Comparative study of GaAs nanostructures synthesized in air and distilled water by picosecond pulsed laser ablation and application in hazardous molecules detection

Abstract

This work explored the fundamental differences/mechanisms between the GaAs substrates ablated in two different media of air and distilled water (DW). A scan area of 5 × 5 mm2 was ablated by a picosecond laser with a pulse duration of 30 ps, a repetition rate of 10 Hz, a wavelength of 1064 nm, and a pulse energy of 2 mJ. The spacing between raster scan lines was varied (0.05–0.35 mm), keeping the scan speed (0.15 mm/s) constant. The obtained GaAs nanostructures (NSs) were thoroughly analyzed using microscopy techniques. A clear increase in separation between the raster scan lines was observed with an increase in the scan spacing for the GaAs NSs fabricated in air, whereas the same result was not observed in DW. Moreover, structures with debris were formed in air irrespective of the spacing, unlike the formation of uniform quasiperiodic GaAs NSs throughout the sample in the case of DW ablation. To the best of our knowledge, there are no reports on the detailed studies involving DW in the fabrication of quasiperiodic NSs of GaAs. Further, these quasiperiodic GaAs NSs formed in DW were coated with a thin layer of gold using the thermal evaporation method, annealed at 400 °C for 1 h in an ambient atmosphere. As a consequence of annealing, Au NPs were uniformly decorated on the quasiperiodic NSs of GaAs imparting plasmonic nature to the whole structures. Subsequently, the Au NPs decorated GaAs NSs were utilized as surface enhanced Raman scattering substrates for the detection of methylene blue (dye molecule) and Thiram (pesticide molecule) at low concentrations.