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 (approximate to 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 m(2) were 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.