Cathodoluminescence imaging on quartz in sandstone

What is the difference between cathodoluminescence and other SEM techniques?

Posted by Delmic on Jan 9, 2020 12:45:00 PM

  • What are the most common SEM techniques for studying materials?

  • What kind of data can you get with these techniques?

  • What makes cathodoluminescence (CL) different from other SEM techniques?

  • 5 advantages of CL imaging


What are the most common SEM techniques for studying materials?


When studying or working with materials, it is essential to understand as much as possible about them. Electron microscopy techniques are a common way to get data, such as material contrast, composition, surface topography and structure. When an electron beam (for example, in a scanning electron microscope) interacts with a material (bulk, thick or thin), multiple processes occur. Such interaction can generate secondary electrons (SE), backscattered electrons (BSE), X-rays. Various techniques exist that harness these signals. The most commonly used techniques are, secondary electron (SE) and  backscattered electron (BSE) detection, electron backscatter diffraction (EBSD) and energy-dispersive x-ray imaging (EDS), can be used to obtain various types of information about the material.


What kind of data can we get with these techniques when we study materials?


cathodoluminescence-solutions-figure1Secondary electrons (SE) detection
is a detection of low-energy electrons, with which it is possible to collect secondary electrons only from the top few nanometers of a material. This technique is sensitive to surface topography and also shows (minor) material contrast. 

Backscattered electrons (BSE) detection is primarily sensitive to density and atomic number and as such can be used to obtain material contrast. 

With electron backscattered diffraction (EBSD) you can look at the crystal structure and crystal orientation.

Energy-dispersive X-ray spectroscopy (EDS) probes core transitions in a material and as such can be used for quantitative elemental analysis 

Next to the above-mentioned signals light can also be generated during the electron beam interaction with a material which is known as cathodoluminescence (CL). 

What makes cathodoluminescence different from other SEM techniques?


Cathodoluminescence provides unique and complementary information to the other SEM based techniques. First of all, it allows observing an emission energy range of 0.5 to 6 eV. In this energy range information about the composition, crystal structure, and the electronic band gap can be obtained for example. Furthermore, trace elements or dopants, can be sensitively detected with CL because they have different transitions than the bulk materials. Similarly, it is possible to look at crystal defects as these can alter the local optical properties of the material. With CL you can image optical resonances in a range of (resonant) photonic systems and you are sensitive to the refractive index of the materials. Overall, it is a powerful tool and a visible measure of what is taking place inside a material or an organism. Combined with other SEM-based techniques, it can be used to produce the most complete material analysis.  Furthermore, it can act as a prescreening tool for more time-consuming and expensive techniques such as mass spectrometry for quantitative isotope analysis.


5 advantages of a CL imaging

  1.  Nanoscale excitation resolution well below the optical diffraction limit

  2. Probeless and contactless inspection technique (compared to near-field microscopy, for example, a physical probe is not required);

  3. Broad band excitation allowing inspection from the deep UV to the infrared spectral range; 

  4. The spectral resolution is high in state-of-the art CL systems allowing high-quality spectroscopy;

  5. The electron penetration depth is tunable, which allows depth-resolved studies and imaging buried structures

If you are looking for more information explaining the basics of cathodoluminescence, make sure to check out our upcoming webinar series called “Cathodoluminescence fundamentals”. The first webinar will focus on CL processes and talk about coherent and incoherent cathodoluminescence. Read more and sign up for it here

Topics: materials science, cathodoluminescence

Thoughts on the various applications, techniques, and complications to be discovered in the fascinating fields of both cathodoluminescence and correlative light and electron microscopy.

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