Nanowires

Introduction

A nanowire can be defined an extremely thin wire with lateral size constrained to tens of nanometers or less and unconstrained longitudinal size, the ratio of the length to width can be greater than 1000. At these scales, quantum mechanical effects are important, hence such wires are also known as "quantum wires". Many different types of nanowires have been developed, including superconducting nanowire (e.g. YBCO), semiconducting nanowire (e.g. silicon nanowires (SiNWs), InP, GaN), metallic nanowire (e.g. Ni, Pt, Au) and insulating nanowire (e.g. SiO₂, TiO₂). Molecular nanowires are composed of repeating molecular units either organic (e.g. DNA) or inorganic (e.g. Mo₆S₉−_xI_x).

Fig 1 SEM of silver nanowires

Nanowire exhibits high flexibility, high strength and uniform morphology. As for their thermoelectric properties, metallic nanowire shows high Seeback coefficient because of the enhanced density of electronic states. Thus it can conduct heat or electricity substantially higher than any bulk material. The crystalline structure of nanowire increases the electrical properties by many fold. The large surface area of nanoparticles provides motivating catalytic properties for nanowire. Considering optical properties, metallic nanowire shows unique plasmon absorption effect.

Fig 2 Nanoarray structure in fiber nanogenerators.

Applications

Nanowires exhibit unique thermal, chemical, electronic, optical and mechanical properties which are not found in bulk materials and which have their related fields of applications.

• Chemical and biological nanosensors: Nanowire sensors have the potential to be smaller, more sensitive, demand less power and react faster than their macroscopic counterparts, which lead to opportunities for the miniaturization of chemical and biological sensors.

• Electronic devices: Nanowires can be used for transistors, which are used widely as fundamental building element in electronic circuits. Due to the unique one-dimensional structure with remarkable optical properties, the nanowire also opens new opportunities for realizing high efficiency photovoltaic devices.

• Nanowire lasers: Nanowire lasers are nano-scaled lasers with potential as optical interconnects and optical data communication on chip. Nanowire lasers are built from III–V semiconductor heterostructures, the high refractive index allows for low optical loss in the nanowire core.

• Nanowire battery: Nanowire battery uses nanowires to increase the surface area of one or both of its electrodes. Some designs based on nanowire materials (silicon, germanium and transition metal oxides) have been announced, which can improve battery performance.