Electrical Properties of Titanium, Zirconium, and Hafnium Films from 300 °K to 1.3 °K

Abstract

Electrical properties of titanium, zirconium, and hafnium films prepared by electron beam evaporation have been measured from 300 °K to 1.3 °K as a function of substrate temperature, film thickness, and substrate material (single-crystal sapphire, Corning 7059 glass, and fused quartz). Zirconium films in the thickness range 2000 Å to 12 000 Å have superconductive transition temperatures near 1.3 °K for films deposited at substrate temperatures of 100 °C and below. Expitaxial growth of titanium is observed on single-crystal sapphire substrates in the temperature range 200 °C to 400 °C on at least two orientations of sapphire. Epitaxial titanium films have a resistance ratio (R300 °K/R4.2 °K) of 24 at a thickness of 12 000 Å and of 8 at 400 Å. This is nearly twice those of the corresponding polycrystalline films on Corning 7059 glass or fused quartz. Films of zirconium and hafnium have an enhanced resistance ratio on sapphire substrates only when deposited at a substrate temperature of 400 °C. Their resistivities at 300 °K are about twice the bulk values for films 7000 Å thick or greater. Superconductivity was not observed for either titanium or hafnium films down to 1.3 °K. Only the hexagonal close-packed crystal structure was found for all three film materials.