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Title: Perspective: Highly stable vapor-deposited glasses

ORCiD logo [1]
  1. Department of Chemistry, University of Wisconsin-Madison, 1101 University Avenue, Madison, Wisconsin 53706, USA
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Sponsoring Org.:
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Journal Article: Publisher's Accepted Manuscript
Journal Name:
Journal of Chemical Physics
Additional Journal Information:
Journal Volume: 147; Journal Issue: 21; Related Information: CHORUS Timestamp: 2018-02-14 22:21:06; Journal ID: ISSN 0021-9606
American Institute of Physics
Country of Publication:
United States

Citation Formats

Ediger, M. D.. Perspective: Highly stable vapor-deposited glasses. United States: N. p., 2017. Web. doi:10.1063/1.5006265.
Ediger, M. D.. Perspective: Highly stable vapor-deposited glasses. United States. doi:10.1063/1.5006265.
Ediger, M. D.. 2017. "Perspective: Highly stable vapor-deposited glasses". United States. doi:10.1063/1.5006265.
title = {Perspective: Highly stable vapor-deposited glasses},
author = {Ediger, M. D.},
abstractNote = {},
doi = {10.1063/1.5006265},
journal = {Journal of Chemical Physics},
number = 21,
volume = 147,
place = {United States},
year = 2017,
month =

Journal Article:
Free Publicly Available Full Text
This content will become publicly available on December 1, 2018
Publisher's Accepted Manuscript

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  • Vapor-deposited organic glasses can show enhanced kinetic stability relative to liquid-cooled glasses. When such stable glasses of model glassformers are annealed above the glass transition temperature T{sub g}, they lose their thermal stability and transform into the supercooled liquid via constant velocity propagating fronts. In this work, we show that vapor-deposited glasses of an organic semiconductor, N,N′-bis(3-methylphenyl)-N,N′-diphenylbenzidine (TPD), also transform via propagating fronts. Using spectroscopic ellipsometry and a new high-throughput annealing protocol, we measure transformation front velocities for TPD glasses prepared with substrate temperatures (T{sub Substrate}) from 0.63 to 0.96 T{sub g}, at many different annealing temperatures. We observe thatmore » the front velocity varies by over an order of magnitude with T{sub Substrate}, while the activation energy remains constant. Using dielectric spectroscopy, we measure the structural relaxation time of supercooled TPD. We find that the mobility of the liquid and the structure of the glass are independent factors in controlling the thermal stability of TPD films. In comparison to model glassformers, the transformation fronts of TPD have similar velocities and a similar dependence on T{sub Substrate}, suggesting universal behavior. These results may aid in designing active layers in organic electronic devices with improved thermal stability.« less
  • Stable non-crystalline toluene films of micrometer and nanometer thicknesses were grown by vapor deposition at distinct rates and probed by fast scanning calorimetry. Fast scanning calorimetry is shown to be extremely sensitive to the structure of the vapor-deposited phase and was used to characterize simultaneously its kinetic stability and its thermodynamic properties. According to our analysis, transformation of vapor-deposited samples of toluene during heating with rates in excess 10{sup 5} K s{sup −1} follows the zero-order kinetics. The transformation rate correlates strongly with the initial enthalpy of the sample, which increases with the deposition rate according to sub-linear law. Analysismore » of the transformation kinetics of vapor-deposited toluene films of various thicknesses reveal a sudden increase in the transformation rate for films thinner than 250 nm. The change in kinetics seems to correlate with the surface roughness scale of the substrate. The implications of these findings for the formation mechanism and structure of vapor-deposited stable glasses are discussed.« less
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  • Glasses of a model smectic liquid crystal-forming molecule, itraconazole, were prepared by vapor deposition onto substrates with temperatures ranging from T substrate = 0.78T g to 1.02T g, where T g (=330 K) is the glass transition temperature. The films were characterized using X-ray scattering techniques. For T substrate near and below T g, glasses with layered smectic-like structures can be prepared and the layer spacing can be tuned by 16% through the choice of T substrate. Remarkably, glasses prepared with T substrate values above T g exhibit levels of structural organization much higher than that of a thermally annealedmore » film. These results are explained by a mechanism based upon a preferred molecular orientation and enhanced molecular motion at the free surface, indicating that molecular organization in the glass is independent of the anchoring preferred at the substrate. Furthermore, these results suggest new strategies for optimizing molecular packing within active layers of organic electronic and optoelectronic devices.« less