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nanocrystals

Nano-scale particles (0-100 nm) of many materials exhibit unique properties that are very distinct from their bulk behavior such as catalytic activity and optoelectronic properties. The ability to reliably manipulate these properties on the nanometer scale has made nanocrystals extremely important in a wide variety of fields from bioimaging to high-performance catalysts, to television screens. The key to harnessing and manipulating the properties of nanocrystals lies in the fine and reliable control of size, shape, and composition. In our lab, we analyze these characteristics of individual nanocrystals using scanning transmission electron microscopy paired with spectroscopy techniques such as energy dispersive x-ray (EDX) spectroscopy and electron energy loss (EEL) spectroscopy. With these tools, we are able to directly observe individual dopant atoms, characterize interfaces between layers of materials in core/shell nanocrystals, and evaluate the shape and structure of individual nanocrystals with a resolution well beyond the reach of other characterization techniques.

 


Figure:Analysis of Ge/Si core/shell nanocrystals using STEM-EDX. Left: HAADF-STEM image of an individual nanocrystal alongside spatially resolved Ge and Si EDX signals. Right: Radially-averaged EDX signal along with a fit idealized error function-based model, allowing us to accurately determine the radial composition of the nanocrystal. All fit parameters are listed in the table, with the interface broadening between the Ge and Si and surface roughness expressed as standard deviations.

Recommended Reading

  1. "Nonthermal Plasma Synthesis of Core/Shell Quantum Dots: Strained Ge/Si Nanocrystals"
    K. I. Hunter, J. T. Held, K. A. Mkhoyan, U. R. Kortshagen
    - ACS App. Mater. Interfaces 9, 8263 (2017)

  2. "Nonequilibrium-Plasma-Synthesized ZnO Nanocrystals with Plasmon Resonance Tunable via Al Doping and Quantum Confinement"
    B. L. Greenberg, S. Ganguly, J. T. Held, N. J. Kramer, K. A. Mkhoyan, E. S. Aydil, U. R. Kortshagen
    - Nano Lett. 15, 8162 (2015)

  3. "High electron mobility in thin films formed via supersonic impact deposition of nanocrystals synthesized in nonthermal plasmas"
    E. Thimsen, M. Johnson, X. Zhang, A. J. Wagner, K. A. Mkhoyan, U. R. Kortshagen, E. S. Aydil
    - Nature Commun. 5, 5822 (2014).     Highlighted on Phys.org.

  4. "Direct observation of core/double-shell architecture of intense dual-mode luminescent tetragonal bipyramidal nanophosphors"
    S. Y. Kim, J. S. Jeong, K. A. Mkhoyan, H. S. Jang
    - Nanoscale 8, 10049 (2016)  Highlighted on Nanoscale Cover.

  5. "Plasmonic Interactions through Chemical Bonds of Surface Ligands on PbSe Nanocrystals"
    A. A. Gunawan, B. D. Chernomordik, D. S. Plemmons, D. D. Deng, E. S. Aydil, K. A. Mkhoyan
    - Chem. Mater. 26, 3328 (2014).

  6. "Phosphorus-Doped Silicon Nanocrystals Exhibiting Mid-Infrared Localized Surface Plasmon Resonance"
    D. J. Rowe, J. S. Jeong, K. A. Mkhoyan, U. R. Kortshagen
    - Nano Lett. 13, 1317 (2013).

  7. "Imaging 'Invisible' Dopant Atoms in Semiconductor Nanocrystals"
    A. A. Gunawan, K. A. Mkhoyan, A. W. Wills, M. G. Thomas, D. J. Norris
    - Nano Lett. 11, 5553 (2011).     Highlighted in Nature Chemistry.


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