Photo-initiated growth of zinc oxide (ZnO) nanorods

A photo-initiated process via femtosecond pulse-induced heterogeneous nucleation in zinc ammine complex (Zn(NH₃)₄²⁺)-based aqueous solution without catalyst and surfactant, followed by hydrothermal treatments for crystal growth into zinc oxide (ZnO) nanorods, was investigated. Flat-top hexagonal ZnO nanorods with smooth planes of diameter ≥ 100 nm and length ≤ 1 μm were grown with laser irradiation, compared to porous rod-like structures without irradiation. The flat-top planes indicate slow growth rate, due to the intermediate step of Zn(NH₃)₄²⁺ decomposition to Zn(OH)₄²⁻, before dehydration to ZnO. Prolonged hydrothermal treatment produced nanotubes and lateral splits due to OH⁻ erosion of the crystal faces. XRD analysis showed a hexagonal crystal structure while photoluminescence study indicated a peak at about 380 nm.     

Selective growth of PbSe on one or both tips of colloidal semiconductor nanorods

PbSe nanocrystals with rock-salt structure are grown on the tips of colloidal CdS and CdSe nanorods. The facets of wurtzite rods provide a substrate with various degrees of reactivity for the growth of PbSe. The presence of dangling Cd bonds may explain subtle differences between nonequivalent facets resulting in the selective nucleation of PbSe only on one of the two tips of each CdS rod. This approach has the potential to facilitate the fabrication of heterostructures with tailored optical and electronic properties.     

Electrical contacts to individual colloidal semiconductor nanorods

We report the results of charge transport studies on single CdTe nanocrystals contacted via evaporated Pd electrodes. Device charging energy, E c, monitored as a function of electrode separation drops suddenly at separations below approximately 55 nm. This drop can be explained by chemical changes induced by the metal electrodes. This explanation is corroborated by ensemble X-ray photoelectron spectroscopy studies of CdTe films as well as single particle measurements by transmission electron microscopy and energy dispersive X-rays. Similar to robust optical behavior obtained when nanocrystals are coated with a protective shell, we find that a protective SiO 2 layer deposited between the nanocrystal and the electrode prevents interface reactions and an associated drop in E c,max. This observation of interface reactivity and its effect on electrical properties has important implications for the integration of nanocrystals into conventional fabrication techniques and may enable novel nanomaterials.     

Fabrication and growth mechanism of hexagonal zinc oxide nanorods via solution process

This article presents, the fabrication of perfectly hexagonal zinc oxide nanorods performed via solution process using zinc nitrate hexahydrate (Zn(NO₃)₂·6H₂O) and hexamethylenetetramine (HMT) at various concentrations of i.e. 1 × 10⁻³ to 10 × 10⁻² M in 50 mL distilled water and refluxed at 100 °C for 1 h. We used HMT because it acts as a template for the nucleation and growth of zinc oxide nanorods, and it also works as a surfactant for the zinc oxide structures. The X-ray diffraction patterns clearly reveal that the grown product is pure zinc oxide. The diameters and lengths of the synthesized nanorods lie in the range of 200–800 nm and 2–4 μm, respectively as observed from the field emission scanning electron microscopy (FESEM). The morphological observation was also confirmed by the transmission electron microscopy (TEM) and clearly consistent with the FESEM observations. The chemical composition was analyzed by the FTIR spectroscopy, and it shows the ZnO band at 405 cm⁻¹. On the basis of these observations, the growth mechanism of ZnO nanostructures was also proposed.     

Nanostructured tellurium semiconductor: from nanoparticles to nanorods

Selective fabrication of single crystalline tellurium nanorods of various lengths and spherical nanoparticles can be easily achieved by a simple hydrothermal reduction method. The product was characterised by X-ray diffraction, transmission electron microscopy, high-resolution transmission electron microscopy, selected area electron diffraction and energy-dispersive X-ray spectroscopy techniques. It was found that when the concentration of orthotelluric acid gradually increased from 4 to 10, 20, 30 and 50?mM with other conditions controlled, the morphology of the tellurium nanocrystals gradually changed from long nanorod to shorter nanorods and eventually became spherical. Based on the experimental results, the morphology control mechanism of tellurium nanocrytals was well reasoned.     

