  Nanowires have been considered for a number of applications in nanometrology.
In such a context, we have explored the possibility of using ultrathin twisted
nanowires as torsion nanobalances to probe forces and torques at molecular
level with high precision, a nanoscale system analogous to the Coulomb's
torsion balance electrometer. In order to achieve this goal, we performed a
first principles investigation on the structural and electronic properties of
twisted silicon nanowires, in their pristine and hydrogenated forms. The
results indicated that wires with pentagonal and hexagonal cross sections are
the thinnest stable silicon nanostructures. Additionally, all wires followed a
Hooke's law behavior for small twisting deformations. Hydrogenation leads to
spontaneous twisting, but with angular spring constants considerably smaller
than the ones for the respective pristine forms. We observed considerable
changes on the nanowire electronic properties upon twisting, which allows to
envision the possibility of correlating the torsional angular deformation with
the nanowire electronic transport. This could ultimately allow a direct access
to measurements on interatomic forces at molecular level.
