Substrate effect on atomic force microscopy-based nanolithography of graphene

Atomic force microscopy (AFM)-based nanolithography is one of the commonly used techniques to fabricate graphene devices on different substrates. However, the patterned graphene varies with different substrate materials. We demonstrate, both experimentally and theoretically, that the required force to pattern graphene and the trench morphology is highly dependent on the substrate hardness and the interfacial adhesion energy between graphene and the substrate. A strong correlation is seen between the cutting force and the average width of the fractured graphene on a variety of substrates. In our experiments, we show that graphene trenches with ultrasmooth edges and narrow width down to 30 nm can be created on soft substrates like gold under small applied forces, while only rough and wide trenches can be obtained on hard substrates (Si and SiO₂). Our studies reveal the effect of graphene-substrate interactions on the mechanics of AFM nanolithography process, thus paving the way for achieving controllable fabrication of graphene-based devices through an appropriate control of applied forces for the target substrate materials.