Number Of Nanorods Research Articles

Two Significant Factors Affecting the Dimensions of the ZnO Nanorods During Chemical Bath Deposition: Precursor Solution Concentration and HMTA Content

The effects of zinc ion concentration and hexamethylene tetramine (HMTA) content of the aqueous precursor solution on the aspect ratios of the one-dimensional (1D) ZnO nanorods during chemical bath deposition (CBD) were investigated. The ZnO nanorods were grown on these seeded substrates by the low-temperature CBD method at 95 °C for 5 h. In the first part of this investigation the zinc nitrate hexahydrate (ZNH) to HMTA molar ratio was kept constant at a ratio of 1:1 for each of the CBD solutions prepared with different Zn^(+2) ion concentrations of 0.025, 0.035, 0.050, and 0.075 M. The number densities of the nanorods (i.e., number of nanorods per unit area) were increased with the increasing concentration. In the second part, the ZNH to HMTA molar ratio was varied to differ from the 1:1 value and, in turn, to obtain the precursor solutions relatively rich in Zn^(+2) or OH^-ions. Here, the concentration of the precursor solution was kept constant at 0.05 M. The lateral growth perpendicular to the c-axis of the ZnO nanorods was found to be suppressed with the increasing HMTA content (e.g., for the ZNH to HMTA molar ratio of 0.4: 1) due to its capping effect. However, the precursor solution containing an excessive amount of HMTA led to a decrease in the probability of crystal growth, which has been attributed to the OH^- ion enrichment.

Investigations of a Statistical and Analytical Method to Find the Relationship between the Morphological and Optical Properties of ZnO Nanoflower Arrays

In this study, a sapphire substrate with a patterned concave structure was used to prepare ZnO film/A-B glue, and the ZnO film/A-B glue with a patterned convex matrix was transferred onto a silicon wafer using the lift-off technology as the seed layer. Then, the hydrothermal method with different Zn(CH3COO)2 and C6H12N4 concentrations as precursors was used to synthesize ZnO nanoflower arrays on the patterned convex ZnO seed layer. XRD pattern, FESEM, FIB, and photoluminescence (PL) spectrometry were employed to observe and analyze the properties of the synthesized ZnO nanoflower arrays. When Zn(CH3COO)2 and C6H12N4 concentrations were 0.01, 0.02, 0.03, and 0.04 M, the average heights of the ZnO nanorods in the ZnO nanoflower arrays were 993, 1500, 1550, and 1650 nm, the average diameters of the ZnO nanorods were 50, 90, 105, and 225 nm, and the aspect ratios (H/D) of the ZnO nanorods were 19.9, 16.7, 14.8, and 7.33, respectively. A simple statistical and analytical method was investigated to estimate the densities (number of nanorods) of the ZnO nanoflower arrays in one 1 μm × 1 μm area. The total surface area (S) of the ZnO nanoflower arrays first increased from 5.05 × 106 and then reached a maximum value of 1.20 × 107 nm2 as Zn(CH3COO)2 and C6H12N4 concentrations increased from 0.01 to 0.02 M. For the systhesized ZnO nanoflower arrays, as the Zn(CH3COO)2 and C6H12N4 concentrations increased from 0.01 to 0.04 M, their total volume (V) increased from the 6.23 × 107 to 5.90 × 108 nm3 and the S/V ratio decreased from 8.10 × 10–2 to 1.84 × 10–2. We found that ZnO nanoflower arrays with Zn(CH3COO)2 and C6H12N4 concentrations of 0.2 M presented the maximum PL emission intensities. The calculated S/V ratios and X-ray photoelectron spectroscopy analyses are used to discuss the reasons for these results.

A Novel Synthesis of ZnO Nanoflower Arrays Using a Lift-Off Technique with Different Thicknesses of Al Sacrificial Layers on a Patterned Sapphire Substrate.

A novel method to synthesize large-scale ZnO nanoflower arrays using a protrusion patterned ZnO seed layer was investigated. Different thicknesses of aluminum (Al) film were deposited on the concave patterned sapphire substrate as a sacrificial layer. ZnO gel was layered onto the Al film as a seed layer and OE-6370HF AB optical glue was used as the adhesive material. A lift-off technique was used to transfer the protrusion patterned ZnO/AB glue seed layer to a P-type Si <100> wafer. The hydrothermal method using Zn(CH3COO)2 and C6H12N4 solutions as liquid precursors was used to synthesize ZnO nanoflower arrays on the patterned seed layer. X-ray diffraction spectra, field-effect scanning electron microscopy, focused ion beam milling (for obtaining cross-sectional views), and photoluminescence (PL) spectrometry were used to analyze the effects that different synthesis times and different thicknesses of Al sacrificial layer had on the properties of ZnO nanoflower arrays. These effects included an increased diameter, and a decreased height, density (i.e., number of nanorods in μm−2), total surface area, total volume, and maximum emission intensity of PL spectrum. We showed that when the synthesis time and the thickness of the Al sacrificial layer were increased, the emission intensities of the ultraviolet light and visible light had different variations.

