Scanning electron microscope
A scanning electron microscope (SEM) is a type of electron microscope that produces images of a sample by scanning the surface with a focused beam of electrons. The electrons interact with atoms in the sample, producing various signals that contain information about the surface topography and composition of the sample. The electron beam is scanned in a raster scan pattern, and the position of the beam is combined with the intensity of the detected signal to produce an image. In the most common SEM mode, secondary electrons emitted by atoms excited by the electron beam are detected using a secondary electron detector. The number of secondary electrons that can be detected, and thus the signal intensity, depends, among other things, on specimen topography. Some SEMs can achieve resolutions better than 1 nanometer.
Image of pollen grains taken on a SEM shows the characteristic depth of field of SEM micrographs
M. von Ardenne's first SEM
SEM with opened sample chamber
Analog type SEM
An electron microscope is a microscope that uses a beam of electrons as a source of illumination. They use electron optics that are analogous to the glass lenses of an optical light microscope to control the electron beam, for instance focusing them to produce magnified images or electron diffraction patterns. As the wavelength of an electron can be up to 100,000 times smaller than that of visible light, electron microscopes have a much higher resolution of about 0.1 nm, which compares to about 200 nm for light microscopes. Electron microscope may refer to:Transmission electron microscopy (TEM) where swift electrons go through a thin sample
Scanning transmission electron microscopy (STEM) which is similar to TEM with a scanned electron probe
Scanning electron microscope (SEM) which is similar to STEM, but with thick samples
Electron microprobe similar to a SEM, but more for chemical analysis
Ultrafast scanning electron microscopy, version of a SEM that can operate very fast
Low-energy electron microscopy (LEEM), used to image surfaces
Photoemission electron microscopy (PEEM) which is similar to LEEM using electrons emitted from surfaces by photons
A transmission electron microscope from 2002
An image of an ant in a scanning electron microscope
Reproduction of an early electron microscope constructed by Ernst Ruska in the 1930s
Image of Bacillus subtilis taken with a 1960s electron microscope