Two-Dimensional Hexagonal Beryllium Sulfide Crystal

Strong Be-Be bonds in double-aromatic bridged Be2(μ-SO) molecules

A bridged Be2(μ-SO) molecule is formed by stabilizing the Be2 dimer using a SO ligand. In this molecule, which is thermodynamically stable, the Be2 moiety behaves as an efficient electron donor toward the SO fragment. The ionic character of Be2δ+ and SOδ- in this molecule is confirmed by NBO analysis. Energy decomposition analysis shows that the strongest attractive interactions in this molecule are the polarization and exchange interactions. Also, Adaptive Natural Density Partitioning (AdNDP) analysis indicates the stability of this molecule, which could be due to the double-aromatic character of this system. Therefore, it seems that the title molecule could be experimentally detected.

Stable Low-Dimensional Boron Chalcogenides from Planar Structural Motifs

There has been growing interest in searching for new low-dimensional (low-D) materials for nanoelectronics and energy applications. Most materials have their structural units extended in three dimensions and connected with chemical bonds. When the dimension is reduced, these bonds will be broken, decreasing the stability and making their experimental realization difficult. Here, we show that stable low-D materials can be made from naturally existing planar structural units. This is demonstrated by first-principles study of boron chalcogenides (B-X), which can have various low-D structures with attractive properties. For example, B₂O₃ can be the thinnest proton-exchange membrane for fuel cells. B-X are wide-gap semiconductors that can complement the narrow-gap 2D metal dichalcogenides for (opto)electronics. Our work sheds light on the stability of low-D materials and suggests guidelines for rational design of new materials.

2D BeP2 monolayer: investigation of electronic and optical properties by driven modulated strain

Recently, the two-dimensional (2D) material beryllium diphosphide (BeP₂) has attracted significant attention for potential device applications due to its Dirac semimetal state, dynamic and thermal stability, and high carrier mobility. In this work, we investigated its electronic and optical properties under biaxial Lagrangian strain using density functional theory (DFT). Electronic band gaps and effective charge carrier mass were highly sensitive to the Lagrangian strain of BeP₂ monolayer. The bandgaps of BeP₂ varied from 0 eV to 0.30 eV for 2% to 8% strain, where the strain range is based on the final stable condition of the system. The absorption spectra for the dielectric properties show the highest absorption peaks in the infrared (IR) region. These abundant strain-dependent studies of the BeP₂ monolayer provide guidelines for its application in infrared sensors and devices.

BeP₂ monolayer is a promising material for the novel IR optical device.

A MoO2 sheet as a promising electrode material: ultrafast Li-diffusion and astonishing Li-storage capacity

The potential of MoO₂ crystal as an electrode material is reported, and nanostructural MoO₂ systems, including nanoparticles, nanospheres, nanobelts and nanowires, were synthesized and proved to be advanced electrode materials. A two-dimensional (2D) geometric structure represents an extreme of surface-to-volume ratio, and thus is more suitable as an electrode material in general. Stimulated by the recent fabrication of 2D MoO₂, we adopted an ab initio molecular dynamics simulation and density functional theory calculation to study the stability and electrochemical properties of a MoO₂ sheet. Identified by a phonon dispersion curve and potential energy curve calculations, the MoO₂ sheet proved to be dynamically and thermally stable. After lithiation, similar to most promising 2D structures, we found that a Li atom can strongly adsorb on a MoO₂ sheet, and the lithiated MoO₂ sheet presented excellent metallic properties. Note that, compared with most promising 2D structures, we unexpectedly revealed that the diffusion barrier of the Li atom on the MoO₂ sheet was much lower and the storage capacity of the MoO₂ sheet was much larger. The calculated energy barrier for the diffusion of Li on the MoO₂ sheet was only 75 meV, and, due to multilayer adsorption, the theoretical capacity of the MoO₂ sheet can reach up to 2513 mA h g^-1. Benefiting from general properties, such as strong Li-binding and excellent conductivity, and unique phenomena, such as ultrafast diffusion capacity and astonishing storage capacity, we highlight a new promising electrode material for the Li-ion battery.

