Please join us May 2nd for a one-hour talk from Paulo Ferreira, International Iberian Nanotechnology Laboratory, titled:
Seeing Small: Revealing the Atomic Structure of Li-ion Battery LiMn2O4 Cathodes and 2D MoS2 Materials by Advanced Electron Microscopy
Abstract – Aberration-Corrected TEM/STEM has emerged as powerful tool for the characterization of
nanomaterials as it enables structural imaging at resolutions below 0.1 nanometers while performing
chemical analysis at the atomic level. In this talk, a brief overview of Aberration-Corrected
TEM/STEM will be presented and related to the quest for investigating nanomaterials. Subsequently,
two examples that demonstrate the power of these techniques in providing scientific insight will be
discussed.
First, the atomic structure of one of the cathode chemistries for Li-ion batteries – Li[Mn2]O4 – will be
presented. This material is particularly appealing due to the moderate capacity and high rate
capabilities associated with its cubic spinel framework, but it suffers from capacity loss, attributed to
the dissolution of Mn to the electrolyte. In this work we use HAADF-STEM to show that a restructured
surface is formed in this material, where a stable surface layer of Mn3O4, followed by Li1+xMn2O4
subsurface with retention of bulk LiMn2O4 is formed. In addition, by using differential phase contrast
(DPC) STEM we were able to determine the Li, Mn and O atomic positions, thus providing a novel
insight into the migration of these species within the structure of LiMn2O4.
In the second part of the talk, the atomic electrostatic configuration of the 2D material MoS2 and some
of its point defects will be presented. The use of DPC-STEM allow us to observe not only the
structure of the materials at atomic level with greater sensitivity, but also to obtain images
proportional to the projected potential, the projected electric field and the projected charge
distribution. In particular, this talk will focus on the investigation of S mono- and divacancy defects in
monolayer MoS2, the two most common point defects associated with the material. The results
indicate a reduction of the experimental projected electric field at the single S vacancy and divacancy
sites, which have strong implications with respect to the properties of MoS2, particularly in relation to
the forces experienced by adatoms on its surface.
Bio – Paulo Ferreira is currently a Full Professor in the Department of Mechanical Engineering at IST,
University of Lisbon, Portugal, as well as the Head of the Advanced Electron Microscopy, Imaging and
Spectroscopy Center and the Leader of the Atomic Structure-Composition of Materials Group at the
International Iberian Nanotechnology Laboratory (INL), Portugal. He is also an Adjunct Professor, Robert &
Jane Mitchell Endowed Faculty Fellowship in Engineering in the Materials Science and Engineering
Program at the University of Texas at Austin, USA. Before joining INL and IST in Portugal, he was Robert &
Jane Mitchell Endowed Faculty in Engineering and Full Professor at the University of Texas at Austin, USA
and the Director of Electron Microscopy at the Texas Materials Institute at the University of Texas at Austin.
He has a Ph.D in Materials Science and Engineering from the University of Illinois, USA and has done his
Post-doctoral work at MIT in Materials Science and Engineering. He concentrates his scientific research in
the areas of Materials Science, Nanomaterials and Electron Microscopy applied to alternative energy
materials and 2D materials. At the educational level, he teaches graduate courses in Nanomaterials and
Nanotechnology, Structure of Materials and Electron Microscopy. In parallel, he has been involved in
initiatives with various American and Portuguese institutions in the areas of Education and Higher
Education, Systems of Innovation, and Science and Technology. He is co-author of three books, namely
“Materials 2000”, IST Press, 2003, “Investing in the Future: University-Industry Collaborations in USA and
Portugal”; and “Nanotechnology for Architects, Designers and Engineers” with co-authors D. Schodek
(Harvard University) and Michael Ashby (University of Cambridge, UK). He is also the author of 214
scientific articles published in international journals, conference proceedings and book chapters. Prof.
Ferreira has also acted as a special advisor to the Minister of Economics and Innovation, Portugal, on
Government Strategy for Science & Technology, and he is part of the Selection Nomination Committee of
the Japan Prize. He is also the Area Director of the UT Austin-Portugal Program and the Vice-President of
the Portuguese Society for Microscopy.
This one-hour seminar will be presented in the ASRC Auditorium and broadcasted via Zoom.
For more information about this hybrid event, please contact:
Leah Abraha
labraha@gc.cuny.edu