Type of Document Master's Thesis Author Nakles, Michael Robert URN etd-07232004-233646 Title Experimental and Modeling Studies of Low-Energy Ion Sputtering for Ion Thrusters Degree Master of Science Department Aerospace and Ocean Engineering Advisory Committee
Advisor Name Title Wang, Joseph J. Committee Chair Domonkos, Matthew Committee Member Hall, Christopher D. Committee Member Keywords
- Ion Propulsion
Date of Defense 2004-07-08 Availability unrestricted AbstractThis thesis investigates low-energy xenon-molybdenum (Xe+-Mo) sputtering
yields for ion energies of 100 eV and less. Sputtering yield data at these energies
are important for ion thruster design and lifetime prediction. The basic
principles of sputtering phenomena are discussed. An overview of various
popular types of experimental sputtering yield methods is presented with an
emphasis on the techniques that have been used to find Xe+-Mo sputtering
yields in the past. Sputtering yields in this study are found through both
models and experiments.
Sputtering yields are calculated using the Sigmund, Bohdansky, Yamamura,
and Wilhelm formulas. The computed sputtering yields for these models
varied widely at low-energy. TRIM (The TRansport of Ions in Matter),
a Monte-Carlo simulation program, was adapted to study sputtering yields,
and energy and angular distributions of sputtered atoms. Simulations were
run at various combinations of ion energy and ion incidence angle. TRIM
did not prove to be an adequate model for low-energy sputtering.
Experimental measurements of sputtering were made using both Rutherford
backscattering spectrometry (RBS) and mass-loss methods. Sputtering
was performed in a small vacuum facility using an ion gun. For the RBS
technique, sputtered material was collected on aluminum foil substrates. The
area density of the deposited Mo film on the substrates was measured using
RBS. These measurements enabled calculation of differential sputtering
yields, which were integrated to find the total sputtering yield. Sputtering
yield was found by the mass-loss technique by simply comparing the
mass of the sample both before and after sputtering using a microbalance.
Sputtering yields at 100 eV, 90 eV, 80 eV, 70 eV, and 60 eV were found
using the RBS technique. The mass-loss technique was only successful in
the 80 eV experiment. The experimental results were unexpected. The measured
sputtering yields were significantly higher than those reported by other
researchers. Also, sputtering yields were found to increase with decreasing
ion energy from 90 eV down to 60 eV.
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