This Materials World Network project focuses on exploring the fundamental mechanisms governing the optical excitations of two specific hybrid material systems of common interest, namely (1) quantum-dot/quantum-well coupled via tunneling and (2) metal/semiconductor coupled via their exciton-plasmon resonance. The goal is to establish the relationships between structure and function in these systems that will create new knowledge with impact on plasmonic and quantum dot lasers, biosensors, and energy conversion. The core innovation lies in fabrication, optical probing and simulation of novel nanoscale hybrid structures and architectures whose geometrical parameters can be systematically tuned. To accomplish this goal requires a concerted effort in nanofabrication, coherent optical spectroscopy and theoretical modeling that is provided by an international collaboration between an American and German research team. The US team consists of researchers at the University of Arkansas who are partners with the University of Oklahoma in an NSF-supported 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 nanostructures. Together, both teams have the experience, talent, and infrastructure needed to develop 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.
Student exchange will also play a significant part of the collaborative effort to accomplish the research goals. For example, students will spend one to two months each year with their international partner pursuing and advancing the understanding of the coupling in hybrid nanostructures and their corresponding thesis research. Since students will eventually work in a global market there is no better preparation for international collaboration. In addition, 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. Students will also be the central element in an aggressive outreach plan to both K-12 American and German students. Their participation will further provide an opportunity for the sharing of cultures.
The discovery of new materials has throughtout history inspired innovation leading to new and better products. The development of iron, steel, silicon, and plastics are evidence of the tremendous impact of new materials on innovation and their revolutionary impact on our economy. We are already aware that materials at the nanosize have unique and extraordinary properties, which unlike their bulk counterparts, depend on size, shape, and surroundings. While this opportunity is already extraordinary, combining two or more nanomaterials to form a coupled system opens the possibility of even more exciting new material properties and potential for economic impact, especially on the next generation of electronic and photonic devices. Basically, the two nanomaterials couple, connect to each other, forming a new material structure that can have a new identity of its own. This is analogous to two atoms coupling together to form a molecule. Unlike natural molecules, however, the states of coupled nanomaterials, such as two quantum dots or a quantum dot and a quantum well, can be engineered and tailored during growth. They can also be manipulated using applied electric, magnetic, or optical fields. We have explored these possibilities with research on the coupled quantum dot and quantum well system. This system can result in enhanced optical sources, as well as new concepts for electronic switching, and optical computing. Our research on this system has discovered and demonstrated for the first time, coherent coupling betweem a quantum dot and quantum well. This means that the coupled system can act as a fast optical switch or can store information as a component of a quantum computer. For example, quantum information processing with a coupled quantum dot and a quantum well offer exciting possibities. In general, the concept of entangled information is based on the coupling between two states. The resulting mixed states can be used for massive parallel processing since many quantum commonations of the two states are possible, not just two. This means that the detailed nature of the interaction and de-coherence processes must be understood. The ability to selectively initialize, control, manipulate, and readout the quantum stateusing optical means is of paramount importance to the realization of quantum computing. Our research has provided some of this understanding.
