Vertical ZnO Nanorods Research Articles

Low temperature growth of ZnO nanorods on flexible polymeric substrates

Vertical ZnO nanorods have been cathodically deposited on conductive polymeric substrates from zinc nitrate electrolyte at low temperatures of 60–80 °C. As-grown ZnO nanorods display a wurzite crystal structure that grows preferentially in the (0 0 2) direction. The interspacing between adjacent lattice fringes is approximately 0.261 nm. The growth rate of ZnO pillars in c-axis is an increasing function of both growth temperature and period. Arrhenius plots determine different stages of apparent activation energy (5.51–8.95 kJ/mol), showing an inhomogeneous surface reactivity on polymeric substrate during the ZnO growth process. This variation of activation energy can be ascribed to the two growth stages of ZnO pillars, the epitaxy and the texture growth.

Optical and physical characteristics of In-doped ZnO nanorods

In this paper the effect of indium dopants on structure, optical, electrical and mechanical properties of ZnO nanorods are studied. The average surface potentials and the surface currents of ZnO:In nanorods were 0.25–0.84 mV and 2.2–200 MΩ-cm, respectively. The turn-on threshold field for the vertical ZnO nanorods was around 2–16 V μm −1. Emission current densities of 3.3–911.4 mA cm −2 were obtained for an electrical field of 60–160 V μm −1. The photoluminescence (PL) spectrum measured at 15–300 K showed that the intensity of the peak at 2.06 eV increased with decreasing temperature, while the peak at 2.06 eV further red shifted and the peak at 3.39 eV blue shifted.

Template Deformation‐Tailored ZnO Nanorod/Nanowire Arrays: Full Growth Control and Optimization of Field‐Emission

AbstractHere, a facile and effective route toward full control of vertical ZnO nanorod (NR)/nanowire (NW) arrays in centimeter‐scale areas and considerable improvement of field‐emission (FE) performance is reported. Controlled deformation of colloidal crystal monolayer templates is introduced by heating near glass‐transition temperature. The NR/NW density, uniformity, and tapering were all adjusted through selection of template size and deformation, and electrolyte composition. In line with the adjustments, the field‐emission performance of the arrays is significantly improved. A low turn‐on electric field of 1.8 V µm−1, a field‐enhancement factor of up to 5 750, and an emitting current density of up to 2.5 mA cm−2 were obtained. These improved parameters would benefit their potential application in cold‐cathode‐based electronics.

Buckling and elastic stability of vertical ZnO nanotubes and nanorods

Buckling and elastic stability study of vertical well aligned ZnO nanorods grown on Si substrate and ZnO nanotubes etched from the same nanorods was done quantitatively by nanoindentation technique. The critical load, modulus of elasticity, and flexibility of the ZnO nanorods and nanotubes were observed and we compared these properties for the two nanostructures. It was observed that critical load of nanorods (2890 μN) was approximately five times larger than the critical load of the nanotubes (687 μN). It was also observed that ZnO nanotubes were approximately five times more flexible (0.32 nm/μN) than the nanorods (0.064 nm/μN). We also calculated the buckling energies of the ZnO nanotubes and nanorods from the force displacement curves. The ratio of the buckling energies was also close to unity due to the increase/decrease of five times for one parameter (critical load) and increase/decrease of five times for the other parameter (displacement) of the two samples. We calculated critical load, critical stress, strain, and Young modulus of elasticity of single ZnO nanorod and nanotube. The high flexibility of the nanotubes and high elasticity of the ZnO nanorods can be used to enhance the efficiency of piezoelectric nanodevices. We used the Euler buckling model and shell cylindrical model for the analysis of the mechanical properties of ZnO nanotubes and nanorods.

Synthesis of Vertical ZnO Nanorods on Glass Substrates by Simple Chemical Method

ZnO nanorods (NRs) have been synthesized by a chemical bath deposition (CBD) method on simple glass substrate that had been precoated by successive ionic layer absorption and reaction (SILAR) with a thin ZnO film. ZnO NR array was obtained by using zinc acetate and hexamethylenetetramine as aqueous solutions at optimized pH concentration and deposition time. X-ray diffraction (XRD) and SEM analysis were used to confirm the growth of ZnO nanorods. The pH and deposition time of the solution was found to influence the growth behavior of ZnO NRs. PL analysis also reflected the growth behavior of ZnO NRs.

Growth of high transmittance vertical aligned ZnO nanorod arrays with polyvinyl alcohol by hydrothermal method

Well-aligned ZnO nanorod arrays were synthesized on SnO 2:F (FTO) glass substrates by hydrothermal method with the addition of polyvinyl alcohol. Morphology and optical properties of the well-aligned ZnO nanorod arrays were studied. The transmittance of the as grown samples was dramatically increased by the addition of polyvinyl alcohol. PVA was regarded to play an important role in improving the optical transmittance and its role in hydrothermal growth process is also discussed in this work.

