Types of Photoemissive Surfaces Classical and NEA

Photoemissive devices can be conveniently divided into two historical (and performance) classes depending upon the material used as the photoemissive layer [5.11]. The first class is the classical group [5.26]. Here the photoemitter is a thin evaporated-layer compound containing an alkali metal or metals (almost always including Cs), one or more other metallic elements from group VB of the periodic table (e.g., Sb), and possibly also oxygen and/or silver [5.27], For ultraviolet applications several other sensor materials are used (e.g., Csl), but such devices become highly specialized and are not discussed further in this chapter [5.28]. 

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