Electron Microscope

What is an electron microscope? 

Electron microscopy (EM) is a technique for obtaining high-resolution images of biological and non-biological samples.

It is used in biomedical research to investigate the detailed structure of tissues, cells, organelles and macromolecular complexes.

EM images use high-resolution electrons (which have very low wavelengths) as a source of light radiation.

Electron microscopy is used in conjunction with various assistive techniques (such as thin sectioning, immuno-labelling, negative staining) to answer specific questions.

History of electron microscope

The electron microscope began in the twentieth century when the first electromagnetic lens was developed.

This opened the door for the possibility of inventing a microscope to use lens principles that could examine the composition of the specimen in greater detail. It had the ability to surpass the capabilities of optical microscopes, which were the first type of microscope at the time.

The invention of the electron microscope

Hans Bush invented the first electromagnetic lens in 1926 and, although he allegedly filed a patent for an electron microscope in 1928, he did not manufacture the microscope.

The first electron microscope was created in 1931 by Ernst Ruska, a physicist at the University of Berlin, and Max Knoll, an electrical engineer.

In the same year, Siemens-Schuckertwerke's scientific director Reinhold Rudenberg received an electron microscope patent.

In 1933, Ernst Ruska further developed an electron microscope developed on the original model that was capable of producing higher resolution images than optical microscopy. In 1937, Manfred von Arden developed the first scanning electron microscope.

Siemens-Schuckertwerke released the first commercial electron microscope to the public in 1938. With this, transmission electron microscopes became more readily available in other regions of the world, including North America.

How the electron microscope works

Thought you knew about the simple microscope if not then please read our previous article Microscope. So for an ordinary microscope, there are essentially four important parts:

• Light source

• The sample

• Lens that makes the sample larger

• Detailed image of the sample you see

In an electron microscope, these four things are slightly different.

• The light source is replaced by a beam of very fast-moving electrons.

• The sample, usually it must be specially prepared and placed inside a vacuum chamber from which the air is pumped (because electrons do not travel very far in the air).

• The lens is replaced by a series of coil-shaped electromagnets through which the electron beam travels. In an electron microscope, the coils bend the electron beam the same way.

• The image formed as a picture (called an electron micrograph) or an image on a TV screen.

Types of electron microscope

There are a few different types of electron microscopes. They all work in different ways. The three most familiar types are the following:

• Transmission electron microscope (TEM)

• Scanning electron microscope (SEM)

• Reflection Electron Microscope (REM)

1. Transmission electron microscope

The transmission electron microscope is a basic type of electron microscope, which directs a high voltage electron beam toward the specimen (specimen) to illuminate and form a detailed image of the specimen.

An electron gun is used to produce an electron beam. The gun is usually fitted with a tungsten filament cathode, which is the source of the electron beam. An anode is used to accelerate the electron beam, and electrostatic and electromagnetic lenses help to focus the beam.

When the electron beam passes through the specimen, it provides an image of a scattered and microstructure of the specimen, which can be viewed through the lens of a microscope.

The most important limitation of transmission microscopes is the need for very thin specimen samples, typically less than 100 nm. As a result, most biological samples need to be chemically fixed and dehydrated, embedded in polymer resins so that it can be visualized with a TEM.

2. Scanning electron microscope

The scanning electron microscope used a technique known as raster scanning to produce enhanced images of the specimen. It directs a focused electron beam to the rectangular region of the sample, which loses energy upon its passing.

Energy is converted into other forms, such as heat, light, secondary electrons, and backscattered electrons.

This is beneficial because it uses surface processes and can, therefore, make images of large samples up to several centimetres in size, and has greater depth of field. Consequently, images of SEM can be good representations of the actual size of the sample.

3. Reflection electron microscope

The reflection electron microscope involves the detection of a beam of scattered electrons that are reflected from the probe sample.

Reflection high energy electron diffraction (RHeED) and reflection high energy loss spectroscopy (RHELS) techniques are often used in this type of microscopy.

Uses of electron microscope

Industry

Electronic microscopy is often used for industrial purposes to aid in the development and manufacturing process of new products.
For example, electronics industries use electron microscopes for high-resolution imaging in the development and manufacturing processes of semiconductors and other electronics. Other industries that we can use also include industries such as aeronautics, automotive, apparel and medicine.

Natural resources

Electron microscopy can be used to characterize and analyze organic materials. Microscopes can provide automated, objective, and quantitative information about the environment.
Additionally, oil and gas companies can use this technology to survey a field and obtain information about it. This can help reduce the risks associated with oil and gas exploration and extraction. For example, quantitative lithotype and porosity characteristics of the environment, such as reservoir, seal and source rocks, can be obtained. It can also help to increase and validate inputs for geological models produced from seismic, wireline, and soil logs.

Forensic Science

We can also use electron microscopy in the forensic sciences. For example, an electron microscope can be used to analyze sharp details of relevant samples, such as gunshot residues or clothing fibres, blood, or other biologicals. Sample of substance.
What's more, it allows forensic scientists to learn more about the crime scene, which can help find more evidence.