Scanning Electron Microscope
The scanning electron microscope (SEM) is a very valuable tool in modern analytics. It has developed into a widely used imaging, examination, and material analysis device, since its invention by Ernst Ruska and Max Knoll in 1931. The most common areas of application include the analysis of surface or material properties of various samples.
The imaging in a scanning electron microscope is based on an electron beam, which is generated from a suitable source (tungsten, lanthanum hexaboride or field emission cathode) and scanned line by line as a tightly focused beam over the specimen. The interaction of the electrons with the object leads to the emission of so-called secondary electrons from the impact site. These are recorded and amplified by a nearby detector. Depending on the generated secondary electron current, a very detailed gray-scale image of the sample surface with a high depth of focus is created as a function of the electron beam position. Since vacuum is required for the electron beam, a suitable object for SEM analysis must be dry and electrically conductive. Otherwise, the image quality would suffer due to charging effects. Modern electron microscopes allow multi-axes positioning of the sample (rotation, translation, inclination).