Electron Microscope – Types, Parts, Application, Advantages, Disadvantages

An electron microscope is a type of microscope that uses a beam of electrons to create an image of a sample. Electron microscopes have a higher resolution than optical microscopes, which use light to form an image, and can be used to observe objects that are too small to be seen with an optical microscope. Electron microscopes are used in a variety of fields, including biology, materials science, and nanotechnology, to study the structure and properties of materials at a very small scale. There are several types of electron microscopes, including transmission electron microscopes, scanning electron microscopes, and scanning transmission electron microscopes, each of which has its own unique set of capabilities and applications.

What is an Electron Microscope?

  • An electron microscope is a microscope, which uses electron beams as a primary source of illumination.
  • An EM uses the same principles of an optical microscope but instead of photons or particles of light, it concentrates electrons, charged particles located on the outside of atoms, onto an object.
  • Electron microscope is used to obtain high-resolution images of biological and non-biological specimens.
  • It is used to study the structure of tissues, cells, organelles, and macromolecular complexes in detail and often used for quality control and failure analysis.
  • These microscopes use electrons of up to 100,000 times shorter wavelength as compared to the visible light photons.
  • Electron microscope a higher resolving power than light microscopes.
  • Instead of glass lenses, EM uses shaped magnetic fields to form an electron-optical lens.
  • In 1931, a physicist and electrical engineer,  Ernst Ruska, and Max Knoll discovered the first transmission electron microscope.
  •  All electron microscopes use a coil of wire wrapped around the outside of a tube (commonly referred to as a solenoid) as an electromagnetic and/or electrostatic lenses.
  • The resolution in Em depends on the wavelength of radiation, Smaller the radiation, greater will be the resolution.

Working Principle of Electron Microscope – how does an electron microscope work?

The working principle of an electron microscope is based on the interaction of a beam of electrons with a sample. In a transmission electron microscope (TEM), a beam of electrons is transmitted through a thin sample, and the resulting image is formed by the electrons that pass through the sample. The electrons are focused by an electron lens, which consists of a series of electromagnets that bend the path of the electrons. The sample is placed on a grid or a specimen holder, and the electrons pass through it and are collected by an electronic detector on the other side. The image is then displayed on a screen or captured by a camera.

In a scanning electron microscope (SEM), a beam of electrons is focused onto the surface of a sample, and the resulting image is formed by the electrons that are reflected or scattered by the sample. The electrons are focused by an electron gun, which consists of a cathode and an anode that generate and accelerate the electrons. The sample is mounted on a stage and is scanned by the beam of electrons, which is rastered over the surface of the sample. As the electrons interact with the sample, they are detected by an electronic detector, and the resulting image is displayed on a screen or captured by a camera.

Scanning transmission electron microscopes (STEM) combine the capabilities of TEMs and SEMs and can be used to create high-resolution images of both the surface and the internal structure of a sample. In a STEM, the beam of electrons is transmitted through a thin sample and is scattered by the sample as it passes through. The scattered electrons are detected by an electronic detector, and the resulting image is displayed on a screen or captured by a camera.

Operating Procedure of Electron microscope

The operating procedure of an electron microscope varies depending on the specific type of electron microscope being used and the sample being studied. However, there are some general steps that are common to most electron microscopes:

  1. Prepare the sample: The sample must be prepared in a specific way before it can be studied with an electron microscope. This may involve thinning the sample, adding a contrast agent, or mounting the sample on a holder or a stage.
  2. Position the sample: The sample is placed in the electron beam and is positioned so that the area of interest is in the field of view. The sample may be moved and rotated to view different areas or to focus on specific features.
  3. Adjust the electron beam: The energy and intensity of the electron beam may be adjusted to optimize the image contrast and to minimize sample damage. The beam may also be focused or rastered over the sample to create a high-resolution image.
  4. Collect and process the image data: The electrons that are scattered or reflected by the sample are detected by an electronic detector and are used to create an image of the sample. The image data may be processed and analyzed using specialized software.
  5. View and analyze the image: The image is displayed on a screen or captured by a camera and can be viewed and analyzed to study the structure and properties of the sample. The image may be magnified, rotated, or enhanced to highlight specific features or to aid in the analysis.

