Composition Dictates Molecular Orientation at the Heterointerfaces of Vapor-Deposited Glasses

Journal Article · Fri Jun 23 00:00:00 EDT 2023 · JACS Au

DOI:https://doi.org/10.1021/jacsau.3c00168· OSTI ID:1986373

Ferron, Thomas J.  ^[1]; Fiori, Marie E.  ^[2]; Ediger, M. D.  ^[2]; DeLongchamp, Dean M.  ^[1]; Sunday, Daniel F.  ^[1]

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1. National Institute of Standards and Technology, Gaithersburg, Maryland 20899, United States
2. Department of Chemistry, University of Wisconsin−Madison, Madison, Wisconsin 53706, United States

Physical vapor deposition (PVD) can prepare organic glasses with a preferred molecular orientation. The relationships between deposition conditions and orientation have been extensively investigated in the film bulk. The role of interfaces on the structure is less well understood and remains a key knowledge gap, as the interfacial region can govern glass stability and optoelectronic properties. Robust experimental characterization has remained elusive due to complexities in interrogating molecular organization in amorphous, organic materials. Polarized soft X-rays are sensitive to both the composition and the orientation of transition dipole moments in the film, making them uniquely suited to probe molecular orientation in amorphous soft matter. Here, we utilize polarized resonant soft X-ray reflectivity (P-RSoXR) to simultaneously depth profile the composition and molecular orientation of a bilayer prepared through the physical vapor deposition of 1,4-di-[4-(N,N-diphenyl)amino]styryl-benzene (DSA-Ph) on a film of aluminum-tris(8-hydroxyquinoline) (Alq3). The bulk orientation of the DSA-Ph layer is controlled by varying deposition conditions. Utilizing P-RSoXR to depth profile the films enables determination of both the bulk orientation of DSA-Ph and the orientation near the Alq3 interface. At the Alq3 surface, DSA-Ph always lies with its long axis parallel to the interface, before transitioning into the bulk orientation. This is likely due to the lower mobility and higher glass transition of Alq3, as the first several monolayers of DSA-Ph deposited on Alq3 appear to behave as a blend. We further show how orientation at the interface correlates with the bulk behavior of a codeposited glass of similar blend composition, demonstrating a straightforward approach to predicting molecular orientation at heterointerfaces. This work provides key insights into how molecules orient during vapor deposition and offers methods to predict this property, a critical step toward controlling interfacial behavior in soft matter.

• Research Organization: National Inst. of Standards and Technology (NIST), Gaithersburg, MD (United States); Lawrence Livermore National Laboratory (LLNL), Livermore, CA (United States); Lawrence Berkeley National Laboratory (LBNL), Berkeley, CA (United States). Advanced Light Source (ALS); Brookhaven National Laboratory (BNL), Upton, NY (United States). National Synchrotron Light Source II (NSLS-II)
• Sponsoring Organization: USDOE Office of Science (SC), Basic Energy Sciences (BES); USDOE Office of Science (SC), Basic Energy Sciences (BES). Materials Sciences & Engineering Division (MSE); USDOE Office of Science (SC), Basic Energy Sciences (BES). Scientific User Facilities (SUF)
• Grant/Contract Number: AC52-07NA27344; DESC0002161; SC0012704; DEAC02-05CH11231; SC0002161; AC02-05CH11231
• OSTI ID: 1986373
• Alternate ID(s): OSTI ID: 1992216
• Journal Information: JACS Au, Journal Name: JACS Au Vol. 3 Journal Issue: 7; ISSN 2691-3704
• Publisher: American Chemical Society
• Country of Publication: United States
• Language: English

Related Subjects

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY
glasses
vapor deposition
organic interfaces
reflectivity
soft X-rays
X-ray spectroscopy