Secondary electron yield enhancement by MgO capping layers

摘要

The yield of secondary electrons emitted from an epitaxial three monolayer (3 ML) NiO(100)/Ag(100) film excited by soft X-ray linearly polarized synchrotron radiation at the Ni L_(2.3) absorption threshold has been measured for different values of the thickness of a MgO(100) capping layer. Compared with the as grown 3 ML NiO(100)/Ag(100) film, we observe a significant enhancement by about a factor 1.2 of the secondary electron emission for the capped 8 ML MgO(100)/3 ML NiO(100)/Ag(100) sample. A further substantial yield enhancement by a factor 1.6 with respect to the uncapped NiO sample is observed after deposition of an additional 8 ML MgO(100) film, for a total capping layer thickness of 16 ML. The observed secondary electron yield enhancement is discussed in terms of modified electronic structure, surface work function changes, and characteristic electron propagation lengths.