One-dimensional nearly free electron states in borophene

Abstract

Two-dimensional boron (borophene) is featured by its structural polymorphs and distinct in-plane anisotropy, opening opportunities to achieve tailored electronic properties by intermixing different phases. Here, using scanning tunneling spectroscopy combined with first-principles calculations, delocalized one-dimensional nearly free electron states (NFE) in the (2,3) or β12 borophene sheet on the Ag (111) surface were observed. The NFE states emerge from a line defect in the borophene, manifested as a structural unit of the (2,2) or χ3 sheet, which creates an in-plane potential well that shifts the states toward the Fermi level. The NFE states are held in the 2D plane of borophene, rather than in the vacuum region as observed in other nanostructures. Furthermore the borophene can provide a rare prototype to further study novel NFE behaviors, which may have potential applications on transport or field emission nanodevices based on boron.

Screening in Graphene: Response to External Static Electric Field and an Image-Potential Problem

“…Moreover, the information on the image-plane position can be useful for the construction of effective potentials in the systems with more complex geometries like fullerens and nanotubes, where the nearly-free states and the super-atomic orbitals, a subject of intense ongoing research, are inherently linked to IPSs in a flat graphene layer [60][61][62][63][64][65][66][67]. We believe that such a study as ours will not only be restricted to the carbon atoms case, since image-potential states can be realized in many other quasi-2D systems of current interest, like phosphorene, silicene and germanene [68], borophene [69], MXenes [70][71][72], and molecular overlayers on graphene [73].…”

Two-Dimensional Borophene: Properties, Fabrication, and Promising Applications

“…Provided that its ideal strength and in-plane stiffness are satisfactorily high, borophene can be used as assist elements for designing composites. Secondly, borophene is suitable for fabricating flexible nanodevices because of the high standards of flexibility against off-plane deformation [32][33][34]. Moreover, because of the powerfully anisotropic structure in borophene, its magnetic and electronic properties can be effectively controlled for multiple applications [35][36][37].…”

Resonant tunneling in disordered borophene nanoribbons with line defects

“…On the other hand, line defects (LDs) exist in diverse 2D materials [33][34][35][36][37][38] and strongly affect their electronic, magnetic, optical, mechanical, and thermal properties [39][40][41][42][43][44][45][46][47][48][49]. Very recently, a specific LD at the interface between (2,2) and (2,3) chains has been widely reported in experiments [50][51][52][53][54][55][56], owing to higher structural stability of borophene in the presence of LDs [52,57]. Specifically, several distinct phases are synthesized from periodic self-assembly of LDs [50][51][52], implying that (2,2) and (2,3) chains function as building blocks to construct novel boron sheets.…”

“…Specifically, several distinct phases are synthesized from periodic self-assembly of LDs [50][51][52], implying that (2,2) and (2,3) chains function as building blocks to construct novel boron sheets. These LDs could considerably mod-ulate the electronic properties of borophene [50,53,58] and improve its mechanical response [57], thus playing an important role in the discovery of exotic quantum phenomena and in device applications. Notice that the LDs in realistic borophene lack long-range order and structural disorder emerges simultaneously [50,52].…”