One-Dimensional MoS2 Nanoscrolls as Miniaturized Memories.

Dimensionality of materials is closely related to their physical properties. For two-dimensional (2D) semiconductors such as monolayer molybdenum disulfide (MoS2), converting them from 2D nanosheets to one-dimensional (1D) nanoscrolls could contribute to remarkable electronic and optoelectronic properties, yet the rolling-up process still lacks sufficient controllability, which limits the development of their device applications. Herein we report a modified solvent evaporation-induced rolling process that halts at intermediate states and achieve MoS2 nanoscrolls with high yield and decent axial uniformity. The accordingly fabricated nanoscroll memories exhibit an on/off ratio of ∼104 and a retention time exceeding 103 s and can realize multilevel storage with pulsed gate voltages. Such open-end, high-curvature, and hollow 1D nanostructures provide new possibilities to manipulate the hysteresis windows and, consequently, the charge storage characteristics of nanoscale field-effect transistors, thereby holding great promise for the development of miniaturized memories.

Large-Substrate-Terrace Confined Growth of Arrayed Ultrathin PtSe2 Ribbons on Step-Bunched Vicinal Au(001) Facets Toward Electrocatalytic Applications.

Ultrathin PtSe2 ribbons can host spin-polarized edge states and distinct edge electrocatalytic activity, emerging as a promising candidate for versatile applications in various fields. However, the direct synthesis is still challenging and the growth mechanism is still unclear. Herein, the arrayed growth of ultrathin PtSe2 ribbons on bunched vicinal Au(001) facets, via a facile chemical vapor deposition (CVD) route is reported. The ultrathin PtSe2 flakes can transform from traditional irregular shapes to desired ribbon shapes by increasing the height of bunched and unidirectionally oriented Au steps (with step height hstep) is found. This crossover, occurring at hstep ≈ 3.0 nm, defines the tailored growth from step-flow to single-terrace-confined modes, as validated by density functional theory calculations of the different system energies. On the millimeter-scale single-crystal Au(001) films with aligned steps, the arrayed ultrathin PtSe2 ribbons with tunable width of ≈20-1000 nm, which are then served as prototype electrocatalysts for hydrogen evolution reaction (HER) is achieved. This work should represent a huge leap in the direct synthesis and the mechanism exploration of arrayed ultrathin transition-metal dichalcogenides (TMDCs) ribbons, which should stimulate further explorations of the edge-related physical properties and practical applications.

Exosomes derived from uMSCs promote hair regrowth in alopecia areata through accelerating human hair follicular keratinocyte proliferation and migration.

Alopecia areata (AA) is a complex genetic disease that results in hair loss due to an autoimmune-mediated attack on the hair follicle. Mesenchymal stem cells (MSCs) have great potential to induce hair regeneration due to their strong secretion ability and multidirectional differentiation. Recent studies have revealed that the therapeutic potential of MSCs comes from their secretion ability, which can produce large amounts of bioactive substances and regulate the key physiological functions of subjects. The secretion products of MSCs, such as vesicles, exosomes, and conditioned media, have significant advantages in preparing of biological products derived from stem cells. Human umbilical cord mesenchymal stem cells (uMSCs) are the best choice for exosome production. uMSCs are obtained from the human umbilical cord. The umbilical cord is easy to obtain, and the efficiency of uMSCs isolation and culture higher than that of obtaining MSCs from bone marrow or adipose tissue. In this study, we investigated the effects of exosomes released from uMSCs in AA mice. In summary, due to easy isolation and cultivation, simple preparation, and convenient storage, it is possible to obtain uMSCs, or uMSCs exosomes for research and clinical treatment.

Designing artificial two-dimensional landscapes via atomic-layer substitution.

Technology advancements in history have often been propelled by material innovations. In recent years, two-dimensional (2D) materials have attracted substantial interest as an ideal platform to construct atomic-level material architectures. In this work, we design a reaction pathway steered in a very different energy landscape, in contrast to typical thermal chemical vapor deposition method in high temperature, to enable room-temperature atomic-layer substitution (RT-ALS). First-principle calculations elucidate how the RT-ALS process is overall exothermic in energy and only has a small reaction barrier, facilitating the reaction to occur at room temperature. As a result, a variety of Janus monolayer transition metal dichalcogenides with vertical dipole could be universally realized. In particular, the RT-ALS strategy can be combined with lithography and flip-transfer to enable programmable in-plane multiheterostructures with different out-of-plane crystal symmetry and electric polarization. Various characterizations have confirmed the fidelity of the precise single atomic layer conversion. Our approach for designing an artificial 2D landscape at selective locations of a single layer of atoms can lead to unique electronic, photonic, and mechanical properties previously not found in nature. This opens a new paradigm for future material design, enabling structures and properties for unexplored territories.

