We report ultrahigh density assembly of aligned single-walled carbon nanotube (SWNT) two-dimensional arrays via AC dielectrophoresis using high-quality surfactant-free and stable SWNT solutions. After optimization of frequency and trapping time, we can reproducibly control the linear density of the SWNT between prefabricated electrodes from 0.5 SWNT/μm to more than 30 SWNT/μm by tuning the concentration of the nanotubes in the solution. Our maximum density of 30 SWNT/μm is the highest for aligned arrays via any solution processing technique reported so far. Further increase of SWNT concentration results in a dense array with multiple layers. We discuss how the orientation and density of the nanotubes vary with concentrations and channel lengths. Electrical measurement data show that the densely packed aligned arrays have low sheet resistances. Selective removal of metallic SWNTs via controlled electrical breakdown produced field-effect transistors with high current on-off ratio. Ultrahigh density alignment reported here will have important implications in fabricating high-quality devices for digital and analog electronics.

We report on high quality individual solution processed single-walled carbon nanotube ͑SWNT͒ field effect transistors assembled from a commercial surfactant free solution via dielectrophoresis. The devices show field effect mobilities up to 1380 cm 2 / V s and on-state conductance up to 6 S. The mobility values are an order of magnitude improvement over previous solution processed SWNT devices and close to the theoretical limit. These results demonstrate that high quality SWNT devices can be obtained from solution processing and will have significant impact in high yield fabrication of SWNT nanoelectronic devices.

We demonstrate solution processable large area field effect transistors (FETs) from aligned arrays of carbon nanotubes (CNTs). Commercially available, surfactant free CNTs suspended in aqueous solution were aligned between source and drain electrodes using ac dielectrophoresis technique. After removing the metallic nanotubes using electrical breakdown, the devices displayed p-type behavior with on-off ratios up to ~ 2 × 10 4 . The measured field effect mobilities are as high as 123 cm 2 /Vs, which is three orders of magnitude higher than typical solution processed organic FET devices.* To whom correspondence should be addressed. E-mail: saiful@mail.ucf.edu † Current Address: Chemical Engineering Department, University of Puerto Rico at Mayaguez, Mayaguez, P.R. 00681-9000Solution processed electronic devices have attracted tremendous attention because of their ease of processablity, low cost of fabrication, and their ability to cover large areas. These devices may be useful for applications such as flexible displays, sensor sheets, radiofrequency (RFIDs) tags, and photovoltaics [1][2]. A significant amount of effort has been dedicated to improve device performance of solution processed organic field effect transistors (FETs). However, typical field effect mobilities for these devices are usually on the order of ~ 0

We present a simple and scalable technique for the fabrication of solution processed & local gated carbon nanotube field effect transistors (CNT-FETs). The approach is based on directed assembly of individual single wall carbon nanotube from dichloroethane via AC dielectrophoresis (DEP) onto pre-patterned source and drain electrodes with a local aluminum gate in the middle. Localgated CNT-FET devices display superior performance compared to global back gate with on-off ratios >104 and maximum subthreshold swings of 170 mV/dec. The local bottom-gated DEP assembled CNT-FETs will facilitate large scale fabrication of complementary metal-oxidesemiconductor (CMOS) compatible nanoelectronic devices.

We present a near IR photoresponse study of large area multi-walled carbon nanotube/poly(3-hexylthiophene)-block-polystyrene polymer (MWNT/P3HT-b-PS) nanocomposite films for different loading ratio of MWNT into the polymer matrix. We show that the photocurrent strongly depends on the position of the laser spot with maximum photocurrent occurring at the metal -film interface. In addition, compared to the pure MWNT film, the photoresponse is much larger in the MWNT/polymer composite films. The time constant for the photoresponse is slow and varies between 0.6 and 1.2 seconds. We explain the photoresponse by Schottky barrier modulation at the metal -film interface.* To whom correspondence should be addressed. E-mail: saiful@mail.ucf.edu Carbon nanotubes (CNTs) are considered to be promising building blocks for nanoelectronic and optical devices due to their special geometry, high electrical conductivity, exceptional mechanical and optical properties [1][2][3]. Recently, photoresponse of CNTs (both in visible and near infrared (NIR) regime) have generated considerable debate in terms of whether the photoresponse is (i) due to photon induced charge carrier (excitonic), (ii) due to heating of the CNT network (bolometric), or (iii) caused by photodesorption of oxygen molecules at the surface of the CNT. In addition, the role of the metal -CNT contact effect on the photoresponse has also been debated. In individual semiconducting single-walled carbon nanotube (SWNT) field effect transistor (FET) devices, Freitag et al. and Qiu et al. explained the photoresponse in the NIR regime using an exciton model [4,5]. Chen et al. showed that in individual SWNT FET device, the reduction of conductivity upon UV illumination is due to desorption of molecular oxygen from the CNT surface which causes a reduction in hole carriers [6]. In contrast, for a large area SWNT film suspended in vacuum, it was argued by Itkis et al. that the NIR photoresponse was due to a bolometric effect, a change in conductivity due to heating of the SWNT network [7]. In a microscopic SWNT film, Levitsky et al also found molecular photodesorption to be responsible for change in conductivity upon near IR illumination [8].Other studies in macroscopic SWNT film show that the maximum photoresponse occurs at the CNT film-metal interface and that the response varies with the position of laser illumination [9][10][11][12]. This effect has been explained using exciton model where CNT-metal interface helps to separate electron and holes to induce a photovoltage. A recent study has shown that muti-walled carbon nanotube (MWNT) film also displays a positional dependent photocurrent [13]. Although there are many studies for the photoresponse in individual CNTs and CNT films, there are almost no studies on CNT/Polymer nanocomposites. Nanocomposites may provide enhanced