Diisopropylammonium Bromide Based Two-Dimensional Ferroelectric Monolayer Molecular Crystal with Large In-Plane Spontaneous Polarization.

In light of their easy processing, light weight and mechanical flexibility, ferroelectric molecular crystal with large spontaneous polarization ( P) is highly desired for many advanced applications. Herein, we report the first theoretical study of two-dimensional (2D) ferroelectric molecular crystals via ab initio calculations. Specifically, we show that diisopropylammonium bromide (DIPAB) based 2D ferroelectric monolayer molecular crystal with large in-plane P of ∼1.

Down-regulation of microRNA-200b is a potential prognostic marker of lung cancer in southern-central Chinese population.

MicroRNAs (miRNAs) may regulate diverse biological processes and play an important role in cancer. And MiRNAs have been proposed as a useful tool for lung cancer diagnosis and therapeutics in cancer. The purpose of the present study was to investigate the association among the expression level of mature miR-200b-5p in peripheral blood and the risk of lung cancer and clinic pathological characteristics.

Highly stable and efficient all-inorganic lead-free perovskite solar cells with native-oxide passivation.

There has been an urgent need to eliminate toxic lead from the prevailing halide perovskite solar cells (PSCs), but the current lead-free PSCs are still plagued with the critical issues of low efficiency and poor stability. This is primarily due to their inadequate photovoltaic properties and chemical stability. Herein we demonstrate the use of the lead-free, all-inorganic cesium tin-germanium triiodide (CsSnGeI) solid-solution perovskite as the light absorber in PSCs, delivering promising efficiency of up to 7.

Copper(i) sulfide: a two-dimensional semiconductor with superior oxidation resistance and high carrier mobility.

Two-dimensional (2D) semiconductors with suitable direct band gaps, high carrier mobility, and excellent open-air stability are especially desirable for material applications. Herein, we show theoretical evidence of a new phase of a copper(i) sulfide (CuS) monolayer, denoted δ-CuS, with both novel electronic properties and superior oxidation resistance. We find that both monolayer and bilayer δ-CuS have much lower formation energy than the known β-CuS phase.

Quasi-1D TiS Nanoribbons: Mechanical Exfoliation and Thickness-Dependent Raman Spectroscopy.

Quasi-one-dimensional (quasi-1D) materials enjoy growing interest due to their unusual physical properties and promise for miniature electronic devices. However, the mechanical exfoliation of quasi-1D materials into thin flakes and nanoribbons received considerably less attention from researchers than the exfoliation of conventional layered crystals. In this study, we investigated the micromechanical exfoliation of representative quasi-1D crystals, TiS whiskers, and demonstrate that they typically split into narrow nanoribbons with very smooth, straight edges and clear signatures of 1D TiS chains.

Diagnosis of nasopharyngeal carcinoma from serum samples using hyperspectral imaging combined with a chemometric method.

Diagnosing nasopharyngeal carcinoma (NPC) is a significant challenge because of the highly complex process. We proposed an approach to diagnose NPC serum using a combination of hyperspectral imaging and weight-based principal component analysis. Samples were prepared by pressing boric acid into pellets for use as the sera substrate.

Insights into High Conductivity of the Two-Dimensional Iodine-Oxidized sp-c-COF.

A recent experiment [ Jin , E. ; Science 2017 , 357 , 673 - 676 ] shows that the conductivity of a two-dimensional (2D) sp-carbon-hybridized π-conjugated covalent organic framework (sp-c-COF) can be enhanced by as much as 12 orders of magnitude after iodine oxidation processing. To understand the physical mechanism underlying such a huge increase in the conductivity, we perform multiscale computations and find that the high conductivity of the iodine-oxidized 2D COF can be attributed to both hole transfer and ion transfer within the 2D COF.

Unravelling the Role of Topological Defects on Catalytic Unzipping of Single-Walled Carbon Nanotubes by Single Transition Metal Atom.

Catalytic unzipping of single-walled carbon nanotubes (SWCNTs) has been experimentally shown to be a viable method to produce graphene nanoribbons (GNRs) with clean and smooth edges for advanced applications, while topological defects (TDs) are inevitably presented in mass produced CNTs (especially the tube end/cap), which may affect the catalytic unzipping. Herein, we theoretically investigate the roles of TDs on the catalytic unzipping of SWCNTs by a single Fe atom in the H environment. Our computation shows that the threshold reaction barriers to the catalytic SWCNT unzipping can be notably reduced by ∼20%-40%, resulting from weakened and elongated local C-C bonds associated with TDs.

