Open Access
Add to BibSonomy
Abstract
VO2 is a very promising material due to its semiconductor-metal phase transition, however, the research on fs laser-induced phase transition is still very controversial, which greatly limits its development in ultrafast optics. In this work, the fs laser-induced changes in the optical properties of VO2 films were studied with a variable-temperature Z-scan. At room temperature, VO2 consistently maintained nonlinear absorption properties at laser repetition frequencies below 10 kHz while laser-induced phase transition properties appeared at higher repetition frequencies. It was found by temperature variation experiments at 100 kHz that the modulation depth of the laser-induced VO2 phase transition was consistent with that of the ambient temperature-induced phase transition, which was increased linearly with thickness, further confirming that the phase transition was caused by the accumulation of thermal effects of a high-repetition-frequency laser. The phase transition process is reversible and causes substantial changes in optical properties of the film, which holds significant promise for all-optical switches and related applications.
© 2022 Optica Publishing Group under the terms of the Optica Open Access Publishing Agreement
1. Introduction
Vanadium oxide (VO2), which is one of the most important phase transition materials, has attracted substantial attention since Morin first discovered its phase transition characteristics in 1959 [1]. At a critical temperature of ∼341 K, VO2 undergoes a reversible transition from a low-temperature semiconducting phase with a monoclinic structure to a high-temperature metallic phase with a tetragonal rutile structure [2,3]. Multiple stimuli, such as thermal radiation, [4,5] electricity, [6,7] THz waves, [8,9] strain, [10,11] and laser irradiation, [12–19] can inspire the semiconductor-metal phase transition of VO2. Owing to the phase transition, the optical properties of VO2 will change significantly, resulting in a range of promising applications, such as photodetectors, [20–22] optical switches, [23–26] smart windows, [27–31] and laser protection [32,33]. Cilento et al. realized an ultrafast optical switch measuring the spectrogram of a supercontinuum light pulse based on the phase transition of a VO2 multifilm when excited by fs near-infrared laser pulses [23]. Zhao et al. achieved the dynamic full-color tunability of high-performance smart windows on an ultraviolet-responsive photochromism/VO2 composite film [27]. Chen et al. used VO2 to protect sensitive infrared detectors from strong laser radiation at 10.6 µm [32]. In these cases, the transmittance of VO2 varied abruptly as the crystalline state changed from semiconducting to metallic under laser action. Lasers play an increasingly important role in inducing VO2 phase transition, as they are widely applied in almost every field of our daily life, including industry, health, business, scientific research, information, and military [34–37].
The realization of VO2 phase transition using laser has been widely reported, and the phase transition is extremely easy to occur when CW and ns lasers are applied to VO2 due to the obvious laser thermal effect, [38–41] but its long response time is not favorable for further applications. Under fs laser action, the VO2 phase transition has been reported to be ultrafast with subfemtosecond time scale [14,42,43]. It remains unclear whether the phase transition is induced directly by a laser or by heat transformation after absorbing light [44–47]. Moreover, some studies have suggested that the change in optical properties is caused by the excitation of the electronic subsystem only and does not involve a structural semiconductor-to-metal phase transition [47,48]. It is of considerable importance to study the optical properties and clarify the mechanism of fs laser-induced phase transition in VO2, which will be helpful in extending its application [49–51].
We prepared a series of VO2 films with different thicknesses using magnetron sputtering. A stylus profilometer, atomic force microscopy (AFM), and X-ray diffraction (XRD) were used to characterize the quality of the obtained VO2 films. The optical properties of these VO2 films during the phase transition were investigated using a home-made variable-temperature Z-scan setup with an excitation of 1040 nm fs pulses, which showed nonlinear absorption and phase transition. The phase transition of the VO2 films was accompanied by a sharp change in transmittance, which was related to the thickness. Further research found that the laser thermal effect under high-repetition-frequency laser excitation played an important role in inducing the phase transition of VO2 films. In addition, the semiconducting VO2 phase exhibited a reverse saturable response, whereas the metallic phase VO2 exhibited a saturable response.
