Home > Electron microscope

1 History

The first electron microscope was built in 1931 by Ernst Ruska and Max Knoll at the Berlin Technische Hochschule. It was greatly developed through the 1950s and has allowed great advances in the natural sciences. The advantage of an electron beam is that it has a much smaller wavelength (see wave-particle duality), which allows a higher resolution - the measure of how close together two things can be before they are seen as one. Light microscopes allow a resolution of about 0.2 micrometres, whereas electron microscopes can have resolutions as low as 0.1 nanometers.

2 Process

High voltage electron beams from a cathodeThe electrode of an electrochemical cell at which reduction occurs is referred to as the cathode . In an electrolytic cell the cathode is negatively charged and in a galvanic cell the cathode is positively charged. The oppositely charged electrode in that are focused by magnetThis article is about magnetized material. Magnet is also the name of a commune in the Allier departement, in France A magnet is an object that has a magnetic field. A so-called permanent magnet is made of a ferromagnetic material. Such materials consistic lenses on to the specimen. They are then magnified by a series of magnetic lenses until they hit photographic plate or light sensitive sensors - which transfer the image to a computer screen. The image produced is called an electron micrograph (EM).

3 Types

The Transmission electron microscope (TEM) produces images by detecting electrons that are transmitted through the sample, while the Scanning electron microscopeant head The scanning electron microscope SEM is a type of electron microscope capable of producing high resolution images of a sample surface. Due to the manner in which the image is created, SEM images have a characteristic 3-dimensional quality and are (SEM) produces images by detecting secondary electrons which are emitted from the surface due to excitation by the primary electron beam.

Generally, the TEM resolution is about an order of magnitude better than the SEM resolution, however, because the SEM image relies on surface processes rather than transmission it is able to image bulk samples and has a much greater depth of view, and so can produce images that are a good representation of the 3D structure of the sample.

A Scanning Transmission Electron Microscope (STEM) is a specific sort of TEM, where the electrons still pass through the specimen, but, as in SEM, the sample is scanned in a raster fashion.

4 Treatment

Samples viewed under an electron microscope have to be treated in many ways:

• Cryofixation - is freezing a specimen so rapidly, to liquid nitrogen temperatures, that the water forms vitreous (non-crystalline) ice. This preserves the specimen in a snapshot of its solution state. This technique produces the best specimen preservation, but isn't applicable to all specimens.
• Fixation - is preserving the sample to make it more realistic. GlutaraldehydeGlutaraldehyde is a colourless liquid used to sterialize medical and dental equipment. It is also used for industrial water treatment and as a chemical preservative. But it is toxic, causing severe eye, nose, throat and lung irritation, along with headach - for hardening - and osmic acid - which stains lipidLipids are fatty acid esters, a class of relatively water-insoluble organic molecules, which are the "basic" components of biological membranes. There are three forms of lipids: phospholipids, steroids. and triglycerides. Lipids consist of a polar or hydrs black - are used.
• Dehydration - is the removing of waterDrinking water This article focuses on water as we experience it every day. The water (molecule) article describes water from a scientific and technical perspective. Water is an abundant substance on Earth. It exists in many forms, such as sea, rain, and to be replaced with an embedding medium such as ethanol or propanone.
• Embedding - supports the tissue for sectioning in a resin such as araldite.
• Sectioning - produces thin slices for mounting. These can be cut on an ultramicrotome with a diamond knife to produce very thin slices.
• Staining - uses metals such as lead and uranium to reflect electrons to give contrast between different structures.
• Ion Beam Milling - thins samples until they are transparent to electrons by firing ions (typically argon) at the surface from an angle and sputtering material from the surface.