Structural, electronic and mechanical properties of double core carbon nanothreads

Abstract

The synthesis of double core carbon nanothreads (NTHs) has been recently achieved through compression of aromatic molecules containing two rings connected by short chains featuring either double or triple bonds (such as stilbene, azobenzene and diphenylacetylene). Their structure are characterized by two conventional 1D NTHs cores, interconnected by covalent bonds arranged in several ways. In this paper, we provide a comprehensive analysis of the possible atomic structures for double core NTHs, evaluate their relative stability, and calculate some electronic and mechanical properties, using Density Functional Theory calculations and Molecular Dynamics simulations. Many isomers are possible for these 1D materials, differing by the intrinsic structure of the cores and the nature of the covalent bonds crosslinking them. For stilbene and diphenylacetylene NTHs, the most stable isomers feature continuous sp3 or sp2 C-C chains connecting the cores, while those that preserve the original unsaturation of the molecule (azo group) are the most stable for azobenzene. The mechanical behavior of these NTHs are similar to that of conventional single core ones, with enhanced 1D strength and stiffness when continuous chains connect the cores. Their electronic behavior range from metallic to insulating depending on the arrangement of the bonds connecting the cores, and the materials with the narrowest band gaps feature electron delocalization along the chain connecting the cores. The variations in properties associated to the presence of bonds connecting the cores bring new opportunities to the design of electronic and optical devices employing this class of strong and flexible materials.