Twisting or untwisting graphene twisted nanoribbons without rotation

The common sense regarding twisting or untwisting a ribbon is that it requires the application of an external rotation to happen. However, at nanoscale, the application of precise amounts of rotation on a nanoribbon is not a trivial task. Here, the concept of an alternative method to add twist to or remove twist from a twisted graphene nanoribbon (TGNR) without rotation is presented and computationally demonstrated. The method consists of suspending a TGNR on two separate substrates and, by changing only their distance, the total amount of twist of the TGNR is shown to change. The possibility of fine-tuning the amount of twist of a TGNR is also shown. The concept is demonstrated through fully atomistic molecular dynamics simulations and numerical calculations of the topological parameters twist and writhe of a TGNR. It is shown that the above process satisfies the so-called linking number theorem of space curves. Besides being capable of precisely determining the total twist of a TGNR, this concept reveals a twist to writhe transition phenomenon that is tension-free and does not require controlling either the nanoribbon end-to-end distance or its critical twist density.