Berlin 2018 – wissenschaftliches Programm

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O: Fachverband Oberflächenphysik

O 57: Electronic structure of surfaces: Spectroscopy, surface states II

O 57.6: Vortrag

Mittwoch, 14. März 2018, 12:00–12:15, MA 042

On multi-electron emission from surfaces — Iuri S. Brandt, Zheng Wei, Jürgen Kirschner, and •Frank O. Schumann — Max-Planck Institut für Mikrostrukturphysik, Halle, Germany

We have studied the electron pair emission process from surfaces due to the impact of a primary positron. The existence of this process implies a two-step scattering event. In the first step the primary positron scatters with a valence band electron. Each particle of the positron-electron pair can collide with another valence electron. We find that the electron pair intensity is on the same scale as the positron-electron pair intensity. This suggests that a significant contribution of the pair intensity is actually due to the emission of three particles. Our instrument is only able to detect two particles in coincidence. We also observe a strong material dependence of the coincidence intensity. In previous studies with primary electron excitation or photon absorption we observed that NiO displays the highest coincidence rate.[1,2] The same observation we have made in this work. We find that NiO has a factor of 3 higher coincidence intensity compared to the Ag(100) substrate. We also note that the pair intensity scales with the single electron rate. The higher the singles rate the higher the coincidence rate. We discuss the fact that very different excitation processes leading to pair emission give similar results.

[1] I.S. Brandt et al., Phys. Rev. B 92, 155106 (2015).

[2] F.O. Schumann et al., Phys. Rev. B 93, 235128 (2016).