Parts of an Electron Microscope

Electron Microscopes contain these following parts;

No.PartDescription
1Electron GunGenerates and accelerates electrons for imaging. In TEM, it consists of a cathode and an anode; in SEM, it has a cathode for generation and an anode for acceleration of electrons.
2Electromagnetic Lens SystemComprises different types of lenses to focus and magnify the electron beam: <br> – Condenser lens: Focuses the electron beam on the specimen. <br> – Objective lens: Magnifies the image after the beam passes through the specimen. <br> – Projector (ocular) lenses: Further magnifies the intermediate image to form the final image.
3Sample Holder/Specimen HolderA platform with a mechanical arm to hold and position the specimen. In TEM, the sample is placed on a grid or holder; in SEM, it’s mounted on a stage that can be moved and positioned under the electron beam.
4Image Viewing and Recording SystemProjects the final image of the specimen onto a fluorescent screen, with a camera located below the screen to record the image.
5DetectorDetects scattered or reflected electrons from the sample to create an image. Various types of detectors can be used, including scintillators, phosphor screens, and CCDs.
6Electronics and Computer SystemControls the microscope’s operation and processes and displays image data. This system may include computers, monitors, and software for microscope control and data analysis.

1. Electron gun

  • The electron gun generates and accelerates the electrons that are used to create the image. In a transmission electron microscope (TEM), the electron gun consists of a cathode and an anode that generate and accelerate the electrons.
  • In a scanning electron microscope (SEM), the electron gun consists of a cathode that generates the electrons and an anode that accelerates them.

2. Electromagnetic lense System

This system allows electrons within a smell energy range to pass through, so that the electrons in the electron beam will have a well-defined energy. In an electron microscope, different types of lenses are used such as;

  • Condenser lens: It focuses the electron beam on the specimen. 
  • objective lens: Electron beam after coming out from the specimen is passed through a second of magnetic coils called the objective lens. It helps in the formation of an intermediate magnified image.
  • Projector (ocular) lenses: It helps in the formation of a final further magnified image.

3. Sample Holder or Specimen Holder

  • It is a platform equipped with a mechanical arm for holding the specimen and controlling its position.
  • The sample stage holds the sample in place and allows it to be moved and positioned in the electron beam. In a TEM, the sample is placed on a grid or a specimen holder, and in a SEM, the sample is mounted on a stage and is scanned by the beam of electrons.

4. Image viewing and Recording System

  • The final image of the specimen is projected on a fluorescent screen. This image is recorded by a camera, which is located below the screen.

5. Detector

  • The detector is used to detect the electrons that are scattered or reflected by the sample and to create an image of the sample.
  • There are several types of detectors that can be used in an electron microscope, including scintillators, phosphor screens, and charge-coupled devices (CCDs).

6. Electronics and computer system

  • The electronics and computer system is used to control the operation of the electron microscope and to process and display the image data.
  • This may include a computer, monitor, and software for controlling the microscope and analyzing the data.

Types of Electron microscope

Electron Microscopes are divided into three classes;

1. Transmission Electron Microscope (TEM)

Transmission electron microscopes (TEMs) are a type of electron microscope that uses a beam of electrons that is transmitted through a thin sample to create an image of the sample’s internal structure. TEMs have a very high resolution and can be used to observe objects at the nanoscale, making them a powerful tool for studying the structure and properties of materials at the atomic level.

In a TEM, the sample is placed on a grid or a specimen holder, and the beam of electrons is focused by an electron lens and transmitted through the sample. The electrons that pass through the sample are collected by an electronic detector on the other side, and the resulting image is displayed on a screen or captured by a camera.

TEMs can be used to study a wide range of samples, including metals, semiconductors, polymers, and biological materials. They are particularly useful for studying the structure and properties of materials at the atomic and molecular level, as well as for imaging defects and impurities in materials. TEMs are also used in the fields of materials science, biology, and nanotechnology to study the structure and properties of materials at the nanoscale.

Transmission Electron Microscope (TEM)
Transmission Electron Microscope (TEM)

Features of Transmission Electron Microscope (TEM)

  • Transmission Electron Microscopes uses a high voltage electron beam to illuminate the specimen and create an image.
  • These electron beams are produced by an electron gun, which is consists of a tungsten filament called Cathode.
  • Then the electron beam is accelerated by an anode typically at +100 keV (40 to 400 keV).
  • The electron beam is focused on the specimen by using an electrostatic and electromagnetic lense.
  • Transmitted through the specimen that is in part transparent to electrons and in part scatters them out of the beam. 
  • The transmitted electron beams are now magnified by the objective lens system of the microscope. 
  • Now the magnified electron image is projected onto a fluorescent viewing screen to see the clear and magnified image of the specimen.
  • The screen is coated with a phosphor or scintillator material such as zinc sulfide. 
  • The image is recorded with a digital camera.

