Silver nano-entities through ultrafast double ablation in aqueous media for surface enhanced Raman scattering and photonics applications

Abstract

We have fabricated stable silver nanoparticles (NPs) and nanostructures (NSs) effectively through double ablation of bulk silver substrate immersed in double distilled water using ∼2 ps laser pulses. The effects of multiple/double/single ablation on silver substrates via surface morphology studies along with average size distribution of Ag NPs were investigated. Prepared Ag NPs in solution exhibited yellow color with an absorption peak near 410 nm, assigned to localized surface Plasmon resonance of nano-sized silver. Depending on the ablation parameters average sizes observed were ∼13 nm/∼17 nm in multiple/double ablation case and ∼7 nm in single ablation case. High resolution transmission electron microscope studies highlighted that most of the Ag NPs were spherical and polycrystalline in nature. Surface morphology of the substrates was characterized by field emission scanning electron microscope and atomic force microscope. A different scenario was observed in the double ablation case compared to single/multiple ablation case. Double ablation resulted in dome like NSs on the substrate with dimensions of few hundreds of nanometers while single ablation did not. Nonlinear optical (NLO) properties of Ag NPs were investigated using Z-scan technique with ∼2 ps pulses and corresponding NLO coefficients were obtained. Surface enhanced Raman scattering (SERS) studies on multiple/double ablated Ag substrates with adsorbed Rhodamine 6G molecules were carried out using excitation wavelengths of 532 nm, 785 nm, and three orders of enhancement in Raman signal intensity was observed. Furthermore, influence of laser fluence on the fabrication of SERS active Ag substrates with double ablation was also investigated. In this case, Raman spectra of adsorbed Research Department eXplosive (RDX) molecules on ablated surfaces were recorded for 532 nm and 785 nm excitation. Enhancements up to 460 were observed from substrates fabricated at fluences of 12 J/cm2, 16 J/cm2 with excitation wavelengths of 532 nm and 785 nm, respectively.