Secondary Electron Emission from Clean Surface of Molybdenum Due to Low-Energy Noble Gas Ions

Secondary electron yields from clean, polycrystalline, molybdenum bombarded by ${\mathrm{He}}^{+}$ and ${\mathrm{Ar}}^{+}$ have been measured for the kinetic energy range 100 eV to 2.5 keV. This covers the transition energy region where electron ejection processes depending on the translational energy of the bombarding particle are superposed on those depending on their potential energies. A definite kinetic energy threshold for electron ejection is observed for ${\mathrm{He}}^{+}$ at about 500 eV and for ${\mathrm{Ar}}^{+}$ at about 700 eV. For ${\mathrm{He}}^{+}$, the yield drops as the energy increases to about 500 eV and, thereafter, increases linearly with energy. In the case of ${\mathrm{Ar}}^{+}$ $\gamma$ is relatively insensitive to beam energy up to the kinetic threshold and, thereafter, increases linearly. The agreement between the observed variation of $\gamma$ with ion kinetic energy and a theoretical calculation of the same is discussed.