vaporliquidsolid

Vapor-liquid-solid, commonly abbreviated as VLS, refers to a growth mechanism used to synthesize one-dimensional nanostructures such as nanowires. In this process, a liquid metal catalyst particle forms a eutectic alloy with the material to be deposited and mediates material addition from the vapor phase.

In VLS growth, vapor-phase precursors are absorbed into the liquid catalyst and dissolved until supersaturation with the desired material is reached. At that point, the solid crystallizes at the liquid–solid interface, and nanowire growth proceeds with the catalyst droplet remaining at the tip. The diameter of the resulting nanowire is controlled by the size of the catalyst droplet and tends to stay relatively constant during growth.

Common materials include silicon grown with gold catalysts, as well as various III–V compounds, II–VI compounds, and other systems using suitable catalyst materials. Growth typically occurs under low-pressure chemical vapor deposition or molecular beam epitaxy, at temperatures above the eutectic temperature of the catalyst–material system. After growth, the droplet can often be left at the tip for continued elongation or removed if required.

Advantages of the VLS mechanism include the ability to produce high-crystal-quality, single-crystalline nanowires with uniform diameters and the potential for incorporating heterostructures or dopants along the wire. Limitations include possible contamination from the catalyst, diffusion of catalyst atoms into the nanowire, sensitivity to surface conditions, and challenges in achieving uniform growth across different materials or large-area production.

Historically, the VLS mechanism was described in the 1960s and has since become a standard approach for nanowire synthesis, with numerous material systems and variations developed, including alternative growth modes such as vapor-solid-solid.