There is only one place to start this story, not in the beginning but bang in the middle. It all started with the attendance of more than 100 research scholars attending a conference in Delft, 1949. This was the first international conference on a microscope which can provide 1000 times better resolution than the regular microscope of that time. Arguably, this can be marked as the true beginning of transmission electron microscope’s global recognition.
In 1931, E. Ruska & M. Knoll was about to design the 1st model of a transmission electron microscope (TEM) sometimes also referred as a conventional transmission electron microscope (CTEM). TEM can generate an image having a resolution much greater than the light microscope. For this E. Ruska also won the Nobel Prize in 1986 and later he died in 1988.
TEM follows the same principle as of light microscope but uses an electron beam instead of a light beam resulting in 1000 times better resolution and magnification up to 5,000,000 times greater than the light microscope.
Instrumentation & Working
- Illumination system- An electron gun transmits the electron beam through the specimen placed on the stage.
- Objective lens & stage- These are the heart of the TEM. Ultra-thin specimens are placed on the stage which is connected to the lens.
- TEM imaging systems- When an electron comes in contact with the stage having the specimen, some gets reflected & some passes through it. This result in the formation of an image due to the interaction of the electron through the specimen. Fluorescent screen is used to detect & magnify the image on to an imaging device and a CCD camera is used as a sensor for the detector.
The image can be manipulated by adjusting the voltage of the gun to accelerate or decrease the speed of an electron as well as changing the electromagnetic wavelength via the solenoids.
- Nanotechnology- Transmission electron microscopy (TEM) has become one of the most powerful techniques in the field of nanotechnology. It is widely used for the determination of shape and size of the nanoparticles. Presence of surface defects can also be confirmed by using TEM. It provides a smaller picture than other scanning microscopes which is useful in observing the size distribution of the nanoparticles. The composition of the nanoparticles can also be characterized by using modern TEM’s.
- Metallurgy- By the time of 1960, it helped metallurgist to bring precision in their crafts by providing the details of surface and defect structure of metals and alloys.
- Information Technology- It can be used for semiconductor analysis and production and the manufacturing of computer and silicon chips. IT companies use TEM to identify damage, defects and fractures to micro-sized particles.
- Chemistry- TEM can provide complete morphological details of any particular chemical by identifying its property and nature.
- Medical Science- As its principle is closely related to the light microscope, its use in the medical field was accepted in between the late 1950s and early 1960s. For extreme cases, TEM’s are still used for comparing blood & tissue samples to find the illness. It is used for identifying viruses or diseases and comparing the patient’s sample with the test sample. It is widely used for investigating specimens related to renal disease, tumor processes and identification of infectious agents.
- Microbiology- TEM can be used to see the interaction between the cell and microorganisms. Small details in the cell or microorganisms down to atomic levels can be examined.
- Forensics- It is useful in examining the gunshot residue. It can also assist in crime scene investigations such as traffic accidents or samples of clothing fiber/blood and so on.
Although it can generate the image of 1nm in size, the images are produced in monochrome texture. Currently, while comparing it with other electron microscopes it can only generate 2-dimensional (2-D) images which are limited to giving details of overall shape, size and surface defects. Also, it is quite large, expensive & sample preparation can be done only by the experts. Only those samples can be used which are electron transparent (very small).
Just imagine that a design proposed by a German physicist and German electrical engineer leads to the development of one of the most important discoveries of that time. TEM might have some limitations when compared to other microscopes used today, but it also has several advantages, especially in those days. It not only surpassed the best magnification power available at that time but also opened the gates to many branches. It can even have an impact after several decades and in the multitude of fields including nanosciences, forensics, life sciences, medical, biological, material research, forensic analysis, gemmology, metallurgy, and others.
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