2. Scanning electron microscope

Scanning Electron Microscope (SEM)
Scanning Electron Microscope (SEM)
  • The heated electron gun releases a narrow electron beam.
  • Now, the Specimen is exposed to these narrow electron beams.
  • These narrow electron beams will rapidly move over or scans the surface of the specimen.
  • As a result, this will emit a shower of secondary electrons and other types of radiations from the outer surface of specimen.
  • The intensity of these secondary electrons depends upon the shape and the chemical composition of the irradiated object.
  • These secondary electrons are collected by a detector, which helps to generate electronic signals.
  • These electronic signals are now scanned in the manner of a television system to produce an image on a cathode ray tube (CRT).
  • The image is recorded by capturing it from the CRT. 
  • The Modern variants of Scanning electron microscopes have the facility to record the photograph by digital camera. This microscope is used to observe the surface structure of microscopic objects.
Scanning electron microscope
Scanning electron microscope | Image Source: www.britannica.com

3. Scanning and Transmission Electron Microscope (STEM)

  • Scanning transmission electron microscopes (STEMs) are a type of electron microscope that combines the capabilities of transmission electron microscopes (TEMs) and scanning electron microscopes (SEMs).
  • STEMs use a beam of electrons that is transmitted through a thin sample and is scattered by the sample as it passes through. The scattered electrons are detected by an electronic detector, and the resulting image is displayed on a screen or captured by a camera.
  • STEMs are particularly useful for studying samples with a high atomic number, such as metals and semiconductors, as they can produce high-resolution images of both the surface and the internal structure of a sample.
  • They are also useful for studying samples that are sensitive to high-energy electrons, as the energy of the electron beam can be adjusted to minimize sample damage.
  • In a STEM, the sample is mounted on a stage and is scanned by the beam of electrons, which is rastered over the surface of the sample. As the electrons interact with the sample, they are detected by an electronic detector, and the resulting image is displayed on a screen or captured by a camera.
  • STEMs can be used to study a wide range of samples, including metals, semiconductors, polymers, and biological materials. They are particularly useful for studying the structure and properties of materials at the nanoscale, as well as for imaging defects and impurities in materials.

4. Other types of Electron Microscope

Except, these two types of Electron Microscopes, there are also present;

a. Reflection electron microscope (REM)

In this microscope, an electron beam is incident on a surface of specimen, and the reflected beam of elastically scattered electrons is detected. 

This technique is typically coupled with reflection high energy electron diffraction (RHEED) and reflection high-energy loss spectroscopy (RHELS).

b. Scanning transmission electron microscope (STEM)

The STEM rasters a focused incident probe across a specimen that (as with the TEM) has been thinned to facilitate the detection of electrons scattered through the specimen.

c. Scanning tunneling microscopy (STM)

In this microscope, a conductive tip held at a voltage is brought near a surface, and a profile can be obtained based on the tunneling probability of an electron from the tip to the sample since it is a function of distance.

d. Environmental electron microscopes

Environmental electron microscopes are specialized types of electron microscopes that are designed to study samples in their native environment, such as in a gas or liquid. These microscopes can be used to study the properties of materials under realistic conditions and are particularly useful for studying materials that are sensitive to the vacuum conditions required for other types of electron microscopes.

e. Low-energy electron microscopes (LEEMs)

LEEMs use a beam of low-energy electrons to create an image of the surface of a sample. LEEMs are particularly useful for studying samples that are sensitive to high-energy electrons, such as organic materials and biological samples.

