  We present the electrical transport characteristics of a batch of
nano-crystalline diamond films of varying nitrogen concentrations and explain
the conduction mechanism by the disordered quasi-superlattice model applied to
semiconductor heterostructures. Synthesized by the hot filament chemical vapour
deposition technique, the degree of structural disorder in the films, confirmed
from Raman spectroscopy, is found to be controllable, resulting in the
transition of conduction mechanism from localized and activated to the metallic
conduction regime. Hence through high field magneto-resistance measurements at
low temperatures we firmly establish a conductivity crossover from hopping to
3D weak localization. The long electronic dephasing time and its weak
temperature dependence suggest the possibility for diamond-based high-speed
device applications.
