| Autor: |
Hauwiller MR; Department of Chemistry , University of California-Berkeley , Berkeley , California , 94720 , United States., Frechette LB; Department of Chemistry , University of California-Berkeley , Berkeley , California , 94720 , United States.; Erwin Schrödinger Institute for Mathematics and Physics , University of Vienna , 1090 Vienna , Austria., Jones MR; Department of Chemistry , University of California-Berkeley , Berkeley , California , 94720 , United States., Ondry JC; Department of Chemistry , University of California-Berkeley , Berkeley , California , 94720 , United States., Rotskoff GM; Courant Institute of Mathematical Sciences , New York University , New York 10012 , United States., Geissler P; Department of Chemistry , University of California-Berkeley , Berkeley , California , 94720 , United States.; Erwin Schrödinger Institute for Mathematics and Physics , University of Vienna , 1090 Vienna , Austria., Alivisatos AP; Department of Chemistry , University of California-Berkeley , Berkeley , California , 94720 , United States.; Department of Materials Science and Engineering , University of California-Berkeley , Berkeley , California , 94720 , United States.; Materials Sciences Division , Lawrence Berkeley National Laboratory , Berkeley , California 94720 , United States.; Kavli Energy NanoScience Institute , University of California-Berkeley and Lawrence Berkeley National Laboratory , Berkeley , California 94720 , United States. |
| Abstrakt: |
Mechanisms of kinetically driven nanocrystal shape transformations were elucidated by monitoring single particle etching of gold nanocrystals using in situ graphene liquid cell transmission electron microscopy (TEM). By systematically changing the chemical potential of the oxidative etching and then quantifying the facets of the nanocrystals, nonequilibrium processes of atom removal could be deduced. Etching at sufficiently high oxidation potentials, both cube and rhombic dodecahedra (RDD)-shaped gold nanocrystals transform into kinetically stable tetrahexahedra (THH)-shaped particles. Whereas {100}-faceted cubes adopt an { hk0}-faceted THH intermediate where h/ k depends on chemical potential, {110}-faceted RDD adopt a {210}-faceted THH intermediate regardless of driving force. For cube reactions, Monte Carlo simulations show that removing 6-coordinate edge atoms immediately reveals 7-coordinate interior atoms. The rate at which these 6- and 7-coordinate atoms are etched is sensitive to the chemical potential, resulting in different THH facet structures with varying driving force. Conversely, when RDD are etched to THH, removal of 6-coordinate edge atoms reveals 6-coordinate interior atoms. Thus, changing the driving force for oxidation does not change the probability of edge atom versus interior atom removal, leading to a negligible effect on the kinetically stabilized intermediate shape. These fundamental insights, facilitated by single-particle liquid-phase TEM imaging, provide important atomic-scale mechanistic details regarding the role of kinetics and chemical driving force in dictating shape transformations at the nanometer length scale. |
