Collaborative Research: Programmable Metal-Assisted Chemical Etching for Three-Dimensional Functional Metamaterials

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Metamaterials are artificially structured materials that exhibit unusual, but advantageous, electromagnetic properties not readily found in nature. The special properties arise from regions of complex structural features organized in a periodic arrangement. Currently, the fabrication of the optical metamaterials is largely based on intrinsic two-dimensional patterning processes, with limited demonstrations of three-dimensional optical metamaterials mostly based on polymer structures. There are no manufacturing techniques for direct fabrication of three-dimensional crystalline semiconductor-based metamaterials. This award explores a unique programmable metal-assisted chemical etching process for the scalable nano-manufacturing of three-dimensional functional metamaterials. Such an approach will overcome the current roadblocks towards integrated photonics based on functional metamaterials to enable complete control of light. The versatile fabrication methodology and materials functionalities will inevitably impact the production of three-dimensional electronics and photonics, tissue engineering, and energy conversion/storage. By engaging students including women and minorities in this emerging field of research, the award activities will help ensure their competence and leadership in today's global environment. Outreach activities targeting high school teachers, students, and the general public will raise awareness and prepare our future workforce to embrace the emerging US nano-manufacturing industry.Metal-assisted chemical etching is an anisotropic solution-based etching method that defies the textbook definition of wet etching. By this technique, three-dimensional high aspect-ratio semiconductor nanostructures are formed by engraving patterned metal template into the body of the semiconductor. Under controlled conditions, etching occurs only at the interface between the metal and the semiconductor. As a result, the metal layer descends or digs into the semiconductor as the underlying semiconductor is eroded. In this study, as etching proceeds, a magnetic field is programmed to guide the movement of ferromagnetic-metal catalyst and arbitrary three-dimensional curvilinear nanostructures are formed by programming the trajectory of the metal catalyst as it engraves into the body of Si or higher index III-V semiconductors. Because of its compatibility with integrated circuit manufacturing, this method is scalable for high-volume manufacturing of highly desired functional optical metamaterials. The collaborative effort with complementary expertise in nanofabrication and photonics, respectively, is positioned to provide a leap-ahead advance in capabilities for manufacturing three-dimensional micro- and nano-scale semiconductor and metallo-dielectric structures with unprecedented control of shape and dimensions, and for development of novel functional optical and other materials and devices.