Application of Electron Microscopes

Electron microscopes are used in a wide variety of fields to study the structure and properties of materials at a very small scale. Some common applications of electron microscopes include:

  1. Materials science: Electron microscopes are used to study the structure and properties of materials at the atomic and molecular level, such as metals, semiconductors, and polymers. They can be used to study the arrangement of atoms in a material, to identify defects and impurities, and to study the corrosion and wear of materials.
  2. Biology: Electron microscopes are used to study the structure of cells and tissues at the molecular level, such as proteins, DNA, and organelles. They can be used to study the structure and function of cells and tissues, to identify abnormalities, and to study the effects of drugs and other treatments.
  3. Nanotechnology: Electron microscopes are used to study the structure and properties of materials at the nanoscale, such as nanotubes, nanoparticles, and nanowires. They are used to study the properties of materials at the nanoscale and to design and fabricate new materials and devices at the nanoscale.
  4. Semiconductor industry: Electron microscopes are used to study the structure and properties of semiconductor materials and devices, such as transistors, integrated circuits, and solar cells. They are used to study the performance and reliability of semiconductor devices and to identify and troubleshoot defects.
  5. Environmental science: Electron microscopes are used to study the structure and properties of environmental samples, such as soil, water, and air. They are used to study the distribution and behavior of contaminants and to understand the impacts of environmental factors on the structure and properties of materials.

Advantages of Electron Microscopes

There are several advantages of electron microscopes compared to other types of microscopes, such as optical microscopes:

  1. High Magnification: Electron Microscopes can Magnifies objects over 500,000x  times.
  2. Higher resolution: Electron microscopes have a much higher resolution than optical microscopes, and can be used to observe objects at the nanoscale. This makes them a powerful tool for studying the structure and properties of materials at the atomic and molecular level.
  3. Greater depth of field: Electron microscopes have a greater depth of field than optical microscopes, which means that they can produce images of objects that have a greater depth or thickness. This makes them useful for studying thick or three-dimensional samples.
  4. Ability to study a wide range of samples: Electron microscopes can be used to study a wide range of samples, including metals, semiconductors, polymers, and biological materials. They are particularly useful for studying samples that are too small, too transparent, or too opaque to be studied with an optical microscope.
  5. Ability to study samples under a variety of conditions: Electron microscopes can be used to study samples under a variety of conditions, such as in a vacuum, in a gas, or in a liquid. This makes them useful for studying samples that are sensitive to the environment or that need to be studied in their native state.
  6. Greater contrast: Electron microscopes can produce images with a high level of contrast, which makes it easier to distinguish between different features in a sample. This is especially useful for studying samples with a complex structure or for identifying defects and impurities in materials.

Limitations of Electron microscope

There are several limitations of electron microscopes, including:

  1. Price: Electron Microscopes are expensive. 
  2. Sample preparation: Electron microscopes require that the sample be prepared in a specific way, such as by thinning it or adding a contrast agent. This can be time-consuming and may alter the properties of the sample.
  3. Sample size: Electron microscopes are limited by the size of the sample that can be studied. Larger samples must be cut or ground into smaller pieces before they can be studied, which can be difficult and may alter the properties of the sample. As the penetration power of the electron beam is very low, the specimen should be ultra-thin.
  4. Image Formation: All images forms in EM, are in black and white.
  5. Sample damage: Electron microscopes can damage samples due to the high energy of the electron beam. This can be a problem when studying sensitive or fragile samples, such as biological materials.
  6. Complexity: Electron microscopes are complex instruments that require specialized training and expertise to operate. They are also expensive and require regular maintenance and calibration to ensure that they are operating correctly. A high vacuum is required for viewing the living material. Affected by magnetic fields.
  7. Limited imaging depth: Electron microscopes have a limited imaging depth and are not able to produce images of objects that are more than a few micrometers below the surface. This can be a problem when studying samples with a complex internal structure.
  8. Sample Type: Live specimens cannot be observed.
  9. Space: EMs are very large in size and must be operated in special rooms.
  10. Operate: It is Expensive to operate. Required expertise to handle it.

Why is electron microscope better than light?

Electron microscopes are generally considered to be more powerful and have a higher resolution than light microscopes, which use light to form an image. There are several reasons for this:

  1. Higher resolution: Electron microscopes have a much higher resolution than light microscopes and can be used to observe objects at the nanoscale. This makes them a powerful tool for studying the structure and properties of materials at the atomic and molecular level.
  2. Greater depth of field: Electron microscopes have a greater depth of field than light microscopes, which means that they can produce images of objects that have a greater depth or thickness. This makes them useful for studying thick or three-dimensional samples.
  3. Ability to study a wide range of samples: Electron microscopes can be used to study a wide range of samples, including metals, semiconductors, polymers, and biological materials. They are particularly useful for studying samples that are too small, too transparent, or too opaque to be studied with a light microscope.
  4. Ability to study samples under a variety of conditions: Electron microscopes can be used to study samples under a variety of conditions, such as in a vacuum, in a gas, or in a liquid. This makes them useful for studying samples that are sensitive to the environment or that need to be studied in their native state.
  5. Greater contrast: Electron microscopes can produce images with a high level of contrast, which makes it easier to distinguish between different features in a sample. This is especially useful for studying samples with a complex structure or for identifying defects and impurities in materials.

