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

Engineering Two-Dimensional Nodal Semimetals in Functionalized Biphenylene by Fluorine Adatoms

We propose a band engineering scheme on the biphenylene network, a newly synthesized carbon allotrope. We illustrate that the electronic structure of the biphenylene network can be significantly altered by controlling conditions affecting the symmetry and destructive interference of wave functions through periodic fluorination. First, we investigate the mechanism for the appearance of a type-II Dirac fermion in a pristine biphenylene network. We show that the essential ingredients are mirror symmetries and stabilization of the compact localized eigenstates via destructive interference. While the former is used for the band-crossing point along high symmetry lines, the latter induces highly inclined Dirac dispersions. Subsequently, we demonstrate the transformation of the biphenylene network's type-II Dirac semimetal phase into various Dirac phases such as type-I Dirac, gapped type-II Dirac, and nodal line semimetals through the deliberate disruption of mirror symmetry or modulation of destructive interference by varying the concentration of fluorine atoms.

Theoretical insights into the structural, electronic and thermoelectric properties of the inorganic biphenylene monolayer

Being motivated by a recently synthesized biphenylene carbon monolayer (BPN), using first principles methods, we have studied its inorganic analogue (B-N analogue) named I-BPN. A comparative study of structural, electronic and mechanical properties between BPN and I-BPN was carried out. Like BPN, the stability of I-BPN was verified in terms of formation energy, phonon dispersion calculations, and mechanical parameters (Young's modulus and Poisson's ratio). The chemical inertness of I-BPN was also investigated by adsorbing an oxygen molecule in an oxygen-rich environment. It has been found that the B-B bond favours the oxygen molecule to be adsorbed through chemisorption. The lattice transport properties reveal that the phonon thermal conductivity of I-BPN is ten times lower than that of BPN. The electronic band structure reveals that I-BPN is a semiconductor with an indirect bandgap of 1.88 eV, while BPN shows metallic behaviour. In addition, we investigated various thermoelectric properties of I-BPN for possible thermoelectric applications. The thermoelectric parameters, such as the Seebeck coefficient, show the highest peak value of 0.00289 V K-1 at 300 K. Electronic transport properties reveal that I-BPN is highly anisotropic along the x and y-axes. Furthermore, the thermoelectric power factor as a function of chemical potential shows a peak value of 0.057 W m-1 K-2 along the x-axis in the p-type doping region. The electronic figure of merit shows a peak value of approximately unity. However, considering lattice thermal conductivity, the peak value of the total figure of merit (ZT) reduces to 0.68(0.46) for p-type and 0.56(0.48) for n-type doping regions along the x(y) direction at 900 K. It is worth noting that our calculated ZT value of I-BPN is higher than that of many other reported B-N composite materials.

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 α, β and γ, were investigated. The structural, mechanical, electronic, and optical properties of these hydrogenated biphenylene configurations were calculated by first-principles calculations. Band gaps with HSE correction were 4.69, 4.42 and 4.39 eV for α, β, and γ configurations, respectively. Among these three configurations, β presents the best electronic performance and special elastic properties (negative Poisson's ratio), while γ exhibits the best elastic properties. In addition, we comprehensively analyze the mechanical properties of these configurations and provide evidence that hydrogenated biphenylene possibly exhibits a negative-Poisson's-ratio along the zigzag and armchair directions when hydrogen atoms are added to biphenylene in certain ways. Furthermore, although the electronic properties of γ are weaker than those of β, they are also excellent. In addition, the binding energies of β and γ are relatively lower, which indicates that β and γ are more stable. Our findings demonstrate that the hydrogenated biphenylene is a promising material with significant application potential in optoelectronic devices.

Size-tunable energy gaps of hydrogen-terminated biphenylene segments

The electronic properties of hydrogen-terminated biphenylene (BP) segments of different sizes on the sub-nanoscale are explored using density functional theory, and the size dependence of the energy gap is evaluated using a structural parameter as a function of the bond lengths and the electronic density contributions. More importantly, the energy gap is observed to decrease linearly with the reduced hydrogen-to-carbon ratio of the corresponding structures, while the decrease-rate undergoes a diminution of four times at a gap of 0.5 eV due to the transformed distribution of the lowest unoccupied molecular orbital. The results give a deep insight into the size-tunable energy gaps of BPs and provide a possibility for the preparation of hydrogen-terminated carbon materials with a desirable energy gap.

