Layer-by-Layer Growth of AA-Stacking MoS₂ for Tunable Broadband Phototransistors

The stacking configuration has been considered as an important additional degree of freedom to tune the physical property of layered materials, such as superconductivity and interlayer excitons. However, the facile growth of highly uniform stacking configuration is still a challenge. Herein, the AA-stacking MoS2 domains with a ratio up to 99.5% has been grown by using the modified chemical vapor deposition through introducing NaCl molecules in the confined space. By tuning the growth time, MoS2 domains would transit from an AA-stacking bilayer to an AAAAA-stacking five-layer. The epitaxial growth mechanism has been insightfully studied, revealing that the critical nucleation size of the AA-stacking bilayer is 5.0 ± 3.0 μm. Through investigation of the photoluminescence, the photoemission, especially the indirect photoexcitation, is dependent on both the stacking fashion and layer number. Furthermore, by studying the gate-tuned MoS2 phototransistors, we found a significant dependence on the stacking configuration of MoS2 of the photoexcitation and a different gate tunable photoresponse. The AAA-stacking trilayer MoS2 phototransistor delivers a photoresponse of 978.14 A W–1 at 550 nm. By correction of the external quantum efficiency with external field and illumination power density, it has been found that the photoresponse tunability is dependent on the layer number due to the strong photogating effect. This strategy provides a general avenue for the epitaxial growth of van der Waals film which will further facilitate the applications in a tunable photodetector

Ionic Liquid-Assisted Synthesis of Hierarchical One-Dimensional MoP/NPC for High-Performance Supercapacitor and Electrocatalysis

The development of advanced nanomaterials with multifunctionalities is an intriguing and challenging approach for utilizing clean and sustainable energy. Herein, we demonstrate the construction of a unique hierarchically structured one-dimensional molybdenum phosphide (MoP) through an ionic liquid-assisted synthesis method. Further, encapsulating with an N, P-codoped carbon shell to form a hybrid multifunctional material (MoP/NPC) was performed for the supercapacitor and electrocatalysis. The as-synthesized MoP/NPC nanostructures possessed a large number of active sites and a shorter ionic diffusion length. As a proof-of-concept application, the symmetric all-solid-state supercapacitor device assembled using MoP/NPC delivers a superior-specific capacitance of 544 F g–1 at 0.5 A g–1, a high specific energy of 76 W h kg–1 at a power density of 503 W kg–1, and outstanding cycling stability. Moreover, MoP/NPC also displays excellent electrocatalytic activity and stability toward hydrogen evolution reaction in a wide pH range (0–14). This study demonstrates an effective strategy for developing transition-metal phosphide-based nanomaterials with outstanding electrochemical performance for future energy conversion and storage

Inducing Temporal and Reversible Autophagy by Nanotopography for Potential Control of Cell Differentiation

Tuning autophagy has become a new strategy to control cell differentiation in tissue engineering. The nanosized surface is well-known for its ability to interfere with intracellular procedures, while its role in autophagy regulation is unclear. In this study, we found that a nanotube (NT) structure was able to induce enhanced mTOR-independent autophagy in osteoblasts compared to a flat surface. Further analysis revealed that autophagy was temporally promoted by NTs in the initial day contact and it was also reversible by exchanging the substrate nanotopographies. Actin filaments were significantly dispersed and there were numerous filopodia on the leading edge of cells grown on the NT surface. Intracellular Ca²⁺ was significantly increased on the NT surface. Moreover, the phenomenon was also found on different nanotopographies as well as in different cell lines. These indicated that cell membrane stretching might be the central regulation factor. Finally, we found that the NT surface exhibited enhanced autophagy-dependent osteogenic differentiation efficacy. In addition, the enhancement on NT surface could be remembered. In conclusion, the nanotopographic surface is able to induce temporal, reversible, and memorable autophagy via cell membrane stretching, which may be used as a versatile method to control cell differentiation

Carbon/Silicon Heterojunction Formed by Inserting Carbon Nanotubes into Silicon Nanotubes: Molecular Dynamics Simulations

Using molecular dynamics (MD) simulations, we report a carbon/silicon (C/Si) heterojunction formed by inserting carbon nanotubes (CNTs) into silicon nanotubes (SiNTs). Due to the weak mechanical property of the SiNTs, insertion of CNTs into them can not only reinforce their mechanical stabilities but also form multiwalled C/Si nanotube heterojunctions. The driving force of the coaxial assembly is primarily the intertube van der Waals (vdW) interactions. The coaxial self-assembly process is strongly tube size dependent, and the intertube distance (Δd) for a successful assembly between the two type nanotubes is around 3.5 Å. Simulations suggest possible bottom-up self-assembly routes for fabrication of novel nanomachines and nanodevices in nanomechanical systems. This study also suggests that the possibility of synthesizing SiNTs with fewer walls, even single-walled SiNT in aid of CNTs

Supramolecular Nanopatterns Self-Assembled by Adenine−Thymine Quartets at the Liquid/Solid Interface

