Nanorod Templates Research Articles

Visible light-driven CdSe nanotube array photocatalyst

Large-scale CdSe nanotube arrays on indium tin oxide (ITO) glass have been synthesized using ZnO nanorod template. The strong visible light absorption in CdSe, its excellent photoresponse, and the large surface area associated with the tubular morphology lead to good visible light-driven photocatalytic capability of these nanotube arrays. Compared to freestanding nanoparticles, such one-piece nanotube arrays on ITO make it very convenient for catalyst recycling after their usage

Study of the optical effects of nanostructure embedded GaN light emitting diodes formed by nanorod template overgrowth

In this paper, we used the finite difference time domain method to study the optical effect of nanostructures produced by the nanorod epitaxial lateral overgrowth (NELO) process on the light extraction of GaN Light Emitting Diode (LED). It was found that these nanostructures produced by NELO served as buffer layers for reducing stress and dislocations, as well as photon blocking layers for reducing the light penetrating sapphire substrates. We studied the effect of the nanostructure shape and density distribution on the light extraction efficiency of GaN LED because various overgrowth conditions can lead to different shapes and distributions of nanostructures. Simulation results showed that curved surface nanopores and dual-sized nanorod structures formed during overgrowth on the nanorod template have an extraction efficiency that is almost 100% higher than that of conventional LEDs, and 30% higher than that of original nanorod embedded LEDs. This is because of the higher probability of photon reflection and the strong surface scattering from the curved surface of nanopores and extra air gap of dual-sized nanorod structures. It was also shown that the density of the nanostructure occupied area affects light extraction. The simulation analysis shows that the light intensity peaks coincide in the locations of the nanopore gathered region, indicating that photon reflection is enhanced by nanopores. Experiments also showed that the electro luminescence emission from LEDs with 12.5% nanostructure density is 30% stronger than that of conventional LED.

Synthesis, characterization and enhanced thermoelectric performance of structurally ordered cable-like novel polyaniline–bismuth telluride nanocomposite

Bismuth telluride (Bi2Te3) nanorods and polyaniline (PANI) nanoparticles have been synthesized by employing solvothermal and chemical oxidative processes, respectively. Nanocomposites, comprising structurally ordered PANI preferentially grown along the surface of a Bi2Te3 nanorods template, are synthesized using in situ polymerization. X-ray powder diffraction, UV–vis and Raman spectral analysis confirm the highly ordered chain structure of PANI on Bi2Te3 nanorods, leading to a higher extent of doping, higher chain mobility and enhancement of the thermoelectric performance. Above 380 K, the PANI–Bi2Te3 nanocomposite with a core–shell/cable-like structure exhibits a higher thermoelectric power factor than either pure PANI or Bi2Te3. At room temperature the thermal conductivity of the composite is lower than that of its pure constituents, due to selective phonon scattering by the nanointerfaces designed in the PANI–Bi2Te3 nanocable structures. The figure of merit of the nanocomposite at room temperature is comparable to the values reported in the literature for bulk polymer-based composite thermoelectric materials.

Inverted Organic Photovoltaic Cells Using Three-Dimensionally Interconnected TiO<SUB>2</SUB> Nanotube Arrays

Here we describe a simple sol-gel method to fabricate inverted organic photovoltaics (OPV) using interconnected TiO2 nanotubes (inter-TiO2 NT) as an efficient electron transport layer. Three-dimensionally inter-TiO2 NT arrays were prepared by spin-coating a TiO2 precursor solution on the ZnO nanorod (NR) template grown via the liquid phase deposition method. Upon etching of ZnO NRs, inter-TiO2 NT arrays were generated, as confirmed by X-ray diffraction (XRD), energy-filtering transmission electron microscopy (EF-TEM) and field-emission scanning electron microscopy (FE-SEM). A blend of poly(3-hexylthiophene) (P3HT) and phenyl-C61-butyric acid methyl ester (PCBM) deeply infiltrated into the pores of inter-TiO2 NT, as revealed by FE-SEM and atomic force microscopy (AFM) images. The power conversion efficiency (PCE) of inter-TiO2 NT-based inverted OPV reached 3.0% at an air mass of 1.5 (100 mW/cm2), which is a 25% performance improvement compared to flat TiO2 films derived from the sol-gel process or commercial paste. The efficiency improvement arises from facilitated charge separation and collection due to the increased TiO2 interface arera and efficient transport pathway.

