The design and performance of a compact fluorescense XAFS apparatus equipped with a microfluidic cell for in situ studies of nanoparticles are described. CdSe nanoparticles were prepared by solution reaction starting from trioctylphosphine-Se. Time-resolved experiments were performed by precisely controlling the reactor coordinates (x,y), allowing the synchrotron X-ray beam to travel along a reactor channel, covering nucleation and initial growth of nanoparticles. Detailed analysis of EXAFS data combined with UV-vis spectra allow reliable estimation of particle size and density in the initial growth that cannot be accessible by conventional optical techniques based on a long-range order. The Se K-XANES spectra are interpreted by multi-scattering calculations providing bond formation kinetics consistent with the EXAFS data.

The nucleation process of CdSe nanocrystals is studied by fluorescence-detected extended x-ray absorption fine structure (EXAFS) using a microreactor and synchrotron radiation. Detailed analysis of in situ Se K-edge EXAFS data measured along a microreactor channel revealed a strong position-dependence which displays a rapid increase in the CdSe phase with time at the initial stage. The results indicate that the CdSe nucleation completes within several seconds starting from trioctylphosphine Se solution and dodecylamine surfactant at 240 °C. This shows the promising capability of in situ EXAFS combined with a microreactor to investigate the nucleation process of nanocrystals synthesized in a solvent.

The initial nucleation and growth processes of CdSe nanocrystals in a microfluidic reactor are studied by in situ extended X-ray absorption fine structure (EXAFS) in conjunction with UV−visible absorbance and photoluminescence spectra. On the basis of a surface reaction kinetics equation, the analytical expressions of the particle size and concentration are proposed. The surface reaction rate constant calibrated by UV−visible absorbance spectra at longer reaction time (>2.4 s) was used to estimate the particle size and concentration within the first 2.4 s of reaction. A burst of nucleation at 1−2 s with the smallest nucleus size of ∼1.3 nm was observed after rapidly heating the reaction solution in the microfluidic reactor. This initial nucleation burst was associated with a rapid particle size increase within ∼3 s, and after that the growth rate was slowed. It is demonstrated that the combination of in situ EXAFS with a microfluidic reactor provides a valuable way for studying the kinetics of nanocrystals synthesis in solution.