Programmable Assembly of Semiconductor Mesostructures via Artificial Phototropism

Plants direct the addition of new biomass to optimize collection of solar insolation via the phototropic response. Artificial phototropism enables the programmable assembly of complex 3D nanoarchitectures with instruction by an incoherent, unstructured, mW cm^-2 intensity light beam. Artificial phototropism has been demonstrated via the light-mediated electrochemical assembly of semiconductor deposits from solution-phase precursor ions. Ordered nanoscale features were uniformly assembled over full macroscale (cm²) areas with feature heights on the order of several um with growth times < 5 min despite no use of patterning or masking agents. In-plane anisotropy was a function of the input polarization. Linearly polarized light resulted in anisotropic lamellar structures with in-plane orientations set by the polarization direction. The structure pitch was dependent on the spectral distribution of the input light with shorter wavelengths effecting higher feature densities. The out-of-plane growth direction was related to the propagation direction of the input light. Time-varying optical inputs enabled programming of 3D intricacy by evolving the in-plane structure along the out-of-plane dimension, e.g. an abrupt reduction in the input wavelength resulted in a concomitant increase in the interfacial density resulting in tuning fork structures. Additional morphological control has also been effected by using multiple simultaneous illumination inputs. Optically based growth modeling indicated that assembly was directed by evolution of the growth front to maximize spatial anisotropy in light collection.