Well-aligned Nanorods Research Articles

Photocatalyst ZnO nanorod arrays on glass substrates: the critical role of seed layer in nanorod alignment and photocatalytic efficiencies

The surfaces of the wet-etched and activated glass substrates were first seeded by a simple dip-coating method using the zinc acetate precursor solutions with and without polyvinyl alcohol (PVA). Then, the substrates with two kinds of freshly prepared seed layers (i.e. with and without PVA) were annealed at 250 and 400 °C. Seed-mediated growth of rod-like zinc oxide (ZnO) nanostructure arrays by a chemical bath deposition was carried out as the second step in the formation of continuous ZnO films. PVA, which was added to the seed precursor solution, increased the vertical alignment of the ZnO nanorods along the c-axis. This was confirmed by the appearance of the strong (002) X-ray diffraction peak and by the cross-sectional scanning electron microscope (SEM) images of the films. Even though the well-aligned nanorods were synthesized on the PVA-modified seed layer, they exhibited poor photocatalytic activities in the degradation of C.I. Acid Red 88 azo dye compared with the more randomly aligned ones. The color removal efficiencies of the “random” nanorods (i.e. without PVA modification) under ultraviolet A light illumination were nearly two times higher than those of the well-aligned nanorods.

Fabrication of ultra-sensitive piperidine chemical sensor with a direct grown well-aligned ZnO nanorods on FTO substrate as a working electrode

In this work, we report a direct growth of well-aligned zinc oxide nanorods (ZNRs) on fluorine doped tin oxide (FTO) substrate by a single step chemical method in an aqueous solution; the synthesized ZNRs were then used for piperidine sensing studies, as a working electrode. The ZNRs were uniformly grown in a large area, highly crystalline, and vertically aligned with an average length and diameter of ~650 nm and ~50 nm, respectively. The vertically aligned ZNRs provide the higher surface area for electrocatalytic activity of piperidine, and thus exhibited an ultra-sensitivity of 527 μAmM−1cm−2, a low detection limit (~60 nM), and a wide linear detection range from 0.1 μM to 200 μM. The improved piperidine sensing response characteristics of direct grown ZNRs on FTO substrate due to the large surface area, higher electrocatalytic activity and the fast electron transfer process, which makes them interesting candidate for fabricating other chemical sensing devices.

Direct growth of self-aligned single-crystalline GaN nanorod array on flexible Ta foil for photocatalytic solar water-splitting

We report the direct growth of self-aligned single crystalline GaN nanorod array on flexible Ta metal foil using laser molecular beam epitaxy. Scanning electron microscopy reveals the vertically aligned nanorods on Ta surface having diameters in the range of 60–80 nm. The nanorods show well-defined hexagonal facets and are quite uniformly distributed across the metal foil. Transmission electron microscopy shows single crystalline nature of the individual rods having c-axis oriented growth with wurtzite structure. Room temperature photoluminescence study exhibits a sharp, intense band-to-band emission without any deep-level bands indicating the excellent optical quality of the GaN nanorod array. X-ray photoemission spectroscopy to elucidate the electronic structure of the nanorods confirms Ga–N bonding and the calculated chemical composition turns out to be slightly Ga rich. Location of valence band maxima also suggests the n-type character of GaN nanorods. The photoelectrochemical water-splitting behaviour of the self-aligned GaN nanorod arrays on Ta foil has been investigated using 1 M oxalic acid as the electrolyte with AM 1.5 G simulated solar radiation under 1 Sun (100 mW/cm2) conditions. The results demonstrate an effective way of fabricating well-aligned GaN nanorods on flexible metal foils for developing simple, relatively inexpensive, and flexible photo-electrodes for photocatalytic solar water-splitting applications.

Improvement of Vacuum Free Hybrid Photovoltaic Performance Based on a Well-Aligned ZnO Nanorod and WO3 as a Carrier Transport Layer.

