Scanning electron microscopy (SEM)

Teemu Karlsson & Päivi M. Kauppila, Geological Survey of Finland, P.O. BOX 1237, FI-70211 Kuopio, FINLAND, e-mail: teemu.karlsson(at)


A scanning electron microscope (SEM) produces images of sample by scanning it with a focused beam of electrons. Its geological applications are widely used e.g. in determining mineral abundances, grain size and microstructures.
Figure 1: A detailed scanning electron microscope (SEM) image of a series of partly filled pits on the surface of a mineral grain. Photo: NASA

Description of the method

With SEM an image of the specimen can be made by accelerating a narrow stream of high-energy electrons towards the sample. Electrons interact and scatter when impacting the sample, revealing information about the sample including texture, chemical composition, and crystalline structure and orientation of sample material. Images of the sample can be produced by mapping the intensity of corresponding scattered electrons and other energy signals. Data is usually collected over a selected area of the sample surface, ranging from approximately 1 cm to 5 microns in width. (Swapp 2014)
The kinetic energy of accelerated electrons is dissipated as a variety of signals produced by electrons hitting the sample surface. The signals include secondary electrons, backscattered electrons (BSE), diffracted electrons (EBSD), photons, visible light and heat. Secondary and backscattered electrons are usually used for imaging the sample; secondary electrons for morphology and topography, and backscattered electrons for composition. (Swapp 2014)

Appropriate applications

The SEM has probably the widest range of applications in the study of solid materials compared to other instruments or methods. The SEM can be used for e.g. the determination of mineral abundances, grain size, grain size distribution of individual minerals and microstructures. (Swapp 2014) It is rapid and accurate method to identify the problematic minerals, i.e. typically sulphide minerals, and also those minerals providing neutralizing capacity in mine wastes. In addition to the aforementioned applications, SEM is optimal in studying weathering state of minerals, particularly sulphide minerals, and their weathering products in mine wastes. SEM can also provide information on the mineral associations of various minerals and element distributions within the minerals. In mining waste characterisation SEM analysis can be used in several ways. In preliminary characterisation it provides data on the overall mineralogy, grain size distribution and elemental deportments of the mine wastes to make an initial assessment of the environmental properties and required waste management procedures of mine wastes. In mine closure phase it is useful for example in studying the weathering state of the wastes to evaluate and decide on the closure technologies.

Different types of SEM setups and variations exist, differences being mainly in the amount and characters of the attached detectors (Swapp 2014):

  • Secondary electron detector for producing SEM images (the most common detector)
  • Scanning electron microscopy (SEM) and electron probe microanalyser (EPMA). See the EPMA-page of SERC (Goodge 2012 a)
  • Energy-Dispersive X-ray Spectroscopy (EDS) detector for acquiring elemental maps or spot chemical analyses. See EDS-page of SERC (Goodge 2012 b)
  • Scanning electron microanalyser + mineral liberation analyser (SEM-MLA)
  • Back-scattered electron detector (BSE) for discrimination of phases based on mean atomic number (See SEM-MLA)
  • Cathodoluminescence (CL) detector for producing high-resolution digital cathodoluminescent images of luminescent materials
  • Diffracted backscattered electron detector (EBSD) for examination of microfabric and crystallographic orientations
  • FE-SEM
Advantages (Swapp 2012)
  • Non-destructive method
  • Easy sample preparation (depending on sample and used application)
  • Rapid data acquisition for many applications
Disadvantages (Swapp 2012)
  • Samples must be solid and fit into the microscope chamber (maximum horizontal size around 10 cm and vertical size usually below 40 mm)
  • Samples must usually be stable in vacuum; samples that may outgas at low pressure include rocks saturated with hydrocarbons, coal, organic materials or swelling clays, although special SEMs exist also for these kind of samples
  • Hard to detect very light elements like H, He and Li
  • Electrically insulated samples must be covered with a thin layer of conducting material (e.g. carbon or gold) to prevent charge build-up.

Method maturity

SEM is well documented and widely used.


Goodge, J. 2012 a. Electron probe micro-analyzer (EPMA) Retrieved Dec. 3 2014, from
Goodge, J. 2012 b. Energy-Dispersive X-Ray Spectroscopy (EDS) Retrieved Dec. 3 2014, from
Swapp, S. 2014 “Scanning Electron Microscope (SEM)”, retrieved August 13, 2014, from