A Honeycomb BeN2 Sheet with a Desirable Direct Band Gap and High Carrier Mobility

Using global particle-swarm optimization method, we report, for the first time, a BeN2 sheet (h-BeN2) with a graphene-like honeycomb lattice but displaying a direct band gap. Symmetry group analysis indicates that the dipole transition is allowed between the conduction band minimum and the valence band maximum. Although the direct band gap of 2.23 eV is close to that (2.14 eV) of MoS2 sheet, the h-BeN2 sheet has additional advantages: the direct band gap feature of the h-BeN2 sheet is quite insensitive to the layer stacking pattern and layer number, in contrast to the well-known direct-to-indirect band gap transition observed in TMDs and h-BN sheets. When rolled up, all the resulting h-BeN2 nanotubes have direct band gaps independent of chirality and diameter. Furthermore, the intrinsic acoustic-phonon-limited carrier mobility of the h-BeN2 sheet can reach ∼10(5) cm(2) V(-1) s(-1) for electron and ∼10(4) cm(2) V(-1) s(-1) for hole, which are higher than that of MoS2 and black phosphorus.

Thermal exfoliation of stoichiometric single-layer silica from the stishovite phase: insight from first-principles calculations

Mechanical cleavage, chemical intercalation and chemical vapor deposition are the main methods that are currently used to synthesize nanosheets or monolayers. Here, we propose a new strategy, thermal exfoliation for the fabrication of silica monolayers. Using a variety of state-of-the-art theoretical calculations we show that a stoichiometric single-layer silica with a tetragonal lattice, T-silica, can be thermally exfoliated from the stishovite phase in a clean environment at room temperature. The resulting single-layer silica is dynamically, thermally, and mechanically stable with exceptional properties, including a large band gap of 7.2 eV, an unusual negative Poisson's ratio, a giant Stark effect, and a high breakdown voltage. Moreover, other analogous structures like single-layer GeO2 can also be obtained by thermal exfoliation of its bulk phase. Our findings are expected to motivate experimental efforts on developing new techniques for the synthesis of monolayer materials.

Spin-dependent electronic transport properties of zigzag silicon carbon nanoribbon

The zigzag SiC nanoribbon devices exhibit a variety of exotic physical properties such as spin filtering, current-limited, and oscillation effects.

Unusual electronic properties and transmission in hexagonal SiB monolayers

After the success of graphene, several two-dimensional (2D) layers have been proposed and investigated both theoretically and experimentally in order to evaluate their structural stability and possible applications of these unusual materials in electronics. Except for graphene, only silicon and germanium were predicted to form semi-metallic honeycomb monolayers, while most of the binary graphene-like compounds are all semiconductors. These predictions have been corroborated for several 2D structures experimentally synthesized. Considering the possibility of finding other candidates in this realm, exhibiting exceptional electron mobility, we have explored low-dimensional silicon-boron compounds containing planar sp(2)-bonding silicon atoms, through first-principles density-functional theory calculations. We have demonstrated that the so-called h-SiB sheet, which is a structural analogue of 2D honeycomb binary compounds, exhibits good structural stability, compared to the structure of silicene, for example, and predicted that this structure is also able to roll up into thermally stable single-walled silicon-boron nanotubes. The h-SiB sheet exhibits a delocalized charge density like in graphene, but the partially filled π band and two highest occupied σ bands are above the Fermi level, leading to the metallic behaviour of this SiB sheet. In this sense, we perform first-principles electron transport calculations, based on the nonequilibrium Green's function formalism, which has demonstrated that h-SiB exhibits higher transmission around the Fermi energy than the transmission in graphene. Our results indicate the unusual conductivity of this new material and open up new possibilities for the realization of metallic graphene-like systems for electronic transport in low dimensions.

Hybrid platforms of graphane–graphene 2D structures: prototypes for atomically precise nanoelectronics

Graphane-based electronics in nanocircuits.