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PubMed Journals Articles About "Resonant Tunneling Induced Enhancement Electron Field Emission Ultra" RSS

16:04 EDT 15th September 2019 | BioPortfolio

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Showing "Resonant Tunneling Induced Enhancement Electron Field Emission Ultra" PubMed Articles 1–25 of 29,000+

Coherent Resonant Tunneling through Double Metallic Quantum-Well States.

Study of resonant tunneling through multi-metallic quantum well (QW) structure is not only important for the fundamental understanding of quantum transport, but also for the great potential to generate advanced functionalities of spintronic devices. However, it remains challenging to engineer such structure due to the short electron phase coherence length in metallic QW system. Here, we demonstrate the successful fabrication of double-QW structure in a single fully epitaxial MTJ heterostructure, where two F...


Conduction mechanisms and voltage drop during field electron emission from diamond needles.

We report results of experimental investigation of field electron emission from diamond nanoemitters. The measurements were performed with single crystal diamond needles fixed at tungsten tips. The voltage drop along diamond needles during emission was revealed and measured using electron energy spectroscopy. The observed linear dependence of the voltage drop in diamond on voltage applied to the tungsten tip is explained in the frame of a simple macroscopic electrical model combining Poole-Frenkel conductio...

Stacking angle-tunable photoluminescence from interlayer exciton states in twisted bilayer graphene.

Twisted bilayer graphene (tBLG) is a metallic material with two degenerate van Hove singularity transitions that can rehybridize to form interlayer exciton states. Here we report photoluminescence (PL) emission from tBLG after resonant 2-photon excitation, which tunes with the interlayer stacking angle, θ. We spatially image individual tBLG domains at room-temperature and show a five-fold resonant PL-enhancement over the background hot-electron emission. Prior theory predicts that interlayer orbitals mix t...


Nano-antenna enhanced waveguide integrated light source based on an MIS tunnel junction.

Ultrafast electro-optical conversion at nanoscale is of fundamental interest for information transfer and optical interconnects. Light emission from a quantum tunnel junction provides an opportunity owing to its unique capability of ultrafast response and small footprint. However, the main challenge to the wide adoption of the tunnel junction is its low emission efficiency caused by the low inelastic electron tunneling proportion and radiation efficiency. In this Letter, an electrically driven silicon light...

Unifying Tunneling Pictures of Strong-Field Ionization with an Improved Attoclock.

We demonstrate a novel attoclock, in which we add a perturbative linearly polarized light field at 400 nm to calibrate the attoclock constructed by an intense circularly polarized field at 800 nm. This approach can be directly implemented to analyze the recent hot and controversial topics involving strong-field tunneling ionization. The generally accepted picture is that tunneling ionization is instantaneous and that the tunneling probability synchronizes with the laser electric field. Alternatively, rece...

Dependence of enhancement factor on electrode size for field emission current from carbon nanotube on silicon wafer.

This work studies the enhancement factor associated with a current emitted from a multi-wall carbon nanotube to an extremely small counter electrode. The experimental data show that the field enhancement factor increases by 1.15 times when the width of the counter electrode increases from 50 to 200 nm. To better understand this enhancement effect, field intensities at the emitter surface are numerically simulated. The experimental work and simulations demonstrate that the observed field enhancement results ...

The field emission of carbon-in-Al4O4C nanoneedles and its failure mechanism: high-field induced shell cracking and chemical Decomposition.

Although ceramic Al4O4C has been found with interesting optical properties recently, the low conductivity makes it difficult to be used in fields related to electron transport. Here, we achieved carbon-in-Al4O4C core-shell nanoneedles via a one-step chemical vapor deposition method. The core with the form of few-layer graphene embedded in amorphous carbon improves the electron transport largely, as the I-V measurement based on a single nanowire. Good field electron emission behavior was observed in these na...

Metal Nanoparticle enhancement of electron transfer to tethered redox centers through self-assembled molecular films.

Metal nanoparticle mediated electron transfer (ET) across an insulator thin film containing nanoparticles with attached redox centers was studied using electrochemical impedance spectroscopy. Specifically, a gold spherical microelectrode was modified with 16-amino-1-hexa-decanethiol creating an insulator film. This was followed by the electrostatic adsorption of gold nanoparticles and the covalent attachment of Os2+ redox centers. A variation of the Creager-Wooster method was developed in order to get quant...

Optical antennas driven by quantum tunneling: a key issues review.