Enhanced Photocatalytic Activity Using Near Visible Light of ZnO Nanorods by Doping with Mn2+ Ions

ZnO is a promising photocatalyst for photocatalytic oxidation of organic compounds under the influence of sunlight that provides clean energy and decomposes sustainable organic pollutants substances. ZnO is found to have non-toxic properties, long-term stability, high carrier mobility, low cost and biocompatibility. However, some disadvantages of ZnO limit its use in photocatalysis. Due to its wide bandgap, ZnO can only be activated under UV illumination. On the other hand, the photo-excited electron-hole pairs that recombine quickly on ZnO surface, suppress its photocatalytic properties. To improve its properties and performance, doping with transition metals was used to improve the optical properties of ZnO. Among the transition metal ions, Manganese (Mn) was commonly used to improve and tune the optical, electrical, diameter, height, and the number of nanorods (NRs) per unit area. Introduction of Mn into ZnO could enhance the photocatalytic activity due to the increase in the defect sites that effectively decreased the recombination of free electrons and holes. This study successfully synthesized ZnO nanorod arrays generated on glass substrates with different concentrations of doping Mn (0, 0.5, 1, 1.5 and 2%) at 100 °C by a simple hydrothermal method. To investigate the structure, morphology and optical properties, ultraviolet-visible spectroscopy (UV-Vis), X-ray diffraction (XRD) and scanning electron microscopy (SEM) were conducted. With the range of Mn doping ≤ 2% mol, the band gap reduced slightly, and the most optimized Mn doping concentration was of 0.5%. Overall, this work shows that the most effective way to increase ZnO’s photocatalytic activity in the visible region by reducing its band gap was the reduction in the size of the material or denaturation of ZnO by certain metals or non-metals.&#x0D;

Trapped modes with extremely high quality factor in a circular array of dielectric nanorods.

In this Letter, we investigate the formation of trapped modes with near-zero group velocities in a ring chain composed of dielectric nanorods. Two kinds of bound modes are successfully identified: the regular below-continuum-resonance (BCR) modes formed at the band edge and importantly the quasi-bound-states-in-the-continuum (BIC) trapped modes (similar to the BIC in the equivalent infinite linear chain). The lowest-order trapped mode possesses the highest Q factor, which scales exponentially with the number of nanorods N as Q∼exp(0.325N) for the BCR and Q∼exp(0.662N) for the quasi-BIC. Interestingly, a moderate high Q factor ∼105 can be obtained for the quasi-BIC mode even with a very small N=8. This suggests that our nanorod-based ring resonator possesses a clear advantage over the linear chain for the same N. Our findings greatly expand the application scope of BIC-based phenomena.

Effect of Indium doping on the photoelectric properties of n-ZnO nanorods/p-GaN heterojunction light-emitting diodes

Indium doped ZnO nanorods had been synthesized on p-GaN films by hydrothermal method at low temperature. The microstructure and morphology would be significantly affected by In doping. With increasing In doping concentration, the average diameter increased and the number of nanorods per area decreased. At the same time, the incorporation of In also affected the optical properties of ZnO nanorods. There was a slight red-shift of UV emission peak related to the combined effect of energy shift and Band-Gap-Renormalization effect. And the intensity of visible emission peak increased due to the increasing oxygen vacancies by In doping. What's more, In doping could shorten the band gap of ZnO. Finally, n-ZnO/p-GaN heterojunction Light-emitting diodes had better conductivity with the increase of In doping concentration.

