  We have fabricated 5 nm ultra-thin NbN nanowires that form a dense and
regular array in the linear channels of mesoporous SBA-15 silica substrates.
Bulk NbN is a well-known classical superconductor with Tc of 16 K. We show
that, by being incorporated into this nanostructure, the composite material
exhibits typical quasi-one-dimensional characteristics. We compare the
superconducting properties with those of superconducting Pb nanowires of same
dimensionality in identical configuration within the linear SBA-15 pores. While
Pb nanowire arrays show a pronounced crossover from 1D superconductivity at
high temperatures to a 3D bulk superconducting state in the low temperature
regime with true zero resistance triggered by transversal Josephson
interaction, this transition appears to be completely absent in the NbN
nanowire array. The small coherence length in NbN, which strongly suppresses
the Josephson coupling is discussed as the origin of this difference.
