Drs. Anil O. Yalcin

Kavli Institute of Nanoscience, Delft University of Technology, Delft, The Netherlands
Authors | Anil O. Yalcin, Zhaochuan Fan, Bart Goris, Wun-Fan Li, Rik S. Koster, Chang-Ming Fang, Alfons van Blaaderen, Marianna Casavola, Frans D. Tichelaar, Sara Bals, Gustaaf Van Tendeloo, Thijs J. H. Vlugt, Daniël Vanmaekelbergh, Henny W. Zandbergen and Marijn A. van Huis. Email | m.a.vanhuis@uu.nl

Application Atomic Resolution Monitoring of Cation Exchange in CdSe-PbSe Heteronanocrystals during Epitaxial Solid–Solid–Vapor Growth
Authors Anil O. Yalcin, Zhaochuan Fan, Bart Goris, Wun-Fan Li, Rik S. Koster, Chang-Ming Fang, Alfons van Blaaderen, Marianna Casavola, Frans D. Tichelaar, Sara Bals, Gustaaf Van Tendeloo, Thijs J. H. Vlugt, Daniël Vanmaekelbergh, Henny W. Zandbergen and Marijn A. van Huis.
Journal Nano Letters, 2014
Sample Nanoparticles
Topic Interface, Diffusion, Growth, hetero-nanoparticle/crystal
Field Material Science, Chemistry, Electronics
Techniques HRSTEM, EDX Mapping
Keywords Colloidal Nanocrystals; Cation Exchange; Molecular Dynamics; Density Functional Theory; In Situ Transmission Electron Microscopy
Publication / D.O.I. Full publication here

Atomic Resolution Monitoring of Cation Exchange in CdSe-PbSe Heteronanocrystals during Epitaxial Solid–Solid–Vapor Growth

 

ABSTRACT: Here, we show a novel solid–solid–vapor (SSV) growth mechanism whereby epitaxial growth of heterogeneous semiconductor nanowires takes place by evaporation-induced cation exchange. During heating of PbSe-CdSe nanodumbbells inside a transmission electron microscope (TEM), we observed that PbSe nanocrystals grew epitaxially at the expense of CdSe nanodomains driven by evaporation of Cd. Analysis of atomic-resolution TEM observations and detailed atomistic simulations reveals that the growth process is mediated by vacancies.
Figure left: HAADF-STEM images and chemical mapping of the nanodumbbells before and after heating. (a) HAADF-STEM image of CdSe-PbSe nanodumbbells. The PbSe tips exhibit brighter contrast than the CdSe nanorods due to Z-contrast. (b,c) Dumbbell HNCs at 160 °C (b) and at 200°C (c), showing gradual extension of PbSe domains at the expense of CdSe. A heating rate of 10 degrees/min was used in the in situ studies and the HNCs were annealed at the indicated temperatures for 5 min before imaging. Dumbbell HNCs with solid arrows transformed totally to brighter contrast with heating. This phenomenon occurred mostly from one side, though it can proceed from both PbSe domains as well (dumbbell with dashed arrows in panel c). (d−o) HAADF-STEM images and corresponding STEM-EDX elemental maps of dumbbell heteronanostructures annealed for 5 min at temperatures of (d−g) 100 °C, (h−k) 170 °C, and (l−o) 200 °C. In panels d−g, HNCs are in original dumbbell state with PbSe tips and CdSe nanorod. In panels h−k, a partially transformed nanorod is present. In panels l−o, two PbSe-CdSe HNCs became full PbSe domains. The Se remains in place during the transformation. Note that the contrast is maximized in each individual image; hence, intensities of different mappings cannot be directly compared. Quantitative analyses are provided in the Supporting Information.
Figure right: Atomic-resolution HAADF-STEM images of CdSe-PbSe HNCs reveals the dynamic growth process. It shows that PbSe has cubic rock salt (RS) crystal structure with a lattice constant(20) of 6.13 Å, whereas CdSe has a hexagonal wurtzite (WZ) crystal structure with lattice parameters(21) a = 4.29 Å and c = 7.01 Å. The CdSe WZ (0002) spacing is 3.5 Å and PbSe RS (200) spacing is 3.1 Å. With heating from 160 °C (a) to 180 °C (b) with a heating rate of 10 degrees/min, WZ CdSe nanorods started to transform to RS PbSe. The insets are Fourier transforms (FTs) taken from the white squares in each image. The spot depicted with an arrow in the inset FT of panel a corresponds to WZ CdSe(0002) spacing. It disappeared in the inset FT of panel b, confirming the WZ to RS transformation.  Movie S4 shows the transformation with atomic resolution. (c) HAADF-STEM image of a PbSe-CdSe dumbbell HNC. Stacking faults and a dislocation are present in the CdSe nanorod domain. The interface at the left-hand side is {111}PbSe/{0001}CdSea (panel d), whereas the interface at the right-hand side is {100}PbSe/{0001}CdSe (panel f).

DENSsolutions Comments

Structure evolution across an interface (e.g. diffusion, growth, chemical reaction, etc.) requires not only crystal structure information, but chemical information both to be known.  HRSTEM images, combining with EDX mapping, provides analysis tool to investigate samples structure as well as chemical environment changes down to nano/atomic scale. During these analyses, the sample stability at elevated temperature is extremely crucial for achieving reliable/interpretable results, simply because longer  time need to be applied for collecting enough signal.
The DENSsolutions heating system provides such an extreme sample stability at the elevated temperature that enables the chemical mapping of this dynamic growth process to be obtained. The researchers use the collect experimental results, as well as detailed atomistic simulations reveal that the growth process is mediated by vacancies.

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