Population statistics of gold nanoparticle morphologies: direct determination by HREM observations

Population distributions of gold nanoparticle morphologies were able to be derived as a function of size by collecting a great number of high-resolution electron microscopy (HREM) images. We observed more than 4000 individual gold nanoparticles (3–18 nm) which were generated from an inert gas aggregation source using helium and deposited on amorphous carbon films. To obtain structural features three-dimensionally and not to miss high-contrast images, 20 photos were taken for each particle by changing tilting angle of a specimen holder in combination with the through-focus procedure. In order to perform reliable structural determinations, HREM images and their tilting sequences were directly compared with multislice-simulation results for icosahedral, decahedral and face-centered cubic morphologies, and finally the population distribution of each morphology was obtained as a function of size. In the present sample, icosahedral particles were dominantly populated over the observed size range and decahedral particles with non-spherical truncated bi-pyramid shape were secondly dominant. Even though a large number of sampling has been done, few crystalline particles were observed. The present experimental statistical results on morphologies provide important information on cluster growth phenomena.