Molecular secondary ion emission from binary collisions

Secondary ions, produced by neutral 1.0 MeV argon beam impact on Al2O3 and LiF thin films, are analyzed by a XY-TOF detection system. Angular distributions and initial velocities are simultaneously determined for ionized species originating from the bulk or from the adsorbate layer. The employed XY-TOF spectrometer was designed to measure accurately radial and axial velocity measurements of positive and negative secondary ions with mass <50 u and desorbed from the surface material in the 100-eV energy range. The analysis shows that high velocity diatomic and triatomic molecules can be also emitted in a process similar to the one involving atomic secondary ions, in which energetic binary collisions causes emission perpendicularly to the beam direction. The initial velocity distribution analysis is shown to be helpful in the identification of chemical species lying either on surface or in the bulk material.