Polarity-Reversed Robust Carrier Mobility in Monolayer MoS₂ Nanoribbons

Using first-principles calculations and deformation potential theory, we investigate the intrinsic carrier mobility (μ) of monolayer MoS₂ sheet and nanoribbons. In contrast to the dramatic deterioration of μ in graphene upon forming nanoribbons, the magnitude of μ in armchair MoS₂ nanoribbons is comparable to its sheet counterpart, albeit oscillating with ribbon width. Surprisingly, a room-temperature transport polarity reversal is observed with μ of hole (h) and electron (e) being 200.52 (h) and 72.16 (e) cm² V^–1s^–1 in sheet, and 49.72 (h) and 190.89 (e) cm² V^–1 s^–1 in 4 nm nanoribbon. The high and robust μ and its polarity reversal are attributable to the different characteristics of edge states inherent in MoS₂ nanoribbons. Our study suggests that width reduction together with edge engineering provide a promising route for improving the transport properties of MoS₂ nanostructures

Hydrogen-Bonded Chains and Networks of Triptycene-Based Triboronic Acid and Tripyridinone

The synthesis of 2,7,14-triptycene triboronic acid <b>1</b> and triptycene tripyridinone <b>2</b>, as well as their packings in the crystalline states, was studied. Both compounds show pronounced aggregation by hydrogen bonding, thus forming supramolecular polymeric chains or interpenetrated networks depending on the solvent mixtures used for crystallization. In all examples, two of the three hydrogen bonding motifs in each molecule formed cyclic dimers, leaving the third site either masked by solvents or for the formation of another hydrogen bond with the dimeric units. The influence of the solvent is discussed

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<p>Endophytic fungi are an integral part and even seen as host organs of plant, influencing physiology, ecology, and development of host plants. However, little is known about micro-ecosystems and functional interactions of endophytic fungi in root-parasitic interactions of Cynomorium songaricum and its host Nitraria tangutorum. Here, distribution and dynamics of endophytic fungi were objectively investigated in their associations with C. songaricum and N. tangutorum based on mycobiome studies using high-throughput sequencing. Results suggest that endophytic fungi may be exchanged between C. songaricum and its host N. tangutorum probably through haustorium, connection of xylem and phloem in the vascular system. The similarity of endophytic fungal composition between C. songaricum and parasitized N. tangutorum was 3.88% which was significantly higher than the fungal similarity of 0.10% observed between C. songaricum and non-parasitized N. tangutorum. The similarities of fungal community in parasitized N. tangutorum were much closer to C. songaricum than to the non-parasitized N. tangutorum. The composition of endophytic fungi in these associations increased in progressive developmental stages of C. songaricum from sprouting to above ground emergence, and decreased subsequently probably due to host recognition and response by fungi. However, the shared fungal operational taxonomic units (OTUs) increased among interactions of C. songaricum with parasitized and non-parasitized N. tangutorum. Studies of bioactivity on culturable endophytic fungi showed that isolates such as Fusarium spp. possess the ability to promote seed germination of C. songaricum. Our study reports for the first time the special ecological system of endophytic fungi in C. songaricum and its host N. tangutorum. Overall, we hypothesize that a deeper understanding of the sharing, movement, and role of endophytic fungi between root-parasitic plant and its host may lead to finding alternative approaches to help increase the output of ethno-pharmacologically important medicinal plants.</p

