The Center for Photonic and Multiscale Nanomaterials (C-PHOM) is a National Science Foundation Materials Research Science and Engineering Center, established in 2011. The center’s research activity is focused on two Interdisciplinary Research Groups (IRG’s): wide-bandgap nanostructured materials for quantum light emitters and advanced electromagnetic metamaterials and near-field tools. The center is housed primarily at the University of Michigan; the Metamaterials IRG is a partnership between the University of Michigan and Purdue University. Other participating institutions include the University of Texas at Austin, University of Illinois Urbana Champaign, Wayne State University, and City College of CUNY.
C-PHOM’s activities are focused on two IRG’s and a coordinated program in diversity, education, and human resources development (EHRD). IRG1 is dedicated to wide-bandgap nanostructured materials for quantum light emitters. The program develops wide-gap materials, particularly GaN-based nanostructures, establishing inorganic semiconductor nanophotonic structures with large bandgap and high exciton binding energy for high-efficiency visible light emitters, lasers, energy conversion, and novel quantum devices. The scope of the research includes the epitaxy and synthesis of GaN-based nanostructures, their structural, electrical, and optical characterization, their application in laser spectroscopy and quantum optical studies, investigation of strong coupling phenomena, polariton lasing, high-efficiency visible LEDs, and microcavity lasers. This effort is centered at the University of Michigan, with partners at the University of Illinois Urbana Champaign and City College CUNY.
IRG2 is focused on advanced electromagnetic metamaterials (MM’s) and near-field tools. Metamaterials are nanostructured mixtures that behave as homogeneous optical materials with electromagnetic properties unattainable with naturally existing materials, such as negative refraction, cloaking, plasmonic hot spots, and super-resolution. This IRG investigates MM’s – particularly chiral, quasiperiodic and hyperbolic MM’s – and MM-inspired structures with unusual properties such as near-field plates and hyperlenses, and develops understanding leading to potential applications in communication, sensing, and imaging (notably sub-wavelength imaging). The IRG consists of a partnership between the University of Michigan and Purdue University, and additional collaborations with Wayne State University and the University of Texas at Austin. Both IRG’s include extensive interactions with national labs (Sandia, Argonne, and NIST) and with overseas institutions.
A key feature of the center is that it provides a framework for the close integration of research with educational and outreach initiatives, at the high school, undergraduate, graduate, and postdoctoral levels. Specific programs include undergraduate involvement in MRSEC research via both a Michigan and an international (“City of Light”) REU program, a focused program for regional high school students from schools with large underrepresented group enrollment, a coordinated system for recruiting underrepresented groups into higher education, and an entrepreneurship program to train PhD students and postdocs and encourage translation of technology developed in the center.
Multiscale Materials for Nanophotonics
The development of new materials has often proven to be the foundation for revolutionary advances in both science and technology; optical materials, for example, are key to high-speed data transmission, through such applications as diode lasers, modulators, detectors, and low-loss optical fibers. The past decade has seen the emergence of powerful techniques to synthesize and control materials on multiple length scales. In photonics, for example, one can now tailor electronic wavefunctions through quantum confinement using materials structured on the 1-10 nm length scale. Control of optical-frequency electromagnetic modes, however, is managed by structures whose characteristic size is on the order of the fraction of a wavelength – typically 10-1000 nm. These structures may range from metamaterials (in which the material nanostructure leads to a homogeneous effective medium) to photonic crystals and microcavities (in which a periodic dielectric structure leads to modification of the optical modes via diffraction). In a multiscale composite, the material structure is controlled on the nanometer to micron scale and beyond, leading to simultaneous control of both the electronic or excitonic properties and the electromagnetic modes of the system. For example, a dense system of quantum dots (QDs) behaves as a continuous medium for light while acting as a set of non-interacting units for the strongly confined electrons; incorporation into a photonic crystal enables manipulation of the light modes interacting with the QD. The control of light-matter interactions leads to such phenomena as enhanced or inhibited light emission, strong coupling (cavity-QED) effects, and single-quantum-dot quantum logic gates.
Materials that are engineered to simultaneously access these multiple length scales are known as multiscale materials. Their development constitutes one of the most exciting frontiers in materials research today. Nanophotonics, defined as the use of multiscale materials to control light-matter interactions through both the electronic wavefunctions and sub-wavelength properties of confined light fields, stands to benefit immensely from the thorough understanding and exploitation of such novel structures.