Stiffness Polypropylene Bismuth bias_mode NUS SrTiO3 China Polydimethylsiloxane ScanningKelvinProbeMicroscopy exfoliate molecular_self_assembly AIN Pinpoint multi_layer C_AFM FM_SKPM VerticalPFM Mechanical&nanotechnology AM-KPFM mechanical property Wonseok Varistor Ecoli CeramicCapacitor SiliconeOxide WS2 SelfAssembly SSRM ItoGlass Bacterium Aluminium_Oxide Sic BreastCancerCell KelvinProbeForceMicroscopy Nanopattern