Tunnel conductance of Watson-Crick nucleoside-base pairs from telegraph noise

International Nuclear Information System (INIS)

Chang Shuai; He Jin; Lin Lisha; Zhang Peiming; Liang Feng; Huang Shuo; Lindsay, Stuart; Young, Michael

2009-01-01

The use of tunneling signals to sequence DNA is presently hampered by the small tunnel conductance of a junction spanning an entire DNA molecule. The design of a readout system that uses a shorter tunneling path requires knowledge of the absolute conductance across base pairs. We have exploited the stochastic switching of hydrogen-bonded DNA base-nucleoside pairs trapped in a tunnel junction to determine the conductance of individual molecular pairs. This conductance is found to be sensitive to the geometry of the junction, but a subset of the data appears to come from unstrained molecular pairs. The conductances determined from these pairs are within a factor of two of the predictions of density functional calculations. The experimental data reproduces the counterintuitive theoretical prediction that guanine-deoxycytidine pairs (3 H-bonds) have a smaller conductance than adenine-thymine pairs (2 H-bonds). A bimodal distribution of switching lifetimes shows that both H-bonds and molecule-metal contacts break.

Coherent tunnelling conductance in normal-metal/d-wave superconductor/normal-metal double tunnel junctions

International Nuclear Information System (INIS)

Dong, Z C; Zheng, Z M; Xing, D Y

2004-01-01

Taking simultaneously into account the electron-injected current from one normal-metal (N) electrode and the hole-injected current from the other N electrode, we study the coherent tunnelling conductance and quantum interference effects in N/d-wave superconductor (S)/N double tunnel junctions. It is found that oscillations of all quasiparticle transport coefficients and the conductance spectrum with quasiparticle energy and thickness of the d-wave S depend to a great extent on the crystal orientation of the d-wave S. The zero-bias conductance peak is gradually lowered with increasing barrier strength and/or temperature, its magnitude exhibiting damped oscillatory behaviour with thickness of S

Systematic study on the tunneling conductance in a normal-metal/px+y ± ipy-x-wave superconductor junction

International Nuclear Information System (INIS)

Jin Biao; Zhang Yinhan; Cheng Qiang

2010-01-01

The chiral p x+y ± ip y-x -wave state is currently considered to be a promising candidate state for Sr 2 RuO 4 in the light of microscopic theories. We theoretically investigate the tunneling conductance in a normal-metal/p x+y ± ip y-x -wave superconductor junction over a wide range of temperature and barrier strength. For a cylindrical Fermi surface with the magnitude of the radius R, the p x+y ± ip y-x -wave gap function exhibits two typical types of nodal structures when R = 1.0 and R=1/√2, respectively. It is found, in particular, that the line shapes of the conductance spectra for R∼1/√2 cases can qualitatively account for the existing in-plane tunneling experiments on Sr 2 RuO 4 .

Spatial effects of Fano resonance in local tunneling conductivity in vicinity of impurity on semiconductor surface

OpenAIRE

Mantsevich, V. N.; Maslova, N. S.

2009-01-01

We present the results of local tunneling conductivity spatial distribution detailed theoretical investigations in vicinity of impurity atom for a wide range of applied bias voltage. We observed Fano resonance in tunneling conductivity resulting from interference between resonant tunneling channel through impurity energy level and direct tunneling channel between the tunneling contact leads. We have found that interference between tunneling channels strongly modifies form of tunneling conduct...

Tunneling conductance in superconductor-hybrid double quantum dots Josephson junction

Science.gov (United States)

Chamoli, Tanuj; Ajay

2018-05-01

The present work deals with the theoretical model study to analyse the tunneling conductance across a superconductor hybrid double quantum dots tunnel junction (S-DQD-S). Recently, there are many experimental works where the Josephson current across such nanoscopic junction is found to be dependent on nature of the superconducting electrodes, coupling of the hybrid double quantum dot's electronic states with the electronic states of the superconductors and nature of electronic structure of the coupled dots. For this, we have attempted a theoretical model containing contributions of BCS superconducting leads, magnetic coupled quantum dot states and coupling of superconducting leads with QDs. In order to include magnetic coupled QDs the contributions of competitive Kondo and Ruderman-Kittel- Kasuya-Yosida (RKKY) interaction terms are also introduced through many body effects in the model Hamiltonian at low temperatures (where Kondo temperature TK tunnel junctions. Tunneling conductance is proportional to DOS, hence we can analyse it's behaviour with the help of DOS.

Spin-dependent tunneling conductance in 2D structures in zero magnetic field

International Nuclear Information System (INIS)

Rozhansky, I.V.; Averkiev, N.S.

2009-01-01

The influence of the spin-orbit interaction on the tunneling between two-dimensional electron layers is considered. A general expression for the tunneling current is obtained with the Rashba and Dresselhaus effects and also elastic scattering of charge carriers on impurities taken into account. It is shown that the particular form of the tunneling conductance as a function of the voltage between layers is extremely sensitive to the relationship between the Rashba and Dresselhaus parameters. This makes it possible to determine the parameters of the spin-orbit interaction and the quantum scattering time directly from measurements of the tunneling conductance in the absence of magnetic field

Electronic-Reconstruction-Enhanced Tunneling Conductance at Terrace Edges of Ultrathin Oxide Films.

Science.gov (United States)

Wang, Lingfei; Kim, Rokyeon; Kim, Yoonkoo; Kim, Choong H; Hwang, Sangwoon; Cho, Myung Rae; Shin, Yeong Jae; Das, Saikat; Kim, Jeong Rae; Kalinin, Sergei V; Kim, Miyoung; Yang, Sang Mo; Noh, Tae Won

2017-11-01

Quantum mechanical tunneling of electrons across ultrathin insulating oxide barriers has been studied extensively for decades due to its great potential in electronic-device applications. In the few-nanometers-thick epitaxial oxide films, atomic-scale structural imperfections, such as the ubiquitously existed one-unit-cell-high terrace edges, can dramatically affect the tunneling probability and device performance. However, the underlying physics has not been investigated adequately. Here, taking ultrathin BaTiO 3 films as a model system, an intrinsic tunneling-conductance enhancement is reported near the terrace edges. Scanning-probe-microscopy results demonstrate the existence of highly conductive regions (tens of nanometers wide) near the terrace edges. First-principles calculations suggest that the terrace-edge geometry can trigger an electronic reconstruction, which reduces the effective tunneling barrier width locally. Furthermore, such tunneling-conductance enhancement can be discovered in other transition metal oxides and controlled by surface-termination engineering. The controllable electronic reconstruction can facilitate the implementation of oxide electronic devices and discovery of exotic low-dimensional quantum phases. © 2017 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

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

International Nuclear Information System (INIS)

Welter, B.

2007-01-01

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 H c2 (T) respectively H c2 (0) are presented and applied to the experimental data. Finally the results of the tunnel-spectroscopy measurements are shown

Tunneling Conductivity and Piezoresistivity of Composites Containing Randomly Dispersed Conductive Nano-Platelets

Science.gov (United States)

Oskouyi, Amirhossein Biabangard; Sundararaj, Uttandaraman; Mertiny, Pierre

2014-01-01

In this study, a three-dimensional continuum percolation model was developed based on a Monte Carlo simulation approach to investigate the percolation behavior of an electrically insulating matrix reinforced with conductive nano-platelet fillers. The conductivity behavior of composites rendered conductive by randomly dispersed conductive platelets was modeled by developing a three-dimensional finite element resistor network. Parameters related to the percolation threshold and a power-low describing the conductivity behavior were determined. The piezoresistivity behavior of conductive composites was studied employing a reoriented resistor network emulating a conductive composite subjected to mechanical strain. The effects of the governing parameters, i.e., electron tunneling distance, conductive particle aspect ratio and size effects on conductivity behavior were examined. PMID:28788580

Atomic site tunneling spectroscopy on high-Tc superconductors

International Nuclear Information System (INIS)

Hasegawa, T.; Nantoh, M.; Takagi, A.; Yamaguchi, W.; Ogino, M.; Kawasaki, M.

1994-01-01

Superconducting gap structures of Bi 2 Sr 2 CaCu 2 O y (BSCCO) and YBa 2 Cu 3 O y (YBCO) have been probed by scanning tunneling microscopy (STM) at cryogenic temperatures. The tunneling conductance curves observed on bulk single crystals of BSCCO and epitaxial thin films of YBCO revealed clear obershooting peaks and flat bottom regions around V=0 with quite low zero-bias conductances of ∝1%. Since the electron tunneling process in STM is essentially incoherent, the present observation is favored by the s-wave pairing mechanism. However, the conductance curves were found to be substantially smeared in comparison with the conventional spectra predicted in the BCS (isotropic s-wave) superconductors, suggesting gap anisotropy. (orig.)

Tunneling conductance oscillations in spin-orbit coupled metal-insulator-superconductor junctions

Science.gov (United States)

Kapri, Priyadarshini; Basu, Saurabh

2018-01-01

The tunneling conductance for a device consisting of a metal-insulator-superconductor (MIS) junction is studied in presence of Rashba spin-orbit coupling (RSOC) via an extended Blonder-Tinkham-Klapwijk formalism. We find that the tunneling conductance as a function of an effective barrier potential that defines the insulating layer and lies intermediate to the metallic and superconducting electrodes, displays an oscillatory behavior. The tunneling conductance shows high sensitivity to the RSOC for certain ranges of this potential, while it is insensitive to the RSOC for others. Additionally, when the period of oscillations is an odd multiple of a certain value of the effective potential, the conductance spectrum as a function of the biasing energy demonstrates a contrasting trend with RSOC, compared to when it is not an odd multiple. The explanations for the observation can be found in terms of a competition between the normal and Andreev reflections. Similar oscillatory behavior of the conductance spectrum is also seen for other superconducting pairing symmetries, thereby emphasizing that the insulating layer plays a decisive role in the conductance oscillations of a MIS junction. For a tunable Rashba coupling, the current flowing through the junction can be controlled with precision.

Conductance of single atoms and molecules studied with a scanning tunnelling microscope

International Nuclear Information System (INIS)

Neel, N; Kroeger, J; Limot, L; Berndt, R

2007-01-01

The conductance of single atoms and molecules is investigated with a low-temperature scanning tunnelling microscope. In a controlled and reproducible way, clean Ag(111) surfaces, individual silver atoms on Ag(111) as well as individual C 60 molecules adsorbed on Cu(100) are contacted with the tip of the microscope. Upon contact the conductance changes discontinuously in the case of the tip-surface junction while the tip-atom and tip-molecule junctions exhibit a continuous transition from the tunnelling to the contact regime

Enhancement of tunnel conductivity by Cooper pair fluctuations in electron-hole bilayer

International Nuclear Information System (INIS)

Efimkin, D K; Lozovik, Yu E

2012-01-01

Influence of Cooper pair fluctuations that are precursor of pairing of electrons and holes located on opposite surfaces of topological insulator film on tunnel conductivity between the surfaces is investigated. Due to restrictions caused by momentum and energy conservation dependence of tunnel conductivity on external bias voltage has peak that becomes more prominent with decreasing of disorder and temperature. We have shown that Cooper pair fluctuations considerably enhance tunneling and height of the peak diverges in vicinity of critical temperature with critical index ν = 2. Width of the peak tends to zero in proximity of critical temperature. Pairing of electrons and holes can be suppressed by disorder and in vicinity of quantum critical point height of the peak also diverges as function of Cooper pair damping with critical index μ = 2.

Infrared spectroscopy of molecular submonolayers on surfaces by infrared scanning tunneling microscopy: tetramantane on Au111.

Science.gov (United States)

Pechenezhskiy, Ivan V; Hong, Xiaoping; Nguyen, Giang D; Dahl, Jeremy E P; Carlson, Robert M K; Wang, Feng; Crommie, Michael F

2013-09-20

We have developed a new scanning-tunneling-microscopy-based spectroscopy technique to characterize infrared (IR) absorption of submonolayers of molecules on conducting crystals. The technique employs a scanning tunneling microscope as a precise detector to measure the expansion of a molecule-decorated crystal that is irradiated by IR light from a tunable laser source. Using this technique, we obtain the IR absorption spectra of [121]tetramantane and [123]tetramantane on Au(111). Significant differences between the IR spectra for these two isomers show the power of this new technique to differentiate chemical structures even when single-molecule-resolved scanning tunneling microscopy (STM) images look quite similar. Furthermore, the new technique was found to yield significantly better spectral resolution than STM-based inelastic electron tunneling spectroscopy, and to allow determination of optical absorption cross sections. Compared to IR spectroscopy of bulk tetramantane powders, infrared scanning tunneling microscopy (IRSTM) spectra reveal narrower and blueshifted vibrational peaks for an ordered tetramantane adlayer. Differences between bulk and surface tetramantane vibrational spectra are explained via molecule-molecule interactions.

A hysteresis phenomenon in NMR spectra of molecular nanomagnets Fe8: a resonant quantum tunneling system

Science.gov (United States)

Yamasaki, Tomoaki; Ueda, Miki; Maegawa, Satoru

2003-05-01

A molecular nanomagnet Fe8 with a total spin S=10 in the ground state attracts much attention as a substance which exhibits the quantum tunneling of magnetization below 300 mK. We performed 1H NMR measurements for a single crystal of Fe8 in temperature range between 20 and 800 mK. The spectra below 300 mK strongly depend on the sequence of the applied field and those in the positive and negative fields are not symmetric about zero field, while they are symmetric above 300 mK. We discuss the origin of this hysteresis phenomenon, relating to the initial spin state of molecules, the resonant quantum tunneling and the nuclear spin relaxation process.

A hysteresis phenomenon in NMR spectra of molecular nanomagnets Fe8: a resonant quantum tunneling system

International Nuclear Information System (INIS)

Yamasaki, Tomoaki; Ueda, Miki; Maegawa, Satoru

2003-01-01

A molecular nanomagnet Fe8 with a total spin S=10 in the ground state attracts much attention as a substance which exhibits the quantum tunneling of magnetization below 300 mK. We performed 1 H NMR measurements for a single crystal of Fe8 in temperature range between 20 and 800 mK. The spectra below 300 mK strongly depend on the sequence of the applied field and those in the positive and negative fields are not symmetric about zero field, while they are symmetric above 300 mK. We discuss the origin of this hysteresis phenomenon, relating to the initial spin state of molecules, the resonant quantum tunneling and the nuclear spin relaxation process

Scanning tunneling spectroscopy study of DNA conductivity

Czech Academy of Sciences Publication Activity Database

Kratochvílová, Irena; Král, Karel; Bunček, M.; Nešpůrek, Stanislav; Todorciuc, Tatiana; Weiter, M.; Navrátil, J.; Schneider, Bohdan; Pavluch, J.

2008-01-01

Roč. 6, č. 3 (2008), s. 422-426 ISSN 1895-1082 R&D Projects: GA AV ČR KAN401770651; GA MŠk OC 137; GA AV ČR KAN400720701; GA AV ČR KAN200100801 Institutional research plan: CEZ:AV0Z10100520; CEZ:AV0Z40500505; CEZ:AV0Z40550506 Keywords : molecular electronics * DNA * scanning tunneling microscopy * conductivity * charge carrier transport Subject RIV: BM - Solid Matter Physics ; Magnetism Impact factor: 0.448, year: 2008

Closed-loop conductance scanning tunneling spectroscopy: demonstrating the equivalence to the open-loop alternative.

Science.gov (United States)

Hellenthal, Chris; Sotthewes, Kai; Siekman, Martin H; Kooij, E Stefan; Zandvliet, Harold J W

2015-01-01

We demonstrate the validity of using closed-loop z(V) conductance scanning tunneling spectroscopy (STS) measurements for the determination of the effective tunneling barrier by comparing them to more conventional open-loop I(z) measurements. Through the development of a numerical model, the individual contributions to the effective tunneling barrier present in these experiments, such as the work function and the presence of an image charge, are determined quantitatively. This opens up the possibility of determining tunneling barriers of both vacuum and molecular systems in an alternative and more detailed manner.

Resonance tunneling electron-vibrational spectroscopy of polyoxometalates.

Science.gov (United States)

Dalidchik, F I; Kovalevskii, S A; Balashov, E M

2017-05-21

The tunneling spectra of the ordered monolayer films of decamolybdodicobaltate (DMDC) compounds deposited from aqueous solutions on HOPG were measured by scanning tunnel microscopy in air. The DMDC spectra, as well as the tunneling spectra of other polyoxometalates (POMs), exhibit well-defined negative differential resistances (NDRs). The mechanism of formation of these spectral features was established from the collection of revealed NDR dependences on the external varying parameters and found to be common to all systems exhibiting Wannier-Stark localization. A model of biresonance tunneling was developed to provide an explanation for the totality of experimental data, both the literature and original, on the tunneling POM probing. A variant of the tunneling electron-vibrational POM spectroscopy was proposed allowing the determination of the three basic energy parameters-energy gaps between the occupied and unoccupied states, frequencies of the vibrational transitions accompanying biresonance electron-tunneling processes, and electron-vibrational interaction constants on the monomolecular level.

Low-temperature conductivity of tunnel-coupled quantum dots system in YBaCuO and LaSrMnO dielectric films

CERN Document Server

Okunev, V D; Isaev, V A; Dyachenko, A T; Klimov, A; Lewandowski, S J

2002-01-01

Paper contains new experimental data concerning investigation into the nature of rho(T) approx = const conductivity segments at T < T sub c for YBaCuO and LaSrMnO dielectric films prepared by means of laser deposition and containing nanocrystalline clusters with metallic conductivity. In YBaCuO epitaxial films with a tetragonal structure rho = rho(T) approx = const (T sub c = 10 K) dependences are observed following the effect of (KrF) excimer laser emission on the specimens, while in LaSrMnO amorphous films (T sub c approx = 160 K) - immediately after they are prepared. rho(T) approx = const effect manifests itself if in the optical spectra of specimens there are regions of absorption by free charge carriers and is associated with a tunnel conductivity of a system of quantum points

Time course and predictors of median nerve conduction after carpal tunnel release.

Science.gov (United States)

Rotman, Mitchell B; Enkvetchakul, Bobby V; Megerian, J Thomas; Gozani, Shai N

2004-05-01

To identify predictors of outcome and of electrophysiologic recovery in patients with carpal tunnel syndrome (CTS) treated by endoscopic carpal tunnel release using a nerve conduction testing system (NC-Stat; NEUROMetrix, Inc, Waltham, MA). Validity of the automated nerve conduction testing system was shown by comparing presurgical distal motor latencies (DMLs) against a reference obtained by referral to an electromyography laboratory. The DML was evaluated in 48 patients with CTS. Measurements were obtained within 1 hour of surgery and at 2 weeks, 6 weeks, 3 months, and 6 months after carpal tunnel release. Presurgical and postsurgical DMLs were then compared and correlated with variables and possible predictors of outcome including age, body mass index, gender, and presurgical DMLs. The automated nerve conduction testing system DMLs matched those of reference electromyography/nerve conduction study values with high correlation. Sensitivity of the automated nerve conduction testing system when compared with a standardized CTS case definition was 89%, with a specificity of 95%. A significant correlation was found between the DML before release and the DML 1 hour after release. Moreover, maximal postsurgical DML improvement was highly dependent on the presurgical DML, with no improvement shown for the 6-ms group. Among the clinical variables of age, gender, and body mass index only age was mildly predictive of postrelease DML changes at 6 months. No other correlations between clinical variables and postsurgical DMLs were significant. In addition the predictive value of age was lost when combined with the presurgical DML in a multivariate analysis. Postsurgical changes in the median nerve DML were highly dependent on the prerelease latency. The sensitivity and specificity of a nerve conduction monitoring system in detecting and aiding in the diagnosis of CTS is useful in the long-term management of patients with CTS and can aid in determining the level of improvement

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

Energy Technology Data Exchange (ETDEWEB)

Wang, R.; Williams, C. C., E-mail: clayton@physics.utah.edu [Department of Physics and Astronomy, University of Utah, Salt Lake City, Utah 84112 (United States)

2015-09-15

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.

The dynamical conductance of graphene tunnelling structures

International Nuclear Information System (INIS)

Zhang Huan; Chan, K S; Lin Zijing

2011-01-01

The dynamical conductances of graphene tunnelling structures were numerically calculated using the scattering matrix method with the interaction effect included in a phenomenological approach. The overall single-barrier dynamical conductance is capacitative. Transmission resonances in the single-barrier structure lead to dips in the capacitative imaginary part of the response. This is different from the ac responses of typical semiconductor nanostructures, where transmission resonances usually lead to inductive peaks. The features of the dips depend on the Fermi energy. When the Fermi energy is below half of the barrier height, the dips are sharper. When the Fermi energy is higher than half of the barrier height, the dips are broader. Inductive behaviours can be observed in a double-barrier structure due to the resonances formed by reflection between the two barriers.

The dynamical conductance of graphene tunnelling structures.

Science.gov (United States)

Zhang, Huan; Chan, K S; Lin, Zijing

2011-12-16

The dynamical conductances of graphene tunnelling structures were numerically calculated using the scattering matrix method with the interaction effect included in a phenomenological approach. The overall single-barrier dynamical conductance is capacitative. Transmission resonances in the single-barrier structure lead to dips in the capacitative imaginary part of the response. This is different from the ac responses of typical semiconductor nanostructures, where transmission resonances usually lead to inductive peaks. The features of the dips depend on the Fermi energy. When the Fermi energy is below half of the barrier height, the dips are sharper. When the Fermi energy is higher than half of the barrier height, the dips are broader. Inductive behaviours can be observed in a double-barrier structure due to the resonances formed by reflection between the two barriers.

Tunneling spectroscopy on grain boundary junctions in electron-doped high-temperature superconductors; Tunnelspektroskopie an Korngrenzenkontakten aus elektronendotierten Hochtemperatur-Supraleitern

Energy Technology Data Exchange (ETDEWEB)

Welter, B.

2007-12-07

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 H{sub c2}(T) respectively H{sub c2}(0) are presented and applied to the experimental data. Finally the results of the tunnel-spectroscopy measurements are shown.

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

International Nuclear Information System (INIS)

Srisongmuang, B.; Ka-oey, A.

2012-01-01

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

Normal-state conductance used to probe superconducting tunnel junctions for quantum computing

Energy Technology Data Exchange (ETDEWEB)

Chaparro, Carlos; Bavier, Richard; Kim, Yong-Seung; Kim, Eunyoung; Oh, Seongshik [Department of Physics and Astronomy, Rutgers, The State University of New Jersey, Piscataway, NJ 08854 (United States); Kline, Jeffrey S; Pappas, David P, E-mail: carlosch@physics.rutgers.ed, E-mail: ohsean@physics.rutgers.ed [National Institute of Standards and Technology, Boulder, CO 80305 (United States)

2010-04-15

Here we report normal-state conductance measurements of three different types of superconducting tunnel junctions that are being used or proposed for quantum computing applications: p-Al/a-AlO/p-Al, e-Re/e-AlO/p-Al, and e-V/e-MgO/p-V, where p stands for polycrystalline, e for epitaxial, and a for amorphous. All three junctions exhibited significant deviations from the parabolic behavior predicted by the WKB approximation models. In the p-Al/a-AlO/p-Al junction, we observed enhancement of tunneling conductances at voltages matching harmonics of Al-O stretching modes. On the other hand, such Al-O vibration modes were missing in the epitaxial e-Re/e-AlO/p-Al junction. This suggests that absence or existence of the Al-O stretching mode might be related to the crystallinity of the AlO tunnel barrier and the interface between the electrode and the barrier. In the e-V/e-MgO/p-V junction, which is one of the candidate systems for future superconducting qubits, we observed suppression of the density of states at zero bias. This implies that the interface is electronically disordered, presumably due to oxidation of the vanadium surface underneath the MgO barrier, even if the interface was structurally well ordered, suggesting that the e-V/e-MgO/p-V junction will not be suitable for qubit applications in its present form. This also demonstrates that the normal-state conductance measurement can be effectively used to screen out low quality samples in the search for better superconducting tunnel junctions.

Josephson tunneling and nanosystems

OpenAIRE

Ovchinnikov, Yurii; Kresin, Vladimir

2010-01-01

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

Electronic structure classifications using scanning tunneling microscopy conductance imaging

International Nuclear Information System (INIS)

Horn, K.M.; Swartzentruber, B.S.; Osbourn, G.C.; Bouchard, A.; Bartholomew, J.W.

1998-01-01

The electronic structure of atomic surfaces is imaged by applying multivariate image classification techniques to multibias conductance data measured using scanning tunneling microscopy. Image pixels are grouped into classes according to shared conductance characteristics. The image pixels, when color coded by class, produce an image that chemically distinguishes surface electronic features over the entire area of a multibias conductance image. Such open-quotes classedclose quotes images reveal surface features not always evident in a topograph. This article describes the experimental technique used to record multibias conductance images, how image pixels are grouped in a mathematical, classification space, how a computed grouping algorithm can be employed to group pixels with similar conductance characteristics in any number of dimensions, and finally how the quality of the resulting classed images can be evaluated using a computed, combinatorial analysis of the full dimensional space in which the classification is performed. copyright 1998 American Institute of Physics

Tunnelling conductive hybrid films of gold nanoparticles and cellulose and their applications as electrochemical electrodes

International Nuclear Information System (INIS)

Liu, Zhiming; Wang, Xuefeng; Wu, Wenjian; Li, Mei

2015-01-01

Conductive hybrid films of metal nanoparticles and polymers have practical applications in the fields of sensing, microelectronics and catalysis, etc. Herein, we present the electrochemical availability of tunnelling conductive hybrid films of gold nanoparticles (GNPs) and cellulose. The hybrid films were provided with stable tunnelling conductive properties with 12 nm GNPs of 12.7% (in weight). For the first time, the conductive hybrid films were used as substrates of electrochemical electrodes to load calmodulin (CaM) proteins for sensing of calcium cations. The electrodes of hybrid films with 20 nm GNPs of 46.7% (in weight) exhibited stable electrochemical properties, and showed significant responses to calcium cations with concentrations as low as 10 −9 M after being loaded with CaM proteins. (paper)

Tunnel magnetoresistance in asymmetric double-barrier magnetic tunnel junctions

International Nuclear Information System (INIS)

Useinov, N.Kh.; Petukhov, D.A.; Tagirov, L.R.

2015-01-01

The spin-polarized tunnel conductance and tunnel magnetoresistance (TMR) through a planar asymmetric double-barrier magnetic tunnel junction (DBMTJ) have been calculated using quasi-classical model. In DBMTJ nanostructure the magnetization of middle ferromagnetic metal layer can be aligned parallel or antiparallel with respect to the fixed magnetizations of the top and bottom ferromagnetic electrodes. The transmission coefficients of an electron to pass through the barriers have been calculated in terms of quantum mechanics. The dependencies of tunnel conductance and TMR on the applied voltage have been calculated in case of non-resonant transmission. Estimated in the framework of our model, the difference between the spin-channels conductances at low voltages was found relatively large. This gives rise to very high magnitude of TMR. - Highlights: • The spin-polarized conductance through the junction is calculated. • Dependencies of the tunnel conductance vs applied bias are shown. • Bias voltage dependence of tunnel magnetoresistance for the structure is shown

Energy-gap spectroscopy of superconductors using a tunneling microscope

International Nuclear Information System (INIS)

Le Duc, H.G.; Kaiser, W.J.; Stern, J.A.

1987-01-01

A unique scanning tunneling microscope (STM) system has been developed for spectroscopy of the superconducting energy gap. High-resolution control of tunnel current and voltage allows for measurement of superconducting properties at tunnel resistance levels 10 2 --10 3 greater than that achieved in prior work. The previously used STM methods for superconductor spectroscopy are compared to those developed for the work reported here. Superconducting energy-gap spectra are reported for three superconductors, Pb, PbBi, and NbN, over a range of tunnel resistance. The measured spectra are compared directly to theory

Dielectric spectra of proteins in conducting media

International Nuclear Information System (INIS)

Ruderman, G.; Xammar Oro, J.R. de

1990-10-01

Dielectric measurements of serum albumin and myoglobin in solutions of varying conductivities were performed. The results presented confirm that also for protein solutions, the Maxwell predictions of a threshold frequency in conducting materials holds. The threshold frequency of a serum albumin solution was experimentally determined. Attention should be recalled that, if the dielectric spectra of proteins solutions want to be measured, three distinct frequency regions are to be observed: a low frequency region, where the sample behaves like a conductor; an intermediate region centered around the threshold frequency, where the free charges partially screen the fixed ones; and a high frequency region where the sample behaves like a good dielectric. (author). 8 refs, 5 figs

Tunneling probe of fluctuating superconductivity in disordered thin films

Science.gov (United States)

Dentelski, David; Frydman, Aviad; Shimshoni, Efrat; Dalla Torre, Emanuele G.

2018-03-01

Disordered thin films close to the superconductor-insulator phase transition (SIT) hold the key to understanding quantum phase transition in strongly correlated materials. The SIT is governed by superconducting quantum fluctuations, which can be revealed, for example, by tunneling measurements. These experiments detect a spectral gap, accompanied by suppressed coherence peaks, on both sides of the transition. Here we describe the insulating side in terms of a fluctuating superconducting field with finite-range correlations. We perform a controlled diagrammatic resummation and derive analytic expressions for the tunneling differential conductance. We find that short-range superconducting fluctuations suppress the coherence peaks even in the presence of long-range correlations. Our approach offers a quantitative description of existing measurements on disordered thin films and accounts for tunneling spectra with suppressed coherence peaks.

Superconducting phonon spectroscopy using a low-temperature scanning tunneling microscope

Science.gov (United States)

Leduc, H. G.; Kaiser, W. J.; Hunt, B. D.; Bell, L. D.; Jaklevic, R. C.

1989-01-01

The low-temperature scanning tunneling microscope (STM) system described by LeDuc et al. (1987) was used to observe the phonon density of states effects in a superconductor. Using techniques based on those employed in macroscopic tunneling spectroscopy, electron tunneling current-voltage (I-V) spectra were measured for NbN and Pb, and dI/dV vs V spectra were measured using standard analog derivative techniques. I-V measurements on NbN and Pb samples under typical STM conditions showed no evidence for multiparticle tunneling effects.

Measured Temperature Dependence of the cos-phi Conductance in Josephson Tunnel Junctions

DEFF Research Database (Denmark)

Sørensen, O. H.; Mygind, Jesper; Pedersen, Niels Falsig

1977-01-01

The temperature dependence of the cosϕ conductance in Sn-O-Sn Josephson tunnel junctions has been measured just below the critical temperature, Tc. From the resonant microwave response at the junction plasma frequency as the temperature is decreased from Tc it is deduced that the amplitude of the...

Size-dependent energy levels of InSb quantum dots measured by scanning tunneling spectroscopy.

Science.gov (United States)

Wang, Tuo; Vaxenburg, Roman; Liu, Wenyong; Rupich, Sara M; Lifshitz, Efrat; Efros, Alexander L; Talapin, Dmitri V; Sibener, S J

2015-01-27

The electronic structure of single InSb quantum dots (QDs) with diameters between 3 and 7 nm was investigated using atomic force microscopy (AFM) and scanning tunneling spectroscopy (STS). In this size regime, InSb QDs show strong quantum confinement effects which lead to discrete energy levels on both valence and conduction band states. Decrease of the QD size increases the measured band gap and the spacing between energy levels. Multiplets of equally spaced resonance peaks are observed in the tunneling spectra. There, multiplets originate from degeneracy lifting induced by QD charging. The tunneling spectra of InSb QDs are qualitatively different from those observed in the STS of other III-V materials, for example, InAs QDs, with similar band gap energy. Theoretical calculations suggest the electron tunneling occurs through the states connected with L-valley of InSb QDs rather than through states of the Γ-valley. This observation calls for better understanding of the role of indirect valleys in strongly quantum-confined III-V nanomaterials.

The tunneling spectra and superconducting gaps observed by using scanning tunneling microscope near the grain-boundary of FeSe0.3Te0.7 films

OpenAIRE

Lin, K. C.; Li, Y. S.; Shen, Y. T.; Wu, M. K.; Chi, C. C.

2013-01-01

We used STM to study the tunneling spectra of FeSe0.3Te0.7 films with two orientations of ab-planes and the connection ramp between them. We have discovered that, using pulse laser deposition (PLD) method, the a- and b-axis of the FeSe0.3Te0.7 film deposited on Ar-ion-milled Magnesium Oxide (MgO) substrate are rotated 45 degree with respect to those of MgO, while the a- and b-axis of the film grown on pristine MgO substrate are parallel to those of MgO. With photolithography and this techniqu...

Aspirated capacitor measurements of air conductivity and ion mobility spectra

International Nuclear Information System (INIS)

Aplin, K.L.

2005-01-01

Measurements of ions in atmospheric air are used to investigate atmospheric electricity and particulate pollution. Commonly studied ion parameters are (1) air conductivity, related to the total ion number concentration, and (2) the ion mobility spectrum, which varies with atmospheric composition. The physical principles of air ion instrumentation are long established. A recent development is the computerized aspirated capacitor, which measures ions from (a) the current of charged particles at a sensing electrode, and (b) the rate of charge exchange with an electrode at a known initial potential, relaxing to a lower potential. As the voltage decays, only ions of higher and higher mobility are collected by the central electrode and contribute to the further decay of the voltage. This enables extension of the classical theory to calculate ion mobility spectra by inverting voltage decay time series. In indoor air, ion mobility spectra determined from both the voltage decay inversion, and an established voltage switching technique, were compared and shown to be of similar shape. Air conductivities calculated by integration were: 5.3±2.5 and 2.7±1.1 fSm -1 , respectively, with conductivity determined to be 3 fSm -1 by direct measurement at a constant voltage. Applications of the relaxation potential inversion method include air ion mobility spectrum retrieval from historical data, and computation of ion mobility spectra in planetary atmospheres

Tunneling spectroscopy study of YBa2Cu3O7 thin films using a cryogenic scanning tunneling microscope

International Nuclear Information System (INIS)

Wilkins, R.; Amman, M.; Soltis, R.E.; Ben-Jacob, E.; Jaklevic, R.C.

1990-01-01

We have measured reproducible tunneling spectra on YBa 2 Cu 3 O 7 (T c ∼85 K) thin films (thickness ∼2 μm) with a cryogenic scanning tunneling microscope. We find that the I-V curves are generally of three types. The most common type, featured in a large majority of the data, shows a region of high conductance at zero bias. The amplitude of this region is inversely proportional to the tunneling resistance between the tip and sample. It is possible that this can be explained in terms of Josephson effects within the films, although an alternative is given based on electronic self-energy corrections. Data showing capacitive charging steps are analyzed in terms of two ultrasmall tunnel junctions in series.. Theoretical fits to the data give specific values of the junction parameters that are consistent with the assumed geometry of the tip probing an individual grain of the film. The third type of I-V curves exhibits negative differential resistance. We conclude that this phenomenon is probably due to tunneling to localized states in the surface oxide. We also present and discuss data with energy-gap-like behavior; the best example gives Δ to be about 27 mV

Physical meaning of conductivity spectra for ZnO ceramics

Institute of Scientific and Technical Information of China (English)

Cheng Peng-Fei; Li Sheng-Tao; Li Jian-Ying; Ding Can; Yang Yan

2012-01-01

With the help of broadband dielectric spectroscopy in a wide temperature and frequency range,the conductivity spectra of ZnO polycrystalline ceramics are measured and the direct-current-like (DC-like) conductivity and relaxation polarization conductivity are observed successively along the frequency axis.According to the classical Debye theory and Cole-Cole equation,the physical meanings of the two conductivities are discussed.It is found that the DC-like conductivity corresponds to electron transportation over the Schottky barrier at the grainboundary.The relaxation polarization conductivity corresponds to electronic trap relaxation of intrinsic point defects (zinc interstitial and oxygen vacancy).When in the high frequency region,the relaxation conductivity obeys the universal law with the index n equal to the index α in the Cole-Cole equation as an indictor of disorder degree.

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

Energy Technology Data Exchange (ETDEWEB)

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

2014-10-21

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

Charge density waves as the origin of dip-hump structures in the differential tunneling conductance of cuprates: The case of d-wave superconductivity

Energy Technology Data Exchange (ETDEWEB)

Gabovich, Alexander M., E-mail: gabovich@iop.kiev.ua; Voitenko, Alexander I., E-mail: voitenko@iop.kiev.ua

2014-08-15

Highlights: • d-Wave superconductivity and charge-density waves compete for the Fermi surface. • Charge-density waves induce pseudogaps and peak-dip-hump structures in cuprates. • Tunnel spectra are non-symmetric due to the dielectric order-parameter phase fixation. • Scatter of the dielectric order parameter smears the tunnel spectra peculiarities. - Abstract: Quasiparticle differential current–voltage characteristics (CVCs) G(V) of non-symmetric tunnel junctions between d-wave superconductors with charge-density waves (CDWs) and normal metals were calculated. The dependences G(V) were shown to have a V-like form at small voltages V and low temperatures, and to be asymmetric at larger V owing to the presence of CDW peak in either of the V-branches. The spatial scatter of the dielectric (CDW) order parameter smears the CDW peak into a hump and induces a peak-dip-hump structure (PDHS) typical of CVCs observed for such junctions. At temperatures larger than the superconducting critical one, the PDHS evolves into a pseudogap depression. The results agree well with the scanning tunneling microscopy data for Bi{sub 2}Sr{sub 2}CaCu{sub 2}O{sub 8+δ} and YBa{sub 2}Cu{sub 3}O{sub 7−δ}. The results differ substantially from those obtained earlier for CDW s-wave superconductors.

S-I-N tunneling spectroscopy of MgB2 superconductor: evidence of two superconducting energy gaps

International Nuclear Information System (INIS)

Sen, Shashwati; Aswal, D.K.; Singh, Ajay; Gadkari, S.C.; Shah, K.; Gupta, S.K.; Sahni, V.C.

2002-01-01

The tunneling spectra of polycrystalline MgB 2 , have been recorded, at different temperatures between 29 K and T c , using planar superconductor- insulating-normal (S-I-N) tunneling spectroscopy. The planar S-I-N tunnel junctions have been fabricated by thermally evaporating Ag electrodes on MgB 2 surface. The naive layer, which forms at the surface of MgB 2 , due to atmospheric degradation, was employed as an insulating layer between Ag electrodes and MgB 2 . We have found presence of two clear superconducting energy gaps in MgB 2 . The magnitudes of these gaps at 29.5 K are 1.8 and 5.9 MeV, respectively. In the vicinity of T c , while larger energy gap obeyed BCS temperature dependence, the smaller energy gap deviated from BCS dependence. All the spectra exhibited zero-bias conductance, which decreased linearly with temperature and vanished at T c . (author)

Magnetic-field-controlled negative differential conductance in scanning tunneling spectroscopy of graphene npn junction resonators

Science.gov (United States)

Li, Si-Yu; Liu, Haiwen; Qiao, Jia-Bin; Jiang, Hua; He, Lin

2018-03-01

Negative differential conductance (NDC), characterized by the decreasing current with increasing voltage, has attracted continuous attention for its various novel applications. The NDC typically exists in a certain range of bias voltages for a selected system and controlling the regions of NDC in curves of current versus voltage (I -V ) is experimentally challenging. Here, we demonstrate a magnetic-field-controlled NDC in scanning tunneling spectroscopy of graphene npn junction resonators. The magnetic field not only can switch on and off the NDC, but also can continuously tune the regions of the NDC in the I -V curves. In the graphene npn junction resonators, magnetic fields generate sharp and pronounced Landau-level peaks with the help of the Klein tunneling of massless Dirac fermions. A tip of scanning tunneling microscope induces a relatively shift of the Landau levels in graphene beneath the tip. Tunneling between the misaligned Landau levels results in the magnetic-field-controlled NDC.

Conductance mechanism in a linear non-conjugated trimethylsilyl-acetylene molecule: tunneling through localized states

NARCIS (Netherlands)

Petrov, E.G.; Marchenko, A.; Kapitanchuk, O.; Katsonis, Nathalie Hélène; Fichou, D.

2014-01-01

The conductance properties of 1,3-(trimethylsilyl)-1-tridecene-6,12-diyne, a non-conjugated trimethylsil-acetylene molecule have been investigated both experimentally and theoretically. Based on scanning tunnelling spectroscopy experiments, a discussion on the mechanisms controlling the charge

The phonon-assisted tunneling mechanism of conduction in ZnO nanowires and films

International Nuclear Information System (INIS)

Pipinys, Povilas; Ohlckers, Per

2010-01-01

The phonon-assisted tunneling (PhAT) model is applied for an explanation of the conductivity dependence on temperature and temperature-dependent I-V characteristics measured by other investigators for zinc oxide (ZnO) nanowires and films. Our proposed model describes well not only conductivity dependence on temperature measured in a wide temperature range, but also temperature-dependent I-V data using the same set of parameters characterizing the material under investigation. The values of active phonons energy are estimated from a fit of the conductivity dependence to temperature data with the PhAT theory.

Hybrid High-Temperature-Superconductor–Semiconductor Tunnel Diode

Directory of Open Access Journals (Sweden)

Alex Hayat

2012-12-01

Full Text Available We report the demonstration of hybrid high-T_{c}-superconductor–semiconductor tunnel junctions, enabling new interdisciplinary directions in condensed matter research. The devices are fabricated by our newly developed mechanical-bonding technique, resulting in high-T_{c}-superconductor–semiconductor tunnel diodes. Tunneling-spectra characterization of the hybrid junctions of Bi_{2}Sr_{2}CaCu_{2}O_{8+δ} combined with bulk GaAs, or a GaAs/AlGaAs quantum well, exhibits excess voltage and nonlinearity, similarly to spectra obtained in scanning-tunneling microscopy, and is in good agreement with theoretical predictions for a d-wave-superconductor–normal-material junction. Additional junctions are demonstrated using Bi_{2}Sr_{2}CaCu_{2}O_{8+δ} combined with graphite or Bi_{2}Te_{3}. Our results pave the way for new methods in unconventional superconductivity studies, novel materials, and quantum technology applications.

Fluctuations of tunneling currents in photonic and polaritonic systems

Science.gov (United States)

Mantsevich, V. N.; Glazov, M. M.

2018-04-01

Here we develop the nonequilibrium Green's function formalism to analyze the fluctuation spectra of the boson tunneling currents. The approach allows us to calculate the noise spectra in both equilibrium and nonequilibrium conditions. The proposed general formalism is applied to several important realizations of boson transport, including the tunneling transport between two reservoirs and the case where the boson current flows through the intermediate region between the reservoirs. Developed theory can be applied for the analysis of the current noise in waveguides, coupled optical resonators, quantum microcavities, etc., where the tunneling of photons, exciton-polaritons, or excitons can be realized.

Conducting Rock Mass Rating for tunnel construction on Mars

Science.gov (United States)

Beemer, Heidi D.; Worrells, D. Scott

2017-10-01

Mars analogue missions provide researchers, scientists, and engineers the opportunity to establish protocols prior to sending human explorers to another planet. This paper investigated the complexity of a team of simulation astronauts conducting a Rock Mass Rating task during Analogue Mars missions. This study was conducted at the Mars Desert Research Station in Hanksville, UT, during field season 2015/2016 and with crews 167,168, and 169. During the experiment, three-person teams completed a Rock Mass Rating task during a three hour Extra Vehicular Activity on day six of their two-week simulation mission. This geological test is used during design and construction of excavations in rock on Earth. On Mars, this test could be conducted by astronauts to determine suitable rock layers for tunnel construction which would provide explorers a permanent habitat and radiation shielding while living for long periods of time on the surface. The Rock Mass Rating system derives quantitative data for engineering designs that can easily be communicated between engineers and geologists. Conclusions from this research demonstrated that it is feasible for astronauts to conduct the Rock Mass Rating task in a Mars simulated environment. However, it was also concluded that Rock Mass Rating task orientation and training will be required to ensure that accurate results are obtained.

Simplified tunnelling current calculation for MOS structures with ultra-thin oxides for conductive atomic force microscopy investigations

International Nuclear Information System (INIS)

Frammelsberger, Werner; Benstetter, Guenther; Stamp, Richard; Kiely, Janice; Schweinboeck, Thomas

2005-01-01

As charge tunnelling through thin and ultra-thin silicon dioxide layers is regarded as the driving force for MOS device degradation the determination and characterisation of electrically week spots is of paramount importance for device reliability and failure analysis. Conductive atomic force microscopy (C-AFM) is able to address this issue with a spatial resolution smaller than the expected breakdown spot. For the determination of the electrically active oxide thickness in practice an easy to use model with sufficient accuracy and which is largely independent of the oxide thickness is required. In this work a simplified method is presented that meets these demands. The electrically active oxide thickness is determined by matching of C-AFM voltage-current curves and a tunnelling current model, which is based on an analytical tunnelling current approximation. The model holds for both the Fowler-Nordheim tunnelling and the direct tunnelling regime with one single tunnelling parameter set. The results show good agreement with macroscopic measurements for gate voltages larger than approximately 0.5-1 V, and with microscopic C-AFM measurements. For this reason arbitrary oxides in the DT and the FNT regime may be analysed with high lateral resolution by C-AFM, without the need of a preselection of the tunnelling regime to be addressed

Spin tunneling and manipulation in nanostructures.

Science.gov (United States)

Sherman, E Ya; Ban, Yue; Gulyaev, L V; Khomitsky, D V

2012-09-01

The results for joint effects of tunneling and spin-orbit coupling on spin dynamics in nanostructures are presented for systems with discrete and continuous spectra. We demonstrate that tunneling plays the crucial role in the spin dynamics and the abilities of spin manipulation by external electric field. This result can be important for design of nanostructures-based spintronics devices.

Direct, coherent and incoherent intermediate state tunneling and scanning tunnel microscopy (STM)

International Nuclear Information System (INIS)

Halbritter, J.

1997-01-01

Theory and experiment in tunneling are still qualitative in nature, which hold true also for the latest developments in direct-, resonant-, coherent- and incoherent-tunneling. Those tunnel processes have recently branched out of the field of ''solid state tunnel junctions'' into the fields of scanning tunnel microscopy (STM), single electron tunneling (SET) and semiconducting resonant tunnel structures (RTS). All these fields have promoted the understanding of tunneling in different ways reaching from the effect of coherence, of incoherence and of charging in tunneling, to spin flip or inelastic effects. STM allows not only the accurate measurements of the tunnel current and its voltage dependence but, more importantly, the easy quantification via the (quantum) tunnel channel conductance and the distance dependence. This new degree of freedom entering exponentially the tunnel current allows an unique identification of individual tunnel channels and their quantification. In STM measurements large tunnel currents are observed for large distances d > 1 nm explainable by intermediate state tunneling. Direct tunneling with its reduced tunnel time and reduced off-site Coulomb charging bridges distances below 1 nm, only. The effective charge transfer process with its larger off-site and on-site charging at intermediate states dominates tunnel transfer in STM, biology and chemistry over distances in the nm-range. Intermediates state tunneling becomes variable range hopping conduction for distances larger than d > 2 nm, for larger densities of intermediate states n 1 (ε) and for larger temperatures T or voltages U, still allowing high resolution imaging

A temperature dependent tunneling study of the spin density wave gap in EuFe2As2 single crystals.

Science.gov (United States)

Dutta, Anirban; Anupam; Hossain, Z; Gupta, Anjan K

2013-09-18

We report temperature dependent scanning tunneling microscopy and spectroscopy measurements on single crystals of EuFe2As2 in the 15-292 K temperature range. The in situ cleaved crystals show atomic terraces with homogeneous tunnel spectra that correlate well with the spin density wave (SDW) transition at a temperature, TSDW ≈ 186 K. Above TSDW the local tunnel spectra show a small depression in the density of states (DOS) near the Fermi energy (EF). The gap becomes more pronounced upon entering the SDW state with a gap value ∼90 meV at 15 K. However, the zero bias conductance remains finite down to 15 K indicating a finite DOS at the EF in the SDW phase. Furthermore, no noticeable change is observed in the DOS at the antiferromagnetic ordering transition of Eu(2+) moments at 19 K.

Design and electrical performance of CdS/Sb2Te3 tunneling heterojunction devices

Science.gov (United States)

Khusayfan, Najla M.; Qasrawi, A. F.; Khanfar, Hazem K.

2018-02-01

In the current work, a tunneling barrier device made of 20 nm thick Sb2Te3 layer deposited onto 500 nm thick CdS is designed and characterized. The design included a Yb metallic substrate and Ag point contact of area of 10-3 cm2. The heterojunction properties are investigated by means of x-ray diffraction and impedance spectroscopy techniques. It is observed that the coating of the Sb2Te3 onto the surface of CdS causes a further deformation to the already strained structure of hexagonal CdS. The designed energy band diagram for the CdS/Sb2Te3 suggests a straddling type of heterojunction with an estimated conduction and valence band offsets of 0.35 and 1.74 eV, respectively. In addition, the analysis of the capacitance-voltage characteristic curve revealed a depletion region width of 14 nm. On the other hand, the capacitance and conductivity spectra which are analyzed in the frequency domain of 0.001-1.80 GHz indicated that the conduction in the device is dominated by the quantum mechanical tunneling in the region below 0.26 GHz and by the correlated barrier hopping in the remaining region. While the modeling of the conductivity spectra allowed investigation of the density of states near Fermi levels and an average scattering time of 1.0 ns, the capacitance spectra exhibited resonance at 0.26 GHz followed by negative differential capacitance effect in the frequency domain of 0.26-1.8 GHz. Furthermore, the evaluation of the impedance and reflection coefficient spectra indicated the usability of these devices as wide range low pass filters with ideal values of voltage standing wave ratios.

Wind-tunnel investigation of an armed mini remotely piloted vehicle. [conducted in Langley V/STOL tunnel

Science.gov (United States)

Phelps, A. E., III

1979-01-01

A wind tunnel investigation of a full scale remotely piloted vehicle (RPV) armed with rocket launchers was conducted. The model had unacceptable longitudinal stability characteristics at negative angles of attack in the original design configuration. The addition of a pair of fins mounted in a V arrangement on the propeller shroud resulted in a configuration with acceptable longitudinal stability characteristics. The addition of wing mounted external stores to the modified configuration resulted in a slight reduction in the longitudinal stability. The lateral directional characteristics of the model were generally good, but the model had low directional stability at low angles of attack. Aerodynamic control power was very strong around all three axes.

Scanning tunneling spectroscopic studies of superconducting NbN single crystal thin films at 4.2 K

International Nuclear Information System (INIS)

Kashiwaya, S.; Koyanagi, M.; Matsuda, M.; Shoji, A.; Shibata, H.

1991-01-01

This paper reports on a Low Temperature Scanning Tunneling Microscope (LTSTM) constructed to study the microscopic properties of superconductors. It has atomic resolution from room temperature to 4.2 K. Conductance spectra obtained between a Pt tip and a NbN thin film agreed well with theoretical curves based on the BCS theory

Temperature and frequency response of conductivity in Ag2S doped chalcogenide glassy semiconductor

Science.gov (United States)

Ojha, Swarupa; Das, Anindya Sundar; Roy, Madhab; Bhattacharya, Sanjib

2018-06-01

The electric conductivity of chalcogenide glassy semiconductor xAg2S-(1-x)(0.5S-0.5Te) has been presented here as a function of temperature and frequency. Formation of different nanocrystallites has been confirmed from X-ray diffraction study. It is also noteworthy that average size of nanocrystallites decreases with the increase of dislocation density. Dc conductivity data have been interpreted using Mott's model and Greaves's model in low and high temperature regions respectively. Ac conductivity above the room temperature has been analyzed using Meyer-Neldel (MN) conduction rule. It is interestingly noted that Correlated Barrier Hopping (CBH) model is the most appropriate conduction mechanism for x = 0.35, where pairs of charge carrier are considered to hop over the potential barrier between the sites via thermal activation. To interpret experimental data for x = 0.45, modified non-overlapping small polaron tunnelling (NSPT) model is supposed to be appropriate model due to tunnelling through grain boundary. The conductivity spectra at various temperatures have been analyzed using Almond-West Formalism (power law model). Scaling of conductivity spectra reveals that electrical relaxation process of charge carriers (polaron) is temperature independent but depends upon the composition of the present chalcogenide glassy system.

The crossover between tunnel and hopping conductivity in granulated films of noble metals

Science.gov (United States)

Kavokin, Alexey; Kutrovskaya, Stella; Kucherik, Alexey; Osipov, Anton; Vartanyan, Tigran; Arakelyan, Sergey

2017-11-01

The conductivity of thin films composed by clusters of gold and silver nanoparticles has been studies in a wide range of temperatures. The switch from a temperature independence to an exponential thermal dependence of the conductivity manifests the crossover between the tunnel and thermally activated hopping regimes of the electronic transport at the temperature of 60 °C. The characteristic thermal activation energy that governs hopping of electrons between nanoparticles is estimated as 1.3 eV. We have achieved a good control of the composition and thicknesses of nano-cluster films by use of the laser ablation method in colloidal solutions.

Confined states of individual type-II GaSb/GaAs quantum rings studied by cross-sectional scanning tunneling spectroscopy.

Science.gov (United States)

Timm, Rainer; Eisele, Holger; Lenz, Andrea; Ivanova, Lena; Vossebürger, Vivien; Warming, Till; Bimberg, Dieter; Farrer, Ian; Ritchie, David A; Dähne, Mario

2010-10-13

Combined cross-sectional scanning tunneling microscopy and spectroscopy results reveal the interplay between the atomic structure of ring-shaped GaSb quantum dots in GaAs and the corresponding electronic properties. Hole confinement energies between 0.2 and 0.3 eV and a type-II conduction band offset of 0.1 eV are directly obtained from the data. Additionally, the hole occupancy of quantum dot states and spatially separated Coulomb-bound electron states are observed in the tunneling spectra.

