007-05-15

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

  3. First Principles Study of Electron Tunneling through Ice

    KAUST Repository

    Cucinotta, Clotilde S.

    2012-10-25

    With the aim of understanding electrochemical scanning tunnel microscopy experiments in an aqueous environment, we investigate electron transport through ice in the coherent limit. This is done by using the nonequilibrium Greens functions method, implemented within density functional theory, in the self-interaction corrected local density approximation. In particular, we explore different ice structures and different Au electrode surface orientations. By comparing the decay coefficient for different thicknesses to the ice complex band structure, we find that the electron transport occurs via tunneling with almost one-dimensional character. The slow decay of the current with the ice thickness is largely due to the small effective mass of the conduction electrons. Furthermore, we find that the calculated tunneling decay coefficients at the Fermi energy are not sensitive to the structural details of the junctions and are at the upper end of the experimental range for liquid water. This suggests that linear response transport measurements are not capable of distinguishing between different ordered ice structures. However, we also demonstrate that a finite bias measurement may be capable of sorting polar from nonpolar interfaces due to the asymmetry of the current-voltage curves for polar interfaces. © 2012 American Chemical Society.

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

    International Nuclear Information System (INIS)

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

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

    OpenAIRE

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

    2007-01-01

    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...

  6. Managing electronic resources a LITA guide

    CERN Document Server

    Weir, Ryan O

    2012-01-01

    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.

  7. Ballistic transport and hot electron spectroscopy in Tunnelling Hot Electron Transfer Amplifier (THETA)

    Science.gov (United States)

    Heiblum, M.

    1987-10-01

    An unambiguous demonstration of ballistic (collisionless) electron transport was done in GaAs with the aid of a Tunnelling Hot Electron Transfer Amplifier (THETA) device. Consequently, interesting quantum related phenomena were observed. Ballistic devices are potentially very fast; current gains as high as 10 were already measured at 77 K.

  8. Ballistic transport and hot electron spectroscopy in Tunneling Hot Electron Transfer Amplifier (THETA)

    Science.gov (United States)

    Heiblum, M.

    1987-10-01

    An unambiguous demonstration of ballistic (collisionless) electron transport was done in GaAs with the aid of a Tunneling Hot Electron Transfer Amplifier (THETA) device. Consequently, interesting quantum related phenomena were observed. Ballistic devices are potentially very fast; current gains as high as 10 were already measured at 77 K.

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

    Science.gov (United States)

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

    1994-01-01

    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.

  10. Scanning electron and tunneling microscopy of palladium-barium emitters

    International Nuclear Information System (INIS)

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

  11. Scanning electron and tunneling microscopy of palladium barium emitters

    Science.gov (United States)

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

    2003-06-01

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

  12. High Performance Resonant Tunneling Electronic Circuit with Suitable Resistance Parameters

    OpenAIRE

    Hsiao Hsuan Cheng; Yen Chun Lin; Chih Chin Yang

    2012-01-01

    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...

  13. Electronic Resource Management Systems in Practice

    Science.gov (United States)

    Grogg, Jill E.

    2008-01-01

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

  14. Implementing CORAL: An Electronic Resource Management System

    Science.gov (United States)

    Whitfield, Sharon

    2011-01-01

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

  15. Environmentally Activated Tunneling Events in a Hybrid Single-Electron Box

    OpenAIRE

    Saira, O. -P.; Mottonen, M.; Maisi, V. F.; Pekola, J.P.

    2010-01-01

    We have measured individual tunneling events and Coulomb step shapes in single-electron boxes with opaque superconductor-normal metal tunnel junctions. We observe anomalous broadening of the Coulomb step with decreasing temperature in a manner that is consistent with activation of first-order tunneling events by an external dissipative electromagnetic environment. We demonstrate that the rates for energetically unfavourable tunneling events saturate to finite values at low t...

  16. Enhancement of Radiative Plasmon Decay by Hot Electron Tunneling.

    Science.gov (United States)

    Wang, Xiao; Braun, Kai; Zhang, Dai; Peisert, Heiko; Adler, Hilmar; Chassé, Thomas; Meixner, Alfred J

    2015-08-25

    Here we demonstrate that photon emission induced by inelastic tunneling through a nanometer single gap between a sharp Au tip and an Au substrate can be significantly enhanced by the illumination of the junction with 634 nm laser light with an electric field component oriented parallel to the tip-axis, i.e., perpendicular to the sample. Analyzing photoluminescence (PL) spectra recorded as a function of bias voltage allows us to distinguish between PL from (1) the decay of electron-hole pairs created by the laser excited sp/d interband transition with a characteristic band at 690 nm and (2) the red-shifted radiative decay of characteristic plasmon modes formed by the gap. Since the electroluminescence spectra (without laser) already show the plasmonic gap modes, we conclude that the enhanced intensity induced by laser illumination originates from the radiative decay of hot electrons closely above the Fermi level via inelastic tunneling and photon emission into the plasmon modes. Since these processes can be independently controlled by laser illumination and the amplitude of the bias voltage, it is of great interest for designing new switchable photon emission plasmonic devices. PMID:26200215

  17. Resonant tunneling of interacting electrons in an AC electric field

    Energy Technology Data Exchange (ETDEWEB)

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

    2013-11-15

    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.

  18. Tunneling electron induced luminescence from porphyrin molecules on monolayer graphene

    Energy Technology Data Exchange (ETDEWEB)

    Geng, Feng; Kuang, Yanmin; Yu, Yunjie; Liao, Yuan; Zhang, Yao; Zhang, Yang; Dong, Zhenchao, E-mail: zcdong@ustc.edu.cn

    2015-01-15

    Using epitaxially grown graphene on Ru(0001) as a decoupling layer, we investigate the evolution of tunneling electron induced luminescence from different number of layers of porphyrin molecules. Light emission spectra and photon maps, acquired via a combined optical setup with scanning tunneling microscopy (STM), indicate that the electronic decoupling effect of a monolayer (ML) graphene alone is still insufficient for generating molecule-specific emission from both the 1st- and 2nd-layer porphyrin molecules. Nevertheless, interestingly, the plasmonic emission is enhanced for the 1st-layer but suppressed for the 2nd-layer in comparison with the plasmonic emission on the monolayer graphene. Intrinsic intramolecular molecular fluorescence occurs at the 3rd-layer porphyrin. Such molecular thickness is about two MLs thinner than previous reports where molecules were adsorbed directly on metals. These observations suggest that the monolayer graphene does weaken the interaction between molecule and metal substrate and contribute to the reduction of nonradiative decay rates. - Highlights: • Showing molecularly resolved photon maps of graphene and porphyrins on it. • Revealing the influence of spacer thickness on molecular electroluminescence. • Graphene does weaken the interaction between molecules and metal substrate.

  19. Probing Nanoscale Electronic and Magnetic Interaction with Scanning Tunneling Spectroscopy

    DEFF Research Database (Denmark)

    Bork, Jakob

    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......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...

  20. Thermoelectric effects in electron chiral tunneling in metallic carbon nanotubes

    Science.gov (United States)

    Parafilo, A. V.; Ilinskaya, O. A.; Krive, I. V.; Park, Y. W.

    2015-12-01

    Thermoelectric effects in a metallic single-wall carbon nanotube in the presence of long-range electrostatic and pseudomagnetic potentials (produced by strain) are considered. It is shown that for strong scattering potentials (chiral tunneling) a pronounced energy "gap" appears in the energy dependence of electron transmission coefficient. This results in strong violation of Wiedemann-Franz law and in a peak-like behavior of thermopower as a function of chemical potential. The electronic figure-of-merit (ZT) is calculated and shown to be sensitive at low temperatures to nanotube chirality. By tuning chemical potential, ZT can reach high values (ZT?5) that makes specially engineered nanotube-based thermocouple to be a promising nano-device with a high thermoelectric performance.

  1. Digital Preservation of Electronic Resources

    Directory of Open Access Journals (Sweden)

    Ramesh C. Gaur,

    2012-07-01

    Full Text Available Due to huge advances in information communication technologies (ICTs, there has been an astronomical growth of e-resources—e-journals, e-books, online databases and so on; libraries spend phenomenally on acquisition of these e- resources as these are very popularly used by the students and researchers.Unfortunately, this growth is accompanied by many threats. Digital content (of the e- resources is fragile andnot durable. Its accessibility and use by future generations depends on technology which very rapidly evolvesand changes. Hence, ensuring access of e-resources for future generation of users is a big challenge forlibraries. The present paper highlights various problems of digital content and elaborates how digital preservationis more demanding and challenging than preserving print copies of journals. It also gives a bird’s eye view of various projects initiated for archiving digital content of scholarly journals.

  2. Digital Preservation of Electronic Resources

    Directory of Open Access Journals (Sweden)

    Ramesh C. Gaur,

    2012-07-01

    Full Text Available Due to huge advances in information communication technologies (ICTs, there has been an astronomicalgrowth of e-resources—e-journals, e-books, online databases and so on; libraries spend phenomenally onacquisition of these e- resources as these are very popularly used by the students and researchers.Unfortunately, this growth is accompanied by many threats. Digital content (of the e- resources is fragile andnot durable. Its accessibility and use by future generations depends on technology which very rapidly evolvesand changes. Hence, ensuring access of e-resources for future generation of users is a big challenge forlibraries. The present paper highlights various problems of digital content and elaborates how digital preservationis more demanding and challenging than preserving print copies of journals. It also gives a bird’s eye viewof various projects initiated for archiving digital content of scholarly journals.

  3. High Performance Resonant Tunneling Electronic Circuit with Suitable Resistance Parameters

    Directory of Open Access Journals (Sweden)

    Hsiao Hsuan Cheng

    2012-10-01

    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.

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

    OpenAIRE

    Wu, Shiwei; Ho, Wilson

    2010-01-01

    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...

  5. dc performance of ballistic tunneling hot-electron transfer amplifiers

    Science.gov (United States)

    Heiblum, M.; Anderson, I. M.; Knoedler, C. M.

    1986-07-01

    Ballistic electron transport through thin n(+)-GaAs layers is investigated experimentally. Measurements were done on tunneling hot-electron-transfer amplifier devices composed of GaAs and AlGaAs layers. In devices with GaAs active regions (bases) of 300 and 800 A, collisionless or ballistic transport was observed. By performing hot-electron energy spectroscopy it is found that the collected ballistic distributions were similar in shape but differed in magnitude. This suggests the existence of a strong scattering mechanism which randomizes the otherwise ballistic electrons. The maximum differential current transfer ratio was 0.9 in devices for which about 75 percent of the injected current traversed the base ballistically. The presence of ballistic transport has also allowed the measurement of the AlGaAs barrier height through observation of the onset of current collection in the devices. Barrier heights higher than those reported by Batey and Wright (1986) have been measured. In addition the effects of grading the collector barrier are shown. The most noted effect in these cases was a higher transfer ratio.

  6. Electronic Single Molecule Identification of Carbohydrate Isomers by Recognition Tunneling

    CERN Document Server

    Im, JongOne; Liu, Hao; Zhao, Yanan; Sen, Suman; Biswas, Sudipta; Ashcroft, Brian; Borges, Chad; Wang, Xu; Lindsay, Stuart; Zhang, Peiming

    2016-01-01

    Glycans play a central role as mediators in most biological processes, but their structures are complicated by isomerism. Epimers and anomers, regioisomers, and branched sequences contribute to a structural variability that dwarfs those of nucleic acids and proteins, challenging even the most sophisticated analytical tools, such as NMR and mass spectrometry. Here, we introduce an electron tunneling technique that is label-free and can identify carbohydrates at the single-molecule level, offering significant benefits over existing technology. It is capable of analyzing sub-picomole quantities of sample, counting the number of individual molecules in each subset in a population of coexisting isomers, and is quantitative over more than four orders of magnitude of concentration. It resolves epimers not well separated by ion-mobility and can be implemented on a silicon chip. It also provides a readout mechanism for direct single-molecule sequencing of linear oligosaccharides.

  7. Spurious signals generated by electron tunneling on large reflector antennas

    Science.gov (United States)

    Higa, W. H.

    1975-01-01

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

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

    International Nuclear Information System (INIS)

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

  9. Dynamics of Managing Electronic Resources: Electronic Resource Management System (ERMS) Initiatives

    OpenAIRE

    John Paul Anbu K.; Sanjay Kataria; Shri Ram

    2013-01-01

    Even after two decades of digital presence in libraries and proliferation of electronic resources (e-resources) in terms of production, acquisition and usage the management of e-resources remains a cumbersome process. The process involved in the management of e-resources has often overwhelmed the library personnel. The life cycle of e-resources, especially in the academic institutions begin with the discovery and identification of the resource and moves on to the trial access, selecting the s...

  10. Non-classical microwave radiation generated by electron transport in a tunnel junction

    Science.gov (United States)

    Qassemi, Farzad; Thibault, Karl; Bertrand Reulet, Bertrand; Blais, Alexandre

    2014-03-01

    Electrons coupled to a bath of photons in a tunnel junction form an interesting platform for many-body quantum phenomena. Recently, squeezing of radiated electromagnetic field due to electron shot noise has been observed [G. Gasse et al PRL 111, 136601 (2013)]. To investigate the relation between photonic and electronic correlation functions, we develop an input-output theory for electron-photon system in a tunnel junction. We show the effect of electronic transport on the equation of motion for the photon fields giving rise to nonclassical effects. In particular, we demonstrate that by modulating the bias voltage across the tunnel junction we can squeeze the radiated light.

  11. Managing Electronic Resources with Open Source Software

    OpenAIRE

    Roën Janyk; Sandra Wong

    2012-01-01

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

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

    Science.gov (United States)

    Hipps, K. W.; Scudiero, L.

    2005-01-01

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

  13. On the Dynamics of Single-Electron Tunneling in Semiconductor Quantum Dots under Microwave Radiation

    OpenAIRE

    Qin, Hua

    2001-01-01

    Efforts are made in this thesis to reveal the dynamics of single-electron tunneling and to realize quantum bits (qubits) in semiconductor quantum dots. At low temperatures, confined single quantum dots and double quantum dots are realized in the twodimensional electron gas (2DEG) of AlGaAs/GaAs heterostructures. For transport studies, quantum dots are coupled to the drain and source contacts via tunnel barriers. Electron-electron interaction in such closed quantum dots leads to...

  14. Direct measurement of electron transfer distance decay constants of single redox proteins by electrochemical tunneling spectroscopy.

    Science.gov (United States)

    Artés, Juan M; Díez-Pérez, Ismael; Sanz, Fausto; Gorostiza, Pau

    2011-03-22

    We present a method to measure directly and at the single-molecule level the distance decay constant that characterizes the rate of electron transfer (ET) in redox proteins. Using an electrochemical tunneling microscope under bipotentiostatic control, we obtained current?distance spectroscopic recordings of individual redox proteins confined within a nanometric tunneling gap at a well-defined molecular orientation. The tunneling current decays exponentially, and the corresponding decay constant (?) strongly supports a two-step tunneling ET mechanism. Statistical analysis of decay constant measurements reveals differences between the reduced and oxidized states that may be relevant to the control of ET rates in enzymes and biological electron transport chains. PMID:21539019

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

    Energy Technology Data Exchange (ETDEWEB)

    Stock, T.; Nogami, J. [Department of Materials Science and Engineering, University of Toronto, Toronto, Ontario M5S 3E4 (Canada)

    2014-02-17

    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.

  16. Quasiballistic electronic transport in a tunneling hot-electron-transfer amplifier

    Science.gov (United States)

    Leo, James; Bending, Simon J.

    1991-01-01

    The operation of a tunneling hot-electron-transfer amplifier has been simulated by treating it as a double-barrier diode where the field across each barrier can be varied independently. Current flow is evaluated by calculating the transmission coefficient of the entire structure starting from a coherent-transport framework and then by phenomenologically introducing both elastic and inelastic scattering of the electrons in the base region between the two barriers. By directly comparing the numerical results with those obtained experimentally, we have been able to establish an upper bound of the mean free path of electrons in the base of around 45 nm.

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

    Energy Technology Data Exchange (ETDEWEB)

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

    2014-08-21

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

  18. Excitation of plasmonic nanoantennas with nonresonant and resonant electron tunnelling

    CERN Document Server

    Uskov, Alexander V; Protsenko, Igor E; Smetanin, Igor V; Bouhelier, Alexandre

    2016-01-01

    A rigorous theory of photon emission accompanied inelastic tunnelling inside the gap of plasmonic nanoantennas has been developed. The disappointingly low efficiency of the electrical excitation of surface plasmon polaritons in these structures can be increased by orders of magnitude when a resonant tunnelling structure is incorporated inside the gap. Resonant tunnelling assisted surface plasmon emitter may become a key element in future electrically-driven nanoplasmonic circuits.

  19. Effect of Quantum Confinement on Electron Tunneling through a Quantum Dot

    OpenAIRE

    Kang, Kicheon; B. I. Min

    1997-01-01

    Employing the Anderson impurity model, we study tunneling properties through an ideal quantum dot near the conductance minima. Considering the Coulomb blockade and the quantum confinement on an equal footing, we have obtained current contributions from various types of tunneling processes; inelastic cotunneling, elastic cotunneling, and resonant tunneling of thermally activated electrons. We have found that the inelastic cotunneling is suppressed in the quantum confinement l...

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

    International Nuclear Information System (INIS)

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

  1. 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

  2. Strong overtones modes in inelastic electron tunneling spectroscopy with cross-conjugated molecules

    DEFF Research Database (Denmark)

    Jørgensen, Jacob Lykkebo; Gagliardi, Alessio; Pecchia, Alessandro; Solomon, Gemma C.

    2013-01-01

    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...

  3. Low-frequency noise in single electron tunneling transistor

    DEFF Research Database (Denmark)

    Tavkhelidze, A.N.; Mygind, Jesper

    1998-01-01

    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.

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

    International Nuclear Information System (INIS)

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

  5. Equilibrium and non-equilibrium electron tunneling via discrete quantum states

    CERN Document Server

    Deshmukh, M M; Pasupathy, A N; Ralph, D C; Deshmukh, Mandar M.; Bonet, Edgar

    2001-01-01

    Tunneling is measured via the quantum levels of a metal nanoparticle. We analyze quantitatively the resonance energies, widths, and amplitudes, both in the regime where only one state is accessible for tunneling and in the non-equilibrium regime when additional states are made accessible one-by-one. For tunneling through one state, our results agree with expectations for sequential tunneling, but in the non-equilibrium regime the resonances are broadened and shifted in ways that require taking into account electron interactions and relaxation.

  6. When does an electron exit a tunneling barrier?

    OpenAIRE

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

    2013-01-01

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

  7. When does an electron exit a tunneling barrier?

    Directory of Open Access Journals (Sweden)

    Ivanov M. Yu.

    2013-03-01

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

  8. Reviewing the Electronic Resources & Libraries Conference

    Science.gov (United States)

    Tijerina, Bonnie

    2008-01-01

    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…

  9. A fullerene molecular tip can detect localized and rectified electron tunneling within a single fullerene–porphyrin pair

    OpenAIRE

    Nishino, Tomoaki; Ito, Takashi; Umezawa, Yoshio

    2005-01-01

    A fullerene molecular tip was used to detect electron tunneling from a single porphyrin molecule. Electron tunneling was found to occur locally from an electron-donating moiety of the porphyrin to the fullerene through charge-transfer interaction between them. In addition, electron tunneling within the single fullerene–porphyrin pair exhibited rectifying behavior in which electrons can be driven only at the direction from the porphyrin to the fullerene. It is demonstrated that localized elect...

  10. Atomic scale imaging and spectroscopy of individual electron trap states using force detected dynamic tunnelling.

    Science.gov (United States)

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

    2009-02-01

    We report the first atomic scale imaging and spectroscopic measurements of electron trap states in completely non-conducting surfaces by dynamic tunnelling force microscopy/spectroscopy. Single electrons are dynamically shuttled to/from individual states in thick films of hafnium silicate and silicon dioxide. The new method opens up surfaces that are inaccessible to the scanning tunnelling microscope for imaging and spectroscopy on an atomic scale. PMID:19417360

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

    CERN Document Server

    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

    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.

  12. Ultralarge area MOS tunnel devices for electron emission

    DEFF Research Database (Denmark)

    Thomsen, Lasse BjØrchmar; Nielsen, Gunver

    2007-01-01

    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.

  13. Bilayer insulator tunnel barriers for graphene-based vertical hot-electron transistors

    Science.gov (United States)

    Vaziri, S.; Belete, M.; Dentoni Litta, E.; Smith, A. D.; Lupina, G.; Lemme, M. C.; Östling, M.

    2015-07-01

    Vertical graphene-based device concepts that rely on quantum mechanical tunneling are intensely being discussed in the literature for applications in electronics and optoelectronics. In this work, the carrier transport mechanisms in semiconductor-insulator-graphene (SIG) capacitors are investigated with respect to their suitability as electron emitters in vertical graphene base transistors (GBTs). Several dielectric materials as tunnel barriers are compared, including dielectric double layers. Using bilayer dielectrics, we experimentally demonstrate significant improvements in the electron injection current by promoting Fowler-Nordheim tunneling (FNT) and step tunneling (ST) while suppressing defect mediated carrier transport. High injected tunneling current densities approaching 103 A cm-2 (limited by series resistance), and excellent current-voltage nonlinearity and asymmetry are achieved using a 1 nm thick high quality dielectric, thulium silicate (TmSiO), as the first insulator layer, and titanium dioxide (TiO2) as a high electron affinity second layer insulator. We also confirm the feasibility and effectiveness of our approach in a full GBT structure which shows dramatic improvement in the collector on-state current density with respect to the previously reported GBTs. The device design and the fabrication scheme have been selected with future CMOS process compatibility in mind. This work proposes a bilayer tunnel barrier approach as a promising candidate to be used in high performance vertical graphene-based tunneling devices.

  14. Bilayer insulator tunnel barriers for graphene-based vertical hot-electron transistors.

    Science.gov (United States)

    Vaziri, S; Belete, M; Dentoni Litta, E; Smith, A D; Lupina, G; Lemme, M C; Östling, M

    2015-08-14

    Vertical graphene-based device concepts that rely on quantum mechanical tunneling are intensely being discussed in the literature for applications in electronics and optoelectronics. In this work, the carrier transport mechanisms in semiconductor-insulator-graphene (SIG) capacitors are investigated with respect to their suitability as electron emitters in vertical graphene base transistors (GBTs). Several dielectric materials as tunnel barriers are compared, including dielectric double layers. Using bilayer dielectrics, we experimentally demonstrate significant improvements in the electron injection current by promoting Fowler-Nordheim tunneling (FNT) and step tunneling (ST) while suppressing defect mediated carrier transport. High injected tunneling current densities approaching 10(3) A cm(-2) (limited by series resistance), and excellent current-voltage nonlinearity and asymmetry are achieved using a 1 nm thick high quality dielectric, thulium silicate (TmSiO), as the first insulator layer, and titanium dioxide (TiO2) as a high electron affinity second layer insulator. We also confirm the feasibility and effectiveness of our approach in a full GBT structure which shows dramatic improvement in the collector on-state current density with respect to the previously reported GBTs. The device design and the fabrication scheme have been selected with future CMOS process compatibility in mind. This work proposes a bilayer tunnel barrier approach as a promising candidate to be used in high performance vertical graphene-based tunneling devices. PMID:26176739

  15. Electron tunnelling through single azurin molecules can be on/off switched by voltage pulses

    Energy Technology Data Exchange (ETDEWEB)

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

    2015-05-04

    Redox metalloproteins are emerging as promising candidates for future bio-optoelectronic and nano-biomemory devices, and the control of their electron transfer properties through external signals is still a crucial task. Here, we show that a reversible on/off switching of the electron current tunnelling through a single protein can be achieved in azurin protein molecules adsorbed on gold surfaces, by applying appropriate voltage pulses through a scanning tunnelling microscope tip. The observed changes in the hybrid system tunnelling properties are discussed in terms of long-sustained charging of the protein milieu.

