Vertically stacked and laterally stitched heterostructures consisting of two-dimensional (2D) transition metal dichalcogenides (TMDCs) are predicted to possess novel electronic and optical properties, which offer opportunities for the development of next-generation electronic and optoelectronic devices. In the present work, we report the temperature-dependent synthesis of 2D TMDC heterostructures on Si/SiO2 substrates, including MoS2–WS2, WS2–MoS2–WS2, Mo1–xWxS2–WS2, and Mo1–xWxS2 alloyed bilayer heterostructures by ambient pressure chemical vapor deposition (CVD). Raman and photoluminescence mapping studies demonstrate that the as-produced heterostructures show distinct structural and optical modulation. Our results indicate that the evolution of various 2D heterostructures originates from the competition between the adsorption and desorption of Mo atoms and the diffusion of W atoms under various growth temperatures. This work sheds light on the design and fabrication of heterostructures using controllable interfaces and junctions of diverse TMDC atomic layers.Keywords: 2D heterosructures; growth mechanism; magnetron sputtering and CVD synthesis; Mo1−xWxS2; MoS2; two-dimensional semiconductor; WS2;

•P-ZnO:Na nanorods have been grown on Si substrates by a catalyst-free CVD method.•P-ZnO:Na nanorods with Na concentration in the range of 1.2–2.1 at.% exhibit p-conductivity.•P-ZnO:Na nanorods/ZnO/n-Si heterostructure shows good rectifying behavior.Na-doped ZnO (ZnO:Na) nanorods have been grown on Si substrates by a catalyst-free chemical vapor deposition method. Element analysis reveals that the doping concentration of Na is in the range of 0.5–3.7 at.%. Morphological and electrical properties of the ZnO nanorods were found to be highly dependent on the Na concentration. Hall measurement indicates the realization of p-ZnO:Na nanorods with hole concentrations in the order of 1015 cm−3. Temperature dependent photoluminescence measurement down to 10 K confirms the shallow acceptor level, which is ∼132 meV. Desirable rectifying behavior has also been observed from the I-V characteristic of the p-ZnO:Na nanorods/ZnO/n-Si structure and the turn on voltage is ∼2.5 V.

•A facile approach for the fabrication of Au/ZnO-hollow-sphere-monolayer thin films.•Both ZnO and Au NPs were deposited by DC magnetron technique.•Au/ZnO hybrid showed enhanced photocatalytic performance for degradation of MO.In this study, we present a facile strategy for the fabrication of Au/ZnO-hollow-sphere-monolayer thin films. ZnO hollow spheres were synthesized by a template technique based on polystyrene (PS). ZnO and Au nanoparticles (NPs) were simultaneously deposited by DC magnetron sputtering. The as-prepared ZnO spheres exhibit a hollow structure with an obvious contrast between the thin ZnO shell and the interior. The Au/ZnO-hollow-sphere-monolayer thin films showed significantly enhanced photocatalytic performance in the degradation of MO compared with that of the ZnO thin film and ZnO-hollow-sphere-monolayer thin films. The observed degradation constant k of MO for the Au/ZnO–400 nm sample was 0.0415 min−1, which is approximately 17 times that of the ZnO thin film (0.0024 min−1) and 3 times that of the ZnO–400 nm sample (0.0128 min−1). The enhancement in photocatalytic activity was attributed to the synergistic effect of the transfer of effective charges from the ZnO conduction band to the plasmonic Au NPs and the light trapping within the ZnO hollow spheres.Download high-res image (108KB)Download full-size image

Hybrid structures composed of layered two-dimensional (2D) transitional metal dichalcogenides have received tremendous attention due to their exceptional tunable optical, electronic, and catalytic properties. In this article, we report the fabrication and novel enhanced photoluminescence (PL) properties of AlN/MoS2 core–shell nanowires. The morphology and composition of the as-prepared AlN/MoS2 core–shell heterostructures were characterized by X-ray diffraction, field-emission scanning electron microscopy, transmission electron microscopy, X-ray photoelectron spectroscopy, and Raman spectroscopy. PL measurements showed that the PL emission of the AlN/MoS2 heterostructures was enhanced with a blue-shift in comparison to that of the MoS2 monolayer grown on a Si/SiO2 substrate. The PL enhancement of the AlN/MoS2 heterostructures was mainly attributed to charge transfer across the interface of the heterostructure. The results presented here provide novel insights into the PL enhancement of MoS2 monolayers.

