二维过渡金属硫化物在肿瘤诊疗一体化中的应用

二维过渡金属硫化物（2D TMDCs）既具有成像能力可用于肿瘤的诊断,又具有光热转换能力可用于肿瘤PTT,因此在肿瘤诊疗一体化中得到广泛应用。为更好了解2D TMDCs在肿瘤诊疗一体化中的应用,综述了与2D TMDCs有关的肿瘤成像方式的利弊,2D TMDCs作为肿瘤诊疗一体化剂的优势,以及其在肿瘤诊疗一体化中的应用,并对2D TMDCs在肿瘤诊疗一体化中的发展前景和面临的挑战进行了讨论。 关键词 二维过渡金属硫化物;成像;PTT;诊疗一体化     

Resolidified Chalcogen Precursors for High-Quality 2D Semiconductor Growth

Two-dimensional (2D) semiconductors including transition metal dichalcogenides (TMDCs) have gained attention in optoelectronics for their extraordinary properties. However, the large amount and locally distributed lattice defects affect the optical properties of 2D TMDCs, and the defects originate from unstable factors in the synthesis process. In this work, we develop a method of pre-melting and resolidification of chalcogen precursors (sulfur and selenium), namely resolidified chalcogen, as precursor for the chemical vapor deposition growth of TMDCs with ultrahigh quality and uniformity. Taking WS₂ as an example, the monolayer WS₂ shows uniform fluorescence intensity and a small full-width at half-maximum of photoluminescence peak at low temperatures with an average value of 13.6±1.9 meV. The defect densities at the interior and edge region are both low and comparable, i.e., (9±3)×10¹² cm⁻² and (10±4)×10¹² cm⁻², indicating its high structural quality and uniformity. This method is universal in growing high quality monolayer MoS₂, WSe₂, MoSe₂, and will benefit their applications.     

Advances in transition metal dichalcogenide-based two-dimensional nanomaterials

Two-dimensional transition metal dichalcogenides (TMDCs) are the layered materials that have gained substantial consideration in a wide range of applications. The TMDCs possess exceptional properties such as high surface-to-volume ratio, excellent charge transfer capacity, mechanical strength, and low bandgap energy. Additionally, TMDCs (MoS₂, WS₂, etc.) are abundant, have a low synthesis cost, and are visible-light-active. The appealing surface morphologies and properties of TMDCs make them an appropriate choice for diverse applications like photocatalytic degradation of hazardous pollutants, energy conversion reactions (electrocatalytic and photocatalytic H₂ production), and energy storage devices (supercapacitors and rechargeable batteries) in addition to bio/chemical sensors. This article addresses the latest trends and advancements in the domain of TMDC-based nanomaterials. The different synthesis routes have been comprehensively reviewed. The challenges faced by TMDCs at a large scale and the future scope have also been discussed.     

TiS2 Monolayer as an Emerging Ultrathin Bifunctional Catalyst: Influence of Defects and Functionalization

We have envisaged the hydrogen evolution and oxygen evolution reactions (HER and OER) on a two-dimensional (2D) noble-metal-free titanium disulfide (TiS₂) monolayer, which belongs to the exciting family of transition metal dichalcogenides (TMDCs). Our theoretical investigation to probe the HER and OER on both the H and T phases of 2D TiS₂ is based on electronic-structure calculations witihin the framework of density functional theory (DFT). Since TiS₂ is the lightest compound among the group-IV TMDCs, it is worth exploring the catalytic activity of a TiS₂ monolayer through the functionalization at the anion (S) site, substituting with P, N, and C dopants as well as by incorporating single sulfur vacancy defects. We have investigated the effect of functionalization and vacancy defects on the structural, electronic, and optical response of a TiS₂ monolayer by determining the density of states, work-function, and optical absorption spectra. We have determined the HER and OER activities for the functionalized and defective TiS₂ monolayers based on the reaction coordinate, which can be constructed from the adsorption free energies of the intermediates (H*, O*, OH* and OOH*, where * denotes the adosrbed state) in the HER and OER mechanisms. Finally, we have shown that TiS₂ monolayers are emerging as a promising material for the HER and OER mechanisms under the influence of functionalization and defects.     

