Measuring Surface Electronic States

Although the electronic states of a material‘s surface are only 2D, they contain a wealth of interesting physics. These states, which differ from the bulk of the material, dominate many phenomena, including electrical conduction, magnetism, and catalysis. They are responsible for nontrivial surface effects observed in topological materials and systems with strong spin-orbit interaction. Surface electronic states also influence the properties of 2D materials like graphene.

Photoemission spectroscopy, which measures the energy and momentum of electrons emitted when photons strike a material, is primarily used by researchers to understand surface phenomena and harness them in practical devices. The high resolution characterizes electron energy, and momentum allows physicists to measure the band structure and the density of states (DOS) in the few surface layers where escaping photoelectrons originate. However, because bulk electrons contribute to photoemission signals, obtaining the electronic states of only the sample’s outermost layer is difficult.

Researchers have developed a new method for determining the electron states of the first surface layer based on a modification technique that liberates electrons using positrons rather than photons.

The team’s technique, auger-mediated positron surface sticking (AMPS), develops magnetically guided, low-energy positron beams for positron annihilation-induced Auger electron spectroscopy, in which positrons projected at the sample form bound states on the sample’s surface.

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