Tuning the electronic and magnetic properties of MoS2 nanotubes with vacancy defects

Impact of ion beam irradiation on two-dimensional MoS2: a molecular dynamics simulation study

Two-dimensional (2D) materials such as MoS₂have extraordinary properties and significant application potential in electronics, optoelectronics, energy storage, bioengineering, etc. To realize the numerous application potential, it is needed to modulate the structure and properties of these 2D materials, for which ion beam irradiation has obvious advantages. This research adopted classical molecular dynamics simulations to study the sputtering of atoms in 2D MoS₂, defect formation and the control rule under Ar ion beam irradiation, considering the influence of ion irradiation parameters (i.e., ion beam energy, ion dose), layer number of 2D MoS₂, substrate. Furthermore, the uniaxial mechanical performance of the ion-irradiated nanostructures was investigated for actual applications loading with mechanical stress/strain. This research could provide important theoretical support for fabricating high-performance 2D MoS₂-based nanodevices by ion beam irradiation method.

Molecular dynamics simulations of ion beam irradiation on graphene/MoS2 heterostructure

The interaction between ion irradiation and two-dimensional (2D) heterostructures is important for the performance modulation and application realization, while few studies have been reported. This paper investigates the influence of Ar ion irradiation on graphene/MoS2 heterostructure by using molecular dynamics (MD) simulations. The generation of defects is studied at first by considering the influence factors (i.e., irradiation energy, dose, stacking order, and substrate). Then uniaxial tensile test simulations are conducted to uncover the evolution of the mechanical performance of graphene/MoS2 heterostructure after being irradiated by ions. At last, the control rule of interlayer distance in graphene/MoS2 heterostructure by ion irradiation is illustrated for the actual applications. This study could provide important guidance for future application in tuning the performance of graphene/MoS2 heterostructure-based devices by ion beam irradiation.

Size-dependent trends in the hydrogen evolution activity and electronic structure of MoS2 nanotubes

The thermodynamics of hydrogen evolution on MoS2 nanotubes is studied for the first time using periodic density functional theory calculations to obtain hydrogen adsorption free energies (ΔG Hads ) on pristine nanotubes and those with S-vacancy defects. Armchair and zigzag MoS2 nanotubes of different diameters, ranging from 12 to 22 Å, are examined. The H adsorption energy is observed to become more favourable (lower ΔG Hads ) as nanotube diameter decreases, with ΔG Hads values ranging from 1.82 to 1.39 eV on the pristine nanotubes, and from 0.03 to -0.30 eV at the nanotube S-vacancy defect sites. An ideal thermoneutral ΔG Hads value of nearly 0 eV is observed at the S-vacancy site on nanotubes around 20 to 22 Å in diameter. For the pristine nanotubes, density of states calculations reveal that electron transfer from S to Mo occurs during H adsorption, and the energy gap between these two states yields a highly reliable linear correlation with ΔG Hads , where a smaller gap leads to a more favourable hydrogen adsorption. For the S-vacancy defect site the H adsorption resembles that on a pure metallic surface, meaning that a traditional d-band centre model can be applied to explain the trends in ΔG Hads . A linear relation between the position of the Mo d-states and ΔG Hads is found, with d-states closer to the Fermi level leading to strong hydrogen adsorption. Overall this work highlights the relevance of MoS2 nanotubes as promising hydrogen evolution catalysts and explains trends in their activity using the energies of the electronic states involved in binding hydrogen.

Topology of transition metal dichalcogenides: the case of the core-shell architecture

