Long Range and Collective Impact of Au Surface Adatoms on Nanofin Growth

In the Au-catalyzed surface-directed vapor–liquid–solid (S-VLS) growth of semiconductor nanowires, individual Au nanodroplets result in the lateral growth of single nanowires per site. However, using the same process, the growth of single nanofins (fins) per catalyst site becomes unpredictable. We show that as the Au catalyst pattern size reduces to the microscale and smaller, the lateral fin growth is suppressed, and instead lateral nanowires prevail. We identify the origin of this phenomenon and reveal a novel aspect of Au catalysis in the growth of the ZnO nanostructures. While a Au nanodroplet drives the elongation of the lateral nanowire on the surface via a VLS process, we show that the surface-adsorbed Au atoms at the vapor–semiconductor interface catalyze the out-of-plane growth on the (0002) ZnO plane, resulting in fins. For instance, as the Au film thickness is increased from 2 to 8 nm, the out-of-plane fin growth rate increases. At and beyond 12 nm thickness, the fin growth abruptly stops, and only nanowires form. We attribute this behavior to a decline in the Au surface adatom concentration in response to the lower chemical potential (Gibbs–Thomson vapor pressure) of Au as the particle size increases. As a result, the fin formation from a given catalyst pattern strongly depends on the arrangement of the neighboring catalyst patterns, their shape, and thickness. These findings enable strategies to facilitate controlled single-fin formation in ordered arrays using micro- and submicrometer-size catalyst patterns.