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Спутники
РН
SpaceX
Роскосмос
NASA
СпутникиРНSpaceXРоскосмосNASAPublication date: 8 July 2026
Source: Journal of Nano Research Vol. 93
Author(s): Nurul Hanis Azhan, Nor Azuana Ramli, Kunio Okimura, Abdul Manaf Hashim
Vanadium dioxide (VO2) is a model correlated oxide whose insulator–metal transition (IMT) can be exploited in a wide range of switching, sensing, and adaptive optical devices. Precise control of its microstructure and stress state is therefore essential for optimizing functionality. In this work, the morphological evolution of VO2 films on Al2O3 (001) substrates deposited by rf sputtering with substrate biasing of 20, 30, and 40 W was investigated using a combined imaging and statistical approach. FE-SEM images revealed a transition from isotropic grain growth at 20 W to the strongly elongated grains at 40 W. Otsu's method was used for grain segmentation, followed by ellipse fitting, which enabled the extraction of aspect ratio (AR) and circularity. Analysis of variance (ANOVA), Welch's ANOVA, and post-hoc comparisons methods confirmed that only film deposited at 40 W showed a significant increase in AR, with the median shifting from ~0.52 to ~0.60. Violin and box plots highlighted wider and multimodal distributions on films deposited with high biasing power. At the same time, histograms confirmed the widest spread at 30 W and a mixed grain size distribution at 40 W. Strain mapping based on AR deviations showed uniform stress at 20 W, localized anisotropy at 30 W, and significant heterogeneous compressive stress at 40 W. A weak but statistically significant Spearman correlation was observed between AR and circularity (ρ = 0.252, p = 0.0000), linking grain elongation to circularity loss, consistent with stress-driven anisotropy in the film deposited with high biasing power. These results demonstrate that substrate biasing resulted in the introduction of grain anisotropy, stress distribution, and microstructural disorder, and thus affects the IMT properties of the VO2 thin films. This combined methodology of images and statistical analysis provides further understanding of both the microstructure and functional performance in correlated oxide films.
[1] Morin, F. J. (1959). Oxides which show a metal-to-insulator transition at the Neel temperature. Physical review letters, 3(1), 34.
[2] Kim, J., & Paik, T. (2021). Recent advances in fabrication of flexible, thermochromic vanadium dioxide films for smart windows. Nanomaterials, 11(10), 2674.
DOI: 10.3390/nano11102674
[3] Warwick, M. E., & Binions, R. (2014). Advances in thermochromic vanadium dioxide films. Journal of Materials Chemistry A, 2(10), 3275-3292.
DOI: 10.1039/c3ta14124a
[4] Yoon, J., Hong, W. K., Kim, Y., & Park, S. Y. (2023). Nanostructured vanadium dioxide materials for optical sensing applications. Sensors, 23(15), 6715.
DOI: 10.3390/s23156715
[5] Kabir, S., Nirantar, S., Zhu, L., Ton-That, C., Jain, S. K., Kayani, A. B. A., ... & Bhaskaran, M. (2020). Phase change vanadium dioxide light sensors. Applied Materials Today, 21, 100833.
[6] Jung, Y., Jeong, J., Qu, Z., Cui, B., Khanda, A., Parkin, S. S., & Poon, J. K. (2021). Observation of optically addressable nonvolatile memory in VO2 at room temperature. Advanced electronic materials, 7(8), 2001142.
[7] Bae, S. H., Lee, S., Koo, H., Lin, L., Jo, B. H., Park, C., & Wang, Z. L. (2013). The memristive properties of a single VO2 nanowire with switching controlled by self‐heating. Advanced Materials, 25(36), 5098-5103.
[8] Valakh, M. Y., Yukhymchuk, V. O., Dzhagan, V. M., Isaieva, O. F., Yefanov, V. S., & Romanyuk, B. M. (2024). Variation of the metal-insulator phase transition temperature in VO2: An overview of some possible implementation methods. Semicond. Physics, Quantum Electronics & Optoelectronics, 27(2), 136.
