Components of the Electron Microscope
The electron microscope is a specialized type of microscope that utilizes a beam of accelerated electrons as its illumination source. This microscopy technique is distinguished by its high-resolution images and is commonly employed in biomedical research to observe the intricate structure of tissues, cells, organelles, and molecules. Below, we outline the essential components of the electron microscope:
Electron Gun
The electron gun (English: Electron Gun) is a critical component that emits electrons when heated. This device is primarily constructed from tungsten, a robust chemical element.
Electromagnetic Lenses
There are three types of electromagnetic lenses within an electron microscope, all of which serve to magnify the image while sustaining clarity and detail. These lenses include:
- The first condenser lens (English: The condenser lens), which focuses the electron beam onto the specimen, while the second condenser lens refines the electrons into a fine bundle.
- The objective lens (English: Objective lens) allows the electron beam exiting the specimen to pass through a second magnetic coil, producing a medium magnified image.
- The ocular lenses (English: Ocular lens) form the third set of magnetic lenses, which provide a final enlarged view of the sample.
Specimen Holder
The specimen holder (English: Specimen holder) is an ultra-thin membrane made of carbon or collodion, secured in place by a metallic grid.
Camera and Fluorescent Screen
The image display and recording system presents the final image on a fluorescent screen made of phosphor, and underneath this screen, a camera is utilized to capture the images.
Types of Electron Microscopes
The following is an overview of the primary types of electron microscopes:
Scanning Electron Microscope
This type of microscope derives its name from the method by which images are created through the scanning of a focused electron beam across the surface of the specimen in a point pattern. The scanning electron microscope provides detailed images of cellular surfaces and whole organisms and can also be used to count particles and determine sizes, relying on the emission of secondary electrons from the specimen’s surface.
Transmission Electron Microscope
This microscope type is used to capture images of internal cellular components, the structure of protein molecules, the arrangement of molecules in viruses, cytoskeletal filaments, and the arrangement of proteins in cell membranes. Images are generated when electrons pass through extremely thin samples.
Advantages of Electron Microscopes
The benefits of using an electron microscope are as follows:
- Exceptional magnification capabilities.
- High resolution.
- Diverse applications.
- Three-dimensional visualization of structures.
- Ability to image small structures.
- Minimal distortion of materials during preparation.
Disadvantages of Electron Microscopes
However, there are several drawbacks associated with electron microscopes, including:
- Requires specialized training for operation.
- High cost, which includes installation and maintenance expenses.
- Inability to visualize live samples.
- Sample preparation is complex, requiring the specimen to be extremely thin, entailing drying and slicing into fine sections due to the low penetration power of the electron beam.
- Often large and heavy, and sensitive to external vibrations.
- Demands substantial electrical energy for operation.
- Artifacts from sample preparation may appear in the final images.