Three dimensional ZnO nanotube arrays and their optical tuning through formation of type-II heterostructures

Abstract

In this paper, we report on the first successful attempt of chemical vapor deposition (CVD) synthesis of well-aligned single-crystalline ZnO nanotube arrays on Mo wire mesh. According to detailed morphology and composition analyses, a rational growth model is proposed to illustrate the growth process of the hollow ZnO nanotubes. Metastable Zn-rich ZnO_x nanorods formed in the early stage are believed to play a vital role towards the formation of nanotube configuration. In addition, we also successfully fabricate ZnO/ ZnS and ZnO/CdS core/shell nanotube arrays by simply depositing ZnS and CdS on the pre-fabricated ZnO nanotubes. Despite the existence of a large lattice mismatch, the grown ZnS and CdS layers are somewhat single-crystalline and show an epitaxial orientation relationship with the inner ZnO, that is, [0001]_{ZnS or CdS}//[0001]_ZnO and (10-10)_{ZnS or CdS}//(10-10)_ZnO. Further, room temperature cathodoluminescence (CL) characterization indicates that after surface decoration, the formed ZnO-based heterostructures show dis- tinguished optical properties. Quenching of 67.2% and 99.7% of ZnO near-band-gap (NBE) emission is ob- served on ZnO/CdS and ZnO/ZnS, respectively. Efficient charge separation resulting from type-II band con- figuration is considered to be responsible for the variation of optical properties. Our method may represent a powerful synthesis platform for creation of ZnO nanotubes and ZnO-based hollow heterostructures with tunable properties

Self-Assembled Vertically Aligned Hetero-Epitaxial ZnO/CdS Core/Shell Array by all CBD Process: Platform for Enhanced Visible-Light-Driven PEC Performance

“…As there are few reports on the heteroepitaxial ZnO/CdS core/shell heterostructure, we compare our observed results first in general with the earlier reported PEC data on ZnO/CdS-based core/shell systems (Table ). There are a few studies on ZnO/CdS core/shell NR arrays covered with some passivation/sensitization layer employed to enhance the absorption as well as photostability of ZnO/CdS NR photoanodes.…”

“…The interplanar spacing of ∼3.3 Å in the shell region is attributed to the (002) plane of wurtzite CdS (JCPDS 41-1049) on the well-oriented ZnO NR core. Moreover, the angle between the lattice fringes of (002) planes of ZnO core ( d 002 ∼ 2.6 Å) and CdS shell ( d 002 ∼ 3.3 Å) is found to be ∼38°, which suggests tilted-epitaxy growth, (002) ZnO //(002) CdS heteroepitaxy, of wurtzite CdS QDs on ZnO NRs. , Furthermore, the corresponding SAED pattern of ZC90 in Figure f is the combination of two sets of diffraction patterns from the ZnO core as well as CdS shell. The clearly observed diffraction spots correlate to the [002] growth direction.…”

“…Moreover, the angle between the lattice fringes of (002) planes of ZnO core (d 002 ∼ 2.6 Å) and CdS shell (d 002 ∼ 3.3 Å) is found to be ∼38°, which suggests tilted-epitaxy growth, (002) ZnO //(002) CdS heteroepitaxy, of wurtzite CdS QDs on ZnO NRs. 47,48 Furthermore, the corresponding SAED pattern of ZC90 in Figure 6f For the ZC0 sample, a clear and abrupt absorption edge at ∼375 nm is ascribed to the direct band gap of wurtzite ZnO (E g ∼ 3.3 eV), and there is low absorbance in the visible region. Deposition of CdS on ZnO NRs absorbance in the visible region is observed, which continues to increase with the eventual evolution of the second absorption edge when the CdS QD-shell becomes conformal.…”

Carbon-Coated Graphitic Carbon Nitride Nanotubes for Supercapacitor Applications

“…Many materials could form three-dimensional (3D) nanotube structures, such as TiO 2 nanotubes, 5,6 carbon nanotubes, 7 and ZnO nanotubes. 8 Generally, materials with a nanotubular morphology could be fabricated by template 9,10 and nontemplate 11,12 methods. The template method needs to introduce a template, either a hard template (e.g., carbon, 5 MnO x 13 ) or a soft template.…”

“…Hollow nanotube structures have many advantages such as large specific surface area and more active sites, which have attracted extensive research interest in supercapacitor, photocatalyst, biochemistry, lithium ion battery, etc. Many materials could form three-dimensional (3D) nanotube structures, such as TiO 2 nanotubes, , carbon nanotubes, and ZnO nanotubes . Generally, materials with a nanotubular morphology could be fabricated by template , and nontemplate , methods.…”