Conductive polymers, i.e. plastics, that conduct electricity, are important in science and technology as they offer the potential for cheap, flexible electronic devices. This work examines the mechanisms by which electrons are transported in such materials, a process that remains far from understood. One of the main results of the work is that the behavior of such materials, at very high densities of charge carriers, is radically different to simple expectations.
In semiconductor nanocrystals, the physical effects of deliberately included impurities, called dopants, may depend on the dopant position with the crystal. To date, there has not been an effective technique to determine the location of individual dopant atoms in nanocrystals. IRG-4 researchers demonstrated that a combination of scanning transmission electron microscopy and electron energy loss spectroscopy can be used to reveal the position of such “invisible” dopants.
Our team has developed a simple solution-based method to fabricate arrays of ZnO nanowires inside of a glass microchannel. The density of the wires is easily controlled by the concentration of the solution used during the seeding step. The resulting devices can be used for fast separations of long DNA by size. The fabrication method developed here is much faster and less expensive than conventional methods to create nanopost arrays, such as electron beam lithography.
Ordering of spherical
particles represents a fundamental topic in materials science and engineering
ranging from the sub-nanometer scale packing of atoms in simple crystals to
micron sized assemblies of colloids.
Auger recombination is an important mechanism that can
limit the performance of solar cells. Ryan Gresback, working with a group at Los Alamos National Lab,
compared Auger recombination rates of direct and indirect band gap
semiconductor quantum dots. While in bulk semiconductors Auger recombination
rates differ by 4-5 orders of magnitude, a striking convergence of Auger
recombination rates in quantum dots of both direct (InAs, PbSe, CdSe) and indirect band
gap (Ge) semiconductors was found. 
Graduate student Wade Luhman has demonstrated a route to enhance the short exciton diffusion length (LD) of organic semiconductors by
combining fluorescent and phosphorescent materials into a single electron
donating thin film. Here, a near-doubling of the diffusion length is realized
in a fluorescent material upon addition of the phosphorescent sensitizer. This
work highlights a novel approach to improve the absorption efficiency of
organic solar cells, and provides fundamental insight into exciton migration in these materials.