Analogous to radio- and microwave antennas, optical nanoantennas are devices that receive and emit radiation at optical frequencies. Until recently, the realization of electrically driven optical antennas was an outstanding challenge in nanophotonics. In this review we discuss and analyze recent reports in which quantum tunneling---specifically inelastic electron tunneling---is harnessed as a means to convert electrical energy into photons, mediated by optical antennas. To aid this analysis we introduce the...

Silicon and germanium terminated (001)-(2x1) diamond surface.

Control over the chemical termination of diamond surfaces has shown great promise in the realization of field-emission applications, the selection of charge states of near-surface colour-centres such as NV, and the realisation of surface-conductive channels for electronic device applications. Experimental investigations of ultra-thin Si and Ge layers yield surface states both within the band-gap and resonant with the underlying diamond valence band. In this report, we report the results of density-functiona...

Scanning Tunneling Microscope-Induced Excitonic Luminescence of a Two-Dimensional Semiconductor.

The long sought-after goal of locally and spectroscopically probing the excitons of two-dimensional (2D) semiconductors is attained using a scanning tunneling microscope (STM). Excitonic luminescence from monolayer molybdenum diselenide (MoSe_{2}) on a transparent conducting substrate is electrically excited in the tunnel junction of an STM under ambient conditions. By comparing the results with photoluminescence measurements, the emission mechanism is identified as the radiative recombination of bright A e...

Ultra-efficient spin-orbit torque induced magnetic switching in W/CoFeB/MgO structures.

The spin-orbit torque (SOT) induced magnetic switching in heavy metal/ferromagnet (HM/FM) structures with perpendicular magnetic anisotropy (PMA) is promising for energy-efficient spintronic devices. Here, we studied the SOT induced magnetic switching in perpendicular W/Co20Fe60B20/MgO structures. We demonstrated the critical current density for the SOT induced switching is as low as 1.15∗10<sup>6</sup> A/cm2 in the presence of an in-plane magnetic field, which is very energy e...

Experimental observation of negative grey trion in electron rich WSe2 monolayer.

We measure the evolution of low temperature photoluminescence in a WSe<sub>2</sub> monolayer with increasing electron concentration level. By comparing non-resonant and resonant laser laser excitation, we find that the formation of negative trions is facilitated by very efficient phonon emission. The most prominent line is photolumienscence spectra in the intermediate range of carrier concentations (below 5×10<sup>12</sup> cm<sup>-2&...

Experimental measurements validate the use of the binary encounter approximation model to accurately compute proton induced dose and radiolysis enhancement from gold nanoparticles.

In protontherapy, it has been suggested that nanoparticles of high-Z material like gold (GNP) be used as radiosensitizers. The origin of this enhancement phenomenon for proton radiation is not yet well understood and additional mechanistic insights are required. Previous works have highlighted the good capabilities of TRAX to reproduce secondary electron emission from gold material. Therefore, TRAX cross sections obtained with the binary encounter approximation (BEA) model for proton ionization were impleme...

Donor-acceptor symmetric and antisymmetric tunneling matrix elements: a pathway model investigation of protein electron transfer.

In protein electron transfer reaction rate calculations, the electronic Hamiltonian is apportioned into donor-acceptor (D-A) and protein bridge subspaces, and a two-state system is defined for the D-A subspace. Löwdin partitioning is used to perform the two-state reductions necessary to compute the tunneling matrix element between D and A sites. Here, a method of performing donor and acceptor state analysis for a non-orthogonal basis set in both the weak and strong electronic coupling regimes is developed....

Resolving the Correlation between Tip-Enhanced Resonance Raman Scattering and Local Electronic States with 1 nm Resolution.

Low-temperature tip-enhanced Raman spectroscopy (TERS) enables chemical identification with single-molecule sensitivity and extremely high spatial resolution even down to the atomic scale. The large enhancement of Raman scattering obtained in TERS can originate from physical and/or chemical enhancement mchanisms. Whereas physical enhancement requires a strong near-field through excitation of localized surface plasmons, chemical enhancement is governed by resonance in the electronic structure of the sample, ...

Directing Single-Molecule Emission with DNA Origami-Assembled Optical Antennas.

We demonstrate the capability of DNA self-assembled optical antennas to direct the emission of an individual fluorophore, which is free to rotate. DNA origami is used to fabricate optical antennas composed of two colloidal gold nanoparticles separated by a predefined gap and to place a single Cy5 fluorophore near the gap center. Although the fluorophore is able to rotate, its excitation and far-field emission is mediated by the antenna, with the emission directionality following a dipolar pattern according ...