Efficient reduction of defects in (1120) non-polar and (1122) semi-polar GaN grown on nanorod templates

(1120) non-polar and (1122) semi-polar GaNs with a low defect density have been achieved by means of an overgrowth on nanorod templates, where a quick coalescence with a thickness even below 1 μm occurs. On-axis and off-axis X-ray rocking curve measurements have shown a massive reduction in the linewidth for our overgrown GaN in comparison with standard GaN films grown on sapphire substrates. Transmission electron microscope observation demonstrates that the overgrowth on the nanorod templates takes advantage of an omni-directional growth around the sidewalls of the nanostructures. The dislocations redirect in basal planes during the overgrowth, leading to their annihilation and termination at voids formed due to a large lateral growth rate. In the non-polar GaN, the priority 〈0001〉 lateral growth from vertical sidewalls of nanorods allows basal plane stacking faults (BSFs) to be blocked in the nanorod gaps; while for semi-polar GaN, the propagation of BSFs starts to be impeded when the growth front is changed to be along inclined 〈0001〉 direction above the nanorods.

Self-Assembly of NiO-Coated ZnO Nanorod Electrodes with Core–Shell Nanostructures as Anode Materials for Rechargeable Lithium-Ion Batteries

A porous nickel hydroxide shell was self-assembled by hydrolysis of aqueous nickel chloride in the presence of hexagonal ZnO nanorod template at room temperature. The nickel hydroxide shell converted to cubic NiO after heat treatment at 500 °C. Galvanostatic charge and discharge results indicated that the NiO-coated ZnO nanorod electrode is capable of delivering a higher capacity than the bare ZnO nanorod and carbon-coated ZnO nanorod electrodes especially in high-rate charge and discharge processes. The presence of porous NiO shell might prevent the disintegration of ZnO nanorods because of the large volume change during charge and discharge. In addition, the porous NiO shell ensured good electrical contact of ZnO with the current collector and facilitated the charge transfer and transport of lithium ions. The amount of NiO coated on ZnO nanorods significantly affected the electrochemical performance of ZnO electrode toward lithium. Insufficient NiO shell would not provide enough electrical conductivity and protection against disintegration. When the NiO content was higher than 32.6 wt %, the electrode performance could be significantly improved.

A Novel Approach to Well‐Aligned TiO2 Nanotube Arrays and Their Enhanced Photocatalytic Performances

A simple route has been developed to prepare well‐aligned TiO2 nanotube arrays, which is based on outward coating of TiO2 and inward etching of Cu(OH)2 nanorod templates. Effects of annealing temperature and time on the crystal size and crystallinity of TiO2 nanotube arrays and photocatalytic activities of TiO2 nanotube arrays for degradation of Rhodamine B in aqueous solution have been investigated. The results indicate that the TiO2 nanotube arrays annealed at 500°C for 2 h possessed an enhanced photocatalytic activity in comparison with the TiO2 nanotube arrays without post heating and commercial anatase TiO2 nanoparticle film and presented a good life cycle performance. Scale‐up of the process has also been demonstrated. Our work opens a new avenue to fabricate free‐standing TiO2 nanotube arrays and demonstrates an excellent photocatalytic performance of the anatase TiO2 nanotube arrays for wastewater treatment. © 2012 American Institute of Chemical Engineers AIChE J, 59: 2134–2144, 2013

