50 research outputs found
Energy-resolved Photoconductivity Mapping in a Monolayer-bilayer WSe2 Lateral Heterostructure
Vertical and lateral heterostructures of van der Waals materials provide
tremendous flexibility for band structure engineering. Since electronic bands
are sensitively affected by defects, strain, and interlayer coupling, the edge
and heterojunction of these two-dimensional (2D) systems may exhibit novel
physical properties, which can be fully revealed only by spatially resolved
probes. Here, we report the spatial mapping of photoconductivity in a
monolayer-bilayer WSe2 lateral heterostructure under multiple excitation
lasers. As the photon energy increases, the light-induced conductivity detected
by microwave impedance microscopy first appears along the hetero-interface and
bilayer edge, then along the monolayer edge, inside the bilayer area, and
finally in the interior of the monolayer region. The sequential emergence of
mobile carriers in different sections of the sample is consistent with the
theoretical calculation of local energy gaps. Quantitative analysis of the
microscopy and transport data also reveals the linear dependence of
photoconductivity on the laser intensity and the influence of interlayer
coupling on carrier recombination. Combining theoretical modeling, atomic scale
imaging, mesoscale impedance microscopy, and device-level characterization, our
work suggests an exciting perspective to control the intrinsic band-gap
variation in 2D heterostructures down to the few-nanometer regime.Comment: 18 pages, 5 figures; Nano Lett., Just Accepted Manuscrip
Unveiling Defect-Mediated Carrier Dynamics in Monolayer Semiconductors by Spatiotemporal Microwave Imaging
The optoelectronic properties of atomically thin transition-metal
dichalcogenides are strongly correlated with the presence of defects in the
materials, which are not necessarily detrimental for certain applications. For
instance, defects can lead to an enhanced photoconduction, a complicated
process involving charge generation and recombination in the time domain and
carrier transport in the spatial domain. Here, we report the simultaneous
spatial and temporal photoconductivity imaging in two types of WS2 monolayers
by laser-illuminated microwave impedance microscopy. The diffusion length and
carrier lifetime were directly extracted from the spatial profile and temporal
relaxation of microwave signals respectively. Time-resolved experiments
indicate that the critical process for photo-excited carriers is the escape of
holes from trap states, which prolongs the apparent lifetime of mobile
electrons in the conduction band. As a result, counterintuitively, the
photoconductivity is stronger in CVD samples than exfoliated monolayers with a
lower defect density. Our work reveals the intrinsic time and length scales of
electrical response to photo-excitation in van der Waals materials, which is
essential for their applications in novel optoelectronic devices.Comment: 21 pages, 4 figure
Preparation of stable magnetic nanofluids containing Fe3O4@PPy nanoparticles by a novel one-pot route
Stable magnetic nanofluids containing Fe3O4@Polypyrrole (PPy) nanoparticles (NPs) were prepared by using a facile and novel method, in which one-pot route was used. FeCl3·6H2O was applied as the iron source, and the oxidizing agent to produce PPy. Trisodium citrate (Na3cit) was used as the reducing reagent to form Fe3O4 NPs. The as-prepared nanofluid can keep long-term stability. The Fe3O4@PPy NPs can still keep dispersing well after the nanofluid has been standing for 1 month and no sedimentation is found. The polymerization reaction of the pyrrole monomers took place with Fe3+ ions as the initiator, in which these Fe3+ ions remained in the solution adsorbed on the surface of the Fe3O4 NPs. Thus, the core-shell NPs of Fe3O4@PPy were obtained. The particle size of the as-prepared Fe3O4@PPy can be easily controlled from 7 to 30 nm by the polymerization reaction of the pyrrole monomers. The steric stabilization and weight of the NPs affect the stability of the nanofluids. The as-prepared Fe3O4@PPy NPs exhibit superparamagnetic behavior
Small genomic insertions form enhancers that misregulate oncogenes
The non-coding regions of tumour cell genomes harbour a considerable fraction of total DNA sequence variation, but the functional contribution of these variants to tumorigenesis is ill-defined. Among these non-coding variants, somatic insertions are among the least well characterized due to challenges with interpreting short-read DNA sequences. Here, using a combination of Chip-seq to enrich enhancer DNA and a computational approach with multiple DNA alignment procedures, we identify enhancer-associated small insertion variants. Among the 102 tumour cell genomes we analyse, small insertions are frequently observed in enhancer DNA sequences near known oncogenes. Further study of one insertion, somatically acquired in primary leukaemia tumour genomes, reveals that it nucleates formation of an active enhancer that drives expression of the LMO2 oncogene. The approach described here to identify enhancer-associated small insertion variants provides a foundation for further study of these abnormalities across human cancers
The impacts of climate change on the Neolithic cultures of Gansu-Qinghai region during the late Holocene Megathermal
The 2nd challenge on remote physiological signal sensing (RePSS)
Abstract
Remote measurement of physiological signals from videos is an emerging topic. The topic draws great interest, but the lack of publicly available benchmark databases and a fair validation platform are hindering its further development. The RePSS Challenge is organized as an annual event for this concern. Here the 2nd RePSS is organized in conjunction with ICCV 2021. The 2nd RePSS contains two competition tracks. Track 1 is to measure inter-beat-intervals (IBI) from facial videos, which requires accurate measurement of each individual pulse peak. Track 2 is about respiration measurement from facial videos, as respiration is another important physiological index related to both health and emotional status. One new dataset is built and shared for Track 2. This paper presents an overview of the challenge, including data, protocol, results, and discussion. We highlighted the top-ranked solutions to provide insight for researchers, and we also outline future directions for this topic and this challenge