What is Cathodoluminescence? Plus how to add it to your SEM/TEM/STEM

Cathodoluminescence (CL) is a scientific analytical technique for characterising composition, optical and electronic properties. This data correlates with morphology, micro-structure, composition and chemistry at the micro- and nanoscale.

This technique can easily be added to your electron micoscope (SEM, TEM or STEM) with systems from Gatan.

Blue Scientific is the official Nordic distributor for Gatan systems for electron microscopes in Norway, Sweden, Denmark, Finland and Iceland. For more information or quotes, please get in touch.

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 Contact us on +44 (0)1223 422 269 or info@blue-scientific.com

  

What is Cathodoluminescence?

Cathodoluminescence (also known as CL) is the emission of photons as light, when a material is stimulated by high energy electrons.

Cathodoluminescence microscopy involves analysing the light or photons (luminescence) that are emitted when a sample is stimulated by the electron beam of an electron microscope. This beam can be focused at sub-nanometer length scales, so you can go beyond going beyond the diffraction limit constraints of optical microscopes, and study optical properties at the nanoscale.

Cathodoluminescence data can also be correlated with other signals, to reveal more information about your sample.

What can you Analyse?

CL can be used in a SEM or STEM (Scanning or Scanning Transmission Electron Microscope) to characterise materials:

  • Composition
  • Optical properties
  • Electronic properties

This data correlates with morphology, micro-structure, composition and chemistry at the micro- and nano-scale.

Advantages of Cathodoluminescence

While there are other techniques for measuring optical properties (eg optical emission spectroscopy, photo-luminescence, electro-luminescence) SEM-based CL has several unique advantages:

  • Sub-nm spatial resolution
  • Data correlates with structural information
  • Wealth of data from the emitted signals: morphology (eg size and shape), composition, chemistry, crystallography, electronic properties and more
CL image of zircon grains
Colour CL images of polished zircon grains in epoxy mount, acquired simultaneously with the Gatan ChromaCL2. Many of the grains are highly zoned, and appear to be igneous in origin. Several have metamorphic rims.

Unique Benefits

These advantages can be used to perform unique studies:

  • Study the optical properties of individual nanostructures and assemblies with optical characterisation below the diffraction limit.
  • Analyse semiconductors: Growth, composition and quantify point and extended defect distributions
  • Characterise optical materials and devices with a spatial resolution better than the diffraction limit of light
  • Reveal texture in minerals – Reconstruct geochemical processes by revealing trace element distributions
  • Measure morphology and composition simultaneously – Fully characterise your sample, correlating shape, size, crystallinity and composition with optical properties
  • Analyse properties without manufacturing a complete device and take non-destructive measurements

Application Areas

The ability to measure optical properties at such a small scale is useful in many areas, including:

  • Light emitting diodes (LEDs)
  • Nanoparticles
  • Oil and geology
  • Optoelectronic and photovoltaic materials
  • Solar cells
  • Phosphors
  • 2D materials
  • Pharmaceuticals
  • Polymers
  • Plasmonics (noble metals)
  • Organic materials

To find out whether CL could be used in your area of research, please get in touch.

Electronics and Optoelectronics

Measure the local electronic band gap in semiconductors and study defect distribution at the micro- and nano-scale. This enables you to examine direct bandgap semiconductors with strong cathodoluminescence (eg GaAs or GaN), as well as indirect semiconductors that emit weak cathodoluminescence (eg silicon).

Variations in luminescence caused by perfect and dislocated crystalline silicon can be used to map defects in integrated circuits. The high spatial resolution is ideal for low-dimensional semiconductor structures such as quantum wells and dots.

Bulk GaN Cathodoluminescence Image
Panchromatic cathodoluminescence image of a bulk GaN sample (acquired in 30 seconds). The dark spots highlight threading dislocations. The dislocation density was calculated as 5 x 105 cm-2. The secondary electron image shows the topography but no contrast.

Geoscience

Studying trace element chemistry and geochemical effects enables you to reconstruct geological processes in rocks and minerals. SEM-based cathodoluminescence reveals internal structures not visible using other techniques. This gives you access to unique information about mineral composition, growth and provenance.

More about SEM-based CL in geology and geoscience

Cathodoluminescence image of sandstone
This CL image of sandstone reveals quartz grains from granite and a metamorphic source with low temperature quartz cement (bluish). There is a later (hotter) reddish overprint along the grain boundaries in the overgrowth. Courtesy of Indiana University.

Material Science

Cathodoluminescence is useful in the development of sensor and communication technologies that involve the interaction of light with metal nanoparticles. Their properties can be measured by surface plasmons and local surface plasmon resonance modes.

There have also been recent publications involving the use of SEM-based cathodoluminescence for studying surface plasmon resonance in metallic nanoparticles, with resolution below the diffraction limit.

CL Image of Plasmonics
Gold prisms in a STEM: Bright field TEM images (a & b) and cathodoluminescence intensity maps (c & d) taken in STEM mode. The variation in size causes a change in the local surface plasmon resonance and the spatial and spectral distribution of luminescence (not shown here). Courtesy of A*STAR IMRE, Singapore.

Organic Molecules and Pharmaceuticals

Many polymers and active ingredients in pharmaceuticals are cathodoluminescent. The signal reveals the chemical structure of molecules, so it can be used to map the distribution of organic molecules with sub-100 nm resolution.

CL Image of Pharmaceutical Drug Distribution
Drug distribution within a pill: The composite image maps the spatial distribution of the micronised drug (salmeterol xinafoate) in green. The secondary electron image shows the non-cathodoluminescent lactose monohydrate in brown. Courtesy of Pfizer UK.

Instrumentation

These systems can be used to add cathodoluminesence to your SEM/TEM. They’re compatible with electron microscopes from major manufacturers – contact us for details.

Gatan Monarc CL dectector

Monarc CL Detector

Next generation system for SEM

  • Unmatched spatial, angular and wavelength resolution
  • Collect hyper-spectral data 30x faster than other CL detectors
  • Large field of view

More details…

Gatan Vulcan

Vulcan CL Detector

For TEM/STEM

  • Analyse a wide range of samples
  • Combine with other techniques
  • Compatible with Gatan EELS systems for correlating absorption and emission processes

More details…

Gatan ChromaCL2

ChromaCL2 iBSED Detector

For geology and geoscience

  • Live, colour CL imaging
  • Reveal geochemical processes
  • Visualise tecture easily
  • Automated montages for a large field of view

More details…

More Information

Blue Scientific is the official distributor of Gatan systems for electron microscopes – including their state-of-the-art cameras, filters and sample preparation equipment. We’re here to provide quotes and help with any queries you have about how they can enhance the capabilities of your microscope – just get in touch:

 Contact us on +44 (0)1223 422 269 or info@blue-scientific.com

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