The discovery of graphene and the rise of two-dimensional (2D) materials came with the necessity of resolving the atomic structure of light atoms in one-atom-thick films. State-of-the-art scanning transmission electron microscopes (STEM) equipped with 5th order aberration correctors, enabled atomic resolution imaging of monolayer materials under low accelerating voltages (<100 kV), and pushed the detection limit of imaging and spectroscopy analysis down to the single-atom level. The use of low-energy electrons has key advantages: most importantly, it can effectively decrease the energy transferred to the atoms and prevent radiation damage, allowing the study of the structure and atomic defects in its pristine from; secondly, low-energy electrons increase the efficiency in valence features in electron energy loss spectroscopy EELS (VEELS) due to an enhanced signal-to-noise ratio. Combined with recent developments in e-beam monochromation, low-voltage electron microscopy (LVEM) improved the attainable energy resolution of EELS beyond <10 meV, thus opening the doors to analyzing vibrational modes at high spatial resolution at structural features such as surfaces, grain boundaries or interfaces .
In this seminar I will discuss the novel capabilities of low-voltage electron microscopy (LVEM), such as four-dimensional (4D) scanning transmission electron microscopes (STEM) and phonon-electron energy loss spectroscopy (EELS), in the characterization of 2D van der Waals-based functional materials and devices, but also extend it to the analysis of more complex 3D oxide heterostructures.
 Krivanek, O., Lovejoy, T., Dellby, N. et al. Vibrational spectroscopy in the electron microscope. Nature 514, 209–212 (2014)
Roger Guzman obtained his PhD in Materials Science and Technology by the Autonomous University of Barcelona (UAB) in 2014, in the Superconducting materials group in the Institute of Materials Science of Barcelona (ICMAB, CSIC), where he started his scientific career in the field of experimental aberration-corrected scanning transmission electron microscopy (STEM). After graduation, he continued his research activity as a post-doc researcher in different national laboratories (Instituto de Nanociencia de Aragón, 2014; Universidad Complutense de Madrid, 2015; Institut de Ciència de Materials de Barcelona, 2016) becoming an expert in the field of analytical STEM. Since 2019, he is part of the research staff at the STEMgroup of the University of Chinese Academy of Sciences, UCAS, Chinese Academy of Sciences, CAS (Beijing, China) as a post-doc and now as a Research Scientist. The group is leaded by Professor Wu Zhou, with the counselling of Professor Steven J. Pennycook as a Distinguished visiting Professor.
His scientific portfolio covers analytical electron microscopy techniques development and fundamental material physics research of strongly-correlated complex oxides such as superconductors, magnetic complex-oxides, multiferroics, and more recently two-dimensional (2D) materials by means of aberration corrected scanning transmission electron microscopy (STEM) and electron energy loss spectroscopy (EELS). My current research projects are devoted to the development and implementation of state-of-the-art STEM analytical tools for the study of low dimensional systems, such as four-dimensional STEM and vibrational electron-energy loss spectroscopy (EELS).