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CQDMs characterization and single particle optical microscope setup. (a) TEM image of a grid containing 1.3nm/2.1nm CdSe/CdS core radius/shell thickness CQDMs. (b) HAADF STEM characterization of a single CdSe/CdS CQDM. (c) EDS measurement on the same particle showing the distribution of cadmium and Selenium throughout the CQDM. (d) Single particle optical microscope comprised of a 4K cryostat, 475nm pulsed laser, Dichroic
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Colloidal Quantum Dots (CQDs), major building blocks in modern opto-electronic devices, have so far been synthesized with only one emission center where the exciton resides. Recent development of coupled Colloidal Quantum Dots Molecules (CQDM), where two core-shell CQDs are fused to form two emission centers in close proximity, allows to explore ho...
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... the studied sample we aim at CQDM with stronger coupling achieved for a CdSe core radius of 1.3nm and the CdS shell thickness of 2.1nm (Supporting Information fig. S11 shows the monomers size dispersion). Figure 1a shows a transmission electron microscopy (TEM) image demonstrating the formation of quantum dot molecules. The high angle annular dark field (HAADF) scanning transmission electron microscopy (STEM) characterization shows the fusion of the two CdSe/CdS nanocrystals forming the CQDMs (Fig. ...
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... shows the monomers size dispersion). Figure 1a shows a transmission electron microscopy (TEM) image demonstrating the formation of quantum dot molecules. The high angle annular dark field (HAADF) scanning transmission electron microscopy (STEM) characterization shows the fusion of the two CdSe/CdS nanocrystals forming the CQDMs (Fig. 1b). ...
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... fig. S11 shows the monomers size dispersion). Figure 1a shows a transmission electron microscopy (TEM) image demonstrating the formation of quantum dot molecules. The high angle annular dark field (HAADF) scanning transmission electron microscopy (STEM) characterization shows the fusion of the two CdSe/CdS nanocrystals forming the CQDMs (Fig. 1b). The core-shell architecture in the CQDMs was maintained as demonstrated by the energy dispersive X-Ray spectroscopy 6 (EDS) measurement on the same particle (Fig. 1c). A continuous distribution of cadmium (both in core and shell) is identified throughout the projection of the CQDM. However, selective regions of the selenium (only in ...
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... The high angle annular dark field (HAADF) scanning transmission electron microscopy (STEM) characterization shows the fusion of the two CdSe/CdS nanocrystals forming the CQDMs (Fig. 1b). The core-shell architecture in the CQDMs was maintained as demonstrated by the energy dispersive X-Ray spectroscopy 6 (EDS) measurement on the same particle (Fig. 1c). A continuous distribution of cadmium (both in core and shell) is identified throughout the projection of the CQDM. However, selective regions of the selenium (only in core) are clearly identified signifying the cores ...
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... with low CQDM concentration, on a silicon substrate which was mounted inside a 4K cryogenic single particle microscope/spectroscopy system wave-plate rotation, upon photon detection in the APD or upon exposure of the EMCCD, we are able, by post processing, to trace each and every detected photon to the relevant respective measurement condition (Fig. 1d). The typical overall measurement time from a single particle is 200 sec. presents 400 consecutive spectra (0.5 sec each frame, the vertical and horizontal polarization replicas are added together). Starting from the simpler CQD spectra, typically it may show blinking and spectral diffusion, and therefore spectral clustering is ...
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... same sequence happens also in case E. However, now it is QD2 which is discharging and transferring the negative surface charge to QD1. Comparing the two emission states from QD1, before and after event E (blue dashed line rectangle and blue rectangle in fig. S10b), now explains the observed large red-shifted emission (the red shift of the blue line from the blue dashed line in ...
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... cases C and F, where charging of QD1 changes the emission from QD2 by less than 1meV, are cases where the positive surface charge, which was created upon excitation of the neutral QD1 and ejection of the hole to a surface trap, is not transferring to the surface of QD2 ( fig. S10a). Thus, the emission of QD2 is hardly changing as predicted by the simulations of such a case ( fig. 5b the red line is close to the red dashed line in the right ...
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... A, illustrated in Fig. S10c, is a special case where both the QDs are getting negatively charged simultaneously. A possible explanation to interpret this case is by a starting point where the two QDs are neutral. However, QD2 contains an electron in an inaccessible trap which cannot deliver the electron back into the QD. However, upon charging of QD1 and surface ...
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... point where the two QDs are neutral. However, QD2 contains an electron in an inaccessible trap which cannot deliver the electron back into the QD. However, upon charging of QD1 and surface charge transfer of a positive charge to the surface of QD2, the electron on the surface is moving to an accessible trap and by that, charging QD2 as well ( fig. ...
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