2. Results and discussion
VO2 films were synthesized on 30 mm × 30 mm BK7 substrates using a reactive magnetron sputtering system (DENTON Discovery 635). A 4-inch V2O3 ceramic target was fixed in the reaction chamber, which was pumped down to 10−4 Pa and held by a rotary pump and cryopump. The Ar gas and Ar + O2 mixed gas were introduced to the vacuum atmosphere; the ratio of Ar/(Ar + O2) was maintained at 7:3, and the pressure was maintained at 7-8 mTorr. The V2O3 films were deposited on BK7 substrates with 200 W of DC power. Finally, the post-annealing process was conducted for approximately 5 minutes at a pressure of 5 mTorr and temperature of 723 K. Continuous VO2 films were obtained after natural cooling of the cavity temperature. A series of VO2 thin films (labeled as S1-S5, as shown in Fig. 1(a)) were synthesized with sputtering times of 5, 8, 12, 15, and 20 minutes. Their corresponding thicknesses were 33.0, 55.8, 71.1, 92.4, and 111.7 nm, respectively, which were tested using a stylus profilometer (Fig. 1(b)). AFM was used to measure the morphology of the VO2 films, as shown in Fig. S1. The AFM results indicate the continuity and homogeneity of our samples, and the corresponding root-mean-square (RMS) roughness values were 2.6, 3.54, 3.90, 4.45, and 5.04 nm (Fig. 1(c)). The XRD pattern (Fig. 1(d)) shows that the prepared samples are all pure VO2(M) phase (JCPDS card NO.72-0514, P21/c, a = 0.574 nm, b = 0.452 nm, c = 0.538 nm, α = γ = 90°, and β = 122.61°), with the main peak corresponding to the (011) plane. To evaluate the ambient temperature-induced phase transition properties, we investigated the variation in the sample transmittance at 1040 nm from 305 to 355 K with a UV-NIR spectrophotometer (Fig. 1(e)). The phase transition of the samples, from the semiconducting to the metallic state, starts at 330 K and completes at 348 K, with an average hysteresis of ∼18 K depending on the direction of the temperature change [52]. The transmittance of the semiconducting phase decreases from 60.5% to 40.2% with increasing thickness, whereas the transmittance of the metallic phase decreases from 52.2% to 15.1%. To quantify the change in transmittance during the phase transition, we define 10 × log10 (Tm/T0) as the modulation depth, where T0 and Tm are the transmittances before and after external induction, respectively. The modulation depth induced by ambient temperature increases from ∼-0.64 to ∼-4.25 dB with increasing VO2 film thickness, and detailed data are summarized in Table 1.
Fig. 1. (a) Photograph of the VO2 films prepared via magnetron sputtering for 5, 8, 12, 15, and 20 minutes, respectively. (b) Thickness of the VO2 films measured using a stylus profilometer. (c) RMS roughness as a function of thickness. Inset shows the surface morphology of the VO2-S5 sample. (d) Typical XRD pattern of all the VO2 films studied. (e) Temperature-dependent transmittance at 1040 nm. Solid and dashed lines represent the heating and cooling processes, respectively.
Table 1. Fundamental information of VO2 films prepared via magnetron sputtering.
The optical properties of the VO2 films during the phase transition process were investigated using a home-built variable-temperature Z-scan setup (Fig. 2). The excitation laser source was a 380 fs-pulsed laser at 1040 nm. The beam was focused with a 150 mm focus lens, and the beam waist radius at the focus was estimated to be ∼44.2 µm. In the experiment, the samples were mounted in a thermostat (Janis ST-500), and the temperature was precisely controlled in the range of 300 K to 350 K by adjusting the liquid nitrogen flow rate and heater.
Fig. 2. Schematic of the variable temperature Z-scan setup. Sample is mounted in a thermostat and then placed on a linear motorized stage.
