kelvin probe force microscopy Heat temperature controller AFM Pzt Iron GalliumPhosphide Nanofiber NtuEee Laser Mosfet polyvinyl acetate Friction Morphology PinPointMode FrequencyModulation Corrosion Electrode Chromium Lattice PtfeMembrane Strontium SurfaceChange Pinpoint FM_SKPM GaP Chungnam_National_University Protein TCS Graphene Potential Sulfur optoelectronics UnivMaryland DNAProtein bias_mode