Rapid, template-free synthesis of macroscale semiconductor nanopatterns via tailored photoexcitation

Abstract

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 morphol. 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 av. E-field vector and with degrees of anisotropy related to the difference in orientation between the two input Efield 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 obsd. 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 addn. accurately reproduced the exptl. obsd. morphologies and indicated that the encoding process was a consequence of the fundamental light-matter interactions during growth. This photoelectrochem. deposition process is unique from other methods of generating ordered mesostructures with electrochem. means as no photomask, no photoactive substrate, no lithog. processing, nor any chem. 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 cm areas required only several minutes. Moreover, films were deposited from aq. soln. using oxide precursors at room temp. with low-intensity illumination (∼10 mW cm^(-2)).