Tunneling spectroscopy of a germanium quantum dot in single-hole transistors with self-aligned electrodes

International Nuclear Information System (INIS)

Chen, G-L; Kuo, David M T; Lai, W-T; Li, P-W

2007-01-01

We have fabricated a Ge quantum dot (QD) (∼10 nm) single-hole transistor with self-aligned electrodes using thermal oxidation of a SiGe-on-insulator nanowire based on FinFET technology. This fabricated device exhibits clear Coulomb blockade oscillations with large peak-to-valley ratio (PVCR) of 250-750 and negative differential conductance with PVCR of ∼12 at room temperature. This reveals that the gate-induced tunneling barrier lowering is effectively suppressed due to the self-aligned electrode structure. The magnitude of tunneling current spectra also reveals the coupling strengths between the energy levels of the Ge QD and electrodes

Tunneling time, exit time and exit momentum in strong field tunnel ionization

International Nuclear Information System (INIS)

Teeny, Nicolas

2016-01-01

Tunnel ionization belongs to the fundamental processes of atomic physics. It is still an open question when does the electron tunnel ionize and how long is the duration of tunneling. In this work we solve the time-dependent Schroedinger equation in one and two dimensions and use ab initio quantum calculations in order to answer these questions. Additionally, we determine the exit momentum of the tunnel ionized electron from first principles. We find out results that are different from the assumptions of the commonly employed two-step model, which assumes that the electron ionizes at the instant of electric field maximum with a zero momentum. After determining the quantum final momentum distribution of tunnel ionized electrons we show that the two-step model fails to predict the correct final momentum. Accordingly we suggest how to correct the two-step model. Furthermore, we determine the instant at which tunnel ionization starts, which turns out to be different from the instant usually assumed. From determining the instant at which it is most probable for the electron to enter the tunneling barrier and the instant at which it exits we determine the most probable time spent under the barrier. Moreover, we apply a quantum clock approach in order to determine the duration of tunnel ionization. From the quantum clock we determine an average tunneling time which is different in magnitude and origin with respect to the most probable tunneling time. By defining a probability distribution of tunneling times using virtual detectors we relate both methods and explain the apparent discrepancy. The results found have in general an effect on the interpretation of experiments that measure the spectra of tunnel ionized electrons, and specifically on the calibration of the so called attoclock experiments, because models with imprecise assumptions are usually employed in order to interpret experimental results.

Tunneling time, exit time and exit momentum in strong field tunnel ionization

Energy Technology Data Exchange (ETDEWEB)

Teeny, Nicolas

2016-10-18

Tunnel ionization belongs to the fundamental processes of atomic physics. It is still an open question when does the electron tunnel ionize and how long is the duration of tunneling. In this work we solve the time-dependent Schroedinger equation in one and two dimensions and use ab initio quantum calculations in order to answer these questions. Additionally, we determine the exit momentum of the tunnel ionized electron from first principles. We find out results that are different from the assumptions of the commonly employed two-step model, which assumes that the electron ionizes at the instant of electric field maximum with a zero momentum. After determining the quantum final momentum distribution of tunnel ionized electrons we show that the two-step model fails to predict the correct final momentum. Accordingly we suggest how to correct the two-step model. Furthermore, we determine the instant at which tunnel ionization starts, which turns out to be different from the instant usually assumed. From determining the instant at which it is most probable for the electron to enter the tunneling barrier and the instant at which it exits we determine the most probable time spent under the barrier. Moreover, we apply a quantum clock approach in order to determine the duration of tunnel ionization. From the quantum clock we determine an average tunneling time which is different in magnitude and origin with respect to the most probable tunneling time. By defining a probability distribution of tunneling times using virtual detectors we relate both methods and explain the apparent discrepancy. The results found have in general an effect on the interpretation of experiments that measure the spectra of tunnel ionized electrons, and specifically on the calibration of the so called attoclock experiments, because models with imprecise assumptions are usually employed in order to interpret experimental results.

Temperature dependence of the cosphi conductance in Josephson tunnel junctions determined from plasma resonance experiments

DEFF Research Database (Denmark)

Pedersen, Niels Falsig; Sørensen, O. H.; Mygind, Jesper

1978-01-01

The microwave response at 9 GHz of Sn-O-Sn tunnel-junction current biased at zero dc voltage has been measured just below the critical temperature Tc of the Sn films. The temperature dependence of the cosφ conductance is determined from the resonant response at the junction plasma frequency fp...

Spin-wave thermal population as temperature probe in magnetic tunnel junctions

Energy Technology Data Exchange (ETDEWEB)

Le Goff, A., E-mail: adrien.le-goff@u-psud.fr; Devolder, T. [Institut d' Electronique Fondamentale, CNRS, Univ. Paris-Sud, Université Paris-Saclay, 91405 Orsay (France); Nikitin, V. [SAMSUNG Electronics Corporation, 601 McCarthy Blvd Milpitas, California 95035 (United States)

2016-07-14

We study whether a direct measurement of the absolute temperature of a Magnetic Tunnel Junction (MTJ) can be performed using the high frequency electrical noise that it delivers under a finite voltage bias. Our method includes quasi-static hysteresis loop measurements of the MTJ, together with the field-dependence of its spin wave noise spectra. We rely on an analytical modeling of the spectra by assuming independent fluctuations of the different sub-systems of the tunnel junction that are described as macrospin fluctuators. We illustrate our method on perpendicularly magnetized MgO-based MTJs patterned in 50 × 100 nm{sup 2} nanopillars. We apply hard axis (in-plane) fields to let the magnetic thermal fluctuations yield finite conductance fluctuations of the MTJ. Instead of the free layer fluctuations that are observed to be affected by both spin-torque and temperature, we use the magnetization fluctuations of the sole reference layers. Their much stronger anisotropy and their much heavier damping render them essentially immune to spin-torque. We illustrate our method by determining current-induced heating of the perpendicularly magnetized tunnel junction at voltages similar to those used in spin-torque memory applications. The absolute temperature can be deduced with a precision of ±60 K, and we can exclude any substantial heating at the spin-torque switching voltage.

Tunneling Conductance in Ferromagnetic Metal/Normal Metal/Spin-Singlet -Wave Ferromagnetic Superconductor Junctions

Directory of Open Access Journals (Sweden)

Hamidreza Emamipour

2013-01-01

Full Text Available In the framework of scattering theory, we study the tunneling conductance in a system including two junctions, ferromagnetic metal/normal metal/ferromagnetic superconductor, where ferromagnetic superconductor is in spin-singlet -wave pairing state. The non-magnetic normal metal is placed in the intermediate layer with the thickness ( which varies from 1 nm to 10000 nm. The interesting result which we have found is the existence of oscillations in conductance curves. The period of oscillations is independent of FS and FN exchange field while it depends on . The obtained results can serve as a useful tool to determine the kind of pairing symmetry in ferromagnetic superconductors.

Effect of the subgap conductance on the metastable states in a Josephson tunnel junction

International Nuclear Information System (INIS)

Cristiano, R.; Pagano, S.; Silvestrini, P.; Gray, K.E.; Liengme, O.

1987-09-01

An investigation of the decay rate of metastable states in Josephson tunnel junctions in presence of thermal noise is presented. We have observed that, in the extremely underdamped regime, there is an exponential temperature dependence of the best fit value for the shunt conductance. Such a dependence shows a close relation with the temperature dependence of the subgap conductance, suggesting that the effective conductance for the escape from the metastable states obeys to a quasi-particle thermal activation mechanism. The introduction of this effective conductance into the lifetime expression for the zero-voltage states leads to significant changes in the width of the switching current distributions. A comparisons of the experimental data with the proposed model is reported. 7 refs., 2 figs

Mechanistic analysis of temperature-dependent current conduction through thin tunnel oxide in n+-polySi/SiO2/n+-Si structures

Science.gov (United States)

Samanta, Piyas

2017-09-01

We present a detailed investigation on temperature-dependent current conduction through thin tunnel oxides grown on degenerately doped n-type silicon (n+-Si) under positive bias ( VG ) on heavily doped n-type polycrystalline silicon (n+-polySi) gate in metal-oxide-semiconductor devices. The leakage current measured between 298 and 573 K and at oxide fields ranging from 6 to 10 MV/cm is primarily attributed to Poole-Frenkel (PF) emission of trapped electrons from the neutral electron traps located in the silicon dioxide (SiO2) band gap in addition to Fowler-Nordheim (FN) tunneling of electrons from n+-Si acting as the drain node in FLOating gate Tunnel OXide Electrically Erasable Programmable Read-Only Memory devices. Process-induced neutral electron traps are located at 0.18 eV and 0.9 eV below the SiO2 conduction band. Throughout the temperature range studied here, PF emission current IPF dominates FN electron tunneling current IFN at oxide electric fields Eox between 6 and 10 MV/cm. A physics based new analytical formula has been developed for FN tunneling of electrons from the accumulation layer of degenerate semiconductors at a wide range of temperatures incorporating the image force barrier rounding effect. FN tunneling has been formulated in the framework of Wentzel-Kramers-Brilloiun taking into account the correction factor due to abrupt variation of the energy barrier at the cathode/oxide interface. The effect of interfacial and near-interfacial trapped-oxide charges on FN tunneling has also been investigated in detail at positive VG . The mechanism of leakage current conduction through SiO2 films plays a crucial role in simulation of time-dependent dielectric breakdown of the memory devices and to precisely predict the normal operating field or applied floating gate (FG) voltage for lifetime projection of the devices. In addition, we present theoretical results showing the effect of drain doping concentration on the FG leakage current.

Magnetic tunnel junctions with monolayer hexagonal boron nitride tunnel barriers

Energy Technology Data Exchange (ETDEWEB)

Piquemal-Banci, M.; Galceran, R.; Bouzehouane, K.; Anane, A.; Petroff, F.; Fert, A.; Dlubak, B.; Seneor, P. [Unité Mixte de Physique, CNRS, Thales, Univ. Paris-Sud, Université Paris-Saclay, Palaiseau 91767 (France); Caneva, S.; Martin, M.-B.; Weatherup, R. S.; Kidambi, P. R.; Robertson, J.; Hofmann, S. [Department of Engineering, University of Cambridge, Cambridge CB21PZ (United Kingdom); Xavier, S. [Thales Research and Technology, 1 avenue Augustin Fresnel, Palaiseau 91767 (France)

2016-03-07

We report on the integration of atomically thin 2D insulating hexagonal boron nitride (h-BN) tunnel barriers into Co/h-BN/Fe magnetic tunnel junctions (MTJs). The h-BN monolayer is directly grown by chemical vapor deposition on Fe. The Conductive Tip Atomic Force Microscopy (CT-AFM) measurements reveal the homogeneity of the tunnel behavior of our h-BN layers. As expected for tunneling, the resistance depends exponentially on the number of h-BN layers. The h-BN monolayer properties are also characterized through integration into complete MTJ devices. A Tunnel Magnetoresistance of up to 6% is observed for a MTJ based on a single atomically thin h-BN layer.

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

International Nuclear Information System (INIS)

Pryadkin, S.L.; Tsoj, V.S.

1988-01-01

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

Tunneling current between graphene layers

OpenAIRE

Poklonski, Nikolai A.; Siahlo, Andrei I.; Vyrko, Sergey A.; Popov, Andrey M.; Lozovik, Yurii E.

2013-01-01

The physical model that allows to calculate the values of the tunneling current be-tween graphene layers is proposed. The tunneling current according to the pro-posed model is proportional to the area of tunneling transition. The calculated value of tunneling conductivity is in qualitative agreement with experimental data.

Thermal conductivity of thin insulating films determined by tunnel magneto-Seebeck effect measurements and finite-element modeling

Science.gov (United States)

Huebner, Torsten; Martens, Ulrike; Walowski, Jakob; Münzenberg, Markus; Thomas, Andy; Reiss, Günter; Kuschel, Timo

2018-06-01

In general, it is difficult to access the thermal conductivity of thin insulating films experimentally by electrical means. Here, we present a new approach utilizing the tunnel magneto-Seebeck effect (TMS) in combination with finite-element modeling (FEM). We detect the laser-induced TMS and the absolute thermovoltage of laser-heated magnetic tunnel junctions with 2.6 nm thin barriers of MgAl2O4 (MAO) and MgO, respectively. A second measurement of the absolute thermovoltage after a dielectric breakdown of the barrier grants insight into the remaining thermovoltage of the stack. Thus, the pure TMS without any parasitic Nernst contributions from the leads can be identified. In combination with FEM via COMSOL, we are able to extract values for the thermal conductivity of MAO (0.7 W (K · m)‑1) and MgO (5.8 W (K · m)‑1), which are in very good agreement with theoretical predictions. Our method provides a new promising way to extract the experimentally challenging parameter of the thermal conductivity of thin insulating films.

Full-dimensional characterization of photoelectron spectra of HOCO− and DOCO− and tunneling facilitated decay of HOCO prepared by anion photodetachment

International Nuclear Information System (INIS)

Wang, Jun; Li, Jun; Guo, Hua; Ma, Jianyi

2014-01-01

The photodetachment of both the HOCO − and DOCO − anions is investigated using full-dimensional quantum wave packets on new ab initio based global potential energy surfaces for both the neutral and anionic species. The calculated electron affinities and neutral fundamental vibrational frequencies of both isotopomers are in good agreement with available experimental data. The measured photoelectron spectra are also accurately reproduced, further validating the accuracy of the potential energy surfaces. In addition, strong mode specificity is found in the lifetimes of the HOCO vibrational features and the tunneling facilitated predissociation rates to H + CO 2 are rationalized using the recently proposed sudden vector projection model

Structural and electrical properties of conducting diamond nanowires.

Science.gov (United States)

Sankaran, Kamatchi Jothiramalingam; Lin, Yen-Fu; Jian, Wen-Bin; Chen, Huang-Chin; Panda, Kalpataru; Sundaravel, Balakrishnan; Dong, Chung-Li; Tai, Nyan-Hwa; Lin, I-Nan

2013-02-01

Conducting diamond nanowires (DNWs) films have been synthesized by N₂-based microwave plasma enhanced chemical vapor deposition. The incorporation of nitrogen into DNWs films is examined by C 1s X-ray photoemission spectroscopy and morphology of DNWs is discerned using field-emission scanning electron microscopy and transmission electron microscopy (TEM). The electron diffraction pattern, the visible-Raman spectroscopy, and the near-edge X-ray absorption fine structure spectroscopy display the coexistence of sp³ diamond and sp² graphitic phases in DNWs films. In addition, the microstructure investigation, carried out by high-resolution TEM with Fourier transformed pattern, indicates diamond grains and graphitic grain boundaries on surface of DNWs. The same result is confirmed by scanning tunneling microscopy and scanning tunneling spectroscopy (STS). Furthermore, the STS spectra of current-voltage curves discover a high tunneling current at the position near the graphitic grain boundaries. These highly conducting regimes of grain boundaries form effective electron paths and its transport mechanism is explained by the three-dimensional (3D) Mott's variable range hopping in a wide temperature from 300 to 20 K. Interestingly, this specific feature of high conducting grain boundaries of DNWs demonstrates a high efficiency in field emission and pave a way to the next generation of high-definition flat panel displays or plasma devices.

Incoherent tunneling and heat dissipation in molecular bridges

International Nuclear Information System (INIS)

Pecchia, A; Gagliardi, A; Solomon, G; Carlo, A Di; Frauenheim, Th; Reimers, J R

2006-01-01

Simulated IV characteristics and inelastic electron tunneling spectra of octanedithiol chemisorbed on gold electrodes are presented. The geometric and electronic structure is obtained from calculations based on a density functional scheme. A non-equilibrium Green's function formalism is employed to deal with the transport aspect of the problem. Both the IV and the calculated spectra show good agreement with experimental results and suggest further details in the assignment and characterization of such spectra

Scanning tunnelling microscope light emission: Finite temperature current noise and over cut-off emission.

Science.gov (United States)

Kalathingal, Vijith; Dawson, Paul; Mitra, J

2017-06-14

The spectral distribution of light emitted from a scanning tunnelling microscope junction not only bears its intrinsic plasmonic signature but is also imprinted with the characteristics of optical frequency fluc- tuations of the tunnel current. Experimental spectra from gold-gold tunnel junctions are presented that show a strong bias (V b ) dependence, curiously with emission at energies higher than the quantum cut-off (eV b ); a component that decays monotonically with increasing bias. The spectral evolution is explained by developing a theoretical model for the power spectral density of tunnel current fluctuations, incorporating finite temperature contribution through consideration of the quantum transport in the system. Notably, the observed decay of the over cut-off emission is found to be critically associated with, and well explained in terms of the variation in junction conductance with V b . The investigation highlights the scope of plasmon-mediated light emission as a unique probe of high frequency fluctuations in electronic systems that are fundamental to the electrical generation and control of plasmons.

Zero-bias peaks in the tunneling conductance of spin-orbit-coupled superconducting wires with and without Majorana end-states.

Science.gov (United States)

Liu, Jie; Potter, Andrew C; Law, K T; Lee, Patrick A

2012-12-28

One of the simplest proposed experimental probes of a Majorana bound state is a quantized (2e(2)/h) value of zero-bias tunneling conductance. When temperature is somewhat larger than the intrinsic width of the Majorana peak, conductance is no longer quantized, but a zero-bias peak can remain. Such a nonquantized zero-bias peak has been recently reported for semiconducting nanowires with proximity induced superconductivity. In this Letter we analyze the relation of the zero-bias peak to the presence of Majorana end states, by simulating the tunneling conductance for multiband wires with realistic amounts of disorder. We show that this system generically exhibits a (nonquantized) zero-bias peak even when the wire is topologically trivial and does not possess Majorana end states. We make comparisons to recent experiments, and discuss the necessary requirements for confirming the existence of a Majorana state.

A graphene solution to conductivity mismatch: spin injection from ferromagnetic metal/graphene tunnel contacts into silicon

Science.gov (United States)

van't Erve, Olaf

2014-03-01

New paradigms for spin-based devices, such as spin-FETs and reconfigurable logic, have been proposed and modeled. These devices rely on electron spin being injected, transported, manipulated and detected in a semiconductor channel. This work is the first demonstration on how a single layer of graphene can be used as a low resistance tunnel barrier solution for electrical spin injection into Silicon at room temperature. We will show that a FM metal / monolayer graphene contact serves as a spin-polarized tunnel barrier which successfully circumvents the classic metal / semiconductor conductivity mismatch issue for electrical spin injection. We demonstrate electrical injection and detection of spin accumulation in Si above room temperature, and show that the corresponding spin lifetimes correlate with the Si carrier concentration, confirming that the spin accumulation measured occurs in the Si and not in interface trap states. An ideal tunnel barrier should exhibit several key material characteristics: a uniform and planar habit with well-controlled thickness, minimal defect / trapped charge density, a low resistance-area product for minimal power consumption, and compatibility with both the FM metal and semiconductor, insuring minimal diffusion to/from the surrounding materials at temperatures required for device processing. Graphene, offers all of the above, while preserving spin injection properties, making it a compelling solution to the conductivity mismatch for spin injection into Si. Although Graphene is very conductive in plane, it exhibits poor conductivity perpendicular to the plane. Its sp2 bonding results in a highly uniform, defect free layer, which is chemically inert, thermally robust, and essentially impervious to diffusion. The use of a single monolayer of graphene at the Si interface provides a much lower RA product than any film of an oxide thick enough to prevent pinholes (1 nm). Our results identify a new route to low resistance-area product spin

Infrared spectra and tunneling dynamics of the N2-D2O and OC-D2O complexes in the v2 bend region of D2O.

Science.gov (United States)

Zhu, Yu; Zheng, Rui; Li, Song; Yang, Yu; Duan, Chuanxi

2013-12-07

The rovibrational spectra of the N2-D2O and OC-D2O complexes in the v2 bend region of D2O have been measured in a supersonic slit jet expansion using a rapid-scan tunable diode laser spectrometer. Both a-type and b-type transitions were observed for these two complexes. All transitions are doubled, due to the heavy water tunneling within the complexes. Assuming the tunneling splittings are the same in K(a) = 0 and K(a) = 1, the band origins, all three rotational and several distortion constants of each tunneling state were determined for N2-D2O in the ground and excited vibrational states, and for OC-D2O in the excited vibrational state, respectively. The averaged band origin of OC-D2O is blueshifted by 2.241 cm(-1) from that of the v2 band of the D2O monomer, compared with 1.247 cm(-1) for N2-D2O. The tunneling splitting of N2-D2O in the ground state is 0.16359(28) cm(-1), which is about five times that of OC-D2O. The tunneling splittings decrease by about 26% for N2-D2O and 23% for OC-D2O, respectively, upon excitation of the D2O bending vibration, indicating an increase of the tunneling barrier in the excited vibrational state. The tunneling splittings are found to have a strong dependence on intramolecular vibrational excitation as well as a weak dependence on quantum number K(a).

Local study of the Mg{sub 1-x}Al{sub x}B{sub 2} single crystals by scanning tunneling spectroscopy in magnetic field up to 3 Tesla

Energy Technology Data Exchange (ETDEWEB)

Giubileo, F. [CNR-INFM Laboratorio Regionale SUPERMAT, Dipartimento di Fisica ' E.R. Caianiello' , Universita degli Studi di Salerno, via Salvador Allende, 84081 Baronissi, SA (Italy)], E-mail: giubileo@sa.infn.it; Bobba, F.; Scarfato, A.; Cucolo, A.M. [CNR-INFM Laboratorio Regionale SUPERMAT, Dipartimento di Fisica ' E.R. Caianiello' , Universita degli Studi di Salerno, via Salvador Allende, 84081 Baronissi, SA (Italy); Kohen, A.; Roditchev, D. [Institut des Nanosciences de Paris, INSP, Universite P. et M. Curie Paris 6, CNRS, UMR 75-88, Paris (France); Zhigadlo, N.D.; Karpinski, J. [Solid State Physics Laboratory, ETH Zurich, CH-8093 Zurich (Switzerland)

2008-04-01

We have performed local tunneling spectroscopy on high quality Mg{sub 1-x}Al{sub x}B{sub 2} single crystals by means of variable temperature scanning tunneling spectroscopy in magnetic field up to 3 Tesla. Single gap conductance spectra due to c-axis tunneling were extensively measured, probing different amplitudes of the three-dimensional {delta}{sub {pi}} as a function of Al content (i.e. as a function of the critical temperature T{sub C}). Temperature and magnetic field dependences of the conductance spectra were studied in S-I-N configuration: the effect of the doping resulted in a monotonous reduction of the locally measured T{sub C} down to 24 K for x = 0.2. The magnetic field dependence was studied in a local way: An estimation for upper critical field H{sub c2} was inferred from the evolution of the tunneling spectra with the field perpendicular to the sample surface, for different doping levels. The high spatial resolution of the STS technique allowed us to evidence possible non-homogeneities of the superconducting properties on the sample surface with variation of in the same sample depending on different local levels of doping. The locally measured upper critical field resulted to vary for different dopings, and the maximum value H{sub c2}{approx_equal}3T was found for samples with T{sub C}=33 K. The evolution of the density of states (DOS) was found to be characterized by two distinct regimes separated by a crossover region. Our results indicate a rapid suppression of the intrinsic term in {pi}-band superconductivity for 0 T < B < 0.5 T. At high fields (0.8 T < B < 3 T) the superconductivity in the {pi}-band survives uniquely due to the coupling to the {sigma}-band. The shape of tunneling spectra suggests an important role played by the quasiparticle inter-band scattering.

Spatially resolved vacuum tunneling spectroscopy on Bi 2Sr 2CaCu 2O 8 by STM at 4.8K

Science.gov (United States)

Renner, Ch.; Fischer, Ø.; Kent, A. D.; Mitzi, D. B.; Kapitulnik, A.

1994-02-01

We report scanning tunneling spectroscopy investigations on in-situ cleaved superconducting Bi 2Sr 2CaCu 2O 8 single crystals. Although many investigators report reproducible tunneling studies on high temperature superconductors, there nevertheless remains uncertainties about the correct intrinsic shape of the tunneling spectra. We have been able to obtain higly reproducible spectra while scanning single crystal surfaces in many different areas and taking a spectra every 5Å along lines of several hundred Ångstroms. Furthermore, we show that the spectra are independent of modifacations of the barrier obtained by changing the tip/sample distance. The experimental density of states clearly shows some filling of the gap which does not fit with a BCS-like s-wave prediction, even if some scattering in the tunneling process is accounted for.

Spatially resolved vacuum tunneling spectroscopy on Bi2Sr2CaCu2O8 by STM at 4.8K

International Nuclear Information System (INIS)

Renner, C.; Fischer, Oe.; Kent, A.D.; Mitzi, D.B.; Kapitulnik, A.

1994-01-01

We report scanning tunneling spectroscopy investigations on in-situ cleaved superconducting Bi 2 Sr 2 CaCu 2 O 8 single crystals. Although many investigators report reproducible tunneling studies on high temperature superconductors, there nevertheless remains uncertainties about the correct intrinsic shape of the tunneling spectra. We have been able to obtain highly reproducible spectra while scanning single crystal surfaces in many different areas and taking a spectra every 5A along lines of several hundred AAngstroms. Furthermore, we show that the spectra are independent of modifications of the barrier obtained by changing the tip/sample distance. The experimental density of states clearly shows some filling of the gap which does not fit with a BCS-like s-wave prediction, even if some scattering in the tunneling process is accounted for. (orig.)

Correlating nerve conduction studies and clinical outcome measures on carpal tunnel syndrome: lessons from a randomized controlled trial

NARCIS (Netherlands)

Schrijver, H.M.; Gerritsen, A.A.M.; Strijers, R.L.; Uitdehaag, B.M.J.; Scholten, R.J.P.M.; de Vet, H.C.W.; Bouter, L.M.

2005-01-01

The reported relationships between nerve conduction studies (NCS) and outcome measures in carpal tunnel syndrome (CTS) are weak to moderate. However, selection of patients may have confounded nonrandomized studies. NCS have potentially great value in selecting patients for a specific treatment and

Ferroelectric tunneling element and memory applications which utilize the tunneling element

Science.gov (United States)

Kalinin, Sergei V [Knoxville, TN; Christen, Hans M [Knoxville, TN; Baddorf, Arthur P [Knoxville, TN; Meunier, Vincent [Knoxville, TN; Lee, Ho Nyung [Oak Ridge, TN

2010-07-20

A tunneling element includes a thin film layer of ferroelectric material and a pair of dissimilar electrically-conductive layers disposed on opposite sides of the ferroelectric layer. Because of the dissimilarity in composition or construction between the electrically-conductive layers, the electron transport behavior of the electrically-conductive layers is polarization dependent when the tunneling element is below the Curie temperature of the layer of ferroelectric material. The element can be used as a basis of compact 1R type non-volatile random access memory (RAM). The advantages include extremely simple architecture, ultimate scalability and fast access times generic for all ferroelectric memories.

Tunneling magnetoresistance and electroresistance in Fe/PbTiO3/Fe multiferroic tunnel junctions

International Nuclear Information System (INIS)

Dai, Jian-Qing

2016-01-01

We perform first-principles electronic structure and spin-dependent transport calculations for a Fe/PbTiO 3 /Fe multiferroic tunnel junction with asymmetric TiO 2 - and PbO-terminated interfaces. We demonstrate that the interfacial electronic reconstruction driven by the in situ screening of ferroelectric polarization, in conjunction with the intricate complex band structure of barrier, play a decisive role in controlling the spin-dependent tunneling. Reversal of ferroelectric polarization results in a transition from insulating to half-metal-like conducting state for the interfacial Pb 6p z orbitals, which acts as an atomic-scale spin-valve by releasing the tunneling current in antiparallel magnetization configuration as the ferroelectric polarization pointing to the PbO-terminated interface. This effect produces large change in tunneling conductance. Our results open an attractive avenue in designing multiferroic tunnel junctions with excellent performance by exploiting the interfacial electronic reconstruction originated from the in situ screening of ferroelectric polarization.

Development of micro-four-point probe in a scanning tunneling microscope for in situ electrical transport measurement.

Science.gov (United States)

Ge, Jian-Feng; Liu, Zhi-Long; Gao, Chun-Lei; Qian, Dong; Liu, Canhua; Jia, Jin-Feng

2015-05-01

Electrons at surface may behave differently from those in bulk of a material. Multi-functional tools are essential in comprehensive studies on a crystal surface. Here, we developed an in situ microscopic four-point probe (4PP) transport measurement system on the basis of a scanning tunneling microscope (STM). In particular, convenient replacement between STM tips and micro-4PPs enables systematic investigations of surface morphology, electronic structure, and electrical transport property of a same sample surface. Performances of the instrument are demonstrated with high-quality STM images, tunneling spectra, and low-noise electrical I-V characteristic curves of a single-layer FeSe film grown on a conductive SrTiO3 surface.

Development of micro-four-point probe in a scanning tunneling microscope for in situ electrical transport measurement

Energy Technology Data Exchange (ETDEWEB)

Ge, Jian-Feng; Liu, Zhi-Long; Gao, Chun-Lei; Qian, Dong; Liu, Canhua, E-mail: canhualiu@sjtu.edu.cn, E-mail: jfjia@sjtu.edu.cn; Jia, Jin-Feng, E-mail: canhualiu@sjtu.edu.cn, E-mail: jfjia@sjtu.edu.cn [Key Laboratory of Artificial Structures and Quantum Control (Ministry of Education), Department of Physics and Astronomy, Shanghai Jiao Tong University, 800 Dongchuan Road, Shanghai 200240 (China)

2015-05-15

Electrons at surface may behave differently from those in bulk of a material. Multi-functional tools are essential in comprehensive studies on a crystal surface. Here, we developed an in situ microscopic four-point probe (4PP) transport measurement system on the basis of a scanning tunneling microscope (STM). In particular, convenient replacement between STM tips and micro-4PPs enables systematic investigations of surface morphology, electronic structure, and electrical transport property of a same sample surface. Performances of the instrument are demonstrated with high-quality STM images, tunneling spectra, and low-noise electrical I-V characteristic curves of a single-layer FeSe film grown on a conductive SrTiO{sub 3} surface.

Scanning tunneling microscope nanoetching method

Science.gov (United States)

Li, Yun-Zhong; Reifenberger, Ronald G.; Andres, Ronald P.

1990-01-01

A method is described for forming uniform nanometer sized depressions on the surface of a conducting substrate. A tunneling tip is used to apply tunneling current density sufficient to vaporize a localized area of the substrate surface. The resulting depressions or craters in the substrate surface can be formed in information encoding patterns readable with a scanning tunneling microscope.

Dependences of the Tunnel Magnetoresistance and Spin Transfer Torque on the Sizes and Concentration of Nanoparticles in Magnetic Tunnel Junctions

Science.gov (United States)

Esmaeili, A. M.; Useinov, A. N.; Useinov, N. Kh.

2018-01-01

Dependences of the tunnel magnetoresistance and in-plane component of the spin transfer torque on the applied voltage in a magnetic tunnel junction have been calculated in the approximation of ballistic transport of conduction electrons through an insulating layer with embedded magnetic or nonmagnetic nanoparticles. A single-barrier magnetic tunnel junction with a nanoparticle embedded in an insulator forms a double-barrier magnetic tunnel junction. It has been shown that the in-plane component of the spin transfer torque in the double-barrier magnetic tunnel junction can be higher than that in the single-barrier one at the same thickness of the insulating layer. The calculations show that nanoparticles embedded in the tunnel junction increase the probability of tunneling of electrons, create resonance conditions, and ensure the quantization of the conductance in contrast to the tunnel junction without nanoparticles. The calculated dependences of the tunnel magnetoresistance correspond to experimental data demonstrating peak anomalies and suppression of the maximum magnetoresistances at low voltages.

Microstructure, electrical conductivity and modulus spectra of CdI{sub 2} doped nanocomposite-electrolytes

Energy Technology Data Exchange (ETDEWEB)

Kundu, Ranadip [Department of Engineering Sciences and Humanities, Siliguri Institute of Technology, Darjeeeling 734009, West Bengal (India); Department of Mechanical Engineering, Jadavpur University, Jadavpur, Kolkata 700032 (India); Roy, Debasish [Department of Mechanical Engineering, Jadavpur University, Jadavpur, Kolkata 700032 (India); Bhattacharya, Sanjib, E-mail: sanjib_ssp@yahoo.co.in [Department of Engineering Sciences and Humanities, Siliguri Institute of Technology, Darjeeeling 734009, West Bengal (India)

2017-02-15

Ionic conductivity and dielectric behavior of Ag{sub 2}O–CdI{sub 2}–CdO nanocomposite system have been studied. X-ray diffraction has been carried out to obtain the crystallite sizes and the growth of CdO dispersed in glass-matrices. Total conductivity of them shows thermally activated nature. It is observed that total conductivity decreases and corresponding activation energy for conduction follows opposite behavior. The high-frequency ac conductivity may correspond to a nonrandom, correlated and sub-diffusive motion of Ag{sup +} ions. Conductivity relaxation time is found to increase. The nature of scaling of the conductivity as well as modulus spectra indicates that the electrical relaxation of Ag{sup +} is temperature independent but depends upon composition.

Tunneling magnetoresistance and electroresistance in Fe/PbTiO{sub 3}/Fe multiferroic tunnel junctions

Energy Technology Data Exchange (ETDEWEB)

Dai, Jian-Qing, E-mail: djqkust@sina.com [School of Materials Science and Engineering, Kunming University of Science and Technology, Kunming 650093 (China)

2016-08-21

We perform first-principles electronic structure and spin-dependent transport calculations for a Fe/PbTiO{sub 3}/Fe multiferroic tunnel junction with asymmetric TiO{sub 2}- and PbO-terminated interfaces. We demonstrate that the interfacial electronic reconstruction driven by the in situ screening of ferroelectric polarization, in conjunction with the intricate complex band structure of barrier, play a decisive role in controlling the spin-dependent tunneling. Reversal of ferroelectric polarization results in a transition from insulating to half-metal-like conducting state for the interfacial Pb 6p{sub z} orbitals, which acts as an atomic-scale spin-valve by releasing the tunneling current in antiparallel magnetization configuration as the ferroelectric polarization pointing to the PbO-terminated interface. This effect produces large change in tunneling conductance. Our results open an attractive avenue in designing multiferroic tunnel junctions with excellent performance by exploiting the interfacial electronic reconstruction originated from the in situ screening of ferroelectric polarization.

Directional scanning tunneling spectroscopy in MgB2

International Nuclear Information System (INIS)

Iavarone, M.; Karapetrov, G.; Koshelev, A.E.; Kwok, W.K.; Crabtree, G.W.; Hinks, D.G.; Cook, R.; Kang, W.N.; Choi, E.M.; Kim, H.J.; Lee, S.I.

2003-01-01

The superconductivity in MgB 2 has a two-band character with the dominating band having a 2D character and the second band being isotropic in the three dimensions. We use tunneling microscopy and spectroscopy to reveal the two distinct energy gaps at Δ 1 =2.3 meV and Δ 2 =7.1 meV. Different spectral weights of the partial superconducting density of states are a reflection of different tunneling directions in this multi-band system. The results are consistent with the existence of two-band superconductivity in the presence of strong interband superconducting pair interaction and quasiparticle scattering. The temperature evolution of the tunneling spectra shows both gaps vanishing at the bulk T c

Charge Islands Through Tunneling

Science.gov (United States)

Robinson, Daryl C.

2002-01-01

It has been recently reported that the electrical charge in a semiconductive carbon nanotube is not evenly distributed, but rather it is divided into charge "islands." This paper links the aforementioned phenomenon to tunneling and provides further insight into the higher rate of tunneling processes, which makes tunneling devices attractive. This paper also provides a basis for calculating the charge profile over the length of the tube so that nanoscale devices' conductive properties may be fully exploited.

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

Science.gov (United States)

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

2005-06-21

The scanning tunneling microscope enables atomic-scale measurements of electron transport through individual molecules. Copper phthalocyanine and magnesium porphine molecules adsorbed on a thin oxide film grown on the NiAl(110) surface were probed. The single-molecule junctions contained two tunneling barriers, vacuum gap, and oxide film. Differential conductance spectroscopy shows that electron transport occurs via vibronic states of the molecules. The intensity of spectral peaks corresponding to the individual vibronic states depends on the relative electron tunneling rates through the two barriers of the junction, as found by varying the vacuum gap tunneling rate by changing the height of the scanning tunneling microscope tip above the molecule. A simple, sequential tunneling model explains the observed trends.

Spatially resolved vacuum tunneling spectroscopy on Bi[sub 2]Sr[sub 2]CaCu[sub 2]O[sub 8] by STM at 4. 8K

Energy Technology Data Exchange (ETDEWEB)

Renner, C; Fischer, Oe; Kent, A D; Mitzi, D B [Univ. of Geneva, DPMC, Geneva (Switzerland) Stanford Univ., Dept. of Applied Physics, CA (United States); Kapitulnik, A [Univ. of Geneva, DPMC, Geneva (Switzerland) Stanford Univ., Dept. of Applied Physics, CA (United States)

1994-02-01

We report scanning tunneling spectroscopy investigations on in-situ cleaved superconducting Bi[sub 2]Sr[sub 2]CaCu[sub 2]O[sub 8] single crystals. Although many investigators report reproducible tunneling studies on high temperature superconductors, there nevertheless remains uncertainties about the correct intrinsic shape of the tunneling spectra. We have been able to obtain highly reproducible spectra while scanning single crystal surfaces in many different areas and taking a spectra every 5A along lines of several hundred AAngstroms. Furthermore, we show that the spectra are independent of modifications of the barrier obtained by changing the tip/sample distance. The experimental density of states clearly shows some filling of the gap which does not fit with a BCS-like s-wave prediction, even if some scattering in the tunneling process is accounted for. (orig.)

Tunneling Anomalous and Spin Hall Effects.

Science.gov (United States)

Matos-Abiague, A; Fabian, J

2015-07-31

We predict, theoretically, the existence of the anomalous Hall effect when a tunneling current flows through a tunnel junction in which only one of the electrodes is magnetic. The interfacial spin-orbit coupling present in the barrier region induces a spin-dependent momentum filtering in the directions perpendicular to the tunneling current, resulting in a skew tunneling even in the absence of impurities. This produces an anomalous Hall conductance and spin Hall currents in the nonmagnetic electrode when a bias voltage is applied across the tunneling heterojunction. If the barrier is composed of a noncentrosymmetric material, the anomalous Hall conductance and spin Hall currents become anisotropic with respect to both the magnetization and crystallographic directions, allowing us to separate this interfacial phenomenon from the bulk anomalous and spin Hall contributions. The proposed effect should be useful for proving and quantifying the interfacial spin-orbit fields in metallic and metal-semiconductor systems.

Single Electron Tunneling

International Nuclear Information System (INIS)

Ruggiero, Steven T.

2005-01-01

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

Fano Description of Single-Hydrocarbon Fluorescence Excited by a Scanning Tunneling Microscope.

Science.gov (United States)

Kröger, Jörg; Doppagne, Benjamin; Scheurer, Fabrice; Schull, Guillaume

2018-06-13

The detection of fluorescence with submolecular resolution enables the exploration of spatially varying photon yields and vibronic properties at the single-molecule level. By placing individual polycyclic aromatic hydrocarbon molecules into the plasmon cavity formed by the tip of a scanning tunneling microscope and a NaCl-covered Ag(111) surface, molecular light emission spectra are obtained that unravel vibrational progression. In addition, light spectra unveil a signature of the molecule even when the tunneling current is injected well separated from the molecular emitter. This signature exhibits a distance-dependent Fano profile that reflects the subtle interplay between inelastic tunneling electrons, the molecular exciton and localized plasmons in at-distance as well as on-molecule fluorescence. The presented findings open the path to luminescence of a different class of molecules than investigated before and contribute to the understanding of single-molecule luminescence at surfaces in a unified picture.

Theory of single-spin inelastic tunneling spectroscopy.

Science.gov (United States)

Fernández-Rossier, J

2009-06-26

I show that recent experiments of inelastic scanning tunneling spectroscopy of single and a few magnetic atoms are modeled with a phenomenological spin-assisted tunneling Hamiltonian so that the inelastic dI/dV line shape is related to the spin spectral weight of the magnetic atom. This accounts for the spin selection rules and dI/dV spectra observed experimentally for single Fe and Mn atoms deposited on Cu2N. In the case of chains of Mn atoms it is found necessary to include both first and second-neighbor exchange interactions as well as single-ion anisotropy.

Theoretical consideration of spin-polarized resonant tunneling in magnetic tunnel junctions

International Nuclear Information System (INIS)

Mu Haifeng; Zhu Zhengang; Zheng Qingrong; Jin Biao; Wang Zhengchuan; Su Gang

2004-01-01

A recent elegant experimental realization [S. Yuasa et al., Science 297 (2002) 234] of the spin-polarized resonant tunneling in magnetic tunnel junctions is interpreted in terms of a two-band model. It is shown that the tunnel magnetoresistance (TMR) decays oscillatorily with the thickness of the normal metal (NM) layer, being fairly in agreement with the experimental observation. The tunnel conductance is found to decay with slight oscillations with the increase of the NM layer thickness, which is also well consistent with the experiment. In addition, when the magnetizations of both ferromagnet electrodes are not collinearly aligned, TMR is found to exhibit sharp resonant peaks at some particular thickness of the NM layer. The peaked TMR obeys nicely a Gaussian distribution against the relative orientation of the magnetizations

Tunneling Photocurrent Assisted by Interlayer Excitons in Staggered van der Waals Hetero-Bilayers.

Science.gov (United States)

Luong, Dinh Hoa; Lee, Hyun Seok; Neupane, Guru Prakash; Roy, Shrawan; Ghimire, Ganesh; Lee, Jin Hee; Vu, Quoc An; Lee, Young Hee

2017-09-01

Vertically stacked van der Waals (vdW) heterostructures have been suggested as a robust platform for studying interfacial phenomena and related electric/optoelectronic devices. While the interlayer Coulomb interaction mediated by the vdW coupling has been extensively studied for carrier recombination processes in a diode transport, its correlation with the interlayer tunneling transport has not been elucidated. Here, a contrast is reported between tunneling and drift photocurrents tailored by the interlayer coupling strength in MoSe 2 /MoS 2 hetero-bilayers (HBs). The interfacial coupling modulated by thermal annealing is identified by the interlayer phonon coupling in Raman spectra and the emerging interlayer exciton peak in photoluminescence spectra. In strongly coupled HBs, positive photocurrents are observed owing to the inelastic band-to-band tunneling assisted by interlayer excitons that prevail over exciton recombinations. By contrast, weakly coupled HBs exhibit a negative photovoltaic diode behavior, manifested as a drift current without interlayer excitonic emissions. This study sheds light on tailoring the tunneling transport for numerous optoelectronic HB devices. © 2017 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

The anisotropic tunneling behavior of spin transport in graphene-based magnetic tunneling junction

Science.gov (United States)

Pan, Mengchun; Li, Peisen; Qiu, Weicheng; Zhao, Jianqiang; Peng, Junping; Hu, Jiafei; Hu, Jinghua; Tian, Wugang; Hu, Yueguo; Chen, Dixiang; Wu, Xuezhong; Xu, Zhongjie; Yuan, Xuefeng

2018-05-01

Due to the theoretical prediction of large tunneling magnetoresistance (TMR), graphene-based magnetic tunneling junction (MTJ) has become an important branch of high-performance spintronics device. In this paper, the non-collinear spin filtering and transport properties of MTJ with the Ni/tri-layer graphene/Ni structure were studied in detail by utilizing the non-equilibrium Green's formalism combined with spin polarized density functional theory. The band structure of Ni-C bonding interface shows that Ni-C atomic hybridization facilitates the electronic structure consistency of graphene and nickel, which results in a perfect spin filtering effect for tri-layer graphene-based MTJ. Furthermore, our theoretical results show that the value of tunneling resistance changes with the relative magnetization angle of two ferromagnetic layers, displaying the anisotropic tunneling behavior of graphene-based MTJ. This originates from the resonant conduction states which are strongly adjusted by the relative magnetization angles. In addition, the perfect spin filtering effect is demonstrated by fitting the anisotropic conductance with the Julliere's model. Our work may serve as guidance for researches and applications of graphene-based spintronics device.

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

International Nuclear Information System (INIS)

Zubkov, Evgeniy

2013-01-01

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

Communication: Tunnelling splitting in the phosphine molecule

Science.gov (United States)

Sousa-Silva, Clara; Tennyson, Jonathan; Yurchenko, Sergey N.

2016-09-01

Splitting due to tunnelling via the potential energy barrier has played a significant role in the study of molecular spectra since the early days of spectroscopy. The observation of the ammonia doublet led to attempts to find a phosphine analogous, but these have so far failed due to its considerably higher barrier. Full dimensional, variational nuclear motion calculations are used to predict splittings as a function of excitation energy. Simulated spectra suggest that such splittings should be observable in the near infrared via overtones of the ν2 bending mode starting with 4ν2.

Studying the influence of substrate conductivity on the optoelectronic properties of quantum dots langmuir monolayer

Science.gov (United States)

Al-Alwani, Ammar J.; Chumakov, A. S.; Begletsova, N. N.; Shinkarenko, O. A.; Markin, A. V.; Gorbachev, I. A.; Bratashov, D. N.; Gavrikov, M. V.; Venig, S. B.; Glukhovskoy, E. G.

2018-04-01

The formation of CdSe quantum dots (QDs) monolayers was studied by Langmuir Blodgett method. The fluorescence (PL) spectra of QD monolayers were investigated at different substrate type (glass, silicon and ITO glass) and the influence of graphene sheets layer (as a conductive surface) on the QDs properties has also been studied. The optoelectronic properties of QDs can be tuned by deposition of insulating nano-size layers of the liquid crystal between QDs and conductive substrate. The monolayer of QDs transferred on conductive surface (glass with ITO) has lowest intensity of PL spectra due to quenching effect. The PL intensity of QDs could be tuned by using various type of substrates or/and by transformed high conductive layer. Also the photooxidation processes of CdSe QDs monolayer on the solid surface can be controlled by selection of suitable substrate. The current-voltage (I–V) characteristics of QDs thin film on ITO surface was studied using scanning tunneling microscope (STM).

Study of tunneling transport in Si-based tunnel field-effect transistors with ON current enhancement utilizing isoelectronic trap

Science.gov (United States)

Mori, Takahiro; Morita, Yukinori; Miyata, Noriyuki; Migita, Shinji; Fukuda, Koichi; Mizubayashi, Wataru; Masahara, Meishoku; Yasuda, Tetsuji; Ota, Hiroyuki

2015-02-01

The temperature dependence of the tunneling transport characteristics of Si diodes with an isoelectronic impurity has been investigated in order to clarify the mechanism of the ON-current enhancement in Si-based tunnel field-effect transistors (TFETs) utilizing an isoelectronic trap (IET). The Al-N complex impurity was utilized for IET formation. We observed three types of tunneling current components in the diodes: indirect band-to-band tunneling (BTBT), trap-assisted tunneling (TAT), and thermally inactive tunneling. The indirect BTBT and TAT current components can be distinguished with the plot described in this paper. The thermally inactive tunneling current probably originated from tunneling consisting of two paths: tunneling between the valence band and the IET trap and tunneling between the IET trap and the conduction band. The probability of thermally inactive tunneling with the Al-N IET state is higher than the others. Utilization of the thermally inactive tunneling current has a significant effect in enhancing the driving current of Si-based TFETs.

First Results at ultra-high Rλ in a wind tunnel

Science.gov (United States)

Kuechler, Christian; Bodenschatz, Eberhard; Bewley, Gregory P.

2017-11-01

With a new active grid installed, the Variable Density Turbulence Tunnel (VDTT) at the Max-Planck-Institute for Dynamics and Self-Organization produced homogeneous turbulence at Reynolds numbers up to Rλ 7500 . The active grid consisted of 111 individually controllable flaps that produced more intense turbulence than classical fixed grids. We varied the Reynolds number by changing the pressure of sulfur hexafluoride gas in the tunnel between 0.5 and 15 bar, which changes the viscosity of the gas. With hot wire probes called NSTAPs that were 30 microns long, we measured velocity spectra and structure functions. While a bottleneck is present in the spectra at Reynolds numbers up to Rλ < 3000 , the bottleneck weakens and disappears at higher Rλ. We compare this observation with measurements made in the field and with computer simulations.

New directions in scanning-tunneling microscopy

International Nuclear Information System (INIS)

Ferrell, T.L.; Warmack, R.J.; Reddick, R.C.

1989-01-01

The tunneling of electrons in scanning-tunneling microscopy (STM) has permitted imaging of the electronic distribution about individual atoms on surfaces. The need for use of conducting surfaces in STM limits its applicability, and new forms of scanning microscopy have emerged as a result of interest in poorly conducting samples. Atomic force microscopy has demonstrated that the force between a surface and a probe tip can be used to image selected materials. Now being developed are magnetic probe STM's and photon tunneling microscopes in which the probe is a sharpened optical fiber. Also of great interest presently is the measurement of differential conductance of surfaces using electron STM's. This method supplies spectral information and contrast enhancement in images. At present there remains much theoretical work to be carried out in order to better characterize related data on inelastic electron tunneling, and valuable insight may be gained from data being gathered on the local work function of materials. As matters stand today, the key problems lie in determining tip and contamination effects, preparation of samples, and understanding conductivity mechanisms in very thin materials on conducting substrates. Resolution of these problems and introduction of new forms of scanning microscopy may permit novel and important applications in biology as well as surface science

Ionic conductivity and Raman spectra of Na--Li, K--Li, and K--Sn β-Al2O3

International Nuclear Information System (INIS)

Kaneda, T.; Bates, J.B.; Wang, J.C.; Engstrom, H.

1979-01-01

The ionic conductivity and Raman spectra of Na, Na--Li, K, K--Li, and K--Sn β-Al 2 O 3 were measured in order to understand the mechanisms of mixed-ion conduction. It was observed that at 300 0 K, for example, the conductivity of a crystal with composition Na 0 . 82 Li 0 . 18 β-Al 2 O 3 was about one-fifth that of pure Na cyrstals, while the conductivity of K 0 . 80 Li 0 . 20 β-Al 2 O 3 was more than three orders of magnitude lower than that of pure K compounds. The results of a model calculation indicated that the Li + ions are the main carrier species in the Na--Li and K--Li mixed compounds. Features observed in the Raman spectra were attributed to paired- and single-ion vibrations. It is concluded that the K + ions which contribute to a band at 69 cm -1 in K β-Al 2 O 3 are the effective carriers for conduction

Interfacial Nb-substitution induced anomalous enhancement of polarization and conductivity in BaTiO3 ferroelectric tunnel junctions

Directory of Open Access Journals (Sweden)

H. F. Li

2014-12-01

Full Text Available Using density functional theory (DFT method combined with non-equilibrium Green’s function approach, we systematically investigated the structural, ferroelectric and electronic transport properties of Pt/BaTiO3/Pt ferroelectric tunnel junctions (FTJ with the interface atomic layers doped by charge neutral NbTi substitution. It is found that interfacial NbTi substitution will produce several anomalous effects such as the vanishing of ferroelectric critical thickness and the decrease of junction resistance against tunneling current. Consequently, the thickness of the ferroelectric thin film (FTF in the FTJ can be reduced, and both the electroresistance effect and sensitivity to external bias of the FTJ are enhanced. Our calculations indicate that the enhancements of conductivity and ferroelectric distortion can coexist in FTJs, which should be important for applications of functional electronic devices based on FTJs.

Phase Structure of Strong-Field Tunneling Wave Packets from Molecules.

Science.gov (United States)

Liu, Ming-Ming; Li, Min; Wu, Chengyin; Gong, Qihuang; Staudte, André; Liu, Yunquan

2016-04-22

We study the phase structure of the tunneling wave packets from strong-field ionization of molecules and present a molecular quantum-trajectory Monte Carlo model to describe the laser-driven dynamics of photoelectron momentum distributions of molecules. Using our model, we reproduce and explain the alignment-dependent molecular frame photoelectron spectra of strong-field tunneling ionization of N_{2} reported by M. Meckel et al. [Nat. Phys. 10, 594 (2014)]. In addition to modeling the low-energy photoelectron angular distributions quantitatively, we extract the phase structure of strong-field molecular tunneling wave packets, shedding light on its physical origin. The initial phase of the tunneling wave packets at the tunnel exit depends on both the initial transverse momentum distribution and the molecular internuclear distance. We further show that the ionizing molecular orbital has a critical effect on the initial phase of the tunneling wave packets. The phase structure of the photoelectron wave packet is a key ingredient for modeling strong-field molecular photoelectron holography, high-harmonic generation, and molecular orbital imaging.

Electric and VLF-MT survey of Tegatayama tunnel; Tegatayama tunnel no denki tansa oyobi VLF tansa

Energy Technology Data Exchange (ETDEWEB)

Nishitani, T [Akita University, Akita (Japan). Mining College

1997-05-27

To survey the structure at the depth between 20 and 30 m, field tests were conducted by means of vertical electric and VFL-MT (magnetotelluric) survey. Tegatayama tunnel has a total length of 276 m, width of 7.5 m, and height of 4.7 m, and the depth from the surface is about 28 m near the top of mountain. Near the tunnel, the thickness of surface soil is about 60 cm, which consists of clay soil including soft mudstone gravel. It was found that terrace deposit is distributed up to the depth of 8 m, and that mudstone is distributed below the depth of 8 m. Weighted four-electrode method was adopted for the vertical electrical survey. Measurements were conducted at the immediately above the tunnel, 10 m apart from the center of tunnel in the right and left, and 20 m apart from the center in the east. For the VLF-MT method, component of frequency 22.2 kHz was used. As a result of the tests, it was difficult to illustrate the existence of tunnel from the vertical electrical survey only at one point. Feature of the tunnel could be well illustrated by means of the VLF-MT method. 3 refs., 9 figs.

