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observed in other publications under pulsed illumination or
depending on the material 23,36,37 . In the experiment, the dark
regions are identical with the elevated areas, which, when
compared with the simulation, equates to a full movement of
the material out of the illuminated regions. This is consistent
with the significantly longer illumination times of 20 h in the
experiment, compared to only a few picoseconds in the simulation.
We conclude that very short cw or pulsed illumination
can induce a double peak with maxima at the interfaces of illuminated
and dark regions, while a longer illumination leads
to a maximum in the dark region.
In both the simulation and in the experiment, the polarization
of the incident light has no or only a minor impact on
the surface modulation. In the experiment, small bead-like
structures of 10 nm to 20 nm height emerge in the valleys.
These are not predicted in the simulation. This difference
could again be due to the different time and length scales of
simulation and experiment. The illumination times of only picoseconds
and stripe sizes of a few nanometres investigated
in the simulation cannot be realized in these experiments and
vice versa.
The reason for this rare (virtual) independence of SRG
formation on polarization could be the high fluence used in
these experiments. While in most SRG experiments, the
azopolymer films are illuminated for a few seconds to several
minutes with intensities in the range of tens to hundreds
of mWcm −2 , here the films are illuminated for 20 hour
with over 150 mWcm −2 and thus with a significantly higher
fluence 4,7,16 . Also in our simulations, the fluence is very
high with ... photons per .. Our experiment and simulation
are thus consistent with publications claiming polarizationindependent
SRG formation under high-intensity cw and
pulsed irradiation 7,20,21,23–26 .
With regard to the cause of photomigration, the simulations
clearly show that the conversion of light-energy into local heat
is a prerequisite for this phenomenon to occur. In the fluence
regime studied here, mass transport appears to take place in
the direction of the negative temperature gradient and can thus
be described my the theory of thermal diffusion 38 .
IV.
CONCLUSIONS
We have carried out a combined experimental and theoretical
study of the surface relief grating formation in the azopolymer
poly-disperse-orange3-methyl-methacrylate. On the experimental
side, azopolymer polymer films were illuminated
with light patterns of bright and dark stripes created by a spatial
light modulator. The surface profile was subsequently
characterized using atom force microscopy. Thus is could be
established that mass transport occurred away from the bright
stripes into the dark stripes. Furthermore, the polarisation direction
was seen to have a minor effect. These experimental
findings were corroborated by atomistic molecular dynamics
simulations that explicitly modelled the photoisomerisation
dynamics and light polarisation. The simulations further
showed that local heating due to light-absorption is necessary
for mass transport to occur. In the high-fluence regime investigated
in this work, mass transport appears to be dominated by
the temperature gradient rather than any more subtle effects
related to the photoisomerisation dynamics.
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ACKNOWLEDGMENTS
We wish to acknowledge the support of the author community
in using REVTEX, offering suggestions and encouragement,
testing new versions, . . . .
DATA AVAILABILITY STATEMENT
The data that support the findings of this study are available
from the corresponding author upon reasonable request.
Appendix A: A little more on appendixes
1. A subsection in an appendix
1 H. Zhang, “Reprocessable photodeformable azobenzene polymers,”
Molecules 26, 4455–4484 (2021).
2 P. Weis, W. Tian, and S. Wu, “Reprocessable photodeformable azobenzene
polymers,” Chem. Eur. J. 24, 6494–6505 (2021).
3 S. Lee, H. S. Kang, and J.-K. Park, “Directional photofluidization lithography:
Micro/nanostructural evolution by photofluidic motions of azobenzene
materials,” Adv. Mater. 24, 2069–2103 (2012).
4 C. J. Barrett, J. Mamiya, K. G. Yager, and T. Ikeda, “Photo-mechanical
effects in azobenzene-containing soft materials,” Soft Matter 3, 1249–1261
(2007).
5 K. G. Yager and C. J. Barrett, “Photomechanical surface patterning in azopolymer
materials,” Macromolecules 39, 9320–9326 (2006).
6 A. Natansohn and P. L. Rochon, “Photoinduced motions in azo-containing
polymers,” Chem. Rev. 102, 4139–4175 (2002).
7 N. K. Viswanathan, D. Y. Kim, S. Bian, J. Williams, W. Liu, L. Li,
L. Samuelson, J. Kumar, and S. K. Tripathy, “Surface relief structures on
azo polymer films,” J. Mater. Chem. 9, 1941–1955 (1999).
8 W.-C. Xu, S. Sun, and S. Wu, “Photoinduced reversible solid-to-liquid transitions
for photoswitchable materials,” Angew. Chem. Int. Ed. 58, 9712–
9740 (2019).
9 J. Konieczkowska, K. Bujak, and E. Schab-Balcerzak, “A short review
of the photomechanical effect in azo-containing amorphous (glassy) polymers,”
eXPRESS Polymer Letters 15, 459–472 (2021).
10 S. De Martino, F. Mauro, and P. Netti, “Photonic applications of azobenzene
molecules embedded in amorphous polymer,” La Rivista del Nuovo
Cimento 43, 599–629 (2020).
11 M. Hendrikx, A. P. Schenning, M. G. Debije, and D. J. Broer, “Lighttriggered
formation of surface topographies in azo polymers,” Crystals 7,
231 (2017).
12 T. Fukuda, H. Matsuda, T. Shiraga, T. Kimura, M. Kato, N. K. Viswanathan,
J. Kumar, and S. K. Tripathy, “Photofabrication of surface relief grating on
films of azobenzene polymer with different dye functionalization,” Macromolecules
33, 4220–4225 (2000).
13 C. J. Barrett, A. L. Natansohn, and P. L. Rochon, “Mechanism of optically
inscribed high-efficiency diffraction gratings in azo polymer films,” The
Journal of Physical Chemistry 100, 8836–8842 (1996).