Collaborative Research: Atomic-Scale Hybrids, Tuning the IR Dielectric Function through Superlattice Design

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Non-Technical Description: The infrared spectral range offers a wealth of technological opportunities, including thermal imaging, ability to see through dust or clouds, chemical identification for medical diagnostics and hazard identification, to name a few. Unlike the visible spectral range where materials such as glass provide exceptionally high performance at extremely low cost, the infrared optical components are typically sensitive to water, opaque in the visible, expensive and/or brittle. Thus, identifying alternative materials or material platforms that can provide the basis of next generation infrared optics and light sources is highly desired. Within the infrared, many polar materials, such as silicon carbide, exhibit crystal vibrations that can be excited using light. This provides opportunities to compress long-wavelength infrared light to nanometer scale lengths, offering the potential to significantly reduce the size of infrared optics. However, these crystal vibrations are material specific and thus, finding the right material in the desired infrared frequency range is challenging. This project investigates novel hybrid materials composed of altering stacking thin layers with potential to modify their crystal vibrations in an effort to change its corresponding infrared properties. The collaborative research seeks to understand how these vibrations are influenced when the layer thickness is reduced to atom-scale thicknesses, and involves a multidisciplinary team of a material scientist, physicist and mechanical engineer to aid in realizing designer infrared materials deemed 'crystalline hybrids'. The project trains graduate and undergraduate students in semiconductor growth, infrared spectroscopy and characterization and theoretical descriptions of complex solids.Technical Description: This project seeks to develop a new class of materials called Crystalline Hybrids (XHs) that offers the promise for realizing user-defined infrared (IR) optical materials. These novel materials can serve as the basis of next generation IR optical components, sources and detector elements. A primary research goal of this collaborative program is to discover theory-guided principles for the rational design of XHs to meet a given application space. The XH approach seeks to modify polar optic phonons within atomically thin layers comprising a multilayered superlattice. Within these structures, the layer thicknesses will be less than the phonon mean-free-path, resulting in quantum confinement and frequency tuning of the vibrational state. Furthermore, the modified bonding at the multiple interfaces within the superlattice structures introduce new interfacial phonons. These modified phonon properties directly influence the infrared response of the material, as it is optic phonons that dominate the IR behavior of polar crystals. The research is focused on superlattices comprised of the near-lattice matched III-V semiconductors InAs, GaSb and AlSb, which eliminate external effects like strain and allow well-controlled experiments to be performed. The project involves a diverse group of graduate and undergraduate students who are trained in the basics of semiconductor growth, IR spectroscopy, theory and first-principles calculations of nanomaterials, enabling them to work at the frontiers of nanophotonics research. The collaboration between material scientists, physicists and engineers broadens the impact of this work.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.