XPS for Elemental Analysis Presentation.pptx

X-ray Photoelectron Spectroscopy (XPS): An Overview

X-ray Photoelectron Spectroscopy (XPS) is a sophisticated and surface-sensitive analytical technique that leverages the photoelectric effect to identify elements present within or on the surface of materials. Beyond mere elemental composition, XPS provides detailed insights into the chemical states of these elements, the electronic structure, and the density of electronic states in the material.

Principles of XPS:
XPS operates by irradiating a material with a beam of X-rays, causing the emission of photoelectrons. The kinetic energy and number of these ejected electrons are measured, allowing for the determination of the elemental composition and chemical state of the elements. This measurement technique is inherently quantitative, offering precise information about the sample's surface composition and chemistry.

Applications and Capabilities:
One of the key strengths of XPS is its ability to not only identify the elements present but also to elucidate their chemical bonding states. This dual capability makes XPS a powerful tool in materials science for understanding the intricate details of chemical processes occurring at surfaces or interfaces.

Elemental and Chemical State Analysis:
XPS can detect all elements except for hydrogen and helium when using laboratory X-ray sources. The technique boasts a detection limit in the parts per thousand range, with parts per million (ppm) sensitivity achievable through extended collection times and focusing on the topmost surface layers. The high sensitivity and specificity of XPS make it invaluable for a wide range of materials, including:
- Inorganic compounds
- Metal alloys
- Polymers
- Catalysts
- Glasses and ceramics
- Paints and inks
- Biological samples and biomaterials

Surface and Depth Profiling:
XPS can perform both surface and depth profiling analyses. Surface profiling involves scanning the surface to map the elemental composition across different regions, whereas depth profiling, when combined with ion-beam etching, allows for the analysis of subsurface layers by sequentially removing material.

Chemical State Information:
The chemical state information provided by XPS is crucial for understanding the nature of chemical bonds and interactions within the material. This capability is particularly important in fields such as catalysis, corrosion studies, and surface treatments, where the chemical state can significantly influence material performance.

Operational Requirements & Advancements:
XPS analysis requires high vacuum (residual gas pressure ~10^-6 Pa) or ultra-high vacuum conditions (p < 10^-7 Pa). However, a notable advancement in the field is the development of ambient-pressure XPS, which enables sample analysis at pressures of a few tens of millibars, expanding the technique's applicability to more diverse and less stable samples.
XPS is a versatile analytical technique that provides detailed insights into the element composition.

1. By Asma Shahi XPS for elemental analysis

2. A sample is irradiated by X-ray beams, which interact with the inner electron shell  of atoms.  Photon energy of the X-rays is transferred to an electron in the inner shell, enabling it (the photoelectron) to escape from the sample surface.  An analyzer measures the kinetic energy of the photoelectron, which is equal to the electron’s binding energy. Knowledge of the binding energy allows identification of the element. Principle: -

3. 3 Information obtained from XPS graph: - X-ray photoelectron spectroscopy detects the electron energies and identifies the elements and oxidation states of the atoms in a sample. The XPS spectrum shows several emitted electrons against their kinetic energy. The XPS method has very important applications on solid surfaces and as a non-destructive method of analysis.

4. This is a typical “survey” or wide-range scan. Scanning from 0-1100 eV it detects an element on the surface that is >0.1 At %. Ex: The surface of a Tape release liner has a silicone coating based on the 2:1:1 ratio of C:O:Si. 4 Line Profiling

5. The shifts in the XPS peak is related to its oxidation state and higher shift in binding energy corresponds to higher oxidation state. Atom loses valence charge, BE increases Atom gains valence charge, BE decreases 5 Oxidation States

6. High resolution C1s spectrum showing Carbon-Oxygen and Fluorocarbon bonding states. 6 Chemical Bonding

7. Oxidized and clean Cr 2p spectra (left). Oxidized and clean Cu 2p spectra (right).
The oxide layer resulted in extra peaks (shoulder at higher BE—left of the main line). 7 Oxidized surfaces

8. When an electronics manufacturer observed a haze on a polyimide film, they suspected chromium residue resulting from a chromium film not being completely etched during the production.
XPS testing produced the following testing survey scan of the hazed area. The survey scan shows the presence of chromium (C1s) in the hazed area, indicating that the chromium film was not completely removed. 8 Contaminated surfaces

9. A depth profile can help one understand how the material changes as a function. Different materials have a different sputter rates so only approximate thickness can be assumed without standards. Ex: Above after a 20 minute profile the thin films of a medical mirror are zirconium oxide, silicon dioxide, aluminum oxide, silver, aluminum oxide and silicon dioxide.). 9 Depth Profiling