Thickness-dependent exciton relaxation dynamics of few-layer rhenium diselenide

Rhenium diselenide(ReSe_(2))has gathered much attention due to its low symmetry of lattice structure,which makes it possess in-plane anisotropic optical,electrical as well as excitonic properties and further enables ReSe_(2)have an important application in optoelectronic devices.Here,we report the thickness-dependent exciton relaxation dynamics of mechanically exfoliated few-layer ReSe_(2)flakes by using time-resolved pump–probe transient transmission spectroscopies.The results reveal two thickness-dependent relaxation processes of the excitons.The fast one correlates with the exciton formation(i.e.,the conversion of hot carriers to excitons),while the slow one is attributed to the exciton recombination dominated by defect-assisted exciton trapping besides photon emission channel.The decrease of scattering probability caused by defects leads to the increase of fast lifetime with thickness,and the increase of slow lifetime with thickness is related to the trap-mediated exciton depopulation induced by surface defects.Polarization-dependent transient spectroscopy indicates the isotropic exciton dynamics in the two-dimensional(2D)plane.These results are insightful for better understanding of excitonic dynamics of ReSe_(2)materials and its application in future optoelectronic and electronic devices.

The copper polymetallic deposits and resource potential in the Tibet Plateau

Many large and super-large copper deposits have been discovered and explored in the Tibet Plateau,which makes it the most important copper resource reserve and development base in China.Based on the work of the research team,the paper summarizes the geological characteristics of the main copper deposits in Tibet and puts forward a further prospecting direction.A series of large accumulated metal deposits or ore districts from subduction of Tethys oceanic crust to India-Asia collisionhave been discovered,such as Duolong Cu(Au)ore district and Jiama copper polymetallic deposit.The ore deposits in the Duolong ore district are located in the lowstand domain,the top of lowstand domain,and the highstand domain of the same magmatic-hydrothermal metallogenic system,and their relative positions are the indicators for related deposits in the Bangong Co-Nujiang metallogenic belt.The polycentric metallogenic model of the Jiama copper polymetallic deposit is an important inspiration for the exploration of the porphyry mineralization related to collision orogeny.Further mineral exploration in the Tibet Plateau should be focused on the continental volcanic rocks related to porphyry-epithermal deposits,orogenic gold deposits,hydrothermal Pb-Zn deposits related to nappe structures,skarn Cu(Au)and polymetallic deposits,and the Miocene W-Sn polymetallic deposits.

Recent Advances in MoiréSuperlattice Structures of Twisted Bilayer and Multilayer Graphene

Twisted bilayer graphene(TBG),which has drawn much attention in recent years,arises from van der Waals materials gathering each component together via van der Waals force.It is composed of two sheets of graphene rotated relatively to each other.Moirépotential,resulting from misorientation between layers,plays an essential role in determining the band structure of TBG,which directly relies on the twist angle.Once the twist angle approaches a certain critical value,flat bands will show up,indicating the suppression of kinetic energy,which significantly enhances the importance of Coulomb interaction between electrons.As a result,correlated states like correlated insulators emerge from TBG.Surprisingly,superconductivity in TBG is also reported in many experiments,which drags researchers into thinking about the underlying mechanism.Recently,the interest in the atomic reconstruction of TBG at small twist angles comes up and reinforces further understandings of properties of TBG.In addition,twisted multilayer graphene receives more and more attention,as they could likely outperform TBG although they are more difficult to handle experimentally.In this review,we mainly introduce theoretical and experimental progress on TBG.Besides the basic knowledge of TBG,we emphasize the essential role of atomic reconstruction in both experimental and theoretical investigations.The consideration of atomic reconstruction in small-twist situations can provide us with another aspect to have an insight into physical mechanism in TBG.In addition,we cover the recent hot topic,twisted multilayer graphene.While the bilayer situation can be relatively easy to resolve,multilayer situations can be really complicated,which could foster more unique and novel properties.Therefore,in the end of the review,we look forward to future development of twisted multilayer graphene.