Nonlocal axial vibration of the multiple Bishop nanorod system

Construction of reliable dynamic models of nanostructures is an important task for design procedures of different nanoresonator devices. Such theoretical models allow as to perform different numerical experiments, which is the key point in the development of advanced nanodevices. This paper presents a new nanoresonator model based on the axial vibration of the elastic multi-nanorod system. It is assumed that the system of multiple nanorods is embedded in an elastic medium. The governing equations of motion of a coupled multi-nanorod system are derived using the Hamilton’s principle, the nonlocal elastic constitutive relation, and Bishop’s rod theory, where effects of inertia of the lateral motion and the shear stiffness are considered. Exact closed form solutions for natural frequencies are obtained for one and multiple nanorod systems with different boundary conditions. Then, results for natural frequencies obtained by the finite difference method are compared with the results obtained analytically. Effects of nonlocal parameter, different rod theories, number of nanorods and stiffness coefficient of an elastic medium on natural frequencies are examined through several numerical examples.

Mn-doping-induced photocatalytic activity enhancement of ZnO nanorods prepared on glass substrates

Mn-doped ZnO nanorods were synthesized on glass substrates via a two-steps process of ultrasonic spray pyrolysis and hydrothermal methods with four different concentrations Mn-doping (0, 1, 3, and 7 mol%). Introduction of Mn into ZnO is known could enhance the photocatalytic activity owing to the increase in the defect sites that effectively suppress the recombination of free electrons and holes. In this study, results show that Mn-doping has effectively modified the nucleations and crystal growth of ZnO, as evidenced by the increasing in the diameter, height, and the number of nanorods per unit area, besides slightly reduced the band gap and increased the oxygen vacancy concentrations in the ZnO lattice. This condition has successfully multiplied the photocatalytic performance of the ZnO nanorods in the degradation of methylene blue (MB) compared to the undoped-ZnO sample where in the typical process the MB can be degraded approximately 77% within only 35 min under a UV light irradiation.

Optimization of the plasmonic nano-rods-based absorption coefficient using TLBO algorithm

We have used the teaching–learning-based optimization (TLBO) algorithm to design the plasmonic nano-rods in order to achieve the maximum absorption coefficient spectrum. In TLBO, a group of learners controls the nano-rod radius, the nano-rods distance, and the number of nano-rods in two dimensions. This approach is useful in optical applications such as solar cell and plasmonic nano antenna.

Vibration insight of a nonlocal viscoelastic coupled multi-nanorod system

Longitudinal vibration of viscoelastic multi-nanorod system (VMNS) is studied. Based on the D' Alembert's principles, nonlocal and viscoelastic constitutive relations, the system of m partial differential equations are derived which described the motion of the presented nano-system. ClampedeClamped and ClampedeFree boundary conditions and two different chain systems, namely “Clamped-Chain” and “Free-Chain” are illustrated. The method of separations of variables and trigonometric method are utilized for solutions. The analytical expressions for critical viscoelastic parameters and asymptotic frequencies are presented. The predicted results are validated with results obtained by direct numerical simulations and results from literature. The effects of nonlocal parameter, number of nanorods, viscoelastic material constant and parameter of viscoelastic layer on the complex eigenvalue are discussed in details.

Lateral growth of ZnO nanorod arrays in polyhedral structures for high on-current field-effect transistors.

Lateral growth of one-dimensional nanostructures is crucial for high performance field-effect transistors (FETs) which can drive a high on-current that is proportional to the number of nanorods (NRs) aligned between electrodes. Hence, it is strongly required to laterally and directly grow a large number of NRs between electrodes. For the first time, we propose a polyhedral-type FET (PH-FET) based on laterally-grown ZnO NRs, which includes circle, square and triangle configurations. The PH-FET structure not only provides a larger contact area than that of the planar parallel-type FET so that a great number of ZnO NRs are aligned between electrodes, but also generates a high on-current in the mA range (i.e., 5.5-6.8 mA). The high on-current PH-FET opens up a new range of applications for power devices where large currents have to be switched.

Novel three-dimensional Co3O4 dendritic superstructures: hydrothermal synthesis, formation mechanism and magnetic properties

Well-defined porous Co3O4 nanodendrites have been synthesized by a simple one-pot hydrothermal method combined with subsequent calcination. Importantly, after thermal treatment, the dendritic morphology could be completely preserved. The as-obtained superstructures are characterized by several techniques, such as powder X-ray diffraction, Fourier transform infrared spectroscopy, X-ray photoemission spectroscopy, elemental analysis, transmission electron microscopy, high-resolution TEM and magnetometry. On the dendritic hierarchical structures, a number of nanorods with different lengths and widths are connected to the main trunk with a diameter of about 50 nm and length of several micrometers. Each branch is about 0.5–1.0 μm with a width ranging from 100 to 400 nm. The possible formation mechanism was proposed on the basis of the contrasting experiments. It demonstrated that trisodium citrate and acetone play important roles in the synthesis of Co3O4 nanodendrites, while the other reaction parameters, such as reaction temperature, concentration of trisodium citrate and reaction time, have close relationships with the final morphology of the Co3O4 products. Optical properties of Co3O4 nanodendrites were characterized by Raman and UV-vis spectroscopy. Magnetic property measurement shows that Co3O4 nanodendrites have a low Neel transition temperature of 35 K. The as-prepared mesoporous Co3O4 nanostructures are expected to have great applications in many fields.

