Glass-like carbon (GC) is a class of nongraphitizing carbon made by firing polymeric precursors such as phenolic resin or furfuryl alcohol resin in an inert atmosphere. Type I GC, which is produced at low temperatures, consists mainly of randomly distributed, curved graphene layer fragments. Type II GC, fabricated at high temperatures, contains self-assembled, fullerene-like, nanometer-sized spheroids dispersed within, and interconnected by, a three-dimensional disordered multilayer graphene matrix. Type II GC can therefore be envisaged as fullerene-like spheroids encased in disordered graphene layers with a nanostructure like that shown in Fig. 1, which has a number of similarities to mechanical metamaterials, but with statistical characteristic building blocks (that is, fullerene-like spheroids) at nanometre scales. It is well known that graphene has very high in-plane strength, while fullerene has a large volume deformation capacity, and so the hybrid type-II GC is expected to have the integrated features of both materials to possess exceptional mechanical properties.
The discovery of fullerene-like spheroids encased in a disordered, multi-layer graphene matrix opens a route for the preparation of new forms of carbon that feature combinations of two or more carbon allotropes. Such combined forms may display properties superior to the properties of either of the components, and perhaps unique combinations of tailored mechanical and electronic properties may be obtained [Z. Zhao et al., Nature Comm. 6, 6212 (2015)].