Flow-based solution-liquid-solid nanowire synthesis

Discovered almost two decades ago, the solution-liquid-solid (SLS) method for semiconductor nanowire synthesis has proven to be an important route to high-quality, single-crystalline anisotropic nanomaterials. In execution, the SLS technique is similar to colloidal quantum-dot synthesis in that it entails the injection of chemical precursors into a hot surfactant solution, but mechanistically it is considered the solution-phase analogue to vapour-liquid-solid (VLS) growth. Both SLS and VLS methods make use of molten metal nanoparticles to catalyse the nucleation and elongation of single-crystalline nanowires. Significantly, however, the methods differ in how chemical precursors are introduced to the metal catalysts. In SLS, precursors are added in a one-off fashion in a flask, whereas in VLS they are carried by a flow of gas through the reaction chamber, and by-products are removed similarly. The ability to dynamically control the introduction of reactants and removal of by-products in VLS synthesis has enabled a degree of synthetic control not possible with SLS growth. We show here that SLS synthesis can be transformed into a continuous technique using a microfluidic reactor. The resulting flow-based SLS ('flow-SLS') platform allows us to slow down the synthesis of nanowires and capture mechanistic details concerning their growth in the solution phase, as well as synthesize technologically relevant axially heterostructured semiconductor nanowires, while maintaining the propensity of SLS for accessing ultrasmall diameters below 10 nm.