4D and In Situ Workshop

Abstract

The need to characterize chemistry, structure and bonding with high spatial resolution has driven the exciting developments in electron energy-loss spectroscopy (EELS) in the scanning transmission electron microscope (STEM) over the last two decades. This has been achieved with the development of high-performance electron monochromators, improved spectrometer electron optics and introduction of new detectors with a high detector quantum efficiency (DQE). This has culminated in achievement of an energy resolution of 4 meV (32 cm-1) or less on a few STEM-EELS instruments. This level of performance is opening new opportunities for the study of both electronic and vibrational excitations using high resolution EELS in the scanning transmission electron microscope (STEM). One of the most exciting, and challenging, research opportunities for high resolution STEM-EELS is to identify functional groups in organic/biological systems and determine their spatial distribution. In the first part of this seminar, I will discuss recent research results demonstrating the use of high-resolution STEM-EELS to identify functional groups in polymers and to use this to spatially map such groups at the dentin-enamel junction (DEJ) to gain insight into biomineralization mechanisms. In many “soft” materials the damage caused by the electron beam limits the data quality that can be achieved, even with the use of “smart” scanning algorithms and machine learning optimizations. The use of cryogenic sample cooling has been employed to dramatic success in the determination of structure of proteins and macromolecules by cryoEM. This requires cryo-transfer of flash frozen samples into the microscope, a capability that, until recently, was not available on STEM-EELS systems capable of ultimate energy resolution. I will report the development of a cryo-transfer system for the monochromated aberration corrected (MAC-) STEM at Oak Ridge national Laboratory (ORNL) and will show early results on the study of several macromolecular systems by vibrational spectroscopy using cryo-STEM-EELS.

About Dr. McComb / Profile
The Ohio State University

David McComb, PhD, is the Director of the Center for Electron Microscopy and Analysis (CEMAS), an Ohio Research Scholar and Professor of Materials Science and Engineering at The Ohio State University. A chemistry graduate from the University of Glasgow, David completed his PhD in Physics at the University of Cambridge. David is an expert in the development and application of electron energy-loss spectroscopy (EELS) as a sub-nanometer scale probe for chemistry, structure, and bonding. He has developed and implemented approaches to studying inorganic, organic, and molecular systems using electron microscopy techniques. He has extensive experience in the application of EELS to the study of problems in sold-state chemistry and materials science, including structural and compositional variations in high-k oxides, short range magnetic order in transition metal oxides, interfaces in fuel cells, photovoltaics, multiferroics and biomaterials. In recent years, he has focused his attention on developing and implementing approaches to studying organic and molecular systems using these methods. He has demonstrated that these methods can be used to obtain unique insights into materials such on polymers for organic photovoltaics, biomineralized tissues, amyloid plaques, wear particles in macrophage cells associated with metal hip implants, molecular fragments associated with degradation of carbon nanotubes in cells and mechanisms for early stage mineralization processes. He is a fellow of the Microscopy Society of America and the Royal Society of Chemistry and the Institute of Materials. In October 2011, he joined The Ohio State University as the founding director of the Center for Electron Microscopy and Analysis (CEMAS). This multidisciplinary facility drives the application of state-of-the-art electron microscopy techniques to strategic research challenges in the physical, engineering, life and medical sciences at Ohio State and beyond.