Herein, we have presented the VO2-S5 film as a representative sample because it possessed the most significant optical properties owing to its maximum thickness. Figure 3 shows Z-scan results with different laser frequencies along both the laser propagation direction (red line, +Z) and the opposite direction (blue line, -Z) at room temperature ∼300 K, which exhibits two different optical variation properties. As shown in Fig. 3(a-c), at laser repetition frequencies below 10 kHz, the transmittance curves along the + Z and -Z directions overlap and exhibit slight decreases from 40.2% to 37.4%. This outcome is caused by the nonlinear absorption of the semiconductor phase, and thermal accumulation or phase transition is not apparent. Continue to increase the laser energy, we can find no laser-induced phase transition occurs (Fig. S2 in Supplement 1) until the sample is broken (∼49.75 mJ/cm2, the damage threshold of all samples see in Table S1), and the sample exhibits nonlinear absorption characteristics with the transmittance signal response increases. For higher laser repetition frequencies of 50 kHz and 100 kHz (Fig. 3(d) and 3(e)), the minimum transmittance at the focal position is significantly reduced to 20.3% and 16.9%, respectively. The transmittance along both the + Z and -Z directions shows an abrupt decrease followed by a slow rise as the phase transition time is shorter than the recovery time, which indicates that the sample first transitions to the metallic phase and then returns to the semiconducting phase as the laser intensity increases and then decreases. The results obtained along + Z and -Z directions no longer overlap but resemble “thermogenic echo” lines, indicating a typical laser thermal accumulation-induced phase transition process. Figure 3(f) is the modulation depth variation under different laser repetitions, which maintains a low value of ∼-0.29 dB below 10 kHz, and increases to ∼-2.85 dB and ∼-3.75 dB at 50 and 100 kHz, respectively. This mainly corresponds to the laser-induced nonlinear optical effects below 10 kHz, and laser thermal accumulation-induced phase transition at 50 kHz and higher.
Fig. 3. (a-e) Z-scan results of the VO2-S5 film at 300 K and 1 µJ with different laser repetition frequencies. (f) Modulation depth as a function of the laser repetition frequency.
In this study, we used 100 kHz laser pulses to realize the phase transition. To investigate the phase transition properties with laser initiation. We performed the laser-energy-dependent Z-scan measurements at different temperatures. From the data at 300 K (Fig. 4(a)), the transmittance remains at an approximately constant value of ∼40.5% below 250 nJ. When the data is enlarged, small reductions (∼0.5% and 2% for 100 and 250 nJ, respectively) appear on the focus of the lens, as shown in Fig. 4 g. The small variation can be attributed to the two-photon absorption of the semiconducting characteristic of VO2, where electrons could simultaneously absorb two photons and transition to an excited state when the fs laser is applied to the sample. Further, we fitted the results using the nonlinear propagation equation [53–55] and obtained the two-photon absorption coefficients (βTPA) of ∼400.95 and ∼573.35 cm/GW for 100 and 250 nJ, respectively.
Fig. 4. (a-f) Variable energy Z-scan results of the VO2-S5 film obtained at different temperatures. (g) Fitted Z-scan results with 100 and 250 nJ at 300 K. (h) VO2 phase transition turn-on threshold as a function of temperature. (i) Saturable absorption coefficient and saturable intensity at 350 K.
Go back to Fig. 4(a), when the energy is increased to 500 nJ, the transmittance begins to decrease abruptly, which is a characteristic of the phase transition induced by a laser. As the energy continues to increase, the transmittance-decreasing region becomes increasingly wider, and the minimum transmittance is maintained at ∼14.6% at the focal position, which corresponds to a modulation depth of ∼-4.29 dB. From Fig. 4(b-d), similar phenomena are observed at temperatures of 310-330 K, except that the energy at which the phase transition occurs decreased as the laser energy increased. Here, the laser intensity at which the transmittance starts to decrease abruptly is defined as the phase transition turn-on threshold. As shown in Fig. 4 h, the phase transition turn-on threshold decreases from 0.42 to 0.04 mJ/cm2 as the temperature increases from 300 K to 330 K and then becomes zero at a higher temperature as the VO2 has completely phase transmitted.
In addition, a small broad peak begins to appear at higher energies since 310 K, which becomes apparent at 340 K and 350 K as the small coordinate display range in Fig. 4(e) and 4(f). This phenomenon mainly originates from the saturable absorption of the metallic VO2. In particular, the transmittance peak height increases gradually as the laser pulse energy increases, which is also direct evidence that the sample has completely transformed into the metallic phase under this condition. The obtained saturable absorption coefficient (βSA) and saturable absorption intensity (Is) are shown in Fig. 4(i). For the VO2 film, the nonlinear absorption coefficient and saturable absorption intensity increase and decrease when laser energy increases, remaining approximately constant at ∼-775.67 cm/GW and ∼206.05 GW/cm2, respectively.
