Investigation of weak interlayer coupling in 2D layered GeS2 from theory to experiment

Interlayer coupling as a unique feature for two-dimensional (2D) materials may influence their thickness-dependent physical properties, especially the bandgap due to quantum confinement effect. Widely-studied 2D materials usually possess strong interlayer coupling such as most of transition metal dichalcogenides (TMDs), PtS2 and so on. However, 2D materials with weak interlayer coupling are rarely referred that mainly focus on ReS2, as well as its counterpart ReSe2. Here we report a new member of weak interlayer coupling 2D materials, germanium disulfide (GeS2). The interlayer interaction in GeS2 is investigated from theory to experiment. By density functional theory calculations, we find that this extraordinarily weak interlayer coupling in GeS2 originates from the weak hybridization of interlayer S atoms. Thickness-dependent Raman spectra of GeS2 flakes exhibit that the Raman peaks remain unchanged when increasing the thickness; and a small first-order temperature coefficient of -0.00857 cm(-1).K-1 is obtained from the temperature-dependent Raman spectra. These experimental results further confirm the weak interlayer coupling in GeS2.

Automated summary

The study reveals that germanium disulfide (GeS2) is a new type of two-dimensional material with weak interlayer coupling, originated from the weak hybridization of interlayer sulfur atoms. The thickness-dependent Raman spectra of GeS2 show minimal changes as thickness increases, and a small first-order temperature coefficient was obtained from temperature-dependent Raman spectra, confirming the weak interlayer coupling in GeS2.