Ultrathin Eardrum-Inspired Self-Powered Acoustic Sensor for Vocal Synchronization Recognition with the Assistance of Machine Learning.

With the rapid development of human-machine interfaces, artificial acoustic sensors play an important role in the hearing impaired. Here, an ultrathin eardrum-like triboelectric acoustic sensor (ETAS) is presented consisting of silver-coated nanofibers, whose thickness is only 40 µm. The sensitivity and frequency response range of the ETAS are closely related to the geometric parameters. The ETAS endows a high sensitivity of 228.5 mV Pa-1 at 95 dB, and the ETAS has a broad frequency response ranging from 20 to 5000 Hz, which can be tuned by adjusting the thickness, size, or shape of the sensor. Cooperating with artificial intelligence (AI) algorithms, the ETAS can achieve real-time voice conversion with a high identification accuracy of 92.64%. Under good working property and the AI system, the ETAS simplifies signal processing and reduces the power consumption. This work presents a strategy for self-power auditory systems, which can greatly accelerate the miniaturization of self-powered systems used in wearable electronics, augmented reality, virtual reality, and control hubs for automation.

Research progress in targeted therapies for gastric cancer.

Patients with advanced gastric cancer experience rapid disease progression with limited survival, high mortality, and a lack of surgical options. Thus, radiochemotherapy or a combination of chemotherapeutics with targeted therapy is the mainstay of treatment. In comparison to the treatment of other malignant tumors, in gastric cancer, the development of molecularly targeted drugs has been relatively slow. Currently, there are two major classes of molecularly targeted drug regimens that have achieved a certain efficacy in clinical practice: anti-vascular endothelial growth factor (anti-VEGF) therapy and anti-epidermal growth factor receptor (anti-EGFR) therapy. Trastuzumab has been approved as the standard of care for first-line treatment in advanced human epidermal growth factor receptor 2 (HER2)-positive gastric cancer. Ramucirumab in combination with paclitaxel is the recommended regimen for second-line treatment, and apatinib is recommended as third-line treatment. This review summarizes the current status of targeted therapies in the treatment of gastric cancer and gives a perspective on the future.

Regulated Expression of an Environmental DNA-Derived Type II Polyketide Gene Cluster in Streptomyces Hosts Identified a New Tetracenomycin Derivative TCM Y.

As bacterial natural products have been proved to be the most important source of many therapeutic medicines, the need to discover novel natural products becomes extremely urgent. Despite the fact that the majority of bacterial species are yet to be cultured in a laboratory setting, and that most of the bacterial natural product biosynthetic genes are silent, "metagenomics technology" offers a solution to help clone natural product biosynthetic genes from environmental samples, and genetic engineering enables the silent biosynthetic genes to be activated. In this work, a type II polyketide biosynthetic gene cluster was identified from a soil metagenomic library and was activated by over-expression of a SARP regulator gene in the gene cluster in Streptomyces hosts. A new tetracenomycin type compound tetracenomycin Y was identified from the fermentation broth. This study shows that metagenomics and genetic engineering could be combined to provide access to new natural metabolites.

Additive manufacturing of patterned 2D semiconductor through recyclable masked growth.

The 2D van der Waals crystals have shown great promise as potential future electronic materials due to their atomically thin and smooth nature, highly tailorable electronic structure, and mass production compatibility through chemical synthesis. Electronic devices, such as field effect transistors (FETs), from these materials require patterning and fabrication into desired structures. Specifically, the scale up and future development of "2D"-based electronics will inevitably require large numbers of fabrication steps in the patterning of 2D semiconductors, such as transition metal dichalcogenides (TMDs). This is currently carried out via multiple steps of lithography, etching, and transfer. As 2D devices become more complex (e.g., numerous 2D materials, more layers, specific shapes, etc.), the patterning steps can become economically costly and time consuming. Here, we developed a method to directly synthesize a 2D semiconductor, monolayer molybdenum disulfide (MoS2), in arbitrary patterns on insulating SiO2/Si via seed-promoted chemical vapor deposition (CVD) and substrate engineering. This method shows the potential of using the prepatterned substrates as a master template for the repeated growth of monolayer MoS2 patterns. Our technique currently produces arbitrary monolayer MoS2 patterns at a spatial resolution of 2 µm with excellent homogeneity and transistor performance (room temperature electron mobility of 30 cm2 V-1 s-1 and on-off current ratio of 107). Extending this patterning method to other 2D materials can provide a facile method for the repeatable direct synthesis of 2D materials for future electronics and optoelectronics.

