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• The same single core / shell semiconductor nanocrystals have been sequen7ally imaged using fluorescence spectroscopy and atomic number contrast scanning transmission electron microscopy (Z-‐STEM)
• This imaging technique will allow inves7ga7on of the structural basis for single nanocrystal fluorescence phenomena including blinking behavior, fluorescence intensity and fluorescence life7me
• An enhanced understanding of single par7cle behavior will allow ra7onal design of more efficient NCs for use in LEDs
Needle in the Hay: Correla7ng the Atomic Structure of a Single Core / Shell Semiconductor Nanocrystal with Its Photophysical Proper7es
Noah Orfield1,6, James R. McBride1,6, Joseph D. Keene1,6, Sandra J. Rosenthal1-‐7
1Departments of Chemistry, 2Interdisciplinary Materials Science, 3Physics and Astronomy, 4Pharmacology, 5Chemical and Biomolecular Engineering, and 6Vanderbilt Ins7tute for Nanoscale Science and Engineering, Vanderbilt University, Nashville, Tennessee 37235, United States. 7Materials Science and Technology Division, Oak Ridge Na7onal Laboratory, Oak Ridge, Tennessee 37831, United States.
Background and Mo7va7on for this Study
Conclusions and Future Direc7ons
References and Funding (1) McBride et al, Nano Le(. 6 (7) 1496-‐1501 2006 (2) McBride et al, Nano Le(. 7 (10) 8358-‐65 2013 (3) Dukes et al, J. Phys. Chem. C 1115 4076-‐81 2011 (4) Kuno et al, J. Chem. Phys. 112 (7) 3117-‐20 2000
This work is funded by the Na=onal Science Founda=on grant CHE1213758
Le<: Summa7on of 1000 fluorescent images of NCs on SiO2 TEM grid substrate, collected with 100 ms acquisi7on 7me. Right: Projec7on of slice indicated by red line in the adjacent summa7on figure over en7re collec7on 7me, illustra7ng the “on” / “off” blinking behavior of the NCs.
Incen=ve for Elucida=ng Blinking / Structure Correla=ons • Blinking is detrimental to the implementa7on of semiconductor
nanocrystals (NCs) in solid state ligh7ng devices and biological tracking • Previous studies disregard defects and irregulari7es in shape, size and
structure of NCs, instead focusing only on ensemble photophysics
Single Nanocrystal Fluorescence Microscopy • Nanocrystals on a SiO2 TEM grid are excited by the 250 kHz, 400 nm output
of a Coherent OPA • Nanocrystal fluorescence is then detected by an Andor EM-‐CCD camera or
a TCSPC system for single-‐photon detec7on
Inves7ga7on of Atomic Structure Correla7on of Fluorescence Microscopy & TEM Le<: Illustra7on of the method implemented to allow correla7on of single NCs on SiO2 TEM windows. 1μm polystyrene beads are used to readily iden7fy corresponding areas on both the op7cal microscope and at low magnifica7on on TEM.
These Z-‐STEM images correspond to the labeled NCs which were iden7fied via correlated op7cal and electron microscopy.
NC4
NC2
NC3
NC6
(a) Close up of a region of the fluorescence image of individual NCs. (b) HAADF TEM image of the same region. (c) Radial filter applied to the image shown in (b) to demonstrate the loca7on of NCs. (d) Cartoon demonstra7ng the posi7on of polystyrene fiducials and NCs.