Non-planar architectures of the traditionally flat 2D materials are emerging as an intriguing paradigm to realize nascent properties within the family of transition metal dichalcogenides (TMDs). These non-planar forms encompass a diversity of curvatures, morphologies, and overall 3D architectures that exhibit unusual characteristics across the hierarchy of length-scales. Topology offers an integrated and unified approach to describe, harness, and eventually tailor non-planar architectures through both local and higher order geometry. Topological design of layered materials intrinsically invokes elements highly relevant to property manipulation in TMDs, such as the origin of strain and its accommodation by defects and interfaces, which have broad implications for improved material design. In this review, we discuss the importance and impact of geometry on the structure and properties of TMDs. We present a generalized geometric framework to classify and relate the diversity of possible non-planar TMD forms. We then examine the nature of curvature in the emerging core-shell architecture, which has attracted high interest due to its versatility and design potential. We consider the local structure of curved TMDs, including defect formation, strain, and crystal growth dynamics, and factors affecting the morphology of core-shell structures, such as synthesis conditions and substrate morphology. We conclude by discussing unique aspects of TMD architectures that can be leveraged to engineer targeted, exotic properties and detail how advanced characterization tools enable detection of these features. Varying the topology of nanomaterials has long served as a potent methodology to engineer unusual and exotic properties, and the time is ripe to apply topological design principles to TMDs to drive future nanotechnology innovation.

3D Nest-Like Architecture of Core-Shell CoFe2O4@1T/2H-MoS2 Composites with Tunable Microwave Absorption Performance

As a promising microwave absorber filler, molybdenum disulfide (MoS₂), because of the unique structure, high electrical conductivity, and polarization effect, is receiving more and more interest. Developing MoS₂-based composites with specific structure and morphology is a hot top in the field of microwave absorbers, because of its strong multiple scattering and reflecting for microwaves as well as its unique interfacial characteristics. Now, with a facile solvothermal method, a novel core-shell CoFe₂O₄@1T/2H-MoS₂ composite is synthesized, where the CoFe₂O₄ nanospheres are entirely embedded in a special three-dimensional (3D) nest-like 1T/2H phase MoS₂. Notably, in comparison with superparamagnetic CoFe₂O₄ nanospheres, the coercivities of as-synthesized CoFe₂O₄@1T/2H-MoS₂ composites greatly increase. Here, 1T/2H-MoS₂ exhibits ferromagnetism superimposed onto large diamagnetism. It is noted that, by adjusting the content of 1T/2H-phase MoS₂, the microwave absorption performance of as-synthesized composites can be effectively tuned. The combination of 1T/2H-MoS₂ with CoFe₂O₄ helps to adjust the permittivity and optimize the impedance matching of the composites. Impressively, a minimum reflection loss (RL_min) of -68.5 dB for the as-synthesized composites with a thickness of 1.81 mm is gained at 13.2 GHz; meanwhile, a broad effective bandwidth of 4.56 GHz ranged from 13.2 to 17.76 GHz is achieved at 1.6 mm. Further, the overall effective bandwidth (RL < -10 dB) is obtained up to 14.5 GHz from 3.5 to 18.0 GHz, covering more than 90% of the measured frequency range. The high microwave absorption performance is ascribed to the special structure design with the core of magnetic CoFe₂O₄ nanospheres and the shell of dielectric nest-like 1T/2H-MoS₂ as well as their appropriate impedance matching. From the perspective of basic research and practical microwave application, this study provides another feasible and effective pathway to design novel MoS₂-based magnetic/dielectric microwave absorbers.

Orientational DNA binding and directed transport on nanomaterial heterojunctions

A deep understanding of the interactions between nanomaterials and biomolecules is critical for biomedical applications of nanomaterials. In this paper, we study the binding patterns, structural stabilities and diffusions of a double stranded DNA (dsDNA) segment on two recently reported graphene derivatives, boronic graphene (BC3) and nitrogenized graphene (C3N), with molecular dynamics (MD) simulations. Our results demonstrate that dsDNA exhibits a highly favored binding mode with an upright orientation on BC3 and C3N, independent of the initial configurations. In contrast to graphene (GRA) which demonstrates a cytotoxic feature, BC3 and C3N show high biocompatibility without causing evident structural distortions to the dsDNA duplex, benefitting from the periodic atomic charge distributions. Most interestingly, highly directional dsDNA transport is realized by formation of BC3/GRA and C3N/GRA in-plane heterojunctions, where the dsDNA migrating direction is uniformly BC3 → GRA → C3N. Furthermore, free energy profiling calculated by the umbrella sampling technique quantitatively supports these observations. Insights from our study would potentiate and guide future studies of graphenic 2D materials and bring about a flourishing new branch of in-plane heterojunction applications as targeted drug delivery templates in biomedical research.