Formation of single crystalline ZnO nanotubes without catalysts and templates

Abstract

Oxide and nitride nanotubes have gained attention for their large surface areas, wide energy band gaps, and hydrophilic natures for various innovative applications. These nanotubes were either grown by templates or multistep processes with uncontrollable crystallinity. Here the authors show that single crystal ZnO nanotubes can be directly grown on planar substrates without using catalysts and templates. These results are guided by the theory of nucleation and the vapor-solid crystal growth mechanism, which is applicable for transforming other nanowires or nanorods into nanotubular structures.

Controlling the Growth Mechanism of ZnO Nanowires by Selecting Catalysts

“…Due to the constraints that originated from liquid-phase catalyst nanoparticles, beyond onedimensional nanowires and nanorods, the VLS process seldom leads to the formation of complex structures. In general, the VS mechanism is the driving force behind the synthesis of many kinds of ZnO architectures and hierarchical nanostructures, such as tetrapods, 24 nanotubes, 25,26 nanoneedles, 27 nanohelices and nanosprings, 28 nanorings, 29 nanodisks, 25,30 nanodonuts, 31 nanobridges and nanonails, 32 nanopins, 33 nanocombs, 34 nanowalls, 35 nanoflowers, and so forth. 36 Under a certain environmental condition it could be controversial how the VLS and the VS mechanisms compete with each other and what roles the catalytic particles play in the growth process.…”

Bubble‐Templated and Flow‐Controlled Synthesis of Macroscopic Silica Tubes Supporting Zinc Oxide Nanostructures

“…We note that ZnO nanotubes and rods of similar dimensions have been grown using chemical vapor deposition. [13] High-resolution transmission electron microscopy The powder X-ray diffraction (XRD) pattern in Figure 2 e complements the SAED pattern. The X-ray data show that the tube contains sufficient amounts of crystalline material to allow for a reliable assignment.…”

Nanostructuration and band gap emission enhancement of ZnO film via electrochemical anodization

“…Nanostructuration of the ZnO films has been reported as one of the possible means to improve its band gap emission and to raise its efficiency as TCO in photovoltaic applications [1,4]. Various morphologies of ZnO nanostructures including nanorods [1,4], nanowalls [5] and single-crystal nanotubes [6] can be synthesized using different methods such as; hydrothermal technique [7], template-assisted growth [8] and ultra-fast microwave method [9]. However, these synthesis routes have disadvantages of (i) poor adhesion to the substrate, making it difficult to integrate them into the device configuration and (ii) presence of structural defects and contaminants inherent of these processing routes, leading to suppression of the UV emission as in the case of photoluminescence (PL), for example [10].…”