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F8.09 - Light-Directed Growth of Complex Three-Dimensional Nanostructures in Photoresponsive Chalcogenide Films: Comparison of Nanophotonic Models and Experiments 
Date/Time:
April 24, 2014   4:30pm - 4:45pm
 
Speaker:
 
 
Se 
 
 
 
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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. Recently, we have reported a novel template-free photo-assisted electrodeposition technique in which ordered mesoscale Se-Te amorphous alloy structures with 50-500 nm scale features evolve spontaneously via dynamic feedback with a polarized monochromatic light source, requiring only mW/cm^2 power densities. These inorganic mesostructures 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. The lamellar stripes were found to have a period of approximately λ/2, where λ is the wavelength of light in the solution, and demonstrated aspect ratios greater than 10. [1] In contrast to conventional lithography, this technique utilizes time-dependent variations in the illumination conditions to directly write complex 3D structures in a bottom-up fashion, with morphology features depending on illumination wavelength, angle, polarization and intensity. Here, we present a simple quantitative nanophotonic model to describe the dynamic feedback process and gain insight into the physical mechanisms governing the temporal evolution of the system. We find that film morphological evolution occurs via faster growth at locations on the film surface with high local optical intensity. Our results are well described by a model that postulates a locally modified electrochemical driving force for film growth proportional to the light-induced quasi-Fermi separation. This model leads to complex lamellar, spiral and branched structures that closely resemble those seen in experiments. Additionally, we demonstrate a Monte Carlo algorithm for interface motion with rate coupled to intensity calculations from full wave finite difference time domain electrodynamic simulations, which allows us to visualize the formation of the phototropic structures. We will discuss the use of this quantitative model to predict formation of complex three-dimensional structures and early stages of growth on patterned surfaces that support resonant modes.[1] B Sadtler, S P Burgos, N A Batara, J A Beardslee, H A Atwater, N S Lewis, “Phototropic growth control of nanoscale pattern formation in photoelectrodeposited Se-Te films”, 2013, Proceedings of the National Academy of Sciences, in press.
 


 
 
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