Structural, mechanical, electronic and optical properties of biphenylene hydrogenation: a first-principles study.

Biphenylene networks typically exhibit a metallic electronic nature, while hydrogenation can open the band gap changing it to a semiconductor. This property makes hydrogenated biphenylene a promising candidate for use in semiconductor optoelectronic materials and devices. In this work, three representative configurations of hydrogenated biphenylene, denoted by , and , were investigated.

The luminescence mechanism of ligand-induced interface states in silicon quantum dots.

Over decades of research on photoluminescence (PL) of silicon quantum dots (Si-QDs), extensive exploratory experiments have been conducted to find ways to improve the photoluminescence quantum yield. However, the complete physical picture of Si-QD luminescence is not yet clear and needs to be studied in depth. In this work, which considers the quantum size effect and surface effect, the optical properties of Si-QDs with different sizes and surface terminated ligands were calculated based on first principles calculations.

Influence of Group-IVA Doping on Electronic and Optical Properties of ZnS Monolayer: A First-Principles Study.

Element doping is a universal way to improve the electronic and optical properties of two-dimensional (2D) materials. Here, we investigate the influence of group-ⅣA element (C, Si, Ge, Sn, and Pb) doping on the electronic and optical properties of the ZnS monolayer with a tetragonal phase by using first-principles calculations. The results indicate that the doping atoms tend to form tetrahedral structures with neighboring S atoms.

A new direct band gap Si-Ge allotrope with advanced electronic and optical properties.

Direct-band silicon materials have been a sought-after material for potential applications in silicon photonics and solar cells. Accordingly, methodologies like nanostructure engineering, alloy engineering and strain engineering have been developed. In this work, the particle swarm optimization (PSO) algorithm is used to design direct-band Si-Ge alloys.

A first-principles study of electronic and optical properties of the tetragonal phase of monolayer ZnS modulated by biaxial strain.

Modulation of the electronic and optical properties of two-dimensional (2D) materials is of great significance for their practical applications. Here, by using first-principles calculations, we study a tetragonal phase of monolayer ZnS, and explore its associated electronic and optical properties under biaxial strain. The results from phonon dispersion and molecular dynamics simulation demonstrate that the tetragonal phase of monolayer ZnS possesses a very high stability.

Electronic and optical properties of hydrogen-terminated biphenylene nanoribbons: a first-principles study.

The electronic structures and optical properties of novel 2D biphenylene and hydrogen-terminated nanoribbons of different widths which are cut from a layer of biphenylene were explored first-principles calculations. The findings of phonon computations demonstrate that such a biphenylene is dynamically stable and shows metallic properties. The crystal orbital Hamilton population analysis indicates that the tetra-ring local structure results in anisotropic mechanical properties.

Luminescence mechanism in hydrogenated silicon quantum dots with a single oxygen ligand.

Though photoluminescence (PL) of Si quantum dots (QDs) has been known for decades and both theoretical and experimental studies have been extensive, their luminescence mechanism has not been elaborated. Several models have been proposed to explain the mechanism. A deep insight into the origin of light emissions in Si QDs is necessary.

Electric Field-Tunable Structural Phase Transitions in Monolayer Tellurium.

Electronic properties of monolayer tellurium (Te) with three proposed atomic configurations under external electric field were investigated through first-principles calculations. The calculated results demonstrate that α-Te and γ-Te have indirect band gaps, whereas β-Te, when no electric field is applied, can be considered as a direct semiconductor. An interesting structural change occurs in α- and γ-phase Te under a specific electric field strength, as does a change in structural chirality.

A first-principles study of strain tuned optical properties in monolayer tellurium.

First-principles calculations are employed to study the optical properties of monolayer Te tuned by biaxial strain. Our results demonstrate that monolayer Te has strong absorption in the visible and ultraviolet regions, and that a structural transition occurs between the α-phase and the β-phase under certain strain. In addition, there is significant optical anisotropy in α- and β-Te, while γ-Te shows isotropic characteristics due to their different structural properties.

A first-principles study of the electrically tunable band gap in few-layer penta-graphene.

The structural and electronic properties of bilayer (AA- and AB-stacked) and tri-layer (AAA-, ABA- and AAB-stacked) penta-graphene (PG) have been investigated in the framework of density functional theory. The present results demonstrate that the ground state energy in AB stacking is lower than that in AA stacking, whereas ABA stacking is found to be the most energetically favorable, followed by AAB and AAA stackings. All considered model configurations are found to be semiconducting, independent of the stacking sequence.

Screening effects on the field enhancement factor of zigzag graphene nanoribbon arrays: a first-principles study.

The field screening effect on the electronic and field-emission properties of zigzag graphene nanoribbons (ZGNRs) has been studied using first-principles calculations. We have systematically investigated the effects of inter-ribbon distance and ribbon width on the work function, field enhancement factor, band gap and edge magnetism of zigzag graphene nanoribbons (ZGNRs). It is found that the work function of ZGNRs increases rapidly as the inter-ribbon distance Dx increases, which is caused by the positive dipole at the edge of the ribbon.

Novel penta-graphene nanotubes: strain-induced structural and semiconductor-metal transitions.

Research into novel one-dimensional (1D) materials and associated structural transitions is of significant scientific interest. It is widely accepted that a 1D system with a short-range interaction cannot have 1D phase transition at finite temperature. Herein, we propose a series of new stable carbon nanotubes by rolling up penta-graphene sheets, which exhibit fascinating well-defined 1D phase transitions triggered by axial strain.

