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.