Weak Interlayer Interaction in 2D Anisotropic GeSe₂

Germanium diselenide (GeSe₂) has recently emerged as a new member of in-plane anisotropic 2D materials, notable for its wide bandgap of 2.74 eV, excellent air stability, and high performance in polarization-sensitive photodetection. However, the interlayer interaction in GeSe₂ has never been reported, which usually plays an important role in layer-number-dependent physical properties. Here, the interlayer coupling in GeSe₂ is systematically investigated from theory to experiment. Unexpectedly, all of density functional theory (DFT) calculations about layer-dependent band structures, cleavage energy, binding energy, translation energy, and interlayer differential charge density demonstrate the much weaker interlayer interaction in GeSe₂ when compared with black phosphorus (BP). Furthermore, both thickness-dependent and temperature-dependent Raman spectra of GeSe₂ flakes, which exhibit no detectable changes of Raman peaks with the increase in thickness and a small first-order temperature coefficient of -0.0095 cm^-1 K^-1, respectively, experimentally confirm the weakly coupled layers in GeSe₂. The results establish GeSe₂ as an unusual member of in-plane anisotropic 2D materials with weak interlayer interaction.