Surface science has always been a important field of study because most chemistry takes place either on the surfaces of materials, or at the interface where two surfaces meet. Electrons in the constituent atoms absorb the incoming energy and are ejected from the sample as photoelectrons.
Photoelectrons emitted from the inner shells of an atom also behave as outgoing waves.
Most techniques that use photons to probe solids are really bulk probes. The beauty of photoelectron spectroscopy and diffraction is that only effects that come from within the first 5 to 10 layers of atoms are measured. By treating the outgoing photoelectron wave as a reference wave and analyzing the interference patterns created with waves scattered from other atoms, it is possible to make a photoelectron hologram. With enough holographic data, true 3-D images of individual atoms can be produced. The surface science experimental station that has been set up by Fadley, Hussain, and their students is located on ALS beamline 9.3.2, a bend- magnet beamline that produces photons between 30 and 1500 electron volts in energy.