143 research outputs found
The Roman Catholic and Lutheran Doctrine of Sin
However, while there are apparent similarities, it must be pointed out that the actual similarity or dissimilarity of churches does not consist in their external rites and ceremonies but in their teachings. Therefore, in order to get an accurate picture, it is necessary that we examine the doctrine of each church. However, since we cannot treat all the doctrines we shall take a basic one, namely, the doctrine of sin. The writer will attempt to set forth the official teachings of both churches on this one doctrine
Dry-transferred CVD graphene for inverted spin valve devices
Integrating high-mobility graphene grown by chemical vapor deposition (CVD)
into spin transport devices is one of the key tasks in graphene spintronics. We
use a van der Waals pickup technique to transfer CVD graphene by hexagonal
boron nitride (hBN) from the copper growth substrate onto predefined Co/MgO
electrodes to build inverted spin valve devices. Two approaches are presented:
(i) a process where the CVD-graphene/hBN stack is first patterned into a bar
and then transferred by a second larger hBN crystal onto spin valve electrodes
and (ii) a direct transfer of a CVD-graphene/hBN stack. We report record high
spin lifetimes in CVD graphene of up to 1.75 ns at room temperature. Overall,
the performances of our devices are comparable to devices fabricated from
exfoliated graphene also revealing nanosecond spin lifetimes. We expect that
our dry transfer methods pave the way towards more advanced device geometries
not only for spintronic applications but also for CVD-graphene-based
nanoelectronic devices in general where patterning of the CVD graphene is
required prior to the assembly of final van der Waals heterostructures.Comment: 5 pages, 3 figure
Nanosecond spin lifetimes in bottom-up fabricated bilayer graphene spin-valves with atomic layer deposited AlO spin injection and detection barriers
We present spin transport studies on bi- and trilayer graphene non-local
spin-valves which have been fabricated by a bottom-up fabrication method. By
this technique, spin injection electrodes are first deposited onto
Si/SiO substrates with subsequent mechanical transfer of a
graphene/hBN heterostructure. We showed previously that this technique allows
for nanosecond spin lifetimes at room temperature combined with carrier
mobilities which exceed 20,000 cm/(Vs). Despite strongly enhanced spin and
charge transport properties, the MgO injection barriers in these devices
exhibit conducting pinholes which still limit the measured spin lifetimes. We
demonstrate that these pinholes can be partially diminished by an oxygen
treatment of a trilayer graphene device which is seen by a strong increase of
the contact resistance area products of the Co/MgO electrodes. At the same
time, the spin lifetime increases from 1 ns to 2 ns. We believe that the
pinholes partially result from the directional growth in molecular beam
epitaxy. For a second set of devices, we therefore used atomic layer deposition
of AlO which offers the possibility to isotropically deposit more
homogeneous barriers. While the contacts of the as-fabricated bilayer graphene
devices are non-conductive, we can partially break the oxide barriers by
voltage pulses. Thereafter, the devices also exhibit nanosecond spin lifetimes.Comment: 6 pages, 4 figure
Spin lifetimes exceeding 12 nanoseconds in graphene non-local spin valve devices
We show spin lifetimes of 12.6 ns and spin diffusion lengths as long as 30.5
\mu m in single layer graphene non-local spin transport devices at room
temperature. This is accomplished by the fabrication of Co/MgO-electrodes on a
Si/SiO substrate and the subsequent dry transfer of a graphene-hBN-stack on
top of this electrode structure where a large hBN flake is needed in order to
diminish the ingress of solvents along the hBN-to-substrate interface.
Interestingly, long spin lifetimes are observed despite the fact that both
conductive scanning force microscopy and contact resistance measurements reveal
the existence of conducting pinholes throughout the MgO spin
injection/detection barriers. The observed enhancement of the spin lifetime in
single layer graphene by a factor of 6 compared to previous devices exceeds
current models of contact-induced spin relaxation which paves the way towards
probing intrinsic spin properties of graphene.Comment: 8 pages, 5 figure
Spin States Protected from Intrinsic Electron-Phonon-Coupling Reaching 100 ns Lifetime at Room Temperature in MoSe
We present time-resolved Kerr rotation measurements, showing spin lifetimes
of over 100 ns at room temperature in monolayer MoSe. These long lifetimes
are accompanied by an intriguing temperature dependence of the Kerr amplitude,
which increases with temperature up to 50 K and then abruptly switches sign.
