Transmission Electron Microscope Imaging

TRANSMISSION ELECTRON MICROSCOPE

1       Major components 

·            Basic unit has microscope column, vacuum system and control panel.

·               Power supply unit- It generates and supplies power to various parts of the basic unit.

·               Electromagnetic lenses- these generate heat. To cool these down, cold water (~20o C) is circulated by the water chiller inside the microscope column.

·           An air compressor does open and close the valves at various points in the column.

 2       Microscope column Копии швейцарских часов

·            Illumination system (electron gun and condenser lenses)

·            Imaging system (objective lens, projector lens)

·            Image translating system (fluorescent screen, digital photographic unit)

2.1    Illumination system

This system contains the electron gun (source of electrons), and the condenser that regulates the intensity of the beam and directs it on to the specimen. The electron gun consists of the filament in a Wehnelt assembly and an anode. The former is a V-shaped tungsten wire and acts as a cathode. When high voltage is applied, it gets heated up and emits electrons. The emitted electrons form a cloud around the tip of filament, and are propelled down the column due to high potential (40-120 kV) generated between the filament and the anode. The electron beam is focused on to the specimen by means of condenser lens. The intensity of illumination is controlled by adjusting the focal length (lens current) of the condenser lens. It is also determined by the size of the aperture, larger the aperture size, more electrons can pass through the condenser and higher is the intensity of illumination.

2.2   Imaging System

 The objective lens forms the initial enlarged image of the specimen. By varying its current, the image of the specimen is focused. The projector lens projects the final magnified image on the screen. By varying the current in the projector lens, the magnification of the projected image can be changed.

 2.3   Image Translating System

EM provides information in the form of variations of electron intensity in the image. To see the information contained by the transmitted electrons they are converted into visible light. This is done by using a fluorescent screen, which when bombarded with electrons, emit photons of visible light, which is with eyes. Images are acquired through a high-resolution digital CCD camera, in conjunction with image processing software (e.g., iTEM of Olympus Soft Imaging System, Germany).