Scanning Electron Microscopy
Electron microscopes utilize highly concentrated electron beams to observe and analyze biological and non-organic specimen. Compared to optical microscopes, electron microscopes have much greater magnification and resolution power. Electron microscopes, in general terms, provide information on topography, morphology and composition of a given sample. There are four main types of electron microscope technologies: scanning electron microscope (SEM), transmission electron microscope (TEM), environmental scanning electron microscope (ESEM) and scanning tunnelling microscope (STM). For this article, I will mainly focus on the scanning electron microscope, it’s history, the technology behind it, it’s use cases and artistic potential.
The history of the electron microscope dates back to the invention of the electromagnetic lens by Hans Busch in 1926, a device which became the underlying technology of the electron microscope by enabling manipulation and focusing of electron beams. However, the first electron microscope was created by two scientists at the University of Berlin, Ernst Ruska and Max Knoll. Upon the invention the patent was acquired by Siemens and further developed until the eventual commercial release of the electron microscope in 1938. In 1986 the inventors of the scanning electron microscope was awarded the Nobel Prize in Physics. Since then, SEM usage became widespread in many industrial, commercial and scientific applications. It is used in industries and fields such as material science, semiconductor / microchip industry, forensic investigation, biological sciences / medical science, archeology and paleontology for the purposes of research, quality control, failure analysis, assembly aid, dating and material identification. It can easily be said that electron microscopy made an immense contribution to nearly all fields of science and industry and it is one of the most important inventions of the last century.
For an SEM to function, an electron beam must first be generated. This is done by applying high electric current to a tungsten wire. The resulting electrons are then guided through a positively charged anode opening onto the specimen. Along the path, the electron beam is shaped and finely focused using magnetic lenses. When the beam reaches on the specimen surface, it knocks out the electrons from the surface of the object, creating what’s called secondary electrons. A secondary electron detector (SE detector) captures secondary electrons to generate image and surface information. Apart from magnification and surface analysis purposes, SEMs can be used for non-destructive chemical analysis. During the operation, x-ray radiation is generated by the electrons knocked out from the surface of the specimen. Using this, an x-ray detector can analyze the data and determine the chemical composition of a sample.
SEMs don’t produce color images naturally, therefore, black and white images are one of the defining aesthetic characteristics of this technology. Another aesthetic characteristic of the SEM is the distinct surface look. Since the generated image is a result of topographical mapping, the visualized information is primarily depth information of the object surface. This distinct look, combined with the extreme magnification presents us something unreal looking, something we normally never see. The images created by SEM devices don’t look photographic (since the process isn’t photographic), they almost resemble computer generated imagery. Recently, artists are starting to make use of the artistic potential of this technology. Such as the artist duo Broomberg & Chanarin using this technology in their work titled Every Piece of Dust on Freud’s Couch. Another example is the work by Donald Weber, titled War Sand. In his work he uses SEM images of particles that are collected at Normandy Beach.
Fig.1 Scanning Electron Microscope Room - NASA/Langley Research Center (NASA-LaRC)
Fig.2 Image of pollen grains taken on an SEM - Dartmouth College Electron Microscope Facility
Fig.3 Electron microscope Siemens, Germany, 1960 - Museum of Science and Technology Belgrade
Fig.5 Image from page 80 of "The electron microscope, its development, present performance and future possibilities" (1948)