Origin of Different Growth Modes for Epitaxial Manganite Films
Origin of Different Growth Modes for Epitaxial Manganite Films
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DOI：
10.1111/jace.12202
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发表时间：
2013-05
影响因子：
3.9
通讯作者：
R. Cai;Yiqian Wang;Xuehua Liu;Weiwei Gao;Yunzhong Chen;Jirong Sun;Yanguo Wang
中科院分区：
文献类型：
--
作者：
R. Cai;Yiqian Wang;Xuehua Liu;Weiwei Gao;Yunzhong Chen;Jirong Sun;Yanguo Wang
用透射电子显微镜对Bi0.4Ca0.6MnO3（BCMO）和La0.67Ca0.33MnO3（LCMO）外延薄膜的微观结构进行了详细的研究。BCMO外延膜（类似于10和类似于40nm）表现出岛状生长模式，而LCMO膜（类似于6和类似于30nm）遵循逐层生长模式。结合外延膜中失配位错的临界厚度模型，引入原子塌缩模型来解释其在锰氧化物薄膜中的形成机制。在沉积初期，由于外延膜和衬底之间的晶格失配而引起的应变可以通过弹性变形来调节。随着薄膜厚度的增加，应变越来越大。当薄膜厚度达到临界厚度时，应变只能通过失配位错的形成来松弛。同时，外延膜的原子结构将重新组织，部分原子开始塌陷，从而形成岛状形貌。一旦塌陷形态形成，这种波状形态的维持取决于沉积原子的原子扩散长度。如果沉积原子的扩散长度长，则岛状形态将不能保持。如果淀积原子的扩散长度较短，岛状形貌将一直保持到外延膜足够厚。这一结果对其它钙钛矿外延薄膜的生长模式有一定的指导意义。
The microstructures of the Bi0.4Ca0.6MnO3 (BCMO) and La0.67Ca0.33MnO3 (LCMO) epitaxial films are investigated by transmission electron microscopy in detail. BCMO epitaxial films (similar to 10 and similar to 40nm) exhibit an island growth mode whereas the LCMO films (similar to 6 and similar to 30nm) follow a layer by layer growth mode. Combined with the critical thickness models for the expected onset of the misfit dislocations in epitaxial films, an atomic collapse model is introduced to explain their mechanism of formation in manganite films. At the beginning of deposition, the strain caused by the lattice mismatch between the epitaxial film and substrate can be accommodated by elastic deformation. With the increase of film thickness, the strain becomes larger and larger. When the film thickness reaches the critical thickness, the strain can only be relaxed by the formation of misfit dislocations. Meanwhile, the atomic configuration of the epitaxial film will reorganize and some atoms begin to collapse, thus an island morphology will be formed. Once the collapse morphology is formed, maintenance of this wave-like morphology depends on atomic diffusion length of the deposited atoms. If the diffusion length of the deposited atoms is long, the island morphology will not be maintained. If the diffusion length of the deposited atoms is short, the island morphology will keep until the epitaxial film is thick enough. The results could shed light on the growth modes for other perovskite epitaxial films.