Electrical and mechanical properties and thermoelectric efficiency enhancement of monolayer and bilayer Si2BN: A first-principle study

Tunable band gap and enhanced thermoelectric performance of tetragonal Germanene under bias voltage and chemical doping

This paper employs the tight-binding model to investigate the thermal properties of tetragonal Germanene (T-Ge) affected by external fields and doping. T-Ge is a two-dimensional material with unique electronic properties, including zero band gap and two Dirac points. The electronic properties of T-Ge can be influenced by bias voltage, which can open its band gap and convert it to a semiconductor due to its buckling structure. The tunable band gap of biased T-Ge, makes it a a promising option for electronic and optoelectronic devices. The band structure of T-Ge is split by the magnetic field, leading to an increases its band edges due to the Zeeman Effect. The findings demonstrate that the thermoelectric properties of T-Ge are highly sensitive to external parameters and modifications of the band structure. The thermal and electrical conductivity of T-Ge increase with increasing temperature due to the rise in thermal energy of charge carriers. The thermoelectric properties of T-Ge decrease with bias voltage due to band gap opening, increase with the magnetic field due to a modifications of the band structure, and increase with chemical potential due to increasing density of charge carriers. By manipulating the band structure of T-Ge through bias voltage and chemical doping, the electrical conductivity can be optimized to achieve higher figure of merit (ZT) and improved thermoelectric performance. The results demonstrate the potential of T-Ge for use in electronic and magnetic devices, opening up new possibilities for further research and development in this field.

Decoupling 1D and 2D features of 2D sp-nanoribbons-the megatom model

The dependence of the electron energy band gap on the width of ansp-nanoribbon is investigated using a generalization of the 1D tight binding model for a chain of atoms. Within the proposed generalization, small linear atomic formations along lines perpendicular to the 2D ribbon axis are modeled as single large atoms calledmegatomswhose properties depend on the type, the size and the atomic conformation. Replacement of a 1D chain of atoms by that of the megatoms is accompanied by the incorporation of zeroth order 2D features into the 1D model approximation of the nanoribbon. We use this model to investigate the oscillating band gap of ansp-nanoribbon in terms of the ribbon's width. Results are presented for the width dependence of the energy gap of the zig-zag Si₂BN nanoribbons.

From Fundamental to CO2 and COCl2 Gas Sensing Properties of Pristine and Defective Si2BN Monolayer

The capability of Si2BN monolayer (Si2BN-ML) in sensing CO2 and COCl2 molecules is investigated by analyzing the structural, electronic, mechanical and gas sensing properties of defect-free and defective Si2BN-ML. Electronic...

Novel high-performance anodic materials for lithium ion batteries: two-dimensional Sn-X (X = C, Si, and Ge) alloy monolayers

Lithium-ion batteries (LIBs) have always been the focus of researchers for energy storage applications. Here, the first-principles density functional theory method was used to explore the possibility of using stanene derived structures as LIB anodes. And such two-dimensional structures are similar to graphene or stanene, but half of the Sn atoms are replaced by group-IV atoms to form new structures, which are called Sn-X (X = C, Si, and Ge). Our calculation results showed that the optimized structure, lattice constant and other parameters are consistent with those reported in previous studies. Meanwhile, we found out that the semiconductor properties of pristine Sn-X transform into metal properties after the adsorption of Li. Then, by calculating the adsorption concentration of Li ions on the Sn-X monolayers, we found that these kinds of materials can meet the requirements of battery anodes very well, not only in terms of their open-circuit voltage, but also storage capacity. For Sn-Si and Sn-Ge, their theoretical capacities can be as high as 1095.78 mA h g^-1 (Li₆Sn-Si) and 840.88 mA h g^-1 (Li₆Sn-Ge). At last, based on the investigation of their diffusion path, Sn-X has been found to have high charge and discharge rates because of its low barrier. By reason of the foregoing, 2D Sn-X monolayers will be excellent battery anodes.

High temperature stability, metallic character and bonding of the Si2BN planar structure

The family of monolayered Si₂BN structures constitute a new class of 2D materials exhibiting metallic character with remarkable stability. Topologically, these structures are very similar to graphene, forming a slightly distorted honeycomb lattice generated by a union of two basic motifs with AA and AB stacking. In the present work we study in detail the structural and electronic properties of these structures in order to understand the factors which are responsible for their structural differences as well as those which are responsible for their metallic behavior and bonding. Their high temperature stability is demonstrated by the calculations of finite temperature phonon modes which show no negative contributions up to and beyond 1000 K. Presence of the negative thermal expansion coefficient, a common feature of one-atom thick 2D structures, is also seen. Comparison of the two motifs reveal the main structural differences to be the differences in their bond angles, which are affected by the third nearest neighbor interactions ofcis-transtype. On the other hand, the electronic properties of these two structures are very similar, including the charge transfers occurring between orbitals and between atoms. Their metallicity is mainly due to thep_zorbitals of Si with a minor contribution from thep_zorbitals of B, while the contribution from thep_zorbitals of N atoms is negligible. There is almost no contributions from the Np_zelectrons to the energy states near the Fermi level, and they form a band well below it. I.e., thep_zelectrons of N are localized mostly at the N atoms and therefore cannot be considered as mobile electrons of thep_zcloud. Moreover, we show that due to the relative positions in the energy axis of the atomic energies of thep_zorbitals of B, N and Si atoms, the density of states (DOS) of Si₂BN can be considered qualitatively as a combination of the DOS of planar hexagonal BN (h-BN) and hypothetically planar silicene (ph-Si). As a result, the Si₂BN behaves electronically at the Fermi level as slightly perturbed ph-Si, having very similar electronic properties as silicene, but with the advantage of having kinetic stability in planar form. As for the bonding, the Si-Si bonds are covalent, while theπback donation mechanism occurs for the B-N bonding, in accordance with the B-N bonding in h-BN.