Fabrication of 2D based pn junctions with improved performance by selective laser annealing

There is a growing body of research on transistors based on nanomaterials such as 2D transition metal dichalcogenides (TMDs) (WS2, MoS2, etc.) and carbon nanotubes (CNTs). Here we co-deposited MoS2 and WS2 as PN junctions. The deposition could be performed on a PCB (printed circuit board) with Cu electrodes. The current-voltage characteristics were obtained using an Arduino board. The effect of laser irradiation could be investigated by studying the IV curves and light sensitivity for the same kind of devices in which one of the Cu electrodes was modified by a laser. The IV curves from the devices with and without laser treatment could be compared to quantify the changes in performance

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