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

    International Nuclear Information System (INIS)

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

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

    Energy Technology Data Exchange (ETDEWEB)

    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

    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.)

  18. Electron transport in AlGaAs/GaAs tunneling hot electron transfer amplifiers

    Science.gov (United States)

    Kim, K.; Hess, K.

    1988-09-01

    A Monte Carlo code has been developed to study electron transport at 4.2 K in AlGaAs/GaAs tunneling hot electron transfer amplifier devices. Our model includes the effects of coupled plasmon-phonon interaction and the Pauli exclusion principle along with more conventional features. The numerical results demonstrate the existence of nearly ballistic transport in the base and the collector barrier, and confirm that the experiments by Heiblum et al. [Phys. Rev. Lett. 55, 2200 (1985)] indeed measure the exact energy distribution of injected ballistic electrons. The device characteristics such as transfer ratio and transit time have also been investigated in detail and are discussed along with the optimum operating conditions.

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

    OpenAIRE

    O.Ya. Farenyuk; A.M. Shvaika

    2006-01-01

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

  20. Photon induced tunneling of electron through a graphene electrostatic barrier

    Energy Technology Data Exchange (ETDEWEB)

    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

    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.

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

    Science.gov (United States)

    Ji, Tao

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

  2. Negative differential resistance in GaN tunneling hot electron transistors

    Energy Technology Data Exchange (ETDEWEB)

    Yang, Zhichao; Nath, Digbijoy; Rajan, Siddharth [Department of Electrical and Computer Engineering, The Ohio State University, Columbus, Ohio 43202 (United States)

    2014-11-17

    Room temperature negative differential resistance is demonstrated in a unipolar GaN-based tunneling hot electron transistor. Such a device employs tunnel-injected electrons to vary the electron energy and change the fraction of reflected electrons, and shows repeatable negative differential resistance with a peak to valley current ratio of 7.2. The device was stable when biased in the negative resistance regime and tunable by changing collector bias. Good repeatability and double-sweep characteristics at room temperature show the potential of such device for high frequency oscillators based on quasi-ballistic transport.

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

    CERN Document Server

    Patapenka, Andrei

    2014-01-01

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

  4. Negative differential resistance in GaN tunneling hot electron transistors

    International Nuclear Information System (INIS)

    Room temperature negative differential resistance is demonstrated in a unipolar GaN-based tunneling hot electron transistor. Such a device employs tunnel-injected electrons to vary the electron energy and change the fraction of reflected electrons, and shows repeatable negative differential resistance with a peak to valley current ratio of 7.2. The device was stable when biased in the negative resistance regime and tunable by changing collector bias. Good repeatability and double-sweep characteristics at room temperature show the potential of such device for high frequency oscillators based on quasi-ballistic transport

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

    OpenAIRE

    Tull, Laura

    2013-01-01

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

  6. Dynamics of Managing Electronic Resources: Electronic Resource Management System (ERMS Initiatives

    Directory of Open Access Journals (Sweden)

    John Paul Anbu K.

    2013-07-01

    Full Text Available Even after two decades of digital presence in libraries and proliferation of electronic resources (e-resources in terms of production, acquisition and usage the management of e-resources remains a cumbersome process. The process involved in the management of e-resources has often overwhelmed the library personnel. The life cycle of e-resources, especially in the academic institutions begin with the discovery and identification of the resource and moves on to the trial access, selecting the specific resource from the gamut of other resources followed by acquisition of the specific resource into the library realm and then felicitating access to the users and then the follow-up of studying the usage of the resource for further continuation of those resources. In between these processes there is the cumbersome chore of going through the licensing agreements and keeping the records correct. All these processes are time consuming and involve a lot of work. These relentless arrays of work have made librarians to look for systems which can save their time and energy and provide efficient management of e-resources. This paper looks at the origin of the ERMS (E-resource Management Systems and the available ERMS in the library digital landscape.

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

    Science.gov (United States)

    Blansit, B D; Connor, E

    1999-07-01

    Changes in the practice of medicine and technological developments offer librarians unprecedented opportunities to select and organize electronic resources, use the Web to deliver content throughout the organization, and improve knowledge at the point of need. The confusing array of available products, access routes, and pricing plans makes it difficult to anticipate the needs of users, identify the top resources, budget effectively, make sound collection management decisions, and organize the resources effectively and seamlessly. The electronic resource marketplace requires much vigilance, considerable patience, and continuous evaluation. There are several strategies that librarians can employ to stay ahead of the electronic resource curve, including taking advantage of free trials from publishers; marketing free trials and involving users in evaluating new products; watching and testing products marketed to the clientele; agreeing to beta test new products and services; working with aggregators or republishers; joining vendor advisory boards; benchmarking institutional resources against five to eight competitors; and forming or joining a consortium for group negotiating and purchasing. This article provides a brief snapshot of leading biomedical resources; showcases several libraries that have excelled in identifying, acquiring, and organizing electronic resources; and discusses strategies and trends of potential interest to biomedical librarians, especially those working in hospital settings. PMID:10427421

  8. Electronic resource management systems a workflow approach

    CERN Document Server

    Anderson, Elsa K

    2014-01-01

    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.

  9. Semantic Web and Electronic Information Resources

    OpenAIRE

    Radovanovic, Danica

    2003-01-01

    The usage of electronic resources depends on good possibilities of searching and the Semantic Web concept can be convenient solution for information retrieval (IR). WWW (World Wide Web) enables, with the help of search engines and huge number of available (meta)information, data that can satisfy user's need for information, 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 possible rel...

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

    CERN Document Server

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

    1999-01-01

    We report about the fabrication and analysis of the properties of Cr/CrO_x/Cr tunnel junctions and SET transistors, prepared by different variants of direct-writing multilayer technique. In all cases, the CrO_x tunnel barriers were formed in air under ambient conditions. From the experiments on single junctions, values for the effective barrier height and thickness were derived. For the Cr/CrO_x/Cr SET transistors we achieved minimal junction areas of 17 x 60 nm^2 using a scanning transmission electron microscope for the e-beam exposure on Si_3N_4 membrane substrate. We discuss the electrical performance of the transistor samples as well as their noise behavior.

  11. Investigation of electron and hole tunneling through thin silicon dioxide films

    International Nuclear Information System (INIS)

    The processes of electrons and holes tunneling through thin silicon dioxide films have been investigated. In parallel with the direct measurement of tunneling current in Si-SiO2-Al structures, an original method, based on the accumulation of charge in Si-SiO2-Si3N4-Al structures, have been used. The current-voltage dependences obtained by two methods for electron tunneling are in agreement and correspond to carrier injection from silicon at a positive voltage on metal according to the Fowler-Nordheim mechanism. The hole tunneling current can be measured only by the charge accumulation method due to a high energy barrier for holes. Possible mechanisms of positive charge accumulation are discussed

  12. 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

  13. Nonconstant electronic density of states tunneling inversion for A15 superconductors: Nb3Sn

    OpenAIRE

    Freericks, J. K.; Liu, A. Y.; Quandt, A.; Geerk, J.

    2002-01-01

    We re-examine the tunneling data on A15 superconductors by performing a generalized McMillan-Rowell tunneling inversion that incorporates a nonconstant electronic density of states obtained from band-structure calculations. For Nb3Sn, we find that the fit to the experimental data can be slightly improved by taking into account the sharp structure in the density of states, but it is likely that such an analysis alone is not enough to completely explain the superconducting tun...

  14. Detecting hydrogen gas by single electron tunneling based sensors: an image processing and simulation study

    OpenAIRE

    ABBASI, H.; KHAJE, M.; H Sedghi

    2015-01-01

    Abstract. We present a hydrogen sensor based on single electron tunneling at two dimensional (2D) hexagonal closed packed arrays of palladium nano-islands. Parameters of the hexagonal closed packed arrays of palladium nanoparticles were extracted from experimental TEM results by image processing methods. Using SIMON simulator, emergences of the coulomb blockade were inspected by studying Current-Voltage (IV) characteristics of equivalent circuits consisting of palladium islands and tunneling ...

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

    OpenAIRE

    García-Lekue, Aran; Sánchez-Portal, Daniel; Arnau, Andrés; Frederiksen, T.

    2011-01-01

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

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

    Energy Technology Data Exchange (ETDEWEB)

    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

    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.

  17. Multi-electron dynamics in the tunnel ionization of correlated quantum systems

    CERN Document Server

    Hollstein, Maximilian

    2015-01-01

    The importance of multi-electron dynamics during the tunnel ionization of a correlated quantum system is investigated. By comparison of the solution of the time-dependent Schr\\"odinger equation (TDSE) with the time-dependent configuration interaction singles approach (TDCIS), we demonstrate the importance of a multi-electron description of the tunnel ionization process especially for weakly confined quantum systems. Within this context, we observe that adiabatic driving by an intense light field can even enhance the correlations between still trapped electrons.

  18. 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 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

  19. Imaging surfaces with reflected electrons from a field emission scanning tunnelling microscope: image contrast mechanisms

    International Nuclear Information System (INIS)

    Electrons backscattered from a scanning tunnelling microscope operating in the field emission mode have been collected to produce images of a rough Si(111) surface. We have obtained a spatial resolution of about 40 nm in such images. Comparison between backscattered electron images and topographic images reveals that edge enhancement and shadowing are important contrast mechanisms. (author)

  20. Novel Transport Mechanism for Interacting Electrons in Disordered Systems: Variable-Range Resonant Tunneling

    OpenAIRE

    Baranovskii, S. D.; Shlimak, I. S.

    1998-01-01

    To interpret recent experimental observations of the phononless hopping conduction, we suggest a novel transport mechanism according to which the current-carrying single electrons move via quantum resonant tunneling between localized states brought into resonance by fast electron hops in their environment.

  1. Probing Nanoscale Electronic and Magnetic Interaction with Scanning Tunneling Spectroscopy

    DEFF Research Database (Denmark)

    Bork, Jakob

    2010-01-01

    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

  2. Competing Anisotropy-Tunneling Correlation of the CoFeB/MgO Perpendicular Magnetic Tunnel Junction: An Electronic Approach.

    Science.gov (United States)

    Yang, Chao-Yao; Chang, Shu-Jui; Lee, Min-Han; Shen, Kuei-Hung; Yang, Shan-Yi; Lin, Horng-Ji; Tseng, Yuan-Chieh

    2015-01-01

    We intensively investigate the physical principles regulating the tunneling magneto-resistance (TMR) and perpendicular magnetic anisotropy (PMA) of the CoFeB/MgO magnetic tunnel junction (MTJ) by means of angle-resolved x-ray magnetic spectroscopy. The angle-resolved capability was easily achieved, and it provided greater sensitivity to symmetry-related d-band occupation compared to traditional x-ray spectroscopy. This added degree of freedom successfully solved the unclear mechanism of this MTJ system renowned for controllable PMA and excellent TMR. As a surprising discovery, these two physical characteristics interact in a competing manner because of opposite band-filling preference in space-correlated symmetry of the 3d-orbital. An overlooked but harmful superparamagnetic phase resulting from magnetic inhomogeneity was also observed. This important finding reveals that simultaneously achieving fast switching and a high tunneling efficiency at an ultimate level is improbable for this MTJ system owing to its fundamental limit in physics. We suggest that the development of independent TMR and PMA mechanisms is critical towards a complementary relationship between the two physical characteristics, as well as the realization of superior performance, of this perpendicular MTJ. Furthermore, this study provides an easy approach to evaluate the futurity of any emerging spintronic candidates by electronically examining the relationship between their magnetic anisotropy and transport. PMID:26596778

  3. Competing Anisotropy-Tunneling Correlation of the CoFeB/MgO Perpendicular Magnetic Tunnel Junction: An Electronic Approach

    Science.gov (United States)

    Yang, Chao-Yao; Chang, Shu-Jui; Lee, Min-Han; Shen, Kuei-Hung; Yang, Shan-Yi; Lin, Horng-Ji; Tseng, Yuan-Chieh

    2015-11-01

    We intensively investigate the physical principles regulating the tunneling magneto-resistance (TMR) and perpendicular magnetic anisotropy (PMA) of the CoFeB/MgO magnetic tunnel junction (MTJ) by means of angle-resolved x-ray magnetic spectroscopy. The angle-resolved capability was easily achieved, and it provided greater sensitivity to symmetry-related d-band occupation compared to traditional x-ray spectroscopy. This added degree of freedom successfully solved the unclear mechanism of this MTJ system renowned for controllable PMA and excellent TMR. As a surprising discovery, these two physical characteristics interact in a competing manner because of opposite band-filling preference in space-correlated symmetry of the 3d-orbital. An overlooked but harmful superparamagnetic phase resulting from magnetic inhomogeneity was also observed. This important finding reveals that simultaneously achieving fast switching and a high tunneling efficiency at an ultimate level is improbable for this MTJ system owing to its fundamental limit in physics. We suggest that the development of independent TMR and PMA mechanisms is critical towards a complementary relationship between the two physical characteristics, as well as the realization of superior performance, of this perpendicular MTJ. Furthermore, this study provides an easy approach to evaluate the futurity of any emerging spintronic candidates by electronically examining the relationship between their magnetic anisotropy and transport.

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

    OpenAIRE

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

    2014-01-01

    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...

  5. Hot electron spectroscopy of carrier relaxation within indirect AlAs tunnel barriers

    Science.gov (United States)

    Sivaraya, S.; Bending, S. J.; Henini, M.

    1999-11-01

    Hot electron spectroscopy has been performed on electrons which have tunneled through indirect AlAs potential barriers in a tunneling hot electron transfer amplifier. We find that only about 1% of the electrons are collected close to their injection energy in stark contrast to an otherwise identical structure with an Al0.5Ga0.5As barrier where this fraction was 30%. Measurements under hydrostatic pressure show clear evidence for the real-space transfer of electrons from the emitter electrode into an X-point barrier subband adjacent to the emitter Fermi band. A detailed analysis of hot electron spectra reveals that the transferred electrons undergo strong inelastic scattering within the AlAs barrier and relax down through the ladder of X-point subbands there before being reemitted into the base layer.

  6. Free online electronic information resources on applied science and technology

    OpenAIRE

    Ghosh, T B.

    2003-01-01

    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 inform...

  7. Electron tunneling pathways and role of adenine in repair of cyclobutane pyrimidine dimer by DNA photolyase.

    Science.gov (United States)

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

    2012-05-16

    Electron tunneling pathways in enzymes are critical to their catalytic efficiency. Through electron tunneling, photolyase, a photoenzyme, splits UV-induced cyclobutane pyrimidine dimer into two normal bases. Here, we report our systematic characterization and analyses of photoinitiated three electron transfer processes and cyclobutane ring splitting by following the entire dynamical evolution during enzymatic repair with femtosecond resolution. We observed the complete dynamics of the reactants, all intermediates and final products, and determined their reaction time scales. Using (deoxy)uracil and thymine as dimer substrates, we unambiguously determined the electron tunneling pathways for the forward electron transfer to initiate repair and for the final electron return to restore the active cofactor and complete the catalytic photocycle. Significantly, we found that the adenine moiety of the unusual bent flavin cofactor is essential to mediating all electron-transfer dynamics through a superexchange mechanism, leading to a delicate balance of time scales. The cyclobutane ring splitting takes tens of picoseconds, while electron-transfer dynamics all occur on a longer time scale. The active-site structural integrity, unique electron tunneling pathways, and the critical role of adenine ensure the synergy of these elementary steps in this complex photorepair machinery to achieve maximum repair efficiency which is close to unity. Finally, we used the Marcus electron-transfer theory to evaluate all three electron-transfer processes and thus obtained their reaction driving forces (free energies), reorganization energies, and electronic coupling constants, concluding that the forward and futile back-electron transfer is in the normal region and that the final electron return of the catalytic cycle is in the inverted region. PMID:22533849

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

    Energy Technology Data Exchange (ETDEWEB)

    Miller, John R.; Beitz, James V.

    1979-01-01

    Electron tunneling leads to transfer of trapped positive, or negative charge tens of angstroms in rigid matrices. Franck-Condon effects give energy specificity to charge transfer and ion recombination, and adds sensitivity to molecular structure, solvation and H/D isotope effects. The specificity is important in photosynthesis and solar energy storage as well as in radiation chemistry. We feel that the question of hopping vs. tunneling is definitely settled in favor of tunneling for intermolecular electron transfer at low temperatures. Hopping cannot yet be conclusively ruled out in reactions of trapped electrons. Hopping is expected to become important in many media near room temperature (T approx. less than 200/sup 0/K).

  9. Dynamic tunneling force microscopy for characterizing electronic trap states in non-conductive surfaces

    Science.gov (United States)

    Wang, R.; Williams, C. C.

    2015-09-01

    Dynamic tunneling force microscopy (DTFM) is a scanning probe technique for real space mapping and characterization of individual electronic trap states in non-conductive films with atomic scale spatial resolution. The method is based upon the quantum mechanical tunneling of a single electron back and forth between a metallic atomic force microscopy tip and individual trap states in completely non-conducting surface. This single electron shuttling is measured by detecting the electrostatic force induced on the probe tip at the shuttling frequency. In this paper, the physical basis for the DTFM method is unfolded through a physical model and a derivation of the dynamic tunneling signal as a function of several experimental parameters is shown. Experimental data are compared with the theoretical simulations, showing quantitative consistency and verifying the physical model used. The experimental system is described and representative imaging results are shown.

  10. Tunneling of electrons via rotor-stator molecular interfaces: combined ab initio and model study

    CERN Document Server

    Petreska, Irina; Pejov, Ljupco; Kocarev, Ljupco

    2015-01-01

    Tunneling of electrons through rotor-stator anthracene aldehyde molecular interfaces is studied with a combined ab initio and model approach. Molecular electronic structure calculated from first principles is utilized to model different shapes of tunneling barriers. Together with a rectangular barrier, we also consider a sinusoidal shape that captures the effects of the molecular internal structure more realistically. Quasiclassical approach with the Simmons' formula for current density is implemented. Special attention is paid on conformational dependence of the tunneling current. Our results confirm that the presence of the side aldehyde group enhances the interesting electronic properties of the pure anthracene molecule, making it a bistable system with geometry dependent transport properties. We also investigate the transition voltage and we show that confirmation dependent field emission could be observed in these molecular interfaces at realistically low voltages. The present study accompanies our previ...

  11. From Tedious to Timely: Screencasting to Troubleshoot Electronic Resource Issues

    Science.gov (United States)

    Hartnett, Eric; Thompson, Carole

    2010-01-01

    The shift from traditional print materials to electronic resources, in conjunction with the rise in the number of distance education programs, has left many electronic resource librarians scrambling to keep up with the resulting inundation of electronic resource problems. When it comes to diagnosing these problems, words do not always convey all…

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

    OpenAIRE

    Blansit, B D; Connor, E

    1999-01-01

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

  13. Highly Efficient Midinfrared On-Chip Electrical Generation of Graphene Plasmons by Inelastic Electron Tunneling Excitation

    CERN Document Server

    Ooi, Kelvin J A; Hsieh, Chang Yu; Tan, Dawn T H; Ang, Lay Kee

    2015-01-01

    Inelastic electron tunneling provides a low-energy pathway for the excitation of surface plasmons and light emission. We theoretically investigate tunnel junctions based on metals and graphene. We show that graphene is potentially a highly efficient material for tunneling excitation of plasmons because of its narrow plasmon linewidths, strong emission, and large tunability in the midinfrared wavelength regime. Compared to gold and silver, the enhancement can be up to 10 times for similar wavelengths and up to 5 orders at their respective plasmon operating wavelengths. Tunneling excitation of graphene plasmons promises an efficient technology for on-chip electrical generation and manipulation of plasmons for graphene-based optoelectronics and nanophotonic integrated circuits.

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

    International Nuclear Information System (INIS)

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

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

    Directory of Open Access Journals (Sweden)

    Madsen Lars B.

    2013-03-01

    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.

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

    OpenAIRE

    Gain, Jatindranath; Sarkar, Madhumita Das; Kundu, Sudakshina

    2010-01-01

    Tunneling of electrons through the barriers in heterostructures has been studied, within unified transfer matrix approach. The effect of barrier width on the transmission coefficient of the electrons has been investigated for different pairs of semi conducting materials that are gaining much importance recently. These pairs include CdS/CdSe, AlGaAs/GaAs and InAs/AlSb. Barrier dimensions have been reduced from 20nm to 5nm to observe the effect of scaling on tunneling properti...

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

    International Nuclear Information System (INIS)

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

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

    International Nuclear Information System (INIS)

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

  19. Constructing a dental electronic information resource (DEIR).

    Science.gov (United States)

    Lang, W P

    1994-04-01

    This paper discusses the construction of a dental electronic information resource (DEIR). Development is based on the Internet gopher client/server model. Information is organized in a series of hierarchical menus. A DEIR can be browsed by traversing the menu hierarchy or by performing keyword searches. Searches can result in a menu of found items from across the Internet. Initially, contents of the DEIR will be text files. Electronic copy will be given to an editorial board that will review submissions for conformity to publication standards. A current estimate for electronic storage costs of a DEIR is $1.25/Mb per year. There will be additional costs associated with any purchases of data (e.g. Current Contents), production of data (e.g. development time), and editorial and managerial activities. The DEIR will be accessible from any computer or terminal that can connect to the Internet. Primary user groups will be faculty, staff, and students of dental schools. However, access to the DEIR will be free, and an extensive user community will be encouraged, including practicing dentists, dental associations, public health agencies, and dental insurance companies. PMID:8005714

  20. 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.

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

    Energy Technology Data Exchange (ETDEWEB)

    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

    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.

  2. Resonant tunneling of electrons in asymmetric double quantum wells under crossed electric and magnetic fields

    International Nuclear Information System (INIS)

    It has been investigated the influence of an uniform electric field, applied in the growth direction, and an uniform magnetic field, perpendicular to this direction, on the resonant tunneling of electrons in a system formed by two asymmetric quantum wells separated by a thin barrier. The semiconductor heterostructure is considered in the effective mass approximation and one band model. The method we have used to calculated the electronic structure is based on the solution of the time-dependent Schroedinger equation using the split-operator technique. The tunneling dynamics in the resonance condition is studied using the time evolution of a wave-packet from which we determine the tunneling time. A comparison with recent experimental data is presented. (author). 10 refs., 4 figs

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

    CERN Document Server

    Gain, Jatindranath; Kundu, Sudakshina

    2010-01-01

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

  4. On the concept of an optimal hot-electron bolometer with NIS tunnel junctions

    Science.gov (United States)

    Kuzmin, Leonid; Golubev, Dmitry

    2002-08-01

    Optimization of the hot-electron bolometer with a normal metal-insulator-superconductor (NIS) tunnel junction as a temperature sensor has been done theoretically. The responsivity and the noise equivalent power (NEP) of the bolometer are obtained numerically for typical experimental parameters. We demonstrate that electron cooling by the NIS junction, which serves as a thermometer, can improve the sensitivity of the device. This effect is especially useful in the presence of a finite power load. Optimization of the hot-electron bolometer in the presence of a finite power load is discussed. It has been shown that the optimal regime can be realized when thermal conductance through the tunnel junctions is larger than the electron-phonon conductance. The electron-phonon noise is negligible and the NEP is determined mainly by the noise of the NIS junctions because of practically full transference of power of the incoming signal to a readout amplifier through the junctions.

