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Published December 3, 2013 | Supplemental Material + Published
Journal Article Open

Phototropic growth control of nanoscale pattern formation in photoelectrodeposited Se-Te films


Photoresponsive materials that adapt their morphologies, growth directions, and growth rates dynamically in response to the local incident electromagnetic field would provide a remarkable route to the synthesis of complex 3D mesostructures via feedback between illumination and the structure that develops under optical excitation. We report the spontaneous development of ordered, nanoscale lamellar patterns in electrodeposited selenium–tellurium (Se–Te) alloy films grown under noncoherent, uniform illumination on unpatterned substrates in an isotropic electrolyte solution. These inorganic nanostructures exhibited phototropic growth in which lamellar stripes grew toward the incident light source, adopted an orientation parallel to the light polarization direction with a period controlled by the illumination wavelength, and showed an increased growth rate with increasing light intensity. Furthermore, the patterns responded dynamically to changes during growth in the polarization, wavelength, and angle of the incident light, enabling the template-free and pattern-free synthesis, on a variety of substrates, of woodpile, spiral, branched, or zigzag structures, along with dynamically directed growth toward a noncoherent, uniform intensity light source. Full-wave electromagnetic simulations in combination with Monte Carlo growth simulations were used to model light–matter interactions in the Se–Te films and produced a model for the morphological evolution of the lamellar structures under phototropic growth conditions. The experiments and simulations are consistent with a phototropic growth mechanism in which the optical near-field intensity profile selects and reinforces the dominant morphological mode in the emergent nanoscale patterns.

Additional Information

© 2013 National Academy of Sciences. Edited by Harry B. Gray, California Institute of Technology, Pasadena, CA, and approved October 8, 2013 (received for review August 16, 2013). Published online before print November 11, 2013. We thank Chi Ma for advice on SEM imaging. XPS was performed at the Molecular Materials Research Center in the Beckman Institute at the California Institute of Technology. SEM and EDS were performed at the Analytical Facility in the Geological and Planetary Sciences Division at the California Institute of Technology. This work is part of the "Light–Material Interactions in Energy Conversion" Energy Frontier Research Center funded by the US Department of Energy, Office of Science, Office of Basic Energy Sciences, under Award DE-SC0001293. B.S. acknowledges the Beckman Institute of the California Institute of Technology for a postdoctoral fellowship. Author contributions: B.S., H.A.A., and N.S.L. designed research; B.S., S.P.B., N.A.B., and J.A.B. performed research; B.S., S.P.B., N.A.B., and J.A.B. analyzed data; and B.S., H.A.A., and N.S.L. wrote the paper. Conflict of interest statement: N.S.L. and B.S. have published a manuscript with Editorial Board Member Harry B. Gray within the last 24 months.

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Published - Sadtler_2013_PNAS.pdf

Supplemental Material - sapp.pdf


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