Surveying electronic bandstructure of smart materials revealed by nano-ARPES

Synchrotron SOLEIL & Université Paris Saclay

Antares beamline

In today's state-of-the-art material science, length scales play a central role on the chemical and electronic properties of many of the most promising materials for the future. During the last decades, we have witnessed exponential advances in the development of different areas of novel nanotechnologies. These virtuoso materials are often initially isolated or synthetized as small crystallites, which makes difficult their precise exploration. Also, they can be difficult to produce, without fluctuations in their chemical composition, bringing out heterogeneities at variable scales.

Polycrystalline materials, with chemically homogeneous and well-structured grains are also frequent, where the crystalline orientation is challenging to unravel as well as the consequences on the transport and magnetic properties are unknown. In the field of nano-objects also, even if these smart "building blocks" may show remarkable properties, they would have remained unexploited if, we had not developed new tools capable of viewing and scrutinizing  ( chemically and electronically) objects on a wide range of scales, from a few microns to a few tens of nanometers.

In the imaging domain, despite the great progress made in spectroscopic microscopy and even the remarkable success achieved, the challenge still remain concerning the precise determination of the chemical and electronic imagery of advances materials, which usually are available as heterogeneous large crystals or tiny homogeneous monocrystals. The challenge is to quantify and analyze the electronic properties of advanced materials on a nano- and micrometer- scale. For such a goal, analysis of the electronic structure must be comprehensive, not only with regard to detection of core levels, but also to disclose the structure of delocalized valence bands, directly responsible for chemical bonds, electrical transport and the thermal and mechanical properties.

Here we report, a recently developed novel X-ray microscope, labelled, k-microscope or Nano-ARPES (Nano Angle Resolved Photoelectron Spectroscopy) recently installed on the ANTARES beamline at the French Synchrotron SOLEIL. This sophisticated instrument is particularly well-suited to provide both high resolved chemical and electronic information in the real and reciprocal space of complex materials with nano-scale resolution. With a spatial resolution of several tens of nanometers, this highly developed microscope is able to carrying out the direct imaging of core levels and their chemical shifts, band electronic structures in reciprocal space and constant energy surfaces in reciprocal space, especially the Fermi surfaces.

(a) Schematic of the different components of the ANTARES k-microscope. (b) ARPES data showing the “d” and “sp” bands of the copper substrate together with the massless π bands of graphene. (c) real-space image of the copper states intensity (red box states of panel(b)) obtained by nano-ARPES mapping presented on a linear scale as a false-color image. The inset of panel (c) shows the sample optical image where the copper border grains are visible. Panel(d) shows the real-space image of graphene grains distribution, obtained by monitoring the graphene states intensity (green box states of panel (b)).

Currently, Permanent Research Staff of the SOLEIL French synchrotron source and Université Paris Saclay, she is also Permanent staff of the Spanish Research Council (CSIC), working in the area of electronic structure of advanced materials. Maria Asensio commenced her academic career in Argentina, where she obtained her PhD in Condense Matter. Then she held several positions at the Autonomous University of Madrid, the University of Warwick and at the Fritz Haber Institute of the Max-Planck in Berlin, Germany. She is author of more than 250 publications, with approximately 4500 cites and more than 100 invited talks in International conferences.