Effect of the co-adsorption of small molecules from air on the properties of penta-graphene and their proton transfer calculation

Penta-graphene has attracted considerable attention due to its unique structure and novel properties. Herein, we studied the effect of the co-adsorption of small molecules from air on the properties of penta-graphene using first-principles calculations. Our results show that oxygen molecules can be self-decomposed on the surface of penta-graphene and the process of O₂ decomposition is an exothermic reaction. On the contrary, the adsorption of H₂O or N₂ molecule on penta-graphene exhibits weak interaction characteristic. For co-adsorption systems, the adsorption of N₂ molecule has no effect on the electronic properties of penta-graphene because the N₂ molecule is more inert than other molecules. Hydrogen bonds (H-bonds) have been observed in the co-adsorption of H₂O and O₂ on penta-graphene. We find that shorter H-bonds lead to higher stability of the systems. We also explore the proton transfer process between H₂O and oxidized penta-graphene. Our results show that the proton transfer process is relatively difficult due to the high energy barrier. However, double-proton transfer is an exothermic process since the energy of the final state is 0.11 eV lower than that of the initial state. These results indicate that the configuration of oxidized penta-graphene is complicated. Our research provides a theoretical basis and important guidance for the experimental synthesis and functionalization of penta-graphene.

Effects of hydrogenation on the tensile and shear mechanical properties of defective penta-graphene

Penta-graphene (PG) is a new theoretical two-dimensional metastable carbon allotrope composed entirely of carbon pentagons. In this paper, molecular dynamics simulations are performed to investigate the effects of the hydrogenation on the tensile and shear mechanical properties, together with the failure mechanism of PG with vacancy defects. The results show that hydrogenation can effectively tune the mechanical properties and failure mechanism of PG with vacancy defects. The defective PG (DPG) with low hydrogenation coverages exhibits obvious plastic deformation features under tensile and shear loading, and pentagon-to-polygon structural transformation is observed, while complete hydrogenation can change the failure mechanism of DPG from plastic deformation to brittle fracture. Both the tensile and shear moduli and elastic limit of DPG first decrease dramatically and then increase slowly with the increase of hydrogenation coverage, while tensile and shear strain increases almost monotonically with rising hydrogenation coverage. Complete hydrogenation can result in large enhancement of tensile and shear elastic stress limit and strain. These results may provide an important guideline for effectively tuning the mechanical properties of PG and other two-dimensional nanomaterials.

The effect of oxidation on the electronic properties of penta-graphene: first-principles calculation

Herein, using first-principles calculations, we systematically studied the effect of oxidation on the structural and electronic properties of penta-graphene. We have found that the oxygen atom prefers to adsorb at the center of the C[double bond, length as m-dash]C bond, and the interaction between the oxygen atom and penta-graphene is a strong chemical bond. When the oxygen coverage increases, the band gap of penta-graphene gradually widens due to the rigid up-shift of the conduction band. More importantly, we found that the oxygen molecule on the penta-graphene surface could self-decompose into oxygen atoms without any metal catalyst. Our calculated results show that penta-graphene would be chemically unstable when it is exposed to air. Therefore, from the application point of view, penta-graphene-based devices must be encapsulated or functionalized before exposure to air. Oxidized penta-graphene exhibits a large band gap, which can facilitate its application as dielectric layers in electronic devices.

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. In the presence of a perpendicular electric field, their band gaps can be significantly reduced and completely closed at a specific critical electric field strength, demonstrating a Stark effect. These findings show that few-layer PG will have tremendous opportunities to be applied in nanoscale electronic and optoelectronic devices owing to its tunable band gap.

Piezoelectric and polarized enhancement by hydrofluorination of penta-graphene

Hydrofluorination can efficiently enhance the piezoelectric response of 2D penta-graphene.