After that, a solution of ethanol and
demineralized water for 5 min was used to clean the surface. A subsequent
treatment was carried out by immersion in a solution of
demineralized water and hydrofluoric acid (HF) for 1 min (first acid
etching). After one washing in demineralized water, the samples were
put in a second hot solution of H2O, sulfuric acid (H2SO4) and hydrochloric
acid (HCl) for 8 min (second acid etching). A final washing
with ethanol and demineralized water was performed