This chapter describes nanowires (NWs), their types, characteristic features, and their use in sensor and transistor applications as well. Introductory part in general explains briefly about nanowires (NWs), their characteristics features, types, as well as their most significant properties. The types of nanowires (NWs) can be of conducting materials such as Ni, Pt, Au; semiconducting materials like Si, InP, GaN; as well as insulating materials like that of SiO2, TiO2, etc. The property of nanowires includes mechanical, electrical, chemical, optical, and thermal properties. Also, a small description of nanowires (NWs) and sensors are explained with their performance parameters. Furthermore, nanowires (NWs)-based transistors are discussed in addition with their characteristics and applications. Finally, this chapter concludes with the significance of nanowires (NWs) in contemporary era.
TopIntroduction
Nanowires are those nanostructures which have diameters (Radial dimension) in the range of nanoscalethat is 10-9 (tens of nanometers) and lateral dimension upto range of micro meter (µm) as shown in Figure.1.
Figure 1. Represents typical Nanowire, which is equivalent to size of biological DNA
Nanowires (NW), can be of conducting materials such as (Al, Pt, Au), while semiconducting materials such as (Si, Ge, GaN) as well of insulating materials such as (SiO2, HfO2 TiO2) etc (Wu et al., 2008). Nanowires can be fabricated by using two approaches such as top-down approach and bottom-up approach but bottom-up is most preferably used because following parameters of Nanowires (Lu et al., 2008) like length, radius, chemical composition and direction of growth can be precisely controlled (Sohn et al., 2009; Yu & Meyyappan, 2006). Nanowires (NW) can used to design various types of sensorsas reported by various investigations (Najam, 2008). Further, because of large Young’s moduli, nanowires (NW) is used to design nano electromechanical systems (NEMS) (Lu et al., 2008). Nanowires (NWs) by virtue of excellent optical, electrical, chemical as well as mechanical properties are considered as popular nanomaterials (Muskins, 2008). The conductivity of Nanowires (NW) can be managed by field-effect mechanism, due to this action it can be used as future generation Transistors, Radom Access Memory (RAM) and advanced sensors (Hochbaum et al., 2008).
As per International Technology Roadmap of Semiconductors (ITRS) future generation transistor size can be scaled down to 18nm and gate length will scaled down to 7nm. At this dimensation conventional MOSFETs proves to be ineffective. Nanowires based MOSFETs are potential candidates at such device size. Moreover, for the diagnosis of diseases the future sensor must have fast real-time response, low cost and high resolution. The amazing properties of Nanowires give born to various types of biosensors, optosensors, gas sensor as well as electrochemical sensors.
Properties of Nanowire
Nanowires (NWs) possess extremely extraordinary properties which makes them useful for Nanoelectronics applications. The various properties are explained as follows:
Electrical Properties
The mechanism such as charge trapping and scattering electrical transport can be controlled easily with respect to both minority and majority carrier in Nanowire (NW). When light falls on Nanowires due to dielectric constant reduces the difference for light absorption by order of magnitude from ~250μm making Nanowires suitable for photovoltaics applications (Boukai et al., 2008).
Thermal Properties
Thermal properties depend upon the scattering of phonon within the Nanowires as thermal transport is due to phonons mostly. Due to small diameter the scattering of phonon reduces leads to reduction in heat transport. Thus making Nanowires suitable for thermoelectric applications (Chan et al., 2008; Cui et al., 2003).
Chemical Properties
Chemical properties depend upon large effective areas and surfaces. As nanowirespossess large area/volume ratio. Thus making Nanowires a potential candidate for Chemical and Sensing applications (Zheng et al., 2004).
Magnetic Property
Because of high energy of anisotropy with a super magnetic in Nanowires making them suitable for electromagnetic applications.
Catalytic Property
The large surface area of Nanowires formed due to transition oxide materials shows inspiring catalytic properties and can be further improved by using gold and platinum.
Types of Nanowires
Nanowires are often of two types because of its structural compositions.
Homogenous Structures
Homogeneous structure based nanowires with only one types of material composition such as Silicon (Si), germanium (Ge), etc.