Secondary Ion Mass Spectroscopy (SIMS)
By bombarding the surface of any material with short pulses of gallium atoms, we can gently sputter molecules from the surface without disturbing the second (or lower) atomic layers. The molecules coming off the surface can be charged or neutral. By using a charged lens, we can extract the ions into a time-of-flight (TOF) mass spectrometer. This provides the weights of any ions sputtered from the surface. The result is a spectrum of the top molecular or atomic layer of a material. This provides the ultimate in surface sensitivity, since if anything is less than one atom thick it isn’t there! This technique is especially useful in surface adhesion and contamination problems. Corrosion can be seen long before even an electron microscope would be able to visualize it.
