MolybdenumDisulfide PinpointPFM Roughness HiVacuum Vortex LiquidCrystal bias_mode TappingMode Mechinical contact Molybdenum_disulfide membrane PvdfBead MultiferroicMaterials FFM TransitionMetal StyreneBeads FrictionForce Vanadate HardDisk Optoelectonics self-assembled_monolayer KPFM BreastCancerCell GranadaUniv UnivMaryland Polystyrene Butterfly HBN Sio2 Blood Ni81Fe19 2-vinylpyridine Techcomp LeakageCurrent