卤化钙钛矿太阳能电池的缺陷容忍及缺陷钝化研究进展

缺陷在钙钛矿太阳能电池的快速发展中起着至关重要的作用。缺陷容忍性,即金属卤化钙钛矿的主导缺陷是浅能级缺陷,它们不会成为强非辐射复合中心,这被认为是金属卤化钙钛矿的独特特性,是其具有高光电转换效率的主要原因。然而,要进一步提高金属卤化钙钛矿的光电转换效率,就需要消除一些可作为非辐射复合中心并严重影响器件性能的少量深能级缺陷,包括点缺陷、晶界、表面和界面等。本文综述了缺陷容忍的研究进展,包括软声子模式和极化子效应。此外,还总结了缺陷钝化的策略,包括通过阳离子或阴离子来钝化离子键,以及通过路易斯酸或路易斯碱来钝化配位键等。     

A bibliometric analysis: Research progress and prospects on transition metal dichalcogenides in the biomedical field

Recent years have witnessed the wide contributions made by transition metal dichalcogenides (TMDCs) to various fields, including the biomedical field. Here, to identify and further promote the development of biomedical TMDCs, we provide a bibliometric analysis of literature regarding TMDCs for biomedical applications. Firstly, general bibliometric distributions of the dataset by year, country, institute, Web of Science category and referenced source are recognized. Following, we carefully explore the research hotspots of the TMDC-related biomedical field, among which biosensing, bioelectronics, cancer theranostics, antibacterial and tissue engineering are identified. The functions of TMDCs in each biomedical scenario, the related properties and research challenges are highlighted. Finally, future prospects are proposed to shed light on the design of novel TMDC-related biomaterials, potential new biomedical applications, as well as their clinical translation.     

Growth of Single-crystalline Transition Metal Dichalcogenides Monolayers with Large-size

Two-dimensional(2D) transition metal dichalcogenides(TMDCs) semiconductors, such as monolayers of molybdenum disulfide(MoS₂) and tungsten disulfide(WS₂) can potentially serve as ultrathin channel materials for building short channel field-effect transistors(FETs) to further extend Moore's Law. It is essential to develop controllable approaches for the synthesis of large single crystals of these 2D semiconductors to promote their practical applications in future electronics. In this short review, we summarized the recent advances on the chemical vapor deposition(CVD) of single crystalline semiconducting 2D TMDCs with a large size. We first discussed the driving force and urgent demands on developing controllable approaches for the growth of large 2D TMDCs single crystals and then summarized the current strategies and representative studies on the CVD growth of large 2D single crystals. Finally, we discussed the challenges and future directions in this topic.     

The cubo-octahedral cluster in the fluorite-type lattice: A theoretical approach

A cubo-octahedral cluster within the anionic sublattice is proposed as an extended defect in the AM₃F₁₀ phases (A = K, Rb; M = Y, Bi). A computer simulation technique is used starting from crystallographic data to determine their validity and to evaluate some physical properties. A simulation study of new point defects in alkaline-earth fluorides doped with tetravalent cations is developed. The cubo-octahedral cluster is shown to be stable when it is introduced within the fluorite lattice. A mechanism is proposed for its formation on the basis of the aggregation of simpler defects.     

From two-dimensional materials to heterostructures

Graphene, hexagonal boron nitride, molybdenum disulphide, and layered transition metal dichalcogenides (TMDCs) represent a class of two-dimensional (2D) atomic crystals with unique properties due to reduced dimensionality. Stacking these materials on top of each other in a controlled fashion can create heterostructures with tailored properties that offers another promising approach to design and fabricate novel electronic devices. In this report, we attempt to review this rapidly developing field of hybrid materials. We summarize the fabrication methods for different 2D materials, the layer-by-layer growth of various vertical heterostructures and their electronic properties. Particular interests are given to in-situ stack aforementioned 2D materials in controlled sequences, and the TMDCs heterostructures.     

TEM observation of the high-temperature metal-insulator transition in Cr-doped V2O3

The high-temperature metal-insulator transition in Cr-doped V₂O₃, (V_1?xCr_x)₂O₃, was investigated by TEM at a composition x = 0.006. Boundaries between the metallic phase and the insulator phase were observed between room temperature and 150°C by both heating and cooling and their crystallographic features were investigated. Boundaries are low-index planes and their orientations are such that the change of dimension by the transition in the direction parallel to the specimen surface is zero. This indicates that the orientation of the boundary is determined by the condition of minimum strain energy. Misfit dislocations parallel to the specimen surface were found to exist under this condition. The motion of the boundaries is fast, but the boundaries can be trapped by defects or at those places where the area of boundaries becomes minimum. The observation is consistent with the existence of the temperature hysteresis of the transition and the discontinuous change of the resistivity-temperature curve of this transition.     

