What Is X-ray Photoelectron Spectroscopy?
X-ray Photoelectron Spectroscopy (XPS), also known as Electron Spectroscopy for Chemical Analysis (ESCA), is a surface-sensitive analytical technique that probes the top 70–100 Å of a sample. The technique is based on photoelectrons emitted from atoms on the sample surface after excitation by x-rays, usually Al K-alpha (1487 eV).
The key strength of XPS is its surface sensitivity. The mean free path of the emitted photoelectrons limits the depth from which they can escape and be detected to the top 70 – 100Å of the surface using the typical Take-off-Angle (TOA, measured between the detector and the surface) of 90° and depending on the element from which the electron originated. Changing this TOA to a more grazing angle can reduce the analytical depth. This makes XPS the ideal technique for the analysis of thin films, surface contaminants, and oxidation/corrosion.
Depth and Angle Profiling
Offers depth profiling and
angle-resolved measurements to examine layered materials and surface composition variations.
Surface-Specific Analysis
Provides detailed chemical and elemental information from the top 7-10nm of a sample, ideal for thin films, coatings, and contamination studies.
Chemical Bonding Insight
Why Use XPS?
X-ray Photoelectron Spectroscopy (XPS) is a highly surface-specific technique that provides detailed chemical and elemental information from the top 7–10 nm of a material. It is ideal for analyzing thin films, surface contamination, oxidation, corrosion, and chemical bonding states. XPS enables both depth profiling and angle-resolved analysis, making it indispensable for understanding surface chemistry in industrial and research applications.
High-Resolution Detection
Advanced Sample Handling
Layered Material Analysis
Argon ion etching enables depth profiling to study composition changes across layers without losing chemical information.
How XPS Works
- Elemental Composition:
- XPS collects a survey spectrum over a wide energy range (-10eV to 1350eV) with high signal strength.
- Elements are identified by the detected peaks.
- Peaks are integrated to give the relative atomic percent of each element, normalized to 100%.
- Chemical Bonding Information:
- XPS takes high-resolution spectra focused on specific elements.
- These spectra use settings that enhance spectral resolution.
- Special models are used to fit each peak and determine their exact positions.
- The positions (binding energies) help identify what types of chemical bonds are present, using reference data.
- Depth Profiles:
- XPS can combine measurements with argon ion etching, which slowly removes material from the surface.
- This allows you to see how the composition changes with depth, useful for analyzing layered materials and estimating layer thickness.
- Angle-Resolved Analysis:
- By changing the angle of measurement, XPS can collect information from different depths without removing material.
- This helps estimate the thickness of layers in your sample.
Equipment Used for XPS
ThermoFisher Nexsa
- Spot Size: 10µm to 400µm.
- Sensitivity: 0.01 atomic % to 0.5 atomic % depending on the element.
- X-ray Source: Monochromated, micro-focused, high-efficiency Al Kα X-ray Anode.
Key differentiators
Strengths
- Provides chemical bonding information from the top 7-10nm not obtainable with any other technique.
- Capable of analyzing conductors and insulators.
- Compatible with a wide variety of sample types.
- Excellent detection limits (part per thousand for some elements) and spectral resolution.
Limitations
- Does not have ppm detection limits.
- Some sample degradation can occur due to heating from x-ray or flood guns.
- Chemical bonding information is not always possible in depth profiles due to reduction of sensitive species by argon ion sputtering.
- Not suited to very rough samples.
Example Outputs
Sample Requirements
XPS can analyze any sample compatible with an Ultra-High Vacuum (10-9 mbar) including polymers, powders, cured adhesives, liquid residues, fibers, viscous oil and gels, and any other solid sample.
- Solid phase.
- Stable under ultra-high vacuum conditions.
- Max dimensions: 60 mm (L) x 60 mm (W) x 20 mm (T).
- Flatter topographies improve signal detection.
- For Powder Samples: 5-10 mg is sufficient (as long as it can cover 0.5 cm x 0.5 cm of foil or Cu tape).
XPS Applications by Industry
Semiconductor & Microelectronics
XPS detects surface contamination, and checks oxidation states that could affect device yield. XPS can measure material work functions, critical for semiconductor performance. Depth profiling verifies thin-film chemistry and reveals interlayer diffusion in multilayer stacks.
Aerospace & Defense
XPS identifies oxidation, corrosion, and contaminants on metals and coatings. It validates surface treatments and supports failure analysis of mission-critical parts, such as delaminations.
Energy & Battery Technology
XPS analyzes electrode surfaces, SEI layers, and catalyst coatings for surface contamination and oxidation states, especially effective when paired with inert gas/vacuum transfer directly into instrument.
Polymers / Coatings / Adhesives
XPS detects contamination, chemical variations, and surface treatments on polymer and coating surfaces. It supports adhesion studies and failure analysis, such as delaminations and discolorations.
Medical Devices & Biotech
XPS verifies surface cleanliness, functionalization, and bioactive coatings and surface treatments. It helps detect residues and ensure material compatibility for regulated applications.
Automotive & Industrial Manufacturing
XPS identifies corrosion products, contaminants, and wear-related chemistry. It verifies pre-coat surface quality and supports root-cause investigations.
Environmental & Catalysis Research
XPS determines oxidation states and surface species on catalysts and environmental samples. It aids in evaluating reaction mechanisms and material degradation.
Techniques That Complement XPS
Similar to XPS but making use of the Auger electron transition, initiated by electrons and not x-rays, capable of smaller (~1µm) spot sizes; best applied to depth profiling experiments. Provides limited chemical information. Similar detection limits. Not able to analyze non-conductive samples.
Why Choose Covalent for Your XPS Needs?
Covalent’s Thermo Scientific Nexsa G2 provides advanced analytical capabilities, excellent signal to noise, accessories for all types of XPS experiments, and a team of XPS scientists with over 20 years of combined experience in XPS and materials science and engineering.
Frequently Asked Questions
How do the accessories help me do different XPS experiments?
Why is having experienced XPS scientists important for understanding my results?
What types of information can XPS provide about my sample?
How should I prepare my sample for XPS to ensure reliable results?
- Avoid contact of any kind with the region of interest.
- Loosely wrap the sample in aluminum foil and secure using double sided tape to the bottom of a rigid container.
- Secure the sample to the bottom of a rigid container with the surface of interest facing up.
What is the analysis depth and spatial resolution of XPS?
- XPS analyzes the top 7-10nm of a surface.
- Spot sizes range from 10 to 400µm (elliptical) and can be adjusted in increments of 5µm.