Ok Jong Mok, Yoon Sangmoon, Lupini Andrew R, Ganesh Panchapakesan, Chisholm Matthew F, Lee Ho Nyung
Materials Science and Technology Division, Oak Ridge National Laboratory, Oak Ridge, TN, 37831, USA.
Center for Nanophase Materials Sciences, Oak Ridge National Laboratory, Oak Ridge, TN, 37831, USA.
Sci Rep. 2020 Jul 9;10(1):11375. doi: 10.1038/s41598-020-68275-w.
ABO delafossites are fascinating materials that exhibit a wide range of physical properties, including giant Rashba spin splitting and anomalous Hall effects, because of their characteristic layered structures composed of noble metal A and strongly correlated BO sublayers. However, thin film synthesis is known to be extremely challenging owing to their low symmetry rhombohedral structures, which limit the selection of substrates for thin film epitaxy. Hexagonal lattices, such as those provided by AlO(0001) and (111) oriented cubic perovskites, are promising candidates for epitaxy of delafossites. However, the formation of twin domains and impurity phases is hard to suppress, and the nucleation and growth mechanisms thereon have not been studied for the growth of epitaxial delafossites. In this study, we report the epitaxial stabilization of a new interfacial phase formed during pulsed-laser epitaxy of (0001)-oriented CuCrO epitaxial thin films on AlO substrates. Through a combined study using scanning transmission electron microscopy/electron-energy loss spectroscopy and density functional theory calculations, we report that the nucleation of a thermodynamically stable, atomically thick CuCrAlO interfacial layer is the critical element for the epitaxy of CuCrO delafossites on AlO substrates. This finding provides key insights into the thermodynamic mechanism for the nucleation of intermixing-induced buffer layers that can be used for the growth of other noble-metal-based delafossites, which are known to be challenging due to the difficulty in initial nucleation.
ABO 铜铁矿是一类迷人的材料，由于其由贵金属 A 和强关联的 BO 子层组成的特征性层状结构，展现出广泛的物理性质，包括巨大的 Rashba 自旋分裂和反常霍尔效应。然而，由于其低对称性的菱面体结构，薄膜合成极具挑战性，这限制了薄膜外延生长的衬底选择。六边形晶格，如由 AlO(0001) 和 (111) 取向的立方钙钛矿提供的晶格，是铜铁矿外延生长的有前途的候选者。然而，孪晶畴和杂质相的形成难以抑制，并且对于外延铜铁矿生长的成核和生长机制尚未进行研究。在本研究中，我们报道了在 AlO 衬底上脉冲激光外延生长 (0001) 取向的 CuCrO 外延薄膜过程中形成的一种新的界面相的外延稳定化。通过结合使用扫描透射电子显微镜/电子能量损失谱和密度泛函理论计算的研究，我们报道热力学稳定的原子级厚度的 CuCrAlO 界面层的成核是 CuCrO 铜铁矿在 AlO 衬底上外延生长的关键要素。这一发现为混合诱导缓冲层成核的热力学机制提供了关键见解，该机制可用于生长其他基于贵金属的铜铁矿，由于初始成核困难，这些铜铁矿的生长具有挑战性。