Quantitative Replacement of Cetyl Trimethylammonium Bromide by Cationic Thiol Ligands on the Surface of Gold Nanorods and Their Extremely Large Uptake by Cancer Cells

Stable and biocompatible: The chemical composition of synthesized cationic thiolate-monolayer-protected gold nanorods was precisely determined. In vitro cell culture experiments showed no cytotoxicity of these nanorods, and the number of nanorods that were taken up by each cancer cell exceeded two million particles (see picture).

Absorption Spectral Simulation of the End-to-End Linked Gold Nanorods Chain Structure

A classical electrostatic simulation model was developed to study the absorption spectral features of the end-to-end linked and equally-spaced n gold nanorods system with n=2 to 20 for the first time. The model calculation takes into account the dipole-dipole interactions only and solved for the mean polarizability of such nano-chain. We modelled the evolution of the longitudinal surface plasmon (SPlong) absorption band of such system in terms of the interparticle spacings and the number of nanorods. In both cases, either the decrease of interparticle spacing or the increase of n, the evolution of the SPlong bands exhibits a clear spectral red-shift similar to other assembled forms reported in literature. The extent of such spectral shift can be as large as more than 100 nm before levelling off. The interparticle dipole-dipole interaction, characterized by the results in the spectral features of SPlong bands, evidences an effective spatial range of ca. 100 nm. Keywords: Surface plasma resonance, gold nanorod, chain structure, end-to-end link, surface plasmon, Raman scattering, fluorescence, laser-induced photoacoustic tomography, polarization, DDA, BEM, FDTD, MLWA, Mie/Drude formalism, polarizability, dipole-dipole interaction, irradiation, electric field, nanorods, End-To-End Rods Chain, FWHM, SPlong band shift

Nanoparticles Change the Ordering Pattern of n-Carboxylic Acids into Nanorods on HOPG

This paper describes the formation of organic nanorods induced by monolayer-protected inorganic nanoparticles. Alkanes and alkane derivatives, such as n-carboxylic acids, self-assemble on highly oriented pyrolytic graphite (HOPG) into a persistent molecular packing structure that is dictated by the epitaxial interaction between the carbon chain plane and the HOPG basal plane. Carboxylic acids form 2-D crystalline layers consisting of nanostripe domains whose periodicity is one or two times the molecular chain length. However, when the molecular ordering occurs in the vicinity of a nanoparticle, this persistent HOPG-dominated nanostripe pattern is disrupted, and nanorods attached to the nanoparticles become the dominant structure. In order to understand the underlying mechanism of the nanoparticle-mediated nanorod formation, the effects of film-forming conditions, carboxylic acid chain length, nanoparticle size, and chemical composition of the nanoparticle are examined. It is determined that carboxylic acid nanorods can be induced by nanoparticles of different core materials including CdSe, CdS, and Au, as long as the protecting monolayer allows sufficient dispersion and colloidal stability of the nanoparticles in solution. A carboxylic chain length range amenable to the nanorod formation is identified, as is the relationship between the nanoparticle size and the number of nanorods per nanoparticle. This study contributes to the understanding of seed-mediated crystallization and molecular ordering. Moreover, it defines the parameters governing solution-based formation of hybrid nanostructures and nanopatterns incorporating dual functionality as defined by the inorganic nanoparticle and organic nanorod, respectively.

In situ real-time investigation of cancer cell photothermolysis mediated by excited gold nanorod surface plasmons

The photothermolysis of living EMT-6 breast tumor cells triggered by gold nanorods (AuNRs) with two-photon irradiation was conducted in situ and under real-time observation. The morphology and plasma membrane permeability of the cells were key indicators to the phenomena. AuNRs with an aspect ratio of 3.92, and a longitudinal absorption peak at 800 nm were synthesized with a seed-mediated method. The nanorods surfaces were further modified with polystyrenesulfonate (PSS) for biocompatibility. The prepared nanorods displayed excellent two-photon photoluminescence imaging. In situ real-time results revealed cavities internal to the cells were created from thermal explosions triggered by AuNRs localized photothermal effect. The cavitation dynamic is energy dependent and responsible for the perforation or sudden rupture of the plasma membrane. The energy threshold for cell therapy depended significantly on the number of nanorods taken up per cell. For an ingested AuNR cluster quantity N ∼ 10–30 per cell, it is found that energy fluences E larger-than 93 mJ/cm 2 led to effective cell destruction in the crumbled form within a very short period. As for a lower energy level E = 18 mJ/cm 2 with N ∼ 60–100, a non-instant, but progressive cell deterioration, is observed.

