  Making use of focused Ga-ion beam (FIB) fabrication technology, the evolution
with device dimension of the low-temperature electrical properties of Nb
nanowires has been examined in a regime where crossover from Josephson-like to
insulating behaviour is evident. Resistance-temperature data for devices with a
physical width of order 100 nm demonstrate suppression of superconductivity,
leading to dissipative behaviour that is shown to be consistent with the
activation of phase-slip below Tc. This study suggests that by exploiting the
Ga-impurity poisoning introduced by the FIB into the periphery of the nanowire,
a central superconducting phase-slip nanowire with sub-10 nm dimensions may be
engineered within the core of the nanowire.
