Nanomorphological investigation of graphite surface after cryo-ultrasonication in liquid nitrogen by atomic force microscopy

Mineral graphite has been effectively used to produce high quality graphene sheets, and a promising top-down approach for the production of graphene from graphite is liquid-phase exfoliation (LPF) because of its versatility and intrinsic ease of operation. Here, the work introduces a novel method for LPF, and they present preliminary results on the effects of ultrasonication assisted LPF of graphite in liquid nitrogen (cryo-ultrasonication at 77 K), comparing it with untreated graphite and graphite exfoliated by ultrasonication in distilled water at room temperature (∼300 K). Atomic force microscopy was employed to investigate and to assess at the nanoscale the effect of the cryo-ultrasonication on the exfoliation of the graphite surface. Various graphene single-layers with an area of >0.2 μm2were obtained after cryo-ultrasonication in liquid nitrogen working at 40 kHz, 100 W for 10 min. The present investigation demonstrates that graphene single-layers can be easily produced by ultrasonication assisted LPF of graphite immersed in liquid nitrogen.