A universal explanation of tunneling conductance in exotic superconductors

OpenAIRE

Hong, Jongbae; Abergel, D. S. L.

2016-01-01

A longstanding mystery in understanding cuprate superconductors is the inconsistency between the experimental data measured by scanning tunneling spectroscopy (STS) and angle-resolved photoemission spectroscopy (ARPES). In particular, the gap between prominent side peaks observed in STS is much bigger than the superconducting gap observed by ARPES measurements. Here, we reconcile the two experimental techniques by generalising a theory which was previously applied to zero-dimensional mesoscop...

Electrical conductivity and modulus formulation in zinc modified bismuth boro-tellurite glasses

Science.gov (United States)

Dhankhar, Sunil; Kundu, R. S.; Dult, Meenakshi; Murugavel, S.; Punia, R.; Kishore, N.

2016-09-01

The ac conductivity of zinc modified tellurium based quaternary glasses having composition 60 TeO2-10 B2O3-(30 - x) Bi2O3-x ZnO; x = 10, 15, 20, 25 and 30 has been investigated in the frequency range 10-1-105 Hz and in temperature range 483-593 K. Frequency and temperature dependent ac conductivity found to obey Jonscher power law modified by Almond-West. DC conductivity, crossover frequency and frequency exponent have been estimated from the fitting of the experimental data of conductivity with Jonscher power law modified by Almond-West. The ac conductivity and its frequency exponent have been analyzed by various theoretical models. In presently studied glasses ac conduction takes place via tunneling of overlapping large polaron tunneling. Activation energy is found to be increased with increase in zinc content and dc conduction takes place via variable range hopping proposed by Mott with some modification suggested by Punia et al. The value of the stretched exponent ( β) obtained by fitting of M^' ' }} reveals the presence of non-Debye type relaxation. Scaling spectra of ac conductivity and electric modulus collapse into a single master curve for all compositions and temperatures, reveals the presence of composition and temperature independent conduction and relaxation process in these glasses. Activation energy of conduction ( W) and electric modulus ( E R ) are nearly equal, indicating that polaron have to overcome the same energy barrier during conduction as well as relaxation processes.

Tunnel magnetoresistance in alumina, magnesia and composite tunnel barrier magnetic tunnel junctions

International Nuclear Information System (INIS)

Schebaum, Oliver; Drewello, Volker; Auge, Alexander; Reiss, Guenter; Muenzenberg, Markus; Schuhmann, Henning; Seibt, Michael; Thomas, Andy

2011-01-01

Using magnetron sputtering, we have prepared Co-Fe-B/tunnel barrier/Co-Fe-B magnetic tunnel junctions with tunnel barriers consisting of alumina, magnesia, and magnesia-alumina bilayer systems. The highest tunnel magnetoresistance ratios we found were 73% for alumina and 323% for magnesia-based tunnel junctions. Additionally, tunnel junctions with a unified layer stack were prepared for the three different barriers. In these systems, the tunnel magnetoresistance ratios at optimum annealing temperatures were found to be 65% for alumina, 173% for magnesia, and 78% for the composite tunnel barriers. The similar tunnel magnetoresistance ratios of the tunnel junctions containing alumina provide evidence that coherent tunneling is suppressed by the alumina layer in the composite tunnel barrier. - Research highlights: → Transport properties of Co-Fe-B/tunnel barrier/Co-Fe-B magnetic tunnel junctions. → Tunnel barrier consists of MgO, Al-Ox, or MgO/Al-Ox bilayer systems. → Limitation of TMR-ratio in composite barrier tunnel junctions to Al-Ox values. → Limitation indicates that Al-Ox layer is causing incoherent tunneling.

The comparison between limited open carpal tunnel release using direct vision and tunneling technique and standard open carpal tunnel release: a randomized controlled trial study.

Science.gov (United States)

Suppaphol, Sorasak; Worathanarat, Patarawan; Kawinwongkovit, Viroj; Pittayawutwinit, Preecha

2012-04-01

To compare the operative outcome of carpal tunnel release between limited open carpal tunnel release using direct vision and tunneling technique (group A) with standard open carpal tunnel release (group B). Twenty-eight patients were enrolled in the present study. A single blind randomized control trial study was conducted to compare the postoperative results between group A and B. The study parameters were Levine's symptom severity and functional score, grip and pinch strength, and average two-point discrimination. The postoperative results between two groups were comparable with no statistical significance. Only grip strength at three months follow up was significantly greater in group A than in group B. The limited open carpal tunnel release in the present study is effective comparable to the standard open carpal tunnel release. The others advantage of this technique are better cosmesis and improvement in grip strength at the three months postoperative period.

Communication: Tunnelling splitting in the phosphine molecule

Energy Technology Data Exchange (ETDEWEB)

Sousa-Silva, Clara; Tennyson, Jonathan; Yurchenko, Sergey N. [Department of Physics and Astronomy, University College London, London WC1E 6BT (United Kingdom)

2016-09-07

Splitting due to tunnelling via the potential energy barrier has played a significant role in the study of molecular spectra since the early days of spectroscopy. The observation of the ammonia doublet led to attempts to find a phosphine analogous, but these have so far failed due to its considerably higher barrier. Full dimensional, variational nuclear motion calculations are used to predict splittings as a function of excitation energy. Simulated spectra suggest that such splittings should be observable in the near infrared via overtones of the ν{sub 2} bending mode starting with 4ν{sub 2}.

Nonreciprocal optical tunnelling through evanescently coupled Tamm states in magnetophotonic crystals

Energy Technology Data Exchange (ETDEWEB)

Fang, Yun-Tuan [Jiangsu Univ., Zhenjiang (China). School of Computer Science and Telecommunication Engineering; Han, Ling [The Second Military Medical Univ., Shanghai (China). Dept. of Radiation Medicine; Gao, Yong-Feng [Jiangsu Univ., Zhenjiang (China). School of Mechanical Engineering

2015-07-01

Evanescently coupled Tamm states are achieved through two magnetophotonic crystals (MPCs) with a pair of coupling prisms. At the wavelengths of coupled Tamm states, a double of nonreciprocal optical tunnelling channels is found through the transmission spectra obtained from a developed transfer matrix method. The nonreciprocal tunnelling wavelength and the interval between two nonreciprocal channels can be adjusted depending on the width of the air gap between two MPCs or the scale invariant of a PC. The nonreciprocal tunnelling is demonstrated through electromagnetic field distribution simulations based on finite element software. Such theoretical results may provide a new method to design tunable optical isolators with a double of channels.

Pre-microscope tunnelling — Inspiration or constraint?

Science.gov (United States)

Walmsley, D. G.

1987-03-01

Before the microscope burst upon the scene, tunnelling had established for itself a substantial niche in the repertoire of the solid state physicist. Over a period of 20 years it has contributed importantly to our understanding of many systems. It elucidated the superconducting state, first by a direct display of the energy gap then by providing detailed information on the phonon spectra and electron-phonon coupling strength in junction electrodes. Its use as a phonon spectrometer was subsequently extended to semiconductors and to the oxides of insulating barriers. Eventually the vibrational spectra of monolayer organic and inorganic adsorbates became amenable with rich scientific rewards. In a few cases electronic transitions have been observed. Plasmon excitation by tunnelling electrons led to insights on the electron loss function in metals at visible frequencies and provided along the way an intriguing light emitting device. With the advent of the microscope it is now appropriate to enquire how much of this experience can profitably be carried over to the new environment. Are we constrained just to repeat the experiments in a new configuration? Happily no. The microscope offers us topographical and spectroscopic information of a new order. One might next ask how great is the contact between the two disciplines? We explore this question and seek to establish where the pre-microscope experience can be helpful in inspiring our use of this marvellous new facility that we know as the scanning tunnelling microscope.

Tunneling from super- to normal-deformed minima in nuclei

International Nuclear Information System (INIS)

Khoo, T. L.

1998-01-01

An excited minimum, or false vacuum, gives rise to a highly elongated superdeformed (SD) nucleus. A brief review of superdeformation is given, with emphasis on the tunneling from the false to the true vacuum, which occurs in the feeding and decay of SD bands. During the feeding process the tunneling is between hot states, while in the decay it is from a cold to a hot state. The γ spectra connecting SD and normal-deformed (ND) states provide information on several physics issues: the decay mechanism; the spin/parity quantum numbers, energies and microscopic structures of SD bands; the origin of identical SD bands; the quenching of pairing with excitation energy; and the chaoticity of excited ND states at 2.5-5 MeV. Other examples of tunneling in nuclei, which are briefly described, include the possible role of tunneling in ΔI = 4 bifurcation in SD bands, sub-barrier fusion and proton emitters

Quantum-Sequencing: Biophysics of quantum tunneling through nucleic acids

Science.gov (United States)

Casamada Ribot, Josep; Chatterjee, Anushree; Nagpal, Prashant

2014-03-01

Tunneling microscopy and spectroscopy has extensively been used in physical surface sciences to study quantum tunneling to measure electronic local density of states of nanomaterials and to characterize adsorbed species. Quantum-Sequencing (Q-Seq) is a new method based on tunneling microscopy for electronic sequencing of single molecule of nucleic acids. A major goal of third-generation sequencing technologies is to develop a fast, reliable, enzyme-free single-molecule sequencing method. Here, we present the unique ``electronic fingerprints'' for all nucleotides on DNA and RNA using Q-Seq along their intrinsic biophysical parameters. We have analyzed tunneling spectra for the nucleotides at different pH conditions and analyzed the HOMO, LUMO and energy gap for all of them. In addition we show a number of biophysical parameters to further characterize all nucleobases (electron and hole transition voltage and energy barriers). These results highlight the robustness of Q-Seq as a technique for next-generation sequencing.

Tunneling from super- to normal-deformed minima in nuclei.

Energy Technology Data Exchange (ETDEWEB)

Khoo, T. L.

1998-01-08

An excited minimum, or false vacuum, gives rise to a highly elongated superdeformed (SD) nucleus. A brief review of superdeformation is given, with emphasis on the tunneling from the false to the true vacuum, which occurs in the feeding and decay of SD bands. During the feeding process the tunneling is between hot states, while in the decay it is from a cold to a hot state. The {gamma} spectra connecting SD and normal-deformed (ND) states provide information on several physics issues: the decay mechanism; the spin/parity quantum numbers, energies and microscopic structures of SD bands; the origin of identical SD bands; the quenching of pairing with excitation energy; and the chaoticity of excited ND states at 2.5-5 MeV. Other examples of tunneling in nuclei, which are briefly described, include the possible role of tunneling in {Delta}I = 4 bifurcation in SD bands, sub-barrier fusion and proton emitters.

Spin polarization at the interface and tunnel magnetoresistance

International Nuclear Information System (INIS)

Itoh, H.; Inoue, J.

2001-01-01

We propose that interfacial states of imperfectly oxidized Al ions may exist in ferromagnetic tunnel junctions with Al-O barrier and govern both the spin polarization and tunnel conductance. It is shown that the spin polarization is positive independent of materials and correlates well with the tunnel magnetoresistance

Conductance and thermopower in molecular nanojunctions

Science.gov (United States)

Sen, Arijit

2013-02-01

Electronic transport through short channels in a molecular junction is an intricate quantum scattering problem [1]. To garner insight on how the structure and the electrical properties of a nanoscale junction are correlated is thus of both fundamental and technological interest [1-3]. As observed experimentally in the last couple of years by several independent research groups [4-5], a two-terminal molecular junction comprising of a simple alkane chain with varying length can exhibit high as well as low conductance. However, what causes the simultaneous unveiling of multiple conductances remained largely obscure. We have recently demonstrated [6] that the binary conductance in these heterostructures is due mainly to two distinct electrode orientations that control the electrode-molecule coupling as well as the tunneling strength through quantum interference following diversity in the electrode band structures. Our detailed analysis on the transmission spectra indicates that even a single-molecule nanojunction can potentially serve as a realistic double-quantum-dot kind of system to yield tunable Fano resonance, as often desired for nanoscale switching. In this talk, I intend to give a brief account of molecular electronics and its future applications along with the challenges and possibilities in the current perspective. A few deliberations may as well include how the inter-dot tunneling strength may affect the non-equilibrium charge transport and thermoelectricity in a myriad of molecular junctions based on different molecular conformations and electrode structures. Finally, I shall try to touch upon the effect of electron-phonon interaction on the nanoscale charge transport, and also, the phonon-mediated thermal transport in molecular nanodevices.

Full-Span Tiltrotor Aeroacoustic Model (TRAM) Overview and 40- by 80-Foot Wind Tunnel Test. [conducted in the 40- by 80-Foot Wind Tunnel at Ames Research Center

Science.gov (United States)

McCluer, Megan S.; Johnson, Jeffrey L.; Rutkowski, Michael (Technical Monitor)

2001-01-01

Most helicopter data trends cannot be extrapolated to tiltrotors because blade geometry and aerodynamic behavior, as well as rotor and fuselage interactions, are significantly different for tiltrotors. A tiltrotor model has been developed to investigate the aeromechanics of tiltrotors, to develop a comprehensive database for validating tiltrotor analyses, and to provide a research platform for supporting future tiltrotor designs. The Full-Span Tiltrotor Aeroacoustic Model (FS TRAM) is a dual-rotor, powered aircraft model with extensive instrumentation for measurement of structural and aerodynamic loads. This paper will present the Full-Span TRAM test capabilities and the first set of data obtained during a 40- by 80-Foot Wind Tunnel test conducted in late 2000 at NASA Ames Research Center. The Full-Span TRAM is a quarter-scale representation of the V-22 Osprey aircraft, and a heavily instrumented NASA and U.S. Army wind tunnel test stand. Rotor structural loads are monitored and recorded for safety-of-flight and for information on blade loads and dynamics. Left and right rotor balance and fuselage balance loads are monitored for safety-of-flight and for measurement of vehicle and rotor aerodynamic performance. Static pressure taps on the left wing are used to determine rotor/wing interactional effects and rotor blade dynamic pressures measure blade airloads. All of these measurement capabilities make the FS TRAM test stand a unique and valuable asset for validation of computational codes and to aid in future tiltrotor designs. The Full-Span TRAM was tested in the NASA Ames Research Center 40- by 80-Foot Wind Tunnel from October through December 2000. Rotor and vehicle performance measurements were acquired in addition to wing pressures, rotor acoustics, and Laser Light Sheet (LLS) flow visualization data. Hover, forward flight, and airframe (rotors off) aerodynamic runs were performed. Helicopter-mode data were acquired during angle of attack and thrust sweeps for

Polymer-mediated tunneling transport between carbon nanotubes in nanocomposites.

Science.gov (United States)

Derosa, Pedro A; Michalak, Tyler

2014-05-01

Electron transport in nanocomposites has attracted a good deal of attention for some time now; furthermore, the ability to control its characteristics is a necessary step in the design of multifunctional materials. When conductive nanostructures (for example carbon nanotubes) are inserted in a non-conductive matrix, electron transport below the percolation threshold is dominated by tunneling and thus the conductive characteristics of the composite depends heavily on the characteristics of the tunneling currents between nanoinserts. A parameter-free approach to study tunneling transport between carbon nanotubes across a polymer matrix is presented. The calculation is done with a combination of Density Functional Theory and Green functions (an approach heavily used in molecular electronics) which is shown here to be effective in this non-resonant transport condition. The results show that the method can effectively capture the effect of a dielectric layer in tunneling transport. The current is found to exponentially decrease with the size of the gap for both vacuum and polymer, and that the polymer layer lowers the tunneling barrier enhancing tunneling conduction. For a polyacrylonitrile matrix, a four-fold decrease in the tunneling constant, compared to tunneling in vacuum, is observed, a result that is consistent with available information. The method is very versatile as any DFT functional (or any other quantum mechanics method) can be used and thus the most accurate method for each particular system can be chosen. Furthermore as more methods become available, the calculations can be revised and improved. This approach can be used to design functional materials for fine-tunning the tunneling transport, for instance, the effect of modifying the nanoinsert-matrix interface (for example, by adding functional groups to carbon nanotubes) can be captured and the comparative performance of each interface predicted by simulation.

MgO magnetic tunnel junctions of enduring F-type upon annealing

International Nuclear Information System (INIS)

Schleicher, F; Halisdemir, U; Urbain, E; Gallart, M; Boukari, S; Beaurepaire, E; Gilliot, P; Bowen, M; Lacour, D; Montaigne, F; Hehn, M

2015-01-01

The authors performed magnetotransport experiments to determine whether annealing alters the oxygen vacancy-mediated tunnelling potential landscape of the central portion of a MgO ultrathin film within sputtered CoFeB/MgO/CoFeB magnetic tunnel junctions. Using the Î rel method reveals a temperature-dependent tunnelling barrier height for a non-annealed barrier that arises from single oxygen vacancies (F centres) and is qualitatively identical to that found for its partly and fully annealed counterparts. Thus these MTJs with F centres remain of F-type upon annealing. This explicitly confirms that the large tunnel-magnetoresistance (TMR) increase upon annealing results mainly from structural modifications of MgO and CoFeB and not from vacancy pairing within the barrier. Photoluminescence spectra performed on both annealed and non-annealed thin MgO films grown on CoFeB electrodes support this conclusion. This work should promote renewed scrutiny over the precise impact of annealing on tunnelling magnetotransport across MgO. (paper)

Tip-Loading, Force-Dependent Tunneling Behavior in Alkanethiol Self-Assembled Monolayers Studied Through Conducting Atomic Force Microscopy

International Nuclear Information System (INIS)

Lee, Min Hyung; Song, Hyun Wook

2013-01-01

The force-dependent tunneling transport in metal/alkanethiol/metal junctions was examined using CAFM. Tunneling current and current density through alkanethiol SAMs increased with increasing tip-loading force in CAFM, which suggests that a potential change in geometry of the molecules under the tip loads influences the transport properties of alkanethiol SAMs. Enhanced intermolecular tunneling transport in the tilted molecular configuration under tip-loading effect is likely responsible for such an increase in tunneling current density. We also demonstrated that through-bond tunneling is a more efficient pathway in alkanethiol SAMs than are intermolecular chain-to-chain pathways, by demonstrating a dependence of current density on the associated tunneling distances. We report a tip-loading, force-dependent tunneling behavior in alkanethiol SAMs using CAFM. A variable tip-loading force applies to alkanethiol SAMs with a standard AFM feedback, and current(I)-voltage(V) characteristics are simultaneously measured while varying the loading forces. In particular, we observe how a tip-loading force in CAFM influences the transport properties of alkanethiol SAMs

Low conductive support for thermal insulation of a sample holder of a variable temperature scanning tunneling microscope.

Science.gov (United States)

Hanzelka, Pavel; Vonka, Jakub; Musilova, Vera

2013-08-01

We have designed a supporting system to fix a sample holder of a scanning tunneling microscope in an UHV chamber at room temperature. The microscope will operate down to a temperature of 20 K. Low thermal conductance, high mechanical stiffness, and small dimensions are the main features of the supporting system. Three sets of four glass balls placed in vertices of a tetrahedron are used for thermal insulation based on small contact areas between the glass balls. We have analyzed the thermal conductivity of the contacts between the balls mutually and between a ball and a metallic plate while the results have been applied to the entire support. The calculation based on a simple model of the setup has been verified with some experimental measurements. In comparison with other feasible supporting structures, the designed support has the lowest thermal conductance.

Scanning tunneling spectroscopy of Pb thin films

Energy Technology Data Exchange (ETDEWEB)

Becker, Michael

2010-12-13

The present thesis deals with the electronic structure, work function and single-atom contact conductance of Pb thin films, investigated with a low-temperature scanning tunneling microscope. The electronic structure of Pb(111) thin films on Ag(111) surfaces is investigated using scanning tunneling spectroscopy (STS). Quantum size effects, in particular, quantum well states (QWSs), play a crucial role in the electronic and physical properties of these films. Quantitative analysis of the spectra yields the QWS energies as a function of film thickness, the Pb bulk-band dispersion in {gamma}-L direction, scattering phase shifts at the Pb/Ag interface and vacuum barrier as well as the lifetime broadening at anti {gamma}. The work function {phi} is an important property of surfaces, which influences catalytic reactivity and charge injection at interfaces. It controls the availability of charge carriers in front of a surface. Modifying {phi} has been achieved by deposition of metals and molecules. For investigating {phi} at the atomic scale, scanning tunneling microscopy (STM) has become a widely used technique. STM measures an apparent barrier height {phi}{sub a}, which is commonly related to the sample work function {phi}{sub s} by: {phi}{sub a}=({phi}{sub s}+{phi}{sub t}- vertical stroke eV vertical stroke)/2, with {phi}{sub t} the work function of the tunneling tip, V the applied tunneling bias voltage, and -e the electron charge. Hence, the effect of the finite voltage in STM on {phi}{sub a} is assumed to be linear and the comparison of {phi}{sub a} measured at different surface sites is assumed to yield quantitative information about work function differences. Here, the dependence of {phi}{sub a} on the Pb film thickness and applied bias voltage V is investigated. {phi}{sub a} is found to vary significantly with V. This bias dependence leads to drastic changes and even inversion of contrast in spatial maps of {phi}{sub a}, which are related to the QWSs in the Pb

The Beginner's Guide to Wind Tunnels with TunnelSim and TunnelSys

Science.gov (United States)

Benson, Thomas J.; Galica, Carol A.; Vila, Anthony J.

2010-01-01

The Beginner's Guide to Wind Tunnels is a Web-based, on-line textbook that explains and demonstrates the history, physics, and mathematics involved with wind tunnels and wind tunnel testing. The Web site contains several interactive computer programs to demonstrate scientific principles. TunnelSim is an interactive, educational computer program that demonstrates basic wind tunnel design and operation. TunnelSim is a Java (Sun Microsystems Inc.) applet that solves the continuity and Bernoulli equations to determine the velocity and pressure throughout a tunnel design. TunnelSys is a group of Java applications that mimic wind tunnel testing techniques. Using TunnelSys, a team of students designs, tests, and post-processes the data for a virtual, low speed, and aircraft wing.

Transparent control of three-body selective destruction of tunneling via unusual states

International Nuclear Information System (INIS)

Luo, Yunrong; Tan, Jintao; Hai, Wenhua; Lu, Gengbiao

2015-01-01

We study transparent control of quantum tunneling via unusual analytical solutions for three bosons held in a driven double-well. Under high-frequency approximation, we analytically obtain the fine band structure and general non-Floquet state. At some collapse points of the quasi-energy spectra, the latter becomes the unusual special states. Based on the analytical results and their numerical correspondences, we clearly reveal the mechanism of coherent tunneling and suggest a scheme to transparently control the tunneling of three bosons from one well to another. The results can be observed with the current experimental capability (Chen et al 2011 Phys. Rev. Lett. 107 210405) (paper)

Charge Transport in 2D DNA Tunnel Junction Diodes

KAUST Repository

Yoon, Minho

2017-11-06

Recently, deoxyribonucleic acid (DNA) is studied for electronics due to its intrinsic benefits such as its natural plenitude, biodegradability, biofunctionality, and low-cost. However, its applications are limited to passive components because of inherent insulating properties. In this report, a metal-insulator-metal tunnel diode with Au/DNA/NiOx junctions is presented. Through the self-aligning process of DNA molecules, a 2D DNA nanosheet is synthesized and used as a tunneling barrier, and semitransparent conducting oxide (NiOx ) is applied as a top electrode for resolving metal penetration issues. This molecular device successfully operates as a nonresonant tunneling diode, and temperature-variable current-voltage analysis proves that Fowler-Nordheim tunneling is a dominant conduction mechanism at the junctions. DNA-based tunneling devices appear to be promising prototypes for nanoelectronics using biomolecules.

Charge Transport in 2D DNA Tunnel Junction Diodes

KAUST Repository

Yoon, Minho; Min, Sung-Wook; Dugasani, Sreekantha Reddy; Lee, Yong Uk; Oh, Min Suk; Anthopoulos, Thomas D.; Park, Sung Ha; Im, Seongil

2017-01-01

Recently, deoxyribonucleic acid (DNA) is studied for electronics due to its intrinsic benefits such as its natural plenitude, biodegradability, biofunctionality, and low-cost. However, its applications are limited to passive components because of inherent insulating properties. In this report, a metal-insulator-metal tunnel diode with Au/DNA/NiOx junctions is presented. Through the self-aligning process of DNA molecules, a 2D DNA nanosheet is synthesized and used as a tunneling barrier, and semitransparent conducting oxide (NiOx ) is applied as a top electrode for resolving metal penetration issues. This molecular device successfully operates as a nonresonant tunneling diode, and temperature-variable current-voltage analysis proves that Fowler-Nordheim tunneling is a dominant conduction mechanism at the junctions. DNA-based tunneling devices appear to be promising prototypes for nanoelectronics using biomolecules.

Electrical conduction of organic ultrathin films evaluated by an independently driven double-tip scanning tunneling microscope.

Science.gov (United States)

Takami, K; Tsuruta, S; Miyake, Y; Akai-Kasaya, M; Saito, A; Aono, M; Kuwahara, Y

2011-11-02

The electrical transport properties of organic thin films within the micrometer scale have been evaluated by a laboratory-built independently driven double-tip scanning tunneling microscope, operating under ambient conditions. The two tips were used as point contact electrodes, and current in the range from 0.1 pA to 100 nA flowing between the two tips through the material can be detected. We demonstrated two-dimensional contour mapping of the electrical resistance on a poly(3-octylthiophene) thin films as shown below. The obtained contour map clearly provided an image of two-dimensional electrical conductance between two point electrodes on the poly(3-octylthiophene) thin film. The conductivity of the thin film was estimated to be (1-8) × 10(-6) S cm(-1). Future prospects and the desired development of multiprobe STMs are also discussed.

Neutrons and numerical methods. A new look at rotational tunneling

Energy Technology Data Exchange (ETDEWEB)

Johnson, M R; Kearley, G J [Institut Max von Laue - Paul Langevin (ILL), 38 - Grenoble (France)

1997-04-01

Molecular modelling techniques are easily adapted to calculate rotational potentials in crystals of simple molecular compounds. A comparison with the potentials obtained from the tunnelling spectra provides a stringent means for validating current methods of calculating Van der Waals, Coulomb and covalent terms. (author). 5 refs.

Derivation of the tunnelling exchange time for the model of trap-assisted tunnelling

International Nuclear Information System (INIS)

Racko, J.; Ballo, P.; Benko, P.; Harmatha, L.; Grmanova, A.; Breza, J.

2014-01-01

We present derivation of the tunnelling exchange times that play the key role in the model of trap assisted tunnelling (TAT) considering the electron and hole exchange processes between the trapping centre lying in the forbidden band of the semiconductor and the conduction band, valence band or a metal. All exchange processes are quantitatively described by respective exchange times. The reciprocal values of these exchange times represent the frequency with which the exchange processes contribute to the probability of occupation of the trap by free charge carriers. The crucial problem in any model of TAT is the calculation of the occupation probability. In our approach this probability is expressed in terms of only thermal and tunnelling exchange times. The concept of tunnelling exchange times presents a dominant contribution to our model of TAT. The new approach allows to simply calculate the probability of occupation of the trapping centre by a free charge carrier and subsequently to get the thermal and tunnelling generation-recombination rates occurring in the continuity equations. This is why the TAT model based on thermal and tunnelling exchange times is suitable for simulating the electrical properties of semiconductor nanostructures in which quantum mechanical phenomena play a key role. (authors)

Tunneling in cuprate and bismuthate superconductors

International Nuclear Information System (INIS)

Zasadzinski, J.F.; Huang, Qiang; Tralshawala, N.

1991-10-01

Tunneling measurements using a point-contact technique are reported for the following high temperature superconducting oxides: Ba 1-x K x BiO 3 (BKBO), Nd 2-x Ce x CuO 4 (NCCO), Bi 2 Sr 2 CaCu 2 O 7 (BSCCO) and Tl 2 Ba 2 CaCu 2 O x (TBCCO). For the bismuthate, BKBO, ideal, S-I-N tunneling characteristics are observed using a Au tip. The normalized conductance is fitted to a BCS density of states and thermal smearing only proving there is no fundamental limitation in BKBO for device applications. For the cuprates, the normalized conductance displays BCS-like characteristics, but with a broadening larger than from thermal smearing. Energy gap values are presented for each material. For BKBO and NCCO the Eliashberg functions, α 2 F(ω), obtained from the tunneling are shown to be in good agreement with neutron scattering results. Proximity effect tunneling studies are reported for Au/BSCCO bilayers and show that the energy gap of BSCCO can be observed through Au layers up to 600 Angstrom thick

Development and trial measurement of synchrotron-radiation-light-illuminated scanning tunneling microscope

International Nuclear Information System (INIS)

Matsushima, Takeshi; Okuda, Taichi; Eguchi, Toyoaki; Ono, Masanori; Harasawa, Ayumi; Wakita, Takanori; Kataoka, Akira; Hamada, Masayuki; Kamoshida, Atsushi; Hasegawa, Yukio; Kinoshita, Toyohiko

2004-01-01

Scanning tunneling microscope (STM) study is performed under synchrotron-radiation-light illumination. The equipment is designed so as to achieve atomic resolution even under rather noisy conditions in the synchrotron radiation facility. By measuring photoexcited electron current by the STM tip together with the conventional STM tunneling current, Si 2p soft-x-ray absorption spectra are successfully obtained from a small area of Si(111) surface. The results are a first step toward realizing a new element-specific microscope

Effects of the finite duration of quantum tunneling in laser-assisted scanning tunneling microscopy

International Nuclear Information System (INIS)

Hagmann, M.J.

1994-01-01

Previous measurements of tunnel conductance in heterostructures and experiments with Josephson junctions suggest quantum tunneling has a definite duration. The authors use semiclassical methods to determine the effects of this delay on the tunneling current in a laser-assisted STM. A planar-planar STM model is used with the exact multiple image potential, and the energy distribution for a free-electron metal. It is necessary to average over the phase at barrier entry, and iteration with back propagated solutions is required to obtain the transmission coefficients for evenly spaced phases and specified energies at barrier entry. The simulations suggest that the dependence of the tunneling current on the wavelength of illumination can serve as a basis for determining the duration of barrier traversal. A power flux density of 10 11 W/m 2 would be required at several wavelengths from 1 to 10 μm. It is possible that thermal effects could be separated from the modeled phenomena by determining the time dependence of the tunneling current with a pulsed laser

Giant tunneling effect of hydrogen dissolved in α-Mn

International Nuclear Information System (INIS)

Kolesnikov, A.I.; Grosse, G.; Wagner, F.E.

1999-01-01

Complete text of publication follows. A neutron diffraction study has shown that H atoms in α-Mn occupy a double-well potential with a distance of l = 0.68 A between the minima. The results of the inelastic neutron scattering study are presented of α-MnH 0.07 and α-MnD 0.05 at temperatures from 1.7 to 200 K over a wide range of energy and momentum transfers. Together with the high-energy bands of the optical vibrations, pronounced peaks at ε = 6.3 and 1.6 meV were observed in the spectra of the samples loaded with H and D, respectively. The temperature, momentum-transfer and isotope dependence of the spectra unambiguously demonstrated the tunneling origin of these peaks. The anomalously high value of the tunneling energy, ε, is presumably due to the short distance, l, between the minima of the double-well potential, which is about half that found in other metal-H systems, while ε increases exponentially with decreasing l 2 . (author)

Resonant tunneling across a ferroelectric domain wall

Science.gov (United States)

Li, M.; Tao, L. L.; Velev, J. P.; Tsymbal, E. Y.

2018-04-01

Motivated by recent experimental observations, we explore electron transport properties of a ferroelectric tunnel junction (FTJ) with an embedded head-to-head ferroelectric domain wall, using first-principles density-functional theory calculations. We consider a FTJ with L a0.5S r0.5Mn O3 electrodes separated by a BaTi O3 barrier layer and show that an in-plane charged domain wall in the ferroelectric BaTi O3 can be induced by polar interfaces. The resulting V -shaped electrostatic potential profile across the BaTi O3 layer creates a quantum well and leads to the formation of a two-dimensional electron gas, which stabilizes the domain wall. The confined electronic states in the barrier are responsible for resonant tunneling as is evident from our quantum-transport calculations. We find that the resonant tunneling is an orbital selective process, which leads to sharp spikes in the momentum- and energy-resolved transmission spectra. Our results indicate that domain walls embedded in FTJs can be used to control the electron transport.

Local X-ray magnetic circular dichroism study of Fe/Cu(111) using a tunneling smart tip

Energy Technology Data Exchange (ETDEWEB)

DiLullo, Andrew; Shirato, Nozomi; Cummings, Marvin [Argonne National Laboratory, 9700 South Cass Avenue, Argonne, IL 60439 (United States); Kersell, Heath; Chang, Hao [Argonne National Laboratory, 9700 South Cass Avenue, Argonne, IL 60439 (United States); Ohio University, Athens, OH 45701 (United States); Rosenmann, Daniel; Miller, Dean; Freeland, John W. [Argonne National Laboratory, 9700 South Cass Avenue, Argonne, IL 60439 (United States); Hla, Saw-Wai [Argonne National Laboratory, 9700 South Cass Avenue, Argonne, IL 60439 (United States); Ohio University, Athens, OH 45701 (United States); Rose, Volker, E-mail: vrose@anl.gov [Argonne National Laboratory, 9700 South Cass Avenue, Argonne, IL 60439 (United States); Argonne National Laboratory, 9700 South Cass Avenue, Argonne, IL 60439 (United States)

2016-01-28

A tunneling smart tip of a synchrotron X-ray scanning tunneling microscope provides simultaneously localized topographic, elemental and magnetic information. Localized spectroscopy with simultaneous topographic, elemental and magnetic information is presented. A synchrotron X-ray scanning tunneling microscope has been employed for the local study of the X-ray magnetic circular dichroism at the Fe L{sub 2,3}-edges of a thin iron film grown on Cu(111). Polarization-dependent X-ray absorption spectra have been obtained through a tunneling smart tip that serves as a photoelectron detector. In contrast to conventional spin-polarized scanning tunneling microscopy, X-ray excitations provide magnetic contrast even with a non-magnetic tip. Intensity variations in the photoexcited tip current point to chemical variations within a single magnetic Fe domain.

Reduction of conductance mismatch in Fe/Al2O3/MoS2 system by tunneling-barrier thickness control

Science.gov (United States)

Hayakawa, Naoki; Muneta, Iriya; Ohashi, Takumi; Matsuura, Kentaro; Shimizu, Jun’ichi; Kakushima, Kuniyuki; Tsutsui, Kazuo; Wakabayashi, Hitoshi

2018-04-01

Molybdenum disulfide (MoS2) among two-dimensional semiconductor films is promising for spintronic devices because it has a longer spin-relaxation time with contrasting spin splitting than silicon. However, it is difficult to fabricate integrated circuits by the widely used exfoliation method. Here, we investigate the contact characteristics in the Fe/Al2O3/sputtered-MoS2 system with various thicknesses of the Al2O3 film. Current density increases with increasing thickness up to 2.5 nm because of both thermally-assisted and direct tunneling currents. On the other hand, it decreases with increasing thickness over 2.5 nm limited by direct tunneling currents. These results suggest that the Schottky barrier width can be controlled by changing thicknesses of the Al2O3 film, as supported by calculations. The reduction of conductance mismatch with this technique can lead to highly efficient spin injection from iron into the MoS2 film.

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

OpenAIRE

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

2005-01-01

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

Electron tunneling in proteins program.

Science.gov (United States)

Hagras, Muhammad A; Stuchebrukhov, Alexei A

2016-06-05

We developed a unique integrated software package (called Electron Tunneling in Proteins Program or ETP) which provides an environment with different capabilities such as tunneling current calculation, semi-empirical quantum mechanical calculation, and molecular modeling simulation for calculation and analysis of electron transfer reactions in proteins. ETP program is developed as a cross-platform client-server program in which all the different calculations are conducted at the server side while only the client terminal displays the resulting calculation outputs in the different supported representations. ETP program is integrated with a set of well-known computational software packages including Gaussian, BALLVIEW, Dowser, pKip, and APBS. In addition, ETP program supports various visualization methods for the tunneling calculation results that assist in a more comprehensive understanding of the tunneling process. © 2016 Wiley Periodicals, Inc. © 2016 Wiley Periodicals, Inc.

Tunnelling anomalous and planar Hall effects (Conference Presentation)

Science.gov (United States)

Matos-Abiague, Alex; Scharf, Benedikt; Han, Jong E.; Hankiewicz, Ewelina M.; Zutic, Igor

2016-10-01

We theoretically show how the interplay between spin-orbit coupling (SOC) and magnetism can result in a finite tunneling Hall conductance, transverse to the applied bias. For two-dimensional tunnel junctions with a ferromagnetic lead and magnetization perpendicular to the current flow, the detected anomalous Hall voltage can be used to extract information not only about the spin polarization but also about the strength of the interfacial SOC. In contrast, a tunneling current across a ferromagnetic barrier on the surface of a three-dimensional topological insulator (TI) can induce a planar Hall response even when the magnetization is oriented along the current flow[1]. The tunneling nature of the states contributing to the planar Hall conductance can be switched from the ordinary to the Klein regimes by the electrostatic control of the barrier strength. This allows for an enhancement of the transverse response and a giant Hall angle, with the tunneling planar Hall conductance exceeding the longitudinal component. Despite the simplicity of a single ferromagnetic region, the TI/ferromagnet system exhibits a variety of functionalities. In addition to a spin-valve operation for magnetic sensing and storing information, positive, negative, and negative differential conductances can be tuned by properly adjusting the barrier potential and/or varying the magnetization direction. Such different resistive behaviors in the same system are attractive for potential applications in reconfigurable spintronic devices. [1] B. Scharf, A. Matos-Abiague, J. E. Han, E. M. Hankiewicz, and I. Zutic, arXiv:1601.01009 (2016).

Comparison of Ares I-X Wind-Tunnel Derived Buffet Environment with Flight Data

Science.gov (United States)

Piatak, David J.; Sekula, Martin K.; Rausch, Russ D.

2011-01-01

The Ares I-X Flight Test Vehicle (FTV), launched in October 2009, carried with it over 243 buffet verification pressure sensors and was one of the most heavily instrumented launch vehicle flight tests. This flight test represented a unique opportunity for NASA and its partners to compare the wind-tunnel derived buffet environment with that measured during the flight of Ares I-X. It is necessary to define the launch vehicle buffet loads to ensure that structural components and vehicle subsystems possess adequate strength, stress, and fatigue margins when the vehicle structural dynamic response to buffet forcing functions are considered. Ares I-X buffet forcing functions were obtained via wind-tunnel testing of a rigid buffet model (RBM) instrumented with hundreds of unsteady pressure transducers designed to measure the buffet environment across the desired frequency range. This paper discusses the comparison of RBM and FTV buffet environments, including fluctuating pressure coefficient and normalized sectional buffet forcing function root-mean-square magnitudes, frequency content of power-spectral density functions, and force magnitudes of an alternating flow phenomena. Comparison of wind-tunnel model and flight test vehicle buffet environments show very good agreement with root-mean-square magnitudes of buffet forcing functions at the majority of vehicle stations. Spectra proved a challenge to compare because of different wind-tunnel and flight test conditions and data acquisition rates. However, meaningful and promising comparisons of buffet spectra are presented. Lastly, the buffet loads resulting from the transition of subsonic separated flow to supersonic attached flow were significantly over-predicted by wind-tunnel results.

Ultrafast scanning tunneling microscopy

Energy Technology Data Exchange (ETDEWEB)

Botkin, D.A. [California Univ., Berkeley, CA (United States). Dept. of Physics]|[Lawrence Berkeley Lab., CA (United States)

1995-09-01

I have developed an ultrafast scanning tunneling microscope (USTM) based on uniting stroboscopic methods of ultrafast optics and scanned probe microscopy to obtain nanometer spatial resolution and sub-picosecond temporal resolution. USTM increases the achievable time resolution of a STM by more than 6 orders of magnitude; this should enable exploration of mesoscopic and nanometer size systems on time scales corresponding to the period or decay of fundamental excitations. USTM consists of a photoconductive switch with subpicosecond response time in series with the tip of a STM. An optical pulse from a modelocked laser activates the switch to create a gate for the tunneling current, while a second laser pulse on the sample initiates a dynamic process which affects the tunneling current. By sending a large sequence of identical pulse pairs and measuring the average tunnel current as a function of the relative time delay between the pulses in each pair, one can map the time evolution of the surface process. USTM was used to measure the broadband response of the STM`s atomic size tunnel barrier in frequencies from tens to hundreds of GHz. The USTM signal amplitude decays linearly with the tunnel junction conductance, so the spatial resolution of the time-resolved signal is comparable to that of a conventional STM. Geometrical capacitance of the junction does not appear to play an important role in the measurement, but a capacitive effect intimately related to tunneling contributes to the measured signals and may limit the ultimate resolution of the USTM.

Magnetic reconstruction induced magnetoelectric coupling and spin-dependent tunneling in Ni/KNbO_3/Ni multiferroic tunnel junctions

International Nuclear Information System (INIS)

Zhang, Hu; Dai, Jian-Qing; Song, Yu-Min

2016-01-01

We investigate the magnetoelectric coupling and spin-polarized tunneling in Ni/KNbO_3/Ni multiferroic tunnel junctions with asymmetric interfaces based on density functional theory. The junctions have two stable polarization states. We predict a peculiar magnetoelectric effect in such junctions originating from the magnetic reconstruction of Ni near the KO-terminated interface. This reconstruction is induced by the reversal of the ferroelectric polarization of KNbO_3. Furthermore, the change in the magnetic ordering filters the spin-dependent current. This effect leads to a change in conductance by about two orders of magnitude. As a result we obtain a giant tunneling electroresistance effect. In addition, there exist sizable tunneling magnetoresistance effects for two polarization states. - Highlights: • We study the ME coupling and electron tunneling in Ni/KNbO_3/Ni junctions. • There is magnetic reconstruction of Ni atoms near the KO-terminated interface. • A peculiar magnetoelectric coupling effect is obtained. • Predicted giant tunneling electroresistance effects.

Stationary spectra of short-wave convective and magnetostatic fluctuations in a finite-pressure plasma and anomalous heat conductivity

International Nuclear Information System (INIS)

Vakulenko, M.O.

1992-01-01

Within the general renormalized statistical approach, the low-frequency short-wave stationary spectra of potential and magnetic perturbations in a finite-pressure plasma, are obtained. Anomalous heat conductivity considerably enhances due to non-linear interaction between magnetic excitations. 11 refs. (author)

Probing Single Nanometer-scale Particles with Scanning Tunneling Microscopy and Spectroscopies

International Nuclear Information System (INIS)

McCarty, G.S.; Love, J.C.; Kushmerick, J.G.; Charles, L.F.; Keating, C.D.; Toleno, B.J.; Lyn, M.E.; Castleman, A.W.; Natan, M.J.; Weiss, P.S.

1999-01-01

Scanning tunneling microscopy can be used to isolate single particles on surfaces for further study. Local optical and electronic properties coupled with topographic information collected by the scanning tunneling microscope (STM) give insight into the intrinsic properties of the species under study. Since each spectroscopic measurement is done on a single particle, each sample is 'monodisperse', regardless of the degree of heterogeneity of the original preparation. We illustrate this with three example systems - a metal cluster of known atomic structure, metal nanoparticles dispersed from colloid suspensions, and metallocarbohedrenes (Met-Cars) deposited with other reaction products. Au and Ag nanoparticles were imaged using a photon emission STM. The threshold voltage, the lowest bias voltage at which photons are produced, was determined for Au nanoparticles. Electronic spectra of small clusters of Ni atoms on MoS 2 were recorded. Preliminary images of Zr-based Met-Car-containing soot were obtained on Au and MoS 2 substrates and partial electronic spectra were recorded of these possible Met-Car particles

A tight binding model study of tunneling conductance spectra of spin and orbitally ordered CMR manganites

Science.gov (United States)

Panda, Saswati; Sahoo, D. D.; Rout, G. C.

2018-04-01

We report here a tight binding model for colossal magnetoresistive (CMR) manganites to study the pseudo gap (PG) behavior near Fermi level. In the Kubo-Ohata type DE model, we consider first and second nearest neighbor interactions for transverse spin fluctuations in core band and hopping integrals in conduction band, in the presence of static band Jahn-Teller distortion. The model Hamiltonian is solved using Zubarev's Green's function technique. The electron density of states (DOS) is found out from the Green's functions. We observe clear PG near Fermi level in the electron DOS.

Quantum description of spin tunneling in magnetic molecules

Science.gov (United States)

Galetti, D.

2007-01-01

Starting from a phenomenological Hamiltonian originally written in terms of angular momentum operators we derive a new quantum angle-based Hamiltonian that allows for a discussion on the quantum spin tunneling. The study of the applicability of the present approach, carried out in calculations with a soluble quasi-spin model, shows that we are allowed to use our method in the description of physical systems such as the Mn12-acetate molecule, as well as the octanuclear iron cluster, Fe8, in a reliable way. With the present description the interpretation of the spin tunneling is seen to be direct, the spectra and energy barriers of those systems are obtained, and it is shown that they agree with the experimental ones.

Anisotropic magnetoresistance and tunneling magnetoresistance of conducting filaments in NiO with different resistance states

Science.gov (United States)

Zhao, Diyang; Qiao, Shuang; Luo, Yuxiang; Chen, Aitian; Zhang, Pengfei; Zheng, Ping; Sun, Zhong; Guo, Minghua; Chiang, F.-K.; Wu, Jian; Luo, Jianlin; Li, Jianqi; Wang, Yayu; Zhao, Yonggang; Tsinghua University Team; Chinese Academy of Sciences Collaboration

Resistive switching (RS) effect in conductor/insulator/conductor thin-film stacks has attracted much attention due to its interesting physics and potentials for applications. NiO is one of the most representative systems and its RS effect has been generally explained by the formation and rupture of Ni related conducting filaments, which are very unique since they are formed by electric forming process. We study the MR behaviors in NiO RS films with different resistance states. Rich and interesting MR behaviors were observed, including the normal and anomalous anisotropic magnetoresistance (AMR) and tunneling magnetoresistance (TMR), etc., which provide new insights into the nature of the filaments and their evolution in the resistive switching process. First-principles calculation reveals the essential role of oxygen migration into the filaments during the RESET process and can account for the experimental results. Our work provides a new avenue for the exploration of the conducting filaments in RS materials, and is significant for understanding the RS mechanism as well as multifunctional device design.

Large tunneling magnetoresistance in octahedral Fe3O4 nanoparticles

Directory of Open Access Journals (Sweden)

Arijit Mitra

2016-05-01

Full Text Available We have observed large tunneling Magnetoresistance (TMR in amine functionalized octahedral nanoparticle assemblies. Amine monolayer on the surface of nanoparticles acts as an insulating barrier between the semimetal Fe3O4 nanoparticles and provides multiple tunnel junctions where inter-granular tunneling is plausible. The tunneling magnetoresistance recorded at room temperature is 38% which increases to 69% at 180 K. When the temperature drops below 150 K, coulomb staircase is observed in the current versus voltage characteristics as the charging energy exceeds the thermal energy. A similar study is also carried out with spherical nanoparticles. A 24% TMR is recorded at room temperature which increases to 41% at 180 K for spherical particles. Mössbauer spectra reveal better stoichiometry for octahedral particles which is attainable due to lesser surface disorder and strong amine coupling at the facets of octahedral Fe3O4 nanoparticles. Less stoichiometric defect in octahedral nanoparticles leads to a higher value of spin polarization and therefore larger TMR in octahedral nanoparticles.

On the flow of an electrically conducting gas past a slender body of revolution placed in a circular wind tunnel in the presence of a crossed magnetic field

International Nuclear Information System (INIS)

Suwa, Shigeaki; Kusukawa, Ken-ichi.

1976-01-01

The wind tunnel interference problem in magnetohydrodynamics, in which an inviscid compressible fluid with small electrical conductivity flows steadily past a slender axi-symmetric pointed body of revolution placed in a cylindrical perfectly insulated wind tunnel, in the presence of a crossed magnetic field, is considered. Using the analytical method which was studied by one of the present authors, the streamlines and the space charge in a cross section are calculated. (auth.)

An update of conditions in the Donkin-Morien tunnels

Energy Technology Data Exchange (ETDEWEB)

Seedsman, R.W. [Seedsman Geotechnics Pty Ltd., Mt. Kembla (Australia)

2009-07-01

Two 7.6 diameter tunnels were constructed in the Donkin-Morien peninsula in Nova Scotia in 1984 and 1985. Ground support designs of the tunnel were based on the identification of rock failure zones using finite element analyses and the Hoek Brown failure criterion. The tunnels were flooded in 1992 when the mining project was abandoned. However, subsequent monitoring data from the tunnels were used to analyze brittle rock behaviour before and after its subsequent dewatering. This paper discussed the results of a feasibility study conducted to compare collapse zones in the roof and sides of the tunnel with results obtained from a simple elastic analysis technique that used brittle parameters, a spalling limit of 5, and a low-dependent shear modulus. Analyses were conducted to examine the potential maximum height of failure as a function of the coal seams. The study showed that coal measure rocks can be analyzed using the brittle failure criterion when both transverse anisotropy and low spalling limits were included. However, it is not possible to determine the contribution of corrosion to the deterioration of the tunnels. The analysis will be used to form a design for re-supporting the tunnels. 7 refs., 2 tabs., 7 figs.

Low frequency noise peak near magnon emission energy in magnetic tunnel junctions

Energy Technology Data Exchange (ETDEWEB)

Liu, Liang; Xiang, Li; Guo, Huiqiang; Wei, Jian, E-mail: weijian6791@pku.edu.cn [International Center for Quantum Materials, School of Physics, Peking University, Beijing 100871, China and Collaborative Innovation Center of Quantum Matter, Beijing (China); Li, D. L.; Yuan, Z. H.; Feng, J. F., E-mail: jiafengfeng@iphy.ac.cn; Han, X. F. [Beijing National Laboratory of Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences, Beijing 100190 (China); Coey, J. M. D. [CRANN and School of Physics, Trinity College, Dublin 2 (Ireland)

2014-12-15

We report on the low frequency (LF) noise measurements in magnetic tunnel junctions (MTJs) below 4 K and at low bias, where the transport is strongly affected by scattering with magnons emitted by hot tunnelling electrons, as thermal activation of magnons from the environment is suppressed. For both CoFeB/MgO/CoFeB and CoFeB/AlO{sub x}/CoFeB MTJs, enhanced LF noise is observed at bias voltage around magnon emission energy, forming a peak in the bias dependence of noise power spectra density, independent of magnetic configurations. The noise peak is much higher and broader for unannealed AlO{sub x}-based MTJ, and besides Lorentzian shape noise spectra in the frequency domain, random telegraph noise (RTN) is visible in the time traces. During repeated measurements the noise peak reduces and the RTN becomes difficult to resolve, suggesting defects being annealed. The Lorentzian shape noise spectra can be fitted with bias-dependent activation of RTN, with the attempt frequency in the MHz range, consistent with magnon dynamics. These findings suggest magnon-assisted activation of defects as the origin of the enhanced LF noise.

Low frequency noise peak near magnon emission energy in magnetic tunnel junctions

Directory of Open Access Journals (Sweden)

Liang Liu

2014-12-01

Full Text Available We report on the low frequency (LF noise measurements in magnetic tunnel junctions (MTJs below 4 K and at low bias, where the transport is strongly affected by scattering with magnons emitted by hot tunnelling electrons, as thermal activation of magnons from the environment is suppressed. For both CoFeB/MgO/CoFeB and CoFeB/AlOx/CoFeB MTJs, enhanced LF noise is observed at bias voltage around magnon emission energy, forming a peak in the bias dependence of noise power spectra density, independent of magnetic configurations. The noise peak is much higher and broader for unannealed AlOx-based MTJ, and besides Lorentzian shape noise spectra in the frequency domain, random telegraph noise (RTN is visible in the time traces. During repeated measurements the noise peak reduces and the RTN becomes difficult to resolve, suggesting defects being annealed. The Lorentzian shape noise spectra can be fitted with bias-dependent activation of RTN, with the attempt frequency in the MHz range, consistent with magnon dynamics. These findings suggest magnon-assisted activation of defects as the origin of the enhanced LF noise.

Measurement of the quantum conductance of germanium by an electrochemical scanning tunneling microscope break junction based on a jump-to-contact mechanism.

Science.gov (United States)

Xie, Xufen; Yan, Jiawei; Liang, Jinghong; Li, Jijun; Zhang, Meng; Mao, Bingwei

2013-10-01

We present quantum conductance measurements of germanium by means of an electrochemical scanning tunneling microscope (STM) break junction based on a jump-to-contact mechanism. Germanium nanowires between a platinum/iridium tip and different substrates were constructed to measure the quantum conductance. By applying appropriate potentials to the substrate and the tip, the process of heterogeneous contact and homogeneous breakage was realized. Typical conductance traces exhibit steps at 0.025 and 0.05 G0. The conductance histogram indicates that the conductance of germanium nanowires is located between 0.02 and 0.15 G0 in the low-conductance region and is free from the influence of substrate materials. However, the distribution of conductance plateaus is too discrete to display distinct peaks in the conductance histogram of the high-conductance region. Copyright © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Tunneling technologies for the collider ring tunnels

International Nuclear Information System (INIS)

Frobenius, P.

