Angle-resolved Auger electron emission from ion-bombarded NaCl surface

Characteristic electron emission spectra obtained from ion-bombarded sodium chloride surface are distinctly different and more complex than such spect ra from metallic sodium. The spectra for sodium halides have been explained recently in a context of the collisional deexcitation model in which the c ore excited sodium ion colliding with a halogen anion captures an electron which activates autoionizing deexcitation channels. However, a controversy has arisen whether the Auger deexcitation process takes place inside the so lid or in vacuum above the surface. In the present work we report on the an gular dependence of the Na Auger electron line positions and intensities. T he source atom energies and basic characteristics of their angular distribu tions are derived from the experimental data. An interpretation of the obse rved angular-dependent line shifts is given in terms of the Doppler effect. The results indicate strongly that the Auger deexcitation processes occur on sodium atoms ejected directionally above the surface due to direct knock -off collisions with primary ions. (C) 2000 Elsevier Science B.V. All right 's reserved.