| Superconducting samples of equal layer thickness have been made by sequential deposition of Nb and Cu on single crystal sapphire substrates. The individual layer thicknesses were varied from 5(ANGSTROM)-5000(ANGSTROM), the total thickness of each sample being kept equal to (TURN)1(mu)m. Both materials grow preferentially perpendicular to the substrate--Cu(111) and Nb(110). Layer thicknesses were determined from the relative position of the superlattice peaks of the Bragg x-ray spectrum of the sample. These results agreed well with the layer thickness determined from the geometric parameters of the system.;The superconducting transition temperature T(,c) of the Nb/Cu superlattices has been investigated as a function of layer thickness. The dependence of T(,c) above 300(ANGSTROM) layer thickness agrees well with the proximity effect theory with no adjustable parameters. Below 300(ANGSTROM), the data in conjunction with the proximity effect theory shows that T(,c) of Nb decreases with layer thickness. This is interpreted in terms of a change in the electronic density of states due to a decrease in the mean free path.;The temperature and angular dependence of the critical fields of the above mentioned samples have also been studied. For layer thickness between 100 (ANGSTROM) and 300 (ANGSTROM), evidence for dimensional crossover has been observed in the temperature dependence. Associated with the crossover we find a change in the angular dependence given by the effective mass theory. This is the first time that a relationship has been observed between dimensional crossover in the temperature dependence and a change in the angular dependence of critical fields. |
