Crystal growth of ZnS nanoparticles during hydrothermal coarsened in 4 M NaOH occurs via a two-stage process. In the first stage, the primary particles grow into a size over hundred times of the original volume. The initial growth rate can be fitted by an asymptotic curve. High-resolution transmission electron microscope (HRTEM) data indicate that in this stage, crystal growth mainly occurs via a multistep crystallographically specific oriented attachment (OA). The higher the coarsening temperature, the earlier the first stage ends. In the second stage, an abrupt transition from asymptotic to square parabola growth kinetics occurs. The crystal growth data can be fitted by a standard Ostwald ripening (OR) model consistent with growth controlled by dissolution/precipitation of ions in solution. HRTEM data indicate that a minor amount of OA-based growth also occurs in the early period of the second stage. A new multistep OA kinetics model analogous to the reaction between molecules was proposed to illustrate the asymptotic growth in the first stage of coarsening. The effect of concentrated NaOH was discussed and proved to be the key that hindered the OR process, attributing to the almost exclusive pure OA-based growth of ZnS particles in the first stage.

We propose and analyze a new approach based on parity-time (PT ) symmetric microcavities with balanced gain and loss to enhance the performance of cavity-assisted metrology. We identify the conditions under which PT -symmetric microcavities allow to improve sensitivity beyond what is achievable in loss-only systems. We discuss its application to the detection of mechanical motion, and show that the sensitivity is significantly enhanced in the vicinity of the transition point from unbroken-to broken-PT regimes. We believe that our results open a new direction for PT -symmetric physical systems and it may find use in ultra-high precision metrology and sensing.PACS numbers: 42.65. Yj, 06.30.Ft, 42.50.Wk Introduction.-The measurement of physical quantities with high precision is the subject of metrology. This has attracted much attention due to the increasing interest in, e.g., gravitational wave detection [1], sensing of nanostructures [2,3], as well as global positioning and navigation [4,5]. Developments in metrology over the past two decades have provided the necessary tools to determine the fundamental limits of measuring physical quantities and the resources required to achieve them [6,7].Among many different approaches, cavity-assisted metrology (CAM), where a high-quality (Q) factor cavity or resonator is coupled to a device under test (DUT), has emerged as a versatile and efficient experimental approach to achieve high-precision measurements. In CAM, the coupling between the resonator and the DUT manifests itself as a back-action-induced resonance frequency shift, resonance mode splitting, or a sideband in the output transmission spectrum [8]. Cavity-assisted metrology has been successfully applied for reading out the state of a qubit [9], measuring tiny mechanical motions [10,[12][13][14][15][16][17]42], and detecting nanoparticles with single-particle resolution [18,19].The readout signal (i.e., the transmission spectrum) of CAM is determined by the sum between the background spectrum of the cavity and the back-action spectrum of the DUT. The background spectrum is determined by the Q of the cavity whereas the back-action spectrum is determined by the strength of the cavity- * Electronic address: jing-zhang@mail.tsinghua.edu.cn † Electronic address: ozdemir@ese.wustl.edu DUT coupling (also dependent on Q) and the quantity to be measured. A broad background spectrum masks the back-action spectrum and decreases signal-to-noise ratio (SNR) [ Fig. 1(a)]. A higher coupling-strength between the cavity and the DUT and a higher Q of the cavity will be helpful to detect very weak signals and enable to resolve fine structures in the output spectra [ Fig. 1(b)]. A higher Q is also necessary to enhance the coupling strength between the cavity and the DUT. For example, for optomechanical resonators, the detection of tiny motions requires a strong optomechanical coupling, which is only possible with an high Q-factor. Therefore, CAM will benefit significantly from a narrower background spectrum which is fundamentally...

