Potassium fluoride,anhydrous
           Potassium fluoride,extra pure
           Potassium fluoride,Granular
           Silicon Dioxide
           Hydrofluoric acid
           Synthetic Cryolite
           Potassium Fluoaluminate
           Ammonium bifluoride
           Potassium Bifluoride
           Aluminium fluoride
           Sodium fluoride
           Potassium Fluorosilicate
           Fluorosilicic Acid
           Sodium silicofluoride
           Potassium Hydroxide Flakes
           Magnesium Fluoride
           Magnesium fluorosilicate
           Barium Fluoride
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To assess the effect of etching on the surface properties, a com-plete chemical and topographical characterization was carried outon samples etched in Hydrofluoric acid  40%.The surface morphology was observed by SEM and the elemen-tal composition was determined by EDS. An XPS analysis similar tothe one described in 2.5 allowed to quantify the elements consti-tuting the first nanometers of the surface and to determine theirchemical state. Following the same methodology as described in 2.3, AFM andWLI measurements were performed on respectively three and tensamples per experimental point. From these measurements, the 3Droughness parameters described were determined.

The observation by TEM of the particles present in suspensionin the DI water used for ultrasonic cleaning of samples etched twohours in Hydrofluoric acid 40% showed the presence of octahedral particles (octa-hedrons) and needle-like particles (needles). The selected area electron diffraction (SAED) pattern of an octa-hedron showed a crystalline structure, which is consistent with their regular shape. The SAED of a needle revealed a texturedpolycrystalline structure. In both patterns, low intensity quasi-amorphous rings were observed. 

SEM observations of the surface in the “as etched” state (no ultrasonic cleaning) after etching in Hydrofluoric acid  40% for: (a) 20 min, (b) 40 min, (c) 60 min, (d) 90 min, (e) 120 min,(f) 120 min (high magnification). After the cleaning procedure, SEM inspection of the samples did not evidence any remaining octahedrons or “adhered layer” on thesurface, confirming the ultrasonic cleaning efficiency. Regardingthe preferentiality of the etching, SEM observations showed thatthe attack was both intergranular and intragranular (grain size ofthe original material measured by the intercept method: 0.3 μm),being slightly faster at the grain boundaries and demon-strated a substantial evolution of the morphology at different scalesdepending on etching time. Nevertheless, observations athigh magnification showed no significant evolution of the granulartexture. On the other hand, the presence of randomly dispersed pitswas detected on the surface.For both AFM and WLI measurements, the texture aspect ratio(Str) approached the value of one when increasing the etching dura-tion, which evidenced that the process leads to an isotropic surface.