Models for Molecular Ion Emission in SIMS

1 Models for Molecular Ion Emission in SIMS As covered in Section 3.3.4, there exist a range of models introduced in an effort to explain the detection of molecular ion emissions resulting from energetic ion impact, albeit if only qualitatively. These models, of which some share many similarities, are described henceforth in a chronological order. 

The Gas Flow model introduced shortly thereafter by the team of Michl (Orth et al. 1982) was developed in an effort to explain the cluster ion emissions recorded fi om fi ozen matrices. This model uses many of the same assumptions used in 

The Nascent Emission model formulated by Plog and Gerhard (Plog and Gerhard 1983a, 1983b) specifies that molecular ions are formed as a result of the sputtering of neutral molecular species (nascent species), which then dissociate on their departure from the surface. As the ions are specified to form as a result of a nonadiabatic 

The Desorption/Ionization model proposed by Pachuta and Cooks (Pachuta and Cooks 1987) introduced the concept of isomerization. In short, this introduced the 

There then remains the question of how the respective positive secondary ions are formed. Two mechanisms prevail in the literature. The first being the association of sputtered neutral elements or molecules of interest with cations sputtered as a positive ion. This then results in a positively charged cluster displaying a sufficient lifetime to allow its detection and the association of sputtered neutral elements or molecules of interest with a cation sputtered as a neutral excited atom. The second describes de-excitation following association via electron emission (an autoionization process) which then results in a positively charged cluster displaying a sufficient lifetime. 

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