SFB Extra Seminar

The properties of two-dimensional materials are strongly influenced by changes of the electronic structure. Angle-resolved photoemission spectroscopy (ARPES) is the ideal tool for obtaining precise information about the electronic states. At the nano-ARPES facility at the Advanced Light Source, we mate the merits of spatial resolution, by focusing the illuminating photon beam, with ARPES, as a detection method. Two methods for focusing are employed: With a zone plate we achieve a spot size of <120 nm diameter, while a reflective capillary focusing optics provides <500 nm spot size. In contrast to the zone plate however, the capillary provides a substantially higher intensity. With an eventual goal of less than 50 nm, nano-ARPES brings k- and energy resolved electronic contrast on the nano- and mesoscale within reach.

I will showcase nano-ARPES results obtained from WS₂ grown on TiO₂ as well as graphene/SiC and CVD grown WS₂ transferred to hexagonal boron nitride. Nano-ARPES allows us to laterally map differences in band bending and changes in the spectral function of these different substrates. However photoemission spectroscopy is not limited to the spectral function. Using higher photon energies we also obtained laterally resolved data of the tungsten and sulfur core levels. This allows us to pinpoint the observed changes in the electronic structure to edges and/or defects in the materials.