Electron Emission from Solids During Ion Bombardment. Theoretical Aspects

Abstract

This contribution is devoted to the theory of ion-induced electron emission from solids, with the emphasis on bulk as opposed to surface processes. With the aim of describing yields and energy spectra of emitted electrons, we discuss pertinent elementary processes, l.e., primary and secondary excitation, electron transport, and escape. I'lith regard to the primary process, proper distinction is made between high-and low-velocity ions, and reference is made to the physics of ion-atom collisions as well as to dielectric stopping theory. The discussion of secondary excitation makes reference to the theory of ionization cascades as well as atomic recoil cascades. Electron transport is considered first in an infinite medium and subsequently, within the diffusion approximation, in a semi-infinite medium. Special attention is paid to pertinent electron mean free paths, inelastic processes being estimated on the basis of the free-electron-gas model of a solid. We find that the neglect of elastic scattering of electrons in most existing treatments of electron emission has severe consequences on the interpretation of structure in measured electron spectra. Comments are made on the escape depth of electrons.

Polyatomic Ion-Induced Electron Emission (IIEE) in Electrospray Thrusters

“…However, difficulties arise with application of the Schou model to polyatomic impacts, and its solution for EMI + should be treated with caution. Schou noted breakdown of his theory at low energies, where the assumption of a cascade ionization no longer holds well [54,55]. Departure from assumed conditions was seen when applying the Schou model to cluster impacts with velocities less than 10 7 cm s −1 , which is again near the classical velocity threshold for IIEE.…”

“…Schou's theory [54] differs greatly from previous semi-empirical models. While it gives an analytical, closed solution with inputs similar to that of the B&F model, it remains the only theory accounting for cascade processes, particularly recoil ionization [29,55]. An adapted solution form for this study is as follows:…”

Design and construction of a secondary electron suppressed Faraday Cup for measurement of beam current in an electrostatics proton accelerator

“…According to the experiments, the angular distribution of the secondary electrons outside the solid is closely proportional to cos Â, where  is the angle of the electron trajectory with respect to the surface normal [8].…”

Calibration of a multiple microchannel plate detectors system by α-induced secondary electrons

“…The observed distributions do not reflect the angular distribution in the bulk since transport in the solid and refraction at the surface affect the electron trajectories. [9][10][11] For electrons created in the bulk, a cos angular dependence is commonly encountered resulting from the path length needed to reach the surface. 8,12 The observed cosine distribution for electrons associated with peaks A and B seems to corroborate the interrow calibration.…”