We demonstrate logic circuits with field-effect transistors based on single carbon nanotubes. Our device layout features local gates that provide excellent capacitive coupling between the gate and nanotube, enabling strong electrostatic doping of the nanotube from p-doping to n-doping and the study of the nonconventional long-range screening of charge along the one-dimensional nanotubes. The transistors show favorable device characteristics such as high gain (>10), a large on-off ratio (>10(5)), and room-temperature operation. Importantly, the local-gate layout allows for integration of multiple devices on a single chip. Indeed, we demonstrate one-, two-, and three-transistor circuits that exhibit a range of digital logic operations, such as an inverter, a logic NOR, a static random-access memory cell, and an ac ring oscillator.

Recently, it was reported that crystals of the organic material dithiophene-tetrathiafulvalene (DT-TTF) have a high field-effect charge carrier mobility of 1.4 cm(2)/(V x s). These crystals were formed by a simple drop-casting method, making this material interesting to investigate for possible applications in low-cost electronics. Here, organic single-crystal field-effect transistors based on materials related to DT-TTF are presented and a clear correlation between the crystal structure and the electrical characteristics is observed. The observed relationship between the mobilities in the different crystal structures is strongly corroborated by calculations of both the molecular reorganization energies and the maximum intermolecular transfer integrals. The most suitable materials described here exhibit mobilities that are among the highest reported for organic field-effect transistors and that are the highest reported for solution-processed materials.

The processing characteristics of organic semiconductors make them potentially useful for electronic applications where low-cost, large area coverage, and structural flexibility are required. 1 Charge carrier mobility is a measure of the quality of organic semiconductors and is a primary factor that determines the performance of organic field effect transistors (OFETs). The highest mobilities are found in single crystals due to molecular ordering that permits good overlapping of the π-π orbitals. A mobility of 1.5 cm 2 /Vs was reported for pentacene, 2 and recently a mobility of 8 cm 2 /Vs was reported for rubrene. 3 These organic crystals were grown from the vapor phase in long and complex experiments. To progress in this field toward device applications, it is very important to search for new molecules that are able to act as organic semiconductors 4 and also to develop easy methods to grow single crystals or films. In this communication, we report on the clear observation of field effect hole mobility in single crystals of the organic semiconductor dithiophene-tetrathiafulvalene (DT-TTF, Figure 1a) grown by drop casting, a very simple method. The maximum mobility observed in these crystals was 1.4 cm 2 /Vs.Tetrathiafulvalene (TTF) and its derivatives are successfully used as building blocks for charge-transfer salts, giving rise to a multitude of organic conductors and superconductors. These conducting salts are prepared mainly as single crystals but also as thin films of nanocrystals supported on dielectric polymers. [5][6][7] The driving force in the crystallization of the salts is the π-π stacking, which permits, together with the S‚‚‚S interactions, an intermolecular electronic transfer responsible for their transport properties. The transport properties of a few single crystals of neutral TTF derivatives have been measured, showing semiconductor character with a roomtemperature conductivity on the order of 10 -5 S/cm. 8-10 Additionally, organic thin films of TTF derivatives have been grown by vacuum deposition techniques, but only their morphology and nanomechanical properties have been studied. 11 However, TTF derivatives have never been used for the preparation of OFETs despite the fact that they are soluble in various solvents, easily chemically modified, and good electron donors.DT-TTF is a particularly promising molecule because it is rigid and completely conjugated, having a low conformational freedom that favors stronger intermolecular interactions and, thus, higher carrier mobilities. Cyclic voltammetry measurements of DT-TTF show two separate reversible one-electron oxidations with E 1/2 1 and E 1/2 2 of 0.78 and 0.96 V, respectively (in DMF/0.1 M TBAPF 6 vs SCE). X-ray studies reveal that the DT-TTF molecules stack uniformly along the b axis in a herringbone pattern ( Figure 1a). 12 Moreover, it is seen that the sulfur atoms also promote interactions between the different DT-TTF stacks within the layer which can lead to electronic dimensionality enhancing 5 (d(S‚‚‚S) ) 3.55 and 3.61 Å). This cr...