Surfactant controlled synthesis of crystalline phosphovanadate nanorods

Phosphovanadate nanorods were obtained in a reaction of vanadium (V) oxide as a precursor and a cationic surfactant, dodecylpyridinium chloride, as structure directing template at pH ∼3 at room temperature. The composition and morphology of the nanorods was established by powder X-ray diffraction (XRD), energy dispersive X-ray analysis (EDAX), fourier transform infra-red spectroscopy (FTIR), thermogravimetric analysis (TGA), transmission electron microscopy (TEM) and atomic force microscopy (AFM). The obtained nanorods have diameters of 40-60 nm with lengths up to 1 μm. The effect of reaction parameters such as concentration of surfactant and pH of the solution on the growth of nanorods has been investigated. A plausible mechanism involving the coalescence of nanoparticle ‘seeds’ leading to one-dimensional nanorods is also discussed. The same reaction when performed under hydrothermal condition, keeping other reaction parameters unchanged, resulted in the formation of phosphovanadate nanospheres of diameter 10-15 nm.     

Photocatalytic paper using zinc oxide nanorods

Zinc oxide (ZnO) nanorods were grown on a paper support prepared from soft wood pulp. The photocatalytic activity of a sheet of paper with ZnO nanorods embedded in its porous matrix has been studied. ZnO nanorods were firmly attached to cellulose fibers and the photocatalytic paper samples were reused several times with nominal decrease in efficiency. Photodegradation of up to 93% was observed for methylene blue in the presence of paper filled with ZnO nanorods upon irradiation with visible light at 963 Wm^–2 for 120 min. Under similar conditions, photodegradation of approximately 35% was observed for methyl orange. Antibacterial tests revealed that the photocatalytic paper inhibits the growth of Escherichia coli under room lighting conditions.     

Photocatalytic paper using zinc oxide nanorods

Abstract

Zinc oxide (ZnO) nanorods were grown on a paper support prepared from soft wood pulp. The photocatalytic activity of a sheet of paper with ZnO nanorods embedded in its porous matrix has been studied. ZnO nanorods were firmly attached to cellulose fibers and the photocatalytic paper samples were reused several times with nominal decrease in efficiency. Photodegradation of up to 93% was observed for methylene blue in the presence of paper filled with ZnO nanorods upon irradiation with visible light at 963 Wm^–2 for 120 min. Under similar conditions, photodegradation of approximately 35% was observed for methyl orange. Antibacterial tests revealed that the photocatalytic paper inhibits the growth of Escherichia coli under room lighting conditions.     

The influence of surface oxide on the growth of metal/semiconductor nanowires

We report the critical effects of oxide on the growth of nanostructures through silicide formation. Under an in situ ultrahigh vacuum transmission electron microscope, it is observed from the conversion of Si nanowires into the metallic PtSi grains epitaxially through controlled reactions between lithographically defined Pt pads and Si nanowires. With oxide, instead of contact area, single crystal PtSi grains start forming either near the center between two adjacent pads or from the ends of Si nanowires, resulting in the heterostructure formation of Si/PtSi/Si. Without oxide, transformation from Si into PtSi begins at the contact area between them, resulting in the heterostructure formation of PtSi/Si/PtSi. The nanowire heterostructures have an atomically sharp interface with epitaxial relationships of Si(20-2)//PtSi(10-1) and Si[111]//PtSi[111]. Additionally, it has been observed that the existence of oxide significantly affects not only the growth position but also the growth behavior and the growth rate by two orders of magnitude. Molecular dynamics simulations have been performed to support our experimental results and the proposed growth mechanisms. In addition to fundamental science, the significance of the study matters for future processing techniques in nanotechnology and related applications as well.     

Radiative melting of crystalline ruthenium oxide nanorods

In this investigation, crystalline ruthenium oxide square nanorods have been observed via scanning electron microscopy (SEM) to melt at significantly lower temperatures than the melting temperature of bulk ruthenium oxide (1200?°C) at a measured substrate temperature of only 180?°C. The heating and subsequent melting of these nanorods occurs as a result of the combined effects of enhanced infrared (IR) absorption by the surface plasmon resonance and the inability of the nanorods to radiate at long wavelengths. This can result in the transfer of energy from a lower temperature body to a higher temperature body. This observation does not violate any thermodynamic laws as the entropy of the system is reduced with the concurrent input of energy.     

Directed spatial organization of zinc oxide nanorods

The ability to precisely place nanomaterials at predetermined locations is necessary for realizing applications using these new materials. Using an organic template, we demonstrate directed growth of zinc oxide (ZnO) nanorods on silver films from aqueous solution. Spatial organization of ZnO nanorods in prescribed arbitrary patterns was achieved, with unprecedented control in selectivity, crystal orientation, and nucleation density. Surprisingly, we found that caboxylate endgroups of omega-alkanethiol molecules strongly inhibit ZnO nucleation. The mechanism for this observed selectivity is discussed.     