1989-01-01

The Texas site chosen for the Superconducting Super Collider has been studied, and it has been determined that proven, conventional technology and accepted engineering practice are suitable for constructing the collider tunnels. The Texas National Research Laboratory Commission report recommended that two types of tunneling machines be used for construction of the tunnels: a conventional hard rock tunnel boring machine (TBM) for the Austin chalk and a double shielded, rotary TBM for the Taylor marl. Since the tunneling machines usually set the pace for the project, efficient planning, operation, and coordination of the tunneling system components will be critical to the schedule and cost of the project. During design, tunneling rate prediction should be refined by focusing on the development of an effective tunneling system and evaluating its capacity to meet or exceed the required schedules. 8 refs., 13 figs

Calculated and experimental low-loss electron energy loss spectra of dislocations in diamond and GaN

CERN Document Server

Jones, R; Gutiérrez-Sosa, A; Bangert, U; Heggie, M I; Blumenau, A T; Frauenheim, T; Briddon, P R

2002-01-01

First-principles calculations of electron energy loss (EEL) spectra for bulk GaN and diamond are compared with experimental spectra acquired with a scanning tunnelling electron microscope offering ultra-high-energy resolution in low-loss energy spectroscopy. The theoretical bulk low-loss EEL spectra, in the E sub g to 10 eV range, are in good agreement with experimental data. Spatially resolved spectra from dislocated regions in both materials are distinct from bulk spectra. The main effects are, however, confined to energy losses lying above the band edge. The calculated spectra for low-energy dislocations in diamond are consistent with the experimental observations, but difficulties remain in understanding the spectra of threading dislocations in GaN.

Band-to-band tunneling distance analysis in the heterogate electron–hole bilayer tunnel field-effect transistor

Energy Technology Data Exchange (ETDEWEB)

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

2016-01-28

In this work, we analyze the behavior of the band-to-band tunneling distance between electron and hole subbands resulting from field-induced quantum confinement in the heterogate electron–hole bilayer tunnel field-effect transistor. We show that, analogously to the explicit formula for the tunneling distance that can be easily obtained in the semiclassical framework where the conduction and valence band edges are allowed states, an equivalent analytical expression can be derived in the presence of field-induced quantum confinement for describing the dependence of the tunneling distance on the body thickness and material properties of the channel. This explicit expression accounting for quantum confinement holds valid provided that the potential wells for electrons and holes at the top and bottom of the channel can be approximated by triangular profiles. Analytical predictions are compared to simulation results showing very accurate agreement.

A Top Pilot Tunnel Preconditioning Method for the Prevention of Extremely Intense Rockbursts in Deep Tunnels Excavated by TBMs

Science.gov (United States)

Zhang, Chuanqing; Feng, Xiating; Zhou, Hui; Qiu, Shili; Wu, Wenping

2012-05-01

The headrace tunnels at the Jinping II Hydropower Station cross the Jinping Mountain with a maximum overburden depth of 2,525 m, where 80% of the strata along the tunnels consist of marble. A number of extremely intense rockbursts occurred during the excavation of the auxiliary tunnels and the drainage tunnel. In particular, a tunnel boring machine (TBM) was destroyed by an extremely intense rockburst in a 7.2-m-diameter drainage tunnel. Two of the four subsequent 12.4-m-diameter headrace tunnels will be excavated with larger size TBMs, where a high risk of extremely intense rockbursts exists. Herein, a top pilot tunnel preconditioning method is proposed to minimize this risk, in which a drilling and blasting method is first recommended for the top pilot tunnel excavation and support, and then the TBM excavation of the main tunnel is conducted. In order to evaluate the mechanical effectiveness of this method, numerical simulation analyses using the failure approaching index, energy release rate, and excess shear stress indices are carried out. Its construction feasibility is discussed as well. Moreover, a microseismic monitoring technique is used in the experimental tunnel section for the real-time monitoring of the microseismic activities of the rock mass in TBM excavation and for assessing the effect of the top pilot tunnel excavation in reducing the risk of rockbursts. This method is applied to two tunnel sections prone to extremely intense rockbursts and leads to a reduction in the risk of rockbursts in TBM excavation.

Tunneling spin injection into single layer graphene.

Science.gov (United States)

Han, Wei; Pi, K; McCreary, K M; Li, Yan; Wong, Jared J I; Swartz, A G; Kawakami, R K

2010-10-15

We achieve tunneling spin injection from Co into single layer graphene (SLG) using TiO₂ seeded MgO barriers. A nonlocal magnetoresistance (ΔR(NL)) of 130  Ω is observed at room temperature, which is the largest value observed in any material. Investigating ΔR(NL) vs SLG conductivity from the transparent to the tunneling contact regimes demonstrates the contrasting behaviors predicted by the drift-diffusion theory of spin transport. Furthermore, tunnel barriers reduce the contact-induced spin relaxation and are therefore important for future investigations of spin relaxation in graphene.

Chiral tunneling in gated inversion symmetric Weyl semimetal

Science.gov (United States)

Bai, Chunxu; Yang, Yanling; Chang, Kai

2016-01-01

Based on the chirality-resolved transfer-matrix method, we evaluate the chiral transport tunneling through Weyl semimetal multi-barrier structures created by periodic gates. It is shown that, in sharp contrast to the cases of three dimensional normal semimetals, the tunneling coefficient as a function of incident angle shows a strong anisotropic behavior. Importantly, the tunneling coefficients display an interesting periodic oscillation as a function of the crystallographic angle of the structures. With the increasement of the barriers, the tunneling current shows a Fabry-Perot type interferences. For superlattice structures, the fancy miniband effect has been revealed. Our results show that the angular dependence of the first bandgap can be reduced into a Lorentz formula. The disorder suppresses the oscillation of the tunneling conductance, but would not affect its average amplitude. This is in sharp contrast to that in multi-barrier conventional semiconductor structures. Moreover, numerical results for the dependence of the angularly averaged conductance on the incident energy and the structure parameters are presented and contrasted with those in two dimensional relativistic materials. Our work suggests that the gated Weyl semimetal opens a possible new route to access to new type nanoelectronic device. PMID:26888491

Tunneling Planar Hall Effect in Topological Insulators: Spin Valves and Amplifiers.

Science.gov (United States)

Scharf, Benedikt; Matos-Abiague, Alex; Han, Jong E; Hankiewicz, Ewelina M; Žutić, Igor

2016-10-14

We investigate tunneling across a single ferromagnetic barrier on the surface of a three-dimensional topological insulator. In the presence of a magnetization component along the bias direction, a tunneling planar Hall conductance (TPHC), transverse to the applied bias, develops. Electrostatic control of the barrier enables a giant Hall angle, with the TPHC exceeding the longitudinal tunneling conductance. By changing the in-plane magnetization direction, it is possible to change the sign of both the longitudinal and transverse differential conductance without opening a gap in the topological surface state. The transport in a topological-insulator-ferromagnet junction can, thus, be drastically altered from a simple spin valve to an amplifier.

Tunneling Negative Magnetoresistance via δ Doping in a Graphene-Based Magnetic Tunnel Junction

International Nuclear Information System (INIS)

Yuan Jian-Hui; Chen Ni; Mo Hua; Zhang Yan; Zhang Zhi-Hai

2016-01-01

We investigate the tunneling magnetoresistance via δ doping in a graphene-based magnetic tunnel junction in detail. It is found that the transmission probability and the conductance oscillates with the position and the aptitude of the δ doping. Also, both the transmission probability and the conductance at the parallel configuration are suppressed by the magnetic field more obviously than that at the antiparallel configuration, which implies a large negative magnetoresistance for this device. The results show that the negative magnetoresistance of over 300% at B = 1.0 T is observed by choosing suitable doped parameters, and the temperature plays an important role in the magnetoresistance. Thus it is possible to open a way to effectively manipulate the magnetoresistance devices, and to make a type of magnetoresistance device by controlling the structural parameter of the δ doping. (paper)

/sup 13/C NMR spectra and electron conduction in 4-substituted diphenylamines

Energy Technology Data Exchange (ETDEWEB)

Filimonov, V.D.; Kogan, R.M.; Tverdokhlebova, N.E.; Shcherbakov, V.V.; Kushnarev, D.F.; Kalabin, G.A.

1986-07-10

The /sup 13/C NMR spectra were recorded for a series of 4-X-diphenylamines, and correlations equations relating the /sup 13/C NMR chemical shifts of the C/sup 1/ and C/sup 4/ positions to the electronic characteristics of the substituent X were obtained. It was established that the conduction of the substituted ring in the 4-X-diphenylamines is practically the same as in 4-X-biphenyls. Joint analysis of the spectral characteristics of the diphenylamines, biphenyls, N-substituted anilines, and carbazoles made it possible to conclude that the increased transmission characteristics of the diphenylamines are determined by the conformational mobility of the two benzene rings and by the unidirectional effect of changes in the introduction and resonance factors with variation in the substituent X.

Spectroscopy of bulk and few-layer superconducting NbSe2 with van der Waals tunnel junctions.

Science.gov (United States)

Dvir, T; Massee, F; Attias, L; Khodas, M; Aprili, M; Quay, C H L; Steinberg, H

2018-02-09

Tunnel junctions, an established platform for high resolution spectroscopy of superconductors, require defect-free insulating barriers; however, oxides, the most common barrier, can only grow on a limited selection of materials. We show that van der Waals tunnel barriers, fabricated by exfoliation and transfer of layered semiconductors, sustain stable currents with strong suppression of sub-gap tunneling. This allows us to measure the spectra of bulk (20 nm) and ultrathin (3- and 4-layer) NbSe 2 devices at 70 mK. These exhibit two distinct superconducting gaps, the larger of which decreases monotonically with thickness and critical temperature. The spectra are analyzed using a two-band model incorporating depairing. In the bulk, the smaller gap exhibits strong depairing in in-plane magnetic fields, consistent with high out-of-plane Fermi velocity. In the few-layer devices, the large gap exhibits negligible depairing, consistent with out-of-plane spin locking due to Ising spin-orbit coupling. In the 3-layer device, the large gap persists beyond the Pauli limit.

Tunneling emission of electrons from semiconductors' valence bands in high electric fields

International Nuclear Information System (INIS)

Kalganov, V. D.; Mileshkina, N. V.; Ostroumova, E. V.

2006-01-01

Tunneling emission currents of electrons from semiconductors to vacuum (needle-shaped GaAs photodetectors) and to a metal (silicon metal-insulator-semiconductor diodes with a tunneling-transparent insulator layer) are studied in high and ultrahigh electric fields. It is shown that, in semiconductors with the n-type conductivity, the major contribution to the emission current is made by the tunneling emission of electrons from the valence band of the semiconductor, rather than from the conduction band

Hoosac tunnel geothermal heat source. Final report

Energy Technology Data Exchange (ETDEWEB)

1982-06-10

The Hoosac Rail Tunnel has been analyzed as a central element in a district heating system for the City of North Adams. The tunnel has been viewed as a collector of the earth's geothermal heat and a seasonal heat storage facility with heat piped to the tunnel in summer from existing facilities at a distance. Heated fluid would be transported in winter from the tunnel to users who would boost the temperature with individual heat pumps. It was concluded the tunnel is a poor source of geothermal heat. The maximum extractable energy is only 2200 million BTU (20000 gallons of oil) at 58/sup 0/F. The tunnel is a poor heat storage facility. The rock conductivity is so high that 75% of the heat injected would escape into the mountain before it could be recaptured for use. A low temperature system, with individual heat pumps for temperature boost could be economically attractive if a low cost fuel (byproduct, solid waste, cogeneration) or a cost effective seasonal heat storage were available.

Fabrication of silver tips for scanning tunneling microscope induced luminescence.

Science.gov (United States)

Zhang, C; Gao, B; Chen, L G; Meng, Q S; Yang, H; Zhang, R; Tao, X; Gao, H Y; Liao, Y; Dong, Z C

2011-08-01

We describe a reliable fabrication procedure of silver tips for scanning tunneling microscope (STM) induced luminescence experiments. The tip was first etched electrochemically to yield a sharp cone shape using selected electrolyte solutions and then sputter cleaned in ultrahigh vacuum to remove surface oxidation. The tip status, in particular the tip induced plasmon mode and its emission intensity, can be further tuned through field emission and voltage pulse. The quality of silver tips thus fabricated not only offers atomically resolved STM imaging, but more importantly, also allows us to perform challenging "color" photon mapping with emission spectra taken at each pixel simultaneously during the STM scan under relatively small tunnel currents and relatively short exposure time.

Wind Tunnel Measurements at LM Wind Power

DEFF Research Database (Denmark)

Bertagnolio, Franck

2012-01-01

This section presents the results obtained during the experimental campaign that was conducted in the wind tunnel at LM Wind Power in Lunderskov from August 16th to 26th, 2010. The goal of this study is to validate the so-called TNO trailing edge noise model through measurements of the boundary...... layer turbulence characteristics and the far-field noise generated by the acoustic scattering of the turbulent boundary layer vorticies as they convect past the trailing edge. This campaign was conducted with a NACA0015 airfoil section that was placed in the wind tunnel section. It is equipped with high...

Spin inelastic electron tunneling spectroscopy on local spin adsorbed on surface.

Science.gov (United States)

Fransson, J

2009-06-01

The recent experimental conductance measurements taken on magnetic impurities on metallic surfaces, using scanning tunneling microscopy technique and suggesting occurrence of inelastic scattering processes, are theoretically addressed. We argue that the observed conductance signatures are caused by transitions between the spin states that have opened due to, for example, exchange coupling between the local spins and the tunneling electrons, and are directly interpretable in terms of inelastic transitions energies. Feasible measurements using spin-polarized scanning tunneling microscopy that would enable new information about the excitation spectrum of the local spins are discussed.

Phantom force induced by tunneling current: a characterization on Si(111).

Science.gov (United States)

Weymouth, A J; Wutscher, T; Welker, J; Hofmann, T; Giessibl, F J

2011-06-03

Simultaneous measurements of tunneling current and atomic forces provide complementary atomic-scale data of the electronic and structural properties of surfaces and adsorbates. With these data, we characterize a strong impact of the tunneling current on the measured force on samples with limited conductivity. The effect is a lowering of the effective gap voltage through sample resistance which in turn lowers the electrostatic attraction, resulting in an apparently repulsive force. This effect is expected to occur on other low-conductance samples, such as adsorbed molecules, and to strongly affect Kelvin probe measurements when tunneling occurs.

Construction monitoring activities in the ESF starter tunnel

International Nuclear Information System (INIS)

Pott, J.; Carlisle, S.

1994-01-01

In situ design verification activities am being conducted in the North Ramp Starter Tunnel of the Yucca Mountain Project Exploratory Studies Facility. These activities include: monitoring the peak particle velocities and evaluating the damage to the rock mass associated with construction blasting, assessing the rock mass quality surrounding the tunnel, monitoring the performance of the installed ground support, and monitoring the stability of the tunnel. In this paper, examples of the data that have been collected and preliminary conclusions from the data are presented

Identification of microorganisms using superconducting tunnel junctions and time-of-flight mass spectrometry

Science.gov (United States)

Ullom, J. N.; Frank, M.; Horn, J. M.; Labov, S. E.; Langry, K.; Benner, W. H.

2000-04-01

We present time-of-flight measurements of biological material ejected from bacterial spores following laser irradiation. Ion impacts are registered on a microchannel plate detector and on a Superconducting Tunnel Junction (STJ) detector. We compare mass spectra obtained with the two detectors. The STJ has better sensitivity to massive ions and also measures the energy of each ion. We show evidence that spores of different bacillus species produce distinctive mass spectra and associate the observed mass peaks with coat proteins.

Identification of microorganisms using superconducting tunnel junctions and time-of-flight mass spectrometry

International Nuclear Information System (INIS)

Ullom, J.N.; Frank, M.; Horn, J.M.; Labov, S.E.; Langry, K.; Benner, W.H.

2000-01-01

We present time-of-flight measurements of biological material ejected from bacterial spores following laser irradiation. Ion impacts are registered on a microchannel plate detector and on a Superconducting Tunnel Junction (STJ) detector. We compare mass spectra obtained with the two detectors. The STJ has better sensitivity to massive ions and also measures the energy of each ion. We show evidence that spores of different bacillus species produce distinctive mass spectra and associate the observed mass peaks with coat proteins

Quantized Majorana conductance

Science.gov (United States)

Zhang, Hao; Liu, Chun-Xiao; Gazibegovic, Sasa; Xu, Di; Logan, John A.; Wang, Guanzhong; van Loo, Nick; Bommer, Jouri D. S.; de Moor, Michiel W. A.; Car, Diana; Op Het Veld, Roy L. M.; van Veldhoven, Petrus J.; Koelling, Sebastian; Verheijen, Marcel A.; Pendharkar, Mihir; Pennachio, Daniel J.; Shojaei, Borzoyeh; Lee, Joon Sue; Palmstrøm, Chris J.; Bakkers, Erik P. A. M.; Sarma, S. Das; Kouwenhoven, Leo P.

2018-04-01

Majorana zero-modes—a type of localized quasiparticle—hold great promise for topological quantum computing. Tunnelling spectroscopy in electrical transport is the primary tool for identifying the presence of Majorana zero-modes, for instance as a zero-bias peak in differential conductance. The height of the Majorana zero-bias peak is predicted to be quantized at the universal conductance value of 2e2/h at zero temperature (where e is the charge of an electron and h is the Planck constant), as a direct consequence of the famous Majorana symmetry in which a particle is its own antiparticle. The Majorana symmetry protects the quantization against disorder, interactions and variations in the tunnel coupling. Previous experiments, however, have mostly shown zero-bias peaks much smaller than 2e2/h, with a recent observation of a peak height close to 2e2/h. Here we report a quantized conductance plateau at 2e2/h in the zero-bias conductance measured in indium antimonide semiconductor nanowires covered with an aluminium superconducting shell. The height of our zero-bias peak remains constant despite changing parameters such as the magnetic field and tunnel coupling, indicating that it is a quantized conductance plateau. We distinguish this quantized Majorana peak from possible non-Majorana origins by investigating its robustness to electric and magnetic fields as well as its temperature dependence. The observation of a quantized conductance plateau strongly supports the existence of Majorana zero-modes in the system, consequently paving the way for future braiding experiments that could lead to topological quantum computing.

Air quality assessment in Salim Slam Tunnel

International Nuclear Information System (INIS)

El-Fadel, M.; Hashisho, Z.; Saikaly, P.

1999-01-01

Full text.Vehicle emissions constitute a serious occupational environmental hazard particularly in confined spaces such as tunnels and underground parking garages. these emissions at elevated concentrations, can cause adverse health effects, which range from nausea and eye irritation to mutagenicity, carcinogenicity and even death. This paper presents an environmental air quality assessment in a tunnel located in a highly congested urban area. For this purpose, air samples were collected and analyzed for the presence of primary air pollutants, priority metals, and volatile organic carbons. Air quality modeling was conducted to simulate variations of pollutant concentrations in the tunnel under worst case scenarios including traffic congestion and no air ventilation. Field measurements and mathematical simulation results were used to develop a strategy for proper air quality management in tunnels

Shot Noise in Negative-Differential-Conductance Devices

National Research Council Canada - National Science Library

Song, W

2003-01-01

The authors have compared the shot-noise properties at T = 4.2 K of a double-barrier resonant-tunneling diode and a superlattice tunnel diode, both of which exhibit negative differential-conductance (NDC...

Superconducting tunnel-junction refrigerator

International Nuclear Information System (INIS)

Melton, R.G.; Paterson, J.L.; Kaplan, S.B.

1980-01-01

The dc current through an S 1 -S 2 tunnel junction, with Δ 2 greater than Δ 1 , when biased with eV 1 +Δ 2 , will lower the energy in S 1 . This energy reduction will be shared by the phonons and electrons. This device is shown to be analogous to a thermoelectric refrigerator with an effective Peltier coefficient π* approx. Δ 1 /e. Tunneling calculations yield the cooling power P/sub c/, the electrical power P/sub e/ supplied by the bias supply, and the cooling efficiency eta=P/sub c//P/sub e/. The maximum cooling power is obtained for eV= +- (Δ 2 -Δ 1 ) and t 1 =T 1 /T/sub c/1 approx. 0.9. Estimates are made of the temperature difference T 2 -T 1 achievable in Al-Pb and Sn-Pb junctions with an Al 2 O 3 tunneling barrier. The performance of this device is shown to yield a maximum cooling efficiency eta approx. = Δ 1 /(Δ 2 -Δ 1 ) which can be compared with that available in an ideal Carnot refrigerator of eta=T 1 /(T 2 -T 1 ). The development of a useful tunnel-junction refrigerator requires a tunneling barrier with an effective thermal conductance per unit area several orders of magnitude less than that provided by the A1 2 O 3 barrier in the Al-Pb and Sn-Pb systems

Prediction of vibration level in tunnel blasting; Tonneru kusshin happa ni yotte reiki sareru shindo no reberu yosoku ho

Energy Technology Data Exchange (ETDEWEB)

Hirata, A. [Kumamoto Industries Univ, Kumamoto (Japan); Yamamoto, M. [Asahi Chemical Industry Co. Ltd., Tokyo (Japan); Inaba, C. [Nishimatsu Construction Co. Ltd., Kanagawa (Japan); Kaneko, K. [Hokkaido Univ (Japan)

1997-08-01

For avoiding the generation of public hazard due to ground vibration causes by blasting in tunneling, it is important to devise a blasting method for ensuring the level of the ground vibration caused thereby under a limit, and an exact predication of ground vibration before blasting is desirable. In this study, the characteristics of the ground vibration caused by tunnel blasting are analyzed, and a summary of amplitude spectra calculating method is described. A theoretical analysis method for predicting the vibration level is proposed based on spectrum-multiplicative method. Vibration caused by multistage blasting in tunneling is most strong and deemed as important. When observing the process of elastic wave motion caused by multistage blasting being measured, the process can be divided into three element processes in frequency area as vibration source spectrum, transmission attenuation spectrum and frequency response function vibrating test, and, with the multiplication of them, the amplitude spectra at an observation portion can be estimated. 12 refs., 12 figs.

On the flow of groundwater in closed tunnels. Generic hydrogeological modelling of nuclear waste repository, SFL 3-5

International Nuclear Information System (INIS)

Holmen, J.G.

1997-06-01

The purpose is to study the flow of groundwater in closed tunnels by use of mathematical models. The calculations were based on three dimensional models, presuming steady state conditions. The stochastic continuum approach was used for representation of a heterogeneous rock mass. The size of the calculated flow is given as a multiple of an unknown regional groundwater flow. The size of the flow in a tunnel has been studied, as regards: Direction of the regional groundwater flow, Tunnel length, width and conductivity; Heterogeneity of the surrounding rock mass; Flow barriers and encapsulation inside a tunnel. The study includes a model of the planned repository for nuclear waste (SFL 3-5). The flow through the tunnels is estimated for different scenarios. The stochastic continuum approach has been investigated, as regards the representation of a scale dependent heterogeneous conductivity. An analytical method is proposed for the scaling of measured conductivity values, the method is consistent with the stochastic continuum approach. Some general conclusions from the work are: The larger the amount of heterogeneity, the larger the expected flow; The effects of the heterogeneity will decrease with increased tunnel length; If the conductivity of the tunnel is smaller than a threshold value, the tunnel conductivity is the most important parameter; If the tunnel conductivity is large and the tunnel is long, the most important parameter is the direction of the regional flow; Given a heterogeneous rock mass, if the tunnel length is shorter than about 500 m, the heterogeneity will be an important parameter, for lengths shorter than about 250 m, probably the most important; The flow through an encapsulation surrounded by a flow barrier is mainly dependent on the conductivity of the barrier. 70 refs, 110 figs, 10 tabs

On the flow of groundwater in closed tunnels. Generic hydrogeological modelling of nuclear waste repository, SFL 3-5

Energy Technology Data Exchange (ETDEWEB)

Holmen, J.G. [Uppsala Univ. (Sweden). Inst. of Earth Sciences]|[Golder Associates AB (Sweden)

1997-06-01

The purpose is to study the flow of groundwater in closed tunnels by use of mathematical models. The calculations were based on three dimensional models, presuming steady state conditions. The stochastic continuum approach was used for representation of a heterogeneous rock mass. The size of the calculated flow is given as a multiple of an unknown regional groundwater flow. The size of the flow in a tunnel has been studied, as regards: Direction of the regional groundwater flow, Tunnel length, width and conductivity; Heterogeneity of the surrounding rock mass; Flow barriers and encapsulation inside a tunnel. The study includes a model of the planned repository for nuclear waste (SFL 3-5). The flow through the tunnels is estimated for different scenarios. The stochastic continuum approach has been investigated, as regards the representation of a scale dependent heterogeneous conductivity. An analytical method is proposed for the scaling of measured conductivity values, the method is consistent with the stochastic continuum approach. Some general conclusions from the work are: The larger the amount of heterogeneity, the larger the expected flow; The effects of the heterogeneity will decrease with increased tunnel length; If the conductivity of the tunnel is smaller than a threshold value, the tunnel conductivity is the most important parameter; If the tunnel conductivity is large and the tunnel is long, the most important parameter is the direction of the regional flow; Given a heterogeneous rock mass, if the tunnel length is shorter than about 500 m, the heterogeneity will be an important parameter, for lengths shorter than about 250 m, probably the most important; The flow through an encapsulation surrounded by a flow barrier is mainly dependent on the conductivity of the barrier. 70 refs, 110 figs, 10 tabs.

Conduction spectroscopy of a proximity induced superconducting topological insulator

Science.gov (United States)

Stehno, M. P.; Hendrickx, N. W.; Snelder, M.; Scholten, T.; Huang, Y. K.; Golden, M. S.; Brinkman, A.

2017-09-01

The combination of superconductivity and the helical spin-momentum locking at the surface state of a topological insulator (TI) has been predicted to give rise to p-wave superconductivity and Majorana bound states. The superconductivity can be induced by the proximity effect of a s-wave superconductor (S) into the TI. To probe the superconducting correlations inside the TI, dI/dV spectroscopy has been performed across such S-TI interfaces. Both the alloyed Bi1.5Sb0.5Te1.7Se1.3 and the stoichiometric BiSbTeSe2 have been used as three-dimensional TI. In the case of Bi1.5Sb0.5Te1.7Se1.3, the presence of disorder induced electron-electron interactions can give rise to an additional zero-bias resistance peak. For the stoichiometric BiSbTeSe2 with less disorder, tunnel barriers were employed in order to enhance the signal from the interface. The general observations in the spectra of a large variety of samples are conductance dips at the induced gap voltage, combined with an increased sub-gap conductance, consistent with p-wave predictions. The induced gap voltage is typically smaller than the gap of the Nb superconducting electrode, especially in the presence of an intentional tunnel barrier. Additional uncovered spectroscopic features are oscillations that are linearly spaced in energy, as well as a possible second order parameter component.

Measurements of temperature characteristics and estimation of terahertz negative differential conductance in resonant-tunneling-diode oscillators

Directory of Open Access Journals (Sweden)

M. Asada

2017-11-01

Full Text Available The temperature dependences of output power, oscillation frequency, and current-voltage curve are measured for resonant-tunneling-diode terahertz (THz oscillators. The output power largely changes with temperature owing to the change in Ohmic loss. In contrast to the output power, the oscillation frequency and current-voltage curve are almost insensitive to temperature. The measured temperature dependence of output power is compared with the theoretical calculation including the negative differential conductance (NDC as a fitting parameter assumed to be independent of temperature. Very good agreement was obtained between the measurement and calculation, and the NDC in the THz frequency region is estimated. The results show that the absolute values of NDC in the THz region significantly decrease relative to that at DC, and increases with increasing frequency in the measured frequency range.

Direct characterization of spin-transfer switching of nano-scale magnetic tunnel junctions using a conductive atomic force microscope

International Nuclear Information System (INIS)

Lee, Jia-Mou; Yang, Dong-Chin; Lee, Ching-Ming; Ye, Lin-Xiu; Chang, Yao-Jen; Wu, Te-ho; Lee, Yen-Chi; Wu, Jong-Ching

2013-01-01

We present an alternative method of spin-transfer-induced magnetization switching for magnetic tunnel junctions (MTJs) using a conductive atomic force microscope (CAFM) with pulsed current. The nominal MTJ cells' dimensions were 200 × 400 nm 2 . The AFM probes were coated with a Pt layer via sputtering to withstand up to several milliamperes. The pulsed current measurements, with pulse duration varying from 5 to 300 ms, revealed a magnetoresistance ratio of up to 120%, and an estimated intrinsic switching current density, based on the thermal activation model, of 3.94 MA cm −2 . This method demonstrates the potential skill to characterize nanometre-scale magnetic devices. (paper)

Steep Turn On/Off Green Tunnel Transistors

Science.gov (United States)

2010-12-17

band tunneling ( BTBT ), in which electrons tunnel across the energy gap of a semiconductor (i.e., valance to conduction band). Subsequent chapters will...discuss the simulation and experimental results of several transistor designs utilizing BTBT as an active “source” and enabler for ultra low voltage...operation. A thorough understanding of the BTBT models is invaluable for future discussions. In this chapter the derivation of the local or constant

Scanning Tunneling Optical Resonance Microscopy

Science.gov (United States)

Bailey, Sheila; Wilt, Dave; Raffaelle, Ryne; Gennett, Tom; Tin, Padetha; Lau, Janice; Castro, Stephanie; Jenkins, Philip; Scheiman, Dave

2003-01-01

Scanning tunneling optical resonance microscopy (STORM) is a method, now undergoing development, for measuring optoelectronic properties of materials and devices on the nanoscale by means of a combination of (1) traditional scanning tunneling microscopy (STM) with (2) tunable laser spectroscopy. In STORM, an STM tip probing a semiconductor is illuminated with modulated light at a wavelength in the visible-to-near-infrared range and the resulting photoenhancement of the tunneling current is measured as a function of the illuminating wavelength. The photoenhancement of tunneling current occurs when the laser photon energy is sufficient to excite charge carriers into the conduction band of the semiconductor. Figure 1 schematically depicts a proposed STORM apparatus. The light for illuminating the semiconductor specimen at the STM would be generated by a ring laser that would be tunable across the wavelength range of interest. The laser beam would be chopped by an achromatic liquid-crystal modulator. A polarization-maintaining optical fiber would couple the light to the tip/sample junction of a commercial STM. An STM can be operated in one of two modes: constant height or constant current. A STORM apparatus would be operated in the constant-current mode, in which the height of the tip relative to the specimen would be varied in order to keep the tunneling current constant. In this mode, a feedback control circuit adjusts the voltage applied to a piezoelectric actuator in the STM that adjusts the height of the STM tip to keep the tunneling current constant. The exponential relationship between the tunneling current and tip-to-sample distance makes it relatively easy to implement this mode of operation. The choice of method by which the photoenhanced portion of the tunneling current would be measured depends on choice of the frequency at which the input illumination would be modulated (chopped). If the frequency of modulation were low enough (typically tunneling current

Modeling the cost-benefit of nerve conduction studies in pre-employment screening for carpal tunnel syndrome.

Science.gov (United States)

Evanoff, Bradley; Kymes, Steve

2010-06-01

The aim of this study was to evaluate the costs associated with pre-employment nerve conduction testing as a screening tool for carpal tunnel syndrome (CTS) in the workplace. We used a Markov decision analysis model to compare the costs associated with a strategy of screening all prospective employees for CTS and not hiring those with abnormal nerve conduction, versus a strategy of not screening for CTS. The variables included in our model included employee turnover rate, the incidence of CTS, the prevalence of median nerve conduction abnormalities, the relative risk of developing CTS conferred by abnormal nerve conduction screening, the costs of pre-employment screening, and the worker's compensation costs to the employer for each case of CTS. In our base case, total employer costs for CTS from the perspective of the employer (cost of screening plus costs for workers' compensation associated with CTS) were higher when screening was used. Median costs per employee position over five years were US$503 for the screening strategy versus US$200 for a no-screening strategy. A sensitivity analysis showed that a strategy of screening was cost-beneficial from the perspective of the employer only under a few circumstances. Using Monte Carlo simulation varying all parameters, we found a 30% probability that screening would be cost-beneficial. A strategy of pre-employment screening for CTS should be carefully evaluated for yield and social consequences before being implemented. Our model suggests such screening is not appropriate for most employers.

External field induced switching of tunneling current in the coupled quantum dots

OpenAIRE

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

2014-01-01

We investigated the tunneling current peculiarities in the system of two coupled by means of the external field quantum dots (QDs) weakly connected to the electrodes in the presence of Coulomb correlations. It was found that tuning of the external field frequency induces fast multiple tunneling current switching and leads to the negative tunneling conductivity. Special role of multi-electrons states was demonstrated. Moreover we revealed conditions for bistable behavior of the tunneling curre...

Carpal tunnel sonography by the rheumatologist versus nerve conduction study by the neurologist

NARCIS (Netherlands)

Swen, WAA; Jacobs, JWG; Bussemaker, FEAM; de Waard, J; Bijlsma, JWJ

Objective. To determine the value of sonogaphy (SG) performed by the rheumatologist to diagnose carpal tunnel syndrome (CTS). Methods. Sixty-three patients with clinical signs of CTS according to the neurologist. based on patient history and clinical examination, were studied. In the 6 weeks prior

On the basically single-type excitation source of resonance in the wind tunnel and in the hydroturbine channel of a hydraulic power plant

Science.gov (United States)

Karavosov, R. K.; Prozorov, A. G.

2012-01-01

We have investigated the spectra of pressure pulsations in the near field of the open working section of the wind tunnel with a vortex flow behind the tunnel blower formed like the flow behind the hydroturbine of a hydraulic power plant. We have made a comparison between the measurement data for pressure pulsations and the air stream velocity in tunnels of the above type and in tunnels in which a large-scale vortex structure behind the blower is not formed. It has been established that the large-scale vortex formation in the incompressible medium behind the blade system in the wind tunnel is a source of narrow-band acoustic radiation capable of exciting resonance self-oscillations in the tunnel channel.

Tunnel - history of

International Nuclear Information System (INIS)

1998-11-01

This book introduces history of tunnel in ancient times, the middle ages and modern times, survey of tunnel and classification of bedrock like environment survey of position, survey of the ground, design of tunnel on basic thing of the design, and design of tunnel of bedrock, analysis of stability of tunnel and application of the data, construction of tunnel like lattice girder and steel fiber reinforced shot crete, and maintenance control and repair of tunnel.

Typical Underwater Tunnels in the Mainland of China and Related Tunneling Technologies

Directory of Open Access Journals (Sweden)

Kairong Hong

2017-12-01

Full Text Available In the past decades, many underwater tunnels have been constructed in the mainland of China, and great progress has been made in related tunneling technologies. This paper presents the history and state of the art of underwater tunnels in the mainland of China in terms of shield-bored tunnels, drill-and-blast tunnels, and immersed tunnels. Typical underwater tunnels of these types in the mainland of China are described, along with innovative technologies regarding comprehensive geological prediction, grouting-based consolidation, the design and construction of large cross-sectional tunnels with shallow cover in weak strata, cutting tool replacement under limited drainage and reduced pressure conditions, the detection and treatment of boulders, the construction of underwater tunnels in areas with high seismic intensity, and the treatment of serious sedimentation in a foundation channel of immersed tunnels. Some suggestions are made regarding the three potential great strait-crossing tunnels—the Qiongzhou Strait-Crossing Tunnel, Bohai Strait-Crossing Tunnel, and Taiwan Strait-Crossing Tunnel—and issues related to these great strait-crossing tunnels that need further study are proposed. Keywords: Underwater tunnel, Strait-crossing tunnel, Shield-bored tunnel, Immersed tunnel, Drill and blast

Conductance in double quantum well systems

International Nuclear Information System (INIS)

Hasbun, J E

2003-01-01

The object of this paper is to review the electronic conductance in double quantum well systems. These are quantum well structures in which electrons are confined in the z direction by large band gap material barrier layers, yet form a free two-dimensional Fermi gas within the sandwiched low band gap material layers in the x-y plane. Aspects related to the conductance in addition to the research progress made since the inception of such systems are included. While the review focuses on the tunnelling conductance properties of double quantum well devices, the longitudinal conductance is also discussed. Double quantum well systems are a more recent generation of structures whose precursors are the well known double-barrier resonant tunnelling systems. Thus, they have electronic signatures such as negative differential resistance, in addition to resonant tunnelling, whose behaviours depend on the wavefunction coupling between the quantum wells. As such, the barrier which separates the quantum wells can be tailored in order to provide better control of the device's electronic properties over their single well ancestors. (topical review)

Tunneling ionization and harmonic generation in two-color fields

International Nuclear Information System (INIS)

Kondo, K.; Kobayashi, Y.; Sagisaka, A.; Nabekawa, Y.; Watanabe, S.

1996-01-01

Tunneling ionization and harmonic generation in two-color fields were studied with a fundamental beam (ω) and its harmonics (2ω,3ω), which were generated by a 100-fs Ti:sapphire laser. Ion yields of atoms and molecules were successfully controlled by means of a change in the relative phase between ω and 3ω pulses. Two-color interference was clearly observed in photoelectron spectra and harmonic spectra. In the ω endash 2ω field even-order harmonics were observed in which the intensity was almost equal to that of the odd harmonics because of an asymmetric optical field. These results were compared with the quasi-static model for ionization and with the quantum theory for harmonic generation. copyright 1996 Optical Society of America

Spectral analysis of meteorites ablated in a wind tunnel

Science.gov (United States)

Drouard, A.; Vernazza, P.; Loehle, S.; Gattacceca, J.; Zander, T.; Eberhart, M.; Meindl, A.; Oefele, R.; Vaubaillon, J.; Colas, F.

2017-09-01

Recently and for the very first time, experiments simulating vaporization of a meteorite sample were performed in a wind tunnel near Stuttgart with the specific aim to record emission spectra of the vaporized material. Using a high enthalpy air plasma flow for modeling an equivalent air friction of an entry speed of about 10 km/s, three meteorite types (H, CM and HED) and two meteoritical analogues (basalt and argillite) were ablated and high resolution spectra were recorded simultaneously. After the identification of all atomic lines, we per- formed a detailed study of our spectra using two approaches: (i) by direct comparison of multiplet in- tensities between the samples and (ii) by computation of a synthetic spectrum to constrain some physical parameters (temperature, elemental abundance). Finally, we compared our results to the elemental composition of our samples and we determined how much compositional information can be retrieved for a given meteor using visible sectroscopy.

Energy gap and surface structure of superconducting diamond films probed by scanning tunneling microscopy

International Nuclear Information System (INIS)

Nishizaki, Terukazu; Takano, Yoshihiko; Nagao, Masanori; Takenouchi, Tomohiro; Kawarada, Hiroshi; Kobayashi, Norio

2007-01-01

We have performed scanning tunneling microscopy/spectroscopy (STM/STS) experiments on (1 1 1)-oriented epitaxial films of heavily boron-doped diamond at T = 0.47 K. The STM topography shows two kinds of atomic structures: a hydrogenated 1 x 1 structure, C(1 1 1)1 x 1:H, and an amorphous structure. On the C(1 1 1)1 x 1:H region, the tunneling spectra show superconducting property with the energy gap Δ = 0.83 meV. The obtained gap ratio 2Δ/k B T c = 3.57 is consistent with the weak-coupling BCS theory

Structural and tunneling properties of Si nanowires

KAUST Repository

Montes Muñoz, Enrique

2013-12-06

We investigate the electronic structure and electron transport properties of Si nanowires attached to Au electrodes from first principles using density functional theory and the nonequilibrium Green\\'s function method. We systematically study the dependence of the transport properties on the diameter of the nanowires, on the growth direction, and on the length. At the equilibrium Au-nanowire distance we find strong electronic coupling between the electrodes and nanowires, which results in a low contact resistance. With increasing nanowire length we study the transition from metallic to tunneling conductance for small applied bias. For the tunneling regime we investigate the decay of the conductance with the nanowire length and rationalize the results using the complex band structure of the pristine nanowires. The conductance is found to depend strongly on the growth direction, with nanowires grown along the ⟨110⟩ direction showing the smallest decay with length and the largest conductance and current.

Structural and tunneling properties of Si nanowires

KAUST Repository

Montes Muñ oz, Enrique; Gkionis, Konstantinos; Rungger, Ivan; Sanvito, Stefano; Schwingenschlö gl, Udo

2013-01-01

We investigate the electronic structure and electron transport properties of Si nanowires attached to Au electrodes from first principles using density functional theory and the nonequilibrium Green's function method. We systematically study the dependence of the transport properties on the diameter of the nanowires, on the growth direction, and on the length. At the equilibrium Au-nanowire distance we find strong electronic coupling between the electrodes and nanowires, which results in a low contact resistance. With increasing nanowire length we study the transition from metallic to tunneling conductance for small applied bias. For the tunneling regime we investigate the decay of the conductance with the nanowire length and rationalize the results using the complex band structure of the pristine nanowires. The conductance is found to depend strongly on the growth direction, with nanowires grown along the ⟨110⟩ direction showing the smallest decay with length and the largest conductance and current.

Structural Safety Assessment of Existing Multiarch Tunnel: A Case Study

Directory of Open Access Journals (Sweden)

Jinxing Lai

2017-01-01

Full Text Available Structural health assessment is one of the key activities in maintaining the performance of a tunnel during its service life. Due to the development of modern detection technology, comprehensive structural health assessment system is being established for operating tunnels. To evaluate the actual operational state of Shitigou tunnel, overall detection of the liner crack, tunnel seepage, and liner void was conducted by employing the modern detection technology, such as crack width monitoring technology, concrete strength monitoring technology, and electromagnetic wave nondestructive monitoring technology. Through the statistical analysis of the detection results, the distribution characteristic, development law, and damage grade of structural defects were obtained. Tunnel liner cracks are mainly located on the middle wall; serious water leakage is encountered on the side wall, middle wall, and vault; the strength of foundation and liner structure of left tunnel does not meet the design requirement; the liner voids are mostly located at the tunnel entrance section, especially, on the tunnel vault; and the proportion of influence factors of structural defects should be considered. The research results presented for this study can serve as references for effective design and health assessment of existing multiarch tunnel projects.

Tunable spin-tunnel contacts to silicon using low-work-function ferromagnets

Science.gov (United States)

Min, Byoung-Chul; Motohashi, Kazunari; Lodder, Cock; Jansen, Ron

2006-10-01

Magnetic tunnel junctions have become ubiquitous components appearing in magnetic random-access memory, read heads of magnetic disk drives and semiconductor-based spin devices. Inserting a tunnel barrier has been key to achieving spin injection from ferromagnetic (FM) metals into GaAs, but spin injection into Si has remained elusive. We show that Schottky barrier formation leads to a huge conductivity mismatch of the FM tunnel contact and Si, which cannot be solved by the well-known method of adjusting the tunnel barrier thickness. We present a radically different approach for spin-tunnelling resistance control using low-work-function ferromagnets, inserted at the FM/tunnel barrier interface. We demonstrate that in this way the resistance-area (RA) product of FM/Al2O3/Si contacts can be tuned over eight orders of magnitude, while simultaneously maintaining a reasonable tunnel spin polarization. This raises prospects for Si-based spintronics and presents a new category of ferromagnetic materials for spin-tunnel contacts in low-RA-product applications.

Effect of resonant tunneling on electroluminescence in nc-Si/SiO2 multilayers-based p-i-n structure

International Nuclear Information System (INIS)

Chen, D.Y.; Wang, Y.Y.; Sun, Y.; He, Y.J.; Zhang, G.

2015-01-01

P-i-n structures with SiO 2 /nc-Si/SiO 2 multilayers as intrinsic layer were prepared in conventional plasma enhanced chemical vapor deposition system. Their carrier transport and electroluminescence properties were investigated. Two resonant tunneling related current peaks with current dropping gradually under forward bias were observed in the current voltage curve. Non-uniformity of the interfaces might be responsible for the gradual dropping of the current. Electroluminescence intensity of the device under bias of 7 V which is near the resonant tunneling peak voltage of 7.2 V was weaker than that under 6.5 V. According to the Gaussian fitting results of the spectra, the intensity of the sub-peak of 650 nm originating from recombination of injected electrons and holes was decreased the most. When resonant tunneling conditions are met, it might be that most of the injected electrons participate in resonant tunneling and fewer in Pool–Frenkel tunneling, which is the main carrier transport mechanism, to contribute to electroluminescence intensity. - Highlights: • Two resonant tunneling peaks with current dropping gradually were observed. • The EL intensity of the structure under resonant tunneling peak voltage is weakened. • P–F tunneling is the main transport mechanism besides resonant tunneling

A method for data base management and analysis for wind tunnel data

Science.gov (United States)

Biser, Aileen O.

1987-01-01

To respond to the need for improved data base management and analysis capabilities for wind-tunnel data at the Langley 16-Foot Transonic Tunnel, research was conducted into current methods of managing wind-tunnel data and a method was developed as a solution to this need. This paper describes the development of the data base management and analysis method for wind-tunnel data. The design and implementation of the software system are discussed and examples of its use are shown.

Atomic-Monolayer MoS2 Band-to-Band Tunneling Field-Effect Transistor

KAUST Repository

Lan, Yann Wen

2016-09-05

The experimental observation of band-to-band tunneling in novel tunneling field-effect transistors utilizing a monolayer of MoS2 as the conducting channel is demonstrated. Our results indicate that the strong gate-coupling efficiency enabled by two-dimensional materials, such as monolayer MoS2, results in the direct manifestation of a band-to-band tunneling current and an ambipolar transport.

Quantum tunneling of magnetization in solids

International Nuclear Information System (INIS)

Stamp, P.C.E.; Barbara, B.

1992-01-01

Magnetic solids should, under certain circumstances, show macroscopic quantum behavior, in which coherence exists between completely distinct magnetization states, each involving a very large number of spins (∼10 12 spins). This article reviews the recent work in this field, concentrating particularly on macroscopic quantum tunneling (MQT) of magnetization. The two main phenomena discussed are the tunneling of magnetization in single-domain particles or grains (in which some 10 3 - 10 4 spins rotate together through an energy barrier), and the tunneling of domain walls in films or in bulk magnets; where walls containing ∼10 10 spins may tunnel off a pinning potential, or from one pinning center to another. Some attention is also given to the quantum nucleation of magnetization reversal in a bulk magnet, and to the quantum motion of other magnetic solitons (such as vortices). After a thorough analysis of the basic grain and wall tunneling phenomena, the authors continue on to a discussion of the various dissipative or decoherence mechanisms, which destroy the phase correlations involved in tunneling. The coupling of grain magnetization to phonons, photons, and electrons is shown to have little consequence for weakly-conducting or insulating grains. Domain walls couple to these and also to magnons and impurities or defects; the 3rd order coupling to magnons can have serious effects, but if one uses pure insulators at low temperatures, these can also be ignored

Effects of temperature and other experimental variables on single molecule vibrational spectroscopy with the scanning tunneling microscope

International Nuclear Information System (INIS)

Lauhon, L. J.; Ho, W.

2001-01-01

Inelastic electron tunneling spectroscopy (IETS) was performed on single molecules with a variable temperature scanning tunneling microscope. The peak intensity, width, position, and line shape of single molecule vibrational spectra were studied as a function of temperature, modulation bias, bias polarity, and tip position for the (C--H,C--D) stretching vibration of acetylene (C 2 H 2 ,C 2 D 2 ) on Cu(001). The temperature broadening of vibrational peaks was found to be a consequence of Fermi smearing as in macroscopic IETS. The modulation broadening of vibrational peaks assumed the expected form for IETS. Extrapolation of the peak width to zero temperature and modulation suggested an intrinsic width of ∼4 meV due primarily to instrumental broadening. The inelastic tunneling cross section at negative bias was reduced by a factor of 1.7 for the C--H stretch mode. Low energy modes of other molecules did not show such a reduction. There was no evidence of a tip-induced Stark shift in the peak positions. The spatial variation of the inelastic signal was measured to determine the junction stability necessary for the acquisition of single molecule vibrational spectra

Which nerve conduction parameters can predict spontaneous electromyographic activity in carpal tunnel syndrome?

Science.gov (United States)

Chang, Chia-Wei; Lee, Wei-Ju; Liao, Yi-Chu; Chang, Ming-Hong

2013-11-01

We investigate electrodiagnostic markers to determine which parameters are the best predictors of spontaneous electromyographic (EMG) activity in carpal tunnel syndrome (CTS). We enrolled 229 patients with clinically proven and nerve conduction study (NCS)-proven CTS, as well as 100 normal control subjects. All subjects were evaluated using electrodiagnostic techniques, including median distal sensory latencies (DSLs), sensory nerve action potentials (SNAPs), distal motor latencies (DMLs), compound muscle action potentials (CMAPs), forearm median nerve conduction velocities (FMCVs) and wrist-palm motor conduction velocities (W-P MCVs). All CTS patients underwent EMG examination of the abductor pollicis brevis (APB) muscle, and the presence or absence of spontaneous EMG activities was recorded. Normal limits were determined by calculating the means ± 2 standard deviations from the control data. Associations between parameters from the NCS and EMG findings were investigated. In patients with clinically diagnosed CTS, abnormal median CMAP amplitudes were the best predictors of spontaneous activity during EMG examination (p95% (positive predictive rate >95%). If the median CMAP amplitude was higher than the normal limit (>4.9 mV), the rate of no spontaneous EMG activity was >94% (negative predictive rate >94%). An abnormal SNAP amplitude was the second best predictor of spontaneous EMG activity (p<0.001; OR 4.13; 95% CI 2.16-7.90), and an abnormal FMCV was the third best predictor (p=0.01; OR 2.10; 95% CI 1.20-3.67). No other nerve conduction parameters had significant power to predict spontaneous activity upon EMG examination. The CMAP amplitudes of the APB are the most powerful predictors of the occurrence of spontaneous EMG activity. Low CMAP amplitudes are strongly associated with spontaneous activity, whereas high CMAP amplitude are less associated with spontaneous activity, implying that needle EMG examination should be recommended for the detection of

Single-molecule conductance of redox molecules in electrochemical scanning tunneling microscopy

DEFF Research Database (Denmark)

Haiss, W.; Albrecht, Tim; van Zalinge, H.

2007-01-01

of a maximum in the I-tunneling versus electrode potential relationship can be fitted by a "soft" gating concept. This arises from large configurational fluctuations of the molecular bridge linked to the gold contacts by flexible chains. This view is incorporated in a formalism that is well-suited for data...... analysis and reproduces in all important respects the 6V6 data for physically sound values of the appropriate parameters. This study demonstrates that fluctuations of isolated configurationally "soft" molecules can dominate charge transport patterns and that theoretical frameworks for compact monolayers...

Force modulation and electrochemical gating of conductance in a cytochrome

Science.gov (United States)

Davis, Jason J.; Peters, Ben; Xi, Wang

2008-09-01

Scanning probe methods have been used to measure the effect of electrochemical potential and applied force on the tunnelling conductance of the redox metalloprotein yeast iso-1-cytochrome c (YCC) at a molecular level. The interaction of a proximal probe with any sample under test will, at this scale, be inherently perturbative. This is demonstrated with conductive probe atomic force microscopy (CP-AFM) current-voltage spectroscopy in which YCC, chemically adsorbed onto pristine Au(111) via its surface cysteine residue, is observed to become increasingly compressed as applied load is increased, with concomitant decrease in junction resistance. Electrical contact at minimal perturbation, where probe-molecule coupling is comparable to that in scanning tunnelling microscopy, brings with it the observation of negative differential resistance, assigned to redox-assisted probe-substrate tunnelling. The role of the redox centre in conductance is also resolved in electrochemical scanning tunnelling microscopy assays where molecular conductance is electrochemically gateable through more than an order of magnitude.

A cryogen-free low temperature scanning tunneling microscope capable of inelastic electron tunneling spectroscopy

Energy Technology Data Exchange (ETDEWEB)

Zhang, Shuai; Huang, Di [State Key Laboratory of Surface Physics, Key Laboratory of Micro and Nano Photonic Structures (MOE), and Department of Physics, Fudan University, Shanghai 200433 (China); Wu, Shiwei, E-mail: swwu@fudan.edu.cn [State Key Laboratory of Surface Physics, Key Laboratory of Micro and Nano Photonic Structures (MOE), and Department of Physics, Fudan University, Shanghai 200433 (China); Collaborative Innovation Center of Advanced Microstructures, Fudan University, Shanghai 200433 (China)

2016-06-15

The design and performance of a cryogen-free low temperature scanning tunneling microscope (STM) housed in ultrahigh vacuum (UHV) are reported. The cryogen-free design was done by directly integrating a Gifford-McMahon cycle cryocooler to a Besocke-type STM, and the vibration isolation was achieved by using a two-stage rubber bellow between the cryocooler and a UHV-STM interface with helium exchange gas cooling. A base temperature of 15 K at the STM was achieved, with a possibility to further decrease by using a cryocooler with higher cooling power and adding additional low temperature stage under the exchange gas interface. Atomically sharp STM images and high resolution dI/dV spectra on various samples were demonstrated. Furthermore, we reported the inelastic tunneling spectroscopy on a single carbon monoxide molecule adsorbed on Ag(110) surface with a cryogen-free STM for the first time. Being totally cryogen-free, the system not only saves the running cost significantly but also enables uninterrupted data acquisitions and variable temperature measurements with much ease. In addition, the system is capable of coupling light to the STM junction by a pair of lens inside the UHV chamber. We expect that these enhanced capabilities could further broaden our views to the atomic-scale world.

A cryogen-free low temperature scanning tunneling microscope capable of inelastic electron tunneling spectroscopy.

Science.gov (United States)

Zhang, Shuai; Huang, Di; Wu, Shiwei

2016-06-01

The design and performance of a cryogen-free low temperature scanning tunneling microscope (STM) housed in ultrahigh vacuum (UHV) are reported. The cryogen-free design was done by directly integrating a Gifford-McMahon cycle cryocooler to a Besocke-type STM, and the vibration isolation was achieved by using a two-stage rubber bellow between the cryocooler and a UHV-STM interface with helium exchange gas cooling. A base temperature of 15 K at the STM was achieved, with a possibility to further decrease by using a cryocooler with higher cooling power and adding additional low temperature stage under the exchange gas interface. Atomically sharp STM images and high resolution dI/dV spectra on various samples were demonstrated. Furthermore, we reported the inelastic tunneling spectroscopy on a single carbon monoxide molecule adsorbed on Ag(110) surface with a cryogen-free STM for the first time. Being totally cryogen-free, the system not only saves the running cost significantly but also enables uninterrupted data acquisitions and variable temperature measurements with much ease. In addition, the system is capable of coupling light to the STM junction by a pair of lens inside the UHV chamber. We expect that these enhanced capabilities could further broaden our views to the atomic-scale world.