Engineering of TMDC–OSC hybrid interfaces: the thermodynamics of unitary and mixed acene monolayers on MoS2

Hybrid systems of two-dimensional (2D) materials such as transition metal dichalcogenides (TMDCs) and organic semiconductors (OSCs) have become subject of great interest for future device architectures. Although OSC–TMDC hybrid systems have been used in first device demonstrations, the precise preparation of ultra-thin OSC films on TMDCs has not been addressed. Due to the weak van der Waals interaction between TMDCs and OSCs, this requires precise knowledge of the thermodynamics at hand. Here, we use temperature-programmed desorption (TPD) and Monte Carlo (MC) simulations of TPD traces to characterize the desorption kinetics of pentacene (PEN) and perfluoropentacene (PFP) on MoS₂ as a model system for OSCs on TMDCs. We show that the monolayers of PEN and PFP are thermally stabilized compared to their multilayers, which allows preparation of nominal monolayers by selective desorption of multilayers. This stabilization is, however, caused by entropy due to a high molecular mobility rather than an enhanced molecule–substrate bond. Consequently, the nominal monolayers are not densely packed films. Molecular mobility can be suppressed in mixed monolayers of PEN and PFP that, due to intermolecular attraction, form highly ordered films as shown by scanning tunneling microscopy. Although this reduces the entropic stabilization, the intermolecular attraction further stabilizes mixed films.

Entropic stabilization enables the fabrication of (perfluoro-)pentacene monolayers on MoS₂ by selective multilayer desorption but reduces order and packing density. Intermolecular attraction allows to create ordered close-packed molecular monolayers.     

Phonon Scattering by Externded Defects in Polycrystalline Graphene

Phonon scattering by static stress fields created by grain boundaries (GBs) in graphene was studied with the deformation potential method. This method provides exact analytical expressions for phonon mean free paths as a result of scattering by GBs with arbitrary geometries in the Born approximation. Two regimes, k^–1 and k^–3, of the mean free path behavior are discovered in the limit of small momenta. The first (dislocation) regime is realized for open configurations in polycrystalline graphene, while the second regime is realized for closed configurations and Stone-Wales defects in pure graphene. The mean free path does not depend on k for any GB in the short-wave limit (large k). Thermal conductivity in graphene with GBs was calculated using the Callaway model which considers both normal phonon processes and umklapp processes. The contribution from these defects to the thermal conductivity is shown to exceed substantially the contribution from point defects and vacancies in a wide range of temperatures.     

Suppression of the Charge Density Wave State in Two-Dimensional 1T-TiSe2 by Atmospheric Oxidation

Two-dimensional (2D) metallic transition-metal dichalcogenides (TMDCs), such as 1T-TiSe₂, have recently emerged as unique platforms for exploring their exciting properties of superconductivity and the charge density wave (CDW). 2D 1T-TiSe₂ undergoes rapid oxidation under ambient conditions, significantly affecting its CDW phase-transition behavior. We comprehensively investigate the oxidation process of 2D TiSe₂ by tracking the evolution of the chemical composition and atomic structure with various microscopic and spectroscopic techniques and reveal its unique selenium-assisting oxidation mechanism. Our findings facilitate a better understanding of the chemistry of ultrathin TMDCs crystals, introduce an effective method to passivate their surfaces with capping layers, and thus open a way to further explore the functionality of these materials toward devices.     

Convection-Flow-Assisted Preparation of a Strong Electron Dopant,Benzyl Viologen,for Surface-Charge Transfer Doping of Molybdenum Disulfide

Transition metal dichalcogenides (TMDCs) have received attention as atomically thin post-silicon semiconducting materials. Tuning the carrier concentrations of the TMDCs is important, but their thin structure requires a non-destructive modulation method. Recently, a surface-charge transfer doping method was developed based on contacting molecules on TMDCs, and the method succeeded in achieving a large modulation of the electronic structures. The successful dopant is a neutral benzyl viologen (BV⁰); however, the problem remains of how to effectively prepare the BV⁰ molecules. A reduction process with NaBH₄ in water has been proposed as a preparation method, but the NaBH₄ simultaneously reacts vigorously with the water. Here, a simple method is developed, in which the reaction vial is placed on a hotplate and a fragment of air-stable metal is used instead of NaBH₄ to prepare the BV⁰ dopant molecules. The prepared BV⁰ molecules show a strong doping ability in terms of achieving a degenerate situation of a TMDC, MoS₂. A key finding in this preparation method is that a convection flow in the vial effectively transports the produced BV⁰ to a collection solvent. This method is simple and safe and facilitates the tuning of the optoelectronic properties of nanomaterials by the easily-handled dopant molecules.     

