Aspect Ratio Of ZnO Nanorods Research Articles

Position-controlled hydrothermal growth of ZnO nanorods on arbitrary substrates with a patterned seed layer via ultraviolet-assisted nanoimprint lithography

A novel technique for the position-controlled growth of ZnO nanorods is established, by combining ultraviolet-assisted nanoimprint lithography (UV-NIL) and hydrothermal growth. Various ZnO nanorod arrays were obtained on silicon substrates, by UV-NIL of ZnO seed patterns with lines of 200 nm wide at a pitch of 1000 nm from a photosensitive ZnO precursor, followed by a position-controlled hydrothermal growth step with varied growth times. It was found that the aspect ratio of ZnO nanorods increased from 2.7 to 11.8 as the growth time was increased from 2 to 6 h. Selected area electron diffraction (SAED) analysis indicates that the root of studied ZnO nanorods consists of both amorphous and polycrystalline phases whereas the stem shows a single-crystalline nature with a preferred (002) growth. ZnO nanorod arrays were also routinely obtained on transparent glass and flexible polyethylene terephthalate (PET). In all cases, ZnO nanorods were observed on both the sidewalls and top surfaces of the ZnO seed patterns with a nanoflower-like structure regardless of substrate substances. This technique offers an alternative method for integrating ZnO nanorods at low temperatures and free of high vacuum, potentially useful in applications such as nanophotonics, photovoltaics and flexible nanoelectronics.

Origin of enhanced photocatalytic activity and photoconduction in high aspect ratio ZnO nanorods

Faceted ZnO nanorods with different aspect ratios were synthesized by a solvothermal method by tuning the reaction time. Increased reaction leads to the formation of high aspect ratio ZnO nanorods largely bound by the prism planes. The high aspect ratio rods showed significantly higher visible light photocatalytic activity when compared to the lower aspect ratio structures. It is proposed that the higher activity is due to better charge separation in the elongated 1D structure. In addition, the fraction of unsaturated Zn(2+) sites is higher on the {1010} facets, leading to better adsorption of oxygen-containing species. These species enhance the production of reactive radicals that are responsible for photodegradation. The photocurrent for these ZnO nanostructures under solar light was measured and a direct correlation between photocurrent and aspect ratio was observed. Since the underlying mechanisms for photodegradation and photocurrent generation are directly related to the efficiency of electron-hole creation and separation, this observation corroborates that the charge separation processes are indeed enhanced in the high aspect ratio structures. The efficiency of photoconduction (electron-hole pair separation) could be further improved by attaching Au nanoparticles on ZnO, which can act as a sink for the electrons. This heterostructure exhibits a high chemisorption of oxygen, which facilitates the production of highly reactive radicals contributing to the high photoreactivity. The suggested mechanisms are applicable to other n-type semiconductor nanostructures with important implications for applications relating to energy and the environment.

Optimization of parameters for the growth of defect free ZnO nanorod arrays with intense UV emission capacity by electrochemcial route

We present the fabrication of highly oriented, well faceted and defect free ZnO nanorods by electrodeposition using ZnCl2 and KCl as the electrolyte. The ZnO nanostructures were prepared on high purity Cu foil, commercial Cu foil, ITO coated glass and Cu (100nm)/Ti (30nm)/Si substrates. We have studied in detail the effects of various growth parameters such as bath temperature, deposition time, precursor concentration and applied potential on the morphology, structural and optical properties of ZnO nanorods. A detailed mechanism and the effects of various process parameters on the formation of defect free (with controlled microstructure of) ZnO nanorods are reported. Our studies confirmed that the bath temperature and the deposition time critically influenced the aspect ratio of ZnO nanorods. For instance, the growth of ZnO nanorods along the lateral direction affected marginally, whereas, along the c-axis, the growth affected significantly with bath temperature as well as with the deposition time. At higher deposition time the shape of ZnO nanostructures got distorted because of reduction in the bulk pH value of the solution. Similarly, at bath temperature greater than 80°C, the ZnO nanorods were misoriented with cauliflower-like microstructure mainly because of reduction in Zn2+ ion concentration. The ZnO nanostructures prepared under the optimized growth conditions showed an intense UV emission without spreading in the visible region as confirmed by photoluminescence spectroscopy, thus demonstrating the formation of defect free structure.

Effects of the aspect ratio on the dye adsorption of ZnO nanorods grown by using a sonochemical method for dye-sensitized solar cells

Well-aligned ZnO nanorods for the photoelectrode of dye-sensitized solar cells (DSSCs) were grown via a sonochemical method, and the effects of their aspect ratios on the dye adsorption in DSSCs were studied. The control of the aspect ratio of well-aligned ZnO nanorods was performed by tuning the mole concentration of zinc acetate dehydrate in the range of 0.04–0.06M. The dye amounts adsorbed in the ZnO nanorods were estimated from the UV-Visible absorbance by using the Beer-Lambert law. The efficiency of DSSCs with ZnO nanorods was measured to investigate the effects of the aspect ratio of the ZnO nanorods on the dye adsorption properties. A change in the aspect ratio of the ZnO nanorods was founded to yield a change in their dye adsorption ability, resulting in a change in the efficiency of the DSSCs.