Scanning Tunnelling Spectroscopic Studies of Dirac Fermions in Graphene and Topological Insulators

Directory of Open Access Journals (Sweden)

wang K.-L.

2012-03-01

Full Text Available We report novel properties derived from scanning tunnelling spectroscopic (STS studies of Dirac fermions in graphene and the surface state (SS of a strong topological insulator (STI, Bi2Se3. For mono-layer graphene grown on Cu by chemical vapour deposition (CVD, strain-induced scalar and gauge potentials are manifested by the charging effects and the tunnelling conductance peaks at quantized energies, respectively. Additionally, spontaneous time-reversal symmetry breaking is evidenced by the alternating anti-localization and localization spectra associated with the zero-mode of two sublattices while global time-reversal symmetry is preserved under the presence of pseudo-magnetic fields. For Bi2Se3 epitaxial films grown on Si(111 by molecular beam epitaxy (MBE, spatially localized unitary impurity resonances with sensitive dependence on the energy difference between the Fermi level and the Dirac point are observed for samples thicker than 6 quintuple layers (QL. These findings are characteristic of the SS of a STI and are direct manifestation of strong topological protection against impurities. For samples thinner than 6-QL, STS studies reveal the openup of an energy gap in the SS due to overlaps of wave functions between the surface and interface layers. Additionally, spin-preserving quasiparticle interference wave-vectors are observed, which are consistent with the Rashba-like spin-orbit splitting.

Large positive spin polarization and giant inverse tunneling magnetoresistance in Fe/PbTiO3/Fe multiferroic tunnel junction

International Nuclear Information System (INIS)

Dai, Jian-Qing; Zhang, Hu; Song, Yu-Min

2014-01-01

We perform first-principles electronic structure and spin-dependent transport calculations of a multiferroic tunnel junction (MFTJ) with an epitaxial Fe/PbTiO 3 /Fe heterostructure. We predict a large positive spin-polarization (SP) and an intriguing giant inverse tunneling magnetoresistance (TMR) ratio in this tunnel junction. We demonstrate that the tunneling properties are determined by ferroelectric (FE) polarization screening and electronic reconstruction at the interface with lower electrostatic potential. The intricate complex band structure of PbTiO 3 , in particular the lowest decay rates concerning Pb 6p z and Ti 3d z2 states near the Γ ¯ point, gives rise to the large positive SP of the tunneling current in the parallel magnetic configuration. However, the giant inverse TMR ratio is attributed to the minority-spin electrons of the interfacial Ti 3d xz +3d yz orbitals which have considerably weight in the extended area around the Γ ¯ point at the Fermi energy and causes remarkable contributions to the conductance in the antiparallel magnetic configuration. - Highlights: • We study spin-dependent tunneling in Fe/PbTiO 3 /Fe multiferroic tunnel junction. • We find a large positive spin polarization in the parallel magnetic configuration. • An intriguing giant inverse TMR ratio (about −2000%) is predicted. • Complex band structure of PbTiO 3 causes the large positive spin polarization. • Negative TMR is due to minority-spin electrons of interfacial Ti d xz +d yz orbitals

Radiation environment in the tunnel of a high-energy proton accelerator at energies near 1 TeV

International Nuclear Information System (INIS)

McCaslin, J.B.; Sun, R.K.S.; Swanson, W.P.

1987-12-01

Neutron energy spectra, fluence distributions and rates in the FNAL Tevatron tunnel are summarized. This work has application to radiation damage to electronics and research equipment at high energy accelerators, as well as to radiological protection. 7 refs., 4 figs

Results for the hybrid laminar flow control experiment conducted in the NASA Langley 8-foot transonic pressure tunnel on a 7-foot chord model

Science.gov (United States)

Bobbitt, Percy J.; Ferris, James C.; Harvey, William D.; Goradia, Suresh H.

1992-01-01

A description is given of the development of, and results from, the hybrid laminar flow control (HLFC) experiment conducted in the NASA LaRC 8 ft Transonic Pressure Tunnel on a 7 ft chord, 23 deg swept model. The methods/codes used to obtain the contours of the HLFC model surface and to define the suction requirements are outlined followed by a discussion of the model construction, suction system, instrumentation, and some example results from the wind tunnel tests. Included in the latter are the effects of Mach number, suction level, and the extent of suction. An assessment is also given of the effect of the wind tunnel environment on the suction requirements. The data show that, at or near the design Mach number, large extents of laminar flow can be achieved with suction mass flows over the first 25 percent, or less, of the chord. Top surface drag coefficients with suction extending from the near leading edge to 20 percent of the chord were approximately 40 percent lower than those obtained with no suction. The results indicate that HLFC can be designed for transonic speeds with lift and drag coefficients approaching those of LFC designs but with much smaller extents and levels of suction.

Nonlinear transport theory in the metal with tunnel barrier

Science.gov (United States)

Zubov, E. E.

2018-02-01

Within the framework of the scattering matrix formalism, the nonlinear Kubo theory for electron transport in the metal with a tunnel barrier has been considered. A general expression for the mean electrical current was obtained. It significantly simplifies the calculation of nonlinear contributions to the conductivity of various hybrid structures. In the model of the tunnel Hamiltonian, all linear and nonlinear contributions to a mean electrical current are evaluated. The linear approximation agrees with results of other theories. For effective barrier transmission ?, the ballistic transport is realised with a value of the Landauer conductivity equal to ?.

Electron tunneling and the energy gap in Bi2Sr2CaCu2Ox

Science.gov (United States)

Lee, Mark; Mitzi, D. B.; Kapitulnik, A.; Beasley, M. R.

1989-01-01

Results of electron tunneling on single crystals of the Bi2Sr2CaCu2Ox superconductor are reported. The junctions show a gap structure with Δ~=25 meV, whose temperature dependence exhibits a qualitatively Bardeen-Cooper-Schrieffer-like behavior with a gap-closing Tc~=81-85 K. Comparisons of these tunneling spectra to those obtained on YBa2Cu3O7-x are made. Evidence that 2Δ/kTc~7 for both Ba2Sr2CaCu2Ox and YBa2Cu3O7-x is also discussed.

Monitoring pilot projects on bored tunnelling : The Second Heinenoord Tunnel and the Botlek Rail Tunnel

NARCIS (Netherlands)

Bakker, K.J.; De Boer, F.; Admiraal, J.B.M.; Van Jaarsveld, E.P.

1999-01-01

Two pilot projects for bored tunnelling in soft soil have been undertaken in the Netherlands. The monitoring was commissioned under the authority of the Centre for Underground Construction (COB). A description of the research related to the Second Heinenoord Tunnel and the Botlek Rail Tunnel will be

The propagation of sound in tunnels

Science.gov (United States)

Li, Kai Ming; Iu, King Kwong

2002-11-01

The sound propagation in tunnels is addressed theoretically and experimentally. In many previous studies, the image source method is frequently used. However, these early theoretical models are somewhat inadequate because the effect of multiple reflections in long enclosures is often modeled by the incoherent summation of contributions from all image sources. Ignoring the phase effect, these numerical models are unlikely to be satisfactory for predicting the intricate interference patterns due to contributions from each image source. In the present paper, the interference effect is incorporated by summing the contributions from the image sources coherently. To develop a simple numerical model, tunnels are represented by long rectangular enclosures with either geometrically reflecting or impedance boundaries. Scale model experiments are conducted for the validation of the numerical model. In some of the scale model experiments, the enclosure walls are lined with a carpet for simulating the impedance boundary condition. Large-scale outdoor measurements have also been conducted in two tunnels designed originally for road traffic use. It has been shown that the proposed numerical model agrees reasonably well with experimental data. [Work supported by the Research Grants Council, The Industry Department, NAP Acoustics (Far East) Ltd., and The Hong Kong Polytechnic University.

Electron tunneling in carbon nanotube composites

International Nuclear Information System (INIS)

Gau, C; Kuo, Cheng-Yung; Ko, H S

2009-01-01

Nanocomposites, such as polymer blending with carbon nanotubes (CNTs), have been shown to have a drastic reduction in the resistivity and become conductive when the CNTs concentration has reached a certain percolation threshold. The reduction could be more than a millionth of the original polymer material. This has been realized as the formation of an infinite cluster of connected CNTs or pathways. Therefore, the conductivity of a nanocomposite should follow that of CNTs. Here we show that the resistivity of a nanocomposite is not governed by the interconnected CNTs, but the polymer between neighboring CNTs. That is, polymer-CNTs exhibit the nature of a conducting polymer, which can be explained as the tunneling of electrons one by one from the first CNT electrode to the next-nearest CNT electrode, forming a CNT/polymer pathway. A conduction model based on the tunneling of electrons passing, one by one, through the polymer gap between two neighboring CNT electrodes is formulated and derived. This model can accurately predict the significant reduction of the polymer-CNTs' resistivity with the addition of CNTs. The temperature effect can be readily incorporated to account for resistivity variation with the temperature of this nanocomposites.

A specific 2,4-disubstituted-adamantane interaction with plasma-grown aluminum oxide. Inelastic-electron-tunneling spectroscopy study

NARCIS (Netherlands)

Meijer, E.W.; Raas, M.C.; Velzen, van P.N.T.

1987-01-01

The interaction of several mono- and disubstituted adamantanes with plasma-grown aluminum oxide has been studied using inelastic-electron-tunneling (IET) spectroscopy. The IET spectra evidence the chemisorption of 2,4-adamantanedione onto the aluminum oxide surface as the carboxylate anion of

Materials and construction techniques for cryogenic wind tunnel facilities for instruction/research use

Science.gov (United States)

Morse, S. F.; Roper, A. T.

1975-01-01

The results of the cryogenic wind tunnel program conducted at NASA Langley Research Center are presented to provide a starting point for the design of an instructional/research wind tunnel facility. The advantages of the cryogenic concept are discussed, and operating envelopes for a representative facility are presented to indicate the range and mode of operation. Special attention is given to the design, construction and materials problems peculiar to cryogenic wind tunnels. The control system for operation of a cryogenic tunnel is considered, and a portion of a linearized mathematical model is developed for determining the tunnel dynamic characteristics.

Water table tests of proposed heat transfer tunnels for small turbine vanes

Science.gov (United States)

Meitner, P. L.

1974-01-01

Water-table flow tests were conducted for proposed heat-transfer tunnels which were designed to provide uniform flow into their respective test sections of a single core engine turbine vane and a full annular ring of helicopter turbine vanes. Water-table tests were also performed for the single-vane test section of the core engine tunnel. The flow in the heat-transfer tunnels was shown to be acceptable.

Investigating the Inter-Tube Conduction Mechanism in Polycarbonate Nanocomposites Prepared with Conductive Polymer-Coated Carbon Nanotubes

KAUST Repository

Ventura, Isaac Aguilar; Zhou, Jian; Lubineau, Gilles

2015-01-01

such as damage-sensitive and history-dependent conductivity because their macroscopic electrical conductivity is largely determined by the tunneling effect at the tube/tube interface. To reduce these issues, new nanocomposites have been developed with CNTs

Design and Development of Low-Cost Water Tunnel for Educational Purpose

Science.gov (United States)

Zahari, M.; Dol, S. S.

2015-04-01

The hydrodynamic behaviour of immersed body is essential in fluid dynamics study. Water tunnel is an example of facility required to provide a controlled condition for fluid flow research. The operational principle of water tunnel is quite similar to the wind tunnel but with different working fluid and higher flow-pumping capacity. Flow visualization in wind tunnel is more difficult to conduct as turbulent flows in wind dissipate quickly whilst water tunnel is more suitable for such purpose due to higher fluid viscosity and wide variety of visualization techniques can be employed. The present work focusses on the design and development of open flow water tunnel for the purpose of studying vortex-induced vibration from turbulent vortex shedding phenomenon. The water tunnel is designed to provide a steady and uniform flow speed within the test section area. Construction details are discussed for development of low-cost water tunnel for quantitative and qualitative fluid flow measurements. The water tunnel can also be used for educational purpose such as fluid dynamics class activity to provide quick access to visualization medium for better understanding of various turbulence motion learnt in class.

Theory of inelastic electron tunneling from a localized spin in the impulsive approximation.

Science.gov (United States)

Persson, Mats

2009-07-31

A simple expression for the conductance steps in inelastic electron tunneling from spin excitations in a single magnetic atom adsorbed on a nonmagnetic metal surface is derived. The inelastic coupling between the tunneling electron and the spin is via the exchange coupling and is treated in an impulsive approximation using the Tersoff-Hamann approximation for the tunneling between the tip and the sample.

Density-matrix approach for the electroluminescence of molecules in a scanning tunneling microscope.

Science.gov (United States)

Tian, Guangjun; Liu, Ji-Cai; Luo, Yi

2011-04-29

The electroluminescence (EL) of molecules confined inside a nanocavity in the scanning tunneling microscope possesses many intriguing but unexplained features. We present here a general theoretical approach based on the density-matrix formalism to describe the EL from molecules near a metal surface induced by both electron tunneling and localized surface plasmon excitations simultaneously. It reveals the underlying physical mechanism for the external bias dependent EL. The important role played by the localized surface plasmon on the EL is highlighted. Calculations for porphyrin derivatives have reproduced corresponding experimental spectra and nicely explained the observed unusual large variation of emission spectral profiles. This general theoretical approach can find many applications in the design of molecular electronic and photonic devices.

A scanning tunneling microscope capable of imaging specified micron-scale small samples

Science.gov (United States)

Tao, Wei; Cao, Yufei; Wang, Huafeng; Wang, Kaiyou; Lu, Qingyou

2012-12-01

We present a home-built scanning tunneling microscope (STM) which allows us to precisely position the tip on any specified small sample or sample feature of micron scale. The core structure is a stand-alone soft junction mechanical loop (SJML), in which a small piezoelectric tube scanner is mounted on a sliding piece and a "U"-like soft spring strip has its one end fixed to the sliding piece and its opposite end holding the tip pointing to the sample on the scanner. Here, the tip can be precisely aligned to a specified small sample of micron scale by adjusting the position of the spring-clamped sample on the scanner in the field of view of an optical microscope. The aligned SJML can be transferred to a piezoelectric inertial motor for coarse approach, during which the U-spring is pushed towards the sample, causing the tip to approach the pre-aligned small sample. We have successfully approached a hand cut tip that was made from 0.1 mm thin Pt/Ir wire to an isolated individual 32.5 × 32.5 μm2 graphite flake. Good atomic resolution images and high quality tunneling current spectra for that specified tiny flake are obtained in ambient conditions with high repeatability within one month showing high and long term stability of the new STM structure. In addition, frequency spectra of the tunneling current signals do not show outstanding tip mount related resonant frequency (low frequency), which further confirms the stability of the STM structure.

A scanning tunneling microscope capable of imaging specified micron-scale small samples.

Science.gov (United States)

Tao, Wei; Cao, Yufei; Wang, Huafeng; Wang, Kaiyou; Lu, Qingyou

2012-12-01

We present a home-built scanning tunneling microscope (STM) which allows us to precisely position the tip on any specified small sample or sample feature of micron scale. The core structure is a stand-alone soft junction mechanical loop (SJML), in which a small piezoelectric tube scanner is mounted on a sliding piece and a "U"-like soft spring strip has its one end fixed to the sliding piece and its opposite end holding the tip pointing to the sample on the scanner. Here, the tip can be precisely aligned to a specified small sample of micron scale by adjusting the position of the spring-clamped sample on the scanner in the field of view of an optical microscope. The aligned SJML can be transferred to a piezoelectric inertial motor for coarse approach, during which the U-spring is pushed towards the sample, causing the tip to approach the pre-aligned small sample. We have successfully approached a hand cut tip that was made from 0.1 mm thin Pt∕Ir wire to an isolated individual 32.5 × 32.5 μm(2) graphite flake. Good atomic resolution images and high quality tunneling current spectra for that specified tiny flake are obtained in ambient conditions with high repeatability within one month showing high and long term stability of the new STM structure. In addition, frequency spectra of the tunneling current signals do not show outstanding tip mount related resonant frequency (low frequency), which further confirms the stability of the STM structure.

Temperature dependence of the cosphi conductance in Josephson tunnel junctions determined from plasma resonance experiments

International Nuclear Information System (INIS)

Pedersen, N.F.; Soerensen, O.H.; Mygind, J.

1978-01-01

The microwave response at 9 GHz of Sn-O-Sn tunnel-junction current biased at zero dc voltage has been measured just below the critical temperature T/sub c/ of the Sn films. The temperature dependence of the cosphi conductance is determined from the resonant response at the junction plasma frequency f/sub p/ as the temperature is decreased from T/sub c/. We used three different schemes for observation of the plasma oscillations: (a) second-harmonic generation (excitation at approx. 4.5 GHz, f/sub p/ approx. 4.5 GHz); (b) mixing (excitations at approx. 9 and approx. 18 GHz, f/sub p/ approx. 9 GHz); (c) parametric half-harmonic oscillation (excitation at approx. 18 GHz, f/sub p/ approx. 9 GHz). Measurements were possible in two temperature intervals; 0.994 or = T/T/sub c/ > or = 0.930, with the result that as the temperature was decreased the cosphi amplitude first increased from about zero to positive values and then at lower temperatures decreased approaching -1 at the lowest temperatures of the experiment

Analysis of heat-transfer measurements from 2 AEDC wind tunnels on the Shuttle external tank

Science.gov (United States)

Nutt, K. W.

1984-01-01

Previous aerodynamic heating tests have been conducted in the AEDC/VKF Supersonic Wind Tunnel (A) to aid in defining the design thermal environment for the space shuttle external tank. The quality of these data has been under discussion because of the effects of low tunnel enthalpy and slow model injection rates. Recently the AEDC/VKF Hypersonic Wind Tunnel (C) has been modified to provide a Mach 4 capability that has significantly higher tunnel enthalpy with more rapid model injection rates. Tests were conducted in Tunnel C at Mach 4 to obtain data on the external tank for comparison with Tunnel A results. Data were obtained on a 0.0175 scale model of the Space Shuttle Integrated Vehicle at Re/ft = 4 x 10 to the 6th power with the tunnel stagnation temperature varying from 740 to 1440 R. Model attitude varied from an angle of attack of -5 to 5 deg and an angle of sideslip of -3 to 3 deg. One set of data was obtained in Tunnel C at Re/ft = 6.9 x 10 to the 6th for comparison with flight data. Data comparisons between the two tunnels for numerous regions on the external tank are given.

Inelastic tunneling of electrons through a quantum dot with an embedded single molecular magnet

Science.gov (United States)

Chang, Bo; Liang, J.-Q.

2010-06-01

We report a theoretical analysis of electron transport through a quantum dot with an embedded biaxial single-molecule magnet (SMM) based on mapping of the many-body interaction-system onto a one-body problem by means of the non-equilibrium Green function technique. It is found that the conducting current exhibits a stepwise behavior and the nonlinear differential conductance displays additional peaks with variation of the sweeping speed and the magnitude of magnetic field. This observation can be interpreted by the interaction of electron-spin with the SMM and the quantum tunneling of magnetization. The inelastic conductance and the corresponding tunneling processes are investigated with normal as well as ferromagnetic electrodes. In the case of ferromagnetic configuration, the coupling to the SMM leads to an asymmetric tunneling magnetoresistance (TMR), which can be enhanced or suppressed greatly in certain regions. Moreover, a sudden TMR-switch with the variation of magnetic field is observed, which is seen to be caused by the inelastic tunneling.

Inelastic tunneling of electrons through a quantum dot with an embedded single molecular magnet

Energy Technology Data Exchange (ETDEWEB)

Chang Bo [Institute of Theoretical Physics and Department of Physics, Shanxi University, Taiyuan, Shanxi 030006 (China); Liang, J.-Q., E-mail: jqliang@sxu.edu.c [Institute of Theoretical Physics and Department of Physics, Shanxi University, Taiyuan, Shanxi 030006 (China)

2010-06-28

We report a theoretical analysis of electron transport through a quantum dot with an embedded biaxial single-molecule magnet (SMM) based on mapping of the many-body interaction-system onto a one-body problem by means of the non-equilibrium Green function technique. It is found that the conducting current exhibits a stepwise behavior and the nonlinear differential conductance displays additional peaks with variation of the sweeping speed and the magnitude of magnetic field. This observation can be interpreted by the interaction of electron-spin with the SMM and the quantum tunneling of magnetization. The inelastic conductance and the corresponding tunneling processes are investigated with normal as well as ferromagnetic electrodes. In the case of ferromagnetic configuration, the coupling to the SMM leads to an asymmetric tunneling magnetoresistance (TMR), which can be enhanced or suppressed greatly in certain regions. Moreover, a sudden TMR-switch with the variation of magnetic field is observed, which is seen to be caused by the inelastic tunneling.

Graphene-Molybdenum Disulfide-Graphene Tunneling Junctions with Large-Area Synthesized Materials.

Science.gov (United States)

Joiner, Corey A; Campbell, Philip M; Tarasov, Alexey A; Beatty, Brian R; Perini, Chris J; Tsai, Meng-Yen; Ready, William J; Vogel, Eric M

2016-04-06

Tunneling devices based on vertical heterostructures of graphene and other 2D materials can overcome the low on-off ratios typically observed in planar graphene field-effect transistors. This study addresses the impact of processing conditions on two-dimensional materials in a fully integrated heterostructure device fabrication process. In this paper, graphene-molybdenum disulfide-graphene tunneling heterostructures were fabricated using only large-area synthesized materials, unlike previous studies that used small exfoliated flakes. The MoS2 tunneling barrier is either synthesized on a sacrificial substrate and transferred to the bottom-layer graphene or synthesized directly on CVD graphene. The presence of graphene was shown to have no impact on the quality of the grown MoS2. The thickness uniformity of MoS2 grown on graphene and SiO2 was found to be 1.8 ± 0.22 nm. XPS and Raman spectroscopy are used to show how the MoS2 synthesis process introduces defects into the graphene structure by incorporating sulfur into the graphene. The incorporation of sulfur was shown to be greatly reduced in the absence of molybdenum suggesting molybdenum acts as a catalyst for sulfur incorporation. Tunneling simulations based on the Bardeen transfer Hamiltonian were performed and compared to the experimental tunneling results. The simulations show the use of MoS2 as a tunneling barrier suppresses contributions to the tunneling current from the conduction band. This is a result of the observed reduction of electron conduction within the graphene sheets.

Outcome of open carpal tunnel release surgery

International Nuclear Information System (INIS)

Khan, A.A.; Ali, H.; Muhammad, G.; Gul, N.; Zardan, K.K.; Mushtaq, M.; Ali, S.; Bhatti, S.N.; Ali, K.; Rashid, B.; Saboor, A.

2015-01-01

Background: Carpel tunnel syndrome is a common compression neuropathy of the median nerve causing pain, numbness and functional dysfunction of the hand. Among the available treatments, surgical release of the nerve is the most effective and acceptable treatment option. The aim of this study was to see the outcomes of surgical release of carpel tunnel using open technique. Method: This descriptive case series was conducted at the Department of neurosurgery, Ayub Teaching Hospital Abbottabad from April 2013 to March 2014. One hundred consecutive patients with carpel tunnel syndrome were included who underwent open carpel tunnel release surgery. They were followed up at 1, 3 and 6 months. Residual pain, numbness and functional improvement of the hand were the main outcome measures. Results: Out of 100 patients, 19 were males. The age ranged from 32 to 50 years with a mean of 39.29±3.99 years. The duration of symptoms was from 5 to 24 months. In the entire series patient functional outcome and satisfaction was 82 percentage at 1 month, 94 percentage at 3 months and 97 percentage at 6 months. 18 percentage patient had residual pain at 1 month post-operative follow-up, 6percentage at 3 months and 3 percentage at 6 month follow-up. Conclusion: Open carpel tunnel release surgery is an effective procedure for compression neuropathy of the median nerve. It should be offered to all patients with moderate to severe pain and functional disability related to carpel tunnel syndrome. (author)

Quantized Majorana conductance

NARCIS (Netherlands)

Zhang, Hao; Liu, Chun Xiao; Gazibegovic, Sasa; Xu, Di; Logan, John A.; Wang, Guanzhong; Van Loo, Nick; Bommer, Jouri D.S.; De Moor, Michiel W.A.; Car, Diana; Op Het Veld, Roy L.M.; Van Veldhoven, Petrus J.; Koelling, Sebastian; Verheijen, Marcel A.; Pendharkar, Mihir; Pennachio, Daniel J.; Shojaei, Borzoyeh; Lee, Joon Sue; Palmstrøm, Chris J.; Bakkers, Erik P.A.M.; Sarma, S. Das; Kouwenhoven, Leo P.

2018-01-01

Majorana zero-modes - a type of localized quasiparticle - hold great promise for topological quantum computing. Tunnelling spectroscopy in electrical transport is the primary tool for identifying the presence of Majorana zero-modes, for instance as a zero-bias peak in differential conductance. The

Intradot spin-flip Andreev reflection tunneling through a ferromagnet-quantum dot-superconductor system with ac field

International Nuclear Information System (INIS)

Song Hongyan; Zhou Shiping

2008-01-01

We investigate Andreev reflection (AR) tunneling through a ferromagnet-quantum dot-superconductor (F-QD-S) system in the presence of an external ac field. The intradot spin-flip scattering in the QD is involved. Using the nonequilibrium Green function and BCS quasiparticle spectrum for superconductor, time-averaged AR conductance is formulated. The competition between the intradot spin-flip scattering and photon-assisted tunneling dominates the resonant behaviors of the time-averaged AR conductance. For weak intradot spin-flip scattering strengths, the AR conductance shows a series of equal interval resonant levels. However, the single-peak at main resonant level develops into a well-resolved double-peak resonance at a strong intradot spin-flip scattering strength. Remarkable, multiple-photon-assisted tunneling that generates photonic sideband peaks with a variable interval has been found. In addition, the AR conductance-bias voltage characteristic shows a transition between the single-peak to double-peak resonance as the ratio of the two tunneling strengths varies

Rotary Balance Wind Tunnel Testing for the FASER Flight Research Aircraft

Science.gov (United States)

Denham, Casey; Owens, D. Bruce

2016-01-01

Flight dynamics research was conducted to collect and analyze rotary balance wind tunnel test data in order to improve the aerodynamic simulation and modeling of a low-cost small unmanned aircraft called FASER (Free-flying Aircraft for Sub-scale Experimental Research). The impetus for using FASER was to provide risk and cost reduction for flight testing of more expensive aircraft and assist in the improvement of wind tunnel and flight test techniques, and control laws. The FASER research aircraft has the benefit of allowing wind tunnel and flight tests to be conducted on the same model, improving correlation between wind tunnel, flight, and simulation data. Prior wind tunnel tests include a static force and moment test, including power effects, and a roll and yaw damping forced oscillation test. Rotary balance testing allows for the calculation of aircraft rotary derivatives and the prediction of steady-state spins. The rotary balance wind tunnel test was conducted in the NASA Langley Research Center (LaRC) 20-Foot Vertical Spin Tunnel (VST). Rotary balance testing includes runs for a set of given angular rotation rates at a range of angles of attack and sideslip angles in order to fully characterize the aircraft rotary dynamics. Tests were performed at angles of attack from 0 to 50 degrees, sideslip angles of -5 to 10 degrees, and non-dimensional spin rates from -0.5 to 0.5. The effects of pro-spin elevator and rudder deflection and pro- and anti-spin elevator, rudder, and aileron deflection were examined. The data are presented to illustrate the functional dependence of the forces and moments on angle of attack, sideslip angle, and angular rate for the rotary contributions to the forces and moments. Further investigation is necessary to fully characterize the control effectors. The data were also used with a steady state spin prediction tool that did not predict an equilibrium spin mode.

Electron-spin polarization in tunnel junctions with ferromagnetic EuS barriers

International Nuclear Information System (INIS)

Hao, X.; Moodera, J.S.; Meservey, R.

1989-01-01

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

Tunneling magnetoresistance in Si nanowires

KAUST Repository

Montes Muñoz, Enrique

2016-11-09

We investigate the tunneling magnetoresistance of small diameter semiconducting Si nanowires attached to ferromagnetic Fe electrodes, using first principles density functional theory combined with the non-equilibrium Green\\'s functions method for quantum transport. Silicon nanowires represent an interesting platform for spin devices. They are compatible with mature silicon technology and their intrinsic electronic properties can be controlled by modifying the diameter and length. Here we systematically study the spin transport properties for neutral nanowires and both n and p doping conditions. We find a substantial low bias magnetoresistance for the neutral case, which halves for an applied voltage of about 0.35 V and persists up to 1 V. Doping in general decreases the magnetoresistance, as soon as the conductance is no longer dominated by tunneling.

Variability in ACL tunnel placement: observational clinical study of surgeon ACL tunnel variability.

Science.gov (United States)

Wolf, Brian R; Ramme, Austin J; Wright, Rick W; Brophy, Robert H; McCarty, Eric C; Vidal, Armando R; Parker, Richard D; Andrish, Jack T; Amendola, Annunziato

2013-06-01

Multicenter and multisurgeon cohort studies on anterior cruciate ligament (ACL) reconstruction are becoming more common. Minimal information exists on intersurgeon and intrasurgeon variability in ACL tunnel placement. Purpose/ The purpose of this study was to analyze intersurgeon and intrasurgeon variability in ACL tunnel placement in a series of The Multicenter Orthopaedic Outcomes Network (MOON) ACL reconstruction patients and in a clinical cohort of ACL reconstruction patients. The hypothesis was that there would be minimal variability between surgeons in ACL tunnel placement. Cross-sectional study; Level of evidence, 3. Seventy-eight patients who underwent ACL reconstruction by 8 surgeons had postoperative imaging with computed tomography, and ACL tunnel location and angulation were analyzed using 3-dimensional surface processing and measurement. Intersurgeon and intrasurgeon variability in ACL tunnel placement was analyzed. For intersurgeon variability, the range in mean ACL femoral tunnel depth between surgeons was 22%. For femoral tunnel height, there was a 19% range. Tibial tunnel location from anterior to posterior on the plateau had a 16% range in mean results. There was only a small range of 4% for mean tibial tunnel location from the medial to lateral dimension. For intrasurgeon variability, femoral tunnel depth demonstrated the largest ranges, and tibial tunnel location from medial to lateral on the plateau demonstrated the least variability. Overall, surgeons were relatively consistent within their own cases. Using applied measurement criteria, 85% of femoral tunnels and 90% of tibial tunnels fell within applied literature-based guidelines. Ninety-one percent of the axes of the femoral tunnels fell within the boundaries of the femoral footprint. The data demonstrate that surgeons performing ACL reconstructions are relatively consistent between each other. There is, however, variability of average tunnel placement up to 22% of mean condylar depth

Effects of tunneling on groundwater flow and swelling of clay-sulfate rocks

Science.gov (United States)

Butscher, Christoph; Einstein, Herbert H.; Huggenberger, Peter

2011-11-01

Swelling of clay-sulfate rocks is a major threat in tunneling. It is triggered by the transformation of the sulfate mineral anhydrite into gypsum as a result of water inflow in anhydrite-containing layers after tunnel excavation. The present study investigates the hydraulic effects of tunneling on groundwater flow and analyzes how hydraulic changes caused by excavation lead to water inflow into anhydrite-containing layers in the tunnel area. Numerical groundwater models are used to conduct scenario simulations that allow one to relate hydrogeological conditions to rock swelling. The influence of the topographic setting, the excavation-damaged zone around the tunnel, the sealing effect of the tunnel liner, and the geological configuration are analyzed separately. The analysis is performed for synthetic situations and is complemented by a case study from a tunnel in Switzerland. The results illustrate the importance of geological and hydraulic information when assessing the risk of swelling at an actual site.

Interaction between groundwater and TBM (Tunnel Boring Machine) excavated tunnels

OpenAIRE

Font Capó, Jordi

2012-01-01

A number of problems, e.g. sudden inflows are encountered during tunneling under the piezometric level, especially when the excavation crosses high transmissivity areas. These inflows may drag materials when the tunnel crosses low competent layers, resulting in subsidence, chimney formation and collapses. Moreover, inflows can lead to a decrease in head level because of aquifer drainage. Tunnels can be drilled by a tunnel boring machine (TBM) to minimize inflows and groundwater impacts, restr...

Tunneling and activity of reticulitermes flavipes (isoptera: rhinotermitidae) exposed to low concentrations of nonrepellent termiticides

Science.gov (United States)

J.E. Mulrooney; P.D. Gerard

2009-01-01

Tunneling and activity bioassays of chlorfenapyr, fipronil, and imidaclopridtreated sand were conducted in the laboratory using Reticulitermes flavipes(Kollar). Termites tunneled significantly less through sand treated with 1.0

Investigation of air flow in open-throat wind tunnels

Science.gov (United States)

Jacobs, Eastman N

1930-01-01

Tests were conducted on the 6-inch wind tunnel of the National Advisory Committee for Aeronautics to form a part of a research on open-throat wind tunnels. The primary object of this part of the research was to study a type of air pulsation which has been encountered in open-throat tunnels, and to find the most satisfactory means of eliminating such pulsations. In order to do this it was necessary to study the effects of different variable on all of the important characteristics of the tunnel. This paper gives not only the results of the study of air pulsations and methods of eliminating them, but also the effects of changing the exit-cone diameter and flare and the effects of air leakage from the return passage. It was found that the air pulsations in the 6-inch wind tunnel could be practically eliminated by using a moderately large flare on the exit cone in conjunction with leakage introduced by cutting holes in the exit cone somewhat aft of its minimum diameter.

Tunneling between edge states in a quantum spin Hall system.

Science.gov (United States)

Ström, Anders; Johannesson, Henrik

2009-03-06

We analyze a quantum spin Hall device with a point contact connecting two of its edges. The contact supports a net spin tunneling current that can be probed experimentally via a two-terminal resistance measurement. We find that the low-bias tunneling current and the differential conductance exhibit scaling with voltage and temperature that depend nonlinearly on the strength of the electron-electron interaction.

Systematic observation of tunneling field-ionization in highly excited Rb Rydberg atoms

International Nuclear Information System (INIS)

Kishimoto, Y.; Tada, M.; Kominato, K.; Shibata, M.; Yamada, S.; Haseyama, T.; Ogawa, I.; Funahashi, H.; Yamamoto, K.; Matsuki, S.

2002-01-01

Pulsed field ionization of high-n (90≤n≤150) manifold states in Rb Rydberg atoms has been investigated in high slew-rate regime. Two peaks in the field ionization spectra were systematically observed for the investigated n region, where the field values at the lower peak do not almost depend on the excitation energy in the manifold, while those at the higher peak increase with increasing excitation energy. The fraction of the higher peak component to the total ionization signals increases with increasing n, exceeding 80% at n=147. Characteristic behavior of the peak component and the comparison with theoretical predictions indicate that the higher peak component is due to the tunneling process. The obtained results show that the tunneling process plays increasingly the dominant role at such highly excited nonhydrogenic Rydberg atoms

Frequency driven inversion of tunnel magnetoimpedance and observation of positive tunnel magnetocapacitance in magnetic tunnel junctions

International Nuclear Information System (INIS)

Parui, Subir; Ribeiro, Mário; Atxabal, Ainhoa; Llopis, Roger; Bedoya-Pinto, Amilcar; Sun, Xiangnan; Casanova, Fèlix; Hueso, Luis E.

2016-01-01

The relevance for modern computation of non-volatile high-frequency memories makes ac-transport measurements of magnetic tunnel junctions (MTJs) crucial for exploring this regime. Here, we demonstrate a frequency-mediated effect in which the tunnel magnetoimpedance reverses its sign in a classical Co/Al 2 O 3 /NiFe MTJ, whereas we only observe a gradual decrease in the tunnel magnetophase. Such effects are explained by the capacitive coupling of a parallel resistor and capacitor in the equivalent circuit model of the MTJ. Furthermore, we report a positive tunnel magnetocapacitance effect, suggesting the presence of a spin-capacitance at the two ferromagnet/tunnel-barrier interfaces. Our results are important for understanding spin transport phenomena at the high frequency regime in which the spin-polarized charge accumulation due to spin-dependent penetration depth at the two interfaces plays a crucial role.

Frequency driven inversion of tunnel magnetoimpedance and observation of positive tunnel magnetocapacitance in magnetic tunnel junctions

Energy Technology Data Exchange (ETDEWEB)

Parui, Subir, E-mail: s.parui@nanogune.eu, E-mail: l.hueso@nanogune.eu; Ribeiro, Mário; Atxabal, Ainhoa; Llopis, Roger [CIC nanoGUNE, 20018 Donostia-San Sebastian (Spain); Bedoya-Pinto, Amilcar [CIC nanoGUNE, 20018 Donostia-San Sebastian (Spain); Max Planck Institute of Microstructure Physics, D-06120 Halle (Germany); Sun, Xiangnan [CIC nanoGUNE, 20018 Donostia-San Sebastian (Spain); National Center for Nanoscience and Technology, 100190 Beijing (China); Casanova, Fèlix; Hueso, Luis E., E-mail: s.parui@nanogune.eu, E-mail: l.hueso@nanogune.eu [CIC nanoGUNE, 20018 Donostia-San Sebastian (Spain); IKERBASQUE, Basque Foundation for Science, 48011 Bilbao (Spain)

2016-08-01

The relevance for modern computation of non-volatile high-frequency memories makes ac-transport measurements of magnetic tunnel junctions (MTJs) crucial for exploring this regime. Here, we demonstrate a frequency-mediated effect in which the tunnel magnetoimpedance reverses its sign in a classical Co/Al{sub 2}O{sub 3}/NiFe MTJ, whereas we only observe a gradual decrease in the tunnel magnetophase. Such effects are explained by the capacitive coupling of a parallel resistor and capacitor in the equivalent circuit model of the MTJ. Furthermore, we report a positive tunnel magnetocapacitance effect, suggesting the presence of a spin-capacitance at the two ferromagnet/tunnel-barrier interfaces. Our results are important for understanding spin transport phenomena at the high frequency regime in which the spin-polarized charge accumulation due to spin-dependent penetration depth at the two interfaces plays a crucial role.

Dihydroazulene photoswitch operating in sequential tunneling regime

DEFF Research Database (Denmark)

Broman, Søren Lindbæk; Lara-Avila, Samuel; Thisted, Christine Lindbjerg

2012-01-01

to electrodes so that the electron transport goes by sequential tunneling. To assure weak coupling, the DHA switching kernel is modified by incorporating p-MeSC6H4 end-groups. Molecules are prepared by Suzuki cross-couplings on suitable halogenated derivatives of DHA. The synthesis presents an expansion of our......, incorporating a p-MeSC6H4 anchoring group in one end, has been placed in a silver nanogap. Conductance measurements justify that transport through both DHA (high resistivity) and VHF (low resistivity) forms goes by sequential tunneling. The switching is fairly reversible and reenterable; after more than 20 ON...

Carpal Tunnel Syndrome

Science.gov (United States)

... a passing cramp? It could be carpal tunnel syndrome. The carpal tunnel is a narrow passageway of ... three times more likely to have carpal tunnel syndrome than men. Early diagnosis and treatment are important ...

Conduction mechanism in assemblies of metal nanoparticles linked by organic molecules

International Nuclear Information System (INIS)

Mueller, K.-H.; Herrmann, J.; Raguse, B.; Baxter, G.; Reda, T.

2002-01-01

Full text: We have investigated theoretically and experimentally electron transport through thin films of gold nanoparticles which are linked by alkanedithiol molecules of different chain lengths. We find that conduction between neighbouring nanoparticles takes place by electron tunnelling along weakly conducting organic linker molecules. Using a tight binding model for the alkanedithiol molecules to describe the tunnelling process we predict the conductivity to decrease exponentially with the length of the molecules. During tunnelling the electron has to overcome a charging energy due to the electron-hole interaction between tunnelling electrons and the corresponding holes left behind on the donor nanoparticle. Experimentally we find that large applied voltages cause nonlinear I-V characteristics and that the temperature dependence of the conductivity does not show Arrhenius behaviour but instead is of the form exp[-(E o /kT) 1/2 ]. Using percolation theory for a network of metal nanoparticles separated by barriers we show that strong disorder caused by variations in nanoparticle size and linker length as well as randomly trapped electric charges on the linker molecules can well explain our experimental data

Horizontal coring using air as the circulating fluid: Some prototype studies conducted in G Tunnel at the Nevada Test Site for the Yucca Mountain Project

International Nuclear Information System (INIS)

Chornack, M.P.; French, C.A.

1989-01-01

Horizontal coring using air as the circulating fluid has been conducted in the G Tunnel Underground Facility (GTUF) at the Nevada Test Site. This work is part of the prototype investigations of hydrogeology for the Yucca Mountain Project. The work is being conducted to develop methods and procedures that will be used at the Department of Energy's Yucca Mountain Site, a candidate site for the nation's first high-level nuclear waste repository, during the site characterization phase of the investigations. The United States Geological Survey (USGS) is conducting this prototype testing under the guidance of the Los Alamos National Laboratory (LANL) and in conjunction with Reynolds Electrical ampersand Engineering Company (REECo), the drilling contractor. 7 refs., 8 figs., 5 tabs

Theory of superconducting tunneling without the tunneling Hamiltonian

International Nuclear Information System (INIS)

Arnold, G.B.

1987-01-01

When a tunneling barrier is nearly transparent, the standard tunneling (or transfer) Hamiltonian approximation fails. The author describes the theory which is necessary for calculating the tunneling current in these cases, and illustrate it by comparing theory and experiment on superconductor/insulator/superconductor (SIS) junctions have ultra-thin tunnel barriers. This theory accurately explains the subgap structure which appears in the dynamical resistance of such SIS junctions, including many observed details which no previous theory has reproduced. The expression for the current through an SIS junction with an ultrathin barrier is given by I(t) = Re{Sigma/sub n/ J/sub n/ (omega/sub o/)e/sup in omega/o/sup t/} where omega/sub o/ = 2eV/h is the Josephson frequency, V is the bias voltage, and the J/sub n/ are voltage dependent coefficients, one for each positive or negative integer, n, and n=0. The relative sign of the terms involving cos(n omega/sub o/t) and sin(n omega/sub o/t) agrees with experiment, in contrast to previous theories of Josephson tunneling

Atomic scale investigations of the gate controlled tunneling effect in graphyne nanoribbon

International Nuclear Information System (INIS)

Yang, Wen; Wang, Lu-Hao; Geng, Yang; Sun, Qing-Qing; Zhou, Peng; Ding, Shi-Jing; Wei Zhang, David

2013-01-01

Configuration and transport properties of zigzag graphyne nanoribbon (n = 2) are investigated by means of the first-principles calculations and non-equilibrium Green's function in this work. We demonstrated the controllability of the graphyne's conductivity by gate bias, and the tunneling behavior induced by gate and drain voltages was investigated systemically. The characteristics of I d -V d , I d -V g , as well as the evolutions of current with electron temperature elevation were explored. The device exhibits a tunneling ratio around 10 3 , and the state art of tunneling operations of the tunneling field effect transistor in this split-new material was achieved

Spin-polarized tunneling through a ferromagnetic insulator

NARCIS (Netherlands)

Kok, M.; Kok, M.; Beukers, J.N.; Brinkman, Alexander

2009-01-01

The polarization of the tunnel conductance of spin-selective ferromagnetic insulators is modeled, providing a generalized concept of polarization including both the effects of electrode and barrier polarization. The polarization model is extended to take additional non-spin-polarizing insulating

Laser-assisted spin-polarized transport in graphene tunnel junctions

International Nuclear Information System (INIS)

Ding Kaihe; Zhu Zhengang; Berakdar, Jamal

2012-01-01

The Keldysh nonequilibrium Green’s function method is utilized to theoretically study spin-polarized transport through a graphene spin valve irradiated by a monochromatic laser field. It is found that the bias dependence of the differential conductance exhibits successive peaks corresponding to the resonant tunneling through the photon-assisted sidebands. The multi-photon processes originate from the combined effects of the radiation field and the graphene tunneling properties, and are shown to be substantially suppressed in a graphene spin valve which results in a decrease of the differential conductance for a high bias voltage. We also discuss the appearance of a dynamical gap around zero bias due to the radiation field. The gap width can be tuned by changing the radiation electric field strength and the frequency. This leads to a shift of the resonant peaks in the differential conductance. We also demonstrate numerically the dependences of the radiation and spin valve effects on the parameters of the external fields and those of the electrodes. We find that the combined effects of the radiation field, the graphene and the spin valve properties bring about an oscillatory behavior in the tunnel magnetoresistance, and this oscillatory amplitude can be changed by scanning the radiation field strength and/or the frequency. (paper)

Tunneling works. Tunnel koji

Energy Technology Data Exchange (ETDEWEB)

Higo, M [Hazam Gumi, Ltd., Tokyo (Japan)

1991-10-25

A mountain tunneling method for rock-beds used to be applied mainly to construction works in the mountains under few restrictions by environmental problems. However, construction works near residential sreas have been increasing. There are such enviromental problems due to tunneling works as vibration, noise, lowering of ground-water level, and influences on other structures. This report mainly describes the measurement examples of vibration and noise accompanied with blasting and the effects of the measures to lessen such influences. When the tunneling works for the railroad was carried out on the natural ground mainly composed of basalt, vibration of the test blasting was measured at three stations with piezoelectric accelerometers. Then, ordinary blasting, mutistage blasting, and ABM blasting methods were used properly besed on the above results, and only a few complaints were made. In the different works, normal noise and low-frequency sound were mesured at 22 stations around the pit mouth. As countermeasures for noise, sound-proof sheets, walls, and single and double doors were installed and foundto be effective. 1 ref., 6 figs., 1 tab.

On the conductive properties of MgO films grown on ultrathin hexagonal close-packed Co(0001) layer

International Nuclear Information System (INIS)

Gladczuk, L.; Aleszkiewicz, M.

2013-01-01

Here we present a scanning tunneling microscopy study of electrical conductivity of (110)-oriented MgO ultrathin films grown on hexagonal close-packed Co(0001) surface by molecular beam epitaxy, being a good candidate for tunneling barrier for future-generation spintronic devices. Three-dimensional growth of the tunneling barrier, expected for compressive strains emerging at the Co/MgO interface, is demonstrated by reflection high-energy electron diffraction and atomic force microscopy. The 5 eV height of the full barrier of MgO is reached at a layer thickness of 4 nm. Thinner MgO layers exhibit randomly distributed spots of the high conductance on the tunneling current map. The current–voltage curves indicate the existence of vacancies in MgO crystal lattice, lowering the resistivity of the tunneling barrier. - Highlights: • Conductivity of MgO barrier in MgO/hexagonal close-packed-Co bilayer • Conductivity strongly varies with MgO thickness • MgO barrier exhibits randomly distributed spots of particularly high conductance • Tunneling current–voltage curves indicate the existence of vacancies in MgO lattice

Investigating the Inter-Tube Conduction Mechanism in Polycarbonate Nanocomposites Prepared with Conductive Polymer-Coated Carbon Nanotubes

KAUST Repository

Ventura, Isaac Aguilar

2015-12-16

A well-known strategy to improve the electrical conductivity of polymers is to dope them with high-aspect-ratio and conductive nanoparticles such as carbon nanotubes (CNTs). However, these nanocomposites also exhibit undesirable properties such as damage-sensitive and history-dependent conductivity because their macroscopic electrical conductivity is largely determined by the tunneling effect at the tube/tube interface. To reduce these issues, new nanocomposites have been developed with CNTs that have been coated with a conductive layer of poly(3,4-ethylenedioxythiophene)poly(styrenesulfonate) (PEDOT/PSS). It has been posited that the insulating region between the CNTs is replaced by a conductive polymer bridge; this has not been proven up to now. We propose here to investigate in-depth how the macroscopic conductivity of these materials is changing when (1) varying the frequency of the electrical loading (impedance spectroscopy), (2) varying the mechanical hydrostatic pressure, and (3) varying the voltage of the electrical loading. The response is systematically compared to the one of conventional carbon nanotube/polycarbonate (CNT/PC) nanocomposites so we can clarify how efficiently the tunneling effect is suppressed from these composites. The objective is to elucidate further the mechanism for conduction in such material formulations.

Tunneling junction as an open system. Normal tunneling

International Nuclear Information System (INIS)

Ono, Y.

1978-01-01

The method of the tunneling Hamiltonian is reformulated in the case of normal tunneling by introducing two independent particle baths. Due to the baths, it becomes possible to realize a final stationary state where the electron numbers of the two electrodes in the tunneling system are maintained constant and where there exists a stationary current. The effect of the bath-system couplings on the current-voltage characteristics of the junction is discussed in relation to the usual expression of the current as a function of voltage. (Auth.)

Note: long-range scanning tunneling microscope for the study of nanostructures on insulating substrates.

Science.gov (United States)

Molina-Mendoza, Aday J; Rodrigo, José G; Island, Joshua; Burzuri, Enrique; Rubio-Bollinger, Gabino; van der Zant, Herre S J; Agraït, Nicolás

2014-02-01

The scanning tunneling microscope (STM) is a powerful tool for studying the electronic properties at the atomic level, however, it is of relatively small scanning range and the fact that it can only operate on conducting samples prevents its application to study heterogeneous samples consisting of conducting and insulating regions. Here we present a long-range scanning tunneling microscope capable of detecting conducting micro and nanostructures on insulating substrates using a technique based on the capacitance between the tip and the sample and performing STM studies.

Note: Long-range scanning tunneling microscope for the study of nanostructures on insulating substrates

Energy Technology Data Exchange (ETDEWEB)

Molina-Mendoza, Aday J., E-mail: aday.molina@uam.es [Departamento de Física de la Materia Condensada, Universidad Autónoma de Madrid, Campus de Cantoblanco, E-28049 Madrid (Spain); Rodrigo, José G.; Rubio-Bollinger, Gabino [Departamento de Física de la Materia Condensada, Universidad Autónoma de Madrid, Campus de Cantoblanco, E-28049 Madrid (Spain); Condensed Matter Physics Center (IFIMAC) and Instituto Universitario de Ciencia de Materiales “Nicolás Cabrera,” Universidad Autónoma de Madrid, Campus de Cantoblanco, E-28049 Madrid (Spain); Island, Joshua; Burzuri, Enrique; Zant, Herre S. J. van der [Kavli Institute of Nanoscience, Delft University of Technology, P.O. Box 5046, 2600 GA Delft (Netherlands); Agraït, Nicolás [Departamento de Física de la Materia Condensada, Universidad Autónoma de Madrid, Campus de Cantoblanco, E-28049 Madrid (Spain); Condensed Matter Physics Center (IFIMAC) and Instituto Universitario de Ciencia de Materiales “Nicolás Cabrera,” Universidad Autónoma de Madrid, Campus de Cantoblanco, E-28049 Madrid (Spain); Instituto Madrileño de Estudios Avanzados en Nanociencia IMDEA-Nanociencia, E-28049 Madrid (Spain)

2014-02-15

The scanning tunneling microscope (STM) is a powerful tool for studying the electronic properties at the atomic level, however, it is of relatively small scanning range and the fact that it can only operate on conducting samples prevents its application to study heterogeneous samples consisting of conducting and insulating regions. Here we present a long-range scanning tunneling microscope capable of detecting conducting micro and nanostructures on insulating substrates using a technique based on the capacitance between the tip and the sample and performing STM studies.

Application of the instanton method for analyzing tunneling splitting spectra of nonrigid molecular systems : II. Excited states

NARCIS (Netherlands)

Iroshnikov, GS; Sukhanov, LP

For nonrigid molecules with two equivalent minima on their potential energy surface, expressions are obtained in terms of the instanton method for the calculation of the magnitude of the tunneling splitting of vibrational levels with the number n greater than or equal to 0 both in the harmonic

Low frequency elastic properties of glasses at low temperatures - implications on the tunneling model

International Nuclear Information System (INIS)

Raychaudhuri, A.K.; Hunklinger, S.

1984-01-01

We have measured the low frequency elastic properties of dielectric, normal conducting and superconducting metallic glasses at audio-frequencies (fapprox.=1 kHz) and temperatures down to 10 mK. Our results are discussed in the framework of the tunneling model of glasses. The major assumption of the tunneling model regarding the tunneling states with long relaxation time has been verified, but discrepancies to high frequency measurements have been found. In addition, our experiments on superconducting metallic glasses seem to indicate that the present treatment of the electron-tunneling state interaction is not sufficient. (orig.)

