Solid-Liquid-Vapor Synthesis of Negative Metal Oxide Nanowire Arrays

Nanowires grown using the vapor-liquid-solid (VLS) mechanism are highly attractive components for functional nanomaterials since they grow along unique crystallographic axes to form defect-free single crystals with well-controlled dimensions. To date, however, these free-standing wires have been put to little use, since their ordered arrangement or placement is highly challenging. Here, we report an approach to create ordered arrays of nanoscale interfaces, in which we utilize the reverse of the VLS mechanism (the solid-liquid-vapor (SLV) mechanism) to etch the inverse of a nanowire, a "negative nanowire", into a single crystal. In this way, we achieve essentially the same array of crystallographic surfaces as would be achieved by growing a large array of nanowires but in a way that creates a single object which is easy to handle. The SLV mechanism is a unique approach in that it is governed by the same crystallography which makes the VLS mechanism attractive but, additionally, poses several key advantages, such as the tendency for negative nanowires to grow along a preferred etch direction inherently leading to arrays of negative nanowires with related alignment and orientation. Here, we present proof-of-principle experiments to show that SLV etching to synthesize negative nanowires can be performed in a nonreactive atmosphere and on single-crystalline zinc oxide and tin(IV) oxide substrates, demonstrating control over shape, size, alignment, and growth direction.