Solution-based Chalcogenide Thin Film Deposition

As a group of promising semiconductor materials, metal chalcogenides in thin film form have been widely used in electronics and optoelectronics applications, such as solar cell devices and photon sensors. Unfortunately, the film size and product throughput are limited by the current vacuum-based thin film deposition techniques. Solution-based thin film deposition could archive a continuous large area thin film deposition of chalcogenides. Also by eliminating the vacuum requirement, the total process cost can be significantly reduced. Here three different routes to deposit the chalcogenide thin film have been studied: from solution-based deposited metal oxide film, from electroplated metal thin film, and from bulk chalcogenide powder. By a hydrogen-assisted selenization process, an oxide thin film of copper, indium, and gallium has been successfully transited to CuIn₁₋ₓGaₓSe₂ chalcopyrite thin film, and the solar deviceshave been fabricated based on this p-type chalcogenide material. In a similar way, a metal stack of copper, zinc, and tin has been converted to Cu₂ZnSnS₄ kesterite thin film solar cell material. The last one, powder molybdenum disulfide is transformed into thin film through a dimensional reduction process with the help of microreactor design and simulation. This research also includes the fabrication of photovoltaic devices, thin film transistors, and their characterizations in both structural and electronic properties. There are advantages and disadvantages from each of these solution-based deposition techniques, and by selecting one of these methods, it could archive a generic process route for a large range of metal chalcogenide thin film deposition

Molecular simulation of adsorption behaviors of methane and carbon dioxide on typical clay minerals

Knowledge of the interaction mechanisms between shale and CH4/CO2 is crucial for the implementation of CO2 sequestration with enhanced CH4 recovery (CS-EGR) in shale reservoir. As one of the main constituents of shale, clay minerals can profoundly affect the storage capacity of gases in nanopores. In this paper, the adsorption behaviors of both CO2 and CH4 on montmorillonite, illite as well as kaolinite under dry condition are investigated by Grand Canonical Monte Carlo (GCMC) simulation. The results exhibit that the maximum adsorption capacity of single-component CH4 and CO2 is associated with the types of clay crystals. Specifically, the montmorillonite has the strongest adsorption capacity for CO2, followed by illite and kaolinite, while the sequence in maximum adsorption capacity of CH4 is predicted in the order of kaolinite > montmorillonite > illite. These discrepancies are closely related to the characteristics of adsorbate molecules as well as the different structures of clay crystals. Meanwhile, the maximum adsorption capacity of CH4 in studied clay minerals gradually decreases as pore size increases, while nanopores with 2-nm basal spacing demonstrate the highest adsorption capacity for CO2. In addition, it is observed that the studied clay minerals tend to preferentially adsorb CO2 rather than CH4 during binary gas mixtures simulation. The selectivity of CH4/CO2 mixtures in montmorillonite and kaolinite exhibits various performances as the adsorption pressure increases, with the selectivity in montmorillonite being the largest, especially at low pressure. The cation exchange significantly enhances the electrostatic interaction with CO2 molecules, leading to a higher loading of CO2 as well as larger value of selectivity. These findings can provide basis and guidance for the CS-EGR project in shale reservoirs

Substantial Progress Yet Significant Opportunity for Improvement in Stroke Care in China

BACKGROUND AND PURPOSE: Stroke is a leading cause of death in China. Yet the adherence to guideline-recommended ischemic stroke performance metrics in the past decade has been previously shown to be suboptimal. Since then, several nationwide stroke quality management initiatives have been conducted in China. We sought to determine whether adherence had improved since then. METHODS: Data were obtained from the 2 phases of China National Stroke Registries, which included 131 hospitals (12 173 patients with acute ischemic stroke) in China National Stroke Registries phase 1 from 2007 to 2008 versus 219 hospitals (19 604 patients) in China National Stroke Registries phase 2 from 2012 to 2013. Multiple regression models were developed to evaluate the difference in adherence to performance measure between the 2 study periods. RESULTS: The overall quality of care has improved over time, as reflected by the higher composite score of 0.76 in 2012 to 2013 versus 0.63 in 2007 to 2008. Nine of 13 individual performance metrics improved. However, there were no significant improvements in the rates of intravenous thrombolytic therapy and anticoagulation for atrial fibrillation. After multivariate analysis, there remained a significant 1.17-fold (95% confidence interval, 1.14-1.21) increase in the odds of delivering evidence-based performance metrics in the more recent time periods versus older data. The performance metrics with the most significantly increased odds included stroke education, dysphagia screening, smoking cessation, and antithrombotics at discharge. CONCLUSIONS: Adherence to stroke performance metrics has increased over time, but significant opportunities remain for further improvement. Continuous stroke quality improvement program should be developed as a national priority in China

Reducing CO₂ to dense nanoporous graphene by Mg/Zn for high power electrochemical capacitors

Converting CO2 to valuable materials is attractive.Herein, we report using simple metallothermic reactions to reduce atmospheric CO2 to dense nanoporous graphene. By using a Zn/Mg mixture as a reductant, the resulted nanoporous graphene exhibits highly desirable properties: high specific surface area of 1900 m2/g, a great conductivity of 1050 S/m and a tap density of 0.63 g/cm3, comparable to activated carbon. The nanoporous graphene contains a fine mesoporous structure constructed by curved few-layer graphene nanosheets. The unique property ensemble enables one of the best high-rate performances reported for electrochemical capacitors: a specific capacitance of ~170F/g obtained at 2000 mV/s and 40 F/g at a frequency of 120 Hz. This simple fabricating strategy conceptually provides opportunities for materials scientists to design and prepare novel carbon materials with metallothermic reactions.This is the publisher’s final pdf. The published article is copyrighted by Elsevier and can be found at: http://www.journals.elsevier.com/nano-energy/.Keywords: Magnesiothermic reduction, Nanoporous graphene, CO₂ reduction, Electrochemical capacitor

Enhanced polarization and abnormal flexural deformation in bent freestanding perovskite oxides

Recent realizations of ultrathin freestanding perovskite oxides offer a unique platform to probe novel properties in two-dimensional oxides. Here, we observe a giant flexoelectric response in freestanding BiFeO3 and SrTiO3 in their bent state arising from strain gradients up to 3.5 × 107 m−1, suggesting a promising approach for realizing ultra-large polarizations. Additionally, a substantial change in membrane thickness is discovered in bent freestanding BiFeO3, which implies an unusual bending-expansion/shrinkage effect in the ferroelectric membrane that has never been seen before in crystalline materials. Our theoretical model reveals that this unprecedented flexural deformation within the membrane is attributable to a flexoelectricity–piezoelectricity interplay. The finding unveils intriguing nanoscale electromechanical properties and provides guidance for their practical applications in flexible nanoelectromechanical systems