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Transition-metal dichalcogenides have promising potentials for high-performance electronic and optoelectronic applications, which could be deeply influenced by defects, including native defects and dopants. Experiments to date have frequently reported p-type conductivity in the WSe 2 monolayer, but the origin remains elusive. Here, using the first-principles calculations, we systematically investigate the point defects in the WSe 2 monolayer and show that: (1) no intrinsic point defect is responsible for the p-type doping; (2) hydrogen interstitials (H i ) are possible sources for n-type conductivity; (3) oxygen substitution of Se (O Se ) can greatly promote the formation of adjacent W vacancy (V W ), and finally make V W relatively shallow acceptors by forming the defect complex n O Se + V W ( n = 1 to 6). Our work reveals that n O Se + V W is the origin of the p-type conductivity in the unintentionally doped WSe 2 monolayer, given that O is present throughout the synthesis conditions of WSe 2 .

Temperature tolerance restricts the distribution of a species. However, the molecular and cellular mechanisms that set the thermal tolerance limits of an organism are poorly understood. Here, we report on the function of dual-specificity phosphatase 1 (DUSP1) in thermal tolerance regulation. Notably, we found that dusp1 -/- zebrafish grew normally but survived within a narrowed temperature range. The higher susceptibility of these mutant fish to both cold and heat challenges was attributed to accelerated cell death caused by aggravated mitochondrial dysfunction and over-production of reactive oxygen species in the gills. The DUSP1-MAPK-DRP1 axis was identified as a key pathway regulating these processes in both fish and human cells. These observations suggest that DUSP1 may play a role in maintaining mitochondrial integrity and redox homeostasis. We therefore propose that maintenance of cellular redox homeostasis may be a key mechanism for coping with cellular thermal stress and that the interplay between signaling pathways regulating redox homeostasis in the most thermosensitive tissue (i.e., gills) may play an important role in setting the thermal tolerance limit of zebrafish.

It is known that carrier mobility in layered semiconductors generally increases from two-dimensions (2D) to three-dimensions due to fewer scattering channels resulting from decreased densities of electron and phonon states. In this work, we find an abnormal decrease of electron mobility from monolayer to bulk MoS 2 . By carefully analyzing the scattering mechanisms, we can attribute such abnormality to the stronger intravalley scattering in the monolayer but weaker intervalley scattering caused by few intervalley scattering channels and weaker corresponding electron-phonon couplings compared to the bulk case. We show that it is the matching between the electronic band structure and phonon spectrum rather than their densities of electronic and phonon states that determines scattering channels. We propose, for the first time, the phonon-energy-resolved matching function to identify the intra- and inter-valley scattering channels. Furthermore, we show that multiple valleys do not necessarily lead to strong intervalley scattering if: (1) the scattering channels, which can be explicitly captured by the distribution of the matching function, are few due to the small matching between the corresponding electron and phonon bands; and/or (2) the multiple valleys are far apart in the reciprocal space and composed of out-of-plane orbitals so that the corresponding electron-phonon coupling strengths are weak. Consequently, the searching scope of high-mobility 2D materials can be reasonably enlarged using the matching function as useful guidance with the help of band edge orbital analysis.

Interlayer interactions play important roles in manipulating the electronic properties of layered semiconductors. One common mechanism is that the valence band maximum (VBM) and the conduction band minimum (CBM) in one layer couple to the VBM and CBM in another layer, respectively, resulting in the decrease of the band gap from the monolayer to the bilayer. Here we report an unusual interlayer coupling mechanism in layered Cu-based ternary chalcogenides CuMCh 2 (M = Sb, Bi; Ch = S, Se) that the CBM in one layer strongly couples to the VBM in the other layer, leading to the band gap increase from the monolayer to the bilayer. Such an unusual interlayer interaction arises from the entangling between the electronic structures and the structures of CuMCh 2 in which the cations M and anions Ch are alternatively arranged at the outmost part of each layer. Consequently, the M atom at the bottom of the upper layer is very close to the Ch atom at the top of the bottom layer, so that the orbitals of the M atom which dominate the CBM can strongly couple to the orbitals of the Ch atom which dominate the VBM, as demonstrated by the orbital hopping integrals obtained from the Wannier function analysis. The exceptional case of the unusual interlayer interaction revealed in this work enriches the diversity of the interlayer interactions in layered materials and is expected to exist in similar layered systems in which cations and anions are alternatively arranged at the outmost part of each layer.

Despite the great appeal of two-dimensional semiconductors for electronics and optoelectronics, to achieve the required charge carrier concentrations by means of chemical doping remains a challenge due to large defect ionization energies (IEs). Here, by decomposing the defect IEs into three parts based on ionization process, we propose a conceptual picture that the large defect IEs are caused by two effects of reduced dimensionality. While the quantum confinement effect makes the neutral single-electron point defect levels deep, the reduced screening effect leads to high energy cost for the electronic relaxation. The first-principles calculations for black phosphorus and MoS 2 do demonstrate the general trend. Using BP monolayer either embedded into dielectric continuum or encapsulated between two hBN layers, we demonstrate the feasibility of increasing the screening to reduce the defect IEs. Our analysis is expected to help achieve effective carrier doping and open ways toward more extensive applications of 2D semiconductors.

Two-dimensional (2D) Dirac materials and boron sheets have attracted intensive interest recently. However, 2D Dirac materials remain rare and difficult to be realized experimentally, and 2D boron sheets generally have high dynamical instability. Stimulated by the experimental observation of Dirac cones in nongraphene-like β 12 boron sheets and based on the understanding of boron sheet electronic organization, we theoretically design new 2D Dirac materials β 12 -XBeB 5 (X = H, F, Cl) with high stability. We confirm β 12 -HBeB 5 as the global energy minimum among its 2D allotropes based on global structure search methods, a strong indication of its experimental feasibility. Our designed β 12 -HBeB 5 has not only a high Fermi velocity, but also a Dirac state very robust against extraordinary large tensile strains, an advantage for flexible electronics applications. Our work opens a new avenue to designing feasible 2D Dirac materials and stabilizing borophene sheets.

Objective: To investigate the changes in the plasma levels of endotoxin in severe burn patients during administration of antibiotics., Methods: Fifty severe burn patients with burn area larger than 30% TBSA were enrolled in the study, and they were respectively treated with Netilmicin (A group), Cefoperazone (B group), Ceftazidime (C group) and Imipenem/Cilastatin (D group). Venous blood samples were harvested for determination of endotoxins levels before treatment and 1, 2, 3, 5, 7 post-treatment day (PTD)., Results: The plasma levels of endotoxin were elevated in different degrees in A, B and C groups. The plasma levels of endotoxin in B group were higher on 1, 2 PTD than on 3, 5, 7 PTD, and they were also higher than that in D group (P < 0.05). The plasma levels of endotoxin in C group reached the peak on 5 PTD [(0.398 +/- 0.172) EU/mL], which were higher than that before treatment [(0.251 +/- 0.142) EU/mL, P < 0.05] and other groups (P < 0.05). The plasma levels of endotoxin in D group were lower on 1, 2 PTD than that before treatment (P < 0.05)., Conclusion: Different amounts of endotoxins can be released after treatment with antibiotics in severe burn patients. Attention should be paid to the effect of antibiotics on the levels of endotoxin in practice.