Mechanistic Origin of the High Performance of Yolk@Shell BiS@N-Doped Carbon Nanowire Electrodes.

High-performance lithium-ion batteries are commonly built with heterogeneous composite electrodes that combine multiple active components for serving various electrochemical and structural functions. Engineering these heterogeneous composite electrodes toward drastically improved battery performance is hinged on a fundamental understanding of the mechanisms of multiple active components and their synergy or trade-off effects. Herein, we report a rational design, fabrication, and understanding of yolk@shell BiS@N-doped mesoporous carbon (C) composite anode, consisting of a BiS nanowire (NW) core within a hollow space surrounded by a thin shell of N-doped mesoporous C.

PCl: A Unique Post-Phosphorene 2D Material with Superior Properties against Oxidation.

Herein, a unique class of post-phosphorene materials, namely, phosphorene halogenides (e.g., α-PCl) with superior oxidation resistance and desirable bandgap characteristics, are proposed.

Application of Electronic Counting Rules for Ligand-Protected Gold Nanoclusters.

Understanding special stability of numerous ligand-protected gold nanoclusters has always been an active area of research. In the past few decades, several theoretical models, including the polyhedral skeletal electron pair theory (PSEPT), superatom complex (SAC), and superatom network (SAN), among others, have been developed for better understanding the stabilities and structures of selected ligand-protected gold nanoclusters. This Account overviews the recently proposed grand unified model (GUM) to offer some new insights into the structures and growth mechanism of nearly all crystallized and predicted ligand-protected gold nanoclusters.

Machine learning and artificial neural network prediction of interfacial thermal resistance between graphene and hexagonal boron nitride.

High-performance thermal interface materials (TIMs) have attracted persistent attention for the design and development of miniaturized nanoelectronic devices; however, a large number of potential new materials exist to form these heterostructures and the explorations of their thermal properties are time consuming and expensive. In this work, we train several supervised machine learning (ML) and artificial neural network (ANN) models to predict the interfacial thermal resistance (R) between graphene and hexagonal boron-nitride (hBN) with only the knowledge of the system temperature, coupling strength between two layers, and in-plane tensile strains. The training data were obtained by high-throughput computations (HTCs) of R using classical molecular dynamics (MD) simulations.

Fabrication and understanding of CuSi-Si@carbon@graphene nanocomposites as high-performance anodes for lithium-ion batteries.

Besides silicon's low electronic conductivity, another critical issue for using silicon as the anode for lithium-ion batteries (LIBs) is the dramatic volume variation (>300%) during lithiation/delithiation processes, which can lead to rapid capacity fading and poor rate capability, thereby hampering silicon's practical applications in batteries. To mitigate these issues, herein, we report our findings on the design and understanding of a self-supported CuSi-Si@carbon@graphene (CuSi-SCG) nanocomposite anode. The nanocomposite is composed of CuSi-Si core and carbon shell with core/shell particles uniformly encapsulated by graphene nanosheets anchored directly on a Cu foil.

Self-scrolling MoS metallic wires.

Two-dimensional (2D) van der Waals (vdW) materials with strong in-plane chemical bonds and weak interaction in the out-of-plane direction have been acknowledged as a basic building block for designing dimensional materials in 0D, 1D, 2D and 3D forms. Compared to the explosive research on 2D vdW materials, quasi-one-dimensional (quasi-1D) vdW materials have received rare attention, despite the fact that they also present rich physics in electronics and engineering implications. Herein, quasi-1D MoS2 nanoscrolls are directly fabricated from CVD-grown 2D triangular MoS2 sheets.

Two-dimensional dry ices with rich polymorphic and polyamorphic phase behavior.

Both carbon dioxide (CO) and water (HO) are triatomic molecules that are ubiquitous in nature, and both are among the five most abundant gases in the Earth's atmosphere. At low temperature and ambient pressure, both CO and HO form molecular crystals--dry ice I and ice I Because water possesses distinctive hydrogen bonds, it exhibits intricate and highly pressure-dependent phase behavior, including at least 17 crystalline ice phases and three amorphous ice phases. In contrast, due to its weak van der Waals intermolecular interactions, CO exhibits fewer crystalline phases except at extremely high pressures, where nonmolecular ordered structures arise.

Determination of CO Adsorption Sites on Gold Clusters Au ( n = 21-25): A Size Region That Bridges the Pyramidal and Core-Shell Structures.