Well-aligned zinc oxide nanorods (WA-ZnO Nrods) with different lengths were synthesized and the effects of the growth times on the optical, morphological, and electrical properties of the WA-ZnO Nrods were examined. We also investigated the application of WA-ZnO Nrods as an electron transport layer (ETL) and tungsten trioxide (WO3) as a hole transport layer (HTL) to vacuum free hybrid photovoltaic (HPV) performance. The eutectic gallium–indium (EGaIn) alloy was used as a top electrode coated using a brush-painting method. A device with the structure of indium tin oxide (ITO)/WA-ZnO Nrods/(P3HT:PCBM)/WO3/EGaIn was optimized and fabricated. The maximum power conversion efficiency (PCE) was ~4.5%. Improvement of the device performance indicates that the well-aligned ZnO Nrods and WO3 can effectively be applied as charge carrier transport layer for vacuum free hybrid (HPV).

Hydrothermal growth of well-aligned TiO2 nanorods on fluorine-doped tin oxide glass

Abstract One-dimensional titanium dioxide nanostructures have been studied intensively and extensively due to their outstanding properties and their diverse technological applications in photovoltaic cells. Interestingly, single crystalline TiO2 nanorods (TiO2 NRs) offer more advantageous compared with TiO2 particles and polycrystalline. TiO2 NRs produce direct electrical pathways of photogenerated carriers as well as large surface areas between NRs. This work presents a synthesis of vertically-aligned and uniform TiO2 NRs that were hydrothermally grown on a transparent conductive fluorine-doped tin oxide (FTO) glass substrate. The substrates were seeded with TiO2 compact layer (CL) using titanium (IV) butoxide as a precursor in HCl solution. Various techniques, including field emission scanning electron microscopy (FE-SEM) and X-ray diffraction (XRD) were employed to investigate the morphology and crystalline structure of the prepared TiO2 NRs. FE-SEM results revealed that the TiO2 NRs showed a rod-like nanostructure which could increase the accessible surface area. In addition, the effect on Ti initial reactant concentration was optimized to have desirable properties on the TiO2 NRs’ density, diameter and length. As a result, the as-prepared TiO2 NRs could have very good prospects in high-performance perovskite solar cell as electron transporting layers.

Template-free synthesis of nanoarrays SnO2 hollow microcubes with high gas-sensing performance to ether

Hierarchical nanoarrays SnO2 hollow microcubes were successfully synthesized by a simple one-pot template-free hydrothermal route without any substrates. The as-prepared products demonstrated novel hollow SnO2 microcubes with side length of 2–3 μm. Noticeably, the SnO2 cubic surfaces exhibited a hierarchical architecture of well-aligned nanorod arrays. The gas-sensing properties indicated that the nanoarrays SnO2 hollow microcubes possessed superior sensitivity towards ether at the heating voltage of 4.5 V. The formation and sensing mechanism of the nanoarrays SnO2 hollow microcubes were proposed in this paper.

Comprehensive Study on the Morphology Control of TiO2 Nanorods on Foreign Substrates by the Hydrothermal Method

The hydrothermal method is a facile route for the synthesis of TiO2 nanostructured materials, but it requires accurate process optimizations and adjustments to circumvent the undesirable morphology products. In this study, systematically controlled experimental studies are carried out under thermodynamic and kinetic considerations to understand the formation of well-aligned TiO2 nanorods during the hydrothermal reaction. In this regard, TiO2 nanorods are synthesized on various types of substrates, including single crystal TiO2 and sapphire, fluorine doped tin oxide, and silicon. Variable growth parameters are classified and investigated for their effects on the morphological evolution of TiO2 nanorods. The preferred morphology of TiO2 nanorods with the {110} facet is confirmed based on the crystallographic results for TiO2 nanorods acquired by extensive transmission electron microscopy studies during the entire growth processes. The presence of the seeds on the substrates is found to be mandatory for the ...

