CVD-Synthesized Gallium-Oxide Thin Films as Protective Coating for Energy Storage Applications
DOI:
https://doi.org/10.66173/jenmas.2026.39Keywords:
Gallium Oxide, Chemical vapor deposition, Thermal Energy Storage System, Coating MaterialsAbstract
The rapid growth of renewable energy integration, particularly Concentrated Solar Power (CSP), has increased demand for reliable and efficient thermal energy storage (TES) systems. Unlike photovoltaics, CSP can provide dispatchable electricity using molten salt, typically an eutectic Nano₃–KNO₃ mixture, due to its broad operating range (200–600 °C), low cost, and scalability. However, long-term operation leads to corrosion and degradation of structural alloys such as stainless steels, reducing component lifespan and increasing maintenance costs. Protective coating materials with high chemical and thermal stability are therefore essential for material compatibility and TES durability. Gallium oxide (Ga₂O₃) emerged as an interesting candidate because of its wide band gap ranging from 4.8 to 5.3 eV, high breakdown field ca. 8 MVcm-1, offering exceptional thermal and chemical stability, even at elevated temperature ca. 1800 °C, which can offer durable, effective, and efficient heat-resistant materials for TES applications. In this presented work, thin films of Ga₂O₃ are synthesized with an apparent roughness of ~1.8 nm as determined from AFM step-height profiles (mean of five measurements; ±0.4 nm) on sapphire substrate using a simple three-zone chemical vapor deposition (CVD) system, as it is cost-effective, scalable, and produces high-quality films. The preheating strategy strongly influenced surface roughness, with moderate preheating (500 °C) yielding smoother films than high-temperature preheating (750 °C). CVD enables precise control of film thickness, crystallinity, and microstructure, underscoring its potential to produce Ga₂O₃ barrier layers that resist molten-salt infiltration and thermal stress. The study provides a controlled growth process and microstructural optimization of Ga₂O₃ films, which will serve as a basis for future corrosion studies and durability testing of functional performance, which are part of the ongoing research. It is also focused on single- and multilayer architectures and protective overlayers to further enhance the corrosion resistance and interfacial stability of TES systems under harsh molten-salt cycling.
References
[1] Anam, B.; Gaston, N. Structural, Thermal, and Electronic Properties of Two-Dimensional Gallium Oxide (β-Ga2O3) from First-Principles Design. ChemPhysChem 2021, 22, 2362–2370. https://doi.org/10.1002/cphc.202100267
[2] Osorio, J.D.; Mehos, M.; Imponenti, L.; Kelly, B.; Price, H.; Torres-Madronero, J.; Rivera-Alvarez, A.; Nieto-Londono, C.; Ni, C.; Yu, Z. Failure Analysis for Molten Salt Thermal Energy Storage Tanks for In-Service CSP Plants; National Renewable Energy Laboratory (NREL), Golden, CO (United States): 2024. https://doi.org/10.2172/2331241
[3] D’Aguanno, B.; Karthik, M.; Grace, A.N.; Floris, A. Thermostatic properties of nitrate molten salts and their solar and eutectic mixtures. Scientific Reports 2018, 8, 10485. https://doi.org/10.1038/s41598-018-28641-1
[4] Li, N.; Wang, Y.; Liu, Q.; Peng, H. Evaluation of Thermal-Physical Properties of Novel Multicomponent Molten Nitrate Salts for Heat Transfer and Storage. Energies 2022, 15, 6591. https://doi.org/10.3390/en15186591
[5] Wang, H.; Li, J.; Zhong, Y.; Liu, X.; Wang, M. Novel Wide-Working-Temperature NaNO3-KNO3-Na2SO4 Molten Salt for Solar Thermal Energy Storage. Molecules 2024, 29, 2328. https://doi.org/10.3390/molecules29102328
