Figure 3: The optical properties and band structure of GeCH₃.

(a) DRA (red) and PL (blue) of GeCH₃. (b) DRA spectra of GeH (blue) and GeCH₃ (red) plotted in Kubelka-Munk function versus photon energy. (c) Electronic band structure of a bilayer GeCH₃ unit cell calculated using the hybrid HSE06 theory including spin-orbit coupling with experimental lattice parameters (3.96 Å) predicting a 1.82 eV direct band gap. The hole and electron effective masses for each extrema are indicated in red. (d) Images of GeCH₃ photoluminescence of crystals (left) and in suspension in isopropanol (right), upon illumination with a handheld 365 nm light. Scale bars, 1 cm. (e) PL intensity of exfoliated GeCH₃ thin flakes having average thicknesses ranging from 13–65 nm. Inset is the raw photoluminescence spectra of flakes with the thickness of 13 nm (wine), 27 nm (violet), 29 nm (orange), 31 nm (olive), 49 nm (magenta) and 65 nm (blue).