Synthesis of Nanowire

There are two basic approaches of synthesizing nanowires: top-down and bottom-up approach. In a top-down approach a large piece of material is cut down to small pieces through different means such as lithography and electrophoresis. Whereas in a bottom-up approach the nanowire is synthesized by the combination of constituents ad-atoms. Most of the synthesis techniques are based on bottom-up approach.

Nanowire structures are grown through several common laboratory techniques including suspension, deposition (electrochemical or otherwise), and VLS growth.

Suspension

A suspended nanowire is a wire produced in a high-vacuum chamber held at the longitudinal extremities. Suspended nanowires can be produced by:

- The chemical etching, or bombardment (typically with highly energetic ions) of a larger wire
- Indenting the tip of a STM in the surface of a metal near its melting point, and then retracting it

VLS Growth

A common technique for creating a nanowire is the Vapor-Liquid-Solid (VLS) synthesis method. This technique uses as source material either laser ablated particles or a feed gas (such as silane). The source is then exposed to a catalyst. For nanowires, the best catalysts are liquid metal (such as gold) nanoclusters, which can either be purchased in colloidal form and deposited on a substrate or self-assembled from a thin film by dewetting. This process can often produce crystalline nanowires in the case of semiconductor materials.

The source enters these nanoclusters and begins to saturate it. Once supersaturation is reached, the source solidifies and grows outward from the nanocluster. The final product’s length can be adjusted by simply turning off the source. Compound nanowires with super-lattices of alternating materials can be created by switching sources while still in the growth phase.

Inorganic nanowires such as Mo6S9-xIx(which are alternatively viewed as cluster polymers) are synthesised in a single-step vapour phase reaction at elevated temperature.

Solution-phase synthesis

Nanowires of many types of materials can be grown in solution. Solution-phase synthesis has the advantage that it can be scaled-up to produce very large quantities of nanowires as compared to methods that produce nanowires on a surface. The polyol synthesis, in which ethylene glycol is both solvent and reducing agent, has proven particularly versatile at producing nanowires of Pb, Pt, and silver