Single gold nanowires with ultrahigh (>10⁴) aspect ratios by triphasic electrodeposition

Due to their superior optical and electrical properties, gold nanowires are used ubiquitously across industries. Current techniques for fabricating such structures are often expensive, involving multiple steps, cleanroom operation, and limited ability for a user to controllably place a nanowire at a desired location. Here, we introduce the concept of triphasic electrodeposition, where metal salts act as antagonistic salts at the liquid|liquid interface, leading to their increased concentration at this phase boundary. We show that the electrodeposition of ultra-high aspect ratio gold nanowires may be achieved in a one-step, one-pot method by submerging a conductor in contact with two phases: an organic phase containing HAuCl₄ and a quaternary ammonium salt, and an aqueous phase containing potassium chloride. Changing electrodeposition parameters in the triphasic system allows tunability of important features of the nanowire, such as size and thickness. Furthermore, this new method provides an impressive ability to choose the geometry and precise positioning of deposited nanowires simply by changing where a liquid|liquid interface contacts the electrode surface.