Abstract
A great variety of two-dimensional (2D) boron allotropes (borophenes) were extensively studied in the past decade in the quest for graphene-like materials with potential for advanced technological applications. Among them, the 2D honeycomb boron is of specific interest as a structural analogue of graphene. Recently it has been synthesized on the Al(111) substrate; however it remains unknown to what extent does honeycomb boron behave like graphene. Here we elucidate the structural and electronic properties of this unusual 2D material with a combination of core-level X-ray spectroscopies, scanning tunneling microscopy, and DFT calculations. We demonstrate that in contrast to graphene on lattice-mismatched metal surfaces, honeycomb boron cannot wiggle like a blanket on Al(111), but rather induces reconstruction of the top metal layer, forming a stoichiometric AlB2 sheet on top of Al. Our conclusions from theoretical modeling are fully supported by X-ray absorption spectra showing strong similarity in the electronic structure of honeycomb boron on Al(111) and thick AlB2 films. On the other hand, a clear separation of the electronic states of the honeycomb boron into π- and σ-subsystems indicates an essentially 2D nature of the electronic system in both one-layer AlB2 and bulk AlB2.
Highlights
Elemental boron is a material famous for its rich phase diagram,[1] with the majority of stable bulk phases composed of interlinked icosahedral B12 clusters
We perform a comparison of the structure, growth processes, and electronic properties of honeycomb boron (HB) on Al(111) with thin films of AlB2 grown on the same substrate and studied by means of synchrotron-based X-ray photoemission spectroscopy (XPS), NEXAFS spectroscopy, scanning tunneling microscopy (STM), low-energy electron diffraction (LEED), and density-functional theory (DFT) calculations. ( epitaxial films of AlB2 may slightly deviate structurally from the parent bulk compound, we refer to the (−B−Al−)n/Al(111) samples as AlB2 films throughout this article based on our interpretation of the data.) We reveal a transition from HB on Al(111) to AlB2 and suggest a model for the HB arrangement on Al(111)
Up to now we demonstrated that XPS results are fully consistent with STM and LEED, allowing us to monitor and control the formation of HB and bulk AlB2 on Al(111) by observing their peculiar spectroscopic signatures
Summary
Elemental boron is a material famous for its rich phase diagram,[1] with the majority of stable bulk phases composed of interlinked icosahedral B12 clusters. Stimulated by the discovery of fascinating electronic properties in graphene, an intense search for two-dimensional (2D) forms of boron started in a quest for unknown phenomena. In contrast to graphene and hexagonal BN, a large variety of 2D boron sheet allotropes (called borophenes) were predicted in a freestanding form[2−4] and supported.[5,6] Essentially, any borophene can be considered as a triangular B lattice with either (less energetically favorable) buckling or (more energetically favorable) periodic vacancies (hollow hexagons, HH) in different motifs and concentrations.[2] For purely planar freestanding borophene this vacancy concentration can vary from 0 for a triangular sheet with no HH to 1/
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
