Particle-induced desorption in mass spectrometry .1. Mechanisms and processes

Desorption of (predominantly) organic molecules, induced by particles with keV to MeV energy incident on a condensed phase target, is the topic of this review. The focus is on MeV atomic ion-induced desorption-plasma desorption (PD). Parallels with keV particle desorption-secondary ion mass spectrometry (SIMS) and fast atom bombardment (FAB)-will be presented more schematically and chiefly for comparison purposes. Current understanding of desorption mechanisms by referring to insights from theory of the processes is surveyed, and the underlying similarities as well as differences between keV and MeV particle desorption are addressed. Several connections between particle-induced desorption and photon-induced desorption (e.g., matrix-assisted laser desorption/ionization-MALDI) are briefly outlined. Results from computer simulations are used to visualize the dynamics of the desorption process. A brief description of experimental characteristics of desorbed species, aimed at elucidating the mechanisms of desorption, is given, partly to illustrate the use of mass spectrometry in fundamental studies of ion-solid interactions. Ionization pathways in PD and molecular SIMS are briefly summarized. No special emphasis is placed in describing the ''generic'' instrumental setup for particle desorption and only specific technical aspects, not treated elsewhere, e.g., time and spatial correlation of the ejected species, are discussed here. In the second part of this review (subsequent article) desorption induced by polyatomic projectiles, and effects accompanying ion ejection, namely secondary electron emission, impact-induced photon emission, and sputtering of clusters (fullerenes in particular), are also reviewed. In conclusion, selected examples for analytical applications of desorption methods that may illustrate current and emerging trends and perspectives are discussed. (C) 1996 John Wiley & Sons, Inc.