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<p>Endophytic fungi are an integral part and even seen as host organs of plant, influencing physiology, ecology, and development of host plants. However, little is known about micro-ecosystems and functional interactions of endophytic fungi in root-parasitic interactions of Cynomorium songaricum and its host Nitraria tangutorum. Here, distribution and dynamics of endophytic fungi were objectively investigated in their associations with C. songaricum and N. tangutorum based on mycobiome studies using high-throughput sequencing. Results suggest that endophytic fungi may be exchanged between C. songaricum and its host N. tangutorum probably through haustorium, connection of xylem and phloem in the vascular system. The similarity of endophytic fungal composition between C. songaricum and parasitized N. tangutorum was 3.88% which was significantly higher than the fungal similarity of 0.10% observed between C. songaricum and non-parasitized N. tangutorum. The similarities of fungal community in parasitized N. tangutorum were much closer to C. songaricum than to the non-parasitized N. tangutorum. The composition of endophytic fungi in these associations increased in progressive developmental stages of C. songaricum from sprouting to above ground emergence, and decreased subsequently probably due to host recognition and response by fungi. However, the shared fungal operational taxonomic units (OTUs) increased among interactions of C. songaricum with parasitized and non-parasitized N. tangutorum. Studies of bioactivity on culturable endophytic fungi showed that isolates such as Fusarium spp. possess the ability to promote seed germination of C. songaricum. Our study reports for the first time the special ecological system of endophytic fungi in C. songaricum and its host N. tangutorum. Overall, we hypothesize that a deeper understanding of the sharing, movement, and role of endophytic fungi between root-parasitic plant and its host may lead to finding alternative approaches to help increase the output of ethno-pharmacologically important medicinal plants.</p

Theoretical Design Study on the Electronic Structures and Phosphorescent Properties of Four Iridium(III) Complexes

<div><p>The geometry structures, electronic structures, absorption, and phosphorescent properties of four Ir(III) complexes have been investigated using the density functional method. Calculations of ionization potential (IP) and electron affinity (EA) were used to evaluate the injection abilities of holes and electrons into these complexes. The result also indicates that the –CF₃ substituent group on the ligand not only change the character of transition but affect the rate and balance of charge transfer. The lowest energy absorption wavelengths are located at 428 nm for <b>1a</b>, 446 nm for <b>1b</b>, 385 nm for <b>2a</b>, and 399 nm for <b>2b</b>, respectively, in good agreement with the energy gap (Δ<i>E</i>_L-H) trend because the HOMO–LUMO transition configurations are predominantly responsible for the <i>S</i>₀→<i>S</i>₁ transition. <b>2b</b> has the 433 nm blue emission, which might be a potential candidate for blue emitters in phosphorescent dopant emitters in organic light emitting diodes (OLEDs). The study could provide constructive information for designing novel OLEDs materials in the future.</p><p><i>[Supplemental materials are available for this article. Go to the publisher's online edition of Molecular Crystals and Liquid Crystals to view the free supplemental file.]</i></p></div

Modulating Carrier Density and Transport Properties of MoS₂ by Organic Molecular Doping and Defect Engineering

Using first-principles calculations, we investigate the effect of molecular doping and sulfur vacancy on the electronic properties and charge modulation of monolayer MoS₂. It is found that tetrathiafulvalene and dimethyl-<i>p</i>-phenylenediamine molecules are effective donors, whereas tetracyanoethylene (TCNE) and tetracyanoquinodimethane (TCNQ) are effective acceptors, and all these molecules are able to shift the work function of MoS₂. For MoS₂ containing sulfur vacancies, these molecules are able to change the position of the defect levels within the band gap and modulate the carrier density around the defect center. Charge transfer analysis shows that TCNE and TCNQ induce a free-carrier depletion of the defect states, which is beneficial for the suppression of the nonradiative trionic decay and a higher excitonic efficiency due to a decrease in the screening of excitons. Furthermore, the effects of molecular adsorption on Seebeck coefficient of MoS₂ are also explored. Our work suggests that an enhanced excitonic efficiency of MoS₂ may be achieved via proper defect engineering and molecular doping arising from the charge density modulation and charge screening

Graphene Helicoid: Distinct Properties Promote Application of Graphene Related Materials in Thermal Management

