891 research outputs found
Electrical observation of a tunable band gap in bilayer graphene nanoribbons at room temperature
We investigate the transport properties of double-gated bilayer graphene
nanoribbons at room temperature. The devices were fabricated using conventional
CMOS-compatible processes. By analyzing the dependence of the resistance at the
charge neutrality point as a function of the electric field applied
perpendicular to the graphene surface, we show that a band gap in the density
of states opens, reaching an effective value of ~sim50 meV. This demonstrates
the potential of bilayer graphene as FET channel material in a conventional
CMOS environment.Comment: 3 pages, 3 figure
Apparent rippling with honeycomb symmetry and tunable periodicity observed by scanning tunneling microscopy on suspended graphene
Suspended graphene is difficult to image by scanning probe microscopy due to
the inherent van-der-Waals and dielectric forces exerted by the tip which are
not counteracted by a substrate. Here, we report scanning tunneling microscopy
data of suspended monolayer graphene in constant-current mode revealing a
surprising honeycomb structure with amplitude of 50200 pm and lattice
constant of 10-40 nm. The apparent lattice constant is reduced by increasing
the tunneling current , but does not depend systematically on tunneling
voltage or scan speed . The honeycomb lattice of the rippling
is aligned with the atomic structure observed on supported areas, while no
atomic corrugation is found on suspended areas down to the resolution of about
pm. We rule out that the honeycomb structure is induced by the feedback
loop using a changing , that it is a simple enlargement effect of
the atomic resolution as well as models predicting frozen phonons or standing
phonon waves induced by the tunneling current. Albeit we currently do not have
a convincing explanation for the observed effect, we expect that our intriguing
results will inspire further research related to suspended graphene.Comment: 10 pages, 7 figures, modified, more detailed discussion on errors in
vdW parameter
Weak localization in ferromagnetic (Ga,Mn)As nanostructures
We report on the observation of weak localization in arrays of (Ga,Mn)As
nanowires at millikelvin temperatures. The corresponding phase coherence length
is typically between 100 nm and 200 nm at 20 mK. Strong spin-orbit interaction
in the material is manifested by a weak anti-localization correction around
zero magnetic field.Comment: 5 pages, 3 figure
Ультрафлокуляция – как метод повышения эффективности процесса извлечения тонкодисперсного угля из хвостов обогащения
На прикладі хвостів вуглезбагачення ОФ "Распадська" (р. Междуріченськ Кемеровської області, РФ) встановлено, що використання ультрафлокулярної обробки дає нижче-наступні переваги при витяганні тонкодисперсного вугілля методом седиментації в радіальному згущувачі:
• зниження витрати флокулянтів – в 2,5-3,5 разу.
• збільшення витягання вугільного концентрату з хвостів на 23…26%.
• зменшення зольності концентрату, вилученого з хвостів з 18 до 12%.
• зменшення вологості прес-фільтраційного кека концентрату, вилученого з хвостів з 40 до 35%.На примере хвостов углеобогащения ОФ "Распадская" (г. Междуреченск Кемеровской области, РФ) установлено, что использование ультрафлокулярной обработки дает нижеследующие преимущества при извлечении тонкодисперсного угля методом седиментации в радиальном сгустителе:
• снижение расхода флокулянтов – в 2,5-3,5 раза.
• увеличение извлечения угольного концентрата из хвостов на 23…26%.
• уменьшение зольности концентрата, извлекаемого из хвостов с 18 до 12%.
• уменьшение влажности пресс-фильтрационного кека концентрата, извлекаемого из хвостов с 40 до 35%
Electrical transport and low-temperature scanning tunneling microscopy of microsoldered graphene
Using the recently developed technique of microsoldering, we perform a
systematic transport study of the influence of PMMA on graphene flakes
revealing a doping effect of up to 3.8x10^12 1/cm^2, but a negligible influence
on mobility and gate voltage induced hysteresis. Moreover, we show that the
microsoldered graphene is free of contamination and exhibits a very similar
intrinsic rippling as has been found for lithographically contacted flakes.
Finally, we demonstrate a current induced closing of the previously found
phonon gap appearing in scanning tunneling spectroscopy experiments, strongly
non-linear features at higher bias probably caused by vibrations of the flake
and a B-field induced double peak attributed to the 0.Landau level of graphene.Comment: 8 pages, 3 figure
Observation of the spin-orbit gap in bilayer graphene by one-dimensional ballistic transport
We report on measurements of quantized conductance in gate-defined quantum
point contacts in bilayer graphene that allow the observation of subband
splittings due to spin-orbit coupling. The size of this splitting can be tuned
from 40 to 80 eV by the displacement field. We assign this gate-tunable
subband-splitting to a gap induced by spin-orbit coupling of Kane-Mele type,
enhanced by proximity effects due to the substrate. We show that this
spin-orbit coupling gives rise to a complex pattern in low perpendicular
magnetic fields, increasing the Zeeman splitting in one valley and suppressing
it in the other one. In addition, we observe the existence of a spin-polarized
channel of 6 e/h at high in-plane magnetic field and of signatures of
interaction effects at the crossings of spin-split subbands of opposite spins
at finite magnetic field.Comment: 5 pages, 4 figures, Supplement 6 figure
Apparent rippling with honeycomb symmetry and tunable periodicity observed by scanning tunneling microscopy on suspended graphene
Suspended graphene is difficult to image by scanning probe microscopy due to the inherent van der Waals and dielectric forces exerted by the tip, which are not counteracted by a substrate. Here, we report scanning tunneling microscopy data of suspended monolayer graphene in constant-current mode, revealing a surprising honeycomb structure with amplitude of 50-200 pm and lattice constant of 10-40 nm. The apparent lattice constant is reduced by increasing the tunneling current I, but does not depend systematically on tunneling voltage V or scan speed v(scan). The honeycomb lattice of the rippling is aligned with the atomic structure observed on supported areas, while no atomic corrugation is found on suspended areas down to the resolution of about 3-4 pm. We rule out that the honeycomb structure is induced by the feedback loop using a changing vscan, that it is a simple enlargement effect of the atomic lattice, as well as models predicting frozen phonons or standing phonon waves induced by the tunneling current. Although we currently do not have a convincing explanation for the observed effect, we expect that our intriguing results will inspire further research related to suspended graphene
Phase coherent transport in (Ga,Mn)As
Quantum interference effects and resulting quantum corrections of the
conductivity have been intensively studied in disordered conductors over the
last decades. The knowledge of phase coherence lengths and underlying dephasing
mechanisms are crucial to understand quantum corrections to the resistivity in
the different material systems. Due to the internal magnetic field and the
associated breaking of time-reversal symmetry quantum interference effects in
ferromagnetic materials have been scarcely explored. Below we describe the
investigation of phase coherent transport phenomena in the newly discovered
ferromagnetic semiconductor (Ga,Mn)As. We explore universal conductance
fluctuations in mesoscopic (Ga,Mn)As wires and rings, the Aharonov-Bohm effect
in nanoscale rings and weak localization in arrays of wires, made of the
ferromagnetic semiconductor material. The experiments allow to probe the phase
coherence length L_phi and the spin flip length L_SO as well as the temperature
dependence of dephasing.Comment: 22 pages, 10 figure
A C*-Algebraic Model for Locally Noncommutative Spacetimes
Locally noncommutative spacetimes provide a refined notion of noncommutative
spacetimes where the noncommutativity is present only for small distances. Here
we discuss a non-perturbative approach based on Rieffel's strict deformation
quantization. To this end, we extend the usual C*-algebraic results to a
pro-C*-algebraic framework.Comment: 13 pages, LaTeX 2e, no figure
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