  The argon content of titanium dioxide doped tantalum pentoxide thin films was
quantified in a spatially resolved way using HAADF images and DualEELS. Films
annealed at 300$^{\circ}$C, 400$^{\circ}$C and 600$^{\circ}$C were investigated
to see if there was a relationship between annealing temperature and bubble
formation. It was shown using HAADF imaging that argon is present in most of
these films and that bubbles of argon start to form after annealing at
400$^{\circ}$C and coarsen after annealing at 600$^{\circ}$C. A semi-empirical
standard was created for the quantification using argon data from the EELS
atlas and experimental data scaled using a Hartree Slater cross section. The
density and pressure of argon within the bubbles was calculated for 35 bubbles
in the 600$^{\circ}$C sample. The bubbles had a mean diameter, density and
pressure of 22\r{A}, 870kg/m$^3$ and 400MPa, respectively. The pressure was
calculated using the Van der Waals equation. The bubbles may affect the
properties of the films, which are used as optical coatings for mirrors in
gravitational wave detectors. This spatially resolved quantification technique
can be readily applied to other small noble gas bubbles in a range of
materials.
