Photoelectron Spectroscopy in Atmosphere (PESA)

Photoelectron Spectroscopy in Atmosphere
This example graph shows a thin film sample’s photoemission work function with Excitation Energy (eV) on the x-axis and standardized photoelectron yield ratio (Yieldn, or Y) on the y-axis. The slope of the linear best-fit for the data is correlated to the thickness of the film, and the y-intercept corresponds to the material Work Function: the maximum energy difference along the valence belt.

Photoelectron Spectroscopy in Atmosphere (PESA) is a technique used to analyze the work function of a surface: i.e., the amount of energy needed to remove an electron from the sample.

Work function is particularly important to measure as it can determine the efficiency and other key properties of junction contacts. It is a fundamental property for Schottky barrier devices used in many of our electronics.

In addition to measuring the work function, PESA can also be used for certain samples to estimate the density of states (DoS), highest occupied molecular orbital (HOMO) energy level, lowest unoccupied molecular orbital (LUMO) energy level, band gap and energy gap.

Strengths
  • No sample preparation required
  • Minimal sample damage
  • High repeatability, even for organic samples
  • Absolute value measurement
  • Easy measurement in air (no vacuum required!)
Limitations
  • Surfaces are often contaminated which can reduce accuracy of measurement
  • Narrow measurement range
  • No way to clean surface in the tool
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Photoelectron Spectroscopy in Atmosphere (PESA)
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Example Outputs

This example graph shows a thin film sample’s photoemission work function with Excitation Energy (eV) on the x-axis and standardized photoelectron yield ratio (Yieldn, or Y) on the y-axis. The slope of the linear best-fit for the data is correlated to the thickness of the film, and the y-intercept corresponds to the material Work Function: the maximum energy difference along the valence belt.

Instruments Used for PESA
Raiken Keiki AC-3

Raiken Keiki AC-3

  • Low Photoexcitation Energy: 5.0 – 6.20 eV
  • Open Counter Electron Detector
  • Nitrogen Substitution-type Grating-method Monochromator
  • Spot Size: 2 x 5 mm (Slit: 1.00mm)
  • Maximum Radiating UV Intensity: 100nW (at 5.9 eV)
Sample Requirements
  • Solids
  • Minimum Sample Size: at least 0.5 by 0.5 cm
  • Maximum Sample Size: 30 x 30 mm
How PESA Works

Photoelectron Spectroscopy in Atmosphere (PESA) is based on the well-known photoelectric effect. Light from a wide-band, deep UV source is passed through a monochromator and focused into a small spot on a sample. The photoelectric effect produces signal electrons at characteristic energy levels related to the photoemission work function of the surface.

The system measures these electron emissions as a function of wavelength. The used of a unique photoelectron detector called Open Counter, allows the measurements in ambient or gas environments as opposed to XPS, which is done under UHV. In the ideal case the electron emission increases linearly as wavelength decreases; this allows analysts to fit a straight line to the data where the y-intercept is a measure of the work function of the surface being measured.

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