Atomic-scale analysis of the physical strength and phonon transport mechanisms of monolayer β-bismuthene

Effects of quantum size on the thermoelectric properties of bismuth

First principles and the Boltzmann transport equation have been combined to investigate the effects of quantum size L/λ, the ratio of quantum confinement length L to thermal de Broglie wavelength λ, on the thermoelectric properties of 2D β-bismuth. It is revealed that the thermoelectric properties of 2D β-bismuth are highly influenced by quantum size, especially when the L/λ is less than 0.1. Specifically, the Seebeck coefficients of both electrons and holes decrease as the L/λ ratio increases, while the electrical and thermal conductivity show the opposite trend. The results also show that 2D bismuth with three or more layers has semimetal properties, with the first observation of a semiconductor-semimetal transition in 2D bismuth. Moreover, the electron affinity, ionization energy, and work function of 2D β-bismuth do not exhibit a significant variation or trend with quantum size effects. The detailed electronic structures provide a fundamental understanding of the thermoelectric properties of bismuth, and the obtained results may provide a deep understanding of the relationship between the quantum size and the thermoelectric properties of 2D β-bismuth.

Optical absorption of bismuthene with a single vacancy: first-principle calculations

The exceptional mechanical, electronic, topological, and optical properties, make bismuthene an ideal candidate for various applications in ultrafast saturation absorption and spintronics. Despite the extensive research efforts devoted to synthesizing this material, the introduction of defects, which can significantly affect its properties, remains a substantial obstacle. In this study, we investigate the transition dipole moment and joint density of states of bismuthene with/without single vacancy defect via energy band theory and interband transition theory. It is demonstrated that the existence of the single defect enhances the dipole transition and joint density of states at lower photon energies, ultimately resulting in an additional absorption peak in the absorption spectrum. Our results suggest that the manipulation of defects in bismuthene has enormous potential for improving the optoelectronic properties of this material.

Atomic-level investigation on the oxidation efficiency and corrosion resistance of lithium enhanced by the addition of two dimensional materials

Understanding the oxidation and corrosion characteristics of Lithium (Li)-based systems is critical to their successful use as a solid fuel in spacecraft, powerplants, rechargeable batteries, submarines, and many other aquatic and corrosive environments. This study offers a systematic roadmap for engineering the oxidation efficiency and corrosion resistance of Li-based systems using ReaxFF-based Reactive Molecular Dynamics (RMD) simulations for the first time. First, we explored the oxidation mechanism of bare Li (Li/O₂) at 1200 K, noticing that the oxidation process quickly ceases due to the creation of a passive oxide film on the Li surface. Afterward, we examined the effect of introducing graphene-oxide (GO) to the oxidation process of Li/O₂. Interestingly, the inclusion of GO establishes a new reaction pathway between Li and O₂, thus significantly improving oxidation efficiency. Additionally, we realized that when the concentration of GO increases in the system, the oxidation rate of Li/O₂ increases considerably. As exposed to O₂ and H₂O, bare Li is observed to be highly corrosion-prone, while graphene (Gr)-coated Li exhibits excellent corrosion resistance, suggesting that Gr might be used as a promising corrosion-protective shield. Overall, this study is intended to serve as a reference for experimental investigations and assist researchers and engineers in designing more efficient Li-based functional systems.

Our ReaxFF RMD simulations uncover that oxidation efficiency and corrosion resistance of Li could be notably enhanced utilizing Graphene Oxide (GO), and Graphene (Gr), respectively.

Bonding, structure, and mechanical stability of 2D materials: the predictive power of the periodic table

This tutorial review describes the ongoing effort to convert main-group elements of the periodic table and their combinations into stable 2D materials, which is sometimes called modern 'alchemy'. Theory is successfully approaching this goal, whereas experimental verification is lagging far behind in the synergistic interplay between theory and experiment. The data collected here gives a clear picture of the bonding, structure, and mechanical performance of the main-group elements and their binary compounds. This ranges from group II elements, with two valence electrons, to group VI elements with six valence electrons, which form not only 1D structures but also, owing to their variable oxidation states, low-symmetry 2D networks. Outside of these main groups reviewed here, predominantly ionic bonding may be observed, for example in group II-VII compounds. Besides high-symmetry graphene with its shortest and strongest bonds and outstanding mechanical properties, low-symmetry 2D structures such as various borophene and tellurene phases with intriguing properties are receiving increasing attention. The comprehensive discussion of data also includes bonding and structure of few-layer assemblies, because the electronic properties, e.g., the band gap, of these heterostructures vary with interlayer layer separation and interaction energy. The available data allows the identification of general relationships between bonding, structure, and mechanical stability. This enables the extraction of periodic trends and fundamental rules governing the 2D world, which help to clear up deviating results and to estimate unknown properties. For example, the observed change of the bond length by a factor of two alters the cohesive energy by a factor of four and the extremely sensitive Young's modulus and ultimate strength by more than a factor of 60. Since the stiffness and strength decrease with increasing atom size on going down the columns of the periodic table, it is important to look for suitable allotropes of elements and binaries in the upper rows of the periodic table when mechanical stability and robustness are issues. On the other hand, the heavy compounds are of particular interest because of their low-symmetry structures with exotic electronic properties.

