Electronic properties, single SWNTs

The first important group of nanomaterials with application in sensors and biosensors field is represented by the CNTs [114], The nanodimensions, surface chemistry and electronic properties of CNT make this material an ideal candidate for chemical and biochemical sensing. There are two main types of CNTs (i) single-walled nanotubes (SWNTs) consisting of single graphite rolled seamlessly wrapped into a cylindrical tube (1-2 nm diameter) represents undoubtedly one of the more remarkable discoveries in the... 

Some extraordinary features have been observed in these studies. Single tubes and bundles, for example, differ significantly in their electronic properties, but also different types of SWNTs among themselves show rather individual characteristics. For instance, there are semiconducting and metalhc nanotubes, different bands are observed in Raman spectra depending on the tubes diameter, etc. This chapter will deal with these and a number of further properties. 

Up to now only the electronic properties of single carbon nanotubes have been regarded. In reality, however, frequent use is being made of multiwalled tubes or of bundles of single-walled species. Their electronic properties differ to some extent from those of isolated SWNT. Yet the growing complexity of the systems increasingly complicates the analytical description of the density of states and band structure. Still some recent publications on the matter discuss the phenomena observed upon the assembly of several tubes. 

The most readily cited examples of this class of nanocomposite are systems based on carbon nanotubes. Carbon nanotubes have many interesting properties, including exceptionally high mechanical strength and remarkably versatile electronic properties. They occur in two distinct forms single-walled nanotubes (SWNTs) and multiwalled nanotubes (MWNTs). Compared with multiwalled nanotubes, single-waUed nanotubes are expensive and difficult to obtain, but they have been of great interest due to their superior electronic, mechanical, and gas adsorption properties. 

Since its discovery [199], CNTs have attracted enormous attention as a novel catalyst material due to their high aspect ratio and unique electronic properties [166,167,172,174,175,177,178,199-206]. CNT is an allotrope of carbon with a cylindrical nanostructure made from curved graphite sheets. CNTs can be classified as single-walled nanotubes (SWNTs), double-walled nanotubes (DWNTs),... 

Research on modeling of endohedral fullerenes within single-walled carbon nanotubes (SWNTs) has received increased attention towards the understanding of their electronic and structural properties [304-307]. However, very recently particular emphasis was given to the endohedral fullerenes N C60 [308-313] and P C60 [314] due to the electron spin on the nitrogen or phosphorus site, respectively. Having an extremely long decoherence time the unpaired electron spin could be used as a qubit within a quantum computer. 

Intermolecular interactions define crucial characteristics of materials for hydrogen storage materials. This topic is discussed in detail in the chapter by Cheng et al. devoted to molecular dynamics simulations of single-walled carbon nanotubes (SWNT) with molecular hydrogen. The properties of modified SWNTs, in the contribution from Politzer et al., are also analyzed from the point of view of potential applications in molecular electronics. 

Double-walled carbon nanotubes (DWNTs), first observed in 1996, constitute a unique family of carbon nanotubes (CNTs). -2 DWNTs occupy a position between the single-walled carbon nanotubes (SWNTs) and the multiwalled carbon nanotubes (MWNTs), as they consist of two concentric cylinders of rolled graphene. DWNTs possess useful electrical and mechanical properties with potential applications. Thus, DWNTs and SWNTs have similar threshold voltages in field electron emission, but the DWNTs exhibit longer lifetimes.3 Unlike SWNTs, which get modified structurally and electronically upon functionalization, chemical functionalization of DWNTs surfaces would lead to novel carbon nanotube materials where the inner tubes are intact. The stability of DWNTs is controlled by the spacing of the inner and outer layers but not by the chirality of the tubes 4 therefore, one obtains a mixture of DWNTs with varying diameters and chirality indices of the inner and outer tubes. DWNTs have been prepared by several techniques, such as arc discharge5 and chemical vapor depo-... 

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