Mark D. Ediger (University of Wisconsin-Madison) presents at the Fred Kavli Special Symposium: From Unit Cell to Biological Cell at the APS March Meeting 2019 in Boston, MA. View abstract below. ------------------------------------------------- The Design And Growth Of Ultra-Stable Glasses ------------------------------------------------- Glasses are generally regarded as highly disordered and the idea of "controlling" molecular packing in glasses is reasonably met with skepticism. However, as glasses are non-equilibrium materials, a vast array of amorphous structures are possible in principle. Physical vapor deposition (PVD) allows a surprising amount of control over molecular packing in glasses and can be used to test the limits of amorphous packing in two ways. PVD can prepare glasses that approach the limits of the most dense and lowest energy amorphous packings that are possible. The activation barriers for rearrangements in these materials are very high, giving rise to high thermal and chemical stability. In addition, PVD allows control over anisotropic packing in glasses. For rod-shaped molecules, for example, glasses can be prepared in which the molecules have a substantial tendency to stand-up or lie-down relative to the substrate. As these materials have applications in organic electronics, an important question is: How much anisotropic order can be added to a glass without destroying key technological advantages such as macroscopic homogeneity? The high density and anisotropic packing of PVD glasses can be explained by a mechanism that is "anti-epitaxial" as structure is templated by the top surface rather than by the underlying substrate.

1. The design and growth of ultra-stable glasses:
Exploring the limits of amorphous packing
Camille Bishop, Madeleine Beasley, Kushal Bagchi, Yue Qiu, Lian Yu,
Mark Ediger (UW-Madison)
Hai Bin Yu, Ranko Richert (Arizona State University)
NSF CHE, NSF MRSEC, and DOE BES
1

2. Glasses are solids with greater variation of
local structure than crystals – and are better
materials for some applications
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3. Knowledge of our universe – brought to you by glass!
3Hubble image
Hubble space
telescope mirror
Macroscopic homogeneity,
compositional flexibility

4. Modern communications depends upon glass
4NASA image
CBS News image
techepics.com
Optical fibers Organic light emitting
diode (OLED) display
Processability

5. The active layers in OLED displays are vapor-deposited organic
semiconductors
• Macroscopic
homogeneity
• Compositional
flexibility
• Non-equilibrium
=> process control
5TPD

6. Can we make better glass?
• What is the densest
possible glass than can
be prepared from a given
molecule?
• What is the most
anisotropic glass that
can be prepared without
sacrificing macroscopic
homogeneity and
compositional flexibility?
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7. Glasses are non-equilibrium
solids without long range order
7Plazek and Magill, JCP 1966
Molarvolume(ml/mol)
Temperature (°C)
crystal
super-
cooled
liquid
glasses
TNB
liquid
Tg

8. Glasses are non-equilibrium
solids without long range order
8Plazek and Magill, JCP 1966
Molarvolume(ml/mol)
Temperature (°C)
crystal
super-
cooled
liquid
glasses
TNB
Can we make these high
density states that are
inaccessible by liquid
cooling? What properties?
Is there an end to this line - a
perfectly packed amorphous
state (an “ideal glass”)?
liquid
Tg

9. The ideal glass?
9Ediger and Harrowell, JCP 2012; Data from Chang and Bestul, JCP 1972
Vanishing
configurational
entropy (by
extrapolation)
defines ideal glass
packing
Random first order
transition predicted
(Kirkpatrick,
Thirumalai and
Wolynes), but liquid
cooling won’t get us
there.

10. Physical vapor deposition can prepare organic
glasses with high density and high kinetic stability
Dalal et al., JPC Lett. (2012) Equivalent to 103 – 1010 years of aging
10
ChangeinFilmThickness(%)
High kinetic stability

11. Log (time)
Retention of
glass packing
upon heating
x 104
Poorly packed glass Well-packed glass
Physical vapor deposition (PVD) utilizes surface mobility to produce
glasses with high density and high kinetic stability (“stable glasses”)
Swallen, Kearns, et al., Science (2007) ; Berthier and Ediger, Physics Today (2016)

12. Computer simulations support surface
equilibration mechanism
• Lyubimov et al., JCP 143, 094502 (2015)
• Coarse-grained TPD
• Low energy; high kinetic stability
12
• Berthier et al., PRL 119, 188002 (2017)
• Polydisperse spheres
• Deposition rate plays the role of cooling
rate

