Reduction BiFeO3 SKPM 3-hexylthiophene BoronNitride phase_change gallium_nitride Chromium aluminum_nitride SKKU IRDetector Laser MetalCompound HanyangUniv Potential Regensburg FrequencyModulation Conductivity lithography BiVO4 KPFM DIWafer Gallium temp_control Varistor Silicon Hexacontane Polyethylene SurfaceOxidation Microchannel TemperatureControl amplitude_modulation KelvinProbeForceMicroscopy NiFe ring shape