New insights into phase transition behavior and electrochemistry corrosion of three-dimensional biphenylene

It is estimated that the annual cost of corrosion in most countries accounts for 3-4% of gross domestic product, far exceeding the losses caused by natural disasters, prompting scientists to continuously search for high-performance anti-corrosion materials. Among these high-performance materials, two-dimensional carbon materials represented by graphene have received widespread attention due to their excellent chemical stability and anti-permeability. However, some studies have found that the poor ability of graphene to bind to the interface and the electrical coupling caused by metallicity make it possible to protect copper from corrosion only for a short period of time. To circumvent these issues, through phase behavior research, interface binding property simulation and corrosion mechanism exploration, we propose a more promising anti-corrosive three-dimensional (3D) biphenylene diamond-like carbon membrane (BP-DLC). The kinetic study results show that due to the Gibbs free energy of biphenylene structures below three layers being lower than 0, few-layer biphenylene can spontaneously generate phase transitions of limited size, forming a biphenylene diamond-like membrane and exhibiting superior mechanical properties and a certain degree of flexibility. Mechanical and electronic performance results further show that there is a strong bonding effect between BP-DLC and the metal surface, which further enhances the bistate heterostructure and prolongs the coating life of BP-DLC materials. Compared with pure graphene and Cu substrates, BP-DLC membranes exhibit stronger corrosion resistance by reducing porosity, increasing charge transfer and hindering the diffusion of corrosion ions to the substrate. This study provides a new strategy for constructing corrosion-resistant materials by designing long-term stable and highly corrosion-resistant diamond-like membranes.

Localized vibrational characteristics of biphenylene strips resulting in length-dependent Raman spectra

The length dependence of the Raman spectra and vibrational properties of biphenylene strips are explored using density functional theory. The Raman intensity of two bands increases and decreases with length due to the enlarging and shrinking of the proportion of effective vibrating units. The red shift of vibrational modes is observed with the increase in length, owing to the various vibrational characteristics of the effective vibrating units. More importantly, a linear relationship between the energy gap and the wavenumber of the shifting Raman bands is obtained. The results allow us to interpret the length-dependence of the Raman spectra from the perspective of localized vibrational characteristics and suggest that Raman spectroscopy can be used as a convenient method to determine the energy gap of nanomaterials.

Biphenylene: A Two-Dimensional Graphene-Based Coating with Superior Anti-Corrosion Performance

Metal corrosion can potentially cause catastrophic engineering accidents threatening personal safety; thus, coating protection is a tremendously valuable anti-corrosion initiative. Recently, biphenylene, a novel two-dimensional (2D) graphene-based material, has achieved a remarkable synthetic breakthrough; the anti-corrosion properties of biphenylene, with its specific pore structure, are predicted to be beneficial in applications of metal corrosion resistance. In this study, the anti-corrosion mechanism of biphenylene is deciphered utilizing first principles and molecular dynamics. The results suggest that biphenylene with tetragonal, hexagonal, and octagonal carbon rings supplies adequate sites for stable O atom adsorption. The charge transfer amounts of +0.477 and +0.420 e facilitate the formation of a compact oxygen-rich layer on the material surface to acquire outstanding anti-corrosion properties. The moderate wettability of biphenylene prevents the water-based solution from encroaching on the biphenylene coating and substrate. In addition, the intensive binding between biphenylene and the aluminum substrate strengthens the integration of the two heterogeneous structures with -413.7 and 415.5 eV, which guarantees the durable application of biphenylene coating.

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. The monolayer ZnS has a direct band gap of 4.20 eV. It changes to an indirect band gap under both compression and tension, exhibiting a decrease in band gap. However, the band gap decreases more slowly under compression compared to the tension process such that the direct band gap remains within −8%, demonstrating excellent endurance under pressure. Fortunately, tetragonal ZnS exhibits a good absorption ability in the ultraviolet (UV) range regardless of strain. Our research results enrich the understanding of monolayer ZnS, which is helpful for the design and application of optoelectronic devices using the material.

The evolution of electronic property for monolayer tetragonal ZnS under biaxial strain.

Effective regulation of the electronic properties of a biphenylene network by hydrogenation and halogenation

The electronic properties of a biphenylene network can be effectively regulated in the range of 0.00–4.86 eV by hydrogenation and halogenation, and some of the obtained functionalized biphenylene networks have the potential to photolyse water.