Direct Evidence of Dirac Signature in Bilayer Germanene Islands on Cu(111)

Abstract

Bernal-stacked bilayer germanene with a stable buckled honeycomb structure has been successfully synthesized on Cu(111). Structural and electronic characterizations as well as theoretical calculations unequivocally demonstrate for the first time the presence of a nearly linear energy dispersion in the vicinity of the Fermi energy, as expected of the Dirac signature for theoretical freestanding germanene.

Recent Progress on Germanene and Functionalized Germanene: Preparation, Characterizations, Applications, and Challenges

“…Unfortunately, the buckled germanene layer also has two parabolic bands that cross the Fermi level at the Γ point, which might suppress the anomalous quantum Hall effect as well as the transport properties that are found in 2D Dirac systems. The strength of the germanene–substrate interaction is weakened in bilayer germanene on Cu(111) surfaces (Figure c), where a V‐shaped differential conductivity curve is shown around the Fermi level as a typical feature of 2D systems (Figure g) . As the STS is an integral result of the density of states, this is not conclusive evidence for Dirac fermions.…”

“…Germanene has been successfully fabricated by epitaxial growth on metallic substrates, such as Pt(111), Al(111), Cu(111), Au(111), and Ag(111) . It was found that the reconstructed germanene on the metallic surface is likely to lose its massless Dirac fermion characteristic due to hybridization, strain, and electronic doping effects .…”

“…c) STM image of 1 × 1 germanene/√3 × √3 Cu(111) ( V = 0.06 V, I = 0.07 nA). Reproduced with permission . Copyright 2017, Wiley‐VCH.…”

“…Inset: STS spectrum collected from the bare Cu(111) and repeatedly verifying the condition of the tip ( V = 1.0 V, I = 0.1 nA). Reproduced with permission . Copyright 2017, Wiley‐VCH.…”

Raman Studies on Silicene and Germanene

“…28 Furthermore, another peak located at 165 cm −1 corresponds to the out-of-plane transverse optical (oTO) phonon branch at G, which is evoked by the larger buckling value compared to that of silicene. 28 Experimentally, germanene has been successfully fabricated on metallic and semiconducting substrates, including Au(111), [64][65][66] Pt(111), 67 Al(111), 68 Cu(111), 69 Sb(111) 70 and molybdenum disulfide, 71 as there is no bulk allotrope of FS germanene in nature. The superstructures are formed on the top of these substrates instead of 1×1 FS germanene, in which different buckling structures and phonon properties are expected.…”