Thickness dependent band structure of α-bismuthene grown on epitaxial graphene

Abstract

Along with the great interest in two-dimensional elemental materials that has emerged in recent years, atomically thin layers of bismuth have attracted attention due to physical properties on account of a strong spin-orbit coupling. Thickness dependent electronic band structure must be explored over the whole Brillouin zone in order to further explore their topological electronic properties. The anisotropic band structures along zig-zag and armchair directions of α-bismuthine (α-Bi) were resolved using the two-dimensional mapping of angle-resolved photoemission spectra. An increase in the number of layers from 1- to 2-bilayers (BLs) shifts a small hole pocket on Γ-X1 line to high wavenumber regions. Subsequently, this hole pocket transforms into an electron pocket, and another hole pocket centred at Γ point appears in the 3 BL α-Bi. Gapless Dirac-cone features with a large anisotropy were clearly resolved on X2 point in the 1-BL and 2-BL α-Bi, which can be attributed to the strong spin-orbit coupling and protection by the nonsymmorphic symmetry of the α-Bi lattice.

Morphology of Bi(110) quantum islands on epitaxial graphene

“…the shorter axis in real space, which corresponds to the zig-zag direction of Bi(110) (see also the inset of figure 2(c)), is aligned approximately with the armchair direction of graphene. However, it is misaligned by ±(1.75 ± 0.5) • , resulting in two sub-domains, as already observed by Takahashi et al [15], and indicated by solid and dotted lines in figure 1(a). For reference, figure 1(b) shows the LEED image for a Bi coverage of 0.15 BL, where the Bi spots are barely visible, i.e.…”

“…The amount was controlled by a quartz crystal microbalance. The thickness calibration was done by observing the conductance oscillations during the deposition of Bi on a Bi(111) film on Si(111) at a substrate temperature of 12 K, and then converting the result from Bi(111) bilayers (1BL = 1.14 × 10 15 atoms cm −2 ) to Bi(110) bilayers (1BL = 1.85 × 10 15 atoms cm −2 [15]). The Bi layers were investigated as deposited and after an annealing step at 410 K for 30 min.…”

“…For these reasons, it is not surprising that the structure of bismuth coatings on graphene has already been the focus of many experiments [15][16][17][18]. In particular, it was found that small ultrathin coverages of Bi on graphene are island-like and have the structure of α-bismuthene [19], i.e.…”

“…However, the conditions under which previous experiments were performed were somewhat different. Takahashi et al deposited Bi on triple-layer graphene/SiC at 100 • C [15], while in other experiments, monolayer graphene was used as the substrate at room temperature (RT) [16,18]. In [15], the experiment was performed on a substrate containing a mixture of monolayer graphene and buffer layer areas.…”

“…Takahashi et al deposited Bi on triple-layer graphene/SiC at 100 • C [15], while in other experiments, monolayer graphene was used as the substrate at room temperature (RT) [16,18]. In [15], the experiment was performed on a substrate containing a mixture of monolayer graphene and buffer layer areas. Therefore, it is obvious that conducting thorough and consistent studies to reveal the details of the structure of ultrathin Bi coatings on graphene formed by the same methodology is desirable and expedient.…”