**1.3 Vapor-solid (VS)**

*Renewable and Sustainable Composites*

classified into the following three groups:

ibbons, nanobelts, or nanocables)

solid with the anisotropic crystallographic structure.

(VS), and the mechanism of solution-liquid-solid (SLS).

**1.1 Vapor-liquid-solid (VLS)**

or superlattices)

According to the dimensions in nanometer scale size, nanostructures can be

a. Zero-dimensional (0D) nanostructures (quantum dots, nanoparticles, or nanoclusters) b. One-dimensional (1D) nanostructures (nanowires, nanorods, nanotubes, nanor-

c. Two-dimensional (2D) nanostructures (super-thin films, multiple-layer films,

In comparison with 0D nanostructures, it is easier to investigate the relationship between the mechanical properties, optical and electronic transport, and the confinement of the size and dimensionality for 1D nanostructures. Moreover, 1D semiconductor nanomaterials have an extremely crucial effect of the active components and interconnect in the nanoscale electronic and photonic devices fabrications.

Up to now, 1D nanostructure is generally used to describe large aspect ratio rods, wires, tubes, and belt and tubes and has been the key point of investigation due to its attractive physical and technological significance in fabricating nanoscale devices. When the radial diameter of the 1D nanostructure is lower than some lengths (the path of the phonon mean free, the light of wavelength, Bohr radius, etc.), the effect of the quantum mechanics will be crucial. Owing to the large surface-to-volume ratio and the confinement of two dimensions, nanowires possess the definitely attractive electronic, magnetic, and optical properties. In addition, because nanowires' aspect ratio is extremely large, the quantum particles (photons, phonons, electrons, etc.) can be conducted directly easily to make the nanowires as the ideal candidate for the energy transport materials to enhance the relevant technique applications [9–17]. Today, numerous approaches have been researched to synthesize 1D nanostructures. Two fundamental steps are essentially involved in the evolution: nucleation and growth. A lot of solid materials with 1D nanostructures in nature are controlled by the bonding in the structure of crystallography in the highly anisotropic. The materials need common growth conditions including chemical vapor deposition (CVD), wet-chemical routs, and template-assistant methods. In classification, all the contemporary approaches are divided into bottom-up and top-down methods. The most important issue for developing a new synthetic method is to control the dimensions, morphology, and uniformity of nanostructures. When making a method to synthesize the nanostructures by the synthetic effects, it is definitely important to control the related morphology (or shape), dimensions, and uniformity simultaneously. To obtain 1D growth nanostructures, several chemical methods were generated. The current common six different strategies are (1) the reduction of a 1D microstructure in size, (2) 0D nanostructure self-assembly, (3) by a capping reagent kinetic control, (4) a template usage for direction, (5) a liquid droplet confinement as in the vapor-liquid-solid process, and (6) the control of a

Generally, there are four popular mechanisms for understanding the synthesis of 1D nanostructure materials. They are the mechanism of vapor-liquid-solid (VLS), the mechanism of oxide-assisted growth (OAG), the mechanism of vapor-solid

In the VLS mechanism, a liquid metal cluster or catalyst, such as Au, Fe, Ni, or Co, is taken as the energetically favorable point of the gas-phase reactant absorption.

**52**

For the mechanism of the vapor-solid (VS), the size of the nucleation site is critical for defining the rod diameter when the vapor supersaturation is appropriately controlled. Metal catalysts are not necessary. Three stages can be summarized as the illustration: (i) The source forms vapor phase, (ii) the vapor is transported by the carrier gas and deposits on the substrate to form crystalline nuclei, and (iii) the defects of the nuclei become the growth points, and the reactive vapor molecules further grow into nanostructures [27, 28].
