20 research outputs found
Electron-beam chemistry in graphene - Effect of environmental SEM parameters on patterning and defect engineering
The engineering of defects in low-dimensional materials can enable the modulation of their optical, electrical, thermal, and structural properties. We have previously shown the ability to engineer precision patterned defects in graphene by electron beam irradiation in a controlled water vapor ambient within an environmental scanning electron microscope (ESEM). However, the relationship between instrumental parameters and structural changes in graphene are unexplored. Here, we investigate the relationships between parameters such as pressure, electron dose, and acceleration voltage on the electronic and structural properties of graphene as probed by Raman spectroscopy. There are dependencies on all of the studied parameters but electron dose is the dominant parameter that shows the most intense levels of structural modulation. Interestingly, control of instrumental parameters allows for the precision tailoring of features such as resolution (as determined by the beamskirting effect), doping, and functionalization – all of which make this process powerful for precision tuning of 2D materials and adds an enhanced technique for the development of next-generation electronics
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GBStools: A Statistical Method for Estimating Allelic Dropout in Reduced Representation Sequencing Data
Reduced representation sequencing methods such as genotyping-by-sequencing (GBS) enable low-cost measurement of genetic variation without the need for a reference genome assembly. These methods are widely used in genetic mapping and population genetics studies, especially with non-model organisms. Variant calling error rates, however, are higher in GBS than in standard sequencing, in particular due to restriction site polymorphisms, and few computational tools exist that specifically model and correct these errors. We developed a statistical method to remove errors caused by restriction site polymorphisms, implemented in the software package GBStools. We evaluated it in several simulated data sets, varying in number of samples, mean coverage and population mutation rate, and in two empirical human data sets (N = 8 and N = 63 samples). In our simulations, GBStools improved genotype accuracy more than commonly used filters such as Hardy-Weinberg equilibrium p-values. GBStools is most effective at removing genotype errors in data sets over 100 samples when coverage is 40X or higher, and the improvement is most pronounced in species with high genomic diversity. We also demonstrate the utility of GBS and GBStools for human population genetic inference in Argentine populations and reveal widely varying individual ancestry proportions and an excess of singletons, consistent with recent population growth
GBStools: A Statistical Method for Estimating Allelic Dropout in Reduced Representation Sequencing Data
Reduced representation sequencing methods such as genotyping-by-sequencing (GBS) enable low-cost measurement of genetic variation without the need for a reference genome assembly. These methods are widely used in genetic mapping and population genetics studies, especially with non-model organisms. Variant calling error rates, however, are higher in GBS than in standard sequencing, in particular due to restriction site polymorphisms, and few computational tools exist that specifically model and correct these errors. We developed a statistical method to remove errors caused by restriction site polymorphisms, implemented in the software package GBStools. We evaluated it in several simulated data sets, varying in number of samples, mean coverage and population mutation rate, and in two empirical human data sets (N = 8 and N = 63 samples). In our simulations, GBStools improved genotype accuracy more than commonly used filters such as Hardy-Weinberg equilibrium p-values. GBStools is most effective at removing genotype errors in data sets over 100 samples when coverage is 40X or higher, and the improvement is most pronounced in species with high genomic diversity. We also demonstrate the utility of GBS and GBStools for human population genetic inference in Argentine populations and reveal widely varying individual ancestry proportions and an excess of singletons, consistent with recent population growth
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Field-free deterministic switching of a perpendicularly polarized magnet using unconventional spin-orbit torques in WTe2
Spin-orbit torque (SOT) driven deterministic control of the magnetization
state of a magnet with perpendicular magnetic anisotropy (PMA) is key to next
generation spintronic applications including non-volatile, ultrafast, and
energy efficient data storage devices. But, field-free deterministic switching
of perpendicular magnetization remains a challenge because it requires an
out-of-plane anti-damping torque, which is not allowed in conventional spin
source materials such as heavy metals (HM) and topological insulators due to
the system's symmetry. The exploitation of low-crystal symmetries in emergent
quantum materials offers a unique approach to achieve SOTs with unconventional
forms. Here, we report the first experimental realization of field-free
deterministic magnetic switching of a perpendicularly polarized van der Waals
(vdW) magnet employing an out-of-plane anti-damping SOT generated in layered
WTe2 which is a low-crystal symmetry quantum material. The numerical
simulations confirm that out-of-plane antidamping torque in WTe2 is responsible
for the observed magnetization switching in the perpendicular direction
Field-free deterministic switching of a perpendicularly polarized magnet using unconventional spin-orbit torques in WTe2
Spin-orbit torque (SOT) driven deterministic control of the magnetization
state of a magnet with perpendicular magnetic anisotropy (PMA) is key to next
generation spintronic applications including non-volatile, ultrafast, and
energy efficient data storage devices. But, field-free deterministic switching
of perpendicular magnetization remains a challenge because it requires an
out-of-plane anti-damping torque, which is not allowed in conventional spin
source materials such as heavy metals (HM) and topological insulators due to
the system's symmetry. The exploitation of low-crystal symmetries in emergent
quantum materials offers a unique approach to achieve SOTs with unconventional
forms. Here, we report the first experimental realization of field-free
deterministic magnetic switching of a perpendicularly polarized van der Waals
(vdW) magnet employing an out-of-plane anti-damping SOT generated in layered
WTe2 which is a low-crystal symmetry quantum material. The numerical
simulations confirm that out-of-plane antidamping torque in WTe2 is responsible
for the observed magnetization switching in the perpendicular direction
Visualizing band structure hybridization and superlattice effects in twisted MoS/WS heterobilayers
A mismatch of atomic registries between single-layer transition metal
dichalcogenides (TMDs) in a two dimensional van der Waals heterostructure
produces a moir\'e superlattice with a periodic potential, which can be
fine-tuned by introducing a twist angle between the materials. This approach is
promising both for controlling the interactions between the TMDs and for
engineering their electronic band structures, yet direct observation of the
changes to the electronic structure introduced with varying twist angle has so
far been missing. Here, we probe heterobilayers comprised of single-layer
MoS and WS with twist angles of , , and and investigate the differences in
their electronic band structure using micro-focused angle-resolved
photoemission spectroscopy. We find strong interlayer hybridization between
MoS and WS electronic states at the -point of
the Brillouin zone, leading to a transition from a direct bandgap in the
single-layer to an indirect gap in the heterostructure. Replicas of the
hybridized states are observed at the centre of twist angle-dependent moir\'e
mini Brillouin zones. We confirm that these replica features arise from the
inherent moir\'e potential by comparing our experimental observations with
density functional theory calculations of the superlattice dispersion. Our
direct visualization of these features underscores the potential of using
twisted heterobilayer semiconductors to engineer hybrid electronic states and
superlattices that alter the electronic and optical properties of 2D
heterostructures.Comment: 31 pages, 6 figures in the main text and 5 figures in the supporting
informatio