NiMoO4 nanorods supported on nickel foam for high-performance supercapacitor electrode materials

Well-aligned hierarchical NiMoO4 nanorods are successfully grown on nickel foam by a facile hydrothermal method, which can be directly used as integrated electrodes for supercapacitors without the addition of other ancillary materials such as binders or additives to enhance electrode cycling stability or conductivity. The samples are characterized by X-ray diffraction, scanning electron microscopy, energy dispersive spectroscopy, Fourier transform infrared, galvanostatic charge-discharge, and electrochemical impedance spectroscopy measurements. The achieved NiMoO4 nanorods are uniformly grown on nickel foam with the average diameter of 100 nm and length of 3 μm. The results indicate that the NiMoO4 nanorod samples deliver high specific capacitances of 3412, 2490, 1740, and 1496 F/g at 1, 4, 7, and 10 A/g, respectively. Furthermore, the excellent rate capability of the NiMoO4 nanorod based supercapacitors has been obtained in the KOH electrolyte, demonstrating that the as-prepared products can be promising electrode materials for supercapacitors.

TiO2 nanorod array film decorated with rGO nanosheets for enhancing photocatalytic and photoelectrochemical properties

A well-aligned TiO2 nanorod array film decorated with reduced graphene oxide(rGO/TNR) was constructed on fluorine-doped tin oxide (FTO) via a one-pot hydrothermal route with the aim of improving the photocatalytic and photoelectrochemical performances. The optimal ratio of components was investigated by changing the GO content that was added to the TiO2 precursor solution. The structure, morphology, composition, optical, photocatalytic and photoelectrochemical properties of the rGO/TNR films were investigated in detail. The resulting rGO/TNR films had a unique microstructure, apparent red shift of the absorption edge and low recombination rate of photoinduced charge carriers. For the degradation of methylene orange (MO) under UV light, the 5 wt%-rGO/TNR film exhibited the best photogradation efficiency of 95.8% in 120 min compared to bare TNR, which had a photogradation efficiency of 41.4%. Moreover, the 5 wt%-rGO/TNR film also showed the highest photocurrent of 110 μA/cm2, which was 6 times higher than that of bare TNR (16 μA/cm2). The excellent performance of the rGO/TNR film may be caused by the synergistic effect of the extended photoresponse range, high adsorption of target molecules and effective photogenerated electron-hole separation via rGO nanosheets as electron collectors and transporters.

Evolution of the composition, structure, and piezoelectric performance of (K1-xNax)NbO3 nanorod arrays with hydrothermal reaction time

Lead-free (K,Na)NbO3 (KNN) nanorod arrays were synthesized with the assistance of a Nb: SrTiO3 single-crystal substrate through the hydrothermal process. The evolutions of the morphology, composition, and structure of the as-synthesized KNN nanorods with the increase in reaction time were investigated. The results confirmed that the increase in reaction time up to 3 h led to the increase in the length and aspect ratio of the well-aligned KNN nanorods. All samples have K-rich orthorhombic crystal structures, while the diffraction peaks shifted towards a higher degree. The peak shifts should be attributed to the increase in the Na content in the KNN lattice, which could decrease the lattice parameters owing to the small ionic radius of Na+ than that of K+. Moreover, the increase in reaction time also resulted in the suppression of oxygen vacancies on the surface of the KNN nanorods. These evolutions of the composition and crystal structure, as well as the decrease in the defect content, lead to great enhancement of the nanorod's piezoelectric response, as their d33 value was increased from 19 to 64 pm/V. These results demonstrated the significant impact of reaction time on the hydrothermal growth of high-performance lead-free KNN one-dimensional nanomaterials.

