Alladi Ramakrishnan Hall

Ab-initio Studies of Carbon-Based Novel Materials

Prof. S. Leoni

Cardiff University, UK

Research on novel carbon allotropes never loses momentum. The expectation of a larger variety than what is known so far is motivated by its ability to form tetrahedral sp3 compounds like diamond, as well as planar sp2 graphite. Between those two limiting geometries a manifold of intermediate cases is known, from fullerenes to nanotubes, from hyperbolic Schwarzites to carbon foams. While the planar sp2 unit implies layers of merged six-rings, as regular triangles tile the Euclidean plane, this is not necessarily true for structures based on sp3 centres. Diamond consists of adamantane-like cages of fused six-rings in chair conformation. On the other hand 3D structures with planar six-rings and tetrahedral centres seem to be intrinsically a problem, unless there is a certain amount of odd rings in the structure. Combination of odd and even rings is key to hard and transparent carbon materials, while entangling 1D nanotubes in regular pattern produces superior hydrogen storage materials. Dirac fermions appears in single sheet graphene, while electronic properties can be further tuned in few-layers gaphites. In the attempt to expand the catalogue of carbons, we have found novel graphenoid strcutures, based on sp2 centers, which nonetheless are not planar, i.e. they represent 3D gaphenes. They define a novel class of compounds, that can be derived from generalised graphite compounds, whereby different tilings of the plane can be used. Along this way, different graphites as well as graphenoid carbons can be obtained, which hosts interesting electronic properties. The chirality of some of them may represent the starting point towards pure carbon 3D Weyl fermion materials, which so far could be realised in exotic materials only. The possibility of experimentally accessing these materials from suitable precursors is also part of this study.