Abstract
Reflection and transmission secondary emission ratios have been measured for a thin Si sample with one surface activated to a state of negative electron affinity. Reflection‐mode gains of 950 were observed at 20‐keV primary energy. The highest transmission secondary emission ratio was 725 at 20‐keV primary energy. The high secondary emission gains result from the effective negative electron affinity at the surface of the sample together with a long escape depth for internal secondaries.