Electron Microscope: Definition, Types, Parts, Application, Advantages, Disadvantages – Video

Electron microscope images

FAQ

What is an electron microscope?

An electron microscope is a type of microscope that uses a beam of electrons to create an image of a sample. Electron microscopes have a higher resolution than optical microscopes, which use light to form an image, and can be used to observe objects that are too small to be seen with an optical microscope. Electron microscopes are used in a variety of fields, including biology, materials science, and nanotechnology, to study the structure and properties of materials at a very small scale. There are several types of electron microscopes, including transmission electron microscopes, scanning electron microscopes, and scanning transmission electron microscopes, each of which has its own unique set of capabilities and applications.

When was the electron microscope invented?

The first electron microscope was developed in the 1930s by German physicist Ernst Ruska and his colleagues at the Technical University of Berlin. Ruska received the Nobel Prize in Physics in 1986 for his work on the development of the electron microscope.
In the early 1930s, Ruska and his colleague Max Knoll developed the first electron microscope, which they called the “transmission electron microscope” (TEM). The TEM used a beam of electrons that was transmitted through a thin sample to create an image of the sample’s internal structure.
In the 1940s, other types of electron microscopes were developed, including the scanning electron microscope (SEM) and the scanning transmission electron microscope (STEM). The SEM used a beam of electrons that was focused onto the surface of a sample to create an image of the sample’s surface features, while the STEM used a beam of electrons that was transmitted through a thin sample and was scattered by the sample as it passed through.
Today, electron microscopes are used in a wide variety of fields to study the structure and properties of materials at the atomic and molecular level. They are an essential tool for scientists and researchers in many fields, including materials science, biology, and nanotechnology.

How much does a electron microscope cost?

The cost of an electron microscope can vary widely depending on the type and capabilities of the microscope. Generally, electron microscopes are more expensive than optical microscopes, due to their higher resolution and specialized features.
A basic transmission electron microscope (TEM) can cost several hundred thousand dollars, while a more advanced TEM with additional features and capabilities can cost several million dollars. A scanning electron microscope (SEM) can also cost several hundred thousand dollars, while a scanning transmission electron microscope (STEM) can cost several million dollars.
In addition to the initial purchase price, there are also ongoing costs associated with operating an electron microscope, including maintenance, repair, and calibration. These costs can vary depending on the type of microscope and the specific needs of the user.
Overall, the cost of an electron microscope can be a significant investment, and it is important to carefully consider the specific needs and budget of an organization when purchasing an electron microscope.

Which lens is used in electron microscope?

Electron microscopes use electron lenses to focus the beam of electrons onto the sample. There are several types of electron lenses that are used in electron microscopes, including:
1. Electromagnetic lenses: Electromagnetic lenses are used in transmission electron microscopes (TEMs) to focus the beam of electrons onto the sample. They consist of a series of electromagnets that bend the path of the electrons and can be used to adjust the focus of the beam.
2. Electrostatic lenses: Electrostatic lenses are used in scanning electron microscopes (SEMs) to focus the beam of electrons onto the sample. They consist of a series of electrostatic plates that are charged to different potentials, which deflect the electrons and focus them onto the sample.
3. Hybrid lenses: Hybrid lenses are a combination of electromagnetic and electrostatic lenses and are used in some types of electron microscopes to focus the beam of electrons onto the sample. Hybrid lenses offer the benefits of both electromagnetic and electrostatic lenses and can be used to achieve a high-resolution image.
In addition to these types of lenses, electron microscopes may also use other types of lenses, such as aberration correctors and condenser lenses, to adjust the focus and contrast of the beam of electrons.

What is the size of electron microscope?