Unusual photocarrier and coherent phonon dynamics behaviors of layered PdSe_(2)unveiled by ultrafast spectroscopy of the edge surface

Layered materials exhibit different electronic and phonon properties along in-plane and out-of-plane directions;existing studies focus on their in-plane behaviors,and the influence of such anisotropies on the dynamics of photocarriers and phonons is unknown.Here,we fabricate layered PdSe_(2)crystals with flat edge surfaces and compare the time-resolved ultrafast spectroscopies on their basal and edge surfaces.Pronounced differences in the transient reflection spectroscopies reveal the inconsistent photocarrier and phonon dynamics behaviors on the two surfaces:the slow hot carrier relaxation process is accelerated and the thermoelasticity-induced longitudinal coherent acoustic phonon oscillation completely vanishes on the edge surface,as compared with the basal surface.Theoretical analysis reveals that the inconsistent hot carrier dynamics originate from the anisotropic properties of low-energy phonons in PdSe_(2),and the absence of phonon oscillation on the edge surface results from the wavevector-limited sensitivity of acoustic B_(1u)mode.Moreover,polarization-dependent spectroscopies indicate the diverse optical anisotropies beyond the in-plane of PdSe_(2).This work provides a new method to explore unique physical properties and modulate the optical anisotropy of layered materials.

Stacking of Exfoliated Two-Dimensional Materials: A Review

In recent years,two-dimensfonal(2D)atomic crystals represented by graphene have opened up new fields of 2D physics.Layered materials with atomic layer thickness are self-assembled into van der Waals heterostructures by weak van der Waals forces without considering lattice matching.Van der Waals heterostructures can not only enhance the performance of its constituent materials but also show new characteristics.High-quality heterostructures require mechanically cleaved intrinsic 2D materials and flexible 2D material stacking techniques.Here,we summarize in detail the reliable exfoliation methods for large-area single-layer 2D materials and the dry and wet stacking techniques with high success rates.The twisted bilayer graphene is used as an example to briefly introduce the single-crystal tearing method,which is currently the most practical method for preparing isotropic twisted heterostructures with high-precision rotation angles.We hope to provide a valuable reference for researchers of 2D materials.

Pulmonary aspergillosis with in-situ pulmonary artery thrombosis: to anti-coagulate or not?

Aspergillus is widespread in the environment and causes a variety of tracheobronchial and pulmonary disorders,depending upon the alterations of immune status of hosts.[1] Among the spectrum of pulmonary aspergillosis (PA),allergic bronchopulmonary aspergillosis,and most chronic pulmonary aspergillosis are considered as noninvasive diseases,whereas invasive pulmonary aspergillosis (IPA) and subacute invasive pulmonary aspergillosis (SAIA) may cause tissue invasion.

A rare 3D hybrid bimetal halide ferroelectric:(3-Hydroxypyrrolidinium)2RbBiBr6

Organic-inorganic hybrid metal halides have gained worldwide attention due to their structural diversity and intriguing physical&chemical properties[1–5].The metal halides hold great promise in micro-and nano-electronics,energy storage,photocatalysis,optoelectronics and photovoltaics[6–9].In particular,photovoltaic devices containing a compositional derivative of the hybrid metal halide methylammonium lead halide(CH_(3)-NH_(3)PbX_(3),X=Cl,Br or I)have demonstrated remarkably high photoconversion efficiencies[10,11].

Sign of differential reflection and transmission in pump-probe spectroscopy of graphene on dielectric substrate

Pump-probe differential reflection and transmission spectroscopy is a very effective tool to study the nonequilibrium carrier dynamics of graphene. The reported sign of differential reflection from graphene is not explicitly explained and not consistent. Here, we study the differential reflection and transmission signals of graphene on a dielectric substrate. The results reveal the sign of differential reflection changes with the incident direction of the probe beam with respect to the substrate. The obtained theory can be applied to predict the differential signals of other two-dimensional materials placed on various dielectric substrates.