Low Temperature Properties of Bismuth Films in Large Electric and Magnetic Fields

Polycrystalline bismuth films were prepared by vacuum deposition onto mica substrates held at 423 K and onto glass substrates held at room temperature . The conductance of these films was monitored continuously as they were actually being deposited, and a complicated dependence of conductance on film thickness was seen. Electron micrographs of the films made at room temperature showed that the average cyrstallite size increased as a function of the evaporation rate that was used in their fabrication. There was no correlation between average crystallite size and evaporation rate for the films made at 423 K. However, the average crystallite size in the films made at 423 K was s larger than the average crystallite size of those films made at room temperature. those films made at room temperature. The films prepared at 423 K were used in subsequent galvanomagnetic and electric field effect measurements made at 4.2 K. Continuous plots of the film resistance as a function of an applied transverse magnetic field were obtained for field values ranging from zero to 5 T. The resistance was seen to increase quadratically wth field for low fields and then to saturate at high fields . Measurements of the Hall voltage as a function of an applied magnetic field revealed an anomalous positive Hall constant at low fields for most of the films . The Hall constant decreased with field from this initial positive value and saturated in the high field region . In some cases, the Hall constant saturated at a positive value, and in other cases, saturation occurred at a negative value. The electric field effect, which is the modulation of the film resistance as a function of an applied transverse electric field, was measured in the presence of an applied transverse magnetic field. A strong dependence of the electric field effect on the magnetic field was seen. Specifically, it was found that the magnitude of the electric field effect increased as a function of the applied magnetic field for fields higher than 2 T