Future Challenges and Prospects of Cluster SIMS

Cluster secondary ion mass spectrometry (SIMS) has considerable promise for use as a mass spectrometric molecular imaging and depth profiling method. Some future challenges for cluster SIMS are readily identified: extend the molecular mass range accessible to focusable small cluster beams; improve data rates for small clusters by moving away from pulsed primary beams; develop imaging modalities for very large cluster beams; develop understanding of parameters governing molecular ejection and ionization to allow improvements in useful ion yields; and develop understanding of matrix effects to allow for quantitative analysis. Efficiency is a central theme of this chapter; it can best be defined in terms of "useful ion yield," that is, the product of the fraction of target molecules consumed that are sputtered intact, the fraction of intact molecules that are ionized, and the fraction of ions that are transmitted and detected.