Date of Award
12-2009
Document Type
Dissertation
Degree Name
Doctor of Philosophy (PhD)
Legacy Department
Physics
Committee Chair/Advisor
Manson, Joseph R
Committee Member
Daw , Murray
Committee Member
Marinescu , Catalina
Committee Member
Tritt , Terry
Abstract
In the initial portion of this dissertation studies of Ar
scattering from Ru(0001) at thermal and hyperthermal energies are
compared to calculations with classical scattering theory. These
data exhibited a number of characteristics that are unusual in
comparison to other systems for which atomic beam experiments have
been carried out under similar conditions. The measured energy
losses were unusually small. Some of the angular distributions
exhibited an anomalous shoulder feature in addition to a broad
peak near the specular direction and quantum mechanical
diffraction was observed under conditions for which it was not
expected. Many of the unusual features observed in the
measurements are explained, but only upon using an effective
surface mass of 2.3 Ru atomic masses, which implies collective
effects in the Ru crystal. The large effective mass, because it
leads to substantially larger Debye-Waller factors, explains and
confirms the observations of diffraction features. It also leads
to the interesting conclusion that Ru is a metal for which atomic
beam scattering measurements in the purely quantum mechanical
regime, where diffraction and single-phonon creation are dominant,
should be possible not only with He atoms, but with many other
atomic species with larger masses.
A useful theoretical expression for interpreting and analyzing
observed scattering intensity spectra for atomic and molecular
collisions with surfaces is the differential reflection
coefficient for a smooth, vibrating surface. This differential
reflection coefficient depends on a parameter, usually expressed
in dimensions of velocity, that arises due to correlated motions
of neighboring regions of the surface and can be evaluated if the
polarization vectors of the phonons near the surface are known. As
a part of this dissertation experimental conditions are suggested
under which this velocity paramenter may be more precisely
measured than it has been in the past.
Experimental data for scattering of argon, neon and xenon atoms
from molten gallium, indium and bismuth surfaces are compared to
calculations with classical scattering theory. The results of the
theory are in reasonable agreement with observed energy resolved
spectra taken at fixed angles, with in-plane angular distribution
distributions, and with the first available out-of-plane angular
distribution spectra for these systems. For all three of the rare
gases, only scattering from liquid Ga required the use of an
effective surface mass equal to 1.65 times the mass of a single Ga
atom. The need for a larger effective mass has been noted
previously for Ar/Ga scattering and is indicative of collective
effects in the liquid Ga. Comparisons with data taken at low
incident energies enables estimates of the physisorption well
depth in the interaction potentials for many of the gas-metal
combinations.
Surface corrugation is considered in a theory for which the
surface corrugation amplitude is estimated from the temperature
dependence of the most probable intensity for energy resolved
scattering distributions. The theory is applied to an
approximation for a sinusoidal surface corrugation. Final energy
resolved spectra, in-plane and out-of-plane angular spectra are
examined that exhibit reasonable agreement with data for
scattering of rare argon from liquid metals. This establishes
benchmark results for the behavior of this theory. Rainbow
scattering is also considered.
Recommended Citation
Hayes, William, "Atom Scattering from Metals" (2009). All Dissertations. 458.
https://tigerprints.clemson.edu/all_dissertations/458