Cellular Uptake and Cytotoxicity of Gold Nanorods: Molecular Origin of Cytotoxicity and Surface Effects

Gold nanorods of different aspect ratios are prepared using the growth-directing surfactant, cetyltrimethylammonium bromide (CTAB), which forms a bilayer on the gold nanorod surface. Toxicological assays of CTAB-capped nanorod solutions with human colon carcinoma cells (HT-29) reveal that the apparent cytotoxicity is caused by free CTAB in solution. Overcoating the nanorods with polymers substantially reduces cytotoxicity. The number of nanorods taken up per cell, for the different surface coatings, is quantitated by inductively coupled plasma mass spectrometry on washed cells; the number of nanorods per cell varies from 50 to 2300, depending on the surface chemistry. Serum proteins from the biological media, most likely bovine serum albumin, adsorb to gold nanorods, leading to all nanorod samples bearing the same effective charge, regardless of the initial nanorod surface charge. The results suggest that physiochemical surface properties of nanomaterials change substantially after coming into contact with biological media. Such changes should be taken into consideration when examining the biological properties or environmental impact of nanoparticles.

Supramolecular structures formed by the self assembly of ionic fullerenes in binary liquid mixtures

The self assembly of C60-N, N′-dimethylpyrrolidinium iodide (C60-DMePyI) in binary liquid mixtures has been investigated. C60-DMePyI self-organized into nanosheets in a mixture of toluene and iodomethane, and aggregated to form nanofibers in toluene. The dimensions of the nanosheets were several micrometers in length and about 100 nm in thickness. Scanning electron microscope observations indicated that a large number of nanorods having a diameter of about 20-nm formed matted nanosheets. When iodomethane alone was used as a solvent, supramolecular structures such as nanofibers and nanosheets were not produced. Structural analyses of the C60-DMePyI aggregates were carried out by laser Raman spectroscopy and x-ray diffraction (XRD). The Raman spectroscopic results suggested that an ordered chain of successive polyiodine units was formed in all the supramolecular aggregates. The XRD studies showed that the crystal systems of the nanosheets and nanofibers were monoclinic, though with different unit cells.

N-Type Field-Effect Transistors Using Multiple Mg-Doped ZnO Nanorods

Nanorod field-effect transistors (FETs) that use multiple Mg-doped ZnO nanorods and a SiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> gate insulator were fabricated and characterized. The use of multiple nanorods provides higher on-currents without significant degradation in threshold voltage shift and subthreshold slopes. It has been observed that the on-currents of the multiple ZnO nanorod FETs increase approximately linearly with the number of nanorods, with on-currents of ~1 muA per nanorod and little change in off-current (~4times10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-12</sup> ). The subthreshold slopes and on-off ratios typically improve as the number of nanorods within the device channel is increased, reflecting good uniformity of properties from nanorod to nanorod. It is expected that Mg dopants contribute to high n-type semiconductor characteristics during ZnO nanorod growth. For comparison, nonintentionally doped ZnO nanorod FETs are fabricated, and show low conductivity to compare with Mg-doped ZnO nanorods. In addition, temperature-dependent current-voltage characteristics of single ZnO nanorod FETs indicate that the activation energy of the drain current is very low (0.05-0.16 eV) at gate voltages both above and below threshold

Silicon Carbide Nanorods and Ceramics from Wood

Japanese cedar carbonized at 700degreesC was vacuum infiltrated with tetraethylorthosilicate (TEOS), and heated for 30 min at 1400, 1600 and 1800degreesC by electric pulse heating. The microstructure was investigated by X-ray diffraction and electron microscopy. Extra peaks in the XRD scans could be traced back to beta-SiC. Preliminary Auger analysis indicated an increase of the Si signal in pore walls. This was considered together with SEM images in agreement with the concept of a reaction layer covering the pore walls. Moreover, a large number of nanorods were present inside the pores. TEM analysis confirmed them to be SiC nanorods grown along the direction.