How do defects affect electronic properties of quantum dot superlattices?
Check out work from Xiaolei Chu, Adam Moulé, and their colleagues at the University of California – Davis and University of California – Irvine, using the Hummingbird Scientific tomography sample holder to perform HAADF-STEM electron tomography on a polycrystalline epitaxially-fused colloidal PbSe quantum dot superlattice. The electron mobility of the tomography sample and the impact of grain boundaries on charge transport are estimated using a kinetic Monte Carlo model.
a) Plan-view and cross-section SEM images of the epi-SL film. b) HAADF-STEM image of the needle-shaped tomography sample with disc-shaped epi-SL layer and all other layers labeled. c) Top, d) bottom, e) cross-section, and f) perspective views of the tomogram of the epi-SL film. Color scale denotes normalized electron density in e– per nm3. g) Exploded view of the seven quantum dot layers in the tomogram, showing the sections of each grain. h) Magnified isosurface plot of two regions of the sample showing variation in neck morphology with green dots representing center-of-mass of each quantum dot. Histograms of i) neck number and j) average neck diameter for all three grains. Copyright © The Royal Society of Chemistry 2020
The high spatial resolution of the tomographic reconstruction enabled mapping of all 1846 quantum dot center-of-mass coordinates as well as the thousands of epitaxial connections (necks). The tomogram reveals the microstructure of the three superlattice grains that make up the sample. A high correlation between neck number per quantum dot and local spatial order is found, suggesting that enhanced neck connectivity leads to reduced defects. Areas of lower neck connectivity and higher incidence of defects were related to position within the superlattice, and therefore tunable by synthesis parameters for future improvement of 3D quantum dot superlattice structural perfection.
Reference: Xiaolei Chu, Hamed Heidari, Alex Abelson, Davis Unruh, Chase Hansen, Caroline Qian, Gergely Zimanyi, Matt Law, and Adam J. Moulé, Journal of Materials Chemistry A 8 18254-18265 (2020) DOI: 10.1039/D0TA06704K
Full paper Copyright © The Royal Society of Chemistry 2020
View All News