Thickness-tuned superconductor-insulator transitions in quench-condensed Mo and MoRu films

The results of studies on superconductor-insulator transitions are reported for Mo and MoRu films of varying thickness deposited on SiO underlayers and on bare glass. The film samples were quench-condensed on glass substrates held at liquid He temperatures. MoRu films on SiO, which offer the most homogeneous film morphology, showed a critical sheet resistance of transition, R(c), of similar to 6.7 k Omega. Both series ofMo films on SiO and MoRu films on bare glass had R(c) similar or equal to 13 k Omega. These values are larger than those previously reported for MoGe, MoSi, and MoC films. For the above films in the insulating region far from the transition, the exponent of the thermally activated resistance ranged from 0.5 to 1.0.