We have studied the electrical conductivity of Cs vapor cells in the
temperature range 190−270 °C with Cs atom density up to 3 × 1014 cm−3. Depending on these parameters controlled independently, two predominant mechanisms are shown to determine the electrical properties of the cells: wall surface conductivity and space conductivity. The latter is caused by thermionic emission of electrons from the “cesiated” surface at submonolayer coverage.
This process has been studied for the case of metal (Ti) and
dielectric (Al2O3) surfaces. The values of the electron emission work
function are found to be 1.38–1.42 V for Ti, 1.4–1.45 V for alumina and 1.39 V for
sapphire. From independent photoemission studies, we also obtain the value of 1.35–1.40 V
for the work function of sapphire. Our measurement technique not requiring internal
electrodes can easily be implemented for studies of charge emission and ionization, in
different types of dielectric cells containing a low density gas medium.