SEM: SCANNING ELECTRON MICROSCOPE

The Scanning Electron Microscope - SEM uses, as radiation source, a beam of electrons with a wavelength shorter than the visible light, that varies between 380 and 760 nanometers and too big to be used in the observation of nano-samples. The beam of electrons is produced by a metallic wire brought to high temperature, therefore the emission of electrons is due to the thermionic effect. When the atoms of the sample surface are struck by the electron beam, they emit "secondary electrons" which are detected and converted into electrical impulses. The electron beam, highly focused, is moved along the surface of the sample, which is analyzed portion per portion, so to obtain the "scan" of the whole sample. SEM provides a complete three-dimensional image of the sample and a very detailed image.