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We systematically introduced defects onto the body of multi-walled carbon nanotubes through an acid treatment, and the evolution of these defects was examined by Raman spectroscopy using different excitation wavelengths. The D and D′ modes are most prominent and responsive to defect formation caused by acid treatment and exhibit dispersive behavior upon changing the excitation wavelengths as expected from the double resonance Raman (DRR) mechanism. Several weaker Raman resonances including D″ and L1 (L2) + D′ modes were also observed at the lower excitation wavelengths (633 and 785 nm). In addition, specific structural defects including the typical pentagon-heptagon structure (Stone–Wales defects) were identified by Raman spectroscopy. In a closer analysis we also observed Haeckelite structures, specifically Ag mode response in R5,7 and O5,6,7.

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Acid-treated and pristine chemical vapor deposition grown multiwalled carbon nanotube (MWNT) and poly(bisphenol A carbonate) (PC) composites were prepared through a simple solution blending with varied nanotube weight fractions. The electrical conductivities of the composites can be described by the scaling law based on percolation theory with unprecedented high saturated ac conductivity of pristine nanotubes (σsat=1598.4 S cm−1, pc=0.19 wt %) and acid-treated nanotubes (σsat=435.4 S cm−1, pc=0.3 wt %), which correlates well with the dc behavior. We attribute the high saturated conductivities to managing the dispersions, rather than looking to have a well dispersed three-dimensional network thin film. The comparison was made between acid-treated nanotubes and pristine nanotube, both dispersed in PC at various loadings. It was found that the pristine nanotubes in PC possessed an even higher conductivity than the more evenly dispersed composites consisting of lightly acid-treated MWNT in PC.

We propose a new architecture as an alternative method when constructing organic photovoltaics (PVs) by addressing the best method to trap resonant light within the devices using fiber optics to concentrate light in the form of a microconcentrator cell (m-C cell). Our initial effort is to address how the m-C cells manage light absorption using a mathematical model that considers all the required parameters including the incident angle, meridional plane, cross sectional area, and path length. By knowing the materials, refractive index, we are able to calculate the optical angular input to achieve maximum absorption of resonant light. We also addressed the complexity of how changing refractive indices in a multilayer device can alter the angular dependence when considering the incident input light. The consequence is that we can ensure efficient absorption of resonant light in a thin film yet without issues of transmission losses which are evident in all other thin film organic PVs.