Electron energy analyzers measure the number of ejected electrons as a function of the electron energies. The analyzers must be located in a high vacuum chamber and isolated from stray magnetic fields (including the earthís) that deflect electrons. Past Auger spectrometers used several types of electron energy analyzers, including spherical sector and cylindrical mirror analyzers. However, modern instruments nearly always incorporate cylindrical mirror analyzers because their high transmission efficiency leads to better signal-to-noise ratios. The schematic shows a cross section of a cylindrical mirror analyzer in red. The primary electron beam hits the sample surface at the source point of the analyzer. Auger electrons move outward in all directions and some pass through the grid covered aperture in the inner cylinder. A variable negative potential on the outer cylinder bends the Auger electrons back through a second aperture on the inner cylinder and then through an exit aperture on the analyzer axis. The energy of transmitted electrons is proportional to the voltage (-V) on the outer cylinder.
Auger Tutorial: Instrumentation
In this Auger Tutorial from EAG Laboratories, we present the history of Auger, as well as the scientific principles behind the instrumentation and data provided by this analytical technique.
In 1923, Pierre Auger discovered the Auger Process and Auger electrons while irradiating samples with X-rays. The idea of using electron-stimulated Auger signals for surface analysis was first suggested in 1953 by J. J. Lander. However, it wasn’t until 1967 that Larry Harris demonstrated the use of differentiation for enhancing the Auger signals. This development provided the necessary sensitivity for useful measurements. Early differentiating instruments used analog circuits and lock-in amplifiers to provide differentiated spectra directly, but more modern instruments acquire electron intensities directly and use computer Display Algorithms to provide differentiated spectra. Today Auger electron spectroscopy is the most frequent analytical method for surfaces, thin-films, and interface compositions. This utility arises from the combination of surface specificity (0.5 to 10 nm), good lateral surface resolution (as little as 10 nm), periodic table coverage (except hydrogen and helium), and reasonable sensitivity (100 ppm for most elements).