Semiconductor nanowires have emerged as a new class of materials with significant potential to reveal new fundamental physics and to propel new applications. This international collaborative research project brings together research teams from USA (University of Cincinnati, and Miami University) and Australia (Australian National University and University of Queensland) with expertise in state-of-the-art semiconductor nanowire heterostructure growth, high resolution electron microscopy, and high resolution optical spectroscopy, to advance the understanding of the electronic landscapes of these unique nanostructures. The overall goal is to understand how nanowire heterostructures affect the physics of electronic states and their interactions. The synergistic, collaborative research of this team will explore three significant research thrusts: (1) Achieving high quality growth of III-V nanowires and radial, axial and hybrid nanowire heterostructures (2) Understanding the physics of these novel nanowire heterostructures (3) Measuring and understanding p- and n- type doping of these structures. These studies are expected to advance the understanding of the nature of quantum confinement in tailored radial and axial heterostructures, how quantum confinement affects the localized and continuum electronic states and their coupling, spins, scattering mechanisms with other elementary excitations in nanowires, as well as interactions with external electric and magnetic fields. This research will directly involve the interaction among and the training of graduate students, postdoctoral fellows and undergraduate students in multi-disciplinary area in an international setting. All participants in this research will be involved in an annual "Saturday International Nano Science and Engineering Day" for area middle school students where potential young scientists and engineers can explore nanoscience in an exciting hands-on environment.
The development of a fundamental understanding of the 0- and 1-dimensional physics of nanowire heterostructures will have strong societal benefits, influencing the development of new thrusts in optoelectronic device technology and ultimately making possible new varieties of sensors and other compact devices. This project will also train our nation?s future workforce in the critical areas of nanoscience and engineering. The exposure of graduate and undergraduate students, as well as postdoctoral fellows, to an international interdisciplinary scientific environment will deepen their understanding of the science involved and inform a more sophisticated perspective on the challenges and effectiveness of international collaboration, a signature of successful 21st research in nanoscience.
This Materials World Network award makes possible a coherent integrated research and education effort among four universities in the US and Australia, on the growth and characterization of semiconductor nanowires as well as the understanding of the physics of their electronic states. This award is jointly funded by the Division of Materials Research in the Mathematical and Physical Sciences Directorate and the Office of International Science and Engineering.
This grant was used to facilitate an intensive international collaborative research program on the physics of semiconductor nanowires between the research group of Prof. Chennupati Jagadish at the Australian National University and the research groups of Howard Jackson and Leigh Smith at the University of Cincinnati (UC), and the research group of Jan Yarrison-Rice at Miami University (MU) in Oxford, OH. The semiconductor nanowire heterostructures were fabricated in Australia, and then studied with a variety of optical techniques at UC and MU. Semiconductor nanowires are uniquely suited for fabricating next-generation devices for ultra-sensitive sensors and for possible quantum computing devices.. The research accomplished by this funding provided new and significant findings on the materials science and physics of these novel nanostructures, as well as a host of broader impact efforts which engaged students from K-12 through post-graduates. INTELLECTUAL MERIT Semiconductor nanowire heteostructures provide tremendous flexibility to engineer and fabricate structures for particular purposes, either for investigations of basic physics, or also as materials for novel nanotechnologies. The work supported by this grant involved investigations of how heterostructures can be utilized to improve or modify the electronic structure of nanowires. The findings and outcomes of this research include: Surface states which adversely affect the lifetime of electrons and holes in nanowires can be eliminated or passivated through optimized growth of outer shells which confine carriers to the interior nanowires. We have shown that InP nanowires can be created in two very different structures: cubic (Zincblende) crystal structure as occurs naturally in bulk materials, and hexagonal (Wurtzite) which can be fabricated by design in semiconductor nanowires. These two crystal structures have very different symmetries which impact their electronic structure. In nanowires where both hexagonal and cubic phases appear simultaneously, electrons and holes can be confined quantum mechanically to the ZB or WZ sections respectively. Because the wavefunctions are spatially separated, the electrons and hole can live for significantly longer than in normal nanowires. We have shown that outer shells can be fabricated which are significantly lattice mismatched and that the resultant strain can be used to tune the energy structures of the internal core. We have developed a new technique, photomodulated Rayleigh scattering, which can be used to investigate the electronic structure of a single nanowire, by looking how polarized light scatters off single semiconductor nanowire nanostructures. These results are of significant importance in learning how to design novel semiconductor heterostructures in order to tune the quantum wavefunctions for particular purposes in these one-dimensional structures. BROADER IMPACTS The research supported by this grant engaged students from K-12, college students, graduate students and High School Teachers. They included: Adding nanoscience and technology courses to the curriculum of both undergraduate nonscience majors, and physics undergraduate and graduate students. Sponsoring 2 high school physics teachers to participate in our research for a summer and to collaborate on developing nanoscience curriculum modules to take back to their respective schools. These educational projects have reached several hundred high school students over the past 4 years. The research groups at both the University of Cincinnati and Miami University ran outreach programs for K-12 graders. Programs ran from an hour to a half a day to short interactions at demonstration tables, and all involved hands-on activities. Many students were minority youths or from low income families or were young women, all of whom are underrepresented in the science and engineering fields. In many cases, teachers of students engaged in these outreach programs were provided with optics kits and educational handouts to use in their classrooms in future years. The PhD research of 5 graduate students was supported by this research grant. The research of two MS students was supported by this grant. Both are now in PhD programs at Virginia Tech and Clemson University. Two undergraduates engaged in Summer research projects supported by this grant. The research groups at UC and MU also directly engaged the public through participation in "Nano Days" at the Cincinnati Museum Center. In conclusion, the ability to study single nanowires and heterostructured nanowire structures with high spatial resolution, high spectral resolution, and to study their behavior as a function of time or through photoinduced current has given us many insights into the nanoscale physics that is foundational for real-world applications.
