Cathodoluminescence

Source: Wikipedia, the free encyclopedia.
Color cathodoluminescence of a diamond in SEM, real colors

Cathodoluminescence is an

cathode ray tube. Cathodoluminescence is the inverse of the photoelectric effect
, in which electron emission is induced by irradiation with photons.

InGaN
polycrystal. The blue and green channels represent real colors, the red channel corresponds to UV emission.

Origin

X-rays, which in turn can scatter as well. Such a cascade of scattering events leads to up to 103 secondary electrons per incident electron.[1] These secondary electrons can excite valence electrons into the conduction band when they have a kinetic energy about three times the band gap
energy of the material .
band structure
, classical semiconductors, insulators, ceramics, gemstones, minerals, and glasses can be treated the same way.

Microscopy

Thin section of quartz from a hydrothermal vein - left in CL and right in transmitted light

In

cathodoluminescence microscope, may be used to examine internal structures of semiconductors, rocks, ceramics, glass
, etc. in order to get information on the composition, growth and quality of the material.

Optical cathodoluminescence microscope

Hot cathode CL microscope

A cathodoluminescence (CL) microscope combines a regular (light optical)

electron beam
.

Using a cathodoluminescence microscope, structures within

fly ash
, etc.

CL color and intensity are dependent on the characteristics of the sample and on the working conditions of the

electron microscopy, cold cathodoluminescence microscopy provides positive ions along with the electrons which neutralize surface charge buildup and eliminate the need for conductive coatings to be applied to the specimens. The "hot cathode" type generates an electron beam by an electron gun with tungsten filament. The advantage of a hot cathode is the precisely controllable high beam intensity allowing to stimulate the emission of light even on weakly luminescing materials (e.g. quartz – see picture). To prevent charging of the sample, the surface must be coated with a conductive layer of gold or carbon. This is usually done by a sputter deposition
device or a carbon coater.

Cathodoluminescence from a scanning electron microscope

Sketch of a cathodoluminescence system: The electron beam passes through a small aperture in the parabolic mirror which collects the light and reflects it into the spectrometer. A charge-coupled device (CCD) or photomultiplier (PMT) can be used for parallel or monochromatic detection, respectively. An electron beam-induced current (EBIC) signal may be recorded simultaneously.
Sketch of a cathodoluminescence objective inserted in a SEM column

In

CCD camera, an entire spectrum can be measured at each point of a map (hyperspectral imaging
). Moreover, the optical properties of an object can be correlated to structural properties observed with the electron microscope.

The primary advantages to the electron microscope based technique is its spatial resolution. In a scanning electron microscope, the attainable resolution is on the order of a few ten nanometers,

quantum dots
.

While an electron microscope with a cathodoluminescence detector provides high magnification, an optical cathodoluminescence microscope benefits from its ability to show actual visible color features directly through the eyepiece. More recently developed systems try to combine both an optical and an electron microscope to take advantage of both these techniques.[5]

Extended applications

Although

integrated circuits
.

Recently, cathodoluminescence performed in electron microscopes is also being used to study

photonic crystals and nanostructured photonic materials.[7]

See also

References

  1. S2CID 56031946
    .
  2. doi:10.1063/1.1656484
    .
  3. S2CID 118314773
    .
  4. S2CID 18003378
    .
  5. ^ "What is Quantitative Cathodoluminescence?". 2023-08-23.
  6. S2CID 119246090
    .
  7. S2CID 31259521
    .

Further reading

External links

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