Cathodoluminescence
Cathodoluminescence is a special form of luminescence , whereby an electron beam coming from an electron source hits a solid surface and this stimulates light , i.e. H. electromagnetic radiation to emit (functional principle of the Braun tube or cathode ray tube ).
Areas of application and experimental setups
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In geology, mineralogy and materials science, an optical cathodoluminescence microscope is used to make internal structures of rock samples, ceramic materials, glasses, etc., visible and thus to obtain information about the structure, origin and quality of the material being examined.
In materials science and semiconductor technology , cathodoluminescence examinations are often carried out in a scanning electron microscope (SEM). Here a highly focused electron beam hits the sample and causes it to emit light from the infrared, visible or UV range, depending on the material. This light is through an optical system, such as. B. an elliptical mirror collected. It is guided out of the SEM via optics and directed onto a detector ( photomultiplier or CCD detector) by a monochromator . Either luminescence spectra can be recorded as a function of the light wavelength / photon energy or an image of the luminescence can be recorded at a certain wavelength, which can then be correlated directly with a secondary electron image of the surface. This information allows conclusions to be drawn about the structure and quality of the semiconductor crystals examined.
An electron microscope with a cathodoluminescence attachment allows significantly higher magnifications, but is more difficult to handle and far more expensive than an optical cathodoluminescence microscope, whose strength lies in showing the actually visible luminescence colors of the samples directly through the eyepiece. The former is therefore of particular importance for the investigation of nanostructured semiconductors, while the latter is used in geology.
The shadow cross tube can still be found in physics lessons at schools and universities as a demonstration device. Using the luminescence of the bulb glass or a fluorescent screen, it allows the study of the generation, propagation and magnetic influence of cathode rays.
Technical application examples
- Picture tubes of televisions and tube monitors
- Vacuum fluorescent display (VFD), also Digitron
- Magic eye (tuning indicator tube)
history
The Ukrainian physicist Johann Puluj is considered to be the discoverer of cathodoluminescence . In 1881 he developed a lamp, later known as the Puluj lamp, which was based on the principle of cathodoluminescence. In 1905 Philipp Lenard received the Nobel Prize in Physics “for his work on cathode rays ” . In his honor, cathodoluminescent substances are also known as Lenard phosphors .
See also
Web links
- AG Bimberg at the TU Berlin
- Microstructure center of the University of Magdeburg
- Paul-Drude Institute CL-Labor
- Cathodoluminescence in Applied Mineralogy - TU Freiberg
Individual evidence
- ^ The Nobel Prize in Physics 1905. Philipp Lenard. Retrieved April 19, 2013 .