Epitaxial growth of the zinc oxide nanorods, their characterization and in vitro biocompatibility studies

Here, we have synthesized Zinc Oxide (ZnO) nanorods at room temperature using zinc acetate and hexamethylenetetramine as precursors followed by characterization using X-ray diffraction (XRD), fourier transform infra red spectroscopy, scanning electron microscopy (SEM) and transmission electron microscopy. The growth of the synthesized ZnO was found to be very close to its hexagonal nature, which is confirmed by XRD. The nanorods were grown perpendicular to the long-axis and grew along the [001] direction, which is the nature of ZnO growth. The morphology of the synthesized ZnO nanorods was also confirmed by SEM. The size of the nanorod was estimated to be around 20-25?nm in diameter and approximately 50-60?nm in length. Our biocompatibility studies using synthesized ZnO showed no significant dose- or time-dependent increase in the formation of free radicals, accumulation of peroxidative products, antioxidant depletion or loss of cell viability on lung epithelial cells.     

Titanium oxide nanotubes with controlled morphology for enhanced bone growth

An array of vertically aligned titanium oxide nanotubes was grown on the surface of titanium substrate by anodization. A chemical treatment with NaOH solution to make them more bioactive with a formation of nanoscale sodium titanate structure. The presence of such treated TiO₂ nanotubes significantly accelerated the kinetics of hydroxyapatite growth by a factor of as much as 7. The adhesion/growth of osteoblast cells is also significantly accelerated by the topography of the TiO₂ nanotubes with the filopodia of the growing cells actually going into the nanotube pores, producing a locked-in cell structure. The number of the adhered cells on the TiO₂ nanotubes increases by as much ∼400% as compared to the Ti metal, most likely caused by the pronounced topological feature, significantly increased surface area, as well as the in-between-nanotube pathways for fluid. Such an array of TiO₂ nanotubes well adherent on Ti implant surface can be useful for accelerated bone growth in orthopaedic/dental applications.     

Glancing angle deposition of crystalline zinc oxide nanorods

Zinc oxide nanorod films produced by glancing angle deposition were fabricated within the parameter space defined by the process variables pitch (nanorod growth per substrate rotation), deposition rate, and throw distance to investigate the effect these parameters have on morphology and crystallinity. Statistical analysis was used to identify important relationships. Final film morphology depends on both pitch and deposition rate, where two growth regimes distinguished by deposition rate are observed and interpreted as arising from competition between geometric shadowing and crystalline growth kinetics. Optimal growth conditions for nanostructured films of isolated zinc oxide nanorods occurred for pitch values of approximately 1 nm to 10 nm. Pole-figure measurements confirm that the films consist of oriented single-crystal nanorods. Films deposited at all pitch values between 0.001 nm to 6.5 μm are crystalline and textured, and greater texturing is achieved for conditions of decreased surface diffusion.     

Nanofabrication of self-organized, three-dimensional epitaxial oxide nanorods

In this article, we address the nanofabrication process of self-organized, three-dimensional (3D) epitaxial oxide nanorods of perovskite La_1−xSr_xMnO₃ and fluorite Gd₂Zr₂O₇ using pulsed laser ablation. These nanorods are epitaxially grown on (001) LaAlO₃ substrate and are well defined with a very narrow size distribution as studied by transmission electron microcopy. All of the nanorods are encapsulated by uniformly thick amorphous-like boundaries. The nanofabrication process leading to formation of 3D nanorods in these systems is discussed by considering the interplay of misfit strain energy and surface energy contributions.     

Growth of tungsten oxide nanorods with carbon caps

Hybrid nanostructures consisting of tungsten oxide nanorods with mushroom-shaped carbon caps were grown on electrochemically etched tungsten tips by thermal chemical vapor deposition with methane and argon. These nanorods grow along the radial direction and are very straight and smooth. Electron microscopy revealed a dominant diameter and length of approximately 50 nm and approximately 0.6 microm, respectively. High-resolution transmission electron microscopy (HRTEM), and electron energy loss spectroscopy (EELS) revealed the presence of crystalline monoclinic W18O49 in the nanorods, and the cap was entirely amorphous carbon. A plausible growth mechanism involves the reduction of tungsten oxide WO3, present on the tungsten surface, by methane at 900 degrees C.