Tailoring CoO–ZnO nanorod and nanotube arrays for Li-ion battery anode materials

Hydrothermal treatment of cobalt nitrate in the presence of ZnO nanorod templates results in the generation of free-standing CoO–ZnO composite arrays on a copper substrate. The result shows that tuning the molar concentration of cobalt nitrate can controllably prepare CoO–ZnO nanotube and ZnCo2O4 hierarchical nanorod structures. The electrochemical properties of the resultant nanorod and nanotube arrays are investigated. Due to the short insertion and extraction length for lithium ions, the free space between the adjacent tubes or rods, and the high contact area, the as-prepared one-dimensional CoO–ZnO composites exhibit excellent cycling performance and high capacities as anode materials for Li-ion batteries.

Template synthesis of PMAA@chitosan hollow nanorods for docetaxel delivery

Nanorods are capable of enhanced intracellular delivery and prolonged blood circulation over their spherical counterparts, and thus can be used as unmatched drug carriers for cancer chemotherapy. An innovative method was developed to synthesize size-tunable, PMAA@chitosan-based, hollow polymeric nanorods for intracellular delivery, by using mesoporous silica nanorod templates. The morphology of the polymeric hollow nanorods was examined by TEM and FT-IR spectra, which indicated a homogeneous three-dimensional structure. An uptake study using human lung carcinoma A-549 cell lines revealed highly efficient cell internalization of the FITC-labeled nanorods, suggesting the potential of utilizing these nanorods as carriers in achieving effective intracellular drug delivery. Cell viability studies of the docetaxel-loaded nanorods yielded consistent results, as the drug-loaded nanorods produced a significantly higher inhibition of the growth of A-549 tumor cells when compared with treatment by free docetaxel. Overall, this preliminary in vitro investigation sheds light on the use of prepared hollow polymeric nanorods for drug delivery applications.

Efficiency and droop improvement in green InGaN/GaN light-emitting diodes on GaN nanorods template with SiO2 nanomasks

This study presents the green InGaN/GaN multiple quantum wells light-emitting diodes (LEDs) grown on a GaN nanorods template with SiO2 nanomasks by metal–organic chemical vapor deposition. By nanoscale epitaxial lateral overgrowth, microscale air voids were formed between nanorods and the threading dislocations were efficiently suppressed. The electroluminescence measurement reveals that the LEDs on nanorods template with SiO2 nanomasks suffer less quantum-confined Stark effect and exhibit higher light output power and lower efficiency droop at a high injection current as compared with conventional LEDs.

Template-guided growth of well-aligned ZnO nanocone arrays on FTO substrate

Well-aligned ZnO nanocone arrays (NCAs) were prepared on fluorine doped tin oxide (FTO) substrates using highly ordered ZnO nanorod arrays (NRAs) as templates to guide the growth via a hydrothermal method. In contrast, only disordered ZnO nanocones on FTO were obtained in the absence of the highly ordered ZnO nanorod templates. The well-aligned ZnO nanocone arrays were characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD), UV–visible absorption, and photoluminescence (PL) spectroscopies. It was found that the highly ordered ZnO NRAs pre-formed on FTO played a critical role in dictating the further growth of the well-aligned ZnO NCAs from them. Significantly, strong light-trapping effect was revealed for the well-aligned ZnO NCAs, which may find important applications in, e.g., photovoltaics.

