Electrical control of nanoscale functionalization in graphene by the scanning probe technique

Functionalized graphene is a versatile material that has well-known physical and chemical properties depending on functional groups and their coverage. However, selective control of functional groups on the nanoscale is hardly achievable by conventional methods utilizing chemical modifications. We demonstrate electrical control of nanoscale functionalization of graphene with the desired chemical coverage of a selective functional group by atomic force microscopy (AFM) lithography and their full recovery through moderate thermal treatments. Surprisingly, our controlled coverage of functional groups can reach 94.9% for oxygen and 49.0% for hydrogen, respectively, well beyond those achieved by conventional methods. This coverage is almost at the theoretical maximum, which is verified through scanning photoelectron microscope measurements as well as first-principles calculations. We believe that the present method is now ready to realize ‘chemical pencil drawing’ of atomically defined circuit devices on top of a monolayer of graphene. Nanoscale functionalized graphenes are fabricated by atomic force microscopy lithography with the desired coverage of a selective functional group using the simple method of the electrical control, and their recovery through moderate thermal treatments. Surprisingly, our controlled coverage of functional groups can reach 94.9% for oxygen and 49.0% for hydrogen, well beyond the coverage achieved by conventional methods. Attaching atoms, such as oxygen and hydrogen, to graphene alters its conductivity and introduces semiconducting bandgaps — a valuable trick for researchers seeking to fine-tune the electrical behavior of this ultrathin material. But achieving nanoscale control over graphene's surface chemistry is challenging; conventional lithographic patterning leaves behind charge scattering centers that can upset device performance. Bae Ho Park from Konkuk University in South Korea and co-workers have discovered a way to ‘draw’ atomically defined circuit patterns on graphene using a conductive atomic force microscope (AFM). By applying either a positive or negative voltage to graphene samples, the team selectively generated small-scale regions of surface oxygen or hydrogen atoms with the scanning AFM tip. Intriguingly, this method yields functional group coverage close to the theoretical maximum — a significant improvement over existing methods.