Manipulation of Nanoscale Pattern Formation in Photoelectrochemically Deposited Chalcogenide Films Using Multiple Beam Illumination

Wednesday, 27 May 2015: 14:40
Williford Room C (Hilton Chicago)
A. Carim, N. Batara, A. Premkumar, H. A. Atwater (California Institute of Technology), and N. S. Lewis (Joint Center for Artificial Photosynthesis)
Photoelectrochemical deposition of semiconducting chalcogenide films resulted in the spontaneous generation of ordered nanostructures wherein the pattern developed is a function of the illumination utilized during growth. Film adopted an ordered, highly anisotropic lamella-type pattern when deposited under conformal illumination with polarized light. Feature size and pitch were controlled the illumination wavelength, direction of anisotropy by the polarization vector and the growth direction by the incident light vector. In order to progress toward generation of intricate, 3-dimensional architectures for specific applications, the manipulation of the pattern formation by utilizing simultaneous illumination from multiple discrete beams during deposition has been investigated. Illumination with two parallel polarized, narrowband sources with two discrete mean wavelengths resulted in patterns with periods that were intermediate of those that would be expected for either source alone and a function of the relative source intensities. The use of two linearly polarized sources with polarization vectors separated by an acute angle produced structures oriented in a direction between the two polarization vectors: this direction was a function of the relative intensities and mean wavelengths of the sources. Illumination with orthogonally polarized sources provided for the generation of mesh-type structures wherein the periodicity and height of pattern in the two orthogonal, in-plane directions could be controlled independently by varying the intensities and wavelengths of the sources.  Modeling of the growth was achieved with a Monte Carlo process wherein the probability of mass-addition was weighted based on simulations of the light-matter interactions in the films.

This photoelectrochemical deposition process is unique from other methods of generating ordered mesostructures with electrochemical means as no photomask, no photoactive substrate, no physically patterned substrate, nor any chemical templating agents (ligands, surfactants) were utilized. Additionally, tuning the deposition potential and electrolyte along with the illumination has enabled control of the material composition. The same general morphology was observed for a range of varying materials. Thus, this process displays significant, increasing potential to possibly enable the generation of complex morphologies for functional materials without some of the limitations imposed by traditional fabrication techniques.