  5. Electronic Resource Management System. Vernetzung von Lizenzinformationen

    Directory of Open Access Journals (Sweden)

    Michaela Selbach

    2014-12-01

    Full Text Available In den letzten zehn Jahren spielen elektronische Ressourcen im Bereich der Erwerbung eine zunehmend wichtige Rolle: Eindeutig lässt sich hier ein Wandel in den Bibliotheken (fort vom reinen Printbestand zu immer größeren E-Only-Beständen feststellen. Die stetig wachsende Menge an E-Ressourcen und deren Heterogenität stellt Bibliotheken vor die Herausforderung, die E-Ressourcen effizient zu verwalten. Nicht nur Bibliotheken, sondern auch verhandlungsführende Institutionen von Konsortial- und Allianzlizenzen benötigen ein geeignetes Instrument zur Verwaltung von Lizenzinformationen, welches den komplexen Anforderungen moderner E-Ressourcen gerecht wird. Die Deutsche Forschungsgemeinschaft (DFG unterstützt ein Projekt des Hochschulbibliothekszentrums des Landes Nordrhein-Westfalen (hbz, der Universitätsbibliothek Freiburg, der Verbundzentrale des Gemeinsamen Bibliotheksverbundes (GBV und der Universitätsbibliothek Frankfurt, in dem ein bundesweit verfügbares Electronic Ressource Managementsystem (ERMS aufgebaut werden soll. Ein solches ERMS soll auf Basis einer zentralen Knowledge Base eine einheitliche Nutzung von Daten zur Lizenzverwaltung elektronischer Ressourcen auf lokaler, regionaler und nationaler Ebene ermöglichen. Statistische Auswertungen, Rechteverwaltung für alle angeschlossenen Bibliotheken, kooperative Datenpflege sowie ein über standardisierte Schnittstellen geführter Datenaustausch stehen bei der Erarbeitung der Anforderungen ebenso im Fokus wie die Entwicklung eines Daten- und Funktionsmodells. In the last few years the importance of electronic resources in library acquisitions has increased significantly. There has been a shift from mere print holdings to both e- and print combinations and even e-only subscriptions. This shift poses a double challenge for libraries: On the one hand they have to provide their e-resource collections to library users in an appealing way, on the other hand they have to manage these collections efficiently. Not only libraries, but also the negotiators of Alliance and National Licences need a software application which helps them to handle these complex licences efficiently. The project presented in this paper aims at developing a national Electronic Resource Management System (ERMS. It is funded by the German Research Foundation/Deutsche Forschungsgemeinschaft (DFG. The project partners are the North Rhine-Westphalian Library Service Centre (hbz, the University Library Johann Christian Senckenberg Frankfurt, the Head Office of the Gemeinsamer Bibliotheksverbund (GBV and the Freiburg University Library. The projected ERMS  will provide a software system with a central knowledge base which supports a unified overview of licence data with a local, regional and national scope. In the current state of development, the focus is on data and function modelling and on designing concepts for rights management, cooperative data management, implementation of interface standards and the intended services such as statistical analyses.

  6. Electron-tunneling studies of the cubic Kondo semiconductors

    International Nuclear Information System (INIS)

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

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

    Directory of Open Access Journals (Sweden)

    O.Ya.Farenyuk

    2006-01-01

    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.

  8. Electron-acoustic phonon field induced tunnel scattering

    Directory of Open Access Journals (Sweden)

    S.V. Melkonyan

    2015-06-01

    Full Text Available Theory of electron-acoustic single phonon scattering has been reconsidered. It is assumed that the non-degenerate semiconductor has a spherical parabolic band structure. In the basis of the reconsideration there is a phenomenon of the tilting of semiconductor bands by the perturbing potential of an electric field. In this case, electron eigenfunctions are not plane waves or Bloch functions. In low-field regime, the expressions for electron intraband transition probability and scattering time are obtained under elastic collision approximation. Dependencies of scattering time on electron energy and uniform electric field are analyzed. The results of corresponding numerical computations for n-Si at 300 K are presented. It is established that there is no fracture on the curve of electron scattering time on the electron energy dependence.

  9. Local imaging of high mobility two-dimensional electron systems with virtual scanning tunneling microscopy

    International Nuclear Information System (INIS)

    Correlated electron states in high mobility two-dimensional electron systems (2DESs), including charge density waves and microemulsion phases intermediate between a Fermi liquid and Wigner crystal, are predicted to exhibit complex local charge order. Existing experimental studies, however, have mainly probed these systems at micron to millimeter scales rather than directly mapping spatial organization. Scanning probes should be well-suited to study the spatial structure of these states, but high mobility 2DESs are found at buried semiconductor interfaces, beyond the reach of conventional scanning tunneling microscopy. Scanning techniques based on electrostatic coupling to the 2DES deliver important insights, but generally with resolution limited by the depth of the 2DES. In this letter, we present our progress in developing a technique called “virtual scanning tunneling microscopy” that allows local tunneling into a high mobility 2DES. Using a specially designed bilayer GaAs/AlGaAs heterostructure where the tunnel coupling between two separate 2DESs is tunable via electrostatic gating, combined with a scanning gate, we show that the local tunneling can be controlled with sub-250?nm resolution

  10. Local imaging of high mobility two-dimensional electron systems with virtual scanning tunneling microscopy

    Energy Technology Data Exchange (ETDEWEB)

    Pelliccione, M. [Department of Applied Physics, Stanford University, 348 Via Pueblo Mall, Stanford, California 94305 (United States); Stanford Institute for Materials and Energy Sciences, SLAC National Accelerator Laboratory, 2575 Sand Hill Road, Menlo Park, California 94025 (United States); Department of Physics, University of California, Santa Barbara, Santa Barbara, California 93106 (United States); Bartel, J.; Goldhaber-Gordon, D. [Stanford Institute for Materials and Energy Sciences, SLAC National Accelerator Laboratory, 2575 Sand Hill Road, Menlo Park, California 94025 (United States); Department of Physics, Stanford University, 382 Via Pueblo Mall, Stanford, California 94305 (United States); Sciambi, A. [Department of Applied Physics, Stanford University, 348 Via Pueblo Mall, Stanford, California 94305 (United States); Stanford Institute for Materials and Energy Sciences, SLAC National Accelerator Laboratory, 2575 Sand Hill Road, Menlo Park, California 94025 (United States); Pfeiffer, L. N.; West, K. W. [Department of Electrical Engineering, Princeton University, Princeton, New Jersey 08544 (United States)

    2014-11-03

    Correlated electron states in high mobility two-dimensional electron systems (2DESs), including charge density waves and microemulsion phases intermediate between a Fermi liquid and Wigner crystal, are predicted to exhibit complex local charge order. Existing experimental studies, however, have mainly probed these systems at micron to millimeter scales rather than directly mapping spatial organization. Scanning probes should be well-suited to study the spatial structure of these states, but high mobility 2DESs are found at buried semiconductor interfaces, beyond the reach of conventional scanning tunneling microscopy. Scanning techniques based on electrostatic coupling to the 2DES deliver important insights, but generally with resolution limited by the depth of the 2DES. In this letter, we present our progress in developing a technique called “virtual scanning tunneling microscopy” that allows local tunneling into a high mobility 2DES. Using a specially designed bilayer GaAs/AlGaAs heterostructure where the tunnel coupling between two separate 2DESs is tunable via electrostatic gating, combined with a scanning gate, we show that the local tunneling can be controlled with sub-250?nm resolution.

  11. Tunneling hot electron transistor as a high power source at terahertz frequencies

    Science.gov (United States)

    Dellow, M. W.; Cronin, N. J.; Bending, S. J.

    1994-11-01

    A novel device is proposed, based upon a tunneling hot electron transfer amplifier, which exhibits the characteristics of negative differential resistance (NDR) coupled with high current gain. The mechanism which produces the NDR is known to be extremely fast. The combination of these features suggests that such a device could be used as a high power source of terahertz radiation.

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

    Science.gov (United States)

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

    2012-06-01

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

  13. Dynamics and pathway of electron tunneling in repair of damaged DNA by photolyase

    Science.gov (United States)

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

    2013-03-01

    Through electron tunneling, photolyase, a photoenzyme, restores damaged DNA into normal bases. Here, we report our systematic characterization and analyses of three electron transfer processes in thymine dimer restoration by following the entire dynamical evolution during enzymatic repair with femtosecond resolution. Using (deoxy)uracil and thymine as dimer substrates, we unambiguously determined the electron tunneling pathways for the forward electron transfer to initiate repairing and for the final electron return to restore the active cofactor and complete the repair photocycle. Significantly, we found that the adenine moiety of the unusual bent cofactor is essential to mediating all electron-transfer dynamics through a super-exchange mechanism, leading to a delicate balance of time scales. The active-site structural integrity, unique electron tunneling pathways and the critical role of adenine assure these elementary dynamics in synergy in this complex photorepair machinery to achieve the maximum repair efficiency close to unity. The authors thank Drs. Chaitanya Sexana, Yi Yang, and Chen Zang for the initial help with experiment, and Prof. Sherwin Singer and Dr. Ali Hassanali for discussion.

  14. Tunnel and pnpn diodes in fast electronics for discrimination and counting devices in nuclear physics

    International Nuclear Information System (INIS)

    With a simple apparatus without power supply, the authors measured the rise time of the pulse produced by the fast switching of a tunnel diode. This time was of the order of 0.5 ns. The addition of a source of current made it possible to mount an ultra-fast amplitude-discrimination trigger working at a nanosecond. Problems of power supply and impedance adaptation make this a delicate experiment to perform successfully. It is particularly difficult to get good trigger threshold stability, as this is very sensitive to the supply voltage. At the present stage of the technique, a bi-stable flip-flop utilizing only one tunnel diode does not offer the operational security which would permit its use in nuclear physics. But it is possible to construct bi-stable flip-flops with two tunnel diodes. A system of n tunnel diodes in series, fed by a constant-current generator, presents n potential stable states. It is therefore possible to construct fast scalers of astonishing simplicity. Unfortunately, up until now zeroing has required the use of slower active or passive elements which do not allow full use to be made of the scaler's capacity. Combinations of tunnel diodes make it easy to construct rather complex electronic commutators. To conclude: the difficulty of using tunnel diode circuits lies essentially in problems of power feed and in linking them with other electronic gear. Nevertheless, their very considerable advantages justify intensive study in order to render them simpler to use. With four-layer diodes similar apparatus, but capable of furnishing considerable power, can be constructed. However, they require high voltages to justify their use in electronic tube circuits. (author)

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

    Scientific Electronic Library Online (English)

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

    2002-06-01

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

  16. Electron-tunneling studies of the cubic Kondo semiconductors

    Energy Technology Data Exchange (ETDEWEB)

    Ekino, Toshikazu; Fujii, Hironobu [Faculty of Integrated Arts and Sciences, Hiroshima Univ., Higashi-Hiroshima (Japan); Katoh, Ken-ichi; Iga, Fumitoshi; Takabatake, Toshiro [Graduate School of Advanced Science of Matter, Hiroshima Univ., Higashi-Hiroshima (Japan)

    1999-02-28

    We present the experimental evidence for the energy gap in cubic Ce{sub 3}Bi{sub 4}Pt{sub 3} and YbB{sub 12} single crystals using break-junction tunneling. The well-defined gap values 2{delta}(4.2 K) = 85 {+-} 20 meV and 220 - 260 meV are obtained for Ce{sub 3}Bi{sub 4}Pt{sub 3} and YbB{sub 12}, respectively. The ratio 2{delta}/k{sub B}T{sub {chi}} for Ce{sub 3}Bi{sub 4}Pt{sub 3} is evaluated to be approx. = 13 with the susceptibility-maximum temperature T{sub {chi}} = 80 K. On the other hand, 2{delta}/k{sub B}T{sub {chi}} approx. = 37 for YbB{sub 12} is much larger than that of Ce{sub 3}Bi{sub 4}Pt{sub 3} in spite of possessing the similar T{sub {chi}} value of 75 K. These results indicate that the characteristic energy for the gap creation in YbB{sub 12} is much higher than that in Ce{sub 3}Bi{sub 4}Pt{sub 3}. (author)

  17. Spin Accumulation Encoded in Electronic Noise for Mesoscopic Billiards with Finite Tunneling Rates

    OpenAIRE

    Ramos, J. G. G. S.; Barbosa, A. L. R.; Bazeia, D.; Hussein, M. S

    2011-01-01

    We study the effects of spin accumulation (inside reservoirs) on electronic transport with tunneling and reflections at the gates of a quantum dot. Within the stub model, the calculation focus on the current-current correlation function for the flux of electrons injected into the quantum dot. The linear response theory used allows to obtain the noise power in the regime of thermal crossover as a function of parameters that reveal the spin polarization at the reservoirs. The ...

  18. 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)

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

    CERN Document Server

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

    1998-01-01

    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.

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

    Energy Technology Data Exchange (ETDEWEB)

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

    1982-04-15

    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.

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

    International Nuclear Information System (INIS)

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

  2. Electronic transport in graphene/CdSe nanoparticle monolayer/graphene tunneling devices

    Science.gov (United States)

    Zhang, Datong; Lu, Chenguang; van der Zande, Arend; Kim, Philip; Herman, Irving P.

    2015-03-01

    We fabricated graphene/CdSe nanoparticle monolayer/graphene sandwich device structures. The CdSe nanoparticle monolayer is formed on a liquid-air surface before transferring it onto the bottom graphene layer that had been micro-exfoliated onto a 285 nm SiO2/Si substrate. The top graphene layer is transferred to the targeted area on the CdSe nanoparticle monolayer via a dry transfer technique. Tunneling-type vertical transport is observed, which is fitted by tunneling models that suggest that ligand shell instead of nanoparticle core is the major barrier of tunneling. Photoconductivity is enhanced but with low exciton separation efficiency when the laser is on the junction area, also suggesting that ligand shell is the major barrier of electronic transport in the sandwich structure.

  3. Strong Asymmetric Charge Carrier Dependence in Inelastic Electron Tunneling Spectroscopy of Graphene Phonons.

    Science.gov (United States)

    Natterer, Fabian D; Zhao, Yue; Wyrick, Jonathan; Chan, Yang-Hao; Ruan, Wen-Ying; Chou, Mei-Yin; Watanabe, Kenji; Taniguchi, Takashi; Zhitenev, Nikolai B; Stroscio, Joseph A

    2015-06-19

    The observation of phonons in graphene by inelastic electron tunneling spectroscopy has been met with limited success in previous measurements arising from weak signals and other spectral features which inhibit a clear distinction between phonons and miscellaneous excitations. Utilizing a back-gated graphene device that allows adjusting the global charge carrier density, we introduce an averaging method where individual tunneling spectra at varying charge carrier density are combined into one representative spectrum. This method improves the signal for inelastic transitions while it suppresses dispersive spectral features. We thereby map the total graphene phonon density of states, in good agreement with density functional calculations. Unexpectedly, an abrupt change in the phonon intensity is observed when the graphene charge carrier type is switched through a variation of the back-gate electrode potential. This sudden variation in phonon intensity is asymmetric in the carrier type, depending on the sign of the tunneling bias. PMID:26196985

  4. User Perception of Electronic Resources in the University of Ilorin

    OpenAIRE

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

    2011-01-01

    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 allu...

  5. "Have I Learnt It?" Evaluating Skills for Resource-based Study Using Electronic Resources.

    Science.gov (United States)

    Macdonald, Janet; Heap, Nick; Mason, Robin

    2001-01-01

    Discussion of electronic information resources and information literacy in higher education focuses on the information handling skills students need and the factors influencing their acquisition in two networked resource-based courses at the United Kingdom Open University. Offers guidelines for course designers incorporating electronic resources

  6. A Diamond Electron Tunneling Micro-Electromechanical Sensor

    Science.gov (United States)

    Albin, Sacharia

    2000-01-01

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

  7. Single-electron tunneling in InP nanowires

    CERN Document Server

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

    2003-01-01

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

  8. Ultralarge area MOS tunnel devices for electron emission

    DEFF Research Database (Denmark)

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

    2007-01-01

    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 ver...

  9. Ultralarge area MOS tunnel devices for electron emission

    OpenAIRE

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

    2008-01-01

    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 ...

  10. Use of Electronic Resources in Scholarly Electronic Journals: A Citation Analysis.

    Science.gov (United States)

    Herring, Susan Davis

    2002-01-01

    Describes a citation analysis of research articles from scholarly electronic journals published in 1999-2000 that focused on the extent to which scholars are using electronic resources and the types and subject areas of online resources that are being referenced. Results indicate a growing reliance on electronic resources, especially…

  11. 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)

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

    Directory of Open Access Journals (Sweden)

    Jun He

    2012-03-01

    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.

  13. Interplay between adsorbate diffusion and electron tunneling at an insulating surface

    International Nuclear Information System (INIS)

    We investigate electron tunneling between defects and mobile adsorbates on the surface of MgO and show that electrons can be transferred to Au and Pt atoms from defects, such as oxygen vacancies, over distances ?20 A even at room temperature. As a result of the surface-mediated interaction following electron transfer, the mobility of these metal atoms is enhanced significantly. Such processes may affect the kinetics of growth and structure of adsorbed clusters and thin films and the interaction of molecules with surfaces.

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

    Science.gov (United States)

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

    2014-06-01

    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.

  15. Electronic effects in scanning tunneling microscopy: Moiré pattern on a graphite surface

    Science.gov (United States)

    Rong, Zhao Y.; Kuiper, Pieter

    1993-12-01

    We observed by scanning tunneling microscopy (STM) a hexagonal superlattice on graphite with a period of 66 Å. Direct measurement of the angle between lattice vectors confirmed that the superlattice is a Moiré pattern caused by a 2.1° rotation of the topmost (0001) plane with respect to the bulk. The STM corrugation of 2.6 Å is not due to physical buckling, but to differences in electronic structure between AA-stacked, normal AB-stacked, and rhombohedral CAB-stacked graphite. The high tunneling current of AA-stacked regions is in agreement with the high density of states at the Fermi level calculated for AA graphite. The Moiré pattern changes, both the amplitude and the shape, with bias voltage. The observation provides a basis for a comparative study of surface electronic structures with different subsurface layer configuration, which is a vital test of our understanding of STM.

  16. Theoretical model for diffusion controlled reactions of solvated electrons, incorporating a tunnelling mechanism

    International Nuclear Information System (INIS)

    The effect on diffusion-controlled reactions, of electron tunnelling from a solvent cavity to a scavenger molecule, is examined. The radial diffusion equation is modified to include a sink term, which varies exponentially with distance from the origin, and thus simulates tunnelling behaviour. An analytical solution is obtained for the steady-state, and applied to diffusion controlled reactions of the solvated electron in media covering a wide range of viscosities. In low viscosity media (eta approximately 10-3kgm-1s-1) reaction can take place at a reactant separation of about two molecular diameters, this distance increases with viscosity, reaching about eight molecular diameters for eta=109(gm-1s-1. The theory is also applied to energy transfer by an exchange mechanism; transfer only begins to take place from distances greater than the encounter distance when the viscosity reaches approximately 105kgm-1s-1. (author)

  17. Using Electronic Resources to Support Problem-Based Learning

    Science.gov (United States)

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

    2012-01-01

    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…

  18. Using Electronic Resources to Support Problem-Based Learning

    Science.gov (United States)

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

    2012-01-01

    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…

  19. What Faculty Think: A Survey on Electronic Resources

    Science.gov (United States)

    Jackson, Millie

    2008-01-01

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

  20. The Role of the Acquisitions Librarian in Electronic Resources Management

    Science.gov (United States)

    Pomerantz, Sarah B.

    2010-01-01

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

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

    Science.gov (United States)

    Rux, Erika; Borchert, Theresa

    2010-01-01

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

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

    Science.gov (United States)

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

    1973-01-01

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

  3. 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

  4. Scanning tunnelling microscopy and electronic structure of Mn clusters on Ag(111)

    Energy Technology Data Exchange (ETDEWEB)

    Kliewer, J.; Berndt, R. [Christian-Albrechts-Universitaet zu Kiel, Institut fuer Experimentelle und Angewandte Physik, Kiel (Germany); Minar, J.; Ebert, H. [University of Munich, Dept. Chemie und Biochemie, Muenchen (Germany)

    2006-01-01

    Small Mn clusters (Mn{sub 1}-Mn{sub 4}) are prepared by manipulation of Mn adatoms on Ag(111) with the tip of a scanning tunnelling microscope. The apparent heights of the clusters are observed to increase monotonously from 1.6 A for a monomer to 2.2 A for a tetramer. Self-consistent calculations of the electronic structure of these clusters are in encouraging agreement with the experimental data. (orig.)

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

    OpenAIRE

    Kuchiev, M. Yu.; Robinson, D.J.

    2007-01-01

    Electron-positron pair creation due to combined nuclear Coulomb and strong laser fields is investigated for the tunneling regime. The energy spectra and angular distributions of the pair are found analytically for the first time. The energy spectrum for each lepton exhibits a sharp maximum located well above the threshold for any polarization of the laser field. The angular distributions of leptons depend on the polarization: for the linear polarization both leptons move predominantly along t...

  6. Electron Tunneling and Hopping Possibilites in RuO2 Thick Films

    OpenAIRE

    Halder, N. C.

    1983-01-01

    It is proposed in this paper that the temperature coefficient of resistivity (TCR) in thick film resistors arises from (i) the usual particle-to-particle conduction, (ii) electron tunneling, and (iii) the phononassisted hopping. Equations for activation energies are derived for the temperature minimum of the resistance with and without hopping. New equations for TCR are suggested. Some extensive calculations of TCR and activation energy have been made for RuO2 thick film resistors, the result...

  7. Room-temperature operation of a tunneling hot-electron transfer amplifier

    Science.gov (United States)

    Moise, T. S.; Kao, Y.-C.; Seabaugh, A. C.

    1994-02-01

    We demonstrate a tunneling hot-electron transfer amplifier that exhibits both dc and rf current gain at room temperature. The measured peak common-emitter current gain of the transistor approaches 7 while the dc differential gain is close to 10. S-parameter measurements, performed at a current density of 1.8×104 A cm-2, yield a current gain cutoff frequency of 6 GHz and a maximum frequency of oscillation of 12.5 GHz.

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

    International Nuclear Information System (INIS)

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

  9. STM Study of Encapsulated Nanometer Size Gold Clusters: Room Temperature Single Electron Tunneling Effects

    Science.gov (United States)

    Hong, S.; Bielefeld, J. D.; Andres, R. P.; Reifenberger, R.

    1997-03-01

    New measurements of I(V,z) from nanometer-size crystalline Au clusters using an UHV STM are reported. In contrast to previous studies,[1,2,3] Au clusters are now encapsulated by dodecanethiol molecules. After encapsulation, the clusters are deposited on either a freshly cleaved MoS2 substrate or on a Au(111) film coated with a self assembled monolayer (SAM) of a double ended thiol, p-xylene-?,?'-dithiol (C_8H_10S2 ). STM images of the encapsulated clusters supported on either substrate reveal a regular, hexagonal closed packed array. I(V,Z) data obtained from isolated clusters exhibit reproducible single electron tunneling behavior. By using the same STM tip, the size dependence of the single electron tunneling features in the I(V,z) data can be studied reliably. By fitting the measured I(V,z) data to the semiclassical theory for Coulomb blockade, the electronic properties of the tunnel junction between cluster and substrate can be determined. \\vspace11pt [1]. M. Dorogi, et al., Phys. Rev. B52, 9071 (1995). [2]. R.P. Andres, et al., Science 272, 1323 (1996). [3]. Samanta, et al., Phys. Rev. B53, 7626 (1996).