Epitaxy of Vertical ZnO Nanorod Arrays on Highly (001)-Oriented ZnO Seed Monolayer by a Hydrothermal Route

A long ZnO nanorod array with good verticality and thin diameter is synthesized from a single solution by the hydrothermal route. Prior to the growth, a ZnO seed layer with the c-axis texturing and the monolayer distribution is deposited on the substrate by a modified sol−gel spin coating process. A molecule adsorption stabilization mechanism is proposed to explain the seed orientation. Factors affecting the ZnO nanorod growth are systematically investigated. The critical conditions for the rod growth are obtained by changing the polyethyleneimine amount and the pH. The results suggest that the verticality of the array depends heavily on the seed orientation. The atomic force microscopy and X-ray diffraction measurements reveal that the crystallinity and the initial strain relaxation determine the growth activation energy and the rod diameter size.

Defect study in ZnO related structures—A multi-spectroscopic approach

ZnO has attracted a great deal of attention in recent years because of its potential applications for fabricating optoelectronic devices. Using a multi-spectroscopic approach including positron annihilation spectroscopy (PAS), deep level transient spectroscopy (DLTS), photoluminescence (PL) and X-ray photoelectron spectroscopy (XPS), we have studied the two observed phenomena from ZnO related structures. They namely included the H 2O 2 pre-treatment induced ohmic to rectifying contact conversion on Au/ n-ZnO contact and the p-type doping by nitrogen ion implantation. The aim of the studies was to offering comprehensive views as to how the defects influenced the structures electrical and optical properties of the structures. It was also shown that PAS measurement using the monoenergetic positron beam could offer valuable information of vacancy type defects in the vertical ZnO nanorod array structure.

Surface states dominative Au Schottky contact on vertical aligned ZnO nanorod arrays synthesized by low-temperature growth

Vertical aligned ZnO nanorod (diameter = 50 nm) arrays on indium tin oxide (ITO) substrates have been grown using a new two-step soft chemical procedure. The resulting current–voltage (I–V) characteristics of the ZnO nanorods exhibited a clear rectifying behaviour. This rectifying behaviour was attributed to the formation of a Schottky contact between the Au coated atomic force microscopy (AFM) tip and ZnO nanorod (nano-M/SC) which was dominated by the surface states in ZnO itself. Photo-assisted conductive AFM (PC-AFM) was used to demonstrate how the I–V characteristics are influenced by the surface states. Our I–V results also showed that the nano-M/SCs had a good photo-electric switching effect at reverse bias.

Variations in the intensity of lasing in vertical ZnO nanorods with polarization of optical excitation

The polarization dependences of emission and optical excitation of an array of vertical ZnO semiconductor nanorods synthesized on the Si (100) substrate are analyzed. Because of the surface charge induced due to the difference between the permittivities of the nanorods and their surroundings, the absorption coefficient and the emission coefficient are different for the light polarized in parallel or perpendicularly to the axes of the nanorods. As a result, the intensity and spectra of luminescence in the array of parallel nanorods are highly sensitive to the polarization of excitation. Study of the behavior of the laser spectrum with the polarization of excitation shows good agreement of the data with the theory of induced charge. The mechanism of lasing is related to the formation of paths of light due to multiple scattering in the array of vertically oriented ZnO nanorods.

Random lasing in vertical ZnO nanorods

Random lasing with coherent feedback is detected in the array of vertical ZnO nanorods synthesized on a Si(100) substrate. Under high-intensity optical pumping at the wavelength of 337.1 nm at room temperature, several narrow laser peaks with the width of 0.1 nm are observed in the wavelength region around 392 nm. The laser radiation is emitted in a direction orthogonal to the axis of the nanorods. Study of the behavior of the laser spectrum with the excited area shows good agreement of the data with the theory of random lasers. The mechanism of laser emission is related to the formation of closed paths of light due to multiple coherent scattering at the vertically oriented ZnO nanorods.

Chemical growth of ZnO nanorod arrays on textured nanoparticle nanoribbons and its second-harmonic generation performance

On the basis of the highly oriented ZnO nanoparticle nanoribbons as the growth seed layer (GSL) and solution growth technique, we have synthesized vertical ZnO nanorod arrays with high density over a large area and multi-teeth brush nanostructure, respectively, according to the density degree of the arrangement of nanoparticle nanoribbons GSL on the glass substrate. This controllable and convenient technique opens the possibility of creating nanostructured film for industrial fabrication and may represent a facile way to get similar structures of other compounds by using highly oriented GSL to promote the vertical arrays growth. The growth mechanism of the formation of the ordered nanorod arrays is also discussed. The second-order nonlinear optical coefficient d 31 of the vertical ZnO nanorod arrays measured by the Maker fringes technique is 11.3 times as large as that of d 36 KH 2PO 4 (KDP).

Buffer layer effect on ZnO nanorods growth alignment

Vertical aligned ZnO nanorods array was fabricated on Si with introducing a ZnO thin film as a buffer layer. Two different nucleation mechanisms were found in growth process. With using Au catalyst, Zn vapor could diffuse into Au nanoclusters with forming a solid solution. Then the ZnO nucleation site is mainly on the catalyst by oxidation of Au/Zn alloy. Without catalyst, nucleation could occur directly on the surface of buffer layer by homoepitaxy. The density and the size of ZnO nanorods could be governed by morphological character of catalyst and buffer layer. The nanorods growth is followed by vapor–solid mechanism.