Random Carbon Nanotube Networks Research Articles

Detection of Nonpolar Molecules by Means of Carrier Scattering in Random Networks of Carbon Nanotubes: Toward Diagnosis of Diseases via Breath Samples

Field effect transistors (FETs) based on random networks (RNs) of single-wall carbon nanotubes (CNTs) have several technological advantages. However, the low sensitivity (or no sensitivity) of RN-CNT sensors to nonpolar molecules is a problematic, negative feature that limits their applications in the detection of a wide variety of diseases via breath samples. In this paper, we show experimental evidence for the detection of both individual nonpolar molecules and patterns of nonpolar molecules, even in the presence of polar molecules in the same environment. We do so by preparing RN-CNT FETs and functionalizing them with organic films that exhibit distinctive electrical and physical (or mechanical) characteristics. Exposing the functionalized RN-CNTs to representative nonpolar breath biomarkers, and, for comparison, to polar molecules in the gas phase, and monitoring the changes in conductance, work function, and organic film thickness show sensitivity toward nonpolar molecules. We explain this observation by carrier scattering as a result of swelling of the organic film upon exposure to (nonpolar) chemical agents. Hence, the sensitivity towards nonpolar molecules can be tailored, even in the presence of polar molecules, by controlling the scattering of charge carrier through deliberate functionalization of CNTs. As examples for the technological impact of our findings, we describe ways to detect lung cancer and kidney disease using specially designed RN-CNT sensor arrays.

A New Method of Carbon‐Nanotube Patterning Using Reduction Potentials

Carbon nanotubes (CNTs) have attracted considerable interest as high-stiffness materials and for use in nanodevices, on account of their extraordinary mechanical, chemical, and electrical properties. There have been several examples of CNTs being used to realize devices and composites. However, several hurdles remain to be overcome before CNT-based technology can be deployed on a commercial scale. Among these hurdles are locating and patterning technologies. So far, films of CNT networks have been patterned in the micrometer regime by a variety of techniques, including using a poly(methyl methacrylate) (PMMA) or poly(dimethylsiloxane) (PDMS) stamp, CO2 snow-jet etching, and O2-plasma etching. [4] However, these methods have limitations in commercial applications, such as lack of scalability, low resolution, and low reliability. This paper reports that noble metals, such as Au, Pt, and Ag, can promote the oxidation of CNTs at a relatively low temperature (350 8C), because of the reduction potential of the CNTs (in this study, oxidation means decomposition to CO2). Based on these phenomena, a nanometer-sized, patterned, random network of CNTs is fabricated. This study also examines the difference in the reduction potentials of single-walled and multiwalled CNTs (SWCNTs and MWCNTs, respectively). Scheme 1 summarizes the experimental procedure used to determine the reduction potential of the CNTs and to obtain the novel nanometer-sized patterns of SWCNTs. In order to make a CNT–metal junction, very thin metal films were deposited on a CNT film using electron-beam evaporation. The samples were then annealed in a box furnace at 350 8C in ambient air. In a reactive environment, a material system can be considered a ‘‘galvanic cell’’ if there is electrical contact between two materials with different reduction potentials, and they are in the same electrolyte. Under these conditions, the corrosion rate of the material with the lower reduction potential can be faster than that of the material with the higher reduction potential. The novel method for patterning CNT films was developed by applying this phenomenon. In order to confine the CNTs to a selected area,

Turning Carbon Nanotubes from Exceptional Heat Conductors into Insulators

Thermal conductivity (kappa) of isolated carbon nanotubes (CNTs) is higher than the kappa of diamond; however, in this Letter we show that the kappa of a packed bed of three-dimensional random networks of single and multiwall CNTs is smaller than that of thermally insulating amorphous polymers. The thermoelectric power (Sigma) of the random network of CNTs was also measured. The Sigma of a single wall nanotube network is very similar to that of isolated nanotubes and, in contrast with kappa, Sigma shows a strong dependence on the tube diameter.