By means of scanning tunneling microscopy (STM), we have observed for the first time well-ordered supramolecular nanopatterns formed by mixing two complementary DNA bases:  adenine (A) and thymine (T), respectively, at the liquid/solid interface. By mixing A and T at a specific mixing molar ratio, cyclic structures that were distinctly different from the structures observed by the individual base molecules separately were formed. From an interplay between the STM findings and self-consistent charge density-functional based tight-binding (SCC-DFTB) calculation method, we suggest formation of A−T−A−T quartets constructed on the basis of A−T base pairing. The formation of the A−T−A−T quartets opens new avenues to use DNA base pairing as a way to form nanoscale surface architecture and biocompatible patterned surfaces particularly via host−guest complexation that might be suitable for drug design, where the target can be trapped inside the cavities of the molecular containers

Point-Defect Mediated Bonding of Pt Clusters on (5,5) Carbon Nanotubes

The adhesion of various sizes of Pt clusters on the metallic (5,5) carbon nanotubes (CNTs) with and without the point defect has been investigated by means of density functional theory (DFT). The calculations show that the binding energies of Ptn (n = 1−6) clusters on the defect free CNTs are more than 2.0 eV. However, the binding energies are increased more than three times on the point defective CNTs. The dramatic increase of the binding energy has been further explained by the partial density of states, deformation charge density, and two population analyses methods (Mulliken and Hirshfeld). The stronger orbital hybridization between the Pt atom and the carbon atom shows larger charge transfers on the defective CNTs than on the defect free CNTs, which allows the strong interaction between Pt clusters and CNTs. On the basis of DFT calculations, CNTs with point defect can be used as the catalyst supports for noble metal nanoparticles adhesion, which can be applied to a series of catalytic reactions, such as fuel cell, hydrogenation, etc

Supramolecular Nanopatterns Self-Assembled by Adenine−Thymine Quartets at the Liquid/Solid Interface

By means of scanning tunneling microscopy (STM), we have observed for the first time well-ordered supramolecular nanopatterns formed by mixing two complementary DNA bases:  adenine (A) and thymine (T), respectively, at the liquid/solid interface. By mixing A and T at a specific mixing molar ratio, cyclic structures that were distinctly different from the structures observed by the individual base molecules separately were formed. From an interplay between the STM findings and self-consistent charge density-functional based tight-binding (SCC-DFTB) calculation method, we suggest formation of A−T−A−T quartets constructed on the basis of A−T base pairing. The formation of the A−T−A−T quartets opens new avenues to use DNA base pairing as a way to form nanoscale surface architecture and biocompatible patterned surfaces particularly via host−guest complexation that might be suitable for drug design, where the target can be trapped inside the cavities of the molecular containers

Multipathway Antibacterial Mechanism of a Nanoparticle-Supported Artemisinin Promoted by Nitrogen Plasma Treatment

Artemisinin has excellent antimalarial, antiparasitic, and antibacterial activities; however, the poor water solubility of artemisinin crystal limits their application in antibiosis. Herein, artemisinin crystal was first composited with silica nanoparticles (SNPs) to form an artemisinin@silica nanoparticle (A@SNP). After treating with nitrogen plasma, the aqueous solubility of plasma-treated A@SNP (A@SNP-p) approaches 42.26%, which is possibly attributed to the exposure of hydrophilic groups such as −OH groups on the SNPs during the plasma process. Compared with the pristine A@SNP, the antibacterial activity of A@SNP-p against both Gram-positive and Gram-negative strains is further enhanced, and its bactericidal rate against both strains exceeded 6 log CFU/mL (>99.9999%), which is contributed by the increased water solubility of the A@SNP-p. A possible multipathway antibacterial mechanism of A@SNP was proposed and preliminarily proved by the changes of intracellular materials of bacteria and the inhibition of bacterial metabolism processes, including the HMP pathway in Gram-negative strain and EMP pathway in Gram-positive strain, after treating with A@SNP-p. These findings from the present work will provide a new view for fabricating artemisinin-based materials as antibiotics

Two-Dimensional π‑Conjugated Metal Bis(dithiolene) Complex Nanosheets as Selective Catalysts for Oxygen Reduction Reaction

Developing high activity and low price catalysts for the oxygen reduction reaction (ORR) is of critical importance for the commercial application of polymer electrolyte membrane fuel cells. On the basis of density functional theory, the catalytic activity of π-conjugated metal bis­(dithiolene) complex nanosheets (MC₄S₄, where M denotes Fe, Co, Ni, Ru, Rh, Pd, Os, Ir, and Pt) for the ORR has been investigated systematically. It is found that the ORR activity of MC₄S₄ is sensitive to the selection of the central metal atom. The adsorption energies of ORR intermediates on MC₄S₄ decrease as the central atom varies from group 8 to group 10. The free energy change of the rate-determining step in the ORR increases in the order of IrC₄S₄ < CoC₄S₄ ≈ RhC₄S₄ < FeC₄S₄ < PdC₄S₄ ≈ PtC₄S₄ < NiC₄S₄ < RuC₄S₄ < OsC₄S₄. Due to the optimal adsorption properties, the IrC₄S₄ nanosheet shows the best ORR catalytic activity among the nine studied MC₄S₄ nanosheets. The free energy change of the rate-determining step in the ORR at high electrode potential follows an inverted volcano curve as a function of the adsorption strength of OH. This work may open new avenues for the development of high-performance ORR catalysts