Energy spectra of sputtered positive ions under Cs+ bombardment

The emission-energy spectra of atomic and molecular secondary ions sputtered from various metals and semiconductors (Al, Cu, In, Si, InP, and InSb) under 5.5-keV Cs+ irradiation were investigated. The emitted ions were detected in a high-sensitivity double-focusing secondary-ion mass spectrometer. Specifically, the energy distributions of Cs+, Cs2+, MCs+, and M+ ions (where M designates one of the target elements) were recorded for emission energies E ⩽ 125 eV. All ion species exhibit a peak at low energy (E < 5 eV), but differ significantly in the respective fall-off to high emission energies. The influence of the oxygen partial pressure in the vicinity of the sputtered surface on the energy spectra was examined for Cs+ ions emitted from Si. With an increase of the ratio r of the O2 flux to the Cs+ flux, the spectra shift to higher emission-energy values, with the total shift amounting to ∼0.45 eV at a value of r ∼ 3.3. Concurrently, the intensity of Cs+ increases by ∼30%. The measured emission distributions of Cs+ ions from different samples were compared with the predictions of the electron-tunneling model of secondary-ion formation. It is found that the experimental spectra can be reproduced quite well when employing specific sets of parameters in that theoretical concept. The possible limitations of such a comparison are discussed.