LIPSS formation by picosecond laser irradiation of magnetron sputtered CGO thin films
Résumé
The interaction between ultrashort laser beam pulses with thin films induces the
formation of surface micro/nanostructures. These laser-induced periodic surface
structures (LIPSS), or ripples, could improve the physico-chemical properties of thin
films including their specific surface. In the case of electrochemical cells made of an
assembly of thin films, they can further improve the performance of the electrode by
increasing the specific contact surface by laser structuring of a wide range of
materials which is an increasingly powerful technique for species active at the
electrode / electrolyte interface.
In this work, a picosecond Nd: YAG laser operating at its third harmonic (λ=355 nm)
is used to irradiate the surface of gadolinium-doped ceria (CGO) thin films, grown by
on yttria-stabilized zirconia (YSZ) by magnetron sputtering. The morphological
characteristics of the thin films and their structuring were observed by high resolution
scanning electron microscopy (HR-SEM). LIPSS are generally produced in a low
fluence laser multi-pulse regime close to the ablation threshold. They were obtained
with the period of approximately 283 nm under appropriate values of laser fluence (F
from 184 to 295 mJ/cm2) and scanning speed (0.2 mm/s to 0.4 mm/s). Exceeding
the threshold leads to surface ablation. In agreement with the literature, it has been
noted that these periodic structures can be classified as Low Spatial Frequency
LIPSS (LSFL) or High Spatial Frequency LIPSS (HSFL). The LSFL period is
generally close to the beam wavelength λ, presenting a period varying in 0.5λ-λ. On
the other hand, HSFL refers to ripples having a period smaller than the beam
wavelength (< 0.5λ). Our work focusses on the optimization of laser parameters to
generate clear and high resolution LSFL/HSFL without ablating the CGO layer.
Using numerical tools for SEM/AFM images, the enhancement of the specific surface
of the CGO films will also be discussed.