To further analyze the phase transition properties, we reorganized the experimental data and obtained the transmittance at different temperatures at laser energies ranging from 100 to 1000 nJ, as shown in Fig. 5. The transmittance at different temperatures varies significantly, even at the same energy. At lower pulse energies of 100 and 250 nJ (see Fig. 5(a) and 5(b)), the film shows a transition from semiconducting to metallic characteristics as the temperature increases, especially at the focus of the laser spot. This can be clearly observed through the enlarged portion of Fig. 5(b); the film exhibits two-photon absorption properties at 300 K (semiconducting phase) with the absorption coefficient of ∼573.35 cm/GW and modulation depth of ∼-0.08 dB and saturable absorption at 350 K (metallic phase) with the saturable absorption coefficient of ∼-253.22 cm/GW and saturable absorption intensity of ∼280.07 GW/cm2. At pulse energies of 500 nJ and higher (see Fig. 5(c-e)), the VO2 film demonstrates a metallic phase at the laser focus, even at room temperature.
Fig. 5. Variable temperature Z-scan results of the VO2-S5 film obtained at different energies. Right panel in (b) is the normalized Z-scan results at 300 K and 350 K.
Similar phenomena were observed in samples with other thickness values, as shown in Fig. S3-S6. For comparison, we combined the normalized Z-scan results at 300 K (room temperature) and 500 nJ (Fig. 6(a)), as the samples underwent the most pronounced laser-induced phase transition. As the samples approaches the laser focal point, the VO2 film characteristics change from semiconducting to metallic. As the thickness increases, the laser-induced phase transition turn-on threshold decreases, manifesting as a wider decreasing region of transmittance, possibly owing to the increased laser absorption with increasing thickness. Here, we also summarize the modulation depth of the samples induced by laser excitation (red dots), which is approximately the same as that of the ambiance temperature-induced phase transition (blue dots). This means that both the laser and temperature can induce phase transitions in VO2 films, and the same effect can be achieved using either method.
Fig. 6. (a) Normalized transmittance of VO2 S1-S5 films. (b) Modulation depth induced by laser (red line, 300 K) and temperature (blue line, from Table 1) variation as a function of sample thickness.
3. Conclusion
In summary, we prepared VO2 films with different thicknesses via magnetron sputtering, and the samples exhibited very desirable crystallinity with phase transition temperatures ranging from 330 to 348 K. Under the excitation of fs laser pulses with a repetition frequency lower than 10 kHz, the VO2 films maintained semiconducting phase characteristics and exhibit nonlinear absorption properties. Under the excitation of fs laser pulses with a repetition frequency higher than 50 kHz, the samples changed from the semiconducting phase to the metallic phase, accompanied by the change of two-photon absorption to saturable absorption. Furthermore, the laser-induced phase transition turn-on threshold decreased with increasing temperature. In this case, the phase transition was mainly induced by the thermal accumulation of laser pulses. The use of optical means to study the change of optical properties and its phase transition mechanism under VO2 fs laser induction in VO2 films will be beneficial for the further development of phase transition materials.
Funding
National Natural Science Foundation of China (11904375, 12174414); Youth Innovation Promotion Association (2019249).
Disclosures
The authors declare no conflicts of interest.
Data availability
Data underlying the results presented in this paper are not publicly available at this time but may be obtained from the authors upon reasonable request.
Supplemental document
See Supplement 1 for supporting content.