The size of an electron microscope can vary widely depending on the type and capabilities of the microscope. Some electron microscopes are relatively small and portable, while others are large and require a dedicated laboratory space.
Transmission electron microscopes (TEMs) are generally larger than scanning electron microscopes (SEMs) and may require a dedicated laboratory space. TEMs can range in size from a few feet to over 10 feet in length and may weigh several thousand pounds.
Scanning electron microscopes (SEMs) are generally smaller than TEMs and can be more portable. SEMs can range in size from a few feet to several feet in length and may weigh several hundred pounds.
Overall, the size of an electron microscope can vary depending on the specific requirements and needs of the user. Some electron microscopes are designed for use in a laboratory or research facility, while others are designed for use in the field or in a manufacturing environment.

Can electron microscopes see living things?

Unlike light microscopes, electron microscopes cannot be used to directly see living organisms since samples must undergo special preparation before being viewed. Rather, electron microscopes attempt to produce a high-resolution “picture” of a moment in living tissue.

Can electron microscopes see atoms?

Yes, electron microscopes are powerful enough to observe individual atoms and can be used to study the structure and properties of materials at the atomic scale. There are several types of electron microscopes that can be used to study atoms, including transmission electron microscopes (TEMs) and scanning transmission electron microscopes (STEMs).
TEMs and STEMs use a beam of electrons that is transmitted through a thin sample to create an image of the sample’s internal structure. The electrons that pass through the sample are scattered by the atoms in the sample, and the resulting pattern of scattering is used to create an image of the sample.
By analyzing the image, scientists can identify the arrangement of atoms in a sample, measure the distance between atoms, and study the chemical bonding between atoms. Electron microscopes are particularly useful for studying materials that have a complex structure or that are made up of a small number of atoms, such as nanomaterials or thin films.
Overall, electron microscopes are an essential tool for studying the structure and properties of materials at the atomic scale and have played a key role in our understanding of the fundamental properties of matter.

Can electron microscopes see color?

Electron microscopes do not use light to form an image, so they do not produce images with color in the same way that optical microscopes do. Instead, they produce black and white images that show the contrast between different features in the sample.
However, it is possible to assign colors to different features in an electron microscope image to highlight specific structures or to make the image more visually appealing. This is often done using software that can analyze the image data and assign colors to different features based on their size, shape, or position.
For example, scientists may assign different colors to different types of atoms in a sample or to different types of molecules in a cell. This can help to identify specific structures or to study the distribution of different molecules in a sample.
Overall, electron microscopes do not produce images with color in the same way that optical microscopes do, but it is possible to use color to highlight specific features in an electron microscope image to aid in the analysis and interpretation of the image.

How powerful is an electron microscope?

Electron microscopes are very powerful instruments that can be used to study the structure and properties of materials at the atomic and molecular level. They have a much higher resolution than optical microscopes and can be used to observe objects that are too small to be seen with an optical microscope.
The power of an electron microscope is often measured in terms of its resolution, which is the smallest distance between two points that can be distinguished by the microscope. The resolution of an electron microscope is typically measured in nanometers (nm), which is one billionth of a meter.
The resolution of an electron microscope depends on the type of electron microscope being used and the specific sample being studied. Transmission electron microscopes (TEMs) and scanning transmission electron microscopes (STEMs) have a higher resolution than scanning electron microscopes (SEMs) and can be used to study the structure of materials at the atomic scale. TEMs and STEMs can have a resolution of 0.1 nm or less, while SEMs typically have a resolution of around 1-2 nm.
Overall, electron microscopes are very powerful instruments that are essential for studying the structure and properties of materials at the atomic and molecular level. They are used in a wide variety of fields, including materials science, biology, and nanotechnology, to study the structure and properties of materials at a very small scale.

Reference

  • https://www.umassmed.edu/cemf/whatisem/
  • https://www.microscopemaster.com/electron-microscope.html
  • https://www.wikilectures.eu/w/Electron_microscopy/principle
  • https://www.biologydiscussion.com/microscope/electron-microscope/electron-microscope-principle-components-specimen-preparation-and-uses/16595
  • https://www.slideshare.net/gangahuvin/electron-microscopy-16995175
  • https://getrevising.co.uk/grids/electron_microscopes_2
  • https://www.yourarticlelibrary.com/microeconomics/working-principle-of-a-electron-microscopes-with-diagram/26479
  • https://en.wikipedia.org/wiki/Electron_microscope

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