Patterning GaSe by High-Powered Laser Beams

We report the high-powered laser modification of the chemical, physical, and structural properties of the two-dimensional (2D) van der Waals material GaSe. Our results show that contrary to expectations and previous reports, GaSe at the periphery of a high-power laser beam does not entirely decompose into Se and Ga₂O₃. In contrast, we find unexpectedly that the Raman signal from GaSe gets amplified around regions where it was not expected to exist. Atomic force microscopy (AFM), dielectric force microscopy (DFM), scanning electron microscopy (SEM), and energy-dispersive X-ray spectroscopy (EDX) results show that laser irradiation induces the formation of nanoparticles. Our analyses demonstrate that, except for a fraction of Ga₂Se₃, these nanoparticles still belong to the GaSe phase but possess different electrical and optical properties. These changes are evidenced in the increased Raman intensity attributed to the near-resonance conditions with the Raman excitation laser. The elemental analysis of nanoparticles shows that the relative selenium content increased to as much as 70% from a 50:50 value in stoichiometric GaSe. This elemental change is related to the formation of the Ga₂Se₃ phase identified by Raman spectroscopy at some locations near the edge. Further, we exploit the localized high-power laser processing of GaSe to induce the formation of Ag-GaSe nanostructures by exposure to a solution of AgNO₃. The selective reaction of AgNO₃ with laser-irradiated GaSe gives rise to composite nanostructures that display photocatalytic activity originally absent in the pristine 2D material. The photocatalytic activity was investigated by the transformation of 4-nitrobenzenethiol to its amino and dimer forms detected in situ by Raman spectroscopy. This work improves the understanding of light-matter interaction in layered systems, offering an approach to the formation of laser-induced composites with added functionality.