Atomic Structures of Metallic and Semiconducting Nanocrystals by Coherent Electron Diffraction

Abstract

The third application of the single-particle diffraction technique is to measure the temperature-dependent structures of individual nanocrystals. Again, Au nanocrystals were studied for this experiment. Experimentally, we recorded diffraction patterns from the same Au nanocrystals at different temperatures. From the diffraction data, we found that the coefficient of thermal expansion (CTE) of TiO2-supported Au nanocrystals is size dependent: the CTE is positive for nanocrystals larger than 7 nanometers in diameter and negative for the smaller nanocrystals. From the diffraction intensity, we also extracted through modeling the mean square displacement of the surface atoms of the Au nanocrystals as a function of temperature, and found that surface atoms have a significantly larger vibration amplitude than the interior atoms.