Growth Mechanisms in Nanocrystalline Lead Sulfide by Stopped-Flow Kinetic Analysis
Bibliographic record
Abstract
The growth mechanisms of thiolate-capped lead sulfide nanocrystals have been elucidated using stopped-flow UV−visible absorption spectroscopy. Spectra were recorded over the range of 0−45 °C at 48 ms intervals during the first 144 s of reaction between Pb(NO 3 ) 2 and Na 2 S in an aqueous solution containing thioglycerol and dithioglycerol capping ligands at pH 11. The spectra were deconvoluted by fitting to three Gaussian curves; the lowest-energy of these corresponded to the first excitonic transition and was used to approximate the average particle radius using a linear relationship between the band gap and the particle diameter for spherical PbS clusters. Kinetic models for oriented attachment (OA) and Ostwald ripening (OR) growth mechanisms were used to interpret the evolution of particle radius with time. Least-squares fitting analysis revealed that OR was the single dominant mechanism of growth in the low temperature range (0−25 °C), while at higher temperatures (30−45 °C) the mechanism was time dependent: within the first 20 s, growth was predominantly by OR; OA was favored thereafter. Parametric optimization showed that OR was controlled by the dissolution kinetics at the particle−matrix interface. The enthalpy (Δ H ‡ ) and entropy (Δ S ‡ ) of activation for the OA process were determined by Eyring treatment to be 12 ± 3 and −160 ± 10 J K −1 mol −1, respectively; the resulting Gibbs free energy of activation (Δ G ‡ ) was 62 ± 6 kJ mol −1 . The very early stages of nanocrystal growth (<0.5 s) were dominated by nucleation processes, and the kinetic data could be fit to neither OR nor OA models.
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How this classification was reachedexpand
Full frame distilled prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. Learned from the 10,348 direct Codex labels and 10,348 direct Gemma labels. Candidate is the union of thresholded teacher heads; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels or direct frontier model labels.
Codex and Gemma teacher scores by category
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.001 | 0.000 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.000 | 0.000 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.000 | 0.000 |
Machine scores (provisional)
The two teacher heads of the student model, read on this work. A score orders the frame for review; it never asserts a category, and the validation status ships verbatim with every row.
Baseline scores from an immature model (maturity gate not passed, 7 training rounds). Scores rank; they never assert a category.
score_only:v0-immature-baseline · verbatim from the scoring run: score_only means the number may rank works, and no category label ships from itClassification
machine, unvalidatedMachine predicted; a candidate call from one teacher head, not a consensus.
How this classification was reached, model by model and score by score, is at the end of the page under "How this classification was reached".