Bagchi Kushal, Jackson Nicholas E, Gujral Ankit, Huang Chengbin, Toney Michael F, Yu Lian, de Pablo Juan J, Ediger M D
Department of Chemistry , University of Wisconsin-Madison , Madison , Wisconsin 53706 , United States.
Institute for Molecular Engineering , University of Chicago , Chicago , Illinois 60637 , United States.
J Phys Chem Lett. 2019 Jan 17;10(2):164-170. doi: 10.1021/acs.jpclett.8b03582. Epub 2018 Dec 31.
Anisotropic molecular packing is a key feature that makes glasses prepared by physical vapor deposition (PVD) unique materials, warranting a mechanistic understanding of how a PVD glass attains its structure. To this end, we use X-ray scattering and ellipsometry to characterize the structure of PVD glasses of tris(8-hydroxyquinoline) aluminum (Alq3), a molecule used in organic electronics, and compare our results to simulations of its supercooled liquid. X-ray scattering reveals a tendency for molecular layering in Alq3 glasses that depends upon the substrate temperature during deposition and the deposition rate. Simulations reveal that the Alq3 supercooled liquid, like liquid metals, exhibits surface layering. We propose that the layering in Alq3 glasses observed here as well as the previously reported bulk dipole orientation are inherited from the surface structure of the supercooled liquid. This work significantly advances our understanding of the mechanism governing the formation of anisotropic structure in PVD glasses.
各向异性分子堆积是通过物理气相沉积（PVD）制备的玻璃成为独特材料的关键特征，这使得有必要从机理上理解PVD玻璃是如何获得其结构的。为此，我们使用X射线散射和椭偏仪来表征用于有机电子学的三（8-羟基喹啉）铝（Alq3）的PVD玻璃的结构，并将我们的结果与它的过冷液体模拟结果进行比较。X射线散射揭示了Alq3玻璃中分子分层的趋势，这种趋势取决于沉积过程中的衬底温度和沉积速率。模拟结果表明，Alq3过冷液体与液态金属一样，表现出表面分层。我们提出，这里观察到的Alq3玻璃中的分层以及先前报道的体偶极取向是从超冷液体的表面结构继承而来的。这项工作极大地推进了我们对PVD玻璃中各向异性结构形成机制的理解。
