Understanding the electroluminescence emitted by single molecules in scanning tunneling microscopy experiments
Bibliographic record
Abstract
We explore theoretically the electroluminescence of single molecules. We adopt a local-electrode framework that is appropriate for scanning tunneling microscopy (STM) experiments where electroluminescence originates from individual molecules of moderate size on complex substrates: Couplings between the STM tip and molecule and between the molecule and multiple substrate sites are treated on the same footing as local electrodes contacting the molecule. Electron flow is modeled with the Lippmann-Schwinger Green's function scattering technique. The evolution of the electronic energy levels of the molecule under bias is modeled assuming the total charge of the molecule to be invariant, consistent with Coulomb blockade considerations, but the electronic occupations of the molecular highest occupied molecular orbital and lowest unoccupied molecular orbital levels vary with changing bias. The photon-emission rate is calculated using Fermi's golden rule. We apply this theoretical approach to the STM/Zn-etioporphyrin/${\text{Al}}_{2}{\text{O}}_{3}/\text{NiAl}(110)$ system and simulate various configurations of coupling strength between the molecule and substrate. We compare our results to the experimental observations of Qiu et al. [Science 299, 542 (2003)] for this system and find that our model provides a comprehensive explanation of a multitude of previously unexplained observations. These include the different types of current-voltage characteristics (CVCs) that are observed experimentally, the observed association of electroluminescence with some CVCs and not others, and key properties of the observed photon spectra. Theoretical predictions are presented for further single-molecule electroluminescence experiments.
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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 | 0.001 | 0.002 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.001 | 0.001 |
| Bibliometrics | 0.000 | 0.000 |
| Science and technology studies | 0.000 | 0.001 |
| Scholarly communication | 0.001 | 0.003 |
| Open science | 0.001 | 0.001 |
| Research integrity | 0.002 | 0.001 |
| 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".