Recent Submissions

  • Mesoscale modeling of quantum yield in nanocrystalline devices

    Irvin, Samantha; Flammer, Philip David; Lusk, Mark; Beach, Joe; van de Lagemaat, Jao; Graf, Peter
    A new solar material features silicon nanocrystals (nc-Si) within an amorphous silicon (a-Si) matrix. The efficiency with which photons are absorbed and converted to electric current depends on the size, orientation, volume fraction, and interface properties of nc-Si. This investigation has resulted in the development of a device level simulator which predicts quantum efficiency and voltage-current character for nc-Si/a-Si systems. These performance measures are calculated as functions of input photon energy. A number of different interactions were combined to completely characterize the device, including optical scattering and absorption, creation of excitons and charge carriers, electrostatic fields, and drift/diffusion of charge carriers.
  • Functionalization of 110 oriented silicon quantum wires

    Lochner, Robert; Li, Huashan; Wu, Zhigang; Lusk, Mark T.
    Silicon nanowires (SiNW) are cylindrical crystals of diamond structured silicon with a length much greater than diameter. Silicon nanowires are ~1-100 nm in diameter, 110 direction dominates for wires less than 10 nm (Wu et al.), and the smallest wire is 1.3 nm diameter (Ma et al.). Electronic properties of silicon nanowires vary with growth orientation, surface restructuring, and attached ligands. Prospects are good for use of silicon nanowires in future nanoelectronics and PV devices.
  • Characterization of molecular magnets using EPR

    Riskey, Kory; Miller, Joel; Simonds, Brian; Taylor, P. Craig
    Molecules involving tetracyanoethylene (TCNE) and transition or rare earth compounds have been found to exhibit magnetic properties at low temperature. One compound, however, with V and TCNE has been found to have an ordering temperature above 300 K. A compound with Fe and TCNE has shown to exhibit 32% more magnetization in molecules than iron metal. Molecular magnet compounds can be dissolved in a solvent, added to a matrix such as a polymer, and do not require metallurgical processing. Since magnetism is a very basic science, application possibilities for molecular magnets are broad, stretching from nanotechnology to high density information storage.
  • Immobilization of heteropolyacids in PEM fuel cell membranes via copolymerization

    Jessop, Jeri D.; Herring, Andrew M.; Horan, James L.; Kuo, Mei-Chen
    Nafion is the current standard by which PEM fuel cell membranes are measured. It is a PFSA (perfluoro sulfonic acid) polymer that is used to conduct ions such as protons. This material is only useful at low temperature (less than 100 degrees celsius) and high relative humidity due to protons being transported by water which is not practical for a fuel cell. Research is currently being done to create a new membrane that does not contain PFSA, instead membranes are made using heteropolyacids (HPAs). HPAs are useful because they are strong inorganic acids that have a high water of hydration, meaning a humidifier may not be necessary in a fuel cell. Another positive aspect of HPAs is the ability of protons to hop from HPA molecule to HPA molecule. One limitation of HPAs is their solubility in water. This research is focused on immobilizing the HPA by functionalizing it with an easily polymerizable group so that it becomes a monomer that can be used to make copolymers. Two HPA systems are being presented here, HPA-ethylene and HPA-butyl acyrlate. It is possible that these systems will be more effective than PFSA membranes.