Carbon nanotube thin-film transistors are expected to enable the fabrication of high-performance, flexible and transparent devices using relatively simple techniques. However, as-grown nanotube networks usually contain both metallic and semiconducting nanotubes, which leads to a trade-off between charge-carrier mobility (which increases with greater metallic tube content) and on/off ratio (which decreases). Many approaches to separating metallic nanotubes from semiconducting nanotubes have been investigated, but most lead to contamination and shortening of the nanotubes, thus reducing performance. Here, we report the fabrication of high-performance thin-film transistors and integrated circuits on flexible and transparent substrates using floating-catalyst chemical vapour deposition followed by a simple gas-phase filtration and transfer process. The resulting nanotube network has a well-controlled density and a unique morphology, consisting of long (~10 µm) nanotubes connected by low-resistance Y-shaped junctions. The transistors simultaneously demonstrate a mobility of 35 cm(2) V(-1) s(-1) and an on/off ratio of 6 × 10(6). We also demonstrate flexible integrated circuits, including a 21-stage ring oscillator and master-slave delay flip-flops that are capable of sequential logic. Our fabrication procedure should prove to be scalable, for example, by using high-throughput printing techniques.

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We theoretically investigate the dependence of exciton transition energies on dielectric constant of surrounding materials. We make a simple model for the relation between dielectric constant of environment and a static dielectric constant describing the effects of electrons in core states, σ bonds and surrounding materials. Although the model is very simple, calculated results well reproduce experimental transition energy dependence on dielectric constant of various surrounding materials.

Carbon nanotube-based solar cells have been extensively studied from the perspective of potential application. Here we demonstrated a significant improvement of the carbon nanotube solar cells by the use of metal oxide layers for efficient carrier transport. The metal oxides also serve as an antireflection layer and an efficient carrier dopant, leading to a reduction in the loss of the incident solar light and an increase in the photocurrent, respectively. As a consequence, the photovoltaic performance of both p-single-walled carbon nanotube (SWNT)/n-Si and n-SWNT/p-Si heterojunction solar cells using MoO x and ZnO layers is improved, resulting in very high photovoltaic conversion efficiencies of 17.0 and 4.0%, respectively. These findings regarding the use of metal oxides as multifunctional layers suggest that metal oxide layers could improve the performance of various electronic devices based on carbon nanotubes.

The optical transition energies, E 11 and E 22 , of single-walled carbon nanotubes (SWNTs) suspended in air have been investigated for 20 species by photoluminescence and excitation spectroscopies. We h a ve studied the environmental e ects in photoluminescence by comparing our results with those for the SWNTs wrapped by sodium-dodecyl-sulfate (SDS), as reported by W eisman et al. The energy di erences between air-suspended and SDS-wrapped SWNTs, E ii = E air ii ; E SDS ii , depends on the chiral vector (n,m), speci cally on the chiral angle and type of SWNT (type-I or type-II). The E 11 and E 22 mostly blueshifted, with the exception of the E 22 of some type-II SWNTs (that have a small chiral angle), which redshifted. With an increase in the chiral angle, the E 11 increased in type-I SWNTs and decreased in type-II SWNTs. In contrast, the E 22 demonstrated opposite dependence on the chiral angle. The di erences in E 11 and E 22 between type-I and type-II disappeared in the SWNTs with chiral angles close to 30 (near armchair). The (n,m) dependence of the environmental e ect on the transition energies can be explained by the di erence in the e ective mass, which c o n tributes to the energy of Coulomb i n teractions between carriers.

We have fabricated n-type carbon nanotube field effect transistors by choosing the contact metal. Single-walled carbon nanotubes were grown directly on a SiO2∕Si substrate by chemical vapor deposition using patterned metal catalysts. Following the nanotube growth, Ca contacts with a small work function were formed by evaporating and lifting off the metal. The devices showed n-type transfer characteristics without any doping into the nanotube channel. In contrast, the devices with Pd contacts showed p-type conduction. These results can be explained by taking into account the work functions of the contact metals.

We have developed a process for chemical purification of carbon nanotubes for solution-processable thin-film transistors (TFTs) having high mobility. Films of the purified carbon nanotubes fabricated by simple drop coating showed carrier mobilities as high as 164 cm 2 V -1 s -1 , normalized transconductances of 0.78 Sm -1 , and on/off current ratios of 10 6 . Such high performance requires the preparation of a suspension of micrometer-long and highly purified semiconducting single-walled carbon nanotubes (SWCNTs). Our purification process includes length and electronic-type selective trapping of SWCNTs using recycling gel filtration with a mixture of surfactants. The results provide an important milestone toward printed high-speed and large-area electronics with roll-to-roll and ink-jet device fabrication.