Greatly improved crystal quality of non‐polar GaN grown on a‐plane GaN nano‐rod template obtained using self‐organised nano‐masks

AbstractWe have developed a simple and effective approach for growth of a‐plane GaN with massively improved crystal quality on a‐plane GaN nanorod template on sapphire. The a‐plane GaN nanorod template is fabricated using self‐organised nickel nano‐masks. X‐ray diffraction rocking curves, measured along both symmetrical and asymmetrical directions, show a massive reduction in full width at half maximum (FWHM), meaning a significant reduction in dislocation density. These are all among best reports although our overgrown layer is only 4‐5 μm, much less than those using any other overgrowth technique. The threading dislocation density has been reduced down to 2.5×108 cm‐2 from typical 9×109 cm‐2 for the a‐plane GaN template on sapphire. The scanning electron microscope measurements show that two kinds of voids have been observed in the cross‐sectional image, which form during the coalescence process of the overgrowth. Taking the advantage of the SiO2 remaining on the top of the nano‐rods, theoretically all dislocations could be effectively blocked. Photoluminescence (PL) measurements have been performed, showing a strong band‐edge emission, which cannot be observed in the a‐plane GaN template on sapphire (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Coaxial multi-shelled TiO2 nanotube arrays for dye sensitized solar cells

The performance of one-dimensional (1D) TiO2 nanotube based dye-sensitized solar cells (DSCs) was limited by the insufficient surface area of TiO2 nanotubes. To solve this issue, coaxial multiple-shelled TiO2 nanotube arrays were successfully synthesized on the transparent conductive oxide (TCO) substrates by using improved ZnO nanorod template assisted layer by layer absorption and reaction (LbL-AR) technique. To fabricate tube-in-tube nanostructures, LbL-AR TiO2 coatings were successively deposited on the exterior walls of the ZnO nanowires and the sacrificial sol–gel ZnO spacers, which were removed together by selective etching to form the hollow tubal structures. The performance of dye-sensitized solar cells (DSCs) increases with increasing the shell number of multi-shelled TiO2 nanotube photoanodes, attributed to the increase of the surface area, which was confirmed by N2 adsorption-desorption isotherms and the dye-loading capacities. A maximum efficiency of 6.2% was achieved for a quintuple shelled TiO2 nanotube photoanode with a short-circuit current density (Jsc) = 15 mA cm2, open-circuit voltage (Voc) = 0.73 V and fill factor (FF) = 0.57.

Investigation of Emission Polarization and Strain in InGaN–GaN Multiple Quantum Wells on Nanorod Epitaxially Lateral Overgrowth Templates

Non-polar (a-plane) InGaN-GaN multiple quantum wells (MQWs) on the GaN nanorod epitaxially lateral overgrowth templates with different nanorod height have been fabricated. The average in-plane strain in the InGaN MQWs has been determined from 2.73 × 10-2 to 2.58 × 10-2 while the nanorod height in templates increases from 0 to 1.7 μm. The polarization ratio of the emission from InGaN MQWs varies from 85 % to 53 % along with the increase of the GaN nanorod height. The reduction of polarization ratio has been attributed to the partial strain relaxation within the epitaxial structures as a result of growth on the GaN nanorod templates and the micro-size air-voids observed in the nanorod templates.

Fabrication of 3D interconnected porousTiO2 nanotubes templatedby poly(vinyl chloride-g-4-vinyl pyridine) for dye-sensitized solar cells

Porous TiO2 nanotube arrays with three-dimensional (3D) interconnectivity wereprepared using a sol–gel process assisted by poly(vinyl chloride-graft-4-vinylpyridine), PVC-g-P4VP graft copolymer and a ZnO nanorod template. A7 µm long ZnO nanorod array was grown from the fluorine-doped tinoxide (FTO) glass via a liquid phase deposition method. TheTiO2 sol–gel solutiontemplated by the PVC-g-P4VP graft copolymer produced a random 3D interconnection betweenthe adjacent ZnO nanorods during spin coating. Upon etching of ZnO,TiO2 nanotubes consisting of 10–15 nm nanoparticles were generated, as confirmed by wide-anglex-ray scattering (WAXS), energy-filtering transmission electron microscopy (EF-TEM) andfield-emission scanning electron microscopy (FE-SEM). The ordered and interconnectednanotube architecture showed an enhanced light scattering effect and increased penetrationof polymer electrolytes in dye-sensitized solar cells (DSSC). The energy conversionefficiency reached 1.82% for liquid electrolyte, and 1.46% for low molecular weight(Mw) and 0.74%for high Mw polymer electrolytes.

