| AVS 63rd International Symposium & Exhibition | |
| Thin Film | Wednesday Sessions |
| Session TF+MI+NS-WeM |
| Session: | ALD and Nanostructures |
| Presenter: | Robin E. Rodriguez, University of Michigan, Ann Arbor |
| Authors: | R.E. Rodriguez, University of Michigan, Ann Arbor D. Das, University of Michigan, Ann Arbor S.P. Agarwal, University of Michigan, Ann Arbor W. Shang, Shanghai Jiao Tong University, China T. Deng, Shanghai Jiao Tong University, China N.P. Dasgupta, University of Michigan, Ann Arbor |
| Correspondent: | Click to Email |
Hierarchical nanostructures found in biology have unique properties that inspire bio-mimetic engineering. These natural nanostructures present design principles of bottom-up nanomanufacturing for materials with tunable properties. For example, structural coloration is a phenomenon observed in a wide range of natural materials that take advantage of nanoscale hierarchical structures to tune their reflection and absorption properties through periodic diffraction and photonic resonances. Here we demonstrate bio-templating via Atomic Layer Deposition (ALD) as an approach to manufacture atomically-precise synthetic materials that manipulate the natural structural coloration found in Morpho butterfly wings for enhanced photocatalytic activity.
Until recently, conventional approaches to bio-templated nanomaterial synthesis have been limited in their ability to create highly conformal 3-D interfaces between temperature- and chemically-sensitive bio materials and functional thin films. ALD is uniquely suited for scalable and conformal bio-templating, which allows us to use the nanoscale structural complexity that nature provides to tune the interfacial properties of natural systems by coating them with functional materials. By varying the geometric and optical properties of the surface, ALD is able to tune structural coloration to manipulate the light absorbing and photocatalytic properties of natural materials with nanostructured surfaces.
Morpho butterflies are particularly interesting examples of structural coloration, which occurs due to hierarchical nanostructures on their wing surfaces. The combination of strong photonic resonances and high surface area in these wings represent an ideal template for photocatalysis. To demonstrate this, proof-of-concept tests were performed on Morpho wings coated by ALD of TiO2 and ZnO. Electron microscopy images showed conformal coating of the wing geometries at the nanoscale. The structural coloration of the butterfly wings could be tuned using this approach, which was modeled using finite-difference time-domain simulations of the modified wing geometry. The viability of this approach was further demonstrated in the photocatalytic degradation of methylele blue dyes in water, which led to an increase in photocatalytic activity relative to planar thin film samples. The ALD deposited materials show superior photocatalytic activity which was attributed to enhanced light absorption and increased surface area from the butterfly’s hierarchical structures.