146 research outputs found
Excitation-Dependent High-Lying Excitonic Exchange via Interlayer Energy Transfer from Lower-to-Higher Bandgap 2D Material
High light absorption (~15%) and strong photoluminescence (PL) emission in
monolayer (1L) transition metal dichalcogenide (TMD) make it an ideal candidate
for optoelectronic applications. Competing interlayer charge (CT) and energy
transfer (ET) processes control the photocarrier relaxation pathways in TMD
heterostructures (HSs). In TMDs, long-distance ET can survive up to several
tens of nm, unlike the CT process. Our experiment shows that an efficient ET
occurs from the 1Ls WSe2-to-MoS2 with an interlayer hBN, due to the resonant
overlapping of the high-lying excitonic states between the two TMDs, resulting
in enhanced HS MoS2 PL emission. This type of unconventional ET from the
lower-to-higher optical bandgap material is not typical in the TMD HSs. With
increasing temperature, the ET process becomes weaker due to the increased
electron-phonon scattering, destroying the enhanced MoS2 emission. Our work
provides new insight into the long-distance ET process and its effect on the
photocarrier relaxation pathways.Comment: 5 figures and SI include
Delineating transcriptional crosstalk between Mycobacterium avium subsp. paratuberculosis and human THP-1 cells at the early stage of infection via dual RNA-seq analysis
Mycobacterium avium subsp. paratuberculosis (MAP) is the causative agent of Johne's disease, a chronic debilitating disease in ruminants. To control this disease, it is crucial to understand immune evasion and the mechanism of persistence by analyzing the early phase interplays of the intracellular pathogens and their hosts. In the present study, host-pathogen interactions at the transcriptomic level were investigated in an in vitro macrophage infection model. When differentiated human THP-1 cells were infected with MAP, the expression of various genes associated with stress responses and metabolism was altered in both host and MAP at 3 h post-infection. MAP upregulates stress-responsive global gene regulators, such as two-component systems and sigma factors, in response to oxidative and cell wall stress. Downstream genes involved in type VII secretion systems, cell wall synthesis (polyketide biosynthesis proteins), and iron uptake were changed in response to the intracellular environment of macrophages. On the host side, upregulation of inflammatory cytokine genes was observed along with pattern recognition receptor genes. Notably, alterations in gene sets involved in arginine metabolism were observed in both the host and MAP, along with significant downregulation of NOS2 expression. These observations suggest that the utilization of metabolites such as arginine by intracellular MAP might affect host NO production. Our dual RNA-seq data can provide novel insights by capturing the global transcriptome with higher resolution, especially in MAP, thus enabling a more systematic understanding of host-pathogen interactions
Genomic diversity of Mycobacterium avium subsp. paratuberculosis: pangenomic approach for highlighting unique genomic features with newly constructed complete genomes
Mycobacterium avium subsp. paratuberculosis (MAP) is a causative agent of Johne's disease, which is a chronic granulomatous enteropathy in ruminants. Determining the genetic diversity of MAP is necessary to understand the epidemiology and biology of MAP, as well as establishing disease control strategies. In the present study, whole genome-based alignment and comparative analysis were performed using 40 publicly available MAP genomes, including newly sequenced Korean isolates. First, whole genome-based alignment was employed to identify new genomic structures in MAP genomes. Second, the genomic diversity of the MAP population was described by pangenome analysis. A phylogenetic tree based on the core genome and pangenome showed that the MAP was differentiated into two major types (C- and S-type), which was in keeping with the findings of previous studies. However, B-type strains were discriminated from C-type strains. Finally, functional analysis of the pangenome was performed using three virulence factor databases (i.e., PATRIC, VFDB, and Victors) to predict the phenotypic diversity of MAP in terms of pathogenicity. Based on the results of the pangenome analysis, we developed a real-time PCR technique to distinguish among S-, B- and C-type strains. In conclusion, the results of our study suggest that the phenotypic differences between MAP strains can be explained by their genetic polymorphisms. These results may help to elucidate the diversity of MAP, extending from genomic features to phenotypic traits
Improving scattering layer through mixture of nanoporous spheres and nanoparticles in ZnO-based dye-sensitized solar cells
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Light-induced charge density wave in LaTe3
When electrons in a solid are excited with light, they can alter the free
energy landscape and access phases of matter that are beyond reach in thermal
equilibrium. This accessibility becomes of vast importance in the presence of
phase competition, when one state of matter is preferred over another by only a
small energy scale that, in principle, is surmountable by light. Here, we study
a layered compound, LaTe, where a small in-plane (a-c plane) lattice
anisotropy results in a unidirectional charge density wave (CDW) along the
c-axis. Using ultrafast electron diffraction, we find that after
photoexcitation, the CDW along the c-axis is weakened and subsequently, a
different competing CDW along the a-axis emerges. The timescales characterizing
the relaxation of this new CDW and the reestablishment of the original CDW are
nearly identical, which points towards a strong competition between the two
orders. The new density wave represents a transient non-equilibrium phase of
matter with no equilibrium counterpart, and this study thus provides a
framework for unleashing similar states of matter that are "trapped" under
equilibrium conditions
Dynamical slowing down in an ultrafast photo-induced phase transition
Complex systems, which consist of a large number of interacting constituents,
often exhibit universal behavior near a phase transition. A slowdown of certain
dynamical observables is one such recurring feature found in a vast array of
contexts. This phenomenon, known as critical slowing down, is well studied
mostly in thermodynamic phase transitions. However, it is less understood in
highly nonequilibrium settings, where the time it takes to traverse the phase
boundary becomes comparable to the timescale of dynamical fluctuations. Using
transient optical spectroscopy and femtosecond electron diffraction, we studied
a photo-induced transition of a model charge-density-wave (CDW) compound,
LaTe. We observed that it takes the longest time to suppress the order
parameter at the threshold photoexcitation density, where the CDW transiently
vanishes. This finding can be quantitatively captured by generalizing the
time-dependent Landau theory to a system far from equilibrium. The experimental
observation and theoretical understanding of dynamical slowing down may offer
insight into other general principles behind nonequilibrium phase transitions
in many-body systems
Dynamic lattice distortions driven by surface trapping in semiconductor nanocrystals
Nonradiative processes limit optoelectronic functionality of nanocrystals and
curb their device performance. Nevertheless, the dynamic structural origins of
nonradiative relaxations in nanocrystals are not understood. Here, femtosecond
electron diffraction measurements corroborated by atomistic simulations uncover
transient lattice deformations accompanying radiationless electronic processes
in semiconductor nanocrystals. Investigation of the excitation energy
dependence shows that hot carriers created by a photon energy considerably
larger than the bandgap induce structural distortions at nanocrystal surfaces
on few picosecond timescales associated with the localization of trapped holes.
On the other hand, carriers created by a photon energy close to the bandgap
result in transient lattice heating that occurs on a much longer 200 ps
timescale, governed by an Auger heating mechanism. Elucidation of the
structural deformations associated with the surface trapping of hot holes
provides atomic-scale insights into the mechanisms deteriorating optoelectronic
performance and a pathway towards minimizing these losses in nanocrystal
devices.Comment: 17 pages, 4 figure
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