Search results for "Tunne"
showing 10 items of 739 documents
Thermal irreversibility in optically labeled low-temperature glasses.
1989
We present an investigation of irreversible features of thermal broadening of persistent spectral holes. The investigation is based on temperature-cycling hole-burning experiments performed with a variety of organic glasses doped with rather different probe molecules. The results show a rich temperature dependence. They can, however, be interpreted in terms of the well-known spectral diffusion models, in which we introduced a freezing condition to account for thermal irreversiblity. There is a tunneling regime for low temperatures and an activated regime for high temperatures. In the tunneling regime the broadening is linear in T; in the activated regime it increases with ${T}^{3/2}$ and lo…
Rational design of new materials for spintronics: Co2FeZ (Z=Al, Ga, Si, Ge)
2008
Spintronic is a multidisciplinary field and a new research area. New materials must be found for satisfying the different types of demands. The search for stable half-metallic ferromagnets and ferromagnetic semiconductors with Curie temperatures higher than room temperature is still a challenge for solid state scientists. A general understanding of how structures are related to properties is a necessary prerequisite for material design. Computational simulations are an important tool for a rational design of new materials. The new developments in this new field are reported from the point of view of material scientists. The development of magnetic Heusler compounds specifically designed as …
Transition from direct to Fowler-Nordheim tunneling in chemically reduced graphene oxide film.
2014
We investigate charge transport in a chemically reduced graphene oxide (RGO) film of sub-micron thickness. The I-V curve of RGO film shows current switching of the order of ∼10(5) above the threshold voltage. We found that the observed I-V curve is consistent with quantum tunnelling based charge transport. The quantum tunnelling based Simmons generalized theory was used to interpret the charge transport mechanism which shows that the current switching phenomenon is associated with transition from direct to Fowler-Nordheim (F-N) tunneling. The absence of current switching in the I-V curve after stripping away the oxygen functional groups from chemically RGO film confirms that the presence of…
Large Tunneling Anisotropic Magneto-Seebeck Effect in a CoPt|MgO|Pt Tunnel Junction
2014
We theoretically investigate the Tunneling Anisotropic Magneto-Seebeck effect in a realistically-modeled CoPt|MgO|Pt tunnel junction using coherent transport calculations. For comparison we study the tunneling magneto-Seebeck effect in CoPt|MgO|CoPt as well. We find that the magneto-Seebeck ratio of CoPt|MgO|Pt exceeds that of CoPt|MgO|CoPt for small barrier thicknesses, reaching 175% at room temperature. This result provides a sharp contrast to the magnetoresistance, which behaves oppositely for all barrier thicknesses and differs by one order of magnitude between devices. Here the magnetoresistance results from differences in transmission brought upon by changing the tunnel junction's mag…
Spintronics and Nanomemory Systems
2017
The chapter presents and explains the possibilities of CNT forest growth on Fe–Pt nanoparticles for the magnetic nanomemory. The magnetoresistance phenomena – giant magnetoresistance and tunnelling magnetoresistance (GMR and TMR) – for nanomemory devices are based on CNTs of various morphologies (i.e. various chiralities, diameters). It includes metal- and semiconductor-like CNTs which can be considered as alternative variants for electromagnetic nanosensoring and magnetic nanomemory. The chapter also presents simulations of Fe–Pt magnetically disordered nanodrops, as well as spin transport models.
Primary thermometry with nanoscale tunnel junctions
1995
We have found current-voltage (I-V) and conductance (dI/dV) characteristics of arrays of nanoscale tunnel junctions between normal metal electrodes to exhibit suitable features for primary thermometry. The current through a uniform array depends on the ratio of the thermal energy kBT and the electrostatic charging energy E c of the islands between the junctions and is completely blocked by Coulomb repulsion at T = 0 and at small voltages eV/2 ≤ Ec. In the opposite limit, kBT ≫ Ec, the width of the conductance minimum scales linearly and universally with T and N, the number of tunnel junctions, and qualifies as a primary thermometer. The zero bias drop in the conductance is proportional to T…
Bright Beaches of Nanoscale Potassium Islands on Graphite in STM Imaging
2008
We demonstrate, via scanning tunneling microscopy (STM) measurements performed at 48 K, the existence of "bright beaches" at the edges of K islands (diameter approximately 5-500 nm) on the graphite surface. The enhanced tunneling current is only observed in monolayer-high islands on graphite, and not in islands of similar geometry on top of a K monolayer film. First-principles density functional calculations and STM simulations suggest that this is an STM field effect, which appears as the positive tip attracts donated electrons back to the metallic K islands. The restored charge accumulates preferentially at the island edges.
Evidence of Band Bending Induced by Hole Trapping at MAPbI3 Perovskite / Metal Interface
2016
International audience; Electron injection by tunneling from a gold electrode and hole transport properties in polycrystalline MAPbI3 has been investigated using variable temperature experiments and numerical simulations. The presence of a large and unexpected band bending at the Au/MAPbI3 interface is revealed and attributed to the trapping of holes, which enhances the injection of electrons via tunneling. These results elucidate the role of volume and interface defects in state-of-the-art hybrid perovskite semiconductors.
Reconstructed bcc Co films on the surface
2007
Abstract Ultrathin epitaxial Co films on Cr ( 1 1 0 ) are examined by scanning tunneling microscopy and spectroscopy (STM and STS). At room temperature Co grows as pseudomorphic bcc layers for the first two monolayers and forms close-packed Co layers with stacking faults for thicker coverages. A periodic lattice distortion appears in two equivalent (3 × 1) reconstruction domains in combination with a regular lattice of dislocation lines oriented along the in-plane close-packed row directions bcc [ 1 1 ¯ 1 ] and bcc [ 1 ¯ 1 1 ] . The reconstruction and the occurrence of dislocation lines are caused by the epitaxial strain. The local density-of-states function is mapped by scanning tunneling …
Maxwell and Sharvin conductance in gold point contacts investigated using TEM-STM
2000
We have investigated the conductance of gold point contacts using a scanning tunneling microscope ~STM! inside a transmission electron microscope ~TEM!. Measuring the conductance of these point contacts as a function of radius, we could directly compare it with theories both in the ballistic regime ~Sharvin! as well as in the diffusive regime ~Maxwell!. The width of the contacts were between a single atom and 20 nm. Using an interpolation formula ~Wexler! between the two limits, we obtain a mean free path of 4 nm, which is about ten times shorter than the room-temperature bulk value. The low value indicates an enhanced scattering, which is not due to high temperature in the point contact, i…