Selective Growth of Pure and Long ZnO Nanowires by Controlled Vapor Concentration Gradients

Abstract

ZnO can appear as nanowires, nanobelts, and nanocombs, which are attractive for various applications. However, this has prevented the growth of desired nanostructures without other trace morphologies. Here we demonstrated a mechanism for selective growth of pure and long ZnO nanowires. This was obtained by placing a gold film at a high-temperature zone so that ZnO nanowires with controllable densities can be grown on adjacent bare substrates at lower temperature zones. The concentration gradients of gold and ZnO vapors are responsible for this selective growth, which could be applicable for selective growth of ZnO nanobelts and nanocombs in the future.

In situobservation of size-scale effects on the mechanical properties of ZnO nanowires

“…In this set-up, the full nanowire-contacts system may be regarded as having a pinned and clamped configuration. Our ZnO nanostructured samples were synthesized by the thermal chemical vapor deposition method, as reported elsewhere [22,23]. Figure 2(c) displays the ZnO nanowire under the compressive/bending state by incremental movement of the piezo-driven gold tip against the AFM tip.…”

Growth direction and morphology of ZnO nanobelts revealed by combiningin situatomic force microscopy and polarized Raman spectroscopy

“…33 Experimental studies using similar equipment have shown that, inside the furnace, the temperature and the ZnO vapor pressure decreases as the distance to the source ͑alumina boat containing ZnO powder͒ increases. [35][36][37] Various morphologies of ZnO nanostructures, with a wide range of aspect ratios, were formed depending on the substrate temperature and distance to the source. [35][36][37] ZnO nanobelts with high w / t were most likely observed on the substrate located close to the ZnO source at a higher temperature, and that observation was made whether a gold catalyst was added to the substrate or not.…”

“…[35][36][37] Various morphologies of ZnO nanostructures, with a wide range of aspect ratios, were formed depending on the substrate temperature and distance to the source. [35][36][37] ZnO nanobelts with high w / t were most likely observed on the substrate located close to the ZnO source at a higher temperature, and that observation was made whether a gold catalyst was added to the substrate or not. 37 Growth at high temperatures and large supersaturation ratio ͑nonequilibrium conditions͒ also leads to ZnO nanostructures with a high density of defects, due to the higher deposition rate of molecular ZnO from the vapor.…”

“…[35][36][37] ZnO nanobelts with high w / t were most likely observed on the substrate located close to the ZnO source at a higher temperature, and that observation was made whether a gold catalyst was added to the substrate or not. 37 Growth at high temperatures and large supersaturation ratio ͑nonequilibrium conditions͒ also leads to ZnO nanostructures with a high density of defects, due to the higher deposition rate of molecular ZnO from the vapor. 38 The introduction of defects, particularly at high temperatures, can increase the growth rate of ZnO nanostructures and the overall size of the synthesis products.…”

In situ probing of electromechanical properties of an individual ZnO nanobelt

“…Our ZnO samples were synthesized by thermal chemical vapor deposition method, as reported elsewhere. 9,10 For in situ electrical measurement, an individual ZnO nanobelt was attached to the electromechanically etched tungsten tip by tungsten deposition using the focused ion beam ͑FIB͒ technique to ensure good electrical contact between the tip and the nanobelt. The different steps of the sample preparation are shown in Figs.…”