Using ab initio simulations we explain the latter behavior in terms of the
intrinsic electron-phonon coupling and the activation of transitions to
secondary valleys. The phonon-assisted scattering of the photo-excited
electron-hole pairs prepares a valley spin polarization within the first few ps
after laser excitation. The sign of the total valley magnetization, and thus
the Kerr amplitude, switches as a function of temperature, as conduction and
valence band states exhibit different phonon-mediated inter-valley scattering
rates. However, the electron-phonon scattering on the ps time scale does not
provide an explanation for the long spin lifetimes. Hence, we deduce that the
initial spin polarization must be transferred into spin states which are
protected from the intrinsic electron-phonon coupling, and are most likely
resident charge carriers which are not part of the itinerant valence or
conduction band states.Comment: 18 pages, 17 figure
How to solve problems in micro- and nanofabrication caused by the emission of electrons and charged metal atoms during e-beam evaporation
We discuss how the emission of electrons and ions during
electron-beam-induced physical vapor deposition can cause problems in micro-
and nanofabrication processes. After giving a short overview of different types
of radiation emitted from an electron-beam (e-beam) evaporator and how the
amount of radiation depends on different deposition parameters and conditions,
we highlight two phenomena in more detail: First, we discuss an unintentional
shadow evaporation beneath the undercut of a resist layer caused by the one
part of the metal vapor which got ionized by electron-impact ionization. These
ions first lead to an unintentional build-up of charges on the sample, which in
turn results in an electrostatic deflection of subsequently incoming ionized
metal atoms towards the undercut of the resist. Second, we show how low-energy
secondary electrons during the metallization process can cause cross-linking,
blisters, and bubbles in the respective resist layer used for defining micro-
and nanostructures in an e-beam lithography process. After the metal
deposition, the cross-linked resist may lead to significant problems in the
lift-off process and causes leftover residues on the device. We provide a
troubleshooting guide on how to minimize these effects, which e.g. includes the
correct alignment of the e-beam, the avoidance of contaminations in the
crucible and, most importantly, the installation of deflector electrodes within
the evaporation chamber.Comment: 13 pages, 7 figure
Nanosecond spin lifetimes in single- and few-layer graphene-hBN heterostructures at room temperature
We present a new fabrication method of graphene spin-valve devices which
yields enhanced spin and charge transport properties by improving both the
electrode-to-graphene and graphene-to-substrate interface. First, we prepare
Co/MgO spin injection electrodes onto Si/SiO. Thereafter, we
mechanically transfer a graphene-hBN heterostructure onto the prepatterned
electrodes. We show that room temperature spin transport in single-, bi- and
trilayer graphene devices exhibit nanosecond spin lifetimes with spin diffusion
lengths reaching 10m combined with carrier mobilities exceeding 20,000
cm/Vs.Comment: 15 pages, 5 figure
Valley lifetimes of conduction band electrons in monolayer WSe
One of the main tasks in the investigation of 2-dimensional transition metal
dichalcogenides is the determination of valley lifetimes. In this work, we
combine time-resolved Kerr rotation with electrical transport measurements to
explore the gate-dependent valley lifetimes of free conduction band electrons
of monolayer WSe. When tuning the Fermi energy into the conduction band we
observe a strong decrease of the respective valley lifetimes which is
consistent with both spin-orbit and electron-phonon scattering. We explain the
formation of a valley polarization by the scattering of optically excited
valley polarized bright trions into dark states by intervalley scattering.
Furthermore, we show that the conventional time-resolved Kerr rotation
measurement scheme has to be modified to account for photo-induced gate
screening effects. Disregarding this adaptation can lead to erroneous
conclusions drawn from gate-dependent optical measurements and can completely
mask the true gate-dependent valley dynamics.Comment: 5 pages, 3 figure
Self-organization on surfaces: foreword
After decades of work, the growth of continuous thin films, i.e.,
two-dimensional structures, is progressively becoming a technological issue
more than a field of fundamental research. Incidentally self-organization of
nanostructures on surfaces is now an important field of research, i.e.,
structures of dimensionality one or zero, with a steep rise of attention in the
past five years. Whereas self-organization was initially motivated by potential
applications, it has up to now essentially contributed to the advancement of
fundamental science in low dimensions, as model systems could be produced that
could not have been fabricated by lithography. This Special Issue aims at
giving a cross-community timely overview of the field. The Issue gathers a
broad panel of articles covering various self-organization mechanisms, specific
structural characterization, physical properties, and current trends in
extending the versatility of growth. The materials mostly covered here are
semiconductors and magnetic materials.Comment: Foreword of the Editor to Special Issue on Self-organization on
surface
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