Transient Superdiffusion of Energetic Carriers in Transition Metal Dichalcogenides Visualized by Ultrafast Pump-Probe Microscopy

Because of the strong Coulomb interaction and quantum confinement effect,2-dimensional transitionmetal dichalcogenides possess a stable excitonic population.To realize excitonic device applications,such as excitonic circuits,switches,and transistors,it is of paramount importance for understanding the optical properties of transition metal dichalcogenides.Furthermore,the strong quantum confinement in 2-dimensional space introduces exotic properties,such as enhanced phonon bottlenecking effect,many-body interaction of excitons,and ultrafast nonequilibrium exciton-exciton annihilation.Exciton diffusion is the primary energy dissipation process and a working horse in excitonic devices.In this work,we investigated time-resolved exciton propagation in monolayer semiconductors of wSe_(2),MowSe_(2),and MoSe_(2),with a home-built femtosecond pump-probe microscope.We observed ultrafast exciton expansion behavior with an equivalent diffusivity of up to 502 cm^(2)s^(-1)at the initial delay time,followed by a slow linear dffusive regime(20.9 cm^(2)s^(-1))in the monolayer WSe_(2).The fast expansion behavior is attributed to energetic carrier-dominated superdiffusive behavior.We found that in the monolayers MowSe_(2)and MoSe_(2),the energetic carrier-induced exciton expansion is much more effective,with diffusivity up to 668 and 2295 cm^(2)s^(-1),respectively.However,the"cold"exciton transport is trap limited in MowSe_(2)and MoSe_(2),leading to negative diffusion behavior at later time.Our findings are helpful to better understand the ultrafast nonlinear diffusive behavior in strongly quantum-confined systems.It may be harnessed to break the limit of conventional slow diffusion of excitons for advancing more efficient and ultrafast optoelectronicdevices.

A multicenter prospective study of next-generation sequencing-based newborn screening for monogenic genetic diseases in China

Background Newborn screening(NBS)is an important and successful public health program that helps improve the long-term clinical outcomes of newborns by providing early diagnosis and treatment of certain inborn diseases.The develop-ment of next-generation sequencing(NGS)technology provides new opportunities to expand current newborn screening methodologies.Methods We designed a a newborn genetic screening(NBGS)panel targeting 135 genes associated with 75 inborn disorders by multiplex PCR combined with NGS.With this panel,a large-scale,multicenter,prospective multidisease analysis was conducted on dried blood spot(DBS)profiles from 21,442 neonates nationwide.Results We presented the positive detection rate and carrier frequency of diseases and related variants in different regions;and 168(0.78%)positive cases were detected.Glucose-6-Phosphate Dehydrogenase deficiency(G6PDD)and phenylketonuria(PKU)had higher prevalence rates,which were significantly different in different regions.The positive detection of G6PD variants was quite common in south China,whereas PAH variants were most commonly identified in north China.In addi-tion,NBGS identified 3 cases with DUOX2 variants and one with SLC25A13 variants,which were normal in conventional NBS,but were confirmed later as abnormal in repeated biochemical testing after recall.Eighty percent of high-frequency gene carriers and 60%of high-frequency variant carriers had obvious regional differences.On the premise that there was no significant difference in birth weight and gestational age,the biochemical indicators of SLC22A5 c.1400C>G and ACADSB c.1165A>G carriers were significantly different from those of non-carriers.Conclusions We demonstrated that NBGS is an effective strategy to identify neonates affected with treatable diseases as a supplement to current NBS methods.Our data also showed that the prevalence of diseases has significant regional charac-teristics,which provides a theoretical basis for screening diseases in different regions.

Highly Fluorescent Semiconducting Two-Dimensional Conjugated Polymer Films Achieved by Side-Chain Engineering Showing Large Exciton Diffusion Length

Semiconducting two-dimensional conjugated polymers(2DCPs)with strong fluorescence emission have great potential for various optoelectronic applications.However,it is enormously challenging to achieve this goal due to the significant compact interlayerπ-πstacking-induced quenching effect in these systems.In this work,we found that highly fluorescent semiconducting 2DCPs can be prepared through an effective side-chain engineering approach in which interlayer spacers are introduced to reduce the fluorescence quenching effect.The obtained two truxene-based 2DCP films that,along with-C6H13 and-C_(12)H_(25)alkyl side chains as interlayer spacers both demonstrate superior fluorescence properties with a high photoluminescence quantum yield of 5.6%and 14.6%,respectively.These are among the highest values currently reported for 2DCP films.Moreover,an ultralong isotropic quasi-twodimensional exciton diffusion length constrained in the plane with its highest value approaching 110 nm was revealed by the transient photoluminescence microscopy technique,suggesting that theπ-conjugated structure in these truxene-based 2DCP films has effectively been extended.This work can enable a broad exploration of highly fluorescent semiconducting 2DCP films for more deeply fundamental properties and optoelectronic device applications.