Journal
PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA
Volume 118, Issue 42, Pages -Publisher
NATL ACAD SCIENCES
DOI: 10.1073/pnas.2111988118
Keywords
organic glass; buried interfaces; X-ray scattering; physical vapor deposition
Categories
Funding
- US Department of Energy, Office of Basic Energy Sciences, Division of Materials Sciences and Engineering [DE-SC0002161]
- NSF through the University of Wisconsin Materials Research Science and Engineering Center [DMR-1720415]
- US Department of Energy, Office of Science, Office of Basic Energy Sciences [DE-AC02-76SF00515]
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Superlattice structures of organic semiconductors Alq3 and DSA-Ph were prepared using PVD to study interfacial packing near buried organic-organic interfaces. Both X-ray scattering and spectroscopic ellipsometry results indicate that the substrate has a negligible influence on the PVD glass structure, suggesting the surface equilibration mechanism can describe PVD glass structure even within the first monolayer deposition on an organic substrate.
Glasses prepared by physical vapor deposition (PVD) are anisotropic, and the average molecular orientation can be varied significantly by controlling the deposition conditions. While previous work has characterized the average structure of thick PVD glasses, most experiments are not sensitive to the structure near an underlying substrate or interface. Given the profound influence of the substrate on the growth of crystalline or liquid crystalline materials, an underlying substrate might be expected to substantially alter the structure of a PVD glass, and this near-interface structure is important for the function of organic electronic devices prepared by PVD, such as organic light-emitting diodes. To study molecular packing near buried organic-organic interfaces, we prepare superlattice structures (stacks of 5- or 10-nm layers) of organic semiconductors, Alq3 (Tris-(8-hydroxyquinoline)aluminum) and DSA-Ph (1,4-di-[4-(N,N-diphenyl)amino]styrylbenzene), using PVD. Superlattice structures significantly increase the fraction of the films near buried interfaces, thereby allowing for quantitative characterization of interfacial packing. Remarkably, both X-ray scattering and spectroscopic ellipsometry indicate that the substrate exerts a negligible influence on PVD glass structure. Thus, the surface equilibration mechanism previously advanced for thick films can successfully describe PVD glass structure even within the first monolayer of deposition on an organic substrate.
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