  Scanning tunneling spectroscopies are performed below 100~mK on
nano-crystalline boron-doped diamond films characterized by Transmission
Electron Microscopy and transport measurements. We demonstrate a strong
correlation between the local superconductivity strength and the granular
structure of the films. The study of the spectral shape, amplitude and
temperature dependence of the superconductivity gap enables us to differentiate
intrinsically superconducting grains that follow the BCS model, from grains
showing a different behavior involving the superconducting proximity effect.
