A platinum aperture from a transmission electron microscope exhibits atomic variations after prolonged exposure to electromagnetic radiation. A gold aperture on the other hand does not. Using a backscatter electron detector we can observe sturctural features of materials below the surface. This is possible because beam electrons passing close to a nucleus (higher atomic number, higher interaction probability, thus higher signal and brighter image) are defracted, over and over until exiting the top of the specimen. Anyway, the above may not be correct and any corrections or comments are encouraged. The question at hand is what happens to a pure platinum aperture, internally, that give the resulting pattern: http://i.imgur.com/u545w.png This was taken using a backscatter electron detector at ~550x in compositional mode.