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.

2. Electron Micoscope

Parts of Light Microscope and its Function

Body Tube - It is the part of the microscope that holds the eyepiece.

Arm - The arm connects the body tube to the base.

Base - As the name suggests, the base is the lowest portion on which the whole structure of the microscope rests.

Eyepiece - It is through the eyepiece that we look at the specimen placed on the stage of the microscope. It contains two or more lenses. The most common magnification for the eyepiece is of 10x, however, they can also be of 2x and 5x.

Objective Lenses - A standard compound microscope contains two primary objective lenses, which can have magnification of 4x, 5x, 10x, 20x, 40x, 50x, and 100x. The magnification values are written on the side of each lens. The objective can be manually rotated to get the lens to give the desired magnification and focus of the specimen.

Stage - is the platform below the objective lens on which the object or specimen to be viewed is placed. There is a hole in the stage through which light beam passes and illuminates the specimen that is to be viewed.

Stage Clips - There are two stage clips, one on each side of the stage. Once the slide containing the specimen is placed on the stage, the stage clips are used to hold the slide in place.

Diaphragm - is located on the lower surface of the stage. It is used to control the amount of light that reaches the specimen through the hole in the stage.

Illuminator - Simple compound microscopes have a mirror that can be moved to adjust the amount of light that is focused on the specimen. However, some advanced types of compound microscopes have their own light source.

The Adjustments - There are two adjustment knobs, the fine adjustment knob and the coarse adjustment knob. The coarse adjustment knob helps in improving the focus at a low power, whereas the fine adjustment knob helps in adjusting the focus of the lenses with higher magnification.

1. Light Microscope

 

Microscope part 1

A microscope (from the Ancient Greek: μικρός, mikrós, "small" and σκοπεῖν, skopeîn, "to look" or "see") is an instrument used to see objects that are too small for the naked eye. The science of investigating small objects using such an instrument is called microscopy. Microscopic means invisible to the eye unless aided by a microscope.

Function of Microscope:

The function of a microscope is to enlarge the visual image of small objects (a telescope, on the other hand, is enlarges the image of distant objects). More specifically, microscopes enlarge the image of objects too small to be seen by the naked eye.

Types of Microscopes

Microscopes need illumination to work. Depending on the source of illumination, these instruments can be divided into two broad categories. They are:

Compound Microscope:
The compound microscope uses light for illumination. Some simple compound microscopes make use of natural light whereas some have an illuminator attached to the base of the microscope that acts as the source of light. The specimen is placed on the stage and observed through different lenses of the microscope, which have varying magnification powers. Dissection microscopes and compound microscopes are a part of this category.

Electron Microscope

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.

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.
• 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.