TipBiasMode KAIST PtfeFilter 2dMaterials CVD Zagreb Growth PS_LDPE Gong Tape PinpointPFM Moire suspended_graphene HOPG UnivCollegeLondon Boron Hexacontane KPFM MolybdenumDisulfide FM_KPFM GalliumPhosphide hetero_structure Polydimethylsiloxane amplitude_modulation kelvin probe force microscopy HighAspect Polytetrafluoroethylene CastIron contact Electrode LiquidCell Cross-section Ferrite polymeric_arrays VerticalPFM