[6] Kunkel, S.; Klasing, F.; Hanke, A.; Bauer, T.; Bonk, A. Concentrating solar power at higher limits: First studies on molten nitrate salts at 600 °C in a 100 kg-scale hot tank. Solar Energy Materials and Solar Cells 2023, 258, 112412. https://doi.org/10.1016/j.solmat.2023.112412
[7] Singh, M.P.; Basu, B.; Chattopadhyay, K. Probing High-Temperature Electrochemical Corrosion of 316 Stainless Steel in Molten Nitrate Salt for Concentrated Solar Power Plants. Journal of Materials Engineering and Performance 2022, 31, 4902–4908. https://doi.org/10.1007/s11665-021-06538-x
[8] Wei, Y.; La, P.; Zheng, Y.; Zhan, F.; Yu, H.; Yang, P.; Zhu, M.; Bai, Z.; Gao, Y. Review of Molten Salt Corrosion in Stainless Steels and Superalloys. Crystals 2025, 15, 237. https://doi.org/10.3390/cryst15030237
[9] Torres-Madroñero, J.L.; Osorio, J.D.; Nieto-Londoño, C.; Ordonez, J.C. Impact of molten salt inflow on the temperature distribution in thermal energy storage tanks at startup for central receiver concentrating solar power plants. Journal of Energy Storage 2025, 117, 116069. https://doi.org/10.1016/j.est.2025.116069
[10] Xiao, T.; Xu, J.; Xie, J.; Dong, X.; Liu, C.; Wang, Y.; Yu, X.; Zhang, L. Advanced encapsulation strategies for high-temperature molten salt: Synthesis methods and performance enhancement. Renewable and Sustainable Energy Reviews 2025, 218, 115818. https://doi.org/10.1016/j.rser.2025.115818
[11] Ding, W.; Bonk, A.; Bauer, T. Corrosion behavior of metallic alloys in molten chloride salts for thermal energy storage in concentrated solar power plants: A review. Frontiers of Chemical Science and Engineering 2018, 12, 564–576. https://doi.org/10.1007/s11705-018-1720-0
[12] Henríquez, M.; Reinoso-Burrows, J.C.; Pastén, R.; Soto, C.; Duran, C.; Olivares, D.; Guerreiro, L.; Cardemil, J.M.; Galleguillos Madrid, F.M.; Fuentealba, E. Long-Term Evaluation of a Ternary Mixture of Molten Salts in Solar Thermal Storage Systems: Impact on Thermophysical Properties and Corrosion. Materials 2024, 17, 4053. https://doi.org/10.3390/ma17164053
[13] Alparone, G.P.; Penney, D.; Sullivan, J.; Edy, J.; Mills, C. Al2O3 Coatings for Protection of Stainless Steel 316L against Corrosion in Zn-Al and Zn-Al-Mg. Coatings 2024, 14, 606. https://doi.org/10.3390/coatings14050606
[14] BROWN, S.D.; KISTLER, S.S. Devitrification of High-SiO2 Glasses of the System Al2O3-SiO2. Journal of the American Ceramic Society 1959, 42, 263–270. https://doi.org/10.1111/j.1151-2916.1959.tb12951.x
[15] Li, X.; Yin, X.; Zhang, L.; He, S. The devitrification kinetics of silica powder heat-treated in different conditions. Journal of Non-Crystalline Solids 2008, 354, 3254–3259. https://doi.org/10.1016/j.jnoncrysol.2008.02.016
[16] Cheng, Z.; Yang, J.; Shao, F.; Zhong, X.; Zhao, H.; Zhuang, Y.; Ni, J.; Tao, S. Thermal Stability of YSZ Coatings Deposited by Plasma Spray–Physical Vapor Deposition. Coatings 2019, 9, 464. https://doi.org/10.3390/coatings9080464
[17] Song, G.; Adamczyk, J.; Park, Y.; Toberer, E.S.; Hogan Jr., C.J. Spray Pyrolysis-Aerosol Deposition for the Production of Thick Yttria-Stabilized Zirconia Coatings. Advanced Engineering Materials 2021, 23, 2100255. https://doi.org/10.1002/adem.202100255
[18] Sato, T.; Koike, Y.; Endo, T.; Shimada, M. Corrosion and strength degradation of Si3N4 and sialons in K2CO3 and K2SO4 melts. Journal of Materials Science 1988, 23, 1405–1410. https://doi.org/10.1007/bf01154608
[19] Heinselman, K.; Walker, P.; Norman, A.; Parilla, P.; Ginley, D.; Zakutayev, A. Performance and reliability of β-Ga2O3 Schottky barrier diodes at high temperature. Journal of Vacuum Science & Technology A 2021, 39. https://doi.org/10.1116/6.0001003
[20] House, S.D.; Jiang, K.; Tang, J.; Davis, R.F.; Porter, L.M.; Das, D.; Chintalapalle V, R. Understanding Phase Stabilization and Transformations in Ga2O3 Wide-Bandgap Semiconductors Through In Situ Transmission Electron Microscopy. Microscopy and Microanalysis 2024, 30. https://doi.org/10.1093/mam/ozae044.794
