Monolayer graphene was fabricated on silicon carbide (SiC) (0001) face by thermal decomposition of SiC single crystal of 5 cm in diameter. The reaction of SiC substrate with aqueous potassium hydroxide (KOH) by photo-electrochemical etching reduced the interaction force between graphene and SiC substrate

and the quasi-free-standing bilayer graphene was obtained by removal of buffer layer between graphene and SiC substrate. Numerous conditions of current densities and illumination intensities were studied. The optimal condition to remove graphene buffer layer

which would synchronously obtain free standing graphene film in the highest quality

was estimated to be in the current intensity of 6 mA·cm-2 when samples held the distance of 3 cm to UV light source. Among three current densities of 3

6 and 9 mA·cm-2

Raman spectra showed that the 6 mA·cm-2 current density was the most suitable for etching process. The decoupling effect of graphene buffer layer showed a positive correlation to UV light intensity in a certain range. Raman and XPS spectra on graphene film prepared under optimized condition showed broken bonds between SiC substrate and in-situ grown buffer layer and characteristics of free standing graphene film. The removal of graphene buffer layer was shown by disappearance of characteristic S1 and S2 peaks of buffer layer in XPS C1s spectra. The chemical reaction dynamics in etching process was proposed by analyzing electrochemical voltage-time curves.