Vertical Zinc Oxide Nanorods Research Articles

A numerical study of ZnO random lasers using FDTD method

In this paper, a 2D strongly disordered a zinc oxide (ZnO) thin film is modelled and simulated to investigate behaviors of ZnO random lasers. In order to observe the scattering and interferes of the electromagnetic waves (EMW), Maxwell’s equations are solved for a transverse magnetic (TM) wave by using finite-difference time-domain (FDTD) method. Perfect electric conductor (PEC) boundary condition is used to truncate the FDTD problem space. The 2D random laser is formed with vertical aligned ZnO nanorods. The size and distribution of ZnO nanorods in the medium are randomly distributed in the air background medium. The intensity of modes and spectrum of ZnO random laser are observed for different EMW excitation values, and different numbers and radii of ZnO nanorods in the medium.

High-Performance Schottky Diode Gas Sensor Based on the Heterojunction of Three-Dimensional Nanohybrids of Reduced Graphene Oxide-Vertical ZnO Nanorods on an AlGaN/GaN Layer.

A Schottky diode based on a heterojunction of three-dimensional (3D) nanohybrid materials, formed by hybridizing reduced graphene oxide (RGO) with epitaxial vertical zinc oxide nanorods (ZnO NRs) and Al0.27GaN0.73(∼25 nm)/GaN is presented as a new class of high-performance chemical sensors. The RGO nanosheet layer coated on the ZnO NRs enables the formation of a direct Schottky contact with the AlGaN layer. The sensing results of the Schottky diode with respect to NO2, SO2, and HCHO gases exhibit high sensitivity (0.88-1.88 ppm-1), fast response (∼2 min), and good reproducibility down to 120 ppb concentration levels at room temperature. The sensing mechanism of the Schottky diode can be explained by the effective modulation of the reverse saturation current due to the change in thermionic emission carrier transport caused by ultrasensitive changes in the Schottky barrier of a van der Waals heterostructure between RGO and AlGaN layers upon interaction with gas molecules. Advances in the design of a Schottky diode gas sensor based on the heterojunction of high-mobility two-dimensional electron gas channel and highly responsive 3D-engineered sensing nanomaterials have potential not only for the enhancement of sensitivity and selectivity but also for improving operation capability at room temperature.

ZnO Nanorod Arrays as Electron Injection Layers for Efficient Organic Light Emitting Diodes

Nanostructured oxide arrays have received significant attention as charge injection and collection electrodes in numerous optoelectronic devices. Zinc oxide (ZnO) nanorods have received particular interest owing to the ease of fabrication using scalable, solution processes with a high degree of control of rod dimension and density. Here, vertical ZnO nanorods as electron injection layers in organic light emitting diodes are implemented for display and lighting purposes. Implementing nanorods into devices with an emissive polymer, poly(9,9‐dioctyluorene‐alt‐benzothiadiazole) (F8BT) and poly(9,9‐di‐n‐octylfluorene‐alt‐N‐(4‐butylphenyl)dipheny‐lamine) (TFB) as an electron blocking layer, brightness and efficiencies up to 8602 cd m−2 and 1.66 cd A−1 are achieved. Simple solution processing methodologies combined with postdeposition thermal processing are highlighted to achieve complete wetting of the nanorod arrays with the emissive polymer. The introduction of TFB to minimize charge leakage and nonradiative exciton decay results in dramatic increases to device yields and provides an insight into the operating mechanism of these devices. It is demonstrated that the detected emission originates from within the polymer layers with no evidence of ZnO band edge or defect emission. The work represents a significant development for the ongoing implementation of ZnO nanorod arrays into efficient light emitting devices.

Effect of seed annealing temperature and growth duration on hydrothermal ZnO nanorod structures and their electrical characteristics

This study investigates the effect of seed annealing temperature and growth duration on the morphology and size of zinc oxide (ZnO) nanostructures. The annealing temperature and growth duration are varied from 100°C to 200°C and from 3h to 9h, respectively. The size of the ZnO nanorods proportionally increases with growth duration, and 150°C annealing temperature produces the maximum length and diameter (i.e., 4000 and 379nm) after 9h of growth process. However, the length and diameter significantly decreases to 3281 and 118nm, respectively, when the annealing temperature increases to 200°C. The aspect ratio for the sample annealed at 150°C is the smallest at approximately 10:1, compared with 15:1 achieved during annealing at 100°C and 25:1 at 200°C, with similar final growth duration of 9h. The ZnO nanorods annealed at 150°C have the lowest resistivity of 6.67×103Ωcm, but this value increases to 13.2×103Ωcm when the annealing temperature reaches 200°C after 9h of growth. Unique ZnO nanorods are formed when bundles of ZnO nanorods grow on top of vertical ZnO nanorods when the seed layer is annealed above 150°C. Based on these results, the resistivity of ZnO nanorods depends on size, growth orientation, and morphology. Uniform ZnO nanorods are successfully observed on 8in. wafer-oxidized silicon, indicating that the process condition carried out in this experiment is reliable.

Vertically aligned smooth ZnO nanorod films for planar device applications

The growth of smooth and continuous zinc oxide (ZnO) films, consisting of densely packed vertical ZnO nanorods with (002) crystal orientation on silicon substrates has been achieved in this work by a chemical solution method. These ZnO thin films have much stronger photoluminescence emission than those from discrete ZnO nanorods under identical conditions. Large area surface acoustic wave devices were fabricated on these films using conventional photolithography, and exhibited two well-defined resonant modes of the Sezawa wave and its harmonic mode.

Field-Emission and Photoelectrical Characteristics of ZnO Nanorods Photodetectors Prepared on Flexible Substrate

Vertical zinc oxide nanorods were synthesized on flexible polyimide (PI) substrate by a low temperature process, aqueous method. The field emission performance of ZnO nanorods can be greatly enhanced by illuminating UV light. It was found that the turn-on electric field can be reduced from 4.3 to 2.0 V/μm and it is attributed to generate a large number of electrons by UV illumination. Compared with the conventional ZnO film photodetectors, the ZnO nanorods photodetectors have much higher photocurrent. As a result, it is attributed to high surface-to-volume ratio of nanorods, which provide an efficient light trapping absorption.

Photoconductive Gain of Vertical ZnO Nanorods on Flexible Polyimide Substrate by Low-Temperature Process

In this investigation, vertical zinc oxide (ZnO) nanorods were synthesized on flexible polyimide (PI) substrate by a simple aqueous method at a low temperature. The PL spectrum and X-ray diffraction (XRD) spectrum showed the ZnO nanorods had a wurtzite hexagonal phase and growth along the c axis direction. A high photoconductive gain and large responsivity suggest that ZnO nanorods were sensitive to UV light that was due to ZnO nanorods had high surface-to-volume ratio of nanorods and provided an efficient light trapping absorption.