Title page for ETD etd-05132002-124451


Type of Document Master's Thesis
Author Shuler, Shelby
Author's Email Address sshuler@vt.edu
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
Abstract
Interactions 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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