Model vapor-deposited glasses: Growth front and composition effects

Lyubimov, Ivan; Ediger, M. D.; Pablo, Juan J. de

doi:10.1063/1.4823769

Cited by 85 publications

(95 citation statements)

References 31 publications

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“…The simulated vapor deposition process is analogous to that reported earlier (9,32). Iterative cycles are repeated until a film with thickness of ∼35 σ bb is grown.…”

Section: Methodsmentioning

confidence: 99%

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Tunable molecular orientation and elevated thermal stability of vapor-deposited organic semiconductors

Dalal

Walters

Lyubimov

et al. 2015

Proc. Natl. Acad. Sci. U.S.A.

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199

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Physical vapor deposition is commonly used to prepare organic glasses that serve as the active layers in light-emitting diodes, photovoltaics, and other devices. Recent work has shown that orienting the molecules in such organic semiconductors can significantly enhance device performance. We apply a high-throughput characterization scheme to investigate the effect of the substrate temperature (T substrate ) on glasses of three organic molecules used as semiconductors. The optical and material properties are evaluated with spectroscopic ellipsometry. We find that molecular orientation in these glasses is continuously tunable and controlled by T substrate /T g , where T g is the glass transition temperature. All three molecules can produce highly anisotropic glasses; the dependence of molecular orientation upon substrate temperature is remarkably similar and nearly independent of molecular length. All three compounds form "stable glasses" with high density and thermal stability, and have properties similar to stable glasses prepared from model glass formers. Simulations reproduce the experimental trends and explain molecular orientation in the deposited glasses in terms of the surface properties of the equilibrium liquid. By showing that organic semiconductors form stable glasses, these results provide an avenue for systematic performance optimization of active layers in organic electronics.glasses | organic semiconductors | molecular orientation | physical vapor deposition | high-throughput characterization

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“…The simulated vapor deposition process is analogous to that reported earlier (9,32). Iterative cycles are repeated until a film with thickness of ∼35 σ bb is grown.…”

Section: Methodsmentioning

confidence: 99%

“…4, Inset). We used a previously described algorithm that mimics the essential features of the deposition process (Materials and Methods) (32). A small number of molecules is introduced to the simulation box in the gas phase and allowed to condense at the free surface of a growing film.…”

mentioning

confidence: 99%

Tunable molecular orientation and elevated thermal stability of vapor-deposited organic semiconductors

Dalal

Walters

Lyubimov

et al. 2015

Proc. Natl. Acad. Sci. U.S.A.

Self Cite

199

351

View full text Add to dashboard Cite

show abstract

“…10,18 This phenomenon was already predicted by random first order transition (RFOT) theory, 19,20 facilitated kinetic Ising model calculations 21,22 and vapour deposition simulations. 23 Experimentally, this phenomenon has also been observed using a variety of techniques in several systems, e.g. secondary mass ion spectroscopy (SIMS), 13,24 ellipsometry, 25 AC-calorimetry, 6,26 differential scanning calorimetry 17 and fast-scanning nanocalorimetry.…”

Section: Introductionmentioning

confidence: 99%

The role of thermodynamic stability in the characteristics of the devitrification front of vapour-deposited glasses of toluene

Ràfols‐Ribé

González-Silveira

Rodríguez-Tinoco

et al. 2017

Phys. Chem. Chem. Phys.

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Physical vapour deposition (PVD) has settled in as an alternative method to prepare glasses with significantly enhanced properties, providing new insights into the understanding of glass transition. One of the striking properties of some PVD glasses is their transformation into liquid via a heterogeneous mechanism that initiates at surfaces/interfaces. Here, we use membrane-based fast-scanning nanocalorimetry (10 4 K s À1) to analyse the variables that govern the transformation mechanism of vapourdeposited toluene glasses with different stabilities. Thin films ranging from 20 to 250 nm were prepared at deposition temperatures between 0.70 and 1.15 times the glass transition temperature. We show how a propagating growth front is the initial transformation mechanism in all the vapour deposited samples, revealing a clear tendency to faster front velocities for less stable samples. Contrary to other glassformers such as indomethacin, toluene shows a one-to-one relationship between limiting fictive temperature and front velocity. We associate this behaviour with the much simpler molecular geometry of toluene, which would prevent the presence of strong preferential molecular arrangements in the glass. However, the propagation distance of the growth front before the homogenous transformation mechanism dominates the transition is found to be dependent on the preparation conditions rather than on the thermal stability of the glass. Understanding the link between the growth variables and the properties of PVD glasses is crucial for finding and developing potential applications of this type of glass.

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“…The key recipe for the formation of such ultrastable glasses is to deposit the materials at substrate temperatures around 0.85T g . This allows molecules to utilize surface mobility and rearrange towards configurations with lower enthalpy [34]. These glasses have properties such as density, elastic modulus, enthalpy and specific heat, which would otherwise be obtained only if ordinary glasses were annealed for thousands of years [33,35,36].…”

mentioning

confidence: 99%