4.1 Introduction

One-dimensional nanostructures have been called by a variety of names including: whiskers, fibers or fibrils, nanowires and nanorods. In many cases, nanotubules and nanocables are also considered one-dimensional structures. Although whiskers and nanorods are in general considered to be shorter than fibers and nanowires, the definition is often a little arbitrary. In addition, one-dimensional structures with diameters ranging from several nanometers to several hundred microns were referred to as whiskers and fibers in the early literature, whereas nanowires and nanorods with diameters not exceeding a few hundred nanometers are used predominantly in the recent literature. One will find, from reading this chapter, the fact that many fundamental understandings and techniques of growth of one-dimensional nanostructures are based on the early work on the growth of whiskers and fibers, albeit with less emphasis on nanometer scale. In this chapter, various terms of one-dimensional structures will be used interchangeably, though nanowires in general have a high aspect ratio than that of nanorods.

Many techniques have been developed in the synthesis and formation of one-dimensional nanostructured materials, though some techniques have been explored extensively, while others have attracted far less attention.

These techniques can be generally grouped into four categories:

1. Spontaneous growth:

   1. Evaporation (or dissolution) condensation

   2. Vapor (or solution) liquid solid (VLS or SLS) growth

   3. Stress induced recrystallization

2. Template-based synthesis:

   1. Electroplating and electrophoretic deposition

   2. Colloid dispersion, melt, or solution filling

   3. Conversion with chemical reaction

3. Electrospinning

4. Lithography

Spontaneous growth, template-based synthesis and electrospinning are considered as a bottom-up approach, whereas lithography is a top-down technique.