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We investigate the optical and transport properties of single GaAs/AlGaAs core-multishell Quantum Well Tube (QWT) nanowire heterostructure. The QWT is defined by a thin (8 nm) GaAs layer embedded inside a thick Al 0.4 Ga 0.6 As shell which surrounds a 50 nm diameter GaAs NW core see Fig.1. The electrons and holes in the thin GaAs shell are radially confined and are free along the nanowire length. The radial confinement results in confined quantum states as shown in the schematics in Fig.1. These nanowires growth was achieved by two temperature MOCVD growth techniques [1, 2]. Optical studies of these nanowires show high quantum efficiency of the QWT ground state photoluminescence compared to the core luminescence. The shift to higher energies above the core corresponds to increasing quantum confinement of the ground state transition of the quantum well tube [1]. The energy eigenvalues depicted in Fig.1 are numerically calculated values of the energies of the electrons and holes confined to the quantum well tube where the hexagonal symmetry of the nanowires is approximated by cylindrical symmetry.

The Cincinnati Engineering Enhanced Math and Science (CEEMS) Program, funded by the National Science Foundation, DUE #1102990, empowers secondary math and science teachers to integrate the engineering design process and challenge-based learning into the courses they teach. Some of the curricular materials developed by CEEMS participating teachers also incorporate the fine arts into the design process, thus increasing student engagement and demonstrating the importance of a multi-disciplinary approach to learning. This paper describes seven challenge-based learning endeavors developed for middle school and high school math classrooms that demonstrate the connection with math and fine arts. One curricular unit is described in detail to highlight the incorporation of engineering design and challenge-based learning, while the other six are summarized to provide other examples. Traditionally, math instruction features the teacher as the “sage on the stage” and students working individually to apply formulas in order to find the “right” answers. In contrast, CEEMS' pedagogical approaches result in student-directed instruction, which includes cooperative learning groups using creativity and critical thinking to develop unique solutions to design challenges.

We review GaAs nanowires and related nanowire heterostructures grown on Si (111) substrates by metal organic chemical vapor deposition via vapor-liquid-solid (VLS) mechanism. Transmission electron microscopy, micro-photoluminescence and micro-Raman spectroscopy have been used to understand the crystal structure, light emission and strain effects on the bandgap energy of GaAs nanowires.

We investigate vertical and defect-free growth of GaAs nanowires on Si (111) substrates via a vapor-liquid-solid (VLS) growth mechanism with Au catalysts by metal-organic chemical vapor deposition (MOCVD). By using annealed thin GaAs buffer layers on the surface of Si substrates, most nanowires are grown on the substrates straight, following (111) direction; by using two temperature growth, the nanowires were grown free from structural defects, such as twin defects and stacking faults. Systematic experiments about buffer layers indicate that V/III ratio of precursor and growth temperature can affect the morphology and quality of the buffer layers. Especially, heterostructural buffer layers grown with different V/III ratios and temperatures and in-situ post-annealing step are very helpful to grow well arranged, vertical GaAs nanowires on Si substrates. The initial nanowires having some structural defects can be defect-free by two-temperature growth mode with improved optical property, which shows us positive possibility for optoelectronic device application. ©2010 IEEE.

We report the effect of V/III ratio and nanowire diameter on the crystal structure and optical properties of InP nanowires. Time -resolved photoluminescence studies have revealed that wurtzite nanowires show longer carrier lifetimes than zinc-blende ones.

Tunable photonic crystal (PC) waveguides have been designed using plane-wave expansion calculations for application to photonic integrated circuits. Wavelength selective propagation has been observed in silicon-on-insulator (SOI) PC waveguides fabricated by electron-beam lithography and inductively coupled plasma etching. Incorporation of DNA into an SOI PC lattice has been demonstrated, and novel tunable PC devices using biophotonic materials have been considered.

Incorporation of DNA into nanoscale wells in a silicon substrate has been demonstrated to show fabrication feasibility for optically tunable photonic crystal waveguides. A change in propagation characteristics due to DNA incorporation has been observed for a silicon-on-insulator photonic crystal waveguide.

We report on room temperature resonant Raman scattering measurements on individual CdS nanowires. We show that spatially-resolved Raman spectroscopy on single nanowires can be used as a tool to study structural and compositional uniformity of the nanowire.

A unique experimental apparatus has been developed for the optical characterization of nanophotonic devices. Grating couplers with nanoscale periodicity have been fabricated on silicon-on-insulator (SOI) substrates by electron beam lithography (EBL) and reactive ion etching (RIE). The coupling efficiency of these gratings has been measured as a function of grating depth and the angle and wavelength of incident radiation. A coupling efficiency of at least 5.2% is demonstrated for 1568 nm light incident at 40°.

The excitonic structure in quantum dots is studied by polarization-resolved spectroscopy. For symmetric dots magneto-PL measurements show that the spin-relaxation time depends on the splitting of the exciton spin states. At magnetic field spin polarization is conserved within the timescale of exciton recombination.

The optical properties of magnetic quantum dots are studied. Micro-photoluminescence spectroscopy reveals that single dot emission lines are broadened due to magnetic moment fluctuations. Polarization resolved measurements show that even at zero field emission from CdMnTe quantum dots is strongly circularly polarized.