Hyperthermal ion /surface collisions at self -assembled monolayer surfaces: Surface analysis and selective chemical modification
Abstract
Collisions of hyperthermal ions (1 to 100 eV) at molecular surfaces contain a center-of-mass energy greater than typical bond energies of that surface. This allows for both bond cleavage and bond formation during the course of hyperthermal ion bombardment, making this a very chemically interesting energy regime to study. The chemical reagent nature of these hyperthermal ionic projectiles permits both surface analysis and surface modification. Surface analysis from bond activation within fluorinated self-assembled monolayer (FSAM) surfaces upon hyperthermal ion bombardment is shown to create unique product ions. Due to the reactive nature of hyperthermal ions at molecular surfaces it is shown that the ions behave as chemical reagents during the course of the interaction with the surface. Bond activation based on the electronic structure of several transition metals as well as the thermochemistry of charge transfer from various reagent ions is explored. Bond cleavage within the F-SAM surface is found to occur from the transfer of either electronic energy (in the case of exothermic projectile ion neutralization) or momentum transfer (in the case of endothermic projectile ion neutralization) with subsequent ionization of characteristic surface species. Reactive collisions at isomeric monolayers are used to draw conclusions regarding adsorption geometries based upon distinctive formation of scattered ions. Chemically selective covalent surface modification is demonstrated through terminal functional group variation. Low energy, 15 eV, bombardment of an alcohol terminated self-assembled monolayer (HO-SAM) surface by tri-coordinated silyl containing cations, i.e. Si(CH3)3+, was observed to transform ca. 30% of the monolayer surface to the corresponding neutral trimethylsilyl ether. This modification was verified through both mass spectrometric and x-ray photoelectron analysis.
Degree
Ph.D.
Advisors
Cooks, Purdue University.
Subject Area
Analytical chemistry
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