These two spectroscopic methods are not the same, but they are very close. The only advantage of AES is the spatial resolution. For AES it may be up to approx 10nm comparing to some microns or tens of micron for XPS. If you don't need high spatial resolution, XPS is better since the interpretation of XPS spectra is easier and you can extract more chemical information. However, sometimes (for some elements in some oxidation states) Auger spectra may be more sensitive to chemical state than XPS spectra.

The fundamental principles of the two techniques are the same. One is a single photo-emission step (XPS), the other is a two-step emission process (AES). Indeed, we can see AES peaks in XPS but not XPS peaks in AES.

A host of reasons exist for why we use an electron gun rather than an x-ray source for laboratory-level AES. We should also remember some practical differences between conventional AES (with an electron gun) and conventional XPS (with an x-ray source).

* AES requires conductive substrates whereas XPS does not

* AES is more surface sensitive and has a higher spatial resolution

* AES is more sensitive to chemical state shifts of the parent element, but the interpretation of the spectra to resolve that information is more difficult in AES than in XPS. This is why the term electron spectroscopy for chemical analysis (ESCA) traditionally only means XPS and not also AES

* Damage to the sample (chemical reaction changes) is induced by an electron beam in AES and by x-rays in XPS

Both techniques can provide useful chemical information, but they are fundamentally different, with different initial and final states.

The electrons detected with each technique come from different locations: XPS - absorbed X-ray energy ejects a core level electron; AES - an electron from a higher energy level fills a core hole and an electron from the same level is ejected. The detected Auger electrons are coming from a region that is much closer to other atoms (hence, bonds, neighboring atoms in crystals, etc), thus is much more sensitive to chemical environment compared to the core-level peaks seen with XPS.

I have not done conventional AES with an electron gun, but I routinely look at both core-level peaks and the Auger regions in my XPS data collection for a consistent and comprehensive picture of the material chemistry, among other properties. There are factors that could contribute to differences in the spectra of electron gun AES versus x-ray AES, but that is probably beyond the scope of your question.

No problem Lynette, I would like to know if these differences give distinctive results or information detected on the end, are same.

The total spectrum of electron gun AES (that I have seen in the literature) includes backscattered electrons and the elastic peak, which are a direct result of using electrons create the core holes. Obviously, these would not be present using X-rays.

For X-rays, there may also be differences in spectra between using a nonmonchromatic source and a source with a monochromator. The first produces satellites in the spectrum (from additional transitions creating X-rays of different excitation energies) which may or many not overlap the Auger region of interest, depending on the sample; with the second, satellites are not seen (monochromator is used to select the desired excitation energy).

The raw spectra from AES and XPS will be different, and will have to be processed and interpreted differently, but in theory, they should give similar information. Ultimately, the specifics of the instrumentation being used and the composition and nature (amorphous, crystalline, etc) of the sample being measured will affect the data that is collected and what can be learned from it. One technique might be better suited than the other for a specific sample and the information you need from it.

Two books you may want to look at, if you need to know more of the details of either AES, XPS, or both:

Carlson, T.A., Photoelectron and Auger Spectroscopy, 1975

Hoffmann, S. Auger- and X-Ray Photoelectron Spectroscopy in Materials Science, 2013

If your university does not have these books, maybe you can get them through an inter-library loan program? Such programs are widely used here in the US; I do not know if the extent of similar programs in other countries.

https://books.google.com/books/about/Photoelectron_and_Auger_spectroscopy.html?id=Ey5RAAAAMAAJ

http://www.springer.com/us/book/9783642273803

Good comments

Differences

Instrumentation and Sample Extraction

ESCA analysis, which is also called X-Ray Photoelectron Spectroscopy (or XPS), uses an x-ray beam to excite atoms on the surface of a solid sample, which results in the emission of photoelectrons. Then, an energy analysis of the photoelectrons is performed to identify both elemental and chemical bonding information.

On the other hand, AES uses an electron beam to excite atoms, which results in the emission of electrons known as Auger electrons. Like ESCA, an energy analysis is then conducted to uncover the analytical information.

Unique Applications

ESCA analysis can analyze oxidation of chromium and iron. This is especially useful for electronics and medical device manufacturers that worry about oxidation leading to product malfunction or failure. For example, an electronics manufacturer discovered a haze on a polyimide film. The manufacturer believed that the haze was from the chromium film that was not completely etched away during manufacturing. ESCA scanned the area and determined that there was in fact a presence of chromium, supporting the manufacturer’s theory.

As for AES, this technique can analyze the chemistry and thickness of passivation layers of stents and small diameter wires. For example, AES was performed on a Nitinol stent to determine any impurities in the oxide layer and the thickness of the layer. Testing revealed that the passivation layer was composed mostly of titanium dioxide and its thickness was approximately 300 angstroms.

When is Each Testing Method Used?

ESCA analysis can be used to:

• Evaluate the passivation of stainless steels and the oxidation of chromium and iron
• Analyze the surface chemistry of polymers, glasses and other insulators
• Resolve issues related to metal interdiffusion, resin-to-metal adhesion or oxidation

AES can be used to:

• Determine the chemical composition of a surfaces and interfaces
• Analyze contamination and stains
• Analyze passivation layers

https://www.innovatechlabs.com/newsroom/975/whats-difference-esca-analysis-auger-electron-spectroscopy/