The Photoelectric Effect #
The photoelectric effect was first discovered by Heinrich Hertz in 1887 and experimentally studied by Philipp Lenard. It remained a puzzling phenomenon until Albert Einstein provided the first theoretical explanation in 1905, proposing that light consists of discrete packets of energy called “photons.” Einstein’s theory showed that electrons are emitted from a material only if the light has a frequency above a certain threshold, supporting the quantum nature of light and leading to the development of quantum theory. This explanation earned Einstein the Nobel Prize and fundamentally changed the understanding of light and energy interaction. The photoelectric effect remains a cornerstone in modern physics.
When radiation with energy above a certain threshold strikes an atom, it can emit an electron – called a photoelectron. If the incoming radiation is below this energy, no emission will occur – instead there will likely be some kind of excitation of electrons into higher orbitals (e.g. FT-IR spectroscopy). The energy threshold to begin exciting electrons is in the UV region.
So when our radiation with enough energy interacts with an atom, and removes an photoelectron – this electron will be released with a given kinetic energy. This kinetic energy is related to that of the incoming radiation, the binding energy of the electron within the atom and a small energy penalty for electron removal, which is called the work function of the spectrometer (Φsp).
Ek = hv – EB – Φsp
Since the properties of hv and Φsp are known, and that of Ek measured – modern spectrometers typically automatically derive the binding energy of a measurement and display the results according to this value.
1
Kahn, A. (2016). “Fermi level, work function and vacuum level.” Materials Horizons 3(1): 7-10.
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Helander, M. G., et al. (2010). “Pitfalls in measuring work function using photoelectron spectroscopy.” Applied Surface Science 256(8): 2602-2605.
