Macroscale Films of Highly Ordered Periodic 3D Semiconductor Nanostructures Generated Via Lithography-Free Photoelectrodeposition

Wednesday, 4 October 2017: 17:10
Chesapeake 6 (Gaylord National Resort and Convention Center)
A. I. Carim, N. A. Batara, A. Premkumar, H. A. Atwater, and N. S. Lewis (California Institute of Technology)
Electrodeposition of Se-Te alloy films under illumination spontaneously generates nanopatterned films with significant periodic order. The feature sizes, periodicities, anisotropies, and orientations of the nanoscale pattern are a function of the exact nature of the optical excitation. Isotropic morphologies consisting of ordered arrays of nanopores were generated using unpolarized illumination whereas linearly polarized light resulted in highly-anisotropic lamellar morphologies with the long axes of the patterns aligned along the E-field vector. The use of two non-orthogonal 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 pattern periodicity was encoded by the illumination spectral profile. A single periodicity in single spatial direction was only generated even with the use of broadband and multimodal spectral profiles and multiple polarization inputs and the 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. Also, additional 3D morphological complexity could be directed by utilizing temporal changes in the illumination; for example, zig-zag structures resulted from oscillation of the illumination incidence back and forth across the surface normal and woodpile structures were generated by periodically switching between orthogonal polarization states.

The nanopatterning process occurred without the use of any type of physical or chemical templating agents: no photomask, patterned substrate nor surfactants/ligands were used to influence the morphology. 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 successfully reproduced the experimentally observed morphologies and indicated that morphology development was a consequence of the fundamental light-matter interactions during growth.