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MICROSCOPE
A microscope (Greek: μικρόν micron = small and σκοπός scopos = aim) is an instrument for viewing objects that are too small to be seen by the naked or unaided eye. The science of investigating small objects using such an instrument is called microscopy, and the term microscopic means minute or very small, not easily visible with the unaided eye. In other words, requiring a microscope to examine.
The most common type of microscope—and the first to be invented—is the optical microscope. This is an optical instrument containing one or more lenses that produce an enlarged image of an object placed in the focal plane of the lens(es). There are, however, many other microscope designs.
Microscope Types
Microscopes can largely be separated into two classes, optical theory microscopes and scanning probe microscopes.
Optical theory microscopes are microscopes which function through the optical theory of lenses in order to magnify the image generated by the passage of a wave through the sample. The waves used are either electromagnetic in optical microscopes or electron beams in electron microscopes.
Optical Microscopes
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Optical microscopes, through their use of visible wavelengths of light, are the simplest and hence most widely used type of microscope. They serve uses in many fields of science, particularly biology and geology.
Optical microscopes use refractive lenses, typically of glass and occasionally of plastic, to focus light into the eye or another light detector. Typical magnification of a light microscope is up to 100x with a resolution of up to 0.2 micrometres. Specialised techniques (eg. scanning confocal microscopy) may exceed this magnification but the resolution is an insurmountable diffraction limit.
Other microscopes which use electromagnetic wavelengths not visible to the human eye are often called optical microscopes. The most common of these, due to its high resolution yet no requirement for a vacuum like electron microscopes, is the x-ray microscope.
Because of their popular use, optical microscopes have many adaptions to facilitate usage and improve image quality.
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Electron microscopes
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Electron microscopes, which use beams of electrons instead of light, are designed for very high magnification usage. Electrons, which have a much smaller wavelength than visible light, allow a much higher resolution. The main limitation of the electron beam is that it must pass through a vacuum as air molecules would otherwise scatter the beam.
Instead of relying on refraction, lenses for electron microscopes are specially designed electromagnets which generates magnetic fields that are approximately parallel to the direction that electrons travel. The electrons are typically detected by a phosphor screen, photographic film or a CCD.
Two major variants of electron microscopes exist:
Scanning probe microscope
In scanning probe microscopy (SPM), a physical probe is used either in close contact to the sample or nearly touching it. By rastering the probe across the sample, and by measuring the interactions between the sharp tip of the probe and the sample, a micrograph is generated. The exact nature of the interactions between the probe and the determines exactly what kind of SPM is being used. Because this kind of microscopy relies on the interactions between the tip and the sample, it generally only measures information about the surface of the sample.
Some kinds of SPMs are:
Other microscopes
Acoustic microscopes use sound waves to measure variations in acoustic impedence. Similar to SONAR in principle, they are used for such jobs as detecting defects in the subsurfaces of materials including those found in integrated circuits.
See also
External links
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