Lee Dong Kyu, Lee Sungwon, Sim Hyeji, Choi Si-Young, Son Junwoo
Department of Materials Science and Engineering, Seoul National University, Seoul 08826, Republic of Korea.
Research Institute of Advanced Materials, Seoul National University, Seoul 08826, Republic of Korea.
Nano Lett. 2025 Jul 23;25(29):11210-11217. doi: 10.1021/acs.nanolett.5c01392. Epub 2025 Jul 11.
High-quality growth manifests the exotic properties of correlated oxides (e.g., VO) in thin film forms, but the defects and cracks that relax the misfit strain energy deteriorate the quality of the metal-insulator transition (MIT) in VO epilayers on thick TiO substrates above the critical thickness (). A new approach must be developed to overcome the fundamental degradation by strain relaxation during the pseudomorphic growth of VO films. Herein, we utilize thin TiO nanomembranes (NM) as a strain-sharing layer to allow the formation of crack-free VO epitaxial films exceeding . While the inhomogeneous strain relaxation induced by cracks occurs in VO films on thick TiO substrates (∼0.5 mm), the homogeneous and relaxed 50-nm-thick VO films are grown by simply converting thick TiO substrates to thin TiO NM (∼8 nm) as a growth template. Atomic-scale characterization reveals that a strong strain gradient was observed in underlying TiO NM as well as VO epilayers at the interface; unlike VO on a thick TiO substrate, this strain sharing by compliant TiO NM suppresses the formation of catastrophic cracks in VO epitaxial layers. Due to the absence of the cracks, excellent MIT steepness (Δ = 4.5 K) and cycle endurance without resistance degradation were achieved in VO films above on TiO NM. Our design of thin film growth will provide a new strategy to utilize a compliance effect to release misfit strain energy and offer a novel platform for advanced epitaxial growth techniques to unrestrictedly design multifunctional heterostructures for advanced electronics.
高质量生长展现了相关氧化物（如VO）以薄膜形式存在时的奇异特性，但在厚TiO衬底上临界厚度以上的VO外延层中，用于释放失配应变能的缺陷和裂纹会降低金属-绝缘体转变（MIT）的质量。必须开发一种新方法来克服VO薄膜赝晶生长过程中因应变弛豫导致的基本退化。在此，我们利用薄TiO纳米膜（NM）作为应变共享层，以形成超过临界厚度的无裂纹VO外延膜。虽然在厚TiO衬底（约0.5毫米）上的VO薄膜中会发生由裂纹引起的不均匀应变弛豫，但通过简单地将厚TiO衬底转变为薄TiO纳米膜（约8纳米）作为生长模板，可以生长出均匀且弛豫的50纳米厚的VO薄膜。原子尺度表征表明，在界面处的底层TiO纳米膜以及VO外延层中均观察到强烈的应变梯度；与在厚TiO衬底上的VO不同，这种由柔顺的TiO纳米膜进行的应变共享抑制了VO外延层中灾难性裂纹的形成。由于不存在裂纹，在TiO纳米膜上厚度超过临界厚度的VO薄膜中实现了优异的MIT陡度（Δ = 4.5 K）和无电阻退化的循环耐久性。我们的薄膜生长设计将提供一种利用柔顺效应释放失配应变能的新策略，并为先进外延生长技术提供一个新颖的平台，以无限制地设计用于先进电子学的多功能异质结构。
