Analysis of N-Heterocyclic Carbenes and Their Monolayers by X-ray Photoelectron Spectroscopy: Peak-Fitting, Effects of Molecular Architecture and Impact of Possible Impurities
Bibliographic record
Abstract
X-ray photoelectron spectroscopy (XPS) is a frequently employed technique for surface characterization, particularly useful in studying self-assembled monolayers (SAMs). Herein, we examine precursors and SAMs of N-heterocyclic carbenes (NHCs) on gold. We establish a reliable and reproducible XPS peak-fitting model for 1,3-diisopropyl-1 H -benzo[ d ]imidazol-3-ium hydrogen carbonate and its CF 3 -tagged derivative to enable accurate detection, quantification, and chemical analysis of NHCs by XPS. The effects of molecular architecture variations on the N 1s peak were investigated and found to be insignificant across a wide range of derivatives. The characteristics of the N 1s peak after deposition on a gold surface were examined. All samples show a symmetric N 1s peak centered around 400.5 eV, with a FWHM ranging from 1.2 to 1.6 eV, which is a 0.6 eV shift compared to the starting hydrogen carbonate precursors, or other salts, which appear at 401.1 eV. Examination of hydrogen carbonate salts during extended irradiation under ultrahigh vacuum illustrates that dehydration and eventually decarboxylation likely take place during the process of measuring the XP spectra. More substantial degradation of the precursors can be observed after 4 h of exposure to the conditions of measurement for simple NHC precursors, with the CF 3 -tagged NHC salts degrading more rapidly within 2 h due to C–F bond cleavage. Common impurities that may result from synthetic conditions and can complicate the N 1s spectra are also presented.
Fetched live from OpenAlex and de-inverted. Abstracts are not stored in this database: the inverted indexes are 8.6 GB of the frame’s 9.3 GB of text, and the host has 13 GB free.
How this classification was reachedexpand
Full frame machine prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. The Gemma side is a direct model label for every work in the frame, read from the title-only record. The Codex side is a classifier learned from the 10,348 direct Codex labels and calibrated to design-weighted sample rates; fields without enough sample support carry no Codex call. Candidate is the union of the two sides; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels.
Distilled classifier scores by category (both heads)
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.000 | 0.001 |
| 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) | 0.001 | 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 itClassification
machine, unvalidatedMachine predicted; a candidate call from one source (direct Gemma or distilled Codex), 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".