Defects in hexagonal vanadium fluoride bronzes: A high resolution electron microscope study

Observations of hexagonal vanadium fluoride bronzes, A_xVF₃, (A = K, Rb, Cs, and Tl; 0.18 ≤ x ≤ 0.32 by high resolution electron imaging showed the presence of several kinds of defects, including stacking faults, overlays, twin boundaries, and different types of antiphase boundaries. These defects were modeled, and the structures confirmed by comparison of calculated and observed images where necessary. The presence of disorder was interpreted as supporting evidence for the tentative phase diagram.     

Suppression of the Charge Density Wave State in Two‐Dimensional 1T‐TiSe2 by Atmospheric Oxidation

Two‐dimensional (2D) metallic transition‐metal dichalcogenides (TMDCs), such as 1T ‐TiSe₂, have recently emerged as unique platforms for exploring their exciting properties of superconductivity and the charge density wave (CDW). 2D 1T ‐TiSe₂ undergoes rapid oxidation under ambient conditions, significantly affecting its CDW phase‐transition behavior. We comprehensively investigate the oxidation process of 2D TiSe₂ by tracking the evolution of the chemical composition and atomic structure with various microscopic and spectroscopic techniques and reveal its unique selenium‐assisting oxidation mechanism. Our findings facilitate a better understanding of the chemistry of ultrathin TMDCs crystals, introduce an effective method to passivate their surfaces with capping layers, and thus open a way to further explore the functionality of these materials toward devices.     

Development and evaluation of osteogenic PMMA bone cement composite incorporating curcumin for bone repairing

Acrylic resin (PMMA - polymethylmethacrylate) is a material widely used in orthopedics to fill gaps or cavities in the bone marrow, bone defects, and implants fixation. However, even if it possesses high mechanical strength and is considered bioinert, its use has various limitations related to the lack of positive additional bioactive effects, such as osteogenesis stimulation. This work reports a preliminary assessment of the effects of curcumin incorporated in PMMA bone cements at different concentrations (4, 5, 7.5, and 10 wt%), and in particular, its osteoinductivity and osteoconductivity in vitro, tested with KUSA-A1 cells. The different samples were characterized using a combination of microscopic and spectroscopic techniques before and after in vitro testing. Results showed that curcumin and PMMA can produce a homogeneous composite material in a wide range of concentrations, up to at least 10 wt%. By increasing the percentage of curcumin both cellular adhesion and bone production are improved, without sacrificing the quality of the bone tissue formed. Addition of curcumin over a threshold of about 5% results in a sudden loss of ultimate strength with an increase of the elongation to failure. Samples containing about 5% of curcumin proved to have good in vitro performances without compromising the mechanical properties. This suggests how curcumin can be considered as a low-cost additive useful not only for its well-known antimicrobial activity but also in the bone regeneration improving the bioactive properties of the PMMA.     

Effect of microstructure of nitrogen-doped graphene on oxygen reduction activity in fuel cells

The development of fuel cells as clean-energy technologies is largely limited by the prohibitive cost of the noble-metal catalysts needed for catalyzing the oxygen reduction reaction (ORR) in fuel cells. A fundamental understanding of catalyst design principle that links material structures to the catalytic activity can accelerate the search for highly active and abundant nonmetal catalysts to replace platinum. Here, we present a first-principles study of ORR on nitrogen-doped graphene in acidic environment. We demonstrate that the ORR activity primarily correlates to charge and spin densities of the graphene. The nitrogen doping and defects introduce high positive spin and/or charge densities that facilitate the ORR on graphene surface. The identified active sites are closely related to doping cluster size and dopant-defect interactions. Generally speaking, a large doping cluster size (number of N atoms >2) reduces the number of catalytic active sites per N atom. In combination with N clustering, Stone-Wales defects can strongly promote ORR. For four-electron transfer, the effective reversible potential ranges from 1.04 to 1.15 V/SHE, depending on the defects and cluster size. The catalytic properties of graphene could be optimized by introducing small N clusters in combination with material defects.     

钠离子电池炭基负极材料研究进展

钠离子电池是目前新兴的低成本储能技术,因在大规模电化学储能中具有较好的应用前景而受到了国内外学者广泛的关注与研究。作为钠离子电池的关键电极材料之一,非石墨的炭质材料因具有储钠活性高、成本低廉、无毒无害等诸多优点,而被认为是钠离子电池实际应用时负极的最佳选择。本文详细综述了目前钠离子电池炭基负极材料的研究进展,重点介绍了炭质材料的储钠机理与特性,分析了炭材料结构与电化学性能之间的关系,探讨了其存在的问题,为钠离子电池炭基负极材料的发展提供有益的认识。