Vertical Growth Of ZnO Nanorods Research Articles

Role of ZnO thin film in the vertically aligned growth of ZnO nanorods by chemical bath deposition

The effect of ZnO thin film on the growth of ZnO nanorods was investigated. ZnO thin films were sputter-deposited on Si substrate with varying the thickness. ZnO nanorods were grown on the thin film using a chemical bath deposition (CBD) method at 90°C. The ZnO thin films showed granular structure and vertical roughness on the surface, which facilitated the vertical growth of ZnO nanorods. The average grain size and the surface roughness of ZnO film increased with an increase in film thickness, and this led to the increase in both the average diameter and the average length of vertically grown ZnO nanorods. In particular, it was found that the average diameter of ZnO nanorods was very close to the average grain size of ZnO thin film, confirming the role of ZnO film as a seed layer for the vertical growth of ZnO nanorods. The CBD growth on ZnO seed layers may provide a facile route to engineering vertically aligned ZnO nanorod arrays.

Fabrication and Characterization of ZnO Nanorods on Multiple Substrates.

In this study, we present the fabrication and characterization of ZnO nanorods (NRs) grown on p-Si, gold (Au) and nickel (Ni) coated on Si wafer, indium tin oxide (ITO), and quartz substrates. The aqueous chemical growth method is used for the vertical growth of ZnO NRs on multiple substrates. The samples are characterized with scanning electron microscope and energy dispersive X-ray spectroscopy to probe into the growth, alignment, density, diameter, and length of ZnO NRs on multiple substrates. It is found that under same conditions, like growth temperature, growth time, and solution concentration, ZnO NRs on ITO and quartz have same length but comparatively larger diameter than on other samples. The effects of growth time on the diameter and length of ZnO NRs are also explored. All the samples are characterized with probe station to look at the current-voltage (I-V) behavior of ZnO NRs on multiple substrates. It is found that ZnO NRs on p-Si show a simple p-n heterojunction diode like behavior. ZnO NRs grown on Au- and Ni-coated Si wafers show Schottky I-V characteristic behaviors while ZnO NRs on ITO show a simple ohmic I-V response with comparatively higher level of current. Finally, the I-V response of ZnO NRs on p-Si is also studied under ultraviolet illumination. Because of the photo-generated carriers in ZnO, the sample shows higher level of current upon illumination.

UV-assisted synthesis of reduced graphene oxide–ZnO nanorod composites immobilized on Zn foil with enhanced photocatalytic performance

ZnO nanorods were hydrothermally grown on Zn foil in an alkaline solution and the immobilized nanorods were subsequently hybridized with reduced graphene oxide (rGO) through UV-assisted photocatalytic reduction of graphene oxide (GO). X-ray diffraction analysis confirmed the vertical growth of ZnO nanorods while the incorporation of rGO to ZnO was investigated by scanning electron microscopy and photoluminescence spectroscopy. The successful photocatalytic reduction of GO was demonstrated by means of Raman spectroscopy and X-ray photoelectron spectroscopy. The photocatalytic behavior and photostability of the sandwich-like rGO–ZnO composite were studied through decolorization of the aqueous solution of acid orange 7 under UV-C illumination. The rGO–ZnO photocatalyst presented higher dye decomposition efficiency than pure ZnO. The hybridization of rGO and ZnO led to a 40 % increase in the pseudo-first-order kinetic model’s rate constant and an enhancement of the photostability. The role of incorporation of rGO in enhancement of the ZnO’s photostability has been elucidated in the light of specific features of the sandwich-like architecture.

Study of NBE emission enhancement with an absence of DL emission from ZnO nanorods through controlled growth on ultra-thin Ag films

ZnO nanorods (NRs) exhibiting enhanced ultra-violet near band edge (UV-NBE) emission without a broad visible deep level (DL) emission has been investigated on catalytically grown ZnO/Ag hybrid nanostructure. The hybrid structure is fabricated in two steps, (1) Thermal evaporation of ultra-thin catalytic layer of Ag with mass thickness ∼1nm on glass substrate followed by annealing process from 50 to 250°C and (2) vertical growth of ZnO NRs by hydrothermal reaction process on all Ag films. The surface properties of Ag layer such as particle size, inter-particle distance, particles number density, surface roughness and surface coverage area were altered through annealing process. Annealing at 100°C modifies Ag from quasi-amorphous to nanocrystalline leading to high density growth and high aspect ratio of ZnO NRs where as a random and less density growth was realized at 250°C due to increase of both particle size and inter-particles distance in Ag layer. X-ray diffraction reveals a predominant growth of (002) plane at 100°C confirming the formation of wurtzite phase of ZnO NRs with highest texture coefficient of 2.35. Raman spectra verify the chemical structure of ZnO with very good crystallinity. Absorption spectra demonstrates the overlapping of surface plasmon resonance (SPR) and exciton bands up to 200°C while the excitonic absorption band is resolved at above 200°C because of the red shift in SPR due to change in surface properties of Ag layer. At 250°C, a broad optical absorption spectra from 300 to 800nm attributed to the dominant properties of SPR and exciton. Besides acting as a catalyst, Ag interlayer enhances the NBE emission at above 200°C through electrons transfer from Ag to ZnO which is quite possible because of the direct contact between them, explained by giving energy band diagram. The morphology is such that there is an increase in passage for light interaction due to less density and random growth of ZnO NRs leading to increase light scattering over absorption of Ag interlayer.

