Some Photoelectric Properties of Evaporated Bismuth Films

Some photoelectric properties of bismuth films deposited on glass by evaporation in high vacuum are investigated. It is shown that the photoelectric emission and threshold wave-length increase with film thickness to a limiting value. DuBridge's method, in which the photoelectric currents are measured at a single incident frequency and variable temperature, was employed in the threshold determinations and an excellent fit of the observed data to the theoretical curves is always obtained for the temperature range -53.8°C to 24.4°C but not for higher temperatures. The maximum threshold wave-length for the bismuth films as determined by the present work is between 2564 and 2600A. The minimum measured threshold wave-length, corresponding to a glass surface thinly spattered with bismuth, is between 2443 and 2506A. Films subject to possible gas contamination and films more carefully protected from such contamination show little difference. Two sets of data, analyzed by Cashman's method, give values of $n$, the exponent of $T$ in the photoelectric emission equation equal to 2.039 and 2.052.