UC San Diego

Gold nanocrystals are increasingly important for a wide range of potential applications in photonics, nanoelectronics, biological imaging, and biosensors. Although various synthesis methods for Au nanocrystals have been developed, most synthesis technique employ surfactants to control shape and/or size. However, we synthesized polyhedral shaped gold nanocrystals in the absence of any foreign catalysts so that we were able to avoid any influences of surfactants on the physical properties of the nanocrystals. We then used coherent diffractive imaging to investigate the nanoscale internal structure, shape, and lattice distortion of the Au nanocrystals and understand growth dynamics and suitability of the synthesis technique. This is the first study of both curvature-induced strain under a locally rounded surface and the effect of thermally induced lattice strain at the nanocrystal- substrate interface in a single Au nanocrystal. It is confirmed that the strain dis- tribution on the locally curved surface of the Au nanoparticle is consistent with the theoretical prediction known as the Young-Laplace effect. In contrast, the strain at the interface with the substrate is anomalous. We attribute it to the dissimilar interfacial energies between Au/Air and Au/Si and to the difference in thermal expansion between the nanocrystal and the substrate during the cooling process. These results indicate that the lattice strain of nanocrystals is influenced both by their interactions with the substrate as well as the geometric details