Twistons in graphene nanoribbons on a substrate

Twisted nanoribbons from two-dimensional materials possess many unusual properties tunable by changing the twist angle, for example, electro- and thermal conductivity, chemical properties, and stability against buckling. New interesting phenomena can be observed when a twisted nanoribbon interacts with a substrate. Here we report the results of a classical molecular dynamics study of a graphene nanoribbon twisted about its long axis and interacting with a graphite substrate. Van der Waals interactions with the substrate lead to localization of twisting and the formation of topological solitons called twistons. The topological charge of a twiston obtained with the twist angle beta multiple of pi can be defined as q = beta/pi; it can be positive or negative. Twistons can move along the nanoribbon with very little radiation in the form of small-amplitude phonons. Scenarios of twiston collisions are described depending on their topological charge and on the nanoribbon width. In narrow nanoribbons twistons collide practically elastically, preserving their profiles and speeds after the collision, and inelasticity of collisions increases with increasing nanoribbon width. Our results contribute to an understanding of the behavior of two-dimensional material nanoribbons on a substrate.