Efficient selection of semiconducting single-walled carbon nanotubes (SWNTs) from as-grown nanotube samples is crucial for their application as printable and flexible semiconductors in field-effect transistors (FETs). In this study, we use atactic poly(9-dodecyl-9-methyl-fluorene) (a-PF-1-12), a polyfluorene derivative with asymmetric side-chains, for the selective dispersion of semiconducting SWNTs with large diameters (>1 nm) from plasma torch-grown SWNTs. Lowering the molecular weight of the dispersing polymer leads to a significant improvement of selectivity. Combining dense semiconducting SWNT networks deposited from an enriched SWNT dispersion with a polymer/metal-oxide hybrid dielectric enables transistors with balanced ambipolar, contact resistance-corrected mobilities of up to 50 cm2·V–1·s–1, low ohmic contact resistance, steep subthreshold swings (0.12–0.14 V/dec) and high on/off ratios (106) even for short channel lengths (<10 μm). These FETs operate at low voltages (<3 V) and show almost no current hysteresis. The resulting ambipolar complementary-like inverters exhibit gains up to 61.

Graphene oxide is a promising solution-processable precursor for the mass production of graphene thin films. However, during the wet chemical oxidation and reduction process toward reduced graphene oxide (rGO) a large number of defects are created. Although it is possible to synthesize rGO with an average defect distance of 3–4 nm, the performance is still limited. Here we demonstrate the partial restoration of the graphene basal plane of rGO by annealing in Ar/H2/isopropanol flow. Detailed statistical Raman analysis over large areas corroborates that the mean defect distance increases from initially 2–3 to 10–12 nm after CVD annealing. Some areas even reach defect distances of up to 18 nm. However, residual manganese impurities from the oxidation process lead to undesired carbon nanotube growth on the substrate under these conditions and had to be removed before the deposition of graphene oxide flakes on the substrate. The observed defect reduction during CVD annealing indicates that the lattice defects in rGO are mostly decorated vacancies that can be healed by addition of carbon under suitable conditions.

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We present an experimental study on the near-field light-matter interaction by tip-enhanced Raman scattering (TERS) with polarized light in three different materials: germanium-doped gallium nitride (GaN), graphene, and carbon nanotubes. We investigate the dependence of the TERS signal on the incoming light polarization and on the sample carrier concentration, as well as the Raman selection rules in the near-field. We explain the experimental data with a tentative quantum mechanical interpretation, which takes into account the role of plasmon polaritons, and the associated evanescent field. The driving force for the breakdown of the classical Raman selection rules in TERS is caused by photon tunneling through the perturbation of the evanescent field, with the consequent polariton annihilation. Predictions based on this quantum mechanical approach are in good agreement with the experimental data, which are shown to be independent of incoming light polarization, leading to new Raman selection rules for TERS.