(using a 40 mA current for 60 s) in a SCD 050 sputtercoater (Oerlikon-Balzers, Balzers,Liechtenstein). These sputtering conditions resulted in a gold layer of 16 nm. Both equipments were available at the National Laboratory of Nanotechnology (LNNano) located in Campinas-SP/Brazil.Analyses of the sample surfaces were performed under vacuum,using a 5 kV acceleration voltage.