An electron microscope is a type of microscope that makes a picture of a sample by sending a beam of electrons through it. Electron microscopes can see things that are too small to be seen with an optical microscope. This is because electron microscopes have a higher resolution than optical microscopes, which use light to make an image. Electron microscopes are used in many fields, like biology, materials science, and nanotechnology, to look at the very small structure and properties of materials.
Electron Microscope Definition
An electron microscope is a type of microscope that is illuminated by a beam of fast-moving electrons. It is a special kind of microscope with high-resolution images that can magnify objects to the size of nanometers. The images are made by using electrons in a vacuum in a controlled way and capturing them on a phosphorescent screen. The first transmission electron microscope was developed by physicist Ernst Ruska and electrical engineer Max Knoll in 1931 and the same principles behind his prototype still govern modern EMs.
Principle of Electron Microscope
Electron microscopes rely on the interaction of an electron beam with a specimen. In a transmission electron microscope (TEM), a beam of electrons is sent through a thin sample, and the electrons that pass through the sample form an image. An electron lens, made up of several electromagnets, focuses electrons by re-directing their trajectory. A specimen is placed on a grid or holder, and electrons are then sent through it and detected by an electronic detector. After that, the image is either projected onto a screen or photographed.
Scanning electron microscopes (SEMs) work by focusing a beam of electrons onto a sample’s surface; the electrons reflected or scattered by the sample are what create the final image. An electron gun uses a cathode and an anode to create and accelerate electrons, which are then focused by the gun. The sample, which is supported on a stage, is raster-scanned by an electron beam. An electronic detector picks up the signals produced by the electrons’ collisions with the sample, and the resulting image can be viewed on a screen or recorded by a camera.
Scanning transmission electron microscopes (STEMs) combine the features of transmission electron microscopes (TEMs) and scanning electron microscopes (SEMs). They can be used to make high-resolution pictures of both the surface and the inside of a sample. In a STEM, the electron beam is sent through a thin sample and scattered by the sample as it goes. An electronic detector picks up the scattered electrons, and the image they make is shown on a screen or captured by a camera.
Procedure of Electron Microscope
How an electron microscope is utilised depends on the type of microscope and the material being examined. Most electron microscopes have their own unique procedures, however there are some common ones as well:
Prepare the sample: Before a sample can be looked at with an electron microscope, it needs to be prepared in a specific way. This could mean making the sample thinner, adding a contrast agent, or putting the sample on a holder or a stage.
Position the sample: The sample is put in the electron beam and moved so that the area of interest is in the field of view. You can move and rotate the sample to look at different areas or zoom in on certain parts.
Adjust the beam: The electron beam’s energy and intensity can be changed to improve the contrast of the image and reduce damage to the sample. A high-resolution image can also be made by focusing the beam on the sample or moving it back and forth over it.
Collect Image data: An electronic detector picks up the scattered or reflected electrons from the sample and uses them to make an image of the sample. Specialized software can be used to process and analyse the image data.
Analyse the image: The image can be shown on a screen or taken with a camera. It can then be viewed and analyzed to learn about the sample’s structure and properties. The image can be enlarged, turned, or improved to bring out certain details or to help with the analysis.
Parts of Electron Microscope
Electron Microscope looks like a tall, vertically mounted vacuum column. It is made up of the following:
Electron gun: The electron gun produces and accelerates the electrons utilised in image creation. The electron gun of a transmission electron microscope (TEM) is composed of a cathode and an anode that create and accelerate electrons. The electron gun of a scanning electron microscope (SEM) comprises of a cathode that produces electrons and an anode that accelerates them.
Condenser lens: The electron beam is focused on the specimen by the condenser lens. The electrons are formed into a thin, tight beam by a second condenser lens. The electron beam coming out of the specimen travels down the second magnetic coil, known as the objective lens, which has a high power and produces the intermediate magnified image.
Specimen Holder: It is a platform with a mechanical arm for holding and controlling the specimen’s location. The sample stage secures the sample and enables for its movement and positioning inside the electron beam.
Image viewing: The specimen’s final image is projected onto a fluorescent screen. This image is captured by a camera positioned beneath the display.
Detector System: The electrons dispersed or reflected by the sample are detected by the detector, which are then employed to form a picture of the sample. Scintillators, phosphor screens, and charge-coupled devices are just a few examples of the detectors that can be employed in an electron microscope.