References
1. F. J. Morin, “Oxides which show a metal-to-insulator transition at the neel temperature,” Phys. Rev. Lett. 3(1), 34–36 (1959). [CrossRef]
2. M. F. Becker, A. B. Buckman, R. M. Walser, T. Lepine, P. Georges, and A. Brun, “Femtosecond laser excitation of the semiconductor-metal phase-transition in VO2,” Appl. Phys. Lett. 65(12), 1507–1509 (1994). [CrossRef]
3. J. B. Goodenough, “The two components of crystallographic transition in VO2,” J. Solid State Chem. 3(4), 490–500 (1971). [CrossRef]
4. X. B. Liu, Q. Wang, X. Q. Zhang, H. Li, Q. Xu, Y. H. Xu, X. Y. Chen, S. X. Li, M. Liu, Z. Tian, C. H. Zhang, C. W. Zou, J. G. Han, and W. L. Zhang, “Thermally dependent dynamic meta-holography using a vanadium dioxide integrated metasurface,” Adv. Opt. Mater. 7(12), 1900175 (2019). [CrossRef]
5. M. M. Qazilbash, M. Brehm, B. G. Chae, P. C. Ho, G. O. Andreev, B. J. Kim, S. J. Yun, A. V. Balatsky, M. B. Maple, F. Keilmann, H. T. Kim, and D. N. Basov, “Mott transition in VO2 revealed by infrared spectroscopy and nano-imaging,” Science 318(5857), 1750–1753 (2007). [CrossRef]
6. J. Jeong, N. Aetukuri, T. Graf, T. D. Schladt, M. G. Samant, and S. S. P. Parkin, “Suppression of metal-insulator transition in VO2 by electric field-induced oxygen vacancy formation,” Science 339(6126), 1402–1405 (2013). [CrossRef]
7. Y. Zhou, X. N. Chen, C. H. Ko, Z. Yang, C. Mouli, and S. Ramanathan, “Voltage-triggered ultrafast phase transition in vanadium dioxide switches,” IEEE Electron Device Lett. 34(2), 220–222 (2013). [CrossRef]
8. M. K. Liu, H. Y. Hwang, H. Tao, A. C. Strikwerda, K. B. Fan, G. R. Keiser, A. J. Sternbach, K. G. West, S. Kittiwatanakul, J. W. Lu, S. A. Wolf, F. G. Omenetto, X. Zhang, K. A. Nelson, and R. D. Averitt, “Terahertz-field-induced insulator-to-metal transition in vanadium dioxide metamaterial,” Nature 487(7407), 345–348 (2012). [CrossRef]
9. P. U. Jepsen, B. M. Fischer, A. Thoman, H. Helm, J. Y. Suh, R. Lopez, and R. F. Haglund, “Metal-insulator phase transition in a VO2 thin film observed with terahertz spectroscopy,” Phys. Rev. B 74(20), 205103 (2006). [CrossRef]
10. J. Cao, E. Ertekin, V. Srinivasan, W. Fan, S. Huang, H. Zheng, J. W. L. Yim, D. R. Khanal, D. F. Ogletree, J. C. Grossmanan, and J. Wu, “Strain engineering and one-dimensional organization of metal-insulator domains in single-crystal vanadium dioxide beams,” Nat. Nanotechnol. 4(11), 732–737 (2009). [CrossRef]
11. D. Lee, J. Lee, K. Song, F. Xue, S. Y. Choi, Y. J. Ma, J. Podkaminer, D. Liu, S. C. Liu, B. Chung, W. J. Fan, S. J. Cho, W. D. Zhou, J. Lee, L. Q. Chen, S. H. Oh, Z. Q. Ma, and C. B. Eom, “Sharpened VO2 phase transition via controlled release of epitaxial strain,” Nano Lett. 17(9), 5614–5619 (2017). [CrossRef]
12. W. R. Roach, “Optical induction and detection of fast phase transition in VO2,” Solid State Commun. 9(9), 551–555 (1971). [CrossRef]
13. S. Lysenko, V. Vikhnin, F. Fernandez, A. Rua, and H. Liu, “Photoinduced insulator-to-metal phase transition in VO2 crystalline films and model of dielectric susceptibility,” Phys. Rev. B 75(7), 075109 (2007). [CrossRef]
