Search results for "Tunnel effect"

Exchange bias in epitaxial Mn2Au (0 0 1)/Fe (0 0 1) bilayers

2019

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…

Phonon contribution to the absorption of ultrasound in amorphous solids at moderately low temperatures

1998

Abstract Sound absorbtion in amorphous solids is considered to be due to the scattering of sound waves from the thermal phonons. It is shown that the dependence of the absorption coefficient on the temperature displays a maximum in the interval 10≲T≲100 K . The frequency dependence of the absorption coefficient is investigated. Numerical calculations for amorphous Mg and Zn illustrate the theoretical results.

Temperature and bias-voltage dependence of atomic-layer-deposited HfO2-based magnetic tunnel junctions

2014

Magnetic tunnel junctions with HfO2 tunnel barriers were prepared through a combination of magnetron sputtering and atomic layer deposition. We investigated the tunneling transport behavior, including the tunnel magnetoresistance ratio and the current-voltage characteristics between room temperature and 2 K. Here, we achieved a tunneling magneto resistance ratio of 10.3% at room temperature and 19.3% at 2 K. Furthermore, we studied the bias-voltage and temperature dependencies and compared the results with those of commonly used alumina- and magnesia-based magnetic tunnel junctions. We observed a polycrystalline/amorphous electrode-barrier system via high-resolution transmission electron mi…

Peculiar aspects of nanocrystal memory cells: Data and extrapolations

2003

Nanocrystal memory cell are a promising candidate for the scaling of nonvolatile memories in which the conventional floating gate is replaced by an array of nanocrystals. The aim of this paper is to present the results of a thorough investigation of the possibilities and the limitations of such new memory cell. In particular, we focus on devices characterized by a very thin tunnel oxide layer and by silicon nanocrystals formed by chemical vapor deposition. The direct tunneling of the electrons through the tunnel oxide, their storage into the silicon nanocrystals, and furthermore, retention, endurance, and drain turn-on effects, well-known issues for nonvolatile memories, are all investigate…

SUBWAVELENGTH OPTICAL DEVICES FOR NANOMETER SCALE APPLICATIONS

2002

Recent progress in near-field optics instrumentation led to a new class of subwavelength optical experiments in which it is intended to use either the optical tunnel effect (OTE) or the lower mode based transmission (LMBT) in order to control the optical transfer between several delocalized detection or injection centers. This paper presents a panel of new theoretical and experimental results computed or observed near various dielectric or metallic patterns, linear, curved, or dashed, integrated in coplanar geometry. In particular, we demonstrate, how an efficient control of light evanescent waves can allow structures of subwavelength cross sections to be addressed.

Energy and entropy barriers of two-level systems in argon clusters: An energy landscape approach

1999

Abstract Free argon clusters containing up to 160 atoms have been studied by means of a numerical algorithm for finding thousands of adjacent minima connected through a first-order saddle point. Many minimum-saddle-minimum systems have been found to be good candidates for forming two-level systems. The ground state splitting has been evaluated by taking into account both energy and entropy barriers. The role of the latter in auenching or enhancing the ground state splitting is discussed with the aid of a simple model potential.

Programming options for nanocrystal MOS memories

2003

Nanocrystal memories represent a promising candidate for the scaling of FLASH memories. In these devices, the charge is not stored in a continuous floating gate but in a discontinuous layer composed by numerous discrete silicon quantum dots well separated one from the other.The nanocrystals of radius of few nanometers are realized by chemical vapor deposition (CVD) of silicon on the tunnel oxide of 2.8 nm of thickness. These islands have been coated with a control oxide of 7 nm formed by CVD and incorporated in Metal-Oxide-Semiconductor structure. The devices are programmed and erased by tunnelling using low voltages and fast times. In addition, the programming can be easily achieved also b…

Symmetry-species conversion in CD3systems

1993

The rates for symmetry-species conversion of CD3 groups are calculated using a model in which the interaction between the quadrupolar moment of the deuterons with electric-field gradient at the site of the nucleus causes symmetry-changing transitions. Just the same phonons are considered for energy conservation as are used to describe the temperature dependence of inelastic neutron scattering experiments. For the conversion rate, a similar temperature dependence is found as has already been obtained for CH3. For temperatures around the tunnelling energy, a behaviour is predicted for CD3 that is different from the behaviour in protonated systems according to all theories known to the authors…

Interference effect in the Landau-Zener tunneling of the antiferromagnetically coupled dimer of single-molecule magnets

2004

Two antiferromagnetically coupled tunneling systems is a minimal model exhibiting the effect of quantum-mechanical phase in the Landau-Zener effect. It is shown that the averaged staying probability oscillates vs resonance shift between the two particles, as well as vs sweeping rate. Such a resonance shift can be produced in Mn-4 dimers by the gradient of the magnetic field.