Physical Electronics 710

ICAL has recently acquired this Scanning Auger NanoProbe, which features EDS (energy-dispersive X-ray spectroscopy) and EBSD (electron backscattered diffraction) capabilities. In Auger spectroscopy (AES), like SEM, a highly focused and energetically well-defined electron beam is incident on the sample, whereupon electrons ejected from the sample are analyzed in terms of their kinetic energy and quantity. Some of these electrons are characteristic Auger electrons and, much like characteristic X-rays, are the fingerprint of the atoms from which they are emitted.

Because of the low kinetic energies of the ejected Auger electrons, their escape depth is limited to a few atomic layers. 

Photo of Scanning Auger Electron Nanoprobe

Thus AES allows analysis of only the top atomic layers of the sample of interest. Therefore, Auger is a surface-sensitive technique (~5 nm) that complements the bulk X-ray microanalysis (~3 μm) of EDS. To allow observation below the surface of the sample, the system is equipped with in situ Ar-ion etching capability for depth profiling of the sample as well as charge compensation for insulating samples. The system operates under ultrahigh vacuum conditions with rapid sample introduction facilities. A secondary electron detector on this system allows high-resolution imaging, as previously described. Excepting hydrogen and helium, all elements can be detected.

In summary, the advantages of AES are:

  • Surface compositional analysis for all elements from Li (Z=3) and heavier of atomic monolayers (~1 nm)
  •  Quantitative analysis and mapping of surface components
  • Sub-micron spatial analysis; enhanced lateral spatial resolution for elemental analysis (<8 nm with a 20kV, 1nA electron beam)
  • Advanced charge compensation system allows for analysis of insulating materials
  • Limited chemical (valence state) information
  • Sputter depth profiling to characterize surficial stratigraphy (three dimensional analysis) using an Ar sputter gun
  • EDS detector for “bulk” compositional analysis and mapping; allows for direct comparison of composition of “bulk” material and surficial composition measured by AES.
  • EBSD detector for in situ phase identification, crystallographic orientation, and crystallographic preferred orientation and residual strain mapping

Further Reading About AES:

  • D. Briggs and M. P. Seah, Practical Surface Analysis by Auger and X-ray Photoelectron Spectroscopy, John Wiley and Sons, New York, 1983.
  • Powell, C.J. and Seah, M.P., 1990. Precision, accuracy, and uncertainty in quantitative surface analyses by Auger‐electron spectroscopy and x‐ray photoelectron spectroscopy. Journal of Vacuum Science & Technology A: Vacuum, Surfaces, and Films, 8(2), pp.735-763.
  • Powell, C.J., Jablonski, A., Werner, W.S. and Smekal, W., 2005. Characterization of thin films on the nanometer scale by Auger electron spectroscopy and X-ray photoelectron spectroscopy. Applied Surface Science, 239(3-4), pp.470-480.
  • Prutton, M., 2006, Scanning Auger Electron Microscopy, Wiley, 368 p.

Please refer to these tutorial websites for further information on instruments and methods described above:

Auger Electron Spectroscopy (AES)

 

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