Enhancement of van der Waals Interlayer Coupling through Polar Janus MoSSe.

Interlayer coupling plays essential roles in the quantum transport, polaritonic, and electrochemical properties of stacked van der Waals (vdW) materials. In this work, we report the unconventional interlayer coupling in vdW heterostructures (HSs) by utilizing an emerging 2D material, Janus transition metal dichalcogenides (TMDs). In contrast to conventional TMDs, monolayer Janus TMDs have two different chalcogen layers sandwiching the transition metal and thus exhibit broken mirror symmetry and an intrinsic vertical dipole moment. Such a broken symmetry is found to strongly enhance the vdW interlayer coupling by as much as 13.2% when forming MoSSe/MoS2 HS as compared to the pristine MoS2 counterparts. Our noncontact ultralow-frequency Raman probe, linear chain model, and density functional theory calculations confirm the enhancement and reveal the origins as charge redistribution in Janus MoSSe and reduced interlayer distance. Our results uncover the potential of tuning interlayer coupling strength through Janus heterostacking.

Direct Observation of Symmetry-Dependent Electron-Phonon Coupling in Black Phosphorus.

Electron-phonon coupling in two-dimensional nanomaterials plays a fundamental role in determining their physical properties. Such interplay is particularly intriguing in semiconducting black phosphorus (BP) due to the highly anisotropic nature of its electronic structure and phonon dispersions. Here we report the direct observation of symmetry-dependent electron-phonon coupling in BP by performing the polarization-selective resonance Raman measurement in the visible and ultraviolet regimes, focusing on the out-of-plane Ag1 and in-plane Ag2 phonon modes. Their intrinsic resonance Raman excitation profiles (REPs) were extracted and quantitatively compared. The in-plane Ag2 mode exhibits remarkably strong resonance enhancement across the excitation wavelengths when the excitation polarization is parallel to the armchair (Ag2//AC) direction. In contrast, a dramatically weak resonance effect was observed for the same mode with the polarization parallel to zigzag (Ag2//ZZ) direction and for the out-of-plane Ag1 mode (Ag1//AC and Ag1//ZZ). Analysis on quantum perturbation theory and first-principles calculations on the anisotropic electron distributions in BP demonstrated that electron-phonon coupling considering the symmetry of the involved excited states and phonon vibration patterns is responsible for this phenomenon. Further analysis of the polarization-dependent REPs for Ag phonons allows us to resolve the existing controversies on the physical origin of Raman anomaly in BP and its dependence on excitation energy, sample thickness, phonon modes, and crystalline orientation. Our study gives deep insights into the underlying interplay between electrons and phonons in BP and paves the way for manipulating the electron-phonon coupling in anisotropic nanomaterials for future device applications.

Recent progress in the tailored growth of two-dimensional hexagonal boron nitride via chemical vapour deposition.

Recent years have witnessed many advances in two-dimensional (2D) hexagonal boron nitride (h-BN) materials in both fundamental research and practical applications. This has ultimately been inspired by the unique electrical and optical properties, as well as the excellent thermal and chemical stability of h-BN. However, controllable and scalable preparation of 2D h-BN materials has been challenging. Very recently, the chemical vapour deposition (CVD) technique has shown great promise for achieving high-quality h-BN samples with excellent layer-number selectivity and large-area uniformity, considerably contributing to the latest advancements of 2D material research. In this tutorial review, we provide a systematic summary of the state-of-the-art in the tailored production of 2D h-BN on various substrates by virtue of CVD routes.

Synthetic Lateral Metal-Semiconductor Heterostructures of Transition Metal Disulfides.

