In-plane anisotropic layered materials such as black phosphorus (BP) have emerged as an important class of two-dimensional (2D) materials that bring a new dimension to the properties of 2D materials, hence providing a wide range of opportunities for developing conceptually new device applications. However, all of recently reported anisotropic 2D materials are relatively narrow-bandgap semiconductors (<2 eV), and there has been no report about this type of materials with wide bandgap, restricting the relevant applications such as polarization-sensitive photodetection in short wave region. Here we present a new member of the family, germanium diselenide (GeSe2) with a wide bandgap of 2.74 eV, and systematically investigate the in-plane anisotropic structural, vibrational, electrical, and optical properties from theory to experiment. Photodetectors based on GeSe2 exhibit a highly polarization-sensitive photoresponse in short wave region due to the optical absorption anisotropy induced by in-plane anisotropy in crystal structure. Furthermore, exfoliated GeSe2 flakes show an outstanding stability in ambient air which originates from the high activation energy of oxygen chemisorption on GeSe2 (2.12 eV) through our theoretical calculations, about three times higher than that of BP (0.71 eV). Such unique in-plane anisotropy and wide bandgap, together with high air stability, make GeSe2 a promising candidate for future 2D optoelectronic applications in short wave region.
In article number 2001483, Tongbo Wei, Feng Ding, Peng Gao, Zhongfan Liu, and co-workers report the direct growth of nano-patterned graphene on an oxide substrate via selective growth on the c-plane of a nano-patterned sapphire substrate, as guided by density functional theory calculations and analogue simulations. The thus obtained nano-patterned graphene shows potential applications such as high-performance light-emitting diodes.
Medicaid is the government insurance program that provides health insurance to the poor. The effect of Medicaid eligibility on children’s health is of great concern. The literature survey demonstrates that Medicaid eligibility largely increased the utilization of medical service. However, there are few studies evaluating the effect of Medicaid eligibility on children’s health conditions. This paper use ‘days of school missed due to illnesses or injury’ as the measurement to illustrate the effect of Medicaid eligibility on children’s health. Four econometric models are used to fully analyze the effect of Medicaid eligibility on children’s health outcome. The four models are probit model, triprobit model, negative binomial model and endogenous negative binomial model. Medicaid eligibility and days of school missed due to illness or injury are positively correlated in all four models.
Fracture mechanics behavior and acoustic emission (AE) characteristics of fractured rock mass are related to underground engineering safety construction, disaster prediction, and early warning. In this study, the failure evolution characteristics of intact and fracture (e.g., single fracture, parallel fractures, cross fractures, and mixed fractures) coal were studied and contrasted with each other on the basis of the distribution of max amplitude of AE. The study revealed some meaningful results, where the value of b (i.e., the distribution characteristic of max amplitude of AE) could represent the failure evolution process of intact and fractured coal. The maximum amplitude distribution of AE events was characterized by Gaussian normal distribution, and the probability of the maximum amplitude of AE events corresponding to 35∼50 dB was the largest. In the stress range of 60∼80%, AE events and maximum amplitude increased rapidly, and the corresponding b value decreased. The energy of AE events showed a downward trend after reaching the maximum value at about 80% stress level. Under the same stress level, the more complex the fracture was, the larger the b value of coal–rock mass was, and the stronger the inhibition effect on the fracture expansion caused by the internal fracture distribution was. Due to the anisotropy of coal–rock mass with a single crack, the distribution of the b value was more discrete, while the anisotropy of coal–rock mass with mixed crack decreased, and the dispersion of the b value decreased. The deformation of cracked coal mainly caused by the adjustment of cracks during the initial loading b value experienced a trend of decreasing first, then increasing, and then decreasing in the loading process. When the load reached 0.8 times of the peak strength, the b value had a secondary decreasing trend, indicating the macroscopic failure of the sample, which could be used as a precursor criterion for the complete failure of coal–rock mass.
Domestic migration workers and inflation are two phenomena attracting attention from worldwide scholars. The article endeavors to accomplish the following three tasks: a) describe the characteristics of inflation and immigration situations in China; b) study the effect of inflation on domestic immigrants' the expenditures; c) understand the effect of inflation on immigrants' happiness and satisfaction. The paper found out that in all the eight expenditure categories, only three categories (food, clothing and housing) are negatively affected by inflation. Other five expenditure categories (health and medical, house equipment, facilities and services, entertainment, educational and cultural activities, transportation and communication, tuition, and miscellaneous) are positively affected by inflation. The biggest reduction of expenditure is in transportation and communication with a coefficient of -0.025. The paper also found out that the lower income group's expenditure is more affected by inflation then higher income group. The paper showed that inflation didn't have a significant effect on people's feeling of happiness and their satisfaction.
Epichlorohydrin (ECH) is mainly an industrial raw material, while it is toxic and dangerous for human health, so finding a simple and effective method for detecting ECH gas is challenging work. Porous SnO2 structures are successfully obtained through a hydrothermal method using SnCl4·5H2O as the tin source and water as the solvent. Ag nanoparticle (NPs) decorated porous SnO2 structures have also been prepared by the impregnation method. The morphology and structure of the as-prepared products were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and the nitrogen adsorption–desorption technique. The as-synthesized nanostructures, with diameters ranging from 4–5 μm, are composed of porous nanosheets with an average thickness of 60 nm. The gas sensing properties of the Ag NPs decorated porous SnO2 structures for ECH gas were investigated in detail, and the results showed that the 10% Ag NPs decorated porous SnO2 structures gas sensor was the optimum sensor, demonstrating a response (S = 50) for 100 ppm of ECH gas, while the working temperature was decreased by about 180 °C. In addition, it showed a low detection level (0.5 ppm) for ECH gas, good reproducibility and repeatability, and long-term stability, implying a promising application in detecting ECH gas.
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