Stress in Evaporated Bismuth Films during and after Deposition

Abstract

Bismuth was deposited onto thin strips of copper in a vacuum of 2∼5×10^-5 torr, and the stress within the films was determined by observing electrically the bending of the strip. Continuous observations of the stress and electrical resistivity of films were simultaneously made during and after the deposition. When a critical thickness d _c is reached during the deposition, a sharp increase in compressive stress occurs, which precisely corresponds to the appearance of conductivity. The stress in bismuth films after the deposition onto substrates at room temperature is tensile (\lesssim5×10⁷dyn/cm²). Electron micrographs show that films close to d _c in thickness are in the final channel stage or the hole stage. The origin of the compressive stress during deposition is discussed.