Scanning Auger Nanoprobe Laboratory

What is Auger Electron Spectroscopy (AES)

Auger Electron Spectroscopy (AES) is an analytical technique that uses a primary electron beam to probe the surface of a solid material. Secondary electrons that are emitted as a result of the Auger process are analyzed and their kinetic energy is determined. The identity and quantity of the elements are determined from the kinetic energy and intensity of the Auger peaks. The nature of the Auger surface analysis process is such that Auger electrons can only escape from the outer 5-50 Ň of a solid surface at their characteristic energy. This effect makes AES an extremely surface sensitive technique. A finely focused electron beam can be scanned to create secondary electron and Auger images, or the beam can be positioned to perform microanalysis of specific sample features. Applications include materials characterization, failure analysis, thin film analysis, and particle identification.

The Auger Process

The basic Auger process starts with removal of an inner shell atomic electron to form a vacancy. Several processes are capable of producing the vacancy, but bombardment with an electron beam is the most common. The inner shell vacancy is filled by a second atomic electron from a higher shell. Energy must be simultaneously released. A third electron, the Auger electron, escapes carrying the excess energy in a radiationless process. The process of an excited ion decaying into a doubly charged ion by ejection of an electron is called the Auger process, named for its discoverer, Pierre Auger. As described, the Auger process requires three electrons, thus we cannot detect H or He but can detect all other elements from Li on up.

The instrument

We have a PHI 700 Scanning Auger Nanoprobe that provides down to 6nm secondary electron image resolution with the sample in the analytical position and 8nm Auger resolution with high elemental sensitivity. The analyzer and the electron gun assembly is coaxial, allowing from greater flexibility in analyzing topographically challenging samples. The system incorporates a low energy ion gun to do light sputter cleaning of the sample surface or sputter depth profiling. The system is fully automated with integrated control software and data processing.

Example Data

In this example, a particle of interest is identified in the SEM micrograph.  Auger survey spectra from areas on and around the particle identify Cu and Ti in the particle residing on an SiO2 surface.  Elemental maps obtained from area containing the particle identify distinct Cu and Ti phases in the particle and the Si from the surrounding substrate.

Specifications

• Secondary Electron Image Resolution: 6 nm

• Auger Electron Analysis Resolution: 8 nm

• Detection Limits: 0.1 to 0.01 atomic%

• Analysis Depth: 5 to 50 Å

• Sample Size: Up to 2" diameter

Sample Restrictions

Samples must be solid and vacuum compatible.  Insulating samples can be more difficult.  Because Auger is a surface sensitive technique, gold or carbon coating must be avoided.

Other sources of information on AES

There are numerous sources of information about the Auger technique and itís applications.

Some Examples are:
Handbook of Auger Electron Spectroscopy, C.L Hedberg (Published by Physical Electronics, Inc.)
Photoelectron and Auger Spectroscopy, T.A. Carlson (Plenum Press New Your, 1975)

For futher information about AES at Stanford, please contact Chuck Hitzman (chitzman@stanford.edu)