Nanopendeo coalescence overgrowth of GaN on etched nanorod array

AbstractThis paper reports the characteristics of gallium nitride layers that have been grown on top of an etched array of nanorods. Nanoimprint lithography has been used to create nanorods on a wafer‐scale that are subsequently passivated to allow selective regrowth from their tips by MOVPE. The first epitaxial growth step favoured lateral growth and the second resulted in a planar coalesced layer of gallium nitride. It was found that smooth planarised overgrowth required careful timing of the growth transition between the two steps and that the crystallographic quality of the overgrown layer was very sensitive to the nanorod template properties, in particular the amount of unpassivated nanorod surface. (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Reduction of Efficiency Droop in InGaN Light-Emitting Diode Grown on Self-Separated Freestanding GaN Substrates

Using a GaN nanorod template in a hydride vapor phase epitaxy (HVPE) system can manufacture a freestanding GaN (FS-GaN) substrate with threading dislocation densities down to ~ 107 cm-2. In this letter, we report InGaN/GaN multiple-quantum-well light-emitting diodes (LEDs) grown on this FS-GaN substrate. The defect densities in the homoepitaxially grown LEDs were substantially reduced, leading to improved light emission efficiency. Compared with the LED grown on sapphire, we obtained a lower forward voltage, smaller diode ideality factor, and higher light-output power in the same structure grown on FS-GaN. The external quantum efficiency (EQE) of LEDs grown on FS-GaN were improved especially at high injection current, which brought the efficiency droop phenomenon greatly reduced at high current density.

Hiearchical ZnO rod-in-tube nano-architecture arrays produced via a two-step hydrothermal and ultrasonication process

Vertically aligned hierarchical ZnO rod-in-tube nano-architecture arrays are produced via a two-step process including an initial hydrothermal reaction followed by ultrasonication growth. The ZnO nanorod arrays grow firstly on FTO glass through a hydrothermal process and then act as templates for the fabrication of rod-in-tube nano-architectures during ultrasonication. The as-prepared ZnO rod-in-tube nano-architectures are assembled by the self-stacking of hexagonal nanorings along with orientation of ZnO nanorod templates. Both hexamethylenetetramine and sodium citrate are found to play key roles in the formation of the novel ZnO rod-in-tube nano-architectures. The power conversion efficiency of dye-sensitized solar cell based on hierarchical ZnO rod-in-tube nano-architectures photoelectrode (0.91%) exhibits a significant improvement (75%) compared to that of ZnO nanorods (0.52%).

ランダム成長ZnOナノロッドによるプラズモン増強ラマン散乱

ランダム成長ZnOナノロッドによるプラズモン増強ラマン散乱

Enhanced Photovoltaic Performance of Nanostructured Hybrid Solar Cell Using Highly Oriented TiO2 Nanotubes

Highly oriented TiO2 nanotubes have been fabricated using ZnO nanorod template through liquid reactive deposition on the ITO substrates. The diameter and length of TiO2 nanotubes can be effectively controlled for the suitable use for a hybrid solar cell by varying the diameter and length of the ZnO nanorod template. A mixture of P3HT/PCBM was infiltrated into the gaps between TiO2 nanotubes to form hybrid solar cells. The open circuit voltage, short circuit current density, fill factor, and power conversion efficiency of the hybrid solar cell using highly oriented TiO2 nanotubes were 646 mV, 9.95 mA cm−2, 51.6%, and 3.32%, respectively, much higher than 1.2% of hybrid solar cell based on ZnO nanorods tested under otherwise identical conditions and significantly higher than 0.7% of the same type hybrid solar cells reported in literature. The enhancement of the power conversion efficiency could be resulted from the highly oriented TiO2 nanotubes with smaller diameter and large specific surface area for the ...