XPS

X-ray Photoelectron Spectroscopy (XPS), also known as Electron Spectroscopy for Chemical Analysis (ESCA), is a non-destructive technique for analyzing the surface chemistry of a solid material.

How it works?

When a solid material is irradiated with a beam of x-ray, electrons are emitted from the material (photoelectric effect). An electron energy analyzer measures the kinetic energy and intensity of the emitted photoelectrons. The x-ray photon energy is also known (Al Kα 1486.7 eV or Mg Kα 1253.7 eV). The difference between the excitation energy and the photoeelctron energy is the binding energy, which is characteristic of the atoms in the test material.

A spectrum of photoelectron intensity over a broad range of binding energy (survey scan) shows all elements present on the sample surface. Subsequent narrow (i.e., high-resolution) scans can be obtained focusing on specific transitions of the elements revealing chemical and electronic state information. The example spectra to the right were taken from a silver sample.

Sample requirements

UHV-compatible solid (i.e., no outgassing)
Maximum diameter: 10 mm
Maximum thickness: 5 mm

What can XPS do?

Element identification and quantification of the top few (1-10) nm of sample.
Chemical state identification of the elements in the sample and information on local bonding environment of atoms.

The Amicus is equipped with a 10-sample carousel and a 10-sample loading cassette. Up to 10 samples can be loaded and analyzed with a single vacuum cycle.

It has a sensitive sample transport chamber which can be loaded in an inert atmosphere in a glovebox and carried to MARL where the samples can be loaded without exposure to air.

The Amicus has a high speed ion gun for quickly milling samples with minimal damage. This allows for depth profiling of thin film materials, i.e., determining chemistry as a function of depth.

The figure to the right shows two depth profiling experiments - one with a 240 nm Au film deposited on Si and one with a 240 nm SiO2 film on Si.
For the Au film, the first scans show Au with no Si. The remaining scans show Si with no Au.
For the SiO2 film, the first scans show O and a Si peak at 103.5 eV. Successive scans show no O and the Si peak is shifted to 99.2 eV for elemental Si.