Understanding and controlling optical excitations in individual hybrid nanostructures

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Hybrid nanostructures, the combination of two or more nanoscale materials to form a new heterostructure, are being actively pursued for a number of potential applications including lightharvesting, quantum dot lasers, chemical and biological sensing, and quantum computation. This interest is driven by the fact that the integration of two nanoscale material systems can lead to structures that exhibit novel properties, such as, enhanced photoluminescence, chemical activity, or carrier transfer, which result from the coupling between the individual components. For example, metals and semiconductors are two classes of materials with very different properties and combining them to form hybrid nanomaterials is of fundamental interest. Whereas metals can confine light on the nanoscale, semiconductors provide switching functionality and their combination promises high-density ultrafast nanophotonic integrated circuitry. Consequently, however, the development and control of the potentially unique properties found in hybrid nanostructures requires a thorough understanding of the coupling between the hybridized component materials.Intellectual Merit - This proposal focuses on exploring the fundamental microscopic mechanisms governing the optical excitations of two specific hybrid material systems of common interest, namely (1) quantum-dot/quantum-well semiconductor based hybrid nanostructures coupled via tunneling and (2) metal/semiconductor hybrid nanostructures coupled via their exciton and plasmon resonances. The goal of the proposed research is to elucidate the mechanisms governing the optical response and energy transfer in well-defined nanoscale hybrid nanostructures. Establishment of the relationships between structure and function in these systems would lead to disruptive new knowledge with impact on a range of applications, including plasmonic and quantum dot lasers, biosensors, and energy conversion. The core innovation in this proposal lies in the fabrication, optical probing and simulation of novel nanoscale hybrid structures and architectures whose geometrical parameters can be systematically tuned.Exploring these hybrid material systems requires a concerted effort in nanofabrication, coherent optical spectroscopy and theoretical modeling, a fundamental reason for proposing an international collaboration between an American and German research team. The American team consists of researchers at the University of Arkansas who are partners with the University of Oklahoma in an NSFsupported Materials Research Science and Engineering Center. This team is especially talented in the growth by molecular beam epitaxy, characterization by scanning tunneling microscopy, and the characterization of the optical behavior of nanostructures and the interactions between them. The German team consists of researchers at the Institut für Physik, at the University of Oldenburg, who have many years of experience in the development and application of ultrafast and nanoscale optical spectroscopy tools to study the coherent optical behavior of both single and arrays of hybrid nanostructures. Together, both teams have the experience, talent, and infrastructure to break new ground in the understanding of the material science and physics of coupling in hybrid nanostructures. The potential for a strong team effort, which has already begun to form over the last year and a half, is evidenced by exchange visits between both teams as well as recent collaborative publication.Broader Impact – From a purely technical point of view, this proposal presents an opportunity for the development of a detailed microscopic understanding of the interactions between the elementary optical excitations of a semiconductor quantum dot, or exciton, and the elementary optical excitation of a metal nanoparticle (MNP), or surface plasmon polariton, as well as the coherent and incoherent resonant coupling between a single quantum dot and quantum well.In addition, since students will eventually work in a global market there is no better preparation for international collaboration than … international collaboration. By working with a team on an international scale there is a new dimension added to student teamwork, requiring students to handle collaboration that is remote, cross-cultural, and linguistically challenging. As part of this proposal an aggressive outreach plan to both K-12 American and German students is presented that will further provide an opportunity for the sharing of cultures. The progress and plans for diversity is also discussed.