Electronic Structures and Optical Properties of 6H- and 3C-SiC Microstructures and Nanostructures from X-ray Absorption Fine Structures, X-ray Excited Optical Luminescence, and Theoretical Studies
Bibliographic record
Abstract
We report a comparative study of the electronic and optical properties of five silicon carbide (SiC) materials of different crystal structures (6H and 3C polytypes), sizes (micro- and nanocrystals), and morphologies (nanowires of SiC−SiO 2 core−shell structures and oxide-free nanowires). X-ray absorption near-edge structures (XANES) at both Si K- and C K-edge have been used to investigate the electronic structures of SiC. Theoretical calculations using density functional theory (DFT), the WIEN2k code are in good accord with the experiment. It is found that both 6H- and 3C-SiC have similar XANES at Si K-edge hence similar local structure at the Si site but slightly and more noticeable difference at the C K-edge, which is due to the difference in band gaps among the polytypes. The spectra of core−shell nanowires are found to have both SiO 2 and SiC contributions in which SiO 2 is dominant. The SiO 2 shell can be almost completely removed by hydrofluoric acid treatment. X-ray excited optical luminescence (XEOL) was used to measure light emission from SiC by tuning the excitation photon energy across both Si K- and C K-edge. Luminescence was observed from all SiC samples upon X-ray excitation, though at different wavelengths depending on the crystal structures and morphologies. By measuring the yield of the total luminescence (300−800 nm) and luminescence at selected wavelengths with excitation photon energy across the absorption edge, we are able to ascribe the luminescence at various wavelengths to surface states and defects, quantum confinement, and SiO 2 surface/SiC-SiO 2 interface in core−shell nanowires. The implications of these findings are discussed.
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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 | 0.000 | 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) | 0.001 | 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".