Controllable assembly of sandwich-structured SnO2/Fe2O3 multilayer nanosheets for high sensitive acetone detection

A new type of hierarchically nonspherical architecture with sandwich-structured multilayer nanosheets has been successfully prepared via a controllable multistep approach in case of SnO2/Fe2O3 heterostructures. The morphological characterization reveals that unique sandwich-structured SnO2/Fe2O3 multilayer nanosheets (MNSs) are constructed via the self-assembly of densely well-aligned Fe2O3 nanorod layers to cover and fill the interlayers of hexagonal SnO2 hollow multilayer nanosheets (HMNs). When used as the sensing materials for acetone detection, the sandwich hetero-nanostructures demonstrate evidently improved sensing performance compared to pure SnO2. The significantly improved sensing performance can be attributed not only to the rational microstructures for fast transfer of gas molecules, but also to the additional effects of loaded Fe2O3 ultrathin nanorods.

Pr3+ doped biphasic TiO2 (rutile-brookite) nanorod arrays grown on activated carbon fibers: Hydrothermal synthesis and photocatalytic properties

Praseodymium-doped biphasic TiO2 (rutile-brookite) nanorod arrays (Pr-TiO2 NRAs) were successfully prepared via a two-step hydrothermal reaction on activated carbon fibers (ACFs) which pre-coated with TiO2 nanoparticles at first step. The bicrystalline arrays grown on ACFs are primarily constructed by the well-aligned TiO2 nanorods growing along [0 0 1] direction, which were indicated by the results of SEM and XRD. The nanorods are uniform in diameter and length with about 250 nm and 2.5 μm. The composite photocatalyst with high specific surface area and well-aligned nanostructure are beneficial to enhance the adsorption capacity and even help to suppress electron-hole recombination effectively, which consequently revealed much better (2 times) catalytic performance than that of commercially available P25 TiO2 on methylene blue(MB) photodegradation. In addition, the existence of praseodymium in TiO2 gives rise to shift of absorption edge towards long wavelength, which was indicated by the results of UV-vis DRS. Photodegradation results reveal that Pr-doping significantly improves the activity of TiO2, which was 20% higher than that of undoped TiO2 NRAs for the photodegradation of MB in aqueous medium under visible light irradiation. Meanwhile, the doped amount of Pr had a tiny influence on the photocatalytic performance of the composites. In our experiment, 3% Pr-doped molar concentration was proven to be the relatively optimal dopant concentration for the doping of TiO2 NRAs. Moreover, the photocatalyst grown on ACFs substrates is favorable to reuse and photodegradation rate kept on 76% even after 4 times of reuse.

Hydrothermally grown of well-aligned ZnONRs: dependence of alignment ordering upon precursor concentration

The well-aligned Zinc Oxide Nanorods (ZnONRs) arrays was obtained through a hydrothermal process at various precursor concentrations (PC) under a growth temperature of 90 °C for an hour. The effect of PC (0.02, 0.03, 0.04, 0.05, and 0.06 M which is denoted as K0.01–K0.06) to the structural, optical, and morfology (diameter, height, slope, and density) of ZnONRs were studied by using X-ray diffraction, UV–Vis spectroscopy, and field emission scanning electron microscopy (FESEM). As-synthesized ZnONRs exhibit an uniform growth direction along the [002] orientations with average diameters in the range of 40–90 nm. These nanorods showed a strong optical absorption peak centering at 367 nm,which is equivalent to optical energy band gap of ZnO 3.37 eV, confirming the formation of ZnONRs. The morfology of ZnONRs in term of diameter, height, slope, and density increases with the PC. The highest density of approximately 182 number/µm−2 with average slope of 6 degree (aligning percentage of 83 ± 12%) was obtained at the PC of K0.04. It is interesting to find that the dye sensitized solar cell utilizing the sample K0.04 showed five times increasing in the power conversion efficiency as compared to that of device utilizing K0.02 sample.

Preparation of 3D hierarchical porous Co3O4 nanostructures with enhanced performance in lithium-ion batteries.

