Electron impact ionization cross sections of Cu and Au between 40 and 250 eV, and the velocity of evaporated atoms

摘要

The total ionization cross sections of Cu and Au were measured with a simple crossedhyphen;beam apparatus for bombarding electron energies between 40 and 250 eV. The maximum cross sections weresgr; lpar;Curpar;equals;lpar;7.6 plusmn; 1.1 times; 10minus;16cm2at95 plusmn; 10thinsp;eVandsgr; lpar;Aurpar; equals;lpar;15.3 plusmn; 2.1rpar; times; 10minus;16cm2at100 plusmn; 10eV. The ratio of the cross sections issgr; lpar;Aurpar;sol;sgr; lpar;Curpar; equals;2.0 plusmn; 0.2between 50 and 180 eV. The shape of our cross section curve for Cu compares well with a previous measurement by Crawford. An evaporation model which predicts thermal equilibrium between a liquid and the atoms evaporating into a vacuum is discussed, and the average velocity of atoms evaporated from an evaporation boat is calculated.