Tunable magnetic states on the zigzag edges of hydrogenated and halogenated group-IV nanoribbons.

The magnetic and electronic properties of hydrogenated and halogenated group-IV zigzag nanoribbons (ZNRs) are investigated by first-principles density functional calculations. Fascinatingly, we find that all the ZNRs have magnetic edges with a rich variety of electronic and magnetic properties tunable by selecting the parent and passivating elements as well as controlling the magnetization direction and external strain. In particular, the electric property of the edge band structure can be tuned from the conducting to insulating with a band gap up to 0.

The fracture behaviors of monolayer phosphorene with grain boundaries under tension: a molecular dynamics study.

The fracture behaviors of monolayer phosphorene (MP) with and without a grain boundary (GB) have been explored by molecular dynamics (MD) simulations. Firstly, in the case of perfect MP, fracture mostly happens on the bond in the zigzag direction when suffering random loading. With the existence of a GB, the crack propagates perpendicular to the GB in different ways under parallel tension to the GB, whereas it propagates along the GB under perpendicular tension to the GB.

Si78 double cage structure and special optical properties.

We performed first-principles calculations to study the structural stability of Si78 clusters with or without hydrogen passivation. The calculations reveal that an endohedral double cage isomer is more stable than the diamond-like structure, whereas the opposite is found for the hydrogen passivated isomers. In particular, the hydrogenated double cage and diamond-like structure may display blue shifts to the visible and UV regions, respectively.

Magnetic evolution and anomalous Wilson transition in diagonal phosphorene nanoribbons driven by strain.

Inducing magnetism in phosphorene nanoribbons (PNRs) is critical for practical applications. However, edge reconstruction and Peierls distortion prevent PNRs from becoming highly magnetized. Using first-principles calculations, we find that relaxed oxygen-saturated diagonal-PNRs (O-d-PNRs) realize stable spin-polarized antiferromagnetic (AFM) coupling, and the magnetism is entirely localized at the saturated edges.

A first-principles study of the electronic structure and mechanical and optical properties of CaAlSiN3.

The mechanical properties, electronic structures and optical properties of CaAlSiN3 were investigated using the first-principles calculations. The elastic constants, bulk moduli, shear moduli, Young's moduli, and Poisson's ratio were obtained. These results indicate that CaAlSiN3 is mechanically stable and a relatively hard material.

Investigation into the mechanical properties of single-walled carbon nanotube heterojunctions.

The mechanical properties of finite-length (6,0)/(8,0) single-walled carbon nanotube (SWCNT) heterojunctions with respect to different kinds of connection segments, either coaxial or bias, are investigated using molecular dynamics simulation calculations. It is found that the resulting significant deformation of structure and significant drop of stress under yielding strain is due to the strain localization. Moreover, the deformation is occurred below the heptagon ring in the thinner segment of the heterojunctions under tension at different temperatures, whereas under compression it occurs on the heptagon ring.

Target molecular simulations of RecA family protein filaments.

Modeling of the RadA family mechanism is crucial to understanding the DNA SOS repair process. In a 2007 report, the archaeal RadA proteins function as rotary motors (linker region: I71-K88) such as shown in Figure 1. Molecular simulations approaches help to shed further light onto this phenomenon.

Modular ion mobility spectrometer for explosives detection using corona ionization.

Ion mobility spectrometry (IMS) has become the most widely used technology for trace explosives detection. A key task in designing IMS systems is to balance the explosives detection performance with size, weight, cost, and safety of the instrument. Commercial instruments are, by and large, equipped with radioactive (63)Ni ionization sources which pose inherent problems for transportation, safety, and waste disposal regulation.

Competitive diamond-like and endohedral fullerene structures of Si70.

We performed first-principles calculations to study the structure and stability of Si(70) cluster. The results from the density functional theory calculation with the Becke-Lee-Yang-Parr and B3LYP exchange-correlation functionals suggest that a diamond-like Si(70) isomer is the most stable structure, in contrast to endohedral fullerenes of Si(70). On the other hand, an endohedral fullerene of Si(16)@Si(54) was found to be slightly lower in energy than the diamond-like Si(70) if the Predew-Burke-Ernzerhof functional is used.

Structural and electronic properties of hydrogen adsorptions on BC₃ sheet and graphene: a comparative study.

We have systematically investigated the effect of hydrogen adsorption on a single BC₃ sheet as well as graphene using first-principles calculations. Specifically, a comparative study of the energetically favorable atomic configurations for both H-adsorbed BC₃ sheets and graphene at different hydrogen concentrations ranging from 1/32 to 4/32 ML and 1/8 to 1 ML was undertaken. The preferred hydrogen arrangement on the single BC₃ sheet and graphene was found to have the same property as that of the adsorbed H atoms on the neighboring C atoms on the opposite sides of the sheet.

Structural and electronic properties of graphene nanotube-nanoribbon hybrids.

The structural and electronic properties of a hybrid of an armchair graphene nanotube and a zigzag graphene nanoribbon are investigated by first-principles spin-polarized calculations. These properties strongly depend either on the nanotube location or on the spin orientation. The interlayer spacing, the transverse distance from the center of the ribbon and the stacking configuration affect the electronic structures.

Predicting Raman spectra using density functional theory.

Accurately computing molecular Raman spectra would enable rapid development of inexpensive and extensive Raman libraries. This is especially beneficial for chemicals that are regulated, toxic, or otherwise difficult to handle. Numerous quantum mechanical methods have been developed that enable computation of Raman spectra.