14. A. Cavalleri, C. Toth, C. W. Siders, J. A. Squier, F. Raksi, P. Forget, and J. C. Kieffer, “Femtosecond structural dynamics in VO2 during an ultrafast solid-solid phase transition,” Phys. Rev. Lett. 87(23), 237401 (2001). [CrossRef]
15. A. Cavalleri, T. Dekorsy, H. H. W. Chong, J. C. Kieffer, and R. W. Schoenlein, “Evidence for a structurally-driven insulator-to-metal transition in VO2: a view from the ultrafast timescale,” Phys. Rev. B 70(16), 161102 (2004). [CrossRef]
16. S. Lysenko, A. J. Rua, V. Vikhnin, J. Jimenez, F. Fernandez, and H. Liu, “Light-induced ultrafast phase transitions in VO2 thin film,” Appl. Surf. Sci. 252(15), 5512–5515 (2006). [CrossRef]
17. F. Guinneton, L. Sauques, J. C. Valmalette, F. Cros, and J. R. Gavarri, “Optimized infrared switching properties in thermochromic vanadium dioxide thin films: role of deposition process and microstructure,” Thin Solid Films 446(2), 287–295 (2004). [CrossRef]
18. H. Liu, O. Vasquez, V. R. Santiago, L. Diaz, and F. E. Fernandez, “Excited state dynamics and semiconductor-to-metallic phase transition of VO2 thin film,” J. Lumin. 108(1-4), 233–238 (2004). [CrossRef]
19. M. F. Becker, A. B. Buckman, R. M. Walser, T. Lepine, P. Georges, and A. Brun, “Femtosecond laser excitation dynamics of the semiconductor-metal phase transition in VO2,” J. Appl. Phys. 79(5), 2404–2408 (1996). [CrossRef]
20. Z. J. Li, Z. P. Hu, J. Peng, C. Z. Wu, Y. C. Yang, F. Feng, P. Gao, J. L. Yang, and Y. Xie, “Ultrahigh infrared photoresponse from core-shell single-domain-VO2/V2O5 heterostructure in nanobeam,” Adv. Funct. Mater. 24(13), 1821–1830 (2014). [CrossRef]
21. J. M. Wu and W. E. Chang, “Ultrahigh responsivity and external quantum efficiency of an ultraviolet-light photodetector based on a single VO2 microwire,” ACS Appl. Mater. Interfaces 6(16), 14286–14292 (2014). [CrossRef]
22. R. Tian, Y. Li, Z. M. Liu, J. Z. Zhou, J. Liu, L. N. Fan, W. Q. Zhao, J. X. Li, X. Zhang, C. Peng, Y. D. Wu, X. H. Wang, and B. Y. Fang, “Broadband nir absorber based on square lattice arrangement in metallic and dielectric state VO2,” Chin. Opt. Lett. 18(5), 052601 (2020). [CrossRef]
23. F. Cilento, C. Giannetti, G. Ferrini, S. Dal Conte, T. Sala, G. Coslovich, M. Rini, A. Cavalleri, and F. Parmigiani, “Ultrafast insulator-to-metal phase transition as a switch to measure the spectrogram of a supercontinuum light pulse,” Appl. Phys. Lett. 96(2), 021102 (2010). [CrossRef]
24. S. A. Pollack, D. B. Chang, F. A. Chudnovky, and I. A. Khakhaev, “Passive-Q switching and mode-locking of er-glass lasers using VO2 mirrors,” J. Appl. Phys. 78(6), 3592–3599 (1995). [CrossRef]
25. M. Soltani, M. Chaker, E. Haddad, R. V. Kruzelecky, and D. Nikanpour, “Optical switching of vanadium dioxide thin films deposited by reactive pulsed laser deposition,” J. Vac. Sci. Technol., A 22(3), 859–864 (2004). [CrossRef]
26. S. H. Chen, H. Ma, X. J. Yi, H. C. Wang, X. Tao, M. X. Chen, X. W. Li, and C. J. Ke, “Optical switch based on vanadium dioxide thin films,” Infrared Phys. Technol. 45(4), 239–242 (2004). [CrossRef]
27. S. W. Zhao, Z. W. Shao, A. B. Huang, S. H. Bao, H. J. Luo, S. D. Ji, P. Jin, and X. Cao, “Dynamic full-color tunability of high-performance smart windows utilizing absorption-emission effect,” Nano Energy 89, 106297 (2021). [CrossRef]
