Superstructures of Cubic and Hexagonal Diamonds Comprising a Family of Novel $s{p}^3$ Superhard Carbon Allotropes

Abstract

Superstructures of cubic and hexagonal diamonds (h- and c-diamond) comprising a family of stable diamond-like $s{p}^3$ hybridized novel carbon allotropes are proposed, which are referred to as U${}_n$-carbon where $n\ge 2$ denotes the number of structural layers in a unit cell. The conventional h- and c-diamond are included in this family as members with $n=2$ and 3, respectively. U${}_n$-carbon ($n=4-6$), which are unveiled energetically and thermodynamically more stable than h-diamond and possess remarkable kinetic stabilities, are shown to be insulators with indirect gaps of $5.6\sim 5.8$ eV, densities of $3.5\sim 3.6$ g/cm${}^3$, bulk modulus of $4.3\sim 4.4\times 10^2$ GPa, and Vickers hardness of $92.9\sim 97.5$ GPa even harder than h- and c-diamond. The simulated x-ray diffraction and Raman spectra are presented for experimental characterization. These new structures of carbon would have a compelling impact in physics, chemistry, materials science and geophysics.

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• Electric Field Effect in Atomically Thin Carbon Films