Morphology Evolution of Gradient-Alloyed Cd_xZn_1–xSe_yS_1–y@ZnS Core–Shell Quantum Dots during Transmission Electron Microscopy Determination: A Route to Illustrate Strain Effects

Abstract

In this work, we reported the morphology evolution (formation of voids & size reduction) of gradient-alloyed Cd x Zn1–x Se y S1–y @ZnS quantum dots under electron irradiation during transmission electron microscopy observation. By investigating the correlations between shell gradients and morphology evolution, the formation of voids can be explained by the continuous electron irradiation-induced atomic movement under interfacial strain. On the other hand, the size reduction can be attributed to the elastic scattering-enabled sputtering of surface atoms. The as-formed voids of Cd x Zn1–x Se y S1–y @ZnS quantum dots with CdS-rich cores are much larger than those of ZnSe-rich ones, and the sizes of voids decreased with the increasing of shell thickness. The comparison of the morphology evolution of Cd x Zn1–x Se y S1–y @ZnS core–shell quantum dots with different composition gradients demonstrated that the size and shape of as-formed voids illustrate the strain characteristics of shell gradient. This provides a guideline to understand the strain effects in gradient-alloyed core–shell quantum dots through transmission electron microscopy measurement. We believe the deep insights into gradient-alloyed Cd x Zn1–x Se y S1–y @ZnS core–shell quantum dots would push forward their optimization toward commercialized light-emitting technology.

Photoluminescence Blinking and Biexciton Auger Recombination in Single Colloidal Quantum Dots with Sharp and Smooth Core/Shell Interfaces

“…QD1, synthesized at a relatively low shell-growth temperature, possesses a sharp core/shell interface, while QD2 has a smooth core/shell interface due to the interdiffusion of ions at the higher shell-growth temperature . The gradient and smooth interface of the QD2 have been verified by the elemental distribution analysis of the energy dispersive spectra, as presented in previous literature Figures d and e show the absorption and emission spectra of QD1 and QD2 in toluene, respectively.…”

“…40 The gradient and smooth interface of the QD2 have been verified by the elemental distribution analysis of the energy dispersive spectra, as presented in previous literature. 5 Figures 1d and 1e show the absorption and emission spectra of QD1 and QD2 in toluene, respectively. The emission peaks of QD1 and QD2 are 544.6 and 514.0 nm, respectively.…”

“…Colloidal semiconductor quantum dots (QDs) show superior optical properties including high photoluminescence (PL) quantum yields (QYs), broad absorption, and narrow emission spectra, − making them promising materials for light-emitting diodes, , lasers, photovoltaic devices, − single-photon sources, and biomedical labels. − Nonetheless, almost all single colloidal QDs exhibit PL blinking, − the random switching between bright (on) and dim/dark (off) states, which is a considerable drawback in QD-based applications, e.g., degrading the performance of lasers and light-emitting diodes, interrupting the photon emission of quantum light sources, and causing difficulty in single-particle tracking …”

Molecular Dynamics Calculations of Grain Boundary Mobility in CdTe

“…This potential is chosen because it both captures accurately the experimental atomic volumes, cohesive energies, and elastic properties of CdTe [12], and predicts the crystalline growth of II-VI compounds correctly [13]. Since the potential has been widely used to study grain structures in CdTe/CdS systems [3,13,14,15,16], knowledge of GB mobilities using the same potential has an additional advantage for comparing to previous studies.…”

Continuously Graded Quantum Dots: Synthesis, Applications in Quantum Dot Light-Emitting Diodes, and Perspectives

“…A novel synthesis for fabricating cg-QDs along the whole radial direction with a large size and nearly free of strain-induced defects still faces tremendous challenges and awaits opportunities in the future …”