NUS_Physics Ptfe phase_change Annealed atomic_layer HOPG hard_disk PhaseChange strontiu_titanate temp Mapping ring shape CP-AFM Beads Barium_titanate Force-distance Piezoresponse OpticalModulator STM Chungnam_National_University PtfeMembrane VortexCore Spincast FloppyDisk SrO KAIST fe_nd_b frequency_modulation MeltingPoint Blend Spain ContactModeDot AM_SKPM Sadowski HexacontaneFilm