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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)