Auger electron spectroscopy
Auger Electron Spectroscopy (AES) is a fundamental analytical technique that is used to analyze the characteristics of different types of surfaces. It is able to ascertain data about the elemental composition and depth profile, as well as produce surface images of various types of conducting and semiconducting materials.
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What is the Auger effect?
The Auger effect occurs when an electron is removed from a low-energy orbital of an atom, usually by colliding it with another electron. 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. This type of electron which is released from an atom in this way is called an Auger electron.
What is Auger electron spectroscopy?
AES is a technique that utilizes the Auger effect in order 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 which 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 is AES used for?
AES is commonly used to identify the elemental composition of the surface of a material and when combined with a fast-moving beam, can be used to map out the surface itself. This can provide a digital image, allowing the user to see the surface itself on a very small scale. It 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.
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 conductors and semiconductors, as they have the ability to easily transfer electrons throughout the material. Therefore, it is generally not suitable for analyzing insulating materials, instead, a different analyzing technique may be preferable. Alternatively, some insulators can be prepared with a conductive coating which 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. Therefore, the time needed to record the required data with acceptable quality may vary case-by-case. The electron beam itself can also be somewhat destructive to certain samples. This means that ideally, the sample must be able to withstand the bombardment from electrons, in order 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 samples such as certain organic and some 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 for more specific areas of a sample, and provides higher quality surface mapping, provided that the material in question is able to conduct an electrical charge.
Sample requirements and preparation
AES is generally able to be used on solid material samples 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 still possible to perform AES, by first applying a conductive coat which will enable to reduce the charge build-up from the electron beam. Otherwise, clean and flat samples are preferred in order to optimize the quality of data acquired.
Need a AES analysis?
Measurlabs offers AES analyses of high quality fast service. 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 through the form below or by emailing us at firstname.lastname@example.org.
Suitable sample matrices
- Metallic samples
- Solid conductive materials
- Identifying elemental composition
- Imaging and elemental mapping of surfaces
- Depths profiling
Frequently asked questions
AES is often used for imaging and elemental mapping of surfaces, identifying the elemental composition of the surface, and depth profiling.
AES is generally only suitable for conducting and semiconducting materials. The electron beam can also be destructive to some sample materials, which can negatively affect the accuracy of the test results.
Solid conductive materials, semiconductors, and metallic samples.
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