Photoelectric Properties of Lead Sulfide near the Threshold Region

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Abstract
The photoemission properties of the (100) surface of lead sulfide prepared by cleaving, cleaving and annealing, and ion bombarding and annealing have been investigated in the region within about 2 eV of the threshold. For the cleaved and annealed, or ion bombarded and annealed surface, the photothreshold is 3.8±0.1 eV giving an electron affinity of 3.4±0.1 eV. This value of electron affinity is lower than the 4.6 eV value previously reported and is found to be primarily dependent on surface preparation; the surface prepared in vacuum by cleaving and annealing or ion bombarding and annealing gives the lower threshold. Surfaces prepared by cleaving in air and then mounting in the vacuum apparatus have a higher threshold and lower yield than those prepared in vacuum. Subsequent anneal and/or ion bombardment of a surface prepared by cleaving in vacuum lowers the threshold and increases the yield even more significantly. Exposure of the freshly cleaved surfaces to oxygen at room temperature indicated a sticking coefficient of less than 10−4.