Scanning Electron Microscopy


Two-quantum photoemission is a process in which two times the photon energy is transferred to the photoelectron. In this process, the photoelectron observed in the vacuum keeps a "memory" of the intermediate empty state by which it transited after its first excitation, and before its second excitation and its final escape. We discuss here the experimental problems involved and the information obtained in the case of the semiconductors Si and InP. We show that ballistic or non-ballistic electrons can be selected by an adequate choice of experimental conditions, yielding information on both the static and dynamic properties of the empty states.

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