SEM-CL Scanning Electron Microscopy – Cathodoluminescence

Introduction to SEM-CL

A cathodoluminescence detector connected to a scanning electron microscope (SEM), field emission microscope (FEM), or electron microprobe (EPMA) can provide high-resolution digital cathodoluminescent (CL) images of luminescent materials. In a scanning electron microscope (SEM), an electron beam from the SEM is used to excite the sample, resulting in the emission of photons. Whether this CL detector is coupled to a SEM, FEM, or EMPA, this method of acquiring a CL image or CL spectrum is known as SEM-CL. SEM-CL is a sophisticated approach to material characterization that provides a unique perspective on materials by utilizing cathodoluminescent signals produced during electron beam excitation. Researchers use this technique to investigate the luminous properties of materials, which aids in understanding their electrical structure, flaws, and compositional changes. MaTestLab is one of the best testing service providers, with the best network of testing laboratories in the USA to conduct SEM-CL tests for our clients.

Principle and Methodology of SEM-CL

The SEM-CL works in the same way as a hot-cathode CL attached to an optical system, in which electrons are created by a heated filament and driven to an anode. In SEM-CL, electrons are accelerated towards the anode using high vacuum (10–5 Torr) and potential differences ranging from 1–30 kV. The sample current can range between 1 pa and 10 nA. 

Focusing electrons on a narrow beam (5 nm to 1 µm) allows for a CL response on a tiny area of the sample.  SEM-CL works on the idea that high-energy electrons from the electron beam interact with the specimen, causing luminescence. The emitted light is then collected and analyzed to determine the material’s qualities. The methodology combines scanning electron microscopy for topographical imaging with cathodoluminescence spectroscopy to investigate the sample’s optical characteristics.

Cathodoluminescence Detector

The primary instrument for SEM-CL is a specialized scanning electron microscope with a cathodoluminescence detector. This detector collects emitted light and generates detailed pictures that show luminescence changes throughout the sample. To collect complete data, the electron beam is excited, and the ensuing signals are detected with precise precision.

Applications of Scanning Electron Microscopy – Cathodoluminescence

CL emissions can offer general information on the trace elements found in minerals or the formation of mechanically induced flaws in crystals. Perhaps more crucially for the geologic context, the distribution of CL in a material reveals basic information about processes such as crystal development, replacement, deformation, and provenance. These apps include:

• Investigations of cementation and diagenesis processes in sedimentary rocks
• The origin of clastic material in sedimentary and metasedimentary rocks
• Details of interior structures in fossils
• Growth/dissolution characteristics in igneous and metamorphic minerals
• Deformation mechanisms in metamorphic rocks.
• Discrimination between generations of the same mineral is due to changes in tiny levels of activator elements.

Strengths and Limitations of Scanning Electron Microscopy – Cathodoluminescence

The advantages of acquiring CL pictures using the SEM-CL over the optical-CL include:

• Better spatial resolution.
• Improved current control
• Creates a color CL image of the sample using the relevant filters or detectors.
• Examination of UV or IR CL responses that differ from those obtained with optical-CL.

The limitations of acquiring CL pictures using the SEM-CL compared to the optical-CL include:

• It is necessary to have an electron beam instrument, such as SEM, FEM, or EMPA.
• Machine time is typically more expensive.
• Conductive coating is required on the sample.
• Nonlinear absorption of RGB filters and problems in appropriate color reintegration
• Problems with phosphorescence in primary CL-emitting materials, including carbonate minerals and apatite.

Other related techniques SEM-cathodoluminescence (SEM-CL) is related to techniques such as electron backscatter diffraction (EBSD), which is used to analyze crystallographic orientation, energy dispersive X-ray spectroscopy (EDS), which is used to determine elemental composition in materials, and cathodoluminescence lifetime imaging (CLLI), which is used to measure the decay time of luminescence emission.