Electronics: Electronics and a computer system are utilised to manage the electron microscope and show processed image data. In some cases, this may contain a computer, a display, and software designed to manage the microscope and analyse the collected data.
3 Types of Electron Microscope
i) Transmission Electron Microscope (TEM)
In light microscopy, differential absorption of light, which depends mainly on staining the specimen, results in the visible differences in various parts of the image. In the TEM, a condense, lens focuses the electron beam onto the specimen and electrons are transmitted through the specimen. The portion of the beam absorbed by specimen is minimal. To be absorbed, an electron must lose all its energy to the specimen. Although not absorbed, these electrons are scattered by the atoms of the specimen.
Image formation in the electron microscope depends on differential scattering of electrons by parts of the specimen. Consider a beam of electrons focused on the screen. If no specimen were present in the column, the screen would be evenly illuminated by the beam of electrons, producing an image that is uniformly bright.
Figure 1: Transmission Electron Microscope Images
By contrast, if a specimen is placed in the path of the beam, some of the electrons strike the specimen and are scattered away. When the electrons come in contact with the sample, it can either be scattered elastically, that is, without any loss of energy, or inelastically, i.e. transferring some of that energy to the atom. Interaction between the incoming fast electron and an atomic nucleus gives rise to elastic scattering. Interaction between the fast electron and atomic electrons results in inelastic scattering. Some of the electrons passing through the specimen are scattered and the remainder is focused to form an image, in a manner analogous to the way an image is formed in a light microscope.
The image can be observed on a phosphorescent screen or recorded, either on a photographic plate or with a high-resolution digital camera. Because the scattered electrons are lost from the beam, the dense regions of the specimen show up in the image as areas of reduced electron flux, which look dark. Scattering of electrons contribute to the contrast. Because the electrons are absorbed by atoms in the air, the entire tube between the electron source and the detector is maintained under an ultrahigh vacuum.
ii) Scanning Electron Microscope (SEM)
The Scanning Electron Microscope (SEM) views the surfaces of specimens. The sample is fixed, dried, and coated with a thin layer of a heavy metal, such as gold or a mixture of gold and palladium. The specimen is, then, scanned with a very narrow beam of electrons. Molecules in the specimen are excited and they release secondary electrons that are captured by a detector, and generating an Image of the specimen’s surface.
Figure 2: Scanning Electron Microscope Images
Contrast arises when different parts of specimen generate differing amounts of secondary electrons as the electrons beam strikes them. Areas which generate large numbers of secondary electrons will appear brighter than areas that generate fewer secondary electrons. The resolving power of scanning electron microscopes, which Is limited by the thickness of the metal coating, is Only about 10 nm, much less than that of transmission electron microscope. The Image produced appear three-dimensional in SEM whereas transmission electron microscope produces two dimensional images.
iii) Scanning and Transmission Microscope
Transmission electron microscopes (TEMs) and scanning electron microscopes (SEMs) are two types of electron microscopes, but scanning transmission electron microscopes (STEMs) combine the best features of both.
During STEM analysis, an electron beam is passed through a thin sample and scattered by the sample. An electronic detector picks up the dispersed electrons, producing a digital or analogue image of the sample. Metals, semiconductors, polymers, and even biological materials can all be analyzed with the use of STEMs.
Electron Microscope Uses
Electron microscopes have several applications due to their ability to examine minute details of materials. The following are some typical electron microscope uses:
Materials science: the electron microscope uses to examine the atomic and molecular structure and properties of materials like metals, semiconductors, and polymers. They can be used to investigate corrosion and wear as well as the orientation of atoms in a material.
Biology Samples: The molecular structure of cells and tissues, including proteins, DNA, and organelles, can be examined with an electron microscope. They can be utilised in the investigation of medication and treatment outcomes, as well as the examination of cellular and tissue structure and function.
Nanotechnology: The structure and behavior of nanoscale materials, such as nanotubes, nanoparticles, and nanowires, are investigated with electron microscopes. Electron microscope uses in the design and fabrication of nanoscale materials and devices as well as the investigation of nanoscale material characteristics.
Semiconductor: Transistors, integrated circuits, and solar cells are just a few examples of the semiconductor technologies and materials that electron microscope uses to investigate. They are put to use in the semiconductor industry for the purpose of analysing and diagnosing device problems.
