How do the different types of electron microscopy work?

Common types of electron microscopy include transmission electron, scanning electron, and reflection electron microscopy. 

1. Electron transmission microscopes use accelerated beams of electrons (through electromagnetic lenses) to produce a highly magnified image. These microscopes use a high voltage electron gun to produce the electron beam. The gun typically features a tungsten filament cathode, which is the origin of the electron beam. To accelerate the electron beams, an anode is used, and the electromagnetic lenses assist in focusing the beam. The electron beam passes through the sample and electrons then scatter or hit a fluorescent screen and produce an image. The image is observed through the objective lens of the microscope. The spatial variations can be analyzed by displaying the image on a fluorescent zinc-sulfide coated screen. It can also be photographed to display the images in real-time by using a digital camera.  
2. Scanning electron microscopy uses a method called raster scanning to generate detailed images of the sample. This method utilizes a beam of electrons to produce signals at the surfaces of samples. Specifically, the beam moves across the sample’s rectangular area, losing energy as it passes through. This transformation of energy produces heat, light, and secondary electrons as a result; this data can then be used to visualize the features and chemical composition of the specimen. SEM produces a 2D image which shows spatial variations and generally has less resolution than TEM. However, it is able to produce images of large samples and has a higher depth of field than TEM.
3. Reflection electron microscopy uses a stream of electrons which bounce off the sample when it is observed. This type of microscopy typically uses methods like reflection high-energy diffraction and reflection high-energy loss spectroscopy to study the topography of structures.