Improved Infrared Optical Constants from Pressed Pellets: II. Ellipsometric <i>n</i> and <i>k</i> Values for Ammonium Sulfate with Variability Analysis
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Bibliographic record
Abstract
Infrared reflectance analysis is facilitated via the comparison of spectra recorded in situ to a databank of actual or synthetic infrared reflectance spectra. It has recently been shown that reference spectra corresponding to the many different morphological forms of the same chemical can be generated synthetically using the imaginary, k, and real, n, components of the complex refractive index, [Formula: see text] = n + i k. One method to obtain the n and k vectors is infrared ellipsometry, which measures the changes in amplitude, tan Ψ, and phase, Δ, of polarized light reflected from the sample both as a function of wavenumber and angle of incidence. The method requires specularly reflected light, so best results are usually obtained with polished planar samples of large surface area. Due to the difficulties of obtaining such samples, however, we investigate the possibility of pressing powders of neat materials and obtaining the corresponding optical constants from the pellets. In this paper, variability in the sample pellet and preparation method is investigated, as is variability in the fitting procedure for the derived optical constants. The n/k vectors are derived from the measured ellipsometric parameters, tan ψ and Δ, as they are fit by an oscillator model which yield n([Formula: see text]) and k([Formula: see text]) vectors as a function of wavenumber, [Formula: see text]. Construction of the oscillator model is not automatic and depends on significant input from the analyst as well as the sample’s physical characteristics. For pellet pressing, the experimental variability was found to be minimized for size-selected powdered samples as gauged by the minimal variance in ψ and Δ for three different pellets; similarly, the analytical precision for multiple measurements of the same pellet was also quite good, suggesting that a pressed pellet is a viable sample preparation method. Experimental variabilities were comparatively small; the greatest variability came in the analytic fitting procedure with differences in the k-peak values up to 10% for only the sharpest bands arising from four different fits to the same data set. The final ellipsometric n/k data are compared to literature values obtained from crystalline ammonium sulfate ((NH 4 ) 2 SO 4 ) samples as well as single-angle reflectance measurements that also used pressed pellets. Comparison with the previous literature values shows generally good agreement, although larger k-values are observed for the independent sets of data derived from pressed pellets. These data are suggested as an improved set of optical constants for (NH 4 ) 2 SO 4 .
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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 | 0.000 | 0.000 |
| Meta-epidemiology (narrow) | 0.001 | 0.001 |
| Meta-epidemiology (broad) | 0.001 | 0.000 |
| Bibliometrics | 0.000 | 0.003 |
| 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) | 0.001 | 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 it