An experimental assessment of proposed universal yield curves for secondary electron emission

A variety of 'Universal Yield Curves' for the secondary emission process have been proposed. A series of precise measurements of the secondary emission properties of a range of related amorphous semiconducting materials, made under UHV on freshly vacuum-cleaved surfaces, and covering a wide range of primary energies, have recently made possible an accurate assessment of the validity of the various UYCs suggested. It is found that no truly universal curve exists; the atomic number of the target materials plays an important part in determining the secondary emission properties. Agarwal's semi-empirical expression, which takes account of the atomic number and weight, is found to give good agreement for all the materials studied. Further theoretical investigation is required.