Controllable epitaxial growth of GeSe2nanostructures and nonlinear optical properties

Germanium diselenide (GeSe₂) has emerged as a new member of anisotropic two-dimensional (2D) materials and gained increasing attention because of its excellent air stability, wide band gap and unique anisotropic properties, which exhibits promising applications in the fields of electronics, optoelectronics and polarized photodetection. However, the controllable epitaxial growth of large-scale and high-quality GeSe₂nanostructures to date remains a big challenge. Herein, GeSe₂nanofilms with lateral size up to centimeter scale have been successfully prepared on mica substrate by employing chemical vapor deposition technique. Experimental results demonstrated that hydrogen is the key factor for the controllable growth of GeSe₂nanostructures and GeSe₂-based heterostructures. Corresponding growth mechanism was proposed based on systematical characterizations. The nonlinear optical properties of as-prepared GeSe₂were investigated by employing open-aperture z-scan technique exhibiting significant saturable and reverse saturable absorption behaviors at wavelengths of 400 nm and 800 nm, respectively. This study provides a new and robust route for fabricating GeSe₂nanostructures and 2D heterostructures, which will benefit the development of GeSe₂-based nonlinear optical and optoelectronic devices.

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.