Type of Document Master's Thesis Author Shuler, Shelby Author's Email Address email@example.com URN etd-05132002-124451 Title Investigation of Gas-Surface Dynamics Using an Ar Atomic Beam and Functionalized Self-Assembled Monolayers Degree Master of Science Department Chemistry Advisory Committee
Advisor Name Title Morris, John R. Committee Chair Crawford, Daniel T. Committee Member Tissue, Brian M. Committee Member Keywords
- self-assembled monolayers (SAMs)
- molecular beam
- ultrahigh vacuum
Date of Defense 2002-04-23 Availability unrestricted AbstractInteractions of gas-phase molecules with surfaces are important in many ordinary
events, such as ozone depletion, corrison of metals, and heterogeneous catalysis. These
processes are controlled by the bonding, diffusion, and reactivity of the impinging gas
species. Our research employs molecular beam techniques and well-characterized
surfaces to study these processes.
The goal of this study is to better understand how the physical and chemical
nature of the surface interface influences energy transfer dynamics in gas-surface
collisions. An atomic beam is used to probe the energy transfer dynamics in collisions of
Argon with model surfaces of functionalized self-assembled monolayers (SAMs)
(1-dodecanethiol and 11-mercapto-1-undecanol) on gold. The beam is directed towards the surface
at an incident angle of 30 degrees and the scattered Ar atoms are detected at the specular angle
of 30 degrees. Time-of-flight scans measure the velocity distributions of atoms leaving the surface,
which correlate with the energy transfer dynamics of the impinging gas atoms.
Gas-surface energy transfer experiments are accomplished by directing an 80 kJ/mol
Ar atomic beam at a clean Au(111) surface and surfaces composed of hydroxyl-terminated
or methyl-terminated SAMs on Au(111). The fractional energy transferred to
the bare gold surface is 69 %, while it is grater than 77 % for the monolayer-covered
surfaces. The extent of thermalization on the surface during the collision is significantly
greater for the methyl-terminated surface than for the hydroxyl-terminated surface. Since the two
monolayers are similar in structure, packing density, and mass, the differences in
scattering dynamics are likely due to a combination of factors that may include
differences in the available energy modes between the two terminal groups and the
hydrogen-bonding nature of the hydroxyl-terminated SAM.
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