Auger Electron Spectroscopy

Auger electron spectroscopy (AES) uses the weak Auger electrons excited in a sample surface by an electron beam to characterize the top ten to twenty five Angstroms of the sample. The Auger electrons generally range between zero and two thousand electron volts in energy.

AES systems operate at ultra-high vacuums, in the range 10-8 to 10-10 torr, comparable to the vacuum of outer space. The vacuum is created by a combination of turbo-molecular pumps and a large main ion pump. At these vacuum levels surface oxidation rates are drastically reduced, meaning that it’s actually possible to look at a fresh unoxidized metal surface. Such a surface can be created by fracturing a sample within the chamber of the AES unit or by sputtering away the surface layers using a beam of energetic argon ions. The latter technique is tremendously useful for analyzing the changing composition of the freshly exposed layers below the outer surface.

A good example of the application of this technique is to analyze a sequence of layers of CVD (chemical vapor deposition) components in an electronic device, peeling them away, one layer at a time. Other examples are determination of the nature of contaminating films on galvanized surfaces, variations in oxygen concentration in mixed oxides, and the nature of discolorations on steels. Combinations of AES and SEM are particularly powerful, using the imaging capabilities of SEM in combination with the surface analytical capabilities of AES.