[21] Sun, S.; Wang, C.; Alghamdi, S.; Zhou, H.; Hao, Y.; Zhang, J. Recent Advanced Ultra-Wide Bandgap β-Ga2O3 Material and Device Technologies. Advanced Electronic Materials 2025, 11, 2300844. https://doi.org/10.1002/aelm.202300844
[22] Zika, F.; Albagul, M.; Zhang, W.; Chodavarapu, S.; Quaglia, R.; Albagul, A. Gallium Oxide and Its Applications in Electronics: An Overview. WSEAS TRANSACTIONS ON ELECTRONICS 2024, 15, 118–127. https://doi.org/10.37394/232017.2024.15.14
[23] Song, Y.; Shoemaker, D.; Leach, J.H.; McGray, C.; Huang, H.-L.; Bhattacharyya, A.; Zhang, Y.; Gonzalez-Valle, C.U.; Hess, T.; Zhukovsky, S.; et al. Ga2O3-on-SiC Composite Wafer for Thermal Management of Ultrawide Bandgap Electronics. ACS Applied Materials & Interfaces 2021, 13, 40817–40829. https://doi.org/10.1021/acsami.1c09736
[24] Cheng, Z.; Wheeler, V.D.; Bai, T.; Shi, J.; Tadjer, M.J.; Feygelson, T.; Hobart, K.D.; Goorsky, M.S.; Graham, S. Integration of polycrystalline Ga2O3 on diamond for thermal management. Applied Physics Letters 2020, 116. https://doi.org/10.1063/1.5125637
[25] Liu, A.-C.; Hsieh, C.-H.; Langpoklakpam, C.; Singh, K.J.; Lee, W.-C.; Hsiao, Y.-K.; Horng, R.-H.; Kuo, H.-C.; Tu, C.-C. State-of-the-Art β-Ga2O3 Field-Effect Transistors for Power Electronics. ACS Omega 2022, 7, 36070–36091. https://doi.org/10.1021/acsomega.2c03345
[26] Li, B.; Wang, Y.; Luo, Z.; Xu, W.; Gong, H.; You, T.; Ou, X.; Ye, J.; Hao, Y.; Han, G. Gallium oxide (Ga2O3) heterogeneous and heterojunction power devices. Fundamental Research 2025, 5, 804–817. https://doi.org/10.1016/j.fmre.2023.10.008
[27] Pearton, S.J.; Ren, F.; Polyakov, A.Y.; Haque, A.; Labed, M.; Rim, Y.S. Status of Ga2O3 for power device and UV photodetector applications. Applied Physics Reviews 2025, 12. https://doi.org/10.1063/5.0285075
[28] Zhong, W.; Liu, Y.; Huang, H.; Sun, Z.; Xin, W.; Liu, W.; Zhao, X.; Long, S.; Xu, H. Ultrathin Ga2O3 Photodetector with Fast Response and Trajectory Tracking Capability Fabricated by Liquid Metal Oxidation. Nano Letters 2024, 24, 13769–13774. https://doi.org/10.1021/acs.nanolett.4c04030.s001
[29] Zhang, J.; Willis, J.; Yang, Z.; Lian, X.; Chen, W.; Wang, L.-S.; Xu, X.; Lee, T.-L.; Chen, L.; Scanlon, D.O.; et al. Deep UV transparent conductive oxide thin films realized through degenerately doped wide-bandgap gallium oxide. Cell Reports Physical Science 2022, 3, 100801. https://doi.org/10.1016/j.xcrp.2022.100801
[30] Zhang, K.; Feng, L.; Wang, L.; Zhu, J.; Zhang, H.; Ha, S.; Sun, J.; Liang, H.; Yang, T. Ga2O3/Ag/Ga2O3-Laminated Film Fabricated at Room Temperature: Toward Applications in Ultraviolet Transparent Highly Conductive Electrodes. Crystals 2023, 13, 1018. https://doi.org/10.3390/cryst13071018
[31] Guo, D.; Wu, Z.; Li, P.; An, Y.; Liu, H.; Guo, X.; Yan, H.; Wang, G.; Sun, C.; Li, L.; et al. Fabrication of β-Ga2O3 thin films and solar-blind photodetectors by laser MBE technology. Optical Materials Express 2014, 4, 1067–1076. https://doi.org/10.1364/ome.4.001067
[32] Sanyal, I.; Nandi, A.; Cherns, D.; Kuball, M. Thermodynamics of Ga2O3 Heteroepitaxy and Material Growth Via Metal Organic Chemical Vapor Deposition. ACS Applied Electronic Materials 2024, 6, 5021–5028. https://doi.org/10.1021/acsaelm.4c00535
[33] Kim, W.; Kim, H.W.; Cho, S.B. Design of optimized halide vapor phase epitaxy (HVPE) conditions for uniform α-Ga2O3 growth based on CFD analysis. Journal of the Korean Ceramic Society 2025. https://doi.org/10.1007/s43207-025-00523-z
[34] Sanchez, F.; Das, D.; Episcopo, N.; Manciu, F.S.; Tan, S.; Shutthanandan, V.; Ramana, C.V. Structure, surface/interface chemistry and optical properties of W-incorporated β-Ga2O3 films made by pulsed laser deposition. RSC Applied Interfaces 2024, 1, 1395–1409. https://doi.org/10.1039/d4lf00257a
