Collisions of ions with surfaces at hyperthermal energies for the chemical analysis and modification of surfaces
Abstract
Collisions of ions with surfaces in the hyperthermal energy range (1–100 eV) are advantageous in that the projectile ion is allowed to perform as a chemical reagent. This is the case because the amount of energy transferred to surface molecules (or to the projectile ion) upon collision is in the range of tens of kcal/mol, about the energies needed to drive many chemical reactions involving covalent bond formation. In this thesis, it is shown that ions colliding with surfaces at hyperthermal energies react selectively at the outermost molecular layers of a surface, providing sensitive chemical analysis and controlled chemical modification to those surfaces. The first example of an ion/surface reaction in this work involves transhalogenation at a fluorinated self-assembled monolayer (F-SAM) surface through dissociative ion/surface reaction. Chemical sputtering and X-ray photoelectron spectroscopy establish that reaction results in transformation of the terminal -CF 3 group on the surface to the terminal -CF2X, where X represents a halogen group contained in the projectile ion. An HO-terminated self-assembled monolayer (HO-SAM) surface is used as the primary substrate for another set of experiments. Silylation and esterification of this surface are achieved through the low-energy (∼15 eV) deposition of ions, such as Si(OCH 3)3+ and C6H5CO +. Chemical sputtering, reactive scattering, and Fourier transform infrared external reflectance spectroscopy demonstrate covalent bond formation and provide quantitative results about the surface modification. The observation of scattered ions arising from these collisions is also useful for the analysis of surfaces. Chemical sputtering, surface-induced dissociation, and reactive scattering yield separate, yet complementary information facilitating surface analysis. Chemical distinction and relative quantitation of surface groups are achieved by scattering the projectile ions, SiCl3+, CF3+, and the molecular ion of pyridine, C 5H5N+·, from various oxygenated surfaces.
Degree
Ph.D.
Advisors
Cooks, Purdue University.
Subject Area
Analytical chemistry
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