SPAHE AND CONFORMATION DESIGN ON CORE-SHELL STRUCTURED NANOCRYSTALLITES: AN IN-SITU SMALL ANGLE X-RAY SCATTERING INSPECTION ON HETEROGENENEOUS NANOCRYSTAL GROWTH
Tsan-Yao Chen1,2*, Po-Wei Yang1, Yu-Ting Liu3
1Department of Engineering and System Science, National Tsing Hua University, Hsinchu, Taiwan
2Institute of Nuclear Engineering and Science, National Tsing Hua University, Hsinchu, Taiwan
3Department of Soil and Environmental Science, National Chung Hsing University, Taichung, Taiwan
* presenting author:Tsan-Yao Chen, email:chencaeser@gmail.com
Here we demonstrate that the intrinsic heterjunction can be manipulated in expected configurations by properly design the sequences of crystal growth at different components in particular at core-shell structured NCs. As elucidated by in-situ small angle X-ray scattering (Fig. 1), the core crystal is grown as nano-disk in shape. The subsequent shell crystal was grown atop radial and facet facets at different rates. Properly control the physiochemical heteroatomic exchange pathways at core-shell interface the initial crystal state confined the subsequent shell crystal growth mechanisms and thus the configurations. In the cases with low heteroatomic exchange (revealed by the interface milting zone), the shell crystal growth follows layer-plus-island (Stranski-Krastanov, SK) thin-film growth mechanism at the interfacet corner sites. In this case opened (low atomic packing density) facets at cylinder face possess the pseudo melting interface (region C in Fig. 1) for nuclear and crystal growth with larger extend of heteroatomic intermix comparing to the close packed facets at radial face. These phenomena further strengthen by doubling the shell to core atomic ratio. By increasing the exchange extent at initial state with prolonged chemical etching time and dose, the crystal was truncated into ellipsoid with isotropic shell thicknesses in different orientations. Taking together, the presented structure confinement approaches enables the facile control of the crystal structure with expected structure in varies energy applications.


Keywords: in-situ SAXS, in-situ WAXS, heterojunction crystal growth, core-shell nanocrystal