Semiconducting polymers play an important role in a wide range of optical and electronic material applications. Polymer thin films that result in the highest performance typically have a complex semicrystalline morphology, indicating that considerable device improvement can be achieved through optimization of microstructural properties. However, the connection between molecular ordering and device performance is difficult to predict due to the current need for a mathematical theory of the physics that dictates charge transport in semiconducting polymers. It is experimentally suggested that efficient transport in such films occurs via connected networks of crystallites. We present an analytical and computational description of semicrystalline conjugated polymer materials that captures the impact of polymer conformation on charge transport in heterogeneous thin films. We first develop an analytical theory for the statistical behavior of a polymer emanating from a crystallite and predict the average distance to the first kink in the chain that traps a charge. We use this analysis to define the conditions for percolation and the consequent efficient transport through a semicrystalline material. We then establish a charge transport model using Monte Carlo simulations that predicts the multi-scale charge transport and crystallite connections. We approximate the thin film as a two-dimensional grid of crystallites embedded in amorphous polymer. The chain conformations in the amorphous region are determined by the wormlike chain model, and the crystallites are assigned fixed mobilities. We use this model to identify limits of charge transport at various time scales for varying fraction of crystallinity.
The use of ZnO nanowires has become a widespread topic of interest in optoelectronics. In order to correctly assess the
quality, functionality, and possible applications of such nanostructures it is important to accurately understand their
electrical and optical properties. Aluminum- and gallium-doped crystalline ZnO nanowires were synthesized using a
low-temperature solution-based process, achieving dopant densities of the order of 1020 cm-3. A non-contact optical
technique, photothermal deflection spectroscopy, is used to characterize ensembles of ZnO nanowires. By modeling the
free charge carrier absorption as a Drude metal, we are able to calculate the free carrier density and mobility.
Determining the location of the dopant atoms in the ZnO lattice is important to determine the doping mechanisms of the
ZnO nanowires. Solid-state NMR is used to distinguish between coordination environments of the dopant atoms.
Helmholtz-Gauss beams can be expressed as a superposition of tilted Gaussian waves, and combining this spectrum
with perturbation theory using the Rytov approximation can be useful in order to study the propagation
of Helmholtz-Gauss beams through random media. We do this by obtaining the second-order statistical properties
of the fields. We compare our results with previously reported calculations for pure Gaussian beams and
nondiffracting beams. Our analysis is restricted to the weak regime of atmospheric fluctuations.
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