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

    DEFF Research Database (Denmark)

    Zhang, Jingdong; Chi, Qijin; Nazmutdinov, R. R.; Zinkicheva, T. T.; Bronshtein, M. D.

    2009-01-01

    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...... 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...... 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...

  11. Three-Dimensional S-Matrix Simulation of Single-Electron Resonant Tunnelling Through Random Ionised Donor States

    OpenAIRE

    MIZUTA, HIROSHI

    1998-01-01

    This paper presents a numerical study of single-electron resonant tunnelling (RT) assisted by a few ionised donors in a laterally-confined resonant tunnelling diode (LCRTD). The 3D multi-mode S-matrix simulation is performed newly introducing the scattering potential of discrete impurities. With a few ionised donors being placed, the calculated energy-dependence of the total transmission rate shows new resonances which are donor-configuration dependent. Visualised electron probability density...

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

    OpenAIRE

    Friis, Esben P.; Jens E. T. Andersen; Kharkats, Yu. I.; Kuznetsov, A. M.; Nichols, R.J.; Zhang, J.-D.; Ulstrup, Jens

    1999-01-01

    In situ scanning tunneling microscopy (STM) of redox molecules, in aqueous solution, shows interesting analogies and differences compared with interfacial electrochemical electron transfer (ET) and ET in homogeneous solution. This is because the redox level represents a deep indentation in the tunnel barrier, with possible temporary electronic population. Particular perspectives are that both the bias voltage and the overvoltage relative to a reference electrode ca...

  13. Magnetic control of resonant tunneling and Kondo effect in a one-electron double quantum dot

    CERN Document Server

    Schr"oer, D M; Eberl, K; Ludwig, S; Kiselev, M N; Altshuler, B L

    2006-01-01

    We present first transport measurements of the Kondo effect in a double quantum dot charged with only one or two electrons, respectively. For the one electron case we observe a surprising quasi-periodic oscillation of the Kondo conductance as a function of a small perpendicular magnetic field |B| \\lesssim 50mT. We interpret this behavior by means of a fine tuning of the interdot tunnel coupling. Such a magnetic field dependent coupling implies important consequences for applications in quantum information processing.

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

    CERN Document Server

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

    2010-01-01

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

  15. Probing flexible conformations in molecular junctions by inelastic electron tunneling spectroscopy

    International Nuclear Information System (INIS)

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

  16. 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.

  17. Single-electron tunneling by using a two-dimensional Corbino nano-scale disk

    Directory of Open Access Journals (Sweden)

    H. Taira

    2015-09-01

    Full Text Available We investigate a single-electron tunneling effect of two-dimensional electron systems formed in the Corbino nano-scale disk. By controlling bias and gate voltages, the transistor using this effect is able to control electrons one by one. The present study focuses on the electronic transmission probability affected by the charging energy in the Corbino-type single-electron transistor. We reformulated the Schrödinger equation for an electron in the Corbino disk in order to consider the effect of the curvature of the disk, taking into account the charging effect on the performance of the Corbino-type single-electron transistor. We formulated the transmission probability of the electron by applying the Wentzel-Kramers-Brillouin (WKB method. The electron’s energy in the formula of the transmission probability is then associated to the energy eigenvalue of the Schrödinger equation for an electron in an effective confining potential. We numerically solved the Schrödinger equation to evaluate the transmission probability. Our results show that the transmission probability strongly depends on the charging energy stored in the Corbino disk depending on its size.

  18. Vibrational Properties of h-BN and h-BN-Graphene Heterostructures Probed by Inelastic Electron Tunneling Spectroscopy

    Science.gov (United States)

    Jung, Suyong; Park, Minkyu; Park, Jaesung; Jeong, Tae-Young; Kim, Ho-Jong; Watanabe, Kenji; Taniguchi, Takashi; Ha, Dong Han; Hwang, Chanyong; Kim, Yong-Sung

    2015-01-01

    Inelastic electron tunneling spectroscopy is a powerful technique for investigating lattice dynamics of nanoscale systems including graphene and small molecules, but establishing a stable tunnel junction is considered as a major hurdle in expanding the scope of tunneling experiments. Hexagonal boron nitride is a pivotal component in two-dimensional Van der Waals heterostructures as a high-quality insulating material due to its large energy gap and chemical-mechanical stability. Here we present planar graphene/h-BN-heterostructure tunneling devices utilizing thin h-BN as a tunneling insulator. With much improved h-BN-tunneling-junction stability, we are able to probe all possible phonon modes of h-BN and graphite/graphene at ? and K high symmetry points by inelastic tunneling spectroscopy. Additionally, we observe that low-frequency out-of-plane vibrations of h-BN and graphene lattices are significantly modified at heterostructure interfaces. Equipped with an external back gate, we can also detect high-order coupling phenomena between phonons and plasmons, demonstrating that h-BN-based tunneling device is a wonderful playground for investigating electron-phonon couplings in low-dimensional systems. PMID:26563740

  19. Vibrational Properties of h-BN and h-BN-Graphene Heterostructures Probed by Inelastic Electron Tunneling Spectroscopy.

    Science.gov (United States)

    Jung, Suyong; Park, Minkyu; Park, Jaesung; Jeong, Tae-Young; Kim, Ho-Jong; Watanabe, Kenji; Taniguchi, Takashi; Ha, Dong Han; Hwang, Chanyong; Kim, Yong-Sung

    2015-01-01

    Inelastic electron tunneling spectroscopy is a powerful technique for investigating lattice dynamics of nanoscale systems including graphene and small molecules, but establishing a stable tunnel junction is considered as a major hurdle in expanding the scope of tunneling experiments. Hexagonal boron nitride is a pivotal component in two-dimensional Van der Waals heterostructures as a high-quality insulating material due to its large energy gap and chemical-mechanical stability. Here we present planar graphene/h-BN-heterostructure tunneling devices utilizing thin h-BN as a tunneling insulator. With much improved h-BN-tunneling-junction stability, we are able to probe all possible phonon modes of h-BN and graphite/graphene at ? and K high symmetry points by inelastic tunneling spectroscopy. Additionally, we observe that low-frequency out-of-plane vibrations of h-BN and graphene lattices are significantly modified at heterostructure interfaces. Equipped with an external back gate, we can also detect high-order coupling phenomena between phonons and plasmons, demonstrating that h-BN-based tunneling device is a wonderful playground for investigating electron-phonon couplings in low-dimensional systems. PMID:26563740

  20. Vibrational Properties of h-BN and h-BN-Graphene Heterostructures Probed by Inelastic Electron Tunneling Spectroscopy

    Science.gov (United States)

    Jung, Suyong; Park, Minkyu; Park, Jaesung; Jeong, Tae-Young; Kim, Ho-Jong; Watanabe, Kenji; Taniguchi, Takashi; Ha, Dong Han; Hwang, Chanyong; Kim, Yong-Sung

    2015-11-01

    Inelastic electron tunneling spectroscopy is a powerful technique for investigating lattice dynamics of nanoscale systems including graphene and small molecules, but establishing a stable tunnel junction is considered as a major hurdle in expanding the scope of tunneling experiments. Hexagonal boron nitride is a pivotal component in two-dimensional Van der Waals heterostructures as a high-quality insulating material due to its large energy gap and chemical-mechanical stability. Here we present planar graphene/h-BN-heterostructure tunneling devices utilizing thin h-BN as a tunneling insulator. With much improved h-BN-tunneling-junction stability, we are able to probe all possible phonon modes of h-BN and graphite/graphene at ? and K high symmetry points by inelastic tunneling spectroscopy. Additionally, we observe that low-frequency out-of-plane vibrations of h-BN and graphene lattices are significantly modified at heterostructure interfaces. Equipped with an external back gate, we can also detect high-order coupling phenomena between phonons and plasmons, demonstrating that h-BN-based tunneling device is a wonderful playground for investigating electron-phonon couplings in low-dimensional systems.

  1. Bistability of single cyclooctadiene molecules on Si(001) induced by inelastic electron tunneling

    Energy Technology Data Exchange (ETDEWEB)

    Nacci, Christophe; Lagoute, Jerome; Liu, Xi; Foelsch, Stefan [Paul Drude Institute for Solid-State Electronics, Hausvogteiplatz 5-7, 10117 Berlin (Germany)

    2008-07-01

    The tip-induced switching of single 1,5 cyclooctadiene molecules (COD) on Si(001) was studied by low-temperature scanning tunneling microscopy. COD (C{sub 8}H{sub 12}) is a cyclic alkene with a twisted boat double-degenerate configuration which adsorbs in two different structures: the so-called bridge structure and the upright structure, with the bridge structure being the prevalent conformation. Time spectroscopy of the tunnel current with the tip positioned over the molecule adsorbed in the bridge structure reveals fluctuations between two levels of current reminiscent to statistical telegraph noise. This behavior is interpreted as a reversible dynamic switching of the adsorbed molecule between two degenerate conformations triggered by inelastic single-electron excitation. First measurements on COD adsorbed in the upright structure reveal a significantly different noise response with an enhanced quantum yield and a lifted degeneracy of the current level population probabilities.

  2. Electron radiation effect on excess currents of GaSb tunnel diodes

    International Nuclear Information System (INIS)

    Straight lines of the volt ampere characteristics VAC of GaSb tunnel diodes were investigated. Four sections with different current transfer mechanisms are distinguished in the region of excess currents on the VAC of intact diodes. An increase in the excess current accompanied by a change in the current transfer mechanisms is observed on certain VAC sections following irradiation by 2.2 MeV electrons. The increase in the excess current is related to the formation and rearrangement of radiation defects responsible for shallow and deep levels in the forbidden GaSb zone. The energy levels measured by method of tunnel spectroscopy are found to be: Esub(c)-0.060 and Esub(c)-0.2 eV in the n-region of the p-n-transition

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

    International Nuclear Information System (INIS)

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

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

    CERN Document Server

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

    2014-01-01

    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...

  5. Tunneling hot-electron transfer amplifier: A hot-electron GaAs device with current gain

    Science.gov (United States)

    Heiblum, M.; Thomas, D. C.; Knoedler, C. M.; Nathan, M. I.

    1985-11-01

    Tunneling hot-electron transfer amplifier (THETA) devices, based on GaAs-AlGaAs heterojunctions, were fabricated and tested. Hot-electron transfer (?) through a 1100-Å base in excess of 70% was found at 4.2 K. This resulted in a corresponding current gain ( ?) in a common emitter configuration of about 2.3. In the temperature range of 4.2-80 K and under constant biasing conditions, ? was nearly temperature independent. Electron energy distributions for motion normal to the layers and electron total energy loss while traversing the device were estimated. Typical widths of the energy distributions were less than 200 meV, and both widths and energy peak positions were only slightly dependent on temperature and initial injection energy.

  6. Single-electron tunneling by using a two-dimensional Corbino nano-scale disk

    Science.gov (United States)

    Taira, H.; Suzuki, A.

    2015-09-01

    We investigate a single-electron tunneling effect of two-dimensional electron systems formed in the Corbino nano-scale disk. By controlling bias and gate voltages, the transistor using this effect is able to control electrons one by one. The present study focuses on the electronic transmission probability affected by the charging energy in the Corbino-type single-electron transistor. We reformulated the Schrödinger equation for an electron in the Corbino disk in order to consider the effect of the curvature of the disk, taking into account the charging effect on the performance of the Corbino-type single-electron transistor. We formulated the transmission probability of the electron by applying the Wentzel-Kramers-Brillouin (WKB) method. The electron's energy in the formula of the transmission probability is then associated to the energy eigenvalue of the Schrödinger equation for an electron in an effective confining potential. We numerically solved the Schrödinger equation to evaluate the transmission probability. Our results show that the transmission probability strongly depends on the charging energy stored in the Corbino disk depending on its size.

  7. 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)

  8. Electron-phonon coupling in C{sub 60} as revealed by scanning tunneling spectroscopy

    Energy Technology Data Exchange (ETDEWEB)

    Franke, Katharina J.; Schulze, Gunnar; Pascual, Jose Ignacio [Freie Universitaet Berlin (Germany); Frederiksen, Thomas; Arnau, Andres [Donostia International Physics Center, Donostia (Spain); Monturet, Sergio [Universite Paul Sabatier, Toulouse (France); Lorente, Nicolas [Centro de Investigaciones en Nanociencia y Nanotecnologia, Bellaterra (Spain)

    2008-07-01

    Electron-phonon coupling is of major importance for charge transport through single molecule tunneling junctions. In most experimental implementations of molecular junctions the electronic coupling of the molecular orbitals with substrate states leads to a significant broadening, thus obscuring electron-phonon coupling effects. Here, we investigate the electronic structure of single C{sub 60} molecules adsorbed on top of a self-assembled pattern of alternating tetraphenyladamantane and C{sub 60}. Scanning tunnelling spectroscopy reveals that these molecules exhibit properties similar to the free molecule, such as a large gap of 3.7 eV and a narrow LUMO resonance of only {approx}60 meV line width. The LUMO resonance is followed by a broad weaker peak at about 240 meV higher energy. By density functional calculations including the Jahn-Teller effect, we show that this broad feature is induced by a complex coupling of the C{sub 60} vibrational eigenmodes with the LUMO resonance.

  9. Atomic-scale mapping of electronic structures across heterointerfaces by cross-sectional scanning tunneling microscopy

    Science.gov (United States)

    Chiu, Ya-Ping; Huang, Bo-Chao; Shih, Min-Chuan; Huang, Po-Cheng; Chen, Chun-Wei

    2015-09-01

    Interfacial science has received much attention recently based on the development of state-of-the-art analytical tools that can create and manipulate the charge, spin, orbital, and lattice degrees of freedom at interfaces. Motivated by the importance of nanoscale interfacial science that governs device operation, we present a technique to probe the electronic characteristics of heterointerfaces with atomic resolution. In this work, the interfacial characteristics of heteroepitaxial structures are investigated and the fundamental mechanisms that pertain in these systems are elucidated through cross-sectional scanning tunneling microscopy (XSTM). The XSTM technique is employed here to directly observe epitaxial interfacial structures and probe local electronic properties with atomic-level capability. Scanning tunneling microscopy and spectroscopy experiments with atomic precision provide insight into the origin and spatial distribution of electronic properties across heterointerfaces. The first part of this report provides a brief description of the cleavage technique and spectroscopy analysis in XSTM measurements. The second part addresses interfacial electronic structures of several model heterostructures in current condensed matter research using XSTM. Topics to be discussed include high-?‘s/III-V’s semiconductors, polymer heterojunctions, and complex oxide heterostructures, which are all material systems whose investigation using this technique is expected to benefit the research community. Finally, practical aspects and perspectives of using XSTM in interface science are presented.

  10. Electronic neural network for dynamic resource allocation

    Science.gov (United States)

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

    1991-01-01

    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.

  11. Improving Electronic Resources through Holistic Budgeting

    Science.gov (United States)

    Kusik, James P.; Vargas, Mark A.

    2009-01-01

    To establish a more direct link between its collections and the educational goals of Saint Xavier University, the Byrne Memorial Library has adopted a "holistic" approach to collection development. This article examines how traditional budget practices influenced the library's selection of resources and describes how holistic collection…

  12. Using Zapier with Trello for Electronic Resources Troubleshooting Workflow

    OpenAIRE

    Meghan Finch

    2014-01-01

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

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

    OpenAIRE

    Micaela Waldman

    2003-01-01

    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 correl...

  14. Euler European Libraries and Electronic Resources in Mathematical Sciences

    CERN Document Server

    The Euler Project. Karlsruhe

    The European Libraries and Electronic Resources (EULER) Project in Mathematical Sciences provides the EulerService site for searching out "mathematical resources such as books, pre-prints, web-pages, abstracts, proceedings, serials, technical reports preprints) and NetLab (for Internet resources), this outstanding engine is capable of simple, full, and refined searches. It also offers a browse option, which responds to entries in the author, keyword, and title fields. Further information about the Project is provided at the EULER homepage.

  15. 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

  16. Single electron turnstile and pump devices using long arrays of small tunnel junctions

    International Nuclear Information System (INIS)

    We have investigated, both experimentally and numerically, single electron tunneling devices of interest for current standard applications. The devices consist of long arrays of small tunnel junctions with gate electrodes capacitively coupled to electrodes inside the arrays. Experiments on arrays of 25 small aluminum tunnel junctions with a single gate electrode capacitively coupled to the center of the array (an ''array turnstile'') have been performed at temperatures down to 40 mK. We observe sharp steps in the I-V characteristics at currents I = ±ef when an rf-signal of frequency f is applied to the gate electrode. The sharp steps can be obtained even without any compensation for background charge. Numerical simulations of a similar device (an ''array pump'') are also presented. This device consists of an array with two gate electrodes where two rf signals with a phase shift of 90deg may be applied. The size of the voltage steps in the I-V characteristics are investigated as a funtion of several parameters. For instance, the dependence of electrode capacitance, number of junctions, and background charge is investigated. (orig.)

  17. Integrating Electronic Resources into the Library Catalog: A Collaborative Approach.

    Science.gov (United States)

    Herrera, Gail; Aldana, Lynda

    2001-01-01

    Describes a project at the University of Mississippi Libraries to catalog purchased electronic resources so that access to these resources is available only via the Web-based library catalog. Discusses collaboration between cataloging and systems personnel; and describes the MARC catalog record field that contains the information needed to locate…

  18. Using XML Technologies to Organize Electronic Reference Resources

    OpenAIRE

    Huser, Vojtech; Del Fiol, Guilherme; Rocha, Roberto A.

    2005-01-01

    Provision of access to reference electronic resources to clinicians is becoming increasingly important. We have created a framework for librarians to manage access to these resources at an enterprise level, rather than at the individual hospital libraries. We describe initial project requirements, implementation details, and some preliminary results.

  19. Access to electronic resources by visually impaired people

    OpenAIRE

    Jenny Craven

    2003-01-01

    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.

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

    CERN Document Server

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

    2005-01-01

    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.

  1. Tunneling hot electron transfer amplifiers /theta/ - Amplifiers operating up to the infrared

    Science.gov (United States)

    Heiblum, M.

    1981-04-01

    A family of three-terminal devices that relies on the transfer of a quasi-monoenergetic hot electron beam through a thin base is described. The results are reviewed and reasons for the poor performances are suggested. The prediction is made that, with a proper choice of parameters, metal-base amplifiers can operate as switches, negative resistance devices, and continuous amplifiers in the subpicosecond range. The two subclasses described are the tunneling emitter (THETA) and the nontunneling emitter (BHETA) amplifiers. In the THETA family, the metal-oxide-metal-oxide-metal (MOMOM), the MOM-semiconductor (MOMS), and the heterojunctions devices are analyzed. It is noted that members of the BHETA family generate quasi-monoenergetic electron beams by injecting electrons by n(+)n(-) or metal-n(-) and that they include a variety of metals and semiconductor combinations.

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

    International Nuclear Information System (INIS)

    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

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

    Energy Technology Data Exchange (ETDEWEB)

    Li, Wei [National Institute of Standards and Technology, Gaithersburg, Maryland 20899 (United States); Key Laboratory for the Physics and Chemistry of Nanodevices and Department of Electronics, Peking University, Beijing 100871 (China); Zhang, Qin; Kirillov, Oleg A.; Levin, Igor; Richter, Curt A.; Gundlach, David J.; Nguyen, N. V., E-mail: Nhan.Nguyen@nist.gov, E-mail: liangxl@pku.edu.cn [National Institute of Standards and Technology, Gaithersburg, Maryland 20899 (United States); Bijesh, R.; Datta, S. [Department of Electrical Engineering, The Pennsylvania State University, University Park, Pennsylvania 16802 (United States); Liang, Yiran; Peng, Lian-Mao; Liang, Xuelei, E-mail: Nhan.Nguyen@nist.gov, E-mail: liangxl@pku.edu.cn [Key Laboratory for the Physics and Chemistry of Nanodevices and Department of Electronics, Peking University, Beijing 100871 (China)

    2014-11-24

    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 Al{sub 2}O{sub 3}/InAs/GaSb layer structure, the barrier height from the top of the InAs and GaSb valence bands to the bottom of the Al{sub 2}O{sub 3} conduction band is inferred from electron emission whereas hole emissions reveal the barrier height from the top of the Al{sub 2}O{sub 3} 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.

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

    International Nuclear Information System (INIS)

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

  5. Consecutive Charging of a Molecule-on-Insulator Ensemble Using Single Electron Tunnelling Methods.

    Science.gov (United States)

    Rahe, Philipp; Steele, Ryan P; Williams, Clayton C

    2016-02-10

    We present the local charge state modification at room temperature of small insulator-supported molecular ensembles formed by 1,1'-ferrocenedicarboxylic acid on calcite. Single electron tunnelling between the conducting tip of a noncontact atomic force microscope (NC-AFM) and the molecular islands is observed. By joining NC-AFM with Kelvin probe force microscopy, successive charge build-up in the sample is observed from consecutive experiments. Charge transfer within the islands and structural relaxation of the adsorbate/surface system is suggested by the experimental data. PMID:26713686

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

    Czech Academy of Sciences Publication Activity Database

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

    2011-01-01

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

  7. 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

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

    OpenAIRE

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

    2005-01-01

    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 a...

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

    DEFF Research Database (Denmark)

    Zhang, Jingdong; Kuznetsov, A.M.; Ulstrup, Jens

    2003-01-01

    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...... 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...

  10. A low temperature scanning tunneling microscope for electronic and force spectroscopy

    International Nuclear Information System (INIS)

    In this article, we describe and test a novel way to extend a low temperature scanning tunneling microscope with the capability to measure forces. The tuning fork that we use for this is optimized to have a high quality factor and frequency resolution. Moreover, as this technique is fully compatible with the use of bulk tips, it is possible to combine the force measurements with the use of superconductive or magnetic tips, advantageous for electronic spectroscopy. It also allows us to calibrate both the amplitude and the spring constant of the tuning fork easily, in situ and with high precision

  11. 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

  12. Building an electronic resource collection a practical guide

    CERN Document Server

    Lee, Stuart D

    2004-01-01

    This practical book guides information professionals step-by-step through building and managing an electronic resource collection. It outlines the range of electronic products currently available in abstracting and indexing, bibliographic, and other services and then describes how to effectively select, evaluate and purchase them.

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

    OpenAIRE

    Love-Rodgers, Christine; Stewart, Rowena

    2006-01-01

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

  14. Opto-electronic studies of semiconductor tunnelling structures and quantum wells

    International Nuclear Information System (INIS)

    This thesis describes optical and electrical studies of two groups of low dimensional semiconductor structures. The majority of the work concerns an optical study of electron populations (n1,n2) in the ground (E1) and first excited (E2) states of the quantum well (QW) regions of various GaAs-AlGaAs double and triple barrier resonant tunnelling structures (DBRTS and TBRTS respectively). The relative populations of the E2 and E1 confined states are determined from analysis of the photoluminescence (PL) intensities. When the structures are biased for tunnelling into the E2 state, rate equation analysis shows that n2/n1 is approximately equal to ?i/?1, where ?i is the E2-E1 intersubband scattering time and ?1 is the tunnelling-out time from E1. The relative electron populations are thus expected to be a sensitive function of the QW and collector barrier widths. The second group of structures studied in this thesis consists of a series of shallow GaAs-AlyGa1-yAs multi-quantum well structures, with aluminium concentrations of 1 to 4.5%. The 1s-2s exciton energy separation is measured from PL excitation (PLE) experiments and is combined with a small correction for the 2s binding energy to give an accurate determination of the exciton binding energy (Ex). It is found that even in these very shallow QW structures there is a marked enhancement in the value of Ex over that in 3D GaAs

  15. 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

  16. Resonant tunneling of 1-dimensional electrons across an array of 3-dimensionally confined potential wells

    Science.gov (United States)

    Allee, D. R.; Chou, S. Y.; Harris, J. S.; Pease, R. F. W.

