Femtosecond Laser Writing of Pd Patterns with Nanoflower Morphology on Silicon

We report a single‑step, maskless route to fabricate palladium patterns directly on silicon using ultrashort‑pulse laser writing under a Pd‑salt solution. Varying the precursor concentration controls the morphology over a broad range. At ~10−6 M, the substrate shows subwavelength ripples characteristic of laser‑induced periodic surface structures (LIPSS) with no detectable Pd. At higher concentrations, the ripples become decorated with Pd nanoparticles, which then coalesce into continuous films that inherit the grooved relief, while at ≥10−3 M nanoflower‑like dendrites emerge. Arbitrary patterns (including line arrays, net‑like lattices, and dot arrays) are written with micrometer pitches and clear gaps between features. Post‑oxidation at 450°C converts Pd to PdO, as confirmed by the ~640 cm−1 Raman band. These Pd and PdO structures, with tunable nanoscale morphology, offer a direct pathway to integrated optical and resistive hydrogen‑sensor elements for on‑chip leak detection and safety monitoring across hydrogen production, storage, and distribution.