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The Auger yield is a measure of the likelihood that an atom in an excited state will de-excite through the Auger effect rather than emitting X-rays. It quantifies the probability of Auger electron emission as a de-excitation process following the ionization of an inner-shell electron.

Understanding Auger Yield

  1. Excited State and De-Excitation:
  • Ionization Event: When an inner-shell electron is ejected from an atom, a vacancy is created in the inner electron shell.
  • De-Excitation Pathways: The atom can return to a lower energy state by filling the vacancy with an electron from a higher shell. This process can result in either:
    • Auger Electron Emission: The energy released in the transition is transferred to another outer-shell electron, which is then ejected as an Auger electron.
    • X-ray Emission: The energy is released as X-ray radiation when the vacancy is filled by an electron from a higher energy level.
  1. Auger Yield Definition:
  • Probability: The Auger yield is defined as the fraction of de-excitation events that result in Auger electron emission. It is a dimensionless quantity typically expressed as a percentage or a ratio.
  • Mathematical Expression: If \( Y_A \) represents the Auger yield, it can be expressed as:
    \[
    Y_A = \frac{\text{Number of Auger Electrons Emitted}}{\text{Total Number of De-excitation Events}}
    \]
  • Complementary Yield: The probability of X-ray emission is \( 1 – Y_A \).

Factors Influencing Auger Yield

  1. Elemental Properties:
  • Atomic Number: Generally, elements with higher atomic numbers tend to have higher Auger yields because the probability of Auger emission increases with the number of electrons and available energy levels.
  • Electron Configuration: The distribution of electrons in various shells affects the likelihood of Auger emission. The yield can vary depending on the specific electronic transitions involved.
  1. Energy Levels:
  • Transition Energies: The energy differences between electron shells influence the relative probability of Auger versus X-ray emission. Larger energy differences may favor X-ray emission.
  1. Electron Shells:
  • Inner vs. Outer Shells: The shell from which the electron is ejected and the shell into which the electron falls can affect the Auger yield. Different shells have different probabilities for Auger transitions.
  1. Chemical Environment:
  • Chemical State: The chemical bonding and environment of the atom can influence the Auger yield. Changes in oxidation state or chemical bonding can alter the energy levels and transition probabilities.

Applications

  1. Surface Analysis:
  • Auger Spectroscopy: Auger yield is important in Auger electron spectroscopy (AES), which is used to analyze surface compositions. The yield helps in understanding the relative intensities of Auger peaks in the spectrum.
  1. Material Science:
  • Material Characterization: Knowledge of Auger yields aids in the characterization of materials, particularly in determining surface composition and chemical states.
  1. Spectroscopy Calibration:
  • Calibration and Analysis: Auger yields are used to calibrate spectrometers and interpret spectra by providing information on the likelihood of Auger versus X-ray emissions.

Summary

The Auger yield is a key parameter in understanding the relative likelihood of Auger electron emission versus X-ray emission following ionization. It is influenced by the atomic and electronic properties of the element, as well as the chemical environment. Understanding Auger yield is essential for interpreting Auger spectra and for applications in surface analysis and material characterization.

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