X-Ray Photoelectron Spectroscopy, or XPS analysis, is a highly flexible, expedient, and accurate form of surface analysis used for component identification, contaminant analysis, and quality assurance in a wide variety of industries. Here is what you need to know about XPS analysis and whether it’s right for your needs:
What is XPS Analysis?
XPS analysis is also known as Electron Spectroscopy for Chemical Analysis (ESCA). It is a surface analysis technique that can identify the elemental composition of a material, as well as providing quantitative and chemical state information about that sample’s surfaces and interfaces.
XPS analysis is highly useful as a surface analysis technique for the identification of both organic and inorganic materials for several reasons:
- It’s accurate: XPS analysis is capable of detecting the spectrum of all surface elements (except, under most circumstances, hydrogen and helium) within ca. 0.1 atomic percent.
- It can determine both surface elements and chemical status: XPS identifies elements by reading the binding energy of their core electrons. This energy also changes relative to the chemical environment of the surface material—this is called its “chemical shift.” By analyzing both the energy reading itself and its chemical shift, XPS can determine both the elements present on the sample material and the material’s chemical composition in a single test. This is why XPS is also called Electron Spectroscopy for Chemical Analysis.
- It’s fast: XPS analysis can take as little as 30 minutes. Clients typically receive their results in a single business day.
How does XPS Analysis Work?
XPS analysis passes an x-ray beam over the surface of the sample being analyzed in order to “excite” the atoms on that surface. Atoms are “excited” when their core electrons absorb the photon energy from the beam as it passes.
When core electrons absorb enough photon energy, they detach from the atom itself and emit out onto the surface of the sample material, where they’re subsequently detected by the testing equipment. The specific amount of binding energy required to cause a core electron to be emitted and detected is unique to each element. By measuring how much energy each electron absorbed before emitting, it’s possible to identify the element the core electron emitted from.
The amount of binding energy required for electron emission changes as well, depending on the chemical environment the element is in at the time of the emission. This is an effect called “chemical shift.” Different chemical compositions also affect emission requirements in unique, highly precise ways.
By measuring how the chemical environment of the sample material affected how much binding energy was required for each core electron to emit, therefore, XPS analysis can successfully identify the atoms present on the surface of the sample material and the chemical environment each element exists in on the material.
For more information on how XPS analysis works, read our full article.
What is XPS Analysis Used For?
Naturally, XPS analysis is primarily used for surface characterization: that is, to identify the atomic and chemical properties of the outermost 10 nanometers (or three atomic layers) of natural or engineered materials such as organic and inorganic compounds, semiconductors, and thin films and coatings.
XPS analysis is commonly used as a quality assurance test in general manufacturing, medical device manufacturing, polymers and plastics, and electronics manufacturing industries. The kind of surface characterization that XPS analysis provides gives these manufacturers a great deal of information about the specifications of their products, such as the product’s thickness and toughness, along with its susceptibility to rust, corrosion, and other forms of contamination.
Here are some real-world examples of how Innovatech has used XPS analysis to solve problems for our clients in the past:
Examples of XPS Analysis Use
1. Analysis of haze on polyimide substrate
An electronics manufacturer suspected a haze they observed on a polyimide film they were producing was a chromium residue contaminant. Innovatech used XPS analysis to scan the hazed area and confirmed the manufacturer’s suspicion: chromium was present in the hazed areas of the film, indicating that chromium film was not completely etched away during the manufacturing process.
2. Analysis of a contaminant on Polyethylene
A plastics manufacturer found a brown-colored contaminant on one of their polyethylene parts. They suspected the contaminant to be rust from a piece of steel that had come into contact with the part. Innovatech used XPS analysis to analyze the thin film left behind on the surface of the polyethylene by the contaminant. Our scan showed the presence of both iron and oxygen on the polyethylene part, supporting the manufacturer’s hypothesis that rust was the contaminant.
3. Stainless steel passivation testing
This is one of the tests Innovatech most commonly uses XPS to accomplish. In order to prevent stainless steel products from rusting, it’s necessary to coat the surface of the steel with a chromium oxide-rich passivation layer. XPS is an ideal way to test whether this layer is sufficient to prevent rust, because it provides both a quantitative measurement of surface impurities on the topmost layer and the required information on the oxidation state of the chromium and iron.
For more information on interpreting XPS analysis results, read our full article.
Is XPS Analysis Right for My Needs?
XPS analysis is probably right for you if you require surface chemistry and/or thickness product testing and…
- Your product is a conductive and/or insulating sample, such as ceramic, polymer, metal, or glass
- You need to find and identify surface contaminants
- You need to understand your product’s adhesion properties, resistance to corrosion, response to friction, and/or response to chemical reactions
XPS analysis is probably NOT right for you if…
- You need to identify the presence of hydrogen and/or helium on the surface of your sample
- Your sample is larger than an inch in any lateral direction and taller than half an inch or smaller than one millimeter
- You need to reproduce results across several samples with a low margin of error
- Your sample cannot withstand a high vacuum environment
For more information on whether XPS analysis is right for you, read our full article.
If you think XPS analysis is the right testing procedure for your needs, contact the experts at Innovatech right away. You can receive results in as little as one business day.
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