• Semmar, Nadjib
• Rabat, Hervé
• Thomann, Anne-Lise
• Karim, Wael
• Tabbal, Malek
• Petit, Agnès

Abstract

In electrochemical cells based on ceramic electrolytes, a thin film of gadolinium-doped cerium oxide (GDC) is deposited between the electrolyte (yttrium-stabilized zirconia, YSZ) and the top electrode to improve resistance to aging. The increase in interface surface area is expected to benefit cell performance. This work investigates the formation of LIPSS (laser-induced periodic surface structures) on the surface of a 600 nm GDC thin film obtained by the magnetron sputtering method on screen-printed YSZ. A picosecond Nd: YAG laser operating at its third harmonic (=355 nm, 40 ps, 10Hz) was used to structure the surface of the GDC/YSZ layer after deposition, using both static and scanning irradiation modes of the laser beam. The various structures formed on the film surface after laser irradiation, mainly quasi-periodic LIPSS, were studied by scanning electron microscopy (SEM) and atomic force microscopy (AFM). Parallel and perpendicular LIPSS were formed simultaneously with periods varying from 220 to 300 nm, depending on beam fluence ranging from 30 to 160 mJ/cm2, and in a spot size of ~500 μm in static mode. The coexistence of the two orientations disappeared at a higher number of shots (N > 20), where only perpendicular structures were formed. Increasing the number of shots up to N> 50 led to a progressive ablation of the film followed by the start of a nano-structuring process of the YSZ substrate. The formation of parallel LIPSS is mainly attributed to the thermochemical process occurring on the GDC/YSZ film at the center of the irradiated zone corresponding to the highest local fluence. The same LIPSS orientations were found in scan mode by varying laser fluence and displacement stage parameters. For the latter mode, the effect of laser irradiation on the elemental composition of the films was studied by energy dispersive X-ray spectroscopy (EDX) and Rutherford backscattering (RBS) to verify the chemical stability of the film in the soft ablation process by accumulation effect. Finally, surface enhancement by LIPSS formation was estimated using atomic force microscopy (AFM) and a geometric surface enhancement coefficient that gave "theoretical" maximum values of 57% and 78% for 1D periodic structures (regular LIPSS) and 2D others respectively.

Topics

• impedance spectroscopy
• surface
• scanning electron microscopy
• thin film
• atomic force microscopy
• physical vapor deposition
• chemical stability
• Yttrium
• aging
• Energy-dispersive X-ray spectroscopy
• ceramic
• Gadolinium
• aging
• Rutherford backscattering spectrometry
• Cerium