CNT-Based Electronic Devices

By leveraging the electronic properties outlined earlier, various electronic devices, including MJs, can be made using CNTs. However, a distinction between metallic 

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Smalley and coworkers sought to employ self-assembly to fabricate CNT-based electronic devices, where individual SWNTs were deposited on chemically functionalized nanolithographic patterns." This method should enable the creation of nanotube-based circuits and structures according to a predesigned pattern. Prior to this approach, it was common for nanotubes to be deposited on an electrode array by either random deposition (i.e., drop casting) or using probe microscopy (AFM or STM) to position CNTs on the electrode. Their approach is an example of using carboxylated CNTs in noncovalent interactions. 

A new approach to improve the performance of solar devices using natural pigments is to employ carbon nanotube (CNT)-based counter-electrodes. As previously reported, the excited dye transfers an electron to Ti02 and so it acquires a positive charge. Then, the cationic molecule subtracts an electron from the counterelectrode which is transported by the electrolyte. This reaction is usually catalyzed by means of conductive and electrocatalytically active species for triiodide reduction of carbon coatings. CNTs have a high superficial area, which represents a very... 

The exploration of biomolecules as components in CNT-based systems is a rapidly flourishing research field. The combination of the CNTs electronic and optical features with those of many biomolecules is appealing for many applications in medicine, optical device technologies and other fields. 

CNT based FETs can outperform the current FET technologies in many ways however, one of the most interesting properties of carbon nanotubes is the ballistic transport of electrons [178], which opens the possibility of constructing FETs that can operate at extremely high frequencies, making them suitable for the next generation electronic devices. Operation of SWCNT transistors has been demonstrated at microwave frequencies (see Fig. 21) [179] and more recently the operation of an SWCNT transistor in the terahertz frequency range was demonstrated [148]. 

The tunable electronic properties of CNTs are being explored for next-generation IC architectures. As you may recall from Chapter 4, traditional Si-based microelectronic devices will likely reach a fundamental limit within the next decade or so, necessitating the active search for replacement materials. Accordingly, an area of intense investigation is molecular electronics - in which the electronic device is built from the placement of individual molecules.Not surprisingly, the interconnects of these devices will likely be comprised of CNTs and other (semi)conductive ID nanostructures such as nanowires. 

Fig. 12 An electronic device based on a single rolled-up sheet of carbon atoms. (From Ref. () In the figure, a CNT (red about 1 nm in diameter) bridges two closely spaced (400 nm apart) platinum electrodes (labeled source and drain) atop a silicon surface coated with an insulating silicon oxide layer. Applying an electric field to the silicon (via a gate electrode, not shown) turns on and off the fiow of current across the nanotube, by controlling the movement of charge carriers onto the nanotube. (View this art in color at www.dekker.com.)...

Figure 3.1 DOS for (11,0) semiconducting (left) and (12,0) metallic (right) CNTs showing van Hove singularities based on a tight-binding model. Reprinted (adapted) with permission from Anantram, M. P., and Leonard, F., Physics of carbon nanotube electronic devices. Rep. Prog. Phys., 2006. 69 pp. 507-561. Copyright (2006) Institute of Physics and lOP Publishing Limited.

In this regard, we compared Au, Ru, and carbon nanotube (CNT) electrodes on molecular electronic devices. (This sub-chapter is mainly based on Ref. [28].) These are a few materials among the employed as an electrode in experiments. Au is the most popular in molecular electronics [29]. Tulevski et al. studied the Ru surface to which a carbon atom was bound by forming a multiple covalent bond [30]. Guo et al. studied CNT electrodes with an amide linkage [31]. Au, CNT, and Ru also represent a material mainly having s, p, and d band characters in the vicinity of their Fermi energies, respectively. 

Contraiy to popular belief, carbon nanotubes (CNTs) were not discovered by lijima in 1991 [1], but rather by Radushkevich and Lukyanovich in 1952 [2,3], who published clear transmission electron micrographs of 50nm diameter mbes made of carbon. Unfortunately, due to the pohlical tensions of the time this work wait largely unnoticed. In fact, with the discovery that CNTs were responsible for the high strength of Damascus steel from the seventeenth century [4], it became clear that thdr advantageous mechanical properties have been employed for some time. Today their novel properties have found use in a number of innovative electronic devices. This chapta details some of the more prominent appUcations based on their excellent field emission behavior. 

CNT-based FETs were used as electronic noses to detect odors. Metal electrodes were patterned over CVD-grown CNTs on an Si02/Si substrate with electron beam lithography to form the FET. To enhance the detection and provide selectivity, single-stranded DNA was deposited and dried on the device (Eigure 7.7a). The sensor was used to detect and distinguish between methanol and propionic acid, as shown in Eigure 7.7b, as well as other odors such as trimethylamine, dinitro-toluene, and dimethyl methylphosphonate. 

The excellent FE properties of CNTs, such as low-voltage operation, good stability, stable and high emission current, and large field enhancement factor, have opened new application fields in CNT-based devices. The use of CNTs as a source of electrons under an applied electric field is one of the most promising applications. As shown in Figure 8.5, it is easy to control the FE pattern of CNTs to... 

Nanoyam is spun from powder- or solution-based polymers. It has superior functional properties, owing to high surface area. Lepro et al. (2010) have developed carbon nanotube nanoyams from CNT forests grown on metallic substrates. They claim that the yams have interesting electrical and mechanical properties and that they could be used for various stractural applications in electronic devices (Bourzac, 2011). 

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