X-RAY PHOTOELECTRON SPECTROSCOPY (XPS)
Description
In the X-ray Photoelectron Spectroscopy (XPS), also
known as Electron Spectroscopy for Chemical Analysis (ESCA), the
sample is irradiated with soft X-rays photons (1-2 keV). The X-ray
excitation of the inner shell electrons of target atoms induces
direct emisssion of photoelectrons.
The energy of photoelectrons is characteristic of the target material,
and measurement of the energy spectrum (number of count vs kinetic/binding
energy) provides valuable information about the top 2-20 atomic
layers,depending on the material studied. Peak position and peak
area are used to evaluate the composition, while the peak shape
give unique information about the chemical shifts or chemical
bonds of the elements.
Modes
of Operation
(1) Energy spectrum.
Survey spectra (typically 0-1000 eV) are measured to estimate
the composition, while high-resolution spectra (within 10-20 eV)
provide information about the chemical bonds.
(2) Mapping.
Choosing the energy of a single peak and scanning the focal point
of the lenses across the sample one gets information about the
lateral distribution of the corresponding species (elemental or
chemical state) on the surface.
(3) Imaging.
Parallel imaging of the whole field of view e.g. by using a second
hemispherical analyser allows real-time capability for chemical
state and elemental imaging with high spatial resolution (<10-15
microns) and high sensitivity.
Applications
The strength
of XPS is its ability to identify different chemical states. This
ability is useful in studies of oxidation/corrosion, adsorption,
catalysis, adhesion failure, thin film growth.
Advanced applications include depth distribution of the composition/chemical
states, assessment of thin film thickness among others.
Instrumentation
The energy spectra
and mapping are available on both, AXIS
165 and AXIS ULTRA. XPS imaging
is available on AXIS ULTRA only.
Examples
Elemental composition and mapping
(NiCo layer)
Chemical shifts (PET sample)
XPS of cokes (I)
XPS of cokes (II)
Imaging (Pt/Au
patterns)
More imaging from Kratos: 5
um Cu-grid and 15
um Au-electrode
Depth profiling of thin films (tungsten oxide)
Angle resolved studies (plasma grown Si-oxide)
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