3-hexylthiophene ForceVolumeImage Fujian suspended_graphene ring shape PANI STO frequency_modulation NCM University_of_Regensburg YszSubstrate ContactModeDot SKKU atomic_steps GalliumPhosphide ContactMode Vinylpyridine margarine PhaseImaging ContactModeDots BTO Ram LiftMode Gold hard_disk Co/Cr/Pt OpticalModulator PFM FrequencyModulation Resistance StrontiumTitanate PinpointNanomechanicalMode FrictionForce TiO2 WS2