Nucleation and Growth of CdSe Nanocrystals in a Binary Ligand System

Abstract

The competing effects of two ligands, oleic acid (OA) and bis-(2,2,4-trimethylpentyl) phosphinic acid (TMPPA), on the nucleation rate and growth of CdSe nanocrystals in octadecene are reported. It is found that TMPPA acts as a high boiling point "nonsolvent" or "nucleating agent". Addition of TMPPA leads to higher initial particle yields and smaller particle diameters. Conversely, oleic acid inhibits nucleation and results in a drastic increase in "early time ripening" (ETR), a phenomenon that causes a rapid reduction in the number of particles within the first minutes of reaction. By controlling the number of nuclei formed with TMPPA and tuning the rate of ETR with oleic acid, high yields of particles can be obtained with sizes between 3 and 7 nm. Furthermore, in the absence of OA, the preparation of very small nanocrystals with diameters approximately 2 nm is facilitated.

In-situ EXAFS study of nucleation process of CdSe nanocrystals

“…3(b) [10,12,29]. This is also confirmed by the red-shift of our UV-vis absorption spectra with time (Fig.…”

Soft‐Lithographed Up‐Converted Distributed Feedback Visible Lasers Based on CdSe–CdZnS–ZnS Quantum Dots

“…Materials: The CdSe cores are prepared by the method reported by van Embden et al [25] Core-shell nanocrystals are made following the recently developed SILAR method. [48][49][50] The final core-shell structure of the sample studied here, with the corresponding number of monolayers (ML), is: CdSe-CdS(1 ML)-Cd 0.5 Zn 0.5 S(1 ML)-ZnS(1 ML) (herein called CdSe-CdZnS-ZnS).…”

“…QDs were composed of 5.3 nm CdSe cores which were overcoated by a 1.2 nm thick CdZnS-ZnS graded shell. [25] Linear and nonlinear optical characterizations of QDs were performed in ethanol (EtOH) solution and in solid films. As shown in Figure 1, the band-edge exciton absorption peak of the QDs in solution occurs at 629 nm.…”

From Hot‐Injection Synthesis to Heating‐Up Synthesis of Cobalt Nanoparticles: Observation of Kinetically Controllable Nucleation

“…Unfortunately, although the direct measurement of nuclei concentration and size distribution is wellestablished for optically active quantum-dot nanoparticles, it is more difficult for particles that are not optically active, such as cobalt nanoparticles. [11,[28][29][30][31] Therefore, we used an indirect method to resolve the final concentration of the full-grown nanoparticles. The concentration can be calculated from the amount of carbonyl present initially and the average size of the nanoparticles at the end of the synthesis if the conversion of cobalt into nanoparticles (crystallization yield) is known.…”