Propriétés photoélectriques des couches minces de calcium

Thin films of calcium were evaporated under ultrahigh vacuum conditions (pressures less than 5 x 10(-10) Torr) onto quartz substrates to a thickness of 20 nm. The photoelectric yield and hence the work function of the layers were determined as a function of thickness. For film thicknesses greater than 10 nm, the work function was constant with a value of 2.87 +/- 0.06 eV. The work function suows minima at film thicknesses of about 2.5 nm and 5.5 nm. Results from films thicker from 5.5 are a good fit to the Fowler function; for thinner films, the results suggest the existence of a second photoelectric threshold with a corresponding work function ø(s). A theory based on the energy states of the surface electrons is proposed to explain both this second threshold and the ir absorption of thin calcium films.