Speaker: David C. Bell, School of Engineering and Applied Sciences, Harvard University

Title: Imaging of quantum materials using low-voltage abberation corrected microscopy

Host: Henny Zandbergen

Abstract
Quantum materials are atomically layered materials such as graphene or hexagonal boron nitride (h-BN). Their properties differ strongly from those of their 3D bulk state. Depending on the composition, quantum materials may act as conductors, insulators, semiconductors or even as superconductors. Especially combinations of different quantum materials are of high interest to explore new phenomena and as the foundation for future electronic devices at the nanometer scale. Our research on quantum materials is widely spread, reaching from defect formation in graphene to the characterization of hybrid quantum materials. We use a C_s corrected Zeiss Libra TEM to investigate chemical vapor deposition (CVD) graphene with added copper and mercury defects. With TEM we address the question, where the Hg and Co atoms are placed on the graphene. At the same time, we observe the effect of the copper and mercury on the pi electrons in graphene with Raman spectroscopy.

In addition, we will present our work utilizing Low-Voltage High-Resolution Electron Microscopy (LV HREM). Low voltage imaging has several significant advantages, including increased cross-sections for inelastic and elastic scattering, increased contrast per electron and improved spectroscopy efficiency, decreased delocalization effects and reduced radiation knock-on damage. Together, these often improve the contrast to damage ratio obtained on a large class of samples.

Low-voltage TEM offers significant improvement in contrast for inorganic materials, biological samples and especially nano-biological samples while retaining atomic resolution.  Our group has shown that spherical aberration corrector in conjunction with electron monochromator at 40 keV takes the user surprisingly close to the lower bound imposed by fifth-order spherical aberration, and enables imaging with an information limit better than 1Å, and a workable resolution of better than 1.4Å. Application of Low-Voltage Electron Microscopy and its development and future directions will be presented.

Keywords: low-voltage; quantum materials; aberration correction

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