Mean-Field Theoretical Study of Bistability in Mixed Azobenzene-Alkylthiol Monolayers
Bibliographic record
Abstract
Azobenzene derivatives exhibit a well-known cis−trans photoinduced isomerization. At the gold surface, scanning tunneling microscopy studies of the azobenzene derivative N -(2-mercaptoethyl)-4-phenylazobenzamide have revealed similar isomerization behavior under the influence of an electric field. The reversible conversion of this adsorbate between a low-current and a high-current isomer shows promise for applications in molecular switching. This paper employs a mean-field theoretical approach to study bistability at medium to high surface coverages of chemisorbed mixed monolayers of azobenzene and dodecanethiol on gold surfaces. We find that the trans isomer dominates the monolayer under most sets of conditions, stabilized both by interactions between its total dipole moment and the field, and by lateral interactions with matrix molecules. Our results also highlight two important effects, which are often overlooked in discussions of bistability in self-assembled monolayers. First, polarizability effects can overcome destabilizing coupling between the permanent dipole moment and the applied field when fields are strong. We find that, at strong negative sample biases, the highly polarizable trans azobenzenes become most prevalent in the monolayer even though they are hindered by unfavorable permanent dipole-field coupling. Second, the more favorable lateral interactions between trans isomers and the dodecanethiol matrix lead to almost full conversion to the trans isomer in the monolayer, at densities well below those for which one would expect the footprint of the molecule to become important.
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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 | 0.001 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.001 | 0.001 |
| Bibliometrics | 0.001 | 0.000 |
| Science and technology studies | 0.000 | 0.001 |
| Scholarly communication | 0.000 | 0.001 |
| Open science | 0.001 | 0.000 |
| Research integrity | 0.001 | 0.001 |
| Insufficient payload (model declined to judge) | 0.002 | 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".