Dental Step Al2O3 Ram ElectrostaticForceMicroscopy Spincast cooling Oxide Flake Vac 3-hexylthiophene CrAu Solution vertical_PFM Nanostructure Sapphire Silver GalliumPhosphide DomainSwitching PolyvinylideneFluoride fluoroalkane Annealing MESA structure PFM cross section LifeScience STM PS_LDPE Boundary SolarCell Carbon LateralForce LateralForceMicroscopy HanyangUniv SPMLabs