Teignmouth Science and Technology Centre (TSTC)
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© 2017 Teignmouth Science and
Technology Centre (TSTC)
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with the express permission of Casa Software Ltd. (known as CasaXPS)
to surface analysis using XPS
(X-Ray Photoelectron Spectroscopy)
x-ray photoelectron spectrum is a sequence of measurements, where each
measurement records the numbers electrons of a given energy for a specific time
interval. The objective is to measure counts per second (CPS) as a function of kinetic
energy (eV) of emission for electrons from atoms in the surface material.
Measured in units of CPSeV, variation in intensity for electrons with differing
emission energies provides a means for characterising the electronic state of
atoms within the sample from which electrons are emitted and offers
quantifiable information about the surface composition.
iXPS data set consists of a spectrum at every pixel in an image. These
spectroscopic image data sets may exhibit lateral differential charging as a
An uneven X-ray flux
of photoelectron emission across the field of view
is not necessarily a problem for quantification where the limits of integration
can be adjusted to accommodate the charging. Neither is it a problem for peak
fitting where peaks can be fixed with respect to the primary peak which can be
allowed to move within limits. However, it is a problem for Principal Component
Analysis (PCA) which is used to improve the signal/noise in the iXPS data set.
PCA recognises different charge shifts as a separate component increasing the
number of components and therefore the possibility that some will be lost in
the noise of the data. Correction of charging at every pixel is therefore
necessary. This page illustrates the steps required to do this.