13. PVD glasses can closely approach ideal glass packing
(Ramos, Oguni, Ishii, and Nakayama)
13Adapted from Ramos, Oguni, Ishii, Nakayama, J. Phys. Chem. B (2011)
PVD glasses of
ethylbenzene deposited
as low as 0.92 Tg (1.04 TK)
have enthalpy expected for the
equilibrated supercooled
liquid.
end of the line for the
liquid state – the ideal glass
Liquid-cooled
glass
TK
PVD glasses

14. PVD glasses can closely approach ideal glass packing,
consistent with random first order transition scenario
14
Beasley, Bishop, Kasting, Ediger (unpublished)
PVD glasses of
ethylbenzene deposited
as low as 0.90 Tg (1.02 TK)
have density expected for the
equilibrated supercooled
liquid
end of the line
for the liquid state
– the ideal glass
Madeleine Beasley

15. 15
How important is a 1%
density increase?
Substantial increases in
photostability
Qiu, Antony, de Pablo, Ediger, JACS (2016)
• 50X increase in
photostability
• Increased density
correlates with OLED
efficiency and device
lifetime (Gonzoles-
Silveira/Rodriguez-
Viejo, Sci. Adv. 2018)
Yue Qiu

16. Residual motion suppressed in high density PVD glasses
16
Yu, Richert et al., PRL 115, 185501 (2015)
Possible physical
picture: Orientation
exploration in a
cone of ~ 3°
(vapor deposited
glass) instead of
~ 7 °(liquid-
cooled glass)

17. Residual motion also be suppressed by aging the liquid-
cooled glass, but it takes a long time
17
For toluene, the
strength of sub-Tg relaxation
appears to an another
indication of approach to
ideal glass state
Yu, Richert et al., PRL 115, 185501 (2015)

18. Stable metallic glasses
• Luo et al., Nature Comm. (2018)
• Zr46Cu46Al8 metallic glass
• Ion beam assisted deposition
• Increased onset temperature
• Increased resistance to
crystallization
18

19. Stable chalcogenide glasses
• Zhang et al., J. Phys. Chem. B. (2017)
• Sb2Se3 chalcogenide glass
• Increased resistance to crystallization 19

20. Stable polymer glasses
20
• Yoon et al, Macromolecules (2017)
• Vacuum pyrolysis of fluoropolymer
• Low enthalpy
• Guo et al., Nat. Mater. (2012)
• MAPLE deposition of poly(methyl
methacrylate)
• Increased kinetic stability

21. 21
What determines the structure of a glass?
Molarvolume(ml/mol)
Temperature (°C)
crystal
super-
cooled
liquid
glasses
TNB
the (isotropic) liquid the (anisotropic) interface

22. PVD glass
on silicon wafer
22
Grazing incidence wide angle x-ray scattering

23. Counts
2D GIWAXS data from Kushal Bagchi
and Camille Bishop.
qxy
qz
23
A sampling of structures of vapor-deposited organic solids.
Can we predict and control?

24. Molecular orientation and anisotropic packing
improves OLED operation
Yokoyama, D. J. Mater. Chem., 2011, 21, 19187-
19202.
N
N
BSB-Cz
Improve charge mobility Improve outcoupling
efficiency
Metal Electrode
Organic Layer
Glass
Substrat
e
Electrode
24

25. PVD glasses prepared from two rod-
like molecules
25Gomez, et al., Soft Matter (2016)

26. 26
Insert giwaxs data here
Itraconazole Posaconazole
Also aligned smectic layering!
PVD glasses with smectic order from
both mesogen and a non-mesogen
Bishop, et al. Unpublished
Aligned smectic layering!

27. Molecular orientation at
liquid surface controls
glass structure
27Ediger, de Pablo, Yu, Acc. Chem. Res. (2019)

28. t = 0 s
Bishop et al. (unpublished)
Smectic-like PVD glasses of posaconazole transform into the
isotropic liquid at Tg + 5 K
t = 120 st = 60 s
t = 300 st = 240 st = 180 s

29. 29
PVD glasses
• useful material properties: high
photostability, low residual mobility
• consistent with “ideal glass” scenario
• structure is inherited from free surface
(“anti-epitaxy”), allowing control over
anisotropy in glasses
• highly anisotropic glasses can be
prepared
• is there a limiting anisotropy, beyond
which amorphous materials cannot be
prepared?
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