28. T. D. Manning, I. P. Parkin, M. E. Pemble, D. Sheel, and D. Vernardou, “Intelligent window coatings: Atmospheric pressure chemical vapor deposition of tungsten-doped vanadium dioxide,” Chem. Mater. 16(4), 744–749 (2004). [CrossRef]
29. S. M. Babulanam, T. S. Eriksson, G. A. Niklasson, and C. G. Granqvist, “Thermochromic VO2 films for energy-efficient windows,” Sol. Energy Mater. 16(5), 347–363 (1987). [CrossRef]
30. N. R. Mlyuka, G. A. Niklasson, and C. G. Granqvist, “Thermochromic VO2-based multilayer films with enhanced luminous transmittance and solar modulation,” Phys. Status Solidi A 206(9), 2155–2160 (2009). [CrossRef]
31. T. C. Chang, X. Cao, L. R. Dedon, S. W. Long, A. B. Huang, Z. W. Shao, N. Li, H. J. Luo, and P. Jin, “Optical design and stability study for ultrahigh-performance and long-lived vanadium dioxide-based thermochromic coatings,” Nano Energy 44, 256–264 (2018). [CrossRef]
32. S. H. Chen, H. Ma, X. J. Yi, T. Xiong, H. C. Wang, and C. J. Ke, “Smart VO2 thin film for protection of sensitive infrared detectors from strong laser radiation,” Sens. Actuators, A 115(1), 28–31 (2004). [CrossRef]
33. O. B. Danilov, A. P. Zhevlakov, A. I. Sidorov, S. A. Tul’skii, I. L. Yachnev, and D. Titterton, “Effect of intense laser radiation on controlled VO2 mirrors,” J. Opt. Technol. 67(6), 526–531 (2000). [CrossRef]
34. L. Civan and S. Kurama, “A review: preparation of functionalised materials/smart fabrics that exhibit thermochromic behaviour,” Mater. Sci. Technol. 37(18), 1405–1420 (2021). [CrossRef]
35. A. Hakami, S. S. Srinivasan, P. K. Biswas, A. Krishnegowda, S. L. Wallen, and E. K. Stefanakos, “Review on thermochromic materials: development, characterization, and applications,” J. Coat. Technol. Res. 19(2), 377–402 (2022). [CrossRef]
36. G. Y. Sun, X. Cao, H. J. Zhou, S. H. Bao, and P. Jin, “A novel multifunctional thermochromic structure with skin comfort design for smart window application,” Sol. Energy Mater. Sol. Cells 159, 553–559 (2017). [CrossRef]
37. C. Garlisi, E. Trepci, X. Li, R. Al Sakkaf, K. Al-Ali, R. P. Nogueira, L. X. Zheng, E. Azar, and G. Palmisano, “Multilayer thin film structures for multifunctional glass: self-cleaning, antireflective and energy-saving properties,” Appl. Energy 264, 114697 (2020). [CrossRef]
38. R. S. Rana, D. D. Nolte, and F. A. Chudnovskii, “Optical bistability from a thermodynamic phase-transition in vanadium dioxide,” Opt. Lett. 17(19), 1385–1387 (1992). [CrossRef]
39. N. Daliran, A. Hatef, and A. Hassanzadeh, “Photothermal bistability in the molecular energy transfer near a VO2@Au nanoshell triggered by the continuous-wave laser,” Optik 264, 169441 (2022). [CrossRef]
40. N. K. Berger and R. Shuker, “Time-resolved characteristics of phase conjugation in metal-semiconductor phase transition in VO2,” Appl. Phys. Lett. 74(19), 2770–2772 (1999). [CrossRef]
41. I. Karakurt, J. Boneberg, P. Leiderer, R. Lopez, A. Halabica, and R. F. Haglund, “Transmission increase upon switching of VO2 thin films on microstructured surfaces,” Appl. Phys. Lett. 91(9), 091907 (2007). [CrossRef]
42. S. Wall, L. Foglia, D. Wegkamp, K. Appavoo, J. Nag, R. F. Haglund, J. Stahler, and M. Wolf, “Tracking the evolution of electronic and structural properties of VO2 during the ultrafast photoinduced insulator-metal transition,” Phys. Rev. B 87(11), 115126 (2013). [CrossRef]
