Laser-Synthesized Amorphous PdSe${}_{2-\mathrm{x}}$ Nanoparticles: A Defect-Rich Platform for High-Efficiency SERS, Photocatalysis, and Photothermal Conversion

Abstract

The control of material properties at the atomic scale remains a central challenge in materials science. Transition metal dichalcogenides (TMDCs) offer remarkable electronic and optical properties, but their functionality is largely dictated by their stable crystalline phases. Here we demonstrate a single-step, ligand-free strategy using femtosecond laser ablation in liquid to transform crystalline, stoichiometric palladium diselenide (PdSe${}_2$) into highly stable, amorphous, and non-stoichiometric nanoparticles (PdSe${}_{2-\mathrm{x}}$, with x$\approx$1). This laser-driven amorphization creates a high density of selenium vacancies and coordinatively unsaturated sites, which unlock a range of emergent functions absent in the crystalline precursor, including plasmon-free surface-enhanced Raman scattering with an enhancement factor exceeding 10${}^6$, a 50-fold increase in photocatalytic activity, and near-infrared photothermal conversion efficiency reaching 83$\%$. Our findings establish laser-induced amorphization as a powerful top-down approach for defect-engineered TMDCs and advances their practical usage in optics, catalysis, and nanomedicine.