X-ray Photoelectron Spectroscopy (XPS)) is a high-precision surface analysis technique that allows for the determination of elemental composition, chemical state, and binding energy of atoms in the material's surface layer (depth of about 1–10 nm). This technique is based on the photoelectric effect, where electrons are ejected from atoms when the material is irradiated by monochromatic X-rays.
In industry, XPS is considered one of the most important tools in the field of quality control, research and development (R&D), and ensuring the performance of advanced materials. From semiconductor wafers, lithium-ion batteries to anti-corrosion coatings, XPS helps manufacturers understand surface chemical characteristics – a decisive factor for product performance and durability.
The operating principle of XPS
When X-rays with a defined energy (e.g., Al Kα = 1486.6 eV) are directed at a sample, electrons in the atom absorb energy and are ejected from the surface. The XPS device measures the kinetic energy of these electrons to determine binding energy (Binding Energy) – a value characteristic of each element and chemical state.
Basic equation: EB = hv - Ek - ɸ where:
EB: Binding energy of the electron,
hv: Energy of the X-ray photon,
Ek: Kinetic energy of the emitted electron,
ɸ : Device escape.
Through the value EBE_BEB, we can determine:
The type of element present on the sample surface,
Chemical state (e.g., Fe²⁺, Fe³⁺; C–O, C=O,...),
Depth distribution of components when combined with ion sputtering (Depth Profiling).
The role of XPS in modern industry
In the era of advanced materials and nanotechnology, the surface of materials plays a key role in most industrial applications. XPS helps control and optimize surface properties, ensuring product quality at the atomic level.
1. Quality Control (Quality Control)
Ensuring the purity of coatings, thin films, or microelectronic components.
Detecting contamination, oxidation, or unwanted changes in chemical state.
Testing the thickness and chemical composition of metal or polymer coatings.
2. Supporting R&D and developing new materials
Analyzing chemical reactions occurring on the surface during processing or operation.
Determining the correlation between surface structure and physical – mechanical properties.
Evaluating the effectiveness of surface treatment methods (such as plasma, laser, ion-beam,...).
3. Product testing and process optimization
Verifying compliance with production standards.
Analyzing surface defects during mass production.
Providing corrective actions or adjustments to manufacturing technology.
Applications of XPS in key industries
1. Semiconductor and microelectronics industry
In microchip production, transistors, and sensors, XPS is used to:
Analyze the oxide layer on silicon (SiO₂, Si₃N₄, HfO₂,...).
Check for surface contamination of the wafer during photolithography or etching.
Study the interface between material layers (interface analysis).
Benefits:
Enhance the reliability of microchips.
Reduce manufacturing errors due to contamination or chemical discrepancies.
Ensure adhesion and electrical stability of thin film layers.
2. Energy and storage materials industry
In the energy sector, XPS is a key tool for studying:
Lithium-ion battery electrode materials (LiCoO₂, LiFePO₄, Si/C,...).
The chemical structure of photocatalysts, electrochemical catalysts.
The mechanism of performance degradation due to surface reactions or the formation of SEI (Solid Electrolyte Interphase).
Specific applications:
Monitor the chemical changes of the electrode surface after multiple charge/discharge cycles.
Analyze the effectiveness of protective coatings in solid-state batteries.
Check the oxidation levels of catalyst compounds on TiO₂, ZnO,...
3. Aerospace industry
In the aerospace field, XPS supports the analysis of anti-corrosion, anti-oxidation, and thermal protection coatings.
Main applications:
Evaluate the durability of Al₂O₃, TiN, or CrN coatings on superalloys.
Detect surface chemical changes due to high temperatures or harsh environments.
Study carbon-fiber composite materials or heat-resistant ceramics.
4. Biomedical and polymer industry
In the research and development of biomaterials, XPS helps examine the surface of polymers, hydrogels, and implant materials.
Typical applications:
Analysis of functional groups on the surface of biomaterials (C–N, C–O, NH₂,...).
Determining the chemical composition of antibacterial or biocompatible coatings.
Evaluating the degree of chemical change after plasma treatment or UV exposure.
5.Advanced and nano materials industry
With the development of nano materials, XPS is an indispensable tool in analyzing structure and surface reactions.
Applications:
Analyzing the chemical structure of metal, oxide, or graphene nanoparticles.
Studying surface effects and oxidation states on nano catalysts.
Quality control of nano coating materials in optics and electronics.
Advanced XPS techniques in industry
Angle-resolved XPS (ARXPS): Determining the structure of thin films according to the angle of electron emission.
Depth profiling XPS: Analyzing the distribution of components with depth using Ar⁺ ion sputtering.
XPS mapping: Creating elemental distribution maps on the sample surface.
HAXPES (Hard X-ray Photoelectron Spectroscopy): Deeper analysis (10–50 nm), suitable for thick films.
Advantages and limitations of XPS in industry
Advantages:
Accurate analysis of composition and chemical states.
High sensitivity, suitable for thin films and nano coatings.
Can be combined with SEM, AFM, AES, or TOF-SIMS to expand the analysis range.
Limitations:
Cannot detect H and He.
Samples need to be conductive or coated with a thin conductive layer to avoid charging.
Must be measured in a high vacuum environment.
Trends and future of XPS in industry
XPS technology is rapidly developing with new directions:
Combining XPS and in-situ measurement: Direct analysis under the operating conditions of the sample (in-operando).
Application of AI and machine learning: Automating spectrum processing and signal recognition.
Environmental XPS: Allows measurement of samples at higher pressures, closer to real conditions.
Conclusion
X-ray photoelectron spectroscopy (XPS) plays a key role in modern industry, especially in fields requiring high surface accuracy such as semiconductors, energy materials, aerospace, biomedical, and nanomaterials. With the ability to deeply analyze surface chemical structures, XPS helps optimize production processes, ensure product quality, and drive technological innovation in the era of advanced materials.