Nanocrystalline boron-doped diamond films, a mixture of BCS-like and non-BCS-like superconducting grains

Scanning tunneling topography and spectroscopy are performed below 100mK on granular nanocrystalline borondoped diamond (BDD) films. We found the superconductivity behavior to follow mainly the granular features of the BDD films. The temperature dependence of the local differential conductance spectra shows our nanocrystalline BDD films as made of grains with a supercondutivity either BCS-like or non- BCS-like. Such a distribution is not discernible in transport measurements, which present a sharp macroscopic superconducting transition at a temperature of a few Kelvins. Our local scanning tunneling microscopies also confirm the good coupling between these grains: only a few opaque interfaces are detected. Such a transparency of intergrain interfaces is responsible for a proximity effect in weakly superconductive grains and an inverse proximity effect in strongly superconducting grains.