Dynamic nuclear polarisation of liquids at one microtesla using circularly polarised RF with application to millimetre resolution MRI.

Magnetic resonance imaging in ultra-low fields is often limited by mediocre signal-to-noise ratio hindering a higher resolution. Overhauser dynamic nuclear polarisation (O-DNP) using nitroxide radicals has been an efficient solution for enhancing the thermal nuclear polarisation. However, the concurrence of positive and negative polarisation enhancements arises in ultra-low fields resulting in a significantly reduced net enhancement, making O-DNP far less attractive. Here, we address this issue by applying ...

Development of Ion Mobility Spectrometry with Novel Atmospheric Electron Emission Ionization for Field Detection of Gaseous and Blister Chemical Warfare Agents.

Drift tube ion mobility spectrometry with a novel atmospheric electron emission (AEE) source was developed for determination of gaseous and blister chemical warfare agents (CWAs) in negative mode. The AEE source was fabricated from an aluminum substrate electrode covered with 1 μm silver nanoparticle-dispersed silicone resin and a thin gold layer. This structure enabled stable tunneling electron emission upon the application of more than 11 V potential under atmospheric pressure. The reactant ion peak (RIP...

Plasmonic Measurement of Electron Transfer Between a Single Metal Nanoparticle and an Electrode through a Molecular Layer.

We study electron transfer associated with electrocatalytic reduction of hydrogen on single platinum nanoparticles separated from an electrode surface with an alkanethiol monolayer using a plasmonic imaging technique. By varying the monolayer thickness, we show that the reaction rate depends on electron tunneling from the electrode to the nanoparticle. The tunneling decay constant is ~4.3 nm-1, which is small compared to those in literature for alkanethiols. We attribute it to a reduced tunneling barrier re...

Optimization of off-axis electron holography performed with femtosecond electron pulses.

We report on electron holography experiments performed with femtosecond electron pulses in an ultrafast coherent Transmission Electron Microscope based on a laser-driven cold field emission gun. We first discuss the experimental requirements related to the long acquisition times imposed by the low emission/probe current available in these instruments. The experimental parameters are first optimized and electron holograms are then acquired in vacuum and on a nano-object showing that useful physical propertie...

Giant Enhancement in the Supercapacitance of NiFe-Graphene Nanocomposites Induced by a Magnetic Field.

The rapid rise in energy demand in the past years has prompted a search for low-cost alternatives for energy storage, supercapacitors being one of the most important devices. It is shown that a dramatic enhancement (≈1100%, from 155 to 1850 F g ) of the specific capacitance of a hybrid stimuli-responsive FeNi -graphene electrode material can be achieved when the charge/discharge cycling is performed in the presence of an applied magnetic field of 4000 G. This result is related to an unprecedented magnetic...

Plasmon Excited Ultrahot Carriers and Negative Differential Photoresponse in a Vertical Graphene van der Waals Heterostructure.

Photogenerated nonequilibrium hot carriers play a key role in graphene's intriguing optoelectronic properties. Compared to conventional photoexcitation, plasmon excitation can be engineered to enhance and control the generation and dynamics of hot carriers. Here, we report an unusual negative differential photoresponse of plasmon-induced "ultrahot" electrons in a graphene-boron nitride-graphene tunneling junction. We demonstrate nanocrescent gold plasmonic nanostructures that substantially enhance the absor...

Rotation of Single-Molecule Emission Polarization by Plasmonic Nanorods.

The strong light-matter interactions between dyes and plasmonic nanoantennas enable the study of fundamental molecular-optical processes. Here, we overcome conventional limitations with high-throughput single-molecule polarization-resolved microscopy to measure dye emission polarization modifications upon near-field coupling to a gold nanorod. We determine that the emission polarization distribution is not only rotated toward the nanorod's dominant localized surface plasmon mode as expected, but is also uni...

Thermodynamic evidence of magnetic-field-induced complete valley polarization in bismuth.

We investigated the fundamental physical properties in the ultra-quantum limit state of bismuth through measurements of magnetoresistance, magnetization, magnetostriction, and ultrasound attenuation in magnetic fields up to 60T. For magnetic fields applied along the bisectrix direction of a single crystal, a drastic sign reversal in magnetostriction was observed at approximately 39T, which could be ascribed to the complete valley polarization in the electron Fermi pockets. The application of magnetic fields...


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