[9] Lu, H., Li, L., Tang, Z., Xu, M., Zheng, Y., Becker, M., ... & He, Y. (2023). Correlation of metal-to-insulator transition and strain state of VO2 thin films on TiO2 (110) substrates. Applied Physics Letters, 123(4).
DOI: 10.1063/5.0152809
[10] Chen, B., Kim, G., Cho, H. J., & Ohta, H. (2022). Room Temperature Insulator‐to‐Metal Transition of VO2/TiO2 Epitaxial Bilayer Films Grown on M‐plane Sapphire Substrates. Advanced Electronic Materials, 8(1), 2100687.
[11] Singh, S., Anand, J. K., Chitnis, U., Garg, S., Arora, K., Goswami, A., & Singh, R. (2025). Controlling the Mott–Peierls transition in epitaxial VO2 (M1) film grown by PLD for near-IR photodetection. Journal of Applied Physics, 137(5).
DOI: 10.1063/5.0244967
[12] Yu, Z., Liu, Y., Zhang, Z., Cheng, M., Zou, Z., Lu, Z., ... & Xiong, R. (2020). Controllable phase transition temperature by regulating interfacial strain of epitaxial VO2 films. Ceramics International, 46(8), 12393-12399.
[13] Azhan, N. H., Su, K., Okimura, K., & Sakai, J. (2015). Radio frequency substrate biasing effects on the insulator-metal transition behavior of reactively sputtered VO2 films on sapphire (001). Journal of Applied Physics, 117(18).
DOI: 10.1063/1.4921105
[14] Azhan, N. H., Okimura, K., Ohtsubo, Y., Kimura, S. I., Zaghrioui, M., & Sakai, J. (2016). Large modification in insulator-metal transition of VO2 films grown on Al2O3 (001) by high energy ion irradiation in biased reactive sputtering. Journal of Applied Physics, 119(5).
DOI: 10.1063/1.4941348
[15] Bangare, S. L., Dubal, A., Bangare, P. S., & Patil, S. (2015). Reviewing Otsu's method for image thresholding. International Journal of Applied Engineering Research, 10(9), 21777-21783.
[16] Jellison Jr, G. E. (1996). The calculation of thin film parameters from spectroscopic ellipsometry data. Thin Solid Films, 290, 40-45.
[17] Azhan, N. H., Su, K., Okimura, K., Zaghrioui, M., & Sakai, J. (2015). Appearance of large crystalline domains in VO2 films grown on sapphire (001) and their phase transition characteristics. Journal of Applied Physics, 117(24).
DOI: 10.1063/1.4923223
[18] Azhan, N. H., Okimura, K., Matsuoka, K., Zaghrioui, M., & Sakai, J. (2017). Recrystallization of VO2 films into (011)-oriented micrometer-sized grains on Al2O3 (001) in biased reactive sputtering. Journal of Vacuum Science & Technology A, 35(6).
DOI: 10.1116/1.4989669
[19] Birkholzer, Y. A., Sotthewes, K., Gauquelin, N., Riekehr, L., Jannis, D., Van Der Minne, E., ... & Rijnders, G. (2022). High-strain-induced local modification of the electronic properties of VO2 thin films. ACS Applied Electronic Materials, 4(12), 6020-6028.
[20] Chang, X., Li, J., Mu, J., Ma, C. H., Huang, W., Zhu, H. F., ... & Shi, Q. (2023). Impact of the uniaxial strain on terahertz modulation characteristics in flexible epitaxial VO2 film across the phase transition. Optics Express, 31(8), 13243-13254.
DOI: 10.1364/oe.488947
[21] Gurunatha, K. L., Sathasivam, S., Li, J., Portnoi, M., Parkin, I. P., & Papakonstantinou, I. (2020). Combined effect of temperature induced strain and oxygen vacancy on metal‐insulator transition of VO2 colloidal particles. Advanced Functional Materials, 30(49), 2005311.
[22] Yamin, T., Wissberg, S., Cohen, H., Cohen-Taguri, G., & Sharoni, A. (2016). Ultrathin films of VO2 on r-cut sapphire achieved by postdeposition etching. ACS applied materials & interfaces, 8(23), 14863-14870.