Auger electron spectroscopy

What is AES analysis used for?

Auger electron spectroscopy is commonly used to determine the elemental composition of the surface of a material. When combined with a fast-moving beam, AES can be used to map out the surface. This can provide a digital image, allowing the user to see the surface on a very small scale. AES can also be used to probe the depth of a sample and identify elements and their oxidation states beneath the material surface. This makes it a very versatile technique to gather various types of data in a relatively short amount of time.

How does Auger electron spectroscopy work?

The Auger effect occurs when an electron is removed from a low-energy orbital of an atom, usually by using an electron beam. When this happens, the atom becomes unstable and requires another electron to fill the new vacancy formed. In order to do this, an electron from a higher energy orbital will drop into this gap, becoming the new core electron.

However, for this to happen, the extra energy of the high-energy electron must first be released. In most cases, this extra energy is released as a photon, such as an X-ray, which is emitted from the atom. In other cases, the extra energy will be transferred by a second electron, which will use it as kinetic energy and break free from the atom, being ejected in the process. The type of electron released from an atom in this way is called an Auger electron.

AES utilizes the Auger effect to gather important information about the surfaces of various materials. When an Auger electron is released, it will have a very specific amount of kinetic energy, which is dependent on the type of atom it was ejected from, and the oxidation state that it is in. Therefore, by detecting these electrons and measuring the energy that they carry, it is possible to gather data about the atoms in the sample and construct an image of its surface.

What are the limitations of AES?

As AES relies on the use of an electron beam to probe a surface, it will only work for analyzing semiconductors and conductors, which have the ability to easily transfer electrons throughout the material. Therefore, it is generally not suitable for analyzing insulating materials. Some insulators can be prepared with a conductive coating that will allow them to be analyzed, though this introduces additional preparation steps.

The probe speed impacts the AES image resolution; the faster a surface is probed, the lower the resolution that can be obtained. Longer scanning periods can improve this, but longer measurement times are needed. The electron beam can also be somewhat destructive to certain samples. This means that ideally, the sample must be able to withstand the bombardment from electrons to provide accurate data and reduce damage to the material.

AES vs XPS - what are the differences and when to use which one?

Both AES and X-ray photoelectron spectroscopy (XPS) revolve around detecting an electron that is ejected from within an atom. However, the key difference is that while in AES the electron is removed by firing a beam of electrons at the target atoms, in XPS X-rays are used to excite and remove the electrons.

This makes them largely similar techniques suitable for slightly different types of samples. To start with, XPS is able to analyze materials that do not conduct electrical charges, which AES cannot. This makes it the better choice for analyzing certain organic and polymeric materials.

On the other hand, AES is generally able to provide higher sensitivity than XPS due to the fact that it is easier to focus a beam of electrons than X-rays. Therefore, it can be used to probe more specific areas of a sample and provides higher-quality surface mapping of suitable samples.

Sample requirements and preparation

AES can generally be used on solid sample materials with little to no specific preparation. As it is usually conducted within a vacuum, the sample must be in a vacuum-stable state. For some insulators, it is possible to perform AES by first applying a conductive coat that will enable reducing the charge build-up from the electron beam. Clean and flat samples are preferred to optimize data quality.

Need an AES analysis?

Measurlabs offers high-quality AES analyses with fast turnaround times. If you have any questions about your sample or its suitability for the method, our experts are always happy to help. You can contact us using the form below.