Lateral heterostructures with planar integrity form the basis of two-dimensional (2D) electronics and optoelectronics. Here we report that, through a two-step chemical vapor deposition (CVD) process, high-quality lateral heterostructures can be constructed between metallic and semiconducting transition metal disulfide (TMD) layers. Instead of edge epitaxy, polycrystalline monolayer MoS2 in such junctions was revealed to nucleate from the vertices of multilayered VS2 crystals, creating one-dimensional junctions with ultralow contact resistance (0.5 kΩ·µm). This lateral contact contributes to 6-fold improved field-effect mobility for monolayer MoS2, compared to the conventional on-top nickel contacts. The all-CVD strategy presented here hence opens up a new avenue for all-2D-based synthetic electronics.

Metallic Vanadium Disulfide Nanosheets as a Platform Material for Multifunctional Electrode Applications.

Nanothick metallic transition metal dichalcogenides such as VS2 are essential building blocks for constructing next-generation electronic and energy-storage applications, as well as for exploring unique physical issues associated with the dimensionality effect. However, such two-dimensional (2D) layered materials have yet to be achieved through either mechanical exfoliation or bottom-up synthesis. Herein, we report a facile chemical vapor deposition route for direct production of crystalline VS2 nanosheets with sub-10 nm thicknesses and domain sizes of tens of micrometers. The obtained nanosheets feature spontaneous superlattice periodicities and excellent electrical conductivities (∼3 × 103 S cm-1), which has enabled a variety of applications such as contact electrodes for monolayer MoS2 with contact resistances of ∼1/4 to that of Ni/Au metals, and as supercapacitor electrodes in aqueous electrolytes showing specific capacitances as high as 8.6 × 102 F g-1. This work provides fresh insights into the delicate structure-property relationship and the broad application prospects of such metallic 2D materials.

Tuning Excitonic Properties of Monolayer MoS2 with Microsphere Cavity by High-Throughput Chemical Vapor Deposition Method.

Tuning the optical properties of 2D direct bandgap semiconductors is crucial for applications in photonic light source, optical communication, and sensing. In this work, the excitonic properties of molybdenum disulphide (MoS2 ) are successfully tuned by directly depositing it onto silica microsphere resonators using chemical vapor deposition method. Multiple whispering gallery mode (WGM) peaks in the emission wavelength range of ≈650-750 nm are observed under continuous wave excitation at room temperature. Time-resolved photoluminescence (TRPL) and femtosecond transient absorption (TA) spectroscopy are conducted to study light-matter interaction dynamics of the MoS2 microcavities. TRPL study suggests radiative recombination rate of carrier-phonon scattering and interband transition processes in MoS2 is enhanced by a factor of ≈1.65 due to Purcell effect in microcavities. TA spectroscopy study shows modulation of the interband transition process mainly occurs at PB-A band with an estimated F ≈ 1.60. Furthermore, refractive index sensing utilizing WGM peaks of MoS2 is established with sensitivity up to ≈150 nm per refractive index unit. The present work provides a large-scale and straightforward method for coupling atomically thin 2D gain media with cavities for high-performance optoelectronic devices and sensors.

Chemical vapour deposition of group-VIB metal dichalcogenide monolayers: engineered substrates from amorphous to single crystalline.

As structural analogues of graphene but with a sizeable band gap, monolayers of group-VIB transition metal dichalcogenides (MX2, M = Mo, W; X = S, Se, Te, etc.) have emerged as the ideal two dimensional prototype for exploring fundamental issues in physics such as valley polarization, and for engineering a wide range of nanoelectronic, optoelectronic and photocatalytic applications. Recently, chemical vapour deposition (CVD) was introduced as a more efficient preparation method than traditional chemical or physical exfoliation options, and has allowed for the successful synthesis of large-area MX2 monolayers possessing a large domain size, high thickness uniformity and continuity, and satisfactory crystal quality. This tutorial review therefore focuses on introducing the more recent advances in the CVD growth of MX2 (MoS2, WS2, MoS2(1-x)Se2xetc.) monolayers via the sulphurisation/decomposition of pre-deposited metal-based precursors, or the one-step reaction and deposition of gaseous metal and chalcogen feedstocks. Differences in growth behaviour caused by commonly used amorphous SiO2/Si, and newly adopted insulating single crystal substrates such as sapphire, mica and SrTiO3, are also comparatively presented. Also discussed are the essential parameters that influence the growth of MX2, such as the temperature, the source-substrate distance and the composition of the carrier gas (Ar/H2). Finally, an assessment is provided for viable future pathways for fine-tuning of the domain size and orientation, thickness uniformity, and the bandgap of MX2 and its alloys.

Unravelling orientation distribution and merging behavior of monolayer MoS2 domains on sapphire.

