Low energy polyatomic ion/surface collisions and their use as a means of surface modification
Abstract
The energy partitioning in low energy (1-100 eV) ion/surface collisions is key to understanding the inelastic, reactive, and soft-landing processes which occur in this low collision energy regime. The thermometer molecule method is used to measure the translational-to-vibrational energy (T${\to}$V) conversion efficiency for a liquid perfluoropolyether (PFPE) surface. Collisions of the ferrocene molecular ion are used to determine the T${\to}$V conversion efficiencies for Si(100) and both fluorinated and deuterated self-assembled monolayer (SAM) surfaces. Fluorocarbon surfaces, liquid PFPE and SAM, have conversion efficiencies of 18% and 19%, while the deuterated and Si(100) surfaces convert 13%. The scattered ion kinetic energies are low, less than 20% of the projectile's translational energy, and the bulk of the energy in the collision process, greater than 60%, is absorbed by the surface. Reactive scattering processes, chemical sputtering and ion/surface reactions, are presented for collisions of various projectile ions with Si(100), liquid PFPE, and fluorocarbon and deuterated SAM surfaces. Reactive collisions of various projectile ions with the liquid and fluorinated SAM surface show that the microstructure or the liquid surface is similar to that of the SAM. Reactive scattering of ferrocene molecular ions from SAM surfaces support the electron transfer mechanism associated with hydrocarbon projectile ion/hydrocarbon SAM surface reactions. The sequence of ion/surface reaction and SID is shown to occur via SID at or near the surface followed by reaction for collisions of OCNCO$\sp{+}$ projectile ions with a fluorinated SAM surface. Chemical modification of fluorinated SAM surfaces is achieved using low energy polyatomic ion/surface reactions, transhalogenation and trans-pseudohalgenation, and ion-assisted neutral annealing. Soft-landing of intact polyatomic ions is shown for various projectiles in fluorinated SAM surfaces. The soft-landed projectiles remain at the surface for several days under vacuum and a few days in ambient laboratory air. Evidence is presented which suggests that the soft-landed material remains at the surface as a charged species.
Degree
Ph.D.
Advisors
Cooks, Purdue University.
Subject Area
Analytical chemistry|Chemistry
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