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Photoelectrons are emitted from a metallic material when it absorbs light radiation. The process was discovered by Heinrich Hertz and later explained by Albert Einstein. Photoelectron spectroscopy is used to study the surface region of a sample material, with X-ray spectroscopy and ultraviolet photoelectron spectroscopy being the two basic types. The latest synchrotron equipment allows for the study of energy ranges between 5 and over 5,000 electron volts. In 2011, photoelectronic spectrometer equipment was developed that can measure the thickness of thin films down to 20 nanometers and can operate in the range of 3.4 to 6.2 electron volts.
A photoelectron is an electron emitted by a substance by the photoelectric effect. The photoelectric effect occurs when a material that is usually metallic in nature absorbs enough light radiation to cause electrons to be emitted from its surface. The discovery of the photoelectric effect was first made in 1887 by Heinrich Hertz, a German physicist, and was later called the Hertz effect. Many researchers have spent time defining its properties over the years, and in 1905, Albert Einstein published findings that it was caused by quanta of light known as photons. Einstein’s clear and elegant explanation of how photoelectrons were produced won him the Nobel Prize in Physics in 1921.
For photoelectrons to be emitted from a surface, the wavelength of the light must be low enough, such as that of UV light. Photoelectron emission is also a key feature that is used in describing the principles of quantum mechanics. The process involves a quanta, or single photon of energy that is absorbed by a solid material if the photon’s energy is greater than the energy of the upper valence band, or outermost electron shell of the material.
Photoelectron spectroscopy is a process in which the kinetic energy of photons emitted from a surface is analyzed to study the surface region of a sample material. Two basic types of the process have been used. X-ray spectroscopy studies the core levels of a material using photon energy ranges from 200 to 2,000 electron volts, and ultraviolet photoelectron spectroscopy uses photon energy levels between 10 and 45 electron volts to study the outer electron or valence shells of the material. As of 2011, the latest synchrotron equipment, which is a magnetic cyclotron that accelerates particles electrostatically, allows for the study of energy ranges between 5 and over 5,000 electron volts so that separate research equipment is no longer needed. However, these machines are expensive and complex, so they are not widely used in the field.
As of 2011, photoelectronic spectrometer equipment with an electron detector capable of operating in open air and atmospheric pressure has been developed, a first in the field. It is capable of measuring the thickness of thin films down to levels down to 20 nanometers or 20 billionths of a metre. The machines are desktop models that use an ultraviolet light source and can operate in the range of 3.4 to 6.2 electron volts. They are used to analyze both metals and semiconductors such as silicon.
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