    A lateral resonant tunneling field effect transistor has been fabricated with a gate electrode in the form of a railway such that the two rails form a lateral double barrier potential at the GaAs/AlGaAs interface. The ties confine the electrons in the third dimension forming an array of potential boxes or three dimensionally confined potential wells. The width of the ties and rails is 50nm; the spacings between the ties and between the two rails are 230nm and 150nm respectively. The ties are 750nm long and extend beyond the the two rails forming one dimensional wires on either side. Conductance oscillations are observed in the drain current at 4.2K as the gate voltage is scanned. Comparison with devices with a solid gate, and with a monorail gate with ties fabricated on the same wafer suggest that these conductance oscillations are electron resonant tunneling from one dimensional wires through the quasi-bound states of the three dimensionally confined potential wells. Comparison with a device with a two rail gate without ties (previously published) indicates that additional confinement due to the ties enhances the strength of the conductance oscillations.

  17. Proton coupled electron transfer tunneling reactions in WO3 and MoO3 nanostructured films

    Science.gov (United States)

    Gavrilyuk, A. I.

    2007-12-01

    WO3 and MoO3 are famous hydrogenphilics, hydrogen loving materials, capable of performing various functions concerning atomic hydrogen. They are active catalysts in photochemical reactions connected with detachment of hydrogen atoms, being, at the same time, capable of accomodating great quantities of the detached hydrogen atoms, and transporting them to other functional materials via employment of various heterostructures. It was shown that tunneling proton-coupled electron transfer is the mechanism of the photochemical hydrogen abstraction reaction on the surface of highly disordered nanostructured WO3 and MoO3 thin films. Specially selected hydrogen donor molecules were adsorbed on the oxide surface bonding via donor-acceptor and hydrogen bonds which yield a decrease in the energy barrier for the hydrogen transfer from the adsorbed hydrogen donor molecule to the oxide surface. The very rough and heterogeneous film surface yields space fluctuations of the energy barrier parameters whereas intermolecular vibrations yield time fluctuations; the fluctuative barrier preparation being responsible for the tunneling photo-stimulated proton-coupled electron transfer.

  18. Resonant tunneling assisted propagation and amplification of plasmons in high electron mobility transistors

    Science.gov (United States)

    Bhardwaj, Shubhendu; Sensale-Rodriguez, Berardi; Xing, Huili Grace; Rajan, Siddharth; Volakis, John L.

    2016-01-01

    A rigorous theoretical and computational model is developed for the plasma-wave propagation in high electron mobility transistor structures with electron injection from a resonant tunneling diode at the gate. We discuss the conditions in which low-loss and sustainable plasmon modes can be supported in such structures. The developed analytical model is used to derive the dispersion relation for these plasmon-modes. A non-linear full-wave-hydrodynamic numerical solver is also developed using a finite difference time domain algorithm. The developed analytical solutions are validated via the numerical solution. We also verify previous observations that were based on a simplified transmission line model. It is shown that at high levels of negative differential conductance, plasmon amplification is indeed possible. The proposed rigorous models can enable accurate design and optimization of practical resonant tunnel diode-based plasma-wave devices for terahertz sources, mixers, and detectors, by allowing a precise representation of their coupling when integrated with other electromagnetic structures.

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

    Science.gov (United States)

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

    2014-07-01

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

  20. Tunneling Hamiltonian

    OpenAIRE

    Kern, Johannes

    2013-01-01

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

  1. Inelastic electron tunneling through degenerate and nondegenerate ground state polymeric junctions

    International Nuclear Information System (INIS)

    Highlights: • Current–voltage characteristics of two polymeric junctions are studied. • Current is reduced in phonon assistant tunneling regime. • Behavior of current is independent of temperature. • Elastic energy changes current drastically. - Abstract: The inelastic electron transport properties through two polymeric (trans-polyacetylene and polythiophene) molecular junctions are studied using Keldysh nonequilibrium Green function formalism. The Hamiltonian of the polymers is described via Su–Schrieffer–Heeger model and the metallic electrodes are modeled by the wide-band approximation. Results show that the step-like behavior of the current–voltage characteristics is deformed in presence of strong electron–phonon interaction. Also, the magnitude of current is slightly decreased in the phonon assistant electron transport regime. In addition, it is observed that the I–V curves are independent of temperature

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

    Energy Technology Data Exchange (ETDEWEB)

    Storgards, J [Departamento de FIsica de Materiales, Facultad de Ciencias FIsicas, Universidad Complutense de Madrid, 28040 Madrid (Spain); Mendez, B [Departamento de FIsica de Materiales, Facultad de Ciencias FIsicas, Universidad Complutense de Madrid, 28040 Madrid (Spain); Piqueras, J [Departamento de FIsica de Materiales, Facultad de Ciencias FIsicas, Universidad Complutense de Madrid, 28040 Madrid (Spain); Chenot, M [Fraunhofer Institute for Solar Energy Systems, 79110 Freiburg (Germany); Dimroth, F [Fraunhofer Institute for Solar Energy Systems, 79110 Freiburg (Germany); Bett, A W [Fraunhofer Institute for Solar Energy Systems, 79110 Freiburg (Germany)

    2004-01-21

    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) using 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 the ternary compound and to donor-acceptor recombination are detected. In addition, with the aid of a scanning tunnelling microscope (STM), local electronic properties, such as conductance and surface energy gap, were studied in sample cross-sections. The results obtained from imaging and spectroscopy modes of STM enabled us to image the single AlGaSb layer.

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

    International Nuclear Information System (INIS)

    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) using 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 the ternary compound and to donor-acceptor recombination are detected. In addition, with the aid of a scanning tunnelling microscope (STM), local electronic properties, such as conductance and surface energy gap, were studied in sample cross-sections. The results obtained from imaging and spectroscopy modes of STM enabled us to image the single AlGaSb layer

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

    Energy Technology Data Exchange (ETDEWEB)

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

    2008-02-15

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

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

    International Nuclear Information System (INIS)

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

  6. Magnetooscillations of the tunneling current between two-dimensional electron systems

    International Nuclear Information System (INIS)

    We calculate electric current caused by electron tunnelling between two-dimensional layers in the magnetic field applied perpendicular to the layers. An elastic scattering of the electrons is taken into account. Analytical results are obtained for two regimes: i) small magnetic field, when the Landau quantization is suppressed by the scattering and the oscillatory part of the current shows nearly harmonic behaviour; ii) high magnetic field, when the Landau levels are well-defined and the conductivity shows series of sharp peaks corresponding to resonant magnetotunneling. In the last case, we used two alternative approaches: self-consistent Born approximation and path integral method, and compared obtained results. (author). 12 refs, 3 figs

  7. 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

  8. Developing an Electronic Resource Management System: Verde from Ex Libris

    Directory of Open Access Journals (Sweden)

    Tamar Sadeh

    2004-10-01

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

  9. Two-photon-induced hot-electron transfer to a single molecule in a scanning tunneling microscope

    International Nuclear Information System (INIS)

    The junction of a scanning tunneling microscope (STM) operating in the tunneling regime was irradiated with femtosecond laser pulses. A photoexcited 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 the polarization measurement. Spatial dependence of the electron-transfer rate exhibits atomic-scale variations. A two-pulse correlation experiment reveals the ultrafast dynamic nature of photoinduced charging process in the STM junction. Results from these experiments are important for understanding photoinduced interfacial charge transfer in many nanoscale inorganic-organic structures.

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

    CERN Document Server

    Viatkina, A V

    2014-01-01

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

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

    International Nuclear Information System (INIS)

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

  12. Why and How to Measure the Use of Electronic Resources

    Directory of Open Access Journals (Sweden)

    Jean Bernon

    2008-11-01

    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.

  13. Access to electronic resources by visually impaired people

    Directory of Open Access Journals (Sweden)

    Jenny Craven

    2003-01-01

    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.

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

    Directory of Open Access Journals (Sweden)

    Chung-Yen Yu

    2014-10-01

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

  15. Practical guide to electronic resources in the humanities

    CERN Document Server

    Dubnjakovic, Ana

    2010-01-01

    From full-text article databases to digitized collections of primary source materials, newly emerging electronic resources have radically impacted how research in the humanities is conducted and discovered. This book, covering high-quality, up-to-date electronic resources for the humanities, is an easy-to-use annotated guide for the librarian, student, and scholar alike. It covers online databases, indexes, archives, and many other critical tools in key humanities disciplines including philosophy, religion, languages and literature, and performing and visual arts. Succinct overviews of key eme

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

    Science.gov (United States)

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

    2015-03-01

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

  17. An atomic switch of electron propagation on Ge (001) by tunneling carrier injection

    Science.gov (United States)

    Komori, Fumio

    2008-03-01

    Reversible switching of electronic conduction through atom manipulation is one of the important subjects of nanoscience. However, different conducting pathways were not clearly observed with atomic resolution. We have demonstrated the correlation between the change of surface atomic position by tunneling carrier injection and that of the reflection of one-dimensional (1D) surface-state electrons on the Ge (001) surface with a low density of heterogeneous Sn-Ge dimers. [1] On the clean Ge(001) surface, two adjacent atoms form a buckled dimer, and the buckling orientation of the Ge dimer can be locally and reversibly controlled by carrier injection to the surface from the STM tip. [2] The unoccupied surface &*circ;-electron behaves like a 1D free electron along the Ge dimer row. When Sn atoms are deposited on the clean Ge(001) surface at room temperature, buckled dimers originating from the Sn atoms are formed at the Ge dimer position in the surface. [3] An atomic switch is realized for the &*circ; electrons in the Ge dimer- row direction by injection carriers to reversibly flip the buckling orientation of a single Sn-Ge dimer in the dimer row. When the Sn atom of the heterogeneous dimer is at the lower position, the 1D electrons are reflected and a standing wave of this state is observed. Whereas, when it is at the upper position, the 1D electrons pass through the heterogeneous dimer, and no standing wave is observed. In this state, the lower atom of the dimer is Ge, and the &*circ; state at the dimer is little different from that of the Ge-Ge dimers. [1] K. Tomatsu, K. Nakatsuji, T. Iimori, Y. Takagi, H. Kusuhara, A. Ishii, F. Komori; Science 315, 1696, 2007. [2] Y. Takagi, Y. Yoshimoto, K. Nakatsuji, F. Komori; Surf. Sci. 559, 1, 2004. [3] K. Tomatsu, K. Nakatsuji, T. Iimori, F. Komori; Surf. Sci. 601, 1736, 2007.

  18. Equilibrium and non-equilibrium electron tunneling via discrete quantum states

    OpenAIRE

    Deshmukh, Mandar M.; Bonet, Edgar; Pasupathy, A. N.; Ralph, D C

    2001-01-01

    Tunneling is measured via the quantum levels of a metal nanoparticle. We analyze quantitatively the resonance energies, widths, and amplitudes, both in the regime where only one state is accessible for tunneling and in the non-equilibrium regime when additional states are made accessible one-by-one. For tunneling through one state, our results agree with expectations for sequential tunneling, but in the non-equilibrium regime the resonances are broadened and shifted in ways ...

  19. Comment on ‘Germanium electron–hole bilayer tunnel field-effect transistors with a symmetrically arranged double gate’

    Science.gov (United States)

    Padilla, J. L.; Alper, C.; Gámiz, F.; Ionescu, A. M.

    2015-12-01

    In this comment we demonstrate that the inclusion of field-induced quantum confinement effects through appropriate discretization of conduction and valence bands refutes the suitability of a germanium electron–hole bilayer tunnel field-effect transistor with symmetrically arranged gates (Jeong et al 2015 Semicond. Sci. Technol. 30 035021). Delayed alignment of the first electron and hole energy subbands in the central gated intrinsic channel region makes the onset of vertical band-to-band tunneling unattainable at low applied voltages for the metal workfunctions used by Jeong et al. Furthermore, quantization effects lead to the appearance of unavoidable parasitic lateral tunneling to the lightly doped drain-source region (LDD), which seriously degrades the switching behavior reported by Jeong et al.

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

    Energy Technology Data Exchange (ETDEWEB)

    Tsang, Juine Kai

    1980-01-01

    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.

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

    Science.gov (United States)

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

    2004-02-01

    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.

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

    Energy Technology Data Exchange (ETDEWEB)

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

    2011-06-22

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

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

    International Nuclear Information System (INIS)

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

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

    Directory of Open Access Journals (Sweden)

    Mohammad Javad Sharifi

    2009-01-01

    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.

  5. Probing the local environment of a single OPE3 molecule using inelastic tunneling electron spectroscopy

    Directory of Open Access Journals (Sweden)

    Riccardo Frisenda

    2015-12-01

    Full Text Available We study single-molecule oligo(phenylene ethynylenedithiol junctions by means of inelastic electron tunneling spectroscopy (IETS. The molecule is contacted with gold nano-electrodes formed with the mechanically controllable break junction technique. We record the IETS spectrum of the molecule from direct current measurements, both as a function of time and electrode separation. We find that for fixed electrode separation the molecule switches between various configurations, which are characterized by different IETS spectra. Similar variations in the IETS signal are observed during atomic rearrangements upon stretching of the molecular junction. Using quantum chemistry calculations, we identity some of the vibrational modes which constitute a chemical fingerprint of the molecule. In addition, changes can be attributed to rearrangements of the local molecular environment, in particular at the molecule–electrode interface. This study shows the importance of taking into account the interaction with the electrodes when describing inelastic contributions to transport through single-molecule junctions.

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

    Science.gov (United States)

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

    2014-10-01

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

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

    International Nuclear Information System (INIS)

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

  8. From the Inside Out: An Organizational View of Electronic Resources and Collection Development.

    Science.gov (United States)

    Younger, Jennifer A.

    2002-01-01

    Discusses electronic resources and collection development. Topics include how electronic resources are changing the world of access to information; how and why scholars and research libraries use electronic resources; digitization initiatives; knowledge and learning via the Web; archiving electronic resources; and building collections versus…

  9. Chiral Enhanced Phonon Excitations in Inelastic Electron Tunneling Spectroscopy of Graphene

    Science.gov (United States)

    Natterer, Fabian Donat

    2015-03-01

    In graphene, phonons are important agents for a wide range of phenomena; they mediate relaxation rates for hot carriers, they lead to van-Hove singularities, and they induce a renormalization of the Fermi velocity due to electron-phonon coupling and many-body interactions. The previous observations of phonons by inelastic electron tunneling spectroscopy (IETS) have been expandable in terms of detail and resolution, due to weak signals and other spectral features which inhibit a clear distinction between phonons and miscellaneous excitations. We find that utilizing a back gated graphene device, where the graphene charge carrier density can be varied in magnitude and sign, allows all the critical point graphene phonons with large density of states to be sampled by IETS with the scanning tunneling microscope, and in good agreement with density functional calculations. In addition, a strong overtone excitation at 360 meV is observed. Quite surprisingly, we observe all the graphene excitations are resonantly enhanced when the charge carrier type is switched, indicating that this amplification occurs whenever the inelastic transition allows a change in the graphene chirality. The chiral enhancement is observed to follow a linear trend with energy and reaches almost an order of magnitude for the highest transition. Our averaging technique suppresses charge carrier dependent excitations, while it improves the signal for inelastic transitions. This approach can be employed as a guide in advanced studies that are relying on gate tunable graphene devices, such as for the detection of spin, vibrational, or rotational excitations in adsorbates. Collaborators: Y. Zhao* , J. Wyrick* , W. Y. Ruan** , Y-H. Chan** , M-Y. Chou** , N. B. Zhitenev* , J. A. Stroscio* : * NIST/CNST, ** Georgia Tech, FDN appreciates funding from the SNF foundation under Project No. 148891.

  10. What Is the Future of Electronic Resource Management Systems?

    Science.gov (United States)

    Tijerina, Bonnie; King, Douglas

    2008-01-01

    In a time of constant change, sometimes it is worthwhile to ruminate on the future and how things ought to be. "Journal of Electronic Resources Librarianship" wanted to capture some of these ruminations from around the field in a new column called "E-Opinions from the Field" where readers are asked to send in their thoughts on a topic and respond…

  11. Think Locally: A Prudent Approach to Electronic Resource Management Systems

    Science.gov (United States)

    Gustafson-Sundell, Nat

    2011-01-01

    A few articles have drawn some amount of attention specifically to the local causes of the success or failure of electronic resource management system (ERMS) implementations. In fact, it seems clear that local conditions will largely determine whether any given ERMS implementation will succeed or fail. This statement might seem obvious, but the…

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

    Science.gov (United States)

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

    1999-01-01

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

  13. Providing Access to Electronic Information Resources in Further Education

    Science.gov (United States)

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

    2004-01-01

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

  14. Electronic Resources: Access and Usage at Ashesi University College

    Science.gov (United States)

    Dadzie, Perpetua S.

    2005-01-01

    Purpose: Sets out to investigate the use of electronic resources by students and faculty of Ashesi University, Ghana, in order to determine the level of use, the type of information accessed and the effectiveness of the library's communication tools for information research. Design/methodology/approach: A questionnaire-based survey was utilized.…

  15. Student Satisfaction with Electronic Library Resources at Wayne State University

    Science.gov (United States)

    Holley, Robert P.; Powell, Ronald R.

    2004-01-01

    This paper reports the results of a survey of student satisfaction with electronic library resources other than the online catalog at Wayne State University. Undertaken in Fall Term 2000 as a class project for a marketing course, a student team designed, administered, and analyzed a survey of a random sample of students. Almost 40% of the…

  16. 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)

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

    2014-10-21

    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.

  17. 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.

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

    Science.gov (United States)

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

    2013-04-10

    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

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

    DEFF Research Database (Denmark)

    Frederiksen, Thomas; Munuera, C.; Ocal, C.; Brandbyge, Mads; Paulsson, Magnus; Sanchez-Portal, D.; Arnau, A.

    2009-01-01

    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 contact...

  20. The cosmo-nucleonic ultra-relativistic quantum electronic tunnelling (URQET) as EM-Signals of QGP

    International Nuclear Information System (INIS)

    The physical reality of nucleonic matters had been endeavoured as a process of super-relativistic cosmo-nucleonic quantum electronic tunnelling, coupling the two. The theory will be beneficial in disclosing the ways to regulate the nuclear synthesis, fusion, fission, solar flares and the cosmic events

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

    OpenAIRE

    Sanna Torma; Pertti Vakkari

    2004-01-01

    This study elaborated relations between digital library use by university faculty, users' discipline and the availability of key resources in the Finnish National Electronic Library (FinELib), Finnish national digital library, by using nationwide representative survey data. The results show that the perceived availability of key electronic resources by researchers in FinELib was a stronger predictor of the frequency and purpose of use of its services than users' discipline. Regardless of disc...

  2. Evaluating the appropriateness of electronic information resources for learning

    Science.gov (United States)

    Nolan, Nathanial S.

    2016-01-01

    Objectives Current US medical students have begun to rely on electronic information repositories—such as UpToDate, AccessMedicine, and Wikipedia—for their pre-clerkship medical education. However, it is unclear whether these resources are appropriate for this level of learning due to factors involving information quality, level of evidence, and the requisite knowledgebase. This study evaluated appropriateness of electronic information resources from a novel perspective: amount of mental effort learners invest in interactions with these resources and effects of the experienced mental effort on learning. Methods Eighteen first-year medical students read about three unstudied diseases in the above-mentioned resources (a total of fifty-four observations). Their eye movement characteristics (i.e., fixation duration, fixation count, visit duration, and task-evoked pupillary response) were recorded and used as psychophysiological indicators of the experienced mental effort. Post reading, students' learning was assessed with multiple-choice tests. Eye metrics and test results constituted quantitative data analyzed according to the repeated Latin square design. Students' perceptions of interacting with the information resources were also collected. Participants' feedback during semi-structured interviews constituted qualitative data and was reviewed, transcribed, and open coded for emergent themes. Results Compared to AccessMedicine and Wikipedia, UpToDate was associated with significantly higher values of eye metrics, suggesting learners experienced higher mental effort. No statistically significant difference between the amount of mental effort and learning outcomes was found. More so, descriptive statistical analysis of the knowledge test scores suggested similar levels of learning regardless of the information resource used. Conclusions Judging by the learning outcomes, all three information resources were found appropriate for learning. UpToDate, however, when used alone, may be less appropriate for first-year medical students' learning as it does not fully address their information needs and is more demanding in terms of cognitive resources invested. PMID:26807049

  3. Use of Electronic Resources in Degree College Libraries in Chandigarh

    Directory of Open Access Journals (Sweden)

    Jaspal Kaur Bhatia

    2011-11-01

    Full Text Available The electronic resources (e-resources available in a library play a prominent role in facilitating access to required information to the users in an easy and expeditious manner. The e-resources, like CD-ROM databases, online journals, online books, OPACs, and the internet, are slowly replacing the importance and usage of print media. A study of 11 degree colleges in Chandigarh, which have students and teachers strength of over 30000, was conducted. For the purpose of the study, a sample selected was 770 which included 60 students and 10 teachers from each of the colleges, respectively. The objectives of this study was to know the usage of e-resources and services by the users of degree college libraries in Chandigarh; find out the impediments encountered by the users while accessing and using the e-resources; and suggest measures to take full advantage of IT to make degree college libraries more digitally resourceful and for providing information services data from the users.teachers and students.to know the impact of e-resources. The data collected was analysed using simple percentage technique.

  4. Non-exponential tunneling and control of microwave absorption lineshapes via Fano resonance for electrons on Helium

    OpenAIRE

    Duki, Solomon; Mathur, Harsh

    2008-01-01

    We consider the application of a small in-plane magnetic field to electrons on a helium surface in a perpendicular magnetic field. Certain states that were bound to the helium surface then dissolve into the continuum turning into long-lived resonances. As a result microwave absorption lines acquire an asymmetric Fano lineshape that is tunable by varying the microwave polarisation or the in-plane magnetic field. Electrons trapped in a formerly bound state will tunnel off the surface of helium;...

  5. Insights into Solid-State Electron Transport through Proteins from Inelastic Tunneling Spectroscopy: The Case of Azurin.

