Surface spectroscopy with high spatial resolution using metastable atoms

Abstract

THE study of surface phenomena is in large part dependent on spectroscopic techniques that are sensitive to only the outermost few layers of the material under consideration. A variety of such techniques are now available, some of which also have the benefit of high spatial resolution1–3. Here we show that metastable atoms—that is, atoms in long-lived excited states—can be used as a sensitive surface probe with high spatial resolution. In contrast to electrons or photons, metastable atoms cannot penetrate into a solid; instead, they are de-excited readily following interaction with the surface electronic orbitals4,5. The de-excitation process is accompanied by the emission of electrons, the energy spectrum of which provides fundamental information about the electronic properties of the surface. High spatial resolution (in the present case, about 5 μm) is achieved by detecting electrons that have been emitted from only a small area of the sample. As the metastable atoms have only thermal kinetic energies, they are essentially nondestructive, making them ideally suited to probing fragile surfaces such as organic layers and biological specimens.