G. Chen et al , Phys. Rev. Lett . (2011), in press.

1. Hot Electron ‘Coolness’ through Tunable Energy Transfer in NanowiresJonathan E. Spanier, Drexel University, DMR 0907381 Harnessing and transfer of excess energy of electrons generated by light via rapid transfer of electrons across semiconductor interfaces is key to developing more efficient solar cells. In addition, hot-electron transfer is one process involved in obtaining a region of negative electrical resistance, a non-linear feature that is important in many advanced electronic devices. We report on highly tunable and fast photo-excited hot electron transfer across the cylindrical interface of a co-axial core-shell semiconductor nanowire hetero-structure. The onset of the negative resistance region is shown to be highly tunable by one of three different modes, owing to the reduced dimensionality of a nanowire. Devices demonstrating adjustable phase shift and frequency multiplication indicate that hot electron transfer processes for constructing complex electronic circuits using far fewer, simpler and much smaller components with the potential for requiring much less energy to operate. Photo-excited electrons within the core of a cylindrical core-shell nanowire gain enough energy from an applied electric field to become hot, as illustrated. Hot electrons possess energy greater than interfacial potential barrier and “spill into” to the lower-mobility sheath. Harnessing this tunable real-space transfer in a device, a tunable negative differential resistance enables complex functionalities, e.g. tunable phase and frequency multiplication, within a single nano-scale device element. G. Chen et al,Phys. Rev. Lett.(2011), in press.

2. Mentored undergraduate team research: integrating device design and measurement with electronic band simulations Jonathan E. Spanier, Drexel University, DMR 0907381 The REU summer research experience program provides a rich and open environment to experience hands-on graduate student and faculty-mentored lab research, and an opportunity to learn and contribute in a team environment. The aim for this specific project is to understand the important role of nanostructure with cylindrical symmetry and specific size confinement in energy band alignment and carrier transport. Creation of a Poisson-Schrodinger solver by the students, including REU participant Kevin Siegl (2010), expanded to include a simple transport model by Ross (2011) permits analysis of experimental data from devices designed and fabricated by Anderson (2011). Drexel REU participants Ross (Haverford College) and Anderson (Rowan Univ.) working on their simulation and device fabrication projects, respectively. Plotted is a calculated electronic band diagram and electron density concentration profiles for core-shell nanowires for a selected doping as produced and used by the REU participants.