Electronic and nuclear effects in ion-induced desorption from NaCl{100}

Multiphoton resonance ionization (MPRI) spectroscopy has been employed to investigate the ejection mechanisms of neutral and ionic particles from an ion-bombarded NaCl{100} single crystal. The results are used to reveal the similarities and the differences between ion bombardment and electron irradiation of alkali halides. The mass spectra of neutral species and positive and negative ions have been measured. The yield of Na⁺ ions is found to be two orders of magnitude higher than in measurements with electron bombardment. It is suggested that the secondary ions are created by direct emission from the collision cascade. The ejection of neutral Na atoms is observed to be very sensitive to the temperature of the target, the angle of incidence, and the state of the surface as determined by the time-of-flight (TOF) measurements. In particular, it is found that most of the neutral Na atoms are emitted with thermal energies, which indicates that desorption via electronic transitions dominates over ejections from collision cascades. The relative yield of the collisional component to the thermal component is found to vary significantly as the surface structure is modified. This investigation emphasizes the importance of measurements with low incident-ion dose which allows one to decouple the single ion/surface interaction from the accumulative effect of ion-induced surface modifications.