conductive FM-KPFM FrictionalForce GaAs optoelectronics Topography LDPE WS2 Sic frequency_modulation Polystyrene OrganicSemiconductor MBE AtomicSteps Graphene Sidewall SSRM DNA UnivCollegeLondon Sio2 Alkane SiliconOxide layers Polymer Al2O3 MoirePattern Insulator FrequencyModulation Piezo Au111 AM_SKPM TempControl Composite ULCA domain_switching