Phonon thermal conductivity of the stanene/hBN van der Waals heterostructure

We use classical non-equilibrium molecular dynamics (NEMD) simulations to investigate the phonon thermal conductivity (PTC) of hexagonal boron nitride (hBN) supported stanene. At first, we examine the length dependent PTCs of bare stanene and hBN, and the stanene/hBN heterostructure and realize the dominance of the hBN layer to dictate the PTC in the heterostructure system. Afterward, we assess the length-independent bulk PTCs of these materials. The bulk PTCs at room temperature are found as ∼15.20 W m-1 K-1, ∼550 W m-1 K-1, and ∼232 W m-1 K-1 for bare stanene and hBN, and stanene/hBN, respectively. Moreover, our simulations reveal that bare stanene exhibits a substantially lower PTC compared to bare hBN, and the predicted PTC of stanene/hBN lies between those of stand-alone stanene and hBN. We also found that the PTC obtained for the stanene/hBN system from NEMD simulations nicely agrees with the theoretical formula developed to predict the PTC of heterostructures of two distinct materials. Temperature studies suggest that the PTC of the stanene/hBN heterostructure system follows a decreasing trend with increasing temperature. Additionally, corresponding phonon density of states (PDOS) and phonon dispersion data are provided to comprehensively understand the phonon properties of bare stanene and hBN, and stanene/hBN. Overall, this NEMD study would offer a deep understating towards the PTC of the stanene/hBN heterostructure and would widen the scope of its successful operations in future nanoelectronic, spintronic, and thermoelectric devices.

Characterization of the mechanical properties of van der Waals heterostructures of stanene adsorbed on graphene, hexagonal boron-nitride and silicon carbide

Stanene has revealed a new horizon in the field of quantum condensed matter and energy conversion devices but its significantly lower tensile strength limits its further applications and effective operation in these nanodevices. Van der Waals heterostructures have given substantial flexibility to integrate different two-dimensional (2D) layered materials over the past few years and have proven highly functional with exceptional features, appealing applications, and innovative physics. Considerable efforts have been made for the preparation, thorough understanding, and applications of van der Waals heterostructures in the fields of electronics and optoelectronics. In this paper, we have executed Molecular Dynamics (MD) simulations to predict the tensile strength of van der Waals heterostructures of stanene (Sn) adsorbed on graphene (Gr), hexagonal boron nitride (hBN), and silicon carbide (SiC) (Sn/Gr, Sn/hBN, and Sn/SiC, respectively) subjected to both armchair and zigzag directional loading at different strain rates for the first time, which has enticing applications in electronic, optoelectronic, energy storage and bio-engineered devices. Among all the van der Waals heterostructures, the Sn/SiC heterostructure exhibits the lowest tensile strength and tensile strain. Furthermore, it has been found that zigzag directional loading could endure more tensile strain before fracture. Besides, it has been disclosed that though the rule of mixtures may accurately reproduce the Young's modulus of these heterostructures, it has limitations to predict the tensile strength. Fracture analysis suggests that for the Sn/hBN heterostructure the fracture initiates from the stanene layer while for the Sn/Gr and Sn/SiC heterostructures the fracture initiates from the Gr and SiC layer, respectively, for both armchair and zigzag directional loading. Overall, this study would aid in the design and efficient operation of Sn/Gr, Sn/hBN, and Sn/SiC heterostructures when subjected to mechanical force.

Nanomechanics of antimonene allotropes under tensile loading

Monolayer antimonene has drawn the attention of research communities due to its promising physical properties. However, the mechanical properties of antimonene have remained largely unexplored. In this work, we investigate the mechanical properties and fracture mechanisms of two stable phases of monolayer antimonene - β-antimonene (puckered structure) and α-antimonene (buckled structure) - through molecular dynamics (MD) simulations. Our simulations reveal that a stronger chiral effect results in a greater anisotropic elastic behavior in α-antimonene than in β-antimonene. We focus on crack-tip stress distribution using local volume averaged virial stress definition and derive the fracture toughness from the crack-line stress. Our calculated crack tip stress distribution ensures the applicability of linear elastic fracture mechanics (LEFM) for cracked antimonene allotropes with considerable accuracy up to a pristine structure. We evaluate the effect of temperature, strain rate, crack-length, and point-defect concentration on the strength and elastic properties. The tensile strength of antimonene degrades significantly with the increase of temperature, crack length and defect concentration. The elastic modulus is found to be less susceptible to temperature variation but is largely affected by the increase in defects. The strain rate exhibits a power law relationship between strength and fracture strain. Finally, we discuss the fracture mechanisms in the light of crack propagation and establish the relationship between the fracture mechanism and the observed anisotropic properties.

Tuning the mechanical properties of functionally graded nickel and aluminium alloy at the nanoscale

We revealed that the mechanical properties of Ni3Al (homogeneous alloy) could be modulated utilizing functional grading.