Transmission Electron Microscopy
Transmission Electron Microscopes (TEM) work similar to light microscopes, but they utilize electrons instead of light. Electrons have wavelike properties. Due to their high energy, electrons have a very short wavelength. This translates into the extremely high resolution of electron microscopes. The electrons pass through the sample like light through a shadow puppet screen. Dense structures absorb a lot of electrons and create a dark spot on the resulting image, just like the shadow of a puppet blocking the light. A TEM image is always black and white; staining techniques only allow increasing the density of certain structures and thereby making them appear darker. To bundle the electrons, the TEM contains strong magnets that are analogous to lenses in the light microscope. To efficiently illuminate the specimen with an electron beam, the sample slice needs to be very thin and the body of the TEM has to be evacuated. 
TEM image of the brush border: These high resolution images enable us to visualize structures as small as the fibers within the microvilli.