Showing papers by "Vittorio Scardaci published in 2007"

Ink-jet printing of carbon nanotube thin film transistors

Abstract: Ink-jet printing is an important process for placing active electronics on plastic substrates. We demonstrate ink-jet printing as a viable method for large area fabrication of carbon nanotube (CNT) thin film transistors (TFTs). We investigate different routes for producing stable CNT solutions ("inks"). These consist of dispersion methods for CNT debundling and the use of different solvents, such as N-methyl-2-pyrrolidone. The resulting printable inks are dispensed by ink-jet onto electrode bearing silicon substrates. The source to drain electrode gap is bridged by percolating networks of CNTs. Despite the presence of metallic CNTs, our devices exhibit field effect behavior, with effective mobility of similar to 0.07 cm(2)/V s and ON/OFF current ratio of up to 100. This result demonstrates the feasibility of ink-jet printing of nanostructured materials for TFT manufacture. (C) 2007 American Institute of Physics.

Photoluminescence spectroscopy of carbon nanotube bundles: Evidence for exciton energy transfer

Abstract: We investigate photoluminescence of nanotube bundles. Their spectra are explained by exciton energy transfer between adjacent tubes, whereby excitation of large gap tubes induces emission from smaller gap ones. The consequent relaxation rate is faster than nonradiative recombination, leading to enhanced photoluminescence of acceptor tubes.

Stabilization and Debundling of single-wall carbon nanotube dispersions in N-methyl-2-pyrrolidone (NMP) by polyvinylpyrrolidone (PVP)

Abstract: We present a simple method to stabilize single-wall carbon nanotube (SWNT) dispersions in N-methyl-2-pyrrolidone (NMP) by polyvinylpyrrolidone (PVP). A significant population of isolated SWNTs as well as small bundles of SWNTs in NMP is obtained by ultrasonic treatment followed by vacuum filtration through glass fiber filters. The resulting dispersions in pure NMP are monitored by photoluminescence (PL) spectroscopy over a period of 3 weeks. The PL intensities of such dispersions decrease with time, suggesting slow microscopic aggregation of nanotubes. However, addition of PVP dramatically improves the stability. In addition, PVP also spontaneously “debundles” some nanotube aggregates, increasing the isolated SWNT population without further ultrasonic treatment.

Carbon nanotube–polymer composites for photonic devices

Abstract: We report the fabrication of high optical quality single wall carbon nanotube polyvinyl alcohol composites and their application in nanotube based photonic devices. These show a broad absorption of semiconductor tubes centred at ∼1.55 μm, the spectral range of interest for optical communications. The films are used as mode-lockers in an erbium doped fibre laser, achieving ∼700 fs mode-locked pulses. Raman spectroscopy shows no damage after a long time continuous laser operation.

Carbon nanotubes for ultrafast photonics

Abstract: We report characterization by absorption and photoluminescence excitation (PLE) spectroscopy of carbon nanotube solutions, which are then used for nanotube-based composite preparation. PLE shows the presence of bundles in the solution. The composite show a saturation intensity of 5 MW/cm 2 and is used in a fibre laser to generate pulses as short as 866 fs at about 1530 nm.

Advanced waveguide lasers fabricated by femtosecond laser writing in an Er: Yb-doped phosphate glass

Abstract: Recently, great effort has been devoted to waveguide lasers, because of their inherent simplicity with respect to fiber lasers. Actually, due to their compactness, such lasers are expected to achieve a higher temporal coherence, making them attracting for fiber optical reflectometry, distribute sensing, and range finding applications. Furthermore, the availablity of fast saturable absorbers based on carbon nanotubes allows for a cheap and reliable implementation of the passive mode-locking technique with the potential for generating high repetition rate pulse trains. Such lasers will provide low-noise and inexpensive pulsed sources for applications in optical communications, optically sampled analog-to-digital converters, and spectral line-by-line pulse shaping. We report here on advanced waveguide lasers, operating both in continuous wave and pulsed regimes, based on active waveguides fabricated by femtosecond laser writing in a phosphate glass substrate. A single longitudinal mode waveguide laser providing more than 50 mW with 21% slope efficiency was demonstrated. Furthermore, by combining a high gain waveguide and an innovated fiber-pigtailed saturable absorber based on carbon nanotubes, a mode-locked ring laser providing transform limited 1.6-ps pulses was also demonstrated.