Electron Microscope and its Functions

As the name suggests, electron microscopes focus electron beams upon the specimen instead of using light. The use of electron helps in viewing the specimen at an extremely high resolution. The camera present within the microscope captures these images to reveal the finer details of the specimen. This microscope can zoom and view the density of a specimen until it is only a micrometer thick and has a magnification ranging between 1,000 - 250,000x on the fluorescent screen. This type of microscope requires a computer software in order to function accurately and yield precise results. These microscopes provide better magnification than the light microscopes.

Parts of Electron Microscope

Electron Gun - The electron gun contains the cathode and control shield or grid. The cathode is the negative electrode through which electrons are generated. The cathode and the control grid are placed above the electron gun, in a separate compartment away from the lenses. This part must be placed accurately for the microscope to generate accurate results.

Anode - is the second electrode of the electron gun and is shaped like a disk. This disk contains an axial opening for the electron beams to pass through it.

Condenser Lens - collects the electron beam, and is responsible for controlling the aperture and focus of the rays. The diameter of the beam can be tweaked in order to get the optimal contrast and brightness.

Objective Aperture Lens - is placed beneath the specimen tray. The focal length of this lens is short and ranges from 1-5 mm. The objective lens helps to generate a real image of the specimen, which is magnified further by the intermediate lens along with the projector lens.

Intermediate Lens - is actually the first projector lens and is placed above the second projector lens. This magnification is further enlarged through the use of the actual projector lens. The projector lens magnifies the image by five times and thus has a 5:1 ratio or range of magnification. The combination of two lenses allows for greater zooming of the image without having to change the actual length of the electron microscope.

Fluorescent Screen - is a transparent sheet which is coated with a phosphoric substance. The coat is applied on the side of the sheet which is facing towards the rays. When the electron rays hit this sheet, it causes the phosphor to fluoresce or illuminate the image of the specimen. This image is simultaneously captured by the image recording device that is placed beneath the fluorescent screen.

Two major variants of electron microscopes exist:

• Scanning electron microscope (SEM): looks at the surface of bulk objects by scanning the surface with a fine electron beam. See also environmental scanning electron microscope (ESEM).
• Transmission electron microscope (TEM): passes electrons through the sample, analogous to basic optical microscopy. This requires careful sample preparation, since electrons are scattered so strongly by most materials.This is a scientific device that allows people to see objects that could normally not be seen by the naked or unaided eye.