Transmission Electron Microscope (TEM) is based on the theory where energetic electrons are imposed on the surface of the experimental nanoparticles to evaluate the morphologic, compositional and crystallographic information of the particles. Tem is the most powerful magnified microscope where 1 nm particle can be also evaluated. Although TEMs produce a two-dimensional images but its high-resolution capacity allow it for a wide range of application including educational, research, and science and industry applications.
History of TEM:
In 1931, Knoll, the inventor of SEM and Ruska collectively invent the electron microscope and demonstrated two dimensional electron images. Later this group developed the first successful TEM with high resolution capacity in 1933 and the first commercial application of TEM was executed in the year of 1939. Further research on the electron microscope stopped due to destruction of new laboratory constructed at Siemens by an air-raid during World War II. After World War II, Ruska resumed work and developed the electron microscope with 100k magnification. In 2008, Jannick Meyer et al. invented new TEM based on the direct visualization techniques using light atoms of carbon and hydrogen.
EMs consists of the following components:
Fig 1: Schematic diagram of Transmission electron Microscopy (TEM)
The following are the important parts of a TEM
- An electron source
- Thermionic Gun
- Electron beam
- Electromagnetic lenses
- Vacuum chamber
- 2 Condensers
- Sample stage
- Phosphor or fluorescent screen
A Transmission Electron Microscope works on the basic principles of an optical microscope.
The basic difference is that in case of TEM electrons replace photons, electromagnetic lenses replace glass lenses and images are mainly viewed on a screen rather than through an optical eyepiece
The important feature of TEM imaging are explained here
1. Transmission Electron Microscopes generate black and white but high-resolution image using the technique of interaction between specially prepared samples and high energetic electrons in a vacuum chamber.
2. Air should be pumped out form vacuum chamber to generate a space where electrons are free to move.
3. The electrons then travel through powerful multiple electromagnetic lenses. These solenoids are tubes with coil surrounding around them.
4. After that the beam passes through the solenoids and makes contact with the screen where the electrons are converted to electromagnetic radiation to form an image.
5. The image can be developed by adjusting the voltage to control the speed of electrons as well as changing the electromagnetic wavelength.
6. The function of coils is to focus the images onto a photographic screen.
7. during the period of transmission phase, the speed of electrons directly proportional to the electronic energy.
8. The lighter zone of the image indicates the area where a larger number of electrons passed through the sample and the darker areas represent the denser areas of the particle.
9. The differences of the contrast of the area provide information on the structure, appearance, shape and size of the particle sample.
10. To obtain a TEM analysis samples need to have certain properties. They need to be sliced thin enough for electrons to pass through, a property known as electron transparency.
11. Samples should withstand the negative pressure in vacuum chamber and for this reason special preparation of the samples before viewing.
12. Different steps of sample preparation include dehydration, sputter coating, cryofixation, sectioning and staining of the samples.
1.A Transmission Electron Microscope have enormous application in different fields such as life sciences, medical, biological, nanotechnology and material research, forensic analysis, gemology and metallurgy as well as industrial research and education
2. TEMs provide not only topographical, morphological, compositional structure but it will also provide crystalline information of the sample.
3. The images help researchers to investigate the samples on a molecular level, making it feasible to analyze the structure and appearance of the samples.
4. Tem provide us the information that is not only needful for the study of crystals and metals, but also has vast industrial applications.
5. TEMs have also application in semiconductor field for the manufacturing of various computer and silicon chips.
6. Technology companies can also TEMs to determine different flaws, fractures and damages in micro subject objects.
7. Academic and research institution can use TEMs for different type of investigative research and studies.
8. Although electron microscopes require specialized training, students can assist professors and learn TEM techniques.
9. The application of TEM will have the huge opportunity to observe a nano-sized world in incredible depth and detail.
A Transmission Electron Microscope is a highly sophisticated instrument that have several advantages.
- TEMs have ability to magnify the sample potentially over one million times or more
- TEMs have a very wide-range of applications and can be use in a variety of different scientific, educational and industrial fields
- TEMs provide the structural information on element and as well as compound structure
- The image quality of the TEM is very god and prominent
- TEMs are able to yield information of surface appearance, size, shape, and structure
- Handling of the TEM is very easy after proper training
The common disadvantages of TEM are given below
- TEMs are very large in size and also very expensive
- sample preparation takes lots of time and laborious
- Potential artifacts from sample preparation
- Special training is required for operation and analysis.
- Samples are limited to those that are electron transparent, able to tolerate the vacuum chamber and small enough to fit in the chamber
- Special housing and maintenance is required for TEMs.
- Images of TEM are black and white