Novel carbon nanotube network deposition technique for electronic device fabrication

AbstractWe present a novel dry and room‐temperature method for the deposition of random carbon nanotube networks (CNTNs) onto various substrates. This method is based on natural charging of carbon nanotube (CNT) bundles in the gas‐phase and their efficient deposition directly downstream of the synthesis reactor by means of an electric field. The density of the deposited CNTNs was controllably adjusted by varying the deposition time and the electric field strength. Application of this deposition technique for the fabrication of single‐walled CNTNbased field‐effect transistors (FETs), where a random CNTN serves as a transport channel, is presented. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Nanotechnology builds flexible electronic circuits from random networks of carbon nanotubes

Nanotechnology builds flexible electronic circuits from random networks of carbon nanotubes

Estimating the yield and characteristics of random network carbon nanotube transistors

The device characteristics of field-effect transistors featuring a random network of carbon nanotubes (CNTs) as a channel material were investigated by means of a numerical simulation. The simulations of the conductivity of CNTs, contact resistances, and metallic to semiconducting ratio indicated that, even with a random network composed of one-third metallic CNTs, the maximum yield rate can be dramatically increased by shortening the CNTs. The error rate can be reduced to 0.0014% when the length of CNTs is one-tenth of the source-to-drain distance. The conductance of the devices, on/off ratio, and methods to improve these characteristics are also discussed.

Percolation in random networks of heterogeneous nanotubes

The electrical performance of random carbon nanotube network transistors is found by Monte Carlo simulation to strongly depend on the nature of the conduction path percolating the network. When the network is percolated only by semiconducting nanotube pathways (OSPs), the transistors can directly achieve both high on current and large on/off current ratio. Based on percolation theory, the present work predicts that there exist specific nanotube coverage domains within which OSP has the highest probability and becomes predominant. Simulation results show that the coverage domains depend on the network dimension, nanotube length, and the fraction of metallic nanotubes.

Carbon nanotube based battery architecture

We have fabricated batteries using a random network of carbon nanotubes serving both as the charge collector and the interface with the active components. Due to the high network conductivity and high porosity, such networks, in combination with nanoscale active components, lead to batteries with excellent energy storage characteristics. In addition the devices can be fabricated using a roll-to-roll or inkjet printing process, the essentials of what can be called “printed power.”

1 ∕ f noise and percolation in carbon nanotube random networks

The 1∕f noise in carbon nanotube random network films has been experimentally and theoretically investigated. The authors have established that the percolation process is the primary physical mechanism influencing the noise level in such films. Using percolation theory, the authors give an expression for the 1∕f noise scaling that describes how noise is affected by design variables of nanotube macrostructures. As expected for percolation networks, the noise amplitude strongly depends on the film homogeneity. This shows that noise analysis could be used as a tool to evaluate the quality of films.

Structure and magnetic properties of nanoparticles trapped in a carbon matrix along with the catalytic growth of carbon nanotubes

The combination of magnetic materials and carbon nanotubes (CNTs) is a promising research direction with a wide range of applications such as magnetic storage and drug delivery free of toxicity. It is well known that some transition metals are mandatory for the nucleation and growth of CNTs by pyrolysis. This paper deals with a new approach where Fe–C nanostructures are developed in a carbon matrix with a random network of CNTs by the polymers pyrolysis (phenol-formaldehyde resins and polyvinyl alcohol) and ferrocene up to 900 °C in inert atmosphere. The proposed method is simple and could be a promising way to produce magnetic nanoparticles coated with carbon as well as CNTs. The characterization (TEM, Mössbauer spectroscopy) and magnetic properties of the carbon–iron system are systematically investigated.

Graph Spectra of Carbon Nanotube Networks: Molecular Communication

ABSTRACTThe integrated application within random carbon nanotube networks (CNT) to carry and fuse information, as well as perform simple sensing, is explored. One may imagine small CNT networks with functionalized nanotubes simultaneously sensing multiple targets in-vivo for unprecedented understanding of biological pathways. This is clearly distinct from the traditional convoluted approach of using CNT networks to construct transistors that are in turn used to construct communication networks. With random CNT network layouts, routing of information is an integral part of the physical layer.A Mathematica analysis for evaluating random CNT networks has been developed and used to verify design characteristics. The graph spectrum of the CNT network is used to determine resistance and electron mobility characteristics. Thus, we have been able to find relationships among CNT network structure and electron mobility. The nanotube density allows for an increase in the number of bits per square meter of information transfer compared to wireless communication. Consider a wireless network; a typical bit-meters/second capacity is limited in a traditional wireless network. The maximum wireless capacity approximation in a wireless broadcast media is contrasted with a CNT network; we look at the efficiency of CNT networks to carry information and compare with theoretical limits.

Random networks of carbon nanotubes as an electronic material

We report on the transport properties of random networks of single-wall carbon nanotubes fabricated into thin-film transistors. At low nanotube densities (∼1 μm−2) the networks are electrically continuous and behave like a p-type semiconductor with a field-effect mobility of ∼10 cm2/V s and a transistor on-to-off ratio ∼105. At higher densities (∼10 μm−2) the field-effect mobility can exceed 100 cm2/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.