  Graphene nanoribbons (GNRs) have the most of the outstanding properties of
pristine graphene plus non-null bandgap. Besides width- and edge-dependent, GNR
band-gap and other electronic properties were shown to change with the
application of twisting along its axis. Twisted GNRs (TGNRs) have already been
produced, but it remains a challenge to control and fine-tune their amount of
torsional strain. Here, based on the strong adhesion between graphene layers, I
proposed a new way to change the amount of twist in a TGNR without rotating its
extremities. By laying the extremities of a TGNR on two separate substrates and
controlling the distance between them, I show by computational simulations that
the total twist of the TGNR can be continuously varied within a certain
interval. This happens because of a topological constraint imposed by the
substrates on the geometric structure of the TGNR, leading to a new kind of
twist-to-writhe conversion (TWC), well-known to happen in twisted structures,
from DNA to marine cables. Regular TWC is controlled by applying tension or
changing the end-to-end distance of the filament, while this new substrate
induced TWC phenomenon relies only on the interactions between the TGNR and
substrate. Possible applications are suggested.