Three-dimensional hierarchical Co3O4 microspheres assembled by well-aligned 1D porous nanorods have been synthesized by hydrothermal methods with the help of CTAB and subsequent heat treatment. The morphology and compositional characteristics of the hierarchical Co3O4 microspheres have been investigated using different techniques. Based on the SEM and TEM analyses, the growth direction of the nanorods is in the [110] direction. The hierarchical Co3O4 microspheres have a comparatively large Brunauer–Emmett–Teller surface area of about 50.2 m2g−1, and pore size distribution is mainly concentrated at 12 nm. On the basis of the time tracking experiment, a possible growth mechanism has been proposed. It demonstrates that the overall mechanism includes nucleation, oriented growth and self-assembly processes. These hierarchical Co3O4 microspheres provide several favorable features for Li-ion battery applications: (1) large Brunauer–Emmett–Teller surface area, (2) porous structure, and (3) hierarchical structure. Therefore, measurement of the electrochemical properties indicates that the specific capacity can maintain a stable value of about 1942 mA h g−1 at a current of 100 mA g−1 within 100 cycles.

Crystallographic plane and topography-dependent growth of semipolar InGaN nanorods on patterned sapphire substrates by molecular beam epitaxy.

A low-cost, high-efficiency, and catalyst-free method for fabricating well-aligned and uniform semipolar InGaN nanorods (NRs) by molecular beam epitaxy (MBE) is proposed using an optimized patterned sapphire substrate (PSS) with high Miller index crystallographic planes. The dense, obliquely aligned, and high-quality semipolar (11[combining macron]02) InGaN NRs are fabricated on hexagonal pyramid arrays of the PSS for the first time in this work. A unique semipolar (11[combining macron]02) and polar (0001) InGaN NR array composite structure is thus achieved on a hexagonal pyramid PSS. The connected, uniform, and obliquely aligned NRs are formed on the PSS with cylindrical arrays. The cylindrical and hexagonal pyramid arrays of PSSs are structured by the standard photolithography process and etching techniques. Both pattern topography and crystallographic plane of the PSS significantly affect the morphology, dimension, and crystallographic orientation of InGaN NRs. It is clearly demonstrated that the PSS with exposed high Miller index crystallographic planes, with well-organized step-terrace structures, facilitates the growth of ordered and dense semipolar InGaN NRs. This work contributes to the thorough understanding of the nucleation and growth mechanisms of InGaN NRs on a high Miller index plane of the PSS with different topographies, as well as of those of controllably fabricating dense and uniform semipolar NRs, thus facilitating the fabrication of NR-based optoelectronic devices with enhanced performance.

C-axis correlated pinning mechanism in vortex liquid and solid phases for Sm123 film with well-aligned BaHfO3 nanorods

Nanorods, which are nano-scaled columnar-shape precipitates, have recently been used to improve critical current density Jc in magnetic fields for REBa2Cu3Oy (RE123, RE: rare earth element) high temperature superconducting tapes/films. However, the flux pinning mechanism of the nanorod is not clear yet. We investigated the Jc and resistivity ρ properties in detail and discussed the flux pinning properties on the basis of the flux pinning state diagram for high-quality Sm123 films with well-aligned 5.6 vol% BaHfO3 nanorods. Plateaus were observed in the field dependence of Jc and ρ at high temperatures above the delocalization temperature. This suggests that nanorod pinning becomes effective in the vortex liquid phase and it grows up when the temperature decreases toward the delocalization temperature. In the ‘many-nanorod’ state in the high temperature region above the delocalization temperature, double peaks in the Fp curves appear due to the coexistence of nanorod pinning and random pinning. At low temperatures below 70 K, however, the well-scaled Fp curves at low fields and temperature dependent (non-scaled) normalized Fp curves are observed. From detailed analysis using the cooperation model of the random and the correlated pinning centers, we found that nanorod pinning is dominant below the matching field and the cooperation between nanorod pinning and random pinning determines the high field Jc properties above the matching field.