Monolayer MoS2 prepared by chemical vapor deposition (CVD) has a highly polycrystalline nature largely because of the coalescence of misoriented domains, which severely hinders its future applications. Identifying and even controlling the orientations of individual domains and understanding their merging behavior therefore hold fundamental significance. In this work, by using single-crystalline sapphire (0001) substrates, we designed the CVD growth of monolayer MoS2 triangles and their polycrystalline aggregates for such purposes. The obtained triangular MoS2 domains on sapphire were found to distributively align in two directions, which, as supported by density functional theory calculations, should be attributed to the relatively small fluctuations of the interface binding energy around the two primary orientations. Using dark-field transmission electron microscopy, we further imaged the grain boundaries of the aggregating domains and determined their prevalent armchair crystallographic orientations with respect to the adjacent MoS2 lattice. The coalescence of individual triangular flakes governed by unique kinetic processes is proposed for the polycrystal formation. These findings are expected to shed light on the controlled MoS2 growth toward predefined domain orientation and large domain size, thus enabling its versatile applications in next-generation nanoelectronics and optoelectronics.

High-quality monolayer graphene synthesis on Pd foils via the suppression of multilayer growth at grain boundaries.

The segregation of carbon from metals in which carbon is highly soluble, such as Ni (≈1.1 atom% at 1000 °C), is a typical method for graphene growth; this method differs from the surface-catalyzed growth of graphene that occurs on other metals such as Cu (<0.04 atom%). It has not been established whether strictly monolayer graphene could be synthesized through the traditional chemical vapor deposition route on metals where carbon is highly soluble, such as Pd (≈3.5 atom%). In this work, this issue is investigated by suppressing the grain boundary segregation using a pretreatment comprising the annealing of the Pd foils; this method was motivated by the fact that the typical thick growths at the grain boundaries revealed that the grain boundary functions as the main segregation channel in polycrystalline metals. To evaluate the high crystallinity of the as-grown graphene, detailed atomic-scale characterization with scanning tunneling microscopy is performed.

Epitaxial monolayer MoS2 on mica with novel photoluminescence.

Molybdenum disulfide (MoS2) is back in the spotlight because of the indirect-to-direct bandgap tunability and valley related physics emerging in the monolayer regime. However, rigorous control of the monolayer thickness is still a huge challenge for commonly utilized physical exfoliation and chemical synthesis methods. Herein, we have successfully grown predominantly monolayer MoS2 on an inert and nearly lattice-matching mica substrate by using a low-pressure chemical vapor deposition method. The growth is proposed to be mediated by an epitaxial mechanism, and the epitaxial monolayer MoS2 is intrinsically strained on mica due to a small adlayer-substrate lattice mismatch (~2.7%). Photoluminescence (PL) measurements indicate strong single-exciton emission in as-grown MoS2 and room-temperature PL helicity (circular polarization ~0.35) on transferred samples, providing straightforward proof of the high quality of the prepared monolayer crystals. The homogeneously strained high-quality monolayer MoS2 prepared in this study could competitively be exploited for a variety of future applications.

Research on cross-platform dissemination of rational and irrational information based on a two-layer network.

Numerous social media platforms have evolved into fertile grounds for the proliferation of irrational information, expanding the avenues of information dissemination. This paper initially utilized the Weibo and Bilibili social platforms as exemplars and devised a cross-platform two-layer network SEIaIbR-FXYaYbZ dissemination model grounded in classical infectious disease models. Subsequently, this research computed the model equilibrium point, basic reproduction number, and information entropy through dynamic equations. Finally, the model equations were fitted to real cases to determine optimal parameter solutions and conduct simulation analysis. The simulation results reveal that: (i) information entropy values on both platforms are low, with irrational information predominantly influencing public opinion; (ii) concerning various types of information, the augmentation of rational information results in a reduction of irrational information, while the quantity of rational information remains largely unaffected by changes in the quantity of irrational information; (iii) examining different platforms for information dissemination, alterations in the circulation rate and quantity of rational information on the Weibo platform impact the quantity of rational and irrational information on the Bilibili platform, while those changes on the Bilibili platform exert minimal influence on public opinion information on the Weibo platform. The results and corresponding strategies obtained from this study on the cross-platform dissemination of rational and irrational information on Weibo and Bilibili can provide a reference for relevant departments to guide the rational development of online information and enhance the effective management of public opinion in social media platforms.