We have carried out comparative studies on transparent conductive thin films made with two kinds of commercial carbon nanotubes: HiPCO and arc-discharge nanotubes. These films have been further exploited as hole-injection electrodes for organic light-emitting diodes (OLEDs) on both rigid glass and flexible substrates. Our experiments reveal that films based on arc-discharge nanotubes are overwhelmingly better than HiPCO-nanotube-based films in all of the critical aspects, including surface roughness, sheet resistance, and transparency. Further improvement in arc-discharge nanotube films has been achieved by using PEDOT passivation for better surface smoothness and using SOCl2 doping for lower sheet resistance. The optimized films show a typical sheet resistance of approximately 160 Omega/ square at 87% transparency and have been used successfully to make OLEDs with high stabilities and long lifetimes.

We report the implementation of continuous, highly flexible, and transparent graphene films obtained by chemical vapor deposition (CVD) as transparent conductive electrodes (TCE) in organic photovoltaic cells. Graphene films were synthesized by CVD, transferred to transparent substrates, and evaluated in organic solar cell heterojunctions (TCE/poly-3,4-ethylenedioxythiophene:poly styrenesulfonate (PEDOT:PSS)/copper phthalocyanine/fullerene/bathocuproine/aluminum). Key to our success is the continuous nature of the CVD graphene films, which led to minimal surface roughness ( approximately 0.9 nm) and offered sheet resistance down to 230 Omega/sq (at 72% transparency), much lower than stacked graphene flakes at similar transparency. In addition, solar cells with CVD graphene and indium tin oxide (ITO) electrodes were fabricated side-by-side on flexible polyethylene terephthalate (PET) substrates and were confirmed to offer comparable performance, with power conversion efficiencies (eta) of 1.18 and 1.27%, respectively. Furthermore, CVD graphene solar cells demonstrated outstanding capability to operate under bending conditions up to 138 degrees , whereas the ITO-based devices displayed cracks and irreversible failure under bending of 60 degrees . Our work indicates the great potential of CVD graphene films for flexible photovoltaic applications.

Preseparated, semiconductive enriched carbon nanotubes hold great potential for thin-film transistors and display applications due to their high mobility, high percentage of semiconductive nanotubes, and room-temperature processing compatibility. Here in this paper, we report our progress on wafer-scale processing of separated nanotube thin-film transistors (SN-TFTs) for display applications, including key technology components such as wafer-scale assembly of high-density, uniform separated nanotube networks, high-yield fabrication of devices with superior performance, and demonstration of organic light-emitting diode (OLED) switching controlled by a SN-TFT. On the basis of separated nanotubes with 95% semiconductive nanotubes, we have achieved solution-based assembly of separated nanotube thin films on complete 3 in. Si/SiO(2) wafers, and further carried out wafer-scale fabrication to produce transistors with high yield (>98%), small sheet resistance ( approximately 25 kOmega/sq), high current density ( approximately 10 microA/microm), and superior mobility ( approximately 52 cm(2) V(-1) s(-1)). Moreover, on/off ratios of >10(4) are achieved in devices with channel length L > 20 microm. In addition, OLED control circuit has been demonstrated with the SN-TFT, and the modulation in the output light intensity exceeds 10(4). Our approach can be easily scaled to large areas and could serve as critical foundation for future nanotube-based display electronics.

We report high-performance fully transparent thin-film transistors (TTFTs) on both rigid and flexible substrates with transfer printed aligned nanotubes as the active channel and indium-tin oxide as the source, drain, and gate electrodes. Such transistors have been fabricated through low-temperature processing, which allowed device fabrication even on flexible substrates. Transparent transistors with high effective mobilities (approximately 1300 cm(2) V(-1) s(-1)) were first demonstrated on glass substrates via engineering of the source and drain contacts, and high on/off ratio (3 x 10(4)) was achieved using electrical breakdown. In addition, flexible TTFTs with good transparency were also fabricated and successfully operated under bending up to 120 degrees . All of the devices showed good transparency (approximately 80% on average). The transparent transistors were further utilized to construct a fully transparent and flexible logic inverter on a plastic substrate and also used to control commercial GaN light-emitting diodes (LEDs) with light intensity modulation of 10(3). Our results suggest that aligned nanotubes have great potential to work as building blocks for future transparent electronics.

We report a comparative study and Raman characterization of the formation of graphene on single crystal Ni (111) and polycrystalline Ni substrates using chemical vapor deposition (CVD). Preferential formation of monolayer/ bilayer graphene on the single crystal surface is attributed to its atomically smooth surface and the absence of grain boundaries. In contrast, CVD graphene formed on polycrystalline Ni leads to a higher percentage of multilayer graphene (g3 layers), which is attributed to the presence of grain boundaries in Ni that can serve as nucleation sites for multilayer growth. Micro-Raman surface mapping reveals that the area percentages of monolayer/bilayer graphene are 91.4% for the Ni (111) substrate and 72.8% for the polycrystalline Ni substrate under comparable CVD conditions. The use of single crystal substrates for graphene growth may open ways for uniform high-quality graphene over large areas. SECTION Nanoparticles and Nanostructures