    Science.gov (United States)

    Yu, Xi; Lovrincic, Robert; Sepunaru, Lior; Li, Wenjie; Vilan, Ayelet; Pecht, Israel; Sheves, Mordechai; Cahen, David

    2015-10-27

    Surprisingly efficient solid-state electron transport has recently been demonstrated through "dry" proteins (with only structural, tightly bound H2O left), suggesting proteins as promising candidates for molecular (bio)electronics. Using inelastic electron tunneling spectroscopy (IETS), we explored electron-phonon interaction in metal/protein/metal junctions, to help understand solid-state electronic transport across the redox protein azurin. To that end an oriented azurin monolayer on Au is contacted by soft Au electrodes. Characteristic vibrational modes of amide and amino acid side groups as well as of the azurin-electrode contact were observed, revealing the azurin native conformation in the junction and the critical role of side groups in the charge transport. The lack of abrupt changes in the conductance and the line shape of IETS point to far off-resonance tunneling as the dominant transport mechanism across azurin, in line with previously reported (and herein confirmed) azurin junctions. The inelastic current and hence electron-phonon interaction appear to be rather weak and comparable in magnitude with the inelastic fraction of tunneling current via alkyl chains, which may reflect the known structural rigidity of azurin. PMID:26381112

  6. Discipline, Availability of Electronic Resources and the Use of Finnish National Electronic Library-- FinELib

    Science.gov (United States)

    Törmä, Sanna; Vakkari, Pertti

    2004-01-01

    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…

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

    Science.gov (United States)

    White, Marilyn; Sanders, Susan

    2009-01-01

    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…

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

    CERN Document Server

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

    2004-01-01

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

  9. Increasing the efficiency of a silicon tunnel MIS injector of hot electrons by using high-K oxides

    Science.gov (United States)

    Vexler, M. I.

    2015-09-01

    It is demonstrated theoretically that replacing silicon dioxide in a metal-insulator-semiconductor (MIS) structure with a double-layer insulator HfO2(ZrO2)/SiO2 must lead to a decrease in the relative contribution of electrons with comparatively low energies to the total tunneling current. As a consequence, a suppression of the current component associated with the charge transport into the valence band of Si or from it is predicted for many regimes, especially of the low-energy part of this component. This effect can improve the efficiency of injection devices, such as a transistor with a tunnel MIS emitter or a resonant-tunneling diode based on a heavily doped MIS structure.

  10. Quantum tunnelling and classical above-barrier transitions in electron detachment from negative ions by negatively charged projectiles

    International Nuclear Information System (INIS)

    A simple model of electron detachment from negative ions by negatively charged projectile impact is developed as a combination of quantum tunnelling and classical field ionization. While the tunnelling theory has been discussed previously by Smirnov and Chibisov, we have substantially amended Solovevs classical model for above-barrier transition. As the most important modification we introduce the concept of decay rate for the classical ensemble related to the quantumstate and evaluate the rate in terms of the simple free-fall atomic model. The present theory compares very well with recent experiments while the isolated application of the tunnelling model and of the classical model yields results that are a factor of two too large and too small, respectively. (author)

  11. 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.)

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

    DEFF Research Database (Denmark)

    Zhang, Jingdong; Chi, Qijin

    2009-01-01

    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.

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

    DEFF Research Database (Denmark)

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

    2009-01-01

    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...... 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...

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

    Directory of Open Access Journals (Sweden)

    O.M. Voitsekhivska

    2011-12-01

    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.

  15. An electronic approach to evaluating healthcare Web resources.

    Science.gov (United States)

    Hodson-Carlton, K; Dorner, J L

    1999-01-01

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

  16. Laser Activated Electron Tunneling Based Mass Spectrometric Imaging of Molecular Architectures of Mouse Brain Revealing Regional Specific Lipids.

    Science.gov (United States)

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

    2016-01-01

    A comprehensive description of overall brain architecture at the molecular level is essential for understanding behavioral and cognitive processes in health and diseases. Although fluorescent labeling of target proteins has been successfully established to visualize a brain connectome, the molecular basis for diverse neurophysiological phenomena remains largely unknown. Here we report a brain-wide, molecular-level, and microscale imaging of endogenous metabolites, in particular, lipids of mouse brain by using laser activated electron tunneling (LAET) and mass spectrometry. In this approach, atomic electron emission along with finely tuned laser beam size provides high resolution that can be down to the sub-micrometer level to display spatial distribution of lipids in mouse brain slices. Electron-directed soft ionization has been achieved through exothermal capture of tunneling photoelectrons as well as unpaired electron-initiated chemical bond cleavages. Regionally specific lipids including saturated, mono-unsaturated, and poly-unsaturated fatty acids as well as other lipids, which may be implicated in neurological signaling pathways, have been discovered by using this laser activated electron tunneling based mass spectrometric imaging (LAET-MSI) technique. PMID:26613184

  17. 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)

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

    2010-12-01

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

  18. Room temperature observation of size dependent single electron tunneling in a sub-2 nm size tunable Pt nanoparticle embedded metal–oxide–semiconductor structure

    International Nuclear Information System (INIS)

    In this paper we report size dependent single electron tunneling behavior at room temperature in a metal–oxide–semiconductor structure with uniformly sized Pt nanoparticles embedded in an Al2O3 dielectric. The sub-2 nm size Pt nanoparticles sandwiched between the Al2O3 layers are deposited by a unique tilted target sputter deposition technique which produces metal nanoparticles as small as 0.5 nm with narrow size distributions at room temperature. The charging behavior of these nanoparticles shows clear single electron tunneling peaks due to the Coulomb blockade effect. Moreover, the average single electron addition energy and height of the single electron tunneling current strongly depend on the size of the Pt nanoparticle. These controllable single electron tunneling behaviors suggest a new route for fabrication of single electron devices.

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

    Science.gov (United States)

    Stachokas, George

    2009-01-01

    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…

  20. 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)

    England, Lenore; Fu, Li

    2011-01-01

    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…

  1. 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)

    England, Lenore; Fu, Li

    2011-01-01

    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…

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

    Science.gov (United States)

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

    1994-06-01

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

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

    Science.gov (United States)

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

    2006-10-01

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

  4. 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.

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

    Energy Technology Data Exchange (ETDEWEB)

    Yang, Zhichao, E-mail: zcyang.phys@gmail.com; Zhang, Yuewei; Nath, Digbijoy N.; Rajan, Siddharth [Department of Electrical and Computer Engineering, The Ohio State University, Columbus, Ohio 43210 (United States); Khurgin, Jacob B. [Department of Electrical and Computer Engineering, The Johns Hopkins University, Baltimore, Maryland 21218 (United States)

    2015-01-19

    We report on Gallium Nitride-based tunneling hot electron transistor amplifier with common-emitter current gain greater than 1. Small signal current gain up to 5 and dc current gain of 1.3?were attained in common-emitter configuration with collector current density in excess of 50?kA/cm{sup 2}. The use of a combination of 1?nm GaN/3?nm AlN layers as an emitter tunneling barrier was found to improve the energy collimation of the injected electrons. These results represent demonstration of unipolar vertical transistors in the III-nitride system that can potentially lead to higher frequency and power microwave devices.

  6. 2-dimensional hyperbolic medium for electrons and photons based on the array of tunnel-coupled graphene nanoribbons

    CERN Document Server

    Iorsh, Ivan

    2015-01-01

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

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

    International Nuclear Information System (INIS)

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

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

    International Nuclear Information System (INIS)

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

  9. Journals, Data and Abstracts Make an Integrated Electronic Resource

    Science.gov (United States)

    Boyce, P.

    1996-12-01

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

  10. Resonant Tunneling and Persistent Current of a Non-interacting and Weakly Interacting One-dimensional Electron Gas

    OpenAIRE

    Krive, I. V.; Sandström, P.

    1997-01-01

    The persistent current for a one-dimensional ring with two tunnel barriers is considered in the limit of weakly interacting electrons. In addition to a small off-resonance current, there are two kinds of resonant behavior; (i) a current independent of the barrier transparency (true resonance) and (ii) a current analogous to the one for a ring with only a single barrier (``semi''-resonance). For a given barrier transparency one or the other type of resonant behavior is realiz...

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

    International Nuclear Information System (INIS)

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

  12. 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 ...

  13. Analysis of Human Resources Management Strategy in China Electronic Commerce Enterprises

    Science.gov (United States)

    Shao, Fang

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

  14. 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

  15. Recognition tunneling

    International Nuclear Information System (INIS)

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

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

    International Nuclear Information System (INIS)

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

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

    Energy Technology Data Exchange (ETDEWEB)

    Galbiati, Marta; Tatay, Sergio; Delprat, Sophie; Khanh, Hung Le; Deranlot, Cyrile; Collin, Sophie; Seneor, Pierre, E-mail: pierre.seneor@thalesgroup.com; Mattana, Richard, E-mail: richard.mattana@thalesgroup.com; Petroff, Frédéric [Unité Mixte de Physique CNRS/Thales, 1 Av. A. Fresnel, 91767 Palaiseau, France and Université Paris-Sud, 91405 Orsay (France); Servet, Bernard [Thales Research and Technology, 1 Av. A. Fresnel, 91767 Palaiseau (France)

    2015-02-23

    Molecular and organic spintronics is an emerging research field which combines the versatility of chemistry with the non-volatility of spintronics. Organic materials have already proved their potential as tunnel barriers (TBs) or spacers in spintronics devices showing sizable spin valve like magnetoresistance effects. In the last years, a large effort has been focused on the optimization of these organic spintronics devices. Insertion of a thin inorganic tunnel barrier (Al{sub 2}O{sub 3} or MgO) at the bottom ferromagnetic metal (FM)/organic interface seems to improve the spin transport efficiency. However, during the top FM electrode deposition, metal atoms are prone to diffuse through the organic layer and potentially short-circuit it. This may lead to the formation of a working but undesired FM/TB/FM magnetic tunnel junction where the organic plays no role. Indeed, establishing a protocol to demonstrate the effective spin dependent transport through the organic layer remains a key issue. Here, we focus on Co/Al{sub 2}O{sub 3}/Alq{sub 3}/Co junctions and show that combining magnetoresistance and inelastic electron tunnelling spectroscopy measurements one can sort out working “organic” and short-circuited junctions fabricated on the same wafer.

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

    Science.gov (United States)

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

    2015-02-01

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

  19. Next Generation Networks for Distributed Electronic Resources: Opportunities and Challenges

    OpenAIRE

    Soysal, Murat

    2014-01-01

    The changes in the lifestyle of the people, new applications, technological developments and the telecommunication market drive the adoption Next Generation Network (NGN) as the new network architecture. NGN has a service-centric architecture which promotes agile creation of services and then maintenance of these services with end-to-end QoS support. In the current era, every internet user is a potential electronic resource user. Due to the transition from the traditional mode of collections ...

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

    Energy Technology Data Exchange (ETDEWEB)

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

    2012-06-04

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

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

    Science.gov (United States)

    Stachokas, George

    2009-01-01

    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…

  2. Effects of Electronic Information Resources Skills Training for Lecturers on Pedagogical Practices and Research Productivity

    Science.gov (United States)

    Bhukuvhani, Crispen; Chiparausha, Blessing; Zuvalinyenga, Dorcas

    2012-01-01

    Lecturers use various electronic resources at different frequencies. The university library's information literacy skills workshops and seminars are the main sources of knowledge of accessing electronic resources. The use of electronic resources can be said to have positively affected lecturers' pedagogical practices and their work in general. The…

  3. Magneto-tunnelling spectroscopy of chiral two-dimensional electron systems

    OpenAIRE

    Pratley, L; Zuelicke, U.

    2013-01-01

    We present a theoretical study of momentum-resolved tunneling between parallel two-dimensional conductors whose charge carriers have a (pseudo-)spin-1/2 degree of freedom that is strongly coupled to their linear orbital momentum. Specific examples are single and bilayer graphene as well as single-layer molybdenum disulphide. Resonant behavior of the differential tunneling conductance exhibited as a function of an in-plane magnetic field and bias voltage is found to be strongly affected by the...

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

    OpenAIRE

    Toroz, Dimitrios; Rontani, Massimo; Corni, Stefano

    2011-01-01

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

  5. Scanning-Tunneling Microscope Imaging of Single-Electron Solitons in a Material with Incommensurate Charge-Density Waves

    Science.gov (United States)

    Brazovskii, Serguei; Brun, Christophe; Wang, Zhao-Zhong; Monceau, Pierre

    2012-03-01

    We report on scanning-tunneling microscopy experiments in a charge-density wave (CDW) system allowing visually capturing and studying in detail the individual solitons corresponding to the self-trapping of just one electron. This “Amplitude Soliton” is marked by vanishing of the CDW amplitude and by the ? shift of its phase. It might be the realization of the spinon—the long-sought particle (along with the holon) in the study of science of strongly correlated electronic systems. As a distinct feature we also observe one-dimensional Friedel oscillations superimposed on the CDW which develop independently of solitons.

  6. Direct current and high frequency performance of thin film InP-based tunneling hot electron transfer amplifiers

    Science.gov (United States)

    Evers, N.; Laskar, J.; Jokerst, N. M.; Moise, T. S.; Kao, Y.-C.

    1997-05-01

    We report the dc and high frequency performance of thin-film InP-based tunneling hot electron transfer amplifiers bonded to a variety of host substrates. The high-frequency device performance is slightly degraded since the InP substrate removal and bonding process for these devices have not yet been optimized. This demonstration represents an important step toward the development of high-frequency, thin-film InP-based electronic devices integrated with conventional Si-based circuit elements.

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

    DEFF Research Database (Denmark)

    Frederiksen, Thomas; Munuera, C.

    2009-01-01

    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.

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

    Science.gov (United States)

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

    2013-02-01

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

  9. 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.)

  10. Electronic Document Management: A Human Resource Management Case Study

    Directory of Open Access Journals (Sweden)

    Thomas Groenewald

    2004-11-01

    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.

  11. Harnessing electronic information resources through prospective consortia approach: a national necessity

    OpenAIRE

    Vasishta, Seema; Dhingra, Navjyoti

    2007-01-01

    Earlier information resources were considered physical entities but now these have evolved from traditional print documents to electronically stored information resources. In this time of lessening finances, myriad forms of resources and rising expectations of user community, libraries face many challenges to operate competently. The demand to provide more electronic information resources often results in a need to find creative ways to get the most out of our limited financial resources. Pre...

  12. Pulse radiolysis study of electron tunneling in an 8 M NaOH glass between 4 and 100 K

    International Nuclear Information System (INIS)

    Pulse radiolysis experiments have been performed in an 8 M NaOH glass between 4 and 100 K and in the time range 10-6 to 10 s. The spur radius was estimated from the decay of the trapped electrons on the red side of the absorption maximum. The spur radius was about 4 nm at 80 K and increased to about 6 nm at 10 K. We studied the decay of trapped electrons in the presence of the following electron scavengers: CrO2-4, Fe(CN)3-6, and NO-2. No temperature dependence was found between 10 and 100 K. To explain the results distance-dependent and/or time-dependent Franck--Condon factors have been introduced. We show that in the time range studied it is not possible to distinguish between direct tunneling and trap-to-trap tunneling. Dry electron scavenging efficiencies and encounter pair formation are expressed in S37. For CrO2-4, Fe(CN)3-6, and NO-2 we found that S37 was 45, 130, and 300 M, respectively

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

    International Nuclear Information System (INIS)

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

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

    CERN Document Server

    Hassel, J; Seppä, H; Hakonen, P J

    2003-01-01

    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.

  15. Tunneling: From Milliseconds to Attoaseconds

    OpenAIRE

    Nimtz, Guenter

    2009-01-01

    How much time does a wave packet spent in tunneling a barrier? Quantum mechanical calculations result in zero time inside a barrier. In the nineties analogous tunneling experiments with microwaves were carried out confirming quantum mechanics. Electron tunneling time is hard to measure being extremely short. However, quite recently the atomic ionization tunneling time has been measured. Experimental data of photonic, phononic, and electronic tunneling time is available now. ...

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

    International Nuclear Information System (INIS)

    In this paper, the electronic transport characteristics of Fe/trans-polyacetylene/Fe magnetic tunnel junctions (MTJs) are investigated using multi-band tight-binding calculations within the framework of nonequilibrium Green function theory. A CH2 radical is added to different positions on the polymer chain and its effects on the tunnelling magnetoresistance of the MTJ are studied. The ferromagnetic electrodes are assumed to be single-band and their tight-binding parameters are chosen in such a way as to simulate the ab initio density functional calculations of the band structure of bcc-Fe along its [001] crystallographic direction. In building the Hamiltonian of the trans-polyacetylene (t-PA) chain, we have assumed an s orbital on the H atoms and one s and three p(px,py,pz) orbitals on the C atoms, and the dimerization effects are taken into account. It is found that moving the radical out of the centre of the polymer chain enhances the tunnelling magnetoresistance of the MTJ.

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

    Science.gov (United States)

    Abedi Ravan, B.

    2012-10-01

    In this paper, the electronic transport characteristics of Fe/trans-polyacetylene/Fe magnetic tunnel junctions (MTJs) are investigated using multi-band tight-binding calculations within the framework of nonequilibrium Green function theory. A CH2 radical is added to different positions on the polymer chain and its effects on the tunnelling magnetoresistance of the MTJ are studied. The ferromagnetic electrodes are assumed to be single-band and their tight-binding parameters are chosen in such a way as to simulate the ab initio density functional calculations of the band structure of bcc-Fe along its [001] crystallographic direction. In building the Hamiltonian of the trans-polyacetylene (t-PA) chain, we have assumed an s orbital on the H atoms and one s and three p(px,py,pz) orbitals on the C atoms, and the dimerization effects are taken into account. It is found that moving the radical out of the centre of the polymer chain enhances the tunnelling magnetoresistance of the MTJ.

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

    Science.gov (United States)

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

    2012-01-01

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

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

    Energy Technology Data Exchange (ETDEWEB)

    Moro-Melgar, Diego, E-mail: diego.moro-melgar@obspm.fr [Observatoire de Paris, LERMA, 77 avenue Denfert Rochereau 75014 Paris (France); Mateos, Javier, E-mail: javierm@usal.es; González, Tomás, E-mail: tomasg@usal.es; Vasallo, Beatriz G., E-mail: bgvasallo@usal.es [Departamento de Física Aplicada, Universidad de Salamanca, Plaza de la Merced s/n, 37008 Salamanca (Spain)

    2014-12-21

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

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

    International Nuclear Information System (INIS)

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

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

    Energy Technology Data Exchange (ETDEWEB)

    SCHNEIDER,LARRY X.

    2000-06-01

    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.

  2. 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

  3. Electron-tunneling studies on CeCoIn5 heavy-fermion thin films and microstructures

    International Nuclear Information System (INIS)

    In many cases, the availability of high-quality thin films of a material under study allows to gain valuable physical insight into its properties. For example, when thin films are available, planar tunneling spectroscopy or quantum mechanical interferometry techniques can be used to probe the electronic properties in a very direct way. In this work, we study the rich but poorly understood electronic properties of the heavy-fermion compound CeCoIn5. Numerous attempts to grow homogeneous CeCoIn5 thin films of the desired quality have not been successful. Our work therefore pursuits two goals: (1) to improve the CeCoIn5 thin film quality using the molecular beam epitaxy and (2) to investigate the low-temperature electronic properties of the CeCoIn5 thin films using direct probing methods.

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

    Directory of Open Access Journals (Sweden)

    M.V. Tkach

    2012-10-01

    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.

  5. Shaping a time-dependent excitation to control the electron distribution function: noise minimization in a tunnel junction

    OpenAIRE

    Gabelli, Julien; Reulet, Bertrand

    2012-01-01

    We report measurements of shot noise in a tunnel junction under bi-harmonic illumination, Vac(t) = Vac1 cos(2\\pi ft) + Vac2 cos(4\\pi ft+ \\phi). The experiment is performed in the quantum regime, hf >> k_BT at low temperature T = 70 mK and high frequency f = 10 GHz. From the measurement of noise at low frequency, we show that we can infer and control the non-equilibrium electronic distribution function by adjusting the amplitudes and phase of the excitation, thus modeling its shape. In particu...

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

    Energy Technology Data Exchange (ETDEWEB)

    Singh, Poonam; Dharmadhikari, C V [Centre for Advanced Studies in Materials Science and Solid State Physics, Department of Physics, University of Pune, Pune 411007 (India)

    2007-04-15

    Comparison of electron transport across dodecanethiol capped Au nanoclusters adsorbed in different locations viz. in an agglomeration, on isolated particle either on the terrace or at the step edge of highly oriented pyrolytic graphite using scanning tunneling microscopy / spectroscopy is carried out. Current-distance measurements on these different locations shows different regimes suggesting different mechanisms for electron transport. Current-voltage measurements at these locations have been carried out and the results are discussed in the light of orthodox theory for electron transport in double-barrier tunnel junction.

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

    Energy Technology Data Exchange (ETDEWEB)

    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

    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.

  8. 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

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

    OpenAIRE

    Kamble M.G; Ghante P. B.

    2012-01-01

    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.

  10. Electronic picture of spin-polarized tunneling with a Cr tip

    Energy Technology Data Exchange (ETDEWEB)

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

    2010-05-15

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

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

    Directory of Open Access Journals (Sweden)

    Ma Jing-Min

    2011-01-01

    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:

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

    OpenAIRE

    Zhong Wenjuan; Wu Xuezhi; Zhao Tieqin

    2014-01-01

    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 resource...

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

    Directory of Open Access Journals (Sweden)

    P?nar Al

    2003-04-01

    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.

  14. Plane-wave based electron tunneling through field emission resonance states

    OpenAIRE

    García-Lekue, Aran; Sánchez-Portal, Daniel; Arnau, Andrés; Wang, L W

    2013-01-01

    Field emission resonances (FERs) on Cu(100) surface are investigated by means of tunneling regime simulations performed with a plane-wave based transport calculation method. FERs are located near the surface and decay into the vacuum, and their accurate simulation requires a faithful description of vacuum states. This type of simulations is thus not possible using the popular transport methods based on atom-centered localized basis sets and the use of plane waves becomes important. We introdu...

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

    OpenAIRE

    Müllegger, Stefan; Tebi, Stefano; Das, Amal K.; Schöfberger, Wolfgang; Faschinger, Felix; Koch, Reinhold

    2014-01-01

    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 spectroscopy together wit...

  16. Ferroelectric tunnel junctions

    OpenAIRE

    Rodriguez Contreras, J.

    2004-01-01

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

  17. Universal Time Tunneling

    OpenAIRE

    Nimtz, Guenter

    2009-01-01

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

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

    OpenAIRE

    Aaron August Lupton; Marcia Kay Salmon

    2012-01-01

    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...

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

    OpenAIRE

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

    2011-01-01

    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...

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

    Energy Technology Data Exchange (ETDEWEB)

    Kuzmin, L [Chalmers University of Technology, S-41296 Gothenburg (Sweden)], E-mail: leonid.kuzmin@mc2.chalmers.se

    2008-02-01

    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.

  1. Design of a novel on-chip electronic refrigerator based on a normal-insulator-superconductor tunnel junction

    International Nuclear Information System (INIS)

    We present a design for a novel electronic refrigerator having a base temperature of about 18 mK when operating from a bath temperature as high as 1.5 K. This all-electronic refrigerator is a factor of 104 smaller and lighter than dilution and adiabatic demagnetization refrigerators, and is compatible with conventional photolithographic fabrication. The refrigerator, based on the unique thermal transport properties of a normal-insulator-superconductor (NIS) tunnel function, preferentially removes electrons whose energy is higher than the Fermi energy from a normal metal. Electrons with an average energy equal to the Fermi energy are returned to the metal by a superconductor contact. Consequently, high energy thermal excitations are removed from the normal metal, thus cooling the electrons. In our configuration, the junction is deposited on a Si3N4 membrane of submicron thickness that thermally isolates the normal electrode from the bath. As a result, both electrons and phonons in the metal are cooled below the bath temperature. We calculate a cooling power of 2 nW at 100 mK, and a base temperature of 18 mK for a refrigerator area of about 100X100?m2. Using 105 such refrigerator circuits, the cooling power can be increased to 200 ?W

  2. 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

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

    Directory of Open Access Journals (Sweden)

    S. A. Ketabi

    2003-12-01

    Full Text Available   In this paper, on the basis of tight-binding model and a generalized Green- function method as well as Lanczos algorithm procedure, the effects of the metal-molecule coupling(MMC strength on the electronic transmission through a metal-single molecule-metal(MMM system is investigated. Using the Landauer formalism we study some of the significant conductance properties of this system as a molecular wire. Our results show that with the increase of the length of the molecule, the conductance of the molecular wire decreases exponentially. With trans-polyacetylene (trans-PA as the molecule, we calculate a characteristic time for electron transmission through the MMM system. This time scale measures the delay caused by tunneling through the MMC. Our calculations show that the conductance is sensitive to the MMC strength. The focus is on the significant relationship between this time scale and the strength of the metal-molecule(trans-PA coupling.

