Linearized secondary-electron cascades from the surfaces of metals. I. Clean surfaces of homogeneous specimens

Abstract

The cascade in the secondary-electron emission from atomically clean and atomically characterized surfaces of metals has been studied in the energy region of shortest inelastic mean free paths ($10 \mathrm{eV}\lesssim E\lesssim 1000 \mathrm{eV}$). Specimen surfaces were cleaned in situ and characterized under ultra-high-vacuum conditions (∼${10}^{-9\mathrm{}}$ Torr) by low-energy electron diffraction and Auger electron spectroscopy. The cascade from clean surfaces was found to consist of linear segments when $logj\left(E\right)\mathrm{}$ was displayed vs $logE$, where $j\left(E\right)\mathrm{}$ is the emission current distribution as a function of the electron kinetic energy $E$. From the linear characteristics and the dependence of emission on primary beam energy $E_p$ it is inferred that the emission current in the cascade is of the form $j\left(E\right)=A{E}^{-m}{E}_p^{-n}$. It is shown that this functional form is compatible with a solution of the Boltzmann diffusion equation. Deviations from linearity are found in the form of a segmented (linear) display where segmentation is caused by internal sources such as Auger electron sources. The linear segments are joined near energies characteristics of bound electrons in the solid. These effects are used to form the basis of a new approach to surface characterization.