Fast vertical growth of ZnO nanorods using a modified chemical bath deposition

In this study, we grew vertical ZnO nanorods on seeded Si (100) substrates using a modified chemical bath deposition (CBD). We investigated the effects of the growth temperature, growth time and concentration on the morphological and structural properties of the ZnO nanorods using field emission gun scanning electron microscopy (FEG-SEM) and X-ray diffraction. This modified CBD method shows improved results over conventional CBD. ZnO nanorods with good structural XRD properties were grown with a very fast growth rate in a wide range of growth conditions and did not require post-growth annealing.

Intermittent spray pyrolytic growth of nanocrystalline and highly oriented transparent conducting ZnO thin films: Effect of solution spray rate

Abstract Uniformly distributed jet of fine droplets was created with control of spray rate ( S f ) to deposit nanocrystalline ZnO thin films by spray pyrolysis technique. X-ray diffraction analysis indicated the polycrystalline film growth with most preferred orientation along c -axis [0 0 2] direction for S f ⩽ 4.5 ml/min, above which films favored [1 0 1] direction. FE-SEM and AFM analysis revealed the uniform vertical growth of ZnO nano-rods for S f = 2.5 ml/min and the film exhibited highest transmittance (95%) with lowest dark resistivity (∼10 −2 Ω-cm). The deposition rate increased due to rise in S f . Alteration of crystallinity, grain size and film thickness with variation in S f lead to variation of band-gap energy from 3.198 eV to 3.302 eV. ZnO film deposited at optimal S f = 2.5 ml/min exhibited maximum electrical conductivity σ = 78.8 Ω −1 -cm −1 , minimum sheet resistance R s = 2.04 × 10 2 Ω/□ and highest figure of merit Φ TC = 2.93 × 10 −3 Ω −1 .

Impact of first-step potential and time on the vertical growth of ZnO nanorods on ITO substrate by two-step electrochemical deposition

Abstract In this study, we analyzed the growth of ZnO nanorods on an ITO (indium doped tin oxide) substrate by electrochemical deposition using a two-step, continuous potential process. We examined the effect of changing the first-step potential as well as the first-step duration on the morphological, structural and optical properties of ZnO nanorods, measured via using field emission scanning electron microscopy (FE-SEM), X-ray diffraction (XRD) and photoluminescence (PL), respectively. As a result, vertical ZnO nanorods were grown on ITO substrate without the need for a template when the first-step potential was set to −1.2 V for a duration of 10 s, and the second-step potential was set to −0.7 V for a duration of 1190 s. The ZnO nanorods on this sample showed the highest XRD (0 0 2)/(1 0 0) peak intensity ratio and the highest PL near band edge emission to deep level emission peak intensity ratio (NBE/DLE). In this study, the nucleation for vertical ZnO nanorod growth on an ITO substrate was found to be affected by changes in the first-step potential and first-step duration.

Vertical growth of ZnO nanorods on ITO substrate by using a two-step-potential electrochemical deposition method

In this study, we grew vertical ZnO nanorods on indium-doped tin-oxide (ITO) substrate by using an electrochemical deposition. For the growth, we used a two-step, continuous potential process without a template, additives, catalysts or a seed buffer layer. The morphological, structural and optical properties of ZnO were investigated using field-emission scanning electron microscopy (FESEM), X-ray diffraction (XRD) and photoluminescence (PL), respectively. The best test conditions resulted in the growth of vertical ZnO nanorods with a height of 550 nm and occurred when a first-step potential of −1.2 V was applied for 10 s, and a second-step potential of −0.7 V was applied for 1190 s. ZnO nanorods grown at the optimized growth condition show the strongest (002) peak intensity in the XRD spectrum and the highest near band edge emission over deep level edge emission (NBE/DLE) peak ratio of 76.26 and the lowest full width at half maximum (FWHM) of 144 meV in the photoluminescence spectrum. In our study, the structural and the optical properties of ZnO nanorods were highly improved, as compared with a constant single potential for 1200 s, when a first-step potential of −1.2 V was applied for 10 s and was followed by a second-step potential of −0.7 V which was applied for 1190 s.

