How X-Ray Photoelectron Spectroscopy/ESCA Works

X-Ray Photoelectron Spectroscopy (XPS), also referred to as Electron Spectroscopy for Chemical Analysis (ESCA) is a surface analysis technique that provides quantitative and chemical state information about a sample material’s surfaces and interfaces.

XPS is an incredibly flexible, sensitive, and efficient analysis technique with applications across a broad range of organic and inorganic materials. Because it detects the spectrum of elements from lithium to uranium with detection limits of ca. 0.1 atomic percent, it is invaluable for identifying surface contaminants. Best of all, analysis can be done in as little as 30 minutes with full results within one business day.

So how does XPS/ESCA deliver results? Read on to learn how scientists perform XPS/ESCA testing and analysis.

How XPS Works

This technique uses an x-ray beam to excite the molecules on the surface of a sample, leading to a release of photoelectrons. By analyzing the energy of these photoelectrons, we can learn crucial elemental and chemical binding information about a material’s surface. Because XPS uses a low-energy electron beam to create a steady charge state at the surface, it is possible to use this test to analyze the surface composition of non-conducting materials.

What XPS Is Used For

XPS is used to analyze solids and powders. By providing insights on the surface chemistry of materials, XPS can resolve issues related to metal interdiffusion, resin-to-metal adhesion, and oxidation. Top applications include:

• Stainless steel passivation: XPS is a powerful tool to analyze the oxidation of chromium and iron at the surface of a sample.

• Plastics analysis: XPS is a favorite analysis technique for companies that use polymers or plastics in the manufacturing process. XPS is ideal for analyzing thin films (e.g., <1000 angstroms) on insulating substrates and for confirming suspected contamination in plastics.

• Quality control across manufacturing sectors: For manufacturers that make products where surface chemistry or thickness is critical to product function and safety, XPS can help ensure that a product adheres to specifications and delivers the expected level of quality.

Case Studies of XPS in Action

Example One: An electronics manufacturer contacted Innovatech because they had discovered hazing on samples of their polyimide film. They suspected the haze was caused by chromium residue, but couldn’t be sure.

Innovatech used ESCA/XPS to analyze the samples. Our survey scan confirmed the presence of chromium in the haze. The company was then able to identify the source of the contamination in their production line and remedy the problem.

Example Two: Customers frequently call on Innovatech to analyze samples of bulk stainless steel, to ensure that it meets industry standards for manufacturing. Stainless steel requires a chromium oxide-rich passivation layer on the surface to prevent rust, so our analysis focuses on analyzing that passivation layer.

With ESCA/XPS, we are able to identify the chromium to iron ratios within the sample. Bulk steel has a chromium to iron ratio of approximately .3, while a well-passivated stainless steel surface will have approximately a 2.0 ratio. This chemical analysis can determine whether a given sample is sufficiently passivated to prevent rust.

How to Analyze an XPS Scan

XPS scans are recognizable for their peaks and jagged lines. But have you ever wondered how to interpret XPS results? XPS analysis is based on the position and intensity of the peaks on the scans.

The location of the peak on the x-axis indicates the elemental and chemical composition and the height of the peak on the y-axis shows how much of a particular element is visible at the surface.

When you work with Innovatech, we provide actionable insights based on a three-part analysis process:

• The survey scan: Identifies the elemental composition of the sample surface.

• The high-resolution multiplex scan: Measures the atomic concentrations of the elements identified in the survey scan. The multiplex scan also measures the chemical environment of each element through its binding energies. Precise determination of binding energies is made by using curve-fitting routines, with a NIST database available for identifying binding energies with actual compounds. (Note: H and He cannot be detected. Detection limits are approximately 0.1 atom percent for most elements.)

• Depth profile: Measures the distribution of elements as a function ion beam etching. Depth resolution is dependent upon the sample and sputtering parameters (ca. 100 Å resolution is not unusual). The typical sputtering rate is 30 Å/min.

Will XPS Analysis Work For You?

Innovatech is a full-service analytical laboratory with a team of experienced scientists ready to recommend the optimal approach to your specific analytical needs — whether it’s XPS or another materials analysis, testing, characterization, or chemical analysis service.

We’d love to discuss your project. Give us a call at 1-888-740-LABS (5227) or 763-231-0150 and let us wow you with our personalized service and fast and accurate turnaround.