A Transmission Electron Microscope (TEM) utilizes energetic electrons to provide morphologic, compositional and crystallographic information on samples.
At a maximum potential magnification of 1 nanometer, TEMs are the most powerful microscopes. TEMs produce high-resolution, two-dimensional images, allowing for a wide range of educational, science and industry applications.
TEM History
Ernst Ruska developed the first electron microscope, a TEM, with the assistance of Max Knolls in 1931. After significant improvements to the quality of magnification, Ruska joined the Sieman’s Company in the late 1930s as an electrical engineer, where he assisted in the manufacturing of his TEM.
TEMs consist of the following components:
- An electron source
- Thermionic Gun
- Electron beam
- Electromagnetic lenses
- Vacuum chamber
- 2 Condensers
- Sample stage
- Phosphor or fluorescent screen
- Computer
A Transmission Electron Microscope functions under the same basic principles as an optical microscope.
In a TEM, electrons replace photons, electromagnetic lenses replace glass lenses and images are viewed on a screen rather than through an eyepiece.
TEM Imaging
A Transmission Electron Microscope produces a high-resolution, black and white image from the interaction that takes place between prepared samples and energetic electrons in the vacuum chamber. Air needs to be pumped out of the vacuum chamber, creating a space where electrons are able to move. The electrons then pass through multiple electromagnetic lenses. These solenoids are tubes with coil wrapped around them. The beam passes through the solenoids, down the column, makes contact with the screen where the electrons are converted to light and form an image. The image can be manipulated by adjusting the voltage of the gun to accelerate or decrease the speed of electrons as well as changing the electromagnetic wavelength via the solenoids.
The coils focus images onto a screen or photographic plate. During transmission, the speed of electrons directly correlates to electron wavelength; the faster electrons move, the shorter wavelength and the greater the quality and detail of the image. The lighter areas of the image represent the places where a greater number of electrons were able to pass through the sample and the darker areas reflect the dense areas of the object. These differences provide information on the structure, texture, shape and size of the sample.
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. Samples need to be able to withstand the vacuum chamber and often require special preparation before viewing. Types of preparation include dehydration, sputter coating of non-conductive materials, cryofixation, sectioning and staining.
TEM Applications
A Transmission Electron Microscope is ideal for a number of different fields such as life sciences, nanotechnology, medical, biological and material research, forensic analysis, gemology and metallurgy as well as industry and education.
TEMs provide topographical, morphological, compositional and crystalline information. The images allow researchers to view samples on a molecular level, making it possible to analyze structure and texture. This information is useful in the study of crystals and metals, but also has industrial applications. TEMs can be used in semiconductor analysis and production and the manufacturing of computer and silicon chips. Technology companies use TEMs to identify flaws, fractures and damages to micro-sized objects; this data can help fix problems and/or help to make a more durable, efficient product.
Colleges and universities can utilize TEMs for research and studies. Although electron microscopes require specialized training, students can assist professors and learn TEM techniques. Students will have the opportunity to observe a nano-sized world in incredible depth and detail.
Advantages
A Transmission Electron Microscope is an impressive instrument with a number of advantages such as:
- TEMs offer the most powerful magnification, potentially over one million times or more
- TEMs have a wide-range of applications and can be utilized in a variety of different scientific, educational and industrial fields
- TEMs provide information on element and compound structure
- Images are high-quality and detailed
- TEMs are able to yield information of surface features, shape, size and structure
- They are easy to operate with proper training
Disadvantages
- Some cons of electron microscopes include:
- TEMs are large and very expensive
- Laborious sample preparation
- Potential artifacts from sample preparation
- Operation and analysis requires special training
- Samples are limited to those that are electron transparent, able to tolerate the vacuum chamber and small enough to fit in the chamber
- TEMs require special housing and maintenance
- Images are black and white
Electron microscopes are sensitive to vibration and electromagnetic fields and must be housed in an area that isolates them from possible exposure. A Transmission Electron Microscope requires constant upkeep including maintaining voltage, currents to the electromagnetic coils and cooling water.
What is the Cost?
TEMs are manufactured by companies such as Zeiss, Jeol, Philips and Hitachi and are extremely expensive. Examples of prices for new TEM models include $95,000 for a Jeol 1200EXII, $95,000 for a Philips EM10 and $100,000 for a Hitachi 7000.
