Effect of Residual Gases on the Properties of Indium Films

Abstract

Indium films have been deposited at pressures less than 10⁻⁹ mm Hg and at higher pressures of specific residual gases. N₂, H₂, 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−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.