Nucleation and Growth Kinetics of CdSe Nanocrystals in Octadecene

Abstract

The growth kinetics of CdSe nanocrystals nucleated from TOPSe and cadmium oleate were investigated in octadecene, a non-coordinating solvent. The effects of temperature and the oleic acid concentration on the kinetics of both nucleation and particle growth were investigated. It was found that increasing oleic acid concentrations led to smaller numbers of nuclei, smaller initial nuclei size, and larger final particle sizes. The rate constant for steady-state CdSe deposition was found to be 2.2 × 10 -6 cm s -1 at ≈ 265 °C, far slower than the diffusion limit. The number of growing particles remained constant following the initial nucleation step. The radius of the primary CdSe nuclei varied from 1.0 ± 0.1 nm down to 0.8 ± 0.2 nm at lower oleic acid concentrations. Between 2 and 8% of the available Cd was consumed during nucleation. From the residual TOPSe and cadmium oleate concentrations at the onset of Ostwald ripening, the solubility of 2.2 nm CdSe in octadecene is measured to be 6.4 × 10 -5 M 2 at 265 °C. The surface free energy of CdSe in octadecene was found to be 0.17 J/cm 2 , which leads to an estimate of a 9% size distribution in the nanocrystals at the moment of nucleation.

High-Temperature Microfluidic Synthesis of CdSe Nanocrystals in Nanoliter Droplets

“…The three temperatures display similar growth curves that flatten at increased residence time, but the higher temperatures shift the traces to higher wavelengths. These curves are similar to the kinetic data reported in previous high-temperature nanocrystal syntheses, 28 which validates our experimental methods. More significantly, Fig.…”

“…In addition, the relatively high oleic acid:Cd ratios (7:1) used are believed to encourage Ostwald ripening, 28 which can explain why the PL peaks in this particular reaction system are not significantly narrower when using droplets.…”

Mechanistic Study of the Formation of Bright White Light-Emitting Ultrasmall CdSe Nanocrystals: Role of Phosphine Free Selenium Precursors

“…During last two decades, formation of metal chalcogenide QDs has been investigated using various trialkylphosphine chalcogenides (R3P=E; E= S, Se, Te) as precursors. [13][14]29,49,[66][67][68] In this context, the chemical identity of an important selenium precursor, which is prepared by dissolving elemental selenium in ODE at high temperature (>180 o C) and used frequently in CdSe QD synthesis 40,52,[69][70][71] has not been resolved.…”

Synthesis kinetics of CdSe quantum dots in trioctylphosphine oxide and in stearic acid

“…The model only simulates QD growth after nucleation and before Ostwald ripening, and it assumes that the number of nuclei remain constant during this period. 24 In that case, the average growth rate v ͑t͒ ͑in moles s −1 ͒, of each QD is approximated by Eq. ͑1͒, where Q is the activation energy ͑in eV molecule −1 ͒, T is temperature ͑in K͒, and k is Boltzmann's constant ͑in eV molecule −1 K −1 ͒, R ͑t͒ is the average QD radius ͑in cm͒, ͓M ͑t͒ ͔ is the molar concentration ͑in moles cm −3 ͒ of the limiting reactant ͑in this case organometallic Cd complexes͒, D o is the diffusion coefficient ͑in cm 2 s −1 ͒, and L D is a characteristic diffusion length ͑in cm͒, which might represent the ligand barrier thickness or a reactant depletion distance in the reaction solvent:…”