VortexCore mechanical property ConductiveAFM FAPbI3 Water WS2 PiezoelectricForceMicroscopy Topography kelvin probe force microscopy HBN pinpoint mode Hafnium_dioxide Nanofiber TransitionMetal PolyStylene PetruPoni DNAProtein Switching Copolymer AM-KPFM PS_PVAC MonoLayer Ram NiFe Spain INSPParis tip_bias_mode NtuEee DNA MagneticArray biocompatible Polyurethane alkanes membrane Polyvinylidene_fluoride