We perform a joint photoelectron spectroscopy and theoretical study to investigate CO adsorption sites on midsized gold clusters, Au ( n = 21-25), a special size region that bridges the highly symmetric pyramidal cluster Au (Li et al. Science 2003, 299, 864) and the prevailing core-shell clusters starting from Au (Schaefer et al. ACS Nano 2014, 8, 7413).

Self-Catalytic Reaction of SO and NH To Produce Sulfamic Acid and Its Implication to Atmospheric Particle Formation.

Sulfur trioxide (SO) is one of the most active chemical species in the atmosphere, and its atmospheric fate has profound implications to air quality and human health. The dominant gas-phase loss pathway for SO is generally believed to be the reaction with water molecules, resulting in sulfuric acid. The latter is viewed as a critical component in the new particle formation (NPF).

Zero-Dimensional Organic-Inorganic Perovskite Variant: Transition between Molecular and Solid Crystal.

Low-dimensional organic-inorganic halide perovskites (OIHPs) have attracted intense interest recently for photovoltaic applications, due to their markedly high chemical stability as compared to the widely studied three-dimensional (3D) counterparts. However, low-dimensional OIHPs usually give much lower device performance than the 3D OIHPs. In particular, for the zero-dimensional (0D) OIHPs, it is believed that the strong intrinsic quantum-confinement effects can lead to extremely low carrier motility, which can severely limit the photovoltaic performance.

[Characteristics of soil phosphorus fractions of different vegetation types in subtropical forests and their driving factors.].

Soil P fraction, microbial biomass P (MBP), and activities of acid phosphomonoesterase (ACP) and phosphodiesterase (PD) were analyzed under evergreen broad-leaved forest, mixed forest and coniferous forest in Daiyun Mountains. The results showed that labile-P comprised only 1.0%-4.

Transition-Metal Dihydride Monolayers: A New Family of Two-Dimensional Ferromagnetic Materials with Intrinsic Room-Temperature Half-Metallicity.

Two-dimensional (2D) ferromagnetic materials with intrinsic half-metallicity are highly desirable for nanoscale spintronic applications. Here, we predict a new and stable family of 2D transition-metal dihydride (MH; M = Sc, Ti, V, Cr, Fe, Co, Ni) monolayers with novel properties. Our density functional theory computation shows that CoH and ScH monolayers are ferromagnetic metals, while the others are antiferromagnetic semiconductors.

Structural evolution and magnetic properties of anionic clusters CrGe (n = 3-14): photoelectron spectroscopy and density functional theory computation.

The structural, electronic and magnetic properties of dual Cr atoms doped germanium anionic clusters, [Formula: see text] (n  =  3-14), have been investigated by using photoelectron spectroscopy in combination with density-functional theory calculations. The low-lying structures of [Formula: see text] are determined by DFT based genetic algorithm optimization. For [Formula: see text] with n  ⩽  8, the structures are bipyramid-based geometries, while [Formula: see text] cluster has an opening cage-like structure, and the half-encapsulated structure is gradually covered by the additional Ge atoms to form closed-cage configuration with one Cr atom interior for n  =  10 to 14.

Criegee intermediate inside fullerene cage: Evidence for size-dependent reactivity.

In the theoretical calculations reported here, we show that the hydration of the Criegee intermediate within the sub-nanospace of fullerene cages occurs differently in different fullerenes, thereby providing evidence for the size-dependent reactivity inside these exotic carbon cages. Upon C or C encapsulation, the Criegee hydration occurs instantaneously without any activation barrier, whereas inside the C cage, the hydration involves a small barrier of 4.4 kcal/mol.

Formation of HONO from the NH-promoted hydrolysis of NO dimers in the atmosphere.

One challenging issue in atmospheric chemistry is identifying the source of nitrous acid (HONO), which is believed to be a primary source of atmospheric "detergent" OH radicals. Herein, we show a reaction route for the formation of HONO species from the NH-promoted hydrolysis of a NO dimer (ONONO), which entails a low free-energy barrier of 0.5 kcal/mol at room temperature.

Understanding the quenching nature of Mn in wide band gap inorganic compounds: design principles for Mn phosphors with higher efficiency.

Mn4+ doped phosphors, as an alternative to rare-earth element doped phosphors, have attracted immense attention owing to their ultrahigh quantum efficiency of red emission for potential applications in high rendering white LEDs (light-emitting diodes). Their performance can be largely affected by quenching phenomena such as thermal quenching, concentration quenching and the quenching induced by some intrinsic/extrinsic defects. However, the quenching mechanisms due to the defect levels and host band are still incompletely understood.