LDPE AM-KPFM piezoelectric force microscopy HanyangUniv SKKU Water Phosphide PMNPT ContactMode UnivCollegeLondon Multiferroic_materials Perovskite LogAmplifier LiquidImaging SRAM small_scan Pinpoint PFM MagneticForceMicroscopy StrontiuTitanate NUS_Physics molecular_beam VerticalPFM CalciumHydroxyapatite Change fifber Biofilm NusEce AIN NUSNNI MagneticPhase Conduct Plug Tapping FuelCell semifluorinated alkane