Effect of residual gases on the properties of indium films

Indium films have been deposited at pressures less than 10-9 mm Hg and at higher pressures of specific residual gases. N2, H 2, CH4, A, CO, and CO2 were found to have no measurable effect on the electrical or superconducting properties of these films when present in partial pressures of 10-5 mm Hg. For oxygen, a pronounced effect was observed when K (the ratio of oxygen molecules to indium atoms striking the substrate) exceeded 3%. The room temperature resistivity increased from 9.0 μohm-cm to 14 μohm-cm, the critical temperature decreased from (3.402±0.005)°K to (3.389±0.002)°K, the effective magnetic penetration depth increased from 630±100 A to over 1000 A. For 10-3<K<3×10-2, a larger apparent penetration depth was observed for films deposited through a mask due to edge effects. It was shown that indium films could be deposited at 100 A/sec on clean, baked substrates at 10-5 mm Hg with characteristics indistinguishable from those of films deposited in ultrahigh vacuum provided the partial pressures of oxygen and water vapor were below 10-7 and 10-5 mm Hg, respectively. © 1961 The American Institute of Physics.