CuFoil Semiconductor Graphene ring shape NUS_NNI_Nanocore temp pinpoint mode Ram Kevlar Inorganic_Compound Potential vertical_PFM Scanning_Thermal_Microscopy Polydimethylsiloxane Sphere Techcomp polyvinyl acetate cross section EFM Copolymer heterojunctions SiliconOxide AAO PatternedSapphireSubstrat MagneticForceMicroscopy SThM Floppy PFM Electrode graphene_hybrid Calcite 3-hexylthiophene Annealed Bacteria PyroelectricDetector