Interactions of glutamine dipeptides with sodium dodecyl sulfate in aqueous solution measured by volume, conductivity, and fluorescence spectra

Energy Technology Data Exchange (ETDEWEB)

Yan Zhenning, E-mail: yanzzn@zzu.edu.cn [Department of Chemistry, Zhengzhou University, Zhengzhou, Henan 450001 (China); Sun Ximeng; Li Weiwei; Li Yu [Department of Chemistry, Zhengzhou University, Zhengzhou, Henan 450001 (China); Wang Jianji [Department of Chemistry, Henan Normal University, Xinxiang, Henan 453007 (China)

2011-10-15

Highlights: > Ion-ion and ion-polar group interactions are dominant interactions. > The SDS addition and temperature increase cause a dehydration effect on dipeptides. > The addition of dipeptide in water decreases the c{sub cmc} of SDS. > Enthalpy-entropy compensation takes place during micellization. > Micelle aggregation number was decreased by addition of glutamine dipeptides. - Abstract: Densities, conductivities, and fluorescence spectra of {l_brace}sodium dodecyl sulfate (SDS) + glutamine dipeptide + water{r_brace} mixtures were measured as a function of temperature. The density data have been utilized to calculate apparent molar volumes, standard partial molar volumes (V{sub 2,{phi}}{sup o}), standard partial molar volumes of transfer from water to aqueous SDS solutions ({Delta}{sub t}V{sup o}), the hydration number, partial molar expansibility (E{sub {phi}}{sup o}), and Hepler's constant of glutamine dipeptides. The critical micellar concentration (c{sub cmc}) and the degree of counterion dissociation of SDS micelles obtained from electrical conductivity data have been estimated at various concentrations of glutamine dipeptide. Thermodynamic parameters of micellization of SDS in aqueous dipeptide solutions have been determined from c{sub cmc} values and an enthalpy-entropy compensation effect was observed for the ternary systems. The pyrene fluorescence spectra were used to study the change of micropolarity produced by the interaction of SDS with glutamine dipeptide, and the aggregation behavior of SDS. The results have been interpreted in terms of solute-solvent interactions and structural changes in the mixed solutions.

A Historical Evaluation of the U16a Tunnel, Nevada National Security Site, Nye County, Nevada Volume 2

Energy Technology Data Exchange (ETDEWEB)

Jones, Roberrt C. [Desert Research Inst. (DRI), Reno, NV (United States); Drollinger, Harold [Desert Research Inst. (DRI), Reno, NV (United States)

2013-06-01

This report presents a historical evaluation of the U16a Tunnel on the Nevada National Security Site in southern Nevada. The work was conducted by the Desert Research Institute at the request of the U.S. Department of Energy, National Nuclear Security Administration Nevada Site Office and the U.S. Department of Defense, Defense Threat Reduction Agency. The U16a Tunnel was used for underground nuclear weapons effects tests in Shoshone Mountain in Area 16 of the Nevada National Security Site. Six nuclear tests were conducted in the U16a Tunnel from 1962 to 1971. These tests are Marshmallow, Gum Drop, Double Play, Ming Vase, Diamond Dust, and Diamond Mine. The U.S. Department of Defense Threat Reduction Agency, with participation from Lawrence Livermore National Laboratory and Las Alamos National Laboratory, sponsored the tests. Fifteen high explosives tests were also conducted at the tunnel. Two were calibration tests during nuclear testing and the remaining were U.S. Department of Defense, Defense Threat Reduction Agency tunnel defeat tests. The U16a Tunnel complex is on the top and slopes of Shoshone Mountain, encompassing an area of approximately 16.7 hectares (41.1 acres). Major modifications to the landscape are a result of three principal activities, road construction and maintenance, mining activities related to development of the tunnel complex, and site preparation for activities related to testing. Forty-seven cultural features were recorded at the portal and on the slopes of Shoshone Mountain. At the portal area, features relate to the mining, construction, testing, and general every day operational support activities within the tunnel. These include concrete foundations for buildings, equipment pads, and rail lines. Features on the slopes above the tunnel relate to tunnel ventilation, borehole drilling, and data recording. Feature types include soil-covered bunkers, concrete foundations, instrument cable holes, drill holes, and ventilation shafts. The U16

A Historical Evaluation of the U16a Tunnel, Nevada National Security Site, Nye County, Nevada Volume 1

Energy Technology Data Exchange (ETDEWEB)

Jones, Robert C. [Desert Research Inst. (DRI), Reno, NV (United States); Drollinger, Harold [Desert Research Inst. (DRI), Reno, NV (United States); Bullard, Thomas F. [Desert Research Inst. (DRI), Reno, NV (United States); Ashbaugh, Laurence J. [Desert Research Inst. (DRI), Reno, NV (United States); Griffin, Wayne R. [Desert Research Inst. (DRI), Reno, NV (United States)

2013-01-01

This report presents a historical evaluation of the U16a Tunnel on the Nevada National Security Site in southern Nevada. The work was conducted by the Desert Research Institute at the request of the U.S. Department of Energy, National Nuclear Security Administration Nevada Site Office and the U.S. Department of Defense, Defense Threat Reduction Agency. The U16a Tunnel was used for underground nuclear weapons effects tests in Shoshone Mountain in Area 16 of the Nevada National Security Site. Six nuclear tests were conducted in the U16a Tunnel from 1962 to 1971. These tests are Marshmallow, Gum Drop, Double Play, Ming Vase, Diamond Dust, and Diamond Mine. The U.S. Department of Defense Threat Reduction Agency, with participation from Lawrence Livermore National Laboratory and Las Alamos National Laboratory, sponsored the tests. Fifteen high explosives tests were also conducted at the tunnel. Two were calibration tests during nuclear testing and the remaining were U.S. Department of Defense, Defense Threat Reduction Agency tunnel defeat tests. The U16a Tunnel complex is on the top and slopes of Shoshone Mountain, encompassing an area of approximately 16.7 hectares (41.1 acres). Major modifications to the landscape are a result of three principal activities, road construction and maintenance, mining activities related to development of the tunnel complex, and site preparation for activities related to testing. Forty-seven cultural features were recorded at the portal and on the slopes of Shoshone Mountain. At the portal area, features relate to the mining, construction, testing, and general every day operational support activities within the tunnel. These include concrete foundations for buildings, equipment pads, and rail lines. Features on the slopes above the tunnel relate to tunnel ventilation, borehole drilling, and data recording. Feature types include soil-covered bunkers, concrete foundations, instrument cable holes, drill holes, and ventilation shafts. The U16

Fire analyses in central and disposal tunnels by APROS

International Nuclear Information System (INIS)

Peltokorpi, L.; Kukkola, T.; Nieminen, J.

2012-12-01

The central tunnels and the disposal tunnels on the north-east disposal area are the target areas of the fire studies. Target is to maintain under pressure in the fire zone in case of a fire. In the central tunnels a fire of a drilling jumbo with moderate fire propagation is used as heat release rate. In the disposal tunnel the heat release rate of a canister transfer and installation vehicle fire received as a result of the pyrolysis analyze as well as an average heat release rate of a van fire are used. Inlet air is to be conducted to the back end of the fire zone and the exhaust is to be lead out from the beginning of the fire zone. The worst location of the fire is in the beginning of the fire zone just below of the exhaust air clap valve. The size of the fire zone does not have big impact on pressure. In all analyzed cases the fire zone remains too long time over pressurized. Inlet air flow of a 30 m 3 /s is too much. The rotation controlled booster blowers will solve the pressure problems of the fire zone in fire cases. The rotation is controlled by the fire zone pressure. The fire of the canister transfer and installation vehicle in the central tunnel will not cause problems. The disposal tunnel fire door should be kept open, if the canister transfer and installation vehicle or the bentonite blocks transfer and installation vehicle is driven into the disposal tunnel. If a fire is caught in the disposal tunnel then the fire zone in the central tunnel is to be closed and the pressure is controlled by the rotation controlled booster blowers. If a personnel car or a van is driven into the disposal tunnel, then fire door of the disposal is to be kept closed against fires in the central tunnel. (orig.)

Quantum theory of tunneling

CERN Document Server

Razavy, Mohsen

2014-01-01

In this revised and expanded edition, in addition to a comprehensible introduction to the theoretical foundations of quantum tunneling based on different methods of formulating and solving tunneling problems, different semiclassical approximations for multidimensional systems are presented. Particular attention is given to the tunneling of composite systems, with examples taken from molecular tunneling and also from nuclear reactions. The interesting and puzzling features of tunneling times are given extensive coverage, and the possibility of measurement of these times with quantum clocks are critically examined. In addition by considering the analogy between evanescent waves in waveguides and in quantum tunneling, the times related to electromagnetic wave propagation have been used to explain certain aspects of quantum tunneling times. These topics are treated in both non-relativistic as well as relativistic regimes. Finally, a large number of examples of tunneling in atomic, molecular, condensed matter and ...

Quantum random number generator based on quantum tunneling effect

OpenAIRE

Zhou, Haihan; Li, Junlin; Pan, Dong; Zhang, Weixing; Long, Guilu

2017-01-01

In this paper, we proposed an experimental implementation of quantum random number generator(QRNG) with inherent randomness of quantum tunneling effect of electrons. We exploited InGaAs/InP diodes, whose valance band and conduction band shared a quasi-constant energy barrier. We applied a bias voltage on the InGaAs/InP avalanche diode, which made the diode works under Geiger mode, and triggered the tunneling events with a periodic pulse. Finally, after data collection and post-processing, our...

Spin heat accumulation induced by tunneling from a ferromagnet.

Science.gov (United States)

Vera-Marun, I J; van Wees, B J; Jansen, R

2014-02-07

An electric current from a ferromagnet into a nonmagnetic material can induce a spin-dependent electron temperature. Here, it is shown that this spin heat accumulation, when created by tunneling from a ferromagnet, produces a non-negligible voltage signal that is comparable to that due to the coexisting electrical spin accumulation and can give a different Hanle spin precession signature. The effect is governed by the spin polarization of the Peltier coefficient of the tunnel contact, its Seebeck coefficient, and the spin heat resistance of the nonmagnetic material, which is related to the electrical spin resistance by a spin-Wiedemann-Franz law. Moreover, spin heat injection is subject to a heat conductivity mismatch that is overcome if the tunnel interface has a sufficiently large resistance.

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

International Nuclear Information System (INIS)

Gauyacq, J-P; Lorente, N

2014-01-01

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

Magnetoresistance of galfenol-based magnetic tunnel junction

International Nuclear Information System (INIS)

Gobaut, B.; Vinai, G.; Castán-Guerrero, C.; Krizmancic, D.; Panaccione, G.; Torelli, P.; Rafaqat, H.; Roddaro, S.; Rossi, G.; Eddrief, M.; Marangolo, M.

2015-01-01

The manipulation of ferromagnetic layer magnetization via electrical pulse is driving an intense research due to the important applications that this result will have on memory devices and sensors. In this study we realized a magnetotunnel junction in which one layer is made of Galfenol (Fe 1-x Ga x ) which possesses one of the highest magnetostrictive coefficient known. The multilayer stack has been grown by molecular beam epitaxy and e-beam evaporation. Optical lithography and physical etching have been combined to obtain 20x20 micron sized pillars. The obtained structures show tunneling conductivity across the junction and a tunnel magnetoresistance (TMR) effect of up to 11.5% in amplitude

Electron tunneling measurements in LaSrCuO and YBaCuO

International Nuclear Information System (INIS)

Moreland, J.; Ekin, J.W.; Goodrich, L.F.; Capobianco, T.E.; Clark, A.F.

1987-01-01

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

Tunneling Spectroscopy of Quantum Hall States in Bilayer Graphene

Science.gov (United States)

Wang, Ke; Harzheim, Achim; Watanabe, Kenji; Taniguchi, Takashi; Kim, Philip

In the quantum Hall (QH) regime, ballistic conducting paths along the physical edges of a sample appear, leading to quantized Hall conductance and vanishing longitudinal magnetoconductance. These QH edge states are often described as ballistic compressible strips separated by insulating incompressible strips, the spatial profiles of which can be crucial in understanding the stability and emergence of interaction driven QH states. In this work, we present tunneling transport between two QH edge states in bilayer graphene. Employing locally gated device structure, we guide and control the separation between the QH edge states in bilayer graphene. Using resonant Landau level tunneling as a spectroscopy tool, we measure the energy gap in bilayer graphene as a function of displacement field and probe the emergence and evolution of incompressible strips.

Rashba and Dresselhaus spin-orbit coupling effects on tunnelling through two-dimensional magnetic quantum systems

International Nuclear Information System (INIS)

Xu Wen; Guo Yong

2005-01-01

We investigate the influence of the Rashba and Dresselhaus spin-orbit coupling interactions on tunnelling through two-dimensional magnetic quantum systems. It is showed that not only Rashba spin-orbit coupling but also Dresselhaus one can affect spin tunnelling properties greatly in such a quantum system. The transmission possibility, the spin polarization and the conductance are obviously oscillated with both coupling strengths. High spin polarization, conductance and magnetic conductance of the structure can be obtained by modulating either Rashba or Dresselhaus coupling strength

Process of long-term tunnel instability by temperature and humidity variation in sedimentary rock

International Nuclear Information System (INIS)

Sawada, Masataka; Okada, Tetsuji; Nakata, Eiji

2009-01-01

It is concerned that tunnels in the sedimentary rock are seriously damaged during the long operation after excavation, while there are various plans to construct significant underground facilities such as a high-level radioactive waste disposal facility. A case history study on tunnel instability is important in order to assess and evaluate tunnel instability behavior. In this respect, an accelerated tunnel deformation test by removing tunnel supports was conducted. Instability of tunnel wall was observed before and after this test in the summer, when it is warm and humid in the test tunnel. Fiber optic sensing detected the instability. Scale of collapsed rock was evaluated from the variation of shape of tunnel cross-section measured by a 3-D lazar measurement tool. The maximum size of collapsed rock block is 1m in diameter. Surrounding sandstone has such a characteristic that crack growth is much faster and its strength decreases gradually in the condition of high relative humidity. Numerical simulation considering this decrease of rock strength reproduced the instable zone around the test tunnel. (author)

Tip preparation for usage in an ultra-low temperature UHV scanning tunneling microscope

Directory of Open Access Journals (Sweden)

S. Ernst, S. Wirth, M. Rams, V. Dolocan and F. Steglich

2007-01-01

Full Text Available This work deals with the preparation and characterization of tungsten tips for the use in UHV low-temperature scanning tunneling microscopy and spectroscopy (STM and STS, respectively. These specific environments require in situ facilities for tip conditioning, for further sharpening of the tips, as well as for reliable tip characterization. The implemented conditioning methods include direct resistive annealing, annealing by electron bombardment, and self-sputtering with noble gas ions. Moreover, results from in situ tip characterization by field emission and STM experiments were compared to ex situ scanning electron microscopy. Using the so-prepared tips, high resolution STM images and tunneling spectra were obtained in a temperature range from ambient down to 350 mK, partially with applied magnetic field, on a variety of materials.

The role of local tunneling states in superconductivity at disordered interfaces

International Nuclear Information System (INIS)

Nguyen, B.D.; Simanek, E.

1982-01-01

The origin of the enhancement of the superconducting transition temperature caused by the presence of disordered interfaces is studied. An enhancement mechanism involving the tunneling of the conduction electrons from metal into the local state coupled to the ''two-level state systems'' in the interfaces region, is considered. In this model, the reduction of the tunneling matrix elements by orthogonality blocking can be avoided. (author)

Spin-dependent tunnelling in magnetic tunnel junctions

International Nuclear Information System (INIS)

Tsymbal, Evgeny Y; Mryasov, Oleg N; LeClair, Patrick R

2003-01-01

The phenomenon of electron tunnelling has been known since the advent of quantum mechanics, but continues to enrich our understanding of many fields of physics, as well as creating sub-fields on its own. Spin-dependent tunnelling (SDT) in magnetic tunnel junctions (MTJs) has recently aroused enormous interest and has developed in a vigorous field of research. The large tunnelling magnetoresistance (TMR) observed in MTJs garnered much attention due to possible applications in non-volatile random-access memories and next-generation magnetic field sensors. This led to a number of fundamental questions regarding the phenomenon of SDT. In this review article we present an overview of this field of research. We discuss various factors that control the spin polarization and magnetoresistance in MTJs. Starting from early experiments on SDT and their interpretation, we consider thereafter recent experiments and models which highlight the role of the electronic structure of the ferromagnets, the insulating layer, and the ferromagnet/insulator interfaces. We also discuss the role of disorder in the barrier and in the ferromagnetic electrodes and their influence on TMR. (topical review)

Hybrid tunnel junction contacts to III–nitride light-emitting diodes

KAUST Repository

Young, Erin C.; Yonkee, Benjamin P.; Wu, Feng; Oh, Sang Ho; DenBaars, Steven P.; Nakamura, Shuji; Speck, James S.

2016-01-01

In this work, we demonstrate highly doped GaN p–n tunnel junction (TJ) contacts on III–nitride heterostructures where the active region of the device and the top p-GaN layers were grown by metal organic chemical vapor deposition and highly doped n-GaN was grown by NH3 molecular beam epitaxy to form the TJ. The regrowth interface in these hybrid devices was found to have a high concentration of oxygen, which likely enhanced tunneling through the diode. For optimized regrowth, the best tunnel junction device had a total differential resistivity of 1.5 × 10−4 Ω cm2, including contact resistance. As a demonstration, a blue-light-emitting diode on a ($20\\bar{2}\\bar{1}$) GaN substrate with a hybrid tunnel junction and an n-GaN current spreading layer was fabricated and compared with a reference sample with a transparent conducting oxide (TCO) layer. The tunnel junction LED showed a lower forward operating voltage and a higher efficiency at a low current density than the TCO LED.

Hybrid tunnel junction contacts to III–nitride light-emitting diodes

KAUST Repository

Young, Erin C.

2016-01-26

In this work, we demonstrate highly doped GaN p–n tunnel junction (TJ) contacts on III–nitride heterostructures where the active region of the device and the top p-GaN layers were grown by metal organic chemical vapor deposition and highly doped n-GaN was grown by NH3 molecular beam epitaxy to form the TJ. The regrowth interface in these hybrid devices was found to have a high concentration of oxygen, which likely enhanced tunneling through the diode. For optimized regrowth, the best tunnel junction device had a total differential resistivity of 1.5 × 10−4 Ω cm2, including contact resistance. As a demonstration, a blue-light-emitting diode on a ($20\\\\bar{2}\\\\bar{1}$) GaN substrate with a hybrid tunnel junction and an n-GaN current spreading layer was fabricated and compared with a reference sample with a transparent conducting oxide (TCO) layer. The tunnel junction LED showed a lower forward operating voltage and a higher efficiency at a low current density than the TCO LED.

Tunneling Splittings in Vibronic Structure of CH_3F^+ ( X^2E): Studied by High Resolution Photoelectron Spectra and AB Initio Theoretical Method

Science.gov (United States)

Mo, Yuxiang; Gao, Shuming; Dai, Zuyang; Li, Hua

2013-06-01

We report a combined experimental and theoretical study on the vibronic structure of CH_3F^+. The results show that the tunneling splittings of vibrational energy levels occur in CH_3F^+ due to the Jahn-Teller effect. Experimentally, we have measured a high resolution ZEKE spectrum of CH_3F up to 3500 cm^-^1 above the ground state. Theoretically, we performed an ab initio calculation based on the diabatic model. The adiabatic potential energy surfaces (APES) of CH_3F^+ have been calculated at the MRCI/CAS/avq(t)z level and expressed by Taylor expansions with normal coordinates as variables. The energy gradients for the lower and upper APES, the derivative couplings between them and also the energies of the APES have been used to determine the coefficients in the Taylor expansion. The spin-vibronic energy levels have been calculated by accounting all six vibrational modes and their couplings. The experimental ZEKE spectra were assigned based on the theoretical calculations. W. Domcke, D. R. Yarkony, and H. Köpple (Eds.), Conical Intersections: Eletronic Structure, Dynamics and Spectroscopy (World Scientific, Singapore, 2004). M. S. Schuurman, D. E. Weinberg, and D. R. Yarkony, J. Chem. Phys. 127, 104309 (2007).

On the time-averaging of ultrafine particle number size spectra in vehicular plumes

Directory of Open Access Journals (Sweden)

X. H. Yao

2006-01-01

Full Text Available Ultrafine vehicular particle (<100 nm number size distributions presented in the literature are mostly averages of long scan-time (~30 s or more spectra mainly due to the non-availability of commercial instruments that can measure particle distributions in the <10 nm to 100 nm range faster than 30 s even though individual researchers have built faster (1–2.5 s scanning instruments. With the introduction of the Engine Exhaust Particle Sizer (EEPS in 2004, high time-resolution (1 full 32-channel spectrum per second particle size distribution data become possible and allow atmospheric researchers to study the characteristics of ultrafine vehicular particles in rapidly and perhaps randomly varying high concentration environments such as roadside, on-road and tunnel. In this study, particle size distributions in these environments were found to vary as rapidly as one second frequently. This poses the question on the generality of using averages of long scan-time spectra for dynamic and/or mechanistic studies in rapidly and perhaps randomly varying high concentration environments. One-second EEPS data taken at roadside, on roads and in tunnels by a mobile platform are time-averaged to yield 5, 10, 30 and 120 s distributions to answer this question.

Charge transport model in nanodielectric composites based on quantum tunneling mechanism and dual-level traps

Energy Technology Data Exchange (ETDEWEB)

Li, Guochang; Chen, George, E-mail: gc@ecs.soton.ac.uk, E-mail: sli@mail.xjtu.edu.cn [State Key Laboratory of Electrical Insulation and Power Equipment, Xi' an Jiaotong University, Xi' an 710049 (China); School of Electronic and Computer Science, University of Southampton, Southampton SO17 1BJ (United Kingdom); Li, Shengtao, E-mail: gc@ecs.soton.ac.uk, E-mail: sli@mail.xjtu.edu.cn [State Key Laboratory of Electrical Insulation and Power Equipment, Xi' an Jiaotong University, Xi' an 710049 (China)

2016-08-08

Charge transport properties in nanodielectrics present different tendencies for different loading concentrations. The exact mechanisms that are responsible for charge transport in nanodielectrics are not detailed, especially for high loading concentration. A charge transport model in nanodielectrics has been proposed based on quantum tunneling mechanism and dual-level traps. In the model, the thermally assisted hopping (TAH) process for the shallow traps and the tunnelling process for the deep traps are considered. For different loading concentrations, the dominant charge transport mechanisms are different. The quantum tunneling mechanism plays a major role in determining the charge conduction in nanodielectrics with high loading concentrations. While for low loading concentrations, the thermal hopping mechanism will dominate the charge conduction process. The model can explain the observed conductivity property in nanodielectrics with different loading concentrations.

Electron Tunneling in Junctions Doped with Semiconductors and Metals.

Science.gov (United States)

Bell, Lloyd Douglas, II

In this study, tunnel junctions incorporating thin layers of semiconductors and metals have been analyzed. Inelastic electron tunneling spectroscopy (IETS) was employed to yield high-resolution vibrational spectra of surface species deposited at the oxide-M_2 interface of M_1-M_1O _{rm x}-M _2 tunneling samples. Analysis was also performed on the elastic component of the tunneling current, yielding information on the tunnel barrier shape. The samples in this research exhibit a wide range of behavior. The IETS for Si, SiO_2, and Ge doped samples show direct evidence of SiH _{rm x} and GeH_ {rm x} formation. The particular species formed is shown to depend on the form of the evaporated dopant. Samples were also made with organic dopants deposited over the evaporated dopants. Many such samples show marked effects of the evaporated dopants on the inelastic peak intensities of the organic dopants. These alterations are correlated with the changed reactivity of the oxide surface coupled with a change in the OH dipole layer density on the oxide. Thicker organic dopant layers cause large changes in the elastic tunneling barrier due to OH layer alterations or the low barrier attributes of the evaporated dopant. In the cases of the thicker layers an extra current-carrying mechanism is shown to be contributing. Electron ejection from charge traps is proposed as an explanation for this extra current. The trend of barrier shape with dopant thickness is examined. Many of these dopants also produce a voltage-induced shift in the barrier shape which is stable at low temperature but relaxes at high temperature. This effect is similar to that produced by certain organic dopants and is explained by metastable bond formation between the surface OH and dopant. Other dopants, such as Al, Mg, and Fe, produce different effects. These dopants cause large I-V nonlinearity at low voltages. This nonlinearity is modeled as a giant zero-bias anomaly (ZBA) and fits are presented which show good

Quantum measurement of coherent tunneling between quantum dots

International Nuclear Information System (INIS)

Wiseman, H. M.; Utami, Dian Wahyu; Sun, He Bi; Milburn, G. J.; Kane, B. E.; Dzurak, A.; Clark, R. G.

2001-01-01

We describe the conditional and unconditional dynamics of two coupled quantum dots when one dot is subjected to a measurement of its occupation number by coupling it to a third readout dot via the Coulomb interaction. The readout dot is coupled to source and drain leads under weak bias, and a tunnel current flows through a single bound state when energetically allowed. The occupation of the quantum dot near the readout dot shifts the bound state of the readout dot from a low conducting state to a high conducting state. The measurement is made by continuously monitoring the tunnel current through the readout dot. We show that there is a difference between the time scale for the measurement-induced decoherence between the localized states of the dots, and the time scale on which the system becomes localized due to the measurement

Thermal stability analysis of thin film Ni-NiOx-Cr tunnel junctions

International Nuclear Information System (INIS)

Krishnan, S.; Emirov, Y.; Bhansali, S.; Stefanakos, E.; Goswami, Y.

2010-01-01

This research reports on the thermal stability of Ni-NiO x -Cr based Metal-Insulator-Metal (MIM) junction. Effect of annealing (250 to 400 o C) on the electrical and physical transport properties of this MIM stack was understood to determine the thermal budget allowable when using these diodes. MIM tunnel junctions were fabricated by sputtering and the NiO x was formed through reactive sputtering. The performance of the tunnel junctions after exposure to elevated temperatures was investigated using current-voltage measurements. This was correlated to the structural properties of the interfaces at different temperatures, characterized by Atomic Force Microscopy, X-ray Diffraction and Transmission Electron Microscopy (TEM). MIM tunnel junctions annealed up to 350 o C demonstrated satisfactory current-voltage characteristics and sensitivity. MIM junctions exhibited improved electrical performance as they were heated to 250 o C (sensitivity of 42 V -1 and a zero-bias resistance of ∼300 Ω) due to improved crystallization of the layers within the stack. At temperatures over 350 o C, TEM and Energy Dispersive Spectra confirmed a breakdown of the MIM structure due to interdiffusion.

Electron tunneling and the energy gap in Bi2Sr2CaCu2O/sub x/

International Nuclear Information System (INIS)

Lee, M.; Mitzi, D.B.; Kapitulnik, A.; Beasley, M.R.

1989-01-01

Results of electron tunneling on single crystals of the Bi 2 Sr 2 CaCu 2 O/sub x/ superconductor are reported. The junctions show a gap structure with Δ≅25 meV, whose temperature dependence exhibits a qualitatively Bardeen-Cooper-Schrieffer-like behavior with a gap-closing T/sub c/≅81--85 K. Comparisons of these tunneling spectra to those obtained on YBa 2 Cu 3 O/sub 7-//sub x/ are made. Evidence that 2Δ/kT/sub c/∼7 for both Ba 2 Sr 2 CaCu 2 O/sub x/ and YBa 2 Cu 3 O/sub 7-//sub x/ is also discussed

The possibility to determine a constant of spin-orbit interaction by scanning tunneling microscopy method

International Nuclear Information System (INIS)

Khotkevich, N.V.; Kolesnichenko, Yu.A.; Vovk, N.P.

2016-01-01

The electron tunneling from the quasi-two-dimensional (surface) states with the spin-orbit interaction into bulk-mode states is studied in the framework of a model of an infinitely thin inhomogeneous tunnel magnetic barrier. The influence of the scattering of quasi-two-dimensional electrons by a single magnetic defect on the tunnel current is analyzed. Analytic formulas for the conductance of a tunnel point-contact as a function of its distance from the defect are obtained. It is shown that the analysis of the local magnetization density around the defect by means of spin-polarized scanning tunneling microscopy allows finding the constant of spin orbit interaction.

Scanning tunneling microscopy/spectroscopy on multi-layered cuprate superconductor Ba2Ca5Cu6O12 (O1-x Fx)2

International Nuclear Information System (INIS)

Sugimoto, A.; Shohara, K.; Ekino, T.; Watanabe, Y.; Harada, Y.; Mikusu, S.; Tokiwa, K.; Watanabe, T.

2009-01-01

Scanning tunneling microscopy/spectroscopy (STM/STS) measurements on multi-layered cuprate superconductor Ba 2 Ca 5 Cu 6 O 12 (O 1-x F x ) 2 are carried out. STM topographies show randomly distributed bright spot structures with a typical spot size of ∼0.8 nm. These bright spots are occupied about 28% per one unit cell of c-plane, which is comparable to the regular amount of apical oxygen of 20% obtained from element analysis. Tunneling spectra simultaneously show both the small and the large gap structures. These gap sizes at 4.9 K are about Δ ∼15 meV and ∼90 meV, respectively. The small gap structure disappears at the temperature close to T C , while the large gap persists up to ∼200 K. Therefore, these features correspond to the superconducting gap and pseudogap, respectively. These facts give evidence for some ordered state with large energy scale even in the superconducting state. For the superconducting gap, the ratio of 2Δ/K B T C = 4.9 is obtained with T C = 70 K, which is determined from temperature dependence of the tunneling spectra.

Experimental hydraulic analysis in conduction tunnels at the trunk section working as a channel considering compound roughness; Analisis hidraulico experimental en tuneles de conduccion en seccion baul trabajando como canal, considerando rugosidades compuestas

Energy Technology Data Exchange (ETDEWEB)

Marengo-Mogollon, Humberto; Cortes-Cortes, Carlos [Comision Federal de Electricidad (Mexico); Arreguin-Cortes, Felipe I [Comision Nacional del Agua (Mexico)

2008-01-15

This paper presents the roughness coefficients of a conduction tunnel at the trunk section working as a channel obtained experimentally using a hydraulic model of the diversion tunnel of the Hydroelectric Project called El Cajon (Mexico). A comparative analysis between experimental and theoretical coefficients obtained in the literature is shown. [Spanish] Se presentan los coeficientes de rugosidad compuesta de un tunel de conduccion en seccion baul trabajando como canal obtenidos en forma experimental en un modelo hidraulico del tunel de desvio del Proyecto Hidroelectrico El Cajon (Mexico). Se muestra un analisis comparativo entre los coeficientes experimentales y los teoricos obtenidos en la literatura.

Tunnel fire dynamics

CERN Document Server

Ingason, Haukur; Lönnermark, Anders

2015-01-01

This book covers a wide range of issues in fire safety engineering in tunnels, describes the phenomena related to tunnel fire dynamics, presents state-of-the-art research, and gives detailed solutions to these major issues. Examples for calculations are provided. The aim is to significantly improve the understanding of fire safety engineering in tunnels. Chapters on fuel and ventilation control, combustion products, gas temperatures, heat fluxes, smoke stratification, visibility, tenability, design fire curves, heat release, fire suppression and detection, CFD modeling, and scaling techniques all equip readers to create their own fire safety plans for tunnels. This book should be purchased by any engineer or public official with responsibility for tunnels. It would also be of interest to many fire protection engineers as an application of evolving technical principles of fire safety.

Proton tunneling in solids

Energy Technology Data Exchange (ETDEWEB)

Kondo, J.

1998-10-01

The tunneling rate of the proton and its isotopes between interstitial sites in solids is studied theoretically. The phonons and/or the electrons in the solid have two effects on the tunneling phenomenon. First, they suppress the transfer integral between two neighbouring states. Second, they give rise to a finite lifetime of the proton state. Usually the second effect is large and the tunneling probability per unit time (tunneling rate) can be defined. In some cases, however, a coherent tunneling is expected and actually observed. (author)

Proton tunneling in solids

International Nuclear Information System (INIS)

Kondo, J.

1998-01-01

The tunneling rate of the proton and its isotopes between interstitial sites in solids is studied theoretically. The phonons and/or the electrons in the solid have two effects on the tunneling phenomenon. First, they suppress the transfer integral between two neighbouring states. Second, they give rise to a finite lifetime of the proton state. Usually the second effect is large and the tunneling probability per unit time (tunneling rate) can be defined. In some cases, however, a coherent tunneling is expected and actually observed. (author)

Apparent Barrier Height in Scanning Tunneling Microscopy Revisited

DEFF Research Database (Denmark)

Olesen, L.; Brandbyge, Mads; Sørensen, Mads Reinholdt

1996-01-01

The apparent barrier height phi(ap), that is, the rate of change of the logarithm of the conductance with tip-sample separation in a scanning tunneling microscope (STM), has been measured for Ni, Pt, and Au single crystal surfaces. The results show that phi(ap) is constant until point contact...... is reached rather than decreasing at small tunneling gap distances, as previously reported. The findings for phi(ap) can be accounted for theoretically by including the relaxations of the tip-surface junction in an STM due to the strong adhesive forces at close proximity. These relaxation effects are shown...

Multiband corrections for the semi-classical simulation of interband tunneling in GaAs tunnel junctions

Science.gov (United States)

Louarn, K.; Claveau, Y.; Hapiuk, D.; Fontaine, C.; Arnoult, A.; Taliercio, T.; Licitra, C.; Piquemal, F.; Bounouh, A.; Cavassilas, N.; Almuneau, G.

2017-09-01

The aim of this study is to investigate the impact of multiband corrections on the current density in GaAs tunnel junctions (TJs) calculated with a refined yet simple semi-classical interband tunneling model (SCITM). The non-parabolicity of the considered bands and the spin-orbit effects are considered by using a recently revisited SCITM available in the literature. The model is confronted to experimental results from a series of molecular beam epitaxy grown GaAs TJs and to numerical results obtained with a full quantum model based on the non-equilibrium Green’s function formalism and a 6-band k.p Hamiltonian. We emphasize the importance of considering the non-parabolicity of the conduction band by two different measurements of the energy-dependent electron effective mass in N-doped GaAs. We also propose an innovative method to compute the non-uniform electric field in the TJ for the SCITM simulations, which is of prime importance for a successful operation of the model. We demonstrate that, when considering the multiband corrections and this new computation of the non-uniform electric field, the SCITM succeeds in predicting the electrical characteristics of GaAs TJs, and are also in agreement with the quantum model. Besides the fundamental study of the tunneling phenomenon in TJs, the main benefit of this SCITM is that it can be easily embedded into drift-diffusion software, which are the most widely-used simulation tools for electronic and opto-electronic devices such as multi-junction solar cells, tunnel field-effect transistors, or vertical-cavity surface-emitting lasers.

Fluctuation Dominated Josephson Tunneling with a Scanning Tunneling Microscope

International Nuclear Information System (INIS)

Naaman, O.; Teizer, W.; Dynes, R. C.

2001-01-01

We demonstrate Josephson tunneling in vacuum tunnel junctions formed between a superconducting scanning tunneling microscope tip and a Pb film, for junction resistances in the range 50--300 k Omega. We show that the superconducting phase dynamics is dominated by thermal fluctuations, and that the Josephson current appears as a peak centered at small finite voltage. In the presence of microwave fields (f=15.0 GHz) the peak decreases in magnitude and shifts to higher voltages with increasing rf power, in agreement with theory

Device-quality tunnel junctions on the high Tc superconductor HgBa2CuO4+δ

International Nuclear Information System (INIS)

Zasadzinski, J.; Chen, J.; Romano, P.; Gray, K.E.; Wagner, J.L.; Hinks, D.G.

1995-01-01

SIN and SIS tunnel junction devices (e.g. photon detectors, logic elements) require quasiparticle characteristics that exhibit sharp current onsets at the gap voltage and very low sub-gap conductances. Progress is reported on the development of such junctions on High Tc cuprates using mechanical point contacts. In general, these contacts display the optimum characteristics that can be obtained from HTS native-surface tunnel barriers. Most cuprates display a sub-gap conductance which monotonically increases with voltage about the minimum value at zero bias. However, tunneling data of unusually high quality have been obtained for the recently discovered Hg-based cuprate, HgBa 2 CuO 4 (T c =96K). SIS' tunneling data using a Nb tip are presented which exhibit very low and flat sub-gap conductances and sharp conductance peaks as expected from a BCS density of states. These results are slightly improved over earlier published results with SIN junctions. Use of the experimental data to simulate the performance of a quasiparticle mixer demonstrates that noise temperatures approaching the quantum limit are possible for SIS and SIN mixers in the range 1-5 THz

In-vehicle nitrogen dioxide concentrations in road tunnels

Science.gov (United States)

Martin, Ashley N.; Boulter, Paul G.; Roddis, Damon; McDonough, Liza; Patterson, Michael; Rodriguez del Barco, Marina; Mattes, Andrew; Knibbs, Luke D.

2016-11-01

There is a lack of knowledge regarding in-vehicle concentrations of nitrogen dioxide (NO2) during transit through road tunnels in urban environments. Furthermore, previous studies have tended to involve a single vehicle and the range of in-vehicle NO2 concentrations that vehicle occupants may be exposed to is not well defined. This study describes simultaneous measurements of in-vehicle and outside-vehicle NO2 concentrations on a route through Sydney, Australia that included several major tunnels, minor tunnels and busy surface roads. Tests were conducted on nine passenger vehicles to assess how vehicle characteristics and ventilation settings affected in-vehicle NO2 concentrations and the in-vehicle-to-outside vehicle (I/O) concentration ratio. NO2 was measured directly using a cavity attenuated phase shift (CAPS) technique that gave a high temporal and spatial resolution. In the major tunnels, transit-average in-vehicle NO2 concentrations were lower than outside-vehicle concentrations for all vehicles with cabin air recirculation either on or off. However, markedly lower I/O ratios were obtained with recirculation on (0.08-0.36), suggesting that vehicle occupants can significantly lower their exposure to NO2 in tunnels by switching recirculation on. The highest mean I/O ratios for NO2 were measured in older vehicles (0.35-0.36), which is attributed to older vehicles having higher air exchange rates. The results from this study can be used to inform the design and operation of future road tunnels and modelling of personal exposure to NO2.

Dynamic Tunnel Usability Study: Format Recommendations for Synthetic Vision System Primary Flight Displays

Science.gov (United States)

Arthur, Jarvis J., III; Prinzel, Lawrence J., III; Kramer, Lynda J.; Bailey, Randall E.

2006-01-01

A usability study evaluating dynamic tunnel concepts has been completed under the Aviation Safety and Security Program, Synthetic Vision Systems Project. The usability study was conducted in the Visual Imaging Simulator for Transport Aircraft Systems (VISTAS) III simulator in the form of questionnaires and pilot-in-the-loop simulation sessions. Twelve commercial pilots participated in the study to determine their preferences via paired comparisons and subjective rankings regarding the color, line thickness and sensitivity of the dynamic tunnel. The results of the study showed that color was not significant in pilot preference paired comparisons or in pilot rankings. Line thickness was significant for both pilot preference paired comparisons and in pilot rankings. The preferred line/halo thickness combination was a line width of 3 pixels and a halo of 4 pixels. Finally, pilots were asked their preference for the current dynamic tunnel compared to a less sensitive dynamic tunnel. The current dynamic tunnel constantly gives feedback to the pilot with regard to path error while the less sensitive tunnel only changes as the path error approaches the edges of the tunnel. The tunnel sensitivity comparison results were not statistically significant.

The ISI Tunnel

Science.gov (United States)

1993-10-01

DP /etc/tunnelvisa p zephyr dark -star TCP /etc/tunnelvisa p zephyr dak’star ICMP /etc/tunnelvisa p zephyr quark MDP /etc/tunnelvisa p zephyr quark ...drax-net-yp 128.9.32.2 1 route add quark -net-yp 128.9.32.3 1 route add vlsi-net-yp 128.9.32.4 1 route add darkstar-net-yp 128.9.32.3 1 route add rocky...TCP /etc/tunnel-visa p zephyr quark ICMP /etc/tunnel-visa p zephyr drax tTI)P /etc/tunnel-visa p zephyr drax TCP /etc/tunnel_visa p zephyr drax ICMP

Tunneling Conductance in Two-Dimensional Junctions between a Normal Metal and a Ferromagnetic Rashba Metal

Science.gov (United States)

Oshima, Daisuke; Taguchi, Katsuhisa; Tanaka, Yukio

2018-03-01

We have studied charge transport in a ferromagnetic Rashba metal (FRM), where both Rashba type spin-orbit coupling (RSOC) and exchange coupling coexist. It has nontrivial metallic states, i.e., a normal Rashba metal (NRM), anomalous Rashba metal (ARM), and Rashba ring metal (RRM), and they are manipulated by tuning the Fermi level with an applied gate voltage. We theoretically studied the tunneling conductance (G) in a normal metal/FRM junction by changing the Fermi level via an applied gate voltage (Vg) on the FRM. We found a wide variation in the Vg dependence of G, which depends on the metallic states. In an NRM, the Vg dependence of G is the same as that in a conventional two-dimensional system. However, in an ARM, the Vg dependence of G is similar to that in a conventional one- (two-)dimensional system for a large (small) RSOC. Furthermore, in an RRM, which is generated by a large RSOC, the Vg dependence of G is similar to that in the one-dimensional system. In addition, these anomalous properties stem from the density of states in the ARM and RRM caused by the large RSOC and exchange coupling rather than the spin-momentum locking of RSOC.

Resonant tunnel magnetoresistance in a double magnetic tunnel junction

KAUST Repository

Useinov, Arthur; Useinov, Niazbeck Kh H; Tagirov, Lenar R.; Kosel, Jü rgen

2011-01-01

We present quasi-classical approach to calculate a spin-dependent current and tunnel magnetoresistance (TMR) in double magnetic tunnel junctions (DMTJ) FML/I/FMW/I/FMR, where the magnetization of the middle ferromagnetic metal layer FMW can

Tunneling magnetoresistance in junctions composed of ferromagnets and time-reversal invariant topological superconductors

International Nuclear Information System (INIS)

Yan, Zhongbo; Wan, Shaolong

2016-01-01

Tunneling magnetoresistance between two ferrromagnets is an issue of fundamental importance in spintronics. In this work, we show that tunneling magnetoresistance can also emerge in junctions composed of ferromagnets and time-reversal invariant topological superconductors without spin-rotation symmetry. Here the physical origin is that when the spin-polarization direction of an injected electron from the ferromagnet lies in the same plane of the spin-polarization direction of Majorana zero modes, the electron will undergo a perfect spin-equal Andreev reflection, while injected electrons with other spin-polarization directions will be partially Andreev reflected and partially normal reflected, which consequently has a lower conductance, and therefore, the magnetoresistance effect emerges. Compared to conventional magnetic tunnel junctions, an unprecedented advantage of the junctions studied here is that arbitrary high tunneling magnetoresistance can be obtained even when the magnetization of the ferromagnets are weak and the insulating tunneling barriers are featureless. Our findings provide a new fascinating mechanism to obtain high tunneling magnetoresistance. (paper)

Tunneling through landsliding zone; Jisuberi chitainai no tunnel seko

Energy Technology Data Exchange (ETDEWEB)

Konbu, A; Hatabu, K; Kano, T [Tekken Corp., Tokyo (Japan)

1994-08-01

At the new tunnel construction site of the Shirakata tunnel on the Obama line in Yamaguchi Prefecture, a landsliding occurred at about 60 meters to the upper portion obliquely to the right hand side of the shaft when the excavation progressed to about 10 meters from the starting side. The landslide caused displacement at the shaft opening and change in the supports. As a result of the re-investigation, it was confirmed that the slide face went through the tunnel cross section. The measures taken were removal of the upper soil and an adoption of the all ground fastening (AGF) method (injection type long tip fastening method) as an auxiliary construction to stop loosening of the natural ground associated with the tunnel excavation. The result was a completion of tunneling the landsliding zone without a problem. This paper reports the AGF method adopted in the above construction, together with the construction works and natural ground conditions. The AGF method is about the same as the pipe roof method with regard to the natural ground accepting mechanism and the materials used. The difference is building an improved body in a limited area in the natural ground around the steel pipes by injecting the fixing material. The use of this method caused no problems in subsidence and displacement in the surrounding ground, and completed the tunneling construction without an unusual event. 1 ref., 7 figs., 2 tabs.

Numerical modeling of time-dependent deformation and induced stresses in concrete pipes constructed in Queenston shale using micro-tunneling technique

Directory of Open Access Journals (Sweden)

Hayder Mohammed Salim Al-Maamori

2018-04-01

Full Text Available Effects of time-dependent deformation (TDD on a tunnel constructed using the micro-tunneling technique in Queenston shale (QS are investigated employing the finite element method. The TDD and strength parameters of the QS were measured from tests conducted on QS specimens soaked in water and lubricant fluids (LFs used in micro-tunneling such as bentonite and polymer solutions. The numerical model was verified using the results of TDD tests performed on QS samples, field measurements of some documented projects, and the closed-form solutions to circular tunnels in swelling rock. The verified model was then employed to conduct a parametric study considering important micro-tunneling design parameters, such as depth and diameter of the tunnel, in situ stress ratio (Ko, and the time lapse prior to replacing LFs with permanent cement grout around the tunnel. It was revealed that the time lapse plays a vital role in controlling deformations and associated stresses developed in the tunnel lining. The critical case of a pipe or tunnel in which the maximum tensile stress develops at its springline occurs when it is constructed at shallow depths in the QS layer. The results of the parametric study were used to suggest recommendations for the construction of tunnels in QS employing micro-tunneling. Keywords: Numerical model, Micro-tunneling, Queenston shale (QS, Lubricant fluids (LFs

A Historical Evaluation of the U12n Tunnel, Nevada National Security Site, Nye County, Nevada Part 1

Energy Technology Data Exchange (ETDEWEB)

Drollinger, Harold [DRI; Jones, Robert C [DRI; Bullard, Thomas F [DRI; Ashbaugh, Laurence J [DRI; Griffin, Wayne R [DRI

2011-06-01

This report presents a historical evaluation of the U12n Tunnel on the Nevada National Security Site (NNSS) in southern Nevada. The work was conducted by the Desert Research Institute at the request of the U.S. Department of Energy, National Nuclear Security Administration Nevada Site Office and the U.S. Department of Defense, Defense Threat Reduction Agency (DTRA). The U12n Tunnel was one of a series of tunnels used for underground nuclear weapons effects tests in Rainier and Aqueduct Mesas. A total of 22 nuclear tests were conducted in the U12n Tunnel from 1967 to 1992. These tests include Midi Mist, Hudson Seal, Diana Mist, Misty North, Husky Ace, Ming Blade, Hybla Fair, Mighty Epic, Diablo Hawk, Miners Iron, Huron Landing, Diamond Ace, Mini Jade, Tomme/Midnight Zephyr, Misty Rain, Mill Yard, Diamond Beech, Middle Note, Misty Echo, Mineral Quarry, Randsburg, and Hunters Trophy. DTRA sponsored all tests except Tomme and Randsburg which were sponsored by the Lawrence Livermore National Laboratory. Midnight Zephyr, sponsored by DTRA, was an add on experiment to the Tomme test. Eleven high explosive tests were also conducted in the tunnel and included a Stemming Plan Test, the Pre-Mill Yard test, the two seismic Non-Proliferation Experiment tests, and seven Dipole Hail tests. The U12n Tunnel complex is composed of the portal and mesa areas, encompassing a total area of approximately 600 acres (240 hectares). Major modifications to the landscape have resulted from four principal activities. These are road construction and maintenance, mining activities related to development of the tunnel complex, site preparation for activities related to testing, and construction of retention ponds. A total of 202 cultural features were recorded for the portal and mesa areas. At the portal area, features relate to the mining, construction, testing, and general everyday operational support activities within the tunnel. These include concrete foundations for buildings, ventilation

Magnetoresistance of galfenol-based magnetic tunnel junction

Energy Technology Data Exchange (ETDEWEB)

Gobaut, B., E-mail: benoit.gobaut@elettra.eu [Sincrotrone Trieste S.C.p.A., S.S. 14 Km 163.5, Area Science Park, 34149 Trieste (Italy); Vinai, G.; Castán-Guerrero, C.; Krizmancic, D.; Panaccione, G.; Torelli, P. [Laboratorio TASC, IOM-CNR, S.S. 14km 163.5, Basovizza, 34149 Trieste (Italy); Rafaqat, H. [Laboratorio TASC, IOM-CNR, S.S. 14km 163.5, Basovizza, 34149 Trieste (Italy); ICTP, Trieste (Italy); Roddaro, S. [Laboratorio TASC, IOM-CNR, S.S. 14km 163.5, Basovizza, 34149 Trieste (Italy); NEST, Scuola Normale Superiore and Istituto Nanoscienze-CNR, Piazza S. Silvestro 12, 56127 Pisa (Italy); Rossi, G. [Laboratorio TASC, IOM-CNR, S.S. 14km 163.5, Basovizza, 34149 Trieste (Italy); Dipartimento di Fisica, Università di Milano, via Celoria 16, 20133 Milano (Italy); Eddrief, M.; Marangolo, M. [Sorbonne Universités, UPMC Paris 06, CNRS-UMR 7588, Institut des Nanosciences de Paris, 75005, Paris (France)

2015-12-15

The manipulation of ferromagnetic layer magnetization via electrical pulse is driving an intense research due to the important applications that this result will have on memory devices and sensors. In this study we realized a magnetotunnel junction in which one layer is made of Galfenol (Fe{sub 1-x}Ga{sub x}) which possesses one of the highest magnetostrictive coefficient known. The multilayer stack has been grown by molecular beam epitaxy and e-beam evaporation. Optical lithography and physical etching have been combined to obtain 20x20 micron sized pillars. The obtained structures show tunneling conductivity across the junction and a tunnel magnetoresistance (TMR) effect of up to 11.5% in amplitude.

Resonant-enhanced spectroscopy of molecular rotations with a scanning tunneling microscope.

Science.gov (United States)

Natterer, Fabian Donat; Patthey, François; Brune, Harald

2014-07-22

We use rotational excitation spectroscopy with a scanning tunneling microscope to investigate the rotational properties of molecular hydrogen and its isotopes physisorbed on the surfaces of graphene and hexagonal boron nitride (h-BN), grown on Ni(111), Ru(0001), and Rh(111). The rotational excitation energies are in good agreement with ΔJ = 2 transitions of freely spinning p-H2 and o-D2 molecules. The variations of the spectral line shapes for H2 among the different surfaces can be traced back to a molecular resonance-mediated tunneling mechanism. Our data for H2/h-BN/Rh(111) suggest a local intrinsic gating on this surface due to lateral static dipoles. Spectra on a mixed monolayer of H2, HD, and D2 display all three J = 0 → 2 rotational transitions, irrespective of tip position, thus pointing to a multimolecule excitation, or molecular mobility in the physisorbed close-packed layer.

Phonon-assisted tunnelling in electrical conductivity of individual carbon nanotubes and networks ones

Energy Technology Data Exchange (ETDEWEB)

Pipinys, P. [Department of Physics, Vilnius Pedagogical University, Studentu 39, LT-08106 Vilnius (Lithuania)], E-mail: pipiniai@takas.lt; Kiveris, A. [Department of Physics, Vilnius Pedagogical University, Studentu 39, LT-08106 Vilnius (Lithuania)], E-mail: studsk@vpu.lt

2008-10-01

Current-voltage (I-V) characteristics of single-wall carbon nanotubes (SWCNT), measured in the low temperatures by Tang et al. [Science 292 (2001) 2462] and transparent SWCNT networks presented by Jaiswal et al. [J. Phys.: Condens. Matter 19 (2007) 446006], are reinterpreted in the framework of phonon-assisted tunnelling theory as a free charge carriers generation mechanism in the strong electrical field. The good fit of the temperature-dependent I-V data in low temperature region (i.e., T<25 K) has been achieved using the phonons of energy <1 meV.

Phonon-assisted tunnelling in electrical conductivity of individual carbon nanotubes and networks ones

International Nuclear Information System (INIS)

Pipinys, P.; Kiveris, A.

2008-01-01

Current-voltage (I-V) characteristics of single-wall carbon nanotubes (SWCNT), measured in the low temperatures by Tang et al. [Science 292 (2001) 2462] and transparent SWCNT networks presented by Jaiswal et al. [J. Phys.: Condens. Matter 19 (2007) 446006], are reinterpreted in the framework of phonon-assisted tunnelling theory as a free charge carriers generation mechanism in the strong electrical field. The good fit of the temperature-dependent I-V data in low temperature region (i.e., T<25 K) has been achieved using the phonons of energy <1 meV

Origin of the water drained by the tunnel Graton

International Nuclear Information System (INIS)

Plata B, A.

1992-12-01

The research of the origin of the water drained by the Graton tunnel was attempted using isotope techniques. During the period of studies (April 1989-October 1992), four field work was executed to sample waters for chemistry, stable isotope and Tritium analysis, an to inject tracers and verify the possible infiltration from the Rimac and Blanco rivers to the tunnel. The results of the stable isotope analysis show that the water drained by the Graton tunnel comes from a basin around 300 meters above the average altitude of the basin where the Graton is located. The Tritium analysis show that the water is relatively modern. Using the model of total mixing, the residence times of the water drained at the km 0.5 and 2.5 are in the order to 45 years. The conductivities of the water of the tunnel is higher than the Rimac river ones because the influence of mine water. The chemical analysis of the water sampled at the downstream end of the tunnel, show that the conservative ions of the water kept almost constant during more than two years. The results of the work with artificial tracer show that there is no significant leakage from the Rimac and Blanco rivers to the Graton tunnel. So far, it can be concluded as a preliminary approach that the Graton tunnel drains relatively modern water originated in another basin. The hydrodynamics of the area of study seems to include a large storage on underground water in the system. The topography, geology and isotopic composition of the water samples, points to the upper Mantaro river basin as the possible source of part of the water drained by the Graton tunnel. (authors). 20 p. 2 figs., 7 ills., 4 tabs

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

Energy Technology Data Exchange (ETDEWEB)

Zubkov, Evgeniy

2013-09-01

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

Measurement of discrete energy-level spectra in individual chemically synthesized gold nanoparticles

DEFF Research Database (Denmark)

Kuemmeth, Ferdinand; Bolotin, Kirill I; Shi, Su-Fei

2008-01-01

We form single-electron transistors from individual chemically synthesized gold nanoparticles, 5-15 nm in diameter, with monolayers of organic molecules serving as tunnel barriers. These devices allow us to measure the discrete electronic energy levels of individual gold nanoparticles that are......, by virtue of chemical synthesis, well-defined in their composition, size and shape. We show that the nanoparticles are nonmagnetic and have spectra in good accord with random-matrix-theory predictions taking into account strong spin-orbit coupling....

