The effective secondary electron yield in the space-charge limited condition

The dependence of the effective secondary electron yield on the potential distribution and the target materials was investigated by means of electron transport simulation in the sheath with the potential distribution calculated for the different emission characteristics of Be (Z=4), C (Z=6), Mo (Z=42) and W (Z=74) as the target materials. For lower primary energy incidence the effective secondary electron yield in the space-charge limited condition (SCLC) is markedly suppressed due to the prompt return of the secondary electrons. For higher energy electrons, the yield is independent of the potential distribution in the sheath and the energy distribution of the emitted electrons is shifted to higher energy direction. This effect would increase the sheath potential resulting in the increase of both ion energy flux to the surface and sputtering yield. Because of their high reflection coefficients this result should be very important for high Z materials but not for low Z materials. (orig.)