[35] Cooke, J.; Sensale-Rodriguez, B.; Ghadbeigi, L. Methods for synthesizing β-Ga2O3 thin films beyond epitaxy. Journal of Physics: Photonics 2021, 3, 032005. https://doi.org/10.1088/2515-7647/ac0db5
[36] Li, X.; Niu, J.; Bai, L.; Jing, X.; Gao, D.; Deng, J.; Lu, F.; Wang, W. Preparation of β-Ga2O3/ε-Ga2O3 type II phase junctions by atmospheric pressure chemical vapor deposition. Ceramics International 2025, 51, 10395–10401. https://doi.org/10.1016/j.ceramint.2024.12.472
[37] Delpech, S.; Carrière, C.; Chmakoff, A.; Martinelli, L.; Rodrigues, D.; Cannes, C. Corrosion Mitigation in Molten Salt Environments. Materials (Basel) 2024, 17. https://doi.org/10.3390/ma17030581
[38] Faisal, N.H.; Rajendran, V.; Prathuru, A.; Hossain, M.; Muthukrishnan, R.; Balogun, Y.; Pancholi, K.; Hussain, T.; Lokachari, S.; Horri, B.A.; et al. Thermal spray coatings for molten salt facing structural parts and enabling opportunities for thermochemical cycle electrolysis. Engineering Reports 2024, 6, e12947. https://doi.org/10.1002/eng2.12947
[39] Dimitrocenko, L.; Strikis, G.; Polyakov, B.; Bikse, L.; Oras, S.; Butanovs, E. The Effect of a Nucleation Layer on Morphology and Grain Size in MOCVD-Grown β-Ga2O3 Thin Films on C-Plane Sapphire. Materials 2022, 15, 8362. https://doi.org/10.3390/ma15238362
[40] Wang, X.; Chen, Z.; Zhang, F.; Saito, K.; Tanaka, T.; Nishio, M.; Guo, Q. Temperature dependence of Raman scattering in β-(AlGa)2O3 thin films. AIP Advances 2016, 6. https://doi.org/10.1063/1.4940763
[41] Chen, Y.; Xia, X.; Liang, H.; Abbas, Q.; Liu, Y.; Du, G. Growth Pressure Controlled Nucleation Epitaxy of Pure Phase ε- and β-Ga2O3 Films on Al2O3 via Metal–Organic Chemical Vapor Deposition. Crystal Growth & Design 2018, 18, 1147–1154. https://doi.org/10.1021/acs.cgd.7b01576
[42] Usseinov, A.; Koishybayeva, Z.; Platonenko, A.; Pankratov, V.; Suchikova, Y.; Akilbekov, A.; Zdorovets, M.; Purans, J.; Popov, A.I. Vacancy Defects in Ga2O3: First-Principles Calculations of Electronic Structure. Materials 2021, 14, 7384. https://doi.org/10.3390/ma14237384
[43] Dong, L.; Jia, R.; Xin, B.; Peng, B.; Zhang, Y. Effects of oxygen vacancies on the structural and optical properties of β-Ga2O3. Scientific Reports 2017, 7, 40160. https://doi.org/10.1038/srep40160
[44] Milchev, A. Nucleation phenomena in electrochemical systems: thermodynamic concepts. ChemTexts 2016, 2, 2. https://doi.org/10.1007/s40828-015-0022-0
[45] Bosi, M.; Seravalli, L.; Mazzolini, P.; Mezzadri, F.; Fornari, R. Thermodynamic and Kinetic Effects on the Nucleation and Growth of ε/κ- or β-Ga2O3 by Metal–Organic Vapor Phase Epitaxy. Crystal Growth & Design 2021, 21, 6393–6401. https://doi.org/10.1021/acs.cgd.1c00863
[46] Xu, Y.; Zhang, C.; Cheng, Y.; Li, Z.; Cheng, Y.n.; Feng, Q.; Chen, D.; Zhang, J.; Hao, Y. Influence of Carrier Gases on the Quality of Epitaxial Corundum-Structured α-Ga2O3 Films Grown by Mist Chemical Vapor Deposition Method. Materials 2019, 12, 3670. https://doi.org/10.3390/ma12223670
[47] Wang, J.; Luo, T.-c.; He, Y.-c.; Wang, G. Chemical reaction-mass transport model of Ga2O3 grown by TEGa in MOCVD and an intelligent system. Journal of Crystal Growth 2023, 618, 127311. https://doi.org/10.1016/j.jcrysgro.2023.127311
[48] Karthika, S.; Radhakrishnan, T.K.; Kalaichelvi, P. A Review of Classical and Nonclassical Nucleation Theories. Crystal Growth & Design 2016, 16, 6663–6681. https://doi.org/10.1021/acs.cgd.6b00794
[49] Yu, H.Z.; Thompson, C.V. Grain growth and complex stress evolution during Volmer–Weber growth of polycrystalline thin films. Acta Materialia 2014, 67, 189–198. https://doi.org/10.1016/j.actamat.2013.12.031
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