We report on the transport properties of random networks of single-wall carbon nanotubes fabricated into thin-film transistors. At low nanotube densities ͑ϳ1 m Ϫ2 ͒ the networks are electrically continuous and behave like a p-type semiconductor with a field-effect mobility of ϳ10 cm 2 /V s and a transistor on-to-off ratio ϳ10 5 . At higher densities ͑ϳ10 m Ϫ2 ͒ the field-effect mobility can exceed 100 cm 2 /V s; however, in this case the network behaves like a narrow band gap semiconductor with a high off-state current. The fact that useful device properties are achieved without precision assembly of the nanotubes suggests the random carbon nanotube networks may be a viable material for thin-film transistor applications.Perhaps the most intriguing electronic property of single-wall carbon nanotubes ͑SWNTs͒ is the high roomtemperature mobility of semiconducting SWNTs ͑s-SWNTs͒ that is more than an order of magnitude larger than the mobility of crystalline Si. 1,2 This high mobility has prompted researchers to fabricate and study field-effect transistors in which a single s-SWNT serves as a high-mobility transport channel. [1][2][3][4][5][6][7] Recent measurements on such devices yield a transconductance per unit channel width greater than that of state-of-the-art Si transistors. 7 However, because of the limited current-carrying capacity of individual SWNTs, many s-SWNTs aligned side by side in a single device would be required in order to surpass the current drive of a Si device. Such precise positioning of SWNTs is beyond the capability of current growth and assembly technology and presents a major technological hurdle for carbon nanotube-based electronic applications.In contrast, random arrays of SWNTs are easily produced either by direct growth on a catalyzed substrate or by deposition onto an arbitrary substrate from a solution of suspended SWNTs. If the density of SWNTs in such an array is sufficiently high, the nanotubes will interconnect and form continuous electrical paths. Such random arrays of SWNTs have not previously been seriously investigated for use as channels in field-effect transistors.In this letter we explore the transport properties of random networks of SWNTs and find that low density networks ͑ϳ1 m Ϫ2 ͒ behave like a p-type semiconducting thin film with a field-effect mobility ϳ10 cm 2 /V s, approximately an order of magnitude larger than the mobility of materials typically used in commercial thin-film transistors, e.g., amorphous Si. These mobility values and correspondingly good electronic quality of the random SWNT network are due to a combination of the low resistance of inter-SWNT contacts and the high mobility of the individual SWNTs, which together compensate for the extremely low fill factor of the network. These initial transport results are promising and indicate that such random nanotube networks ͑easily produced with no need for precision assembly͒ form an interest-ing electronic material that has potential for use in thin-filmtransistor applications to produce active electronic...

We report the use of carbon nanotubes as a sensor for chemical nerve agents. Thin-film transistors constructed from random networks of single-walled carbon nanotubes were used to detect dimethyl methylphosphonate (DMMP), a simulant for the nerve agent sarin. These sensors are reversible and capable of detecting DMMP at sub-ppb concentration levels, and they are intrinsically selective against interferent signals from hydrocarbon vapors and humidity. We provide additional chemical specificity by the use of filters coated with chemoselective polymer films. These results indicate that the electronic detection of sub-ppb concentrations of nerve agents and potentially other chemical warfare agents is possible with simple-to-fabricate carbon nanotube devices.

Nanometer-sized metal particles (e.g., gold and silver) are certain to be important fundamental building blocks of future nanoscale electronic and optical devices. However, there are numerous challenges and questions which must be addressed before nanoparticle technologies can be implemented successfully. For example, basic capping ligand chemistrysnanoparticle electronic function relationships must be addressed in greater detail. New methods for assembling nanoparticles together into higher-order arrays with more complex electronic functions are also required. This review highlights our recent progress toward characterizing electron transport in gold nanoparticles as a function of capping ligand charge state. These studies have shown that single electron tunneling energies can be manipulated predictably via pH-induced charge changes of surfacebound thiol capping ligands. We also show that rigid phenylacetylene molecules are useful bridges for assembling gold and silver nanoparticles into arrays of two, three, and four particles with psuedo D ∞h , D 3h , and T d symmetries. These nanoparticle "molecules" interact electromagnetically in a manner qualitatively consistent with dipole coupling models.

A method for synthesizing hollow nanoscopic polypyrrole and poly(N-methylpyrrole) capsules is described. The method employs gold nanoparticles as templates for polymer nucleation and growth. Etching the gold leaves a structurally intact hollow polymer capsule with a shell thickness governed by polymerization time (ca. 5 to >100 nm) and a hollow core diameter dictated by the diameter of the template particle (ca. 5−200 nm). Transport rates of gold etchant through the polymer shell to the gold core were found to depend on the oxidation state of the polymer, those rates being a factor of 3 greater for the reduced form of the polymer. We show for the first time that not only is the particle a useful template material but also that it can be employed to deliver guest molecules into the capsule core. For example, ligands attached to the gold surface prior to poly(N-methylpyrrole) formation remained trapped inside the hollow capsule following polymer formation and gold etching.

We report the development of high-mobility carbon-nanotube thin-film transistors fabricated on a polymeric substrate. The active semiconducting channel in the devices is composed of a random two-dimensional network of single-walled carbon nanotubes (SWNTs). The devices exhibit a field-effect mobility of 150cm2∕Vs and a normalized transconductance of 0.5mS∕mm. The ratio of on-current (Ion) to off-current (Ioff) is ∼100 and is limited by metallic SWNTs in the network. With electronic purification of the SWNTs and improved gate capacitance we project that the transconductance can be increased to ∼10–100mS∕mm with a significantly higher value of Ion∕Ioff, thus approaching crystalline semiconductor-like performance on polymeric substrates.