An electron microscope (EM’s) is a versatile technique to see the 3D image of sample by using a beam of electron. This technique is very useful to reveal the structure of smaller objects. We know that the wavelength of electron using this microscope is 100,000 times shorter than that of visible light photon. This microscope provides a good resolving power than light microscopes for having the shorter wavelengths of electron used in this technique.
The ultra structure of specimen samples like cells, large molecules, biopsy samples, microorganisms, metals, and crystals can be investigated easily by applying this technique. This microscopic system is a crucial technique in the field of quality control and failure analysis in the industrial sectors.
What is an Electron Microscope?
A beam of accelerated electrons from the source is used in electron microscopic system to illuminate the specimen sample clearly. It contains high resolution power and has the ability to magnify objects in nanometer level. This advance type microscope was constructed by a German engineer Ernst Ruska in 1931.
Principle of Electron microscope
A beam of electron is firstly generated from the gun of electrons. There has two sets of condenser lenses which focuses the generated electron beam on the sample surface and then into a thin tight beam. An accelerating voltage is then applied between the tungsten filament and anode for moving down the electron beam through the column. It is important to use very thinner specimen sample for this microscopic system.
Then the generated electron beam passes through the sample easily. The electrons are scattered from the sample based on the thickness or refractive index of different parts of the sample specimen. It is generally seen that the more scattered electrons are generated from the denser regions in the specimen.
The scattered electron is then passes through the objective lens, which has high resolution power to form the nice magnified image. The final magnified image is then produced by the ocular lenses.
Structure of electron microscope
The structure of this microscope is shown below:
Types of Electron microscope
There exist two types of electron microscope which are given below:
Scanning Electron Microscope (SEM)
It is used a focused beam of electrons for scanning a sample surface to generate a high resolution image. We get the surface composition and topographical information of sample from this microscope.
An electron gun produces electrons and passes through a series of lenses and apertures creating a focused beam. The generated focused beam is then interacts with the surface of a sample.
The sample is kept in a vacuum stage depends on the microscope’s design. Scan coils help to scan across the sample surface by controlling the position of the electron beam above the objective lens. Then a number of signals are generated in the form of secondary electrons, backscattered electrons, and characteristic X-rays which are then detected by detectors. The detector has the ability to create a good image to display it on a computer screen.
Transmission Electron Microscope (TEM)
There are mainly three components in this microscope namely an electron source; a series of electromagnetic lenses; and a sensitive optical detector. A beam of accelerated electron is produced by a high-voltage electron gun. The electron beam is then focused onto the ultra-thin sample to produce an image onto a photosensitive screen.
Parts of Electron Microscope
Electron Microscope consists of the following parts:
Electron gun: It is a heated tungsten filament and has the ability to generate electrons.
Electromagnetic lenses: These lenses can focus the beam of electron on the sample specimen surface. The transmitted electron beam is then passed through the second of magnetic coils called the objective lens. It has high resolution power and forms the intermediate magnified image.
A projector or ocular lenses are then produce the final further magnified image. Actually each type of lens acts as an image magnifier to reveal an incredible level of detail topographical information about the specimen.
Specimen Holder: It is made by an extremely thin film of carbon or collodion attached with a metal grid.
Image viewing and Recording System: The final image of the specimen is viewd on a fluorescent screen. A camera records the specimen image for further analyses.
Operating Procedure of Electron microscope
The standard operating procedure of an electron microscope is discussed below:
Sample preparation: The sample should be properly before placing it in this instrument. The prepared sample is then placed in a sample holder for analysis.
Sample position: The sample should be placed in such a position where electron beams are passed easily.
Electron beam adjustment: The generated electron beam should be adjusted to to create a high-resolution image and to minimize sample damage.
Collect and process the image data: The scattered or reflected beam of electrons by the sample specimen is then detected by an electronic detector to generate an image of the specimen. The generated image data can be processed and analyzed by helping with specialized software. The generated image is then captured by a camera which can be magnified, rotated, or enhanced to further analyses.
Sample preparation procedure for electron microscope analysis
It should be stabilized an organism/sample’s mobile macrostructure for analysis. Then the sample must be stored in a lower temperature to preserve its state. During analysis, it must remove water form a specimen and embedded in resin to be sectioned properly. The sample specimen should be cut into thin strips that are semitransparent to electrons. Finally the sample can placed on a copper grid.
Advantages of Electron microscope
The magnification as well as higher resolution power of this microscopy is perfect for various analyses.
The images of sample from this microscope have a greater depth or thickness.
This microscope is used for a lot of analyses purposes for its versatility.
This microscope can produce images with a high level of contrast which make it different from optical microscope.
Limitations of Electron microscope
It cannot be observed a live specimen by this tool.
The penetration of generated electron beam is not very high; as a result the sample specimen should be ultra-thin for observation clearly.
It requires an experienced person for analysis by this microscope.
It is very expensive to build this microscope as well as maintenance.
Applications of Electron Microscope
Electron microscope is very essential tool in the quality control and assurance laboratories for different analysis of atomic structures, and drug development.
This microscope is used to test various diseases including tumors.
This microscope is used in various electronic industries to create high-resolution 2D and 3D imaging, semiconductor inspection, and computer chip manufacturing purposes.
It is used in forensic laboratories the analysis of gunshot residue, identification of firearm, gemstones and jewelry investigations, examinations of non-conducting materials, and etc.
It is used to know the morphological information about rocks and minerals.
References
Ruska, E. (1987). The development of the electron microscope and of electron microscopy. Reviews of modern physics, 59(3), 627.
Zworykin, V. K. (1945). Electron Optics and their Electron Microscope. John Wiley & Sons.
Frequently Asked Questions (FAQ’s)
What is the definition of electron microscope?
An electron microscope uses a beam of energetic electron targeted on sample surface to create high-resolution 2D and 3D image.
What are the uses of electron microscope?
This microscope is used in QC lab, QA lab, Pathological lab, forensic lab, electronic lab, and various research labs for analyses.
What are the types of electron microscope?
This microscope has two types namely Scanning Electron Microscope (SEM) and Transmission Electron Microscope (TEM).
What are the parts of electron microscope?
This microscope contains sample holder, lenses, electron gun and recording system.
What are the electron microscope magnification and resolution?
It produces an image with resolution as great as 0.1nm. The magnification of this microscope is ×500000.
What are the functions of electron microscope?
This microscope provides a greater depth or thickness of the specimen to know the morphological characteristics properly.
What are the advantages of electron microscope?
This tool provides perfect magnification as well as higher resolution power to reveal the morphological characteristics of specimen.
