X-Ray Photoelectron Spectroscopy Applications

Improving energy storage is crucial for transitioning to carbon-neutral technologies. Advancements in battery research require a comprehensive understanding of cell materials, necessitating the use of various analytical techniques. 

Surface analysis, particularly X-ray photoelectron spectroscopy (XPS), is one of the leading methods used, in part due to the technique’s ability to detect lithium and other light elements. XPS and related surface analysis methods reveal the chemistry of a sample’s outermost atomic layers, which are vital in battery materials such as electrodes or separators due to their contact with the electrolyte and influence on device performance over time.

Surface chemistry plays a crucial role in the performance of catalysts, and XPS has been a valuable tool for assessing both active and support materials. By quantifying the chemical states at the surface, XPS enables investigation of batch failures and provides insights into changes in catalytic activity throughout the material’s lifecycle.

Precise control of the biological activity of surfaces is becoming increasingly important for applications in biomedical research. Over the years, there has been a focus on modifying the surface chemistry of in-vivo medical devices like stents and joint replacements to ensure stability within the patient and offer additional advantages such as drug elution. These processes are now being expanded to include the use of active nanoparticles for antimicrobial coatings on fabrics and surfaces, as well as improving the comfort of devices like contact lenses. XPS has emerged as a crucial technique in the development of such materials.

The development and use of 2D materials has grown rapidly over the last decade, since the award of the Nobel prize to Geim and Novoselov in 2010 for the isolation of graphene. The ultra-thin nature of the films, and the importance of chemical modification in tuning their performance to meet the requirements of an application, means that XPS and other surface analysis techniques are ideally suited to their characterization. 

XPS can help identify the root cause of failures resulting from contamination or defects. When the issue resides at the surface or an interface, XPS and XPS depth profiling can be employed to determine the chemical changes responsible for defects or delamination.

Enhancing the efficiency of solar cells is a significant focus of research to decarbonize energy generation. Advanced photovoltaic devices employ intricate material compositions or layer structures to optimize sunlight-to-electricity conversion. XPS, along with complementary techniques like ultraviolet photoelectron spectroscopy (UPS) and reflection electron energy loss spectroscopy (REELS), can be employed in tandem to comprehensively investigate the chemical composition and electronic structure of newly developed solar cell materials.

Thin, transparent coatings are applied to glass surfaces to impart beneficial properties for automotive, architectural, and biological applications. Whether they aim to provide anti-reflective properties or ensure that a drug can be stored safely in a vial, the layers applied to the surface can be quite complex. XPS depth profiling using either monatomic or gas cluster ion sources is an ideal way to verify the correctness of the created layer structure.  

Modern semiconductor devices consist of ultra-thin layers deposited on substrates, sometimes doped to refine their performance. Techniques such as XPS depth profiling, angle resolved XPS, ISS, UPS, and REELS are crucial for comprehending these layer structures and confirming their integrity. While XPS may lack the spatial resolution to identify features on patterned wafers, surface analysis methods are valuable for assessing bond pad conformity, developing ultra-thin layers for chip design, and measuring layered materials like OLEDs or displays.

XPS helps analysts investigate various surface issues on metal and oxide surfaces. Passivation layers used for steel protection can be efficiently investigated using XPS due to their thin nature. Measuring the composition and thickness of these protective oxide films on metals makes it possible to understand and adjust their performance. The chemistry of oxide and metal surfaces holds significance across a wide range of applications, including pigments, catalysis, glass coatings, and biomaterials.

In the past thirty years, XPS has emerged as a key analytical technique for studying polymeric materials, primarily due to advancements in insulator analysis and the introduction of gas cluster ion sources. In addition to identifying and quantifying elemental and chemical state and detecting organic and inorganic contaminants, XPS now allows for more advanced analysis. It can investigate surface uniformity, which is crucial when applying surface treatments to achieve specific properties. Using gas cluster ion sources enables probing of interfacial chemistry by selectively removing surface material and measuring the remaining components without damaging the underlying chemistry, a limitation observed with monatomic ion beams.