Fig. 6: Raman spectroscopy results for the GeSn bilayer.
From: Covalent bonded bilayers from germanene and stanene with topological giant capacitance effects
a The individual thickness of the Ge and Sn layers is estimated at ~0.3 nm. The Ge–Ge E1g and A1g modes are marked in black and red, respectively. The broad blue peak is attributed to surface phonons. b The \({A}_{{{{\rm{1g}}}}}^{{\prime} }\) in GeSn bilayer can be well fitted with a Lorentzian form (in red), showing that the peak is well defined and has a narrow FWHM ≈ 25 cm−1. c A schematic representation of the E1g and A1g vibrational modes in the Ge–Ge and Sn-Sn layers. d The transverse Ge–Sn \({A}_{{{{\rm{1g}}}}}^{{\prime} }\) vibration. The local Ge–Sn pyramidal cluster is shown in yellow. k is the Ge–Ge spring constant and k2 is the spring constant for the Ge–Sn bond. Ge and Sn atoms are shown in blue and red, respectively.
