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The Secret Behind XPS: How It Detects What’s Around an Atom!
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The Secret Behind XPS: How It Detects What’s Around an Atom!

XPS and Its Role in Identifying Chemical Environments

Introduction to XPS

  • X-ray Photoelectron Spectroscopy (XPS) serves two main purposes: identifying elemental composition and distinguishing chemical environments of elements.
  • Elemental information is obtained from survey spectra, while high-resolution spectra provide insights into the chemical environment.

Understanding Chemical Environment through XPS

  • The standard XPS survey spectrum for phosphorus indicates the presence of carbon, hydrogen, and oxygen; however, XPS cannot detect hydrogen.
  • Carbon exhibits different chemical environments based on its bonding situation, which can be analyzed through high-resolution spectra.

Analyzing Peaks in High-Resolution Spectra

  • The carbon 1s peak consists of three distinct peaks due to varying environments around carbon atoms.
  • Each peak corresponds to a specific type of environment:
  • Peak A represents one environment,
  • Peak B represents another,
  • Peak C indicates yet another.

Importance of Neighboring Elements and Oxidation States

  • The area under each peak correlates with the number of carbon atoms present; larger areas indicate more atoms.
  • Neighboring elements significantly influence binding energy; for example, replacing oxygen with nitrogen alters the binding energy observed in XPS.

Trends in Binding Energy Changes

  • Binding energy varies depending on neighboring atoms; changing from carbon to nitrogen or fluorine affects this energy level.
  • Observations show that introducing more electronegative elements increases binding energy due to electron withdrawal from host elements.

Effects of Oxidation State on Binding Energy

  • Titanium's oxidation states (0, II, IV) demonstrate how changes in oxidation state lead to variations in binding energy.
  • This variation provides critical information about the chemical state and environment surrounding titanium within compounds.
Playlists: XPS - X-rays Photoelectron Spectroscopy
Video description

How XPS identified the Chemical Environment of the element? X-ray Photoelectron Spectroscopy (XPS) is uses for the following two purposes 1- Surface sensitivity (∼10 nm) - elemental information , which can be identified by the survey spectra 2- Its ability to distinguish in *chemical environment*, which can be achieved by running the high resolution spectra Let's discuss it in details Chemical environment: It includes factors like nearest neighbor elements, oxidation state of the elements, which affects the BE of the Auger electrons and Photoelectrons Peaks. For example, the BE of a carbon atom in a C=O bond will be different from that in C-H or C- N, or C- F2 bonds. Let’s just focus the XPS survey spectra of polyethylene terephthalate (PET) and high-resolution spectra of C 1s (Ref to video). The relative area under each peak (refer to video) shows the number of carbon atoms present in each environment. How neighbor elements changes the BE of the core element? Chemical State Binding Energy C- C 285 eV C-N 286 eV C-O 286.5 eV C=O 288 eV CF2 292 eV CF3 294 eV Similarly, How the oxidation states changes the BE of the element? Oxidation State Chemical State Binding Energy Ti (0) Ti 453.9 eV Ti (II) TiO 455.2 eV Ti (IV) TiO2 458.7 eV As it has been shown that Ti(0), Ti (II) and T (IV) shows different BE because of the different oxidation states. This can be only accomplished by running high resolution XPS spectra. To sum up, the chemical environment, which is composed of neighbor elements and oxidation states are easily identified by the high resolution XPS spectra. We simply see variation in the BE and then it confirms variation in the chemical environment. Cheers! Please subscribe to my channel and share it.