Article

Beyond Chemical Composition: How Surface Science Can Measure Electronic Properties

Surface Analysis Spotlight: XPS

by Sarah Zaccarine XPS Scientist

X-ray photoelectron spectroscopy (XPS) is a widely utilized technique for analyzing surface composition and chemical states. In many applications, scientists and engineers need complementary information to optimize a material’s performance in a device, including details about optical and electronic properties. This is critical for systems including semiconductors, photovoltaics, sensors, (opto)electronics, batteries, and other chemical redox systems.

Modern XPS instruments have evolved to include complementary techniques that provide deeper insights into electron behavior, chemical bonding, and material properties. These advancements enable researchers to go beyond traditional surface chemical analysis, addressing challenges in material science and device engineering. PHI XPS instruments offer multiple complementary techniques to obtain insights into optical and electronic properties during the same experiment.

Reflection Electron Energy Loss Spectroscopy (REELS): REELS complements XPS by providing optical and chemical information. It is used for:

• Measuring optical band gaps, critical for semiconductors and optoelectronic devices.
• Determining hydrogen content, which is particularly relevant in thin films and hydrogen storage materials.
• Analyzing carbon hybridization, offering insights into organic and inorganic materials.

Ultraviolet Photoelectron Spectroscopy (UPS): UPS employs low-energy UV photons instead of X-rays, achieving higher spectral resolution. This method allows researchers to:

• Study the valence band structure in detail.
• Measure work function and ionization potential, key parameters in electronic device design and characterization.

Low-energy Inverse Photoemission Spectroscopy (LEIPS): IPES probes the conduction band by analyzing unoccupied electronic states. Key applications include:

• Investigating the electronic structure of metals and conductive materials.
• Measuring electron affinity, crucial for understanding charge transport mechanisms.
• The low energy of LEIPS is critical for studying beam-sensitive materials, such as organic semiconductors, without causing damage; this is not possible with traditional IPES and is only available on PHI XPS instruments.

Combined, UPS and LEIPS offer analysis of the full electronic band gap, while REELS provides insight into optical and dielectric properties of a material. By leveraging these advanced techniques, researchers can unlock a holistic understanding of material surfaces and interfaces, enabling breakthroughs in material design and application.

To learn more about the options available on PHI XPS instruments for optical and electronic property analysis, please visit Dr. Sarah Zaccarine’s poster during the upcoming PCSI-50 Conference in Konda, HI starting January 19.  She will be giving a short presentation on January 20 at 9:10 am and her poster will be available for viewing and discussion throughout the week.

For more information on the differences between REELS, UPS, and LEIPS and detailed guidance on designing a sample and experiment for this type of analysis, please watch the recent two-part installment in the PHI webinar series. Dr. James Johns discusses these topics in detail in Part 1 and Part 2, available now on the PHI YouTube channel.