Visualization of graphene formation in nanoscale by in situ transmission electron microscopy: A Review

In situ transmission electron microscopy (TEM) observation of the graphene synthesis by solid phase reaction is dealt with. For this purpose, metal-included and pristine (metal free) amorphous carbon nanofibers (CNFs) were fabricated on an edge of a graphite foil by Ar ion irradiation (Ar ion irradiation method) with and without a supply of metals at room temperature, respectively. In Ar ion irradiation method, any kinds of metals could be included in CNFs. Cu-coated pristine CNFs were also prepared. The graphite foils thus prepared were cut into small pieces to be mounted directly on a TEM sample holder equipped with a piezo-controlled nanoprobe to, measure their current-voltage characteristics in direct current (DC) and field emission (FE) modes. Depending on the included metal element in the CNFs, different types of nanocarbons, such as graphene, ring-shaped graphene, and carbon nanotubes (CNTs), were formed from amorphous CNF during the electron current flow by solid phase reaction. Here, dependence of included metal on the nanocarbon formation is reviewed, together with the visualization of graphene sheet formation in nanoscale during the electron current flow for the Cu-coated pristine CNFs. It is believed that the graphene formation by solid phase reaction is essential also for the growth area (position) control of graphene nano-ribbon.