- 标题
- 摘要
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- 实验方案
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A New Family of Two-Dimensional Topological Materials: CdX (X?=?F, Cl, Br, and I)
摘要： Two-dimensional (2D) transition-metal halides have attracted great interest owing to their versatile applications in electronics, optoelectronics, and renewable energy storage/conversions. Using first-principles calculations, it is proposed that a new series of 2D transition-metal halide CdX (X ? F, Cl, Br, and I) monolayers with honeycomb lattice structure show topological properties. When omitting the spin–orbital coupling (SOC) effect, all of them behave as Dirac semimetal whose Fermi surface is composed of two Dirac points at high symmetry K and K’ points in Brillouin zone. When considering the SOC effect, CdCl, CdBr, and CdI monolayers behave as topological insulators with global band gap, whereas CdF is converted from Dirac semimetal into topological metal with local band gap. The nontrivial topological properties are further proved by their nontrivial edge states. The fascinating properties of the CdX (X ? F, Cl, Br, and I) monolayers show their potential for future quantum computing and next generation of high-speed electronic devices.
关键词： topological insulators,topological metals,two-dimensional transition-metal halides
更新于2025-09-23 15:23:52
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Control on Dimensions and Supramolecular Chirality of Self-Assemblies through Light and Metal Ions
摘要： Precise control over helical chirality and dimensions of molecular self-assemblies, a remaining challenge for both chemists and materials scientists, is the key to manipulate the property and performance of supramolecular materials. Herein, we report that a cholesterol-azopyridine conjugate could self-assemble into organogels with photo-controllable dimensional transition from 2D microbelts to 1D nanotubes and finally to 0D nanoparticles. The E/Z-Photoisomerization of the 4-azopyridine unit is the major driving force for the dimensional transformation. Furthermore, the self-assembled structures were observed to exhibit metal ion-mediated helicity inversion through the metal coordination. These observations were collectively confirmed by several techniques including scanning electron microscopy, atomic force microscope, circular dichroism, and X-ray crystallography. The rational design of building blocks for the construction of dimension and chirality controllable self-assembly systems may lead to versatile applications in smart display, advanced optoelectronic device, and supramolecular asymmetric catalysis.
关键词： photoisomerization,dimensional transition,supramolecular chirality,metal coordination,self-assembly
更新于2025-09-23 15:21:21
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Two-dimensional transition metal dichalcogenides mediated long range surface plasmon resonance biosensors
摘要： Two-dimensional transition metal dichalcogenides (TMDCs), as promising alternative plasmon supporting materials to graphene, exhibit potential applications in sensing. Here, we propose a TMDCs-mediated long range surface plasmon resonance (LRSPR) imaging biosensor, which shows tremendous improvements in both imaging sensitivity (> ×2) and detection accuracy (> ×10) as compared to conventional surface plasmon resonance (cSPR) biosensor. It is found that the imaging sensitivity of the LRSPR biosensor can be enhanced by the integration of TMDC layers, which is di?erent from the previously reported graphene-mediated cSPR imaging sensor whose imaging sensitivity decreases with the number of graphene layers. This imaging sensitivity enhancement e?ect for the TMDCs-mediated LRSPR sensor originates from the propagating nature of the LRSPR at both interfaces of sensing medium/gold and gold/cytop layer (with matching refractive index as sensing medium). By tuning the thickness of gold ?lm and cytop layer, it is possible to achieve optimized imaging sensitivity for LRSPR sensor with any known integrated number of TMDC layers and the analyte refractive index. The proposed TMDCs-mediated LRSPR imaging sensor could provide potential applications in chemical sensing and biosensing applications.
关键词： detection accuracy,biosensor,long range surface plasmon resonance,Two-dimensional transition metal dichalcogenides,imaging sensitivity
更新于2025-09-23 15:21:01
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[IEEE 2019 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC) - Munich, Germany (2019.6.23-2019.6.27)] 2019 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC) - Direct Laser Synthesis of Two-Dimensional Transition Metal Dichalcogenides
摘要： The emergence of nanomaterials with their often superior mechanical, electronic and optical properties compared with bulk form demands a robust technology that can synthesize, modify and pattern scalably and cost effectively. This can be fulfilled via laser processing protocols which produce such materials with both high precision and excellent spatial controllability [1]. Direct laser synthesis of nanomaterials such as graphene and nano-structured metal oxides have been explored thoroughly for a wide range of applications [2,3]. However, to date, there are only a few reports associated with the laser processing of two-dimensional transition metal dichalcogenides (2D-TMDCs) [4]. These mainly utilize laser radiation for thinning TMDC films through sublimation down to a single molecular thickness [1]. However, this top-down approach is not practical for large- area and scalable production. In addition, further processing steps such as lithographic patterning are then required for discrete device fabrication. Here we present a novel method for the local synthesis and patterning of two-dimensional MoS2 and WS2 layers. The synthesis of these materials is achieved by spatially selective, visible laser irradiation of suitable precursors coated on the surface of planar substrates under ambient, room temperature conditions. The non- exposed precursor regions are then completely removed in a single step, revealing the synthesised 2D-TMDCs. This method can produce micro-patterned films with lateral dimensions that approach the diffraction limit of the focused laser beam. An example of such laser synthesised MoS2 tracks can be seen in the optical microscopy image of Figure 1(a) where it clearly shows a well-defined micro-pattern without any precursor residue. Using this method, we have achieved local synthesis of of MoS2 and WS2 with thickness down to three molecular layers for MoS2 and monolayer WS2 on various glass and crystalline substrates. The quality and thickness of the resulting films can be tuned by modifying the precursor chemistry and laser parameters. Different microprobe and spectroscopic spectroscopy, photoluminescence spectroscopy (PL) and X-ray photoelectron spectroscopy (XPS) have been used to assess the quality and thickness of the deposited MoS2 and WS2 structures. Finally, we have demonstrated the electronic functionality of our films by fabricating a thin film transistor (TFT). The transfer characteristics (source-drain current vs gate voltage) of such a TFT using a laser-synthesised MoS2 channel is shown in Figure 1(b).
关键词： Two-Dimensional Transition Metal Dichalcogenides,WS2,MoS2,Direct Laser Synthesis,Thin Film Transistor
更新于2025-09-11 14:15:04
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monolayers on the hBN-layer thickness
摘要： The optical properties of two-dimensional transition-metal dichalcogenide monolayers, such as MoS2 or WSe2 are dominated by excitons, Coulomb bound electron-hole pairs. Screening effects due to the presence of hexagonal-boron nitride (hBN) surrounding layers have been investigated by solving the Bethe-Salpeter equation on top of GW wave functions in density functional theory calculations. We have calculated the dependence of both the quasiparticle gap and the binding energy of the neutral exciton ground-state Eb as a function of the hBN-layer thickness. This paper demonstrates that the effects of screening at this level of theory are more short ranged than is widely believed. The encapsulation of a WSe2 monolayer by three sheets of hBN (～1 nm) already yields a 20% decrease in Eb, whereas the maximal reduction is 27% for thick hBN. We have performed similar calculations in the case of a WSe2 monolayer deposited on stacked hBN layers. These results are compared to the recently proposed quantum electrostatic heterostructure approach.
关键词： GW wave functions,density functional theory,hexagonal-boron nitride,two-dimensional transition-metal dichalcogenide,Bethe-Salpeter equation,exciton
更新于2025-09-04 15:30:14