Materials Science Applications of Transmission Electron Microscopy at the National Center for Electron Microscopy | Advanced Materials and Process Engineering Laboratory

GUEST SPEAKER:
Colin Ophus
Staff Scientist
National Center for Electron Microscope, Molecular Foundry Lawrence Berkeley National Laboratory

Tuesday, October 14th 11:00-12:00PM AMPEL 311, 2355 East Mall (Brimacombe Bldg).

ABSTRACT:

The transmission electron microscope (TEM) has emerged as one of the preeminent characterization tools for materials science. It has the ability to characterize materials on length scales ranging from macroscopic (grain boundaries, inclusions, etc) to atomic (interfaces, dopants, individual atomic columns or even atoms). The two primary operating modes are scanning transmission electron microscope (STEM) and phase-contrast high-resolution transmission electron microscope (HRTEM). HRTEM measurements are faster in both real space and diffraction space, but often require scattering simulations to interpret the results. STEM typically provides easier image interpretation (espically using annular dark field detectors), but requires higher beam doses and longer electron collection times. This easy mapping of measurements onto structure makes STEM an ideal tool for 3D tomographic reconstructions of sample volumes. Both imaging modes can be used for spectroscopy by measuring the electron energy losses. STEM probes also generate spatially-localized secondary electrons and x-rays which can be used to measure surface structures or spectroscopically determine local composition respectively. With the widespread adoption of aberration-correction electron optics, both STEM and HRTEM has now reached resolutions below 0.05 nm.

In this talk I will introduce the theoretical background of HRTEM plane wave and STEM probe formation, beam-sample interaction and electron detection. I will discuss image interpretation of atomic resolution micrographs for both bright-field (black atom) and dark-field modes (white atom). I will show experimental examples for many different TEM operating modes, including imaging core-shell precipitates (AlLiSc alloys and B-doped C nanospheres), epitaxial multilayers (perovskites and GaPAs), 3D tomography at both nanometer and atomic scale, grain boundaries of graphene, platinum-sapphire interfaces, ultrahigh precision measurements of SiN4, liquid-cell tomography, and other examples if time permits.