The liquid-phase exfoliation of tin(II) sulfide to produce SnS nanosheets in N-methyl-2-pyrrolidone is reported. The material is characterized by Raman spectroscopy, atomic force microscopy, ...lattice-resolution scanning transmission electron microscope imaging, and energy dispersive X-ray spectrum imaging. Quantum chemical calculations on the optoelectronic characteristics of bulk and 10-layer down to monolayer SnS have been performed using a quantum chemical density functional tight-binding approach. The optical properties of the SnS and centrifugally fractionated SnS nanosheet dispersions were compared to that predicted by theory. Through centrifugation, bilayer SnS nanosheets can be produced size-selectively. The scalable solution processing of semiconductor SnS nanosheets is the key to their commercial exploitation and is potentially an important step toward the realization of a future electronics industry based on two-dimensional materials.
This book examines the formation of the Chinese empire through its reorganization and reinterpretation of its basic spatial units: the human body, the household, the city, the region, and the world. ...The central theme of the book is the way all these forms of ordered space were reshaped by the project of unification and how, at the same time, that unification was constrained and limited by the necessary survival of the units on which it was based. Consequently, as Mark Edward Lewis shows, each level of spatial organization could achieve order and meaning only within an encompassing, superior whole: the body within the household, the household within the lineage and state, the city within the region, and the region within the world empire, while each level still contained within itself the smaller units from which it was formed. The unity that was the empire's highest goal avoided collapse back into the original chaos of nondistinction only by preserving within itself the very divisions on the basis of family or region that it claimed to transcend.
Phosphorene, or two-dimensional (2D) black phosphorus (BP) was the first synthetic 2D elemental allotrope beyond graphene to be isolated and studied. It is useful due to its high p-type carrier ...mobility and direct band gap that is tunable in the range
ca.
0.3-2 eV thus bridging the energy gap between graphene and transition metal dichalcogenides such as molybdenum disulfide. Beyond the 'Scotch-Tape' method that was used to isolate the first samples of 2D BP for prototype studies, a range of potentially scalable solution processing techniques emerged later that can produce electronics grade material. This feature article focuses on such solution-process routes to 2D BP and highlights challenges in processing the material, mainly caused by its susceptibility to oxidation, as well as illuminating new avenues and opportunities in the area.
This feature article discusses solution-phase routes to semiconducting two-dimensional black phosphorus ('phosphorene') and highlights challenges in processing the material as well as illuminating new avenues and opportunities in the area.
The incidence of neonatal sepsis in India is the highest in the world. Evidence regarding its risk factors can guide clinical practice and prevention strategies.
To review, assess and synthesize the ...available literature from India on the risk factors of sepsis among neonates.
A systematic review was conducted. We searched PubMed, CINAHL, Scopus, Web of Science, Popline, IndMed, Indian Science Abstracts and Google Scholar from inception up to March 23, 2018 to identify observational analytical studies reporting on risk factors of laboratory-confirmed neonatal sepsis in India. Two authors independently screened studies (title, abstract and full-text stages), extracted data, and assessed quality. A random-effects meta-analysis was performed as substantial heterogeneity was anticipated. Subgroup and sensitivity analyses were additionally performed. Effect size in our review included odds ratio and standardized mean difference.
Fifteen studies were included from 11,009 records, of which nine were prospective in design. Birthweight and gestational age at delivery were the most frequently reported factors. On meta-analyses, it was found that male sex (OR: 1.3, 95% CI: 1.02, 1.68), out born neonates (OR: 5.5, 95% CI: 2.39, 12.49), need for artificial ventilation (OR: 5.61; 95% CI: 8.21, 41.18), gestational age <37 weeks (OR: 2.05; 95% CI:1.40, 2.99) and premature rupture of membranes (OR:11.14, 95% CI: 5.54, 22.38) emerged as risk factors for neonatal sepsis. Included studies scored lowest on exposure assessment and confounding adjustment, which limited comparability. Inadequacy and variation in definitions and methodology affected the quality of included studies and increased heterogeneity.
Male neonates, outborn admissions, need for artificial ventilation, gestational age <37 weeks and premature rupture of membranes are risk factors for sepsis among neonates in India. Robustly designed and reported research is urgently needed to confirm the role of other risk factors of neonatal sepsis in India.
A new wet chemistry approach, based on the hot-injection–thermolytic decomposition of the single-source precursor Mo2O2S2(S2COEt)2 in oleylamine, is described for the production of nanodimensional ...1H-MoS2@oleylamine. High quality freestanding MoS2 nanosheets capped with oleylamine have been prepared and subjected to detailed compositional analyses for the first time. The selection of the appropriate reaction temperatures (200–325 °C) in the simple yet robust procedure allows control of the lateral nanosheet dimensions which range from 4.5 to 11.5 nm, as 1H-MoS2@oleylamine entities which maintain a consistent chemical composition (MoS2·oleylamine0.28–0.33). This work provides the first example of atomic resolution STEM imaging of these fine-scale nanosheet materials, providing new insights into their morphology and demonstrating that those freestanding MoS2 nanosheets are pure, highly crystalline, randomly oriented monolayers. The 1H-MoS2@oleylamine samples were analyzed by attenuated total reflectance FT-infrared spectroscopy (ATR-FTIR), transmission electron microscope (TEM) imaging, aberration corrected scanning transmission electron microscope (STEM) imaging, energy dispersive X-ray (EDX) spectrum imaging, powder X-ray diffractometry (p-XRD), thermogravimetric analysis (TGA), and Raman spectroscopy. Composite materials of the as-synthesized MoS2 nanosheets and exfoliated graphene were then used to construct coin-cell supercapacitor electrodes with a specific capacitance of 50 mF/cm2, demonstrating its utility as an energy storage material.
