Evolution of the size and shape of 2D nanosheets during ultrasonic fragmentation

Abstract

2-dimensional (2D) nanosheets such as graphene, graphene oxide, boron nitride or transition metal
\ndichalcogenides can be produced on a large scale by exfoliation techniques. The lateral shape of these
\n2D materials is typically considered random and irregular, and their average size is often estimated
\nusing techniques characterized by strong approximations or poor statistical significance. Here we
\nmeasure in a quantitative, objective way the size and shape of 2D monoatomic nanosheets using
\na combination of optical, electronic and scanning probe techniques. We measure, one by one, the
\nsize and shape of thousands of sheets of graphene oxide as they undergo a standard ultrasonication
\ntreatment. Using automatic image processing and statistical modelling we identify two different
\nfragmentation processes in 2D at the nanoscale, related to two populations of nanosheets described
\nby gamma and exponential size distributions respectively. The two populations of sheets coexist
\nduring the fragmentation process, each one retaining its average size and shape. Our results explain
\nthe size reduction commonly observed in nanosheets upon sonication as an effect of changes in the
\nrespective weights of the two populations of nanosheets present in the material.