Effect of Ag doping on hydrothermally grown ZnO thin-film electronic synapse device

The present paper reports the effect of silver (Ag) doping on hydrothermally grown zinc oxide (ZnO) thin-film memristor-based electronic synapse devices. The morphological, structural and electrical characterizations of the zinc oxide memristor devices were carried out using scanning electron microscopy, X-ray diffraction and a programmable electrochemical workstation, respectively. The crystallographic orientation was detected along the (002) plane with well-aligned and compact zinc oxide nanorods for silver-doped zinc oxide memristor devices. An analog memory with a synaptic weight behavior similar to that of a biological synapse was observed for the developed devices. The morphological, structural, electrical and resistive switching mechanism studies clearly show improved performance of silver-doped zinc oxide devices over that of the bare zinc oxide device. Furthermore, the conduction mechanism of the devices follows the ohmic and space-charge-limited conduction theories. The present report is useful for the development and optimization of zinc oxide-based electronic synaptic devices for neuromorphic applications.

Strongly enhanced irreversibility field and flux pinning force density in SmBa2Cu3Oy-coated conductors with well-aligned BaHfO3 nanorods

A high flux pinning performance was obtained for a 3.8 vol % BaHfO3-doped SmBa2Cu3Oy superconducting film on a metallic substrate. At a temperature of 77.3 K, an irreversibility field of 16.8 T and the maximum flux pinning force density of 32.5 GN/m3 in fields applied parallel to the c-axis of the film were achieved, which are the highest values reported thus far for REBa2Cu3Oy films, to our knowledge. The introduction of well-aligned BaHfO3 nanorods with a high number density into REBa2Cu3Oy films with little or no degradation of the critical temperature is an effective method for improving the flux pinning performance.

Facile hydrothermal synthesis and characterization of cesium-doped PbI2 nanostructures for optoelectronic, radiation detection and photocatalytic applications

Low-temperature hydrothermal-assisted synthesis of pure and cesium (Cs) (1, 3, 5, 7 and 10 wt%) doped lead iodide (PbI2) nanorods and nanosheets have been achieved successfully for the first time. The structural and vibrational studies confirm the formation of a 2H-polytypic PbI2 predominantly. Scanning electron microscope analysis confirms the formation of well-aligned nanorods of average size ~ 100 nm at low concentration and nanosheets of average thicknesses in the range of ~ 20–40 nm at higher concentrations of Cs doping. The presence of Cs doping was confirmed by energy dispersive X-ray study. Ultra-violet-visible absorbance spectra were recorded, and energy gap was calculated in the range of 3.33 to 3.45 eV for pure and Cs-doped PbI2 nanostructures which is higher than the bulk value (i.e., ~ 2.27 eV) due to quantum confinement effect. Dielectric constant, loss, and AC conductivity studies have been done. Enhancement in Gamma linear absorption coefficient due to Cs doping confirms the suitability of prepared nanostructures for radiation detection applications. Furthermore, the photocatalytic performance of the synthesized nanostructures was evaluated in the decolorization of methyl green (MG) and methyl orange (MO) under the illumination of visible light (λ > 420 nm). The observed photocatalytic activity for 5 and 7 wt% Cs-doped PbI2 was observed to be more than pure PbI2 and also > 10 times higher than the commercially available photocatalysts. The results suggest that the prepared nanostructures are highly applicable in optoelectronic, radiation detection and many other applications.

Nanoscale electrical properties of ZnO nanorods grown by chemical bath deposition.

Well-aligned zinc oxide nanorod arrays (ZNAs) synthesized using chemical bath deposition were fabricated on a gallium-doped zinc oxide substrate, and the effects of varying the precursor concentrations on the growth and nanoscale electrical properties of the ZNAs were investigated. The as-synthesized ZNAs were characterized using field-emission scanning electron microscopy (FESEM), atomic force microscopy (AFM), conducting atomic force microscopy (CAFM), and scanning surface potential microscopy (SSPM). The FESEM and AFM images show that the growth rate in terms of length and diameter is highly sensitive to the precursor concentration. CAFM and SSPM analyses indicate that when concentrations of both the zinc acetate and hexamethylenetetramine solutions were 30 mM, the coverage percentages of the recordable and conducting regions on the ZNA surface were 48.3% and 0.9%, which is suitable for application in resistive random access memory devices.