  We explore the effects of sample dimensionality on vortex pinning in a
type-II, low-$T_C$, s-wave superconductor, NbN, in the presence of a
perpendicular magnetic field, $H$. We find significant differences in the phase
diagrams in the magnetic field--temperature plane between 3-dimensional (3D)
and 2-dimensional (2D) NbN films. The differences are most striking close to
the normal-superconductor phase transition. We establish that these variances
have their origin in the differing pinning properties in two different
dimensions. We obtain the pinning strength quantitatively in both the
dimensions from two independent transport measurements performed in two
different regimes of vortex-motion -- (i) thermally assisted flux-flow (TAFF)
regime and (ii) flux flow (FF) regime. Both the measurements consistently show
that both the pinning potential and the zero-field free-energy barrier to
depinning in the 3D superconductor are at least an order of magnitude stronger
than that in the 2D superconductor. Further, we probed the dynamics of pinning
in both 2D and 3D superconductor through voltage fluctuation spectroscopy. We
find that the mechanism of vortex pinning-depinning is qualitatively similar
for the 3D and 2D superconductors. The voltage-fluctuations arising from
vortex-motion are found to be correlated only in the 2D superconductor. We
establish this to be due to the presence of long-range phase fluctuations near
the Berezinskii-Kosterlitz-Thouless (BKT) type superconducting transition in
2-dimensional superconductors.
