Thin Film Materials Research Center, Korea Institute of Science and Technology (KIST) (Seoul, KR) scientists have manufactured AA' graphite with a new stacking feature of graphene and developed its fabrication by chemical vapor deposition. Graphene is stacked in the sequence of AA' where alternate graphene layers exhibiting the AA' stacking are translated by a half hexagon (1.23 .ANG.). AA' graphite has an interplanar spacing of about 3.44 .ANG. larger than that of the conventional AB stacked graphite (3.35 .ANG.) that has been known as the only crystal of pure graphite. This may allow the AA' stacked graphite to have unique physical and chemical characteristics, say inventors Jae-Kap Lee, So-Hyung Lee, Jae-Pyoung Ahn, Seung-Cheol Lee and Wook-Seong Lee in U.S. Patent Application 20100028573.
FIG. 7A is a TEM (transmission electron microscope) image showing AA' graphite in the form of a nano-flake synthesized by a CVD method according to method created at KIST, and FIG. 7B is an HRTEM (high-resolution transmission electron microscope) image showing graphene fringes of the AA' stacked nano-flakes where an interplanar spacing is measured to be 3.44 .ANG
Stacked AA graphite was synthesized using a high-density DC plasma in hydrogen-methane mixtures. Graphene layers have been grown epitaxially with 2-1 registration between the AA graphitic edges and the surface of diamond.
Graphite is a representative graphitic material, and is composed of graphene i.e., a single layer trigonal carbon honeycomb. Thus, graphite is named as a layered structure and can be classified into AB or AA graphite according to stacking types of graphene. It has been well known that AB stacked graphite (or AB graphite) is the only stable crystalline that exists in nature (FIG. 1) (i.e., AB graphite: stable graphite with an interplanar spacing of 3.35 .ANG.) since 1924
However the AA stacking of graphene is not present in pure graphite because it is energically unstable. AA stacked graphite (or AA graphite) (FIG. 2) can appear only when Li intercalates into graphene layers of AB graphite (i.e., AA graphite: unstable graphite with an interplanar spacing of about 3.53 .ANG.). Disordered graphite (in lack of the order in stacking graphene), termed turbostratic (FIG. 3) suggested by Biscoe et al. [Journal of Applied Physics 13 (1942) 364], is the generally accepted alternative stacking arrangement for graphitic materials. This has been extended to include multi-wall carbon nanotubes (MW CNTs) discovered by IIjima in 1991.
FIG. 1 is a view showing the structure of AB stacked graphite where graphene is stacked in the sequence of AB.
FIG. 2 is a planar view showing the structure of AA stacked graphite where graphene is stacked in the sequence of AA
FIG. 3 is a planar view showing the structure of turbostratic graphite where graphene is stacked disorderly.
FIG. 4 is a plane view showing the structure of AA' stacked graphite according to KIST's discovery, where graphene is stacked in the sequence of AA'.
FIG. 5 shows a crystal structure of the AA' stacking, assigned to a space group of a hexagonal (simple hexagonal, space group p6/mmm #191).