The extremely high thermal conductivity of graphene has received great attention both in experiments and calculations. Obviously, new features in thermal properties are of primary importance for application of graphene-based materials in thermal management in nanoscale. Here, we studied the thermal conductivity of graphene helicoid, a newly reported graphene-related nanostructure, using molecular dynamics simulation. Interestingly, in contrast to the converged cross-plane thermal conductivity in multilayer graphene, axial thermal conductivity of graphene helicoid keeps increasing with thickness with a power law scaling relationship, which is a consequence of the divergent in-plane thermal conductivity of two-dimensional graphene. Moreover, the large overlap between adjacent layers in graphene helicoid also promotes higher thermal conductivity than multilayer graphene. Furthermore, in the small strain regime (<10%), compressive strain can effectively increase the thermal conductivity of graphene helicoid, while in the ultra large strain regime (∼100% to 500%), tensile strain does not decrease the heat current, unlike that in generic solid-state materials. Our results reveal that the divergence in thermal conductivity, associated with the anomalous strain dependence and the unique structural flexibility, makes graphene helicoid a new platform for studying fascinating phenomena of key relevance to the scientific understanding and technological applications of graphene-related materials

Plasmonic Nanochemistry Based on Nanohole Array

We show that the growth of Ag nanoparticles (NPs) follows the areas of maximum plasmonic field in nanohole arrays (NAs). We thus obtain Ag NP rings not connected to the metallic rim of the nanoholes. The photocatalytic effect resulting from the enhanced <i>E</i>-field of NAs boosts the reaction and is responsible for the site selectivity. The strategy, using plasmonics to control a chemical reaction, can be expanded to organic reactions, for example, synthesis of polypyrrole. After the NA film is removed, ordered ring-shaped Ag NPs are easily obtained, inspiring a facile micropatterning method. Overall, the results reported in this work will contribute to the control of chemical reactions at the nanoscale and are promising to inspire a facile way to pursue patterned chemical reactions

Resonant Optical Transmission through Topologically Continuous Films

A continuous thick (≥100 nm) Ag film is generally optically nontransparent, but here we show that <i>via</i> a dedicated structuring it can be made transparent. The enhanced optical transmission is realized by preparing metal films with a periodic array of hollow nanocones <i>via</i> an inexpensive and versatile colloidal lithography technique. These topologically continuous films possess the structural feature of sharp top tips and bottom nanoholes, leading to an effective resonance mode of coupling between the surface plasmons around the holes and cone tips. This introduces a resonant optical transmission that is much affected by the thickness and height of the hollow nanocones. Moreover, the topologically continuous films are highly sensitive to the surrounding environment, indicating great potential for plasmonic sensors. The experimental results are in good agreement with numerical simulations. On the basis of the hollow element and enhanced optical performance, hollow nanocone array films can be used as photosensitive microreactors, isolated cell culture bases, <i>etc.</i> This provides a combination of high optical sensitivity and chemistry in microcavities

Anisotropic Wetting Characteristics of Water Droplets on Phosphorene: Roles of Layer and Defect Engineering

We study the wetting behavior of water droplets on pristine and defective phosphorene using molecular dynamics simulations. It is found that unlike prototypical two-dimensional materials such as graphene and MoS₂, phosphorene exhibits an anisotropic contact angle along armchair and zigzag directions. This anisotropy is tunable with increasing the number of layers and vacancy concentration. More specifically, the water contact angles decrease with increasing the number of layers, indicating the importance of water–substrate interactions. The contact angles along both armchair and zigzag directions increase with the increasing vacancy concentration, and the anisotropy disappears when the defect concentration is high. For an in-plane pristine-defective phosphorene heterostructure, when the junction is zigzag-oriented, a spontaneous diffusion of water droplets from the defective region to the pristine region occurs; when the junction is armchair-oriented, however, the spontaneous motion is suppressed. The energetic factor plays a role for the difference in the motion of water droplets along zigzag and armchair directions. Our work highlights the unique and fascinating directional wetting behavior of water droplets on phosphorene