ABSTRACT
When one speaks of a ‘spectrum’, the dispersed array of colours from a luminous body comes to mind; however, in the most general sense, a spectrum is a record of the energy and probability of transitions between states of a substance. In electron spectroscopy the ‘spectrum’ takes the form of the energy distribution of electrons emanating from a sample. Electron spectroscopies are classified according to the phenomena giving rise to these electrons; historically, each technique has acquired an acronym until today one finds a veritable alphabet soup of electron spectroscopies in the scientific literature. For example, PES refers to photoelectron spectroscopy, a technique in which the detected electrons are emitted after the absorption of a photon induces transitions into the continuum beyond the first ionization potential of the sample. Electronimpact spectroscopies, the subject of this entry, entail the excitation of a transition by an electron impinging upon a sample with the subsequent measurement of the energy of the scattered electron. The spectrum is the scattered-electron intensity as a function of the difference between the incident-and scattered-electron energies-the energy loss.
