Unraveling the strain tuning mechanism of interlayer excitons in WSe2/MoSe2heterostructure.

Atomically thin transition metal dichalcogenides (TMDs) exhibit rich excitonic physics, due to reduced dielectric screening and strong Coulomb interactions. Especially, some attractive topics in modern condensed matter physics, such as correlated insulator, superconductivity, topological excitons bands, are recently reported in stacking two monolayer (ML) TMDs. Here, we clearly reveal the tuning mechanism of tensile strain on interlayer excitons (IEXs) and intralayer excitons (IAXs) in WSe2/MoSe2heterostructure (HS) at low temperature. We utilize the cryogenic tensile strain platform to stretch the HS, and measure by micro-photoluminescence (µ-PL). The PL peaks redshifts of IEXs and IAXs in WSe2/MoSe2HS under tensile strain are well observed. The first-principles calculations by using density functional theory reveals the PL peaks redshifts of IEXs and IAXs origin from bandgap shrinkage. The calculation results also show the Mo-4d states dominating conduction band minimum shifts of the ML MoSe2plays a dominant role in the redshifts of IEXs. This work provides new insights into understanding the tuning mechanism of tensile strain on IEXs and IAXs in two-dimensional (2D) HS, and paves a way to the development of flexible optoelectronic devices based on 2D materials.

Impact of dyslipidemia on the cumulative pregnancy outcomes after first ovarian stimulation.

Objectives: To investigate the cumulative live birth rate (CLBR) according to lipid metabolism in patients with or without polycystic ovarian syndrome (PCOS) undergoing their first complete in vitro fertilization/intracytoplasmic sperm injection (IVF/ICSI) cycles. Patients: A total of 1,470 patients with PCOS and 3,232 patients without PCOS who underwent their first complete IVF/ICSI cycles from January 2016 to June 2018 were included. During a minimum of 2 years of follow-up, they had achieved at least one live birth or used all available embryos. The cumulative pregnancy outcomes were compared based on the patients' blood lipid parameters, including triglycerides (TG), total cholesterol (TC), low-density lipoprotein cholesterol (LDL-C) and high-density lipoprotein cholesterol (HDL-C), in the two populations. Patients with an abnormal level of one or more of these four indicators were considered the dyslipidemia group. Patients whose four indicators were normal were considered the control group. Results: Among 1,470 patients with PCOS, the cumulative pregnancy outcomes were similar in the dyslipidemia group and control group. Logistic regression analysis showed that the TC levels were significantly negatively associated with the cumulative live birth rate (CLBR) after adjustment for confounding factors such as age and BMI (aOR 0.81, 95% CI 0.66-0.98, P<0.05). Among the 3,232 patients without PCOS, there was no significant difference in the cumulative pregnancy outcomes between the dyslipidemia group and the control group. No significant correlations were found in other logistic regression analyses. Conclusions: TC negatively impacts the CLBR after first ovarian stimulation in PCOS patients. PCOS patients with dyslipidemia caused by elevated TC may have a poor CLBR.

Exploring the emerging of electronic and magnetic properties with adatom adsorption on a novel semiconductor monolayer: N2P6.

The effect of adsorbed adatoms on the structural stability and electronic properties of monolayer N2P6 have been systematically studied via first-principles simulation methods. It is found that pristine N2P6 is an indirect 0.21 eV band gap semiconductor, with a pleated honeycomb-like structure similar to phosphorene. The calculation results show that adsorbed adatoms can modify the properties of monolayer N2P6 effectively. The degree of local distortion strongly depends on the electronegativity and size of adatoms, also the adsorption energy ranges from 0.3 to 5.8 eV depending on the species of adatoms. The electronic properties show metallic behavior with several adsorbed metal atoms (Li, Na, Al, K, Cu, Ni, and Zn) and some non-metal atoms (H, F, P, and Cl), while adsorbed O, S, Ca, and Si atoms still remain semiconductors. The systems of Ni and Zn adatoms show ferromagnetic behavior, and adsorbed Mg exhibits a half-metallic character. Our theoretical studies indicate that N2P6 possesses potential application in the field of gas sensors.