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

    Science.gov (United States)

    DeLoach, Richard; Micol, John R.

    2011-01-01

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

  5. Electronic Safety Resource Tools -- Supporting Hydrogen and Fuel Cell Commercialization

    Energy Technology Data Exchange (ETDEWEB)

    Barilo, Nick F.

    2014-09-29

    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.

  6. eFG: an electronic resource for Fusarium graminearum.

    Science.gov (United States)

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

    2013-01-01

    Fusarium graminearum is a plant pathogen, which causes crop diseases and further leads to huge economic damage worldwide in past decades. Recently, the accumulation of different types of molecular data provides insights into the pathogenic mechanism of F. graminearum, and might help develop efficient strategies to combat this destructive fungus. Unfortunately, most available molecular data related to F. graminearum are distributed in various media, where each single source only provides limited information on the complex biological systems of the fungus. In this work, we present a comprehensive database, namely eFG (Electronic resource for Fusarium graminearum), to the community for further understanding this destructive pathogen. In particular, a large amount of functional genomics data generated by our group is deposited in eFG, including protein subcellular localizations, protein-protein interactions and orthologous genes in other model organisms. This valuable knowledge can not only help to disclose the molecular underpinnings of pathogenesis of the destructive fungus F. graminearum but also help the community to develop efficient strategies to combat this pathogen. To our best knowledge, eFG is the most comprehensive functional genomics database for F. graminearum until now. The eFG database is freely accessible at http://csb.shu.edu.cn/efg/ with a user-friendly and interactive interface, and all data can be downloaded freely. DATABASE URL: http://csb.shu.edu.cn/efg/ PMID:23798489

  7. Controlling user access to electronic resources without password

    Science.gov (United States)

    Smith, Fred Hewitt

    2015-06-16

    Described herein are devices and techniques for remotely controlling user access to a restricted computer resource. The process includes pre-determining an association of the restricted computer resource and computer-resource-proximal environmental information. Indicia of user-proximal environmental information are received from a user requesting access to the restricted computer resource. Received indicia of user-proximal environmental information are compared to associated computer-resource-proximal environmental information. User access to the restricted computer resource is selectively granted responsive to a favorable comparison in which the user-proximal environmental information is sufficiently similar to the computer-resource proximal environmental information. In at least some embodiments, the process further includes comparing user-supplied biometric measure and comparing it with a predetermined association of at least one biometric measure of an authorized user. Access to the restricted computer resource is granted in response to a favorable comparison.

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

    Directory of Open Access Journals (Sweden)

    Reuter Dirk

    2010-01-01

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

  9. Electronic Resource Management 2.0: Using Web 2.0 Technologies as Cost-Effective Alternatives to an Electronic Resource Management System

    Science.gov (United States)

    Murray, Adam

    2008-01-01

    Designed to assist with the management of e-resources, electronic resource management (ERM) systems are time- and fund-consuming to purchase and maintain. Questions of system compatibility, data population, and workflow design/redesign can be difficult to answer; sometimes those answers are not what we'd prefer to hear. The two primary functions…

  10. Organization of adenine on Ag(111) and correlated interfacial electronic structure measured with low temperature scanning tunneling microscopy

    Science.gov (United States)

    Pearl, Thomas P.; Andrews, Katie M.; Davis, Bryce F.

    2010-03-01

    Low temperature scanning tunneling microscopy and spectroscopy has been used to observe the organization of the nucleobase adenine on the Ag(111) surface as well as to resolve modifications to Ag(111) surface electronic structure. Multiple hydrogen bonding interactions between adenine adsorbates dictate the formation of dimers on the surface as well as long range order of molecular domains, which have limited commensuration with the Ag(111) lattice. Differential conductance spectroscopy recorded at 15 K reveals an upward energetic shift of the Shockley-type surface state native to Ag(111) from a band edge of -67 meV on the clean surface to+82.5 meV recorded over adenine islands. Differential conductance maps show free-electron like scattering in the adenine domains. Dispersion of the parallel wave vector of scattered electrons in the adenine domains is compared to the dispersion for electron scattering in bare silver and the ratio of effective masses for electrons in those bands is 1.1 ± 0.05. It is hypothesized that this shift occurs due to a combination of effects brought on by the adsorption of adenine including changes in work function and dipole-induced screening of the first image potential.

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

    Energy Technology Data Exchange (ETDEWEB)

    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

    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.

  12. Electron tunneling experiments on La-substituted Kondo-semiconductor CeRhAs

    International Nuclear Information System (INIS)

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

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

    International Nuclear Information System (INIS)

    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 104 photons/s for sensitive imaging applications by keeping the device far from saturation by employing an appropriate reset frequency

  14. 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

  15. Carrier-envelope phase-dependent electron tunneling in a coupled double-quantum-dot system driven by a few-cycle laser pulse

    International Nuclear Information System (INIS)

    We theoretically investigate the dependence of the electron tunneling on the carrier-envelope phase of a few-cycle laser pulse in a coupled double-quantum-dot system, and we show that the electron tunneling between coupled quantum dots is very sensitive to the carrier-envelope phase under a change of the parameters of the system. This in turn provides an additional means to measure the carrier-envelope phase of a laser pulse at lower laser intensity regime in the solid-state nanostructure.

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

    Directory of Open Access Journals (Sweden)

    ??? Li-Hsiang Lai

    2001-04-01

    Full Text Available

    ???85-97

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

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

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

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

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

    Science.gov (United States)

    Yamada, Toshishige; Kwak, Dochan (Technical Monitor)

    2000-01-01

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

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

    International Nuclear Information System (INIS)

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

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

    Directory of Open Access Journals (Sweden)

    Steven Shapiro

    2010-01-01

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

  20. Issues in Electronic Resource Services in K-12 School Library Settings.

    Science.gov (United States)

    Farmer, Leslie S. J.

    2002-01-01

    Discusses the unique factors that online electronic resources pose in school library settings. Topics include the appropriateness of online electronic resources; strategic planning for Internet access, including acceptable use policies; administrative issues; selection and acquisition; organization; and intellectual access, including library…

  1. What Do Libraries Really Do with Electronic Resources? The Practice in 2003

    Science.gov (United States)

    Shorten, Jay

    2005-01-01

    One hundred fourteen academic libraries in the United States and Canada are surveyed for the organization of electronic resources within their home page and their cataloguing practice. The majority provide access to databases, electronic resources, subject guides, ready reference, and their own catalogue both on their home page and within their…

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

    Science.gov (United States)

    England, Lenore; Fu, Li; Miller, Stephen

    2011-01-01

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

  3. Using a Decision Grid Process to Build Consensus in Electronic Resources Cancellation Decisions

    Science.gov (United States)

    Foudy, Gerri; McManus, Alesia

    2005-01-01

    Many libraries are expending an increasing part of their collections budgets on electronic resources. At the same time many libraries, especially those which are state funded, face diminishing budgets and high rates of inflation for serials subscriptions in all formats, including electronic resources. Therefore, many libraries need to develop ways…

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

    OpenAIRE

    Steven Shapiro

    2010-01-01

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

  5. Developing Humanities Collections in the Digital Age: Exploring Humanities Faculty Engagement with Electronic and Print Resources

    Science.gov (United States)

    Kachaluba, Sarah Buck; Brady, Jessica Evans; Critten, Jessica

    2014-01-01

    This article is based on quantitative and qualitative research examining humanities scholars' understandings of the advantages and disadvantages of print versus electronic information resources. It explores how humanities' faculty members at Florida State University (FSU) use print and electronic resources, as well as how they perceive these…

  6. Bridging the Two Cultures: A Collaborative Approach to Managing Electronic Resources.

    Science.gov (United States)

    Dupuis, John; Ryan, Patti

    2002-01-01

    Highlights an example of cross-discipline collaboration in an academic library and describes a collaborative approach to managing electronic resources that is used at York University (Canada). Explains a model in which a science librarian and a humanities/social science librarian work together to manage electronic resources. (Author/LRW)

  7. Electronic resource management practical perspectives in a new technical services model

    CERN Document Server

    Elguindi, Anne

    2012-01-01

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

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

    Science.gov (United States)

    Hulseberg, Anna; Monson, Sarah

    2009-01-01

    Electronic resources, the tools we use to manage them, and the needs and expectations of our users are constantly evolving; at the same time, the roles, responsibilities, and workflow of the library staff who manage e-resources are also in flux. Recognizing a need to be more intentional and proactive about how we manage e-resources, the…

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

    Science.gov (United States)

    Hulseberg, Anna; Monson, Sarah

    2009-01-01

    Electronic resources, the tools we use to manage them, and the needs and expectations of our users are constantly evolving; at the same time, the roles, responsibilities, and workflow of the library staff who manage e-resources are also in flux. Recognizing a need to be more intentional and proactive about how we manage e-resources, the…

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

    Science.gov (United States)

    Tenopir, Carol

    2003-01-01

    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…

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

    Energy Technology Data Exchange (ETDEWEB)

    Borovkov, Vsevolod I. [Institute of Chemical Kinetics and Combustion of SB RAS, ul. Institutskaya, 3, Novosibirsk 630090 (Russian Federation); Novosibirsk State University, ul. Pirogova, 2, Novosibirsk 630090 (Russian Federation)], E-mail: borovkov@kinetics.nsc.ru

    2008-10-15

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

  12. Room-temperature tunnel current amplifier and experimental setup for high resolution electronic spectroscopy in millikelvin STM experiments

    OpenAIRE

    Le Sueur, H.; Joyez, P

    2006-01-01

    The spectroscopic resolution of tunneling measurements performed with a scanning tunneling microscope is ultimately limited by the temperature at which the experiment is performed. To take advantage of the potential high spectroscopic resolution associated with operating an STM in a dilution refrigerator we have designed a room temperature tunnel current amplifier having very small back-action on the tunnel contact and allowing to nearly reach the predicted energy resolution...

  13. Cataloguing the Chameleon: A Guide to Electronic Resources

    OpenAIRE

    Cox, Joseph P.; Dekker, Jennifer

    1999-01-01

    This manual was created to bridge the gap in guidelines for describing internet resources during the long period when AACR2 was updating its rules for cataloguing. Librarians needed interim procedures and Cataloguing the Chameleon was a set of guidelines recommended by the Cataloguing Internet Resources Project based at the University of Toronto's Faculty of Information Studies.

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

    Science.gov (United States)

    Pan, Denise

    2009-01-01

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

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

    CERN Document Server

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

    1998-01-01

    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.

  16. Determination of carbide structures on an Mo(110) surface by scanning tunneling microscopy and low energy electron diffraction

    Science.gov (United States)

    Yu, De-Wei; Wu, Yi-Hsueh; Lin, Rong-Bin; Lo, Rong-Li

    2008-04-01

    Surface properties of transition metals can be modified considerably by forming carbide overlayers. In this study we fabricated molybdenum carbide overlayers by carburizing the Mo(110) surface with ethylene (C2H4) and successfully determined their real space structures by using low energy electron diffraction (LEED) and scanning tunneling microscopy (STM). With various carburization recipes, three carbon-terminated structures {\\scriptsize \\bigl (\\matrix {5 & 0 \\cr {-2} & 6 }\\bigr)} , (12 × 4)-2C, and (4 × 4) of coverages 1/30,1/24, and 1/16 monolayer (ML) were formed on the surface, respectively. Since the carbide overlayers were formed at high temperatures, inward diffusion of carbon atoms played a key role in structure formation.

  17. Determination of carbide structures on an Mo(110) surface by scanning tunneling microscopy and low energy electron diffraction

    International Nuclear Information System (INIS)

    Surface properties of transition metals can be modified considerably by forming carbide overlayers. In this study we fabricated molybdenum carbide overlayers by carburizing the Mo(110) surface with ethylene (C2H4) and successfully determined their real space structures by using low energy electron diffraction (LEED) and scanning tunneling microscopy (STM). With various carburization recipes, three carbon-terminated structures ((5)/-2/(0)/6), (12 x 4)-2C, and (4 x 4) of coverages 1/30,1/24, and 1/16 monolayer (ML) were formed on the surface, respectively. Since the carbide overlayers were formed at high temperatures, inward diffusion of carbon atoms played a key role in structure formation

  18. 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

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

    Energy Technology Data Exchange (ETDEWEB)

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

    1997-02-07

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

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

    CERN Document Server

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

    2009-01-01

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

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

    Science.gov (United States)

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

    1950-01-01

    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.

  2. Single-Nanoparticle Collision Events: Tunneling Electron Transfer on a Titanium Dioxide Passivated n-Silicon Electrode.

    Science.gov (United States)

    Ahn, Hyun S; Bard, Allen J

    2015-11-01

    Single-nanoparticle collisions were observed on an n-type silicon electrode (600??m diameter) passivated by a thin layer of amorphous TiO2, where the current steps occurred by tunneling electron transfer. The observed collision frequency was in reasonable agreement with that predicted from theory. The isolated electrode, after a collision experiment, with a Pt/TiO2/n-Si architecture was shown to retain the photoelectrochemical properties of n-Si without photocorrosion or current decay. The Pt/TiO2/n-Si electrode produced 19?mA?cm(-2) of photocurrent density under 100?mW?cm(-2) irradiation from a xenon lamp during oxygen evolution without current fading for over 12?h. PMID:26377039

  3. Si/SiGe electron resonant tunneling diodes with graded spacer wells

    International Nuclear Information System (INIS)

    Resonant tunneling diodes have been fabricated using graded Si1-xGex (x=0.3->0.0) spacer wells and strained Si0.4Ge0.6 barriers on a relaxed Si0.7Ge0.3 n-type substrate which demonstrates negative differential resistance at up to 100 K. This design is aimed at reducing the voltage at which the peak current density is achieved. Peak current densities of 0.08A/cm2 with peak-to-valley current ratios of 1.67 have been achieved for a low peak voltage of 40 mV at 77 K. This represents an improvement of over an order of magnitude compared to previous work. [copyright] 2001 American Institute of Physics

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

    Science.gov (United States)

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

    2014-11-01

    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

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

    International Nuclear Information System (INIS)

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

  6. Interaction-dependent photon-assisted tunneling in optical lattices: a quantum simulator of strongly-correlated electrons and dynamical Gauge fields

    Science.gov (United States)

    Bermudez, Alejandro; Porras, Diego

    2015-10-01

    We introduce a scheme that combines photon-assisted tunneling (PAT) by a moving optical lattice with strong Hubbard interactions, and allows for the quantum simulation of paradigmatic quantum many-body models. We show that, in a certain regime, this quantum simulator yields an effective Hubbard Hamiltonian with tunable bond-charge interactions, a model studied in the context of strongly-correlated electrons. In a different regime, we show how to exploit a correlated destruction of tunneling to explore Nagaoka ferromagnetism at finite Hubbard repulsion. By changing the photon-assisted tunneling parameters, we can also obtain a t-J model with independently controllable tunneling t, super-exchange interaction J, and even a Heisenberg-Ising anisotropy. Hence, the full phase diagram of this paradigmatic model becomes accessible to cold-atom experiments, departing from the region t\\gg J allowed by standard single-band Hubbard Hamiltonians in the strong-repulsion limit. We finally show that, by generalizing the PAT scheme, the quantum simulator yields models of dynamical Gauge fields, where atoms of a given electronic state dress the tunneling of the atoms with a different internal state, leading to Peierls phases that mimic a dynamical magnetic field.

  7. Electron tunneling studies of spin-flip scattering with native and artificial rare-earth barriers

    International Nuclear Information System (INIS)

    Both artificial and native rare earth (RE) tunnel barriers have been successfully fabricated. Artificial barriers are of the form M-REOx-M (M = Al, Pb, PbBi; RE = Ho, Dy, Gd, Lu), and native barriers are of the form RE-REOx-s (S = Pb, PbBi; RE = Dy, Ho). Artificial barriers are formed by oxidizing a thin (5-20 angstrom) film of evaporated RE. Current-Voltage characteristics (I-V) produced by Al-REOx-Al junctions shown substantial gap depression and gap smearing for magnetic rare earths (Ho, Dy, Gd). Using the Abrikosov-Gorkov (AG) theory of spin-flip scattering, we have successfully fit gap-depressed I-V's. Since the actual experimental temperature (T = 0.93 degree K) corresponds to a high reduced temperature (T/Tc) for Al, the AG predicted temperature dependence of the pair potential was necessary to obtain good fits. Our tunneling experiments utilize a variety of fabrication geometries. Our results do not support the view that contact between Al and the REOx barrier is responsible for gap depression. Instead, they indicate that gap depression is caused by inter-diffusion of Al and RE at the metal-metal interface. Native Dy barriers have been fabricated in-situ using a wet-oxygen ambient. The presence of water was found to be crucial for the formation of low leakage (0.6%) barriers. PbBi counter-electrodes show no sign-of-gap depression, despite clean contact with the DyOx barriers. Barrier characteristics for native RE barriers are quite different from those of artificial RE barriers. Native RE dV/dI's are quite symmetric corresponding to rectangular (flat) WKB barriers. The average height and width are 1.02 eV and 27.8 A, respectively. IETS has been performed for both HoOx and DyOx barriers. We report new quantitative results for barrier phonons in both HoOx and DyOx

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

    DEFF Research Database (Denmark)

    Kuznetsov, A.M.; Ulstrup, Jens

    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...... 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...

  9. 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

  10. Electronic transport through EuO spin-filter tunnel junctions

    KAUST Repository

    Jutong, Nuttachai

    2012-11-12

    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 Δ1 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.

  11. 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)

  12. Identifying highly conducting Au–C links through inelastic electron tunneling spectroscopy.

    Czech Academy of Sciences Publication Activity Database

    Foti, G.; Vázquez, Héctor; Sanchez-Portal, D.; Arnau, A.; Frederiksen, T.

    2014-01-01

    Ro?. 118, OCT (2014), s. 27106-27112. ISSN 1932-7447 Institutional support: RVO:68378271 Keywords : molecular electronics * alkanes * tin-functionalization * anchoring groups * vibrational spectroscopy Subject RIV: CF - Physical ; Theoretical Chemistry Impact factor: 4.772, year: 2014

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

    Scientific Electronic Library Online (English)

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

    2002-06-01

    Full Text Available 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.

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

    Science.gov (United States)

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

    2013-11-01

    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

  15. Approach to surface structure determination with the scanning tunneling microscope: Multiple-gap imaging and electron-scattering quantum-chemistry theory

    International Nuclear Information System (INIS)

    We have successfully developed and tested a method of quantitative surface structure determination using scanning tunneling microscopy (STM). Image simulations of the c(2x2) S on Mo(100) chemisorption system were calculated as a function of surface and tip structure using electron-scattering quantum-chemistry STM theory. STM images with a wide range of tunneling gap resistance values were acquired in a ''multiple-gap'' mode which preserves information on the z separation and lateral registry between the images under different tunneling conditions. The best fit of a numerical comparison of the image simulations with experimental data simultaneously determined two structural parameters of the surface. The STM results differ from those of dynamical LEED by approximately 0.1 A, which we estimate to be the level of accuracy obtainable with the present implementation of the method

  16. Collection Development of Electronic Information Resources in Turkish University Libraries

    OpenAIRE

    Tonta, Yaşar

    2001-01-01

    The number of information sources available through both printed and electronic media are ever increasing. Even libraries with sizable collection development budgets are having difficulties in coping with this increase. Yet with the development of new technologies, the possibilities of innovative interlibrary cooperation projects emerge: libraries combining their efforts through various consortia are trying to get access to electronic information sources more economically. In this paper, we b...

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

    Directory of Open Access Journals (Sweden)

    Mallinath Kumbar

    2012-12-01

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

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

    OpenAIRE

    Ingutia-Oyieke, Lilian; Dick, Archie L.

    2010-01-01

    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...

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

    OpenAIRE

    Mallinath Kumbar; G. Kiran kumar

    2012-01-01

    Purpose: This study evaluates the use of electronic resources among the faculty in five autonomous Engineering Colleges in Bengaluru. It evaluates the purpose,benefits, preference of web browsers, search engines, file formats, problem faced,and search patterns as the key parameters. It highlights some problems,constraints and forward suggestions for better use of electronic resources.Methodology/Approach: The structured questionnaire is used for data collection besides personal interview and ...

  20. Assessment of the utilisation of Makerere University electronic information resources by academic staff; challenges and prospects

    OpenAIRE

    Agaba, Didace Mulamira

    2005-01-01

    The study investigated the utilization of electronic information resources by the academic staff of Makerere University in Uganda. It examined academic staff awareness of the resources’ availability, the types of resources provided by the University Library , factors affecting their utilization, problems faced, and it offers recommendations for the way forward. The study was both qualitative and quantitative in nature, employing questionnaire, interview and content analysis methods. Findings ...

  1. Electronic resources and institutional repositories in informal scholarly communication and publishing

    OpenAIRE

    Galina Russell, I.

    2009-01-01

    The aim of institutional repositories is to aid the management and dissemination of the increasingly copious amount of scholarly electronic resources produced by academics. To date most research has focused on the impact for formal scholarly publishing. The purpose of this exploratory study is to discover the impact of IRs on the visibility and use of digital resources with particular focus on resources outside the formal publishing framework. An online survey and interviews wi...

  2. An Evaluation of Electronic Product Design Education Using Hypermedia-Resourced Learning Environments

    Science.gov (United States)

    Page, Tom; Thorsteinsson, Gisli

    2006-01-01

    The work outlined here provides a comprehensive report and formative observations of the development and implementation of hypermedia resources for learning and teaching used in conjunction with a managed learning environment (MLE). These resources are used to enhance teaching and learning of an electronics module in product design at final year…

  3. NRC Clients' Perceptions of Electronic Resources and Use of CISTI's Virtual Library.

    Science.gov (United States)

    Belzile, Sylvie; Kneale, Jean; Young, Ian; Summers, Randy; Colbourne, David

    1999-01-01

    Discusses a study of use of the Web-based virtual library at CISTI (Canada Institute for Scientific and Technical Information) by NRC (National Research Council of Canada). Results indicate that NRC staff is favorably inclined toward electronic resources and that a positive correlation exists between use of digital resources and perception and…

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

    Science.gov (United States)

    Downey, Kay

    2012-01-01

    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…

  5. A Study on Developing Evaluation Criteria for Electronic Resources in Evaluation Indicators of Libraries

    Science.gov (United States)

    Noh, Younghee

    2010-01-01

    This study aimed to improve the current state of electronic resource evaluation in libraries. While the use of Web DB, e-book, e-journal, and other e-resources such as CD-ROM, DVD, and micro materials is increasing in libraries, their use is not comprehensively factored into the general evaluation of libraries and may diminish the reliability of…

  6. 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)

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

    International Nuclear Information System (INIS)

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

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

    Science.gov (United States)

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

    2015-03-01

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

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

    Energy Technology Data Exchange (ETDEWEB)

    Benabbas, Abdelkrim; Salna, Bridget; Sage, J. Timothy; Champion, Paul M., E-mail: champ@neu.edu [Department of Physics and Center for Interdisciplinary Research on Complex Systems,Northeastern University, Boston, Massachusetts 02115 (United States)

    2015-03-21

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

  10. 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

  11. Strong overtones modes in inelastic electron tunneling spectroscopy with cross-conjugated molecules

    DEFF Research Database (Denmark)

    Jørgensen, Jacob Lykkebo; Gagliardi, Alessio; Pecchia, Alessandro; Solomon, Gemma C.

