Molecular modeling of vapor-deposited polymer glasses

Lin, Po‐Han; Lyubimov, Ivan; Yu, Lian; Ediger, M. D.; Pablo, Juan J. de

doi:10.1063/1.4876078

Cited by 35 publications

(51 citation statements)

References 45 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…We find that for T s > 850K the two different types of glasses have comparable densities whereas for T s < 850K the PVD glasses have a larger density than the melt-quenched glasses by up to 1.5%. The lower potential energy and the higher density of the PVD glasses are in good agreement with experimental findings for the ultrastable organic glasses [8,20], which shows that the stability in the two classes of materials follow a similar trend.…”

Section: Resultssupporting

confidence: 88%

Increased stability of CuZrAl metallic glasses prepared by physical vapor deposition

Bokas

Zhao

Morgan

et al. 2017

Journal of Alloys and Compounds

View full text Add to dashboard Cite

We carried out molecular dynamics simulations (MD) using realistic empirical potentials for the vapor deposition (VD) of CuZrAl glasses. VD glasses have higher densities and lower potential and inherent structure energies than the melt-quenched glasses for the same alloys. The optimal substrate temperature for the deposition process is 0.625×T g . In VD metallic glasses (MGs), the total number of icosahedral like clusters is higher than in the melt-quenched MGs. Surprisingly, the VD glasses have a lower degree of chemical mixing than the melt-quenched glasses. The reason for it is that the melt-quenched MGs can be viewed as frozen liquids, which means that their chemical order is the same as in the liquid state. In contrast, during the formation of the VD MGs, the absence of the liquid state results in the creation of a different chemical order with more Zr-Zr homonuclear bonds compared with the melt-quenched MGs. In order to obtain MGs from melt-quench technique with similarly low energies as in the VD process, the cooling rate during quenching would have to be many orders of magnitude lower than currently accessible to MD simulations. The method proposed in this manuscript is a more efficient way to create MGs by using MD simulations.

show abstract

Section: Resultssupporting

confidence: 88%

Increased stability of CuZrAl metallic glasses prepared by physical vapor deposition

Bokas

Zhao

Morgan

et al. 2017

Journal of Alloys and Compounds

View full text Add to dashboard Cite

show abstract

“…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%

“…Whereas one might expect all glasses to be isotropic because of their structural disorder, Yokoyama et al and other groups have shown that molecular orientation in vapor-deposited glasses can be quite anisotropic (3,4,8,9) and depend upon deposition conditions (3). It has recently been suggested that orientation resulting from deposition could be used as a figure of merit to identify promising compounds for these applications (10).…”

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

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

show abstract

“…[1][2][3] In particular, physical vapor deposition can prepare organic glasses with exceptional thermal stability if the deposition conditions are chosen appropriately; [4][5][6] transformation to the supercooled liquid has been observed to occur at temperatures up to 35 K higher than the glass transition temperature (T g ) of the liquidcooled glass. 7 Stable glasses also have high density 6,[8][9][10][11] and low enthalpy [5][6][7][12][13][14][15] and can exhibit useful anisotropic structures 16 as evidenced by birefringence, 10,11,17 dichroism, 17 and X-ray scattering. 14,15,18,19 These solid-state properties are lost on transformation to the equilibrium supercooled liquid, so high thermal stability is important for extending the range of applications for these materials.…”

Section: Introductionmentioning

confidence: 99%

Thermal stability of vapor-deposited stable glasses of an organic semiconductor

Walters

Richert

Ediger

2015

The Journal of Chemical Physics

Self Cite

View full text Add to dashboard Cite

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 Tg, 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 (TSubstrate) from 0.63 to 0.96 Tg, at many different annealing temperatures. We observe that the front velocity varies by over an order of magnitude with TSubstrate, 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 TSubstrate, suggesting universal behavior. These results may aid in designing active layers in organic electronic devices with improved thermal stability.

show abstract

Molecular modeling of vapor-deposited polymer glasses

Cited by 35 publications

References 45 publications

Increased stability of CuZrAl metallic glasses prepared by physical vapor deposition

Increased stability of CuZrAl metallic glasses prepared by physical vapor deposition

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

Thermal stability of vapor-deposited stable glasses of an organic semiconductor

Contact Info

Product

Resources

About