First-Principles Study of Fe Adsorption and Its Effects on the Mechanical and Electrical Properties of Monolayer and Bilayer Biphenylene Networks

Abstract: Biphenylene network (BPN) is a 2D carbon allotrope that exhibits promising potential for applications. In this work, we systematically investigated the adsorption characteristics of Fe atoms on monolayer and bilayer BPN. Structural optimization and adsorption energy analysis reveal that, for monolayer BPN, the average adsorption gradually enhances with increasing Fe coverage, indicating a strengthening of Fe-substrate interactions. The most stable configuration is identified at an Fe/C ratio of 50 %. For bilayer BPN, the energetically preferred adsorption site for Fe atom is located at the center of the interlayer four-membered ring, with an average adsorption energy of -4.3 eV. Mechanical properties are further evaluated for pristine and Fe-decorated BPN. The results demonstrate that monolayer and bilayer BPN possess relatively high in-plane Young's and shear moduli, indicative of excellent in-plane mechanical stability. Fe adsorption is found to have only a minor effect on the in-plane mechanical properties of both monolayer and bilayer BPN, suggesting that the in-plane stiffness is predominantly governed by the intrinsic carbon framework. In contrast, the out-of-plane mechanical response of bilayer BPN is significantly affected by Fe incorporation. The effective out-of-plane elastic constant C33 of pristine bilayer BPN is calculated to be 24.59 GPa, indicating relatively weak interlayer interactions and facile deformation along the out-of-plane direction. Notably, this property can be substantially enhanced by interlayer Fe adsorption, with C33 increasing dramatically to 515.63 GPa upon an Fe/C ratio of 25 %. The calculations on pristine and Fe-decorated BPN reveal pronounced anisotropy in the conductivity, with the value along one direction being significantly higher than that along the other. At 300 K, the overall conductivity is on the order of 10^5 S/m.