energy such as wind and solar energy has attracted enormous interest for its significant roles in mitigating CO 2 emissions and reducing dependence on petrochemicals. [1,2] At the heart of the CO 2 conversion technology, electrocatalysts are needed to promote a critical reaction, CO 2 reduction reaction (CO 2 RR) that determines the efficiency and selectivity. To date, the electrocatalysts have confronted severe bottlenecks issue: poor selectivity about various accessory products in CO 2 conversion process, and loss of efficiency toward competing hydrogen evolution. [3] The former involves associated multielectron transfer process and is difficult to accurately control the reaction process by external conditions, [4] while the latter is mainly due to the fact that the equilibrium potentials for most of the CO 2 RR are very close to hydrogen evolution reaction (HER) toward undesirable side-products in aqueous electrolytes, which degrades the electrocatalytic performance during the CO 2 RR process. [5,6] Therefore, CO 2 RR is much more complex than other energy-related electrochemical reactions such as oxygen reduction reaction (ORR) and oxygen evolution reaction (OER), and it is still a great challenge to design and synthesize electrocatalytic materials with higher product selectivity and catalytic activity for CO 2 RR.Among the electrocatalysts including metals oxides and metal-doped carbon materials, single-atom catalysts (SACs) represent an exciting class of catalysts with monodispersed metal catalytic centers and have emerged as the frontier science in both homogeneous and heterogeneous catalysis, including CO 2 conversion. [7][8][9][10] This type of catalysts contains M-N-C moiety with single atoms and is common in building metalorganic frameworks (MOFs), [11] covalent organic frameworks (COFs) [12] with transition metal macrocyclic clusters, such as porphyrin, phthalocyanine, and tetraazannulene, as well as metal-doped carbon materials [13] (e.g., graphene, carbon nanotubes, fullerene). In nature, the biomolecules, like chlorophyll (Mg-porphyrin) in leaves, and iron porphyrins in cytochrome c oxidase in blood cells, have similar structures as SACs, with special ability in photosynthesis and transforming CO 2 from cells with high efficiency and selectivity. [14] Through the selection of appropriate motifs, the construction principles of Direct conversion of CO 2 into carbon-neutral fuels or industrial chemicals holds a great promise for renewable energy storage and mitigation of greenhouse gas emission. However, experimentally finding an electrocatalyst for specific final products with high efficiency and high selectivity poses serious challenges due to multiple electron transfer, complicated intermediates, and numerous reaction pathways in electrocatalytic CO 2 reduction. Here, an intrinsic descriptor that correlates the catalytic activity with the topological, bonding, and electronic structures of catalytic centers on M-N-C based single-atom catalysts is discovered. The "volcano"-shaped relationships betwee...

Owing to the characteristics of mimicking human skin's function and transmitting sensory signals, electronic skin (eskin), as an emerging and exciting research field, has inspired tremendous efforts in the biomedical field. However, it is frustrating that most e-skins are prone to bacterial infections, resulting a serious threat to human health. Therefore, the construction of e-skin with an integrated perceptual signal and antibacterial properties is highly desirable. Herein, the dynamic supramolecular hydrogel was prepared through a freezing/thawing method by cross-linking the conductive graphene (G), biocompatible polyvinyl alcohol (PVA), self-adhesive polydopamine (PDA), and in situ formation antibacterial silver nanoparticles (AgNPs). Having fabricated the hierarchical network structure, the PVA−G−PDA−AgNPs composite hydrogel with a tensile strength of 1.174 MPa and an elongation of 331% paves way for flexible e-skins. Notably, the PVA−G−PDA−AgNPs hydrogel exhibits outstanding antibacterial activity to typical pathogenic microbes (e.g., Gram-negative Escherichia coli and Gram-positive Staphylococcus aureus), which effectively prevents bacterial infections that harm human health. With self-adhesiveness to various surfaces and excellent conductivity, the PVA−G−PDA−AgNPs composite hydrogel was used as strain sensors to detect a variety of macroscale and microscale human motions successfully. Meanwhile, the excellent rehealing property allows the hydrogel to recycle as a new sensor to detect large-scale human activities or tiny movement. Based on these remarkable features, the antibacterial, self-adhesive, recyclable, and tough conductive composite hydrogels possess the great promising application in biomedical materials.

In this work, crystal growth kinetics of surfactant-free nanocrystalline SnO2 in distilled water at 175-250 degrees C were investigated. The growth rate followed the type of asymptotic curve in hundreds of hours, which could be fitted by the multistep oriented attachment (OA) kinetic model. High-resolution transmission electron microscope (HRTEM) data also indicated crystal growth occurring via the multistep OA mechanism. During the growth of SnO2, the concentration of Sn ions in the aqueous solution was examined. It reveals that the unsaturated situation of SnO2 results in crystal growth via the pure OA mechanism. A growth model of self-integration of conjugated nanocrystals was discussed for understanding the OA behavior.

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Uniformly aligned single crystal arrays of C8-BTBT were prepared by the LSVC method and their OFETs exhibit high mobility with uniform distribution.

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