    2013-01-01

    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 ...

  12. Low energy anomalies in electron tunneling through strongly asymmetric Majorana nanowire

    OpenAIRE

    Shkop, A. D.; Parafilo, A. V.; Krive, I. V.; Shekhter, R.I.

    2016-01-01

    Electron transport through Majorana nanowire with strongly asymmetric couplings to normal metal leads is considered. In three terminal geometry (electrically grounded nanowire) it is shown that the presence of unbiased electrode restores zero-bias anomaly even for strong Majorana energy splitting. For effectively two-terminal geometry we show that electrical current through asymmetric Majorana junction is qualitatively different from the analogous current through a resonant (Breit-Wigner) level.

  13. Resonant Tunneling in a Dissipative Environment

    OpenAIRE

    Bomze, Yu.; Mebrahtu, H.; Borzenets, I.; Makarovski, A.; Finkelstein, G.

    2010-01-01

    We measure tunneling through a single quantum level in a carbon nanotube quantum dot connected to resistive metal leads. For the electrons tunneling to/from the nanotube, the leads serve as a dissipative environment, which suppresses the tunneling rate. In the regime of sequential tunneling, the height of the single-electron conductance peaks increases as the temperature is lowered, although it scales more weekly than the conventional 1/T. In the resonant tunneling regime (t...

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

    Energy Technology Data Exchange (ETDEWEB)

    Warburton, William K

    2009-03-06

    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.

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

    International Nuclear Information System (INIS)

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

  16. Field emission spectroscopy evidence for dual-barrier electron tunnelling in nanographite

    Energy Technology Data Exchange (ETDEWEB)

    Bandurin, D. A.; Kleshch, V. I. [Department of Physics, M.V. Lomonosov Moscow State University, Moscow 119991 (Russian Federation); Mingels, S.; Lützenkirchen-Hecht, D.; Müller, G. [FB C Physics Department, University of Wuppertal, 42119 Wuppertal (Germany); Obraztsov, A. N., E-mail: obraz@polly.phys.msu.ru [Department of Physics, M.V. Lomonosov Moscow State University, Moscow 119991 (Russian Federation); Department of Physics and Mathematics, University of Eastern Finland, Joensuu 80101 (Finland)

    2015-06-08

    Nanocarbon films with upstanding flake-like graphite crystallites of nanometre thickness were fabricated by carbon condensation from a methane–hydrogen gas mixture activated by a direct-current discharge. The nanographite (NG) crystallites are composed of a few graphene layers. The adjacent atomic layers are connected partially at the edges of the crystallites to form strongly curved graphene structures. The extraordinary field emission (FE) properties were revealed for the NG films with an average current density of a few mA/cm{sup 2}, reproducibly obtained at a macroscopic applied field of about 1?V/?m. The integral FE current–voltage curves and electron spectra (FEES) of NG cathodes with multiple emitters were measured in a triode configuration. Most remarkably, above a threshold field, two peaks were revealed in FEES with different field-dependent shifts to lower energies. This behaviour evidences electron emission through a dual potential barrier, corresponding to carbon–carbon heterostructure formed as a result of the graphene bending.

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

    Science.gov (United States)

    Barbier, Patricia

    2007-01-01

    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.

  18. Electronic Information Resources in Undergraduate Education: An Exploratory Study of Opportunities for Student Learning and Independence.

    Science.gov (United States)

    McDowell, Liz

    2002-01-01

    This qualitative interview-based study examines lecturer perspectives on the roles of electronic information resources in undergraduate education. Highlights include electronic academic libraries; changes toward more constructivist approaches to learning; information quality on the Web; plagiarism; information use; information literacy; and…

  19. Numerical modelling of emission of a two-level atom near a metal nanoparticle with account for tunnelling of an electron from an atom into a particle

    Science.gov (United States)

    Fedorovich, S. V.; Protsenko, I. E.

    2016-01-01

    We report the results of numerical modelling of emission of a two-level atom near a metal nanoparticle under resonant interaction of light with plasmon modes of the particle. Calculations have been performed for different polarisations of light by a dipole approximation method and a complex multipole method. Depending on the distance between a particle and an atom, the contribution of the nonradiative process of electron tunnelling from a two-level atom into a particle, which is calculated using the quasi-classical approximation, has been taken into account and assessed. We have studied spherical gold and silver particles of different diameters (10 – 100 nm). The rates of electron tunnelling and of spontaneous decay of the excited atomic state are found. The results can be used to develop nanoscale plasmonic emitters, lasers and photodetectors.

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

    OpenAIRE

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

    1993-01-01

    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...

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

    DEFF Research Database (Denmark)

    Chi, Qijin; Farver, O; Ulstrup, Jens

    2005-01-01

    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 i...

  2. Electronic textbooks as a professional resource after dental school.

    Science.gov (United States)

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

    2012-05-01

    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

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

    Directory of Open Access Journals (Sweden)

    Aaron August Lupton

    2012-01-01

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

  4. 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

    CERN Photo Service

    2008-01-01

    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.

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

    Science.gov (United States)

    Foster, Anita; Williams, Sarah C.

    2010-01-01

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

  6. The National Site Licensing of Electronic Resources: An Institutional Perspective

    Directory of Open Access Journals (Sweden)

    Xiaohua Zhu

    2011-06-01

    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.

  7. Library Electronic Resource Sharing Among Liberal Arts Colleges: ACS Palladian Alliance Project

    Directory of Open Access Journals (Sweden)

    Wenxian Zhang

    1997-03-01

    Full Text Available ?Effective electronic resource sharing is critical to library information services of the 1990s. Explosion of data and increased cost of information force libraries to work together, and technological advancements present the library service profession a platform for resource sharing. The Palladian Alliance Project of the Associated Colleges of the South is designed to provides ACS member institutions an effective means to enhance information access for their faculty and students, and achieve significant cost containment in the years to come.

  8. Evaluating a scalable model for implementing electronic health records in resource-limited settings

    OpenAIRE

    Were, Martin C.; Emenyonu, Nneka; Achieng, Marion; Shen, Changyu; Ssali, John; Masaba, John P M; William M. Tierney

    2010-01-01

    Current models for implementing electronic health records (EHRs) in resource-limited settings may not be scalable because they fail to address human-resource and cost constraints. This paper describes an implementation model which relies on shared responsibility between local sites and an external three-pronged support infrastructure consisting of: (1) a national technical expertise center, (2) an implementer's community, and (3) a developer's community. This model was used to implement an op...

  9. Connecting knowledge resources to the veterinary electronic health record: opportunities for learning at point of care.

    Science.gov (United States)

    Alpi, Kristine M; Burnett, Heidi A; Bryant, Sheila J; Anderson, Katherine M

    2011-01-01

    Electronic health records (EHRs) provide clinical learning opportunities through quick and contextual linkage of patient signalment, symptom, and diagnosis data with knowledge resources covering tests, drugs, conditions, procedures, and client instructions. This paper introduces the EHR standards for linkage and the partners-practitioners, content publishers, and software developers-necessary to leverage this possibility in veterinary medicine. The efforts of the American Animal Hospital Association (AAHA) Electronic Health Records Task Force to partner with veterinary practice management systems to improve the use of controlled vocabulary is a first step in the development of standards for sharing knowledge at the point of care. The Veterinary Medical Libraries Section (VMLS) of the Medical Library Association's Task Force on Connecting the Veterinary Health Record to Information Resources compiled a list of resources of potential use at point of care. Resource details were drawn from product Web sites and organized by a metric used to evaluate medical point-of-care resources. Additional information was gathered from questions sent by e-mail and follow-up interviews with two practitioners, a hospital network, two software developers, and three publishers. Veterinarians with electronic records use a variety of information resources that are not linked to their software. Systems lack the infrastructure to use the Infobutton standard that has been gaining popularity in human EHRs. While some veterinary knowledge resources are digital, publisher sites and responses do not indicate a Web-based linkage of veterinary resources with EHRs. In order to facilitate lifelong learning and evidence-based practice, veterinarians and educators of future practitioners must demonstrate to veterinary practice software developers and publishers a clinically-based need to connect knowledge resources to veterinary EHRs. PMID:22023919

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

    Directory of Open Access Journals (Sweden)

    Aarnio Matti

    2006-05-01

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

  11. Considering Point-of-Care Electronic Medical Resources in Lieu of Traditional Textbooks for Medical Education.

    Science.gov (United States)

    Hale, LaDonna S; Wallace, Michelle M; Adams, Courtney R; Kaufman, Michelle L; Snyder, Courtney L

    2015-09-01

    Selecting resources to support didactic courses is a critical decision, and the advantages and disadvantages must be carefully considered. During clinical rotations, students not only need to possess strong background knowledge but also are expected to be proficient with the same evidence-based POC resources used by clinicians. Students place high value on “real world” learning and therefore may place more value on POC resources that they know practicing clinicians use as compared with medical textbooks. The condensed nature of PA education requires students to develop background knowledge and information literacy skills over a short period. One way to build that knowledge and those skills simultaneously is to use POC resources in lieu of traditional medical textbooks during didactic training. Electronic POC resources offer several advantages over traditional textbooks and should be considered as viable options in PA education. PMID:26309211

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

    Science.gov (United States)

    Berman, Diana; Walker, Matthew; Krim, Jacqueline

    2012-02-01

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

  13. Eavesdropping on Electronic Guidebooks Observing Learning Resources in Shared Listening Environments

    CERN Document Server

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

    2002-01-01

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

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

    OpenAIRE

    Rusbridge, Chris

    2000-01-01

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

  15. Eavesdropping on Electronic Guidebooks: Observing Learning Resources in Shared Listening Environments

    OpenAIRE

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

    2002-01-01

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

  16. Superluminal Tunneling Devices

    CERN Document Server

    Nimtz, G

    2002-01-01

    Photonic tunneling permits superluminal signal transmission. The principle of causality is not violated but the time duration between cause and effect can be shortened compared with an interaction exchange with velocity of light. This outstanding property can be applied to speed-up photonic signal modulation and transmission as well as to improve micro-electronic devices. Superluminal photonic signal transmission have been presented at microwave and infrared frequencies already. Presumably superluminal photonic and electronic devices can become reality having in mind the experimental evidence of the universal tunneling time of photons and of electrons.

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

    Energy Technology Data Exchange (ETDEWEB)

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

    2000-02-09

    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.

  18. Cost-Benefit Analysis of Electronic Information Resources: An Evaluation of the Middle East Technical University Library

    OpenAIRE

    Bat?, Hacer

    2006-01-01

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

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

    International Nuclear Information System (INIS)

    We report the tunneling spectroscopy investigation in an atomic scale gap filled with liquid 4He using mechanically controllable break junction (MCBJ) technique. In order to assure the filling of liquid 4He into the gap, we construct a cryostat with an inner chamber for the tunneling spectroscopy inside the vacuum jacket of the liquid 4He bath. MCBJ apparatus is installed in the inner chamber with a flexible bellows. After filling inner chamber with liquid 4He below 4.2 K, Au electrical electrodes were stretched by the mechanical force generated by a piezo device. We observed the increase of the tunnel conductance through liquid 4He compared to that in the vacuum environment.

  20. Implementation of an Electronic Resource Assessment System in an Academic Library

    Science.gov (United States)

    Xu, Fei

    2010-01-01

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

  1. Use of Electronic Information Resources among Research Scholars in the Islamia University of Bahawalpur, Pakistan

    Science.gov (United States)

    Amjad, Anam; Ahmed, Shamshad; Bin Naeem, Salman

    2013-01-01

    This study examined the use of electronic resources among academic scholars of The Islamia University of Bahawalpur (IUB), Punjab, Pakistan. A quantitative survey was found most convenient and useful for this study. The total population of the study was 169 research students in IUB. The response rate was 79% and 133 utilizable responses were coded…

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

    Science.gov (United States)

    Koehn, Shona L.; Hawamdeh, Suliman

    2010-01-01

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

  3. Specific Features of Development of Electronic Information and Education Resources for the Distant Learning Systems ??????????? ???????? ??????????? ?????????????-??????????????? ???????? ??? ?????? ?????????????? ????????

    Directory of Open Access Journals (Sweden)

    Sergienko Yelena A.

    2012-07-01

    Full Text Available The article is analyzed the features of distance learning and forms of its realization, is devoted to research existing technologies and tools of distance learning, as well as their possible applications in modern education system. Presents the potential for electronic information-educational resources for distance education systems.? ?????? ???????? ?????? ???????????? ?????????????? ???????? ? ???? ??? ??????????. ??????????? ?????????? ? ???????? ?????????????? ????????, ? ????? ??????????? ?? ?????????? ? ??????????? ??????? ???????????. ???????????? ??????????? ???????? ??????????? ?????????????- ??????????????? ???????? ??? ?????? ?????????????? ???????????.

  4. What Do Community College Libraries Do with Electronic Resources? The Practice in 2003

    Science.gov (United States)

    Shorten, Jay

    2004-01-01

    One hundred fourteen community college libraries in the United States and Canada are surveyed for the organization of electronic resources within their home page and their cataloguing practice. The majority provide access to databases, ready reference, and their own catalogue both on their home page and within their web site. They do not usually…

  5. A Mid-infrared Digital Electronic Camera System for Assessing Natural Resources

    Science.gov (United States)

    Water strongly absorbs mid-infrared (1300-2500 nm) radiation, resulting in this region of the spectrum being sensitive to the water content within features. Little information is available on using an electronic digital camera filtered to this region of the spectrum to assess natural resources. Th...

  6. A Survey of the Use of Electronic Resources at Seven Universities in Wuhan, China

    Science.gov (United States)

    Zhang, Liyi; Ye, Pinghao; Liu, Qihua

    2011-01-01

    Purpose: The purpose of this paper is to report on users' information behaviour in China, a topic which has not been researched extensively. The aim is to help producers and providers collect and develop more electronic resources. Design/methodology/approach: The study investigates users' information behaviour at seven "211 Project" universities…

  7. Innovative's Electronic Resource Management as catalyst for change at Glasgow University Library

    OpenAIRE

    Galloway, L

    2006-01-01

    In March 2003 Glasgow University Library joined with Innovative and several other Innovative customers to develop a new Electronic Resource Management (ERM) module. This paper will outline the ways in which the development and implementation of ERM has acted as a catalyst and facilitator for further enhancements and developments in the area of e-journals at Glasgow University Library.

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

    International Nuclear Information System (INIS)

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

  9. Resonance tunneling spectroscopy of heteropoly compounds

    Science.gov (United States)

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

    2012-12-01

    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.

  10. Resonance tunneling spectroscopy of heteropoly compounds

    Energy Technology Data Exchange (ETDEWEB)

    Dalidchik, F. I., E-mail: domfdal@mail.ru; Budanov, B. A.; Kolchenko, N. N.; Balashov, E. M.; Kovalevskii, S. A. [Russian Academy of Sciences, Semenov Institute of Chemical Physics (Russian Federation)

    2012-12-15

    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.

  11. Tunneling in Fractional Quantum Hall line junctions

    OpenAIRE

    Aranzana, Manuel; Regnault, Nicolas; Jolicoeur, Thierry

    2005-01-01

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

  12. Attosecond tunnelling interferometry

    Science.gov (United States)

    Pedatzur, O.; Orenstein, G.; Serbinenko, V.; Soifer, H.; Bruner, B. D.; Uzan, A. J.; Brambila, D. S.; Harvey, A. G.; Torlina, L.; Morales, F.; Smirnova, O.; Dudovich, N.

    2015-10-01

    Attosecond physics offers new insights into ultrafast quantum phenomena involving electron dynamics on the fastest measurable timescales. The rapid progress in this field enables us to re-visit one of the most fundamental strong-field phenomena: field-induced tunnel ionization. In this work, we employ high-harmonic generation to probe the electron wavefunction during field-induced tunnelling through a potential barrier. By using a combination of strong and weak driving laser fields, we modulate the atomic potential barrier on optical subcycle timescales. This induces a temporal interferometer between attosecond bursts originating from consecutive laser half-cycles. Our study provides direct insight into the basic properties of field-induced tunnelling, following the evolution of the electronic wavefunction within a temporal window of approximately 200 attoseconds.

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

    International Nuclear Information System (INIS)

    High resolution transmission electron microscopy, 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 (TMJs), deposited on various single crystalline substrates (a-plane sapphire, MgO(100) and Si(111)). They allow for providing a correlation between these magnetic properties and the fine structure investigated at atomic scale. The Al2O3 tunnel barrier is always amorphous and contains a large concentration of Co atoms, which, however, is significantly reduced when using a sapphire substrate. The Co layer is polycrystalline and shows larger grains for films grown on a sapphire substrate. The VSM investigation reveals in-plane anisotropy only for samples grown on a sapphire substrate. The FMR spectra of the TMJs are compared to the obtained ones with a single Co and Co2MnGe films of identical thickness deposited on a sapphire substrate. As expected, two distinct modes are detected in the TMJs while only one mode is observed in each single film. For the TMJ grown on a sapphire substrate, the FMR behavior does not significantly differ from the superposition of the individual spectra of the single films, allowing for a conclusion that the exchange coupling between the two magnetic layers is too small to give rise to observable shifts. For TMJs grown on a Si or on a MgO substrate, the resonance spectra reveal one mode which is nearly identical to the obtained one in the single Co film, while the other observed resonance shows a considerably smaller intensity and cannot be described using the magnetic parameters appropriate to the single Co2MnGe film. The large Co concentration in the Al2O3 interlayer prevents for a simple interpretation of the observed spectra when using Si or MgO substrates. - Highlights: • Tunnel magnetic junctions have been grown on different substrates. • Their nanoscale structure has been studied and compared to the magnetic properties. • Inter-diffusion to the tunnel barrier has been observed. • Differences between tunnel junctions have a direct impact on magnetic properties

  14. Transmission electron microscopy and ferromagnetic resonance investigations of tunnel magnetic junctions using Co{sub 2}MnGe Heusler alloys as magnetic electrodes

    Energy Technology Data Exchange (ETDEWEB)

    Belmeguenai, M., E-mail: belmeguenai.mohamed@univ-paris13.fr [LSPM (CNRS-UPR 3407), Université Paris 13, 99 avenue Jean-Baptiste Clément, 93430 Villetaneuse (France); Genevois, C. [Groupe de Physique des Matériaux, UMR CNRS 6634, Site Universitaire du Madrillet, BP12, 76801 Saint Etienne du Rouvray cedex (France); Zighem, F.; Roussigné, Y.; Chérif, S.M. [LSPM (CNRS-UPR 3407), Université Paris 13, 99 avenue Jean-Baptiste Clément, 93430 Villetaneuse (France); Westerholt, K. [Institut für Experimentelle Physik, Ruhr-Universität Bochum, 44780 Bochum (Germany); El Bahoui, A.; Fnidiki, A. [Groupe de Physique des Matériaux, UMR CNRS 6634, Site Universitaire du Madrillet, BP12, 76801 Saint Etienne du Rouvray cedex (France); Moch, P. [LSPM (CNRS-UPR 3407), Université Paris 13, 99 avenue Jean-Baptiste Clément, 93430 Villetaneuse (France)

    2014-01-31

    High resolution transmission electron microscopy, 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 Co{sub 2}MnGe(13 nm)/Al{sub 2}O{sub 3}(3 nm)/Co(13 nm) tunnel magnetic junctions (TMJs), deposited on various single crystalline substrates (a-plane sapphire, MgO(100) and Si(111)). They allow for providing a correlation between these magnetic properties and the fine structure investigated at atomic scale. The Al{sub 2}O{sub 3} tunnel barrier is always amorphous and contains a large concentration of Co atoms, which, however, is significantly reduced when using a sapphire substrate. The Co layer is polycrystalline and shows larger grains for films grown on a sapphire substrate. The VSM investigation reveals in-plane anisotropy only for samples grown on a sapphire substrate. The FMR spectra of the TMJs are compared to the obtained ones with a single Co and Co{sub 2}MnGe films of identical thickness deposited on a sapphire substrate. As expected, two distinct modes are detected in the TMJs while only one mode is observed in each single film. For the TMJ grown on a sapphire substrate, the FMR behavior does not significantly differ from the superposition of the individual spectra of the single films, allowing for a conclusion that the exchange coupling between the two magnetic layers is too small to give rise to observable shifts. For TMJs grown on a Si or on a MgO substrate, the resonance spectra reveal one mode which is nearly identical to the obtained one in the single Co film, while the other observed resonance shows a considerably smaller intensity and cannot be described using the magnetic parameters appropriate to the single Co{sub 2}MnGe film. The large Co concentration in the Al{sub 2}O{sub 3} interlayer prevents for a simple interpretation of the observed spectra when using Si or MgO substrates. - Highlights: • Tunnel magnetic junctions have been grown on different substrates. • Their nanoscale structure has been studied and compared to the magnetic properties. • Inter-diffusion to the tunnel barrier has been observed. • Differences between tunnel junctions have a direct impact on magnetic properties.

  15. Lateral ordering of PTCDA on the clean and the oxygen pre-covered Cu(100) surface investigated by scanning tunneling microscopy and low energy electron diffraction

    OpenAIRE

    Gärtner, Stefan; Fiedler, Benjamin; Bauer, Oliver; Marele, Antonela; Sokolowski, Moritz M

    2014-01-01

    We have investigated the adsorption of perylene-3,4,9,10-tetracarboxylic acid dianhydride (PTCDA) on the clean and on the oxygen pre-covered Cu(100) surface [referred to as (?2 × 2?2)R45° – 2O/Cu(100)] by scanning tunneling microscopy (STM) and low energy electron diffraction (LEED). Our results confirm the (4?2 × 5?2)R45° superstructure of PTCDA/Cu(100) reported by A. Schmidt et al. [J. Phys. Chem. 1995, 99,11770–11779]. However, contrary to Schmidt et al., we have no indication for a ...

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

    OpenAIRE

    Belmeguenai, M.; Genevois, C.; Zighem, F.; Roussigné, Y; Chérif, S-M.; Westerholt, K.; Bahoui, A. El; Fnidiki, A.; Moch, P.

    2013-01-01

    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 magnetic properties...

  17. 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

  18. Recognition Tunneling

    OpenAIRE

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

    2010-01-01

    Single molecules in a tunnel junction can now be interrogated reliably using chemically-functionalized electrodes. Monitoring stochastic bonding fluctuations between a ligand bound to one electrode and its target bound to a second electrode (“tethered molecule-pair” configuration) gives insight into the nature of the intermolecular bonding at a single molecule-pair level, and defines the requirements for reproducible tunneling data. Simulations show that there is an instability in the tunnel ...

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

    Science.gov (United States)

    Webster, Peter

    2006-01-01

    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…

  20. Knowledge and use of electronic information resources by medical sciences faculty at The University of the West Indies

    OpenAIRE

    Renwick, Shamin

    2005-01-01

    Objective: The objective was to determine faculty's knowledge of electronic resources, access to a computer, use of electronic resources (both number and frequency) available at the Medical Sciences Library (MSL), and the areas of training needed and to identify areas for further research.