Tellurite And Fluorotellurite Glasses For Active And Passive

7. Surface properties; MDO 255
quantitative elemental analysis, but is difficult to obtain accurately, particularly for multi-
component materials (see below).
Photoemission from electronic levels with a non-zero orbital angular momentum (j),
i.e. for electronic levels higher in energy than the s level, such as p, d, f, etc., results in a
spin-orbit doublet [3]. For degenerate p sub-shells, the ratio of the XPS peak areas of sub-
shells is ½ (e.g. Zn2p1/2 and Zn2p3/2), ⅔ for d sub-shells (e.g. Te3d3/2 and Te3d5/2), ¾ for f
sub-shells (e.g. W4f5/2 and W4f7/2) etc. A multicomponent glass for example, containing
d- and f-block elements such as zinc, tellurium, and tungsten, as well as lighter elements,
such as sodium, fluorine and oxygen, will result in a complex XPS spectrum with
multiple peaks, corresponding to the s, p, d, and f levels of the elements present, as well
as their loss tails and associated features.
In general, the photoelectron cross-section increases with increasing angular
momentum of the orbital; therefore the electron with the largest j value (e.g. Te3d) of a
given core shell results in the most intense XPS peak, and is most appropriate for semi-
quantitative chemical analysis [3]. The positions, widths, and areas of the peaks can then
be measured from wide and high resolution scans, and semi-quantitative analysis
performed with the appropriate sensitivity factors (which vary from spectrometer to
spectrometer). Overlapping peaks can be deconvoluted with Gaussian-Lorentzian fitting,
and attributed to different chemical species in the sample.
Peak areas are used to calculate the relative concentrations of species in the sample.
The ratio in atomic concentration of species A, and species B is given by equation (7.4).
[ A]
σ bζ
bλbη
bI
a
=
[ B]
σ ζ λ η I
a
a
a
a
b
(7.4)