Coating Thickness Software for Eagle µ-EDXRF Systems

There are three “default” kV excitation options in FunMaster (20, 30 or 40kV). Where a fast throughput is
required (no time to wait for vacuum pump down) and the selected analyte line energies allow, sample
measurements are made in air typically at 30 or 40kV. Where lower energy analyte lines are of interest e.g.
Au(M), Al(K), etc., a vacuum spectrometer environment is necessary and tube voltages of 20kV typically
used. However, other tube kV may be defined (i.e. 15kV), as used for the example “Cr on Steel” in this
manual.
NOTE: In practice as far as the influence of the scatter spectra has on subsequent FP calculations,
it is normally sufficient just to collect all scatter spectra data under vacuum and not both air &
vacuum unless, of course, all coating calibrations are to be made in an air filled sample chamber.
The important requirement is that a scatter spectrum contains sufficient statistically-valid data.
Apart from the kV and air/vac conditions, other settings used for scatter spectrum collection may differ from
those used for the actual calibrations — in particular the Amplifier Time Constant (i.e. the setting that
determines system throughput & energy resolution), tube current and measurement time. For example, at a
40kV (or other) excitation voltage a minimal TC setting (e.g. 2.5µs or 3.2µs DPP) would be used to collect a
scatter spectrum with a tube current setting to attain a maximum DT=30 to 35%. The low TC enables a
higher throughput (i.e. more data collectable in a shorter clock time) because of the lower overall system
dead time (DT) but of course at a poorer energy resolution. The poorer spectral resolution does not
degrade the required information contained in a scatter spectrum but would not necessarily be the
conditions used or indeed recommended for the actual analysis.
Typical scatter spectra collection conditions should be set as to enable sufficient data (a minimum of 10^6
total counts) to be collected within whatever time is needed - typically at least 1000 seconds. Therefore at
the required tube kV setting, a tube current sufficient to produce an input CPS that yields a DT of 35% or
less. A typical scatter spectrum, as obtained from a poly-capillary system, is shown in Figure 1.
Figure 1. Wax “scatter/excitation” spectrum for a polycapillary lens
system
1.2.1 Collection of Scatter Spectrum 8