Globally 113 702 confirmed (4125 new) 4012 deaths (203 new) China 80 924 confirmed (20 new) 3140 deaths (17 new) Outside of China 32 778 confirmed (4105 new) 872 deaths (186 new) 109 countries/territories/ areas (5 new) WHO RISK ASSESSMENT China Very High Regional Level Very High Global Level Very High HIGHLIGHTS • 5 new countries/territories/areas (Brunei Darussalam, Mongolia, Cyprus, Guernsey and Panama) have reported cases of COVID-19 in the past 24 hours. 1 https://www.iatatravelcentre.com/international-travel-document-news/1580226297.htm 2 https://pandemic.internationalsos.com/2019-ncov/ncov-travel-restrictions-flight-operations-and-screening 3 https://www.iata.org/en/pressroom/pr/2020-03-02-01/ 4 https://www.who.int/ith/2019-nCoV_advice_for_international_traffic-rev/en/

Benefiting from the superior electron mobility and good air‐stability, the emerging layered bismuth oxyselenide (Bi2O2Se) nanosheet has received considerable attention with the promising prospects for electronics and optoelectronics applications. However, the high charge carrier concentration and bolometric effect of Bi2O2Se give rise to the high dark current and relatively slow photoresponse, which severely impede further improvement of the performance of Bi2O2Se based photodetectors. Here, a WSe2/Bi2O2Se Van der Waals p‐n heterostructure is reported with a pronounced rectification ratio of 105 and a low reverse dark current of 10−11 A, as well as an enhanced light on/off ratio up to 618 under 532 nm light illumination. The device also exhibits a fast response speed of 2.6 µs and a broadband detection capability from 365 to 2000 nm due to the efficient charge separation and strong interlayer coupling at the interface of the two flakes. Importantly, the built‐in potential in the WSe2/Bi2O2Se heterostructure offers a competitive self‐powered photodetector with the light on/off ratio above 105 and a photovoltaic responsivity of 284 mA W−1. The WSe2/Bi2O2Se heterostructure shows promising potentials for high‐performance self‐driven photodetector applications.

Background:The ongoing outbreak of novel corona virus disease 2019 in Wuhan, China, is arousing international concern. This study evaluated whether and when the infected but asymptomatic cases during the incubation period could infect others. Methods:We collected data on demographic characteristics, exposure history, and symptom onset day of the confirmed cases, which had been announced by the Chinese local authorities. We evaluated the potential of transmission during the incubation period in 50 infection clusters, including 124 cases. All the secondary cases had a history of contact with their first-generation cases prior to symptom onset. Results:The estimated mean incubation period for COVID-19 was 4.9 days (95% confidence interval [CI], 4.4 to 5.4) days, ranging from 0.8 to 11.1 days (2.5th to 97.5th percentile). The observed mean and standard deviation (SD) of serial interval was 4.1±3.3 days, with the 2.5th and 97.5th percentiles at -1 and 13 days. The infectious curve showed that in 73.0% of the secondary cases, their date of getting infected was before symptom onset of the first-generation cases, particularly in the last three days of the incubation period. Conclusions:The results indicated the transmission of COVID-9 occurs among close contacts during the incubation period, which may lead to a quarantine loophole.Strong and effective countermeasures should be implemented to prevent or mitigate asymptomatic transmission during the incubation period in populations at high risk.

and zhaoys@sustc.edu.cn † Supplemental Materials available: Detailed sample characterizations (including crystal structure and pressure-dependence of lattice parameters of layered ReS 2 , enthalpy curve of ReS 2 as a function of pressure, schematics of electrical resistance measurements in DAC, and electrical resistance results using large volume press).‡ Equal contribution. ABSTRACT: Triclinic rhenium disulphide (ReS 2 ) is a promising candidate for postsilicon electronics because of its unique optic-electronic properties. The electrical and optical properties of ReS 2 under high pressure, however, remain unclear. Here we present a joint experimental and theoretical study on the structure, electronic and vibrational properties, and visible-light responses of ReS 2 up to 50 GPa. There is a direct to indirect band gap transition in 1T-ReS 2 under low pressure regime up to 5GPa. Upon further compression, 1T-ReS 2 undergoes a structural transition to distorted-1T′ phase at 7.7 GPa, followed by the isostructural metallization at 38.5GPa. Both in situ Raman spectrum and electronic structure analysis reveal that interlayer sulphur-sulphur interaction is greatly enhanced during compression, leading to the remarkable modifications on the electronic properties observed in our subsequent experimental measurements, such as band gap closure and enhanced photo-responsiveness. This study demonstrates the critical role of pressure in tuning materials properties and the potential usage of layered ReS 2 for pressure-responsive optoelectronic applications.