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Isotopic fractionation in sputtering


Spicklemire, Stephen James (1990) Isotopic fractionation in sputtering. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/XEGH-4365.


Isotopic fractionation due to sputtering has been investigated via a collector type experiment in which targets of known isotopic composition have been bombarded with several keV Ar+ and Xe+ ions with fluences down to 3.0x1014 ions/cm2 , believed to be the lowest fluences for which such detailed measurements have ever been made. The isotopes were sputtered onto carbon collectors and analyzed with Secondary Ion Mass Spectroscopy (SIMS.) There is clear indication of preferential effects several times that predicted by the dominant analytical theory. Results also show a fairly strong angular variation in the fractionation. The maximum effect is usually seen in the near normal direction, measured from the target surface, falling continuously, by a few percent in some cases, to a minimum in the oblique direction. Measurements have been made using Mo isotopes: 100Mo and 92Mo and a liquid metal system of In:Ga eutectic. The light isotope of Mo is found to suffer a 53 ± 5‰ (note: 1.0‰ ≡ 0.1%) enrichment in the sputtered flux in the near normal direction, compared to the steady state near normal sputtered composition, under 5.0 keV Xe+ bombardment of 3.0 x 1014 ions/cm2. In the liquid metal study only the angular dependence of the fractionation could be measured due to the lack of a well defined reference and the nature of the liquid surface, which is able to 'repair' itself during the course of a bombardment. The results show that 113In is preferentially sputtered over 115In in the near normal direction by about 8.7 ± 2.7‰ compared to the oblique direction. 69Ga, on the other hand, is sputtered preferentially over 71Ga in the oblique direction by about 13 ± 4.4‰ with respect to the near normal direction.

Item Type:Thesis (Dissertation (Ph.D.))
Subject Keywords:Physics
Degree Grantor:California Institute of Technology
Division:Physics, Mathematics and Astronomy
Major Option:Physics
Thesis Availability:Public (worldwide access)
Research Advisor(s):
  • Tombrello, Thomas A.
Thesis Committee:
  • Unknown, Unknown
Defense Date:5 January 1990
Non-Caltech Author Email:spicklemire (AT)
Record Number:CaltechTHESIS:07282014-093054555
Persistent URL:
Default Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:8612
Deposited By: Benjamin Perez
Deposited On:28 Jul 2014 17:02
Last Modified:09 Nov 2022 19:20

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