On the Electronic, Mechanical and Optical Properties of Superhard Cross-Linked Carbon Nanotubes (Tubulanes)

We have investigated the electronic, optical, and mechanical properties of six structures belonging to the Tubulanes-cross-linked carbon nanotube family, using Density Functional Theory (DFT) with the Generalized Gradient Approximation (GGA) and the Perdew–Burke–Ernzerhof (PBE) functional. Our results highlight the remarkable anisotropic mechanical behavior of these materials, distinguishing them from isotropic structures, such as diamond. Notably, the 8-tetra-22 structure has a higher Young’s modulus (YM) along the z-direction compared to diamond. Unlike diamonds, the mechanical properties of Tubulanes are direction-dependent, exhibiting significant variations in Young’s Modulus (2.3 times). Additionally, the Poisson’s ratio is highly anisotropic, with at least one direction exhibiting a value close to zero. The inherent anisotropy of these materials enables tunable mechanical properties that depend on the direction of applied stress. Regarding their electronic properties, all Tubulane structures studied possess indirect electronic band gaps, dominated by 2p orbitals. The band dispersion is relatively high, with band gaps ranging from 0.46 to 2.74 eV, all of which are smaller than that of diamond. Notably, the 16-tetra-22 structure exhibits the smallest bandgap (0.46 eV), making it particularly interesting for electronic applications. Additionally, these structures exhibit porosity, which offers advantages over denser materials, such as diamond. Given recent advances in the synthesis of 3D carbon-based materials, the synthesis of tubulane-like structures is within current technological capabilities.