Electrochemically Controlled Nanopore and Crystal Structure Evolution in Zinc Oxide Nanorods

We investigate high aspect ratio ZnO nanorods during Li-battery cycling by stepwise characterization of their crystal structures and porosities. During the cycling, nonporous ZnO nanorods become porous and, as a result, the surface area of ZnO nanorods increases significantly. As the Li amount inserted and extracted increases, it was observed that nanopores progress from the surfaces to the cores of ZnO nanorods. Also, in the crystal structure viewpoint, the original single-crystalline structure of the pristine ZnO nanorods gradually turns into the polycrystalline during the pore progression. This investigation not only delivers detailed information on the morphology and crystal structures of one-dimensional ZnO nanostructures during the course of Li-battery operations, but also suggests that battery processes can be a useful means to manipulate the crystal structure and porosity of ZnO nanostructures.

Growth of high aspect ratio ZnO nanorods by solution process: Effect of polyethyleneimine

High aspect ratio ZnO nanorods were grown vertically on ZnO seed layer deposited silicon, glass and polyimide substrates by a solution process at low-temperature using zinc nitrate hexahydrate and hexamethylenetetramine. We studied the effect of polyethlyeneimine (PEI) on the growth of ZnO nanorods. It was found that PEI has a prominent effect on controlling the aspect ratio of ZnO nanorods in solution. The morphological and photoluminescence properties of the ZnO nanorods were also examined with varying the growth temperature (60–90°C).

Effect of the ZnO Rods Growth Time to the Conductivity of ZnO Thin Film Combined with N3 Dye

In this work, ZnO nanorod has been grown by hydrothermal solution method. The samples were prepared by two stages. The first stage was seeding process where the ZnO nanoparticles are spin-casted onto ITO coated glasses and the second stage was hydrothermal process. The morphology of nanorods were investigated by using scanning electron microscope (SEM) and different of length and diameter of nanorods with different growth durations have been observed. The differences of diameters and aspect ratio of nanorods have affected the optical and electrical properties of the ZnO-coated thin film with dye due to its surface area and morphologies of growth rod. Aspect ratio of ZnO nanorods increases by increasing the reaction time (growth time). From the band gap energy study, the thin film with the longest ZnO nanorods growth time has the lowest band gap energy (3.55 eV). The higher aspect ratio of the nanorod affected the conductivity, by increasing the conductivity when combined with N3 dye.

Fabrication of ZnO Nanorods in One Pot via Solvothermal Method

AbstractIn this article, we reported a low temperature solvothermal method to synthesize ZnO nanorods in one pot. In order to study the growth mechanism of ZnO nanorods, various preparative parameters, such as zinc species concentration, the molar concentration ratio of hydroxide [OH‐] to zinc species [Zn2+], and surfactants, have been systematically examined. According to the analysis, the aspect ratio of ZnO nanorods was enlarged with the increase of the concentration ratio of [OH‐] to [Zn2+]. However, the mean diameter only causes subtle change. Additionally, the influence of surfactants was studied by two different kinds of surfactant, ethylenediamine (EDA) and hexadecylamine (HDA). From transmission electron microscopy analysis, the aspect ratio of ZnO nanorods was similar to that without adding surfactant. However, the green emission caused by oxygen defects or others can be omitted while the surfactants were added into the reaction. Herein, the growth mechanism was proposed to relate to the element of coordination polyhedron presented in the interface. When terminal vertex bonds with more growth units, the interface has higher growth rate for the crystal formation. Besides, the reaction medium also affects the growth mechanism of ZnO nanorods. In an alkali medium, the larger hindrance effect of ONa‐ ions at the interface of (0001) and ( 01 1¯ 1¯ ) faces, the growth rates of (0001) and ( 01 1¯ 1¯ ) faces have a great hindrance relative to other crystal faces.

Preparation of ZnO nanorods by microemulsion synthesis and their application as a CO gas sensor

Zinc oxide nanorods with different surface area were synthesized by surfactant assisted microemulsion method. The alkyl chain length of surfactant would affect aspect ratio of ZnO nanorods. ZnO nanorods synthesized by ethyl benzene acid sodium salt (EBS), which is surfactant with short alkyl chain length, show higher aspect ratio than ones by dodecyl benzene sulfonic acid sodium salt (DBS). These nanorods had diameters in the range of 80–300 nm and length of up to several microns. The Brunauer–Emmett–Teller (BET) surface area of the ZnO nanorods was strongly affected by the morphology of the nanorods. The BET surface area of the nanorods synthesized with EBS was higher than the surface area of the nanorods synthesized with DBS (20.2 and 14.1 m 2/g for EBS and DBS, respectively). The response of ZnO nanorods to CO in air was strongly affected by surface area, defects and oxygen vacancies. The results demonstrate that the microemulsion synthesis is an easy and useful method to synthesize ZnO nanorods with large aspect ratio, which may enhance their gas sensing properties.

Modulation of field emission properties of vertically aligned ZnO nanorods with aspect ratio and number density

Vertically aligned ZnO nanorod arrays with different aspect ratios were synthesized by hybrid wet chemical route. Modulation of the field emission properties (FE) with aspect ratio of ZnO nanorods was examined. With the increase in the aspect ratio, the emission current density increases from 0.02 to 8 μA/cm 2 at 7.0 V/μm. Turn-on voltage was seen to decrease from 9.6 to 7 V/μm at a current density of 10 μA/cm 2 with the increase in aspect ratio in the ZnO films. The interrelation between the FE characteristics (emission thresholds, current density, surface uniformity, etc.) and microstructure of the ZnO nanostructure obtained from scanning electron microscopy (SEM) and atomic force microscopy (AFM) was discussed. Quality of the ZnO nanorods was also examined by using Raman spectroscopy and Fourier transformed infrared spectroscopy (FTIR). It was found that the observed enhancements of FE characteristics could mainly be attributed to the increase in aspect ratio and associated number density of ZnO nanorods.