Fundamental Insights into Nanowire Diameter Modulation and the Liquid/Solid Interface

Controlled modulation of diameter along the axis of nanowires can enhance nanowire-based device functionality, but the potential for achieving such structures with arbitrary diameter ratios has not been explored. Here, we use a theoretical approach that considers changes in the volume, wetting angle, and three-dimensional morphology of seed particles during nanowire growth to understand and guide nanowire diameter modulation. We use our experimental results from diameter-modulated InN and GaN nanowires and extend our analysis to consider the potential and limitations for diameter modulation in other materials systems. We show that significant diameter modulations can be promoted for seed materials that enable substantial compositional and surface energy changes. Furthermore, we apply our model to provide insights into the morphology of the liquid/solid interface. Our approach can be used to understand and guide nanowire diameter modulation, as well as probe fundamental phenomena during nanowire growth

Phalaena plecta

Semiconducting nanowires have unique properties that are distinct from their bulk counterparts, but realization of their full potential will be ultimately dictated by the ability to control nanowire structure, composition, and size with high accuracy. Here, we report a simple, yet versatile, approach to modulate in situ the diameter, length, and composition of individual segments within (In,Ga)N nanowires by tuning the seed particle supersaturation and size via the supply of III and V sources during the growth. By elucidating the underlying mechanisms controlling structural evolution, we demonstrate the synthesis of axial InN/InGaN nanowire heterojunctions in the nonpolar <i>m</i>-direction. Our approach can be applied to other materials systems and provides a foundation for future development of complex nanowire structures with enhanced functionality

Role of Au in the Growth and Nanoscale Optical Properties of ZnO Nanowires

Metallic nanoparticles play a crucial role in nanowire growth and have profound consequences on nanowire morphology and their physical properties. Here, we investigate the evolving role of the Au nanoparticle during ZnO nanowire growth and its effects on nanoscale photoemission of the nanowires. We observe the transition from Au-assisted to non-assisted growth mechanisms during a single nanowire growth, with significant changes in growth rates during these two regimes. This transition occurs through the reduction of oxygen partial pressure, which modifies the ZnO facet stability and increases Au diffusion. Nanoscale quenching of ZnO cathodoluminescence occurs near the Au nanoparticle due to excited electron diffusion to the nanoparticle. Thus, the Au nanoparticle is critically linked to the nanowire growth mechanism and corresponding growth rate through the energy of its interface with the ZnO nanowire, and its presence modifies nanowire optical properties on the nanoscale

The Growth and Optical Properties of ZnO Nanowalls

Nanowalls are novel nanostructures whose networked morphology holds potential for applications such as solar cells and gas sensors. The realization of such nanowall-based devices depends directly on a comprehensive understanding of the nanowall growth, namely, its competition with nanowire growth and the role of seed particles. We induced a morphological evolution from nanowires to nanowalls by increasing source flux during vapor transport and condensation growth. Nanowall growth kinetics indicates that their morphological dominance was driven by a time-dependent curvature of the nanowall growth facet. Nanowalls have excellent crystalline quality and strong near-band-edge luminescence and were found to grow by a combination of Au- and nonassisted mechanisms, resulting in Au nanoparticles within 300 nm of the substrate whose positions were associated with the origin of green luminescence. These results imply that the growth mechanism causes nanoscale structural variations, which in turn locally affect the optical properties of nanowalls