Ultra-short pulsed laser deposition of thin silver films for surface enhanced Raman scattering

Nanostructured thin films have been obtained by ultra-short pulsed laser deposition (PLD) of silver performed in vacuum. The ablation source used in these experiments was a frequency doubled (λ = 527 nm) Nd:glass laser with a pulse duration of 250 fs. The films have been characterized by UV–vis spectroscopy, atomic force microscopy and transmission electron microscopy. The surface enhanced Raman scattering activity results, investigated by Raman scattering of rhodamine B adsorbed onto rough silver substrates, are strongly related to the effective surface area (ESA) of the silver surfaces. Surprisingly, silver films obtained by ultra-short PLD are very similar to those obtained by short PLD. With the aim of explaining this likeness, the dynamics of plasmas induced by short and ultra-short laser pulses have been studied by optical emission spectroscopy and fast imaging. Composition, velocity, excitation temperature and density of short and ultra‐short plasmas are quite similar, showing that film properties are strongly related to the plasma features.