Title page for ETD etd-07232004-233646


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
  • Sputtering
Date of Defense 2004-07-08
Availability unrestricted
Abstract
This 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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