Unveiling the Multiradical Character of the Biphenylene Network and Its Anisotropic Charge Transport

Abstract

Recent progress in the on-surface synthesis and characterization of nanomaterials is facilitating the realization of new carbon allotropes, such as nanoporous graphenes, graphynes, and 2D π-conjugated polymers. One of the latest examples is the biphenylene network (BPN), which was recently fabricated on gold and characterized with atomic precision. This gapless 2D organic material presents uncommon metallic conduction, which could help develop innovative carbon-based electronics. Here, using first principles calculations and quantum transport simulations, we provide new insights into some fundamental properties of BPN, which are key for its further technological exploitation. We predict that BPN hosts an unprecedented spin-polarized multiradical ground state, which has important implications for the chemical reactivity of the 2D material under practical use conditions. The associated electronic band gap is highly sensitive to perturbations, as seen in finite temperature (300 K) molecular dynamics simulations, but the multiradical character remains stable. Furthermore, BPN is found to host in-plane anisotropic (spin-polarized) electrical transport, rooted in its intrinsic structural features, which suggests potential device functionality of interest for both nanoelectronics and spintronics.

The electronic and interfacial properties of a vdW heterostructure composed of penta-PdSe2and biphenylene monolayers

“…27 From the device's perspective, a large rectification ratio of up to 6.3 Â 10 5 for PdSe 2 /MoTe 2 , 30 39 synthesized an ultra-flat metallic carbon sheet, namely the biphenylene network (BPN), which is composed of tetra-, hexa-, and octa-gonal rings and features pure sp 2hybridization. By using first-principles calculations, some theoretical studies have also confirmed metallicity, 40 magnetic and topological ordering, 41 anisotropic charge transport, 42 and remarkable negative thermal expansion 43 in the BPN monolayer, which extend the functionality of this sheet for advanced nanodevices. From the perspective of heterojunctions, it would be interesting to explore how the BPN sheet interacts with penta-PdSe 2 to form a heterostructure.…”

Topologically Frustrated Graphene Antidot Lattice Semiconductors with Room-Temperature Magnetism

“…Recent theoretical studies have demonstrated that the magnetism of two-dimensional carbon-based materials is determined by the characteristics of their open-shell building block molecules. − Therefore, seeking strong magnetic coupling build blocks of GALs is the prerequisite to achieve room-temperature magnetic GALs. The building blocks of magnetic GALs could be viewed as open-shell graphene nanoflakes (GNFs), which are arbitrarily shaped and finitely sized graphene fragments with multiradical character. − The main magnetic mechanism of GNFs is involved with topological frustration in the graphene network, which is a phenomenon when π electron networks with certain topologies are unable to pair all p z orbitals simultaneously to form π bonds, which generates uncompensated radicals. , Recently, considerable topologically frustrated magnetic GNFs have been synthesized on metal surfaces in experiments, such as [ n ]­triangulene and their polymer. − Notably, one biradicaloid GNF, named heptauthrene, has been synthesized recently and exhibits strong intramolecular ferromagnetic coupling strength .…”

Unveiling the formation mechanism of the biphenylene network

“…30 The ultra-flat network is achieved by the intermolecular HF zipping between self-assembled poly(2,5-difluoro-para-phenylene) (PFPP) chains on the Au(111) surface after annealing to 700 K. 30 The experimental observation and further theoretical investigations have demonstrated that the BPN exhibits uncommon metallic conduction, which is of great value in the development of carbon-based electronic materials. [30][31][32] Despite the experimental success, the underlying mechanism for the intermolecular HF zipping still remains unclear. Therefore, a complete theoretical understanding of the intermolecular HF zipping on the Au(111) surface is crucial for the rational design of new on-surface synthesis protocols making use of such reactions.…”