Photothermal characterization of thermochromic materials \nfor tunable thermal devices
Bibliographic record
Abstract
The optical and infrared properties in thermochromic materials have been deeply investigated in the last years due to the large variety of photonic devices that can be realised thanks to the metal/insulator phase transition: “smart” windows which autonomously control sun rays into a room, thermally controllable localized-plasmon, hysteresis enhancement of a phase transition by nanoparticulation, optical memory by the means of phase transition, and ultrafast switching of the photonic stop band in photonic crystals. \nAmong the thermocromic materials (niobium dioxide, vanadium sesquioxide etc..) vanadium dioxide (VO2) represents the most widely used for many applications [1]. Its crystalline lattice exhibits an abrupt semiconductor-to-metal phase transition at a temperature of about TC≈68°C, characterized by a change of the crystalline cell from monoclinic to tetragonal, and consequently by an ultrafast change in the optical and IR properties (i.e. reflectivity and emissivity). \nIn this paper we show how photothermal techniques may represent a useful non-destructive and non contact tool to study the optical and thermal properties changes of vanadium dioxide thin films (both single layer and multilayers deposited onto a silicon substrate [2,3]) during the phase transition. We have performed the standard optical and infrared measurements of reflectance, transmittance, and emittance by changing the temperature of the vanadium dioxide film from 20°C (below Tc) to 90°C (above Tc) so to determine the entity of the thermal hysteresis loops and compare the refractive index in both metallic and semiconductor states with respect to the reference values. We have applied photothermal radiometry (PTR) by using a diode laser modulated at a frequency in the range 1Hz -100 kHz, and a MCZT infrared detector, in order to measure the effective thermal parameters of the structure, as well as the induced emissivity changes from the vanadium dioxide film. \nExperimental results show how PTR represent an good tool for a quantitative measurement of the thermal properties of vanadium dioxide thin films. \n \nAcknowledgments \nThis work has been performed in the framework of a collaboration between Sapienza University of Rome and the Defence R&D Canada Valcartier research center. Part of the work has been granted by Italian Ministry of Defence.
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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) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.001 | 0.000 |
| Bibliometrics | 0.000 | 0.001 |
| Science and technology studies | 0.000 | 0.001 |
| Scholarly communication | 0.000 | 0.002 |
| Open science | 0.001 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.016 | 0.001 |
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".