Electrically Addressable Hybrid Architectures of Zinc Oxide Nanowires Grown on Aligned Carbon Nanotubes

The fabrication and characterization of hybrid architectures of ZnO nanowires (ZNWs) grown on organized carbon nanotubes (CNTs), by a two‐step chemical vapor deposition (CVD) process involving CNT growth from a hydrocarbon source followed by ZNW growth using a Zn metal source, is reported. The ZNWs grow uniformly and radially from individual CNTs and CNT bundles, and the aligned morphology of the CNTs is not disturbed by the ZNW growth process. The nucleation and growth of ZnO crystals on CNTs are analyzed in relation to the classical vapor–solid mechanism. Importantly, the CNTs make uniform and distributed electrical contact to the ZNWs, with up to a 1000‐fold yield advantage over conventional ZNW growth on a flat substrate. Hybrid ZNW/CNT sheets are fabricated by scalable CVD, rolling, and printing methods; and their electrical properties, which are governed by transport through the anisotropic CNT network, are characterized. Functional interaction between the ZNWs and CNTs is demonstrated by photoconductive behavior and photocurrent generation of the hybrid material under UV illumination. There is significant future opportunity to extend these processing methods to fabricate other functional oxides on CNTs, and to build devices that harness the attractive properties of ZNWs and CNTs with high volumetric efficiency over large areas.     

Enhanced solar-driven water splitting by ZnO/CdTe heterostructure thin films-based photocatalysts

Solar-driven hydrogen production by water splitting using a photocatalyst is considered the most effective approach to produce hydrogen. Hydrogen is the most suitable renewable energy source. The efficiency of hydrogen production is still low. The efficiency of hydrogen production through photocatalysis can be enhanced by preparing a suitable and efficient photocatalyst. In this work, ZnO thin films were deposited on CdTe thin films at 600 °C, 650 °C, and 700 °C temperatures to form ZnO/CdTe heterostructure thin films by chemical vapor deposition (CVD) as photoelectrodes for water splitting. The photoelectrochemical properties showed that ZnO/CdTe heterostructure thin films have better photocurrent response compared to pristine ZnO and CdTe thin films. EIS results showed that the charge transfer at the electrode-electrolyte interface for ZnO/CdTe heterostructure thin films is much better than that of the pristine ZnO film. The ZnO/CdTe-700 °C heterostructure thin film has a 112-fold higher rate of photocatalytic hydrogen generation than pure ZnO.     

A facile room temperature chemical route to Pt nanocube/carbon nanotube heterostructures with enhanced electrocatalysis

The fascinating heterostructure of carbon nanotube-supported metal nanoparticles continues to attract interest for developing electrocatalysts for energy sciences. Here, we report the fabrication of noble metal nanocubes carbon nanotube nanocomposites through an electroless deposition route. The as-synthesized carbon nanotubes-supported Pt nanocubes with high active and selective {1 0 0} surfaces display excellent electrocatalytic activities towards the oxygen reduction reaction, which can/will replace current/state of the art cathode catalysts in fuel cells, and thereby improve the catalytic performance and utilization efficiency. The methodology presented here could be further extended to fabricate other one-dimensional materials/noble metal nanostructures.     

Properties and applications of quantum dot heterostructures grown by molecular beam epitaxy

One of the main directions of contemporary semiconductor physics is the production and study of structures with a dimension less than two: quantum wires and quantum dots, in order to realize novel devices that make use of low-dimensional confinement effects. One of the promising fabrication methods is to use self-organized three-dimensional (3D) structures, such as 3D coherent islands, which are often formed during the initial stage of heteroepitaxial growth in lattice-mismatched systems. This article is intended to convey the flavour of the subject by focussing on the structural, optical and electronic properties and device applications of self-assembled quantum dots and to give an elementary introduction to some of the essential characteristics.     

Structural and compositional evolution of FePt nanocubes in oganometallic synthesis

In this study, the mechanisms for the formation of FePt nanocubes via pyrolysis of iron pentacarbonate [Fe(CO)₅] and platinum(II) acetylacetonate [Pt(acac)₂] were investigated. The time evolution of the structure, morphology, and composition of the FePt nanocubes was probed by transmission electron microscopy (TEM) at different reaction stages. On the basis of the detailed characterization, we determined the following aspects of the reaction mechanism: (1) The FePt nanocubes are rapidly formed at 160°C to 180°C by the decomposition of the precursors, and the formation of the FePt nanocubes is dominated by the nucleation of Pt-rich species followed by a slow deposition process of Fe atoms. (2) A thin Fe atomic layer is present on the FePt nanocubes, which does not influence their phase transition into a fct structure. (3) The use of Fe(CO)₅ is the key factor leading to the anisotropic growth of the FePt nanocubes, and the Fe(CO)₅/Pt(acac)₂ molar ratio not only determines the composition of the resulting FePt nanocubes but also affects their morphology and structures.     

Study of the growth,and effects of filament to substrate distance on the structural and optical properties of Si/SiC core–shell nanowires synthesized by hot-wire chemical vapor deposition

Silicon/silicon carbide (Si/SiC) core–shell nanowires grown on quartz substrates by hot-wire chemical vapor deposition were studied. Nickel was used as a catalyst to induce the growth of these core–shell nanowires followed by the vapor–solid–solid growth mechanism. The nanowires were grown by varying substrate-to-filament distance; d_s-f from 1.9 to 3.1 cm with an interval of 0.4 cm. Lower d_s-f produced a high density of straight core–shell nanowires. A highly crystalline single crystal Si core of the nanowires was produced at lower d_s-f as well. Presence of Si and SiC nano-crystallites embedded within an amorphous matrix in the shell of the nanowires exhibited a high intensity of photoluminescence emission spectra from 600 to 1000 nm. The effects of the d_s-f on the structural and optical properties of the nanowires are discussed.