Electron Microscope

An electron microscope is a microscope that illuminates with a beam of accelerated electrons. It’s a high-resolution microscope that can magnify things from nanometres. This is possible by the controlled utilisation of electrons in a vacuum caught on a phosphorescent screen.

The first Electron Microscope was built in 1931 by Ernst Ruska (1906-1988), a German engineer and academic professor, and the same principles that guided his prototype still govern modern EMs.

Wavelength of De Broglie

In 1923, Prince Louis-Victor de Broglie (1892–1987), a French physics graduate student, made a radical proposal based on the hope that nature is symmetric. If EM radiation possesses both particle and wave properties, nature would be symmetric if matter possessed both particle and wave properties. If what we once considered an unequivocal wave (EM radiation) is also a particle, then what we once thought an unequivocal particle (matter) might also be a wave. De Broglie’s suggestion, presented as part of his doctoral thesis, was met with some scepticism.

De Broglie used both relativity and quantum mechanics to develop his proposal that all particles have a wavelength, which is given as

λ = h/p

where h denotes Planck’s constant and p denotes momentum. This is known as the de Broglie wavelength. (Note that this is already true for photons based on the equation.)

p = h/λ

Interference is the distinguishing feature of a wave. If matter is a wave, it must interact in constructive and destructive ways. Why isn’t this more commonly observed? The answer is that a wave must interact with an object about the same size as its wavelength to produce significant interference effects. Because h is so small, especially for macroscopic objects. For example, a 3-kg bowling ball moving at 10 m/s has

λ = h/p = 6.63 × 10 − 34 J ⋅ s (3 kg) (10 m/s) = 2 × 10 − 35 m

Here are a few working principles of an Electronic Microscope

To understand the definition, morphology, and composition of electronic microscopes, we will have to employ signals generated by the interaction of an electron beam with the material.

• The electron cannon produces electrons.

• The electron beam is focused on the specimen and converted into a narrow tight beam by two pairs of condenser lenses.

• An accelerating voltage (usually between 100 kV and 1000 kV) is supplied between the tungsten filament and anode to transport electrons down the column.

• The specimen to be viewed is created exceedingly thin, at least 200 times thinner than the optical microscope specimens. Ultra-thin sections with a thickness of 20-100 nm are cut and placed on the specimen holder.

• The electrons are dispersed when the electrical beam travels through the specimen, depending on the thickness or refractive index of various portions of the specimen.

• Since fewer electrons reach that area of the screen, the denser portions of the specimen scatter more electrons and look darker in the picture. Transparent areas, on the other hand, are brighter.

• The electron beam leaves the specimen and travels to the objective lens, which has a high magnification power and creates the intermediate magnified picture.

• The ocular lenses create the final enlarged picture.

Principle

• A stream of electrons passes through the item, with electric and magnetic fields focusing the electrons that carry the object’s information.

• The electron microscope has a high resolving power due to its shorter wavelength, which is inversely proportional to the wavelength.

Construction

• An electron microscope is similar to an optical microscope in appearance. Electrons can be focused using either a magnetic lens or an electrostatic lens. Usually, magnetic lenses are used to focus electron microscopes.

The fundamental steps in all EMs

• The Electron Source (typically a heated tungsten or field emission filament) generates a stream of high voltage electrons (usually 5-100 KeV) that are accelerated toward the specimen in a vacuum using a positive electrical potential.

• This stream is confined and focused into a thin, focused monochromatic beam using metal apertures and magnetic lenses.

• This beam is focused on the sample using a magnetic lens.

• Within the irradiated sample, interactions occur, influencing the electron beam.

• These connections and impacts are identified and represented graphically.

• At the end of the nineteenth century, physicists realised that the only way to improve microscopic examination was to use much lower wavelengths of radiation.

• Although Louis deBroglie proved in 1924 that a particle beam travelling in a vacuum needs to behave as a form of very short wavelength radiation, it was Ernst Ruska who made the leap to use electrons’ wave-like properties to build the first EM and improve on the microscopic examination.

Currently, two types of electron microscopes are used in biological and preclinical research: the transmission electron microscope (TEM) and the scanning electron microscope (SEM); TEM and SEM are sometimes combined into a single tool, the scanning transmission electron microscope (STEM).

Electron Microscopes in action

• It’s used in the industry for quality assurance and failure analysis.

• It’s used to investigate the structure of various living and non-living elements.

• It is used in microbiology to examine microorganisms such as bacteria and viruses.

• It’s used to find a flaw or weakness in building material.

• It’s used to investigate a material’s crystal structure.

• It’s used in particle adsorption on surfaces.

Benefits of Electron Microscopes

• Electron microscopes magnify things by a factor of 500,000.

• Preparation seldom causes the material to become distorted.

• We can study a higher depth of field with EM.

• It is capable of resolving objects as small as 200 nm.

Drawbacks of Electron Microscopes

• The cost of an electron microscope is high.

• It is not possible to view live specimens.

• Because EMs are so enormous, they must be operated in specialised rooms.

• The specimen must be ultra-thin because the electron beam penetrating power is so low.

• In EM, all picture types are black and white.

• Viewing live material needs a high vacuum.

• One needs specialised knowledge to deal with it.

• Magnetic fields have an impact.

Conclusion

There are two kinds of electron microscopes. The transmission electron microscope (TEM) accelerates electrons emitted from a hot filament (the cathode). Before passing through the sample, the beam is widened. A magnetic lens focuses the image of the beam onto a fluorescent screen, a photographic plate, or (most likely) a CCD (light-sensitive camera), from which it is transferred to a computer. Here it examines a thin sample in a vacuum. The TEM is similar to an optical microscope. It can, however, resolve details as small as 0.1 nm (1010 m) at magnifications up to 100 million times the original object’s size. The TEM has allowed us to see individual atoms and the cell structure.