Measurement and statistical analysis of single-molecule current-voltage characteristics, transition voltage spectroscopy, and tunneling barrier height.

Science.gov (United States)

Guo, Shaoyin; Hihath, Joshua; Díez-Pérez, Ismael; Tao, Nongjian

2011-11-30

We report on the measurement and statistical study of thousands of current-voltage characteristics and transition voltage spectra (TVS) of single-molecule junctions with different contact geometries that are rapidly acquired using a new break junction method at room temperature. This capability allows one to obtain current-voltage, conductance voltage, and transition voltage histograms, thus adding a new dimension to the previous conductance histogram analysis at a fixed low-bias voltage for single molecules. This method confirms the low-bias conductance values of alkanedithiols and biphenyldithiol reported in literature. However, at high biases the current shows large nonlinearity and asymmetry, and TVS allows for the determination of a critically important parameter, the tunneling barrier height or energy level alignment between the molecule and the electrodes of single-molecule junctions. The energy level alignment is found to depend on the molecule and also on the contact geometry, revealing the role of contact geometry in both the contact resistance and energy level alignment of a molecular junction. Detailed statistical analysis further reveals that, despite the dependence of the energy level alignment on contact geometry, the variation in single-molecule conductance is primarily due to contact resistance rather than variations in the energy level alignment.

Temperature Dependent Electron Transport Properties of Gold Nanoparticles and Composites: Scanning Tunneling Spectroscopy Investigations.

Science.gov (United States)

Patil, Sumati; Datar, Suwarna; Dharmadhikari, C V

2018-03-01

Scanning tunneling spectroscopy (STS) is used for investigating variations in electronic properties of gold nanoparticles (AuNPs) and its composite with urethane-methacrylate comb polymer (UMCP) as function of temperature. Films are prepared by drop casting AuNPs and UMCP in desired manner on silicon substrates. Samples are further analyzed for morphology under scanning electron microscopy (SEM) and atomic force microscopy (AFM). STS measurements performed in temperature range of 33 °C to 142 °C show systematic variation in current versus voltage (I-V) curves, exhibiting semiconducting to metallic transition/Schottky behavior for different samples, depending upon preparation method and as function of temperature. During current versus time (I-t) measurement for AuNPs, random telegraphic noise is observed at room temperature. Random switching of tunneling current between two discrete levels is observed for this sample. Power spectra derived from I-t show 1/f2 dependence. Statistical analysis of fluctuations shows exponential behavior with time width τ ≈ 7 ms. Local density of states (LDOS) plots derived from I-V curves of each sample show systematic shift in valance/conduction band edge towards/away from Fermi level, with respect to increase in temperature. Schottky emission is best fitted electron emission mechanism for all samples over certain range of bias voltage. Schottky plots are used to calculate barrier heights and temperature dependent measurements helped in measuring activation energies for electron transport in all samples.

Development of the tunneling junction simulation environment for scanning tunneling microscope evaluation

International Nuclear Information System (INIS)

Gajewski, Krzysztof; Piasecki, Tomasz; Kopiec, Daniel; Gotszalk, Teodor

2017-01-01

Proper configuration of scanning tunneling microscope electronics plays an important role in the atomic scale resolution surface imaging. Device evaluation in the tunneling contact between scanning tip and sample may be prone to the surface quality or mechanical disturbances. Thus the use of tunneling junction simulator makes electronics testing more reliable and increases its repeatability. Here, we present the theoretical background enabling the proper selection of electronic components circuitry used as a tunneling junction simulator. We also show how to simulate mechanics related to the piezoelectric scanner, which is applied in real experiments. Practical use of the proposed simulator and its application in metrological characterization of the developed scanning tunneling microscope is also shown. (paper)

Tunneling current into the vortex lattice states of s-and p- wave superconductors

International Nuclear Information System (INIS)

Kowalewski, L.; Nogala, M.M.; Thomas, M.; Wojciechowski, R.J.

2000-01-01

The tunneling current between the metallic tip of a scanning microscope and s- and p-wave superconductors in quantizing magnetic field is investigated. The differential conductance is calculated both as a function of bias voltage at the centre of the vortex line and for varying position of the scanning tunneling microscope tip at a stable voltage. (author)

Fabrication of magnetic tunnel junctions with a single-crystalline LiF tunnel barrier

Science.gov (United States)

Krishna Narayananellore, Sai; Doko, Naoki; Matsuo, Norihiro; Saito, Hidekazu; Yuasa, Shinji

2018-04-01

We fabricated Fe/LiF/Fe magnetic tunnel junctions (MTJs) by molecular beam epitaxy on a MgO(001) substrate, where LiF is an insulating tunnel barrier with the same crystal structure as MgO (rock-salt type). Crystallographical studies such as transmission electron microscopy and nanobeam electron diffraction observations revealed that the LiF tunnel barrier is single-crystalline and has a LiF(001)[100] ∥ bottom Fe(001)[110] crystal orientation, which is constructed in the same manner as MgO(001) on Fe(001). Also, the in-plane lattice mismatch between the LiF tunnel barrier and the Fe bottom electrode was estimated to be small (about 0.5%). Despite such advantages for the tunnel barrier of the MTJ, the observed tunnel magnetoresistance (MR) ratio was low (˜6% at 20 K) and showed a significant decrease with increasing temperature (˜1% at room temperature). The results imply that indirect tunneling and/or thermally excited carriers in the LiF tunnel barrier, in which the current basically is not spin-polarized, play a major role in electrical transport in the MTJ.

Nb/NiCu bilayers in single and stacked superconductive tunnel junctions: preliminary results

International Nuclear Information System (INIS)

Pepe, G.P.; Ruotolo, A.; Parlato, L.; Peluso, G.; Ausanio, G.; Carapella, G.; Latempa, R.

2004-01-01

We present preliminary experimental results concerning both single and stacked tunnel junctions in which one of the electrodes was formed by a superconductor/ferromagnet (S/F) bi-layer. In particular, in the stacked configuration a Nb/NiCu bi-layer was used as the intermediate electrode, and it was probed by tunneling on both sides. Tunnel junctions have been characterized in terms of current-voltage characteristics (IVC), and differential conductance. Preliminary steady-state injection-detection measurements performed in the stacked devices at T=4.2 K are also presented and discussed

Development and Evaluation of Solar Tunnel Dryer for Commercial Fish Drying

Science.gov (United States)

Mohod, A. G.; Khandetod, Y. P.; Shrirame, H. Y.

2014-01-01

The local practice of drying fish in open sun drying poses problems such as high moisture content, uncontrolled drying and contamination. These problems can be avoided by proper use of improved methods such as the solar tunnel dryer, which results in faster drying of fish. The semi cylindrical walk-in type natural convection solar tunnel dryer, having drying area of 37.5 m2 was developed and evaluated for the drying of fish products in comparison with the conventional method of open sun drying. The experiments were conducted without fish and with fish to evaluate the performance of solar tunnel dryer. The average rise in temperature inside the solar tunnel dryer was found to be 11.24 °C and 18.29 °C over the ambient temperature during no load test in winter and summer respectively. The average 28 % saving in time was observed for selected fish drying using solar tunnel dryer over open sun drying method with average drying efficiency of 19 %. The economics was calculated for drying of prawns ( Parapaeneopsis stylifera) by solar tunnel dryer and open sun drying system on the basis of business as a whole. The economics of the solar tunnel dryer is presented in term of Net present worth, Benefit-Cost Ratio, Payback period, Profitability index and Internal rate of return. The pay back period for solar tunnel dryer was found to be 2.84 years.

Chloride Transport in Undersea Concrete Tunnel

Directory of Open Access Journals (Sweden)

Yuanzhu Zhang

2016-01-01

Full Text Available Based on water penetration in unsaturated concrete of underwater tunnel, a diffusion-advection theoretical model of chloride in undersea concrete tunnel was proposed. The basic parameters including porosity, saturated hydraulic conductivity, chloride diffusion coefficient, initial water saturation, and moisture retention function of concrete specimens with two water-binder ratios were determined through lab-scale experiments. The variation of chloride concentration with pressuring time, location, solution concentration, initial saturation, hydraulic pressure, and water-binder ratio was investigated through chloride transport tests under external water pressure. In addition, the change and distribution of chloride concentration of isothermal horizontal flow were numerically analyzed using TOUGH2 software. The results show that chloride transport in unsaturated concrete under external water pressure is a combined effect of diffusion and advection instead of diffusion. Chloride concentration increased with increasing solution concentration for diffusion and increased with an increase in water pressure and a decrease in initial saturation for advection. The dominant driving force converted with time and saturation. When predicting the service life of undersea concrete tunnel, it is suggested that advection is taken into consideration; otherwise the durability tends to be unsafe.

ONKALO 3D tunnel seismic investigations at Olkiluoto in 2009

International Nuclear Information System (INIS)

Cosma, C.; Enescu, N.; Balu, L.; Jacome, M.

2011-02-01

POSIVA Oy conducts bedrock investigations at the spent nuclear fuel final disposal site at Olkiluoto, in western Finland. The excavation of the access tunnel to the repository hosts the ONKALO underground rock characterization facility. The investigations carried out at ONKALO focus on the bedrock and groundwater conditions prevailing on the final disposal site and how construction work affects them. Tunnel seismic investigations were carried out in July 2009, as an extension of similar work performed in December 2007. The main objective of the tunnel seismic investigations have been to demonstrate the possibility to detect, locate and image cost effectively steeply and gently dipping fractures, at the side and/or below the tunnel and to characterize the volume of rock surrounding a 250 m long segment of the ONKALO tunnel. The survey was conducted at a depth of 350 m, over a 240 m long line of 3-components receivers, spaced at 3m intervals. Seismic signals were produced along two lines, on the tunnel wall and floor, with source points spaced at 1m. A timedistributed swept-impact, the Vibsist-250 hydraulic source, was used. The source was hosted on a mini excavator. Receiver holes approximately 0.4 m deep were drilled prior to the survey, horizontally into the tunnel wall. One of the procedures used for data stacking and migration is based on a proprietary method combining the DMO (Dip Move Out) correction and an expression of the Radon Transform. Horizontal and vertical migrated profiles were computed both for the P wave and S wave reflected wave fields. A true 3D migration technique (Image Point migration) was used to create 3D migrated sections oriented to incremental azimuths around the tunnel, the result being a cylindrical imaging volume. A general conclusion is that seismic surveys along the tunnel can economically be used for rock mass characterization. High quality results can be obtained by operations in tunnel working conditions, provided that due

Resonant tunneling via spin-polarized barrier states in a magnetic tunnel junction

NARCIS (Netherlands)

Jansen, R.; Lodder, J.C.

2000-01-01

Resonant tunneling through states in the barrier of a magnetic tunnel junction has been analyzed theoretically for the case of a spin-polarized density of barrier states. It is shown that for highly spin-polarized barrier states, the magnetoresistance due to resonant tunneling is enhanced compared

Quantum tunneling time

International Nuclear Information System (INIS)

Wang, Z.S.; Lai, C.H.; Oh, C.H.; Kwek, L.C.

2004-01-01

We present a calculation of quantum tunneling time based on the transition duration of wave peak from one side of a barrier to the other. In our formulation, the tunneling time comprises a real and an imaginary part. The real part is an extension of the phase tunneling time with quantum corrections whereas the imaginary time is associated with energy derivatives of the probability amplitudes

Electronic tunneling through a potential barrier on the surface of a topological insulator

Science.gov (United States)

Zhou, Benliang; Zhou, Benhu; Zhou, Guanghui

2016-12-01

We investigate the tunneling transport for electrons on the surface of a topological insulator (TI) through an electrostatic potential barrier. By using the Dirac equation with the continuity conditions for all segments of wave functions at the interfaces between regions inside and outside the barrier, we calculate analytically the transmission probability and conductance for the system. It is demonstrated that, the Klein paradox can also been observed in the system same as in graphene system. Interestingly, the conductance reaches the minimum value when the incident electron energy is equal to the barrier strength. Moreover, with increasing barrier width, the conductance turns up some tunneling oscillation peaks, and larger barrier strength can cause lower conductance, shorter period but larger oscillation amplitude. The oscillation amplitude decreases as the barrier width increases, which is similar as that of the system consisting of the compressive uniaxial strain applied on a TI, but somewhat different from that of graphene system where the oscillation amplitude is a constant. The findings here imply that an electrostatic barrier can greatly influence the electron tunneling transport of the system, and may provide a new way to realize directional filtering of electrons.

Magnetic field mediated conductance oscillation in graphene p–n junctions

Science.gov (United States)

Cheng, Shu-Guang

2018-04-01

The electronic transport of graphene p–n junctions under perpendicular magnetic field is investigated in theory. Under low magnetic field, the transport is determined by the resonant tunneling of Landau levels and conductance versus magnetic field shows a Shubnikov–de Haas oscillation. At higher magnetic field, the p–n junction subjected to the quasi-classical regime and the formation of snake states results in periodical backscattering and transmission as magnetic field varies. The conductance oscillation pattern is mediated both by magnetic field and the carrier concentration on bipolar regions. For medium magnetic field between above two regimes, the combined contributions of resonant tunneling, snake states oscillation and Aharanov–Bohm interference induce irregular oscillation of conductance. At very high magnetic field, the system is subjected to quantum Hall regime. Under disorder, the quantum tunneling at low magnetic field is slightly affected and the oscillation of snake states at higher magnetic field is suppressed. In the quantum Hall regime, the conductance is a constant as predicted by the mixture rule.

Degradation of magnetic tunnel junctions with thin AlOx barrier

Directory of Open Access Journals (Sweden)

Tadashi Mihara, Yoshinari Kamakura, Masato Morifuji and Kenji Taniguchi

2007-01-01

Full Text Available The degradation of magnetic tunnel junctions (MTJs with AlOx barrier was experimentally investigated. Constant voltage stress (CVS measurement was carried out to monitor the time evolution of the conductance and tunneling magnetoresistance (TMR of MTJs. The gradual increase of the stress-induced leakage current (SILC was observed prior to the breakdown, following a power law function of stress time with an exponent of about 0.2–0.4, which is similar to the case of the ultrathin gate oxide films in MOSFETs. The measured TMR for SILC suggests that the spin-dependent current component would be involved in the early stage of degradation, while spin-independent conduction becomes dominant before the breakdown resulting in a decrease of TMR.

Laboratory Study of the Influence of Substrate Type and Temperature on the Exploratory Tunneling by Formosan Subterranean Termite

Directory of Open Access Journals (Sweden)

Bal K. Gautam

2012-06-01

Full Text Available Using two-dimensional foraging arenas, laboratory tests were conducted to investigate the effect of soil type, soil moisture level and ambient temperature on the exploratory tunneling by Coptotermes formosanus Shiraki. In choice arenas consisting of two substrate types having two moisture levels each, and conducted at a constant temperature of 22 °C, a significantly greater proportion of termites aggregated in sand than in sandy loam. Similarly, the length of excavated tunnels was also increased in sand. In a given substrate, termite aggregation or tunnel length did not differ between 5% and 15% moisture levels. In no-choice tests, where three different substrates (sand, sandy loam and silt loam were tested at two temperatures (22 °C and 28 °C, excavations were significantly greater in sand than either sandy loam or silt loam at 22 °C. Fewer primary tunnels were constructed in sandy loam than in sand and fewer branched tunnels than either in sand or silt loam. No significant difference in either tunnel length or number of primary or branched tunnels was found between these two temperatures.

Band Alignment in MoS2/WS2 Transition Metal Dichalcogenide Heterostructures Probed by Scanning Tunneling Microscopy and Spectroscopy.

Science.gov (United States)

Hill, Heather M; Rigosi, Albert F; Rim, Kwang Taeg; Flynn, George W; Heinz, Tony F

2016-08-10

Using scanning tunneling microscopy (STM) and scanning tunneling spectroscopy (STS), we examine the electronic structure of transition metal dichalcogenide heterostructures (TMDCHs) composed of monolayers of MoS2 and WS2. STS data are obtained for heterostructures of varying stacking configuration as well as the individual monolayers. Analysis of the tunneling spectra includes the influence of finite sample temperature, yield information about the quasi-particle bandgaps, and the band alignment of MoS2 and WS2. We report the band gaps of MoS2 (2.16 ± 0.04 eV) and WS2 (2.38 ± 0.06 eV) in the materials as measured on the heterostructure regions and the general type II band alignment for the heterostructure, which shows an interfacial band gap of 1.45 ± 0.06 eV.

Rock mechanical conditions at the Aespoe HRL. A study of the correlation between geology, tunnel maintenance and tunnel shape

International Nuclear Information System (INIS)

Andersson, Christer; Soederhaell, Joergen

2001-12-01

Maintenance records including scaling, shotcreting and bolting have been kept since the excavation start of Aespoe HRL 1990 together with records of groundwater flow and all other activities taking place in the tunnels. When the facility was constructed one objective was to limit the rock support as much as possible. The reason for this was that it should be possible to go back and easily study the exposed rock surface. Support during the operational phase has only been carried out where and when necessary. This type of maintenance and its location is documented in the digital database each time. The maintenance records have been compiled and areas requiring more maintenance than average noted. An interview has also been held with one of the miners conducting scaling and bolting in the tunnel. His experiences together with the study of the database maintenance records led to the selection of certain areas in the tunnel to be studied by numerical modelling. The probable reason for the need of additional maintenance in all areas, not only these numerically modelled, has been investigated. Almost all maintenance in the main tunnel both during construction and the operational phase has been located in the widened curves of the access tunnel. The maintenance is also located in areas containing veins or intrusions of Smaaland granite or fine-grained granite. These areas are often located in fracture zones of different sizes or show an increasing fracture frequency. The areas numerically modelled indicate stress concentrations or unloaded stress conditions. The stress concentrations are created by the geometry of the niches and side-tunnels in relation to the in situ stress field. The angle between the tunnel and the major principal stress has an impact on the need for maintenance. The areas with the largest angles towards the principal stress direction need more maintenance than the areas almost parallel to the major principal stress direction. The maintenance work in

Measuring fire size in tunnels

International Nuclear Information System (INIS)

Guo, Xiaoping; Zhang, Qihui

2013-01-01

A new measure of fire size Q′ has been introduced in longitudinally ventilated tunnel as the ratio of flame height to the height of tunnel. The analysis in this article has shown that Q′ controls both the critical velocity and the maximum ceiling temperature in the tunnel. Before the fire flame reaches tunnel ceiling (Q′ 1.0), Fr approaches a constant value. This is also a well-known phenomenon in large tunnel fires. Tunnel ceiling temperature shows the opposite trend. Before the fire flame reaches the ceiling, it increases very slowly with the fire size. Once the flame has hit the ceiling of tunnel, temperature rises rapidly with Q′. The good agreement between the current prediction and three different sets of experimental data has demonstrated that the theory has correctly modelled the relation among the heat release rate of fire, ventilation flow and the height of tunnel. From design point of view, the theoretical maximum of critical velocity for a given tunnel can help to prevent oversized ventilation system. -- Highlights: • Fire sizing is an important safety measure in tunnel design. • New measure of fire size a function of HRR of fire, tunnel height and ventilation. • The measure can identify large and small fires. • The characteristics of different fire are consistent with observation in real fires

Microwave-induced co-tunneling in single electron tunneling transistors

DEFF Research Database (Denmark)

Ejrnaes, M.; Savolainen, M.; Manscher, M.

2002-01-01

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......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...

Influence of trap-assisted tunneling on trap-assisted tunneling current in double gate tunnel field-effect transistor

International Nuclear Information System (INIS)

Jiang Zhi; Zhuang Yi-Qi; Li Cong; Wang Ping; Liu Yu-Qi

2016-01-01

Trap-assisted tunneling (TAT) has attracted more and more attention, because it seriously affects the sub-threshold characteristic of tunnel field-effect transistor (TFET). In this paper, we assess subthreshold performance of double gate TFET (DG-TFET) through a band-to-band tunneling (BTBT) model, including phonon-assisted scattering and acoustic surface phonons scattering. Interface state density profile (D it ) and the trap level are included in the simulation to analyze their effects on TAT current and the mechanism of gate leakage current. (paper)

Structure and tunneling dynamics in a model system of peptide co-solvents: Rotational spectroscopy of the 2,2,2-trifluoroethanol⋯water complex

Energy Technology Data Exchange (ETDEWEB)

Thomas, Javix; Xu, Yunjie, E-mail: yunjie.xu@ualberta.ca [Department of Chemistry, University of Alberta, Edmonton, Alberta T6G 2G2 (Canada)

2014-06-21

The hydrogen-bonding topology and tunneling dynamics of the binary adduct, 2,2,2-trifluoroethanol (TFE)⋯water, were investigated using chirped pulse and cavity based Fourier transform microwave spectroscopy with the aid of high level ab initio calculations. Rotational spectra of the most stable binary TFE⋯water conformer and five of its deuterium isotopologues were assigned. A strong preference for the insertion binding topology where water is inserted into the existing intramolecular hydrogen-bonded ring of TFE was observed. Tunneling splittings were detected in all of the measured rotational transitions of TFE⋯water. Based on the relative intensity of the two tunneling components and additional isotopic data, the splitting can be unambiguously attributed to the tunneling motion of the water subunit, i.e., the interchange of the bonded and nonbonded hydrogen atoms of water. The absence of any other splitting in the rotational transitions of all isotopologues observed indicates that the tunneling between g+ and g− TFE is quenched in the TFE⋯H{sub 2}O complex.

Current evidence for effectiveness of interventions for cubital tunnel syndrome, radial tunnel syndrome, instability, or bursitis of the elbow: a systematic review.

Science.gov (United States)

Rinkel, Willem D; Schreuders, Ton A R; Koes, Bart W; Huisstede, Bionka M A

2013-12-01

To provide an evidence-based overview of the effectiveness of interventions for 4 nontraumatic painful disorders sharing the anatomic region of the elbow: cubital tunnel syndrome, radial tunnel syndrome, elbow instability, and olecranon bursitis. The Cochrane Library, PubMed, Embase, PEDro, and CINAHL were searched to identify relevant reviews and randomized clinical trials (RCTs). Two reviewers independently extracted data and assessed the quality of the methodology. A best-evidence synthesis was used to summarize the results. One systematic review and 6 RCTs were included. For the surgical treatment of cubital tunnel syndrome (1 review, 3 RCTs), comparing simple decompression with anterior ulnar nerve transposition, no evidence was found in favor of either one of these. Limited evidence was found in favor of medial epicondylectomy versus anterior transposition and for early postoperative therapy versus immobilization. No evidence was found for the effect of local steroid injection in addition to splinting. No RCTs were found for radial tunnel syndrome. For olecranon bursitis (1 RCT), limited evidence for effectiveness was found for methylprednisolone acetate injection plus naproxen. Concerning elbow instability, including 2 RCTs, one showed that nonsurgical treatment resulted in similar results compared with surgery, whereas the other found limited evidence for the effectiveness in favor of early mobilization versus 3 weeks of immobilization after surgery. In this review no, or at best, limited evidence was found for the effectiveness of nonsurgical and surgical interventions to treat painful cubital tunnel syndrome, radial tunnel syndrome, elbow instability, or olecranon bursitis. Well-designed and well-conducted RCTs are clearly needed in this field.

Thermovoltages in vacuum tunneling investigated by scanning tunneling microscopy

OpenAIRE

Hoffmann, D. H.; Rettenberger, Armin; Grand, Jean Yves; Läuger, K.; Leiderer, Paul; Dransfeld, Klaus; Möller, Rolf

1995-01-01

By heating the tunneling tip of a scanning tunneling microscope the thermoelectric properties of a variable vacuum barrier have been investigated. The lateral variation of the observed thermovoltage will be discussed for polycrystalline gold, stepped surfaces of silver, as well as for copper islands on silver.

Analytical model for vibration prediction of two parallel tunnels in a full-space

Science.gov (United States)

He, Chao; Zhou, Shunhua; Guo, Peijun; Di, Honggui; Zhang, Xiaohui

2018-06-01

This paper presents a three-dimensional analytical model for the prediction of ground vibrations from two parallel tunnels embedded in a full-space. The two tunnels are modelled as cylindrical shells of infinite length, and the surrounding soil is modelled as a full-space with two cylindrical cavities. A virtual interface is introduced to divide the soil into the right layer and the left layer. By transforming the cylindrical waves into the plane waves, the solution of wave propagation in the full-space with two cylindrical cavities is obtained. The transformations from the plane waves to cylindrical waves are then used to satisfy the boundary conditions on the tunnel-soil interfaces. The proposed model provides a highly efficient tool to predict the ground vibration induced by the underground railway, which accounts for the dynamic interaction between neighbouring tunnels. Analysis of the vibration fields produced over a range of frequencies and soil properties is conducted. When the distance between the two tunnels is smaller than three times the tunnel diameter, the interaction between neighbouring tunnels is highly significant, at times in the order of 20 dB. It is necessary to consider the interaction between neighbouring tunnels for the prediction of ground vibrations induced underground railways.

Pain and Function Following Revision Cubital Tunnel Surgery.

Science.gov (United States)

Davidge, Kristen M; Ebersole, Gregory C; Mackinnon, Susan E

2017-11-01

The purpose of this study was to determine pain and functional outcomes following revision cubital tunnel surgery and to identify predictors of poor postoperative outcome. A retrospective cohort study was conducted of all patients undergoing revision cubital tunnel surgery over a 5-year period at a high-volume peripheral nerve center. Intraoperative findings, demographic and injury factors, and outcomes were reviewed. Average pain, worst pain, and impact of pain on self-perceived quality of life were each measured using a 10-cm visual analog scale (VAS). Function was evaluated using pinch and grip strength, as well as the Disabilities of the Arm, Shoulder and Hand (DASH) questionnaire. Differences in preoperative and postoperative pain, strength, and DASH were analyzed using nonparametric tests. Predictors of postoperative average pain were evaluated using odds ratios and linear regression analyses. The final cohort consisted of 50 patients (mean age: 46.3 ± 12.5 years; 29 [68%] male) undergoing 52 revision ulnar nerve transpositions (UNTs). Pain VAS scores decreased significantly following revision UNT. Strength and DASH scores demonstrated nonsignificant improvements postoperatively. Worse preoperative pain and greater than 1 prior cubital tunnel procedure were significant predictors of worse postoperative average pain VAS scores. Patients can and do improve following revision cubital tunnel surgery, particularly as it relates to pain. Intraoperative findings during the revision procedure suggest that adherence to specific principles in the primary operation is key to prevention of secondary cubital tunnel syndrome.

Symmetric and Asymmetric Magnetic Tunnel Junctions with Embedded Nanoparticles: Effects of Size Distribution and Temperature on Tunneling Magnetoresistance and Spin Transfer Torque.

Science.gov (United States)

Useinov, Arthur; Lin, Hsiu-Hau; Lai, Chih-Huang

2017-08-21

The problem of the ballistic electron tunneling is considered in magnetic tunnel junction with embedded non-magnetic nanoparticles (NP-MTJ), which creates additional conducting middle layer. The strong temperature impact was found in the system with averaged NP diameter d av  tunneling magnetoresistance (TMR) voltage behaviors. The low temperature approach also predicts step-like TMR and quantized in-plane spin transfer torque (STT) effects. The robust asymmetric STT respond is found due to voltage sign inversion in NP-MTJs with barrier asymmetry. Furthermore, it is shown how size distribution of NPs as well as quantization rules modify the spin-current filtering properties of the nanoparticles in ballistic regime. Different quantization rules for the transverse component of the wave vector are considered to overpass the dimensional threshold (d av  ≈ 1.8 nm) between quantum well and bulk-assisted states of the middle layer.

User manual for NASA Lewis 10 by 10 foot supersonic wind tunnel. Revised

Science.gov (United States)

Soeder, Ronald H.

1995-01-01

This manual describes the 10- by 10-Foot Supersonic Wind Tunnel at the NASA Lewis Research Center and provides information for users who wish to conduct experiments in this facility. Tunnel performance operating envelopes of altitude, dynamic pressure, Reynolds number, total pressure, and total temperature as a function of test section Mach number are presented. Operating envelopes are shown for both the aerodynamic (closed) cycle and the propulsion (open) cycle. The tunnel test section Mach number range is 2.0 to 3.5. General support systems, such as air systems, hydraulic system, hydrogen system, fuel system, and Schlieren system, are described. Instrumentation and data processing and acquisition systems are also described. Pretest meeting formats and schedules are outlined. Tunnel user responsibility and personnel safety are also discussed.

Flight and full-scale wind-tunnel comparison of pressure distributions from an F-18 aircraft at high angles of attack. [Conducted in NASA Ames Research Center's 80 by 120 ft wind tunnel

Science.gov (United States)

Fisher, David F.; Lanser, Wendy R.

1994-01-01

Pressure distributions were obtained at nearly identical fuselage stations and wing chord butt lines in flight on the F-18 HARV at NASA Dryden Flight Research Center and in the NASA Ames Research Center's 80 by 120 ft wind tunnel on a full-scale F/A-18 aircraft. The static pressures were measured at the identical five stations on the forebody, three stations on the left and right leading-edge extensions, and three spanwise stations on the wing. Comparisons of the flight and wind-tunnel pressure distributions were made at alpha = 30 deg, 45 deg, and 60 deg/59 deg. In general, very good agreement was found. Minor differences were noted at the forebody at alpha = 45 deg and 60 deg in the magnitude of the vortex footprints and a Mach number effect was noted at the leading-edge extension at alpha = 30 deg. The inboard leading edge flap data from the wind tunnel at alpha = 59 deg showed a suction peak that did not appear in the flight data. This was the result of a vortex from the corner of the leading edge flap whose path was altered by the lack of an engine simulation in the wind tunnel.

Documentation and archiving of the Space Shuttle wind tunnel test data base. Volume 1: Background and description

Science.gov (United States)

Romere, Paul O.; Brown, Steve Wesley

1995-01-01

Development of the space shuttle necessitated an extensive wind tunnel test program, with the cooperation of all the major wind tunnels in the United States. The result was approximately 100,000 hours of space shuttle wind tunnel testing conducted for aerodynamics, heat transfer, and structural dynamics. The test results were converted into Chrysler DATAMAN computer program format to facilitate use by analysts, a very cost effective method of collecting the wind tunnel test results from many test facilities into one centralized location. This report provides final documentation of the space shuttle wind tunnel program. The two-volume set covers evolution of space shuttle aerodynamic configurations and gives wind tunnel test data, titles of wind tunnel data reports, sample data sets, and instructions for accessing the digital data base.

Anisotropic superconductivity in β-(BDA-TTP)2SbF6: STM spectroscopy

Science.gov (United States)

Nomura, K.; Muraoka, R.; Matsunaga, N.; Ichimura, K.; Yamada, J.

2009-03-01

We have investigated the gap symmetry in the superconducting phase of β-(BDA-TTP)2SbF6 with use of the scanning tunneling microscope (STM). The tunneling spectra obtained on the conducting surface show a clear superconducting gap structure. Its functional form is of V-shaped similarly to κ-(BEDT-TTF)2X and suggests the anisotropic superconducting gap with line nodes. For lateral surfaces the shape of tunneling spectra varies from the U-shape with relatively large gap to the V-shape with small gap depending on the tunneling direction alternately twice between directional angle 0 and π. From the analysis of conductance curve taking the k dependence of the tunneling probability into account, it is found that the gap has maximum near the a* and c* axes and the nodes appear along near a*+c* and the a-c* directions. These indicate that the d like superconducting pair is formed in this system as the case of κ-(BEDT-TTF)2X. This node direction is consistent with the theoretical prediction based on the spin fluctuation mechanism. However, the zero-bias conductance peak has not been observed yet.

Anisotropic superconductivity in β-(BDA-TTP)2SbF6: STM spectroscopy

International Nuclear Information System (INIS)

Nomura, K.; Muraoka, R.; Matsunaga, N.; Ichimura, K.; Yamada, J.

2009-01-01

We have investigated the gap symmetry in the superconducting phase of β-(BDA-TTP) 2 SbF 6 with use of the scanning tunneling microscope (STM). The tunneling spectra obtained on the conducting surface show a clear superconducting gap structure. Its functional form is of V-shaped similarly to κ-(BEDT-TTF) 2 X and suggests the anisotropic superconducting gap with line nodes. For lateral surfaces the shape of tunneling spectra varies from the U-shape with relatively large gap to the V-shape with small gap depending on the tunneling direction alternately twice between directional angle 0 and π. From the analysis of conductance curve taking the k dependence of the tunneling probability into account, it is found that the gap has maximum near the a* and c* axes and the nodes appear along near a*+c* and the a-c* directions. These indicate that the d x 2 -y 2 like superconducting pair is formed in this system as the case of κ-(BEDT-TTF) 2 X. This node direction is consistent with the theoretical prediction based on the spin fluctuation mechanism. However, the zero-bias conductance peak has not been observed yet

Macroscopic quantum tunneling in Josephson tunnel junctions and Coulomb blockade in single small tunnel junctions

International Nuclear Information System (INIS)

Cleland, A.N.

1991-04-01

Experiments investigating the process of macroscopic quantum tunneling in a moderately-damped, resistively shunted, Josephson junction are described, followed by a discussion of experiments performed on very small capacitance normal-metal tunnel junctions. The experiments on the resistively-shunted Josephson junction were designed to investigate a quantum process, that of the tunneling of the Josephson phase variable under a potential barrier, in a system in which dissipation plays a major role in the dynamics of motion. All the parameters of the junction were measured using the classical phenomena of thermal activation and resonant activation. Theoretical predictions are compared with the experimental results, showing good agreement with no adjustable parameters; the tunneling rate in the moderately damped (Q ∼ 1) junction is seen to be reduced by a factor of 300 from that predicted for an undamped junction. The phase is seen to be a good quantum-mechanical variable. The experiments on small capacitance tunnel junctions extend the measurements on the larger-area Josephson junctions from the region in which the phase variable has a fairly well-defined value, i.e. its wavefunction has a narrow width, to the region where its value is almost completely unknown. The charge on the junction becomes well-defined and is predicted to quantize the current through the junction, giving rise to the Coulomb blockade at low bias. I present the first clear observation of the Coulomb blockade in single junctions. The electrical environment of the tunnel junction, however, strongly affects the behavior of the junction: higher resistance leads are observed to greatly sharpen the Coulomb blockade over that seen with lower resistance leads. I present theoretical descriptions of how the environment influences the junctions; comparisons with the experimental results are in reasonable agreement

Diesel oil pool fire characteristic under natural ventilation conditions in tunnels with roof openings.

Science.gov (United States)

Wang, Yanfu; Jiang, Juncheng; Zhu, Dezhi

2009-07-15

In order to research the fire characteristic under natural ventilation conditions in tunnels with roof openings, full-scale experiment of tunnel fire is designed and conducted. All the experimental data presented in this paper can be further applied for validation of numerical simulation models and reduced-scale experimental results. The physical model of tunnel with roof openings and the mathematical model of tunnel fire are presented in this paper. The tunnel fire under the same conditions as experiment is simulated using CFD software. From the results, it can be seen that most smoke is discharged directly off the tunnel through roof openings, so roof openings are favorable for exhausting smoke. But along with the decrease of smoke temperatures, some smoke may backflow and mix with the smoke-free layer below, which leads to fall in visibility and is unfavorable for personnel evacuation. So it is necessary to research more efficient ways for improving the smoke removal efficiency, such as early fire detection systems, adequate warning signs and setting tunnel cap.

High conductivity carbon nanotube wires from radial densification and ionic doping

Science.gov (United States)

Alvarenga, Jack; Jarosz, Paul R.; Schauerman, Chris M.; Moses, Brian T.; Landi, Brian J.; Cress, Cory D.; Raffaelle, Ryne P.

2010-11-01

Application of drawing dies to radially densify sheets of carbon nanotubes (CNTs) into bulk wires has shown the ability to control electrical conductivity and wire density. Simultaneous use of KAuBr4 doping solution, during wire drawing, has led to an electrical conductivity in the CNT wire of 1.3×106 S/m. Temperature-dependent electrical measurements show that conduction is dominated by fluctuation-assisted tunneling, and introduction of KAuBr4 significantly reduces the tunneling barrier between individual nanotubes. Ultimately, the concomitant doping and densification process leads to closer packed CNTs and a reduced charge transfer barrier, resulting in enhanced bulk electrical conductivity.

About tunnelling times

International Nuclear Information System (INIS)

Olkhovsky, V.S.; Recami, E.

1991-08-01

In this paper, first we critically analyse the main theoretical definitions and calculations of the sub-barrier tunnelling and reflection times. Secondly, we propose a new, physically sensible definition of such durations, on the basis of a recent general formalism (already tested for other types of quantum collisions). At last, we discuss some results regarding temporal evolution of the tunnelling processes, and in particular the ''particle'' speed during tunnelling. (author). 36 refs, 1 fig

The effect of density-of-state tails on band-to-band tunneling: Theory and application to tunnel field effect transistors

Science.gov (United States)

Sant, S.; Schenk, A.

2017-10-01

It is demonstrated how band tail states in the semiconductor influence the performance of a Tunnel Field Effect Transistor (TFET). As a consequence of the smoothened density of states (DOS) around the band edges, the energetic overlap of conduction and valence band states occurs gradually at the onset of band-to-band tunneling (BTBT), thus degrading the sub-threshold swing (SS) of the TFET. The effect of the band tail states on the current-voltage characteristics is modelled quantum-mechanically based on the idea of zero-phonon trap-assisted tunneling between band and tail states. The latter are assumed to arise from a 3-dimensional pseudo-delta potential proposed by Vinogradov [1]. This model potential allows the derivation of analytical expressions for the generation rate covering the whole range from very strong to very weak localization of the tail states. Comparison with direct BTBT in the one-band effective mass approximation reveals the essential features of tail-to-band tunneling. Furthermore, an analytical solution for the problem of tunneling from continuum states of the disturbed DOS to states in the opposite band is found, and the differences to direct BTBT are worked out. Based on the analytical expressions, a semi-classical model is implemented in a commercial device simulator which involves numerical integration along the tunnel paths. The impact of the tail states on the device performance is analyzed for a nanowire Gate-All-Around TFET. The simulations show that tail states notably impact the transfer characteristics of a TFET. It is found that exponentially decaying band tails result in a stronger degradation of the SS than tail states with a Gaussian decay of their density. The developed model allows more realistic simulations of TFETs including their non-idealities.

The benefits of conducting factory performance tests for main mine fans

Energy Technology Data Exchange (ETDEWEB)

Ray, R.E.Jr. [PB Americas Inc., New York, NY (United States); Gamble, G.A. [Clarage Twin City Fan Co., Akron, OH (United States)

2010-07-01

Axial flow fans used in underground mining are also commonly used in subway tunnel ventilation fans to provide an evacuation path during a tunnel fire emergency. The axial flow fans provide sufficient air velocity to the fire site to prevent backlayering of smoke against the incoming airflow. Since the tunnels are used by the public, advance testing of fans and motors is conducted to confirm that the equipment will perform as specified during a fire. This paper discussed some of the advantages derived from conducting fan factory tests for tunnel projects that would also apply to mining applications. It also described other benefits from testing that are unique to mining. External factors that may cause the fan performance to vary considerably from the predicted performance measured at the factory were also discussed. These included air density changes and system effects produced by poorly designed shaft configurations and fan inlet ductwork. 11 refs., 6 figs.

Temperature dependent tunneling study of CaFe{sub 1.96}Ni{sub 0.04}As{sub 2} single crystals

Energy Technology Data Exchange (ETDEWEB)

Dutta, Anirban, E-mail: adatta@iitk.ac.in; Gupta, Anjan K. [Department of Physics, IIT Kanpur, Kanpur-208 016 (India); Thamizhavel, A. [Department of Condensed Matter Physics and Materials Science, Tata Institute of Fundamental Research, Homi Bhabha Road, Colaba, Mumbai-400 005 (India)

2014-04-24

We report on temperature dependent scanning tunneling microscopy and spectroscopy studies on CaFe{sub 1.96}Ni{sub 0.04}As{sub 2} single crystals in 5.4 – 19.7 K temperature range across the normal metal - superconductor transition temperature, T{sub C} = 14K. The in-situ cleaved crystals show reasonably flat surface with signatures of atomic resolution. The tunnel spectra show significant spatial inhomogeneity below T{sub C}, which reduces significantly as the temperature goes above the T{sub C}. We discuss these results in terms of an inhomogeneous electronic phase that may exist due to the vicinity of this composition to the quantum critical point.

Enhanced Tunnel Spin Injection into Graphene using Chemical Vapor Deposited Hexagonal Boron Nitride

Science.gov (United States)

Kamalakar, M. Venkata; Dankert, André; Bergsten, Johan; Ive, Tommy; Dash, Saroj P.

2014-01-01

The van der Waals heterostructures of two-dimensional (2D) atomic crystals constitute a new paradigm in nanoscience. Hybrid devices of graphene with insulating 2D hexagonal boron nitride (h-BN) have emerged as promising nanoelectronic architectures through demonstrations of ultrahigh electron mobilities and charge-based tunnel transistors. Here, we expand the functional horizon of such 2D materials demonstrating the quantum tunneling of spin polarized electrons through atomic planes of CVD grown h-BN. We report excellent tunneling behavior of h-BN layers together with tunnel spin injection and transport in graphene using ferromagnet/h-BN contacts. Employing h-BN tunnel contacts, we observe enhancements in both spin signal amplitude and lifetime by an order of magnitude. We demonstrate spin transport and precession over micrometer-scale distances with spin lifetime up to 0.46 nanosecond. Our results and complementary magnetoresistance calculations illustrate that CVD h-BN tunnel barrier provides a reliable, reproducible and alternative approach to address the conductivity mismatch problem for spin injection into graphene. PMID:25156685

Analog/RF performance of two tunnel FETs with symmetric structures

Science.gov (United States)

Chen, Shupeng; Liu, Hongxia; Wang, Shulong; Li, Wei; Wang, Qianqiong

2017-11-01

In this paper, the radio frequency and analog performance of two tunnel field-effect transistors with symmetric structures are analyzed. The symmetric U-shape gate tunnel field-effect transistor (SUTFET) and symmetric tunnel field-effect transistor (STFET) are investigated by Silvaco Atlas simulation. The basic electrical properties and the parameters related to frequency and analog characteristics are analyzed. Due to the lower off-state leakage current, the STFET has better power consumption performance. The SUTFET obtains larger operating current (242 μA/μm), transconductance (490 μS/μm), output conductance (494 μS/μm), gain bandwidth product (3.2 GHz) and cut-off frequency (27.7 GHz). The simulation result of these two devices can be used as a guideline for their analog/RF applications.

Ultrafast terahertz control of extreme tunnel currents through single atoms on a silicon surface

DEFF Research Database (Denmark)

Jelic, Vedran; Iwaszczuk, Krzysztof; Nguyen, Peter H.

2017-01-01

scanning tunnelling microscopy (THz-STM) in ultrahigh vacuum as a new platform for exploring ultrafast non-equilibrium tunnelling dynamics with atomic precision. Extreme terahertz-pulse-driven tunnel currents up to 10(7) times larger than steady-state currents in conventional STM are used to image...... terahertz-induced band bending and non-equilibrium charging of surface states opens new conduction pathways to the bulk, enabling extreme transient tunnel currents to flow between the tip and sample.......Ultrafast control of current on the atomic scale is essential for future innovations in nanoelectronics. Extremely localized transient electric fields on the nanoscale can be achieved by coupling picosecond duration terahertz pulses to metallic nanostructures. Here, we demonstrate terahertz...

Influence of microclimatic conditions under high tunnels on the physiological and productive responses in blueberry 'O'Neal'

Directory of Open Access Journals (Sweden)

Jorge Retamal-Salgado

2015-09-01

Full Text Available Blueberry (Vaccinium corymbosum L. production under tunnels has spread in recent years. However, there is little information on the productive and physiological responses of blueberry grown under high tunnels. The objective of this research was to evaluate the effect of high tunnel microclimate on the physiological and productive responses of blueberries. A total of 1296 plants of highbush blueberry 'O'Neal' were grown in high tunnels, leaving the same amount of plants under open fields (control. Environmental temperature (T, °C and relative humidity (RH, %, diffuse and total photosynthetically active radiation (PARdiffuse and PARtotal, /conductance (g s, mmol nr² s-1 and maximum photochemical efficiency of photosystem II (Fv/Fm of the leaf were measured. Fruit yield, date of harvest initiation and fruit growth rate were also determined. The maximum T was on average 10-12 °C higher inside the high tunnel than the control, whereas the minimum T averaged only 2-5 °C higher. PARtotal decreased an average of 25% under tunnel, while levels of PARdiffuse increased more than 150%. The g s ranged between 42% and 99% higher in the high tunnel compared to the control, and was positive and statistically related (r² = 0.69** to PARdiffuse variations. Blueberries under high tunnel recorded an accumulated yield 44% higher, while harvest started 14 d earlier compared to control. The results suggest that high tunnels in blueberries increases fruit yield and improves precocity due to higher temperatures during the flowering stage and fruit set. Particular light conditions under tunnels would favor higher leaf stomatal conductance in this crop.

First-principles investigation of quantum transport in GeP3 nanoribbon-based tunneling junctions

Science.gov (United States)

Wang, Qiang; Li, Jian-Wei; Wang, Bin; Nie, Yi-Hang

2018-06-01

Two-dimensional (2D) GeP3 has recently been theoretically proposed as a new low-dimensional material [ Nano Lett. 17(3), 1833 (2017)]. In this manuscript, we propose a first-principles calculation to investigate the quantum transport properties of several GeP3 nanoribbon-based atomic tunneling junctions. Numerical results indicate that monolayer GeP3 nanoribbons show semiconducting behavior, whereas trilayer GeP3 nanoribbons express metallic behavior owing to the strong interaction between each of the layers. This behavior is in accordance with that proposed in two-dimensional GeP3 layers. The transmission coefficient T( E) of tunneling junctions is sensitive to the connecting formation between the central monolayer GeP3 nanoribbon and the trilayer GeP3 nanoribbon at both ends. The T( E) value of the bottom-connecting tunneling junction is considerably larger than those of the middle-connecting and top-connecting ones. With increases in gate voltage, the conductances increase for the bottom-connecting and middle-connecting tunneling junctions, but decrease for the top-connecting tunneling junctions. In addition, the conductance decreases exponentially with respect to the length of the central monolayer GeP3 nanoribbon for all the tunneling junctions. I-V curves show approximately linear behavior for the bottom-connecting and middle-connecting structures, but exhibit negative differential resistance for the top-connecting structures. The physics of each phenomenon is analyzed in detail.

Clinical Study on Five Cases of Carpal tunnel syndrome

Directory of Open Access Journals (Sweden)

Kim Il Hwan

2001-12-01

Full Text Available Objections : The purpose of the study was to evaluate the effectiveness of treating the carpal tunnel syndrome by using both the Herbal Acupuncture and herbal medicine therapy on five cases. Methods : For the Herbal Acupuncture, Jungseonguhhyl No. 1 and Hwanglyunhaedoktang were used. For the herbal medicine, Dangguihwalhyul-tang was used. The patients were treated once in every two days; the result was evaluated after ten treatments. Patients' conditions were monitored through their testimony, phalen's test, nerve conduction study and electromyography. Results : In all five cases, the patients showed improvement; in four cases, the patients no longer had most of the clinical symptoms. Based on the result of the nerve conduction study, for the four cases in which the patients no longer displayed most of the clinical symptoms, their nerve conduction rate improved; for the remaining one case, the patient's nerve conduction rate deteriorated. Conclusions : The results of this study demonstrate that combining the Herbal Acupuncture and herbal medicine therapy can have noticeable effects in treating the carpal tunnel syndrome; developing more variety of the herbal acupuncture would lead to even better treatment results.

Drill and blast tunnelling; Konvensjonell drift av tunneler

Energy Technology Data Exchange (ETDEWEB)

Roenn, Paal-Egil

1997-12-31

This thesis treats drill and blast tunnelling. The rapid technological advance necessitates revised and updated design criteria, quality requirements and quality control. In situ blast experiments were carried out in order to test new methods and improve the basis for calculation and design. The main topics of the experiments were (1) longer rounds and increased drillhole diameter, (2) emulsion slurry as explosives in tunnelling, and (3) electronic detonators in contour blasting. The experiments show that it is technically feasible to blast rounds of up to 8.6 m length. Using current technology, the economical optimum round length is substantially shorter. Dust, low visibility, noise and toxic fumes are occupational environmental strains for the tunnel workers. Several of the environmental factors are strongly influenced by the type of explosives used. For example, emulsion slurry resulted in 4 to 5 times better visibility than Anolit and the concentration of respirable dust and total dust was reduced by 30-50 %. Electronic detonators were tested and found to give a higher percentage of remaining drillholes in the contour than Nonel detonators. The thesis includes a chapter on economic design of hydropower tunnels. 42 refs., 83 figs., 45 tabs.

Resonant tunnel magnetoresistance in double-barrier planar magnetic tunnel junctions

KAUST Repository

Useinov, A. N.

2011-08-24

We present a theoretical approach to calculate the spin-dependent current and tunnel magnetoresistance (TMR) in a double-barrier magnetic tunnel junction (DMTJ), in which the magnetization of the middle ferromagnetic metal layer can be aligned parallel or antiparallel in relation to the fixed magnetizations of the left and right ferromagnetic electrodes. The electron transport through the DMTJ is considered as a three-dimensional problem, taking into account all transmitting electron trajectories as well as the spin-dependent momentum conservation law. The dependence of the transmission coefficient and spin-polarized currents on the applied voltage is derived as an exact solution to the quantum-mechanical problem for the spin-polarized transport. In the range of the developed physical model, the resonant tunneling, nonresonant tunneling, and enhanced spin filtering can be explained; the simulation results are in good agreement with experimental data.

Resonant tunnel magnetoresistance in double-barrier planar magnetic tunnel junctions

KAUST Repository

Useinov, A. N.; Kosel, Jü rgen; Useinov, N. Kh.; Tagirov, L. R.

2011-01-01

We present a theoretical approach to calculate the spin-dependent current and tunnel magnetoresistance (TMR) in a double-barrier magnetic tunnel junction (DMTJ), in which the magnetization of the middle ferromagnetic metal layer can be aligned parallel or antiparallel in relation to the fixed magnetizations of the left and right ferromagnetic electrodes. The electron transport through the DMTJ is considered as a three-dimensional problem, taking into account all transmitting electron trajectories as well as the spin-dependent momentum conservation law. The dependence of the transmission coefficient and spin-polarized currents on the applied voltage is derived as an exact solution to the quantum-mechanical problem for the spin-polarized transport. In the range of the developed physical model, the resonant tunneling, nonresonant tunneling, and enhanced spin filtering can be explained; the simulation results are in good agreement with experimental data.

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

OpenAIRE

Saffarzadeh, Alireza; Daqiq, Reza

2009-01-01

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

Photon-Assisted Resonant Chiral Tunneling Through a Bilayer Graphene Barrier

OpenAIRE

Phillips A. H.; Mina A. N.

2011-01-01

The electronic transport property of a bilayer graphene is investigated under the effect of an electromagnetic field. We deduce an expression for the conductance by solving the Dirac equation. This conductance depends on the barrier height for graphene and the energy of the induced photons. A resonance oscillatory behavior of the conductance is observed. These oscillations are strongly depends on the barrier height for chiral tunneling through graphene. This oscillatory behavio...

Wave Pattern Peculiarities of Different Types of Explosions Conducted at Semipalatinsk Test Site

Science.gov (United States)

Sokolova, Inna

2014-05-01

The historical seismograms of the explosions conducted at the STS in 1949 - 1989 are of great interest for the researchers in the field of monitoring. Large number of air (86), surface (30) and underground nuclear explosions were conducted here in boreholes and tunnels (340). In addition to nuclear explosions, large chemical explosions were conducted at the Test Site. It is known that tectonic earthquakes occur on the Test Site territory and near it. Since 2005 the Institute of Geophysical Researches conducts works on digitizing the historical seismograms of nuclear explosions. Currently, the database contains more than 6000 digitized seismograms of nuclear explosions used for investigative monitoring tasks, major part of them (4000) are events from the STS region. Dynamic parameters of records of air, surface and underground nuclear explosions, as well as large chemical explosions with compact charge laying were investigated for seismic stations located on the territory of Kazakhstan using digitized records of the STS events. In addition, the comparison between salvo wave pattern and single explosions was conducted. The records of permanent and temporary seismic stations (epicentral distances range 100 - 800 km) were used for the investigations. Explosions spectra were analyzed, specific features of each class of events were found. The seismograms analysis shows that the wave pattern depends significantly on the explosion site and on the source type.

Influence of trap-assisted tunneling on trap-assisted tunneling current in double gate tunnel field-effect transistor

Science.gov (United States)

Zhi, Jiang; Yi-Qi, Zhuang; Cong, Li; Ping, Wang; Yu-Qi, Liu

2016-02-01

Trap-assisted tunneling (TAT) has attracted more and more attention, because it seriously affects the sub-threshold characteristic of tunnel field-effect transistor (TFET). In this paper, we assess subthreshold performance of double gate TFET (DG-TFET) through a band-to-band tunneling (BTBT) model, including phonon-assisted scattering and acoustic surface phonons scattering. Interface state density profile (Dit) and the trap level are included in the simulation to analyze their effects on TAT current and the mechanism of gate leakage current. Project supported by the National Natural Science Foundation of China (Grant Nos. 61574109 and 61204092).

Temperature dependence of interlayer coupling in perpendicular magnetic tunnel junctions with GdOX barriers

Science.gov (United States)

Newhouse-Illige, T.; Xu, Y. H.; Liu, Y. H.; Huang, S.; Kato, H.; Bi, C.; Xu, M.; LeRoy, B. J.; Wang, W. G.

