Scanning Auger Microscopy

pic49The field emission Auger microprobe is a high-sensitivity instrument for surface analysis. It has very high spatial resolution, with a minimum probe diameter of 8nm, and high energy resolution. Using a hemispherical electrostatic energy analyser with a large acceptance angle and a multi-channel detector, elements can be detected with concentrations as low as 0.2 atomic%, although higher concentrations are required for accurate quantification.

An incorporated SEM provides images of the sample and an EDXS detector provides quick preview analysis allowing precise selection of the location for point spectra, line scans, depth profiling, and Auger image mapping. EDXS is a very unusual capability in an Auger instrument; this JAMP was the first where an EDXS detector was successfully installed, overcoming challenges of the UHV environment.

Selected volumes can be milled away with the in-situ ion gun, allowing depth profiling to a depth of a few hundred nanometres. The ion beam can also be used to remove contamination and to neutralize surface charging for non-conductive samples.

In Auger electron spectroscopy a primary electron beam excites atoms at the surface of a material. The atoms return to a lower energy state by emitting either an x-ray or an Auger electron, both of which have energies characteristic of the emitting atom. An electrostatic energy analyser separates the electrons by energy and then a multi-channel detector counts the electrons and outputs an electron energy spectrum, which is used to identify the elements in the analysed material. Auger electrons have very low energies so only electrons emitted from very close (0-6 nm) to the surface escape the material and are detected for analysis.

Auger electron spectroscopy is, however, a very sensitive technique for surface analysis, with a quoted detection limit on the order of 0.1 atomic%. It can be used for quantitative analysis and mapping of most elements above He. Also, for many elements’ fine details within the energy spectrum give information about the chemical state.