A facile catalyst-free approach using a simple thermal transport method has been developed to fabricate high-density AlN nanotips on flexible carbon cloth at large scales for use as field emission (FE) emitters. The AlN nanotips exhibit good performance as flexible cold-cathode electron emitters, with a very low turn-on electric field of 1.1–2.3 V μm−1, a low threshold electric field of 1.5–2.5 V μm−1, and a high emission current density. The excellent field emission properties of the AlN nanotips are attributed to the large field enhancement factor of 6895 as well as the combined effect of the tip profile of the AlN nanostructures and the excellent electron transport path of the conductive carbon cloth substrate.

Wurtzite aluminum gallium nitride (AlxGa1−xN) nanostructures with manifold morphologies, including nanonails, nanoneedles, nanorods, nanoflowers, nanomultipods and nanotowers, have been fabricated on bare Si (100) substrates by a simple halide chemical vapor deposition process. The detailed morphological and structural characteristics of these nanostructures have been examined by field emission scanning electron microscopy, X-ray diffraction spectroscopy, and transmission electron microscopy. All AlxGa1−xN nanostructures exhibit a hexagonal wurtzite single-phase structure and a preferred orientation along the [0001] direction. The evolution of the various AlxGa1−xN nanostructures has been systematically investigated in terms of the saturation vapor pressure of the precursors by tuning the growth parameters. A vapor–solid growth mechanism combined with the surface diffusion process is responsible for the formation and evolution of the series of nanostructures.

ZnO nanorods on Si substrates have been synthesized by a simple vapor phase transport method. A two-step surface modification, which involves coating with a very thin AlN layer followed by Ar+ plasma etching treatment, has been employed to enhance the field emission (FE) properties of ZnO nanorods. Compared with the FE properties of as-grown ZnO nanorods, the turn on field of the two-step surface modified ZnO nanorods decreased to 42% from 16.0 to 6.8 V μm−1 at the current density of 10 μA cm−2, and the FE current density increased by about 40 times, reaching as high as 4.1 mA cm−2 at an electric field of 17.4 V μm−1. It has been proposed that the enhancement in the field emission properties is due to the reduction of the effective work function and the low electron affinity of the thin AlN coating layer, as well as the enhanced local field near the reduced tips of the ZnO nanorods. This study provides an effective approach for enhancing the FE properties of semiconductor emitters.

In this work, we describe compositionally tunable AlxGa1−xN nanowires (0.66 ≤ x ≤ 1) grown on Si (1 0 0) substrates using a chemical vapor deposition (CVD) process. The composition of AlxGa1−xN nanowires may be tuned by adjusting the vapor temperature of the AlCl3 and GaCl3 used in its production. The structural, chemical and optical properties of the AlxGa1−xN nanowires are investigated using X-ray diffractometry (XRD), field emission scanning electron microscopy (FESEM), X-ray energy-dispersive spectroscopy (EDS), transmission electron microscopy (TEM) and Raman spectroscopy. All the AlxGa1−xN nanowires exhibit a preferred c  -axis orientation. Raman analysis shows that the E22 phonon exhibits two-mode behavior. The positions of the AlN-like E22, GaN-like E22 and A1(TO) modes shift toward higher frequencies as the amount of Al increases. The growth of these AlxGa1−xN nanowires has been proposed to follow a vapor–solid–solid (VSS) mechanism.