Size dependence of the Tc and the superconducting energy gap in   nanocrystalline thin films of Nb
  In nanocrystalline Nb films, the superconducting Tc decreases with a reduction in the average particle size below 20nm. We correlate the decrease in Tc with a reduction in the superconducting energy gap measured by point contact spectroscopy. Consistent with the Anderson criterion, no superconducting transition was observed for sizes below 8 nm. We show that the size-dependence of the superconducting properties in this intermediate coupling Type II superconductor is governed by changes in the electronic density of states rather than by phonon softening. 
Sangita Bose, Pratap Raychaudhuri, Rajarshi Banerjee, Parinda Vasa and   Pushan Ayyub