The Ohio State University
Wednesday, May 15, 2019
The electronic, mechanical, or thermal properties of functional materials are often controlled by the atomic scale structure and defects within the material, and therefore the precise atomic scale characterization becomes very important. We present novel ways to determine the atomic-tonanoscale origins of important properties of materials using high resolution 4-dimensional scanning transmission electron microscopy (4D-STEM) and fluctuation microscopy, combined with advanced computational simulations and in situ settings. Three topics will be present; First, we show our recent study on the point defect complexes and their impact to the electronic properties of β-Ga2O3, an ultra-wide bandgap transparent conductive oxide that has recently gained significant attention. We show that the unique structure of the divacancy - cation interstitial complex that we observed in β-Ga2O3 directly correlates with the density functional theory calculation, and that correlating the STEM data to the results from deep-level optical spectroscopy identifies the origin of the specific trap state within the band gap. Second, we will show the recent progress on the direct determination of medium range atomic ordering (MRO) that contributes to the nanoscale structural heterogeneity in disordered (amorphous) materials and glasses. Using 4DSTEM combined with mesoscale deformation simulation, we determine the detailed type, size, and volume fraction of MRO that correlate to the shear banding and ductility of metallic glasses. Finally, we present a novel quantitative STEM approach to determine the thermal interface resistance that is critical for thermal engineering of novel electronic devices and heterostructures. This new method is based on quantifying the Debye-Waller factor, the attenuation of the scattering intensity due to thermal vibration, in in situ thermal settings that will enable the determination of the local temperature of the material with unprecedented resolution and precision.