The beam is created in exactly the same way as in a scanning electron microscope (SEM). The electrons emitted from the cathode are accelerated to the anode. The acceleration voltages in transmission electron microscopes usually lie between 80kV and 300kV.
The condenser lenses are responsible for lighting the sample. The objective lens creates an enlarged image of the object behind the electron transparent sample. This is enlarged even more by following lenses (diffraction lens, intermediate lens, projective lens) and displayed on a projection screen or via a CCD camera on a monitor. The resolution is determined by the diameter of the beam. A TEM may have a scanning unit on it which guides the electron beam over the sample in lines (STEM scanning transmission electron microscope).
In addition to standard light field and dark field images, due to additional detector systems, modern TEMs offer a range of possibilities for obtaining information. EDX and EELS detectors serve the chemical analysis in the nanometer area. Electron energy loss spectroscopy (EELS) gives information about the chemical composition and bonds in the area of the sample tested and is also the basis for recording energy filtered maps of element distribution (EFTEM). High angle annular darkfield (HAADF) detectors and electron diffraction in the selected area electron diffraction (SAED) or convergent electron diffraction (CBED) mode enable crystallographic information to be obtained; Lorentz lens systems allow magnetic domains in materials to be mapped.
Electron probe micro analysis