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What is an Electron Microscope? Principles of Operation and Applications
Electron microscopes are frequently mentioned in the context of observing objects by magnifying images multiple times to clearly display extremely small items. This device is primarily used in laboratories for inspection and repair. To understand what an electron microscope is, its structure, and its applications, let’s delve into the article below!
What is an Electron Microscope?
The electron microscope was invented in 1938 by E. Ruska and Van Borries in the USA. It is a scientific device used to observe the structure of objects with extremely small sizes. This device operates on the principle of using accelerated electron waves at high voltages to observe, with voltages ranging from several tens to several hundreds of kV.
Electron microscopes are widely used in research at laboratories, nanotechnology centers, and universities. In these settings, the structure of a sample can be observed in detail, providing information about the sample’s function. The results obtained can be utilized by other agencies and organizations.
In what year was the electron microscope born? (Photo: Internet)
If optical microscopes use visible light to observe samples, electron microscopes utilize a beam of electrons to create images of the specimen. Since the wavelength of visible light is much larger than that of electrons, using electron waves in an electron microscope provides significantly higher resolution and magnification. This allows for detailed observation of much smaller objects compared to optical microscopes.
Instead of glass lenses, electron microscopes use electromagnetic lenses to focus the electron beam. Electron microscopes require a vacuum environment to operate effectively. Therefore, the electron microscope system must be placed in a high vacuum chamber.
Classification of Electron Microscopes
Classification by Operating Mechanism
Electron microscopes are commonly divided into two types: Scanning Electron Microscopes (SEM) and Transmission Electron Microscopes (TEM). So, what are the differences between these two types of electron microscopes?
The most significant difference between TEM and SEM is that SEM creates images by detecting scattered or reflected electrons, whereas TEM uses transmitted electrons (electrons passing through the sample) to generate images. Therefore, TEM provides valuable information about the internal structure of the sample, such as morphology, crystal structure, and stress state information. SEM, on the other hand, provides information about the surface and composition of the sample.
Due to the requirement for transmitted electrons, TEM samples must be very thin, typically less than 150nm, or must provide high-resolution images, such as those under 30nm. This specific requirement does not apply to SEM images.
Classification by Size and Type of Device
Handheld Electron Microscopes:
These microscopes are characterized by their portability, convenience, and good image quality, making them widely used for tasks requiring high mobility such as field research and investigations.
Benchtop Electron Microscopes:
With high magnification, these microscopes are trusted for use in laboratories, clinics, and inspection and repair facilities. Some models are equipped with built-in LCD screens or projectors, making observation easier, quicker, and more accurate. Users can actively adjust the samples as needed during observation.
Structure of Electron Microscopes
Each type of electron microscope has a different structure. Specifically:
Structure of a TEM (Transmission Electron Microscope):
- Electron Source
- Condenser Lens
- Electron Gun
- Objective Lens
- Sample
- Projector Lens
- Intermediate Lens
- Fluorescent Screen
Structure of an SEM (Scanning Electron Microscope):
- Electron Source
- Condenser Lens
- Electron Gun
- Objective Lens
- Sample
- Scanning Coils, Scanning Circuit
- Image Amplifier
- Detector
- CRT (Cathode Ray Tube)
- Deflection Coils
Structure of TEM and SEM electron microscopes (Photo: Internet)
Operating Principle of Electron Microscopes
All types of electron microscopes use electrostatic or electromagnetic lenses to control the path of electrons. Glass lenses, used in light microscopes, do not affect the electron beam.
An electromagnetic lens contains a solenoid or a coil around the outside of a tube, creating a magnetic field. The electron beam passes through the center of the solenoids as it travels down the column of the electron microscope toward the sample. Electrons are very sensitive to magnetic fields, allowing for precise control by varying the current through the lens.
The faster the electrons move, the shorter their wavelength. The resolving power of electron microscopes is directly related to the wavelength of the radiation used to create the image. Decreasing the wavelength increases the resolution.
The resolution of an electron microscope increases if the accelerating voltage of the electron beam increases. The accelerating voltage of the electron microscope beam is measured in kilovolts (kV).
Applications of Electron Microscopes
Today, electron microscopes are used in a wide variety of fields. Most commonly, they are used in medical and biological research to study the detailed structures of cells, tissues, and organelles. This is because electron microscopes can view microscopic structures of samples far more clearly than optical microscopes. So, what are the specific applications of electron microscopes? Here are some key applications:
In Medicine
Electron microscopes are used to research and analyze small-sized samples. They support the use of cameras to record images or directly project observed samples onto screens for diagnostic purposes, determining disease manifestations, and identifying causes of illness.
In Forensics
Along with high-magnification camera technology, electron microscopes aid authorities in their investigations. Handheld electron microscopes can be easily transported and allow for the precise and clear collection of data.
In Education
Images captured by electron microscopes are extremely useful in teaching. Some devices have USB connections that easily link the microscope’s images to large projection screens for classroom use.
Compact tabletop electron microscopes are commonly used in research and teaching (Photo: Internet)
In Field Research
Electron microscopes are incredibly useful tools for researchers. Given the frequent need for mobility, researchers can simply carry a handheld electron microscope, a laptop, and a USB connection to perform their work efficiently.
In Industrial Applications
In this sector, electron microscopes are used to support new products and manufacturing processes. These devices help analyze industrial defects and can control processes in various industries. For example, high-resolution electron microscopes are widely applied in the production and development of semiconductors and other electronic devices.
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Conclusion
It is evident that electron microscopes are becoming increasingly essential and widely used in many specialized fields such as research, inspection, analysis, and evaluation due to their outstanding features. Hopefully, through this article, readers have gained a clear understanding of what an electron microscope is and the remarkable advantages this device offers.
