Quantitative Broadband Optical Spectroscopy of Freestanding Ti <sub>3</sub> C <sub>2</sub> T <sub> <i>x</i> </sub> MXene Films: Unveiling Intrinsic Bulk Charge Carrier Dynamics
Bibliographic record
Abstract
Micrometer-thick freestanding MXene films offer a rare opportunity to probe intrinsic bulk optical and electronic properties without the influence of a substrate. Yet, quantitative optical constants over a broadband spectral range remain elusive due to the mechanically flexible nature of such films. Here, we report the first comprehensive far-infrared-to-ultraviolet (150–36,000 cm –1 ) optical spectroscopic study of freestanding Ti 3 C 2 T x MXene films with thicknesses of 1 and 4 μm. By a combination of attaching the freestanding films on flat and smooth brass plates and using an in situ metal-evaporation method, we obtained highly reliable reflectance spectra. Kramers–Kronig analysis, coupled with a two-Drude-Lorentz model, reveals multiple free-carrier populations at the Fermi level, yielding carrier densities of 7.31 × 10 21 and 7.50 × 10 21 cm –3 and mobilities of 8.15 and 4.98 cm 2 V –1 s –1 for the 1- and 4-μm-thick freestanding films, respectively. The spectra further identify a 1.61 eV feature arising from interband-plasmon coupling and a 3.84 eV interband transition, with small thickness dependence, highlighting the bulk-dominated plasmonic response in micrometer-scale films. This work establishes a quantitative, noncontact framework for mapping intrinsic charge dynamics in MXenes, unlocking pathways for their integration into broadband plasmonic, optoelectronic, infrared, and THz devices.
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How this classification was reachedexpand
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 | 0.002 | 0.000 |
| Meta-epidemiology (narrow) | 0.001 | 0.001 |
| Meta-epidemiology (broad) | 0.003 | 0.000 |
| Bibliometrics | 0.001 | 0.001 |
| Science and technology studies | 0.001 | 0.001 |
| Scholarly communication | 0.001 | 0.001 |
| Open science | 0.001 | 0.001 |
| Research integrity | 0.001 | 0.000 |
| Insufficient payload (model declined to judge) | 0.000 | 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; both teacher heads agree on what is shown here.
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".