Thursday, 1 June 2017: 11:00
Grand Salon D - Section 19 (Hilton New Orleans Riverside)
Template-free photoelectrodeposition of semiconducting chalcogen alloys resulted in the spontaneous generation of highly periodic nanostructured films over macroscopic length scales. The exact nature of the optical excitation was encoded in the deposit morphology in terms of the feature sizes, periodicities, anisotropies, and orientations of the nanoscale pattern. The use of unpolarized light generated isotropic morphologies consisting of ordered arrays of nanopores whereas linearly polarized light resulted in a highly-anisotropic lamellar morphologies with the long axes of the patterns aligned along the E-field vector. Utilization of two same-wavelength, non-orthogonally polarized sources simultaneously generated patterns oriented along the average E-field vector and with degrees of anisotropy related to the difference in orientation between the two input E-field vectors and the phase correlation between the sources. The illumination spectral profile encoded the pattern periodicity and feature width. A single periodicity in a single in-plane direction was consistently observed even with the use of broadband and multimodal spectral profiles and this periodicity was found to be sensitive to all investigated tuning of such profiles. The incidence of the illumination set the direction the material grew from the substrate, mimicking natural phototropism: grazing illumination resulted in growth at significant angle to the surface normal. Modeling of the growth using a combination of full-wave electromagnetic simulations of light absorption and scattering coupled with Monte Carlo simulations of mass addition accurately reproduced the experimentally observed morphologies and indicated that the encoding process was a consequence of the fundamental light-matter interactions during growth.
This photoelectrochemical deposition process is unique from other methods of generating ordered mesostructures with electrochemical means as no photomask, no photoactive substrate, no lithographic processing, nor any chemical templating agents (ligands, surfactants) were utilized. Illumination was simply conformal over the entire substrate surface (no far-field spatial modulation was used nor required). Complete nanoscale patterning over cm2 areas required only several minutes. Moreover, films were deposited from aqueous solution using oxide precursors at room temperature with low-intensity illumination (~10 mW cm-2). Thus, this process displays significant potential to possibly enable the generation of complex morphologies for functional materials without several limitations imposed by traditional fabrication techniques.