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Physics Seminars-Cardiff Bremen

Photoemission Electron Microscopy, a technique for every occasion

Speaker: Prof. Giovanni Zamborlini (Karl-Franzens University of Graz, Austria)
Date: Tuesday 23 January 2024
Time: 15:00
Venue: Zoom

Photoemission electron microscopes (PEEMs) are incredibly powerful and versatile tools for investigating the chemical and physical properties of surfaces with spatial resolution. Thanks to their electron lens system, they can capture both spatial and angular information of the photoemitted electrons, making them suitable to measure electron momenta (and thus the material's band structure) from selected areas (usually few Ám wide) of the surface. As PEEMs are full-field instruments, they can collect a wide range of photoelectron angles within a single acquisition. They can also be coupled with pulsed light sources, such as high harmonic generation or UV-pulsed sources, in a pump-probe scheme that allows for performing time-resolved experiments with femtosecond resolution. Moreover, by inserting an electron mirror within the optical path, it is possible to simultaneously probe both the electron momenta and their spin character. The versatility of these instruments allows for the study of completely different systems, from molecular overlayers, single crystal surfaces to 2D materials. The aim of this talk is to showcase examples where the PEEM capabilities can be fully exploited to unravel the physical properties of the selected systems. At first, it will be shown how angle-resolved photoemission measurements can benefit from the full-field acquisition scheme, enabling the probing of energy level alignment and the molecular conformation of self-assembled porphyrin films atop the oxygen-passivated iron surface (O-Fe) [1]. Passivating iron with oxygen quenches the molecule-metal interaction, favoring self-assembly. Moreover, oxygen adsorption strongly modifies the electronic properties of the pristine surface, enhancing electron correlation. The spin-dependent electronic structure can be accessed by spin-resolved PEEM measurements coupled with state-of-the-art theoretical methods that go beyond the one-electron approximation, thus including the effect of electron correlation [2]. Finally, I will show the ability of the set-up to perform time-resolved ARPES in a pump-probe configuration (with pump pulses in a very broad photon energy range) while almost preserving the state-of-the-art resolution in momentum space. We benchmark our set-up through a series of experiments on an Au(111) surface and tr-ARPES measurements on a bismuth selenide (Bi2Se3) crystal [3]. [1] D. M. Janas et. al. Inorganica Chimica Acta 557, 121705 (2023). [2] D. M. Janas et. al. Advanced Materials 35, 2205698 (2023). [3] S. Ponzoni et al. Advanced Physics Research 2, 2200016 (2023). .