PVAC solar_cell PANI Photovoltaics Vinylpyridine GaN HexacontaneFilm Piezo FrequencyModulation Al2O3 atomic_steps cross section StyreneBeads PtfeFilter Oxidation Optical LMF Fet HDD Polydimethylsiloxane FrictionForce Etch Hexacontane Annealing mfm_amplitude Hysteresys Fiber Graphite TemperatureControlledAFM Liquid Chloroform ForceVolumeMapping Varistor GranadaUniv ferromagnetic