Electrochemical fabrication of oriented ZnO nanorods on TiO<SUB align="right">2 nanotubes

We report the ability to use TiO2 nanotube as a guide layer to achieve the vertical growth of ZnO nanorods, in additive–free bath. First, we focused on the anodisation conditions (cell voltage and anodisation time) to produce TiO2 nanotube thin films grown from a 1.5 µm thick Ti layer sputtered onto Si. Highly organised titania nanotubes were obtained in glycerol viscous electrolyte. In a second step, the electrochemical growth of ZnO grains has been investigated from a zinc nitrate bath at 70°C on both Ti foil and TiO2 nanotubes. ZnO deposition mechanism has been highlighted through the electrochemical experiments in conjunction with XRD technique and scanning electron microscopy (SEM) examinations. On Ti foils, we show that addition of additives is required to obtain a highly oriented nanostructured ZnO deposit. On TiO2 nanotubes, additives are not necessary to obtain such a deposit: Titania nanotubes can be used to guide the vertical growth of hybrid nanoarchitectured ZnO/TiO2 electrode.

Vertical Growth of ZnO Nanorods Prepared on an ITO-Coated Glass Substrate by Hydrothermal-Electrochemical Deposition

In this study, ZnO nanorods were grown on indium-tin oxide (ITO)-coated glass substrate using a hydrothermal-electrochemical method in a Zn(NO3)2 aqueous solution. To optimize the properties of ZnO nanorods grown on the ITO-coated glass substrate, the effects of growth parameters, such as the thickness of ZnO seed layer (0–70 nm), the addition of NaOH additive, the applied potential (−0.6–−1.2 V), and the growth temperature (120–180°C) were examined with respect to the morphological, structural, photoluminescence, and transmittance properties of the nanorods. An improvement in the UV–visible ratio of the ZnO nanorods was obtained by increasing the thickness of the seed layer and by increasing the applied potential and the growth temperature with the addition of a NaOH solution. Based on the combined results of this study, the vertical ZnO nanorods produced on the ITO-coated glass substrate hold great promise for use in the development of high-performance optoelectronic devices and other applications.

Hydrothermal Growth of Vertical ZnO Nanorods

Vertically aligned, single crystalline ZnO nanorods with a high packing density and diameter of ∼60 nm have been successfully synthesized via a low‐temperature hydrothermal route on glass substrates pre‐deposited with a ZnO seeding layer. The seeding layer exhibits an epitaxial effect on the growth and alignment of the ZnO nanorods. This epitaxial effect can arise from two considerations, namely the crystalline orientation and surface roughness of the seeding layer, which can be controlled by the curing temperature. The ZnO seeding layer that was cured at 350°C exhibited a preferred (0002) crystalline orientation of wurtzite hexagonal structure and a low surface roughness. It was demonstrated to promote the vertical growth of ZnO nanorods. The ZnO nanorods grew in an almost linear relationship with hydrothermal time up to 8 h, but thereafter started to dissolve as the reaction time extended beyond 8 h, due to competition from the homogeneous nucleation of ZnO microparticles in the solution.

Seed layer-free synthesis and characterization of vertically grown ZnO nanorod array via the stepwise solution route

A novel stepwise method was developed for the deposition of ZnO nanorod array (NRA) from the simple inorganic aqueous solution. Different from the traditional one-pot synthesis route, merely a thin liquid precursor layer adsorbed on the substrate instead of the bulk solution underwent the reaction at elevated temperature in a typical deposition cycle. Sparse and vertically grown wurtzite ZnO NRA was deposited on seed layer-free glass substrate after 20 cycles (in typically 20 min). Each individual ZnO rod possessed the well-defined hexagonal facet, the side length of about 150 nm, the aspect ratio of 2:3, and the small size dispersity. Also the overall ZnO NRA exhibited high ultraviolet photoluminescence and weak blue emission, indicating its good optical properties. Mechanism analysis indicated that, the decrease of the supersaturation degree in solution after the climax in the reaction period of each deposition cycle is the root cause of the sparse nucleation and the vertical growth of ZnO nanorods. The work has opened up a novel stepwise approach toward high quality ZnO NRA, being valuable for extending the synthetic methods of semiconductor nanostructures in mild solutions.