Description of the influence of charging on the measurement of the secondary electron yield of MgO

The influence of charging on the secondary electron emission yield (σ) measurements of MgO is studied. This is done by measuring σ as a function of the primary energy (Ep) of the electron beam of thin layers of MgO deposited on Si. At high Ep, σ decreases when the primary current or the layer thickness increases. At low Ep, we find that σ increases somewhat due to charging. As a result of the measurement technique σ can become smaller than 1, even when Ep is in the energy range where σ is expected to be larger than 1. Furthermore, we observe for some samples the onset of a conduction mechanism at high primary currents. Monte Carlo calculations show that a potential barrier in front of the sample can arise, leading to a partial recapture of the generated secondary electrons. This causes σ to decrease at high Ep. A simplified analytical model is presented to calculate the effect of charging of the sample on the measured value of σ.