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We present an enhanced method for synthesizing sheets of borophane. Despite the challenges associated with low efficiency, we discovered that incorporating hydrochloric acid into the ion-exchange reaction significantly improved the production yield from 20% to over 50%. After a thorough examination of the reaction, we gained insight into the underlying mechanisms and found that the use of hydrochloric acid provides two key benefits: accelerated production of borophene and isolation of high-purity products. This method has the potential to pave the way for the production of novel topological 2D materials with potential industrial applications.

Sn atomic layers attract considerable interest owing to their spin-related physical properties caused by their strong spin–orbit interactions. We performed Sn intercalation into the graphene/SiC(0001) interface and found a new type of Sn atomic layer. Sn atoms occupy on-top sites of Si-terminated SiC(0001) with in-plane Sn–Sn bondings, resulting in a triangular lattice. Angle-resolved photoemission spectroscopy revealed characteristic dispersions at and points, which agreed well with density functional theory calculations. The Sn triangular lattice atomic layer at the interface showed no oxidation upon exposure to air, which is useful for characterization and device fabrication ex situ. [ABSTRACT FROM AUTHOR]

The symmetry of a surface or interface plays an important role in determining the spin splitting and texture of a two-dimensional band. Spin-polarized bands of a triangular lattice atomic layer (TLAL) consisting of Sn on a SiC(0001) substrate is investigated by spin- and angle-resolved photoelectron spectroscopy. Surprisingly, both Zeeman- and Rashba-type spin-split bands, without and with spin degeneracy, respectively, coexist at a K point of the Sn TLAL. The K point has a threefold symmetry without inversion symmetry according to the crystal structure including the SiC periodicity, meaning that the Zeeman-type is consistent with the symmetry of the lattice while the Rashba-type is inconsistent. Our density functional calculations reveal that the charge density distribution of the Rashba-type (Zeeman-type) band shows (no) inversion symmetry at the K point. Therefore, the symmetry of the charge density distribution agrees with both types of the spin splitting. [ABSTRACT FROM AUTHOR]

Electronic states of the topological insulator Bi1-xSbx, which is nontrivial in terms of both the Z2 index and the mirror Chern number, were studied by quasiparticle interference (QPI) using low-temperature scanning tunneling spectroscopy. Our Fourier-transform analysis of the QPI patterns reveals the dispersion of the two surface bands above the Fermi energy (EF). Absence of the surface band crossing is unambiguously confirmed, which allowed us to elucidate the mirror Chern number of this system is -1. We also found that Co atoms deposited onto a clean surface of Bi1-xSbx create impurity states with a clover-leaf-like shape at around 80 meV above EF. While additional spin-flipping scatterings due to those Co atoms cannot be detected by QPI because of the inherent absence of interference between states with antiparallel spins, we observed clear enhancement of spin-conserving scatterings after Co deposition. [ABSTRACT FROM AUTHOR]

We present a method of producing a densely ordered array of epitaxial graphene nanoribbons (GNRs) using vicinal SiC surfaces as a template, which consists of ordered pairs of (0001) terraces and nanofacets. Controlled selective growth of graphene on approximately 10 nm wide (0001) terraces with 10 nm spatial intervals allows GNR formation. By selecting the vicinal direction of SiC substrate, [11̅ 00], well-ordered GNRs with predominantly armchair edges are obtained. These structures, the high-density GNRs, enable us to observe the electronic structure at K points by angle-resolved photoemission spectroscopy, showing a clear band-gap opening of at least 0.14 eV. [ABSTRACT FROM AUTHOR]

Graphene, a two-dimensional carbon crystal with a gas of massless Dirac fermions, has promise as a material that is useful in photonic and optoelectronic devices. A comprehensive understanding of carrier cooling in photoexcited graphene is necessary for their applications, however, as competing cooling processes, electron-phonon scattering, and supercollisions, complicate the problem. Specifically, in energy harvesting, supercollision promotes further carrier cooling and, therefore, leads to lower efficiency, placing doubt on the feasibility of device applications. Here we present evidence of suppressed supercollisions in trilayer graphene on a SiC(0001) substrate by directly observing photoexcited carriers and numerically analyzing a phenomenological two-temperature model. Knowing that supercollisions restrict the capabilities of graphene-based devices, our results provide a breakthrough for improving their performance. [ABSTRACT FROM AUTHOR]

Honeycomb structures of group IV elements can host massless Dirac fermions with nontrivial Berry phases. Their potential for electronic applications has attracted great interest and spurred a broad search for new Dirac materials especially in monolayer structures. We present a detailed investigation of the β12 sheet, which is a borophene structure that can form spontaneously on a Ag(111) surface. Our tight-binding analysis revealed that the lattice of the β12 sheet could be decomposed into two triangular sublattices in a way similar to that for a honeycomb lattice, thereby hosting Dirac cones. Furthermore, each Dirac cone could be split by introducing periodic perturbations representing overlayer-substrate interactions. These unusual electronic structures were confirmed by angle-resolved photoemission spectroscopy and validated by first-principles calculations. Our results suggest monolayer boron as a new platform for realizing novel high-speed low-dissipation devices. [ABSTRACT FROM AUTHOR]

Epitaxial graphene growth on SiC surfaces is considered advantageous in terms of device application. However, the first graphitic layer on SiC transforms to a buffer layer because of strong coupling with the substrate. The properties of several subsequent layers are also significantly degraded. One method to decouple graphene from the substrate is Si intercalation. In the present work, we report observation and analysis of interface structures formed by Si intercalation in between the graphene layer and the SiC(0001) surface depending on Si coverage and influence of these interfaces on graphene electronic structure by means of low-energy electron diffraction (LEED), scanning tunneling microscopy (STM), angle-resolved photoemission spectroscopy (ARPES), and theoretical first-principles calculations. The STM appearance of observed periodic interface structures strongly resembles previously known Si-rich phases on the SiC(0001) surface. Based on the observed range of interface structures we discuss the mechanism of graphene layer decoupling and differences in stability of the Si-rich phases on clean SiC(0001) and in the graphene/SiC(0001) interface region. We also discuss a possibility to tune graphene electronic properties by interface engineering. [ABSTRACT FROM AUTHOR]

The search for metallic boron allotropes has attracted great attention in the past decades and recent theoretical works predict the existence of metallicity in monolayer boron. Here, we synthesize the β12-sheet monolayer boron on a Ag(111) surface and confirm the presence of metallic boron-derived bands using angle-resolved photoemission spectroscopy. The Fermi surface is composed of one electron pocket at the Spoint and a pair of hole pockets near the X point, which is supported by the first-principles calculations. The metallic boron allotrope in β12 sheet opens the way to novel physics and chemistry in material science. [ABSTRACT FROM AUTHOR]