1,707 research outputs found
Electrical spin injection in p-type Si using Fe/MgO contacts
We report the successful electrical creation of spin polarization in p-type
Si at room temperature by using an epitaxial MgO(001) tunnel barrier and
Fe(001) electrode. Reflection high-energy electron diffraction observations
revealed that epitaxial Fe/MgO(001) tunnel contacts can be grown on a (2 x 1)
reconstructed Si surface whereas tunnel contacts grown on the (1 x 1) Si
surface were polycrystalline. Transmission electron microscopy images showed a
more flat interface for the epitaxial Fe/MgO/Si compared to that of the
polycrystalline structure. For the Fe/MgO/p-Si devices, the Hanle and inverted
Hanle effects were clearly observed at 300 K by using a three-terminal
configuration, proving that spin polarization can be induced in the Si at room
temperature. Effective spin lifetimes deduced from the width of the Hanle curve
were 95 +/- 6 ps and 143 +/- 10 ps for the samples with polycrystalline and
epitaxial MgO tunnel contacts, respectively. The observed difference can be
qualitatively explained by the local magnetic field induced by the larger
roughness of the interface of the polycrystalline sample. The sample with
epitaxial Fe/MgO tunnel contact showed higher magnitude of the spin
accumulation with a nearly symmetric behavior with respect to the bias polarity
whereas that of the polycrystalline MgO sample exhibited a quite asymmetric
evolution. This might be attributed to the higher degree of spin polarization
of the epitaxial Fe/MgO(001) tunnel contact, which acts as a spin filter. Our
experimental results suggest that an epitaxial MgO barrier is beneficial for
creating spins in Si.Comment: Paper presented at SPIE Nanoscience + Engineering, Spintronics V
session in San Diego, US on August 13th, 201
Spin effects in single-electron transport through carbon nanotube quantum dots
We investigate the total spin in an individual single-wall carbon nanotube
quantum dot with various numbers of electrons in a shell by using the ratio of
the saturation currents of the first steps of Coulomb staircases for positive
and negative biases. The current ratio reflects the total-spin transition that
is increased or decreased when the dot is connected to strongly asymmetric
tunnel barriers. Our results indicate that total spin states with and without
magnetic fields can be traced by this method.Comment: 5pages, 5figures, accepted for publication in Phys. Rev.
Heavy-Ion Rutherford Backscattering Spectrometry : A Comparison of ¹¹B with ⁴He Ions
The Rutherford backscattering spectrometry was examined with ¹¹B and ⁴He ions. Backscattering spectra improve in the mass resolution, the depth resolution and the channeling minimum yield when 6 MeV ¹¹B ions are used instead of 2 MeV ⁴He ions, which have been used commonly. Then the terminal voltage of a 1.7 MV tandem Cockcroft-Walton accelerator was calibrated by means of a combination of the ²⁷Al(p, γ)²⁸Si resonance method and a new iterative method using ¹H and ⁴He ions. The true terminal voltage of the accelerator is lower than the corresponding nominal values, and the deviation quadratically increases with increasing voltage
Discovery reach for wino and higgsino dark matter with a disappearing track signature at a 100 TeV collider
Within the theory of supersymmetry, the lightest neutralino is a dark matter
candidate and is often assumed to be the lightest supersymmetric particle (LSP)
as well. If the neutral wino or higgsino is dark matter, the upper limit of the
LSP mass is determined by the observed relic density of dark matter. If the LSP
is a nearly-pure neutral state of the wino or higgsino, the lightest chargino
state is expected to have a significant lifetime due to a tiny mass difference
between the LSP and the chargino. This article presents discovery potential of
the 100 TeV future circular hadron collider (FCC) for the wino and higgsino
dark matter using a disappearing-track signature. The search strategy to extend
the discovery reach to the thermal limits of wino/higgsino dark matter is
discussed with detailed studies on the background rate and the reference design
of the FCC-hadron detector under possible running scenarios of the FCC-hadron
machine. A proposal of modifying the detector layout and several ideas to
improve the sensitivity further are also discussed.Comment: 10 pages, 7 figures, 4 table
On the X-ray Image of The Crab Nebula: Comparison with Chandra Observations
An axisymmetric model for the Crab Nebula is constructed to examine the flow
dynamics in the nebula. The model is based on that of Kennel and Coroniti
(1984), although we assume that the kinetic-energy-dominant wind is confined in
an equatorial region. The evolution of the distribution function of the
electron-positron plasma flowing out in the nebula is calculated. Given viewing
angles, we reproduce an image of the nebula and compare it with Chandra
observation.
The reproduced image is not a ring-like but rather 'lip-shaped'. It is found
that the assumption of toroidal field does not reproduce the Chandra image. We
must assume that there is disordered magnetic field with an amplitude as large
as the mean toroidal field. In addition, the brightness contrast between the
front and back sides of the ring cannot be reproduced if we assume that the
magnetization parameter is as small as . The brightness
profile along the semi-major axis of the torus is also examined. The
non-dissipative, ideal-MHD approximation in the nebula appears to break down.
We speculate that if the magnetic energy is released by some process that
produce turbulent field in the nebula flow and causes heating and acceleration,
e.g. by magnetic reconnection, then the present difficulties may be resolved
(i.e. we can reproduce a ring image, and a higher brightness contrast). Thus,
the magnetization parameter can be larger than previously expected.Comment: 8 pages, 4 figures. accepted for publication in MNRA
X-ray magnetic circular dichroism and photoemission study of the diluted ferromagnetic semiconductor ZnCrTe
We have performed x-ray magnetic circular dichroism (XMCD) and valence-band
photoemission studies of the diluted ferromagnetic semiconductor
ZnCrTe. XMCD signals due to ferromagnetism were observed at the Cr
2p absorption edge. Comparison with atomic multiplet calculations suggests that
the magnetically active component of the Cr ion was divalent under the
tetrahedral crystal field with tetragonal distortion along the crystalline a-,
b-, and c-axes. In the valence-band spectra, spectral weight near the Fermi
level was strongly suppressed, suggesting the importance of Jahn-Teller effect
and the strong Coulomb interaction between the Cr 3d electrons
Formation of new crystal faces on TiO2 particles by treatment with aqueous HF solution or hot sulfuric acid
We have demonstrated that new crystal faces are generated on anatase and rutile TiO2 particles by means of chemical etching in aqueous hydrofluoric acid or hot sulfuric acid. In the treatment with aqueous hydrofluoric acid, the {112} face of anatase particles and the {021} face of rutile particles are newly formed. When treated with hot sulfuric acid, anatase particles exposed the {122} face and rutile particles exposed the {001}, {010}, {021} and {121} faces. In both cases, anatase particles are etched at a higher rate than rutile particles. The etched particles are expected to show photocatalytic properties unique to the crystal faces. For example, the {112} face of anatase particles is demonstrated to be active in the oxidation of Pb2+ ions
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