Printing homogeneous single-layer oxidized graphene (SOG) via excimer UV for engineering graphene FETs

UV treatment is a feasible method to produce homogeneous graphene oxide (GO), which is not only crucial to unlocking its enormous potential applications but also allows us to adjust graphene FET characteristics. However, the oxidation rate of graphene under a UV environment is highly sensitive to UV bandwidth and irradiation time. In this work, we utilize an excimer UV in an ambient environment to synthesize single-layer oxidized graphene (SOG). First, we discuss multiple oxidation phases and defect types by analyzing correlations between XPS and Raman spectra. The main three stages are namely, polymer residual cleaning, oxidation, and defective lattice. Nonetheless, the optimal condition lies within 60 s of UV irradiation with ~20% oxygen content as epoxide (C-O-C) groups on the graphene plane. AFM and TEM images confirm the preservation of graphene lattice at optimized oxidation conditions with an average thickness of 0.79 nm. Additionally, we exploited this technique to modify the performance of CVD-graphene FETs. Since SOG exhibits insulating electrical properties compared to monolayer graphene, we employed e-beam lithography and PMMA mask to isolate and pattern graphene channels in FETs. As result, UV patterned devices show well-defined edges with homogeneous epoxide groups at their boundaries compared to plasma etching which typically shows highly defective edges inhibiting random functionalities. This opens up the possibility of printing numerous graphene-SOG interfaces for a wide range of applications where the graphene boundary sharpness is only limited by lithography precision.