2018-02-01

Perpendicular magnetic tunnel junctions with GdOX tunneling barriers have shown a unique voltage controllable interlayer magnetic coupling effect. Here, we investigate the quality of the GdOX barrier and the coupling mechanism in these junctions by examining the temperature dependence of the tunneling magnetoresistance and the interlayer coupling from room temperature down to 11 K. The barrier is shown to be of good quality with the spin independent conductance only contributing a small portion, 14%, to the total room temperature conductance, similar to AlOX and MgO barriers. The interlayer coupling, however, shows an anomalously strong temperature dependence including sign changes below 80 K. This non-trivial temperature dependence is not described by previous models of interlayer coupling and may be due to the large induced magnetic moment of the Gd ions in the barrier.

Step tunneling enhanced asymmetry in metal-insulator-insulator-metal (MIIM) diodes for rectenna applications

Science.gov (United States)

Alimardani, N.; Conley, J. F.

2013-09-01

We combine nanolaminate bilayer insulator tunnel barriers (Al2O3/HfO2, HfO2/Al2O3, Al2O3/ZrO2) deposited via atomic layer deposition (ALD) with asymmetric work function metal electrodes to produce MIIM diodes with enhanced I-V asymmetry and non-linearity. We show that the improvements in MIIM devices are due to step tunneling rather than resonant tunneling. We also investigate conduction processes as a function of temperature in MIM devices with Nb2O5 and Ta2O5 high electron affinity insulators. For both Nb2O5 and Ta2O5 insulators, the dominant conduction process is established as Schottky emission at small biases and Frenkel-Poole emission at large biases. The energy depth of the traps that dominate Frenkel-Poole emission in each material are estimated.

STM tunneling through a quantum wire with a side-attached impurity

International Nuclear Information System (INIS)

Kwapinski, T.; Krawiec, M.; Jalochowski, M.

2008-01-01

The STM tunneling through a quantum wire (QW) with a side-attached impurity (atom, island) is investigated using a tight-binding model and the non-equilibrium Keldysh Green function method. The impurity can be coupled to one or more QW atoms. The presence of the impurity strongly modifies the local density of states of the wire atoms, thus influences the STM tunneling through all the wire atoms. The transport properties of the impurity itself are also investigated mainly as a function of the wire length and the way it is coupled to the wire. It is shown that the properties of the impurity itself and the way it is coupled to the wire strongly influence the STM tunneling, the density of states and differential conductance

Electrical installations of the Channel tunnel; Installations electriques du Tunnel sous la Manche

Energy Technology Data Exchange (ETDEWEB)

Kersabiec, G. de [Eurotunnel, Folkestone (United Kingdom)

2002-08-01

Like an underground factory, the railway and auxiliary equipments of the Channel tunnel between France and UK, need a reliable and redundant power supply with a high quality maintenance. This article presents: the design criteria of the power distribution systems, the installation itself and the organisation of its exploitation: 1 - transportation system of the Channel tunnel (loads to supply, exploitation imperatives, fundamental criteria); 2 - external power sources (connection to the UK and French grids, values used by the national grids); 3 - exploitation criteria, tunnel design; 4 - description (main UK and French power stations, 25 kV traction network, 21 kV distribution network, tunnels, lighting in railway tunnels, supply of terminals, earthing network); 5 - exploitation; 6 - maintenance and quality. (J.S.)

A Historical Evaluation of the U12n Tunnel, Nevada national Security Site, Nye County, Nevada Part 2 of 2

Energy Technology Data Exchange (ETDEWEB)

Drollinger, Harold [DRI; Jones, Robert C [DRI; Bullard, Thomas F [DRI; Ashbaugh, Laurence J [DRI; Griffin, Wayne R

2011-06-01

This report presents a historical evaluation of the U12n Tunnel on the Nevada National Security Site (NNSS) in southern Nevada. The work was conducted by the Desert Research Institute at the request of the U.S. Department of Energy, National Nuclear Security Administration Nevada Site Office and the U.S. Department of Defense, Defense Threat Reduction Agency (DTRA). The U12n Tunnel was one of a series of tunnels used for underground nuclear weapons effects tests in Rainier and Aqueduct Mesas. A total of 22 nuclear tests were conducted in the U12n Tunnel from 1967 to 1992. These tests include Midi Mist, Hudson Seal, Diana Mist, Misty North, Husky Ace, Ming Blade, Hybla Fair, Mighty Epic, Diablo Hawk, Miners Iron, Huron Landing, Diamond Ace, Mini Jade, Tomme/Midnight Zephyr, Misty Rain, Mill Yard, Diamond Beech, Middle Note, Misty Echo, Mineral Quarry, Randsburg, and Hunters Trophy. DTRA sponsored all tests except Tomme and Randsburg which were sponsored by the Lawrence Livermore National Laboratory. Midnight Zephyr, sponsored by DTRA, was an add on experiment to the Tomme test. Eleven high explosive tests were also conducted in the tunnel and included a Stemming Plan Test, the Pre-Mill Yard test, the two seismic Non-Proliferation Experiment tests, and seven Dipole Hail tests. The U12n Tunnel complex is composed of the portal and mesa areas, encompassing a total area of approximately 600 acres (240 hectares). Major modifications to the landscape have resulted from four principal activities. These are road construction and maintenance, mining activities related to development of the tunnel complex, site preparation for activities related to testing, and construction of retention ponds. A total of 202 cultural features were recorded for the portal and mesa areas. At the portal area, features relate to the mining, construction, testing, and general everyday operational support activities within the tunnel. These include concrete foundations for buildings, ventilation

Heavy-Atom Tunneling Calculations in Thirteen Organic Reactions: Tunneling Contributions are Substantial, and Bell's Formula Closely Approximates Multidimensional Tunneling at ≥250 K.

Science.gov (United States)

Doubleday, Charles; Armas, Randy; Walker, Dana; Cosgriff, Christopher V; Greer, Edyta M

2017-10-09

Multidimensional tunneling calculations are carried out for 13 reactions, to test the scope of heavy-atom tunneling in organic chemistry, and to check the accuracy of one-dimensional tunneling models. The reactions include pericyclic, cycloaromatization, radical cyclization and ring opening, and S N 2. When compared at the temperatures that give the same effective rate constant of 3×10 -5  s -1 , tunneling accounts for 25-95 % of the rate in 8 of the 13 reactions. Values of transmission coefficients predicted by Bell's formula, κ Bell  , agree well with multidimensional tunneling (canonical variational transition state theory with small curvature tunneling), κ SCT . Mean unsigned deviations of κ Bell vs. κ SCT are 0.08, 0.04, 0.02 at 250, 300 and 400 K. This suggests that κ Bell is a useful first choice for predicting transmission coefficients in heavy-atom tunnelling. © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

Macroscopic quantum tunneling in Josephson tunnel junctions and Coulomb blockade in single small tunnel junctions

International Nuclear Information System (INIS)

Cleland, A.N.

1991-01-01

Experiments investigated the process of macroscopic quantum tunneling in a moderately-damped, resistively shunted, Josephson junction are described, followed by a discussion of experiments performed on very-small-capacitance normal-metal tunnel junctions. The experiments on the resistively-shunted Josephson junction were designed to investigate a quantum process, that of the tunneling of the Josephson-phase variable under a potential barrier, in a system in which dissipation plays a major role in the dynamics of motion. All the parameters of the junction were measured using the classical phenomena of thermal activation and resonant activation. Theoretical predictions are compared with the experimental results, showing good agreement with no adjustable parameters. The experiments on small-capacitance tunnel junctions extend the measurements on the large-area Josephson junctions from the region in which the phase variable has a fairly well-defined value, i.e. its wave function has a narrow width, to the region where its value is almost completely unknown. The charge on the junction becomes well-defined and is predicted to quantize the current through the junction, giving rise to the Coulomb blockade at low bias

Enhancement of tunneling current in phosphorene tunnel field effect transistors by surface defects.

Science.gov (United States)

Lu, Juan; Fan, Zhi-Qiang; Gong, Jian; Chen, Jie-Zhi; ManduLa, Huhe; Zhang, Yan-Yang; Yang, Shen-Yuan; Jiang, Xiang-Wei

2018-02-21

The effects of the staggered double vacancies, hydrogen (H), 3d transition metals, for example cobalt, and semiconductor covalent atoms, for example, germanium, nitrogen, phosphorus (P) and silicon adsorption on the transport properties of monolayer phosphorene were studied using density functional theory and non-equilibrium Green's function formalism. It was observed that the performance of the phosphorene tunnel field effect transistors (TFETs) with an 8.8 nm scaling channel length could be improved most effectively, if the adatoms or vacancies were introduced at the source channel interface. For H and P doped devices, the upper limit of on-state currents of phosphorene TFETs were able to be quickly increased to 2465 μA μm -1 and 1652 μA μm -1 , respectively, which not only outperformed the pristine sample, but also met the requirements for high performance logic applications for the next decade in the International Technology Roadmap for Semiconductors (ITRS). It was proved that the defect-induced band gap states make the effective tunneling path between the conduction band (CB) and valence band (VB) much shorter, so that the carriers can be injected easily from the left electrode, then transfer to the channel. In this regard, the tunneling properties of phosphorene TFETs can be manipulated using surface defects. In addition, the effects of spin polarization on the transport properties of doped phosphorene TFETs were also rigorously considered, H and P doped TFETs could achieve a high ON current of 1795 μA μm -1 and 1368 μA μm -1 , respectively, which is closer to realistic nanodevices.

Ge/Si(001) heterostructures with dense arrays of Ge quantum dots: morphology, defects, photo-emf spectra and terahertz conductivity.

Science.gov (United States)

Yuryev, Vladimir A; Arapkina, Larisa V; Storozhevykh, Mikhail S; Chapnin, Valery A; Chizh, Kirill V; Uvarov, Oleg V; Kalinushkin, Victor P; Zhukova, Elena S; Prokhorov, Anatoly S; Spektor, Igor E; Gorshunov, Boris P

2012-07-23

: Issues of Ge hut cluster array formation and growth at low temperatures on the Ge/Si(001) wetting layer are discussed on the basis of explorations performed by high resolution STM and in-situ RHEED. Dynamics of the RHEED patterns in the process of Ge hut array formation is investigated at low and high temperatures of Ge deposition. Different dynamics of RHEED patterns during the deposition of Ge atoms in different growth modes is observed, which reflects the difference in adatom mobility and their 'condensation' fluxes from Ge 2D gas on the surface for different modes, which in turn control the nucleation rates and densities of Ge clusters. Data of HRTEM studies of multilayer Ge/Si heterostructures are presented with the focus on low-temperature formation of perfect films.Heteroepitaxial Si p-i-n-diodes with multilayer stacks of Ge/Si(001) quantum dot dense arrays built in intrinsic domains have been investigated and found to exhibit the photo-emf in a wide spectral range from 0.8 to 5 μm. An effect of wide-band irradiation by infrared light on the photo-emf spectra has been observed. Photo-emf in different spectral ranges has been found to be differently affected by the wide-band irradiation. A significant increase in photo-emf is observed in the fundamental absorption range under the wide-band irradiation. The observed phenomena are explained in terms of positive and neutral charge states of the quantum dot layers and the Coulomb potential of the quantum dot ensemble. A new design of quantum dot infrared photodetectors is proposed.By using a coherent source spectrometer, first measurements of terahertz dynamical conductivity (absorptivity) spectra of Ge/Si(001) heterostructures were performed at frequencies ranged from 0.3 to 1.2 THz in the temperature interval from 300 to 5 K. The effective dynamical conductivity of the heterostructures with Ge quantum dots has been discovered to be significantly higher than that of the structure with the same amount of bulk

Transport and Quantum Coherence in Graphene Rings: Aharonov-Bohm Oscillations, Klein Tunneling, and Particle Localization

Science.gov (United States)

Filusch, Alexander; Wurl, Christian; Pieper, Andreas; Fehske, Holger

2018-06-01

Simulating quantum transport through mesoscopic, ring-shaped graphene structures, we address various quantum coherence and interference phenomena. First, a perpendicular magnetic field, penetrating the graphene ring, gives rise to Aharonov-Bohm oscillations in the conductance as a function of the magnetic flux, on top of the universal conductance fluctuations. At very high fluxes, the interference gets suppressed and quantum Hall edge channels develop. Second, applying an electrostatic potential to one of the ring arms, nn'n- or npn-junctions can be realized with particle transmission due to normal tunneling or Klein tunneling. In the latter case, the Aharonov-Bohm oscillations weaken for smooth barriers. Third, if potential disorder comes in to play, both Aharonov-Bohm and Klein tunneling effects rate down, up to the point where particle localization sets in.

Effects of ultrashort laser pulses on angular distributions of photoionization spectra.

Science.gov (United States)

Ooi, C H Raymond; Ho, W L; Bandrauk, A D

2017-07-27

We study the photoelectron spectra by intense laser pulses with arbitrary time dependence and phase within the Keldysh framework. An efficient semianalytical approach using analytical transition matrix elements for hydrogenic atoms in any initial state enables efficient and accurate computation of the photoionization probability at any observation point without saddle point approximation, providing comprehensive three dimensional photoelectron angular distribution for linear and elliptical polarizations, that reveal the intricate features and provide insights on the photoionization characteristics such as angular dispersions, shift and splitting of photoelectron peaks from the tunneling or above threshold ionization(ATI) regime to non-adiabatic(intermediate) and multiphoton ionization(MPI) regimes. This facilitates the study of the effects of various laser pulse parameters on the photoelectron spectra and their angular distributions. The photoelectron peaks occur at multiples of 2ħω for linear polarization while  odd-ordered peaks are suppressed in the direction perpendicular to the electric field. Short pulses create splitting and angular dispersion where the peaks are strongly correlated to the angles. For MPI and elliptical polarization with shorter pulses the peaks split into doublets and the first peak vanishes. The carrier envelope phase(CEP) significantly affects the ATI spectra while the Stark effect shifts the spectra of intermediate regime to higher energies due to interference.

Vacuum phonon tunneling.

Science.gov (United States)

Altfeder, Igor; Voevodin, Andrey A; Roy, Ajit K

2010-10-15

Field-induced phonon tunneling, a previously unknown mechanism of interfacial thermal transport, has been revealed by ultrahigh vacuum inelastic scanning tunneling microscopy (STM). Using thermally broadened Fermi-Dirac distribution in the STM tip as in situ atomic-scale thermometer we found that thermal vibrations of the last tip atom are effectively transmitted to sample surface despite few angstroms wide vacuum gap. We show that phonon tunneling is driven by interfacial electric field and thermally vibrating image charges, and its rate is enhanced by surface electron-phonon interaction.

Breaking through the tranfer tunnel

CERN Document Server

Laurent Guiraud

2001-01-01

This image shows the tunnel boring machine breaking through the transfer tunnel into the LHC tunnel. Proton beams will be transferred from the SPS pre-accelerator to the LHC at 450 GeV through two specially constructed transfer tunnels. From left to right: LHC Project Director, Lyn Evans; CERN Director-General (at the time), Luciano Maiani, and Director for Accelerators, Kurt Hubner.

New Tunneling Features in Polar III-Nitride Resonant Tunneling Diodes

Directory of Open Access Journals (Sweden)

Jimy Encomendero

2017-10-01

Full Text Available For the past two decades, repeatable resonant tunneling transport of electrons in III-nitride double barrier heterostructures has remained elusive at room temperature. In this work we theoretically and experimentally study III-nitride double-barrier resonant tunneling diodes (RTDs, the quantum transport characteristics of which exhibit new features that are unexplainable using existing semiconductor theory. The repeatable and robust resonant transport in our devices enables us to track the origin of these features to the broken inversion symmetry in the uniaxial crystal structure, which generates built-in spontaneous and piezoelectric polarization fields. Resonant tunneling transport enabled by the ground state as well as by the first excited state is demonstrated for the first time over a wide temperature window in planar III-nitride RTDs. An analytical transport model for polar resonant tunneling heterostructures is introduced for the first time, showing a good quantitative agreement with experimental data. From this model we realize that tunneling transport is an extremely sensitive measure of the built-in polarization fields. Since such electric fields play a crucial role in the design of electronic and photonic devices, but are difficult to measure, our work provides a completely new method to accurately determine their magnitude for the entire class of polar heterostructures.

Increased Mach Number Capability for the NASA Glenn 10x10 Supersonic Wind Tunnel

Science.gov (United States)

Slater, J. W.; Saunders, J. D.

2015-01-01

Computational simulations and wind tunnel testing were conducted to explore the operation of the Abe Silverstein Supersonic Wind Tunnel at the NASA Glenn Research Center at test section Mach numbers above the current limit of Mach 3.5. An increased Mach number would enhance the capability for testing of supersonic and hypersonic propulsion systems. The focus of the explorations was on understanding the flow within the second throat of the tunnel, which is downstream of the test section and is where the supersonic flow decelerates to subsonic flow. Methods of computational fluid dynamics (CFD) were applied to provide details of the shock boundary layer structure and to estimate losses in total pressure. The CFD simulations indicated that the tunnel could be operated up to Mach 4.0 if the minimum width of the second throat was made smaller than that used for previous operation of the tunnel. Wind tunnel testing was able to confirm such operation of the tunnel at Mach 3.6 and 3.7 before a hydraulic failure caused a stop to the testing. CFD simulations performed after the wind tunnel testing showed good agreement with test data consisting of static pressures along the ceiling of the second throat. The CFD analyses showed increased shockwave boundary layer interactions, which was also observed as increased unsteadiness of dynamic pressures collected in the wind tunnel testing.

Histological Observation of Regions around Bone Tunnels after Compression of the Bone Tunnel Wall in Ligament Reconstruction

International Nuclear Information System (INIS)

Maeda, Shintaro; Ishikawa, Hiroki; Tanigawa, Naoaki; Miyazaki, Kyosuke; Shioda, Seiji

2012-01-01

The objectives of this study were to investigate the time-course of influence of compression of bone tunnel wall in ligament reconstruction on tissue around the bone tunnel and to histologically examine the mechanism of preventing the complication of bone tunnel dilation, using rabbit tibia. A model in which the femoral origin of the extensor digitorum longus tendon was cut and inserted into a bone tunnel made proximal to the tibia was prepared in the bilateral hind legs of 20 Japanese white rabbits. In each animal, a tunnel was made using a drill only in the right leg, while an undersized bone tunnel was made by drilling and then dilated by compression using a dilator to the same tunnel size as that in the right leg. Animals were sacrificed at 0, 2, 4, 8 and 12 weeks after surgery (4 animals at each time point). Observation of bone tunnels by X-ray radiography showed osteosclerosis in the 2- and 4-week dilation groups. Osteosclerosis appeared as white lines around the bone tunnel on X-ray radiography. This suggests that dilation promotes callus formation in the bone tunnel wall and prevents the complication of bone tunnel enlargement after ligament reconstruction

Facility Closure Report for Tunnel U16a, Area 16, Nevada Test Site, Nevada

International Nuclear Information System (INIS)

2009-01-01

U16a is not listed in the Federal Facility Agreement and Consent Order. The closure of U16a was sponsored by the Defense Threat Reduction Agency (DTRA) and performed with the cooperation of the U.S. Department of Energy, National Nuclear Security Administration Nevada Site Office and the Nevada Division of Environmental Protection. This report documents closure of this site as identified in the DTRA Fiscal Year 2008 Statement of Work, Task 6.3. Closure activities included: (1) Removing and disposing of a shack and its contents; (2) Disposing of debris from within the shack and in the vicinity of the tunnel entrance; (3) Verifying that the tunnel is empty; (4) Welding screened covers over tunnel vent holes to limit access and allow ventilation; and (5) Constructing a full-tunnel cross-section fibercrete bulkhead to prevent access to the tunnel Field activities were conducted from July to August 2008.

Infrared Spectra of the 10-μm Bands of 1,2-Difluoroethane and 1,1,2-Trifluoroethane: Vibrationally Mediated Torsional Tunneling in 1,1,2-Trifluoroethane

Science.gov (United States)

Stone, Stephen C.; Miller, C. Cameron; Philips, Laura A.; Andrews, A. M.; Fraser, G. T.; Pate, B. H.; Xu, Li-Hong

1995-12-01

The 3-MHz-resolution infrared spectra of the 10-μm bands of thegaucheconformer of 1,2-difluoroethane (HFC152) and theC1-symmetry conformer of 1,1,2-trifluoroethane (HFC143) have been measured using a molecular-beam electric-resonance optothermal spectrometer with a tunable microwave-sideband CO2laser source. For 1,2-difluoroethane, two bands have been studied, the ν17B-symmetry C-F stretch at 1077.3 cm-1and the ν13B-symmetry CH2rock at 896.6 cm-1. Both bands are well fit to a asymmetric-rotor Hamiltonian to better than 0.5 MHz. The ν13band is effectively unperturbed, while the ν17band is weakly perturbed, as shown by the large change in centrifugal distortion constants from the ground state values. Two bands have also been studied for 1,1,2-trifluoroethane, the ν11symmetric CF2stretch at 1077.2 cm-1and the ν13C-C stretch at 905.1 cm-1. One of the two bands, ν11, is unperturbed and fit to near the experimental precision. The ν13vibration, on the other hand, is weakly perturbed by an interaction with a nearby state. This perturbation leads to a doubling or splitting of the lines, due to a perturbation-induced lifting of the degeneracy of the symmetric and antisymmetric tunneling states associated with tunneling between the two equivalentC1forms. For theJ,Kastates studied, the splittings are as large as 37 MHz. Combining this observation with published low-resolution far-infrared measurements of torsional sequence-band and hot-band frequencies and calculations from an empirical torsional potential allows us to identify the perturbing state as ν17+ 6ν18. Here, ν17is the CF2twist and ν18is the torsion. The matrix element responsible for this interaction exchanges eight vibrational quanta!

Tensile strained Ge tunnel field-effect transistors: k · p material modeling and numerical device simulation

International Nuclear Information System (INIS)

Kao, Kuo-Hsing; De Meyer, Kristin; Verhulst, Anne S.; Van de Put, Maarten; Soree, Bart; Magnus, Wim; Vandenberghe, William G.

2014-01-01

Group IV based tunnel field-effect transistors generally show lower on-current than III-V based devices because of the weaker phonon-assisted tunneling transitions in the group IV indirect bandgap materials. Direct tunneling in Ge, however, can be enhanced by strain engineering. In this work, we use a 30-band k · p method to calculate the band structure of biaxial tensile strained Ge and then extract the bandgaps and effective masses at Γ and L symmetry points in k-space, from which the parameters for the direct and indirect band-to-band tunneling (BTBT) models are determined. While transitions from the heavy and light hole valence bands to the conduction band edge at the L point are always bridged by phonon scattering, we highlight a new finding that only the light-hole-like valence band is strongly coupling to the conduction band at the Γ point even in the presence of strain based on the 30-band k · p analysis. By utilizing a Technology Computer Aided Design simulator equipped with the calculated band-to-band tunneling BTBT models, the electrical characteristics of tensile strained Ge point and line tunneling devices are self-consistently computed considering multiple dynamic nonlocal tunnel paths. The influence of field-induced quantum confinement on the tunneling onset is included. Our simulation predicts that an on-current up to 160 (260) μA/μm can be achieved along with on/off ratio > 10 6 for V DD  = 0.5 V by the n-type (p-type) line tunneling device made of 2.5% biaxial tensile strained Ge

Tensile strained Ge tunnel field-effect transistors: k · p material modeling and numerical device simulation

Energy Technology Data Exchange (ETDEWEB)

Kao, Kuo-Hsing; De Meyer, Kristin [IMEC, Kapeldreef 75, 3001 Leuven (Belgium); Department of Electrical Engineering, Katholieke Universiteit Leuven, 3000 Leuven (Belgium); Verhulst, Anne S. [IMEC, Kapeldreef 75, 3001 Leuven (Belgium); Van de Put, Maarten; Soree, Bart; Magnus, Wim [IMEC, Kapeldreef 75, 3001 Leuven (Belgium); Department of Physics, Universiteit Antwerpen, 2000 Antwerpen (Belgium); Vandenberghe, William G. [Department of Materials Science and Engineering, University of Texas at Dallas, Richardson, Texas 75080 (United States)

2014-01-28

Group IV based tunnel field-effect transistors generally show lower on-current than III-V based devices because of the weaker phonon-assisted tunneling transitions in the group IV indirect bandgap materials. Direct tunneling in Ge, however, can be enhanced by strain engineering. In this work, we use a 30-band k · p method to calculate the band structure of biaxial tensile strained Ge and then extract the bandgaps and effective masses at Γ and L symmetry points in k-space, from which the parameters for the direct and indirect band-to-band tunneling (BTBT) models are determined. While transitions from the heavy and light hole valence bands to the conduction band edge at the L point are always bridged by phonon scattering, we highlight a new finding that only the light-hole-like valence band is strongly coupling to the conduction band at the Γ point even in the presence of strain based on the 30-band k · p analysis. By utilizing a Technology Computer Aided Design simulator equipped with the calculated band-to-band tunneling BTBT models, the electrical characteristics of tensile strained Ge point and line tunneling devices are self-consistently computed considering multiple dynamic nonlocal tunnel paths. The influence of field-induced quantum confinement on the tunneling onset is included. Our simulation predicts that an on-current up to 160 (260) μA/μm can be achieved along with on/off ratio > 10{sup 6} for V{sub DD} = 0.5 V by the n-type (p-type) line tunneling device made of 2.5% biaxial tensile strained Ge.

Tunnel fire testing and modeling the Morgex North tunnel experiment

CERN Document Server

Borghetti, Fabio; Gandini, Paolo; Frassoldati, Alessio; Tavelli, Silvia

2017-01-01

This book aims to cast light on all aspects of tunnel fires, based on experimental activities and theoretical and computational fluid dynamics (CFD) analyses. In particular, the authors describe a transient full-scale fire test (~15 MW), explaining how they designed and performed the experimental activity inside the Morgex North tunnel in Italy. The entire organization of the experiment is described, from preliminary evaluations to the solutions found for management of operational difficulties and safety issues. This fire test allowed the collection of different measurements (temperature, air velocity, smoke composition, pollutant species) useful for validating and improving CFD codes and for testing the real behavior of the tunnel and its safety systems during a diesel oil fire with a significant heat release rate. Finally, the fire dynamics are compared with empirical correlations, CFD simulations, and literature measurements obtained in other similar tunnel fire tests. This book will be of interest to all ...

Optimization of a tunneling barrier in magnetic tunneling junction by tilted-plasma oxidation

International Nuclear Information System (INIS)

Nam, C.H.; Shim, Heejae; Kim, K.S.; Cho, B.K.

2004-01-01

Oxidation of an AlO x insulating barrier in a magnetic tunneling junction (MTJ) was carried out by a tilted-plasma oxidation method. It was found that the tilted-plasma oxidation induced a gradual change in the extent of oxidation of an insulating layer, which consequently led to a gradual change in the tunneling magnetoresistance (TMR) and specific junction resistance (RA) of the MTJ. We found a linear relation in the TMR versus RA curve with positive and negative slopes for less- and overoxidized junctions, respectively, and a parabolic relation for optimally oxidized junctions. The crossover in the TMR versus RA curves provides an effective and useful way to optimize (and monitor) the oxidation condition of a tunneling barrier in MTJs especially of a tunneling barrier less than 10 A thick. The tunneling junctions were also investigated after thermal annealing at various temperatures. The observations after thermal annealing were found to be consistent with transmission electrons microscopy images and a scenario of the partial formation of an additional ultrathin tunneling barrier at the top surface of the bottom magnetic layer

On the tunneling of full-vector X-Waves through a slab under frustrated total reflection condition

KAUST Repository

Salem, Mohamed; Bagci, Hakan

2012-01-01

Tunneling of full-vector X-Waves through a dielectric slab under frustrated total reflection condition is investigated. Full-vector X-Waves are obtained by superimposing transverse electric and magnetic polarization components, which are derived from the scalar X-Wave solution. The analysis of reflection and transmission at the dielectric interfaces is carried out analytically in a straightforward fashion using vector Bessel beam expansion. Investigation of the fields propagating away from the farther end of the slab (transmitted fields) shows an advanced (superluminal) transmission of the X-Wave peak. Additionally, a similar advanced reflection is also observed. The apparent tunneling of the peak is shown to be due to the phase shift in the fields' spectra and not to be causally related to the incident peak. © 2012 IEEE.

On the tunneling of full-vector X-Waves through a slab under frustrated total reflection condition

KAUST Repository

Salem, Mohamed

2012-07-01

Tunneling of full-vector X-Waves through a dielectric slab under frustrated total reflection condition is investigated. Full-vector X-Waves are obtained by superimposing transverse electric and magnetic polarization components, which are derived from the scalar X-Wave solution. The analysis of reflection and transmission at the dielectric interfaces is carried out analytically in a straightforward fashion using vector Bessel beam expansion. Investigation of the fields propagating away from the farther end of the slab (transmitted fields) shows an advanced (superluminal) transmission of the X-Wave peak. Additionally, a similar advanced reflection is also observed. The apparent tunneling of the peak is shown to be due to the phase shift in the fields\\' spectra and not to be causally related to the incident peak. © 2012 IEEE.

Spin-polarized scanning tunneling microscopy: breakthroughs and highlights.

Science.gov (United States)

Bode, Matthias

2012-01-01

The principle of scanning tunneling microscopy, an imaging method with atomic resolution capability invented by Binnig and Rohrer in 1982, can be adapted for surface magnetism studies by using magnetic probe tips. The contrast mechanism of this so-called spin-polarized scanning tunneling microscopy, or SP-STM, relies on the tunneling magneto-resistance effect, i.e. the tip-sample distance as well as the differential conductance depend on the relative magnetic orientation of tip and sample. To illustrate the working principle and the unique capabilities of SP-STM, this compilation presents some key experiments which have been performed on various magnetic surfaces, such as the topological antiferromagnet Cr(001), a double-layer of Fe which exhibits a stripe- domain pattern with about 50 nm periodicity, and the Mn monolayer on W(110), where the combination of experiment and theory reveal an antiferromagnetic spin cycloid. Recent experimental results also demonstrate the suitability of SP-STM for studies of dynamic properties, such as the spin relaxation time of single magnetic nanostructures.

Force and light tuning vertical tunneling current in the atomic layered MoS2.

Science.gov (United States)

Li, Feng; Lu, Zhixing; Lan, Yann-Wen; Jiao, Liying; Xu, Minxuan; Zhu, Xiaoyang; Zhang, Xiankun; Wu, Hualin; Qi, Junjie

2018-07-06

In this work, the vertical electrical transport behavior of bilayer MoS 2 under the coupling of force and light was explored by the use of conductive atomic force microscopy. We found that the current-voltage behavior across the tip-MoS 2 -Pt junction is a tunneling current that can be well fitted by a Simmons approximation. The transport behavior is direct tunneling at low bias and Fowler-Nordheim tunneling at high bias, and the transition voltage and tunnel barrier height are extracted. The effect of force and light on the effective band gap of the junction is investigated. Furthermore, the source-drain current drops surprisingly when we continually increase the force, and the dropping point is altered by the provided light. This mechanism is responsible for the tuning of tunneling barrier height and width by force and light. These results provide a new way to design devices that take advantage of ultrathin two-dimensional materials. Ultrashort channel length electronic components that possess tunneling current are important for establishing high-efficiency electronic and optoelectronic systems.

Quantum mechanical tunneling in chemical physics

CERN Document Server

Nakamura, Hiroki

2016-01-01

Quantum mechanical tunneling plays important roles in a wide range of natural sciences, from nuclear and solid-state physics to proton transfer and chemical reactions in chemistry and biology. Responding to the need for further understanding of multidimensional tunneling, the authors have recently developed practical methods that can be applied to multidimensional systems. Quantum Mechanical Tunneling in Chemical Physics presents basic theories, as well as original ones developed by the authors. It also provides methodologies and numerical applications to real molecular systems. The book offers information so readers can understand the basic concepts and dynamics of multidimensional tunneling phenomena and use the described methods for various molecular spectroscopy and chemical dynamics problems. The text focuses on three tunneling phenomena: (1) energy splitting, or tunneling splitting, in symmetric double well potential, (2) decay of metastable state through tunneling, and (3) tunneling effects in chemical...

ANALYSIS OF FACTORS CAUSING WATER DAMAGE TO LOESS DOUBLE-ARCHED TUNNEL BASED ON TFN-AHP

Directory of Open Access Journals (Sweden)

Mao Zheng-jun

2017-04-01

Full Text Available In order to analysis the factors causing water damage to loess double-arched tunnel, this paper conducts field investigation on water damage to tunnels on Lishi-Jundu Expressway in Shanxi, China, confirms its development characteristics, builds an index system (covering 36 evaluation indexes for construction condition, design stage, construction stage, and operation stage for the factors causing water damage to loess double-arched tunnel, applies TFN-AHP (triangular fuzzy number-analytic hierarchy process in calculating the weight of indexes at different levels, and obtains the final sequence of weight of the factors causing water seepage to loess double-arched tunnel. It is found out that water damage to loess double-arched tunnel always develops in construction joints, expansion joints, settlement joints, and lining joints of tunnel and even around them; there is dotted water seepage, linear water seepage, and planar water seepage according to the trace and scope of water damage to tunnel lining. The result shows that water damage to loess double-arched tunnel mainly refers to linear water seepage, planar water seepage is also developed well, and partition and equipment box at the entrance and exit of tunnel are prone to water seepage; construction stage is crucial for controlling water damage to loess double-arched tunnel, atmospheric precipitation is the main water source, and the structure defect of double-arched tunnel increases the possibility of water seepage; the final sequence for weight of various factors is similar to the actual result.

Tunneling into quantum wires: regularization of the tunneling Hamiltonian and consistency between free and bosonized fermions

OpenAIRE

Filippone, Michele; Brouwer, Piet

2016-01-01

Tunneling between a point contact and a one-dimensional wire is usually described with the help of a tunneling Hamiltonian that contains a delta function in position space. Whereas the leading order contribution to the tunneling current is independent of the way this delta function is regularized, higher-order corrections with respect to the tunneling amplitude are known to depend on the regularization. Instead of regularizing the delta function in the tunneling Hamiltonian, one may also obta...

Effect of simulated in-flight thrust reversing on vertical-tail loads of F-18 and F-15 airplane models. [conducted in the Langley 16-foot transonic tunnel

Science.gov (United States)

Bare, E. A.; Berrier, B. L.; Capone, F. J.

1981-01-01

Investigations were conducted in the Langley 16-Foot Transonic Tunnel to provide data on a 0.10-scale model of the prototype F-18 airplane and a 0.047-scale model of the F-15 three-surface configuration (canard, wing, and horizontal tails). Test data were obtained at static conditions and at Mach numbers from 0.6 to 1.2 over an angle-of-attack range from 2 deg to 15 deg. Nozzle pressure ratio was varied from jet off to about 8.0.

Static and wind tunnel near-field/far-field jet noise measurements from model scale single-flow base line and suppressor nozzles. Summary report. [conducted in the Boeing large anechoic test chamber and the NASA-Ames 40by 80-foot wind tunnel

Science.gov (United States)

Jaeck, C. L.

1977-01-01

A test program was conducted in the Boeing large anechoic test chamber and the NASA-Ames 40- by 80-foot wind tunnel to study the near- and far-field jet noise characteristics of six baseline and suppressor nozzles. Static and wind-on noise source locations were determined. A technique for extrapolating near field jet noise measurements into the far field was established. It was determined if flight effects measured in the near field are the same as those in the far field. The flight effects on the jet noise levels of the baseline and suppressor nozzles were determined. Test models included a 15.24-cm round convergent nozzle, an annular nozzle with and without ejector, a 20-lobe nozzle with and without ejector, and a 57-tube nozzle with lined ejector. The static free-field test in the anechoic chamber covered nozzle pressure ratios from 1.44 to 2.25 and jet velocities from 412 to 594 m/s at a total temperature of 844 K. The wind tunnel flight effects test repeated these nozzle test conditions with ambient velocities of 0 to 92 m/s.

Photoluminescence spectra of n-doped double quantum wells in a parallel magnetic field

International Nuclear Information System (INIS)

Huang, D.; Lyo, S.K.

1999-01-01

We show that the photoluminescence (PL) line shapes from tunnel-split ground sublevels of n-doped thin double quantum wells (DQW close-quote s) are sensitively modulated by an in-plane magnetic field B parallel at low temperatures (T). The modulation is caused by the B parallel -induced distortion of the electronic structure. The latter arises from the relative shift of the energy-dispersion parabolas of the two quantum wells (QW close-quote s) in rvec k space, both in the conduction and valence bands, and formation of an anticrossing gap in the conduction band. Using a self-consistent density-functional theory, the PL spectra and the band-gap narrowing are calculated as a function of B parallel , T, and the homogeneous linewidths. The PL spectra from symmetric and asymmetric DQW close-quote s are found to show strikingly different behavior. In symmetric DQW close-quote s with a high density of electrons, two PL peaks are obtained at B parallel =0, representing the interband transitions between the pair of the upper (i.e., antisymmetric) levels and that of the lower (i.e., symmetric) levels of the ground doublets. As B parallel increases, the upper PL peak develops an N-type kink, namely a maximum followed by a minimum, and merges with the lower peak, which rises monotonically as a function of B parallel due to the diamagnetic energy. When the electron density is low, however, only a single PL peak, arising from the transitions between the lower levels, is obtained. In asymmetric DQW close-quote s, the PL spectra show mainly one dominant peak at all B parallel close-quote s. In this case, the holes are localized in one of the QW close-quote s at low T and recombine only with the electrons in the same QW. At high electron densities, the upper PL peak shows an N-type kink like in symmetric DQW close-quote s. However, the lower peak is absent at low B parallel close-quote s because it arises from the inter-QW transitions. Reasonable agreement is obtained with recent

A Lightweight Radio Propagation Model for Vehicular Communication in Road Tunnels.

Directory of Open Access Journals (Sweden)

Muhammad Ahsan Qureshi

Full Text Available Radio propagation models (RPMs are generally employed in Vehicular Ad Hoc Networks (VANETs to predict path loss in multiple operating environments (e.g. modern road infrastructure such as flyovers, underpasses and road tunnels. For example, different RPMs have been developed to predict propagation behaviour in road tunnels. However, most existing RPMs for road tunnels are computationally complex and are based on field measurements in frequency band not suitable for VANET deployment. Furthermore, in tunnel applications, consequences of moving radio obstacles, such as large buses and delivery trucks, are generally not considered in existing RPMs. This paper proposes a computationally inexpensive RPM with minimal set of parameters to predict path loss in an acceptable range for road tunnels. The proposed RPM utilizes geometric properties of the tunnel, such as height and width along with the distance between sender and receiver, to predict the path loss. The proposed RPM also considers the additional attenuation caused by the moving radio obstacles in road tunnels, while requiring a negligible overhead in terms of computational complexity. To demonstrate the utility of our proposed RPM, we conduct a comparative summary and evaluate its performance. Specifically, an extensive data gathering campaign is carried out in order to evaluate the proposed RPM. The field measurements use the 5 GHz frequency band, which is suitable for vehicular communication. The results demonstrate that a close match exists between the predicted values and measured values of path loss. In particular, an average accuracy of 94% is found with R2 = 0.86.

Tunnelling of a molecule

International Nuclear Information System (INIS)

Jarvis, P.D.; Bulte, D.P.

1998-01-01

A quantum-mechanical description of tunnelling is presented for a one-dimensional system with internal oscillator degrees of freedom. The 'charged diatomic molecule' is frustrated on encountering a barrier potential by its centre of charge not being coincident with its centre of mass, resulting in transitions amongst internal states. In an adiabatic limit, the tunnelling of semiclassical coherent-like oscillator states is shown to exhibit the Hartman and Bueuttiker-Landauer times t H and t BL , with the time dependence of the coherent state parameter for the tunnelled state given by α(t) = α e -iω(t+Δt) , Δt = t H - it BL . A perturbation formalism is developed, whereby the exact transfer matrix can be expanded to any desired accuracy in a suitable limit. An 'intrinsic' time, based on the oscillator transition rate during tunnelling, transmission or reflection, is introduced. In simple situations the resulting intrinsic tunnelling time is shown to vanish to lowest order. In the general case a particular (nonzero) parametrisation is inferred, and its properties discussed in comparison with the literature on tunnelling times for both wavepackets and internal clocks. Copyright (1998) CSIRO Australia

Influence of quasiparticle multi-tunneling on the energy flow through the superconducting tunnel junction

International Nuclear Information System (INIS)

Samedov, V. V.; Tulinov, B. M.

2011-01-01

Superconducting tunnel junction (STJ) detector consists of two layers of superconducting material separated by thin insulating barrier. An incident particle produces in superconductor excess nonequilibrium quasiparticles. Each quasiparticle in superconductor should be considered as quantum superposition of electron-like and hole-like excitations. This duality nature of quasiparticle leads to the effect of multi-tunneling. Quasiparticle starts to tunnel back and forth through the insulating barrier. After tunneling from biased electrode quasiparticle loses its energy via phonon emission. Eventually, the energy that equals to the difference in quasiparticle energy between two electrodes is deposited in the signal electrode. Because of the process of multi-tunneling, one quasiparticle can deposit energy more than once. In this work, the theory of branching cascade processes was applied to the process of energy deposition caused by the quasiparticle multi-tunneling. The formulae for the mean value and variance of the energy transferred by one quasiparticle into heat were derived. (authors)

Interaction between electrons and tunneling levels in metallic glasses

International Nuclear Information System (INIS)

Black, J.L.; Gyorffy, B.L.

1978-01-01

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

Enhanced MRI in carpal tunnel syndrome

International Nuclear Information System (INIS)

Hayakawa, Katsuhiko; Nakane, Takashi; Kobayashi, Shigeru; Asai, Takahiro; Wada, Kunio; Yoshizawa, Hidezo

1998-01-01

In this study, we performed contrast-enhanced MRI in patients with idiopathic carpal tunnel syndrome and examined the morphologic change in the carpal tunnel. In the transverse section of the opening of carpal tunnel where scaphoid and pisiform bones are figured out, we measured and examined 4 items, viz. the soft carpal tunnel volume, flat rate of median nerve, position of median nerve and thickness of palmer ligaments composing the base of carpal tunnel, with an image analyzer attached to the MRI apparatus. Whereas the average carpal tunnel volume in 12 hands of normal controls was 166.8 mm 2 , that in 74 hands of carpal tunnel syndrome was 207.2 mm 2 , a significant increase compared with the normal controls. The flat rate of median nerve was 46% in the controls, but that was 37.5% in the carpal tunnel syndrome, a significant flattening was noted. We connected the peaks of the scaphoid node and pisiform bone with a line and named it standard line. When we observed the position of median nerve in the carpal tunnel, the nerve in 9 of 12 hands, 75%, lay below the standard line in the controls, but the nerve in 65 of 74 hands, 87.8%, lay above the standard line in the carpal tunnel syndrome, clearly showing that the median nerve had shifted to the palmar side. Regarding these morphologic changes of the carpal tunnel, the internal pressure of the carpal tunnel is considered to be raised with swelling of the soft tissues mainly composing the inside of carpal tunnel, thus the area of cross section of carpal tunnel to be increased, the median nerve to be shifted to the palmar side and the median nerve to be compressed by the transverse carpal ligament at that time. Although we can observe these morphological changes readily in MRI images, these images show only the results of carpal tunnel syndrome after all, and do not specify the direct causes. However, we believe that these facts are important factors in the manifestation of idiopathic carpal tunnel syndrome. (author)

A Historical Evaluation of the U12t Tunnel, Nevada Test Site, Nye County, Nevada, Volume 6 of 6

Energy Technology Data Exchange (ETDEWEB)

Harold Drollinger; Robert C. Jones; and Thomas F. Bullard; Desert Research Institute, Laurence J. Ashbaugh, Southern Nevada Courier Service and Wayne R. Griffin, Stoller-Navarro Joint Venture

2009-02-01

This report presents a historical evaluation of the U12t Tunnel on the Nevada Test Site in southern Nevada. The work was conducted by the Desert Research Institute at the request of the U.S. Department of Energy, National Nuclear Security Administration Nevada Site Office and the U.S. Department of Defense, Defense Threat Reduction Agency (DTRA). The U12t Tunnel is one of a series of tunnels used for underground nuclear weapons effects tests on the east side of Rainier and Aqueduct Mesas. Six nuclear weapons effects tests, Mint Leaf, Diamond Sculls, Husky Pup, Midas Myth/Milagro, Mighty Oak, and Mission Ghost, and one high explosive test, SPLAT, were conducted within the U12t Tunnel from 1970 to 1987. All six of the nuclear weapons effects tests and the high explosive test were sponsored by DTRA. Two conventional weapons experiments, Dipole Knight and Divine Eagle, were conducted in the tunnel portal area in 1997 and 1998. These experiments were sponsored by the Defense Special Weapons Agency. The U12t Tunnel complex is composed of the Portal and Mesa Areas and includes an underground tunnel with a main access drift and nine primary drifts, a substantial tailings pile fronting the tunnel portal, a series of discharge ponds downslope of the tailings pile, and two instrumentation trailer parks and 16 drill holes on top of Aqueduct Mesa. A total of 89 cultural features were recorded: 54 at the portal and 35 on the mesa. In the Portal Area, cultural features are mostly concrete pads and building foundations; other features include the portal, rail lines, the camel back, ventilation and cooling system components, communication equipment, and electrical equipment. On the mesa are drill holes, a few concrete pads, a loading ramp, and electrical equipment.

A Historical Evaluation of the U12t Tunnel, Nevada Test Site, Nye County, Nevada, Volume 1 of 6

Energy Technology Data Exchange (ETDEWEB)

Drollinger, Harold [Desert Research Institute (DRI), Nevada System of Higher Education, Reno,NV (United States); Jones, Robert C. [Desert Research Institute (DRI), Nevada System of Higher Education, Reno,NV (United States); Bullard, Thomas F. [Desert Research Institute (DRI), Nevada System of Higher Education, Reno,NV (United States); Ashbaugh, Laurence J. [Southern Nevada Courier Service, NV (United States); Griffin, Wayne R. [Stoller-Navarro Joint Venture, Las Vegas, NV (United States)

2009-02-01

This report presents a historical evaluation of the U12t Tunnel on the Nevada Test Site in southern Nevada. The work was conducted by the Desert Research Institute at the request of the U.S. Department of Energy, National Nuclear Security Administration Nevada Site Office and the U.S. Department of Defense, Defense Threat Reduction Agency (DTRA). The U12t Tunnel is one of a series of tunnels used for underground nuclear weapons effects tests on the east side of Rainier and Aqueduct Mesas. Six nuclear weapons effects tests, Mint Leaf, Diamond Sculls, Husky Pup, Midas Myth/Milagro, Mighty Oak, and Mission Ghost, and one high explosive test, SPLAT, were conducted within the U12t Tunnel from 1970 to 1987. All six of the nuclear weapons effects tests and the high explosive test were sponsored by DTRA. Two conventional weapons experiments, Dipole Knight and Divine Eagle, were conducted in the tunnel portal area in 1997 and 1998. These experiments were sponsored by the Defense Special Weapons Agency. The U12t Tunnel complex is composed of the Portal and Mesa Areas and includes an underground tunnel with a main access drift and nine primary drifts, a substantial tailings pile fronting the tunnel portal, a series of discharge ponds downslope of the tailings pile, and two instrumentation trailer parks and 16 drill holes on top of Aqueduct Mesa. A total of 89 cultural features were recorded: 54 at the portal and 35 on the mesa. In the Portal Area, cultural features are mostly concrete pads and building foundations; other features include the portal, rail lines, the camel back, ventilation and cooling system components, communication equipment, and electrical equipment. On the mesa are drill holes, a few concrete pads, a loading ramp, and electrical equipment.

Probing spin-polarized tunneling at high bias and temperature with a magnetic tunnel transistor

NARCIS (Netherlands)

Park, B.G.; Banerjee, T.; Min, B.C.; Sanderink, Johannes G.M.; Lodder, J.C.; Jansen, R.

2005-01-01

The magnetic tunnel transistor (MTT) is a three terminal hybrid device that consists of a tunnel emitter, a ferromagnetic (FM) base, and a semiconductor collector. In the MTT with a FM emitter and a single FM base, spin-polarized hot electrons are injected into the base by tunneling. After

Control of tunneling in heterostructures

International Nuclear Information System (INIS)

Volokhov, V M; Tovstun, C A; Ivlev, B

2007-01-01

A tunneling current between two rectangular potential wells can be effectively controlled by applying an external ac field. A variation of the ac frequency by 10% may lead to the suppression of the tunneling current by two orders of magnitude, which is a result of quantum interference under the action of the ac field. This effect of destruction of tunneling can be used as a sensitive control of tunneling current across nanosize heterostructures

Josephson current at atomic scale: Tunneling and nanocontacts using a STM

International Nuclear Information System (INIS)

Rodrigo, J.G.; Crespo, V.; Vieira, S.

2006-01-01

Using a scanning tunneling microscope, STM, with a superconducting tip, we have measured the Josephson current in atomic size tunnel junctions and contacts with a small number of quantum channels of conduction. We analyze our results in terms of the Ivanchenko and Zil'berman model for phase diffusion. The effect of the thermal energy and the electromagnetic environment on the Josephson current is discussed in terms of the transmissions of the individual quantum channels. These results suppose an initial step to the control of Scanning Josephson Spectroscopy at atomic level

Nanoelectromechanical switch operating by tunneling of an entire C-60 molecule

DEFF Research Database (Denmark)

Danilov, Andrey V.; Hedegård, Per; Golubev, Dimitrii S.

2008-01-01

(i) the relative contribution of tunneling, current induced heating and thermal fluctuations to the switching mechanism, (ii) the voltage dependent energy barrier (similar to 100-200 meV) separating the two states of the switch and (iii) the switching attempt frequency, omega(0) corresponding to a 2......We present a solid state single molecule electronic device where switching between two states with different conductance happens predominantly by tunneling of an entire C-60 molecule. This conclusion is based on a novel statistical analysis of similar to 10(5) switching events. The analysis yields...

Hybrid Wing Body Model Identification Using Forced-Oscillation Water Tunnel Data

Science.gov (United States)

Murphy, Patrick C.; Vicroy, Dan D.; Kramer, Brian; Kerho, Michael

2014-01-01

Static and dynamic testing of the NASA 0.7 percent scale Hybrid Wing Body (HWB) configuration was conducted in the Rolling Hills Research Corporation water tunnel to investigate aerodynamic behavior over a large range of angle-of-attack and to develop models that can predict aircraft response in nonlinear unsteady flight regimes. This paper reports primarily on the longitudinal axis results. Flow visualization tests were also performed. These tests provide additional static data and new dynamic data that complement tests conducted at NASA Langley 14- by 22-Foot Subsonic Tunnel. HWB was developed to support the NASA Environmentally Responsible Aviation Project goals of lower noise, emissions, and fuel burn. This study also supports the NASA Aviation Safety Program efforts to model and control advanced transport configurations in loss-of-control conditions.

Wind tunnel evaluation of the RAAMP sampler. Final report

International Nuclear Information System (INIS)

Vanderpool, R.W.; Peters, T.M.

1994-11-01

Wind tunnel tests of the Department of Energy RAAMP (Radioactive Atmospheric Aerosol Monitoring Program) monitor have been conducted at wind speeds of 2 km/hr and 24 km/hr. The RAAMP sampler was developed based on three specific performance objectives: (1) meet EPA PM10 performance criteria, (2) representatively sample and retain particles larger than 10 microm for later isotopic analysis, (3) be capable of continuous, unattended operation for time periods up to 2 months. In this first phase of the evaluation, wind tunnel tests were performed to evaluate the sampler as a potential candidate for EPA PM10 reference or equivalency status. As an integral part of the project, the EPA wind tunnel facility was fully characterized at wind speeds of 2 km/hr and 24 km/hr in conjunction with liquid test aerosols of 10 microm aerodynamic diameter. Results showed that the facility and its operating protocols met or exceeded all 40 CFR Part 53 acceptance criteria regarding PM10 size-selective performance evaluation. Analytical procedures for quantitation of collected mass deposits also met 40 CFR Part 53 criteria. Modifications were made to the tunnel's test section to accommodate the large dimensions of the RAAMP sampler's instrument case

Charge and spin current oscillations in a tunnel junction induced by magnetic field pulses

Energy Technology Data Exchange (ETDEWEB)

Dartora, C.A., E-mail: cadartora@eletrica.ufpr.br [Electrical Engineering Department, Federal University of Parana (UFPR), C.P. 19011 Curitiba, 81.531-970 PR (Brazil); Nobrega, K.Z., E-mail: bzuza1@yahoo.com.br [Federal Institute of Education, Science and Technolgy of Maranhão (IFMA), Av. Marechal Castelo Branco, 789, São Luís, 65.076-091 MA (Brazil); Cabrera, G.G., E-mail: cabrera@ifi.unicamp.br [Instituto de Física ‘Gleb Wataghin’, Universidade Estadual de Campinas (UNICAMP), C.P. 6165, Campinas 13.083-970 SP (Brazil)

2016-08-15

Usually, charge and spin transport properties in tunnel junctions are studied in the DC bias regime and/or in the adiabatic regime of time-varying magnetic fields. In this letter, the temporal dynamics of charge and spin currents in a tunnel junction induced by pulsed magnetic fields is considered. At low bias voltages, energy and momentum of the conduction electrons are nearly conserved in the tunneling process, leading to the description of the junction as a spin-1/2 fermionic system coupled to time-varying magnetic fields. Under the influence of pulsed magnetic fields, charge and spin current can flow across the tunnel junction, displaying oscillatory behavior, even in the absence of DC bias voltage. A type of spin capacitance function, in close analogy to electric capacitance, is predicted.