Ecology Studies: The field of environmental science electron microscope uses to investigate the composition and composition of environmental samples like dirt, water, and air. Ecology influences have an effect on the structure and properties of materials, therefore studying their distribution and behavior is important.
Electron Microscopes Advantages
When compared to optical microscopes, electron microscopes provide a number of benefits. There are the advantages of electron microscope:
High resolution: When compared to optical microscopes, electron microscopes are able to create more detailed images of samples due to their better resolution. This is because electrons’ wavelength is substantially shorter than that of light, allowing for sharper pictures to be taken.
High magnification: Electron microscopes have the ability to magnify samples up to several million times, which enables scientists to examine extremely minute characteristics and structures.
3D Sample Study: The ability to investigate materials in three dimensions is a major advantage of electron microscopes, which allow for in-depth analysis of the subject under examination.
Variety of Samples: Electron microscopes can be used to examine a broad variety of samples, including those from biology, chemistry, and materials science, as well as microelectronics.
In Natural State: Electron microscopes allow researchers to examine items as they are found in nature, without subjecting them to any kind of artificial alteration, such as drying or staining. This is directly important when analysing biological samples that could be harmed during sample preparation.
Different Heat: Some electron microscopes feature a cryo-stage, enabling scientists to investigate samples at extremely low temperatures. The ability to control the temperature is helpful for investigating materials that are affected by drastic shifts in ambient conditions.
Study in a vacuum: Samples can be studied in a vacuum free from environmental influences; electron microscopes function in a vacuum. It’s crucial for examining samples that can’t stand being exposed to air or other impurities.
Electron Microscope Limitations
Preparing the sample: For an electron microscope to work, the sample needs to be thin enough to let the electron beam pass through. To do this, the sample must be prepared in a certain way, which may include cutting, embedding, and slicing it. This can take a lot of time and might damage the sample.
Dehydrating Sample: In order to use an electron microscope to study something, the sample must be dehydrated, because water absorbs electrons and makes it hard to make a clear image. Some samples, especially biological ones, can also be damage by being too dry.
Sample conductivity: To be looked at with an electron microscope, samples must be conductive, because the electron beam is drawn to charged particles. In order to study something, it must be covered with a conductive material, like gold or platinum.
Sample Artifacts: The process of preparing the sample can cause artefacts, or distortions, in the sample, which can change how accurate the image is.
Sample damage: An electron microscopes electron beam can damage the sample, especially if it is exposed to the beam for a long time.
More Expensive: Electron microscopes are expensive tools that can only be used by people who have had special training. Some researchers may not be able to get to them because of this.
Low Image Depth: The depth of field in an electron microscope image is limited, which makes it hard to study samples that are thick or have many layers.
Electron Microscope Images
Figure 3: Electron Microscope Images
Figure 4: Scanning Electron Microscope Images
Figure 5: Transmission Electron Microscope Images
Figure 6: Virus Under Electron Microscope
Figure 7: Electron Microscope Images of Atoms
Figure 8: Electron Microscope Image of An Atom
Figure 9: Electron Microscopic Image of Atom
Figure 10: Sperm under Electron Microscope
Figure 11: Crystals under Electron Microscope
FAQs on Electron Microscope Types and Uses with Diagram
A high-resolution image of a sample can be created by an electron microscope, which uses a focused stream of electrons.
A group of scientists at the Technical University of Berlin, led by Ernst Ruska and Max Knoll in the 1930s developed the electron microscope.
A scanning electron microscope (SEM) is a type of electron microscope that uses a beam of electrons to make a high-resolution image of a sample. It works by moving a focused beam of electrons over the surface of the sample and picking up the electrons that are scattered or reflected by the surface.
As electrons are significantly smaller than the wavelengths of visible light, it is impossible to directly observe them using a microscope or other optical instrument. Nevertheless, using various types of microscopes, it is possible to study the effects of electrons on materials.
Electron microscopes are specialized instruments that use a beam of electrons to produce a high-resolution image of a sample.
A scanning electron microscope (SEM) is a type of microscope that uses a beam of electrons to produce high-resolution images of the surface of a sample.
The cost of an electron microscope can vary significantly depending on the type and complexity of the instrument. Simple, low-resolution transmission electron microscopes (TEMs) can cost tens of thousands of dollars, while high-resolution, specialized TEMs and scanning electron microscopes (SEMs) can cost hundreds of thousands or even millions of dollars.