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types of electron microscopes used in the medical science field

by:Marslite     2020-01-08
The first microscope zoomed in the object with light.
They are called optical microscopy and are still widely used today, but their resolution is limited by the wavelength of light.
The best optical microscope can be enlarged no more than 2000 times.
The wavelength of electrons is much smaller.
According to the prediction of quantum theory, all particles have waves-
The electron microscope can enlarge the object 2 million times, and the resolution is three orders of magnitude thinner than the optical microscope.
Although the optical microscope uses a transparent lens, light-
The electronic beam used in the electron microscope bends the light through a refractive material and does not pass through any physical material.
Since the electron is a charged particle, the electron microscope uses a magnetic field to bend the electron beam.
Bottom left: Transmission electron micrograph of a strain of bacteria.
The following rights: chaetae of scanning electron microscope (bristles)
The first electron microscope is a transmission electron microscope (TEM)
The date was 1938.
In the TEM, the electron beam focusing through the electrostatic lens and the electromagnetic lens enters the sample.
Electrons interact with the sample, some electrons pass through the sample, and others are scattered.
The result is two-
Size image inside the sample.
For observation by transmission electron microscopy, the sample was prepared by cutting the diamond knife on the ultra-thin slice, and the thickness of the resulting slice was less than 100 nm.
Just like chemical staining of samples under an optical microscope for observation, samples of TEM may be dyed by heavy metals scattered on the electron beam.
Scanning electron microscope in scanning electron microscope (SEM)
The electron beam is directed through the surface of the sample, thus drawing a map of the entire sample field.
This \"map\" is called a raster pattern.
Electrons interact with the surface and experience several different effects.
The detector sends the information to the computer, which processes it and generates the image.
Scanning electron microscopy has great depth of field and yield
Size image.
SEM images only include information about the surface of the object because the electron beam does not penetrate the sample.
The effects experienced by electrons in SEM provide information about different types of samples.
The main means of collecting information in a scanning electron microscope is secondary electrons, in which case secondary electrons are electrons produced by primary radiation.
In addition, different materials emit X-
Rays in a specific spectrum when exposed to radiation, so detect and analyze these features X-
The light provides information about the atomic composition of the sample.
In some scanning electron microscopy, the principle of cathode light emission is used.
This effect occurs when an electron hits a half electron.
Conductive surfaces, most commonly used in traditional television sets, but can also be used for SEM when special optical detectors are integrated into the device.
This principle is most useful in the application of materials science and minerals.
Because the surface must be half
Conductor, cathode light can only be used to study non-
Metal material. Back-
The scattering of electrons is similar to reflection and refraction light;
Electrons hold the same energy, but change direction when they encounter surfaces.
Because they have wave-like properties, electrons can interfere with each other.
That is, they can increase or decrease the wavelength of each other.
These effects are used to reflect high energy electron diffraction (RHEED)
Where electrons are directed to the surface of the crystal at a shallow angle to gather information about the surface.
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