43. B. T. O’Callahan, A. C. Jones, J. H. Park, D. H. Cobden, J. M. Atkin, and M. B. Raschke, “Inhomogeneity of the ultrafast insulator-to-metal transition dynamics of VO2,” Nat. Commun. 6(1), 6849 (2015). [CrossRef]
44. Z. Yang, C. Y. Ko, and S. Ramanathan, “Oxide electronics utilizing ultrafast metal-insulator transitions,” Annu. Rev. Mater. Res. 41(1), 337–367 (2011). [CrossRef]
45. D. Wegkamp, M. Herzog, L. Xian, M. Gatti, P. Cudazzo, C. L. McGahan, R. E. Marvel, R. F. Haglund, A. Rubio, M. Wolf, and J. Stahler, “Instantaneous band gap collapse in photoexcited monoclinic VO2 due to photocarrier doping,” Phys. Rev. Lett. 113(21), 216401 (2014). [CrossRef]
46. P. Baum, D. S. Yang, and A. H. Zewail, “4D visualization of transitional structures in phase transformations by electron diffraction,” Science 318(5851), 788–792 (2007). [CrossRef]
47. V. R. Morrison, R. P. Chatelain, K. L. Tiwari, A. Hendaoui, A. Bruhacs, M. Chaker, and B. J. Siwick, “A photoinduced metal-like phase of monoclinic VO2 revealed by ultrafast electron diffraction,” Science 346(6208), 445–448 (2014). [CrossRef]
48. B. Q. Wang, S. H. Chen, Z. L. Huang, and M. Fu, “Optical nonlinearities of nanostructured VO2 thin films with low phase transition temperature,” Appl. Surf. Sci. 258(14), 5319–5322 (2012). [CrossRef]
49. M. A. Kats, D. Sharma, J. Lin, P. Genevet, R. Blanchard, Z. Yang, M. M. Qazilbash, D. N. Basov, S. Ramanathan, and F. Capasso, “Ultra-thin perfect absorber employing a tunable phase change material,” Appl. Phys. Lett. 101(22), 221101 (2012). [CrossRef]
50. Y. Ren, T. L. Zhou, C. Jiang, and B. Tang, “Thermally switching between perfect absorber and asymmetric transmission in vanadium dioxide-assisted metamaterials,” Opt. Express 29(5), 7666–7679 (2021). [CrossRef]
51. J. T. Liu, H. Yang, V. Khayrudinov, H. Lipsanen, H. K. Nie, K. J. Yang, B. T. Zhang, and J. L. He, “Ultrafast carrier dynamics and nonlinear optical response of InAsP nanowires,” Photonics Res. 9(9), 1811–1819 (2021). [CrossRef]
52. J. Hiltunen, J. Puustinen, A. Sitomaniemi, S. Pearce, M. Charlton, and J. Lappalainen, “Self-modulation of ultra-fast laser pulses with 1550 nm central wavelength in VO2 thin films,” Appl. Phys. Lett. 102(12), 121111 (2013). [CrossRef]
53. L. Wang, S. F. Zhang, N. McEvoy, Y. Y. Sun, J. W. Huang, Y. F. Xie, N. N. Dong, X. Y. Zhang, I. M. Kislyakov, J. M. Nunzi, L. Zhang, and J. Wang, “Nonlinear optical signatures of the transition from semiconductor to semimetal in PtSe2,” Laser Photonics Rev. 13(8), 1900052 (2019). [CrossRef]
54. H. Ma, Y. A. Zhao, Y. C. Shao, Y. F. Lian, W. L. Zhang, G. H. Hu, Y. X. Leng, and J. D. Shao, “Principles to tailor the saturable and reverse saturable absorption of epsilon-near-zero material,” Photonics Res. 9(5), 678–686 (2021). [CrossRef]
55. Z. X. Yang, L. L. Han, Q. Yang, X. H. Ren, S. Z. U. Din, X. Y. Zhang, J. C. Leng, J. B. Zhang, B. T. Zhang, K. J. Yang, J. L. He, C. L. Li, and J. Wang, “Two-dimensional tellurium saturable absorber for ultrafast solid-state laser,” Chin. Opt. Lett. 19(3), 031401 (2021). [CrossRef]
