Low-Frequency Noise Spectroscopy at Nanoscale: Carbon Nanotube Materials and Devices

This section presents brief description of peculiarities of carbon materials and advantages of noise spectsroscopy for the study of unique carbon nanotubes (CNT) materials and devices. In general, carbon is truly an extraordinary material with physical structures spanning three dimensional (3D) graphite, two-dimensional (2D) graphene and zero-dimensional (0D) buckyballs or buckminster fullerine spheres. It is not surprising that the structural characteristics of carbon thus yield band diagrams displaying a diverse array of physical properties. When a 2D graphene sheet is rolled into a cylinder, a one-dimensional (1D) or quasi-1D form of carbon results, namely CNTs, which have been one of the most extensively studied materials since their discovery. A single rolled-up sheet of graphene results in a single-walled nanotube (SWNT) with a typical diameter of 1 – 2 nm. The rolling direction is characterized by a chiral index ( , ) n m . Achiral zigzag ( ,0) n and armchair ( , ) n n CNTs are distinguished from the rest (chiral CNTs). Armchair tubes are always metallic, while zigzag tubes can be semiconducting or metallic (Reich et al., 2004). Multi-walled nanotubes (MWNTs) consist of concentric cylinders with an interlayer spacing of 0.3 – 0.4 nm, and diameters that are at least an order of magnitude larger than SWNTs, between 10 – 30 nm. CNTs have high elastic modulus, strength, show efficient conductivity of heat, exhibit high thermal and chemical stability, flexibility, low mass density, and unique electrical properties (metallic conductivity and semiconductivity) which makes them excellent candidates for nano-devices and polymer composite materials (Sánchez-Pomales et al., 2010; Service, 1998). At the same time the CNTs are extremely difficult to manage due to their low solubility in both aqueous and organic solvents, which restrict the extent of their applications. Therefore one of the main challenges is the need for the development of new functionalization chemistries that can increase the solubility of CNTs without altering their CNTs properties. Transport in the CNTs of molecular SWand MWNT-field-effect transistors (FETs) is dominated by holes and, at room temperature, it appears to be diffusive (Martel et al., 1998). Using the gate electrode, the conductance of a SWNT-FET is modulated