Chang, Jui-Hsien (2008) Ultra low energy gold cluster ion beams for SIMS applications. PhD thesis, University of Warwick.

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Abstract

The purpose of work was to obtain gold and possible other negative ion
cluster beams where each constituent atom in the cluster carried an energy
≤ 1 keV, using the floating low energy ion gun (FLIGTM), and to test these in
secondary ion mass spectrometry. The heavy negative metal cluster is worth
researching because (i) there is the possibility of generating high secondary
ion/sputter yields, and (ii) negative ions would be useful for insulators.
The sputter cluster ion source (SCIS) developed in the University of
Antwerp (Belgium) was selected because it can emit cluster ions of pure
materials as well as compounds. Gold was chosen due to its high mass and thus
high sputter rate. The source was retrofitted to a FLIG column by designing
matched ion optics based on simulation, a new mass separator, vacuum devices
and power supplies. The ion gun of SCIS-FLIG was then tested and
characterised, and defects were improved. As the result, ultra low energy gold
cluster ions were obtained for the first time. The ratio of IAu1-:IAu2-:IAu3- is
about 13:1.2:1, and a maximum 1 keV Au1
– current density of 38 μA cm-2 was
obtained at the sample, which is superior to any reported negative gold cluster
ions source. Ions with higher energy (up to 3.7 keV) and positive ions were also
obtained. A preliminary study of the usefulness of the gold cluster ions in SIMS
depth profiling with a silicon sample was conducted afterwards. Nonlinear
sputtering with E0 ≤ 1 keV was observed for the first time. The sputter rates of
the ions are higher than that of O2
+ and Cs+. Gold deposition due to Au3
–
bombardment (E0 = 0.33 keV) was observed at a dose ≤ 0.54×1017 cm-2,
otherwise sputtering can be achieved with dose ≥ 1×1017 cm-2. A peculiar
observation is the time dependent evolution of the bombarded silicon surface
during subsequent atmospheric exposure. Further work in obtaining a more
reliable and long-lived source and a higher current density at the sample is
recommended.

Item Type:	Thesis or Dissertation (PhD)
Subjects:	Q Science > QC Physics
Library of Congress Subject Headings (LCSH):	Ion bombardment, Sputtering (Physics), Gold, Secondary ion mass spectrometry
Official Date:	August 2008
Dates:	Date Event August 2008 Submitted
Institution:	University of Warwick
Theses Department:	Department of Physics
Thesis Type:	PhD
Publication Status:	Unpublished
Supervisor(s)/Advisor:	Dowsett, M. G.
Sponsors:	Engineering and Physical Sciences Research Council (EPSRC)
Extent:	xvi, 133 leaves : ill., charts
Language:	eng
URI:	http://wrap.warwick.ac.uk/id/eprint/3639

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