Copper nanoparticles (Cu‐NPs) have a wide range of applications as heterogeneous catalysts. In this study, a novel green biosynthesis route for producing Cu‐NPs using the metal‐reducing bacterium, ...Shewanella oneidensis is demonstrated. Thin section transmission electron microscopy shows that the Cu‐NPs are predominantly intracellular and present in a typical size range of 20–40 nm. Serial block‐face scanning electron microscopy demonstrates the Cu‐NPs are well‐dispersed across the 3D structure of the cells. X‐ray absorption near‐edge spectroscopy and extended X‐ray absorption fine‐structure spectroscopy analysis show the nanoparticles are Cu(0), however, atomic resolution images and electron energy loss spectroscopy suggest partial oxidation of the surface layer to Cu2O upon exposure to air. The catalytic activity of the Cu‐NPs is demonstrated in an archetypal “click chemistry” reaction, generating good yields during azide‐alkyne cycloadditions, most likely catalyzed by the Cu(I) surface layer of the nanoparticles. Furthermore, cytochrome deletion mutants suggest a novel metal reduction system is involved in enzymatic Cu(II) reduction and Cu‐NP synthesis, which is not dependent on the Mtr pathway commonly used to reduce other high oxidation state metals in this bacterium. This work demonstrates a novel, simple, green biosynthesis method for producing efficient copper nanoparticle catalysts.
A novel green biosynthesis route for the production of functional copper nanoparticles (Cu‐NPs) using a metal‐reducing bacterium is reported. Detailed characterization reveals well‐dispersed Cu(0) nanoparticles with a thin, stable Cu2O surface layer. The catalytic activity of the biogenic Cu‐NPs is demonstrated for a range of “click chemistry” azide‐alkyne cycloaddition reactions, and the commercial potential of this approach discussed.
We demonstrate a new design of graphene liquid cell consisting of a thin lithographically patterned hexagonal boron nitride crystal encapsulated on both sides with graphene windows. The ultrathin ...window liquid cells produced have precisely controlled volumes and thicknesses and are robust to repeated vacuum cycling. This technology enables exciting new opportunities for liquid cell studies, providing a reliable platform for high resolution transmission electron microscope imaging and spectral mapping. The presence of water was confirmed using electron energy loss spectroscopy (EELS) via the detection of the oxygen K-edge and measuring the thickness of full and empty cells. We demonstrate the imaging capabilities of these liquid cells by tracking the dynamic motion and interactions of small metal nanoparticles with diameters of 0.5–5 nm. We further present an order of magnitude improvement in the analytical capabilities compared to previous liquid cell data with 1 nm spatial resolution elemental mapping achievable for liquid encapsulated bimetallic nanoparticles using energy dispersive X-ray spectroscopy (EDXS).
We report the electrochemical detection of the redox active cardiac biomarker myoglobin (Mb) using aptamer-functionalized black phosphorus nanostructured electrodes by measuring direct electron ...transfer. The as-synthesized few-layer black phosphorus nanosheets have been functionalized with poly-l-lysine (PLL) to facilitate binding with generated anti-Mb DNA aptamers on nanostructured electrodes. This aptasensor platform has a record-low detection limit (∼0.524 pg mL–1) and sensitivity (36 μA pg–1 mL cm–2) toward Mb with a dynamic response range from 1 pg mL–1 to 16 μg mL–1 for Mb in serum samples. This strategy opens up avenues to bedside technologies for multiplexed diagnosis of cardiovascular diseases in complex human samples.
Atomically thin black phosphorus (BP) has attracted considerable interest due to its unique properties, such as an infrared band gap that depends on the number of layers and excellent electronic ...transport characteristics. This material is known to be sensitive to light and oxygen and degrades in air unless protected with an encapsulation barrier, limiting its exploitation in electrical devices. We present a new scalable technique for nanopatterning few layered BP by direct electron beam exposure of encapsulated crystals, achieving a spatial resolution down to 6 nm. By encapsulating the BP with single layer graphene or hexagonal boron nitride (hBN), we show that a focused electron probe can be used to produce controllable local oxidation of BP through nanometre size defects created in the encapsulation layer by the electron impact. We have tested the approach in the scanning transmission electron microscope (STEM) and using industry standard electron beam lithography (EBL). Etched regions of the BP are stabilized by a thin passivation layer and demonstrate typical insulating behavior as measured at 300 and 4.3 K. This new scalable approach to nanopatterning of thin air sensitive crystals has the potential to facilitate their wider use for a variety of sensing and electronics applications.
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